The Inhibitory Function Of Mesenchymal Stem Cells In Colitis-associated Colorectal Cancer

The connection between inflammation and tumor development was noticed after Virchow demonstrated that the site of chronic inflammation tended to occur cancer. Colorectal cancer which includes hereditary, sporadic and colitis-associated colorectal cancer (CAC) is one of the most common malignant. More and more evidences show that chronic inflammation of colon is an important factor for the progression of colorectal cancer.Mesenchymal stem cells (MSCs), which are derived from a variety of tissues and fibroblast-like morphology, have the capability of self-renewal and differentiation. MSCs can migrate to the site of damaged tissue induced by inflammation and play an anti-inflammatory effect through regulation the function of immune cells, like dendritic cells, natural killer cells (NK cells), T cells, and B cells.Previous studies have produced controversial results regarding whether mesenchymal stem cells (MSCs) promote or inhibit tumor development. Given the dual role of MSCs in inflammation and cancer, in this study the colitis-associated colorectal cancer (CAC) model was used to examine whether umbilical cord tissue-derived MSCs could prevent neoplasm by inhibiting chronic inflammation.1. MSCs can decrease the incidence of colitis-related neoplasmCAC model was successfully induced by injecting mice with AOM and 2% DSS. We noticed that mice treated with MSCs had less macroscopic tumors and longer colon length. Moreover, immunohistochemical analysis showed that Ki-67 and PCNA was lower in colon tissues of mice treated with MSCs than those without treatment. These data confirmed that MSCs could inhibit the development of tumor in CAC model.2. MSCs can migrate to colon and alleviate the pathology of DSS-induced chronic colitisWe then detected the migration activity of MSCs in mice through tail vein injection. In tumor group, which mice were treated with AOM and 2%DSS, MSCs were detected in colon. These results indicated that MSCs could migrate to colon tissues when the intestinal epithelium of mice was damaged by DSS. To confirm that MSCs inhibit carcinogenesis through inhibition of colonic inflammation, mice in tumor group were sacrificed on day 32. We found that MSCs treatments significantly alleviated chronic inflammation with increased body weight and colon length and lower level of inflammation. The expressions of IL-1β, IL-6 and TNF-α in colon were examined, which were reduced after MSCs treatment. These results consistently demonstrated that during the development of CAC, MSC had the protective function on DSS-induced colitis by inhibiting excessive inflammation in colon tissues.3. Treg cells are up-regulated in the progression of chronic colitisTo detect the regulatory effect of MSCs on immune cells, Flow cytometry was used to analyze changes of adaptive immune cells in mesenteric lymph nodes after MSCs treatment for 33 days. We found that Treg cells were significantly up-regulated by MSCs treatment. In addition, Foxp3 stained by immunohistochemistry showed that Treg cells infiltrated in intestinal stromal more in MSCs treated group than those in untreated group. Therefore, these results indicated that MSCs indeed were involved in inducing Treg cells to suppress colitis. In vitro, after naive CD4+T cells co-cultured with MSCs for 3 days, compared to the group with neutralizing antibody of TGF-β, the CD4+Foxp3+T cells were increased significantly. Moreover, the conditioned medium of MSCs was then used to stimulate Jurkat cells. Mechanically, phosphorylation-Smad2 was activated after 30min treated with MSCs. These data suggest that MSCs secreting TGF-β increased the CD4+Foxp3+T cell populations via activating phosphorylation of Smad2.To sum up, we found that MSCs can inhibit the colitis at colitis stage and eventually suppress the development of colon cancer at tumor stage. Importantly, Treg cells were accumulated in colon tissues by MSCs treatment. MSCs can also raise the expression of Foxp3 in naive CD4+T cells and activated TGF-β-Smad2 signal. Our research makes an important theoretical basis for the clinical application of MSCs which can suppress chronic inflammation, and then suppress the development of CAC.