in vasculoangiogenesis and hematopoiesis

Signaling by vascular endothelial growth factors (VEGFs) through VEGF receptors (VEGFRs) plays important roles in vascu-lar development and hematopoiesis. The authors analyzed the function of VEGF-C signaling through both VEGFR-2 and VEGFR-3 in vasculoangiogenesis and he-matopoiesis using a coculture of para-aortic splanchnopleural mesoderm (P-Sp) explants from mouse embryos with stromal cells (OP9). Vasculogenesis and angiogenesis were evaluated by the ex-tent of vascular bed and network forma-tion, respectively. Addition of VEGF-C to the P-Sp culture enhanced vascular bed formation and suppressed definitive he-matopoiesis. Both vascular bed and net-work formations were completely sup-pressed by addition of soluble VEGFR-1–Fc competitor protein. Formation 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–deficient embryos show the abnormal vasculature and se-vere anemia. Consistent with these in vivo findings, vascular bed formation in the P-Sp from the VEGFR-3–deficient em-bryos was enhanced to that in wild-type or heterozygous embryos, and hemato-poiesis was severely suppressed. When VEGFR-3–Fc chimeric protein was added to trap endogenous VEGF-C in the P-Sp culture of the VEGFR-3–deficient em-bryos, vascular bed formation was sup-pressed and hematopoiesis was par-tially rescued. These results demonstrate that because VEGF-C signaling through VEGFR-2workssynergisticallywithVEGF-A, the binding of VEGF-C to VEGFR-3 conse-quently regulates VEGFR-2 signaling. In VEGFR-3–deficient embryos, an excess of VEGF-C signals through VEGFR-2 in-duced the disturbance of vasculogenesis and hematopoiesis during embryogen-esis. This indicates that elaborated con-trol through VEGFR-3 signaling is critical in vasculoangiogenesis and hematopoi-esis. (Blood. 2000;96:3793-3800) © 2000 by The American Society of Hematolog