Objective: To investigate the role of TGF-beta1 and STAT3 signaling in liver fibrosis using a rat model system and to determine the therapeutic mechanism of AG490 in relation to this signaling pathway.
Methods: Rats were randomly divided into a control group and DENA-induced liver fibrosis model group, and then subdivided into AG490 treatment groups. During fibrosis development, liver tissue samples were collected at different time points (0, 4 and 8 weeks) and evaluated according to the Scheuer scoring system. Expression of STAT3, TGFbeta1, alpha-SMA, E-cadherin, MMP2 and TIMP1 was measured by PCR (mRNA) and immunohistochemistry and western blotting (protein).
Results: Increasing degrees of inflammation and fibrosis were observed in liver tissues of DENA-treated rats throughout model establishment. The mRNA expression of TGFbeta1 and STAT3 was significantly increased in DENA-induced rats with advanced fibrosis (AF) compared to those with early fibrosis (EF) (P = 0.034 and P = 0.012 respectively). The protein expression of TGF-beta1, phospho-Smad2, alpha-SMA, E-cadherin, STAT3 and phospho-STAT3 was significantly increased in DENA-induced rats with AF compared to the unmodeled control group (P = 0.048, P = 0.003, P = 0.002, P = 0.028, P = 0.009 and P = 0.039). The protein expression of E-cadherin was lower in the DENA-induced rats with AF than in those with EF (P = 0.026). STAT3 and TGF-beta1 co-expression was detected in AF tissues. DENA-induced AG490-treated rats with AF showed substantially lower protein expression of STAT3, TGF-beta1, MMP2 and TIMP1 compared to DENA-induced untreated rats with AF (P = 0.006, P = 0.018, P = 0.010 and P = 0.005); in addition, the degrees of fibrosis and inflammation were also greatly reduced in the DENA-induced AG490-treated rats with AF compared to DENA-induced untreated rats with AF (P = 0.042 and P = 0.021). Conclusions STAT3 signal transduction may regulate the TGF-beta1 pathway and affect liver fibrosis, especially in the advanced phase. AG490 can inhibit TGFbeta1-STAT3 signaling, resulting in reversal of liver fibrosis.