Long term treatment of neonatal aortic smooth muscle cells with βVLDL induces cholesterol accumulation

Abstract

A model for smooth muscle derived foam cells was developed by treating smooth muscle cells isolated from the aortae of neonatal rabbits with βVLDL for up to 1 month. Hyperlipidemic βVLDL isolated from cholesterol fed rabbits induced proliferation of the cells that were maintained in lipid deficient serum. In addition, the lipoprotein fraction stimulated [ 14C]oleic acid incorporation into [ 14C]cholesteryl ester, even in cultures that had been chronically exposed to the lipoprotein. The accumulation of cholesterol was evaluated and small amounts of cholesteryl ester were demonstrated in cultures treated for 3 days with βVLDL. However, continued exposure to the lipoprotein resulted in larger elevations in total cholesterol, approximately 65% of which was in the esterified form in cultures treated with 100 wg OVLDL/ml for 24 days. When cholesterol levels were examined as a function of time, it was determined that both total cholesterol and cholesteryl ester levels increased. Approximately 2–3 weeks after lipoprotein was introduced to the culture, maximum levels were attained. Triglyceride levels were also measured and found to increase more than two-fold in cultures that had been incubated in the presence of βVLDL for 24 days, when compared to cultures incubated in its absence. Examination of the cultures by electron microscopy revealed intracytoplasmic lipid droplets in βVLDL treated cells. These results suggest that βVLDL treatment of neonatal aortic smooth muscle cells provides an ideal model in which to study the lipid laden smooth muscle cells that characterize the atherosclerotic plaque.