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

Abstract

Abstract Signaling by vascular endothelial growth factors (VEGFs) through VEGF receptors (VEGFRs) plays important roles in vascular development and hematopoiesis. The authors analyzed the function of VEGF-C signaling through both VEGFR-2 and VEGFR-3 in vasculoangiogenesis and hematopoiesis 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 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 completely suppressed 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 severe anemia. Consistent with these in vivo findings, vascular bed formation in the P-Sp from the VEGFR-3–deficient embryos was enhanced to that in wild-type or heterozygous embryos, 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 VEGFR-3–deficient embryos, vascular bed formation was suppressed and hematopoiesis was partially rescued. These results demonstrate that because VEGF-C signaling through VEGFR-2 works synergistically with VEGF-A, the binding of VEGF-C to VEGFR-3 consequently regulates VEGFR-2 signaling. In VEGFR-3–deficient embryos, an excess of VEGF-C signals through VEGFR-2 induced the disturbance of vasculogenesis and hematopoiesis during embryogenesis. This indicates that elaborated control through VEGFR-3 signaling is critical in vasculoangiogenesis and hematopoiesis.