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P065. IL-33/ST2 axis modulates epithelial repair and gut mucosal wound healing in DSS-colitic mice

L.R. Lopetuso1,2, C. De Salvo2, H. Senkfor2, X.-M. Wang2, D.W. Abbott2, F. Scaldaferri1, A. Gasbarrini1, T.T. Pizarro2, 1Catholic University of Sacred Heart, Internal Medicine and Gastroenterology, Rome, Italy, 2Case Western Reserve University, Pathology, Cleveland, OH, United States

Background

IL-33 and its receptor, ST2, are important factors in IBD. However, animal studies have yielded ambiguous results, reporting both pathogenic and protective functions. The aim was to characterize and functionally evaluate the precise role of the IL-33/ST2 axis following acute epithelial injury and mucosal repair in DSS-induced colitic mice.

Methods

DSS was administered for 5d to C57/BL6 wild-type (WT), IL-33 KO and ST2 KO mice to induce colitis. DSS was then replaced with regular drinking water for 2 wks (recovery period). Another group of WT mice received DSS for 5d and IL-33 (33 ug/kg, i.p.) or vehicle (VEH) every other day during the recovery period. Mice were sacrificed either after DSS challenge or after 1 or 2 wks of recovery; control mice (CT) not exposed to DSS were sacrificed at similar time points, at which time colons were harvested. Body weight, occult blood test, and stool consistency were measured daily to calculate Disease Activity Index (DAI), and endoscopic and histological evaluation of colons were performed using established scoring systems. IHC, qPCR and Western blots were done on full-thickness colons for IL-33 and ST2 localization, mRNA expression, and evaluation of protein isoforms, respectively.

Results

DSS administered to WT mice resulted in increased body weight loss and DAI. More severe colitis was observed following DSS+1wk recovery vs. after 5d of DSS, which decreased after DSS+2wks recovery. IL-33 mRNA transcripts were dramatically elevated after DSS, and even more so following DSS+recovery vs. CT, but similar to CT after DSS+2wks recovery. ST2 mRNA expression was also increased after DSS+recovery vs. CT, while no difference was found between 5d of DSS challenge and CT and after DSS+2wks recovery. Full-length, bioactive IL33 (31 kDa), ST2L (76 kDa) and sST2 (52 kDa) were expressed in all experimental groups; the cleaved, less active form of IL33 (24 kDa) was increased in only DSS exposed mice vs. CT. IHC showed intense IL-33 and ST2 staining within the inflamed and ulcerated mucosa of DSS-treated mice. ST2 staining was more evident during the recovery phase following DSS, notably localized to subepithelial myofibroblasts in close proximity to areas of re-epithelialization. Remarkably, both IL-33 and ST2 KO mice showed increased colonic inflammation after 2 wks recovery compared to after 5d DSS and vs also WT, suggesting the importance of IL-33/ST2 axis in mucosal healing. Likewise, IL-33 treatment of WT mice resulted in increased body weight, reduced DAI, and decreased colonic inflammation after 2 wks recovery vs. VEH.

Conclusion

Our results suggest that activation of the IL-33/ST2 axis promotes epithelial repair and mucosal healing following acute epithelial injury during DSS-induced colitis.