Induction of vascular endothelial growth factor and hypoxia-inducible factor-1α by global ischemia in rat brain

Abstract

Vascular endothelial growth factor is an angiogenic and neurotrophic peptide whose expression is transcriptionally induced in hypoxic tissues through the action of hypoxia-inducible factor-1α. To determine if this signaling pathway is activated in the ischemic brain, and might therefore participate in adaptive processes such as angiogenesis and neuroprotection, we examined the expression of vascular endothelial growth factor and hypoxia-inducible factor-1α in cerebral cortex and hippocampus following transient global cerebral ischemia in the rat. Northern analysis showed ischemia-inducible expression of multiple vascular endothelial growth factor messenger ribonucleic acid splice variants between 4 and 24 h. Western analysis and immunocytochemistry demonstrated the concerted induction of vascular endothelial growth factor and hypoxia-inducible factor-1α in the same, apparently neuronal, cells in vulnerable regions of cortex and hippocampus after 15 min of ischemia, which persisted for as long as 4 to 72 h of reperfusion. These findings demonstrate that hypoxia-sensitive vascular endothelial growth factor signaling can be induced in neurons in global cerebral ischemia in vivo, and are consistent with the hypothesis that ischemic insults trigger hypoxia-sensing and adaptive downstream molecular responses in central neurons.