Cysteine regulation of protein function--as exemplified by NMDA-receptor modulation

A novel dual-function fluorescent probe for the detection of cysteine and its applications in vitro

A fluorescent probe of both colorimetric and ratiometric type for highly selective and sensitive detection of Cys (cysteine) is very important in biological analysis. In this work, a new colorimetric and ratiometric fluorescent probe ((E)-2-(2-(5-(4-(acryloyloxy)phenyl)furan-2-yl)vinyl)-3-methylbenzo[d]thiazol-3-ium iodide, LP-1) was designed and synthesized for the detection of Cys. The reaction mechanism of LP-1 toward Cys involves a conjugate addition reaction between Cys and the α,β-unsaturated carbonyl group, leading to the formation of an intermediate thioether, followed by intramolecular cyclization to produce the desired compounds LP-1-OH. At this point, the ICT process is activated, significantly increasing the fluorescence intensity of the molecules. Meanwhile, LP-1 is highly selective and sensitive to Cys identification under optimized experimental conditions. LP-1 shows a good linear relationship in the range of Cys concentration from 0.40 μM to 40 μM (R2 = 0.9942) and the limit of detection (LOD) of Cys is 0.19 μM. In addition, we have developed a simple, portable and low-cost smartphone-based high-sensitivity Cys detection method based on naked eye obvious color detection. LP-1 also has low cell toxicity and can be successfully used for biological imaging of Cys, suggesting that it is a promising biological application tool for Cys detection.

Decreased levels of hydrogen sulfide in the hypothalamic paraventricular nucleus contribute to sympathetic hyperactivity induced by cerebral infarction

Paroxysmal sympathetic hyperactivity (PSH) is a common clinical feature secondary to ischemic stroke (IS), but its mechanism is poorly understood. We aimed to investigate the role of H2S in the pathogenesis of PSH. IS patients were divided into malignant (MCI) and non-malignant cerebral infarction (NMCI) group. IS in rats was induced by the right middle cerebral artery occlusion (MCAO). H2S donor (NaHS) or inhibitor (aminooxy-acetic acid, AOAA) were microinjected into the hypothalamic paraventricular nucleus (PVN). Compared with the NMCI group, patients in the MCI group showed PSH, including tachycardia, hypertension, and more plasma norepinephrine (NE) that was positively correlated with levels of creatine kinase, glutamate transaminase, and creatinine respectively. The 1-year survival rate of patients with high plasma NE levels was lower. The hypothalamus of rats with MCAO showed increased activity, especially in the PVN region. The levels of H2S in PVN of the rats with MCAO were reduced, while the blood pressure and renal sympathetic discharge were increased, which could be ameliorated by NaHS and exacerbated by AOAA. NaHS completely reduced the disulfide bond of NMDAR1 in PC12 cells. The inhibition of NMDAR by MK-801 microinjected in PVN of rats with MCAO also could lower blood pressure and renal sympathetic discharge. In conclusion, PSH may be associated with disease progression and survival in patients with IS. Decreased levels of H2S in PVN were involved in regulating sympathetic efferent activity after cerebral infarction. Our results might provide a new strategy and target for the prevention and treatment of PSH.

A new lysosome-targeted Cys probe and its application in biology and food samples

Cysteine (Cys) is a sulfur-containing amino acid that plays an important role in living systems. The most common way to supplement the body with exogenous Cys is through the consumption of Cys-rich foods. Therefore, it is important to detect and analyze Cys in living systems and food samples. However, most of the Cys fluorescent probes developed so far are limited to the detection of the cellular environment only, and very few probes can take into account the detection of Cys in plant roots and food samples. In this paper, a novel fluorescent probe LN-NCS targeting the detection of Cys in lysosomes was designed and synthesized by modifying the naphthalimide fluorophore. The probe LN-NCS has a large Stokes shift (140 nm), low cytotoxicity, low detection limit (16.3 nM), and high selectivity, and probe LN-NCS reacts with Cys to produce the compound LN-NH2 with good fluorescence quantum yield (Ф = 0.81). Probe LN-NCS can be used to detect Cys in cells, zebrafish, plant roots, food samples, and environmental water samples. In addition, by modeling cellular inflammation, we have demonstrated that probe LN-NCS can detect changes in Cys concentration induced by cellular inflammation, providing a potential tool to better study the cellular inflammatory environment.

A simple indanone-based red emission fluorescent probe for the rapid detection of cysteine in vitro and in vivo

Cysteine is a vital biothiols that plays an important role in numerous physiological and pathological processes. The development of simple molecule tools for detection and analysis Cys in subcellar environment is significant for further exploring their pathophysiological. In this work, a simple but activated fluorescent probe AMIA was constructed with a donor-π-accepter (D- π -A) structure, which using an indanone as the electron-withdrawing unit acting as the fluorophore, dimethylamino group attached to the position 4 of the benzene ring as the electron-donating, two double bonds as the linker group, and the acryloyl ester group as the trigger and response unit. This probe AMIA was exhibited highly selective and sensitive response to Cys over other amino acids and ions under physiological conditions. It was found that AMIA showed a red turn-on fluorescence response at 630 nm towards Cys with a large stroke shift of 170 nm and a very low detection limit of 26.3 nM. HRMS, 1H NMR and TD-DFT calculation further confirmed that the response mechanism is the Cys triggered the addition-cyclization reaction between AMIA' acryloyl group and Cys' sulfhydryl and amino unit, leading to the release of a red fluorescent dye AMIA-OH, which can be identified by naked eyes. Furthermore, AMIA was successfully applied for simultaneous determination of Cys in living cells and zebrafish with lower cytotoxicity and good cell permeability. We hope that this novel indanone-based probe AMIA will provide a new reference for visualized Cys in other complex biological system.

Schizophrenia and Glutathione: A Challenging Story

Schizophrenia (SZ) is a devastating mental illness with a complex and heterogeneous clinical state. Several conditions like symptoms, stage and severity of the disease are only some of the variables that have to be considered to define the disorder and its phenotypes. SZ pathophysiology is still unclear, and the diagnosis is currently relegated to the analysis of clinical symptoms; therefore, the search for biomarkers with diagnostic relevance is a major challenge in the field, especially in the era of personalized medicine. Though the mechanisms implicated in SZ are not fully understood, some processes are beginning to be elucidated. Oxidative stress, and in particular glutathione (GSH) dysregulation, has been demonstrated to play a crucial role in SZ pathophysiology. In fact, glutathione is a leading actor of oxidative-stress-mediated damage in SZ and appears to reflect the heterogeneity of the disease. The literature reports differing results regarding the levels of glutathione in SZ patients. However, each GSH state may be a sign of specific symptoms or groups of symptoms, candidating glutathione as a biomarker useful for discriminating SZ phenotypes. Here, we summarize the literature about the levels of glutathione in SZ and analyze the role of this molecule and its potential use as a biomarker.

PDI augments kainic acid-induced seizure activity and neuronal death by inhibiting PP2A-GluA2-PICK1-mediated AMPA receptor internalization in the mouse hippocampus

Protein disulfide isomerase (PDI) is a redox-active enzyme and also serves as a nitric oxide donor causing S-nitrosylation of cysteine residues in various proteins. Although PDI knockdown reduces α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR)-mediated neuronal activity, the underlying mechanisms are largely unknown. In the present study, we found that under physiological condition PDI knockdown increased CaMKII activity (phosphorylation) in the mouse hippocampus. However, PDI siRNA inhibited protein phosphatase (PP) 2A-mediated GluA2 S880 dephosphorylation by increasing PP2A oxidation, independent of S-nitrosylation. PDI siRNA also enhanced glutamate ionotropic receptor AMPA type subunit 1 (GluA1) S831 and GluA2 S880, but not GluA1 S845 and GluA2 Y869/Y873/Y876 phosphorylations, concomitant with the enhanced protein interacting with C kinase 1 (PICK1)-mediated AMPAR internalization. Furthermore, PDI knockdown attenuated seizure activity and neuronal damage in response to kainic acid (a non-desensitizing agonist of AMPAR). Therefore, these findings suggest that PDI may regulate surface AMPAR expression through PP2A-GluA2-PICK1 signaling pathway, and that PDI may be one of the therapeutic targets for epilepsy via AMPAR internalization without altering basal neurotransmission.

Rational design of a novel acryl-modified CQDs fluorescent probe for highly selective detection and imaging of cysteine in vitro and in vivo

A novel fluorescent nanoprobe CQDs-O-Acryl has been designed and synthesized to directly and accurately identify Cys over other biothiols in PBS (10 mM, pH 7.4) buffer. The carbon quantum dots (CQDs-OH) (λ_ex/em maxima = 495/525 nm) were fabricated by a solvothermal method using resorcinol as the carbon source. The CQDs-O-Acryl was achieved through covalently grafting the acryloyl group on the surface of carbon quantum dots by nuclear reaction based on static quenching. The structure and morphology of CQDs-OH and CQDs-O-Acryl have been characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and UV-vis absorption spectroscopy. Upon the addition of Cys, the ester bond of CQDs-O-Acryl has been broken, and the free CQDs were released by conjugated addition and cyclization reactions successively, emitting strong green fluorescence at 525 nm (λ_ex = 495 nm). Under the optimized conditions, CQDs-O-Acryl exhibited good sensing of Cys within the range 0.095-16 μM (the LOD of 0.095 μM). Due to the high sensitivity, reliability, fast fluorescence response (10 min), and low toxicity of CQDs-O-Acryl, it was successfully applied to fluorescence imaging of Cys in A549 cells and zebrafish.

In vivo 'turn on' fluorescence detection of free cysteine in zebrafish kidney and liver

Cysteine is directly associated with a wide range of biological processes. Besides its essential role in protein synthesis, cysteine undergoes a variety of post-translational modifications which modulate several physiological processes. Dysregulated cysteine metabolism is associated with several neurodegenerative disorders. Accordingly, restoring cysteine balance has therapeutic benefits. It is therefore essential to detect the presence of endogenous free cysteine in order to understand different physiological modes of action inside the cell. Here, a carbazole-pyridoxal conjugate system (CPLC) has been developed to detect endogenous free cysteine in the liver and kidney of an adult zebrafish. In consequence, we have also determined the fluorescence intensity statistics of zebrafish kidney and liver images. CPLC interacts in a very fascinating way with two cysteine molecules through chemodosimetric and chemosensing approaches which are conclusively proved by different spectroscopic analyses (UV-vis, fluorescence, NMR) and theoretical calculations (DFT). The detection limit of CPLC towards cysteine is 0.20 μM. Moreover, this preliminary experiment has been done using HuH-7 cell line to check the permeability of CPLC, interaction with cysteine intracellularly, and assessment of the toxicity of CPLC, if any, before performing details in-vivo experiments in zebrafish model.

Coumarin-Based Fluorescence Probe for Differentiated Detection of Biothiols and Its Bioimaging in Cells

In this work, a coumarin derivative, SWJT-14, was synthesized as a fluorescence probe to distinguish cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) in aqueous solutions. The detection limit of Cys, Hcy and GSH for the probe was 0.02 μM, 0.42 μM and 0.92 μM, respectively, which was lower than biothiols in cells. The probe reacted with biothiols to generate different products with different conjugated structures. Additionally, it could distinguish Cys, Hcy and GSH using fluorescence and UV-Vis spectra. The detection mechanism was confirmed by MS. SWJT-14 was successfully used in cellular experiments and detected both endogenous and exogenous biothiols.

Aberrant protein S-nitrosylation contributes to hyperexcitability-induced synaptic damage in Alzheimer's disease: Mechanistic insights and potential therapies

Alzheimer's disease (AD) is arguably the most common cause of dementia in the elderly and is marked by progressive synaptic degeneration, which in turn leads to cognitive decline. Studies in patients and in various AD models have shown that one of the early signatures of AD is neuronal hyperactivity. This excessive electrical activity contributes to dysregulated neural network function and synaptic damage. Mechanistically, evidence suggests that hyperexcitability accelerates production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) that contribute to neural network impairment and synapse loss. This review focuses on the pathways and molecular changes that cause hyperexcitability and how RNS-dependent posttranslational modifications, represented predominantly by protein S-nitrosylation, mediate, at least in part, the deleterious effects of hyperexcitability on single neurons and the neural network, resulting in synaptic loss in AD.

Regulation of macrophage activation by S-Nitrosothiols following ozone-induced lung injury

Acute exposure to ozone causes oxidative stress, characterized by increases in nitric oxide (NO) and other reactive nitrogen species in the lung. NO has been shown to modify thiols generating S-nitrosothiols (SNOs); this results in altered protein function. In macrophages this can lead to changes in inflammatory activity which impact the resolution of inflammation. As SNO formation is dependent on the redox state of both the NO donor and the recipient thiol, the local microenvironment plays a key role in its regulation. This dictates not only the chemical feasibility of SNO formation but also mechanisms by which they may form. In these studies, we compared the ability of the SNO donors, ethyl nitrite (ENO), which targets both hydrophobic and hydrophilic thiols, SNO-propanamide (SNOPPM) which targets hydrophobic thiols, and S-nitroso-N-acetylcysteine. (SNAC) which targets hydrophilic thiols. to modify macrophage activation following ozone exposure. Mice were treated with air or ozone (0.8 ppm, 3 h) followed 1 h later by intranasal administration of ENO, SNOPPM or SNAC (1-500 μM) or appropriate controls. Mice were euthanized 48 h later. Each of the SNO donors reduced ozone-induced inflammation and modified the phenotype of macrophages both within the lung lining fluid and the tissue. ENO and SNOPPM were more effective than SNAC. These findings suggest that the hydrophobic SNO thiol pool targeted by SNOPPM and ENO plays a major role in regulating macrophage phenotype following ozone induced injury.

S-Glutathionylation and S-Nitrosylation in Mitochondria: Focus on Homeostasis and Neurodegenerative Diseases

Redox post-translational modifications are derived from fluctuations in the redox potential and modulate protein function, localization, activity and structure. Amongst the oxidative reversible modifications, the S-glutathionylation of proteins was the first to be characterized as a post-translational modification, which primarily protects proteins from irreversible oxidation. However, a growing body of evidence suggests that S-glutathionylation plays a key role in core cell processes, particularly in mitochondria, which are the main source of reactive oxygen species. S-nitrosylation, another post-translational modification, was identified >150 years ago, but it was re-introduced as a prototype cell-signaling mechanism only recently, one that tightly regulates core processes within the cell’s sub-compartments, especially in mitochondria. S-glutathionylation and S-nitrosylation are modulated by fluctuations in reactive oxygen and nitrogen species and, in turn, orchestrate mitochondrial bioenergetics machinery, morphology, nutrients metabolism and apoptosis. In many neurodegenerative disorders, mitochondria dysfunction and oxidative/nitrosative stresses trigger or exacerbate their pathologies. Despite the substantial amount of research for most of these disorders, there are no successful treatments, while antioxidant supplementation failed in the majority of clinical trials. Herein, we discuss how S-glutathionylation and S-nitrosylation interfere in mitochondrial homeostasis and how the deregulation of these modifications is associated with Alzheimer’s, Parkinson’s, amyotrophic lateral sclerosis and Friedreich’s ataxia.

Posttranslational S-nitrosylation modification regulates HMGB1 secretion and promotes its proinflammatory and neurodegenerative effects

Nuclear protein high-mobility group box 1 (HMGB1) can be actively secreted by activated immune cells and functions as a proinflammatory cytokine. Regulation of HMGB1 secretion is critical for treatment of HMGB1-mediated inflammation and related diseases. This study demonstrates that S-nitrosylation (SNO; the covalent binding of nitric oxide [NO] to cysteine thiols) by inducible nitric oxide synthase (iNOS)-derived NO at Cys106 is essential and sufficient for inflammation-elicited HMGB1 secretion. iNOS deletion or inhibition or Cys106Ser mutation prevents lipopolysaccharide (LPS)- and/or poly(I:C)-elicited HMGB1 secretion. NO donors induce SNO of HMGB1 and reproduce inflammogen-triggered HMGB1 secretion. SNO of HMGB1 promotes its proinflammatory and neurodegenerative effects. Intranigral HMGB1 injection induces chronic microglial activation, dopaminergic neurodegeneration, and locomotor deficits, the key features of Parkinson’s disease (PD), in wild-type, but not Mac1 (CD11b/CD18)-deficient, mice. This study indicates pivotal roles for SNO modification in HMGB1 secretion and HMGB1-Mac1 interaction for inflammatory neurodegeneration, identifying a mechanistic basis for PD development.

Regulation of HMGB1 secretion is critical for the treatment of HMGB1-mediated inflammation and related diseases. Yang et al. demonstrate that posttranslational S-nitrosylation modification (the covalent binding of nitric oxide to protein cysteine thiols) regulates HMGB1 secretion and promotes its proinflammatory and neurodegenerative effects, thereby contributing to Parkinson’s disease pathogenesis.

Genetics-informed precision treatment formulation in schizophrenia and bipolar disorder

Genetically informed drug development and repurposing is an attractive prospect for improving patient outcomes in psychiatry; however, the effectiveness of these endeavors is confounded by heterogeneity. We propose an approach that links interventions implicated by disorder-associated genetic risk, at the population level, to a framework that can target these compounds to individuals. Specifically, results from genome-wide association studies are integrated with expression data to prioritize individual "directional anchor" genes for which the predicted risk-increasing direction of expression could be counteracted by an existing drug. While these compounds represent plausible therapeutic candidates, they are not likely to be equally efficacious for all individuals. To account for this heterogeneity, we constructed polygenic scores restricted to variants annotated to the network of genes that interact with each directional anchor gene. These metrics, which we call a pharmagenic enrichment score (PES), identify individuals with a higher burden of genetic risk, localized in biological processes related to the candidate drug target, to inform precision drug repurposing. We used this approach to investigate schizophrenia and bipolar disorder and reveal several compounds targeting specific directional anchor genes that could be plausibly repurposed. These genetic risk scores, mapped to the networks associated with target genes, revealed biological insights that cannot be observed in undifferentiated genome-wide polygenic risk score (PRS). For example, an enrichment of these partitioned scores in schizophrenia cases with otherwise low PRS. In summary, genetic risk could be used more specifically to direct drug repurposing candidates that target particular genes implicated in psychiatric and other complex disorders.

Biomarker-responsive Fluorescent Probes for In Vivo Imaging of Liver Injury

Liver injury-related diseases have aroused widespread concern due to its extreme unpredictability, acute onset, and severe consequences. Nowadays, the clinical prediction and assessment of liver injury mainly focus on histopathological and serological approaches, which undergoes a tedious process and sometimes requires invasive biopsy. Over the past decades, fluorescence imaging technique have emerged as a rising star for the diagnosis of diseases owing to its noninvasiveness, high fidelity and ease of operation. On regard to liver injury, the fluorescent probes have been delicately designed to response a variety of endogenous biomolecules to precisely offer comprehensive information about the lesion site. Herein, we make a brief summary and discussion about the design strategies and applications of the recently reported fluorescent biosensors responsive to a series of biomarkers involved in the liver injury. The potential prospects and remaining challenges are also discussed to promote the progression in this field.

Amyloid-β disrupts unitary calcium entry through endothelial NMDA receptors in mouse cerebral arteries

Transient increases in intracellular Ca2+ activate endothelium-dependent vasodilatory pathways. This process is impaired in cerebral amyloid angiopathy, where amyloid-β(1-40) accumulates around blood vessels. In neurons, amyloid-β impairs the Ca2+-permeable N-methyl-D-aspartate receptor (NMDAR), a mediator of endothelium-dependent dilation in arteries. We hypothesized that amyloid-β(1-40) reduces NMDAR-elicited Ca2+ signals in mouse cerebral artery endothelial cells, blunting dilation. Cerebral arteries isolated from 4-5 months-old, male and female cdh5:Gcamp8 mice were used for imaging of unitary Ca2+ influx through NMDAR (NMDAR sparklets) and intracellular Ca2+ transients. The NMDAR agonist NMDA (10 µmol/L) increased frequency of NMDAR sparklets and intracellular Ca2+ transients in endothelial cells; these effects were prevented by NMDAR antagonists D-AP5 and MK-801. Next, we tested if amyloid-β(1-40) impairs NMDAR-elicited Ca2+ transients. Cerebral arteries incubated with amyloid-β(1-40) (5 µmol/L) exhibited reduced NMDAR sparklets and intracellular Ca2+ transients. Lastly, we observed that NMDA-induced dilation of pial arteries is reduced by acute intraluminal amyloid-β(1-40), as well as in a mouse model of Alzheimer's disease, the 5x-FAD, linked to downregulation of Grin1 mRNA compared to wild-type littermates. These data suggest that endothelial NMDAR mediate dilation via Ca2+-dependent pathways, a process disrupted by amyloid-β(1-40) and impaired in 5x-FAD mice.

Progress and Pitfalls in Developing Agents to Treat Neurocognitive Deficits Associated with Schizophrenia

Cognitive impairments associated with schizophrenia (CIAS) represent a central element of the symptomatology of this severe mental disorder. CIAS substantially determine the disease prognosis and hardly, if at all, respond to treatment with currently available antipsychotics. Remarkably, all drugs presently approved for the treatment of schizophrenia are, to varying degrees, dopamine D₂/D₃ receptor blockers. In turn, rapidly growing evidence suggests the immense significance of systems other than the dopaminergic system in the genesis of CIAS. Accordingly, current efforts addressing the unmet needs of patients with schizophrenia are primarily based on interventions in other non-dopaminergic systems. In this review article, we provide a brief overview of the available evidence on the importance of specific systems in the development of CIAS. In addition, we describe the promising targets for the development of new drugs that have been used so far. In doing so, we present the most important candidates that have been investigated in the field of the specific systems in recent years and present a summary of the results available at the time of drafting this review (May 2022), as well as the currently ongoing studies.

The two-steps reaction fluorescent probe for the selective detection of cysteine and its applications

We reported the specific fluorescent probe (MC-BOD-XDS) with two-steps reaction based on monomercapto-coumarin-BODIPY for selective detection of cysteine，high activty mercapto-coumarin as the multiple reaction group instead of a group internal standard fluorophore. The reaction mechanism of MC-BOD-XDS for detecting cysteine was different from the reported probes about the nucleophilic  aromatic substitution reaction (SNAr) of chlorinated BODIPY. The fluorescent color of MC-BOD-XDS changed from yellow to red, and then to orange. The linear calibration diagram showed that it can potentially be used for quantitatively detection of Cys. Its potential applications were demonstrated by employing it for detection of Cys in artificial urine and in fluorescent imaging in HeLa cells.

Pillars and Gaps of S-Nitrosylation-Dependent Epigenetic Regulation in Physiology and Cancer

Nitric oxide (NO) is a diffusible signaling molecule produced by three isoforms of nitric oxide synthase, which release NO during the metabolism of the amino acid arginine. NO participates in pathophysiological responses of many different tissues, inducing concentration-dependent effect. Indeed, while low NO levels generally have protective effects, higher NO concentrations induce cytotoxic/cytostatic actions. In recent years, evidences have been accumulated unveiling S-nitrosylation as a major NO-dependent post-translational mechanism ruling gene expression. S-nitrosylation is a reversible, highly regulated phenomenon in which NO reacts with one or few specific cysteine residues of target proteins generating S-nitrosothiols. By inducing this chemical modification, NO might exert epigenetic regulation through direct effects on both DNA and histones as well as through indirect actions affecting the functions of transcription factors and transcriptional co-regulators. In this light, S-nitrosylation may also impact on cancer cell gene expression programs. Indeed, it affects different cell pathways and functions ranging from the impairment of DNA damage repair to the modulation of the activity of signal transduction molecules, oncogenes, tumor suppressors, and chromatin remodelers. Nitrosylation is therefore a versatile tool by which NO might control gene expression programs in health and disease.

The metabolic signaling of the nucleoredoxin-like 2 gene supports brain function

The nucleoredoxin gene NXNL2 encodes for two products through alternative splicing, rod-derived cone viability factor-2 (RdCVF2) that mediates neuronal survival and the thioredoxin-related protein (RdCVF2L), an enzyme that regulates the phosphorylation of TAU. To investigate the link between NXNL2 and tauopathies, we studied the Nxnl2 knockout mouse (Nxnl2-/-). We established the expression pattern of the Nxnl2 gene in the brain using a Nxnl2 reporter mouse line, and characterized the behavior of the Nxnl2-/- mouse at 2 months of age. Additionally, long term potentiation and metabolomic from hippocampal specimens were collected at 2 months of age. We studied TAU oligomerization, phosphorylation and aggregation in Nxnl2-/- brain at 18 months of age. Finally, newborn Nxnl2-/- mice were treated with adeno-associated viral vectors encoding for RdCVF2, RdCVF2L or both and measured the effect of this therapy on long-term potential, glucose metabolism and late-onset tauopathy. Nxnl2-/- mice at 2 months of age showed severe behavioral deficiency in fear, pain sensitivity, coordination, learning and memory. The Nxnl2-/- also showed deficits in long-term potentiation, demonstrating that the Nxnl2 gene is involved in regulating brain functions. Dual delivery of RdCVF2 and RdCVF2L in newborn Nxnl2-/- mice fully correct long-term potentiation through their synergistic action. The expression pattern of the Nxnl2 gene in the brain shows a predominant expression in circumventricular organs, such as the area postrema. Glucose metabolism of the hippocampus of Nxnl2-/- mice at 2 months of age was reduced, and was not corrected by gene therapy. At 18-month-old Nxnl2-/- mice showed brain stigmas of tauopathy, such as oligomerization, phosphorylation and aggregation of TAU. This late-onset tauopathy can be prevented, albeit with modest efficacy, by recombinant AAVs administrated to newborn mice. The Nxnl2-/- mice have memory dysfunction at 2-months that resembles mild-cognitive impairment and at 18-months exhibit tauopathy, resembling to the progression of Alzheimer's disease. We propose the Nxnl2-/- mouse is a model to study multistage aged related neurodegenerative diseases. The NXNL2 metabolic and redox signaling is a new area of therapeutic research in neurodegenerative diseases.

Nicotinamide Adenine Dinucleotide Phosphate Oxidases Are Everywhere in Brain Disease, but Not in Huntington's Disease?

Huntington’s disease (HD) is an inherited neurodegenerative disorder characterized by neuronal loss and tissue atrophy mainly in the striatum and cortex. In the early stages of the disease, impairment of neuronal function, synaptic dysfunction and white matter loss precedes neuronal death itself. Relative to other neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease and Amyotrophic Lateral Sclerosis, where the effects of either microglia or NADPH oxidases (NOXs) are recognized as important contributors to disease pathogenesis and progression, there is a pronounced lack of information in HD. This information void contrasts with evidence from human HD patients where blood monocytes and microglia are activated well before HD clinical symptoms (PET scans), and the clear signs of oxidative stress and inflammation in post mortem HD brain. Habitually, NOX activity and oxidative stress in the central nervous system (CNS) are equated with microglia, but research of the last two decades has carved out important roles for NOX enzyme function in neurons. Here, we will convey recent information about the function of NOX enzymes in neurons, and contemplate on putative roles of neuronal NOX in HD. We will focus on NOX-produced reactive oxygen species (ROS) as redox signaling molecules in/among neurons, and the specific roles of NOXs in important processes such as neurogenesis and lineage specification, neurite outgrowth and growth cone dynamics, and synaptic plasticity where NMDAR-dependent signaling, and long-term depression/potentiation are redox-regulated phenomena. HD animal models and induced pluripotent stem cell (iPSC) studies have made it clear that the very same physiological processes are also affected in HD, and we will speculate on possible roles for NOX in the pathogenesis and development of disease. Finally, we also take into account the limited information on microglia in HD and relate this to any contribution of NOX enzymes.

A near-infrared fluorescence turn-on probe based on Michael addition-intramolecular cyclization for specific detection of cysteine and its applications in environmental water and milk samples and living cells

Owing to its important biological functions in many physiological and pathological processes, it is necessary to develop efficient and appropriate detection methods for monitoring the levels of Cys in biological systems. Based on this, a novel rhodol-isophorone derivative (RHI) was designed and synthesized as a reaction-based fluorescence probe for specific detection of Cys with high sensitivity and large Stokes shift (155 nm). This probe was composed of an acrylate moiety (recognition group) and a rhodol-isophorone derivative (fluorophore). Probe RHI could react with Cys rapidly (15 min) with a 100-fold fluorescence enhancement. The limit of detection value was calculated to be 0.168 μM. When Cys was added, the color of the probe RHI solution turned from yellow to blue, indicating that Cys could be monitored by the naked eye. In addition, probe RHI was successfully utilized for detecting Cys in environmental water and milk samples. More importantly, the probe could be applied to imaging Cys in living cells with low cytotoxicity and good biocompatibility.

Sulphide activity-dependent multicolor emission dye and its applications in in vivo imaging

Reactive sulfur species (RSS) play pivotal roles in various pathological and physiological processes. There exists an intricate relevance in generation and metabolism among these substances. Although they are nucleophilic, there are still some differences in their reactivity. There are many methods to detect them by using reactive fluorescent probes, but the systematic study of their reactivity is still lacking. In our study, we designed a multiple reaction site fluorescent probe based on benzene conjugated benzopyrylium and NBD. The study revealed that besides both biothiols and hydrogen sulfide, sulfur dioxide (SO₂) can cleave the ether bond. There are two reaction forms for GSH with low reactivity: cutting the ether bond and adding the conjugated double bond of benzopyrylium. Nevertheless, Cys/Hcy with higher activity can further rearrange with NBD after cutting the ether bond. In addition, SO₂ can not only cleave the ether bond, but also continue to add the conjugated double bond of benzopyrylium. The above processes lead to multicolor emission of the probe, thus realizing the characteristic analysis of different sulfides. Thus the probe can be used for the detection of sulfide in mitochondria, and further for the imaging of sulfide in cells and zebrafish. This effective analysis method will provide a broad application prospect for practical applications.

A fluorescent probe with dual acrylate sites for discrimination of different concentration ranges of cysteine in living cells

Monitoring of cysteine (Cys) is of significant importance for studying Cys-involved biological functions and clinically diagnosing Cys-related diseases. Recently, few fluorescent probes with two different reacting sites were reported to be capable of sensing different concentration ranges of Cys with distinct fluorescence signals, particularly suiting for bioimaging. However, due to relative sophisticated synthesis and moderate selectivity, the applications of these probes were still severely restricted. In this work, we proposed a novel probe design strategy by utilizing two same reacting groups, instead of two different reacting groups, to simplify the synthesis route and minimize the interference from competing species. Same reacting groups in a probe with different steric hindrances could exhibit different reactivities to Cys. This probe showed distinguishable fluorescence peak wavelengths towards low and high concentration ranges of Cys, giving green and blue emissions, respectively. Moreover, this probe was successfully applied for monitoring of Cys concentration in living cells. We believe this work provided a simpler strategy for dual-site fluorescent probes to sense difference concentration ranges of Cys, which may inspire more probe design in future.

Protein Transnitrosylation Signaling Networks Contribute to Inflammaging and Neurodegenerative Disorders

Significance: Physiological concentrations of nitric oxide (NO^•) and related reactive nitrogen species (RNS) mediate multiple signaling pathways in the nervous system. During inflammaging (chronic low-grade inflammation associated with aging) and in neurodegenerative diseases, excessive RNS contribute to synaptic and neuronal loss. "NO signaling" in both health and disease is largely mediated through protein S-nitrosylation (SNO), a redox-based posttranslational modification with "NO" (possibly in the form of nitrosonium cation [NO⁺]) reacting with cysteine thiol (or, more properly, thiolate anion [R-S^-]). Recent Advances: Emerging evidence suggests that S-nitrosylation occurs predominantly via transnitros(yl)ation. Mechanistically, the reaction involves thiolate anion, as a nucleophile, performing a reversible nucleophilic attack on a nitroso nitrogen to form an SNO-protein adduct. Prior studies identified transnitrosylation reactions between glyceraldehyde-3-phosphate dehydrogenase (GAPDH)-nuclear proteins, thioredoxin-caspase-3, and X-linked inhibitor of apoptosis (XIAP)-caspase-3. Recently, we discovered that enzymes previously thought to act in completely disparate biochemical pathways can transnitrosylate one another during inflammaging in an unexpected manner to mediate neurodegeneration. Accordingly, we reported a concerted tricomponent transnitrosylation network from Uch-L1-to-Cdk5-to-Drp1 that mediates synaptic damage in Alzheimer's disease. Critical Issues: Transnitrosylation represents a critical chemical mechanism for transduction of redox-mediated events to distinct subsets of proteins. Although thousands of thiol-containing proteins undergo S-nitrosylation, how transnitrosylation regulates a myriad of neuronal attributes is just now being uncovered. In this review, we highlight recent progress in the study of the chemical biology of transnitrosylation between proteins as a mechanism of disease. Future Directions: We discuss future areas of study of protein transnitrosylation that link our understanding of aging, inflammation, and neurodegenerative diseases. Antioxid. Redox Signal. 35, 531-550.

Andrographolide improves PCP-induced schizophrenia-like behaviors through blocking interaction between NRF2 and KEAP1

Schizophrenia is one of the foremost psychological illness around the world, and recent evidence shows that inflammation and oxidative stress may play a critical role in the etiology of schizophrenia. Andrographolide is a diterpenoid lactone from Andrographis paniculate, which has shown anti-inflammation and anti-oxidative effects. In this study, we explored whether andrographolide can improve schizophrenia-like behaviors through its inhibition of inflammation and oxidative stress in Phencyclidine (PCP)-induced mouse model of schizophrenia. We found that abnormal behavioral including locomotor activity, forced swimming and novel object recognition were ameliorated following andrographolide administration (5 mg/kg and 10 mg/kg). Andrographolide inhibited PCP-induced production of inflammatory cytokines, decreased p-p65, p-IκBα, p-p38 and p-ERK1/2 in the prefrontal cortex. Andrographolide significantly declined the level of MDA and GSH, as well as elevated the activity of SOD, CAT and GCH-px. In addition, andrographolide increased expression of NRF-2, HO-1 and NQO-1, promoted nuclear translocation of NRF-2 through blocking the interaction between NRF-2 and KEAP1, which may be associated with directly binding to NRF-2. Furthermore, antioxidative effects and anti-schizophrenia-like behaviors of andrographolide were compromised by the application of NRF-2 inhibitor ML385. In conclusion, these results suggested that andrographolide improved oxidative stress and schizophrenia-like behaviors induced by PCP through increasing NRF-2 pathway.

Fluorescence Probe for Imaging N-Methyl-d-aspartate Receptors and Monitoring GSH Selectively Using Two-Photon Microscopy

N-Methyl-d-aspartate (NMDA) is an excitotoxic amino acid used to identify a specific subset of glutamate receptors. The activity of NMDA receptors is closely related to the redox level of the biological system. Glutathione (GSH) as an antioxidant plays a key role with regard to modulation of the redox environment. In this work we designed and developed a GSH-specific fluorescent probe with the capability of targeting NMDA receptors, which was composed of a two-photon naphthalimide fluorophore, a GSH-reactive group sulfonamide, and an ifenprodil targeting group for the NMDA receptor. This probe exhibited high selectivity toward GSH in comparison to other similar amino acids. Two-photon fluorescence microscopy allowed this probe to successfully monitor GSH in neuronal cells and hippocampal tissues with an excitation at 750 nm. It could serve as a potential practical imaging tool to explore the function of GSH and related biological processes in the brain.

Effect of Lenalidomide on Pentylenetetrazole-Induced Clonic Seizure Threshold in Mice: A Role for N-Methyl-D-Aspartic Acid Receptor/Nitric Oxide Pathway

Background and Purpose

Accumulating evidence suggest that lenalidomide, a structural analog of thalidomide, has neuro-modulatory and neuroprotective properties. In the present study, we investigated effects of acute administration of lenalidomide on clonic seizure threshold in mice induced by pentylenetetrazole (PTZ) and possible role of N-methyl-D-aspartic acid receptor (NMDAR) and nitric oxide (NO) pathway.

Methods

We have utilized a clonic model of seizure in NMRI mice induced by PTZ to evaluate the potential effect of lenalidomide on seizure threshold. Different doses of lenalidomide (5, 10, 20, and 50 mg/kg, intraperitoneal [i.p.]) were administered 1 hour before PTZ. To evaluate probable role of NMDAR/NO signaling, the non-selective NO synthase inhibitor L-N^G-nitroarginine methyl ester (L-NAME; 10 mg/kg, i.p.), neuronal NOS (nNOS) inhibitor 7-nitroindazole (7-NI; 30 mg/kg, i.p.), selective inducible NOS inhibitor aminoguanidine (AG; 100 mg/kg, i.p.), selective NMDAR antagonist MK-801 (0.01 mg/kg, i.p.), and selective NMDAR agonist D-serine (30 mg/kg, i.p.) were injected 15 minutes before lenalidomide.

Results

Lenalidomide at 10 and 20 mg/kg significantly elevated the PTZ-induced seizure thresholds. Interestingly, L-NAME (10 mg/kg, i.p), 7-NI (30 mg/kg, i.p), and AG (100 mg/kg, i.p) reversed the anticonvulsive effect of lenalidomide (10 mg/kg). Moreover, treatment with the NMDAR agonist D-serine (30 mg/kg, i.p.) did not alter the anticonvulsive properties of lenalidomide (10 mg/kg, i.p). However, the NMDAR antagonist MK-801 (0.01 mg/kg, i.p) significantly reversed the anticonvulsive effects of lenalidomide (10 mg/kg).

Conclusions

Our study demonstrated a role for the NMDAR/NO pathway in the anticonvulsive effects of lenalidomide on the PTZ-induced clonic seizures in mice.

Structure modulation on fluorescent probes for biothiols and the reversible imaging of glutathione in living cells

The detection of small molecular biothiols (cysteine, homocysteine and glutathione) is of great importance, as they involve in a series of physiological and pathological processes and are associated with many diseases. To realize the real-time monitoring of a specific biothiol, a rapid and reversible probe is required. Therefore, three probes, namely, o-MNPy, m-MNPy and p-MNPy, with pyridine substituted α, β-unsaturated ketone as the recognition site, were reported here, and the reactivity of the recognition site was finely tuned by the connection mode of the pyridine unit. To single out the optimal one, the response performances of three probes toward each biothiol were systemically studied, taking the differences of the intracellular contents of three biothiols into account during the evaluation. Biothiols reacted with the probes through Michael addition, and results showed that the slight structural variations could affect the performances of the probes obviously. p-MNPy with the pyridine unit connected to the recognition site through the para-position of the nitrogen atom, revealed the best sensing ability among the three probes. It demonstrated rapid response, good selectivity and sensitivity, excellent pH adaptability to Cys and GSH, and displayed reversible detection toward GSH. Finally, p-MNPy was successfully applied to track the GSH fluctuations under the oxidative stress stimulated by H₂O₂ in living cells.

A reversible fluorescent probe for GSH was obtained through structure modulation, by which the intracellular GSH fluctuation was imaged.

Drugs Based on NMDAR Hypofunction Hypothesis in Schizophrenia

Treatments for negative symptoms and cognitive dysfunction in schizophrenia remain issues that psychiatrists around the world are trying to solve. Their mechanisms may be associated with N-methyl-D-aspartate receptors (NMDARs). The NMDAR hypofunction hypothesis for schizophrenia was brought to the fore mainly based on the clinical effects of NMDAR antagonists and anti-NMDAR encephalitis pathology. Drugs targeted at augmenting NMDAR function in the brain seem to be promising in improving negative symptoms and cognitive dysfunction in patients with schizophrenia. In this review, we list NMDAR-targeted drugs and report on related clinical studies. We then summarize their effects on negative symptoms and cognitive dysfunction and analyze the unsatisfactory outcomes of these clinical studies according to the improved glutamate hypothesis that has been revealed in animal models. We aimed to provide perspectives for scientists who sought therapeutic strategies for negative symptoms and cognitive dysfunction in schizophrenia based on the NMDAR hypofunction hypothesis.

The Extracellular Domains of GluN Subunits Play an Essential Role in Processing NMDA Receptors in the ER

N-methyl-D-aspartate receptors (NMDARs) belong to a family of ionotropic glutamate receptors that play essential roles in excitatory neurotransmission and synaptic plasticity in the mammalian central nervous system (CNS). Functional NMDARs consist of heterotetramers comprised of GluN1, GluN2A-D, and/or GluN3A-B subunits, each of which contains four membrane domains (M1 through M4), an intracellular C-terminal domain, a large extracellular N-terminal domain composed of the amino-terminal domain and the S1 segment of the ligand-binding domain (LBD), and an extracellular loop between M3 and M4, which contains the S2 segment of the LBD. Both the number and type of NMDARs expressed at the cell surface are regulated at several levels, including their translation and posttranslational maturation in the endoplasmic reticulum (ER), intracellular trafficking via the Golgi apparatus, lateral diffusion in the plasma membrane, and internalization and degradation. This review focuses on the roles played by the extracellular regions of GluN subunits in ER processing. Specifically, we discuss the presence of ER retention signals, the integrity of the LBD, and critical N-glycosylated sites and disulfide bridges within the NMDAR subunits, each of these steps must pass quality control in the ER in order to ensure that only correctly assembled NMDARs are released from the ER for subsequent processing and trafficking to the surface. Finally, we discuss the effect of pathogenic missense mutations within the extracellular domains of GluN subunits with respect to ER processing of NMDARs.

Targeting redox-altered plasticity to reactivate synaptic function: A novel therapeutic strategy for cognitive disorder

Redox-altered plasticity refers to redox-dependent reversible changes in synaptic plasticity via altering functions of key proteins, such as N-methyl-d-aspartate receptor (NMDAR). Age-related cognitive disorders includes Alzheimer's disease (AD), vascular dementia (VD), and age-associated memory impairment (AAMI). Based on the critical role of NMDAR-dependent long-term potentiation (LTP) in memory, the increase of reactive oxygen species in cognitive disorders, and the sensitivity of NMDAR to the redox status, converging lines have suggested the redox-altered NMDAR-dependent plasticity might underlie the synaptic dysfunctions associated with cognitive disorders. In this review, we summarize the involvement of redox-altered plasticity in cognitive disorders by presenting the available evidence. According to reports from our laboratory and other groups, this "redox-altered plasticity" is more similar to functional changes rather than organic injuries, and strategies targeting redox-altered plasticity using pharmacological agents might reverse synaptic dysfunctions and memory abnormalities in the early stage of cognitive disorders. Targeting redox modifications for NMDARs may serve as a novel therapeutic strategy for memory deficits.

Ultrasensitive and selective fluorescent sensor for cysteine and application to drug analysis and bioimaging

A fluorescent sensor based on coumarin-maleimide conjugate was developed for efficient discrimination of Cys from Hcy and GSH in both organic and aqueous solution. Addition of Cys to the non-fluorescent sensor solution in DMF induced bright blue fluorescence and enhanced the fluorescence intensity by 320-fold while other amino acids and biothiols (Gly, Hcy, GSH, Glu, Val, Tyr, Arg, Trp, Lys, His, Leu, Phe, Asp and Met) did not bring about remarked change. The sensor responds to Cys extremely rapidly. If Cys was added to the sensor solution, the fluorescence intensity increased by 170-fold immediately and attained the maximum value in 5 min. A linear relationship was observed between Cys concentration within 2-20 μM and the fluorescence intensity of the sensor solution. The detection limit of the sensor toward Cys is as low as 4.7 nM. The sensor is also effective for specific detection of Cys in aqueous (DMF/H₂O = 9:1, v/v) solution. Practical application of the sensor to drug analysis and bioimaging of living Hela cells has been verified. Possible sensing mechanism of the sensor toward Cys has been proposed.

A modular template for the design of thiol-triggered sensors and prodrugs

A unique reaction between thiols (RSH) and alkyl sulfonylbenzothiazole was discovered. This reaction was specific for thiols and produced a sulfinic acid (RSO₂H) as the intermediate, which further triggered an intramolecular cyclization to release a -OH containing payload. This reaction was used to develop thiol-triggered fluorescent sensors and prodrugs. The modular design of this template provides tunability of the release profiles of the payloads.

A novel near-infrared fluorescent probe based on isophorone for the bioassay of endogenous cysteine

A dicyanoisophorone/acrylate-combined probe (DDP) was synthesized and designed as a near-infrared (NIR) fluorescent sensor for the rapid identification of Cys over Hcy and GSH in aqueous solution with a large Stokes shift (143 nm). The detection limit of Cys was 1.23 μM, which was lower than that of the intracellular Cys concentration. DDP was cell membrane-permeable and had been successfully applied to the detection of intracellular Cys in HeLa cells. The detection mechanism was determined by ¹H NMR titration, MS and DFT calculations.

Nitric Oxide and S-Nitrosylation in Cardiac Regulation: G Protein-Coupled Receptor Kinase-2 and β-Arrestins as Targets

Cardiac diseases including heart failure (HF), are the leading cause of morbidity and mortality globally. Among the prominent characteristics of HF is the loss of β-adrenoceptor (AR)-mediated inotropic reserve. This is primarily due to the derangements in myocardial regulatory signaling proteins, G protein-coupled receptor (GPCR) kinases (GRKs) and β-arrestins (β-Arr) that modulate β-AR signal termination via receptor desensitization and downregulation. GRK2 and β-Arr2 activities are elevated in the heart after injury/stress and participate in HF through receptor inactivation. These GPCR regulators are modulated profoundly by nitric oxide (NO) produced by NO synthase (NOS) enzymes through S-nitrosylation due to receptor-coupled NO generation. S-nitrosylation, which is NO-mediated modification of protein cysteine residues to generate an S-nitrosothiol (SNO), mediates many effects of NO independently from its canonical guanylyl cyclase/cGMP/protein kinase G signaling. Herein, we review the knowledge on the NO system in the heart and S-nitrosylation-dependent modifications of myocardial GPCR signaling components GRKs and β-Arrs.

Protein disulfide isomerase-mediated S-nitrosylation facilitates surface expression of P2X7 receptor following status epilepticus

Background

P2X7 receptor (P2X7R) is an ATP-gated nonselective cationic channel playing important roles in a variety of physiological functions, including inflammation, and apoptotic or necrotic cell death. An extracellular domain has ten cysteine residues forming five intrasubunit disulfide bonds, which are needed for the P2X7R trafficking to the cell surface and the recognition of surface epitopes of apoptotic cells and bacteria. However, the underlying mechanisms of redox/S-nitrosylation of cysteine residues on P2X7R and its role in P2X7R-mediated post-status epilepticus (SE, a prolonged seizure activity) events remain to be answered.

Methods

Rats were given pilocarpine (380 mg/kg i.p.) to induce SE. Animals were intracerebroventricularly infused N^ω-nitro-l-arginine methyl ester hydrochloride (L-NAME, a NOS inhibitor) 3 days before SE, or protein disulfide isomerase (PDI) siRNA 1 day after SE using an osmotic pump. Thereafter, we performed Western blot, co-immunoprecipitation, membrane fraction, measurement of S-nitrosylated (SNO)-thiol and total thiol, Fluoro-Jade B staining, immunohistochemistry, and TUNEL staining.

Results

SE increased S-nitrosylation ratio of P2X7R and the PDI-P2X7R bindings, which were abolished by L-NAME and PDI knockdown. In addition, both L-NAME and PDI siRNA attenuated SE-induced microglial activation and astroglial apoptosis. L-NAME and PDI siRNA also ameliorated the increased P2X7R surface expression induced by SE.

Conclusions

These findings suggest that PDI-mediated redox/S-nitrosylation may facilitate the trafficking of P2X7R, which promotes microglial activation and astroglial apoptosis following SE. Therefore, our findings suggest that PDI-mediated regulations of dynamic redox status and S-nitrosylation of P2X7R may be a critical mechanism in the neuroinflammation and astroglial death following SE.

Redox Post-translational Modifications of Protein Thiols in Brain Aging and Neurodegenerative Conditions-Focus on S-Nitrosation

Reactive oxygen species and reactive nitrogen species (RONS) are by-products of aerobic metabolism. RONS trigger a signaling cascade that can be transduced through oxidation-reduction (redox)-based post-translational modifications (redox PTMs) of protein thiols. This redox signaling is essential for normal cellular physiology and coordinately regulates the function of redox-sensitive proteins. It plays a particularly important role in the brain, which is a major producer of RONS. Aberrant redox PTMs of protein thiols can impair protein function and are associated with several diseases. This mini review article aims to evaluate the role of redox PTMs of protein thiols, in particular S-nitrosation, in brain aging, and in neurodegenerative diseases. It also discusses the potential of using redox-based therapeutic approaches for neurodegenerative conditions.

Potential Roles of Redox Dysregulation in the Development of Schizophrenia

Converging evidence implicates redox dysregulation as a pathological mechanism driving the emergence of psychosis. Increased oxidative damage and decreased capacity of intracellular redox modulatory systems are consistent findings in persons with schizophrenia as well as in persons at clinical high risk who subsequently developed frank psychosis. Levels of glutathione, a key regulator of cellular redox status, are reduced in the medial prefrontal cortex, striatum, and thalamus in schizophrenia. In humans with schizophrenia and in rodent models recapitulating various features of schizophrenia, redox dysregulation is linked to reductions of parvalbumin containing gamma-aminobutyric acid (GABA) interneurons and volumes of their perineuronal nets, white matter abnormalities, and microglia activation. Importantly, the activity of transcription factors, kinases, and phosphatases regulating diverse aspects of neurodevelopment and synaptic plasticity varies according to cellular redox state. Molecules regulating interneuron function under redox control include NMDA receptor subunits GluN1 and GluN2A as well as KEAP1 (regulator of transcription factor NRF2). In a rodent schizophrenia model characterized by impaired glutathione synthesis, the Gclm knockout mouse, oxidative stress activated MMP9 (matrix metalloprotease 9) via its redox-responsive regulatory sites, causing a cascade of molecular events leading to microglia activation, perineural net degradation, and impaired NMDA receptor function. Molecular pathways under redox control are implicated in the etiopathology of schizophrenia and are attractive drug targets for individualized drug therapy trials in the contexts of prevention and treatment of psychosis.

Multiple cellular targets involved in the antidepressant-like effect of glutathione

A previous study demonstrated that glutathione (GSH) produces specific antidepressant-like effect in the forced swimming test (FST), a predictive test of antidepressant activity. The present study investigated the involvement of multiple cellular targets implicated in the antidepressant-like effect of GSH in the FST. The antidepressant-like effect of GSH (300 nmol/site, icv) lasted up to 3 h when mice were submitted to FST. The central administration of oxidized GSH (GSSG, 3-300 nmol/site) did not alter the behavior of mice submitted to the FST. Furthermore, the combined treatment of sub-effective doses of GSH (100 nmol/site, icv) with a sub-effective dose of classical antidepressants (fluoxetine 10 mg/kg, and imipramine 5 mg/kg, ip) presented synergistic effect by decreasing the immobility time in the FST. The antidepressant-like effect of GSH was abolished by prazosin (1 mg/kg, ip, α₁-adrenoceptor antagonist), baclofen (1 mg/kg, ip, GABAB receptor agonist), bicuculline (1 mg/kg, ip, GABAA receptor antagonist), l-arginine (750 mg/kg, ip, NO precursor), SNAP (25 μg/site, icv, NO donor), but not by yohimbine (1 mg/kg, ip, α₂-adrenoceptor antagonist). The NMDA receptor antagonists, MK-801(0.001 mg/kg, ip) or GMP (0.5 mg/kg, ip), potentiated the effect of a sub-effective dose of GSH in the FST. These results suggest that the antidepressant-like effect induced by GSH is connected to the activation of α1 adrenergic and GABAA receptors, as well as the inhibition of GABAB and NMDA receptors and NO biosyntesis. We speculate that redox-mediated signaling on the extracelular portion of cell membrane receptors would be a common mechanism of action of GSH.

A HIF1a-Dependent Pro-Oxidant State Disrupts Synaptic Plasticity and Impairs Spatial Memory in Response to Intermittent Hypoxia

Sleep apnea causes cognitive deficits and is associated with several neurologic diseases. Intermittent hypoxia (IH) is recognized as a principal mediator of pathophysiology associated with sleep apnea, yet the basis by which IH contributes to impaired cognition remains poorly defined. Using a mouse model exposed to IH, this study examines how the transcription factor, hypoxia inducible factor 1a (HIF1a), contributes to disrupted synaptic physiology and spatial memory. In wild-type mice, impaired performance in the Barnes maze caused by IH coincided with a loss of NMDA receptor (NMDAr)-dependent long-term potentiation (LTP) in area CA1 and increased nuclear HIF1a within the hippocampus. IH-dependent HIF1a signaling caused a two-fold increase in expression of the reactive oxygen species (ROS) generating enzyme NADPH oxidase 4 (NOX4). These changes promoted a pro-oxidant state and the downregulation of GluN1 within the hippocampus. The IH-dependent effects were not present in either mice heterozygous for Hif1a (HIF1a^+/-) or wild-type mice treated with the antioxidant manganese (III) tetrakis(1-methyl-4-pyridyl) porphyrin (MnTMPyP). Our findings indicate that HIF1a-dependent changes in redox state are central to the mechanism by which IH disrupts hippocampal synaptic plasticity and impairs spatial memory. This mechanism may enhance the vulnerability for cognitive deficit and lower the threshold for neurologic diseases associated untreated sleep apnea.

NMDA Receptor Antagonists: Repositioning of Memantine as a Multitargeting Agent for Alzheimer's Therapy

Alzheimer's disease (AD) is a progressive neurodegenerative disease that causes problems with memory, thinking, and behavior. Currently, there is no drug that can reduce the pathological events of this degenerative disease but symptomatic relief is possible that can abate the disease condition. N-methyl-D-aspartate (NMDA) receptors exert a critical role for synaptic plasticity as well as transmission. Overstimulation of glutamate receptors, predominantly NMDA type, may cause excitotoxic effects on neurons and is recommended as a mechanism for neurodegeneration. Atypical activation of the NMDA receptor has been suggested for AD by synaptic dysfunction. NMDA receptor antagonists especially memantine block the NMDA receptor and can reduce the influx of calcium (Ca2+) ions into neuron, thus, toxic intracellular events are not activated. This review represents the role of NMDA receptors antagonists as potential therapeutic agents to reduce AD. Moreover, this review highlights the repositioning of memantine as a potential novel therapeutic multitargeting agent for AD.

How the Local Environment of Functional Sites Regulates Protein Function

Proteins form complex biological machineries whose functions in the cell are highly regulated at both the cellular and molecular levels. Cellular regulation of protein functions involves differential gene expressions, post-translation modifications, and signaling cascades. Molecular regulation, on the other hand, involves tuning an optimal local protein environment for the functional site. Precisely how a protein achieves such an optimal environment around a given functional site is not well understood. Herein, by surveying the literature, we first summarize the various reported strategies used by certain proteins to ensure their correct functioning. We then formulate three key physicochemical factors for regulating a protein's functional site, namely, (i) its immediate interactions, (ii) its solvent accessibility, and (iii) its conformational flexibility. We illustrate how these factors are applied to regulate the functions of free/metal-bound Cys and Zn sites in proteins.

PDI-Mediated Reduction of Disulfide Bond on PSD95 Increases Spontaneous Seizure Activity by Regulating NR2A-PSD95 Interaction in Epileptic Rats Independent of S-Nitrosylation

Postsynaptic density-95 (PSD95), a major scaffolding protein, is critical in coupling N-methyl-D-aspartate receptor (NMDAR) to cellular signaling networks in the central nervous system. A couple of cysteine residues in the N-terminus of PSD95 are potential sites for disulfide bonding, S-nitrosylation and/or palmitoylation. Protein disulfide isomerase (PDI) reduces disulfide bonds (S-S) to free thiol (-SH) on various proteins. However, the involvement of PDI in disulfide bond formation/S-nitrosylation of PSD95 and its role in epilepsy are still unknown. In the present study, acute seizure activity significantly increased the bindings of PDI to NR2A, but not to PSD95, while it decreased the NR2A–PSD95 binding. In addition, pilocarpine-induced seizures increased the amount of nitrosylated (SNO-) thiols, not total (free and SNO-) thiols, on PSD95. Unlike acute seizure, spontaneous seizing rats showed the increases in PDI–PSD95 binding, total- and SNO-thiol levels on PSD95, and NR2A–PSD95 interaction. PDI siRNA effectively reduced spontaneous seizure activity with decreases in total thiol level on PSD95 and NR2A–PSD95 association. These findings indicate that PDI-mediated reduction of disulfide-bond formations may facilitate the NR2A–PSD95 binding and contribute to spontaneous seizure generation in epileptic animals.