title: Flt-1 (VEGFR-1) coordinates discrete stages of blood vessel formation.
abstract: In developing blood vessel networks, the overall level of vessel branching often correlates with angiogenic sprout initiations, but in some pathological situations, increased sprout initiations paradoxically lead to reduced vessel branching and impaired vascular function. We examine the hypothesis that defects in the discrete stages of angiogenesis can uniquely contribute to vessel branching outcomes.
  
  
  
  Time-lapse movies of mammalian blood vessel development were used to define and quantify the dynamics of angiogenic sprouting. We characterized the formation of new functional conduits by classifying discrete sequential stages-sprout initiation, extension, connection, and stability-that are differentially affected by manipulation of vascular endothelial growth factor-A (VEGF-A) signalling via genetic loss of the receptor flt-1 (vegfr1). In mouse embryonic stem cell-derived vessels genetically lacking flt-1, overall branching is significantly decreased while sprout initiations are significantly increased. Flt-1(-/-) mutant sprouts are less likely to retract, and they form increased numbers of connections with other vessels. However, loss of flt-1 also leads to vessel collapse, which reduces the number of new stable conduits. Computational simulations predict that loss of flt-1 results in ectopic Flk-1 signalling in connecting sprouts post-fusion, causing protrusion of cell processes into avascular gaps and collapse of branches. Thus, defects in stabilization of new vessel connections offset increased sprout initiations and connectivity in flt-1(-/-) vascular networks, with an overall outcome of reduced numbers of new conduits.
  
  
  
  These results show that VEGF-A signalling has stage-specific effects on vascular morphogenesis, and that understanding these effects on dynamic stages of angiogenesis and how they integrate to expand a vessel network may suggest new therapeutic strategies.
authors.affiliation: Department of Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA Center for Heart and Regenerative Medicine Research, Virginia Tech Carilion Research Institute, Roanoke, VA 24014, USA.
authors.forename: John C
authors.initials: JC
authors.lastname: Chappell
authors.affiliation: Department of Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Julia G
authors.initials: JG
authors.lastname: Cluceru
authors.affiliation: Curriculum in Genetics and Molecular Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Jessica E
authors.initials: JE
authors.lastname: Nesmith
authors.affiliation: Department of Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA Lineberger Comprehensive Cancer Center, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Kevin P
authors.initials: KP
authors.lastname: Mouillesseaux
authors.affiliation: Center for Heart and Regenerative Medicine Research, Virginia Tech Carilion Research Institute, Roanoke, VA 24014, USA.
authors.forename: Vanessa B
authors.initials: VB
authors.lastname: Bradley
authors.affiliation: Center for Heart and Regenerative Medicine Research, Virginia Tech Carilion Research Institute, Roanoke, VA 24014, USA.
authors.forename: Caitlin M
authors.initials: CM
authors.lastname: Hartland
authors.affiliation: Department of Biomedical Engineering and Institute for Computational Medicine, Johns Hopkins University, Baltimore, MD 21218, USA.
authors.forename: Yasmin L
authors.initials: YL
authors.lastname: Hashambhoy-Ramsay
authors.affiliation: Department of Biomedical Engineering, University of Virginia, Charlottesville, VA 22908, USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Walpole
authors.affiliation: Department of Biomedical Engineering, University of Virginia, Charlottesville, VA 22908, USA.
authors.forename: Shayn M
authors.initials: SM
authors.lastname: Peirce
authors.affiliation: Department of Biomedical Engineering and Institute for Computational Medicine, Johns Hopkins University, Baltimore, MD 21218, USA.
authors.forename: Feilim
authors.initials: F
authors.lastname: Mac Gabhann
authors.affiliation: Department of Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA Curriculum in Genetics and Molecular Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA Lineberger Comprehensive Cancer Center, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA McAllister Heart Institute, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA bautch@med.unc.edu.
authors.forename: Victoria L
authors.initials: VL
authors.lastname: Bautch
mesh_terms: D000818:Animals; D001808:Blood Vessels / Q000196:embryology / Q000378:metabolism*; D048430:Cell Shape; D002478:Cells, Cultured; D003198:Computer Simulation; D053595:Embryonic Stem Cells / Q000378:metabolism*; D066026:Endothelial Progenitor Cells / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D051379:Mice; D018715:Microscopy, Video; D008955:Models, Cardiovascular; D009010:Monte Carlo Method; D009024:Morphogenesis; D018919:Neovascularization, Physiologic; D010641:Phenotype; D015398:Signal Transduction; D013997:Time Factors; D059008:Time-Lapse Imaging; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism; D040281:Vascular Endothelial Growth Factor Receptor-1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D042461:Vascular Endothelial Growth Factor A; C467480:vascular endothelial growth factor A, mouse; C501163:Flt1 protein, mouse; D040281:Vascular Endothelial Growth Factor Receptor-1
keywords: Angiogenesis; Computational model; ES cells; Flt-1; VEGF-A