Stat3 confers resistance against hypoxia/reoxygenation-induced oxidative injury in hepatocytes through upregulation of Mn-SOD

Background/Aims Hypoxia/reoxygenation (H/R) causes oxidative stress to the cell and induces apoptotic cell death. Signal transducer and activator of transcription-3 (Stat3) is one of the most important molecules involved in the initiation of liver development and regeneration, and has recently been shown to protect cells against various pathogens. In order to investigate the hepatoprotective effects of Stat3, we examined whether it protects against H/R-induced injury in primary hepatocytes. Methods Primary cultured hepatocytes were prepared from SD rats. Adenoviruses and cytokines were added 2 days and 1 h prior to the H/R insult, respectively. Hepatocytes and culture media were harvested for the assays before and after H/R insult. Results Interleukin-6 and cardiotropin-1, which may function mainly through Stat3 activation, protected cells from H/R-induced apoptosis. Adenoviral overexpression of the constitutively activated form of Stat3 (Stat3-C) reduced H/R-induced apoptosis as well as generation of reactive oxygen species (ROS) in hepatocytes. Interestingly, Stat3-C induced Mn-SOD, but not Cu/Zn-SOD, both at the protein and mRNA levels. Overexpression of Mn-SOD significantly reduced H/R-induced ROS and apoptosis by inhibiting redox-sensitive activation of caspase-3 activity. Conclusions Stat3 protects hepatocytes from H/R-induced cell injury at least partly by upregulating Mn-SOD and inactivating caspase-3.