Neuronal glutathione deficiency and age-dependent neurodegeneration in the EAAC1 deficient mouse

L-Cysteine mitigates ROS-induced apoptosis and neurocognitive deficits by protecting against endoplasmic reticulum stress and mitochondrial dysfunction in mouse neuronal cells

Oxidative stress and mitochondrial dysfunction play critical roles in neurodegenerative diseases. Glutathione (GSH), a key brain antioxidant, helps to neutralize reactive oxygen species (ROS) and maintain redox balance. We investigated the effectiveness of L-cysteine (L-Cys) in preventing apoptosis induced by the ROS generator 2,3-dimethoxy-1,4-naphthoquinone (DMNQ) in mouse hippocampal neuronal HT22 cells, as well as alleviating memory and cognitive impairments caused by the GSH synthesis inhibitor L-buthionine sulfoximine (BSO) in mice. DMNQ-induced apoptotic events in HT22 cells, including elevated cytosolic and mitochondrial ROS levels, DNA fragmentation, endoplasmic reticulum stress, and mitochondrial damage-mediated apoptotic pathways were dose-dependently abrogated by L-Cys (0.5-2 mM). The reduced intracellular GSH level, caused by DMNQ treatment, was restored by L-Cys cotreatment. Although L-Cys did not significantly restore GSH in the presence of BSO, it prevented DMNQ-induced ROS elevation, mitochondrial damage, and apoptosis. Furthermore, compared to N-acetylcysteine and GSH, L-Cys had higher 2,2-diphenyl-1-picrylhydrazyl and 2,2-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid radical-scavenging activity. L-Cys also restored mitochondrial respiration capacity in DMNQ-treated HT22 cells by reversing mitochondrial fission-fusion dynamic balance. BSO administration (500 mg/kg/day) in mice led to neuronal deficits, including memory and cognitive impairments, which were effectively mitigated by oral L-Cys (15 or 30 mg/kg/day). L-Cys also reduced BSO-induced ROS levels in the mice hippocampus and cortex. These findings suggest that even though it does not contribute to intracellular GSH synthesis, exogenous L-Cys protects neuronal cells against oxidative stress-induced mitochondrial damage and apoptosis, by acting as a ROS scavenger, which is beneficial in ameliorating neurocognitive deficits caused by oxidative stress.

Hydrogen Sulfide: A Versatile Molecule and Therapeutic Target in Health and Diseases

In recent years, research has unveiled the significant role of hydrogen sulfide (H2S) in many physiological and pathological processes. The role of endogenous H2S, H2S donors, and inhibitors has been the subject of studies that have aimed to investigate this intriguing molecule. The mechanisms by which H2S contributes to different diseases, including inflammatory conditions, cardiovascular disease, viral infections, and neurological disorders, are complex. Despite noteworthy progress, several questions remain unanswered. H2S donors and inhibitors have shown significant therapeutic potential for various diseases. This review summarizes our current understanding of H2S-based therapeutics in inflammatory conditions, cardiovascular diseases, viral infections, and neurological disorders.

Increased forebrain EAAT3 expression confers resilience to chronic stress

Depression is a disabling and highly prevalent psychiatric illness. Multiple studies have linked glutamatergic dysfunction with the pathophysiology of depression, but the exact alterations in the glutamatergic system that contribute to depressive-like behaviors are not fully understood. Recent evidence suggests that a decreased level in neuronal glutamate transporter (EAAT3), known to control glutamate levels and limit the activation of glutamate receptors at synaptic sites, may contribute to the manifestation of a depressive phenotype. Here, we tested the possibility that increased EAAT3 expression at excitatory synapses could reduce the susceptibility of mice to develop depressive-like behaviors when challenged to a 5-week unpredictable chronic mild stress (UCMS) protocol. Mice overexpressing EAAT3 in the forebrain (EAAT3glo/CMKII) and control littermates (EAAT3glo) were assessed for depressive-like behaviors and long-term memory performance after being subjected to UCMS conditions. We found that, after UCMS, EAAT3glo/CMKII mice did not exhibit depressive-like behaviors or memory alterations observed in control mice. Moreover, we found that EAAT3glo/CMKII mice did not show alterations in phasic dopamine release in the nucleus accumbens neither in long-term synaptic plasticity in the CA1 region of the hippocampus after UCMS, as observed in control littermates. Altogether these results suggest that forebrain EAAT3 overexpression may be related to a resilient phenotype, both at behavioral and functional level, to the deleterious effect of chronic stress, highlighting the importance of neuronal EAAT3 in the pathophysiology of depressive-like behaviors.

Glutamatergic Neurotransmission in Aging and Neurodegenerative Diseases: A Potential Target to Improve Cognitive Impairment in Aging

Aging is characterized by the decline in many of the individual's capabilities. It has been recognized that the brain undergoes structural and functional changes during aging that are occasionally associated with the development of neurodegenerative diseases. In this sense, altered glutamatergic neurotransmission, which involves the release, binding, reuptake, and degradation of glutamate (Glu) in the brain, has been widely studied in physiological and pathophysiological aging. In particular, changes in glutamatergic neurotransmission are exacerbated during neurodegenerative diseases and are associated with cognitive impairment, characterized by difficulties in memory, learning, concentration, and decision-making. Thus, in the present manuscript, we aim to highlight the relevance of glutamatergic neurotransmission during cognitive impairment to develop novel strategies to prevent, ameliorate, or delay cognitive decline. To achieve this goal, we provide a comprehensive review of the changes reported in glutamatergic neurotransmission components, such as Glu transporters and receptors during physiological aging and in the most studied neurodegenerative diseases. Finally, we describe the current therapeutic strategies developed to target glutamatergic neurotransmission.

Amino acid transporters in neurological disorders and neuroprotective effects of cysteine derivatives

For most diseases and disorders occurring in the brain, the full causes behind them are yet unknown, but many show signs of dysfunction of amino acid transporters or abnormalities in amino acid metabolism. The blood-brain barrier (BBB) plays a key role in supporting the function of the central nervous system (CNS). Because of its unique structure, the BBB can maintain the optimal environment for CNS by controlling the passage of hydrophilic molecules from blood to the brain. Nutrients, such as amino acids, can cross the BBB via specific transporters. Many amino acids are essential for CNS function, and dysfunction of these amino acid transporters can lead to abnormalities in amino acid levels. This has been linked to causes behind certain genetic brain diseases, such as schizophrenia, autism spectrum disorder, and Huntington's disease (HD). One example of crucial amino acids is L-Cys, the rate-limiting factor in the biosynthesis of an important antioxidant, glutathione (GSH). Deficiency of L-Cys and GSH has been linked to oxidative stress and has been shown as a plausible cause behind certain CNS diseases, like schizophrenia and HD. This review presents the current status of potential L-Cys therapies and gives future directions that can be taken to improve amino acid transportation related to distinct CNS diseases.

Erythroid Differentiation Regulator 1 as a Regulator of Neuronal GSH Synthesis

Erythroid differentiation regulator 1 (Erdr1) is a cytokine known to play important roles in cell survival under stressful conditions, maintenance of cellular growth homeostasis, and activation of the immune system. However, the impact of Erdr1 on neurons remains undefined. In this study, we present novel evidence that Erdr1 plays a role in regulating glutathione (GSH) synthesis via glutamate transporter-associated protein 3-18 (GTRAP3-18), an anchor protein in the endoplasmic reticulum that holds excitatory amino acid carrier 1 (EAAC1) in neurons. Both DNA microarray and quantitative real-time PCR analyses revealed an approximately 2-fold increase in Erdr1 levels in the hippocampus of GTRAP3-18-deficient mice compared to those of wild-type mice. Knockdown of Erdr1 in vitro resulted in a decrease in GTRAP3-18 levels, leading to an increase in EAAC1 expression and intracellular GSH levels, and subsequently, cytoprotective effects against oxidative stress. Our findings shed light on the regulatory mechanisms involving Erdr1, GTRAP3-18, EAAC1, and GSH in the context of neuronal defense against oxidative stress. Understanding the intricate interplay among these molecules may pave the way for the development of promising therapeutic strategies for neurodegenerative disorders.

A Red-Emission Fluorescent Probe for Intracellular Biothiols and Hydrogen Sulfide Imaging in Living Cells

This research centers on the development and synthesis of a longwave fluorescence probe, labeled as 60T, designed for the simultaneous detection of hydrogen sulfide, cysteine/homocysteine, and glutathione. The probe showcases a swift response, good linearity range, and heightened sensitivity, boasting that the detection limits of the probe for Cys, Hcy, GSH and H2S were 0.140, 0.202, 0.259 and 0.396 μM, respectively. Notably, its efficacy in monitoring thiol status changes in live MCF-7 cells is underscored by a substantial decrease in fluorescence intensity upon exposure to the thiol trapping reagent, N-ethyl maleimide (NEM). With an impressive red emission signal at 630 nm and a substantial Stokes shift of 80 nm, this probe exhibits remarkable sensitivity and selectivity for biothiols and H2S, indicating promising applications in the diagnosis and surgical navigation of relevant cancers.

The role of glutamate and glutamine metabolism and related transporters in nerve cells

BACKGROUND

Glutamate and glutamine are the most abundant amino acids in the blood and play a crucial role in cell survival in the nervous system. Various transporters found in cell and mitochondrial membranes, such as the solute carriers (SLCs) superfamily, are responsible for maintaining the balance of glutamate and glutamine in the synaptic cleft and within cells. This balance affects the metabolism of glutamate and glutamine as non-essential amino acids.

AIMS

This review aims to provide an overview of the transporters and enzymes associated with glutamate and glutamine in neuronal cells.

DISCUSSION

We delve into the function of glutamate and glutamine in the nervous system by discussing the transporters involved in the glutamate-glutamine cycle and the key enzymes responsible for their mutual conversion. Additionally, we highlight the role of glutamate and glutamine as carbon and nitrogen donors, as well as their significance as precursors for the synthesis of reduced glutathione (GSH).

CONCLUSION

Glutamate and glutamine play a crucial role in the brain due to their special effects. It is essential to focus on understanding glutamate and glutamine metabolism to comprehend the physiological behavior of nerve cells and to treat nervous system disorders and cancer.

EAAT3 impedes oligodendrocyte remyelination in chronic cerebral hypoperfusion-induced white matter injury

BACKGROUND

Chronic cerebral hypoperfusion-induced demyelination causes progressive white matter injury, although the pathogenic pathways are unknown.

METHODS

The Single Cell Portal and PanglaoDB databases were used to analyze single-cell RNA sequencing experiments to determine the pattern of EAAT3 expression in CNS cells. Immunofluorescence (IF) was used to detect EAAT3 expression in oligodendrocytes and oligodendrocyte progenitor cells (OPCs). EAAT3 levels in mouse brains were measured using a western blot at various phases of development, as well as in traumatic brain injury (TBI) and intracerebral hemorrhage (ICH) mouse models. The mouse bilateral carotid artery stenosis (BCAS) model was used to create white matter injury. IF, Luxol Fast Blue staining, and electron microscopy were used to investigate the effect of remyelination. 5-Ethynyl-2-Deoxy Uridine staining, transwell chamber assays, and IF were used to examine the effects of OPCs' proliferation, migration, and differentiation in vivo and in vitro. The novel object recognition test, the Y-maze test, the rotarod test, and the grid walking test were used to examine the impact of behavioral modifications.

RESULTS

A considerable amount of EAAT3 was expressed in OPCs and mature oligodendrocytes, according to single-cell RNA sequencing data. During multiple critical phases of mouse brain development, there were no substantial changes in EAAT3 levels in the hippocampus, cerebral cortex, or white matter. Furthermore, neither the TBI nor ICH models significantly affected the levels of EAAT3 in the aforementioned brain areas. The chronic white matter injury caused by BCAS, on the other hand, resulted in a strikingly high level of EAAT3 expression in the oligodendroglia and white matter. Correspondingly, blocking EAAT3 assisted in the recovery of cognitive and motor impairment as well as the restoration of cerebral blood flow following BCAS. Furthermore, EAAT3 suppression was connected to improved OPCs' survival and proliferation in vivo as well as faster OPCs' proliferation, migration, and differentiation in vitro. Furthermore, this study revealed that the mTOR pathway is implicated in EAAT3-mediated remyelination.

CONCLUSIONS

Our findings provide the first evidence that abnormally high levels of oligodendroglial EAAT3 in chronic cerebral hypoperfusion impair OPCs' pro-remyelination actions, hence impeding white matter repair and functional recovery. EAAT3 inhibitors could be useful in the treatment of ischemia demyelination.

The "molecular soldiers" of the CNS: Astrocytes, a comprehensive review on their roles and molecular signatures

For a long time, neurons held the position of central players in the nervous system. Since there are far more astrocytes than neurons in the brain, it makes us wonder if these cells just take up space and support the neurons or if they are actively participating in central nervous system (CNS) homeostasis. Now, astrocytes' contribution to CNS physiology is appreciated as they are known to regulate ion and neurotransmitter levels, synapse formation and elimination, blood-brain barrier integrity, immune function, cerebral blood flow, and many more. In many neurological and psychiatric disorders, astrocyte functions are altered. Advancements in microscopic and transcriptomic tools revealed populations of astrocytes with varied morphology, electrophysiological properties, and transcriptomic profiles. Neuron-circuit-specific functions and neuron-specific interactions of astroglial subpopulations are found, which suggests that diversity is essential in carrying out diverse region-specific CNS functions. Investigations on heterogeneous astrocyte populations are revealing new astrocyte functions and their role in pathological conditions, opening a new therapeutic avenue for targeting neurological conditions. The true extent of astrocytic heterogeneity and its functional implications are yet to be fully explored. This review summarizes essential astrocytic functions and their relevance in pathological conditions and discusses astrocytic diversity in relation to morphology, function, and gene expression throughout the CNS.

Neuronal Senescence in the Aged Brain

Cellular senescence is a highly complicated cellular state that occurs throughout the lifespan of an organism. It has been well-defined in mitotic cells by various senescent features. Neurons are long-lived post-mitotic cells with special structures and functions. With age, neurons display morphological and functional changes, accompanying alterations in proteostasis, redox balance, and Ca2+ dynamics; however, it is ambiguous whether these neuronal changes belong to the features of neuronal senescence. In this review, we strive to identify and classify changes that are relatively specific to neurons in the aging brain and define them as features of neuronal senescence through comparisons with common senescent features. We also associate them with the functional decline of multiple cellular homeostasis systems, proposing the possibility that these systems are the main drivers of neuronal senescence. We hope this summary will serve as a steppingstone for further inputs on a comprehensive but relatively specific list of phenotypes for neuronal senescence and in particular their underlying molecular events during aging. This will in turn shine light on the association between neuronal senescence and neurodegeneration and lead to the development of strategies to perturb the processes.

Targeting ferroptosis opens new avenues for the development of novel therapeutics

Ferroptosis is an iron-dependent form of regulated cell death with distinct characteristics, including altered iron homeostasis, reduced defense against oxidative stress, and abnormal lipid peroxidation. Recent studies have provided compelling evidence supporting the notion that ferroptosis plays a key pathogenic role in many diseases such as various cancer types, neurodegenerative disease, diseases involving tissue and/or organ injury, and inflammatory and infectious diseases. Although the precise regulatory networks that underlie ferroptosis are largely unknown, particularly with respect to the initiation and progression of various diseases, ferroptosis is recognized as a bona fide target for the further development of treatment and prevention strategies. Over the past decade, considerable progress has been made in developing pharmacological agonists and antagonists for the treatment of these ferroptosis-related conditions. Here, we provide a detailed overview of our current knowledge regarding ferroptosis, its pathological roles, and its regulation during disease progression. Focusing on the use of chemical tools that target ferroptosis in preclinical studies, we also summarize recent advances in targeting ferroptosis across the growing spectrum of ferroptosis-associated pathogenic conditions. Finally, we discuss new challenges and opportunities for targeting ferroptosis as a potential strategy for treating ferroptosis-related diseases.

Glutathione-Mediated Neuroprotective Effect of Purine Derivatives

Numerous basic studies have reported on the neuroprotective properties of several purine derivatives such as caffeine and uric acid (UA). Epidemiological studies have also shown the inverse association of appropriate caffeine intake or serum urate levels with neurodegenerative diseases such as Alzheimer disease (AD) and Parkinson's disease (PD). The well-established neuroprotective mechanisms of caffeine and UA involve adenosine A2A receptor antagonism and antioxidant activity, respectively. Our recent study found that another purine derivative, paraxanthine, has neuroprotective effects similar to those of caffeine and UA. These purine derivatives can promote neuronal cysteine uptake through excitatory amino acid carrier protein 1 (EAAC1) to increase neuronal glutathione (GSH) levels in the brain. This review summarizes the GSH-mediated neuroprotective effects of purine derivatives. Considering the fact that GSH depletion is a manifestation in the brains of AD and PD patients, administration of purine derivatives may be a new therapeutic approach to prevent or delay the onset of these neurodegenerative diseases.

N-Acetylcysteine Amide against Aβ-Induced Alzheimer's-like Pathology in Rats

Oxidative stress with a depletion of glutathione is a key factor in the initiation and progression of Alzheimer's disease (AD). N-Acetylcysteine (NAC), a glutathione precursor, provides neuroprotective effects in AD animal models. Its amide form, N-Acetylcysteine amide (NACA), has an extended bioavailability compared to NAC. This study evaluates the neuroprotective effects of NACA against Aβ1-42 peptide-induced AD-like pathology in rats. Male Wistar rats (2.5 months old) were divided into five groups: Normal Control (NC), Sham (SH), Aβ, Aβ + NACA and NACA + Aβ + NACA (n = 8 in all groups). AD-like pathology was induced by the intracerebroventricular infusion of Aβ1-42 peptide into the lateral ventricle. NACA (75 mg/kg) was administered either as a restorative (i.e., injection of NACA for 7 consecutive days after inducing AD-like pathology (Aβ + N group)), or as prophylactic (for 7 days before and 7 days after inducing the pathology (N + Aβ + N group)). Learning and memory, neurogenesis, expression of AD pathology markers, antioxidant parameters, neuroprotection, astrogliosis and microgliosis were studied in the hippocampus and the prefrontal cortex. All data were analyzed with a one-way ANOVA test followed by Bonferroni's multiple comparison test. NACA treatment reversed the cognitive deficits and reduced oxidative stress in the hippocampus and prefrontal cortex. Western blot analysis for Tau, Synaptophysin and Aβ, as well as a histopathological evaluation through immunostaining for neurogenesis, the expression of neurofibrillary tangles, β-amyloid peptide, synaptophysin, neuronal morphology and gliosis, showed a neuroprotective effect of NACA. In conclusion, this study demonstrates the neuroprotective effects of NACA against β-amyloid induced AD-like pathology.

Pharmacological Inhibition of Ferroptosis as a Therapeutic Target for Neurodegenerative Diseases and Strokes

Emerging evidence suggests that ferroptosis, a unique regulated cell death modality that is morphologically and mechanistically different from other forms of cell death, plays a vital role in the pathophysiological process of neurodegenerative diseases, and strokes. Accumulating evidence supports ferroptosis as a critical factor of neurodegenerative diseases and strokes, and pharmacological inhibition of ferroptosis as a therapeutic target for these diseases. In this review article, the core mechanisms of ferroptosis are overviewed and the roles of ferroptosis in neurodegenerative diseases and strokes are described. Finally, the emerging findings in treating neurodegenerative diseases and strokes through pharmacological inhibition of ferroptosis are described. This review demonstrates that pharmacological inhibition of ferroptosis by bioactive small-molecule compounds (ferroptosis inhibitors) could be effective for treatments of these diseases, and highlights a potential promising therapeutic avenue that could be used to prevent neurodegenerative diseases and strokes. This review article will shed light on developing novel therapeutic regimens by pharmacological inhibition of ferroptosis to slow down the progression of these diseases in the future.

Antioxidant Therapy Reduces Oxidative Stress, Restores Na,K-ATPase Function and Induces Neuroprotection in Rodent Models of Seizure and Epilepsy: A Systematic Review and Meta-Analysis

Epilepsy is a neurological disorder characterized by epileptic seizures resulting from neuronal hyperexcitability, which may be related to failures in Na,K-ATPase activity and oxidative stress participation. We conducted this study to investigate the impact of antioxidant therapy on oxidative stress, Na,K-ATPase activity, seizure factors, and mortality in rodent seizure/epilepsy models induced by pentylenetetrazol (PTZ), pilocarpine (PILO), and kainic acid (KA). After screening 561 records in the MEDLINE, EMBASE, Web of Science, Science Direct, and Scopus databases, 22 were included in the systematic review following the PRISMA guidelines. The meta-analysis included 14 studies and showed that in epileptic animals there was an increase in the oxidizing agents nitric oxide (NO) and malondialdehyde (MDA), with a reduction in endogenous antioxidants reduced glutathione (GSH) and superoxide dismutase (SO). The Na,K-ATPase activity was reduced in all areas evaluated. Antioxidant therapy reversed all of these parameters altered by seizure or epilepsy induction. In addition, there was a percentage decrease in the number of seizures and mortality, and a meta-analysis showed a longer seizure latency in animals using antioxidant therapy. Thus, this study suggests that the use of antioxidants promotes neuroprotective effects and mitigates the effects of epilepsy. The protocol was registered in the Prospective Register of Systematic Reviews (PROSPERO) CRD42022356960.

Targeting the Cysteine Redox Proteome in Parkinson's Disease: The Role of Glutathione Precursors and Beyond

Encouraging recent data on the molecular pathways underlying aging have identified variants and expansions of genes associated with DNA replication and repair, telomere and stem cell maintenance, regulation of the redox microenvironment, and intercellular communication. In addition, cell rejuvenation requires silencing some transcription factors and the activation of pluripotency, indicating that hidden molecular networks must integrate and synchronize all these cellular mechanisms. Therefore, in addition to gene sequence expansions and variations associated with senescence, the optimization of transcriptional regulation and protein crosstalk is essential. The protein cysteinome is crucial in cellular regulation and plays unexpected roles in the aging of complex organisms, which show cumulative somatic mutations, telomere attrition, epigenetic modifications, and oxidative dysregulation, culminating in cellular senescence. The cysteine thiol groups are highly redox-active, allowing high functional versatility as structural disulfides, redox-active disulfides, active-site nucleophiles, proton donors, and metal ligands to participate in multiple regulatory sites in proteins. Also, antioxidant systems control diverse cellular functions, including the transcription machinery, which partially depends on the catalytically active cysteines that can reduce disulfide bonds in numerous target proteins, driving their biological integration. Since we have previously proposed a fundamental role of cysteine-mediated redox deregulation in neurodegeneration, we suggest that cellular rejuvenation of the cysteine redox proteome using GSH precursors, like N-acetyl-cysteine, is an underestimated multitarget therapeutic approach that would be particularly beneficial in Parkinson's disease.

Appraising the Role of Astrocytes as Suppliers of Neuronal Glutathione Precursors

The metabolism and intercellular transfer of glutathione or its precursors may play an important role in cellular defense against oxidative stress, a common hallmark of neurodegeneration. In the 1990s, several studies in the Neurobiology field led to the widely accepted notion that astrocytes produce large amounts of glutathione that serve to feed neurons with precursors for glutathione synthesis. This assumption has important implications for health and disease since a reduction in this supply from astrocytes could compromise the capacity of neurons to cope with oxidative stress. However, at first glance, this shuttling would imply a large energy expenditure to get to the same point in a nearby cell. Thus, are there additional underlying reasons for this expensive mechanism? Are neurons unable to import and/or synthesize the three non-essential amino acids that are the glutathione building blocks? The rather oxidizing extracellular environment favors the presence of cysteine (Cys) as cystine (Cis), less favorable for neuronal import. Therefore, it has also been proposed that astrocytic GSH efflux could induce a change in the redox status of the extracellular space nearby the neurons, locally lowering the Cis/Cys ratio. This astrocytic glutathione release would also increase their demand for precursors, stimulating Cis uptake, which these cells can import, further impacting the local decline of the Cis/Cys ratio, in turn, contributing to a more reduced extracellular environment and subsequently favoring neuronal Cys import. Here, we revisit the experimental evidence that led to the accepted hypothesis of astrocytes acting as suppliers of neuronal glutathione precursors, considering recent data from the Human Protein Atlas. In addition, we highlight some potential drawbacks of this hypothesis, mainly supported by heterogeneous cellular models. Finally, we outline additional and more cost-efficient possibilities by which astrocytes could support neuronal glutathione levels, including its shuttling in extracellular vesicles.

Defects in Glutathione System in an Animal Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a progredient neurodegenerative disease characterized by a degeneration of the first and second motor neurons. Elevated levels of reactive oxygen species (ROS) and decreased levels of glutathione, which are important defense mechanisms against ROS, have been reported in the central nervous system (CNS) of ALS patients and animal models. The aim of this study was to determine the cause of decreased glutathione levels in the CNS of the ALS model wobbler mouse. We analyzed changes in glutathione metabolism in the spinal cord, hippocampus, cerebellum, liver, and blood samples of the ALS model, wobbler mouse, using qPCR, Western Blot, HPLC, and fluorometric assays. Here, we show for the first time a decreased expression of enzymes involved in glutathione synthesis in the cervical spinal cord of wobbler mice. We provide evidence for a deficient glutathione metabolism, which is not restricted to the nervous system, but can be seen in various tissues of the wobbler mouse. This deficient system is most likely the reason for an inefficient antioxidative system and, thus, for elevated ROS levels.

Nox4-and Tf/TfR-mediated peroxidation and iron overload exacerbate neuronal ferroptosis after intracerebral hemorrhage: Involvement of EAAT3 dysfunction

Intracerebral hemorrhage (ICH) induces high mortality and disability. Neuronal death is the principal factor to unfavourable prognosis in ICH. However, the mechanisms underlying this association remain unclear. In this study, we investigated the molecular mechanisms by which neuronal ferroptosis occurs after ICH and whether the use of corresponding modulators can inhibit neuronal death and improve early outcomes in a rat ICH model. Our findings indicated that Nox4 and TF/TfR were upregulated in the perihematomal tissues of ICH rats. Oxidative stress and iron overload induced by Nox4 and TF/TfR promoted neuronal ferroptosis post-ICH. In contrast, application of Nox4-siRNA and the deferoxamine (DFO) attenuated peroxidation and iron deposition in the hemorrhagic brain, alleviated neuronal ferroptosis, and improved sensorimotor function in ICH rats. Additionally, our findings indicated that the post-ICH neuronal reduced glutathione (GSH) depletion were not related to dysfunctional glutamine delivery in astrocytes but rather to downregulation of EAAT3 due to lipid peroxidation-induced dysfunction in the neuronal membrane. These findings indicate that ferroptosis is involved in neuronal death in model rats with collagenase-induced ICH. Oxidative stress and iron overload induced by Nox4 and TF/TfR exacerbate ferroptosis after ICH, while Nox4 downregulation and iron chelation exert neuroprotective effects. The present results highlight the cysteine importer EAAT3 as a potential biomarker of ferroptosis and provide insight into the neuronal death process that occurs following ICH, which may aid in the development of translational treatment strategies for ICH.

DOPA pheomelanin is increased in nigral neuromelanin of Parkinson's disease

Neuromelanin (NM) in dopaminergic neurons of human substantia nigra (SN) has a melanic component that consists of pheomelanin and eumelanin moieties and has been proposed as a key factor contributing to dopaminergic neuron vulnerability in Parkinson's disease (PD). While eumelanin is considered as an antioxidant, pheomelanin and related oxidative stress are associated with compromised drug and metal ion binding and melanoma risk. Using postmortem SN from patients with PD or Alzheimer's disease (AD) and unaffected controls, we identified increased L-3,4-dihydroxyphenylalanine (DOPA) pheomelanin and increased ratios of dopamine (DA) pheomelanin markers to DA in PD SN compared to controls. Eumelanins derived from both DOPA and DA were reduced in PD group. In addition, we report an increase in DOPA pheomelanin relative to DA pheomelanin in PD SN. In AD SN, we observed unaltered melanin markers despite reduced DOPA compared to controls. Furthermore, synthetic DOPA pheomelanin induced neuronal cell death in vitro while synthetic DOPA eumelanin showed no significant effect on cell viability. Our findings provide insights into the different roles of pheomelanin and eumelanin in PD pathophysiology. We anticipate our study will lead to further investigations on pheomelanin and eumelanin individually as biomarkers and possibly therapeutic targets for PD.

Advances of H2S in Regulating Neurodegenerative Diseases by Preserving Mitochondria Function

Neurotoxicity is induced by different toxic substances, including environmental chemicals, drugs, and pathogenic toxins, resulting in oxidative damage and neurodegeneration in mammals. The nervous system is extremely vulnerable to oxidative stress because of its high oxygen demand. Mitochondria are the main source of ATP production in the brain neuron, and oxidative stress-caused mitochondrial dysfunction is implicated in neurodegenerative diseases. H2S was initially identified as a toxic gas; however, more recently, it has been recognized as a neuromodulator as well as a neuroprotectant. Specifically, it modulates mitochondrial activity, and H2S oxidation in mitochondria produces various reactive sulfur species, thus modifying proteins through sulfhydration. This review focused on highlighting the neuron modulation role of H2S in regulating neurodegenerative diseases through anti-oxidative, anti-inflammatory, anti-apoptotic and S-sulfhydration, and emphasized the importance of H2S as a therapeutic molecule for neurological diseases.

Multiple low-dose radiation-induced neuronal cysteine transporter expression and oxidative stress are rescued by N-acetylcysteine in neuronal SH-SY5Y cells

Recently, several studies have demonstrated that low-dose radiation (LDR) therapy has positively impacts on the treatment of Alzheimer's disease (AD). LDR suppresses the production of pro-neuroinflammation molecules and improves cognitive function in AD. However, it is unclear whether direct exposure to LDR causes beneficial effects and what mechanism is involved in neuronal cells. In this study, we first determined the effect of high-dose radiation (HDR) alone on C6 cells and SH-SY5Y cells. We found that SH-SY5Y cells were more vulnerable than C6 cells to HDR. Moreover, in neuronal SH-SY5Y cells exposed to single or multiple LDR, N-type cells showed decreased cell viability with increasing radiation exposure time and frequency, but S-type cells were unaffected. Multiple LDR increased proapoptotic molecules such as p53, Bax and cleaved caspase-3, and decreased anti-apoptotic molecule (Bcl₂). Multiple LDR also generated free radicals in neuronal SH-SY5Y cells. We detected a change in the expression of the neuronal cysteine transporter EAAC1. Pretreatment with N-acetylcysteine (NAC) rescued the increased in EAAC1 expression and the generation of ROS in neuronal SH-SY5Y cells after multiple LDR. Furthermore, we verified whether the increased in EAAC1 expression induces cell defense or cell death promotion signaling. We showed that transient overexpression of EAAC1 reduced the multiple LDR-induced p53 overexpression in neuronal SH-SY5Y cells. Our results indicate that neuronal cells can be injured by increased production of ROS not only by HDR but also by multiple LDR, which suggests that combination treatment with anti-free radical agents such as NAC may be useful in multiple LDR therapy.

The Protective Role of Glutathione on Zinc-Induced Neuron Death after Brain Injuries

Glutathione (GSH) is necessary for maintaining physiological antioxidant function, which is responsible for maintaining free radicals derived from reactive oxygen species at low levels and is associated with improved cognitive performance after brain injury. GSH is produced by the linkage of tripeptides that consist of glutamic acid, cysteine, and glycine. The adequate supplementation of GSH has neuroprotective effects in several brain injuries such as cerebral ischemia, hypoglycemia, and traumatic brain injury. Brain injuries produce an excess of reactive oxygen species through complex biochemical cascades, which exacerbates primary neuronal damage. GSH concentrations are known to be closely correlated with the activities of certain genes such as excitatory amino acid carrier 1 (EAAC1), glutamate transporter-associated protein 3-18 (Gtrap3-18), and zinc transporter 3 (ZnT3). Following brain-injury-induced oxidative stress, EAAC1 function is negatively impacted, which then reduces cysteine absorption and impairs neuronal GSH synthesis. In these circumstances, vesicular zinc is also released into the synaptic cleft and then translocated into postsynaptic neurons. The excessive influx of zinc inhibits glutathione reductase, which inhibits GSH's antioxidant functions in neurons, resulting in neuronal damage and ultimately in the impairment of cognitive function. Therefore, in this review, we explore the overall relationship between zinc and GSH in terms of oxidative stress and neuronal cell death. Furthermore, we seek to understand how the modulation of zinc can rescue brain-insult-induced neuronal death after ischemia, hypoglycemia, and traumatic brain injury.

Understanding the Molecular Progression of Chronic Traumatic Encephalopathy in Traumatic Brain Injury, Aging and Neurodegenerative Disease

Traumatic brain injury (TBI) is one of the leading causes of death and disability among children and adults in America. In addition, the acute morbidity caused by TBI is implicated in the development of devastating neuropsychiatric and neurodegenerative sequela. TBI is associated with the development of a neurodegenerative condition termed 'Punch Drunk syndrome' or 'dementia pugilistica', and the more recently renamed 'chronic traumatic encephalopathy'. Chronic traumatic encephalopathy (CTE) is a slowly progressive neurodegenerative condition caused by a single or repetitive blow to the head. CTE was first described in boxers and was later found to be associated with other contact sports and military combat. It is defined by a constellation of symptoms consisting of mood disorders, cognitive impairment, and memory loss with or without sensorimotor changes. It is also a Tauopathy characterized by the deposition of hyperphosphorylated Tau protein in the form of neurofibrillary tangles, astrocytoma tangles, and abnormal neurites found in clusters around small vessels, typically at the sulcal depths. Oxidative stress, neuroinflammation, and glutaminergic toxicity caused due to the insult play a role in developing this pathology. Additionally, the changes in the brain due to aging also plays an important role in the development of this condition. In this review, we discuss the molecular mechanisms behind the development of CTE, as well as genetic and environmental influences on its pathophysiology.

Neuronal Oxidative Stress Promotes α-Synuclein Aggregation In Vivo

Both genetic and environmental factors increase risk for Parkinson's disease. Many of the known genetic factors influence α-synuclein aggregation or degradation, whereas most of the identified environmental factors produce oxidative stress. Studies using in vitro approaches have identified mechanisms by which oxidative stress can accelerate the formation of α-synuclein aggregates, but there is a paucity of evidence supporting the importance of these processes over extended time periods in brain. To assess this issue, we evaluated α-synuclein aggregates in brains of three transgenic mouse strains: hSyn mice, which overexpress human α-synuclein in neurons and spontaneously develop α-synuclein aggregates; EAAT3^-/- mice, which exhibit a neuron-specific impairment in cysteine uptake and resultant neuron-selective chronic oxidative stress; and double-transgenic hSyn/EAAT3^-/- mice. Aggregate formation was evaluated by quantitative immunohistochemistry for phosphoserine 129 α-synuclein and by an α-synuclein proximity ligation assay. Both methods showed that the double transgenic hSyn/EAAT3^-/- mice exhibited a significantly higher α-synuclein aggregate density than littermate hSyn mice in each brain region examined. Negligible aggregate formation was observed in the EAAT3^-/- mouse strain, suggesting a synergistic rather than additive interaction between the two genotypes. A similar pattern of results was observed in assessments of motor function: the pole test and rotarod test. Together, these observations indicate that chronic, low-grade neuronal oxidative stress promotes α-synuclein aggregate formation in vivo. This process may contribute to the mechanism by which environmentally induced oxidative stress contributes to α-synuclein pathology in idiopathic Parkinson's disease.

Glutathione Depletion and MicroRNA Dysregulation in Multiple System Atrophy: A Review

Multiple system atrophy (MSA) is a rare neurodegenerative disease characterized by parkinsonism, cerebellar impairment, and autonomic failure. Although the causes of MSA onset and progression remain uncertain, its pathogenesis may involve oxidative stress via the generation of excess reactive oxygen species and/or destruction of the antioxidant system. One of the most powerful antioxidants is glutathione, which plays essential roles as an antioxidant enzyme cofactor, cysteine-storage molecule, major redox buffer, and neuromodulator, in addition to being a key antioxidant in the central nervous system. Glutathione levels are known to be reduced in neurodegenerative diseases. In addition, genes regulating redox states have been shown to be post-transcriptionally modified by microRNA (miRNA), one of the most important types of non-coding RNA. miRNAs have been reported to be dysregulated in several diseases, including MSA. In this review, we focused on the relation between glutathione deficiency, miRNA dysregulation and oxidative stress and their close relation with MSA pathology.

An indanone-based fluorescent probe for detection and imaging of Cys/Hcy in living cells

Effective detection of Cys and Hcy plays an important role in the diagnosis of diseases. In this work, a novel indanone-based fluorescent probe INIAc-CN for sensitively and effectively detecting Cys and Hcy was developed. The probe exhibited weak fluorescence, but obvious fluorescent enhancement after reacted with Cys/Hcy. Moreover, the good anti-interference and low cytotoxicity of the probe made it successfully applied for monitoring Cys and Hcy of in living cells.

Developmental neurotoxicity of silver nanoparticles: the current state of knowledge and future directions

The increasing production and use of silver nanoparticles (AgNPs) as an antimicrobial agent in an array of medical and commercial products, including those designed for infants and children, poses a substantial risk of exposure during the developmental period. This review summarizes current knowledge on developmental neurotoxicity of AgNPs in both pre- and post-natal stages with a focus on the biological specificity of immature organisms that predisposes them to neurotoxic insults as well as the molecular mechanisms underlying AgNP-induced neurotoxicity. The current review revealed that AgNPs increase the permeability of the blood-brain barrier (BBB) and selectively damage neurons in the brain of immature rats exposed pre and postnatally. Among the AgNP-induced molecular mechanisms underlying toxic insult is cellular stress, which can consequently lead to cell death. Glutamatergic neurons and NMDAR-mediated neurotransmission also appear to be a target for AgNPs during the postnatal period of exposure. Collected data indicate also that our current knowledge of the impact of AgNPs on the developing nervous system remains insufficient and further studies are required during different stages of development with investigation of environmentally-relevant doses of exposure.

Mutant Huntingtin Derails Cysteine Metabolism in Huntington's Disease at Both Transcriptional and Post-Translational Levels

Cysteine is a semi-essential amino acid that not only plays an essential role as a component of protein synthesis, but also in the generation of numerous sulfur-containing molecules such as the antioxidant glutathione and coenzyme A. We previously showed that the metabolism of cysteine is dysregulated in Huntington's disease (HD), a neurodegenerative disorder triggered by the expansion of polyglutamine repeats in the protein huntingtin. In this study, we showed that cysteine metabolism is compromised at multiple levels in HD, both transcriptional and post-translational. Accordingly, restoring cysteine homeostasis may be beneficial in HD.

Enhancement of Phosphorylation and Transport Activity of the Neuronal Glutamate Transporter Excitatory Amino Acid Transporter 3 by C3bot and a 26mer C3bot Peptide

In primary murine hippocampal neurons we investigated the regulation of EAAT3-mediated glutamate transport by the Clostridium botulinum C3 transferase C3bot and a 26mer peptide derived from full length protein. Incubation with either enzyme-competent C3bot or enzyme-deficient C3bot156–181 peptide resulted in the upregulation of glutamate uptake by up to 22% compared to untreated cells. A similar enhancement of glutamate transport was also achieved by the classical phorbol-ester-mediated activation of protein kinase C subtypes. Yet comparable, effects elicited by C3 preparations seemed not to rely on PKCα, γ, ε, or ζ activation. Blocking of tyrosine phosphorylation by tyrosine kinase inhibitors prevented the observed effect mediated by C3bot and C3bot 26mer. By using biochemical and molecular biological assays we could rule out that the observed C3bot and C3bot 26mer-mediated effects solely resulted from enhanced transporter expression or translocation to the neuronal surface but was rather mediated by transporter phosphorylation at tyrosine residues that was found to be significantly enhanced following incubation with either full length protein or the 26mer C3 peptide.

Changes of Serum Homocysteine and Vitamin B12, but Not Folate Are Correlated With Obsessive-Compulsive Disorder: A Systematic Review and Meta-Analysis of Case-Control Studies

Background

Obsessive-compulsive disorder (OCD) a complex neuropsychiatric disorder, is characterized by irresistible obsessive thinking and compulsive behavior. Folate is a member of water-soluble vitamins in the human body and sustains many normal daily activities (e.g., exercise, sleep, and memory). Homocysteine, a sulfur-containing non-essential amino acid, has been investigated in numerous psychiatric disorders (e.g., OCD). Vitamin B12 is a type of complex organic compound with cobalt contained. Moreover, vitamin B12 and folate deficiency and high levels of homocysteine were found to have an effect on brain functions and also lead to non-specific psychiatric symptoms.

Objectives

This study aimed to confirm the epidemiological evidence of OCD and investigate whether vitamin B12, folate, and homocysteine have an effect on the etiology of OCD.

Methods

A systematic search was conducted on eight databases (i.e., PubMed, Embase, Web of Science, the Cochrane Library, China Biology Medicine disc, China National Knowledge Infrastructure, Wanfang Database, China Science and Technology Journal Database), and the retrieval time was up to March 2021. The available articles involving patients with OCD with/without abnormal serum levels of vitamin B12, folate, and homocysteine were comprehensively reviewed and analyzed.

Results

A total of 5 studies involving 309 patients were included in this meta-analysis, including 172 cases in the experimental group and 137 in the control group. The content of folate in the OCD group was not significantly different from that in the control group (SMD = -0.089, 95%CI -0.755 to 0.577, p = 0.794). And serum homocysteine was significantly higher in the patients with OCD (SMD = 1.132, 95%CI 0.486 to 1.778, p = 0.001). Vitamin B12 was significantly lower in patients with OCD (SMD = -0.583, 95%CI -0.938 to -0.229, p = 0.001).

Conclusions

This meta-analysis shows serum high levels of homocysteine, low levels of vitamin B12, and normal folate level are closely correlated with OCD. However, high-quality case-control studies should be further conducted to explore the correlation between serum levels of vitamin B12, folate, homocysteine, and OCD.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021262161; PROSPERO (Number CRD#42021262161).

Nuclear and Cytoplasmatic Players in Mitochondria-Related CNS Disorders: Chromatin Modifications and Subcellular Trafficking

Aberrant mitochondrial phenotypes are common to many central nervous system (CNS) disorders, including neurodegenerative and neurodevelopmental diseases. Mitochondrial function and homeostasis depend on proper control of several biological processes such as chromatin remodeling and transcriptional control, post-transcriptional events, vesicle and organelle subcellular trafficking, fusion, and morphogenesis. Mutation or impaired regulation of major players that orchestrate such processes can disrupt cellular and mitochondrial dynamics, contributing to neurological disorders. The first part of this review provides an overview of a functional relationship between chromatin players and mitochondria. Specifically, we relied on specific monogenic CNS disorders which share features with mitochondrial diseases. On the other hand, subcellular trafficking is coordinated directly or indirectly through evolutionarily conserved domains and proteins that regulate the dynamics of membrane compartments and organelles, including mitochondria. Among these “building blocks”, longin domains and small GTPases are involved in autophagy and mitophagy, cell reshaping, and organelle fusion. Impairments in those processes significantly impact CNS as well and are discussed in the second part of the review. Hopefully, in filling the functional gap between the nucleus and cytoplasmic organelles new routes for therapy could be disclosed.

Developmental impact of glutamate transporter overexpression on dopaminergic neuron activity and stereotypic behavior

Obsessive-compulsive disorder (OCD) is a disabling condition that often begins in childhood. Genetic studies in OCD have pointed to SLC1A1, which encodes the neuronal glutamate transporter EAAT3, with evidence suggesting that increased expression contributes to risk. In mice, midbrain Slc1a1 expression supports repetitive behavior in response to dopaminergic agonists, aligning with neuroimaging and pharmacologic challenge studies that have implicated the dopaminergic system in OCD. These findings suggest that Slc1a1 may contribute to compulsive behavior through altered dopaminergic transmission; however, this theory has not been mechanistically tested. To examine the developmental impact of Slc1a1 overexpression on compulsive-like behaviors, we, therefore, generated a novel mouse model to perform targeted, reversible overexpression of Slc1a1 in dopaminergic neurons. Mice with life-long overexpression of Slc1a1 showed a significant increase in amphetamine (AMPH)-induced stereotypy and hyperlocomotion. Single-unit recordings demonstrated that Slc1a1 overexpression was associated with increased firing of dopaminergic neurons. Furthermore, dLight1.1 fiber photometry showed that these behavioral abnormalities were associated with increased dorsal striatum dopamine release. In contrast, no impact of overexpression was observed on anxiety-like behaviors or SKF-38393-induced grooming. Importantly, overexpression solely in adulthood failed to recapitulate these behavioral phenotypes, suggesting that overexpression during development is necessary to generate AMPH-induced phenotypes. However, doxycycline-induced reversal of Slc1a1/EAAT3 overexpression in adulthood normalized both the increased dopaminergic firing and AMPH-induced responses. These data indicate that the pathologic effects of Slc1a1/EAAT3 overexpression on dopaminergic neurotransmission and AMPH-induced stereotyped behavior are developmentally mediated, and support normalization of EAAT3 activity as a potential treatment target for basal ganglia-mediated repetitive behaviors.

N-Acetyl-Cysteine: Modulating the Cysteine Redox Proteome in Neurodegenerative Diseases

In the last twenty years, significant progress in understanding the pathophysiology of age-associated neurodegenerative diseases has been made. However, the prevention and treatment of these diseases remain without clinically significant therapeutic advancement. While we still hope for some potential genetic therapeutic approaches, the current reality is far from substantial progress. With this state of the issue, emphasis should be placed on early diagnosis and prompt intervention in patients with increased risk of neurodegenerative diseases to slow down their progression, poor prognosis, and decreasing quality of life. Accordingly, it is urgent to implement interventions addressing the psychosocial and biochemical disturbances we know are central in managing the evolution of these disorders. Genomic and proteomic studies have shown the high molecular intricacy in neurodegenerative diseases, involving a broad spectrum of cellular pathways underlying disease progression. Recent investigations indicate that the dysregulation of the sensitive-cysteine proteome may be a concurrent pathogenic mechanism contributing to the pathophysiology of major neurodegenerative diseases, opening new therapeutic opportunities. Considering the incidence and prevalence of these disorders and their already significant burden in Western societies, they will become a real pandemic in the following decades. Therefore, we propose large-scale investigations, in selected groups of people over 40 years of age with decreased blood glutathione levels, comorbidities, and/or mild cognitive impairment, to evaluate supplementation of the diet with low doses of N-acetyl-cysteine, a promising and well-tolerated therapeutic agent suitable for long-term use.

Neuron-glia (mis)interactions in brain energy metabolism during aging

Life expectancy in humans is increasing, resulting in a growing aging population, that is accompanied by an increased disposition to develop cognitive deterioration. Hypometabolism is one of the multiple factors related to inefficient brain function during aging. This review emphasizes the metabolic interactions between glial cells (astrocytes, oligodendrocytes, and microglia) and neurons, particularly, during aging. Glial cells provide support and protection to neurons allowing adequate synaptic activity. We address metabolic coupling from the expression of transporters, availability of substrates, metabolic pathways, and mitochondrial activity. In aging, the main metabolic exchange machinery is altered with inefficient levels of nutrients and detrimental mitochondrial activity that results in high reactive oxygen species levels and reduced ATP production, generating a highly inflammatory environment that favors deregulated cell death. Here, we provide an overview of the glial-to-neuron mechanisms, from the molecular components to the cell types, emphasizing aging as the crucial risk factor for developing neurodegenerative/neuroinflammatory diseases.

Rapid Regulation of Glutamate Transport: Where Do We Go from Here?

Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system (CNS). A family of five Na⁺-dependent transporters maintain low levels of extracellular glutamate and shape excitatory signaling. Shortly after the research group of the person being honored in this special issue (Dr. Baruch Kanner) cloned one of these transporters, his group and several others showed that their activity can be acutely (within minutes to hours) regulated. Since this time, several different signals and post-translational modifications have been implicated in the regulation of these transporters. In this review, we will provide a brief introduction to the distribution and function of this family of glutamate transporters. This will be followed by a discussion of the signals that rapidly control the activity and/or localization of these transporters, including protein kinase C, ubiquitination, glutamate transporter substrates, nitrosylation, and palmitoylation. We also include the results of our attempts to define the role of palmitoylation in the regulation of GLT-1 in crude synaptosomes. In some cases, the mechanisms have been fairly well-defined, but in others, the mechanisms are not understood. In several cases, contradictory phenomena have been observed by more than one group; we describe these studies with the goal of identifying the opportunities for advancing the field. Abnormal glutamatergic signaling has been implicated in a wide variety of psychiatric and neurologic disorders. Although recent studies have begun to link regulation of glutamate transporters to the pathogenesis of these disorders, it will be difficult to determine how regulation influences signaling or pathophysiology of glutamate without a better understanding of the mechanisms involved.

Regulation of NRG-1-ErbB4 signaling and neuroprotection by exogenous neuregulin-1 in a mouse model of epilepsy

Temporal lobe epilepsy (TLE) is the most common form of focal epilepsy. Dysregulation of glutamate transporters has been a common finding across animal models of epilepsy and in patients with TLE. In this study, we investigate NRG-1/ErbB4 signaling in epileptogenesis and the neuroprotective effects of NRG-1 treatment in a mouse model of temporal lobe epilepsy. Using immunohistochemistry, we report the first evidence for NRG-1/ErbB4-dependent selective upregulation of glutamate transporter EAAC1 and bihemispheric neuroprotection by exogeneous NRG-1 in the intrahippocampal kainic acid (IHKA) model of TLE. Our findings provide evidence that dysregulation of glutamate transporter EAAC1 contributes to the development of epilepsy and can be therapeutically targeted to reduce neuronal death following IHKA-induced status epilepticus (SE).

Brain areas involved with obsessive-compulsive disorder present different DNA methylation modulation

Background

Obsessive-compulsive disorder (OCD) is characterized by intrusive thoughts and repetitive actions, that presents the involvement of the cortico-striatal areas. The contribution of environmental risk factors to OCD development suggests that epigenetic mechanisms may contribute to its pathophysiology. DNA methylation changes and gene expression were evaluated in post-mortem brain tissues of the cortical (anterior cingulate gyrus and orbitofrontal cortex) and ventral striatum (nucleus accumbens, caudate nucleus and putamen) areas from eight OCD patients and eight matched controls.

Results

There were no differentially methylated CpG (cytosine-phosphate-guanine) sites (DMSs) in any brain area, nevertheless gene modules generated from CpG sites and protein-protein-interaction (PPI) showed enriched gene modules for all brain areas between OCD cases and controls. All brain areas but nucleus accumbens presented a predominantly hypomethylation pattern for the differentially methylated regions (DMRs). Although there were common transcriptional factors that targeted these DMRs, their targeted differentially expressed genes were different among all brain areas. The protein-protein interaction network based on methylation and gene expression data reported that all brain areas were enriched for G-protein signaling pathway, immune response, apoptosis and synapse biological processes but each brain area also presented enrichment of specific signaling pathways. Finally, OCD patients and controls did not present significant DNA methylation age differences.

Conclusions

DNA methylation changes in brain areas involved with OCD, especially those involved with genes related to synaptic plasticity and the immune system could mediate the action of genetic and environmental factors associated with OCD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12863-021-00993-0.

Effects of Panthenol and N-Acetylcysteine on Changes in the Redox State of Brain Mitochondria under Oxidative Stress In Vitro

The glutathione system in the mitochondria of the brain plays an important role in maintaining the redox balance and thiol–disulfide homeostasis, whose violations are the important component of the biochemical shifts in neurodegenerative diseases. Mitochondrial dysfunction is known to be accompanied by the activation of free radical processes, changes in energy metabolism, and is involved in the induction of apoptotic signals. The formation of disulfide bonds is a leading factor in the folding and maintenance of the three-dimensional conformation of many specific proteins that selectively accumulate in brain structures during neurodegenerative pathology. In this study, we estimated brain mitochondria redox status and functioning during induction of oxidative damage in vitro. We have shown that the development of oxidative stress in vitro is accompanied by inhibition of energy metabolism in the brain mitochondria, a shift in the redox potential of the glutathione system to the oxidized side, and activation of S-glutathionylation of proteins. Moreover, we studied the effects of pantothenic acid derivatives—precursors of coenzyme A (CoA), primarily D-panthenol, that exhibit high neuroprotective activity in experimental models of neurodegeneration. Panthenol contributes to the significant restoration of the activity of enzymes of mitochondrial energy metabolism, normalization of the redox potential of the glutathione system, and a decrease in the level of S-glutathionylated proteins in brain mitochondria. The addition of succinate and glutathione precursor N-acetylcysteine enhances the protective effects of the drug.

Enhanced Vascular Permeability by Microbubbles and Ultrasound in Drug Delivery

Ultrasound and microbubbles, an ultrasound contrast agent, have recently increased attention to developing novel drug delivery systems. Ultrasound exposure can induce mechanical effects derived from microbubbles behaviors such as an expansion, contraction, and collapse depending on ultrasound conditions. These mechanical effects induce several biological effects, including enhancement of vascular permeability. For drug delivery, one promising approach is enhancing vascular permeability using ultrasound and microbubbles, resulting in improved drug transport to targeted tissues. This approach is applied to several tissues and drugs to cure diseases. This review describes the enhancement of vascular permeability by ultrasound and microbubbles and its therapeutic application, including our recent study. We also discuss the current situation of the field and its potential future perspectives.

Protective Role of Glutathione in the Hippocampus after Brain Ischemia

Stroke is a major cause of death worldwide, leading to serious disability. Post-ischemic injury, especially in the cerebral ischemia-prone hippocampus, is a serious problem, as it contributes to vascular dementia. Many studies have shown that in the hippocampus, ischemia/reperfusion induces neuronal death through oxidative stress and neuronal zinc (Zn²⁺) dyshomeostasis. Glutathione (GSH) plays an important role in protecting neurons against oxidative stress as a major intracellular antioxidant. In addition, the thiol group of GSH can function as a principal Zn²⁺ chelator for the maintenance of Zn²⁺ homeostasis in neurons. These lines of evidence suggest that neuronal GSH levels could be a key factor in post-stroke neuronal survival. In neurons, excitatory amino acid carrier 1 (EAAC1) is involved in the influx of cysteine, and intracellular cysteine is the rate-limiting substrate for the synthesis of GSH. Recently, several studies have indicated that cysteine uptake through EAAC1 suppresses ischemia-induced neuronal death via the promotion of hippocampal GSH synthesis in ischemic animal models. In this article, we aimed to review and describe the role of GSH in hippocampal neuroprotection after ischemia/reperfusion, focusing on EAAC1.

Glutamate metabolism and recycling at the excitatory synapse in health and neurodegeneration

Glutamate is the primary excitatory neurotransmitter of the brain. Cellular homeostasis of glutamate is of paramount importance for normal brain function and relies on an intricate metabolic collaboration between neurons and astrocytes. Glutamate is extensively recycled between neurons and astrocytes in a process known as the glutamate-glutamine cycle. The recycling of glutamate is closely linked to brain energy metabolism and is essential to sustain glutamatergic neurotransmission. However, a considerable amount of glutamate is also metabolized and serves as a metabolic hub connecting glucose and amino acid metabolism in both neurons and astrocytes. Disruptions in glutamate clearance, leading to neuronal overstimulation and excitotoxicity, have been implicated in several neurodegenerative diseases. Furthermore, the link between brain energy homeostasis and glutamate metabolism is gaining attention in several neurological conditions. In this review, we provide an overview of the dynamics of synaptic glutamate homeostasis and the underlying metabolic processes with a cellular focus on neurons and astrocytes. In particular, we review the recently discovered role of neuronal glutamate uptake in synaptic glutamate homeostasis and discuss current advances in cellular glutamate metabolism in the context of Alzheimer's disease and Huntington's disease. Understanding the intricate regulation of glutamate-dependent metabolic processes at the synapse will not only increase our insight into the metabolic mechanisms of glutamate homeostasis, but may reveal new metabolic targets to ameliorate neurodegeneration.

Altered Grooming Syntax and Amphetamine-Induced Dopamine Release in EAAT3 Overexpressing Mice

The excitatory amino acid transporter EAAT3 plays an important role in the neuronal uptake of glutamate regulating the activation of glutamate receptors. Polymorphisms in the gene-encoding EAAT3 have been associated with obsessive-compulsive disorder (OCD), although the mechanisms underlying this relationship are still unknown. We recently reported that mice with increased EAAT3 expression in forebrain neurons (EAAT3 ^{g lo} /CMKII) display behavioral and synaptic features relevant to OCD, including increased grooming, higher anxiety-like behavior and altered cortico-striatal synaptic function. The dopamine neurotransmitter system is implicated in ritualistic behaviors. Indeed, dopaminergic neurons express EAAT3, and mice lacking EAAT3 exhibit decreased dopamine release and decreased expression of the dopamine D1 receptor. Moreover, EAAT3 plays a role on the effect of the psychostimulant amphetamine. As such, we sought to determine if the OCD-like behavior in EAAT3 ^{g lo} /CMKII mice is accompanied by altered nigro-striatal dopaminergic transmission. The aim of this study was to analyze dopamine transmission both in basal conditions and after an acute challenge of amphetamine, using behavioral, neurochemical, molecular, and cellular approaches. We found that in basal conditions, EAAT3 ^{g lo} /CMKII mice performed more grooming events and that they remained in phase 1 of the grooming chain syntax compared with control littermates. Administration of amphetamine increased the number of grooming events in control mice, while EAAT3 ^{g lo} /CMKII mice remain unaffected. Interestingly, the grooming syntax of amphetamine-control mice resembled that of EAAT3 ^{g lo} /CMKII mice in basal conditions. Using in vivo microdialysis, we found decreased basal dopamine levels in EAAT3 ^{g lo} /CMKII compared with control mice. Unexpectedly, we found that after acute amphetamine, EAAT3 ^{g lo} /CMKII mice had a higher release of dopamine compared with that of control mice, suggesting that EAAT3 overexpression leads to increased dopamine releasability. To determine postsynaptic effect of EAAT3 overexpression over dopamine transmission, we performed Western blot analysis of dopaminergic proteins and found that EAAT3 ^{g lo} /CMKII mice have higher expression of D2 receptors, suggesting a higher inhibition of the indirect striatal pathway. Together, the data indicate that EAAT3 overexpression impacts on dopamine transmission, making dopamine neurons more sensitive to the effect of amphetamine and leading to a disbalance between the direct and indirect striatal pathways that favors the performance of repetitive behaviors.

Glutamic Acid Transporters: Targets for Neuroprotective Therapies in Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disease in middle-aged and elderly individuals. At present, no effective drug has been developed to treat PD. Although a variety of drugs exist for the symptomatic treatment of PD, they all have strong side effects. Most studies on PD mainly focus on dopaminergic neurons. This review highlights the function of glutamic acid transporters (GLTs), including excitatory amino acid transporters (EAATs) and vesicular glutamate transporters (VGLUTs), during the development of PD. In addition, using bioinformatics, we compared the expression of different types of glutamate transporter genes in the cingulate gyrus of PD patients and healthy controls. More importantly, we suggest that the functional roles of glutamate transporters may prove beneficial in the treatment of PD. In summary, VGLUTs and EAATs may be potential targets in the treatment of PD. VGLUTs and EAATs can be used as clinical drug targets to achieve better efficacy. Through this review article, we hope to enable future researchers to improve the condition of PD patients.

Constitutive Endocytosis of the Neuronal Glutamate Transporter Excitatory Amino Acid Transporter-3 Requires ARFGAP1

The eukaryotic endocytic pathway regulates protein levels available at the plasma membrane by recycling them into specific endosomal compartments. ARFGAP1 is a component of the coat protein I (COPI) complex but it also plays a role in promoting adapter protein-2 (AP-2) mediated endocytosis. The excitatory amino acid transporter-3 (EAAT3) mediates the reuptake of glutamate from the synaptic cleft to achieve rapid termination of synaptic transmission at glutamatergic synapses. In this study, we identified two interacting proteins of EAAT3 by mass spectrometry (MS) ARFGAP1 and ARF6. We explored the role of ARFGAP1 and ARF6 in the endocytosis of EAAT3. Our data revealed that ARFGAP1 plays a role in the recycling of EAAT3, by utilizing its GTPase activating protein (GAP) activity and ARF6 acting as the substrate. ARFGAP1 promotes cargo sorting of EAAT3 via a single phenylalanine residue (F508) located at the C-terminus of the transporter. ARFGAP1-promoted AP-2 dependent endocytosis is abolished upon neutralizing F508. We utilized a heterologous expression system to identify an additional motif in the C-terminus of EAAT3 that regulates its endocytosis. Impairment in endocytosis did not affect somatodendritic targeting in cultured hippocampal neurons. Our findings support a model where endocytosis of EAAT3 is a multifactorial event regulated by ARFGAP1, occurring via the C-terminus of the transporter, and is the first study to examine the role of ARFGAP1 in the endocytosis of a transport protein.

Glutathione in the Brain

Glutathione (GSH) is the most abundant non-protein thiol, and plays crucial roles in the antioxidant defense system and the maintenance of redox homeostasis in neurons. GSH depletion in the brain is a common finding in patients with neurodegenerative diseases, such as Alzheimer’s disease and Parkinson’s disease, and can cause neurodegeneration prior to disease onset. Excitatory amino acid carrier 1 (EAAC1), a sodium-dependent glutamate/cysteine transporter that is selectively present in neurons, plays a central role in the regulation of neuronal GSH production. The expression of EAAC1 is posttranslationally controlled by the glutamate transporter-associated protein 3–18 (GTRAP3-18) or miR-96-5p in neurons. The regulatory mechanism of neuronal GSH production mediated by EAAC1 may be a new target in therapeutic strategies for these neurodegenerative diseases. This review describes the regulatory mechanism of neuronal GSH production and its potential therapeutic application in the treatment of neurodegenerative diseases.

α-synuclein aggregates induce c-Abl activation and dopaminergic neuronal loss by a feed-forward redox stress mechanism

Oxidative stress and α-synuclein aggregation both drive neurodegeneration in Parkinson's disease, and the protein kinase c-Abl provides a potential amplifying link between these pathogenic factors. Suppressing interactions between these factors may thus be a viable therapeutic approach for this disorder. To evaluate this possibility, pre-formed α-synuclein fibrils (PFFs) were used to induce α-synuclein aggregation in neuronal cultures. Exposure to PFFs induced oxidative stress and c-Abl activation in wild-type neurons. By contrast, α-synuclein - deficient neurons, which cannot form α-synuclein aggregates, failed to exhibit either oxidative stress or c-Abl activation. N-acetyl cysteine, a thiol repletion agent that supports neuronal glutathione metabolism, suppressed the PFF - induced redox stress and c-Abl activation in the wild-type neurons, and likewise suppressed α-synuclein aggregation. Parallel findings were observed in mouse brain: PFF-induced α-synuclein aggregation in the substantia nigra was associated with redox stress, c-Abl activation, and dopaminergic neuronal loss, along with microglial activation and motor impairment, all of which were attenuated with oral N-acetyl cysteine. Similar results were obtained using AAV-mediated α-synuclein overexpression as an alternative means of driving α-synuclein aggregation in vivo. These findings show that α-synuclein aggregates induce c-Abl activation by a redox stress mechanism. c-Abl activation in turn promotes α-synuclein aggregation, in a feed-forward interaction. The capacity of N-acetyl cysteine to interrupt this interaction adds mechanistic support its consideration as a therapeutic in Parkinson's disease.

The Role of Non-Coding RNAs in the Neuroprotective Effects of Glutathione

The establishment of antioxidative defense systems might have been mandatory for most living beings with aerobic metabolisms, because oxygen consumption produces adverse byproducts known as reactive oxygen species (ROS). The brain is especially vulnerable to the effect of ROS, since the brain has large amounts of unsaturated fatty acids, which are a target of lipid oxidation, as well as comparably high-energy consumption compared to other organs that results in ROS release from mitochondria. Thus, dysregulation of the synthesis and/or metabolism of antioxidants-particularly glutathione (GSH), which is one of the most important antioxidants in the human body-caused oxidative stress states that resulted in critical diseases, including neurodegenerative diseases in the brain. GSH plays crucial roles not only as an antioxidant but also as an enzyme cofactor, cysteine storage form, the major redox buffer, and a neuromodulator in the central nervous system. The levels of GSH are precisely regulated by uptake systems for GSH precursors as well as GSH biosynthesis and metabolism. The rapid advance of RNA sequencing technologies has contributed to the discovery of numerous non-coding RNAs with a wide range of functions. Recent lines of evidence show that several types of non-coding RNAs, including microRNA, long non-coding RNA and circular RNA, are abundantly expressed in the brain, and their activation or inhibition could contribute to neuroprotection through the regulation of GSH synthesis and/or metabolism. Interestingly, these non-coding RNAs play key roles in gene regulation and growing evidence indicates that non-coding RNAs interact with each other and are co-regulated. In this review, we focus on how the non-coding RNAs modulate the level of GSH and modify the oxidative stress states in the brain.