Temporal and spatial expression of neuropilin-1 in focal cerebral ischemic brain
Neuropilin-1 is a receptor for vascular endothelial grow factor 165 isoform (VEGF165) and plays roles in vasculogenesis and angiogenesis. Neuropilin-1 also binds to semaphorin III which is an inhibitor to axon guidance signal. To seek evidence that neuropilin-1 may play roles in ischemic brain, we examined the temporal and spatial profiles of its expression after focal cerebral ischemia. Male Wistar Rats (n=42) were subjected to 1h to 28 days of embolic middle cerebral artery (MCA) occlusion. Expression of neuropilin-1 was measured by Northern blot, in situ hybridization and immunohistochemistry. Upregulation of neuropilin-1 mRNA was detected in the ischemic hemisphere on Northern blots at 2h and persisted at least 28 days after ischemia. In situ hybridization revealed increased mRNA in the ischemic injury neurons around the boundary of the ischemic lesion at 4h to 48h after ischemia. Seven to twenty-eight days after ischemia, neuropilin-1 mRNA was localized to vessels within the ischemic lesion. Immunostaining for neuropilin-1 showed that some of the ischemic neurons were neuropilin-1 immunoreactive at 2h to 4h after ischemia, and cerebral blood vessels within the ischemic lesion were neuropilin-1 immunoreactive at 2 days to 28 days after ischemia. In addition, hypertrophic astrocytes around the boundary of the ischemic lesion were neuropilin-1 immunoreactive at 1 day to 28 days after ischemia. Double immunofluorescent staining for neuropilin-1 and VEGF showed that neuropilin-1 immunoreactive vessels and astrocytes exhibited VEGF immunoreactivity. Thus our data suggest that upregulation of neuropilin-1 may play a role in angiogenesis in ischemic brain.