INTESTINAL EPITHELIAL BARRIER FUNCTION AND DEFENSE

肠道黏膜是口腔耐受和防御有害生物的免疫器官。为了使抗原与树突状抗原呈递细胞相互作用，这些蛋白质必须以受控的方式穿过肠上皮。因此，肠上皮细胞屏障的调节对肠道免疫和炎症的发展至关重要，但其机制在很大程度上是未知的。紧密连接复合体是极化上皮细胞最顶端的一个特化膜结构域，它不仅为阻止溶质和病原体的胞外运输创造了初级屏障，而且还限制了膜脂和蛋白的后期扩散，以维持细胞极性。初步实验表明，最近发现的紧密连接相关蛋白claudin家族成员在人小肠上皮细胞和大肠中表达。此外，在肠上皮细胞中，claudins的表达可受到炎症介质的调控，并发生经上皮耐药。细菌毒素可以与cladin结合，因此病原体可以直接靶向紧密连接相关蛋白来改变肠上皮细胞的功能。然而，肠上皮细胞分化过程中claudin表达的调控机制以及宿主防御过程中claudin在肠上皮屏障调控中的作用尚不清楚。总的假设是，调节肠上皮细胞中claudin的表达和细胞分布的机制对维持肠屏障至关重要。本研究的总体目标是表征claudin在肠上皮细胞中的生物学功能，明确细胞因子和内毒素诱导的claudin在肠上皮细胞中表达调控的分子机制。

The intestinal mucosa constitutes an immunological organ were oral tolerance and defense against harmful organisms develops. For antigens to interact with dendritic antigen-presenting cells, these proteins must cross the intestinal epithelium in a controlled manner. The regulation of the intestinal epithelial cell barrier is therefore central to the development intestinal immunity and inflammation, but the mechanisms are largely unknown. The tight junctional complex is a specialized membrane domain at the most apical region of polarized epithelial cells that not only creates the primary barrier to prevent paracellular transport of solutes and pathogens but also restricts that later diffusion of membrane lipids and proteins to maintain the cellular polarity. Preliminary experiments demonstrate that members of the recently identified claudin family of tight junction associated proteins are expressed in human intestinal epithelial cells of the small and large intestine. In addition, the expression of claudins can be regulated by inflammatory mediators together with the development of transepithelial resistance in intestinal epithelial cells. Bacterial toxins can bind to claudins thus pathogens may be able to target tight junction associated proteins directly to alter intestinal epithelial cell function. However, the mechanisms regulating claudin expression during intestinal epithelial cell differentiation and the role of claudins in the regulation of the intestinal epithelial barrier during host defense is unknown. The overall hypothesis is that mechanisms regulating the expression and the cellular distribution of claudins in intestinal epithelial cells are essential to maintain the intestinal barrier. The overall goals of this proposal are to characterize the biological functions of claudins in intestinal epithelial cells and to define the cytokine and endotoxin induced molecular mechanisms, which regulate claudin expression in intestinal epithelial cells.