Retinoic acid receptor-related orphan receptor α reduces lipid droplets by upregulating neutral cholesterol ester hydrolase 1 in macrophages

Abstract

BACKGROUND: Neutral cholesterol ester hydrolase 1 (NCEH1) catalyzes the hydrolysis of cholesterol ester (CE) in macrophages. Genetic ablation of NCEH1 promotes CE-laden macrophages and the development of atherosclerosis in mice. Dysregulation of NCEH1 levels is involved in the pathogenesis of multiple disorders including metabolic diseases and atherosclerosis; however, relatively little is known regarding the mechanisms regulating NCEH1. Retinoic acid receptor-related orphan receptor α (RORα)-deficient mice exhibit several phenotypes indicative of aberrant lipid metabolism, including dyslipidemia and increased susceptibility to atherosclerosis. RESULTS: In this study, inhibition of lipid droplet formation by RORα positively regulated NCEH1 expression in macrophages. In mammals, the NCEH1 promoter region was found to harbor putative RORα response elements (ROREs). Electrophoretic mobility shift, chromatin immunoprecipitation, and luciferase reporter assays showed that RORα binds and responds to ROREs in human NCEH1. Moreover, NCEH1 was upregulated through RORα via a phorbol myristate acetate-dependent mechanism during macrophage differentiation from THP1 cells. siRNA-mediated knockdown of RORα significantly downregulated NCEH1 expression and accumulated lipid droplets in human hepatoma cells. In contrast, NCEH1 expression and removal of lipid droplets were induced by RORα agonist treatments and RORα overexpression in macrophages. CONCLUSION: These data strongly suggested that NCEH1 is a direct RORα target, defining potential new roles for RORα in the inhibition of lipid droplet formation through NCEH1.