1
|
Altered Behavioral Responses Show GABA Sensitivity in Muscleblind-Like 2-Deficient Mice: Implications for CNS Symptoms in Myotonic Dystrophy. eNeuro 2022; 9:ENEURO.0218-22.2022. [PMID: 36150891 PMCID: PMC9557336 DOI: 10.1523/eneuro.0218-22.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Revised: 09/08/2022] [Accepted: 09/13/2022] [Indexed: 01/17/2023] Open
Abstract
Considerable evidence from mouse models and human postmortem brain suggests loss of Muscleblind-like protein 2 (MBNL2) function in brain is a major driver of CNS symptoms in Myotonic dystrophy type 1 (DM1). Increased hypersomnia, fatigue, and surgical complications associated with general anesthesia suggest possible sensitivity to GABAergic inhibition in DM1. To test the hypothesis that MBNL2 depletion leads to behavioral sensitivity to GABAA receptor (GABAA-R) modulation, Mbnl2 knock-out (KO) and wild-type (WT) littermates were treated with the anesthetic sevoflurane, the benzodiazepine diazepam, the imidazopyridine zolpidem, and the benzodiazepine rescue agent, flumazenil (Ro 15-1788), and assessed for various behavioral metrics. Mbnl2 KO mice exhibited delayed recovery following sevoflurane, delayed emergence and recovery from zolpidem, and enhanced sleep time at baseline that was modulated by flumazenil. A significantly higher proportion of Mbnl2 KO mice also loss their righting reflex [loss of righting reflex (LORR)] from a standard diazepam dose. We further examined whether MBNL2 depletion affects total GABAA-R mRNA subunit levels and validated RNA-sequencing data of mis-spliced Gabrg2, whose isoform ratios are known to regulate GABA sensitivity and associated behaviors. While no other GABAA-R subunit mRNA levels tested were altered in Mbnl2 KO mouse prefrontal cortex, Gabrg2S/L mRNA ratio levels were significantly altered. Taken together, our findings indicate that loss of MBNL2 function affects GABAergic function in a mouse model of myotonic dystrophy (DM1).
Collapse
|
2
|
Activation of the Rat α1β2ε GABA A Receptor by Orthosteric and Allosteric Agonists. Biomolecules 2022; 12:biom12070868. [PMID: 35883422 PMCID: PMC9312946 DOI: 10.3390/biom12070868] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Revised: 06/10/2022] [Accepted: 06/17/2022] [Indexed: 02/04/2023] Open
Abstract
GABAA receptors are a major contributor to fast inhibitory neurotransmission in the brain. The receptors are activated upon binding the transmitter GABA or allosteric agonists including a number of GABAergic anesthetics and neurosteroids. Functional receptors can be formed by various combinations of the nineteen GABAA subunits cloned to date. GABAA receptors containing the ε subunit exhibit a significant degree of constitutive activity and have been suggested to be unresponsive to allosteric agents. In this study, we have characterized the functional properties of the rat α1β2ε GABAA receptor. We confirm that the α1β2ε receptor exhibits a higher level of constitutive activity than typical of GABAA receptors and show that it is inefficaciously activated by the transmitter and the allosteric agonists propofol, pentobarbital, and allopregnanolone. Manipulations intended to alter ε subunit expression and receptor stoichiometry were largely without effect on receptor properties including sensitivity to GABA and allosteric agonists. Surprisingly, amino acid substitutions at the conserved 9' and 6' positions in the second transmembrane (TM2) domain in the ε subunit did not elicit the expected functional effects of increased constitutive activity and resistance to the channel blocker picrotoxin, respectively. We tested the accessibility of TM2 residues mutated to cysteine using the cysteine-modifying reagent 4-(hydroxymercuri)benzoic acid and found a unique pattern of water-accessible residues in the ε subunit.
Collapse
|
3
|
Potier B, Lallemant L, Parrot S, Huguet-Lachon A, Gourdon G, Dutar P, Gomes-Pereira M. DM1 Transgenic Mice Exhibit Abnormal Neurotransmitter Homeostasis and Synaptic Plasticity in Association with RNA Foci and Mis-Splicing in the Hippocampus. Int J Mol Sci 2022; 23:ijms23020592. [PMID: 35054778 PMCID: PMC8775431 DOI: 10.3390/ijms23020592] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2021] [Revised: 12/31/2021] [Accepted: 01/02/2022] [Indexed: 02/01/2023] Open
Abstract
Myotonic dystrophy type 1 (DM1) is a severe neuromuscular disease mediated by a toxic gain of function of mutant RNAs. The neuropsychological manifestations affect multiple domains of cognition and behavior, but their etiology remains elusive. Transgenic DMSXL mice carry the DM1 mutation, show behavioral abnormalities, and express low levels of GLT1, a critical regulator of glutamate concentration in the synaptic cleft. However, the impact of glutamate homeostasis on neurotransmission in DM1 remains unknown. We confirmed reduced glutamate uptake in the DMSXL hippocampus. Patch clamp recordings in hippocampal slices revealed increased amplitude of tonic glutamate currents in DMSXL CA1 pyramidal neurons and DG granule cells, likely mediated by higher levels of ambient glutamate. Unexpectedly, extracellular GABA levels and tonic current were also elevated in DMSXL mice. Finally, we found evidence of synaptic dysfunction in DMSXL mice, suggestive of abnormal short-term plasticity, illustrated by an altered LTP time course in DG and in CA1. Synaptic dysfunction was accompanied by RNA foci accumulation in localized areas of the hippocampus and by the mis-splicing of candidate genes with relevant functions in neurotransmission. Molecular and functional changes triggered by toxic RNA may induce synaptic abnormalities in restricted brain areas that favor neuronal dysfunction.
Collapse
Affiliation(s)
- Brigitte Potier
- LuMIn, CNRS FRE2036, ENS Paris-Saclay, CentraleSupelec, Université Paris-Saclay, 91190 Gif-sur-Yvette, France; (B.P.); (P.D.)
| | - Louison Lallemant
- Centre de Recherche en Myologie, Institut de Myologie, Inserm, Sorbonne Université, 75013 Paris, France; (L.L.); (A.H.-L.)
| | - Sandrine Parrot
- Lyon Neuroscience Research Center, Inserm U1028, CNRS UMR5292, Université Lyon 1, 69500 Bron, France;
| | - Aline Huguet-Lachon
- Centre de Recherche en Myologie, Institut de Myologie, Inserm, Sorbonne Université, 75013 Paris, France; (L.L.); (A.H.-L.)
| | - Geneviève Gourdon
- Centre de Recherche en Myologie, Institut de Myologie, Inserm, Sorbonne Université, 75013 Paris, France; (L.L.); (A.H.-L.)
- Correspondence: (G.G.); (M.G.-P.)
| | - Patrick Dutar
- LuMIn, CNRS FRE2036, ENS Paris-Saclay, CentraleSupelec, Université Paris-Saclay, 91190 Gif-sur-Yvette, France; (B.P.); (P.D.)
| | - Mário Gomes-Pereira
- Centre de Recherche en Myologie, Institut de Myologie, Inserm, Sorbonne Université, 75013 Paris, France; (L.L.); (A.H.-L.)
- Correspondence: (G.G.); (M.G.-P.)
| |
Collapse
|
4
|
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.
Collapse
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.
| |
Collapse
|
5
|
Castellano D, Shepard RD, Lu W. Looking for Novelty in an "Old" Receptor: Recent Advances Toward Our Understanding of GABA ARs and Their Implications in Receptor Pharmacology. Front Neurosci 2021; 14:616298. [PMID: 33519367 PMCID: PMC7841293 DOI: 10.3389/fnins.2020.616298] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2020] [Accepted: 12/14/2020] [Indexed: 12/16/2022] Open
Abstract
Diverse populations of GABAA receptors (GABAARs) throughout the brain mediate fast inhibitory transmission and are modulated by various endogenous ligands and therapeutic drugs. Deficits in GABAAR signaling underlie the pathophysiology behind neurological and neuropsychiatric disorders such as epilepsy, anxiety, and depression. Pharmacological intervention for these disorders relies on several drug classes that target GABAARs, such as benzodiazepines and more recently neurosteroids. It has been widely demonstrated that subunit composition and receptor stoichiometry impact the biophysical and pharmacological properties of GABAARs. However, current GABAAR-targeting drugs have limited subunit selectivity and produce their therapeutic effects concomitantly with undesired side effects. Therefore, there is still a need to develop more selective GABAAR pharmaceuticals, as well as evaluate the potential for developing next-generation drugs that can target accessory proteins associated with native GABAARs. In this review, we briefly discuss the effects of benzodiazepines and neurosteroids on GABAARs, their use as therapeutics, and some of the pitfalls associated with their adverse side effects. We also discuss recent advances toward understanding the structure, function, and pharmacology of GABAARs with a focus on benzodiazepines and neurosteroids, as well as newly identified transmembrane proteins that modulate GABAARs.
Collapse
Affiliation(s)
- David Castellano
- Synapse and Neural Circuit Research Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States
| | - Ryan David Shepard
- Synapse and Neural Circuit Research Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States
| | - Wei Lu
- Synapse and Neural Circuit Research Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States
| |
Collapse
|
6
|
Recurrent seizures cause immature brain injury and changes in GABA a receptor α1 and γ2 subunits. Epilepsy Res 2020; 163:106328. [DOI: 10.1016/j.eplepsyres.2020.106328] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2020] [Revised: 03/05/2020] [Accepted: 03/31/2020] [Indexed: 02/07/2023]
|
7
|
Stefanits H, Milenkovic I, Mahr N, Pataraia E, Baumgartner C, Hainfellner JA, Kovacs GG, Kasprian G, Sieghart W, Yilmazer-Hanke D, Czech T. Alterations in GABAA Receptor Subunit Expression in the Amygdala and Entorhinal Cortex in Human Temporal Lobe Epilepsy. J Neuropathol Exp Neurol 2020; 78:1022-1048. [PMID: 31631219 DOI: 10.1093/jnen/nlz085] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2019] [Revised: 07/06/2019] [Indexed: 12/14/2022] Open
Abstract
The amygdala has long been implicated in the pathophysiology of human temporal lobe epilepsy (TLE). The different nuclei of this complex structure are interconnected and share reciprocal connections with the hippocampus and other brain structures, partly via the entorhinal cortex. Expression of GABAA receptor subunits α1, α2, α3, α5, β2, β2/3, and γ2 was evaluated by immunohistochemistry in amygdala specimens and the entorhinal cortex of 12 TLE patients and 12 autopsy controls. A substantial decrease in the expression of α1, α2, α3, and β2/3 subunits was found in TLE cases, accompanied by an increase of γ2 subunit expression in many nuclei. In the entorhinal cortex, the expression of all GABAA receptor subunits was decreased except for the α1 subunit, which was increased on cellular somata. The overall reduction in α subunit expression may lead to decreased sensitivity to GABA and its ligands and compromise phasic inhibition, whereas upregulation of the γ2 subunit might influence clustering and kinetics of receptors and impair tonic inhibition. The description of these alterations in the human amygdala is important for the understanding of network changes in TLE as well as the development of subunit-specific therapeutic agents for the treatment of this disease.
Collapse
Affiliation(s)
- Harald Stefanits
- Department of Neurosurgery, Institute of Neurology, Department of Neurology, Department of Biomedical Imaging and Image Guided Therapy, Center for Brain Research, Department of Molecular Neurosciences, Medical University of Vienna, Vienna, Austria; Second Neurological Department, General Hospital Hietzing, Vienna, Austria; and Clinical Neuroanatomy, Neurology Department, Medical Faculty, Ulm University, Ulm, Germany
| | - Ivan Milenkovic
- Department of Neurosurgery, Institute of Neurology, Department of Neurology, Department of Biomedical Imaging and Image Guided Therapy, Center for Brain Research, Department of Molecular Neurosciences, Medical University of Vienna, Vienna, Austria; Second Neurological Department, General Hospital Hietzing, Vienna, Austria; and Clinical Neuroanatomy, Neurology Department, Medical Faculty, Ulm University, Ulm, Germany
| | - Nina Mahr
- Department of Neurosurgery, Institute of Neurology, Department of Neurology, Department of Biomedical Imaging and Image Guided Therapy, Center for Brain Research, Department of Molecular Neurosciences, Medical University of Vienna, Vienna, Austria; Second Neurological Department, General Hospital Hietzing, Vienna, Austria; and Clinical Neuroanatomy, Neurology Department, Medical Faculty, Ulm University, Ulm, Germany
| | - Ekaterina Pataraia
- Department of Neurosurgery, Institute of Neurology, Department of Neurology, Department of Biomedical Imaging and Image Guided Therapy, Center for Brain Research, Department of Molecular Neurosciences, Medical University of Vienna, Vienna, Austria; Second Neurological Department, General Hospital Hietzing, Vienna, Austria; and Clinical Neuroanatomy, Neurology Department, Medical Faculty, Ulm University, Ulm, Germany
| | - Christoph Baumgartner
- Department of Neurosurgery, Institute of Neurology, Department of Neurology, Department of Biomedical Imaging and Image Guided Therapy, Center for Brain Research, Department of Molecular Neurosciences, Medical University of Vienna, Vienna, Austria; Second Neurological Department, General Hospital Hietzing, Vienna, Austria; and Clinical Neuroanatomy, Neurology Department, Medical Faculty, Ulm University, Ulm, Germany
| | - Johannes A Hainfellner
- Department of Neurosurgery, Institute of Neurology, Department of Neurology, Department of Biomedical Imaging and Image Guided Therapy, Center for Brain Research, Department of Molecular Neurosciences, Medical University of Vienna, Vienna, Austria; Second Neurological Department, General Hospital Hietzing, Vienna, Austria; and Clinical Neuroanatomy, Neurology Department, Medical Faculty, Ulm University, Ulm, Germany
| | - Gabor G Kovacs
- Department of Neurosurgery, Institute of Neurology, Department of Neurology, Department of Biomedical Imaging and Image Guided Therapy, Center for Brain Research, Department of Molecular Neurosciences, Medical University of Vienna, Vienna, Austria; Second Neurological Department, General Hospital Hietzing, Vienna, Austria; and Clinical Neuroanatomy, Neurology Department, Medical Faculty, Ulm University, Ulm, Germany
| | - Gregor Kasprian
- Department of Neurosurgery, Institute of Neurology, Department of Neurology, Department of Biomedical Imaging and Image Guided Therapy, Center for Brain Research, Department of Molecular Neurosciences, Medical University of Vienna, Vienna, Austria; Second Neurological Department, General Hospital Hietzing, Vienna, Austria; and Clinical Neuroanatomy, Neurology Department, Medical Faculty, Ulm University, Ulm, Germany
| | - Werner Sieghart
- Department of Neurosurgery, Institute of Neurology, Department of Neurology, Department of Biomedical Imaging and Image Guided Therapy, Center for Brain Research, Department of Molecular Neurosciences, Medical University of Vienna, Vienna, Austria; Second Neurological Department, General Hospital Hietzing, Vienna, Austria; and Clinical Neuroanatomy, Neurology Department, Medical Faculty, Ulm University, Ulm, Germany
| | - Deniz Yilmazer-Hanke
- Department of Neurosurgery, Institute of Neurology, Department of Neurology, Department of Biomedical Imaging and Image Guided Therapy, Center for Brain Research, Department of Molecular Neurosciences, Medical University of Vienna, Vienna, Austria; Second Neurological Department, General Hospital Hietzing, Vienna, Austria; and Clinical Neuroanatomy, Neurology Department, Medical Faculty, Ulm University, Ulm, Germany
| | - Thomas Czech
- Department of Neurosurgery, Institute of Neurology, Department of Neurology, Department of Biomedical Imaging and Image Guided Therapy, Center for Brain Research, Department of Molecular Neurosciences, Medical University of Vienna, Vienna, Austria; Second Neurological Department, General Hospital Hietzing, Vienna, Austria; and Clinical Neuroanatomy, Neurology Department, Medical Faculty, Ulm University, Ulm, Germany
| |
Collapse
|
8
|
Sieghart W, Savić MM. International Union of Basic and Clinical Pharmacology. CVI: GABAA Receptor Subtype- and Function-selective Ligands: Key Issues in Translation to Humans. Pharmacol Rev 2018; 70:836-878. [DOI: 10.1124/pr.117.014449] [Citation(s) in RCA: 105] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
|
9
|
Lorenz-Guertin JM, Bambino MJ, Jacob TC. γ2 GABA AR Trafficking and the Consequences of Human Genetic Variation. Front Cell Neurosci 2018; 12:265. [PMID: 30190672 PMCID: PMC6116786 DOI: 10.3389/fncel.2018.00265] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2018] [Accepted: 08/02/2018] [Indexed: 11/13/2022] Open
Abstract
GABA type A receptors (GABAARs) mediate the majority of fast inhibitory neurotransmission in the central nervous system (CNS). Most prevalent as heteropentamers composed of two α, two β, and a γ2 subunit, these ligand-gated ionotropic chloride channels are capable of extensive genetic diversity (α1-6, β1-3, γ1-3, δ, 𝜀, 𝜃, π, ρ1-3). Part of this selective GABAAR assembly arises from the critical role for γ2 in maintaining synaptic receptor localization and function. Accordingly, mutations in this subunit account for over half of the known epilepsy-associated genetic anomalies identified in GABAARs. Fundamental structure-function studies and cellular pathology investigations have revealed dynamic GABAAR trafficking and synaptic scaffolding as critical regulators of GABAergic inhibition. Here, we introduce in vitro and in vivo findings regarding the specific role of the γ2 subunit in receptor trafficking. We then examine γ2 subunit human genetic variation and assess disease related phenotypes and the potential role of altered GABAAR trafficking. Finally, we discuss new-age imaging techniques and their potential to provide novel insight into critical regulatory mechanisms of GABAAR function.
Collapse
Affiliation(s)
- Joshua M Lorenz-Guertin
- Department of Pharmacology and Chemical Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Matthew J Bambino
- Department of Pharmacology and Chemical Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Tija C Jacob
- Department of Pharmacology and Chemical Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| |
Collapse
|
10
|
Kisiel M, Jatczak M, Brodzki M, Mozrzymas JW. Spontaneous activity, singly bound states and the impact of alpha 1Phe64 mutation on GABA AR gating in the novel kinetic model based on the single-channel recordings. Neuropharmacology 2017; 131:453-474. [PMID: 29162430 DOI: 10.1016/j.neuropharm.2017.11.030] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2017] [Revised: 10/25/2017] [Accepted: 11/17/2017] [Indexed: 12/31/2022]
Abstract
GABAA receptor is the primary mediator of inhibition in the adult mammalian brain. Our recent studies revealed that a classic gating scheme for GABAAR needed to be updated with an intermediate step (flipping) and that the α1Phe64 mutation at the GABA binding site affects this transition. However, description of flipping at the single-channel level remains incomplete. In particular, its role in singly-bound and spontaneous activity remains unknown. We have performed thus single-channel recordings over wide range of agonist concentration for wild-type α1β2γ2L receptors and α1Phe64 mutants. For WT receptors we observed relatively frequent brief spontaneous openings which were also present at low [GABA]. However, closed times distributions for spontaneous activity and at low [GABA] were clearly different indicating that a proportion of short-lived openings were due to liganded, most likely singly bound receptors. Increasing [GABA] resulted in prolongation of bursts and increased occurrence of bursts with long openings and short closures. Mutations of α1Phe64 residue dramatically affected the open and closed time distributions at high and saturating [GABA], especially in the case of cysteine mutants. However, this mutation weakly affected spontaneous or singly bound activity. Model fitting of our single-channel data led us to propose a novel and, to our knowledge, most complete GABAAR kinetic model in which flipping occurs in singly and doubly bound states. However, spontaneous activity did not reveal involvement of flipping. Moreover, we report that α1Phe64 mutation affects not only the flipping but also the opening/closing transitions indicating its generalized impact on the receptor gating.
Collapse
Affiliation(s)
- Magdalena Kisiel
- Laboratory of Neuroscience, Department of Biophysics, Wrocław Medical University, Wrocław 50-368, Poland.
| | - Magdalena Jatczak
- Laboratory of Neuroscience, Department of Biophysics, Wrocław Medical University, Wrocław 50-368, Poland; Department of Physiology and Molecular Neurobiology, Wrocław University, Wrocław 50-335, Poland
| | - Marek Brodzki
- Laboratory of Neuroscience, Department of Biophysics, Wrocław Medical University, Wrocław 50-368, Poland; Department of Physiology and Molecular Neurobiology, Wrocław University, Wrocław 50-335, Poland
| | - Jerzy W Mozrzymas
- Laboratory of Neuroscience, Department of Biophysics, Wrocław Medical University, Wrocław 50-368, Poland.
| |
Collapse
|
11
|
Wang HY, Sun J, Xia LY, Li YH, Chen Z, Wu FG. Permeabilization-Tolerant Plasma Membrane Imaging Reagent Based on Amine-Rich Glycol Chitosan Derivatives. ACS Biomater Sci Eng 2017; 3:2570-2578. [DOI: 10.1021/acsbiomaterials.7b00448] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Hong-Yin Wang
- State
Key Laboratory of Bioelectronics, School of Biological Science and
Medical Engineering, Southeast University, 2 Sipailou Road, Nanjing 210096, P. R. China
| | - Jie Sun
- State
Key Laboratory of Bioelectronics, School of Biological Science and
Medical Engineering, Southeast University, 2 Sipailou Road, Nanjing 210096, P. R. China
| | - Liu-Yuan Xia
- State
Key Laboratory of Bioelectronics, School of Biological Science and
Medical Engineering, Southeast University, 2 Sipailou Road, Nanjing 210096, P. R. China
| | - Yan-Hong Li
- State
Key Laboratory of Bioelectronics, School of Biological Science and
Medical Engineering, Southeast University, 2 Sipailou Road, Nanjing 210096, P. R. China
| | - Zhan Chen
- Department
of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
| | - Fu-Gen Wu
- State
Key Laboratory of Bioelectronics, School of Biological Science and
Medical Engineering, Southeast University, 2 Sipailou Road, Nanjing 210096, P. R. China
| |
Collapse
|
12
|
Taylor-Wells J, Hawkins J, Colombo C, Bermudez I, Jones AK. Cloning and functional expression of intracellular loop variants of the honey bee (Apis mellifera) RDL GABA receptor. Neurotoxicology 2017; 60:207-213. [DOI: 10.1016/j.neuro.2016.06.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Revised: 05/26/2016] [Accepted: 06/07/2016] [Indexed: 01/20/2023]
|
13
|
Hung KL, Liang JS, Wang JS, Chen HJ, Lin LJ, Lu JF. Association of a novel GABRG2 splicing variation and a PTGS2/COX-2 single nucleotide polymorphism with Taiwanese febrile seizures. Epilepsy Res 2017; 129:1-7. [DOI: 10.1016/j.eplepsyres.2016.11.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Revised: 11/07/2016] [Accepted: 11/12/2016] [Indexed: 01/20/2023]
|
14
|
Mutagenesis and computational docking studies support the existence of a histamine binding site at the extracellular β3+β3− interface of homooligomeric β3 GABA A receptors. Neuropharmacology 2016; 108:252-63. [DOI: 10.1016/j.neuropharm.2016.04.042] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Revised: 04/06/2016] [Accepted: 04/28/2016] [Indexed: 12/31/2022]
|
15
|
Botzolakis EJ, Gurba KN, Lagrange AH, Feng HJ, Stanic AK, Hu N, Macdonald RL. Comparison of γ-Aminobutyric Acid, Type A (GABAA), Receptor αβγ and αβδ Expression Using Flow Cytometry and Electrophysiology: EVIDENCE FOR ALTERNATIVE SUBUNIT STOICHIOMETRIES AND ARRANGEMENTS. J Biol Chem 2016; 291:20440-61. [PMID: 27493204 DOI: 10.1074/jbc.m115.698860] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Indexed: 01/23/2023] Open
Abstract
The subunit stoichiometry and arrangement of synaptic αβγ GABAA receptors are generally accepted as 2α:2β:1γ with a β-α-γ-β-α counterclockwise configuration, respectively. Whether extrasynaptic αβδ receptors adopt the analogous β-α-δ-β-α subunit configuration remains controversial. Using flow cytometry, we evaluated expression levels of human recombinant γ2 and δ subunits when co-transfected with α1 and/or β2 subunits in HEK293T cells. Nearly identical patterns of γ2 and δ subunit expression were observed as follows: both required co-transfection with α1 and β2 subunits for maximal expression; both were incorporated into receptors primarily at the expense of β2 subunits; and both yielded similar FRET profiles when probed for subunit adjacency, suggesting similar underlying subunit arrangements. However, because of a slower rate of δ subunit degradation, 10-fold less δ subunit cDNA was required to recapitulate γ2 subunit expression patterns and to eliminate the functional signature of α1β2 receptors. Interestingly, titrating γ2 or δ subunit cDNA levels progressively altered GABA-evoked currents, revealing more than one kinetic profile for both αβγ and αβδ receptors. This raised the possibility of alternative receptor isoforms, a hypothesis confirmed using concatameric constructs for αβγ receptors. Taken together, our results suggest a limited cohort of alternative subunit arrangements in addition to canonical β-α-γ/δ-β-α receptors, including β-α-γ/δ-α-α receptors at lower levels of γ2/δ expression and β-α-γ/δ-α-γ/δ receptors at higher levels of expression. These findings provide important insight into the role of GABAA receptor subunit under- or overexpression in disease states such as genetic epilepsies.
Collapse
Affiliation(s)
| | | | - Andre H Lagrange
- the Departments of Neurology, Pharmacology, and the Veterans Affairs Tennessee Valley Healthcare System, Nashville, Tennessee 37212, and
| | | | - Aleksandar K Stanic
- the Department of Obstetrics and Gynecology, University of Wisconsin, Madison, Wisconsin 53792
| | | | - Robert L Macdonald
- the Departments of Neurology, Pharmacology, and Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee 37240-7915,
| |
Collapse
|
16
|
Wang HY, Hua XW, Jia HR, Li C, Lin F, Chen Z, Wu FG. Universal Cell Surface Imaging for Mammalian, Fungal, and Bacterial Cells. ACS Biomater Sci Eng 2016; 2:987-997. [DOI: 10.1021/acsbiomaterials.6b00130] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- Hong-Yin Wang
- State
Key Laboratory of Bioelectronics, School of Biological Science and
Medical Engineering, Southeast University, Nanjing 210096, P. R. China
| | - Xian-Wu Hua
- State
Key Laboratory of Bioelectronics, School of Biological Science and
Medical Engineering, Southeast University, Nanjing 210096, P. R. China
| | - Hao-Ran Jia
- State
Key Laboratory of Bioelectronics, School of Biological Science and
Medical Engineering, Southeast University, Nanjing 210096, P. R. China
| | - Chengcheng Li
- State
Key Laboratory of Bioelectronics, School of Biological Science and
Medical Engineering, Southeast University, Nanjing 210096, P. R. China
| | - Fengming Lin
- State
Key Laboratory of Bioelectronics, School of Biological Science and
Medical Engineering, Southeast University, Nanjing 210096, P. R. China
| | - Zhan Chen
- Department
of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan, United States
| | - Fu-Gen Wu
- State
Key Laboratory of Bioelectronics, School of Biological Science and
Medical Engineering, Southeast University, Nanjing 210096, P. R. China
| |
Collapse
|
17
|
Brodzki M, Rutkowski R, Jatczak M, Kisiel M, Czyzewska MM, Mozrzymas JW. Comparison of kinetic and pharmacological profiles of recombinant α1γ2L and α1β2γ2L GABAA receptors - A clue to the role of intersubunit interactions. Eur J Pharmacol 2016; 784:81-9. [PMID: 27179992 DOI: 10.1016/j.ejphar.2016.05.015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2015] [Revised: 05/10/2016] [Accepted: 05/10/2016] [Indexed: 11/25/2022]
Abstract
The fastest inhibitory mechanism in the CNS is mediated by ionotropic GABAA receptors and it is known that subunit composition critically determines their properties. While a typical GABAA receptor consists of two α, two β and one γ/δ subunit, there are some exceptions, e.g. αβ receptors. Functional α1γ2 GABAA receptors can be expressed in recombinant model (Verdoorn et al., 1990) and although their role remains unknown, it seems appealing to extend their characterization to further explore the structure-function relationship of GABAA receptors. Intriguingly, this receptor is lacking canonical GABA binding sites but it can be activated by GABA and dose-response relationships for α1β2γ2L and α1γ2L receptors overlap. Deactivation kinetics was similar for both receptors but the percentage of the fast component was smaller in the case of α1γ2L receptors and, consequently, the mean deactivation time constant was slower. The rate and extent of macroscopic desensitization were smaller in the case of α1γ2L receptors but they showed slower recovery. Both receptor types had a similar proton sensitivity showing only subtle but significant differences in pH effects on deactivation. Flurazepam exerted a similar effect on both receptors but the rapid deactivation components were differently affected and an opposite effect was observed on desensitization extent. Rebound currents evoked by pentobarbital were undistinguishable for both receptor types. Taking altogether, although some significant differences were found, α1β2γ2L and α1γ2L receptors showed unforeseen similarity. We propose that functioning of GABAA receptors might rely on subunit-subunit cooperative interactions to a larger extent than believed so far.
Collapse
Affiliation(s)
- Marek Brodzki
- Laboratory of Neuroscience, Department of Biophysics, Wrocław Medical University, ul. Chałubińskiego 3, 50-358 Wrocław, Poland; Department of Animal Molecular Physiology, Institute of Experimental Biology, University of Wrocław, ul. Cybulskiego 30, 50-205 Wrocław, Poland.
| | - Radoslaw Rutkowski
- Laboratory of Neuroscience, Department of Biophysics, Wrocław Medical University, ul. Chałubińskiego 3, 50-358 Wrocław, Poland
| | - Magdalena Jatczak
- Laboratory of Neuroscience, Department of Biophysics, Wrocław Medical University, ul. Chałubińskiego 3, 50-358 Wrocław, Poland; Department of Animal Molecular Physiology, Institute of Experimental Biology, University of Wrocław, ul. Cybulskiego 30, 50-205 Wrocław, Poland
| | - Magdalena Kisiel
- Laboratory of Neuroscience, Department of Biophysics, Wrocław Medical University, ul. Chałubińskiego 3, 50-358 Wrocław, Poland
| | - Marta M Czyzewska
- Laboratory of Neuroscience, Department of Biophysics, Wrocław Medical University, ul. Chałubińskiego 3, 50-358 Wrocław, Poland
| | - Jerzy W Mozrzymas
- Laboratory of Neuroscience, Department of Biophysics, Wrocław Medical University, ul. Chałubińskiego 3, 50-358 Wrocław, Poland; Department of Animal Molecular Physiology, Institute of Experimental Biology, University of Wrocław, ul. Cybulskiego 30, 50-205 Wrocław, Poland
| |
Collapse
|
18
|
Nakamura T, Arima-Yoshida F, Sakaue F, Nasu-Nishimura Y, Takeda Y, Matsuura K, Akshoomoff N, Mattson SN, Grossfeld PD, Manabe T, Akiyama T. PX-RICS-deficient mice mimic autism spectrum disorder in Jacobsen syndrome through impaired GABAA receptor trafficking. Nat Commun 2016; 7:10861. [PMID: 26979507 PMCID: PMC4799364 DOI: 10.1038/ncomms10861] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Accepted: 01/27/2016] [Indexed: 11/09/2022] Open
Abstract
Jacobsen syndrome (JBS) is a rare congenital disorder caused by a terminal deletion of the long arm of chromosome 11. A subset of patients exhibit social behavioural problems that meet the diagnostic criteria for autism spectrum disorder (ASD); however, the underlying molecular pathogenesis remains poorly understood. PX-RICS is located in the chromosomal region commonly deleted in JBS patients with autistic-like behaviour. Here we report that PX-RICS-deficient mice exhibit ASD-like social behaviours and ASD-related comorbidities. PX-RICS-deficient neurons show reduced surface γ-aminobutyric acid type A receptor (GABAAR) levels and impaired GABAAR-mediated synaptic transmission. PX-RICS, GABARAP and 14-3-3ζ/θ form an adaptor complex that interconnects GABAAR and dynein/dynactin, thereby facilitating GABAAR surface expression. ASD-like behavioural abnormalities in PX-RICS-deficient mice are ameliorated by enhancing inhibitory synaptic transmission with a GABAAR agonist. Our findings demonstrate a critical role of PX-RICS in cognition and suggest a causal link between PX-RICS deletion and ASD-like behaviour in JBS patients.
Collapse
Affiliation(s)
- Tsutomu Nakamura
- Laboratory of Molecular and Genetic Information, Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan
| | - Fumiko Arima-Yoshida
- Division of Neuronal Network, Department of Basic Medical Sciences, Institute of Medical Science, The University of Tokyo, Minato-ku, Tokyo 108-8639, Japan
| | - Fumika Sakaue
- Laboratory of Molecular and Genetic Information, Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan
| | - Yukiko Nasu-Nishimura
- Laboratory of Molecular and Genetic Information, Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan
| | - Yasuko Takeda
- Laboratory of Molecular and Genetic Information, Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan
| | - Ken Matsuura
- Laboratory of Molecular and Genetic Information, Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan
| | - Natacha Akshoomoff
- Department of Psychiatry, School of Medicine, University of California, San Diego, La Jolla, California 92093, USA
| | - Sarah N Mattson
- Department of Psychology, San Diego State University, San Diego, California 92120, USA
| | - Paul D Grossfeld
- Department of Pediatrics, School of Medicine, University of California, San Diego, San Diego, California 92123, USA
| | - Toshiya Manabe
- Division of Neuronal Network, Department of Basic Medical Sciences, Institute of Medical Science, The University of Tokyo, Minato-ku, Tokyo 108-8639, Japan
| | - Tetsu Akiyama
- Laboratory of Molecular and Genetic Information, Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan
| |
Collapse
|
19
|
Stojanovic T, Capo I, Aronica E, Adle-Biassette H, Höger H, Sieghart W, Kovacs GG, Milenkovic I. The α1, α2, α3, and γ2 subunits of GABAA receptors show characteristic spatial and temporal expression patterns in rhombencephalic structures during normal human brain development. J Comp Neurol 2015; 524:1805-24. [PMID: 26518133 DOI: 10.1002/cne.23923] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2015] [Revised: 10/24/2015] [Accepted: 10/28/2015] [Indexed: 01/13/2023]
Abstract
γ-Aminobutyric acid (GABA) is the most abundant inhibitory neurotransmitter in adult mammalian brain, mediating its actions chiefly via a pentameric chloride ion channel, the GABAA receptor. Nineteen different subunits (α1-6, β1-3, γ1-3, δ, ε, π, θ, ρ1-3) can give rise to multiple receptor subtypes that are the site of action of many clinically important drugs. In the developing brain, however, GABAA receptors mediate excitatory actions due to an increased chloride concentration within neurons and seem to control cell proliferation, migration, differentiation, synapse maturation, and cell death. Little is known about the distribution of single subunits in the human brain. Here we describe developmental changes in the immunohistochemical distribution of four subunits (α1, α2, α3, and γ2) in the human rhombencephalon. The γ2 was the most abundant subunit in all rhombencephalic structures during development and in adults, whereas α subunits showed a structure- and age-characteristic distribution. The α1 was expressed prenatally in the molecular and Purkinje cell layer, but only postnatally in the granule cell layer and the dentate nucleus. Expression was completely absent in the inferior olivary nucleus. The α2 gradually increased during development, showing some layer specificity in the cerebellar cortex. The α3-immunoreactivity in the cerebellar cortex was relatively weak, but it was abundantly observed in different cell populations in the subcortical cerebellar structures. Structure- and age-characteristic colocalization between subunits during development suggests differences in GABAA receptor composition. Interestingly, subunit expression in several instances differed between human and rodent brain, underlining the importance of immunohistochemical studies in humans.
Collapse
Affiliation(s)
- Tamara Stojanovic
- Institute of Neurology, Neurodegeneration Research Group, Medical University of Vienna, Vienna, Austria
| | - Ivan Capo
- Department of Histology and Embryology, Medical Faculty, Vojvodina, Serbia
| | - Eleonora Aronica
- Department of (Neuro)Pathology, Academic Medical Center, University of Amsterdam, The Netherlands; SEIN - Stichting Epilepsie Instellingen Nederland, Heemstede, The Netherlands; Swammerdam Institute for Life Sciences, Center for Neuroscience, University of Amsterdam, The Netherlands
| | - Homa Adle-Biassette
- Inserm U1141, Paris, France; Univ. Paris Diderot, Sorbonne Paris Cité, UMRS 676, Paris, France, Department of Pathology, Lariboisière Hospital, APHP, Paris, France
| | - Harald Höger
- Division of Laboratory Animal Science and Genetics, Medical University of Vienna, Vienna, Austria
| | - Werner Sieghart
- Department of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - Gabor G Kovacs
- Institute of Neurology, Neurodegeneration Research Group, Medical University of Vienna, Vienna, Austria
| | - Ivan Milenkovic
- Institute of Neurology, Neurodegeneration Research Group, Medical University of Vienna, Vienna, Austria.,Department of Neurology, Medical University of Vienna, Vienna, Austria
| |
Collapse
|
20
|
Zai CC, Zai GC, Tiwari AK, Manchia M, de Luca V, Shaikh SA, Strauss J, Kennedy JL. Association study of GABRG2 polymorphisms with suicidal behaviour in schizophrenia patients with alcohol use disorder. Neuropsychobiology 2015; 69:154-8. [PMID: 24776921 DOI: 10.1159/000358839] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Accepted: 01/20/2014] [Indexed: 11/19/2022]
Abstract
BACKGROUND Schizophrenia is a severe neuropsychiatric disorder where the role of γ-aminobutyric acid (GABA), an inhibitory neurotransmitter, has been implicated in its aetiopathophysiology. Several genes coding for GABAA subunits, including the GABRG2 gene that encodes the γ2 subunit, are clustered at 5q31-q35, a chromosomal region that is associated with schizophrenia in genome scan studies. We recently reported GABRG2 to be associated with schizophrenia in our case-control and family samples. METHODS We tested eight single-nucleotide polymorphisms spanning the GABRG2 gene for an association with suicidal behaviour in our schizophrenia sample of European ancestry (n = 197), taking into account history of alcohol abuse or dependence. RESULTS We found the haplotypes of the rs183294 and rs209356 markers to be significantly associated with history of suicide attempt (p < 0.01) as well as suicide specifier scores (p < 0.05). The association appeared to be originating in patients with a history of alcohol dependence or abuse. CONCLUSIONS Taken together, the results of the present study suggest that GABRG2 may be involved in suicidal behaviour in schizophrenia patients with alcohol dependence or abuse, but replications are required. These results may help in the discovery of novel treatments for alcoholism and/or prevention of suicide.
Collapse
Affiliation(s)
- Clement C Zai
- Neurogenetics Section, Neuroscience Research Department, Centre for Addiction and Mental Health, Toronto, Ont., Canada
| | | | | | | | | | | | | | | |
Collapse
|
21
|
Three epilepsy-associated GABRG2 missense mutations at the γ+/β- interface disrupt GABAA receptor assembly and trafficking by similar mechanisms but to different extents. Neurobiol Dis 2014; 68:167-79. [PMID: 24798517 DOI: 10.1016/j.nbd.2014.04.015] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2014] [Revised: 04/22/2014] [Accepted: 04/25/2014] [Indexed: 11/23/2022] Open
Abstract
We compared the effects of three missense mutations in the GABAA receptor γ2 subunit on GABAA receptor assembly, trafficking and function in HEK293T cells cotransfected with α1, β2, and wildtype or mutant γ2 subunits. The mutations R82Q and P83S were identified in families with genetic epilepsy with febrile seizures plus (GEFS+), and N79S was found in a single patient with generalized tonic-clonic seizures (GTCS). Although all three mutations were located in an N-terminal loop that contributes to the γ+/β- subunit-subunit interface, we found that each mutation impaired GABAA receptor assembly to a different extent. The γ2(R82Q) and γ2(P83S) subunits had reduced α1β2γ2 receptor surface expression due to impaired assembly into pentamers, endoplasmic reticulum (ER) retention and degradation. In contrast, γ2(N79S) subunits were efficiently assembled into GABAA receptors with only minimally altered receptor trafficking, suggesting that N79S was a rare or susceptibility variant rather than an epilepsy mutation. Increased structural variability at assembly motifs was predicted by R82Q and P83S, but not N79S, substitution, suggesting that R82Q and P83S substitutions were less tolerated. Membrane proteins with missense mutations that impair folding and assembly often can be "rescued" by decreased temperatures. We coexpressed wildtype or mutant γ2 subunits with α1 and β2 subunits and found increased surface and total levels of both wildtype and mutant γ2 subunits after decreasing the incubation temperature to 30°C for 24h, suggesting that lower temperatures increased GABAA receptor stability. Thus epilepsy-associated mutations N79S, R82Q and P83S disrupted GABAA receptor assembly to different extents, an effect that could be potentially rescued by facilitating protein folding and assembly.
Collapse
|
22
|
Denman RB, Xie W, Merz G, Sung YJ. GABAAergic stimulation modulates intracellular protein arginine methylation. Neurosci Lett 2014; 572:38-43. [PMID: 24793772 DOI: 10.1016/j.neulet.2014.04.036] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2014] [Revised: 03/26/2014] [Accepted: 04/22/2014] [Indexed: 10/25/2022]
Abstract
Changes in cytoplasmic pH are known to regulate diverse cellular processes and influence neuronal activities. In neurons, the intracellular alkalization is shown to occur after stimulating several channels and receptors. For example, it has previously demonstrated in P19 neurons that a sustained intracellular alkalinization can be mediated by the Na(+)/H(+) antiporter. In addition, the benzodiazepine binding subtypes of the γ-amino butyric acid type A (GABAA) receptor mediate a transient intracellular alkalinization when they are stimulated. Because the activities of many enzymes are sensitive to pH shift, here we investigate the effects of intracellular pH modulation resulted from stimulating GABAA receptor on the protein arginine methyltransferases (PRMT) activities. We show that the major benzodiazepine subtype (2α1, 2β2, 1γ2) is constitutively expressed in both undifferentiated P19 cells and retinoic acid (RA) differentiated P19 neurons. Furthermore stimulation with diazepam and, diazepam plus muscimol produce an intracellular alkalinization that can be detected ex vivo with the fluorescence dye. The alkalinization results in significant perturbation in protein arginine methylation activity as measured in methylation assays with specific protein substrates. Altered protein arginine methylation is also observed when cells are treated with the GABAA agonist muscimol but not an antagonist, bicuculline. These data suggest that pH-dependent and pH-independent methylation pathways can be activated by GABAAergic stimulation, which we verified using hippocampal slice preparations from a mouse model of fragile X syndrome.
Collapse
Affiliation(s)
- Robert B Denman
- Department of Molecular Biology, New York State Institute for Basic Research in Developmental Disabilities, 1050 Forest Hill Road, Staten Island, New York, NY 10314, USA
| | - Wen Xie
- Division of Hematology and Medical Oncology, Department of Medicine, Weill Medical College of Cornell University, New York, NY 1065, USA
| | - George Merz
- Department of Developmental Neurobiology, New York State Institute for Basic Research in Developmental Disabilities, 1050 Forest Hill Road, Staten Island, New York, NY 10314, USA
| | - Ying-Ju Sung
- Department of Basic Sciences, The Commonwealth Medical College, 525 Pine Street, Scranton, PA 18509, USA.
| |
Collapse
|
23
|
Monoterpene α-thujone exerts a differential inhibitory action on GABA(A) receptors implicated in phasic and tonic GABAergic inhibition. Eur J Pharmacol 2013; 702:38-43. [PMID: 23376563 DOI: 10.1016/j.ejphar.2013.01.032] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2012] [Revised: 01/08/2013] [Accepted: 01/16/2013] [Indexed: 11/22/2022]
Abstract
A monoterpene ketone, α-thujone originally attracted attention as a major natural ingredient of absinthe and was suspected to cause adverse effects such as hallucinations and seizures in persons excessively consuming this beverage. Although subsequent studies ruled out any major role of α-thujone in the "absynthism", it was found that at high doses it may induce epileptic activity pointing to an interaction with GABAergic inhibition. Indeed, subsequent studies, including those from this laboratory, showed that α-thujone inhibits GABAergic currents. However, GABAA receptors are extremely heterogeneous and in the present study we have investigated the effect of α-thujone on different recombinant GABAA receptors (α1β2γ2L, α1β2, α1β2δ and α4β2δ) relevant to phasic or tonic forms of inhibition. We report that α-thujone inhibits all considered receptor types by a qualitatively similar mechanism but the strongest effect is observed for α1β2δ receptors, suggesting that tonic currents might be more sensitive to α-thujone than the phasic ones. Moreover, we demonstrate that tonic currents, mimicked by response to a submicromollar GABA concentration (0.3 μM) in cultured neurons, showed a substantially larger sensitivity to α-thujone than responses elicited by higher [GABA] (more similar to phasic currents) or Inhibitory Postsynaptic Currents in the same preparation. Importantly, the extent of tonic current inhibition by α-thujone was as strong as in the case of currents mediated by α1β2δ receptors. Altogether, these data provide evidence that different GABAA receptor subtypes show distinct sensitivities to α-thujone and suggest that this compound may differentially affect tonic and phasic components of GABAergic inhibition.
Collapse
|
24
|
Verdurand M, Fillman SG, Shannon Weickert C, Zavitsanou K. Increases in [3H]muscimol and [3H]flumazenil binding in the dorsolateral prefrontal cortex in schizophrenia are linked to α4 and γ2S mRNA levels respectively. PLoS One 2013; 8:e52724. [PMID: 23320076 PMCID: PMC3540049 DOI: 10.1371/journal.pone.0052724] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2012] [Accepted: 11/21/2012] [Indexed: 11/30/2022] Open
Abstract
Background GABAA receptors (GABAAR) are composed of several subunits that determine sensitivity to drugs, synaptic localisation and function. Recent studies suggest that agonists targeting selective GABAAR subunits may have therapeutic value against the cognitive impairments observed in schizophrenia. In this study, we determined whether GABAAR binding deficits exist in the dorsolateral prefrontal cortex (DLPFC) of people with schizophrenia and tested if changes in GABAAR binding are related to the changes in subunit mRNAs. The GABA orthosteric and the benzodiazepine allosteric binding sites were assessed autoradiographically using [3H]Muscimol and [3H]Flumazenil, respectively, in a large cohort of individuals with schizophrenia (n = 37) and their matched controls (n = 37). We measured, using qPCR, mRNA of β (β1, β2, β3), γ (γ1, γ2, γ2S for short and γ2L for long isoform, γ3) and δ subunits and used our previous measurements of GABAAR α subunit mRNAs in order to relate mRNAs and binding through correlation and regression analysis. Results Significant increases in both [3H]Muscimol (p = 0.016) and [3H]Flumazenil (p = 0.012) binding were found in the DLPFC of schizophrenia patients. Expression levels of mRNA subunits measured did not show any significant difference in schizophrenia compared to controls. Regression analysis revealed that in schizophrenia, the [3H]Muscimol binding variance was most related to α4 mRNA levels and the [3H]Flumazenil binding variance was most related to γ2S subunit mRNA levels. [3H]Muscimol and [3H]Flumazenil binding were not affected by the lifetime anti-psychotics dose (chlorpromazine equivalent). Conclusions We report parallel increases in orthosteric and allosteric GABAAR binding sites in the DLPFC in schizophrenia that may be related to a “shift” in subunit composition towards α4 and γ2S respectively, which may compromise normal GABAergic modulation and function. Our results may have implications for the development of treatment strategies that target specific GABAAR receptor subunits.
Collapse
Affiliation(s)
- Mathieu Verdurand
- Schizophrenia Research Institute, Sydney, Australia
- ANSTO LifeSciences, Australian Nuclear Science and Technology Organization, Sydney, Australia
| | - Stu G. Fillman
- Schizophrenia Research Institute, Sydney, Australia
- Schizophrenia Research Laboratory, Neuroscience Research Australia, Sydney, Australia
- School of Psychiatry, University of New South Wales, Sydney, Australia
| | - Cynthia Shannon Weickert
- Schizophrenia Research Institute, Sydney, Australia
- Schizophrenia Research Laboratory, Neuroscience Research Australia, Sydney, Australia
- School of Psychiatry, University of New South Wales, Sydney, Australia
| | - Katerina Zavitsanou
- Schizophrenia Research Institute, Sydney, Australia
- Schizophrenia Research Laboratory, Neuroscience Research Australia, Sydney, Australia
- School of Psychiatry, University of New South Wales, Sydney, Australia
- * E-mail:
| |
Collapse
|
25
|
Shu HJ, Bracamontes J, Taylor A, Wu K, Eaton MM, Akk G, Manion B, Evers AS, Krishnan K, Covey DF, Zorumski CF, Steinbach JH, Mennerick S. Characteristics of concatemeric GABA(A) receptors containing α4/δ subunits expressed in Xenopus oocytes. Br J Pharmacol 2012; 165:2228-43. [PMID: 21950777 DOI: 10.1111/j.1476-5381.2011.01690.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
BACKGROUND AND PURPOSE GABA(A) receptors mediate both synaptic and extrasynaptic actions of GABA. In several neuronal populations, α4 and δ subunits are key components of extrasynaptic GABA(A) receptors that strongly influence neuronal excitability and could mediate the effects of neuroactive agents including neurosteroids and ethanol. However, these receptors can be difficult to study in native cells and recombinant δ subunits can be difficult to express in heterologous systems. EXPERIMENTAL APPROACH We engineered concatemeric (fused) subunits to ensure δ and α4 subunit expression. We tested the pharmacology of the concatemeric receptors, compared with a common synaptic-like receptor subunit combination (α1 +β2 +γ2L), and with free-subunit α4/δ receptors, expressed in Xenopus oocytes. KEY RESULTS δ-β2 -α4 +β2-α4 cRNA co-injected into Xenopus oocytes resulted in GABA-gated currents with the expected pharmacological properties of α4/δ-containing receptors. Criteria included sensitivity to agonists of different efficacy, sensitivity to the allosteric activator pentobarbital, and modulation of agonist responses by DS2 (4-chloro-N-[2-(2-thienyl)imidazo[1,2-a]pyridine-3-yl benzamide; a δ-selective positive modulator), furosemide, and Zn(2+) . We used the concatemers to examine neurosteroid sensitivity of extrasynaptic-like, δ-containing receptors. We found no qualitative differences between extrasynaptic-like receptors and synaptic-like receptors in the actions of either negative or positive neurosteroid modulators of receptor function. Quantitative differences were explained by the partial agonist effects of the natural agonist GABA and by a mildly increased sensitivity to low steroid concentrations. CONCLUSIONS AND IMPLICATIONS The neurosteroid structure-activity profile for α4/δ-containing extrasynaptic receptors is unlikely to differ from that of synaptic-like receptors such as α1/β2/γ2-containing receptors.
Collapse
Affiliation(s)
- Hong-Jin Shu
- Department of Psychiatry, Washington University School of Medicine, St. Louis, Missouri, USA
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
26
|
Benzodiazepines modulate GABAA receptors by regulating the preactivation step after GABA binding. J Neurosci 2012; 32:5707-15. [PMID: 22539833 DOI: 10.1523/jneurosci.5663-11.2012] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
GABA(A) receptors (GABA(A)Rs) composed of αβγ subunits are allosterically modulated by the benzodiazepines (BDZs). Agonists at the BDZ binding site potentiate submaximal GABA responses by increasing the apparent affinity of GABA(A)Rs for GABA. Although BDZs were initially thought to affect the binding of GABA agonists, recent studies suggest an effect on receptor gating; however, the involvement of preactivation steps in the modulation by BDZs has not been considered. Consequently, we examined whether BDZ agonists could exert their modulatory effect by displacing the equilibrium between resting and preactivated states of recombinant α1β2γ2 GABA(A)Rs expressed in Xenopus oocytes. For GABA and the partial agonists 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol and piperidine-4-sulfonic acid, we examined BDZ modulation using a simple three-step model incorporating agonist binding, receptor preactivation, and channel opening. The model accounted for diazepam modulation simply by increasing the preactivation constant by approximately fourfold. To assess whether BDZs preferentially affected a specific GABA binding site, pentameric concatamers were used. This demonstrated that single GABA-binding site mutant receptors were equally sensitive to modulation by BDZs compared with wild-type counterparts. Overall, our results suggest that BDZs affect the preactivation step to cause a global conformational rearrangement of GABA(A)Rs, thereby modulating receptor function.
Collapse
|