title: In vivo and in vitro uptake and degradation of acetylated low density lipoprotein by rat liver endothelial, Kupffer, and parenchymal cells.
abstract: Isolation and separation of rat liver cells into endothelial, Kupffer, and parenchymal cell fractions were performed at different times after injection of human 125I-acetyl low density lipoproteins (LDL). In order to minimize degradation and redistribution of the injected lipoprotein during cell isolation, a low temperature (8 degrees C) procedure was applied. Ten min after injection, isolated endothelial cells contained 5 times more acetyl-LDL apoprotein per mg of cell protein than the Kupffer cells and 31 times more than the hepatocytes. A similar relative importance of the different cell types in the uptake of acetyl-LDL was observed 30 min after injection. For studies on the in vitro interaction of endothelial and Kupffer cells with acetyl-LDL, the cells were isolated with a collagenase perfusion at 37 degrees C. Pure endothelial (greater than 95%) and purified Kupffer cells (greater than 70%) were obtained by a two-step elutriation method. It is demonstrated that the rat liver endothelial cell possesses a high affinity receptor specific for the acetyl-LDL because a 35-fold excess of unlabeled acetyl-LDL inhibits association of the labeled compound for 70%, whereas unlabeled native human LDL is ineffective. Binding to the acetyl-LDL receptor is coupled to rapid uptake and degradation of the apolipoprotein. Addition of the lysosomotropic agents chloroquine (50 microM) or NH4Cl (10 mM) resulted in more than 90% inhibition of the high affinity degradation, indicating that this occurs in the lysosomes. With the purified Kupffer cell fraction, the cell association and degradation of acetyl-LDL was at least 4 times less per mg of cell protein than with the pure endothelial cells. Although cells isolated with the cold pronase technique are also still able to bind and degrade acetyl-LDL, it appeared that 40-60% of the receptors are destroyed or inactivated during the isolation procedure. It is concluded that the rat liver endothelial cell is the main cell type responsible for acetyl-LDL uptake.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001692:Biological Transport; D004727:Endothelium / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D007728:Kupffer Cells / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008099:Liver / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D011770:Pyruvate Kinase / Q000378:metabolism; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011973:Receptors, LDL
chemical_list: D008077:Lipoproteins, LDL; D011956:Receptors, Cell Surface; D011973:Receptors, LDL; C032629:acetyl-LDL; D011770:Pyruvate Kinase