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Li X, Guo S, Sun Y, Ding J, Chen C, Wu Y, Li P, Sun T, Wang X. GABRG2 mutations in genetic epilepsy with febrile seizures plus: structure, roles, and molecular genetics. J Transl Med 2024; 22:767. [PMID: 39143639 PMCID: PMC11323400 DOI: 10.1186/s12967-024-05387-1] [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] [Received: 03/25/2024] [Accepted: 06/10/2024] [Indexed: 08/16/2024] Open
Abstract
Genetic epilepsy with febrile seizures plus (GEFS+) is a genetic epilepsy syndrome characterized by a marked hereditary tendency inherited as an autosomal dominant trait. Patients with GEFS+ may develop typical febrile seizures (FS), while generalized tonic-clonic seizures (GTCSs) with fever commonly occur between 3 months and 6 years of age, which is generally followed by febrile seizure plus (FS+), with or without absence seizures, focal seizures, or GTCSs. GEFS+ exhibits significant genetic heterogeneity, with polymerase chain reaction, exon sequencing, and single nucleotide polymorphism analyses all showing that the occurrence of GEFS+ is mainly related to mutations in the gamma-aminobutyric acid type A receptor gamma 2 subunit (GABRG2) gene. The most common mutations in GABRG2 are separated in large autosomal dominant families, but their pathogenesis remains unclear. The predominant types of GABRG2 mutations include missense (c.983A → T, c.245G → A, p.Met199Val), nonsense (R136*, Q390*, W429*), frameshift (c.1329delC, p.Val462fs*33, p.Pro59fs*12), point (P83S), and splice site (IVS6+2T → G) mutations. All of these mutations types can reduce the function of ion channels on the cell membrane; however, the degree and mechanism underlying these dysfunctions are different and could be linked to the main mechanism of epilepsy. The γ2 subunit plays a special role in receptor trafficking and is closely related to its structural specificity. This review focused on investigating the relationship between GEFS+ and GABRG2 mutation types in recent years, discussing novel aspects deemed to be great significance for clinically accurate diagnosis, anti-epileptic treatment strategies, and new drug development.
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Affiliation(s)
- Xinxiao Li
- Department of Neurosurgery, The Fifth Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan, 450052, People's Republic of China.
| | - Shengnan Guo
- Department of Rehabilitative Medicine, The Fifth Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan, 450052, People's Republic of China
| | - Yangyang Sun
- Ningxia Key Laboratory of Cerebrocranial Disease, The Incubation Base of National Key Laboratory, Ningxia Medical University, Yinchuan, Ningxia, 750001, People's Republic of China
| | - Jiangwei Ding
- Department of Neurosurgery, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan, 450052, People's Republic of China
| | - Chao Chen
- Department of Neurosurgery, The Fifth Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan, 450052, People's Republic of China
| | - Yuehui Wu
- Department of Neurosurgery, The Fifth Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan, 450052, People's Republic of China
| | - Peidong Li
- Department of Neurosurgery, The Fifth Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan, 450052, People's Republic of China
| | - Tao Sun
- Ningxia Key Laboratory of Cerebrocranial Disease, The Incubation Base of National Key Laboratory, Ningxia Medical University, Yinchuan, Ningxia, 750001, People's Republic of China.
| | - Xinjun Wang
- Department of Neurosurgery, The Fifth Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan, 450052, People's Republic of China.
- Department of Neurosurgery, The Third Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan, 450052, People's Republic of China.
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Modarres Mousavi SM, Alipour F, Noorbakhsh F, Jafarian M, Ghadipasha M, Gharehdaghi J, Kellinghaus C, Speckmann EJ, Stummer W, Khaleghi Ghadiri M, Gorji A. Clinical Correlation of Altered Molecular Signatures in Epileptic Human Hippocampus and Amygdala. Mol Neurobiol 2024; 61:725-752. [PMID: 37658249 PMCID: PMC10861640 DOI: 10.1007/s12035-023-03583-6] [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] [Received: 12/26/2022] [Accepted: 08/14/2023] [Indexed: 09/03/2023]
Abstract
Widespread alterations in the expression of various genes could contribute to the pathogenesis of epilepsy. The expression levels of various genes, including major inhibitory and excitatory receptors, ion channels, cell type-specific markers, and excitatory amino acid transporters, were assessed and compared between the human epileptic hippocampus and amygdala, and findings from autopsy controls. Moreover, the potential correlation between molecular alterations in epileptic brain tissues and the clinical characteristics of patients undergoing epilepsy surgery was evaluated. Our findings revealed significant and complex changes in the expression of several key regulatory genes in both the hippocampus and amygdala of patients with intractable epilepsy. The expression changes in various genes differed considerably between the epileptic hippocampus and amygdala. Different correlation patterns were observed between changes in gene expression and clinical characteristics, depending on whether the patients were considered as a whole or were subdivided. Altered molecular signatures in different groups of epileptic patients, defined within a given category, could be viewed as diagnostic biomarkers. Distinct patterns of molecular changes that distinguish these groups from each other appear to be associated with epilepsy-specific functional consequences.
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Affiliation(s)
| | - Fatemeh Alipour
- Shefa Neuroscience Research Center, Khatam Alanbia Hospital, Tehran, Iran
| | - Farshid Noorbakhsh
- Shefa Neuroscience Research Center, Khatam Alanbia Hospital, Tehran, Iran
| | - Maryam Jafarian
- Shefa Neuroscience Research Center, Khatam Alanbia Hospital, Tehran, Iran
| | - Masoud Ghadipasha
- Legal Medicine Research Center, Legal Medicine Organization, Tehran, Iran
| | - Jaber Gharehdaghi
- Legal Medicine Research Center, Legal Medicine Organization, Tehran, Iran
| | | | - Erwin-Josef Speckmann
- Department of Neurosurgery, Westfälische Wilhelms-Universität Münster, Münster, Germany
- Epilepsy Research Center, Westfälische Wilhelms-Universität Münster, Münster, Germany
| | - Walter Stummer
- Department of Neurosurgery, Westfälische Wilhelms-Universität Münster, Münster, Germany
| | | | - Ali Gorji
- Shefa Neuroscience Research Center, Khatam Alanbia Hospital, Tehran, Iran.
- Department of Neurosurgery, Westfälische Wilhelms-Universität Münster, Münster, Germany.
- Epilepsy Research Center, Westfälische Wilhelms-Universität Münster, Münster, Germany.
- Department of Neuroscience, Mashhad University of Medical Sciences, Mashhad, Iran.
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Radosavljevic M, Svob Strac D, Jancic J, Samardzic J. The Role of Pharmacogenetics in Personalizing the Antidepressant and Anxiolytic Therapy. Genes (Basel) 2023; 14:genes14051095. [PMID: 37239455 DOI: 10.3390/genes14051095] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Revised: 05/12/2023] [Accepted: 05/15/2023] [Indexed: 05/28/2023] Open
Abstract
Pharmacotherapy for neuropsychiatric disorders, such as anxiety and depression, has been characterized by significant inter-individual variability in drug response and the development of side effects. Pharmacogenetics, as a key part of personalized medicine, aims to optimize therapy according to a patient's individual genetic signature by targeting genetic variations involved in pharmacokinetic or pharmacodynamic processes. Pharmacokinetic variability refers to variations in a drug's absorption, distribution, metabolism, and elimination, whereas pharmacodynamic variability results from variable interactions of an active drug with its target molecules. Pharmacogenetic research on depression and anxiety has focused on genetic polymorphisms affecting metabolizing cytochrome P450 (CYP) and uridine 5'-diphospho-glucuronosyltransferase (UGT) enzymes, P-glycoprotein ATP-binding cassette (ABC) transporters, and monoamine and γ-aminobutyric acid (GABA) metabolic enzymes, transporters, and receptors. Recent pharmacogenetic studies have revealed that more efficient and safer treatments with antidepressants and anxiolytics could be achieved through genotype-guided decisions. However, because pharmacogenetics cannot explain all observed heritable variations in drug response, an emerging field of pharmacoepigenetics investigates how epigenetic mechanisms, which modify gene expression without altering the genetic code, might influence individual responses to drugs. By understanding the epi(genetic) variability of a patient's response to pharmacotherapy, clinicians could select more effective drugs while minimizing the likelihood of adverse reactions and therefore improve the quality of treatment.
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Affiliation(s)
- Milica Radosavljevic
- Institute of Pharmacology, Clinical Pharmacology and Toxicology, Faculty of Medicine, University of Belgrade, 11000 Belgrade, Serbia
| | - Dubravka Svob Strac
- Laboratory for Molecular Neuropsychiatry, Division of Molecular Medicine, Rudjer Boskovic Institute, 10000 Zagreb, Croatia
| | - Jasna Jancic
- Clinic of Neurology and Psychiatry for Children and Youth, Faculty of Medicine, University of Belgrade, 11000 Belgrade, Serbia
| | - Janko Samardzic
- Institute of Pharmacology, Clinical Pharmacology and Toxicology, Faculty of Medicine, University of Belgrade, 11000 Belgrade, Serbia
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Byun JI. Management of convulsive status epilepticus: recent updates. ENCEPHALITIS 2023; 3:39-43. [PMID: 37469676 PMCID: PMC10295829 DOI: 10.47936/encephalitis.2022.00087] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2022] [Revised: 10/31/2022] [Accepted: 11/15/2022] [Indexed: 07/21/2023] Open
Abstract
Convulsive status epilepticus (SE) is a medical emergency associated with high morbidity and mortality. Recently, clinical trials and meta-analyses investigating medical treatment of SE have been published. Benzodiazepine is well known as the first-line treatment for SE. Recent evidence suggests the equivalence of intravenous fosphenytoin, valproate, and levetiracetam for treatment of established SE. There is lack of evidence regarding treatment for refractory SE. Intravenous midazolam is commonly used, and recent evidence supports the use of ketamine. Additional studies are needed to improve the management of convulsive SE.
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Affiliation(s)
- Jung-Ick Byun
- Department of Neurology, Kyung Hee University Hospital at Gangdong, Kyung Hee University College of Medicine, Seoul, Korea
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Novel variants in GABA A receptor subunits: A possible association with benzodiazepine resistance in patients with drug-resistant epilepsy. Epilepsy Res 2023; 189:107056. [PMID: 36469977 DOI: 10.1016/j.eplepsyres.2022.107056] [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: 10/01/2021] [Revised: 10/12/2022] [Accepted: 11/22/2022] [Indexed: 11/24/2022]
Abstract
Benzodiazepines (BDZ) such as diazepam and lorazepam are popular as first-line treatment for acute seizures due to their rapid action and high efficacy. However, long-term usage of BDZ leads to benzodiazepine resistance, a phenomenon whose underlying mechanisms are still being investigated. One of the hypothesised mechanisms contributing to BDZ resistance is the presence of mutations in benzodiazepine-sensitive receptors. While a few genetic variants have been reported previously, knowledge of relevant pathogenic variants is still scarce. We used Sanger Sequencing to detect variants in the ligand-binding domain of BDZ-sensitive GABAA receptor subunits α1-3 and 5 expressed in resected brain tissues of drug-resistant epilepsy (DRE) patients with a history of BDZ resistance and found two previously unreported predicted pathogenic frameshifting variants - NM_000807.4(GABRA2):c.367_368insG and NM_000810.4(GABRA5):c.410del - significantly enriched in these patients. The findings were further explored in resected DRE brain tissues through cellular electrophysiological experiments.
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Morina IY, Mikhrina AL, Mikhailova EV, Vataev SI, Hismatullina ZR, Romanova IV. Analysis of the Hypothalamic Orexinergic System in Rats with Different Forms of Genetically Determined Epilepsy. J EVOL BIOCHEM PHYS+ 2022. [DOI: 10.1134/s0022093022060242] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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GABA A receptor proline 273 at the interdomain interface of the β 2 subunit regulates entry into desensitization and opening/closing transitions. Life Sci 2022; 308:120943. [PMID: 36096246 DOI: 10.1016/j.lfs.2022.120943] [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: 05/31/2022] [Revised: 08/29/2022] [Accepted: 09/06/2022] [Indexed: 11/23/2022]
Abstract
AIMS GABAA receptors belong to Cys-loop ion channel family and mediate inhibition in the brain. Despite the abundance of structural data on receptor structure, the molecular scenarios of activation are unknown. In this study we investigated the role of a β2P273 residue in channel gating transitions. This residue is located in a central position of the M2-M3 linker of the interdomain interface, expected to be predisposed to interact with another interfacial element, the β1-β2 loop of the extracellular side. The interactions occurring on this interface have been reported to couple agonist binding to channel gating. MAIN METHODS We recorded micro- and macroscopic current responses of recombinant GABAA receptors mutated at the β2P273 residue (to A, K, E) to saturating GABA. Electrophysiological data served as basis to kinetic modeling, used to decipher which gating transition were affected by mutations. KEY FINDINGS Mutations of this residue impaired macroscopic desensitization and accelerated current deactivation with P273E mutant showing greatest deviation from wild-type. Single-channel analysis revealed alterations mainly in short-lived shut times and shortening of openings, resulting in dramatic changes in intraburst open probability. Kinetic modeling indicated that β2P273 mutants show diminished entry into desensitized and open states as well as faster channel closing transitions. SIGNIFICANCE In conclusion, we demonstrate that β2P273 of the M2-M3 linker is a crucial element of the ECD-TMD interface regulating the receptor's ability to undergo late gating transitions. Henceforth, this region could be an important target for new pharmacological tools affecting GABAAR-mediated inhibition.
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Tong X, Zhang Z, Zhu J, Li S, Qu S, Qin B, Guo Y, Chen R. A Comparison of Epileptogenic Effect of Status Epilepticus Treated With Diazepam, Midazolam, and Pentobarbital in the Mouse Pilocarpine Model of Epilepsy. Front Neurol 2022; 13:821917. [PMID: 35669869 PMCID: PMC9163813 DOI: 10.3389/fneur.2022.821917] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Accepted: 04/19/2022] [Indexed: 11/13/2022] Open
Abstract
Status epilepticus (SE) is a medical emergency associated with acute severe systemic damage and high mortality. Moreover, symptomatic SE is one of the highest risk factors for epileptogenesis. While the antiepileptic drugs (AEDs) are chosen in favor of acute control of SE, the potential short-term and long-term effects of such AEDs have been ignored in clinics. In this study, we hypothesized that AEDs that are used to control acute SE might affect the feasibility for the chronic development of epileptogenesis after SE. Therefore, we sought to compare the epileptogenic effects of SE that are terminated by three AEDs, i.e., diazepam, midazolam, and pentobarbital, which are widely used as first-line anti-SE AEDs. For this purpose, we used a mouse model of SE induced by intraperitoneal (i.p.) injection of lithium chloride (LiCl)-pilocarpine. The pilocarpine-induced SE was terminated with diazepam, midazolam, or pentobarbital. Then we compared short-term and long-term effects of SE with different AED treatments by examining SE-associated mortality and behavioral spontaneous recurrent seizures (SRSs) and by using magnetic resonance imaging (MRI) and immunohistochemistry to evaluate pathological and cellular alterations of mice in the different treatment groups. We found that i.p. injections of diazepam (5 mg/kg), midazolam (10 mg/kg), and pentobarbital (37.5 mg/kg) were able to terminate acute pilocarpine-SE effectively, while pentobarbital treatment showed less neuroprotective action against lethality in the short phase following SE. Long-term evaluation following SE revealed that SE treated with midazolam had resulted in relatively less behavioral SRS, less hippocampal atrophy, and milder neuronal loss and gliosis. Our data revealed an obvious advantage of midazolam vs. diazepam or pentobarbital in protecting the brain from epileptogenesis. Therefore, if midazolam provides as strong action to quench SE as other AEDs in clinics, midazolam should be the first choice of anti-SE AEDs as it provides additional benefits against epileptogenesis.
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Affiliation(s)
- Xiangzhen Tong
- Guangdong Province Key Laboratory of Psychiatric Disorders, Department of Neurobiology, School of Basic Medical Sciences, Southern Medical University, Guangzhou, China
| | - Zizhu Zhang
- Guangdong Province Key Laboratory of Psychiatric Disorders, Department of Neurobiology, School of Basic Medical Sciences, Southern Medical University, Guangzhou, China
| | - Jianping Zhu
- Guangdong Province Key Laboratory of Psychiatric Disorders, Department of Neurobiology, School of Basic Medical Sciences, Southern Medical University, Guangzhou, China
| | - Shuji Li
- Guangdong Province Key Laboratory of Psychiatric Disorders, Department of Neurobiology, School of Basic Medical Sciences, Southern Medical University, Guangzhou, China
| | - Shaogang Qu
- Department of Neurology, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Bing Qin
- Epilepsy Center and Department of Neurosurgery, The First Affiliated Hospital, Jinan University, Guangzhou, China
- *Correspondence: Bing Qin
| | - Yanwu Guo
- Guangdong Provincial Key Laboratory on Brain Function Repair and Regeneration, Department of Neurosurgery, The National Key Clinic Specialty, The Engineering Technology Research Center of Education Ministry of China, Zhujiang Hospital, Southern Medical University, Guangzhou, China
- Yanwu Guo
| | - Rongqing Chen
- Guangdong Province Key Laboratory of Psychiatric Disorders, Department of Neurobiology, School of Basic Medical Sciences, Southern Medical University, Guangzhou, China
- Guangdong Provincial Key Laboratory on Brain Function Repair and Regeneration, Department of Neurosurgery, The National Key Clinic Specialty, The Engineering Technology Research Center of Education Ministry of China, Zhujiang Hospital, Southern Medical University, Guangzhou, China
- Key Laboratory of Mental Health of the Ministry of Education, Guangdong-Hong Kong-Macao Greater Bay Area Center for Brain Science and Brain-Inspired Intelligence, Southern Medical University, Guangzhou, China
- Rongqing Chen ;
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Why won't it stop? The dynamics of benzodiazepine resistance in status epilepticus. Nat Rev Neurol 2022; 18:428-441. [PMID: 35538233 DOI: 10.1038/s41582-022-00664-3] [Citation(s) in RCA: 31] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/19/2022] [Indexed: 11/08/2022]
Abstract
Status epilepticus is a life-threatening neurological emergency that affects both adults and children. Approximately 36% of episodes of status epilepticus do not respond to the current preferred first-line treatment, benzodiazepines. The proportion of episodes that are refractory to benzodiazepines is higher in low-income and middle-income countries (LMICs) than in high-income countries (HICs). Evidence suggests that longer episodes of status epilepticus alter brain physiology, thereby contributing to the emergence of benzodiazepine resistance. Such changes include alterations in GABAA receptor function and in the transmembrane gradient for chloride, both of which erode the ability of benzodiazepines to enhance inhibitory synaptic signalling. Often, current management guidelines for status epilepticus do not account for these duration-related changes in pathophysiology, which might differentially impact individuals in LMICs, where the average time taken to reach medical attention is longer than in HICs. In this Perspective article, we aim to combine clinical insights and the latest evidence from basic science to inspire a new, context-specific approach to efficiently managing status epilepticus.
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10
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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: 0.7] [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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Syed P, Durisic N, Harvey RJ, Sah P, Lynch JW. Effects of GABA A Receptor α3 Subunit Epilepsy Mutations on Inhibitory Synaptic Signaling. Front Mol Neurosci 2020; 13:602559. [PMID: 33328885 PMCID: PMC7714833 DOI: 10.3389/fnmol.2020.602559] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Accepted: 10/02/2020] [Indexed: 11/13/2022] Open
Abstract
Missense mutations T166M, Q242L, T336M, and Y474C in the GABAA receptor (GABAAR) α3 subunit gene are associated with epileptic seizures, dysmorphic features, intellectual disability, and developmental delay. When incorporated into GABAARs expressed in oocytes, all mutations are known to reduce GABA-evoked whole-cell currents. However, their impact on the properties of inhibitory synaptic currents (IPSCs) is unknown, largely because it is difficult to establish, much less control, the stoichiometry of GABAAR expressed in native neuronal synapses. To circumvent this problem, we employed a HEK293 cell-neuron co-culture expression system that permits the recording of IPSCs mediated by a pure population of GABAARs with a defined stoichiometry. We first demonstrated that IPSCs mediated by α3-containing GABAARs (α3β3γ2) decay significantly slower than those mediated by α1-containing isoforms (α1β2γ2 or α1β3γ2). GABAAR α3 mutations did not affect IPSC peak amplitudes or 10-90% rise times, but three of the mutations affected IPSC decay. T336M significantly accelerated the IPSC decay rate whereas T166M and Y474C had the opposite effect. The acceleration of IPSC decay kinetics caused by the T366M mutation was returned to wild-type-like values by the anti-epileptic medication, midazolam. Quantification experiments in HEK293 cells revealed a significant reduction in cell-surface expression for all mutants, in agreement with previous oocyte data. Taken together, our results show that impaired surface expression and altered IPSC decay rates could both be significant factors underlying the pathologies associated with these mutations.
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Affiliation(s)
- Parnayan Syed
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
| | - Nela Durisic
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
| | - Robert J Harvey
- School of Health and Behavioural Sciences, University of the Sunshine Coast, Maroochydore, QLD, Australia.,Sunshine Coast Health Institute, Birtinya, QLD, Australia
| | - Pankaj Sah
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia.,Department of Biology, Joint Center for Neuroscience and Neural Engineering, Southern University of Science and Technology, Shenzhen, China
| | - Joseph W Lynch
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
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Thakran S, Guin D, Singh P, Singh P, Kukal S, Rawat C, Yadav S, Kushwaha SS, Srivastava AK, Hasija Y, Saso L, Ramachandran S, Kukreti R. Genetic Landscape of Common Epilepsies: Advancing towards Precision in Treatment. Int J Mol Sci 2020; 21:E7784. [PMID: 33096746 PMCID: PMC7589654 DOI: 10.3390/ijms21207784] [Citation(s) in RCA: 42] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Revised: 10/09/2020] [Accepted: 10/14/2020] [Indexed: 12/15/2022] Open
Abstract
Epilepsy, a neurological disease characterized by recurrent seizures, is highly heterogeneous in nature. Based on the prevalence, epilepsy is classified into two types: common and rare epilepsies. Common epilepsies affecting nearly 95% people with epilepsy, comprise generalized epilepsy which encompass idiopathic generalized epilepsy like childhood absence epilepsy, juvenile myoclonic epilepsy, juvenile absence epilepsy and epilepsy with generalized tonic-clonic seizure on awakening and focal epilepsy like temporal lobe epilepsy and cryptogenic focal epilepsy. In 70% of the epilepsy cases, genetic factors are responsible either as single genetic variant in rare epilepsies or multiple genetic variants acting along with different environmental factors as in common epilepsies. Genetic testing and precision treatment have been developed for a few rare epilepsies and is lacking for common epilepsies due to their complex nature of inheritance. Precision medicine for common epilepsies require a panoramic approach that incorporates polygenic background and other non-genetic factors like microbiome, diet, age at disease onset, optimal time for treatment and other lifestyle factors which influence seizure threshold. This review aims to comprehensively present a state-of-art review of all the genes and their genetic variants that are associated with all common epilepsy subtypes. It also encompasses the basis of these genes in the epileptogenesis. Here, we discussed the current status of the common epilepsy genetics and address the clinical application so far on evidence-based markers in prognosis, diagnosis, and treatment management. In addition, we assessed the diagnostic predictability of a few genetic markers used for disease risk prediction in individuals. A combination of deeper endo-phenotyping including pharmaco-response data, electro-clinical imaging, and other clinical measurements along with genetics may be used to diagnose common epilepsies and this marks a step ahead in precision medicine in common epilepsies management.
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Affiliation(s)
- Sarita Thakran
- Genomics and Molecular Medicine Unit, Institute of Genomics and Integrative Biology (IGIB), Council of Scientific and Industrial Research (CSIR), Delhi 110007, India; (S.T.); (D.G.); (P.S.); (P.S.); (S.K.); (C.R.); (S.Y.)
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India;
| | - Debleena Guin
- Genomics and Molecular Medicine Unit, Institute of Genomics and Integrative Biology (IGIB), Council of Scientific and Industrial Research (CSIR), Delhi 110007, India; (S.T.); (D.G.); (P.S.); (P.S.); (S.K.); (C.R.); (S.Y.)
- Department of Bioinformatics, Delhi Technological University, Shahbad Daulatpur, Main Bawana Road, Delhi 110042, India;
| | - Pooja Singh
- Genomics and Molecular Medicine Unit, Institute of Genomics and Integrative Biology (IGIB), Council of Scientific and Industrial Research (CSIR), Delhi 110007, India; (S.T.); (D.G.); (P.S.); (P.S.); (S.K.); (C.R.); (S.Y.)
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India;
| | - Priyanka Singh
- Genomics and Molecular Medicine Unit, Institute of Genomics and Integrative Biology (IGIB), Council of Scientific and Industrial Research (CSIR), Delhi 110007, India; (S.T.); (D.G.); (P.S.); (P.S.); (S.K.); (C.R.); (S.Y.)
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India;
| | - Samiksha Kukal
- Genomics and Molecular Medicine Unit, Institute of Genomics and Integrative Biology (IGIB), Council of Scientific and Industrial Research (CSIR), Delhi 110007, India; (S.T.); (D.G.); (P.S.); (P.S.); (S.K.); (C.R.); (S.Y.)
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India;
| | - Chitra Rawat
- Genomics and Molecular Medicine Unit, Institute of Genomics and Integrative Biology (IGIB), Council of Scientific and Industrial Research (CSIR), Delhi 110007, India; (S.T.); (D.G.); (P.S.); (P.S.); (S.K.); (C.R.); (S.Y.)
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India;
| | - Saroj Yadav
- Genomics and Molecular Medicine Unit, Institute of Genomics and Integrative Biology (IGIB), Council of Scientific and Industrial Research (CSIR), Delhi 110007, India; (S.T.); (D.G.); (P.S.); (P.S.); (S.K.); (C.R.); (S.Y.)
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India;
| | - Suman S. Kushwaha
- Department of Neurology, Institute of Human Behaviour and Allied Sciences, Dilshad Garden, Delhi 110095, India;
| | - Achal K. Srivastava
- Department of Neurology, All India Institute of Medical Sciences, Ansari Nagar, New Delhi 110029, India;
| | - Yasha Hasija
- Department of Bioinformatics, Delhi Technological University, Shahbad Daulatpur, Main Bawana Road, Delhi 110042, India;
| | - Luciano Saso
- Department of Physiology and Pharmacology “Vittorio Erspamer”, Sapienza University of Rome, P. le Aldo Moro 5, 00185 Rome, Italy;
| | - Srinivasan Ramachandran
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India;
- G N Ramachandran Knowledge Centre, Council of Scientific and Industrial Research (CSIR)—Institute of Genomics and Integrative Biology (IGIB), New Delhi 110007, India
| | - Ritushree Kukreti
- Genomics and Molecular Medicine Unit, Institute of Genomics and Integrative Biology (IGIB), Council of Scientific and Industrial Research (CSIR), Delhi 110007, India; (S.T.); (D.G.); (P.S.); (P.S.); (S.K.); (C.R.); (S.Y.)
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India;
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13
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Jatczak-Śliwa M, Kisiel M, Czyzewska MM, Brodzki M, Mozrzymas JW. GABA A Receptor β 2E155 Residue Located at the Agonist-Binding Site Is Involved in the Receptor Gating. Front Cell Neurosci 2020; 14:2. [PMID: 32116555 PMCID: PMC7026498 DOI: 10.3389/fncel.2020.00002] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Accepted: 01/06/2020] [Indexed: 12/02/2022] Open
Abstract
GABAA receptors (GABAARs) play a crucial role in mediating inhibition in the adult brain. In spite of progress in describing (mainly) the static structures of this receptor, the molecular mechanisms underlying its activation remain unclear. It is known that in the α1β2γ2L receptors, the mutation of the β2E155 residue, at the orthosteric binding site, strongly impairs the receptor activation, but the molecular and kinetic mechanisms of this effect remain elusive. Herein, we investigated the impact of the β2E155C mutation on binding and gating of the α1β2γ2L receptor. To this end, we combined the macroscopic and single-channel analysis, the use of different agonists [GABA and muscimol (MSC)] and flurazepam (FLU) as a modulator. As expected, the β2E155C mutation caused a vast right shift of the dose–response (for GABA and MSC) and, additionally, dramatic changes in the time course of current responses, indicative of alterations in gating. Mutated receptors showed reduced maximum open probability and enhanced receptor spontaneous activity. Model simulations for macroscopic currents revealed that the primary effect of the mutation was the downregulation of the preactivation (flipping) rate. Experiments with MSC and FLU further confirmed a reduction in the preactivation rate. Our single-channel analysis revealed the mutation impact mainly on the second component in the shut times distributions. Based on model simulations, this finding further confirms that this mutation affects mostly the preactivation transition, supporting thus the macroscopic data. Altogether, we provide new evidence that the β2E155 residue is involved in both binding and gating (primarily preactivation).
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Affiliation(s)
- Magdalena Jatczak-Śliwa
- Laboratory of Neuroscience, Department of Biophysics, Wrocław Medical University, Wrocław, Poland.,Department of Molecular Physiology and Neurobiology, University of Wrocław, Wrocław, Poland
| | - Magdalena Kisiel
- Laboratory of Neuroscience, Department of Biophysics, Wrocław Medical University, Wrocław, Poland
| | | | - Marek Brodzki
- Laboratory of Neuroscience, Department of Biophysics, Wrocław Medical University, Wrocław, Poland.,Department of Molecular Physiology and Neurobiology, University of Wrocław, Wrocław, Poland
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Naimo GD, Guarnaccia M, Sprovieri T, Ungaro C, Conforti FL, Andò S, Cavallaro S. A Systems Biology Approach for Personalized Medicine in Refractory Epilepsy. Int J Mol Sci 2019; 20:E3717. [PMID: 31366017 PMCID: PMC6695675 DOI: 10.3390/ijms20153717] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2019] [Revised: 07/22/2019] [Accepted: 07/28/2019] [Indexed: 02/01/2023] Open
Abstract
Epilepsy refers to a common chronic neurological disorder that affects all age groups. Unfortunately, antiepileptic drugs are ineffective in about one-third of patients. The complex interindividual variability influences the response to drug treatment rendering the therapeutic failure one of the most relevant problems in clinical practice also for increased hospitalizations and healthcare costs. Recent advances in the genetics and neurobiology of epilepsies are laying the groundwork for a new personalized medicine, focused on the reversal or avoidance of the pathophysiological effects of specific gene mutations. This could lead to a significant improvement in the efficacy and safety of treatments for epilepsy, targeting the biological mechanisms responsible for epilepsy in each individual. In this review article, we focus on the mechanism of the epilepsy pharmacoresistance and highlight the use of a systems biology approach for personalized medicine in refractory epilepsy.
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Affiliation(s)
- Giuseppina Daniela Naimo
- Institute for Biomedical Research and Innovation, National Research Council, Contrada Burga, Piano Lago, 87050 Mangone (CS) and Via Paolo Gaifami 18, 95126 Catania, Italy
| | - Maria Guarnaccia
- Institute for Biomedical Research and Innovation, National Research Council, Contrada Burga, Piano Lago, 87050 Mangone (CS) and Via Paolo Gaifami 18, 95126 Catania, Italy
| | - Teresa Sprovieri
- Institute for Biomedical Research and Innovation, National Research Council, Contrada Burga, Piano Lago, 87050 Mangone (CS) and Via Paolo Gaifami 18, 95126 Catania, Italy
| | - Carmine Ungaro
- Institute for Biomedical Research and Innovation, National Research Council, Contrada Burga, Piano Lago, 87050 Mangone (CS) and Via Paolo Gaifami 18, 95126 Catania, Italy
| | - Francesca Luisa Conforti
- Department of Pharmacy, Health and Nutritional Sciences, University of Calabria, Rende, 87036 Cosenza, Italy
| | - Sebastiano Andò
- Department of Pharmacy, Health and Nutritional Sciences, University of Calabria, Rende, 87036 Cosenza, Italy
- Centro Sanitario, University of Calabria, Via Pietro Bucci, 87036 Arcavacata di Rende (CS), Italy
| | - Sebastiano Cavallaro
- Institute for Biomedical Research and Innovation, National Research Council, Contrada Burga, Piano Lago, 87050 Mangone (CS) and Via Paolo Gaifami 18, 95126 Catania, Italy.
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15
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Lorenz-Guertin JM, Bambino MJ, Jacob TC. γ2 GABA AR Trafficking and the Consequences of Human Genetic Variation. Front Cell Neurosci 2018; 12:265. [PMID: 30190672 PMCID: PMC6116786 DOI: 10.3389/fncel.2018.00265] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2018] [Accepted: 08/02/2018] [Indexed: 11/13/2022] Open
Abstract
GABA type A receptors (GABAARs) mediate the majority of fast inhibitory neurotransmission in the central nervous system (CNS). Most prevalent as heteropentamers composed of two α, two β, and a γ2 subunit, these ligand-gated ionotropic chloride channels are capable of extensive genetic diversity (α1-6, β1-3, γ1-3, δ, 𝜀, 𝜃, π, ρ1-3). Part of this selective GABAAR assembly arises from the critical role for γ2 in maintaining synaptic receptor localization and function. Accordingly, mutations in this subunit account for over half of the known epilepsy-associated genetic anomalies identified in GABAARs. Fundamental structure-function studies and cellular pathology investigations have revealed dynamic GABAAR trafficking and synaptic scaffolding as critical regulators of GABAergic inhibition. Here, we introduce in vitro and in vivo findings regarding the specific role of the γ2 subunit in receptor trafficking. We then examine γ2 subunit human genetic variation and assess disease related phenotypes and the potential role of altered GABAAR trafficking. Finally, we discuss new-age imaging techniques and their potential to provide novel insight into critical regulatory mechanisms of GABAAR function.
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Affiliation(s)
- Joshua M Lorenz-Guertin
- Department of Pharmacology and Chemical Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Matthew J Bambino
- Department of Pharmacology and Chemical Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Tija C Jacob
- Department of Pharmacology and Chemical Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
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16
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The genetic variant "C588T" of GABARG2 is linked to childhood idiopathic generalized epilepsy and resistance to antiepileptic drugs. Seizure 2018; 60:39-43. [PMID: 29894917 DOI: 10.1016/j.seizure.2018.06.004] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Revised: 06/03/2018] [Accepted: 06/05/2018] [Indexed: 11/21/2022] Open
Abstract
PURPOSE Previous studies have suggested that GABARG2 (Gamma-Aminobutyric acid type A Receptor Gamma 2 subunit) could be a gene of interest in genetic epilepsy; through possible associations with increased epilepsy susceptibility or resistance to antiepileptic drugs. The present study was designed to explore whether the GABARG2 C588 T (rs211037) genetic variant predicts susceptibility to epilepsy and pharmacoresistance among Egyptian children with Idiopathic Generalized Epilepsy (IGE). METHODS A cohort of 210 Egyptian children was divided into two groups for this case-control study: group (I) included 100 children with IGE, group (II) comprised of 110 paediatric healthy controls. PCR-RFLP was used to amplify the C588 T polymorphism of the GABARG2 gene, which was digested with APOI restriction enzymes. RESULTS There was a higher frequency of the TT genotype (P = 0.004) and T allele (P = 0.002) of the C588 T polymorphism of the GABARG2 gene in patients than controls. Besides, there was a substantial increase of the T allele among drug-resistant patients compared with those responding to antiepileptic drugs (P = 0.00015). Children with the C allele were four times more likely to be responsive to antiepileptic drugs than non-C-allele-carriers. CONCLUSION The C588 T polymorphism of GABARG2 is associated with an increased risk of developing childhood IGE and may modulate patients' response to antiepileptic drugs.
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17
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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: 1.5] [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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18
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Durisic N, Keramidas A, Dixon CL, Lynch JW. SAHA (Vorinostat) Corrects Inhibitory Synaptic Deficits Caused by Missense Epilepsy Mutations to the GABA A Receptor γ2 Subunit. Front Mol Neurosci 2018; 11:89. [PMID: 29628874 PMCID: PMC5876238 DOI: 10.3389/fnmol.2018.00089] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2018] [Accepted: 03/06/2018] [Indexed: 11/22/2022] Open
Abstract
The GABAA receptor (GABAAR) α1 subunit A295D epilepsy mutation reduces the surface expression of α1A295Dβ2γ2 GABAARs via ER-associated protein degradation. Suberanilohydroxamic acid (SAHA, also known as Vorinostat) was recently shown to correct the misfolding of α1A295D subunits and thereby enhance the functional surface expression of α1A295Dβ2γ2 GABAARs. Here we investigated whether SAHA can also restore the surface expression of γ2 GABAAR subunits that incorporate epilepsy mutations (N40S, R43Q, P44S, R138G) known to reduce surface expression via ER-associated protein degradation. As a control, we also investigated the γ2K289M epilepsy mutation that impairs gating without reducing surface expression. Effects of mutations were evaluated on inhibitory postsynaptic currents (IPSCs) mediated by the major synaptic α1β2γ2 GABAAR isoform. Recordings were performed in neuron-HEK293 cell artificial synapses to minimise contamination by GABAARs of undefined subunit composition. Transfection with α1β2γ2N40S, α1β2γ2R43Q, α1β2γ2P44S and α1β2γ2R138G subunits produced IPSCs with decay times slower than those of unmutated α1β2γ2 GABAARs due to the low expression of mutant γ2 subunits and the correspondingly high expression of slow-decaying α1β2 GABAARs. SAHA pre-treatment significantly accelerated the decay time constants of IPSCs consistent with the upregulation of mutant γ2 subunit expression. This increase in surface expression was confirmed by immunohistochemistry. SAHA had no effect on either the IPSC kinetics or surface expression levels of α1β2γ2K289M GABAARs, confirming its specificity for ER-retained mutant γ2 subunits. We also found that α1β2γ2K289M GABAARs and SAHA-treated α1β2γ2R43Q, α1β2γ2P44S and α1β2γ2R138G GABAARs all mediated IPSCs that decayed at significantly faster rates than wild type receptors as temperature was increased from 22 to 40°C. This may help explain why these mutations cause febrile seizures (FS). Given that SAHA is approved by therapeutic regulatory agencies for human use, we propose that it may be worth investigating as a treatment for epilepsies caused by the N40S, R43Q, P44S and R138G mutations. Although SAHA has already been proposed as a therapeutic for patients harbouring the α1A295D epilepsy mutation, the present study extends its potential utility to a new subunit and four new mutations.
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Affiliation(s)
- Nela Durisic
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
| | - Angelo Keramidas
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
| | - Christine L Dixon
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
| | - Joseph W Lynch
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
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19
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Oyrer J, Maljevic S, Scheffer IE, Berkovic SF, Petrou S, Reid CA. Ion Channels in Genetic Epilepsy: From Genes and Mechanisms to Disease-Targeted Therapies. Pharmacol Rev 2018; 70:142-173. [PMID: 29263209 DOI: 10.1124/pr.117.014456] [Citation(s) in RCA: 163] [Impact Index Per Article: 27.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Accepted: 10/02/2017] [Indexed: 12/19/2022] Open
Abstract
Epilepsy is a common and serious neurologic disease with a strong genetic component. Genetic studies have identified an increasing collection of disease-causing genes. The impact of these genetic discoveries is wide reaching-from precise diagnosis and classification of syndromes to the discovery and validation of new drug targets and the development of disease-targeted therapeutic strategies. About 25% of genes identified in epilepsy encode ion channels. Much of our understanding of disease mechanisms comes from work focused on this class of protein. In this study, we review the genetic, molecular, and physiologic evidence supporting the pathogenic role of a number of different voltage- and ligand-activated ion channels in genetic epilepsy. We also review proposed disease mechanisms for each ion channel and highlight targeted therapeutic strategies.
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Affiliation(s)
- Julia Oyrer
- The Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Melbourne, Australia (J.O., S.M., I.E.S., S.P., C.A.R.); Department of Medicine, Austin Health, University of Melbourne, Heidelberg West, Melbourne, Australia (I.E.S., S.F.B.); and Department of Paediatrics, University of Melbourne, Royal Children's Hospital, Melbourne, Australia (I.E.S.)
| | - Snezana Maljevic
- The Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Melbourne, Australia (J.O., S.M., I.E.S., S.P., C.A.R.); Department of Medicine, Austin Health, University of Melbourne, Heidelberg West, Melbourne, Australia (I.E.S., S.F.B.); and Department of Paediatrics, University of Melbourne, Royal Children's Hospital, Melbourne, Australia (I.E.S.)
| | - Ingrid E Scheffer
- The Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Melbourne, Australia (J.O., S.M., I.E.S., S.P., C.A.R.); Department of Medicine, Austin Health, University of Melbourne, Heidelberg West, Melbourne, Australia (I.E.S., S.F.B.); and Department of Paediatrics, University of Melbourne, Royal Children's Hospital, Melbourne, Australia (I.E.S.)
| | - Samuel F Berkovic
- The Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Melbourne, Australia (J.O., S.M., I.E.S., S.P., C.A.R.); Department of Medicine, Austin Health, University of Melbourne, Heidelberg West, Melbourne, Australia (I.E.S., S.F.B.); and Department of Paediatrics, University of Melbourne, Royal Children's Hospital, Melbourne, Australia (I.E.S.)
| | - Steven Petrou
- The Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Melbourne, Australia (J.O., S.M., I.E.S., S.P., C.A.R.); Department of Medicine, Austin Health, University of Melbourne, Heidelberg West, Melbourne, Australia (I.E.S., S.F.B.); and Department of Paediatrics, University of Melbourne, Royal Children's Hospital, Melbourne, Australia (I.E.S.)
| | - Christopher A Reid
- The Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Melbourne, Australia (J.O., S.M., I.E.S., S.P., C.A.R.); Department of Medicine, Austin Health, University of Melbourne, Heidelberg West, Melbourne, Australia (I.E.S., S.F.B.); and Department of Paediatrics, University of Melbourne, Royal Children's Hospital, Melbourne, Australia (I.E.S.)
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20
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Basak S, Schmandt N, Gicheru Y, Chakrapani S. Crystal structure and dynamics of a lipid-induced potential desensitized-state of a pentameric ligand-gated channel. eLife 2017; 6:23886. [PMID: 28262093 PMCID: PMC5378477 DOI: 10.7554/elife.23886] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Accepted: 03/04/2017] [Indexed: 12/14/2022] Open
Abstract
Desensitization in pentameric ligand-gated ion channels plays an important role in regulating neuronal excitability. Here, we show that docosahexaenoic acid (DHA), a key ω−3 polyunsaturated fatty acid in synaptic membranes, enhances the agonist-induced transition to the desensitized state in the prokaryotic channel GLIC. We determined a 3.25 Å crystal structure of the GLIC-DHA complex in a potentially desensitized conformation. The DHA molecule is bound at the channel-periphery near the M4 helix and exerts a long-range allosteric effect on the pore across domain-interfaces. In this previously unobserved conformation, the extracellular-half of the pore-lining M2 is splayed open, reminiscent of the open conformation, while the intracellular-half is constricted, leading to a loss of both water and permeant ions. These findings, in combination with spin-labeling/EPR spectroscopic measurements in reconstituted-membranes, provide novel mechanistic details of desensitization in pentameric channels. DOI:http://dx.doi.org/10.7554/eLife.23886.001 The nerve cells (or neurons) in the brain communicate with each other by releasing chemicals called neurotransmitters that bind to ion channels on neighboring neurons. This ultimately causes ions to flow in or out of the receiving neuron through these ion channels; this ion flow determines how the neuron responds. One family of ion channels that is found at the junction between neurons, and between neurons and muscle fibers, is known as the pentameric ligand-gated ion channels (or pLGICs). These channels act as ‘gates’ that open to allow ions through them when a neurotransmitter binds to the channel. In addition to the open ‘active’ state, the channels can take on two different ‘inactive’ states that do not allow ions to pass through the channel: a closed (resting) state and a desensitized state (that is still bound to the neurotransmitter). Understanding how channels switch between these states is important for designing drugs that correct problems that cause the channels to work incorrectly. Problems that affect the desensitized state have been linked to neurological disorders such as epilepsy. Medically important molecules such as anesthetics and alcohols are thought to affect desensitization, and drugs that target desensitized ion channels may present ways of treating neurological disorders with fewer side effects. Docosahexaenoic acid (DHA) is an abundant lipid molecule that is present in the membranes of neurons. It is one of the key ingredients in fish oil supplements and is thought to enhance learning and memory. DHA affects the desensitization of pLGICs but it is not clear exactly how it does so. Basak et al. now show that DHA affects a bacterial pLGIC in the same way as it affects human channels – by enhancing desensitization. Using a technique called X-ray crystallography to analyze the channel while bound to DHA revealed a previously unobserved channel structure. The DHA molecule binds to a site at the edge of the channel and causes a change in its structure that leaves the upper part of the channel open while the lower part is constricted. Basak et al. predict that molecules such as anesthetics target this desensitized state. The next step will be to obtain the structures of bacterial and human pLGIC channels in a natural membrane environment. This will allow us to better understand the changes in structure that the channels go through as they transmit signals between neurons, and so help in the development of new treatments for neurological disorders. DOI:http://dx.doi.org/10.7554/eLife.23886.002
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Affiliation(s)
- Sandip Basak
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, United States
| | - Nicolaus Schmandt
- Department of Neuroscience, School of Medicine, Case Western Reserve University, Cleveland, United States
| | - Yvonne Gicheru
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, United States
| | - Sudha Chakrapani
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, United States
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Botzolakis EJ, Gurba KN, Lagrange AH, Feng HJ, Stanic AK, Hu N, Macdonald RL. Comparison of γ-Aminobutyric Acid, Type A (GABAA), Receptor αβγ and αβδ Expression Using Flow Cytometry and Electrophysiology: EVIDENCE FOR ALTERNATIVE SUBUNIT STOICHIOMETRIES AND ARRANGEMENTS. J Biol Chem 2016; 291:20440-61. [PMID: 27493204 DOI: 10.1074/jbc.m115.698860] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Indexed: 01/23/2023] Open
Abstract
The subunit stoichiometry and arrangement of synaptic αβγ GABAA receptors are generally accepted as 2α:2β:1γ with a β-α-γ-β-α counterclockwise configuration, respectively. Whether extrasynaptic αβδ receptors adopt the analogous β-α-δ-β-α subunit configuration remains controversial. Using flow cytometry, we evaluated expression levels of human recombinant γ2 and δ subunits when co-transfected with α1 and/or β2 subunits in HEK293T cells. Nearly identical patterns of γ2 and δ subunit expression were observed as follows: both required co-transfection with α1 and β2 subunits for maximal expression; both were incorporated into receptors primarily at the expense of β2 subunits; and both yielded similar FRET profiles when probed for subunit adjacency, suggesting similar underlying subunit arrangements. However, because of a slower rate of δ subunit degradation, 10-fold less δ subunit cDNA was required to recapitulate γ2 subunit expression patterns and to eliminate the functional signature of α1β2 receptors. Interestingly, titrating γ2 or δ subunit cDNA levels progressively altered GABA-evoked currents, revealing more than one kinetic profile for both αβγ and αβδ receptors. This raised the possibility of alternative receptor isoforms, a hypothesis confirmed using concatameric constructs for αβγ receptors. Taken together, our results suggest a limited cohort of alternative subunit arrangements in addition to canonical β-α-γ/δ-β-α receptors, including β-α-γ/δ-α-α receptors at lower levels of γ2/δ expression and β-α-γ/δ-α-γ/δ receptors at higher levels of expression. These findings provide important insight into the role of GABAA receptor subunit under- or overexpression in disease states such as genetic epilepsies.
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Affiliation(s)
| | | | - Andre H Lagrange
- the Departments of Neurology, Pharmacology, and the Veterans Affairs Tennessee Valley Healthcare System, Nashville, Tennessee 37212, and
| | | | - Aleksandar K Stanic
- the Department of Obstetrics and Gynecology, University of Wisconsin, Madison, Wisconsin 53792
| | | | - Robert L Macdonald
- the Departments of Neurology, Pharmacology, and Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee 37240-7915,
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22
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Wijckmans E, Nys M, Debaveye S, Brams M, Pardon E, Willegems K, Bertrand D, Steyaert J, Efremov R, Ulens C. Functional and Biochemical Characterization of Alvinella pompejana Cys-Loop Receptor Homologues. PLoS One 2016; 11:e0151183. [PMID: 26999666 PMCID: PMC4801368 DOI: 10.1371/journal.pone.0151183] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Accepted: 02/24/2016] [Indexed: 11/22/2022] Open
Abstract
Cys-loop receptors are membrane spanning ligand-gated ion channels involved in fast excitatory and inhibitory neurotransmission. Three-dimensional structures of these ion channels, determined by X-ray crystallography or electron microscopy, have revealed valuable information regarding the molecular mechanisms underlying ligand recognition, channel gating and ion conductance. To extend and validate the current insights, we here present promising candidates for further structural studies. We report the biochemical and functional characterization of Cys-loop receptor homologues identified in the proteome of Alvinella pompejana, an extremophilic, polychaete annelid found in hydrothermal vents at the bottom of the Pacific Ocean. Seven homologues were selected, named Alpo1-7. Five of them, Alpo2-6, were unidentified prior to this study. Two-electrode voltage clamp experiments revealed that wild type Alpo5 and Alpo6, both sharing remarkably high sequence identity with human glycine receptor α subunits, are anion-selective channels that can be activated by glycine, GABA and taurine. Furthermore, upon expression in insect cells fluorescence size-exclusion chromatography experiments indicated that four homologues, Alpo1, Alpo4, Alpo6 and Alpo7, can be extracted out of the membrane by a wide variety of detergents while maintaining their oligomeric state. Finally, large-scale purification efforts of Alpo1, Alpo4 and Alpo6 resulted in milligram amounts of biochemically stable and monodisperse protein. Overall, our results establish the evolutionary conservation of glycine receptors in annelids and pave the way for future structural studies.
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Affiliation(s)
- Eveline Wijckmans
- Department of Cellular and Molecular Medicine, Laboratory of Structural Neurobiology, University of Leuven, Leuven, Belgium
| | - Mieke Nys
- Department of Cellular and Molecular Medicine, Laboratory of Structural Neurobiology, University of Leuven, Leuven, Belgium
- * E-mail:
| | - Sarah Debaveye
- Department of Cellular and Molecular Medicine, Laboratory of Structural Neurobiology, University of Leuven, Leuven, Belgium
| | - Marijke Brams
- Department of Cellular and Molecular Medicine, Laboratory of Structural Neurobiology, University of Leuven, Leuven, Belgium
| | - Els Pardon
- Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium
- Structural Biology Research Center, VIB, Brussels, Belgium
| | - Katrien Willegems
- Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium
- Structural Biology Research Center, VIB, Brussels, Belgium
| | | | - Jan Steyaert
- Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium
- Structural Biology Research Center, VIB, Brussels, Belgium
| | - Rouslan Efremov
- Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium
- Structural Biology Research Center, VIB, Brussels, Belgium
| | - Chris Ulens
- Department of Cellular and Molecular Medicine, Laboratory of Structural Neurobiology, University of Leuven, Leuven, Belgium
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Hammer H, Ebert B, Jensen HS, Jensen AA. Functional characterization of the 1,5-benzodiazepine clobazam and its major active metabolite N-desmethylclobazam at human GABA(A) receptors expressed in Xenopus laevis oocytes. PLoS One 2015; 10:e0120239. [PMID: 25798598 PMCID: PMC4370687 DOI: 10.1371/journal.pone.0120239] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2014] [Accepted: 02/04/2015] [Indexed: 12/13/2022] Open
Abstract
The 1,5-benzodiazepine clobazam is indicated for the adjunctive treatment of seizures associated with Lennox-Gastaut syndrome in patients 2 years of age or older in the United States, and for treatment of anxiety and various forms of epilepsy elsewhere. Clobazam has been reported to exhibit different in vivo adverse effects and addiction liability profile than the classic 1,4-benzodiazepines. In this study, it was investigated whether the in vitro pharmacological properties of clobazam and its major active metabolite N-desmethylclobazam could explain some of these clinical differences. The functional properties of the two 1,5-benzodiazepines were characterized at the human γ-aminobutyric acid type A receptor (GABAAR) subtypes α1β2γ2S, α2β2γ2S, α3β2γ2S, α5β2γ2S and α6β2δ expressed in Xenopus laevis oocytes by use of two-electrode voltage-clamp electrophysiology and compared to those exhibited by the 1,4-benzodiazepine clonazepam. All three compounds potentiated GABA EC20-evoked responses through the α1,2,3,5β2γ2S GABAARs in a reversible and concentration-dependent manner, with each displaying similar EC50 values at the four subtypes. Furthermore, the degrees of potentiation of the GABA EC20 currents through the four receptors mediated by saturating modulator concentrations did not differ substantially for any of the three benzodiazepines. The three compounds were substantially less potent (200-3900 fold) as positive allosteric modulators at the α6β2δ GABAAR than at the α1,2,3,5β2γ2S receptors. Interestingly, however, clobazam and especially N-desmethylclobazam were highly efficacious potentiators of α6β2δ receptor signaling. Although this activity component is unlikely to contribute to the in vivo effects of clobazam/N-desmethylclobazam, the 1,5-benzodiazepine could constitute an interesting lead for novel modulators targeting this low-affinity binding site in GABAARs. In conclusion, the non-selective modulation exerted by clobazam, N-desmethylclobazam and clonazepam at the α1β2γ2S, α2β2γ2S, α3β2γ2S and α5β2γ2S GABAARs indicate that the observed clinical differences between clobazam and 1,4-benzodiazepines are likely to arise from factors other than their respective pharmacological properties at the GABAARs as investigated here.
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Affiliation(s)
- Harriet Hammer
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | | | | | - Anders A. Jensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- * E-mail:
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24
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Peng X, Hughes EG, Moscato EH, Parsons TD, Dalmau J, Balice-Gordon RJ. Cellular plasticity induced by anti-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor encephalitis antibodies. Ann Neurol 2015; 77:381-98. [PMID: 25369168 PMCID: PMC4365686 DOI: 10.1002/ana.24293] [Citation(s) in RCA: 98] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2014] [Revised: 09/19/2014] [Accepted: 10/22/2014] [Indexed: 02/06/2023]
Abstract
Objective Autoimmune-mediated anti–α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) encephalitis is a severe but treatment-responsive disorder with prominent short-term memory loss and seizures. The mechanisms by which patient antibodies affect synapses and neurons leading to symptoms are poorly understood. Methods The effects of patient antibodies on cultures of live rat hippocampal neurons were determined with immunostaining, Western blot, and electrophysiological analyses. Results We show that patient antibodies cause a selective decrease in the total surface amount and synaptic localization of GluA1- and GluA2-containing AMPARs, regardless of receptor subunit binding specificity, through increased internalization and degradation of surface AMPAR clusters. In contrast, patient antibodies do not alter the density of excitatory synapses, N-methyl-D-aspartate receptor (NMDAR) clusters, or cell viability. Commercially available AMPAR antibodies directed against extracellular epitopes do not result in a loss of surface and synaptic receptor clusters, suggesting specific effects of patient antibodies. Whole-cell patch clamp recordings of spontaneous miniature postsynaptic currents show that patient antibodies decrease AMPAR-mediated currents, but not NMDAR-mediated currents. Interestingly, several functional properties of neurons are also altered: inhibitory synaptic currents and vesicular γ-aminobutyric acid transporter (vGAT) staining intensity decrease, whereas the intrinsic excitability of neurons and short-interval firing increase. Interpretation These results establish that antibodies from patients with anti-AMPAR encephalitis selectively eliminate surface and synaptic AMPARs, resulting in a homeostatic decrease in inhibitory synaptic transmission and increased intrinsic excitability, which may contribute to the memory deficits and epilepsy that are prominent in patients with this disorder.
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Affiliation(s)
- Xiaoyu Peng
- Department of Neuroscience, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA
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25
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Abstract
Since their introduction in the 1960s, benzodiazepines (BZs) remain one of the most commonly prescribed medications, acting as potent sedatives, hypnotics, anxiolytics, anticonvulsants, and muscle relaxants. The primary neural action of BZs and related compounds is augmentation of inhibitory transmission, which occurs through allosteric modulation of the gamma-aminobutyric acid (GABA)-induced current at the gamma-aminobutyric acid receptor (GABAAR). The discovery of the BZ-binding site on GABAARs encouraged many to speculate that the brain produces its own endogenous ligands to this site (Costa & Guidotti, 1985). The romanticized quest for endozepines, endogenous ligands to the BZ-binding site, has uncovered a variety of ligands that might fulfill this role, including oleamides (Cravatt et al., 1995), nonpeptidic endozepines (Rothstein et al., 1992), and the protein diazepam-binding inhibitor (DBI) (Costa & Guidotti, 1985). Of these ligands, DBI, and affiliated peptide fragments, is the most extensively studied endozepine. The quest for the "brain's Valium" over the decades has been elusive as mainly negative allosteric modulatory effects have been observed (Alfonso, Le Magueresse, Zuccotti, Khodosevich, & Monyer, 2012; Costa & Guidotti, 1985), but recent evidence is accumulating that DBI displays regionally discrete endogenous positive modulation of GABA transmission through activation of the BZ receptor (Christian et al., 2013). Herein, we review the literature on this topic, focusing on identification of the endogenous molecule and its region-specific expression and function.
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Lachance-Touchette P, Choudhury M, Stoica A, Di Cristo G, Cossette P. Single-cell genetic expression of mutant GABAA receptors causing Human genetic epilepsy alters dendritic spine and GABAergic bouton formation in a mutation-specific manner. Front Cell Neurosci 2014; 8:317. [PMID: 25352779 PMCID: PMC4196543 DOI: 10.3389/fncel.2014.00317] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2014] [Accepted: 09/21/2014] [Indexed: 11/13/2022] Open
Abstract
Mutations in genes encoding for GABAA receptor subunits is a well-established cause of genetic generalized epilepsy. GABA neurotransmission is implicated in several developmental processes including neurite outgrowth and synapse formation. Alteration in excitatory/inhibitory synaptic activities plays a critical role in epilepsy, thus here we investigated whether mutations in α1 subunit of GABAA receptor may affect dendritic spine and GABAergic bouton formation. In particular, we examined the effects of three mutations of the GABRA1 gene (D219N, A322D and K353delins18X) that were found in a cohort of French Canadian families with genetic generalized epilepsy. We used a novel single-cell genetic approach, by preparing cortical organotypic cultures from GABRA1flox/flox mice and simultaneously inactivating endogenous GABRA1 and transfecting mutant α1 subunits in single glutamatergic pyramidal cells and basket GABAergic interneurons by biolistic transfection. We found that GABRA1−/− GABAergic cells showed reduced innervation field, which was rescued by co-expressing α1-A322D and α1-WT but not α1-D219N. We further found that the expression of the most severe GABRA1 missense mutation (α1-A322D) induced a striking increase of spine density in pyramidal cells along with an increase in the number of mushroom-like spines. In addition, α1-A322D expression in GABAergic cells slightly increased perisomatic bouton density, whereas other mutations did not alter bouton formation. All together, these results suggest that the effects of different GABAAR mutations on GABAergic bouton and dendritic spine formation are specific to the mutation and cannot be always explained by a simple loss-of-function gene model. The use of single cell genetic manipulation in organotypic cultures may provide a better understanding of the specific and distinct neural circuit alterations caused by different GABAA receptor subunit mutations and will help define the pathophysiology of genetic generalized epilepsy syndromes.
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Affiliation(s)
- Pamela Lachance-Touchette
- Centre d'Excellence en Neuromique de l'Université de Montréal, Centre de Recherche, Centre Hospitalier de l'Université de Montréal, Université de Montréal Montréal, QC, Canada
| | - Mayukh Choudhury
- Centre Hospitalier Universitaire Sainte-Justine, Université de Montréal Montréal, QC, Canada
| | - Ana Stoica
- Centre d'Excellence en Neuromique de l'Université de Montréal, Centre de Recherche, Centre Hospitalier de l'Université de Montréal, Université de Montréal Montréal, QC, Canada
| | - Graziella Di Cristo
- Centre Hospitalier Universitaire Sainte-Justine, Université de Montréal Montréal, QC, Canada
| | - Patrick Cossette
- Centre d'Excellence en Neuromique de l'Université de Montréal, Centre de Recherche, Centre Hospitalier de l'Université de Montréal, Université de Montréal Montréal, QC, Canada
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27
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Nah SY. Ginseng ginsenoside pharmacology in the nervous system: involvement in the regulation of ion channels and receptors. Front Physiol 2014; 5:98. [PMID: 24678300 PMCID: PMC3958645 DOI: 10.3389/fphys.2014.00098] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2013] [Accepted: 02/27/2014] [Indexed: 01/05/2023] Open
Abstract
Ginseng, the root of Panax ginseng C.A. Meyer, is one of the oldest traditional medicines and is thought to be a tonic. It has been claimed that ginseng may improve vitality and health. Recent studies have advanced ginseng pharmacology and shown that ginseng has various pharmacological effects in the nervous system. Ginsenosides, steroid glycosides extracted from ginseng, were one of the first class of biologically active plant glycosides identified. The diverse pharmacological effects of ginsenosides have been investigated through the regulation of various types of ion channels and receptors in neuronal cells and heterologous expression systems. Ginsenoside Rg3 regulates voltage-gated ion channels such as Ca(2+), K(+), and Na(+) channels, and ligand-gated ion channels such as GABAA, 5-HT3, nicotinic acetylcholine, and N-methyl-D-aspartate (NMDA) receptors through interactions with various sites including channel blocker binding sites, toxin-binding sites, channel gating regions, and allosteric channel regulator binding sites when the respective ion channels or receptors are stimulated with depolarization or ligand treatment. Treatment with ginsenoside Rg3 has been found to stabilize excitable cells by blocking influxes of cations such as Ca(2+) and Na(+), or by enhancing Cl(-) influx. The aim of this review is to present recent findings on the pharmacological functions of the ginsenosides through the interactions with ion channels and receptors. This review will detail the pharmacological applications of ginsenosides as neuroprotective drugs that target ion channels and ligand-gated ion channels.
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Affiliation(s)
- Seung-Yeol Nah
- Ginsentology Research Laboratory, Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University Seoul, South Korea
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28
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Abstract
The γ-aminobutyric acid receptor type A (GABAA receptor) is a ligand-gated chloride channel that mediates major inhibitory functions in the central nervous system. GABAA receptors function mainly as pentamers containing α, β, and either γ or δ subunits. A number of antiepileptic drugs have agonistic effects on GABAA receptors. Hence, dysfunctions of GABAA receptors have been postulated to play important roles in the etiology of epilepsy. In fact, mutations or genetic variations of the genes encoding the α1, α6, β2, β3, γ2, or δ subunits (GABRA1, GABRA6, GABRB2, GABRB3, GABRG2, and GABRD, respectively) have been associated with human epilepsy, both with and without febrile seizures. Epilepsy resulting from mutations is commonly one of following, genetic (idiopathic) generalized epilepsy (e.g., juvenile myoclonic epilepsy), childhood absence epilepsy, genetic epilepsy with febrile seizures, or Dravet syndrome. Recently, mutations of GABRA1, GABRB2, and GABRB3 were associated with infantile spasms and Lennox-Gastaut syndrome. These mutations compromise hyperpolarization through GABAA receptors, which is believed to cause seizures. Interestingly, most of the insufficiencies are not caused by receptor gating abnormalities, but by complex mechanisms, including endoplasmic reticulum (ER)-associated degradation, nonsense-mediated mRNA decay, intracellular trafficking defects, and ER stress. Thus, GABAA receptor subunit mutations are now thought to participate in the pathomechanisms of epilepsy, and an improved understanding of these mutations should facilitate our understanding of epilepsy and the development of new therapies.
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Greenfield LJ. Molecular mechanisms of antiseizure drug activity at GABAA receptors. Seizure 2013; 22:589-600. [PMID: 23683707 PMCID: PMC3766376 DOI: 10.1016/j.seizure.2013.04.015] [Citation(s) in RCA: 115] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2013] [Revised: 04/16/2013] [Accepted: 04/17/2013] [Indexed: 02/09/2023] Open
Abstract
The GABAA receptor (GABAAR) is a major target of antiseizure drugs (ASDs). A variety of agents that act at GABAARs s are used to terminate or prevent seizures. Many act at distinct receptor sites determined by the subunit composition of the holoreceptor. For the benzodiazepines, barbiturates, and loreclezole, actions at the GABAAR are the primary or only known mechanism of antiseizure action. For topiramate, felbamate, retigabine, losigamone and stiripentol, GABAAR modulation is one of several possible antiseizure mechanisms. Allopregnanolone, a progesterone metabolite that enhances GABAAR function, led to the development of ganaxolone. Other agents modulate GABAergic "tone" by regulating the synthesis, transport or breakdown of GABA. GABAAR efficacy is also affected by the transmembrane chloride gradient, which changes during development and in chronic epilepsy. This may provide an additional target for "GABAergic" ASDs. GABAAR subunit changes occur both acutely during status epilepticus and in chronic epilepsy, which alter both intrinsic GABAAR function and the response to GABAAR-acting ASDs. Manipulation of subunit expression patterns or novel ASDs targeting the altered receptors may provide a novel approach for seizure prevention.
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Affiliation(s)
- L John Greenfield
- Dept. of Neurology, University of Arkansas for Medical Sciences, 4301W. Markham St., Slot 500, Little Rock, AR 72205, United States.
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30
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Chaumont S, André C, Perrais D, Boué-Grabot E, Taly A, Garret M. Agonist-dependent endocytosis of γ-aminobutyric acid type A (GABAA) receptors revealed by a γ2(R43Q) epilepsy mutation. J Biol Chem 2013; 288:28254-65. [PMID: 23935098 DOI: 10.1074/jbc.m113.470807] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
GABA-gated chloride channels (GABAARs) trafficking is involved in the regulation of fast inhibitory transmission. Here, we took advantage of a γ2(R43Q) subunit mutation linked to epilepsy in humans that considerably reduces the number of GABAARs on the cell surface to better understand the trafficking of GABAARs. Using recombinant expression in cultured rat hippocampal neurons and COS-7 cells, we showed that receptors containing γ2(R43Q) were addressed to the cell membrane but underwent clathrin-mediated dynamin-dependent endocytosis. The γ2(R43Q)-dependent endocytosis was reduced by GABAAR antagonists. These data, in addition to a new homology model, suggested that a conformational change in the extracellular domain of γ2(R43Q)-containing GABAARs increased their internalization. This led us to show that endogenous and recombinant wild-type GABAAR endocytosis in both cultured neurons and COS-7 cells can be amplified by their agonists. These findings revealed not only a direct relationship between endocytosis of GABAARs and a genetic neurological disorder but also that trafficking of these receptors can be modulated by their agonist.
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Affiliation(s)
- Severine Chaumont
- From the Université Bordeaux, Institut de Neurosciences Cognitives et Intégratives d'Aquitaine (INCIA), UMR 5287, F-33000 Bordeaux, France
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31
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Christian CA, Herbert AG, Holt RL, Peng K, Sherwood KD, Pangratz-Fuehrer S, Rudolph U, Huguenard JR. Endogenous positive allosteric modulation of GABA(A) receptors by diazepam binding inhibitor. Neuron 2013; 78:1063-74. [PMID: 23727119 DOI: 10.1016/j.neuron.2013.04.026] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/12/2013] [Indexed: 11/30/2022]
Abstract
Benzodiazepines (BZs) allosterically modulate γ-aminobutyric acid type-A receptors (GABAARs) to increase inhibitory synaptic strength. Diazepam binding inhibitor (DBI) protein is a BZ site ligand expressed endogenously in the brain, but functional evidence for BZ-mimicking positive modulatory actions has been elusive. We demonstrate an endogenous potentiation of GABAergic synaptic transmission and responses to GABA uncaging in the thalamic reticular nucleus (nRT) that is absent in both nm1054 mice, in which the Dbi gene is deleted, and mice in which BZ binding to α3 subunit-containing GABAARs is disrupted. Viral transduction of DBI into nRT is sufficient to rescue the endogenous potentiation of GABAergic transmission in nm1054 mice. Both mutations enhance thalamocortical spike-and-wave discharges characteristic of absence epilepsy. Together, these results indicate that DBI mediates endogenous nucleus-specific BZ-mimicking ("endozepine") roles to modulate nRT function and suppress thalamocortical oscillations. Enhanced DBI signaling might serve as a therapy for epilepsy and other neurological disorders.
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Affiliation(s)
- Catherine A Christian
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA 94305, USA.
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32
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Bazyan AS, van Luijtelaar G. Neurochemical and behavioral features in genetic absence epilepsy and in acutely induced absence seizures. ISRN NEUROLOGY 2013; 2013:875834. [PMID: 23738145 PMCID: PMC3664506 DOI: 10.1155/2013/875834] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/21/2013] [Accepted: 02/06/2013] [Indexed: 02/08/2023]
Abstract
The absence epilepsy typical electroencephalographic pattern of sharp spikes and slow waves (SWDs) is considered to be due to an interaction of an initiation site in the cortex and a resonant circuit in the thalamus. The hyperpolarization-activated cyclic nucleotide-gated cationic I h pacemaker channels (HCN) play an important role in the enhanced cortical excitability. The role of thalamic HCN in SWD occurrence is less clear. Absence epilepsy in the WAG/Rij strain is accompanied by deficiency of the activity of dopaminergic system, which weakens the formation of an emotional positive state, causes depression-like symptoms, and counteracts learning and memory processes. It also enhances GABAA receptor activity in the striatum, globus pallidus, and reticular thalamic nucleus, causing a rise of SWD activity in the cortico-thalamo-cortical networks. One of the reasons for the occurrence of absences is that several genes coding of GABAA receptors are mutated. The question arises: what the role of DA receptors is. Two mechanisms that cause an infringement of the function of DA receptors in this genetic absence epilepsy model are proposed.
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Affiliation(s)
- A. S. Bazyan
- Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Science, Russian Federation, 5A Butlerov Street, Moscow 117485, Russia
| | - G. van Luijtelaar
- Biological Psychology, Donders Centre for Cognition, Donders Institute for Brain, Cognition and Behavior, Radboud University Nijmegen, P.O. Box 9104, 6500 HE Nijmegen, The Netherlands
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Keramidas A, Lynch JW. An outline of desensitization in pentameric ligand-gated ion channel receptors. Cell Mol Life Sci 2013; 70:1241-53. [PMID: 22936353 PMCID: PMC11113241 DOI: 10.1007/s00018-012-1133-z] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2012] [Revised: 07/28/2012] [Accepted: 08/13/2012] [Indexed: 10/27/2022]
Abstract
Pentameric ligand-gated ion channel (pLGIC) receptors exhibit desensitization, the progressive reduction in ionic flux in the prolonged presence of agonist. Despite its pathophysiological importance and the fact that it was first described over half a century ago, surprisingly little is known about the structural basis of desensitization in this receptor family. Here, we explain how desensitization is defined using functional criteria. We then review recent progress into reconciling the structural and functional basis of this phenomenon. The extracellular-transmembrane domain interface is a key locus. Activation is well known to involve conformational changes at this interface, and several lines of evidence suggest that desensitization involves a distinct conformational change here that is incompatible with activation. However, major questions remain unresolved, including the structural basis of the desensitization-induced agonist affinity increase and the mechanism of pore closure during desensitization.
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Affiliation(s)
- Angelo Keramidas
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072 Australia
| | - Joseph W. Lynch
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072 Australia
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD 4072 Australia
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Reid CA, Kim T, Phillips AM, Low J, Berkovic SF, Luscher B, Petrou S. Multiple molecular mechanisms for a single GABAA mutation in epilepsy. Neurology 2013; 80:1003-8. [PMID: 23408872 DOI: 10.1212/wnl.0b013e3182872867] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE To understand the molecular basis and differential penetrance of febrile seizures and absence seizures in patients with the γ2(R43Q) GABA receptor mutation. METHODS Spike-and-wave discharges and thermal seizure susceptibility were measured in heterozygous GABA γ2 knock-out and GABA γ2(R43Q) knock-in mice models crossed to different mouse strains. RESULTS By comparing the GABA γ2 knock-out with the GABA γ2(R43Q) knock-in mouse model we show that haploinsufficiency underlies the genesis of absence seizures but cannot account for the thermal seizure susceptibility. Additionally, while the expression of the absence seizure phenotype was very sensitive to mouse background genetics, the thermal seizure phenotype was not. CONCLUSIONS Our results show that a single gene mutation can cause distinct seizure phenotypes through independent molecular mechanisms. A lack of effect of genetic background on thermal seizure susceptibility is consistent with the higher penetrance of febrile seizures compared to absence seizures seen in family members with the mutation. These mouse studies help to provide a conceptual framework within which clinical heterogeneity seen in genetic epilepsy can be explained.
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Affiliation(s)
- Christopher A Reid
- Florey Institute of Neuroscience and Mental Health, The University of Melbourne, Australia.
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35
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Kim YO, Kim MK, Nam TS, Jang SY, Park KW, Kim EY, Rho YI, Woo YJ. Mutation Screening of the γ-Aminobutyric Acid Type-A Receptor Subunit γ2 Gene in Korean Patients with Childhood Absence Epilepsy. J Clin Neurol 2012; 8:271-5. [PMID: 23323135 PMCID: PMC3540286 DOI: 10.3988/jcn.2012.8.4.271] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2011] [Revised: 04/16/2012] [Accepted: 04/16/2012] [Indexed: 11/25/2022] Open
Abstract
Background and Purpose Since the γ-aminobutyric acid type-A receptor subunit γ2 gene (GABRG2) mutation was discovered in an Australian family with childhood absence epilepsy (CAE) and febrile convulsions, a few screening studies for the GABRG2 mutation have been conducted in sporadic individuals with CAE from other ethnic groups. The aim of this study was to determine whether or not the previously reported genetic mutations and single-nucleotide polymorphisms (SNPs) of GABRG2 can be reproduced in sporadic Korean individuals with CAE, compared to healthy Korean individuals. Methods Thirty-five children with CAE in Chonnam National University Hospital and healthy controls (n=207) were enrolled, and the medical records of patients with CAE were reviewed. CAE was diagnosed according to the Classification and Terminology of the International League Against Epilepsy. All nine exons of GABRG2 were directly sequenced. In addition, the two SNPs found in our CAE patients were analyzed: C315T in exon 3 (E3) and C588T in exon 5 (E5). The frequencies of the two SNPs in the CAE patients were compared with data from healthy controls (for E3 and E5) and from previously reported Korean population data (only for E3). Results No mutation of GABRG2 was found in our CAE patients. In addition, the allele and genotype frequencies of the two polymorphisms did not differ significantly between CAE patients, healthy controls, and the Korean general population (p>0.05). Conclusions Our study of sporadic Korean individuals with CAE found no evidence that GABRG2 contributes to the genetic basis of CAE.
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Affiliation(s)
- Young Ok Kim
- Department of Pediatrics, Chonnam National University Medical School, Gwangju, Korea
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Seymour VAL, Curmi JP, Howitt SM, Casarotto MG, Laver DR, Tierney ML. Selective modulation of different GABAA receptor isoforms by diazepam and etomidate in hippocampal neurons. Int J Biochem Cell Biol 2012; 44:1491-500. [PMID: 22704937 DOI: 10.1016/j.biocel.2012.06.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2011] [Revised: 05/29/2012] [Accepted: 06/04/2012] [Indexed: 10/28/2022]
Abstract
Diazepam modulation of native γ2-containing GABA(A) (γGABA(A)) receptors increases channel conductance by facilitating protein interactions involving the γ2-subunit amphipathic (MA) region, which is found in the cytoplasmic loop between transmembrane domains 3 and 4 (Everitt et al., 2009). However, many drugs, predicted to act on different GABA(A) receptor subtypes, increase channel conductance leading us to hypothesize that conductance variation in GABA(A) receptors may be a general property, mediated by protein interactions involving the cytoplasmic MA stretch of amino acids. In this study we have tested this hypothesis by potentiating extrasynaptic GABA(A) currents with etomidate and examining the ability of peptides mimicking either the γ2- or δ-subunit MA region to affect conductance. In inside-out hippocampal patches from newborn rats the general anesthetic etomidate potentiated GABA currents, producing either an increase in open probability and single-channel conductance or an increase in open probability, as described previously (Seymour et al., 2009). In patches displaying high conductance channels application of a δ((392-422)) MA peptide, but not a scrambled version or the equivalent γ2((381-403)) MA peptide, reduced the potentiating effects of etomidate, significantly reducing single-channel conductance. In contrast, when GABA currents were potentiated by the γ2-specific drug diazepam the δ MA peptide had no effect. These data reveal that diazepam and etomidate potentiate different extrasynaptic GABA(A) receptor subtypes but both drugs modulate conductance similarly. One interpretation of the data is that these drugs elicit potentiation through protein interactions and that the MA peptides compete with these interactions to disrupt this process.
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Affiliation(s)
- Victoria A L Seymour
- The John Curtin School of Medical Research, The Australian National University, Canberra, ACT 2601, Australia
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Carpenter TS, Lau EY, Lightstone FC. A role for loop F in modulating GABA binding affinity in the GABA(A) receptor. J Mol Biol 2012; 422:310-23. [PMID: 22659322 DOI: 10.1016/j.jmb.2012.05.025] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Revised: 05/08/2012] [Accepted: 05/17/2012] [Indexed: 10/28/2022]
Abstract
The brain's major inhibitory neuroreceptor is the ligand-gated ion channel γ-aminobutyric acid (GABA) type A receptor (GABAR). GABARs exist in a variety of different subunit combinations that act to modulate the physiological behavior of GABAR by altering its pharmacological profile, as well as its affinity for GABA. While the α(1)β(2)γ(2) subtype is one of the most prevalent GABARs, the less populous α(6)β(3)δ subtype has much higher GABA sensitivity. Previous studies identified residues crucial for GABA binding; however, the specific molecular differences responsible for this diverse sensitivity are not known. Furthermore, the role of loop F is a divisive subject, with conflicting evidence for ligand binding function. Using homology modeling, ligand docking, and molecular dynamics simulations, we investigated the GABA binding sites of the two receptor subtypes. Simulations identified seven residues that consistently interacted with GABA in both subtypes: αF65, αR132, βL99, βE155, βR/K196, βY205, and βR207. Residue substitution at position β196 (arginine in α(6)β(3)δ, lysine in α(1)β(2)γ(2)) resulted in a shift in GABA binding. However, the major difference between the two binding sites was the magnitude of loop F involvement, with a greater contribution in the α(6)β(3)δ receptor. Free energy calculations confirm that the α(6)β(3)δ binding pocket has an increased affinity for GABA. Thus, the possible role for loop F across the GABAR family is to modulate GABA affinity.
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Affiliation(s)
- Timothy S Carpenter
- Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
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Ponnala S, Chaudhari JR, Jaleel MA, Bhiladvala D, Kaipa PR, Das UN, Hasan Q. Role of MDR1 C3435T and GABRG2 C588T gene polymorphisms in seizure occurrence and MDR1 effect on anti-epileptic drug (phenytoin) absorption. Genet Test Mol Biomarkers 2012; 16:550-7. [PMID: 22239287 DOI: 10.1089/gtmb.2011.0225] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
AIMS To assess the role of MDR1 and gamma-aminobutyric acid receptor-gamma 2 sub unit (GABRG2) gene polymorphism in seizure susceptibility in generalized seizure (GS) and febrile seizure (FS) patients and to evaluate MDR1 C3435T gene polymorphism's role in absorption of the anti-epileptic drug, phenytoin (PHT) in a cohort of patients. METHODS One hundred twenty-seven cases of seizure (86 GS and 41 FS) patients were analyzed for MDR1 C3435T and GABRG2 C588T gene polymorphisms using restriction fragment length polymorphism-polymerase chain reaction. Serum PHT levels were analyzed. RESULTS The T allele of MDR1 C3435T and GABRG2 C588T gene polymorphism was higher in GS in the Indian population compared with controls. From the data in GS, CT and TT genotype carriers of the MDR1 gene and TT genotype carriers of the GABRG2 gene had more recurrent seizures compared with others. MDR1 T allele carriers in the seizure reoccurrence (SR) group of GS and FS were high compared with the well-controlled seizure group (with no seizures after treatment). TT genotype carriers in SR group were high in FS (with regard to MDR1 gene polymorphism) and GS (with regard to GABRG2 gene polymorphism) compared with a well-controlled seizure group. MDR1 C3435T gene polymorphism affects serum PHT levels (p<0.015). Association of dose PHT ratio and genotype groups of MDR1 C3435T gene polymorphism showed a significant association (p<0.05). MDR1*CC genotype was more common in cases with low serum PHT levels.In addition, it is evident that CT and TT genotype carriers have a high percentage of SR with elevated serum PHT levels. CONCLUSIONS Our results show that the MDR1 3435T and GABRG2 588T alleles play a role in seizure occurrence. Moreover, the MDR1 3435T allele also affects PHT absorption. We suggest MDR1 C3435T and GABRG2 C588T genotyping would be of value in order to lower the risk of concentration-dependent drug toxicity and for better patient management.
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Affiliation(s)
- Shivani Ponnala
- Department of Cancer Biology and Pharmacology, University of Illinois College of Medicine at Peoria, Peoria, Illinois, USA.
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Wang Q, Lynch JW. Activation and desensitization induce distinct conformational changes at the extracellular-transmembrane domain interface of the glycine receptor. J Biol Chem 2011; 286:38814-38824. [PMID: 21917927 DOI: 10.1074/jbc.m111.273631] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Most ligand-gated channels exhibit desensitization, which is the progressive fading of ionic current in the prolonged presence of agonist. This process involves conformational changes that close the channel despite continued agonist binding. Despite the physiological and pathological importance of desensitization, little is known about the conformational changes that underlie this process in any Cys-loop ion channel receptor. Here we employed voltage clamp fluorometry to identify conformational changes that occur with a similar time course as the current desensitization rate in both slow- and fast-desensitizing α1 glycine receptor chloride channels. Voltage clamp fluorometry provides a direct indication of conformational changes that occur in the immediate vicinity of residues labeled with environmentally sensitive fluorophores. We compared the rates of current desensitization and fluorescence changes at nine labeled extracellular sites in both wild type slow-desensitizing and mutated (A248L) fast-desensitizing glycine receptors. As labels attached to three sites at the interface between the ligand binding domain and transmembrane domain reported fluorescence responses that changed in parallel with the current desensitization rate, we concluded that they experienced local conformational changes associated with desensitization. These labeled sites included A52C in loop 2, Q219C in the pre-M1 domain, and M227C in the M1 domain. Activation and desensitization were accompanied by physically distinct conformational changes at each labeled site. Because activation is mediated by a specific reorganization of molecular interactions at the extracellular-transmembrane domain interface, we propose that desensitization is mediated by a distinct set of conformational changes that prevents this reorganization from occurring, thereby favoring channel closure.
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Affiliation(s)
- Qian Wang
- Queensland Brain Institute and School of Biomedical Sciences, University of Queensland, Brisbane QLD 4072, Australia
| | - Joseph W Lynch
- Queensland Brain Institute and School of Biomedical Sciences, University of Queensland, Brisbane QLD 4072, Australia.
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Lachance-Touchette P, Brown P, Meloche C, Kinirons P, Lapointe L, Lacasse H, Lortie A, Carmant L, Bedford F, Bowie D, Cossette P. Novel α1 and γ2 GABAA receptor subunit mutations in families with idiopathic generalized epilepsy. Eur J Neurosci 2011; 34:237-49. [PMID: 21714819 DOI: 10.1111/j.1460-9568.2011.07767.x] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Epilepsy is a heterogeneous neurological disease affecting approximately 50 million people worldwide. Genetic factors play an important role in both the onset and severity of the condition, with mutations in several ion-channel genes being implicated, including those encoding the GABA(A) receptor. Here, we evaluated the frequency of additional mutations in the GABA(A) receptor by direct sequencing of the complete open reading frame of the GABRA1 and GABRG2 genes from a cohort of French Canadian families with idiopathic generalized epilepsy (IGE). Using this approach, we have identified three novel mutations that were absent in over 400 control chromosomes. In GABRA1, two mutations were found, with the first being a 25-bp insertion that was associated with intron retention (i.e. K353delins18X) and the second corresponding to a single point mutation that replaced the aspartate 219 residue with an asparagine (i.e. D219N). Electrophysiological analysis revealed that K353delins18X and D219N altered GABA(A) receptor function by reducing the total surface expression of mature protein and/or by curtailing neurotransmitter effectiveness. Both defects would be expected to have a detrimental effect on inhibitory control of neuronal circuits. In contrast, the single point mutation identified in the GABRG2 gene, namely P83S, was indistinguishable from the wildtype subunit in terms of surface expression and functionality. This finding was all the more intriguing as the mutation exhibited a high degree of penetrance in three generations of one French Canadian family. Further experimentation will be required to understand how this mutation contributes to the occurrence of IGE in these individuals.
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Affiliation(s)
- Pamela Lachance-Touchette
- Centre for Excellence in Neuromics of University of Montreal, CHUM Research Center, 1560 Sherbrooke est, Montreal, QC, Canada H2L 4M1
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McClelland S, Dubé CM, Yang J, Baram TZ. Epileptogenesis after prolonged febrile seizures: mechanisms, biomarkers and therapeutic opportunities. Neurosci Lett 2011; 497:155-62. [PMID: 21356275 DOI: 10.1016/j.neulet.2011.02.032] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2011] [Accepted: 02/15/2011] [Indexed: 01/08/2023]
Abstract
Epidemiological and recent prospective analyses of long febrile seizures (FS) and febrile status epilepticus (FSE) support the idea that in some children, such seizures can provoke temporal lobe epilepsy (TLE). Because of the high prevalence of these seizures, if epilepsy was to arise as their direct consequence, this would constitute a significant clinical problem. Here we discuss these issues, and describe the use of animal models of prolonged FS and of FSE to address the following questions: Are long FS epileptogenic? What governs this epileptogenesis? What are the mechanisms? Are there any predictive biomarkers of the epileptogenic process, and can these be utilized, together with information about the mechanisms of epileptogenesis, for eventual prevention of the TLE that results from long FS and FSE.
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Affiliation(s)
- Shawn McClelland
- Department of Anatomy/Neurobiology, University of California, Irvine, CA 92697-4475, USA
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Różycka A, Dorszewska J, Jagodziński PP. Zaburzenia czynności kanałów jonowych w patogenezie padaczek idiopatycznych. Neurol Neurochir Pol 2011; 45:42-56. [PMID: 21384293 DOI: 10.1016/s0028-3843(14)60059-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Yin W, Majumder S, Clayton T, Petrou S, VanLinn ML, Namjoshi OA, Ma C, Cromer BA, Roth BL, Platt DM, Cook JM. Design, synthesis, and subtype selectivity of 3,6-disubstituted β-carbolines at Bz/GABA(A)ergic receptors. SAR and studies directed toward agents for treatment of alcohol abuse. Bioorg Med Chem 2010; 18:7548-64. [PMID: 20888240 PMCID: PMC2972656 DOI: 10.1016/j.bmc.2010.08.049] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2010] [Revised: 08/25/2010] [Accepted: 08/26/2010] [Indexed: 11/29/2022]
Abstract
A series of 3,6-disubstituted β-carbolines was synthesized and evaluated for their in vitro affinities at α(x)β(3)γ(2) GABA(A)/benzodiazepine receptor subtypes by radioligand binding assays in search of α(1) subtype selective ligands to treat alcohol abuse. Analogues of β-carboline-3-carboxylate-t-butyl ester (βCCt, 1) were synthesized via a CDI-mediated process and the related 6-substituted β-carboline-3-carboxylates 6 including WYS8 (7) were synthesized via a Sonogashira or Stille coupling processes from 6-iodo-βCCt (5). The bivalent ligands of βCCt (32 and 33) were also designed and prepared via a palladium-catalyzed homocoupling process to expand the structure-activity relationships (SAR) to larger ligands. Based on the pharmacophore/receptor model, a preliminary SAR study on 34 analogues illustrated that large substituents at position-6 of the β-carbolines were well tolerated. As expected, these groups are proposed to project into the extracellular domain (L(Di) region) of GABA(A)/Bz receptors (see 32 and 33). Moreover, substituents located at position-3 of the β-carboline nucleus exhibited a conserved stereo interaction in lipophilic pocket L(1), while N(2) presumably underwent a hydrogen bonding interaction with H(1). Three novel β-carboline ligands (βCCt, 3PBC and WYS8), which preferentially bound to α1 BzR subtypes permitted a comparison of the pharmacological efficacies with a range of classical BzR antagonists (flumazenil, ZK93426) from several different structural groups and indicated these β-carbolines were 'near GABA neutral antagonists'. Based on the SAR, the most potent (in vitro) α(1) selective ligand was the 6-substituted acetylenyl βCCt (WYS8, 7). Earlier both βCCt and 3PBC had been shown to reduce alcohol self-administration in alcohol preferring (P) and high alcohol drinking (HAD) rats but had little or no effect on sucrose self-administration.(1-3) Moreover, these two β-carbolines were orally active, and in addition, were anxiolytic in P rats but were only weakly anxiolytic in rodents. These data prompted the synthesis of the β-carbolines presented here.
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Affiliation(s)
- Wenyuan Yin
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI, 53201-0413
| | - Samarpan Majumder
- Department of Pharmacology and Division of Medicinal Chemistry, University of North Carolina-Chapel Hill Medical School and School of Pharmacy and NIMH Psychoactive Drug Screening Program, 120 Mason Farm Road, 4072 Genetics Medicine Bldg, Chapel Hill, NC 27599-7365
| | - Terry Clayton
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI, 53201-0413
| | - Steven Petrou
- Howard Florey Institute, University of Melbourne, Parkville, VIC 3010, Australia
| | - Michael L. VanLinn
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI, 53201-0413
| | | | - Chunrong Ma
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI, 53201-0413
| | - Brett A. Cromer
- Howard Florey Institute, University of Melbourne, Parkville, VIC 3010, Australia
- Department of Pharmacology, University of Melbourne, Parkville, VIC 3010, Australia
| | - Bryan L. Roth
- Department of Pharmacology and Division of Medicinal Chemistry, University of North Carolina-Chapel Hill Medical School and School of Pharmacy and NIMH Psychoactive Drug Screening Program, 120 Mason Farm Road, 4072 Genetics Medicine Bldg, Chapel Hill, NC 27599-7365
| | - Donna M. Platt
- Harvard Medical School, New England Primate Research Center, One Pine Hill Drive, Box 9102, Southborough, MA 01772-9102
| | - James M. Cook
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI, 53201-0413
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Abstract
The GABAA-receptor γ2 Subunit R43Q Mutation Linked to Childhood Absence Epilepsy and Febrile Seizures Causes Retention of α1 β2γ2S Receptors in the Endoplasmic Reticulum Kang J, Macdonald RL J Neurosci 2004;24:8672–8677 The GABAA-receptor γ2 subunit mutation R43Q is an autosomal dominant mutation associated with childhood absence epilepsy and febrile seizures. Previously, we demonstrated that homozygous α1 β3 γ2L(R43Q)-receptor whole-cell currents had reduced amplitude with unaltered time course, suggesting reduced cell-surface expression of functional receptors. In human embryonic kidney 293-T cells, we demonstrate that both heterozygous and homozygous α1 β2 γ2S(R43Q) GABAA-receptor current amplitudes were reduced when receptors were assembled from coexpressed α1, β2, and γ2S subunits and from β2- α1 tandem subunits coexpressed with the γ2L subunit. By using fluorescence confocal microscopy, we demonstrated that mutant receptors containing enhanced yellow fluorescent protein-tagged γ2S subunits had reduced surface expression and were retained in the endoplasmic reticulum. In addition, by using biotinylation of surface receptors and immunoblotting, we confirmed that α1 β2 γ2S(R43Q)-receptors had reduced surface expression. These results provide evidence that the γ2S(R43Q) mutation impaired GABAA-receptor function by compromising receptor trafficking and reducing surface expression. Altered Expression of the δ Subunit of the GABAA Receptor in a Mouse Model of Temporal Lobe Epilepsy Peng Z, Huang CS, Stell BM, Mody I, Houser CR J Neurosci 2004;24:8629–8639 δ Subunit–containing GABAA receptors are located predominantly at nonsynaptic sites in the dentate gyrus, where they may play important roles in controlling neuronal excitability through tonic inhibition and responses to GABA spillover. Immunohistochemical methods were used to determine whether δ subunit expression was altered after pilocarpine-induced status epilepticus in C57BL/6 mice in ways that could increase excitability of the dentate gyrus. In pilocarpine-treated animals, the normal diffuse labeling of the δ subunit in the dentate molecular layer was decreased by 4 days after status epilepticus (latent period) and remained low throughout the period of chronic seizures. In contrast, diffuse labeling of α4 and γ2 subunits, potentially interrelated GABAA-receptor subunits, was increased during the chronic period. Interestingly, δ subunit labeling of many interneurons progressively increased after pilocarpine treatment. Consistent with the observed changes in δ subunit labeling, physiological studies revealed increased excitability in the dentate gyrus of slices obtained from the pilocarpine-treated mice and demonstrated that physiologic concentrations of the neurosteroid tetrahydrodeoxycorticosterone were less effective in reducing excitability in the pilocarpine-treated animals than in controls. The findings support the idea that alterations in nonsynaptic δ subunit–containing GABAA receptors in both principal cells and interneurons could contribute to increased seizure susceptibility in the hippocampal formation in a temporal lobe epilepsy model.
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He X, Hesse LM, Hazarika S, Masse G, Harmatz JS, Greenblatt DJ, Court MH. Evidence for oxazepam as an in vivo probe of UGT2B15: oxazepam clearance is reduced by UGT2B15 D85Y polymorphism but unaffected by UGT2B17 deletion. Br J Clin Pharmacol 2010; 68:721-30. [PMID: 19916996 DOI: 10.1111/j.1365-2125.2009.03519.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
AIMS Although in vitro studies indicate that oxazepam is an isoform-selective substrate probe for UDP-glucuronosyltransferase 2B15, the utility of this drug as an in vivo probe is uncertain. The main aim of this study was to determine whether common missense polymorphisms in the UGT2B15 gene (D85Y and K523T) are associated with altered oxazepam pharmacokinetics and pharmacodynamics. We also determined the possible influence of a common deletion polymorphism in the gene encoding UGT2B17, which shows substantial substrate specificity overlap with UGT2B15. METHODS Thirty healthy male subjects were administered 15 mg of oxazepam by mouth followed by plasma oxazepam concentration monitoring for 36 h, and pharmacodynamic testing for 8 h. Genotypes were determined by genomic polymerase chain reaction and commercial 5'-nuclease assays. RESULTS Allele frequencies for D85Y, K523T, UGT2B17del were 47%, 23% and 19%, respectively. Median oxazepam apparent oral clearance was significantly lower in 85YY subjects (1.62 ml min(-1) kg(-1)) compared with 85DD subjects (3.35 ml min(-1) kg(-1); P= 0.003, Student-Newman-Keuls test), whereas 85DY subjects were intermediate (2.34 ml min(-1) kg(-1); P= 0.018 vs. 85DD, P= 0.034 vs. 85YY). Regression analysis indicated that UGT2B15 D85Y genotype accounted for 34% of interindividual variability. However, neither UGT2B15 K523T nor UGT2B17del was associated with altered oxazepam disposition. Furthermore, no differences in pharmacodynamic measures, including quantitative electroencephalography, digit-symbol substitution test, self- or observer-rated visual analogue scales, could be demonstrated for any of the polymorphisms evaluated. CONCLUSIONS These results identify UGT2B15 D85Y as a major determinant of oxazepam clearance, and indicate that oxazepam may be useful as an in vivo probe for glucuronidation by UGT2B15.
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Affiliation(s)
- Xi He
- Laboratory of Comparative and Molecular Pharmacogenomics and Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, MA 02111, USA
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Wimmer VC, Reid CA, So EYW, Berkovic SF, Petrou S. Axon initial segment dysfunction in epilepsy. J Physiol 2010; 588:1829-40. [PMID: 20375142 DOI: 10.1113/jphysiol.2010.188417] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The axon initial segment (AIS) contains the site of action potential initiation and plays a major role in neuronal excitability. AIS function relies on high concentrations of different ion channels and complex regulatory mechanisms that orchestrate molecular microarchitecture. We review recent evidence that a large number of ion channels associated with epilepsy are enriched at the AIS, making it a 'hotspot' for epileptogenesis. Furthermore, we present novel data on the clustering of GABRgamma2 receptors in the AIS of cortical and hippocampal neurons in a knock in mouse model of a human genetic epilepsy. This article highlights the molecular coincidence of epilepsy mutations at the AIS and reviews pathogenic mechanisms converging at the AIS.
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Affiliation(s)
- Verena C Wimmer
- Florey Neuroscience Institutes, University of Melbourne, Parkville 3010, Victoria, Australia
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Galanopoulou AS. Mutations affecting GABAergic signaling in seizures and epilepsy. Pflugers Arch 2010; 460:505-23. [PMID: 20352446 DOI: 10.1007/s00424-010-0816-2] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2009] [Revised: 02/18/2010] [Accepted: 02/23/2010] [Indexed: 02/02/2023]
Abstract
The causes of epilepsies and epileptic seizures are multifactorial. Genetic predisposition may contribute in certain types of epilepsies and seizures, whether idiopathic or symptomatic of genetic origin. Although these are not very common, they have offered a unique opportunity to investigate the molecular mechanisms underlying epileptogenesis and ictogenesis. Among the implicated gene mutations, a number of GABAA receptor subunit mutations have been recently identified that contribute to several idiopathic epilepsies, febrile seizures, and rarely to certain types of symptomatic epilepsies, like the severe myoclonic epilepsy of infancy. Deletion of GABAA receptor genes has also been linked to Angelman syndrome. Furthermore, mutations of proteins controlling chloride homeostasis, which indirectly defines the functional consequences of GABAA signaling, have been identified. These include the chloride channel 2 (CLCN2) and the potassium chloride cotransporter KCC3. The pathogenic role of CLCN2 mutations has not been clearly demonstrated and may represent either susceptibility genes or, in certain cases, innocuous polymorphisms. KCC3 mutations have been associated with hereditary motor and sensory polyneuropathy with corpus callosum agenesis (Andermann syndrome) that often manifests with epileptic seizures. This review summarizes the recent progress in the genetic linkages of epilepsies and seizures to the above genes and discusses potential pathogenic mechanisms that contribute to the age, sex, and conditional expression of these seizures in carriers of these mutations.
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Affiliation(s)
- Aristea S Galanopoulou
- Saul R. Korey Department of Neurology and Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, 1410 Pelham Parkway South, Kennedy Center Room 306, Bronx, NY 10461, USA.
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Increase of GABAA receptor-mediated tonic inhibition in dentate granule cells after traumatic brain injury. Neurobiol Dis 2010; 38:464-75. [PMID: 20304069 DOI: 10.1016/j.nbd.2010.03.012] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2009] [Revised: 03/10/2010] [Accepted: 03/10/2010] [Indexed: 10/19/2022] Open
Abstract
Traumatic brain injury (TBI) can result in altered inhibitory neurotransmission, hippocampal dysfunction, and cognitive impairments. GABAergic spontaneous and miniature inhibitory postsynaptic currents (sIPSCs and mIPSCs) and tonic (extrasynaptic) whole cell currents were recorded in control rat hippocampal dentate granule cells (DGCs) and at 90days after controlled cortical impact (CCI). At 34 degrees C, in CCI DGCs, sIPSC frequency and amplitude were unchanged, whereas mIPSC frequency was decreased (3.10+/-0.84Hz, n=16, and 2.44+/-0.67Hz, n=7, p<0.05). At 23 degrees C, 300nM diazepam increased peak amplitude of mIPSCs in control and CCI DGCs, but the increase was 20% higher in control (26.81+/-2.2pA and 42.60+/-1.22pA, n=9, p=0.031) compared to CCI DGCs (33.46+/-2.98pA and 46.13+/-1.09pA, n=10, p=0.047). At 34 degrees C, diazepam did not prolong decay time constants (6.59+/-0.12ms and 6.62+/-0.98ms, n=9, p=0.12), the latter suggesting that CCI resulted in benzodiazepine-insensitive pharmacology in synaptic GABA(A) receptors (GABA(A)Rs). In CCI DGCs, peak amplitude of mIPSCs was inhibited by 100microM furosemide (51.30+/-0.80pA at baseline and 43.50+/-5.30pA after furosemide, n=5, p<0.001), a noncompetitive antagonist of GABA(A)Rs with an enhanced affinity to alpha4 subunit-containing receptors. Potentiation of tonic current by the GABA(A)R delta subunit-preferring competitive agonist THIP (1 and 3microM) was increased in CCI DGCs (47% and 198%) compared to control DGCs (13% and 162%), suggesting the presence of larger tonic current in CCI DGCs; THIP (1microM) had no effect on mIPSCs. Taken together, these results demonstrate alterations in synaptic and extrasynaptic GABA(A)Rs in DGCs following CCI.
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Goldschen-Ohm MP, Wagner DA, Petrou S, Jones MV. An epilepsy-related region in the GABA(A) receptor mediates long-distance effects on GABA and benzodiazepine binding sites. Mol Pharmacol 2009; 77:35-45. [PMID: 19846749 DOI: 10.1124/mol.109.058289] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The GABA(A) receptor mutation gamma(2)R43Q causes absence epilepsy in humans. Homology modeling suggests that gamma(2)Arg43, gamma(2)Glu178, and beta(2)Arg117 participate in a salt-bridge network linking the gamma(2) and beta(2) subunits. Here we show that several mutations at these locations exert similar long-distance effects on other intersubunit interfaces involved in GABA and benzodiazepine binding. These mutations alter GABA-evoked receptor kinetics by slowing deactivation, enhancing desensitization, or both. Kinetic modeling and nonstationary noise analysis for gamma(2)R43Q reveal that these effects are due to slowed GABA unbinding and slowed recovery from desensitization. Both gamma(2)R43Q and beta(2)R117K also speed diazepam dissociation from the receptor's benzodiazepine binding interface, as assayed by the rate of decay of diazepam-induced potentiation of GABA-evoked currents. These data demonstrate that gamma(2)Arg43 and beta(2)Arg117 similarly regulate the stability of both the GABA and benzodiazepine binding sites at the distant beta/alpha and alpha/gamma intersubunit interfaces, respectively. A simple explanation for these results is that gamma(2)Arg43 and beta(2)Arg117 participate in interactions between the gamma(2) and beta(2) subunits, disruptions of which alter the neighboring intersubunit binding sites in a similar fashion. In addition, gamma(2)Arg43 and gamma(2)Glu178 regulate desensitization, probably mediated within the transmembrane domains near the pore. Therefore, mutations at the gamma/beta intersubunit interface have specific long-distance effects that are propagated widely throughout the GABA(A) receptor protein.
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