The transcription factor Nrf2 promotes survival by enhancing the expression of uncoupling protein 3 under conditions of oxidative stress

A novel redox regulator, MnTnBuOE-2-PyP5+, enhances normal hematopoietic stem/progenitor cell function

The signaling of reactive oxygen species (ROS) is essential for the maintenance of normal cellular function. However, whether and how ROS regulate stem cells are unclear. Here, we demonstrate that, in transgenic mice expressing the human manganese superoxide dismutase (MnSOD) gene, a scavenger of ROS in mitochondria, the number and function of mouse hematopoietic stem/progenitor cells (HSPC) under physiological conditions are enhanced. Importantly, giving MnTnBuOE-2-PyP⁵⁺(MnP), a redox- active MnSOD mimetic, to mouse primary bone marrow cells or to C57B/L6 mice significantly enhances the number of HSPCs. Mechanistically, MnP reduces superoxide to hydrogen peroxide, which activates intracellular Nrf2 signaling leading to the induction of antioxidant enzymes, including MnSOD and catalase, and mitochondrial uncoupling protein 3. The results reveal a novel role of ROS signaling in regulating stem cell function, and suggest a possible beneficial effect of MnP in treating pathological bone marrow cell loss and in increasing stem cell population for bone marrow transplantation.

Aspalathin Protects the Heart against Hyperglycemia-Induced Oxidative Damage by Up-Regulating Nrf2 Expression

Aspalathin (ASP) can protect H9c2 cardiomyocytes against high glucose (HG)-induced shifts in myocardial substrate preference, oxidative stress, and apoptosis. The protective mechanism of ASP remains unknown. However, as one of possible, it is well known that phytochemical flavonoids reduce oxidative stress via nuclear factor (erythroid-derived 2)-like 2 (Nrf2) activation resulting in up-regulation of antioxidant genes and enzymes. Therefore, we hypothesized that ASP protects the myocardium against HG- and hyperglycemia-induced oxidative damage by up-regulating Nrf2 expression in H9c2 cardiomyocytes and diabetic (db/db) mice, respectively. Using an oxidative stress RT² Profiler PCR array, ASP at a dose of 1 µM was demonstrated to protect H9c2 cardiomyocytes against HG-induced oxidative stress, but silencing of Nrf2 abolished this protective response of ASP and exacerbated cardiomyocyte apoptosis. Db/db mice and their non-diabetic (db/+) littermate controls were subsequently treated daily for six weeks with either a low (13 mg/kg) or high (130 mg/kg) ASP dose. Compared to nondiabetic mice the db/db mice presented increased cardiac remodeling and enlarged left ventricular wall that occurred concomitant to enhanced oxidative stress. Daily treatment of mice with ASP at a dose of 130 mg/kg for six weeks was more effective at reversing complications than both a low dose ASP or metformin, eliciting enhanced expression of Nrf2 and its downstream antioxidant genes. These results indicate that ASP maintains cellular homeostasis and protects the myocardium against hyperglycemia-induced oxidative stress through activation of Nrf2 and its downstream target genes.

The Role of the Nrf2/ARE Antioxidant System in Preventing Cardiovascular Diseases

It is widely believed that consuming foods and beverages that have high concentrations of antioxidants can prevent cardiovascular diseases and many types of cancer. As a result, many articles have been published that give the total antioxidant capacities of foods in vitro. However, many antioxidants behave quite differently in vivo. Some of them, such as resveratrol (in red wine) and epigallocatechin gallate or EGCG (in green tea) can activate the nuclear erythroid-2 like factor-2 (Nrf2) transcription factor. It is a master regulator of endogenous cellular defense mechanisms. Nrf2 controls the expression of many antioxidant and detoxification genes, by binding to antioxidant response elements (AREs) that are commonly found in the promoter region of antioxidant (and other) genes, and that control expression of those genes. The mechanisms by which Nrf2 relieves oxidative stress and limits cardiac injury as well as the progression to heart failure are described. Also, the ability of statins to induce Nrf2 in the heart, brain, lung, and liver is mentioned. However, there is a negative side of Nrf2. When over-activated, it can cause (not prevent) cardiovascular diseases and multi-drug resistance cancer.

Redox biology and the interface between bioenergetics, autophagy and circadian control of metabolism

Understanding molecular mechanisms that underlie the recent emergence of metabolic diseases such as diabetes and heart failure has revealed the need for a multi-disciplinary research integrating the key metabolic pathways which change the susceptibility to environmental or pathologic stress. At the physiological level these include the circadian control of metabolism which aligns metabolism with temporal demand. The mitochondria play an important role in integrating the redox signals and metabolic flux in response to the changing activities associated with chronobiology, exercise and diet. At the molecular level this involves dynamic post-translational modifications regulating transcription, metabolism and autophagy. In this review we will discuss different examples of mechanisms which link these processes together. An important pathway capable of linking signaling to metabolism is the post-translational modification of proteins by O-linked N-acetylglucosamine (O-GlcNAc). This is a nutrient regulated protein modification that plays an important role in impaired cellular stress responses. Circadian clocks have also emerged as critical regulators of numerous cardiometabolic processes, including glucose/lipid homeostasis, hormone secretion, redox status and cardiovascular function. Central to these pathways are the response of autophagy, bioenergetics to oxidative stress, regulated by Keap1/Nrf2 and mechanisms of metabolic control. The extension of these ideas to the emerging concept of bioenergetic health will be discussed.

Maternal obesity reduces oxidative capacity in fetal skeletal muscle of Japanese macaques

Maternal obesity is proposed to alter the programming of metabolic systems in the offspring, increasing the risk for developing metabolic diseases; however, the cellular mechanisms remain poorly understood. Here, we used a nonhuman primate model to examine the impact of a maternal Western-style diet (WSD) alone, or in combination with obesity (Ob/WSD), on fetal skeletal muscle metabolism studied in the early third trimester. We find that fetal muscle responds to Ob/WSD by upregulating fatty acid metabolism, mitochondrial complex activity, and metabolic switches (CPT-1, PDK4) that promote lipid utilization over glucose oxidation. Ob/WSD fetuses also had reduced mitochondrial content, diminished oxidative capacity, and lower mitochondrial efficiency in muscle. The decrease in oxidative capacity and glucose metabolism was persistent in primary myotubes from Ob/WSD fetuses despite no additional lipid-induced stress. Switching obese mothers to a healthy diet prior to pregnancy did not improve fetal muscle mitochondrial function. Lastly, while maternal WSD alone led only to intermediary changes in fetal muscle metabolism, it was sufficient to increase oxidative damage and cellular stress. Our findings suggest that maternal obesity or WSD, alone or in combination, leads to programmed decreases in oxidative metabolism in offspring muscle. These alterations may have important implications for future health.

The role of Nrf2 in skeletal muscle contractile and mitochondrial function

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that confers cellular protection by upregulating antioxidant enzymes in response to oxidative stress. However, Nrf2 function within skeletal muscle remains to be further elucidated. We examined the role of Nrf2 in determining muscle phenotype using young (3 mo) and older (12 mo) Nrf2 wild-type (WT) and knockout (KO) mice. Basally, the absence of Nrf2 did not impact mitochondrial content. In intermyofibrillar mitochondria, lack of Nrf2 resulted in a 40% reduction in state 4 respiration, which coincided with a 68% increase in reactive oxygen species (ROS) emission. Nrf2 abrogation impaired in situ muscle performance, characterized by a 48% greater rate of fatigue and a 35% decrease in force within the first 5 min of stimulation. Acute treadmill exercise resulted in a 1.5-fold increase in Nrf2 activation via enhanced DNA binding in WT animals. In response to training, cytochrome-c oxidase activity increased by 20% in the WT animals; however, this response was attenuated in KO mice. Nrf2 protein was reduced 30% by training. Despite this, exercise training normalized respiration, ROS production, and muscle performance in KO mice. Our results suggest that Nrf2 transcriptional activity is increased by exercise and that Nrf2 is required for the maintenance of basal mitochondrial function as well as for the normal increase in specific mitochondrial proteins in response to training. Nonetheless, the decrements in mitochondrial function in Nrf2 KO muscle can be rescued by exercise training, suggesting that this restorative function operates via a pathway independent of Nrf2.

Increased Energy Expenditure, Ucp1 Expression, and Resistance to Diet-induced Obesity in Mice Lacking Nuclear Factor-Erythroid-2-related Transcription Factor-2 (Nrf2)

The NRF2 (also known as NFE2L2) transcription factor is a critical regulator of genes involved in defense against oxidative stress. Previous studies suggest thatNrf2plays a role in adipogenesisin vitro, and deletion of theNrf2gene protects against diet-induced obesity in mice. Here, we demonstrate that resistance to diet-induced obesity inNrf2(-/-)mice is associated with a 20-30% increase in energy expenditure. Analysis of bioenergetics revealed thatNrf2(-/-)white adipose tissues exhibit greater oxygen consumption. White adipose tissue showed a >2-fold increase inUcp1gene expression. Oxygen consumption is also increased nearly 2.5-fold inNrf2-deficient fibroblasts. Oxidative stress induced by glucose oxidase resulted in increasedUcp1expression. Conversely, antioxidant chemicals (such asN-acetylcysteine and Mn(III)tetrakis(4-benzoic acid)porphyrin chloride) and SB203580 (a known suppressor ofUcp1expression) decreasedUcp1and oxygen consumption inNrf2-deficient fibroblasts. These findings suggest that increasing oxidative stress by limitingNrf2function in white adipocytes may be a novel means to modulate energy balance as a treatment of obesity and related clinical disorders.

The cardioprotective compound cloxyquin uncouples mitochondria and induces autophagy

Mitochondrial quality control mechanisms have been implicated in protection against cardiac ischemia-reperfusion (IR) injury. Previously, cloxyquin (5-chloroquinolin-8-ol) was identified via phenotypic screening as a cardioprotective compound. Herein, cloxyquin was identified as a mitochondrial uncoupler in both isolated heart mitochondria and adult cardiomyocytes. Additionally, cardiomyocytes isolated from transgenic mice expressing green fluorescent protein-tagged microtubule-associated protein light chain 3 showed increased autophagosome formation with cloxyquin treatment. The autophagy inhibitor chloroquine abolished cloxyquin-induced cardioprotection in both cellular and perfused heart (Langendorff) models of IR injury. Finally, in an in vivo murine left anterior descending coronary artery occlusion model of IR injury, cloxyquin significantly reduced infarct size from 31.4 ± 3.4% to 16.1 ± 2.2%. In conclusion, the cardioprotective compound cloxyquin simultaneously uncoupled mitochondria and induced autophagy. Importantly, autophagy appears to be required for cloxyquin-induced cardioprotection.

The emerging role of Nrf2 in mitochondrial function

The transcription factor NF-E2 p45-related factor 2 (Nrf2; gene name NFE2L2) allows adaptation and survival under conditions of stress by regulating the gene expression of diverse networks of cytoprotective proteins, including antioxidant, anti-inflammatory, and detoxification enzymes as well as proteins that assist in the repair or removal of damaged macromolecules. Nrf2 has a crucial role in the maintenance of cellular redox homeostasis by regulating the biosynthesis, utilization, and regeneration of glutathione, thioredoxin, and NADPH and by controlling the production of reactive oxygen species by mitochondria and NADPH oxidase. Under homeostatic conditions, Nrf2 affects the mitochondrial membrane potential, fatty acid oxidation, availability of substrates (NADH and FADH2/succinate) for respiration, and ATP synthesis. Under conditions of stress or growth factor stimulation, activation of Nrf2 counteracts the increased reactive oxygen species production in mitochondria via transcriptional upregulation of uncoupling protein 3 and influences mitochondrial biogenesis by maintaining the levels of nuclear respiratory factor 1 and peroxisome proliferator-activated receptor γ coactivator 1α, as well as by promoting purine nucleotide biosynthesis. Pharmacological Nrf2 activators, such as the naturally occurring isothiocyanate sulforaphane, inhibit oxidant-mediated opening of the mitochondrial permeability transition pore and mitochondrial swelling. Curiously, a synthetic 1,4-diphenyl-1,2,3-triazole compound, originally designed as an Nrf2 activator, was found to promote mitophagy, thereby contributing to the overall mitochondrial homeostasis. Thus, Nrf2 is a prominent player in supporting the structural and functional integrity of the mitochondria, and this role is particularly crucial under conditions of stress.

4-Hydroxynonenal induces Nrf2-mediated UCP3 upregulation in mouse cardiomyocytes

4-Hydroxy-2-nonenal (HNE) is a highly cytotoxic product of lipid peroxidation. Nevertheless, at low concentrations, it is able to mediate cell signaling and to activate protective pathways, including that of the transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2). In addition, HNE activates uncoupling proteins (UCPs), mitochondrial inner membrane proteins that mediate uncoupling of oxidative phosphorylation and have been proposed to protect against oxidative stress. It is not known, however, whether HNE might induce UCP expression via Nrf2 to cause mitochondrial uncoupling. We investigated the effects of HNE on UCP3 expression in mouse cardiomyocytes and the involvement of Nrf2. HNE induced the nuclear accumulation of Nrf2 and enhanced UCP3 expression, effects prevented by the antioxidant N-acetylcysteine. ChIP assays indicated that Nrf2 bound to the Ucp3 promoter after HNE treatment, increasing its expression. Cardiomyocytes treated with Nrf2- or UCP3-specific siRNA were less tolerant to HNE as reflected by increased cell death, and Nrf2 siRNA prevented HNE-induced UCP3 upregulation. The treatment with HNE greatly altered cardiomyocyte bioenergetics, increasing the proton leak across the inner mitochondrial membrane and severely decreasing the maximal respiratory capacity and the respiratory reserve capacity. These findings confirm that low HNE doses activate Nrf2 in cardiomyocytes and provide the first evidence of Nrf2 binding to the Ucp3 promoter in response to HNE, leading to increased protein expression. These results suggest that the upregulation of UCP3 mediated by Nrf2 in response to HNE might be important in the protection of the heart under conditions of oxidative stress such as ischemia-reperfusion.

Altered Oxygen Utilisation in Rat Left Ventricle and Soleus after 14 Days, but Not 2 Days, of Environmental Hypoxia

The effects of environmental hypoxia on cardiac and skeletal muscle metabolism are dependent on the duration and severity of hypoxic exposure, though factors which dictate the nature of the metabolic response to hypoxia are poorly understood. We therefore set out to investigate the time-dependence of metabolic acclimatisation to hypoxia in rat cardiac and skeletal muscle. Rats were housed under normoxic conditions, or exposed to short-term (2 d) or sustained (14 d) hypoxia (10% O₂), after which samples were obtained from the left ventricle of the heart and the soleus for assessment of metabolic regulation and mitochondrial function. Mass-corrected maximal oxidative phosphorylation was 20% lower in the left ventricle following sustained but not short-term hypoxia, though no change was observed in the soleus. After sustained hypoxia, the ratio of octanoyl carnitine- to pyruvate- supported respiration was 11% and 12% lower in the left ventricle and soleus, respectively, whilst hexokinase activity increased by 33% and 2.1-fold in these tissues. mRNA levels of PPARα targets fell after sustained hypoxia in both tissues, but those of PPARα remained unchanged. Despite decreased Ucp3 expression after short-term hypoxia, UCP3 protein levels and mitochondrial coupling remained unchanged. Protein carbonylation was 40% higher after short-term but not sustained hypoxic exposure in the left ventricle, but was unchanged in the soleus at both timepoints. Our findings therefore demonstrate that 14 days, but not 2 days, of hypoxia induces a loss of oxidative capacity in the left ventricle but not the soleus, and a substrate switch away from fatty acid oxidation in both tissues.

Antioxidant responses and cellular adjustments to oxidative stress

Redox biological reactions are now accepted to bear the Janus faceted feature of promoting both physiological signaling responses and pathophysiological cues. Endogenous antioxidant molecules participate in both scenarios. This review focuses on the role of crucial cellular nucleophiles, such as glutathione, and their capacity to interact with oxidants and to establish networks with other critical enzymes such as peroxiredoxins. We discuss the importance of the Nrf2-Keap1 pathway as an example of a transcriptional antioxidant response and we summarize transcriptional routes related to redox activation. As examples of pathophysiological cellular and tissular settings where antioxidant responses are major players we highlight endoplasmic reticulum stress and ischemia reperfusion. Topologically confined redox-mediated post-translational modifications of thiols are considered important molecular mechanisms mediating many antioxidant responses, whereas redox-sensitive microRNAs have emerged as key players in the posttranscriptional regulation of redox-mediated gene expression. Understanding such mechanisms may provide the basis for antioxidant-based therapeutic interventions in redox-related diseases.

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Antioxidant responses are crucial for both redox signaling and redox damage.

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Glutathione-mediated reactions and Nrf2-Keap1 pathway are key antioxidant responses.

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Redox-related post-translational modifications activate specific signaling pathways.

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Redox-sensitive microRNAs contribute to redox-mediated gene expression regulation.

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ER stress and ischemia-reperfusion are antioxidant-related pathophysiological events.

Inflammation, oxidative stress and postoperative atrial fibrillation in cardiac surgery

Postoperative atrial fibrillation (POAF) is a common complication of cardiac surgery that occurs in up to 60% of patients. POAF is associated with increased risk of cardiovascular mortality, stroke and other arrhythmias that can impact on early and long term clinical outcomes and health economics. Many factors such as disease-induced cardiac remodelling, operative trauma, changes in atrial pressure and chemical stimulation and reflex sympathetic/parasympathetic activation have been implicated in the development of POAF. There is mounting evidence to support a major role for inflammation and oxidative stress in the pathogenesis of POAF. Both are consequences of using cardiopulmonary bypass and reperfusion following ischaemic cardioplegic arrest. Subsequently, several anti-inflammatory and antioxidant drugs have been tested in an attempt to reduce the incidence of POAF. However, prevention remains suboptimal and thus far none of the tested drugs has provided sufficient efficacy to be widely introduced in clinical practice. A better understanding of the cellular and molecular mechanisms responsible for the onset and persistence of POAF is needed to develop more effective prediction and interventions.

Emerging functional cross-talk between the Keap1-Nrf2 system and mitochondria

Nuclear factor erythroid-derived 2-related factor 2 (Nrf2) was originally identified as a positive regulator of drug detoxifying enzyme gene expression during exposure to environmental electrophiles. Currently, Nrf2 is known to regulate the expression of hundreds of cytoprotective genes to counteract endogenously or exogenously generated oxidative stress. Furthermore, when activated in human tumors by somatic mutations, Nrf2 confers growth advantages and chemoresistance by regulating genes involved in various processes such as the pentose phosphate pathway and nucleotide synthesis in addition to antioxidant proteins. Interestingly, increasing evidence shows that Nrf2 is associated with mitochondrial biogenesis during environmental stresses in certain tissues such as the heart. Furthermore, SKN-1, a functional homolog of Nrf2 in C. elegans, is activated by mitochondrial reactive oxygen species and extends life span by promoting mitochondrial homeostasis (i.e., mitohormesis). Similarly, Nrf2 activation was recently observed in the heart of surfeit locus protein 1 (Surf1) -/- mice in which cellular respiration was decreased due to cytochrome c oxidase defects. In this review, we critically examine the relationship between Nrf2 and mitochondria and argue that the Nrf2 stress pathway intimately communicates with mitochondria to maintain cellular homeostasis during oxidative stress.

Genetic deletion in uncoupling protein 3 augments 18F-fluorodeoxyglucose cardiac uptake in the ischemic heart

Background

We investigated the effects of uncoupling protein 3 (UCP3) genetic deletion on ¹⁸F-fluorodeoxyglucose (FDG) cardiac uptake by positron emission tomography (PET)/computed tomography (CT) dedicated animal system after permanent coronary artery ligation.

Methods

Cardiac ¹⁸F-FDG PET/CT was performed in UCP3 knockout (UCP3^−/−) and wild-type (WT) mice one week after induction of myocardial infarction or sham procedure.

Results

In sham-operated mice no difference in left ventricular (LV) volume was detectable between WT and UCP3^−/−. After myocardial infarction, LV volume was higher in both WT and UCP3^−/− compared to sham animals, with a significant interaction (p < 0.05) between genotype and myocardial infarction. In sham-operated animals no difference in FDG standardized uptake value (SUV) was detectable between WT (1.8 ± 0.6) and UCP3^−/− (1.8 ± 0.6). After myocardial infarction SUV was significantly higher in remote areas than in infarcted territories in both UCP3−/− and WT mice (both p < 0.01). Moreover, in remote areas, SUV was significantly higher (p < 0.001) in UCP3−/− as compared to WT, while in the infarcted territory SUV was comparable (p = 0.29). A significant relationship (r = 0.68, p < 0.001) between LV volume and SUV was found.

Conclusions

In a mice model of permanent coronary occlusion, UCP3 deficiency results in a metabolic shift that favored glycolytic metabolism and increased FDG uptake in remote areas.

How the mitochondrion was shaped by radical differences in substrates: what carnitine shuttles and uncoupling tell us about mitochondrial evolution in response to ROS

As free-living organisms, alpha-proteobacteria produce reactive oxygen species (ROS) that diffuse into the surroundings; once constrained inside the archaeal ancestor of eukaryotes, however, ROS production presented evolutionary pressures - especially because the alpha-proteobacterial symbiont made more ROS, from a variety of substrates. I previously proposed that ratios of electrons coming from FADH2 and NADH (F/N ratios) correlate with ROS production levels during respiration, glucose breakdown having a much lower F/N ratio than longer fatty acid (FA) breakdown. Evidently, higher endogenous ROS formation did not hinder eukaryotic evolution, so how were its disadvantages mitigated? I propose that the resulting selection pressures favoured the evolution of a variety of eukaryotic 'innovations': peroxisomes for FA breakdown, carnitine shuttles, the linkage of beta-oxidation to antioxidant properties, uncoupling proteins (UCPs) and using mitochondrial uncoupling during beta-oxidation to reduce ROS. Recently observed relationships between peroxisomes and mitochondria further support the model.

The Nrf2 regulatory network provides an interface between redox and intermediary metabolism

Nuclear factor-erythroid 2 p45-related factor 2 (Nrf2, also called Nfe2l2) is a transcription factor that regulates the cellular redox status. Nrf2 is controlled through a complex transcriptional/epigenetic and post-translational network that ensures its activity increases during redox perturbation, inflammation, growth factor stimulation and nutrient/energy fluxes, thereby enabling the factor to orchestrate adaptive responses to diverse forms of stress. Besides mediating stress-stimulated induction of antioxidant and detoxification genes, Nrf2 contributes to adaptation by upregulating the repair and degradation of damaged macromolecules, and by modulating intermediary metabolism. In the latter case, Nrf2 inhibits lipogenesis, supports β-oxidation of fatty acids, facilitates flux through the pentose phosphate pathway, and increases NADPH regeneration and purine biosynthesis; these observations suggest Nrf2 directs metabolic reprogramming during stress.

Effects of cannabinoid receptor type 2 on endogenous myocardial regeneration by activating cardiac progenitor cells in mouse infarcted heart

Cannabinoid receptor type 2 (CB2) activation is recently reported to promote proliferation of some types of resident stem cells (e.g., hematopoietic stem/progenitor cell or neural progenitor cell). Resident cardiac progenitor cell (CPC) activation and proliferation are crucial for endogenous cardiac regeneration and cardiac repair after myocardial infarction (MI). This study aims to explore the role and possible mechanisms of CB2 receptor activation in enhancing myocardial repair. Our results revealed that CB2 receptor agonist AM1241 can significantly increase CPCs by c-kit and Runx1 staining in ischemic myocardium as well as improve cardiomyocyte proliferation. AM1241 also decreased serum levels of MDA, TNF-α and IL-6 after MI. In addition, AM1241 can ameliorate left ventricular ejection fraction and fractional shortening, and reduce fibrosis. Moreover, AM1241 treatment markedly increased p-Akt and HO-1 expression, and promoted Nrf-2 nuclear translocation. However, PI3K inhibitor wortmannin eliminated these cardioprotective roles of AM1241. In conclusion, AM1241 could induce myocardial regeneration and improve cardiac function, which might be associated with PI3K/Akt/Nrf2 signaling pathway activation. Our findings may provide a promising strategy for cardiac endogenous regeneration after MI.

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.