Inhibition of the JNK/AP-1 pathway reduces neuronal death and improves behavioral outcome after neonatal hypoxic–ischemic brain injury

Perinatal hypoxic–ischemic (HI) brain damage continues to be a major clinical problem. We investigated the contribution of the MAP kinase c-Jun N-terminal kinase (JNK), to neonatal HI brain damage. JNK regulates several transcriptional (via AP-1 activation) and non-transcriptional processes involved in brain damage such as inflammation and cell death/survival.P7 rats were subjected to HI by unilateral carotid artery occlusion and hypoxia. HI-induced activation of cerebral AP-1 peaked at 3–6 h post-HI. Intraperitoneal administration of the JNK-inhibitor TAT-JBD immediately after HI prevented AP-1 activation. TAT-JBD treatment within 3 h after HI reduced early neuronal damage by ∼30%. JNK/AP-1 inhibition did not reduce HI-induced cytokine/chemokine expression. Analysis of indicators of apoptotic cell death revealed that TAT-JBD markedly reduced the HI-induced increase in active caspase 3. However, the upstream mediators of apoptosis: active caspase 8, cleaved Bid, mitochondrial cytochrome c release and caspase 9 cleavage were not reduced after TAT-JBD. TAT-JBD inhibited the HI-induced increase in Smac/DIABLO, an inhibitor of IAPs that prevent activation of caspase 3. TAT-JBD treatment also reduced cleavage of α-fodrin, indicating that calpain-mediated brain damage was reduced. Neuroprotection by TAT-JBD treatment was long-lasting as gray- and white matter damage was diminished by ∼50% at 14 weeks post-HI concomitantly with marked improvement of sensorimotor behavior and cognitive functioning.In conclusion, JNK inhibition by TAT-JBD treatment reduced neonatal HI brain damage with a therapeutic window of 3 h and long-lasting anatomical and behavioral improvements. We propose that inhibition of mitochondrial Smac/DIABLO release and calpain activation contribute to neuroprotection by TAT-JBD.