Bone morphogenetic protein 4 differently promotes distinct VE-cadherin+ precursor stages during the definitive hematopoietic development from embryonic stem cell-derived mesodermal cells
Definitive hematopoietic cells develop from the fetal liver kinase 1 (Flk1)+ mesodermal cells during the in vitro differentiation of mouse embryonic stem cells (ESCs). VE-cadherin+CD41-CD45- (V+41-45-) hemogenic endothelial cells (HECs) and VE-cadherin+CD41+CD45- (V+41+45-) cells mediate the definitive hematopoietic development from Flk1+ cells. Bone morphogenetic protein 4 (BMP4) is known to be essential for the formation of mesoderm. However, the role of BMP4 in the differentiation of the VE-cadherin+ definitive hematopoietic precursors from the mesoderm has been elusive. We addressed this issue using a co-aggregation culture of ESC-derived Flk1+ cells with OP9 stromal cells. This culture method induced V+41-45- cells, V+41+45- cells, and CD45+ cells from Flk1+ cells. V+41+45- cells possessed the potentials of erythromyeloid and T-lymphoid differentiation. When Flk1+ cells were cultured in the presence of a high concentration of BMP4, the generation of V+41-45- cells was enhanced. The increase of V+41-45- cells led to the subsequent increase of V+41+45- cells and CD45+ cells. The addition of BMP4 also increased hematopoietic colony-forming cells of various lineages. Furthermore, BMP4 promoted the expansion of V+41+45- cells independently of the preceding V+41-45- cell stage. These results suggest that BMP4 has promotive effects on the differentiation of V+41-45- HECs from Flk1+ mesodermal cells and the subsequent proliferation of V+41+45- hematopoietic precursors. These findings may provide insights for establishing a culture system to induce definitive hematopoietic stem cells from ESCs
