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


CONCLUSIONS
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.
Gu
Li
L
Department of Pulmonary Medicine, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences, Beijing 100071, China.
Zhu
Yuan-Jue
YJ
Yang
Xiao
X
Guo
Zi-Jian
ZJ
Xu
Wen-Bing
WB
Tian
Xin-Lun
XL
D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D005347:Fibroblasts / Q000502:physiology*; D017930:Genes, Reporter / Q000235:genetics; D006801:Humans; D008168:Lung / Q000166:cytology*; D051379:Mice; D010957:Plasmids / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics* / Q000502:physiology*; D051785:Smad Proteins / Q000235:genetics / Q000502:physiology*; D051900:Smad3 Protein / Q000096:biosynthesis / Q000235:genetics; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000502:physiology*
D051785:Smad Proteins; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta