Transient and sustained oxidative stress differentially activate the JNK1/2 pathway and apoptotic phenotype in H9c2 cells

The aim of this study was to investigate the activation of JNK1/2 signalling pathway and the respective cellular phenotype of H9c2 cardiac myoblasts during two distinct types of oxidative insult. We examined the dose- and time-dependent activation of JNK1/2 pathway by exogenous H2O2, both under transient and sustained stimulation. At 2 h of either sustained or transient treatment, maximal phosphorylation of c-Jun was observed, coincidently with the activation of nuclear JNK1/2; under sustained stress, these phosphorylation levels remained elevated above basal for up to 6 h, whereas under transient stress they declined to basal ones within 4 h of withdrawal. Furthermore, the JNK1/2 selective inhibitor SP600125 abolished the c-jun phosphorylation induced by oxidative stress. Our results using cell viability assays and light microscopy revealed that sustained H2O2 stimulation significantly and time-dependently decreased H9c2 viability, in contrast to transient stimulation; SP600125 (10 microM) abolished cell death induced by sustained as well as cell survival induced by transient oxidative stress. Hoechst staining showed an increase in DNA condensation during sustained, but not during transient stimulation. Moreover, from the antioxidants tested, catalase and superoxide dismutase prevented oxidative stress-induced cell death. Flow cytometry studies reconfirmed that sustained oxidative stress induced apoptosis, whereas transient resulted in the recovery of cardiac myoblasts within 24 h. We conclude that in H9c2 myoblasts, sustained activation of JNK1/2 signalling pathway during oxidative stimulation is followed by an apoptotic phenotype, while transient JNK1/2 activation correlates well with cell survival, suggesting a dual role of this signalling pathway in cell fate determination.