Neurodegeneration, Neuroprotection, and Disease-Oriented NeuroscienceResearch PaperI.c.v administration of an endothelin ETB receptor agonist stimulates vascular endothelial growth factor-A production and activates vascular endothelial growth factor recep

Vascular endothelial growth factors (VEGFs), a family of angiogenic factors, are upregulated by nerve injuries. To clarify the extracellular signals involved in VEGF production in the brain, the effects of endothelins (ETs), a family of vasoconstricting peptides, were examined. I.c.v. administration of 500 pmol/d Ala1,3,11,15-ET-1, an ETB receptor agonist, increased the level of VEGF-A mRNA in the rat cerebrum, whereas those of VEGF-B, placental growth factor (PLGF), angiopoietin (ANG)-1, and ANG-2 mRNAs were not largely affected by Ala1,3,11,15-ET. The ET-induced increases in cerebrum VEGF-A mRNA were reduced by coadministration of 1 nmol/d BQ788, an ETB antagonist. Ala1,3,11,15-ET-1 also stimulated the production of VEGF-A proteins in the cerebrum. Immunohistochemical observations in the cerebrum of Ala1,3,11,15-ET-1-infused rats showed that glial fibrillary acidic protein (GFAP)-positive astrocytes had VEGF-A immunoreactivity. Neurons, microglia, and brain capillary endothelial cells in the Ala1,3,11,15-ET-1-infused rats did not show VEGF-A reactivity. The i.c.v. administration of Ala1,3,11,15-ET-1 stimulated tyrosine phosphorylations of VEGF-R1 and R2 receptors in the rat cerebrum, whereas expression levels of total VEGF-R1 and R2 proteins were not largely changed. Immunoreactivity of tyrosine-phosphorylated VEGF-R1 was selectively shown in GFAP-positive astrocytes in the cerebrum of Ala1,3,11,15-ET-1-infused rats. Tyrosine-phosphorylated VEGF-R2 proteins were present in astrocytes and brain capillary endothelial cells. These findings indicate that activation of brain ETB receptors increases production of VEGF-A and stimulates VEGF receptor signaling in the brain.

▶Roles of endothelin (ET) receptors on brain VEGF signals were examined. ▶I.c.v. administration of Ala1,3,11,15-ET-1 increased production of VEGF-A. ▶Tyrosine phosphorylations of VEGF receptors were induced by Ala1,3,11,15-ET-1. ▶Histological observations showed that astrocytes had VEGF-A and phosphorylated VEGF receptors.