A peptide inhibitor of c-Jun NH2-terminal kinase reduces myocardial ischemia-reperfusion injury and infarct size in vivo

The c-Jun NH2-terminal kinase ( JNK) pathway of the mitogen-activated protein kinase ( MAPK) signaling cascade regulates cell function and survival after stress stimulation. Equally robust studies reported dichotomous results suggesting both protective and detrimental effects of JNK during myocardial ischemia-reperfusion ( I/R). The lack of a highly specific JNK inhibitor contributed to this controversy. We recently developed a cell-penetrating, protease-resistant peptide inhibitor of JNK, D-JNKI-1. Here we report on the effects of D-JNKI-1 in myocardial I/R. D-JNKI-1 was tested in isolated-perfused adult rat hearts. Increased activation of JNK, p38-MAPK, and extracellular signal-regulated kinase-1/2 ( ERK1/2), as assessed by kinase assays and Western blotting, occurred during I/R. D-JNKI-1 delivered before onset of ischemia prevented the increase in JNK activity while not affecting ERK1/2 and p38-MAPK activation. JNK inhibition reduced ischemic injury, as manifested by increased time to contracture ( P < 0.05) and decreased left ventricular end-diastolic pressure during ischemia ( P < 0.01), and enhanced posthypoxic recovery of systolic and diastolic function ( P < 0.01). D-JNKI-1 reduced mitochondrial cytochrome-c release, caspase-3 activation, and the number of apoptotic cells determined by terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling ( P < 0.05), indicating suppression of the mitochondrial machinery of apoptosis. D-JNKI-1 delivered at the time of reperfusion did not improve functional recovery but still prevented apoptosis. In vivo, D-JNKI-1 reduced infarct size after coronary artery occlusion and reperfusion by similar to 50% ( P < 0.01). In conclusion, D-JNKI-1 is an important compound that can be used in preclinical models to investigate the role of JNK signaling in vivo. Inhibition of JNK during I/R is cardioprotective in anesthetized rats in vivo.