The role of curli fibrils in modulating immune responses in the gut

描述(申请人提供)：淀粉样蛋白是一种蛋白质沉积，具有保守的纤维状交叉β片状四级结构。人类体内产生了60多种不同的淀粉样蛋白。虽然这些蛋白质中的少数几个的功能已被证实，包括胰岛淀粉样多肽和几种多肽激素，但许多其他淀粉样蛋白的作用仍不清楚。有趣的是，很少有细菌被证明能产生淀粉样蛋白。包括大肠杆菌在内的肠道细菌生物膜中发现的卷曲纤维 和肠沙门氏菌血清型。鼠伤寒杆菌是迄今为止特征最明确的细菌淀粉样蛋白。最近，我们发现Toll样受体2既识别宿主淀粉样蛋白β-淀粉样蛋白1-42，又识别卷曲淀粉样蛋白纤维，这是由于它们共同的β-Sheet结构保守(19，20)。此外，我们和其他人证明了TLR2与TLR1二聚化对于识别β-淀粉样蛋白1-42和卷曲淀粉样蛋白纤维(21)是必要的。肠上皮细胞表达的TLR2有助于调节肠屏障功能(5)。然而，淀粉样蛋白对肠上皮屏障的影响仍不清楚。通过这一应用，我们将研究细菌和宿主淀粉样蛋白对肠道免疫反应的贡献。我们的中心假设是，通过TLR2/TLR1复合体检测到淀粉样蛋白在肠道上皮细胞中产生保护性免疫反应，通过激活PI3K途径增强肠上皮屏障。这反过来又会导致 紧密连接蛋白的增加。我们将使用共生生物体E.coliNissle以及纯化的卷曲纤维和血清淀粉样蛋白A1(SAA1)来验证我们的假设，SAA1是炎症时在肠道中产生的一种宿主淀粉样蛋白。这项研究的基本原理是，更好地了解Nissle或宿主淀粉样蛋白SAA卷曲纤维促进上皮屏障功能的机制，将有助于从机制上更好地理解免疫系统在动态平衡和炎症过程中如何调节肠上皮屏障。

DESCRIPTION (provided by applicant): Amyloids are protein deposits that possess a conserved fibrillar cross-β sheet quartenary structure. More than 60 different amyloidogenic proteins are produced in humans. While the function of few of these proteins has been demonstrated including, islet-amyloid polypeptide and several peptide hormones, the role of many other amyloids remain unknown. Interestingly, few bacteria have been shown to produce amyloids. Curli fibers found in the biofilms of enteric bacteria including Escherichia coli and Salmonella enterica serovar. Typhimurium are the best-characterized bacterial amyloid to date. Recently, we discovered that Toll-like receptor (TLR) 2 recognizes both β-amyloid 1-42, a host amyloid, and curli amyloid fibers due to their conserved common β-sheet structure (19, 20). Moreover, we and others demonstrated that the dimerization of TLR2 with TLR1 is necessary for the recognition of β-amyloid 1-42 and curli amyloid fibers (21). TLR2 expressed by the intestinal epithelial cells contribute to the regulation of the intestinal barrier function (5). Nonetheless, the affects of amyloids on the intestinal epithelial barrier remain unknown. With this application we will investigate the contribution of bacterial and host amyloids to intestinal immune responses. Our central hypothesis is that the detection of amyloids via the TLR2/TLR1 complex generates a protective immune response in the gut epithelium leading to reinforcement of the intestinal epithelial barrier via activation of the PI3K pathway. This, in turn, leads to an increase in tight junction proteins. We will test our hypothesis using the commensal organism E. coli Nissle, as well as purified curli fibers and serum amyloid A1 (SAA1), a host amyloid produced in the gut upon inflammation. The rationale for the proposed research is that a better understanding of the mechanisms by which curli fibers of Nissle or host amyloid SAA promote epithelial barrier function will lead to a better mechanistic understanding of how intestinal epithelial barrier is regulated by the immune system during homeostasis and inflammation.