The Conundrum of Hydrogen Peroxide Signaling and the Emerging Role of Peroxiredoxins as Redox Relay Hubs

Tsa1 is the dominant peroxide scavenger and a source of H2O2-dependent GSSG production in yeast

Hydrogen peroxide (H2O2) is an important biological molecule, functioning both as a second messenger in cell signaling and, especially at higher concentrations, as a cause of cell damage. Cells harbor multiple enzymes that have peroxide reducing activity in vitro. However, the contribution of each of these enzymes towards peroxide scavenging in vivo is less clear. Therefore, to directly investigate in vivo peroxide scavenging, we used the genetically encoded peroxide probes, roGFP2-Tsa2ΔCR and HyPer7, to systematically screen the peroxide scavenging capacity of baker's yeast thiol and heme peroxidase mutants. We show that the 2-Cys peroxiredoxin Tsa1 alone is responsible for almost all exogenous H2O2 and tert-butyl hydroperoxide scavenging. Furthermore, Tsa1 can become an important source of H2O2-dependent cytosolic glutathione disulfide production. The two catalases and cytochrome c peroxidase only produce observable scavenging defects at higher H2O2 concentrations when these three heme peroxidases are removed in combination. We also analyzed the reduction of Tsa1 in vitro, revealing that the enzyme is efficiently reduced by thioredoxin-1 with a rate constant of 2.8 × 106 M-1s-1 but not by glutaredoxin-2. Tsa1 reduction by reduced glutathione occurs nonenzymatically with a rate constant of 2.9 M-1s-1. Hence, the observed Tsa1-dependent glutathione disulfide production in yeast probably requires the oxidation of thioredoxins. Our findings clarify the importance of the various thiol and heme peroxidases for peroxide removal and suggest that most thiol peroxidases have alternative or specialized functions in specific subcellular compartments.

Decoding bacterial communication: Intracellular signal transduction, quorum sensing, and cross-kingdom interactions

This review provides a comprehensive analysis of the intricate architecture of bacterial sensing systems, with a focus on signal transduction mechanisms and their critical roles in microbial physiology. It highlights quorum sensing (QS), quorum quenching (QQ), and quorum sensing interference (QSI) as fundamental processes driving bacterial communication, influencing gene expression, biofilm formation, and interspecies interactions. The analysis explores the importance of diffusible signal factors (DSFs) and secondary messengers such as cAMP and c-di-GMP in modulating microbial behaviors. Additionally, cross-kingdom signaling, where bacterial signals impact host-pathogen dynamics and ecological balance, is systematically reviewed. This review introduces "signalomics", an novel interdisciplinary framework integrating genomics, proteomics, and metabolomics to offer a holistic framework for understanding microbial communication and evolution. These findings hold significant implications for various domains, including food preservation, agriculture, and human health.

Peroxiredoxin 2 mediates redox-stimulated adaptations to oxidative phosphorylation induced by contractile activity in human skeletal muscle myotubes

Skeletal muscle generates superoxide during contractions, which is converted to hydrogen peroxide (H2O2). H2O2 has been proposed to activate signalling pathways and transcription factors that regulate adaptive responses to exercise, but the concentration required to oxidize and activate key redox-sensitive signalling proteins in vitro is much higher than the typical intracellular levels seen in muscle after exercise. We hypothesized that 2-Cys-peroxiredoxins (PRDX), which rapidly oxidize in the presence of physiological concentrations of H2O2, serve as intermediary signalling molecules and play a crucial role in activating adaptive pathways following muscle contractions. This study has examined the human muscle myotube responses to contractile activity, or exposure to low extracellular concentrations (2.5-5 μM) of H2O2 and whether knock down of muscle PRDX2 alters the differential gene expression (DEG) that results from these stresses. Exposure of human skeletal muscle myotubes to a 15 min period of aerobic electrically stimulated isometric contractions or 5 μM H2O2 induced substantial changes in DEG with modification of many genes associated with adaptations of skeletal muscle to contractile activity. Common DEG in these conditions included upregulation of genes associated with increased mitochondrial oxidative phosphorylation, including COX1, COX2, COX3 and ATP6. In myotubes with PRDX2 knock down (94 % decrease in PRDX2 mRNA), the upregulation of genes associated with increased mitochondrial oxidative phosphorylation was abolished following contractile activity or exposure to H2O2. These data indicate that a common effect of contractile activity and exposure to "physiological" levels of H2O2 in human myotubes is to increase the expression of multiple genes associated with increased mitochondrial oxidative phosphorylation. Furthermore, these effects were abolished in PRDX2 knock down myotubes indicating that adaptations to upregulate multiple genes related to increased mitochondrial capacity in human muscle myotubes in response to exercise is both redox regulated and requires PRDX2 as an essential mediator of the effects of H2O2.

Self-supported electrochemical sensor based on uniform palladium nanoparticles functionalized porous graphene film for monitoring H2O2 released from living cells

Graphene film has been considered a promising material for the construction of self-supported electrodes due to its favorable flexibility and high conductivity. However, the film fabricated from pristine graphene or conventional graphene sheet reduced graphene oxide processes limited electrocatalytic performance. Decorating active metal species or incorporating heteroatoms into the graphene framework have been proved to be effective methods to enhance the electrocatalytic efficiency of graphene film-based self-supported electrodes. Herein, we present a freestanding electrode composed of uniform Pd nanoparticles decorating N,S co-doped porous graphene film (Pd/NSPGF) and explore its practical application in differentiating various human colon cell types by in situ tracking the amount of H2O2 secreted from live cells. Our findings reveal that, on the one hand, the NSPGF has abundant surface and inner pores, which promote active site exposure, and mass diffusion during electrochemical reactions; on the other hand, the substitutional doping of the graphene framework with heteroatoms (e.g., N or S) can tailor its electronic and chemical properties, and facilitate the uniform loading of high-density Pd nanoparticles. Moreover, the intrinsic activity of Pd/NSPGF is regulated by the interaction of Pd nanoparticles with the NSPGF support. Taking the advantages of morphology and composition, the self-supported Pd/NSPGF electrode displays remarkable electrochemical performance with a wide linear range up to 2.0 mM, low detection limit of 0.1 μM (S/N = 3), high sensitivity of 665 µA cm-2 mM-1, and good selectivity. When applied in real-time tracking of the H2O2 released from normal human colon epithelial cells and human colorectal cancer cells, the Pd/NSPGF-based electrochemical sensing system can distinguish the cell types by testing the number of extracellular H2O2 molecules released per cell, which holds considerable potential for early detection and monitoring of disease-related clinical specimens.

Redox proteomic analysis of H2O2 -treated Jurkat cells and effects of bicarbonate and knockout of peroxiredoxins 1 and 2

Oxidation of thiol proteins and redox signaling occur in cells exposed to H2O2 but mechanisms are unclear. We used redox proteomics to seek evidence of oxidation of specific proteins either by a mechanism involving reaction of H2O2 with CO2/bicarbonate to give the more reactive peroxymonocarbonate, or via a relay involving peroxiredoxins (Prdxs). Changes in oxidation state of specific Cys-SH residues on treating Jurkat T lymphoma cells with H2O2 were measured by isotopically labeling reduced thiols and analysis by mass spectrometry. The effects of bicarbonate and of knocking out either Prdx1 or Prdx2 were examined. Approximately 14,000 Cys-peptides were detected, of which ∼1 % underwent 2-10 fold loss in thiol content with H2O2. Those showing the most oxidation were not affected by the presence of bicarbonate or knockout of either Prdx. Consistent with previous evidence that bicarbonate potentiates inactivation of glyceraldehyde-3-phosphate dehydrogenase, the GAPDH active site Cys residues were significantly more sensitive to H2O2 when bicarbonate was present. Several other proteins were identified as promising candidates for further investigation. Although we identified some potential protein candidates for Prdx-dependent oxidation, most of the significant differences between KO and WT cells were seen in proteins for which H2O2 unexpectedly increased their CysSH content over untreated cells. We conclude that facilitation of protein oxidation by bicarbonate or Prdx-mediated relays is restricted to a small number of proteins and is insufficient to explain the majority of the oxidation of the cell thiols that occured in response to H2O2.

Reactive oxygen species promote endurance exercise-induced adaptations in skeletal muscles

The discovery that contracting skeletal muscle generates reactive oxygen species (ROS) was first reported over 40 years ago. The prevailing view in the 1980s was that exercise-induced ROS production promotes oxidation of proteins and lipids resulting in muscle damage. However, a paradigm shift occurred in the 1990s as growing research revealed that ROS are signaling molecules, capable of activating transcriptional activators/coactivators and promoting exercise-induced muscle adaptation. Growing evidence supports the notion that reduction-oxidation (redox) signaling pathways play an important role in the muscle remodeling that occurs in response to endurance exercise training. This review examines the specific role that redox signaling plays in this endurance exercise-induced skeletal muscle adaptation. We begin with a discussion of the primary sites of ROS production in contracting muscle fibers followed by a summary of the antioxidant enzymes involved in the regulation of ROS levels in the cell. We then discuss which redox-sensitive signaling pathways promote endurance exercise-induced muscle adaptation and debate the strength of the evidence supporting the notion that redox signaling plays an essential role in muscle adaptation to endurance exercise training. In hopes of stimulating future research, we highlight several important unanswered questions in this field.

Mitochondrial Sulfenated-Protein-Targeted Covalent Immobilization Boosting Efficient Copper(II) Depletion for Enhanced Cancer Treatment

Copper plays a vital role in cellular metabolism and oxidative stress regulation. Visualizing and controlling the copper level in mitochondrion have been proven to be promising and efficient strategies for the diagnosis and treatment of triple-negative breast cancer (TNBC). However, developing an advanced probe for simultaneous visualization and depletion of mitochondrial copper remains a huge challenge. Herein, we for the first time report a mitochondria-anchorable, copper-responsive, and depleting probe d-IR-DPA and evaluate its potential for quantitative visualization of intratumoral copper(II) and anti-TNBC in vivo. Taking advantage of the mitochondrion-targeting and sulfenated-protein-mediated covalent immobilization characteristics, this probe not only enables the quantitative detection of Cu2+ levels in various types of tumors through ratiometric photoacoustic (PA680 nm/PA800 nm) imaging but also scavenges the mitochondrial Cu2+, simultaneously igniting increased oxidative stress and mitochondrial membrane damage and eventually leading to severe TNBC cell apoptosis. More notably, the depletion of Cu2+ by d-IR-DPA can alter the cellular metabolic pathway from oxidative phosphorylation to glycolysis, inducing energy deprivation and significant suppression of TNBC tumor in living mice. Our probe may provide a valuable and powerful means for the effective treatment of TNBC as well as other copper-associated diseases.

Methods to monitor mitochondrial disulfide bonds

Mitochondria contain numerous proteins that utilize the chemistry of cysteine residues, which can be reversibly oxidized. These proteins are involved in mitochondrial biogenesis, protection against oxidative stress, metabolism, energy transduction to adenosine triphosphate, signaling and cell death among other functions. Many proteins located in the mitochondrial intermembrane space are imported by the mitochondrial import and assembly pathway the activity of which is based on the reversible oxidation of cysteine residues and oxidative trapping of substrates. Oxidative modifications of cysteine residues are particularly difficult to study because of their labile character. Here we present techniques that allow for monitoring the oxidative state of mitochondrial proteins as well as to investigate the mitochondrial import and assembly pathway. This chapter conveys basic concepts on sample preparation and techniques to monitor the redox state of cysteine residues in mitochondrial proteins as well as the strategies to study mitochondrial import and assembly pathway.

Exploring the unmapped cysteine redox proteoform landscape

Cysteine redox proteoforms define the diverse molecular states that proteins with cysteine residues can adopt. A protein with one cysteine residue must adopt one of two binary proteoforms: reduced or oxidized. Their numbers scale: a protein with 10 cysteine residues must assume one of 1,024 proteoforms. Although they play pivotal biological roles, the vast cysteine redox proteoform landscape comprising vast numbers of theoretical proteoforms remains largely uncharted. Progress is hampered by a general underappreciation of cysteine redox proteoforms, their intricate complexity, and the formidable challenges that they pose to existing methods. The present review advances cysteine redox proteoform theory, scrutinizes methodological barriers, and elaborates innovative technologies for detecting unique residue-defined cysteine redox proteoforms. For example, chemistry-enabled hybrid approaches combining the strengths of top-down mass spectrometry (TD-MS) and bottom-up mass spectrometry (BU-MS) for systematically cataloguing cysteine redox proteoforms are delineated. These methods provide the technological means to map uncharted redox terrain. To unravel hidden redox regulatory mechanisms, discover new biomarkers, and pinpoint therapeutic targets by mining the theoretical cysteine redox proteoform space, a community-wide initiative termed the "Human Cysteine Redox Proteoform Project" is proposed. Exploring the cysteine redox proteoform landscape could transform current understanding of redox biology.

Mitochondrial Physiology of Cellular Redox Regulations

Mitochondria (mt) represent the vital hub of the molecular physiology of the cell, being decision-makers in cell life/death and information signaling, including major redox regulations and redox signaling. Now we review recent advances in understanding mitochondrial redox homeostasis, including superoxide sources and H2O2 consumers, i.e., antioxidant mechanisms, as well as exemplar situations of physiological redox signaling, including the intramitochondrial one and mt-to-cytosol redox signals, which may be classified as acute and long-term signals. This review exemplifies the acute redox signals in hypoxic cell adaptation and upon insulin secretion in pancreatic beta-cells. We also show how metabolic changes under these circumstances are linked to mitochondrial cristae narrowing at higher intensity of ATP synthesis. Also, we will discuss major redox buffers, namely the peroxiredoxin system, which may also promote redox signaling. We will point out that pathological thresholds exist, specific for each cell type, above which the superoxide sources exceed regular antioxidant capacity and the concomitant harmful processes of oxidative stress subsequently initiate etiology of numerous diseases. The redox signaling may be impaired when sunk in such excessive pro-oxidative state.

Mitochondria in Retinal Ganglion Cells: Unraveling the Metabolic Nexus and Oxidative Stress

This review explored the role of mitochondria in retinal ganglion cells (RGCs), which are essential for visual processing. Mitochondrial dysfunction is a key factor in the pathogenesis of various vision-related disorders, including glaucoma, hereditary optic neuropathy, and age-related macular degeneration. This review highlighted the critical role of mitochondria in RGCs, which provide metabolic support, regulate cellular health, and respond to cellular stress while also producing reactive oxygen species (ROS) that can damage cellular components. Maintaining mitochondrial function is essential for meeting RGCs' high metabolic demands and ensuring redox homeostasis, which is crucial for their proper function and visual health. Oxidative stress, exacerbated by factors like elevated intraocular pressure and environmental factors, contributes to diseases such as glaucoma and age-related vision loss by triggering cellular damage pathways. Strategies targeting mitochondrial function or bolstering antioxidant defenses include mitochondrial-based therapies, gene therapies, and mitochondrial transplantation. These advances can offer potential strategies for addressing mitochondrial dysfunction in the retina, with implications that extend beyond ocular diseases.

Ten "Cheat Codes" for Measuring Oxidative Stress in Humans

Formidable and often seemingly insurmountable conceptual, technical, and methodological challenges hamper the measurement of oxidative stress in humans. For instance, fraught and flawed methods, such as the thiobarbituric acid reactive substances assay kits for lipid peroxidation, rate-limit progress. To advance translational redox research, we present ten comprehensive "cheat codes" for measuring oxidative stress in humans. The cheat codes include analytical approaches to assess reactive oxygen species, antioxidants, oxidative damage, and redox regulation. They provide essential conceptual, technical, and methodological information inclusive of curated "do" and "don't" guidelines. Given the biochemical complexity of oxidative stress, we present a research question-grounded decision tree guide for selecting the most appropriate cheat code(s) to implement in a prospective human experiment. Worked examples demonstrate the benefits of the decision tree-based cheat code selection tool. The ten cheat codes define an invaluable resource for measuring oxidative stress in humans.

Role of mitochondria in pathogenesis and therapy of renal fibrosis

Renal fibrosis, specifically tubulointerstitial fibrosis, represents the predominant pathological consequence observed in the context of progressive chronic kidney conditions. The pathogenesis of renal fibrosis encompasses a multifaceted interplay of mechanisms, including but not limited to interstitial fibroblast proliferation, activation, augmented production of extracellular matrix (ECM) components, and impaired ECM degradation. Notably, mitochondria, the intracellular organelles responsible for orchestrating biological oxidation processes in mammalian cells, assume a pivotal role within this intricate milieu. Mitochondrial dysfunction, when manifest, can incite a cascade of events, including inflammatory responses, perturbed mitochondrial autophagy, and associated processes, ultimately culminating in the genesis of renal fibrosis. This comprehensive review endeavors to furnish an exegesis of mitochondrial pathophysiology and biogenesis, elucidating the precise mechanisms through which mitochondrial aberrations contribute to the onset and progression of renal fibrosis. We explored how mitochondrial dysfunction, mitochondrial cytopathy and mitochondrial autophagy mediate ECM deposition and renal fibrosis from a multicellular perspective of mesangial cells, endothelial cells, podocytes, macrophages and fibroblasts. Furthermore, it succinctly encapsulates the most recent advancements in the realm of mitochondrial-targeted therapeutic strategies aimed at mitigating renal fibrosis.

Antioxidant Enzymes and Their Potential Use in Breast Cancer Treatment

According to the World Health Organization (WHO), breast cancer (BC) is the deadliest and the most common type of cancer worldwide in women. Several factors associated with BC exert their effects by modulating the state of stress. They can induce genetic mutations or alterations in cell growth, encouraging neoplastic development and the production of reactive oxygen species (ROS). ROS are able to activate many signal transduction pathways, producing an inflammatory environment that leads to the suppression of programmed cell death and the promotion of tumor proliferation, angiogenesis, and metastasis; these effects promote the development and progression of malignant neoplasms. However, cells have both non-enzymatic and enzymatic antioxidant systems that protect them by neutralizing the harmful effects of ROS. In this sense, antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), thioredoxin reductase (TrxR), and peroxiredoxin (Prx) protect the body from diseases caused by oxidative damage. In this review, we will discuss mechanisms through which some enzymatic antioxidants inhibit or promote carcinogenesis, as well as the new therapeutic proposals developed to complement traditional treatments.

The cytosolic hyperoxidation-sensitive and -robust Leishmania peroxiredoxins cPRX1 and cPRX2 are both dispensable for parasite infectivity

Typical two-cysteine peroxiredoxins (2-Cys-PRXs) are H2O2-metabolizing enzymes whose activity relies on two cysteine residues. Protists of the family Trypanosomatidae invariably express one cytosolic 2-Cys-PRX (cPRX1). However, the Leishmaniinae sub-family features an additional isoform (cPRX2), almost identical to cPRX1, except for the lack of an elongated C-terminus with a Tyr-Phe (YF) motif. Previously, cytosolic PRXs were considered vital components of the trypanosomatid antioxidant machinery. Here, we shed new light on the properties, functions and relevance of cPRXs from the human pathogen Leishmania infantum. We show first that LicPRX1 is sensitive to inactivation by hyperoxidation, mirroring other YF-containing PRXs participating in redox signaling. Using genetic fusion constructs with roGFP2, we establish that LicPRX1 and LicPRX2 can act as sensors for H2O2 and oxidize protein thiols with implications for signal transduction. Third, we show that while disrupting the LicPRX-encoding genes increases susceptibility of L. infantum promastigotes to external H2O2in vitro, both enzymes are dispensable for the parasites to endure the macrophage respiratory burst, differentiate into amastigotes and initiate in vivo infections. This study introduces a novel perspective on the functions of trypanosomatid cPRXs, exposing their dual roles as both peroxidases and redox sensors. Furthermore, the discovery that Leishmania can adapt to the absence of both enzymes has significant implications for our understanding of Leishmania infections and their treatment. Importantly, it questions the conventional notion that the oxidative response of macrophages during phagocytosis is a major barrier to infection and the suitability of cPRXs as drug targets for leishmaniasis.

Temporal coordination of the transcription factor response to H2O2 stress

Oxidative stress from excess H2O2 activates transcription factors that restore redox balance and repair oxidative damage. Although many transcription factors are activated by H2O2, it is unclear whether they are activated at the same H2O2 concentration, or time. Dose-dependent activation is likely as oxidative stress is not a singular state and exhibits dose-dependent outcomes including cell-cycle arrest and cell death. Here, we show that transcription factor activation is both dose-dependent and coordinated over time. Low levels of H2O2 activate p53, NRF2 and JUN. Yet under high H2O2, these transcription factors are repressed, and FOXO1, NF-κB, and NFAT1 are activated. Time-lapse imaging revealed that the order in which these two groups of transcription factors are activated depends on whether H2O2 is administered acutely by bolus addition, or continuously through the glucose oxidase enzyme. Finally, we provide evidence that 2-Cys peroxiredoxins control which group of transcription factors are activated.

Glutathione Protects other Cellular Thiols against Oxidation by CuII-Dp44mT

Cu-thiosemicarbazones have been intensively investigated for their application in cancer therapy or as antimicrobials. Copper(II)-di-2-pyridylketone-4,4-dimethyl-thiosemicarbazone (CuII-Dp44mT) showed anticancer activity in the submicromolar concentration range in cell culture. The interaction of CuII-Dp44mT with thiols leading to their depletion or inhibition was proposed to be involved in this activity. Indeed, CuII-Dp44mT can catalyze the oxidation of thiols although with slow kinetics. The present work aims to obtain insights into the catalytic activity and selectivity of CuII-Dp44mT toward the oxidation of different biologically relevant thiols. Reduced glutathione (GSH), L-cysteine (Cys), N-acetylcysteine (NAC), D-penicillamine (D-Pen), and the two model proteins glutaredoxin (Grx) and thioredoxin (Trx) were investigated. CuII-Dp44mT catalyzed the oxidation of these thiols with different kinetics, with rates in the following order D-Pen>Cys≫NAC>GSH and Trx>Grx. CuII-Dp44mT was more efficient than CuII chloride for the oxidation of NAC and GSH, but not D-Pen and Cys. In mixtures of biologically relevant concentrations of GSH and either Cys, Trx, or Grx, the oxidation kinetics and spectral properties were similar to that of GSH alone, indicating that the interaction of these thiols with CuII-Dp44mT is dominated by GSH. Hence GSH could protect other thiols against potential deleterious oxidation by CuII-Dp44mT.

Restricted glycolysis is a primary cause of the reduced growth rate of zinc-deficient yeast cells

Zinc is required for many critical processes, including intermediary metabolism. In Saccharomyces cerevisiae, the Zap1 activator regulates the transcription of ∼80 genes in response to Zn supply. Some Zap1-regulated genes are Zn transporters that maintain Zn homeostasis, while others mediate adaptive responses that enhance fitness. One adaptive response gene encodes the 2-cysteine peroxiredoxin Tsa1, which is critical to Zn-deficient (ZnD) growth. Depending on its redox state, Tsa1 can function as a peroxidase, a protein chaperone, or a regulatory redox sensor. In a screen for possible Tsa1 regulatory targets, we identified a mutation (cdc19S492A) that partially suppressed the tsa1Δ growth defect. The cdc19S492A mutation reduced activity of its protein product, pyruvate kinase isozyme 1 (Pyk1), implicating Tsa1 in adapting glycolysis to ZnD conditions. Glycolysis requires activity of the Zn-dependent enzyme fructose-bisphosphate aldolase 1, which was substantially decreased in ZnD cells. We hypothesized that in ZnD tsa1Δ cells, the loss of a compensatory Tsa1 regulatory function causes depletion of glycolytic intermediates and restricts dependent amino acid synthesis pathways, and that the decreased activity of Pyk1S492A counteracted this depletion by slowing the irreversible conversion of phosphoenolpyruvate to pyruvate. In support of this model, supplementing ZnD tsa1Δ cells with aromatic amino acids improved their growth. Phosphoenolpyruvate supplementation, in contrast, had a much greater effect on growth rate of WT and tsa1Δ ZnD cells, indicating that inefficient glycolysis is a major factor limiting yeast growth. Surprisingly however, this restriction was not primarily due to low fructose-bisphosphate aldolase 1 activity, but instead occurs earlier in glycolysis.

Superoxidase dismutases (SODs) in the European eel: Gene characterization, expression response to temperature combined with hormonal maturation and possible migratory implications

Superoxide dismutases (SODs) are antioxidant enzymes that protect cells from oxidation. Three SODs have been identified in mammals, but there is limited information in teleosts. This study investigates SODs in the European eel and their expression patterns during testis maturation. Phylogenetic and synteny analyses revealed SODs paralogs and their evolution in vertebrates. The eel possesses one SOD1 and two SOD2/3 (a and b), indicating SOD2 and SOD3 duplication in elopomorphs. SODs expression were then evaluated in various male and female tissues. SOD1 is more expressed in females, while SOD2a and SOD2b dominate brain-pituitary-gonad tissues in both sexes. SOD3a showed predominant expression in the ovary and the male livers, whereas SOD3b was found in the pituitary and brain of both sexes. The effects of different maturation protocols (standard hormonal treatment vs. same protocol preceded with cold seawater pre-treatment) on SODs expression during testis maturation were evaluated. Salinity increase at the onset of standard treatment at 20 °C, simulating early migration, upregulated SOD1, SOD2a, and SOD2b, coinciding with spermatogonia type A differentiated cells dominance. Thereafter, SOD2a and SOD3a decreased, while SOD2b increased during hormonal treatment-induced spermatogenesis. Pre-treatment with seawater at 10 °C, mimicking the conditions at the beginning of the seawater migration, downregulated SOD1 but increased SOD3a expression. Finally, the standard hormonal treatment, replicating spawning at higher temperatures, downregulated SOD1 in eels without any pre-treatment while SOD2a expression increased in pre-treated eels. This study revealed tissue-specific, sex-dependent, and maturation-related SOD expression patterns, predicting SODs dynamic expression profiles during their reproductive migration.

Reactive oxygen species and cell signaling. Review

Reactive oxygen species (ROS) is a term encompassing a group of highly reactive oxygen-derived molecules. In physiological systems, ROS production exists in concert with antioxidant defenses, which safeguard cells against higher, toxic levels of ROS. Oxidative stress, coined as "oxidative distress", is "a serious imbalance between the generation of ROS and antioxidant defenses in favor of ROS, causing excessive oxidative damage to biomolecules". At physiological levels, ROS are essential for many cellular processes, which is known as "oxidative eustress". Oxidants like hydrogen peroxide (H2O2) activate signaling pathways like mitogen-activated protein kinases (MAPK)s and phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt). ROS activate transcription factors like nuclear factor erythroid 2-related factor 2 (Nrf2), hypoxia-inducible factor 1α (HIF-1α), activator protein 1 (AP-1), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Redox signaling through H2O2 mainly occurs through reversible oxidation of protein cysteine thiolate residues (RS-) to form sulfenic acids (RSOH). An unresolved question is that the reaction rate of H2O2 with protein thiols is very low. In cells, the reaction of H2O2 with protein thiols is likely to be outcompeted by faster reactions of H2O2 with peroxiredoxins and glutathione peroxidases. A novel mechanism being explored is that H2O2 could react with peroxiredoxins that act as reactive redox sensor proteins, leading to peroxiredoxin-mediated relays. Very few redox signaling pathways have been well characterized. Improved understanding of precise mechanisms by which ROS regulate signaling pathways and the role of cellular sensors, is essential for deciphering their roles in physiological and pathological conditions.

Peroxisomal hydrogen peroxide signaling: A new chapter in intracellular communication research

Hydrogen peroxide (H2O2), a natural metabolite commonly found in aerobic organisms, plays a crucial role in numerous cellular signaling processes. One of the key organelles involved in the cell's metabolism of H2O2 is the peroxisome. In this review, we first provide a concise overview of the current understanding of H2O2 as a molecular messenger in thiol redox signaling, along with the role of peroxisomes as guardians and modulators of cellular H2O2 balance. Next, we direct our focus toward the recently identified primary protein targets of H2O2 originating from peroxisomes, emphasizing their importance in unraveling the complex interplay between peroxisomal H2O2 and cell signaling. We specifically focus on three areas: signaling through peroxiredoxin redox relay complexes, calcium signaling, and phospho-signaling. Finally, we highlight key research directions that warrant further investigation to enhance our comprehension of the molecular and biochemical mechanisms linking alterations in peroxisomal H2O2 metabolism with disease.

Was hydrogen peroxide present before the arrival of oxygenic photosynthesis? The important role of iron(II) in the Archean ocean

We address the chemical/biological history of H2O2 back at the times of the Archean eon (2.5-3.9 billion years ago (Gya)). During the Archean eon the pO2 was million-fold lower than the present pO2, starting to increase gradually from 2.3 until 0.6 Gya, when it reached ca. 0.2 bar. The observation that some anaerobic organisms can defend themselves against O2 has led to the view that early organisms could do the same before oxygenic photosynthesis had developed at about 3 Gya. This would require the anaerobic generation of H2O2, and here we examine the various mechanisms which were suggested in the literature for this. Given the concentration of Fe2+ at 20-200 μM in the Archean ocean, the estimated half-life of H2O2 is ca. 0.7 s. The oceanic H2O2 concentration was practically zero. We conclude that early organisms were not exposed to H2O2 before the arrival of oxygenic photosynthesis.

Dual role of PRDX1 in redox-regulation and tumorigenesis: Past and future

Tumour cells often display an active metabolic profile, leading to the intracellular accumulation of reactive oxygen species. As a member of the peroxidase family, peroxiredoxin 1 (PRDX1) functions generally in protecting against cell damage caused by H2O2. Additionally, PRDX1 plays a role as a molecular chaperone in various malignant tumours, exhibiting either tumour-promoting or tumour-suppressing effects. Currently, PRDX1-targeting drugs have demonstrated in vitro anticancer effects, indicating the potential of PRDX1 as a molecular target. Here we discussed the diverse functions of PRDX1 in tumour biology and provided a comprehensive analysis of the therapeutic potential of targeting PRDX1 signalling across various types of cancer.

Fingerprint of the oxido-reductase ERO1: A protein disulfide bond producer and supporter of cancer

Endoplasmic reticulum oxidoreductin 1 (ERO1) alpha (ERO1A) is an endoplasmic reticulum (ER)-localized protein disulfide oxidoreductase, involved in the disulfide bond formation of proteins. ERO1's activity in oxidative protein folding is redundant in higher eukaryotes and its loss is well compensated. Although it is dispensable in non-cancer cells, high ERO1 levels are seen with different cancers and predict their malignant phenotype. ERO1 fosters tumor aggressiveness and the response to drug therapy in hypoxic and highly metastatic tumors. It regulates vascular endothelial growth factor (VEGF) levels, oxidative folding and N-glycosylation in hypoxic conditions, boosting tumor fitness and angiogenesis on multiple levels. In addition, ERO1 regulates protein death ligand-1 (PD-L1) on tumors, interfering with the related immune surveillance mechanism, hence acting on the tumors' response to immune check-point inhibitors (ICI). This all points to inhibition of ERO1 as an effective pharmacological tool, selectively targeting tumors while sparing non-cancer cells from cytotoxicity. The critical discussion here closely examines the molecular basis for ERO1's involvement in tumors and ERO1 inhibition strategies for their treatment.

Glutathione and glutathione-dependent enzymes: From biochemistry to gerontology and successful aging

The tripeptide glutathione (GSH), namely γ-L-glutamyl-L-cysteinyl-glycine, is an ubiquitous low-molecular weight thiol nucleophile and reductant of utmost importance, representing the central redox agent of most aerobic organisms. GSH has vital functions involving also antioxidant protection, detoxification, redox homeostasis, cell signaling, iron metabolism/homeostasis, DNA synthesis, gene expression, cysteine/protein metabolism, and cell proliferation/differentiation or death including apoptosis and ferroptosis. Various functions of GSH are exerted in concert with GSH-dependent enzymes. Indeed, although GSH has direct scavenging antioxidant effects, its antioxidant function is substantially accomplished by glutathione peroxidase-catalyzed reactions with reductive removal of H2O2, organic peroxides such as lipid hydroperoxides, and peroxynitrite; to this antioxidant activity also contribute peroxiredoxins, enzymes further involved in redox signaling and chaperone activity. Moreover, the detoxifying function of GSH is basically exerted in conjunction with glutathione transferases, which have also antioxidant properties. GSH is synthesized in the cytosol by the ATP-dependent enzymes glutamate cysteine ligase (GCL), which catalyzes ligation of cysteine and glutamate forming γ-glutamylcysteine (γ-GC), and glutathione synthase, which adds glycine to γ-GC resulting in GSH formation; GCL is rate-limiting for GSH synthesis, as is the precursor amino acid cysteine, which may be supplemented as N-acetylcysteine (NAC), a therapeutically available compound. After its cell export, GSH is degraded extracellularly by the membrane-anchored ectoenzyme γ-glutamyl transferase, a process occurring, as GSH synthesis and export, in the γ-glutamyl cycle. GSH degradation occurs also intracellularly by the cytoplasmic enzymatic ChaC family of γ-glutamyl cyclotransferase. Synthesis and degradation of GSH, together with its export, translocation to cell organelles, utilization for multiple essential functions, and regeneration from glutathione disulfide by glutathione reductase, are relevant to GSH homeostasis and metabolism. Notably, GSH levels decline during aging, an alteration generally related to impaired GSH biosynthesis and leading to cell dysfunction. However, there is evidence of enhanced GSH levels in elderly subjects with excellent physical and mental health status, suggesting that heightened GSH may be a marker and even a causative factor of increased healthspan and lifespan. Such aspects, and much more including GSH-boosting substances administrable to humans, are considered in this state-of-the-art review, which deals with GSH and GSH-dependent enzymes from biochemistry to gerontology, focusing attention also on lifespan/healthspan extension and successful aging; the significance of GSH levels in aging is considered also in relation to therapeutic possibilities and supplementation strategies, based on the use of various compounds including NAC-glycine, aimed at increasing GSH and related defenses to improve health status and counteract aging processes in humans.

Studying the Human Microbiota: Advances in Understanding the Fundamentals, Origin, and Evolution of Biological Timekeeping

The recently observed circadian oscillations of the intestinal microbiota underscore the profound nature of the human-microbiome relationship and its importance for health. Together with the discovery of circadian clocks in non-photosynthetic gut bacteria and circadian rhythms in anucleated cells, these findings have indicated the possibility that virtually all microorganisms may possess functional biological clocks. However, they have also raised many essential questions concerning the fundamentals of biological timekeeping, its evolution, and its origin. This narrative review provides a comprehensive overview of the recent literature in molecular chronobiology, aiming to bring together the latest evidence on the structure and mechanisms driving microbial biological clocks while pointing to potential applications of this knowledge in medicine. Moreover, it discusses the latest hypotheses regarding the evolution of timing mechanisms and describes the functions of peroxiredoxins in cells and their contribution to the cellular clockwork. The diversity of biological clocks among various human-associated microorganisms and the role of transcriptional and post-translational timekeeping mechanisms are also addressed. Finally, recent evidence on metabolic oscillators and host-microbiome communication is presented.

Glutathione kinetically outcompetes reactions between dimedone and a cyclic sulfenamide or physiological sulfenic acids

Dimedone and its derivates are used as selective probes for the nucleophilic detection of sulfenic acids in biological samples. Qualitative analyses suggested that dimedone also reacts with cyclic sulfenamides. Furthermore, under physiological conditions, dimedone must compete with the highly concentrated nucleophile glutathione. We therefore quantified the reaction kinetics for a cyclic sulfenamide model peptide and the sulfenic acids of glutathione and a model peroxiredoxin in the presence or absence of dimedone and glutathione. We show that the cyclic sulfenamide is stabilized at lower pH and that it reacts with dimedone. While reactions between dimedone and sulfenic acids or the cyclic sulfenamide have similar rate constants, glutathione kinetically outcompetes dimedone as a nucleophile by several orders of magnitude. Our comparative in vitro and intracellular analyses challenge the selectivity of dimedone. Consequently, the dimedone labeling of cysteinyl residues inside living cells points towards unidentified reaction pathways or unknown, kinetically competitive redox species.

Caenorhabditis elegans as an in vivo model for the identification of natural antioxidants with anti-aging actions

Natural antioxidants have recently emerged as a highly exciting and significant topic in anti-aging research. Diverse organism models present a viable protocol for future research. Notably, many breakthroughs on natural antioxidants have been achieved in the nematode Caenorhabditis elegans, an animal model frequently utilized for the study of aging research and anti-aging drugs in vivo. Due to the conservation of signaling pathways on oxidative stress resistance, lifespan regulation, and aging disease between C. elegans and multiple high-level organisms (humans), as well as the low and controllable cost of time and labor, it gradually develops into a trustworthy in vivo model for high-throughput screening and validation of natural antioxidants with anti-aging actions. First, information and models on free radicals and aging are presented in this review. We also describe indexes, detection methods, and molecular mechanisms for studying the in vivo antioxidant and anti-aging effects of natural antioxidants using C. elegans. It includes lifespan, physiological aging processes, oxidative stress levels, antioxidant enzyme activation, and anti-aging pathways. Furthermore, oxidative stress and healthspan improvement induced by natural antioxidants in humans and C. elegans are compared, to understand the potential and limitations of the screening model in preclinical studies. Finally, we emphasize that C. elegans is a useful model for exploring more natural antioxidant resources and uncovering the mechanisms underlying aging-related risk factors and diseases.

Redox-stress response resistance (RRR) mediated by hyperoxidation of peroxiredoxin 2 in senescent cells

Aging is closely related to redox regulation. In our previous work, we proposed a new concept, "redox-stress response capacity (RRC)," and found that the decline in RRC was a dynamic characteristic of aging. However, the mechanism of RRC decline during aging remains unknown. In this study, using the senescent human fibroblast cell model and Caenorhabditis elegans model, we identified that peroxiredoxin 2 (PRDX2), as a hydrogen peroxide (H2O2) sensor, was involved in mediating RRC. PRDX2 knockdown led to a decline of RRC and accelerated senescence in fibroblasts and prdx-2 mutant C. elegans also showed decreased RRC. The mechanism study showed that the decreased sensor activity of PRDX2 was related to the increase in hyperoxidation of PRDX2 in senescent cells. Moreover, the level of PRDX2 hyperoxidation also increased in old C. elegans. Simultaneous overexpression of both PRDX2 and sulfiredoxin (SRX) rescued the reduced RRC and delayed senescence. The increase in PRDX2 hyperoxidation in senescent cells led to a decrease in its sensor activity, resulting in the decreased cellular response to H2O2, which is similar to the mechanism of insulin resistance due to the lower insulin receptor sensitivity. Treatment of young cells with a high level of H2O2 to induce a higher level of PRDX2-SO3 resulted in mimicking the RRC decline in senescent cells, which is also similar to a model of insulin resistance induced by high levels of insulin. All these results thrillingly indicate that there is an insulin-resistance-like phenomenon in senescent cells, we named it redox-stress response resistance, RRR. RRR in senescent cells is an important new discovery that explains RRC decline during aging and reveals the internal relationship between redox regulation and aging from a new perspective.

The multifaceted nature of peroxiredoxins in chemical biology

Peroxiredoxins (Prx), thiol-dependent peroxidases, were first identified as H2O2 detoxifiers, and more recently as H2O2 sensors, intermediates in redox-signaling pathways, metabolism modulators, and chaperones. The multifaceted nature of Prx is not only dependent on their peroxidase activity but also strongly associated with specific protein-protein interactions that are being identified, and where the Prx oligomerization dynamics plays a role. Their oxidation by a peroxide substrate forms a sulfenic acid that opens a route to channel the redox signal to diverse protein targets. Recent research underscores the importance of different Prx isoforms in the cellular processes behind disease development with potential therapeutic applications.

Pitfalls of Mitochondrial Redox Signaling Research

Redox signaling from mitochondria (mt) to the cytosol and plasma membrane (PM) has been scarcely reported, such as in the case of hypoxic cell adaptation or (2-oxo-) 2-keto-isocaproate (KIC) β-like-oxidation stimulating insulin secretion in pancreatic β-cells. Mutual redox state influence between mitochondrial major compartments, the matrix and the intracristal space, and the cytosol is therefore derived theoretically in this article to predict possible conditions, when mt-to-cytosol and mt-to-PM signals may occur, as well as conditions in which the cytosolic redox signaling is not overwhelmed by the mitochondrial antioxidant capacity. Possible peroxiredoxin 3 participation in mt-to-cytosol redox signaling is discussed, as well as another specific case, whereby mitochondrial superoxide release is diminished, whereas the matrix MnSOD is activated. As a result, the enhanced conversion to H2O2 allows H2O2 diffusion into the cytosol, where it could be a predominant component of the H2O2 release. In both of these ways, mt-to-cytosol and mt-to-PM signals may be realized. Finally, the use of redox-sensitive probes is discussed, which disturb redox equilibria, and hence add a surplus redox-buffering to the compartment, where they are localized. Specifically, when attempts to quantify net H2O2 fluxes are to be made, this should be taken into account.

Seasonal Changes in Photoperiod: Effects on Growth and Redox Signaling Patterns in Atlantic Salmon Postsmolts

Farmed Atlantic salmon reared under natural seasonal changes in sea-cages had an elevated consumption of antioxidants during spring. It is, however, unclear if this response was caused by the increase in day length, temperature, or both. The present study examined redox processes in Atlantic salmon that were reared in indoor tanks at constant temperature (9 °C) under a simulated natural photoperiod. The experiment lasted for 6 months, from vernal to autumnal equinoxes, with the associated increase and subsequent decrease in day length. We found that intracellular antioxidants were depleted, and there was an increase in malondialdehyde (MDA) levels in the liver and muscle of Atlantic salmon with increasing day length. Antioxidant enzyme activity in liver and muscle and their related gene profiles was also affected, with a distinct upregulation of genes involved in maintaining redox homeostasis, such as peroxiredoxins in the brain in April. This study also revealed a nuclear factor-erythroid 2-related factor 2 (Nrf2)-mediated oxidative stress response in muscle and liver, suggesting that fish integrate environmental signals through redox signaling pathways. Furthermore, growth and expression profiles implicated in growth hormone (GH) signaling and cell cycle regulation coincided with stress patterns. The results demonstrate that a change in photoperiod without the concomitant increase in temperature is sufficient to stimulate growth and change the tissue oxidative state in Atlantic salmon during spring and early summer. These findings provide new insights into redox regulation mechanisms underlying the response to the changing photoperiod, and highlight a link between oxidative status and physiological function.

S-nitroso-glutathione (GSNO) inhibits hydrogen peroxide production by alpha-ketoglutarate dehydrogenase: An investigation into sex and diet effects

Pyruvate dehydrogenase (PDH) and α-ketoglutarate dehydrogenase (KGDH) are vital sources of hydrogen peroxide (H₂O₂) and key sites for redox regulation. Here, we report KGDH is more sensitive to inhibition by S-nitroso-glutathione (GSNO) when compared to PDH and deactivation of both enzymes by nitro modification is affected by sex and diet. Liver mitochondria from male C57BL/6N mice displayed a robust inhibition of H₂O₂ production after exposure to 500-2000 μM GSNO. H₂O₂ genesis by PDH was not significantly affected by GSNO. Purified KGDH of porcine heart origin displayed a ∼82% decrease in H₂O₂ generating activity at 500 μM GSNO, which was mirrored by a decrease in NADH production. By contrast, H₂O₂- and NADH-producing activity of purified PDH was only minimally affected by an incubation in 500 μM GSNO. Incubations in GSNO had no significant effect on the H₂O₂-generating activity of KGDH and PDH in female liver mitochondria when compared to samples collected from males, which was attributed to higher GSNO reductase (GSNOR) activity. High fat feeding augmented the GSNO-mediated inhibition of KGDH in liver mitochondria from male mice. Exposure of male mice to a HFD also resulted in a significant decrease in the GSNO-mediated inhibition of H₂O₂ genesis by PDH, an effect not observed in mice fed a control-matched diet (CD). Female mice displayed higher resistance to the GSNO-induced inhibition of H₂O₂ production, regardless of being fed a CD or HFD. However, exposure to a HFD did result in a small but significant decrease in H₂O₂ production by KGDH and PDH when female liver mitochondria were treated with GSNO. Although, the effect was less when compared to their male counterparts. Collectively, we show for the first time GSNO deactivates H₂O₂ production by α-keto acid dehydrogenases and we demonstrate that sex and diet are determinants for the nitro-inhibition of both KGDH and PDH.

Redox-regulated chaperones in cell stress responses

Proteostasis and redox homeostasis are tightly interconnected and most protein quality control pathways are under direct redox regulation which allow cells to immediately respond to oxidative stress conditions. The activation of ATP-independent chaperones serves as a first line of defense to counteract oxidative unfolding and aggregation of proteins. Conserved cysteine residues evolved as redox-sensitive switches which upon reversible oxidation induce substantial conformational rearrangements and the formation of chaperone-active complexes. In addition to harnessing unfolding proteins, these chaperone holdases interact with ATP-dependent chaperone systems to facilitate client refolding and restoring proteostasis during stress recovery. This minireview gives an insight into highly orchestrated mechanisms regulating the stress-specific activation and inactivation of redox-regulated chaperones and their role in cell stress responses.

New insights into posttranslational modifications of proteins during bull sperm capacitation

BACKGROUND

Due to the unique nature of spermatozoa, which are transcriptionally and translationally silent, the regulation of capacitation is based on the formation of posttranslational modifications of proteins (PTMs). However, the interactions between different types of PTMs during the capacitation remain unclear. Therefore, we aimed to unravel the PTM-based regulation of sperm capacitation by considering the relationship between tyrosine phosphorylation and reversible oxidative PTMs (oxPTMs), i.e., S-nitrosylation and S-glutathionylation. Since reversible oxPTMs may be closely related to peroxyredoxin (PRDX) activity, the second aim was to verify the role of PRDXs in the PTM-based regulation of capacitation.

METHODS

Cryopreserved bull sperm were capacitated in vitro with or without PRDX inhibitor. Qualitative parameters of sperm and symptoms characteristic of capacitation were analyzed. Posttranslational protein modifications (S-nitrosylation, S-glutathionylation, tyrosine phosphorylation) were investigated at the cellular level (flow cytometry, fluorescence microscopy) and at the proteomic level (fluorescent gel-based proteomic approach).

RESULTS

Zona-pellucida binding proteins (ACRBP, SPAM1, ZAN, ZPBP1 and IZUMO4) were particularly rich in reversible oxPTMs. Moreover, numerous flagellar proteins were associated with all analyzed types of PTMs, which indicates that the direction of posttranslational modifications was integrated. Inhibition of PRDX activity during capacitation caused an increase in S-nitrosylation and S-glutathionylation and a decrease in tyrosine phosphorylation. Inhibition of PRDXs caused GAPDHS to undergo S-glutathionylation and the GSTO2 and SOD2 enzymes to undergo denitrosylation. Moreover, PRDX inhibition caused the AKAP proteins to be dephosphorylated.

CONCLUSIONS

Our research provides evidence that crosstalk occurs between tyrosine phosphorylation and reversible oxPTMs during bull sperm capacitation. This study demonstrates that capacitation triggers S-nitrosylation and S-glutathionylation (and reverse reactions) of zona-pellucida binding proteins, which may be a new important mechanism that determines the interaction between sperms and oocytes. Moreover, TCA-related and flagellar proteins, which are particularly rich in PTMs, may play a key role in sperm capacitation. We propose that the deglutathionylation of ODFs and IZUMO4 proteins is a new hallmark of bull sperm capacitation. The obtained results indicate a relationship between PRDX activity and protein phosphorylation, S-glutathionylation and S-nitrosylation. The activity of PRDXs may be crucial for maintaining redox balance and for providing proper PKA-mediated protein phosphorylation during capacitation. Video Abstract.

Expression of the H2O2 Biosensor roGFP-Tpx1.C160S in Fission and Budding Yeasts and Jurkat Cells to Compare Intracellular H2O2 Levels, Transmembrane Gradients, and Response to Metals

Intracellular hydrogen peroxide (H2O2) levels can oscillate from low, physiological concentrations, to intermediate, signaling ones, and can participate in toxic reactions when overcoming certain thresholds. Fluorescent protein-based reporters to measure intracellular H2O2 have been developed in recent decades. In particular, the redox-sensitive green fluorescent protein (roGFP)-based proteins fused to peroxiredoxins are among the most sensitive H2O2 biosensors. Using fission yeast as a model system, we recently demonstrated that the gradient of extracellular-to-intracellular peroxides through the plasma membrane is around 300:1, and that the concentration of physiological H2O2 is in the low nanomolar range. Here, we have expressed the very sensitive probe roGFP2-Tpx1.C169S in two other model systems, budding yeast and human Jurkat cells. As in fission yeast, the biosensor is ~40–50% oxidized in these cell types, suggesting similar peroxide steady-state levels. Furthermore, probe oxidation upon the addition of extracellular peroxides is also quantitatively similar, suggesting comparable plasma membrane H2O2 gradients. Finally, as a proof of concept, we have applied different concentrations of zinc to all three model systems and have detected probe oxidation, demonstrating that an excess of this metal can cause fluctuations of peroxides, which are moderate in yeasts and severe in mammalian cells. We conclude that the principles governing H2O2 fluxes are very similar in different model organisms.

Temporal Coordination of the Transcription Factor Response to H2O2 stress

The p53 and FOXO transcription factors (TFs) share many similarities despite their distinct evolutionary origins. Both TFs are activated by a variety of cellular stresses and upregulate genes in similar pathways including cell-cycle arrest and apoptosis. Oxidative stress from excess H2O2 activates both FOXO1 and p53, yet whether they are activated at the same time is unclear. Here we found that cells respond to high H2O2 levels in two temporal phases. In the first phase FOXO1 rapidly shuttles to the nucleus while p53 levels remain low. In the second phase FOXO1 exits the nucleus and p53 levels rise. We found that other oxidative stress induced TFs are activated in the first phase with FOXO1 (NF-κB, NFAT1), or the second phase with p53 (NRF2, JUN) but not both following H2O2 stress. The two TF phases result in large differences in gene expression patterns. Finally, we provide evidence that 2-Cys peroxiredoxins control the timing of the TF phases in response to H2O2.

Interactions of reactive sulfur species with metalloproteins

Reactive sulfur species (RSS) entail a diverse family of sulfur derivatives that have emerged as important effector molecules in H₂S-mediated biological events. RSS (including H₂S) can exert their biological roles via widespread interactions with metalloproteins. Metalloproteins are essential components along the metabolic route of oxygen in the body, from the transport and storage of O₂, through cellular respiration, to the maintenance of redox homeostasis by elimination of reactive oxygen species (ROS). Moreover, heme peroxidases contribute to immune defense by killing pathogens using oxygen-derived H₂O₂ as a precursor for stronger oxidants. Coordination and redox reactions with metal centers are primary means of RSS to alter fundamental cellular functions. In addition to RSS-mediated metalloprotein functions, the reduction of high-valent metal centers by RSS results in radical formation and opens the way for subsequent per- and polysulfide formation, which may have implications in cellular protection against oxidative stress and in redox signaling. Furthermore, recent findings pointed out the potential role of RSS as substrates for mitochondrial energy production and their cytoprotective capacity, with the involvement of metalloproteins. The current review summarizes the interactions of RSS with protein metal centers and their biological implications with special emphasis on mechanistic aspects, sulfide-mediated signaling, and pathophysiological consequences. A deeper understanding of the biological actions of reactive sulfur species on a molecular level is primordial in H₂S-related drug development and the advancement of redox medicine.

The Effects of Antioxidant Nutraceuticals on Cellular Sulfur Metabolism and Signaling

Significance: Nutraceuticals are ingested for health benefits, in addition to their general nutritional value. These dietary supplements have become increasingly popular since the late 20th century and they are a rapidly expanding global industry approaching a half-trillion U.S. dollars annually. Many nutraceuticals are promulgated as potent antioxidants. Recent Advances: Experimental support for the efficacy of nutraceuticals has lagged behind anecdotal exuberance. However, accumulating epidemiological evidence and recent, well-controlled clinical trials are beginning to support earlier animal and in vitro studies. Although still somewhat limited, encouraging results have been suggested in essentially all organ systems and against a wide range of pathophysiological conditions. Critical Issues: Health benefits of "antioxidant" nutraceuticals are largely attributed to their ability to scavenge oxidants. This has been criticized based on several factors, including limited bioavailability, short tissue retention time, and the preponderance of endogenous antioxidants. Recent attention has turned to nutraceutical activation of downstream antioxidant systems, especially the Keap1/Nrf2 (Kelch like ECH associated protein 1/nuclear factor erythroid 2-related factor 2) axis. The question now becomes, how do nutraceuticals activate this axis? Future Directions: Reactive sulfur species (RSS), including hydrogen sulfide (H2S) and its metabolites, are potent activators of the Keap1/Nrf2 axis and avid scavengers of reactive oxygen species. Evidence is beginning to accumulate that a variety of nutraceuticals increase cellular RSS by directly providing RSS in the diet, or through a number of catalytic mechanisms that increase endogenous RSS production. We propose that nutraceutical-specific targeting of RSS metabolism will lead to the design and development of even more efficacious antioxidant therapeutic strategies. Antioxid. Redox Signal. 38, 68-94.

Hydrogen peroxide detoxification through the peroxiredoxin/thioredoxin antioxidant system: A look at the pancreatic β-cell oxidant defense

Reactive oxygen species (ROS), such as hydrogen peroxide, are formed when molecular oxygen obtains additional electrons, increasing its reactivity. While low concentrations of hydrogen peroxide are necessary for regulation of normal cellular signaling events, high concentrations can be toxic. To maintain this balance between beneficial and deleterious concentrations of hydrogen peroxide, cells utilize antioxidants. Our recent work supports a primary role for peroxiredoxin, thioredoxin, and thioredoxin reductase as the oxidant defense pathway used by insulin-producing pancreatic β-cells. These three players work in an antioxidant cycle based on disulfide exchange, with oxidized targets ultimately being reduced using electrons provided by NADPH. Peroxiredoxins also participate in hydrogen peroxide-based signaling through disulfide exchange with redox-regulated target proteins. This chapter will describe the catalytic mechanisms of thioredoxin, thioredoxin reductase, and peroxiredoxin and provide an in-depth look at the roles these enzymes play in antioxidant defense pathways of insulin-secreting β-cells. Finally, we will evaluate the physiological relevance of peroxiredoxin-mediated hydrogen peroxide signaling as a regulator of β-cell function.

Oxidative Stress and Mitochondrial Dysfunction in Chronic Kidney Disease

The kidney contains many mitochondria that generate ATP to provide energy for cellular processes. Oxidative stress injury can be caused by impaired mitochondria with excessive levels of reactive oxygen species. Accumulating evidence has indicated a relationship between oxidative stress and kidney diseases, and revealed new insights into mitochondria-targeted therapeutics for renal injury. Improving mitochondrial homeostasis, increasing mitochondrial biogenesis, and balancing mitochondrial turnover has the potential to protect renal function against oxidative stress. Although there are some reviews that addressed this issue, the articles summarizing the relationship between mitochondria-targeted effects and the risk factors of renal failure are still few. In this review, we integrate recent studies on oxidative stress and mitochondrial function in kidney diseases, especially chronic kidney disease. We organized the causes and risk factors of oxidative stress in the kidneys based in their mitochondria-targeted effects. This review also listed the possible candidates for clinical therapeutics of kidney diseases by modulating mitochondrial function.

MITF Is Regulated by Redox Signals Controlled by the Selenoprotein Thioredoxin Reductase 1

TR1 and other selenoproteins have paradoxical effects in melanocytes and melanomas. Increasing selenoprotein activity with supplemental selenium in a mouse model of UV-induced melanoma prevents oxidative damage to melanocytes and delays melanoma tumor formation. However, TR1 itself is positively associated with progression in human melanomas and facilitates metastasis in melanoma xenografts. Here, we report that melanocytes expressing a microRNA directed against TR1 (TR1low) grow more slowly than control cell lines and contain significantly less melanin. This phenotype is associated with lower tyrosinase (TYR) activity and reduced transcription of tyrosinase-like protein-1 (TYRP1). Melanoma cells in which the TR1 gene (TXNRD1) was disrupted using Crispr/Cas9 showed more dramatic effects including the complete loss of the melanocyte-specific isoform of MITF; other MITF isoforms were unaffected. We provide evidence that TR1 depletion results in oxidation of MITF itself. This newly discovered mechanism for redox modification of MITF has profound implications for controlling both pigmentation and tumorigenesis in cells of the melanocyte lineage.

Interplay of carbon dioxide and peroxide metabolism in mammalian cells

The carbon dioxide/bicarbonate (CO₂/HCO₃^-) molecular pair is ubiquitous in mammalian cells and tissues, mainly as a result of oxidative decarboxylation reactions that occur during intermediary metabolism. CO₂ is in rapid equilibrium with HCO₃^-via the hydration reaction catalyzed by carbonic anhydrases. Far from being an inert compound in redox biology, CO₂ enhances or redirects the reactivity of peroxides, modulating the velocity, extent, and type of one- and two-electron oxidation reactions mediated by hydrogen peroxide (H₂O₂) and peroxynitrite (ONOO^-/ONOOH). Herein, we review the biochemical mechanisms by which CO₂ engages in peroxide-dependent reactions, free radical production, redox signaling, and oxidative damage. First, we cover the metabolic formation of CO₂ and its connection to peroxide formation and decomposition. Next, the reaction mechanisms, kinetics, and processes by which the CO₂/peroxide interplay modulates mammalian cell redox biology are scrutinized in-depth. Importantly, CO₂ also regulates gene expression related to redox and nitric oxide metabolism and as such influences oxidative and inflammatory processes. Accumulated biochemical evidence in vitro, in cellula, and in vivo unambiguously show that the CO₂ and peroxide metabolic pathways are intertwined and together participate in key redox events in mammalian cells.

Effect of Peroxiredoxin 6 on p53 Transcription Factor Level

Peroxiredoxin 6 (Prdx6) is an important antioxidant enzyme with multiple functions in the cell. Prdx6 neutralizes a wide range of hydroperoxides, participates in phospholipid metabolism and cell membrane repair, and in transmission of intracellular and intercellular signals. Disruption of normal Prdx6 expression in the cell leads to the development of pathological conditions. Decrease in the Prdx6 concentration leads to increase in oxidative damage to the cell. At the same time, hyperproduction of Prdx6 is associated with increase in antioxidant status, suppression of apoptosis, and carcinogenesis. Currently, mechanisms of carcinogenic action of peroxiredoxins are poorly understood. In this work we established that the 3-4-fold increase in Prdx6 production in mouse embryonic fibroblast 3T3 cells leads to the 4-5-fold decrease in the level of oncosuppressor p53. At the same time, hyperproduction of Prdx6 leads to the increased expression of RELA and HIF1A, which have oncogenic effects. The 3-4-fold increase in intracellular Prdx6 increases intensity of cell proliferation by 20-30%, promotes increase in antioxidant activity by 30-50%, and increases radioresistance of the transfected 3T3 cells by 30-40%. Increase of the level of intranuclear Prdx6 leads to the decrease in expression of the DNA repair genes in response to radiation, indicating decrease in the genomic DNA damage. This work discusses possible molecular mechanisms of p53 suppression during Prdx6 hyperproduction, which could be used in the development of new approaches in cancer therapy.

Pulmonary hypertension and oxidative stress: Where is the link?

Oxidative stress can be associated with hyperoxia and hypoxia and is characterized by an increase in reactive oxygen (ROS) and nitrogen (RNS) species generated by an underlying disease process or by supplemental oxygen that exceeds the neutralization capacity of the organ system. ROS and RNS acting as free radicals can inactive several enzymes and vasodilators in the nitric oxide pathway promoting pulmonary vasoconstriction resulting in persistent pulmonary hypertension of the newborn (PPHN). Studies in animal models of PPHN have shown high ROS/RNS that is further increased by hyperoxic ventilation. In addition, antioxidant therapy increased PaO2 in these models, but clinical trials are lacking. We recommend targeting preductal SpO2 between 90 and 97%, PaO2 between 55 and 80 mmHg and avoiding FiO2 > 0.6-0.8 if possible during PPHN management. This review highlights the role of oxidative and nitrosative stress markers on PPHN and potential therapeutic interventions that may alleviate the consequences of increased oxidant stress during ventilation with supplemental oxygen.

Mitochondrial trafficking and redox/phosphorylation signaling supporting cell migration phenotypes

Regulation of cell signaling cascades is critical in making sure the response is activated spatially and for a desired duration. Cell signaling cascades are spatially and temporally controlled through local protein phosphorylation events which are determined by the activation of specific kinases and/or inactivation of phosphatases to elicit a complete and thorough response. For example, A-kinase-anchoring proteins (AKAPs) contribute to the local regulated activity protein kinase A (PKA). The activity of kinases and phosphatases can also be regulated through redox-dependent cysteine modifications that mediate the activity of these proteins. A primary example of this is the activation of the epidermal growth factor receptor (EGFR) and the inactivation of the phosphatase and tensin homologue (PTEN) phosphatase by reactive oxygen species (ROS). Therefore, the local redox environment must play a critical role in the timing and magnitude of these events. Mitochondria are a primary source of ROS and energy (ATP) that contributes to redox-dependent signaling and ATP-dependent phosphorylation events, respectively. The strategic positioning of mitochondria within cells contributes to intracellular gradients of ROS and ATP, which have been shown to correlate with changes to protein redox and phosphorylation status driving downstream cellular processes. In this review, we will discuss the relationship between subcellular mitochondrial positioning and intracellular ROS and ATP gradients that support dynamic oxidation and phosphorylation signaling and resulting cellular effects, specifically associated with cell migration signaling.

Defining roles of specific reactive oxygen species (ROS) in cell biology and physiology

'Reactive oxygen species' (ROS) is a generic term that defines a wide variety of oxidant molecules with vastly different properties and biological functions that range from signalling to causing cell damage. Consequently, the description of oxidants needs to be chemically precise to translate research on their biological effects into therapeutic benefit in redox medicine. This Expert Recommendation article pinpoints key issues associated with identifying the physiological roles of oxidants, focusing on H₂O₂ and O₂^.-. The generic term ROS should not be used to describe specific molecular agents. We also advocate for greater precision in measurement of H₂O₂, O₂^.- and other oxidants, along with more specific identification of their signalling targets. Future work should also consider inter-organellar communication and the interactions of redox-sensitive signalling targets within organs and whole organisms, including the contribution of environmental exposures. To achieve these goals, development of tools that enable site-specific and real-time detection and quantification of individual oxidants in cells and model organisms are needed. We also stress that physiological O₂ levels should be maintained in cell culture to better mimic in vivo redox reactions associated with specific cell types. Use of precise definitions and analytical tools will help harmonize research among the many scientific disciplines working on the common goal of understanding redox biology.

Auranofin and Pharmacologic Ascorbate as Radiomodulators in the Treatment of Pancreatic Cancer

Pancreatic cancer accounts for nearly one fourth of all new cancers worldwide. Little progress in the development of novel or adjuvant therapies has been made over the past few decades and new approaches to the treatment of pancreatic cancer are desperately needed. Pharmacologic ascorbate (P-AscH⁻, high-dose, intravenous vitamin C) is being investigated in clinical trials as an adjunct to standard-of-care chemoradiation treatments. In vitro, P-AscH⁻ has been shown to sensitize cancer cells to ionizing radiation in a manner that is dependent on the generation of H₂O₂ while simultaneously protecting normal tissue from radiation damage. There is renewed interest in Auranofin (Au), an FDA-approved medication utilized in the treatment of rheumatoid arthritis, as an anti-cancer agent. Au inhibits the thioredoxin antioxidant system, thus increasing the overall peroxide burden on cancer cells. In support of current literature demonstrating Au’s effectiveness in breast, colon, lung, and ovarian cancer, we offer additional data that demonstrate the effectiveness of Au alone and in combination with P-AscH⁻ and ionizing radiation in pancreatic cancer treatment. Combining P-AscH⁻ and Au in the treatment of pancreatic cancer may confer multiple mechanisms to increase H₂O₂-dependent toxicity amongst cancer cells and provide a promising translatable avenue by which to enhance radiation effectiveness and improve patient outcomes.