Background: Transforming growth factor-beta (TGF-beta)/Smad3 signalling plays a central role in tissue fibrogenesis, acting as a potent stimulus of extracellular matrix (ECM) protein accumulation. The aim of this study was to evaluate the potential role of Smad3 in the pathogenesis of colonic fibrosis induced by trinitrobenzene sulfonic acid (TNBS) in Smad3 null mice.
Materials and methods: Chronic colitis-associated fibrosis was induced in 15 Smad3 null and 13 wild-type mice by intra-rectal administration of TNBS. Each mouse received an incremental dose of TNBS (0.5-1.0 mg per week) over a 6-week period. The colon was excised for macroscopic examination and histological, morphometric and immunohistochemical analyses. For immunohistochemistry, alpha-smooth muscle actin (alpha-SMA), collagen types I-III, TGF-beta1, connective tissue growth factor (CTGF), Smad3, Smad7, and CD3 antibodies were used.
Results: At macroscopic examination, the colon of Smad3 wild-type mice appeared significantly harder, thicker and shorter than that of the Smad3 null mice. Of the wild-type mice, 50% presented colonic adhesions and strictures. Histological and morphometric evaluation revealed a significantly higher degree of colonic fibrosis and accumulation of collagen in the Smad3 wild-type compared to null mice, whereas the degree of colonic inflammation did not differ between the two groups of mice. Immunohistochemical evaluation showed a marked increase in CTGF, collagen I-III, TGF-beta and Smad3 staining in the colon of Smad3 wild-type compared to null mice, whereas Smad7 was increased only in null mice.
Conclusions: These results indicate that Smad3 loss confers resistance to the development of TNBS-induced colonic fibrosis. The reduced fibrotic response appears to be due to a reduction in fibrogenic mesenchymal cell activation and ECM production and accumulation. Smad3 could be a novel target for potential treatment of intestinal fibrosis, especially in inflammatory bowel disease.