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Onishi Y, Yamamura Y, Hosogi M, Higashi H, Ogita K, Kinjo T, Uno K, Yoneda Y, Kuramoto N. Long-lasting increases in GABA B receptor subunit levels in hippocampal dentate gyrus of mice with a single systemic injection of trimethyltin. Heliyon 2024; 10:e29713. [PMID: 38720739 PMCID: PMC11076641 DOI: 10.1016/j.heliyon.2024.e29713] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Revised: 03/13/2024] [Accepted: 04/14/2024] [Indexed: 05/12/2024] Open
Abstract
We have recently shown delayed increases in GABAB receptor (GABABR) subunit protein levels in the hippocampal dentate gyrus (DG), but not in the pyramidal CA1 and CA3 regions, at 15-30 days after the systemic single administration of trimethyltin (TMT) in mice. An attempt was thus made to determine whether the delayed increases return to the control levels found in naive mice afterward. In the DG on hippocampal slices obtained at 90 days after the administration, however, marked increases were still seen in protein levels of both GABABR1 and GABABR2 subunits without significant changes in calbindin and glial fibrillary acidic protein (GFAP) levels on immunoblotting analysis. Fluoro-Jade B staining clearly revealed the absence of degenerated neurons from the DG at 90 days after the administration. Although co-localization was invariably detected between GABABR2 subunit and GFAP in the DG at 30 days on immunohistochemical analysis, GABABR2-positive cells did not merge well with GFAP-positive cells in the DG at 90 days. These results suggest that both GABABR1 and GABABR2 subunits would be tardily and sustainably up-regulated by cells other than neurons and astrocytes in the murine DG at 90 days after a systemic single injection of TMT.
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Affiliation(s)
- Yuki Onishi
- Laboratory of Molecular Pharmacology,Faculty of Pharmaceutical Sciences, Setsunan University, Hirakata, Osaka, 573-0101, Japan
- The Institute of Prophylactic Pharmacology, Kita-Shinagawa, Shinagawa, 140-0001, Tokyo, Japan
| | - Yusuke Yamamura
- Laboratory of Pharmacology, Faculty of Pharmaceutical Sciences, Setsunan University, Hirakata, Osaka, 573-0101, Japan
| | - Misa Hosogi
- Laboratory of Molecular Pharmacology,Faculty of Pharmaceutical Sciences, Setsunan University, Hirakata, Osaka, 573-0101, Japan
| | - Hiroshi Higashi
- Laboratory of Molecular Pharmacology,Faculty of Pharmaceutical Sciences, Setsunan University, Hirakata, Osaka, 573-0101, Japan
| | - Kiyokazu Ogita
- Laboratory of Pharmacology, Faculty of Pharmaceutical Sciences, Setsunan University, Hirakata, Osaka, 573-0101, Japan
- The Institute of Prophylactic Pharmacology, Kita-Shinagawa, Shinagawa, 140-0001, Tokyo, Japan
| | - Toshihiko Kinjo
- Laboratory of Molecular Pharmacology,Faculty of Pharmaceutical Sciences, Setsunan University, Hirakata, Osaka, 573-0101, Japan
- The Institute of Prophylactic Pharmacology, Kita-Shinagawa, Shinagawa, 140-0001, Tokyo, Japan
| | - Kyosuke Uno
- Laboratory of Molecular Pharmacology,Faculty of Pharmaceutical Sciences, Setsunan University, Hirakata, Osaka, 573-0101, Japan
- The Institute of Prophylactic Pharmacology, Kita-Shinagawa, Shinagawa, 140-0001, Tokyo, Japan
| | - Yukio Yoneda
- The Institute of Prophylactic Pharmacology, Kita-Shinagawa, Shinagawa, 140-0001, Tokyo, Japan
| | - Nobuyuki Kuramoto
- Laboratory of Molecular Pharmacology,Faculty of Pharmaceutical Sciences, Setsunan University, Hirakata, Osaka, 573-0101, Japan
- Laboratory of Pharmacology, Faculty of Pharmaceutical Sciences, Setsunan University, Hirakata, Osaka, 573-0101, Japan
- The Institute of Prophylactic Pharmacology, Kita-Shinagawa, Shinagawa, 140-0001, Tokyo, Japan
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Onishi Y, Yamamura Y, Hosogi M, Higashi H, Ogita K, Kinjo T, Uno K, Yoneda Y, Kuramoto N. Delayed Expression of Both GABA BR1 and GABA BR2 Subunits in Murine Hippocampal Dentate Gyrus After a Single Systemic Injection of Trimethyltin. Neurochem Res 2022; 47:2780-2792. [PMID: 35737203 DOI: 10.1007/s11064-022-03652-7] [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] [Received: 03/31/2022] [Revised: 05/26/2022] [Accepted: 06/06/2022] [Indexed: 11/24/2022]
Abstract
Trimethyltin (TMT) has been used as a cytotoxin to neurons rather than glial cells in the mammalian hippocampus. The systemic administration of TMT led to declined fluorescence of ZnAF-2 DA staining as a marker of intact mossy fibers and increased fluorescence of Fluoro-Jade B staining as a marker of degenerated neurons during the initial 2 to 5 days after the administration with later ameliorations within 30 days in the hippocampal dentate gyrus (DG) and CA3 region in mice. On immunoblotting analysis, both GABABR1 and GABABR2 subunit levels increased during 15 to 30 days after TMT along with significant decreases in glutamatergic GluA1 and GluA2/3 receptor subunit levels during 2 to 7 days in the DG, but not in other hippocampal regions such as CA1 and CA3 regions. Immunohistochemical analysis revealed the constitutive and inducible expression of GABABR2 subunit in cells immunoreactive to an astrocytic marker as well as neuronal markers in the DG with the absence of neither GABABR1a nor GABABR1b subunit from cells positive to an astrocytic marker. These results suggest that both GABABR1 and GABABR2 subunits may be up-regulated in cells other than neurons and astroglia in the DG at a late stage of TMT intoxication in mice.
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Affiliation(s)
- Yuki Onishi
- Laboratories of Molecular Pharmacology, Faculty of Pharmaceutical Sciences, Setsunan University, 45-1 Nagaotoge-cho, Hirakata, Osaka, 573-0101, Japan
- The Institute of Prophylactic Pharmacology, Kita-Shinagawa, Shinagawa, Tokyo, 140-0001, Japan
- Laboratory of Pharmacology, Faculty of Pharmaceutical Sciences, Hiroshima International University, Hiroshima, 737-0112, Japan
| | - Yusuke Yamamura
- Laboratories of Pharmacology, Faculty of Pharmaceutical Sciences, Setsunan University, Hirakata, Osaka, 573-0101, Japan
| | - Misa Hosogi
- Laboratories of Molecular Pharmacology, Faculty of Pharmaceutical Sciences, Setsunan University, 45-1 Nagaotoge-cho, Hirakata, Osaka, 573-0101, Japan
| | - Hiroshi Higashi
- Laboratories of Molecular Pharmacology, Faculty of Pharmaceutical Sciences, Setsunan University, 45-1 Nagaotoge-cho, Hirakata, Osaka, 573-0101, Japan
| | - Kiyokazu Ogita
- Laboratories of Pharmacology, Faculty of Pharmaceutical Sciences, Setsunan University, Hirakata, Osaka, 573-0101, Japan
- The Institute of Prophylactic Pharmacology, Kita-Shinagawa, Shinagawa, Tokyo, 140-0001, Japan
- Setsunan University, 17-8 Ikedanakamachi, Neyagawa, Osaka, 572-8508, Japan
| | - Toshihiko Kinjo
- Laboratories of Molecular Pharmacology, Faculty of Pharmaceutical Sciences, Setsunan University, 45-1 Nagaotoge-cho, Hirakata, Osaka, 573-0101, Japan
- The Institute of Prophylactic Pharmacology, Kita-Shinagawa, Shinagawa, Tokyo, 140-0001, Japan
| | - Kyosuke Uno
- Laboratories of Molecular Pharmacology, Faculty of Pharmaceutical Sciences, Setsunan University, 45-1 Nagaotoge-cho, Hirakata, Osaka, 573-0101, Japan
- The Institute of Prophylactic Pharmacology, Kita-Shinagawa, Shinagawa, Tokyo, 140-0001, Japan
| | - Yukio Yoneda
- The Institute of Prophylactic Pharmacology, Kita-Shinagawa, Shinagawa, Tokyo, 140-0001, Japan
| | - Nobuyuki Kuramoto
- Laboratories of Molecular Pharmacology, Faculty of Pharmaceutical Sciences, Setsunan University, 45-1 Nagaotoge-cho, Hirakata, Osaka, 573-0101, Japan.
- Laboratories of Pharmacology, Faculty of Pharmaceutical Sciences, Setsunan University, Hirakata, Osaka, 573-0101, Japan.
- The Institute of Prophylactic Pharmacology, Kita-Shinagawa, Shinagawa, Tokyo, 140-0001, Japan.
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D'Onofrio G, Riva A, Di Rosa G, Cali' E, Efthymiou S, Gitto E, Madia F, Accogli A, Zara F, Houlden H, Salpietro V, Striano P, Soler D. Paroxysmal limb dystonias associated with GABBR2 pathogenic variant: A case-based literature review. Brain Dev 2022; 44:469-473. [PMID: 35414446 DOI: 10.1016/j.braindev.2022.03.010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Revised: 03/28/2022] [Accepted: 03/29/2022] [Indexed: 11/18/2022]
Abstract
BACKGROUND De novo mutations in the GABBR2 (Gamma-Aminobutyric acid Type B Receptor Subunit 2) gene have recently been reported to be associated with a form of early-infantile epileptic encephalopathy (EIEE59; OMIM# 617904), as well as a Rett syndrome (RTT)-like disorder defined as a neurodevelopmental disorder with poor language and loss of hand skills (NDPLHS; OMIM# 617903). METHODS We describe a pediatric case carrying a de novo GABBR2 pathogenic variant and showing a phenotype encompassing RTT, epilepsy, generalized hypotonia with a paroxysmal limb dystonia. RESULTS A 11-year-old girl, born to non-consanguineous parents after an uneventful pregnancy, had developmental delay and generalized hypotonia. At age 3.5 months she presented with infantile spasms with an electroencephalographic pattern of hypsarrhythmia. After treatment with clonazepam and prednisolone, she became seizure-free with a slow background electrical activity. Brain magnetic resonance imaging was normal. Paroxysmal dystonic posturing of the extremities, especially the upper limbs, have been observed since the age of 3 years. Motor stereotypies, non-epileptic episodes of hyperventilation and breath-holding were also reported. The girl suffered from feeding difficulties requiring gastrostomy at the age of 8. Exome sequencing (ES) revealed a de novo GABBR2 pathogenic variant (NM_005458:c.G2077T:p.G693W). CONCLUSION Paroxysmal limb dystonias, especially in the context of neurodevelopmental disorder featuring epilepsy, generalized hypotonia and RTT-like features should lead to the suspect of GABBR2 mutations.
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Affiliation(s)
- Gianluca D'Onofrio
- Department of Neurosciences Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health (DiNOGMI), University of Genoa, Via Gerolamo Gaslini 5, 16147 Genoa, Italy; Pediatric Neurology and Muscular Diseases Unit, IRCCS Istituto "Giannina Gaslini", Via Gerolamo Gaslini 5, 16147 Genoa, Italy
| | - Antonella Riva
- Department of Neurosciences Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health (DiNOGMI), University of Genoa, Via Gerolamo Gaslini 5, 16147 Genoa, Italy; Pediatric Neurology and Muscular Diseases Unit, IRCCS Istituto "Giannina Gaslini", Via Gerolamo Gaslini 5, 16147 Genoa, Italy
| | - Gabriella Di Rosa
- Child Neuropsychiatry Unit, Department of Pediatrics, University of Messina, Messina 98100, Italy
| | - Elisa Cali'
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology and The National Hospital for Neurology and Neurosurgery, Gower Street, London WC1E 6BT, United Kingdom
| | - Stephanie Efthymiou
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology and The National Hospital for Neurology and Neurosurgery, Gower Street, London WC1E 6BT, United Kingdom
| | - Eloisa Gitto
- Intensive Neonatal and Pediatric Care Unit, Department of Pediatrics, University of Messina, Messina 98100, Italy
| | - Francesca Madia
- Unit of Medical Genetics, IRCCS Istituto "Giannina Gaslini", Via Gerolamo Gaslini 5, 16147 Genoa, Italy
| | - Andrea Accogli
- Division of Medical Genetics, Department of Specialized Medicine, Montreal Children's Hospital, McGill University Health Centre (MUHC), Montreal, Canada; Department of Human Genetics, McGill University, Montreal, QC, Canada
| | - Federico Zara
- Department of Neurosciences Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health (DiNOGMI), University of Genoa, Via Gerolamo Gaslini 5, 16147 Genoa, Italy; Unit of Medical Genetics, IRCCS Istituto "Giannina Gaslini", Via Gerolamo Gaslini 5, 16147 Genoa, Italy
| | - Henry Houlden
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology and The National Hospital for Neurology and Neurosurgery, Gower Street, London WC1E 6BT, United Kingdom
| | - Vincenzo Salpietro
- Department of Neurosciences Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health (DiNOGMI), University of Genoa, Via Gerolamo Gaslini 5, 16147 Genoa, Italy; Pediatric Neurology and Muscular Diseases Unit, IRCCS Istituto "Giannina Gaslini", Via Gerolamo Gaslini 5, 16147 Genoa, Italy; Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology and The National Hospital for Neurology and Neurosurgery, Gower Street, London WC1E 6BT, United Kingdom
| | - Pasquale Striano
- Department of Neurosciences Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health (DiNOGMI), University of Genoa, Via Gerolamo Gaslini 5, 16147 Genoa, Italy; Pediatric Neurology and Muscular Diseases Unit, IRCCS Istituto "Giannina Gaslini", Via Gerolamo Gaslini 5, 16147 Genoa, Italy
| | - Doriette Soler
- Department of Paediatrics, Mater dei Hospital, Msida, Malta.
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Wang Y, Chen YJ, Xiang C, Jiang GW, Xu YD, Yin LM, Zhou DD, Liu YY, Yang YQ. Discovery of potential asthma targets based on the clinical efficacy of Traditional Chinese Medicine formulas. JOURNAL OF ETHNOPHARMACOLOGY 2020; 252:112635. [PMID: 32004629 DOI: 10.1016/j.jep.2020.112635] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2019] [Revised: 01/23/2020] [Accepted: 01/24/2020] [Indexed: 06/10/2023]
Abstract
ETHNOPHARMACOLOGICAL RELEVANCE Standard therapy for asthma, a highly heterogeneous disease, is primarily based on bronchodilators and immunosuppressive drugs, which confer short-term symptomatic relief but not a cure. It is difficult to discover novel bronchodilators, although potential new targets are emerging. Traditional Chinese Medicine (TCM) formulas have been used to treat asthma for more than 2000 years, forming the basis for representative asthma treatments. AIM OF THE STUDY Based on the efficacy of TCM formulas, anti-asthmatic herbal compounds bind proteins are potential targets for asthma therapy. This analysis will provide new drug targets and discovery strategies for asthma therapy. MATERIALS AND METHODS A list of candidate herbs for asthma was selected from the classical formulas (CFs) of TCM for the treatment of wheezing or dyspnea recorded in Treatise on Cold Damage and Miscellaneous Diseases (TCDMD) and from modern herbal formulas identified in the SAPHRON TCM Database using the keywords "wheezing" or "dyspnea". Compounds in the selected herbs and compounds that directly bind target proteins were acquired by searching the Herbal Ingredients' Targets Database (HITD), TCM Data Bank (TCMDB) and TCM Integrated Database (TCMID). Therapeutic targets of conventional medicine (CM) for asthma were collected by searching Therapeutic Target Database (TTD), DrugBank and PubMed as supplements. Finally, the enriched gene ontology (GO) terms of the targets were obtained using the Database for Annotation Visualization and Integrated Discovery (DAVID) and protein-protein interactions (PPI) networks were constructed using Search Tool for the Retrieval of Interacting Genes/Proteins (STRING). The effects of two selected TCM compounds, kaempferol and ginkgolide A, on cellular resistance in human airway smooth muscle cells (ASMCs) and pulmonary resistance in a mouse model were investigated. RESULTS The list of 32 candidate herbs for asthma was selected from 10 CFs for the treatment of wheezing or dyspnea recorded in TCDMD and 1037 modern herbal formulas obtained from the SAPHRON TCM Database. A total of 130 compounds from the 32 selected herbs and 68 herbal compounds directly bind target proteins were acquired from HITD and TCMDB. Eighty-eight therapeutic targets of CM for asthma were collected by searching TTD and PubMed as supplements. DAVID and STRING analyses showed targets of TCM formulas are primarily related to cytochrome P450 (CYP) family, transient receptor potential (TRP) channels, matrix metalloproteinases (MMPs) and ribosomal protein. Both TCM formulas and CM act on the same types of targets or signaling pathways, such as G protein-coupled receptors (GPCRs), steroid hormone receptors (SHRs), and JAK-STAT signaling pathway. The proteins directly targeted by herbal compounds, TRPM8, TRPA1, TRPV3, CYP1B1, CYP2B6, CYP1A2, CYP3A4, CYP1A1, PPARA, PPARD, NR1I2, MMP1, MMP2, ESR1, ESR2, RPLP0, RPLP1 and RPLP2, are potential targets for asthma therapy. In vitro results showed kaempferol (1 × 10-2 mM) and ginkgolide A (1 × 10-5 mM) significantly increased the cell index (P < 0.05 vs. histamine, n = 3) and therefore relaxed human ASMCs. In vivo results showed kaempferol (145 μg/kg) and ginkgolide A (205 μg/kg) significantly reduced pulmonary resistance (P < 0.05 vs. methacholine, n = 6). CONCLUSION Potential target discovery for asthma treatment based on the clinical effectiveness of TCM is a feasible strategy.
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Affiliation(s)
- Yu Wang
- International Union Laboratory on Acupuncture Based Target Discovery, International Joint Laboratory on Acupuncture Neuro-immunology, Shanghai Research Institute of Acupuncture and Meridian, Yue Yang Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai, 201203, China; Experiment Center for Science and Technology, Shanghai University of Traditional Chinese Medicine, Shanghai, 201203, China
| | - Yan-Jiao Chen
- International Union Laboratory on Acupuncture Based Target Discovery, International Joint Laboratory on Acupuncture Neuro-immunology, Shanghai Research Institute of Acupuncture and Meridian, Yue Yang Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai, 201203, China
| | - Cheng Xiang
- International Union Laboratory on Acupuncture Based Target Discovery, International Joint Laboratory on Acupuncture Neuro-immunology, Shanghai Research Institute of Acupuncture and Meridian, Yue Yang Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai, 201203, China
| | - Guang-Wei Jiang
- International Union Laboratory on Acupuncture Based Target Discovery, International Joint Laboratory on Acupuncture Neuro-immunology, Shanghai Research Institute of Acupuncture and Meridian, Yue Yang Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai, 201203, China
| | - Yu-Dong Xu
- International Union Laboratory on Acupuncture Based Target Discovery, International Joint Laboratory on Acupuncture Neuro-immunology, Shanghai Research Institute of Acupuncture and Meridian, Yue Yang Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai, 201203, China
| | - Lei-Miao Yin
- International Union Laboratory on Acupuncture Based Target Discovery, International Joint Laboratory on Acupuncture Neuro-immunology, Shanghai Research Institute of Acupuncture and Meridian, Yue Yang Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai, 201203, China
| | - Dong-Dong Zhou
- International Union Laboratory on Acupuncture Based Target Discovery, International Joint Laboratory on Acupuncture Neuro-immunology, Shanghai Research Institute of Acupuncture and Meridian, Yue Yang Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai, 201203, China
| | - Yan-Yan Liu
- International Union Laboratory on Acupuncture Based Target Discovery, International Joint Laboratory on Acupuncture Neuro-immunology, Shanghai Research Institute of Acupuncture and Meridian, Yue Yang Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai, 201203, China
| | - Yong-Qing Yang
- International Union Laboratory on Acupuncture Based Target Discovery, International Joint Laboratory on Acupuncture Neuro-immunology, Shanghai Research Institute of Acupuncture and Meridian, Yue Yang Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai, 201203, China.
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Sereikaite V, Fritzius T, Kasaragod VB, Bader N, Maric HM, Schindelin H, Bettler B, Strømgaard K. Targeting the γ-Aminobutyric Acid Type B (GABA B) Receptor Complex: Development of Inhibitors Targeting the K + Channel Tetramerization Domain (KCTD) Containing Proteins/GABA B Receptor Protein-Protein Interaction. J Med Chem 2019; 62:8819-8830. [PMID: 31509708 DOI: 10.1021/acs.jmedchem.9b01087] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Targeting multiprotein receptor complexes, rather than receptors directly, is a promising concept in drug discovery. This is particularly relevant to the GABAB receptor complex, which plays a prominent role in many brain functions and diseases. Here, we provide the first studies targeting a key protein-protein interaction of the GABAB receptor complex-the interaction with KCTD proteins. By employing the μSPOT technology, we first defined the GABAB receptor-binding epitope mediating the KCTD interaction. Subsequently, we developed a highly potent peptide-based inhibitor that interferes with the KCTD/GABAB receptor complex and efficiently isolates endogenous KCTD proteins from mouse brain lysates. X-ray crystallography and SEC-MALS revealed inhibitor induced oligomerization of KCTD16 into a distinct hexameric structure. Thus, we provide a template for modulating the GABAB receptor complex, revealing a fundamentally novel approach for targeting GABAB receptor-associated neuropsychiatric disorders.
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Affiliation(s)
- Vita Sereikaite
- Center for Biopharmaceuticals, Department of Drug Design and Pharmacology , University of Copenhagen , 2100 Copenhagen , Denmark
| | - Thorsten Fritzius
- Department of Biomedicine , University of Basel , CH-4056 Basel , Switzerland
| | - Vikram B Kasaragod
- Rudolf Virchow Center for Experimental Biomedicine , University of Würzburg , 97080 Würzburg , Germany
| | - Nicole Bader
- Rudolf Virchow Center for Experimental Biomedicine , University of Würzburg , 97080 Würzburg , Germany
| | - Hans M Maric
- Center for Biopharmaceuticals, Department of Drug Design and Pharmacology , University of Copenhagen , 2100 Copenhagen , Denmark
| | - Hermann Schindelin
- Rudolf Virchow Center for Experimental Biomedicine , University of Würzburg , 97080 Würzburg , Germany
| | - Bernhard Bettler
- Department of Biomedicine , University of Basel , CH-4056 Basel , Switzerland
| | - Kristian Strømgaard
- Center for Biopharmaceuticals, Department of Drug Design and Pharmacology , University of Copenhagen , 2100 Copenhagen , Denmark
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Structural basis for auxiliary subunit KCTD16 regulation of the GABA B receptor. Proc Natl Acad Sci U S A 2019; 116:8370-8379. [PMID: 30971491 DOI: 10.1073/pnas.1903024116] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Metabotropic GABAB receptors mediate a significant fraction of inhibitory neurotransmission in the brain. Native GABAB receptor complexes contain the principal subunits GABAB1 and GABAB2, which form an obligate heterodimer, and auxiliary subunits, known as potassium channel tetramerization domain-containing proteins (KCTDs). KCTDs interact with GABAB receptors and modify the kinetics of GABAB receptor signaling. Little is known about the molecular mechanism governing the direct association and functional coupling of GABAB receptors with these auxiliary proteins. Here, we describe the high-resolution structure of the KCTD16 oligomerization domain in complex with part of the GABAB2 receptor. A single GABAB2 C-terminal peptide is bound to the interior of an open pentamer formed by the oligomerization domain of five KCTD16 subunits. Mutation of specific amino acids identified in the structure of the GABAB2-KCTD16 interface disrupted both the biochemical association and functional modulation of GABAB receptors and G protein-activated inwardly rectifying K+ channel (GIRK) channels. These interfacial residues are conserved among KCTDs, suggesting a common mode of KCTD interaction with GABAB receptors. Defining the binding interface of GABAB receptor and KCTD reveals a potential regulatory site for modulating GABAB-receptor function in the brain.
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Frangaj A, Fan QR. Structural biology of GABA B receptor. Neuropharmacology 2018; 136:68-79. [PMID: 29031577 PMCID: PMC5897222 DOI: 10.1016/j.neuropharm.2017.10.011] [Citation(s) in RCA: 58] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2017] [Revised: 10/09/2017] [Accepted: 10/11/2017] [Indexed: 11/17/2022]
Abstract
Metabotropic GABAB receptor is a G protein-coupled receptor (GPCR) that mediates slow and prolonged inhibitory neurotransmission in the brain. It functions as a constitutive heterodimer composed of the GABAB1 and GABAB2 subunits. Each subunit contains three domains; the extracellular Venus flytrap module, seven-helix transmembrane region and cytoplasmic tail. In recent years, the three-dimensional structures of GABAB receptor extracellular and intracellular domains have been elucidated. These structures reveal the molecular basis of ligand recognition, receptor heterodimerization and receptor activation. Here we provide a brief review of the GABAB receptor structures, with an emphasis on describing the different ligand-bound states of the receptor. We will also compare these with the known structures of related GPCRs to shed light on the molecular mechanisms of activation and regulation in the GABAB system, as well as GPCR dimers in general. This article is part of the "Special Issue Dedicated to Norman G. Bowery".
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Affiliation(s)
- Aurel Frangaj
- Department of Pharmacology, Columbia University, New York, NY 10032, USA
| | - Qing R Fan
- Department of Pharmacology, Columbia University, New York, NY 10032, USA; Department of Pathology & Cell Biology, Columbia University, New York, NY 10032, USA.
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9
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Fatemi SH, Folsom TD. GABA receptor subunit distribution and FMRP-mGluR5 signaling abnormalities in the cerebellum of subjects with schizophrenia, mood disorders, and autism. Schizophr Res 2015; 167:42-56. [PMID: 25432637 PMCID: PMC5301472 DOI: 10.1016/j.schres.2014.10.010] [Citation(s) in RCA: 58] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/02/2014] [Revised: 10/06/2014] [Accepted: 10/08/2014] [Indexed: 12/24/2022]
Abstract
Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the brain. GABAergic receptor abnormalities have been documented in several major psychiatric disorders including schizophrenia, mood disorders, and autism. Abnormal expression of mRNA and protein for multiple GABA receptors has also been observed in multiple brain regions leading to alterations in the balance between excitatory/inhibitory signaling in the brain with potential profound consequences for normal cognition and maintenance of mood and perception. Altered expression of GABAA receptor subunits has been documented in fragile X mental retardation 1 (FMR1) knockout mice, suggesting that loss of its protein product, fragile X mental retardation protein (FMRP), impacts GABAA subunit expression. Recent postmortem studies from our laboratory have shown reduced expression of FMRP in the brains of subjects with schizophrenia, bipolar disorder, major depression, and autism. FMRP acts as a translational repressor and, under normal conditions, inhibits metabotropic glutamate receptor 5 (mGluR5)-mediated signaling. In fragile X syndrome (FXS), the absence of FMRP is hypothesized to lead to unregulated mGluR5 signaling, ultimately resulting in the behavioral and intellectual impairments associated with this disorder. Our laboratory has identified changes in mGluR5 expression in autism, schizophrenia, and mood disorders. In the current review article, we discuss our postmortem data on GABA receptors, FMRP, and mGluR5 levels and compare our results with other laboratories. Finally, we discuss the interactions between these molecules and the potential for new therapeutic interventions that target these interconnected signaling systems.
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Affiliation(s)
- S Hossein Fatemi
- Department of Psychiatry, Division of Neuroscience Research, University of Minnesota Medical School, 420 Delaware St SE, MMC 392, Minneapolis, MN 55455, USA; Department of Neuroscience, University of Minnesota Medical School, 321 Church St. SE, Minneapolis, MN 55455, USA.
| | - Timothy D Folsom
- Department of Psychiatry, Division of Neuroscience Research, University of Minnesota Medical School, 420 Delaware St SE, MMC 392, Minneapolis, MN 55455, USA.
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Filipeanu CM. Temperature-Sensitive Intracellular Traffic of α2C-Adrenergic Receptor. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2015; 132:245-65. [DOI: 10.1016/bs.pmbts.2015.02.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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Fan WM, Ma XH, Xiao L, Chen LP, He XY, Shi BY. Expression of truncated γ-aminobutyric acid B receptor in liver fibrosis in rats. Shijie Huaren Xiaohua Zazhi 2014; 22:4456-4460. [DOI: 10.11569/wcjd.v22.i29.4456] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
AIM: To investigate the expression of truncated γ-aminobutyric acid B receptor 1 (GABBR1) in liver fibrosis in rats.
METHODS: Sprague-Dawley rats were divided into three groups: a normal control group, a model group and a treatment group. Liver fibrosis was induced with carbon tetrachloride (CCl4) in rats of the model group and treatment group, and the normal control group was given olive oil. The treatment group was additionally given GABA. Western blot analysis and PCR were performed to detect the expression of GABBR1 protein and mRNA.
RESULTS: Both Western blot and PCR analyses indicated the presence of a truncated GABBR1 in rats of the three groups. DNA sequencing and NCBI blast sequence analysis confirmed that the protein is GABBR1e. PCR results showed that the mRNA expression level of GABBR1e in the model group was higher than those in the GABA group and the control group. However, there was no significant difference in the protein expression level of GABBR1e among the three groups.
CONCLUSION: Our findings suggest the expression of GABBR1e in liver tissue. The role of GABBR1e in liver fibrosis and its biological significance still need further research.
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Tao YX, Conn PM. Chaperoning G protein-coupled receptors: from cell biology to therapeutics. Endocr Rev 2014; 35:602-47. [PMID: 24661201 PMCID: PMC4105357 DOI: 10.1210/er.2013-1121] [Citation(s) in RCA: 96] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Accepted: 03/14/2014] [Indexed: 12/13/2022]
Abstract
G protein-coupled receptors (GPCRs) are membrane proteins that traverse the plasma membrane seven times (hence, are also called 7TM receptors). The polytopic structure of GPCRs makes the folding of GPCRs difficult and complex. Indeed, many wild-type GPCRs are not folded optimally, and defects in folding are the most common cause of genetic diseases due to GPCR mutations. Both general and receptor-specific molecular chaperones aid the folding of GPCRs. Chemical chaperones have been shown to be able to correct the misfolding in mutant GPCRs, proving to be important tools for studying the structure-function relationship of GPCRs. However, their potential therapeutic value is very limited. Pharmacological chaperones (pharmacoperones) are potentially important novel therapeutics for treating genetic diseases caused by mutations in GPCR genes that resulted in misfolded mutant proteins. Pharmacoperones also increase cell surface expression of wild-type GPCRs; therefore, they could be used to treat diseases that do not harbor mutations in GPCRs. Recent studies have shown that indeed pharmacoperones work in both experimental animals and patients. High-throughput assays have been developed to identify new pharmacoperones that could be used as therapeutics for a number of endocrine and other genetic diseases.
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Affiliation(s)
- Ya-Xiong Tao
- Department of Anatomy, Physiology, and Pharmacology (Y.-X.T.), College of Veterinary Medicine, Auburn University, Auburn, Alabama 36849-5519; and Departments of Internal Medicine and Cell Biology (P.M.C.), Texas Tech University Health Science Center, Lubbock, Texas 79430-6252
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13
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Distinct human and mouse membrane trafficking systems for sweet taste receptors T1r2 and T1r3. PLoS One 2014; 9:e100425. [PMID: 25029362 PMCID: PMC4100762 DOI: 10.1371/journal.pone.0100425] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2014] [Accepted: 05/27/2014] [Indexed: 11/23/2022] Open
Abstract
The sweet taste receptors T1r2 and T1r3 are included in the T1r taste receptor family that belongs to class C of the G protein-coupled receptors. Heterodimerization of T1r2 and T1r3 is required for the perception of sweet substances, but little is known about the mechanisms underlying this heterodimerization, including membrane trafficking. We developed tagged mouse T1r2 and T1r3, and human T1R2 and T1R3 and evaluated membrane trafficking in human embryonic kidney 293 (HEK293) cells. We found that human T1R3 surface expression was only observed when human T1R3 was coexpressed with human T1R2, whereas mouse T1r3 was expressed without mouse T1r2 expression. A domain-swapped chimera and truncated human T1R3 mutant showed that the Venus flytrap module and cysteine-rich domain (CRD) of human T1R3 contain a region related to the inhibition of human T1R3 membrane trafficking and coordinated regulation of human T1R3 membrane trafficking. We also found that the Venus flytrap module of both human T1R2 and T1R3 are needed for membrane trafficking, suggesting that the coexpression of human T1R2 and T1R3 is required for this event. These results suggest that the Venus flytrap module and CRD receive taste substances and play roles in membrane trafficking of human T1R2 and T1R3. These features are different from those of mouse receptors, indicating that human T1R2 and T1R3 are likely to have a novel membrane trafficking system.
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14
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Giachino C, Barz M, Tchorz JS, Tome M, Gassmann M, Bischofberger J, Bettler B, Taylor V. GABA suppresses neurogenesis in the adult hippocampus through GABAB receptors. Development 2013; 141:83-90. [PMID: 24284211 DOI: 10.1242/dev.102608] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Adult neurogenesis is tightly regulated through the interaction of neural stem/progenitor cells (NSCs) with their niche. Neurotransmitters, including GABA activation of GABAA receptor ion channels, are important niche signals. We show that adult mouse hippocampal NSCs and their progeny express metabotropic GABAB receptors. Pharmacological inhibition of GABAB receptors stimulated NSC proliferation and genetic deletion of GABAB1 receptor subunits increased NSC proliferation and differentiation of neuroblasts in vivo. Cell-specific conditional deletion of GABAB receptors supports a cell-autonomous role in newly generated cells. Our data indicate that signaling through GABAB receptors is an inhibitor of adult neurogenesis.
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Affiliation(s)
- Claudio Giachino
- Embryology and Stem Cell Biology, Department of Biomedicine, University of Basel, Mattenstrasse 28, CH-4058 Basel, Switzerland
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15
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Kostakis E, Smith C, Jang MK, Martin SC, Richards KG, Russek SJ, Gibbs TT, Farb DH. The neuroactive steroid pregnenolone sulfate stimulates trafficking of functional N-methyl D-aspartate receptors to the cell surface via a noncanonical, G protein, and Ca2+-dependent mechanism. Mol Pharmacol 2013; 84:261-74. [PMID: 23716622 DOI: 10.1124/mol.113.085696] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
N-methyl D-aspartate (NMDA) receptors (NMDARs) mediate fast excitatory synaptic transmission and play a critical role in synaptic plasticity associated with learning and memory. NMDAR hypoactivity has been implicated in the pathophysiology of schizophrenia, and clinical studies have revealed reduced negative symptoms of schizophrenia with a dose of pregnenolone that elevates serum levels of the neuroactive steroid pregnenolone sulfate (PregS). This report describes a novel process of delayed-onset potentiation whereby PregS approximately doubles the cell's response to NMDA via a mechanism that is pharmacologically and kinetically distinct from rapid positive allosteric modulation by PregS. The number of functional cell-surface NMDARs in cortical neurons increases 60-100% within 10 minutes of exposure to PregS, as shown by surface biotinylation and affinity purification. Delayed-onset potentiation is reversible and selective for expressed receptors containing the NMDAR subunit subtype 2A (NR2A) or NR2B, but not the NR2C or NR2D, subunits. Moreover, substitution of NR2B J/K helices and M4 domain with the corresponding region of NR2D ablates rapid allosteric potentiation of the NMDA response by PregS but not delayed-onset potentiation. This demonstrates that the initial phase of rapid positive allosteric modulation is not a first step in NMDAR upregulation. Delayed-onset potentiation by PregS occurs via a noncanonical, pertussis toxin-sensitive, G protein-coupled, and Ca(2+)-dependent mechanism that is independent of NMDAR ion channel activation. Further investigation into the sequelae for PregS-stimulated trafficking of NMDARs to the neuronal cell surface may uncover a new target for the pharmacological treatment of disorders in which NMDAR hypofunction has been implicated.
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Affiliation(s)
- Emmanuel Kostakis
- Laboratory of Molecular Neurobiology, Department of Pharmacology & Experimental Therapeutics, Boston University School of Medicine, Boston, MA, USA
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16
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Hearing MC, Zink AN, Wickman K. Cocaine-induced adaptations in metabotropic inhibitory signaling in the mesocorticolimbic system. Rev Neurosci 2012; 23:325-51. [PMID: 22944653 DOI: 10.1515/revneuro-2012-0045] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2012] [Accepted: 06/11/2012] [Indexed: 12/17/2022]
Abstract
The addictive properties of psychostimulants such as cocaine are rooted in their ability to activate the mesocorticolimbic dopamine (DA) system. This system consists primarily of dopaminergic projections arising from the ventral tegmental area (VTA) and projecting to the limbic and cortical brain regions, such as the nucleus accumbens (NAc) and prefrontal cortex (PFC). While the basic anatomy and functional relevance of the mesocorticolimbic DA system is relatively well-established, a key challenge remaining in addiction research is to understand where and how molecular adaptations and corresponding changes in function of this system facilitate a pathological desire to seek and take drugs. Several lines of evidence indicate that inhibitory signaling, particularly signaling mediated by the Gi/o class of heterotrimeric GTP-binding proteins (G proteins), plays a key role in the acute and persistent effects of drugs of abuse. Moreover, recent evidence argues that these signaling pathways are targets of drug-induced adaptations. In this review we discuss inhibitory signaling pathways involving DA and the inhibitory neurotransmitter GABA in two brain regions - the VTA and PFC - that are central to the effects of acute and repeated cocaine exposure and represent sites of adaptations linked to addiction-related behaviors including sensitization, craving, and relapse.
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Affiliation(s)
- Matthew C Hearing
- Department of Pharmacology, University of Minnesota, Minneapolis, MN, USA
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17
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Kaeser GE, Rabe BA, Saha MS. Cloning and characterization of GABAA α subunits and GABAB subunits in Xenopus laevis during development. Dev Dyn 2011; 240:862-73. [PMID: 21384470 DOI: 10.1002/dvdy.22580] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/17/2011] [Indexed: 11/08/2022] Open
Abstract
Gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the adult nervous system, acts via two classes of receptors, the ionotropic GABA(A) and metabotropic GABA(B) receptors. During the development of the nervous system, GABA acts in a depolarizing, excitatory manner and plays an important role in various neural developmental processes including cell proliferation, migration, synapse formation, and activity-dependent differentiation. Here we describe the spatial and temporal expression patterns of the GABA(A) and GABA(B) receptors during early development of Xenopus laevis. Using in situ hybridization and qRT-PCR, GABA(A) α2 was detected as a maternal mRNA. All other α-subunits were first detected by tailbud through hatching stages. Expression of the various subunits was seen in the brain, spinal cord, cranial ganglia, olfactory epithelium, pineal, and pituitary gland. Each receptor subunit showed a distinctive, unique expression pattern, suggesting these receptors have specific functions and are regulated in a precise spatial and temporal manner.
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Affiliation(s)
- Gwendolyn E Kaeser
- Department of Biology, The College of William and Mary, Integrated Science Center, Williamsburg, Virginia, USA
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18
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Abstract
In 1950, γ-aminobutyric acid (GABA) was discovered in the brain and in 1967 it was recognized as an inhibitory neurotransmitter. The discovery of the benzodiazepines Librium® (launched in 1960) and Valium® by Sternbach initiated huge research activities resulting in 50 marketed drugs. In 1975, Haefely found that GABA is involved in the actions of benzodiazepines. The baclofen-sensitive, bicuculline-insensitive GABAB receptor was discovered by Bowery in 1980, and the baclofen-insensitive, bicuculline-insensitive GABAC receptor by Johnston in 1984. Barnard & Seeburg reported the cloning of the GABAA receptor in 1987, Cutting the GABAC receptor in 1991 and Bettler the GABAB1a and GABAB1b receptors in 1997. Six groups cloned the GABAB2 receptor in 1998/1999 showing that the GABAB receptor functions as a heterodimer with GABAB1b/GABAB2 mediating postsynaptic inhibition and GABAB1a/GABAB2 mediating presynaptic inhibition. Möhler and McKernan dissected the pharmacology of the benzodiazepine-receptor subtypes. Antagonists and positive allosteric modulators of GABAB receptors were discovered in 1987 and 2001, respectively. GABA transporter inhibitor, tiagabine, was launched in 1996, a GABA aminotransferase inhibitor, vigabatrin, in 1998 and a glutamic acid decarboxylase activator, pregabalin, in 2004. Most recently, brain-penetrating GABAC-receptor antagonists were reported in 2009.
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Fukui M, Ozawa S, Nakamichi N, Nakazato R, Takarada T, Yoneda Y. Gradual downregulation of protein expression of the partner GABA(B)R2 subunit during postnatal brain development in mice defective of GABA(B)R1 subunit. J Pharmacol Sci 2010; 115:45-55. [PMID: 21160134 DOI: 10.1254/jphs.10254fp] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
Abstract
We have previously shown the functional expression of GABA(B) receptors (GABA(B)R) composed of GABA(B)R1 and GABA(B)R2 subunits with ability to promote proliferation and neuronal differentiation in cultured neural progenitor cells (NPC) isolated from embryonic mouse brains. In this study, we evaluated postnatal changes in the expression profiles of different markers for progenitor, neuronal, astroglial, and microglial cells in brains of GABA(B)R1-null mice. Consistent with undifferentiated murine NPC cultured with epidermal growth factor, a significant and selective decrease was seen in mRNA expression of the proneural gene Mash1 in brains of GABA(B)R1-null mice at 1 day after birth. The expression of several NPC marker proteins was similarly decreased in brains of both wild-type and GABA(B)R1-null mice from 1 to 7 days after birth, while slight changes were induced in both mRNA and proteins for neuronal, astroglial, and microglial markers between wild-type and GABA(B)R1-null mouse brains within this developmental stage. In particular discrete brain structures of adult GABA(B)R1-null mice at 56 days after birth, a significant decrease was seen in neuronal marker protein levels along with a significant increase in both astroglial and microglial marker protein expression. Although no significant difference was found in mRNA expression of the partner GABA(B)R2 subunit between wild-type and GABA(B)R1-null mouse brains, GABA(B)R2 subunit protein levels were gradually declined during postnatal development within 56 days after birth in GABA(B)R1-null mouse brains. These results suggest that GABA(B)R2 protein levels are closely correlated with the partner subunit GABA(B)R1 protein levels in mouse brains during postnatal development in vivo.
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Affiliation(s)
- Masaki Fukui
- Kanazawa University Graduate School of Natural Science and Technology, Kanazawa, Japan
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20
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Naseer M, Lee H, Ullah N, Ullah I, Park M, Kim M. siRNA-mediated GABAB receptor at early fetal rat brain upon acute and chronic ethanol exposure: Down regulation of PKA and p-CREB expression. Synapse 2010; 65:109-18. [DOI: 10.1002/syn.20824] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Heterodimerization of the GABAB receptor-implications for GPCR signaling and drug discovery. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2010; 58:63-91. [PMID: 20655478 DOI: 10.1016/s1054-3589(10)58003-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The identification of the molecular nature of the GABA(B) receptor and the demonstration of its heterodimeric structure has led to extensive studies investigating the mechanism of activation and signaling. Phylogenetic studies suggest that the formation of the heterodimer is a relatively recent event arising in conjunction with the evolution of the central nervous system. Heterodimerization has now been demonstrated for many other G-protein-coupled receptors (GPCRs) and plays a role in signaling and trafficking. This presents both challenges and opportunities for GPCR drug discovery. In the case of the GABA(B) receptor the best hope for the development of new drugs directed at this receptor is from allosteric modulators. This chapter summarizes our current understanding of the molecular function of the GABA(B) receptor and recent developments in the identification of allosteric modulators. The broader implication of heterodimerization on GPCR function and drug discovery is also discussed.
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22
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Constitutive, agonist-accelerated, recycling and lysosomal degradation of GABA(B) receptors in cortical neurons. Mol Cell Neurosci 2008; 39:628-37. [PMID: 18948198 DOI: 10.1016/j.mcn.2008.09.004] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2008] [Revised: 09/09/2008] [Accepted: 09/15/2008] [Indexed: 01/27/2023] Open
Abstract
Endocytosis is considered as an important mechanism for regulating cell surface numbers and thereby signaling strength of G protein-coupled receptors. Currently, little is known about the endocytotic pathways of GABA(B) receptors in neurons. Here we report that GABA(B) receptors are constitutively internalized presumably via clathrin-dependent endocytosis in cultured cortical neurons. Colocalization of GABA(B) receptors with endosomal marker proteins indicated sorting of GABA(B) receptors from early endosomes to recycling endosomes and to lysosomes. Cell surface biotinylation experiments revealed fast constitutive recycling of GABA(B) receptors as the predominant pathway that was accelerated by the GABA(B) receptor agonist baclofen. Finally, degradation of GABA(B) receptors in lysosomes was demonstrated by their intracellular accumulation upon inhibition of lysosomal proteases and by blocking recycling which resulted in the redirection of receptors to lysosomes for degradation. These data imply rapid constitutive - agonist-accelerated - recycling of GABA(B) receptors presumably via clathrin-coated pits and their final targeting to lysosomes for degradation.
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Ben-Ari Y, Gaiarsa JL, Tyzio R, Khazipov R. GABA: a pioneer transmitter that excites immature neurons and generates primitive oscillations. Physiol Rev 2007; 87:1215-84. [PMID: 17928584 DOI: 10.1152/physrev.00017.2006] [Citation(s) in RCA: 892] [Impact Index Per Article: 52.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Developing networks follow common rules to shift from silent cells to coactive networks that operate via thousands of synapses. This review deals with some of these rules and in particular those concerning the crucial role of the neurotransmitter gamma-aminobuytric acid (GABA), which operates primarily via chloride-permeable GABA(A) receptor channels. In all developing animal species and brain structures investigated, neurons have a higher intracellular chloride concentration at an early stage leading to an efflux of chloride and excitatory actions of GABA in immature neurons. This triggers sodium spikes, activates voltage-gated calcium channels, and acts in synergy with NMDA channels by removing the voltage-dependent magnesium block. GABA signaling is also established before glutamatergic transmission, suggesting that GABA is the principal excitatory transmitter during early development. In fact, even before synapse formation, GABA signaling can modulate the cell cycle and migration. The consequence of these rules is that developing networks generate primitive patterns of network activity, notably the giant depolarizing potentials (GDPs), largely through the excitatory actions of GABA and its synergistic interactions with glutamate signaling. These early types of network activity are likely required for neurons to fire together and thus to "wire together" so that functional units within cortical networks are formed. In addition, depolarizing GABA has a strong impact on synaptic plasticity and pathological insults, notably seizures of the immature brain. In conclusion, it is suggested that an evolutionary preserved role for excitatory GABA in immature cells provides an important mechanism in the formation of synapses and activity in neuronal networks.
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Affiliation(s)
- Yehezkel Ben-Ari
- Insititut de Neurobiologie de la Méditerranée, Institut National de la Santé et de la Recherche Médicale U. 29, Marseille, France.
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Grampp T, Sauter K, Markovic B, Benke D. Gamma-aminobutyric acid type B receptors are constitutively internalized via the clathrin-dependent pathway and targeted to lysosomes for degradation. J Biol Chem 2007; 282:24157-65. [PMID: 17581821 DOI: 10.1074/jbc.m702626200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Receptor internalization is recognized as an important mechanism for rapidly regulating cell surface numbers of receptors. However, there are conflicting results on the existence of rapid endocytosis of gamma-aminobutyric acid, type B (GABAB) receptors. Therefore, we analyzed internalization of GABAB receptors expressed in HEK 293 cells qualitatively and quantitatively using immunocytochemical, cell surface enzyme-linked immunosorbent assay, and biotinylation methods. The data indicate the existence of rapid constitutive receptor internalization, with the first endocytosed receptors being observed in proximity of the plasma membrane after 10 min. After 120 min, a loss of about 40-50% of cell surface receptors was detected. Stimulation of GABAB receptors with GABA or baclofen did not enhance endocytosis of receptors, indicating the lack of agonist-induced internalization. The data suggest that GABAB receptors were endocytosed via the classical dynamin- and clathrin-dependent pathway and accumulated in an endosomal sorting compartment before being targeted to lysosomes for degradation. No evidence for recycling of receptors back to the cell surface was found. In conclusion, the results indicate the presence of constitutive internalization of GABAB receptors via clathrin-coated pits, which resulted in lysosomal degradation of the receptors.
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Affiliation(s)
- Thomas Grampp
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich 8057, Switzerland
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Frisullo G, Della Marca G, Mirabella M, Caggiula M, Broccolini A, Rubino M, Mennuni G, Tonali PA, Batocchi AP. A human anti-neuronal autoantibody against GABAB receptor induces experimental autoimmune agrypnia. Exp Neurol 2007; 204:808-18. [PMID: 17336294 DOI: 10.1016/j.expneurol.2007.01.012] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2006] [Revised: 01/10/2007] [Accepted: 01/11/2007] [Indexed: 11/18/2022]
Abstract
In the serum and cerebrospinal fluid of a patient with recurrent acute episodes of respiratory crises, autonomic symptoms and total insomnia (agrypnia), we identified a novel anti-neural complement fixing antibody directed against GABA(B) receptor (GABA(B)R). Patient purified IgG recognized a band of approximately 110 kDa on protein extracts of mouse cerebellum, cortex and brainstem and immunolabelled cultured Chinese hamster ovary (CHO) cells, transfected with human GABA(B)R1 and rat GABA(B)R2 receptors. Western blot analysis of transfected CHO homogenates showed the same band using both patient purified IgG and anti-GABA(B)R1 antibody. In order to verify the pathogenic role of these purified antibodies, we injected patient IgG intrathecally into cisterna magna of C57BL/6 mice pre-implanted with EEG electrodes and we observed severe ataxia followed by breathing depression and total suppression of slow wave sleep, as evidenced by EEG recording, in a dose-dependent manner. Immunohistochemistry on brain sections of mice injected with patient IgG showed the simultaneous presence of bound human IgG and C5b-9 deposits on Purkinje cells and cerebellar granular layer. After incubation with anti-GABA(B)R antibody, a marked reduction of receptor immunostaining was found with relative sparing of neuronal architecture. In conclusion we recognized an anti-neuronal autoantibody directed against GABA(B)R that is associated with autoimmune agrypnia and we showed that our patient purified IgG was able to induce in mice experimental autoimmune agrypnia characterized by a complex neurological syndrome affecting several CNS functions.
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Affiliation(s)
- Giovanni Frisullo
- Department of Neuroscience, Institute of Neurology, Catholic University, Largo Gemelli 8, 00168 Rome, Italy
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Luyt K, Slade TP, Dorward JJ, Durant CF, Wu Y, Shigemoto R, Mundell SJ, Váradi A, Molnár E. Developing oligodendrocytes express functional GABA(B) receptors that stimulate cell proliferation and migration. J Neurochem 2007; 100:822-40. [PMID: 17144904 DOI: 10.1111/j.1471-4159.2006.04255.x] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
GABA(B) receptors (GABA(B)Rs) are involved in early events during neuronal development. The presence of GABA(B)Rs in developing oligodendrocytes has not been established. Using immunofluorescent co-localization, we have identified GABA(B)R proteins in O4 marker-positive oligodendrocyte precursor cells (OPCs) in 4-day-old mouse brain periventricular white matter. In culture, OPCs, differentiated oligodendrocytes (DOs) and type 2 astrocytes (ASTs) express both the GABA(B1abcdf) and GABA(B2) subunits of the GABA(B)R. Using semiquantitative PCR analysis with GABA(B)R isoform-selective primers we found that the expression level of GABA(B1abd) was substantially higher in OPCs or ASTs than in DOs. In contrast, the GABA(B2) isoform showed a similar level of expression in OPCs and DOs, and a significantly higher level in ASTs. This indicates that the expression of GABA(B1) and GABA(B2) subunits are under independent control during oligodendroglial development. Activation of GABA(B)Rs using the selective agonist baclofen demonstrated that these receptors are functionally active and negatively coupled to adenylyl cyclase. Manipulation of GABA(B)R activity had no effect on OPC migration in a conventional agarose drop assay, whereas baclofen significantly increased OPC migration in a more sensitive transwell microchamber-based assay. Exposure of cultured OPCs to baclofen increased their proliferation, providing evidence for a functional role of GABA(B)Rs in oligodendrocyte development. The presence of GABA(B)Rs in developing oligodendrocytes provides a new mechanism for neuronal-glial interactions during development and may offer a novel target for promoting remyelination following white matter injury.
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Affiliation(s)
- Karen Luyt
- Medical Research Council Centre for Synaptic Plasticity, Department of Anatomy, University of Bristol, Bristol, UK
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Sun D, Huang W, Hwang YY, Zhang Y, Zhang Q, Li MD. Regulation by nicotine of Gpr51 and Ntrk2 expression in various rat brain regions. Neuropsychopharmacology 2007; 32:110-6. [PMID: 16794563 DOI: 10.1038/sj.npp.1301134] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Our previous genetic studies demonstrated that variants of the gamma-Aminobutyric acid B receptor subunit 2 (GPR51) and neurotrophic tyrosine kinase receptor type 2 (NTRK2) genes are significantly associated with nicotine dependence (ND) in smokers. However, whether such genetic associations lead to changes in the expression of the two genes in response to nicotine remains undetermined. In this study, we investigated the regulatory effect of nicotine on the expression of Gpr51 and Ntrk2 in seven rat brain regions during the administration of nicotine in a daily dose of 3.15 mg/kg for 7 days. With quantitative real-time RT-PCR, we found that nicotine increased the mRNA of Gpr51 by 70, 78, and 32% in the amygdala, striatum, and prefrontal cortex (PFC), respectively, but decreased by 54% in the nucleus accumbens (NA). The Gpr51 protein was upregulated by nicotine in the amygdala (26%), striatum (73%), PFC (28%), and medial basal hypothalamus (MBH; 19%) but downregulated in the NA (-72%). Similarly, the mRNA level of Ntrk2 was enhanced by nicotine in the striatum (86%) and PFC (38%), but decreased in the NA (-46%) and ventral tegmental area (VTA; -49%). A significant change in protein expression was also obtained for Ntrk2 in the PFC (24%), MBH (33%), NA (-33%), and VTA (-70%). Interestingly, these two genes showed a closely coordinated expression pattern in response to nicotine in most of the brain regions examined. In summary, our results demonstrate that the expression of Gpr51 and Ntrk2 is significantly regulated by nicotine at both the mRNA and protein levels in various brain regions, which provides further evidence that these two genes are involved in the etiology of ND, as reported in our previous genetic association studies in humans.
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Affiliation(s)
- Dongxiao Sun
- Section of Neurobiology, Department of Psychiatric Medicine, University of Virginia, Charlottesville, VA 22911, USA
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Abstract
In the basal ganglia the effects of gamma-aminobutyrate (GABA) are mediated by both ionotropic (GABA(A)) and metabotropic (GABA(B)) receptors. Although the existence and widespread distribution in the CNS of the GABA(B) receptor had been established in the 1980s the field of GABA(B) research was revolutionized with the discovery that two related G-protein-coupled receptors (GPCRs) needed to dimerize to form the functional GABA(B) receptor at the cell surface. This finding lead to a number of studies of oligomerization in GPCRs and detailed pharmacological studies of the cloned receptors and their splice variants. Particular interest has focused on the proteins interacting with the receptor which may be important in mediating the longer term signalling effects of the receptor and modifying its cellular localization or physiology. The cloning of the GABA(B) receptors also lead to the identification of the first compounds interacting in an allosteric fashion with the receptor some of which may have therapeutic value. Most recently "knockouts" of both the GABA(B) subunits have been produced where in general as expected there is a loss of the majority of the inhibitory effects of the GABA(B) receptor.
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Affiliation(s)
- Piers C Emson
- The Babraham Institute, Babraham Research Campus, Cambridge CB2 4AT, UK.
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29
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Kornau HC. GABAB receptors and synaptic modulation. Cell Tissue Res 2006; 326:517-33. [PMID: 16932937 DOI: 10.1007/s00441-006-0264-7] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2006] [Accepted: 05/31/2006] [Indexed: 12/18/2022]
Abstract
GABA(B) receptors modulate transmitter release and postsynaptic membrane potential at various types of central synapses. They function as heterodimers of two related seven-transmembrane domain receptor subunits. Trafficking, activation and signalling of GABA(B) receptors are regulated both by allosteric interactions between the subunits and by the binding of additional proteins. Recent studies have shed light on the roles of GABA(B) receptors in plasticity processes at excitatory synapses. This review summarizes our knowledge of the localization, structure and function of GABA(B) receptors in the central nervous system and their use as drug targets for neurological and psychiatric disorders.
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Affiliation(s)
- Hans-Christian Kornau
- Center for Molecular Neurobiology (ZMNH), University of Hamburg, Falkenried 94, 20251 Hamburg, Germany.
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30
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Villalba RM, Raju DV, Hall RA, Smith Y. GABA(B) receptors in the centromedian/parafascicular thalamic nuclear complex: an ultrastructural analysis of GABA(B)R1 and GABA(B)R2 in the monkey thalamus. J Comp Neurol 2006; 496:269-87. [PMID: 16538684 DOI: 10.1002/cne.20950] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Strong gamma-aminobutyric acid type B (GABA(B)) receptor binding has been shown throughout the thalamus, but the distribution of the two GABA(B) receptor subunits, GABA(B) receptor subunit 1 (GABA(B)R1) and GABA(B) receptor subunit 2 (GABA(B)R2), remains poorly characterized. In primates, the caudal intralaminar nuclei, centromedian and parafascicular (CM/PF), are an integral part of basal ganglia circuits and a main source of inputs to the striatum. In this study, we analyzed the subcellular and subsynaptic distribution of GABA(B) receptor subunits by using light and electron microscopic immunocytochemical techniques. Quantitative immunoperoxidase and immunogold analysis showed that both subunits display a similar pattern of distribution in CM/PF, being expressed largely at extrasynaptic and perisynaptic sites in neuronal cell bodies, dendrites, and axon-like processes and less abundantly in axon terminals. Postsynaptic GABA(B)R1 labeling was found mostly on the plasma membrane (70-80%), whereas GABA(B)R2 was more evenly distributed between the plasma membrane and intracellular compartments of CM/PF neurons. A few axon terminals forming symmetric and asymmetric synapses were also labeled for GABA(B)R1 and GABA(B)R2, but the bulk of presynaptic labeling was expressed in small axon-like processes. About 20% of presynaptic vesicle-containing dendrites of local circuit neurons displayed GABA(B)R1/R2 immunoreactivity. Vesicular glutamate transporters (vGluT1)-containing terminals forming asymmetric synapses expressed GABA(B)R1 and/or displayed postsynaptic GABA(B)R1 at the edges of their asymmetric specialization. Overall, these findings provide evidence for multiple sites where GABA(B) receptors could modulate GABAergic and glutamatergic transmission in the primate CM/PF complex.
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Affiliation(s)
- Rosa M Villalba
- Yerkes National Primate Research Center, Emory University, Atlanta, Georgia 30322, USA.
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31
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Lambrecht NWG, Yakubov I, Zer C, Sachs G. Transcriptomes of purified gastric ECL and parietal cells: identification of a novel pathway regulating acid secretion. Physiol Genomics 2006; 25:153-65. [PMID: 16403840 DOI: 10.1152/physiolgenomics.00271.2005] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The gastric entero-chromaffin-like (ECL) cell plays a key regulatory role in peripheral regulation of acid secretion due to the release of histamine that stimulates acid secretion by the parietal cell. Studies in intact animals, gastric glands, and isolated cells after short-term culture have shown expression of stimulatory CCK2 and PAC1 and inhibitory SST2 and Gal1 receptors as well as histidine decarboxylase. However, the pattern of its gene expression as a neuroendocrine cell has not been explored. Comparison of gene expression by 95% pure ECL cells obtained by density gradient, elutriation, and fluorescence-assisted cell sorting with isolates of the intact fundic gastric epithelium (i.e., "subtractive hybridization") identified a variety of additional expressed gene families characteristic of this neuroendocrine cell. These include genes 1) involved in neuropeptide synthesis and secretory vesicle exocytosis, 2) involved in control of inflammation, 3) implicated in healing of the epithelium, 4) encoding inhibitory Gi protein-coupled receptors, 5) playing a role in neuroendocrine regulation of food intake, and 6) encoding proteins likely involved in maintenance of circadian rhythm, in addition to the ECL cell-specific genes histidine decarboxylase and monoamine transporter. Particularly, the inhibitory apelin receptor gene, APJ, was highly expressed in the ECL cell preparation. Because parietal cells express apelin, immunohistochemical and functional studies showed that there is an inhibitory feed back loop between the parietal and ECL cell during gastrin stimulation, providing evidence for a novel pathway of downregulation of acid secretion due to interaction between these two cell types.
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Affiliation(s)
- Nils W G Lambrecht
- Department of Pathology, David Geffen School of Medicine, University of California Los Angeles, California, USA.
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32
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Krogsgaard-Larsen P, Frølund B, Liljefors T. GABAA Agonists and Partial Agonists: THIP (Gaboxadol) as a Non‐Opioid Analgesic and a Novel Type of Hypnotic1. GABA 2006; 54:53-71. [PMID: 17175810 DOI: 10.1016/s1054-3589(06)54003-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Povl Krogsgaard-Larsen
- Department of Medicinal Chemistry, The Danish University of Pharmaceutical Sciences, 2 Universitetsparken, DK-2100 Copenhagen, Denmark
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33
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Lacey CJ, Boyes J, Gerlach O, Chen L, Magill PJ, Bolam JP. GABA(B) receptors at glutamatergic synapses in the rat striatum. Neuroscience 2005; 136:1083-95. [PMID: 16226840 DOI: 10.1016/j.neuroscience.2005.07.013] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2005] [Revised: 06/06/2005] [Accepted: 07/01/2005] [Indexed: 12/12/2022]
Abstract
Although multiple effects of GABA(B) receptor activation on synaptic transmission in the striatum have been described, the precise locations of the receptors mediating these effects have not been determined. To address this issue, we carried out pre-embedding immunogold electron microscopy in the rat using antibodies against the GABA(B) receptor subunits, GABA(B1) and GABA(B2). In addition, to investigate the relationship between GABA(B) receptors and glutamatergic striatal afferents, we used antibodies against the vesicular glutamate transporters, vesicular glutamate transporter 1 and vesicular glutamate transporter 2, as markers for glutamatergic terminals. Immunolabeling for GABA(B1) and GABA(B2) was widely and similarly distributed in the striatum, with immunogold particles localized at both presynaptic and postsynaptic sites. The most commonly labeled structures were dendritic shafts and spines, as well as terminals forming asymmetric and symmetric synapses. In postsynaptic structures, the majority of labeling associated with the plasma membrane was localized at extrasynaptic sites, although immunogold particles were also found at the postsynaptic specialization of some symmetric, putative GABAergic synapses. Labeling in axon terminals was located within, or at the edge of, the presynaptic active zone, as well as at extrasynaptic sites. Double labeling for GABA(B) receptor subunits and vesicular glutamate transporters revealed that labeling for both GABA(B1) and GABA(B2) was localized on glutamatergic axon terminals that expressed either vesicular glutamate transporter 1 or vesicular glutamate transporter 2. The patterns of innervation of striatal neurons by the vesicular glutamate transporter 1- and vesicular glutamate transporter 2-positive terminals suggest that they are selective markers of corticostriatal and thalamostriatal afferents, respectively. These results thus provide evidence that presynaptic GABA(B) heteroreceptors are in a position to modulate the two major excitatory inputs to striatal spiny projection neurons arising in the cortex and thalamus. In addition, presynaptic GABA(B) autoreceptors are present on the terminals of spiny projection neurons and/or striatal GABAergic interneurons. Furthermore, the data indicate that GABA may also affect the excitability of striatal neurons via postsynaptic GABA(B) receptors.
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Affiliation(s)
- C J Lacey
- Medical Research Council Anatomical Neuropharmacology Unit, Department of Pharmacology, University of Oxford, Oxford OX1 3TH, UK
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34
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Prinster SC, Hague C, Hall RA. Heterodimerization of G Protein-Coupled Receptors: Specificity and Functional Significance. Pharmacol Rev 2005; 57:289-98. [PMID: 16109836 DOI: 10.1124/pr.57.3.1] [Citation(s) in RCA: 302] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
G protein-coupled receptors (GPCRs) are cell surface receptors that mediate physiological responses to a diverse array of stimuli. GPCRs have traditionally been thought to act as monomers, but recent evidence suggests that GPCRs may form dimers (or higher-order oligomers) as part of their normal trafficking and function. In fact, certain GPCRs seem to have a strict requirement for heterodimerization to attain proper surface expression and functional activity. Even those GPCRs that do not absolutely require heterodimerization may still specifically associate with other GPCR subtypes, sometimes resulting in dramatic effects on receptor pharmacology, signaling, and/or internalization. Understanding the specificity and functional significance of GPCR heterodimerization is of tremendous clinical importance since GPCRs are the molecular targets for numerous therapeutic drugs.
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Affiliation(s)
- Steven C Prinster
- Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322, USA
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35
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Krogsgaard-Larsen P, Frølund B, Liljefors T, Ebert B. GABA(A) agonists and partial agonists: THIP (Gaboxadol) as a non-opioid analgesic and a novel type of hypnotic. Biochem Pharmacol 2005; 68:1573-80. [PMID: 15451401 DOI: 10.1016/j.bcp.2004.06.040] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2004] [Accepted: 06/30/2004] [Indexed: 01/07/2023]
Abstract
The GABA(A) receptor system is implicated in a number of central nervous system (CNS) disorders, making GABA(A) receptor ligands interesting as potential therapeutic agents. Only a few different classes of structures are currently known as ligands for the GABA recognition site on the hetero-pentameric GABA(A) receptor complex, reflecting the very strict structural requirements for GABA(A) receptor recognition and activation. A large number of the compounds showing agonist activity at the GABA(A) receptor site are structurally derived from the GABA(A) agonists muscimol, THIP (Gaboxadol), or isoguvacine, which we developed at the initial stage of the project. Using recombinant GABA(A) receptors, functional selectivity has been shown for a number of compounds, including THIP, showing subunit-dependent potency and maximal response. The pharmacological and clinical activities of THIP probably reflect its potent effects at extrasynaptic GABA(A) receptors insensitive to benzodiazepines and containing alpha(4)beta(3)delta subunits. The results of ongoing clinical studies on the effect of the partial GABA(A) agonist THIP on human sleep pattern show that the functional consequences of a directly acting agonist are distinctly different from those seen after administration of GABA(A) receptor modulators, such as benzodiazepines. In the light of the interest in partial GABA(A) receptor agonists as potential therapeutics, structure-activity studies of a number of analogues of 4-PIOL, a low-efficacy partial GABA(A) agonist derived from THIP, have been performed. In this connection, a series of GABA(A) ligands has been developed showing pharmacological profiles ranging from low-efficacy partial GABA(A) agonist activity to selective antagonist effect.
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Affiliation(s)
- Povl Krogsgaard-Larsen
- Department of Medicinal Chemistry, The Danish University of Pharmaceutical Sciences, 2 Universitetsparken, DK-2100 Copenhagen, Denmark.
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36
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Steiger JL, Bandyopadhyay S, Farb DH, Russek SJ. cAMP response element-binding protein, activating transcription factor-4, and upstream stimulatory factor differentially control hippocampal GABABR1a and GABABR1b subunit gene expression through alternative promoters. J Neurosci 2005; 24:6115-26. [PMID: 15240803 PMCID: PMC6729677 DOI: 10.1523/jneurosci.1200-04.2004] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Expression of metabotropic GABA(B) receptors is essential for slow inhibitory synaptic transmission in the CNS, and disruption of GABA(B) receptor-mediated responses has been associated with several disorders, including neuropathic pain and epilepsy. The location of GABA(B) receptors in neurons determines their specific role in synaptic transmission, and it is believed that sorting of subunit isoforms, GABA(B)R1a and GABA(B)R1b, to presynaptic or postsynaptic membranes helps to determine this role. GABA(B)R1a and GABA(B)R1b are thought to arise by alternative splicing of heteronuclear RNA. We now demonstrate that alternative promoters, rather than alternative splicing, produce GABA(B)R1a and GABA(B)R1b isoforms. Our data further show that subunit gene expression in hippocampal neurons is mediated by the cAMP response element-binding protein (CREB) by binding to unique cAMP response elements in the alternative promoter regions. Double-stranded oligonucleotide decoys selectively alter levels of endogenous GABA(B)R1a and GABA(B)R1b in primary hippocampal neurons, and CREB knock-out mice show changes in levels of GABA(B)R1a and GABA(B)R1b transcripts, consistent with decoy competition experiments. These results demonstrate a critical role of CREB in transcriptional mechanisms that control GABA(B)R1 subunit levels in vivo. In addition, the CREB-related factor activating transcription factor-4 (ATF4) has been shown to interact directly with GABA(B)R1 in neurons, and we show that ATF4 differentially regulates GABA(B)R1a and GABA(B)R1b promoter activity. These results, together with our finding that the depolarization-sensitive upstream stimulatory factor (USF) binds to a composite CREB/ATF4/USF regulatory element only in the absence of CREB binding, indicate that selective control of alternative GABA(B)R1 promoters by CREB, ATF4, and USF may dynamically regulate expression of their gene products in the nervous system.
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Affiliation(s)
- Janine L Steiger
- Laboratory of Molecular Neurobiology, Department of Pharmacology, Boston University School of Medicine, Boston, Massachusetts 02118, USA
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37
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McDonald AJ, Mascagni F, Muller JF. Immunocytochemical localization of GABABR1 receptor subunits in the basolateral amygdala. Brain Res 2004; 1018:147-58. [PMID: 15276873 DOI: 10.1016/j.brainres.2004.05.053] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/13/2004] [Indexed: 10/26/2022]
Abstract
Gamma-aminobutyric acid B (GABAB) receptors (GBRs) are G-protein-coupled receptors that mediate a slow, prolonged form of inhibition in the basolateral amygdala (ABL) and other brain areas. Recent studies indicate that this receptor is a heterodimer consisting of GABABR1 (GBR1) and GABABR2 subunits. In the present investigation, antibodies to the GABABR1 subunit were used to study the neuronal localization of GBRs in the rat ABL. GBR immunoreactivity was mainly found in spine-sparse interneurons and astrocytes at the light microscopic level. Very few pyramidal neurons exhibited perikaryal staining. Dual-labeling immunofluorescence analysis indicated that each of the four main subpopulations of interneurons exhibited GBR immunoreactivity. Virtually 100% of large CCK+ neurons in the basolateral and lateral nuclei were GBR+. In the basolateral nucleus 72% of somatostatin (SOM), 73% of parvalbumin (PV) and 25% of VIP positive interneurons were GBR+. In the lateral nucleus 50% of somatostatin, 30% of parvalbumin and 27% of VIP positive interneurons were GBR+. Electron microscopic (EM) analysis revealed that most of the light neuropil staining seen at the light microscopic level was due to the staining of dendritic shafts and spines, most of which probably belonged to spiny pyramidal cells. Very few axon terminals (Ats) were GBR+. In summary, this investigation demonstrates that the distal dendrites of pyramidal cells, and varying percentages of each of the four main subpopulations of interneurons in the ABL, express GBRs. Because previous studies suggest that GBR-mediated inhibition modulates NMDA-dependent EPSPs in the ABL, these receptors may play an important role in neuronal plasticity related to emotional learning.
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Affiliation(s)
- Alexander J McDonald
- Department of Pharmacology, Physiology, and Neuroscience, University of South Carolina School of Medicine, Columbia, SC 29208, USA.
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38
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Thuault SJ, Brown JT, Sheardown SA, Jourdain S, Fairfax B, Spencer JP, Restituito S, Nation JHL, Topps S, Medhurst AD, Randall AD, Couve A, Moss SJ, Collingridge GL, Pangalos MN, Davies CH, Calver AR. The GABAB2 subunit is critical for the trafficking and function of native GABAB receptors. Biochem Pharmacol 2004; 68:1655-66. [PMID: 15451409 DOI: 10.1016/j.bcp.2004.07.032] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2004] [Accepted: 07/12/2004] [Indexed: 11/25/2022]
Abstract
Studies in heterologous systems have demonstrated that heterodimerisation of the two GABA(B) receptor subunits appears to be crucial for the trafficking and signalling of the receptor. Gene targeting of the GABA(B1) gene has demonstrated that the expression of GABA(B1) is essential for GABA(B) receptor function in the central nervous system (CNS). However, the contribution of the GABA(B2) subunit in the formation of native GABA(B) receptors is still unclear, in particular whether other proteins can substitute for this subunit. We have created a transgenic mouse in which the endogenous GABA(B2) gene has been mutated in order to express a C-terminally truncated version of the protein. As a result, the GABA(B1) subunit does not reach the cell surface and concomitantly both pre- and post-synaptic GABA(B) receptor functions are abolished. Taken together with previous gene deletion studies for the GABA(B1) subunit, this suggests that classical GABA(B) function in the brain is exclusively mediated by GABA(B1/2) heteromers.
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Affiliation(s)
- Seb J Thuault
- Neurology and GI CEDD, GlaxoSmithKline, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK
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39
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Charara A, Galvan A, Kuwajima M, Hall RA, Smith Y. An electron microscope immunocytochemical study of GABA(B) R2 receptors in the monkey basal ganglia: a comparative analysis with GABA(B) R1 receptor distribution. J Comp Neurol 2004; 476:65-79. [PMID: 15236467 DOI: 10.1002/cne.20210] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Functional gamma-aminobutyric acid (GABA)(B) receptors are heterodimers made up of GABA(B) R1 and GABA(B) R2 subunits. The subcellular localization of GABA(B) R2 receptors remains poorly known in the central nervous system. Therefore, we performed an ultrastructural analysis of the localization of GABA(B) R2 receptor immunoreactivity in the monkey basal ganglia. Furthermore, to characterize better the neuronal sites at which GABA(B) R1 and GABA(B) R2 may interact to form functional receptors, we compared the relative distribution of immunoreactivity of the two GABA(B) receptors in various basal ganglia nuclei. Light to moderate GABA(B) R2 immunoreactivity was found in cell bodies and neuropil elements in all basal ganglia nuclei. At the electron microscope level, GABA(B) R2 immunoreactivity was commonly expressed postsynaptically, although immunoreactive preterminal axonal segments were also frequently encountered, particularly in the globus pallidus and substantia nigra, where they accounted for the third of the total number of GABA(B) R2-containing elements. A few labeled terminals that displayed the ultrastructural features of glutamatergic boutons were occasionally found in most basal ganglia nuclei, except for the subthalamic nucleus, which was devoid of GABA(B) R2-immunoreactive boutons. The relative distribution of GABA(B) R2 immunoreactivity in the monkey basal ganglia was largely consistent with that of GABA(B) R1, but some exceptions were found, most noticeably in the globus pallidus and substantia nigra, which contained a significantly larger proportion of presynaptic elements labeled for GABA(B) R1 than GABA(B) R2. These findings suggest the possible coexistence and heterodimerization of GABA(B) R1 and GABA(B) R2 at various pre- and postsynaptic sites, but also raise the possibility that the formation of functional GABA(B) receptors in specific compartments of basal ganglia neurons relies on mechanisms other than GABA(B) R1/R2 heterodimerization.
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Affiliation(s)
- Ali Charara
- Yerkes National Primate Research Center, Emory University, Atlanta, Georgia 30322, USA
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Bettler B, Kaupmann K, Mosbacher J, Gassmann M. Molecular structure and physiological functions of GABA(B) receptors. Physiol Rev 2004; 84:835-67. [PMID: 15269338 DOI: 10.1152/physrev.00036.2003] [Citation(s) in RCA: 636] [Impact Index Per Article: 31.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
GABA(B) receptors are broadly expressed in the nervous system and have been implicated in a wide variety of neurological and psychiatric disorders. The cloning of the first GABA(B) receptor cDNAs in 1997 revived interest in these receptors and their potential as therapeutic targets. With the availability of molecular tools, rapid progress was made in our understanding of the GABA(B) system. This led to the surprising discovery that GABA(B) receptors need to assemble from distinct subunits to function and provided exciting new insights into the structure of G protein-coupled receptors (GPCRs) in general. As a consequence of this discovery, it is now widely accepted that GPCRs can exist as heterodimers. The cloning of GABA(B) receptors allowed some important questions in the field to be answered. It is now clear that molecular studies do not support the existence of pharmacologically distinct GABA(B) receptors, as predicted by work on native receptors. Advances were also made in clarifying the relationship between GABA(B) receptors and the receptors for gamma-hydroxybutyrate, an emerging drug of abuse. There are now the first indications linking GABA(B) receptor polymorphisms to epilepsy. Significantly, the cloning of GABA(B) receptors enabled identification of the first allosteric GABA(B) receptor compounds, which is expected to broaden the spectrum of therapeutic applications. Here we review current concepts on the molecular composition and function of GABA(B) receptors and discuss ongoing drug-discovery efforts.
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Affiliation(s)
- Bernhard Bettler
- Pharmazentrum, Dept. of Clinical-Biological Sciences, Institute of Physiology, Univ. of Basel, Klingelbergstr. 50, CH-4056 Basel, Switzerland.
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41
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Meyer MH, Etienne W, Meyer RA. Altered mRNA expression of genes related to nerve cell activity in the fracture callus of older rats: A randomized, controlled, microarray study. BMC Musculoskelet Disord 2004; 5:24. [PMID: 15291962 PMCID: PMC512295 DOI: 10.1186/1471-2474-5-24] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/25/2004] [Accepted: 08/03/2004] [Indexed: 01/10/2023] Open
Abstract
Background The time required for radiographic union following femoral fracture increases with age in both humans and rats for unknown reasons. Since abnormalities in fracture innervation will slow skeletal healing, we explored whether abnormal mRNA expression of genes related to nerve cell activity in the older rats was associated with the slowing of skeletal repair. Methods Simple, transverse, mid-shaft, femoral fractures with intramedullary rod fixation were induced in anaesthetized female Sprague-Dawley rats at 6, 26, and 52 weeks of age. At 0, 0.4, 1, 2, 4, and 6 weeks after fracture, a bony segment, one-third the length of the femur, centered on the fracture site, including the external callus, cortical bone, and marrow elements, was harvested. cRNA was prepared and hybridized to 54 Affymetrix U34A microarrays (3/age/time point). Results The mRNA levels of 62 genes related to neural function were affected by fracture. Of the total, 38 genes were altered by fracture to a similar extent at the three ages. In contrast, eight neural genes showed prolonged down-regulation in the older rats compared to the more rapid return to pre-fracture levels in younger rats. Seven genes were up-regulated by fracture more in the younger rats than in the older rats, while nine genes were up-regulated more in the older rats than in the younger. Conclusions mRNA of 24 nerve-related genes responded differently to fracture in older rats compared to young rats. This differential expression may reflect altered cell function at the fracture site that may be causally related to the slowing of fracture healing with age or may be an effect of the delayed healing.
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Affiliation(s)
- Martha H Meyer
- Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Carolinas Medical Center, P.O. Box 32861, Charlotte, NC 28232-2861 USA
| | - Wiguins Etienne
- Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Carolinas Medical Center, P.O. Box 32861, Charlotte, NC 28232-2861 USA
| | - Ralph A Meyer
- Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Carolinas Medical Center, P.O. Box 32861, Charlotte, NC 28232-2861 USA
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Abstract
The GABA(A) receptor system is implicated in a number of neurological and psychiatric diseases, making GABA(A) receptor ligands interesting as potential therapeutic agents. Only a few different classes of structures are currently known as ligands for the GABA recognition site on the hetero-pentameric GABA(A) receptor complex, reflecting the very strict structural requirements for GABA(A) receptor recognition and activation. Within the series of compounds showing agonist activity at the GABA(A) receptor site that have been developed, most of the ligands are structurally derived from the GABA(A) agonists muscimol, THIP, or isoguvacine, which we developed in the initial stages of the project. Using recombinant GABA(A) receptors, functional selectivity was demonstrated for a number of compounds, including THIP, showing highly subunit-dependent potency and maximal response. In light of the interest in partial GABA(A) receptor agonists as potential therapeutics, structure-activity studies of a number of analogs of 4-PIOL, a low-efficacy partial GABA(A) agonist derived from THIP, have been performed. In this connection, a series of GABA(A) ligands has been developed that exhibit pharmacological profiles from moderately potent low-efficacy partial GABA(A) agonist activity to potent and selective antagonist effects. Very little information is available on direct-acting GABA(A) receptor agonists in clinical studies. However, the results of clinical studies on the effect of the partial GABA(A) agonist THIP on human sleep patterns show that the functional consequences of a direct-acting agonist are different from those seen after the administration of GABA(A) receptor modulators, such as benzodiazepines and barbiturates.
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Affiliation(s)
- Povl Krogsgaard-Larsen
- Department of Medicinal Chemistry, The Royal Danish School of Pharmacy, 2 Universitetsparken, DK 2100 Copenhagen, Denmark.
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Binet V, Brajon C, Le Corre L, Acher F, Pin JP, Prézeau L. The heptahelical domain of GABA(B2) is activated directly by CGP7930, a positive allosteric modulator of the GABA(B) receptor. J Biol Chem 2004; 279:29085-91. [PMID: 15126507 PMCID: PMC2557059 DOI: 10.1074/jbc.m400930200] [Citation(s) in RCA: 170] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The gamma-aminobutyric acid, type B (GABA(B)) receptor is well recognized as being composed of two subunits, GABA(B1) and GABA(B2). Both subunits share structural homology with other class-III G-protein-coupled receptors. They are composed of two main domains: a heptahelical domain (HD) typical of all G-protein-coupled receptors and a large extracellular domain (ECD). Although GABA(B1) binds GABA, GABA(B2) is required for GABA(B1) to reach the cell surface. However, it is still not demonstrated whether the association of these two subunits is always required for function in the brain. Indeed, GABA(B2) plays a major role in the coupling of the heteromer to G-proteins, such that it is possible that GABA(B2) can transmit a signal in the absence of GABA(B1). Today only ligands interacting with GABA(B1) ECD have been identified. Thus, the compounds acting exclusively on the GABA(B2) subunit will be helpful in analyzing the specific role of this subunit in the brain. Here, we explored the mechanism of action of CGP7930, a compound described as a positive allosteric regulator of the GABA(B) receptor. We showed that it activates the wild type GABA(B) receptor but with a low efficacy. The GABA(B2) HD is necessary for this effect, although one cannot exclude that CGP7930 could also bind to GABA(B1). Of interest, CGP7930 could activate GABA(B2) expressed alone and is the first described agonist of GABA(B2). Finally, we show that CGP7930 retains its agonist activity on a GABA(B2) subunit deleted of its ECD. This demonstrates that the HD of GABA(B2) behaves similar to a rhodopsin-like receptor, because it can reach the cell surface alone, can couple to G-protein, and be activated by agonists. These data open new strategies for studying the mechanism of activation of GABA(B) receptor and examine any possible role of homomeric GABA(B2) receptors.
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Affiliation(s)
- Virginie Binet
- LGF, Laboratoire de génomique fonctionnelle
CNRS : UPR2580141, Rue de la Cardonille
34094 MONTPELLIER CEDEX 5,FR
| | - Carole Brajon
- LGF, Laboratoire de génomique fonctionnelle
CNRS : UPR2580141, Rue de la Cardonille
34094 MONTPELLIER CEDEX 5,FR
| | - Laurent Le Corre
- CBPT, Chimie et biochimie pharmacologiques et toxicologiques
CNRS : UMR8601CNRS : IFR95Université Paris Descartes - Paris V45 Rue des Saints-Pères
75270 PARIS CEDEX 06,FR
| | - Francine Acher
- CBPT, Chimie et biochimie pharmacologiques et toxicologiques
CNRS : UMR8601CNRS : IFR95Université Paris Descartes - Paris V45 Rue des Saints-Pères
75270 PARIS CEDEX 06,FR
| | - Jean-Philippe Pin
- LGF, Laboratoire de génomique fonctionnelle
CNRS : UPR2580141, Rue de la Cardonille
34094 MONTPELLIER CEDEX 5,FR
| | - Laurent Prézeau
- LGF, Laboratoire de génomique fonctionnelle
CNRS : UPR2580141, Rue de la Cardonille
34094 MONTPELLIER CEDEX 5,FR
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44
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Abstract
G protein-coupled receptors (GPCRs) modulate diverse physiological and behavioral signaling pathways by virtue of changes in receptor activation and inactivation states. Functional changes in receptor properties include dynamic interactions with regulatory molecules and trafficking to various cellular compartments at various stages of the life cycle of a GPCR. This review focuses on trafficking of GPCRs to the cell surface, stabilization there, and agonist-regulated turnover. GPCR interactions with a variety of newly revealed partners also are reviewed with the intention of provoking further analysis of the relevance of these interactions in GPCR trafficking, signaling, or both. The disease consequences of mislocalization of GPCRs also are described.
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Affiliation(s)
- Christopher M Tan
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA
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45
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Boyes J, Bolam JP. The subcellular localization of GABA(B) receptor subunits in the rat substantia nigra. Eur J Neurosci 2004; 18:3279-93. [PMID: 14686901 DOI: 10.1111/j.1460-9568.2003.03076.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The inhibitory effects of GABA within the substantia nigra (SN) are mediated in part by metabotropic GABA(B) receptors. To better understand the mechanisms underlying these effects, we have examined the subcellular localization of the GABA(B) receptor subunits, GABA(B1) and GABA(B2), in SN neurons and afferents using pre-embedding immunocytochemistry combined with anterograde or retrograde labelling. In both the SN pars compacta (SNc) and pars reticulata (SNr), GABA(B1) and GABA(B2) showed overlapping, but distinct, patterns of immunolabelling. GABA(B1) was more strongly expressed by putative dopaminergic neurons in the SNc than by SNr projection neurons, whereas GABA(B2) was mainly expressed in the neuropil of both regions. Immunogold labelling for GABA(B1) and GABA(B2) was localized in presynaptic and postsynaptic elements throughout the SN. The majority of labelling was intracellular or was associated with extrasynaptic sites on the plasma membrane. In addition, labelling for both subunits was found on the presynaptic and postsynaptic membranes at symmetric, putative GABAergic synapses, including those formed by anterogradely labelled striatonigral and pallidonigral terminals. Labelling was also observed on the presynaptic membrane and at the edge of the postsynaptic density at asymmetric, putative excitatory synapses. Double immunolabelling, using the vesicular glutamate transporter 2, revealed the glutamatergic nature of many of the immunogold-labelled asymmetric synapses. The widespread distribution of GABA(B) subunits in the SNc and SNr suggests that GABA(B)-mediated effects in these regions are likely to be more complex than previously described, involving presynaptic autoreceptors and heteroreceptors, and postsynaptic receptors on different populations of SN neurons.
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Affiliation(s)
- Justin Boyes
- MRC Anatomical Neuropharmacology Unit, University of Oxford, Oxford OX1 3TH, UK
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46
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Martin SC, Steiger JL, Gravielle MC, Lyons HR, Russek SJ, Farb DH. Differential expression of ?-aminobutyric acid type B receptor subunit mRNAs in the developing nervous system and receptor coupling to adenylyl cyclase in embryonic neurons. J Comp Neurol 2004; 473:16-29. [PMID: 15067715 DOI: 10.1002/cne.20094] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
gamma-Aminobutyric acid type B receptors (GABA(B)Rs) mediate both slow inhibitory synaptic activity in the adult nervous system and motility signals for migrating embryonic cortical cells. Previous papers have described the expression of GABA(B)Rs in the adult brain, but the expression and functional significance of these gene products in the embryo are largely unknown. Here we examine GABA(B)R expression from rat embryonic day 10 (E10) to E18 compared with adult and ask whether embryonic cortical neurons contain functional GABA(B)R. GABA(B)R1 transcript levels greatly exceed GABA(B)R2 levels in the developing neural tube at E11, and olfactory bulb and striatum at E17 but equalize in most regions of adult nervous tissue, except for the glomerular and granule cell layers of the main olfactory bulb and the striatum. Consistent with expression differences, the binding affinity of GABA for GABA(B)Rs is significantly lower in adult striatum compared with cerebellum. Multiple lines of evidence from in situ hybridization, RNase protection, and real-time PCR demonstrate that GABA(B)R1a, GABA(B)R1b, GABA(B)R1h (a subunit subtype, lacking a sushi domain, that we have identified in embryonic rat brain), GABA(B)R2, and GABA(B)L transcript levels are not coordinately regulated. Despite the functional requirement for a heterodimer of GABA(B)R subunits, the expression of each subunit mRNA is under independent control during embryonic development, and, by E18, GABA(B)Rs are negatively coupled to adenylyl cyclase in neocortical neurons. The presence of embryonic GABA(B)R transcripts and protein and functional receptor coupling indicates potentially important roles for GABA(B)Rs in modulation of synaptic transmission in the developing embryonic nervous system.
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Affiliation(s)
- Stella C Martin
- Laboratory of Molecular Neurobiology, Department of Pharmacology, Boston University School of Medicine, Boston, Massachusetts 02118-2394, USA
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47
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Burman KJ, Ige AO, White JH, Marshall FH, Pangalos MN, Emson PC, Minson JB, Llewellyn-Smith IJ. GABAB receptor subunits, R1 and R2, in brainstem catecholamine and serotonin neurons. Brain Res 2003; 970:35-46. [PMID: 12706246 DOI: 10.1016/s0006-8993(02)04269-5] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
GABA(B) receptors have been implicated in the GABAergic modulation of catecholaminergic and serotonergic pathways in the central nervous system. The GABA(B) receptor may require two subunits, GABA(B)R1 and GABA(B)R2, for functional activity. Using dual immunofluorescent labelling on adjacent cryostat sections, we investigated the presence of immunoreactivity for the GABA(B)R1 and GABA(B)R2 subunits in brainstem catecholamine (tyrosine hydroxylase-immunoreactive) and serotonin (tryptophan hydroxylase-immunoreactive) neurons. All neurons (>98%) examined in catecholamine groups A1, A2, A5, A6, C1, and serotonin groups B1-3 and B6-8 were immunoreactive for the GABA(B)R1 subunit. All A5 and A6 neurons (>97%) and at least 86% of A1, A2, C1, B2, B3, B7 and B8 neurons examined were GABA(B)R2-immunoreactive. The proportion of neurons with immunoreactivity for the GABA(B)R2 subunit varied between 0% and 99% for B1 neurons, and between 35% and 93% for B6 neurons. Statistical analysis showed that similar proportions of sampled neurons were immunoreactive for GABA(B)R1 and GABA(B)R2 in the A1, A5, A6, C1, B2 and B7 cell groups, whereas a smaller proportion of A2, B1, B3, B6 and B8 neurons were GABA(B)R2-immunoreactive than GABA(B)R1-immunoreactive. In general, our results suggest that GABA(B)R1 and GABA(B)R2 co-exist in the great majority of brainstem catecholamine and serotonin neurons. In the neurons that lack GABA(B)R2, the GABA(B)R1 subunit may act alone or with another protein.
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Affiliation(s)
- Kathleen J Burman
- Cardiovascular Neuroscience Group, Cardiovascular Medicine & Centre for Neuroscience, Flinders University of South Australia, Bedford Park, SA 5042, Australia.
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48
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Hirst WD, Babbs AJ, Green A, Minton JAL, Shaw TE, Wise A, Rice SQ, Pangalos MN, Price GW. Pharmacological characterisation of a cell line expressing GABA B1b and GABA B2 receptor subunits. Biochem Pharmacol 2003; 65:1103-13. [PMID: 12663046 DOI: 10.1016/s0006-2952(02)01658-1] [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: 11/26/2022]
Abstract
The gamma-aminobutyric acid (GABA(B)) receptor has been shown to be a heterodimer consisting of two receptor subunits, GABA(B1) and GABA(B2). We have stably co-expressed these two subunits in a CHO cell line, characterised its pharmacology and compared it to the native receptor in rat brain membranes. Radioligand binding using [3H]CGP54626A demonstrated a similar rank order of potency between recombinant and native receptors: CGP62349>CGP54626A>SCH 50911>3-aminopropylphosphinicacid(3-APPA)>GABA>baclofen>saclofen>phaclofen. However, differences were observed in the affinity of agonists, which were higher at the native receptor, suggesting that in the recombinant system a large number of the receptors were in the low agonist affinity state. In contrast, [35S]GTPgammaS binding studies did not show any differences between recombinant and native receptors with the full agonists GABA and 3-APPA. Measurement of cAMP accumulation in the cells revealed a degree of endogenous coupling of the receptors to G-proteins. This is most likely to be due to the high expression levels of receptors (B(max)=22.5+/-2.5pmol/mg protein) in this experimental system. There was no evidence of GABA(B2) receptors, when expressed alone, binding [3H]CGP54626A, [3H]GABA, [3H]3-APPA nor of GABA having any effect on basal [35S]GTPgammaS binding or cAMP levels.
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Affiliation(s)
- Warren D Hirst
- Neurology and GI Centre of Excellence for Drug Discovery, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK.
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49
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Bäckberg M, Collin M, Ovesjö ML, Meister B. Chemical coding of GABA(B) receptor-immunoreactive neurones in hypothalamic regions regulating body weight. J Neuroendocrinol 2003; 15:1-14. [PMID: 12535164 DOI: 10.1046/j.1365-2826.2003.00843.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Gamma-aminobutyric acid (GABA) interacts with hypothalamic neuronal pathways regulating feeding behaviour. GABA has been reported to stimulate feeding via both ionotropic GABA(A) and metabotropic GABA(B) receptors. The functional form of the GABA(B) receptor is a heterodimer consisting of GABA(B) receptor-1 (GABA(B)R1) and GABA(B) receptor-2 (GABA(B)R2) proteins. Within the heterodimer, the GABA-binding site is localized to GABA(B)R1. In the present study, we used an antiserum to the GABA(B)R1 protein in order to investigate the cellular localization of GABA(B)R1-immunoreactive neurones in discrete hypothalamic regions implicated in the control of body weight. The colocalization of GABA(B)R1 immunoreactivity with different chemical messengers that regulate food intake was analysed. GABA(B)R1-immunoreactive cell bodies were found in the periventricular, paraventricular (PVN), supraoptic, arcuate, ventromedial hypothalamic, dorsomedial hypothalamic, tuberomammillary nuclei and lateral hypothalamic area (LHA). Direct double-labelling showed that glutamic acid decarboxylase (GAD)-positive terminals were in close contact with GABA(B)R1-containing cell bodies located in all these regions. In the ventromedial part of the arcuate nucleus, GABA(B)R1-immunoreactive cell bodies were found to contain neuropeptide Y, agouti-related peptide (AGRP) and GAD. In the ventrolateral part of the arcuate nucleus, GABA(B)R1-immunoreactive cell bodies were shown to contain pro-opiomelanocortin and cocaine- and amphetamine-regulated transcript. In the LHA, GABA(B)R1 immunoreactivity was present in both melanin-concentrating hormone- and orexin-containing cell populations. In the tuberomammillary nucleus, GABA(B)R1-immunoreactive cell bodies expressed histidine decarboxylase, a marker for histamine-containing neurones. In addition, GAD and AGRP were found to be colocalized in some nerve terminals surrounding GABA(B)R1-immunoreactive cell bodies in the parvocellular part of the PVN. The results may provide a morphological basis for the understanding of how GABA regulates the hypothalamic control of food intake and body weight via GABA(B) receptors.
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Affiliation(s)
- M Bäckberg
- Department of Neuroscience, The Retzius Laboratory, Karolinska Institutet, Stockholm, Sweden
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50
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Simeone TA, Donevan SD, Rho JM. Molecular biology and ontogeny of gamma-aminobutyric acid (GABA) receptors in the mammalian central nervous system. J Child Neurol 2003; 18:39-48; discussion 49. [PMID: 12661937 DOI: 10.1177/08830738030180012101] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
gamma-Aminobutyric acid (GABA) is the predominant inhibitory neurotransmitter in the mammalian central nervous system. After release from nerve terminals, GABA binds to at least two classes of postsynaptic receptors (ie, GABAA and GABAB), which are nearly ubiquitous in the brain. GABAA receptors are postsynaptic heteropentameric complexes that display unique physiologic and pharmacologic properties based on subunit composition. Activation of GABAA receptors in mature neurons results in membrane hyperpolarization, which is mediated principally by inward chloride flux, whereas in early stages of brain development, GABAA receptor activation causes depolarization of the postsynaptic membrane. GABA, receptors reside both presynaptically and postsynaptically, exist as heterodimers and are coupled to voltage-dependent ion channels through interactions with heterotrimeric G proteins. This review summarizes the molecular biology and ontogeny of GABAA and GABAB receptors, highlighting some of their putative roles during normal brain development as well as in disease states such as epilepsy.
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Affiliation(s)
- Timothy A Simeone
- Interdepartmental Program in Neuroscience, University of Utah, Salt Lake City, UT, USA
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