Increased Lysosomal Exocytosis Induced by Lysosomal Ca2+ Channel Agonists Protects Human Dopaminergic Neurons from α-Synuclein Toxicity

TPCs: FROM PLANT TO HUMAN

In 2005, the Arabidopsis thaliana two-pore channel TPC1 channel was identified as a vacuolar Ca2+-release channel. In 2009, three independent groups published studies on mammalian TPCs as nicotinic acid adenine dinucleotide phosphate (NAADP)-activated endolysosomal Ca2+ release channels, results that were eventually challenged by two other groups, claiming mammalian TPCs to be phosphatidylinositol-3,5-bisphosphate [PI(3,5)P2]-activated Na+ channels. By now this dispute seems to have been largely reconciled. Lipophilic small molecule agonists of TPC2, mimicking either the NAADP or the PI(3,5)P2 mode of channel activation, revealed, together with structural evidence, that TPC2 can change its selectivity for Ca2+ versus Na+ in a ligand-dependent fashion (N- vs. P-type activation). Furthermore, the NAADP-binding proteins Jupiter microtubule-associated homolog 2 protein (JPT2) and Lsm12 were discovered, corroborating the hypothesis that NAADP activation of TPCs only works in the presence of these auxiliary NAADP-binding proteins. Pathophysiologically, loss or gain of function of TPCs has effects on autophagy, exocytosis, endocytosis, and intracellular trafficking, e.g., LDL cholesterol trafficking leading to fatty liver disease or viral and bacterial toxin trafficking, corroborating the roles of TPCs in infectious diseases such as Ebola or COVID-19. Defects in the trafficking of epidermal growth factor receptor and β1-integrin suggested roles in cancer. In neurodegenerative lysosomal storage disease models, P-type activation of TPC2 was found to have beneficial effects on both in vitro and in vivo hallmarks of Niemann-Pick disease type C1, Batten disease, and mucolipidosis type IV. Here, we cover the latest on the structure, function, physiology, and pathophysiology of these channels with a focus initially on plants followed by mammalian TPCs, and we discuss their potential as drug targets, including currently available pharmacology.

KCTD20 suppression mitigates excitotoxicity in tauopathy patient organoids

Excitotoxicity is a major pathologic mechanism in patients with tauopathy and other neurodegenerative diseases. However, the key neurotoxic drivers and the most effective strategies for mitigating these degenerative processes are unclear. Here, we show that glutamate treatment of induced pluripotent stem cell (iPSC)-derived cerebral organoids induces tau oligomerization and neurodegeneration and that these phenotypes are enhanced in organoids derived from tauopathy patients. Using a genome-wide CRISPR interference (CRISPRi) screen, we find that the suppression of KCTD20 potently ameliorates tau pathology and neurodegeneration in glutamate-treated organoids and mice, as well as in transgenic mice overexpressing mutant human tau. KCTD20 suppression reduces oligomeric tau and improves neuron survival by activating lysosomal exocytosis, which clears pathological tau. Our results show that glutamate signaling can induce neuronal tau pathology and identify KCTD20 suppression and lysosomal exocytosis as effective strategies for clearing neurotoxic tau species.

Small-molecule activation of TFEB alleviates Niemann-Pick disease type C via promoting lysosomal exocytosis and biogenesis

Niemann-Pick disease type C (NPC) is a devastating lysosomal storage disease characterized by abnormal cholesterol accumulation in lysosomes. Currently, there is no treatment for NPC. Transcription factor EB (TFEB), a member of the microphthalmia transcription factors (MiTF), has emerged as a master regulator of lysosomal function and promoted the clearance of substrates stored in cells. However, it is not known whether TFEB plays a role in cholesterol clearance in NPC disease. Here, we show that transgenic overexpression of TFEB, but not TFE3 (another member of MiTF family) facilitates cholesterol clearance in various NPC1 cell models. Pharmacological activation of TFEB by sulforaphane (SFN), a previously identified natural small-molecule TFEB agonist by us, can dramatically ameliorate cholesterol accumulation in human and mouse NPC1 cell models. In NPC1 cells, SFN induces TFEB nuclear translocation via a ROS-Ca2+-calcineurin-dependent but MTOR-independent pathway and upregulates the expression of TFEB-downstream genes, promoting lysosomal exocytosis and biogenesis. While genetic inhibition of TFEB abolishes the cholesterol clearance and exocytosis effect by SFN. In the NPC1 mouse model, SFN dephosphorylates/activates TFEB in the brain and exhibits potent efficacy of rescuing the loss of Purkinje cells and body weight. Hence, pharmacological upregulating lysosome machinery via targeting TFEB represents a promising approach to treat NPC and related lysosomal storage diseases, and provides the possibility of TFEB agonists, that is, SFN as potential NPC therapeutic candidates.

Rab27b Promotes Lysosomal Function and Alpha-Synuclein Clearance in Neurons

Alpha-synuclein (αsyn) is the key pathogenic protein implicated in synucleinopathies including Parkinson's disease (PD) and dementia with Lewy bodies (DLB). In these diseases, αsyn is thought to spread between cells where it accumulates and induces pathology; however, mechanisms that drive its propagation or aggregation are poorly understood. We have previously reported that the small GTPase Rab27b is elevated in human PD and DLB and that it can mediate the autophagic clearance and toxicity of αsyn in a paracrine αsyn cell culture model. Here, we expanded our previous work and characterized the role of Rab27b in neuronal lysosomal processing and αsyn clearance. We found that Rab27b KD in this αsyn-inducible neuronal model resulted in lysosomal dysfunction and increased αsyn levels in lysosomes. Similar lysosomal proteolytic defects and enzymatic dysfunction were observed in both primary neuronal cultures and brain lysates from male and female Rab27b knock-out (KO) mice. αSyn aggregation was exacerbated in Rab27b KO neurons upon treatment with αsyn preformed fibrils. We found no changes in lysosomal counts or lysosomal pH in either model, but we did identify changes in acidic vesicle trafficking and in lysosomal enzyme maturation and localization, which may drive lysosomal dysfunction and promote αsyn aggregation. Rab27b OE enhanced lysosomal activity and reduced insoluble αsyn accumulation. Finally we found elevated Rab27b levels in human postmortem incidental Lewy body disease subjects relative to healthy controls. These data suggest the role of Rab27b in neuronal lysosomal activity and identify it as a potential therapeutic target in synucleinopathies.

Carbonic anhydrase inhibition ameliorates tau toxicity via enhanced tau secretion

Tauopathies are neurodegenerative diseases that manifest with intracellular accumulation and aggregation of tau protein. These include Pick's disease, progressive supranuclear palsy, corticobasal degeneration and argyrophilic grain disease, where tau is believed to be the primary disease driver, as well as secondary tauopathies, such as Alzheimer's disease. There is a need to develop effective pharmacological therapies. Here we tested >1,400 clinically approved compounds using transgenic zebrafish tauopathy models. This revealed that carbonic anhydrase (CA) inhibitors protected against tau toxicity. CRISPR experiments confirmed that CA depletion mimicked the effects of these drugs. CA inhibition promoted faster clearance of human tau by promoting lysosomal exocytosis. Importantly, methazolamide, a CA inhibitor used in the clinic, also reduced total and phosphorylated tau levels, increased neuronal survival and ameliorated neurodegeneration in mouse tauopathy models at concentrations similar to those seen in people. These data underscore the feasibility of in vivo drug screens using zebrafish models and suggest serious consideration of CA inhibitors for treating tauopathies.

Mesenchymal stem cell exosomes enhance the development of hair follicle to ameliorate androgenetic alopecia

BACKGROUND

Mesenchymal stem cells (MSCs) and their secretome have significant potential in promoting hair follicle development. However, the effects of MSC therapy have been reported to vary due to their heterogeneous characteristics. Different sources of MSCs or culture systems may cause heterogeneity of exosomes.

AIM

To define the potential of human adipose-derived MSC exosomes (hADSC-Exos) and human umbilical cord-derived MSC exosomes (hUCMSC-Exos) for improving dermal papillary cell proliferation in androgenetic alopecia.

METHODS

We conducted liquid chromatography-mass spectrometry proteomic analysis of hADSC-Exos and hUCMSC-Exos. Liquid chromatography-mass spectrometry suggested that hADSC-Exos were related to metabolism and immunity. Additionally, the hADSC-Exo proteins regulated the cell cycle and other 9 functional groups.

RESULTS

We verified that hADSC-Exos inhibited glycogen synthase kinase-3β expression by activating the Wnt/β-catenin signaling pathway via cell division cycle protein 42, and enhanced dermal papillary cell proliferation and migration. Excess dihydrotestosterone caused androgenetic alopecia by shortening the hair follicle growth phase, but hADSC-Exos reversed these effects.

CONCLUSION

This study indicated that hair development is influenced by hADSC-Exo-mediated cell-to-cell communication via the Wnt/β-catenin pathway.

Alpha-Synuclein Inhibits the Secretion of Extracellular Vesicles through Disruptions in YKT6 Lipidation

Parkinson's disease is characterized by the presence of alpha-synuclein (α-syn) primarily containing Lewy bodies in neurons. Despite decades of extensive research on α-syn accumulation, its molecular mechanisms have remained largely unexplored. Recent studies by us and others have suggested that extracellular vesicles (EVs), especially exosomes, can mediate the release of α-syn from cells and inhibiting this pathway could result in increased intracellular α-syn levels. In this study, we have discovered that elevated levels of α-syn themselves lead to reduced α-syn -containing EVs in α-syn-inducible H4 cells and induced pluripotent stem cell-derived dopaminergic (DA) neurons from both sexes. Our investigations have revealed that the impairment in EV secretion is not due to their generation but rather a consequence of changes in a soluble N-ethylmaleimide-sensitive factor attachment protein receptor protein, YKT6. Specifically, as α-syn levels increase, membrane-associated YKT6 is reduced. Pharmacological inhibition of farnesylation using FTI has led to decreased EV secretion and subsequent elevated levels of α-syn. In summary, our findings suggest that increased levels of α-syn impair YKT6-mediated EV secretion, establishing a detrimental cycle of intracellular α-syn accumulation in human DA neurons.

Lysosomes' fallback strategies: more than just survival or death

Lysosomes are heterogeneous, acidic organelles whose proper functionality is critically dependent on maintaining the integrity of their membranes and the acidity within their lumen. When subjected to stress, the lysosomal membrane can become permeabilized, posing a significant risk to the organelle's survival and necessitating prompt repair. Although numerous mechanisms for lysosomal repair have been identified in recent years, the progression of lysosome-related diseases is more closely linked to the organelle's alternative strategies when repair mechanisms fail, particularly in the contexts of aging and pathogen infection. This review explores lysosomal responses to damage, including the secretion of lysosomal contents and the interactions with lysosome-associated organelles in the endolysosomal system. Furthermore, it examines the role of organelles outside this system, such as the endoplasmic reticulum (ER) and Golgi apparatus, as auxiliary organelles of the endolysosomal system. These alternative strategies are crucial to understanding disease progression. For instance, the secretion and spread of misfolded proteins play key roles in neurodegenerative disease advancement, while pathogen escape via lysosomal secretion and lysosomotropic drug expulsion underlie cancer treatment resistance. Reexamining these lysosomal fallback strategies could provide new perspectives on lysosomal biology and their contribution to disease progression.

Cholesterol-mediated Lysosomal Dysfunction in APOE4 Astrocytes Promotes α-Synuclein Pathology in Human Brain Tissue

The pathological hallmark of neurodegenerative disease is the aberrant post-translational modification and aggregation of proteins leading to the formation of insoluble protein inclusions. Genetic factors like APOE4 are known to increase the prevalence and severity of tau, amyloid, and α-Synuclein inclusions. However, the human brain is largely inaccessible during this process, limiting our mechanistic understanding. Here, we developed an iPSC-based 3D model that integrates neurons, glia, myelin, and cerebrovascular cells into a functional human brain tissue (miBrain). Like the human brain, we found pathogenic phosphorylation and aggregation of α-Synuclein is increased in the APOE4 miBrain. Combinatorial experiments revealed that lipid-droplet formation in APOE4 astrocytes impairs the degradation of α-synuclein and leads to a pathogenic transformation that seeds neuronal inclusions of α-Synuclein. Collectively, this study establishes a robust model for investigating protein inclusions in human brain tissue and highlights the role of astrocytes and cholesterol in APOE4-mediated pathologies, opening therapeutic opportunities.

Homeostasis and metabolism of iron and other metal ions in neurodegenerative diseases

As essential micronutrients, metal ions such as iron, manganese, copper, and zinc, are required for a wide range of physiological processes in the brain. However, an imbalance in metal ions, whether excessive or insufficient, is detrimental and can contribute to neuronal death through oxidative stress, ferroptosis, cuproptosis, cell senescence, or neuroinflammation. These processes have been found to be involved in the pathological mechanisms of neurodegenerative diseases. In this review, the research history and milestone events of studying metal ions, including iron, manganese, copper, and zinc in neurodegenerative diseases such as Parkinson's disease (PD), Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD), will be introduced. Then, the upstream regulators, downstream effector, and crosstalk of mental ions under both physiologic and pathologic conditions will be summarized. Finally, the therapeutic effects of metal ion chelators, such as clioquinol, quercetin, curcumin, coumarin, and their derivatives for the treatment of neurodegenerative diseases will be discussed. Additionally, the promising results and limitations observed in clinical trials of these metal ion chelators will also be addressed. This review will not only provide a comprehensive understanding of the role of metal ions in disease development but also offer perspectives on their modulation for the prevention or treatment of neurodegenerative diseases.

Canonical and noncanonical autophagy: involvement in Parkinson's disease

Autophagy is the major degradation process in cells and is involved in a variety of physiological and pathological functions. While macroautophagy, which employs a series of molecular cascades to form ATG8-coated double membrane autophagosomes for degradation, remains the well-known type of canonical autophagy, microautophagy and chaperon-mediated autophagy have also been characterized. On the other hand, recent studies have focused on the functions of autophagy proteins beyond intracellular degradation, including noncanonical autophagy, also known as the conjugation of ATG8 to single membranes (CASM), and autophagy-related extracellular secretion. In particular, CASM is unique in that it does not require autophagy upstream mechanisms, while the ATG8 conjugation system is involved in a manner different from canonical autophagy. There have been many reports on the involvement of these autophagy-related mechanisms in neurodegenerative diseases, with Parkinson's disease (PD) receiving particular attention because of the important roles of several causative and risk genes, including LRRK2. In this review, we will summarize and discuss the contributions of canonical and noncanonical autophagy to cellular functions, with a special focus on the pathogenesis of PD.

Lysosomal Channels as New Molecular Targets in the Pharmacological Therapy of Neurodegenerative Diseases via Autophagy Regulation

Besides controlling several organellar functions, lysosomal channels also guide the catabolic "self-eating" process named autophagy, which is mainly involved in protein and organelle quality control. Neuronal cells are particularly sensitive to the rate of autophagic flux either under physiological conditions or during the degenerative process. Accordingly, neurodegeneration occurring in Parkinson's (PD), Alzheimer's (AD), and Huntington's Diseases (HD), and Amyotrophic Lateral Sclerosis (ALS) as well as Lysosomal Storage Diseases (LSD) is partially due to defective autophagy and accumulation of toxic aggregates. In this regard, dysfunction of lysosomal ionic homeostasis has been identified as a putative cause of aberrant autophagy. From a therapeutic perspective, Transient Receptor Potential Channel Mucolipin 1 (TRPML1) and Two-Pore Channel isoform 2 (TPC2), regulating lysosomal homeostasis, are now considered promising druggable targets in neurodegenerative diseases. Compelling evidence suggests that pharmacological modulation of TRPML1 and TPC2 may rescue the pathological phenotype associated with autophagy dysfunction in AD, PD, HD, ALS, and LSD. Although pharmacological repurposing has identified several already used drugs with the ability to modulate TPC2, and several tools are already available for the modulation of TRPML1, many efforts are necessary to design and test new entities with much higher specificity in order to reduce dysfunctional autophagy during neurodegeneration.

The autophagy-lysosome pathway: a potential target in the chemical and gene therapeutic strategies for Parkinson's disease

Parkinson's disease is a common neurodegenerative disease with movement disorders associated with the intracytoplasmic deposition of aggregate proteins such as α-synuclein in neurons. As one of the major intracellular degradation pathways, the autophagy-lysosome pathway plays an important role in eliminating these proteins. Accumulating evidence has shown that upregulation of the autophagy-lysosome pathway may contribute to the clearance of α-synuclein aggregates and protect against degeneration of dopaminergic neurons in Parkinson's disease. Moreover, multiple genes associated with the pathogenesis of Parkinson's disease are intimately linked to alterations in the autophagy-lysosome pathway. Thus, this pathway appears to be a promising therapeutic target for treatment of Parkinson's disease. In this review, we briefly introduce the machinery of autophagy. Then, we provide a description of the effects of Parkinson's disease-related genes on the autophagy-lysosome pathway. Finally, we highlight the potential chemical and genetic therapeutic strategies targeting the autophagy-lysosome pathway and their applications in Parkinson's disease.

INPP4B promotes PDAC aggressiveness via PIKfyve and TRPML-1-mediated lysosomal exocytosis

Aggressive solid malignancies, including pancreatic ductal adenocarcinoma (PDAC), can exploit lysosomal exocytosis to modify the tumor microenvironment, enhance motility, and promote invasiveness. However, the molecular pathways through which lysosomal functions are co-opted in malignant cells remain poorly understood. In this study, we demonstrate that inositol polyphosphate 4-phosphatase, Type II (INPP4B) overexpression in PDAC is associated with PDAC progression. We show that INPP4B overexpression promotes peripheral dispersion and exocytosis of lysosomes resulting in increased migratory and invasive potential of PDAC cells. Mechanistically, INPP4B overexpression drives the generation of PtdIns(3,5)P2 on lysosomes in a PIKfyve-dependent manner, which directs TRPML-1 to trigger the release of calcium ions (Ca2+). Our findings offer a molecular understanding of the prognostic significance of INPP4B overexpression in PDAC through the discovery of a novel oncogenic signaling axis that orchestrates migratory and invasive properties of PDAC via the regulation of lysosomal phosphoinositide homeostasis.

Potential application of natural compounds in ischaemic stroke: Focusing on the mechanisms underlying "lysosomocentric" dysfunction of the autophagy-lysosomal pathway

Ischaemic stroke (IS) is the second leading cause of death and a major cause of disability worldwide. Currently, the clinical management of IS still depends on restoring blood flow via pharmacological thrombolysis or mechanical thrombectomy, with accompanying disadvantages of narrow therapeutic time window and risk of haemorrhagic transformation. Thus, novel pathophysiological mechanisms and targeted therapeutic candidates are urgently needed. The autophagy-lysosomal pathway (ALP), as a dynamic cellular lysosome-based degradative process, has been comprehensively studied in recent decades, including its upstream regulatory mechanisms and its role in mediating neuronal fate after IS. Importantly, increasing evidence has shown that IS can lead to lysosomal dysfunction, such as lysosomal membrane permeabilization, impaired lysosomal acidity, lysosomal storage disorder, and dysfunctional lysosomal ion homeostasis, which are involved in the IS-mediated defects in ALP function. There is tightly regulated crosstalk between transcription factor EB (TFEB), mammalian target of rapamycin (mTOR) and lysosomal function, but their relationship remains to be systematically summarized. Notably, a growing body of evidence emphasizes the benefits of naturally derived compounds in the treatment of IS via modulation of ALP function. However, little is known about the roles of natural compounds as modulators of lysosomes in the treatment of IS. Therefore, in this context, we provide an overview of the current understanding of the mechanisms underlying IS-mediated ALP dysfunction, from a lysosomal perspective. We also provide an update on the effect of natural compounds on IS, according to their chemical structural types, in different experimental stroke models, cerebral regions and cell types, with a primary focus on lysosomes and autophagy initiation. This review aims to highlight the therapeutic potential of natural compounds that target lysosomal and ALP function for IS treatment.

Neuropathology in an α-synuclein preformed fibril mouse model occurs independent of the Parkinson's disease-linked lysosomal ATP13A2 protein

Loss-of-function mutations in the ATP13A2 (PARK9) gene are implicated in early-onset autosomal recessive Parkinson's disease (PD) and other neurodegenerative disorders. ATP13A2 encodes a lysosomal transmembrane P5B-type ATPase that is highly expressed in brain and specifically within the substantia nigra pars compacta (SNc). Recent studies have revealed its normal role as a lysosomal polyamine transporter, although its contribution to PD-related pathology remains unclear. Cellular studies report that ATP13A2 can regulate α-synuclein (α-syn) secretion via exosomes. However, the relationship between ATP13A2 and α-syn in animal models remains inconclusive. ATP13A2 knockout (KO) mice exhibit lysosomal abnormalities and reactive astrogliosis but do not develop PD-related neuropathology. Studies manipulating α-syn levels in mice lacking ATP13A2 indicate minimal effects on pathology. The delivery of α-syn preformed fibrils (PFFs) into the mouse striatum is a well-defined model to study the development and spread of α-syn pathology. In this study we unilaterally injected wild-type (WT) and homozygous ATP13A2 KO mice with mouse α-syn PFFs in the striatum and evaluated mice for neuropathology after 6 months. The distribution, spread and extent of α-syn aggregation in multiple regions of the mouse brain was largely independent of ATP13A2 expression. The loss of nigrostriatal pathway dopaminergic neurons and their nerve terminals induced by PFFs were equivalent in WT and ATP13A2 KO mice. Reactive astrogliosis was induced equivalently by α-syn PFFs in WT and KO mice but was already significantly higher in ATP13A2 KO mice due to pre-existing reactive gliosis. We did not identify asymmetric motor disturbances, microglial activation, or axonal damage induced by α-syn PFFs in WT or KO mice. Although α-syn PFFs induce an increase in lysosomal number in the SNc in general, TH-positive dopaminergic neurons did not exhibit either increased lysosomal area or intensity, regardless of genotype. Our study evaluating the spread of α-syn pathology reveals no exacerbation of α-syn pathology, neuronal loss, astrogliosis or motor deficits in ATP13A2 KO mice, suggesting that selective lysosomal abnormalities resulting from ATP13A2 loss do not play a major role in α-syn clearance or propagation in vivo.

Interplay of α-Synuclein Oligomers and Endoplasmic Reticulum Stress in Parkinson'S Disease: Insights into Cellular Dysfunctions

Oligomeric forms of α-synuclein (α-syn) are critical in the formation of α-synuclein fibrils, exhibiting neurotoxic properties that are pivotal in the pathogenesis of Parkinson's disease (PD). A salient feature of this pathology is the disruption of the protein folding capacity of the endoplasmic reticulum (ER), leading to a perturbation in the ER's protein quality control mechanisms. The accumulation of unfolded or misfolded proteins instigates ER stress. However, the onset of ER stress and the consequent activation of the Unfolded Protein Response (UPR) and Endoplasmic Reticulum-Associated Degradation (ERAD) pathways do not merely culminate in apoptosis when they fail to restore cellular homeostasis. More critically, this condition initiates a cascade of reactions involving ER-related structures and organelles, resulting in multifaceted cellular damage and, potentially, a feedback loop that precipitates neuroinflammation. In this review, we elucidate the interplay between UPR and ERAD, as well as the intricate crosstalk among the ER and other organelles such as mitochondria, lysosomes, and the Golgi apparatus, underscoring their roles in the neurodegenerative process.

Lysosome quality control in health and neurodegenerative diseases

Lysosomes are acidic organelles involved in crucial intracellular functions, including the degradation of organelles and protein, membrane repair, phagocytosis, endocytosis, and nutrient sensing. Given these key roles of lysosomes, maintaining their homeostasis is essential for cell viability. Thus, to preserve lysosome integrity and functionality, cells have developed a complex intracellular system, called lysosome quality control (LQC). Several stressors may affect the integrity of lysosomes, causing Lysosomal membrane permeabilization (LMP), in which membrane rupture results in the leakage of luminal hydrolase enzymes into the cytosol. After sensing the damage, LQC either activates lysosome repair, or induces the degradation of the ruptured lysosomes through autophagy. In addition, LQC stimulates the de novo biogenesis of functional lysosomes and lysosome exocytosis. Alterations in LQC give rise to deleterious consequences for cellular homeostasis. Specifically, the persistence of impaired lysosomes or the malfunctioning of lysosomal processes leads to cellular toxicity and death, thereby contributing to the pathogenesis of different disorders, including neurodegenerative diseases (NDs). Recently, several pieces of evidence have underlined the importance of the role of lysosomes in NDs. In this review, we describe the elements of the LQC system, how they cooperate to maintain lysosome homeostasis, and their implication in the pathogenesis of different NDs.

The endolysosomal system in conventional and unconventional protein secretion

Most secreted proteins are transported through the "conventional" endoplasmic reticulum-Golgi apparatus exocytic route for their delivery to the cell surface and release into the extracellular space. Nonetheless, formative discoveries have underscored the existence of alternative or "unconventional" secretory routes, which play a crucial role in exporting a diverse array of cytosolic proteins outside the cell in response to intrinsic demands, external cues, and environmental changes. In this context, lysosomes emerge as dynamic organelles positioned at the crossroads of multiple intracellular trafficking pathways, endowed with the capacity to fuse with the plasma membrane and recognized for their key role in both conventional and unconventional protein secretion. The recent recognition of lysosomal transport and exocytosis in the unconventional secretion of cargo proteins provides new and promising insights into our understanding of numerous physiological processes.

Calcium Deregulation in Neurodegeneration and Neuroinflammation in Parkinson's Disease: Role of Calcium-Storing Organelles and Sodium-Calcium Exchanger

Parkinson's disease (PD) is a progressive neurodegenerative disorder that lacks effective treatment strategies to halt or delay its progression. The homeostasis of Ca2+ ions is crucial for ensuring optimal cellular functions and survival, especially for neuronal cells. In the context of PD, the systems regulating cellular Ca2+ are compromised, leading to Ca2+-dependent synaptic dysfunction, impaired neuronal plasticity, and ultimately, neuronal loss. Recent research efforts directed toward understanding the pathology of PD have yielded significant insights, particularly highlighting the close relationship between Ca2+ dysregulation, neuroinflammation, and neurodegeneration. However, the precise mechanisms driving the selective loss of dopaminergic neurons in PD remain elusive. The disruption of Ca2+ homeostasis is a key factor, engaging various neurodegenerative and neuroinflammatory pathways and affecting intracellular organelles that store Ca2+. Specifically, impaired functioning of mitochondria, lysosomes, and the endoplasmic reticulum (ER) in Ca2+ metabolism is believed to contribute to the disease's pathophysiology. The Na+-Ca2+ exchanger (NCX) is considered an important key regulator of Ca2+ homeostasis in various cell types, including neurons, astrocytes, and microglia. Alterations in NCX activity are associated with neurodegenerative processes in different models of PD. In this review, we will explore the role of Ca2+ dysregulation and neuroinflammation as primary drivers of PD-related neurodegeneration, with an emphasis on the pivotal role of NCX in the pathology of PD. Consequently, NCXs and their interplay with intracellular organelles may emerge as potentially pivotal players in the mechanisms underlying PD neurodegeneration, providing a promising avenue for therapeutic intervention aimed at halting neurodegeneration.

MCOLN1/TRPML1 in the lysosome: a promising target for autophagy modulation in diverse diseases

MCOLN1/TRPML1 is a nonselective cationic channel specifically localized to the late endosome and lysosome. With its property of mediating the release of several divalent cations such as Ca2+, Zn2+ and Fe2+ from the lysosome to the cytosol, MCOLN1 plays a pivotal role in regulating a variety of cellular events including endocytosis, exocytosis, lysosomal biogenesis, lysosome reformation, and especially in Macroautophagy/autophagy. Autophagy is a highly conserved catabolic process that maintains cytoplasmic integrity by removing superfluous proteins and damaged organelles. Acting as the terminal compartments, lysosomes are crucial for the completion of the autophagy process. This review delves into the emerging role of MCOLN1 in controlling the autophagic process by regulating lysosomal ionic homeostasis, thereby governing the fundamental functions of lysosomes. Furthermore, this review summarizes the physiological relevance as well as molecular mechanisms through which MCOLN1 orchestrates autophagy, consequently influencing mitochondria turnover, cell apoptosis and migration. In addition, we have illustrated the implications of MCOLN1-regulated autophagy in the pathological process of cancer and myocardial ischemia-reperfusion (I/R) injury. In summary, given the involvement of MCOLN1-mediated autophagy in the pathogenesis of cancer and myocardial I/R injury, targeting MCOLN1 May provide clues for developing new therapeutic strategies for the treatment of these diseases. Exploring the regulation of MCOLN1-mediated autophagy in diverse diseases contexts will surely broaden our understanding of this pathway and offer its potential as a promising drug target.Abbreviation: CCCP:carbonyl cyanide3-chlorophenylhydrazone; CQ:chloroquine; HCQ: hydroxychloroquine;I/R: ischemia-reperfusion; MAP1LC3/LC3:microtubule associated protein 1 light chain 3; MCOLN1/TRPML1:mucolipin TRP cation channel 1; MLIV: mucolipidosis type IV; MTORC1:MTOR complex 1; ROS: reactive oxygenspecies; SQSTM1/p62: sequestosome 1.

The ion channels of endomembranes

The endomembrane system consists of organellar membranes in the biosynthetic pathway [endoplasmic reticulum (ER), Golgi apparatus, and secretory vesicles] as well as those in the degradative pathway (early endosomes, macropinosomes, phagosomes, autophagosomes, late endosomes, and lysosomes). These endomembrane organelles/vesicles work together to synthesize, modify, package, transport, and degrade proteins, carbohydrates, and lipids, regulating the balance between cellular anabolism and catabolism. Large ion concentration gradients exist across endomembranes: Ca2+ gradients for most endomembrane organelles and H+ gradients for the acidic compartments. Ion (Na+, K+, H+, Ca2+, and Cl-) channels on the organellar membranes control ion flux in response to cellular cues, allowing rapid informational exchange between the cytosol and organelle lumen. Recent advances in organelle proteomics, organellar electrophysiology, and luminal and juxtaorganellar ion imaging have led to molecular identification and functional characterization of about two dozen endomembrane ion channels. For example, whereas IP3R1-3 channels mediate Ca2+ release from the ER in response to neurotransmitter and hormone stimulation, TRPML1-3 and TMEM175 channels mediate lysosomal Ca2+ and H+ release, respectively, in response to nutritional and trafficking cues. This review aims to summarize the current understanding of these endomembrane channels, with a focus on their subcellular localizations, ion permeation properties, gating mechanisms, cell biological functions, and disease relevance.

Extracellular vesicles contain filamentous alpha-synuclein and facilitate the propagation of Parkinson's pathology

Parkinson's disease (PD) is characterized by the pathological deposition of a-synuclein (a-syn) inclusions, known as Lewy bodies/neurites. Emerging evidence suggests that extracellular vesicles (EVs) play a role in facilitating the spreading of Lewy pathology between the peripheral nervous system and the central nervous system. We analyzed serum EVs obtained from patients with PD (n = 142), multiple system atrophy (MSA) (n = 18), progressive supranuclear palsy (PSP) (n = 28), rapid eye movement sleep behavior disorder (n = 31), and controls (n = 105). While we observed a significant reduction in the number of EVs in PD compared to controls (p = 0.006), we also noted a substantial increase in filamentous α-synuclein within EVs in PD compared to controls (p < 0.0001), MSA (0.012), and PSP (p = 0.03). Further analysis unveiled the role of EVs in facilitating the transmission of filamentous α-synuclein between neurons and from peripheral blood to the CNS. These findings highlight the potential utility of serum α-synuclein filaments within EVs as diagnostic markers for synucleinopathies and underscore the significance of EVs in promoting the dissemination of filamentous α-synuclein throughout the entire body.

Transient Receptor Potential Channels in the Healthy and Diseased Blood-Brain Barrier

The large family of transient receptor potential (TRP) channels are integral membrane proteins that function as environmental sensors and act as ion channels after activation by mechanical (touch), physical (heat, pain), and chemical stimuli (pungent compounds such as capsaicin). Most TRP channels are localized in the plasma membrane of cells but some of them are localized in membranes of organelles and function as intracellular Ca2+-ion channels. TRP channels are involved in neurological disorders but their precise role(s) and relevance in these disorders are not clear. Endothelial cells of the blood-brain barrier (BBB) express TRP channels such as TRP vanilloid 1-4 and are involved in thermal detection by regulating BBB permeability. In neurological disorders, TRP channels in the BBB are responsible for edema formation in the brain. Therefore, drug design to modulate locally activity of TRP channels in the BBB is a hot topic. Today, the application of TRP channel antagonists against neurological disorders is still limited.

Modulation of Cisplatin Sensitivity through TRPML1-Mediated Lysosomal Exocytosis in Ovarian Cancer Cells: A Comprehensive Metabolomic Approach

BACKGROUND

The lysosome has emerged as a promising target for overcoming chemoresistance, owing to its role in facilitating the lysosomal sequestration of drugs. The lysosomal calcium channel TRPML1 not only influences lysosomal biogenesis but also coordinates both endocytosis and exocytosis. This study explored the modulation of cisplatin sensitivity by regulating TRPML1-mediated lysosomal exocytosis and identified the metabolomic profile altered by TRPML1 inhibition.

METHODS

We used four types of ovarian cancer cells: two cancer cell lines (OVCAR8 and TOV21G) and two patient-derived ovarian cancer cells. Metabolomic analyses were conducted to identify altered metabolites by TRPML1 inhibition.

RESULTS

Lysosomal exocytosis in response to cisplatin was observed in resistant cancer cells, whereas the phenomenon was absent in sensitive cancer cells. Through the pharmacological intervention of TRPML1, lysosomal exocytosis was interrupted, leading to the sensitization of resistant cancer cells to cisplatin treatment. To assess the impact of lysosomal exocytosis on chemoresistance, we conducted an untargeted metabolomic analysis on cisplatin-resistant ovarian cancer cells with TRPML1 inhibition. Among the 1446 differentially identified metabolites, we focused on 84 significant metabolites. Metabolite set analysis revealed their involvement in diverse pathways.

CONCLUSIONS

These findings collectively have the potential to enhance our understanding of the interplay between lysosomal exocytosis and chemoresistance, providing valuable insights for the development of innovative therapeutic strategies.

Electrochemical Detection of Dopamine Release from Living Neurons Using Graphene Oxide-Incorporated Polypyrrole/Gold Nanocluster Hybrid Nanopattern Arrays

Stem-cell-based therapeutics have shown immense potential in treating various diseases that are currently incurable. In particular, partial recovery of Parkinson's disease, which occurs due to massive loss or abnormal functionality of dopaminergic (DAnergic) neurons, through the engraftment of stem-cell-derived neurons ex vivo is reported. However, precise assessment of the functionality and maturity of DAnergic neurons is still challenging for their enhanced clinical efficacy. Here, a novel conductive cell cultivation platform, a graphene oxide (GO)-incorporated metallic polymer nanopillar array (GOMPON), that can electrochemically detect dopamine (DA) exocytosis from living DAnergic neurons, is reported. In the cell-free configuration, the linear range is 0.5-100 µm, with a limit of detection of 33.4 nm. Owing to its excellent biocompatibility, a model DAnergic neuron (SH-SY5Y cell) can be cultivated and differentiated on the platform while their DA release can be quantitatively measured in a real-time and nondestructive manner. Finally, it is showed that the functionality of the DAnergic neurons derived from stem cells can be precisely assessed via electrochemical detection of their DA exocytosis. The developed GOMPON is highly promising for a wide range of applications, including real-time monitoring of stem cell differentiation into neuronal lineages, evaluating differentiation protocols, and finding practical stem cell therapies.

Lysosomes in senescence and aging

Dysfunction of lysosomes, the primary hydrolytic organelles in animal cells, is frequently associated with aging and age-related diseases. At the cellular level, lysosomal dysfunction is strongly linked to cellular senescence or the induction of cell death pathways. However, the precise mechanisms by which lysosomal dysfunction participates in these various cellular or organismal phenotypes have remained elusive. The ability of lysosomes to degrade diverse macromolecules including damaged proteins and organelles puts lysosomes at the center of multiple cellular stress responses. Lysosomal activity is tightly regulated by many coordinated cellular processes including pathways that function inside and outside of the organelle. Here, we collectively classify these coordinated pathways as the lysosomal processing and adaptation system (LYPAS). We review evidence that the LYPAS is upregulated by diverse cellular stresses, its adaptability regulates senescence and cell death decisions, and it can form the basis for therapeutic manipulation for a wide range of age-related diseases and potentially for aging itself.

Crater-like nanoelectrode arrays for electrochemical detection of dopamine release from neuronal cells

Stem cell therapy has shown great potential in treating various incurable diseases using conventional chemotherapy. Parkinson's disease (PD)-a neurodegenerative disease-has been reported to be caused by quantitative loss or abnormal functionality of dopaminergic neurons (DAnergic neurons). To date, stem cell therapies have shown some potential in treating PD throughex vivoengraftment of stem-cell-derived neurons. However, accurately identifying the differentiation and non-invasively evaluating the functionality and maturity of DAnergic neurons are formidable challenges in stem cell therapies. These strategies are important in enhancing the efficacy of stem cell therapies. In this study, we report a novel cell cultivation platform, that is, a nanocrater-like electrochemical nanoelectrode array (NCENA) for monitoring dopamine (DA) release from neurons to detect exocytotic DA release from DAnergic neurons. In particular, the developed NCENA has a nanostructure in which three-dimensional porous gold nanopillars are uniformly arranged on conductive electrodes. The developed NCENA exhibited great DA sensing capabilities with a linear range of 0.39-150μM and a limit of detection of 1.16μM. Furthermore, the nanotopographical cues provided by the NCENA are suitable for cell cultivation with enhanced cellular adhesion. Finally, we successfully analysed the functionality and maturity of differentiated neurons on the NCENA through its excellent sensing ability for exocytotic DA.

Increased expression or activation of TRPML1 reduces hepatic storage of toxic Z alpha-1 antitrypsin

Mutant Z alpha-1 antitrypsin (ATZ) accumulates in globules in the liver and is the prototype of proteotoxic hepatic disease. Therapeutic strategies aiming at clearance of polymeric ATZ are needed. Transient receptor potential mucolipin-1 (TRPML1) is a lysosomal Ca2+ channel that maintains lysosomal homeostasis. In this study, we show that by increasing lysosomal exocytosis, TRPML1 gene transfer or small-molecule-mediated activation of TRPML1 reduces hepatic ATZ globules and fibrosis in PiZ transgenic mice that express the human ATZ. ATZ globule clearance induced by TRPML1 occurred without increase in autophagy or nuclear translocation of TFEB. Our results show that targeting TRPML1 and lysosomal exocytosis is a novel approach for treatment of the liver disease due to ATZ and potentially other diseases due to proteotoxic liver storage.

Enzymatic properties and clinical associations of serum alpha-galactosidase A in Parkinson's disease

OBJECTIVE

Recent studies have revealed an association between Parkinson's disease (PD) and Fabry disease, a lysosomal storage disorder; however, the underlying mechanisms remain to be elucidated. This study aimed to investigate the enzymatic properties of serum alpha-galactosidase A (GLA) and compared them with the clinical parameters of PD.

METHODS

The study participants consisted of 66 sporadic PD patients and 52 controls. We measured serum GLA activity and calculated the apparent Michaelis constant (Km ) and maximal velocity (Vmax ) by Lineweaver-Burk plot analysis. Serum GLA protein concentration was measured by enzyme-linked immunosorbent assay. We examined the potential correlations between serum GLA activity and GLA protein concentration and clinical features and the plasma neurofilament light chain (NfL) level.

RESULTS

Compared to controls, PD patients showed significantly lower serum GLA activity (P < 0.0001) and apparent Vmax (P = 0.0131), but no change in the apparent Km value. Serum GLA protein concentration was lower in the PD group (P = 0.0168) and was positively associated with GLA activity. Serum GLA activity and GLA protein concentration in the PD group showed a negative correlation with age. Additionally, serum GLA activity was negatively correlated with the motor severity score and the level of plasma NfL, and was positively correlated with the score of frontal assessment battery.

INTERPRETATION

This study highlights that the lower serum GLA activity in PD is the result of a quantitative decrement of GLA protein in the serum and that it may serve as a biomarker of disease severity.

Statins suppress cell-to-cell propagation of α-synuclein by lowering cholesterol

Cell-to-cell propagation of protein aggregates has been implicated in the progression of neurodegenerative diseases. However, the underlying mechanism and modulators of this process are not fully understood. Here, we screened a small-molecule library in a search for agents that suppress the propagation of α-synuclein and mutant huntingtin (mHtt). These screens yielded several molecules, some of which were effective against both α-synuclein and mHtt. Among these molecules, we focused on simvastatin and pravastatin. Simvastatin administration in a transgenic model of synucleinopathy effectively ameliorated behavioral deficits and α-synuclein accumulation, whereas pravastatin had no effect. Because only simvastatin enters the brain effectively, these results suggest that inhibition of brain cholesterol synthesis is important in simvastatin effects. In cultured cells, accumulation of intracellular cholesterol, induced by genetic ablation of the NPC1 gene or by pharmacological treatment with U18666A, increased α-synuclein aggregation and secretion. In contrast, lowering cholesterol using methyl-β-cyclodextrin or statins reversed α-synuclein aggregation and secretion in NPC1-knockout cells. Consistent with these observations, feeding a high-fat diet aggravated α-synuclein pathology and behavioral deficits in the preformed fibril-injected mouse model, an effect that was also reversed by simvastatin administration. These results suggest that statins suppress propagation of protein aggregates by lowering cholesterol in the brain.

Induction of lysosomal exocytosis and biogenesis via TRPML1 activation for the treatment of uranium-induced nephrotoxicity

Uranium (U) is a well-known nephrotoxicant which forms precipitates in the lysosomes of renal proximal tubular epithelial cells (PTECs) after U-exposure at a cytotoxic dose. However, the roles of lysosomes in U decorporation and detoxification remain to be elucidated. Mucolipin transient receptor potential channel 1 (TRPML1) is a major lysosomal Ca2+ channel regulating lysosomal exocytosis. We herein demonstrate that the delayed administration of the specific TRPML1 agonist ML-SA1 significantly decreases U accumulation in the kidney, mitigates renal proximal tubular injury, increases apical exocytosis of lysosomes and reduces lysosomal membrane permeabilization (LMP) in renal PTECs of male mice with single-dose U poisoning or multiple-dose U exposure. Mechanistic studies reveal that ML-SA1 stimulates intracellular U removal and reduces U-induced LMP and cell death through activating the positive TRPML1-TFEB feedback loop and consequent lysosomal exocytosis and biogenesis in U-loaded PTECs in vitro. Together, our studies demonstrate that TRPML1 activation is an attractive therapeutic strategy for the treatment of U-induced nephrotoxicity.

Synaptic mechanisms underlying onset and progression of memory deficits caused by hippocampal and midbrain synucleinopathy

Cognitive deficits, including working memory, and visuospatial deficits are common and debilitating in Parkinson's disease. α-synucleinopathy in the hippocampus and cortex is considered as the major risk factor. However, little is known about the progression and specific synaptic mechanisms underlying the memory deficits induced by α-synucleinopathy. Here, we tested the hypothesis that pathologic α-Synuclein (α-Syn), initiated in different brain regions, leads to distinct onset and progression of the pathology. We report that overexpression of human α-Syn in the murine mesencephalon leads to late onset memory impairment and sensorimotor deficits accompanied by reduced dopamine D1 expression in the hippocampus. In contrast, human α-Syn overexpression in the hippocampus leads to early memory impairment, altered synaptic transmission and plasticity, and decreased expression of GluA1 AMPA-type glutamate receptors. These findings identify the synaptic mechanisms leading to memory impairment induced by hippocampal α-synucleinopathy and provide functional evidence of the major neuronal networks involved in disease progression.

Autolysosomal exocytosis of lipids protect neurons from ferroptosis

During oxidative stress neurons release lipids that are internalized by glia. Defects in this coordinated process play an important role in several neurodegenerative diseases. Yet, the mechanisms of lipid release and its consequences on neuronal health are unclear. Here, we demonstrate that lipid-protein particle release by autolysosome exocytosis protects neurons from ferroptosis, a form of cell death driven by lipid peroxidation. We show that during oxidative stress, peroxidated lipids and iron are released from neurons by autolysosomal exocytosis which requires the exocytic machinery VAMP7 and syntaxin 4. We observe membrane-bound lipid-protein particles by TEM and demonstrate that these particles are released from neurons using cryoEM. Failure to release these lipid-protein particles causes lipid hydroperoxide and iron accumulation and sensitizes neurons to ferroptosis. Our results reveal how neurons protect themselves from peroxidated lipids. Given the number of brain pathologies that involve ferroptosis, defects in this pathway likely play a key role in the pathophysiology of neurodegenerative disease.

Parkinson's disease-associated ATP13A2/PARK9 functions as a lysosomal H+,K+-ATPase

Mutations in the human ATP13A2 (PARK9), a lysosomal ATPase, cause Kufor-Rakeb Syndrome, an early-onset form of Parkinson's disease (PD). Here, we demonstrate that ATP13A2 functions as a lysosomal H⁺,K⁺-ATPase. The K⁺-dependent ATPase activity and the lysosomal K⁺-transport activity of ATP13A2 are inhibited by an inhibitor of sarco/endoplasmic reticulum Ca²⁺-ATPase, thapsigargin, and K⁺-competitive inhibitors of gastric H⁺,K⁺-ATPase, such as vonoprazan and SCH28080. Interestingly, these H⁺,K⁺-ATPase inhibitors cause lysosomal alkalinization and α-synuclein accumulation, which are pathological hallmarks of PD. Furthermore, PD-associated mutants of ATP13A2 show abnormal expression and function. Our results suggest that the H⁺/K⁺-transporting function of ATP13A2 contributes to acidification and α-synuclein degradation in lysosomes.

The synthetic TRPML1 agonist ML-SA1 rescues Alzheimer-related alterations of the endosomal-autophagic-lysosomal system

Abnormalities in the endosomal-autophagic-lysosomal (EAL) system are an early event in Alzheimer's disease (AD) pathogenesis. However, the mechanisms underlying these abnormalities are unclear. The transient receptor potential channel mucolipin 1(TRPML1, also known as MCOLN1), a vital endosomal-lysosomal Ca2+ channel whose loss of function leads to neurodegeneration, has not been investigated with respect to EAL pathogenesis in late-onset AD (LOAD). Here, we identify pathological hallmarks of TRPML1 dysregulation in LOAD neurons, including increased perinuclear clustering and vacuolation of endolysosomes. We reveal that induced pluripotent stem cell (iPSC)-derived human cortical neurons expressing APOE ε4, the strongest genetic risk factor for LOAD, have significantly diminished TRPML1-induced endolysosomal Ca2+ release. Furthermore, we found that blocking TRPML1 function in primary neurons by depleting the TRPML1 agonist PI(3,5)P2 via PIKfyve inhibition, recreated multiple features of EAL neuropathology evident in LOAD. This included increased endolysosomal Ca2+ content, enlargement and perinuclear clustering of endolysosomes, autophagic vesicle accumulation and early endosomal enlargement. Strikingly, these AD-like neuronal EAL defects were rescued by TRPML1 reactivation using its synthetic agonist ML-SA1. These findings implicate defects in TRPML1 in LOAD EAL pathogenesis and present TRPML1 as a potential therapeutic target.

Characterization of Endo-Lysosomal Cation Channels Using Calcium Imaging

Endo-lysosomes are membrane-bound acidic organelles that are involved in endocytosis, recycling, and degradation of extracellular and intracellular material. The membranes of endo-lysosomes express several Ca²⁺-permeable cation ion channels, including two-pore channels (TPC1-3) and transient receptor potential mucolipin channels (TRPML1-3). In this chapter, we will describe four different state-of-the-art Ca²⁺ imaging approaches, which are well-suited to investigate the function of endo-lysosomal cation channels. These techniques include (1) global cytosolic Ca²⁺ measurements, (2) peri-endo-lysosomal Ca²⁺ imaging using genetically encoded Ca²⁺ sensors that are directed to the cytosolic endo-lysosomal membrane surface, (3) Ca²⁺ imaging of endo-lysosomal cation channels, which are engineered in order to redirect them to the plasma membrane in combination with approaches 1 and 2, and (4) Ca²⁺ imaging by directing Ca²⁺ indicators to the endo-lysosomal lumen. Moreover, we will review useful small molecules, which can be used as valuable tools for endo-lysosomal Ca²⁺ imaging. Rather than providing complete protocols, we will discuss specific methodological issues related to endo-lysosomal Ca²⁺ imaging.

The role of lysosomes in metabolic and autoimmune diseases

Lysosomes are catabolic organelles that contribute to the degradation of intracellular constituents through autophagy and of extracellular components through endocytosis, phagocytosis and macropinocytosis. They also have roles in secretory mechanisms, the generation of extracellular vesicles and certain cell death pathways. These functions make lysosomes central organelles in cell homeostasis, metabolic regulation and responses to environment changes including nutrient stresses, endoplasmic reticulum stress and defects in proteostasis. Lysosomes also have important roles in inflammation, antigen presentation and the maintenance of long-lived immune cells. Their functions are tightly regulated by transcriptional modulation via TFEB and TFE3, as well as by major signalling pathways that lead to activation of mTORC1 and mTORC2, lysosome motility and fusion with other compartments. Lysosome dysfunction and alterations in autophagy processes have been identified in a wide variety of diseases, including autoimmune, metabolic and kidney diseases. Deregulation of autophagy can contribute to inflammation, and lysosomal defects in immune cells and/or kidney cells have been reported in inflammatory and autoimmune pathologies with kidney involvement. Defects in lysosomal activity have also been identified in several pathologies with disturbances in proteostasis, including autoimmune and metabolic diseases such as Parkinson disease, diabetes mellitus and lysosomal storage diseases. Targeting lysosomes is therefore a potential therapeutic strategy to regulate inflammation and metabolism in a variety of pathologies.

Pharmacological inhibition of lysosomal two-pore channel 2 (TPC2) confers neuroprotection in stroke via autophagy regulation

Lysosomal function and organellar Ca²⁺ homeostasis become dysfunctional in Stroke causing disturbances in autophagy, the major process for the degradation of abnormal protein aggregates and dysfunctional organelles. However, the role of autophagy in Stroke is controversial since excessive or prolonged autophagy activation exacerbates ischemic brain injury. Of note, glutamate evokes NAADP-dependent Ca²⁺ release via lysosomal TPC2 channels thus controlling basal autophagy. Considering the massive release of excitotoxins in Stroke, autophagic flux becomes uncontrolled with abnormal formation of autophagosomes causing, in turn, disruption of excitotoxins clearance and neurodegeneration. Here, a fine regulation of autophagy via a proper pharmacological modulation of lysosomal TPC2 channel has been tested in preclinical Stroke models. Primary cortical neurons were subjected to oxygen and glucose deprivation+reoxygenation to reproduce in vitro brain ischemia. Focal brain ischemia was induced in rats by transient middle cerebral artery occlusion (tMCAO). Under these conditions, TPC2 protein expression as well as autophagy and endoplasmic reticulum (ER) stress markers were studied by Western blotting, while TPC2 localization and activity were measured by immunocytochemistry and single-cell video-imaging, respectively. TPC2 protein expression and immunosignal were highly modulated in primary cortical neurons exposed to extreme hypoxic conditions causing dysfunction in organellar Ca²⁺ homeostasis, ER stress and autophagy-induced cell death. TPC2 knocking down and pharmacological inhibition by Ned-19 during hypoxia induced neuroprotection. The effect of Ned-19 was reversed by the permeable form of TPC2 endogenous agonist, NAADP-AM. Of note, Ned-19 prevented ER stress, as measured by GRP78 (78 kDa glucose-regulated protein) protein reduction and caspase 9 downregulation. In this way Ned-19 restored organellar Ca²⁺ level. Interestingly, Ned-19 reduced the infarct volume and neurological deficits in rats subjected to tMCAO and prevented hypoxia-induced cell death by blocking autophagic flux. Collectively, the pharmacological inhibition of TPC2 lysosomal channel by Ned-19 protects from focal ischemia by hampering a hyperfunctional autophagy.

Role of Astrocytes in Parkinson's Disease Associated with Genetic Mutations and Neurotoxicants

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons and the aggregation of Lewy bodies in the basal ganglia, resulting in movement impairment referred to as parkinsonism. However, the etiology of PD is not well known, with genetic factors accounting only for 10-15% of all PD cases. The pathogenetic mechanism of PD is not completely understood, although several mechanisms, such as oxidative stress and inflammation, have been suggested. Understanding the mechanisms of PD pathogenesis is critical for developing highly efficacious therapeutics. In the PD brain, dopaminergic neurons degenerate mainly in the basal ganglia, but recently emerging evidence has shown that astrocytes also significantly contribute to dopaminergic neuronal death. In this review, we discuss the role of astrocytes in PD pathogenesis due to mutations in α-synuclein (PARK1), DJ-1 (PARK7), parkin (PARK2), leucine-rich repeat kinase 2 (LRRK2, PARK8), and PTEN-induced kinase 1 (PINK1, PARK6). We also discuss PD experimental models using neurotoxins, such as paraquat, rotenone, 6-hydroxydopamine, and MPTP/MPP+. A more precise and comprehensive understanding of astrocytes' modulatory roles in dopaminergic neurodegeneration in PD will help develop novel strategies for effective PD therapeutics.

Lysosomal Ion Channels: What Are They Good For and Are They Druggable Targets?

Lysosomes play fundamental roles in material digestion, cellular clearance, recycling, exocytosis, wound repair, Ca²⁺ signaling, nutrient signaling, and gene expression regulation. The organelle also serves as a hub for important signaling networks involving the mTOR and AKT kinases. Electrophysiological recording and molecular and structural studies in the past decade have uncovered several unique lysosomal ion channels and transporters, including TPCs, TMEM175, TRPMLs, CLN7, and CLC-7. They underlie the organelle's permeability to major ions, including K⁺, Na⁺, H⁺, Ca²⁺, and Cl^-. The channels are regulated by numerous cellular factors, ranging from H⁺ in the lumen and voltage across the lysosomal membrane to ATP in the cytosol to growth factors outside the cell. Genetic variations in the channel/transporter genes are associated with diseases that include lysosomal storage diseases and neurodegenerative diseases. Recent studies with human genetics and channel activators suggest that lysosomal channels may be attractive targets for the development of therapeutics for the prevention of and intervention in human diseases.

Lysosomal Potassium Channels

Lysosomes are acidic membrane-bound organelles that use hydrolytic enzymes to break down material through pathways such as endocytosis, phagocytosis, mitophagy, and autophagy. To function properly, intralysosomal environments are strictly controlled by a set of integral membrane proteins such as ion channels and transporters. Potassium ion (K⁺) channels are a large and diverse family of membrane proteins that control K⁺ flux across both the plasma membrane and intracellular membranes. In the plasma membrane, they are essential in both excitable and non-excitable cells for the control of membrane potential and cell signaling. However, our understanding of intracellular K⁺ channels is very limited. In this review, we summarize the recent development in studies of K⁺ channels in the lysosome. We focus on their characterization, potential roles in maintaining lysosomal membrane potential and lysosomal function, and pathological implications.

Role of Ceramides and Lysosomes in Extracellular Vesicle Biogenesis, Cargo Sorting and Release

Cells have the ability to communicate with their immediate and distant neighbors through the release of extracellular vesicles (EVs). EVs facilitate intercellular signaling through the packaging of specific cargo in all type of cells, and perturbations of EV biogenesis, sorting, release and uptake is the basis of a number of disorders. In this review, we summarize recent advances of the complex roles of the sphingolipid ceramide and lysosomes in the journey of EV biogenesis to uptake.

Neurodegenerative Lysosomal Storage Disorders: TPC2 Comes to the Rescue!

Lysosomal storage diseases (LSDs) resulting from inherited gene mutations constitute a family of disorders that disturb lysosomal degradative function leading to abnormal storage of macromolecular substrates. In most LSDs, central nervous system (CNS) involvement is common and leads to the progressive appearance of neurodegeneration and early death. A growing amount of evidence suggests that ion channels in the endolysosomal system play a crucial role in the pathology of neurodegenerative LSDs. One of the main basic mechanisms through which the endolysosomal ion channels regulate the function of the endolysosomal system is Ca2+ release, which is thought to be essential for intracellular compartment fusion, fission, trafficking and lysosomal exocytosis. The intracellular TRPML (transient receptor potential mucolipin) and TPC (two-pore channel) ion channel families constitute the main essential Ca2+-permeable channels expressed on endolysosomal membranes, and they are considered potential drug targets for the prevention and treatment of LSDs. Although TRPML1 activation has shown rescue effects on LSD phenotypes, its activity is pH dependent, and it is blocked by sphingomyelin accumulation, which is characteristic of some LSDs. In contrast, TPC2 activation is pH-independent and not blocked by sphingomyelin, potentially representing an advantage over TRPML1. Here, we discuss the rescue of cellular phenotypes associated with LSDs such as cholesterol and lactosylceramide (LacCer) accumulation or ultrastructural changes seen by electron microscopy, mediated by the small molecule agonist of TPC2, TPC2-A1-P, which promotes lysosomal exocytosis and autophagy. In summary, new data suggest that TPC2 is a promising target for the treatment of different types of LSDs such as MLIV, NPC1, and Batten disease, both in vitro and in vivo.

Alpha-Synuclein: The Spark That Flames Dopaminergic Neurons, In Vitro and In Vivo Evidence

Mitochondria, α-syn fibrils and the endo-lysosomal system are key players in the pathophysiology of Parkinson’s disease. The toxicity of α-syn is amplified by cell-to-cell transmission and aggregation of endogenous species in newly invaded neurons. Toxicity of α-syn PFF was investigated using primary cultures of dopaminergic neurons or on aged mice after infusion in the SNpc and combined with mild inhibition of GBA. In primary dopaminergic neurons, application of α-syn PFF induced a progressive cytotoxicity associated with mitochondrial dysfunction, oxidative stress, and accumulation of lysosomes suggesting that exogenous α-syn reached the lysosome (from the endosome). Counteracting the α-syn endocytosis with a clathrin inhibitor, dopaminergic neuron degeneration was prevented. In vivo, α-syn PFF induced progressive neurodegeneration of dopaminergic neurons associated with motor deficits. Histology revealed progressive aggregation of α-syn and microglial activation and accounted for the seeding role of α-syn, injection of which acted as a spark suggesting a triggering of cell-to-cell toxicity. We showed for the first time that a localized SNpc α-syn administration combined with a slight lysosomal deficiency and aging triggered a progressive lesion. The cellular and animal models described could help in the understanding of the human disease and might contribute to the development of new therapies.

TPC2 rescues lysosomal storage in mucolipidosis type IV, Niemann-Pick type C1, and Batten disease

Lysosomes are cell organelles that degrade macromolecules to recycle their components. If lysosomal degradative function is impaired, e.g., due to mutations in lysosomal enzymes or membrane proteins, lysosomal storage diseases (LSDs) can develop. LSDs manifest often with neurodegenerative symptoms, typically starting in early childhood, and going along with a strongly reduced life expectancy and quality of life. We show here that small molecule activation of the Ca²⁺‐permeable endolysosomal two‐pore channel 2 (TPC2) results in an amelioration of cellular phenotypes associated with LSDs such as cholesterol or lipofuscin accumulation, or the formation of abnormal vacuoles seen by electron microscopy. Rescue effects by TPC2 activation, which promotes lysosomal exocytosis and autophagy, were assessed in mucolipidosis type IV (MLIV), Niemann–Pick type C1, and Batten disease patient fibroblasts, and in neurons derived from newly generated isogenic human iPSC models for MLIV and Batten disease. For in vivo proof of concept, we tested TPC2 activation in the MLIV mouse model. In sum, our data suggest that TPC2 is a promising target for the treatment of different types of LSDs, both in vitro and in‐vivo.

The Zinc Ionophore Clioquinol Reduces Parkinson's Disease Patient-Derived Brain Extracts-Induced Neurodegeneration

Parkinson's disease (PD) is pathologically characterized by intracellular α-synuclein-rich protein aggregates, named Lewy bodies (LB), and by the progressive loss of dopaminergic neurons in the substantia nigra. Several heavy metals, including zinc (Zn), have been suggested to play a role in PD progression, although the exact role of Zn in neurodegeneration remains to be fully elucidated. To address this gap, we investigated the effects of Zn modulation on the progression of degeneration in mice injected with PD patient-derived LB-extracts carrying toxic α-synuclein aggregates. Zn modulation was achieved using either a clioquinol-enriched diet, a Zn ionophore that redistributes cellular Zn, or a Zn-enriched diet that increases Zn levels. Clioquinol treatment significantly prevented dopaminergic neurodegeneration and reduced α-synuclein-associated pathology in LB-injected mice, while no differences were observed with Zn supplementation. Biochemical analyses further demonstrate that the expression levels of vesicle-specific Zn transporter ZnT3 in the striatum of LB-injected mice treated with clioquinol were decreased, suggesting an intracellular redistribution of Zn. Additionally, we found that clioquinol modulates the autophagy-lysosomal pathway by enhancing lysosomal redistribution within the neuronal compartments. Collectively, we found that in vivo pharmacological chelation of Zn, by dampening Zn-mediated cytotoxicity, can result in an overall attenuation of PD-linked lysosomal alterations and dopaminergic neurodegeneration. The results support zinc chelation as a disease-modifying strategy for treating PD.

Targeting Macroautophagy as a Therapeutic Opportunity to Treat Parkinson's Disease

Macroautophagy, an evolutionary conserved catabolic process in the eukaryotic cell, regulates cellular homeostasis and plays a decisive role in self-engulfing proteins, protein aggregates, dysfunctional or damaged organelles, and invading pathogens. Growing evidence from in vivo and in vitro models shows that autophagy dysfunction plays decisive role in the pathogenesis of various neurodegenerative diseases, including Parkinson's disease (PD). PD is an incurable and second most common neurodegenerative disease characterised by neurological and motor dysfunction accompanied of non-motor symptoms that can also reduce the life quality of patients. Despite the investment in research, the aetiology of the disease is still unknown and the therapies available are aimed mostly at ameliorating motor symptoms. Hence, therapeutics regulating the autophagy pathway might play an important role controlling the disease progression, reducing neuronal loss and even ameliorating non-motor symptoms. In this review, we highlight potential therapeutic opportunities involved in different targeting options like an initiation of autophagy, Leucine-rich repeat kinase 2 (LRRK2) inhibition, mitophagy, lysosomes, lipid metabolism, immune system, gene expression, biomarkers, and also non-pharmacological interventions. Thus, strategies to identify therapeutics targeting the pathways modulating autophagy might hold a future for therapy development against PD.