Smad3 knock-out mice as a useful model to study intestinal fibrogenesis

To evaluate the possible differences in morphology and immunohistochemical expression of CD3, transforming growth factor beta1 (TGF-beta1), Smad7, alpha-smooth muscle actin (alpha-Sma), and collagen types I-VII of small and large intestine in Smad3 null and wild-type mice.

Ten null and ten wild-type adult mice were sacrificed at 4 mo of age and the organs (esophagus, small and large bowel, ureters) were collected for histology (hematoxylin and eosin, Masson thrichrome, silver staining), morphometry and immunohistochemistry analysis. TGF-beta1 levels of intestinal tissue homogenates were assessed by ELISA.

No macroscopic intestinal lesions were detected both in null and wild-type mice. Histological and morphometric evaluation revealed a significant reduction in muscle layer thickness of small and large intestine in null mice as compared to wild-type mice. Immunohistochemistry evaluation showed a significant increase of CD3+ T cell, TGF-beta1 and Smad7 staining in the small and large intestine mucosa of Smad3 null mice as compared to wild-type mice. Alpha-Sma and collagen I-VII staining of small and large intestine did not differ between the two groups of mice. TGF-beta1 levels of colonic tissue homogenates were significantly higher in null mice than in wild-type mice. In preliminary experiments a significant reduction of TNBS-induced intestinal fibrosis was observed in null mice as compared to wild-type mice.

Smad3 null mice are a useful model to investigate the in vivo role of the TGF-beta/Smad signalling pathway in intestinal inflammation and fibrosis.