Mechanisms of NMDA receptor regulation

Sex-biased zinc responses modulate ribosomal protein expression, protein synthesis and social defects in Cttnbp2 mutant mice

Autism spectrum disorders (ASD) are neurodevelopmental conditions influenced by genetic mutations, dietary factors, and sex-specific mechanisms, yet the interplay of these factors remains elusive. Here, we investigate the sex-biased responses of mutant mice carrying an ASD-associated mutation in Cttnbp2 to dietary zinc supplementation using behavioral assays, proteomic and bioinformatic analyses, and puromycin pulse labeling to assess protein synthesis. Our results demonstrate that zinc supplementation enhances ribosomal protein expression and protein synthesis and increases the density and size of dendritic spines in male Cttnbp2 mutant mice, alleviating male-biased social deficits. Analyses of neuronal cultures further revealed that neurons, not astrocytes, respond to zinc to enhance protein synthesis. In contrast, female Cttnbp2 mutants exhibit resilience to differential zinc intake, even under zinc deprivation. Elevated mTOR phosphorylation and increased protein levels of translational initiation factors in female brains may provide a protective mechanism, reducing their sensitivity to zinc deficiency. Cttnbp2 mutations heighten male vulnerability to zinc deprivation, impairing social behaviors. These findings highlight zinc-regulated ribosomal protein expression and protein synthesis as critical mediators of sex-specific ASD phenotypes, offering new insights into dietary interventions.

Anticonvulsant effect of Stachydrine on pentylenetetrazole-induced kindling seizure mouse model via Notch and NMDAR signaling pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Stachydrine (STA), the principal bioactive alkaloid of Leonurus japonicus (Motherwort/"Yi Mu Cao"), may derive its ethnopharmacological relevance for epilepsy management from the botanical origin-Motherwort's documented traditional use in treating seizures and other neurological cardiovascular diseases.

AIM OF THE STUDY

To validate STA's ethnomedicinal claim an anticonvulsant by mechanistically interrogating its dual modulation of Notch1-driven neuroinflammation and NMDA receptor-mediated excitotoxicity, which are two key hallmarks of chronic epileptogenesis.

MATERIALS AND METHODS

Male C57BL/6 mice were divided into three groups to evaluate the neuroprotective and an anticonvulsant effects of STA in the PTZ-induced seizure model: Control group, PTZ group, and PTZ + STA group. Behavioral seizure scoring and cognitive tests were integrated with EEG recordings to assess neuronal synchronization. Molecular mechanisms were dissected via hippocampal immunohistochemistry and Western blotting.

RESULTS

Our results showed that daily oral administration of STA for a duration of 25 days significantly reduced seizure scores. EEG recordings indicated that STA treatment resulted in a notable reduction in both total brainwave power and firing amplitude within the groups receiving STA. Furthermore, STA administration provided cognitive protection against kindling-associated deficits, as demonstrated by improved alteration behavior and recognition index in Y-maze and object recognition tests. STA administration reduced neuronal loss and glial cell activation. Additionally, significant downregulation of NMDA receptor subunits, CAMK2, caspase-3, Notch1, and Hes1 expression levels was observed following STA administration.

CONCLUSION

These findings suggest that STA provides neuroprotection against PTZ-induced epilepsy by modulating the Notch and NMDA receptor pathways, thus addressing neuroinflammation and apoptosis resulting from excitotoxicity.

The roles of mitochondria in global and local intracellular calcium signalling

Activation of Ca2+ channels in Ca2+ stores in organelles and the plasma membrane generates cytoplasmic calcium ([Ca2+]c) signals that control almost every aspect of cell function, including metabolism, vesicle fusion and contraction. Mitochondria have a high capacity for Ca2+ uptake and chelation, alongside efficient Ca2+ release mechanisms. Still, mitochondria do not store Ca2+ in a prolonged manner under physiological conditions and lack the capacity to generate global [Ca2+]c signals. However, mitochondria take up Ca2+ at high local [Ca2+]c signals that originate from neighbouring organelles, and also during sustained global elevations of [Ca2+]c. Accumulated Ca2+ in the mitochondria stimulates oxidative metabolism and upon return to the cytoplasm, can produce spatially confined rises in [Ca2+]c to exert control over processes that are sensitive to Ca2+. Thus, the mitochondrial handling of [Ca2+]c is of physiological relevance. Furthermore, dysregulation of mitochondrial Ca2+ handling can contribute to debilitating diseases. We discuss the mechanisms and relevance of mitochondria in local and global calcium signals.

N-methyl-d-aspartate receptors (NMDARs): a glutamate-activated cation channel with biased signaling and therapeutic potential in brain disorders

N-methyl-d-aspartate receptors (NMDARs) are a type of calcium-permeable ion channel receptors that are extensively distributed throughout the body, composed of various subunits. The presence of diverse ligands and subcellular localizations of the receptors confer biased signaling and distinct functional roles. Activation of the NMDARs induces calcium influx, which plays a pivotal role in neurotransmitter release, synaptic plasticity, and intracellular signaling. Differential localization of NMDARs at synaptic and extrasynaptic sites results in divergent physiological effects; excessive or insufficient activation of NMDARs disrupts calcium homeostasis, leading to neuronal damage and subsequent neurological dysfunction as well as related diseases. Therefore, it is crucial to develop drugs targeting NMDAR with high efficacy with low toxicity for treating disorders associated with NMDARs abnormalities. In this review, we summarize both fundamental and clinical studies on NMDARs while discussing potential therapeutic targets aimed at modulating ion channel activity through regulating mechanisms, subunit rearrangement, membrane expression, and the specific targeting of synaptic versus extrasynaptic NMDARs. Our goal is to provide new insights for innovative drug development.

Advances in Alzheimer's Therapy: Exploring Neuropathological Mechanisms to Revolutionize the Future Therapeutic Landscape

Alzheimer's disease (AD) is still an excessively complicated neurological disorder that impacts millions of individuals globally. The ideal defensive feature of the central nervous system (CNS) is the intimate junction of endothelial cells, which functions as a biological barrier to safely control molecular transport throughout the brain. The blood-brain barrier (BBB) comprises tightly locked astrocyte cell junctions on CNS blood capillaries. This biological barrier shields the brain from hazardous toxins by preventing the entry of polar medications, cells, and ions. However, it is very challenging to provide any treatment to the brain for neurodegenerative illnesses like Alzheimer's. Different causative mechanisms, such as amyloid-β (Aβ) plaques, tubulin-associated unit (Tau) tangles, and neuroinflammation, cause neuronal dysfunction, leading to dementia and memory loss in the subject. Several treatments are approved for AD therapy, whereas most only help treat related symptoms. Disappointingly, current remedies have not been able to control the progression of AD due to associated side effects. Specific pathogenic mechanisms are involved in the initiation and development of this disease. Therefore, the expected survival of a patient with AD is limited and is approximately ten years. Hence, the pathogenic mechanism behind AD progression must be understood to better comprehend and improve the overall survival rate. This review highlighted the recent insights into AD pathogenesis, molecular mechanisms, advancements in theragnostic techniques, the existing updates of clinical trials, and emerging innovations for AD medicinal development. That has helped researchers develop other strategies to address the shortcomings of traditional medications.

Ion Channels and G-Protein-Coupled Receptors Involved in the Development of Chronic Post-ischemic Pain (CPIP): A Model of Complex Regional Pain Syndrome (CRPS-I)

Chronic pain is a physical and emotional sensation that exceeds biological necessity. Complex regional pain syndrome (CRPS) is considered a chronic primary pain condition that can arise after limb trauma, such as surgery, ischemia, and fractures. This type of pain is a multifactorial disorder that predominantly affects one body extremity and occurs either without initial nerve injury (CRPS-I) or with partial or complete nerve injury (CRPS-II). Therefore, CRPS-I is still a painful and debilitating condition without a complete understanding of its underlying mechanisms. This gap in knowledge about CRPS-I pathophysiology contributes to patient suffering, as there is still no standard pharmacological treatment. Preclinical research uses diverse models of CRPS-I, such as chronic post-ischemia pain (CPIP), to better understand its pain activation pathways. Various mechanisms continue to emerge in CPIP, including the role of different G-protein-coupled receptors (GPCRs) and ion channels. In this review, we will focus on the mechanisms surrounding these different GPCRs and ion channels in a model of CRPS-I-induced nociception in rodents (the CPIP model). To date, the primary targets studied in CPIP pathophysiology include transient receptor potential (TRP) and N-methyl-D-aspartate (NMDA) ion channels, as well as cannabinoid, bradykinin, adenosine, adrenergic, and endothelin GPCRs.

Unveiling chiral amino acid alterations and glycine dysregulation in late-life depression through targeted metabolomics

Background

Late-life depression (LLD) is a major depressive disorder that is highly prevalent among older people, and there are currently no validated biomarkers for the diagnosis and treatment of LLD. Although dysregulated amino acid metabolism has been increasingly implicated in neuropsychiatric disorders, including LLD, most existing studies overlook the chiral nature of amino acids, potentially leading to inaccurate or incomplete findings. To address this gap, this study aimed to precisely characterize the serum chiral amino acid profiles in patients with LLD and identify potential biomarkers.

Methods

Using liquid chromatography tandem mass spectrometry combined with a chiral derivatization technique, the serum levels of 34 amino acids were analyzed in 53 LLD patients and 37 healthy controls (HCs).

Results

Significant alterations in both D- and L-enantiomers were observed, including reduced levels of D-methionine, D-glutamic acid, D-threonine, and L-threonine, alongside elevated glycine levels in LLD compared to HCs. The combination of D-methionine and glycine demonstrated moderate discriminatory power for distinguishing LLD from HCs, with an area under the curve of 0.71. Notably, glycine levels were significantly lower in antidepressant treatment responders than in non-responders. Additionally, D- and L-glutamic acid levels were differentially associated with specific cognitive function indicators.

Discussion

These findings underscore the importance of accounting for amino acid chirality in biomarker research and highlight chiral amino acids as promising candidates for the diagnosis of LLD and the prediction of treatment response.

Novel 2-Pyrrolidone Derivatives as Negative Allosteric Modulators of GluN2B-Containing NMDA Receptors

This patent highlight describes a series of novel 2-pyrrolidone derivatives that act as negative allosteric modulators (NAMs) of GluN2B-containing N-methyl-d-aspartic acid receptors (NMDARs). These compounds target the ifenprodil binding site of the NMDA receptor and exhibit enhanced metabolic stability compared to traditional phenolic-based molecules.

Editorial to the Special Issue "Glycine-(and D-Serine)-Related Neurotransmission: Promising Therapeutic Targets with Still Unsolved Problems"

Glycine (Gly) is a peculiar neurotransmitter (NT) in the Central Nervous System (CNS) exhibiting dual functions: it is mostly inhibitory, in different CNS areas, when it activates the ionotropic Gly receptors (GlyRs) [...].

CPEB3 can regulate seizure susceptibility by inhibiting the transcriptional activity of STAT3 on NMDARs expression

BACKGROUND

The pathogenesis of epilepsy is complex, and current antiepileptic drugs do not effectively control the seizures. Cytoplasmic polyadenylation element-binding protein 3 (CPEB3) regulates neuronal excitability, but its mechanism of action in epilepsy is not clear. In this paper, we investigated the effect of CPEB3 on seizures and elucidated its underlying molecular mechanism.

METHODS

Bioinformatics-based search for genes closely associated with epilepsy. Changes in expression and cellular localization of CPEB3 in epilepsy were verified by western blotting (WB) and Immunofluorescence staining. Subsequently, The adeno-associated virus was employed to overexpress or knockdown in mice. Behavioral experiments verified the effect of CPEB3 on epileptic phenotype, and the molecular mechanism of CPEB3 affecting epileptic phenotype was explored by WB, real-time quantitative polymerase chain reaction (RT-qPCR), RNA immunoprecipitation (RIP), and chromatin immunoprecipitation (CHIP).

RESULTS

The results were that CPEB3 was downregulated epilepsy in model mice and patients with temporal lobe epilepsy and co-expressed with neurons. Behavioral experiments have shown that CPEB3 negatively regulates epilepsy phenotype in mice. In addition, exogenous CPEB3 can also bind to the mRNA of signal transducer and activator of transcription 3 (STAT3) and inhibit its translation, resulting in lower levels of STAT3 and p-STAT3, reduced nuclear translocation of STAT3, and decreased STAT3-mediated transcriptional activity of GluN1, GluN2A, and GluN2B, suppressing the expression of NMDAR subunits, which attenuate the seizure degree and susceptibility of epileptic mice.

CONCLUSION

These findings suggest that CPEB3 may influence excitability and susceptibility in epileptic mice by regulating STAT3 translation and transcriptional activities to promote NMDARs expression. This mechanism could offer insights into novel therapeutic targets for epilepsy.

The Balance in the Head: How Developmental Factors Explain Relationships Between Brain Asymmetries and Mental Diseases

Cerebral lateralisation is a core organising principle of the brain that is characterised by a complex pattern of hemispheric specialisations and interhemispheric interactions. In various mental disorders, functional and/or structural hemispheric asymmetries are changed compared to healthy controls, and these alterations may contribute to the primary symptoms and cognitive impairments of a specific disorder. Since multiple genetic and epigenetic factors influence both the pathogenesis of mental illness and the development of brain asymmetries, it is likely that the neural developmental pathways overlap or are even causally intertwined, although the timing, magnitude, and direction of interactions may vary depending on the specific disorder. However, the underlying developmental steps and neuronal mechanisms are still unclear. In this review article, we briefly summarise what we know about structural, functional, and developmental relationships and outline hypothetical connections, which could be investigated in appropriate animal models. Altered cerebral asymmetries may causally contribute to the development of the structural and/or functional features of a disorder, as neural mechanisms that trigger neuropathogenesis are embedded in the asymmetrical organisation of the developing brain. Therefore, the occurrence and severity of impairments in neural processing and cognition probably cannot be understood independently of the development of the lateralised organisation of intra- and interhemispheric neuronal networks. Conversely, impaired cellular processes can also hinder favourable asymmetry development and lead to cognitive deficits in particular.

Signaling in autism: Relevance to nutrients and sex

Autism spectrum disorders (ASD) are substantially heterogeneous neuropsychiatric conditions with over a thousand associated genetic factors and various environmental influences, such as infection and nutrition. Additionally, males are four times more likely than females to be affected. This heterogeneity underscores the need to uncover common molecular features within ASD. Recent studies have revealed interactions among genetic predispositions, environmental factors, and sex that may be critical to ASD etiology. This review focuses on emerging evidence for the impact of nutrients-particularly zinc and amino acids-on ASD, as demonstrated in mouse models and human studies. These nutrients have been shown to influence synaptic signaling, dendritic spine formation, and behaviors linked to autism. Furthermore, sex-based differences in nutritional requirements, especially for zinc and amino acids, may contribute to the observed male bias in autism, indicating that interactions between nutrients and genetic factors could be integral to understanding and potentially mitigating ASD symptoms.

Regulation of NMDAR activation efficiency by environmental factors and subunit composition

NMDA receptors (NMDAR) convert the major excitatory neurotransmitter glutamate into a synaptic signal. A key question is how efficiently the ion channel opens in response to the rapid exposure to presynaptic glutamate release. Here, we applied glutamate to single channel outside-out patches and measured the successes of channel openings and the latency to first opening to assay the activation efficiency of NMDARs under different physiological conditions and with different human subunit compositions. For GluN1/GluN2A receptors, we find that various factors, including intracellular ATP and GTP, can enhance the efficiency of activation presumably via the intracellular C-terminal domain. Notably, an energy-based internal solution or increasing the time between applications to increase recovery time improved efficiency. However, even under these optimized conditions and with a 1-s glutamate application, there remained around 10-15% inefficiency. Channel activation became more inefficient with brief synaptic-like pulses of glutamate at 2 ms. Of the different NMDAR subunit compositions, GluN2B-containing NMDARs showed the lowest success rate and longest latency to first openings, highlighting that they display the most distinct activation mechanism. In contrast, putative triheteromeric GluN1/GluN2A/GluN2B receptors showed high activation efficiency. Despite the low open probability, NMDARs containing either GluN2C or GluN2D subunits displayed high activation efficiency, nearly comparable with that for GluN2A-containing receptors. These results highlight that activation efficiency in NMDARs can be regulated by environmental surroundings and varies across different subunits.

RBM4-mediated intron excision of Hsf1 induces BDNF for cerebellar foliation

Brain-derived neurotrophic factor (BDNF) plays important roles in brain development and neural function. Constitutive knockout of the splicing regulator RBM4 reduces BDNF expression in the developing brain and causes cerebellar hypoplasia, an autism-like feature. Here, we show that Rbm4 knockout induced intron 6 retention of Hsf1, leading to downregulation of HSF1 protein and its downstream target BDNF. RBM4-mediated Hsf1 intron excision regulated BDNF expression in cultured granule cells. Ectopic expression of HSF1 restored cerebellar foliation and motor learning of Rbm4-knockout mice, indicating a critical role for RBM4-HSF1-BDNF in cerebellar foliation. Moreover, N-methyl-D-aspartate receptor (NMDAR) signaling promoted the expression and nuclear translocation of RBM4, and hence increased the expression of both HSF and BDNF. A short CU-rich motif was responsible for NMDAR- and RBM4-mediated intron excision. Finally, RBM4 and polypyrimidine tract binding (PTB) proteins play antagonistic roles in intron excision, suggesting a role for splicing regulation in BDNF expression.

Lutein, a versatile carotenoid: Insight on neuroprotective potential and recent advances

BACKGROUND

Neurodegenerative diseases (NDDs) are a diverse group of neurological disorders with progressive neuronal loss at specific brain regions, leading to impaired cognitive functioning, loss of neuroplasticity, severe neurological impairment, and dementia. The incidence of neurodegenerative diseases is increasing at an alarming rate with current treatments struggling to barely prolong the inevitable. The desperation to discover a therapeutic agent to treat neurodegenerative diseases and to aid in the process of healthy recovery has opened a gateway into natural pigments.

HYPOTHESIS

The xanthophyll pigment lutein may bear the potential as a therapeutic agent against NDDs.

RESULTS

Lutein plays an important role in brain development, cognitive functioning, and improving neuroplasticity. In vitro and in vivo studies revealed the neuroprotective properties of lutein against NDDs such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and cerebral ischemia. The neuroprotective effect of lutein is evidenced by the reduction of free radicals and the simultaneous strengthening of the endogenous antioxidant systems by activating the NRF-2/ERK/AKT pathway. Further, it effectively suppressed mitochondrial aberrations, excitotoxicity, overaccumulation of metals, and its resultant complications. The immunomodulatory activity of lutein prevents neuroinflammation by hindering NF-κB nuclear translocation, regulation of NIK/IKK, PI3K/AKT, MAPK/ERK, JNK pathways, and ICAM-1 downregulation. Lutein also rescued the dysregulated cholinergic system and resolved memory defects. Along with its neuroprotective properties, lutein also improved neuroplasticity by enabling neurogenesis through increased GAP-43, NCAM, and BDNF levels.

CONCLUSION

Lutein exhibits strong neuroprotective activities against various NDDs. Though the investigations are in the exploratory phase, this review presents the consolidation of scattered evidence of the neuroprotective properties of lutein and urges its further exploration in clinical studies.

Role of astrocytes in Alzheimer's disease pathogenesis and the impact of exercise-induced remodeling

Alzheimer's disease (AD) is a prevalent and debilitating brain disorder that worsens progressively with age, characterized by cognitive decline and memory impairment. The accumulation of amyloid-beta (Aβ) leading to amyloid plaques and hyperphosphorylation of Tau, resulting in intracellular neurofibrillary tangles (NFTs), are primary pathological features of AD. Despite significant research investment and effort, therapies targeting Aβ and NFTs have proven limited in efficacy for treating or slowing AD progression. Consequently, there is a growing interest in non-invasive therapeutic strategies for AD prevention. Exercise, a low-cost and non-invasive intervention, has demonstrated promising neuroprotective potential in AD prevention. Astrocytes, among the most abundant glial cells in the brain, play essential roles in various physiological processes and are implicated in AD initiation and progression. Exercise delays pathological progression and mitigates cognitive dysfunction in AD by modulating astrocyte morphological and phenotypic changes and fostering crosstalk with other glial cells. This review aims to consolidate the current understanding of how exercise influences astrocyte dynamics in AD, with a focus on elucidating the molecular and cellular mechanisms underlying astrocyte remodeling. The review begins with an overview of the neuropathological changes observed in AD, followed by an examination of astrocyte dysfunction as a feature of the disease. Lastly, the review explores the potential therapeutic implications of exercise-induced astrocyte remodeling in the context of AD.

Efficacy of GluN2B-Containing NMDA receptor antagonist for antitumor and antidepressant therapy in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is the predominant subtype of lung cancer. Evidence suggests that the ionotropic glutamate receptor N-methyl-D-aspartate (NMDA) receptor, a critical molecule in the central nervous system, is expressed in NSCLC. However, the specific expression patterns, subcellular localization, functional modulation, and pathological implications of NMDA receptor subtypes in NSCLC have not been fully elucidated. In this study, we employed a multi-disciplinary approach, combining biochemical and molecular biology with electrophysiological recordings and behavioral assays, to investigate these aspects. We reveal the expression of GluN2B-containing NMDA receptors in A549 and H460 NSCLC cell lines and the induction of NMDA receptor-mediated currents by glutamate in A549 cells. Furthermore, the GluN2B-specific inhibitors ifenprodil and Ro 25-6981 significantly reduced cell viability and migration, while promoting apoptosis. Importantly, intraperitoneal administration of ifenprodil in nude mice inhibited the growth of subcutaneous tumors derived from A549 and H460 cells and ameliorated depression-like behaviors. These findings underscore the potential antiproliferative effects of ifenprodil and Ro 25-6981 and suggest that GluN2B-containing NMDA receptors may represent novel therapeutic targets for NSCLC, with the added benefit of potential antidepressant action.

Neuroplasticity in the transition from acute to chronic pain

Acute pain is a transient sensation that typically serves as part of the body's defense mechanism. However, in certain patients, acute pain can evolve into chronic pain, which persists for months or even longer. Neuroplasticity refers to the capacity for variation and adaptive alterations in the morphology and functionality of neurons and synapses, and it plays a significant role in the transmission and modulation of pain. In this paper, we explore the molecular mechanisms and signaling pathways underlying neuroplasticity during the transition of pain. We also examine the effects of neurotransmitters, inflammatory mediators, and central sensitization on neuroplasticity, as well as the potential of neuroplasticity as a therapeutic strategy for preventing chronic pain. The aims of this article is to clarify the role of neuroplasticity in the transformation from acute pain to chronic pain, with the hope of providing a novel theoretical basis for unraveling the pathogenesis of chronic pain and offering more effective strategies and approaches for its diagnosis and treatment.

Caveolae with GLP-1 and NMDA Receptors as Crossfire Points for the Innovative Treatment of Cognitive Dysfunction Associated with Neurodegenerative Diseases

Some neurodegenerative diseases may be characterized by continuing behavioral and cognitive dysfunction that encompasses memory loss and/or apathy. Alzheimer's disease is the most typical type of such neurodegenerative diseases that are characterized by deficits of cognition and alterations of behavior. Despite the huge efforts against Alzheimer's disease, there has yet been no successful treatment for this disease. Interestingly, several possible risk genes for cognitive dysfunction are frequently expressed within brain cells, which may also be linked to cholesterol metabolism, lipid transport, exosomes, and/or caveolae formation, suggesting that caveolae may be a therapeutic target for cognitive dysfunctions. Interestingly, the modulation of autophagy/mitophagy with the alteration of glucagon-like peptide-1 (GLP-1) and N-methyl-d-aspartate (NMDA) receptor signaling may offer a novel approach to preventing and alleviating cognitive dysfunction. A paradigm showing that both GLP-1 and NMDA receptors at caveolae sites may be promising and crucial targets for the treatment of cognitive dysfunctions has been presented here, which may also be able to modify the progression of Alzheimer's disease. This research direction may create the potential to move clinical care toward disease-modifying treatment strategies with maximal benefits for patients without detrimental adverse events for neurodegenerative diseases.

Glucose-6-phosphate dehydrogenase alleviates epileptic seizures by repressing reactive oxygen species production to promote signal transducer and activator of transcription 1-mediated N-methyl-d-aspartic acid receptors inhibition

The pathogenesis of epilepsy remains unclear; however, a prevailing hypothesis suggests that the primary underlying cause is an imbalance between neuronal excitability and inhibition. Glucose-6-phosphate dehydrogenase (G6PD) is a key enzyme in the pentose phosphate pathway, which is primarily involved in deoxynucleic acid synthesis and antioxidant defense mechanisms and exhibits increased expression during the chronic phase of epilepsy, predominantly colocalizing with neurons. G6PD overexpression significantly reduces the frequency and duration of spontaneous recurrent seizures. Furthermore, G6PD overexpression enhances signal transducer and activator of transcription 1 (STAT1) expression, thus influencing N-methyl-d-aspartic acid receptors expression, and subsequently affecting seizure activity. Importantly, the regulation of STAT1 by G6PD appears to be mediated primarily through reactive oxygen species signaling pathways. Collectively, our findings highlight the pivotal role of G6PD in modulating epileptogenesis, and suggest its potential as a therapeutic target for epilepsy.

Molecular mechanism of ligand gating and opening of NMDA receptor

Glutamate transmission and activation of ionotropic glutamate receptors are the fundamental means by which neurons control their excitability and neuroplasticity1. The N-methyl-D-aspartate receptor (NMDAR) is unique among all ligand-gated channels, requiring two ligands-glutamate and glycine-for activation. These receptors function as heterotetrameric ion channels, with the channel opening dependent on the simultaneous binding of glycine and glutamate to the extracellular ligand-binding domains (LBDs) of the GluN1 and GluN2 subunits, respectively2,3. The exact molecular mechanism for channel gating by the two ligands has been unclear, particularly without structures representing the open channel and apo states. Here we show that the channel gate opening requires tension in the linker connecting the LBD and transmembrane domain (TMD) and rotation of the extracellular domain relative to the TMD. Using electron cryomicroscopy, we captured the structure of the GluN1-GluN2B (GluN1-2B) NMDAR in its open state bound to a positive allosteric modulator. This process rotates and bends the pore-forming helices in GluN1 and GluN2B, altering the symmetry of the TMD channel from pseudofourfold to twofold. Structures of GluN1-2B NMDAR in apo and single-liganded states showed that binding of either glycine or glutamate alone leads to distinct GluN1-2B dimer arrangements but insufficient tension in the LBD-TMD linker for channel opening. This mechanistic framework identifies a key determinant for channel gating and a potential pharmacological strategy for modulating NMDAR activity.

Dynamic role of GlyT1 as glycine sink or source: Pharmacological implications for the gain control of NMDA receptors

Glycine transporter 1 (GlyT1) mediates the termination of inhibitory glycinergic receptor signaling in the spinal cord and brainstem, and is also present diffusely in the forebrain. Here, it regulates the ambient glycine concentration and influences the 'glycine' site occupancy of N-methyl-d-aspartate receptors (NMDARs). GlyT1 is a reversible transporter with a substantial, but not excessive, sodium-motive force for uphill transport. This study investigates its role as a potential source of glycine supply, either by reverse uptake or heteroexchange. Indeed, glutamate alone does not induce NMDAR current in "naive" oocytes co-expressing GluN1/GluN2A and GlyT1, a previously characterized cellular model. However, after substantial intracellular glycine accumulation, GlyT1 reverses its transport mode, and begins to release glycine into the external compartment, allowing NMDAR activation by glutamate alone. These uptake-dependent glutamate currents were blocked by ALX-5407 and potentiated by sarcosine, a specific inhibitor and substrate of GlyT1, respectively, suggesting a higher occupancy of the co-agonist site when GlyT1 functions as a glycine source either by reversed-uptake or by heteroexchange. These two glycine release mechanisms can be distinguished by their voltage dependence, as the reversed-uptake cycle decreases at hyperpolarized potentials, whereas heteroexchange electroneutrality preserves glycine efflux and NMDAR activation at these potentials. These results establish GlyT1-mediated efflux as a positive regulator of NMDAR coagonist site occupancy, and demonstrate the efficacy of sarcosine heteroexchange in enhancing coagonist site occupancy. Because NMDAR facilitation by GlyT1-inhibitors and sarcosine relies on different transport mechanisms, their actions may be a source of variability in reversing NMDAR hypofunction in schizophrenia.

Interactions Involving Glycine and Other Amino Acid Neurotransmitters: Focus on Transporter-Mediated Regulation of Release and Glycine-Glutamate Crosstalk

Glycine plays a pivotal role in the Central Nervous System (CNS), being a major inhibitory neurotransmitter as well as a co-agonist of Glutamate at excitatory NMDA receptors. Interactions involving Glycine and other neurotransmitters are the subject of different studies. Functional interactions among neurotransmitters include the modulation of release through release-regulating receptors but also through transporter-mediated mechanisms. Many transporter-mediated interactions involve the amino acid transmitters Glycine, Glutamate, and GABA. Different studies published during the last two decades investigated a number of transporter-mediated interactions in depth involving amino acid transmitters at the nerve terminal level in different CNS areas, providing details of mechanisms involved and suggesting pathophysiological significances. Here, this evidence is reviewed also considering additional recent information available in the literature, with a special (but not exclusive) focus on glycinergic neurotransmission and Glycine-Glutamate interactions. Some possible pharmacological implications, although partly speculative, are also discussed. Dysregulations in glycinergic and glutamatergic transmission are involved in relevant CNS pathologies. Pharmacological interventions on glycinergic targets (including receptors and transporters) are under study to develop novel therapies against serious CNS pathological states including pain, schizophrenia, epilepsy, and neurodegenerative diseases. Although with limitations, it is hoped to possibly contribute to a better understanding of the complex interactions between glycine-mediated neurotransmission and other major amino acid transmitters, also in view of the current interest in potential drugs acting on "glycinergic" targets.

Disease-Associated Variants in GRIN1, GRIN2A and GRIN2B genes: Insights into NMDA Receptor Structure, Function, and Pathophysiology

N-methyl-D-aspartate receptors (NMDARs) are a subtype of ionotropic glutamate receptors critical for synaptic transmission and plasticity, and for the development of neural circuits. Rare or de-novo variants in GRIN genes encoding NMDAR subunits have been associated with neurodevelopmental disorders characterized by intellectual disability, developmental delay, autism, schizophrenia, or epilepsy. In recent years, some disease-associated variants in GRIN genes have been characterized using recombinant receptors expressed in non-neuronal cells, and a few variants have also been studied in neuronal preparations or animal models. Here we review the current literature on the functional evaluation of human disease-associated variants in GRIN1, GRIN2A and GRIN2B genes at all levels of analysis. Focusing on the impact of different patient variants at the level of receptor function, we discuss effects on receptor agonist and co-agonist affinity, channel open probability, and receptor cell surface expression. We consider how such receptor-level functional information may be used to classify variants as gain-of-function or loss-of-function, and discuss the limitations of this classification at the synaptic, cellular, or system level. Together this work by many laboratories worldwide yields valuable insights into NMDAR structure and function, and represents significant progress in the effort to understand and treat GRIN disorders. Keywords: NMDA receptor , GRIN genes, Genetic variants, Electrophysiology, Synapse, Animal models.

NMDA Receptor Antagonists: Emerging Insights into Molecular Mechanisms and Clinical Applications in Neurological Disorders

Neurodegenerative disorders (NDs) include a range of chronic conditions characterized by progressive neuronal loss, leading to cognitive, motor, and behavioral impairments. Common examples include Alzheimer's disease (AD) and Parkinson's disease (PD). The global prevalence of NDs is on the rise, imposing significant economic and social burdens. Despite extensive research, the mechanisms underlying NDs remain incompletely understood, hampering the development of effective treatments. Excitotoxicity, particularly glutamate-mediated excitotoxicity, is a key pathological process implicated in NDs. Targeting the N-methyl-D-aspartate (NMDA) receptor, which plays a central role in excitotoxicity, holds therapeutic promise. However, challenges, such as blood-brain barrier penetration and adverse effects, such as extrapyramidal effects, have hindered the success of many NMDA receptor antagonists in clinical trials. This review explores the molecular mechanisms of NMDA receptor antagonists, emphasizing their structure, function, types, challenges, and future prospects in treating NDs. Despite extensive research on competitive and noncompetitive NMDA receptor antagonists, the quest for effective treatments still faces significant hurdles. This is partly because the same NMDA receptor that necessitates blockage under pathological conditions is also responsible for the normal physiological function of NMDA receptors. Allosteric modulation of NMDA receptors presents a potential alternative, with the GluN2B subunit emerging as a particularly attractive target due to its enrichment in presynaptic and extrasynaptic NMDA receptors, which are major contributors to excitotoxic-induced neuronal cell death. Despite their low side-effect profiles, selective GluN2B antagonists like ifenprodil and radiprodil have encountered obstacles such as poor bioavailability in clinical trials. Moreover, the selectivity of these antagonists is often relative, as they have been shown to bind to other GluN2 subunits, albeit minimally. Recent advancements in developing phenanthroic and naphthoic acid derivatives offer promise for enhanced GluN2B, GluN2A or GluN2C/GluN2D selectivity and improved pharmacodynamic properties. Additional challenges in NMDA receptor antagonist development include conflicting preclinical and clinical results, as well as the complexity of neurodegenerative disorders and poorly defined NMDA receptor subtypes. Although multifunctional agents targeting multiple degenerative processes are also being explored, clinical data are limited. Designing and developing selective GluN2B antagonists/modulators with polycyclic moieties and multitarget properties would be significant in addressing neurodegenerative disorders. However, advancements in understanding NMDA receptor structure and function, coupled with collaborative efforts in drug design, are imperative for realizing the therapeutic potential of these NMDA receptor antagonists/modulators.

Investigation of metal ion binding biomolecules one molecule at a time

Metal ions can perform multiple roles ranging from regulatory to structural and are crucial for cell function. While some metal ions like Na+ are ubiquitously present at high concentrations, other ions, especially Ca2+ and transition metals, such as Zn2+ or Cu+/2+ are regulated. The concentrations above or below the physiological range cause severe changes in the behavior of biomolecules that bind them and subsequently affect the cell wellbeing. This has led to the development of specialized protocols to study metal ion binding biomolecules in bulk conditions that mimic the cell environment. Recently, there is growing evidence of influence of post-transcriptional and post-translational modifications on the affinity of the metal ion binding sites. However, such targets are difficult to obtain in amounts required for classical biophysical experiments. Single molecule techniques have revolutionized the field of biophysics, molecular and structural biology. Their biggest advantage is the ability to observe each molecule's interaction independently, without the need for synchronization. An additional benefit is its extremely low sample consumption. This feature allows characterization of designer biomolecules or targets obtained coming from natural sources. All types of biomolecules, including proteins, DNA and RNA were characterized using single molecule methods. However, one group is underrepresented in those studies. These are the metal ion binding biomolecules. Single molecule experiments often require separate optimization, due to extremely different concentrations used during the experiments. In this review we focus on single molecule methods, such as single molecule FRET, nanopores and optical tweezers that are used to study metal ion binding biomolecules. We summarize various examples of recently characterized targets and reported experimental conditions. Finally, we discuss the potential promises and pitfalls of single molecule characterization on metal ion binding biomolecules.