VEGFR1 stimulates a CXCR4-dependent translocation of megakaryocytes to the vascular niche, enhancing platelet production in mice

Abstract

It has previously been reported that VEGF-A stimulates megakaryocyte (MK) maturation in vitro. Here we show that treatment of mice with the isoform VEGF-A165 resulted in a significant increase in circulating numbers of platelets. Using specific VEGFR1 and VEGFR2 blocking mAbs and selective VEGFR1 and 2 agonists, PIGF-2 and VEGF-E, respectively, we show directly that stimulation of VEGFR1, but not VEGFR2, increases circulating platelet numbers in vivo. Using flow cytometric analysis of harvested MKs, we show that while PIGF does not change the absolute numbers of MKs present in the bone marrow and the spleen, it increases both their maturation and cell-surface expression of CXCR4 in the bone marrow. Histology of the bone marrow revealed a redistribution of MKs from the endosteal to the vascular niche in response to both VEGF-A165 and PIGF-2 treatment in vivo. Antagonism of CXCR4 suppressed both the VEGFR1-stimulated redistribution of megakyocytes within the bone marrow compartment and the VEGF-A165-induced thrombocytosis. In conclusion, we define a novel proinflammatory VEGFR1-mediated pathway that stimulates the maturation and upregulation of CXCR4 on megakaryocytes, leading to their redistribution within the bone marrow environment, thereby enhancing platelet production in vivo. © 2012 by The American Society of Hematology.