title: Flt-1, but not Flk-1 mediates hyperpermeability through activation of the PI3-K/Akt pathway.
abstract: Vascular endothelial growth factor (VEGF), a potent mediator of endothelial proliferation and migration, has an important role also in brain edema formation during hypoxia and ischemia. VEGF binds to the tyrosine kinase receptors Flt-1 and Flk-1. Yet, their relative importance for hypoxia-induced hyperpermeability is not well understood. We used an in vitro blood-brain barrier (BBB) model consisting of porcine brain microvascular endothelial cells (BMEC) to determine the role of Flt-1 in VEGF-induced endothelial cell (EC) barrier dysfunction. Soluble Flt-1 abolished hypoxia/VEGF-induced hyperpermeability. Furthermore, selective antisense oligonucleotides to Flt-1, but not to Flk-1, inhibited hypoxia-induced permeability changes. Consistent with these data, addition of the receptor-specific homolog placenta-derived growth factor, which binds Flt-1 but not Flk-1, increased endothelial permeability to the same extent as VEGF, whereas adding VEGF-E, a viral VEGF molecule from the orf virus family activating Flk-1 and neuropilin-1, but not Flt-1, did not show any effect. Using the carcinoma submandibular gland cell line (CSG), only expressing Flt-1, it was demonstrated that activation of Flt-1 is sufficient to induce hyperpermeability by hypoxia and VEGF. Hyperpermeability, induced by hypoxia/VEGF, depends on activation of phosphatidylinositol 3-kinase/Akt (PI3-K/Akt), nitric oxide synthase (NOS) and protein kinase G (PKG). The activation of the PI3-K/Akt pathway by hypoxia was confirmed using an in vivo mice hypoxia model. These results demonstrate that hypoxia/VEGF-induced hyperpermeability can be mediated by activation of Flt-1 independently on the presence of Flk-1 and indicate a central role for activation of the PI3-K/Akt pathway, followed by induction of NOS and PKG activity.
authors.affiliation: Max-Planck Institute for Heart and Lung Research, Bad Nauheim, Germany.
authors.forename: Carsten
authors.initials: C
authors.lastname: Vogel
authors.forename: Alexander
authors.initials: A
authors.lastname: Bauer
authors.forename: Marion
authors.initials: M
authors.lastname: Wiesnet
authors.forename: Klaus T
authors.initials: KT
authors.lastname: Preissner
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Schaper
authors.forename: Hugo H
authors.initials: HH
authors.lastname: Marti
authors.forename: Silvia
authors.initials: S
authors.lastname: Fischer
mesh_terms: D000818:Animals; D001812:Blood-Brain Barrier; D001921:Brain / Q000378:metabolism; D045744:Cell Line, Tumor; D004285:Dogs; D042783:Endothelial Cells / Q000378:metabolism; D005786:Gene Expression Regulation; D008297:Male; D051379:Mice; D010100:Oxygen / Q000378:metabolism; D010539:Permeability; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D013552:Swine; D040281:Vascular Endothelial Growth Factor Receptor-1 / Q000378:metabolism*; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism*
chemical_list: D019869:Phosphatidylinositol 3-Kinases; D040281:Vascular Endothelial Growth Factor Receptor-1; D040301:Vascular Endothelial Growth Factor Receptor-2; D051057:Proto-Oncogene Proteins c-akt; D010100:Oxygen