Transforming growth factor-β1 downregulation of Smad1 gene expression in rat hepatic stellate cells

Smads are intracellular signaling molecules of the transforming growth factor-β (TGF-β) superfamily that play an important role in the activation of hepatic stellate cells (HSCs) and hepatic fibrosis. Excepting the regulation of Smad7, receptor-regulated Smad gene expression is still unclear. We employed rat HSCs to investigate the expression and regulation of the Smad1 gene, which is a bone morphogenetic protein (BMP) receptor-regulated Smad. We found that the expression and phosphorylation of Smad1 are increased during the activation of HSCs. Moreover, TGF-β significantly inhibits Smad1 gene expression in HSCs in a time- and dose-dependent manner. Furthermore, although both TGF-β1 and BMP2 stimulate the activation of HSCs, they have different effects on HSC proliferation. In conclusion, Smad1 expression and phosphorylation are increased during the activation of HSCs and TGF-β1 significantly inhibits the expression of the Smad1 gene.