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P002. The potential role of IL‑33 in inflammatory-associated gut fibrosis: Induction of pro-fibrogenic gene expression and myofibroblast hypertrophy

B. Mattioli1, C. De Salvo2, L. Pastorelli3, R.R. Garg2, M. Campieri4, G. Poggioli1, T. Pizarro T2

1Policlinico S. Orsola Malpigli-Università Di Bologna, Instituto di Clinica Chirurgica e Cardiochirurgia II Clinica Chirurgica e Terapia Chirurgica, Bologna, Italy; 2Case Western Reserve University, Department of Pathology, Cleveland, United States; 3IRCCS Policlinico San Donato, Milan, Italy; 4University of Bologna, Italy

Background: Intestinal fibrosis is a serious complication of IBD, with more than a third of Crohn's disease (CD) patients developing a fibrostenosing phenotype with formation of strictures that will require surgical intervention. Remarkably, SAMP1/YitFc (SAMP) mice, a spontaneous model of CD, develop gut fibrosis; Increased levels of IL‑33, a member of the IL‑1 cytokine family, is associated with IBD. Emerging evidence suggests its potential role in liver and cutaneous fibrosis, as well as myofibroblast-associated colonic ulcerations. The aim of this study was to evaluate the role of IL‑33 as a potential mediator of profibrotic events leading to intestinal fibrosis and possible stricture formation.

Methods: A detailed Histologic time course study, Trichrome staining and IHC for IL‑33, was performed on SAMP and control AKR (parental strain) mice. qRT-PCR was done on full-thickness ilea for the profibrogenic genes, collagen (coll)‑1, coll‑3, CTGF and IGF‑1. Exogenous IL‑33 or vehicle was administered daily for 7d to AKR, AntiST2 or vehicle was administered 2 times week/6weeks to SAMP, and ileal tissues evaluated as above. Finally, microarray analysis was performed on IL‑33 stimulated subepithelial myofibroblasts (SEMFs).

Results: SAMP mice displayed macroscopic and microscopic features resembling human intestinal firbosis. IL‑33 and ST2 staining was present within the inflamed lamina propria of SAMP, localized to SEMFs and in areas with increased collagen deposition. Fibrosis was first observed at 20 wks, and reached its peak by 50 wks of age. mRNA expression of coll‑1 (4.74±0.69-fold; P = 0.001), coll‑3 (4.92±1.05-fold; P = 0.01), IGF1 (12.9±3.45; P = 0.006), and CTGF (3.29±0.69; P = 0.004) was dramatically elevated in SAMP vs. AKR ilea. IL‑33 treatment of AKR mice induced a marked hypertrophy of the muscularis propria (4.13±0.74-fold; P < 0.0001), and mRNA expression of coll‑1 (5.16±0.89-fold; P = 0.0009), coll‑3 (1.97±0.14-fold; P = 0.01), IGF‑1 (9.32±2.27-fold; P = 0.004) vs. vehicle controls. Microarray data confirmed these trends, displaying a global increase in profibrogenic gene expression. AntiST2 treatment induced a reduction of fibrosis and inflammatory scores as well as a trend in the decrease of profibrotic gene expression.

Conclusions: SAMP mice represent a valuable model to study mechanism underlying intestinal fibrosis. Our data using this model suggest an important role for IL‑33 in intestinal fibrosis as a potential target for the treatment of IBD-associated fibrosis and stricture formation.