Activation of AMPK/MnSOD signaling mediates anti-apoptotic effect of hepatitis B virus in hepatoma cells

AIM: To investigate the anti-apoptotic capability of the hepatitis B virus(HBV) in the HepG2 hepatoma cell line and the underlying mechanisms.METHODS: Cell viability and apoptosis were measured by MTT assay and flow cytometry, respectively. Targeted knockdown of manganese superoxide dismutase(Mn SOD), AMP-activated protein kinase(AMPK) and hepatitis B virus X protein(HBx) genes as well as AMPK agonist AICAR and antagonist compound C were employed to determine the correlations of expression of these genes.RESULTS: HBV markedly protected the hepatoma cells from growth suppression and cell death in the condition of serum deprivation. A decrease of superoxide anion production accompanied with an increase of Mn SOD expression and activity was found in Hep G2.215 cells. Moreover, AMPK activation contributed to the up-regulation of Mn SOD. HBx protein was identified to induce the expression of AMPK and Mn SOD. CONCLUSION: Our results suggest that HBV suppresses mitochondrial superoxide level and exerts an antiapoptotic effect by activating AMPK/Mn SOD signaling pathway, which may provide a novel pharmacological strategy to prevent HCC.

Role of activin A in carbon tetrachloride-induced acute liver injury

AIM: To investigate the expression and role of activin A in a mouse model of acute chemical liver injury. METHODS: Acute liver injury in C57BL/6 male mice was induced by intraperitoneal injection with carbon tetrachloride (CCl4 ) (0.5 mL/kg, body weight) dissolved in olive oil (1:19 v/v). Mice were sacrificed 1, 3, 5 and 7 d after the treatment. The levels of alanine aminotrans-ferase (ALT) and aspartate aminotransferase (AST) in serum were examined and pathological changes of liver observed by hematoxylin and eosin staining to evaluate the liver injury. Activin A protein levels in serum and hepatic tissue homogenate of mice were detected by enzyme-linked immunosorbent assay, and the expres-sion pattern of activin A protein in livers of mice was examined by immunohistochemistry. Activin type Ⅱ A receptor (ActRⅡA) and Smad3 expressions in the liver were analyzed by real-time quantitative reverse transcription-polymerase chain reaction. In order to further investigate the role of activin A, we also utilized activin A blocking experiment by anti-activin A antibody (500 μg/kg, body weight) injection into mouse tail vein. RESULTS: In CCl4-treated mice, serum ALT and AST levels were significantly increased, compared with that in control mice (P<0.01). Furthermore, the serious necrosis was observed around hepatic portal areas in CCl4-treated mice. Simultaneously, activin A levels in serum and hepatic tissue homogenate of mice treated with CCl4 for 1, 3 and 5 d increased significantly, com-pared with that in control mice (P<0.01). Activin A protein expression in hepatocytes not within the ne-crotic area was also upregulated in mice following CCl4 treatment. Not only activin A, but also ActRⅡA and activin signaling molecule Smad3 mRNA expressions in injury liver induced by CCl4 were significantly higher than that in control liver. In addition, levels of serum ALT and AST in CCl4-treated mice were significantly decreased by injection of anti-activin A antibody to block endogenous activin A action, compared with that in CCl4-treated mice by injection of immunoglobulin G instead of anti-activin A antibody (P<0.01), and the severity of liver injury was also reduced remarkably. CONCLUSION: These data show that activin A is in-volved in CCl4-induced acute liver injury. Blocking ac-tivin A actions may be a therapeutic approach for acute liver injury.