title: Expression of Iron-Related Proteins at the Neurovascular Unit Supports Reduction and Reoxidation of Iron for Transport Through the Blood-Brain Barrier.
abstract: The mechanisms for iron transport through the blood-brain barrier (BBB) remain a controversy. We analyzed for expression of mRNA and proteins involved in oxidation and transport of iron in isolated brain capillaries from dietary normal, iron-deficient, and iron-reverted rats. The expression was also investigated in isolated rat brain endothelial cells (RBECs) and in immortalized rat brain endothelial (RBE4) cells grown as monoculture or in hanging culture inserts with defined BBB properties. Transferrin receptor 1, ferrireductases Steap 2 and 3, divalent metal transporter 1 (DMT1), ferroportin, soluble and glycosylphosphatidylinositol (GPI)-anchored ceruloplasmin, and hephaestin were all expressed in brain capillaries in vivo and in isolated RBECs and RBE4 cells. Gene expression of DMT1, ferroportin, and soluble and GPI-anchored ceruloplasmin were significantly higher in isolated RBECs with induced BBB properties. Primary pericytes and astrocytes both expressed ceruloplasmin and hephaestin, and RBECs, pericytes, and astrocytes all exhibited ferrous oxidase activity. The coherent protein expression of these genes was demonstrated by immunocytochemistry. The data show that brain endothelial cells provide the machinery for receptor-mediated uptake of ferric iron-containing transferrin. Ferric iron can then undergo reduction to ferrous iron by ferrireductases inside endosomes followed by DMT1-mediated pumping into the cytosol and subsequently cellular export by ferroportin. The expression of soluble ceruloplasmin by brain endothelial cells, pericytes, and astrocytes that together form the neurovascular unit (NVU) provides the ferroxidase activity necessary to reoxidize ferrous iron once released inside the brain.
authors.affiliation: Laboratory of Neurobiology, Biomedicine Group, Department of Health Science and Technology, Aalborg University, Fr. Bajers Vej 3B, 1.216, 9220, Aalborg, Denmark. abl@hst.aau.dk.
authors.forename: Annette
authors.initials: A
authors.lastname: Burkhart
authors.affiliation: Laboratory of Neurobiology, Biomedicine Group, Department of Health Science and Technology, Aalborg University, Fr. Bajers Vej 3B, 1.216, 9220, Aalborg, Denmark.
authors.forename: Tina
authors.initials: T
authors.lastname: Skjørringe
authors.affiliation: Laboratory of Neurobiology, Biomedicine Group, Department of Health Science and Technology, Aalborg University, Fr. Bajers Vej 3B, 1.216, 9220, Aalborg, Denmark.
authors.forename: Kasper Bendix
authors.initials: KB
authors.lastname: Johnsen
authors.affiliation: Department of Biomedicine, Aarhus University, Aarhus, Denmark.
authors.forename: Piotr
authors.initials: P
authors.lastname: Siupka
authors.affiliation: Laboratory of Neurobiology, Biomedicine Group, Department of Health Science and Technology, Aalborg University, Fr. Bajers Vej 3B, 1.216, 9220, Aalborg, Denmark.
authors.forename: Louiza Bohn
authors.initials: LB
authors.lastname: Thomsen
authors.affiliation: Department of Biomedicine, Aarhus University, Aarhus, Denmark.
authors.forename: Morten Schallburg
authors.initials: MS
authors.lastname: Nielsen
authors.affiliation: Pharmacosmos A/S, Holbæk, Denmark.
authors.forename: Lars Lykke
authors.initials: LL
authors.lastname: Thomsen
authors.affiliation: Laboratory of Neurobiology, Biomedicine Group, Department of Health Science and Technology, Aalborg University, Fr. Bajers Vej 3B, 1.216, 9220, Aalborg, Denmark.
authors.forename: Torben
authors.initials: T
authors.lastname: Moos
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000378:metabolism; D001692:Biological Transport; D001808:Blood Vessels / Q000378:metabolism*; D001812:Blood-Brain Barrier / Q000378:metabolism*; D002196:Capillaries / Q000378:metabolism; D042783:Endothelial Cells / Q000378:metabolism; D005786:Gene Expression Regulation; D007501:Iron / Q000378:metabolism*; D008297:Male; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D010084:Oxidation-Reduction; D020286:Pericytes / Q000378:metabolism; D017208:Rats, Wistar
chemical_list: D026901:Membrane Transport Proteins; D007501:Iron
keywords: Ceruloplasmin; DMT1; Endothelial; Ferroportin; Hephaestin; Pericyte