Subcellular site of superoxide dismutase expression differentially controls AP-1 activity and injury in mouse liver following ischemia/reperfusion

Acute damage following ischemia and reperfusion (I/R) in the liver is in part caused by the generation of reactive oxygen species, such as superoxides, during the reperfusion event. Gene therapy directed at attenuating mitochondrial superoxide production following warm I/R injury in the liver has demonstrated great promise in reducing acute hepatocellular damage. In the present study, we have compared the: therapeutic effects of ectopic expression of mitochondrial (MnSOD) and cytoplasmic (Cu/ZnSOD) superoxide dismutase using recombinant adenoviral vectors for reducing I/R damage in the liver. Consistent with previous observations, recombinant adenoviral delivery of MnSOD to the liver significantly attenuated both acute liver damage and AP-1 activation following I/R injury to the livers of mice. However, ectopic expression of Cu/ZnSOD diminished neither I/R-induced elevations in serum alanine transaminase (ALT) nor AP-1 activation. Interestingly, baseline activation of AP-1 before I/R-induced injury was seen in livers infected with recombinant Ad.Cu/ZnSOD, but not Ad.MnSOD or Ad.LacZ, vectors. The level of Cu/ZnSOD-induced AP-1 activation was significantly reduced by ablation of Kupffer cells or by coexpression of catalase, suggesting that increased H2O2 production facilitated by Cu/ZnSOD in hepatocytes and/or Kupffer cells may be responsible for AP-1 activation. In vitro reconstitution studies using hepatocyte and macrophage cell lines demonstrated that Cu/ZnSOD overexpression induces AP-1 in both cell types, and that secretion of a Cu/ZnSOD-induced macrophage factor is capable of elevating AP-1 in hepatocytes. In summary, our findings demonstrate that subcellular sites of superoxide production in the liver can differentially affect the outcome of I/R injury in the liver and selectively influence AP-1 activation.