Smad3 mediates TGF-β1-induced collagen gel contraction by human lung fibroblasts

Transforming growth factor-β1 (TGF-β1) is a key mediator in tissue repair and fibrosis. Using small interference RNA (siRNA), the role of Smad2 and Smad3 in TGF-β stimulation of human lung fibroblast contraction of collagenous matrix and induction of α-SMA and the role of α-SMA in contraction were assessed. HFL-1 cells were transfected with Smad2, Smad3 or control-siRNA, and cultured in floating Type I collagen gels ±−TGF-β1. TGF-β1 augmented gel contraction in Smad2-siRNA- and control-siRNA-treated cells, but had no effect in Smad3-siRNA-treated cells. Similarly, TGF-β1 upregulated α-SMA in Smad2-siRNA- and control-siRNA-treated cells, but had no effect on Smad3-siRNA-treated cells. α-SMA-siRNA-treated cells did not contact the collagen gels with or without TGF-β1, suggesting α-SMA is required for gel contraction. Thus, Smad3 mediates TGF-β1-induced contraction and α-SMA induction in human lung fibroblasts. Smad3, therefore, could be a target for blocking contraction of human fibrotic tissue induced by TGF-β1.