HIF-1α attenuates neuronal apoptosis by upregulating EPO expression following cerebral ischemia-reperfusion injury in a rat MCAO model

Hypoxia-inducible factor-1α (HIF-1α) is a key transcriptional factor in response to hypoxia and is involved in ischemic stroke. In the present study, the potential for HIF-1α to inhibit neuronal apoptosis through upregulating erythropoietin (EPO) was investigated in a transient middle cerebral artery occlusion (tMCAO) rat stroke model. For this purpose, a recombinant adenovirus expressing HIF-1α was engineered (Ad-HIF-1α). Control adenovirus (Ad group), Ad-HIF-1α (Ad-HIF-1α group) or Ad-HIF-1α in addition to erythropoietin mimetic peptide-9 (EMP9), an EPO-receptor (-R) antagonist (Ad-HIF-1α+EMP9 group), were used for an intracranial injection into rat ischemic penumbra 1 h following MCAO. All rats demonstrated functional improvement following tMCAO, while the improvement rate was faster in rats treated by Ad-HIF-1α compared with all other groups. The EPO-R inhibitor partially reversed the benefits of Ad-HIF-1α. Apoptosis induced by tMCAO was significantly inhibited by Ad-HIF-1α (P<0.05). The expression of HIF-1α, evaluated by immunohistochemistry either in neurons or astrocytes, was upregulated by Ad-HIF-1α. Both EPO mRNA and protein expression were increased by Ad-HIF-1α, however, there was no significant change of EPO-R either on an mRNA level or protein level. Furthermore, EMP9 did not change the EPO expression which was upregulated by Ad-HIF-1α. Activated caspase 3 in neurons was suppressed by Ad-HIF-1α. Activated caspase 3 downregulated by HIF-1α was partially blocked by EMP9. Altogether, the present data demonstrated that HIF-1α attenuates neuronal apoptosis partially through upregulating EPO following cerebral ischemia in rat. Thus, upregulating HIF-1α subsequent to a stroke may be a potential treatment for ischemic stroke.