title: Up-Regulation of Excitatory Amino Acid Transporters EAAT1 and EAAT2 by ß-Klotho.
abstract: OBJECTIVE
  Klotho, a transmembrane protein expressed in chorioid plexus of the brain, kidney, and several other tissues, is required for inhibition of 1,25(OH)2D3 formation by FGF23. The extracellular domain of Klotho protein could be cleaved off, thus being released into blood or cerebrospinal fluid. At least in part by exerting β-glucuronidase activity, soluble klotho regulates several ion channels and carriers. Klotho protein deficiency accelerates the appearance of age related disorders including neurodegeneration and muscle wasting and eventually leads to premature death. The present study explored the effect of Klotho protein on the excitatory glutamate transporters EAAT1 (SLC1A3) and EAAT2 (SLC1A2), Na+ coupled carriers clearing excitatory amino acids from the synaptic cleft and thus participating in the regulation of neuronal excitability.
  
  
  METHODS
  cRNA encoding EAAT1 or EAAT2 was injected into Xenopus laevis oocytes and glutamate (2 mM)-induced inward current (IGlu) taken as measure of glutamate transport. Measurements were made without or with prior 24 h treatment with soluble ß-Klotho protein (30 ng/ml) in the absence and presence of β-glucuronidase inhibitor D-saccharic acid 1,4-lactone monohydrate (DSAL,10 µM).
  
  
  RESULTS
  IGlu was observed in EAAT1 and in EAAT2 expressing oocytes but not in water injected oocytes. In both, EAAT1 and EAAT2 expressing oocytes IGlu was significantly increased by treatment with soluble ß-Klotho protein, an effect reversed by DSAL. Treatment with ß-klotho protein increased significantly the maximal transport rate without significantly modifying the affinity of the carriers.
  
  
  CONCLUSIONS
  ß-Klotho up-regulates the excitatory glutamate transporters EAAT1 and EAAT2 and thus participates in the regulation of neuronal excitation.
authors.affiliation: Department of Physiology I, University of Tx00FC;bingen, Tx00FC;bingen, Germany.
authors.forename: Jamshed
authors.initials: J
authors.lastname: Warsi
authors.forename: Abeer
authors.initials: A
authors.lastname: Abousaab
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D027341:Excitatory Amino Acid Transporter 1 / Q000235:genetics / Q000378:metabolism*; D027342:Excitatory Amino Acid Transporter 2; D000089703:Fibroblast Growth Factor-23; D050491:Glutamate Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D018698:Glutamic Acid / Q000494:pharmacology; D006801:Humans; D007546:Isoquinolines / Q000494:pharmacology; D000090265:Klotho Proteins; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D008565:Membrane Proteins / Q000494:pharmacology*; D008845:Microinjections; D009154:Mutation / Q000235:genetics; D009865:Oocytes; D018408:Patch-Clamp Techniques; D015854:Up-Regulation / Q000187:drug effects* / Q000235:genetics; D014981:Xenopus
chemical_list: D027341:Excitatory Amino Acid Transporter 1; D027342:Excitatory Amino Acid Transporter 2; C000717427:FGF23 protein, human; D050491:Glutamate Plasma Membrane Transport Proteins; D007546:Isoquinolines; C538995:KLB protein, human; D008565:Membrane Proteins; C493397:SLC1A2 protein, human; C493394:SLC1A3 protein, human; D018698:Glutamic Acid; C051345:1,2-dehydrosalsolinol; D000089703:Fibroblast Growth Factor-23; D000090265:Klotho Proteins