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Journal of Lipid Research, Vol. 47, 492-503, March 2006
Copyright © 2006 by American Society for Biochemistry and Molecular Biology

Hepatic SR-BI-mediated cholesteryl ester selective uptake occurs with unaltered efficiency in the absence of cellular energy

Chris J. Harder, Gerard Vassiliou¹, Heidi M. McBride and Ruth McPherson²

Lipoprotein and Atherosclerosis Group, University of Ottawa Heart Institute, Ottawa, Ontario, Canada K1Y 4W7

Published, JLR Papers in Press, December 7, 2005.

¹ Deceased May 9, 2005.

² To whom correspondence should be addressed. e-mail: rmcpherson{at}ottawaheart.ca

Scavenger receptor class B type I (SR-BI) plays a critical role in the delivery of HDL cholesterol and cholesteryl esters (CEs) to liver and steroidogenic tissues by a selective process that does not result in significant degradation of HDL protein. Recently, SR-BI-mediated endocytosis and recycling of HDL have been demonstrated. However, it remains unclear whether efficient SR-BI-mediated selective uptake occurs strictly at the plasma membrane or at additional sites along its endocytic itinerary. To examine the requirement for SR-BI endocytosis in HDL selective uptake, we determined the effects of energy depletion on the levels of cell-associated HDL protein and CE in primary mouse hepatocytes. Compared with CHO cells, we observed a much larger energy-dependent effect on CE uptake in primary mouse hepatocytes. Although varying the levels of caveolin-1 and carboxyl ester lipase altered the efficiency of selective uptake, neither was able to account for the energy-dependent component of HDL-CE uptake. Finally, we demonstrate that the hepatocyte-specific, energy-dependent effects on HDL-apolipoprotein A-I and -CE uptake are independent of SR-BI and are not required to achieve efficient SR-BI-mediated selective uptake of CE. Together, these data support the conclusion that neither the intracellular trafficking of HDL nor any energy-dependent cellular process affects the ability of the cell to maximally acquire CE through SR-BI-mediated selective uptake from HDL.

Supplementary key words scavenger receptor class B type I • high density lipoprotein • hepatocytes • endocytosis • reverse cholesterol transport

Abbreviations: apoA-I, apolipoprotein A-I; Cav-1, caveolin-1; CE, cholesteryl ester; CEL, carboxyl ester lipase; CFP, cyan fluorescent protein; COE, cholesteryl oleoyl ether; RFP, red fluorescent protein; SR-BI, scavenger receptor class B type I; YFP, yellow fluorescent protein

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