TRIM21在炎症性肠病发病过程中的免疫调节作用机制研究

Inflammatory bowel disease (IBD), comprising of ulcerative colitis and Crohn’s disease, is chronic, relapsing and remitting inflammatory disease of the gastrointestinal tract. Abnormal immune responses in intestinal mucosa toward commensal bacterial flora may be associated with the etiology and pathogenesis of human IBD. Tripartite motif-containing (TRIM)21 functions as an E3 ubiquitination ligase and plays an important role in the pathogenesis of autoimmune diseases through ubiquitination. However, the potential roles of TRIM21 in the pathogenesis of IBD are still unknown. In our preliminary experiments, we have found that TRIM21 was mainly expressed in CD4+ T cells and markedly decreased in inflamed mucosa of IBD patients compared with healthy controls. Ectopic expression of TRIM21 inhibited IBD CD4+ T cells to produce TNF-a、IFN-g、IL-17A and RORC, whereas downregulated expression of TRIM21 had opposite effects compared with controls, suggesting that TRIM21 may play an important role in regulating T helper (Th)1 and Th17 cell differentiation in the pathogenesis of IBD. Thus, TRIM21 is supposed to be involved in the development of inflammation in intestinal mucosa, particularly in human IBD. In this study, we will study the expression of TRIM21 in peripheral blood CD4+ T cells and inflamed mucosa from IBD patients, and investigate the potential role in regulating T cell immune responses in intestinal mucosa. TRIM21 knockout mice will be generated in our laboratory and an acute or chronic experimental colitis model in mice will be also established to determine the development of intestinal mucosal inflammation and phenotypic changes of mucosal immune cells. This work will clarify the potential role of TRIM21 in the pathogenesis of IBD, and provide an important theoretical basis for IBD immune therapy.

炎症性肠病（IBD）是发生在胃肠道原因不明的慢性复发性炎症性疾病，可能与肠黏膜免疫应答异常等有关。TRIM21是E3泛素化连接酶，在一些自身免疫性疾病发病过程中起到重要免疫调节作用，但其在IBD发病过程中的作用机制仍不清楚。前期我们研究发现TRIM21在活动期IBD患者肠黏膜组织中表达降低，其主要表达在CD4+ T细胞；体外转染TRIM21可抑制IBD患者外周血CD4+ T细胞TNF-a、IFN-g、IL-17A和RORC表达。据此提出TRIM21可能参与了IBD肠黏膜内Th1和Th17细胞介导的免疫病理损伤。本课题着重研究TRIM21在IBD中的表达和对肠黏膜组织内CD4+ T细胞的免疫调节效应，阐明其在IBD发生过程中的免疫调节作用机制。构建TRIM21基因敲除小鼠，建立急性和慢性结肠炎小鼠模型，观察肠黏膜组织炎症发展变化和各种免疫细胞的功能变化，为临床上治疗IBD寻求新的治疗靶点。

炎症性肠病（IBD）是一种慢性非特异性炎性疾病，它的发病机制与异常的肠黏膜免疫应答相关。TRIM21是一种E3泛素化连接酶，它对免疫应答反应有重要的调节作用，但其在IBD发病过程中的作用机制仍不清楚。本课题通过qPCR检测发现活动期IBD患者炎症肠黏膜组织表达TRIM21明显降低。而使用免疫组化染色也发现克罗恩病（CD）和溃疡性结肠炎（UC）患者炎症肠黏膜组织内TRIM21阳性细胞也明显降低。同时发现TRIM21主要表达在CD4+ T细胞。另外，我们还发现TRIM21在UC相关癌变（CAC）和结肠癌组织中表达降低。为了进一步确认TRIM21发挥功能的作用通路，我们使用软件分析预测TRIM21的靶基因是IRF3，使用qPCR发现IRF3在活动期IBD患者炎症肠黏膜组织中表达明显增高，并且IRF3主要表达在CD20+ B细胞和CD4+ T细胞。我们进一步分离了健康者、活动期CD和UC患者外周血CD4+ T细胞进行体外培养，并使用慢病毒包装的LV-sh-TRIM21和LV-TRIM21进行体外转染，发现TRIM21可抑制IRF3表达。同时建立了Trim21基因敲除小鼠结肠炎模型，发现Trim21基因敲除小鼠通过促进Th1和Th17细胞增殖分化，加重TNBS诱导的结肠炎症发生。另外，我们还利用Trim21基因敲除小鼠和野生型小鼠，使用偶氮甲烷（AOM）和葡聚糖硫酸钠盐（DSS）诱导小鼠发生CAC模型，结果表明TRIM21在CAC中表达降低，并通过调节上皮细胞增殖、粘附、组织重塑和血管生成以及促炎症反应来负向调节肠黏膜上皮癌变。因此，通过本课题的研究我们着重阐明了TRIM21可负调节IBD CD4+ T细胞中IRF3的表达，参与了IBD肠黏膜内Th1和Th17细胞介导的免疫损伤。同时TRIM21分子还参与了结肠炎相关癌变的发生发展，为IBD和CAC的防治提供了重要的理论依据。