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Papers In Press, published online ahead of print October 24, 2007 J. Lipid Res., doi:10.1194/jlr.M700200-JLR200
Molecular medicine, Columia university, New York, NY 10032
Corresponding Author: ly2159{at}columbia.edu
This study compares the roles of ABCG1 and SR-BI singly or together in promoting net cellular cholesterol efflux to plasma HDL containing active LCAT. In transfected cells SR-BI promoted free cholesterol efflux to HDL but this was offset by an increased uptake of HDL CE into cells, resulting in no net efflux. Co-expression of SR-BI with ABCG1 inhibited the ABCG1-mediated net cholesterol efflux to HDL apparently by promoting the reuptake of CE from media. However, ABCG1-mediated cholesterol efflux was not altered in cholesterol loaded, SR-BI deficient macrophages. Briefly cultured macrophages collected from SR-BI-/- mice loaded with AcLDL in the peritoneal cavity, did exhibit reduced efflux to HDL. However, this was due to reduced expression of ABCG1 and ABCA1, likely reflecting increased macrophage cholesterol efflux to apoE-enriched HDL during loading in SR-BI-/- mice. In conclusion, cellular SR-BI does not promote net cholesterol efflux from cells to plasma HDL containing active LCAT, due to reuptake of HDL CE into cells. Previous findings of increased atherosclerosis in mice transplanted with SR-B1 deficient bone marrow probably cannot be explained by a defect in macrophage cholesterol efflux.
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