Cysteine-3635 is responsible for skeletal muscle ryanodine receptor modulation by NO

Physiological role for S-nitrosylation of RyR1 in skeletal muscle function and development

Excitation-contraction coupling in skeletal muscle myofibers depends upon Ca2+ release from the sarcoplasmic reticulum through the ryanodine receptor/Ca2+-release channel RyR1. The RyR1 contains ∼100 Cys thiols of which ∼30 comprise an allosteric network subject to posttranslational modification by S-nitrosylation, S-palmitoylation and S-oxidation. However, the role and function of these modifications is not understood. Although aberrant S-nitrosylation of multiple unidentified sites has been associated with dystrophic diseases, malignant hyperthermia and other myopathic syndromes, S-nitrosylation in physiological situations is reportedly specific to a single (1 of ∼100) Cys in RyR1, Cys3636 in a manner gated by pO2. Using mice expressing a form of RyR1 with a Cys3636→Ala point mutation to prevent S-nitrosylation at this site, we showed that Cys3636 was the principal target of endogenous S-nitrosylation during normal muscle function. The absence of Cys3636 S-nitrosylation suppressed stimulus-evoked Ca2+ release at physiological pO2 (at least in part by altering the regulation of RyR1 by Ca2+/calmodulin), eliminated pO2 coupling, and diminished skeletal myocyte contractility in vitro and measures of muscle strength in vivo. Furthermore, we found that abrogation of Cys3636 S-nitrosylation resulted in a developmental defect reflected in diminished myofiber diameter, altered fiber subtypes, and altered expression of genes implicated in muscle development and atrophy. Thus, our findings establish a physiological role for pO2-coupled S-nitrosylation of RyR1 in skeletal muscle contractility and development and provide foundation for future studies of RyR1 modifications in physiology and disease.

Protein S-Nitrosylation: A Chemical Modification with Ubiquitous Biological Activities

Nitric oxide (NO) induces protein posttranslational modification (PTM), known as S-nitrosylation, which has started to gain attention as a critical regulator of thousands of substrate proteins. However, our understanding of the biological consequences of this emerging PTM is incomplete because of the limited number of identified S-nitrosylated proteins (S-NO proteins). Recent advances in detection methods have effectively contributed to broadening the spectrum of discovered S-NO proteins. This article briefly reviews the progress in S-NO protein detection methods and discusses how these methods are involved in characterizing the biological consequences of this PTM. Additionally, we provide insight into S-NO protein-related diseases, focusing on the role of these proteins in mitigating the severity of infectious diseases.

Biology of cognitive aging across species

Aging is associated with cognitive decline, which can critically affect quality of life. Examining the biology of cognitive aging across species will lead to a better understanding of the fundamental mechanisms involved in this process, and identify potential interventions that could help to improve cognitive function in aging individuals. This minireview aimed to explore the mechanisms and processes involved in cognitive aging across a range of species, from flies to rodents, and covers topics, such as the role of reactive oxygen species and autophagy/mitophagy in cognitive aging. Overall, this literature provides a comprehensive overview of the biology of cognitive aging across species, highlighting the latest research findings and identifying potential avenues for future research. Geriatr Gerontol Int 2024; 24: 15-24.

Cysteines 1078 and 2991 cross-linking plays a critical role in redox regulation of cardiac ryanodine receptor (RyR)

The most common cardiac pathologies, such as myocardial infarction and heart failure, are associated with oxidative stress. Oxidation of the cardiac ryanodine receptor (RyR2) Ca²⁺ channel causes spontaneous oscillations of intracellular Ca²⁺, resulting in contractile dysfunction and arrhythmias. RyR2 oxidation promotes the formation of disulfide bonds between two cysteines on neighboring RyR2 subunits, known as intersubunit cross-linking. However, the large number of cysteines in RyR2 has been a major hurdle in identifying the specific cysteines involved in this pathology-linked post-translational modification of the channel. Through mutagenesis of human RyR2 and in-cell Ca²⁺ imaging, we identify that only two cysteines (out of 89) in each RyR2 subunit are responsible for half of the channel's functional response to oxidative stress. Our results identify cysteines 1078 and 2991 as a redox-sensitive pair that forms an intersubunit disulfide bond between neighboring RyR2 subunits during oxidative stress, resulting in a pathological "leaky" RyR2 Ca²⁺ channel.

nNOS-derived NO modulates force production and iNO-derived NO the excitability in C2C12-derived 3D tissue engineering skeletal muscle via different NO signaling pathways

Nitric oxide (NO) is a bioactive gas produced by one of the three NO synthases: neuronal NOS (nNOS), inducible (iNOS), and endothelial NOS (eNOS). NO has a relevant modulatory role in muscle contraction; this takes place through two major signaling pathways: (i) activation of soluble guanylate cyclase and, thus, protein kinase G or (ii) nitrosylation of sulfur groups of cysteine. Although it has been suggested that nNOS-derived NO is the responsible isoform in muscle contraction, the roles of eNOS and iNOS and their signaling pathways have not yet been clarified. To elucidate the action of each pathway, we optimized the generation of myooids, an engineered skeletal muscle tissue based on the C2C12 cell line. In comparison with diaphragm strips from wild-type mice, 180 myooids were analyzed, which expressed all relevant excitation–contraction coupling proteins and both nNOS and iNOS isoforms. Along with the biochemical results, myooids treated with NO donor (SNAP) and unspecific NOS blocker (L-NAME) revealed a comparable NO modulatory effect on force production as was observed in the diaphragm strips. Under the effects of pharmacological tools, we analyzed the myooids in response to electrical stimulation of two possible signaling pathways and NO sources. The nNOS-derived NO exerted its negative effect on force production via the sGG-PKG pathway, while iNOS-derived NO increased the excitability in response to sub-threshold electrical stimulation. These results strengthen the hypotheses of previous reports on the mechanism of action of NO during force production, showed a novel function of iNOS-derived NO, and establish the myooid as a novel and robust alternative model for pathophysiological skeletal muscle research.

Positive Aspects of Oxidative Stress at Different Levels of the Human Body: A Review

Oxidative stress is the subject of numerous studies, most of them focusing on the negative effects exerted at both molecular and cellular levels, ignoring the possible benefits of free radicals. More and more people admit to having heard of the term "oxidative stress", but few of them understand the meaning of it. We summarized and analyzed the published literature data in order to emphasize the importance and adaptation mechanisms of basal oxidative stress. This review aims to provide an overview of the mechanisms underlying the positive effects of oxidative stress, highlighting these effects, as well as the risks for the population consuming higher doses than the recommended daily intake of antioxidants. The biological dose-response curve in oxidative stress is unpredictable as reactive species are clearly responsible for cellular degradation, whereas antioxidant therapies can alleviate senescence by maintaining redox balance; nevertheless, excessive doses of the latter can modify the redox balance of the cell, leading to a negative outcome. It can be stated that the presence of oxidative status or oxidative stress is a physiological condition with well-defined roles, yet these have been insufficiently researched and explored. The involvement of reactive oxygen species in the pathophysiology of some associated diseases is well-known and the involvement of antioxidant therapies in the processes of senescence, apoptosis, autophagy, and the maintenance of cellular homeostasis cannot be denied. All data in this review support the idea that oxidative stress is an undesirable phenomenon in high and long-term concentrations, but regular exposure is consistent with the hormetic theory.

Stability of S-nitrosothiols and S-nitrosylated proteins: A struggle for cellular existence!

Nitric oxide is a well-known gasotransmitter molecule that covalently docks to sulfhydryl groups of proteins resulting in S-nitrosylation of proteins and nonprotein thiols that serve a variety of cellular processes including cGMP signaling, vasodilatation, neurotransmission, ion-channel modulation, and cardiac signaling. S-nitrosylation is an indispensable modification like phosphorylation that directly regulates the functionality of numerous proteins. However, recently there has been a controversy over the stability of S-nitrosylated proteins (PSNOs) within the cell. It has been argued that PSNOs formed within the cell is a transient intermediate step to more stable disulfide formation and disulfides are the predominant end effector modifications in NO-mediated signaling. The present article accumulates state-of-the-art evidence from numerous research that strongly supports the very existence of PSNOs within the cell and attempts to put an end to the controversy. This review illustrates critical points including comparative bond dissociation energies of S-NO bond, the half-life of S-nitrosothiols and PSNOs, cellular concentrations of PSNOs, X ray crystallographic studies on PSNOs, and stability of PSNOs at physiological concentration of antioxidants. These logical evidence cumulatively support the endogenous stability and inevitable existence of PSNOs/RSNOs within the cell that directly regulate the functionality of proteins and provide valuable insight into understanding stable S-nitrosylation mediated cell signaling.

Implications of Oxidative and Nitrosative Post-Translational Modifications in Therapeutic Strategies against Reperfusion Damage

Post-translational modifications based on redox reactions "switch on-off" the biological activity of different downstream targets, modifying a myriad of processes and providing an efficient mechanism for signaling regulation in physiological and pathological conditions. Such modifications depend on the generation of redox components, such as reactive oxygen species and nitric oxide. Therefore, as the oxidative or nitrosative milieu prevailing in the reperfused heart is determinant for protective signaling, in this review we defined the impact of redox-based post-translational modifications resulting from either oxidative/nitrosative signaling or oxidative/nitrosative stress that occurs during reperfusion damage. The role that cardioprotective conditioning strategies have had to establish that such changes occur at different subcellular levels, particularly in mitochondria, is also presented. Another section is devoted to the possible mechanism of signal delivering of modified proteins. Finally, we discuss the possible efficacy of redox-based therapeutic strategies against reperfusion damage.

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.

Skeletal muscle redox signaling in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by synovitis and the presence of serum autoantibodies. In addition, skeletal muscle weakness is a common comorbidity that contributes to inability to work and reduced quality of life. Loss in muscle mass cannot alone account for the muscle weakness induced by RA, but instead intramuscular dysfunction appears as a critical factor underlying the decreased force generating capacity for patients afflicted by arthritis. Oxidative stress and associated oxidative post-translational modifications have been shown to contribute to RA-induced muscle weakness in animal models of arthritis and patients with RA. However, it is still unclear how and which sources of reactive oxygen and nitrogen species (ROS/RNS) that are involved in the oxidative stress that drives the progression toward decreased muscle function in RA. Nevertheless, mitochondria, NADPH oxidases (NOX), nitric oxide synthases (NOS) and phospholipases (PLA) have all been associated with increased ROS/RNS production in RA-induced muscle weakness. In this review, we aim to cover potential ROS sources and underlying mechanisms of oxidative stress and loss of force production in RA. We also addressed the use of antioxidants and exercise as potential tools to counteract oxidative stress and skeletal muscle weakness.

Ryanodine receptor remodeling in cardiomyopathy and muscular dystrophy caused by lamin A/C gene mutation

Mutations in the lamin A/C gene (LMNA), which encodes A-type lamins, cause several diseases called laminopathies, the most common of which is dilated cardiomyopathy with muscular dystrophy. The role of Ca2+ regulation in these diseases remain poorly understood. We now show biochemical remodeling of the ryanodine receptor (RyR)/intracellular Ca2+ release channel in heart samples from human subjects with LMNA mutations, including protein kinase A-catalyzed phosphorylation, oxidation and depletion of the stabilizing subunit calstabin. In the LmnaH222P/H222P murine model of Emery-Dreifuss muscular dystrophy caused by LMNA mutation, we demonstrate an age-dependent biochemical remodeling of RyR2 in the heart and RyR1 in skeletal muscle. This RyR remodeling is associated with heart and skeletal muscle dysfunction. Defective heart and muscle function are ameliorated by treatment with a novel Rycal small molecule drug (S107) that fixes 'leaky' RyRs. SMAD3 phosphorylation is increased in hearts and diaphragms of LmnaH222P/H222P mice, which enhances NADPH oxidase binding to RyR channels, contributing to their oxidation. There is also increased generalized protein oxidation, increased calcium/calmodulin-dependent protein kinase II-catalyzed phosphorylation of RyRs and increased protein kinase A activity in these tissues. Our data show that RyR remodeling plays a role in cardiomyopathy and skeletal muscle dysfunction caused by LMNA mutation and identify these Ca2+ channels as a potential therapeutic target.

The functional significance of redox-mediated intersubunit cross-linking in regulation of human type 2 ryanodine receptor

The type 2 ryanodine receptor (RyR2) plays a key role in the cardiac intracellular calcium (Ca²⁺) regulation. We have previously shown that oxidative stress activates RyR2 in rabbit cardiomyocytes by promoting the formation of disulfide bonds between neighboring RyR2 subunits. However, the functional significance of this redox modification for human RyR2 (hRyR2) remains largely unknown. Here, we studied the redox regulation of hRyR2 in HEK293 cells transiently expressing the ryr2 gene. Analysis of hRyR2 cross-linking and of the redox-GFP readout response to diamide oxidation revealed that hRyR2 cysteines involved in the intersubunit cross-linking are highly sensitive to oxidative stress. In parallel experiments, the effect of diamide on endoplasmic reticulum (ER) Ca²⁺ release was studied in cells co-transfected with hRyR2, ER Ca²⁺ pump (SERCA2a) and the ER-targeted Ca²⁺ sensor R-CEPIA1er. Expression of hRyR2 and SERCA2a produced “cardiac-like” Ca²⁺ waves due to spontaneous hRyR2 activation. Incubation with diamide caused a fast decline of the luminal ER Ca²⁺ (or ER Ca²⁺ load) followed by the cessation of Ca²⁺ waves. The maximal effect of diamide on ER Ca²⁺ load and Ca²⁺ waves positively correlates with the maximum level of hRyR2 cross-linking, indicating a functional significance of this redox modification. Furthermore, the level of hRyR2 cross-linking positively correlates with the degree of calmodulin (CaM) dissociation from the hRyR2 complex. In skeletal muscle RyR (RyR1), cysteine 3635 (C3635) is viewed as dominantly responsible for the redox regulation of the channel. Here, we showed that the corresponding cysteine 3602 (C3602) in hRyR2 does not participate in intersubunit cross-linking and plays a limited role in the hRyR2 regulation by CaM during oxidative stress. Collectively, these results suggest that redox-mediated intersubunit cross-linking is an important regulator of hRyR2 function under pathological conditions associated with oxidative stress.

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Oxidative stress promotes cardiac ryanodine receptor (RyR2) intersubunit crosslinking.

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Human RyR2 crosslinking promotes Ca leak and calmodulin dissociation.

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RyR2 C3602 is not involved in crosslinking, slightly affects calmodulin binding.

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RyR2 crosslinking is an important pathology related RyR2 regulator.

Understanding How Phosphorylation and Redox Modifications Regulate Cardiac Ryanodine Receptor Type 2 Activity to Produce an Arrhythmogenic Phenotype in Advanced Heart Failure

Heart failure (HF) is a global pandemic with significant mortality and morbidity. Despite current medications, 50% of individuals die within 5 years of diagnosis. Of these deaths, 30-50% will be a result of sudden cardiac death from ventricular arrhythmias. This review discusses two stress-induced mechanisms, phosphorylation from chronic β-adrenoceptor (β-AR) stimulation and thiol modifications from oxidative stress, and how they modulate the cardiac ryanodine receptor type 2 (RyR2) and foster an arrhythmogenic phenotype. Calcium (Ca²⁺) is the ubiquitous secondary messenger of excitation-contraction coupling and provides a common pathway for contractile dysfunction and arrhythmia genesis. In a healthy heart, Ca²⁺ is released from the sarcoplasmic reticulum (SR) by RyR2. The open probability of RyR2 is under the dynamic influence of co-proteins, ions, and kinases that are in strict balance to ensure normal physiological functioning. In HF, chronic β-AR activity and production of reactive oxygen species and reactive nitrogen species provide two stress-induced mechanisms uncoupling RyR2 control, resulting in pathological diastolic SR Ca²⁺ leak. This increased cytosolic [Ca²⁺] promotes Ca²⁺ extrusion via the local Na⁺/Ca²⁺ exchanger, resulting in net sarcolemmal depolarization, delayed after depolarization and ventricular arrhythmia. Experimental models researching oxidative stress and phosphorylation have aimed to identify how post-translational modifications to the RyR2 macromolecular complex, and the associated Na⁺/Ca²⁺ cycling proteins, result in pathological Ca²⁺ handling and diastolic leak. However, the causative molecular changes remain controversial and undefined. Through understanding the molecular mechanisms that produce an arrhythmic phenotype, novel therapeutic targets to treat HF and prevent its malignant course can be identified.

Antioxidant supplements and endurance exercise: Current evidence and mechanistic insights

Antioxidant supplements are commonly consumed by endurance athletes to minimize exercise-induced oxidative stress, with the intention of enhancing recovery and improving performance. There are numerous commercially available nutritional supplements that are targeted to athletes and health enthusiasts that allegedly possess antioxidant properties. However, most of these compounds are poorly investigated with respect to their in vivo redox activity and efficacy in humans. Therefore, this review will firstly provide a background to endurance exercise-related redox signalling and the subsequent adaptations in skeletal muscle and vascular function. The review will then discuss commonly available compounds with purported antioxidant effects for use by athletes. N-acetyl cysteine may be of benefit over the days prior to an endurance event; while chronic intake of combined 1000 mg vitamin C + vitamin E is not recommended during periods of heavy training associated with adaptations in skeletal muscle. Melatonin, vitamin E and α-lipoic acid appear effective at decreasing markers of exercise-induced oxidative stress. However, evidence on their effects on endurance performance are either lacking or not supportive. Catechins, anthocyanins, coenzyme Q10 and vitamin C may improve vascular function, however, evidence is either limited to specific sub-populations and/or does not translate to improved performance. Finally, additional research should clarify the potential benefits of curcumin in improving muscle recovery post intensive exercise; and the potential hampering effects of astaxanthin, selenium and vitamin A on skeletal muscle adaptations to endurance training. Overall, we highlight the lack of supportive evidence for most antioxidant compounds to recommend to athletes.

Preclinical model systems of ryanodine receptor 1-related myopathies and malignant hyperthermia: a comprehensive scoping review of works published 1990-2019

BACKGROUND

Pathogenic variations in the gene encoding the skeletal muscle ryanodine receptor (RyR1) are associated with malignant hyperthermia (MH) susceptibility, a life-threatening hypermetabolic condition and RYR1-related myopathies (RYR1-RM), a spectrum of rare neuromuscular disorders. In RYR1-RM, intracellular calcium dysregulation, post-translational modifications, and decreased protein expression lead to a heterogenous clinical presentation including proximal muscle weakness, contractures, scoliosis, respiratory insufficiency, and ophthalmoplegia. Preclinical model systems of RYR1-RM and MH have been developed to better understand underlying pathomechanisms and test potential therapeutics.

METHODS

We conducted a comprehensive scoping review of scientific literature pertaining to RYR1-RM and MH preclinical model systems in accordance with the PRISMA Scoping Reviews Checklist and the framework proposed by Arksey and O'Malley. Two major electronic databases (PubMed and EMBASE) were searched without language restriction for articles and abstracts published between January 1, 1990 and July 3, 2019.

RESULTS

Our search yielded 5049 publications from which 262 were included in this review. A majority of variants tested in RYR1 preclinical models were localized to established MH/central core disease (MH/CCD) hot spots. A total of 250 unique RYR1 variations were reported in human/rodent/porcine models with 95% being missense substitutions. The most frequently reported RYR1 variant was R614C/R615C (human/porcine total n = 39), followed by Y523S/Y524S (rabbit/mouse total n = 30), I4898T/I4897T/I4895T (human/rabbit/mouse total n = 20), and R163C/R165C (human/mouse total n = 18). The dyspedic mouse was utilized by 47% of publications in the rodent category and its RyR1-null (1B5) myotubes were transfected in 23% of publications in the cellular model category. In studies of transfected HEK-293 cells, 57% of RYR1 variations affected the RyR1 channel and activation core domain. A total of 15 RYR1 mutant mouse strains were identified of which ten were heterozygous, three were compound heterozygous, and a further two were knockout. Porcine, avian, zebrafish, C. elegans, canine, equine, and drosophila model systems were also reported.

CONCLUSIONS

Over the past 30 years, there were 262 publications on MH and RYR1-RM preclinical model systems featuring more than 200 unique RYR1 variations tested in a broad range of species. Findings from these studies have set the foundation for therapeutic development for MH and RYR1-RM.

Physical exercise: An inducer of positive oxidative stress in skeletal muscle aging

Oxidative stress is the core of most pathological situations, and its attribution toward disease conversion is not yet well established. The adaptive capacity of a cell can overcome ROS-induced pathology. However, when a cell fails to extend its maximum adaptive capacity against oxidative stress, it could lead a cell to misbehave or defunct from its normal functions. Any type of physical activity can increase the cells' maximum adaptive capacity, but aging can limit this. However, whether aging is the initiating point of reducing cells' adaptive capacity against oxidative stress or oxidative stress can induce the aging process is a mystery, and it could be the key to solving several uncured diseases. Paradoxically, minimum ROS is needed for cellular homeostasis. Nevertheless, finding factors that can limit or nullify the production of ROS for cellular homeostasis is a million-dollar question. Regular physical exercise is considered to be one of the factors that can limit the production of ROS and increase the ROS-induced benefits in the cells through inducing minimum oxidative stress and increasing maximum adapting capacity against oxidative stress-induced damages. The type and intensity of exercise that can produce such positive effects in the cells remain unclear. Therefore, this review discusses how physical exercise can help to produce minimal positive oxidative stress in preventing skeletal muscle aging.

Mitochondrial oxidative stress induces leaky ryanodine receptor during mechanical ventilation

RATIONALE

Ventilator-induced diaphragm dysfunction (VIDD) increases morbidity and mortality in critical care patients. Although VIDD has been associated with mitochondrial oxidative stress and calcium homeostasis impairment, the underling mechanisms are still unknown. We hypothesized that diaphragmatic mitochondrial oxidative stress causes remodeling of the ryanodine receptor (RyR1)/calcium release channel, contributing to sarcoplasmic reticulum (SR) Ca²⁺ leak, proteolysis and VIDD.

METHOD

In mice diaphragms mechanically ventilated for short (6 h) and long (12 h) period, we assessed mitochondrial ROS production, mitochondrial aconitase activity as a marker of mitochondrial oxidative stress, RyR1 remodeling and function, Ca²⁺ dependent proteolysis, TGFβ1 and STAT3 pathway, muscle fibers cross-sectional area, and diaphragm specific force production, with or without the mitochondrial targeted anti-oxidant peptide d-Arg-2', 6'-dimethyltyrosine-Lys-Phe-NH₂ (SS31).

MEASUREMENTS AND MAIN RESULTS

6 h of mechanical ventilation (MV) resulted in increased mitochondrial ROS production, reduction of mitochondrial aconitase activity, increased oxidation, S-nitrosylation, S-glutathionylation and Ser-2844 phosphorylation of RyR1, depletion of stabilizing subunit calstabin1 from RyR1, increased SR Ca²⁺ leak. Preventing mROS production by SS31 treatment does not affect the TGFβ1 and STAT3 activation, which suggests that mitochondrial oxidative stress is a downstream pathway to TGFβ1 and STAT3, early involved in VIDD. This is further supported by the fact that SS-31 rescue all the other described cellular events and diaphragm contractile dysfunction induced by MV, while SS20, an analog of SS31 lacking antioxidant properties, failed to prevent these cellular events and the contractile dysfunction. Similar results were found in ventilated for 12 h. Moreover, SS31 treatment prevented calpain1 activity and diaphragm atrophy observed after 12 h of MV. This study emphasizes that mitochondrial oxidative stress during 6 h-MV contributes to SR Ca²⁺ leak via RyR1 remodeling, and diaphragm weakness, while longer periods of MV (12 h) were also associated with increased Ca²⁺-dependent proteolysis and diaphragm atrophy.

Activated Thiol Sepharose-based proteomic approach to quantify reversible protein oxidation

Reactive oxygen species (ROS) can act as second messengers in various signaling pathways, and abnormal oxidation contributes to multiple diseases, including cancer. Detecting and quantifying protein oxidation is crucial for a detailed understanding of reduction-oxidation reaction (redox) signaling. We developed an Activated Thiol Sepharose-based proteomic (ATSP) approach to quantify reversible protein oxidation. ATSP can enrich H2O2-sensitive thiol peptides, which are more likely to contain reactive cysteines involved in redox signaling. We applied our approach to analyze hereditary leiomyomatosis and renal cell carcinoma (HLRCC), a type of kidney cancer that harbors fumarate hydratase (FH)-inactivating mutations and has elevated ROS levels. Multiple proteins were oxidized in FH-deficient cells, including many metabolic proteins such as the pyruvate kinase M2 isoform (PKM2). Treatment of HLRCC cells with dimethyl fumarate or PKM2 activators altered PKM2 oxidation levels. Finally, we found that ATSP could detect Src homology region 2 domain-containing phosphatase-2 and PKM2 oxidation in cells stimulated with platelet-derived growth factor. This newly developed redox proteomics workflow can detect reversible oxidation of reactive cysteines and can be employed to analyze multiple physiologic and pathologic conditions.-Xu, Y., Andrade, J., Ueberheide, B., Neel, B. G. Activated Thiol Sepharose-based proteomic approach to quantify reversible protein oxidation.

[Neuronal cell death induced by the disruption of endoplasmic reticulum-mediated Ca2+ signaling]

For the function and survival of neurons in the central nervous system, it is indispensable that the intracellular Ca²⁺ dynamics are properly controlled. The endoplasmic reticulum (ER), a major intracellular Ca²⁺ store, plays an important role in the control of the intracellular Ca²⁺ dynamics in neurons through the supply and uptake of Ca²⁺. It has been suggested that the disruption of ER Ca²⁺ signaling is involved in neuronal cell death in various pathological conditions. Therefore, the disruption of ER Ca²⁺ signaling has attracted attention as a novel mechanism for neurodegenerative diseases including Alzheimer's disease. In this review, we introduce the latest findings including our research on the relationship between the disruption of ER Ca²⁺ signaling and neuronal cell death. In addition, we will introduce recent developments on the technology for visualizing intraluminal Ca²⁺ dynamics within the ER, which is indispensable for promoting research in this field.

Protein S-Nitrosylation: Determinants of Specificity and Enzymatic Regulation of S-Nitrosothiol-Based Signaling

SIGNIFICANCE

Protein S-nitrosylation, the oxidative modification of cysteine by nitric oxide (NO) to form protein S-nitrosothiols (SNOs), mediates redox-based signaling that conveys, in large part, the ubiquitous influence of NO on cellular function. S-nitrosylation regulates protein activity, stability, localization, and protein-protein interactions across myriad physiological processes, and aberrant S-nitrosylation is associated with diverse pathophysiologies. Recent Advances: It is recently recognized that S-nitrosylation endows S-nitroso-protein (SNO-proteins) with S-nitrosylase activity, that is, the potential to trans-S-nitrosylate additional proteins, thereby propagating SNO-based signals, analogous to kinase-mediated signaling cascades. In addition, it is increasingly appreciated that cellular S-nitrosylation is governed by dynamically coupled equilibria between SNO-proteins and low-molecular-weight SNOs, which are controlled by a growing set of enzymatic denitrosylases comprising two main classes (high and low molecular weight). S-nitrosylases and denitrosylases, which together control steady-state SNO levels, may be identified with distinct physiology and pathophysiology ranging from cardiovascular and respiratory disorders to neurodegeneration and cancer.

CRITICAL ISSUES

The target specificity of protein S-nitrosylation and the stability and reactivity of protein SNOs are determined substantially by enzymatic machinery comprising highly conserved transnitrosylases and denitrosylases. Understanding the differential functionality of SNO-regulatory enzymes is essential, and is amenable to genetic and pharmacological analyses, read out as perturbation of specific equilibria within the SNO circuitry.

FUTURE DIRECTIONS

The emerging picture of NO biology entails equilibria among potentially thousands of different SNOs, governed by denitrosylases and nitrosylases. Thus, to elucidate the operation and consequences of S-nitrosylation in cellular contexts, studies should consider the roles of SNO-proteins as both targets and transducers of S-nitrosylation, functioning according to enzymatically governed equilibria.

Comparison of Activity, Expression, and S-Nitrosylation of Calcium Transfer Proteins between Pale, Soft, and Exudative and Red, Firm, and Non-exudative Pork during Post-Mortem Aging

The research was performed to investigate the difference of activity, expression, and S-nitrosylation of calcium transfer proteins between pale, soft, and exudative (PSE) and red, firm, and non-exudative (RFN) pork. Seven PSE and seven RFN pork longissimus thoracis (LT) muscles were chosen according to pH and L* at 1 h post-mortem and identified by drip loss at 24 h. The nitric oxide synthase (NOS) activity and neuronal nitric oxide synthase (nNOS) expression showed a significant difference between two groups ( p < 0.05). PSE meat had a considerably higher sarcoplasmic calcium concentration compared to RFN meat at 1 h post-mortem aging ( p < 0.05). In PSE meat, the expression of ryanodine receptor 1 (RyR1) and sarcoplasmic reticulum calcium ATPase 1 (SERCA1) was lower than that in RFN meat, while the relative S-nitrosylation level of RyR1 and SERCA1 was higher ( p < 0.05). In addition, a lower activity of SERCA was detected in PSE meat compared to RFN meat ( p < 0.05). Those results indicate that S-nitrosylation of RyR1 and SERCA1 can putatively play a crucial part in regulating calcium homeostasis. A high level of RyR1 and SERCA1 S-nitrosylation can induce the imbalance of calcium in cytoplasm, leading to accelerated pH decline and the development of PSE meat.

Redox Dependent Modifications of Ryanodine Receptor: Basic Mechanisms and Implications in Heart Diseases

Heart contraction vitally depends on tightly controlled intracellular Ca regulation. Because contraction is mainly driven by Ca released from the sarcoplasmic reticulum (SR), this organelle plays a particularly important role in Ca regulation. The type two ryanodine receptor (RyR2) is the major SR Ca release channel in ventricular myocytes. Several cardiac pathologies, including myocardial infarction and heart failure, are associated with increased RyR2 activity and diastolic SR Ca leak. It has been suggested that the increased RyR2 activity plays an important role in arrhythmias and contractile dysfunction. Several studies have linked increased SR Ca leak during myocardial infarction and heart failure to the activation of RyR2 in response to oxidative stress. This activation might include direct oxidation of RyR2 as well as indirect activation via phosphorylation or altered interactions with regulatory proteins. Out of ninety cysteine residues per RyR2 subunit, twenty one were reported to be in reduced state that could be potential targets for redox modifications that include S-nitrosylation, S-glutathionylation, and disulfide cross-linking. Despite its clinical significance, molecular mechanisms of RyR dysfunction during oxidative stress are not fully understood. Herein we review the most recent insights into redox-dependent modulation of RyR2 during oxidative stress and heart diseases.

Calcium Release Mediated by Redox-Sensitive RyR2 Channels Has a Central Role in Hippocampal Structural Plasticity and Spatial Memory

AIMS

Previous studies indicate that hippocampal synaptic plasticity and spatial memory processes entail calcium release from intracellular stores mediated by ryanodine receptor (RyR) channels. In particular, RyR-mediated Ca²⁺ release is central for the dendritic spine remodeling induced by brain-derived neurotrophic factor (BDNF), a neurotrophin that stimulates complex signaling pathways leading to memory-associated protein synthesis and structural plasticity. To examine if upregulation of ryanodine receptor type-2 (RyR2) channels and the spine remodeling induced by BDNF entail reactive oxygen species (ROS) generation, and to test if RyR2 downregulation affects BDNF-induced spine remodeling and spatial memory.

RESULTS

Downregulation of RyR2 expression (short hairpin RNA [shRNA]) in primary hippocampal neurons, or inhibition of nitric oxide synthase (NOS) or NADPH oxidase, prevented agonist-mediated RyR-mediated Ca²⁺ release, whereas BDNF promoted cytoplasmic ROS generation. RyR2 downregulation or inhibitors of N-methyl-d-aspartate (NMDA) receptors, or NOS or of NADPH oxidase type-2 (NOX2) prevented RyR2 upregulation and the spine remodeling induced by BDNF, as did incubation with the antioxidant agent N-acetyl l-cysteine. In addition, intrahippocampal injection of RyR2-directed antisense oligodeoxynucleotides, which caused significant RyR2 downregulation, caused conspicuous defects in a memorized spatial memory task.

INNOVATION

The present novel results emphasize the key role of redox-sensitive Ca²⁺ release mediated by RyR2 channels for hippocampal structural plasticity and spatial memory.

CONCLUSION

Based on these combined results, we propose (i) that BDNF-induced RyR2-mediated Ca²⁺ release and ROS generation via NOS/NOX2 are strictly required for the dendritic spine remodeling and the RyR2 upregulation induced by BDNF, and (ii) that RyR2 channel expression is crucial for spatial memory processes. Antioxid. Redox Signal. 29, 1125-1146.

Role of Endoplasmic Reticulum-Mediated Ca2+ Signaling in Neuronal Cell Death

SIGNIFICANCE

Properly controlled intracellular Ca²⁺ dynamics is crucial for regulation of neuronal function and survival in the central nervous system. The endoplasmic reticulum (ER), a major intracellular Ca²⁺ store, plays a critical role as a source and sink for neuronal Ca²⁺. Recent Advances: Accumulating evidence indicates that disrupted ER Ca²⁺ signaling is involved in neuronal cell death under various pathological conditions, providing novel insight into neurodegenerative disease mechanisms.

CRITICAL ISSUES

We summarize current knowledge concerning the relationship between abnormal ER Ca²⁺ dynamics and neuronal cell death. We also introduce recent technical advances for probing ER intraluminal Ca²⁺ dynamics with unprecedented spatiotemporal resolution.

FUTURE DIRECTIONS

Further studies on ER Ca²⁺ signaling are expected to provide progress for unmet medical needs in neurodegenerative disease. Antioxid. Redox Signal. 29, 1147-1157.

Computational Structural Biology of S-nitrosylation of Cancer Targets

Nitric oxide (NO) plays an essential role in redox signaling in normal and pathological cellular conditions. In particular, it is well known to react in vivo with cysteines by the so-called S-nitrosylation reaction. S-nitrosylation is a selective and reversible post-translational modification that exerts a myriad of different effects, such as the modulation of protein conformation, activity, stability, and biological interaction networks. We have appreciated, over the last years, the role of S-nitrosylation in normal and disease conditions. In this context, structural and computational studies can help to dissect the complex and multifaceted role of this redox post-translational modification. In this review article, we summarized the current state-of-the-art on the mechanism of S-nitrosylation, along with the structural and computational studies that have helped to unveil its effects and biological roles. We also discussed the need to move new steps forward especially in the direction of employing computational structural biology to address the molecular and atomistic details of S-nitrosylation. Indeed, this redox modification has been so far an underappreciated redox post-translational modification by the computational biochemistry community. In our review, we primarily focus on S-nitrosylated proteins that are attractive cancer targets due to the emerging relevance of this redox modification in a cancer setting.

Role of defective Ca2+ signaling in skeletal muscle weakness: Pharmacological implications

The misbehaving attitude of Ca²⁺ signaling pathways could be the probable reason in many muscular disorders such as myopathies, systemic disorders like hypoxia, sepsis, cachexia, sarcopenia, heart failure, and dystrophy. The present review throws light upon the calcium flux regulating signaling channels like ryanodine receptor complex (RyR1), SERCA (Sarco-endoplasmic Reticulum Calcium ATPase), DHPR (Dihydropyridine Receptor) or Cav1.1 and Na+/Ca²⁺ exchange pump in detail and how remodelling of these channels contribute towards disturbed calcium homeostasis. Understanding these pathways will further provide an insight for establishing new therapeutic approaches for the prevention and treatment of muscle atrophy under stress conditions, targeting calcium ion channels and associated regulatory proteins.

Matrix vesicles induce calcification of recipient vascular smooth muscle cells through multiple signaling pathways

In patients with chronic kidney and end-stage renal diseases, the major risk factor for progression of arterial calcification is the presence of existing (baseline) calcification. Here, we tested whether calcification of arteries is extended from calcified vascular smooth muscle cells (VSMCs) to adjacent normal cells by matrix vesicle-induced alteration of cell signaling. Matrix vesicles isolated from VSMC of rats with chronic kidney disease were co-cultured with VSMCs from normal littermates. Endocytosis of vesicles by recipient cells was confirmed by confocal microscopy. The addition of cellular matrix vesicles with characteristics of exosomes and low fetuin-A content enhanced the calcification of recipient VSMC. Further, only cellular-derived matrix vesicles induced an increase in intracellular calcium ion concentration, NOX1 (NADPH oxidase) and the anti-oxidant superoxide dismutase-2 in recipient normal VSMC. The increase in intracellular calcium ion concentration was due to release from endoplasmic reticulum and partially attributed to the activation of both NOX1 and mitogen-activated protein kinase (MEK1 and Erk1/2) signaling, since inhibiting both pathways blocked the increase in intracellular calcium ion in recipient VSMC. In contrast, matrix vesicles isolated from the media had no effect on the intracellular calcium ion concentration or MEK1 signaling, and did not induce calcification. However, media matrix vesicles did increase Erk1/2, although not to the level of cellular matrix vesicles, and NOX1 expression. Blockade of NOX activity further inhibited the cellular matrix vesicle-induced accelerated calcification of recipient VSMC, suggesting a potential therapeutic role of such inhibition. Thus, addition of cellular-derived matrix vesicles from calcifying VSMC can accelerate calcification by inducing cell signaling changes and phenotypic alteration of recipient VSMC.

[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.

Applications of Reactive Cysteine Profiling

Cysteine thiols are involved in a diverse set of biological transformations, including nucleophilic and redox catalysis, metal coordination and formation of both dynamic and structural disulfides. Often posttranslationally modified, cysteines are also frequently alkylated by electrophilic compounds, including electrophilic metabolites, drugs, and natural products, and are attractive sites for covalent probe and drug development. Quantitative proteomics combined with activity-based protein profiling has been applied to annotate cysteine reactivity, susceptibility to posttranslational modifications, and accessibility to chemical probes, uncovering thousands of functional and small-molecule targetable cysteines across a diverse set of proteins, proteome-wide in an unbiased manner. Reactive cysteines have been targeted by high-throughput screening and fragment-based ligand discovery efforts. New cysteine-reactive electrophiles and compound libraries have been synthesized to enable inhibitor discovery broadly and to minimize nonspecific toxicity and off-target activity of compounds. With the recent blockbuster success of several covalent inhibitors, and the development of new chemical proteomic strategies to broadly identify reactive, ligandable and posttranslationally modified cysteines, cysteine profiling is poised to enable the development of new potent and selective chemical probes and even, in some cases, new drugs.

Transient receptor potential channel 6 regulates abnormal cardiac S-nitrosylation in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is an X-linked disorder with dystrophin loss that results in skeletal and cardiac muscle weakening and early death. Loss of the dystrophin-sarcoglycan complex delocalizes nitric oxide synthase (NOS) to alter its signaling, and augments mechanosensitive intracellular Ca²⁺ influx. The latter has been coupled to hyperactivation of the nonselective cation channel, transient receptor potential canonical channel 6 (Trpc6), in isolated myocytes. As Ca²⁺ also activates NOS, we hypothesized that Trpc6 would help to mediate nitric oxide (NO) dysregulation and that this would be manifest in increased myocardial S-nitrosylation, a posttranslational modification increasingly implicated in neurodegenerative, inflammatory, and muscle disease. Using a recently developed dual-labeling proteomic strategy, we identified 1,276 S-nitrosylated cysteine residues [S-nitrosothiol (SNO)] on 491 proteins in resting hearts from a mouse model of DMD (dmd^mdx:utrn^+/-). These largely consisted of mitochondrial proteins, metabolic regulators, and sarcomeric proteins, with 80% of them also modified in wild type (WT). S-nitrosylation levels, however, were increased in DMD. Genetic deletion of Trpc6 in this model (dmd^mdx:utrn^+/-:trpc6^-/-) reversed ∼70% of these changes. Trpc6 deletion also ameliorated left ventricular dilation, improved cardiac function, and tended to reduce fibrosis. Furthermore, under catecholamine stimulation, which also increases NO synthesis and intracellular Ca²⁺ along with cardiac workload, the hypernitrosylated state remained as it did at baseline. However, the impact of Trpc6 deletion on the SNO proteome became less marked. These findings reveal a role for Trpc6-mediated hypernitrosylation in dmd^mdx:utrn^+/- mice and support accumulating evidence that implicates nitrosative stress in cardiac and muscle disease.

Regulation of protein function by S-nitrosation and S-glutathionylation: processes and targets in cardiovascular pathophysiology

Decades of chemical, biochemical and pathophysiological research have established the relevance of post-translational protein modifications induced by processes related to oxidative stress, with critical reflections on cellular signal transduction pathways. A great deal of the so-called ‘redox regulation’ of cell function is in fact mediated through reactions promoted by reactive oxygen and nitrogen species on more or less specific aminoacid residues in proteins, at various levels within the cell machinery. Modifications involving cysteine residues have received most attention, due to the critical roles they play in determining the structure/function correlates in proteins. The peculiar reactivity of these residues results in two major classes of modifications, with incorporation of NO moieties (S-nitrosation, leading to formation of proteinS-nitrosothiols) or binding of low molecular weight thiols (S-thionylation, i.e. in particularS-glutathionylation,S-cysteinylglycinylation andS-cysteinylation). A wide array of proteins have been thus analyzed in detail as far as their susceptibility to either modification or both, and the resulting functional changes have been described in a number of experimental settings. The present review aims to provide an update of available knowledge in the field, with a special focus on the respective (sometimes competing and antagonistic) roles played by proteinS-nitrosations andS-thionylations in biochemical and cellular processes specifically pertaining to pathogenesis of cardiovascular diseases.

The structural basis of ryanodine receptor ion channel function

Large-conductance Ca²⁺ release channels known as ryanodine receptors (RyRs) mediate the release of Ca²⁺ from an intracellular membrane compartment, the endo/sarcoplasmic reticulum. There are three mammalian RyR isoforms: RyR1 is present in skeletal muscle; RyR2 is in heart muscle; and RyR3 is expressed at low levels in many tissues including brain, smooth muscle, and slow-twitch skeletal muscle. RyRs form large protein complexes comprising four 560-kD RyR subunits, four ∼12-kD FK506-binding proteins, and various accessory proteins including calmodulin, protein kinases, and protein phosphatases. RyRs share ∼70% sequence identity, with the greatest sequence similarity in the C-terminal region that forms the transmembrane, ion-conducting domain comprising ∼500 amino acids. The remaining ∼4,500 amino acids form the large regulatory cytoplasmic "foot" structure. Experimental evidence for Ca²⁺, ATP, phosphorylation, and redox-sensitive sites in the cytoplasmic structure have been described. Exogenous effectors include the two Ca²⁺ releasing agents caffeine and ryanodine. Recent work describing the near atomic structures of mammalian skeletal and cardiac muscle RyRs provides a structural basis for the regulation of the RyRs by their multiple effectors.

Chronicles of a reductase: Biochemistry, genetics and physio-pathological role of GSNOR

S-nitrosylation is a major redox posttranslational modification involved in cell signaling. The steady state concentration of S-nitrosylated proteins depends on the balance between the relative ability to generate nitric oxide (NO) via NO synthase and to reduce nitrosothiols by denitrosylases. Numerous works have been published in last decades regarding the role of NO and S-nitrosylation in the regulation of protein structure and function, and in driving cellular activities in vertebrates. Notwithstanding an increasing number of observations indicates that impairment of denitrosylation equally affects cellular homeostasis, there is still no report providing comprehensive knowledge on the impact that denitrosylation has on maintaining correct physiological processes and organ activities. Among denitrosylases, S-nitrosoglutathione reductase (GSNOR) represents the prototype enzyme to disclose how denitrosylation plays a crucial role in tuning NO-bioactivity and how much it deeply impacts on cell homeostasis and human patho-physiology. In this review we attempt to illustrate the history of GSNOR discovery and provide the evidence so far reported in support of GSNOR implications in development and human disease.

NO-sGC Pathway Modulates Ca2+ Release and Muscle Contraction in Zebrafish Skeletal Muscle

Vertebrate skeletal muscle contraction and relaxation is a complex process that depends on Ca²⁺ ions to promote the interaction of actin and myosin. This process can be modulated by nitric oxide (NO), a gas molecule synthesized endogenously by (nitric oxide synthase) NOS isoforms. At nanomolar concentrations NO activates soluble guanylate cyclase (sGC), which in turn activates protein kinase G via conversion of GTP into cyclic GMP. Alternatively, NO post-translationally modifies proteins via S-nitrosylation of the thiol group of cysteine. However, the mechanisms of action of NO on Ca²⁺ homeostasis during muscle contraction are not fully understood and we hypothesize that NO exerts its effects on Ca²⁺ homeostasis in skeletal muscles mainly through negative modulation of Ca²⁺ release and Ca²⁺ uptake via the NO-sGC-PKG pathway. To address this, we used 5–7 days-post fecundation-larvae of zebrafish, a well-established animal model for physiological and pathophysiological muscle activity. We evaluated the response of muscle contraction and Ca²⁺ transients in presence of SNAP, a NO-donor, or L-NAME, an unspecific NOS blocker in combination with specific blockers of key proteins of Ca²⁺ homeostasis. We also evaluate the expression of NOS in combination with dihydropteridine receptor, ryanodine receptor and sarco/endoplasmic reticulum Ca²⁺ ATPase. We concluded that endogenous NO reduced force production through negative modulation of Ca²⁺ transients via the NO-sGC pathway. This effect could be reversed using an unspecific NOS blocker or sGC blocker.

How widespread is stable protein S-nitrosylation as an end-effector of protein regulation?

Over the last 25 years protein S-nitrosylation, also known more correctly as S-nitrosation, has been progressively implicated in virtually every nitric oxide-regulated process within the cardiovascular system. The current, widely-held paradigm is that S-nitrosylation plays an equivalent role as phosphorylation, providing a stable and controllable post-translational modification that directly regulates end-effector target proteins to elicit biological responses. However, this concept largely ignores the intrinsic instability of the nitrosothiol bond, which rapidly reacts with typically abundant thiol-containing molecules to generate more stable disulfide bonds. These protein disulfides, formed via a nitrosothiol intermediate redox state, are rationally anticipated to be the predominant end-effector modification that mediates functional alterations when cells encounter nitrosative stimuli. In this review we present evidence and explain our reasoning for arriving at this conclusion that may be controversial to some researchers in the field.

Muscle Weakness in Rheumatoid Arthritis: The Role of Ca2+ and Free Radical Signaling

In addition to the primary symptoms arising from inflammatory processes in the joints, muscle weakness is commonly reported by patients with rheumatoid arthritis (RA). Muscle weakness not only reduces the quality of life for the affected patients, but also dramatically increases the burden on society since patients' work ability decreases. A 25–70% reduction in muscular strength has been observed in pateints with RA when compared with age-matched healthy controls. The reduction in muscle strength is often larger than what could be explained by the reduction in muscle size in patients with RA, which indicates that intracellular (intrinsic) muscle dysfunction plays an important role in the underlying mechanism of muscle weakness associated with RA. In this review, we highlight the present understanding of RA-associated muscle weakness with special focus on how enhanced Ca^2 + release from the ryanodine receptor and free radicals (reactive oxygen/nitrogen species) contributes to muscle weakness, and recent developments of novel therapeutic interventions.

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Muscle weakness is commonly reported by patients with rheumatoid arthritis (RA).

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Intrinsic muscle weakness is important in the underlying mechanisms of muscle weakness associated with rheumatoid arthritis.

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Enhanced Ca^2 + release and peroxynitrite-induced stress contributes to RA-induced muscle weakness.

Calcium-Dependent Structural Dynamics of a Spin-Labeled RyR Peptide Bound to Calmodulin

We have used chemical synthesis, electron paramagnetic resonance (EPR), and circular dichroism to detect and analyze the structural dynamics of a ryanodine receptor (RyR) peptide bound to calmodulin (CaM). The skeletal muscle calcium release channel RyR1 is activated by Ca²⁺-free CaM and inhibited by Ca²⁺-bound CaM. To probe the structural mechanism for this regulation, wild-type RyRp and four spin-labeled derivatives were synthesized, each containing the nitroxide probe 2,2,6,6-tetramethyl-piperidine-1-oxyl-4-amino-4-carboxylic acid substituted for a single amino acid. In 2,2,6,6-tetramethyl-piperidine-1-oxyl-4-amino-4-carboxylic acid, the probe is rigidly and stereospecifically coupled to the α-carbon, enabling direct detection by EPR of peptide backbone structural dynamics. In the absence of CaM, circular dichroism indicates a complete lack of secondary structure, while 40% trifluoroethanol (TFE) induces >90% helicity and is unperturbed by the spin label. The EPR spectrum of each spin-labeled peptide indicates nanosecond dynamic disorder that is substantially reduced by TFE, but a significant gradient in dynamics is observed, decreasing from N- to C-terminus, both in the presence and absence of TFE. When bound to CaM, the probe nearest RyRp's N-terminus shows rapid rotational motion consistent with peptide backbone dynamics of a locally unfolded peptide, while the other three sites show substantial restriction of dynamics, consistent with helical folding. The two N-terminal sites, which bind to the C-lobe of CaM, do not show a significant Ca²⁺-dependence in mobility, while both C-terminal sites, which bind to the N-lobe of CaM, are significantly less mobile in the presence of bound Ca²⁺. These results support a model in which the interaction of RyR with CaM is nonuniform along the peptide, and the primary effect of Ca²⁺ is to increase the interaction of the C-terminal portion of the peptide with the N-terminal lobe of CaM. These results provide, to our knowledge, new insight into the Ca²⁺-dependent regulation of RyR by CaM.

Spinal Cord Injury Leads to Hyperoxidation and Nitrosylation of Skeletal Muscle Ryanodine Receptor-1 Associated with Upregulation of Nicotinamide Adenine Dinucleotide Phosphate Oxidase 4

Spinal cord injury (SCI) results in marked atrophy and dysfunction of skeletal muscle. There are currently no effective treatments for SCI-induced muscle atrophy or the dysfunction of the remaining muscle tissue. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-4 (Nox4) produces reactive oxygen species (ROS) in sarcoplasmic reticulum (SR) and has been identified as an important O2 sensor in skeletal muscle. Ryanodine receptors (RyRs) are calcium (Ca2+) channels that are responsible for Ca2+ release from SR. In skeletal muscle, type1 RyR (RyR1) is predominantly functional. RyR1 is regulated by multiple proteins, including calstabin1, which assures that they close appropriately once contraction has ceased. RyR1 function is also regulated by oxidation and redox-dependent cysteine nitrosylation. Excessive oxidation/nitrosylation of RyR1 is associated with dissociation of calstabin1 and reduced muscle force generation. However, whether Nox4 levels in skeletal muscle are elevated or whether RyR1 is oxidized or nitrosylated after SCI has not been determined. In this study, we examined Nox4 expression, oxidation/nitrolysation status, and association of calstabin1 with RyR1 in skeletal muscle derived from rats that were subjected to T4 complete transection (SCI), and observed elevated expression of Nox4 messenger RNA and protein in muscle after SCI associated with enhanced binding of Nox4 to RyR1, increased oxidation and nitrosylation of RyR1, and dissociation of calstabin1 from RyR1 in SCI rat muscle. Our data suggest that RyR1 dysfunction resulting from excessive oxidation/nitrosylation may contribute to reduced specific force after SCI and suggest that Nox4 may be the source of ROS responsible for increased oxidation and nitrosylation of RyR1.

The role of S-nitrosoglutathione reductase (GSNOR) in human disease and therapy

S-nitrosoglutathione reductase (GSNOR), or ADH5, is an enzyme in the alcohol dehydrogenase (ADH) family. It is unique when compared to other ADH enzymes in that primary short-chain alcohols are not its principle substrate. GSNOR metabolizes S-nitrosoglutathione (GSNO), S-hydroxymethylglutathione (the spontaneous adduct of formaldehyde and glutathione), and some alcohols. GSNOR modulates reactive nitric oxide (•NO) availability in the cell by catalyzing the breakdown of GSNO, and indirectly regulates S-nitrosothiols (RSNOs) through GSNO-mediated protein S-nitrosation. The dysregulation of GSNOR can significantly alter cellular homeostasis, leading to disease. GSNOR plays an important regulatory role in smooth muscle relaxation, immune function, inflammation, neuronal development and cancer progression, among many other processes. In recent years, the therapeutic inhibition of GSNOR has been investigated to treat asthma, cystic fibrosis and interstitial lung disease (ILD). The direct action of •NO on cellular pathways, as well as the important regulatory role of protein S-nitrosation, is closely tied to GSNOR regulation and defines this enzyme as an important therapeutic target.

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

Vascular tone of resistance arteries and arterioles determines peripheral vascular resistance, contributing to the regulation of blood pressure and blood flow to, and within the body's tissues and organs. Ion channels in the plasma membrane and endoplasmic reticulum of vascular smooth muscle cells (SMCs) in these blood vessels importantly contribute to the regulation of intracellular Ca2+ concentration, the primary determinant of SMC contractile activity and vascular tone. Ion channels provide the main source of activator Ca2+ that determines vascular tone, and strongly contribute to setting and regulating membrane potential, which, in turn, regulates the open-state-probability of voltage gated Ca2+ channels (VGCCs), the primary source of Ca2+ in resistance artery and arteriolar SMCs. Ion channel function is also modulated by vasoconstrictors and vasodilators, contributing to all aspects of the regulation of vascular tone. This review will focus on the physiology of VGCCs, voltage-gated K+ (KV) channels, large-conductance Ca2+-activated K+ (BKCa) channels, strong-inward-rectifier K+ (KIR) channels, ATP-sensitive K+ (KATP) channels, ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), and a variety of transient receptor potential (TRP) channels that contribute to pressure-induced myogenic tone in resistance arteries and arterioles, the modulation of the function of these ion channels by vasoconstrictors and vasodilators, their role in the functional regulation of tissue blood flow and their dysfunction in diseases such as hypertension, obesity, and diabetes. © 2017 American Physiological Society. Compr Physiol 7:485-581, 2017.

Transcriptional and post-translational regulation of pannexins

Pannexins are a 3-membered family of proteins that form large pore ion and metabolite channels in vertebrates. The impact of pannexins on vertebrate biology is intricately tied to where and when they are expressed, and how they are modified, once produced. The purpose of this review is therefore to outline our current understanding of transcriptional and post-translational regulation of pannexins. First, we briefly summarize their discovery and characteristics. Next, we describe several aspects of transcriptional regulation, including cell and tissue-specific expression, dynamic expression over development and disease, as well as new insights into the underlying molecular machinery involved. Following this, we delve into the role of post-translational modifications in the regulation of trafficking and channel properties, highlighting important work on glycosylation, phosphorylation, S-nitrosylation and proteolytic cleavage. Embedded throughout, we also highlight important knowledge gaps and avenues of future research. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.

GSNOR Deficiency Enhances In Situ Skeletal Muscle Strength, Fatigue Resistance, and RyR1 S-Nitrosylation Without Impacting Mitochondrial Content and Activity

AIM

Nitric oxide (NO) plays important, but incompletely defined roles in skeletal muscle. NO exerts its regulatory effects partly though S-nitrosylation, which is balanced by denitrosylation by enzymes such as S-nitrosoglutathione reductase (GSNOR), whose functions in skeletal muscle remain to be fully deciphered.

RESULTS

GSNOR null (GSNOR^-/-) tibialis anterior (TA) muscles showed normal growth and were stronger and more fatigue resistant than controls in situ. However, GSNOR^-/- lumbrical muscles showed normal contractility and Ca²⁺ handling in vitro, suggesting important differences in GSNOR function between muscles or between in vitro and in situ environments. GSNOR^-/- TA muscles exhibited normal mitochondrial content, and capillary densities, but reduced type IIA fiber content. GSNOR inhibition did not impact mitochondrial respiratory complex I, III, or IV activities. These findings argue that enhanced GSNOR^-/- TA contractility is not driven by changes in mitochondrial content or activity, fiber type, or blood vessel density. However, loss of GSNOR led to RyR1 hypernitrosylation, which is believed to increase muscle force output under physiological conditions. cGMP synthesis by soluble guanylate cyclase (sGC) was decreased in resting GSNOR^-/- muscle and was more responsive to agonist (DETANO, BAY 41, and BAY 58) stimulation, suggesting that GSNOR modulates cGMP production in skeletal muscle.

INNOVATION

GSNOR may act as a "brake" on skeletal muscle contractile performance under physiological conditions by modulating nitrosylation/denitrosylation balance.

CONCLUSIONS

GSNOR may play important roles in skeletal muscle contractility, RyR1 S-nitrosylation, fiber type specification, and sGC activity. Antioxid. Redox Signal. 26, 165-181.

Ryanodine receptor modification and regulation by intracellular Ca2+ and Mg2+ in healthy and failing human hearts

RATIONALE

Heart failure is a multimodal disorder, of which disrupted Ca²⁺ homeostasis is a hallmark. Central to Ca²⁺ homeostasis is the major cardiac Ca²⁺ release channel - the ryanodine receptor (RyR2) - whose activity is influenced by associated proteins, covalent modification and by Ca²⁺ and Mg²⁺. That RyR2 is remodelled and its function disturbed in heart failure is well recognized, but poorly understood.

OBJECTIVE

To assess Ca²⁺ and Mg²⁺ regulation of RyR2 from left ventricles of healthy, cystic fibrosis and failing hearts, and to correlate these functional changes with RyR2 modifications and remodelling.

METHODS AND RESULTS

The function of RyR2 from left ventricular samples was assessed using lipid bilayer single-channel measurements, whilst RyR2 modification and protein:protein interactions were determined using Western Blots and co-immunoprecipitation. In all failing hearts there was an increase in RyR2 activity at end-diastolic cytoplasmic Ca²⁺ (100nM), a decreased cytoplasmic [Ca²⁺] required for half maximal activation (K_a) and a decrease in inhibition by cytoplasmic Mg²⁺. This was accompanied by significant hyperphosphorylation of RyR2 S²⁸⁰⁸ and S²⁸¹⁴, reduced free thiol content and a reduced interaction with FKBP12.0 and FKBP12.6. Either dephosphorylation of RyR2 using PP1 or thiol reduction using DTT eliminated any significant difference in the activity of RyR2 from healthy and failing hearts. We also report a subgroup of RyR2 in failing hearts that were not responsive to regulation by intracellular Ca²⁺ or Mg²⁺.

CONCLUSION

Despite different aetiologies, disrupted RyR2 Ca²⁺ sensitivity and biochemical modification of the channel are common constituents of failing heart RyR2 and may underlie the pathological disturbances in intracellular Ca²⁺ signalling.

Modeling Local X-ROS and Calcium Signaling in the Heart

Stretching single ventricular cardiac myocytes has been shown experimentally to activate transmembrane nicotinamide adenine dinucleotide phosphate oxidase type 2 to produce reactive oxygen species (ROS) and increase the Ca2+ spark rate in a process called X-ROS signaling. The increase in Ca2+ spark rate is thought to be due to an increase in ryanodine receptor type 2 (RyR2) open probability by direct oxidation of the RyR2 protein complex. In this article, a computational model is used to examine the regulation of ROS and calcium homeostasis by local, subcellular X-ROS signaling and its role in cardiac excitation-contraction coupling. To this end, a four-state RyR2 model was developed that includes an X-ROS-dependent RyR2 mode switch. When activated, [Ca2+]i-sensitive RyR2 open probability increases, and the Ca2+ spark rate changes in a manner consistent with experimental observations. This, to our knowledge, new model is used to study the transient effects of diastolic stretching and subsequent ROS production on RyR2 open probability, Ca2+ sparks, and the myoplasmic calcium concentration ([Ca2+]i) during excitation-contraction coupling. The model yields several predictions: 1) [ROS] is produced locally near the RyR2 complex during X-ROS signaling and increases by an order of magnitude more than the global ROS signal during myocyte stretching; 2) X-ROS activation just before the action potential, corresponding to ventricular filling during diastole, increases the magnitude of the Ca2+ transient; 3) during prolonged stretching, the X-ROS-induced increase in Ca2+ spark rate is transient, so that long-sustained stretching does not significantly increase sarcoplasmic reticulum Ca2+ leak; and 4) when the chemical reducing capacity of the cell is decreased, activation of X-ROS signaling increases sarcoplasmic reticulum Ca2+ leak and contributes to global oxidative stress, thereby increases the possibility of arrhythmia. The model provides quantitative information not currently obtainable through experimental means and thus provides a framework for future X-ROS signaling experiments.

Muscle redox signalling pathways in exercise. Role of antioxidants

Recent research highlights the importance of redox signalling pathway activation by contraction-induced reactive oxygen species (ROS) and nitric oxide (NO) in normal exercise-related cellular and molecular adaptations in skeletal muscle. In this review, we discuss some potentially important redox signalling pathways in skeletal muscle that are involved in acute and chronic responses to contraction and exercise. Specifically, we discuss redox signalling implicated in skeletal muscle contraction force, mitochondrial biogenesis and antioxidant enzyme induction, glucose uptake and muscle hypertrophy. Furthermore, we review evidence investigating the impact of major exogenous antioxidants on these acute and chronic responses to exercise. Redox signalling pathways involved in adaptive responses in skeletal muscle to exercise are not clearly elucidated at present, and further research is required to better define important signalling pathways involved. Evidence of beneficial or detrimental effects of specific antioxidant compounds on exercise adaptations in muscle is similarly limited, particularly in human subjects. Future research is required to not only investigate effects of specific antioxidant compounds on skeletal muscle exercise adaptations, but also to better establish mechanisms of action of specific antioxidants in vivo. Although we feel it remains somewhat premature to make clear recommendations in relation to application of specific antioxidant compounds in different exercise settings, a bulk of evidence suggests that N-acetylcysteine (NAC) is ergogenic through its effects on maintenance of muscle force production during sustained fatiguing events. Nevertheless, a current lack of evidence from studies using performance tests representative of athletic competition and a potential for adverse effects with high doses (>70mg/kg body mass) warrants caution in its use for performance enhancement. In addition, evidence implicates high dose vitamin C (1g/day) and E (≥260 IU/day) supplementation in impairments to some skeletal muscle cellular adaptations to chronic exercise training. Thus, determining the utility of antioxidant supplementation in athletes likely requires a consideration of training and competition periodization cycles of athletes in addition to type, dose and duration of antioxidant supplementation.

Nitric Oxide-induced Activation of the Type 1 Ryanodine Receptor Is Critical for Epileptic Seizure-induced Neuronal Cell Death

Status epilepticus (SE) is a life-threatening emergency that can cause neurodegeneration with debilitating neurological disorders. However, the mechanism by which convulsive SE results in neurodegeneration is not fully understood. It has been shown that epileptic seizures produce markedly increased levels of nitric oxide (NO) in the brain, and that NO induces Ca²⁺ release from the endoplasmic reticulum via the type 1 ryanodine receptor (RyR1), which occurs through S-nitrosylation of the intracellular Ca²⁺ release channel. Here, we show that through genetic silencing of NO-induced activation of the RyR1 intracellular Ca²⁺ release channel, neurons were rescued from seizure-dependent cell death. Furthermore, dantrolene, an inhibitor of RyR1, was protective against neurodegeneration caused by SE. These results demonstrate that NO-induced Ca²⁺ release via RyR is involved in SE-induced neurodegeneration, and provide a rationale for the use of RyR1 inhibitors for the prevention of brain damage following SE.

Muscle redox disturbances and oxidative stress as pathomechanisms and therapeutic targets in early-onset myopathies

Because of their contractile activity and their high oxygen consumption and metabolic rate, skeletal muscles continually produce moderate levels of reactive oxygen and nitrogen species (ROS/RNS), which increase during exercise and are buffered by multiple antioxidant systems to maintain redox homeostasis. Imbalance between ROS/RNS production and elimination results in oxidative stress (OxS), which has been implicated in ageing and in numerous human diseases, including cancer, diabetes or age-related muscle loss (sarcopenia). The study of redox homeostasis in muscle was hindered by its lability, by the many factors influencing technical OxS measures and by ROS/RNS important roles in signaling pathways and adaptative responses to muscle contraction and effort, which make it difficult to define a threshold between physiological signaling and pathological conditions. In the last years, new tools have been developed that facilitate the study of these key mechanisms, and deregulation of redox homeostasis has emerged as a key pathogenic mechanism and potential therapeutic target in muscle conditions. This is in particular the case for early-onset myopathies, genetic muscle diseases which present from birth or early childhood with muscle weakness interfering with ambulation and often with cardiac or respiratory failure leading to premature death. Inherited defects of the reductase selenoprotein N in SEPN1-related myopathy leads to chronic OxS of monogenic origin as a primary disease pathomechanism. In myopathies associated with mutations of the genes encoding the calcium channel RyR1, the extracellular matrix protein collagen VI or the sarcolemmal protein dystrophin (Duchenne Muscular Dystrophy), OxS has been identified as a relevant secondary pathophysiological mechanism. OxS being drug-targetable, it represents an interesting therapeutic target for these incurable conditions, and following preclinical correction of the cell or animal model phenotype, the first clinical trials with the antioxidants N-acetylcysteine (SEPN1- and RYR1-related myopathies) or epigallocatechin-gallate (DMD) have been launched recently. In this review, we provide an overview of the mechanisms involved in redox regulation in skeletal muscle, the technical tools available to measure redox homeostasis in muscle cells, the bases of OxS as a primary or secondary pathomechanism in early-onset myopathies and the innovative clinical trials with antioxidants which are currently in progress for these so-far untreatable infantile muscle diseases. Progress in our knowledge of redox homeostasis defects in these rare muscle conditions may be useful as a model paradigm to understand and treat other conditions in which OxS is involved, including prevalent conditions with major socioeconomic impact such as insulin resistance, cachexia, obesity, sarcopenia or ageing.