Vascular Endothelial Growth Factor Receptor-2 Inhibition Promotes Cell Death and Limits Endothelial Cell Proliferation in a Neonatal Rodent Model of Stroke

Abstract

Background and Purpose— Recent studies in neonatal rodent stroke models suggest that recovery is due in part to upregulation of hypoxia-inducible factor-1-a and its downstream target, vascular endothelial growth factor. Vascular endothelial growth factor is upregulated after a hypoxic insult and is involved in neuronal survival, angiogenesis, and neurogenesis during the recovery process. Methods— We performed a 1.5-hour transient middle cerebral artery occlusion in 10-day-old rats with injury verified by diffusion-weighted MRI during occlusion to determine the effects of vascular endothelial growth factor receptor-2 (VEGFR2) inhibition on injury, apoptosis, and angiogenesis. Two days after reperfusion, the pups received either the VEGFR inhibitor, SU5416 (10 mg/kg per dose) or vehicle (1% dimethyl sulfoxide) for 3 days. Results— VEGFR2 inhibition worsened injury 7 days after injury when compared with the vehicle-treated and injury-alone groups ( P <0.01). Furthermore, receptor inhibition was associated with increased VEGFR2 expression 5 days after injury ( P <0.05) and increased spectrin cleavage with a shift in favor of the calpain-mediated, caspase-3-independent cleavage ( P <0.01). Increased areas of cleaved caspase-3 staining were seen in treated rats at 7 days ( P <0.01) There were no differences in gliosis or macrophage recruitment as measured by glial fibrillary acidic protein and Iba-1 expression at this time point. Lastly, VEGFR2 inhibition did not affect the overall vessel surface area but reduced endothelial cell proliferation in injured caudate. Conclusions— Inhibition of VEGFR2 signaling worsens injury, affects cell death, and reduces endothelial cell proliferation after neonatal stroke. Injury exacerbation may be in part due to a shift of cell fate from apoptosis to necrosis on the continuum spectrum of cell death as well as effects on angiogenesis in the injured brain.