title: Expression of the human isoform of glutamate dehydrogenase, hGDH2, augments TCA cycle capacity and oxidative metabolism of glutamate during glucose deprivation in astrocytes.
abstract: A key enzyme in brain glutamate homeostasis is glutamate dehydrogenase (GDH) which links carbohydrate and amino acid metabolism mediating glutamate degradation to CO2and expanding tricarboxylic acid (TCA) cycle capacity with intermediates, i.e. anaplerosis. Humans express two GDH isoforms, GDH1 and 2, whereas most other mammals express only GDH1. hGDH1 is widely expressed in human brain while hGDH2 is confined to astrocytes. The two isoforms display different enzymatic properties and the nature of these supports that hGDH2 expression in astrocytes potentially increases glutamate oxidation and supports the TCA cycle during energy-demanding processes such as high intensity glutamatergic signaling. However, little is known about how expression of hGDH2 affects the handling of glutamate and TCA cycle metabolism in astrocytes. Therefore, we cultured astrocytes from cerebral cortical tissue of hGDH2-expressing transgenic mice. We measured glutamate uptake and metabolism using [3H]glutamate, while the effect on metabolic pathways of glutamate and glucose was evaluated by use of13C and14C substrates and analysis by mass spectrometry and determination of radioactively labeled metabolites including CO2, respectively. We conclude that hGDH2 expression increases capacity for uptake and oxidative metabolism of glutamate, particularly during increased workload and aglycemia. Additionally, hGDH2 expression increased utilization of branched-chain amino acids (BCAA) during aglycemia and caused a general decrease in oxidative glucose metabolism. We speculate, that expression of hGDH2 allows astrocytes to spare glucose and utilize BCAAs during substrate shortages. These findings support the proposed role of hGDH2 in astrocytes as an important fail-safe during situations of intense glutamatergic activity. GLIA 2017;65:474-488.
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Science, University of Copenhagen, Copenhagen, 2100, Denmark.
authors.forename: Jakob D
authors.initials: JD
authors.lastname: Nissen
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Science, University of Copenhagen, Copenhagen, 2100, Denmark.
authors.forename: Kasper
authors.initials: K
authors.lastname: Lykke
authors.affiliation: Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, Leipzig, 02109, Germany.
authors.forename: Jaroslaw
authors.initials: J
authors.lastname: Bryk
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Science, University of Copenhagen, Copenhagen, 2100, Denmark.
authors.forename: Malin H
authors.initials: MH
authors.lastname: Stridh
authors.affiliation: Neurology Laboratory, School of Health Sciences, Faculty of Medicine, University of Crete, Heraklion, Crete, Greece.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Zaganas
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Science, University of Copenhagen, Copenhagen, 2100, Denmark.
authors.forename: Dorte M
authors.initials: DM
authors.lastname: Skytt
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Science, University of Copenhagen, Copenhagen, 2100, Denmark.
authors.forename: Arne
authors.initials: A
authors.lastname: Schousboe
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Science, University of Copenhagen, Copenhagen, 2100, Denmark.
authors.forename: Lasse K
authors.initials: LK
authors.lastname: Bak
authors.affiliation: Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, Leipzig, 02109, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Enard
authors.affiliation: Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, Leipzig, 02109, Germany.
authors.forename: Svante
authors.initials: S
authors.lastname: Pääbo
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Science, University of Copenhagen, Copenhagen, 2100, Denmark.
authors.forename: Helle S
authors.initials: HS
authors.lastname: Waagepetersen
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D002245:Carbon Dioxide / Q000493:pharmacokinetics; D002247:Carbon Isotopes / Q000493:pharmacokinetics; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D002952:Citric Acid Cycle / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D015971:Gene Expression Regulation, Enzymologic; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D005947:Glucose / Q000172:deficiency*; D005969:Glutamate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D013401:Sugar Alcohol Dehydrogenases / Q000378:metabolism; D014316:Tritium / Q000493:pharmacokinetics
chemical_list: D002247:Carbon Isotopes; D005904:Glial Fibrillary Acidic Protein; D020033:Protein Isoforms; D014316:Tritium; D002245:Carbon Dioxide; D018698:Glutamic Acid; D013401:Sugar Alcohol Dehydrogenases; C095946:galactitol 2-dehydrogenase; D005969:Glutamate Dehydrogenase; C521120:GLUD2 protein, human; D005947:Glucose
keywords: amino acid; anaplerosis; brain; hypoglycemic; isotopic labeling