Activation of the JNK pathway is important for cardiomyocyte death in response to simulated ischemia

Multiple signaling pathways, including the c-Jun N-terminal kinase (JNK) pa thway, are activated in myocardial ischemia and reperfusion (MI/R) and corr elate with cell death. However, the role of the JNK pathway in MI/R-induced cell death is poorly understood. In a rabbit model, we found that ischemia followed by reperfusion resulted in JNK activation which could be detected in cytosol as well as in mitochondria. To address the functional role of t he JNK activation, we examined the consequences of blockade of JNK activati on in isolated cardiomyocytes under conditions of simulated ischemia. The J NK activity was stimulated similar to sixfold by simulated ischemia and rep erfusion (simulated MI). When a dominant negative mutant of JNK kinase-2 (d nJNKK2), an upstream regulator of JNK, and JNK-interacting protein-1 (JIP-1 ) were expressed in myocytes by recombinant adenovirus, the activation of J NK by simulated MI was reduced 53%, Furthermore, the TNF alpha-activated JN K activity in H9c2 cells was completely abolished by dnJNKK2 and JIP-1, In correlation, when dnJNKKS and JIP-1 were expressed in cardiomyocytes, both constructs significantly reduced cell death after simulated MI compared to vector controls. We conclude that activation of the JNK cascade is importan t for cardiomyocyte death in response to simulated ischemia.