Oligodendroglial GABAergic Signaling: More Than Inhibition!

TMS-EEG evidence links random exploration to inhibitory mechanisms in the dorsolateral prefrontal cortex

Adaptive decision-making in uncertain environments requires balancing exploration and exploitation. Computational models distinguish between directed exploration, involving deliberate information-seeking, and random exploration, characterized by stochastic variability. The neural correlates of these strategies have been investigated in previous studies. However, while prior research implicates the dorsolateral prefrontal cortex (DLPFC) in random exploration, its underlying excitatory and inhibitory mechanisms remain unclear. Understanding these processes is essential for explaining how individuals adapt to a dynamic environment. To investigate this, we combined transcranial magnetic stimulation (TMS) with electroencephalography (EEG) to directly assess cortical excitatory and inhibitory functions. Twenty-five healthy participants completed the Horizon Task, a behavioral paradigm designed to dissociate directed and random exploration, and after the task, they received single-pulse TMS over the DLPFC. The TMS-evoked potentials (TEPs) N45, P60, and N100 were examined as neurophysiological markers of GABAA, GABAB, and glutamate activity. Results revealed a significant positive correlation between the N100 amplitude at the right DLPFC and random exploration, suggesting that GABAB-mediated inhibition plays a key role in stochastic decision-making. Additionally, a correlation between the decision noise parameter in the logistic model and the N100 amplitude further validated this association. These findings highlight the importance of prefrontal inhibition in exploratory behavior and underscore the utility of TMS-EEG in uncovering the neural mechanisms underlying adaptive decision-making.

Repeated sevoflurane exposure causes hypomyelination in the prefrontal cortex of adult male mice

As one of the most commonly used general anesthetics (GAs) in surgery, numerous studies have demonstrated the detrimental effects of sevoflurane exposure on myelination in the developing and elderly brain. However, the impact of sevoflurane exposure on intact myelin structure in the adult brain is barely discovered. Here, we show that repeated sevoflurane exposure, but not single exposure, causes hypomyelination and abnormal ultrastructure of myelin sheath in the prefrontal cortex (PFC) of adult male mice, which is considered as a critical brain region for general anesthesia mediated consciousness change. Furthermore, disrupted proliferation of oligodendrocyte precursor cells (OPCs) contributes to repeated sevoflurane exposure-induced myelin defect. This may be owing to an accumulated tuberous sclerosis complex 1 (TSC1) expression and inhibition of mammalian target of rapamycin (mTOR) signaling, leading to the unbalance of TSC1-mTORC1 activity after repeated sevoflurane exposure, which is critical for proper myelination of the central nervous system (CNS). Moreover, repeated sevoflurane exposure aggregates myelination defect in the cuprizone-induced demyelination model. Together, our present work establishes the role of sevoflurane exposure in myelin integrity in the PFC of the adult male mice and provides a new insight to elucidate the mechanism of GAs-induced brain dysfunctions.

Evidence of the "hit and run" characteristics of Cerebroprotein Hydrolysate-I in the treatment of neonatal HIE based on pharmacokinetic and pharmacological studies

Hypoxic ischemic encephalopathy (HIE) is the leading cause of neonatal mortality and disability, but its treatment options are very limited and there is an urgent need to further improve treatment outcomes. The present study aims to reveal the therapeutic effects, action pattern, and potential mechanisms of Cerebroprotein hydrolysate-I (CH-I), a mixture of hydrolyzed peptides and amino acids, for the management of HIE. To simulate the complex pathogenesis of HIE more accurately, we innovatively constructed a "triple hit" neonatal HIE rat model. The efficacy of CH-1 was examined in this model, and it was found that CH-I treatment not only significantly improved the behavior and small molecule metabolism disorders of neonatal HIE rats, but also reduced intracerebral neuronal apoptosis, neuroinflammation, and oxidative stress levels. In addition, the neuroprotective effect of CH-I was also confirmed in the hypoxic oligodendrocyte precursor cell model. We innovatively found that CH-I could reverse myelin damage induced by HIE modeling via activating the Wnt/β-catenin signaling pathway. More importantly, a robust quantitative analysis assay for the main peptides in CH-I was developed based on LC-MS/MS system combining Skyline software. Then the pharmacokinetics of the main peptides was studied based on 'relative exposure approach' combining 'mixed calibration curves' strategy. The transient exposure of peptides in vivo indicated that CH-I should exert neuroprotective effects through the "hit and run" pattern.

Genetic Downregulation of GABAB Receptors from Oligodendrocyte Precursor Cells Protects Against Demyelination in the Mouse Spinal Cord

GABAergic signaling and GABAB receptors play crucial roles in regulating the physiology of oligodendrocyte-lineage cells, including their proliferation, differentiation, and myelination. Therefore, they are promising targets for studying how spinal oligodendrocyte precursor cells (OPCs) respond to injuries and neurodegenerative diseases like multiple sclerosis. Taking advantage of the temporally controlled and cell-specific genetic downregulation of GABAB receptors from OPCs, our investigation addresses their specific influence on OPC behavior in the gray and white matter of the mouse spinal cord. Our results show that, while GABAB receptors do not significantly alter spinal cord myelination under physiological conditions, they distinctly regulate the OPC differentiation and Ca2+ signaling. In addition, we investigate the impact of OPC-GABAB receptors in two models of toxic demyelination, namely, the cuprizone and the lysolecithin models. The genetic downregulation of OPC-GABAB receptors protects against demyelination and oligodendrocyte loss. Additionally, we observe the enhanced resilience to cuprizone-induced pathological alterations in OPC Ca2+ signaling. Our results provide valuable insights into the potential therapeutic implications of manipulating GABAB receptors in spinal cord OPCs and deepen our understanding of the interplay between GABAergic signaling and spinal cord OPCs, providing a basis for future research.

Integrated electrophysiological and genomic profiles of single cells reveal spiking tumor cells in human glioma

Prior studies have described the complex interplay that exists between glioma cells and neurons; however, the electrophysiological properties endogenous to glioma cells remain obscure. To address this, we employed Patch-sequencing (Patch-seq) on human glioma specimens and found that one-third of patched cells in IDH mutant (IDHmut) tumors demonstrate properties of both neurons and glia. To define these hybrid cells (HCs), which fire single, short action potentials, and discern if they are of tumoral origin, we developed the single cell rule association mining (SCRAM) computational tool to annotate each cell individually. SCRAM revealed that HCs possess select features of GABAergic neurons and oligodendrocyte precursor cells, and include both tumor and non-tumor cells. These studies characterize the combined electrophysiological and molecular properties of human glioma cells and describe a cell type in human glioma with unique electrophysiological and transcriptomic properties that may also exist in the non-tumor brain.

Metabolomics-Based Effects of a Natural Product on Remyelination After Cerebral Ischemia Injury Via GABABR-pCREB-BDNF Pathway

BACKGROUND

Yi-Qi-Tong-Luo Granules (YQTLs) is a natural compound of Traditional Chinese Medicine authorized by China Food and Drug Administration (CFDA). These granules are employed in the convalescent stage of cerebral infarction and render notable clinical efficacy. This study aims to uncover the underlying mechanisms of YQTLs on remyelination after cerebral ischemia injury.

MATERIALS AND METHODS

We established cerebral ischemia model in rats using microsphere-induced multiple cerebral infarction (MCI). We evaluated the pharmacological effects of YQTLs on MCI rats, through Morri's water maze test, open field test, hematoxylin and eosin staining, and glycine silver immersion. We employed liquid chromatography mass spectrometry metabolomics to identify differential metabolites. Enzyme-linked immunosorbent assay was utilized to measure the release of neurotrophins, while immunofluorescence staining was used to assess oligodendrocyte precursor cells differences and myelin regeneration. We used Western blotting to validate the protein expression of remyelination-associated signaling pathways.

RESULTS

YQTLs significantly improves cognitive function following cerebral ischemia injury. Pathological tissue staining revealed that YQTLs administration inhibits neuronal denaturation and neurofibrillary tangles. We identified 141 differential metabolites among the sham, MCI, and YQTLs-treated MCI groups. Among these metabolites, neurotransmitters were identified, and notably, gamma-aminobutyric acid (GABA) showed marked improvement in the YQTLs group. The induction of neurotrophins, such as brain-derived neurotrophic factor (BDNF) and PDGFAA, upregulation of olig2 and MBP expression, and promotion of remyelination were evident in YQTLs-treated MCI groups. Gamma-aminobutyric acid B receptors (GABABR), pERK/extracellular regulated MAP kinase, pAKT/protein kinase B, and pCREB/cAMP response element-binding were upregulated following YQTLs treatment.

CONCLUSION

YQTLs enhance the binding of GABA to GABABR, thereby activating the pCREB/BDNF signaling pathway, which in turn increases the expression of downstream myelin-associated proteins and promotes remyelination and cognitive function.

Interaction between Oligodendrocytes and Interneurons in Brain Development and Related Neuropsychiatric Disorders

A variety of neurological and psychiatric disorders have recently been shown to be highly associated with the abnormal development and function of oligodendrocytes (OLs) and interneurons. OLs are the myelin-forming cells in the central nervous system (CNS), while interneurons are important neural types gating the function of excitatory neurons. These two types of cells are of great significance for the establishment and function of neural circuits, and they share similar developmental origins and transcriptional architectures, and interact with each other in multiple ways during development. In this review, we compare the similarities and differences in these two cell types, providing an important reference and further revealing the pathogenesis of related brain disorders.

Sleep, Glial Function, and the Endocannabinoid System: Implications for Neuroinflammation and Sleep Disorders

The relationship between sleep, glial cells, and the endocannabinoid system represents a multifaceted regulatory network with profound implications for neuroinflammation and cognitive function. The molecular underpinnings of sleep modulation by the endocannabinoid system and its influence on glial cell activity are discussed, shedding light on the reciprocal relationships that govern these processes. Emphasis is placed on understanding the role of glial cells in mediating neuroinflammatory responses and their modulation by sleep patterns. Additionally, this review examines how the endocannabinoid system interfaces with glia-immune signaling to regulate inflammatory cascades within the central nervous system. Notably, the cognitive consequences of disrupted sleep, neuroinflammation, and glial dysfunction are addressed, encompassing implications for neurodegenerative disorders, mood disturbances, and cognitive decline. Insights into the bidirectional modulation of cognitive function by the endocannabinoid system in the context of sleep and glial activity are explored, providing a comprehensive perspective on the potential mechanisms underlying cognitive impairments associated with sleep disturbances. Furthermore, this review examines potential therapeutic avenues targeting the endocannabinoid system to mitigate neuroinflammation, restore glial homeostasis, and normalize sleep patterns. The identification of novel therapeutic targets within this intricate regulatory network holds promise for addressing conditions characterized by disrupted sleep, neuroinflammation, and cognitive dysfunction. This work aims to examine the complexities of neural regulation and identify potential avenues for therapeutic intervention.

Oligodendrocyte precursor cells: the multitaskers in the brain

In the central nervous system, oligodendrocyte precursor cells (OPCs) are recognized as the progenitors responsible for the generation of oligodendrocytes, which play a critical role in myelination. Extensive research has shed light on the mechanisms underlying OPC proliferation and differentiation into mature myelin-forming oligodendrocytes. However, recent advances in the field have revealed that OPCs have multiple functions beyond their role as progenitors, exerting control over neural circuits and brain function through distinct pathways. This review aims to provide a comprehensive understanding of OPCs by first introducing their well-established features. Subsequently, we delve into the emerging roles of OPCs in modulating brain function in both healthy and diseased states. Unraveling the cellular and molecular mechanisms by which OPCs influence brain function holds great promise for identifying novel therapeutic targets for central nervous system diseases.

Neuronal activity and remyelination: new insights into the molecular mechanisms and therapeutic advancements

This article reviews the role of neuronal activity in myelin regeneration and the related neural signaling pathways. The article points out that neuronal activity can stimulate the formation and regeneration of myelin, significantly improve its conduction speed and neural signal processing ability, maintain axonal integrity, and support axonal nutrition. However, myelin damage is common in various clinical diseases such as multiple sclerosis, stroke, dementia, and schizophrenia. Although myelin regeneration exists in these diseases, it is often incomplete and cannot promote functional recovery. Therefore, seeking other ways to improve myelin regeneration in clinical trials in recent years is of great significance. Research has shown that controlling neuronal excitability may become a new intervention method for the clinical treatment of demyelinating diseases. The article discusses the latest research progress of neuronal activity on myelin regeneration, including direct or indirect stimulation methods, and the related neural signaling pathways, including glutamatergic, GABAergic, cholinergic, histaminergic, purinergic and voltage-gated ion channel signaling pathways, revealing that seeking treatment strategies to promote myelin regeneration through precise regulation of neuronal activity has broad prospects.

Interactions of glial cells with neuronal synapses, from astrocytes to microglia and oligodendrocyte lineage cells

The mammalian brain is a complex organ comprising neurons, glia, and more than 1 × 10¹⁴ synapses. Neurons are a heterogeneous group of electrically active cells, which form the framework of the complex circuitry of the brain. However, glial cells, which are primarily divided into astrocytes, microglia, oligodendrocytes (OLs), and oligodendrocyte precursor cells (OPCs), constitute approximately half of all neural cells in the mammalian central nervous system (CNS) and mainly provide nutrition and tropic support to neurons in the brain. In the last two decades, the concept of "tripartite synapses" has drawn great attention, which emphasizes that astrocytes are an integral part of the synapse and regulate neuronal activity in a feedback manner after receiving neuronal signals. Since then, synaptic modulation by glial cells has been extensively studied and substantially revised. In this review, we summarize the latest significant findings on how glial cells, in particular, microglia and OL lineage cells, impact and remodel the structure and function of synapses in the brain. Our review highlights the cellular and molecular aspects of neuron-glia crosstalk and provides additional information on how aberrant synaptic communication between neurons and glia may contribute to neural pathologies.

Characterizing the Neuron-Glial Interactions by the Co-cultures of Human iPSC-Derived Oligodendroglia and Neurons

Induced pluripotent stem cell (iPSC) techniques have had considerable breakthroughs in modeling human neurological diseases. Multiple protocols inducing neurons, astrocytes, microglia, oligodendrocytes, and endothelial cells have been well-established thus far. However, these protocols have limitations, including the long time period to get cells of interest or the challenge of culturing more than one cell type simultaneously. Protocols for handling multiple cell types within a shorter time period are still being established. Here we describe a simple and reliable co-culture system to study interactions between neurons and oligodendrocyte precursor cells (OPC) in health and in disease.

GABAB receptor agonist baclofen promotes central nervous system remyelination

Promoting remyelination is considered as a potential neurorepair strategy to prevent/limit the development of permanent neurological disability in patients with multiple sclerosis (MS). To this end, a number of clinical trials are investigating the potential of existing drugs to enhance oligodendrocyte progenitor cell (OPC) differentiation, a process that fails in chronic MS lesions. We previously reported that oligodendroglia express GABA_B receptors (GABA_B Rs) both in vitro and in vivo, and that GABA_B R-mediated signaling enhances OPC differentiation and myelin protein expression in vitro. Our goal here was to evaluate the pro-remyelinating potential of GABA_B R agonist baclofen (Bac), a clinically approved drug to treat spasticity in patients with MS. We first demonstrated that Bac increases myelin protein production in lysolecithin (LPC)-treated cerebellar slices. Importantly, Bac administration to adult mice following induction of demyelination by LPC injection in the spinal cord resulted in enhanced OPC differentiation and remyelination. Thus, our results suggest that Bac repurposing should be considered as a potential therapeutic strategy to stimulate remyelination in patients with MS.

GABA Receptor Agonists Protect From Excitotoxic Damage Induced by AMPA in Oligodendrocytes

Oligodendrocytes are the myelin forming cells of the central nervous system, and their vulnerability to excitotoxicity induced by glutamate contributes to the pathogenesis of neurological disorders including brain ischemia and neurodegenerative diseases, such as multiple sclerosis. In addition to glutamate receptors, oligodendrocytes express GABA receptors (GABAR) that are involved in their survival and differentiation. The interactions between glutamate and GABAergic systems are well documented in neurons, under both physiological and pathological conditions, but this potential crosstalk in oligodendrocytes has not been studied in depth. Here, we evaluated the protective effect of GABAR agonists, baclofen (GABAB) and muscimol (GABAA), against AMPA-induced excitotoxicity in cultured rat oligodendrocytes. First, we observed that both baclofen and muscimol reduced cell death and caspase-3 activation after AMPA insult, proving their oligoprotective potential. Interestingly, analysis of the cell-surface expression of calcium-impermeable GluR2 subunits in oligodendrocytes revealed that GABAergic agonists significantly reverted GluR2 internalization induced by AMPA. We determined that baclofen and muscimol also impaired AMPA-induced intracellular calcium increase and subsequent mitochondrial membrane potential alteration, ROS generation, and calpain activation. However, AMPA-triggered activation of Src, Akt, JNK and CREB was not affected by baclofen or muscimol. Overall, our results suggest that GABAR activation initiates alternative molecular mechanisms that attenuate AMPA-mediated apoptotic excitotoxicity in oligodendrocytes by interfering with expression of GluR subunits in membranes and with calcium-dependent intracellular signaling pathways. Together, these findings provide evidence of GABAR agonists as potential oligodendroglial protectants in central nervous system disorders.

Impaired bidirectional communication between interneurons and oligodendrocyte precursor cells affects social cognitive behavior

Cortical neural circuits are complex but very precise networks of balanced excitation and inhibition. Yet, the molecular and cellular mechanisms that form the balance are just beginning to emerge. Here, using conditional γ-aminobutyric acid receptor B1- deficient mice we identify a γ-aminobutyric acid/tumor necrosis factor superfamily member 12-mediated bidirectional communication pathway between parvalbumin-positive fast spiking interneurons and oligodendrocyte precursor cells that determines the density and function of interneurons in the developing medial prefrontal cortex. Interruption of the GABAergic signaling to oligodendrocyte precursor cells results in reduced myelination and hypoactivity of interneurons, strong changes of cortical network activities and impaired social cognitive behavior. In conclusion, glial transmitter receptors are pivotal elements in finetuning distinct brain functions.

Early postnatal interruption of the bidirectional GABA/TNFSF12 signaling between parvalbumin-positive interneurons and oligodendrocyte precursor cells impairs correct prefrontal cortical network activity and social cognitive behavior later in life.

Ischemic Stroke and Sleep: The Linking Genetic Factors

This review summarizes the available data about genetic factors which can link ischemic stroke and sleep. Sleep patterns (subjective and objective measures) are characterized by heritability and comprise up to 38-46%. According to Mendelian randomization analysis, genetic liability for short sleep duration and frequent insomnia symptoms is associated with ischemic stroke (predominantly of large artery subtype). The potential genetic links include variants of circadian genes, genes encoding components of neurotransmitter systems, common cardiovascular risk factors, as well as specific genetic factors related to certain sleep disorders.

Clemastine Ameliorates Myelin Deficits via Preventing Senescence of Oligodendrocytes Precursor Cells in Alzheimer's Disease Model Mouse

Disrupted myelin and impaired myelin repair have been observed in the brains of patients and various mouse models of Alzheimer's disease (AD). Clemastine, an H1-antihistamine, shows the capability to induce oligodendrocyte precursor cell (OPC) differentiation and myelin formation under different neuropathological conditions featuring demyelination via the antagonism of M1 muscarinic receptor. In this study, we investigated if aged APPSwe/PS1dE9 mice, a model of AD, can benefit from chronic clemastine treatment. We found the treatment reduced brain amyloid-beta deposition and rescued the short-term memory deficit of the mice. The densities of OPCs, oligodendrocytes, and myelin were enhanced upon the treatment, whereas the levels of degraded MBP were reduced, a marker for degenerated myelin. In addition, we also suggest the role of clemastine in preventing OPCs from entering the state of cellular senescence, which was shown recently as an essential causal factor in AD pathogenesis. Thus, clemastine exhibits therapeutic potential in AD via preventing senescence of OPCs.

A novel hypothesis for COVID-19 pathogenesis: Retinol depletion and retinoid signaling disorder

The SARS-CoV-2 virus has caused a worldwide COVID-19 pandemic. In less than a year and a half, more than 200 million people have been infected and more than four million have died. Despite some improvement in the treatment strategies, no definitive treatment protocol has been developed. The pathogenesis of the disease has not been clearly elucidated yet. A clear understanding of its pathogenesis will help develop effective vaccines and drugs. The immunopathogenesis of COVID-19 is characteristic with acute respiratory distress syndrome and multiorgan involvement with impaired Type I interferon response and hyperinflammation. The destructive systemic effects of COVID-19 cannot be explained simply by the viral tropism through the ACE2 and TMPRSS2 receptors. In addition, the recently identified mutations cannot fully explain the defect in all cases of Type I interferon synthesis. We hypothesize that retinol depletion and resulting impaired retinoid signaling play a central role in the COVID-19 pathogenesis that is characteristic for dysregulated immune system, defect in Type I interferon synthesis, severe inflammatory process, and destructive systemic multiorgan involvement. Viral RNA recognition mechanism through RIG-I receptors can quickly consume a large amount of the body's retinoid reserve, which causes the retinol levels to fall below the normal serum levels. This causes retinoid insufficiency and impaired retinoid signaling, which leads to interruption in Type I interferon synthesis and an excessive inflammation. Therefore, reconstitution of the retinoid signaling may prove to be a valid strategy for management of COVID-19 as well for some other chronic, degenerative, inflammatory, and autoimmune diseases.

Receptor-Receptor Interactions and Glial Cell Functions with a Special Focus on G Protein-Coupled Receptors

The discovery that receptors from all families can establish allosteric receptor-receptor interactions and variably associate to form receptor complexes operating as integrative input units endowed with a high functional and structural plasticity has expanded our understanding of intercellular communication. Regarding the nervous system, most research in the field has focused on neuronal populations and has led to the identification of many receptor complexes representing an important mechanism to fine-tune synaptic efficiency. Receptor-receptor interactions, however, also modulate glia-neuron and glia-glia intercellular communication, with significant consequences on synaptic activity and brain network plasticity. The research on this topic is probably still at the beginning and, here, available evidence will be reviewed and discussed. It may also be of potential interest from a pharmacological standpoint, opening the possibility to explore, inter alia, glia-based neuroprotective therapeutic strategies.