VEGF-C signaling pathways through VEGFR-2 and VEGFR-3 in vasculoangiogenesis and hematopoiesis

Signaling by vascular endothelial growth factors (VEGFs) through VEGF recep tors (VEGFRs) plays important roles in vascular development and hematopoies is. The authors analyzed the function of VEGF-C signaling through both VEGF R-2 and VEGFR-3 in vasculoangiogenesis and hematopoiesis using a coculture of paraaortic splanchnopleural mesoderm (P-Sp) explants from mouse embryos with stromal cells (OP9), Vasculogenesis and angiogenesis were evaluated by the extent of Vascular bed and network formation, respectively Addition of VEGF-C to the P-Sp culture enhanced vascular bed formation and suppressed definitive hematopoiesis. Both Vascular bed and network formations were com pletely suppressed by addition of soluble VEGFR-1-Fc competitor protein, Fo rmation of vascular beds but not networks could be rescued by VEGF-C in the presence of the competitor, while both were rescued by VEGF-A. VEGFR-3-def icient embryos show the abnormal vasculature and severe anemia, consistent with these in vivo findings, vascular bed formation in the P-Sp from the VE GFR-3-deficient embryos was enhanced to that in wild-type or heterozygous e mbryos, and hematopoiesis was severely suppressed. When VEGFR-3-Fc chimeric protein was added to trap endogenous VEGF-C in the P-Sp culture of the VEG FR-3-deficient embryos, vascular bed formation was suppressed and hematopoi esis was partially rescued. These results demonstrate that because VEGF-C s ignaling through VEGFR-2 works synergistically with VEGF-A, the binding of VEGF-C to VEGFR-3 consequently regulates VEGFR-2 signaling. In VEGFR-3-defi cient embryos, an excess of VEGF-C signals through VEGFR-2 induced the dist urbance of vasculogenesis and hematopoiesis during embryogenesis, This indi cates that elaborated control through VEGFR-3 signaling is critical in vasc uloangiogenesis and hematopoiesis. (C) 2000 by The American Society of Hema tology.