Early activation of transcription factor NF-κB during ischemia in perfused rat heart

Abstract

The transcription factor nuclear factor kappaB (NF-kappaB) regulates multiple immediate-early gene expressions involved in immune and inflammatory responses and cellular defenses. Ischemia-reperfusion induces many immediate-early gene expressions, but little is known about the NF-kappaB activation in myocardium during ischemia and reperfusion. This study demonstrated that ischemia alone rapidly induced NF-kappaB activation in the myocardium of isolated working rat hearts. Electrophoretic mobility shift assay showed that NF-kappaB binding activity significantly increased in the nucleus after 5 min of ischemia and remained elevated for up to 30 min. Western blot analysis suggested that the levels of inhibitory IkappaBalpha protein in the cytoplasm became markedly decreased at 4, 5, 7.5, and 10 min of ischemia but were gradually restored following 10 min of ischemia. Reduction of IkappaBalpha protein in the cytoplasm by ischemia resulted in NF-kappaB translocation to the nucleus. Northern blot hybridization showed that IkappaBalpha mRNA levels were not significantly elevated during myocardial ischemia. Pyrrolidine dithiocarbamate, an antioxidant, significantly inhibited the loss of IkappaBalpha protein from the cytoplasm and prevented NF-kappaB binding activity in the nucleus. Reperfusion following short periods of ischemia augmented NF-kappaB binding activity in the nucleus induced by ischemia. The results suggest that early activation of NF-kappaB induced by ischemia in the myocardium could be a signal mechanism for controlling and regulating immediate-early gene expression during ischemia-reperfusion.