Peroxiredoxins: a historical overview and speculative preview of novel mechanisms and emerging concepts in cell signaling

Thiol-based mechanisms of the thioredoxin and glutaredoxin systems: implications for diseases in the cardiovascular system

Reactive oxygen species (ROS) and the cellular thiol redox state are crucial mediators of multiple cell processes like growth, differentiation, and apoptosis. Excessive ROS production or oxidative stress is associated with several diseases, including cardiovascular disorders like ischemia-reperfusion. To prevent ROS-induced disorders, the heart is equipped with effective antioxidant systems. Key players in defense against oxidative stress are members of the thioredoxin-fold family of proteins. Of these, thioredoxins and glutaredoxins maintain a reduced intracellular redox state in mammalian cells by the reduction of protein thiols. The reversible oxidation of Cys-Gly-Pro-Cys or Cys-Pro(Ser)-Tyr-Cys active site cysteine residues is used in reversible electron transport. Thioredoxins and glutaredoxins belong to corresponding systems consisting of NADPH, thioredoxin reductase, and thioredoxin or NADPH, glutathione reductase, glutathione, and glutaredoxin, respectively. Thioredoxin as well as glutaredoxin activities appear to be very important for the progression and severity of several cardiovascular disorders. These proteins function not only as antioxidants, they inhibit or activate apoptotic signaling molecules like apoptosis signal-regulating kinase 1 and Ras or transcription factors like NF-kappaB. Thioredoxin activity is regulated by the endogenous inhibitor thioredoxin-binding protein 2 (TBP-2), indicating an important role of the balance between thioredoxin and TBP-2 levels in cardiovascular diseases. In this review, we will summarize cardioprotective effects of endogenous thioredoxin and glutaredoxin systems as well as the high potential in clinical applications of exogenously applied thioredoxin or glutaredoxin or the induction of endogenous thioredoxin and glutaredoxin systems.

Oxidative stress mediates tau-induced neurodegeneration in Drosophila

Markers of oxidative damage have been detected in brain tissue from patients with Alzheimer disease (AD) and other neurodegenerative disorders. These findings implicate oxidative injury in the neurodegenerative process, but whether oxidative stress is a cause or a consequence of neurotoxicity remains unclear. We used a Drosophila model of human tauopathies to investigate the role of oxidative stress in neurodegeneration. Genetic and pharmacological manipulation of antioxidant defense mechanisms significantly modified neurodegeneration in our model, suggesting that oxidative stress plays a causal role in neurotoxicity. We demonstrate that the JNK signaling pathway is activated in our model, which is in agreement with previous findings in AD tissue. Furthermore, we show that the extent of JNK activation correlates with the degree of tau-induced neurodegeneration. Finally, our findings suggest that oxidative stress acts not to promote tau phosphorylation, but to enhance tau-induced cell cycle activation. In summary, our study identifies oxidative stress as a causal factor in tau-induced neurodegeneration in Drosophila.

Aspects of the biological redox chemistry of cysteine: from simple redox responses to sophisticated signalling pathways

The last decade has witnessed an increased interest in cysteine modifications such as sulfenic and sulfinic acids, thiyl radicals, sulfenyl-amides and thiosulfinates, which come together to enable redox sensing, activation, catalysis, switching and cellular signalling. While glutathionylation, sulfenyl-amide formation and disulfide activation are examples of relatively simple redox responses, the sulfinic acid switch in peroxiredoxin enzymes is part of a complex signalling system that involves sulfenic and sulfinic acids and interacts with kinases and sulfiredoxin. Although the in vivo evaluation of sulfur species is still complicated by a lack of appropriate analytical techniques, research into biological sulfur species has gained considerable momentum and promises further excitement in the future.

Targeted disruption of peroxiredoxin 6 gene renders the heart vulnerable to ischemia-reperfusion injury

Peroxiredoxin 6 (Prdx6) is a novel peroxidase enzyme belonging to the Prdx family, which in mammals contains five more peroxiredoxins (Prdx1–Prdx5). Like glutathione peroxidase (GSHPx) and catalase, Prdx6 possesses H2O2-scavenging activities, and, like the former, it also removes hydroperoxides. Since significant amounts of catalase and GSHPx are present in the heart contributing toward the attenuation of H2O2 and hydroperoxides formed during ischemia-reperfusion injury and thereby providing cardioprotection, we asked whether Prdx6 also has any role in this process. In the present study we used Prdx6−/− mice to assess the role of Prdx6 in ischemic injury. Western blot analysis revealed the absence of any Prdx activity in the Prdx6−/− mouse heart, while the GSHPx-1 and catalase levels remained unchanged. Randomly selected hearts from Prdx6−/− mice and wild-type mice were subjected to 30 min of global ischemia followed by 120 min of reperfusion at normothermia. The hearts from the Prdx6−/− mice were more susceptible to ischemic reperfusion injury as evidenced by reduced recovery of left ventricular function, increased myocardial infarct size, and higher amount of apoptotic cardiomyocytes compared with wild-type mouse hearts. These Prdx6−/− hearts were also subjected to a higher amount of oxidative stress as evidenced by the presence of higher amount of malondialdehyde. The present study thus indicates a nonredundant role of Prdx6 in myocardial ischemic reperfusion injury as catalase, and GSHPx could not make up for the deficiency of Prdx6 activities.

Regulation of the yeast TSA1 peroxiredoxin by ZAP1 is an adaptive response to the oxidative stress of zinc deficiency

Zinc deficiency is a potential risk factor for disease in humans because it leads to increased oxidative stress and DNA damage. We show here that the yeast Saccharomyces cerevisiae also experiences oxidative stress when zinc-deficient, and we have identified one mechanism yeast cells use to defend themselves against this stress. The Zap1p transcription factor is a central player in the response of yeast to zinc deficiency. To identify genes important for growth in low zinc, DNA microarrays were used to identify genes directly regulated by Zap1p. We found that the TSA1 gene is one such Zap1p target whose expression is increased under zinc deficiency. TSA1 encodes a cytosolic thioredoxin-dependent peroxidase responsible for degrading hydrogen peroxide and organic hydroperoxides. Consistent with its regulation by Zap1p, we showed that tsa1delta mutants have a growth defect in low zinc that can be suppressed by zinc but not by other metals. Anaerobic conditions also suppressed the tsa1delta low zinc growth defect indicating that oxidative stress is the likely cause of the poor growth. Consistent with this hypothesis, we demonstrated that zinc deficiency causes increased reactive oxygen species in wild type cells and that this increase is further exacerbated in tsa1delta mutants. The role of this regulation by Zap1p in limiting oxidative stress in low zinc was confirmed when the Zap1p-binding site was specifically mutated in the chromosomal TSA1 promoter. Thus, we conclude that TSA1 induction by Zap1p is an adaptive response to deal with the increased oxidative stress caused by zinc deficiency.

Oxidative stress impairs heme detoxification in the midgut of the cattle tick, Rhipicephalus (Boophilus) microplus

In the cattle tick Rhipicephalus (Boophilus) microplus digestion of blood is intracellular, accomplished by the so-called digest cells that fill the midgut lumen. Hydrolysis of hemoglobin in the digestive vesicles of these cells results in the release of large amounts of heme, a pro-oxidant compound, whose iron atom, together with H(2)O(2), may participate in the Fenton reaction and lead to the production of hydroxyl radicals. Here, we investigated the role of catalase, an enzyme responsible for H(2)O(2) detoxification. Fully engorged female ticks injected with 3-amino-1,2,4-triazole (AT), a catalase inhibitor, showed increased H(2)O(2) in the gut, together with diminished life span and lower egg-laying rates. Increased mortality observed upon AT injection was reversed by further injection of exogenous catalase, 2 days after AT treatment, confirming that increased death was due to inhibition of this enzyme by AT. In primary cultures of digest cells, intracellular H(2)O(2) is limited to specific organelles, while treatment with AT in vitro resulted in increased H(2)O(2) spreading all over the cell, confirming the role of catalase in regulating H(2)O(2) levels. Ticks fed on a calf that had been injected with AT showed marked inhibition of catalase activity in the gut and diminished life span, oviposition and engorgement. Digest cells of these ticks had an altered morphology, showing heme spread all over the cytosol, instead of being limited to the hemosomes. The amount of aggregated heme found in isolated hemosome was also strongly decreased in AT-treated cattle. All together, our results indicate that catalase performs an important role in the control of redox balance in R. microplus, which dramatically affects hemosome formation and stability. This enzyme may be a target in the development of new methods for tick control.

Redox control of neural function: background, mechanisms, and significance

The redox environment within neural cells is dependent on a series of redox couples. The glutathione disulfide/ glutathione (GSSG/GSH) redox pair forms the major redox couple in cells and as such plays a critical role in regulating redox-dependent cellular functions. Not only does GSH act as an antioxidant but it also can modulate the activity of a variety of different proteins via S-glutathionylation of cysteine sulfhydryl groups. The thioredoxin system also makes a significant contribution to the redox environment by reducing inter- and intrachain protein disulfide bonds as well as maintaining the activity of important antioxidant enzymes such as peroxiredoxins and methionine sulfoxide reductases. The redox environment affects the activity and function of a number of different protein phosphatases, protein kinases, and transcription factors. The sum of these effects will determine how changes in the redox environment alter overall cellular function, thereby playing a fundamental role in regulating neural cell fate and physiology.

Oxidative stress in ALS: A mechanism of neurodegeneration and a therapeutic target

The cause(s) of amyotrophic lateral sclerosis (ALS) is not fully understood in the vast majority of cases and the mechanisms involved in motor neuron degeneration are multi-factorial and complex. There is substantial evidence to support the hypothesis that oxidative stress is one mechanism by which motor neuron death occurs. This theory becomes more persuasive with the discovery that mutation of the anti-oxidant enzyme, superoxide dismutase 1 (SOD1), causes disease in a significant minority of cases. However, the precise mechanism(s) by which mutant SOD1 leads to motor neuron degeneration have not been defined with certainty, and trials of anti-oxidant therapies have been disappointing. Here, we review the evidence implicating oxidative stress in ALS pathogenesis, discuss how oxidative stress may affect and be affected by other proposed mechanisms of neurodegeneration, and review the trials of various anti-oxidants as potential therapies for ALS.

Oxidative stress and growth-regulating intracellular signaling pathways in cardiac myocytes

The toxic effects of oxidative stress on cells (including cardiac myocytes, the contractile cells of the heart) are well known. However, an increasing body of evidence has suggested that increased production of reactive oxygen species (ROS) promotes cardiac myocyte growth. Thus, ROS may be 'second messenger' molecules in their own right, and growth-promoting neurohumoral agonists might exert their effects by stimulating production of ROS. The authors review the principal growth-promoting intracellular signaling pathways that are activated by ROS in cardiac myocytes, namely the mitogen-activated protein kinase cascades (extracellular signal-regulated kinases 1/2, c-Jun N-terminal kinases, and p38-mitogen-activated protein kinases) and the phosphoinositide 3-kinase/protein kinase B (Akt) pathway. Possible mechanisms are discussed by which these pathways are activated by ROS, including the oxidation of active site cysteinyl residues of protein and lipid phosphatases with their consequent inactivation, the potential involvement of protein kinase C or the apoptosis signal-regulating kinase 1, and the current models for the activation of the guanine nucleotide binding protein Ras.

The thioredoxin system in cancer

Thioredoxin (Trx), NADPH and thioredoxin reductase (TrxR) comprise a thioredoxin system which exists in nearly all living cells. It functions in thiol-dependent thiol-disulfide exchange reactions crucial to control of the reduced intracellular redox environment, cellular growth, defense against oxidative stress or control of apoptosis and has multi-facetted roles in mammalian cells including implications in cancer. Eg reduced Trx activates DNA binding of transcription factors and is involved in antioxidant defense through repair of oxidatively damaged proteins or as an electron donor to peroxiredoxins. The Trx system functions in synthesis of deoxyribonucleotides for DNA synthesis, both replication and repair, by ribonucleotide reductase. Trx and truncated Trx (Trx80) act in modulation of immune cell function. TrxR isoforms in the cytosol and the mitochondria are essential selenoenzymes with a selenocysteine in the active site. These enzymes display a remarkably broad substrate specificity but are also targets for existing chemotherapeutic drugs. Mammalian TrxR enzymes are linked to selenium metabolism as a result of being selenoproteins, but can also directly reduce low molecular selenium compounds like selenite and have been implicated in the chemoprevention effects of selenium against cancer. Numerous scientific reports describe higher expression of Trx and TrxR in some, but not all tumors. Some data suggest that high Trx could be linked to resistance to chemotherapies while others suggest that high Trx and TrxR may induce apoptosis and reduce the mitotic index of certain tumors linked to the p53 dependent cell death. Recent data suggest that TrxR is essential for the carcinogenic process and invasive phenotype of cancer. Both Trx and TrxR have been regarded as interesting targets for chemotherapy.

Oxidative stress in Schizosaccharomyces pombe: different H2O2 levels, different response pathways

Schizosaccharomyces pombe triggers different signalling pathways depending on the severity of the oxidative stress exerted, the main ones being the Pap1 and the Sty1 pathways. The Pap1 transcription factor is more sensitive to hydrogen peroxide (H(2)O(2)) than the MAP kinase Sty1 pathway, and is designed to induce adaptation, rather than survival, responses. The peroxiredoxin Tpx1 acts as a H(2)O(2) sensor and the upstream activator of the Pap1 pathway. Therefore, sensitivity to H(2)O(2) depends on this thioredoxin peroxidase. In order to achieve maximal activation of the MAP kinase pathway, the concentration of H(2)O(2) needs to be at least fivefold higher than that to fully activate Pap1. Tpx1 is a H(2)O(2) scavenger, thus its peroxidase activity is essential for aerobic growth. As described for other eukaryotic peroxiredoxins, high doses of H(2)O(2) temporarily inactivate Tpx1 and delay Pap1 activation, whereas the Sty1 pathway remains fully functional under these conditions. As part of the Sty1-dependent transcriptional response, the expression of Srx1 is induced and this reductase re-activates the over-oxidised Tpx1. Therefore, the antioxidant pathways of the fission yeast are perfectly designed so that the transcriptional programs triggered by the different signalling pathways never overlap.

Proteins identified as targets of the acyl glucuronide metabolite of mycophenolic acid in kidney tissue from mycophenolate mofetil treated rats

Covalent binding of the acyl glucuronide (AcMPAG) metabolite of the immunosuppressant mycophenolic acid (MPA) to proteins is considered a possible initiating event for organ toxicity. Since the kidney is involved in the formation and excretion of AcMPAG, it can be hypothesized that this tissue may be exposed to relatively high concentrations of this metabolite and would, therefore, be a particularly suitable organ to investigate AcMPAG protein targets. In the present study we identified potential AcMPAG target proteins in kidney tissues from Wistar rats treated with mycophenolate mofetil (40 mg/kg/day over 21 days). Proteins were separated by 2-DE and covalent protein adducts were detected by Western blotting with an antibody specific for MPA/AcMPAG. The corresponding coomassie blue stained proteins from parallel gels were subjected to in-gel tryptic digestion and peptides were characterized on a Q-TOF Ultima Global. The protein targets were further verified by immunoprecipitation with anti-MPA/AcMPAG antibody to purify the modified proteins followed by 1-DE and MS analysis. Database searches revealed several AcMPAG target proteins that could be related to ultrastructural abnormalities, metabolic effects, and altered oxidative stress/detoxification responses. Predominately cytosolic proteins such as selenium binding protein, protein disulfide isomerase, aldehyde dehydrogenase, triosephosphate isomerase, and kidney aminoacylase were involved in adduct formation. Two cytoskeletal proteins tropomyosin 1 and 4 as well as the antioxidant proteins peroxiredoxin 3 and 6 were also targets of AcMPAG. Functional consequences from these protein modifications remain to be demonstrated.

Characterization of cell wall associated proteins of a Staphylococcus aureus isolated from bovine mastitis case by a proteomic approach

Staphylococcus aureus causes different pathologies in humans and animals. In particular, it is involved in intramammary infections in cows, causing economic losses and milk-safety problems. Although it is well-known that surface components (proteins and capsular polysaccharides) and exotoxins are virulence factors involved in the pathogenesis of bovine mastitis, less is known about the precise biochemical identity of such molecules. Therefore, mapping of surface proteins using specific disease- and environment-isolates provides a benchmark for strain comparison of pathogens with different pathogenic characteristics and antibiotic resistance mechanism and can aid in defining specific vaccine and therapeutic targets. In this study, we used a proteomic approach on protein extracts of lysostaphin-treated S. aureus in isotonic conditions, to produce a reproducible and well resolved 2-D electrophoresis (2-DE) reference map of surface associated proteins of isolated S. aureus from a case of bovine mastitis. The most abundant protein components were identified by Matrix assisted laser desorption ionisation-time of flight (MALDI-TOF) mass spectrometry.

The Prx Q protein ofArabidopsis thalianais a member of the luminal chloroplast proteome

Peroxiredoxins have been discovered in many organisms ranging from eubacteria to mammals, and their known biological functions include both oxidant defense and signal transduction. The genome of Arabidopsis thaliana encodes for ten individual peroxiredoxins, of which four are located in the chloroplast. The best-characterized member of the chloroplast peroxiredoxins is 2-Cys Prx that is associated with the stroma side of the thylakoid membrane and is considered to participate in antioxidant defense and protection of photosynthesis. This study addressed the chloroplast peroxiredoxin Prx Q and showed that its subcellular location is the lumen of the thylakoid membrane. To get insight in the biological function of the Prx Q protein of Arabidopsis, the protein levels of the Prx Q protein in thylakoid membranes were studied under different light conditions and oxidative stress. A T-DNA knockout mutant of Prx Q did not show any visible phenotype and had normal photosynthetic performance with a slightly increased oxygen evolving activity.

Structural and biochemical characterization of a mitochondrial peroxiredoxin from Plasmodium falciparum

Plasmodium falciparum possesses a single mitochondrion with a functional electron transport chain. During respiration, reactive oxygen species are generated that need to be removed to protect the organelle from oxidative damage. In the absence of catalase and glutathione peroxidase, the parasites rely primarily on peroxiredoxin-linked systems for protection. We have analysed the biochemical and structural features of the mitochondrial peroxiredoxin and thioredoxin of P. falciparum. The mitochondrial localization of both proteins was confirmed by expressing green fluorescent protein fusions in parasite erythrocytic stages. Recombinant protein was kinetically characterized using the cytosolic and the mitochondrial thioredoxin (PfTrx1 and PfTrx2 respectively). The peroxiredoxin clearly preferred PfTrx2 to PfTrx1 as a reducing partner, reflected by the KM values of 11.6 microM and 130.4 microM respectively. Substitution of the two dyads asparagine-62/tyrosine-63 and phenylalanine-139/alanine-140 residues by aspartate-phenylalaine and valine-serine, respectively, reduced the KM for Trx1 but had no effect on the KM of Trx2 suggesting some role for these residues in the discrimination between the two substrates. Solution studies suggest that the protein exists primarily in a homodecameric form. The crystal structure of the mitochondrial peroxiredoxin reveals a fold typical of the 2-Cys class peroxiredoxins and a dimeric form with an intermolecular disulphide bridge between Cys67 and Cys187. These results show that the mitochondrial peroxiredoxin of P. falciparum occurs in both dimeric and decameric forms when purified under non-reducing conditions.

2-Cys peroxiredoxins from Schistosoma japonicum: The expression profile and localization in the life cycle

Peroxiredoxin (Prx) is known to be an antioxidant protein that protects the organisms against various oxidative stresses and functions as a signal transductor. Here, we determined the full-length cDNA sequences of three types of Prx from an Asian blood fluke, Schistosoma japonicum: Prx-1, Prx-2 and Prx-3. According to the deduced amino acid sequences, only Prx-3 had a mitochondria-targeting sequence. Using RT-PCR, it was shown that these Prx genes were constitutively expressed in the eggs, cercariae and adult worms of the schistosome. Western blot analysis using antisera specific for each Prx revealed that all the three Prx proteins existed in these developmental stages. By immunolocalization analysis, Prx-1 existed on the surface of a miracidium and in the space between a miracidium and an eggshell. Furthermore, Prx-1 was deposited in the host tissues around the eggs. In adult worms, Prx-1 was not only expressed in the tegument, but also contained in their excretory/secretory products. The surface of the 7 day-schistosomula was stained with anti-Prx-1 antiserum. On the other hand, Prx-2 only existed inside the miracidia in eggs. In addition, Prx-2 was mainly detected in the sub-tegumental tissues, parenchyma, vitelline gland and gut epithelium of the adult worms, but was not detected in the tegument of adults and schistosomula. Taken together with previous reports by other investigators, these data suggest that Prx-1 acts to protect the parasite against the ROS produced by host immune cells, and that Prx-2 plays important roles in intracellular redox signaling and/or in the reduction of ROS generated through the hemoglobinolytic process in the digestive tract.

Proteomic analysis of phosphorylation, oxidation and nitrosylation in signal transduction

Signal transduction pathways control cell fate, survival and function. They are organized as intricate biochemical networks which enable biochemical protein activities, crosstalk and subcellular localization to be integrated and tuned to produce highly specific biological responses in a robust and reproducible manner. Post translational Modifications (PTMs) play major roles in regulating these processes through a wide variety of mechanisms that include changes in protein activities, interactions, and subcellular localizations. Determining and analyzing PTMs poses enormous challenges. Recent progress in mass spectrometry (MS) based proteomics have enhanced our capability to map and identify many PTMs. Here we review the current state of proteomic PTM analysis relevant for signal transduction research, focusing on two areas: phosphorylation, which is well established as a widespread key regulator of signal transduction; and oxidative modifications, which from being primarily viewed as protein damage now start to emerge as important regulatory mechanisms.

Extracellular thioredoxin and thioredoxin-binding protein 2 in control of cancer

Thioredoxin-1 (TRX) is a redox-active protein with multiple intracellular and extracellular functions. Intracellular redox balance is maintained by the TRX family and its related molecules. Extracellular TRX shows cytoprotective effects, while truncated Trx80 has more mitogenic activity. Exogenously administered TRX does not promote the growth of cancer in vivo and shows anti-chemotactic effect for neutrophils and anti-inflammatory functions. Thioredoxin is released from cells in response to oxidative stress and TRX levels in plasma or serum are good markers for oxidative stress associated with cancer. Thioredoxin-binding protein 2 (TBP-2) is an endogenous negative regulator of TRX and a tumor suppressor.

Redox-sensitive kinases of the nuclear factor-kappaB signaling pathway

NF-kappaB is an inducible transcription factor that plays a role in the expression of over one hundred genes involved in immunity, inflammation, proliferation, and in defense against apoptosis. NF-kappaB has been known to be redox regulated for some time and is a direct target for oxidation that can affect its ability to bind to DNA. Reactive oxygen species (ROS) have been identified as second messengers in cells, and play a role in receptor signaling and posttranslation modification of signaling molecules. These posttranslation modifications include oxidations of critical cysteines to sulfenic acids or mixed disulfides, which can affect the activity of proteins. Many kinases involved in direct or indirect activation of NF-kappaB are affected by oxidants and therefore, have the potential to alter NF-kappaB activity. This review will provide a summary of the NF-kappaB family, their activation and regulation, followed by a summary of cytoplasmic and nuclear kinases in this pathway whose activity is affected by oxidants. Additionally, recent investigations have revealed that the JNK signaling pathway, which is known to be redox regulated, and pro-apoptotic, is inhibited by NF-kappaB signaling. The crosstalk of NF-kappaB with other signaling pathways is therefore critical for cellular fate, notably survival or cell death under oxidative conditions, and will also be reviewed.

Thioredoxins, glutaredoxins, and glutathionylation: new crosstalks to explore

Oxidants are widely considered as toxic molecules that cells have to scavenge and detoxify efficiently and continuously. However, emerging evidence suggests that these oxidants can play an important role in redox signaling, mainly through a set of reversible post-translational modifications of thiol residues on proteins. The most studied redox system in photosynthetic organisms is the thioredoxin (TRX) system, involved in the regulation of a growing number of target proteins via thiol/disulfide exchanges. In addition, recent studies suggest that glutaredoxins (GRX) could also play an important role in redox signaling especially by regulating protein glutathionylation, a post-translational modification whose importance begins to be recognized in mammals while much less is known in photosynthetic organisms. This review focuses on oxidants and redox signaling with particular emphasis on recent developments in the study of functions, regulation mechanisms and targets of TRX, GRX and glutathionylation. This review will also present the complex emerging interplay between these three components of redox-signaling networks.

Oxidative stress and neurodegeneration: where are we now?

The brain and nervous system are prone to oxidative stress, and are inadequately equipped with antioxidant defense systems to prevent 'ongoing' oxidative damage, let alone the extra oxidative damage imposed by the neurodegenerative diseases. Indeed, increased oxidative damage, mitochondrial dysfunction, accumulation of oxidized aggregated proteins, inflammation, and defects in protein clearance constitute complex intertwined pathologies that conspire to kill neurons. After a long lag period, therapeutic and other interventions based on a knowledge of redox biology are on the horizon for at least some of the neurodegenerative diseases.

Attenuation of doxorubicin-induced contractile and mitochondrial dysfunction in mouse heart by cellular glutathione peroxidase

The cardiac toxicity of doxorubicin (DOX), a potent anticancer anthracycline antibiotic, is believed to be mediated through the generation of reactive oxygen species (ROS) in cardiomyocytes. This study aims to determine the function of cellular glutathione peroxidase (Gpx1), which is located in both mitochondria and cytosol, in defense against DOX-induced cardiomyopathy using a line of transgenic mice with cardiac overexpression of Gpx1. The Gpx1-overexpressing hearts were markedly more resistant than nontransgenic hearts to DOX-induced acute functional derangements, including impaired contractility and diastolic properties, decreased coronary flow rate, and reduced heart rate. In addition, DOX treatment impairs mitochondrial function of nontransgenic hearts as evident in a decreased rate of NAD-linked State 3 respiration, presumably a result of inactivation of complex I activity. This is associated with increases in the rates of NAD- and FAD-linked State 4 respiration and declines in P/O ratio, suggesting that the electron transfer and oxidative phosphorylation are uncoupled in these mitochondrial samples. These functional deficits of mitochondria could be largely prevented by Gpx1 overexpression. Taken together, these studies provide new evidence to further support the role of ROS, particularly H(2)O(2) and/or fatty acid hydroperoxides, in causing contractile and mitochondrial dysfunction in mouse hearts acutely exposed to DOX.

Endogenous anti-oxidants in pregnancy and preeclampsia

Oxidative stress has been implicated in a wide variety of diseases and degenerative states including cancer, rheumatoid arthritis, cardiovascular disease and ageing. There is now considerable evidence to suggest that pregnancy leads to the generation of an increased oxidative burden, but whether this overwhelms the anti-oxidant capacity within the placenta and/or the peripheral circulation remains a point of conjecture. There is little doubt that oxidative stress is a significant contributor in the pathogenesis of preeclampsia. The use of exogenous anti-oxidants such as vitamins C and E in the prevention of preeclampsia is the subject of several large clinical trials currently being conducted in many countries around the world. The results of these studies are eagerly awaited, but what of the endogenous anti-oxidant systems that have evolved to combat the oxidative burden associated with living in an aerobic environment? This review will focus on several important anti-oxidant enzyme systems, their role in pregnancy and the evidence to suggest that endogenous anti-oxidants are important in the development of complications of pregnancy such as preeclampsia.

Human retinoic acid receptor-related orphan receptor alpha1 overexpression protects neurones against oxidative stress-induced apoptosis

Retinoic acid receptor-related orphan receptor alpha (RORalpha) is a transcription factor belonging to the superfamily of nuclear receptors. Disruption of the Rora gene in the mouse results in a defect in the development of Purkinje cells leading to a cerebellar atrophy, which suggests a neuroprotective role for RORalpha. To test this hypothesis, the survival rate of lentiviral-mediated human RORalpha1-overexpressing neurones has been evaluated in response to different stressors disturbing the redox homeostasis, such as beta-amyloid peptide, c(2)-ceramide and H(2)O(2). We show that overexpression of human RORalpha1 provides neuroprotection by increasing the expression of the antioxidant proteins glutathione peroxidase 1 and peroxiredoxin 6, leading to a reduction in the accumulation of stress-induced reactive oxygen species. We further demonstrate that the neuroprotective effect of RORalpha is predominantly mediated by glutathione peroxidase 1 and peroxiredoxin 6. These results suggest a new role for RORalpha in the control of the neuronal oxidative stress and thus represents a new transcription factor of interest in the regulation of reactive oxygen species-induced neurodegenerative processes during ageing.

Transforming growth factor-beta1 induces the non-classical secretion of peroxiredoxin-I in A549 cells

Recent studies found that peroxiredoxin-I (Prx-I) is secreted from A549 cells although it does not contain a signal peptide and is known to be a cytosolic protein. Transforming growth factor-beta1 (TGF-beta1) treatment dramatically enhanced Prx-I secretion from A549 cells, and this effect was not inhibited by brefeldin A. Further investigation revealed that A549 cells constitutively secrete TGF-beta1. Furin, a TGF-beta1-converting enzyme, was also highly activated in A549 cells. Ectopic expression of alpha(1)-antitrypsin Portland (alpha(1)-PDX), a potent furin inhibitor, blocked both TGF-beta1 activation and Prx-I secretion. Our findings collectively suggest that non-classical secretion of Prx-I is induced by TGF-beta1, which is constitutively activated by furin in A549 cells.

Engineering functional artificial hybrid proteins between poplar peroxiredoxin II and glutaredoxin or thioredoxin

The existence of natural peroxiredoxin-glutaredoxin hybrid enzymes in several bacteria is in line with previous findings indicating that poplar peroxiredoxin II can use glutaredoxin as an electron donor. This peroxiredoxin remains however unique since it also uses thioredoxin with a quite good efficiency. Based on the existing fusions, we have created artificial enzymes containing a poplar peroxiredoxin module linked to glutaredoxin or thioredoxin modules. The recombinant fusion enzymes folded properly into non-covalently bound homodimers or homotetramers. Two of the three protein constructs exhibit peroxidase activity, a reaction where the two modules need to function together, but they also display enzymatic activities specific of each module. In addition, mass spectrometry analyses indicate that the Prx module can be both glutathiolated or overoxidized in vitro. This is discussed in the light of the Prx reactivity.

Reactive oxygen species-mediated mitochondria-to-nucleus signaling: a key to aging and radical-caused diseases

Mitochondria-generated reactive oxygen species have been implicated as a common feature that connects aging of organisms and age-related diseases. Efficient elimination of these radicals by antioxidants correlates with increased life span. Understanding how the mitochondrion signals to the nucleus to regulate antioxidant proteins might be a key to aging processes and treatment of human diseases.

Redox balance mechanisms in Schistosoma mansoni rely on peroxiredoxins and albumin and implicate peroxiredoxins as novel drug targets

Schistosoma mansoni, a causative agent of schistosomiasis, resides in the hepatic portal circulation of their human host up to 30 years without being eliminated by the host immune attack. Production of an antioxidant "firewall," which would neutralize the oxidative assault generated by host immune defenses, is one proposed survival mechanism of the parasite. Schistosomes lack catalase, the main H2O2-neutralizing enzyme of many organisms, and their glutathione peroxidases are in the phospholipid class with poor reactivity toward H2O2. Evidence implicates peroxiredoxins (Prx) as providing the main enzymatic activity to reduce H2O2 in the parasite. Quantitative monitoring of Prx mRNAs during parasite life cycle indicated that Prx proteins are differentially expressed, with highest expression occurring in adult stages (oxidative resistant stages). Incubation of schistosomula with Prx1 double-stranded RNA knocked down total Prx enzymatic activity and resulted in lowered survival of cultured parasites compared with controls demonstrating that Prx are essential parasite proteins. These results represent the first report of lethal gene silencing in Schistosoma. Investigation of downstream effects of Prx silencing revealed an abrupt increase of lipid peroxides and the generation of several oxidized proteins. Using mass spectrometry, parasite albumin and actin were identified as the main oxidized proteins. Gene expression analysis showed that schistosome albumin was induced by oxidative stress. This study highlights Prx proteins as essential parasite proteins and potential new targets for anti-schistosome drug development and albumin as a novel, sacrificial oxidant scavenging protein in parasite redox regulation.

Molecular mechanism of the reduction of cysteine sulfinic acid of peroxiredoxin to cysteine by mammalian sulfiredoxin

Among many proteins with cysteine sulfinic acid (Cys-SO2H) residues, the sulfinic forms of certain peroxiredoxins (Prxs) are selectively reduced by sulfiredoxin (Srx) in the presence of ATP. All Srx enzymes contain a conserved cysteine residue. To elucidate the mechanism of the Srx-catalyzed reaction, we generated various mutants of Srx and examined their interaction with PrxI, their ATPase activity, and their ability to reduce sulfinic PrxI. Our results suggest that three surface-exposed amino acid residues, corresponding to Arg50, Asp57, and Asp79 of rat Srx, are critical for substrate recognition. The presence of the sulfinic form (but not the reduced form) of PrxI induces the conserved cysteine of Srx to take the gamma-phosphate of ATP and then immediately transfers the phosphate to the sulfinic moiety of PrxI to generate a sulfinic acid phosphoryl ester (Prx-Cys-S(=O)OPO3(2-)). This ester is reductively cleaved by a thiol molecule (RSH) such as GSH, thioredoxin, and dithiothreitol to produce a disulfide-S-monoxide (Prx-Cys-S(=O)-S-R). The disulfide-S-monoxide is further reduced through the oxidation of three thiol equivalents to complete the catalytic cycle and regenerate Prx-Cys-SH.

Hydrogen peroxide: a signaling messenger

Hydrogen peroxide (H2O2) is a well-documented component of living cells. It plays important roles in host defense and oxidative biosynthetic reactions. In addition there is growing evidence that at low levels, H2O2 also functions as a signaling agent, particularly in higher organisms. This review evaluates the evidence that H2O2 functions as a signaling agent in higher organisms in light of the known biology and biochemistry of H2O2. All aerobic organisms studied to date from prokaryotes to humans appear to tightly regulate their intracellular H2O2 concentrations at relatively similar levels. Multiple biochemical strategies for rapidly reacting with these low endogenous levels of H2O2 have been elucidated from the study of peroxidases and catalases. Well-defined biochemical pathways involved in the response to exogenous H2O2 have been described in both prokaryotes and yeast. In animals and plants, regulated enzymatic systems for generating H2O2 have been described. In addition oxidation-dependent steps in signal transduction pathways are being uncovered, and evidence is accumulating regarding the nature of the specific reactive oxygen species involved in each of these pathways. Application of physiologic levels of H2O2 to mammalian cells has been shown to stimulate biological responses and to activate specific biochemical pathways in these cells.

Single-site oxidation, cysteine 108 to cysteine sulfinic acid, in D-amino acid oxidase from Trigonopsis variabilis and its structural and functional consequences

One of the primary sources of enzyme instability is protein oxidative modification triggering activity loss or denaturation. We show here that the side chain of Cys108 is the main site undergoing stress-induced oxidation in Trigonopsis variabilis d-amino acid oxidase, a flavoenzyme employed industrially for the conversion of cephalosporin C. High-resolution anion-exchange chromatography was used to separate the reduced and oxidized protein forms, which constitute, in a molar ratio of about 3:1, the active biocatalyst isolated from the yeast. Comparative analysis of their tryptic peptides by electrospray tandem mass spectrometry allowed unequivocal assignment of the modification as the oxidation of Cys108 into cysteine sulfinic acid. Cys108 is likely located on a surface-exposed protein region within the flavin adenine dinucleotide (FAD) binding domain, but remote from the active center. Its oxidized side chain was remarkably stable in solution, thus enabling the relative biochemical characterization of native and modified enzyme forms. The oxidation of Cys108 causes a global conformational response that affects the protein environment of the FAD cofactor. In comparison with the native enzyme, it results in a fourfold-decreased specific activity, reflecting a catalytic efficiency for reduction of dioxygen lowered by about the same factor, and a markedly decreased propensity to aggregate under conditions of thermal denaturation. These results open up unprecedented routes for stabilization of the oxidase and underscore the possible significance of protein chemical heterogeneity for biocatalyst function and stability.

The Saccharomyces cerevisiae proteome of oxidized protein thiols: contrasted functions for the thioredoxin and glutathione pathways

Protein thiol oxidation subserves important biological functions and constitutes a sequel of reactive oxygen species toxicity. We developed two distinct thiol-labeling approaches to identify oxidized cytoplasmic protein thiols in Saccharomyces cerevisiae. Inone approach, we used N-(6-(biotinamido)hexyl)-3'-(2'-pyridyldithio)-propionamide to purify oxidized protein thiols, and in the other, we used N-[(14)C]ethylmaleimide to quantify this oxidation. Both approaches showed a large number of the same proteins with oxidized thiols ( approximately 200), 64 of which were identified by mass spectrometry. We show that, irrespective of its mechanism, protein thiol oxidation is dependent upon molecular O(2). We also show that H(2)O(2) does not cause de novo protein thiol oxidation, but rather increases the oxidation state of a select group of proteins. Furthermore, our study reveals contrasted differences in the oxidized proteome of cells upon inactivation of the thioredoxin or GSH pathway suggestive of very distinct thiol redox control functions, assigning an exclusive role for thioredoxin in H(2)O(2) metabolism and the presumed thiol redox buffer function for GSH. Taken together, these results suggest the high selectivity of cytoplasmic protein thiol oxidation.

Transformation of adult retina from the regenerative to the axonogenesis state activates specific genes in various subsets of neurons and glial cells

The purpose of this study was to identify the gene expression profile of the regenerating retina in vitro. To achieve this goal, three experimental groups were studied: (1) an injury control group (OC-LI group) that underwent open crush (OC) of the optic nerve and lens injury (LI) in vivo; (2) an experimental group (OC-LI-R group) that comprised animals treated like those in the OC-LI group except that retinal axons were allowed to regenerate (R) in vitro; and (3) an experimental group (OC-LI-NR group) that comprised animals treated as those in the OC-LI group, except that the retinas were cultured in vitro with the retinal ganglion cell (RGC) layer facing upwards to prevent axonal regeneration (NR). Gene expression in each treatment group was compared to that of untreated controls. Immunohistochemistry was used to examine whether expression of differentially regulated genes also occurred at the protein level and to localize these proteins to the respective retinal cells. Genes that were regulated belonged to different functional categories such as antioxidants, antiapoptotic molecules, transcription factors, secreted signaling molecules, inflammation-related genes, and others. Comparison of changes in gene expression among the various treatment groups revealed a relatively small cohort of genes that was expressed in different subsets of cells only in the OC-LI-R group; these genes can be considered to be regeneration-specific. Our findings demonstrate that axonal regeneration of RGC involves an orchestrated response of all retinal neurons and glia, and could provide a platform for the development of therapeutic strategies for the regeneration of injured ganglion cells.

Effective detection of peptides containing cysteine sulfonic acid using matrix-assisted laser desorption/ionization and laser desorption/ionization on porous silicon mass spectrometry

Cysteine sulfonic acid-containing peptides, being typical acidic peptides, exhibit low response in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. In this study, matrix conditions and the effect of diammonium hydrogencitrate (DAHC) as additive were investigated for ionization of cysteine sulfonic acid-containing peptides in MALDI. A matrix-free ionization method, desorption/ionization on porous silicon (DIOS), was also utilized to evaluate the effect of DAHC. When equimolar three-component mixtures of peptides carrying free cysteine, cysteine sulfonic acid, and carbamidomethyl cysteine were measured by MALDI using a common matrix, alpha-cyano-4-hydroxycinnamic acid (CHCA), no signal corresponding to cysteine sulfonic acid-containing peptide could be observed in the mass spectrum. However, by addition of DAHC to CHCA, the peaks of cysteine sulfonic acid-containing peptides were successfully observed, as well as when using 2,4,6-trihydroxyacetophenone (THAP) and 2,6-dihydroxyacetophenone with DAHC. In the DIOS mass spectra of these analytes, the use of DAHC also enhanced the peak intensity of the cysteine sulfonic acid-containing peptides. On the basis of studies with these model peptides, tryptic digests of oxidized peroxiredoxin 6 were examined as a complex peptide mixture by MALDI and DIOS. In MALDI, the peaks of cysteine sulfonic acid-containing peptides were observed when using THAP/DAHC as the matrix, but this was not so with CHCA. In DIOS, the signal from cysteine sulfonic acid-containing peptides was suppressed; however, the use of DAHC significantly enhanced the signal intensity with an increase in the number of observed peptides and increased signal-to-noise ratio in the DIOS spectra. The results show that DAHC in the matrix or on the DIOS chip decreases discrimination and suppression effects in addition to suppressing alkali-adduct ions, which leads to a beneficial effect on protonation of peptides containing cysteine sulfonic acid.

Redox modifications of protein-thiols: emerging roles in cell signaling

Glutathione represents the major low molecular weight antioxidant redox recycling thiol in mammalian cells and plays a central role in the cellular defence against oxidative damage. Classically glutathione has been known to provide the cell with a reducing environment in addition to maintaining the proteins in a reduced state. Emerging evidences suggest that the glutathione redox status may entail dynamic regulation of protein function by reversible disulfide bond formation. The formation of inter- and intramolecular disulfides as well as mixed disulfides between protein cysteines and glutathione, i.e., S-glutathiolation, has now been associated with the stabilization of extracellular proteins, protection of proteins against irreversible oxidation of critical cysteine residues, and regulation of enzyme functions and transcription. Regulation of DNA binding of redox-dependent transcription factors such as nuclear factor-kappaB, p53, and activator protein-1, has been suggested as one of the mechanisms by which cells may transduce oxidative stress redox signaling into an inducible expression of a wide variety of genes implicated in cellular changes such as proliferation, differentiation, and apoptosis. However, the molecular mechanisms linking the glutathione cellular redox state to a reversible oxidation of various signaling proteins are still poorly understood. This commentary discusses the emerging concept of protein-S-thiolation, protein-S-nitrosation and protein-SH (formation of sulfenic, sulfinic and sulfonic acids) in redox signaling during normal physiology and under oxidative stress in controlling the cellular processes.

Thiol redox control via thioredoxin and glutaredoxin systems

The Trx (thioredoxin) and Grx (glutaredoxin) systems control cellular redox potential, keeping a reducing thiol-rich intracellular state, which on generation of reactive oxygen species signals through thiol redox control mechanisms. Here, we give a brief overview of the human Trx and Grx systems. The main part focuses on our current knowledge about mitochondrial Grx2, which facilitates mitochondrial redox homoeostasis during oxidative stress-induced apoptosis.

2-Cys peroxiredoxin function in intracellular signal transduction: therapeutic implications

H(2)O(2) is a reactive oxygen species that has drawn much interest because of its role as a second messenger in receptor-mediated signaling. Mammalian 2-Cys peroxiredoxins have been shown to eliminate efficiently the H(2)O(2) generated in response to receptor stimulation. 2-Cys peroxiredoxins are members of a novel peroxidase family that catalyze the H(2)O(2) reduction reaction in the presence of thioredoxin, thioredoxin reductase and NADPH. Several lines of evidence suggest that 2-Cys peroxiredoxins have dual roles as regulators of the H(2)O(2) signal and as defenders of oxidative stress. In particular, 2-Cys peroxiredoxin appears to provide selective, specific and localized control of receptor-mediated signal transduction. Thus, the therapeutic potential of 2-Cys peroxiredoxins is clear for diseases, such as cancer and cardiovascular diseases, that involve reactive oxygen species.