1
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Howes OD, Dawkins E, Lobo MC, Kaar SJ, Beck K. New drug treatments for schizophrenia: a review of approaches to target circuit dysfunction. Biol Psychiatry 2024:S0006-3223(24)01349-0. [PMID: 38815885 DOI: 10.1016/j.biopsych.2024.05.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/29/2023] [Revised: 04/23/2024] [Accepted: 05/14/2024] [Indexed: 06/01/2024]
Abstract
Schizophrenia is a leading cause of global disease burden. Current drug treatments are associated with significant side-effects and have limited efficacy for many patients; highlighting the need to develop new approaches that target other aspects of the neurobiology of schizophrenia. Preclinical, in vivo imaging, post-mortem, genetic and pharmacological studies have highlighted the key role of cortical GABA-glutamatergic microcircuits and their projections to subcortical dopaminergic circuits in the pathoetiology of negative, cognitive and psychotic symptoms. Antipsychotics primarily act downstream of the dopaminergic component of this circuit. However, multiple drugs are currently in development that could target other elements of this circuit to treat schizophrenia. These include drugs for GABA or glutamatergic targets, including glycine transporters, d-amino acid oxidase, sodium channels or potassium channels. Other drugs in development are likely to primarily act on pathways that regulate the dopaminergic system such as muscarinic or trace amine receptors or serotonin 2A receptors, whilst phosphodiesterase 10 A inhibitors are being developed to modulate the downstream consequences of dopaminergic dysfunction. Our review considers where new drugs may act on this circuit and their latest clinical trial evidence in terms of indication, efficacy and side-effects. Limitations of the circuit model, including whether there are neurobiologically distinct subgroups of patients, and future directions are also considered. Several drugs based on the mechanisms reviewed have promising clinical data, with the muscarinic agonist KarXT most advanced. If they are approved for clinical use, they have the potential to revolutionise understanding of the pathophysiology and treatment of schizophrenia.
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Affiliation(s)
- Oliver D Howes
- Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK; Institute of Clinical Sciences, Faculty of Medicine, Imperial College London, London, UK; South London and Maudsley NHS Foundation Trust, Maudsley Hospital, London, UK.
| | - Eleanor Dawkins
- Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK; South London and Maudsley NHS Foundation Trust, Maudsley Hospital, London, UK
| | - Maria C Lobo
- South London and Maudsley NHS Foundation Trust, Maudsley Hospital, London, UK
| | - Stephen J Kaar
- Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK; Division of Psychology and Mental Health, School of Health Sciences, Faculty of Biology, Medicine and health, The University of Manchester, Manchester, UK; Greater Manchester Mental Health NHS Foundation Trust, Manchester, UK
| | - Katherine Beck
- Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK; South London and Maudsley NHS Foundation Trust, Maudsley Hospital, London, UK
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2
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Wei Y, Li R, Meng Y, Hu T, Zhao J, Gao Y, Bai Q, Li N, Zhao Y. Transport mechanism and pharmacology of the human GlyT1. Cell 2024; 187:1719-1732.e14. [PMID: 38513663 DOI: 10.1016/j.cell.2024.02.026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2023] [Revised: 12/09/2023] [Accepted: 02/21/2024] [Indexed: 03/23/2024]
Abstract
The glycine transporter 1 (GlyT1) plays a crucial role in the regulation of both inhibitory and excitatory neurotransmission by removing glycine from the synaptic cleft. Given its close association with glutamate/glycine co-activated NMDA receptors (NMDARs), GlyT1 has emerged as a central target for the treatment of schizophrenia, which is often linked to hypofunctional NMDARs. Here, we report the cryo-EM structures of GlyT1 bound with substrate glycine and drugs ALX-5407, SSR504734, and PF-03463275. These structures, captured at three fundamental states of the transport cycle-outward-facing, occluded, and inward-facing-enable us to illustrate a comprehensive blueprint of the conformational change associated with glycine reuptake. Additionally, we identified three specific pockets accommodating drugs, providing clear insights into the structural basis of their inhibitory mechanism and selectivity. Collectively, these structures offer significant insights into the transport mechanism and recognition of substrate and anti-schizophrenia drugs, thus providing a platform to design small molecules to treat schizophrenia.
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Affiliation(s)
- Yiqing Wei
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China; College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Renjie Li
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China; College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yufei Meng
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China; College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Tuo Hu
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China; College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jun Zhao
- Peking University Institute of Advanced Agricultural Sciences, Shandong Laboratory of Advanced Agricultural Sciences at Weifang, Weifang, Shandong 261000, China
| | - Yiwei Gao
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China; College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Qinru Bai
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China; College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Na Li
- Heart Center and Beijing Key Laboratory of Hypertension, Beijing Chaoyang Hospital, Capital Medical University, Beijing 100020, China
| | - Yan Zhao
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China; State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China.
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3
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Miyazaki T. Identification of a novel enzyme and the regulation of key enzymes in mammalian taurine synthesis. J Pharmacol Sci 2024; 154:9-17. [PMID: 38081683 DOI: 10.1016/j.jphs.2023.11.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2023] [Revised: 10/31/2023] [Accepted: 11/16/2023] [Indexed: 12/18/2023] Open
Abstract
Taurine has many pharmacological roles on various tissues. The maintenance of abundant taurine content in the mammalian body through endogenous synthesis, in addition to exogenous intake, is the essential factor for morphological and functional maintenances in most tissues. The synthesis of taurine from sulfur-containing amino acids is influenced by various factors. Previous literature findings indicate the influence of the intake of proteins and sulfur-containing amino acids on the activity of the rate-limiting enzymes cysteine dioxygenase and cysteine sulfinate decarboxylase. In addition, the regulation of the activity and expression of taurine-synthesis enzymes by hormones, bile acids, and inflammatory cytokines through nuclear receptors have been reported in liver and reproductive tissues. Furthermore, flavin-containing monooxygenase subtype 1 was recently identified as the taurine-synthesis enzyme that converts hypotaurine to taurine. This review introduces the novel taurine synthesis enzyme and the nuclear receptor-associated regulation of key enzymes in taurine synthesis.
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Affiliation(s)
- Teruo Miyazaki
- Joint Research Center, Tokyo Medical University Ibaraki Medical Center, 3-20-1 Chuo, Ami, Ibaraki, 300-0395, Japan.
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4
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Bian X, Zhu J, Jia X, Liang W, Yu S, Li Z, Zhang W, Rao Y. Suggestion of creatine as a new neurotransmitter by approaches ranging from chemical analysis and biochemistry to electrophysiology. eLife 2023; 12:RP89317. [PMID: 38126335 PMCID: PMC10735228 DOI: 10.7554/elife.89317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2023] Open
Abstract
The discovery of a new neurotransmitter, especially one in the central nervous system, is both important and difficult. We have been searching for new neurotransmitters for 12 y. We detected creatine (Cr) in synaptic vesicles (SVs) at a level lower than glutamate and gamma-aminobutyric acid but higher than acetylcholine and 5-hydroxytryptamine. SV Cr was reduced in mice lacking either arginine:glycine amidinotransferase (a Cr synthetase) or SLC6A8, a Cr transporter with mutations among the most common causes of intellectual disability in men. Calcium-dependent release of Cr was detected after stimulation in brain slices. Cr release was reduced in Slc6a8 and Agat mutants. Cr inhibited neocortical pyramidal neurons. SLC6A8 was necessary for Cr uptake into synaptosomes. Cr was found by us to be taken up into SVs in an ATP-dependent manner. Our biochemical, chemical, genetic, and electrophysiological results are consistent with the possibility of Cr as a neurotransmitter, though not yet reaching the level of proof for the now classic transmitters. Our novel approach to discover neurotransmitters is to begin with analysis of contents in SVs before defining their function and physiology.
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Affiliation(s)
- Xiling Bian
- Laboratory of Neurochemical Biology, PKU-IDG/McGovern Institute for Brain Research, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Department of Chemical Biology, College of Chemistry and Chemical Engineering, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking UniversityBeijingChina
- Chinese Institute for Brain Research (CIBR)BeijingChina
| | - Jiemin Zhu
- Laboratory of Neurochemical Biology, PKU-IDG/McGovern Institute for Brain Research, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Department of Chemical Biology, College of Chemistry and Chemical Engineering, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking UniversityBeijingChina
- Chinese Institute for Brain Research (CIBR)BeijingChina
| | - Xiaobo Jia
- Laboratory of Neurochemical Biology, PKU-IDG/McGovern Institute for Brain Research, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Department of Chemical Biology, College of Chemistry and Chemical Engineering, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking UniversityBeijingChina
- Chinese Institute for Brain Research (CIBR)BeijingChina
| | - Wenjun Liang
- Chinese Institutes of Medical Research, Capital Medical UniversityBeijingChina
- Changping Laboratory, Yard 28, Science Park Road, Changping DistrictBeijingChina
| | - Sihan Yu
- Laboratory of Neurochemical Biology, PKU-IDG/McGovern Institute for Brain Research, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Department of Chemical Biology, College of Chemistry and Chemical Engineering, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking UniversityBeijingChina
- Changping Laboratory, Yard 28, Science Park Road, Changping DistrictBeijingChina
| | - Zhiqiang Li
- Laboratory of Neurochemical Biology, PKU-IDG/McGovern Institute for Brain Research, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Department of Chemical Biology, College of Chemistry and Chemical Engineering, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking UniversityBeijingChina
| | - Wenxia Zhang
- Laboratory of Neurochemical Biology, PKU-IDG/McGovern Institute for Brain Research, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Department of Chemical Biology, College of Chemistry and Chemical Engineering, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking UniversityBeijingChina
- Chinese Institutes of Medical Research, Capital Medical UniversityBeijingChina
- Institute of Molecular Physiology, Shenzhen Bay LaboratoryShenzhenChina
| | - Yi Rao
- Laboratory of Neurochemical Biology, PKU-IDG/McGovern Institute for Brain Research, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Department of Chemical Biology, College of Chemistry and Chemical Engineering, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking UniversityBeijingChina
- Chinese Institute for Brain Research (CIBR)BeijingChina
- Chinese Institutes of Medical Research, Capital Medical UniversityBeijingChina
- Changping Laboratory, Yard 28, Science Park Road, Changping DistrictBeijingChina
- Institute of Molecular Physiology, Shenzhen Bay LaboratoryShenzhenChina
- Research Unit of Medical Neurobiology, Chinese Academy of Medical SciencesBeijingChina
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5
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Forty Four Years With Baruch Kanner and The Chloride Ion. Neurochem Res 2021; 47:3-8. [PMID: 33929682 DOI: 10.1007/s11064-021-03330-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Revised: 04/14/2021] [Accepted: 04/15/2021] [Indexed: 10/21/2022]
Abstract
Baruch Kanner and this author have had parallel careers investigating neurotransmitter transporters. At multiple times during their careers, they have found themselves collaborating or competing, but always learning from each other. This commentary elaborates on the interactions between the Kanner and Rudnick laboratories, with a focus on transporters in the Neurotransmitter: Sodium Symporter (NSS) family of amino acid and amine transporters. A key focus of these interactions is the mechanism by which chloride ions activate and drive transport.
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6
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Danbolt NC, López-Corcuera B, Zhou Y. Reconstitution of GABA, Glycine and Glutamate Transporters. Neurochem Res 2021; 47:85-110. [PMID: 33905037 PMCID: PMC8763731 DOI: 10.1007/s11064-021-03331-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 04/13/2021] [Accepted: 04/15/2021] [Indexed: 10/25/2022]
Abstract
In contrast to water soluble enzymes which can be purified and studied while in solution, studies of solute carrier (transporter) proteins require both that the protein of interest is situated in a phospholipid membrane and that this membrane forms a closed compartment. An additional challenge to the study of transporter proteins has been that the transport depends on the transmembrane electrochemical gradients. Baruch I. Kanner understood this early on and first developed techniques for studying plasma membrane vesicles. This advanced the field in that the experimenter could control the electrochemical gradients. Kanner, however, did not stop there, but started to solubilize the membranes so that the transporter proteins were taken out of their natural environment. In order to study them, Kanner then had to find a way to reconstitute them (reinsert them into phospholipid membranes). The scope of the present review is both to describe the reconstitution method in full detail as that has never been done, and also to reveal the scientific impact that this method has had. Kanner's later work is not reviewed here although that also deserves a review because it too has had a huge impact.
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Affiliation(s)
- Niels Christian Danbolt
- Neurotransporter Group, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, 0317, Oslo, Norway.
| | - Beatriz López-Corcuera
- Departamento de Biología Molecular, Universidad Autónoma de Madrid, Madrid, Spain.,Centro de Biología Molecular "Severo Ochoa" Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, Madrid, Spain.,IdiPAZ, Hospital Universitario La Paz, Madrid, Spain
| | - Yun Zhou
- Neurotransporter Group, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, 0317, Oslo, Norway
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7
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Fairweather SJ, Shah N, Brӧer S. Heteromeric Solute Carriers: Function, Structure, Pathology and Pharmacology. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 21:13-127. [PMID: 33052588 DOI: 10.1007/5584_2020_584] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Solute carriers form one of three major superfamilies of membrane transporters in humans, and include uniporters, exchangers and symporters. Following several decades of molecular characterisation, multiple solute carriers that form obligatory heteromers with unrelated subunits are emerging as a distinctive principle of membrane transporter assembly. Here we comprehensively review experimentally established heteromeric solute carriers: SLC3-SLC7 amino acid exchangers, SLC16 monocarboxylate/H+ symporters and basigin/embigin, SLC4A1 (AE1) and glycophorin A exchanger, SLC51 heteromer Ost α-Ost β uniporter, and SLC6 heteromeric symporters. The review covers the history of the heteromer discovery, transporter physiology, structure, disease associations and pharmacology - all with a focus on the heteromeric assembly. The cellular locations, requirements for complex formation, and the functional role of dimerization are extensively detailed, including analysis of the first complete heteromer structures, the SLC7-SLC3 family transporters LAT1-4F2hc, b0,+AT-rBAT and the SLC6 family heteromer B0AT1-ACE2. We present a systematic analysis of the structural and functional aspects of heteromeric solute carriers and conclude with common principles of their functional roles and structural architecture.
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Affiliation(s)
- Stephen J Fairweather
- Research School of Biology, Australian National University, Canberra, ACT, Australia. .,Resarch School of Chemistry, Australian National University, Canberra, ACT, Australia.
| | - Nishank Shah
- Research School of Biology, Australian National University, Canberra, ACT, Australia
| | - Stefan Brӧer
- Research School of Biology, Australian National University, Canberra, ACT, Australia.
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8
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Nałęcz KA. Amino Acid Transporter SLC6A14 (ATB 0,+) - A Target in Combined Anti-cancer Therapy. Front Cell Dev Biol 2020; 8:594464. [PMID: 33195271 PMCID: PMC7609839 DOI: 10.3389/fcell.2020.594464] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2020] [Accepted: 09/30/2020] [Indexed: 12/12/2022] Open
Abstract
Cancer cells are characterized by quick growth and proliferation, demanding constant supply of various nutrients. Several plasma membrane transporters delivering such compounds are upregulated in cancer. Solute carrier family 6 member 14 (SLC6A14), known as amino acid transporter B0,+ (ATB0,+) transports all amino acids with exception of the acidic ones: aspartate and glutamate. Its malfunctioning is correlated with several pathological states and it is upregulated in solid tumors. The high expression of SLC6A14 is prognostic and unfavorable in pancreatic cancer, while in breast cancer it is expressed in estrogen receptor positive cells. As many plasma membrane transporters it resides in endoplasmic reticulum (ER) membrane after translation before further trafficking through Golgi to the cell surface. Transporter exit from ER is strictly controlled. The proper folding of SLC6A14 was shown to be controlled from the cytoplasmic side by heat shock proteins, further exit from ER and formation of coatomer II (COPII) coated vesicles depends on specific interaction with COPII cargo-recognizing subunit SEC24C, phosphorylated by kinase AKT. Inhibition of heat shock proteins, known to be upregulated in cancer, directs SLC6A14 to degradation. Targeting proteins regulating SLC6A14 trafficking is proposed as an additional pharmacological treatment of cancer.
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Affiliation(s)
- Katarzyna A Nałęcz
- Laboratory of Transport Through Biomembranes, Nencki Institute of Experimental Biology, Warsaw, Poland
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9
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Rudnick G, Sandtner W. Serotonin transport in the 21st century. J Gen Physiol 2019; 151:1248-1264. [PMID: 31570504 PMCID: PMC6829555 DOI: 10.1085/jgp.201812066] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Accepted: 08/24/2019] [Indexed: 12/16/2022] Open
Abstract
Rudnick and Sandtner review the history of serotonin transporter research in light of structural and electrophysiological advances. Serotonin (5-hydroxytryptamine [5-HT]) is accumulated within nerve endings by the serotonin transporter (SERT), which terminates its extracellular action and provides cytoplasmic 5-HT for refilling of synaptic vesicles. SERT is the target for many antidepressant medications as well as psychostimulants such as cocaine and ecstasy (3,4-methylenedioxymethamphetamine). SERT belongs to the SLC6 family of ion-coupled transporters and is structurally related to several other transporter families. SERT was studied in the 1970s and 1980s using membrane vesicles isolated from blood platelets. These studies led to a proposed stoichiometry of transport that has been challenged by high-resolution structures of SERT and its homologues and by studies of SERT electrophysiology. Here, we review the original evidence alongside more recent structural and electrophysiological evidence. A self-consistent picture emerges with surprising insights into the ion fluxes that accompany 5-HT transport.
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Affiliation(s)
- Gary Rudnick
- Department of Pharmacology, Yale University School of Medicine, New Haven, CT
| | - Walter Sandtner
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
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10
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Affiliation(s)
- Christopher L. Cioffi
- Departments of Basic and Clinical Sciences and Pharmaceutical Sciences, Albany College of Pharmacy and Health Sciences , Albany, NY, USA
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11
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Wellendorph P, Jacobsen J, Skovgaard-Petersen J, Jurik A, Vogensen SB, Ecker G, Schousboe A, Krogsgaard-Larsen P, Clausen RP. γ-Aminobutyric Acid and Glycine Neurotransmitter Transporters. METHODS AND PRINCIPLES IN MEDICINAL CHEMISTRY 2017. [DOI: 10.1002/9783527679430.ch4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- Petrine Wellendorph
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Julie Jacobsen
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Jonas Skovgaard-Petersen
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Andreas Jurik
- University of Vienna; Department of Pharmaceutical Chemistry; Althanstrasse 14, A-1090 Vienna Austria
| | - Stine B. Vogensen
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Gerhard Ecker
- University of Vienna; Department of Pharmaceutical Chemistry; Althanstrasse 14, A-1090 Vienna Austria
| | - Arne Schousboe
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Povl Krogsgaard-Larsen
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Rasmus P. Clausen
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
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12
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Eskandari S, Willford SL, Anderson CM. Revised Ion/Substrate Coupling Stoichiometry of GABA Transporters. ADVANCES IN NEUROBIOLOGY 2017; 16:85-116. [PMID: 28828607 DOI: 10.1007/978-3-319-55769-4_5] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The purpose of this review is to highlight recent evidence in support of a 3 Na+: 1 Cl-: 1 GABA coupling stoichiometry for plasma membrane GABA transporters (SLC6A1 , SLC6A11 , SLC6A12 , SLC6A13 ) and how the revised stoichiometry impacts our understanding of the contribution of GABA transporters to GABA homeostasis in synaptic and extrasynaptic regions in the brain under physiological and pathophysiological states. Recently, our laboratory probed the GABA transporter stoichiometry by analyzing the results of six independent measurements, which included the shifts in the thermodynamic transporter reversal potential caused by changes in the extracellular Na+, Cl-, and GABA concentrations, as well as the ratio of charge flux to substrate flux for Na+, Cl-, and GABA under voltage-clamp conditions. The shifts in the transporter reversal potential for a tenfold change in the external concentration of Na+, Cl-, and GABA were 84 ± 4, 30 ± 1, and 29 ± 1 mV, respectively. Charge flux to substrate flux ratios were 0.7 ± 0.1 charges/Na+, 2.0 ± 0.2 charges/Cl-, and 2.1 ± 0.1 charges/GABA. We then compared these experimental results with the predictions of 150 different transporter stoichiometry models, which included 1-5 Na+, 0-5 Cl-, and 1-5 GABA per transport cycle. Only the 3 Na+: 1 Cl-: 1 GABA stoichiometry model correctly predicts the results of all six experimental measurements. Using the revised 3 Na+: 1 Cl-: 1 GABA stoichiometry, we propose that the GABA transporters mediate GABA uptake under most physiological conditions. Transporter-mediated GABA release likely takes place under pathophysiological or extreme physiological conditions.
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Affiliation(s)
- Sepehr Eskandari
- Biological Sciences Department, California State Polytechnic University, Pomona, CA, 91768, USA.
| | - Samantha L Willford
- Biological Sciences Department, California State Polytechnic University, Pomona, CA, 91768, USA
| | - Cynthia M Anderson
- Biological Sciences Department, California State Polytechnic University, Pomona, CA, 91768, USA
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13
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Abstract
Glycine, besides exerting essential metabolic functions, is an important inhibitory neurotransmitter in caudal areas of the central nervous system and also a positive neuromodulator at excitatory glutamate-mediated synapses. Glial cells provide metabolic support to neurons and modulate synaptic activity. Six transporters belonging to three solute carrier families (SLC6, SLC38, and SLC7) are capable of transporting glycine across the glial plasma membrane. The unique glial glycine-selective transporter GlyT1 (SLC6) is the main regulator of synaptic glycine concentrations, assisted by the neuronal GlyT2. The five additional glycine transporters ATB0,+, SNAT1, SNAT2, SNAT5, and LAT2 display broad amino acid specificity and have differential contributions to glial glycine transport. Glial glycine transporters are divergent in sequence but share a similar architecture displaying the 5 + 5 inverted fold originally characterized in the leucine transporter LeuT. The availability of protein crystals solved at high resolution for prokaryotic and, more recently, eukaryotic homologues of this superfamily has advanced significantly our understanding of the mechanism of glycine transport.
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14
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Cioffi CL, Liu S, Wolf MA, Guzzo PR, Sadalapure K, Parthasarathy V, Loong DTJ, Maeng JH, Carulli E, Fang X, Karunakaran K, Matta L, Choo SH, Panduga S, Buckle RN, Davis RN, Sakwa SA, Gupta P, Sargent BJ, Moore NA, Luche MM, Carr GJ, Khmelnitsky YL, Ismail J, Chung M, Bai M, Leong WY, Sachdev N, Swaminathan S, Mhyre AJ. Synthesis and Biological Evaluation of N-((1-(4-(Sulfonyl)piperazin-1-yl)cycloalkyl)methyl)benzamide Inhibitors of Glycine Transporter-1. J Med Chem 2016; 59:8473-94. [PMID: 27559615 DOI: 10.1021/acs.jmedchem.6b00914] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
We previously disclosed the discovery of rationally designed N-((1-(4-(propylsulfonyl)piperazin-1-yl)cycloalkyl)methyl)benzamide inhibitors of glycine transporter-1 (GlyT-1), represented by analogues 10 and 11. We describe herein further structure-activity relationship exploration of this series via an optimization strategy that primarily focused on the sulfonamide and benzamide appendages of the scaffold. These efforts led to the identification of advanced leads possessing a desirable balance of excellent in vitro GlyT-1 potency and selectivity, favorable ADME and in vitro pharmacological profiles, and suitable pharmacokinetic and safety characteristics. Representative analogue (+)-67 exhibited robust in vivo activity in the cerebral spinal fluid glycine biomarker model in both rodents and nonhuman primates. Furthermore, rodent microdialysis experiments also demonstrated that oral administration of (+)-67 significantly elevated extracellular glycine levels within the medial prefrontal cortex (mPFC).
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Affiliation(s)
- Christopher L Cioffi
- Department of Medicinal Chemistry, AMRI , East Campus, 3 University Place, Rensselaer, New York 12144, United States
| | - Shuang Liu
- Department of Medicinal Chemistry, AMRI , East Campus, 3 University Place, Rensselaer, New York 12144, United States
| | - Mark A Wolf
- Department of Medicinal Chemistry, AMRI , East Campus, 3 University Place, Rensselaer, New York 12144, United States
| | - Peter R Guzzo
- Department of Medicinal Chemistry, AMRI , East Campus, 3 University Place, Rensselaer, New York 12144, United States
| | - Kashinath Sadalapure
- Discovery Research and Development Chemistry, Singapore Research Center, AMRI , 61 Science Park Road, Science Park III, 117525, Singapore
| | - Visweswaran Parthasarathy
- Discovery Research and Development Chemistry, Singapore Research Center, AMRI , 61 Science Park Road, Science Park III, 117525, Singapore
| | - David T J Loong
- Discovery Research and Development Chemistry, Singapore Research Center, AMRI , 61 Science Park Road, Science Park III, 117525, Singapore
| | - Jun-Ho Maeng
- Discovery Research and Development Chemistry, Singapore Research Center, AMRI , 61 Science Park Road, Science Park III, 117525, Singapore
| | - Edmund Carulli
- Discovery Research and Development Chemistry, Singapore Research Center, AMRI , 61 Science Park Road, Science Park III, 117525, Singapore
| | - Xiao Fang
- Discovery Research and Development Chemistry, Singapore Research Center, AMRI , 61 Science Park Road, Science Park III, 117525, Singapore
| | - Kalesh Karunakaran
- Discovery Research and Development Chemistry, Singapore Research Center, AMRI , 61 Science Park Road, Science Park III, 117525, Singapore
| | - Lakshman Matta
- Discovery Research and Development Chemistry, Singapore Research Center, AMRI , 61 Science Park Road, Science Park III, 117525, Singapore
| | - Sok Hui Choo
- Discovery Research and Development Chemistry, Singapore Research Center, AMRI , 61 Science Park Road, Science Park III, 117525, Singapore
| | - Shailijia Panduga
- Discovery Research and Development Chemistry, Singapore Research Center, AMRI , 61 Science Park Road, Science Park III, 117525, Singapore
| | - Ronald N Buckle
- Department of Medicinal Chemistry, AMRI , East Campus, 3 University Place, Rensselaer, New York 12144, United States
| | - Randall N Davis
- Department of Medicinal Chemistry, AMRI , East Campus, 3 University Place, Rensselaer, New York 12144, United States
| | - Samuel A Sakwa
- Department of Medicinal Chemistry, AMRI , East Campus, 3 University Place, Rensselaer, New York 12144, United States
| | - Priya Gupta
- Discovery Research and Development Chemistry, Singapore Research Center, AMRI , 61 Science Park Road, Science Park III, 117525, Singapore
| | - Bruce J Sargent
- Department of Medicinal Chemistry, AMRI , East Campus, 3 University Place, Rensselaer, New York 12144, United States
| | - Nicholas A Moore
- Department of Medicinal Chemistry, AMRI , East Campus, 3 University Place, Rensselaer, New York 12144, United States
| | - Michele M Luche
- Bothell Research Center, AMRI , 22215 26th Ave SE, Bothell, Washington 98021-4425, United States
| | - Grant J Carr
- Bothell Research Center, AMRI , 22215 26th Ave SE, Bothell, Washington 98021-4425, United States
| | - Yuri L Khmelnitsky
- Drug Metabolism and Pharmacokinetics, AMRI , East Campus, 17 University Place, Rensselaer, New York 12144, United States
| | - Jiffry Ismail
- Drug Metabolism and Pharmacokinetics, AMRI , East Campus, 17 University Place, Rensselaer, New York 12144, United States
| | - Mark Chung
- Discovery Research and Development Chemistry, Singapore Research Center, AMRI , 61 Science Park Road, Science Park III, 117525, Singapore
| | - Mei Bai
- Discovery Research and Development Chemistry, Singapore Research Center, AMRI , 61 Science Park Road, Science Park III, 117525, Singapore
| | - Wei Yee Leong
- Discovery Research and Development Chemistry, Singapore Research Center, AMRI , 61 Science Park Road, Science Park III, 117525, Singapore
| | - Nidhi Sachdev
- Discovery Research and Development Chemistry, Singapore Research Center, AMRI , 61 Science Park Road, Science Park III, 117525, Singapore
| | - Srividya Swaminathan
- Discovery Research and Development Chemistry, Singapore Research Center, AMRI , 61 Science Park Road, Science Park III, 117525, Singapore
| | - Andrew J Mhyre
- Bothell Research Center, AMRI , 22215 26th Ave SE, Bothell, Washington 98021-4425, United States
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Aroeira RI, Vaz SH, Sebastião AM, Valente CA. BDNF modulates glycine uptake in hippocampal synaptosomes by decreasing membrane insertion of glycine transporter 2. Neurochem Int 2016; 99:94-102. [PMID: 27296115 DOI: 10.1016/j.neuint.2016.06.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2016] [Revised: 06/07/2016] [Accepted: 06/09/2016] [Indexed: 12/18/2022]
Abstract
Glycine transporter 2 (GlyT2) is localized in the nerve terminals of glycinergic neurons, promoting glycine uptake and ensuring the refilling of glycinergic vesicles. Brain-derived neurotrophic factor (BDNF) activates its high affinity TrkB receptors, which occur in two isoforms, full length (TrkB-FL) and truncated (TrkB-T1/T2). After BDNF binding to TrkB receptor, several intracellular cascades are triggered, specifically PLC, Akt and MAPK signalling pathways. We herein show that BDNF decreases [(3)H]glycine uptake mediated by GlyT2 in isolated nerve endings (synaptosomes) obtained from rat hippocampus, by reducing the maximum velocity (Vmax) of transport while not influencing the transporter affinity constant (Km) for glycine. Western Blot analysis detected both TrkB receptor isoforms in the synaptosomes but the BDNF effect seems to be mediated by TrkB-FL since: 1) the tyrosine kinase inhibitor, k252a, prevented the effect of BDNF, and 2) the effect of BDNF was lost in the presence of specific inhibitors of TrkB signalling pathways, namely U73122, LY294002 and U0126 (inhibitors of PLC, Akt and MAPK pathways, respectively). Monensin, a transporter recycling inhibitor, prevented the BDNF action upon glycine uptake, suggesting that BDNF reduces GlyT2 insertion in the plasma membrane. It is concluded that BDNF effect upon glycine uptake into glycinergic nerve terminals requires the activation of the TrkB-FL receptor and its canonical signalling pathways and occurs by inhibiting GlyT2 membrane incorporation.
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Affiliation(s)
- Rita I Aroeira
- Faculdade de Medicina, Universidade de Lisboa, Av. Prof. Egas Moniz, 1649-028, Lisboa, Portugal; Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Av. Prof. Egas Moniz, 1649-028, Lisboa, Portugal
| | - Sandra H Vaz
- Faculdade de Medicina, Universidade de Lisboa, Av. Prof. Egas Moniz, 1649-028, Lisboa, Portugal; Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Av. Prof. Egas Moniz, 1649-028, Lisboa, Portugal
| | - Ana M Sebastião
- Faculdade de Medicina, Universidade de Lisboa, Av. Prof. Egas Moniz, 1649-028, Lisboa, Portugal; Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Av. Prof. Egas Moniz, 1649-028, Lisboa, Portugal
| | - Cláudia A Valente
- Faculdade de Medicina, Universidade de Lisboa, Av. Prof. Egas Moniz, 1649-028, Lisboa, Portugal; Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Av. Prof. Egas Moniz, 1649-028, Lisboa, Portugal.
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16
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Glycine transporter2 inhibitors: Getting the balance right. Neurochem Int 2015; 98:89-93. [PMID: 26723543 DOI: 10.1016/j.neuint.2015.12.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Revised: 11/13/2015] [Accepted: 12/18/2015] [Indexed: 12/28/2022]
Abstract
Neurotransmitter transporters are targets for a wide range of therapeutically useful drugs. This is because they have the capacity to selectively manipulate the dynamics of neurotransmitter concentrations and thereby enhance or diminish signalling through particular brain pathways. High affinity glycine transporters (GlyTs) regulate extracellular concentrations of glycine and provide novel therapeutic targets for neurological disorders.
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17
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Aroeira RI, Sebastião AM, Valente CA. BDNF, via truncated TrkB receptor, modulates GlyT1 and GlyT2 in astrocytes. Glia 2015. [DOI: 10.1002/glia.22884] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Affiliation(s)
- Rita I. Aroeira
- Faculty of Medicine, Institute of Pharmacology and Neurosciences, and Unit of Neurosciences, Institute of Molecular Medicine, University of Lisbon; Av. Prof. Egas Moniz Lisbon Portugal
| | - Ana M. Sebastião
- Faculty of Medicine, Institute of Pharmacology and Neurosciences, and Unit of Neurosciences, Institute of Molecular Medicine, University of Lisbon; Av. Prof. Egas Moniz Lisbon Portugal
| | - Cláudia A. Valente
- Faculty of Medicine, Institute of Pharmacology and Neurosciences, and Unit of Neurosciences, Institute of Molecular Medicine, University of Lisbon; Av. Prof. Egas Moniz Lisbon Portugal
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18
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Long-term application of glycine transporter inhibitors acts antineuropathic and modulates spinal N-methyl-D-aspartate receptor subunit NR-1 expression in rats. Anesthesiology 2014; 121:160-9. [PMID: 24598217 DOI: 10.1097/aln.0000000000000203] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
BACKGROUND Dysfunction of spinal glycinergic neurotransmission is a major pathogenetic factor in neuropathic pain. The synaptic glycine concentration is controlled by the two glycine transporters (GlyT) 1 and 2. GlyT inhibitors act antinociceptive in various animal pain models when applied as bolus. Yet, in some studies, severe neuromotor side effects were reported. The aim of the current study was to elucidate whether continuous inhibition of GlyT ameliorates neuropathic pain without side effects and whether protein expression of GlyT1, GlyT2, or N-methyl-D-aspartate receptor subunit NR-1 in the spinal cord is affected. METHODS In the chronic constriction injury model of neuropathic pain, male Wistar rats received specific GlyT1 and GlyT2 inhibitors (ALX5407 and ALX1393; Sigma-Aldrich, St. Louis, MO) or vehicle for 14 days via subcutaneous osmotic infusion pumps (n = 6). Mechanical allodynia and thermal hyperalgesia were assessed before, after chronic constriction injury, and every 2 days during substance application. At the end of behavioral assessment, the expression of GlyT1, GlyT2, and NR-1 in the spinal cord was determined by Western blot analysis. RESULTS Both ALX5407 and ALX1393 ameliorated thermal hyperalgesia and mechanical allodynia in a time- and dose-dependent manner. Respiratory or neuromotor side effects were not observed. NR-1 expression in the ipsilateral spinal cord was significantly reduced by ALX5407, but not by ALX1393. The expression of GlyT1 and GlyT2 remained unchanged. CONCLUSIONS Continuous systemic inhibition of GlyT significantly ameliorates neuropathic pain in rats. Thus, GlyT represent promising targets in pain research. Modulation of N-methyl-D-aspartate receptor expression might represent a novel mechanism for the antinociceptive action of GyT1 inhibitors.
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19
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The relationship between glycine transporter 1 occupancy and the effects of the glycine transporter 1 inhibitor RG1678 or ORG25935 on object retrieval performance in scopolamine impaired rhesus monkey. Psychopharmacology (Berl) 2014; 231:511-9. [PMID: 24051602 DOI: 10.1007/s00213-013-3260-0] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/08/2013] [Accepted: 08/19/2013] [Indexed: 12/17/2022]
Abstract
Reduced NMDA receptor functioning is hypothesized to underlie the cognitive and negative symptoms associated with schizophrenia. However, because direct activation of the NMDA receptor is accompanied by neurotoxicity, mechanisms that activate the glycine co-agonist site on the NMDA receptor could carry greater therapeutic potential. In the current study, the effects of two glycine transporter 1 (GlyT1) inhibitors, RG1678 and ORG25935, were characterized in the object-retrieval detour (ORD) task in scopolamine-impaired rhesus monkeys and, using positron emission tomography (PET), the GlyT1 occupancy to efficacy relationship of each compound was established. Scopolamine exerted a significant decrease in accuracy in the ORD task. Lower doses of RG1678 (0.3 and 1.0 mg/kg, p.o.) significantly attenuated the impact of scopolamine, whereas the highest dose tested (1.8 mg/kg) did not. The predicted GlyT1 occupancies of RG1678 at the effective doses were ~10 and 30 %. ORG25935 (0.1, 0.3, and 1 mg/kg, p.o.) also significantly attenuated the impact of scopolamine on the ORD task, whereas 3 mg/kg did not. The predicted GlyT1 occupancies of ORG25935 at the effective doses ranged from 16 to 80 %. These data suggest that GlyT1 inhibitors have the potential to improve performance on prefrontal cortex-dependent tests such as the ORD task, but that efficacy is lost when higher occupancies are achieved. Importantly, recent Ph2B data published by Roche suggests that low but not high doses of RG1678 improved negative symptoms in patients with schizophrenia, highlighting the potential translational nature of the current preclinical findings.
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20
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GlyT-1 Inhibitors: From Hits to Clinical Candidates. SMALL MOLECULE THERAPEUTICS FOR SCHIZOPHRENIA 2014. [DOI: 10.1007/7355_2014_53] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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21
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Lipid inhibitors of high affinity glycine transporters: identification of a novel class of analgesics. Neurochem Int 2013; 73:211-6. [PMID: 24036283 DOI: 10.1016/j.neuint.2013.08.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2013] [Revised: 08/13/2013] [Accepted: 08/13/2013] [Indexed: 11/23/2022]
Abstract
Glycine plays a key role in regulating inhibitory neurotransmission in the spinal cord and concentrations of glycine in the CNS are regulated by two subtypes of high affinity glycine transporters, GlyT1 and GlyT2. In this mini review we will discuss a series of lipid inhibitors of GlyT2 that show promise as analgesics in the treatment of neuropathic and inflammatory pain. N-arachidonyl-glycine inhibits the rate of transport by GlyT2, but has very little or no activity on GlyT1. We will discuss structure-activity studies of the actions of related lipids on GlyT2 and also the characterization of a more potent lipid inhibitor of GlyT2, oleoyl-l-carnitine. Both N-arachidonyl-glycine and oleoyl-l-carnitine show specificity for GlyT2 over GlyT1, which has allowed the use of chimeric GlyT1/GlyT2 transporters to begin characterizing the molecular basis for specificity and mechanism of action of these lipid inhibitors. Although our understanding of the molecular basis for lipid inhibition is still in its infancy, it appears that extracellular loop 4 of GlyT2 plays an important role in the inhibitory mechanism.
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22
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GlyT1 and GlyT2 in brain astrocytes: expression, distribution and function. Brain Struct Funct 2013; 219:817-30. [DOI: 10.1007/s00429-013-0537-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2012] [Accepted: 03/02/2013] [Indexed: 11/25/2022]
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Abstract
The solute carrier 6 (SLC6) family of the human genome comprises transporters for neurotransmitters, amino acids, osmolytes and energy metabolites. Members of this family play critical roles in neurotransmission, cellular and whole body homeostasis. Malfunction or altered expression of these transporters is associated with a variety of diseases. Pharmacological inhibition of the neurotransmitter transporters in this family is an important strategy in the management of neurological and psychiatric disorders. This review provides an overview of the biochemical and pharmacological properties of the SLC6 family transporters.
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Affiliation(s)
- Stefan Bröer
- Research School of Biology, Australian National University, Canberra, ACT, Australia.
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24
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Omoto JJ, Maestas MJ, Rahnama-Vaghef A, Choi YE, Salto G, Sanchez RV, Anderson CM, Eskandari S. Functional consequences of sulfhydryl modification of the γ-aminobutyric acid transporter 1 at a single solvent-exposed cysteine residue. J Membr Biol 2012; 245:841-57. [PMID: 22918627 PMCID: PMC3505503 DOI: 10.1007/s00232-012-9492-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2012] [Accepted: 07/16/2012] [Indexed: 11/18/2022]
Abstract
The aims of this study were to optimize the experimental conditions for labeling extracellularly oriented, solvent-exposed cysteine residues of γ-aminobutyric acid transporter 1 (GAT1) with the membrane-impermeant sulfhydryl reagent [2-(trimethylammonium)ethyl]methanethiosulfonate (MTSET) and to characterize the functional and pharmacological consequences of labeling on transporter steady-state and presteady-state kinetic properties. We expressed human GAT1 in Xenopus laevis oocytes and used radiotracer and electrophysiological methods to assay transporter function before and after sulfhydryl modification with MTSET. In the presence of NaCl, transporter exposure to MTSET (1–2.5 mM for 5–20 min) led to partial inhibition of GAT1-mediated transport, and this loss of function was completely reversed by the reducing reagent dithiothreitol. MTSET treatment had no functional effect on the mutant GAT1 C74A, whereas the membrane-permeant reagents N-ethylmaleimide and tetramethylrhodamine-6-maleimide inhibited GABA transport mediated by GAT1 C74A. Ion replacement experiments indicated that MTSET labeling of GAT1 could be driven to completion when valproate replaced chloride in the labeling buffer, suggesting that valproate induces a GAT1 conformation that significantly increases C74 accessibility to the extracellular fluid. Following partial inhibition by MTSET, there was a proportional reduction in both the presteady-state and steady-state macroscopic signals, and the functional and pharmacological properties of the remaining signals were indistinguishable from those of unlabeled GAT1. Therefore, covalent modification of GAT1 at C74 results in completely nonfunctional as well as electrically silent transporters.
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Affiliation(s)
- Jaison J Omoto
- Biological Sciences Department, California State Polytechnic University, Pomona, 3801 West Temple Avenue, Pomona, CA 91768-4032, USA
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25
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Glycine reuptake inhibitor RG1678: a pharmacologic characterization of an investigational agent for the treatment of schizophrenia. Neuropharmacology 2011; 62:1152-61. [PMID: 22138164 DOI: 10.1016/j.neuropharm.2011.11.008] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2011] [Revised: 11/02/2011] [Accepted: 11/16/2011] [Indexed: 11/20/2022]
Abstract
Dysfunctional N-methyl-d-aspartate (NMDA) receptor neurotransmission has been implicated in the pathophysiology of schizophrenia. It is thought that this abnormal functioning can be corrected by increasing availability of the NMDA co-agonist glycine through inhibition of glycine transporter type 1 (GlyT1). Herein is described the pharmacologic profile of RG1678, a potent and noncompetitive glycine reuptake inhibitor. In vitro, RG1678 noncompetitively inhibited glycine uptake at human GlyT1 with a concentration exhibiting half-maximal inhibition (IC(50)) of 25 nM and competitively blocked [(3)H]ORG24598 binding sites at human GlyT1b in membranes from Chinese hamster ovary cells. In hippocampal CA1 pyramidal cells, RG1678 enhanced NMDA-dependent long-term potentiation at 100 nM but not at 300 nM. In vivo, RG1678 dose-dependently increased cerebrospinal fluid and striatal levels of glycine measured by microdialysis in rats. Additionally RG1678 attenuated hyperlocomotion induced by the psychostimulant d-amphetamine or the NMDA receptor glycine site antagonist L-687,414 in mice. RG1678 also prevented the hyper-response to d-amphetamine challenge in rats treated chronically with phencyclidine, an NMDA receptor open-channel blocker. In the latter experiment, a decrease in ex vivo striatal [(3)H]raclopride binding was also measured. These data demonstrate that RG1678 is a potent, noncompetitive glycine reuptake inhibitor that can modulate both glutamatergic and dopaminergic neurotransmission in animal experiments that model aspects of schizophrenia. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.
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26
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Kristensen AS, Andersen J, Jørgensen TN, Sørensen L, Eriksen J, Loland CJ, Strømgaard K, Gether U. SLC6 neurotransmitter transporters: structure, function, and regulation. Pharmacol Rev 2011; 63:585-640. [PMID: 21752877 DOI: 10.1124/pr.108.000869] [Citation(s) in RCA: 591] [Impact Index Per Article: 45.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The neurotransmitter transporters (NTTs) belonging to the solute carrier 6 (SLC6) gene family (also referred to as the neurotransmitter-sodium-symporter family or Na(+)/Cl(-)-dependent transporters) comprise a group of nine sodium- and chloride-dependent plasma membrane transporters for the monoamine neurotransmitters serotonin (5-hydroxytryptamine), dopamine, and norepinephrine, and the amino acid neurotransmitters GABA and glycine. The SLC6 NTTs are widely expressed in the mammalian brain and play an essential role in regulating neurotransmitter signaling and homeostasis by mediating uptake of released neurotransmitters from the extracellular space into neurons and glial cells. The transporters are targets for a wide range of therapeutic drugs used in treatment of psychiatric diseases, including major depression, anxiety disorders, attention deficit hyperactivity disorder and epilepsy. Furthermore, psychostimulants such as cocaine and amphetamines have the SLC6 NTTs as primary targets. Beginning with the determination of a high-resolution structure of a prokaryotic homolog of the mammalian SLC6 transporters in 2005, the understanding of the molecular structure, function, and pharmacology of these proteins has advanced rapidly. Furthermore, intensive efforts have been directed toward understanding the molecular and cellular mechanisms involved in regulation of the activity of this important class of transporters, leading to new methodological developments and important insights. This review provides an update of these advances and their implications for the current understanding of the SLC6 NTTs.
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Affiliation(s)
- Anders S Kristensen
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Copenhagen, Denmark.
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27
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Bakkar W, Ma CL, Pabba M, Khacho P, Zhang YL, Muller E, Martina M, Bergeron R. Chronically saturating levels of endogenous glycine disrupt glutamatergic neurotransmission and enhance synaptogenesis in the CA1 region of mouse hippocampus. Synapse 2011; 65:1181-95. [PMID: 21633974 DOI: 10.1002/syn.20956] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2011] [Accepted: 05/18/2011] [Indexed: 11/08/2022]
Abstract
Glycine serves a dual role in neurotransmission. It is the primary inhibitory neurotransmitter in the spinal cord and brain stem and is also an obligatory coagonist at the excitatory glutamate, N-methyl-D-aspartate receptor (NMDAR). Therefore, the postsynaptic action of glycine should be strongly regulated to maintain a balance between its inhibitory and excitatory inputs. The glycine concentration at the synapse is tightly regulated by two types of glycine transporters, GlyT1 and GlyT2, located on nerve terminals or astrocytes. Genetic studies demonstrated that homozygous (GlyT1-/-) newborn mice display severe sensorimotor deficits characterized by lethargy, hypotonia, and hyporesponsivity to tactile stimuli and ultimately die in their first postnatal day. These symptoms are similar to those associated with the human disease glycine encephalopathy in which there is a high level of glycine in cerebrospinal fluid of affected individuals. The purpose of this investigation is to determine the impact of chronically high concentrations of endogenous glycine on glutamatergic neurotransmission during postnatal development using an in vivo mouse model (GlyT1+/-). The results of our study indicate the following; that compared with wild-type mice, CA1 pyramidal neurons from mutants display significant disruptions in hippocampal glutamatergic neurotransmission, as suggested by a faster kinetic of NMDAR excitatory postsynaptic currents, a lower reduction of the amplitude of NMDAR excitatory postsynaptic currents by ifenprodil, no difference in protein expression for NR2A and NR2B but a higher protein expression for PSD-95, an increase in their number of synapses and finally, enhanced neuronal excitability.
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Affiliation(s)
- Wafae Bakkar
- Ottawa Hospital Research Institute, Ottawa, Ontario, Canada
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28
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Howard A, Hirst BH. The Glycine Transporter GLYT1 in Human Intestine: Expression and Function. Biol Pharm Bull 2011; 34:784-8. [DOI: 10.1248/bpb.34.784] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Alison Howard
- Epithelial Research Group, Institute for Cell and Molecular Biosciences, Faculty of Medical Sciences, Newcastle University
| | - Barry Hugo Hirst
- Epithelial Research Group, Institute for Cell and Molecular Biosciences, Faculty of Medical Sciences, Newcastle University
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29
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Anderson CM, Kidd PD, Eskandari S. GATMD: γ-aminobutyric acid transporter mutagenesis database. DATABASE-THE JOURNAL OF BIOLOGICAL DATABASES AND CURATION 2010; 2010:baq028. [PMID: 21131297 PMCID: PMC2997607 DOI: 10.1093/database/baq028] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Since the cloning of the first γ-aminobutyric acid (GABA) transporter (GAT1; SLC6A1) from rat brain in 1990, more than 50 published studies have provided structure-function information on investigator-designed rat and mouse GAT1 mutants. To date, more than 200 of 599 GAT1 residues have been subjected to mutagenesis experiments by substitution with different amino acids, and the resulting transporter functional properties have significantly advanced our understanding of the mechanism of Na+- and Cl⁻-coupled GABA transport by this important member of the neurotransmitter:sodium symporter family. Moreover, many studies have addressed the functional consequences of amino acid deletion or insertion at various positions along the primary sequence. The enormity of this growing body of structure-function information has prompted us to develop GABA Transporter Mutagenesis Database (GATMD), a web-accessible, relational database of manually annotated biochemical, functional and pharmacological data reported on GAT1-the most intensely studied GABA transporter isoform. As of the last update of GATMD, 52 GAT1 mutagenesis papers have yielded 3360 experimental records, which collectively contain a total of ∼100 000 annotated parameters. Database URL: http://physiology.sci.csupomona.edu/GATMD/
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Affiliation(s)
- Cynthia M Anderson
- Biological Sciences Department, California State Polytechnic University, Pomona, CA 91768-4032, USA
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30
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Eulenburg V, Gomeza J. Neurotransmitter transporters expressed in glial cells as regulators of synapse function. ACTA ACUST UNITED AC 2010; 63:103-12. [PMID: 20097227 DOI: 10.1016/j.brainresrev.2010.01.003] [Citation(s) in RCA: 135] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2009] [Revised: 01/18/2010] [Accepted: 01/20/2010] [Indexed: 11/16/2022]
Abstract
Synaptic neurotransmission at high temporal and spatial resolutions requires efficient removal and/or inactivation of presynaptically released transmitter to prevent spatial spreading of transmitter by diffusion and allow for fast termination of the postsynaptic response. This action must be carefully regulated to result in the fine tuning of inhibitory and excitatory neurotransmission, necessary for the proper processing of information in the central nervous system. At many synapses, high-affinity neurotransmitter transporters are responsible for transmitter deactivation by removing it from the synaptic cleft. The most prevailing neurotransmitters, glutamate, which mediates excitatory neurotransmission, as well as GABA and glycine, which act as inhibitory neurotransmitters, use these uptake systems. Neurotransmitter transporters have been found in both neuronal and glial cells, thus suggesting high cooperativity between these cell types in the control of extracellular transmitter concentrations. The generation and analysis of animals carrying targeted disruptions of transporter genes together with the use of selective inhibitors have allowed examining the contribution of individual transporter subtypes to synaptic transmission. This revealed the predominant role of glial expressed transporters in maintaining low extrasynaptic neurotransmitter levels. Additionally, transport activity has been shown to be actively regulated on both transcriptional and post-translational levels, which has important implications for synapse function under physiological and pathophysiological conditions. The analysis of these mechanisms will enhance not only our understanding of synapse function but will reveal new therapeutic strategies for the treatment of human neurological diseases.
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Affiliation(s)
- Volker Eulenburg
- Department for Neurochemistry, Max-Planck Institute for Brain Research, 60529 Frankfurt, Germany.
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31
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Cherubino F, Bossi E, Miszner A, Ghezzi C, Peres A. Transient currents in the glycine cotransporter GlyT1 reveal different steps in transport mechanism. J Mol Neurosci 2009; 41:243-51. [PMID: 19711201 DOI: 10.1007/s12031-009-9281-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2009] [Accepted: 07/28/2009] [Indexed: 11/30/2022]
Abstract
The relation between presteady-state (transient) currents elicited by voltage steps in the absence of organic substrate and transport-associated currents in the presence of glycine was investigated in Xenopus oocytes expressing the neuronal glycine transporter GlyT1b. Saturating amounts of glycine converted the transient currents in steady transport currents. Analysis of the transient currents abolished by the substrate confirmed the intramembrane nature of the underlying charge movement process. The sigmoidal Q/V relationship had a moderate slope consistent with the known GlyT1b stoichiometry. The transient currents were best fitted by the sum of two exponentials, with the slow time constant (tau (slow)) being in the order of tens of milliseconds. The apparent affinity for glycine was in the micromolar range and voltage-dependent, slightly decreasing at positive potentials. Numerical simulations show that a simplified, three-state model is sufficient to explain the main features of GlyT1b operation.
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López-Corcuera B, Geerlings A, Aragón C. Glycine neurotransmitter transporters: an update. Mol Membr Biol 2009. [DOI: 10.1080/09687680010028762] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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Mongeon R, Gleason MR, Masino MA, Fetcho JR, Mandel G, Brehm P, Dallman JE. Synaptic homeostasis in a zebrafish glial glycine transporter mutant. J Neurophysiol 2008; 100:1716-23. [PMID: 18715895 DOI: 10.1152/jn.90596.2008] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Truncated escape responses characteristic of the zebrafish shocked mutant result from a defective glial glycine transporter (GlyT1). In homozygous GlyT1 mutants, irrigating brain ventricles with glycine-free solution rescues normal swimming. Conversely, elevating brain glycine levels restores motility defects. These experiments are consistent with previous studies that demonstrate regulation of global glycine levels in the CNS as a primary function of GlyT1. As GlyT1 mutants mature, their ability to mount an escape response naturally recovers. To understand the basis of this recovery, we assay synaptic transmission in primary spinal motor neurons by measuring stimulus-evoked postsynaptic potentials. At the peak of the motility defect, inhibitory synaptic potentials are both significantly larger and more prolonged indicating a prominent role for GlyT1 in shaping fast synaptic transmission. However, as GlyT1 mutants naturally regain their ability to swim, the amplitude of inhibitory potentials decreases to below wild-type levels. In parallel with diminishing synaptic potentials, the glycine concentration required to evoke the mutant motility defect increases 61-fold during behavioral recovery. Behavioral recovery is also mirrored by a reduction in the levels of both glycine receptor protein and transcript. These results suggest that increased CNS glycine tolerance and reduced glycine receptor expression in GlyT1 mutants reflect compensatory mechanisms for functional recovery from excess nervous system inhibition.
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Affiliation(s)
- Rebecca Mongeon
- Howard Hughes Medical Institute, Department of Neurobiology and Behavior, State University of New York, Stony Brook, NY, USA
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34
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The phosphatidylinositol 3-kinase inhibitor LY 294002 inhibits GlyT1-mediated glycine uptake. Brain Res 2008; 1227:42-51. [DOI: 10.1016/j.brainres.2008.06.078] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2008] [Revised: 05/16/2008] [Accepted: 06/15/2008] [Indexed: 11/22/2022]
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35
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Armsen W, Himmel B, Betz H, Eulenburg V. The C-terminal PDZ-ligand motif of the neuronal glycine transporter GlyT2 is required for efficient synaptic localization. Mol Cell Neurosci 2007; 36:369-80. [PMID: 17851090 DOI: 10.1016/j.mcn.2007.07.011] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2007] [Revised: 07/13/2007] [Accepted: 07/24/2007] [Indexed: 11/28/2022] Open
Abstract
The neuronal glycine transporter 2 (GlyT2) belongs to the large SLC6 family of Na+/Cl--dependent neurotransmitter transporters. At its extreme C-terminus, GlyT2 carries a type III PDZ domain binding motif (PDZ-ligand motif), which interacts with the PDZ domain protein syntenin-1. Here, we investigated the physiological role of the GlyT2 PDZ-ligand motif by a loss-of-function approach. Inactivation of the PDZ-ligand motif did not impair the localization, glycosylation and transport function of recombinant GlyT2 expressed in HEK293T cells. However, in transfected hippocampal neurons, the synaptic localization of GlyT2 was significantly reduced upon PDZ-ligand motif inactivation. Co-localization of GlyT2 with marker proteins of excitatory and inhibitory synapses was decreased by down to 50% upon PDZ-ligand motif deletion as compared to the wild-type protein. These data indicate that the C-terminal PDZ-ligand motif of GlyT2 plays an important role in transporter trafficking to and/or stabilization at synaptic sites.
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Affiliation(s)
- Wencke Armsen
- Department of Neurochemistry, Max-Planck Institute for Brain Research, Deutschordenstrasse 46, 60528 Frankfurt am Main, Germany
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36
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Romero-Calderón R, Shome RM, Simon AF, Daniels RW, DiAntonio A, Krantz DE. A screen for neurotransmitter transporters expressed in the visual system of Drosophila melanogaster identifies three novel genes. Dev Neurobiol 2007; 67:550-69. [PMID: 17443808 DOI: 10.1002/dneu.20342] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The fly eye provides an attractive substrate for genetic studies, and critical transport activities for synaptic transmission and pigment biogenesis in the insect visual system remain unknown. We therefore screened for transporters in Drosophila melanogaster that are down-regulated by genetically ablating the eye. Using a large panel of transporter specific probes on Northern blots, we identified three transcripts that are down-regulated in flies lacking eye tissue. Two of these, CG13794 and CG13795, are part of a previously unknown subfamily of putative solute carriers within the neurotransmitter transporter family. The third, CG4476, is a member of a related subfamily that includes characterized nutrient transporters expressed in the insect gut. Using imprecise excision of a nearby transposable P element, we have generated a series of deletions in the CG4476 gene. In fast phototaxis assays, CG4476 mutants show a decreased behavioral response to light, and the most severe mutant behaves as if it were blind. These data suggest an unforeseen role for the "nutrient amino acid transporter" subfamily in the nervous system, and suggest new models to study transport function using the fly eye.
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Affiliation(s)
- Rafael Romero-Calderón
- Interdepartmental Ph.D. Program in Neuroscience, University of California, Los Angeles, California 90095-1761, USA
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37
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Shigeri Y, Shimamoto K. [Pharmacology of inhibitory amino acid transporters (GABA transporters and glycine transporters)]. Nihon Yakurigaku Zasshi 2006; 127:279-87. [PMID: 16755080 DOI: 10.1254/fpj.127.279] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
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38
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Abstract
Glycine has multiple neurotransmitter functions in the central nervous system (CNS). In the spinal cord and brainstem of vertebrates, it serves as a major inhibitory neurotransmitter. In addition, it participates in excitatory neurotransmission by modulating the activity of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors. The extracellular concentrations of glycine are regulated by Na+/Cl(-)-dependent glycine transporters (GlyTs), which are expressed in neurons and adjacent glial cells. Considerable progress has been made recently towards elucidating the in vivo roles of GlyTs in the CNS. The generation and analysis of animals carrying targeted disruptions of GlyT genes (GlyT knockout mice) have allowed investigators to examine the different contributions of individual GlyT subtypes to synaptic transmission. In addition, they have provided animal models for two hereditary human diseases, glycine encephalopathy and hyperekplexia. Selective GlyT inhibitors have been shown to modulate neurotransmission and might constitute promising therapeutic tools for the treatment of psychiatric and neurological disorders such as schizophrenia and pain. Therefore, pharmacological and genetic studies indicate that GlyTs are key regulators of both glycinergic inhibitory and glutamatergic excitatory neurotransmission. This chapter describes our present understanding of the functions of GlyTs and their involvement in the fine-tuning of neuronal communication.
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Affiliation(s)
- J Gomeza
- Department of Pharmacology, The Panum Institute, University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen, Denmark.
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39
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Tian H, Vogel R, Amici L, Tamagnan G, Baldwin RM. Radiosynthesis of 3-(3-[18F]fluoropropoxy)-4-(benzyloxy)-N-[(1-dimethylaminocyclopentyl)methyl]-5-methoxybenzamide, a potential PET radiotracer for the glycine transporter GlyT-2. J Labelled Comp Radiopharm 2006. [DOI: 10.1002/jlcr.1145] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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40
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Baliova M, Jursky F. Calpain Sensitive Regions in the N-terminal Cytoplasmic Domains of Glycine Transporters GlyT1A and GlyT1B. Neurochem Res 2005; 30:1093-100. [PMID: 16292501 DOI: 10.1007/s11064-005-7520-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/18/2005] [Indexed: 10/25/2022]
Abstract
Glycine transporters are members of the Na+/Cl- dependent transporter gene family and play crucial roles in regulating inhibitory as well as excitatory neurotransmission. In this report we show that calcium elevation in spinal cord synaptosomes decreases the levels of glycine transporter, GlyT1, N-terminal immunoreactivity, and that this decrease can be blocked by calpain inhibitor. Sequencing of GST fusion proteins containing the N-terminal domains of GlyT1A and B splice variants cleaved with rat recombinant calpain identified calpain cleavage sites after glycine 17 in GlyT1B and N-terminally of the first conserved arginine residue in both GlyT1A and GlyT1B. Expression in HEK293 cells revealed that truncation of the N-terminus of GlyT1 results in significant inhibition of glycine uptake. A syntaxin1A GST fusion protein was able to pull-down N-terminally deleted GlyT1, indicating that calpain cleavage does not eliminate syntaxin1A binding. These results suggest that calpain cleavage may regulate the transport activity/turnover of GlyT1 in vivo by cleaving its N-terminal domain.
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Affiliation(s)
- Martina Baliova
- Department of Neurobiology, Institute of Molecular Biology, Slovak Academy of Sciences, Bratislava, Slovakia.
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41
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Slassi A, Egle I. Recent progress in the use of glycine transporter-1 inhibitors for the treatment of central and peripheral nervous system diseases. Expert Opin Ther Pat 2005. [DOI: 10.1517/13543776.14.2.201] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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42
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Affiliation(s)
- D Attwell
- Department of Physiology, University College London, Gower Street, London WC1E 6BT, UK
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43
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Petkó M, Veress G, Vereb G, Storm-Mathisen J, Antal M. Commissural propriospinal connections between the lateral aspects of laminae III-IV in the lumbar spinal cord of rats. J Comp Neurol 2005; 480:364-77. [PMID: 15558798 DOI: 10.1002/cne.20356] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
It has been established that there is a strong functional link between sensory neural circuits on the two sides of the spinal cord. In one of our recent studies we provided a morphological confirmation of this functional phenomenon, presenting evidence for the presence of a direct commissural connection between the lateral aspects of the dorsal horn on the two sides of the lumbar spinal cord. By using a combination of neural tracing and immunocytochemical detection of neural markers like vesicular glutamate transporters, glutamic acid decarboxylase, glycine transporter, and met-enkephalin (which are characteristic of various subsets of excitatory and inhibitory neurons), we investigated here the distribution, synaptic relations, and neurochemical characteristics of the commissural axon terminals. We found that the cells of origin of commissural fibers in the lateral aspect of the dorsal horn were confined to laminae III-IV and projected to the corresponding area of the contralateral gray matter. Most of the commissural axon terminals established synaptic contacts with dendrites. Axospinous or axosomatic synaptic contacts were found in limited numbers. We demonstrated that interactions among commissural neurons also exist. More than three-fourths of the labeled axon terminals were immunostained for glutamic acid decarboxylase and/or glycine transporter, but none of them showed positive immunoreaction for met-enkephalin and vesicular glutamate transporters. The results indicate that there is a substantial reciprocal commissural synaptic interaction between the lateral aspects of laminae III-IV on the two sides of the lumbar spinal cord and that this pathway may transmit both inhibitory and excitatory signals to their postsynaptic targets.
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Affiliation(s)
- Mihály Petkó
- Department of Anatomy, Histology and Embryology, Faculty of Medicine, Medical and Health Science Center, University of Debrecen, H-4012 Debrecen, Hungary
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Abstract
Nervous systems are generally composed of two cell types-neurons and glia. Early studies of neurons revealed that these cells can conduct electrical currents, immediately implying that they have roles in the relay of information throughout the nervous system. Roles for glia have, until recently, remained obscure. The importance of glia in regulating neuronal survival had been long recognized. However, this trophic support function has hampered attempts to address additional, more active functions of these cells in the nervous system. In this chapter, recent efforts to reveal some of these additional functions are described. Evidence supporting a role for glia in synaptic development and activity is presented, as well as experiments suggesting glial guidance of neuronal migration and process outgrowth. Roles for glia in influencing the electrical activity of neurons are also discussed. Finally, an exciting system is described for studying glial cells in the nematode C. elegans, in which recent studies suggest that glia are not required for neuronal viability.
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Affiliation(s)
- Shai Shaham
- The Rockefeller University, New York, New York 10021, USA
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45
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Foltz M, Oechsler C, Boll M, Kottra G, Daniel H. Substrate specificity and transport mode of the proton-dependent amino acid transporter mPAT2. ACTA ACUST UNITED AC 2004; 271:3340-7. [PMID: 15291811 DOI: 10.1111/j.1432-1033.2004.04268.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The PAT2 transporter has been shown to act as an electrogenic proton/amino acid symporter. The PAT2 cDNA has been cloned from various human, mouse and rat tissues and belongs to a group of four genes (pat1 to pat4) with PAT3 and PAT4 still resembling orphan transporters. The first immunolocalization studies demonstrated that the PAT2 protein is found in the murine central nervous system in neuronal cells with a proposed role in the intra and/or intercellular amino acid transport. Here we provide a detailed analysis of the transport mode and substrate specificity of the murine PAT2 transporter after expression in Xenopus laevis oocytes, by electrophysiological techniques and flux studies. The structural requirements to the PAT2 substrates - when considering both low and high affinity type substrates - are similar to those reported for the PAT1 protein with the essential features of a free carboxy group and a small side chain. For high affinity binding, however, PAT2 requires the amino group to be located in an alpha-position, tolerates only one methyl function attached to the amino group and is highly selective for the L-enantiomers. Electrophysiological analysis revealed pronounced effects of membrane potential on proton binding affinity, but substrate affinities and maximal transport currents only modestly respond to changes in membrane voltage. Whereas substrate affinity is dependent on extracellular pH, proton binding affinity to PAT2 is substrate-independent, favouring a sequential binding of proton followed by substrate. Maximal transport currents are substrate-dependent which suggests that the translocation of the loaded carrier to the internal side is the rate-limiting step.
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Affiliation(s)
- Martin Foltz
- Molecular Nutrition Unit, Center of Life and Food Sciences, Technical University of Munich, Germany
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46
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Ho KK, Appell KC, Baldwin JJ, Bohnstedt AC, Dong G, Guo T, Horlick R, Islam KR, Kultgen SG, Masterson CM, McDonald E, McMillan K, Morphy JR, Rankovic Z, Sundaram H, Webb M. 2-(Aminomethyl)-benzamide-based glycine transporter type-2 inhibitors. Bioorg Med Chem Lett 2004; 14:545-8. [PMID: 14698200 DOI: 10.1016/j.bmcl.2003.09.080] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Structure-activity studies on benzamide 1 obtained from library screening led to the discovery of a novel series of potent and selective glycine transporter type-2 inhibitors.
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Affiliation(s)
- Koc-Kan Ho
- Pharmacopeia, Inc., PO Box 5350, Princeton, NJ 08543-5350, USA.
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47
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Vandenberg RJ, Ju P, Aubrey KR, Ryan RM, Mitrovic AD. Allosteric modulation of neurotransmitter transporters at excitatory synapses. Eur J Pharm Sci 2004; 23:1-11. [PMID: 15324920 DOI: 10.1016/j.ejps.2004.05.006] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2003] [Revised: 05/10/2004] [Accepted: 05/18/2004] [Indexed: 10/26/2022]
Abstract
The regulation of glutamate and glycine concentrations within excitatory synapses plays an important role in maintaining a dynamic signalling process between neurones, but the failure to regulate the concentrations of these neurotransmitters has been implicated in the pathogenesis of various neurological disorders. In this review we shall discuss how glutamate and glycine transporters regulate synaptic concentrations of these neurotransmitters and how endogenous allosteric modulators influence transporter function. Whilst glutamate transport inhibitors are unlikely to be of therapeutic value because their potential to cause excitoxicity and cell death, a greater understanding of how endogenous compounds allosterically modulate glutamate transporters may provide alternate drug targets. On the other hand, there are some promising drugs that inhibit glycine transporters, which are being trialled as an alternate treatment for schizophrenia. We shall discuss how the activity of one such compound may be expected to influence excitatory neurotransmission.
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Affiliation(s)
- Robert J Vandenberg
- Department of Pharmacology, Institute for Biomedical Research, University of Sydney, Sydney 2006, NSW, Australia.
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48
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Bradaïa A, Schlichter R, Trouslard J. Role of glial and neuronal glycine transporters in the control of glycinergic and glutamatergic synaptic transmission in lamina X of the rat spinal cord. J Physiol 2004; 559:169-86. [PMID: 15235081 PMCID: PMC1665078 DOI: 10.1113/jphysiol.2004.068858] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Using whole cell voltage clamp recordings from lamina X neurones in rat spinal cord slices, we investigated the effect of glycine transporter (GlyT) antagonists on both glycinergic inhibitory postsynaptic current (IPSCs) and glutamatergic excitatory postsynaptic current (EPSCs). We used ORG 24598 and ORG 25543, selective antagonists of the glial GlyT (GlyT1) and neuronal GlyT (GlyT2), respectively. In rats (P12-P16) and in the presence of kynurenic acid, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and bicuculline, ORG 24598 and ORG 25543 applied individually at a concentration of 10 microm induced a mean inward current of -10/-50 pA at -60 mV and increased significantly the decay time constants of miniature (mIPSCs), spontaneous (sIPSCs) and electrically evoked glycinergic (eIPSCs) inhibitory postsynaptic currents. ORG 25543, but not ORG 24598, decreased the frequency of mIPSCs and sIPSCs. Replacing extracellular sodium with N-methyl-d-glucamine or superfusing the slice with micromolar concentrations of glycine also increased the decay time constant of glycinergic IPSCs. By contrast, the decay time constant, amplitude and frequency of miniature GABAergic IPSCs recorded in the presence of strychnine were not affected by ORG 24598 and ORG 25543. In the presence of strychnine, bicuculline and CNQX, we recorded electrically evoked NMDA receptor-mediated EPSCs (eEPSCs). eEPSCs were suppressed by 30 micromd-2-amino-5-phosphonovalerate (APV), an antagonist of the NMDA receptor, and by 30 microm dichlorokynurenic acid (DCKA), an antagonist of the glycine site of the NMDA receptor. Glycine (1-5 microm) and d-serine (10 microm) increased the amplitude of eEPSCs whereas l-serine had no effect. ORG 24598 and ORG 25543 increased significantly the amplitude of NMDA receptor-mediated eEPSCs without affecting the amplitude of non-NMDA receptor-mediated eEPSCs. We conclude that blocking glial and/or neuronal glycine transporters increased the level of glycine in spinal cord slices, which in turn prolonged the duration of glycinergic synaptic current and potentiated the NMDA-mediated synaptic response.
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Affiliation(s)
- Amyaouch Bradaïa
- Laboratoire de Neurophysiologie Cellulaire et Intégrée, UMR 7519 CNRS/ULP, 21 rue R. Descartes, 67084 Strasbourg Cedex, France
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49
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Lim R, Hoang P, Berger AJ. Blockade of glycine transporter-1 (GLYT-1) potentiates NMDA receptor-mediated synaptic transmission in hypoglossal motorneurons. J Neurophysiol 2004; 92:2530-7. [PMID: 15175365 DOI: 10.1152/jn.01123.2003] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
NMDA receptor (NMDAR)-mediated spontaneous miniature excitatory postsynaptic currents (mEPSCs) are potentiated by exogenously applied glycine. In this study, we have investigated the effect of blocking glycine uptake on NMDAR-mediated responses from hypoglossal motorneurons (HMs) of rats. We have used N[3-(4'-fluorophenyl)-3-(4'-phenylphenoxy)-propyl]sarcosine (NFPS; 500 nM), an antagonist of glycine transporter-1 (GLYT1), to study the effect of blocking endogenous glycine uptake on NMDAR-mediated synaptic transmission. We show that the charge transfer of NMDAR-mediated mEPSCs was enhanced after NFPS application in neonate (P2-4) and juvenile rats (P8-11), but this enhancement was statistically significant only in the former group. Spontaneous and evoked EPSCs showed a significant increase in NMDAR-mediated charge transfer in both neonates and juveniles. The greater increase observed in spontaneous EPSCs may be due to increased release of glycine from glycinergic terminals in the absence of tetrodotoxin (TTX). Brief application of NMDA onto HMs showed that extrasynaptic NMDARs may be potentiated by NFPS only in the presence of extracellularly applied glycine. Immunohistochemistry of GLYT1 and -2 shows labeling throughout the hypoglossal nucleus. GLYT1 labeling is diffuse and becomes more intense and uniform during development consistent with its glial localization. In contrast, GLYT2 labeling is intense throughout the nucleus and increases in intensity with age. Our results demonstrate the glycine binding site of the NMDAR is not saturated in the brain stem slice during the first 2 wk of development. We suggest that modulation of glycine concentration by GLYT1 is an important mechanism to regulate NMDAR-mediated synaptic transmission.
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Affiliation(s)
- Rebecca Lim
- Dept. of Physiology and Biophysics, School of Medicine, University of Washington, Box 357290, Seattle, WA 98195-7290, USA
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50
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Ju P, Aubrey KR, Vandenberg RJ. Zn2+ Inhibits Glycine Transport by Glycine Transporter Subtype 1b. J Biol Chem 2004; 279:22983-91. [PMID: 15031290 DOI: 10.1074/jbc.m312484200] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In the central nervous system, glycine is a co-agonist with glutamate at the N-methyl-D-aspartate subtype of glutamate receptors and also an agonist at inhibitory, strychnine-sensitive glycine receptors. The GLYT1 subtypes of glycine transporters (GLYTs) are responsible for regulation of glycine at excitatory synapses, whereas a combination of GLYT1 and GLYT2 subtypes of glycine transporters are used at inhibitory glycinergic synapses. Zn2+ is stored in synaptic vesicles with glutamate in a number of regions of the brain and is believed to play a role in modulation of excitatory neurotransmission. In this study we have investigated the actions of Zn2+ on the glycine transporters, GLYT1b and GLYT2a, expressed in Xenopus laevis oocytes and we demonstrate that Zn2+ is a noncompetitive inhibitor of GLYT1 but has no effect on GLYT2. We have also investigated the molecular basis for these differences and the relationship between the Zn2+ and proton binding sites on GLYT1. Using site-directed mutagenesis, we identified 2 histidine residues, His-243 in the large second extracellular loop (ECL2) and His-410 in the fourth extracellular loop (ECL4), as two coordinates in the Zn2+ binding site of GLYT1b. In addition, our study suggests that the molecular determinants of proton regulation of GLYT1b are localized to the 2 histidine residues (His-410 and His-421) of ECL4. The ability of Zn2+ and protons to regulate the rate of glycine transport by interacting with residues situated in ECL4 of GLYT1b suggests that this region may influence the substrate translocation mechanism.
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Affiliation(s)
- Pengchu Ju
- Department of Pharmacology, Institute for Biomedical Research, University of Sydney, Sydney, New South Wales 2006, Australia
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