VEGF-induced growth cone enhancement is diminished by inhibiting tyrosine-residue 1214 of VEGFR-2

Abstract

Axonal outgrowth is of paramount significance for establishing the intricate neuronal network both during embryogenesis and nerve regeneration. Vascular endothelial growth factor (VEGF), which is known for its essential role in vascular sprouting and its involvement in cancer, has recently been found to exert a trophic activity on neurons leading to an increased axonal outgrowth. Although two receptors, VEGFR-2 and neuropilin-1, were identified on neurons, the signaling pathways associated with them are not well understood. The aim of this study was to analyze the influence of VEGF on the growth cone morphology and motility of dorsal root ganglia (DRG) neurons. Moreover, we aimed for a deeper understanding of VEGFR-2 on growth cones that potentially mediates the stimulating and attractive effects. We cultivated chicken DRG in medium containing mouse VEGF and analyzed growth cone size. The data presented here show a positive effect of VEGF on growth cone size. Furthermore, we interrupted the activity of VEGFR-2 by either blocking the tyrosine residue 1214 (tyr1214) or by inhibiting the receptor phosphorylation with axitinib, a novel small molecule, which has recently entered phase III trials for cancer treatment. Disruption of the VEGFR-2 leads to a significantly diminished growth cone size. Based on these findings, we propose a positive effect of VEGF on peripheral nervous system growth cone size and show for the first time quantitative data to underline this hypothesis. Additionally, we propose that VEGFR-2 and especially the tyr1214-dependent pathway of VEGFR-2 are of importance in VEGF signaling in the growth cone of DRG neurons.