Su1742 Mesenchymal Stem Cells Ameliorate Experimental Colitis by Secretion of TNF-Alfa Stimulated Gene/Protein 6 and Not by Gut-Homing

Abstract

Background Mesenchymal stem cells (MSCs) have been candidate as therapeutic treatment for several immune diseases including inflammatory bowel disease (IBD). Although most of beneficial effects are explained by MSC engrafting at the site of tissue injury with modulation of inflammatory reactions, the mechanisms by which MSCs exert their activities need to be clarified. Aim of this study was to investigate the mechanisms underlying the therapeutic efficacy of MSCs in experimental model of colitis. Methods Colitis was induced in C57BL6 mice by 3% DSS treatment for 10 days. MSCs were isolated from bone marrow of wild type (WT) and GFP-transgenic C57BL6 mice, cultured for 4 weeks and then sorted for Sca-1+, CD31-, cocktail lineagesurface markers. At day 5 of colitic induction the mice were treated intraperitoneally with a single injection of 3x106 GFP-MSC free or encapsulated MSC cells, or in alternative with 5 daily injections of recombinant TNF α-stimulating gene protein 6 (rTSG-6) each of 4 μg. Body weight and disease activity index (DAI) were monitored daily and the damage of murine colonic mucosa was evaluated by endoscopic and histological scores. To follow the migratory activity of the MSCs, GFP-MSCs were injected intraperitoneally in healthy or colitic mice at day 5 and their presence was assessed by flow cytometry after 24 and 48 hours in the colon and mesenteric lymph nodes. Levels of TSG-6, IL-6 and IFN-γ were measured in serum and in mucosal extracts by ELISA, while MMP activities were quantified by WB. Results We found that one injected, MSCs remain into the peritoneal cavity, where they aggregate along with macrophages and lymphocytes, generating organized structures. Only a small fraction (, 1%) of cells reached the inflamed colon. Furthermore, encapsulated MSCs and implanted into peritoneal cavity displayed comparable therapeutic efficacy with free MSCs suggesting that the gut homing was not relevant for their efficacy. In vitro and in vivo assays have demonstrated that MSCs secrete a multipotent anti-inflammatory protein TSG-6 able to reduce the damage to the colon. In fact, rTSG-6 treatment improved survival rate and DSS-induced colitis by reducing both systemic and mucosal levels of IL6, IFN-γ, neutrophil infiltration, and MMP activities. Conclusions Overall, these data indicate that the MSC gut-homing is not relevant for exerting their immunomodulatory effects, but MSCs dampen the mucosal inflammatory response at distance by releasing the potent antiinflammatory protein TSG6.