Cholesteryl ester synthesis in macrophages: stimulation by p-very low density lipoproteins from cholesterol-fed animals

Animals fed cholesterol accumulate several types of cholesterol-rich lipoproteins in their plasma and ultimately develop cholesteryl ester deposition in tissue macrophages. Previous studies in the cholesterol-fed dog have shown that one class of cholesterol-rich lipoproteins, P-migrating very low density lipoproteins (P-VLDI,, density < 1.006 g/ml), possesses a unique ability to produce cellular cholesteryl ester accumulation when incubated with mouse peritoneal macrophages in vitro. This accumulation results from the receptor-mediated uptake of P-VLDL with subsequent lysosomal hydrolysis of the lipoprotein and re-esterification of the liberated cholesterol. In the current studies, we demonstrate that P-VLDL obtained from cholesterol-fed animals of several other species, including monkeys, rabbits, and rats, also causes cholesteryl ester accumulation in monolayers of mouse peritoneal macrophages, as monitored by an increase in the rate at which the cells incorporate exogenous ['4<:]oleate into cholesteryl [14C]oleate. Like canine P-VLDL,, the P-VLDL from these three other species were effective at low concentrations and exhibited saturation kinetics, suggesting that they, too, entered macrophages by receptormediated endocytosis. Very IOM. density lipoprotein (VLDL) frum normal animals and low density lipoprotein (LDL) from normal and cholesterol-fed monkeys, rats, and rabbits did not stimulate cholesteryl ester synthesis in mouse peritoneal macrophages. In addition to their effects on mouse macrophages, the P-VLDL from cholesterol-fed dogs and rabbits stimulated cholesteryl vster synthesis in cultured human monocytes. The current findings suggest that P-VLDL from cholesterol-fed animals has the general property of stimulating cholesteryl ester synthesis and accumulation in macrophages. Mahley, R. W., T. L. Innerarity, M. S. Brown, Y. K. Ho, and J. L. Goldstein. Cholesteryl ester synthesis in macrophages: stimulation by P-very low density lipoproteins from cholesterol-fed aninials o f several species. ,/. Lipid R a . 1980. 21: 970-980. Supplementary key words athet-oscler-osis ' cell sui-tare receptors . familial hypercholesterolemia . fibroblasts . hyperlipidemia A characteristic accompaniment of p ro found hyperlipidemia in cholesterol-fed animals is t he appearance of abnormal cholesterol-rich lipoproteins with the density of very low density lipoproteins (VLDL, density < 1.006 giml) (1 , 2). I n contrast t o normal triglyceride-carrying VLDL, Ivhich shows pre-P-mobility o n electrophoresis, these abnormal cholesterol-rich lipoproteins have @-mobility and a r e designated as P-VLDL ( I ) . T h e accumulation of PVLDL in the bloodstream of cholesterol-fed animals is associated with t h e deposition of large amounts of cholesteryl esters in macrophages in a variety of tissues in vivo (2-4) I n a previous study, tve observed that P-VLDL f rom hyperlipidemic dogs has a specific ability to produce cholesteryl ester deposition in monolayers of mouse peritoneal macrophages ( 5 ) . This effect was attributable to a high affinity binding site on t he macrophage surface that recognized t h e PVLDL a n d facilitated its uptake by the cell a n d degradation by cellular lysosomes (5). A portion of t he cholesterol liberated f rom the degraded PAbbi-rviations: HDL,,, ( holesterol-incliice[l high densit) lipoprotein containing apoproteins A-1 and E: apo F. HDI.,., HDL,. c011taining predominantly apo E; VLDL. vel-y l o w density lipoproteins with pr r -p mobility on electrophoresis. containing apoproteins B and (;; P-VLDL, VLDL with P-mobility on elec.tr-ophoresis, ( 0 1 1 taining apoproteins B and E; IDL. intermediate density Iipoprowin; LDL. low density lipoprotein: HDI.. high density lipoprotein: M E M . minimum essential medium; DMEM, Dulbecco's modified Eagle's medium; FCS, fetal calf serum; FH, familial ti) percholestei-oleniia. ' Gladstone Foundation Laboratories for CardiovasrulalDisease. P . 0 . Box 40608. San Francisco General Hospital, Sa11 Francisco, (;.4 94140. ' Departnient of Molecular Genetics. Lni\ersit) of' Texas Health Science Center at Dallas, 5323 Harry Hines Blvtl. Dallas. T r x a 55235. 970 Journal of Lipid Research Volume 2 1 , 1980 at P E N N S T A T E U N IV E R S IT Y , on F ebuary 1, 2013 w w w .j.org D ow nladed fom VLDL particles was re-esterified and stored by the cell as cholesteryl ester. T h e accumulation of these cholesteryl esters could be followed in two ways: I ) by measurement of the mass of esterified cholesterol within the cell and 2) by measurement of the rate at which the macrophages incorporated exogenous ['4C]oleate into cholesteryl [14C]oleate. Stimulation of the latter re-esterification reaction was proportional to the amount of P-VLDL taken u p and degraded by the cells (5). Other lipoproteins from hyperlipidemic dogs, including LDL, HDL,, apo E HDL,, and typical HDL, were much less effective than P-VLDL in stimulating cholesteryl ester formation in macrophages. Normal VLDL and other lipoproteins from normal dogs and normal humans were similarly ineffective in stimulating cholesteryl ester accumulation in macrophages (5). In the current studies, we have extended these data by investigating lipoproteins isolated from hyperlipidemic animals from three other species: monkeys, rats, and rabbits. We have investigated the effects of these lipoproteins on cholesterol metabolism in mouse and rabbit peritoneal macrophages and in human cells, including cultured fibroblasts and cultured monocytes. The results show that the ability to stimulate cholesteryl ester synthesis in macrophages is a general characteristic of cholesterol-rich P-VLDL from all of these animal