Redox Regulation of NF-κB and AP-1 in Ischemic Reperfused Heart

Abstract

Two redox-sensitive transcription factors, AP-1 and NF-κB, have been implicated in the regulation of apoptosis induced by myocardial ischemia and reperfusion. Hearts adapted to ischemic stress by cyclic episodes of short durations of ischemia and reperfusion attenuate apoptotic cell death. This study was designed to examine the pattern of expression of these transcription factors and the redox sensitive transacting molecule, AP-1, NF-κB, and-Bcl-2, during ischemia/ reperfusion and myocardial adaptation to ischemia. NF-κB binding activity was low in nonischemic control heart. Fifteen minutes of ischemia resulted in translocation of NF-κB from cytosol to nucleus followed by activation. The binding activity of NF-κB was further enhanced after 60 min of ischemia. An even higher degree of NF-κB binding was noticed in the ischemically adapted myocardium. In contrast, AP-1 binding activity was highest for the hearts subjected to 15 min of ischemia followed by 2 hr of reperfusion. AP-1 binding was higher in the ischemically adapted heart as compared to the control. The Bcl-2 gene, which was found to be present in the control hearts, had lowered expression after 15 min of ischemia and 2 hr of reperfusion. Significant upregulation of Bcl-2 mRNA was noticed in the ischemically adapted hearts. Apoptotic cardiomyocytes were found only in the hearts that were reperfused for at least 90 min. No apoptosis occurred in hearts subjected up to 1 hr of ischemia or ischemic adaptation. Prolonged reperfusion, and not ischemia up to 1 hr, can induce cardiomyocyte apoptosis. In concert, ischemic/reperfusion increases the nuclear binding of both AP-1 and NF-κB, but downregulates Bcl-2 gene. Ischemic adaptation attenuates apoptotic cell death, further increases NF-κB binding activity and Bcl-2 gene induction, but reduces AP-1 binding activity. These results suggest that AP-1, NF-κB, and Bcl-2 are differentially regulated by ischemia/reperfusion and ischemic adaptation.