Effect of the protease inhibitor MG132 on the transforming growth factor-β/Smad signaling pathway in HSC-T6 cells.

The activation of hepatic stellate cells (HSCs) and their transformation to myofibroblasts are the key steps in the pathological progress of liver fibrosis. The transforming growth factor-β (TGFβ)/Smad pathway is involved in the proliferation and collagen synthesis of HSCs. This study aimed to examine the effect of the protease inhibitor MG132 on the signaling pathway of TGFβ/Smad in HSC-T6 cells and seek a novel therapeutic approach for liver fibrosis. The HSC-T6 cells were treated with MG132 at different concentrations (0-10 μmol/L). Cell proliferation was detected by MTT method. The mRNA and protein expression levels of TGFβ1, Smad3 and Smad7 were determined in HSC-T6 cells by real-time PCR and Western blotting, respectively, after treatment with MG132 at different concentrations (1, 2, 3 μmol/L) or RPMI1640 alone (serving as control). The results showed that MG132 could inhibit the proliferation of HSC-T6 cells in a dose-dependent manner, and the IC(50) of MG132 was 6.84 μmol/L. After treatment with MG132 at 1, 2 or 3 μmol/L for 24 h, the mRNA expression levels of TGF-β1 and Smad3 were significantly decreased (P<0.05), but the Smad7 mRNA expression had no significant change (P>0.05). There was also a significant decrease in the protein expression level of TGF-β1 and Smad3 (P<0.05). However, the expression of Smad7 protein was substantially increased when compared with the control group (P<0.05). It was concluded that the inhibition of TGFβ/Smad pathway in HSC-T6 cells by MG132 can reduce the production of profibrosis factors (TGFβ1, Smad3) and promote the expression of anti-fibrosis factor (Smad7), suggesting that MG132 may become a potential therapeutic alternative for liver fibrosis.