Flagellin-Induced Gut Epithelial Chemokine Secretion

描述(由申请人提供)：肠道上皮调节维持生命的营养物质的吸收，同时防止大量和多样化的细菌种群在这一表面定居。虽然在传统上，肠道上皮被认为主要通过充当被动的、尽管具有高度选择性的屏障来完成这些任务，但过去十几年的研究表明，事实上，肠道上皮在保护宿主免受可在肠道表面定居的共生和潜在致病细菌的影响方面发挥着非常积极的作用。因此，了解细菌、上皮细胞和免疫细胞之间的相互作用对于了解肠道细菌的发病机制、食源性病原体的系统性感染以及肠道慢性炎症性疾病具有似乎不适当的针对共生肠道微生物区系的免疫反应是重要的。我们在这一建议下进行的细菌上皮相互作用的体外建模表明，作为鞭毛的主要结构成分，细菌鞭毛蛋白连接Toll样受体5(TLR5)是激活肠上皮细胞天然免疫信号的主要方式。鞭毛蛋白由许多病原体和共生微生物释放，但TLR5的表达极化到上皮的基底外侧表面，从而最大限度地减少了共生细菌释放的鞭毛蛋白对促炎信号的激活。相反，鞭毛病原体可以堵塞上皮或改变上皮细胞中的囊泡运输，从而激活模型上皮中的TLR5信号。这种TLR5信号利用了核因子？B、MAPK和JAK-STAT信号转导通路，导致了基因表达的瞬间爆发，似乎是为了直接排斥细菌、招募/激活免疫细胞和防止细胞凋亡。这种基因表达的诱导被认为可以保护宿主免受病原体的侵袭，但也可能导致与许多肠道感染相关的炎性后遗症。此外，一些病原体，如鼠伤寒沙门氏菌，具有一种特殊的机制，在感应到上皮细胞时调节鞭毛单体的释放，这表明一些病原体可能“故意”触发TLR5的激活，以帮助它们的传播。到目前为止进行的体内研究与这两种可能性都是一致的。然而，这类研究的范围太有限，无法合理地了解鞭毛蛋白-TLR5在体内相互作用的重要性，更不用说阐明鞭毛蛋白诱导的信号可能影响宿主-细菌相互作用在健康和疾病中的结果的机制。因此，为了填补这一知识空白，我们概述了一系列实验，以确定体内对鞭毛的先天免疫反应影响宿主-细菌相互作用结果的机制。公共卫生相关性：在发达国家和发展中国家，沙门氏菌仍然是最多产和最普遍的微生物致病原因之一。由沙门氏菌引起的人类疾病可分为两大类：1)肠道限制性自限性胃肠炎和伤寒。我们的研究表明，沙门氏菌鞭毛蛋白与宿主蛋白Toll样受体5的相互作用在这两种疾病过程中都起着关键作用。因此，我们建议了解这种相互作用在小鼠疾病模型中的作用。

DESCRIPTION (provided by applicant): The intestinal epithelium mediates the absorption of life-sustaining nutrients while protecting against the large and diverse population of bacteria that colonize this surface. While, classically, the gut epithelium was thought to manage these tasks primarily by functioning as a passive, albeit highly selective, barrier, research over the last dozen years has demonstrated that, in fact, the gut epithelium plays a very active role in protecting the host from both the commensal and potentially pathogenic bacteria that can colonize this surface. Consequently, understanding the interactions between bacteria, epithelial cells, and immune cells is important to understanding bacterial pathogenesis in the gut, systemic infection by food-borne pathogens, and chronic inflammatory diseases of the intestine in which there is a seemingly inappropriate immune response directed at the commensal enteric microflora. Our in vitro modeling of bacterial epithelial-interactions performed under this proposal revealed that ligation of toll-like receptor 5 (TLR5) by bacterial flagellin, the primary structural component of flagella, is a dominant means of activating innate immune signaling in intestinal epithelial cells. Flagellin is released by a number of pathogens and commensal microbes but TLR5 expression is polarized to the basolateral surface of the epithelium thus minimizing activation of pro-inflammatory signaling by flagellin released from commensal bacteria. Conversely, flagellated pathogens that can breech the epithelium or alter vesicular trafficking in epithelial cells activates TLR5-signaling in model epithelium. Such TLR5 signaling utilizes the NF-?B, MAPK and JaK-STAT signal transduction pathways result in a transient burst of gene expression seemingly designed to directly repel bacteria, recruit/activate immune cells, and prevent apoptosis. Such induction of gene expression can be envisaged to protect the host from pathogens but may contribute to the inflammatory sequellae associated with many enteric infections. Furthermore, that some pathogens such as Salmonella typhimurium have a specific mechanism that mediates release of flagellin monomers upon sensing of epithelial cells suggest that some pathogens might "deliberately" trigger TLR5 activation to aid in their dissemination. The in vivo studies performed to date are consistent with both of these possibilities. However, such studies have been far too limited in scope to provide a reasonable sense of the importance of the flagellin-TLR5 interaction in vivo let alone elucidate the mechanisms by which flagellin-induced signaling might affect the outcomes of host-bacteria interactions in health and disease. Thus, to fill this gap of knowledge, we outline a series of experiments to determine the mechanisms by which innate immune responses to flagellin affect the outcomes of host-bacterial interactions in vivo. PUBLIC HEALTH RELEVANCE: Salmonella remain amongst the most prolific and ubiquitous microbial causes of disease in both developed and developing countries. Human disease caused by Salmonella can be divided into 2 primary categories: 1) gut-restricted self-limiting gastroenteritis and Typhoid fever. Our research indicates that the interaction of the Salmonella protein flagellin with a host protein toll-like receptor 5 plays a key role in both disease processes. Thus, we propose to understand the role of the interaction in mouse models of disease.