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Abstract
Vascular endothelial growth factor (VEGF) has roles in neurogenesis in addition to angiogenesis. VEGF-B/VEGFR-1 signalling can promote neurogenesis in development and following injury. VEGFR-3 is expressed in developing brain and promotes adult subventricular zone (SVZ) neurogenesis. Hypoxic-ischemic (HI) brain injury and visual dysfunction in newborns carry high mortality and morbidity, requiring novel neuroprotective strategies. Neonatal HI has various phases of injury affecting brain and retina, and therapeutic targets include reducing inflammation and cellular excitation and promoting tissue regeneration.
Fluorescent immunohistochemistry was undertaken using primary antibodies to VEGFR-1-3, VEGF-A-C, and neural stem cell (NSC), neuronal and glial cell markers. A developmental expression profile of VEGFR1-3, VEGF-A-C and cellular associations was examined in embryonic day (E) 13 to postnatal day (P) 23 rat brain and eye tissue. A rat model of neonatal HI brain injury was also used to compare expression profiles in HI injured forebrain and retina to controls. VEGF-C or saline were then administered via intracerebroventricular injection following HI to assess potential neuroprotective effects.
VEGFR-3 expression was high in embryonic ventricular zone (VZ), radial glia, olfactory bulb and optic cup, on NSCs and neuroblasts. Postnatally, VEGFR-3 was decreased on NSCs, but increased on neurons, astrocytes, and oligodendroglia. High expression in choroid plexus and retinal pigment epithelium (RPE) was noted. VEGF-C expression was associated with VEGFR-3 throughout development, highest in embryonic stages.
VEGFR-1 was expressed from E13 in VZ, SVZ and rostral migratory stream on NSCs, and on neurons and astrocytes postnatally. VEGFR-2 expression was lower in immature neurogenic zones, but increased postnatally. VEGF-B, but not VEGF-A, was detected in embryonic VZ. High VEGFR-1 expression was found in retinal ganglion cell layer (GCL), with disruption in after HI. VEGFR-2 expression in GCL was absent in controls but upregulated after P7 HI.
After HI, VEGFR-3 was upregulated in neurogenic regions and the peri-infarct zone on NSCs and astrocytes. VEGF-C treatment enhanced neurogenic and astrocytic responses, and induced choroid plexus proliferation.
These results suggest that VEGF-B/VEGFR-1, and VEGF-C/VEGFR-3 signalling promote neurogenesis in developing retina and forebrain, and support the potential of VEGF-C treatment to enhance endogenous NSC responses after neonatal HI injury.