Involvement of TGF-β1/Smad3 Signaling in Carbon Tetrachloride-Induced Acute Liver Injury in Mice

Transforming growth factor-beta1 (TGF-β1) is a major factor in pathogenesis of chronic hepatic injury. Carbon tetrachloride (CCl(4)) is a liver toxicant, and CCl(4)-induced liver injury in mouse is a classical animal model of chemical liver injury. However, it is still unclear whether TGF-β1 is involved in the process of CCl(4)-induced acute chemical liver injury. The present study aimed to evaluate the role of TGF-β1 and its signaling molecule Smad3 in the acute liver injury induce by CCl(4). The results showed that CCl(4) induced acute liver injury in mice effectively confirmed by H&E staining of liver tissues, and levels of not only liver injury markers serum ALT and AST, but also serum TGF-β1 were elevated significantly in CCl(4)-treated mice, compared with the control mice treated with olive oil. Our data further revealed that TGF-β1 levels in hepatic tissue homogenate increased significantly, and type II receptor of TGF-β (TβRII) and signaling molecules Smad2, 3, mRNA expressions and Smad3 and phospho-Smad3 protein levels also increased obviously in livers of CCl(4)-treated mice. To clarify the effect of the elevated TGF-β1/Smad3 signaling on CCl(4)-induced acute liver injury, Smad3 in mouse liver was overexpressed in vivo by tail vein injection of Smad3-expressing plasmids. Upon CCl(4) treatment, Smad3-overexpressing mice showed more severe liver injury identified by H&E staining of liver tissues and higher serum ALT and AST levels. Simultaneously, we found that Smad3-overexpressing mice treated with CCl(4) showed more macrophages and neutrophils infiltration in liver and inflammatory cytokines IL-1β and IL-6 levels increment in serum when compared with those in control mice treated with CCl(4). Moreover, the results showed that the apoptosis of hepatocytes increased significantly, and apoptosis-associated proteins Bax, cytochrome C and the cleaved caspase 3 expressions were up-regulated in CCl(4)-treated Smad3-overexpressing mice as well. These results suggested that TGF-β1/Smad3 signaling was activated during CCl(4)-induced acute liver injury in mice, and Smad3 overexpression aggravated acute liver injury by promoting inflammatory cells infiltration, inflammatory cytokines release and hepatocytes apoptosis. In conclusion, the activation of TGF-β signaling contributes to the CCl(4)-induced acute liver injury. Thus, TGF-β1/Smad3 may serve as a potential target for acute liver injury therapy.