Hypoxia-inducible factor 1 contributes to N-acetylcysteine's protection in stroke

Stroke is a leading cause of adult morbidity and mortality with very limited treatment options. Evidence from preclinical models of ischemic stroke has demonstrated that the antioxidant N-acetylcysteine (NAC) effectively protects the brain from ischemic injury. Here, we evaluated a new pathway through which NAC exerted its neuroprotection in a transient cerebral ischemia animal model. Our results demonstrated that pretreatment with NAC increased protein levels of hypoxia-inducible factor-1α (HIF-1α), the regulatable subunit of HIF-1, and its target proteins erythropoietin (EPO) and glucose transporter (GLUT)-3, in the ipsilateral hemispheres of rodents subjected to 90 min middle cerebral artery occlusion (MCAO) and 24 h reperfusion. Interestingly, after NAC pretreatment and stroke, the contralateral hemisphere also demonstrated increased levels of HIF-1α, EPO, and GLUT-3, but to a lesser extent. Suppressing HIF-1 activity with two widely used pharmacological inhibitors, YC-1 and 2ME2, and specific knockout of neuronal HIF-1α abolished NAC's neuroprotective effects. The results also showed that YC-1 and 2ME2 massively enlarged infarcts, indicating that their toxic effect was larger than just abolishing NAC's neuroprotective effects. Furthermore, we determined the mechanism of NAC-mediated HIF-1α induction. We observed that NAC pretreatment upregulated heat-shock protein 90 (Hsp90) expression and increased the interaction of Hsp90 with HIF-1α in ischemic brains. The enhanced association of Hsp90 with HIF-1α increased HIF-1α stability. Moreover, Hsp90 inhibition attenuated NAC-induced HIF-1α protein accumulation and diminished NAC-induced neuroprotection in the MCAO model. These results strongly indicate that HIF-1 plays an important role in NAC-mediated neuroprotection and provide a new molecular mechanism involved in the antioxidant's neuroprotection in ischemic stroke.