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Arias HR, Pierce SR, Germann AL, Xu SQ, Ortells MO, Sakamoto S, Manetti D, Romanelli MN, Hamachi I, Akk G. Chemical, Pharmacological, and Structural Characterization of Novel Acrylamide-Derived Modulators of the GABA A Receptor. Mol Pharmacol 2023; 104:115-131. [PMID: 37316350 PMCID: PMC10441626 DOI: 10.1124/molpharm.123.000692] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Revised: 05/22/2023] [Accepted: 06/01/2023] [Indexed: 06/16/2023] Open
Abstract
Acrylamide-derived compounds have been previously shown to act as modulators of members of the Cys-loop transmitter-gated ion channel family, including the mammalian GABAA receptor. Here we have synthesized and functionally characterized the GABAergic effects of a series of novel compounds (termed "DM compounds") derived from the previously characterized GABAA and the nicotinic α7 receptor modulator (E)-3-furan-2-yl-N-p-tolyl-acrylamide (PAM-2). Fluorescence imaging studies indicated that the DM compounds increase apparent affinity to the transmitter by up to 80-fold in the ternary αβγ GABAA receptor. Using electrophysiology, we show that the DM compounds, and the structurally related (E)-3-furan-2-yl-N-phenylacrylamide (PAM-4), have concurrent potentiating and inhibitory effects that can be isolated and observed under appropriate recording conditions. The potentiating efficacies of the DM compounds are similar to those of neurosteroids and benzodiazepines (ΔG ∼ -1.5 kcal/mol). Molecular docking, functionally confirmed by site-directed mutagenesis experiments, indicate that receptor potentiation is mediated by interactions with the classic anesthetic binding sites located in the transmembrane domain of the intersubunit interfaces. Inhibition by the DM compounds and PAM-4 was abolished in the receptor containing the α1(V256S) mutation, suggestive of similarities in the mechanism of action with that of inhibitory neurosteroids. Functional competition and mutagenesis experiments, however, indicate that the sites mediating inhibition by the DM compounds and PAM-4 differ from those mediating the action of the inhibitory steroid pregnenolone sulfate. SIGNIFICANCE STATEMENT: We have synthesized and characterized the actions of novel acrylamide-derived compounds on the mammalian GABAA receptor. We show that the compounds have concurrent potentiating effects mediated by the classic anesthetic binding sites, and inhibitory actions that bear mechanistic resemblance to but do not share binding sites with, the inhibitory steroid pregnenolone sulfate.
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Affiliation(s)
- Hugo R Arias
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Spencer R Pierce
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Allison L Germann
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Sophia Q Xu
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Marcelo O Ortells
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Seiji Sakamoto
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Dina Manetti
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Maria Novella Romanelli
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Itaru Hamachi
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
| | - Gustav Akk
- Department of Pharmacology and Physiology, Oklahoma State University College of Osteopathic Medicine, Tahlequah, Oklahoma (H.R.A.); Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri (S.R.P., A.L.G., S.Q.X., G.A.); Facultad de Medicina, Universidad de Morón, Morón, and CONICET, Argentina (M.O.O.); Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan (S.S., I.H.); Department of Neurosciences, Psychology, Drug Research and Child Health Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Florence, Italy (D.M., M.N.R.); The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, Missouri (G.A.)
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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.
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Wang M, Cotter E, Wang YJ, Fu X, Whittsette AL, Lynch JW, Wiseman RL, Kelly JW, Keramidas A, Mu TW. Pharmacological activation of ATF6 remodels the proteostasis network to rescue pathogenic GABA A receptors. Cell Biosci 2022; 12:48. [PMID: 35477478 PMCID: PMC9044816 DOI: 10.1186/s13578-022-00783-w] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2022] [Accepted: 04/05/2022] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Genetic variants in the subunits of the gamma-aminobutyric acid type A (GABAA) receptors are implicated in the onset of multiple pathologic conditions including genetic epilepsy. Previous work showed that pathogenic GABAA subunits promote misfolding and inefficient assembly of the GABAA receptors, limiting receptor expression and activity at the plasma membrane. However, GABAA receptors containing variant subunits can retain activity, indicating that enhancing the folding, assembly, and trafficking of these variant receptors offers a potential opportunity to mitigate pathology associated with genetic epilepsy. RESULTS Here, we demonstrate that pharmacologically enhancing endoplasmic reticulum (ER) proteostasis using small molecule activators of the ATF6 (Activating Transcription Factor 6) signaling arm of the unfolded protein response (UPR) increases the assembly, trafficking, and surface expression of variant GABAA receptors. These improvements are attributed to ATF6-dependent remodeling of the ER proteostasis environment, which increases protein levels of pro-folding ER proteostasis factors including the ER chaperone BiP (Immunoglobulin Binding Protein) and trafficking receptors, such as LMAN1 (Lectin Mannose-Binding 1) and enhances their interactions with GABAA receptors. Importantly, we further show that pharmacologic ATF6 activators increase the activity of GABAA receptors at the cell surface, revealing the potential for this strategy to restore receptor activity to levels that could mitigate disease pathogenesis. CONCLUSIONS These results indicate that pharmacologic ATF6 activators offer an opportunity to restore GABAA receptor activity in diseases including genetic epilepsy and point to the potential for similar pharmacologic enhancement of ER proteostasis to improve trafficking of other disease-associated variant ion channels implicated in etiologically-diverse diseases.
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Affiliation(s)
- Meng Wang
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave, Cleveland, OH, 44106, USA
| | - Edmund Cotter
- Queensland Brain Institute, the University of Queensland, Brisbane, QLD, 4072, Australia
| | - Ya-Juan Wang
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave, Cleveland, OH, 44106, USA
| | - Xu Fu
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave, Cleveland, OH, 44106, USA
| | - Angela L Whittsette
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave, Cleveland, OH, 44106, USA
| | - Joseph W Lynch
- Queensland Brain Institute, the University of Queensland, Brisbane, QLD, 4072, Australia
| | - R Luke Wiseman
- Department of Molecular Medicine, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA, 92037, USA
| | - Jeffery W Kelly
- Department of Molecular Medicine, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA, 92037, USA
| | - Angelo Keramidas
- Queensland Brain Institute, the University of Queensland, Brisbane, QLD, 4072, Australia.
| | - Ting-Wei Mu
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave, Cleveland, OH, 44106, USA.
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Pierce SR, Germann AL, Steinbach JH, Akk G. The Sulfated Steroids Pregnenolone Sulfate and Dehydroepiandrosterone Sulfate Inhibit the α1 β3 γ2L GABA A Receptor by Stabilizing a Novel Nonconducting State. Mol Pharmacol 2022; 101:68-77. [PMID: 34853153 PMCID: PMC8969134 DOI: 10.1124/molpharm.121.000385] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Accepted: 11/21/2021] [Indexed: 02/03/2023] Open
Abstract
The GABAA receptor is inhibited by the endogenous sulfated steroids pregnenolone sulfate (PS) and dehydroepiandrosterone sulfate (DHEAS). It has been proposed in previous work that these steroids act by enhancing desensitization of the receptor. Here, we have investigated the modulatory effects of the steroids on the human α1β3γ2L GABAA receptor. Using electrophysiology and quantitative model-based data analysis, we show that exposure to the steroid promotes occupancy of a nonconducting state that retains high affinity to the transmitter but whose properties differ from those of the classic, transmitter-induced desensitized state. From the analysis of the inhibitory actions of two combined steroids, we infer that PS and DHEAS act through shared or overlapping binding sites. SIGNIFICANCE STATEMENT: Previous work has proposed that sulfated neurosteroids inhibit the GABAA receptor by enhancing the rate of entry into the desensitized state. This study shows that the inhibitory steroids pregnenolone sulfate and dehydroepiandrosterone sulfate act through a common interaction site by stabilizing a distinct nonconducting state.
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Affiliation(s)
- Spencer R Pierce
- Department of Anesthesiology (S.R.P., A.L.G., J.H.S., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Allison L Germann
- Department of Anesthesiology (S.R.P., A.L.G., J.H.S., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Joe Henry Steinbach
- Department of Anesthesiology (S.R.P., A.L.G., J.H.S., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Gustav Akk
- Department of Anesthesiology (S.R.P., A.L.G., J.H.S., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
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Activation of the α1β2γ2L GABA A Receptor by Physiological Agonists. Biomolecules 2021; 11:biom11121864. [PMID: 34944508 PMCID: PMC8699469 DOI: 10.3390/biom11121864] [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: 11/18/2021] [Revised: 12/02/2021] [Accepted: 12/09/2021] [Indexed: 11/21/2022] Open
Abstract
The Cl− permeable GABAA receptor is a major contributor to cellular inhibition in the brain. The receptor is normally activated by synaptically-released or ambient GABA but is sensitive to a number of physiological compounds such as β-alanine, taurine, and neurosteroids that, to various degrees, activate the receptor and modulate responses either to the transmitter or to each other. Here, we describe α1β2γ2L GABAA receptor activation and modulation by combinations of orthosteric and allosteric activators. The overall goal was to gain insight into how changes in the levels of endogenous agonists modulate receptor activity and influence cellular inhibition. Experimental observations and simulations are described in the framework of a cyclic concerted transition model. We also provide general analytical solutions for the analysis of electrophysiological data collected in the presence of combinations of active compounds.
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Lycksell M, Rovšnik U, Bergh C, Johansen NT, Martel A, Porcar L, Arleth L, Howard RJ, Lindahl E. Probing solution structure of the pentameric ligand-gated ion channel GLIC by small-angle neutron scattering. Proc Natl Acad Sci U S A 2021; 118:e2108006118. [PMID: 34504004 PMCID: PMC8449418 DOI: 10.1073/pnas.2108006118] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/26/2021] [Indexed: 02/03/2023] Open
Abstract
Pentameric ligand-gated ion channels undergo subtle conformational cycling to control electrochemical signal transduction in many kingdoms of life. Several crystal structures have now been reported in this family, but the functional relevance of such models remains unclear. Here, we used small-angle neutron scattering (SANS) to probe ambient solution-phase properties of the pH-gated bacterial ion channel GLIC under resting and activating conditions. Data collection was optimized by inline paused-flow size-exclusion chromatography, and exchanging into deuterated detergent to hide the micelle contribution. Resting-state GLIC was the best-fit crystal structure to SANS curves, with no evidence for divergent mechanisms. Moreover, enhanced-sampling molecular-dynamics simulations enabled differential modeling in resting versus activating conditions, with the latter corresponding to an intermediate ensemble of both the extracellular and transmembrane domains. This work demonstrates state-dependent changes in a pentameric ion channel by SANS, an increasingly accessible method for macromolecular characterization with the coming generation of neutron sources.
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Affiliation(s)
- Marie Lycksell
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, 10691 Stockholm, Sweden
| | - Urška Rovšnik
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, 10691 Stockholm, Sweden
| | - Cathrine Bergh
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, 10044 Stockholm, Sweden
| | - Nicolai T Johansen
- Structural Biophysics, X-ray and Neutron Science, The Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Anne Martel
- Institut Laue-Langevin, 38042 Grenoble, France
| | | | - Lise Arleth
- Structural Biophysics, X-ray and Neutron Science, The Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Rebecca J Howard
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, 10691 Stockholm, Sweden
| | - Erik Lindahl
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, 10691 Stockholm, Sweden;
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, 10044 Stockholm, Sweden
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Terejko K, Michałowski MA, Iżykowska I, Dominik A, Brzóstowicz A, Mozrzymas JW. Mutations at the M2 and M3 Transmembrane Helices of the GABA ARs α 1 and β 2 Subunits Affect Primarily Late Gating Transitions Including Opening/Closing and Desensitization. ACS Chem Neurosci 2021; 12:2421-2436. [PMID: 34101432 PMCID: PMC8291490 DOI: 10.1021/acschemneuro.1c00151] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
![]()
GABA type A receptors
(GABAARs) belong to the pentameric
ligand-gated ion channel (pLGIC) family and play a crucial role in
mediating inhibition in the adult mammalian brain. Recently, a major
progress in determining the static structure of GABAARs
was achieved, although precise molecular scenarios underlying conformational
transitions remain unclear. The ligand binding sites (LBSs) are located
at the extracellular domain (ECD), very distant from the receptor
gate at the channel pore. GABAAR gating is complex, comprising
three major categories of transitions: openings/closings, preactivation,
and desensitization. Interestingly, mutations at, e.g., the ligand
binding site affect not only binding but often also more than one
gating category, suggesting that structural determinants for distinct
conformational transitions are shared. Gielen and co-workers (2015)
proposed that the GABAAR desensitization gate is located
at the second and third transmembrane segment. However, studies of
our and others’ groups indicated that other parts of the GABAAR macromolecule might be involved in this process. In the
present study, we asked how selected point mutations (β2G254V, α1G258V, α1L300V,
and β2L296V) at the M2 and M3 transmembrane segments
affect gating transitions of the α1β2γ2 GABAAR. Using high resolution macroscopic
and single-channel recordings and analysis, we report that these substitutions,
besides affecting desensitization, also profoundly altered openings/closings,
having some minor effect on preactivation and agonist binding. Thus,
the M2 and M3 segments primarily control late gating transitions of
the receptor (desensitization, opening/closing), providing a further
support for the concept of diffuse gating mechanisms for conformational
transitions of GABAAR.
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Affiliation(s)
- Katarzyna Terejko
- Department of Biophysics and Neuroscience, Wrocław Medical University, ul. Chałubińskiego 3A, 50-368 Wrocław, Poland
| | - Michał A. Michałowski
- Department of Biophysics and Neuroscience, Wrocław Medical University, ul. Chałubińskiego 3A, 50-368 Wrocław, Poland
- Department of Molecular Physiology and Neurobiology, University of Wrocław, ul. Sienkiewicza 21, 50-335 Wrocław, Poland
| | - Ilona Iżykowska
- Department of Biophysics and Neuroscience, Wrocław Medical University, ul. Chałubińskiego 3A, 50-368 Wrocław, Poland
| | - Anna Dominik
- Department of Biophysics and Neuroscience, Wrocław Medical University, ul. Chałubińskiego 3A, 50-368 Wrocław, Poland
| | - Aleksandra Brzóstowicz
- Department of Biophysics and Neuroscience, Wrocław Medical University, ul. Chałubińskiego 3A, 50-368 Wrocław, Poland
| | - Jerzy W. Mozrzymas
- Department of Biophysics and Neuroscience, Wrocław Medical University, ul. Chałubińskiego 3A, 50-368 Wrocław, Poland
- Department of Molecular Physiology and Neurobiology, University of Wrocław, ul. Sienkiewicza 21, 50-335 Wrocław, Poland
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Electrophysiology of ionotropic GABA receptors. Cell Mol Life Sci 2021; 78:5341-5370. [PMID: 34061215 PMCID: PMC8257536 DOI: 10.1007/s00018-021-03846-2] [Citation(s) in RCA: 41] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 04/02/2021] [Accepted: 04/23/2021] [Indexed: 10/30/2022]
Abstract
GABAA receptors are ligand-gated chloride channels and ionotropic receptors of GABA, the main inhibitory neurotransmitter in vertebrates. In this review, we discuss the major and diverse roles GABAA receptors play in the regulation of neuronal communication and the functioning of the brain. GABAA receptors have complex electrophysiological properties that enable them to mediate different types of currents such as phasic and tonic inhibitory currents. Their activity is finely regulated by membrane voltage, phosphorylation and several ions. GABAA receptors are pentameric and are assembled from a diverse set of subunits. They are subdivided into numerous subtypes, which differ widely in expression patterns, distribution and electrical activity. Substantial variations in macroscopic neural behavior can emerge from minor differences in structure and molecular activity between subtypes. Therefore, the diversity of GABAA receptors widens the neuronal repertoire of responses to external signals and contributes to shaping the electrical activity of neurons and other cell types.
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Germann AL, Pierce SR, Tateiwa H, Sugasawa Y, Reichert DE, Evers AS, Steinbach JH, Akk G. Intrasubunit and Intersubunit Steroid Binding Sites Independently and Additively Mediate α1 β2 γ2L GABA A Receptor Potentiation by the Endogenous Neurosteroid Allopregnanolone. Mol Pharmacol 2021; 100:19-31. [PMID: 33958479 DOI: 10.1124/molpharm.121.000268] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2021] [Accepted: 04/22/2021] [Indexed: 12/18/2022] Open
Abstract
Prior work employing functional analysis, photolabeling, and X-ray crystallography have identified three distinct binding sites for potentiating steroids in the heteromeric GABAA receptor. The sites are located in the membrane-spanning domains of the receptor at the β-α subunit interface (site I) and within the α (site II) and β subunits (site III). Here, we have investigated the effects of mutations to these sites on potentiation of the rat α1β2γ2L GABAA receptor by the endogenous neurosteroid allopregnanolone (3α5αP). The mutations were introduced alone or in combination to probe the additivity of effects. We show that the effects of amino acid substitutions in sites I and II are energetically additive, indicating independence of the actions of the two steroid binding sites. In site III, none of the mutations tested reduced potentiation by 3α5αP, nor did a mutation in site III modify the effects of mutations in sites I or II. We infer that the binding sites for 3α5αP act independently. The independence of steroid action at each site is supported by photolabeling data showing that mutations in either site I or site II selectively change steroid orientation in the mutated site without affecting labeling at the unmutated site. The findings are discussed in the context of linking energetic additivity to empirical changes in receptor function and ligand binding. SIGNIFICANCE STATEMENT: Prior work has identified three distinct binding sites for potentiating steroids in the heteromeric γ-aminobutyric acid type A receptor. This study shows that the sites act independently and additively in the presence of the steroid allopregnanolone and provide estimates of energetic contributions made by steroid binding to each site.
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Affiliation(s)
- Allison L Germann
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Spencer R Pierce
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Hiroki Tateiwa
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Yusuke Sugasawa
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - David E Reichert
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Alex S Evers
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Joe Henry Steinbach
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
| | - Gustav Akk
- Departments of Anesthesiology (A.L.G., S.R.P., H.T., A.S.E., J.H.S., G.A.) and Radiology (D.E.R.), and the Taylor Family Institute for Innovative Psychiatric Research (D.E.R., A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri; and Department of Anesthesiology and Pain Medicine, Juntendo University School of Medicine, Tokyo, Japan (Y.S.)
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10
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Akk G. Meet Our Editorial Board Member. Curr Neuropharmacol 2020. [PMCID: PMC7903496 DOI: 10.2174/1570159x1901201214092532] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Affiliation(s)
- Gustav Akk
- Department of Anesthesiology Washington University School of Medicine St. Louis, MO, United States
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11
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Akk G, Germann AL, Sugasawa Y, Pierce SR, Evers AS, Steinbach JH. Enhancement of Muscimol Binding and Gating by Allosteric Modulators of the GABA A Receptor: Relating Occupancy to State Functions. Mol Pharmacol 2020; 98:303-313. [PMID: 32873746 PMCID: PMC7472144 DOI: 10.1124/molpharm.120.000066] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Accepted: 07/17/2020] [Indexed: 01/08/2023] Open
Abstract
Muscimol is a psychoactive isoxazole derived from the mushroom Amanita muscaria and a potent orthosteric agonist of the GABAA receptor. The binding of [3H]muscimol has been used to evaluate the distribution of GABAA receptors in the brain, and studies of modulation of [3H]muscimol binding by allosteric GABAergic modulators such as barbiturates and steroid anesthetics have provided insight into the modes of action of these drugs on the GABAA receptor. It has, however, not been feasible to directly apply interaction parameters derived from functional studies to describe the binding of muscimol to the receptor. Here, we employed the Monod-Wyman-Changeux concerted transition model to analyze muscimol binding isotherms. We show that the binding isotherms from recombinant α1β3 GABAA receptors can be qualitatively predicted using electrophysiological data pertaining to properties of receptor activation and desensitization in the presence of muscimol. The model predicts enhancement of [3H]muscimol binding in the presence of the steroids allopregnanolone and pregnenolone sulfate, although the steroids interact with distinct sites and either enhance (allopregnanolone) or reduce (pregnenolone sulfate) receptor function. We infer that the concerted transition model can be used to link radioligand binding and electrophysiological data. SIGNIFICANCE STATEMENT: The study employs a three-state resting-active-desensitized model to link radioligand binding and electrophysiological data. We show that the binding isotherms can be qualitatively predicted using parameters estimated in electrophysiological experiments and that the model accurately predicts the enhancement of [3H]muscimol binding in the presence of the potentiating steroid allopregnanolone and the inhibitory steroid pregnenolone sulfate.
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Affiliation(s)
- Gustav Akk
- Department of Anesthesiology (G.A., A.L.G., Y.S., S.R.P., A.S.E., J.H.S.) and the Taylor Family Institute for Innovative Psychiatric Research (G.A., A.S.E., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
| | - Allison L Germann
- Department of Anesthesiology (G.A., A.L.G., Y.S., S.R.P., A.S.E., J.H.S.) and the Taylor Family Institute for Innovative Psychiatric Research (G.A., A.S.E., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
| | - Yusuke Sugasawa
- Department of Anesthesiology (G.A., A.L.G., Y.S., S.R.P., A.S.E., J.H.S.) and the Taylor Family Institute for Innovative Psychiatric Research (G.A., A.S.E., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
| | - Spencer R Pierce
- Department of Anesthesiology (G.A., A.L.G., Y.S., S.R.P., A.S.E., J.H.S.) and the Taylor Family Institute for Innovative Psychiatric Research (G.A., A.S.E., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
| | - Alex S Evers
- Department of Anesthesiology (G.A., A.L.G., Y.S., S.R.P., A.S.E., J.H.S.) and the Taylor Family Institute for Innovative Psychiatric Research (G.A., A.S.E., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
| | - Joe Henry Steinbach
- Department of Anesthesiology (G.A., A.L.G., Y.S., S.R.P., A.S.E., J.H.S.) and the Taylor Family Institute for Innovative Psychiatric Research (G.A., A.S.E., J.H.S.), Washington University School of Medicine, St. Louis, Missouri
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12
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Pierce SR, Germann AL, Evers AS, Steinbach JH, Akk G. Reduced Activation of the Synaptic-Type GABA A Receptor Following Prolonged Exposure to Low Concentrations of Agonists: Relationship between Tonic Activity and Desensitization. Mol Pharmacol 2020; 98:762-769. [PMID: 32978327 DOI: 10.1124/molpharm.120.000088] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Accepted: 09/09/2020] [Indexed: 01/16/2023] Open
Abstract
Synaptic GABAA receptors are alternately exposed to short pulses of a high, millimolar concentration of GABA and prolonged periods of low, micromolar concentration of the transmitter. Prior work has indicated that exposure to micromolar concentrations of GABA can both activate the postsynaptic receptors generating sustained low-amplitude current and desensitize the receptors, thereby reducing the peak amplitude of subsequent synaptic response. However, the precise relationship between tonic activation and reduction of peak response is not known. Here, we have measured the effect of prolonged exposure to GABA or the combination of GABA and the neurosteroid allopregnanolone, which was intended to desensitize a fraction of receptors, on a subsequent response to a high concentration of agonist in human α1β3γ2L receptors expressed in Xenopus oocytes. We show that the reduction in the peak amplitude of the post-exposure test response correlates with the open probability of the preceding desensitizing response. Curve fitting of the inhibitory relationship yielded an IC50 of 12.5 µM and a Hill coefficient of -1.61. The activation and desensitization data were mechanistically analyzed in the framework of a three-state Resting-Active-Desensitized model. Using the estimated affinity, efficacy, and desensitization parameters, we calculated the amount of desensitization that would accumulate during a long (2-minute) application of GABA or GABA plus allopregnanolone. The results indicate that accumulation of desensitization depends on the level of activity rather than agonist or potentiator concentration per se. We estimate that in the presence of 1 µM GABA, approximately 5% of α1β3γ2L receptors are functionally eliminated because of desensitization. SIGNIFICANCE STATEMENT: We present an analytical approach to quantify and predict the loss of activatable GABAA receptors due to desensitization in the presence of transmitter and the steroid allopregnanolone. The findings indicate that the peak amplitude of the synaptic response is influenced by ambient GABA and that changes in ambient concentrations of the transmitter and other GABAergic agents can modify tonically and phasically activated synaptic receptors in opposite directions.
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Affiliation(s)
- Spencer R Pierce
- Department of Anesthesiology (S.R.P., A.L.G., A.S.E., J.H.S., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Allison L Germann
- Department of Anesthesiology (S.R.P., A.L.G., A.S.E., J.H.S., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Alex S Evers
- Department of Anesthesiology (S.R.P., A.L.G., A.S.E., J.H.S., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Joe Henry Steinbach
- Department of Anesthesiology (S.R.P., A.L.G., A.S.E., J.H.S., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Gustav Akk
- Department of Anesthesiology (S.R.P., A.L.G., A.S.E., J.H.S., G.A.) and the Taylor Family Institute for Innovative Psychiatric Research (A.S.E., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
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13
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Sugasawa Y, Cheng WW, Bracamontes JR, Chen ZW, Wang L, Germann AL, Pierce SR, Senneff TC, Krishnan K, Reichert DE, Covey DF, Akk G, Evers AS. Site-specific effects of neurosteroids on GABA A receptor activation and desensitization. eLife 2020; 9:55331. [PMID: 32955433 PMCID: PMC7532004 DOI: 10.7554/elife.55331] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Accepted: 09/20/2020] [Indexed: 12/16/2022] Open
Abstract
This study examines how site-specific binding to three identified neurosteroid-binding sites in the α1β3 GABAA receptor (GABAAR) contributes to neurosteroid allosteric modulation. We found that the potentiating neurosteroid, allopregnanolone, but not its inhibitory 3β-epimer epi-allopregnanolone, binds to the canonical β3(+)–α1(-) intersubunit site that mediates receptor activation by neurosteroids. In contrast, both allopregnanolone and epi-allopregnanolone bind to intrasubunit sites in the β3 subunit, promoting receptor desensitization and the α1 subunit promoting effects that vary between neurosteroids. Two neurosteroid analogues with diazirine moieties replacing the 3-hydroxyl (KK148 and KK150) bind to all three sites, but do not potentiate GABAAR currents. KK148 is a desensitizing agent, whereas KK150 is devoid of allosteric activity. These compounds provide potential chemical scaffolds for neurosteroid antagonists. Collectively, these data show that differential occupancy and efficacy at three discrete neurosteroid-binding sites determine whether a neurosteroid has potentiating, inhibitory, or competitive antagonist activity on GABAARs.
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Affiliation(s)
- Yusuke Sugasawa
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States
| | - Wayland Wl Cheng
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States
| | - John R Bracamontes
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States
| | - Zi-Wei Chen
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States.,Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, United States
| | - Lei Wang
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States
| | - Allison L Germann
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States
| | - Spencer R Pierce
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States
| | - Thomas C Senneff
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States
| | - Kathiresan Krishnan
- Department of Developmental Biology, Washington University in St. Louis, St. Louis, United States
| | - David E Reichert
- Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, United States.,Department of Radiology, Washington University in St. Louis, St. Louis, United States
| | - Douglas F Covey
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States.,Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, United States.,Department of Developmental Biology, Washington University in St. Louis, St. Louis, United States.,Department of Psychiatry, Washington University in St. Louis, St. Louis, United States
| | - Gustav Akk
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States.,Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, United States
| | - Alex S Evers
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, United States.,Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, United States.,Department of Developmental Biology, Washington University in St. Louis, St. Louis, United States
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14
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A novel de novo variant of GABRA1 causes increased sensitivity for GABA in vitro. Sci Rep 2020; 10:2379. [PMID: 32047208 PMCID: PMC7012862 DOI: 10.1038/s41598-020-59323-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Accepted: 01/28/2020] [Indexed: 12/14/2022] Open
Abstract
The GABRA1 gene encodes one of the most conserved and highly expressed subunits of the GABAA receptor family. Variants in this gene are causatively implicated in different forms of epilepsy and also more severe epilepsy-related neurodevelopmental syndromes. Here we study functional consequences of a novel de novo missense GABRA1 variant, p.(Ala332Val), identified through exome sequencing in an individual affected by early-onset syndromic epileptic encephalopathy. The variant is localised within the transmembrane domain helix 3 (TM3) and in silico prediction algorithms suggested this variant to be likely pathogenic. In vitro assessment revealed unchanged protein levels, regular assembly and forward trafficking to the cell surface. On the functional level a significant left shift of the apparent GABA potency in two-electrode voltage clamp electrophysiology experiments was observed, as well as changes in the extent of desensitization. Additionally, apparent diazepam potency was left shifted in radioligand displacement assays. During prenatal development mainly alpha2/3 subunits are expressed, whereas after birth a switch to alpha1 occurs. The expression of alpha1 in humans is upregulated during the first years. Thus, the molecular change of function reported here supports pathogenicity and could explain early-onset of seizures in the affected individual.
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15
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Yang J, Li N, Zhen Y, Huang Q. γ-aminobutyric acid alleviates LPS-induced acute lung injury in mice through upregulating type B receptors. Arch Med Sci 2019; 19:1116-1123. [PMID: 37560718 PMCID: PMC10408013 DOI: 10.5114/aoms.2019.89984] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/26/2019] [Accepted: 10/23/2019] [Indexed: 08/11/2023] Open
Abstract
INTRODUCTION In recent years, studies have shown that GABA has a certain therapeutic effect on acute lung injury (ALI), but its specific mechanism has not been fully elucidated. The study was designed to investigate the protective effect and mechanism of γ-aminobutyric acid (GABA) on ALI induced by lipopolysaccharide (LPS) in mice. MATERIAL AND METHODS C57BL/6 mice were randomly divided into a control group, LPS group, LPS + GABA (10 mg/kg) group and LPS + dexamethasone (Dex, 5 mg/kg) group. The survival rate of each group was observed at different time points after modeling. The levels of tumor necrosis factor α (TNF-α), interleukin (IL) 1β, 10, myeloperoxidase (MPO) and the cell count and protein concentration in bronchoalveolar lavage fluid (BALF) were measured. Lung histopathology and the expression of GABA receptors were observed by HE staining and immunohistochemistry respectively. Lung water content was assessed by wet-dry weight ratio. RESULTS GABA could significantly improve the survival rate and prolong the survival time of animals, alleviate the degree of inflammatory injury and pulmonary edema, reduce the content of MPO, down-regulate the levels of pro-inflammatory cytokines IL-1β and TNF-α, and up-regulate the expression of anti-inflammatory cytokine IL-10. Moreover, GABA could significantly decrease the expression of type A receptors and enhance type B receptors. CONCLUSIONS GABA can effectively alleviate ALI induced by LPS in mice, and its effect may be related to the upregulation of type B receptors.
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Affiliation(s)
- Jing Yang
- Pediatric Department, Qilu Hospital of Shandong University (Qingdao), Qingdao, China
| | - Na Li
- Pediatric Department, Qilu Hospital of Shandong University (Qingdao), Qingdao, China
| | - Yuanyuan Zhen
- Pediatric Department, Qilu Hospital of Shandong University (Qingdao), Qingdao, China
| | - Qikun Huang
- Pediatric Department, Qilu Hospital of Shandong University (Qingdao), Qingdao, China
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16
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Pierce SR, Senneff TC, Germann AL, Akk G. Steady-state activation of the high-affinity isoform of the α4β2δ GABA A receptor. Sci Rep 2019; 9:15997. [PMID: 31690811 PMCID: PMC6831628 DOI: 10.1038/s41598-019-52573-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Accepted: 10/18/2019] [Indexed: 12/18/2022] Open
Abstract
Activation of GABAA receptors consisting of α4, β2 (or β3), and δ subunits is a major contributor to tonic inhibition in several brain regions. The goal of this study was to analyze the function of the α4β2δ receptor in the presence of GABA and other endogenous and clinical activators and modulators under steady-state conditions. We show that the receptor has a high constitutive open probability (~0.1), but is only weakly activated by GABA that has a maximal peak open probability (POpen,peak) of 0.4, taurine (maximal POpen,peak = 0.4), or the endogenous steroid allopregnanolone (maximal POpen,peak = 0.2). The intravenous anesthetic propofol is a full agonist (maximal POpen,peak = 0.99). Analysis of currents using a cyclic three-state Resting-Active-Desensitized model indicates that the maximal steady-state open probability of the α4β2δ receptor is ~0.45. Steady-state open probability in the presence of combinations of GABA, taurine, propofol, allopregnanolone and/or the inhibitory steroid pregnenolone sulfate closely matched predicted open probability calculated assuming energetic additivity. The results suggest that the receptor is active in the presence of physiological concentrations of GABA and taurine, but, surprisingly, that receptor activity is only weakly potentiated by propofol.
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Affiliation(s)
- Spencer R Pierce
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Thomas C Senneff
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Allison L Germann
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Gustav Akk
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, 63110, USA. .,The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, MO, 63110, USA.
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