Hepatic SR-BI-mediated cholesteryl ester selective uptake occurs with unaltered efficiency in the absence of cellular energy.
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.
Harder
Chris J
CJ
Lipoprotein and Atherosclerosis Group, University of Ottawa Heart Institute, Ottawa, Ontario, Canada K1Y 4W7.
Vassiliou
Gerard
G
McBride
Heidi M
HM
McPherson
Ruth
R
D000818:Animals; D016466:CHO Cells; D002788:Cholesterol Esters / Q000378:metabolism*; D006224:Cricetinae; D004705:Endocytosis / Q000502:physiology; D022781:Hepatocytes / Q000378:metabolism; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008099:Liver / Q000166:cytology; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D051122:Scavenger Receptors, Class B / Q000378:metabolism*; D013997:Time Factors
D002788:Cholesterol Esters; D008075:Lipoproteins, HDL; D051122:Scavenger Receptors, Class B