Effect of cyclic stretching and TGF-beta on the SMAD pathway in fibroblasts

Tissue engineering requires the response of the cells to different stimuli inducing the synthesis of the extracellular matrix (ECM). It was been shown that mechanical and biochemical stimuli acted on the synthesis of ECM, particularly type I and III collagens. Growth factors implied in transduction pathways are multiple, but the main is TGF-beta. Member of the transforming growth factor-beta (TGF-beta) family bind to type II and type I serine/threonine kinase receptors, which initiate intracellular signals through activation of SMADs proteins. Nevertheless, the effects of mechanical stress of this pathway remain unknown. The aim of this work was to study the pathway of TGF-beta via the SMADs proteins under mechanical (stretching) and biochemical (TGF-beta) stimulations. Endogenous SMADs expression and its modulation by biochemical and mechanical stimulations were evaluated by both flow cytometry and confocal microscopy. Our results demonstrate that 10 ng of TGF-beta and stretching (5%, 1 Hz) applied during 15 min induced a negative feed back loop which blocks the signalling pathway to control TGF-beta activity. This inhibition effect was raised after 1 h of stimulation. Nevertheless, these preliminary studies should be continued by study of expression and localization of inhibitory SMADs (SMAD7).