Nitric oxide-induced persistent inhibition and nitrosylation of active site cysteine residues of mitochondrial cytochrome-c oxidase in lung endothelial cells

The Role of Protein S-Nitrosylation in Mitochondrial Quality Control in Central Nervous System Diseases

S-Nitrosylation is a reversible covalent post-translational modification. Under physiological conditions, S-nitrosylation plays a dynamic role in a wide range of biological processes by regulating the function of substrate proteins. Like other post-translational modifications, S-nitrosylation can affect protein conformation, activity, localization, aggregation, and protein interactions. Aberrant S-nitrosylation can lead to protein misfolding, mitochondrial fragmentation, synaptic damage, and autophagy. Mitochondria are essential organelles in energy production, metabolite biosynthesis, cell death, and immune responses, among other processes. Mitochondrial dysfunction can result in cell death and has been implicated in the development of many human diseases. Recent evidence suggests that S-nitrosylation and mitochondrial dysfunction are important modulators of the progression of several diseases. In this review, we highlight recent findings regarding the aberrant S- nitrosylation of mitochondrial proteins that regulate mitochondrial biosynthesis, fission and fusion, and autophagy. Specifically, we discuss the mechanisms by which S-nitrosylated mitochondrial proteins exercise mitochondrial quality control under pathological conditions, thereby influencing disease. A better understanding of these pathological events may provide novel therapeutic targets to mitigate the development of neurological diseases.

Nitric oxide-induced endoplasmic reticulum stress of Schistosoma japonicum inhibits the worm development in rats

Schistosomiasis, caused by Schistosoma spp., is a zoonotic parasitic disease affecting human health. Rattus norvegicus (rats) are a non-permissive host of Schistosoma, in which the worms cannot mature and cause typical egg granuloma. We previously demonstrated that inherent high levels of nitric oxide (NO), produced by inducible NO synthase (iNOS), is a key molecule in blocking the development of S. japonicum in rats. To further explore the mechanism of NO inhibiting S. japonicum development in rats, we performed S-nitrosocysteine proteomics of S. japonicum collected from infected rats and mice. The results suggested that S. japonicum in rats may have undergone endoplasmic reticulum (ER) stress. Interestingly, we found that the ER of S. japonicum in rats showed marked damage, while the ER of the worm in iNOS-/- rats and mice were relatively normal. Moreover, the expression of ER stress markers in S. japonicum from WT rats was significantly increased, compared with S. japonicum from iNOS-/- rats and mice. Using the NO donor sodium nitroprusside in vitro, we demonstrated that NO could induce ER stress in S. japonicum in a dose-dependent manner, and the NO-induced ER stress in S. japonicum could be inhibited by ER stress inhibitor 4-Phenyl butyric acid. We further verified that inhibiting ER stress of S. japonicum in rats promoted parasite development and survival. Furthermore, we demonstrated that NO-induced ER stress of S. japonicum was related to the efflux of Ca2+ from ER and the impairment of mitochondrial function. Collectively, these findings show that high levels of NO in rats could induce ER stress in S. japonicum by promoting the efflux of Ca2+ from ER and damaging the mitochondrial function, which block the worm development. Thus, this study further clarifies the mechanism of anti-schistosome in rats and provides potential strategies for drug development against schistosomiasis and other parasitosis.

Roles of Protein S-Nitrosylation in Endothelial Homeostasis and Dysfunction

Significance: Nitric oxide (NO) plays several distinct roles in endothelial homeostasis. Except for activating the guanylyl cyclase enzyme-dependent cyclic guanosine monophosphate signaling pathway, NO can bind reactive cysteine residues in target proteins, a process known as S-nitrosylation (SNO). SNO is proposed to explain the multiple biological functions of NO in the endothelium. Investigating the targets and mechanism of protein SNO in endothelial cells (ECs) can provide new strategies for treating endothelial dysfunction-related diseases. Recent Advances: In response to different environments, proteomics has identified multiple SNO targets in ECs. Functional studies confirm that SNO regulates NO bioavailability, inflammation, permeability, oxidative stress, mitochondrial function, and insulin sensitivity in ECs. It also influences EC proliferation, migration, apoptosis, and transdifferentiation. Critical Issues: Single-cell transcriptomic analysis of ECs isolated from different mouse tissues showed heterogeneous gene signatures. However, litter research focuses on the heterogeneous properties of SNO proteins in ECs derived from different tissues. Although metabolism reprogramming plays a vital role in endothelial functions, little is known about how protein SNO regulates metabolism reprogramming in ECs. Future Directions: Precisely deciphering the effects of protein SNO in ECs isolated from different tissues under different conditions is necessary to further characterize the relationship between protein SNO and endothelial dysfunction-related diseases. In addition, identifying SNO targets that can influence endothelial metabolic reprogramming and the underlying mechanism can offer new views on the crosstalk between metabolism and post-translational protein modification. Antioxid. Redox Signal. 40, 186-205.

Neuronal loss of NCLX-dependent mitochondrial calcium efflux mediates age-associated cognitive decline

Mitochondrial calcium overload contributes to neurodegenerative disease development and progression. We recently reported that loss of the mitochondrial sodium/calcium exchanger (NCLX), the primary mechanism of mCa2+ efflux, promotes mCa2+ overload, metabolic derangement, redox stress, and cognitive decline in models of Alzheimer's disease (AD). However, whether disrupted mCa2+ signaling contributes to neuronal pathology and cognitive decline independent of pre-existing amyloid or tau pathology remains unknown. Here, we generated mice with neuronal deletion of the mitochondrial sodium/calcium exchanger (NCLX, Slc8b1 gene), and evaluated age-associated changes in cognitive function and neuropathology. Neuronal loss of NCLX resulted in an age-dependent decline in spatial and cued recall memory, moderate amyloid deposition, mild tau pathology, synaptic remodeling, and indications of cell death. These results demonstrate that loss of NCLX-dependent mCa2+ efflux alone is sufficient to induce an Alzheimer's disease-like pathology and highlights the promise of therapies targeting mCa2+ exchange.

NO and Heme Proteins: Cross-Talk between Heme and Cysteine Residues

Heme proteins are a diverse group that includes several unrelated families. Their biological function is mainly associated with the reactivity of the heme group, which-among several other reactions-can bind to and react with nitric oxide (NO) and other nitrogen compounds for their production, scavenging, and transport. The S-nitrosylation of cysteine residues, which also results from the reaction with NO and other nitrogen compounds, is a post-translational modification regulating protein activity, with direct effects on a variety of signaling pathways. Heme proteins are unique in exhibiting this dual reactivity toward NO, with reported examples of cross-reactivity between the heme and cysteine residues within the same protein. In this work, we review the literature on this interplay, with particular emphasis on heme proteins in which heme-dependent nitrosylation has been reported and those for which both heme nitrosylation and S-nitrosylation have been associated with biological functions.

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

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

Reappraisal of metabolic dysfunction in neurodegeneration: Focus on mitochondrial function and calcium signaling

The cellular and molecular mechanisms that drive neurodegeneration remain poorly defined. Recent clinical trial failures, difficult diagnosis, uncertain etiology, and lack of curative therapies prompted us to re-examine other hypotheses of neurodegenerative pathogenesis. Recent reports establish that mitochondrial and calcium dysregulation occur early in many neurodegenerative diseases (NDDs), including Alzheimer's disease, Parkinson's disease, Huntington's disease, and others. However, causal molecular evidence of mitochondrial and metabolic contributions to pathogenesis remains insufficient. Here we summarize the data supporting the hypothesis that mitochondrial and metabolic dysfunction result from diverse etiologies of neuropathology. We provide a current and comprehensive review of the literature and interpret that defective mitochondrial metabolism is upstream and primary to protein aggregation and other dogmatic hypotheses of NDDs. Finally, we identify gaps in knowledge and propose therapeutic modulation of mCa2+ exchange and mitochondrial function to alleviate metabolic impairments and treat NDDs.

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

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

Molecular mechanisms by which iNOS uncoupling can induce cardiovascular dysfunction during sepsis: Role of posttranslational modifications (PTMs)

Human sepsis is the result of a multifaceted pathological process causing marked dysregulation of cardiovascular responses. A more sophisticated understanding of the pathogenesis of sepsis is certainly prerequisite. Evidence from studies provide further insight into the role of inducible nitric oxide synthase (iNOS) isoform. Results on inhibition of iNOS in sepsis models remain inconclusive. Concern has been devoted to improving our knowledge and understanding of the role of iNOS. The aim of this review is to define the role of iNOS in redox homeostasis disturbance, the detailed mechanisms linking iNOS and posttranslational modifications (PTMs) to cardiovascular dysfunctions, and their future implications in sepsis settings. Many questions related to the iNOS and PTMs still remain open, and much more work is needed on this.

Thioredoxin Network in Plant Mitochondria: Cysteine S-Posttranslational Modifications and Stress Conditions

Plants are sessile organisms presenting different adaptation mechanisms that allow their survival under adverse situations. Among them, reactive oxygen and nitrogen species (ROS, RNS) and H₂S are emerging as components not only of cell development and differentiation but of signaling pathways involved in the response to both biotic and abiotic attacks. The study of the posttranslational modifications (PTMs) of proteins produced by those signaling molecules is revealing a modulation on specific targets that are involved in many metabolic pathways in the different cell compartments. These modifications are able to translate the imbalance of the redox state caused by exposure to the stress situation in a cascade of responses that finally allow the plant to cope with the adverse condition. In this review we give a generalized vision of the production of ROS, RNS, and H₂S in plant mitochondria. We focus on how the principal mitochondrial processes mainly the electron transport chain, the tricarboxylic acid cycle and photorespiration are affected by PTMs on cysteine residues that are produced by the previously mentioned signaling molecules in the respiratory organelle. These PTMs include S-oxidation, S-glutathionylation, S-nitrosation, and persulfidation under normal and stress conditions. We pay special attention to the mitochondrial Thioredoxin/Peroxiredoxin system in terms of its oxidation-reduction posttranslational targets and its response to environmental stress.

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.

Myalgic encephalomyelitis or chronic fatigue syndrome: how could the illness develop?

A model of the development and progression of chronic fatigue syndrome (myalgic encephalomyelitis), the aetiology of which is currently unknown, is put forward, starting with a consideration of the post-infection role of damage-associated molecular patterns and the development of chronic inflammatory, oxidative and nitrosative stress in genetically predisposed individuals. The consequences are detailed, including the role of increased intestinal permeability and the translocation of commensal antigens into the circulation, and the development of dysautonomia, neuroinflammation, and neurocognitive and neuroimaging abnormalities. Increasing levels of such stress and the switch to immune and metabolic downregulation are detailed next in relation to the advent of hypernitrosylation, impaired mitochondrial performance, immune suppression, cellular hibernation, endotoxin tolerance and sirtuin 1 activation. The role of chronic stress and the development of endotoxin tolerance via indoleamine 2,3-dioxygenase upregulation and the characteristics of neutrophils, monocytes, macrophages and T cells, including regulatory T cells, in endotoxin tolerance are detailed next. Finally, it is shown how the immune and metabolic abnormalities of chronic fatigue syndrome can be explained by endotoxin tolerance, thus completing the model.

Regulation of Cell Survival, Apoptosis, and Epithelial-to-Mesenchymal Transition by Nitric Oxide-Dependent Post-Translational Modifications

SIGNIFICANCE

Nitric oxide (NO) is a physiopathological messenger generating different reactive nitrogen species (RNS) according to hypoxic, acidic and redox conditions. Recent Advances: RNS and reactive oxygen species (ROS) promote relevant post-translational modifications, such as nitrosation, nitration, and oxidation, in critical components of cell proliferation and death, epithelial-to-mesenchymal transition, and metastasis.

CRITICAL ISSUES

The pro- or antitumoral properties of NO are dependent on local concentration, redox state, cellular status, duration of exposure, and compartmentalization of NO generation. The increased expression of NO synthase has been associated with cancer progression. However, the experimental strategies leading to high intratumoral NO generation have been shown to exert antitumoral properties. The effect of NO and ROS on cell signaling is critically altered by factors modulating tumor progression such as oxygen content, metabolism, and inflammatory response. The review describes the alteration of key components involved in cell survival and death, metabolism, and metastasis induced by RNS- and ROS-related post-translational modifications.

FUTURE DIRECTIONS

The identification of the molecular targets affected by nitrosation, nitration, and oxidation, as well as their interactions with other post-translational modifications, will improve the understanding on the complex signaling and cell fate decision in cancer. The therapeutic NO-based strategies have to address the complex crosstalk among NO and ROS with regard to critical components affecting tumor cell survival, metabolism, and metastasis in the progression of cancer, as well as close interaction with ionizing radiation and chemotherapy.

The Endoplasmic Reticulum Stress Response in Neuroprogressive Diseases: Emerging Pathophysiological Role and Translational Implications

The endoplasmic reticulum (ER) is the main cellular organelle involved in protein synthesis, assembly and secretion. Accumulating evidence shows that across several neurodegenerative and neuroprogressive diseases, ER stress ensues, which is accompanied by over-activation of the unfolded protein response (UPR). Although the UPR could initially serve adaptive purposes in conditions associated with higher cellular demands and after exposure to a range of pathophysiological insults, over time the UPR may become detrimental, thus contributing to neuroprogression. Herein, we propose that immune-inflammatory, neuro-oxidative, neuro-nitrosative, as well as mitochondrial pathways may reciprocally interact with aberrations in UPR pathways. Furthermore, ER stress may contribute to a deregulation in calcium homoeostasis. The common denominator of these pathways is a decrease in neuronal resilience, synaptic dysfunction and even cell death. This review also discusses how mechanisms related to ER stress could be explored as a source for novel therapeutic targets for neurodegenerative and neuroprogressive diseases. The design of randomised controlled trials testing compounds that target aberrant UPR-related pathways within the emerging framework of precision psychiatry is warranted.

'SNO'-Storms Compromise Protein Activity and Mitochondrial Metabolism in Neurodegenerative Disorders

The prevalence of neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD), is currently a major public health concern due to the lack of efficient disease-modifying therapeutic options. Recent evidence suggests that mitochondrial dysfunction and nitrosative/oxidative stress are key common mediators of pathogenesis. In this review, we highlight molecular mechanisms linking NO-dependent post-translational modifications, such as cysteine S-nitrosylation and tyrosine nitration, to abnormal mitochondrial metabolism. We further discuss the hypothesis that pathological levels of NO compromise brain energy metabolism via aberrant S-nitrosylation of key enzymes in the tricarboxylic acid (TCA) cycle and oxidative phosphorylation, contributing to neurodegenerative conditions. A better understanding of these pathophysiological events may provide a potential pathway for designing novel therapeutics to ameliorate neurodegenerative disorders.

Comparative biochemistry of cytochrome c oxidase in animals

Cytochrome c oxidase (COX), the terminal enzyme of the electron transport system, is central to aerobic metabolism of animals. Many aspects of its structure and function are highly conserved, yet, paradoxically, it is also an important model for studying the evolution of the metabolic phenotype. In this review, part of a special issue honouring Peter Hochachka, we consider the biology of COX from the perspective of comparative and evolutionary biochemistry. The approach is to consider what is known about the enzyme in the context of conventional biochemistry, but focus on how evolutionary researchers have used this background to explore the role of the enzyme in biochemical adaptation of animals. In synthesizing the conventional and evolutionary biochemistry, we hope to identify synergies and future research opportunities. COX represents a rare opportunity for researchers to design studies that span the breadth of biology: molecular genetics, protein biochemistry, enzymology, metabolic physiology, organismal performance, evolutionary biology, and phylogeography.

Targeting nitric oxide and NMDA receptor-associated pathways in treatment of high grade glial tumors. Hypotheses for nitro-memantine and nitrones

Glioblastoma multiforme (GBM) is a devastating brain cancer with no curative treatment. Targeting Nitric Oxide (NO) and glutamatergic pathways may help as adjunctive treatments in GBM. NO at low doses promotes tumorigenesis, while at higher levels (above 300 nM) triggers apoptosis. Gliomas actively secrete high amounts of glutamate which activates EGR signaling and mediates degradation of peritumoral tissues via excitotoxic injury. Memantine inhibits NMDA-subtype of glutamate receptors (NMDARs) and induces autophagic death of glioma cells in vitro and blocks glioma growth in vivo. Nitro-memantines may exert further benefits by limiting NMDAR signaling and by delivery of NO to the areas of excessive NMDAR activity leading NO-accumulation at tumoricidal levels within gliomas. Due to the duality of NO in tumorigenesis, agents which attenuate NO levels may also act beneficial in treatment of GBM. Nitrone compounds including N-tert-Butyl-α-phenylnitrone (PBN) and its disulfonyl-phenyl derivative, OKN-007 suppress free radical formation in experimental cerebral ischemia. OKN-007 failed to show clinical efficacy in stroke, but trials demonstrated its high biosafety in humans including elderly subjects. PBN inhibits the signaling pathways of NF-κB, inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX). In animal models of liver cancer and glioblastoma, OKN-007 seemed more efficient than PBN in suppression of cell proliferation, microvascular density and in induction of apoptosis. OKN-007 also inhibits SULF2 enzyme, which promotes tumor growth via versatile pathways. We assume that nitromemantines may be more beneficial concomitant with chemo-radiotherapy while nitrones alone may act useful in suppressing basal tumor growth and angiogenesis.

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.

iNOS-derived nitric oxide promotes glycolysis by inducing pyruvate kinase M2 nuclear translocation in ovarian cancer

Aerobic glycolysis is essential for tumor growth and survival. Activation of multiple carcinogenic signals contributes to metabolism reprogramming during malignant transformation of cancer. Recently nitric oxide has been noted to promote glycolysis but the mechanism remains elusive. We report here the dual role of nitric oxide in glycolysis: low/physiological nitric oxide (≤ 100 nM) promotes glycolysis for ATP production, oxidative defense and cell proliferation of ovary cancer cells, whereas excess nitric oxide (≥ 500 nM) inhibits it. Nitric oxide has a positive effect on glycolysis by inducing PKM2 nuclear translocation in an EGFR/ERK2 signaling-dependent manner. Moreover, iNOS induced by mild inflammatory stimulation increased glycolysis and cell proliferation by producing low doses of nitric oxide, while hyper inflammation induced iNOS inhibited it by producing excess nitric oxide. Finally, iNOS expression is abnormally increased in ovarian cancer tissues and is correlated with PKM2 expression. Overexpression of iNOS is associated with aggressive phenotype and poor survival outcome in ovarian cancer patients. Our study indicated that iNOS/NO play a dual role of in tumor glycolysis and progression, and established a bridge between iNOS/NO signaling pathway and EGFR/ERK2/PKM2 signaling pathway, suggesting that interfering glycolysis by targeting the iNOS/NO/PKM2 axis may be a valuable new therapeutic approach of treating ovarian cancer.

Lipid peroxidation as risk factor for endothelial dysfunction in antiphospholipid syndrome patients

The aim of this study was to evaluate oxidative stress markers and it relations to endothelial damage as risk factor for thrombosis in patients with primary (PAPS) and secondary (SAPS) antiphospholipid syndrome (APS) in correlation to traditional risk factors. Flow-mediated (FMD) and nitroglycerine (NMD)-induced dilation of the brachial artery were studied in 140 APS patients (90 PAPS, 50 SAPS) and 40 controls matched by age, sex, and conventional risk factors for atherosclerosis. Markers of oxidative stress, lipid hydroperoxydes (LOOH), advanced oxidation protein products (AOPP), total sulfhydryl groups (tSHG), and paraoxonase 1 activity (PON1) were determined by spectrophotometric method. Oxidative stress dominates in APS patients. LOOH and AOPP correlate to lipid fractions (p < 0.05), unlike PON1, tSHG that correlated to antiphospholipid antibody positivity (p < 0.05). FMD was lower in APS patients comparing to controls (p < 0.001). Cholesterol is independent variable for FMD impairment in control group (p = 0.011); LOOH in PAPS (p = 0.004); LOOH, aCL, and triglycerides in SAPS patients (p = 0.009, p = 0.049, and p = 0.012, respectively). Combined predictive of aCL and LOOH is better for FMD impairment than LOOH alone in both PAPS and SAPS patients (AUC 0.727, p = 0.001, 95 % CI 0.616-0.837 and AUC 0.824, p˂0.001, 95 % CI 0.690-0.957, respectively). Lipid peroxidation is independent predictor for endothelial dysfunction in APS patients. We demonstrated synergistic effect of aCL and LOOH as risk for endothelial impairment in both PAPS and SAPS patients.

Nitrosative Stress, Hypernitrosylation, and Autoimmune Responses to Nitrosylated Proteins: New Pathways in Neuroprogressive Disorders Including Depression and Chronic Fatigue Syndrome

Nitric oxide plays an indispensable role in modulating cellular signaling and redox pathways. This role is mainly effected by the readily reversible nitrosylation of selective protein cysteine thiols. The reversibility and sophistication of this signaling system is enabled and regulated by a number of enzymes which form part of the thioredoxin, glutathione, and pyridoxine antioxidant systems. Increases in nitric oxide levels initially lead to a defensive increase in the number of nitrosylated proteins in an effort to preserve their function. However, in an environment of chronic oxidative and nitrosative stress (O&NS), nitrosylation of crucial cysteine groups within key enzymes of the thioredoxin, glutathione, and pyridoxine systems leads to their inactivation thereby disabling denitrosylation and transnitrosylation and subsequently a state described as "hypernitrosylation." This state leads to the development of pathology in multiple domains such as the inhibition of enzymes of the electron transport chain, decreased mitochondrial function, and altered conformation of proteins and amino acids leading to loss of immune tolerance and development of autoimmunity. Hypernitrosylation also leads to altered function or inactivation of proteins involved in the regulation of apoptosis, autophagy, proteomic degradation, transcription factor activity, immune-inflammatory pathways, energy production, and neural function and survival. Hypernitrosylation, as a consequence of chronically elevated O&NS and activated immune-inflammatory pathways, can explain many characteristic abnormalities observed in neuroprogressive disease including major depression and chronic fatigue syndrome/myalgic encephalomyelitis. In those disorders, increased bacterial translocation may drive hypernitrosylation and autoimmune responses against nitrosylated proteins.

Post-Translational Modifications of Cardiac Mitochondrial Proteins in Cardiovascular Disease: Not Lost in Translation

Protein post-translational modifications (PTMs) are crucial in regulating cellular biology by playing key roles in processes such as the rapid on and off switching of signaling network and the regulation of enzymatic activities without affecting gene expressions. PTMs lead to conformational changes in the tertiary structure of protein and resultant regulation of protein function such as activation, inhibition, or signaling roles. PTMs such as phosphorylation, acetylation, and S-nitrosylation of specific sites in proteins have key roles in regulation of mitochondrial functions, thereby contributing to the progression to heart failure. Despite the extensive study of PTMs in mitochondrial proteins much remains unclear. Further research is yet to be undertaken to elucidate how changes in the proteins may lead to cardiovascular and metabolic disease progression in particular. We aimed to summarize the various types of PTMs that occur in mitochondrial proteins, which might be associated with heart failure. This study will increase the understanding of cardiovascular diseases through PTM.

Functional Impact of Ryanodine Receptor Oxidation on Intracellular Calcium Regulation in the Heart

Type 2 ryanodine receptor (RyR2) serves as the major intracellular Ca²⁺ release channel that drives heart contraction. RyR2 is activated by cytosolic Ca²⁺ via the process of Ca²⁺-induced Ca²⁺ release (CICR). To ensure stability of Ca²⁺ dynamics, the self-reinforcing CICR must be tightly controlled. Defects in this control cause sarcoplasmic reticulum (SR) Ca²⁺ mishandling, which manifests in a variety of cardiac pathologies that include myocardial infarction and heart failure. These pathologies are also associated with oxidative stress. Given that RyR2 contains a large number of cysteine residues, it is no surprise that RyR2 plays a key role in the cellular response to oxidative stress. RyR's many cysteine residues pose an experimental limitation in defining a specific target or mechanism of action for oxidative stress. As a result, the current understanding of redox-mediated RyR2 dysfunction remains incomplete. Several oxidative modifications, including S-glutathionylation and S-nitrosylation, have been suggested playing an important role in the regulation of RyR2 activity. Moreover, oxidative stress can increase RyR2 activity by forming disulfide bonds between two neighboring subunits (intersubunit cross-linking). Since intersubunit interactions within the RyR2 homotetramer complex dictate the channel gating, such posttranslational modification of RyR2 would have a significant impact on RyR2 function and Ca²⁺ regulation. This review summarizes recent findings on oxidative modifications of RyR2 and discusses contributions of these RyR2 modifications to SR Ca²⁺ mishandling during cardiac pathologies.

Signaling and stress: The redox landscape in NOS2 biology

Nitric oxide (NO) has a highly diverse range of biological functions from physiological signaling and maintenance of homeostasis to serving as an effector molecule in the immune system. However, deleterious as well as beneficial roles of NO have been reported. Many of the dichotomous effects of NO and derivative reactive nitrogen species (RNS) can be explained by invoking precise interactions with different targets as a result of concentration and temporal constraints. Endogenous concentrations of NO span five orders of magnitude, with levels near the high picomolar range typically occurring in short bursts as compared to sustained production of low micromolar levels of NO during immune response. This article provides an overview of the redox landscape as it relates to increasing NO concentrations, which incrementally govern physiological signaling, nitrosative signaling and nitrosative stress-related signaling. Physiological signaling by NO primarily occurs upon interaction with the heme protein soluble guanylyl cyclase. As NO concentrations rise, interactions with nonheme iron complexes as well as indirect modification of thiols can stimulate additional signaling processes. At the highest levels of NO, production of a broader range of RNS, which subsequently interact with more diverse targets, can lead to chemical stress. However, even under such conditions, there is evidence that stress-related signaling mechanisms are triggered to protect cells or even resolve the stress. This review therefore also addresses the fundamental reactions and kinetics that initiate signaling through NO-dependent pathways, including processes that lead to interconversion of RNS and interactions with molecular targets.

Alpha-lipoic acid supplementation protects enzymes from damage by nitrosative and oxidative stress

BACKGROUND

S-nitrosylation of mitochondrial enzymes involved in energy transfer under nitrosative stress may result in ATP deficiency. We investigated whether α-lipoic acid, a powerful antioxidant, could alleviate nitrosative stress by regulating S-nitrosylation, which could result in retaining the mitochondrial enzyme activity.

METHODS

In this study, we have identified the S-nitrosylated forms of subunit 1 of dihydrolipoyllysine succinyltransferase (complex III), and subunit 2 of the α-ketoglutarate dehydrogenase complex by implementing a fluorescence-based differential quantitative proteomics method.

RESULTS

We found that the activities of these two mitochondrial enzymes were partially but reversibly inhibited by S-nitrosylation in cultured endothelial cells, and that their activities were partially restored by supplementation of α-lipoic acid. We show that protein S-nitrosylation affects the activity of mitochondrial enzymes that are central to energy supply, and that α-lipoic acid protects mitochondrial enzymes by altering S-nitrosylation levels.

CONCLUSIONS

Inhibiting protein S-nitrosylation with α-lipoic acid seems to be a protective mechanism against nitrosative stress.

GENERAL SIGNIFICANCE

Identification and characterization of these new protein targets should contribute to expanding the therapeutic power of α-lipoic acid and to a better understanding of the underlying antioxidant mechanisms.

Manganese (III) meso-tetrakis N-ethylpyridinium-2-yl porphyrin acts as a pro-oxidant to inhibit electron transport chain proteins, modulate bioenergetics, and enhance the response to chemotherapy in lymphoma cells

The manganese porphyrin, manganese (III) meso-tetrakis N-ethylpyridinium-2-yl porphyrin (MnTE-2-PyP(5+)), acts as a pro-oxidant in the presence of intracellular H2O2. Mitochondria are the most prominent source of intracellular ROS and important regulators of the intrinsic apoptotic pathway. Due to the increased oxidants near and within the mitochondria, we hypothesized that the mitochondria are a target of the pro-oxidative activity of MnTE-2-PyP(5+) and that we could exploit this effect to enhance the chemotherapeutic response in lymphoma. In this study, we demonstrate that MnTE-2-PyP(5+) modulates the mitochondrial redox environment and sensitizes lymphoma cells to antilymphoma chemotherapeutics. MnTE-2-PyP(5+) increased dexamethasone-induced mitochondrial ROS and oxidation of the mitochondrial glutathione pool in lymphoma cells. The combination treatment induced glutathionylation of Complexes I, III, and IV in the electron transport chain, and decreased the activity of Complexes I and III, but not the activity of Complex IV. Treatment with the porphyrin and dexamethasone also decreased cellular ATP levels. Rho(0) malignant T-cells with impaired mitochondrial electron transport chain function were less sensitive to the combination treatment than wild-type cells. These findings suggest that mitochondria are important for the porphyrin's ability to enhance cell death. MnTE-2-PyP(5+) also augmented the effects of 2-deoxy-D-glucose (2DG), an antiglycolytic agent. In combination with 2DG, MnTE-2-PyP(5+) increased protein glutathionylation, decreased ATP levels more than 2DG treatment alone, and enhanced 2DG-induced cell death in primary B-ALL cells. MnTE-2-PyP(5+) did not enhance dexamethasone- or 2DG-induced cell death in normal cells. Our findings suggest that MnTE-2-PyP(5+) has potential as an adjuvant for the treatment of hematologic malignancies.

The many roads to mitochondrial dysfunction in neuroimmune and neuropsychiatric disorders

BACKGROUND

Mitochondrial dysfunction and defects in oxidative metabolism are a characteristic feature of many chronic illnesses not currently classified as mitochondrial diseases. Examples of such illnesses include bipolar disorder, multiple sclerosis, Parkinson's disease, schizophrenia, depression, autism, and chronic fatigue syndrome.

DISCUSSION

While the majority of patients with multiple sclerosis appear to have widespread mitochondrial dysfunction and impaired ATP production, the findings in patients diagnosed with Parkinson's disease, autism, depression, bipolar disorder schizophrenia and chronic fatigue syndrome are less consistent, likely reflecting the fact that these diagnoses do not represent a disease with a unitary pathogenesis and pathophysiology. However, investigations have revealed the presence of chronic oxidative stress to be an almost invariant finding in study cohorts of patients afforded each diagnosis. This state is characterized by elevated reactive oxygen and nitrogen species and/or reduced levels of glutathione, and goes hand in hand with chronic systemic inflammation with elevated levels of pro-inflammatory cytokines.

SUMMARY

This paper details mechanisms by which elevated levels of reactive oxygen and nitrogen species together with elevated pro-inflammatory cytokines could conspire to pave a major road to the development of mitochondrial dysfunction and impaired oxidative metabolism seen in many patients diagnosed with these disorders.

The S-nitrosylation status of PCNA localized in cytosol impacts the apoptotic pathway in a Parkinson's disease paradigm

It is generally accepted that nitric oxide (NO) or its derivatives, reactive nitrogen species (RNS), are involved in the development of Parkinson's disease (PD). Recently, emerging evidence in the study of PD has indicated that protein S-nitrosylation triggers the signaling changes in neurons. In this study, SH-SY5Y cells treated with rotenone were used as a model of neuronal death in PD. The treated cells underwent significant apoptosis, which was accompanied by an increase in intracellular NO in a rotenone dose-dependent manner. The CyDye switch approach was employed to screen for changes in S-nitrosylated (SNO) proteins in response to the rotenone treatment. Seven proteins with increased S-nitrosylation were identified in the treated SH-SY5Y cells, which included proliferating cell nuclear antigen (PCNA). Although PCNA is generally located in the nucleus and participates in DNA replication and repair, significant PCNA was identified in the SH-SY5Y cytosol. Using immunoprecipitation and pull-down approaches, PCNA was found to interact with caspase-9; using mass spectrometry, the two cysteine residues PCNA-Cys81 and -Cys162 were identified as candidate S-nitrosylated residues. In addition, the evidence obtained from in vitro and the cell model studies indicated that the S-nitrosylation of PCNA-Cys81 affected the interaction between PCNA and caspase-9. Furthermore, the interaction of PCNA and caspase-9 partially blocked caspase-9 activation, indicating that the S-nitrosylation of cytosolic PCNA may be a mediator of the apoptotic pathway.

Cancer cell metabolism and the modulating effects of nitric oxide

Altered metabolic phenotype has been recognized as a hallmark of tumor cells for many years, but this aspect of the cancer phenotype has come into greater focus in recent years. NOS2 (inducible nitric oxide synthase of iNOS) has been implicated as a component in many aggressive tumor phenotypes, including melanoma, glioblastoma, and breast cancer. Nitric oxide has been well established as a modulator of cellular bioenergetics pathways, in many ways similar to the alteration of cellular metabolism observed in aggressive tumors. In this review we attempt to bring these concepts together with the general hypothesis that one function of NOS2 and NO in cancer is to modulate metabolic processes to facilitate increased tumor aggression. There are many mechanisms by which NO can modulate tumor metabolism, including direct inhibition of respiration, alterations in mitochondrial mass, oxidative inhibition of bioenergetic enzymes, and the stimulation of secondary signaling pathways. Here we review metabolic alterations in the context of cancer cells and discuss the role of NO as a potential mediator of these changes.

S-nitrosation of mitochondrial connexin 43 regulates mitochondrial function

S-nitrosation (SNO) of connexin 43 (Cx43)-formed channels modifies dye uptake in astrocytes and gap junctional communication in endothelial cells. Apart from forming channels at the plasma membrane of several cell types, Cx43 is also located at the inner membrane of myocardial subsarcolemmal mitochondria (SSM), but not in interfibrillar mitochondria (IFM). The absence or pharmacological blockade of mitochondrial Cx43 (mtCx43) reduces dye and potassium uptake. Lack of mtCx43 is associated with loss of endogenous cardioprotection by ischemic preconditioning (IPC), which is mediated by formation of reactive oxygen species (ROS). Whether or not mitochondrial Lucifer Yellow (LY), ion uptake, or ROS generation are affected by SNO of mtCx43 and whether or not cardioprotective interventions affect SNO of mtCx43 remains unknown. In SSM from rat hearts, application of NO donors (48 nmol to 1 mmol) increased LY uptake (0.5 mmol SNAP 38.4 ± 7.1 %, p < 0.05; 1 mmol GSNO 28.1 ± 7.4 %, p < 0.05) and the refilling rate of potassium (SNAP 227.9 ± 30.1 %, p < 0.05; GSNO 122.6 ± 28.1 %, p < 0.05). These effects were absent following blockade of Cx43 hemichannels by carbenoxolone as well as in IFM lacking Cx43. Unlike potassium, the sodium permeability was not affected by application of NO. Furthermore, mitochondrial ROS formation was increased following NO application compared to control SSM (0.5 mmol SNAP 22.9 ± 1.8 %, p < 0.05; 1 mmol GSNO 40.6 ± 7.1 %, p < 0.05), but decreased in NO treated IFM compared to control (0.5 mmol SNAP 14.4 ± 4 %, p < 0.05; 1 mmol GSNO 13.8 ± 4 %, p < 0.05). NO donor administration to isolated SSM increased SNO of mtCx43 by 109.2 ± 15.8 %. Nitrite application (48 nmol) to mice was also associated with elevated SNO of mtCx43 by 59.3 ± 18.2 % (p < 0.05). IPC by four cycles of 5 min of ischemia and 5 min of reperfusion increased SNO of mtCx43 by 41.6 ± 1.7 % (p < 0.05) when compared to control perfused rat hearts. These data suggest that SNO of mtCx43 increases mitochondrial permeability, especially for potassium and leads to increased ROS formation. The increased amount of SNO mtCx43 by IPC or nitrite administration may link NO and Cx43 in the signal transduction cascade of cardioprotective interventions.

α-Lipoic acid protects mitochondrial enzymes and attenuates lipopolysaccharide-induced hypothermia in mice

Hypothermia is a key symptom of sepsis, but the mechanism(s) leading to hypothermia during sepsis is largely unknown and thus no effective therapy is available for hypothermia. Therefore, it is important to investigate the mechanism and develop effective therapeutic methods. Lipopolysaccharide (LPS)-induced hypothermia accompanied by excess nitric oxide (NO) production leads to a reduction in energy production in wild-type mice. However, mice lacking inducible nitric oxide synthase did not suffer from LPS-induced hypothermia, suggesting that hypothermia is associated with excess NO production during sepsis. This observation is supported by the treatment of wild-type mice with α-lipoic acid (LA) in that it effectively attenuates LPS-induced hypothermia with decreased NO production. We also found that LA partially restored ATP production, and activities of the mitochondrial enzymes involved in energy metabolism, which were inhibited during sepsis. These data suggest that hypothermia is related to mitochondrial dysfunction, which is probably compromised by excess NO production and that LA administration attenuates hypothermia mainly by protecting mitochondrial enzymes from NO damage.

Hydrochlorothiazide attenuates lithium-induced nephrogenic diabetes insipidus independently of the sodium-chloride cotransporter

Lithium is the most common cause of nephrogenic diabetes insipidus (Li-NDI). Hydrochlorothiazide (HCTZ) combined with amiloride is the mainstay treatment in Li-NDI. The paradoxical antidiuretic action of HCTZ in Li-NDI is generally attributed to increased sodium and water uptake in proximal tubules as a compensation for increased volume loss due to HCTZ inhibition of the Na-Cl cotransporter (NCC), but alternative actions for HCTZ have been suggested. Here, we investigated whether HCTZ exerted an NCC-independent effect in Li-NDI. In polarized mouse cortical collecting duct (mpkCCD) cells, HCTZ treatment attenuated the Li-induced downregulation of aquaporin-2 (AQP2) water channel abundance. In these cells, amiloride reduces cellular Li influx through the epithelial sodium channel (ENaC). HCTZ also reduced Li influx, but to a lower extent. HCTZ increased AQP2 abundance on top of that of amiloride and did not affect the ENaC-mediated transcellular voltage. MpkCCD cells did not express NCC mRNA or protein. These data indicated that in mpkCCD cells, HCTZ attenuated lithium-induced downregulation of AQP2 independently of NCC and ENaC. Treatment of Li-NDI NCC knockout mice with HCTZ revealed a significantly reduced urine volume, unchanged urine osmolality, and increased cortical AQP2 abundance compared with Li-treated NCC knockout mice. HCTZ treatment further resulted in reduced blood Li levels, creatinine clearance, and alkalinized urinary pH. Our in vitro and in vivo data indicate that part of the antidiuretic effect of HCTZ in Li-NDI is NCC independent and may involve a tubuloglomerular feedback response-mediated reduction in glomerular filtration rate due to proximal tubular carbonic anhydrase inhibition.

Aberrant protein s-nitrosylation in neurodegenerative diseases

S-Nitrosylation is a redox-mediated posttranslational modification that regulates protein function via covalent reaction of nitric oxide (NO)-related species with a cysteine thiol group on the target protein. Under physiological conditions, S-nitrosylation can be an important modulator of signal transduction pathways, akin to phosphorylation. However, with aging or environmental toxins that generate excessive NO, aberrant S-nitrosylation reactions can occur and affect protein misfolding, mitochondrial fragmentation, synaptic function, apoptosis or autophagy. Here, we discuss how aberrantly S-nitrosylated proteins (SNO-proteins) play a crucial role in the pathogenesis of neurodegenerative diseases, including Alzheimer's and Parkinson's diseases. Insight into the pathophysiological role of aberrant S-nitrosylation pathways will enhance our understanding of molecular mechanisms leading to neurodegenerative diseases and point to potential therapeutic interventions.

Nitric oxide modulates mitochondrial activity and apoptosis through protein S-nitrosylation for preimplantation embryo development

PURPOSE

Previous studies reported that patients with endometriosis had excess nitric oxide (NO) in the reproductive tract and poor embryo development in IVF cycles. This study aims to elucidate the effects of NO on early embryo development.

METHODS

Zygotes from superovulated B6CBF1 mice were cultured to blastocysts in a variety of media. Sodium nitroprusside (SNP) and N(G)-nitro-L-arginine (LNA) were added to the culture medium as a NO donor and a NO synthase inhibitor, respectively. The localization and fluorescence intensity of S-nitrosylated (SNO) proteins within 2-cell stage embryos were analyzed with confocal microscopy. Apoptosis and ATP production in the blastocysts were measured.

RESULT(S)

Subsequent to NO exposure, the SNO proteins mainly colocalized with the mitochondria and endoplasmic reticulum and the intensity of SNO proteins increased. The addition of a quanylate cyclase inhibitor and a cyclic GMP mimic agent induced nonsignificant changes in SNO proteins, whereas addition of a superoxide scavenger or a reduced form of glutathione rescued the embryos from the effects of NO. However, superoxide scavenger supplementation resulted in decreased blastocyst ATP production.

CONCLUSION(S)

Elevated NO exerts deleterious effects on embryo development, possibly through protein S-nitrosylation in the mitochondria and endoplasmic reticulum. Including glutathione as a component in the culture medium might counteract this effect.

Redox signaling pathways involved in neuronal ischemic preconditioning

There is extensive evidence that the restoration of blood flow following cerebral ischemia contributes greatly to the pathophysiology of ischemia mediated brain injury. The initiating stimulus of reperfusion injury is believed to be the excessive production of reactive oxygen (ROS) and nitrogen (RNS) species by the mitochondria. ROS and RNS generation leads to mitochondrial protein, lipid and DNA oxidation which impedes normal mitochondrial physiology and initiates cellular death pathways. However not all ROS and RNS production is detrimental. It has been demonstrated that low levels of ROS production are protective and may serve as a trigger for activation of ischemic preconditioning. Ischemic preconditioning is a neuroprotective mechanism which is activated upon a brief sublethal ischemic exposure and is sufficient to provide protection against a subsequent lethal ischemic insult. Numerous proteins and signaling pathways have been implicated in the ischemic preconditioning neuroprotective response. In this review we examine the origin and mechanisms of ROS and RNS production following ischemic/reperfusion and the role of free radicals in modulating proteins associated with ischemic preconditioning neuroprotection.

Vascular endothelial cells mediate mechanical stimulation-induced enhancement of endothelin hyperalgesia via activation of P2X2/3 receptors on nociceptors

Endothelin-1 (ET-1) is unique among a broad range of hyperalgesic agents in that it induces hyperalgesia in rats that is markedly enhanced by repeated mechanical stimulation at the site of administration. Antagonists to the ET-1 receptors, ET(A) and ET(B), attenuated both initial as well as stimulation-induced enhancement of hyperalgesia (SIEH) by endothelin. However, administering antisense oligodeoxynucleotide to attenuate ET(A) receptor expression on nociceptors attenuated ET-1 hyperalgesia but had no effect on SIEH, suggesting that this is mediated via a non-neuronal cell. Because vascular endothelial cells are both stretch sensitive and express ET(A) and ET(B) receptors, we tested the hypothesis that SIEH is dependent on endothelial cells by impairing vascular endothelial function with octoxynol-9 administration; this procedure eliminated SIEH without attenuating ET-1 hyperalgesia. A role for protein kinase Cε (PKCε), a second messenger implicated in the induction and maintenance of chronic pain, was explored. Intrathecal antisense for PKCε did not inhibit either ET-1 hyperalgesia or SIEH, suggesting no role for neuronal PKCε; however, administration of a PKCε inhibitor at the site of testing selectively attenuated SIEH. Compatible with endothelial cells releasing ATP in response to mechanical stimulation, P2X(2/3) receptor antagonists eliminated SIEH. The endothelium also appears to contribute to hyperalgesia in two ergonomic pain models (eccentric exercise and hindlimb vibration) and in a model of endometriosis. We propose that SIEH is produced by an effect of ET-1 on vascular endothelial cells, sensitizing its release of ATP in response to mechanical stimulation; ATP in turn acts at the nociceptor P2X(2/3) receptor.

Effect of S-nitrosoglutathione on renal mitochondrial function: a new mechanism for reversible regulation of manganese superoxide dismutase activity?

Mitochondria are at the heart of all cellular processes as they provide the majority of the energy needed for various metabolic processes. Nitric oxide has been shown to have numerous roles in the regulation of mitochondrial function. Mitochondria have enormous pools of glutathione (GSH≈5-10 mM). Nitric oxide can react with glutathione to generate a physiological molecule, S-nitrosoglutathione (GSNO). The impact GSNO has on mitochondrial function has been intensively studied in recent years, and several mitochondrial electron transport chain complex proteins have been shown to be targeted by GSNO. In this study we investigated the effect of GSNO on mitochondrial function using normal rat proximal tubular kidney cells (NRK cells). GSNO treatment of NRK cells led to mitochondrial membrane depolarization and significant reduction in activities of mitochondrial complex IV and manganese superoxide dismutase enzyme (MnSOD). MnSOD is a critical endogenous antioxidant enzyme that scavenges excess superoxide radicals in the mitochondria. The decrease in MnSOD activity was not associated with a reduction in its protein levels and treatment of NRK cell lysate with dithiothreitol (a strong sulfhydryl-group-reducing agent) restored MnSOD activity to control values. GSNO is known to cause both S-nitrosylation and S-glutathionylation, which involve the addition of NO and GS groups, respectively, to protein sulfhydryl (SH) groups of cysteine residues. Endogenous GSH is an essential mediator in S-glutathionylation of cellular proteins, and the current studies revealed that GSH is required for MnSOD inactivation after GSNO or diamide treatment in rat kidney cells as well as in isolated kidneys. Further studies showed that GSNO led to glutathionylation of MnSOD; however, glutathionylated recombinant MnSOD was not inactivated. This suggests that a more complex pathway, possibly involving the participation of multiple proteins, leads to MnSOD inactivation after GSNO treatment. The major highlight of these studies is the fact that dithiothreitol can restore MnSOD activity after GSNO treatment. To our knowledge, this is the first study showing that MnSOD activity can be reversibly regulated in vivo, through a mechanism involving thiol residues.

Selective vulnerability of synaptic signaling and metabolism to nitrosative stress

SIGNIFICANCE

Nitric oxide (NO) plays diverse physiological roles in the central nervous system, where it modulates neuronal communication, regulates blood flow, and contributes to the innate immune responses. In a number of brain pathologies, the excessive production of NO also leads to the formation of reactive and toxic intermediates generically termed reactive nitrogen species (RNS). RNS cause irreversible or poorly reversible damage to brain cells.

RECENT ADVANCES

Recent work in the field focused on the ability of NO and RNS to yield protein modifications, including the S-nitrosation of cysteine residues, which, in many instances, impact cellular functions and viability.

CRITICAL ISSUES

The vast majority of neuropathological studies focus on the loss of cell viability, but nitrosative stress may also strongly impair the functions of neuronal processes: axonal projections and dendritic trees. The functional integrity of axons and dendrites critically depends on local metabolism and effective delivery of metabolic enzymes and organelles. Here, we summarize the existing literature describing the effects of nitrosative stress on the major pathways of energetic metabolism: glycolysis, tricarboxylic acid cycle, and mitochondrial respiration, with the emphasis on modifications of protein thiols.

FUTURE DIRECTIONS

We propose that axons and dendrites are highly vulnerable to nitrosative stress because of their low glycolytic capacity and high dependence on timely delivery of metabolic enzymes and organelles from the cell body. Thus, supplementation with the end products of glycolysis, pyruvate or lactate, may help preserve metabolism in distal neuronal processes and protect or restore synaptic function in the ailing brain.

Established Principles and Emerging Concepts on the Interplay between Mitochondrial Physiology and S-(De)nitrosylation: Implications in Cancer and Neurodegeneration

S-nitrosylation is a posttranslational modification of cysteine residues that has been frequently indicated as potential molecular mechanism governing cell response upon redox unbalance downstream of nitric oxide (over)production. In the last years, increased levels of S-nitrosothiols (SNOs) have been tightly associated with the onset of nitroxidative stress-based pathologies (e.g., cancer and neurodegeneration), conditions in which alterations of mitochondrial homeostasis and activation of cellular processes dependent on it have been reported as well. In this paper we aim at summarizing the current knowledge of mitochondria-related proteins undergoing S-nitrosylation and how this redox modification might impact on mitochondrial functions, whose impairment has been correlated to tumorigenesis and neuronal cell death. In particular, emphasis will be given to the possible, but still neglected implication of denitrosylation reactions in the modulation of mitochondrial SNOs and how they can affect mitochondrion-related cellular process, such as oxidative phosphorylation, mitochondrial dynamics, and mitophagy.

Redox regulation of mitochondrial function

Redox-dependent processes influence most cellular functions, such as differentiation, proliferation, and apoptosis. Mitochondria are at the center of these processes, as mitochondria both generate reactive oxygen species (ROS) that drive redox-sensitive events and respond to ROS-mediated changes in the cellular redox state. In this review, we examine the regulation of cellular ROS, their modes of production and removal, and the redox-sensitive targets that are modified by their flux. In particular, we focus on the actions of redox-sensitive targets that alter mitochondrial function and the role of these redox modifications on metabolism, mitochondrial biogenesis, receptor-mediated signaling, and apoptotic pathways. We also consider the role of mitochondria in modulating these pathways, and discuss how redox-dependent events may contribute to pathobiology by altering mitochondrial function.

Intrarenal dopamine modulates progressive angiotensin II-mediated renal injury

It is well-recognized that excessive angiotensin II (ANG II) can mediate progressive renal injury. Previous studies by us and others have indicated that dopamine may modulate actions of ANG II in the kidney. The current studies investigated whether altering intrarenal dopamine levels affected ANG II-mediated renal fibrosis. We utilized a model of increased intrarenal dopamine, catechol-O-methyl-transferase knockout (COMT KO) mice, which have increased kidney dopamine levels due to deletion of a major intrarenal dopamine-metabolizing enzyme. In wild-type mice, chronic ANG II infusion increased renal expression of both of the major dopamine-metabolizing enzymes, COMT and monoamine oxidase. After 8 wk of ANG II infusion, there were no significant differences in blood pressure between wild-type and COMT KO mice. Compared with wild-type, COMT KO mice had decreased albuminuria and tubulointerstitial injury. In response to ANG II infusion, there was decreased expression of both glomerular and tubulointerstitial injury markers (fibronectin, connective tissue growth factor, fibroblast-specific protein-1, collagen I, podocyte vascular endothelial growth factor) in COMT KO mice. We recently reported that ANG II-mediated tubulointerstitial fibrosis is mediated by src-dependent epidermal growth factor receptor (EGFR) activation. In aromatic l-amino acid decarboxylase knockout (AADC KO) mice, a model of intrarenal dopamine deficiency due to selective proximal tubule AADC deletion, which inhibits intrarenal dopamine synthesis, ANG II infusion further increased expression of p-src and pTyr845-EGFR. In contrast, their expression was markedly attenuated in COMT KO mice. These results demonstrate a role for intrarenal dopamine to buffer the detrimental effects of ANG II upon the kidney.

Estrogen-responsive nitroso-proteome in uterine artery endothelial cells: role of endothelial nitric oxide synthase and estrogen receptor-β

Covalent adduction of a NO moiety to cysteines (S-nitrosylation or SNO) is a major route for NO to directly regulate protein functions. In uterine artery endothelial cells (UAEC), estradiol-17β (E2) rapidly stimulated protein SNO that maximized within 10-30 min post-E2 exposure. E2-bovine serum albumin stimulated protein SNO similarly. Stimulation of SNO by both was blocked by ICI 182, 780, implicating mechanisms linked to specific estrogen receptors (ERs) localized on the plasma membrane. E2-induced protein SNO was attenuated by selective ERβ, but not ERα, antagonists. A specific ERβ but not ERα agonist was able to induce protein SNO. Overexpression of ERβ, but not ERα, significantly enhanced E2-induced SNO. Overexpression of both ERs increased basal SNO, but did not further enhance E2-stimulated SNO. E2-induced SNO was inhibited by N-nitro-L-arginine-methylester and specific endothelial NO synthase (eNOS) siRNA. Thus, estrogen-induced SNO is mediated by endogenous NO via eNOS and mainly ERβ in UAEC. We further analyzed the nitroso-proteomes by CyDye switch technique combined with two-dimensional (2D) fluorescence difference gel electrophoresis. Numerous nitrosoprotein (spots) were visible on the 2D gel. Sixty spots were chosen and subjected to matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Among the 54 identified, nine were novel SNO-proteins, 32 were increased, eight were decreased, and the rest were unchanged by E2. Tandom MS identified Cys139 as a specific site for SNO in GAPDH. Pathway analysis of basal and estrogen-responsive nitroso-proteomes suggested that SNO regulates diverse protein functions, directly implicating SNO as a novel mechanism for estrogen to regulate uterine endothelial function and thus uterine vasodilatation.

Oxidative stress is associated with liver damage, inflammatory status, and corticosteroid therapy in patients with systemic lupus erythematosus

Oxidative stress exerts an important role on the pathophysiological mechanisms of systemic lupus erythematosus (SLE). This study investigated oxidative stress in patients with SLE and its correlation with disease activity, corticosteroid therapy, and liver function biomarkers. The study included 58 patients with SLE and 105 healthy volunteers. Patients showed oxidative stress increase evaluated by tert-butyl hydroperoxide-initiated chemiluminescence (CL-LOOH), advanced oxidation protein products (AOPP), and nitric oxide metabolites. C-reactive protein (CRP) was associated with CL-LOOH and with AOPP. Aspartate aminotransferase correlated significantly with CL-LOOH and with AOPP. Patients with disease activity showed an inverse significant correlation of daily prednisone doses and CL-LOOH and a direct correlation with total antioxidant capacity. In conclusion, patients with SLE have persistent lipoperoxidation and protein oxidation even with inactive disease or mild disease activity. The significant correlation between oxidative stress and CRP suggests that, despite clinical remission, the persistence of an inflammatory condition favors oxidative stress. Oxidative stress was associated with liver enzymes, and this relationship seems to support the hypothesis of drug-induced oxidative stress with consequent liver injury. In relation to non-active disease, patients with active SLE did not present oxidative stress and antioxidant capacity changes, due to the antioxidant drugs used in SLE treatment, especially prednisone.

High sodium intake increases HCO(3)- absorption in medullary thick ascending limb through adaptations in basolateral and apical Na+/H+ exchangers

A high sodium intake increases the capacity of the medullary thick ascending limb (MTAL) to absorb HCO(3)(-). Here, we examined the role of the apical NHE3 and basolateral NHE1 Na(+)/H(+) exchangers in this adaptation. MTALs from rats drinking H(2)O or 0.28 M NaCl for 5-7 days were perfused in vitro. High sodium intake increased HCO(3)(-) absorption rate by 60%. The increased HCO(3)(-) absorptive capacity was mediated by an increase in apical NHE3 activity. Inhibiting basolateral NHE1 with bath amiloride eliminated 60% of the adaptive increase in HCO(3)(-) absorption. Thus the majority of the increase in NHE3 activity was dependent on NHE1. A high sodium intake increased basolateral Na(+)/H(+) exchange activity by 89% in association with an increase in NHE1 expression. High sodium intake increased apical Na(+)/H(+) exchange activity by 30% under conditions in which basolateral Na(+)/H(+) exchange was inhibited but did not change NHE3 abundance. These results suggest that high sodium intake increases HCO(3)(-) absorptive capacity in the MTAL through 1) an adaptive increase in basolateral NHE1 activity that results secondarily in an increase in apical NHE3 activity; and 2) an adaptive increase in NHE3 activity, independent of NHE1 activity. These studies support a role for NHE1 in the long-term regulation of renal tubule function and suggest that the regulatory interaction whereby NHE1 enhances the activity of NHE3 in the MTAL plays a role in the chronic regulation of HCO(3)(-) absorption. The adaptive increases in Na(+)/H(+) exchange activity and HCO(3)(-) absorption in the MTAL may play a role in enabling the kidneys to regulate acid-base balance during changes in sodium and volume balance.