Effect of TGF-beta/Smad signaling pathway on lung myofibroblast differentiation

Acta Pharmacol Sin. 2007 Mar;28(3):382-91. doi: 10.1111/j.1745-7254.2007.00468.x.


Aim: Myofibroblasts play important roles in the pathogenesis of lung fibrosis. Transforming growth factor (TGF)-beta 1 has been widely recognized as a key fibrogenic cytokine. The major signaling pathway of (TGF)-beta(1) is through cytoplasmic Smad proteins. Our study investigated the role of individual (TGF)-beta(1)/Smad signal proteins in mediating alpha-smooth muscle actin (alpha-SMA) gene expression, which is a well-known key marker of myofibroblast differentiation.

Methods: We transiently cotransfected alpha-SMA promoter-luciferase fusion plasmid (p895-Luc) and Smad expression plasmids and measured Luc activity in (TGF)-beta(1)-treated human fetal lung fibroblasts. We induced Smad3 knockout mice lung fibrosis by bleomycin. alpha-SMA protein expression was assessed by Western blotting. Collagen protein was analyzed by measuring hydroxyprolin. Myofibroblast morphology was assessed by immunohistochemistry.

Results: We found that the overexpression of Smad3, not Smad2 markedly increased (TGF)-beta(1)-induced alpha-SMA promoter activity and alpha-SMA protein expression in vitro, whereas the overexpression of dominant negative mutant Smad3 and Smad7 repressed (TGF)-beta(1)-induced alpha-SMA gene expression. Compared to wild-type mice, Smad3 knockout mice showed attenuated lung fibrosis after bleomycin treatment, manifested by lower collagen production and myofibroblast differentiation.

Conclusion: Our study suggested (TGF)-beta(1)/Smad3 is a major pathway which regulated the myofibroblast differentiation. This result indicates a potential significance for future attempts of attenuating the progression of human lung fibrosis by the inhibition of the Smad3 cascade.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Differentiation / physiology*
  • Fibroblasts / physiology*
  • Genes, Reporter / genetics
  • Humans
  • Lung / cytology*
  • Mice
  • Plasmids / genetics
  • Signal Transduction / genetics*
  • Signal Transduction / physiology*
  • Smad Proteins / genetics
  • Smad Proteins / physiology*
  • Smad3 Protein / biosynthesis
  • Smad3 Protein / genetics
  • Transfection
  • Transforming Growth Factor beta / genetics
  • Transforming Growth Factor beta / physiology*


  • Smad Proteins
  • Smad3 Protein
  • Transforming Growth Factor beta