Anti-inflammatory role of MUC1 mucin

描述（由申请人提供）：铜绿假单胞菌（PA）是一种机会性细菌病原体，可导致许多临床重要的肺部疾病，包括肺炎和囊性纤维化（CF）。就CF而言，患者发病和死亡的主要原因是气道阻塞，这是由于存在粘稠而坚韧的粘液，这些粘液被PA严重感染。由于PA暴露在正常和CF个体的呼吸系统中都存在，CF患者中这种病原体的“选择性”感染表明存在一种非CF气道中不存在的致病机制。关于CF的病因，人们提出了许多不同的理论。我们的实验室进行了有趣的观察，发现气道上皮细胞表面的MUC1粘蛋白是通过细菌鞭毛蛋白介导的PA的特异性结合位点。MUC1糖蛋白的结构表明，在与鞭毛蛋白相互作用后，它作为一种受体在细胞内传递信号。我们使用转基因小鼠阻断MUC1表达（MUC1敲除小鼠），初步研究表明，与野生型小鼠相比，MUC1敲除小鼠在PA鞭毛蛋白刺激后，肺部PA清除率增加，气道白细胞募集更多，支气管肺泡灌洗液中促炎细胞因子水平更高。有趣的是，TLR5是另一种细胞表面受体，在与鞭毛蛋白结合后产生细胞内信号通路。基于这种相似性，我们进行了进一步的实验来研究MUC1和TLR5的功能关系。我们观察到MUC1的表达在正常肺细胞中抑制鞭毛蛋白- tlr5信号通路，而在CF气道上皮细胞中不抑制。基于这些结果，我们提出MUC1是一种抗炎细胞表面受体，至少部分通过拮抗鞭毛蛋白tlr5信号传导起作用。在本提案中，我们将通过确定MUC1衰减TLR5信号转导的机制来验证我们的理论。该项目的成功完成将为MUC1在炎症、先天免疫和CF早期PA感染中的作用提供重要的见解。

DESCRIPTION (provided by applicant): Pseudomonas aeruginosa (PA) is an opportunistic bacterial pathogen responsible for a number of clinically important lung diseases including pneumonia and cystic fibrosis (CF). In the case of CF, the major cause of morbidity and mortality among afflicted patients is airway obstruction due to the presence of thick and tenacious mucus that becomes heavily infected with PA. Because PA exposure occurs in the respiratory system of both normal and CF individuals, "selective"' infection by this pathogen among CF patients suggests the presence of a disease-causing mechanism that is not present in non-CF airways. A number of different theories have been proposed to account for the etiology of CF. Our laboratory made the interesting observation that MUC1 mucin on the surface of airway epithelial cells is a specific binding site for PA mediated through bacterial flagellin. The structure of the MUC1 glycoprotein suggests that it acts as a receptor to transmit signals intracellularly following interaction with flagellin. Using mice genetically modified to block MUC1 expression (MUC1 knockout mice), our preliminary studies showed that, compared with wild type mice, Muc1 knockout animals exhibited increased PA clearance from the lungs and greater recruitment of airway leukocytes and higher levels of the proinflammatory cytokines in bronchoalveolar lavage fluid following PA flagellin stimulation. Interestingly, TLR5 is another cell surface receptor that generates an intracellular signaling pathway following binding to flagellin. Based on this similarity, we conducted additional experiments to investigate the functional relationship between MUC1 and TLR5. We observed that expression of MUC1 inhibited the flagellin-TLR5 signaling pathway in normal lung cells but not CF airway epithelial cells. Based on these results, we formed the hypothesis that MUC1 is an anti-inflammatory cell surface receptor that acts, at least in part, through antagonism of flagellin-TLR5 signaling. In this proposal, we will test our theory by determining the mechanisms by which MUC1 attenuates TLR5 signal transduction. Successful completion of this project will provide important insights for the role of MUC1 in inflammation, innate immunity, and the early stages of PA infection in CF.