Defective ATP13A2-ITCH-ALIX signaling impairs intraluminal vesicle biogenesis and increases neuronal vulnerability.

ATP13A2 is a lysosomal P5B-type ATPase whose loss-of-function mutations are associated with a spectrum of neurodegenerative disorders, including early-onset Parkinson's disease, Kufor-Rakeb syndrome, neuronal ceroid lipofuscinosis, hereditary spastic paraplegia, and amyotrophic lateral sclerosis. Although ATP13A2 is known to contribute to lysosomal homeostasis and, thereby, to neuronal degeneration, emerging evidence suggests that it may also influence exosome biology. However, the mechanisms by which endogenous ATP13A2 regulates exosome biogenesis and the relevance of this process to neuronal vulnerability remain unclear. In the present study, using multiple ATP13A2-deficient human cell models, we demonstrated that ATP13A2 deficiency impairs intraluminal vesicle (ILV) biogenesis and reduces exosome secretion across diverse cellular contexts. Loss of ATP13A2 did not markedly affect endocytosis, early endosome abundance, or multivesicular body formation, but it consistently reduced ILV density within multivesicular bodies. Mechanistically, ATP13A2 deficiency promoted lysosome-associated accumulation of the E3 ubiquitin ligase ITCH, which enhanced ubiquitin-proteasome-dependent degradation of ALG-2-interacting protein X (ALIX), a critical adaptor of the endosomal sorting complex required for transport machinery that mediates ILV membrane remodeling. Restoration of ALIX expression or reduction of Itchy E3 ubiquitin-protein ligase (ITCH) activity rescued the ILV biogenesis defects in ATP13A2-deficient neuronal cells. Furthermore, dysregulation of the ATP13A2-ITCH-ALIX pathway increased neuronal susceptibility to mitochondrial stress, whereas restoration of ALIX or reduction of ITCH activity markedly improved neuronal survival. Together, these results identify an ATP13A2-ITCH-ALIX signaling axis linking lysosomal dysfunction to impaired ILV biogenesis and exosome regulation. Our study suggests that defective ILV biogenesis contributes to neuronal vulnerability and that modulation of the ATP13A2-ITCH-ALIX pathway may represent a therapeutic strategy for ATP13A2-associated neurodegeneration.