Cholesterol esterification and cholesteryl ester accumulation in cultured pigeon and monkey arterial smooth muscle cells

Abstract

Aortic smooth muscle cells from atherosclerosis-susceptible White Carneau and resistant Show Racer pigeons were grown in culture utilizing conditions identical to those developed for the culture of rhesus monkey arterial smooth muscle cells and skin fibroblasts. Pigeon smooth muscle cells had ultrastructural and growth characteriscis similar to mammalian smooth muscle cells in culture including growth in multiple overlapping layers, numerous pinocytic vesicles, and abundant myofilaments. Cells were incubated for 24 to 72 hr with culture medium containing either lipoprotein deficient serum, fetal calf serum, normocholesterolemic pigeon serum or hypercholesterolemic pigeon serum, and differences in cholesterol content and in the rate of cholesterol esterification were studied. Although there was substantial variability in the absolute cholesterol content among different cell lines, cells of the same type behaved similarly in their response to the various test sera. Generally, the higher the cholesterol content of the culture medium the greater the cholesterol content of the cells. There were, however, considerable differences in the magnitude and pattern of response among the different cell types. Incubation with 10% hypercholesterolemic serum resulted in an increase of similar magnitude in the free cholesterol content of all cell lines. This was not true, however, for the accumulation of cholesteryl esters. Incubation with 10% hypercholesterolemic serum produced a marked increase in the cholesteryl ester content of monkey skin fibroblasts and smooth muscle cells while producing only a slight increase in the cholesteryl ester content of pigeon smooth muscle cells unless very high concentrations of hypercholesterolemic serum were used. Monkey skin fibroblasts were the most responsive to cholesteryl ester accumulation with a greater than 28-fold increase in cholesteryl ester content occurring when incubated with hypercholesterolemic serum. Incubation for 24 hr with hypercholesterolemic serum stimulated cholesterol esterification 4 to 8-fold in monkey cells in a manner that paralleled the time course of accumulation of cholesteryl esters, while no stimulation in cholesterol esterification occurred in pigeon cells, consistent with their lack of ability to accumulate large amounts of cholesteryl esters. No differences in the response to either normal or hypercholesterolemic serum were seen between smooth muscle cells from atherosclerosis-susceptible White Carneau and resistant Show Racer pigeons. There were, however, major differences between pigeon and monkey cells. Although results indicate that the mechanism of accumulation of cholesteryl esters by pigeon smooth muscle cells may be different than for mammalian cells, no differences were seen in any of the parameters measured that might help to explain the difference in susceptibility to atherosclerosis of the two breeds of pigeons.