Signal transduction by reactive oxygen species

Destroy and exploit: catalyzed removal of hydroperoxides from the endoplasmic reticulum

Peroxidases are enzymes that reduce hydroperoxide substrates. In many cases, hydroperoxide reduction is coupled to the formation of a disulfide bond, which is transferred onto specific acceptor molecules, the so-called reducing substrates. As such, peroxidases control the spatiotemporal distribution of diffusible second messengers such as hydrogen peroxide (H₂O₂) and generate new disulfides. Members of two families of peroxidases, peroxiredoxins (Prxs) and glutathione peroxidases (GPxs), reside in different subcellular compartments or are secreted from cells. This review discusses the properties and physiological roles of PrxIV, GPx7, and GPx8 in the endoplasmic reticulum (ER) of higher eukaryotic cells where H₂O₂ and—possibly—lipid hydroperoxides are regularly produced. Different peroxide sources and reducing substrates for ER peroxidases are critically evaluated. Peroxidase-catalyzed detoxification of hydroperoxides coupled to the productive use of disulfides, for instance, in the ER-associated process of oxidative protein folding, appears to emerge as a common theme. Nonetheless, in vitro and in vivo studies have demonstrated that individual peroxidases serve specific, nonoverlapping roles in ER physiology.

Metabolic plasticity and hematopoietic stem cell biology

PURPOSE OF REVIEW

Hematopoietic stem cells (HSCs) residing in the hypoxic niches can both self-renew and give rise to progeny. Multiple regulatory mechanisms for these cellular processes have been identified. Emerging evidence has revealed that metabolism and bioenergetics play important roles in determining stem cell fate in concert with other regulatory networks. In this review, we will discuss recent advances in this field.

RECENT FINDINGS

Recent studies have helped define and redefine metabolic regulation of HSCs. Resting quiescent stem cells use primarily anaerobic glycolysis for energy production and this metabolic program is required to maintain a functional quiescent state. However, when they exit this state and rapidly proliferate and differentiate into different blood cell types, a robust up-regulation of energy metabolism is expected to meet the quickly rising energy demand. Dysregulation of metabolism in HSCs results in various blood disorders, including leukemia.

SUMMARY

Energy metabolism and HSC activity influence and interlink each other in a highly sophisticated and orchestrated manner. Understanding metabolic regulation of HSC function has significant implications for HSC-based therapies and leukemogenesis research.

Role of reactive oxygen species-mediated signaling in aging

SIGNIFICANCE

Redox biology is a rapidly developing area of research due to the recent evidence for general importance of redox control for numerous cellular functions under both physiological and pathophysiological conditions. Understanding of redox homeostasis is particularly relevant to the understanding of the aging process. The link between reactive oxygen species (ROS) and accumulation of age-associated oxidative damage to macromolecules is well established, but remains controversial and applies only to a subset of experimental models. In addition, recent studies show that ROS may function as signaling molecules and that dysregulation of this process may also be linked to aging.

RECENT ADVANCES

Many protein factors and pathways that control ROS production and scavenging, as well as those that regulate cellular redox homeostasis, have been identified. However, much less is known about the mechanisms by which redox signaling pathways influence longevity. In this review, we discuss recent advances in the understanding of the molecular basis for the role of redox signaling in aging.

CRITICAL ISSUES

Recent studies allowed identification of previously uncharacterized redox components and revealed complexity of redox signaling pathways. It would be important to identify functions of these components and elucidate how distinct redox pathways are integrated with each other to maintain homeostatic balance.

FUTURE DIRECTIONS

Further characterization of processes that coordinate redox signaling, redox homeostasis, and stress response pathways should allow researchers to dissect how their dysregulation contributes to aging and pathogenesis of various age-related diseases, such as diabetes, cancer and neurodegeneration.

Sustained production of ROS triggers compensatory proliferation and is required for regeneration to proceed

A major issue in regenerative medicine is the role of injury in promoting cell plasticity. Here we explore the function of reactive oxygen species (ROS) induced through lesions in adult zebrafish. We show that ROS production, following adult fin amputation, is tightly regulated in time and space for at least 24 hours, whereas ROS production remains transient (2 hours) in mere wound healing. In regenerative tissue, ROS signaling triggers two distinct parallel pathways: one pathway is responsible for apoptosis, and the other pathway is responsible for JNK activation. Both events are involved in the compensatory proliferation of stump epidermal cells and are necessary for the progression of regeneration. Both events impact the Wnt, SDF1 and IGF pathways, while apoptosis only impacts progenitor marker expression. These results implicate oxidative stress in regeneration and provide new insights into the differences between healing and regeneration.

Unearthing the secrets of mitochondrial ROS and glutathione in bioenergetics

During the cellular oxidation of fuels, electrons are used to power the proton pumps of the mitochondrial electron transport chain (ETC) and ultimately drive ATP synthesis and the reduction of molecular oxygen to water. During these oxidative processes, some electrons can 'spin off' during fuel oxidation and electron transport to univalently reduce O2, forming reactive oxygen species (ROS). In excess, ROS can be detrimental; however, at low concentrations oxyradicals are essential signaling molecules. Mitochondria thus use a battery of systems to finely control types and levels of ROS, including antioxidants. Several antioxidant systems depend on glutathione. Here, we review mitochondrial ROS homeostatic systems, including emerging knowledge about roles of glutathione in redox balance and the control of protein function by post-translational modification.

Inhibition of glutathione biosynthesis alters compartmental redox status and the thiol proteome in organogenesis-stage rat conceptuses

Developmental signals that control growth and differentiation are regulated by environmental factors that generate reactive oxygen species (ROS) and alter steady-state redox environments in tissues and fluids. Protein thiols are selectively oxidized and reduced in distinct spatial and temporal patterns in conjunction with changes in glutathione/glutathione disulfide (GSH/GSSG) and cysteine/cystine (Cys/CySS) redox potentials (E(h)) to regulate developmental signaling. The purpose of this study was to measure compartment-specific thiol redox status in cultured organogenesis-stage rat conceptuses and to evaluate the impact of thiol oxidation on the redox proteome. The visceral yolk sac (VYS) has the highest initial (0 h) total intracellular GSH (GSH+2GSSG) concentration (5.5 mM) and the lowest Eh (-223 mV) as determined by HPLC analysis. Total embryo (EMB) GSH concentrations ranged lower (3.2 mM) and were only slightly more oxidized than the VYS. Total GSH concentrations in yolk sac fluid (YSF) and amniotic fluid (AF) are >500-fold lower than in tissues and are highly oxidized (YSF E(h)=-121 mV and AF E(h)=-49 mV). Steady-state total Cys concentrations (Cys+2CySS) were significantly lower than GSH in tissues but were otherwise equal in VYS and EMB near 0.5 mM. On gestational day 11, total GSH and Cys concentrations in EMB and VYS increase significantly over the 6h time course while E(h) remains relatively constant. The Eh (GSH/GSSG) in YSF and AF become more reduced over time while E(h) (Cys/CySS) become more oxidized. Addition of L-buthionine-S,R-sulfoximine (BS0) to selectively inhibit GSH synthesis and mimic the effects of some GSH-depleting environmental chemicals significantly decreased VYS and EMB GSH and Cys concentrations and increased Eh over the 6h exposure period, showing a greater overall oxidation. In the YSF, BSO caused a significant increase in total Cys concentrations to 1.7 mM but did not significantly change the E(h) for Cys/CySS. A significant net oxidation was seen in the BSO-treated AF compartment after 6 h. Biotinylated iodoacetamide (BIAM) labeling of proteins revealed the significant thiol oxidation of many EMB proteins following BSO treatment. Quantitative changes in the thiol proteome, associated with developmentally relevant pathways, were detected using isotope coded affinity tag (ICAT) labeling and mass spectroscopy. Adaptive pathways were selectively enriched with increased concentrations of proteins involved in mRNA processing (splicesome) and mRNA stabilization (glycolysis, GAPDH), as well as protein synthesis (aminoacyl-tRNA) and protein folding (antigen processing, Hsp70, protein disulfide isomerase). These results show the ability of chemical and environmental modulators to selectively alter compartmental intracellular and extracellular GSH and Cys concentrations and change their corresponding E(h) within the intact viable conceptus. The altered E(h) were also of sufficient magnitude to alter the redox proteome and change relative protein concentrations, suggesting that the mechanistic links through which environmental factors inform and regulate developmental signaling pathways may be discovered using systems developmental biology techniques.

A mediator of singlet oxygen responses in Chlamydomonas reinhardtii and Arabidopsis identified by a luciferase-based genetic screen in algal cells

All cells produce reactive oxygen species (ROS) as by-products of their metabolism. In addition to being cytotoxic, ROS act as regulators of a wide range of developmental and physiological processes. Little is known about the molecular mechanisms underlying the perception of ROS and initiation of cellular responses in eukaryotes. Using the unicellular green alga Chlamydomonas reinhardtii, we developed a genetic screen for early components of singlet oxygen signaling. Here, we report the identification of a small zinc finger protein, methylene blue sensitivity (MBS), that is required for induction of singlet oxygen-dependent gene expression and, upon oxidative stress, accumulates in distinct granules in the cytosol. Loss-of-function mbs mutants produce singlet oxygen but are unable to fully respond to it at the level of gene expression. Knockout or knockdown of the homologous genes in the higher plant model Arabidopsis thaliana results in mutants that are hypersensitive to photooxidative stress, whereas overexpression produces plants with elevated stress tolerance. Together, our data indicate an important and evolutionarily conserved role of the MBS protein in ROS signaling and provide a strategy for engineering stress-tolerant plants.

Genome-wide expression analysis of rice aquaporin genes and development of a functional gene network mediated by aquaporin expression in roots

The world population continually faces challenges of water scarcity for agriculture. A common strategy called water-balance control has evolved to adapt plant growth to these challenges. Aquaporins are a family of integral membrane proteins that play a central role in water-balance control. In this study, we identified 34 members of the rice aquaporin gene family, adding a novel member to the previous list. A combination of phylogenetic tree and anatomical meta-expression profiling data consisting of 983 Affymetrix arrays and 209 Agilent 44 K arrays was used to identify tissue-preferred aquaporin genes and evaluate functional redundancy among aquaporin family members. Eight aquaporins showed root-preferred expression in the vegetative growth stage, while 4 showed leaf/shoot-preferred expression. Integrating stress-induced expression patterns into phylogenetic tree and semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) analyses revealed that 3 rice aquaporin genes were markedly downregulated and 4 were upregulated by water deficiency in the root, suggesting that these candidate genes are key regulators of water uptake from the soil. Finally, we constructed a functional network of genes mediated by water stress and refined the network by confirming the differential expression using RT-PCR and real-time PCR. Our data will be useful to elucidate the molecular mechanism of water-balance control in rice root.

Oxidative stress and redox regulation of gametogenesis, fertilization, and embryonic development

Oxidative stress caused by elevated reactive oxygen species (ROS) is one of the predominant causes of both male and female infertility. Oxidative stress conditions cause either cell death or senescence by oxidation of cellular molecules including nucleic acid, proteins, and lipids. It is particularly important to minimize oxidative stress when in vitro fertilization is performed for the purpose of assisted reproduction. The problems associated with assisted reproductive technology are becoming evident, and it is now the time to clarify its mechanisms and cope with them. On the other hand, the beneficial roles of ROS, such as intracellular signaling, have become evident. The antithetical functions of ROS make it more difficult to overcome the problems caused by oxidative stress. Despite the difficulty in understanding mammalian reproduction, the mechanisms and problems can be gradually unveiled by advanced technology such as genetic modification of animals.

Antidiabetic potential of the heme oxygenase-1 inducer curcumin analogues

Although there is a therapeutic treatment to combat diabetes, the identification of agents that may deal with its more serious aspects is an important medical field for research. Diabetes, which contributes to the risk of cardiovascular disease, is associated with a low-grade chronic inflammation (inflammatory stress), oxidative stress, and endoplasmic reticulum (ER) stress. Because the integration of these stresses is critical to the pathogenesis of diabetes, agents and cellular molecules that can modulate these stress responses are emerging as potential targets for intervention and treatment of diabetic diseases. It has been recognized that heme oxygenase-1 (HO-1) plays an important role in cellular protection. Because HO-1 can reduce oxidative stress, inflammatory stress, and ER stress, in part by exerting antioxidant, anti-inflammatory, and antiapoptotic effects, HO-1 has been suggested to play important roles in pathogenesis of diabetes. In the present review, we will explore our current understanding of the protective mechanisms of HO-1 in diabetes and present some emerging therapeutic options for HO-1 expression in treating diabetic diseases, together with the therapeutic potential of curcumin analogues that have their ability to induce HO-1 expression.

Co-occurrence of tetraspanin and ROS generators: Conservation in protein cross-linking and other developmental processes

The nematode exoskeleton, commonly called the cuticle, is a highly structured extracellular matrix mainly composed of collagen. Secreted collagen molecules from the underlying epidermal cells are cross-linked via their tyrosyl residues. Reactive oxygen species (ROS) are required for the cross-linking reaction to produce tyrosyl radicals. The conserved ROS generator enzyme in C. elegans, BLI-3/CeDUOX1, a homolog of dual oxidases (DUOXs), is responsible for production of hydrogen peroxide. The ROS generation system must be properly controlled since ROS are highly reactive molecules that irreversibly inhibit the functions of cellular components such as nucleic acids and proteins. We recently reported that the ROS generation system directed by BLI-3 requires the tetraspanin protein, TSP-15. Herein we outline the process of cuticle development with a focus on the molecular roles of TSP-15 in the BLI-3 system. We also propose the co-occurrence of tetraspanin and ROS generators by convergent evolution.

Redox signaling in pathophysiology of hypertension

Reactive oxygen species (ROS) are products of normal cellular metabolism and derive from various sources in different cellular compartments. Oxidative stress resultant from imbalance between ROS generation and antioxidant defense mechanisms is important in pathogenesis of cardiovascular diseases, such as hypertension, heart failure, atherosclerosis, diabetes, and cardiac hypertrophy. In this review we focus on hypertension and address sources of cellular ROS generation, mechanisms involved in regulation of radical homeostasis, superoxide dismutase isoforms in pathophysiology of hypertension; as well as radical intracellular signaling and phosphorylation processes in proteins of the affected cardiovascular tissues. Finally, we discuss the transcriptional factors involved in redox-sensitive gene transcription and antioxidant response, as well as their roles in hypertension.

Contribution of S6K1/MAPK signaling pathways in the response to oxidative stress: activation of RSK and MSK by hydrogen peroxide

Cells respond to different kind of stress through the coordinated activation of signaling pathways such as MAPK or p53. To find which molecular mechanisms are involved, we need to understand their cell adaptation. The ribosomal protein, S6 kinase 1 (S6K1), is a common downstream target of signaling by hormonal or nutritional stress. Here, we investigated the initial contribution of S6K1/MAPK signaling pathways in the cell response to oxidative stress produced by hydrogen peroxide (H₂O₂). To analyze S6K1 activation, we used the commercial anti-phospho-Thr389-S6K1 antibody most frequently mentioned in the bibliography. We found that this antibody detected an 80-90 kDa protein that was rapidly phosphorylated in response to H₂O₂ in several human cells. Unexpectedly, this phosphorylation was insensitive to both mTOR and PI3K inhibitors, and knock-down experiments showed that this protein was not S6K1. RSK and MSK proteins were candidate targets of this phosphorylation. We demonstrated that H₂O₂ stimulated phosphorylation of RSK and MSK kinases at residues that are homologous to Thr389 in S6K1. This phosphorylation required the activity of either p38 or ERK MAP kinases. Kinase assays showed activation of RSK and MSK by H₂O₂. Experiments with mouse embryonic fibroblasts from p38 animals’ knockout confirmed these observations. Altogether, these findings show that the S6K1 signaling pathway is not activated under these conditions, clarify previous observations probably misinterpreted by non-specific detection of proteins RSK and MSK by the anti-phospho-Thr389-S6K1 antibody, and demonstrate the specific activation of MAPK signaling pathways through ERK/p38/RSK/MSK by H₂O₂.

Therapeutic roles of heme oxygenase-1 in metabolic diseases: curcumin and resveratrol analogues as possible inducers of heme oxygenase-1

Metabolic diseases, such as insulin resistance, type II diabetes, and obesity, are associated with a low-grade chronic inflammation (inflammatory stress), oxidative stress, and endoplasmic reticulum (ER) stress. Because the integration of these stresses is critical to the pathogenesis of metabolic diseases, agents and cellular molecules that can modulate these stress responses are emerging as potential targets for intervention and treatment of metabolic diseases. It has been recognized that heme oxygenase-1 (HO-1) plays an important role in cellular protection. Because HO-1 can reduce inflammatory stress, oxidative stress, and ER stress, in part by exerting antioxidant, anti-inflammatory, and antiapoptotic effects, HO-1 has been suggested to play important roles in pathogenesis of metabolic diseases. In the present review, we will explore our current understanding of the protective mechanisms of HO-1 in metabolic diseases and present some emerging therapeutic options for HO-1 expression in treating metabolic diseases, together with the therapeutic potential of curcumin and resveratrol analogues that have their ability to induce HO-1 expression.

HIF-1 mediates metabolic responses to intratumoral hypoxia and oncogenic mutations

Hypoxia occurs frequently in human cancers and induces adaptive changes in cell metabolism that include a switch from oxidative phosphorylation to glycolysis, increased glycogen synthesis, and a switch from glucose to glutamine as the major substrate for fatty acid synthesis. This broad metabolic reprogramming is coordinated at the transcriptional level by HIF-1, which functions as a master regulator to balance oxygen supply and demand. HIF-1 is also activated in cancer cells by tumor suppressor (e.g., VHL) loss of function and oncogene gain of function (leading to PI3K/AKT/mTOR activity) and mediates metabolic alterations that drive cancer progression and resistance to therapy. Inhibitors of HIF-1 or metabolic enzymes may impair the metabolic flexibility of cancer cells and make them more sensitive to anticancer drugs.

Steap4 plays a critical role in osteoclastogenesis in vitro by regulating cellular iron/reactive oxygen species (ROS) levels and cAMP response element-binding protein (CREB) activation

Iron is essential for osteoclast differentiation, and iron overload in a variety of hematologic diseases is associated with excessive bone resorption. Iron uptake by osteoclast precursors via the transferrin cycle increases mitochondrial biogenesis, reactive oxygen species production, and activation of cAMP response element-binding protein, a critical transcription factor downstream of receptor activator of NF-κB-ligand-induced calcium signaling. These changes are required for the differentiation of osteoclast precursors to mature bone-resorbing osteoclasts. However, the molecular mechanisms regulating cellular iron metabolism in osteoclasts remain largely unknown. In this report, we provide evidence that Steap4, a member of the six-transmembrane epithelial antigen of prostate (Steap) family proteins, is an endosomal ferrireductase with a critical role in cellular iron utilization in osteoclasts. Specifically, we show that Steap4 is the only Steap family protein that is up-regulated during osteoclast differentiation. Knocking down Steap4 expression in vitro by lentivirus-mediated short hairpin RNAs inhibits osteoclast formation and decreases cellular ferrous iron, reactive oxygen species, and the activation of cAMP response element-binding protein. These results demonstrate that Steap4 is a critical enzyme for cellular iron uptake and utilization in osteoclasts and, thus, indispensable for osteoclast development and function.

Sestrin-2, a repressor of PDGFRβ signalling, promotes cigarette-smoke-induced pulmonary emphysema in mice and is upregulated in individuals with COPD

Chronic obstructive pulmonary disease (COPD) is a leading cause of morbidity and mortality worldwide. COPD is caused by chronic exposure to cigarette smoke and/or other environmental pollutants that are believed to induce reactive oxygen species (ROS) that gradually disrupt signalling pathways responsible for maintaining lung integrity. Here we identify the antioxidant protein sestrin-2 (SESN2) as a repressor of PDGFRβ signalling, and PDGFRβ signalling as an upstream regulator of alveolar maintenance programmes. In mice, the mutational inactivation of Sesn2 prevents the development of cigarette-smoke-induced pulmonary emphysema by upregulating PDGFRβ expression via a selective accumulation of intracellular superoxide anions (O₂⁻). We also show that SESN2 is overexpressed and PDGFRβ downregulated in the emphysematous lungs of individuals with COPD and to a lesser extent in human lungs of habitual smokers without COPD, implicating a negative SESN2-PDGFRβ interrelationship in the pathogenesis of COPD. Taken together, our results imply that SESN2 could serve as both a biomarker and as a drug target in the clinical management of COPD.

NRF2 and p53: Januses in cancer?

The transcription factor nuclear factor (erythroid-derived 2)-like 2, also known as NFE2L2 or NRF2, is a master regulator of the anti-oxidative stress response and positively controls the expression of a battery of anti-oxidative stress response proteins and enzymes implicated in detoxification and glutathione generation. Although its detoxifying activity is important in cancer prevention, it has recently been shown that cancer cells also exploit its protective functions to thrive and resist chemotherapy. NRF2 was also shown to the pentose phosphate pathway and glutaminolysis, which promotes purine synthesis for supporting rapid proliferation and glutathione for providing anti-oxidative stress protection. Evidence obtained from cancer patients and cell lines suggest that NRF2 is highly active in a variety of human cancers and is associated with aggressiveness. p53 is a tumor suppressor that also promotes an anti-oxidative stress metabolic program and glutaminolysis. Here we will discuss the similarities between NRF2 and p53 and review evidence that p53 might be exploited by cancer cells to gain protection against oxidative stress, as is the case for NRF2. We discuss findings of co-regulation between these transcription factors and propose possible therapeutic strategies that can be used for treatment of cancers that harbor WT p53 and express high levels of NRF2.

Preventive or potential therapeutic value of nutraceuticals against ionizing radiation-induced oxidative stress in exposed subjects and frequent fliers

Humans are constantly exposed to ionizing radiation deriving from outer space sources or activities related to medical care. Absorption of ionizing radiation doses over a prolonged period of time can result in oxidative damage and cellular dysfunction inducing several diseases, especially in ageing subjects. In this report, we analyze the effects of ionizing radiation, particularly at low doses, in relation to a variety of human pathologies, including cancer, and cardiovascular and retinal diseases. We discuss scientific data in support of protection strategies by safe antioxidant formulations that can provide preventive or potential therapeutic value in response to long-term diseases that may develop following exposure.

Nano-nutrition of chicken embryos. The effect of silver nanoparticles and ATP on expression of chosen genes involved in myogenesis

It has been suggested that the quantity and quality of nutrients stored in the egg might not be optimal for the fast rate of chicken embryo development in modern broilers, and embryos could be supplemented with nutrients by in ovo injection. Recent experiments showed that in ovo feeding reduces post-hatch mortality and skeletal disorders and increases muscle growth and breast meat yield. Adenosine triphosphate (ATP) is a "ready for use" energetic molecule, while nanoparticles of silver (Nano-Ag) may penetrate tissues as well as cells and localise inside cells. In this investigation, we hypothesised that silver nanoparticles could be used as a protective carrier for ATP as well as an active agent. ATP and/or an ATP complex with Nano-Ag would be delivered to the muscle cells as a gene expression regulator and promoter of growth and development of embryo breast muscle. A collection of 160 broiler eggs was randomly divided into a Control group without injection and injected groups with hydrocolloids of Nano-Ag, ATP or a complex of Nano-Ag and ATP (Nano-Ag/ATP). The embryos were evaluated on day 20 of incubation. The results indicate that the application of ATP to chicken embryos increases expression of fibroblast growth factor 2 (FGF2), vascular endothelial growth factor (VEGF) and Na(+)/K(+) transporting ATPase (ATP1A1), which may indicate that an extra energy source can enhance molecular mechanisms of muscle cell proliferation. Nano-Ag also up-regulated expression of FGF2, VEGF, ATP1A1 and, also up-regulated expression of myogenic differentiation 1(MyoD1), affecting cell differentiation. The results indicate that ATP and Nano-Ag may accelerate growth and maturation of muscle cells.

Mitochondrial fission-fusion as an emerging key regulator of cell proliferation and differentiation

Mitochondrial shape change, brought about by molecules that promote either fission or fusion between individual mitochondria, has been documented in several model systems. However, the deeper significance of mitochondrial shape change has only recently begun to emerge: among others, it appears to play a role in the regulation of cell proliferation. Here, I review the emerging interplay between mitochondrial fission-fusion components with cell cycle regulatory machineries and how that may impact cell differentiation. Regulation of mitochondrial shape may modulate mitochondrial metabolism and/or energetics to promote crosstalk between signaling components and the cell cycle machinery. Focused research in this area will reveal the exact role of mitochondria in development and disease, specifically in stem cell regulation and tumorigenesis. Such research may also reveal whether and how the endosymbiotic event that gave rise to the mitochondrion was crucial for the evolution of cell cycle regulatory mechanisms in eukaryotes that are absent in prokaryotes.

Hyperoxia-triggered aversion behavior in Drosophila foraging larvae is mediated by sensory detection of hydrogen peroxide

Reactive oxygen species (ROS) in excess have been implicated in numerous chronic illnesses, including asthma, diabetes, aging, cardiovascular disease, and neurodegenerative illness. However, at lower concentrations, ROS can also serve essential routine functions as part of cellular signal transduction pathways. As products of atmospheric oxygen, ROS-mediated signals can function to coordinate external environmental conditions with growth and development. A central challenge has been a mechanistic distinction between the toxic effects of oxidative stress and endogenous ROS functions occurring at much lower concentrations. Drosophila larval aerotactic behavioral assays revealed strong developmentally regulated aversion to mild hyperoxia mediated by H2O2-dependent activation of class IV multidendritic (mdIV) sensory neurons expressing the Degenerin/epithelial Na(+) channel subunit, Pickpocket1 (PPK1). Electrophysiological recordings in foraging-stage larvae (78-84 h after egg laying [AEL]) demonstrated PPK1-dependent activation of mdIV neurons by nanomolar levels of H2O2 well below levels normally associated with oxidative stress. Acute sensitivity was reduced > 100-fold during the larval developmental transition to wandering stage (> 96 h AEL), corresponding to a loss of hyperoxia aversion behavior during the same period. Degradation of endogenous H2O2 by transgenic overexpression of catalase in larval epidermis caused a suppression of hyperoxia aversion behavior. Conversely, disruption of endogenous catalase activity using a UAS-CatRNAi transposon resulted in an enhanced hyperoxia-aversive response. These results demonstrate an essential role for low-level endogenous H2O2 as an environment-derived signal coordinating developmental behavioral transitions.

Mitochondrial dysfunction indirectly elevates ROS production by the endoplasmic reticulum

Mitochondrial dysfunction is often associated with increased reactive oxygen species (ROS) production by the organelle itself. Leadsham et al. (2013) now show that the link between mitochondrial damage and ROS is more complicated, at least in yeast, where signals from damaged mitochondria increase ROS production from the endoplasmic reticulum surface.

Aberrant protein s-nitrosylation in neurodegenerative diseases

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

Current status of NADPH oxidase research in cardiovascular pharmacology

The implications of reactive oxygen species in cardiovascular disease have been known for some decades. Rationally, therapeutic antioxidant strategies combating oxidative stress have been developed, but the results of clinical trials have not been as good as expected. Therefore, to move forward in the design of new therapeutic strategies for cardiovascular disease based on prevention of production of reactive oxygen species, steps must be taken on two fronts, ie, comprehension of reduction-oxidation signaling pathways and the pathophysiologic roles of reactive oxygen species, and development of new, less toxic, and more selective nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitors, to clarify both the role of each NADPH oxidase isoform and their utility in clinical practice. In this review, we analyze the value of NADPH oxidase as a therapeutic target for cardiovascular disease and the old and new pharmacologic agents or strategies to prevent NADPH oxidase activity. Some inhibitors and different direct or indirect approaches are available. Regarding direct NADPH oxidase inhibition, the specificity of NADPH oxidase is the focus of current investigations, whereas the chemical structure-activity relationship studies of known inhibitors have provided pharmacophore models with which to search for new molecules. From a general point of view, small-molecule inhibitors are preferred because of their hydrosolubility and oral bioavailability. However, other possibilities are not closed, with peptide inhibitors or monoclonal antibodies against NADPH oxidase isoforms continuing to be under investigation as well as the ongoing search for naturally occurring compounds. Likewise, some different approaches include inhibition of assembly of the NADPH oxidase complex, subcellular translocation, post-transductional modifications, calcium entry/release, electron transfer, and genetic expression. High-throughput screens for any of these activities could provide new inhibitors. All this knowledge and the research presently underway will likely result in development of new drugs for inhibition of NADPH oxidase and application of therapeutic approaches based on their action, for the treatment of cardiovascular disease in the next few years.

S-glutathionylation in monocyte and macrophage (dys)function

Atherosclerosis is a chronic inflammatory disease involving the accumulation of monocytes and macrophages in the vascular wall. Monocytes and macrophages play a central role in the initiation and progression of atherosclerotic lesion development. Oxidative stress, which occurs when reactive oxygen species (ROS) overwhelm cellular antioxidant systems, contributes to the pathophysiology of many chronic inflammatory diseases, including atherosclerosis. Major targets of ROS are reactive thiols on cysteine residues in proteins, which when oxidized can alter cellular processes, including signaling pathways, metabolic pathways, transcription, and translation. Protein-S-glutathionylation is the process of mixed disulfide formation between glutathione (GSH) and protein thiols. Until recently, protein-S-glutathionylation was associated with increased cellular oxidative stress, but S-glutathionylation of key protein targets has now emerged as a physiologically important redox signaling mechanism, which when dysregulated contributes to a variety of disease processes. In this review, we will explore the role of thiol oxidative stress and protein-S-glutathionylation in monocyte and macrophage dysfunction as a mechanistic link between oxidative stress associated with metabolic disorders and chronic inflammatory diseases, including atherosclerosis.

The redox biochemistry of protein sulfenylation and sulfinylation

Controlled generation of reactive oxygen species orchestrates numerous physiological signaling events (Finkel, T. (2011) Signal transduction by reactive oxygen species. J. Cell Biol. 194, 7-15). A major cellular target of reactive oxygen species is the thiol side chain (RSH) of Cys, which may assume a wide range of oxidation states (i.e. -2 to +4). Within this context, Cys sulfenic (Cys-SOH) and sulfinic (Cys-SO2H) acids have emerged as important mechanisms for regulation of protein function. Although this area has been under investigation for over a decade, the scope and biological role of sulfenic/sulfinic acid modifications have been recently expanded with the introduction of new tools for monitoring cysteine oxidation in vitro and directly in cells. This minireview discusses selected recent examples of protein sulfenylation and sulfinylation from the literature, highlighting the role of these post-translational modifications in cell signaling.

Role of nrf2 in oxidative stress and toxicity

Organismal life encounters reactive oxidants from internal metabolism and environmental toxicant exposure. Reactive oxygen and nitrogen species cause oxidative stress and are traditionally viewed as being harmful. On the other hand, controlled production of oxidants in normal cells serves useful purposes to regulate signaling pathways. Reactive oxidants are counterbalanced by complex antioxidant defense systems regulated by a web of pathways to ensure that the response to oxidants is adequate for the body's needs. A recurrent theme in oxidant signaling and antioxidant defense is reactive cysteine thiol-based redox signaling. The nuclear factor erythroid 2-related factor 2 (Nrf2) is an emerging regulator of cellular resistance to oxidants. Nrf2 controls the basal and induced expression of an array of antioxidant response element-dependent genes to regulate the physiological and pathophysiological outcomes of oxidant exposure. This review discusses the impact of Nrf2 on oxidative stress and toxicity and how Nrf2 senses oxidants and regulates antioxidant defense.

ROS sets the stage for macrophage differentiation

While M1 macrophages are highly pro-inflammatory and microbicidal, M2 macrophages and the related tumor associated macrophages (TAMs) regulate tissue remodeling and angiogenesis and can display immunomodulatory activity. In July issue of Cell Research, Zhang et al. show that ROS production, critical for the activation and functions of M1 macrophages, is necessary for the differentiation of M2 macrophages and TAMs, and that antioxidant therapy blocks TAM differentiation and tumorigenesis in mouse models of cancer.

Beyond oxidative stress: an immunologist's guide to reactive oxygen species

Reactive oxygen species (ROS) react preferentially with certain atoms to modulate functions ranging from cell homeostasis to cell death. Molecular actions include both inhibition and activation of proteins, mutagenesis of DNA and activation of gene transcription. Cellular actions include promotion or suppression of inflammation, immunity and carcinogenesis. ROS help the host to compete against microorganisms and are also involved in intermicrobial competition. ROS chemistry and their pleiotropy make them difficult to localize, to quantify and to manipulate - challenges we must overcome to translate ROS biology into medical advances.

Redox environment, free radical, and oxidative DNA damage

SIGNIFICANCE

Effective redox homeostasis is critical, and disruption of this process can have important cellular consequences. An array of systems protect the cell from potentially damaging reactive oxygen species (ROS), however if these systems are overwhelmed, for example, in aberrantly functioning cells, ROS can have a number of detrimental consequences, including DNA damage. Oxidative DNA damage can be repaired by a number of DNA repair pathways, such as base excision repair (BER).

RECENT ADVANCES

The role of ROS in oxidative DNA damage is well established, however, there is an emerging role for ROS and the redox environment in modulating the efficiency of DNA repair pathways targeting oxidative DNA lesions.

CRITICAL ISSUES

Oxidative DNA damage and modulation of DNA damage and repair by the redox environment are implicated in a number of diseases. Understanding how the redox environment plays such a critical role in DNA damage and repair will allow us to further understand the far reaching cellular consequence of ROS.

FUTURE DIRECTIONS

In this review, we discuss the detrimental effects of ROS, oxidative DNA damage repair, and the redox systems that exist to control redox homeostasis. We also describe how DNA pathways can be modulated by the redox environment and how the redox environment and oxidative DNA damage plays a role in disease.

Mitochondria as oxidative signaling organelles in T-cell activation: physiological role and pathological implications

Early scientific reports limited the cell biological role of reactive oxygen species (ROS) to the cause of pathological damage. However, extensive research performed over the last decade led to a wide recognition of intracellular oxidative/redox signaling as a crucial mechanism of homeostatic regulation. Amongst different cellular processes known to be influenced by redox signaling, T-cell activation is one of the most established. Numerous studies reported an indispensible role for ROS as modulators of T-cell receptor-induced transcription. Nevertheless, mechanistic details regarding signaling pathways triggered by ROS are far from being delineated. The nature and interplay between enzymatic sources involved in the generation of "oxidative signals" are also a matter of ongoing research. In particular, active participation of the mitochondrial respiratory chain as ROS producer constitutes an intriguing issue with various implications for bioenergetics of activated T cells as well as for T-cell-mediated pathologies. The aim of the current review is to address these interesting concepts.

Epigenetic silencing mediates mitochondria stress-induced longevity

Reactive oxygen species (ROS) play complex roles in aging, having both damaging effects and signaling functions. Transiently elevating mitochondrial stress, including mitochondrial ROS (mtROS), elicits beneficial responses that extend lifespan. However, these adaptive, longevity-signaling pathways remain poorly understood. We show here that Tel1p and Rad53p, homologs of the mammalian DNA damage response kinases ATM and Chk2, mediate a hormetic mtROS longevity signal that extends yeast chronological lifespan. This pathway senses mtROS in a manner distinct from the nuclear DNA damage response and ultimately imparts longevity by inactivating the histone demethylase Rph1p specifically at subtelomeric heterochromatin, enhancing binding of the silencing protein Sir3p, and repressing subtelomeric transcription. These results demonstrate the existence of conserved mitochondria-to-nucleus stress-signaling pathways that regulate aging through epigenetic modulation of nuclear gene expression.

From top-down to bottom-up: computational modeling approaches for cellular redoxin networks

SIGNIFICANCE

Thioredoxin, glutaredoxin, and peroxiredoxin systems play critical roles in a large number of redox-sensitive cellular processes. These systems are linked to each other by coupled redox cycles and common reaction intermediates into a larger network. Given the scale and connectivity of this network, computational approaches are required to analyze its dynamics and organization.

RECENT ADVANCES

Theoretical advances, as well as new redox proteomic methods, have led to the development of both top-down and bottom-up systems biology approaches to analyze the these systems and the network as a whole. Top-down approaches have been based on modifications to the Nernst equation or on graph theoretical approaches, while bottom-up approaches have been based on kinetic or stoichiometric modeling techniques.

CRITICAL ISSUES

This review will consider the rationale behind these approaches and focus on their advantages and limitations. Further, the review will discuss modeling standards to ensure model accuracy and availability.

FUTURE DIRECTIONS

Top-down and bottom-up approaches have distinct strengths and limitations in describing cellular redoxin networks. The availability of methods to overcome these limitations, together with the adoption of common modeling standards, is expected to increase the pace of model-led discovery within the redox biology field.

Using exomarkers to assess mitochondrial reactive species in vivo

BACKGROUND

The ability to measure the concentrations of small damaging and signalling molecules such as reactive oxygen species (ROS) in vivo is essential to understanding their biological roles. While a range of methods can be applied to in vitro systems, measuring the levels and relative changes in reactive species in vivo is challenging.

SCOPE OF REVIEW

One approach towards achieving this goal is the use of exomarkers. In this, exogenous probe compounds are administered to the intact organism and are then transformed by the reactive molecules in vivo to produce a diagnostic exomarker. The exomarker and the precursor probe can be analysed ex vivo to infer the identity and amounts of the reactive species present in vivo. This is akin to the measurement of biomarkers produced by the interaction of reactive species with endogenous biomolecules.

MAJOR CONCLUSIONS AND GENERAL SIGNIFICANCE

Our laboratories have developed mitochondria-targeted probes that generate exomarkers that can be analysed ex vivo by mass spectrometry to assess levels of reactive species within mitochondria in vivo. We have used one of these compounds, MitoB, to infer the levels of mitochondrial hydrogen peroxide within flies and mice. Here we describe the development of MitoB and expand on this example to discuss how better probes and exomarkers can be developed. This article is part of a Special Issue entitled Current methods to study reactive oxygen species - pros and cons and biophysics of membrane proteins. Guest Editor: Christine Winterbourn.

Can mitochondrial dysfunction be initiated by dissociative electron attachment to xenobiotics?

Resonance attachment of low-energy electrons to xenobiotic molecules, 2,4-dichlorophenoxyacetic acid (2,4-D), dichlorodiphenyltrichloroethane (DDT) and dichlorodiphenyldichloroethylene (DDE), was investigated under gas-phase conditions by means of complementary experimental techniques. Electron transmission spectroscopy (ETS) and dissociative electron attachment spectroscopy (DEAS), in the 0-6 eV and 0-15 eV energy range, respectively, were applied with the aim of modeling the behavior of these pesticide molecules under reductive conditions in vivo. Formation of long-lived parent molecular anions and fragment negative ions was observed at incident electron energies very close to zero, in agreement with the results of density functional theory calculations. The gas-phase DEA process, analogous to dissociative electron transfer in solution, was considered as a model for the initial step which occurs in the intermembrane space of mitochondria when a xenobiotic molecule captures an electron "leaked" from the respiratory chain. A possible involvement of the fragments produced by DEA to the pesticides under investigation into cellular processes is discussed. It is concluded that the free radicals and potential DNA adducts formed by DEA are expected to be dangerous for mitochondrial functionalities, while several of the products observed could act as messenger molecules, thus interfering with the normal cellular signaling pathways.

Redox regulation of protein kinases

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

Generation 9 polyamidoamine dendrimer encapsulated platinum nanoparticle mimics catalase size, shape, and catalytic activity

Poly(amidoamine) (PAMAM) encapsulated platinum nanoparticles were synthesized and used as catalase mimics. Acetylated generation 9 (Ac-G9) PAMAM dendrimer with a molecular size around 10 nm was used as a template to synthesize platinum nanoparticles. The feeding molar ratio of Pt(4+) and Ac-G9 is 2048, and the synthesized platinum nanoparticle (Ac-G9/Pt NP) has an average size of 3.3 nm. Ac-G9/Pt NP has a similar molecular size and globular shape with catalase (~11 nm). The catalytic activity of Ac-G9/Pt NP on the decomposition of H2O2 is approaching that of catalase at 37 °C. Ac-G9/Pt NP shows differential response to the changes of pH and temperature compared with catalase, which can be explained by different catalytic mechanisms of Ac-G9/Pt NP and catalase. Ac-G9/Pt NP also shows horseradish peroxidase activity and is able to scavenge free radicals such as di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium (DPPH). Furthermore, Ac-G9/Pt NP shows excellent biocompatibility on different cell lines and can down-regulate H2O2-induced intracellular reactive oxygen species (ROS) in these cells. These results suggest that dendrimers are promising mimics of proteins with different sizes and Ac-G9/Pt NP can be used as an alternative candidate of catalase to decrease oxidation stress in cells.

Targeting the redox balance in inflammatory skin conditions

Reactive oxygen species (ROS) can be both beneficial and deleterious. Under normal physiological conditions, ROS production is tightly regulated, and ROS participate in both pathogen defense and cellular signaling. However, insufficient ROS detoxification or ROS overproduction generates oxidative stress, resulting in cellular damage. Oxidative stress has been linked to various inflammatory diseases. Inflammation is an essential response in the protection against injurious insults and thus important at the onset of wound healing. However, hampered resolution of inflammation can result in a chronic, exaggerated response with additional tissue damage. In the pathogenesis of several inflammatory skin conditions, e.g., sunburn and psoriasis, inflammatory-mediated tissue damage is central. The prolonged release of excess ROS in the skin can aggravate inflammatory injury and promote chronic inflammation. The cellular redox balance is therefore tightly regulated by several (enzymatic) antioxidants and pro-oxidants; however, in case of chronic inflammation, the antioxidant system may be depleted, and prolonged oxidative stress occurs. Due to the central role of ROS in inflammatory pathologies, restoring the redox balance forms an innovative therapeutic target in the development of new strategies for treating inflammatory skin conditions. Nevertheless, the clinical use of antioxidant-related therapies is still in its infancy.

NAD(P)H quinone oxidoreductase 1 (NQO1)-bioactivated pronqodine A regulates prostaglandin release from human synovial sarcoma cells

Natural products have contributed to the elucidation of biological mechanisms as well as drug discovery research. Even now, the expectation for natural products is undiminished. We screened prostaglandin release inhibitors that had no effect on in vitro cyclooxygenase activity derived from natural product sources and discovered pronqodine A. Using spectral analysis and total synthesis, the structure of pronqodine A was shown to be a benzo[d]isothiazole-4,7-dione analogue. Evaluation of the biological activity of pronqodine A revealed that the NAD(P)H dehydrogenase quinone 1 (NQO1) converted pronqodine A into a two-electron reductive form. The reductive form underwent autoxidation and reversed to its native form immediately with the generation of reactive oxygen species. Further investigations proved that pronqodine A inhibited cyclooxygenase enzyme activity only in the presence of NQO1. Pronqodine A acts as a potential bioreductive compound, inhibiting prostaglandin release in selectively activated NQO1-expressing cells.

Oxidative damage induced by chlorpyrifos in the hepatic and renal tissue of Kunming mice and the antioxidant role of vitamin E

Chlorpyrifos is a broad-spectrum, chlorinated organophosphate pesticide employed for pest control in various agricultural and animal husbandries. Acute and chronic exposure to CPF can elicit several adverse effects, including oxidative stress. We investigated neurotoxicity of CPF-treated mice, and evaluated the antioxidant effect of vitamin E against oxidative stress and histological changes in the livers and kidneys of CPF-treated mice. Kunming mice were divided randomly into five exposure groups of six: (A) peanut oil; (B) 3mg/kg CPF; (C) 6 mg/kg CPF; (D) 12 mg/kg CPF; (E) vitamin E (100 mg/kg), 3h after administration of CPF (12 mg/kg) and used as a post-treatment group. Oral administration of high-dose groups (12 mg/kg) CPF led to a significant increase in levels of reactive oxygen species, DNA-protein crosslinks, 8-hydroxy-2-deoxyguanosine and malondialdehyde, decreases in acetylcholinesterase activity and glutathione level, as well as causing hepatic and renal histopathological change. Except for AChE activity levels, administration of vitamin E to CPF-treated mice restored these biochemical parameters to within normal levels, and resulted in overall improvement in damage to livers and kidneys. These data suggest that oxidative stress is involved in CPF-induced toxicity and that vitamin E can protect against the tissue damage induced by CPF.

Oxidative stress and free-radical oxidation in bcg granulomatosis development

Background. Little is known about the role of free-radical and oxidative stress signaling in granuloma maturation and resolution. We aimed to study the activity of free-radical oxidation processes in the dynamics of BCG-induced generalized granulomatosis in mice. Methods. Chronic granulomatous inflammation was induced in male BALB/c mice by intravenously injecting the BCG vaccine, and the production of oxidative stress (activity of free-radical oxidation processes) and histological changes in the lungs, liver, and peritoneal exudate were measured 3, 30, 60, and 90 days after infection. Results. The tuberculous granuloma numerical density and diameter continuously increased from day 30 to day 90, and the macrophage content within the granulomas progressively diminished with a concomitant elevation in the number of epithelioid cells. The activity of the free-radical oxidation processes in the liver (i.e., the intensity of the homogenate chemiluminescence) reached a maximum at postinfection day 60 and subsequently began to decrease. The peak generation of reactive oxygen species by phagocytes in the peritoneal exudate (measured using flow cytometry) was also shifted in time and fell on day 30. Conclusions. The rise in the steady-state concentration of H₂O₂ in the liver of mice with BCG-induced granulomatosis is not related to local H₂O₂ production by phagocytes, and a decrease in the severity of generalized inflammation precedes the resolution of local inflammation.