Role of Autophagy in Phosphatidyl- Glycerol Facilitated Cholesterol Clearance from the Endolysosomal System of Npc-1 Deficient Cells

Abstract

Niemann Pick Type C (NPC) Disease is a rare lysosomal storage disorder in which one of the genes that codes for either the NPC-1 or NPC-2 pro-tein is mutated, causing cell lysosomes to accumu-late cholesterol and lipids. Previous studies discov-ered that a unique late endosomal/lysosomal phos-pholipid, lysobisphosphatidic acid (LPBA), is in-volved in cholesterol clearance from late endo-somes. It has also been shown that exogenous treat-ment of the NPC-1 deficient cells with LBPA’s precur-sor, phosphatidylglycerol (PG), leads to LBPA enrich-ment and subsequent endolysosomal cholesterol clearance. Autophagy is a mechanism of cellular clearance in the endolysomal system and we are in-terested to see if it is a partial route in cholesterol clearance during PG treatment of NPC-1 deficient cells. To do so, we silenced the gene that codes for an essential protein in the autophagy pathway, mak-ing the cells autophagy deficient. We then treated the cells with PG, measured the amount of choles-terol clearance in those cells, and compared it to cells with normal autophagy. We found significantly less cholesterol clearance by PG in cells with defec-tive autophagy, confirming that autophagy is in-volved as a partial route in cholesterol clearance dur-ing PG treatment, but not enough of a difference to conclude that it is a major underlying mechanism.