Localization of avβ6 integrin- TGF-β1/Smad3, mTOR and PPARgg in experimental colorectal fibrosis

A simultaneous action of several pro-fibrotic mediators appears relevant in the development of fibrosis. There are evidences that transforming growth factor-β (TGF-β)/Smad3 pathway forms with avβ6 integrin, mammalian target of Rapamycin (mTOR) and peroxisome proliferator-activated receptor-g (PPARg) a complex signalling network with extensive crosstalk and strong effects on fibrosis development. The present study evaluated the expression of TGFβ, Smad3, avβ6 integrin, mTOR and PPARg in 2, 4, 6-trinitrobenzenesulphonic acid (TNBS)-induced colorectal fibrosis in Smad3 wild-type (WT) and null mice. Smad3 WT mice treated with TNBS developed a marked colorectal fibrosis and showed a concomitant up-regulation of TGFβ, Smad3, avβ6 and mTOR and a reduction of PPARg expression. On the other hand, Smad3 Null mice similarly treated with TNBS did not develop fibrosis and showed a very low or even absent expression of TGFβ, Smad3, avβ6 and mTOR and a marked over-expression of PPARg. At the same time the expression of a-smooth muscle actin (a marker of activated myofibroblasts), collagen I-III and connective tissue growth factor (a downstream effector of TGFβ/Smad3-induced extracellular matrix proteins) were upregulated in Smad3 WT mice treated with TNBS compared to Null TNBS-treated mice. These preliminary results suggest a possible interaction between these pro-fibrotic molecules in the development of intestinal fibrosis.