Role of TLR4 in Acute and Chronic Murine Colitis

描述(申请人提供)：肠道上皮和肠道相关的粘膜免疫系统必须一方面对致病菌产生炎症反应，同时积极地将炎症限制在共生生物上。炎症性肠病(IBD)在遗传易感宿主发生触发事件后发展。第一个被鉴定为克罗恩病疾病易感基因的基因是CARD15/NOD2，一种细胞内病原体识别受体(PRR)。克罗恩病相关的CARD15/NOD2基因的多态导致了一种蛋白质，其激活核因子-kB的能力因肽聚糖的反应而受损。这一数据表明，对共生细菌或致病菌的先天免疫反应缺陷可能会导致慢性肠炎。Toll样受体(TLRs)也是PRRs。PAMP与其各自的TLR结合导致NF-kB激活和细菌的清除。TLR4是存在于革兰氏阴性菌上的脂多糖受体。这一应用源于我们令人惊讶的初步观察，即TLR4(TLR4-/-)零突变小鼠在服用葡聚糖硫酸钠后结肠炎的临床症状增加，中性粒细胞浸润减少，细菌易位增加。在MyD88-/-小鼠中也观察到了类似的结果，表明这是TLR4下游的主要途径，解释了这种表型。基于我们的初步数据，我们希望检验这一假说，即通过TLR4信号是产生对肠损伤的急性炎症反应并限制慢性肠炎发展所必需的。我们将利用R21的支持来建立强大的动物模型，建立TLR4在肠道炎症的起始和持续过程中的需求。

DESCRIPTION (provided by applicant): The intestinal epithelium and gut-associated mucosal immune system must on the one (1) hand generate an inflammatory response to pathogenic bacteria while actively limiting inflammation to commensal organisms. Inflammatory bowel disease (IBD) develops in the genetically-susceptible host following a triggering event. The first gene to be identified as a disease-susceptibility gene in Crohn's disease is CARD15/NOD2, an intracellular pathogen-recognition receptor (PRR). Crohn's disease-associated polymorphisms in the CARD15/NOD2 gene result in a protein that is impaired in its ability to activate NF-kB in response to peptidoglycan. This data suggests that a defect in the innate immune response to commensal or pathogenic bacteria may culminate in chronic intestinal inflammation. Toll-like receptors (TLRs) are also PRRs. Binding of PAMPs to their respective TLRs results in NF-kB activation and clearance of bacteria. TLR4 is the receptor for lipopolysaccharide (LPS) present on Gram-negative bacteria. This application emanates from our surprising preliminary observation that mice with a null mutation in TLR4 (TLR4-/-) have increased clinical symptoms of colitis following administration of dextran sodium sulfate, a paucity of neutrophilic infiltration, and increased bacterial translocation. Similar results were observed in MyD88-/- mice suggesting this is the dominant pathway downstream of TLR4 accounting for this phenotype. Based on our preliminary data, we wish to test the hypothesis that signaling through TLR4 is required for the generation of an acute inflammatory response to intestinal injury and limiting the development of chronic intestinal inflammation. We will use the support from this R21 to generate robust animal models that establish the requirement for TLR4 in the initiation and perpetuation of intestinal inflammation.