Acid phospholipase A1 promotes lysosomal membrane catabolism

Abstract

The molecular mechanisms of lysosomal glycerophospholipid (GPL) catabolism are incompletely understood. Here, we report that acid phospholipase A1 (APLA1), formerly known as palmitoyl-protein thioesterase 2 (PPT2), is required for efficient GPL degradation. Deletion of APLA1 in human cells results in excess accumulation of phospholipids within lysosomes # a pathological condition termed phospholipidosis. APLA1 activity depends on interactions with negatively charged GPLs and is inhibited by phospholipidosis-inducing cationic amphiphilic drugs. Hydrolysis of zwitterionic, but not anionic, GPLs requires co-activation of APLA1 by the lysosome-specific lipid bis(monoacylglycero)phosphate. Upon pharmacological mTORC inhibition, which increases lysosomal GPL turnover, APLA1-deficient cells exhibit massive accumulation of multilamellar membranes in lysosomes and reduced cytosolic triacylglycerol stores. APLA1 acts in concert with lysosomal phospholipase A2 (PLA2G15). Combined APLA1/PLA2G15-deficiency leads to a severe reduction in acid phospholipase A1/A2 activity, thereby exacerbating phospholipidosis. Our observations provide detailed mechanistic insights into lysosomal GPL catabolism, a crucial pathway for maintaining lipid homeostasis.