Effects of stretch on cell proliferattion of fibroblast and collagen metabolism

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Although dermal fibroblasts receive stretch and relaxation exerted by muscle movement, biological effects of the mechanical force on the cells remains unclear. In the present study to assess effects of stretch and relaxation on cell proliferation and myofibroblast differentiation of dermal fibroblasts, cells were loaded in a biaxial strain device, which was controlled with computer. Cells were subjected to cyclic sigmoidal stretch and relaxation six cycles/min with 10% maximum change. Cell number was increased in strained cells compared with non-strained ones, and transforming growth factor-β1(TGF-β1)showed an additional effect to the strain-induced stimulation of cell proliferation. Immunoblot assay showed that level of α-smooth muscle actin(SMA)expression of cells , either enhanced by TGF-β1 or not, was decreased by cyclic strain. Flow cytometry suggested that all cells, either stimulated with TGF-β1 or not, decrease the SMA expression in response to strain. Immunofluorescence microscopy showed that there were star-like, spreaded cells that were highly positive for SMA and spindle cells that were negative or slightly positive for SMA, and that a ratio of the former cells to the latter ones was decreased in response to the cyclic strain. Conditioned medium form cells subjected to the cyclic strain had no effects on both cell proliferation and SMA expression of non-strained cells, indicating that the strain-induced effects are not medicated through autocrine mechanism. Genistein abolished both the stimulatory effect of strain on cell proliferation and its suppressive effect on SMA expression, whereas staurosporine or pertussistoxin did not. These data indicatethat the strain-induced effects on both cell proliferation and SMA expression are mediated by tyrosine kinase-dependent mechanism.