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Magro G. Early Polytherapy for Probably Benzodiazepine Refractory Naïve Status Epilepticus (Stage 1 Plus). Neurol Int 2025; 17:11. [PMID: 39852775 PMCID: PMC11767287 DOI: 10.3390/neurolint17010011] [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: 12/16/2024] [Revised: 01/10/2025] [Accepted: 01/16/2025] [Indexed: 01/26/2025] Open
Abstract
Stage 1 Plus is defined here as a naïve, previously untreated, status epilepticus (SE) that is probably refractory to Benzodiazepines (BDZ). These cases include not only prolonged SE as previously proposed by the author (SE lasting > 10 min) but also other cases notoriously associated with BDZ refractoriness such as the absence of prominent motor phenomena and acute etiology (especially primary central nervous system etiology). Interestingly, the absence of prominent motor phenomena as is the case of non convulsive SE might implicitly fall in the category of prolonged SE due to the delay in recognition and treatment. Future studies should help identify other factors associated with BDZ refractoriness, therefore widening the definition of Stage 1 Plus. The appropriate timing for defining prolonged SE may also differ depending on different etiology. Consequently, in future tailored models of SE, the definition of prolonged SE could be enhanced by defining it for a longer duration than Tx, a time point that changes based on different etiologies (x), Tx being much shorter than 10 min in acute etiologies. These cases of naïve probably BDZ refractory SE (Stage 1 Plus) might require a different approach: combined polytherapy from the start. The objective of this review is to provide pathophysiological and pre-clinical evidence, mostly from animal studies, for the different approach of combined polytherapy from the start for those cases of SE falling in the definition of Stage 1 Plus.
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Affiliation(s)
- Giuseppe Magro
- Department of Neuroscience, "Giovanni Paolo II" Hospital, Lamezia Terme, 88046 Catanzaro, Italy
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2
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Michałowski MA, Kłopotowski K, Wiera G, Czyżewska MM, Mozrzymas JW. Molecular mechanisms of the GABA type A receptor function. Q Rev Biophys 2025; 58:e3. [PMID: 39806800 DOI: 10.1017/s0033583524000179] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2025]
Abstract
The GABA type A receptor (GABAAR) belongs to the family of pentameric ligand-gated ion channels and plays a key role in inhibition in adult mammalian brains. Dysfunction of this macromolecule may lead to epilepsy, anxiety disorders, autism, depression, and schizophrenia. GABAAR is also a target for multiple physiologically and clinically relevant modulators, such as benzodiazepines (BDZs), general anesthetics, and neurosteroids. The first GABAAR structure appeared in 2014, but the past years have brought a particularly abundant surge in structural data for these receptors with various ligands and modulators. Although the open conformation remains elusive, this novel information has pushed the structure-function studies to an unprecedented level. Electrophysiology, mutagenesis, photolabeling, and in silico simulations, guided by novel structural information, shed new light on the molecular mechanisms of receptor functioning. The main goal of this review is to present the current knowledge of GABAAR functional and structural properties. The review begins with an outline of the functional and structural studies of GABAAR, accompanied by some methodological considerations, especially biophysical methods, enabling the reader to follow how major breakthroughs in characterizing GABAAR features have been achieved. The main section provides a comprehensive analysis of the functional significance of specific structural elements in GABAARs. We additionally summarize the current knowledge on the binding sites for major GABAAR modulators, referring to the molecular underpinnings of their action. The final chapter of the review moves beyond examining GABAAR as an isolated macromolecule and describes the interactions of the receptor with other proteins in a broader context of inhibitory plasticity. In the final section, we propose a general conclusion that agonist binding to the orthosteric binding sites appears to rely on local interactions, whereas conformational transitions of bound macromolecule (gating) and allosteric modulation seem to reflect more global phenomena involving vast portions of the macromolecule.
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Affiliation(s)
- Michał A Michałowski
- Faculty of Medicine, Department of Biophysics and Neuroscience, Wroclaw Medical University, Wrocław, Poland
| | - Karol Kłopotowski
- Faculty of Medicine, Department of Biophysics and Neuroscience, Wroclaw Medical University, Wrocław, Poland
| | - Grzegorz Wiera
- Faculty of Medicine, Department of Biophysics and Neuroscience, Wroclaw Medical University, Wrocław, Poland
| | - Marta M Czyżewska
- Faculty of Medicine, Department of Biophysics and Neuroscience, Wroclaw Medical University, Wrocław, Poland
| | - Jerzy W Mozrzymas
- Faculty of Medicine, Department of Biophysics and Neuroscience, Wroclaw Medical University, Wrocław, Poland
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3
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Nors JW, Endres Z, Goldschen-Ohm MP. GABA A receptor subunit M2-M3 linkers have asymmetric roles in pore gating and diazepam modulation. Biophys J 2024; 123:2085-2096. [PMID: 38400541 PMCID: PMC11309982 DOI: 10.1016/j.bpj.2024.02.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Revised: 01/19/2024] [Accepted: 02/20/2024] [Indexed: 02/25/2024] Open
Abstract
GABAA receptors (GABAARs) are neurotransmitter-gated ion channels critical for inhibitory synaptic transmission as well as the molecular target for benzodiazepines (BZDs), one of the most widely prescribed class of psychotropic drugs today. Despite structural insight into the conformations underlying functional channel states, the detailed molecular interactions involved in conformational transitions and the physical basis for their modulation by BZDs are not fully understood. We previously identified that alanine substitution at the central residue in the α1 subunit M2-M3 linker (V279A) enhances the efficiency of linkage between the BZD site and the pore gate. Here, we expand on this work by investigating the effect of alanine substitutions at the analogous positions in the M2-M3 linkers of β2 (I275A) and γ2 (V290A) subunits, which together with α1 comprise typical heteromeric α1β2γ2 synaptic GABAARs. We find that these mutations confer subunit-specific effects on the intrinsic pore closed-open equilibrium and its modulation by the BZD diazepam (DZ). The mutations α1(V279A) or γ2(V290A) bias the channel toward a closed conformation, whereas β2(I275A) biases the channel toward an open conformation to the extent that the channel becomes leaky and opens spontaneously in the absence of agonist. In contrast, only α1(V279A) enhances the efficiency of DZ-to-pore linkage, whereas mutations in the other two subunits have no effect. These observations show that the central residue in the M2-M3 linkers of distinct subunits in synaptic α1β2γ2 GABAARs contribute asymmetrically to the intrinsic closed-open equilibrium and its modulation by DZ.
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Affiliation(s)
- Joseph W Nors
- Department of Neuroscience, University of Texas at Austin, Austin, Texas; Department of Molecular and Cellular Physiology, Stanford University, Stanford, California
| | - Zachary Endres
- Department of Neuroscience, University of Texas at Austin, Austin, Texas
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4
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Naylor DE. In the fast lane: Receptor trafficking during status epilepticus. Epilepsia Open 2023; 8 Suppl 1:S35-S65. [PMID: 36861477 PMCID: PMC10173858 DOI: 10.1002/epi4.12718] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2022] [Accepted: 02/23/2023] [Indexed: 03/03/2023] Open
Abstract
Status epilepticus (SE) remains a significant cause of morbidity and mortality and often is refractory to standard first-line treatments. A rapid loss of synaptic inhibition and development of pharmacoresistance to benzodiazepines (BZDs) occurs early during SE, while NMDA and AMPA receptor antagonists remain effective treatments after BZDs have failed. Multimodal and subunit-selective receptor trafficking within minutes to an hour of SE involves GABA-A, NMDA, and AMPA receptors and contributes to shifts in the number and subunit composition of surface receptors with differential impacts on the physiology, pharmacology, and strength of GABAergic and glutamatergic currents at synaptic and extrasynaptic sites. During the first hour of SE, synaptic GABA-A receptors containing γ2 subunits move to the cell interior while extrasynaptic GABA-A receptors with δ subunits are preserved. Conversely, NMDA receptors containing N2B subunits are increased at synaptic and extrasynaptic sites, and homomeric GluA1 ("GluA2-lacking") calcium permeant AMPA receptor surface expression also is increased. Molecular mechanisms, largely driven by NMDA receptor or calcium permeant AMPA receptor activation early during circuit hyperactivity, regulate subunit-specific interactions with proteins involved with synaptic scaffolding, adaptin-AP2/clathrin-dependent endocytosis, endoplasmic reticulum (ER) retention, and endosomal recycling. Reviewed here is how SE-induced shifts in receptor subunit composition and surface representation increase the excitatory to inhibitory imbalance that sustains seizures and fuels excitotoxicity contributing to chronic sequela such as "spontaneous recurrent seizures" (SRS). A role for early multimodal therapy is suggested both for treatment of SE and for prevention of long-term comorbidities.
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Affiliation(s)
- David E Naylor
- VA Greater Los Angeles Healthcare System, Department of Neurology, David Geffen School of Medicine at UCLA, and The Lundquist Institute at Harbor-UCLA Medical Center, Los Angeles, California, USA
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5
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Hernandez CC, Shen Y, Hu N, Shen W, Narayanan V, Ramsey K, He W, Zou L, Macdonald RL. GABRG2 Variants Associated with Febrile Seizures. Biomolecules 2023; 13:414. [PMID: 36979350 PMCID: PMC10046037 DOI: 10.3390/biom13030414] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2022] [Revised: 02/13/2023] [Accepted: 02/17/2023] [Indexed: 02/24/2023] Open
Abstract
Febrile seizures (FS) are the most common form of epilepsy in children between six months and five years of age. FS is a self-limited type of fever-related seizure. However, complicated prolonged FS can lead to complex partial epilepsy. We found that among the GABAA receptor subunit (GABR) genes, most variants associated with FS are harbored in the γ2 subunit (GABRG2). Here, we characterized the effects of eight variants in the GABAA receptor γ2 subunit on receptor biogenesis and channel function. Two-thirds of the GABRG2 variants followed the expected autosomal dominant inheritance in FS and occurred as missense and nonsense variants. The remaining one-third appeared as de novo in the affected probands and occurred only as missense variants. The loss of GABAA receptor function and dominant negative effect on GABAA receptor biogenesis likely caused the FS phenotype. In general, variants in the GABRG2 result in a broad spectrum of phenotypic severity, ranging from asymptomatic, FS, genetic epilepsy with febrile seizures plus (GEFS+), and Dravet syndrome individuals. The data presented here support the link between FS, epilepsy, and GABRG2 variants, shedding light on the relationship between the variant topological occurrence and disease severity.
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Affiliation(s)
- Ciria C. Hernandez
- Life Sciences Institute, University of Michigan, Ann Arbor, MI 48109, USA
| | - Yanwen Shen
- Department of Pediatrics, Seventh Medical Center of Chinese PLA General Hospital, Beijing 100010, China
| | - Ningning Hu
- Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Wangzhen Shen
- Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Vinodh Narayanan
- Center for Rare Childhood Disorders, Translational Genomics Research Institute, Phoenix, AZ 85004, USA
| | - Keri Ramsey
- Center for Rare Childhood Disorders, Translational Genomics Research Institute, Phoenix, AZ 85004, USA
| | - Wen He
- Department of Pediatrics, Seventh Medical Center of Chinese PLA General Hospital, Beijing 100010, China
| | - Liping Zou
- Department of Pediatrics, Seventh Medical Center of Chinese PLA General Hospital, Beijing 100010, China
| | - Robert L. Macdonald
- Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
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6
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Goldschen-Ohm MP. Benzodiazepine Modulation of GABA A Receptors: A Mechanistic Perspective. Biomolecules 2022; 12:1784. [PMID: 36551212 PMCID: PMC9775625 DOI: 10.3390/biom12121784] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2022] [Revised: 11/23/2022] [Accepted: 11/26/2022] [Indexed: 12/05/2022] Open
Abstract
Benzodiazepines (BZDs) are a class of widely prescribed psychotropic drugs that target GABAA receptors (GABAARs) to tune inhibitory synaptic signaling throughout the central nervous system. Despite knowing their molecular target for over 40 years, we still do not fully understand the mechanism of modulation at the level of the channel protein. Nonetheless, functional studies, together with recent cryo-EM structures of GABAA(α1)2(βX)2(γ2)1 receptors in complex with BZDs, provide a wealth of information to aid in addressing this gap in knowledge. Here, mechanistic interpretations of functional and structural evidence for the action of BZDs at GABAA(α1)2(βX)2(γ2)1 receptors are reviewed. The goal is not to describe each of the many studies that are relevant to this discussion nor to dissect in detail all the effects of individual mutations or perturbations but rather to highlight general mechanistic principles in the context of recent structural information.
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7
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Kłopotowski K, Czyżewska MM, Mozrzymas JW. Glycine substitution of α1F64 residue at the loop D of GABA A receptor impairs gating - Implications for importance of binding site-channel gate linker rigidity. Biochem Pharmacol 2021; 192:114668. [PMID: 34216603 DOI: 10.1016/j.bcp.2021.114668] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Revised: 06/27/2021] [Accepted: 06/28/2021] [Indexed: 12/29/2022]
Abstract
GABAA receptors (GABAARs) play a crucial role in mediating inhibition in adult mammalian brains. In the recent years, an impressive progress in revealing the static structure of GABAARs was achieved but the molecular mechanisms underlying their conformational transitions remain elusive. Phenylalanine 64 (α1F64) is located at the loop D of the orthosteric binding site of GABAAR and was found to directly interact with GABA molecule. Mutations of α1F64 were demonstrated to affect not only binding but also some gating properties. Loop D is a rigid β strand which seems to be particularly suitable to convey activatory signaling from the ligand binding site (LBS) to the gate at the channel pore. To test this scenario, we have investigated the substitution of α1F64 with glycine, the smallest amino acid, widely recognized as a rigidity "reducer" of protein structures. To this end, we assessed the impact of the α1F64G mutation in the α1β2γ2L type of GABAARs on gating properties by analyzing both macroscopic responses to rapid agonist applications and single-channel currents. We found that this substitution dramatically altered all gating features of the receptor (opening/closing, preactivation and desensitization) which contrasts with markedly weaker effects of previously considered substitutions (α1F64L and α1F64A). In particular, α1F64G mutation practically abolished the desensitization process. At the same time, the α1F64G mutant maintained gating integrity manifested as single-channel activity in the form of clusters. We conclude that rigidity of the loop D plays a crucial role in conveying the activation signal from the LBS to the channel gate.
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Affiliation(s)
- Karol Kłopotowski
- Wroclaw Medical University, Department of Biophysics and Neuroscience, Chalubinskiego 3A, Wroclaw, Dolnośląskie PL 50-368, +48 71 784 15 51, Poland.
| | - Marta M Czyżewska
- Wroclaw Medical University, Department of Biophysics and Neuroscience, Chalubinskiego 3A, Wroclaw, Dolnośląskie PL 50-368, +48 71 784 15 51, Poland
| | - Jerzy W Mozrzymas
- Wroclaw Medical University, Department of Biophysics and Neuroscience, Chalubinskiego 3A, Wroclaw, Dolnośląskie PL 50-368, +48 71 784 15 51, Poland.
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8
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Nors JW, Gupta S, Goldschen-Ohm MP. A critical residue in the α 1M2-M3 linker regulating mammalian GABA A receptor pore gating by diazepam. eLife 2021; 10:64400. [PMID: 33591271 PMCID: PMC7899671 DOI: 10.7554/elife.64400] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Accepted: 02/15/2021] [Indexed: 01/29/2023] Open
Abstract
Benzodiazepines (BZDs) are a class of widely prescribed psychotropic drugs that modulate activity of GABAA receptors (GABAARs), neurotransmitter-gated ion channels critical for synaptic transmission. However, the physical basis of this modulation is poorly understood. We explore the role of an important gating domain, the α1M2–M3 linker, in linkage between the BZD site and pore gate. To probe energetics of this coupling without complication from bound agonist, we use a gain of function mutant (α1L9'Tβ2γ2L) directly activated by BZDs. We identify a specific residue whose mutation (α1V279A) more than doubles the energetic contribution of the BZD positive modulator diazepam (DZ) to pore opening and also enhances DZ potentiation of GABA-evoked currents in a wild-type background. In contrast, other linker mutations have little effect on DZ efficiency, but generally impair unliganded pore opening. Our observations reveal an important residue regulating BZD-pore linkage, thereby shedding new light on the molecular mechanism of these drugs.
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Affiliation(s)
- Joseph W Nors
- University of Texas at Austin, Department of Neuroscience, Austin, United States
| | - Shipra Gupta
- University of Texas at Austin, Department of Neuroscience, Austin, United States
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9
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Brams M, Govaerts C, Kambara K, Price KL, Spurny R, Gharpure A, Pardon E, Evans GL, Bertrand D, Lummis SCR, Hibbs RE, Steyaert J, Ulens C. Modulation of the Erwinia ligand-gated ion channel (ELIC) and the 5-HT 3 receptor via a common vestibule site. eLife 2020; 9:e51511. [PMID: 31990273 PMCID: PMC7015668 DOI: 10.7554/elife.51511] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Accepted: 01/27/2020] [Indexed: 01/13/2023] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) or Cys-loop receptors are involved in fast synaptic signaling in the nervous system. Allosteric modulators bind to sites that are remote from the neurotransmitter binding site, but modify coupling of ligand binding to channel opening. In this study, we developed nanobodies (single domain antibodies), which are functionally active as allosteric modulators, and solved co-crystal structures of the prokaryote (Erwinia) channel ELIC bound either to a positive or a negative allosteric modulator. The allosteric nanobody binding sites partially overlap with those of small molecule modulators, including a vestibule binding site that is not accessible in some pLGICs. Using mutagenesis, we extrapolate the functional importance of the vestibule binding site to the human 5-HT3 receptor, suggesting a common mechanism of modulation in this protein and ELIC. Thus we identify key elements of allosteric binding sites, and extend drug design possibilities in pLGICs with an accessible vestibule site.
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Affiliation(s)
- Marijke Brams
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, Faculty of Medicine, KU LeuvenLeuvenBelgium
| | - Cedric Govaerts
- Laboratory for the Structure and Function of Biological Membranes, Center for Structural Biology and Bioinformatics, Université libre de BruxellesBrusselsBelgium
| | | | - Kerry L Price
- Department of Biochemistry, University of CambridgeCambridgeUnited Kingdom
| | - Radovan Spurny
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, Faculty of Medicine, KU LeuvenLeuvenBelgium
| | - Anant Gharpure
- Department of Neuroscience, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Biophysics, University of Texas Southwestern Medical CenterDallasUnited States
| | - Els Pardon
- Structural Biology Brussels, Vrije Universiteit BrusselBrusselsBelgium
- VIB-VUB Center for Structural Biology, VIBBrusselsBelgium
| | - Genevieve L Evans
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, Faculty of Medicine, KU LeuvenLeuvenBelgium
| | | | - Sarah CR Lummis
- Department of Biochemistry, University of CambridgeCambridgeUnited Kingdom
| | - Ryan E Hibbs
- Department of Neuroscience, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Biophysics, University of Texas Southwestern Medical CenterDallasUnited States
| | - Jan Steyaert
- Structural Biology Brussels, Vrije Universiteit BrusselBrusselsBelgium
- VIB-VUB Center for Structural Biology, VIBBrusselsBelgium
| | - Chris Ulens
- Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, Faculty of Medicine, KU LeuvenLeuvenBelgium
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10
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Jiang XM, Wang WP, Liu ZH, Yin HJ, Ma H, Feng N, Wang L, Huang HH, Wang XL. 2-(4-methyl-thiazol-5-yl) ethyl nitrate maleate-potentiated GABA A receptor response in hippocampal neurons. CNS Neurosci Ther 2018; 24:1231-1240. [PMID: 30039924 DOI: 10.1111/cns.13033] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2018] [Revised: 06/15/2018] [Accepted: 06/25/2018] [Indexed: 12/31/2022] Open
Abstract
AIMS 2-(4-methyl-thiazol-5-yl) ethyl nitrate maleate (NMZM), a derivative of clomethiazole (CMZ), had been investigated for the treatment of Alzheimer's disease (AD). The beneficial effects of NMZM in AD included reversing cognitive deficit, improving learning and memory as well as neuroprotection. The pharmacological effects of NMZM on GABAA receptors were reported previously; however, the mechanisms were unclear and were explored therefore. RESULTS In this study, we demonstrated that NMZM improved learning and memory by alleviating scopolamine-induced long-term potentiation (LTP) suppression in the dentate gyrus of rats, indicating that NMZM had protective effects against scopolamine-induced depression of LTP. Next, we investigated the action of NMZM on GABAA receptors in hippocampal neurons and the binding site of NMZM on GABAA receptors. NMZM directly activated GABAA receptors in hippocampal neurons in a weak manner. However, NMZM could potentiate the response of GABAA receptors to GABA and NMZM positively modulated GABAA receptors with an EC50 value of 465 μmol/L at 3 μmol/L GABA while this potentiation at low concentration of GABA (1, 3 μmol/L) was more significant than that at high concentration (10, 30 μmol/L). In addition, NMZM could enhance GABA currents after using diazepam and pentobarbital, the positive modulators of GABAA receptors. NMZM could not affect the etomidate-potentiated GABAA current. It suggested that the binding site of NMZM on GABAA receptors is the same as etomidate. CONCLUSIONS These results provided support for the neuroprotective effect of NMZM, which was partly dependent on the potentiation of GABAA receptors. The etomidate binding site might be a new target for neuronal protection and for drug development.
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Affiliation(s)
- Xiao-Mei Jiang
- State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of MateriaMedica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China
| | - Wei-Ping Wang
- State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of MateriaMedica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China
| | - Zhi-Hui Liu
- State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of MateriaMedica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China
| | - Hua-Jing Yin
- State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of MateriaMedica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China
| | - Hao Ma
- State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of MateriaMedica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China
| | - Nan Feng
- State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of MateriaMedica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China
| | - Ling Wang
- State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of MateriaMedica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China
| | - Hai-Hong Huang
- State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of MateriaMedica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China
| | - Xiao-Liang Wang
- State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of MateriaMedica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China
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11
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Pflanz NC, Daszkowski AW, Cornelison GL, Trudell JR, Mihic SJ. An intersubunit electrostatic interaction in the GABA A receptor facilitates its responses to benzodiazepines. J Biol Chem 2018; 293:8264-8274. [PMID: 29622679 DOI: 10.1074/jbc.ra118.002128] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Revised: 04/04/2018] [Indexed: 02/01/2023] Open
Abstract
Benzodiazepines are positive allosteric modulators of the GABAA receptor (GABAAR), acting at the α-γ subunit interface to enhance GABAAR function. GABA or benzodiazepine binding induces distinct conformational changes in the GABAAR. The molecular rearrangements in the GABAAR following benzodiazepine binding remain to be fully elucidated. Using two molecular models of the GABAAR, we identified electrostatic interactions between specific amino acids at the α-γ subunit interface that were broken by, or formed after, benzodiazepine binding. Using two-electrode voltage clamp electrophysiology in Xenopus laevis oocytes, we investigated these interactions by substituting one or both amino acids of each potential pair. We found that Lys104 in the α1 subunit forms an electrostatic bond with Asp75 of the γ2 subunit after benzodiazepine binding and that this bond stabilizes the positively modified state of the receptor. Substitution of these two residues to cysteine and subsequent covalent linkage between them increased the receptor's sensitivity to low GABA concentrations and decreased its response to benzodiazepines, producing a GABAAR that resembles a benzodiazepine-bound WT GABAAR. Breaking this bond restored sensitivity to GABA to WT levels and increased the receptor's response to benzodiazepines. The α1 Lys104 and γ2 Asp75 interaction did not play a role in ethanol or neurosteroid modulation of GABAAR, suggesting that different modulators induce different conformational changes in the receptor. These findings may help explain the additive or synergistic effects of modulators acting at the GABAAR.
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Affiliation(s)
- Natasha C Pflanz
- Department of Neuroscience, Division of Pharmacology and Toxicology, Waggoner Center for Alcohol and Addiction Research, Institutes for Neuroscience and Cell and Molecular Biology, University of Texas, Austin, Texas 78712
| | - Anna W Daszkowski
- Department of Neuroscience, Division of Pharmacology and Toxicology, Waggoner Center for Alcohol and Addiction Research, Institutes for Neuroscience and Cell and Molecular Biology, University of Texas, Austin, Texas 78712
| | - Garrett L Cornelison
- Department of Neuroscience, Division of Pharmacology and Toxicology, Waggoner Center for Alcohol and Addiction Research, Institutes for Neuroscience and Cell and Molecular Biology, University of Texas, Austin, Texas 78712
| | - James R Trudell
- Department of Anesthesia, Stanford University School of Medicine, Stanford, California 94305
| | - S John Mihic
- Department of Neuroscience, Division of Pharmacology and Toxicology, Waggoner Center for Alcohol and Addiction Research, Institutes for Neuroscience and Cell and Molecular Biology, University of Texas, Austin, Texas 78712.
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12
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Hernandez CC, Zhang Y, Hu N, Shen D, Shen W, Liu X, Kong W, Jiang Y, Macdonald RL. GABA A Receptor Coupling Junction and Pore GABRB3 Mutations are Linked to Early-Onset Epileptic Encephalopathy. Sci Rep 2017; 7:15903. [PMID: 29162865 PMCID: PMC5698489 DOI: 10.1038/s41598-017-16010-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Accepted: 10/11/2017] [Indexed: 12/17/2022] Open
Abstract
GABAA receptors are brain inhibitory chloride ion channels. Here we show functional analyses and structural simulations for three de novo missense mutations in the GABAA receptor β3 subunit gene (GABRB3) identified in patients with early-onset epileptic encephalopathy (EOEE) and profound developmental delay. We sought to obtain insights into the molecular mechanisms that might link defects in GABAA receptor biophysics and biogenesis to patients with EOEE. The mutant residues are part of conserved structural domains such as the Cys-loop (L170R) and M2-M3 loop (A305V) that form the GABA binding/channel gating coupling junction and the channel pore (T288N), which are functionally coupled during receptor activation. The mutant coupling junction residues caused rearrangements and formation of new hydrogen bonds in the open state, while the mutant pore residue reshaped the pore cavity. Whereas mutant coupling junction residues uncoupled during activation and caused gain of function, the mutant pore residue favoured low conductance receptors and differential sensitivity to diazepam and loss of function. These data reveal novel molecular mechanisms by which EOEE-linked mutations affect GABAA receptor function.
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Affiliation(s)
- Ciria C Hernandez
- Department of Neurology, Vanderbilt University, Nashville, TN., 37240-7915., USA. .,University of Michigan, Life Sciences Institute, 210 Washtenaw Ave., Room 6115, Ann Arbor, MI, 48109-2216, USA.
| | - Yujia Zhang
- Department of Pediatrics, Peking University First Hospital, Beijing, 100034, China
| | - Ningning Hu
- Department of Neurology, Vanderbilt University, Nashville, TN., 37240-7915., USA
| | - Dingding Shen
- The Graduate Program of Neuroscience, Vanderbilt University, Nashville, 37240-7915., TN, USA
| | - Wangzhen Shen
- Department of Neurology, Vanderbilt University, Nashville, TN., 37240-7915., USA
| | - Xiaoyan Liu
- Department of Pediatrics, Peking University First Hospital, Beijing, 100034, China
| | - Weijing Kong
- Department of Pediatrics, Peking University First Hospital, Beijing, 100034, China
| | - Yuwu Jiang
- Department of Pediatrics, Peking University First Hospital, Beijing, 100034, China.
| | - Robert L Macdonald
- Department of Neurology, Vanderbilt University, Nashville, TN., 37240-7915., USA.
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Shen D, Hernandez CC, Shen W, Hu N, Poduri A, Shiedley B, Rotenberg A, Datta AN, Leiz S, Patzer S, Boor R, Ramsey K, Goldberg E, Helbig I, Ortiz-Gonzalez XR, Lemke JR, Marsh ED, Macdonald RL. De novo GABRG2 mutations associated with epileptic encephalopathies. Brain 2017; 140:49-67. [PMID: 27864268 PMCID: PMC5226060 DOI: 10.1093/brain/aww272] [Citation(s) in RCA: 81] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2016] [Revised: 09/05/2016] [Accepted: 09/10/2016] [Indexed: 12/17/2022] Open
Abstract
Epileptic encephalopathies are a devastating group of severe childhood onset epilepsies with medication-resistant seizures and poor developmental outcomes. Many epileptic encephalopathies have a genetic aetiology and are often associated with de novo mutations in genes mediating synaptic transmission, including GABAA receptor subunit genes. Recently, we performed next generation sequencing on patients with a spectrum of epileptic encephalopathy phenotypes, and we identified five novel (A106T, I107T, P282S, R323W and F343L) and one known (R323Q) de novo GABRG2 pathogenic variants (mutations) in eight patients. To gain insight into the molecular basis for how these mutations contribute to epileptic encephalopathies, we compared the effects of the mutations on the properties of recombinant α1β2γ2L GABAA receptors transiently expressed in HEK293T cells. Using a combination of patch clamp recording, immunoblotting, confocal imaging and structural modelling, we characterized the effects of these GABRG2 mutations on GABAA receptor biogenesis and channel function. Compared with wild-type α1β2γ2L receptors, GABAA receptors containing a mutant γ2 subunit had reduced cell surface expression with altered subunit stoichiometry or decreased GABA-evoked whole-cell current amplitudes, but with different levels of reduction. While a causal role of these mutations cannot be established directly from these results, the functional analysis together with the genetic information suggests that these GABRG2 variants may be major contributors to the epileptic encephalopathy phenotypes. Our study further expands the GABRG2 phenotypic spectrum and supports growing evidence that defects in GABAergic neurotransmission participate in the pathogenesis of genetic epilepsies including epileptic encephalopathies.
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Affiliation(s)
- Dingding Shen
- 1 The Graduate Program of Neuroscience, Vanderbilt University, Nashville, TN 37232, USA
| | - Ciria C Hernandez
- 2 Department of Neurology, Vanderbilt University, Nashville, TN 37240, USA
| | - Wangzhen Shen
- 2 Department of Neurology, Vanderbilt University, Nashville, TN 37240, USA
| | - Ningning Hu
- 2 Department of Neurology, Vanderbilt University, Nashville, TN 37240, USA
| | - Annapurna Poduri
- 3 Epilepsy Genetics Program and the Department of Neurology, Boston Children's Hospital, Boston, MA 02115, USA
- 4 Harvard Medical School, Boston, MA 02115, USA
| | - Beth Shiedley
- 3 Epilepsy Genetics Program and the Department of Neurology, Boston Children's Hospital, Boston, MA 02115, USA
| | - Alex Rotenberg
- 3 Epilepsy Genetics Program and the Department of Neurology, Boston Children's Hospital, Boston, MA 02115, USA
| | - Alexandre N Datta
- 5 Division of Pediatric Neurology and Developmental Medicine, University of Basel Children's Hospital, Basel 4056, Switzerland
| | - Steffen Leiz
- 6 Clinic for Children and Adolescents Dritter Orden, Divison of Neuropediatrics, München, 80638 Germany
| | - Steffi Patzer
- 7 Clinic for Children and Adolescents, Halle/Saale, 06097 Germany
| | - Rainer Boor
- 8 Department of Pediatric Neurology, Kiel University, Kiel 24118 Germany; Northern German Epilepsy Centre for Children and Adolescents, Schwentinental - Raisdorf, 24223 Germany
| | - Kerri Ramsey
- 9 Center for Rare Childhood Disorders, Translational Genomics Research Institute, Phoenix, 85004 AZ, USA
| | - Ethan Goldberg
- 10 Departments of Neurology and Paediatrics, Division of Child Neurology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104, USA
- 11 Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA
| | - Ingo Helbig
- 10 Departments of Neurology and Paediatrics, Division of Child Neurology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104, USA
- 11 Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA
| | - Xilma R Ortiz-Gonzalez
- 10 Departments of Neurology and Paediatrics, Division of Child Neurology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104, USA
- 11 Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA
| | - Johannes R Lemke
- 12 Institute of Human Genetics, University of Leipzig Hospitals and Clinics, Leipzig, 04103 Germany
| | - Eric D Marsh
- 10 Departments of Neurology and Paediatrics, Division of Child Neurology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104, USA
- 11 Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA
| | - Robert L Macdonald
- 2 Department of Neurology, Vanderbilt University, Nashville, TN 37240, USA
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Hernandez CC, Klassen TL, Jackson LG, Gurba K, Hu N, Noebels JL, Macdonald RL. Deleterious Rare Variants Reveal Risk for Loss of GABAA Receptor Function in Patients with Genetic Epilepsy and in the General Population. PLoS One 2016; 11:e0162883. [PMID: 27622563 PMCID: PMC5021343 DOI: 10.1371/journal.pone.0162883] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Accepted: 08/30/2016] [Indexed: 12/02/2022] Open
Abstract
Genetic epilepsies (GEs) account for approximately 50% of all seizure disorders, and familial forms include mutations in single GABAA receptor subunit genes (GABRs). In 144 sporadic GE cases (GECs), exome sequencing of 237 ion channel genes identified 520 GABR variants. Among these variants, 33 rare variants in 11 GABR genes were present in 24 GECs. To assess functional risk of variants in GECs, we selected 8 variants found in GABRA, 3 in GABRB, and 3 in GABRG and compared them to 18 variants found in the general population for GABRA1 (n = 9), GABRB3 (n = 7), and GABRG2 (n = 2). To identify deleterious variants and gain insight into structure-function relationships, we studied the gating properties, surface expression and structural perturbations of the 32 variants. Significant reduction of GABAA receptor function was strongly associated with variants scored as deleterious and mapped within the N-terminal and transmembrane domains. In addition, 12 out of 17 variants mapped along the β+/α- GABA binding interface, were associated with reduction in channel gating and were predicted to cause structural rearrangements of the receptor by in silico simulations. Missense or nonsense mutations of GABRA1, GABRB3 and GABRG2 primarily impair subunit biogenesis. In contrast, GABR variants affected receptor function by impairing gating, suggesting that different mechanisms are operating in GABR epilepsy susceptibility variants and disease-causing mutations. The functional impact of single GABR variants found in individuals with sporadic GEs warrants the use of molecular diagnosis and will ultimately improve the treatment of genetic epilepsies by using a personalized approach.
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Affiliation(s)
- Ciria C. Hernandez
- Department of Neurology, Vanderbilt University, Nashville, Tennessee, 37232, United States of America
- * E-mail: (RLM); (CCH)
| | - Tara L. Klassen
- Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, V6S 1Z3, Canada
| | - Laurel G. Jackson
- Program in Neuroscience, Vanderbilt University, Nashville, Tennessee, 37232, United States of America
| | - Katharine Gurba
- Program in Neuroscience, Vanderbilt University, Nashville, Tennessee, 37232, United States of America
| | - Ningning Hu
- Department of Neurology, Vanderbilt University, Nashville, Tennessee, 37232, United States of America
| | - Jeffrey L. Noebels
- Department of Neurology, Baylor College of Medicine, Houston, Texas, 77030, United States of America
| | - Robert L. Macdonald
- Department of Neurology, Vanderbilt University, Nashville, Tennessee, 37232, United States of America
- * E-mail: (RLM); (CCH)
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15
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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: 1.4] [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.
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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
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16
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Janve VS, Hernandez CC, Verdier KM, Hu N, Macdonald RL. Epileptic encephalopathy de novo GABRB mutations impair γ-aminobutyric acid type A receptor function. Ann Neurol 2016; 79:806-825. [PMID: 26950270 PMCID: PMC5014730 DOI: 10.1002/ana.24631] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2015] [Revised: 03/04/2016] [Accepted: 03/05/2016] [Indexed: 01/27/2023]
Abstract
OBJECTIVE The Epi4K Consortium recently identified 4 de novo mutations in the γ-aminobutyric acid type A (GABAA ) receptor β3 subunit gene GABRB3 and 1 in the β1 subunit gene GABRB1 in children with one of the epileptic encephalopathies (EEs) Lennox-Gastaut syndrome (LGS) and infantile spasms (IS). Because the etiology of EEs is often unknown, we determined the impact of GABRB mutations on GABAA receptor function and biogenesis. METHODS GABAA receptor α1 and γ2L subunits were coexpressed with wild-type and/or mutant β3 or β1 subunits in HEK 293T cells. Currents were measured using whole cell and single channel patch clamp techniques. Surface and total expression levels were measured using flow cytometry. Potential structural perturbations in mutant GABAA receptors were explored using structural modeling. RESULTS LGS-associated GABRB3(D120N, E180G, Y302C) mutations located at β+ subunit interfaces reduced whole cell currents by decreasing single channel open probability without loss of surface receptors. In contrast, IS-associated GABRB3(N110D) and GABRB1(F246S) mutations at β- subunit interfaces produced minor changes in whole cell current peak amplitude but altered current deactivation by decreasing or increasing single channel burst duration, respectively. GABRB3(E180G) and GABRB1(F246S) mutations also produced spontaneous channel openings. INTERPRETATION All 5 de novo GABRB mutations impaired GABAA receptor function by rearranging conserved structural domains, supporting their role in EEs. The primary effect of LGS-associated mutations was reduced GABA-evoked peak current amplitudes, whereas the major impact of IS-associated mutations was on current kinetic properties. Despite lack of association with epilepsy syndromes, our results suggest GABRB1 as a candidate human epilepsy gene. Ann Neurol 2016;79:806-825.
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Affiliation(s)
- Vaishali S Janve
- Graduate Program of Neuroscience, Vanderbilt University, Nashville, TN
| | | | | | - Ningning Hu
- Department of Neurology, Vanderbilt University, Nashville, TN
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17
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Olsen RW. Allosteric ligands and their binding sites define γ-aminobutyric acid (GABA) type A receptor subtypes. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2015; 73:167-202. [PMID: 25637441 DOI: 10.1016/bs.apha.2014.11.005] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
GABAA receptors (GABA(A)Rs) mediate rapid inhibitory transmission in the brain. GABA(A)Rs are ligand-gated chloride ion channel proteins and exist in about a dozen or more heteropentameric subtypes exhibiting variable age and brain regional localization and thus participation in differing brain functions and diseases. GABA(A)Rs are also subject to modulation by several chemotypes of allosteric ligands that help define structure and function, including subtype definition. The channel blocker picrotoxin identified a noncompetitive channel blocker site in GABA(A)Rs. This ligand site is located in the transmembrane channel pore, whereas the GABA agonist site is in the extracellular domain at subunit interfaces, a site useful for low energy coupled conformational changes of the functional channel domain. Two classes of pharmacologically important allosteric modulatory ligand binding sites reside in the extracellular domain at modified agonist sites at other subunit interfaces: the benzodiazepine site and the high-affinity, relevant to intoxication, ethanol site. The benzodiazepine site is specific for certain GABA(A)R subtypes, mainly synaptic, while the ethanol site is found at a modified benzodiazepine site on different, extrasynaptic, subtypes. In the transmembrane domain are allosteric modulatory ligand sites for diverse chemotypes of general anesthetics: the volatile and intravenous agents, barbiturates, etomidate, propofol, long-chain alcohols, and neurosteroids. The last are endogenous positive allosteric modulators. X-ray crystal structures of prokaryotic and invertebrate pentameric ligand-gated ion channels, and the mammalian GABA(A)R protein, allow homology modeling of GABA(A)R subtypes with the various ligand sites located to suggest the structure and function of these proteins and their pharmacological modulation.
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Affiliation(s)
- Richard W Olsen
- Department of Molecular & Medical Pharmacology, David Geffen School of Medicine at UCLA, Los Angeles, California, USA.
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18
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Abstract
The ATP activation signal in trimeric P2X2 receptors propagates down individual subunits before spreading to all three at the level of the pore. P2X2 receptor channel, a homotrimer activated by the binding of extracellular adenosine triphosphate (ATP) to three intersubunit ATP-binding sites (each located ∼50 Å from the ion permeation pore), also shows voltage-dependent activation upon hyperpolarization. Here, we used tandem trimeric constructs (TTCs) harboring critical mutations at the ATP-binding, linker, and pore regions to investigate how the ATP activation signal is transmitted within the trimer and how signals generated by ATP and hyperpolarization converge. Analysis of voltage- and [ATP]-dependent gating in these TTCs showed that: (a) Voltage- and [ATP]-dependent gating of P2X2 requires binding of at least two ATP molecules. (b) D315A mutation in the β-14 strand of the linker region connecting the ATP-binding domains to the pore-forming helices induces two different gating modes; this requires the presence of the D315A mutation in at least two subunits. (c) The T339S mutation in the pore domains of all three subunits abolishes the voltage dependence of P2X2 gating in saturating [ATP], making P2X2 equally active at all membrane potentials. Increasing the number of T339S mutations in the TTC results in gradual changes in the voltage dependence of gating from that of the wild-type channel, suggesting equal and independent contributions of the subunits at the pore level. (d) Voltage- and [ATP]-dependent gating in TTCs differs depending on the location of one D315A relative to one K308A that blocks the ATP binding and downstream signal transmission. (e) Voltage- and [ATP]-dependent gating does not depend on where one T339S is located relative to K308A (or D315A). Our results suggest that each intersubunit ATP-binding signal is directly transmitted on the same subunit to the level of D315 via the domain that contributes K308 to the β-14 strand. The signal subsequently spreads equally to all three subunits at the level of the pore, resulting in symmetric and independent contributions of the three subunits to pore opening.
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Affiliation(s)
- Batu Keceli
- Division of Biophysics and Neurobiology, Department of Molecular Physiology, National Institute for Physiological Sciences, Aichi 444-8585, Japan
| | - Yoshihiro Kubo
- Division of Biophysics and Neurobiology, Department of Molecular Physiology, National Institute for Physiological Sciences, Aichi 444-8585, Japan Department of Physiological Sciences, The Graduate University for Advanced Studies, School of Life Science, Kanagawa 240-0155, Japan
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19
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Seeking potential anticonvulsant agents that target GABAA receptors using experimental and theoretical procedures. J Comput Aided Mol Des 2014; 28:1217-32. [PMID: 25298123 DOI: 10.1007/s10822-014-9798-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2014] [Accepted: 09/27/2014] [Indexed: 12/27/2022]
Abstract
The aim of this study was to identify compounds that possess anticonvulsant activity by using a pentylenetetrazol (PTZ)-induced seizure model. Theoretical studies of a set of ligands, explored the binding affinities of the ligands for the GABA(A) receptor (GABA(A)R), including some benzodiazepines. The ligands satisfy the Lipinski rules and contain a pharmacophore core that has been previously reported to be a GABA(A)R activator. To select the ligands with the best physicochemical properties, all of the compounds were analyzed by quantum mechanics and the energies of the highest occupied molecular orbital and lowest unoccupied molecular orbital were determined. Docking calculations between the ligands and the GABA(A)R were used to identify the complexes with the highest Gibbs binding energies. The identified compound D1 (dibenzo(b,f)(1,4)diazocine-6,11(5H,12H)-dione) was synthesized, experimentally tested, and the GABA(A)R-D1 complex was submitted to 12-ns-long molecular dynamics (MD) simulations to corroborate the binding conformation obtained by docking techniques. MD simulations were also used to analyze the decomposition of the Gibbs binding energy of the residues involved in the stabilization of the complex. To validate our theoretical results, molecular docking and MD simulations were also performed for three reference compounds that are currently in commercial use: clonazepam (CLZ), zolpidem and eszopiclone. The theoretical results show that the GABA(A)R-D1, and GABA(A)R-CLZ complexes bind to the benzodiazepine binding site, share a similar map of binding residues, and have similar Gibbs binding energies and entropic components. Experimental studies using a PTZ-induced seizure model showed that D1 possesses similar activity to CLZ, which corroborates the predicted binding free energy identified by theoretical calculations.
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20
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Abstract
The GABA(A) receptors are the major inhibitory neurotransmitter receptors in mammalian brain. Each isoform consists of five homologous or identical subunits surrounding a central chloride ion-selective channel gated by GABA. How many isoforms of the receptor exist is far from clear. GABA(A) receptors located in the postsynaptic membrane mediate neuronal inhibition that occurs in the millisecond time range; those located in the extrasynaptic membrane respond to ambient GABA and confer long-term inhibition. GABA(A) receptors are responsive to a wide variety of drugs, e.g. benzodiazepines, which are often used for their sedative/hypnotic and anxiolytic effects.
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Affiliation(s)
- Erwin Sigel
- Institute of Biochemistry and Molecular Medicine, University of Bern, CH-3012 Bern, Switzerland.
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