Alpha-smooth muscle actin expression upregulates fibroblast contractile activity

To evaluate whether alpha -smooth muscle actin (alpha -SMA) plays a role in fibroblast contractility, we first compared the contractile activity of rat subcutaneous fibroblasts (SCFs), expressing low levels of alpha -SMA, with that of lung fibroblasts (LFs), expressing high levels of alpha -SMA, with the use of silicone substrates of different stiffness degrees. On medium stiffness substrates the percentage of cells, producing wrinkles was similar to that of alpha -SMA-positive cells in each fibroblast population. On high stiffness substrates, wrinkle production was limited to a subpopulation of LFs very positive for alpha -SMA. In a second approach, we measured the isotonic contraction of SCF- and LF-populated attached collagen lattices. SCFs exhibited 41% diameter reduction compared with 63% by LFs. TGF beta1 increased alpha -SMA expression and lattice contraction by SCFs to the levels of LFs; TGF beta -antagonizing agents reduced alpha -SMA expression and lattice contraction by LFs to the level of SCFs. Finally, 3T3 fibroblasts transiently or permanently transfected with alpha -SMA cDNA exhibited a significantly higher lattice contraction compared with wild-type 3T3 fibroblasts or to fibroblasts transfected. with alpha -cardiac and beta- or gamma -cytoplasmic actin. This took place in the absence of any change in smooth muscle or nonmuscle myosin heavy-chain expression. Our results indicate that an increased alpha -SMA expression is sufficient to enhance fibroblast contractile activity.