title: High-density lipoprotein protects macrophages from oxidized low-density lipoprotein-induced apoptosis by promoting efflux of 7-ketocholesterol via ABCG1.
abstract: Oxidized sterols consumed in the diet or formed on low-density lipoprotein (LDL) are toxic to endothelial cells and macrophages and are thought to have a central role in promoting atherogenesis. The ATP-binding cassette transporter ABCG1 was recently shown to promote efflux of cholesterol from macrophages to high-denisty lipoprotein (HDL). We show that HDL protects macrophages from apoptosis induced by loading with free cholesterol or oxidized LDL. The protective effect of HDL was reduced in Abcg1(-/-) macrophages, especially after loading with oxidized LDL. Similarly, HDL exerted a protective effect against apoptosis induced by 7-ketocholesterol, the major oxysterol present in oxidized LDL and atherosclerotic lesions, in Abcg1(+/+), but not in Abcg1(-/-) macrophages. In transfected 293 cells, efflux of 7-ketocholesterol and related oxysterols was completely dependent on expression of ABCG1 and the presence of HDL in media. In contrast, ABCA1 and apoA-1 did not stimulate the efflux of 7-ketocholesterol into media. HDL stimulated the efflux of 7-ketocholesterol from Abcg1(+/+), but not from Abcg1(-/-) macrophages. In Abcg1(-/-) mice fed a high-cholesterol diet, plasma levels of 7-ketocholesterol were reduced, whereas their macrophages accumulated 7-ketocholesterol. These findings indicate a specific role for ABCG1 in promoting efflux of 7-ketocholesterol and related oxysterols from macrophages onto HDL and in protecting these cells from oxysterol-induced cytotoxicity.
authors.affiliation: Division of Molecular Medicine, Department of Medicine, Columbia University, New York, NY 10032, USA. nt2188@columbia.edu
authors.forename: Naoki
authors.initials: N
authors.lastname: Terasaka
authors.forename: Nan
authors.initials: N
authors.lastname: Wang
authors.forename: Laurent
authors.initials: L
authors.lastname: Yvan-Charvet
authors.forename: Alan R
authors.initials: AR
authors.lastname: Tall
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis; D002478:Cells, Cultured; D006801:Humans; D007653:Ketocholesterols / Q000378:metabolism*; D008074:Lipoproteins / Q000235:genetics / Q000378:metabolism*; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D014162:Transfection
chemical_list: C577836:ABCA1 protein, human; C419353:ABCG1 protein, human; C487540:ABCG1 protein, mouse; D064286:ATP Binding Cassette Transporter 1; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters; D007653:Ketocholesterols; D008074:Lipoproteins; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; C099252:oxidized low density lipoprotein; C003001:7-ketocholesterol