Platelet-activating factor directly stimulates in vitro migration of endothelial cells and promotes in vivo angiogenesis by a heparin-dependent mechanism.

The aim of the present study was to investigate the angiogenic properties of platelet-activating factor (PAF). In vitro PAF was shown to induce a dose-dependent migration of human endothelial cells (EC) across the polycarbonate filters in Boyden's chambers. In contrast, D-PAF, the biologically inactive enantiomer, and Lyso-PAF did not stimulate a significant migration of EC. This effect of PAF was not associated with a proliferative response of EC to this mediator. Moreover, the ability of PAF to stimulate the migration of EC was independent of the presence of heparin in the medium. WEB 2170, a specific PAF receptor antagonist, prevented the migration of EC induced by PAF, thus suggesting a receptor-dependent stimulation. The expression of PAF receptor gene by EC was confirmed by reverse transcriptase-PCR and Southern blot analysis. The in vivo angiogenic effect of PAF was studied in mice using a model in which Matrigel was used for the delivery of mediators. PAF induced a dose-dependent angiogenic response, which at pharmacologic concentrations (1-5 mu M) did not require heparin, but at physiologic concentrations (5-50 nM) required the presence of heparin at doses that were not angiogenic per se. The angiogenesis induced by 50 nM PAF was, indeed, inhibited both by protamine and by the PAF receptor antagonist WEB 2170. The angiogenic effect of D-PAF and Lyso-PAF was not significant. Neutralizing Abs to basic fibroblast growth factor induced a slight but not statistically significant reduction of the angiogenesis induced by PAF.