Abstract 227: Lipophagy’s About Face as Early Macrophage Foam Cells Transition to Late Stages
Efflux of cellular sterol from macrophage foam cells plays an important role in limiting atherosclerotic lesion progression. Recently, lysosomes were shown to participate in efflux of cytoplasmic lipid droplet (LD) sterol through lipophagy. Lipophagy is a form of autophagy that mobilizes cholesteryl ester (CE) and triglyceride (TG) from LDs to lysosomes for degradation. In early atherosclerosis, lipophagy helps clear cytoplasmic sterol. However, in advanced atherosclerosis, macrophage lysosomes are impaired by excess sterol. We hypothesized that lipophagic delivery of LD CE to impaired lysosomes adds to lysosomal sterol burden exacerbating lysosome dysfunction and cellular sterol accumulation rather than promoting sterol clearance. To test this, we induced lysosome CE loading in THP-1 macrophages with aggregated LDL (aggLDL). This elevated lysosomal pH and led to accumulation of autophagic flux markers (LC3 and p62, >2 fold) and the LD coat protein adipophilin (6 fold) in lysosomes without altering lysosomal and upstream autophagic markers. This suggests lipophagy remained active despite the lysosome dysfunction and contributed to lysosomal sterol buildup. Triglyceride rich particles (TRP) have been shown to restore lysosome function and promote clearance of excess sterol from lysosomes and cells. If lipophagy is quantitatively important in late stage foam cells, TRP should reduce the aggLDL-induced lysosomal accrual of lipophagic markers. VLDL treatment of aggLDL-loaded cells restored lysosomal pH and cleared cellular sterol, in addition to, decreasing LC3-II and p62 in whole cells and isolated lysosomes (>2 fold) and reducing the fluorescent colocalization of LC3 with lysosomes by 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 lysosome function 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 cells but only as an adjunct to interventions that restore lysosome function.
Author Disclosures: C. Netherland-Van Dyke: None. C. Romer: None. G. Jerome: None.
This research has received full or partial funding support from the American Heart Association.
- © 2014 by American Heart Association, Inc.