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Whittsette AL, Wang YJ, Mu TW. The endoplasmic reticulum membrane complex promotes proteostasis of GABA A receptors. iScience 2022; 25:104754. [PMID: 35938049 PMCID: PMC9352529 DOI: 10.1016/j.isci.2022.104754] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Revised: 06/30/2022] [Accepted: 07/07/2022] [Indexed: 11/29/2022] Open
Abstract
The endoplasmic reticulum membrane complex (EMC) plays a critical role in the biogenesis of tail-anchored proteins and a subset of multi-pass membrane proteins in the endoplasmic reticulum (ER). However, because of nearly exclusive expression of neurotransmitter-gated ion channels in the central nervous system (CNS), the role of the EMC in their biogenesis is not well understood. In this study, we demonstrated that the EMC positively regulates the surface trafficking and thus function of endogenous γ-aminobutyric acid type A (GABAA) receptors, the primary inhibitory ion channels in the mammalian brain. Moreover, among ten EMC subunits, EMC3 and EMC6 have the most prominent effect, and overexpression of EMC3 or EMC6 is sufficient to restore the function of epilepsy-associated GABAA receptor variants. In addition, EMC3 and EMC6 demonstrate endogenous interactions with major neuroreceptors, which depends on their transmembrane domains, suggesting a general role of the EMC in the biogenesis of neuroreceptors.
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Affiliation(s)
- Angela L. Whittsette
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Ya-Juan Wang
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Ting-Wei Mu
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Avenue, Cleveland, OH 44106, USA
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2
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Fu YL, Han DY, Wang YJ, Di XJ, Yu HB, Mu TW. Remodeling the endoplasmic reticulum proteostasis network restores proteostasis of pathogenic GABAA receptors. PLoS One 2018; 13:e0207948. [PMID: 30481215 PMCID: PMC6258528 DOI: 10.1371/journal.pone.0207948] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Accepted: 11/08/2018] [Indexed: 01/12/2023] Open
Abstract
Biogenesis of membrane proteins is controlled by the protein homeostasis (proteostasis) network. We have been focusing on protein quality control of γ-aminobutyric acid type A (GABAA) receptors, the major inhibitory neurotransmitter-gated ion channels in mammalian central nervous system. Proteostasis deficiency in GABAA receptors causes loss of their surface expression and thus function on the plasma membrane, leading to epilepsy and other neurological diseases. One well-characterized example is the A322D mutation in the α1 subunit that causes its extensive misfolding and expedited degradation in the endoplasmic reticulum (ER), resulting in autosomal dominant juvenile myoclonic epilepsy. We aimed to correct misfolding of the α1(A322D) subunits in the ER as an approach to restore their functional surface expression. Here, we showed that application of BIX, a specific, potent ER resident HSP70 family protein BiP activator, significantly increases the surface expression of the mutant receptors in human HEK293T cells and neuronal SH-SY5Y cells. BIX attenuates the degradation of α1(A322D) and enhances their forward trafficking and function. Furthermore, because BiP is one major target of the two unfolded protein response (UPR) pathways: ATF6 and IRE1, we continued to demonstrate that modest activations of the ATF6 pathway and IRE1 pathway genetically enhance the plasma membrane trafficking of the α1(A322D) protein in HEK293T cells. Our results underlie the potential of regulating the ER proteostasis network to correct loss-of-function protein conformational diseases.
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Affiliation(s)
- Yan-Lin Fu
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States of America
| | - Dong-Yun Han
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States of America
| | - Ya-Juan Wang
- Center for Proteomics and Bioinformatics and Department of Epidemiology and Biostatistics, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States of America
| | - Xiao-Jing Di
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States of America
| | - Hai-Bo Yu
- School of Chemistry and Molecular Bioscience & Molecular Horizons, University of Wollongong, Wollongong, Australia
| | - Ting-Wei Mu
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States of America
- * E-mail:
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3
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Di XJ, Wang YJ, Han DY, Fu YL, Duerfeldt AS, Blagg BSJ, Mu TW. Grp94 Protein Delivers γ-Aminobutyric Acid Type A (GABAA) Receptors to Hrd1 Protein-mediated Endoplasmic Reticulum-associated Degradation. J Biol Chem 2016; 291:9526-39. [PMID: 26945068 DOI: 10.1074/jbc.m115.705004] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Indexed: 11/06/2022] Open
Abstract
Proteostasis maintenance of γ-aminobutyric acid type A (GABAA) receptors dictates their function in controlling neuronal inhibition in mammalian central nervous systems. However, as a multisubunit, multispan, integral membrane protein, even wild type subunits of GABAA receptors fold and assemble inefficiently in the endoplasmic reticulum (ER). Unassembled and misfolded subunits undergo ER-associated degradation (ERAD), but this degradation process remains poorly understood for GABAA receptors. Here, using the α1 subunits of GABAA receptors as a model substrate, we demonstrated that Grp94, a metazoan-specific Hsp90 in the ER lumen, uses its middle domain to interact with the α1 subunits and positively regulates their ERAD. OS-9, an ER-resident lectin, acts downstream of Grp94 to further recognize misfolded α1 subunits in a glycan-dependent manner. This delivers misfolded α1 subunits to the Hrd1-mediated ubiquitination and the valosin-containing protein-mediated extraction pathway. Repressing the initial ERAD recognition step by inhibiting Grp94 enhances the functional surface expression of misfolding-prone α1(A322D) subunits, which causes autosomal dominant juvenile myoclonic epilepsy. This study clarifies a Grp94-mediated ERAD pathway for GABAA receptors, which provides a novel way to finely tune their function in physiological and pathophysiological conditions.
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Affiliation(s)
- Xiao-Jing Di
- From the Department of Physiology and Biophysics
| | - Ya-Juan Wang
- Center for Proteomics and Bioinformatics and Department of Epidemiology and Biostatistics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106
| | - Dong-Yun Han
- From the Department of Physiology and Biophysics
| | - Yan-Lin Fu
- From the Department of Physiology and Biophysics
| | - Adam S Duerfeldt
- the Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, and
| | - Brian S J Blagg
- the Department of Medicinal Chemistry, University of Kansas, Lawrence, Kansas 66045
| | - Ting-Wei Mu
- From the Department of Physiology and Biophysics,
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4
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Desrues L, Lefebvre T, Lecointre C, Schouft MT, Leprince J, Compère V, Morin F, Proust F, Gandolfo P, Tonon MC, Castel H. Down-regulation of GABA(A) receptor via promiscuity with the vasoactive peptide urotensin II receptor. Potential involvement in astrocyte plasticity. PLoS One 2012; 7:e36319. [PMID: 22563490 PMCID: PMC3341351 DOI: 10.1371/journal.pone.0036319] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2011] [Accepted: 04/02/2012] [Indexed: 02/07/2023] Open
Abstract
GABAA receptor (GABAAR) expression level is inversely correlated with the proliferation rate of astrocytes after stroke or during malignancy of astrocytoma, leading to the hypothesis that GABAAR expression/activation may work as a cell proliferation repressor. A number of vasoactive peptides exhibit the potential to modulate astrocyte proliferation, and the question whether these mechanisms may imply alteration in GABAAR-mediated functions and/or plasma membrane densities is open. The peptide urotensin II (UII) activates a G protein-coupled receptor named UT, and mediates potent vasoconstriction or vasodilation in mammalian vasculature. We have previously demonstrated that UII activates a PLC/PIPs/Ca2+ transduction pathway, via both Gq and Gi/o proteins and stimulates astrocyte proliferation in culture. It was also shown that UT/Gq/IP3 coupling is regulated by the GABAAR in rat cultured astrocytes. Here we report that UT and GABAAR are co-expressed in cerebellar glial cells from rat brain slices, in human native astrocytes and in glioma cell line, and that UII inhibited the GABAergic activity in rat cultured astrocytes. In CHO cell line co-expressing human UT and combinations of GABAAR subunits, UII markedly depressed the GABA current (β3γ2>α2β3γ2>α2β1γ2). This effect, characterized by a fast short-term inhibition followed by drastic and irreversible run-down, is not relayed by G proteins. The run-down partially involves Ca2+ and phosphorylation processes, requires dynamin, and results from GABAAR internalization. Thus, activation of the vasoactive G protein-coupled receptor UT triggers functional inhibition and endocytosis of GABAAR in CHO and human astrocytes, via its receptor C-terminus. This UII-induced disappearance of the repressor activity of GABAAR, may play a key role in the initiation of astrocyte proliferation.
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Affiliation(s)
- Laurence Desrues
- Inserm U982, Laboratory of Neuronal and Neuroendocrine Communication and Differentiation, Astrocyte and Vascular Niche, University of Rouen, Mont-Saint-Aignan, France
- Institute of Research and Biomedical Innovation (IRIB), Normandy University PRES, University of Rouen, Mont-Saint-Aignan, France
| | - Thomas Lefebvre
- Inserm U982, Laboratory of Neuronal and Neuroendocrine Communication and Differentiation, Astrocyte and Vascular Niche, University of Rouen, Mont-Saint-Aignan, France
- Institute of Research and Biomedical Innovation (IRIB), Normandy University PRES, University of Rouen, Mont-Saint-Aignan, France
| | - Céline Lecointre
- Inserm U982, Laboratory of Neuronal and Neuroendocrine Communication and Differentiation, Astrocyte and Vascular Niche, University of Rouen, Mont-Saint-Aignan, France
- Institute of Research and Biomedical Innovation (IRIB), Normandy University PRES, University of Rouen, Mont-Saint-Aignan, France
| | - Marie-Thérèse Schouft
- Inserm U982, Laboratory of Neuronal and Neuroendocrine Communication and Differentiation, Astrocyte and Vascular Niche, University of Rouen, Mont-Saint-Aignan, France
- Institute of Research and Biomedical Innovation (IRIB), Normandy University PRES, University of Rouen, Mont-Saint-Aignan, France
| | - Jérôme Leprince
- Inserm U982, Laboratory of Neuronal and Neuroendocrine Communication and Differentiation, Astrocyte and Vascular Niche, University of Rouen, Mont-Saint-Aignan, France
- Institute of Research and Biomedical Innovation (IRIB), Normandy University PRES, University of Rouen, Mont-Saint-Aignan, France
| | - Vincent Compère
- Inserm U982, Laboratory of Neuronal and Neuroendocrine Communication and Differentiation, Astrocyte and Vascular Niche, University of Rouen, Mont-Saint-Aignan, France
- Institute of Research and Biomedical Innovation (IRIB), Normandy University PRES, University of Rouen, Mont-Saint-Aignan, France
- Department of Anesthesiology and Critical Care, Rouen University Hospital, Rouen, France
| | - Fabrice Morin
- Inserm U982, Laboratory of Neuronal and Neuroendocrine Communication and Differentiation, Astrocyte and Vascular Niche, University of Rouen, Mont-Saint-Aignan, France
- Institute of Research and Biomedical Innovation (IRIB), Normandy University PRES, University of Rouen, Mont-Saint-Aignan, France
| | - François Proust
- Inserm U982, Laboratory of Neuronal and Neuroendocrine Communication and Differentiation, Astrocyte and Vascular Niche, University of Rouen, Mont-Saint-Aignan, France
- Institute of Research and Biomedical Innovation (IRIB), Normandy University PRES, University of Rouen, Mont-Saint-Aignan, France
- Department of Neurosurgery, Rouen University Hospital, Rouen, France
| | - Pierrick Gandolfo
- Inserm U982, Laboratory of Neuronal and Neuroendocrine Communication and Differentiation, Astrocyte and Vascular Niche, University of Rouen, Mont-Saint-Aignan, France
- Institute of Research and Biomedical Innovation (IRIB), Normandy University PRES, University of Rouen, Mont-Saint-Aignan, France
| | - Marie-Christine Tonon
- Inserm U982, Laboratory of Neuronal and Neuroendocrine Communication and Differentiation, Astrocyte and Vascular Niche, University of Rouen, Mont-Saint-Aignan, France
- Institute of Research and Biomedical Innovation (IRIB), Normandy University PRES, University of Rouen, Mont-Saint-Aignan, France
| | - Hélène Castel
- Inserm U982, Laboratory of Neuronal and Neuroendocrine Communication and Differentiation, Astrocyte and Vascular Niche, University of Rouen, Mont-Saint-Aignan, France
- Institute of Research and Biomedical Innovation (IRIB), Normandy University PRES, University of Rouen, Mont-Saint-Aignan, France
- * E-mail:
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5
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Cuzon Carlson VC, Yeh HH. GABAA receptor subunit profiles of tangentially migrating neurons derived from the medial ganglionic eminence. Cereb Cortex 2010; 21:1792-802. [PMID: 21148088 DOI: 10.1093/cercor/bhq247] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
During rodent corticogenesis, a sizeable subpopulation of γ-aminobutyric acid (GABA)ergic interneurons arises extracortically from the medial ganglionic eminence (MGE). These neurons progressively acquire responsiveness to GABA in the course of corticopetal tangential migration, a process regulated by ambient GABA and mediated by GABA(A) receptors. Here, we combined patch clamp electrophysiology and single-cell reverse transcription-polymerase chain reaction to examine GABA(A) receptor expression in green fluorescent MGE-derived (eGFP+) cells in telencephalic slices from gestational day 14.5 BAC-Lhx6 embryos. GABA concentration-response curves revealed lower apparent affinity and efficacy in eGFP+ cells in and around the MGE than their counterparts in the cortex. Pharmacological tests revealed subunit-selective response profiles in the MGE and cortex consistent with differential expression of GABA(A) receptor isoforms. Profiling of GABA(A) receptor subunit transcripts (α1-5, β1-3, and γ1-3, δ) uncovered increased expression of the α1-, α2-, α5-, γ2-, and γ3-subunit messenger RNAs in the cortex. We propose that the dynamic expression of certain GABA(A) receptor subunits contributes to assembling receptor isoforms that confer functional attributes important in regulating the migration and maturation of primordial GABAergic cortical interneurons.
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Affiliation(s)
- Verginia C Cuzon Carlson
- Department of Physiology and Neurobiology, Dartmouth Medical School, Dartmouth-Hitchcock Medical Center, Lebanon, NH 03756, USA
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6
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Abstract
Status epilepticus is a neurological emergency that results in mortality and neurological morbidity. It has been postulated that the reduction of inhibitory transmission during status epilepticus results from a rapid modification of GABA(A) receptors. However, the mechanism(s) that contributes to this modification has not been elucidated. We report, using an in vitro model of status epilepticus combined with electrophysiological and cellular imaging techniques, that prolonged epileptiform bursting results in a reduction of GABA-mediated synaptic inhibition. Furthermore, we found that constitutive internalization of GABA(A) receptors is rapid and accelerated by the increased neuronal activity associated with seizures. Inhibition of neuronal activity reduced the rate of internalization. These findings suggest that the rate of GABA(A) receptor internalization is regulated by neuronal activity and its acceleration contributes to the reduction of inhibitory transmission observed during prolonged seizures.
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7
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Gilbert SL, Zhang L, Forster ML, Anderson JR, Iwase T, Soliven B, Donahue LR, Sweet HO, Bronson RT, Davisson MT, Wollmann RL, Lahn BT. Trak1 mutation disrupts GABA(A) receptor homeostasis in hypertonic mice. Nat Genet 2005; 38:245-50. [PMID: 16380713 DOI: 10.1038/ng1715] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2005] [Accepted: 09/12/2005] [Indexed: 02/06/2023]
Abstract
Hypertonia, which results from motor pathway defects in the central nervous system (CNS), is observed in numerous neurological conditions, including cerebral palsy, stroke, spinal cord injury, stiff-person syndrome, spastic paraplegia, dystonia and Parkinson disease. Mice with mutation in the hypertonic (hyrt) gene exhibit severe hypertonia as their primary symptom. Here we show that hyrt mutant mice have much lower levels of gamma-aminobutyric acid type A (GABA(A)) receptors in their CNS, particularly the lower motor neurons, than do wild-type mice, indicating that the hypertonicity of the mutants is likely to be caused by deficits in GABA-mediated motor neuron inhibition. We cloned the responsible gene, trafficking protein, kinesin binding 1 (Trak1), and showed that its protein product interacts with GABA(A) receptors. Our data implicate Trak1 as a crucial regulator of GABA(A) receptor homeostasis and underscore the importance of hyrt mice as a model for studying the molecular etiology of hypertonia associated with human neurological diseases.
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Affiliation(s)
- Sandra L Gilbert
- Howard Hughes Medical Institute and Department of Human Genetics, University of Chicago, Chicago, Illinois 60637, USA
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Christie SB, Li RW, Miralles CP, Yang BY, De Blas AL. Clustered and non-clustered GABAA receptors in cultured hippocampal neurons. Mol Cell Neurosci 2005; 31:1-14. [PMID: 16181787 DOI: 10.1016/j.mcn.2005.08.014] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2005] [Revised: 08/17/2005] [Accepted: 08/23/2005] [Indexed: 12/31/2022] Open
Abstract
In cultured hippocampal neurons, gamma2 subunit-containing GABA(A) Rs form large postsynaptic clusters at GABAergic synapses and small clusters outside GABAergic synapses. We now show that a pool of non-clustered gamma2 subunit-containing GABA(A) Rs are also present at the cell surface. We also demonstrate that myc- or EGFP-tagged gamma2, alpha2, beta3 or alpha1 subunits expressed in these neurons assemble with endogenous subunits, forming GABA(A) Rs that target large postsynaptic clusters, small clusters outside GABAergic synapses or a pool of non-clustered surface GABA(A) Rs. In contrast, myc- or EGFP-tagged delta subunits only form non-clustered GABA(A) Rs, which can be induced to form clusters by antibody capping. A myc-tagged chimeric gamma2 subunit possessing the large intracellular loop (IL) of the delta-subunit IL (myc gamma2S/delta-IL) assembled into GABA(A) Rs, but it did not form clusters, therefore behaving like the delta subunit. Thus, the large intracellular loops of gamma2 and delta play an important role in determining the synaptic clustering/non-clustering capacity of the GABA(A) Rs.
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Affiliation(s)
- S B Christie
- Department of Physiology and Neurobiology, University of Connecticut, 3107 Horsebarn Hill Rd., U-4156, Storrs, CT 06269, USA
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10
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Hamilton NM, Cooke AJ. α-Subunit selective modulators of GABAAreceptor function as CNS therapeutics. Expert Opin Ther Pat 2005. [DOI: 10.1517/13543776.12.10.1491] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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11
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Lüscher B, Keller CA. Regulation of GABAA receptor trafficking, channel activity, and functional plasticity of inhibitory synapses. Pharmacol Ther 2004; 102:195-221. [PMID: 15246246 DOI: 10.1016/j.pharmthera.2004.04.003] [Citation(s) in RCA: 201] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Neural inhibition in the brain is mainly mediated by ionotropic gamma-aminobutyric acid type A (GABA(A)) receptors. Different subtypes of these receptors, distinguished by their subunit composition, are either concentrated at postsynaptic sites where they mediate phasic inhibition or found at perisynaptic and extrasynaptic locations where they prolong phasic inhibition and mediate tonic inhibition, respectively. Of special interest are mechanisms that modulate the stability and function of postsynaptic GABA(A) receptor subtypes and that are implicated in functional plasticity of inhibitory transmission in the brain. We will summarize recent progress on the classification of synaptic versus extrasynaptic receptors, the molecular composition of the postsynaptic cytoskeleton, the function of receptor-associated proteins in trafficking of GABA(A) receptors to and from synapses, and their role in post-translational signaling mechanisms that modulate the stability, density, and function of GABA(A) receptors in the postsynaptic membrane.
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Affiliation(s)
- Bernhard Lüscher
- Department of Biology, Pennsylvania State University, University Park, PA 16802, USA.
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12
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Charych EI, Yu W, Miralles CP, Serwanski DR, Li X, Rubio M, De Blas AL. The brefeldin A-inhibited GDP/GTP exchange factor 2, a protein involved in vesicular trafficking, interacts with the β subunits of the GABAA receptors. J Neurochem 2004; 90:173-89. [PMID: 15198677 DOI: 10.1111/j.1471-4159.2004.02481.x] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We have found that the brefeldin A-inhibited GDP/GTP exchange factor 2 (BIG2) interacts with the beta subunits of the gamma-aminobutyric acid type-A receptor (GABA(A)R). BIG2 is a Sec7 domain-containing guanine nucleotide exchange factor known to be involved in vesicular and protein trafficking. The interaction between the 110 amino acid C-terminal fragment of BIG2 and the large intracellular loop of the GABA(A)R beta subunits was revealed with a yeast two-hybrid assay. The native BIG2 and GABA(A)Rs interact in the brain since both coprecipitated from detergent extracts with either anti-GABA(A)R or anti-BIG2 antibodies. In transfected human embryonic kidney cell line 293 cells, BIG2 promotes the exit of GABA(A)Rs from endoplasmic reticulum. Double label immunofluorescence of cultured hippocampal neurons and electron microscopy immunocytochemistry of rat brain tissue show that BIG2 concentrates in the trans-Golgi network. BIG2 is also present in vesicle-like structures in the dendritic cytoplasm, sometimes colocalizing with GABA(A)Rs. BIG2 is present in both inhibitory GABAergic synapses that contain GABA(A)Rs and in asymmetric excitatory synapses. The results are consistent with the hypotheses that the interaction of BIG2 with the GABA(A)R beta subunits plays a role in the exocytosis and trafficking of assembled GABA(A)R to the cell surface.
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Affiliation(s)
- Erik I Charych
- Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut, USA
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13
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Liang J, Cagetti E, Olsen RW, Spigelman I. Altered Pharmacology of Synaptic and Extrasynaptic GABAA Receptors on CA1 Hippocampal Neurons Is Consistent with Subunit Changes in a Model of Alcohol Withdrawal and Dependence. J Pharmacol Exp Ther 2004; 310:1234-45. [PMID: 15126642 DOI: 10.1124/jpet.104.067983] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Previously, we reported (Cagetti, Liang, Spigelman, and Olsen, 2003) that chronic intermittent ethanol (CIE) treatment leads to signs of alcohol dependence, including anxiety and hyperactivity, accompanied by reduced synaptic gamma-aminobutyric acid (A) receptor (GABAAR) function and altered sensitivity to its allosteric modulators consistent with a measured switch in subunit composition. In this study, we separated the synaptic and extrasynaptic components of GABAAR activation in recordings from pyramidal CA1 cells of hippocampal slices and demonstrated marked differences in the responsiveness of synaptic and extrasynaptic GABAARs to agonists and allosteric modulators in control rats, and in the way they are altered following CIE treatment. Notably, tonic inhibition mediated by extrasynaptic GABAARs was differentially sensitive to the partial agonist gaboxadol (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol; THIP) and the allosteric modulator zolpidem, compared with the miniature inhibitory synaptic currents (mIPSCs) in the same cells from saline-treated rats. After CIE treatment, potentiation of tonic currents by diazepam and zolpidem was lost, whereas potentiation by the alpha4 subunit-preferring benzodiazepine Ro15-4513 (ethyl 8-azido-6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a]-[1,4]benzodiazepine-3-carboxylate) and THIP was only partially reduced. Potentiation of synaptic GABAAR currents by zolpidem was eliminated after CIE, whereas THIP slightly inhibited mIPSCs from control rats and greatly enhanced them after CIE treatment. These results are consistent with alpha1 subunit decreases at synaptic and extrasynaptic GABAARs, whereas alpha4 subunits are increased at synaptic and decreased at extrasynaptic GABAARs. Behaviorally, THIP was active as a hypnotic and anxiolytic but not as an anti-convulsant against pentylenetetrazol seizures in control rats. Only slight tolerance was observed to the sleep time, but not to the anxiolytic, effect of THIP after CIE. Thus, differential alterations in synaptic and extrasynaptic GABAARs appear to play an important role in the brain plasticity of alcohol dependence, and withdrawal signs may be profitably treated with GABAergic drugs such as THIP, which does not show cross-tolerance with ethanol.
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Affiliation(s)
- Jing Liang
- Division of Oral Biology and Medicine, School of Dentistry, UCLA, Los Angeles, CA 90095-1668, USA
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Blair RE, Sombati S, Lawrence DC, McCay BD, DeLorenzo RJ. Epileptogenesis Causes Acute and Chronic Increases in GABAA Receptor Endocytosis That Contributes to the Induction and Maintenance of Seizures in the Hippocampal Culture Model of Acquired Epilepsy. J Pharmacol Exp Ther 2004; 310:871-80. [PMID: 15084648 DOI: 10.1124/jpet.104.068478] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Altered GABAergic inhibitory tone has been observed in association with a number of both acute and chronic models of epilepsy and is believed to be the result, in part, of a decrease in function of the postsynaptic GABAA receptor (GABAAR). This study was carried out to investigate if alterations in receptor internalization contribute to the decrease in GABAAR function observed with epilepsy, utilizing the hippocampal neuronal culture model of low-Mg2+-induced spontaneous recurrent epileptiform discharges (SREDs). Analysis of GABAAR function in "epileptic" cultures showed a 62% reduction in [3H]flunitrazepam binding to the GABAA alpha receptor subunit and a 50% decrease in GABA currents when compared with controls. Confocal microscopy analysis of immunohistochemical staining of GABAAR beta2/beta3 subunit expression revealed approximately a 30% decrease of membrane staining in hippocampal cultures displaying SREDs immediately after low-Mg2+ treatment and in the chronic epileptic state. Low-Mg2+-treated cultures internalized antibody labeled GABAA receptor with an increase in rate of 68% from control. Inhibition of GABAAR endocytosis in epileptic cultures resulted in both a recovery to control levels of membrane GABAA beta2/beta3 immunostaining and a total blockade of SREDs. These results indicate that altered GABAAR endocytosis contributes to the decrease in GABAAR expression and function observed in this in vitro model of epilepsy and plays a role in causing and maintaining SREDs. Understanding the mechanisms underlying altered GABAA R recycling may offer new insights into the pathophysiology of epilepsy and provide novel therapeutic strategies to treat this major neurological condition.
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Affiliation(s)
- Robert E Blair
- Department of Neurology, Virginia Commonwealth University, School of Medicine, P.O. Box 980599, Richmond, VA 23298, USA.
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15
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Kittler JT, Moss SJ. Modulation of GABAA receptor activity by phosphorylation and receptor trafficking: implications for the efficacy of synaptic inhibition. Curr Opin Neurobiol 2003; 13:341-7. [PMID: 12850219 DOI: 10.1016/s0959-4388(03)00064-3] [Citation(s) in RCA: 239] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Fast synaptic inhibition in the brain is largely mediated by GABA(A) receptors. These ligand-gated ion channels are crucial in the control of cell and network activity. Therefore, modulating their function or cell surface stability will have major consequences for neuronal excitation. It has become clear that the stability and activity of GABA(A) receptors at synapses can be dynamically modulated by receptor trafficking and phosphorylation. Here, we discuss these regulatory mechanisms, and their consequences for the efficacy of GABA(A) receptor mediated synaptic inhibition.
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Affiliation(s)
- Josef T Kittler
- Medical Research Council Laboratory of Molecular Cell Biology and Department of Pharmacology, University College London, Gower Street, London WC1E 6BT, UK
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Fritschy JM, Brünig I. Formation and plasticity of GABAergic synapses: physiological mechanisms and pathophysiological implications. Pharmacol Ther 2003; 98:299-323. [PMID: 12782242 DOI: 10.1016/s0163-7258(03)00037-8] [Citation(s) in RCA: 244] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
gamma-Aminobutyric acid(A) (GABA(A)) receptors mediate most of the fast inhibitory neurotransmission in the CNS. They represent a major site of action for clinically relevant drugs, such as benzodiazepines and ethanol, and endogenous modulators, including neuroactive steroids. Alterations in GABA(A) receptor expression and function are thought to contribute to prevalent neurological and psychiatric diseases. Molecular cloning and immunochemical characterization of GABA(A) receptor subunits revealed a multiplicity of receptor subtypes with specific functional and pharmacological properties. A major tenet of these studies is that GABA(A) receptor heterogeneity represents a key factor for fine-tuning of inhibitory transmission under physiological and pathophysiological conditions. The aim of this review is to highlight recent findings on the regulation of GABA(A) receptor expression and function, focusing on the mechanisms of sorting, targeting, and synaptic clustering of GABA(A) receptor subtypes and their associated proteins, on trafficking of cell-surface receptors as a means of regulating synaptic (and extrasynaptic) transmission on a short-time basis, on the role of endogenous neurosteroids for GABA(A) receptor plasticity, and on alterations of GABA(A) receptor expression and localization in major neurological disorders. Altogether, the findings presented in this review underscore the necessity of considering GABA(A) receptor-mediated neurotransmission as a dynamic and highly flexible process controlled by multiple mechanisms operating at the molecular, cellular, and systemic level. Furthermore, the selected topics highlight the relevance of concepts derived from experimental studies for understanding GABA(A) receptor alterations in disease states and for designing improved therapeutic strategies based on subtype-selective drugs.
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Affiliation(s)
- Jean-Marc Fritschy
- Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
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