Glucocorticoids Stimulate Cholesteryl Ester Formation in Human Smooth Muscle Cells

Abstract

Abstract The aim of the present study was to investigate the effect of synthetic glucocorticoid dexamethasone (Dex) on cholesterol esterification in cultured human smooth muscle cells (SMC). In labeled SMC, Dex stimulated the esterification of [ 3 H]cholesterol in a dose-dependent manner. This effect was specific for glucocorticoid hormones and could be inhibited by cycloheximide (3 ng/mL), actinomycin D (10 −5 mol/L), and the specific glucocorticoid antagonist RU 486 (10 −8 mol/L). When plasma membrane was selectively labeled with trace quantities of [ 3 H]cholesterol (0.25 μCi/mL, 1 hour, 10°C), Dex (10 −8 mol/L) caused a net flux of free [ 3 H]cholesterol into the cells. Moreover, Dex (10 −8 mol/L, 24 hours) stimulated the esterification of sterols, newly synthesized from [ 14 C]mevalonate (10 μCi/mL, 4 hours) and lowered the amount of [ 14 C]sterols susceptible for cholesterol oxidase. The incorporation of [ 14 C]oleic acid into cholesteryl esters was markedly higher in Dex-pretreated SMC than in the control cells (2.1±0.07 and 1.4±0.1 pmol/h/μg protein, respectively, P <.01). At the time, cholesteryl ester hydrolysis in Dex-treated cells was reduced (72±8 pmol cholesteryl esters/h per milligram versus 130±10 in the control cells). HDL 3 -mediated [ 3 H]cholesterol efflux was also inhibited in Dex-treated cells; moreover, HDL 3 (40 μg/mL, 24 hours) had practically no effect on [ 3 H]cholesteryl ester content in Dex-treated SMC but caused a 50% reduction of [ 3 H]cholesteryl esters in the control cells. Thus, in human SMC glucocorticoids alter the redistribution of cholesterol between the pools of free and esterified cholesterol, paralleled by the change in acyl coenzyme A:cholesteryl acyltransferase and neutral cholesteryl ester hydrolase activities, leading to the impaired HDL 3 -mediated cholesterol efflux.