The role of apolipoprotein A-I and apolipoprotein A-II in high-density lipoprotein binding to human adipocyte plasma membranes.
Adipocyte plasma membranes purified from omental fat tissue biopsies of massively obese subjects possess specific binding sites for high-density lipoprotein (HDL3). This binding was independent of apolipoprotein E as HDL3 isolated from plasma of an apolipoprotein E-deficient individual was bound to a level comparable to that of normal HDL3. To examine the importance of apolipoprotein A-I, the major HDL3 apolipoprotein, in the specific binding of HDL3 to human adipocytes, HDL3 modified to contain varying proportions of apolipoproteins A-I and A-II was prepared by incubating normal HDL3 particles with different amounts of purified apolipoprotein A-II. As the apolipoproteins A-I-to-A-II ratio in HDL3 decreased, the binding of these particles to adipocyte plasma membranes was reduced. Compared to control HDL3, a 92 +/- 3.1% reduction (mean +/- S.E., n = 3) in maximum binding capacity was observed along with an increased binding affinity for HDL3 particles in which almost all of the apolipoprotein A-I had been replaced by A-II. The uptake of HDL cholesteryl ester by intact adipocytes as monitored by [3H]cholesteryl ether labeled HDL3, was also significantly reduced (about 35% reduction, P less than 0.005) by substituting apolipoprotein A-II for A-I in HDL3. These data suggest that HDL binding to human adipocyte membranes is mediated primarily by apolipoprotein A-I and that optimal delivery of cholesteryl ester from HDL to human adipocytes is also dependent on apolipoprotein A-I.
D000273:Adipose Tissue / Q000378:metabolism*; D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D001054:Apolipoproteins A / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D002788:Cholesterol Esters / Q000378:metabolism; D006801:Humans; D007457:Iodine Radioisotopes; D008075:Lipoproteins, HDL / Q000378:metabolism*; D053440:Lipoproteins, HDL3; D009765:Obesity / Q000378:metabolism
D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D001054:Apolipoproteins A; D002788:Cholesterol Esters; D007457:Iodine Radioisotopes; D008075:Lipoproteins, HDL; D053440:Lipoproteins, HDL3