Protein Kinase C-Dependent Effects of Neurosteroids on Synaptic GABAA Receptor Inhibition Require the δ-Subunit

GABAAR-δ-subunit mediates increased GABAergic inhibition in cardiac DMV neurons after high-fat diet

Activity of cardiac-projecting neurons in the dorsal motor nucleus of the vagus (CVNDMV) is vital in cardiac reflexes contributing to maintaining cardiovascular health. However, how this population adapts to metabolic challenges, such as high-fat diet (HFD), is unclear. This study aimed to identify neuroplasticity changes induced by HFD in CVNDMV. Using whole-cell patch-clamp electrophysiology, we found that 15-day HFD feeding increased tonic, but not phasic, gamma-aminobutyric acid type A (GABAA) inhibitory neurotransmission, exclusive to CVNDMV. Single-cell quantitative reverse-transcription PCR (scRT-qPCR) analysis revealed a higher number of CVNDMV expressing GABAA receptor δ-subunit (GABAA(δ)R) in HFD compared to normal fat diet (NFD). Deletion of GABAA(δ)R in ChAT-positive motor neurons abolished HFD-induced increased tonic GABAA neurotransmission in CVNDMV. Altogether, this evidence suggests that CVNDMV exhibits early onset HFD-induced increased GABAergic neurotransmission, likely mediated by GABAA(δ)R. This increased inhibitory tone could explain previously reported reduced cardiac vagal motor output, thus contributing to poor cardiometabolic health after HFD.

Multifaceted Actions of Neurosteroids

Background and purpose

Neurosteroids modulate neuronal function and are promising therapeutic agents for neuropsychiatric disorders. Neurosteroid analogues are approved for treating postpartum depression and are of interest in other disorders. GABA-A receptors are well characterized targets of natural neurosteroids, but other biological pathways are likely relevant to therapeutic mechanisms and/or to off-target effects. We performed hypothesis-generating in silico analyses and broad in vitro biological screens to assess the range of actions of neurosteroids analogues of varying structural attributes.

Key Results

We employed in silico molecular similarity analysis and network pharmacology to elucidate likely targets. This analysis confirmed likely targets beyond GABA-A receptors. We then functionally screened 19 distinct neurosteroid structures across 78 targets representing interconnected signaling pathways, complemented with a limited screen of kinase activation. Results revealed unanticipated modulation of targets by neurosteroids with some structural selectivity. Many compounds-initiated androgen receptor translocation with little or no enantioselectivity. Modulation of multiple G-protein receptors was also unexpected.

Conclusions and implications

Neurosteroids are ascendant treatments in neuropsychiatry, but their full spectrum of actions remains unclear. This virtual and biological screening discovery approach opens new vistas for exploring mechanism of neurosteroids analogues. The multifaceted approach provides an unbiased, holistic exploration of the potential effects of neurosteroids across various molecular targets and provides a platform for future validation studies to aid drug discovery.

The roles of RACK1 in the pathogenesis of Alzheimer's disease

The receptor for activated C kinase 1 (RACK1) is a protein that plays a crucial role in various signaling pathways and is involved in the pathogenesis of Alzheimer's disease (AD), a prevalent neurodegenerative disease. RACK1 is highly expressed in neuronal cells of the central nervous system and regulates the pathogenesis of AD. Specifically, RACK1 is involved in regulation of the amyloid-β precursor protein processing through α- or β-secretase by binding to different protein kinase C isoforms. Additionally, RACK1 promotes synaptogenesis and synaptic plasticity by inhibiting N-methyl-D-aspartate receptors and activating gamma-aminobutyric acid A receptors, thereby preventing neuronal excitotoxicity. RACK1 also assembles inflammasomes that are involved in various neuroinflammatory pathways, such as nuclear factor-kappa B, tumor necrosis factor-alpha, and NOD-like receptor family pyrin domain-containing 3 pathways. The potential to design therapeutics that block amyloid-β accumulation and inflammation or precisely regulate synaptic plasticity represents an attractive therapeutic strategy, in which RACK1 is a potential target. In this review, we summarize the contribution of RACK1 to the pathogenesis of AD and its potential as a therapeutic target.

The Role of Extrasynaptic GABA Receptors in Postpartum Depression

Postpartum depression is a serious disease with a high incidence and severe impact on pregnant women and infants, but its mechanism remains unclear. Recent studies have shown that GABA receptors, especially extrasynaptic receptors, are closely associated with postpartum depression. There are many different structures of GABA receptors, so different types of receptors have different functions, even though they transmit information primarily through GABA. In this review, we focus on the function of GABA receptors, especially extrasynaptic GABA receptors, and their association with postpartum depression. We have shown that the extrasynaptic GABA receptor has a significant impact on the activity and function of neurons through tonic inhibition. The extrasynaptic receptor and its ligands undergo drastic changes during pregnancy and childbirth. Abnormal changes or the body's inability to adjust and recover may be an important cause of postpartum depression. Finally, by reviewing the mechanisms of several novel antidepressants, we suggest that extrasynaptic receptors may be potential targets for the treatment of postpartum depression.

Gabrb2 knock-out mice exhibit double-directed PMDD-like symptoms: GABAAR subunits, neurotransmitter metabolism disruption, and allopregnanolone binding

Background: Premenstrual dysphoric disorder (PMDD) is a severe mood disorder with pathological changes rooted in GABRB2 copy number variation. Here, we aimed to elucidate the gene dose effect and allopregnanolone binding mechanism of Gabrb2 on possible PMDD-like and comorbid phenotypes in knockout mice.

Methods: PMDD-like behaviors of Gabrb2-knockout mice were measured through various tests. Western Blot and ELISA were used to detect changes in the GABAAR subunits and related neurotransmitter changes in mice respectively for the internal mechanism. The response of mice to allopregnanolone (ALLO) was examined through an exogenous ALLO injection, then validated by the patch-clamp technique to elaborate the potential mechanism of ALLO-mediated GABAAR.

Results: Gabrb2-knockout mice displayed changes in anxiety-like and depression-like emotions opposite to PMDD symptoms, changes in social, learning, and memory capacities similar to PMDD symptoms, and pain threshold changes opposite to PMDD symptoms. GABAAR δ subunit expression in the brains of the Gabrb2-knockout mice was significantly higher than that of Wild-type mice (P<0.05). Gabrb2-knockout mice demonstrated neurotransmitter metabolism disturbance of GABA, Glu, acetylcholine, DA, norepinephrine, and epinephrine. Moreover, Gabrb2-knockout mice did not display the expected phenotypic effect after ALLO injection. Relative to WT mice, the knockout of the β2 subunit gene enhanced the agonistic effect of ALLO on GABAA receptors in cortical neuronal cells.

Conclusions: GABAAR β 2 regulates PMDD-like behaviors. The ALLO binding site may not be located on β two subunits, abnormal δ and ε subunit expression in the mouse brain and the disturbance of neurotransmitters may result in ALLO sensitivity.

Zolpidem Profoundly Augments Spared Tonic GABAAR Signaling in Dentate Granule Cells Ipsilateral to Controlled Cortical Impact Brain Injury in Mice

Type A GABA receptors (GABA_ARs) are pentameric combinations of protein subunits that give rise to tonic (I_TonicGABA) and phasic (i.e., synaptic; I_SynapticGABA) forms of inhibitory GABA_AR signaling in the central nervous system. Remodeling and regulation of GABA_AR protein subunits are implicated in a wide variety of healthy and injury-dependent states, including epilepsy. The present study undertook a detailed analysis of GABA_AR signaling using whole-cell patch clamp recordings from mouse dentate granule cells (DGCs) in coronal slices containing dorsal hippocampus at 1–2 or 8–13 weeks after a focal, controlled cortical impact (CCI) or sham brain injury. Zolpidem, a benzodiazepine-like positive modulator of GABA_ARs, was used to test for changes in GABA_AR signaling of DGCs due to its selectivity for α₁ subunit-containing GABA_ARs. Electric charge transfer and statistical percent change were analyzed in order to directly compare tonic and phasic GABA_AR signaling and to account for zolpidem’s ability to modify multiple parameters of GABA_AR kinetics. We observed that baseline I_TonicGABA is preserved at both time-points tested in DGCs ipsilateral to injury (Ipsi-DGCs) compared to DGCs contralateral to injury (Contra-DGCs) or after sham injury (Sham-DGCs). Interestingly, application of zolpidem resulted in modulation of I_TonicGABA across groups, with Ipsi-DGCs exhibiting the greatest responsiveness to zolpidem. We also report that the combination of CCI and acute application of zolpidem profoundly augments the proportion of GABA_AR charge transfer mediated by tonic vs. synaptic currents at both time-points tested, whereas gene expression of GABA_AR α₁, α₂, α₃, and γ₂ subunits is unchanged at 8–13 weeks post-injury. Overall, this work highlights the shift toward elevated influence of tonic inhibition in Ipsi-DGCs, the impact of zolpidem on all components of inhibitory control of DGCs, and the sustained nature of these changes in inhibitory tone after CCI injury.