The enhanced cellular uptake of very-low-density lipoprotein enriched in apolipoprotein E.
We have recently reported an increased clearance of plasma very-low-density lipoprotein (VLDL) after intravenous injection of apolipoprotein (apo) E in Watanabe heritable hyperlipidemic (WHHL) rabbits. In the present study, we have investigated the cellular uptake of VLDL enriched in apo E (VLDL-E) which had been incubated with purified rabbit apo E. VLDL-E was taken up approx. 2-fold more than VLDL in human skin fibroblast, human monocyte-derived macrophage and Hep G2 cell and its degradation was least in macrophage. To characterize the binding of VLDL-E, we performed a binding assay using hepatic endosome isolated from estradiol-treated rats and we observed both increased EDTA-sensitive and -resistant binding of VLDL-E on endosome. Ligand blotting of hepatic endosome demonstrated two major bands of LDL receptor (130 and 260 kDa protein) and a minor band of LDL receptor-related protein (580 kDa protein) with a ligand of VLDL-E. These results suggested that VLDL-E was endocytosed in liver through a similar pathway among three cell types, and enrichment of apo E in VLDL enhanced the uptake of VLDL not only via an EDTA-sensitive binding site (classical LDL receptor) but also via other binding sites including an EDTA-resistant binding site and an LDL receptor-related protein.
Mokuno
H
H
3rd Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
Yamada
N
N
Shimano
H
H
Ishibashi
S
S
Mori
N
N
Takahashi
K
K
Oka
T
T
Yoon
T H
TH
Takaku
F
F
D000818:Animals; D001057:Apolipoproteins E / Q000378:metabolism*; D001667:Binding, Competitive; D006528:Carcinoma, Hepatocellular; D004492:Edetic Acid / Q000494:pharmacology; D004705:Endocytosis; D004958:Estradiol / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D008079:Lipoproteins, VLDL / Q000378:metabolism*; D008099:Liver / Q000378:metabolism / Q000648:ultrastructure; D008113:Liver Neoplasms; D046911:Macromolecular Substances; D008264:Macrophages / Q000378:metabolism; D008970:Molecular Weight; D009000:Monocytes / Q000378:metabolism; D011817:Rabbits; D011973:Receptors, LDL / Q000378:metabolism; D014407:Tumor Cells, Cultured
D001057:Apolipoproteins E; D008079:Lipoproteins, VLDL; D046911:Macromolecular Substances; D011973:Receptors, LDL; D004958:Estradiol; D004492:Edetic Acid