Cholesteryl ester accumulation in macrophages resulting from receptor-mediated uptake and degradation of hypercholesterolemic canine beta-very low density lipoproteins

Abstract

The synthesis and accumulation of cholesteryl esters by monolayers of mouse peritoneal macrophages was stimulated 20- to 160-fold by incubation with beta-migrating very low density lipoproteins (beta-VLDL, density less than 1.006 g/ml) isolated from the plasma of cholesterol-fed dogs. Three other cholesterol-rich lipoprotein fractions obtained from the plasma of the same hypercholesterolemic dogs, including low density lipoprotein (LDL), cholesterol-induced high density lipoprotein (HDLc), and apo-E HDLc, had little to no stimulatory effect. Plasma VLDL (density less than 1.006 g/ml) from normal dogs did not increase cholesteryl ester formation in macrophages. The enhancement in cholesteryl ester synthesis and accumulation by hypercholesterolemic canine beta-VLDL was due to the presence of a high affinity binding site on the macrophage cell surface that mediated the uptake and lysosomal degradation of the beta-VLDL. Competition studies with fucoidin and dextran sulfate indicated that the receptor for canine beta-VLDL was different from that previously described for human acetylated low density lipoprotein (acetyl-LDL). Prior incubation of macrophage monolayers with either unlabeled canine beta-VLDL or human acetyl-LDL, both of which raised the cellular content of cholesteryl esters, reduced the ability of the cells to degrade 125I-labeled beta-VLDL, suggesting that the receptor for beta-VLDL is subject to regulation. The current findings indicate: 1) that macrophages possess a high affinity receptor that recognizes one of the four cholesterol-rich lipoproteins present in the plasma of cholesterol-fed dogs, beta-VLDL, and 2) that the receptor-mediated ingestion of beta-VLDL leads to cholesteryl ester deposition in these cells.