Enhanced Fibroblast Contraction of 3D Collagen Lattices and Integrin Expression by TGF-beta1 and -beta3: Mechanoregulatory Growth Factors?

Generation of contractile forces as fibroblasts attach and migrate through collagenous substrates is a fundamental behavior, yet its regulation and consequences are obscure. Although the transforming growth factor-betas (TGF-beta) are similarly important in fibrosis and tissue repair, their role in contraction is controversial. Using a quantitative, 3D collagen culture model we have measured the effects of TGF-beta1 and -beta3 on contractile forces generated by human dermal fibroblasts. Maximal stimulation was between 7.5 and 15 ng/ml of TGF-beta1. Higher doses were inhibitory (30 ng/ml), giving a bell-shaped dose response. The initial rate of force generation was increased sevenfold (15 ng/ml). A similar response pattern was seen with TGF-beta3 alone. However, the addition of both isoforms together stimulated a biphasic increase in force generation, suggesting that there was a distinct temporal cooperativity between the two isforms. This very early onset (10-20 min) of stimulation suggested that TGF-beta might act through cell attachment and integrin function and the effect of TFG-beta on expression of fibronectin (FnR) and vitronectin (VnR) integrin receptors was monitored over the same time scale. TGF-beta1 dramatically up-regulated VnR expression, relative to FnR, over time but the optimal time for this was 2-4 h later than that of force stimulation. It is concluded that TGF-beta1 and -beta3 behave here primarily as mechanoregulatory growth factors and that stimulation of integrin expression may be a consequence of the altered cell stress.