Overexpression of estrogen receptor α increases hepatic cholesterogenesis, leading to biliary hypersecretion in mice

Abstract

We explored whether there is an "estrogen-ERα-SREBP-2" (for estrogen-estrogen receptor subtype α-sterol-regulatory element binding protein-2) pathway for regulating hepatic cholesterol biosynthesis in ovariectomized AKR mice treated with 17β-estradial (E2) at 6 μg/day or E2 plus the antiestrogenic agent ICI 182,780 at 125 μg/day and on chow or fed a high-cholesterol (1%) diet for 14 days. To monitor changes in cholesterol biosynthesis and newly synthesized cholesterol secreted into bile, incorporation into digitonin-precipitable sterols in mice treated with 25 mCi of [3H]water was measured in extracts of liver and extrahepatic organs 1 h later and in hepatic biles 6 h later. ERα upregulated SREBP-2, with resulting activation of SREBP-2-responsive genes in the cholesterol biosynthetic pathway. The E2-treated mice continued to synthesize cholesterol in spite of its excess availability from high dietary cholesterol, which reflects a loss in controlling the negative feedback regulation of cholesterol synthesis. These alterations augmented biliary cholesterol secretion and enhanced the lithogenicity of bile. However, these lithogenic effects of E2 were fully blocked by ICI 182,780. We conclude that during estrogen treatment, more newly synthesized cholesterol determined by the estrogen-ERα-SREBP-2 pathway is secreted into bile, leading to biliary cholesterol hypersecretion. These studies provide insights into therapeutic approaches to cholesterol gallstones in high-risk subjects, especially those exposed to high levels of estrogen. Copyright © 2006 by the American Society for Biochemistry and Molecular Biology, Inc.