Ileal Bile Acid Transporter Metabolism and Regulation

描述(申请人提供)：本申请的目的是促进我们对维持胆汁酸的肠-肝循环的转运途径的理解，调节胆汁酸的流量，并保护胆汁酸引起的损伤。这一建议的基础是我们最近确定的异构体有机溶质转运体Osta-Ostb，作为肠道胆汁酸运输的主要机制。在这一应用中，我们将重点关注支持Osta-Ostb维持胆汁酸稳态的机制，以及Osta-Ostb在肠和结肠上皮中的细胞保护作用。我们以前的研究表明，Osta-/-小鼠的肠道胆汁酸吸收受到损害，但并未被消除。基于这些发现，在特定目的1中的研究旨在验证ABC转运蛋白MRP3和MRP4负责残余胆汁酸的转运并保护OSTA缺失小鼠的回肠上皮免受胆汁酸损伤的假设。我们的研究表明，Osta-Ostb的表达受到底物的密切调控，以平衡胆汁酸通量和细胞内浓度。因此，Osta-Ostb表达的失调可能会显著改变胆汁酸和脂肪代谢，这突显了最近发现的Osta-OSTb在胆结石患者回肠中表达降低的重要性。我们的工作表明，在Osta-/-小鼠中，胆汁酸合成的调节发生了深刻的变化。基于这些观察，在特殊目的2中的研究旨在阐明OSTA缺失小鼠胆汁酸稳态改变的机制。在结肠中，内源细菌菌群将胆汁酸转化为更疏水的物种，能够被动地扩散到上皮细胞中。然而，对胆汁酸输出和保护结肠细胞免受胆汁酸损伤的机制知之甚少。我们的初步数据表明，与对照组相比，Osta-/-小鼠更容易受到葡聚糖硫酸钠诱导的结肠损伤。这些发现强调了最近观察到溃疡性结肠炎患者结肠中OSTA表达显著减少的重要性。基于这些发现，在特定目标3中的研究旨在检验Osta-Ostb负责结肠基底外侧胆汁酸运输和保护结肠免受胆汁酸细胞毒性影响的假设。这项工作的长期目标是了解胆汁酸的区隔和肠肝循环的控制机制，以及它们与人类胃肠道和代谢性疾病的关系。

DESCRIPTION (provided by applicant): The goal of this application is to advance our understanding of the transport pathways that maintain the enterohepatic circulation of bile acids, regulate bile acid flux, and protect against bile acid-induced injury. The foundation for this proposal is our recent identification of the heteromeric Organic Solute Transporter, Osta-Ostb, as a major mechanism for intestinal bile acid transport. In this application, we will focus on the mechanisms that support Osta-Ostb to maintain bile acid homeostasis and on the cytoprotective role of Osta-Ostb in the intestinal and colonic epithelium. Our previous studies demonstrated that intestinal bile acid absorption is impaired but not abolished in Osta-/- mice. Based on those findings, the studies in Specific Aim 1 are designed to test the hypothesis that the ABC transporters Mrp3 and Mrp4 are responsible for the residual bile acid transport and serve to protect the ileal epithelium from bile acid-induced damage in the Osta null mice. Our studies demonstrated that expression of Osta-Ostb is closely regulated by substrate to balance the bile acid flux and intracellular concentration. As such, dysregulation of Osta-Ostb expression may significantly alter bile acid and lipid metabolism, underscoring the importance of the recent finding that OSTa-OSTb expression is decreased in ileum from gallstone patients. Our work showed that the regulation of bile acid synthesis is profoundly altered in Osta-/- mice. Based on these observations, the studies in Specific Aim 2 are designed to elucidate the mechanisms responsible for the altered bile acid homeostasis in the Osta null mice. In the colon, the endogenous bacterial flora convert bile acids to more hydrophobic species capable of passively diffusing into epithelial cells. However, little is known about the mechanisms engaged to export bile acids and protect the colonocyte against bile acid-induced damage. Our preliminary data suggest that Osta-/- mice are more susceptible to dextran sodium sulfate-induced colonic injury as compared to littermate controls. These findings underscore the importance of the recent observation that OSTa expression is dramatically reduced in colon from patients with ulcerative colitis. Based on these findings, the studies in Specific Aim 3 are designed to test the hypothesis that Osta-Ostb is responsible for colonic basolateral bile acid transport and functions to protect the colon from the cytotoxic effects of bile acids. The long-term goal of this work is to understand the mechanisms that control the compartmentalization and enterohepatic circulation of bile acids and their relationship to human gastrointestinal and metabolic disease.