Dermo+间质细胞在肠道免疫反应中的作用机制研究

The intestine contains the largest number of immune cells, which act together with the intestinal epithelial cells, goblet cell-generated mucus gel, the anti-microbe polypeptides, and IgA molecules in the mucus, to prevent the invasion of the commensal bacteria and maintain the homeostasis of the intestinal immune system. Disruption of this homeostasis leads to the development of inflammatory bowel diseases (IBD) and likely colorectal cancer. It has been long known that intestine contains mesenchymal/stromal cells, including SMA+ or SMA- myofibroblasts, pericytes, fibroblasts, and other mesoderm-derived cells. There is lack of definite markers to label these stromal subpopulations in vivo. The mixed stromal cell cultures show characteristics of mesenchymal stem cells (MSCs). It is well established that MSCs isolated from the bone marrow or adipose tissues have potent immune regulatory activities and have been tested to treat some immune disorders including IBD. However, little is known whether intestinal stromal cells play a role in the intestinal immunity. Using lineage tracing technology with bone marrow MSC markers, we identified two subpopulations of stromal cells (Prx1 and Dermo1) in the intestine that have MSC tri-lineage differentiation potentials. Ablation of Dermo1+ stromal cells leads to IBD, whereas ablation of Prx1+ cells showed no such phenotype. The IBD development is associated with activation of Th17 cells. We also found that ablation of Dermo1+ cells decreased the number of goblet cells and Mucin production. Based on these preliminary results, we hypothesize that Dermo1+ stromal cells regulates intestine immunity via maintaining the epithelial mucosal barrier and acting on innate and adaptive immune cells. In addition to consolidating the above findings, we are planning to study the molecular mechanisms by which Dermo1+ stromal cells regulate the integrity of intestinal epithelial barrier, and the cytokines/growth factors secreted by Dermo1+ cells, and test the cytokines/growth factors in the development of DSS-induced colitis and AOM/DSS-induced colorectal tumors. Finally, we are going to test the repairing ability of endogenous and bone marrow Dermo1+ cells in treating IBD, and to test the presence of Dermo1+ cells in the development and progression of human IBD and colorectal tumors. This project will advance our understanding of intestinal immunity and development of IBD and identify new targets for IBD therapy.

肠道是最大的免疫器官，肠道中上皮细胞、免疫细胞、间质细胞等和肠道微生物相互作用维持免疫稳态。肠道稳态失衡促进肠炎发生并诱发结直肠癌。肠道间质细胞特异标志物的缺乏导致间质细胞亚群的种类、分布、及其对肠道免疫稳态的作用等研究无法深入进行。预实验结果：谱系示踪技术发现骨髓间充质干细胞marker Dermo1和Prx1可标记肠道间质细胞，特异清除Dermo1+细胞引起小鼠自发性肠炎，伴有IL-17等炎性细胞因子的升高。据此, 我们推断肠道Dermo1+细胞在维持肠道免疫微环境以及肠道炎症性疾病的发生发展过程中起重要作用。我们拟研究Dermo1+间质细胞在肠道的免疫稳态、肠炎症性疾病发生，以及炎症引起的结直肠癌发生中的作用，及其调节粘膜免疫屏障、通过释放细胞因子调节上皮细胞和免疫细胞的机制。最后我们拟研究骨髓中相应的间质细胞亚群在肠炎治疗中的作用。这将是首次系统研究内源性间质细胞在肠道免疫中的作用

肠炎的发生在全世界呈上升趋势，但是我们对肠炎的致病机制并不清楚。本研究发现了位于肠道间质的一类具有间充质干细胞功能的—Dermo+细胞，在肠炎发生中有重要作用。首先通过谱系示踪我们发现了在肠道中存在多种间质细胞亚群，但是只有在去除Dermo+细胞才会发生肠炎。我们的研究发现，Dermo+细胞在正常情况下，间质细胞能够分泌Wnt分子促进杯状细胞分化，并且维持免疫屏障阻止细菌侵入。在DSS诱导的肠炎模型中，免疫屏障被打破，细菌侵入时，Dermo+细胞能够激活TLR4-p38MAPK-Cox2-PGE2信号通路进而抑制巨噬细胞和中性粒细胞的活性，抑制炎症的发生。去除这个通路中的任何一个分子都会使炎症加剧但是不影响肠道隐窝的内稳态，同时我们也证实TGF和RelA没有参与Dermo+细胞抑制肠炎发生的作用。这些发现表明肠道中存在的Dermo+谱系细胞在维持肠道免疫屏障和促进先天免疫细胞活性中发挥重要作用。鉴于这类细胞在抑制肠炎发生发展中的重要作用，我们认为Dermo+间质细胞可以作为抑制和治疗肠炎的靶点。