Abstract 227: Lipophagy’s About Face as Early Macrophage Foam Cells Transition to Late Stages

Efflux of cellular sterolfrom macrophage foam cellsplays an important role in limiting atherosclerotic lesion progression. Recently, lysosomeswere shown to participate in efflux of cytoplasmic lipid droplet (LD) sterolthrough lipophagy. Lipophagy is a form of autophagy that mobilizes cholesteryl ester(CE) and triglyceride (TG) from LDs to lysosomesfor degradation. In early atherosclerosis, lipophagy helps clear cytoplasmic sterol. However, in advanced atherosclerosis, macrophage lysosomesare impaired by excess sterol. We hypothesized that lipophagic delivery of LD CE to impaired lysosomesadds to lysosomal sterolburden exacerbating lysosomedysfunction and cellular sterolaccumulation rather than promoting sterolclearance. To test this, we induced lysosomeCE loading in THP-1 macrophages with aggregated LDL (aggLDL). This elevated lysosomalpH and led to accumulation of autophagic flux markers (LC3 and p62, >2 fold) and the LD coat protein adipophilin (6 fold) in lysosomeswithout altering lysosomaland upstream autophagic markers. This suggests lipophagy remained active despite the lysosomedysfunction and contributed to lysosomal sterolbuildup. Triglyceride rich particles (TRP) have been shown to restore lysosomefunction and promote clearance of excess sterolfrom lysosomesand cells. If lipophagy is quantitatively important in late stage foam cells, TRP should reduce the aggLDL-induced lysosomalaccrual of lipophagic markers. VLDL treatment of aggLDL- loaded cellsrestored lysosomalpH and cleared cellular sterol, in addition to, decreasing LC3-II and p62 in whole cells and isolated lysosomes(>2 fold) and reducing the fluorescent colocalizationof LC3 with lysosomesby 37.9%. VLDL also increased autophagic LD targeting (26.3% LC3 colocalization) and delivery to lysosomes(24.6% LAMP-1 colocalization) for degradation. In conclusion, TRP restores lysosomefunction including the hydrolysis and clearance of LD CE through lipophagy in aggLDL-loaded macrophages. These data indicate that lipophagy is a potential target for therapy in late-stage foam cellsbut only as an adjunct to interventions that restore lysosomefunction.