Lysosomal cholesterol derived from mildly oxidized low density lipoproteinis resistant to efflux

In atherosclerotic lesions, macrophages store lipid in cytoplasmic inclusio ns and lysosomes, Regression studies show that lysosomal lipid is not as ea sily cleared as cytoplasmic inclusion lipid, Macrophages enriched with mild ly oxidized low density lipoprotein (oxLDL) accumulate cholesteryl ester (C E) and free cholesterol (FC) in lysosomes, We examined whether lysosomal st ores of cholesterol from oxLDL are cleared from THP-1 and mouse macrophages , As in previous studies, oxLDL-enriched THP-1 macrophages accumulated subs tantial lysosomal cholesterol, Surprisingly, less than 12% of oxLDL-derived lysosomal CE was cleared to efficient FC accepters (e.g., cyclodextrins, a polipoprotein/phosphatidylcholine vesicles, and fetal bovine serum), Filipi n staining showed that lysosomes of oxLDL-treated THP-1 cells contained FC, and despite removal of most of the cell FC (70-80%) by incubation with cyc lodextrins, filipin staining of FC in lysosomes did not diminish, Also, whe n THP-1 macrophages were incubated with [H-3]CE oxLDL, 73-76% of the [H-3]C E,as retained in a lysosomal hydrolysis resistant pool, In contrast, greate r than 90% of acetylated low density lipoprotein (acLDL) [H-3]CE was hydrol yzed, Furthermore, [H-3]FC liberated from oxLDL [H-3]CE was released at a s lower rate to cyclodextrins than was [H-3]FC from acLDL [H-3]CE. In contras t, only 27% of oxLDL [H-3]CE was resistant to hydrolysis in mouse macrophag es, and the [H-3]FC generated from oxLDL and acLDL [H-3]CE was released to cyclodextrins at similar rates. We conclude that lack of hydrolysis and eff lux of oxLDL cholesterol is not exclusively inherent in oxLDL, but also req uires specific cell factors present in one cell type but not the other.