Why the Cell's Recycling System Breaks

Etiological and Mechanistic Analysis of Autolysosomal Acidification Failure in Neuronal Autophagy

Benjamin Aaron Gustafsson AdultCognitiveDisease.com

---

1. Introduction: The Thermodynamic Imperative of Lysosomal pH in Neuronal Homeostasis

The survival of post-mitotic neurons is predicated on the efficient clearance of intracellular waste, a task largely delegated to the autophagy-lysosomal pathway (ALP). Unlike proliferative cells, which can dilute aggregated proteins and damaged organelles through cell division, neurons must actively degrade these substrates to prevent cytotoxicity over a lifespan that can span decades. The fulcrum of this degradative capacity is the lysosomal proton gradient. The maintenance of a highly acidic luminal pH (typically 4.5–5.0) is not merely a passive environmental requirement for hydrolase activity; it is an electrochemical potential energy source that drives solute transport, calcium buffering, and the fusion of autophagosomes with lysosomes.¹

The failure to acidify the autolysosome constitutes a catastrophic event in neuronal physiology. When the proton gradient dissipates, proteolytic enzymes such as cathepsins become catalytically inert. This results in the accumulation of undigested autophagic substrates—including amyloid-beta (Aβ), alpha-synuclein, and defective mitochondria—within the lumen of "giant" autolysosomes.³ This pathological state, termed "lysosomal storage," is a convergent feature of major neurodegenerative disorders, including Alzheimer’s disease (AD), Parkinson’s disease (PD), and Amyotrophic Lateral Sclerosis (ALS).³

This report provides an exhaustive analysis of the multifactorial etiologies underlying autolysosomal acidification failure in neurons. We dissect the biophysical collapse of the V-ATPase proton pump, the disruption of ion counter-transport systems, the dysregulation of kinase signaling networks, the failure of fusion machinery, and the impact of environmental toxins and glial dysfunction.

2. The V-ATPase Complex: Structural Integrity,

Assembly, and Chaperone Defects

The primary engine of lysosomal acidification is the Vacuolar-type H+-ATPase (V-ATPase), a rotary nanomotor that couples ATP hydrolysis to proton translocation. The complex is composed of two domains: the cytosolic V1 domain (subunits A–H), responsible for ATP hydrolysis, and the membrane-embedded V0 domain (subunits a, c, c'', d, e), which functions as the proton pore.⁶ In neurons, the integrity of this complex is paramount, and its dysfunction is the most direct cause of acidification failure. 2.1 Structural Vulnerability and Ischemic Dissociation The V-ATPase is a dynamic complex. The V1 and V0 domains can reversibly dissociate, a regulatory mechanism used to conserve ATP during starvation or glucose deprivation. However, in pathological states such as ischemic stroke, this dissociation becomes irreversible. Studies indicate that the A subunit of the V1 sector and the V0a1 subunit are susceptible to rapid degradation or dissociation following cerebral artery occlusion, halting proton pumping immediately.⁷ Furthermore, the V-ATPase serves as a signaling hub, interacting with the Ragulator complex to sense amino acids and regulate mTORC1. Dysfunction in the pump therefore creates a dual deficit: a failure of degradation (pH elevation) and a failure of metabolic signaling (mTORC1 dysregulation).² 2.2 The Critical Role of V-ATPase Assembly Factors Efficient proton pumping requires the precise assembly of the V-ATPase in the endoplasmic reticulum (ER) prior to its trafficking to the lysosome. This process is orchestrated by a suite of dedicated assembly factors, the failure of which leads to a paucity of functional pumps. 2.2.1 VMA21: The Master Chaperone VMA21 is an essential ER-resident chaperone that orchestrates the assembly of the V0 proton-translocating pore. It binds to the hydrophobic subunits (c, c'', d) and prevents their premature degradation. Crucially, VMA21 possesses an ER-retrieval motif. It escorts the nascent V0 domain to the Golgi to allow V1 binding but is then retrieved back to the ER to catalyze further assembly cycles.8 Pathogenic mutations that reduce VMA21 expression or impair its retrieval function lead to X-linked Myopathy with Excessive Autophagy (XMEA). In this condition, the assembly of the V0 domain is stalled; fewer pumps reach the lysosome, resulting in a chronic elevation of lysosomal pH. This de-acidification blocks the final step of autophagy, causing the accumulation of massive, non-degradative autophagic vacuoles that eventually consume the cytoplasm.9 2.2.2 The TLDc Protein Family and Oxidative Protection Recent genomic screens have identified the TLDc domain-containing proteins—specifically NCOA7, OXR1, and TBC1D24—as critical regulators of V-ATPase function. These proteins associate with the V-ATPase and appear to stabilize the complex, particularly under conditions of oxidative stress.¹¹ Mutations in TBC1D24 are linked to epilepsy and neurodegeneration, suggesting that the failure to stabilize the proton pump against the high oxidative load of the neuronal environment contributes to acidification defects. Similarly, DMXL2 is required for the V0/V1 interaction, and its deficiency leads to Ohtahara syndrome, a severe epileptic encephalopathy.¹¹ 2.3 Presenilin-1: A Non-Canonical V-ATPase Chaperone One of the most significant breakthroughs in understanding Alzheimer’s pathology is the identification of Presenilin-1 (PS1) as a specific chaperone for the V0a1 subunit of the V-ATPase, a function independent of its role in the γ-secretase complex.

● Mechanism of Chaperoning: The PS1 holoprotein aids in the N-glycosylation of the

V0a1 subunit within the ER. Glycosylation is a critical quality control step; without it, V0a1 is misfolded and targeted for ER-associated degradation (ERAD) rather than being trafficked to the lysosome.¹²

● FAD Mutations: Familial Alzheimer's Disease (FAD) mutations in PSEN1 disrupt this

chaperone function. Consequently, neurons from FAD patients exhibit a drastic reduction in lysosomal V0a1 levels, leading to a pH elevation from ~4.5 to >6.0.¹³

● Calcium Dysregulation: The failure of acidification in PS1 mutants triggers secondary

calcium defects. The lysosomal calcium channel TRPML1 is pH-sensitive; abnormal alkalization leads to dysregulated calcium efflux, which further impairs the fusion of autophagosomes with lysosomes, creating a feed-forward loop of proteostatic failure.¹³ 3. The Amyloidogenic Blockade: Metabolite-Driven

Inhibition

In addition to chaperone failure, the accumulation of specific protein aggregates can directly inhibit the catalytic activity of the V-ATPase. This phenomenon is central to the "inside-out" hypothesis of amyloid toxicity in Alzheimer’s Disease. 3.1 The APP-βCTF Inhibitory Axis While extracellular amyloid-beta (Aβ) plaques are the hallmark of AD, intracellular accumulation of the β-C-terminal fragment of APP (APP-βCTF) appears to be the primary driver of acidification failure.³

● Steric Inhibition: APP-βCTF accumulates in the endolysosomal membranes of AD

neurons and binds directly to the V-ATPase complex. This binding event allosterically inhibits the pump or destabilizes the V0-V1 coupling, effectively "jamming" the motor.¹⁶

● The YENPTY Phosphorylation Switch: The toxicity of APP-βCTF is regulated by

phosphorylation at the tyrosine-682 residue within its YENPTY internalization motif. Kinases such as Fyn, which are upregulated in AD brains, phosphorylate this site. Phosphorylated APP-βCTF exhibits a significantly higher affinity for the V-ATPase, exacerbating the acidification defect.¹⁶

● Down Syndrome: This mechanism is prevalent in Down Syndrome (Trisomy 21), where

the extra copy of the APP gene drives the overproduction of APP-βCTF. This leads to "endosomal-lysosomal meltdown"—the formation of giant, neutral autolysosomes that fail to degrade Aβ, leading to early-onset AD pathology.¹⁵ 3.2 PICALM and Sorting Defects The phosphatidylinositol binding clathrin assembly protein (PICALM), a top genetic risk factor for AD, regulates the sorting of SNAREs (like VAMP8) and autophagic precursors. Reduced PICALM levels, often observed in AD brains, impair the delivery of V-ATPase subunits and fusion machinery to the autophagosome. This trafficking defect acts synergistically with APP-βCTF inhibition to compromise lysosomal acidity.¹⁹ 4. Ion Homeostasis: The Counter-Ion Imperative Proton pumping is electrogenic; the accumulation of H+ ions generates a transmembrane voltage (positive inside) that opposes further pumping. To sustain acidification, this electrical potential must be dissipated by a "shunt" current—either the influx of anions (Cl-) or the efflux of cations (K+, Na+). 4.1 Chloride Transport: The ClC-7/OSTM1 Complex ClC-7 is a 2Cl-/1H+ antiporter that localizes to lysosomes and is critical for providing the chloride counter-ion flux. ● Mechanism: By transporting two Clions into the lumen for every proton exported, ClC-7 neutralizes the membrane potential, allowing the V-ATPase to pump against the concentration gradient.

● OSTM1 Interaction: ClC-7 is obligatorily associated with OSTM1 (Osteopetrosis

Associated Transmembrane Protein 1), a heavily glycosylated beta-subunit that shields ClC-7 from lysosomal proteases.²⁰

● Neuronal Phenotypes: Loss of either ClC-7 or OSTM1 leads to osteopetrosis and severe

neurodegeneration (neuronal ceroid lipofuscinosis). While some studies debated the pH effect in non-neuronal cells, functional assays in neurons confirm that ClC-7 is essential for deep acidification. Furthermore, luminal chloride may directly activate cathepsin C and other hydrolases, meaning ClC-7 loss creates a "double hit": pH elevation and ionic imbalance.²¹ 4.2 Potassium Channels: TMEM175 and Membrane Potential TMEM175 is a non-canonical K+ channel identified as a major genetic risk factor for Parkinson’s Disease.²⁴

● pH Plasticity: Unlike ClC-7, which facilitates deep acidification, TMEM175 appears to act

as a "leak" channel or potential regulator. It is crucial for lysosomal pH plasticity—the ability of the organelle to adjust its pH in response to metabolic demand. Dysfunction of TMEM175 leads to a unstable pH (either hyper-acidic or alkaline depending on the context), which impairs the degradation of alpha-synuclein.¹⁸

● Mechanistic Link: By conducting K+, TMEM175 sets the resting membrane potential of

the lysosome. Defects in this channel hyperpolarize the membrane, altering the electrochemical driving force for the V-ATPase. 4.3 Calcium Channelopathies: TRPML1 and TPC2 Lysosomal calcium release is essential for fusion and fission events. Disruption of these channels affects pH indirectly by blocking the delivery of pumps or regulating membrane dynamics.

Channel Function Role in Disease Link

Acidification

Failure

TRPML1 Ca2+ Release Required for Mucolipidosis IV, (PI(3,5)P2 autophagosome-ly AD, PD ²⁵ activated) sosome fusion. Loss prevents the "hybrid" organelle from acquiring somatic V-ATPases. pH-dependent gating creates a feedback loop.

TPC2 Na+/Ca2+ Release Agonist-Depende AD, LSDs ²⁷

(NAADP activated) nt: NAADP

activation can cause alkalinization (acting as a proton leak). PI(3,5)P2 activation supports acidification/fusion. Hyperactivity in AD leads to alkalinization. 4.4 Zinc Dyshomeostasis: ATP13A2 (PARK9) ATP13A2 is a P5-type ATPase that transports polyamines and heavy metals (Zn2+, Mn2+) across the lysosomal membrane.

● Zinc Toxicity: Loss of ATP13A2 leads to the accumulation of Zinc in the mitochondria and

lysosomes. Excess lysosomal Zinc inhibits V-ATPase function and hydrolase activity, leading to pH elevation.²⁹

● Mitochondrial Coupling: The resulting mitochondrial dysfunction (ROS production)

further oxidizes lysosomal membrane proteins, exacerbating the acidification defect.³⁰ 5. Kinase Signaling and Trafficking Networks in

Parkinson’s Disease

In Parkinson’s Disease, acidification failure is often a downstream consequence of dysregulated kinase signaling that mislocalizes lysosomes to cellular regions where acidification is inefficient. 5.1 LRRK2 Hyperactivity and the Rab Phosphorylation Cascade Mutations in LRRK2 (e.g., G2019S) increase its kinase activity, leading to the hyperphosphorylation of a subset of Rab GTPases, including Rab8, Rab10, and Rab29.³² 5.1.1 The "LYTL" Pathway and Centrosomal Trapping Lysosomes typically undergo retrograde transport to the perinuclear region (soma) to mature and acidify. This positioning is controlled by the interplay between kinesin (anterograde) and dynein (retrograde) motors.

● Mechanism: LRRK2 phosphorylates Rab10 on the lysosomal surface. Phospho-Rab10

recruits the effector RILPL1. The Rab10-RILPL1 complex interacts with the p150Glued subunit of dynactin, but rather than promoting transport, it anchors lysosomes to the centrosome or interferes with motor coordination.³⁴

● Consequence: This "Lysosomal Tubulation/sorting driven by LRRK2" (LYTL) pathway

disrupts normal trafficking dynamics. Lysosomes become trapped in peripheral or centrosomal clusters, preventing their maturation. Peripheral lysosomes are notoriously less acidic than their somatic counterparts.³⁶ ● PPM1H Regulation: The phosphatase PPM1H normally dephosphorylates Rab10, counteracting LRRK2. Loss of PPM1H mimics LRRK2 hyperactivity, locking lysosomes in this pathological, poorly acidified state.³⁸ 5.2 Transcriptional Repression of the CLEAR Network Beyond trafficking, LRRK2 negatively regulates the MiT/TFE family of transcription factors (TFEB, TFE3, MITF), which control the Coordinated Lysosomal Expression and Regulation (CLEAR) gene network.

● Nuclear Exclusion: LRRK2 signaling promotes the phosphorylation and cytoplasmic

sequestration of TFEB/TFE3. This reduces the transcription of V-ATPase subunits and cathepsins. Thus, the neuron is starved of the very components needed to maintain low pH.³⁹ 5.3 Rab29 and TGN-Lysosome Trafficking Rab29 (PARK16) recruits LRRK2 to the Trans-Golgi Network (TGN) and lysosomes. Overexpression of Rab29 induces TGN fragmentation and lysosomal clustering. This structural collapse disrupts the sorting of nascent V-ATPase complexes from the Golgi to the lysosome, preventing the replenishment of the proton pump pool.⁴⁰ 5.4 Glucocerebrosidase (GBA1) and Lipid-Induced Leak Mutations in GBA1 reduce the activity of beta-glucocerebrosidase (GCase), leading to the accumulation of glucosylceramide (GlcCer) and glucosylsphingosine.

● Membrane Permeabilization: These lipids stabilize toxic alpha-synuclein oligomers and

alter the biophysical properties of the lysosomal membrane. High levels of sphingolipids induce membrane permeabilization or "proton leak," making it thermodynamically impossible for the V-ATPase to maintain a gradient.²⁴

● Feedback Loop: GCase itself requires acidic pH to function. The lipid-induced

alkalinization inhibits the remaining enzyme, creating a catastrophic feed-forward loop.⁴³ 6. The Fusion Machinery: SNAREs and Tethers Acidification of the autophagosome occurs largely after fusion with a competent lysosome. Therefore, fusion failure is functionally equivalent to acidification failure. 6.1 The Neuronal SNARE Switch: SNAP29 vs. SNAP47 Recent evidence delineates two distinct SNARE complexes for autophagy, a distinction critical for neuronal survival. ● Starvation Autophagy: Utilizes STX17-SNAP29-VAMP8.

● Basal/Selective Autophagy: Utilizes STX17-SNAP47-VAMP8.⁴⁴

● The "Default" Complex: Neurons are rarely starved; they rely on constitutive (basal) autophagy to clear aggregates. Therefore, they depend heavily on SNAP47. SNAP47 is

recruited to autophagosomes via binding to PI(4,5)P2 and ATG8s. Disruptions in phosphoinositide signaling prevents SNAP47 recruitment, blocking fusion.⁴⁴

● Metabolic Regulation: In nutrient-rich conditions (typical for most neurons), SNAP29 is

O-GlcNAcylated, which inhibits its participation in fusion complexes. This enforces

reliance on SNAP47. Metabolic disorders (diabetes) that alter O-GlcNAcylation levels can therefore dysregulate this switch, stalling neuronal autophagy.⁴⁴ 6.2 The HOPS Complex and VPS41 The HOPS complex (Homotypic Fusion and Protein Sorting) tethers the autophagosome to the lysosome.

● VPS41: This subunit is specific for HOPS function in fusion (as opposed to the CORVET

complex in endosomes). VPS41 mutations or deficiency lead to the accumulation of undegraded autophagosomes. VPS41 is also required for the neuroprotective clearance of alpha-synuclein.⁴⁶ ● WDR91 Competition: The protein WDR91 competes with VPS41 for binding to Rab7. Pathological upregulation of WDR91 sequesters Rab7, preventing HOPS assembly and blocking fusion. This results in "HOPS bodies"—enlarged, neutral endolysosomal compartments.⁴⁶ 6.3 EPG5 and Specificity EPG5 is a tether that confers specificity to the fusion process, ensuring autophagosomes fuse with degradative lysosomes and not other organelles. EPG5 mutations (Vici syndrome) prevent the recruitment of Rab7 and V-ATPases to the fusion site, resulting in a failure to acidify the resulting hybrid organelle.⁴⁹ 7. The Axonal Transport Challenge Neurons face a topological hurdle: autophagosomes form distally in the axon but must travel to the soma to find acidic lysosomes. 7.1 The Acidification Gradient Lysosomal pH is graded along the axon: distal lysosomes are neutral (pH ~6–7), while somatic lysosomes are acidic (pH ~4.5–5).⁵⁰ Maturation and acidification occur during retrograde transport.

● Dynein/Dynactin Failure: Mutations in the dynein motor or its regulator dynactin

(p150Glued) stall retrograde transport. Autophagosomes remain stranded in the distal axon, unable to access the somatic V-ATPase pool. This leads to axonal swellings filled with neutral, aggregate-laden vacuoles.⁵¹

● Snapin: The adaptor protein Snapin is required to link dynein to late endosomes. Loss of

Snapin prevents the retrograde transport of acidification machinery, leading to generalized lysosomal immaturity.⁵³ 7.2 Local Mitophagy and PINK1/Parkin While bulk autophagy requires retrograde transport, damaged mitochondria can be degraded locally.

● Mechanism: PINK1 accumulates on the outer membrane of depolarized mitochondria

and recruits Parkin. This initiates the local formation of autophagosomes.

● Failure Mode: In PINK1 or Parkin mutants, this local recognition fails. Furthermore, even if

autophagosomes form, the lack of local acidic lysosomes (due to transport defects) prevents degradation. The result is the accumulation of "mitophagic intermediates" that cannot be cleared.⁵⁴ PINK1 deficiency also impairs the phosphorylation of Ubiquitin, a signal required for autophagy receptors (like Optineurin) to bridge the mitochondrion to the autophagosome.⁵⁵ 8. Glial-Neuronal Crosstalk: Non-Cell-Autonomous

Mechanisms

Neuronal acidification is heavily influenced by the supporting glial cells. Dysfunction in microglia or astrocytes transmits toxicity to neurons. 8.1 Microglia: The PS1 Phosphorylation Switch In microglia, lysosomal acidification is regulated differently than in neurons.

● Ser367 Phosphorylation: While neuronal PS1 acts as a chaperone, microglial PS1

regulates acidification via phosphorylation at Serine 367. Unphosphorylated PS1 in microglia destabilizes V-ATPase V0a1, raising pH. Conversely, phosphorylated PS1 binds Annexin A2, which facilitates the interaction of VAMP8 with Syntaxin 17, enabling fusion.⁵⁶

● Impact: Microglial acidification failure prevents the clearance of amyloid plaques and

myelin debris, leading to a chronic inflammatory state that is toxic to neighboring neurons. 8.2 Progranulin (GRN) and Myelin Clearance Progranulin is essential for microglial lysosomal function. GRN deficiency (linked to FTD) causes a reduction in Cathepsin D activity and acidification failure. Microglia become engorged with undigested myelin debris, transitioning to a senescent, neurotoxic phenotype that damages neuronal networks.⁵⁷ 8.3 Astrocyte Toxicity and Exosomes

● SUMF1 Deletion: In Multiple Sulfatase Deficiency (MSD), astrocytes lacking SUMF1

accumulate lysosomal storage material. These astrocytes fail to provide metabolic support (lactate) to neurons and cannot clear neurotransmitters, causing neuronal death via non-cell-autonomous mechanisms.⁵⁸

● Toxic Exosomes: Dysfunctional astrocytes secrete exosomes containing mutant proteins

(e.g., SOD1 in ALS) and undigested cargo. Neurons endocytose these exosomes, effectively inheriting the astrocyte's "trash." This overwhelming load saturates the neuronal lysosomal system, leading to secondary acidification failure.⁶⁰ 9. Environmental Toxins and Pharmacological Agents External agents can mimic genetic defects by chemically attacking the V-ATPase or disrupting membrane integrity. 9.1 Heavy Metals: Lead (Pb) and Cadmium (Cd) ● Mechanism: Lead and Cadmium are potent neurotoxins that induce oxidative stress. They can displace essential divalent cations (Zn2+, Mg2+) required for ATPase function. Cadmium increases BBB permeability and accumulates in neurons, where it oxidizes the cysteine residues of the V-ATPase, directly inactivating the pump.⁶¹

● Estrogen Mimicry: Cadmium acts as a metalloestrogen, potentially dysregulating

hormonal signaling pathways that control lysosomal biogenesis.⁶² 9.2 Pesticides: Rotenone, Paraquat, and Chlorpyrifos

● Rotenone/Paraquat: These agents inhibit mitochondrial Complex I. Since V-ATPase

acidification is ATP-dependent, the resulting energy crisis leads to immediate alkalization. Rotenone also inhibits the Mitochondrial Calcium Uniporter (MCU), disrupting the Ca2+ signaling required for TPC2/TRPML1 function.⁶³

● Chlorpyrifos (CPF): Exposure to CPF has been linked to dopaminergic loss and

increased alpha-synuclein phosphorylation (pS129), correlating with autophagic flux inhibition.⁶⁴ 9.3 Pharmacological Agents

● Chloroquine (CQ): A lysosomotropic weak base. It diffuses into the lysosome, becomes

protonated, and is trapped. This accumulation chemically buffers the pH, neutralizing acidity. It also induces Golgi disorganization, further impairing the delivery of lysosomal enzymes.⁶⁵ ● Proton Pump Inhibitors (PPIs): Drugs like Lansoprazole, while targeting gastric pumps, have been associated with neuropathy and potentially dementia. The mechanism may involve off-target inhibition of V-ATPases or alterations in lysosomal enzyme processing.²⁴ 10. Therapeutic Horizons Understanding the diversity of acidification defects opens new avenues for therapy beyond simple autophagy induction.

Therapeutic Target Mechanism Status/Reference

Strategy

Acidic Lysosomal Lumen Delivery of acidic Preclinical ¹⁸

Nanoparticles polymers directly to (PLGA-aNP) the lysosome to

lower pH mechanically.

Nucleolipids Lysosomal Lipid prodrugs that Preclinical ⁶⁷

Membrane release organic acids upon lysosomal uptake.

V-ATPase V-ATPase Small molecules Discovery ⁶⁸

Agonists (e.g., soluble

adenylyl cyclase modulators) that allosterically enhance pumping.

Etidronate V-ATPase/Ataxin-2 Bisphosphonate Clinical

that modulates repurposing ⁶⁹ V-ATPase and lowers Ataxin-2 levels.

TPC2 Agonists TPC2 Channel Compounds like Preclinical ²⁸

TPC2-A1-P that

activate TPC2 to promote acidification and exocytosis (distinct from NAADP).

C381 Progranulin/Lysoso Small molecule that Preclinical ⁷¹

me restores lysosomal function and cognition in PD/FTD models.

Clioquinol Zinc/pH Chelator that Preclinical ⁷²

restores pH by reducing lysosomal zinc burden. 11. Conclusion The failure of autolysosomal acidification in neurons is a complex, convergent phenotype arising from genetic mutations (V-ATPase, PS1, LRRK2), structural failures (assembly chaperones), trafficking defects (axonal transport, SNARE switching), and environmental insults (toxins, drugs). It is the "Achilles' heel" of the post-mitotic neuron. The resulting accumulation of undegraded substrates creates a toxic feedback loop that exacerbates the initial defect. Future therapeutic success will likely depend on precision medicine approaches that identify the specific cause of acidification failure—be it a broken pump, a missing chaperone, or a traffic jam—and target it with specific modulators or acidifying agents.

Works cited

1. Falace A, Volpedo G, Scala M, Zara F, Striano P, Fassio A. V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities. Cells 2024;13(17):1441. DOI 10.3390/cells13171441.

2. Falace A, Volpedo G, Scala M, Zara F, Striano P, Fassio A. V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities. Cells 2024;13(17). DOI 10.3390/cells13171441.

3. Nixon RA. Autophagy-lysosomal-associated neuronal death in neurodegenerative disease. Acta Neuropathol 2024;148(1):42. DOI 10.1007/s00401-024-02799-7.

4. Zhang W, Xu J, Dong J, Huang Z, Cao L. Acidification Deficiency of Autolysosomes Induces Neuronal Autophagic Amyloid-β Plaques in Alzheimer's Disease. Neurosci Bull 2023;39(5):873-876. DOI 10.1007/s12264-022-01002-9.

5. Klein AD, Mazzulli JR. Is Parkinson’s disease a lysosomal disorder?. Brain 2018;141(8):2255-2262.awy147.

   Find this paper

6. Collins MP, Forgac M. Regulation and function of V-ATPases in physiology and disease. Biochim Biophys Acta Biomembr 2020;1862(12):183341. DOI 10.1016/j.bbamem.2020.183341.

7. Shi GS, Qin QL, Huang C, Li ZR, Wang ZH, Wang YY, et al.. The Pathological Mechanism of Neuronal Autophagy-Lysosome Dysfunction After Ischemic Stroke. Cell Mol Neurobiol 2023;43(7):3251-3263. DOI 10.1007/s10571-023-01382-0.

8. Wang H, Bueler SA, Rubinstein JL. Structural basis of V-ATPase V _O region assembly by Vma12p, 21p, and 22p. Proceedings of the National Academy of Sciences 2023;120(6). DOI 10.1073/pnas.2217181120.

9. Ramachandran N, Munteanu I, Wang P, Ruggieri A, Rilstone JJ, Israelian N, et al.. VMA21 deficiency prevents vacuolar ATPase assembly and causes autophagic vacuolar myopathy. Acta Neuropathol 2013;125(3):439-57. DOI 10.1007/s00401-012-1073-6.

10. Cocchiararo I, Cattaneo O, Rajendran J, Chabry F, Cornut M, Soldati H, et al.. Identification of a muscle-specific isoform of VMA21 as a potent actor in X-linked myopathy with excessive autophagy pathogenesis. Hum Mol Genet 2023;32(24):3374-3389. DOI 10.1093/hmg/ddad164.

11. Falace A, Volpedo G, Scala M, Zara F, Striano P, Fassio A. V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities. Cells 2024;13(17). DOI 10.3390/cells13171441.

12. Sun Y, Islam S, Michikawa M, Zou K. Presenilin: A Multi-Functional Molecule in the Pathogenesis of Alzheimer's Disease and Other Neurodegenerative Diseases. Int J Mol Sci 2024;25(3). DOI 10.3390/ijms25031757.

13. Lee JH, McBrayer MK, Wolfe DM, Haslett LJ, Kumar A, Sato Y, et al.. Presenilin 1 Maintains Lysosomal Ca(2+) Homeostasis via TRPML1 by Regulating vATPase-Mediated Lysosome Acidification. Cell Rep 2015;12(9):1430-44.2015.07.050.

    Find this paper

14. Deaton CA, Johnson GVW. Presenilin 1 Regulates Membrane Homeostatic Pathways that are Dysregulated in Alzheimer's Disease. J Alzheimers Dis 2020;77(3):961-977. DOI 10.3233/JAD-200598.

15. Jiang Y, Sato Y, Im E, Berg M, Bordi M, Darji S, et al.. Lysosomal Dysfunction in Down Syndrome Is APP-Dependent and Mediated by APP-βCTF (C99). J Neurosci 2019;39(27):5255-5268. DOI 10.1523/JNEUROSCI.0578-19.2019.

16. Lysosomal dysfunction in Down Syndrome and Alzheimer mouse models is caused by selective v-ATPase inhibition by Tyr682 phosphorylated APP βCTF | bioRxiv, accessed November 19, 2025, DOI 10.1101/2022.06.02.494546">https://www.biorxiv.org/content/10.1101/2022.06.02.494546

17. Too Basic: APP β-CTF's YENTPY Motif Binds Proton Pump, Thwarts Lysosomes - Alzforum, accessed November 19, 2025, https://www.alzforum.org/news/research-news/too-basic-app-v-ctfs-yentpy-mo tif-binds-proton-pump-thwarts-lysosomes

18. Lo CH, Zeng J. Defective lysosomal acidification: a new prognostic marker and therapeutic target for neurodegenerative diseases. Transl Neurodegener 2023;12(1):29. DOI 10.1186/s40035-023-00362-0.

19. Kim Y, Ha TY, Lee MS, Chang KA. Regulatory Mechanisms and Therapeutic Implications of Lysosomal Dysfunction in Alzheimer's Disease. Int J Biol Sci 2025;21(3):1014-1031. DOI 10.7150/ijbs.103028.

20. Schrecker M, Korobenko J, Hite RK. Cryo-EM structure of the lysosomal chloride-proton exchanger CLC-7 in complex with OSTM1. eLife 2020;9. DOI 10.7554/elife.59555.

21. Zifarelli G. The Role of the Lysosomal Cl(-)/H(+) Antiporter ClC-7 in Osteopetrosis and Neurodegeneration. Cells 2022;11(3). DOI 10.3390/cells11030366.

22. Kasper D, Planells‐Cases R, Fuhrmann JC, Scheel O, Zeitz O, Ruether K, et al.. Loss of the chloride channel ClC‐7 leads to lysosomal storage disease and neurodegeneration. The EMBO Journal 2005;24(5):1079-1091. DOI 10.1038/sj.emboj.7600576.

23. ClC-7 drives intraphagosomal chloride accumulation to support hydrolase activity and phagosome resolution | Journal of Cell Biology | Rockefeller University Press, accessed November 19, 2025, https://rupress.org/jcb/article/222/6/e202208155/213990/ClC-7-drives-intraphago somal-chloride-accumulation

24. Giuliano S, Montemagno C, Domdom M, Teisseire M, Brest P, Klionsky DJ, et al.. Should evidence of an autolysosomal de-acidification defect in Alzheimer and Parkinson diseases call for caution in prescribing chronic PPI and DMARD?. Autophagy 2023;19(10):2800-2806. DOI 10.1080/15548627.2023.2214960.

25. Santoni G, Maggi F, Amantini C, Marinelli O, Nabissi M, Morelli MB. Pathophysiological Role of Transient Receptor Potential Mucolipin Channel 1 in Calcium-Mediated Stress-Induced Neurodegenerative Diseases. Frontiers in Physiology 2020;11. DOI 10.3389/fphys.2020.00251.

26. Bhattacharjee A, Abuammar H, Juhász G. Lysosomal activity depends on TRPML1-mediated Ca(2+) release coupled to incoming vesicle fusions. J Biol Chem 2024;300(12):107911. DOI 10.1016/j.jbc.2024.107911.

27. Lloyd-Evans E. Acidic Ca(2+) stores in neurodegeneration. Messenger (Los Angel) 2016;5(1-2):37-55. DOI 10.1166/msr.2016.1054.

28. Agonist-mediated switching of ion selectivity in TPC2 differentially promotes lysosomal function | eLife, accessed November 19, 2025, https://elifesciences.org/articles/54712

29. van Veen S, Sørensen DM, Holemans T, Holen HW, Palmgren MG, Vangheluwe P. Cellular function and pathological role of ATP13A2 and related P-type transport ATPases in Parkinson's disease and other neurological disorders. Front Mol Neurosci 2014;7:48.ol.2014.00048.

    Find this paper

30. Rajagopalan S, Rane A, Chinta SJ, Andersen JK. Regulation of ATP13A2 via PHD2-HIF1α Signaling Is Critical for Cellular Iron Homeostasis: Implications for Parkinson's Disease. The Journal of Neuroscience 2016;36(4):1086-1095. DOI 10.1523/jneurosci.3117-15.2016.

31. Tsunemi T, Krainc D. Zn²⁺ dyshomeostasis caused by loss of ATP13A2/PARK9 leads to lysosomal dysfunction and alpha-synuclein accumulation. Hum Mol Genet 2014;23(11):2791-801. DOI 10.1093/hmg/ddt572.

32. Eguchi T, Kuwahara T, Sakurai M, Komori T, Fujimoto T, Ito G, et al.. LRRK2 and its substrate Rab GTPases are sequentially targeted onto stressed lysosomes and maintain their homeostasis. Proceedings of the National Academy of Sciences 2018;115(39). DOI 10.1073/pnas.1812196115.

33. Insights into the cellular consequences of LRRK2-mediated Rab protein

phosphorylation, accessed November 19, 2025, https://portlandpress.com/biochemsoctrans/article/51/2/587/232776/Insights-intothe-cellular-consequences-of-LRRK2

34. Lara Ordóñez AJ, Fasiczka R, Fernández B, Naaldijk Y, Fdez E, Blanca Ramírez M, et al.. The LRRK2 signaling network converges on a centriolar phospho-Rab10/RILPL1 complex to cause deficits in centrosome cohesion and cell polarization. Biol Open 2022;11(8). DOI 10.1242/bio.059468.

35. Bonet-Ponce L, Kluss JH, Cookson MR. Mechanisms of lysosomal tubulation and sorting driven by LRRK2. Biochem Soc Trans 2024;52(4):1909-1919. DOI 10.1042/BST20240087.

36. Lysosomal positioning regulates Rab10 phosphorylation at LRRK2-positive lysosomes, accessed November 19, 2025, https://www.biorxiv.org/content/

37. Kluss JH, Beilina A, Williamson CD, Lewis PA, Cookson MR, Bonet-Ponce L. Lysosomal positioning regulates Rab10 phosphorylation at LRRK2 ⁺ lysosomes. Proceedings of the National Academy of Sciences 2022;119(43). DOI 10.1073/pnas.2205492119.

38. Kluss JH, Beilina A, Williamson CD, Lewis PA, Cookson MR, Bonet-Ponce L. Lysosomal positioning regulates Rab10 phosphorylation at LRRK2(+) lysosomes. Proc Natl Acad Sci U S A 2022;119(43):e2205492119. DOI 10.1073/pnas.2205492119.

39. Yadavalli N, Ferguson SM. LRRK2 suppresses lysosome degradative activity in macrophages and microglia through MiT-TFE transcription factor inhibition. Proceedings of the National Academy of Sciences 2023;120(31). DOI 10.1073/pnas.2303789120.

40. Mamais A, Kluss JH, Bonet-Ponce L, Landeck N, Langston RG, Smith N, et al.. Mutations in LRRK2 linked to Parkinson disease sequester Rab8a to damaged lysosomes and regulate transferrin-mediated iron uptake in microglia. PLOS Biology 2021;19(12):e3001480. DOI 10.1371/journal.pbio.3001480.

41. Berwick DC, Heaton GR, Azeggagh S, Harvey K. LRRK2 Biology from structure to dysfunction: research progresses, but the themes remain the same. Mol Neurodegener 2019;14(1):49. DOI 10.1186/s13024-019-0344-2.

42. Genetic variations in GBA1 and LRRK2 genes: Biochemical and clinical consequences in Parkinson disease - Frontiers, accessed November 19, 2025, https://www.frontiersin.org/journals/neurology/articles/ full

43. Stojkovska I, Krainc D, Mazzulli JR. Molecular mechanisms of α-synuclein and GBA1 in Parkinson's disease. Cell Tissue Res 2018;373(1):51-60. DOI 10.1007/s00441-017-2704-y.

44. Jian F, Wang S, Tian R, Wang Y, Li C, Li Y, et al.. The STX17-SNAP47-VAMP7/VAMP8 complex is the default SNARE complex mediating autophagosome-lysosome fusion. Cell Res 2024;34(2):151-168. DOI 10.1038/s41422-023-00916-x.

45. Jian F, Wang S, Tian R, Wang Y, Li C, Li Y, et al.. The STX17-SNAP47-VAMP7/VAMP8 complex is the default SNARE complex mediating autophagosome–lysosome fusion. Cell Research 2024;34(2):151-168. DOI 10.1038/s41422-023-00916-x.

VAMP8_complex_is_the_default_SNARE_complex_mediating_autophagosome-ly sosome_fusion

46. van der Beek J, de Heus C, Sanza P, Liv N, Klumperman J. Loss of the HOPS complex disrupts early-to-late endosome transition, impairs endosomal recycling and induces accumulation of amphisomes. Molecular Biology of the Cell 2024;35(3). DOI 10.1091/mbc.E23-08-0328.

47. van der Welle REN, Jobling R, Burns C, Sanza P, van der Beek JA, Fasano A, et al.. Neurodegenerative VPS41 variants inhibit HOPS function and mTORC1‐dependent TFEB/TFE3 regulation. EMBO Molecular Medicine 2021;13(5). DOI 10.15252/emmm.202013258.

48. Xing R, Zhou H, Jian Y, Li L, Wang M, Liu N, et al.. The Rab7 effector WDR91 promotes autophagy-lysosome degradation in neurons by regulating lysosome fusion. J Cell Biol 2021;220(8). DOI 10.1083/jcb.202007061.

49. Dafsari HS, Schuler J, Schober E, Möller B, Antebi A, Fanto M, et al.. The space-time continuum in neurological disorders of the autophagosome-lysosome fusion machinery. Autophagy Reports 2025;4(1). DOI 10.1080/27694127.2025.2560903.

50. Ferguson SM. Axonal transport and maturation of lysosomes. Current Opinion in Neurobiology 2018;51:45-51. DOI 10.1016/j.conb.2018.02.020.

51. The Rab7-Epg5 and Rab39-ema modules cooperately position autophagosomes for efficient lysosomal fusions - bioRxiv, accessed November 19, 2025, DOI 10.1101/2024.08.16.608254">https://www.biorxiv.org/content/10.1101/2024.08.16.608254

52. Driving autophagy – the role of molecular motors | Journal of Cell Science, accessed November 19, 2025, https://journals.biologists.com/jcs/article/137/3/jcs260481/342997/Driving-autopha gy-the-role-of-molecular-motors

53. Ferguson SM. Axonal transport and maturation of lysosomes. Curr Opin Neurobiol 2018;51:45-51. DOI 10.1016/j.conb.2018.02.020.

54. Mitophagy of damaged mitochondria occurs locally in distal neuronal axons and requires PINK1 and Parkin | Journal of Cell Biology | Rockefeller University Press, accessed November 19, 2025, https://rupress.org/jcb/article/206/5/655/37725/Mitophagy-of-damaged-mitocho ndria-occurs-locally

55. Defective PTEN-induced kinase 1/Parkin mediated mitophagy and neurodegenerative diseases - Frontiers, accessed November 19, 2025, https://www.frontiersin.org/journals/cellular-neuroscience/articles/ 022.1031153/full

56. Quick JD, Silva C, Wong JH, Lim KL, Reynolds R, Barron AM, et al.. Lysosomal acidification dysfunction in microglia: an emerging pathogenic mechanism of neuroinflammation and neurodegeneration. J Neuroinflammation 2023;20(1):185. DOI 10.1186/s12974-023-02866-y.

57. Wu Y, Shao W, Todd TW, Tong J, Yue M, Koga S, et al.. Microglial lysosome dysfunction contributes to white matter pathology and TDP-43 proteinopathy in GRN-associated FTD. Cell Rep 2021;36(8):109581.2021.109581.

58. Astrocyte dysfunction triggers neurodegeneration in a lysosomal storage

Di Malta C, Fryer JD, Settembre C, Ballabio A. Astrocyte dysfunction triggers neurodegeneration in a lysosomal storage disorder. Proceedings of the National Academy of Sciences 2012;109(35). DOI 10.1073/pnas.1209577109.

59. Di Malta C, Fryer JD, Settembre C, Ballabio A. Astrocyte dysfunction triggers neurodegeneration in a lysosomal storage disorder. Proc Natl Acad Sci U S A 2012;109(35):E2334-42. DOI 10.1073/pnas.1209577109.

60. Ikezu T, Yang Y, Verderio C, Krämer-Albers E. Extracellular Vesicle-Mediated Neuron–Glia Communications in the Central Nervous System. The Journal of Neuroscience 2024;44(40):e1170242024. DOI 10.1523/jneurosci.1170-24.2024.

61. Bakulski KM, Seo YA, Hickman RC, Brandt D, Vadari HS, Hu H, et al.. Heavy Metals Exposure and Alzheimer's Disease and Related Dementias. J Alzheimers Dis 2020;76(4):1215-1242. DOI 10.3233/JAD-200282.

62. Wang B, Du Y. Cadmium and its neurotoxic effects. Oxid Med Cell Longev 2013;2013:898034. DOI 10.1155/2013/898034.

63. Anirudhan A, Mattethra GC, Alzahrani KJ, Banjer HJ, Alzahrani FM, Halawani IF, et al.. Eleven Crucial Pesticides Appear to Regulate Key Genes That Link MPTP Mechanism to Cause Parkinson's Disease through the Selective Degeneration of Dopamine Neurons. Brain Sci 2023;13(7). DOI 10.3390/brainsci13071003.

64. The Pesticide Chlorpyrifos Increases the Risk of Parkinson's Disease - bioRxiv, accessed November 19, 2025, DOI 10.1101/2025.03.13.643184">https://www.biorxiv.org/content/10.1101/2025.03.13.643184

65. Mauthe M, Orhon I, Rocchi C, Zhou X, Luhr M, Hijlkema KJ, et al.. Chloroquine inhibits autophagic flux by decreasing autophagosome-lysosome fusion. Autophagy 2018;14(8):1435-1455. DOI 10.1080/15548627.2018.1474314.

66. Bourdenx M, Daniel J, Genin E, Soria FN, Blanchard-Desce M, Bezard E, et al.. Nanoparticles restore lysosomal acidification defects: Implications for Parkinson and other lysosomal-related diseases. Autophagy 2016;12(3):472-83. DOI 10.1080/15548627.2015.1136769.

67. Nucleolipid Acid-Based Nanocarriers Restore Neuronal Lysosomal Acidification Defects, accessed November 19, 2025, https://www.frontiersin.org/journals/chemistry/articles/ 4/full

68. Aldrich LN, Kuo S, Castoreno AB, Goel G, Kuballa P, Rees MG, et al.. Discovery of a Small-Molecule Probe for V-ATPase Function. Journal of the American Chemical Society 2015;137(16):5563-5568. DOI 10.1021/jacs.5b02150.

69. Kim G, Nakayama L, Blum JA, Akiyama T, Boeynaems S, Chakraborty M, et al.. Genome-wide CRISPR screen reveals v-ATPase as a drug target to lower levels of ALS protein ataxin-2. Cell Rep 2022;41(4):111508.2022.111508.

    Find this paper

70. Prat Castro S, Kudrina V, Jaślan D, Böck J, Scotto Rosato A, Grimm C. Neurodegenerative Lysosomal Storage Disorders: TPC2 Comes to the Rescue!. Cells 2022;11(18). DOI 10.3390/cells11182807.

71. Vest RT, Chou C, Zhang H, Haney MS, Li L, Laqtom NN, et al.. Small molecule C381 targets the lysosome to reduce inflammation and ameliorate disease in models of neurodegeneration. Proceedings of the National Academy of Sciences 2022;119(11). DOI 10.1073/pnas.2121609119.

72. Wallings R, Connor-Robson N, Wade-Martins R. LRRK2 interacts with the vacuolar-type H+-ATPase pump a1 subunit to regulate lysosomal function. Hum Mol Genet 2019;28(16):2696-2710. DOI 10.1093/hmg/ddz088.

The Validity Ledger

The argument above is only as strong as its weakest load-bearing joint, and the reader is owed an explicit accounting of where it stands on the ground and where it stands on inference.