Human erythropoietin induces a pro-angiogenic phenotype in cultured endothelial cells and stimulates neovascularization in vivo

Hematopoietic and endothelial cell lineages share common progenitors. Accor dingly, cytokines formerly thought to be specific for the hematopoietic sys tem have been shown to affect several functions in endothelial cells, inclu ding angiogenesis. In this study, we investigated the angiogenic potential of erythropoietin (Epo), the main hormone regulating proliferation, differe ntiation, and survival of erythroid cells. Epo receptors (EpoRs) have been identified in the human EA.hy926 endothelial cell line by Western blot anal ysis. Also, recombinant human Epo (rHuEpo) stimulates Janus Kinase-2 (JAK-2 ) phosphorylation, cell proliferation, and matrix metalloproteinase-2 (MMP- 2) production in EA.hy926 cells and significantly enhances their differenti ation into vascular structures when seeded on Matrigel. In vivo, rHuEpo ind uces a potent angiogenic response in the chick embryo chorioallantoic membr ane (CAM). Accordingly, endothelial cells of the CAM vasculature express Ep oRs, as shown by immunostaining with an anti-EpoR antibody. The angiogenic response of CAM blood vessels to rHuEpo was comparable to that elicited by the prototypic angiogenic cytokine basic fibroblast growth factor (FGF2), i t occurred in the absence of a significant mononuclear cell infiltrate, and it was not mimicked by endothelin-1 (ET-1) treatment. Taken together, thes e data demonstrate the ability of Epo to interact directly with endothelial cells and to elicit an angiogenic response in vitro and in vivo and thus a ct as a bona fide direct angiogenic factor. (C) 1999 by The American Societ y of Hematology.