Cholestasis and the Unfolded Protein Response

描述（由申请人提供）：胆汁淤积性肝病是美国进行性肝病的高度流行原因，是肝移植的常见适应症。不幸的是，目前的医学疗法是没有治愈性的，可能无法阻止疾病的进展。在过去的十年中，未折叠蛋白反应（UPR），一种对内质网（ER）应激的适应性细胞反应，已被牵连到许多肝脏疾病的发病机制。然而，UPR在肝胆盐毒性和胆汁淤积性肝病中的作用仍有待研究。X-box binding protein 1-spliced（XBP 1 s）是UPR的一个关键调节分子，我们的初步数据表明它对胆盐损伤具有保护作用。该提议的中心假设是，在胆汁淤积期间，XBP 1对肝脏具有保护作用，并且XBP 1的减弱的肝脏表达导致肝脏胆盐转运蛋白的表达减少和对肝脏胆盐肝损伤的易感性增加。 因此，在本提案中，我们将向小鼠喂食补充胆酸的饲料，并确定XBP 1和下游靶点在肝胆盐损伤中的作用（具体目标#1）。 CYP 7a 1是胆盐合成的限速步骤，抑制CYP 7a 1的表达和活性可以作为减少胆盐池的负反馈机制。我们目前的初步数据表明，激活肝脏UPR显着降低表达， 肝脏CYP 7a 1，可能通过XBP 1 s介导的途径。因此，我们将确定未折叠蛋白应答和XBP 1抑制肝Cyp 7a 1表达、功能和胆盐合成（具体目标#2）。 最后，为了直接确定肝脏XBP 1 s表达的减弱会增加对胆盐肝毒性的易感性，我们将开发具有肝脏特异性XBP 1缺失的遗传修饰小鼠。我们将开发肝脏特异性XBP 1（-/-）小鼠，以确认XBP 1在肝胆盐损伤中的保护作用，并定义其保护机制（具体目标#3）。 虽然这项提案的重点是肝脏XBP 1，但长期目标是开发一系列研究，以确定可作为治疗胆汁淤积性肝病的治疗靶点的UPR信号通路。 该提案利用最先进的小鼠遗传学、分子生物学和脂质生化技术来进一步了解XBP 1在胆盐损伤和胆汁淤积中的保护作用。 确定XBP 1 s信号通路的作用及其对胆盐诱导的肝损伤的影响的研究可能会为治疗胆汁淤积性肝病的药物开发确定一种新的途径和潜在的靶点。

DESCRIPTION (provided by applicant): Cholestatic liver diseases are highly prevalent causes of progressive liver disease in the United States and are a common indication for liver transplantation. Unfortunately, current medical therapies are not curative and may not prevent disease progression. Over the past decade, the Unfolded Protein Response (UPR), an adaptive cellular response to Endoplasmic Reticulum (ER) stress, has been implicated in the pathogenesis of many liver diseases. The role of the UPR in hepatic bile salt toxicity and cholestatic liver disease, however, remains unexplored. X-box binding protein 1-spliced (XBP1s) is a key regulatory molecule of the UPR that our preliminary data indicates is protective from bile salt injury. The central hypothesis of this proposal is that XBP1s is protective to the live during cholestasis~ and attenuated hepatic expression of XBP1s results in diminished expression of liver bile salt transporters and increased susceptibility to hepatic bile salt liver injury. Thus, in this proposal we will feed diets supplemented with cholic acid to mice and define the role of XBP1s and downstream targets in hepatic bile salt injury (Specific Aim #1). CYP7a1 is the rate-limiting step in bile salt synthesis, and inhibition of CYP7a1 expression and activity can act as a negative feedback mechanism to reduce the bile salt pool. We present preliminary data indicating that activation of the hepatic UPR markedly reduces expression of hepatic CYP7a1, likely via a XBP1s- mediated pathway. Thus, we will determine that the Unfolded Protein Response and XBP1s suppress hepatic Cyp7a1 expression, function and bile salt synthesis (Specific Aim #2). Finally, in order to directly determine that attenuation of hepatic XBP1s expression increases susceptibility to bile salt hepatotoxicity, we will develop genetically-modified mice with a liver-specific deletion of XBP1. We will develop liver-specific XBP1(-/-) mice in order to confirm the protective role, and define the protective mechanisms, of XBP1s in liver bile salt injury (Specific Aim #3). While this proposal focuses on hepatic XBP1s, the long-term goal is to develop a line of research to identify UPR signaling pathways that can serve as therapeutic targets for the treatment of cholestatic liver diseases. This proposal utilizes state-of-the-art mouse genetics, molecular biology and lipid biochemical techniques to further our understanding of the protective role of XBP1s in bile salt injury and cholestasis. Investigations identifying the role of the XBP1s signaling pathway and its effects on bile salt-induced liver injury may identify a novel pathway and potential targets for drug development to treat cholestatic liver diseases.