17β-estradiol regulates adenosine triphosphate-binding cassette transporters A1 expression via estrogen receptor A to increase macrophage cholesterol efflux.

Abstract

The liver is the focus of research on the effects of estrogen on cholesterol metabolism. Few studies have investigated the effects of estrogen on macrophages despite the significance of cells in atherosclerosis. The purpose of this study is to examine the effect of estrogen on macrophage cholesterol efflux. Macrophage cholesterol efflux, oil red O staining, RT-qPCR, Western blotting analyses were used to determine cholesterol metabolize and the expressions of adenosine triphosphate (ATP)-binding cassette transporter G1 (ABCG1) and ATP-binding cassette transporter A1 (ABCA1) in J774A.1 cells, and the effect of these treatments was compared to without adding 17β-estradiol (E2). Gain and loss of estrogen receptor alpha (ERα), liver X receptor α (LXRα) were conducted to study interactions between E2, ERα, LXRα and ABCA. Finally, in mice, we validate the relationship between ERα and ABCA1. E2 increases cholesterol efflux from macrophages and decreases the formation of lipid droplets and positively regulates the expression of ABCA1. This suggests that estrogen receptors (ERs) directly regulate ABCA1 translation. We suppressed ERα, which decreased the mRNA and protein expression of ABCA1. At the mRNA level, E2 treatment could partially counteract these phenomena, but not at the protein level. ABCA1 expression decreased after LXRα was inhibited. This suggests that ABCA1 translation is directly regulated by ERα. In the ovariectomized mouse model of ABCA1 protein expression was significantly reduced in the peritoneal macrophages of the ovariectomy (OVX) group. ABCA1 protein expression was greater in the E2+OVX group than in the OVX group. E2 contributes to the positive regulation of ABCA1 expression and promotes cholesterol efflux in macrophages by binding to ERα. The effect is independent of ABCA1 transcription regulation by LXRα.