Hepatic Deletion of Smad7 in Mouse Leads to Spontaneous Liver Dysfunction and Aggravates Alcoholic Liver Injury

BACKGROUND: TGF-β has been known to play an important role in various liver diseases including fibrosis and alcohol-induced fatty liver. Smad7 is an intracellular negative regulator of TGF-β signaling. It is currently unclear whether endogenous Smad7 has an effect on liver function and alcoholic liver damage. METHODOLOGY/PRINCIPAL FINDINGS: We used Cre/loxP system by crossing Alb-Cre mice with Smad7(loxP/loxP) mice to generate liver-specific deletion of Smad7 with loss of the indispensable MH2 domain. Alcoholic liver injury was achieved by feeding mice with a liquid diet containing 5% ethanol for 6 weeks, followed by a single dose of ethanol gavage. Deletion of Smad7 in the liver was associated with increased Smad2/3 phosphorylation in the liver or upon TGF-β treatment in primary hepatocytes. The majority of mice with liver specific deletion of Smad7 (Smad7(liver-KO)) were viable and phenotypically normal, accompanied by only slight or no reduction of Smad7 expression in the liver. However, about 30% of Smad7(liver-KO) mice with high efficiency of Smad7 deletion had spontaneous liver dysfunction, demonstrated as low body weight, overall deterioration, and increased serum levels of AST and ALT. Degeneration and elevated apoptosis of liver cells were observed with these mice. TGF-β-induced epithelial to mesenchymal transition (EMT) was accelerated in Smad7-deleted primary hepatocytes. In addition, alcohol-induced liver injury and steatosis were profoundly aggravated in Smad7 deficient mice, associated with upregulation of critical genes involved in lipogenesis and inflammation. Furthermore, alcohol-induced ADH1 expression was significantly abrogated by Smad7 deletion in hepatocytes. CONCLUSION/SIGNIFICANCE: In this study, we provided in vivo evidence revealing that endogenous Smad7 plays an important role in liver function and alcohol-induced liver injury.