title: VEGFR3 does not sustain retinal angiogenesis without VEGFR2.
abstract: Angiogenesis, the formation of new blood vessels, is regulated by vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs). VEGFR2 is abundant in the tip cells of angiogenic sprouts, where VEGF/VEGFR2 functions upstream of the delta-like ligand 4 (DLL4)/Notch signal transduction pathway. VEGFR3 is expressed in all endothelia and is indispensable for angiogenesis during early embryonic development. In adults, VEGFR3 is expressed in angiogenic blood vessels and some fenestrated endothelia. VEGFR3 is abundant in endothelial tip cells, where it activates Notch signaling, facilitating the conversion of tip cells to stalk cells during the stabilization of vascular branches. Subsequently, Notch activation suppresses VEGFR3 expression in a negative feedback loop. Here we used conditional deletions and a Notch pathway inhibitor to investigate the cross-talk between VEGFR2, VEGFR3, and Notch in vivo. We show that postnatal angiogenesis requires VEGFR2 signaling also in the absence of Notch or VEGFR3, and that even small amounts of VEGFR2 are able to sustain angiogenesis to some extent. We found that VEGFR2 is required independently of VEGFR3 for endothelial DLL4 up-regulation and angiogenic sprouting, and for VEGFR3 functions in angiogenesis. In contrast, VEGFR2 deletion had no effect, whereas VEGFR3 was essential for postnatal lymphangiogenesis, and even for lymphatic vessel maintenance in adult skin. Knowledge of these interactions and the signaling functions of VEGFRs in blood vessels and lymphatic vessels is essential for the therapeutic manipulation of the vascular system, especially when considering multitargeted antiangiogenic treatments.
authors.affiliation: Wihuri Research Institute and Translational Cancer Biology Program, Biomedicum Helsinki, University of Helsinki, FIN-00014 Helsinki, Finland;
authors.forename: Georgia
authors.initials: G
authors.lastname: Zarkada
authors.affiliation: Wihuri Research Institute and Translational Cancer Biology Program, Biomedicum Helsinki, University of Helsinki, FIN-00014 Helsinki, Finland;
authors.forename: Krista
authors.initials: K
authors.lastname: Heinolainen
authors.affiliation: Lymphatic Development Laboratory, Cancer Research UK London Research Institute, London WC2A 3LY, United Kingdom; Rudbeck Laboratory, Department of Immunology, Genetics, and Pathology, Uppsala University, 751 85 Uppsala, Sweden; and.
authors.forename: Taija
authors.initials: T
authors.lastname: Makinen
authors.affiliation: The Laboratory of Vascular Biology, School of Medicine, Keio University, Shinjuku-ku, Tokyo 160-8582, Japan.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Kubota
authors.affiliation: Wihuri Research Institute and Translational Cancer Biology Program, Biomedicum Helsinki, University of Helsinki, FIN-00014 Helsinki, Finland; kari.alitalo@helsinki.fi.
authors.forename: Kari
authors.initials: K
authors.lastname: Alitalo
mesh_terms: D000818:Animals; D051379:Mice; D018919:Neovascularization, Physiologic; D012171:Retinal Vessels / Q000254:growth & development*; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000502:physiology*; D040321:Vascular Endothelial Growth Factor Receptor-3 / Q000502:physiology*
chemical_list: D040301:Vascular Endothelial Growth Factor Receptor-2; D040321:Vascular Endothelial Growth Factor Receptor-3
keywords: Notch; VEGFC; VEGFD; anti-angiogenesis; lymphangiogenesis