DPP4通过调控CD103+DC功能参与肠道炎症的作用机制研究

Dipeptidyl peptidase-4 (DPP4) is a type-II integral transmembrane glycoprotein that has recently gained attention owing to its role in the catalytic degradation of incretins. In addition to its well-known peptidase activity, DPP4 also possesses non-catalytic functions through its interaction with ligands. DPP4 plays a critical role in the regulation of metabolism and immune response. Studies indicated that inhibition of DPP4 catalytic functions ameliorates the development of colitis in animal model. Unexpectedly, our preliminary data demonstrated that the intestine inflammation was significantly worse in DPP4-/- mice with DSS-induced colitis, where the catalytic function of DPP4 was abrogated. These data suggest that the non-catalytic functions of DPP4 is more important than catalytic function in controlling the intestinal inflammation during the colitis. Furthermore, we found that the DPP4 was abundantly expressed on the intestine tolerogenic dendritic cell(DC), and the adoptive infusion of DPP4+ CD103+DC attenuated the inflammatory response in the DPP4-/- mouse with DSS-induced colitis. Thus, we speculate that a crucial role by non-catalytic functions of DPP4 acted in control the inflammation response, and its mechanism may be related to the regulation of tolerogenic CD103+DC function. With the help of knockout mice, bone marrow chimeras, animal model of colitis and clinical sample, our project aims to clarify the mechanism by which DPP4 ameliorates the colitis by regulating the CD103+DC function, and provide a reliable theoretical basis for the new strategies of IBD treatment.

DPP4是一种II型跨膜糖蛋白，具有酶学和非酶学两种功能，在代谢和免疫调节中发挥重要作用。文献报道抑制DPP4酶活性可以缓解肠道炎症，但申请者前期研究发现：在DPP4酶功能丧失的DPP4-/-小鼠中，肠道炎症反而明显加重，提示DPP4非酶学功能在限制肠炎进展中发挥关键性作用；进一步发现CD103+DC（肠道耐受型DC）表达的DPP4在肠炎中明显下降，过继野生型小鼠的CD103+DC可以明显缓解DPP4-/-小鼠肠炎模型的炎症反应。据此，申报者推测DPP4非酶学功能在控制肠道炎症中发挥重要作用，其机制可能通过调控耐受型CD103+DC功能有关。为证实上述假设，本项目拟借助基因敲除小鼠、骨髓移植嵌合小鼠、动物模型等多种实验技术手段，并结合临床样本，明确DPP4通过调控CD103+DC功能参与维持肠道免疫稳态。本项目有助于揭示DPP4在肠道炎症的作用及机制，可望为IBD的临床治疗提供新靶点。

炎症性肠病是以慢性肠道炎症为特征的自身免疫性疾病，目前机制不清，治疗手段有限。 DPP4是一种II型跨膜糖蛋白，表达于多种细胞。DPP4具有酶学和非酶学两种功能，在代谢和免疫调节中发挥重要作用。目前 DPP4的研究主要集中于代谢性疾病，如糖尿病及相关并发症等。然而，对于DPP4在IBD中的作用机制至仍不明确。相对于酶学功能，DPP4非酶学功能在肠道炎症中发挥显著重要的炎症抑制作用，表现为DPP4−/−小鼠的肠道炎症明显加重、体重下降明显、组肠道长度显著低于WT组，炎性细胞因子表达升高，而给与DPP4酶抑制剂后体重则无明显差异。DPP4主要表达于髓系细胞上，并主要表达于CD103+DC和CD4+T细胞上，同时肠道炎症环境抑制DPP4在CD103+DC上表达，DPP4底物利拉鲁肽liraglutide对CD103+DC和Treg的不存在影响。利用WT和DPP4−/−骨髓嵌合体小鼠，结果显示髓系细胞表达的DPP4对肠道炎症具有缓解作用，利用过继输注WT和DPP4−/−小鼠的CD103+DC，证实了DPP4通过调控CD103+DC功能控制肠道炎症。分选WT或DPP4−/−小鼠的CD45RBhigh CD4+T 细胞，分别过继至 Rag2−/−小鼠建立肠炎模型，发现CD4+T 细胞表达的 DPP4 对肠道炎症无影响；同时予以WT 小鼠的 CD45RBhigh CD4+T 细胞分别与 DPP4−/−或 WT 小鼠的 Treg同时输注至 Rag2−/−小鼠。每日监测小鼠体重以及粪便性质及出血，我们发现Treg是否表达DPP4不影响其免疫抑制功能。为排除T细胞表达DPP4对研究DPP4对CD103+DC功能的影响，利用DPP4−/−:Rag2−/−双基因敲除小鼠建立肠道炎症模型，结果显示DPP4−/−:Rag2−/−双基因敲除小鼠的肠道炎症比 Rag2−/−显小鼠明显更严重，体重下降更明显，进一步明确了CD103+DC缓解肠道炎症须借助于DPP4。此外，CD103+DC维持Treg功能、抑制Th1/Th17反应须借助于其表达的DPP4。

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