Protective Role of Sirtuin3 (SIRT3) in Oxidative Stress Mediated by Hepatitis B Virus X Protein Expression

The hepatitis B virus (HBV) infection is accompanied by the induction of oxidative stress, especially mediated by HBV X protein (HBx). Oxidative stress has been implicated in a series of pathological states, such as DNA damage, cell survival and apoptosis. However, the host factor by which cells protect themselves under this oxidative stress is poorly understood. In this study, we first confirmed that HBV infection significantly induced oxidative stress. Moreover, viral protein HBx plays a major role in the oxidative stress induced by HBV. Importantly, we found that mitochondrial protein SIRT3 overexpression could decrease reactive oxygen species (ROS) induced by HBx while SIRT3 knockdown increased HBx-induced ROS. Importantly, SIRT3 overexpression abolished oxidative damage of HBx-expressing cells as evidenced by γH2AX and AP sites measurements. In contrast, SIRT3 knockdown promoted HBx-induced oxidative damage. In addition, we also observed that oxidant H2O2 markedly promoted HBV replication while the antioxidant N-acetyl-L-cysteine (NAC) inhibited HBV replication. Significantly, SIRT3 overexpression inhibited HBV replication by reducing cellular ROS level. Collectively, these data suggest HBx expression induces oxidative stress, which promotes cellular oxidative damage and viral replication during HBV pathogenesis. Mitochondrial protein SIRT3 protected HBx expressing-cells from oxidative damage and inhibited HBV replication possibly by decreased cellular ROS level. These studies shed new light on the physiological significance of SIRT3 on HBx-induced oxidative stress, which can contribute to the liver pathogenesis.