Xian-Ming Du1, Mi-Jurng Kim1, Liming Hou1, Wilfried Le Goff1, M John Chapman1, Miranda Van Eck1, Linda K Curtiss1, John R Burnett1, Sian P Cartland1, Carmel M Quinn1, Maaike Kockx1, Anatol Kontush1, Kerry-Anne Rye1, Leonard Kritharides1, Wendy Jessup2. 1. From the Centre for Vascular Research, University of New South Wales, Sydney, New South Wales, Australia (X.-M.D., M.-J.K., L.H., S.P.C., C.M.Q., K.-A.R); INSERM, UMR_1166, Research Institute of Cardiovascular Disease, Metabolism and Nutrition, Pitié-Salpétrière University Hospital, Paris, France (W.L.G., M.J.C., A.K.); Université Pierre et Marie Curie-Paris 6, Paris, France (W.L.G., M.J.C., A.K.); Division of Biopharmaceutics, Leiden Academic Centre for Drug Research, Leiden, The Netherlands (M.V.E.); Department of Immunology and Microbial Science, The Scripps Research Institute, La Jolla, CA (L.K.C.); Department of Clinical Biochemistry, Royal Perth Hospital, Perth, Western Australia, Australia (J.R.B.); School of Medicine and Pharmacology, University of Western Australia, Crawley, Western Australia, Australia (J.R.B.); Atherosclerosis Laboratory, ANZAC Research Institute, University of Sydney, Sydney, New South Wales, Australia (M.K., L.K., W.J.); and Department of Cardiology, Concord Hospital, Sydney, New South Wales, Australia (L.K.). 2. From the Centre for Vascular Research, University of New South Wales, Sydney, New South Wales, Australia (X.-M.D., M.-J.K., L.H., S.P.C., C.M.Q., K.-A.R); INSERM, UMR_1166, Research Institute of Cardiovascular Disease, Metabolism and Nutrition, Pitié-Salpétrière University Hospital, Paris, France (W.L.G., M.J.C., A.K.); Université Pierre et Marie Curie-Paris 6, Paris, France (W.L.G., M.J.C., A.K.); Division of Biopharmaceutics, Leiden Academic Centre for Drug Research, Leiden, The Netherlands (M.V.E.); Department of Immunology and Microbial Science, The Scripps Research Institute, La Jolla, CA (L.K.C.); Department of Clinical Biochemistry, Royal Perth Hospital, Perth, Western Australia, Australia (J.R.B.); School of Medicine and Pharmacology, University of Western Australia, Crawley, Western Australia, Australia (J.R.B.); Atherosclerosis Laboratory, ANZAC Research Institute, University of Sydney, Sydney, New South Wales, Australia (M.K., L.K., W.J.); and Department of Cardiology, Concord Hospital, Sydney, New South Wales, Australia (L.K.). wendy.jessup@sydney.edu.au.
Abstract
RATIONALE: High-density lipoprotein (HDL) is a heterogeneous population of particles. Differences in the capacities of HDL subfractions to remove cellular cholesterol may explain variable correlations between HDL-cholesterol and cardiovascular risk and inform future targets for HDL-related therapies. The ATP binding cassette transporter A1 (ABCA1) facilitates cholesterol efflux to lipid-free apolipoprotein A-I, but the majority of apolipoprotein A-I in the circulation is transported in a lipidated state and ABCA1-dependent efflux to individual HDL subfractions has not been systematically studied. OBJECTIVE: Our aims were to determine which HDL particle subfractions are most efficient in mediating cellular cholesterol efflux from foam cell macrophages and to identify the cellular cholesterol transporters involved in this process. METHODS AND RESULTS: We used reconstituted HDL particles of defined size and composition, isolated subfractions of human plasma HDL, cell lines stably expressing ABCA1 or ABCG1, and both mouse and human macrophages in which ABCA1 or ABCG1 expression was deleted. We show that ABCA1 is the major mediator of macrophage cholesterol efflux to HDL, demonstrating most marked efficiency with small, dense HDL subfractions (HDL3b and HDL3c). ABCG1 has a lesser role in cholesterol efflux and a negligible role in efflux to HDL3b and HDL3c subfractions. CONCLUSIONS: Small, dense HDL subfractions are the most efficient mediators of cholesterol efflux, and ABCA1 mediates cholesterol efflux to small dense HDL and to lipid-free apolipoprotein A-I. HDL-directed therapies should target increasing the concentrations or the cholesterol efflux capacity of small, dense HDL species in vivo.
RATIONALE: High-density lipoprotein (HDL) is a heterogeneous population of particles. Differences in the capacities of HDL subfractions to remove cellular cholesterol may explain variable correlations between HDL-cholesterol and cardiovascular risk and inform future targets for HDL-related therapies. The ATP binding cassette transporter A1 (ABCA1) facilitates cholesterol efflux to lipid-free apolipoprotein A-I, but the majority of apolipoprotein A-I in the circulation is transported in a lipidated state and ABCA1-dependent efflux to individual HDL subfractions has not been systematically studied. OBJECTIVE: Our aims were to determine which HDL particle subfractions are most efficient in mediating cellular cholesterol efflux from foam cell macrophages and to identify the cellular cholesterol transporters involved in this process. METHODS AND RESULTS: We used reconstituted HDL particles of defined size and composition, isolated subfractions of human plasma HDL, cell lines stably expressing ABCA1 or ABCG1, and both mouse and human macrophages in which ABCA1 or ABCG1 expression was deleted. We show that ABCA1 is the major mediator of macrophage cholesterol efflux to HDL, demonstrating most marked efficiency with small, dense HDL subfractions (HDL3b and HDL3c). ABCG1 has a lesser role in cholesterol efflux and a negligible role in efflux to HDL3b and HDL3c subfractions. CONCLUSIONS: Small, dense HDL subfractions are the most efficient mediators of cholesterol efflux, and ABCA1 mediates cholesterol efflux to small dense HDL and to lipid-free apolipoprotein A-I. HDL-directed therapies should target increasing the concentrations or the cholesterol efflux capacity of small, dense HDL species in vivo.
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