Glutaredoxin modulates platelet-derived growth factor-dependent cell signaling by regulating the redox status of low molecular weight protein-tyrosine phosphatase

Disulfide stress and its role in cardiovascular diseases

Cardiovascular disease (CVD) is one of the leading causes of mortality in humans, and oxidative stress plays a pivotal role in disease progression. This phenomenon typically arises from weakening of the cellular antioxidant system or excessive accumulation of peroxides. This review focuses on a specialized form of oxidative stress-disulfide stress-which is triggered by an imbalance in the glutaredoxin and thioredoxin antioxidant systems within the cell, leading to the accumulation of disulfide bonds. The genesis of disulfide stress is usually induced by extrinsic pathological factors that disrupt the thiol-dependent antioxidant system, manifesting as sustained glutathionylation of proteins, formation of abnormal intermolecular disulfide bonds between cysteine-rich proteins, or irreversible oxidation of thiol groups to sulfenic and sulfonic acids. Disulfide stress not only precipitates the collapse of the antioxidant system and the accumulation of reactive oxygen species, exacerbating oxidative stress, but may also initiate cellular inflammation, autophagy, and apoptosis through a cascade of signaling pathways. Furthermore, this review explores the detrimental effects of disulfide stress on the progression of various CVDs including atherosclerosis, hypertension, myocardial ischemia-reperfusion injury, diabetic cardiomyopathy, cardiac hypertrophy, and heart failure. This review also proposes several potential therapeutic avenues to improve the future treatment of CVDs.

Structural and functional fine mapping of cysteines in mammalian glutaredoxin reveal their differential oxidation susceptibility

Protein-S-glutathionylation is a post-translational modification involving the conjugation of glutathione to protein thiols, which can modulate the activity and structure of key cellular proteins. Glutaredoxins (GLRX) are oxidoreductases that regulate this process by performing deglutathionylation. However, GLRX has five cysteines that are potentially vulnerable to oxidative modification, which is associated with GLRX aggregation and loss of activity. To date, GLRX cysteines that are oxidatively modified and their relative susceptibilities remain unknown. We utilized molecular modeling approaches, activity assays using recombinant GLRX, coupled with site-directed mutagenesis of each cysteine both individually and in combination to address the oxidizibility of GLRX cysteines. These approaches reveal that C8 and C83 are targets for S-glutathionylation and oxidation by hydrogen peroxide in vitro. In silico modeling and experimental validation confirm a prominent role of C8 for dimer formation and aggregation. Lastly, combinatorial mutation of C8, C26, and C83 results in increased activity of GLRX and resistance to oxidative inactivation and aggregation. Results from these integrated computational and experimental studies provide insights into the relative oxidizability of GLRX's cysteines and have implications for the use of GLRX as a therapeutic in settings of dysregulated protein glutathionylation.

Function and regulation of GPX4 in the development and progression of fibrotic disease

Fibrosis is a common feature of fibrotic diseases that poses a serious threat to global health due to high morbidity and mortality in developing countries. There exist some chemical compounds and biomolecules associated with the development of fibrosis, including cytokines, hormones, and enzymes. Among them, glutathione peroxidase 4 (GPX4), as a selenoprotein antioxidant enzyme, is widely found in the embryo, testis, brain, liver, heart, and photoreceptor cells. Moreover, it is shown that GPX4 elicits diverse biological functions by suppressing phospholipid hydroperoxide at the expense of decreased glutathione (GSH), including loss of neurons, autophagy, cell repair, inflammation, ferroptosis, apoptosis, and oxidative stress. Interestingly, these processes are intimately related to the occurrence of fibrotic disease. Recently, GPX4 has been reported to exhibit a decline in fibrotic disease and inhibit fibrosis, suggesting that alterations of GPX4 can change the course or dictate the outcome of fibrotic disease. In this review, we summarize the role and underlying mechanisms of GPX4 in fibrosis diseases such as lung fibrosis, liver fibrosis, kidney fibrosis, cardiac fibrosis, and myelofibrosis.

Role of cassava CC-type glutaredoxin MeGRXC3 in regulating sensitivity to mannitol-induced osmotic stress dependent on its nuclear activity

BACKGROUND

We previously identified six drought-inducible CC-type glutaredoxins in cassava cultivars, however, less is known about their potential role in the molecular mechanism by which cassava adapted to abiotic stress.

RESULTS

Herein, we investigate one of cassava drought-responsive CC-type glutaredoxins, namely MeGRXC3, that involved in regulation of mannitol-induced inhibition on seed germination and seedling growth in transgenic Arabidopsis. MeGRXC3 overexpression up-regulates several stress-related transcription factor genes, such as PDF1.2, ERF6, ORA59, DREB2A, WRKY40, and WRKY53 in Arabidopsis. Protein interaction assays show that MeGRXC3 interacts with Arabidopsis TGA2 and TGA5 in the nucleus. Eliminated nuclear localization of MeGRXC3 failed to result mannitol-induced inhibition of seed germination and seedling growth in transgenic Arabidopsis. Mutation analysis of MeGRXC3 indicates the importance of conserved motifs for its transactivation activity in yeast. Additionally, these motifs are also indispensable for its functionality in regulating mannitol-induced inhibition of seed germination and enhancement of the stress-related transcription factors in transgenic Arabidopsis.

CONCLUSIONS

MeGRXC3 overexpression confers mannitol sensitivity in transgenic Arabidopsis possibly through interaction with TGA2/5 in the nucleus, and nuclear activity of MeGRXC3 is required for its function.

Dysregulation of nitric oxide synthases during early and late pathophysiological conditions of diabetes mellitus leads to amassing of microvascular impedement

Diabetes is a major killer worldwide and its unprecedented rise poses a serious threat to mankind. According to recent estimation, 387 million people worldwide are affected from the disease with a prevalence rate of 8.3 and 46.3 % still remains undiagnosed. Important characteristics of diabetes are abnormalities of the physiological signalling functions of reactive oxygen species and reactive nitrogen species. Increased oxidative stress contributes to the activation of stress-sensitive intracellular signalling pathways and the development of gene products that trigger cellular damage and contribute to the vascular complications of diabetes. Growing evidence from studies into many diseases suggests that the pathogenesis of diabetes, obesity, cancer, ageing, inflammation, neurodegenerative disorders, hypertension, apoptosis, cardiovascular diseases, and heart failure are correlated with oxidative stress. This leads to cell metabolism and cell-cell homeostasis to be complexly dysregulated. This review focuses to investigate the status of oxidative stress, nitric oxide and reactive species in early and diabetes. Significance of nitric oxide synthases Evidences has accumulated indicating that the generation of reactive oxygen species (oxidative stress) may play an important role in the etiology of diabetic complications thus attention was given on the reactive oxygen and reactive nitrogen species and their potential role in pathogenesis. Additionally, the therapeutic advances in diabetes management are included. Nanotechnology, statins and stem cell technology are some techniques which can be considered to have a possible future in the treatment sector of diabetes.

PTP-MEG2 regulates quantal size and fusion pore opening through two distinct structural bases and substrates

Tyrosine phosphorylation of secretion machinery proteins is a crucial regulatory mechanism for exocytosis. However, the participation of protein tyrosine phosphatases (PTPs) in different exocytosis stages has not been defined. Here we demonstrate that PTP-MEG2 controls multiple steps of catecholamine secretion. Biochemical and crystallographic analyses reveal key residues that govern the interaction between PTP-MEG2 and its substrate, a peptide containing the phosphorylated NSF-pY⁸³ site, specify PTP-MEG2 substrate selectivity, and modulate the fusion of catecholamine-containing vesicles. Unexpectedly, delineation of PTP-MEG2 mutants along with the NSF binding interface reveals that PTP-MEG2 controls the fusion pore opening through NSF independent mechanisms. Utilizing bioinformatics search and biochemical and electrochemical screening approaches, we uncover that PTP-MEG2 regulates the opening and extension of the fusion pore by dephosphorylating the DYNAMIN2-pY¹²⁵ and MUNC18-1-pY¹⁴⁵ sites. Further structural and biochemical analyses confirmed the interaction of PTP-MEG2 with MUNC18-1-pY¹⁴⁵ or DYNAMIN2-pY¹²⁵ through a distinct structural basis compared with that of the NSF-pY⁸³ site. Our studies thus provide mechanistic insights in complex exocytosis processes.

Genome-wide expression analysis suggests glutaredoxin genes response to various stresses in cotton

Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species (ROS) and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Glutaredoxins (GRXs) are ubiquitous oxidoreductase enzymes involved in diverse cellular processes and play a key role in oxidative stress responsive mechanisms. This study was aimed to explore the structure-function relationship and to provide a framework for functional validation and biochemical characterization of various GRX members. In this study, our analysis revealed the presence of 127 genes encoding GRX proteins in G. hirsutum. A total of 758 genes from two typical monocot and nine dicot species were naturally divided into four classes based on phylogenetic analysis. The classification was supported with organization of conserved protein motifs and sequence logos comparison between cotton, rice and Arabidopsis. Cotton GRX gene family has underwent strong purifying selection with limited functional divergence. A good collinearity was observed in the synteny analysis of four Gossypium species. Majority of cotton GRXs were influenced by various phytohormones and abiotic stress conditions during expression analysis, suggesting an important role of GRX proteins in response to oxidative stress. Cis-regulatory elements, gene enrichments and co-expression network analysis also support their predicted role against various abiotic stresses. Whole genome and segmental duplication were determined to be the two major impetuses for the expansion of gene numbers during the evolution. The identification of GRX genes showing differential expression in specific tissues or in response to environmental stimuli provides a new avenue for in-depth characterization of selected genes of importance. This study will further broaden our insights into the evolution and functional elucidation of GRX gene family in cotton.

Identification of Maize CC-Type Glutaredoxins That Are Associated with Response to Drought Stress

Global maize cultivation is often adversely affected by drought stress. The CC-type glutaredoxin (GRX) genes form a plant-specific subfamily that regulate plant growth and respond to environmental stresses. However, how maize CC-type GRX (ZmGRXCC) genes respond to drought stress remains unclear. We performed a TBLASTN search to identify ZmGRXCCs in the maize genome and verified the identified sequences using the NCBI conservative domain database (CDD). We further established a phylogenetic tree using Mega7 and surveyed known cis-elements in the promoters of ZmGRXCCs using the PlantCARE database. We found twenty-one ZmGRXCCs in the maize genome by a genome-wide investigation and compared their phylogenetic relationships with rice, maize, and Arabidopsis. The analysis of their redox active sites showed that most of the 21 ZmGRXCCs share similar structures with their homologs. We assessed their expression at young seedlings and adult leaves under drought stress and their expression profiles in 15 tissues, and found that they were differentially expressed, indicating that different ZmGRXCC genes have different functions. Notably, ZmGRXCC14 is up-regulated at seedling, V12, V14, V16, and R1 stages. Importantly, significant associations between genetic variation in ZmGRXCC14 and drought tolerance are found at the seedling stage. These results will help to advance the study of the function of ZmGRXCCs genes under drought stress and understand the mechanism of drought resistance in maize.

Identification and characterization of drought-responsive CC-type glutaredoxins from cassava cultivars reveals their involvement in ABA signalling

BACKGROUND

CC-type glutaredoxins (GRXs) are plant-specific glutaredoxin, play regulatory roles in response of biotic and abiotic stress. However, it is not clear whether the CC-type GRXs are involve in drought response in cassava (Manihot esculenta), an important tropical tuber root crop.

RESULTS

Herein, genome-wide analysis identified 18 CC-type GRXs in the cassava genome, of which six (namely MeGRXC3, C4, C7, C14, C15, and C18) were induced by drought stress in leaves of two cassava cultivars Argentina 7 (Arg7) and South China 124 (SC124). Exogenous abscisic acid (ABA) application induced the expression of all the six CC-type GRXs in leaves of both Arg7 and SC124 plants. Overexpression of MeGRXC15 in Arabidopsis (Col-0) increases tolerance of ABA on the sealed agar plates, but results in drought hypersensitivity in soil-grown plants. The results of microarray assays show that MeGRXC15 overexpression affected the expression of a set of transcription factors which involve in stress response, ABA, and JA/ET signalling pathway. The results of protein interaction analysis show that MeGRXC15 can interact with TGA5 from Arabidopsis and MeTGA074 from cassava.

CONCLUSIONS

CC-type glutaredoxins play regulatory roles in cassava response to drought possibly through ABA signalling pathway.

Tumor-secreted Pros1 inhibits macrophage M1 polarization to reduce antitumor immune response

Tyro3, Axl, Mer (TAM) receptor tyrosine kinases reduce inflammatory, innate immune responses. We demonstrate that tumor-secreted protein S (Pros1), a Mer/Tyro3 ligand, decreased macrophage M1 cytokine expression in vitro and in vivo. In contrast, tumor cells with CRISPR-based deletion of Pros1 failed to inhibit M1 polarization. Tumor cell-associated Pros1 action was abrogated in macrophages from Mer- and Tyro3- but not Axl-KO mice. In addition, several other murine and human tumor cell lines suppressed macrophage M1 cytokine expression induced by IFN-γ and LPS. Investigation of the suppressive pathway demonstrated a role for PTP1b complexing with Mer. Substantiating the role of PTP1b, M1 cytokine suppression was also lost in macrophages from PTP1b-KO mice. Mice bearing Pros1-deficient tumors showed increased innate and adaptive immune infiltration, as well as increased median survival. TAM activation can also inhibit TLR-mediated M1 polarization. Treatment with resiquimod, a TLR7/8 agonist, did not improve survival in mice bearing Pros1-secreting tumors but doubled survival for Pros1-deleted tumors. The tumor-derived Pros1 immune suppressive system, like PD-L1, was cytokine responsive, with IFN-γ inducing Pros1 transcription and secretion. Inhibition of Pros1/TAM interaction represents a potential novel strategy to block tumor-derived immune suppression.

Glutaredoxin 1 mediates the protective effect of steady laminar flow on endothelial cells against oxidative stress-induced apoptosis via inhibiting Bim

Endothelial cell apoptosis induced by oxidative stress is an early event in the development of atherosclerosis. Several antioxidant enzymes which can cope with oxidative stress are up-regulated by the anti-atherogenic laminar blood flow often seen in straight or unbranched regions of blood vessels. However, the molecular mechanism responsible for flow-induced beneficial effects is incompletely understood. Here we report the role of glutaredoxin 1 (Grx1), an antioxidant enzyme, in flow-mediated protective effect in endothelial cells. Specifically, we found that Grx1 is markedly up-regulated by the steady laminar flow. Increasing Grx1 reduces the pro-apoptotic protein Bim expression through regulating Akt-FoxO1 signaling and also attenuates H2O2-induced Bim activation via inhibiting JNK phosphorylation, subsequently preventing the apoptosis of endothelial cells. Grx1 knockdown abolishes the inhibitory effect of steady laminar flow on Bim. The inhibitory effect of Grx1 on Bim is dependent on Grx1's thioltransferase activity. These findings indicate that Grx1 induction plays a key role in mediating the protective effect of laminar blood flow and suggest that Grx1 may be a potential therapeutic target for atherosclerosis.

Redox regulation of the tumor suppressor PTEN by the thioredoxin system and cumene hydroperoxide

Intracellular redox status influences the oxidation and enzyme activity of the tumor suppressor phosphatase and tensin homolog on chromosome 10 (PTEN). Cumene hydroperoxide (CuHP), an organic hydroperoxide, is a known tumor promoter. However, molecular targets and action mechanism of CuHP in tumor promotion have not been well characterized. In this study, we investigated the effect of CuHP on the redox state of PTEN in HeLa cells. In addition, the intracellular reducing system of oxidized PTEN was analyzed using a biochemical approach and the effect of CuHP on this reducing system was also analyzed. While PTEN oxidized by hydrogen peroxide is progressively converted to its reduced form, PTEN was irreversibly oxidized by exposure to CuHP in HeLa cells. A combination of protein fractionation and mass analysis showed that the reducing system of PTEN was comprised of NADPH, thioredoxin reductase (TrxR), and thioredoxin (Trx). Although CuHP-mediated PTEN oxidation was not reversible in cells, CuHP-oxidized PTEN was reactivated by the exogenous Trx system, indicating that the cellular Trx redox system for PTEN is inactivated by CuHP. We present evidence that PTEN oxidation and the concomitant inhibition of thioredoxin by CuHP results in irreversible oxidation of PTEN in HeLa cells. In addition, ablation of peroxiredoxin (Prdx) enhanced CuHP-induced PTEN oxidation in cells. These results provide a new line of evidence that PTEN might be a crucial determinant of cell fate in response to cellular oxidative stress induced by organic hydroperoxides.

Low molecular weight protein tyrosine phosphatase: Multifaceted functions of an evolutionarily conserved enzyme

Originally identified as a low molecular weight acid phosphatase, LMW-PTP is actually a protein tyrosine phosphatase that acts on many phosphotyrosine-containing cellular proteins that are primarily involved in signal transduction. Differences in sequence, structure, and substrate recognition as well as in subcellular localization in different organisms enable LMW-PTP to exert many different functions. In fact, during evolution, the LMW-PTP structure adapted to perform different catalytic actions depending on the organism type. In bacteria, this enzyme is involved in the biosynthesis of group 1 and 4 capsules, but it is also a virulence factor in pathogenic strains. In yeast, LMW-PTPs dephosphorylate immunophilin Fpr3, a peptidyl-prolyl-cis-trans isomerase member of the protein chaperone family. In humans, LMW-PTP is encoded by the ACP1 gene, which is composed of three different alleles, each encoding two active enzymes produced by alternative RNA splicing. In animals, LMW-PTP dephosphorylates a number of growth factor receptors and modulates their signalling processes. The involvement of LMW-PTP in cancer progression and in insulin receptor regulation as well as its actions as a virulence factor in a number of pathogenic bacterial strains may promote the search for potent, selective and bioavailable LMW-PTP inhibitors.

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.

Regulation of protein tyrosine phosphatase oxidation in cell adhesion and migration

SIGNIFICANCE

Redox-regulated control of protein tyrosine phosphatases (PTPs) through inhibitory reversible oxidation of their active site is emerging as a novel and general mechanism for control of cell surface receptor-activated signaling. This mechanism allows for a previously unrecognized crosstalk between redox regulators and signaling pathways, governed by, for example, receptor tyrosine kinases and integrins, which control cell proliferation and migration.

RECENT ADVANCES

A large number of different molecules, in addition to hydrogen peroxide, have been found to induce PTP inactivation, including lipid peroxides, reactive nitrogen species, and hydrogen sulfide. Characterization of oxidized PTPs has identified different types of oxidative modifications that are likely to display differential sensitivity to various reducing systems. Accumulating evidence demonstrates that PTP oxidation occurs in a temporally and spatially restricted manner. Studies in cell and animal models indicate altered PTP oxidation in models of common diseases, such as cancer and metabolic/cardiovascular disease. Novel methods have appeared that allow characterization of global PTP oxidation.

CRITICAL ISSUES

As the understanding of the molecular and cellular biology of PTP oxidation is developing, it will be important to establish experimental procedures that allow analyses of PTP oxidation, and its regulation, in physiological and pathophysiological settings. Future studies should also aim to establish specific connections between various oxidants, specific PTPs, and defined signaling contexts.

FUTURE DIRECTIONS

Modulation of PTP activity still appears as a valid strategy for correction or inhibition of dys-regulated cell signaling. Continued studies on PTP oxidation might present yet unrecognized means to exploit this regulatory mechanism for pharmacological purposes.

Oxidative stress in diabetes: implications for vascular and other complications

In recent decades, oxidative stress has become a focus of interest in most biomedical disciplines and many types of clinical research. Increasing evidence shows that oxidative stress is associated with the pathogenesis of diabetes, obesity, cancer, ageing, inflammation, neurodegenerative disorders, hypertension, apoptosis, cardiovascular diseases, and heart failure. Based on these studies, an emerging concept is that oxidative stress is the “final common pathway” through which the risk factors for several diseases exert their deleterious effects. Oxidative stress causes a complex dysregulation of cell metabolism and cell–cell homeostasis; in particular, oxidative stress plays a key role in the pathogenesis of insulin resistance and β-cell dysfunction. These are the two most relevant mechanisms in the pathophysiology of type 2 diabetes and its vascular complications, the leading cause of death in diabetic patients.

Regulation of Monocyte Adhesion and Migration by Nox4

We showed that metabolic disorders promote thiol oxidative stress in monocytes, priming monocytes for accelerated chemokine-induced recruitment, and accumulation at sites of vascular injury and the progression of atherosclerosis. The aim of this study was to identify both the source of reactive oxygen species (ROS) responsible for thiol oxidation in primed and dysfunctional monocytes and the molecular mechanisms through which ROS accelerate the migration and recruitment of monocyte-derived macrophages. We found that Nox4, a recently identified NADPH oxidase in monocytes and macrophages, localized to focal adhesions and the actin cytoskeleton, and associated with phospho-FAK, paxillin, and actin, implicating Nox4 in the regulation of monocyte adhesion and migration. We also identified Nox4 as a new, metabolic stress-inducible source of ROS that controls actin S-glutathionylation and turnover in monocytes and macrophages, providing a novel mechanistic link between Nox4-derived H₂O₂ and monocyte adhesion and migration. Actin associated with Nox4 was S-glutathionylated, and Nox4 association with actin was enhanced in metabolically-stressed monocytes. Metabolic stress induced Nox4 and accelerated monocyte adhesion and chemotaxis in a Nox4-dependent mechanism. In conclusion, our data suggest that monocytic Nox4 is a central regulator of actin dynamics, and induction of Nox4 is the rate-limiting step in metabolic stress-induced monocyte priming and dysfunction associated with accelerated atherosclerosis and the progression of atherosclerotic plaques.

Redox regulation of protein kinases

Protein kinases represent one of the largest families of genes found in eukaryotes. Kinases mediate distinct cellular processes ranging from proliferation, differentiation, survival, and apoptosis. Ligand-mediated activation of receptor kinases can lead to the production of endogenous hydrogen peroxide (H₂O₂) by membrane-bound NADPH oxidases. In turn, H₂O₂ can be utilized as a secondary messenger in signal transduction pathways. This review presents an overview of the molecular mechanisms involved in redox regulation of protein kinases and its effects on signaling cascades. In the first half, we will focus primarily on receptor tyrosine kinases (RTKs), whereas the latter will concentrate on downstream non-receptor kinases involved in relaying stimulant response. Select examples from the literature are used to highlight the functional role of H₂O₂ regarding kinase activity, as well as the components involved in H₂O₂ production and regulation during cellular signaling. In addition, studies demonstrating direct modulation of protein kinases by H₂O₂ through cysteine oxidation will be emphasized. Identification of these redox-sensitive residues may help uncover signaling mechanisms conserved within kinase subfamilies. In some cases, these residues can even be exploited as targets for the development of new therapeutics. Continued efforts in this field will further basic understanding of kinase redox regulation, and delineate the mechanisms involved in physiological and pathological H₂O₂ responses.

S-glutathionylation of LMW-PTP regulates VEGF-mediated FAK activation and endothelial cell migration

Although promising, the ability to regulate angiogenesis through delivery of VEGF remains an unrealized goal. We have shown previously that physiological levels of peroxynitrite (1 µM) are required for a VEGF-mediated angiogenic response, yet the redox-regulated mechanisms that govern the VEGF signal remain unexplored. We assessed the impact of VEGF and peroxynitrite on modifying redox-state, the level of reduced-glutathione (GSH) and S-glutathionylation on regulation of the low molecular weight protein tyrosine phosphatase (LMW-PTP) and focal adhesion kinase (FAK), which are key mediators of VEGF-mediated cell migration. Stimulation of human microvascular endothelial (HME) cells with VEGF (20 ng/ml) or peroxynitrite (1 µM) caused an immediate and reversible negative-shift in the cellular redox-state and thiol oxidation of LMW-PTP, which culminated in cell migration. VEGF causes reversible S-glutathionylation of LMW-PTP, which inhibits its phosphorylation and activity, and causes the transient activation of FAK. Modulating the redox-state using decomposing peroxynitrite (FeTPPS, 2.5 µM) or the GSH-precursor [N-acetylcysteine (NAC), 1 mM] caused a positive-shift of the redox-state and prevented VEGF-mediated S-glutathionylation and oxidative inhibition of LMW-PTP. NAC and FeTPPS prevented the activation of FAK, its association with LMW-PTP and cell migration. Inhibiting LMW-PTP expression markedly enhanced FAK activation and cell migration. Although mild oxidative stress achieved by combining VEGF with 0.1-0.2 mM peroxynitrite augmented cell migration, an acute shift to oxidative stress achieved by combining VEGF with 0.5 mM peroxynitrite induced and sustained FAK activation, and LMW-PTP S-glutathionylation, resulting in LMW-PTP inactivation and inhibited cell migration. In conclusion, our findings demonstrate that a balanced redox-state is required for VEGF to facilitate reversible S-glutathionylation of LMW-PTP, FAK activation and endothelial cell migration. Shifting the redox-state to reductive stress or oxidative stress inhibited the VEGF-mediated angiogenic response.

Induction of oxidative stress in kidney

Oxidative stress has a critical role in the pathophysiology of several kidney diseases, and many complications of these diseases are mediated by oxidative stress, oxidative stress-related mediators, and inflammation. Several systemic diseases such as hypertension, diabetes mellitus, and hypercholesterolemia; infection; antibiotics, chemotherapeutics, and radiocontrast agents; and environmental toxins, occupational chemicals, radiation, smoking, as well as alcohol consumption induce oxidative stress in kidney. We searched the literature using PubMed, MEDLINE, and Google scholar with “oxidative stress, reactive oxygen species, oxygen free radicals, kidney, renal injury, nephropathy, nephrotoxicity, and induction”. The literature search included only articles written in English language. Letters or case reports were excluded. Scientific relevance, for clinical studies target populations, and study design, for basic science studies full coverage of main topics, are eligibility criteria for articles used in this paper.

Protein glutathionylation in the regulation of peroxiredoxins: a family of thiol-specific peroxidases that function as antioxidants, molecular chaperones, and signal modulators

SIGNIFICANCE

Reversible protein glutathionylation plays an important role in cellular regulation, signaling transduction, and antioxidant defense. This redox-sensitive mechanism is involved in regulating the functions of peroxiredoxins (Prxs), a family of ubiquitously expressed thiol-specific peroxidase enzymes. Glutathionylation of certain Prxs at their active-site cysteines not only provides reducing equivalents to support their peroxidase activity but also protects Prxs from irreversible hyperoxidation. Typical 2-Cys Prx also functions as a molecular chaperone when it exists as a decamer and/or higher molecular weight complexes. The hyperoxidized sulfinic derivative of 2-Cys Prx is reactivated by sulfiredoxin (Srx). In this review, the roles of glutathionylation in the regulation of Prxs are discussed with respect to their molecular structure and functions as antioxidants, molecular chaperones, and signal modulators.

RECENT ADVANCES

Recent findings reveal that glutathionylation regulates the quaternary structure of Prx. Glutathionylation of Prx I at Cys(83) converts the decameric Prx to its dimers with the loss of chaperone activity. The findings that dimer/oligomer structure specific Prx I binding proteins, e.g., phosphatase and tensin homolog (PTEN) and mammalian Ste20-like kinase-1 (MST1), regulate cell cycle and apoptosis, respectively, suggest a possible link between glutathionylation and those signaling pathways.

CRITICAL ISSUES

Knowing how glutathionylation affects the interaction between Prx I and its nearly 20 known interacting proteins, e.g., PTEN and MST1 kinase, would reveal new insights on the physiological functions of Prx.

FUTURE DIRECTIONS

In vitro studies reveal that Prx oligomerization is linked to its functional changes. However, in vivo dynamics, including the effect by glutathionylation, and its physiological significance remain to be investigated.

NADPH oxidase 4 mediates monocyte priming and accelerated chemotaxis induced by metabolic stress

OBJECTIVE

Metabolic disorders increase monocyte chemoattractant protein-1 (MCP-1)-induced monocyte chemotaxis in mice. The goal of this study was to determine the molecular mechanisms responsible for the enhanced responsiveness of monocytes to chemoattractants induced by metabolic stress.

METHODS AND RESULTS

Chronic exposure of monocytes to diabetic conditions induced by human LDL plus high D-glucose concentrations (LDL+HG) promoted NADPH Oxidase 4 (Nox4) expression, increased intracellular H(2)O(2) formation, stimulated protein S-glutathionylation, and increased chemotaxis in response to MCP-1, platelet-derived growth factor B, and RANTES. Both H(2)O(2) added exogenously and overexpression of Nox4 mimicked LDL+HG-induced monocyte priming, whereas Nox4 knockdown protected monocytes against metabolic stress-induced priming and accelerated chemotaxis. Exposure of monocytes to LDL+HG promoted the S-glutathionylation of actin, decreased the F-actin/G-actin ratio, and increased actin remodeling in response to MCP-1. Preventing LDL+HG-induced protein S-glutathionylation by overexpressing glutaredoxin 1 prevented monocyte priming and normalized monocyte chemotaxis in response to MCP-1. Induction of hypercholesterolemia and hyperglycemia in C57BL/6 mice promoted Nox4 expression and protein S-glutathionylation in macrophages, and increased macrophage recruitment into MCP-1-loaded Matrigel plugs implanted subcutaneous in these mice.

CONCLUSIONS

By increasing actin-S-glutathionylation and remodeling, metabolic stress primes monocytes for chemoattractant-induced transmigration and recruitment to sites of vascular injury. This Nox4-dependent process provides a novel mechanism through which metabolic disorders promote atherogenesis.

PDGF: the nuts and bolts of signalling toolbox

PDGF is a growth factor and is extensively involved in multi-dimensional cellular dynamics. It switches on a plethora of molecules other than its classical pathway. It is engaged in various transitions of development; however, if the unleashed potentials lead astray, it brings forth tumourigenesis. Conventionally, it has been assumed that the components of this signalling pathway show fidelity and act with a high degree of autonomy. However, as illustrated by the PDGF signal transduction, reinterpretation of recent data suggests that machinery is often shared between multiple pathways, and other components crosstalk to each other through multiple mechanisms. It is important to note that metastatic cascade is an intricate process that we have only begun to understand in recent years. Many of the early steps of this PDGF cascade are not readily targetable in the clinic. In this review, we will unravel the paradoxes with reference to mitrons and cellular plasticity and discuss how disruption of signalling cascade triggers cellular proliferation phase transition and metastasis. We will also focus on the therapeutic interventions to counteract resultant molecular disorders.

Redox regulation of protein tyrosine phosphatases: structural and chemical aspects

Protein tyrosine phosphatases (PTPs) are important targets of the H(2)O(2) that is produced during mammalian signal transduction. H(2)O(2)-mediated inactivation of PTPs also may be important in various pathophysiological conditions involving oxidative stress. Here we review the chemical and structural biology of redox-regulated PTPs. Reactions of H(2)O(2) with PTPs convert the catalytic cysteine thiol to a sulfenic acid. In PTPs, the initially generated sulfenic acid residues have the potential to undergo secondary reactions with a neighboring amide nitrogen or cysteine thiol residue to yield a sulfenyl amide or disulfide, respectively. The chemical mechanisms by which formation of sulfenyl amide and disulfide linkages can protect the catalytic cysteine residue against irreversible overoxidation to sulfinic and sulfonic oxidation states are described. Due to the propensity for back-door and distal cysteine residues to engage with the active-site cysteine after oxidative inactivation, differences in the structures of the oxidatively inactivated PTPs may stem, to a large degree, from differences in the number and location of cysteine residues surrounding the active site of the enzymes. PTPs with key cysteine residues in structurally similar locations may be expected to share similar mechanisms of oxidative inactivation.

Glutathionylation of peroxiredoxin I induces decamer to dimers dissociation with concomitant loss of chaperone activity

Reversible protein glutathionylation, a redox-sensitive regulatory mechanism, plays a key role in cellular regulation and cell signaling. Peroxiredoxins (Prxs), a family of peroxidases that is involved in removing H(2)O(2) and organic hydroperoxides, are known to undergo a functional change from peroxidase to molecular chaperone upon overoxidation of its catalytic cysteine. The functional change is caused by a structural change from low molecular weight oligomers to high molecular weight complexes that possess molecular chaperone activity. We reported earlier that Prx I can be glutathionylated at three of its cysteine residues, Cys52, -83, and -173 [Park et al. (2009) J. Biol. Chem., 284, 23364]. In this study, using analytical ultracentrifugation analysis, we reveal that glutathionylation of Prx I, WT, or its C52S/C173S double mutant shifted its oligomeric status from decamers to a population consisting mainly of dimers. Cys83 is localized at the putative dimer-dimer interface, implying that the redox status of Cys83 may play an important role in stabilizing the oligomeric state of Prx I. Studies with the Prx I (C83S) mutant show that while Cys83 is not essential for the formation of high molecular weight complexes, it affects the dimer-decamer equilibrium. Glutathionylation of the C83S mutant leads to accumulation of dimers and monomers. In addition, glutathionylation of Prx I, both the WT and C52S/C173S mutants, greatly reduces their molecular chaperone activity in protecting citrate synthase from thermally induced aggregation. Together, these results reveal that glutathionylation of Prx I promotes changes in its quaternary structure from decamers to smaller oligomers and concomitantly inactivates its molecular chaperone function.

12/15-lipoxygenase-derived lipid peroxides control receptor tyrosine kinase signaling through oxidation of protein tyrosine phosphatases

Protein tyrosine phosphatases (PTPs) are regulated through reversible oxidation of the active-site cysteine. Previous studies have implied soluble reactive oxygen species (ROS), like H(2)O(2), as the mediators of PTP oxidation. The potential role(s) of peroxidized lipids in PTP oxidation have not been described. This study demonstrates that increases in cellular lipid peroxides, induced by disruption of glutathione peroxidase 4, induce cellular PTP oxidation and reduce the activity of PDGF receptor targeting PTPs. These effects were accompanied by site-selective increased PDGF beta-receptor phosphorylation, sensitive to 12/15-lipoxygenase (12/15-LOX) inhibitors, and increased PDGF-induced cytoskeletal rearrangements. Importantly, the 12/15-LOX-derived 15-OOH-eicosatetraenoic acid lipid peroxide was much more effective than H(2)O(2) in induction of in vitro PTP oxidation. Our study thus establishes that lipid peroxides are previously unrecognized inducers of oxidation of PTPs. This identifies a pathway for control of receptor tyrosine kinase signaling, which might also be involved in the etiology of diseases associated with increased lipid peroxidation.

Thiol redox systems and protein kinases in hepatic stellate cell regulatory processes

Hepatic stellate cells (HSC) are the major producers of collagen in the liver and their conversion from resting cells to a proliferating, contractile and fibrogenic phenotype ('activation') is a critical step, leading to liver fibrosis characterized by deposition of excessive extracellular matrix. Cytokines, growth factors, reactive oxygen and nitrogen species (ROS/RNS), lipid peroxides and their products deriving from hepatocytes, Kupffer cells and other cells converge on HSC and influence their activation. This review focuses on glutathione and thioredoxin pathways, with particular emphasis on their role in HSC. These two systems have been shown to act in the metabolism of hydrogen peroxide, control of thiol redox balance and regulation of signalling pathways. Particular attention is paid to mitochondria and NADPH oxidase. Detailed knowledge of specific signalling, redox conditions and apoptotic processes will be of help in devising proper pharmacological treatments for liver fibrosis.

Oxidative stress, nitric oxide, and diabetes

In the recent decades, oxidative stress has become focus of interest in most biomedical disciplines and many types of clinical research. Increasing evidence from research on several diseases show that oxidative stress is associated with the pathogenesis of diabetes, obesity, cancer, ageing, inflammation, neurodegenerative disorders, hypertension, apoptosis, cardiovascular diseases, and heart failure. Based on this research, the emerging concept is that oxidative stress is the "final common pathway", through which risk factors of several diseases exert their deleterious effects. Oxidative stress causes a complex dysregulation of cell metabolism and cell-cell homeostasis. In this review, we discuss the role of oxidative stress in the pathogenesis of insulin resistance and beta-cell dysfunction. These are the two most relevant mechanisms in the pathophysiology of type 2 diabetes, and in the pathogenesis of diabetic vascular complications, the leading cause of death in diabetic patients.

Roles of oxidative stress and redox regulation in atherosclerosis

Oxidative stress is believed to be a cause of aging and cardiovascular disorders. In response to inflam-mation or endothelial cell injury, production of reactive oxygen species (ROS) is enhanced in vascular cells. These changes contribute to the initiation of atherosclerosis. Vascular cells possess anti-oxidant systems to protect against oxidative stress, in addition to the redox system. The redox status of pro-tein thiols is important for cellular functions. The Akt signaling pathway exerts effects on survival and apoptosis, and is regulated by the glutathione (GSH)/glutaredoxin (GRX)-dependent redox sys-tem. Sex hormones such as estrogens protect against oxidative stress by protecting the Akt signaling pathway but the physiological role of the extracellular GSH/GRX system has not been clarified, although found an increase in the levels of S-glutathionylated serum proteins in patients with athero-sclerosis obliterans. The results suggested that impaired serum redox potential is a marker of the development vascular dysfunction and estrogen has a possible role in the prevention of atherosclerosis.

Reactive oxygen species mediate mitogenic growth factor signaling pathways in human leiomyoma smooth muscle cells

Uterine leiomyomas are benign uterine tumors characterized by extracellular matrix remodeling, increased collagen deposition, and increased smooth muscle cell (SMC) proliferation. The reactive oxygen species (ROS) producing NADPH oxidase complex has been shown to be involved in the signaling pathways of several growth factors, cytokines, and vasoactive agents that stimulate proliferation of a variety of cell types. Our objective was to test the hypothesis that ROS derived from NADPH oxidase is a necessary component of the MAP kinase mitogenic pathway activated by platelet derived growth factor (PDGF) and epidermal growth factor (EGF) in leiomyoma SMCs (LSMCs). Primary cell cultures of LSMCs were used as our experimental model. Our results showed that stimulation of these cells with PDGF or EGF caused a marked increase in intracellular ROS production and that the NADPH oxidase inhibitor, DPI, blocks ROS production. In addition, inhibition of ROS production by NADPH oxidase inhibitors blocked, in a dose-dependent manner, the EGF- and PDGF-induced increase in [(3)H]thymidine incorporation by LSMCs. Furthermore, an exogenous source of ROS, hydrogen peroxide, was sufficient to stimulate [(3)H]thymidine incorporation in LSMCs but did not affect COL1A2 and COL3A1 mRNA levels. Inhibition of the NADPH oxidase complex decreased PDGF-induced MAPK1/MAPK3 activation, whereas exogenous hydrogen peroxide induced MAPK1/MAPK3 activation. This article is the first report suggesting the presence of the NADPH oxidase system and its importance in mitogenic signaling pathways in LSMCs. The necessity of NADPH oxidase-derived ROS for EGF and PDGF signaling pathways leading to cell proliferation points to another potential therapeutic target for treatment and/or prevention of uterine leiomyomas.

Vascular actions of insulin with implications for endothelial dysfunction

Hemodynamic actions of insulin depend largely on the hormone's ability to stimulate synthesis and release of endothelial mediators, whose balanced activity ensures dynamic control of vascular function. Nitric oxide (NO), endothelin-1 (ET-1), and reactive oxygen species (ROS) are important examples of endothelial mediators with opposing properties on vascular tone, hemostatic processes, and vascular permeability. Reduced NO bioavailability, resulting from either insufficient production or increased degradation of NO, characterizes endothelial dysfunction. In turn, endothelial dysfunction predicts vascular complications of metabolic and hemodynamic disorders. In the cardiovascular system, insulin stimulates the production and release of NO, ET-1, and ROS via activation of distinct intracellular signaling pathways. Under insulin-resistant conditions, increased insulin concentrations and/or impaired insulin-signaling pathways in the vasculature may contribute to imbalance in secretion of endothelial mediators that promote pathogenesis of vascular abnormalities. This short review describes signaling pathways involved in insulin-stimulated release of NO, ROS, and ET-1 and suggests possible molecular mechanisms by which abnormal insulin signaling may contribute to endothelial dysfunction.

Thiol oxidative stress induced by metabolic disorders amplifies macrophage chemotactic responses and accelerates atherogenesis and kidney injury in LDL receptor-deficient mice

BACKGROUND

Strengthening the macrophage glutathione redox buffer reduces macrophage content and decreases the severity of atherosclerotic lesions in LDL receptor-deficient (LDLR(-/-)) mice, but the underlying mechanisms were not clear. This study examined the effect of metabolic stress on the thiol redox state, chemotactic activity in vivo, and the recruitment of macrophages into atherosclerotic lesions and kidneys of LDL-R(-/-) mice in response to mild, moderate, and severe metabolic stress.

METHODS AND RESULTS

Reduced glutathione (GSH) and glutathione disulfide (GSSG) levels in peritoneal macrophages isolated from mildly, moderately, and severe metabolically-stressed LDL-R(-/-) mice were measured by HPLC, and the glutathione reduction potential (E(h)) was calculated. Macrophage E(h) correlated with the macrophage content in both atherosclerotic (r(2)=0.346, P=0.004) and renal lesions (r(2)=0.480, P=0.001) in these mice as well as the extent of both atherosclerosis (r(2)=0.414, P=0.001) and kidney injury (r(2)=0.480, P=0.001). Compared to LDL-R(-/-) mice exposed to mild metabolic stress, macrophage recruitment into MCP-1-loaded Matrigel plugs injected into LDL-R(-/-) mice increased 2.6-fold in moderately metabolically-stressed mice and 9.8-fold in severely metabolically-stressed mice. The macrophage E(h) was a strong predictor of macrophage chemotaxis (r(2)=0.554, P<0.001).

CONCLUSIONS

Thiol oxidative stress enhances macrophage recruitment into vascular and renal lesions by increasing the responsiveness of macrophages to chemoattractants. This novel mechanism contributes at least in part to accelerated atherosclerosis and kidney injury associated with dyslipidemia and diabetes in mice.

Tailoring a low-molecular weight protein tyrosine phosphatase into an efficient reporting protein

Fusion reporter methods are important tools for biology and biotechnology. An ideal reporter protein in a fusion system should have little effects on its fusion partner and provide an easy and accurate readout. Therefore, a small monomeric protein with high activity for detection assays often has advantages as a reporter protein. For this purpose, we have tailored the human B-form low-molecular-weight phosphotyrosyl phosphatase (HPTP-B) to increase its general applicability as a potent reporter protein. With the aim to eliminate interference from cysteine residues in the native HPTP-B, combined with a systematic survey of N- and C-terminal truncated variants, a series of cysteine to serine mutations were introduced, which allowed isolation of an engineered soluble protein with suitable biophysical properties. When we deleted both the first six residues and the last two residues, we still obtained a soluble mutant protein with correct folding and similar activity with wild-type protein. This mutant with two cysteine to serine mutations, HPTP-B(NDelta6-CDelta2-C90S-C109S), has good potential as an optimal reporter.

Dehydroepiandrosterone augments sensitivity to gamma-ray irradiation in human H4 neuroglioma cells through down-regulation of Akt signaling

Dehydroepiandrosterone (DHEA) modulates sensitivity to radiation-induced injury in human neuroglioma cells (H4) through effects on Akt signalling by glutathione (GSH)-dependent redox regulation. Previous treatment of H4 cells with DHEA for 18 h reduced the gamma-ray-induced phosphorylation of Akt, activated p21(waf1) synthesis and up-regulated phosphorylation of Rb independent of p53. These reactions were followed by a decrease in cell number and an increase in apoptosis and G(2)/M checkpoint arrest. The suppression of phosphorylation of Akt by DHEA was due to regulation of the dephosphorylation by protein phosphatase 2A (PP2A). DHEA up-regulated the expression of gamma-glutamylcysteine synthetase, a rate-limiting enzyme of glutathione (GSH) synthesis, and the levels of GSH to maintain PP2A activity. The results suggested that DHEA increases the sensitivity of cells to gamma-ray irradiation by inducing apoptosis and cell cycle arrest through GSH-dependent regulation of the reduced form of PP2A to down-regulate the Akt signalling pathway.

Positive and negative regulation of insulin signaling by reactive oxygen and nitrogen species

Regulated production of reactive oxygen species (ROS)/reactive nitrogen species (RNS) adequately balanced by antioxidant systems is a prerequisite for the participation of these active substances in physiological processes, including insulin action. Yet, increasing evidence implicates ROS and RNS as negative regulators of insulin signaling, rendering them putative mediators in the development of insulin resistance, a common endocrine abnormality that accompanies obesity and is a risk factor of type 2 diabetes. This review deals with this dual, seemingly contradictory, function of ROS and RNS in regulating insulin action: the major processes for ROS and RNS generation and detoxification are presented, and a critical review of the evidence that they participate in the positive and negative regulation of insulin action is provided. The cellular and molecular mechanisms by which ROS and RNS are thought to participate in normal insulin action and in the induction of insulin resistance are then described. Finally, we explore the potential usefulness and the challenges in modulating the oxidant-antioxidant balance as a potentially promising, but currently disappointing, means of improving insulin action in insulin resistance-associated conditions, leading causes of human morbidity and mortality of our era.

Molecular mechanisms and clinical implications of reversible protein S-glutathionylation

Sulfhydryl chemistry plays a vital role in normal biology and in defense of cells against oxidants, free radicals, and electrophiles. Modification of critical cysteine residues is an important mechanism of signal transduction, and perturbation of thiol-disulfide homeostasis is an important consequence of many diseases. A prevalent form of cysteine modification is reversible formation of protein mixed disulfides (protein-SSG) with glutathione (GSH). The abundance of GSH in cells and the ready conversion of sulfenic acids and S-nitroso derivatives to S-glutathione mixed disulfides suggests that reversible S-glutathionylation may be a common feature of redox signal transduction and regulation of the activities of redox sensitive thiol-proteins. The glutaredoxin enzyme has served as a focal point and important tool for evolution of this regulatory mechanism, because it is a specific and efficient catalyst of protein-SSG deglutathionylation. However, mechanisms of control of intracellular Grx activity in response to various stimuli are not well understood, and delineation of specific mechanisms and enzyme(s) involved in formation of protein-SSG intermediates requires further attention. A large number of proteins have been identified as potentially regulated by reversible S-glutathionylation, but only a few studies have documented glutathionylation-dependent changes in activity of specific proteins in a physiological context. Oxidative stress is a hallmark of many diseases which may interrupt or divert normal redox signaling and perturb protein-thiol homeostasis. Examples involving changes in S-glutathionylation of specific proteins are discussed in the context of diabetes, cardiovascular and lung diseases, cancer, and neurodegenerative diseases.

Protein tyrosine phosphatases: regulatory mechanisms

Protein-tyrosine phosphatases are tightly controlled by various mechanisms, ranging from differential expression in specific cell types to restricted subcellular localization, limited proteolysis, post-translational modifications affecting intrinsic catalytic activity, ligand binding and dimerization. Here, we review the regulatory mechanisms found to control the classical protein-tyrosine phosphatases.

Redox signals in wound healing

Physical trauma represents one of the most primitive challenges that threatened survival. Healing a problem wound requires a multi-faceted comprehensive approach. First and foremost, the wound environment will have to be made receptive to therapies. Second, the appropriate therapeutic regimen needs to be identified and provided while managing systemic limitations that could secondarily limit the healing response. Unfortunately, most current solutions seem to aim at designing therapeutic regimen with little or no consideration of the specific details of the wound environment and systemic limitations. One factor that is centrally important in making the wound environment receptive is correction of wound hypoxia. Recent work have identified that oxygen is not only required to disinfect wounds and fuel healing but that oxygen-dependent redox-sensitive signaling processes represent an integral component of the healing cascade. Over a decade ago, it was proposed that in biological systems oxidants are not necessarily always the triggers for oxidative damage and that oxidants such as H2O2 could actually serve as signaling messengers and drive several aspects of cellular signaling. Today, that concept is much more developed and mature. Evidence supporting the role of oxidants such as H2O2 as signaling messenger is compelling. A complete understanding of the continuum between the classical and emergent roles of oxygen requires a thorough consideration of current concepts in redox biology. The objective of this review is to describe our current understanding of how redox-sensitive processes may drive dermal tissue repair.

Mechanisms of reversible protein glutathionylation in redox signaling and oxidative stress

Reversible protein S-glutathionylation (protein-SSG) is an important post-translational modification, providing protection of protein cysteines from irreversible oxidation and serving to transduce redox signals. Analogous to phosphatases, glutaredoxin (GRx) enzymes catalyze deglutathionylation of proteins, regulating diverse intracellular signaling pathways. Recently, other enzymes have been reported to exhibit deglutathionylating activity, but their contribution to intracellular protein deglutathionylation is uncertain. Currently, no enzyme has been shown to serve as a catalyst of S-glutathionylation in situ, although potential prototypes are reported, including human GRx1 and the pi isoform of glutathione-S-transferase (GSTpi). Further insight into cellular mechanisms of protein glutathionylation and deglutathionylation will enrich our understanding of redox signal transduction and potentially identify new therapeutic targets for diseases in which oxidative stress perturbs normal redox signaling. Accordingly, this review focuses primarily on mechanisms of catalysis in mammalian systems.

Glutaredoxin Mediates Akt and eNOS Activation by Flow in a Glutathione Reductase-Dependent Manner

Objective— The glutathione (GSH)/glutaredoxin (Grx) system regulates activities of many redox sensitive enzymes. This system has been shown to protect cells from hydrogen peroxide–induced apoptosis by regulating the redox state of Akt. Grx can be regulated by redox state; the oxidized Grx is selectively recycled to the reduced form by GSH. Flow can maintain endothelial cells in a reduced state by activating glutathione reductase (GR) and increasing the GSH/GSSG ratio. Because steady laminar flow exerts an antioxidant effect, we hypothesized that Grx mediates flow induced Akt and eNOS phosphorylation in a GR dependent manner.

Methods and Results— Exposure of endothelial cells (ECs) to physiological steady laminar flow (shear stress=12 dyn/cm 2 ) for 5 minutes significantly increased Grx activity (1.9±0.2-fold), and also increased Akt and eNOS phosphorylation. Overexpression of GFP-GR in ECs significantly increased Grx activity by 1.6±0.1-fold. Pretreatment with the GR inhibitor 1,3-bis[2-chloroethyl]-1-nitrosourea (BCNU) for 30 minutes dramatically reduced Grx activity and inhibited the increase in Akt and eNOS phosphorylation induced by flow. Overexpression of wild-type Grx in ECs increased both Akt and eNOS phosphorylation. In contrast, a mutated Grx (C22S/C25S), which lacks thioltransferase activity, had no effect. Therefore, flow-induced Akt and eNOS phosphorylation depend on Grx thioltransferase activity. Downregulation of Grx by small interfering RNA decreased flow induced Akt and eNOS phosphorylation.

Conclusions— These data suggest that Grx is an important mediator for flow-induced Akt and eNOS activation, and Grx activity depends on GR-mediated changes in EC redox state.