Angiogenesis induced in vivo by hepatocyte growth factor is mediated by platelet-activating factor synthesis from macrophages

This study shows that the neoangiogenesis induced by hepatocyte growth factor (HGF) was associated with a local synthesis of platelet-activating factor (PAF) and was inhibited by the specific PAF receptor antagonist WEB 2170 in a murine model in which matrigel was injected s.c. as a substratum for angiogenesis. The synthesis of PAF was concomitant with the early migration of endothelial cells and infiltration of MAC-1-positive macrophages. Infiltration of lymphocytes and polymorphonuclear leukocytes was never observed. In vitro studies demonstrated that mouse peritoneal macrophages, but not two murine microvascular endothelial cell lines or human and bovine endothelial cells from large vessels, synthesized PAF after stimulation with HGF. Furthermore, macrophages expressed the transcript of HGF receptor encoded by the MET proto-oncogene and migrated after HGF challenge. The binding of HGF to its receptor was followed by the activation of the receptor tyrosine kinase domain and phosphorylation of the beta subunit. Leukocyte depletion with 5-fluorouracil and anti-MAC-1 Ab added to matrigel prevented the infiltration of macrophages, the synthesis of PAF and the angiogenesis induced by HGF. PAF extracted and purified from mice challenged with HGF induced a rapid angiogenic response, inhibited by WEB 2170. These results suggest that the angiogenic effect of HGF in vivo is mediated, at least in part, by PAF synthesized from macrophages infiltrating the matrigel plug.