title: Soluble Flt-1 regulates Flk-1 activation to control hematopoietic and endothelial development in an oxygen-responsive manner.
abstract: Vascular endothelial growth factor (VEGF) and the vascular endothelial growth factor receptors (VEGFRs) regulate the development of hemogenic mesoderm. Oxygen concentration-mediated activation of hypoxia-inducible factor targets such as VEGF may serve as the molecular link between the microenvironment and mesoderm-derived blood and endothelial cell specification. We used controlled-oxygen microenvironments to manipulate the generation of hemogenic mesoderm and its derivatives from embryonic stem cells. Our studies revealed a novel role for soluble VEGFR1 (sFlt-1) in modulating hemogenic mesoderm fate between hematopoietic and endothelial cells. Parallel measurements of VEGF and VEGFRs demonstrated that sFlt-1 regulates VEGFR2 (Flk-1) activation in both a developmental-stage-dependent and oxygen-dependent manner. Early transient Flk-1 signaling occurred in hypoxia because of low levels of sFlt-1 and high levels of VEGF, yielding VEGF-dependent generation of hemogenic mesoderm. Sustained (or delayed) Flk-1 activation preferentially yielded hemogenic mesoderm-derived endothelial cells. In contrast, delayed (sFlt-1-mediated) inhibition of Flk-1 signaling resulted in hemogenic mesoderm-derived blood progenitor cells. Ex vivo analyses of primary mouse embryo-derived cells and analysis of transgenic mice secreting a Flt-1-Fc fusion protein (Fc, the region of an antibody which is constant and binds to receptors) support a hypothesis whereby microenvironmentally regulated blood and endothelial tissue specification is enabled by the temporally variant control of the levels of Flk-1 activation. Disclosure of potential conflicts of interest is found at the end of this article.
authors.affiliation: Department of Chemical Engineering and Applied Chemistry, Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Kelly A
authors.initials: KA
authors.lastname: Purpura
authors.forename: Sophia H L
authors.initials: SH
authors.lastname: George
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Dang
authors.forename: Kyunghee
authors.initials: K
authors.lastname: Choi
authors.forename: Andras
authors.initials: A
authors.lastname: Nagy
authors.forename: Peter W
authors.initials: PW
authors.lastname: Zandstra
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D019070:Cell Lineage; D053595:Embryonic Stem Cells / Q000166:cytology / Q000378:metabolism; D042783:Endothelial Cells / Q000166:cytology* / Q000378:metabolism; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000378:metabolism; D008648:Mesoderm / Q000166:cytology; D051379:Mice; D008813:Mice, Inbred ICR; D008822:Mice, Transgenic; D009154:Mutation; D010100:Oxygen / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism*; D040281:Vascular Endothelial Growth Factor Receptor-1 / Q000235:genetics / Q000378:metabolism*; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000235:genetics / Q000378:metabolism*
chemical_list: D011993:Recombinant Fusion Proteins; D042461:Vascular Endothelial Growth Factor A; C467480:vascular endothelial growth factor A, mouse; C501163:Flt1 protein, mouse; D040281:Vascular Endothelial Growth Factor Receptor-1; D040301:Vascular Endothelial Growth Factor Receptor-2; D010100:Oxygen