Rab27B-外泌体途径介导CD4+T细胞功能在溃疡性结肠炎肠黏膜炎症中的机制研究

Intercellular communication of immune cells is critical to elicit inflammatory responses, which was once considered to be mainly mediated by cytokines. Recent researches show that exosome-mediated intercellular communication is common among immune cells, exerting pro-inflammatory or immune-regulatory effects. Rab27B is the key player in the intracellular transport and secretion of exosome. Previously, we found that Rab27B- positive immune cells were significantly increased in the intestinal mucosa of patients with active ulcerative colitis, and colocalized with CD4+ T cells. We also observed that exosome derived from CD4+ T cells which were isolated from peripheral blood of patients with ulcerative colitis contained significantly more miR-155 than that from healthy controls. Several studies revealed that miR-155 could promote the differentiation of CD4+ T cells towards Th1/Th17 cells. Our hypothesis is that Rab27B-exosomal pathway mediates the transfer of miR-155 among CD4+ T cells and consequently promote Th1/Th17 differentiation in ulcerative colitis, which contributes to the development of mucosal inflammation. We attempt to prove the hypothesis through researches in colonic mucosa biopsies and peripheral blood from UC patients, colonic tissue from DSS-induced colitis model, T cell transfer colitis model as well as Transwell co-culture system.

免疫细胞间的信息传递是炎症反应的重要环节, 既往认为该过程主要由细胞因子介导。近期研究发现，免疫细胞间外泌体的传递普遍存在并发挥重要促炎及免疫调节作用。Rab27B是外泌体转运、分泌过程中的关键分子。我们前期研究发现，溃疡性结肠炎（UC）患者活动期肠黏膜中Rab27B阳性免疫细胞的数量显著高于对照，并与CD4+ T细胞共定位。UC患者外周血CD4+T细胞经体外分离、活化后分泌的外泌体中miR-155含量显著高于对照。之前多项研究表明，miR-155可促进CD4+T细胞向Th1/Th17方向分化。我们假设：UC中CD4+ T细胞可能通过Rab27B-外泌体途径传递miR-155，诱导CD4+ T细胞向Th1/Th17分化，从而促进肠道炎症发展。本项目拟利用UC患者肠黏膜、外周血标本，DSS肠炎小鼠肠组织，T细胞过继小鼠肠炎模型及Transwell共培养体系等对该假设进行验证。

免疫细胞间的信息传递是炎症反应的重要环节,近期研究发现，免疫细胞间外泌体的传递普遍存在并发挥重要促炎及免疫调节作用。免疫细胞间可通过外泌体传递具有促炎或抑炎作用的miRNAs，介导对其靶基因转录后水平的调控，从而发挥对受体细胞炎症反应的调节，这是近期免疫学研究领域的重要发现之一。Rab27B，小GTP酶（small GTPase）家族成员，是外泌体转运、分泌过程中的关键分子之一。近期研究表明，Rab27敲除，通过抑制外泌体生成，可明显削弱Treg细胞的免疫调节作用，为Rab27参与免疫细胞间的免疫调节提供了可靠依据。本课题组研究发现，溃疡性结肠炎(UC)患者活动期肠黏膜中Rab27B阳性免疫细胞数目显著增高，并与CD4+T细胞共定位；溃疡性结肠炎(UC)患者活动期外周血CD4+ T细胞中Rab27B蛋白及mRNA水平明显增高,同时外泌体中miR-155含量明显增多。Rab27B敲除或抑制外泌体生成，体外活化诱导CD4+T细胞向TH1/Th17分化受到抑制，同时外泌体中miR-155含量明显减少。miR-155可促进CD4+T细胞向TH1/Th17的分化。综上，本研究提示Rab27B-外泌体途径可能通过介导 CD4+T 细胞间 miR-155 的传递，诱导 CD4+T 细胞向 Th1/Th17 方向分化，可能是溃疡性结肠炎肠道炎症发生发展的重要机制。本研究提示Rab27B介导的外泌体途径可能成为溃疡性结肠炎临床诊疗新的有效靶点，从而为诊疗策略、药物研发提供了新的思路。