title: Integrin-dependent and -independent functions of astrocytic fibronectin in retinal angiogenesis.
abstract: Fibronectin (FN) is a major component of the extracellular matrix and functions in cell adhesion, cell spreading and cell migration. In the retina, FN is transiently expressed and assembled on astrocytes (ACs), which guide sprouting tip cells and deposit a provisional matrix for sprouting angiogenesis. The precise function of FN in retinal angiogenesis is largely unknown. Using genetic tools, we show that astrocytes are the major source of cellular FN during angiogenesis in the mouse retina. Deletion of astrocytic FN reduces radial endothelial migration during vascular plexus formation in a gene dose-dependent manner. This effect correlates with reduced VEGF receptor 2 and PI3K/AKT signalling, and can be mimicked by selectively inhibiting VEGF-A binding to FN through intraocular injection of blocking peptides. By contrast, AC-specific replacement of the integrin-binding RGD sequence with FN-RGE or endothelial deletion of itga5 shows little effect on migration and PI3K/AKT signalling, but impairs filopodial alignment along AC processes, suggesting that FN-integrin α5β1 interaction is involved in filopodial adhesion to the astrocytic matrix. AC FN shares its VEGF-binding function and cell-surface distribution with heparan-sulfate (HS), and genetic deletion of both FN and HS together greatly enhances the migration defect, indicating a synergistic function of FN and HS in VEGF binding. We propose that in vivo the VEGF-binding properties of FN and HS promote directional tip cell migration, whereas FN integrin-binding functions to support filopodia adhesion to the astrocytic migration template.
authors: Vascular Biology Laboratory, London Research Institute - Cancer Research UK, London WC2A 3PX, UK.
authors: Denise
authors: D
authors: Stenzel
authors: Andrea
authors: A
authors: Lundkvist
authors: Dominique
authors: D
authors: Sauvaget
authors: Marta
authors: M
authors: Busse
authors: Mariona
authors: M
authors: Graupera
authors: Arjan
authors: A
authors: van der Flier
authors: Errol S
authors: ES
authors: Wijelath
authors: Jacqueline
authors: J
authors: Murray
authors: Michael
authors: M
authors: Sobel
authors: Mercedes
authors: M
authors: Costell
authors: Seiichiro
authors: S
authors: Takahashi
authors: Reinhard
authors: R
authors: Fässler
authors: Yu
authors: Y
authors: Yamaguchi
authors: David H
authors: DH
authors: Gutmann
authors: Richard O
authors: RO
authors: Hynes
authors: Holger
authors: H
authors: Gerhardt
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D002465:Cell Movement; D005109:Extracellular Matrix / Q000378:metabolism; D005353:Fibronectins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D006497:Heparan Sulfate / Q000378:metabolism; D039081:Integrin alpha5beta1 / Q000737:chemistry / Q000378:metabolism; D016023:Integrins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D018919:Neovascularization, Physiologic; D009842:Oligopeptides / Q000737:chemistry; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D054730:Protein Interaction Domains and Motifs; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D012171:Retinal Vessels / Q000254:growth & development* / Q000294:innervation / Q000378:metabolism*; D015398:Signal Transduction; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism
chemical_list: D005353:Fibronectins; D006497:Heparan Sulfate; D039081:Integrin alpha5beta1; D016023:Integrins; D009842:Oligopeptides; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D042461:Vascular Endothelial Growth Factor A; D040301:Vascular Endothelial Growth Factor Receptor-2; C467480:vascular endothelial growth factor A, mouse; C047981:arginyl-glycyl-aspartic acid