GPR30 and Hepatic Cholesterol Homeostasis

 描述(申请人提供)：流行病学和临床研究发现，在所研究的所有人群中，胆固醇结石在所有年龄段的女性中都比男性更常见。积累的证据表明，女性使用口服避孕药和结合雌激素显著增加了胆结石的患病率。前列腺癌患者接受雌激素治疗也会产生类似的致石作用。这些发现清楚地表明，与男性相比，女性患胆结石的风险增加与肝脏代谢胆固醇对雌激素的反应方式不同有关。我们已发表的研究证实，雌激素通过激活肝脏中经典的雌激素受体α(ERα)，而不是ERβ，在促进胆结石形成中发挥关键作用。然而，随着一种新的雌激素受体--G蛋白偶联受体30(GPR30)的发现，介导雌激素在胆结石形成中的致石作用的机制变得更加复杂。我们的遗传学发现支持GPR30作为一种新的胆结石基因Lith18的候选基因。然而，确定GPR30的致石机制一直是人们感兴趣的焦点，因为目前尚不清楚GPR30是否在雌激素诱导的胆结石中发挥主要作用，以及它是否独立于ERα或与ER GR30共同作用于诱导胆结石形成。我们假设GPR30也参与雌激素依赖的致石作用，独立于ERα发挥作用，因为GPR30和ERα都可以通过不同的途径促进雌激素诱导的胆结石的形成。这一假设是基于我们的新的初步数据，该数据表明，喂养致石饲料8周后，去卵巢的GPR30(+/+)/ERα(-/-)小鼠仍然对高剂量雌激素产生胆结石。相比之下，接受雌激素治疗的GPR30(-/-)/ERα(-/-)小鼠的胆结石患病率明显低于GPR30(+/+)/ERα(+/+)小鼠。因此，我们计划通过追求以下三个具体目标来实现我们的目标：第一，我们将研究决定胆固醇胆石症易感性的GPR30的表型特征。其次，我们将研究GPR30的激活是否通过表皮生长因子受体(EGFR)途径抑制肝脏胆汁酸的合成而导致胆汁结石形成，以响应高水平的雌激素。第三，我们将阐明GPR30在肝脏胆汁胆固醇高分泌和胆汁动力低下中的关键作用，这是胆固醇晶体快速生长的原因。这些研究在概念上和实验方法上都具有创新性，因为区分GPR30和ERα的致石作用，并进一步研究雌激素如何通过GPR30产生致石作用，将有助于阐明雌激素诱导胆结石形成的所有分子机制。计划中的实验策略是全面的，但也是可行的。这个项目将帮助我们通过GPR30或ERα或两者兼而有之，对雌激素诱导的胆结石的发病机制有新的认识。

 DESCRIPTION (provided by applicant): Epidemiological and clinical studies have found that cholesterol gallstones are more prevalent in women than in men at all ages in every population studied. Accumulated evidence shows that the use of oral contraceptives and conjugated estrogens in women significantly increases the prevalence of gallstones. Estrogen therapy to men with prostatic cancer also leads to similar lithogenic effects. These findings clearly demonstrate that the increased risk of developing gallstones in women compared to men is related to differences in how the liver metabolizes cholesterol in response to estrogen. Our published studies have established a critical role for estrogen in enhancing cholelithogenesis by activating the classical estrogen receptor α (ERα), but not ERβ in the liver. However, the mechanisms mediating estrogen's lithogenic actions on gallstone formation have become more complicated with the identification of a novel estrogen receptor, the G protein-coupled receptor 30 (GPR30). Our genetic findings support the candidacy of GPR30 as a compelling gene underlying a new gallstone gene Lith18. However, identifying the lithogenic mechanisms of GPR30 has been a focal point of interest because it is still unknown whether GPR30 plays a major role in estrogen-induced gallstones and whether it acts independently of or in conjunction with ERα on inducing gallstone formation. We hypothesize that GPR30 is also involved in estrogen-dependent lithogenic actions, working independently of ERα, as both GPR30 and ERα can work through different pathways to promote the formation of estrogen-induced gallstones. This hypothesis is based on our new preliminary data showing that fed a lithogenic diet for 8 wk, ovariectomized GPR30(+/+)/ERα(-/-) mice still form gallstones in response to high doses of estrogen. By contrast, the prevalence of gallstones is significantly reduced in estrogen-treated GPR30(-/-)/ERα(-/-) mice compared to GPR30(+/+)/ERα(+/+) mice. Therefore, we plan to accomplish our goals by pursuing the following three specific aims: First, we will investigate the phenotypic characterization of GPR30 that determines susceptibility to cholesterol cholelithiasis. Second, we will study whether the activation of GPR30 leads to the lithogenesis of bile by inhibiting hepatic bile acid synthesis through the epidermal growth factor receptor (EGFR) pathway in response to high levels of estrogen. Third, we will elucidate the critical role of GPR30 in hepatic hypersecretion of biliary cholesterol and gallbladder hypomotility that accounts for rapid growth of cholesterol crystals. The proposed studies are innovative both conceptually and in the implementation of experimental approaches because distinguishing the lithogenic actions of GPR30 from those of ERα and further investigating how estrogen produces lithogenic actions through GPR30 will elucidate all the molecular mechanisms behind the formation of estrogen-induced gallstones. The planned experimental strategies are comprehensive, yet feasible. This project will help us gain novel mechanistic insight into the pathogenesis of estrogen-induced gallstones through GPR30 or ERα or both.