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

Abstract

Lipophagy, a selective form of autophagy, has the potential to aid in clearance of sterol from macrophage foam cells by moving cytoplasmic lipid to lysosomes for removal. However, in advanced atherosclerosis, macrophage foam cells retain most of their cholesterol in large, lipid-swollen lysosomes and this inhibits lysosome function, 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 lysosome function and dramatically reduce lysosome and cell sterol content. Given that triglyceride is able to restore lysosome function 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 lysosomal dysfunction similar to that of advanced lesions. Then cells were chased with either media alone or media containing 30μg/mL VLDL for three days. The VLDL chase produced 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 droplet marker adipophilin following the VLDL chase. We also found a significant increase (24.6%) in association of adipophilin with the lysosomal marker LAMP-1. These results suggest that VLDL uptake by foam cells increases the lipophagic targeting of lipid-droplet components to lysosomes and increases clearance of this material (as identified by decreased LC3). Thus, VLDL-mediated restoration of lipophagic clearance of cellular sterol by lysosomal hydrolysis has the potential to be an important mechanism for reducing lipid burden in late-stage foam cells and possibly other neutral lipid-engorged tissues.