Angiopoietin‐1 but not angiopoietin‐2 promotes neutrophil viability: Role of interleukin‐8 and platelet‐activating factor

Abstract

We reported that the angiopoietins (Ang1 and Ang2) induce platelet activating factor (PAF) synthesis from endothelial cells and neutrophils. Since PAF can promote neutrophil viability, we addressed whether Ang1 and/or Ang2 could modulate neutrophil survival. Viability was assessed by flow cytometry using apoptotic and necrotic markers. Basal neutrophil viability from 0 to 24 hours post‐isolation decreased from 98% to ≈50%. Treatment with pro‐survival mediators such as interleukin‐8 (IL‐8; 25 nM) and PAF (100 nM) increased neutrophil viability by 22 and 35% (raising it from 56 to 69 and 76%) respectively. Treatment with Ang1 (0.001– 10 nM) increased neutrophil viability by up to 40%, while Ang2 had no effect. Combination of IL‐8 or PAF with Ang1 (10 nM) further increased neutrophil viability by 44 and 67% respectively. We also observed that Ang1, but not Ang2, can promote IL‐8 release and that a pretreatment of the neutrophils with blocking anti‐IL‐8 antibodies inhibited the pro‐survival effect of IL‐8 and Ang1 by 82 and 66% respectively. Pretreatment with a PAF receptor antagonist did abrogate PAF pro‐survival activity, without affecting Ang1‐induced neutrophil viability. Our data are the first one to report Ang1 pro‐survival activity on neutrophils, which is mainly driven through IL‐8 release. This work was supported by the Canadian Institutes of Health Research and the Heart and Stroke Foundation of Quebec.