Macrophage colony stimulating factor modulates the development of hematopoiesis by stimulating the differentiation of endothelial cells in the AGM region

Definitive hematopoietic stem cells arise in the aorta-gonad-mesonephros (AGM) region from hemangioblasts, common precursors for hematopoietic and endothelial cells. Previously, we showed that multipotential hematopoietic progenitors and endothelial cells were massively produced in primary culture of the AGM region in the presence of oncostatin M. Here we describe a role for macrophage-colony-stimulating factor (M-CSF) in the development of hematopoietic and endothelial cells in AGM culture. The number of hematopoietic progenitors including multipotential cells was significantly increased in the AGM culture of op/op embryos. The addition of M-CSF to op/op AGM culture decreased colony-forming unit (CFU)-GEMM, granulocyte macrophage-CFU, and erythroid-CFU, but it increased CFU-M. On the other hand, the number of cells expressing endothelial markers, vascular endothelial-cadherin, intercellular adhesion molecule 2, and Flk-1 was reduced in op/op AGM culture. The M-CSF receptor was expressed in PCLP1(+)CD45(-) cells, the precursors of endothelial cells, and M-CSF up-regulated the expression of more mature endothelial cell markers-VCAM-1, PECAM-1, and E-selectin-in PCLP1(+)CD45(-) cells. These results suggest that M-CSF modulates the development of hematopoiesis by stimulating the differentiation of PCLP-1(+)CD45(-) cells to endothelial cells in the AGM region.