INTESTINAL EPITHELIAL BARRIER FUNCTION AND DEFENSE

肠粘膜构成免疫器官，是口服耐受和防御有害生物的发展。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于肠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。紧密连接复合物是极化上皮细胞最顶端区域的特化膜结构域，其不仅产生主要屏障以防止溶质和病原体的细胞旁转运，而且还限制膜脂质和蛋白质的随后扩散以维持细胞极性。初步实验表明，最近鉴定的紧密连接相关蛋白的claudin家族的成员在小肠和大肠的人肠上皮细胞中表达。此外，炎症介质可调节claudins的表达，并与肠上皮细胞跨上皮抵抗的发展有关。细菌毒素可以结合到密封蛋白，因此病原体可以能够直接靶向紧密连接相关蛋白以改变肠上皮细胞功能。然而，在肠上皮细胞分化过程中调节claudin表达的机制以及在宿主防御过程中claudins在调节肠上皮屏障中的作用尚不清楚。总体假设是，调节肠上皮细胞中claudins的表达和细胞分布的机制对于维持肠屏障是必不可少的。该提案的总体目标是表征肠上皮细胞中claudin的生物学功能，并确定调节肠上皮细胞中claudin表达的细胞因子和内毒素诱导的分子机制。

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.