Mammalian lysophagy: mechanisms and pathophysiological implications

Lysophagy is a form of selective macroautophagy/autophagy that preserves lysosomal integrity by eliminating damaged lysosomes. Lysosomal membrane permeabilization can arise from diverse physiological and pathological insults, including proteotoxic stress, crystalline particles, pathogens and chemical perturbations, and occurs along a continuum ranging from transient nanoscale lesions to catastrophic rupture. Cells respond to lysosomal injury through a hierarchical quality-control network in which membrane repair, lysophagic removal and lysosomal regeneration operate in a coordinated manner. Damage recognition involves sensing of exposed lumenal glycans and membrane lipids, followed by ubiquitin-dependent tagging that recruits selective autophagy receptors and activates the core autophagy machinery to form lysophagosomes. Lysophagy is closely integrated with membrane repair pathways, metabolic signaling and innate immune responses that together determine lysosomal fate. Dysregulated lysosomal quality control has been implicated in diverse diseases, including neurodegeneration, infection, cancer and chronic inflammatory disorders. In this review, we summarize current mechanistic insights and emerging experimental approaches for studying lysosomal quality control and lysophagy in mammalian cells.Abbreviations: ALR, autophagic lysosome reformation; ALS, amyotrophic lateral sclerosis; ATG8, mammalian Atg8-family protein; ER, endoplasmic reticulum; ESCRT, endosomal sorting complexes required for transport; LAMPs, lysosome associated membrane proteins; LIR, LC3-interacting region; LLOMe, L-leucyl-L-leucine methyl ester; LMP, lysosomal membrane permeabilization; PITT, phosphoinositide-initiated membrane tethering and lipid transport; PtdIns3K, class III phosphatidylinositol 3-kinase; PtdIns3P, phosphatidylinositol-3-phosphate; PtdIns4P, phosphatidylinositol-4-phosphate; ROS, reactive oxygen species; V-ATPase, vacuolar-type H+ -ATPase