Apolipoprotein A-I is necessary for the in vivo formation of high density lipoprotein competent for scavenger receptor BI-mediated cholesteryl ester-selective uptake.
The severe depletion of cholesteryl ester (CE) in steroidogenic cells of apoA-I(-/-) mice suggests that apolipoprotein (apo) A-I plays a specific role in the high density lipoprotein (HDL) CE-selective uptake process mediated by scavenger receptor BI (SR-BI) in vivo. The nature of this role, however, is unclear because a variety of apolipoproteins bind to SR-BI expressed in transfected cells. In this study the role of apoA-I in SR-BI-mediated HDL CE-selective uptake was tested via analyses of the biochemical properties of apoA-I(-/-) HDL and its interaction with SR-BI on adrenocortical cells, hepatoma cells, and cells expressing a transfected SR-BI. apoA-I(-/-) HDL are large heterogeneous particles with a core consisting predominantly of CE and a surface enriched in phospholipid, free cholesterol, apoA-II, and apoE. Functional analysis showed apoA-I(-/-) HDL to bind to SR-BI with the same or higher affinity as compared with apoA-I(+/+) HDL, but apoA-I(-/-) HDL showed a 2-3-fold decrease in the V(max) for CE transfer from the HDL particle to adrenal cells. These results indicate that the absence of apoA-I results in HDL particles with a reduced capacity for SR-BI-mediated CE-selective uptake. The reduced V(max) illustrates that HDL properties necessary for binding to SR-BI are distinct from those properties necessary for the transfer of HDL CE from the core of the HDL particle to the plasma membrane. The reduced V(max) for HDL CE-selective uptake likely contributes to the severe reduction in CE accumulation in steroidogenic cells of apoA-I(-/-) mice.
Temel
Ryan E
RE
Department of Pharmacological Sciences, University Medical Center, State University of New York, Stony Brook, New York 11794, USA.
Walzem
Rosemary L
RL
Banka
Carole L
CL
Williams
David L
DL
D000818:Animals; D016632:Apolipoprotein A-I / Q000502:physiology*; D001667:Binding, Competitive; D018955:CD36 Antigens / Q000378:metabolism*; D002478:Cells, Cultured; D002788:Cholesterol Esters / Q000378:metabolism*; D007700:Kinetics; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008565:Membrane Proteins; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010316:Particle Size; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D051122:Scavenger Receptors, Class B
D016632:Apolipoprotein A-I; D018955:CD36 Antigens; D002788:Cholesterol Esters; D008075:Lipoproteins, HDL; D008565:Membrane Proteins; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B