GABAA receptor plasticity in Jurkat T cells

β subunits of GABAA receptors form proton-gated chloride channels: Insights into the molecular basis

Gamma-aminobutyric acid type A receptors (GABA_ARs) are ligand gated channels mediating inhibition in the central nervous system. Here, we identify a so far undescribed function of β-subunit homomers as proton-gated anion channels. Mutation of a single H267A in β3 subunits completely abolishes channel activation by protons. In molecular dynamic simulations of the β3 crystal structure protonation of H267 increased the formation of hydrogen bonds between H267 and E270 of the adjacent subunit leading to a pore stabilising ring formation and accumulation of Cl^- within the transmembrane pore. Conversion of these residues in proton insensitive ρ1 subunits transfers proton-dependent gating, thus highlighting the role of this interaction in proton sensitivity. Activation of chloride and bicarbonate currents at physiological pH changes (pH₅₀ is in the range 6- 6.3) and kinetic studies suggest a physiological role in neuronal and non-neuronal tissues that express beta subunits, and thus as potential novel drug target.

Beta subunits of GABAA receptors are unexpectedly shown to form homomeric proton gated ion channels attributable to a single histidine residue.

Downregulation of miR-185 is a common pathogenic event in 22q11.2 deletion syndrome-related and idiopathic schizophrenia

Schizophrenia (SCZ) is known as a complicated mental disease with an unknown etiology. The microdeletion of 22q11.2 is the most potent genetic risk factor. Researchers are still trying to find which genes in the deletion region are linked to SCZ. MIR185, encoding microRNA (miR)-185, is present in the minimal 1.5 megabase deletion. Nonetheless, the miR-185 expression profile and its corresponding target genes in animal models and patients with 22q11.2 deletion syndrome (22q11.2DS) imply that more study is required about miR-185 and its corresponding downstream pathways within idiopathic SCZ. The expression of hsa-miR-185-5p and its corresponding target gene, shisa family member 7 (SHISA7), sometimes called CKAMP59, were evaluated in the peripheral blood (PB) samples of Iranian Azeri patients with idiopathic SCZ and healthy subjects, matched by gender and age as control groups by quantitative polymerase chain reaction (qPCR). Fifty SCZ patients (male/female: 22/28, age (mean ± standard deviation (SD)): 35.9 ± 5.6) and 50 matched healthy controls (male/female: 23/27, age (mean ± SD): 34.7 ± 5.4) were enrolled. The expression of hsa-miR-185-5p in the PB samples from subjects with idiopathic SCZ was substantially lower than in that of control groups (posterior beta = -0.985, adjusted P-value < 0.0001). There was also a difference within the expression profile between female and male subgroups (posterior beta = -0.86, adjusted P-value = 0.046 and posterior beta = -1.015, adjusted P-value = 0.004, in turn). Nevertheless, no significant difference was present in the expression level of CKAMP59 between PB samples from patients and control groups (adjusted P-value > 0.999). The analysis of the receiver operating characteristic (ROC) curve suggested that hsa-miR-185-5p may correctly distinguish subjects with idiopathic SCZ from healthy people (the area under curve (AUC) value: 0.722). Furthermore, there was a strong positive correlation between the expression pattern of the abovementioned genes in patients with SCZ and healthy subjects (r = 0.870, P < 0.001 and r = 0.812, P < 0.001, respectively), indicating that this miR works as an enhancer. More research is needed to determine if the hsa-miR-185-5p has an enhancer activity. In summary, this is the first research to highlight the expression of the miR-185 and CKAMP59 genes in the PB from subjects with idiopathic SCZ. Our findings suggest that gene expression alterations mediated by miR-185 may play a role in the pathogenesis of idiopathic and 22q11.2DS SCZ. It is worth noting that, despite a substantial and clear relationship between CKAMP59 and hsa-miR-185-5p, indicating an interactive network, their involvement in the development of SCZ should be reconsidered based on the whole blood sample since the changed expression level of CKAMP59 was not significant. Further research with greater sample sizes and particular leukocyte subsets can greatly make these results stronger.

The Case for Clinical Trials with Novel GABAergic Drugs in Diabetes Mellitus and Obesity

Obesity and diabetes mellitus have become the surprising menaces of relative economic well-being worldwide. Gamma amino butyric acid (GABA) has a prominent role in the control of blood glucose, energy homeostasis as well as food intake at several levels of regulation. The effects of GABA in the body are exerted through ionotropic GABAA and metabotropic GABAB receptors. This treatise will focus on the pharmacologic targeting of GABAA receptors to reap beneficial therapeutic effects in diabetes mellitus and obesity. A new crop of drugs selectively targeting GABAA receptors has been under investigation for efficacy in stroke recovery and cognitive deficits associated with schizophrenia. Although these trials have produced mixed outcomes the compounds are safe to use in humans. Preclinical evidence is summarized here to support the rationale of testing some of these compounds in diabetic patients receiving insulin in order to achieve better control of blood glucose levels and to combat the decline of cognitive performance. Potential therapeutic benefits could be achieved (i) By resetting the hypoglycemic counter-regulatory response; (ii) Through trophic actions on pancreatic islets, (iii) By the mobilization of antioxidant defence mechanisms in the brain. Furthermore, preclinical proof-of-concept work, as well as clinical trials that apply the novel GABAA compounds in eating disorders, e.g., olanzapine-induced weight-gain, also appear warranted.

Activation of GABA(A) receptors inhibits T cell proliferation

BACKGROUND

The major sites for fast synaptic inhibition in the central nervous system (CNS) are ion channels activated by γ-aminobutyric acid (GABA). These receptors are referred as GABA(A) receptors (GABA(A)R). Recent evidence indicates a role of GABA(A)R in modulating the immune response. This work aimed to discern the role of GABA and GABA(A)Rs in human and mouse T cell activity.

METHODS

Mouse splenocytes or human peripheral blood mononuclear cells (PBMCs) were activated with anti-CD3 antibodies and the proliferation of both CD8+ and CD4+ T cells assessed through flow cytometry. Subsequently, the effects on T cell proliferation of either GABA(A)R modulation by diazepam that is also capable of activating mitochondrial based translocator protein (TSPO), alprazolam and allopregnanolone or inhibition by bicucculine methiodide (BMI) and (1,2,5,6-Tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) were assessed.

RESULTS

Positive modulation of GABA(A)Rs either by benzodiazepines or the neurosteroid allopregnanolone inhibits both mouse and human T cell proliferation. GABAergic inhibition of T cell proliferation by benzodiazepines could be rescued by GABA(A)R blocking. Our data suggest that benzodiazepines influence T cell proliferation through both TSPO and GABA(A)Rs activation.

CONCLUSIONS

We conclude that activation of GABA(A)Rs provides immunosuppression by inhibiting T cell proliferation.

Development of GABAA Receptor Subtype-Selective Imidazobenzodiazepines as Novel Asthma Treatments

Recent studies have demonstrated that subtype-selective GABAA receptor modulators are able to relax precontracted human airway smooth muscle ex vivo and reduce airway hyper-responsiveness in mice upon aerosol administration. Our goal in this study was to investigate systemic administration of subtype-selective GABAA receptor modulators to alleviate bronchoconstriction in a mouse model of asthma. Expression of GABAA receptor subunits was identified in mouse lungs, and the effects of α4-subunit-selective GABAAR modulators, XHE-III-74EE and its metabolite XHE-III-74A, were investigated in a murine model of asthma (ovalbumin sensitized and challenged BALB/c mice). We observed that chronic treatment with XHE-III-74EE significantly reduced airway hyper-responsiveness. In addition, acute treatment with XHE-III-74A but not XHE-III-74EE decreased airway eosinophilia. Immune suppressive activity was also shown in activated human T-cells with a reduction in IL-2 expression and intracellular calcium concentrations [Ca(2+)]i in the presence of GABA or XHE-III-74A, whereas XHE-III-74EE showed only partial reduction of [Ca(2+)]i and no inhibition of IL-2 secretion. However, both compounds significantly relaxed precontracted tracheal rings ex vivo. Overall, we conclude that the systemic delivery of a α4-subunit-selective GABAAR modulator shows good potential for a novel asthma therapy; however, the pharmacokinetic properties of this class of drug candidates have to be improved to enable better beneficial systemic pharmacodynamic effects.

GABAergic signalling in the immune system

The GABAergic system is the main inhibitory neurotransmitter system in the central nervous system (CNS) of vertebrates. Signalling of the transmitter γ-aminobutyric acid (GABA) via GABA type A receptor channels or G-protein-coupled type B receptors is implicated in multiple CNS functions. Recent findings have implicated the GABAergic system in immune cell functions, inflammatory conditions and diseases in peripheral tissues. Interestingly, the specific effects may vary between immune cell types, with stage of activation and be altered by infectious agents. GABA/GABA-A receptor-mediated immunomodulatory functions have been unveiled in immune cells, being present in T lymphocytes and regulating the migration of Toxoplasma-infected dendritic cells. The GABAergic system may also play a role in the regulation of brain resident immune cells, the microglial cells. Activation of microglia appears to regulate the function of GABAergic neurotransmission in neighbouring neurones through changes induced by secretion of brain-derived neurotrophic factor. The neurotransmitter-driven immunomodulation is a new but rapidly growing field of science. Herein, we review the present knowledge of the GABA signalling in immune cells of the periphery and the CNS and raise questions for future research.