Role and regulation of beta-catenin in cholestatic liver disease

 描述(申请人提供)：原发性硬化性胆管炎(PSC)是一种罕见的、慢性的、原因不明的淤胆性肝病，其特征是肝内和肝外胆管的进行性炎症和纤维化。目前，尚无有效的药物治疗方法，肝移植仍是终末期PSC患者唯一延长生命的治疗选择。尽管进行了广泛的研究，但对PSC的发病机制仍不完全清楚。其中一个高度相关的机制是有毒胆汁酸(BA)在肝脏中的积累。我们最近证明，在两种胆汁淤积模型(胆管结扎(BDL)和0.1%3，5-二乙氧基甲酰-1，4-二氢-碰撞碱(DDC)饮食)中，肝脏特异的连接蛋白基因敲除小鼠(Alb-creü-catenin KO；KO1)在肝损伤、纤维化和不典型胆管增殖(ADP)方面表现出显著的减少。此外，我们观察到BDL后KO1的总肝脏BA减少，伴随着法尼醇X受体(FXR)激活的增强。这导致了一个新的作用的发现，在调节BA的合成和运输中，通过与核内的FXR结合，？连环素。此外，抑制ç-catenin会激活FXR池，而FXR池通常对BA刺激没有反应。因此，该方案的主要假设是，在胆汁淤积过程中抑制？-catenin可能通过物理上抑制FXR的激活来抑制BA的生物合成，从而减轻损伤和疾病的进展。此外，抑制？-catenin的策略可能与目前利用FXR激动剂的治疗方法结合使用，以提高治疗效果。在目标1中，我们将研究通过？catenin基因敲除降低BA毒性对小鼠胆汁淤积性肝损伤的影响。我们假设，在胆汁淤积的阻塞性、化学性和遗传性模型中，通过抑制β-连环蛋白来减少毒性BA可以延迟或减轻疾病的严重程度。在目标2中，我们将描述FXR/？-catenin联合在胆汁淤积中的作用和调节。要做到这一点，首先要验证FXR的激活是胆汁淤积后的保护机制，然后分析FXR/？连环蛋白在胆汁淤积过程中的动态变化。我们还将在体内和体外确定上游Wnt信号在FXR/？-catenin关联中的作用。在目标3中，我们将确定FXR/？-catenin关联的治疗和预后相关性。首先，我们将直接比较外源性抑制与FXR激动剂联合使用与单独使用激动剂缓解胆汁淤积性损伤。最后，我们将在PSC患者移植后活组织检查中，将B-catenin定位作为FXR活性和肝功能的替代指标。因此，拨款中建议的研究将进一步加深我们对-catenin在胆汁淤积性疾病(如PSC)中的作用的了解，预期结果可能具有重要的预后和治疗意义。

 DESCRIPTION (provided by applicant): Primary sclerosing cholangitis (PSC) is a rare, chronic, cholestatic liver disease of unknown etiology characterized by progressive inflammation and fibrosis of the intrahepatic and extrahepatic biliary ducts. Currently, there are no effective medical therapies available, and liver transplantation remains the only life-extending treatment option for patients with end-stage PSC. Despite extensive research, the pathogenetic mechanisms of PSC are still incompletely understood. One mechanism that is highly relevant is the accumulation of toxic bile acids (BA) in the liver. We have recently demonstrated that liver-specific ß-catenin knockout mice (Alb-cre ß-catenin KO; KO1) exhibit a dramatic decrease in liver injury, fibrosis, and atypical ductular proliferation (ADP) in two models of cholestasis (bil duct ligation (BDL) and 0.1% 3,5- diethoxycarbonyl-1,4-dihydro-collidine (DDC) diet). Furthermore, we observed decreased total hepatic BA in KO1 after BDL, concomitant with enhanced farnesoid X receptor (FXR) activation. This led to the discovery of a novel role for ß-catenin in regulating BA synthesis and transport through association with FXR in the nucleus. Furthermore, inhibition of ß-catenin activates a pool of FXR that is normally unresponsive to BA stimulation. Thus, the overarching hypothesis of the proposal is that suppressing ß-catenin during cholestasis may alleviate injury and progression of the disease through inhibition of BA biosynthesis by physically inhibiting FXR activation. Further, strategies that suppress ß-catenin could potentially be used in conjunction with current therapeutics that utilize FXR agonists in order to enhance the effectiveness of treatment. In aim 1, we will investigate the impact of reduced BA toxicity through ß-catenin knockdown on murine cholestatic liver injury. We hypothesize that reduction of toxic BA through ß-catenin inhibition would delay the onset or alleviate the severity of disease in obstructive, chemical, and genetic models of cholestasis. In aim 2 we will characterize the role and regulation of FXR/ß-catenin association in cholestasis. This will be accomplished by first verifying FXR activation as the protective mechanism after BDL through use of FXR-ß-catenin double KO mice, and then analyzing the dynamics of FXR/ß-catenin association and activity during cholestasis. We will also determine the contribution of upstream Wnt signaling to FXR/ß-catenin association both in vivo and in vitro. In aim 3, we will determine the therapeutic and prognostic relevance of FXR/ß -catenin association. First, we will directly compare the exogenous inhibition of ß-catenin in conjunction with an FXR agonist to the use of agonist alone in alleviating cholestatic injury. Finally, we will correlate ß-catenin localization as a surrogate for FXR activity with hepatic function in PSC patient biopsies post-transplant. Thus, the proposed studies in the grant will further our understanding of the role of -catenin in cholestatic diseases such as PSC and the expected outcomes may have significant prognostic and therapeutic implications.