Cerebral ischemia is encompassed by cerebrovascular apoptosis, yet the mechanisms behind apoptosis regulation are not fully understood. We previously demonstrated inhibition of endothelial apoptosis by vascular endothelial growth factor (VEGF) through upregulation of poly(ADP-ribose)-polymerase (PARP) expression. However, PARP overactivation through oxidative stress can lead to necrosis. This study tested the hypothesis that neuropilin-1 (NP-1), an alternative VEGF receptor, regulates the response to cerebral ischemia by modulating PARP expression and, in turn, apoptosis inhibition by VEGF. In endothelial cell culture, NP-1 colocalized with VEGF receptor-2 (VEGFR-2) and acted as its coreceptor. This significantly enhanced VEGF-induced PARP mRNA and protein expression demonstrated by receptor-specific inhibitors and VEGF-A isoforms. NP-1 augmented the inhibitory effect of VEGF/VEGFR-2 interaction on apoptosis induced by adhesion inhibition through the αV-integrin inhibitor cRGDfV. NP-1/VEGFR-2 signal transduction involved JNK and Akt. In rat models of permanent and temporary middle cerebral artery occlusion, the ischemic cerebral hemispheres displayed endothelial and neuronal apoptosis next to increased endothelial NP-1 and VEGFR-2 expression compared to non-ischemic cerebral hemispheres, sham-operated or untreated controls. Increased vascular superoxide dismutase-1 and catalase expression as well as decreased glycogen reserves indicated oxidative stress in the ischemic brain. Of note, protein levels of intact PARP remained stable despite pro-apoptotic conditions through increased PARP mRNA production during cerebral ischemia. In conclusion, NP-1 is upregulated in conditions of imminent cerebrovascular apoptosis to reinforce apoptosis inhibition and modulate VEGF-dependent PARP expression and activation. We propose that NP-1 is a key modulator of VEGF maintaining cerebrovascular integrity during ischemia. Modulating the function of NP-1 to target PARP could help to prevent cellular damage in cerebrovascular disease.
Keywords: %HLV(ec); A7R; Apoptosis; B-cell lymphoma 2 protein; BSA; Bcl-2; Cerebral ischemia; Cerebrovascular disease; EC; GAPDH; HUVEC; IO; IR; ISL assay; MCAO; NF-κB; NP-1; Neuropilin-1; PARP; PAS; Rat middle cerebral artery occlusion model; SOD-1; STATs; SU5416; VEGF; VEGFR-2; Vascular endothelial growth factor; bovine serum albumin; cRGDfV; edema-corrected ischemic lesion volume; endothelial cells; glyceraldehyde-3-phosphate dehydrogenase; human umbilical vein endothelial cells; in situ-ligation assay; ischemia–occlusion model; ischemia–reperfusion model; middle cerebral artery occlusion; neuropilin-1; neuropilin-1 inhibitor [ATWLPPR]; nuclear factor κ-light-chain-enhancer of activated B-cells; periodic acid-Schiff reaction staining; poly(ADP-ribose)-polymerase; signal transducers and activators of transcription; superoxide dismutase-1; tyrosine-kinase inhibitor of vascular endothelial growth factor receptor-2 [3-[(2,4-di-methylpyrrol-5-yl)-methylidene]-indolin-2-one]; vascular endothelial growth factor; vascular endothelial growth factor receptor-2; αV-integrin inhibitor cyclo-[Arg-Gly-Asp-D-Phe-Val].
© 2013.