Abstract 433: Lipophagy Aids in VLDL-Mediated Lysosomal Sterol Clearance from Macrophage Foam Cells

Lipophagy, a selective form of autophagy, has the potential to aid in clearance of sterolfrom macrophage foam cellsby moving cytoplasmic lipid to lysosomesfor removal. However, in advanced atherosclerosis, macrophage foam cellsretain most of their cholesterol in large, lipid-swollen lysosomesand this inhibits lysosomefunction, including digestion of autophagic-derived lipids. Triglyceride rich particles are also found in atherosclerotic lesions and we have shown that in sterol-engorged cells uptake of triglyceride-rich particles can restore lysosomefunction and dramatically reduce lysosomeand cell sterolcontent. Given that triglyceride is able to restore lysosomefunction and lysosome-mediated removal of sterol, we investigated the role of lipophagy in this restoration. We loaded THP-1 macrophages with 50μg/mL aggregated LDL (aggLDL) for six days to produce sterol-mediated lysosomaldysfunction similar to that of advanced lesions. Then cells were chasedwith either media alone or media containing 30μg/mL VLDL for three days. The VLDL chaseproduced a 23% decrease in the autophagic marker LC3 compared to controls. Fluorescence microscopy confirmed a decrease in overall LC3 levels but also revealed a 26.3% increase in LC3 colocalization with the lipid dropletmarker adipophilin following the VLDL chase. We also found a significant increase (24.6%) in association of adipophilin with the lysosomalmarker LAMP-1. These results suggest that VLDL uptake by foam cellsincreases the lipophagic targeting of lipid-dropletcomponents to lysosomesand increases clearance of this material (as identified by decreased LC3). Thus, VLDL-mediated restoration of lipophagic clearance of cellular sterolby lysosomalhydrolysis has the potential to be an important mechanism for reducing lipid burden in late-stage foam cellsand possibly other neutral lipid-engorged tissues.