Objectives: Although animal studies demonstrated that Smad7 induction ameliorates TGF-β/SMAD-mediated fibrogenesis, its role in human hepatic diseases is rather obscure. Our study explored the activation status of TGF-β/activin pathway in patients with chronic liver diseases, and how it is affected by successful antiviral treatment in chronic HBV hepatitis (CHB).
Methods: Thirty-seven CHB patients (19 with active disease, 14 completely remitted on long-term antiviral treatment and 4 with relapse after treatment withdrawal), 18 patients with chronic HCV hepatitis, 12 with non-alcoholic fatty liver disease (NAFLD), and 3 controls were enrolled in the study. Liver mRNA levels of CTGF, all TGF-β/activin isoforms, their receptors and intracellular mediators (SMADs) were evaluated using qRT-PCR and were correlated with the grade of liver inflammation and fibrosis staging. The expression and localization of pSMAD2 and pSMAD3 were assessed by immunohistochemistry.
Results: TGF-β signalling is activated in CHB patients with active disease, while SMAD7 is up-regulated during the resolution of inflammation after successful treatment. SMAD7 overexpression was also observed in NAFLD patients exhibiting no or minimal fibrosis, despite the activation of TGF-β/activin signaling.
Conclusions: SMAD7 overexpression might represent a mechanism limiting TGF-β-mediated fibrogenesis in human hepatic diseases; therefore, SMAD7 induction likely represents a candidate for novel therapeutic approaches.
Keywords: Chronic HBV hepatitis; Non-alcoholic fatty liver disease; SMAD7; TGF-β signaling.