During vein graft adaptation to the arterial circulation, vascular endothelial growth factor (VEGF) A expression transiently increases before becoming downregulated; however, the role of VEGF-A in venous remodeling is not clear. In addition, although VEGF-A stimulates angiogenesis and determines arterial identity in nascent arterial endothelial cells (EC), the role of VEGF-A in regulating identity in adult venous EC is also not clear.EC, wild type (EphB4+/+) or heterozygous knockout (EphB4+/-), were stimulated with VEGF-A (0-100 ng/mL) and examined with quantitative polymerase chain reaction and western blotting.VEGF-A (100 ng/mL) inhibited expression of EphB4 and stimulated expression of delta-like ligand 4 (dll4) but did not stimulate either notch or EphrinB2 expression in adult venous EC. Pretreatment with VEGF receptor 2-neutralizing antibody abolished VEGF-stimulated downregulation of EphB4 but not the upregulation of dll4. Pretreatment with PD98059 or wortmannin showed that VEGF-A downregulation of EphB4 and upregulation of dll4 are mitogen-activated protein kinase kinase and extracellular signal-regulated kinase dependent but phosphatidylinositol 3 kinase-Akt independent. Compared with VEGF-induced EphB4 downregulation and dll4 upregulation in control EC, reduced EphB4 signaling in EphB4+/- EC showed even further downregulation of EphB4 and upregulation of dll4.Despite the genetic programming of arterial and venous EC fate, VEGF-A can repress venous identity in adult venous EC without induction of arterial identity. These changes in adult EC in vitro recapitulate the changes in identity described during vein graft adaptation to the arterial environment in vivo.