Re: 자가포식을 위한 엔도좀, 자가포식체, 리소좀 ... 세포 수리기관 탐구

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Nat Rev Drug Discov

. 2019 Sep 2;18(12):923–948. doi: 10.1038/s41573-019-0036-1

Lysosomes as a therapeutic target

Srinivasa Reddy Bonam 1,2, Fengjuan Wang 1,2, Sylviane Muller 1,2,3,4,✉

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PMCID: PMC7097195  PMID: 31477883

Abstract

Lysosomes are membrane-bound organelles with roles in processes involved in degrading and recycling cellular waste, cellular signalling and energy metabolism. Defects in genes encoding lysosomal proteins cause lysosomal storage disorders, in which enzyme replacement therapy has proved successful. Growing evidence also implicates roles for lysosomal dysfunction in more common diseases including inflammatory and autoimmune disorders, neurodegenerative diseases, cancer and metabolic disorders. With a focus on lysosomal dysfunction in autoimmune disorders and neurodegenerative diseases — including lupus, rheumatoid arthritis, multiple sclerosis, Alzheimer disease and Parkinson disease — this Review critically analyses progress and opportunities for therapeutically targeting lysosomal proteins and processes, particularly with small molecules and peptide drugs.

요약

리소좀은

세포 폐기물의 분해 및 재활용, 세포 신호 전달, 에너지 대사에 관여하는 막 결합 소기관입니다.

리소좀 단백질을 암호화하는 유전자의 결함은

리소좀 축적 장애를 유발하며,

이 질환에는 효소 대체 요법이 효과적인 것으로 입증되었습니다.

또한, 염증 및 자가 면역 질환, 신경 퇴행성 질환, 암, 대사 장애 등

더 흔한 질환에도 리소좀 기능 장애가 관련되어 있다는 증거가 점점 더 많아지고 있습니다.

자가면역 질환과 신경퇴행성 질환

(루푸스, 류마티스 관절염, 다발성 경화증, 알츠하이머 병, 파킨슨 병 등)에서의 리소좀 기능 장애에 초점을 맞춰,

이 리뷰는 리소좀 단백질과 과정(특히 소분자 및 펩타이드 약물)을

치료적으로 표적화하는 데 대한 진전과 기회를 비판적으로 분석합니다.

Subject terms: Drug discovery, Autoimmune diseases, Inflammatory diseases, Neurodegenerative diseases, Lysosomes

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Defective lysosomal function has been implicated in diseases ranging from rare lysosomal storage disorders to more common diseases including inflammatory and autoimmune disorders, neurodegenerative diseases, cancer and metabolic disorders. Here, Muller and colleagues provide an overview of the physiological and pathological roles of lysosomes and assess the progress and opportunities for therapeutically targeting lysosomal proteins and processes.

Introduction

Discovered in the 1950s by Christian de Duve, lysosomes are membrane-bound vesicles containing numerous hydrolytic enzymes that can break down biological polymers such as proteins, lipids, nucleic acids and polysaccharides1,2. Lysosomes have long been known to have a key role in the degradation and recycling of extracellular material via endocytosis and phagocytosis, and intracellular material via autophagy (reviewed elsewhere2–5) (Fig. 1). The products of lysosomal degradation through these processes can be trafficked to the Golgi apparatus for reuse or for release from the cell through lysosomal exocytosis, which is important in immune system processes. In addition, it has become clear more recently that lysosomes have an important role in other cellular processes including nutrient sensing and the control of energy metabolism3,5–7 (Fig. 1).

리소좀 기능 장애는 희귀한 리소좀 저장 질환부터 염증성 및 자가면역 질환, 신경퇴행성 질환, 암, 대사 장애 등 다양한 질환과 연관되어 있습니다. 본 논문에서 Muller와 동료들은 리소좀의 생리적 및 병리적 역할을 개괄하고, 리소좀 단백질 및 과정을 치료적으로 표적화하는 데 대한 진전과 기회를 평가합니다.

서론

1950년대 크리스티안 드 뒤베에 의해 발견된 리소좀은

단백질, 지질, 핵산, 다당류 등 생물학적 폴리머를 분해할 수 있는

수많은 가수분해 효소를 함유한 막으로 둘러싸인 소체입니다1,2.

리소좀은

내포작용 및 식작용을 통해 세포외 물질의 분해 및 재활용,

그리고 자가포식을 통해 세포내 물질의 분해 및 재활용에 중요한 역할을 하는 것으로 오랫동안 알려져 왔습니다

(다른 문헌에서 검토됨2–5) (그림 1).

이러한 과정 통해 생성된 리소좀 분해 제품은

재사용을 위해 골지체로 운반되거나,

면역 체계 과정에 중요한 역할을 하는 리소좀 분비(lysosomal exocytosis)를 통해

세포 밖으로 방출될 수 있습니다.

최근에는

리소좀이 영양소 감지 및 에너지 대사 조절 등

다른 세포 과정에도 중요한 역할을 한다는 것이 명확해졌습니다3,5–7 (그림 1).

Fig. 1. The central position of lysosomes at the crossroads of major autophagic pathways.

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a | Functional lysosomes are involved in the degradation (endocytic and autophagic) and regulation of exogenous and endogenous cellular material, including recycling processes. Extracellular material endocytosed by the endosomes and intracellular cargo internalized by the autophagosomes fuse with lysosomes for degradation, which produces energy (ATP production) and source molecules for the macromolecules. Mechanistic target of rapamycin complex 1 (mTORC1) plays a key role in lysosomal nutrient sensing signals (lysosome-to-nucleus axis) to regulate energy metabolism. Factors such as energy levels, type of pH, ion channel regulation and others decide the fate of the catabolic process. During lysosomal exocytosis, the lysosomal content favours plasma membrane (PM) repair, bone resorption, immune response and elimination of pathogenic stores. 

b | The lysosome is the ultimate cell compartment that digests unwanted protein materials generated by macroautophagy, microautophagy (pathways during which the cytoplasmic material is trapped in the lysosome by a process of membrane invagination) and chaperone-mediated autophagy (CMA). In general, lipid droplets (LDs) are degraded by lipophagy, a subtype of macroautophagy, which is activated by cytosolic lipases. CMA has also been demonstrated to participate in the degradation of LDs in which perilipin (PLIN2/3) proteins are phosphorylated (P) by AMP-activated protein kinase (AMPK) with the help of the HSPA8 chaperone. Mechanistic target of rapamycin complex 2 (mTORC2) and AKT (also known as protein kinase B) are negative regulators of CMA, where they exert their effect on the translocation complex of CMA. In situations of starvation, negative regulators are controlled by pleckstrin homology domain and leucine-rich repeat protein phosphatase (PHLPP). Lysosomal stability effects the transcription factor EB (TFEB) translation to the nucleus in which TFEB binds to the coordinated lysosomal expression‎ and regulation (CLEAR) motifs to regulate the transcription of genes. EF1a, elongation factor 1a; Lys, lysosome; Rac1, Ras-related C3 botulinum toxin substrate 1.

a | 기능적 리소좀은 외인성 및 내인성 세포 물질의 분해(내포작용 및 자식작용) 및 조절, 재활용 과정에 관여합니다. 엔도좀에 의해 내포된 세포외 물질과 오토파고좀에 의해 내재화된 세포 내 화물은 리소좀과 융합되어 분해되며, 이 과정에서 에너지(ATP 생성)와 대분자 합성에 필요한 원료 분자가 생성됩니다. 라파마이신 복합체 1(mTORC1)은 리소좀 영양 감지 신호(리소좀-핵 축)를 통해 에너지 대사 조절에 핵심적인 역할을 합니다. 에너지 수준, pH 유형, 이온 채널 조절 등 다양한 요인이 분해 과정의 운명을 결정합니다. 리소좀의 분비 과정에서 리소좀 내 내용은 세포막(PM) 복구, 골 흡수, 면역 반응 및 병리적 저장물의 제거에 기여합니다.

b | 리소좀은 거대자가포식, 미세자가포식(세포질 물질이 막의 침입에 의해 리소좀에 갇히는 과정) 및 샤페론 매개자가포식(CMA)에 의해 생성된 불필요한 단백질 물질을 소화하는 궁극적인 세포 소기관입니다. 일반적으로 지질 방울(LD)은 세포질 리파아제에 의해 활성화되는 마크로오토파지의 하위 유형인 리포파지에 의해 분해됩니다. CMA는 또한 AMPK(AMP 활성화 단백질 키나제)의 도움으로 HSPA8 분자 샤페론의 작용으로 perilipin(PLIN2/3) 단백질이 인산화(P)되는 LD의 분해에 참여하는 것으로 입증되었습니다. 라파마이신 복합체 2(mTORC2)와 AKT(단백질 키나제 B로도 알려져 있음)는 CMA의 음성 조절자로, CMA의 전위 복합체에 영향을 미칩니다. 굶주림 상태에서는 음성 조절자가 플렉스트린 호모로지 도메인과 류신 풍부 반복 단백질 인산화효소(PHLPP)에 의해 조절됩니다. 리소좀 안정성은 전사 인자 EB (TFEB)가 핵으로의 번역에 영향을 미치며, TFEB는 조정된 리소좀 발현 및 조절 (CLEAR) 모티프에 결합하여 유전자의 전사를 조절합니다. EF1a, 연장 인자 1a; Lys, 리소좀; Rac1, Ras 관련 C3 보툴리눔 독소 기질 1.

Alterations in lysosomal functions, either in the fusion processes involved in the general pathways mentioned above or related to the function of lysosomal enzymes and non-enzymatic proteins, can result in broad detrimental effects, including failure to clear potentially toxic cellular waste, inflammation, apoptosis and dysregulation of cellular signalling8. Such defects have been implicated in many diseases, ranging from rare lysosomal storage disorders (LSDs), which are caused by the dysfunction of particular lysosomal proteins, to more common autoimmune and neurodegenerative disorders5,9,10. Despite some limitations, impressive results have been achieved in treating several LSDs through enzyme replacement therapy (ERT). In addition, substantial efforts have been focused on therapeutically targeting the autophagy processes upstream of lysosomes11–14. However, there has so far been less attention on investigating the potential to directly target lysosomes with small molecules and peptide drugs.

Nevertheless, with recent advances in understanding of lysosomal function and dysfunction in diseases, promising novel opportunities for therapeutic intervention through targeting lysosomes specifically are beginning to emerge. This Review will provide a brief overview of lysosomal biogenesis, structure and function, and describe the role of lysosomal dysfunction in LSDs as well as other, more common diseases. Specifically, the article will focus on organ-specific and non-organ-specific autoimmune diseases, including lupus, rheumatoid arthritis (RA) and multiple sclerosis (MS), as these have not been extensively reviewed elsewhere, but will also briefly highlight neurodegenerative disorders such as Alzheimer disease (AD) and Parkinson disease (PD), to further illustrate the breadth and nature of the emerging therapeutic opportunities. The current ‘toolbox’ of pharmacological agents that modulate lysosomal functions and emerging novel targets and strategies in this set of indications will be highlighted. It should be noted that therapeutic approaches to treat inflammatory and autoimmune diseases aim to inhibit the deleterious excessive lysosomal activity, whereas lysosomal activation would be the goal in the treatment of neurodegenerative diseases. Although beyond the scope of this review, such approaches may have applications in other diseases in which lysosomes may play a role, including cancer, metabolic diseases and ageing (reviewed elsewhere15,16).

리소좀 기능의 변화,

특히 위에서 언급된 일반적인 경로에 관여하는 융합 과정이나 리소좀 효소 및 비효소 단백질의 기능과 관련된 변화는

잠재적으로 독성 세포 폐기물의 제거 실패, 염증, 세포 사멸 및 세포 신호전달의 이상과 같은

광범위한 유해 효과를 초래할 수 있습니다.

이러한 결함은

특정 리소좀 단백질의 기능 장애로 인한 희귀한 리소좀 저장 장애 (LSDs)부터

더 흔한 자가면역 및 신경퇴행성 질환까지

다양한 질환과 연관되어 있습니다5,9,10.

몇 가지 한계가 있지만,

효소 대체 요법(ERT)을 통해 여러 LSD의 치료에 인상적인 결과가 달성되었습니다.

enzyme replacement therapy (ERT)

또한,

리소좀의 상류에 있는 자가포식 과정을 치료적으로 표적으로 하는 데

상당한 노력이 집중되어 왔습니다11–14.

그러나,

지금까지는 소분자 및 펩티드 약물을 사용하여 리소좀을 직접 표적으로 하는 가능성에 대한 연구는

그다지 주목을 받지 못했습니다.

그러나

리소좀의 기능과 질환에서의 기능 장애에 대한 이해가 최근 진전되면서,

리소좀을 특정적으로 표적화하는 것을 통해

치료적 개입의 유망한 새로운 기회가 점차 등장하고 있습니다.

이 리뷰는

리소좀의 생합성, 구조 및 기능을 간략히 개요하고,

LSDs뿐만 아니라 다른 일반적인 질환에서의 리소좀 기능 장애의 역할을 설명할 것입니다.

특히, 이 논문은 다른 곳에서 충분히 검토되지 않은

장기 특이적 및 비장기 특이적 자가면역 질환인

루푸스, 류마티스 관절염 (RA) 및 다발성 경화증 (MS)에 초점을 맞출 것이며,

알츠하이머 병 (AD)과 파킨슨 병 (PD)과 같은 신경퇴행성 질환을 간략히 언급하여

새롭게 등장하는 치료 기회들의 폭과 특성을 더욱 명확히 할 것입니다.

리소좀 기능을 조절하는 약리학적 제제의 현재 '도구 상자'와

이 질환군에서 새롭게 등장하는 표적 및 전략이 강조될 것입니다.

치료적 접근법은

염증성 및 자가면역 질환의 경우 유해한 과도한 리소좀 활동을 억제하는 것을 목표로 하며,

반면 신경퇴행성 질환의 치료에서는 리소좀 활성화를 목표로 합니다.

이 리뷰의 범위를 넘어서는 내용이지만,

이러한 접근법은 리소좀이 역할을 할 수 있는 다른 질환,

예를 들어 암, 대사 질환 및 노화(다른 곳에서 검토됨15,16)에도 적용될 수 있습니다.

Lysosomal biogenesis, structure and function

The formation of mature lysosomes is a complex process, which involves the fusion of late endosomes that contain material taken up at the cell surface with transport vesicles that bud from the trans-Golgi network5,8,17. These vesicles contain nearly 60 different hydrolytic enzymes (grouped into nucleases, proteases, phosphatases, lipases, sulfatases and others), which are synthesized in the endoplasmic reticulum and delivered to the transport vesicles via diverse systems, such as mannose-6-phosphate tags that are recognized by mannose-6-phosphate receptors (MPRs) at the membrane8,18 or glucocerebrosidase (GCase) that is transported to lysosomes by lysosomal integral membrane protein-2, an ubiquitously expressed type III transmembrane glycoprotein mainly located in endosomes and lysosomes19.

리소좀 생합성, 구조 및 기능

성숙한 리소좀의 형성은 복잡한 과정으로,

세포 표면에서 흡수된 물질을 포함하는 후기 엔도좀과

트랜스 골지 네트워크에서 분비되는 운반 소체 간의 융합을 포함합니다5,8,17.

이 소포체에는

핵산 분해 효소,

단백질 분해 효소,

인산화 효소,

지질 분해 효소,

황산화 효소 등 약 60종의 다양한 가수분해 효소가 포함되어 있으며,

이 효소들은 내소체에서 합성되어 다양한 시스템을 통해 운반 소포체로 전달됩니다.

nucleases, proteases, phosphatases, lipases, sulfatases and others

예를 들어,

막에 존재하는 만노스-6-인산 수용체(MPRs)에 의해 인식되는 만노스-6-인산 태그8,18 또는

리소좀 내막 단백질-2(LISP-2)에 의해 리소좀으로 운반되는 글루코세레브로시다제(GCase) 등이 있습니다.

LISP-2는

주로 엔도좀과 리소좀에 존재하는 보편적으로 발현되는 유형 III 막 단백질입니다19.

Mature lysosomes have an acidic internal pH, at which the lysosomal hydrolases are active, and a lining known as a glycocalyx that protects the internal lysosomal perimeter from the acidic environment of the lumen5,8,20. This acidic environment is maintained through the activity of a vacuolar-type proton adenosine triphosphatase (v-ATPase), which harnesses energy from hydrolysing ATP to drive the translocation of protons through a V0 membrane domain (reviewed elsewhere5,21). Other key lysosomal proteins include structural proteins such as lysosome-associated membrane protein 1 (LAMP1); proteins involved in trafficking and fusion, such as soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and RAB GTPases; transporters such as LAMP2A, which has a key role in chaperone-mediated autophagy (CMA); and ion channels such as the chloride channel ClC7 and the cation channel mucolipin 1, a member of the transient receptor potential (TRP) family that is also known as TRPML1 (refs22,23). Most of the proteins are delivered through the clathrin adaptor protein 3-alkaline phosphatase (ALP) pathway, but some proteins are translocated through the lysosome-associated-protein transmembrane-5, a protein that is preferentially expressed in immune cells3,24.

성숙한 리소좀은

리소좀 가수분해 효소가 활성 상태를 유지하는 산성 내부 pH를 가지고 있으며,

내부 리소좀 경계를 산성 환경으로부터 보호하는 글리코칼릭스라는 내벽을 갖추고 있습니다5,8,20.

이 산성 환경은

리소좀-형 프로톤 아데노신 삼인산 분해효소(v-ATPase)의 활성을 통해 유지됩니다.

이 효소는

ATP 가수분해로부터 에너지를 얻어

V0 막 영역을 통해 프로톤을 이동시킵니다(기타 문헌 참조5,21).

다른 주요 리소좀 단백질에는

구조 단백질인 리소좀 연관 막 단백질 1(LAMP1);

수송 및 융합에 관여하는 단백질인 용해성 N-에틸말레이미드 감수성 인자 부착 단백질 수용체(SNAREs RAB GTPase; 수송체인 LAMP2A, 는 샤페론 매개 자가포식 (CMA)에서 중요한 역할을 합니다.

그리고

염소 이온 채널 ClC7 및 양이온 채널 뮤코리핀 1과 같은 이온 채널도 있습니다.

뮤코리핀 1은 TRPML1이라고도 알려진

일시적 수용체 잠재력 (TRP) 계열에 속합니다 (참조 22,23).

대부분의 단백질은

클라트린 어댑터 단백질 3-알칼리성 포스파타제(ALP) 경로를 통해 전달되지만,

일부 단백질은 면역 세포에서 주로 발현되는 리소좀 관련 단백질 막을 통과하는 5번 단백질을 통해 전달됩니다3,24.

.

Although the concept still remains controversial, two lysosome species — conventional or secretory — are often distinguished based on their physical, biochemical and functional properties. Catabolism is the main function of conventional lysosomes, and several other lysosome-related organelles (LROs), such as melanosomes, the late endosomal major histocompatibility complex class II (MHCII) compartment (MIIC), lytic granules from neutrophils, eosinophils, basophils, mast cells, CD8+ T cells and platelets, complement these functions8,25–29. Many of the LROs act as professional secretory organelles. LROs share with lysosomes the majority of typical characteristics (acidic environment, lysosomal transmembrane proteins, fusion property to phagosomes and others), in addition to particular properties resulting from their specific cargoes (for example, melanosomes contain melanosome-specific transmembrane glycoprotein, and natural killer cells and CD8+ T cells contain perforins and granzymes). The detailed mechanisms of biogenesis and secretion of LROs remain unclear, although it is known that genetic defects in LROs are involved in rare autosomal recessive disorders characterized by reduced pigmentation, such as Chediak–Higashi disease and Hermansky–Pudlak syndrome30. Secretory lysosomes contain many more proteins in addition to those contained in conventional lysosomes, and they participate in multiple cell functions such as plasma membrane repair, tissue and bone regeneration, apoptotic cell death, cholesterol homeostasis, pathogen defence and cell signalling8.

Lysosomal biogenesis and function are regulated by the basic helix–loop–helix leucine zipper transcription factor EB (TFEB) and the coordinated lysosomal expression‎ and regulation (CLEAR) network4,31,32 (Fig. 2). For example, autophagy, a crucial process in immunity and autoimmunity33, is transcriptionally regulated by TFEB31. Interestingly, lysosomal exocytosis, which is important in many immune functions, also depends on TFEB activation31,32. Moreover, it has been demonstrated that TFEB orchestrates lysosomal Ca2+ signalling34. The fact that multiple lysosomal processes are dependent on TFEB activation strengthens its role as a master regulator in lysosomal functions. Like other transcription factors, TFEB undergoes phosphorylation and dephosphorylation via different cytosolic and lysosomal pathways (Fig. 2), processes regulated by mechanistic target of rapamycin complex 1 (mTORC1), a master controller of cell growth35,36.

이 개념은 여전히 논란의 여지가 있지만,

물리적, 생화학적 및 기능적 특성에 따라

두 가지 유형의 리소좀(전통적 또는 분비형)이 구분됩니다.

전통적 리소좀의 주요 기능은 분해이며,

멜라노좀, 후기 엔도소체 주요 조직 적합성 복합체 II(MHCII) 구역(MIIC),

중성구, 호산구, 기저구, 비만세포, CD8+ T 세포 및 혈소판에서 발견되는 용해 소체 등

여러 리소좀 관련 소기관(LROs)이 이 기능을 보완합니다8,25–29.

많은 LRO는 전문 분비 소기관으로 작용합니다. LRO는 리소좀과 대부분의 일반적인 특성(산성 환경, 리소좀 막 단백질, 파고소체와의 융합 특성 등)을 공유하며, 특정 화물에서 비롯된 독특한 특성을 추가로 가지고 있습니다(예: 멜라노소메는 멜라노소메 특이적 막 단백질을 포함하며, 자연살해 세포와 CD8+ T 세포는 퍼포린과 그라니메인을 포함합니다). LRO의 생성과 분비 메커니즘은 아직 명확히 밝혀지지 않았지만, LRO의 유전적 결함이 체다이크-히가시 병과 헤르만스키-푸들락 증후군과 같은 희귀한 상염색체 열성 질환에 관여한다는 것은 알려져 있습니다. 이러한 질환은 색소 감소 증상을 특징으로 합니다.30 분비 리소좀은 전통적인 리소좀에 포함된 단백질보다 훨씬 많은 단백질을 포함하며, 세포막 수리, 조직 및 뼈 재생, 세포 사멸, 콜레스테롤 균형, 병원체 방어 및 세포 신호전달 등 다양한 세포 기능에 참여합니다8.

리소좀의 생성과 기능은 기본 헬릭스-루프-헬릭스 류신 지퍼 전사 인자 EB (TFEB)와 조율된 리소좀 발현 및 조절 (CLEAR) 네트워크에 의해 조절됩니다4,31,32 (그림 2).

예를 들어, 면역 및 자가 면역에 중요한 과정인 자가포식33은 TFEB에 의해 전사적으로 조절됩니다31. 흥미롭게도, 여러 면역 기능에 중요한 리소좀의 세포외 분비도 TFEB의 활성화에 의존합니다31,32. 또한, TFEB가 리소좀의 Ca2+ 신호 전달을 조율한다는 것이 입증되었습니다34. 여러 리소좀 과정이 TFEB 활성화에 의존한다는 사실은 TFEB가 리소좀 기능의 주요 조절자 역할을 강화합니다. 다른 전사 인자와 마찬가지로 TFEB는 세포질과 리소좀 경로를 통해 인산화 및 탈인산화 과정을 거칩니다(그림 2), 이 과정은 세포 성장의 주요 조절자인 기계적 표적 라파마이신 복합체 1(mTORC1)에 의해 조절됩니다35,36

Fig. 2. Lysosomal molecular sites and processes as possible targets for therapeutic strategies.

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After their synthesis in the rough endoplasmic reticulum (RER), the substrates (cargo) that are intended to be degraded through the endo-lysosomal pathway are transported to lysosomes via the trans-Golgi network (TGN). Among the key enzymatic systems that are involved in the lysosomal enzyme transportation of cargos from Golgi to lysosomes, the best studied is the mannose-6-phosphate (M6P) receptor (MPR) system, which binds newly synthesized lysosomal hydrolases in the TGN and delivers them to pre-lysosomal compartments. A few components synthesized in the late Golgi compartment are delivered directly to lysosomes via the 3-alkaline phosphatase (ALP) pathway. Lysosomal components, such as enzymes (lytic enzymes and kinases), membrane-bound proteins/complexes (mechanistic target of rapamycin (mTOR)), transporters and ion channels (vacuolar-type proton adenosine triphosphatase (v-ATPase), TRPML1 and osteopetrosis associated transmembrane protein 1 (Ostm1)) and chaperone-mediated transportation are the best-known targeting sites for lysosomal dysfunction. As depicted in the figure, many pharmacological antagonists and agonists exert activities that potentially correct lysosomal dysfunction and therefore represent potential effective pharmacological tools. CLEAR, coordinated lysosomal expression‎ and regulation; CQ, chloroquine; HCQ, hydroxychloroquine; mTORC1, mTOR complex 1; PtdIns(3,5)P2, phosphatidylinositol-3,5-bisphosphate; RAPTOR, regulatory-associated protein of mTOR; SER, smooth endoplasmic reticulum; TFEB, transcription factor EB.

거친 내소체(RER)에서 합성된 후, 내소체-리소좀 경로를 통해 분해될 예정인 기질(화물)은 트랜스 골지 네트워크(TGN)를 통해 리소좀으로 운반됩니다. 골지체에서 리소좀으로 화물을 운반하는 리소좀 효소 운반 시스템 중 가장 잘 연구된 것은 TGN에서 새롭게 합성된 리소좀 가수분해 효소를 결합하고 이를 전리소좀 구역으로 전달하는 만노스-6-인산(M6P) 수용체(MPR) 시스템입니다. 골지체 후기 구역에서 합성된 일부 성분은 3-알칼리 포스파타제(ALP) 경로를 통해 직접 리소좀으로 전달됩니다. 리소좀 구성 요소로는 효소(리틱 효소 및 키나제), 막 결합 단백질/복합체(mTOR), 운반체 및 이온 채널(v-ATPase, TRPML1, Ostm1) 등이 있습니다. 및 분자 샤페론 매개 수송은 리소좀 기능 장애의 가장 잘 알려진 표적 부위입니다. 그림에서 보여지듯이, 많은 약리학적 길항제와 작용제는 리소좀 기능 장애를 잠재적으로 교정하는 활동을 발휘하며 따라서 잠재적으로 효과적인 약리학적 도구로 작용할 수 있습니다.

CLEAR, 리소좀의 명확하고 조율된 발현 및 조절; CQ, 클로로퀸; HCQ, 하이드록시클로로퀸; mTORC1, mTOR 복합체 1; PtdIns(3,5)P2, 포스파티딜이노시톨-3,5-비스포스페이트; RAPTOR, mTOR의 조절 관련 단백질; SER, 평활 소포체; TFEB, 전사 인자 EB.

Lysosomes are at the crossroads of various degradative pathways, including endocytosis (phagocytosis) and autophagy (Fig. 1). Three main forms of autophagy have been described: macroautophagy (the most extensively characterized form), microautophagy and CMA. At the initiation of macroautophagy, a double-membrane sequestering compartment termed the phagophore, which contains cytoplasmic material, is formed and matures into a vesicle called the autophagosome. The cargo is degraded into vacuoles issued from the fusion of autophagic vesicles and lysosomes (called autolysosomes), and the resulting short products are released back into the cytosol for reuse or, according to sometimes contested observations, possibly dispatched into the MIIC for ultimate processing and MHCII molecule loading for presentation to CD4+ T cells37,38. In contrast to macroautophagy, microautophagy is characterized by direct lysosomal engulfment of cytosolic material into lysosomes, via the formation of characteristic invaginations of the lysosomal membrane. The third major form of autophagy is CMA, which involves the recognition of substrate proteins containing a KFERQ-like motif by a HSPA8/HSC70-containing complex (Fig. 1b). In CMA, two proteins have a key role: HSPA8 ensures the selectivity of proteins, which will be degraded via the CMA pathway; and LAMP2A translocates the targeted cytosolic proteins across the lysosomal membrane (reviewed elsewhere7). The terminal step of autophagy is called autophagic lysosome reformation, in which tubular proto-lysosomes are extruded from autolysosomes (containing lysosomal membrane components) and mature into functional lysosomes39. This step is not solely a lysosomal biogenesis process; it also includes a series of elements that are tightly correlated with the regulation of autophagy40.

리소좀은

세포 내 삼투 (식세포 작용) 및 자가포식 (그림 1)을 비롯한 다양한 분해 경로의 교차점에 위치합니다.

자가포식에는 세 가지 주요 형태가 있습니다: 

거대자가포식 (가장 널리 알려진 형태),

미세자가포식 및 CMA.

대식작용의 초기 단계에서,

세포질 물질을 포함하는 이중막 격리 구역인 파고포어가 형성되고,

이는 자식소체라고 불리는 소포로 성숙합니다.

a double-membrane sequestering compartment termed the phagophore, which contains cytoplasmic material, is formed and matures into a vesicle called the autophagosome.

화물은

오토파고소체와 리소좀의 융합으로 형성된 오토리소좀(autolysosome)에서 소포체로 분해되며,

생성된 짧은 분자는 재사용을 위해 세포질로 방출되거나,

때로는 논란의 여지가 있는 관찰에 따르면 MIIC로 전달되어 최종 처리 및 MHCII 분자 부하를 통해

CD4+ T 세포에 제시될 수 있습니다37,38.

fusion of autophagic vesicles and lysosomes (called autolysosomes), and the resulting short products are released back into the cytosol for reuse or, according to sometimes contested observations, possibly dispatched into the MIIC for ultimate processing and MHCII molecule loading for presentation to CD4+ T cells.

거대자가포식과는 달리,

미세자가포식은 리소좀 막의 특징적인 함입 형성을 통해

세포질 물질이 리소좀으로 직접 포획되는 것이 특징입니다.

자가포식의 세 번째 주요 형태는 CMA로,

HSPA8/HSC70을 포함하는 복합체에 의해 KFERQ와 유사한 모티프를 포함하는

기질 단백질이 인식되는 과정이 포함됩니다(그림 1b).

CMA에서 두 가지 단백질이

핵심 역할을 합니다:

HSPA8은 CMA 경로를 통해 분해될 단백질의 선택성을 보장하며,

LAMP2A는 표적 세포질 단백질을 리소좀 막을 통해 이동시킵니다(기타 문헌 참조7).

자가포식의 마지막 단계는

자가포식 리소좀 재형성이라고 불리며,

이 단계에서 관형 원시 리소좀이 오토리소좀(리소좀 막 성분을 포함)에서 배출되어

기능적인 리소좀으로 성숙합니다39.

In combination with autophagy, lysosomes are involved in both innate and adaptive immune functions, including foreign material recognition (bacterial, parasitic and viral), activation of pattern recognition receptors (such as Toll-like receptors (TLRs) and nucleotide oligomerization domain-like receptor), antigen processing and presentation, especially in the context of MHCII molecules, T cell homeostasis, antibody production and induction of various immune signals (co-stimulation and cytokine secretion)41. Besides being a degradative organelle, the lysosome has recently been recognized as a cellular signalling platform3,42. It plays an important role in nutrient sensing through mTORC1 and other additional protein complexes, or the so-called ‘lysosome nutrient sensing machinery’. The discovery of a stress-induced lysosome-to-nucleus signalling mechanism through TFEB further supports the key role of lysosomes in cellular signalling36.

이 단계는

리소좀 생합성 과정에 그치지 않고,

자가포식 조절과 밀접하게 관련된 일련의 요소들도 포함합니다40.

자가포식과 함께 리소좀은

이물질 인식(박테리아, 기생충 및 바이러스),

패턴 인식 수용체(Toll-like receptor (TLR) 및 뉴클레오티드 올리고머화 도메인-like receptor 등)의 활성화,

항원 처리 및 제시(특히 MHCII 분자,

T 세포의 항상성, 항체 생산 및 다양한 면역 신호 유도(공극 자극 및 사이토킨 분비)41.

분해 기관으로서의 역할 외에도,

리소좀은 최근 세포 신호 전달 플랫폼으로 인정받았습니다3,42.

foreign material recognition (bacterial, parasitic and viral),

activation of pattern recognition receptors (such as Toll-like receptors (TLRs) and

nucleotide oligomerization domain-like receptor),

antigen processing and presentation,

especially in the context of MHCII molecules,

T cell homeostasis, antibody production and induction of various immune signals

(co-stimulation and cytokine secretion)

이는 mTORC1 및 기타 추가 단백질 복합체를 통해

영양소 감지에 중요한 역할을 하며,

이른바 ‘리소좀 영양소 감지 기계’로 알려져 있습니다.

‘lysosome nutrient sensing machinery

TFEB를 통한 스트레스 유발 리소좀-핵 신호 전달 메커니즘의 발견은

리소좀이 세포 신호 전달에서 핵심적인 역할을 한다는 것을 더욱 뒷받침합니다36.

Lysosome dysfunction in diseases

The lysosome occupies a central position in the maintenance of cellular homeostasis, being involved in the exclusion of infectious agents from penetrating host tissue and concomitantly promoting immune regulation. Lysosomes must therefore be able to respond quickly, with increased or decreased functions, to various metabolic conditions aimed at protecting cells from death or damage. Lysosomes are very diverse in size and shape. For reasons that are not totally understood — possibly according to their position in the cytosol43 and/or their composition — some lysosomes in a single cell are more prone to act and defend cells. Given the wide range of functions of lysosomes in all metabolic compartments of the cell, any dysregulation of their activity could lead to the impairment of various elements of the cellular metabolic machinery (including the transport and biogenesis of sugar (glycolysis), lipids, proteins and nucleic acids) and of metabolic pathways, phagocytosis, endocytosis and autophagy. Although the underlying mechanisms are far from being fully deciphered, it has been seen that lysosomal dysfunction or defects in fusion with vesicles containing cargo are commonly observed abnormalities in proteinopathic neurodegenerative diseases. Dysfunctions of lysosomes can affect the proper activity of other organelles such as peroxisomes and mitochondria, leading to excessive production of reactive oxygen species with pathological features associated with ageing, cancer, chronic inflammation, neurological diseases, male infertility and infections.

Such dysregulation is thus central to LSDs, and also implicated in a wide range of other disorders, including autoimmune and neurological disorders, in which the autophagy–lysosomal network under the control of TFEB has attracted considerable attention.

질병에서의 리소좀 기능 장애

리소좀은

세포 내 항상성 유지에 중심적인 역할을 하며,

감염성 인자가 호스트 조직에 침투하는 것을 차단하고 동시에 면역 조절을 촉진합니다.

따라서

리소좀은 세포를 죽음이나 손상으로부터 보호하기 위해

다양한 대사 조건에 신속히 대응하여 기능이 증가하거나 감소해야 합니다.

리소좀은

크기와 모양이 매우 다양합니다.

아직 완전히 이해되지 않은 이유 — 아마도 세포질 내 위치43과/또는 구성에 따라 —

단일 세포 내 일부 리소좀은

세포를 보호하고 방어하는 데 더 취약합니다.

세포의 모든 대사 구획에서 리소좀이 수행하는 기능의 범위가 광범위하기 때문에,

리소좀의 활동이 조절되지 않으면

세포 대사 기전(당(글리코리시스)의 수송 및 생합성, 지질, 단백질 및 핵산 등)과 대사 경로,

식세포 작용, 세포 내 흡수 및 자가포식 등 다양한 요소가 손상될 수 있습니다.

기본 메커니즘은 아직 완전히 규명되지 않았지만,

리소좀 기능 장애나 화물 함유 소체와의 융합 결함은

단백질 병리성 신경퇴행성 질환에서 흔히 관찰되는 이상 현상입니다.

리소좀 기능 장애는

과산화체와 미토콘드리아와 같은 다른 세포 소기관의 정상적인 활동을 방해하여

노화, 암, 만성 염증, 신경 질환, 남성 불임, 감염과 관련된 병리적 특징을 가진

활성 산소 종의 과도한 생산을 유발할 수 있습니다.

따라서 이러한 조절 장애는

LSD의 핵심적인 요소이며,

TFEB의 제어 하에 있는 자가포식-리소좀 네트워크가 주목을 받고 있는

자가면역 및 신경계 질환을 비롯한 다양한 다른 질환에도 관련이 있습니다.

Lysosomal storage disorders

LSDs are a heterogeneous group of about 50 inherited metabolic disorders, which have an incidence of ~1 in 5,000 live births44. These disorders and their treatment have been reviewed extensively elsewhere45,46, and so will only be covered relatively briefly here. The mutations responsible for most LSDs have been largely elucidated (Tables 1,2), and many result in the dysfunction of a particular lysosomal hydrolase, leading to the accumulation of the substrate of that hydrolase. For example, in Gaucher disease, the sphingolipid glucocerebroside accumulates in cells (particularly macrophages) and organs, including the liver and spleen, owing to deficiency in the enzyme GCase24,66. In certain LSDs, the resultant pathology can be explained by the nature of molecules that accumulate (Tables 1,2). Thus, the abundance of cerebrosides and gangliosides that deposit in the central nervous system (CNS) of patients with sphingolipid storage disorders, such as type II (acute infantile neuronopathic) Gaucher disease, underlies the severe neurological symptoms of such disorders67,68. In patients with Pompe disease, which is caused by α-glucosidase deficiency, the high levels of non-degraded glycogen that accumulate in muscles could explain the observed myopathy69,70. However, how the undegraded material accumulates and causes the observed cellular and organ pathology in many other LSDs remains unclear.

리소좀 축적 장애

LSD는 약 50개의 유전성 대사 장애로 구성된 이질적인 그룹으로, 생아 5,000명 중 약 1명의 비율로 발생합니다44. 이 질환과 그 치료법은 다른 문헌에서 광범위하게 검토되었으며45,46, 여기서는 상대적으로 간략히만 다룰 것입니다. 대부분의 LSD를 유발하는 돌연변이는 대부분 규명되었으며(표 1,2),

많은 경우 특정 리소좀 가수분해 효소의 기능 장애를 초래하여

해당 효소의 기질 축적을 유발합니다.

예를 들어,

Gaucher 병에서는 GCase24,66 효소의 결핍으로 인해

스핑고리피드인 글루코세레브로사이드가 세포(특히 대식세포)와 간, 비장 등 장기에 축적됩니다.

일부 LSD에서는 축적되는 분자의 특성으로 인해 발생하는 병리학적 변화가 설명될 수 있습니다(표 1,2).

예를 들어,

스핑고리피드 저장 장애(예: 유형 II(급성 영아 신경병증형) Gaucher 병) 환자의

중추 신경계(CNS)에 축적되는 세레브로사이드와 간글리오사이드의 풍부함이

이러한 장애의 심각한 신경학적 증상을 설명합니다67,68.

포메 병(α-글루코시다아제 결핍으로 인한 질환) 환자의 경우,

근육에 축적되는 비분해된 글리코겐의 높은 수준이 관찰된 근육병을 설명할 수 있습니다69,70.

그러나

다른 많은 LSD에서 분해되지 않은 물질이 어떻게 축적되어 관찰된

세포 및 장기 병리를 유발하는지는 여전히 명확하지 않습니다.

Table 1.

Approved enzyme replacement therapies for lysosomal storage disorders

Lysosomal storage disorderDefective enzymeEnzyme replacement therapies

Type 1 Gaucher disease	β-GCase	Imiglucerase, velaglucerase alfa and taliglucerase alfa
Fabry disease	α-Galactosidase A	Agalsidase beta and agalsidase alfa
Late infantile neuronal ceroid lipofuscinosis type 2 (CLN2 disease)	Tripeptidyl-peptidase 1	Cerliponase alfa
MPS I (Hurler–Scheie and Scheie syndromes)	α-Iduronidase	Laronidase
MPS II (Hunter syndrome)	Iduronidase-2-sulfatase	Idursulfase and idursulfase beta
MPS IV (Morquio syndrome A)	N-acetylgalactosamine-6-sulfate sulfatase	Elosulfase
MPS VI (Maroteaux–Lamy syndrome)	N-acetylgalactosamine-4-sulfatase (arylsulfatase B)	Galsulfase
MPS VII (Sly syndrome)	β-Glucoronidase	Vestronidase alfa
Pompe disease	α-Glucosidase	Alglucosidase alfa
Wolman disease	Lysosomal acid lipase deficiency	Sebelipase alfa

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GCase, glucocerebrosidase; MPS, mucopolysaccharidosis.

Table 2.

Selected diseases associated with lysosomal dysfunction

DiseaseLysosomal dysfunctionObservations/comments

Lysosomal storage disordera
Aspartylglucosaminuria	Aspartylglucosaminidase	Accumulation of unmodified aspartylglucosamine in lysosomes cause progressive mental health problems with skeletal and connective tissue abnormalities in humans45,46
α-Mannosidosis	α-d-Mannosidase	Caused by genetic mutation in the gene MAN2B1 (ref.47)
		Reduction of α-d-mannosidases causes reduced lysosomal breakdown of mannose-based oligosaccharides in many tissues47
		Inherited LSD characterized by immune deficiency (susceptibility to infections including pulmonary infections), facial and skeletal abnormalities, hearing impairment and intellectual deficit47
Fabry disease	α-Galactosidase	Reduced lysosomal metabolism of α-galactosyl lipids, globotriaosylceramides, causes vascular diseases (cardio, cerebro and renal diseases) in patients45,46
Gaucher disease (types 1, 2 and 3)	β-GCase	Accumulation of glucosylceramides in leukocytes (especially in macrophages) leads to abnormalities in the visceral organs (type 1) and neurological defects in both children and adults (types 2 and 3)45,46
GM1 gangliosidosis	β-Galactosidase	Abnormal lysosomal storage of GM1-ganglioside (oligosaccharides) causes skeletal manifestations and neurological impairment in humans45,46
Krabbe disease (globoid cell leukodystrophy)	Galactocerebrosidase	Defects in the galactocerebrosidase provoke accumulation of galactosylceramide and galactosylsphingosine (psychosine). Patients’ brain histology shows myelin loss, neuroinflammation and axonal degeneration48
Metachromatic leukodystrophy	Arylsulfatase A or saposin-B (activator protein; rare cases)	Defects in the enzymes lead to the accumulation of sulfogalactosylceramide in major organs. It affects the different age groups of humans with development signs and symptoms of the disease45,46
Mucopolysaccharidoses	Enzymes involved in mucopolysaccharide catabolism	Accumulation of mucopolysaccharides within lysosomes leads to skeletal and joint abnormalities in humans45,46
Multiple sulfatase deficiency	SUMF1 (formylglycine-generating enzyme needed to activate sulfatases)	Abnormal accumulation of multiple, including sulfated, glycosaminoglycans causes neurodegeneration and psychomotor retardation in humans49
Pompe disease	α-Glucosidase	Accumulated undegraded glycogen in the muscles and peripheral nerves was observed in humans45,46
Sandhoff disease	β-Hexosaminidase A and B	Enzyme defects cause GM2-ganglioside accumulation in lysosomes, which induces nervous system damage in humans45,46
Mucolipidosis (type II and III)	N-acetyl glucosamine phosphoryl transferase α/β	Enzyme deficiency results in accumulation of unphosphorylated glycoproteins, which causes motor function and neurological disorders in humans45
Mucolipidosis IV	Mucolipin-I	Defects in this lysosomal membrane protein (Ca2+ channel) cause accumulation of mucopolysaccharides and lipids, thereby resulting in hepatosplenomegaly, dysmorphic features and neurological disorders in humans45
Cystinosis	Cystinosin (cysteine transporter)	Defects in this lysosomal transporter, cystinosin, cause accumulation of cystine in different organs, first in kidneys and later in other organs in humans45,46
Danon disease	LAMP2	Defects in LAMP2 (especially LAMP2B) cause accumulation of glycogen and other autophagic components in cardiomyocytes of humans, which results in cardiac diseases50
		LAMP2B is highly expressed in the brain, cardiac and skeletal muscles51
Free sialic acid storage disorder	Sialin	Defects in this sialic acid transporter cause accumulation of free sialic acid in organs, which ultimately leads to different disorders (muscular, cerebellar, CNS and other) in humans52
NPC1	Membrane protein involved in lipid transport	Defects in Niemann–Pick C1 and C2 proteins lead to accumulation of cholesterol and glycosphingolipids in lysosomes and cause hepatic, pulmonary and neuropsychiatric disorders in humans45,46
NPC2	Soluble cholesterol-binding protein
Autoimmune diseases
SLE	Lysosomal maturation	Lysosome fragility in humans was observed53
		Macrophages with impaired lysosomal maturation were observed in lupus (MRL/lpr) mice54
SjS	Abnormal elevated levels of lysosomal enzymes (glycosidases and proteases)	Observed in the leukocytes of patients with SjS55
		Defective autophagy processes observed in SGs of MRL/lpr mice56
Crohn’s disease	Abnormal lysosomal pH	Deregulation of proton-sensing G protein-coupled receptor (GPR65) was observed in both mice and human57
Rheumatoid arthritis	Lysosomal hydrolases	In humans, different cathepsins, acid phosphatases and others are involved in the inflammation and joint damage58
CIDP	Alterations in the lysosomal CMA pathway	Increased LAMP2A expression‎ was observed in mice sciatic nerves59
Multiple sclerosis	Lysosomal acidification	Defects in the lysosomal compartment lead to defects in lipid droplet degradation in human neuronal cells60
ALS	Defects in endo-lysosomal trafficking	Spinal cord motor neurons of sporadic patients with ALS were shown positive for autolysosomal inclusions61
		Mouse spinal cord motor (hSOD1G93A)-mimicking human disease model showed lysosomal defects and impaired mitophagy61
Neurodegenerative diseases
Alzheimer disease	Unbalanced lysosomal luminal pH	In humans, defective presenilin-1 dependent v-ATPase function was observed in the case of lysosomal acidification. Lysosomal non-specific cathepsins generate the β-amyloid protein and hyperphosphorylated tau proteins62,63
Parkinson disease	Alterations in the lysosomal CMA pathway	Selective loss of GCase in lysosomes relates to the decreased amount of LAMP2A and increased cathepsins A and D in humans64
Huntington disease	Alterations in the lysosomal transport pathway	Polyglutamine-expanded huntingtin protein accumulation changes the lysosomal enzyme activity and TFEB expression‎ in mice. In addition, accumulation of lipofuscin (non-degradable intra-lysosomal polymer) in neuronal lysosomes prevents clearance65

아스파르틸글루코사미누리아 아스파르틸글루코사미나아제 리소좀 내 미변화 아스파르틸글루코사민의 축적은 인간에서 진행성 정신 건강 문제와 골격 및 결합 조직 이상을 유발합니다.45,46

α-만노시도시스 α-d-만노시다아제 MAN2B1 유전자 변이로 인해 발생합니다(참조47)

α-d-만노시다아제의 감소는 많은 조직에서 만노스 기반 올리고사카라이드의 리소좀 분해 감소로 이어집니다47

유전성 LSD 면역 결핍(폐 감염을 포함한 감염에 대한 취약성), 얼굴 및 골격 이상, 청력 장애 및 지적 장애를 특징으로 합니다47

파브리 병 α-갈락토시다제 α-갈락토실 지질 및 글로보트리아오실세라마이드의 리소좀 대사 감소로 인해 혈관 질환(심장, 뇌, 신장 질환)이 발생합니다45,46

가우처 병(1형, 2형, 3형) β-GCase 백혈구(특히 대식세포)에 글루코실세라마이드가 축적되어 내장 기관의 이상(1형) 및 어린이와 성인 모두에서 신경학적 결손(2형 및 3형)을 유발합니다45,46

GM1 간글리오시도시스 β-갈락토시다아제 GM1-간글리오시드(올리고사카라이드)의 리소좀 내 비정상적 축적은 인간에서 골격 이상과 신경학적 장애를 유발합니다45,46

크라브병 (글로보이드 세포 백질 이영양증) 갈락토세레브로시다아제 갈락토세레브로시다아제의 결함은 갈락토실세라마이드와 갈락토실스핑고신(사이코신)의 축적을 유발합니다. 환자의 뇌 조직학은 마이엘린 손실, 신경염증 및 축삭 퇴행을 보여줍니다48

메타크로마틱 백질 이영양증 아릴설파타제 A 또는 사포신-B(활성 단백질; 드문 사례) 해당 효소의 결함은 주요 장기에 설포갈락토실세라마이드의 축적을 유발합니다. 이는 인간의 다양한 연령층에서 질병의 발달 증상 및 증상을 나타냅니다45,46

뮤코다당체증 뮤코다당체 분해에 관여하는 효소 리소좀 내 뮤코다당체의 축적은 인간에서 골격 및 관절 이상을 유발합니다45,46

다중 설파타제 결핍 SUMF1 (설파타제를 활성화하는 포르밀글리신 생성 효소) 설포화 글리코사미노글리칸을 포함한 다중 글리코사미노글리칸의 비정상적 축적은 인간에서 신경퇴행과 운동 발달 지연을 유발합니다49

폼페 병 α-글루코시다제 근육과 말초 신경에 분해되지 않은 글리코겐이 축적되는 것이 인간에서 관찰되었습니다45,46

샌드호프 병 β-헥소사미나제 A 및 B 효소 결핍으로 리소좀 내 GM2-간글리오시드 축적이 발생하여 인간에서 신경계 손상을 유발합니다45,46

뮤코리피도시스 (형 II 및 III) N-아세틸 글루코사민 포스포릴 트랜스퍼레이즈 α/β 효소 결핍으로 인산화되지 않은 글리코프로틴이 축적되어 인간에서 운동 기능 및 신경학적 장애를 유발합니다45

뮤코리피도시스 IV 뮤코리핀-I 이 리소좀 막 단백질(Ca2+ 채널)의 결함은 뮤코다당류와 지질의 축적을 유발하여 인간에서 간비대, 기형적 특징 및 신경계 장애를 초래합니다45

시스티노시스 시스티노신(시스테인 운반체) 이 리소좀 운반체인 시스티노신의 결함은 다양한 장기에서 시스티인의 축적을 유발하며, 처음에는 신장에서 시작되어 이후 다른 장기에서도 발생합니다.45,46

다논 병 LAMP2 LAMP2(특히 LAMP2B)의 결함은 인간 심근 세포에서 글리코겐 및 기타 자식작용 성분의 축적을 유발하여 심장 질환을 초래합니다.50

LAMP2B는 뇌, 심장 및 골격근에서 고도로 발현됩니다51

자유 시알산 저장 장애 시알린 이 시알산 운반체 결함은 장기 내 자유 시알산의 축적을 유발하며, 이는 결국 인간에서 근육, 소뇌, 중추신경계 및 기타 장애를 초래합니다52

NPC1 지질 운반에 관여하는 막 단백질 니만-픽 C1 및 C2 단백질의 결함은 리소좀 내 콜레스테롤과 글리코스핑고리피드의 축적을 유발하며, 인간에서 간, 폐 및 신경정신과적 장애를 유발합니다45,46

NPC2 용해성 콜레스테롤 결합 단백질

자가면역 질환

SLE 리소좀 성숙 인간에서 리소좀의 취약성이 관찰되었습니다53

루푸스 (MRL/lpr) 마우스에서 리소좀 성숙 장애를 보이는 대식세포가 관찰되었습니다54.

SjS 리소좀 효소 (글리코시다아제 및 프로테아제)의 비정상적인 상승 SjS 환자의 백혈구에서 관찰됨55.

MRL/lpr 마우스의 SG에서 관찰된 자가포식 과정의 결함56.

크론병 리소좀 pH 이상 프로톤 감지 G 단백질 결합 수용체(GPR65)의 조절 장애가 쥐와 인간에서 모두 관찰됨57

류마티스 관절염 리소좀 가수분해 효소 인간에서 다양한 카테프신, 산성 인산분해효소 등이 염증과 관절 손상에 관여함58

CIDP 리소좀 CMA 경로의 변화 마우스의坐골 신경에서 LAMP2A 발현 증가가 관찰됨59

다발성 경화증 리소좀 산성화 인간 신경 세포에서 리소좀 부위의 결함이 지질 방울 분해 결함을 유발함60

ALS 엔도-리소좀 교통 장애 ALS 환자의 척수 운동 신경 세포에서 자식소체 포함물이 양성으로 확인됨61

인간 질환을 모방한 쥐의 척수 운동 신경 (hSOD1G93A) 모델에서 리소좀 결함과 미토파지 장애가 관찰되었습니다61

신경퇴행성 질환

알츠하이머 병 리소좀 내강 pH 불균형 인간에서 리소좀 산성화 시 프레세닐린-1 의존성 v-ATPase 기능 결함이 관찰되었습니다. 리소좀 비특이적 카테프신은 β-아밀로이드 단백질과 과인산화 타우 단백질을 생성합니다62,63

파킨슨병 리소좀 CMA 경로의 변화 인간에서 리소좀 내 GCase의 선택적 손실은 LAMP2A의 감소와 카테프신 A 및 D의 증가와 관련이 있습니다64

헌팅턴 병 리소좀 수송 경로의 변화 폴리글루타민 확장형 헌팅틴 단백질의 축적은 쥐에서 리소좀 효소 활성과 TFEB 발현을 변화시킵니다. 또한, 신경 세포 리소좀 내 비분해성 리포푸신(리소좀 내 폴리머)의 축적은 제거를 방해합니다65

This list is not exhaustive; it highlights representative families of pathological indications in which lysosomal dysfunctions have been described. ALS, amytrophic lateral sclerosis; CIDP, chronic inflammatory demyelinating polyneuropathy; CMA, chaperone-mediated autophagy; CNS, central nervous system; GCase, glucocerebrosidase; LAMP2, lysosome-associated membrane protein 2; LSD, lysosomal storage disorder; MRL, Murphy Roths Large; NPC, Niemann–Pick disease type C; SG, salivary gland; SjS, Sjögren’s syndrome; SLE, systemic lupus erythematosus; TFEB, transcription factor EB; v-ATPase, vacuolar-type proton adenosine triphosphatase. aThe presentation of the successive sections follows the text, namely, LSDs, autoimmune diseases and neurodegenerative diseases.

이 목록은 완전하지 않습니다. 이 목록은 리소좀 기능 장애가 보고된 병리적 증상의 대표적 가족을 강조합니다. ALS, 근위축성 측삭 경화증; CIDP, 만성 염증성 탈수초성 다발 신경병증; CMA, 샤페론 매개 자가포식; CNS, 중추 신경계; GCase, 글루코세레브로시다아제; LAMP2, 리소좀 관련 막 단백질 2; LSD, 리소좀 축적 장애; MRL, Murphy Roths Large; NPC, Niemann–Pick 질병 유형 C; SG, 타액선; SjS, 시그렌 증후군; SLE, 전신성 홍반성 루푸스; TFEB, 전사 인자 EB; v-ATPase, 소포형 프로톤 아데노신 삼인산 분해효소. a본문의 순서에 따라 각 섹션은 LSD, 자가면역 질환, 신경퇴행성 질환의 순으로 제시됩니다.

The accumulation of such undigested macromolecules or monomers in LSDs instigates the formation of secondary products, which ultimately escape from the endosomal–autophagic–lysosomal pathways9,71 and lead to multiple consequences that affect most organs, including the brain, liver, spleen, heart, eyes, muscles and bone (Table 2). Most, if not all, organelles are altered in LSDs, including endosomes, autophagosomes and lysosomes, and their functions in lysosomal formation/reformation and fusion of endosomes or autophagosomes to lysosomes are abnormal. Alterations in several autophagy processes have also been described in LSDs. Thus, deregulated mitophagy, which results in the accumulation of damaged mitochondria, occurs in LSDs, leading to major inflammatory consequences in specific tissues67,72. Perturbations in mitochondrial dynamics are frequently observed, which have been linked to the increased production of reactive oxygen species, ATP production and Ca2+ imbalance. In LSDs, reduced macroautophagy activity (with a decreased autophagic flux) rather than hyperactive autophagy processes, as seen in numerous autoimmune diseases, seems to be responsible for the accumulation of non-degraded cytoplasmic proteins such as α-synuclein, huntingtin (HTT) and others73. Mucolipidosis type IV (Table 2), a disease characterized by severe neurological and ophthalmological abnormalities, is caused by mutations in the MCOLN1 gene and is inherited in an autosomal recessive manner. This gene encodes a non-selective cation channel, mucolipin 1, which has recently been shown to be required for efficient fusion of both late endosomes and autophagosomes with lysosomes74,75. Impaired autophagosome degradation results in the accumulation of autophagosomes in LSDs76. Microautophagy processes that do not involve de novo synthesis of nascent vacuoles also appear to be impaired in LSDs, and were notably revealed in primary myoblasts from patients with the muscle-wasting condition Pompe disease77. Finally, defective CMA components, such as LAMP2A, could also lead to lysosomal dysfunction. For example, mutations in the LAMP2 gene have been claimed to cause Danon disease (inherited in an X-linked dominant pattern)51. Further investigations are needed to support this assertion.

LSD에서 이러한 소화되지 않은 거대 분자나 단량체의 축적은

2차 생성물의 형성을 유발하며,

이는 결국 엔도소체-자식소체-리소소체 경로를 벗어나9,71

뇌, 간, 비장, 심장, 눈, 근육 및 뼈를 포함한 대부분의 장기에 영향을 미치는

다양한 결과를 초래합니다(표 2).

endosomal–autophagic–lysosomal pathways

https://www.nature.com/articles/cdd2008168

엔도좀, 자가포식소체, 리소좀을 비롯한 대부분의 세포 소기관이

LSD에서 변형되며,

리소좀 형성/재형성 및 엔도좀 또는 자가포식소체가 리소좀으로 융합되는 기능에

이상이 생깁니다.

endosomes, autophagosomes and lysosomes

LSD에서는 여러 자가포식 과정의 변화도 보고되었습니다.

따라서,

손상된 미토콘드리아의 축적을 초래하는 조절 장애된 미토파지가 LSD에서 발생하며,

이는 특정 조직에서 주요 염증성 결과를 초래합니다67,72.

미토콘드리아 동역학의 장애가 자주 관찰되며,

이는 활성 산소 종의 증가, ATP 생산 및 Ca2+ 불균형과 연관되어 있습니다.

LSD에서는,

수많은 자가면역질환에서 볼 수 있는 자가포식 과정의 과잉 활동보다는,

거대자가포식 활동의 감소(자가포식 플럭스의 감소)가

α-시누클레인, 헌팅틴 (HTT) 등 분해되지 않은 세포질 단백질의 축적의 원인이 되는 것으로 보입니다73.

Mucolipidosis type IV(표 2)는 심각한 신경학적 및 안과적 이상을 특징으로 하는 질환으로, MCOLN1 유전자 변이로 인해 발생하며 상염색체 열성 유전 방식으로 유전됩니다. 이 유전자는 비선택적 양이온 채널인 뮤코리핀 1을 암호화하며, 최근에 후기 소포체와 오토파고좀이 리소좀과 효율적으로 융합하는 데 필요한 것으로 밝혀졌습니다74,75. 오토파고좀 분해 장애는 LSD에서 오토파고좀의 축적을 초래합니다76. 신생 소포의 신규 합성을 포함하지 않는 미세 자식작용 과정도 LSD에서 손상된 것으로 나타났으며, 근육 위축 질환인 포메 병 환자의 원발성 근모세포에서 특히 밝혀졌습니다77.

마지막으로,

LAMP2A와 같은 CMA 구성 요소의 결함도 리소좀 기능 장애를 유발할 수 있습니다.

예를 들어,

LAMP2 유전자 변이가 X-연관 우성 유전 패턴으로 유전되는 Danon 질환을 유발한다는 주장이 제기되었습니다51.

이 주장을 뒷받침하기 위해 추가 연구가 필요합니다.

Autoimmune disorders

Lysosomes are involved in pathways central to the immune system, including the degradation of intracellular and extracellular material, plasma membrane repair, cell death signalling, cell homeostasis and death. Although the direct involvement of lysosomes in immunity is far from fully understood, it has long been expected that lysosome dysfunction will have a major impact in immune diseases (Table 2). Strikingly, however, this field has not been extensively explored. However, elevated levels of lysosomal enzyme activity have been reported to occur in several autoimmune diseases, such as RA, systemic lupus erythematosus (SLE), dermatomyositis and psoriasis3,14,17,18,20–23.

As discussed, autophagosomes formed during the autophagy process must fuse with lysosomes to generate peptide epitopes for further processing, clear possibly deleterious apoptotic debris, fuel the amino acid pool and produce energy (Fig. 1). Any deviation in this complex processing will affect crucial immune cell functions, such as the control of cytokine release, autoimmune cell anergy and programmed cell death of type I (apoptosis) and type II (autophagy). Secretory lysosomes regulate the release of both pro-inflammatory and anti-inflammatory cytokines, in a process that is dependent on the type of stimulation. In addition, lysosomes degrade glucocorticoid receptors, which are essential to bind glucocorticoids, although the reasons are not known78. In this complex system, lysosomes execute anti-inflammatory action via the phospholipase A2 and cyclooxygenase-2 pathways, and also induce inflammation through the IL-1β–caspase-1 pathway. In both conditions (pro-inflammatory and anti-inflammatory), lysosomes act as indirect precursors for autoimmunity. However, induction and suppression of inflammatory signals are stimulus dependent78.

자가면역 질환

리소좀은

세포 내외 물질의 분해, 세포막 수리, 세포 사멸 신호전달, 세포 항상성 및 사멸과 같은

면역 체계의 핵심 경로에 관여합니다.

리소좀의 면역 체계에 대한 직접적인 역할은 아직 완전히 이해되지 않았지만,

리소좀 기능 장애가 면역 질환에 큰 영향을 미칠 것으로 오랫동안 예상되어 왔습니다(표 2).

그러나

이 분야는 아직 충분히 탐구되지 않았습니다.

그럼에도 불구하고

류마티스 관절염(RA), 전신성 홍반성 루푸스(SLE), 피부근육염 및 건선과 같은

여러 자가면역 질환에서 리소좀 효소 활성도가 증가했다는 보고가 있습니다3,14,17,18,20–23.

앞서 설명한 바와 같이,

자가포식 과정에서 형성된 자식포는 리소좀과 융합하여

추가 처리를 위한 펩티드 에피토프를 생성하고,

유해할 가능성이 있는 세포 사멸 잔해를 제거하며,

아미노산 풀에 연료를 공급하고 에너지를 생성해야 합니다(그림 1).

이 복잡한 처리 과정에 어떤 편차가 발생하면

사이토카인 방출 제어,

자가 면역 세포 무감작,

제 1형(아폽토시스) 및 제 2형(자가포식)의 프로그램된 세포 사멸과 같은

중요한 면역 세포 기능에 영향을 미칩니다.

분비 리소좀은

자극의 유형에 따라 염증 유발 및 항염증성 사이토카인의 방출을 조절합니다.

또한 리소좀은 글루코코르티코이드 수용체를 분해하며,

이는 글루코코르티코이드 결합에 필수적이지만

그 이유는 알려지지 않았습니다78.

이 복잡한 시스템에서 리소좀은

인산리파아제 A2 및 사이클로옥시게나제-2 경로를 통해

항염증 작용을 수행하며,

IL-1β–카스파제-1 경로를 통해 염증을 유도합니다.

두 조건(염증 촉진 및 염증 억제)에서 리소좀은

자가면역의 간접적 전구체로 작용합니다.

그러나

염증 신호의 유도 및 억제는 자극에 의존적입니다78.

Lysosomal cathepsins have a central role in degrading biological macromolecules in the lysosomes and in the immune response. There are approximately 12 members in this large protease family, most of which are endopeptidases that can cleave peptide bonds of their protein substrates79,80. Cathepsins A and G are serine proteases, cathepsins D and E are aspartic proteases and cathepsins B, C, F, H, K, L, O, S, V, X and W are cysteine proteases. For example, cathepsin S is responsible for the degradation of antigens (and autoantigens) in antigen-presenting cells (dendritic cells, macrophages and B cells), and is therefore involved at an upstream level in the presentation of MHCII–(auto)antigenic peptide complexes to CD4+ T cells81. Cathepsin L preferentially cleaves peptide bonds with aromatic residues in the P2 position and hydrophobic residues in the P3 position. It is central in antigen processing, bone resorption, tumour invasion and metastasis, and turnover of intracellular and secreted proteins involved in growth regulation. Cathepsin L-deficient mice display less adipose tissue, lower serum glucose and insulin levels, more insulin receptor subunits, more glucose transporter type 4 and more fibronectin than wild-type controls82. Cathepsin G is primarily known for its function in killing and digestion of engulfed pathogens83. It is also involved in connective tissue remodelling at sites of inflammation84. Anti-neutrophil cytoplasmic antibodies reacting with cathepsin G have been identified in some patients with SLE85.

리소좀 카테프신은

리소좀 내 생물학적 대분자의 분해 및 면역 반응에서 중심적인 역할을 합니다.

이 대규모 프로테아제 가족에는 약 12개의 구성원이 있으며,

대부분은 단백질 기질의 펩타이드 결합을 절단하는 내분해 효소입니다79,80.

카테프신 A와 G는 세린 프로테아제,

카테프신 D와 E는 아스파르트산 프로테아제이며,

카테프신 B, C, F, H, K, L, O, S, V, X 및 W는 시스테인 프로테아제입니다.

예를 들어,

카테프신 S는 항원 제시 세포(수지상 세포, 대식세포 및 B 세포)에서 항원(및 자가항원)의 분해에 관여하며,

따라서 MHCII–(자가)항원 펩타이드 복합체의 CD4+ T 세포 제시 과정의 상류 단계에 관여합니다81.

카테프신 L은

P2 위치에 아로마틱 잔기, P3 위치에 친수성 잔기를 가진 펩타이드 결합을 선택적으로 절단합니다.

이는 항원 처리, 골 흡수, 종양 침윤 및 전이, 성장 조절에 관여하는

세포 내 및 분비 단백질의 회전에 중심적인 역할을 합니다.

카테프신 L 결핍 마우스는 야생형 대조군에 비해 지방 조직이 적고, 혈청 글루코스 및 인슐린 수치가 낮으며, 인슐린 수용체 서브유닛, 글루코스 운반체 유형 4 및 피브로네кти인이 더 많습니다82. 카테프신 G는 주로 포식된 병원체를 죽이고 분해하는 기능으로 알려져 있습니다83. 또한 염증 부위에서 결합 조직 재모델링에 관여합니다84. 카테프신 G와 반응하는 항중성구 세포질 항체가 일부 루푸스 환자에서 확인되었습니다85.

Lupus

Abnormal antigen processing and presentation is known to be one of the upstream events that perturb immune responses in SLE86. Because this process is mediated through lysosomes, it was rational to speculate that lysosomal functions could be altered in lupus. Interestingly, hypotheses were raised in the 1960s on the ‘lysosomal fragility’ in lupus, but without much further pursuit87. The composition and fluidity of the lysosomal membrane are effectively crucial in the regulation of lysosomal fusion with other vesicular organelles and for lysosomal uptake of macromolecules. The integrity of the lysosomal membrane also ensures the prevention of release of lysosomal enzymes into the cytoplasm. Some lysosomal enzymes released from ‘fragile’ lysosomes were regarded potentially harmful in lupus88.

Lysosomes are abnormal in splenic B cells from Fas-deficient Murphy Roths Large (MRL)/lpr mice, a mouse model of lupus, compared with B cells from healthy CBA/J mice89. TFEB expression‎ was increased, indicating an enhanced biogenesis of lysosomes, and the lysosomal volume was raised. The expression‎ levels of LAMP1 and cathepsin D were also increased. These results reinforce previous data showing that the expression‎ and activity of some lysosomal enzymes (such as cathepsins S, L and B) that play important roles in antigen processing are altered in lupus and other autoimmune diseases90,91.

Substantial variations of the acidic endo-lysosomal pH also occur in MRL/lpr mice, being raised by 2 pH units in splenic B cells53,92. This pH change could dramatically influence the activity of soluble lysosomal hydrolases (such as cathepsins) as well as lysosomal membrane proteins (such as LAMPs) that are critical for lysosome activity. pH may also affect the elimination of immune complexes that accumulate in lupus as a result of deficits in complement, lower expression‎ of scavenger receptors, increased expression‎ of Fcγ receptors and other reasons93. These immune complexes, which contain non-selective IgG antibodies or autoantibodies associated with autoantigen (including some apoptotic debris), can initiate inflammation of tissues once deposited (for example, in the kidneys and the skin) and generate a cascade of deleterious effects, such as the release of harmful cytokines and chemokines54.

Recent studies have highlighted the key role of mammalian target of rapamycin complex 2 (mTORC2) in the disruption of lysosome acidification that occurs in this process94. In normal conditions, the regulation of lysosomal acidification requires cleavage of the RAB small GTPase RAB39a, occurring on the surface of phagocytic vesicles by locally activated caspase-194. This finely regulated process requires the association of cofilin with actin that surrounds the vesicle and recruits caspase-11, which then activates caspase-1 (ref.94). In lupus-prone macrophages, chronically active mTORC2 enhances cofilin phosphorylation, thereby hampering its association with actin and affecting the downstream cascade of events leading to the appropriate acidification of lysosomes94. The importance of mTORC1 and mTORC2 has been established earlier in lupus T cells, and in particular, in this context, mTORC1 activity was increased whereas mTORC2 activity was reduced95.

In addition, lysosomal cathepsin K was seen to contribute to the pathological events that develop in Faslpr mice, another model of lupus disease, in part through its activity in TLR-7 proteolytic processing and subsequent effects on regulatory T cells. Cathepsin K-deficiency in Faslpr mice reduced all kidney pathological manifestations (glomerulus and tubulointerstitial scores, glomerulus complement C3 fraction and IgG deposition, chemokine expression‎ and macrophage infiltration) and decreased the levels of potentially pathogenic serum autoantibodies96.

In line with these internal alterations of lysosomes, notably those related to cathepsin functioning, deregulation of autophagy has been reported to contribute to lupus pathology92,97–100. Autophagy failures have been described in the lymphocytes of MRL/lpr mice and (NZBxNZW)F1 mice56,92,97,101 (two spontaneous murine models of systemic autoimmunity of distinct genetic origins and that display different MHC haplotypes) as well as in T and B lymphocytes of patients with SLE97,98,100. Murine and human T cells from the peripheral blood showed a significant accumulation of autophagic vacuoles compared with normal97. The underlying reasons for the dysfunctions in autophagy observed in lupus are not clearly understood, but several independent investigations have identified risk loci spanning autophagy-linked genes in patients with lupus102–106.

루푸스

항원 처리 및 제시의 이상은

SLE에서 면역 반응을 방해하는 상류 사건 중 하나로 알려져 있습니다86.

이 과정이 리소좀을 통해 매개되기 때문에,

루푸스에서 리소좀 기능이 변화될 수 있다는 가설이 제기되었습니다.

흥미롭게도 1960년대에는

루푸스에서의 '리소좀 취약성'에 대한 가설이 제기되었지만,

이후 추가 연구는 거의 이루어지지 않았습니다87.

리소좀 막의 구성과 유동성은

리소좀과 다른 소포체와의 융합 조절 및 리소좀의 대분자 흡수에서 효과적으로 중요합니다.

리소좀 막의 무결성은

리소좀 효소의 세포질로의 방출을 방지합니다.

‘취약한’ 리소좀에서 방출된 일부 리소좀 효소는

루푸스에서 잠재적으로 유해할 수 있다고 간주되었습니다88.

루푸스 모델 마우스인 Fas 결핍 Murphy Roths Large (MRL)/lpr 마우스의 비장 B 세포는 건강한 CBA/J 마우스의 B 세포와 비교해 리소좀이 이상을 보였습니다89. TFEB 발현이 증가해 리소좀 생성이 증가했으며, 리소좀 부피도 증가했습니다. LAMP1과 카테프신 D의 발현 수준도 증가했습니다. 이 결과는 루푸스와 다른 자가면역 질환에서 항원 처리에서 중요한 역할을 하는 일부 리소좀 효소(예: 카테프신 S, L, B)의 발현과 활성이 변화한다는 이전 데이터를 강화합니다90,91.

MRL/lpr 마우스에서 산성 엔도-리소좀 pH의 상당한 변동도 관찰되었으며, 비장 B 세포에서 2 pH 단위 증가했습니다53,92. 이 pH 변화는 용해성 리소좀 가수분해 효소(예: 카테프신) 및 리소좀 막 단백질(예: LAMPs)의 활성에 극적인 영향을 미칠 수 있습니다. pH는 보체 결핍, scavenger 수용체 발현 감소, Fcγ 수용체 발현 증가 등 다양한 이유로 루푸스에서 축적되는 면역 복합체의 제거에도 영향을 미칠 수 있습니다93. 이 면역 복합체는 비특이적 IgG 항체나 자가항원(일부 세포 사멸 잔여물 포함)과 연관된 자가항체를 포함하며, 조직에 침착될 경우(예: 신장 및 피부) 염증을 유발하고 유해한 사이토킨 및 케모카인의 방출 등 유해한 효과의 연쇄 반응을 일으킬 수 있습니다54.

최근 연구들은 이 과정에서 발생하는 리소좀 산성화 장애에 있어 포유류 라파마이신 표적 복합체 2(mTORC2)의 핵심 역할을 강조했습니다94. 정상 조건에서 리소좀 산성화 조절은 식세포 소체 표면에서 국소적으로 활성화된 카스파제-1에 의해 RAB 소형 GTPase RAB39a가 분해되는 과정을 통해 이루어집니다94. 이 정교하게 조절되는 과정은 소포를 둘러싼 액틴과 코필린의 결합을 통해 카스파제-11을 모집하고, 이는 다시 카스파제-1을 활성화합니다(참조94). 루푸스 발병 경향이 있는 대식세포에서 만성적으로 활성화된 mTORC2는 코필린의 인산화를 촉진하여 액틴과의 결합을 방해하고, 이는 리소좀의 적절한 산성화로 이어지는 하류 사건의 연쇄 반응을 방해합니다94. mTORC1과 mTORC2의 중요성은 루푸스 T 세포에서 이전에 확립되었으며, 특히 이 맥락에서 mTORC1 활성은 증가한 반면 mTORC2 활성은 감소했습니다95.

또한, 루푸스 질환의 또 다른 모델인 Faslpr 마우스에서 리소좀 카테프신 K가 TLR-7 단백질 분해 처리 및 이후 조절 T 세포에 미치는 영향 등을 통해 병리적 사건의 발생에 기여하는 것으로 관찰되었습니다. Faslpr 마우스에서 카테프신 K 결핍은 신장 병리학적 소견(글omerulus 및 tubulointerstitial 점수, 글omerulus 보체 C3 분율 및 IgG 침착, 화학유인물질 발현 및 대식세포 침윤)을 모두 감소시켰으며, 잠재적으로 병리학적 혈청 자가항체 수준을 감소시켰습니다96.

리소좀의 이러한 내부 변화, 특히 카텝신 기능과 관련된 변화에 따라, 자가포식 조절 장애가 루푸스 병리에 기여하는 것으로 보고되었습니다92,97–100. 자가포식 장애는 MRL/lpr 마우스 및 (NZBxNZW)F1 마우스56,92,97,101 (유전적 기원이 다르며 서로 다른 MHC 일배체형을 나타내는 두 가지 자연 발생적인 전신 자가면역 마우스 모델)의 림프구와 SLE 환자의 T 및 B 림프구에서 보고되었습니다97,98,100. 말초혈에서 채취한 쥐와 인간의 T 세포는 정상에 비해 자식 세포의 축적이 현저하게 증가했습니다97. 루푸스에서 관찰되는 자가포식 기능 장애의 근본적인 원인은 명확하게 밝혀지지 않았지만, 여러 독립적인 연구에서 루푸스 환자에서 자가포식과 관련된 유전자를 포함하는 위험 유전자 위치를 확인했습니다102–106.

Sjögren’s syndrome

Recent studies have demonstrated an increase in the level of macroautophagy in salivary gland T lymphocytes and in tears and conjunctival epithelial cells of patients with primary Sjögren’s syndrome (SjS)107,108. Alteration of CMA activity was also recently found to occur in the salivary glands of MRL/lpr mice that develop a secondary SjS-like disease56. Lysosomes, which as discussed are mechanistically involved at the downstream level of both macroautophagy and CMA, were found to be altered in salivary glands. Flow cytometry analyses revealed that the mean pH of acidic vesicles in MRL/lpr salivary glands was significantly higher compared with those in mouse control glands and the ATP content was significantly diminished in MRL/lpr salivary gland cells56. Furthermore, amounts of several leukocyte glycosidases and proteases were revealed to be increased in leukocytes of patients with SjS in comparison with healthy controls55. Notably, raised levels of the lysosomal enzymes glucosidase, β-glucuronidase and dipeptidyl peptidase I are involved in the tissue injury in SjS55. Increased expression‎ of lacrimal gland cathepsin S was also reported, which may have application as a diagnostic tool in SjS91. Two members of the RAS oncogene family, RAB3D and RAB27, were found to be implicated in the regulation of cathepsin S secretion levels in SjS109. In vitro studies on lacrimal gland acinar cells suggested further that secreted IFNγ from acinar cells increases cathepsin S expression‎ and that IFNγ stimulated the MHCII-mediated antigen presentation in ocular pathogenesis of SjS110.

쇼그렌 증후군

최근 연구에서

원발성 시그렌 증후군 (SjS) 환자의 침샘 T 림프구 및 눈물과 결막 상피 세포에서

대식자식 자식작용의 수준이 증가했다는 것이 밝혀졌습니다107,108.

MRL/lpr 마우스에서 이차성 SjS 유사 질환을 발병한 경우 침샘에서

CMA 활성의 변화가 최근에 발견되었습니다56.

리소좀은 앞서 논의된 바와 같이

대식작용과 CMA의 하류 단계에서 기계적으로 관여하는 것으로 알려져 있으며,

침샘에서 변화가 관찰되었습니다.

유동세포계측 분석 결과, MRL/lpr 침샘의 산성 소체 평균 pH는 마우스 대조군 침샘에 비해 유의미하게 높았으며, MRL/lpr 침샘 세포의 ATP 함량은 유의미하게 감소했습니다56. 또한, SjS 환자의 백혈구에서 건강한 대조군에 비해 여러 백혈구 글리코시다제와 프로테아제의 양이 증가한 것으로 밝혀졌습니다55. 특히, 리소좀 효소인 글루코시다제, β-글루쿠로니다제 및 디펩티딜 페プチ다제 I의 증가된 수준은 SjS에서의 조직 손상과 관련이 있습니다55. 눈물샘 카테프신 S의 발현 증가도 보고되었으며, 이는 SjS의 진단 도구로 활용될 수 있습니다91. RAS 종양 유전자 가족의 두 구성원인 RAB3D와 RAB27이 SjS에서 카테프신 S 분비 수준 조절에 관여한다는 것이 밝혀졌습니다109. 체외 연구에서 눈물샘 아세리나 세포에서 분비된 IFNγ가 카테프신 S 발현을 증가시키고, IFNγ가 SjS110의 안구 병리에서 MHCII 매개 항원 제시를 자극한다는 것이 제안되었습니다.

Rheumatoid arthritis

Lysosomal cathepsins have important roles in the induction and diagnosis of RA, and levels of several cathepsins (B, D, G, K, L and S) that are present in the serum and synovial fluid of patients have been proposed as a basis for RA diagnosis111–116. Cathepsin S and cathepsin L are highly expressed in synovial macrophages and thymic cortical cells. They each exert essential roles in the positive selection of T cells and antigen presentation, respectively, and participate in the local inflammation and matrix degradation that occurs in joints116. Cathepsin B is involved in collagen degradation, which leads to joint destruction in RA112,117. Expression‎ of cathepsin G, which participates in joint inflammation through its chemoattractant activity, has been shown to be raised in the synovial fluid of patients with RA when compared with individuals with osteoarthritis115. Autoantibodies reacting with cathepsin G were also identified in patients with RA85. Compared with patients with osteoarthritis, cathepsin K expression‎ was found to be elevated in RA113, and genetic deletion of this particular cathepsin was shown to reduce inflammation and bone erosion in RA conditions via TLR mediation118.

Neurological autoimmune diseases

MS, myasthenia gravis, Guillain–Barré syndrome, chronic inflammatory demyelinating polyneuropathy (CIDP), neuromyelitis optica and neuropsychiatric lupus are neurological diseases induced by abnormal autoimmunity62,119–123. Neurological autoimmunity against various proteins, such as myelin in MS or N-methyl-d-aspartate receptor in neuropsychiatric lupus62,123,124, can affect various structures within the CNS and peripheral nervous system, with diverse consequences. Although the exact cause of amyotrophic lateral sclerosis (ALS) still remains unknown, studies support the existence of autoimmune mechanisms, and ALS is therefore also included in this section. Indeed, autoantibodies against ganglioside GM1 and GD1a, sulfoglucuronylparagloboside, neurofilament proteins, FAS/CD95 and voltage-gated Ca2+ channels have all been reported in patients with ALS (reviewed elsewhere125).

In general, the origin of the breakdown in immune tolerance that occurs in this set of neurological diseases is not known. Only recently have investigations discovered that autophagy processes are altered in some of these diseases59,62,126–130. In MS and in experimental autoimmune encephalomyelitis, an experimental model of MS, upregulation of the protein kinase mTOR has been described, and treatment with rapamycin/sirolimus (an immunosuppressant that inhibits mTOR and consequently stimulates macroautophagy) ameliorates some clinical and histological signs of the disease131. Increased levels of macroautophagy markers were measured in the blood and brain of patients with MS122,132. However, impaired macroautophagy was found in the spinal cord of experimental autoimmune encephalomyelitis mice133. In a rat model mimicking human CIDP, both macroautophagy and CMA processes were found to be hyperactivated in lymphatic system cells and non-neuronal cells (sciatic nerves) of peripheral nervous system cells59. In ALS, current data are conflicted62. Some data suggest an activation of macroautophagy processes with an accumulation of autophagosomes in brain tissues of patients with ALS, or an increase of autophagic vacuoles, aggregated ubiquitin and SOD1 proteins associated with MAP1LC3B-II in motor neurons of mice developing an ALS-like disease134,135. In contrast, other data suggest a reduction of autophagy activity136,137. Mutations in SQSTM1, valosin-containing protein, dynactin (a protein complex that activates the dynein motor protein, enabling intracellular transport) and RAB7 (a member of small GTPases that is important in the process of endosomes and autophagosomes maturation) have also been described in ALS138–141. Further studies are required to better understand the type and extent of autophagy dysfunction in this family of complex diseases.

There are only a few published studies on lysosomal dysfunction in neurological autoimmune diseases (Table 2). These notably include lysosome fragility, which was observed in patients with MS in the white matter of cerebral tissue, an area of the CNS that is mainly made up of myelinated axons142. Lysosome fragility was also suspected in SLE (see above) and other rheumatic autoimmune diseases, albeit in other organs53,58,92. As noted above, significant variations in lysosomal pH have been measured in autoimmune conditions such as lupus and SjS, but to our knowledge such studies conducted in the brain or elements of the peripheral nervous system of patients or animal models with neurological autoimmune diseases have not been published78.

In CIDP, it has been shown that Schwann cells dedifferentiate into immature states and that these dedifferentiated cells activate lysosomal and proteasomal protein degradation systems143,144. Based on these observations, Schwann cells have been claimed to actively participate in demyelinating processes via this dedifferentiation process, but the mechanism involved remains undefined145. In the rat model of CIDP mentioned above, it was shown that LAMP2A expression‎ was drastically increased in the sciatic nerve macrophages and reduced macroautophagy was observed in Schwann cells and macrophages59.

In MS, studies conducted on white matter demonstrated that lysosomes are involved in myelin sheath degeneration as well as in the fragmented protein formation. Lysosomal swelling was observed near the degenerated materials of astrocytes146, and an accumulation of lipids was found60. It has been hypothesized that lysosomal swelling/permeabilization might cause the release of hydrolases in the cytosol, where they affect native proteins147.

In ALS, patients also show dysfunctions in the endo/lysosomal pathways, which affect both lower and upper motor neurons (Table 2). Cathepsin B was particularly found to be involved in the motor neuron degeneration, whereas cathepsins H, L and D were not significantly affected148. A cDNA microarray analysis on post-mortem spinal cord specimens of four sporadic patients with ALS revealed major changes in the expression‎ of mRNA in 60 genes including increased expression‎ of cathepsins B and D149. Several disease-causing mutations in genes related to autophagy have been identified, such as SOD1, TDP643, FUS, UBQLN2, OPTN, SQSTM1 and C9orf72 (refs61,150), but none of them code for lysosomal proteins. So, a crucial remaining issue is to clearly determine whether the lysosomal abnormalities that are observed are linked to intrinsic defaults of lysosomes or result from upstream dysregulation in autophagosome formation and fusion61,62,151.

Neurodegenerative disorders

Insufficient clearance of neurotoxic proteins by the autophagy–lysosomal network has been implicated in numerous neurodegenerative disorders152. In disorders such as AD, Huntington disease (HD) and PD, modified or misfolded proteins abnormally accumulate in specific regions of the brain. Accumulation of aggregated proteins is also seen in ALS (see above). These abnormal proteins form deposits in intracellular inclusions or extracellular aggregates, which are characteristic for each disease153–155. Although there has been substantial research in this field, it is still unclear why sophisticated ‘quality-control’ systems, such as the lysosome–autophagosome system in particular, fail in certain circumstances to protect the brain against such protein accumulation156.

In AD, one of the most common neurodegenerative disorders, some alterations in the endo/lysosomal pathways have been described (reviewed elsewhere157,158). The amyloid precursor protein (APP) is cleaved by β- and γ-secretases into amyloid-β peptide (Aβ) fragments, particularly Aβ40 and Aβ42 (ref.159). These fragments are found in the amyloid plaques that are one of the hallmarks of AD (the other being neurofibrillary tangles containing phosphorylated tau), and have been widely considered to have an important role in AD pathogenesis159,160. Cell-based experiments have demonstrated that lysosomal cathepsins have a role in the generation of Aβ peptides (through cathepsins D and E) and the degradation of Aβ peptides (by cathepsin B)161. Lysosomal dysfunction has been observed in patients with AD162,163, and accumulation of the Aβ42 fragment in neuronal cells was shown to lead to lysosomal membrane alterations, which cause neuronal cell death63. In this context, it is noteworthy that inhibition of cathepsin D, which is involved in the lysosomal dysfunction and notably in the cleavage of the tau protein into tangle-like fragments, diminishes its hyperphosphorylation in the brain of patients with AD164. In addition, patients with AD with an inherited form of the disease may carry mutations in the presenilin proteins (PSEN1 and PSEN2), APP or apolipoprotein E, resulting in increased production of the longer form of the Aβ fragment (reviewed elsewhere165). Mutation of PSEN1, for instance, leads to direct disruption of the lysosomal acidification due to impaired delivery of the V0A1 subunit of v-ATPase, a proton pump responsible for controlling the intracellular and extracellular pH of cells. The acidification deficit causes excessive release of lysosomal Ca2+ through TRPML1 channels, which has numerous deleterious effects166. These findings strongly support the hypothesis that dysfunction of endo/lysosomal pathways is pivotal in AD.

Approximately 15% of patients with PD have a family history of the disorder, although the underlying molecular mechanisms remain unclear. In the context of lysosomal dysfunction, it is notable that the most common of the known PD genetic mutations are in GBA1 (encoding the lysosomal β-GCAse) — the same gene that underlies Gaucher disease — which are present in up to 10% of patients with PD in the United States167. GBA1 mutations are also associated with dementia with Lewy bodies167. Several other genes linked to PD are directly or indirectly related to the endo/lysosomal machinery, such as mutations in SNCA (coding for α-synuclein)63,168. A hallmark of PD is the presence in neurons of protein inclusions called Lewy bodies, which are mainly composed of fibrillar α-synuclein. The α-synuclein protein is normally degraded by the lysosomes through the CMA pathway, but macro-aggregates of α-synuclein mutants, which display a longer half-life compared with the non-aggregated wild-type protein, are not degraded by this pathway and, rather, would be degraded via the macroautophagy pathway169–172. It was further shown that the mutant proteins bind to LAMP2A and inhibit the translocation of other substrates and, therefore, their final degradation170. Biochemical analyses suggest that α-synuclein is mainly degraded by lysosomal proteases and notably by cathepsin D, rather than by non-lysosomal proteases (for example, calpain I)173,174. Accumulation of α-synuclein was observed in cathepsin D-deficient mice, whereas, conversely, the accumulation of α-synuclein aggregates was reduced in transgenic mice that overexpressed this cathepsin, resulting in protection of dopaminergic neuronal cells from damage175.

HD is a rare autosomal-dominant neurodegenerative disease caused by an aberrant expansion of CAG trinucleotide repeats within exon 1 of the HTT gene, which results in the production of aggregation-prone HTT mutants (mHTT) that are detrimental to neurons176,177. Whereas HTT has a protective role against neuronal apoptosis, accumulation of mHTT, however, induces pathophysiological consequences including lysosomal and autophagy dysfunctions. Thus, mHTT perturbs post-Golgi trafficking to lysosomal compartments by delocalizing the optineurin/RAB8 complex, which, in turn, affects lysosomal function177. Excessive mHTT induces accumulation of clathrin adaptor complex 1 in the Golgi and an increase of clathrin-coated vesicles in the vicinity of Golgi cisternae177. The activity of several cathepsins such as B, D, E, L and Z has also been linked to HD63,80,174,177–179. Cathepsin D is responsible for full degradation of HTT but is less efficient at degrading mHTT, which is processed by cathepsin L180,181. Cathepsin Z also cleaves HTT and elongated polyglutamine tracts182,183. Thus, lysosomal modulators acting on cathepsin activity might have beneficial effects in the treatment of HD. Notably, hyperexpression‎ of cathepsin D (and cathepsin B) was shown to protect primary neurons against mHTT toxicity179. Alterations in macroautophagy, mitophagy and CMA have also been implicated in HD184,185. CMA activity was increased in response to macroautophagy failure in the early stages of HD186, a result supported by the findings that HSPA8 and LAMP2A have important roles in the clearance of HTT187 and that shRNA-mediated silencing of LAMP2A increased the aggregation of mHTT188. Other studies focusing on the HTT secretory pathway revealed that mHTT secretion is mediated by the Ca2+-dependent lysosomal exostosis mechanism via the synaptotagmin 7 sensor in neuro2A cells189. The extracellular release of mHTT was efficiently inhibited by the phosphoinositide 3-kinase and sphingomyelinase inhibitors Ly294002 and GW4869. HD-dependent perinuclear localization of lysosomes was also demonstrated190.

Increasing evidence thus implicates lysosomal (and autophagy) dysfunction in the pathogenesis of neurodegenerative disorders62,63,127,128,130,191,192. TFEB has received particular attention in this regard193–195, with recent data suggesting that TFEB is selectively lost in patients with AD (as well as ALS)196. Increasing TFEB activity might therefore prevent neuronal death and restore neuronal function in certain neurodegenerative diseases, including PD194.

Lysosomes as therapeutic targets

Given the evidence discussed above, the various lysosomal pathways and their components could represent potential pharmacological targets for a wide range of diseases. When considering lysosomes as targets, it is important to note the need for specificity; that is, agents that will not target all lysosomes, but will specifically target those lysosomes/lysosomal proteins that are defective in certain organs, tissues or cells. In addition, inhibitors or activators of lysosomal components may be required, depending on the disease context.

There has been considerable interest in therapeutically targeting different autophagy pathways, including lysosome-dependent pathways, and progress in the discovery and development of small molecules and biologics that target these processes has been reviewed extensively11,119–122,197,198. However, very few therapies that specifically target lysosomal components have so far been generated and found to be effective in clinical trials, with one general exception — the development of ERTs and small-molecule drugs for LSDs (Box 1). This topic has recently been comprehensively reviewed46 and so will not be discussed in depth here.

It is important to target lysosomes and not the whole autophagy process for several reasons. First, regarding safety, the integral role of lysosomes in several key physiological processes means that therapeutic windows for pharmacological intervention with unacceptable side effects may be limited. For example, azithromycin, an antibiotic with anti-inflammatory properties that is used in the treatment of patients with chronic inflammatory lung diseases such as cystic fibrosis, was found to block autophagy in macrophages, inhibiting intracellular killing of mycobacteria within them and, thereby, increasing the risk of mycobacterial infection204. Second, in some diseases, autophagy may be enhanced in certain tissues or organs but compromised in others, for example in the spleen and salivary glands of MRL/lpr mice56. This phenomenon makes it highly challenging to identify a single drug able to correct a failure, unless a cell-specific targeting molecule could be incorporated into the autophagy activator/inhibitor to enable tissue specificity205. Again, the precise targeting of lysosomes in specialized cells may circumvent the complexity of dysregulation mechanisms of autophagy processes in pathophysiological settings14,56,206,207.

As indicated, the current arsenal of lysosome-specific targeted drugs is small. In fact, many drugs claimed to target lysosomal components have also been found to be capable of interacting with several non-lysosomal receptors, limiting their efficacy and safety12. One example is provided by chloroquine (CQ), a 4-aminoquinoline compound, and its derivative hydroxychloroquine (HCQ), which are widely prescribed to patients with rheumatic diseases, and historically also for the prophylaxis and treatment of malaria (Fig. 3). CQ and HCQ are lysosomotropic agents and as such they raise intralysosomal pH, thereby affecting overall lysosomal function and impairing autophagic protein degradation (Fig. 2). Although the mechanism of action of these agents is not fully elucidated, it is well established that CQ and HCQ display pleiotropic activity208–210 and have important deleterious properties. In certain settings, they have been claimed to operate by interacting directly with TLR ligands and not through an effect on the lysosomal pH, for example211. Toxicity of CQ/HCQ, in particular in the eye (cornea and macula) and the occurrence of cardiomyopathies212, remains a major limitation. The observed ocular toxicity is related to the total cumulative dose rather than the daily dose; therefore, it becomes a serious potential problem in the cases of long-term use. Several HCQ analogues and mimics have been designed that aim to retain the therapeutic activity without secondary effects213,214.

Fig. 3. Structures of selected pharmacological molecules designed to correct lysosomal dysregulation in disease.

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Small molecules and peptides highlighted in this figure are activators and inhibitors of lysosomal constituents targeting mechanistic target of rapamycin (mTOR), vacuolar-type proton adenosine triphosphatase (v-ATPase), TRPML1, PIK kinase and HSPA8. For details, see the text and accompanying tables.

Furthermore, most, if not all, of the small molecules that have so far been identified and investigated as modulators of autophagy and/or lysosomal functions exhibit complex pleiotropic properties affecting the overall function of lysosomes, and also different autophagy pathways (for example, mTOR-dependent and mTOR-independent pathways), as well as other quality-control mechanisms that affect the cell life/death balance. As discussed below, several widely used molecules exert dual, sometimes opposite, effects on upstream and downstream molecular events of the autophagy–lysosomal network.

Several robust assays to characterize autophagy activators and inhibitors, as well as lysosomal effectors, are currently available and validated (Table 3). However, each assay has inherent biases, and so it is necessary to use several independent, in vitro and in vivo approaches to ascertain the reactivity and specificity of novel molecules able to modulate these pathways (Box 2).

Table 3.

Measurements used to assess lysosomal dysfunction

Lysosomal characteristicMethodsComments

Total volume (number and size)	Fluorescence measurement (flow cytometry or fluorescence microscopy) of cellular staining of acidotropic dyes, such as LysoTracker dyes92,215	Simple to use but is not quantitative as stated by the manufacturer; can be adapted to clinical trial settings
	Western blot and fluorescence imaging of lysosomal markers such as LAMP1, LAMP2 etc.216,217	Simple but does not provide information on subcell populations89; can be adapted to clinical trial settings
	Electron microscopy218	Provides morphological information but laborious and semiquantitative
Biogenesis and activation status	Western blot and qPCR of TFEB (and also other family members)219,220	Simple but does not provide information on subcell populations; can be adapted to clinical trial settings
	Fluorescence imaging of the nuclear translocation of TFEB-GFP219	Limited usage in primary cells as they are hard to transfect
pH	Ratiometric fluorescence measurement with LysoSensor Yellow/Blue92,221 or Oregon-Green 488 dye222	The dyes can have an alkalinizing effect on lysosomes and affect the accuracy of results223
Degradation ability	Fluorescence measurement of the degradation of labelled BSA (DQ-BSA Green/Red)57	Requires loading of BSA molecules to lysosomes by endocytosis and could potentially interfere with normal lysosomal function224
Protease expression‎	Western blot measurement of cathepsins92, thiol reductase etc.	Simple but does not provide information on subcell populations; can be adapted to clinical trial settings
Protease activity	Fluorescence measurement of the cleavage of cathepsin substrates by Magic Red Cathepsin (B, K and L) kit225	N/A
Membrane stability	Membrane stability assay with acridine orange226	Phototoxic and stains nucleus as well227
Membrane integrity	Lysosomal galectin puncta assay224	N/A
	Cell fractionation to detect lysosomal content in cytosol216	Limited sensitivity as it fails to detect small amounts of lysosomal content224
Local calcium level	Live cell imaging of genetically encoded Ca2+ indicator: GCaMP3-ML134	Limited usage in primary cells as they are hard to transfect

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BSA, bovine serum albumin; LAMP, lysosome-associated membrane protein; N/A, not available; qPCR, quantitative PCR; TFEB, transcription factor EB.

In this regard, the tremendous work in recent years to establish international guidelines for standardizing research in autophagy — and, in particular, to propose relevant methodologies for monitoring autophagy that are accepted by the whole community — is unique231,232. A better definition of terms and concepts has also been adopted by the community, leading to much easier understanding between researchers worldwide233. These guidelines and definitions should be used by investigators eval‎uating new molecules designed to selectively target key steps of autophagy or developing new high-throughput screening methods for autophagy-modulating pharmacological molecules. However, even the more sophisticated and detailed assays will not recapitulate the full complexity of integrated living systems, which can only be established in clinical trials.

Box 1 Enzyme replacement therapies for lysosomal storage disorders.

Enzyme replacement therapy (ERT) for lysosomal storage disorders (LSD) involves administration of a functional version of the defective enzyme in the particular LSD. Following administration, the enzyme is delivered to the target cells (typically mediated by mannose or mannose-6-phosphate receptors), where it breaks down its substrate in lysosomes, thereby ameliorating the LSD46.

The approach was pioneered with the use of glucocerebrosidase (GCase) purified from placentae in the 1980s to treat patients with Gaucher disease, and a recombinant version of GCase was then introduced in the 1990s199. Following the success of this approach in treating Gaucher disease, other recombinant enzymes have been approved for other LSDs, including Fabry disease, mucopolysaccharidosis (MPS) I, MPS II, MPS VI and Pompe disease (Table 1), and many further ERTs for other LSDs are in clinical trials200.

Although ERT has provided an effective treatment for patients with some LSDs, it has limitations. Recombinant enzymes administered by intravenous injection are not able to cross the blood–brain barrier, and so are not effective for central nervous system manifestations of LSDs201. Low expression‎ of the receptors that mediate delivery on the cell surface of target cells can also be a challenge for the effectiveness of ERT for some LSDs46. For example, in Pompe disease, the level of expression‎ of mannose receptors on skeletal muscle cells is low, necessitating high doses of ERT to achieve a therapeutic effect202. Numerous developments are being studied to address such limitations, with a focus on enzyme modifications that enable better access of enzymes to their receptors and on nanomaterials that enable safe and efficient delivery of enzymes via intra-cerebroventricular/intrathecal administration10,46,200,203.

Box 2 Methods to examine lysosomal dysfunction in disease.

Several parameters have been used to eval‎uate lysosomal functions (Table 2). Alteration of lysosomal volume is an important sign of lysosomal dysfunction; it has been observed in various diseases, such as autoimmune syndromes, cancers and lysosomal storage diseases215. It can be measured by staining cells with acidotropic dyes such as LysoTracker dyes and immunoblot of lysosomal membrane proteins such as lysosome-associated membrane protein 1 (LAMP1). Variation of lysosomal volume is often related to changes in lysosomal biogenesis, which can be assessed by the expression‎ level and cellular location of transcription factor EB (TFEB). However, precise determination of lysosomal functions relies on measurement of lysosomal luminal pH and degradation activity. Several fluorescence probes that measure lysosomal pH (Table 2) are commercially available. Abnormal lysosomal pH affects lysosomal degradation activity, which can be followed, for example, by detecting the degradation of endocytosed fluorescence DQ-BSA57. In complement, the activity of specific enzymes, such as cathepsins B, D and L, can be tested using commercially available kits. Other lysosomal parameters can be eval‎uated to deepen the examination of lysosomal status, including lysosomal membrane stability and integrity and lysosomal Ca2+ ion signalling, for example (Table 2). Lysosomal function is essentially linked with autophagy activity as autophagy is a lysosomal-dependent degradation pathway. Thus, a series of methods routinely applied for assessing macroautophagy in mouse models and patients with autoimmune diseases is summarized89. To ascertain the extent of autophagy defects, a combination of techniques, such as western blot and flow cytometry, measurement of autophagy makers, fluorescent imaging and electron microscopy, in the presence and absence of lysosomal protease inhibitors, is recommended. Several review articles have described reliable methods dedicated to the measurement of chaperone-mediated autophagy (CMA) activity228–230. Increased expression‎ levels of LAMP2A and HSPA8, two key players in CMA, have been shown to occur in a mouse model of lupus92. However, it should be noted that increased expression‎ levels of HSPA8 and LAMP2A starting from a total lysate is only indicative of CMA upregulation; this test is not sufficient to allow any firm conclusion, and it is necessary to examine their expression‎ levels in purified lysosomes or in lysosome-enriched fractions.

Pharmacological regulators of lysosomal activity

The pipeline of specific agonists and antagonists of autophagic activity is currently small, particularly for CMA (Tables 4,5; Figs 2,3). However, high-throughput screening programmes to identify such small molecules are ongoing, which should yield additional therapeutic targets and useful tools. Small molecules that specifically target lysosomes are even rarer (Table 4; Fig. 2). Small-molecule drugs developed specifically for particular LSDs, including substrate reduction therapies and small-molecule chaperones, have reached the market, but other small-molecule candidates for more common diseases are at an earlier stage of development. These molecules that more specifically act on lysosomes, some of which have been discovered by high-throughput screening, mostly target LAMP2A, various lysosomal enzymes such as cathepsins, acid sphingomyelinase, α-galactosidase A and acid β-glucocerebrosidase, and chaperones such as HSPA8 and β-N-acetyl hexosaminidase. Although not solely present in lysosomes, v-ATPase, a proton pump responsible for controlling the intracellular and extracellular pH of cells, and TRPML1, a cation channel located within endosomal and lysosomal membranes, are also pertinent targets.

Table 4.

Pharmacological modulators of lysosome functions: targets and disease indication

Pharmacological agent/companyMechanismStage of developmentComments

LSD substrate reduction therapy
Miglustat/Actelion	Inhibitor of GCS	Marketed	Used in various LSDs, Gaucher disease and NPC; therapeutic efficiency in long-term studies in Gaucher disease type 1 with adverse effects like gastrointestinal discomfort, tremors and weight loss234
Eliglustat/Genzyme	Inhibitor of GCS	Marketed	Does not cross the blood–brain barrier; used in non-neuronopathic Gaucher disease; superior efficacy to miglustat and other treatments in type 1 Gaucher disease235
Lucerastat/Idorsia Pharmaceuticals	Inhibitor of GCS	Phase III	Miglustat analogue with lesser side effects; 1,000 mg two times a day for 12 weeks was highly tolerable in patients with Fabry disease236; effective in a mouse model of GM2 gangliosidosis with improved neurological performance237
Ibiglustat/Genzyme	Inhibitor of GCS	Phase II	Clinically eval‎uated in Fabry disease, Gaucher disease type 3 and Parkinson disease; efficient in neuropathological and behavioural outcomes associated with Gaucher disease238
Genistein	Kinase inhibitor	Phase III	Inhibition of glycosaminoglycans in fibroblasts from patients with MPS III; improved hair morphology and cognitive functions in patients with MPS IIIA and IIIB239; TFEB function modulator240
Odiparcil (IVA336)/Inventiva Pharma	Inhibitor of glycosaminoglycans accumulation	Phase II	Improved clinical symptoms in MPS VI mice241; superior biodistribution in comparison with enzyme replacement therapies241; phase II clinical trial in patients with MPS VI ongoing (NCT03370653)
LSD chaperone therapy
Migalastat/Amicus Therapeutics	Assists α-galactosidase A conformation	Marketed	Oral chaperone therapy for Fabry disease by increasing catalytic enzyme activity; efficacious against mostly patients with GLA gene mutations
Afegostat (isofagomine)/Amicus Therapeutics and Shire plc	Inhibitor of β-glucosidase	Failed in phase II	Binds to N370S glucocerebrosidase mutant; assists in the folding and transportation of enzymes from the endoplasmic reticulum to lysosomes242; pH-dependent activity
Pyrimethamine	Competitive inhibitor of β-hexosaminidase	Phase I	Effective in Sandhoff and Tay–Sachs diseases; binds selectively to the active site of domain II in β-hexosaminidase; side effects at >75 mg per day
Ambroxol (Mucoslovan)/Boehringer Ingelheim	pH-dependent effect on β-glucosidase	Suspended phase I/II	Effective in Gaucher disease with improved neurological symptoms; a GCase chaperone, which also acts on other pathways, such as mitochondria, lysosomal biogenesis and the secretory pathway243
N-Octyl-β-valienamine	β-GCase inhibitor	Preclinical	Epimer of N-octyl-4-epi-β-valienamine for Gaucher disease
N-Acetylcysteine	Assists α-glucosidase in a pH- and temperature-dependent manner	Preclinical	Allosteric chaperone active in Pompe disease244
5-(4-(4-Acetylphenyl)piperazin-1-ylsulfonyl)-6-chloroindolin-2-one	Inhibitor of acid α-glucosidase	Preclinical	Non-iminosugar chaperone; highest chaperone activity against acid α-glucosidase245
1-Deoxynojirimycin/ Amicus Therapeutics	Inhibitor of acid α-glucosidase	Phase II	Effective against different mutant forms of acid α-glucosidase; roles in protein trafficking and stabilization of some mutant forms of acid α-glucosidase246
α-Lobeline and 3,4,7-trihydroxyisoflavone	β-Galactocerebrosidase	Preclinical	Effective in fibroblast cells from patients with Krabbe disease247
N-Octyl-4-epi-β-valienamine	Retains β-galactosidase catalytic activity	Preclinical	Effective in a mouse model of GM1 gangliosidosis248
5N,6S-(N′-butyliminomethylidene)-6-thio-1-deoxygalactonojirimycin	Competitive inhibitor of β-galactosidase	Preclinical	N′-Butyl moiety selectively binds to the active site of β-galactosidase; protects the enzyme from degradation due to temperature fluctuation; used in GM1 gangliosidosis249
NCGC607	Assists the conformation of GCase activity	Preclinical	Reduced lysosomal substrate storage and α-synuclein levels in cell-based assays250
Lysosomal acidification inhibitors
Chloroquine	Inhibition of lysosomal acidification	Tool compound/phase IV	Increases Treg cell expansion and alleviates EAE symptoms251; completed phase IV clinical trials in autoimmune hepatitis (NCT01980745)
Hydroxychloroquine	Inhibition of lysosomal acidification	Tool compound/phase IV	Blocks the autoreactive T cell responses in SLE, RA, SjS and others252; ongoing end-stage clinical trials alone or in combination in SLE (NCT00413361), SjS (NCT01601028), RA (NCT03085940) and others
NH4Cl	Inhibition of lysosomal acidification	Tool compound	N/A
Monensin	Inhibition of lysosomal acidification	Tool compound	N/A
mTOR inhibitors
Rapamycin/sirolimus	Antifungal metabolite produced by Streptomyces hygroscopicus; binds to the FK506-binding protein (FKBP12), resulting in allosteric mTOR inhibition	Tool compound	Used in the treatment of many diseases, including SLE253 and RA254 and others
Cathepsin inhibitors
CA030, CA-074 and their analogues	Cathepsin B inhibitor	Preclinical	High amounts of cathepsin B in patients with RA compared with patients with osteoarthritis112; promising results in melanoma metastases in mice255
Pepstatin A	Cathepsin D inhibitor	Tool compound	Reduction of renal fibrosis in mouse models of CKD256
α1-Antichymotrypsin and phenylmethylsulfonyl fluoride	Cathepsin G inhibitor	Preclinical	Increased cathepsin G in patients with RA compared with patients with osteoarthritis115; monocyte chemotactic activity in the synovial fluid of patients with RA was directly proportional to cathepsin G expression‎
CLIK-148, CLIK-181 and CLIK-195	Cathepsin L inhibitor	Preclinical	Inhibitors obtained as leads from in vitro and in vivo studies; high expression‎ of cathepsin L in patients with RA compared with patients with osteoarthritis257; siRNA-mediated inhibition protected mice from autoimmune diabetes258; inhibition with oxocarbazate prevented virus (coronavirus and Ebola pseudotype virus) entry into cells259
LHVS and CLIK-60	Cathepsin S inhibitor	Preclinical	Cathepsin S inhibitors (CLIK-6O) inhibited autoantigen presentation in mouse model of SjS79,260; cathepsin S-deficient mice are less susceptible to collagen-induced arthritis261
RO5461111/Roche	Cathepsin S inhibitor	Preclinical	Inhibition of cathepsin S has beneficial effects in SLE262 and SjS263 via inhibiting autoantigen presentation; cathepsin S, from tears of patients with SjS, enhanced the degradation of tear proteins264
CLIK-164 and SB-357114/GlaxoSmithKline	Cathepsin K inhibitor	Preclinical	Inhibition of cathepsin K reduced collagen degradation in osteoporosis conditions265,266
L-006235	Cathepsin K inhibitor	Preclinical	Inhibition of cathepsin K exerted analgesia in a rat model of osteoarthritis267
PADK, SD1002 and SD1003	Cathepsin B and L inhibitor	Preclinical	Cathepsin B and L modulators decreased protein accumulation in Alzheimer disease via cathepsin upregulation268
v-ATPase inhibitors
Bafilomycin A1	A macrolide antibiotic isolated from Streptomyces griseus; a potent and selective inhibitor of v-ATPases, via the V0 c subunit in the lysosomal lumen	Tool compound	Reduced lymphoblastic leukaemia by inhibiting the autophagic process and activating the apoptosis pathway via mitochondria269
Concanamycin A	A macrolide antibiotic isolated from Streptomyces diastatochromogenes; a selective inhibitor of v-ATPases via V0 c subunit	Tool compound	N/A
FR167356	A selective inhibitor of osteoclast v-ATPases and relatively less potent inhibitor of other v-ATPases	Preclinical	Effective in osteoporosis and metastatic bone disease270
Salicylihalamide A	First isolated from the marine sponge Haliclona; a selective inhibitor of mammalian v-ATPases via V0 domain	Tool compound/preclinical	Anticancer activity via v-ATPase inhibition271
Saliphenylhalamide	Synthetic molecule; inhibitor of v-ATPases	Preclinical	A derivative of salicylihalamide A with anticancer effects in cancer cell lines (including drug-resistant)
SB 242784/SmithKline Beecham Biologicals	Synthetic molecule; inhibitor of v-ATPases	Preclinical	Selectively inhibits osteoclast v-ATPases and alleviates the clinical signs of osteoporosis and metastatic bone disease270,272
BRD1240/Harvard University	Small molecule; exerts lysosomal acidification by inhibition of v-ATPases	Tool compound	Anticancer activity via inhibiting lysosomal enzymes273
Ion channel modulators
ML-SA1	TRPML1 agonist	Tool compound/preclinical	Important role in lysosomal exocytosis22; induces secretion of lysosomal acid phosphatases and LAMP1 expression‎22
SF-22	TRPML1/3 agonist	Preclinical	May have therapeutic uses in vaccines, autoimmune diseases and infectious diseases (WO2015118167A1)274
MK6-83	TRPML1 agonist	Preclinical	N/A
PIK kinase modulators
YM-201636	PIKfyve kinase inhibitor	Preclinical	Used in antiretroviral therapy; inhibits glucose influx in adipocytes; dysregulated autophagy-induced cell death in neuronal cells275
Apilimod (LAM-002A (apilimoddimesylate)/STA-5326)/AI Therapeutics	PIKfyve kinase inhibitor	Phase I	An inhibitor of T helper 1 and T helper 17 cell responses in autoimmune diseases276–278; under phase 1 study in subjects with relapsed or refractory B cell non-Hodgkin’s lymphoma (NCT02594384)
Chaperone modulators
P140 peptide (Lupuzor)/ImmuPharma	CMA inhibitor	Phase III	Binds HSPA8 and blocks dysregulated chaperone-mediated activity in SLE92,101, SjS56 and CIDP59
VER-155008	HSP70 inhibitor	Tool compound/preclinical	Therapeutic effects in lung cancer279 and Alzheimer disease280
Humanin	CMA activator	Preclinical	Mitochondria-associated peptide that binds HSP90 to facilitate substrate translocation281
Miscellaneous
Lonafarnib/Eiger BioPharmaceuticals	Lysosomal activator	Preclinical	A known anticancer molecule; inhibits farnesyl transferase and reduces tauopathy in mice by activating lysosomal degradative process282; possible therapeutic option for neurodegenerative diseases

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CIDP, chronic inflammatory demyelinating polyneuropathy; CKD, chronic kidney disease; CLIK, cathepsin L inhibitor Katunuma; CMA, chaperone-mediated autophagy; EAE, experimental autoimmune encephalomyelitis; GCase, glucocerebrosidase; GCS, glucosylceramide synthase; LAMP1, lysosome-associated membrane protein 1; LSD, lysosomal storage disorder; LHVS, morpholinurea-leucine-homophenylalanin-vinyl phenyl-sulfone; MPS, mucopolysaccharidosis; mTOR, mechanistic target of rapamycin; N/A, not available; NPC, Niemann–Pick disease type C; PADK, Z-Phe-Ala-diazomethylketone; PIK, phosphatidylinositol-3-phosphate 5-kinase; PIKfyve, FYVE finger-containing phosphoinositide kinase; RA, rheumatoid arthritis; siRNA, small interfering RNA; SjS, Sjögren’s syndrome; SLE, systemic lupus erythematosus; TFEB, transcription factor EB; Treg cell, regulatory T cell; v-ATPase, vacuolar-type proton adenosine triphosphatase.

Table 5.

Pharmacological modulators of lysosome functions: patents

Patent numberAssigneeTitleYear filed/ published/grantedCompositionTarget diseases

US8829204B2	Vertex Pharmaceuticals Inc., Cambridge, MA (USA)	Modulators of ATP-binding cassette transporters	2014	Novel synthetic compounds	Sjögren’s syndrome, LSD and many other diseases
US20140072540A1	The Board of Trustees of the University of Illinois, Urbana, IL (USA)	Compositions and methods for the treatment of Krabbe and other neurodegenerative diseases	2014	Inhibitors, which modulate lysosomal function	Neurodegenerative diseases
US20160051629A1 (WO/2014/170892)	Yeda Research and Development Co. Ltd, Rehovot (Israel)	Inhibition of RIP kinases for treating lysosomal storage diseases	2016	RIP inhibitors are compounds or pharmaceutical compositions and some types of IL-1β antagonists	LSD
WO2018005713A1	Liang Congxin, Palm Beach Gardens, FL 33418 (USA)	Piperazine derivatives as TRPML modulators	2016	Novel piperazine derivatives	Targets lysosomal dysfunction associated with TRPML
EP2744821B1	University of Dundee (UK)	Inhibitors against endosomal/lysosomal enzymes	2016	Protease inhibitor and conjugates	Diseases which need protease inhibition
US9265735B2	The Research Foundation for Msta Hygiene, Inc., Menands, NY (USA)	Methods for screening to identify therapeutic agents for Alzheimer disease and use thereof	2016	Agents that modulate lysosomal function	Alzheimer disease
US9469683B2	Biomarin Pharmaceutical Inc., Novato, CA (USA)	Lysosomal targeting peptides and uses thereof	2016	Peptides	LSD
US9717737B2 (WO2015/124120)	The University of Hong Kong, Hong Kong (China)	Vacuolin-1 as an inhibitor of autophagy and endosomal trafficking and the use thereof for inhibiting tumour progression	2017	Vacuolin-1 and structural analogue	Cancer and other diseases
WO2017040971A1	Biomarin Pharmaceutical Inc., Novato, CA (USA)	Methods of using inhibitors of PIKfyve for the treatment of lysosomal storage disorders and neurodegenerative diseases	2017	Methods and chemicals which are pharmaceutically acceptable	LSD and neurodegenerative diseases
WO2006007560A3	Icahn School of Medicine at Mount Sinai, New York, NY (USA); the Trustees of the University of Pennsylvania, Philadelphia, PA (USA)	Targeted protein replacement for the treatment of lysosomal storage disorders	2017	Compositions and methods for enzyme replacement therapies of LSDs	LSD
WO2018208630A1	Calygene Biotechnology Inc., Camden, DE (USA)	Aryl-sulfonamide and aryl-sulfone derivatives as TRPML modulators	2018	Aryl or heteroaryl compounds	Diseases related to lysosomal functions
US20180110798A1	The United States of America, as represented by the Secretary, Department of Health and Human Services, Rockville, MD (USA)	Cyclodextrin for the treatment of lysosomal storage diseases	2018	Cyclodextrin compounds	LSD

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The list of patents was generated by searching several databases (EPO (Espacenet), USPTO and others) from 2014 to early 2019 using keywords — lysosomal modulators or modulation, lysosomal protein inhibitors (mucolipin, vacuolins, and so forth), lysosomal enzyme inhibitors and lysosome function modulators — and selecting only the chemical modulators/inhibitors that act on lysosomal function. Patents are arranged based on the year filed, published or granted. LSD, lysosomal storage disorder; PIKfyve, FYVE finger-containing phosphoinositide kinase; RIP, receptor-interacting protein kinase; SjS, Sjögren’s syndrome; TRPML, transient receptor potential mucolipin.

Below and in Table 4, we summarize the availability of pharmacological tool compounds and progress in drug development, where applicable, for each broad target class.

Substrate reduction therapies and small-molecule chaperones

In addition to ERTs for LSDs (Box 1), drug discovery programmes have also focused on alternative small molecule-based approaches, which may be particularly relevant for LSDs that affect the CNS, due to the lack of blood–brain barrier penetration by ERTs283.

Small molecules used in substrate reduction therapies prevent the accumulation of substrates of the defective enzymes in LSDs by inhibiting enzymes involved in substrate production284. Miglustat was the first such drug to be approved in the early 2000s by the US Food and Drug Administration and the European Medicines Agency for Gaucher disease and in 2009 for Niemann–Pick disease type C in Europe. This iminosugar inhibits glucosylceramide synthase (GCS), which catalyses the initial step in formation of many glycosphingolipids. Within cells, glycosphingolipids tend to localize to the outer leaflet of the plasma membrane; they cycle within the cell through endocytic pathways that involve the lysosome. Inhibition of GCS therefore reduces the deleterious accumulation of glycosphingolipids within lysosomes with potential therapeutic benefits in diseases like LSDs. Miglustat also inhibits disaccharidases in the gastrointestinal tract, resulting in diarrhoea as a side effect285. Eliglustat, another GCS inhibitor that does not penetrate the CNS, was also approved for Gaucher disease in 2014. Other GCS inhibitors in clinical development include lucerastat, a miglustat analogue with an improved safety profile that is currently in a phase III trial for Fabry disease (FD)236,286, and ibiglustat, which penetrates the CNS. The latter is in clinical development for FD (phase II), for Gaucher disease type 3 (phase II) and for patients with PD who carry a mutation in GBA (phase II). Recent findings generated in a small number of patients have suggested a possible link between PD and FD287, which also exists between patients with PD and Gaucher disease who have GBA mutations (see above). Finally, genistein, a pleotropic natural product that inhibits kinases involved in the regulation of proteoglycan biosynthesis and also affects TFEB function, is in a phase III trial for Sanfilippo syndrome288.

Substrate mimetics that inhibit lysosomal enzymes have also been found to stabilize mutated enzymes in LSDs, thereby leading to restoration of some enzyme activity when suitable subinhibitory concentrations are used, as the enzyme remains stable and functional after dissociation of the inhibitor46,283. The pioneering example of this approach is migalastat, described above, that binds to the active site of α-galactosidase A, which is mutated in FD, and stabilizes the mutant enzyme. Other examples of this strategy include afegostat in Gaucher disease (which failed in a phase II clinical trial in 2009 due to lack of efficacy), pyrimethamine in Sandhoff disease and Tay–Sachs disease, and ambroxol in Gaucher disease with neurological symptoms (Table 4). Agents that are at earlier developmental stages include N-octyl-β-valienamine, a competitive inhibitor of β-glucosidase, for Gaucher disease; N-acetylcysteine for Pompe disease; α-lobeline, 3,4,7-trihydroxyisoflavone and azasugar in Krabbe disease; and N-octyl-4-epi-β-valienamine and 5N,6S-(N′-butyliminomethylidene)-6-thio-1-deoxygalactonojirimycin indicated in GM1 gangliosidosis289. The chemical structures of these pharmacological chaperones have been described recently290,291. Finally, an alternative strategy for stabilizing mutant enzymes, by binding away from the active site, is also being investigated. A promising example of this approach is NCGC607, a non-inhibitory small-molecule chaperone of GCase discovered by screening for molecules that improved the activity of the mutant enzyme46,250. Treatment with NCGC607 reduced lysosomal substrate storage and α-synuclein levels in dopaminergic neurons derived from induced pluripotent stem cells from patients with Gaucher disease with parkinsonism46,250. Further testing of NCGC607 in patients with PD and GBA mutations is awaited. Although promising, conflicting viewpoints still remain on the strength of such small molecule-based approaches, primarily because these compounds bind to the catalytic site of enzymes, which may be a risk at high concentrations if they inhibit rather than increase activity291,292. More clinical trials are therefore required in order to analyse the robustness of this approach.

Cathepsin modulators

Robust genetic and pharmacological preclinical investigations have consistently showed that regulating cathepsin activity can favourably improve pathological features in certain autoimmune and inflammatory diseases. Inhibitors of several cathepsins (B, D, L, K and S) have been described174,293 and their activity has been eval‎uated in rheumatic autoimmune diseases (such as SLE, RA and SjS) and neurodegenerative disorders, notably in AD294 (Table 4). Selective inhibition of cathepsin S with a potent active site inhibitor known as RO5461111 (Roche) mitigated disease in MRL/lpr lupus-prone mice, by reducing priming of T and B cells by dendritic cells, and plasma cell generation262. Promising data have also been generated in murine models, in the context of diabetic nephropathy and cardiovascular diseases295. Further studies based on cathepsin S inhibitors should eval‎uate the clinical safety and utility of treating patients affected by autoimmune and inflammatory diseases295. Cathepsin K, which is highly expressed by osteoclasts and very efficiently degrades type I collagen, the major component of the organic bone matrix, is also a potential target for modulating lysosomal dysfunction in some of the disorders discussed above, such as SLE96. Yet further investigations with selective cathepsin K inhibitors are required to determine whether this targeted strategy might apply in SLE and other inflammatory conditions in which articular manifestations are a major component (RA, ankylosing spondylitis, psoriatic arthritis and others). It should be noted, however, that various cathepsin K inhibitors have been pursued for postmenopausal osteoporosis, including odanacatib (Merck) which reached phase III trials296. Although odanacatib was effective, its development was discontinued in 2016 due to an increased risk of stroke in treated patients. Other cathepsin inhibitors and their context of clinical eval‎uation are listed in Table 4.

Despite multiple efforts to develop selective pharmacologic cathepsin modulators, important concerns still remain with regard to off-target effects due to activity against other cathepsins or towards cathepsins present at non-relevant or unwanted sites. Nonetheless, the underlying biology and clinical effects of certain cathepsin inhibitors or activators remain of considerable interest and could guide future therapeutic approaches.

v-ATPase inhibitors

As reported below, v-ATPase, a multisubunit ATP-driven proton pump, is best known for its role in acidification of endosomes and lysosomes. Regulating the function of v-ATPase may impact lysosomal activity and, hence, the acidification of specialized cells and diverse signalling pathways, such as autophagy. v-ATPase inhibitors like bafilomycin A1 and concanamycin A are non-selective compounds (Table 4; Fig. 3) that inhibit both mammalian and non-mammalian v-ATPases, which control the lysosomal pH of acidic vesicles via a manner that is not fully understood (Fig. 2). Through this mechanism, bafilomycin A1 inhibits autophagic flux by preventing the acidification of endosomes and lysosomes297. Bafilomycin and CQ also affect mitochondrial functions, as discovered recently using intact neurons298. Benzolactoneenamides (salicylihalamide A, lobatamides and oximidines; Table 4; Figs 2,3) are much more selective v-ATPase inhibitors299 than bafilomycin A1 and concanamycin A, but also much less potent. Further investigations into v-ATPase regulation of signalling pathways are needed to identify specific and safe molecules that regulate this vital proton pump300.

Ion channel modulators

As discussed above, lysosomal ion channels are master elements of lysosome activity and, thereby, of cell homeostasis. In the family of TRP channels, TRML1 is essential, being widely expressed in late endosomes and lysosomes, and preferentially associates with LAMP1 in the lysosomal membrane22,301,302. Genetic mutations leading to inactivation of TRPML1 cause a rare genetic disorder called mucolipidosis type IV (MLIV). Pharmacological activation of TRPML1 ameliorated some lysosomal functions that are classically associated with MLIV, NPCs and certain LSDs (Tables 2,4; Fig. 2). Thus, the small molecule SF-22 (Fig. 3), which was identified in a screen for TRPML3 activators, was defined as an activator of both TRPML3 and TRPML1 (ref.274), and displayed an additive effect in combination with the endogenous activator phosphatidylinositol-3,5-bisphosphate (PtdIns(3,5)P2)274,303. An analogue of SF-22, in which chlorine on the thiophene had been replaced by a methyl group, showed greater efficacy on TRPML1 activation303,304. Another molecule called ML-SA1 (Figs 2,3), acting as a mucolipin synthetic agonist, also showed an additive effect with endogenous PtdIns(3,5)P2 on TRPML1 channels305. It is important to note that in neurological diseases, as well as in other indications in which lysosomal acidification is defective (see above), interfering with TRML1 may have contraindications.

Phosphatidylinositol kinase modulators

A central modulator of lysosomes is the lipid kinase FYVE finger-containing phosphoinositide kinase (PIKfyve), which converts phosphatidylinositol-3-phosphate into PtdIns(3,5)P2. The latter regulates Ca2+ release from the lysosome lumen and is required for acidification by v-ATPase. Inactivation of PIKfyve leads to many pathophysiological problems including neurodegeneration and immune dysfunction, mostly related to impaired autophagic flux and alteration of lysosomes (trafficking, Ca2+ transport, biogenesis and swelling)306. The small-molecule apilimod (Fig. 3; Table 4) was originally identified as an inhibitor of TLR-induced IL-12 and IL-23, and later found to be a highly specific inhibitor of PIKfyve276. Apilimod was eval‎uated in clinical trials involving several hundred patients with T helper 1 and T helper 17 cell-mediated inflammatory diseases such as Crohn’s disease, RA and psoriasis277,278. It was well tolerated in more than 700 human subjects (normal healthy volunteers and patients with inflammatory disease), but the clinical trials did not meet their primary endpoints and further development was abandoned. Apilimod is currently being eval‎uated in a clinical trial (NCT02594384) aimed at defining a maximum tolerated dose in patients with B cell non-Hodgkin lymphoma and monitoring safety, pharmacokinetics, pharmacodynamics and preliminary efficacy307. YM-201636 is another selective inhibitor of PIKfyve (Table 4; Fig. 3). This inhibitor contains a FYVE-type zinc finger domain. YM-201636 was found to significantly reduce the survival of primary mouse hippocampal neurons in culture and reversibly impair endosomal trafficking in NIH3T3 cells, mimicking the effect produced by depleting PIKfyve with small interfering RNA. It was also found to block retroviral exit by budding from cells275. From a clinical perspective, although targeting PIKfyve is highly promising, further work is required to pave a way towards a future treatment.

Farnesyl transferase inhibitors

Several molecules with farnesyl transferase inhibitory activity have been developed. However, some earlier compounds were found to have major side effects, and their development was discontinued. Lonafarnib (SCH66336; Eiger Biopharmaceuticals), a synthetic tricyclic halogenated carboxamide, has recently shown some promise in a transgenic mouse, which expresses human tau carrying a P301L mutation282 (Table 4). These mice develop tangles in the hippocampus, amygdala, entorhinal cortex and cerebral cortex by 16 weeks, and about 60% of hippocampal neurons die at about 22 weeks. Compared with untreated mice, mice that received lonafarnib displayed less abnormal behaviour and half of the tangles in the hippocampi and cortices. Treatment also prevented brain atrophy that typically occurs in these transgenic mice, while reducing microgliosis in the hippocampus and tempering astrogliosis in the cortex. Mechanistic studies have shown in lonafarnib-treated mice that substrates were more efficiently delivered to lysosomes, their degradation products disappeared faster and the organelles were more readily degraded, specifically by improving lysosome efficiency. Knowing that lonafarnib is already approved for use in humans for other indications (cancer, and ongoing eval‎uation for progeria and hepatitis delta virus infection), it might therefore be repurposed for use in patients with tauopathy. In this class of farnesyl transferase inhibitors, tipifarnib (R115777; Johnson & Johnson) might also display interesting therapeutic properties as it has been seen to block lysosomal-dependent degradation of bortezomib-induced aggresomes without inhibition of the early steps of autophagy. Kura-oncology in-licenced tipifarnib in 2014.

Chaperone modulators

Molecules targeting chaperone proteins involved in lysosomal function have also been designed for potential therapeutic applications. One of these molecules is VER-155008, a small-molecule inhibitor of HSPA8, a key element of CMA308,309. VER-155008 binds to the nucleotide binding domain of HSPA8 and HSP70, and acts as an ATP-competitive inhibitor of ATPase and chaperone activity. In a mouse model of AD (5XFAD mice), intraperitoneal treatment with VER-155008 reduced the two main pathological features of AD (amyloid plaques and paired helical filament tau accumulation) and improved object recognition, location and episodic-like memory280.

Another molecule, the 21-mer phosphopeptide P140 (Table 4; Fig. 3), was also shown to interact with HSPA8 (Fig. 2)310 and lodge in the HSPA8 nucleotide binding domain92,311. P140 and VER-155008, however, do not have the same mechanism of action, and their effects were not additive312. P140 is a phosphorylated analogue of a nominal peptide that was initially spotted in a cellular screening assay using overlapping peptides covering the whole spliceosomal U1-70K protein and CD4+ T cells collected from the lymph nodes of lupus-prone MRL/lpr mice313. P140 peptide enters B cells via a clathrin coat-dependent endocytosis process to reach early endosomes and then late endosomes/lysosomes92. It affects CMA that is hyperactivated in lupus, likely by hampering the CMA-mediating chaperone HSPA8 (ref.101). P140 peptide reduces the excessive expression‎ of HSPA8 and LAMP2A observed in lupus mice, alters the (auto)antigen presentation by MHCII molecules in the MIIC compartment and, consequently, attenuates the activation of autoreactive T cells92. A significant diminution of MHC molecule expression‎ at the surface of antigen-presenting cells was measured in mice that received the P140 peptide intravenously and on patient’s peripheral cells treated ex vivo with the peptide92,101,314. As a downstream consequence, the activation of autoreactive B cells and their differentiation into autoantibody-secreting cells is repressed101,314. T cells from patients with lupus are no longer responders ex vivo to peptides encompassing CD4+ T cell epitopes315. The effect of P140 on CMA was demonstrated in vitro, using a fibroblast cell line that stably expresses a CMA reporter53,92. P140, which selectively targets the CMA/lysosome process and has no effect on mitophagy316, has been eval‎uated in murine models mimicking other rheumatic diseases with very promising results, notably in mice developing SjS features56, in mice with neuropsychiatric lupus symptoms62 and in rats that develop a CIDP-like disease with disturbance of both CMA and macroautophagy in sciatic nerves59. In clinical trials that included patients with SLE, P140 formulated in mannitol was found to be safe and non-immunogenic after several subcutaneous administrations of peptide312,317,318. P140 showed significant efficacy in a multicentre, double-blind, phase II trial317. This peptide is currently being eval‎uated in phase III trials in the United States, Europe and Mauritius. In continuation, an open-label trial including several hundred patients with lupus worldwide is planned.

Another peptide has been discovered that, in contrast to P140, activates CMA319. This 24-mer peptide called humanin was originally identified from surviving neurons in patients with AD, and was found to directly enhance CMA activity by increasing substrate binding and translocation into lysosomes. Humanin interacts with HSP90 and stabilizes the binding of this chaperone to CMA cargos as they bind to the lysosomal membrane. These results are important as humanin had been shown to possess some cardioprotective and neuroprotective properties in diseases such as AD, cardiovascular disease, stroke, myocardial infarction, diabetes and cancer320.

Emerging potential lysosomal therapeutic targets

In addition to the targets discussed above, there are a few emerging potential lysosomal therapeutic targets for which there is strong biological validation, but not yet any small molecules in development that target them. An example with likely pharmacological tractability is a lysosomal K+ channel called TMEM175, which is important for maintaining the membrane potential and pH stability in lysosomes321. Deficiency in TMEM175 may play a critical role in PD pathogenicity322. Importantly, the structure of TMEM175 has been recently refined323.

Another target for which ligands have not yet been validated is the KCNQ2/3 channel (also named M-channel or Kv7.2/7.3 channel). It has been shown in NPC1 disease that reduced cholesterol efflux from lysosomes aberrantly modifies neuronal firing patterns324. This disruption of lysosomal cholesterol efflux with decreases in PtdIns(4,5)P2-dependent KCNQ2/3 channel activity may lead to the aberrant neuronal activity. The cholesterol transporter and PtdIns(4,5)P2 floppase, ABCA1, is responsible for the decline in PtdIns(4,5)P2 that consequently modifies the electrical properties of NPC1 disease neurons. Dysfunction in the activity of KCNQ2/3 or altered levels of PtdIns(4,5)P2, due notably to genetic mutations, might also be involved in other neuropathies (for example, some forms of epilepsy, HD, PD, AD, ALS and Friedrich ataxia). Although further experiments are needed to validate the link discovered between hyperexcitability and cell death in NPC1 disease and other neurodegenerative diseases, small molecules such as retigabine, an anti-convulsant drug that keeps KCNQ2/3 channels open, might represent important therapeutic tools324,325. Other channel opener ligands of KCNQ2/Q3 include ICA-069673 and its derivatives.

Another promising therapeutic target is sphingomyelin phosphodiesterase 1 (SMPD1). Defects in the gene encoding SMPD1 cause Niemann–Pick disease type A and type B. SMPD1 converts sphingomyelin to ceramide, and also has phospholipase C activity. Reduced activity of acid sphingomyelinase, associated with a marked decrease in lysosomal stability, has been described in patients with Niemann–Pick disease, a phenotype that was corrected by treating cells with recombinant HSP70326.

Finally, as LAMP2A, a specific lysosomal protein that displays a decisive role in CMA, has been shown to be overexpressed in certain pathological settings such as certain cancers and inflammatory diseases (autoimmune or non-autoimmune), downregulating its expression‎ might be therapeutically beneficial53,327. As mentioned above, however, in other indications there is a defect in LAMP2A. The latter can be due to reduced stability of the CMA receptor and not to decreased de novo synthesis (for example, in ageing)328 or can result from aggregation to the lysosomal membrane of pathogenic proteins such as α-synuclein, ubiquitin carboxy-terminal hydrolase L1 (a deubiquitinating enzyme) and mutant tau, known to amass in neurodegenerative disorders (see above). Targeting LAMP2A therefore remains a challenge, although several strategies may be envisaged, for example by controlling de novo synthesis, by hampering its multimerization into lysosomes (possibly via HSP90 and/or other chaperones) or by regulating the degradation rate of LAMP2A monomers (for reuse) into lysosomes.

신규 잠재적 리소좀 치료 표적

위에서 논의된 표적 외에도, 강력한 생물학적 검증은 있지만 아직 해당 표적을 표적으로 하는 개발 중인 소분자가 없는 몇 가지 신규 잠재적 리소좀 치료 표적이 있습니다. 약리학적 접근 가능성이 높은 예시로는 리소좀 내 막 전위와 pH 안정성을 유지하는 데 중요한 역할을 하는 리소좀 K+ 채널인 TMEM175가 있습니다321. TMEM175의 결핍은 파킨슨병(PD)의 병리학적 기전에 중요한 역할을 할 수 있습니다322. 중요하게도, TMEM175의 구조는 최근에 정교하게 재구성되었습니다323.

리간드가 아직 검증되지 않은 또 다른 표적은 KCNQ2/3 채널(M-채널 또는 Kv7.2/7.3 채널로도 알려져 있음)입니다. NPC1 질환에서 리소좀으로부터의 콜레스테롤 배출 감소가 신경 세포의 발화 패턴을 비정상적으로 변화시킨다는 것이 밝혀졌습니다324. 리소좀 콜레스테롤 배출의 장애와 PtdIns(4,5)P2 의존성 KCNQ2/3 채널 활성의 감소는 비정상적인 신경 세포 활성을 유발할 수 있습니다. 콜레스테롤 운반체이자 PtdIns(4,5)P2 플로파제인 ABCA1은 PtdIns(4,5)P2의 감소에 책임이 있으며, 이는 NPC1 질환 신경 세포의 전기적 특성을 변화시킵니다. KCNQ2/3의 활동 장애나 PtdIns(4,5)P2 수준의 변화(특히 유전적 변이 때문)는 다른 신경병증(예: 일부 형태의 간질, HD, PD, AD, ALS 및 Friedrich 운동실조증)에도 관여할 수 있습니다. NPC1 질환과 다른 신경퇴행성 질환에서 과흥분성과 세포 사멸 간의 연관성을 검증하기 위해 추가 실험이 필요하지만, KCNQ2/3 채널을 개방 상태로 유지하는 항경련제인 레티가빈과 같은 소분자는 중요한 치료 도구로 작용할 수 있습니다324,325. KCNQ2/Q3 채널 개방제 리간드에는 ICA-069673 및 그 유도체가 포함됩니다.

또 다른 유망한 치료 표적은 스핑고미엘린 포스포디에스테라제 1 (SMPD1)입니다. SMPD1을 암호화하는 유전자의 결함은 니만-픽병 A형과 B형을 유발합니다. SMPD1은 스핑고미엘린을 세라마이드로 변환하고, 포스포리파제 C 활성도 가지고 있습니다. 니만-픽 병 환자에게서 리소좀 안정성의 현저한 감소와 연관된 산성 스핑고미엘리나제 활성 감소가 보고되었으며, 이 현상은 재조합 HSP70으로 세포를 처리함으로써 교정되었습니다326.

마지막으로, CMA에서 결정적인 역할을 하는 특정 리소좀 단백질인 LAMP2A는 특정 병리학적 상태(예: 특정 암 및 염증성 질환(자가면역 또는 비자가면역))에서 과발현되는 것으로 확인되었습니다. 따라서 그 발현을 억제하는 것이 치료적으로 유익할 수 있습니다53,327. 그러나 위에서 언급된 것처럼 다른 적응증에서는 LAMP2A에 결함이 존재합니다. 후자는 CMA 수용체의 안정성 감소 때문일 수 있으며(예: 노화 시)328, 또는 α-시누클린, 유비퀴틴 카르복시말단 가수분해효소 L1(유비퀴틴 제거 효소) 및 신경퇴행성 질환에서 축적되는 것으로 알려진 돌연변이 타우와 같은 병리적 단백질의 리소좀 막에 대한 집적 때문일 수 있습니다(위 참조). 따라서 LAMP2A를 표적화하는 것은 여전히 도전 과제이지만, 몇 가지 전략이 고려될 수 있습니다. 예를 들어, 신규 합성을 조절하거나, 리소좀 내 다중체 형성을 방해하는 방법(HSP90 및/또는 다른 분자 샤페론 via를 통해) 또는 LAMP2A 단량체의 분해 속도를 조절하여 리소좀 내 재사용을 촉진하는 방법 등이 있습니다.

Challenges and outlook

Current research into lysosomal function and dysfunction is revealing novel roles of lysosomes in disease pathogenesis and highlighting new opportunities to treat such lysosomal and autophagy-related diseases. As in the case of autophagy modulation14,56,207, lysosomal activation or inhibition must be investigated with caution, as lysosomal activity can be abnormally reduced or enhanced in some organs or tissues and not in others, and, at another scale, lysosome activity can be altered in certain lysosomes and not in others within the same cell. Biodistribution studies in vivo must be undertaken to avoid accumulation of pharmaceuticals in healthy organs or tissues. There is an obvious requirement for safety, to ensure that a drug used as a lysosome modulator for a particular type of lysosomal disease does not increase vulnerability to another disease.

There is still much to be learned about the intimate working of lysosomes. This is due to the abundance of constitutive elements that comprise these vesicles, the added complexity resulting from their plasticity (ion channels and transporters, acidification and swelling) and the vast amount of proteins and peptides that are translocated into lysosomes and digested by lytic enzymes. Sensitive analysis methods have allowed important information to be generated about lysosomal membrane proteins, a large majority of which are transporters8. However, many questions remain related to how their expression‎ is regulated and how they regulate their translocator and chaperoning activities. For example, certain cells only contain so-called secretory lysosomes (as in cytotoxic T cells), whereas other cell subsets contain both conventional and secretory lysosomes (as in platelets). Considering the large family of endo-lysosomal vesicles, the whole notion of ‘secretory’ and ‘conventional’ lysosomes remains a matter of debate. In many instances, lysosomes act as a basal cell metabolism organelle; whereas in other cases, they assist in the regulation of homeostasis through unconventional secretory pathways, known as lysosomal exocytosis, and different signalling mechanisms.

Although several assays used to measure the activity of lysosomes have been validated worldwide (Box 2; Table 3), they have their limitations, including issues associated with reliability, performance and sensitivity, notably in vivo. Another level of complexity comes from the inherent organelle heterogeneity, which is an issue of tremendous importance. Unfortunately, with the tools and equipment we have in hand today, it is virtually impossible to examine what happens in the lysosomes of an individual patient. The introduction of microfluidic single-cell analysis technologies has enabled cellular populations to be characterized and huge advances to be performed. However, the level of precision has not yet been achieved at the level of lysosomes (0.2–0.5 μm). We know that lysosomes are heterogeneous in nature, composition and activity even in ‘normal’ settings; they are not all equally competent for autophagy or any other types of activity. Currently, this is obviously the focus of intense research.

Although a certain number of preclinical studies involving lysosomal regulators have been conducted over the years, only a small number of lysosome-targeted therapeutics have so far moved into clinical development. One of the biggest advances in developing such strategies would be the identification of a genetic signature that would allow those patients most likely to respond to a specific therapy to be selected. However, at this stage of our knowledge of specific lysosome-directed drugs and intrinsic lysosomal failures, genetic features that might predict potential responders are still lacking (with the exception of LSDs). Further investigations are required to achieve this level of knowledge, which obviously will also depend on the type of disease, heterogeneity and frequency.

Another issue associated with the development of lysosome-targeted therapeutics relates to delivery. The use of nanovectors represents an attractive delivery method, owing, in particular, to their unique ability to penetrate across cell barriers and, via the endo-lysosomal pathway, to preferentially home in on organelles such as lysosomes. Several nanoscale galenic forms have been developed to serve as vectors or carriers of proteins, peptides or nucleic acids, and a vast literature describes the many advantages of using such nanostructures in nanomedicine. However, safety is a concern as some carbon nanostructures have been claimed to induce nanotoxicity, accompanied by the induction of autophagy and lysosomal dysfunction329–332 (reviewed elsewhere333–336).

The purpose of this Review is to gain awareness of the importance of lysosomes in disease, and to encourage the development of novel lysosomal targeted drugs. However, more research is needed to characterize components that are specifically linked to the lysosome, such as LAMP2A and HSPA8, and to more clearly define their specific involvement in lysosome biogenesis and metabolism. Special attention should be given to the mode of administration of lysosome-targeted medications in order to minimize toxicity and promote specific targeting. It is our hope that a large field of therapeutic applications could emerge from such investigations, encompassing rare and common autoimmune, neurodegenerative and metabolic diseases, as well as cancer, senescence and ageing.

도전 과제 및 전망

리소좀 기능 및 기능 장애에 대한 현재의 연구는 질병 발병에서 리소좀의 새로운 역할을 밝히고 있으며, 리소좀 및 자가포식 관련 질병을 치료할 수 있는 새로운 기회를 강조하고 있습니다.

자가포식 조절의 경우14,56,207과 마찬가지로, 리소좀의 활성화 또는 억제는 일부 기관이나 조직에서는 비정상적으로 감소하거나 강화될 수 있고, 또 다른 규모에서는 동일한 세포 내의 일부 리소좀에서만 리소좀의 활동이 변화될 수 있기 때문에 신중하게 조사해야 합니다. 생체 내 약물 분포 연구를 수행하여 건강한 장기나 조직에 약물이 축적되지 않도록 해야 합니다. 특정 유형의 리소좀 질환 치료를 위해 리소좀 조절제로 사용되는 약물이 다른 질환에 대한 취약성을 증가시키지 않도록 안전성을 확보하는 것이 필수적입니다.

리소좀의 내부 작동 메커니즘에 대해 아직 많은 것이 알려지지 않았습니다. 이는 리소좀을 구성하는 기본 요소들의 풍부함, 이들의 가소성(이온 채널과 운반체, 산성화 및 부종)으로 인한 추가적인 복잡성, 그리고 리소좀으로 운반되어 리소좀 분해 효소에 의해 분해되는 단백질과 펩타이드의 방대한 양 때문입니다. 민감한 분석 방법은 리소좀 막 단백질에 대한 중요한 정보를 제공했으며, 이 중 대부분은 운반체입니다8. 그러나 그들의 발현 조절 방식과 운반체 및 분자 접힘 보조 활동 조절 메커니즘에 대한 많은 질문이 남아 있습니다. 예를 들어, 일부 세포는 이른바 분비형 리소좀(세포독성 T 세포에서처럼)만을 포함하지만, 다른 세포 하위 집합은 전통적 리소좀과 분비형 리소좀을 모두 포함합니다(혈소판에서처럼). 엔도-리소좀 소포의 대규모 가족을 고려할 때, ‘분비형'과 '일반형’ 리소좀의 개념은 여전히 논쟁의 대상입니다. 많은 경우 리소좀은 기초 세포 대사 소기관으로 기능하지만, 다른 경우 비전형적인 분비 경로인 리소좀 분비와 다양한 신호 전달 메커니즘을 통해 항상성 조절에 기여합니다.

리소좀 활성을 측정하기 위해 전 세계적으로 검증된 여러 분석법이 존재합니다(상자 2; 표 3). 그러나 신뢰성, 성능, 민감도(특히 in vivo에서)와 관련된 한계가 있습니다. 또 다른 복잡성은 내재된 소기관 이질성에서 비롯되며, 이는 엄청난 중요성을 지닌 문제입니다. 불행히도 현재 보유한 도구와 장비로는 개별 환자의 리소좀에서 발생하는 현상을 조사하는 것이 사실상 불가능합니다. 마이크로 유체 단일 세포 분석 기술의 도입으로 세포 집단을 특성화하고 엄청난 발전을 이룰 수 있게 되었습니다. 그러나 리소좀 수준(0.2~0.5μm)에서는 아직 그 정밀도가 달성되지 않았습니다. 리소좀은 ‘정상’ 상태에서도 본질, 구성 및 활동이 이질적이며, 모든 리소좀이 자가포식이나 다른 유형의 활동을 똑같이 수행할 수 있는 것은 아닙니다. 현재 이는 분명히 집중적인 연구의 초점입니다.

수년간 리소좀 조절 인자를 대상으로 한 전임상 연구가 진행되었지만, 현재까지 임상 개발 단계로 진입한 리소좀 표적 치료제는 극히 드뭅니다. 이러한 전략 개발의 가장 큰 진전은 특정 치료법에 가장 잘 반응할 가능성이 높은 환자를 선별할 수 있는 유전적 특성을 식별하는 것입니다. 그러나 현재 특정 리소좀 표적 약물과 내재적 리소좀 기능 장애에 대한 지식 단계에서, 잠재적 반응자를 예측할 수 있는 유전적 특징은 여전히 부족합니다(LSD를 제외하고). 이 수준의 지식을 달성하기 위해서는 추가 연구가 필요하며, 이는 당연히 질병의 유형, 이질성 및 빈도에 따라 달라질 것입니다.

리소좀 표적 치료제 개발과 관련된 또 다른 문제는 전달입니다. 나노벡터는 세포 장벽을 관통하는 독특한 능력과 엔도-리소좀 경로를 통해 리소좀과 같은 세포 소기관에 선택적으로 침투하는 특성 때문에 매력적인 전달 방법으로 주목받고 있습니다. 단백질, 펩티드 또는 핵산의 벡터 또는 운반체로 사용하기 위해 여러 가지 나노 규모의 제형이 개발되었으며, 나노 의학에서 이러한 나노 구조를 사용하는 것의 많은 이점을 설명하는 방대한 문헌이 있습니다. 그러나 일부 탄소 나노 구조는 자가포식 및 리소좀 기능 장애를 유발하는 나노 독성을 유발한다고 주장되어 안전성이 우려되고 있습니다329–332 (다른 문헌에서 검토됨333–336).

이 리뷰의 목적은 리소좀이 질병에서 차지하는 중요성을 인식하고, 새로운 리소좀 표적 약물의 개발을 장려하는 것입니다. 그러나 리소좀과 특이적으로 연관된 구성 요소(예: LAMP2A 및 HSPA8)를 특성화하고, 이러한 구성 요소가 리소좀 생성과 대사에서 구체적으로 어떻게 관여하는지 명확히 정의하기 위해 추가 연구가 필요합니다. 리소좀 표적 약물의 투여 방법을 신중히 고려하여 독성을 최소화하고 특정 표적화를 촉진하는 것이 중요합니다. 이러한 연구를 통해 희귀 및 일반적인 자가면역 질환, 신경퇴행성 질환, 대사 질환, 암, 노화 및 노화 관련 질환을 포함하는 광범위한 치료 응용 분야가 등장할 것으로 기대됩니다.

Acknowledgements

The authors apologize to all those whose work is not cited due to space limitations. They gratefully acknowledge Hélène Jeltsch-David for critically reading the manuscript. This research was funded by the French Centre National de la Recherche Scientifique, Région Alsace, the Laboratory of Excellence Medalis (ANR-10-LABX-0034), Initiative of Excellence (IdEx), Strasbourg University, and ImmuPharma France. S.M. is grateful to the University of Strasbourg Institute for Advanced Study (USIAS) for funding F.W., and acknowledges the support of the TRANSAUTOPHAGY COST Action (CA15138), the Club francophone de l’autophagie (CFATG) and the European Regional Development Fund of the European Union in the framework of the INTERREG V Upper Rhine programme.

Glossary

Endocytosis

A vesicle-mediated process by which cells engulf membrane and extracellular materials. Several endocytic pathways — phagocytosis, pinocytosis and receptor-mediated endocytosis — utilize different mechanisms to internalize material. Clathrin-mediated endocytosis is the major endocytic pathway in mammalian cells.

Phagocytosis

An endocytic process by which certain cells called phagocytes (for example, macrophages) internalize large particles (>0.5 µm) such as bacteria, other microorganisms, foreign particles or aged red blood cells, for example, to form a phagosome.

Autophagy

A vital, finely-regulated and evolutionarily-conserved intracellular pathway that continuously degrades, recycles and clears unnecessary or dysfunctional cellular components. Autophagy is crucial for cell adaptation to the environment and to maintain cell homeostasis, especially under stress conditions.

Golgi apparatus

Cytosolic apparatus, meant for the regulation of proteins (modification, storing and transportation) and some forms of lipids to the other cytosolic compartments via the trans-Golgi network or outside the cell.

Lysosomal exocytosis

A process of the secretory pathway in which lysosomes are fused with the plasma membrane and empty their contents outside the cell. This process plays an important role in plasma membrane repair, bone resorption, immune response and elimination of pathogenic stores (mainly in lysosomal storage disorders).

Lysosomal storage disorders

(LSDs). A group of heterogeneous disorders caused by defects in the lysosomal enzymes leading to the accumulation of unmodified or unprocessed components in the lysosomes, which ultimately influence other vital pathways in the cells. LSDs implicate various vital systems of the human body including the skeleton, brain, skin, heart and central nervous system, which are connected with different metabolic pathways.

Rheumatoid arthritis

(RA). An autoimmune disease involving inflammation and degeneration of the joints that affects an estimated 1% of the population, making it the most common inflammatory arthritis.

Multiple sclerosis

(MS). A demyelinating disease in which the myelin sheaths wrapped around nerve fibres in the central nervous system are progressively destroyed by immune cells and possibly also by autoantibodies.

Parkinson disease

(PD). A neurodegenerative disorder with symptoms including slowness of movement and a loss of fine motor control, owing to the degeneration of dopamine-producing neurons in the substantia nigra.

Chaperone-mediated autophagy

(CMA). A selective autophagy pathway in which proteins that contain a signal KFERQ-like sequence are targeted by HSAP8/HSC70 chaperones and translocated into lysosomes via LAMP2A.

Transcription factor EB

(TFEB). A protein that plays a pivotal role in the regulation of basic cellular processes, such as lysosomal biogenesis and autophagy. It controls lysosomal function via the coordinated lysosomal expression‎ and regulation (CLEAR) gene network (including genes coding for hydrolases, lysosomal membrane proteins and the proton pump v-ATPase complex), and additional lysosome-related processes such as autophagy, endocytosis and exocytosis.

Macroautophagy

A finely-regulated process during which the cell forms a double-membrane sequestering compartment named the phagophore, which matures into the autophagosome.

Autophagosome

A double membrane-bound vesicle, which encloses cellular constituents and fuses with lysosomes to form phagolysosomes where the engulfed material is digested or degraded and either released extracellularly via exocytosis or released intracellularly to undergo further processing.

Mitophagy

A key process that selectively disrupts damaged mitochondria by autolysosomal degradation, preventing excessive reactive oxygen species and activation of cell death.

Huntingtin

(HTT). Discovered in 1993, HTT is a protein of 348 kDa that is widely expressed within the central nervous system. Its structure has been elucidated recently by cryo-electron microscopy. The protein is essential for embryonic development and neurogenesis. It is involved in transcription, vesicle transport, protein trafficking, endocytosis and autophagy.

Systemic lupus erythematosus

(SLE). A chronic, relapsing–remitting autoinflammatory syndrome that has multiple and heterogeneous symptoms, including arthralgia, swollen joints, fever, fatigue, chest pain, kidney inflammation, cardiovascular disease and neuropsychiatric complications. Its aetiology is mostly unknown.

Sjögren’s syndrome

(SjS). A multifactorial systemic autoimmune disorder characterized by lymphocytic infiltrates in exocrine organs. Symptoms include dry eyes, dry mouth and parotid enlargement, and serious complications include fatigue, chronic pain, neuropathies and lymphomas.

Myasthenia gravis

Caused by antibodies targeting the muscle acetylcholine receptor or other neuromuscular junction proteins such as muscle-specific kinase. These antibodies compromise communication between nerves and muscles, leading to muscular weakness and fatigue.

Chronic inflammatory demyelinating polyneuropathy

(CIDP). A progressive autoimmune disorder in which peripheral nerves (roots and trunks) and brachial plexuses are damaged owing to demyelination. It causes muscle weakness, sensory loss and reduced reflexes.

Neuromyelitis optica

Also known as Devic’s syndrome, this disease is characterized by an inflammation and demyelination of the optic nerve (optic neuritis) and the spinal cord (myelitis). Antibodies reacting with aquaporin-4 water channels in the brains of patients are implicated in neuromyelitis optica.

Amyotrophic lateral sclerosis

(ALS). Also known as motor neuron disease, this disease generally starts with muscle twitching and weakness in a limb, or slurred speech. It can affect control of the muscles needed to move, speak, eat and breathe, and can be fatal.

Tau

A major microtubule-associated protein of a mature neuron. Hyperphosphorylated tau accumulates with ubiquitin in ageing neurons as the neurofibrillary tangles that were identified in numerous neurodegenerative diseases called tauopathies that include Alzheimer disease.

Fabry disease

(FD). A progressive, X-linked inherited, multisystemic lysosomal storage disorder caused by GLA mutations, resulting in α-galactosidase deficiency and accumulation of lysosomal substrate.

Author contributions

All authors made substantial, direct and intellectual contribution to the work and approved it for publication.

Competing interests

S.M. discloses the following conflicts of interest: research funding (paid to institution) and a past consultant for ImmuPharma; co-inventor of CNRS-ImmuPharma patents on P140 peptide; owns ImmuPharma shares. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. S.R.B. and F.W. declare no competing interests.

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