Angiopoietin-1 (Ang1) and -2 (Ang2) are endothelial growth factors that bind to the tyrosine kinase receptor Tie2 and contribute to orchestrate blood vessel formation during angiogenesis. Ang1 mediates vessel maturation and integrity by the recruitment of pericytes. In contrast, Ang2 is classically considered as a Tie2 antagonist, counteracting the stabilizing action of Ang1. Inflammation exists in a mutually dependent association with angiogenesis and we have therefore studied the capacity of angiopoietins to modulate proinflammatory activities, namely Pselectin translocation and neutrophil adhesion onto endothelial cells. We observed that both Ang1 and Ang2 increased these biologic activities. Furthermore, combination of Ang1/Ang2 induced an additive effect on neutrophil adhesion but not on P-selectin translocation. In an attempt to clarify this phenomenon, we found that angiopoietins can directly activate neutrophils through

The acute increase in vascular permeability produced by vascular endothelial growth factor (VEGF-A165) requires activation of endothelial Flk-1 receptors (VEGFR-2) and stimulation of platelet-activating factor (PAF) synthesis. Like PAF, VEGF-A165 promotes translocation of P-selectin to the endothelial cell (EC) surface. However, the mechanisms involved remain unknown. By treating human umbilical vein endothelial cells (HUVECs) with VEGF analogs, we show that activation of VEGFR-1 or VEGFR-2 or both induced a rapid and transient translocation of endothelial P-selectin and neutrophil adhesion to activated ECs. The effects mediated by VEGF-A165 and VEGF-A121 (VEGFR-1/VEGFR-2 agonists) were blocked by a selective VEGFR-2 inhibitor, SU1498. VEGF-A165 was twice as potent as VEGF-A121, which can be explained by the binding capacity of VEGF-A165 to its coreceptor neuropilin-1 (NRP-1). Indeed, treatment with NRP-1 antagonist (GST-Ex7) reduced the effect of VEGF-A165 to the levels observed upon stimulation with VEGF-A121. Finally, the use of selective PAF receptor antagonists reduced VEGF-A165–mediated P-selectin translocation. Together, these data show that maximal P-selectin translocation and subsequent neutrophil adhesion was mediated by VEGF-A165 on the activation of VEGFR-2/NRP-1 complex and required PAF synthesis.