In situ analysis of protein S-glutathionylation in lung tissue using glutaredoxin-1-catalyzed cysteine derivatization

Local fractal dimension of collagen detects increased spatial complexity in fibrosis

Increase of collagen content and reorganization characterizes fibrosis but quantifying the latter remains challenging. Spatially complex structures are often analyzed via the fractal dimension; however, established methods for calculating this quantity either provide a single dimension for an entire object or a spatially distributed dimension that only considers binary images. These neglect valuable information related to collagen density in images of fibrotic tissue. We sought to develop a fractal analysis that can be applied to 3-dimensional (3D) images of fibrotic tissue. A fractal dimension map for each image was calculated by determining a single fractal dimension for a small area surrounding each image pixel, using fiber thickness as the third dimension. We found that this local fractal dimension increased with age and with progression of fibrosis regardless of collagen content. Our new method of distributed 3D fractal analysis can thus distinguish between changes in collagen content and organization induced by fibrosis.

Glutaredoxin attenuates glutathione levels via deglutathionylation of Otub1 and subsequent destabilization of system xC. SCIENCE ADVANCES 2023;9:eadi5192. [PMID: 37703360 PMCID: PMC10499329 DOI: 10.1126/sciadv.adi5192]

Glutathione (GSH) is a critical component of the cellular redox system that combats oxidative stress. The glutamate-cystine antiporter, system xC-, is a key player in GSH synthesis that allows for the uptake of cystine, the rate-limiting building block of GSH. It is unclear whether GSH or GSH-dependent protein oxidation [protein S-glutathionylation (PSSG)] regulates the activity of system xC-. We demonstrate that an environment of enhanced PSSG promotes GSH increases via a system xC--dependent mechanism. Absence of the deglutathionylase, glutaredoxin (GLRX), augmented SLC7A11 protein and led to significant increases of GSH content. S-glutathionylation of C23 or C204 of the deubiquitinase OTUB1 promoted interaction with the E2-conjugating enzyme UBCH5A, leading to diminished ubiquitination and proteasomal degradation of SLC7A11 and augmentation of GSH, effects that were reversed by GLRX. These findings demonstrate an intricate link between GLRX and GSH via S-glutathionylation of OTUB1 and system xC- and illuminate a previously unknown feed-forward regulatory mechanism whereby enhanced GSH protein oxidation augments cellular GSH.

Regulation of hyperoxia-induced neonatal lung injury via post-translational cysteine redox modifications

Preterm infants and patients with lung disease often have excess fluid in the lungs and are frequently treated with oxygen, however long-term exposure to hyperoxia results in irreversible lung injury. Although the adverse effects of hyperoxia are mediated by reactive oxygen species, the full extent of the impact of hyperoxia on redox-dependent regulation in the lung is unclear. In this study, neonatal mice overexpressing the beta-subunit of the epithelial sodium channel (β-ENaC) encoded by Scnn1b and their wild type (WT; C57Bl6) littermates were utilized to study the pathogenesis of high fraction inspired oxygen (FiO2)-induced lung injury. Results showed that O2-induced lung injury in transgenic Scnn1b mice is attenuated following chronic O2 exposure. To test the hypothesis that reversible cysteine-redox-modifications of proteins play an important role in O2-induced lung injury, we performed proteome-wide profiling of protein S-glutathionylation (SSG) in both WT and Scnn1b overexpressing mice maintained at 21% O2 (normoxia) or FiO2 85% (hyperoxia) from birth to 11-15 days postnatal. Over 7700 unique Cys sites with SSG modifications were identified and quantified, covering more than 3000 proteins in the lung. In both mouse models, hyperoxia resulted in a significant alteration of the SSG levels of Cys sites belonging to a diverse range of proteins. In addition, substantial SSG changes were observed in the Scnn1b overexpressing mice exposed to hyperoxia, suggesting that ENaC plays a critically important role in cellular regulation. Hyperoxia-induced SSG changes were further supported by the results observed for thiol total oxidation, the overall level of reversible oxidation on protein cysteine residues. Differential analyses reveal that Scnn1b overexpression may protect against hyperoxia-induced lung injury via modulation of specific processes such as cell adhesion, blood coagulation, and proteolysis. This study provides a landscape view of protein oxidation in the lung and highlights the importance of redox regulation in O2-induced lung injury.

Oxidative stress-induced FABP5 S-glutathionylation protects against acute lung injury by suppressing inflammation in macrophages

Oxidative stress contributes to the pathogenesis of acute lung injury. Protein S-glutathionylation plays an important role in cellular antioxidant defense. Here we report that the expression of deglutathionylation enzyme Grx1 is decreased in the lungs of acute lung injury mice. The acute lung injury induced by hyperoxia or LPS is significantly relieved in Grx1 KO and Grx1^fl/flLysM^cre mice, confirming the protective role of Grx1-regulated S-glutathionylation in macrophages. Using a quantitative redox proteomics approach, we show that FABP5 is susceptible to S-glutathionylation under oxidative conditions. S-glutathionylation of Cys127 in FABP5 promotes its fatty acid binding ability and nuclear translocation. Further results indicate S-glutathionylation promotes the interaction of FABP5 and PPARβ/δ, activates PPARβ/δ target genes and suppresses the LPS-induced inflammation in macrophages. Our study reveals a molecular mechanism through which FABP5 S-glutathionylation regulates macrophage inflammation in the pathogenesis of acute lung injury.

Redox-dependent regulation plays a key role in the pathogenesis of acute lung injury, but its mechanism is unclear. Here the authors show Grx1-regulated S-glutathionylation of FABP5 controls macrophage inflammation and alleviates acute lung injury.

Dysregulation of the glutaredoxin/S-glutathionylation redox axis in lung diseases

Glutathione is a major redox buffer, reaching millimolar concentrations within cells and high micromolar concentrations in airways. While glutathione has been traditionally known as an antioxidant defense mechanism that protects the lung tissue from oxidative stress, glutathione more recently has become recognized for its ability to become covalently conjugated to reactive cysteines within proteins, a modification known as S-glutathionylation (or S-glutathiolation or protein mixed disulfide). S-glutathionylation has the potential to change the structure and function of the target protein, owing to its size (the addition of three amino acids) and charge (glutamic acid). S-glutathionylation also protects proteins from irreversible oxidation, allowing them to be enzymatically regenerated. Numerous enzymes have been identified to catalyze the glutathionylation/deglutathionylation reactions, including glutathione S-transferases and glutaredoxins. Although protein S-glutathionylation has been implicated in numerous biological processes, S-glutathionylated proteomes have largely remained unknown. In this paper, we focus on the pathways that regulate GSH homeostasis, S-glutathionylated proteins, and glutaredoxins, and we review methods required toward identification of glutathionylated proteomes. Finally, we present the latest findings on the role of glutathionylation/glutaredoxins in various lung diseases: idiopathic pulmonary fibrosis, asthma, and chronic obstructive pulmonary disease.

Nitric oxide and its derivatives in the cancer battlefield

Elevated levels of reactive nitrogen species, alteration in redox balance and deregulated redox signaling are common hallmarks of cancer progression and chemoresistance. However, depending on the cellular context, distinct reactive nitrogen species are also hypothesized to mediate cytotoxic activity and are thus used in anticancer therapies. We present here the dual face of nitric oxide and its derivatives in cancer biology. Main derivatives of nitric oxide, such as nitrogen dioxide and peroxynitrite cause cell death by inducing protein and lipid peroxidation and/or DNA damage. Moreover, they control the activity of important protein players within the pro- and anti-apoptotic signaling pathways. Thus, the control of intracellular reactive nitrogen species may become a sophisticated tool in anticancer strategies.

Reducing protein oxidation reverses lung fibrosis

Idiopathic pulmonary fibrosis is characterized by excessive deposition of collagen in the lung, leading to chronically impaired gas exchange and death1-3. Oxidative stress is believed to be critical in this disease pathogenesis4-6, although the exact mechanisms remain enigmatic. Protein S-glutathionylation (PSSG) is a post-translational modification of proteins that can be reversed by glutaredoxin-1 (GLRX)7. It remains unknown whether GLRX and PSSG play a role in lung fibrosis. Here, we explored the impact of GLRX and PSSG status on the pathogenesis of pulmonary fibrosis, using lung tissues from subjects with idiopathic pulmonary fibrosis, transgenic mouse models and direct administration of recombinant Glrx to airways of mice with existing fibrosis. We demonstrate that GLRX enzymatic activity was strongly decreased in fibrotic lungs, in accordance with increases in PSSG. Mice lacking Glrx were far more susceptible to bleomycin- or adenovirus encoding active transforming growth factor beta-1 (AdTGFB1)-induced pulmonary fibrosis, whereas transgenic overexpression of Glrx in the lung epithelium attenuated fibrosis. We furthermore show that endogenous GLRX was inactivated through an oxidative mechanism and that direct administration of the Glrx protein into airways augmented Glrx activity and reversed increases in collagen in mice with TGFB1- or bleomycin-induced fibrosis, even when administered to fibrotic, aged animals. Collectively, these findings suggest the therapeutic potential of exogenous GLRX in treating lung fibrosis.

Assessment of glutathione/glutathione disulphide ratio and S-glutathionylated proteins in human blood, solid tissues, and cultured cells

Glutathione (GSH) is the major non-protein thiol in humans and other mammals, which is present in millimolar concentrations within cells, but at much lower concentrations in the blood plasma. GSH and GSH-related enzymes act both to prevent oxidative damage and to detoxify electrophiles. Under oxidative stress, two GSH molecules become linked by a disulphide bridge to form glutathione disulphide (GSSG). Therefore, assessment of the GSH/GSSG ratio may provide an estimation of cellular redox metabolism. Current evidence resulting from studies in human blood, solid tissues, and cultured cells suggests that GSH also plays a prominent role in protein redox regulation via S -glutathionylation, i.e., the conjugation of GSH to reactive protein cysteine residues. A number of methodologies that enable quantitative analysis of GSH/GSSG ratio and S-glutathionylated proteins (PSSG), as well as identification and visualization of PSSG in tissue sections or cultured cells are currently available. Here, we have considered the main methodologies applied for GSH, GSSG and PSSG detection in biological samples. This review paper provides an up-to-date critical overview of the application of the most relevant analytical, morphological, and proteomics approaches to detect and analyse GSH, GSSG and PSSG in mammalian samples as well as discusses their current limitations.

Biotin Switch Assays for Quantitation of Reversible Cysteine Oxidation

Thiol groups in protein cysteine residues can be subjected to different oxidative modifications by reactive oxygen/nitrogen species. Reversible cysteine oxidation, including S-nitrosylation, S-sulfenylation, S-glutathionylation, and disulfide formation, modulate multiple biological functions, such as enzyme catalysis, antioxidant, and other signaling pathways. However, the biological relevance of reversible cysteine oxidation is typically underestimated, in part due to the low abundance and high reactivity of some of these modifications, and the lack of methods to enrich and quantify them. To facilitate future research efforts, this chapter describes detailed procedures to target the different modifications using mass spectrometry-based biotin switch assays. By switching the modification of interest to a biotin moiety, these assays leverage the high affinity between biotin and avidin to enrich the modification. The use of stable isotope labeling and a range of selective reducing agents facilitate the quantitation of individual as well as total reversible cysteine oxidation. The biotin switch assay has been widely applied to the quantitative analysis of S-nitrosylation in different disease models and is now also emerging as a valuable research tool for other oxidative cysteine modifications, highlighting its relevance as a versatile, robust strategy for carrying out in-depth studies in redox proteomics.

Attenuation of lung fibrosis in mice with a clinically relevant inhibitor of glutathione-S-transferase π

Idiopathic pulmonary fibrosis (IPF) is a debilitating lung disease characterized by excessive collagen production and fibrogenesis. Apoptosis in lung epithelial cells is critical in IPF pathogenesis, as heightened loss of these cells promotes fibroblast activation and remodeling. Changes in glutathione redox status have been reported in IPF patients. S-glutathionylation, the conjugation of glutathione to reactive cysteines, is catalyzed in part by glutathione-S-transferase π (GSTP). To date, no published information exists linking GSTP and IPF to our knowledge. We hypothesized that GSTP mediates lung fibrogenesis in part through FAS S-glutathionylation, a critical event in epithelial cell apoptosis. Our results demonstrate that GSTP immunoreactivity is increased in the lungs of IPF patients, notably within type II epithelial cells. The FAS-GSTP interaction was also increased in IPF lungs. Bleomycin- and AdTGFβ-induced increases in collagen content, α-SMA, FAS S-glutathionylation, and total protein S-glutathionylation were strongly attenuated in Gstp-/- mice. Oropharyngeal administration of the GSTP inhibitor, TLK117, at a time when fibrosis was already apparent, attenuated bleomycin- and AdTGFβ-induced remodeling, α-SMA, caspase activation, FAS S-glutathionylation, and total protein S-glutathionylation. GSTP is an important driver of protein S-glutathionylation and lung fibrosis, and GSTP inhibition via the airways may be a novel therapeutic strategy for the treatment of IPF.

The relevance of tissue thiol histochemistry to diagnostic hematopathology

Expression analyses suggest that alterations of the antioxidant state of some diffuse large B-cell lymphomas can assist prognosis; reversibly oxidized thiols may serve as a surrogate marker for identifying such cases. Little is known about the distribution of free thiols and reversibly oxidized thiols in human tissues. We developed a staining technique that enables visualization of tissue thiols in situ using bright field microscopy and validated it using gastrointestinal tissue specimens. We used our thiol staining technique to assess benign tonsillectomy and diffuse large B-cell lymphoma specimens. The gastrointestinal series revealed the presence of free thiols within epithelial cells and cells of the lamina propria. Staining for reversibly oxidized thiols was robust in gastric foveolar cells, intestinal goblet cells and the mucus they produce. Tonsillectomy specimens exhibited diffuse presence of free thiols. Staining for reversibly oxidized thiols was confined to germinal center macrophages and sinus histiocytes. Among the diffuse large B-cell lymphoma specimens, we observed strong staining for free thiols within malignant cells. By contrast to benign B-cells, the malignant cells demonstrated pronounced and diffuse staining for reversibly oxidized thiols. We demonstrated intrinsic differences between benign and malignant cells.

Proteome-wide identification and quantification of S-glutathionylation targets in mouse liver

Protein S-glutathionylation is a reversible post-translational modification regulating sulfhydryl homeostasis. However, little is known about the proteins and pathways regulated by S-glutathionylation in whole organisms and current approaches lack the sensitivity to examine this modification under basal conditions. We now report the quantification and identification of S-glutathionylated proteins from animal tissue, using a highly sensitive methodology combining high-accuracy proteomics with tandem mass tagging to provide precise, extensive coverage of S-glutathionylated targets in mouse liver. Critically, we show significant enrichment of S-glutathionylated mitochondrial and Krebs cycle proteins, identifying that S-glutathionylation is heavily involved in energy metabolism processes in vivo. Furthermore, using mice nulled for GST Pi (GSTP) we address the potential for S-glutathionylation to be mediated enzymatically. The data demonstrate the impact of S-glutathionylation in cellular homeostasis, particularly in relation to energy regulation and is of significant interest for those wishing to examine S-glutathionylation in an animal model.

Temporal changes in glutaredoxin 1 and protein s-glutathionylation in allergic airway inflammation

INTRODUCTION

Asthma is a chronic inflammatory disorder of the airways, involving oxidative stress. Upon oxidative stress, glutathione covalently binds to protein thiols to protect them against irreversible oxidation. This posttranslational modification, known as protein S-glutathionylation, can be reversed by glutaredoxin 1 (Glrx1) under physiological condition. Glrx1 is known to increase in the lung tissues of a murine model of allergic airway inflammation. However, the temporal relationship between levels of Glrx1, protein S-glutathionylation, and glutathione in the lungs with allergic airway inflammation is not clearly understood.

METHODS

BALB/c mice received 3 aerosol challenges with ovalbumin (OVA) following sensitization to OVA. They were sacrificed at 6, 24, 48, or 72 h, or 8 days (5 mice per group), and the levels of Glrx1, protein S-glutathionylation, glutathione, and 25 cytokines/chemokines were evaluated in bronchoalveolar lavage fluid (BALF) and/or lung tissue.

RESULTS

Levels of Glrx1 in BALF were significantly elevated in the OVA 6 h (final challenge) group compared to those in the control, with concurrent increases in protein S-glutathionylation levels in the lungs, as well as total glutathione (reduced and oxidized) and oxidized glutathione in BALF. Protein S-glutathionylation levels were attenuated at 24 h, with significant increases in Glrx1 levels in lung tissues at 48 and 72 h. Glrx1 in alveolar macrophages was induced after 6 h. Glrx1 levels concomitantly increased with Th2/NF-κB-related cytokines and chemokines in BALF.

CONCLUSIONS

The temporal relationships of Glrx1 with protein S-glutathionylation, glutathione, and cytokines/chemokines were observed as dynamic changes in lungs with allergic airway inflammation, suggesting that Glrx1 and protein-SSG redox status may play important roles in the development of allergic airway inflammation.

Biochemical methods for monitoring protein thiol redox states in biological systems

Oxidative post-translational modifications of proteins resulting from events that increase cellular oxidant levels play important roles in physiological and pathophysiological processes. Evaluation of alterations to protein redox states is increasingly common place because of methodological advances that have enabled detection, quantification and identification of such changes in cells and tissues. This mini-review provides a synopsis of biochemical methods that can be utilized to monitor the array of different oxidative and electrophilic modifications that can occur to protein thiols and can be important in the regulatory or maladaptive impact oxidants can have on biological systems. Several of the methods discussed are valuable for monitoring the redox state of established redox sensing proteins such as Keap1.

Glutaredoxin-1 attenuates S-glutathionylation of the death receptor fas and decreases resolution of Pseudomonas aeruginosa pneumonia

RATIONALE

The death receptor Fas is critical for bacterial clearance and survival of mice after Pseudomonas aeruginosa infection.

OBJECTIVES

Fas ligand (FasL)-induced apoptosis is augmented by S-glutathionylation of Fas (Fas-SSG), which can be reversed by glutaredoxin-1 (Grx1). Therefore, the objective of this study was to investigate the interplay between Grx1 and Fas in regulating the clearance of P. aeruginosa infection.

METHODS

Lung samples from patients with bronchopneumonia were analyzed by immunofluorescence. Primary tracheal epithelial cells, mice lacking the gene for Grx1 (Glrx1(-/-)), Glrx1(-/-) mice treated with caspase inhibitor, or transgenic mice overexpressing Grx1 in the airway epithelium were analyzed after infection with P. aeruginosa.

MEASUREMENTS AND MAIN RESULTS

Patient lung samples positive for P. aeruginosa infection demonstrated increased Fas-SSG compared with normal lung samples. Compared with wild-type primary lung epithelial cells, infection of Glrx1(-/-) cells with P. aeruginosa showed enhanced caspase 8 and 3 activities and cell death in association with increases in Fas-SSG. Infection of Glrx1(-/-) mice with P. aeruginosa resulted in enhanced caspase activity and increased Fas-SSG as compared with wild-type littermates. Absence of Glrx1 significantly enhanced bacterial clearance, and decreased mortality postinfection with P. aeruginosa. Inhibition of caspases significantly decreased bacterial clearance postinfection with P. aeruginosa, in association with decreased Fas-SSG. In contrast, transgenic mice that overexpress Grx1 in lung epithelial cells had significantly higher lung bacterial loads, enhanced mortality, decreased caspase activation, and Fas-SSG in the lung after infection with P. aeruginosa, compared with wild-type control animals.

CONCLUSIONS

These results suggest that S-glutathionylation of Fas within the lung epithelium enhances epithelial apoptosis and promotes clearance of P. aeruginosa and that glutaredoxin-1 impairs bacterial clearance and increases the severity of pneumonia in association with deglutathionylation of Fas.

Redox proteomics: from bench to bedside

In general protein posttranslation modifications (PTMs) involve the covalent addition of functional groups or molecules to specific amino acid residues in proteins. These modifications include phosphorylation, glycosylation, S-nitrosylation, acetylation, lipidation, among others (Angew Chem Int Ed Engl 44(45):7342-7372, 2005). Although other amino acids can undergo different kinds of oxidative posttranslational modifications (oxPTMs) (Exp Gerontol 36(9):1495-1502, 2001), in this chapter oxPTM will be considered specifically related to Cysteine oxidation, and redox proteomics here is translated as a comprehensive investigation of oxPTMs, in biological systems, using diverse technical approaches. Protein Cysteine residues are not the only amino acid that can be target for oxidative modifications in proteins (Exp Gerontol 36(9):1495-1502, 2001; Biochim Biophys Acta 1814(12):1785-1795, 2011), but certainly it is among the most reactive amino acid (Nature 468(7325):790-795, 2010). Interestingly, it is one of the least abundant amino acid, but it often occurs in the functional sites of proteins (J Mol Biol 404(5):902-916, 2010). In addition, the majority of the Cysteine oxidations are reversible, indicating potential regulatory mechanism of proteins. The global analysis of oxPTMs has been increasingly recognized as an important area of proteomics, because not only maps protein caused by reactive oxygen species (ROS) and reactive nitrogen species (RNS), but also explores protein modulation involving ROS/RNS. Furthermore, the tools and strategies to study this type oxidation are also very abundant and developed, offering high degree of accuracy on the results. As a consequence, the redox proteomics field focuses very much on analyzing Cysteine oxidation in proteins under several experimental conditions and diseases states. Therefore, the identification and localization of oxPTMs within cellular milieu became critical to understand redox regulation of proteins in physiological and pathological conditions, and consequently an important information to develop better strategies for treatment and prevention of diseases associated with oxidative stress.There is a wide range of techniques available to investigate oxPTMs, including gel-based and non-gel-based separation approaches to be combined with sophisticated methods of detection, identification, and quantification of these modifications. The strategies and approaches to study oxPTMs and the respective applications related to physiological and pathological conditions will be discussed in more detail in this chapter.

Emerging mechanisms of glutathione-dependent chemistry in biology and disease

Glutathione has traditionally been considered as an antioxidant that protects cells against oxidative stress. Hence, the loss of reduced glutathione and formation of glutathione disulfide is considered a classical parameter of oxidative stress that is increased in diseases. Recent studies have emerged that demonstrate that glutathione plays a more direct role in biological and pathophysiological processes through covalent modification to reactive cysteines within proteins, a process known as S-glutathionylation. The formation of an S-glutathionylated moiety within the protein can lead to structural and functional modifications. Activation, inactivation, loss of function, and gain of function have all been attributed to S-glutathionylation. In pathophysiological settings, S-glutathionylation is tightly regulated. This perspective offers a concise overview of the emerging field of protein thiol redox modifications. We will also cover newly developed methodology to detect S-glutathionylation in situ, which will enable further discovery into the role of S-glutathionylation in biology and disease.

Sustained Glutathione Deficiency Interferes with the Liver Response to TNF-α and Liver Regeneration after Partial Hepatectomy in Mice

Glutathione (GSH) is a critical intracellular antioxidant that is active in free radical scavenging and as a reducing equivalent in biological reactions. Recent studies have suggested that GSH can affect cellular function at the level of gene transcription as well, in particular by affecting NF-κB activation. Additionally, increased or decreased GSH levels in vitro have been tied to increased or decreased hepatocyte proliferation, respectively. Here, we investigated the effect of GSH on the liver's response to TNF-α injection and 2/3 partial hepatectomy (PH), using mice deficient for the modifier subunit of glutamate-cysteine ligase (GCLM), the rate-limiting enzyme in de novo GSH synthesis. We demonstrate that Gclm^-/- mice have a delay in IκBα degradation after TNF-α injection, resulting in delayed NF-κB nuclear translocation. These mice display profound deficiencies in GSH levels both before and during regeneration, and after PH, Gclm^-/- mice have an overall delay in cell cycle progression, with slower DNA synthesis, mitosis, and expression of cell cycle proteins. Moreover, there is a delay in expression of downstream targets of NF-κB in the regenerating liver in Gclm^-/- mice. These data suggest that GSH may play a role in hepatic NF-κB activation in vivo, which is necessary for accurate timing of liver regeneration.

Strategies to decrease ongoing oxidant burden in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a leading cause of mortality and morbidity globally, and its development is mainly associated with tobacco/biomass smoke-induced oxidative stress. Hence, targeting systemic and local oxidative stress with agents that can balance the antioxidant/redox system can be expected to be useful in the treatment of COPD. Preclinical and clinical trials have revealed that antioxidants/redox modulators can detoxify free radicals and oxidants, control expression of redox and glutathione biosynthesis genes, chromatin remodeling and inflammatory gene expression; and are especially useful in preventing COPD exacerbations. In this review, various novel approaches and problems associated with these approaches in COPD are reviewed.

Chasing cysteine oxidative modifications: proteomic tools for characterizing cysteine redox status

Redox-proteomics involves the large scale analysis of oxidative protein post-translational modifications. In particular, cysteine residues have become the subject of intensifying research interest because of their redox-reactive thiol side chain. Certain reactive cysteine residues can function as redox-switches, which sense changes in the local redox-environment by flipping between the reduced and oxidized state. Depending on the reactive oxygen or nitrogen species, cysteine residues can receive one of several oxidative modifications, each with the potential to confer a functional effect. Modification of these redox-switches has been found to play an important role in oxidative-signaling in the cardiovascular system and elsewhere. Due to the labile and dynamic nature of these modifications, several targeted approaches have been developed to enrich, identify and characterize the status of these critical residues. Here, we review the various proteomic strategies and limitations for the large scale analysis of the different oxidative cysteine modifications.

S-glutathiolation in life and death decisions of the cell

Reversible S-glutathiolation of specific proteins at sensitive cysteines provides a powerful mechanism for the dynamic, post-translational regulation of many cellular processes, including apoptosis. Critical in ascribing any regulatory function to S-glutathiolation is its reversibility, mainly regulated by glutaredoxins. Apoptosis is a controlled form of cell death that plays fundamental roles during embryonic development, tissue homeostasis and some diseases. Much of what happens during the demolition phase of apoptosis is orchestrated primarily by caspases, the final executioners of cell death. Recent findings support an essential role for S-glutathiolation in apoptosis, often at the level of caspases or their inactive precursors, and several studies have demonstrated the importance of glutaredoxins in protecting against apoptosis. These observations have contributed to recent advances in apoptosis research. However, the effective relevance of protein S-glutathiolation and the precise molecular targets in apoptotic signalling remain unresolved and a key challenge for future research.

Measurement of extracellular (exofacial) versus intracellular protein thiols

In recent years, the importance of compartmentalization in redox signaling has been realized. A number of specific thiol pools exist both inside and outside the cell, and these thiols are regulated via unique mechanisms and serve specific roles in cell signaling. This chapter covers some of the methodologies available for the interrogation of thiol status in various cellular compartments, with a focus on mitochondrial, cytosolic, and exofacial thiols. Finally, the relevance of these thiols to pathological disease states, in particular cancer, will be discussed. The chapters in the remainder of this volume more than adequately cover the diversity of thiol modifications, describing the specific biochemical nature of these reactions, ranging from S-nitrosation through glutathionylation, to oxidation and beyond. Therefore, this topic will not be further addressed here. Similarly, general methodological considerations are considered to have been dealt with in the remainder of this volume, including requirements for subdued lighting, avoidance of reducing agents and transition metals in media, and rapid sample preparation with adequate control over temperature and pH.

Ablation of glutaredoxin-1 attenuates lipopolysaccharide-induced lung inflammation and alveolar macrophage activation

Protein S-glutathionylation (PSSG), a reversible posttranslational modification of reactive cysteines, recently emerged as a regulatory mechanism that affects diverse cell-signaling cascades. The extent of cellular PSSG is controlled by the oxidoreductase glutaredoxin-1 (Grx1), a cytosolic enzyme that specifically de-glutathionylates proteins. Here, we sought to evaluate the impact of the genetic ablation of Grx1 on PSSG and on LPS-induced lung inflammation. In response to LPS, Grx1 activity increased in lung tissue and bronchoalveolar lavage (BAL) fluid in WT (WT) mice compared with PBS control mice. Glrx1(-/-) mice consistently showed slight but statistically insignificant decreases in total numbers of inflammatory cells recovered by BAL. However, LPS-induced concentrations of IL-1β, TNF-α, IL-6, and Granulocyte/Monocyte Colony-Stimulating Factor (GM-CSF) in BAL were significantly decreased in Glrx1(-/-) mice compared with WT mice. An in situ assessment of PSSG reactivity and a biochemical evaluation of PSSG content demonstrated increases in the lung tissue of Glrx1(-/-) animals in response to LPS, compared with WT mice or PBS control mice. We also demonstrated that PSSG reactivity was prominent in alveolar macrophages (AMs). Comparative BAL analyses from WT and Glrx1(-/-) mice revealed fewer and smaller AMs in Glrx1(-/-) mice, which showed a significantly decreased expression of NF-κB family members, impaired nuclear translocation of RelA, and lower levels of NF-κB-dependent cytokines after exposure to LPS, compared with WT cells. Taken together, these results indicate that Grx1 regulates the production of inflammatory mediators through control of S-glutathionylation-sensitive signaling pathways such as NF-κB, and that Grx1 expression is critical to the activation of AMs.

Dual role of vitamin C utilization in NO2-induced oxidative stress in lung tissues of mice

Earlier studies with in vitro models have revealed that application of vitamin C can act as a primary NO(2) absorption substrate to contribute to NO(2)-induced cellular injury. In the present study, we showed that the pharmacological application of vitamin C had dual role in lungs of mice exposed to NO(2), with an exacerbated oxidative stress occurring at low concentrations, as indicated by excessive reactive oxygen species production and lipid peroxidation. However, at high concentrations, vitamin C functioned as an antioxidant removing reactive oxygen species and maintaining a reducing status in cells, alleviating NO(2)-induced oxidative toxicity.

Glutaredoxin 1 regulates cigarette smoke-mediated lung inflammation through differential modulation of I{kappa}B kinases in mice: impact on histone acetylation

Glutaredoxin 1 (Glrx1) is a small dithiol protein that regulates the cellular redox state and redox-dependent signaling pathways via modulation of protein glutathionylation. IkappaB kinase (IKK), an essential enzyme for NF-kappaB activation, can be subjected to S-glutathionylation leading to alteration of its activity. However, the role of Glrx1 in cigarette smoke (CS)-induced lung inflammation and chromatin modifications are not known. We hypothesized that Glrx1 regulates the CS-induced lung inflammation and chromatin modifications via differential regulation of IKKs by S-glutathionylation in mouse lung. Glrx1 knockout (KO) and wild-type (WT) mice were exposed to CS for 3 days and determined the role of Glrx1 in regulation of proinflammatory response in the lung. Neutrophil influx in bronchoalveolar lavage fluid and proinflammatory cytokine release in lung were increased in Glrx1 KO mice compared with WT mice exposed to CS, which was associated with augmented nuclear translocation of RelA/p65 and its phospho-acetylation. Interestingly, phosphorylated and total levels of IKKalpha, but not total and phosphorylated IKKbeta levels, were increased in lungs of Glrx1 KO mice compared with WT mice exposed to CS. Ablation of Glrx1 leads to increased CS-induced IKKbeta glutathionylation rendering it inactive, whereas IKKalpha was activated resulting in increased phospho-acetylation of histone H3 in mouse lung. Thus, targeted disruption of Glrx1 regulates the lung proinflammatory response via histone acetylation specifically by activation of IKKalpha in response to CS exposure. Overall, our study suggests that S-glutathionylation and phosphorylation of IKKalpha plays an important role in histone acetylation on proinflammatory gene promoters and NF-kappaB-mediated abnormal and sustained lung inflammation in pathogenesis of chronic inflammatory lung diseases.

Protocols for the detection of s-glutathionylated and s-nitrosylated proteins in situ

The oxidation of protein cysteine residues represents significant posttranslational modifications that impact a wide variety of signal transduction cascades and diverse biological processes. Oxidation of cysteines occurs through reactions with reactive oxygen as well as nitrogen species. These oxidative events can lead to irreversible modifications, such as the formation of sulfonic acids, or manifest as reversible modifications such as the conjugation of glutathione with the cysteine moiety, a process termed S-glutathionylation (also referred to as S-glutathiolation, or protein mixed disulfides). Similarly, S-nitrosothiols can also react with the thiol group in a process known as S-nitrosylation (or S-nitrosation). It is the latter two events that have recently come to the forefront of cellular biology through their ability to reversibly impact numerous cellular processes. Herein we describe two protocols for the detection of S-glutathionylated or S-nitrosylated proteins in situ. The protocol for the detection of S-glutathionylated proteins relies on the catalytic specificity of glutaredoxin-1 for the reduction of S-glutathionylated proteins. The protocol for the detection of S-nitrosylated proteins represents a modification of the previously described biotin switch protocol, which relies on ascorbate in the presence of chelators to decompose S-nitrosylated proteins. These techniques can be applied in situ to elucidate which compartments in tissues are affected in diseased states whose underlying pathologies are thought to represent a redox imbalance.