Glucocorticoid receptor regulates ATP-binding cassette transporter-A1 expression and apolipoprotein-mediated cholesterol efflux from macrophages

Objective: The ATP-binding cassette transporter-A1 (ABCA1) regulates cholesterol efflux from cells and is involved in high-density lipoprotein metabolism and atherogenesis. The objective of this study was to investigate the effect of dexamethasone (Dex) and other glucocorticoid receptor (GR) ligands on apolipoprotein AI-mediated cholesterol efflux from macrophages and ABCA1 expression in them. Methods and Results: Dex, a GR agonist, decreased ABCA1 mRNA levels in a dose- and time-dependent fashion, and RU486, a GR antagonist, reversed the inhibitory effect of Dex. The effects of Dex and RU486 on ABCA1 protein levels and apolipoprotein AI-mediated cholesterol efflux from the macrophages were consistent with these changes in mRNA levels. Transfected RAW264.7, together with a human ABCA1 promoter-luciferase construct, inhibited transcriptional activity by Dex and overexpression of human GR. Transrepression by GR was not mediated by liver X receptor (LXR), because there were no differences in the effects of the GR ligands on promoter activity between a reporter construct with mutations at the LXR binding site and one without the mutations, and no changes were brought about in ABCG1 and ABCG4 expression by GR ligands. Conclusions: Our results showed that GR ligands affected ABCA1 expression and cholesterol efflux from macrophages, which are regulated by GR through a LXR-independent mechanism.