The Role of Myeloid-derived Cells in Ulcerative Colitis-Associated Colorectal Cancer
|Course||Department of Gastroenterology,|
|Keywords||MDSCs UCRCC AOM DSS mouse model|
Background:Ulcerative colitis (UC) is one of the idiopathic inflammatory bowel diseases of the large bowel, the etiology of which is not completely discovered. Patients with UC have a high risk of developing colorectal cancer (CRC). It is hard to obtain certain clinical cases in a short time, so it is necessary to establish an animal model of ulcerative colitis neoplasia. In recent years, there are several animal models of ulcerative colitis-associated colorectal cancer (UCACC). However, the model using DSS needs a long period to induce UCACC, and the incidence of induced tumors is relatively low[1.2]. It is reported that a single intraperitoneal administration of azoxymethane (AOM) combined with one cycle of2%dextran sodium sulfate (DSS, molecular weight36,000-50,000) can established an efficient animal models in20weeks. Myeloid-derived suppressor cells (MDSCs) are heterogeneous populations of cells composed of precursors of macrophages, granulocytes, dendritic cells, and myeloid cells at earlier stages of differentiation. In mice, these myeloid cells are characterized as Gr-1+CDllb+cells. Disturbances in cytokine and chemokine balance, inducecd by tumor growth, infection, immune stress and even vaccination, can alter the hemeostasis of this population leading to its accumulation in the secondary lymphoid organs and, ultimately, influencing their maturation toward a suppressive phenotype. In the present study, we explore a newly UCACC mouse model in which colonic tumors developed within10weeks, when mice were given a single small doses of AOM (10mg/kgWt) by intraperitoneal injection followed by3cycles of7days oral exposure (in drinking water) to DSS (molecular weight36,000-50,000,3%). We investigated the roles of MDSCs in the development of UCRCC, and thus provide a potential therapeutic target for anti-cancer therapy.Objective:We try to establish an animal model of UCRCC, and the role of myeloid derived suppressed cells in the development of UCRCC was studied. Methods:Male C57BL/6mice aged5-6weeks were quarantined for the first7days, and then randomized into four groups, such as AOM+DSS group (Group A,10), DSS group (Group B,10), AOM group (Group C,10) and no-treatment control group (Group D,10). Group A was given a single intraperitoneal injection of AOM (10mg/kg body weight).1week later, the animals were exposure to3%DSS (MW36-50kD) in drinking water for7days, followed by14days of normal water. This cycle was repeated3times. Groups B and C were given DSS or AOM alone, respectively. Group D was untreated. All mice were killed by ether overdose after the last cycle. The large bowels were flushed with saline, and were cut open longitudinally along the main axis, and then washed with saline. After that, the large bowels were fixed in10%buffered formalin for at least24h. Histological examination was performed on paraffin-embedded sections after hematoxylin and eosin (H&E) staining. Fluorescent immunohistochemistry (FIHC) was performed to study the expression of MDSCs. The proportion of MDSCs in marrow and spleen was measured by flow cytometry.Results:1. During the experiment bloody stools were observed at the5th day in groups A and B, and were alleviated in the fllowing14days. The mean of body weight in groups A and B were significantly smaller than that of group D (P<0.05). After exposure to3cycles of3%DSS, masses were found in the5/10mice (50%) which were in the distal colon, and middle next, and none in the proximal colon. There was no tumor in the other2groups.2. MDSCs were positive in the large bowels of groups A and B, but negative in the other2groups3(P<0.05). The proportion of marrow and spleen MDSCs in tumor bearing mice was significantly higher than in normal mice (P<0.05). Accompanying with tumor progression, the proportion of marrow and spleen MDSCs increased gradually.Conclusion:1. The research indicates that a small dosage of AOM combined with3cycles of DSS (MW36-50kDa) can induce tumors in the distal and middle colons of male C57BL/6mice, and the procedures may provide an efficient mouse model for investigatingUCACC.2. The recruitment of MDSCs in marrow, spleen and tumor areas may play a significant role in the development of tumors.