Two gallstone (Lith) genes, Lith9 and Lith18, produces a synergistic effect in enhancing cholelithogenesis by promoting hepatic secretion of biliary cholesterol in female mice
Authors: Wang David , Wang Helen 
Published: May 2023

Estrogen is a critical risk factor for cholesterol gallstone disease because women are twice as likely as men to form gallstones. We have identified that the G protein-coupled receptor 30 (GPR30), a new estrogen receptor, is a novel gallstone gene named Lith18 in mice. Supersaturated bile is mainly caused by persistent hepatic cholesterol hypersecretion, which is a prerequisite for gallstone formation. To explore the mechanisms underlying the critical role of GPR30 in promoting hepatic hypersecretion of biliary cholesterol and estrogen-induced gallstones in females, we tested the hypothesis that GPR30 may activate the ATP-binding cassette sterol efflux transporters G5 and G8 (ABCG5/G8), i.e., Lith9, on the canalicular membrane of hepatocytes, leading to a significant increase in hepatic cholesterol output and saturation of bile and enhancing cholelithogenesis. Methods: GPR30 and ABCG8 knockout (KO) mice on a gallstone-resistant AKR genetic background were created, respectively. The biliary and gallstone phenotypes, as well as cholesterol crystallization in gallbladder bile were studied in ovariectomized (OVX) GPR30 KO, ABCG8 KO, and wild-type (WT) mice injected intramuscularly with the potent GPR30-selective agonist G-1 at 0 or 1 μg/day and fed a lithogenic diet for 8 wk. Results: Compared to that in OVX WT mice receiving no G-1, hepatic expression of Abcg5/g8 is significantly increased by G-1 treatment in OVX WT, but not GPR30 or ABCG8 KO, mice fed the lithogenic diet. Moreover, no changes are found in hepatic expression of Abcb4 or Abcb11 for biliary phospholipid and bile acid secretion in these OVX mice treated with G-1 for 8 wk, suggesting that GPR30 activated by G-1 could promote biliary cholesterol hypersecretion by stimulating hepatic expression of Abcg5/G8 in mice. Feeding the lithogenic diet for 8 wk induces gallstone formation in 10% of OVX WT mice receiving no G-1. By contrast, G-1 treatment drastically increases gallstone prevalence to 80% in OVX WT mice. Many solid cholesterol monohydrate crystals embedded within mucin gels are observed in the remaining (20%) mice. However, no gallstones are found in OVX GPR30 KO or ABCG8 KO mice even treated with G-1 and fed the lithogenic diet for 8 wk. Moreover, gallbladder bile is unsaturated with cholesterol in two groups of KO mice. These results show that activation of GPR30 by G-1 enhances susceptibility to gallstone formation by stimulating hepatic Abcg5/g8 expression for promoting hepatic cholesterol hypersecretion in female mice. Conclusions: This study provides direct evidence for the first time that the interaction of GPR30 and ABCG5/G8, i.e., two Lith genes ( Lith9 and Lith18), exerts a synergistic lithogenic effect on promoting hepatic hypersecretion of biliary cholesterol, thereby leading to supersaturated bile and increased prevalence of cholesterol gallstone formation in female mice. NIH R01 DK126369 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.