S-nitrosylation of AMPA receptor GluA1 regulates phosphorylation, single-channel conductance, and endocytosis

A discrete subpopulation of PFC-LHb neurons govern cocaine place preference

Addiction is a complex behavioral disorder characterized by compulsive drug-seeking and drug use despite harmful consequences. The prefrontal cortex (PFC) plays a crucial role in cocaine addiction, involving decision-making, impulse control, memory, and emotional regulation. The PFC interacts with the brain's reward system, including the ventral tegmental area (VTA) and nucleus accumbens (NAc). The PFC also projects to the lateral habenula (LHb), a brain region critical for encoding negative reward and regulating the reward system. In the current study, we examined the role of PFC-LHb projections in regulating cocaine reward-related behaviors. We found that optogenetic stimulation of the PFC-LHb circuit during cocaine conditioning abolished cocaine preference without causing aversion. In addition, increased c-fos expression in LHb neurons was observed in animals that received optic stimulation during cocaine conditioning, supporting the circuit's involvement in cocaine preference regulation. Molecular analysis in animals that received optic stimulation revealed that cocaine-induced alterations in the expression of GluA1 subunit of AMPA receptor was normalized to saline levels in a region-specific manner. Moreover, GluA1 serine phosphorylation on S845 and S831 were differentially altered in LHb and VTA but not in the PFC. Together these findings highlight the critical role of the PFC-LHb circuit in controlling cocaine reward-related behaviors and shed light on the underlying mechanisms. Understanding this circuit's function may provide valuable insights into addiction and contribute to developing targeted treatments for substance use disorders.

miR-429-3p mediates memory decline by targeting MKP-1 to reduce surface GluA1-containing AMPA receptors in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a leading cause of dementia in the elderly. Mitogen-activated protein kinase phosphatase 1 (MKP-1) plays a neuroprotective role in AD. However, the molecular mechanisms underlying the effects of MKP-1 on AD have not been extensively studied. MicroRNAs (miRNAs) regulate gene expression at the post-transcriptional level, thereby repressing mRNA translation. Here, we reported that the microRNA-429-3p (miR-429-3p) was significantly increased in the brain of APP23/PS45 AD model mice and N2AAPP AD model cells. We further found that miR-429-3p could downregulate MKP-1 expression by directly binding to its 3'-untranslated region (3' UTR). Inhibition of miR-429-3p by its antagomir (A-miR-429) restored the expression of MKP-1 to a control level and consequently reduced the amyloidogenic processing of APP and Aβ accumulation. More importantly, intranasal administration of A-miR-429 successfully ameliorated the deficits of hippocampal CA1 long-term potentiation and spatial learning and memory in AD model mice by suppressing extracellular signal-regulated kinase (ERK1/2)-mediated GluA1 hyperphosphorylation at Ser831 site, thereby increasing the surface expression of GluA1-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs). Together, these results demonstrate that inhibiting miR-429-3p to upregulate MKP-1 effectively improves cognitive and synaptic functions in AD model mice, suggesting that miR-429/MKP-1 pathway may be a novel therapeutic target for AD treatment.

"NO" Time in Fear Response: Possible Implication of Nitric-Oxide-Related Mechanisms in PTSD

Post-traumatic stress disorder (PTSD) is a psychiatric condition characterized by persistent fear responses and altered neurotransmitter functioning due to traumatic experiences. Stress predominantly affects glutamate, a neurotransmitter crucial for synaptic plasticity and memory formation. Activation of the N-Methyl-D-Aspartate glutamate receptors (NMDAR) can trigger the formation of a complex comprising postsynaptic density protein-95 (PSD95), the neuronal nitric oxide synthase (nNOS), and its adaptor protein (NOS1AP). This complex is pivotal in activating nNOS and nitric oxide (NO) production, which, in turn, activates downstream pathways that modulate neuronal signaling, including synaptic plasticity/transmission, inflammation, and cell death. The involvement of nNOS and NOS1AP in the susceptibility of PTSD and its comorbidities has been widely shown. Therefore, understanding the interplay between stress, fear, and NO is essential for comprehending the maintenance and progression of PTSD, since NO is involved in fear acquisition and extinction processes. Moreover, NO induces post-translational modifications (PTMs), including S-nitrosylation and nitration, which alter protein function and structure for intracellular signaling. Although evidence suggests that NO influences synaptic plasticity and memory processing, the specific role of PTMs in the pathophysiology of PTSD remains unclear. This review highlights pathways modulated by NO that could be relevant to stress and PTSD.

Inhibition of ANXA2 activity attenuates epileptic susceptibility and GluA1 phosphorylation

INTRODUCTION

Annexin A2 (ANXA2) participates in the pathology of a variety of diseases. Nevertheless, the impact of ANXA2 on epilepsy remains to be clarified.

AIMS

Hence, the study aimed at investigating the underlying role of ANXA2 in epilepsy through behavioral, electrophysiological, and pathological analyses.

RESULTS

It was found that ANXA2 was markedly upregulated in the cortical tissues of temporal lobe epilepsy patients (TLE), kainic acid (KA)-induced epilepsy mice, and in a seizure-like model in vitro. ANXA2 silencing in mice suppressed first seizure latency, number of seizures, and seizure duration in behavioral analysis. In addition, abnormal brain discharges were less frequent and shorter in the hippocampal local field potential (LFP) record. Furthermore, the results showed that the frequency of miniature excitatory postsynaptic currents was decreased in ANXA2 knockdown mice, indicating that the excitatory synaptic transmission is reduced. Co-immunoprecipitation (COIP) experiments demonstrated that ANXA2 interacted with the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) subunit GluA1. Moreover, ANXA2 knockdown decreased GluA1 expression on the cell surface and its phosphorylation onserine 831 and serine 845, related to the decreased phosphorylation levels mediated by protein kinases A and C (PKA and PKC).

CONCLUSIONS

This study covers a previously unknown and key function of ANXA2 in epilepsy. These findings indicate that ANXA2 can regulate excitatory synaptic activity mediated by AMPAR subunit GluA1 to improve seizure activity, which can provide novel insights for the treatment and prevention of epilepsy.

The PrLGlu→avBNSTGABA circuit rapidly modulates depression-like behaviors in male mice

Depression is a global disease with a high prevalence. Here, we examine the role of the circuit from prelimbic mPFC (PrL) to the anterior ventral bed nucleus of the stria terminalis (avBNST) in depression-like mice through behavioral tests, immunofluorescence, chemogenetics, optogenetics, pharmacology, and fiber photometry. Mice exposed to chronic restraint stress with individual housing displayed depression-like behaviors. Optogenetic or chemogenetic activation of the avBNST-projecting glutamatergic neurons in the PrL had an antidepressant effect. Moreover, we found that α-amino-3-hydroxy-5-methyl-4-isoxazole-propionicacid receptors (AMPARs) play a dominant role in this circuit. Systemic administration of ketamine profoundly alleviated depression-like behaviors in the mice and rapidly rescued the decreased activity in the PrLGlu→avBNSTGABA circuit. Furthermore, the fast-acting effect of ketamine on depressive behaviors was diminished when the circuit was inhibited. To summarize, activating the PrLGlu→avBNSTGABA circuit quickly ameliorated depression-like behaviors. Thus, we propose the PrLGlu→avBNSTGABA circuit as a target for fast regulation of depression.

Nitric Oxide: Physiological Functions, Delivery, and Biomedical Applications

Nitric oxide (NO) is a gaseous molecule that has a central role in signaling pathways involved in numerous physiological processes (e.g., vasodilation, neurotransmission, inflammation, apoptosis, and tumor growth). Due to its gaseous form, NO has a short half-life, and its physiology role is concentration dependent, often restricting its function to a target site. Providing NO from an external source is beneficial in promoting cellular functions and treatment of different pathological conditions. Hence, the multifaceted role of NO in physiology and pathology has garnered massive interest in developing strategies to deliver exogenous NO for the treatment of various regenerative and biomedical complexities. NO-releasing platforms or donors capable of delivering NO in a controlled and sustained manner to target tissues or organs have advanced in the past few decades. This review article discusses in detail the generation of NO via the enzymatic functions of NO synthase as well as from NO donors and the multiple biological and pathological processes that NO modulates. The methods for incorporating of NO donors into diverse biomaterials including physical, chemical, or supramolecular techniques are summarized. Then, these NO-releasing platforms are highlighted in terms of advancing treatment strategies for various medical problems.

Enhanced AMPAR-dependent synaptic transmission by S-nitrosylation in the vmPFC contributes to chronic inflammatory pain-induced persistent anxiety in mice

Chronic pain patients often have anxiety disorders, and some of them suffer from anxiety even after analgesic administration. In this study, we investigated the role of AMPAR-mediated synaptic transmission in the ventromedial prefrontal cortex (vmPFC) in chronic pain-induced persistent anxiety in mice and explored potential drug targets. Chronic inflammatory pain was induced in mice by bilateral injection of complete Freund's adjuvant (CFA) into the planta of the hind paws; anxiety-like behaviours were assessed with behavioural tests; S-nitrosylation and AMPAR-mediated synaptic transmission were examined using biochemical assays and electrophysiological recordings, respectively. We found that CFA induced persistent upregulation of AMPAR membrane expression and function in the vmPFC of anxious mice but not in the vmPFC of non-anxious mice. The anxious mice exhibited higher S-nitrosylation of stargazin (an AMPAR-interacting protein) in the vmPFC. Inhibition of S-nitrosylation by bilaterally infusing an exogenous stargazin (C302S) mutant into the vmPFC rescued the surface expression of GluA1 and AMPAR-mediated synaptic transmission as well as the anxiety-like behaviours in CFA-injected mice, even after ibuprofen treatment. Moreover, administration of ZL006, a small molecular inhibitor disrupting the interaction of nNOS and PSD-95 (20 mg·kg-1·d-1, for 5 days, i.p.), significantly reduced nitric oxide production and S-nitrosylation of AMPAR-interacting proteins in the vmPFC, resulting in anxiolytic-like effects in anxious mice after ibuprofen treatment. We conclude that S-nitrosylation is necessary for AMPAR trafficking and function in the vmPFC under chronic inflammatory pain-induced persistent anxiety conditions, and nNOS-PSD-95 inhibitors could be potential anxiolytics specific for chronic inflammatory pain-induced persistent anxiety after analgesic treatment.

The role of post-translational modifications in synaptic AMPA receptor activity

AMPA-type receptors for the neurotransmitter glutamate are very dynamic entities, and changes in their synaptic abundance underlie different forms of synaptic plasticity, including long-term synaptic potentiation (LTP), long-term depression (LTD) and homeostatic scaling. The different AMPA receptor subunits (GluA1-GluA4) share a common modular structure and membrane topology, and their intracellular C-terminus tail is responsible for the interaction with intracellular proteins important in receptor trafficking. The latter sequence differs between subunits and contains most sites for post-translational modifications of the receptors, including phosphorylation, O-GlcNAcylation, ubiquitination, acetylation, palmitoylation and nitrosylation, which affect differentially the various subunits. Considering that each single subunit may undergo modifications in multiple sites, and that AMPA receptors may be formed by the assembly of different subunits, this creates multiple layers of regulation of the receptors with impact in synaptic function and plasticity. This review discusses the diversity of mechanisms involved in the post-translational modification of AMPA receptor subunits, and their impact on the subcellular distribution and synaptic activity of the receptors.

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.

Tuning brain networks: The emerging role of transcranial direct current stimulation on structural plasticity

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique (NIBS) that has been proven to promote beneficial effects in a range of neurological and psychiatric disorders. Unfortunately, although has been widely investigated, the mechanism comprehension around tDCS effects presents still some gaps. Therefore, scientists are still trying to uncover the cellular and molecular mechanisms behind its positive effects to permit a more suitable application. Experimental models have provided converging evidence that tDCS elicits improvements in learning and memory by modulating both excitability and synaptic plasticity in neurons. Recently, among tDCS neurobiological effects, neural synchronization and dendritic structural changes have been reported in physiological and pathological conditions, suggesting possible effects at the neuronal circuit level. In this review, we bring in to focus the emerging effects of tDCS on the structural plasticity changes and neuronal rewiring, with the intent to match these two aspects with the underpinning molecular mechanisms identified so far, providing a new perspective to work on to unveil novel tDCS therapeutic use to treat brain dysfunctions.

Facial Stimulation Induces Long-Term Potentiation of Mossy Fiber-Granule Cell Synaptic Transmission via GluN2A-Containing N-Methyl-D-Aspartate Receptor/Nitric Oxide Cascade in the Mouse Cerebellum

Long-term synaptic plasticity in the cerebellar cortex is a possible mechanism for motor learning. Previous studies have demonstrated the induction of mossy fiber-granule cell (MF-GrC) synaptic plasticity under in vitro and in vivo conditions, but the mechanisms underlying sensory stimulation-evoked long-term synaptic plasticity of MF-GrC in living animals are unclear. In this study, we investigated the mechanism of long-term potentiation (LTP) of MF-GrC synaptic transmission in the cerebellum induced by train of facial stimulation at 20 Hz in urethane-anesthetized mice using electrophysiological recording, immunohistochemistry techniques, and pharmacological methods. Blockade of GABA_A receptor activity and repetitive facial stimulation at 20 Hz (240 pulses) induced an LTP of MF-GrC synapses in the mouse cerebellar cortical folium Crus II, accompanied with a decrease in paired-pulse ratio (N2/N1). The facial stimulation-induced MF-GrC LTP was abolished by either an N-methyl-D-aspartate (NMDA) receptor blocker, i.e., D-APV, or a specific GluNR2A subunit-containing NMDA receptor antagonist, PEAQX, but was not prevented by selective GluNR2B or GluNR2C/D subunit-containing NMDA receptor blockers. Application of GNE-0723, a selective and brain-penetrant-positive allosteric modulator of GluN2A subunit-containing NMDA receptors, produced an LTP of N1, accompanied with a decrease in N2/N1 ratio, and occluded the 20-Hz facial stimulation-induced MF-GrC LTP. Inhibition of nitric oxide synthesis (NOS) prevented the facial stimulation-induced MF-GrC LTP, while activation of NOS produced an LTP of N1, with a decrease in N2/N1 ratio, and occluded the 20-Hz facial stimulation-induced MF-GrC LTP. In addition, GluN2A-containing NMDA receptor immunoreactivity was observed in the mouse cerebellar granular layer. These results indicate that facial stimulation at 20 Hz induced LTP of MF-GrC synaptic transmission via the GluN2A-containing NMDA receptor/nitric oxide cascade in mice. The results suggest that the sensory stimulation-evoked LTP of MF-GrC synaptic transmission in the granular layer may play a critical role in cerebellar adaptation to native mossy fiber excitatory inputs and motor learning behavior in living animals.

Cocaine-induced projection-specific and cell type-specific adaptations in the nucleus accumbens

Cocaine craving, seeking, and relapse are mediated, in part, by cocaine-induced adaptive changes in the brain reward circuits. The nucleus accumbens (NAc) integrates and prioritizes different emotional and motivational inputs to the reward system by processing convergent glutamatergic projections from the medial prefrontal cortex, basolateral amygdala, ventral hippocampus, and other limbic and paralimbic brain regions. Medium spiny neurons (MSNs) are the principal projection neurons in the NAc, which can be divided into two major subpopulations, namely dopamine receptor D1- versus D2-expressing MSNs, with complementing roles in reward-associated behaviors. After cocaine experience, NAc MSNs exhibit complex and differential adaptations dependent on cocaine regimen, withdrawal time, cell type, location (NAc core versus shell), and related input and output projections, or any combination of these factors. Detailed characterization of these cellular adaptations has been greatly facilitated by the recent development of optogenetic/chemogenetic techniques combined with transgenic tools. In this review, we discuss such cell type- and projection-specific adaptations induced by cocaine experience. Specifically, (1) D1 and D2 NAc MSNs frequently exhibit differential adaptations in spinogenesis, glutamatergic receptor trafficking, and intrinsic membrane excitability, (2) cocaine experience differentially changes the synaptic transmission at different afferent projections onto NAc MSNs, (3) cocaine-induced NAc adaptations exhibit output specificity, e.g., being different at NAc-ventral pallidum versus NAc-ventral tegmental area synapses, and (4) the input, output, subregion, and D1/D2 cell type may together determine cocaine-induced circuit plasticity in the NAc. In light of the projection- and cell-type specificity, we also briefly discuss ensemble and circuit mechanisms contributing to cocaine craving and relapse after drug withdrawal.

Nitrergic modulation of ion channel function in regulating neuronal excitability

Nitric oxide (NO) signaling in the brain provides a wide range of functional properties in response to neuronal activity. NO exerts its effects through different signaling pathways, namely, through the canonical soluble guanylyl cyclase-mediated cGMP production route and via post-translational protein modifications. The latter pathways comprise cysteine S-nitrosylation and 3-nitrotyrosination of distinct tyrosine residues. Many ion channels are targeted by one or more of these signaling routes, which leads to their functional regulation under physiological conditions or facilities their dysfunction leading to channelopathies in many pathologies. The resulting alterations in ion channel function changes neuronal excitability, synaptic transmission, and action potential propagation. Transient and activity-dependent NO production mediates reversible ion channel modifications via cGMP and S-nitrosylation signaling, whereas more pronounced and longer-term NO production during conditions of elevated oxidative stress leads to increasingly cumulative and irreversible protein 3-nitrotyrosination. The complexity of this regulation and vast variety of target ion channels and their associated functional alterations presents a challenging task in assessing and understanding the role of NO signaling in physiology and disease.

Understanding the role of S-nitrosylation/nitrosative stress in inflammation and the role of cellular denitrosylases in inflammation modulation: Implications in health and diseases

S-nitrosylation is a very fundamental post-translational modification of protein and non-protein thiols due the involvement of it in a variety of cellular processes including activation/inhibition of several ion channels such as ryanodine receptor in the cardiovascular system; blood vessel dilation; cGMP signaling and neurotransmission. S-nitrosothiol homeostasis in the cell is tightly regulated and perturbations in homeostasis result in an altered redox state leading to a plethora of disease conditions. However, the exact role of S-nitrosylated proteins and nitrosative stress metabolites in inflammation and in inflammation modulation is not well-reviewed. The cell utilizes its intricate defense mechanisms i.e. cellular denitrosylases such as Thioredoxin (Trx) and S-nitrosoglutathione reductase (GSNOR) systems to combat nitric oxide (NO) pathology which has also gained current attraction as novel anti-inflammatory molecules. This review attempts to provide state-of-the-art knowledge from past and present research on the mechanistic role of nitrosative stress intermediates (RNS, OONO^-, PSNO) in pulmonary and autoimmune diseases and how cellular denitrosylases particularly GSNOR and Trx via imparting opposing effects can modulate and reduce inflammation in several health and disease conditions. This review would also bring into notice the existing gaps in current research where denitrosylases can be utilized for ameliorating inflammation that would leave avenues for future therapeutic interventions.

Inhibition of neuroinflammatory nitric oxide signaling suppresses glycation and prevents neuronal dysfunction in mouse prion disease

Several neurodegenerative diseases associated with protein misfolding (Alzheimer's and Parkinson's disease) exhibit oxidative and nitrergic stress following initiation of neuroinflammatory pathways. Associated nitric oxide (NO)-mediated posttranslational modifications impact upon protein functions that can exacerbate pathology. Nonenzymatic and irreversible glycation signaling has been implicated as an underlying pathway that promotes protein misfolding, but the direct interactions between both pathways are poorly understood. Here we investigated the therapeutic potential of pharmacologically suppressing neuroinflammatory NO signaling during early disease progression of prion-infected mice. Mice were injected daily with an NO synthase (NOS) inhibitor at early disease stages, hippocampal gene and protein expression levels of oxidative and nitrergic stress markers were analyzed, and electrophysiological characterization of pyramidal CA1 neurons was performed. Increased neuroinflammatory signaling was observed in mice between 6 and 10 wk postinoculation (w.p.i.) with scrapie prion protein. Their hippocampi were characterized by enhanced nitrergic stress associated with a decline in neuronal function by 9 w.p.i. Daily in vivo administration of the NOS inhibitor L-NAME between 6 and 9 w.p.i. at 20 mg/kg prevented the functional degeneration of hippocampal neurons in prion-diseased mice. We further found that this intervention in diseased mice reduced 3-nitrotyrosination of triose-phosphate isomerase, an enzyme involved in the formation of disease-associated glycation. Furthermore, L-NAME application led to a reduced expression of the receptor for advanced glycation end-products and the diminished accumulation of hippocampal prion misfolding. Our data suggest that suppressing neuroinflammatory NO signaling slows functional neurodegeneration and reduces nitrergic and glycation-associated cellular stress.

Phosphorylation of AMPA receptor subunit GluA1 regulates clathrin-mediated receptor internalization

Synaptic strength is altered during synaptic plasticity by controlling the number of AMPA receptors (AMPARs) at excitatory synapses. During long-term potentiation and synaptic up-scaling, AMPARs are accumulated at synapses to increase synaptic strength. Neuronal activity leads to phosphorylation of AMPAR subunit GluA1 and subsequent elevation of GluA1 surface expression, either by an increase in receptor forward trafficking to the synaptic membrane or a decrease in receptor internalization. However, the molecular pathways underlying GluA1 phosphorylation-induced elevation of surface AMPAR expression are not completely understood. Here, we employ fluorescence recovery after photobleaching (FRAP) to reveal that phosphorylation of GluA1 Serine 845 (S845) predominantly plays a role in receptor internalization than forward trafficking during synaptic plasticity. Notably, internalization of AMPARs depends upon the clathrin adaptor, AP2, which recruits cargo proteins into endocytic clathrin coated pits. In fact, we further reveal that an increase in GluA1 S845 phosphorylation by two distinct forms of synaptic plasticity diminishes the binding of the AP2 adaptor, reducing internalization, and resulting in elevation of GluA1 surface expression. We thus demonstrate a mechanism of GluA1 phosphorylation-regulated clathrin-mediated internalization of AMPARs.

Nitric Oxide Regulates GluA2-Lacking AMPAR Contribution to Synaptic Transmission of CA1 Apical but Not Basal Dendrites

The mechanisms of synaptic plasticity differ in distinct local circuits. In the CA1 region of the hippocampus, the mechanisms of long-term potentiation (LTP) at apical dendrites in stratum radiatum and basal dendrites in stratum oriens involve different molecular cascades. For instance, participation of nitric oxide in LTP induction was shown to be necessary only for apical dendrites. This phenomenon may play a key role in information processing in CA1, and one of the reasons for this difference may be differing synaptic characteristics in these regions. Here, we compared the synaptic responses to stimulation of apical and basal dendrites of CA1 pyramidal neurons and found a difference in the current–voltage characteristics of these inputs, which is presumably due to a distinct contribution of GluA2-lacking AMPA receptors to synaptic transmission. In addition, we obtained data that indicate the presence of these receptors in pyramidal dendrites in both stratum radiatum and stratum oriens. We also demonstrated that inhibition of NO synthase reduced the contribution of GluA2-lacking AMPA receptors at apical but not basal dendrites, and inhibition of soluble guanylate cyclase did not affect this phenomenon.

Yin and Yang in Post-Translational Modifications of Human D-Amino Acid Oxidase

In the central nervous system, the flavoprotein D-amino acid oxidase is responsible for catabolizing D-serine, the main endogenous coagonist of N-methyl-D-aspartate receptor. Dysregulation of D-serine brain levels in humans has been associated with neurodegenerative and psychiatric disorders. This D-amino acid is synthesized by the enzyme serine racemase, starting from the corresponding L-enantiomer, and degraded by both serine racemase (via an elimination reaction) and the flavoenzyme D-amino acid oxidase. To shed light on the role of human D-amino acid oxidase (hDAAO) in D-serine metabolism, the structural/functional relationships of this enzyme have been investigated in depth and several strategies aimed at controlling the enzymatic activity have been identified. Here, we focused on the effect of post-translational modifications: by using a combination of structural analyses, biochemical methods, and cellular studies, we investigated whether hDAAO is subjected to nitrosylation, sulfhydration, and phosphorylation. hDAAO is S-nitrosylated and this negatively affects its activity. In contrast, the hydrogen sulfide donor NaHS seems to alter the enzyme conformation, stabilizing a species with higher affinity for the flavin adenine dinucleotide cofactor and thus positively affecting enzymatic activity. Moreover, hDAAO is phosphorylated in cerebellum; however, the protein kinase involved is still unknown. Taken together, these findings indicate that D-serine levels can be also modulated by post-translational modifications of hDAAO as also known for the D-serine synthetic enzyme serine racemase.

Emerging Moonlighting Functions of the Branched-Chain Aminotransferase Proteins

Significance: Unique to the branched-chain aminotransferase (BCAT) proteins is their redox-active CXXC motif. Subjected to post-translational modification by reactive oxygen species and reactive nitrogen species, these proteins have the potential to adopt numerous cellular roles, which may be fundamental to their role in oncogenesis and neurodegenerative diseases. An understanding of the interplay of the redox regulation of BCAT with important cell signaling mechanisms will identify new targets for future therapeutics. Recent Advances: The BCAT proteins have been assigned novel thiol oxidoreductase activity that can accelerate the refolding of proteins, in particular when S-glutathionylated, supporting a chaperone role for BCAT in protein folding. Other metabolic proteins were also shown to have peroxide-mediated redox associations with BCAT, indicating that the cellular function of BCAT is more diverse. Critical Issues: While the role of branched-chain amino acid metabolism and its metabolites has dominated aspects of cancer research, less is known about the role of BCAT. The importance of the CXXC motif in regulating the BCAT activity under hypoxic conditions, a characteristic of tumors, has not been addressed. Understanding how these proteins operate under various cellular redox conditions will become important, in particular with respect to their moonlighting roles. Future Directions: Advances in the quantification of thiols, their measurement, and the manipulation of metabolons that rely on redox-based interactions should accelerate the investigation of the cellular role of moonlighting proteins such as BCAT. Given the importance of cross talk between signaling pathways, research should focus more on these "housekeeping" proteins paying attention to their wider application. Antioxid. Redox Signal. 34, 1048-1067.

The allosteric interplay between S-nitrosylation and glycine binding controls the activity of human serine racemase

Human serine racemase (hSR) catalyzes the biosynthesis of D-serine, an obligatory co-agonist of the NMDA receptors. It was previously found that the reversible S-nitrosylation of Cys113 reduces hSR activity. Here, we show by site-directed mutagenesis, fluorescence spectroscopy, mass spectrometry, and molecular dynamics that S-nitrosylation stabilizes an open, less-active conformation of the enzyme. The reaction of hSR with either NO or nitroso donors is conformation-dependent and occurs only in the conformation stabilized by the allosteric effector ATP, in which the ε-amino group of Lys114 acts as a base toward the thiol group of Cys113. In the closed conformation stabilized by glycine-an active-site ligand of hSR-the side chain of Lys114 moves away from that of Cys113, while the carboxyl side-chain group of Asp318 moves significantly closer, increasing the thiol pK_a and preventing the reaction. We conclude that ATP binding, glycine binding, and S-nitrosylation constitute a three-way regulation mechanism for the tight control of hSR activity. We also show that Cys113 undergoes H₂ O₂ -mediated oxidation, with loss of enzyme activity, a reaction also dependent on hSR conformation.

Molecular Mechanisms That Link Oxidative Stress, Inflammation, and Fibrosis in the Liver

Activated hepatic stellate cells (HSCs) and myofibroblasts are the main producers of extracellular matrix (ECM) proteins that form the fibrotic tissue that leads to hepatic fibrosis. Reactive oxygen species (ROS) can directly activate HSCs or induce inflammation or programmed cell death, especially pyroptosis, in hepatocytes, which in turn activates HSCs and fibroblasts to produce ECM proteins. Therefore, antioxidants and the nuclear factor E2-related factor-2 signaling pathway play critical roles in modulating the profibrogenic response. The master proinflammatory factors nuclear factor-κB (NF-κB) and the nucleotide-binding oligomerization domain (NOD)-like receptor protein 3 (NLRP3) inflammasome may coordinate to produce and activate profibrogenic molecules such as interleukins 1β and 18, which effectively activate HSCs, to produce large amounts of fibrotic proteins. Furthermore, the NLRP3 inflammasome activates pro-caspase 1, which is upregulated by NF-κB, to produce caspase 1, which induces pyroptosis via gasdermin and the activation of HSCs. ROS play central roles in the activation of the NF-κB and NLRP3 signaling pathways via IκB (an inhibitor of NF-κB) and thioredoxin-interacting protein, respectively, thereby linking the molecular mechanisms of oxidative stress, inflammation and fibrosis. Elucidating these molecular pathways may pave the way for the development of therapeutic tools to interfere with specific targets.

Emerging role of AMPA receptor subunit GluA1 in synaptic plasticity: Implications for Alzheimer's disease

It is well established that GluA1 mediated synaptic plasticity plays a central role in the early development of AD. The complex cellular and molecular mechanisms that enable GluA1‐related synaptic regulation remain to fully understood. Particularly, understanding the mechanisms that disrupt GluA1 related synaptic plasticity is central to the development of disease‐modifying therapies which are sorely needed as the incidence of AD rises. We surmise that the published evidence establishes deficits in synaptic plasticity as a central factor of AD aetiology. We additionally highlight potential therapeutic strategies for the treatment of AD, and we delve into the roles of GluA1 in learning and memory. Particularly, we review the current understanding of the molecular interactions that confer the actions of this ubiquitous excitatory receptor subunit including post‐translational modification and accessory protein recruitment of the GluA1 subunit. These are proposed to regulate receptor trafficking, recycling, channel conductance and synaptic transmission and plasticity.

Subunit-Specific Augmentation of AMPA Receptor Ubiquitination by Phorbol Ester

Excitatory neurotransmission relies on the precise targeting of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors to the neuronal plasma membrane. Activity-dependent ubiquitination of AMPA receptor (AMPAR) subunits sorts internalised receptors to late endosomes for degradation, which ultimately determines the number of AMPARs on neuronal membrane. Our recent study has demonstrated a functional cross-talk between the phosphorylation and ubiquitination of the GluA1 subunit in mammalian central neurons. However, the existence of such a cross modulation for the GluA2 subunit remains unknown. Here, we have shown that bicuculline induced GluA2 ubiquitination on the same lysine residues (Lys-870 and Lys-882) in the C-terminal as those elicited by the AMPA treatment. Interestingly, bicuculline-induced ubiquitination was markedly enhanced by the phospho-mimetic GluA2 S880E mutant. Pharmacological activation of protein kinase C (PKC) by phorbol ester, which mediates the phosphorylation of GluA2 at Ser-880, augmented bicuculline-induced ubiquitination of GluA2 in cultured neurons. This effect was specific for the GluA2 subunit because phorbol ester did not alter the level of GluA1 ubiquitination. However, phorbol ester-induced enhancement of GluA2 ubiquitination did not require Ser-880 phosphorylation. This suggests that pseudo-phosphorylation of Ser-880 is sufficient but is not necessary for the augmentation of bicuculline-induced GluA2 ubiquitination. Collectively, these data provide the first demonstration of subunit-specific modulation of AMPAR ubiquitination by the PKC-dependent signalling pathway in mammalian central neurons.

Alzheimer's Disease: A Contextual Link with Nitric Oxide Synthase

Nitric oxide (NO) is a gasotransmitter with pleiotropic effects which has made a great impact on biology and medicine. A multidimensional neuromodulatory role of NO has been shown in the brain with specific reference to neurodegenerative disorders like Alzheimer's disease (AD) and cognitive dysfunction. It has been found that NO/cGMP signalling pathway has an important role in learning and memory. Initially, it was considered that indirectly NO exerted neurotoxicity in AD via glutamatergic excitotoxicity. However, considering the early development of cognitive functions involved in the learning memory process including long term potentiation and synaptic plasticity, NO has a crucial role. Increasing evidence uncovered the above facts that isoforms of NOS viz endothelial NO synthase (eNOS), neuronal NO synthase (nNOS) and inducible NO synthase (iNOS) having a variable expression in AD are mainly responsible for learning and memory activities. In this review, we focus on the role of NOS isoforms in AD parallel to NO. Further, this review provides convergent evidence that NO could provide a therapeutic avenue in AD via modulation of the relevant NOS expression.

Zeta Inhibitory Peptide attenuates learning and memory by inducing NO-mediated downregulation of AMPA receptors

Zeta inhibitory peptide (ZIP), a PKMζ inhibitor, is widely used to interfere with the maintenance of acquired memories. ZIP is able to erase memory even in the absence of PKMζ, via an unknown mechanism. We found that ZIP induces redistribution of the AMPARGluA1 in HEK293 cells and primary cortical neurons, and decreases AMPAR-mediated currents in the nucleus accumbens (NAc). These effects were mimicked by free arginine or by a modified ZIP in which all but the arginine residues were replaced by alanine. Redistribution was blocked by a peptidase-resistant version of ZIP and by treatment with the nitric oxide (NO)-synthase inhibitor L-NAME. ZIP increased GluA1-S831 phosphorylation and ZIP-induced redistribution was blocked by nitrosyl-mutant GluA1-C875S or serine-mutant GluA1-S831A. Introducing the cleavable arginine-alanine peptide into the NAc attenuated expression of cocaine-conditioned reward. Together, these results suggest that ZIP may act as an arginine donor, facilitating NO-dependent downregulation of AMPARs, thereby attenuating learning and memory.

Zeta inhibitory peptide (ZIP) impairs the maintenance of acquired memories. ZIP is known as an inhibitor of PKMζ. Here, the authors unveil how ZIP impairs memory maintenance acting as an arginine donor, facilitating NO-dependent down-regulation of AMPARs, independently of its action on PKMζ.

Effect of Nitrosative Stress on the S-Nitroso-Proteome of Paracoccidioides brasiliensis

The fungi Paracoccidioides brasiliensis and Paracoccidioides lutzii are the causative agents of paracoccidioidomycosis (PCM), a systemic mycosis endemic to Latin America. This fungus is considered a facultative intracellular pathogen that is able to survive and replicate inside macrophages. The survival of the fungus during infection depends on its adaptability to various conditions, such as nitrosative/oxidative stress produced by the host immune cells, particularly alveolar macrophages. Currently, there is little knowledge about the Paracoccidioides spp. signaling pathways involved in the fungus evasion mechanism of the host defense response. However, it is known that some of these pathways are triggered by reactive oxygen species and reactive nitrogen species (ROS/RNS) produced by host cells. Considering that the effects of NO (nitric oxide) on pathogens are concentration dependent, such effects could alter the redox state of cysteine residues by influencing (activating or inhibiting) a variety of protein functions, notably S-nitrosylation, a highly important NO-dependent posttranslational modification that regulates cellular functions and signaling pathways. It has been demonstrated by our group that P. brasiliensis yeast cells proliferate when exposed to low NO concentrations. Thus, this work investigated the modulation profile of S-nitrosylated proteins of P. brasiliensis, as well as identifying S-nitrosylation sites after treatment with RNS. Through mass spectrometry analysis (LC-MS/MS) and label-free quantification, it was possible to identify 474 proteins in the S-nitrosylated proteome study. With this approach, we observed that proteins treated with NO at low concentrations presented a proliferative response pattern, with several proteins involved in cellular cycle regulation and growth being activated. These proteins appear to play important roles in fungal virulence. On the other hand, fungus stimulated by high NO concentrations exhibited a survival response pattern. Among these S-nitrosylated proteins we identified several potential molecular targets for fungal disease therapy, including cell wall integrity (CWI) pathway, amino acid and folic acid metabolisms. In addition, we detected that the transnitrosylation/denitrosylation redox signaling are preserved in this fungus. Finally, this work may help to uncover the beneficial and antifungal properties of NO in the P. brasiliensis and point to useful targets for the development of antifungal drugs.

nNOS-expressing neurons in the vmPFC transform pPVT-derived chronic pain signals into anxiety behaviors

Anxiety is common in patients suffering from chronic pain. Here, we report anxiety-like behaviors in mouse models of chronic pain and reveal that nNOS-expressing neurons in ventromedial prefrontal cortex (vmPFC) are essential for pain-induced anxiety but not algesia, using optogenetic and chemogenetic strategies. Additionally, we determined that excitatory projections from the posterior subregion of paraventricular thalamic nucleus (pPVT) provide a neuronal input that drives the activation of vmPFC nNOS-expressing neurons in our chronic pain models. Our results suggest that the pain signal becomes an anxiety signal after activation of vmPFC nNOS-expressing neurons, which causes subsequent release of nitric oxide (NO). Finally, we show that the downstream molecular mechanisms of NO likely involve enhanced glutamate transmission in vmPFC CaMKIIα-expressing neurons through S-nitrosylation-induced AMPAR trafficking. Overall, our data suggest that pPVT excitatory neurons drive chronic pain-induced anxiety through activation of vmPFC nNOS-expressing neurons, resulting in NO-mediated AMPAR trafficking in vmPFC pyramidal neurons.

Chronic pain usually induces anxiety. Here, the authors report that vmPFC nNOS-expressing neurons are activated by excitatory inputs from pPVT during chronic pain and subsequently induce anxiety-like behaviors in mice through promoting AMPAR trafficking.

Fear renewal requires nitric oxide signaling in the lateral amygdala

Fear renewal is defined as return of the conditioned fear responses after extinction when a conditioned stimulus (CS) is given outside of the extinction context. Previously, we have suggested that extinction induces S-nitrosylation of GluA1 in the lateral amygdala (LA), and that the extinction-induced S-nitrosylation of GluA1 lowers the threshold of GluA1 phosphorylation (at Ser 831) which is required for fear renewal. This fits nicely with the fact that fear renewal is induced by weak stimuli. However, it has not been tested whether S-nitrosylation of GluA1 in the LA is indeed required for fear renewal. In the present study, we used three different chemicals to impede protein S-nitrosylation via distinct mechanisms. Fear renewal was inhibited by microinjection of 7-Nitroindazole (nNOS inhibitor), and ZL006 (a blocker of PSD-95-nNOS interaction) before fear renewal. Furthermore, fear renewal was also attenuated by microinjection of a strong antioxidant (N-acetyl cysteine), which scavenges reactive oxygen including nitric oxide, into the LA before each extinction training. These findings suggest that protein S-nitrosylation is required for fear renewal.

Amperometric measurements of cocaine cue and novel context-evoked glutamate and nitric oxide release in the nucleus accumbens core

Cue-induced reinstatement of cocaine seeking after self-administration (SA) and extinction relies on glutamate release in the nucleus accumbens core (NAcore), which activates neuronal nitric oxide synthase interneurons. Nitric oxide (NO) is required for structural plasticity in NAcore medium spiny neurons, as well as cued cocaine seeking. However, NO release in the NAcore during reinstatement has yet to be directly measured. Furthermore, the temporal relationship between glutamate release and the induction of an NO response also remains unknown. Using wireless amperometric recordings in awake behaving rats, we quantified the magnitude and temporal dynamics of novel context- and cue-induced reinstatement-evoked glutamate and NO release in the NAcore. We found that re-exposure to cocaine-conditioned stimuli following SA and extinction increased extracellular glutamate, leading to release of NO in the NAcore. In contrast, exposing drug-naïve rats to a novel context led to a lower magnitude rise in glutamate in the NAcore relative to cue-induced reinstatement. Interestingly, novel context exposure evoked a higher magnitude NO response relative to cue-induced reinstatement. Despite differences in magnitude, novel context evoked-NO release in the NAcore was also temporally delayed when compared to glutamate. These results demonstrate a dissociation between the magnitude of cocaine cue- and novel context-evoked glutamate and NO release in the NAcore, yet similarity in the temporal dynamics of their release. Together, these data contribute to a greater understanding of the relationship between glutamate and NO, two neurotransmitters implicated in encoding the valence of distinct contextual stimuli.

Modulation of AMPA Receptors by Nitric Oxide in Nerve Cells

Nitric oxide (NO) is a gaseous molecule with a large number of functions in living tissue. In the brain, NO participates in numerous intracellular mechanisms, including synaptic plasticity and cell homeostasis. NO elicits synaptic changes both through various multi-chain cascades and through direct nitrosylation of targeted proteins. Along with the N-methyl-d-aspartate (NMDA) glutamate receptors, one of the key components in synaptic functioning are α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors—the main target for long-term modifications of synaptic effectivity. AMPA receptors have been shown to participate in most of the functions important for neuronal activity, including memory formation. Interactions of NO and AMPA receptors were observed in important phenomena, such as glutamatergic excitotoxicity in retinal cells, synaptic plasticity, and neuropathologies. This review focuses on existing findings that concern pathways by which NO interacts with AMPA receptors, influences properties of different subunits of AMPA receptors, and regulates the receptors’ surface expression.

Enhancing Plasticity Mechanisms in the Mouse Motor Cortex by Anodal Transcranial Direct-Current Stimulation: The Contribution of Nitric Oxide Signaling

Consistent body of evidence shows that transcranial direct-current stimulation (tDCS) over the primary motor cortex (M1) facilitates motor learning and promotes recovery after stroke. However, the knowledge of molecular mechanisms behind tDCS effects needs to be deepened for a more rational use of this technique in clinical settings. Here we characterized the effects of anodal tDCS of M1, focusing on its impact on glutamatergic synaptic transmission and plasticity. Mice subjected to tDCS displayed increased long-term potentiation (LTP) and enhanced basal synaptic transmission at layer II/III horizontal connections. They performed better than sham-stimulated mice in the single-pellet reaching task and exhibited increased forelimb strength. Dendritic spine density of layer II/III pyramidal neurons was also increased by tDCS. At molecular level, tDCS enhanced: 1) BDNF expression, 2) phosphorylation of CREB, CaMKII, and GluA1, and 3) S-nitrosylation of GluA1 and HDAC2. Blockade of nitric oxide synthesis by L-NAME prevented the tDCS-induced enhancement of GluA1 phosphorylation at Ser831 and BDNF levels, as well as of miniature excitatory postsynaptic current (mEPSC) frequency, LTP and reaching performance. Collectively, these findings demonstrate that anodal tDCS engages plasticity mechanisms in the M1 and highlight a role for nitric oxide (NO) as a novel mediator of tDCS effects.

S-Nitrosylation: An Emerging Paradigm of Redox Signaling

Nitric oxide (NO) is a highly reactive molecule, generated through metabolism of L-arginine by NO synthase (NOS). Abnormal NO levels in mammalian cells are associated with multiple human diseases, including cancer. Recent studies have uncovered that the NO signaling is compartmentalized, owing to the localization of NOS and the nature of biochemical reactions of NO, including S-nitrosylation. S-nitrosylation is a selective covalent post-translational modification adding a nitrosyl group to the reactive thiol group of a cysteine to form S-nitrosothiol (SNO), which is a key mechanism in transferring NO-mediated signals. While S-nitrosylation occurs only at select cysteine thiols, such a spatial constraint is partially resolved by transnitrosylation, where the nitrosyl moiety is transferred between two interacting proteins to successively transfer the NO signal to a distant location. As NOS is present in various subcellular locales, a stress could trigger concerted S-nitrosylation and transnitrosylation of a large number of proteins involved in divergent signaling cascades. S-nitrosylation is an emerging paradigm of redox signaling by which cells confer protection against oxidative stress.

The AMPA Receptor Code of Synaptic Plasticity

Changes in the properties and postsynaptic abundance of AMPA-type glutamate receptors (AMPARs) are major mechanisms underlying various forms of synaptic plasticity, including long-term potentiation (LTP), long-term depression (LTD), and homeostatic scaling. The function and the trafficking of AMPARs to and from synapses is modulated by specific AMPAR GluA1-GluA4 subunits, subunit-specific protein interactors, auxiliary subunits, and posttranslational modifications. Layers of regulation are added to AMPAR tetramers through these different interactions and modifications, increasing the computational power of synapses. Here we review the reliance of synaptic plasticity on AMPAR variants and propose "the AMPAR code" as a conceptual framework. The AMPAR code suggests that AMPAR variants will be predictive of the types and extent of synaptic plasticity that can occur and that a hierarchy exists such that certain AMPARs will be disproportionally recruited to synapses during LTP/homeostatic scaling up, or removed during LTD/homeostatic scaling down.

Priming of microglia with IFN-γ slows neuronal gamma oscillations in situ

Type II IFN (IFN-γ) is a proinflammatory T lymphocyte cytokine that serves in priming of microglia-resident CNS macrophages-during the complex microglial activation process under pathological conditions. Priming generally permits an exaggerated microglial response to a secondary inflammatory stimulus. The impact of primed microglia on physiological neuronal function in intact cortical tissue (in situ) is widely unknown, however. We explored the effects of chronic IFN-γ exposure on microglia in hippocampal slice cultures, i.e., postnatal parenchyma lacking leukocyte infiltration (adaptive immunity). We focused on fast neuronal network waves in the gamma-band (30-70 Hz). Such gamma oscillations are fundamental to higher brain functions, such as perception, attention, and memory, and are exquisitely sensitive to metabolic and oxidative stress. IFN-γ induced substantial morphological changes and cell population expansion in microglia as well as moderate up-regulation of activation markers, MHC-II, CD86, IL-6, and inducible nitric oxide synthase (iNOS), but not TNF-α. Cytoarchitecture and morphology of pyramidal neurons and parvalbumin-positive inhibitory interneurons were well-preserved. Notably, gamma oscillations showed a specific decline in frequency of up to 8 Hz, which was not mimicked by IFN-α or IL-17 exposure. The rhythm disturbance was caused by moderate microglial nitric oxide (NO) release demonstrated by pharmacological microglia depletion and iNOS inhibition. In conclusion, IFN-γ priming induces substantial proliferation and moderate activation of microglia that is capable of slowing neural information processing. This mechanism might contribute to cognitive impairment in chronic brain disease featuring elevated IFN-γ levels, blood-brain barrier leakage, and/or T cell infiltration, well before neurodegeneration occurs.

Chronic Ethanol Consumption Impairs the Tactile-Evoked Long-Term Depression at Cerebellar Molecular Layer Interneuron-Purkinje Cell Synapses in vivo in Mice

The cerebellum is sensitive to ethanol (EtOH) consumption. Chronic EtOH consumption impairs motor learning by modulating the cerebellar circuitry synaptic transmission and long-term plasticity. Under in vitro conditions, acute EtOH inhibits both parallel fiber (PF) and climbing fiber (CF) long-term depression (LTD). However, thus far it has not been investigated how chronic EtOH consumption affects sensory stimulation-evoked LTD at the molecular layer interneurons (MLIs) to the Purkinje cell (PC) synapses (MLI-PC LTD) in the cerebellar cortex of living animals. In this study, we investigated the effect of chronic EtOH consumption on facial stimulation-evoked MLI-PC LTD, using an electrophysiological technique as well as pharmacological methods, in urethane-anesthetized mice. Our results showed that facial stimulation induced MLI–PC LTD in the control mice, but it could not be induced in mice with chronic EtOH consumption (0.8 g/kg; 28 days). Blocking the cannabinoid type 1 (CB1) receptor activity with AM-251, prevented MLI-PC LTD in the control mice, but revealed a nitric oxide (NO)-dependent long-term potentiation (LTP) of MLI–PC synaptic transmission (MLI-PC LTP) in the EtOH consumption mice. Notably, with the application of a NO donor, S-nitroso-N-Acetyl-D, L-penicillamine (SNAP) alone prevented the induction of MLI–PC LTD, but a mixture of SNAP and AM-251 revealed an MLI-PC LTP in control mice. In contrast, inhibiting NO synthase (NOS) revealed the facial stimulation-induced MLI-PC LTD in EtOH consumption mice. These results indicate that long-term EtOH consumption can impair the sensory stimulation-induced MLI–PC LTD via the activation of a NO signaling pathway in the cerebellar cortex in vivo in mice. Our results suggest that the chronic EtOH exposure causes a deficit in the cerebellar motor learning function and may be involved in the impaired MLI–PC GABAergic synaptic plasticity.

Increased thioredoxin-interacting protein in brain of mice exposed to chronic stress

Chronic stress is a key contributor to depression. Previous studies have shown that oxidative stress and inflammation are increased by chronic stress and in subjects with depression. Thioredoxin is a small redox protein that regulates cellular redox balance and signaling. This protein can reverse protein cysteine oxidative modifications such as sulfenylation and nitrosylation, and inhibit stress-regulated apoptosis signal-regulating kinase 1 pathway. Therefore thioredoxin plays an important role in cellular defense against oxidative stress. Thioredoxin-interacting protein is an endogenous thioredoxin inhibitor. In the present study, to understand the role of thioredoxin in chronic stress and depression, we have investigated thioredoxin, thioredoxin-interacting protein, sulfenylation, nitrosylation and apoptosis signal-regulating kinase 1 phosphorylation in brain of mice exposed to chronic unpredictable stress (CUS). We found that mice exposed to CUS displayed decreased exploratory, increased anhedonic and increased despair depressive-like behaviours. We also found that although CUS had no effect on thioredoxin protein levels, it significantly increased levels of thioredoxin-interacting protein in mouse hippocampus and frontal cortex. CUS also increased protein cysteine sulfenylation, protein cysteine nitrosylation and apoptosis signal-regulating kinase 1 phosphorylation in mouse hippocampus and frontal cortex. These findings suggest that chronic stress may upregulate thioredoxin-interacting protein, subsequently inhibiting thioredoxin activity and enhancing oxidative protein cysteine modification and apoptosis signal-regulating kinase 1 pathway. These results also indicate that thioredoxin-interacting protein may have potential for depression treatment.

GSK3β activity alleviates epileptogenesis and limits GluA1 phosphorylation

BACKGROUND

Glycogen synthase kinase-3β (GSK3β) is a key regulator of cellular homeostasis. In neurons, GSK3β contributes to the control of neuronal transmission and plasticity, but its role in epilepsy remains to be defined.

METHODS

Biochemical and electrophysiological methods were used to assess the role of GSK3β in regulating neuronal transmission and epileptogenesis. GSK3β activity was increased genetically in GSK3β[S9A] mice. Its effects on neuronal transmission and epileptogenesis induced by kainic acid were assessed by field potential recordings in mice brain slices and video electroencephalography in vivo. The ion channel expression was measured in brain samples from mice and followed by analysis in samples from patients with temporal lobe epilepsy or focal cortical dysplasia in correlation to GSK3β phosphorylation.

FINDINGS

Higher GSK3β activity decreased the progression of kainic acid induced epileptogenesis. At the biochemical level, higher GSK3β activity increased the expression of hyperpolarization-activated cyclic nucleotide-gated (HCN) channel 4 under basal conditions and in the epileptic mouse brain and decreased phosphorylation of the glutamate α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit GluA1 at Serine 831 under basal conditions. Moreover, we found a significant correlation between higher inhibitory GSK3β phosphorylation at Serine 9 and higher activating GluA1 phosphorylation at Serine 845 in brain samples from epileptic patients.

INTERPRETATION

Our data imply GSK3β activity in the protection of neuronal networks from hyper-activation in response to epileptogenic stimuli and indicate that the anti-epileptogenic function of GSK3β involves modulation of HCN4 level and the synaptic AMPA receptors pool.

PDI Knockdown Inhibits Seizure Activity in Acute Seizure and Chronic Epilepsy Rat Models via S-Nitrosylation-Independent Thiolation on NMDA Receptor

Redox modulation and S-nitrosylation of cysteine residues are the post-translational modifications of N-methyl-D-aspartate receptor (NMDAR) to regulate its functionality. Recently, we have reported that protein disulfide isomerase (PDI) reduces disulfide bond (S-S) to free thiol (-SH) on NMDAR. Since PDI is a modulator of S-nitrosylation on various proteins, it is noteworthy whether PDI affects S-nitrosylation of NMDAR in acute seizure and chronic epilepsy models. In the present study, we found that acute seizures in response to pilocarpine and spontaneous seizures in chronic epilepsy rats led to the reduction in S-nitrosylated thiol (SNO-thiol)-to-total thiol ratio on NMDAR, while they elevated nitric oxide (NO) level and S-nitrosylation on NMDAR. N-nitro-L-arginine methyl ester (L-NAME, a non-selective NOS inhibitor) did not affect seizure activities in both models, although it decreased SNO-thiol levels on NMDAR. However, PDI knockdown effectively inhibited pilocarpine-induced acute seizures and spontaneous seizures in chronic epilepsy rats, accompanied by increasing the SNO-thiol-to-total thiol ratio on NMDAR due to diminishing the amounts of total thiols on GluN1 and GluN2A. Therefore, these findings indicate that PDI may not be a NO donor or a denitrosylase for NMDAR, and that PDI knockdown may inhibit seizure activity by the S-nitrosylation-independent thiolation on NMDAR.

Redox Signaling in Neurotransmission and Cognition During Aging

SIGNIFICANCE

Oxidative stress increases in the brain with aging and neurodegenerative diseases. Previous work emphasized irreversible oxidative damage in relation to cognitive impairment. This research has evolved to consider a continuum of alterations, from redox signaling to oxidative damage, which provides a basis for understanding the onset and progression of cognitive impairment. This review provides an update on research linking redox signaling to altered function of neural circuits involved in information processing and memory. Recent Advances: Starting in middle age, redox signaling triggers changes in nervous system physiology described as senescent physiology. Hippocampal senescent physiology involves decreased cell excitability, altered synaptic plasticity, and decreased synaptic transmission. Recent studies indicate N-methyl-d-aspartate and ryanodine receptors and Ca²⁺ signaling molecules as molecular substrates of redox-mediated senescent physiology.

CRITICAL ISSUES

We review redox homeostasis mechanisms and consider the chemical character of reactive oxygen and nitrogen species and their role in regulating different transmitter systems. In this regard, senescent physiology may represent the co-opting of pathways normally responsible for feedback regulation of synaptic transmission. Furthermore, differences across transmitter systems may underlie differential vulnerability of brain regions and neuronal circuits to aging and disease.

FUTURE DIRECTIONS

It will be important to identify the intrinsic mechanisms for the shift in oxidative/reductive processes. Intrinsic mechanism will depend on the transmitter system, oxidative stressors, and expression/activity of antioxidant enzymes. In addition, it will be important to identify how intrinsic processes interact with other aging factors, including changes in inflammatory or hormonal signals. Antioxid. Redox Signal. 28, 1724-1745.

Glucocorticoid Upregulates Thioredoxin-interacting Protein in Cultured Neuronal Cells

Previous studies have shown that chronic stress and chronic stress hormone treatment induce oxidative damage in rodents. Thioredoxin (Trx) is a small redox protein that plays an important role in regulation of oxidative protein cysteine modification. A Trx reduced state is maintained by thioredoxin reductase (TrxR), and the thioredoxin-interacting protein (Txnip) is an endogenous inhibitor of Trx. The purpose of this study was to investigate the effects of chronic treatment with stress hormone corticosterone on Trx, TrxR and Txnip in cultured neuronal cells. Using immunoblotting analysis we found that although chronic corticosterone treatment had no effect on Trx and TrxR protein levels, this treatment significantly increased Txnip protein levels. Using immunocytochemistry we also found that chronic corticosterone treatment increased Txnip in both nucleus and cytosol, while glucocorticoid receptor inhibitor RU486 can block corticosterone-increased Txnip protein levels. Using biotin switch, dimedone conjugation and CRISPR/Cas9 methods we found that chronic corticosterone treatment increased protein nitrosylation and sulfenylation, while knocking out Txnip blocked corticosterone-induced protein nitrosylation and sulfenylation. Since Trx can reduce cysteine oxidative protein modification such as nitrosylation and sulfenylation, our findings suggest that chronic corticosterone treatment may upregulate Txnip by targeting glucocorticoid receptor, subsequently inhibiting Trx activity and enhancing oxidative protein cysteine modification, which contributes to corticosterone-caused oxidative damage.

Developmental Alcohol Exposure Impairs Activity-Dependent S-Nitrosylation of NDEL1 for Neuronal Maturation

Neuronal nitric oxide synthase is involved in diverse signaling cascades that regulate neuronal development and functions via S-Nitrosylation-mediated mechanism or the soluble guanylate cyclase (sGC)/cyclic guanosine monophosphate (cGMP) pathway activated by nitric oxide. Although it has been studied extensively in vitro and in invertebrate animals, effects on mammalian brain development and underlying mechanisms remain poorly understood. Here we report that genetic deletion of "Nos1" disrupts dendritic development, whereas pharmacological inhibition of the sGC/cGMP pathway does not alter dendritic growth during cerebral cortex development. Instead, nuclear distribution element-like (NDEL1), a protein that regulates dendritic development, is specifically S-nitrosylated at cysteine 203, thereby accelerating dendritic arborization. This post-translational modification is enhanced by N-methyl-D-aspartate receptor-mediated neuronal activity, the main regulator of dendritic formation. Notably, we found that disruption of S-Nitrosylation of NDEL1 mediates impaired dendritic maturation caused by developmental alcohol exposure, a model of developmental brain abnormalities resulting from maternal alcohol use. These results highlight S-Nitrosylation as a key activity-dependent mechanism underlying neonatal brain maturation and suggest that reduction of S-Nitrosylation of NDEL1 acts as a pathological factor mediating neurodevelopmental abnormalities caused by maternal alcohol exposure.

AMPA-Type Glutamate Receptor Conductance Changes and Plasticity: Still a Lot of Noise

Twenty years ago, we reported from the Collingridge Lab that a single-channel conductance increase through α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type ionotropic glutamate receptors (AMPARs) could mediate one form of plasticity associated with long-term potentiation (LTP) in the hippocampus (Benke et al., Nature 395:793-797, 1998). Revealed through peak-scaled non-stationary fluctuation analysis (PS-NSFA, also known as noise analysis), this component of LTP could be exclusively mediated by direct increases in channel conductance or by increases in the number of high conductance synaptic AMPARs. Re-evaluation of our original data in the light of the molecular details regarding AMPARs, conductance changes and plasticity suggests that insertion of high-conductance GluA1 homomers can account for our initial findings. Any potential cost associated with manufacture or trafficking of new receptors could be mitigated if pre-existing synaptic AMPARs also undergo a modest conductance change. The literature suggests that the presence of high conductance AMPARs and/or GluA1 homomers confers an unstable synaptic state, suggesting state transitions. An experimental paradigm is proposed to differentiate these possibilities. Validation of this state diagram could provide insight into development, disease pathogenesis and treatment.

[Physiological roles of redox signals in relation to synaptic plasticity and brain functions]

In our classical knowledge, redox molecules, including reactive oxygen species (ROS), nitric oxide (NO) and hydrogen sulfide, are considered to be generated as byproducts of aerobic metabolism and act as harmful oxidants of macromolecules, such as proteins and lipids. On the other hands, recently, expressions of enzymes producing redox molecules are identified and reported to be expressed in wide range of tissues, including brain. Moreover, activities of some of these enzymes are revealed to be regulated by physiological signals (e.g. calcium). These observations suggest that redox molecules act as physiological messengers and have biological functions. Actually, recent studies indicate possible involvement of redox signals in functional modification of proteins essential for synaptic plasticity in cultured cells and acute slice preparations. For example, S-nitrosylation of type 1 ryanodine receptor, an intracellular calcium-release channel, is revealed to be essential for NO-induced calcium release (NICR) and synaptic plasticity in cerebellar Purkinje cells. Further studies on mutant animals deficient in redox-modification site may clarify essential role of redox signals in brain functions in vivo.

Regulation of AMPA Receptor Trafficking by Protein Ubiquitination

The molecular mechanisms underlying plastic changes in the strength and connectivity of excitatory synapses have been studied extensively for the past few decades and remain the most attractive cellular models of learning and memory. One of the major mechanisms that regulate synaptic plasticity is the dynamic adjustment of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptor content on the neuronal plasma membrane. The expression of surface AMPA receptors (AMPARs) is controlled by the delicate balance between the biosynthesis, dendritic transport, exocytosis, endocytosis, recycling and degradation of the receptors. These processes are dynamically regulated by AMPAR interacting proteins as well as by various post-translational modifications that occur on their cytoplasmic domains. In the last few years, protein ubiquitination has emerged as a major regulator of AMPAR intracellular trafficking. Dysregulation of AMPAR ubiquitination has also been implicated in the pathophysiology of Alzheimer’s disease. Here we review recent advances in the field and provide insights into the role of protein ubiquitination in regulating AMPAR membrane trafficking and function. We also discuss how aberrant ubiquitination of AMPARs contributes to the pathogenesis of various neurological disorders, including Alzheimer’s disease, chronic stress and epilepsy.

Chronic treatment with Tempol during acquisition or withdrawal from CPP abolishes the expression of cocaine reward and diminishes oxidative damage

In previous studies, we reported that pretreatment with the antioxidant Tempol attenuated the development and expression of cocaine-induced psychomotor sensitization in rats and diminished cocaine-induced oxidative stress (OS) in the prefrontal cortex (PFC) and nucleus accumbens (NAc), suggesting a potential role for Tempol in interfering with cocaine-related psychomotor sensitization. The aim of the current study was to examine the role of Tempol in reward and reinforcement using the conditioned place preference (CPP) paradigm. We found that administration of Tempol during the conditioning session abolished the expression of cocaine-induced CPP. We also found that OS was significantly elevated following the establishment of CPP, and that cocaine-induced OS was significantly diminished by pretreatment with Tempol during conditioning. Furthermore, we found that repeated, but not single, administration of Tempol for seven days during withdrawal from CPP resulted in significant attenuation in the expression of CPP. Moreover, Tempol did not affect the expression of food reward. Taken together, these findings provide evidence for the involvement of Tempol in regulating cocaine rewarding properties without affecting natural rewards. Since Tempol was found to be effective in reducing OS and expression of CPP following withdrawal, it may be a potential treatment for cocaine addiction.

The role of hypernitrosylation in the pathogenesis and pathophysiology of neuroprogressive diseases

There is a wealth of data indicating that de novo protein S-nitrosylation in general and protein transnitrosylation in particular mediates the bulk of nitric oxide signalling. These processes enable redox sensing and facilitate homeostatic regulation of redox dependent protein signalling, function, stability and trafficking. Increased S-nitrosylation in an environment of increasing oxidative and nitrosative stress (O&NS) is initially a protective mechanism aimed at maintaining protein structure and function. When O&NS becomes severe, mechanisms governing denitrosylation and transnitrosylation break down leading to the pathological state referred to as hypernitrosylation (HN). Such a state has been implicated in the pathogenesis and pathophysiology of several neuropsychiatric and neurodegenerative diseases and we investigate its potential role in the development and maintenance of neuroprogressive disorders. In this paper, we propose a model whereby the hypernitrosylation of a range of functional proteins and enzymes lead to changes in activity which conspire to produce at least some of the core abnormalities contributing to the development and maintenance of pathology in these illnesses.

Gasotransmitter Heterocellular Signaling

SIGNIFICANCE

The family of gasotransmitter molecules, nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), has emerged as an important mediator of numerous cellular signal transduction and pathophysiological responses. As such, these molecules have been reported to influence a diverse array of biochemical, molecular, and cell biology events often impacting one another. Recent Advances: Discrete regulation of gasotransmitter molecule formation, movement, and reaction is critical to their biological function. Due to the chemical nature of these molecules, they can move rapidly throughout cells and tissues acting on targets through reactions with metal groups, reactive chemical species, and protein amino acids.

CRITICAL ISSUES

Given the breadth and complexity of gasotransmitter reactions, this field of research is expanding into exciting, yet sometimes confusing, areas of study with significant promise for understanding health and disease. The precise amounts of tissue and cellular gasotransmitter levels and where they are formed, as well as how they react with molecular targets or themselves, all remain poorly understood.

FUTURE DIRECTIONS

Elucidation of specific molecular targets, characteristics of gasotransmitter molecule heterotypic interactions, and spatiotemporal formation and metabolism are all important to better understand their true pathophysiological importance in various organ systems. Antioxid. Redox Signal. 26, 936-960.

The Nucleus Accumbens: Mechanisms of Addiction across Drug Classes Reflect the Importance of Glutamate Homeostasis

The nucleus accumbens is a major input structure of the basal ganglia and integrates information from cortical and limbic structures to mediate goal-directed behaviors. Chronic exposure to several classes of drugs of abuse disrupts plasticity in this region, allowing drug-associated cues to engender a pathologic motivation for drug seeking. A number of alterations in glutamatergic transmission occur within the nucleus accumbens after withdrawal from chronic drug exposure. These drug-induced neuroadaptations serve as the molecular basis for relapse vulnerability. In this review, we focus on the role that glutamate signal transduction in the nucleus accumbens plays in addiction-related behaviors. First, we explore the nucleus accumbens, including the cell types and neuronal populations present as well as afferent and efferent connections. Next we discuss rodent models of addiction and assess the viability of these models for testing candidate pharmacotherapies for the prevention of relapse. Then we provide a review of the literature describing how synaptic plasticity in the accumbens is altered after exposure to drugs of abuse and withdrawal and also how pharmacological manipulation of glutamate systems in the accumbens can inhibit drug seeking in the laboratory setting. Finally, we examine results from clinical trials in which pharmacotherapies designed to manipulate glutamate systems have been effective in treating relapse in human patients. Further elucidation of how drugs of abuse alter glutamatergic plasticity within the accumbens will be necessary for the development of new therapeutics for the treatment of addiction across all classes of addictive substances.

Cysteine 893 is a target of regulatory thiol modifications of GluA1 AMPA receptors

Recent studies indicate that glutamatergic signaling involves, and is regulated by, thiol modifying and redox-active compounds. In this study, we examined the role of a reactive cysteine residue, Cys-893, in the cytosolic C-terminal tail of GluA1 AMPA receptor as a potential regulatory target. Elimination of the thiol function by substitution of serine for Cys-893 led to increased steady-state expression level and strongly reduced interaction with SAP97, a major cytosolic interaction partner of GluA1 C-terminus. Moreover, we found that of the three cysteine residues in GluA1 C-terminal tail, Cys-893 is the predominant target for S-nitrosylation induced by exogenous nitric oxide donors in cultured cells and lysates. Co-precipitation experiments provided evidence for native association of SAP97 with neuronal nitric oxide synthase (nNOS) and for the potential coupling of Ca²⁺-permeable GluA1 receptors with nNOS via SAP97. Our results show that Cys-893 can serve as a molecular target for regulatory thiol modifications of GluA1 receptors, including the effects of nitric oxide.