A plasma lipoprotein containing only apolipoprotein E and with gamma mobility on electrophoresis releases cholesterol from cells.
Previous studies have identified lipid-poor high density lipoproteins with electrophoretic pre-beta mobility as the initial acceptors of cell-derived cholesterol in human plasma. These lipoproteins contain apolipoprotein A-I (apo A-I) as their sole apolipoprotein. In the present study, incubation of human plasma with [3H]cholesterol-laden skin fibroblasts has led to the identification of another lipoprotein that serves as a potent initial acceptor of cell-derived cholesterol. This lipoprotein, which we term gamma-LpE, exhibits gamma mobility on agarose gel electrophoresis. As determined by nondenaturing PAGE and by electron microscopy, the size of the spherical particle ranges between 12 and 16 nm. SDS/PAGE and subsequent immunoblotting identified apoE as its sole apolipoprotein. Plasma from normal and apoA-I-deficient mice, but not from apoE-deficient mice, released [3H]cholesterol from fibroblasts into a gamma-migrating lipoprotein. Cell culture media from hepatoma cells or mouse peritoneal macrophages, both of which contain apoE of cellular origin, also promoted efflux of [3H]cholesterol from fibroblasts into a gamma-migrating fraction. This was not observed with cell culture medium from fibroblasts alone. In conclusion, our results strongly indicate the presence in human plasma of a lipoprotein containing only apoE, gamma-LpE, which is secreted by peripheral cells and is a potent acceptor of cell-derived cholesterol.
Huang
Y
Y
Institut für Arterioskleroseforschung, Universität Münster, Federal Republic of Germany.
von Eckardstein
A
A
Wu
S
S
Maeda
N
N
Assmann
G
G
D000818:Animals; D016632:Apolipoprotein A-I / Q000172:deficiency; D001057:Apolipoproteins E / Q000172:deficiency / Q000302:isolation & purification / Q000378:metabolism*; D001693:Biological Transport, Active; D001797:Blood Protein Electrophoresis; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008074:Lipoproteins / Q000097:blood* / Q000302:isolation & purification / Q000378:metabolism; D051379:Mice
D016632:Apolipoprotein A-I; D001057:Apolipoproteins E; D008074:Lipoproteins; D002784:Cholesterol