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Maintaining the correct balance in neuronal activation is of paramount importance to normal brain function. Imbalances due to changes in excitation or inhibition can lead to a variety of disorders ranging from the clinically extreme (e.g. epilepsy) to the more subtle (e.g. anxiety). In the brain, the most common inhibitory synapses are regulated by...
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... regarding the order of subunits in the pent- amer has been provided by studies elucidating the GABA- and benzodiazepine-binding sites in the receptor [12], by the forced assembly of concatenated subunits [13] and by homology to the acetylcholine receptor [14]. The GABA A receptor contains two low-affinity GABA-binding sites, located at the interfaces between α and β subunits, and a single benzodiazepine site formed between the α and γ sub- units ( Figure 1). Thus the final structural organization of subunits is now established as -γ -(Bz)-α-(GABA)-β-α- (GABA)-β- [13] (Figure 1). ...
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... GABA A receptor contains two low-affinity GABA-binding sites, located at the interfaces between α and β subunits, and a single benzodiazepine site formed between the α and γ sub- units ( Figure 1). Thus the final structural organization of subunits is now established as -γ -(Bz)-α-(GABA)-β-α- (GABA)-β- [13] (Figure 1). Particularly intriguing is the observation that αβγ receptors are formed preferentially, at the expense of αβ receptor formation, when all three subunits are co-expressed [15]. ...
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... with a requirement for these assembly signals to be located at (or near) inter-subunit contact points, the α/γ signals identified to date are located proximal (with respect to the primary structure) to the GABA-and benzodiazepine- binding sites formed at subunit interfaces (in the quaternary structure) between the α-β and α-γ subunits respectively (Figure 1). However, structural predictions of the quaternary structure of GABA A receptors do not predict the α 1 (RQS) signal to be located at subunit interfaces (Figure 2), suggesting that either a transient interaction occurs during receptor assembly, or that this signal plays a conformational role in the presentation of the subunit interface, or both. ...
Citations
... Not surprisingly, in the first experimental design, we demonstrated that BTBR mice displayed an increased seizure susceptibility to chemoconvulsants antagonizing, with different mechanisms of action (Sperk et al., 2004;Mizielinska et al., 2006), GABA A receptors. This phenomenon is consistent with the dysfunction of inhibitory transmission observed in different brain regions in BTBR mice (Han et al., 2014;Cherubini et al., 2022). ...
Background: Autism spectrum disorders (ASDs) are one of the most severe chronic childhood disorders in terms of prevalence, morbidity, and impact on society. Interestingly, several systematic reviews and meta-analyses documented a bidirectional link between epilepsy and ASD, supporting the hypothesis that both disorders may have common neurobiological pathways. According to this hypothesis, an imbalance of the excitatory/inhibitory (E/I) ratio in several brain regions may represent a causal mechanism underpinning the co-occurrence of these neurological diseases.
Methods: To investigate this bidirectional link, we first tested the seizure susceptibility to chemoconvulsants acting on GABAergic and glutamatergic systems in the BTBR mice, in which an imbalance between E/I has been previously demonstrated. Subsequently, we performed the PTZ kindling protocol to study the impact of seizures on autistic-like behavior and other neurological deficits in BTBR mice.
Results: We found that BTBR mice have an increased susceptibility to seizures induced by chemoconvulsants impairing GABA A neurotransmission in comparison to C57BL/6J control mice, whereas no significant difference in seizure susceptibility was observed after administration of AMPA, NMDA, and Kainate. This data suggests that deficits in GABAergic neurotransmission can increase seizure susceptibility in this strain of mice. Interestingly, BTBR mice showed a longer latency in the development of kindling compared to control mice. Furthermore, PTZ-kindling did not influence autistic-like behavior in BTBR mice, whereas it was able to significantly increase anxiety and worsen cognitive performance in this strain of mice. Interestingly, C57BL/6J displayed reduced sociability after PTZ injections, supporting the hypothesis that a tight connection exists between ASD and epilepsy.
Conclusion: BTBR mice can be considered a good model to study epilepsy and ASD contemporarily. However, future studies should shed light on the mechanisms underpinning the co-occurrence of these neurological disorders in the BTBR model.
... In this model, a decrease in the H4 acetylation level leads to the chronic downregulation of c-fos transcription, while an increase in H3 acetylation contributes to the chronic upregulation of BDNF transcription [126]. As the most important inhibitory neurotransmitter closely related to epilepsy, γ-aminobutyric acid (GABA) synthesis is catalyzed by GAD, and the production process is also regulated by acetylation modification [134,135]. In TLE patients and pilocarpine-induced epilepsy models, decreased expression of GAD is associated with decreased H3 acetylation in hippocampal neurons. ...
Epilepsy is a common and severe chronic neurological disorder. Recently, post-translational modification (PTM) mechanisms, especially protein acetylation modifications, have been widely studied in various epilepsy models or patients. Acetylation is regulated by two classes of enzymes, histone acetyltransferases (HATs) and histone deacetylases (HDACs). HATs catalyze the transfer of the acetyl group to a lysine residue, while HDACs catalyze acetyl group removal. The expression of many genes related to epilepsy is regulated by histone acetylation and deacetylation. Moreover, the acetylation modification of some non-histone substrates is also associated with epilepsy. Various molecules have been developed as HDAC inhibitors (HDACi), which have become potential antiepileptic drugs for epilepsy treatment. In this review, we summarize the changes in acetylation modification in epileptogenesis and the applications of HDACi in the treatment of epilepsy as well as the mechanisms involved. As most of the published research has focused on the differential expression of proteins that are known to be acetylated and the knowledge of whole acetylome changes in epilepsy is still minimal, a further understanding of acetylation regulation will help us explore the pathological mechanism of epilepsy and provide novel ideas for treating epilepsy.
... Through pre-or posttranslational processes, these mutations affect GABAA receptor function and/or biogenesis [22]. The exonic rs211037 polymorphism, interestingly, has no effect on the amino acid sequence (Asn196Asn) [23,24]. Synonymous mutations have been linked to the likelihood of various complicated disorders in recent genomic research. ...
Idiopathic generalized epilepsy (IGE) is the most prevalent type of epilepsy with genetic origin. Mutations in ion channel genes have been identified as a common cause of IGE. Several studies have reported various epilepsy risk variants of GABRG2 (gamma-aminobutyric acid type A receptor subunit gamma2 subunit) gene in different ethnic groups, but the results are inconsistent. The purpose of this case-control research is to determine if GABRG2 polymorphisms contribute to IGE susceptibility and antiepileptic drug resistance in Pakistani population. For this purpose, we genotyped exon2, exon5 (C540T and C588T), exon7 (T813C), exon8 (K289M), and exon9 of GABRG2 gene by restriction fragment length polymorphism and Sanger’s sequencing in 87 drug-responsive idiopathic generalized epilepsy patients, 55 drug-resistant epilepsy patients, and 83 healthy controls. Restriction fragment length polymorphism (RFLP) and sequencing results indicated only C588T polymorphism in the studied subjects. The comparison of genotypic and allelic frequencies showed significant differences between IGE patients and control groups ( P = 0.008 and odds ratio = 4.2 ) and nonsignificant association of C588T polymorphism in antiseizure medication-resistant patients ( P = 0.9 ). Our findings showed that C588T polymorphism of GABRG2 is a risk variant for IGE in Pakistani population. Further studies are required to validate the results.
... Reductions of a1subuint can decrease the presence in the cell surface of GABA-A receptors. 37 A large French Canadian family with JME showed Ala322Asp mutation in GABRA1. Compared with wild-type receptors, GABA-A receptors with the mutant subunit show weak GABA-activated currents in vitro. ...
Gamma-aminobutyric acid type A (GABA-A) receptor subunit gene mutations, which include GABRA1, GABRB3, GABRD, and GABRG2, are often involved in several genetic epilepsy syndromes and other neuropsychiatric diseases like autism spectrum disorder, schizophrenia, and anxiety. GABA-A are ligand-gated ionic channels, and are involved firstly in the fast inhibitory synaptic transmission of the central nervous system. The GABA receptors include the ionotropic GABA-A and GABA-C receptors and the metabotropic GABA-B receptors. According to the site in which mutations occur, they cause disorders in channel opening, “lock-and-pull” receptor system functioning, and capable of causing a specific epilepsy phenotype. The aim of this article is to summarize the most recent literature findings, considering genetic mutations, clinical features, genotype/phenotype correlation, and therapy about neurodevelopment diseases correlated to GABA receptors dysfunction, in particular epilepsy. According to our findings, we conclude that further mutation analysis could permit genotype–phenotype correlation and give more information about the best efficient treatment, even if—at present—more clinical and genetic studies are necessary.
... This receptor is pentameric, composed of two α1, two β2, and one γ2 subunits in the mammalian brain. Alteration in the expression and function of these subunits by events such as mutation, trauma, and hypoxia may interfere with inhibition of excitation, consequently contributing to epileptogenesis [5]. ...
... These mutations influence the GABAA receptors by alteration of receptor function and/or impairment of receptor biogenesis through pre-or posttranslational mechanisms [32]. Interestingly, the exonic rs211037 polymorphism does not change the amino acid sequence (Asn196Asn) [5,6]. Recent genetic studies showed that synonymous mutations can be implicated in the risk of some complex disorders. ...
Gamma-aminobutyric acid receptor (GABA-A) is the most common receptor of fast synaptic inhibition in the human brain. Gamma protein encoded by GABRG2 gene, is one of the subunits of GABA-A receptor which plays essential role in the function of this receptor. Several studies have identified various febrile seizures (FS) and epilepsy risk variants of GABRG2 gene in different populations, but some others did not support these results. The aim of this case-control study is to investigate whether the GABRG2 polymorphisms contribute with susceptibility for FS and epilepsy in a pooled data of three cohorts from Malaysia (composed of Malay, Chinese, and Indian), Hong Kong, and Korea. Furthermore, the pooled dataset of these cohorts with previous reports were meta-analyzed for determining the risk effect size of the rs211037 polymorphism on FS and SE. The rs211037, rs210987, rs440218, rs2422106, rs211014 and rs401750 were genotyped in the 6442 subjects (1729 epilepsy and 4713 controls). Results of case-control study showed associations between rs211037 with the risk of SE in the pooled data from all cohorts (T vs. C: P = 3 × 10−5 and TT vs. CC: P = 2 × 10−5) and with the risk of partial seizure in the combined data of Malaysia and Hong Kong (both T vs. C and TT vs. CC: P = 2 × 10−6). The rs211037-rs210987 and rs2422106-rs211014-rs401750 haplotypes were also associated with susceptibility to SE in Chinese. Meta-analysis of all Asians identified association between rs211037 and FS and SE (T vs. C: P = 4 × 10−4 and P = 4 × 10−3, respectively). In conclusion, rs211037 alone may be a risk factor for FS, partial seizure, and SE and in linkage disequilibrium with rs210987 can contribute with FS and SE in Asians, particularly in Chinese.
... Epilepsy is a prevalent and serious neurological disorder characterized by spontaneous sudden abnormal neuronal discharges, and affects 1-2 % of the worldwide population [1,2]. Synaptic hyperexcitability, mainly caused by the imbalance of the neurotransmission systems between excitation and inhibition, in particular the glutamate and gamma-aminobutyric acid (GABA), plays a vital role in the pathogenesis of epilepsy [3]. GABA is synthesized by the glutamate decarboxylases (GADs), including isoforms of GAD67 (GAD1) and GAD65 (GAD2). ...
Recent studies have shown that histone acetylation is involved with the regulation of enzyme glutamate decarboxylases (GADs), including GAD67 and GAD65. Here, we investigated the histone acetylation modifications of GADs in the pathogenesis of epilepsy and explored the therapeutic effect of a novel second-generation histone deacetylase inhibitor (HDACi) JNJ-26481585 in epilepsy animals. We revealed the suppression of GADs protein and mRNA level, and histone hypoacetylation in patients with temporal lobe epilepsy and pilocarpine-induced epilepsy mice model. Double-immunofluorescence also indicated that the hypoacetyl-H3 was located in hippocampal GAD67/GAD65 positive neurons in epilepsy mice. JNJ-26481585 significantly reversed the decrease of the GAD67/GAD65 both protein and mRNA levels, and the histone hypoacetylation of GABAergic neurons in epilepsy mice. Meanwhile, single-cell real-time PCR performed in GFP-GAD67/GAD65 transgenic mice demonstrated that JNJ-26481585 induced increase of GAD67/GAD65 mRNA level in GABAergic neurons. Furthermore, JNJ-26481585 significantly alleviated the epileptic seizures in mice model. Together, our findings demonstrate inhibition of GADs gene via histone acetylation plays an important role in the pathgenesis of epilepsy, and suggest JNJ-26481585 as a promising therapeutic strategy for epilepsy.
... GABAA receptors are pentameric chloride ion channels formed from various combinations of proteins encoded by α (α1-α6), β (β1-β3), γ (γ1-γ3), δ, ε, π, θ, and ρ (ρ1-ρ3). [10] The major isoforms of the GABAA receptor consist α, β, and γ subunits and show a regional heterogeneity that is associated with distinct physiological effects. The α1β2γ2 subunits combination is the major subtype (60%) and most abundant in almost all regions of the brain. ...
Aim:
This study is focused on GABRG2 gene sequence variations in patients with mesial temporal lobe epilepsy (mTLE). The GABAAreceptor is a heteropentameric receptor and alpha-1 beta-2 gamma-2 subunits combination is most abundant and present in almost all regions of the brain. The gamma-2 subunit (GABRG2) gene mutations have been reported in different epilepsy pathologies. In the present study we have looked for GABRG2 gene sequence variations in patients with mTLE.
Materials and methods:
Twenty patients (12 females and eight males, age 4.6-38 years) with MTLE were recruited for this investigation. Patients were recommended for epilepsy surgery after all clinical investigations as per the epilepsy protocol. Ethnically matched glioma or meningioma patients were considered as nonepileptic controls. During temporal lobectomy of amygdalohippocampectomy, hippocampal brain tissue samples were resected guided by intraoperative electrocorticography (ECoG) activity. All 11 exons of GABRG2 gene with their flanking intronic regions were amplified by polymerase chain reaction (PCR) and screened by DNA sequencing analysis for sequence variations.
Statistical analysis used:
Comparison of allele frequencies between patient and control groups was determined using a c(2) test.
Results and conclusions:
Total five DNA sequence variations were identified, three in exonic regions (c.643A > G, rs211035), (c.T > A, rs424740), and (c.C > T, rs418210) and two in intronic regions (c.751 + 41A > G, rs211034) and (c.751 + 52G > A, rs 34281163). Allele frequencies of variants identified in this study did not differ between patients and normal controls. Thus, we conclude that GABRG2 gene may not be playing significant role in the development of epilepsy or as a susceptibility gene in patients with MTLE in Indian population.
... The lack of responsiveness in excised patches is not due to detection failure as cells did not respond to GABA even in recordings performed in the whole-cell configuration (Fig. 6). Taken together with our staining and biochemical experiments, we conclude that the K353delins18X mutation completely eliminates surface expression of mature GABA A receptors, an observation supported by the fact that the a-subunit is required for the formation of functional receptors (Mizielinska et al., 2006). In contrast, we routinely recorded GABA-mediated responses from the cells expressing the a1 D219N and the c2 P83S subunit mutations (Fig. 5A, lower row). ...
... Kang et al. suggest that premature translation can produce mRNA degradation through the activation of molecular pathways such as nonsense-mediated decay and reduced mutant a1 subunit mRNA. Because the a1 subunit is essential for the formation of functional GABA A receptors, a decrease in this subunit will also result in a decrease in surface GABA A receptors (Mizielinska et al., 2006). In an intact neuronal system, the two novel GABRA1 mutants, D219N and K353delins18X, could prove to be deleterious by causing an imbalance between excitation and inhibition. ...
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.
... Gammaaminobutyric acid (GABA) is a crucial inhibitory neurotransmitter that attenuates electrical excitability. Polymorphisms in GABA subunits may be associated with anxiety, neuronal irritability and seizure susceptibility [ 27 ]. ...
... The subunit composition of the ionotropic GABA A receptor (GABA A R) is as varied (α1 through α6, β1 through β3, γ1 through γ3, δ, ɛ, ρ1 through ρ3, θ, and π). This leads to a potentially very high number of possible subunit combinations; however, it is assumed that only 20-30 functional combinations exist in vivo (for review, see Mizielinska et al., 2006). ...
... 2E-F), it was of special interest to investigate the precise subunit composition of these receptors. In mammals, six α, three β, and three γ subunits exist and assemble into typical, pentameric GABA A Rs. Several additional subunits (e.g., δ, ρ, and ɛ) have been described in certain subtypes of functional GABA A Rs (Mizielinska et al., 2006). In heterologous expression systems, channels require only the presence of α, β, and γ subunits to mimic the full repertoire of native channel functions (for review, see Hevers and Luddens, 1998). ...
The involvement of neurotransmission in neuronal development is a generally accepted concept. Nevertheless, the precise regulation of neurotransmitter receptor expression is still unclear. To investigate the expression profiles of the most important ionotropic neurotransmitter receptors, namely GABA(A) receptors (GABA(A)Rs), NMDA receptors (NMDARs), and AMPA receptors (AMPARs), quantitative RT-PCR, immunoblot analysis and patch clamp studies were performed in in vitro-generated neural stem cells (NSCs). This clearly defined cell line is closely related to radial glia cells, the stem cells in the neonate brain. We found functional GABA(A)Rs of the subunit composition alpha2, beta3, and gamma1 to be expressed. Unexpectedly, functional ionotropic glutamate receptors were absent. However, NSCs expressed the NMDAR subunits NR2A and NR3A, and the AMPAR subunit GluR4 at the protein level, and GluR3 at the mRNA level. The overexpression of functional NMDARs in NSCs led to an increased mRNA level of AMPAR subunits, indicating a role in synaptogenesis. Early neuronal markers remained unchanged. These data extend our knowledge about ionotropic neurotransmitter receptor expression during neuronal development and will aid further investigations on activity-dependent neurogenesis.
