Intricacies of GABAA Receptor Function: The Critical Role of the β3 Subunit in Norm and Pathology

Phenols and GABAA receptors: from structure and molecular mechanisms action to neuropsychiatric sequelae

γ-Aminobutyric acid type A receptors (GABAARs) are members of the pentameric ligand-gated ion channel (pLGIC) family, which are widespread throughout the invertebrate and vertebrate central nervous system. GABAARs are engaged in short-term changes of the neuronal concentrations of chloride (Cl-) and bicarbonate (HCO3 -) ions by their passive permeability through the ion channel pore. GABAARs are regulated by various structurally diverse phenolic substances ranging from simple phenols to complex polyphenols. The wide chemical and structural variability of phenols suggest similar and different binding sites on GABAARs, allowing them to manifest themselves as activators, inhibitors, or allosteric ligands of GABAAR function. Interest in phenols is associated with their great potential for GABAAR modulation, but also with their subsequent negative or positive role in neurological and psychiatric disorders. This review focuses on the GABAergic deficit hypotheses during neurological and psychiatric disorders induced by various phenols. We summarize the structure-activity relationship of general phenol groups concerning their differential roles in the manifestation of neuropsychiatric symptoms. We describe and analyze the role of GABAAR subunits in manifesting various neuropathologies and the molecular mechanisms underlying their modulation by phenols. Finally, we discuss how phenol drugs can modulate GABAAR activity via desensitization and resensitization. We also demonstrate a novel pharmacological approach to treat neuropsychiatric disorders via regulation of receptor phosphorylation/dephosphorylation.

Bibliometric Analysis on GABA-A Receptors Research Based on CiteSpace and VOSviewer

Background

GABA-A receptors are the primary mediators of brain inhibitory neurotransmission. In the past years, many studies focused on this channel to decipher the pathogenesis of related diseases but lacked bibliometric analysis research. This study aims to explore the research status and identify the research trends of GABA-A receptor channels.

Methods

Publications related to GABA-A receptor channels were retrieved from the Web of Science Core Collection from 2012 to 2022. After screening, the VOSviewer 1.6.18 and Citespace 5.8 R3 were used for bibliometric analysis from journals, countries, institutions, authors, co-cited references and keywords.

Results

We included 12,124 publications in the field of GABA-A receptor channels for analysis. The data shows that although there was a slight decrease in annual publications from 2012 to 2021, it remained at a relatively high level. Most publications were in the domain of neuroscience. Additionally, the United States was the most prolific country, followed by China. Univ Toronto was the most productive institution, and James M Cook led essential findings in this field. Furthermore, brain activation, GABAAR subunits expression, modulation mechanism in pain and anxiety behaviors and GABA and dopamine were paid attention to by researchers. And top research frontiers were molecular docking, autoimmune encephalitic series, obesity, sex difference, diagnosis and management, EEG and KCC2.

Conclusion

Taken together, academic attention on GABA-A receptor channels was never neglected since 2012. Our analysis identified key information, such as core countries, institutions and authors in this field. Molecular docking, autoimmune encephalitic series, obesity, sex difference, diagnosis and management, EEG and KCC2 will be the future research direction.

Zinc Inhibits the GABAAR/ATPase during Postnatal Rat Development: The Role of Cysteine Residue

Zinc ions (Zn²⁺) are concentrated in various brain regions and can act as a neuromodulator, targeting a wide spectrum of postsynaptic receptors and enzymes. Zn²⁺ inhibits the GABA_ARs, and its potency is profoundly affected by the subunit composition and neuronal developmental stage. Although the extracellular amino acid residues of the receptor's hetero-oligomeric structure are preferred for Zn²⁺ binding, there are intracellular sites that, in principle, could coordinate its potency. However, their role in modulating the receptor function during postembryonic development remains unclear. The GABA_AR possesses an intracellular ATPase that enables the energy-dependent anion transport via a pore. Here, we propose a mechanistic and molecular basis for the inhibition of intracellular GABA_AR/ATPase function by Zn²⁺ in neonatal and adult rats. The enzymes within the scope of GABA_AR performance as Cl^-ATPase and then as Cl^-, HCO₃^-ATPase form during the first week of postnatal rat development. In addition, we have shown that the Cl^-ATPase form belongs to the β1 subunit, whereas the β3 subunit preferably possesses the Cl^-, HCO₃^-ATPase activity. We demonstrated that a Zn²⁺ with variable efficacy inhibits the GABA_AR as well as the ATPase activities of immature or mature neurons. Using fluorescence recording in the cortical synaptoneurosomes (SNs), we showed a competitive association between Zn²⁺ and NEM in parallel changes both in the ATPase activity and the GABA_AR-mediated Cl^- and HCO₃^- fluxes. Finally, by site-directed mutagenesis, we identified in the M3 domain of β subunits the cysteine residue (C313) that is essential for the manifestation of Zn²⁺ potency.

Using Machine Learning to Explore Shared Genetic Pathways and Possible Endophenotypes in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a heterogeneous condition, characterized by complex genetic architectures and intertwined genetic/environmental interactions. Novel analysis approaches to disentangle its pathophysiology by computing large amounts of data are needed. We present an advanced machine learning technique, based on a clustering analysis on genotypical/phenotypical embedding spaces, to identify biological processes that might act as pathophysiological substrates for ASD. This technique was applied to the VariCarta database, which contained 187,794 variant events retrieved from 15,189 individuals with ASD. Nine clusters of ASD-related genes were identified. The 3 largest clusters included 68.6% of all individuals, consisting of 1455 (38.0%), 841 (21.9%), and 336 (8.7%) persons, respectively. Enrichment analysis was applied to isolate clinically relevant ASD-associated biological processes. Two of the identified clusters were characterized by individuals with an increased presence of variants linked to biological processes and cellular components, such as axon growth and guidance, synaptic membrane components, or transmission. The study also suggested other clusters with possible genotype-phenotype associations. Innovative methodologies, including machine learning, can improve our understanding of the underlying biological processes and gene variant networks that undergo the etiology and pathogenic mechanisms of ASD. Future work to ascertain the reproducibility of the presented methodology is warranted.

Physiological Role of ATPase for GABAA Receptor Resensitization

γ-Aminobutyric acid type A receptors (GABA_ARs) mediate primarily inhibitory synaptic transmission in the central nervous system. Following fast-paced activation, which provides the selective flow of mainly chloride (Cl⁻) and less bicarbonate (HCO₃⁻) ions via the pore, these receptors undergo desensitization that is paradoxically prevented by the process of their recovery, referred to as resensitization. To clarify the mechanism of resensitization, we used the cortical synaptoneurosomes from the rat brain and HEK 293FT cells. Here, we describe the effect of γ-phosphate analogues (γPAs) that mimic various states of ATP hydrolysis on GABA_AR-mediated Cl⁻ and HCO₃⁻ fluxes in response to the first and repeated application of the agonist. We found that depending on the presence of bicarbonate, opened and desensitized states of the wild or chimeric GABA_ARs had different sensitivities to γPAs. This study presents the evidence that recovery of neuronal Cl⁻ and HCO₃⁻ concentrations after desensitization is accompanied by a change in the intracellular ATP concentration via ATPase performance. The transition between the desensitization and resensitization states was linked to changes in both conformation and phosphorylation. In addition, the chimeric β3 isoform did not exhibit the desensitization of the GABA_AR-mediated Cl⁻ influx but only the resensitization. These observations lend a new physiological significance to the β3 subunit in the manifestation of GABA_AR resensitization.

Significance of GABAA Receptor for Cognitive Function and Hippocampal Pathology

The hippocampus is a primary area for contextual memory, known to process spatiotemporal information within a specific episode. Long-term strengthening of glutamatergic transmission is a mechanism of contextual learning in the dorsal cornu ammonis 1 (CA1) area of the hippocampus. CA1-specific immobilization or blockade of α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA) receptor delivery can impair learning performance, indicating a causal relationship between learning and receptor delivery into the synapse. Moreover, contextual learning also strengthens GABA_A (gamma-aminobutyric acid) receptor-mediated inhibitory synapses onto CA1 neurons. Recently we revealed that strengthening of GABA_A receptor-mediated inhibitory synapses preceded excitatory synaptic plasticity after contextual learning, resulting in a reduced synaptic excitatory/inhibitory (E/I) input balance that returned to pretraining levels within 10 min. The faster plasticity at inhibitory synapses may allow encoding a contextual memory and prevent cognitive dysfunction in various hippocampal pathologies. In this review, we focus on the dynamic changes of GABA_A receptor mediated-synaptic currents after contextual learning and the intracellular mechanism underlying rapid inhibitory synaptic plasticity. In addition, we discuss that several pathologies, such as Alzheimer’s disease, autism spectrum disorders and epilepsy are characterized by alterations in GABA_A receptor trafficking, synaptic E/I imbalance and neuronal excitability.