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Colucci E, Anshari ZR, Patiño-Ruiz MF, Nemchinova M, Whittaker J, Slotboom DJ, Guskov A. Mutation in glutamate transporter homologue GltTk provides insights into pathologic mechanism of episodic ataxia 6. Nat Commun 2023; 14:1799. [PMID: 37002226 PMCID: PMC10066184 DOI: 10.1038/s41467-023-37503-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2022] [Accepted: 03/20/2023] [Indexed: 04/03/2023] Open
Abstract
Episodic ataxias (EAs) are rare neurological conditions affecting the nervous system and typically leading to motor impairment. EA6 is linked to the mutation of a highly conserved proline into an arginine in the glutamate transporter EAAT1. In vitro studies showed that this mutation leads to a reduction in the substrates transport and an increase in the anion conductance. It was hypothesised that the structural basis of these opposed functional effects might be the straightening of transmembrane helix 5, which is kinked in the wild-type protein. In this study, we present the functional and structural implications of the mutation P208R in the archaeal homologue of glutamate transporters GltTk. We show that also in GltTk the P208R mutation leads to reduced aspartate transport activity and increased anion conductance, however a cryo-EM structure reveals that the kink is preserved. The arginine side chain of the mutant points towards the lipidic environment, where it may engage in interactions with the phospholipids, thereby potentially interfering with the transport cycle and contributing to stabilisation of an anion conducting state.
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Affiliation(s)
- Emanuela Colucci
- Groningen Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG, Groningen, the Netherlands
| | - Zaid R Anshari
- Groningen Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG, Groningen, the Netherlands
| | - Miyer F Patiño-Ruiz
- Groningen Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG, Groningen, the Netherlands
| | - Mariia Nemchinova
- Groningen Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG, Groningen, the Netherlands
| | - Jacob Whittaker
- Groningen Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG, Groningen, the Netherlands
| | - Dirk J Slotboom
- Groningen Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG, Groningen, the Netherlands.
| | - Albert Guskov
- Groningen Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG, Groningen, the Netherlands.
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2
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Sun P, Han Y, Hu K, Huang S, Wang M, Zhou K, Fu L, Chen H, Tang G. Synthesis and biological evaluation of Al[18F]-NOTA-IPB-PDL1P as a molecular probe for PET imaging of PD-L1 positive tumors. Bioorg Chem 2022; 122:105682. [DOI: 10.1016/j.bioorg.2022.105682] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Revised: 02/07/2022] [Accepted: 02/09/2022] [Indexed: 11/02/2022]
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3
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Kovermann P, Engels M, Müller F, Fahlke C. Cellular Physiology and Pathophysiology of EAAT Anion Channels. Front Cell Neurosci 2022; 15:815279. [PMID: 35087380 PMCID: PMC8787812 DOI: 10.3389/fncel.2021.815279] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Accepted: 12/13/2021] [Indexed: 11/17/2022] Open
Abstract
Excitatory amino acid transporters (EAATs) optimize the temporal resolution and energy demand of mammalian excitatory synapses by quickly removing glutamate from the synaptic cleft into surrounding neuronal and glial cells and ensuring low resting glutamate concentrations. In addition to secondary active glutamate transport, EAATs also function as anion channels. The channel function of these transporters is conserved in all homologs ranging from archaebacteria to mammals; however, its physiological roles are insufficiently understood. There are five human EAATs, which differ in their glutamate transport rates. Until recently the high-capacity transporters EAAT1, EAAT2, and EAAT3 were believed to conduct only negligible anion currents, with no obvious function in cell physiology. In contrast, the low-capacity glutamate transporters EAAT4 and EAAT5 are thought to regulate neuronal signaling as glutamate-gated channels. In recent years, new experimental approaches and novel animal models, together with the discovery of a human genetic disease caused by gain-of-function mutations in EAAT anion channels have enabled identification of the first physiological and pathophysiological roles of EAAT anion channels.
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4
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Lin L, Xiang X, Su S, Liu S, Xiong Y, Ma H, Yuan G, Nie D, Tang G. Biological Evaluation of [ 18F]AlF-NOTA-NSC-GLU as a Positron Emission Tomography Tracer for Hepatocellular Carcinoma. Front Chem 2021; 9:630452. [PMID: 33937189 PMCID: PMC8085524 DOI: 10.3389/fchem.2021.630452] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2020] [Accepted: 02/23/2021] [Indexed: 12/29/2022] Open
Abstract
Purpose: N-(2-[18F]fluoropropionyl)-L-glutamate ([18F]FPGLU) for hepatocellular carcinoma (HCC) imaging has been performed in our previous studies, but its radiosynthesis method and stability in vivo need to be improved. Hence, we evaluated the synthesis and biological properties of a simple [18F]-labeled glutamate analog, [18F]AlF-1,4,7-triazacyclononane-1,4,7-triacetic-acid-2-S-(4-isothiocyanatobenzyl)-l-glutamate ([18F]AlF-NOTA-NSC-GLU), for HCC imaging. Procedures: [18F]AlF-NOTA-NSC-GLU was synthesized via a one-step reaction sequence from NOTA-NSC-GLU. In order to investigate the imaging value of [18F]AlF-NOTA-NSC-GLU in HCC, we conducted positron emission tomography/computed tomography (PET/CT) imaging and competitive binding of [18F]AlF-NOTA-NSC-GLU in human Hep3B tumor-bearing mice. The transport mechanism of [18F]AlF-NOTA-NSC-GLU was determined by competitive inhibition and protein incorporation experiments in vitro. Results: [18F]AlF-NOTA-NSC-GLU was prepared with an overall radiochemical yield of 29.3 ± 5.6% (n = 10) without decay correction within 20 min. In vitro competitive inhibition experiments demonstrated that the Na+-dependent systems XAG-, B0+, ASC, and minor XC- were involved in the uptake of [18F]AlF-NOTA-NSC-GLU, with the Na+-dependent system XAG- possibly playing a more dominant role. Protein incorporation studies of the Hep3B human hepatoma cell line showed almost no protein incorporation. Micro-PET/CT imaging with [18F]AlF-NOTA-NSC-GLU showed good tumor-to-background contrast in Hep3B human hepatoma-bearing mouse models. After [18F]AlF-NOTA-NSC-GLU injection, the tumor-to-liver uptake ratio of [18F]AlF-NOTA-NSC-GLU was 2.06 ± 0.17 at 30 min post-injection. In vivo competitive binding experiments showed that the tumor-to-liver uptake ratio decreased with the addition of inhibitors to block the XAG system. Conclusions: We have successfully synthesized [18F]AlF-NOTA-NSC-GLU as a novel PET tracer with good radiochemical yield and high radiochemical purity. Our findings indicate that [18F]AlF-NOTA-NSC-GLU may be a potential candidate for HCC imaging. Also, a further biological evaluation is underway.
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Affiliation(s)
- Liping Lin
- Department of Radiology Intervention and Medical Imaging, Guangdong Engineering Research Center for Medical Radiopharmaceuticals Translational Application, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Xianhong Xiang
- Department of Radiology Intervention and Medical Imaging, Guangdong Engineering Research Center for Medical Radiopharmaceuticals Translational Application, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Shu Su
- Department of Radiology Intervention and Medical Imaging, Guangdong Engineering Research Center for Medical Radiopharmaceuticals Translational Application, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Shaoyu Liu
- Department of Radiology Intervention and Medical Imaging, Guangdong Engineering Research Center for Medical Radiopharmaceuticals Translational Application, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Ying Xiong
- Department of Radiology Intervention and Medical Imaging, Guangdong Engineering Research Center for Medical Radiopharmaceuticals Translational Application, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Hui Ma
- Department of Radiology Intervention and Medical Imaging, Guangdong Engineering Research Center for Medical Radiopharmaceuticals Translational Application, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Gongjun Yuan
- Department of Radiology Intervention and Medical Imaging, Guangdong Engineering Research Center for Medical Radiopharmaceuticals Translational Application, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Dahong Nie
- Department of Radiology Intervention and Medical Imaging, Guangdong Engineering Research Center for Medical Radiopharmaceuticals Translational Application, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China.,Department of Radiotherapy, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Ganghua Tang
- Department of Radiology Intervention and Medical Imaging, Guangdong Engineering Research Center for Medical Radiopharmaceuticals Translational Application, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China.,Nanfang PET Center, Department of Nuclear Medicine, Nanfang Hospital, Southern Medical University, Guangzhou, China
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5
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Sears SM, Hewett SJ. Influence of glutamate and GABA transport on brain excitatory/inhibitory balance. Exp Biol Med (Maywood) 2021; 246:1069-1083. [PMID: 33554649 DOI: 10.1177/1535370221989263] [Citation(s) in RCA: 64] [Impact Index Per Article: 21.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
An optimally functional brain requires both excitatory and inhibitory inputs that are regulated and balanced. A perturbation in the excitatory/inhibitory balance-as is the case in some neurological disorders/diseases (e.g. traumatic brain injury Alzheimer's disease, stroke, epilepsy and substance abuse) and disorders of development (e.g. schizophrenia, Rhett syndrome and autism spectrum disorder)-leads to dysfunctional signaling, which can result in impaired cognitive and motor function, if not frank neuronal injury. At the cellular level, transmission of glutamate and GABA, the principle excitatory and inhibitory neurotransmitters in the central nervous system control excitatory/inhibitory balance. Herein, we review the synthesis, release, and signaling of GABA and glutamate followed by a focused discussion on the importance of their transport systems to the maintenance of excitatory/inhibitory balance.
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Affiliation(s)
- Sheila Ms Sears
- Department of Biology, Program in Neuroscience, 2029Syracuse University, Syracuse, NY 13244, USA
| | - Sandra J Hewett
- Department of Biology, Program in Neuroscience, 2029Syracuse University, Syracuse, NY 13244, USA
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6
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Role of Excitatory Amino Acid Carrier 1 ( EAAC1) in Neuronal Death and Neurogenesis After Ischemic Stroke. Int J Mol Sci 2020; 21:ijms21165676. [PMID: 32784778 PMCID: PMC7460875 DOI: 10.3390/ijms21165676] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Revised: 08/03/2020] [Accepted: 08/05/2020] [Indexed: 12/24/2022] Open
Abstract
Although there have been substantial advances in knowledge regarding the mechanisms of neuron death after stroke, effective therapeutic measures for stroke are still insufficient. Excitatory amino acid carrier 1 (EAAC1) is a type of neuronal glutamate transporter and considered to have an additional action involving the neuronal uptake of cysteine, which acts as a crucial substrate for glutathione synthesis. Previously, our lab demonstrated that genetic deletion of EAAC1 leads to decreased neuronal glutathione synthesis, increased oxidative stress, and subsequent cognitive impairment. Therefore, we hypothesized that reduced neuronal transport of cysteine due to deletion of the EAAC1 gene might exacerbate neuronal injury and impair adult neurogenesis in the hippocampus after transient cerebral ischemia. EAAC1 gene deletion profoundly increased ischemia-induced neuronal death by decreasing the antioxidant capacity. In addition, genetic deletion of EAAC1 also decreased the overall neurogenesis processes, such as cell proliferation, differentiation, and survival, after cerebral ischemia. These studies strongly support our hypothesis that EAAC1 is crucial for the survival of newly generated neurons, as well as mature neurons, in both physiological and pathological conditions. Here, we present a comprehensive review of the role of EAAC1 in neuronal death and neurogenesis induced by ischemic stroke, focusing on its potential cellular and molecular mechanisms.
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7
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Tajan M, Hock AK, Blagih J, Robertson NA, Labuschagne CF, Kruiswijk F, Humpton TJ, Adams PD, Vousden KH. A Role for p53 in the Adaptation to Glutamine Starvation through the Expression of SLC1A3. Cell Metab 2018; 28:721-736.e6. [PMID: 30122553 PMCID: PMC6224545 DOI: 10.1016/j.cmet.2018.07.005] [Citation(s) in RCA: 139] [Impact Index Per Article: 23.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Revised: 05/29/2018] [Accepted: 07/09/2018] [Indexed: 12/24/2022]
Abstract
Numerous mechanisms to support cells under conditions of transient nutrient starvation have been described. Several functions of the tumor-suppressor protein p53 can contribute to the adaptation of cells to metabolic stress and help cancer cell survival under nutrient-limiting conditions. We show here that p53 promotes the expression of SLC1A3, an aspartate/glutamate transporter that allows the utilization of aspartate to support cells in the absence of extracellular glutamine. Under glutamine deprivation, SLC1A3 expression maintains electron transport chain and tricarboxylic acid cycle activity, promoting de novo glutamate, glutamine, and nucleotide synthesis to rescue cell viability. Tumor cells with high levels of SLC1A3 expression are resistant to glutamine starvation, and SLC1A3 depletion retards the growth of these cells in vitro and in vivo, suggesting a therapeutic potential for SLC1A3 inhibition.
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Affiliation(s)
- Mylène Tajan
- The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
| | - Andreas K Hock
- Cancer Research UK Beatson Institute, Switchback Road, Glasgow G61 1BD, UK
| | - Julianna Blagih
- The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
| | - Neil A Robertson
- Institute of Cancer Sciences, University of Glasgow, Garscube Estate, Glasgow G61 1BD, UK
| | | | - Flore Kruiswijk
- Cancer Research UK Beatson Institute, Switchback Road, Glasgow G61 1BD, UK
| | - Timothy J Humpton
- Cancer Research UK Beatson Institute, Switchback Road, Glasgow G61 1BD, UK
| | - Peter D Adams
- Institute of Cancer Sciences, University of Glasgow, Garscube Estate, Glasgow G61 1BD, UK; Sanford Burnham Prebys Medical Discovery Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Karen H Vousden
- The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK.
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8
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Lewis MH, Lindenmaier Z, Boswell K, Edington G, King MA, Muehlmann AM. Subthalamic nucleus pathology contributes to repetitive behavior expression and is reversed by environmental enrichment. GENES BRAIN AND BEHAVIOR 2018; 17:e12468. [PMID: 29457676 DOI: 10.1111/gbb.12468] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2017] [Revised: 02/06/2018] [Accepted: 02/14/2018] [Indexed: 01/09/2023]
Abstract
Repetitive motor behaviors are common in neurodevelopmental, psychiatric and neurological disorders. Despite their prevalence in certain clinical populations, our understanding of the neurobiological cause of repetitive behavior is lacking. Likewise, not knowing the pathophysiology has precluded efforts to find effective drug treatments. Our comparisons between mouse strains that differ in their expression of repetitive behavior showed an important role of the subthalamic nucleus (STN). In mice with high rates of repetitive behavior, we found significant differences in dendritic spine density, gene expression and neuronal activation in the STN. Taken together, these data show a hypoglutamatergic state. Furthermore, by using environmental enrichment to reduce repetitive behavior, we found evidence of increased glutamatergic tone in the STN with our measures of spine density and gene expression. These results suggest the STN is a major contributor to repetitive behavior expression and highlight the potential of drugs that increase STN function to reduce repetitive behavior in clinical populations.
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Affiliation(s)
- M H Lewis
- Department of Psychiatry, University of Florida, Gainesville, Florida
| | - Z Lindenmaier
- Department of Psychiatry, University of Florida, Gainesville, Florida
| | - K Boswell
- Department of Psychiatry, University of Florida, Gainesville, Florida
| | - G Edington
- Department of Psychiatry, University of Florida, Gainesville, Florida
| | - M A King
- Department of Psychiatry, University of Florida, Gainesville, Florida
| | - A M Muehlmann
- Department of Psychiatry, University of Florida, Gainesville, Florida
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9
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Perkins EM, Suminaite D, Clarkson YL, Lee SK, Lyndon AR, Rothstein JD, Wyllie DJ, Tanaka K, Jackson M. Posterior cerebellar Purkinje cells in an SCA5/SPARCA1 mouse model are especially vulnerable to the synergistic effect of loss of β-III spectrin and GLAST. Hum Mol Genet 2016; 25:4448-4461. [PMID: 28173092 PMCID: PMC5409221 DOI: 10.1093/hmg/ddw274] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Revised: 08/05/2016] [Accepted: 08/11/2016] [Indexed: 12/26/2022] Open
Abstract
Clinical phenotypes of spinocerebellar ataxia type-5 (SCA5) and spectrin-associated autosomal recessive cerebellar ataxia type-1 (SPARCA1) are mirrored in mice lacking β-III spectrin (β-III-/-). One function of β-III spectrin is the stabilization of the Purkinje cell-specific glutamate transporter EAAT4 at the plasma membrane. In β-III-/- mice EAAT4 levels are reduced from an early age. In contrast levels of the predominant cerebellar glutamate transporter GLAST, expressed in Bergmann glia, only fall progressively from 3 months onwards. Here we elucidated the roles of these two glutamate transporters in cerebellar pathogenesis mediated through loss of β-III spectrin function by studying EAAT4 and GLAST knockout mice as well as crosses of both with β-III-/- mice. Our data demonstrate that EAAT4 loss, but not abnormal AMPA receptor composition, in young β-III-/- mice underlies early Purkinje cell hyper-excitability and that subsequent loss of GLAST, superimposed on the earlier deficiency of EAAT4, is responsible for Purkinje cell loss and progression of motor deficits. Yet the loss of GLAST appears to be independent of EAAT4 loss, highlighting that other aspects of Purkinje cell dysfunction underpin the pathogenic loss of GLAST. Finally, our results demonstrate that Purkinje cells in the posterior cerebellum of β-III-/- mice are most susceptible to the combined loss of EAAT4 and GLAST, with degeneration of proximal dendrites, the site of climbing fibre innervation, most pronounced. This highlights the necessity for efficient glutamate clearance from these regions and identifies dysregulation of glutamatergic neurotransmission particularly within the posterior cerebellum as a key mechanism in SCA5 and SPARCA1 pathogenesis.
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Affiliation(s)
- Emma M. Perkins
- The Centre for Integrative Physiology, The University of Edinburgh, Hugh Robson Building, George Square, Edinburgh, UK
| | - Daumante Suminaite
- The Centre for Integrative Physiology, The University of Edinburgh, Hugh Robson Building, George Square, Edinburgh, UK
| | - Yvonne L. Clarkson
- The Centre for Integrative Physiology, The University of Edinburgh, Hugh Robson Building, George Square, Edinburgh, UK
| | - Sin Kwan Lee
- The Centre for Integrative Physiology, The University of Edinburgh, Hugh Robson Building, George Square, Edinburgh, UK
| | - Alastair R. Lyndon
- School of Energy, Geoscience, Infrastructure and Society, Heriot-Watt University, John Muir Building, Riccarton, Edinburgh, UK
| | - Jeffrey D. Rothstein
- Department of Neurology and Neuroscience, Johns Hopkins University, School of Medicine, Baltimore, MD, USA
| | - David J.A. Wyllie
- The Centre for Integrative Physiology, The University of Edinburgh, Hugh Robson Building, George Square, Edinburgh, UK
- Centre for Brain Development and Repair, Institute for Stem Cell Biology and Regenerative Medicine, Bangalore, India
| | - Kohichi Tanaka
- Laboratory of Molecular Neuroscience, Medical Research Institute, Tokyo Medical and Dental University, Bunkyo-Ku, Tokyo, Japan
| | - Mandy Jackson
- The Centre for Integrative Physiology, The University of Edinburgh, Hugh Robson Building, George Square, Edinburgh, UK
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10
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Lazo-Gómez R, Tapia R. Motor Alterations Induced by Chronic 4-Aminopyridine Infusion in the Spinal Cord In vivo: Role of Glutamate and GABA Receptors. Front Neurosci 2016; 10:200. [PMID: 27242406 PMCID: PMC4860413 DOI: 10.3389/fnins.2016.00200] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2016] [Accepted: 04/25/2016] [Indexed: 12/13/2022] Open
Abstract
Motor neuron (MN) degeneration is the pathological hallmark of MN diseases, a group of neurodegenerative disorders clinically manifested as muscle fasciculations and hyperreflexia, followed by paralysis, respiratory failure, and death. Ample evidence supports a role of glutamate-mediated excitotoxicity in motor death. In previous work we showed that stimulation of glutamate release from nerve endings by perfusion of the K+-channel blocker 4-aminopyridine (4-AP) in the rat hippocampus induces seizures and neurodegeneration, and that AMPA infusion in the spinal cord produces paralysis and MN death. On these bases, in this work we have tested the effect of the chronic infusion of 4-AP in the spinal cord, using implanted osmotic minipumps, on motor activity and on MN survival, and the mechanisms underlying this effect. 4-AP produced muscle fasciculations and motor deficits assessed in two motor tests, which start 2–3 h after the implant, which ameliorated spontaneously within 6–7 days, but no neurodegeneration. These effects were prevented by both AMPA and NMDA receptors blockers. The role of GABAA receptors was also explored, and we found that chronic infusion of bicuculline induced moderate MN degeneration and enhanced the hyperexcitation produced by 4-AP. Unexpectedly, the GABAAR agonist muscimol also induced motor deficits and failed to prevent the MN death induced by AMPA. We conclude that motor alterations induced by chronic 4-AP infusion in the spinal cord in vivo is due to ionotropic glutamate receptor overactivation and that blockade of GABAergic neurotransmission induces MN death under chronic conditions. These results shed light on the role of glutamatergic and GABAergic neurotransmission in the regulation of MN excitability in the spinal cord.
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Affiliation(s)
- Rafael Lazo-Gómez
- División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México México, México
| | - Ricardo Tapia
- División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México México, México
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11
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Rimmele TS, Rosenberg PA. GLT-1: The elusive presynaptic glutamate transporter. Neurochem Int 2016; 98:19-28. [PMID: 27129805 DOI: 10.1016/j.neuint.2016.04.010] [Citation(s) in RCA: 88] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Revised: 04/21/2016] [Accepted: 04/22/2016] [Indexed: 01/09/2023]
Abstract
Historically, glutamate uptake in the CNS was mainly attributed to glial cells for three reasons: 1) none of the glutamate transporters were found to be located in presynaptic terminals of excitatory synapses; 2) the putative glial transporters, GLT-1 and GLAST are expressed at high levels in astrocytes; 3) studies of the constitutive GLT-1 knockout as well as pharmacological studies demonstrated that >90% of glutamate uptake into forebrain synaptosomes is mediated by the operation of GLT-1. Here we summarize the history leading up to the recognition of GLT-1a as a presynaptic glutamate transporter. A major issue now is understanding the physiological and pathophysiological significance of the expression of GLT-1 in presynaptic terminals. To elucidate the cell-type specific functions of GLT-1, a conditional knockout was generated with which to inactivate the GLT-1 gene in different cell types using Cre/lox technology. Astrocytic knockout led to an 80% reduction of GLT-1 expression, resulting in intractable seizures and early mortality as seen also in the constitutive knockout. Neuronal knockout was associated with no obvious phenotype. Surprisingly, synaptosomal uptake capacity (Vmax) was found to be significantly reduced, by 40%, in the neuronal knockout, indicating that the contribution of neuronal GLT-1 to synaptosomal uptake is disproportionate to its protein expression (5-10%). Conversely, the contribution of astrocytic GLT-1 to synaptosomal uptake was much lower than expected. In contrast, the loss of uptake into liposomes prepared from brain protein from astrocyte and neuronal knockouts was proportionate with the loss of GLT-1 protein, suggesting that a large portion of GLT-1 in astrocytic membranes in synaptosomal preparations is not functional, possibly because of a failure to reseal. These results suggest the need to reinterpret many previous studies using synaptosomal uptake to investigate glutamate transport itself as well as changes in glutamate homeostasis associated with normal functions, neurodegeneration, and response to drugs.
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Affiliation(s)
- Theresa S Rimmele
- Department of Neurology and the F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, MA 02115, USA
| | - Paul A Rosenberg
- Department of Neurology and the F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, MA 02115, USA; Program in Neuroscience, Harvard Medical School, Boston, MA 02115, USA.
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12
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Eid T, Gruenbaum SE, Dhaher R, Lee TSW, Zhou Y, Danbolt NC. The Glutamate-Glutamine Cycle in Epilepsy. ADVANCES IN NEUROBIOLOGY 2016; 13:351-400. [PMID: 27885637 DOI: 10.1007/978-3-319-45096-4_14] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Epilepsy is a complex, multifactorial disease characterized by spontaneous recurrent seizures and an increased incidence of comorbid conditions such as anxiety, depression, cognitive dysfunction, and sudden unexpected death. About 70 million people worldwide are estimated to suffer from epilepsy, and up to one-third of all people with epilepsy are expected to be refractory to current medications. Development of more effective and specific antiepileptic interventions is therefore requisite. Perturbations in the brain's glutamate-glutamine cycle, such as increased extracellular levels of glutamate, loss of astroglial glutamine synthetase, and changes in glutaminase and glutamate dehydrogenase, are frequently encountered in patients with epilepsy. Hence, manipulations of discrete glutamate-glutamine cycle components may represent novel approaches to treat the disease. The goal of his review is to discuss some of the glutamate-glutamine cycle components that are altered in epilepsy, particularly neurotransmitters and metabolites, enzymes, amino acid transporters, and glutamate receptors. We will also review approaches that potentially could be used in humans to target the glutamate-glutamine cycle. Examples of such approaches are treatment with glutamate receptor blockers, glutamate scavenging, dietary intervention, and hypothermia.
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Affiliation(s)
- Tore Eid
- Department of Laboratory Medicine, Yale School of Medicine, 330 Cedar Street, 208035, New Haven, CT, 06520-8035, USA.
| | - Shaun E Gruenbaum
- Department of Anesthesiology, Yale School of Medicine, New Haven, CT, USA
| | - Roni Dhaher
- Department of Laboratory Medicine, Yale School of Medicine, 330 Cedar Street, 208035, New Haven, CT, 06520-8035, USA
| | - Tih-Shih W Lee
- Department of Psychiatry, Yale School of Medicine, New Haven, CT, USA
| | - Yun Zhou
- Department of Molecular Medicine, Institute for Basic Medical Sciences, University of Oslo, Oslo, Norway
| | - Niels Christian Danbolt
- Department of Molecular Medicine, Institute for Basic Medical Sciences, University of Oslo, Oslo, Norway
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13
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Zhou Y, Danbolt NC. Glutamate as a neurotransmitter in the healthy brain. J Neural Transm (Vienna) 2014; 121:799-817. [PMID: 24578174 PMCID: PMC4133642 DOI: 10.1007/s00702-014-1180-8] [Citation(s) in RCA: 527] [Impact Index Per Article: 52.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Accepted: 02/11/2014] [Indexed: 12/13/2022]
Abstract
Glutamate is the most abundant free amino acid in the brain and is at the crossroad between multiple metabolic pathways. Considering this, it was a surprise to discover that glutamate has excitatory effects on nerve cells, and that it can excite cells to their death in a process now referred to as "excitotoxicity". This effect is due to glutamate receptors present on the surface of brain cells. Powerful uptake systems (glutamate transporters) prevent excessive activation of these receptors by continuously removing glutamate from the extracellular fluid in the brain. Further, the blood-brain barrier shields the brain from glutamate in the blood. The highest concentrations of glutamate are found in synaptic vesicles in nerve terminals from where it can be released by exocytosis. In fact, glutamate is the major excitatory neurotransmitter in the mammalian central nervous system. It took, however, a long time to realize that. The present review provides a brief historical description, gives a short overview of glutamate as a transmitter in the healthy brain, and comments on the so-called glutamate-glutamine cycle. The glutamate transporters responsible for the glutamate removal are described in some detail.
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Affiliation(s)
- Y. Zhou
- The Neurotransporter Group, Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, Blindern, P.O. Box 1105, 0317 Oslo, Norway
| | - N. C. Danbolt
- The Neurotransporter Group, Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, Blindern, P.O. Box 1105, 0317 Oslo, Norway
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Petr GT, Bakradze E, Frederick NM, Wang J, Armsen W, Aizenman E, Rosenberg PA. Glutamate transporter expression and function in a striatal neuronal model of Huntington's disease. Neurochem Int 2013; 62:973-81. [PMID: 23507328 DOI: 10.1016/j.neuint.2013.02.026] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2012] [Revised: 02/26/2013] [Accepted: 02/28/2013] [Indexed: 11/26/2022]
Abstract
Excitotoxicity may contribute to the pathogenesis of Huntington's disease. High affinity Na+ dependent glutamate transporters, residing in the plasma membrane, clear glutamate from the extracellular space and are the primary means of protection against excitotoxicity. Many reports suggest that Huntington's disease is associated with a decrease in the expression and function of glutamate transporters. We studied the expression and function of these transporters in a cellular model of Huntington's disease, STHdh(Q111/Q111) and STHdh(Q7/Q7) cells. We found that only GLT-1b and EAAC1 were expressed in these cell lines and only EAAC1 significantly contributed to the glutamate uptake. Surprisingly, there was an increase in Na+-dependent glutamate uptake in STHdh(Q111/Q111) cells accompanied by an increase in surface expression of EAAC1. We studied the influence of the Akt pathway on EAAC1 mediated uptake, since EAAC1 surface expression is influenced by Akt and previous studies have shown increased Akt expression in STHdh(Q111/Q111) cells. Glutamate uptake was inhibited by Akt pathway inhibitors in both the STHdh(Q7/Q7) and the STHdh(Q111/Q111) cell lines. We found no difference in Akt activation between the two cell lines under our conditions of culture. Therefore a difference in Akt activation does not seem to explain the increase in EAAC1 mediated uptake in the STHdh(Q111/Q111) cells.
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Affiliation(s)
- Geraldine T Petr
- Department of Neurology and the F.M. Kirby Neurobiology Center, Children's Hospital Boston, Boston, MA 02115, USA
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15
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Abstract
The mammalian genome contains four genes encoding GABA transporters (GAT1, slc6a1; GAT2, slc6a13; GAT3, slc6a11; BGT1, slc6a12) and five glutamate transporter genes (EAAT1, slc1a3; EAAT2, slc1a2; EAAT3, slc1a1; EAAT4, slc1a6; EAAT5, slc1a7). These transporters keep the extracellular levels of GABA and excitatory amino acids low and provide amino acids for metabolic purposes. The various transporters have different properties both with respect to their transport functions and with respect to their ability to act as ion channels. Further, they are differentially regulated. To understand the physiological roles of the individual transporter subtypes, it is necessary to obtain information on their distributions and expression levels. Quantitative data are important as the functional capacity is limited by the number of transporter molecules. The most important and most abundant transporters for removal of transmitter glutamate in the brain are EAAT2 (GLT-1) and EAAT1 (GLAST), while GAT1 and GAT3 are the major GABA transporters in the brain. EAAT3 (EAAC1) does not appear to play a role in signal transduction, but plays other roles. Due to their high uncoupled anion conductance, EAAT4 and EAAT5 seem to be acting more like inhibitory glutamate receptors than as glutamate transporters. GAT2 and BGT1 are primarily expressed in the liver and kidney, but are also found in the leptomeninges, while the levels in brain tissue proper are too low to have any impact on GABA removal, at least in normal young adult mice. The present review will provide summary of what is currently known and will also discuss some methodological pitfalls.
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Affiliation(s)
- Yun Zhou
- The Neurotransporter Group, Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
| | - Niels Christian Danbolt
- The Neurotransporter Group, Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
- *Correspondence: Niels Christian Danbolt, The Neurotransporter Group, Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, P.O. Box 1105 Blindern, Oslo N-0317, Norway e-mail:
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16
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Jungblut M, Tiveron MC, Barral S, Abrahamsen B, Knöbel S, Pennartz S, Schmitz J, Perraut M, Pfrieger FW, Stoffel W, Cremer H, Bosio A. Isolation and characterization of living primary astroglial cells using the new GLAST-specific monoclonal antibody ACSA-1. Glia 2012; 60:894-907. [PMID: 22374709 DOI: 10.1002/glia.22322] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2011] [Accepted: 02/14/2012] [Indexed: 12/23/2022]
Abstract
Astrocytes show large morphological and functional heterogeneity and are involved in many aspects of neural function. Progress in defining astrocyte subpopulations has been hampered by the lack of a suitable antibody for their direct detection and isolation. Here, we describe a new monoclonal antibody, ACSA-1, which was generated by immunization of GLAST1 knockout mice. The antibody specifically detects an extracellular epitope of the astrocyte-specific L-glutamate/L-aspartate transporter GLAST (EAAT1, Slc1a3). As shown by immunohistochemistry, immunocytochemistry, and flow cytometry, ACSA-1 was cross-reactive for mouse, human, and rat. It labeled virtually all astrocytes positive for GFAP, GS, BLBP, RC2, and Nestin, including protoplastic, fibrous, and reactive astrocytes as well as Bergmann glia, Müller glia, and radial glia. Oligodendrocytes, microglia, neurons, and neuronal progenitors were negative for ACSA-1. Using an immunomagnetic approach, we established a method for the isolation of GLAST-positive cells with high purity. Binding of the antibody to GLAST and subsequent sorting of GLAST-positive cells neither interfered with cellular glutamate transport nor compromised astrocyte viability in vitro. The ACSA-1 antibody is not only a valuable tool to identify and track astrocytes by immunostaining, but also provides the possibility of separation and further analysis of pure astrocytes.
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Affiliation(s)
- Melanie Jungblut
- Miltenyi Biotec GmbH, Friedrich-Ebert-Straße 68, Bergisch Gladbach, Germany
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17
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Volknandt W, Karas M. Proteomic analysis of the presynaptic active zone. Exp Brain Res 2012; 217:449-61. [DOI: 10.1007/s00221-012-3031-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2011] [Accepted: 02/04/2012] [Indexed: 02/06/2023]
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18
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Rowley NM, Madsen KK, Schousboe A, Steve White H. Glutamate and GABA synthesis, release, transport and metabolism as targets for seizure control. Neurochem Int 2012; 61:546-58. [PMID: 22365921 DOI: 10.1016/j.neuint.2012.02.013] [Citation(s) in RCA: 115] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2012] [Accepted: 02/09/2012] [Indexed: 11/17/2022]
Abstract
The synthesis, release, reuptake, and metabolism of the excitatory and inhibitory neurotransmitters glutamate and GABA, respectively, are tightly controlled. Given the role that these two neurotransmitters play in normal and abnormal neurotransmission, it is important to consider the processes whereby they are regulated. This brief review is focused entirely on the metabolic aspects of glutamate and GABA synthesis and neurotransmission. It describes in limited detail the synthesis, release, reuptake, metabolism, cellular compartmentation and pharmacology of the glutamatergic and GABAergic synapse. This review also provides a summary and brief description of the pathologic and phenotypic features of the various genetic animal models that have been developed in an effort to provide a greater understanding of the role that each of the aforementioned metabolic processes plays in controlling excitatory and inhibitory neurotransmission and how their use will hopefully facilitate the development of safer and more efficacious therapies for the treatment of epilepsy and other neurological disorders.
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Affiliation(s)
- Nicole M Rowley
- Department of Pharmacology and Toxicology, Anticonvulsant Drug Development Program, University of Utah, 417 Wakara Way, Suite 3211, Salt Lake City, UT 84108, USA
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19
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Schraven SP, Franz C, Rüttiger L, Löwenheim H, Lysakowski A, Stoffel W, Knipper M. Altered phenotype of the vestibular organ in GLAST-1 null mice. J Assoc Res Otolaryngol 2012; 13:323-33. [PMID: 22350511 DOI: 10.1007/s10162-011-0311-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2011] [Accepted: 12/21/2011] [Indexed: 01/11/2023] Open
Abstract
Various studies point to a crucial role of the high-affinity sodium-coupled glutamate aspartate transporter GLAST-1 for modulation of excitatory transmission as shown in the retina and the CNS. While 2-4-month-old GLAST-1 null mice did not show any functional vestibular abnormality, we observed profound circling behavior in older (7 months) animals lacking GLAST-1. An unchanged total number of otoferlin-positive vestibular hair cells (VHCs), similar ribbon numbers in VHCs, and an unchanged VGLUT3 expression in type II VHCs were detected in GLAST-1 null compared to wild-type mice. A partial loss of supporting cells and an apparent decline of a voltage-gated channel potassium subunit (KCNQ4) was observed in postsynaptic calyceal afferents contacting type I VHCs, together with a reduction of neurofilament- (NF200-) and vesicular glutamate transporter 1- (VGLUT1-) positive calyces in GLAST-1 null mice. Taken together, GLAST-1 deletion appeared to preferentially affect the maintenance of a normal postsynaptic/neuronal phenotype, evident only with increasing age.
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Affiliation(s)
- Sebastian P Schraven
- Department of Otolaryngology, Tübingen Hearing Research Centre (THRC), Molecular Physiology of Hearing, University of Tübingen, Elfriede-Aulhorn-Str. 5, 72076 Tübingen, Germany
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20
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Napier IA, Mohammadi SA, Christie MJ. Glutamate transporter dysfunction associated with nerve injury-induced pain in mice. J Neurophysiol 2012; 107:649-57. [DOI: 10.1152/jn.00763.2011] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Dysfunction at glutamatergic synapses has been proposed as a mechanism in the development of neuropathic pain. Here we sought to determine whether peripheral nerve injury-induced neuropathic pain results in functional changes to primary afferent synapses. Signs of neuropathic pain as well as an induction of glial fibrillary acidic protein in immunostained spinal cord sections 4 days after partial ligation of the sciatic nerve indicated the induction of neuropathic pain. We found that following nerve injury, no discernable change to kinetics of dl-α-amino-3-hydroxy-5-methylisoxazole-propionic acid (AMPA) or N-methyl-d-aspartate receptor (NMDAR)-mediated evoked excitatory postsynaptic currents (eEPSCs) could be observed in dorsal horn (lamina I/II) neurons compared with those of naïve mice. However, we did find that nerve injury was accompanied by slowed decay of the early phase of eEPSCs in the presence of glutamate transporter inhibition by the competitive nontransportable inhibitor dl-threo-β-benzyloxyaspartic acid (TBOA). Concomitantly, expression patterns for the two major glutamate transporters in the spinal cord, excitatory amino acid transporters (EAAT) 1 and EAAT2, were found to be reduced at this time (4 days postinjury). We then sought to directly determine whether nerve injury results in glutamate spillover to NMDARs at dorsal horn synapses. By employing the use-dependent NMDAR blocker (±)MK-801 to block subsynaptic receptors, we found that although TBOA-induced spillover to extrasynaptic receptors trended to increased activation of these receptors after nerve injury, this was not significant compared with naïve mice. Together, these results suggest the development of neuropathic pain involves subtle changes to glutamate transporter expression and function that could contribute to neuropathic pain during excessive synaptic activity.
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Affiliation(s)
- Ian A. Napier
- Discipline of Pharmacology, University of Sydney, New South Wales, Australia
| | - Sarasa A. Mohammadi
- Discipline of Pharmacology, University of Sydney, New South Wales, Australia
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Karaca M, Frigerio F, Maechler P. From pancreatic islets to central nervous system, the importance of glutamate dehydrogenase for the control of energy homeostasis. Neurochem Int 2011; 59:510-7. [DOI: 10.1016/j.neuint.2011.03.024] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2010] [Revised: 03/21/2011] [Accepted: 03/23/2011] [Indexed: 11/25/2022]
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22
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Ferraro TN, Smith GG, Schwebel CL, Doyle GA, Ruiz SE, Oleynick JU, Lohoff FW, Berrettini WH, Buono RJ. Confirmation of multiple seizure susceptibility QTLs on chromosome 15 in C57BL/6J and DBA/2J inbred mice. Physiol Genomics 2010; 42A:1-7. [PMID: 20571108 DOI: 10.1152/physiolgenomics.00096.2010] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To confirm seizure susceptibility (SZS) quantitative trait loci (QTLs) on chromosome (chr) 15 identified previously using C57BL/6J (B6) and DBA/2J (D2) mice and to refine their genomic map position, we studied a set of three congenic strains in which overlapping segments of chr 15 from D2 were transferred onto the B6 background. We measured thresholds for generalized electroshock seizure (GEST) and maximal electroshock seizure (MEST) in congenic strains and B6-like littermates and also tested their responses to kainic acid (KA) and pentylenetetrazol (PTZ). Results document that MEST is significantly lower in strains 15M and 15D, which harbor medial and distal (telomeric) segments of chr 15 (respectively) from D2, compared with strain 15P, which harbors the proximal (acromeric) segment of chr 15 from D2, and with control littermates. Congenic strains 15P and 15M exhibited greater KA SZS compared with strain 15D and B6-like controls. All congenic strains were similar to controls with regard to PTZ SZS. Taken together, results suggest there are multiple SZS QTLs on chr 15 and that two QTLs harbor gene variants that affect MEST and KA SZS independently. The MEST QTL is refined to a 19 Mb region flanked by rs13482630 and D15Mit159. This interval contains 350 genes, 183 of which reside in areas where the polymorphism rate between B6 and D2 is high. The KA QTL interval spans a 65 Mb region flanked by markers D15Mit13 and rs31271969. It harbors 83 genes in highly polymorphic areas, 310 genes in all. Complete dissection of these loci will lead to identification of genetic variants that influence SZS in mice and provide a better understanding of seizure biology.
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Affiliation(s)
- T N Ferraro
- Center for Neurobiology and Behavior, Department of Psychiatry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-3403, USA.
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23
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Loss of beta-III spectrin leads to Purkinje cell dysfunction recapitulating the behavior and neuropathology of spinocerebellar ataxia type 5 in humans. J Neurosci 2010; 30:4857-67. [PMID: 20371805 DOI: 10.1523/jneurosci.6065-09.2010] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Mutations in SPTBN2, the gene encoding beta-III spectrin, cause spinocerebellar ataxia type 5 in humans (SCA5), a neurodegenerative disorder resulting in loss of motor coordination. How these mutations give rise to progressive ataxia and what the precise role beta-III spectrin plays in normal cerebellar physiology are unknown. We developed a mouse lacking full-length beta-III spectrin and found that homozygous mice reproduced features of SCA5 including gait abnormalities, tremor, deteriorating motor coordination, Purkinje cell loss, and cerebellar atrophy (molecular layer thinning). In vivo analysis reveals an age-related reduction in simple spike firing rate in surviving beta-III(-/-) Purkinje cells, whereas in vitro studies show these neurons to have reduced spontaneous firing, smaller sodium currents, and dysregulation of glutamatergic neurotransmission. Our data suggest an early loss of EAAT4- (protein interactor of beta-III spectrin) and a subsequent loss of GLAST-mediated uptake may play a role in neuronal pathology. These findings implicate a loss of beta-III spectrin function in SCA5 pathogenesis and indicate that there are at least two physiological effects of beta-III spectrin loss that underpin a progressive loss of inhibitory cerebellar output, namely an intrinsic Purkinje cell membrane defect due to reduced sodium currents and alterations in glutamate signaling.
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24
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Tissue specificity of mitochondrial glutamate pathways and the control of metabolic homeostasis. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:965-72. [PMID: 18486589 DOI: 10.1016/j.bbabio.2008.04.031] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2008] [Revised: 04/11/2008] [Accepted: 04/22/2008] [Indexed: 11/24/2022]
Abstract
Glutamate is implicated in numerous metabolic and signalling functions that vary according to specific tissues. Glutamate metabolism is tightly controlled by activities of mitochondrial enzymes and transmembrane carriers, in particular glutamate dehydrogenase and mitochondrial glutamate carriers that have been identified in recent years. It is remarkable that, although glutamate-specific enzymes and transporters share similar properties in most tissues, their regulation varies greatly according to particular organs in order to achieve tissue specific functions. This is illustrated in this review when comparing glutamate handling in liver, brain, and pancreatic beta-cells. We describe the main cellular glutamate pathways and their specific functions in different tissues, ultimately contributing to the control of metabolic homeostasis at the organism level.
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25
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Genoud C, Quairiaux C, Steiner P, Hirling H, Welker E, Knott GW. Plasticity of astrocytic coverage and glutamate transporter expression in adult mouse cortex. PLoS Biol 2007; 4:e343. [PMID: 17048987 PMCID: PMC1609127 DOI: 10.1371/journal.pbio.0040343] [Citation(s) in RCA: 215] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2005] [Accepted: 08/17/2006] [Indexed: 11/19/2022] Open
Abstract
Astrocytes play a major role in the removal of glutamate from the extracellular compartment. This clearance limits the glutamate receptor activation and affects the synaptic response. This function of the astrocyte is dependent on its positioning around the synapse, as well as on the level of expression of its high-affinity glutamate transporters, GLT1 and GLAST. Using Western blot analysis and serial section electron microscopy, we studied how a change in sensory activity affected these parameters in the adult cortex. Using mice, we found that 24 h of whisker stimulation elicited a 2-fold increase in the expression of GLT1 and GLAST in the corresponding cortical column of the barrel cortex. This returns to basal levels 4 d after the stimulation was stopped, whereas the expression of the neuronal glutamate transporter EAAC1 remained unaltered throughout. Ultrastructural analysis from the same region showed that sensory stimulation also causes a significant increase in the astrocytic envelopment of excitatory synapses on dendritic spines. We conclude that a period of modified neuronal activity and synaptic release of glutamate leads to an increased astrocytic coverage of the bouton-spine interface and an increase in glutamate transporter expression in astrocytic processes.
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Affiliation(s)
- Christel Genoud
- Départment de Biologie Cellulaire et de Morphologie, Lausanne, Switzerland
| | - Charles Quairiaux
- Départment de Biologie Cellulaire et de Morphologie, Lausanne, Switzerland
| | - Pascal Steiner
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts, United States of America
- Faculté des Sciences de la Vie, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland
| | - Harald Hirling
- Faculté des Sciences de la Vie, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland
| | - Egbert Welker
- Départment de Biologie Cellulaire et de Morphologie, Lausanne, Switzerland
| | - Graham W Knott
- Départment de Biologie Cellulaire et de Morphologie, Lausanne, Switzerland
- * To whom correspondence should be addressed. E-mail:
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26
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Mori T, Tanaka K, Buffo A, Wurst W, Kühn R, Götz M. Inducible gene deletion in astroglia and radial glia--a valuable tool for functional and lineage analysis. Glia 2006; 54:21-34. [PMID: 16652340 DOI: 10.1002/glia.20350] [Citation(s) in RCA: 296] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Astrocytes are thought to play a variety of key roles in the adult brain, such as their participation in synaptic transmission, in wound healing upon brain injury, and adult neurogenesis. However, to elucidate these functions in vivo has been difficult because of the lack of astrocyte-specific gene targeting. Here we show that the inducible form of Cre (CreERT2) expressed in the locus of the astrocyte-specific glutamate transporter (GLAST) allows precisely timed gene deletion in adult astrocytes as well as radial glial cells at earlier developmental stages. Moreover, postnatal and adult neurogenesis can be targeted at different stages with high efficiency as it originates from astroglial cells. Taken together, this mouse line will allow dissecting the molecular pathways regulating the diverse functions of astrocytes as precursors, support cells, repair cells, and cells involved in neuronal information processing.
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Affiliation(s)
- Tetsuji Mori
- Institute of Stem Cell Research, GSF-National Research Center for Environment and Health, Neuherberg/Munich, Germany
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27
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González-Mejia ME, Morales M, Hernández-Kelly LCR, Zepeda RC, Bernabé A, Ortega A. Glutamate-dependent translational regulation in cultured Bergmann glia cells: involvement of p70S6K. Neuroscience 2006; 141:1389-98. [PMID: 16766130 DOI: 10.1016/j.neuroscience.2006.04.076] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2005] [Revised: 04/20/2006] [Accepted: 04/26/2006] [Indexed: 11/15/2022]
Abstract
Glutamate, the main excitatory amino acid transmitter in the vertebrate brain is involved in the dynamic changes in protein repertoire that underlie synaptic plasticity. Activity-dependent differential expression patterns occur not only in neurons but also in glial cells. In fact, a membrane to nuclei signaling has been described after ionotropic glutamate receptor stimulation in cultured chick cerebellar Bergmann glia cells. In order to characterize other levels of protein expression regulation, we explored the effect of glutamate treatment in [35S]-methionine incorporation into newly synthesized polypeptides. A time-dependent modification in protein synthesis was found. An important component of translational control is the ribosomal S6 protein kinase. Threonine phosphorylation renders the kinase active increasing translation initiation. Glutamate exposure results in ribosomal S6 protein kinase Thr389 phosphorylation in a dose and time-dependent manner that matches perfectly with the overall protein synthesis profile detected upon the excitatory amino acid. Pharmacological characterization of the receptors involved suggests the participation of both ionotropic as well as metabotropic glutamate receptors. The non-receptor tyrosine kinase Src, phosphatidylinositol 3-kinase, protein kinase B and the mammalian target of rapamycin are mediators of the glutamate effect. These results not only demonstrate that glutamate receptors activation is critically involved in translational control in glial cells adjacent to synaptic processes like cerebellar Bergmann glia cells, but also further strengthen the notion of an active participation of glial cells in synaptic transmission.
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Affiliation(s)
- M E González-Mejia
- Departamento de Genética y Biología Molecular, Centro de Investigación y de Estudios Avanzados Unidad Zacatenco, Apartado Postal 14-740, México DF 0300, Mexico
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28
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Niederberger E, Schmidtko A, Coste O, Marian C, Ehnert C, Geisslinger G. The glutamate transporter GLAST is involved in spinal nociceptive processing. Biochem Biophys Res Commun 2006; 346:393-9. [PMID: 16765320 DOI: 10.1016/j.bbrc.2006.05.163] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2006] [Accepted: 05/13/2006] [Indexed: 12/19/2022]
Abstract
GLAST and GLT-1 are the most abundant glutamate transporters in the CNS and protect neurons from glutamate neurotoxicity. Here, we investigated the role of GLAST in spinal nociceptive processing. GLAST protein expression was not altered after treatment of rats with either formalin or zymosan. Surprisingly, knock-down of GLAST in the spinal cord using antisense-oligonucleotides decreased glutamate concentrations in cerebrospinal fluid (CSF) and reduced the nociceptive behaviour in the rat formalin assay. However, it did not influence thermal hyperalgesia in the zymosan-induced paw inflammation model indicating that GLAST is associated with spontaneous rather than inflammatory nociception. Mechanisms that might explain the decreased response in the formalin assay may include compensatory activation of other glutamate transporters, inhibition of glutamate release or disturbance of glutamate recycling. In conclusion, these data suggest that inhibition of GLAST expression in the spinal cord reduces excitatory synaptic activity and thereby spontaneous responses after nociceptive stimulation of the paw.
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Affiliation(s)
- Ellen Niederberger
- pharmazentrum frankfurt/ZAFES, Klinikum der Johann Wolfgang Goethe-Universität Frankfurt, Theodor Stern Kai 7, Frankfurt am Main, Germany.
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29
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Takatsuru Y, Takayasu Y, Iino M, Nikkuni O, Ueda Y, Tanaka K, Ozawa S. Roles of glial glutamate transporters in shaping EPSCs at the climbing fiber-Purkinje cell synapses. Neurosci Res 2006; 54:140-8. [PMID: 16377014 DOI: 10.1016/j.neures.2005.11.002] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2005] [Revised: 11/01/2005] [Accepted: 11/02/2005] [Indexed: 11/17/2022]
Abstract
Glial glutamate transporters, GLAST and GLT-1, are co-localized in processes of Bergmann glia (BG) wrapping excitatory synapses on Purkinje cells (PCs). Although GLAST is expressed six-fold more abundantly than GLT-1, no change is detected in the kinetics of climbing fiber (CF)-mediated excitatory postsynaptic currents (CF-EPSCs) in PCs in GLAST(-/-) mice compared to the wild-type mice (WT). Here we aimed to clarify the mechanism(s) underlying this unexpected finding using a selective GLT-1 blocker, dihydrokainate (DHK), and a novel antagonist of glial glutamate transporter, (2S,3S)-3-[3-(4-methoxybenzoylamino)benzyloxy]aspartate (PMB-TBOA). In the presence of cyclothiazide (CTZ), which attenuates the desensitization of AMPA receptors, DHK prolonged the decay time constant (tau(w)) of CF-EPSCs in WT, indicating that GLT-1 plays a partial role in the removal of glutamate. The application of 100 nM PMB-TBOA, which inhibited CF-mediated transporter currents in BG by approximately 80%, caused no change in tau(w) in WT in the absence of CTZ, whereas it prolonged tau(w) in the presence of CTZ. This prolonged value of tau(w) was similar to that in GLAST(-/-) mice in the presence of CTZ. These results indicate that glial glutamate transporters can apparently retain the fast decay kinetics of CF-EPSCs if a small proportion ( approximately 20%) of functional transporters is preserved.
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Affiliation(s)
- Yusuke Takatsuru
- Department of Neurophysiology, Gunma University Graduate School of Medicine, Maebashi, Gunma 371-8511, Japan.
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30
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Shen Y, Linden DJ. Long-term potentiation of neuronal glutamate transporters. Neuron 2005; 46:715-22. [PMID: 15924858 DOI: 10.1016/j.neuron.2005.04.033] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2004] [Revised: 02/02/2005] [Accepted: 04/28/2005] [Indexed: 01/21/2023]
Abstract
Persistent, use-dependent modulation of synaptic strength has been demonstrated for fast synaptic transmission mediated by glutamate and has been hypothesized to underlie persistent behavioral changes ranging from memory to addiction. Glutamate released at synapses is sequestered by the action of excitatory amino acid transporters (EAATs) in glia and postsynaptic neurons. So, the efficacy of glutamate transporter function is crucial for regulating glutamate spillover to adjacent presynaptic and postsynaptic receptors and the consequent induction of plastic or excitotoxic processes. Here, we report that tetanic stimulation of cerebellar climbing fiber-Purkinje cell synapses results in long-term potentiation (LTP) of a climbing fiber-evoked glutamate transporter current recorded in Purkinje cells. This LTP is postsynaptically expressed and requires activation of an mGluR1/PKC cascade. Together with a simultaneously induced long-term depression (LTD) of postsynaptic AMPA receptors, this might reflect an integrated antiexcitotoxic cellular response to strong climbing fiber synaptic activation, as occurs following an ischemic episode.
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Affiliation(s)
- Ying Shen
- Department of Neuroscience, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, Maryland 21205, USA
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31
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Selkirk JV, Nottebaum LM, Vana AM, Verge GM, Mackay KB, Stiefel TH, Naeve GS, Pomeroy JE, Petroski RE, Moyer J, Dunlop J, Foster AC. Role of the GLT-1 subtype of glutamate transporter in glutamate homeostasis: the GLT-1-preferring inhibitor WAY-855 produces marginal neurotoxicity in the rat hippocampus. Eur J Neurosci 2005; 21:3217-28. [PMID: 16026460 DOI: 10.1111/j.1460-9568.2005.04162.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Glutamate is the major excitatory neurotransmitter in the central nervous system and is tightly regulated by cell surface transporters to avoid increases in concentration and associated neurotoxicity. Selective blockers of glutamate transporter subtypes are sparse and so knock-out animals and antisense techniques have been used to study their specific roles. Here we used WAY-855, a GLT-1-preferring blocker, to assess the role of GLT-1 in rat hippocampus. GLT-1 was the most abundant transporter in the hippocampus at the mRNA level. According to [(3)H]-l-glutamate uptake data, GLT-1 was responsible for approximately 80% of the GLAST-, GLT-1-, and EAAC1-mediated uptake that occurs within dissociated hippocampal tissue, yet when this transporter was preferentially blocked for 120 h with WAY-855 (100 microm), no significant neurotoxicity was observed in hippocampal slices. This is in stark contrast to results obtained with TBOA, a broad-spectrum transport blocker, which, at concentrations that caused a similar inhibition of glutamate uptake (10 and 30 microm), caused substantial neuronal death when exposed to the slices for 24 h or longer. Likewise, WAY-855, did not significantly exacerbate neurotoxicity associated with simulated ischemia, whereas TBOA did. Finally, intrahippocampal microinjection of WAY-855 (200 and 300 nmol) in vivo resulted in marginal damage compared with TBOA (20 and 200 nmol), which killed the majority of both CA1-4 pyramidal cells and dentate gyrus granule cells. These results indicate that selective inhibition of GLT-1 is insufficient to provoke glutamate build-up, leading to NMDA receptor-mediated neurotoxic effects, and suggest a prominent role of GLAST and/or EAAC1 in extracellular glutamate maintenance.
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Affiliation(s)
- Julie V Selkirk
- Neurosciences Department, Neurocrine Biosciences Inc., 12970 El Camino Real, San Diego, CA 92130, USA.
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