1
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Chen M, Koopmans F, Paliukhovich I, van der Spek SJF, Dong J, Smit AB, Li KW. Blue Native PAGE-Antibody Shift in Conjunction with Mass Spectrometry to Reveal Protein Subcomplexes: Detection of a Cerebellar α1/α6-Subunits Containing γ-Aminobutyric Acid Type A Receptor Subtype. Int J Mol Sci 2023; 24:ijms24087632. [PMID: 37108794 PMCID: PMC10143440 DOI: 10.3390/ijms24087632] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Revised: 04/07/2023] [Accepted: 04/17/2023] [Indexed: 04/29/2023] Open
Abstract
The pentameric γ-Aminobutyric acid type A receptors (GABAARs) are ligand-gated ion channels that mediate the majority of inhibitory neurotransmission in the brain. In the cerebellum, the two main receptor subtypes are the 2α1/2β/γ and 2α6/2β/δ subunits. In the present study, an interaction proteomics workflow was used to reveal additional subtypes that contain both α1 and α6 subunits. Immunoprecipitation of the α6 subunit from mouse brain cerebellar extract co-purified the α1 subunit. In line with this, pre-incubation of the cerebellar extract with anti-α6 antibodies and analysis by blue native gel electrophoresis mass-shifted part of the α1 complexes, indicative of the existence of an α1α6-containing receptor. Subsequent mass spectrometry of the blue native gel showed the α1α6-containing receptor subtype to exist in two main forms, i.e., with or without Neuroligin-2. Immunocytochemistry on a cerebellar granule cell culture revealed co-localization of α6 and α1 in post-synaptic puncta that apposed the presynaptic marker protein Vesicular GABA transporter, indicative of the presence of this synaptic GABAAR subtype.
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Affiliation(s)
- Miao Chen
- Department of Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Amsterdam Neuroscience, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
| | - Frank Koopmans
- Department of Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Amsterdam Neuroscience, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
| | - Iryna Paliukhovich
- Department of Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Amsterdam Neuroscience, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
| | - Sophie J F van der Spek
- Department of Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Amsterdam Neuroscience, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
| | - Jian Dong
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Amsterdam Neuroscience, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
| | - August B Smit
- Department of Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Amsterdam Neuroscience, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
| | - Ka Wan Li
- Department of Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Amsterdam Neuroscience, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
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2
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Guzikowski NJ, Kavalali ET. Nano-organization of spontaneous GABAergic transmission directs its autonomous function in neuronal signaling. Cell Rep 2022; 40:111172. [PMID: 35947950 PMCID: PMC9392417 DOI: 10.1016/j.celrep.2022.111172] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2021] [Revised: 04/12/2022] [Accepted: 07/15/2022] [Indexed: 01/04/2023] Open
Abstract
Earlier studies delineated the precise arrangement of proteins that drive neurotransmitter release and postsynaptic signaling at excitatory synapses. However, spatial organization of neurotransmission at inhibitory synapses remains unclear. Here, we took advantage of the molecularly specific interaction of antimalarial artemisinins and the inhibitory synapse scaffold protein, gephyrin, to probe the functional organization of gamma-aminobutyric acid A receptor (GABAAR)-mediated neurotransmission in central synapses. Short-term application of artemisinins severely contracts the size and density of gephyrin and GABAaR γ2 subunit clusters. This size contraction elicits a neuronal activity-independent increase in Bdnf expression due to a specific reduction in GABAergic spontaneous, but not evoked, neurotransmission. The same functional effect could be mimicked by disruption of microtubules that link gephyrin to the neuronal cytoskeleton. These results suggest that the GABAergic postsynaptic apparatus possesses a concentric center-surround organization, where the periphery of gephyrin clusters selectively maintains spontaneous GABAergic neurotransmission facilitating its autonomous function regulating Bdnf expression.
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Affiliation(s)
- Natalie J. Guzikowski
- Department of Pharmacology, Vanderbilt University, Nashville, TN 37240-7933, USA,Vanderbilt Brain Institute, Vanderbilt University, Nashville, TN 37240-7933, USA
| | - Ege T. Kavalali
- Department of Pharmacology, Vanderbilt University, Nashville, TN 37240-7933, USA,Vanderbilt Brain Institute, Vanderbilt University, Nashville, TN 37240-7933, USA,Lead contact,Correspondence:
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3
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Tipton AE, Russek SJ. Regulation of Inhibitory Signaling at the Receptor and Cellular Level; Advances in Our Understanding of GABAergic Neurotransmission and the Mechanisms by Which It Is Disrupted in Epilepsy. Front Synaptic Neurosci 2022; 14:914374. [PMID: 35874848 PMCID: PMC9302637 DOI: 10.3389/fnsyn.2022.914374] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2022] [Accepted: 05/17/2022] [Indexed: 11/13/2022] Open
Abstract
Inhibitory signaling in the brain organizes the neural circuits that orchestrate how living creatures interact with the world around them and how they build representations of objects and ideas. Without tight control at multiple points of cellular engagement, the brain’s inhibitory systems would run down and the ability to extract meaningful information from excitatory events would be lost leaving behind a system vulnerable to seizures and to cognitive decline. In this review, we will cover many of the salient features that have emerged regarding the dynamic regulation of inhibitory signaling seen through the lens of cell biology with an emphasis on the major building blocks, the ligand-gated ion channel receptors that are the first transduction point when the neurotransmitter GABA is released into the synapse. Epilepsy association will be used to indicate importance of key proteins and their pathways to brain function and to introduce novel areas for therapeutic intervention.
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Affiliation(s)
- Allison E. Tipton
- Graduate Program for Neuroscience, Boston University, Boston, MA, United States
- Biomolecular Pharmacology Program, Boston University School of Medicine, Boston, MA, United States
- Boston University MD/PhD Training Program, Boston, MA, United States
| | - Shelley J. Russek
- Biomolecular Pharmacology Program, Boston University School of Medicine, Boston, MA, United States
- Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine, Boston, MA, United States
- Center for Systems Neuroscience, Boston University, Boston, MA, United States
- Boston University MD/PhD Training Program, Boston, MA, United States
- *Correspondence: Shelley J. Russek,
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4
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Bai G, Zhang M. Inhibitory postsynaptic density from the lens of phase separation. OXFORD OPEN NEUROSCIENCE 2022; 1:kvac003. [PMID: 38596704 PMCID: PMC10913824 DOI: 10.1093/oons/kvac003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/18/2022] [Revised: 02/22/2022] [Accepted: 02/22/2022] [Indexed: 04/11/2024]
Abstract
To faithfully transmit and decode signals released from presynaptic termini, postsynaptic compartments of neuronal synapses deploy hundreds of various proteins. In addition to distinct sets of proteins, excitatory and inhibitory postsynaptic apparatuses display very different organization features and regulatory properties. Decades of extensive studies have generated a wealth of knowledge on the molecular composition, assembly architecture and activity-dependent regulatory mechanisms of excitatory postsynaptic compartments. In comparison, our understanding of the inhibitory postsynaptic apparatus trails behind. Recent studies have demonstrated that phase separation is a new paradigm underlying the formation and plasticity of both excitatory and inhibitory postsynaptic molecular assemblies. In this review, we discuss molecular composition, organizational and regulatory features of inhibitory postsynaptic densities through the lens of the phase separation concept and in comparison with the excitatory postsynaptic densities.
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Affiliation(s)
- Guanhua Bai
- School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China
| | - Mingjie Zhang
- School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China
- Greater Bay Biomedical Innocenter, Shenzhen Bay Laboratory, Shenzhen 518036, China
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5
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Garcia JD, Gookin SE, Crosby KC, Schwartz SL, Tiemeier E, Kennedy MJ, Dell'Acqua ML, Herson PS, Quillinan N, Smith KR. Stepwise disassembly of GABAergic synapses during pathogenic excitotoxicity. Cell Rep 2021; 37:110142. [PMID: 34936876 PMCID: PMC8824488 DOI: 10.1016/j.celrep.2021.110142] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Revised: 09/17/2021] [Accepted: 11/23/2021] [Indexed: 12/16/2022] Open
Abstract
GABAergic synaptic inhibition controls neuronal firing, excitability, and synaptic plasticity to regulate neuronal circuits. Following an acute excitotoxic insult, inhibitory synapses are eliminated, reducing synaptic inhibition, elevating circuit excitability, and contributing to the pathophysiology of brain injuries. However, mechanisms that drive inhibitory synapse disassembly and elimination are undefined. We find that inhibitory synapses are disassembled in a sequential manner following excitotoxicity: GABAARs undergo rapid nanoscale rearrangement and are dispersed from the synapse along with presynaptic active zone components, followed by the gradual removal of the gephyrin scaffold, prior to complete elimination of the presynaptic terminal. GABAAR nanoscale reorganization and synaptic declustering depends on calcineurin signaling, whereas disassembly of gephyrin relies on calpain activation, and blockade of both enzymes preserves inhibitory synapses after excitotoxic insult. Thus, inhibitory synapse disassembly occurs rapidly, with nanoscale precision, in a stepwise manner and most likely represents a critical step in the progression of hyperexcitability following excitotoxicity.
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Affiliation(s)
- Joshua D Garcia
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045, USA
| | - Sara E Gookin
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045, USA
| | - Kevin C Crosby
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045, USA
| | - Samantha L Schwartz
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045, USA
| | - Erika Tiemeier
- Department of Anesthesiology, Neuronal Injury Program, University of Colorado School of Medicine, Anschutz Medical Campus, 12801 East 17th Avenue, Aurora, CO 80045, USA
| | - Matthew J Kennedy
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045, USA
| | - Mark L Dell'Acqua
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045, USA
| | - Paco S Herson
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045, USA; Department of Anesthesiology, Neuronal Injury Program, University of Colorado School of Medicine, Anschutz Medical Campus, 12801 East 17th Avenue, Aurora, CO 80045, USA
| | - Nidia Quillinan
- Department of Anesthesiology, Neuronal Injury Program, University of Colorado School of Medicine, Anschutz Medical Campus, 12801 East 17th Avenue, Aurora, CO 80045, USA
| | - Katharine R Smith
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045, USA.
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6
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Kuljis DA, Micheva KD, Ray A, Wegner W, Bowman R, Madison DV, Willig KI, Barth AL. Gephyrin-Lacking PV Synapses on Neocortical Pyramidal Neurons. Int J Mol Sci 2021; 22:ijms221810032. [PMID: 34576197 PMCID: PMC8467468 DOI: 10.3390/ijms221810032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Revised: 09/01/2021] [Accepted: 09/07/2021] [Indexed: 11/26/2022] Open
Abstract
Gephyrin has long been thought of as a master regulator for inhibitory synapses, acting as a scaffold to organize γ-aminobutyric acid type A receptors (GABAARs) at the post-synaptic density. Accordingly, gephyrin immunostaining has been used as an indicator of inhibitory synapses; despite this, the pan-synaptic localization of gephyrin to specific classes of inhibitory synapses has not been demonstrated. Genetically encoded fibronectin intrabodies generated with mRNA display (FingRs) against gephyrin (Gephyrin.FingR) reliably label endogenous gephyrin, and can be tagged with fluorophores for comprehensive synaptic quantitation and monitoring. Here we investigated input- and target-specific localization of gephyrin at a defined class of inhibitory synapse, using Gephyrin.FingR proteins tagged with EGFP in brain tissue from transgenic mice. Parvalbumin-expressing (PV) neuron presynaptic boutons labeled using Cre- dependent synaptophysin-tdTomato were aligned with postsynaptic Gephyrin.FingR puncta. We discovered that more than one-third of PV boutons adjacent to neocortical pyramidal (Pyr) cell somas lack postsynaptic gephyrin labeling. This finding was confirmed using correlative fluorescence and electron microscopy. Our findings suggest some inhibitory synapses may lack gephyrin. Gephyrin-lacking synapses may play an important role in dynamically regulating cell activity under different physiological conditions.
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Affiliation(s)
- Dika A. Kuljis
- Center for the Neural Basis of Cognition, Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA; (D.A.K.); (A.R.); (R.B.)
| | - Kristina D. Micheva
- Department of Molecular and Cellular Physiology, Stanford University, Palo Alto, CA 94304, USA; (K.D.M.); (D.V.M.)
| | - Ajit Ray
- Center for the Neural Basis of Cognition, Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA; (D.A.K.); (A.R.); (R.B.)
| | - Waja Wegner
- Optical Nanoscopy in Neuroscience, Center for Nanoscale Microscopy and Molecular Physiology of the Brain, University Medical Center Göttingen, 37075 Göttingen, Germany; (W.W.); (K.I.W.)
- Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Ryan Bowman
- Center for the Neural Basis of Cognition, Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA; (D.A.K.); (A.R.); (R.B.)
| | - Daniel V. Madison
- Department of Molecular and Cellular Physiology, Stanford University, Palo Alto, CA 94304, USA; (K.D.M.); (D.V.M.)
| | - Katrin I. Willig
- Optical Nanoscopy in Neuroscience, Center for Nanoscale Microscopy and Molecular Physiology of the Brain, University Medical Center Göttingen, 37075 Göttingen, Germany; (W.W.); (K.I.W.)
- Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Alison L. Barth
- Center for the Neural Basis of Cognition, Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA; (D.A.K.); (A.R.); (R.B.)
- Correspondence: ; Tel.: +1-412-268-1198
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7
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Wagner S, Lee C, Rojas L, Specht CG, Rhee J, Brose N, Papadopoulos T. The α3 subunit of GABA A receptors promotes formation of inhibitory synapses in the absence of collybistin. J Biol Chem 2021; 296:100709. [PMID: 33901490 PMCID: PMC8141935 DOI: 10.1016/j.jbc.2021.100709] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Revised: 04/14/2021] [Accepted: 04/22/2021] [Indexed: 01/03/2023] Open
Abstract
Signaling at nerve cell synapses is a key determinant of proper brain function, and synaptic defects—or synaptopathies—are at the basis of many neurological and psychiatric disorders. Collybistin (CB), a brain-specific guanine nucleotide exchange factor, is essential for the formation of γ-aminobutyric acidergic (GABAergic) postsynapses in defined regions of the mammalian forebrain, including the hippocampus and basolateral amygdala. This process depends on a direct interaction of CB with the scaffolding protein gephyrin, which leads to the redistribution of gephyrin into submembranous clusters at nascent inhibitory synapses. Strikingly, synaptic clustering of gephyrin and GABAA type A receptors (GABAARs) in several brain regions, including the cerebral cortex and certain thalamic areas, is unperturbed in CB-deficient mice, indicating that the formation of a substantial subset of inhibitory postsynapses must be controlled by gephyrin-interacting proteins other than CB. Previous studies indicated that the α3 subunit of GABAARs (GABAAR-α3) binds directly and with high affinity to gephyrin. Here, we provide evidence (i) that a homooligomeric GABAAR-α3A343W mutant induces the formation of submembranous gephyrin clusters independently of CB in COS-7 cells, (ii) that gephyrin clustering is unaltered in the neuronal subpopulations endogenously expressing the GABAAR-α3 in CB-deficient brains, and (iii) that exogenous expression of GABAAR-α3 partially rescues impaired gephyrin clustering in CB-deficient hippocampal neurons. Our results identify an important role of GABAAR-α3 in promoting gephyrin-mediated and CB-independent formation of inhibitory postsynapses.
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Affiliation(s)
- Sven Wagner
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - ChoongKu Lee
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Lucia Rojas
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Christian G Specht
- Diseases and Hormones of the Nervous System (DHNS), Inserm U1195, Université Paris-Saclay, Le Kremlin-Bicêtre, France
| | - JeongSeop Rhee
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
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8
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George S, Chiou TT, Kanamalla K, De Blas AL. Recruitment of Plasma Membrane GABA-A Receptors by Submembranous Gephyrin/Collybistin Clusters. Cell Mol Neurobiol 2021; 42:1585-1604. [PMID: 33547626 DOI: 10.1007/s10571-021-01050-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Accepted: 01/23/2021] [Indexed: 11/29/2022]
Abstract
It has been shown that subunit composition is the main determinant of the synaptic or extrasynaptic localization of GABAA receptors (GABAARs). Synaptic and extrasynaptic GABAARs are involved in phasic and tonic inhibition, respectively. It has been proposed that synaptic GABAARs bind to the postsynaptic gephyrin/collybistin (Geph/CB) lattice, but not the typically extrasynaptic GABAARs. Nevertheless, there are no studies of the direct binding of various types of GABAARs with the submembranous Geph/CB lattice in the absence of other synaptic proteins, some of which are known to interact with GABAARs. We have reconstituted GABAARs of various subunit compositions, together with the Geph/CB scaffold, in HEK293 cells, and have investigated the recruitment of surface GABAARs by submembranous Geph/CB clusters. Results show that the typically synaptic α1β3γ2 GABAARs were trapped by submembranous Geph/CB clusters. The α5β3γ2 GABAARs, which are both synaptic and extrasynaptic, were also trapped by Geph/CB clusters. Extrasynaptic α4β3δ GABAARs consistently showed little or no trapping by the Geph/CB clusters. However, the extrasynaptic α6β3δ, α1β3, α6β3 (and less α4β3) GABAARs were highly trapped by the Geph/CB clusters. AMPA and NMDA glutamate receptors were not trapped. The results suggest: (I) in the absence of other synaptic molecules, the Geph/CB lattice has the capacity to trap not only synaptic but also several typically extrasynaptic GABAARs; (II) the Geph/CB lattice is important but does not play a decisive role in the synaptic localization of GABAARs; and (III) in neurons there must be mechanisms preventing the trapping of several typically extrasynaptic GABAARs by the postsynaptic Geph/CB lattice.
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Affiliation(s)
- Shanu George
- Department of Physiology and Neurobiology, University of Connecticut, 75 North Eagleville Road, U-3156, Storrs, CT, 06269-3156, USA
| | - Tzu-Ting Chiou
- Department of Physiology and Neurobiology, University of Connecticut, 75 North Eagleville Road, U-3156, Storrs, CT, 06269-3156, USA
| | - Karthik Kanamalla
- Department of Physiology and Neurobiology, University of Connecticut, 75 North Eagleville Road, U-3156, Storrs, CT, 06269-3156, USA
| | - Angel L De Blas
- Department of Physiology and Neurobiology, University of Connecticut, 75 North Eagleville Road, U-3156, Storrs, CT, 06269-3156, USA.
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9
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Shimell JJ, Shah BS, Cain SM, Thouta S, Kuhlmann N, Tatarnikov I, Jovellar DB, Brigidi GS, Kass J, Milnerwood AJ, Snutch TP, Bamji SX. The X-Linked Intellectual Disability Gene Zdhhc9 Is Essential for Dendrite Outgrowth and Inhibitory Synapse Formation. Cell Rep 2020; 29:2422-2437.e8. [PMID: 31747610 DOI: 10.1016/j.celrep.2019.10.065] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2018] [Revised: 09/09/2019] [Accepted: 10/13/2019] [Indexed: 11/29/2022] Open
Abstract
Palmitoylation is a reversible post-translational lipid modification that facilitates vesicular transport and subcellular localization of modified proteins. This process is catalyzed by ZDHHC enzymes that are implicated in several neurological and neurodevelopmental disorders. Loss-of-function mutations in ZDHHC9 have been identified in patients with X-linked intellectual disability (XLID) and associated with increased epilepsy risk. Loss of Zdhhc9 function in hippocampal cultures leads to shorter dendritic arbors and fewer inhibitory synapses, altering the ratio of excitatory-to-inhibitory inputs formed onto Zdhhc9-deficient cells. While Zdhhc9 promotes dendrite outgrowth through the palmitoylation of the GTPase Ras, it promotes inhibitory synapse formation through the palmitoylation of another GTPase, TC10. Zdhhc9 knockout mice exhibit seizure-like activity together with increased frequency and amplitude of both spontaneous and miniature excitatory and inhibitory postsynaptic currents. These findings present a plausible mechanism for how the loss of ZDHHC9 function may contribute to XLID and epilepsy.
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Affiliation(s)
- Jordan J Shimell
- Department of Cellular and Physiological Sciences, Djavad Mowafaghian Centre for Brain Health, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC V6T 1Z3, Canada
| | - Bhavin S Shah
- Department of Cellular and Physiological Sciences, Djavad Mowafaghian Centre for Brain Health, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC V6T 1Z3, Canada
| | - Stuart M Cain
- Michael Smith Laboratories, Djavad Mowafaghian Centre for Brain Health, University of British Columbia, 2215 Wesbrook Mall, Vancouver, BC V6T 1Z3, Canada
| | - Samrat Thouta
- Michael Smith Laboratories, Djavad Mowafaghian Centre for Brain Health, University of British Columbia, 2215 Wesbrook Mall, Vancouver, BC V6T 1Z3, Canada
| | - Naila Kuhlmann
- Montreal Neurological Institute, Department of Neurology and Neurosurgery, McGill University, 3801 University Street, Montreal, QC H3A 2B4, Canada
| | - Igor Tatarnikov
- Montreal Neurological Institute, Department of Neurology and Neurosurgery, McGill University, 3801 University Street, Montreal, QC H3A 2B4, Canada
| | - D Blair Jovellar
- Department of Cellular and Physiological Sciences, Djavad Mowafaghian Centre for Brain Health, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC V6T 1Z3, Canada
| | - G Stefano Brigidi
- Department of Cellular and Physiological Sciences, Djavad Mowafaghian Centre for Brain Health, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC V6T 1Z3, Canada
| | - Jennifer Kass
- Michael Smith Laboratories, Djavad Mowafaghian Centre for Brain Health, University of British Columbia, 2215 Wesbrook Mall, Vancouver, BC V6T 1Z3, Canada
| | - Austen J Milnerwood
- Montreal Neurological Institute, Department of Neurology and Neurosurgery, McGill University, 3801 University Street, Montreal, QC H3A 2B4, Canada
| | - Terrance P Snutch
- Michael Smith Laboratories, Djavad Mowafaghian Centre for Brain Health, University of British Columbia, 2215 Wesbrook Mall, Vancouver, BC V6T 1Z3, Canada
| | - Shernaz X Bamji
- Department of Cellular and Physiological Sciences, Djavad Mowafaghian Centre for Brain Health, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC V6T 1Z3, Canada.
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10
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Pizzarelli R, Griguoli M, Zacchi P, Petrini EM, Barberis A, Cattaneo A, Cherubini E. Tuning GABAergic Inhibition: Gephyrin Molecular Organization and Functions. Neuroscience 2020; 439:125-136. [PMID: 31356900 PMCID: PMC7351109 DOI: 10.1016/j.neuroscience.2019.07.036] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2019] [Revised: 07/16/2019] [Accepted: 07/17/2019] [Indexed: 01/15/2023]
Abstract
To be highly reliable, synaptic transmission needs postsynaptic receptors (Rs) in precise apposition to the presynaptic release sites. At inhibitory synapses, the postsynaptic protein gephyrin self-assembles to form a scaffold that anchors glycine and GABAARs to the cytoskeleton, thus ensuring the accurate accumulation of postsynaptic receptors at the right place. This protein undergoes several post-translational modifications which control protein-protein interaction and downstream signaling pathways. In addition, through the constant exchange of scaffolding elements and receptors in and out of synapses, gephyrin dynamically regulates synaptic strength and plasticity. The aim of the present review is to highlight recent findings on the functional role of gephyrin at GABAergic inhibitory synapses. We will discuss different approaches used to interfere with gephyrin in order to unveil its function. In addition, we will focus on the impact of gephyrin structure and distribution at the nanoscale level on the functional properties of inhibitory synapses as well as the implications of this scaffold protein in synaptic plasticity processes. Finally, we will emphasize how gephyrin genetic mutations or alterations in protein expression levels are implicated in several neuropathological disorders, including autism spectrum disorders, schizophrenia, temporal lobe epilepsy and Alzheimer's disease, all associated with severe deficits of GABAergic signaling. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.
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Affiliation(s)
- Rocco Pizzarelli
- European Brain Research Institute (EBRI), Fondazione Rita Levi-Montalcini, Roma, Italy
| | - Marilena Griguoli
- European Brain Research Institute (EBRI), Fondazione Rita Levi-Montalcini, Roma, Italy
| | - Paola Zacchi
- Department of Life Sciences, University of Trieste, Trieste, Italy
| | - Enrica Maria Petrini
- Fondazione Istituto Italiano di Tecnologia (IIT), Department of Neuroscience and Brain Technologies, Plasticity of inhibitory networks Unit, Genoa, Italy
| | - Andrea Barberis
- Fondazione Istituto Italiano di Tecnologia (IIT), Department of Neuroscience and Brain Technologies, Plasticity of inhibitory networks Unit, Genoa, Italy
| | - Antonino Cattaneo
- European Brain Research Institute (EBRI), Fondazione Rita Levi-Montalcini, Roma, Italy; Scuola Normale Superiore, Pisa, Italy
| | - Enrico Cherubini
- European Brain Research Institute (EBRI), Fondazione Rita Levi-Montalcini, Roma, Italy; Scuola Internazionale Superiore di Studi Avanzati, Trieste, Italy.
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11
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Barker JS, Hines RM. Regulation of GABA A Receptor Subunit Expression in Substance Use Disorders. Int J Mol Sci 2020; 21:ijms21124445. [PMID: 32580510 PMCID: PMC7352578 DOI: 10.3390/ijms21124445] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Revised: 06/17/2020] [Accepted: 06/19/2020] [Indexed: 01/02/2023] Open
Abstract
The modulation of neuronal cell firing is mediated by the release of the neurotransmitter GABA (γ-aminobuytric acid), which binds to two major families of receptors. The ionotropic GABAA receptors (GABAARs) are composed of five distinct subunits that vary in expression by brain region and cell type. The action of GABA on GABAARs is modulated by a variety of clinically and pharmacologically important drugs such as benzodiazepines and alcohol. Exposure to and abuse of these substances disrupts homeostasis and induces plasticity in GABAergic neurotransmission, often via the regulation of receptor expression. Here, we review the regulation of GABAAR subunit expression in adaptive and pathological plasticity, with a focus on substance use. We examine the factors influencing the expression of GABAAR subunit genes including the regulation of the 5′ and 3′ untranslated regions, variations in DNA methylation, immediate early genes and transcription factors that regulate subunit expression, translational and post-translational modifications, and other forms of receptor regulation beyond expression. Advancing our understanding of the factors regulating GABAAR subunit expression during adaptive plasticity, as well as during substance use and withdrawal will provide insight into the role of GABAergic signaling in substance use disorders, and contribute to the development of novel targeted therapies.
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12
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Nitric Oxide Signaling Strengthens Inhibitory Synapses of Cerebellar Molecular Layer Interneurons through a GABARAP-Dependent Mechanism. J Neurosci 2020; 40:3348-3359. [PMID: 32169968 DOI: 10.1523/jneurosci.2211-19.2020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2019] [Revised: 01/13/2020] [Accepted: 03/03/2020] [Indexed: 12/21/2022] Open
Abstract
Nitric oxide (NO) is an important signaling molecule that fulfills diverse functional roles as a neurotransmitter or diffusible second messenger in the developing and adult CNS. Although the impact of NO on different behaviors such as movement, sleep, learning, and memory has been well documented, the identity of its molecular and cellular targets is still an area of ongoing investigation. Here, we identify a novel role for NO in strengthening inhibitory GABAA receptor-mediated transmission in molecular layer interneurons of the mouse cerebellum. NO levels are elevated by the activity of neuronal NO synthase (nNOS) following Ca2+ entry through extrasynaptic NMDA-type ionotropic glutamate receptors (NMDARs). NO activates protein kinase G with the subsequent production of cGMP, which prompts the stimulation of NADPH oxidase and protein kinase C (PKC). The activation of PKC promotes the selective strengthening of α3-containing GABAARs synapses through a GΑΒΑ receptor-associated protein-dependent mechanism. Given the widespread but cell type-specific expression of the NMDAR/nNOS complex in the mammalian brain, our data suggest that NMDARs may uniquely strengthen inhibitory GABAergic transmission in these cells through a novel NO-mediated pathway.SIGNIFICANCE STATEMENT Long-term changes in the efficacy of GABAergic transmission is mediated by multiple presynaptic and postsynaptic mechanisms. A prominent pathway involves crosstalk between excitatory and inhibitory synapses whereby Ca2+-entering through postsynaptic NMDARs promotes the recruitment and strengthening of GABAA receptor synapses via Ca2+/calmodulin-dependent protein kinase II. Although Ca2+ transport by NMDARs is also tightly coupled to nNOS activity and NO production, it has yet to be determined whether this pathway affects inhibitory synapses. Here, we show that activation of NMDARs trigger a NO-dependent pathway that strengthens inhibitory GABAergic synapses of cerebellar molecular layer interneurons. Given the widespread expression of NMDARs and nNOS in the mammalian brain, we speculate that NO control of GABAergic synapse efficacy may be more widespread than has been appreciated.
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13
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Zhou X, Bessereau JL. Molecular Architecture of Genetically-Tractable GABA Synapses in C. elegans. Front Mol Neurosci 2019; 12:304. [PMID: 31920535 PMCID: PMC6920096 DOI: 10.3389/fnmol.2019.00304] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Accepted: 11/26/2019] [Indexed: 12/18/2022] Open
Abstract
Inhibitory synapses represent a minority of the total chemical synapses in the mammalian brain, yet proper tuning of inhibition is fundamental to shape neuronal network properties. The neurotransmitter γ-aminobutyric acid (GABA) mediates rapid synaptic inhibition by the activation of the type A GABA receptor (GABAAR), a pentameric chloride channel that governs major inhibitory neuronal transduction in the nervous system. Impaired GABA transmission leads to a variety of neuropsychiatric diseases, including schizophrenia, autism, epilepsy or anxiety. From an evolutionary perspective, GABAAR shows remarkable conservations, and are found in all eukaryotic clades and even in bacteria and archaea. Specifically, bona fide GABAARs are found in the nematode Caenorhabditis elegans. Because of the anatomical simplicity of the nervous system and its amenability to genetic manipulations, C. elegans provide a powerful system to investigate the molecular and cellular biology of GABA synapses. In this mini review article, we will introduce the structure of the C. elegans GABAergic system and describe recent advances that have identified novel proteins controlling the localization of GABAARs at synapses. In particular, Ce-Punctin/MADD-4 is an evolutionarily-conserved extracellular matrix protein that behaves as an anterograde synaptic organizer to instruct the excitatory or inhibitory identity of postsynaptic domains.
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Affiliation(s)
- Xin Zhou
- Univ Lyon, Université Claude Bernard Lyon 1, CNRS UMR 5310, INSERM U 1217, Institut NeuroMyoGène, Lyon, France
| | - Jean-Louis Bessereau
- Univ Lyon, Université Claude Bernard Lyon 1, CNRS UMR 5310, INSERM U 1217, Institut NeuroMyoGène, Lyon, France
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14
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Dong JX, Lee Y, Kirmiz M, Palacio S, Dumitras C, Moreno CM, Sando R, Santana LF, Südhof TC, Gong B, Murray KD, Trimmer JS. A toolbox of nanobodies developed and validated for use as intrabodies and nanoscale immunolabels in mammalian brain neurons. eLife 2019; 8:48750. [PMID: 31566565 PMCID: PMC6785268 DOI: 10.7554/elife.48750] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Accepted: 09/18/2019] [Indexed: 12/30/2022] Open
Abstract
Nanobodies (nAbs) are small, minimal antibodies that have distinct attributes that make them uniquely suited for certain biomedical research, diagnostic and therapeutic applications. Prominent uses include as intracellular antibodies or intrabodies to bind and deliver cargo to specific proteins and/or subcellular sites within cells, and as nanoscale immunolabels for enhanced tissue penetration and improved spatial imaging resolution. Here, we report the generation and validation of nAbs against a set of proteins prominently expressed at specific subcellular sites in mammalian brain neurons. We describe a novel hierarchical validation pipeline to systematically evaluate nAbs isolated by phage display for effective and specific use as intrabodies and immunolabels in mammalian cells including brain neurons. These nAbs form part of a robust toolbox for targeting proteins with distinct and highly spatially-restricted subcellular localization in mammalian brain neurons, allowing for visualization and/or modulation of structure and function at those sites.
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Affiliation(s)
- Jie-Xian Dong
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, United States
| | - Yongam Lee
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, United States
| | - Michael Kirmiz
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, United States
| | - Stephanie Palacio
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, United States
| | - Camelia Dumitras
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, United States
| | - Claudia M Moreno
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, United States.,Department of Physiology and Biophysics, University of Washington, Seattle, United States
| | - Richard Sando
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford School of Medicine, Stanford, United States
| | - L Fernando Santana
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, United States
| | - Thomas C Südhof
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford School of Medicine, Stanford, United States
| | - Belvin Gong
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, United States
| | - Karl D Murray
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, United States
| | - James S Trimmer
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, United States.,Department of Physiology and Membrane Biology, University of California, Davis, Davis, United States
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15
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Specht CG. Fractional occupancy of synaptic binding sites and the molecular plasticity of inhibitory synapses. Neuropharmacology 2019; 169:107493. [PMID: 30648560 DOI: 10.1016/j.neuropharm.2019.01.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2018] [Revised: 12/01/2018] [Accepted: 01/09/2019] [Indexed: 01/20/2023]
Abstract
The postsynaptic density (PSD) at inhibitory synapses is a complex molecular assembly that serves as a platform for the interaction of neurotransmitter receptors, scaffold and adapter proteins, cytoskeletal elements and signalling molecules. The stability of the PSD depends on a multiplicity of interactions linking individual components. At the same time the PSD retains a substantial degree of flexibility. The continuous exchange of synaptic molecules and the preferential addition or removal of certain components induce plastic changes in the synaptic structure. This property necessarily implies that interactors are in dynamic equilibrium and that not all synaptic binding sites are occupied simultaneously. This review discusses the molecular plasticity of inhibitory synapses in terms of the connectivity of their components. Whereas stable protein complexes are marked by stoichiometric relationships between subunits, the majority of synaptic interactions have fractional occupancy, which is here defined as the non-saturation of synaptic binding sites. Fractional occupancy can have several causes: reduced kinetic or thermodynamic stability of the interactions, an imbalance in the concentrations or limited spatio-temporal overlap of interacting proteins, negative cooperativity or mutually exclusive binding. The role of fractional occupancy in the regulation of synaptic structure and function is explored based on recent data about the connectivity of inhibitory receptors and scaffold proteins. I propose that the absolute quantification of interactors and their stoichiometry at identified synapses can provide new mechanistic insights into the dynamic properties of inhibitory PSDs at the molecular level. This article is part of the special issue entitled 'Mobility and trafficking of neuronal membrane proteins'.
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Affiliation(s)
- Christian G Specht
- École Normale Supérieure, PSL Research University, CNRS, Inserm, Institute of Biology (IBENS), Paris, 75005, France.
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16
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Groeneweg FL, Trattnig C, Kuhse J, Nawrotzki RA, Kirsch J. Gephyrin: a key regulatory protein of inhibitory synapses and beyond. Histochem Cell Biol 2018; 150:489-508. [DOI: 10.1007/s00418-018-1725-2] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/07/2018] [Indexed: 12/26/2022]
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17
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Gamlin CR, Yu WQ, Wong ROL, Hoon M. Assembly and maintenance of GABAergic and Glycinergic circuits in the mammalian nervous system. Neural Dev 2018; 13:12. [PMID: 29875009 PMCID: PMC5991458 DOI: 10.1186/s13064-018-0109-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Accepted: 05/06/2018] [Indexed: 12/19/2022] Open
Abstract
Inhibition in the central nervous systems (CNS) is mediated by two neurotransmitters: gamma-aminobutyric acid (GABA) and glycine. Inhibitory synapses are generally GABAergic or glycinergic, although there are synapses that co-release both neurotransmitter types. Compared to excitatory circuits, much less is known about the cellular and molecular mechanisms that regulate synaptic partner selection and wiring patterns of inhibitory circuits. Recent work, however, has begun to fill this gap in knowledge, providing deeper insight into whether GABAergic and glycinergic circuit assembly and maintenance rely on common or distinct mechanisms. Here we summarize and contrast the developmental mechanisms that regulate the selection of synaptic partners, and that promote the formation, refinement, maturation and maintenance of GABAergic and glycinergic synapses and their respective wiring patterns. We highlight how some parts of the CNS demonstrate developmental changes in the type of inhibitory transmitter or receptor composition at their inhibitory synapses. We also consider how perturbation of the development or maintenance of one type of inhibitory connection affects other inhibitory synapse types in the same circuit. Mechanistic insight into the development and maintenance of GABAergic and glycinergic inputs, and inputs that co-release both these neurotransmitters could help formulate comprehensive therapeutic strategies for treating disorders of synaptic inhibition.
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Affiliation(s)
- Clare R Gamlin
- Department of Biological Structure, University of Washington, Seattle, WA, USA
| | - Wan-Qing Yu
- Department of Biological Structure, University of Washington, Seattle, WA, USA
| | - Rachel O L Wong
- Department of Biological Structure, University of Washington, Seattle, WA, USA
| | - Mrinalini Hoon
- Department of Biological Structure, University of Washington, Seattle, WA, USA. .,Department of Ophthalmology and Visual Sciences, University of Wisconsin, Madison, WI, USA.
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18
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Lorenz-Guertin JM, Jacob TC. GABA type a receptor trafficking and the architecture of synaptic inhibition. Dev Neurobiol 2018; 78:238-270. [PMID: 28901728 PMCID: PMC6589839 DOI: 10.1002/dneu.22536] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2017] [Revised: 09/08/2017] [Accepted: 09/08/2017] [Indexed: 12/21/2022]
Abstract
Ubiquitous expression of GABA type A receptors (GABAA R) in the central nervous system establishes their central role in coordinating most aspects of neural function and development. Dysregulation of GABAergic neurotransmission manifests in a number of human health disorders and conditions that in certain cases can be alleviated by drugs targeting these receptors. Precise changes in the quantity or activity of GABAA Rs localized at the cell surface and at GABAergic postsynaptic sites directly impact the strength of inhibition. The molecular mechanisms constituting receptor trafficking to and from these compartments therefore dictate the efficacy of GABAA R function. Here we review the current understanding of how GABAA Rs traffic through biogenesis, plasma membrane transport, and degradation. Emphasis is placed on discussing novel GABAergic synaptic proteins, receptor and scaffolding post-translational modifications, activity-dependent changes in GABAA R confinement, and neuropeptide and neurosteroid mediated changes. We further highlight modern techniques currently advancing the knowledge of GABAA R trafficking and clinically relevant neurodevelopmental diseases connected to GABAergic dysfunction. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 78: 238-270, 2018.
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Affiliation(s)
- Joshua M Lorenz-Guertin
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, 15261
| | - Tija C Jacob
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, 15261
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19
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Yamasaki T, Hoyos-Ramirez E, Martenson JS, Morimoto-Tomita M, Tomita S. GARLH Family Proteins Stabilize GABA A Receptors at Synapses. Neuron 2017; 93:1138-1152.e6. [PMID: 28279354 DOI: 10.1016/j.neuron.2017.02.023] [Citation(s) in RCA: 95] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2015] [Revised: 05/26/2016] [Accepted: 02/09/2017] [Indexed: 10/20/2022]
Abstract
Ionotropic neurotransmitter receptors mediate fast synaptic transmission by functioning as ligand-gated ion channels. Fast inhibitory transmission in the brain is mediated mostly by ionotropic GABAA receptors (GABAARs), but their essential components for synaptic localization remain unknown. Here, we identify putative auxiliary subunits of GABAARs, which we term GARLHs, consisting of LH4 and LH3 proteins. LH4 forms a stable tripartite complex with GABAARs and neuroligin-2 in the brain. Moreover, LH4 is required for the synaptic localization of GABAARs and inhibitory synaptic transmission in the hippocampus. Our findings propose GARLHs as the first identified auxiliary subunits for anion channels. These findings provide new insights into the regulation of inhibitory transmission and the molecular constituents of native anion channels in vivo.
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Affiliation(s)
- Tokiwa Yamasaki
- Department of Cellular and Molecular Physiology, Program in Cellular Neuroscience, Neurodegeneration and Repair, Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Erika Hoyos-Ramirez
- Department of Cellular and Molecular Physiology, Program in Cellular Neuroscience, Neurodegeneration and Repair, Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06520, USA
| | - James S Martenson
- Department of Cellular and Molecular Physiology, Program in Cellular Neuroscience, Neurodegeneration and Repair, Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Megumi Morimoto-Tomita
- Department of Cellular and Molecular Physiology, Program in Cellular Neuroscience, Neurodegeneration and Repair, Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Susumu Tomita
- Department of Cellular and Molecular Physiology, Program in Cellular Neuroscience, Neurodegeneration and Repair, Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06520, USA.
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20
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Majoul IV, Ernesti JS, Butkevich EV, Duden R. Drebrins and Connexins: A Biomedical Perspective. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1006:225-247. [DOI: 10.1007/978-4-431-56550-5_13] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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21
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Nguyen QA, Horn ME, Nicoll RA. Distinct roles for extracellular and intracellular domains in neuroligin function at inhibitory synapses. eLife 2016; 5. [PMID: 27805570 PMCID: PMC5098909 DOI: 10.7554/elife.19236] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2016] [Accepted: 11/01/2016] [Indexed: 11/17/2022] Open
Abstract
Neuroligins (NLGNs) are postsynaptic cell adhesion molecules that interact trans-synaptically with neurexins to mediate synapse development and function. NLGN2 is only at inhibitory synapses while NLGN3 is at both excitatory and inhibitory synapses. We found that NLGN3 function at inhibitory synapses in rat CA1 depends on the presence of NLGN2 and identified a domain in the extracellular region that accounted for this functional difference between NLGN2 and 3 specifically at inhibitory synapses. We further show that the presence of a cytoplasmic tail (c-tail) is indispensible, and identified two domains in the c-tail that are necessary for NLGN function at inhibitory synapses. These domains point to a gephyrin-dependent mechanism that is disrupted by an autism-associated mutation at R705 and a gephyrin-independent mechanism reliant on a putative phosphorylation site at S714. Our work highlights unique and separate roles for the extracellular and intracellular regions in specifying and carrying out NLGN function respectively. DOI:http://dx.doi.org/10.7554/eLife.19236.001
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Affiliation(s)
- Quynh-Anh Nguyen
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, United States.,Neuroscience Graduate Program, University of California, San Francisco, San Francisco, United States
| | - Meryl E Horn
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, United States.,Neuroscience Graduate Program, University of California, San Francisco, San Francisco, United States
| | - Roger A Nicoll
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, United States.,Department of Physiology, University of California, San Francisco, San Francisco, United States
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22
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Alvarez FJ. Gephyrin and the regulation of synaptic strength and dynamics at glycinergic inhibitory synapses. Brain Res Bull 2016; 129:50-65. [PMID: 27612963 DOI: 10.1016/j.brainresbull.2016.09.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Revised: 08/23/2016] [Accepted: 09/05/2016] [Indexed: 01/23/2023]
Abstract
Glycinergic synapses predominate in brainstem and spinal cord where they modulate motor and sensory processing. Their postsynaptic mechanisms have been considered rather simple because they lack a large variety of glycine receptor isoforms and have relatively simple postsynaptic densities at the ultrastructural level. However, this simplicity is misleading being their postsynaptic regions regulated by a variety of complex mechanisms controlling the efficacy of synaptic inhibition. Early studies suggested that glycinergic inhibitory strength and dynamics depend largely on structural features rather than on molecular complexity. These include regulation of the number of postsynaptic glycine receptors, their localization and the amount of co-localized GABAA receptors and GABA-glycine co-transmission. These properties we now know are under the control of gephyrin. Gephyrin is the first postsynaptic scaffolding protein ever discovered and it was recently found to display a large degree of variation and regulation by splice variants, posttranslational modifications, intracellular trafficking and interactions with the underlying cytoskeleton. Many of these mechanisms are governed by converging excitatory activity and regulate gephyrin oligomerization and receptor binding, the architecture of the postsynaptic density (and by extension the whole synaptic complex), receptor retention and stability. These newly uncovered molecular mechanisms define the size and number of gephyrin postsynaptic regions and the numbers and proportions of glycine and GABAA receptors contained within. All together, they control the emergence of glycinergic synapses of different strength and temporal properties to best match the excitatory drive received by each individual neuron or local dendritic compartment.
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Affiliation(s)
- Francisco J Alvarez
- Department of Physiology, Emory University, Atlanta, GA 30322-3110, United States.
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23
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Fu YL, Wang YJ, Mu TW. Proteostasis Maintenance of Cys-Loop Receptors. ION CHANNELS AS THERAPEUTIC TARGETS, PART A 2016; 103:1-23. [DOI: 10.1016/bs.apcsb.2015.11.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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24
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Arslan A, von Engelhardt J, Wisden W. Cytoplasmic domain of δ subunit is important for the extra-synaptic targeting of GABAA receptor subtypes. J Integr Neurosci 2015; 13:617-31. [PMID: 25233879 DOI: 10.1142/s0219635214500228] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
GABA(A) receptors (GABA(A)Rs) are hetero-pentameric chloride channels and the primary sites for fast synaptic inhibition. We have expressed recombinant γ2 and δ subunits of GABA(A)Rs in cultured hippocampal neurons to analyze the membrane targeting of synaptic and extra-synaptic GABA(A)Rs, a phenomenon not well understood. Our data demonstrate that the synaptic targeting of γ2-containing GABA(A)Rs (γ2-GABA(A)Rs) does not depend on the cytoplasmic loop of γ2 subunit, in parallel with previous findings, showing that the synaptic localization of γ2-GABA(A)Rs requires the TM4 domain of γ2 rather than the large cytoplasmic loop. On the other hand, we showed here that the extrasynaptic targeting of the δ-containing GABA(A)Rs (δ-GABA(A)Rs) depends on the cytoplasmic loop of δ subunit via an active or a passive mechanism. We also show that the amino acid sequences of δ loop is highly conserved across the whole span of vertebrate evolution suggesting an active role of δ loop in extra-synaptic targeting of corresponding receptor subtypes.
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Affiliation(s)
- Ayla Arslan
- Department of Clinical Neurobiology, University of Heidelberg, Im Neuenheimer Feld 364, 69120 Heidelberg, Germany , Department of Molecular Biology and Genetics, Faculty of Engineering and Natural Sciences, Üsküdar University, Altunizade Mah. Haluk Türksoy Sok. No: 14, PK 34662 Üsküdar/İstanbul, Turkey
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25
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C. elegans Punctin Clusters GABAA Receptors via Neuroligin Binding and UNC-40/DCC Recruitment. Neuron 2015; 86:1407-19. [DOI: 10.1016/j.neuron.2015.05.013] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Revised: 02/13/2015] [Accepted: 03/27/2015] [Indexed: 12/21/2022]
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26
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Functions of kinesin superfamily proteins in neuroreceptor trafficking. BIOMED RESEARCH INTERNATIONAL 2015; 2015:639301. [PMID: 26075252 PMCID: PMC4449888 DOI: 10.1155/2015/639301] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/23/2015] [Revised: 04/22/2015] [Accepted: 04/27/2015] [Indexed: 11/18/2022]
Abstract
Synaptic plasticity is widely regarded as the cellular basis of learning and memory. Understanding the molecular mechanism of synaptic plasticity has been one of center pieces of neuroscience research for more than three decades. It has been well known that the trafficking of α-amino-3-hydroxy-5-methylisoxazoloe-4-propionic acid- (AMPA-) type, N-methyl-D-aspartate- (NMDA-) type glutamate receptors to and from synapses is a key molecular event underlying many forms of synaptic plasticity. Kainate receptors are another type of glutamate receptors playing important roles in synaptic transmission. In addition, GABA receptors also play important roles in modulating the synaptic plasticity. Kinesin superfamily proteins (also known as KIFs) transport various cargos in both anterograde and retrograde directions through the interaction with different adaptor proteins. Recent studies indicate that KIFs regulate the trafficking of NMDA receptors, AMPA receptors, kainate receptors, and GABA receptors and thus play important roles in neuronal activity. Here we review the essential functions of KIFs in the trafficking of neuroreceptor and synaptic plasticity.
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27
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Choii G, Ko J. Gephyrin: a central GABAergic synapse organizer. Exp Mol Med 2015; 47:e158. [PMID: 25882190 DOI: 10.1038/emm.2015.5] [Citation(s) in RCA: 91] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2014] [Accepted: 12/18/2014] [Indexed: 01/22/2023] Open
Abstract
Gephyrin is a central element that anchors, clusters and stabilizes glycine and γ-aminobutyric acid type A receptors at inhibitory synapses of the mammalian brain. It self-assembles into a hexagonal lattice and interacts with various inhibitory synaptic proteins. Intriguingly, the clustering of gephyrin, which is regulated by multiple posttranslational modifications, is critical for inhibitory synapse formation and function. In this review, we summarize the basic properties of gephyrin and describe recent findings regarding its roles in inhibitory synapse formation, function and plasticity. We will also discuss the implications for the pathophysiology of brain disorders and raise the remaining open questions in this field.
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Affiliation(s)
- Gayoung Choii
- Department of Biochemistry, College of Life Science and Biotechnology, Yonsei University, Seoul, Korea
| | - Jaewon Ko
- 1] Department of Biochemistry, College of Life Science and Biotechnology, Yonsei University, Seoul, Korea [2] Department of Psychiatry, Yonsei University College of Medicine, Seoul, Korea
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28
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Kalbouneh H, Schlicksupp A, Kirsch J, Kuhse J. Cyclin-dependent kinase 5 is involved in the phosphorylation of gephyrin and clustering of GABAA receptors at inhibitory synapses of hippocampal neurons. PLoS One 2014; 9:e104256. [PMID: 25093719 PMCID: PMC4122414 DOI: 10.1371/journal.pone.0104256] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Accepted: 07/10/2014] [Indexed: 11/19/2022] Open
Abstract
CDK5 has been implicated in neural functions including growth, neuronal migration, synaptic transmission and plasticity of excitatory chemical synapses. Here we report robust effects of CDK5 on phosphorylation of the postsynaptic scaffold protein gephyrin and clustering of inhibitory GABAA receptors in hippocampal neurons. shRNA-mediated knockdown of CDK5 and pharmacological inhibition of cyclin-dependent kinases reduced phosphorylated gephyrin clusters and postsynaptic γ2-containing GABAA receptors. Phosphorylation of S270 is antagonized by PP1/PP2a phosphatase and site-directed mutagenesis and in vitro phosphorylation experiments indicate that S270 is a putative CDK5 phosphorylation site of gephyrin. Our data suggest that CDK5 plays an essential role for the stability of gephyrin-dependent GABAA receptor clusters in hippocampal neurons.
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Affiliation(s)
- Heba Kalbouneh
- Department of Anatomy and Cell Biology, University of Heidelberg, Heidelberg, Germany
| | - Andrea Schlicksupp
- Department of Anatomy and Cell Biology, University of Heidelberg, Heidelberg, Germany
| | - Joachim Kirsch
- Department of Anatomy and Cell Biology, University of Heidelberg, Heidelberg, Germany
| | - Jochen Kuhse
- Department of Anatomy and Cell Biology, University of Heidelberg, Heidelberg, Germany
- * E-mail:
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Gephyrin clusters are absent from small diameter primary afferent terminals despite the presence of GABA(A) receptors. J Neurosci 2014; 34:8300-17. [PMID: 24920633 DOI: 10.1523/jneurosci.0159-14.2014] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Whereas both GABA(A) receptors (GABA(A)Rs) and glycine receptors (GlyRs) play a role in control of dorsal horn neuron excitability, their relative contribution to inhibition of small diameter primary afferent terminals remains controversial. To address this, we designed an approach for quantitative analyses of the distribution of GABA(A)R-subunits, GlyR α1-subunit and their anchoring protein, gephyrin, on terminals of rat spinal sensory afferents identified by Calcitonin-Gene-Related-Peptide (CGRP) for peptidergic terminals, and by Isolectin-B4 (IB4) for nonpeptidergic terminals. The approach was designed for light microscopy, which is compatible with the mild fixation conditions necessary for immunodetection of several of these antigens. An algorithm was designed to recognize structures with dimensions similar to those of the microscope resolution. To avoid detecting false colocalization, the latter was considered significant only if the degree of pixel overlap exceeded that expected from randomly overlapping pixels given a hypergeometric distribution. We found that both CGRP(+) and IB4(+) terminals were devoid of GlyR α1-subunit and gephyrin. The α1 GABA(A)R was also absent from these terminals. In contrast, the GABA(A)R α2/α3/α5 and β3 subunits were significantly expressed in both terminal types, as were other GABA(A)R-associated-proteins (α-Dystroglycan/Neuroligin-2/Collybistin-2). Ultrastructural immunocytochemistry confirmed the presence of GABA(A)R β3 subunits in small afferent terminals. Real-time quantitative PCR (qRT-PCR) confirmed the results of light microscopy immunochemical analysis. These results indicate that dorsal horn inhibitory synapses follow different rules of organization at presynaptic versus postsynaptic sites (nociceptive afferent terminals vs inhibitory synapses on dorsal horn neurons). The absence of gephyrin clusters from primary afferent terminals suggests a more diffuse mode of GABA(A)-mediated transmission at presynaptic than at postsynaptic sites.
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Petrini EM, Ravasenga T, Hausrat TJ, Iurilli G, Olcese U, Racine V, Sibarita JB, Jacob TC, Moss SJ, Benfenati F, Medini P, Kneussel M, Barberis A. Synaptic recruitment of gephyrin regulates surface GABAA receptor dynamics for the expression of inhibitory LTP. Nat Commun 2014; 5:3921. [PMID: 24894704 PMCID: PMC4059940 DOI: 10.1038/ncomms4921] [Citation(s) in RCA: 131] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Accepted: 04/17/2014] [Indexed: 11/09/2022] Open
Abstract
Postsynaptic long-term potentiation of inhibition (iLTP) can rely on increased GABAA receptors (GABA(A)Rs) at synapses by promoted exocytosis. However, the molecular mechanisms that enhance the clustering of postsynaptic GABA(A)Rs during iLTP remain obscure. Here we demonstrate that during chemically induced iLTP (chem-iLTP), GABA(A)Rs are immobilized and confined at synapses, as revealed by single-particle tracking of individual GABA(A)Rs in cultured hippocampal neurons. Chem-iLTP expression requires synaptic recruitment of the scaffold protein gephyrin from extrasynaptic areas, which in turn is promoted by CaMKII-dependent phosphorylation of GABA(A)R-β3-Ser(383). Impairment of gephyrin assembly prevents chem-iLTP and, in parallel, blocks the accumulation and immobilization of GABA(A)Rs at synapses. Importantly, an increase of gephyrin and GABA(A)R similar to those observed during chem-iLTP in cultures were found in the rat visual cortex following an experience-dependent plasticity protocol that potentiates inhibitory transmission in vivo. Thus, phospho-GABA(A)R-β3-dependent accumulation of gephyrin at synapses and receptor immobilization are crucial for iLTP expression and are likely to modulate network excitability.
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Affiliation(s)
- Enrica Maria Petrini
- Department of Neuroscience and Brain Technologies, The Italian Institute of Technology, Via Morego 30, 16163 Genova, Italy
| | - Tiziana Ravasenga
- Department of Neuroscience and Brain Technologies, The Italian Institute of Technology, Via Morego 30, 16163 Genova, Italy
| | - Torben J Hausrat
- Center for Molecular Neurobiology (ZMNH), University Medical Center Hamburg Eppendorf, D-20251 Hamburg, Germany
| | - Giuliano Iurilli
- Department of Neuroscience and Brain Technologies, The Italian Institute of Technology, Via Morego 30, 16163 Genova, Italy
| | - Umberto Olcese
- Department of Neuroscience and Brain Technologies, The Italian Institute of Technology, Via Morego 30, 16163 Genova, Italy
| | - Victor Racine
- Institute of Molecular and Cell Biology, Proteos, Singapore 138673, Singapore
| | - Jean-Baptiste Sibarita
- 1] Interdisciplinary Institute for Neuroscience, University of Bordeaux, F-33000 Bordeaux, France [2] CNRS UMR 5297, F-33000 Bordeaux, France
| | - Tija C Jacob
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
| | - Stephen J Moss
- Department of Neuroscience, Tufts University, 136 Harrison Avenue, Arnold 207 Boston, Massachusetts 0211, USA
| | - Fabio Benfenati
- 1] Department of Neuroscience and Brain Technologies, The Italian Institute of Technology, Via Morego 30, 16163 Genova, Italy [2] Department of Experimental Medicine, University of Genova, 16163 Genova, Italy
| | - Paolo Medini
- Department of Neuroscience and Brain Technologies, The Italian Institute of Technology, Via Morego 30, 16163 Genova, Italy
| | - Matthias Kneussel
- Center for Molecular Neurobiology (ZMNH), University Medical Center Hamburg Eppendorf, D-20251 Hamburg, Germany
| | - Andrea Barberis
- Department of Neuroscience and Brain Technologies, The Italian Institute of Technology, Via Morego 30, 16163 Genova, Italy
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31
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Abstract
The neurotransmitters GABA and glycine mediate fast synaptic inhibition by activating ligand-gated chloride channels--namely, type A GABA (GABA(A)) and glycine receptors. Both types of receptors are anchored postsynaptically by gephyrin, which self-assembles into a scaffold and interacts with the cytoskeleton. Current research indicates that postsynaptic gephyrin clusters are dynamic assemblies that are held together and regulated by multiple protein-protein interactions. Moreover, post-translational modifications of gephyrin regulate the formation and plasticity of GABAergic synapses by altering the clustering properties of postsynaptic scaffolds and thereby the availability and function of receptors and other signalling molecules. Here, we discuss the formation and regulation of the gephyrin scaffold, its role in GABAergic and glycinergic synaptic function and the implications for the pathophysiology of brain disorders caused by abnormal inhibitory neurotransmission.
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32
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Srivastava AK, Schwartz CE. Intellectual disability and autism spectrum disorders: causal genes and molecular mechanisms. Neurosci Biobehav Rev 2014; 46 Pt 2:161-74. [PMID: 24709068 DOI: 10.1016/j.neubiorev.2014.02.015] [Citation(s) in RCA: 139] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2013] [Revised: 01/30/2014] [Accepted: 02/12/2014] [Indexed: 12/19/2022]
Abstract
Intellectual disability (ID) and autism spectrum disorder (ASD) are the most common developmental disorders present in humans. Combined, they affect between 3 and 5% of the population. Additionally, they can be found together in the same individual thereby complicating treatment. The causative factors (genes, epigenetic and environmental) are quite varied and likely interact so as to further complicate the assessment of an individual patient. Nonetheless, much valuable information has been gained by identifying candidate genes for ID or ASD. Understanding the etiology of either ID or ASD is of utmost importance for families. It allows a determination of the risk of recurrence, the possibility of other comorbidity medical problems, the molecular and cellular nature of the pathobiology and hopefully potential therapeutic approaches.
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Affiliation(s)
- Anand K Srivastava
- J.C. Self Research Institute, Greenwood Genetic Center, Greenwood, SC, USA
| | - Charles E Schwartz
- J.C. Self Research Institute, Greenwood Genetic Center, Greenwood, SC, USA.
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Fritschy JM, Panzanelli P. GABAAreceptors and plasticity of inhibitory neurotransmission in the central nervous system. Eur J Neurosci 2014; 39:1845-65. [DOI: 10.1111/ejn.12534] [Citation(s) in RCA: 144] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2014] [Revised: 01/29/2014] [Accepted: 01/29/2014] [Indexed: 12/11/2022]
Affiliation(s)
- Jean-Marc Fritschy
- Institute of Pharmacology and Toxicology; University of Zurich; Winterthurerstrasse 190 8057 Zurich Switzerland
- Neuroscience Center Zurich; University of Zurich and ETH; Zurich Switzerland
| | - Patrizia Panzanelli
- Department of Neuroscience Rita Levi Montalcini; University of Turin; Turin Italy
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34
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Dixon C, Sah P, Lynch JW, Keramidas A. GABAA receptor α and γ subunits shape synaptic currents via different mechanisms. J Biol Chem 2014; 289:5399-411. [PMID: 24425869 DOI: 10.1074/jbc.m113.514695] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Synaptic GABAA receptors (GABAARs) mediate most of the inhibitory neurotransmission in the brain. The majority of these receptors are comprised of α1, β2, and γ2 subunits. The amygdala, a structure involved in processing emotional stimuli, expresses α2 and γ1 subunits at high levels. The effect of these subunits on GABAAR-mediated synaptic transmission is not known. Understanding the influence of these subunits on GABAAR-mediated synaptic currents may help in identifying the roles and locations of amygdala synapses that contain these subunits. Here, we describe the biophysical and synaptic properties of pure populations of α1β2γ2, α2β2γ2, α1β2γ1 and α2β2γ1 GABAARs. Their synaptic properties were examined in engineered synapses, whereas their kinetic properties were studied using rapid agonist application, and single channel recordings. All macropatch currents activated rapidly (<1 ms) and deactivated as a function of the α-subunit, with α2-containing GABAARs consistently deactivating ∼10-fold more slowly. Single channel analysis revealed that the slower current decay of α2-containing GABAARs was due to longer burst durations at low GABA concentrations, corresponding to a ∼4-fold higher affinity for GABA. Synaptic currents revealed a different pattern of activation and deactivation to that of macropatch data. The inclusion of α2 and γ1 subunits slowed both the activation and deactivation rates, suggesting that receptors containing these subunits cluster more diffusely at synapses. Switching the intracellular domains of the γ2 and γ1 subunits substantiated this inference. Because this region determines post-synaptic localization, we hypothesize that GABAARs containing γ1 and γ2 use different mechanisms for synaptic clustering.
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Affiliation(s)
- Christine Dixon
- From the Queensland Brain Institute, University of Queensland, Brisbane, Queensland, Australia 4072
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35
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Rahman J, Latal AT, Besser S, Hirrlinger J, Hülsmann S. Mixed miniature postsynaptic currents resulting from co-release of glycine and GABA recorded from glycinergic neurons in the neonatal respiratory network. Eur J Neurosci 2013; 37:1229-41. [DOI: 10.1111/ejn.12136] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2012] [Revised: 12/17/2012] [Accepted: 12/18/2012] [Indexed: 12/28/2022]
Affiliation(s)
| | - A. Tobias Latal
- DFG Research Center for Molecular Physiology of the Brain (CMPB); University of Göttingen; Göttingen; Germany
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36
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Kowalczyk S, Winkelmann A, Smolinsky B, Förstera B, Neundorf I, Schwarz G, Meier JC. Direct binding of GABAA receptor β2 and β3 subunits to gephyrin. Eur J Neurosci 2012. [PMID: 23205938 DOI: 10.1111/ejn.12078] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
GABAergic transmission is essential to brain function, and a large repertoire of GABA type A receptor (GABA(A) R) subunits is at a neuron's disposition to serve this function. The glycine receptor (GlyR)-associated protein gephyrin has been shown to be essential for the clustering of a subset of GABA(A) R. Despite recent progress in the field of gephyrin-dependent mechanisms of postsynaptic GABA(A) R stabilisation, the role of gephyrin in synaptic GABA(A) R localisation has remained a complex matter with many open questions. Here, we analysed comparatively the interaction of purified rat gephyrin and mouse brain gephyrin with the large cytoplasmic loops of GABA(A) R α1, α2, β2 and β3 subunits. Binding affinities were determined using surface plasmon resonance spectroscopy, and showed an ~ 20-fold lower affinity of the β2 loop to gephyrin as compared to the GlyR β loop-gephyrin interaction. We also probed in vivo binding in primary cortical neurons by the well-established use of chimaeras of GlyR α1 that harbour respective gephyrin-binding motifs derived from the different GABA(A) R subunits. These studies identify a novel gephyrin-binding motif in GABA(A) R β2 and β3 large cytoplasmic loops.
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Affiliation(s)
- Sarah Kowalczyk
- Department of Chemistry, Institute of Biochemistry, University of Cologne, Cologne, Germany
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37
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Fritschy JM, Panzanelli P, Tyagarajan SK. Molecular and functional heterogeneity of GABAergic synapses. Cell Mol Life Sci 2012; 69:2485-99. [PMID: 22314501 PMCID: PMC11115047 DOI: 10.1007/s00018-012-0926-4] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2011] [Revised: 01/16/2012] [Accepted: 01/19/2012] [Indexed: 01/07/2023]
Abstract
Knowledge of the functional organization of the GABAergic system, the main inhibitory neurotransmitter system, in the CNS has increased remarkably in recent years. In particular, substantial progress has been made in elucidating the molecular mechanisms underlying the formation and plasticity of GABAergic synapses. Evidence available ascribes a key role to the cytoplasmic protein gephyrin to form a postsynaptic scaffold anchoring GABA(A) receptors along with other transmembrane proteins and signaling molecules in the postsynaptic density. However, the mechanisms of gephyrin scaffolding remain elusive, notably because gephyrin can auto-aggregate spontaneously and lacks PDZ protein interaction domains found in a majority of scaffolding proteins. In addition, the structural diversity of GABA(A) receptors, which are pentameric channels encoded by a large family of subunits, has been largely overlooked in these studies. Finally, the role of the dystrophin-glycoprotein complex, present in a subset of GABAergic synapses in cortical structures, remains ill-defined. In this review, we discuss recent results derived mainly from the analysis of mutant mice lacking a specific GABA(A) receptor subtype or a core protein of the GABAergic postsynaptic density (neuroligin-2, collybistin), highlighting the molecular diversity of GABAergic synapses and its relevance for brain plasticity and function. In addition, we discuss the contribution of the dystrophin-glycoprotein complex to the molecular and functional heterogeneity of GABAergic synapses.
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Affiliation(s)
- Jean-Marc Fritschy
- Institute of Pharmacology and Toxicology, University of Zurich, Switzerland.
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38
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Körber C, Richter A, Kaiser M, Schlicksupp A, Mükusch S, Kuner T, Kirsch J, Kuhse J. Effects of distinct collybistin isoforms on the formation of GABAergic synapses in hippocampal neurons. Mol Cell Neurosci 2012; 50:250-9. [DOI: 10.1016/j.mcn.2012.05.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2011] [Revised: 05/06/2012] [Accepted: 05/25/2012] [Indexed: 11/25/2022] Open
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39
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Elimination of inhibitory synapses is a major component of adult ocular dominance plasticity. Neuron 2012; 74:374-83. [PMID: 22542189 DOI: 10.1016/j.neuron.2012.03.015] [Citation(s) in RCA: 155] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/23/2012] [Indexed: 11/23/2022]
Abstract
During development, cortical plasticity is associated with the rearrangement of excitatory connections. While these connections become more stable with age, plasticity can still be induced in the adult cortex. Here we provide evidence that structural plasticity of inhibitory synapses onto pyramidal neurons is a major component of plasticity in the adult neocortex. In vivo two-photon imaging was used to monitor the formation and elimination of fluorescently labeled inhibitory structures on pyramidal neurons. We find that ocular dominance plasticity in the adult visual cortex is associated with rapid inhibitory synapse loss, especially of those present on dendritic spines. This occurs not only with monocular deprivation but also with subsequent restoration of binocular vision. We propose that in the adult visual cortex the experience-induced loss of inhibition may effectively strengthen specific visual inputs with limited need for rearranging the excitatory circuitry.
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40
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Wu X, Wu Z, Ning G, Guo Y, Ali R, Macdonald RL, De Blas AL, Luscher B, Chen G. γ-Aminobutyric acid type A (GABAA) receptor α subunits play a direct role in synaptic versus extrasynaptic targeting. J Biol Chem 2012; 287:27417-30. [PMID: 22711532 DOI: 10.1074/jbc.m112.360461] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
GABA(A) receptors (GABA(A)-Rs) are localized at both synaptic and extrasynaptic sites, mediating phasic and tonic inhibition, respectively. Previous studies suggest an important role of γ2 and δ subunits in synaptic versus extrasynaptic targeting of GABA(A)-Rs. Here, we demonstrate differential function of α2 and α6 subunits in guiding the localization of GABA(A)-Rs. To study the targeting of specific subtypes of GABA(A)-Rs, we used a molecularly engineered GABAergic synapse model to precisely control the GABA(A)-R subunit composition. We found that in neuron-HEK cell heterosynapses, GABAergic events mediated by α2β3γ2 receptors were very fast (rise time ∼2 ms), whereas events mediated by α6β3δ receptors were very slow (rise time ∼20 ms). Such an order of magnitude difference in rise time could not be attributed to the minute differences in receptor kinetics. Interestingly, synaptic events mediated by α6β3 or α6β3γ2 receptors were significantly slower than those mediated by α2β3 or α2β3γ2 receptors, suggesting a differential role of α subunit in receptor targeting. This was confirmed by differential targeting of the same δ-γ2 chimeric subunits to synaptic or extrasynaptic sites, depending on whether it was co-assembled with the α2 or α6 subunit. In addition, insertion of a gephyrin-binding site into the intracellular domain of α6 and δ subunits brought α6β3δ receptors closer to synaptic sites. Therefore, the α subunits, together with the γ2 and δ subunits, play a critical role in governing synaptic versus extrasynaptic targeting of GABA(A)-Rs, possibly through differential interactions with gephyrin.
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Affiliation(s)
- Xia Wu
- Department of Biology, Huck Institutes of Life Sciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA
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41
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The residence time of GABA(A)Rs at inhibitory synapses is determined by direct binding of the receptor α1 subunit to gephyrin. J Neurosci 2011; 31:14677-87. [PMID: 21994384 DOI: 10.1523/jneurosci.2001-11.2011] [Citation(s) in RCA: 121] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The majority of fast synaptic inhibition in the brain is mediated by benzodiazepine-sensitive α1-subunit-containing GABA type A receptors (GABA(A)Rs); however, our knowledge of the mechanisms neurons use to regulate their synaptic accumulation is rudimentary. Using immunoprecipitation, we demonstrate that GABA(A)Rs and gephyrin are intimately associated at inhibitory synapses in cultured rat neurons. In vitro we reveal that the E-domain of gephyrin directly binds to the α1 subunit with an affinity of ∼20 μm, mediated by residues 360-375 within the intracellular domain of this receptor subunit. Mutating residues 360-375 decreases both the accumulation of α1-containing GABA(A)Rs at gephyrin-positive inhibitory synapses in hippocampal neurons and the amplitude of mIPSCs. We also demonstrate that the affinity of gephyrin for the α1 subunit is modulated by Thr375, a putative phosphorylation site. Mutation of Thr375 to a phosphomimetic, negatively charged amino acid decreases both the affinity of the α1 subunit for gephyrin, and therefore receptor accumulation at synapses, and the amplitude of mIPSCs. Finally, single-particle tracking reveals that gephyrin reduces the diffusion of α1-subunit-containing GABA(A)Rs specifically at inhibitory synapses, thereby increasing their confinement at these structures. Our results suggest that the direct binding of gephyrin to residues 360-375 of the α1 subunit and its modulation are likely to be important determinants for the stabilization of GABA(A)Rs at synaptic sites, thereby modulating the strength of synaptic inhibition.
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42
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Sheng M, Kim E. The postsynaptic organization of synapses. Cold Spring Harb Perspect Biol 2011; 3:cshperspect.a005678. [PMID: 22046028 DOI: 10.1101/cshperspect.a005678] [Citation(s) in RCA: 375] [Impact Index Per Article: 28.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The postsynaptic side of the synapse is specialized to receive the neurotransmitter signal released from the presynaptic terminal and transduce it into electrical and biochemical changes in the postsynaptic cell. The cardinal functional components of the postsynaptic specialization of excitatory and inhibitory synapses are the ionotropic receptors (ligand-gated channels) for glutamate and γ-aminobutyric acid (GABA), respectively. These receptor channels are concentrated at the postsynaptic membrane and embedded in a dense and rich protein network comprised of anchoring and scaffolding molecules, signaling enzymes, cytoskeletal components, as well as other membrane proteins. Excitatory and inhibitory postsynaptic specializations are quite different in molecular organization. The postsynaptic density of excitatory synapses is especially complex and dynamic in composition and regulation; it contains hundreds of different proteins, many of which are required for cognitive function and implicated in psychiatric illness.
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Affiliation(s)
- Morgan Sheng
- The Department of Neuroscience, Genentech Incorporated, San Francisco, California 94080, USA
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43
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Patrizi A, Viltono L, Frola E, Harvey K, Harvey RJ, Sassoè-Pognetto M. Selective localization of collybistin at a subset of inhibitory synapses in brain circuits. J Comp Neurol 2011; 520:130-41. [DOI: 10.1002/cne.22702] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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44
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Maric HM, Mukherjee J, Tretter V, Moss SJ, Schindelin H. Gephyrin-mediated γ-aminobutyric acid type A and glycine receptor clustering relies on a common binding site. J Biol Chem 2011; 286:42105-42114. [PMID: 22006921 DOI: 10.1074/jbc.m111.303412] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Gephyrin is the major protein determinant for the clustering of inhibitory neurotransmitter receptors. Earlier analyses revealed that gephyrin tightly binds to residues 398-410 of the glycine receptor β subunit (GlyR β) and, as demonstrated only recently, also interacts with GABA(A) receptors (GABA(A)Rs) containing the α1, α2, and α3 subunits. Here, we dissect the molecular basis underlying the interactions between gephyrin and GABA(A)Rs containing these α-subunits and compare them to the crystal structure of the gephyrin-GlyR β complex. Biophysical and biochemical assays revealed that, in contrast to its tight interaction with GlyR β, gephyrin only loosely interacts with GABA(A)R α2, whereas it has an intermediate affinity for the GABA(A)R α1 and α3 subunits. Despite the wide variation in affinities and the low overall sequence homology among the identified receptor subunits, competition assays confirmed the receptor-gephyrin interaction to be a mutually exclusive process. Selected gephyrin point mutants that critically weaken complex formation with GlyR β also abolished the GABA(A)R α1 and α3 interactions. Additionally, we identified a common binding motif with two conserved aromatic residues that are central for gephyrin binding. Consistent with the biochemical data, mutations of the corresponding residues within the cytoplasmic domain of α2 subunit-containing GABA(A)Rs attenuated clustering of these receptors at postsynaptic sites in hippocampal neurons. Taken together, our experiments provide key insights regarding similarities and differences in the complex formation between gephyrin and GABA(A)Rs compared with GlyRs and, hence, the accumulation of these receptors at postsynaptic sites.
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Affiliation(s)
- Hans-Michael Maric
- Rudolf Virchow Center for Experimental Biomedicine, Institute of Structural Biology, University of Würzburg, Josef-Schneider-Strasse 2, 97080 Würzburg, Germany
| | - Jayanta Mukherjee
- Department of Neuroscience, Tufts University, Boston, Massachusetts 02111
| | - Verena Tretter
- Department of Biochemistry and Molecular Biology, Medical University Vienna/Center for Brain Research, Spitalgasse 4, 1090 Vienna, Austria
| | - Stephen J Moss
- Department of Neuroscience, Tufts University, Boston, Massachusetts 02111
| | - Hermann Schindelin
- Rudolf Virchow Center for Experimental Biomedicine, Institute of Structural Biology, University of Würzburg, Josef-Schneider-Strasse 2, 97080 Würzburg, Germany.
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45
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Bouthour W, Leroy F, Emmanuelli C, Carnaud M, Dahan M, Poncer JC, Lévi S. A human mutation in Gabrg2 associated with generalized epilepsy alters the membrane dynamics of GABAA receptors. Cereb Cortex 2011; 22:1542-53. [PMID: 21908847 DOI: 10.1093/cercor/bhr225] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Neuronal activity modulates the membrane diffusion of postsynaptic γ-aminobutyric acid (GABA)(A) receptors (GABA(A)Rs), thereby regulating the efficacy of GABAergic synapses. The K289M mutation in GABA(A)Rs subunit γ2 has been associated with the generalized epilepsy with febrile seizures plus (GEFS+) syndrome. This mutation accelerates receptor deactivation and therefore reduces inhibitory synaptic transmission. Yet, it is not clear why this mutation specifically promotes febrile seizures. We show that upon raising temperature both the number of GABA(A)Rs clusters and the frequency of miniature inhibitory postsynaptic currents decreased in neurons expressing the K289M mutant but not wild-type (WT) recombinant γ2. Single-particle tracking experiments revealed that raising temperature increases the membrane diffusion of synaptic GABA(A)Rs containing the K289M mutant but not WT recombinant γ2. This effect was mediated by enhanced neuronal activity as it was blocked by glutamate receptor antagonists and was mimicked by the convulsant 4-aminopyridine. Our data suggest the K289M mutation in γ2 confers GABA(A)Rs with enhanced sensitivity of their membrane diffusion to neuronal activity. Enhanced activity during hyperthermia may then trigger the escape of receptors from synapses and thereby further reduce the efficacy of GABAergic inhibition. Alteration of the membrane diffusion of neurotransmitter receptors therefore represents a new mechanism in human epilepsy.
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Affiliation(s)
- Walid Bouthour
- Institut National de la Santé et de la Recherche Médicale, Unité Mixte de Recherche en Santé 839, 75005 Paris, France
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46
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Tretter V, Kerschner B, Milenkovic I, Ramsden SL, Ramerstorfer J, Saiepour L, Maric HM, Moss SJ, Schindelin H, Harvey RJ, Sieghart W, Harvey K. Molecular basis of the γ-aminobutyric acid A receptor α3 subunit interaction with the clustering protein gephyrin. J Biol Chem 2011; 286:37702-11. [PMID: 21880742 DOI: 10.1074/jbc.m111.291336] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The multifunctional scaffolding protein gephyrin is a key player in the formation of the postsynaptic scaffold at inhibitory synapses, clustering both inhibitory glycine receptors (GlyRs) and selected GABA(A) receptor (GABA(A)R) subtypes. We report a direct interaction between the GABA(A)R α3 subunit and gephyrin, mapping reciprocal binding sites using mutagenesis, overlay, and yeast two-hybrid assays. This analysis reveals that critical determinants of this interaction are located in the motif FNIVGTTYPI in the GABA(A)R α3 M3-M4 domain and the motif SMDKAFITVL at the N terminus of the gephyrin E domain. GABA(A)R α3 gephyrin binding-site mutants were unable to co-localize with endogenous gephyrin in transfected hippocampal neurons, despite being able to traffic to the cell membrane and form functional benzodiazepine-responsive GABA(A)Rs in recombinant systems. Interestingly, motifs responsible for interactions with GABA(A)R α2, GABA(A)R α3, and collybistin on gephyrin overlap. Curiously, two key residues (Asp-327 and Phe-330) in the GABA(A)R α2 and α3 binding sites on gephyrin also contribute to GlyR β subunit-E domain interactions. However, isothermal titration calorimetry reveals a 27-fold difference in the interaction strength between GABA(A)R α3 and GlyR β subunits with gephyrin with dissociation constants of 5.3 μm and 0.2 μm, respectively. Taken together, these observations suggest that clustering of GABA(A)R α2, α3, and GlyRs by gephyrin is mediated by distinct mechanisms at mixed glycinergic/GABAergic synapses.
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Affiliation(s)
- Verena Tretter
- Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Spitalgasse 4, 1090 Vienna, Austria
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Kuzirian MS, Paradis S. Emerging themes in GABAergic synapse development. Prog Neurobiol 2011; 95:68-87. [PMID: 21798307 DOI: 10.1016/j.pneurobio.2011.07.002] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2011] [Revised: 06/30/2011] [Accepted: 07/03/2011] [Indexed: 12/25/2022]
Abstract
Glutamatergic synapse development has been rigorously investigated for the past two decades at both the molecular and cell biological level yet a comparable intensity of investigation into the cellular and molecular mechanisms of GABAergic synapse development has been lacking until relatively recently. This review will provide a detailed overview of the current understanding of GABAergic synapse development with a particular emphasis on assembly of synaptic components, molecular mechanisms of synaptic development, and a subset of human disorders which manifest when GABAergic synapse development is disrupted. An unexpected and emerging theme from these studies is that glutamatergic and GABAergic synapse development share a number of overlapping molecular and cell biological mechanisms that will be emphasized in this review.
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Affiliation(s)
- Marissa S Kuzirian
- Brandeis Univeristy, Department of Biology, National Center for Behavioral Genomics, Volen Center for Complex Systems, Waltham, MA 02453, USA
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Luscher B, Fuchs T, Kilpatrick CL. GABAA receptor trafficking-mediated plasticity of inhibitory synapses. Neuron 2011; 70:385-409. [PMID: 21555068 DOI: 10.1016/j.neuron.2011.03.024] [Citation(s) in RCA: 316] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/30/2011] [Indexed: 12/22/2022]
Abstract
Proper developmental, neural cell-type-specific, and activity-dependent regulation of GABAergic transmission is essential for virtually all aspects of CNS function. The number of GABA(A) receptors in the postsynaptic membrane directly controls the efficacy of GABAergic synaptic transmission. Thus, regulated trafficking of GABA(A) receptors is essential for understanding brain function in both health and disease. Here we summarize recent progress in the understanding of mechanisms that allow dynamic adaptation of cell surface expression and postsynaptic accumulation and function of GABA(A) receptors. This includes activity-dependent and cell-type-specific changes in subunit gene expression, assembly of subunits into receptors, as well as exocytosis, endocytic recycling, diffusion dynamics, and degradation of GABA(A) receptors. In particular, we focus on the roles of receptor-interacting proteins, scaffold proteins, synaptic adhesion proteins, and enzymes that regulate the trafficking and function of receptors and associated proteins. In addition, we review neuropeptide signaling pathways that affect neural excitability through changes in GABA(A)R trafficking.
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Affiliation(s)
- Bernhard Luscher
- Department of Biology, Pennsylvania State University, University Park, PA 16802, USA.
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Papadopoulos T, Soykan T. The role of collybistin in gephyrin clustering at inhibitory synapses: facts and open questions. Front Cell Neurosci 2011; 5:11. [PMID: 21738498 PMCID: PMC3125517 DOI: 10.3389/fncel.2011.00011] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2011] [Accepted: 06/13/2011] [Indexed: 11/13/2022] Open
Abstract
Collybistin (Cb) is a brain-specific GDP/GTP-exchange factor, which interacts with the inhibitory receptor anchoring protein gephyrin. Data from mice carrying an inactivated Cb gene indicate that Cb is required for the formation and maintenance of gephyrin and gephyrin-dependent GABA(A) receptor (GABA(A)R) clusters at inhibitory postsynapses in selected regions of the mammalian forebrain. However, important aspects of how Cb's GDP/GTP-exchange activity, structure, and regulation contribute to gephyrin and GABA(A)R clustering, as well as its role in synaptic plasticity, remain poorly understood. Here we review the current state of knowledge about Cb's function and address open questions concerning its contribution to synapse formation, maintenance, plasticity, and adaptive changes in response to altered network activity.
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Affiliation(s)
- Theofilos Papadopoulos
- Department of Molecular Neurobiology, Max-Planck Institute of Experimental Medicine , Göttingen, Germany
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Sassoè-Pognetto M, Frola E, Pregno G, Briatore F, Patrizi A. Understanding the molecular diversity of GABAergic synapses. Front Cell Neurosci 2011; 5:4. [PMID: 21713106 PMCID: PMC3112311 DOI: 10.3389/fncel.2011.00004] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2011] [Accepted: 05/23/2011] [Indexed: 01/17/2023] Open
Abstract
GABAergic synapses exhibit a high degree of subcellular and molecular specialization, which contrasts with their apparent simplicity in ultrastructural appearance. Indeed, when observed in the electron microscope, GABAergic synapses fit in the symmetric, or Gray’s type II category, being characterized by a relatively simple postsynaptic specialization. The inhibitory postsynaptic density cannot be readily isolated, and progress in understanding its molecular composition has lagged behind that of excitatory synapses. However, recent studies have brought significant progress in the identification of new synaptic proteins, revealing an unexpected complexity in the molecular machinery that regulates GABAergic synaptogenesis. In this article, we provide an overview of the molecular diversity of GABAergic synapses, and we consider how synapse specificity may be encoded by selective trans-synaptic interactions between pre- and postsynaptic adhesion molecules and secreted factors that reside in the synaptic cleft. We also discuss the importance of developing cataloguing tools that could be used to decipher the molecular diversity of synapses and to predict alterations of inhibitory transmission in the course of neurological diseases.
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Affiliation(s)
- Marco Sassoè-Pognetto
- Department of Anatomy, Pharmacology and Forensic Medicine, University of Turin Torino, Italy
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