Vascular endothelial growth factor (VEGF), best known for its role in mediating angiogenesis, also influences various aspects of neuronal function, including acting as a chemoattractant to promote granule cell (GC) migration during cerebellar development. Noting that N-methyl-D-aspartate (NMDA)–type glutamate receptors (NMDARs), like the VEGF receptor Flk1, are found in developing GCs and have been implicated in their migration, Meissirel et al. explored a possible link between these two types of receptors. Calcium imaging revealed that VEGF enhanced the NMDAR-mediated calcium signal in GCs isolated from mice before the development of functional GC synapses, an effect blocked by an antibody directed against Flk1 (αFlk1) or by pharmacological inhibition of its activity. Calcium imaging of human embryonic kidney (HEK) 293 cells heterologously expressing Flk1 with the NMDAR NR1 and NR2B subunits confirmed that VEGF acted through Flk1 to enhance the NMDR-mediated calcium signal, and patch-clamp analysis of cerebellar slices showed that VEGF acted through Flk1 to potentiate NMDAR-mediated inward current in GCs. Flk1 coimmunoprecipitated with NR1 and NR2B from GCs and transfected HEK-293 cells, and VEGF increased the numbers of Flk1 clusters and Flk1-NRB2 co-clusters on the GC surface. VEGF stimulated the activation of GC Src-family tyrosine kinases (SFKs) and increased phosphorylation of NRB2. Mutational analyses of transfected HEK-293 cells indicated that VEGF activated Flk1 to stimulate the SFK-dependent tyrosine phosphorylation of NRB2, and thereby the ability of VEGF to enhance the NMDR-mediated calcium signal, a conclusion confirmed by pharmacological analyses in GCs. GC migration toward VEGF in vitro was blocked by the NMDAR antagonist D-APV (D-2-amino-5-phosphono-valerate), and analyses of the effects of D-APV and αFlk1 on GC migration in cerebellar slices were consistent with Flk1 and NMDAR mediating GC migration through a common pathway. Thus, the authors conclude that VEGF acts through SFKs to enhance NMDAR signaling and thereby promote GC migration.
C. Meissirel, C. Ruiz de Almodovar, E. Knevels, C. Coulon, N. Chounlamountri, I. Segura, P. de Rossi, S. Vinckier, K. Anthonis, B. Deléglise, M. de Mol, C. Ali, K. Dassonville, E. Loyens, J. Honnorat, Y. Michotte, V. Rogemond, I. Smolders, T. Voets, D. Vivien, P. Vanden Berghe, L. Van Den Bosch, W. Robberecht, A. Chédotal, S. Oliviero, M. Dewerchin, D. Schmucker, N. Thomasset, P. Salin, P. Carmeliet, VEGF modulates NMDA receptors activity in cerebellar granule cells through Src-family kinases before synapse formation. Proc. Natl. Acad. Sci. U.S.A. 108, 13782–13787 (2011). [Abstract] [Full Text]