Caspase-3 and the regulation of hypoxic neuronal death by vascular endothelial growth factor

Vascular endothelial growth factor (VEGF) has neurotrophic and neuroprotective as well as angiogenic properties, but the pathways involved in VEGF-mediated neuronal survival have not been identified. We found previously that VEGF protects cultured neural cells from death induced by serum withdrawal or hypoxia via the activation of VEGF-2/fetal liver kinase-1 receptors, phosphatidylinositol 3'-kinase, Akt and nuclear factor-kappa B. We now report that in mouse cortical neuron cultures subjected to hypoxia, the neuroprotective effect of VEGF involves suppression of cell-death pathways mediated by caspase-3. Exposure to hypoxia for 24 h caused the death of 71+/-4% of cultured neurons; this was reduced to 40+/-1% by VEGF (n=3, P<0.005) and to 44+/-1% by the caspase-3 inhibitor benzyloxycarbonyl-DEVD-fluoromethyl ketone (n=3, P<0.005). VEGF inhibited the activation of caspase-3 as measured by the 17-20-kDa caspase-3 cleavage product, and immunolocalization of VEGF and activated caspase-3 showed segregated expression in separate neuronal populations. An antisense, but not sense, oligodeoxyribonucleotide directed against VEGF increased the proportion of neurons expressing activated caspase-3, and correspondingly reduced the viability of hypoxic neurons by 37+/-2% (n=3, P<0.005). These findings suggest that VEGF protects neurons from hypoxic injury by inhibiting the activation of caspase-3, and could therefore act as an endogenous neuroprotective factor in cerebral ischemia.