Persistence of TGF-β1 induction of increased fibroblast contractility

Fibroblast contraction of collagen gels is regarded as a model of wound contraction. Transforming growth factor “TGF”-β added to such gels can augment contraction consistent with its suggested role as a mediator of fibrotic repair. Since fibroblasts isolated from fibrotic tissues have been suggested to express a "fibrotic phenotype," we hypothesized that TGF-β exposure may lead to a persistent increase in fibroblasts' contractility. To evaluate this question, confluent human fetal lung fibroblasts were treated with serum-free Dulbecco modified Eagle medium “DMEM”, with or without 100 nM TGF-β1, TGF-β2, or TGF-β3 for 48 h. Fibroblasts were then trypsinized and cast into gels composed of native type I collagen isolated from rat tail tendons. After 20 min for gelation, the gels were released and maintained in serum-free DMEM. TGF-β-pretreated fibroblasts caused significantly more rapid gel contraction “52.5 ± 0.6, 50.9 ± 0.2, and 50.3 ± 0.5% by TGF-β1, -β2, and -β3 pretreated fibroblasts, respectively” than control fibroblasts “74.0 ± 0.3%, P < 0.01”. This effect is concentration dependent “50-200 nM”, and all three isoforms had equal activity. The effect of TGF-β1, however, persisted for only a short period of time following the removal of TGF-β, and was lost with sequential passage. These observations suggest that the persistent increase in collagen-gel contractility, mediated by fibroblasts from fibrotic tissues, would not appear to be solely due to previous exposure of these cells to TGF-β.