OBJECTIVE: Cholesterol efflux is achieved by several mechanisms. This study examines contributions of these pathways to efflux to human serum. METHODS AND RESULTS: Human fibroblasts were stably transfected with SR-BI while ABCA1 was upregulated. Quantitation of cholesterol efflux to human serum demonstrated that there was efflux from cells without either protein. Expression of ABCA1 produced a small increase in efflux, whereas SR-BI expression had a dramatic impact. To quantitate ABCA1 and SR-BI contribution, fibroblasts were pretreated with Probucol and BLT-1 to, respectively, inhibit these efflux proteins. Exposing SR-BI-expressing fibroblasts to BLT-1 inhibited efflux by 67%. Probucol pretreatment of ABCA1-expressing fibroblasts reduced efflux to serum by 26%. A large fraction of total efflux was uninhibited. For both J774 and mouse peritoneal macrophages, contributions of either ABCA1 or SR-BI to efflux to serum were low, with background/uninhibited efflux contributing from 70% to 90% of total efflux. CONCLUSIONS: We have shown that ABCA1-mediated efflux to serum responds to the pool of lipid-free/poor apolipoproteins, whereas phospholipid-containing particles mediate SR-BI efflux. Although SR-BI and ABCA1 contribute to efflux from fibroblasts and cholesterol-enriched macrophages, a large proportion of the total efflux to human serum is mediated by a mechanism that is neither SR-BI nor ABCA1.
OBJECTIVE:Cholesterol efflux is achieved by several mechanisms. This study examines contributions of these pathways to efflux to human serum. METHODS AND RESULTS:Human fibroblasts were stably transfected with SR-BI while ABCA1 was upregulated. Quantitation of cholesterol efflux to human serum demonstrated that there was efflux from cells without either protein. Expression of ABCA1 produced a small increase in efflux, whereas SR-BI expression had a dramatic impact. To quantitate ABCA1 and SR-BI contribution, fibroblasts were pretreated with Probucol and BLT-1 to, respectively, inhibit these efflux proteins. Exposing SR-BI-expressing fibroblasts to BLT-1 inhibited efflux by 67%. Probucol pretreatment of ABCA1-expressing fibroblasts reduced efflux to serum by 26%. A large fraction of total efflux was uninhibited. For both J774 and mouse peritoneal macrophages, contributions of either ABCA1 or SR-BI to efflux to serum were low, with background/uninhibited efflux contributing from 70% to 90% of total efflux. CONCLUSIONS: We have shown that ABCA1-mediated efflux to serum responds to the pool of lipid-free/poor apolipoproteins, whereas phospholipid-containing particles mediate SR-BI efflux. Although SR-BI and ABCA1 contribute to efflux from fibroblasts and cholesterol-enriched macrophages, a large proportion of the total efflux to human serum is mediated by a mechanism that is neither SR-BI nor ABCA1.
Authors: Sandhya Sankaranarayanan; Ginny Kellner-Weibel; Margarita de la Llera-Moya; Michael C Phillips; Bela F Asztalos; Robert Bittman; George H Rothblat Journal: J Lipid Res Date: 2011-09-27 Impact factor: 5.922
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Authors: Avery L McIntosh; Barbara P Atshaves; Huan Huang; Adalberto M Gallegos; Ann B Kier; Friedhelm Schroeder Journal: Lipids Date: 2008-06-07 Impact factor: 1.880
Authors: Sandhya Sankaranarayanan; John F Oram; Bela F Asztalos; Ashley M Vaughan; Sissel Lund-Katz; Maria Pia Adorni; Michael C Phillips; George H Rothblat Journal: J Lipid Res Date: 2008-09-30 Impact factor: 5.922