From oxygen sensing to heart failure: role of thioredoxin

Role of Oxidative Stress in Heart Failure: Insights from Gene Transfer Studies

Under physiological circumstances, there is an exquisite balance between reactive oxygen species (ROS) production and ROS degradation, resulting in low steady-state ROS levels. ROS participate in normal cellular function and in cellular homeostasis. Oxidative stress is the state of a transient or a persistent increase of steady-state ROS levels leading to disturbed signaling pathways and oxidative modification of cellular constituents. It is a key pathophysiological player in pathological hypertrophy, pathological remodeling, and the development and progression of heart failure. The heart is the metabolically most active organ and is characterized by the highest content of mitochondria of any tissue. Mitochondria are the main source of ROS in the myocardium. The causal role of oxidative stress in heart failure is highlighted by gene transfer studies of three primary antioxidant enzymes, thioredoxin, and heme oxygenase-1, and is further supported by gene therapy studies directed at correcting oxidative stress linked to metabolic risk factors. Moreover, gene transfer studies have demonstrated that redox-sensitive microRNAs constitute potential therapeutic targets for the treatment of heart failure. In conclusion, gene therapy studies have provided strong corroborative evidence for a key role of oxidative stress in pathological remodeling and in the development of heart failure.

Redox Regulation in Aging Lungs and Therapeutic Implications of Antioxidants in COPD

Mammals, including humans, are aerobic organisms with a mature respiratory system to intake oxygen as a vital source of cellular energy. Despite the essentiality of reactive oxygen species (ROS) as byproducts of aerobic metabolism for cellular homeostasis, excessive ROS contribute to the development of a wide spectrum of pathological conditions, including chronic lung diseases such as COPD. In particular, epithelial cells in the respiratory system are directly exposed to and challenged by exogenous ROS, including ozone and cigarette smoke, which results in detrimental oxidative stress in the lungs. In addition, the dysfunction of redox regulation due to cellular aging accelerates COPD pathogenesis, such as inflammation, protease anti-protease imbalance and cellular apoptosis. Therefore, various drugs targeting oxidative stress-associated pathways, such as thioredoxin and N-acetylcysteine, have been developed for COPD treatment to precisely regulate the redox system. In this review, we present the current understanding of the roles of redox regulation in the respiratory system and COPD pathogenesis. We address the insufficiency of current COPD treatment as antioxidants and discuss future directions in COPD therapeutics targeting oxidative stress while avoiding side effects such as tumorigenesis.

Thioredoxin-1 attenuates sepsis-induced cardiomyopathy after cecal ligation and puncture in mice

BACKGROUND

Sepsis is a leading cause of mortality among patients in intensive care units across the USA. Thioredoxin-1 (Trx-1) is an essential 12 kDa cytosolic protein that, apart from maintaining the cellular redox state, possesses multifunctional properties. In this study, we explored the possibility of controlling adverse myocardial depression by overexpression of Trx-1 in a mouse model of severe sepsis.

METHODS

Adult C57BL/6J and Trx-1Tg/+ mice were divided into wild-type sham (WTS), wild-type cecal ligation and puncture (WTCLP), Trx-1Tg/+sham (Trx-1Tg/+S), and Trx-1Tg/+CLP groups. Cardiac function was evaluated before surgery, 6 and 24 hours after CLP surgery. Immunohistochemical and Western blot analysis were performed after 24 hours in heart tissue sections.

RESULTS

Echocardiography analysis showed preserved cardiac function in the Trx-1Tg/+ CLP group compared with the WTCLP group. Similarly, Western blot analysis revealed increased expression of Trx-1, heme oxygenase-1 (HO-1), survivin (an inhibitor of apoptosis [IAP] protein family), and decreased expression of thioredoxin-interacting protein (TXNIP), caspase-3, and 3- nitrotyrosine in the Trx-1Tg/+CLP group compared with the WTCLP group. Immunohistochemical analysis showed reduced 4-hydroxynonenal, apoptosis, and vascular leakage in the cardiac tissue of Trx-1Tg/+CLP mice compared with mice in the WTCLP group.

CONCLUSIONS

Our results indicate that overexpression of Trx-1 attenuates cardiac dysfunction during CLP. The mechanism of action may involve reduction of oxidative stress, apoptosis, and vascular permeability through activation of Trx-1/HO-1 and anti-apoptotic protein survivin.

Melatonin rescues cardiac thioredoxin system during ischemia-reperfusion injury in acute hyperglycemic state by restoring Notch1/Hes1/Akt signaling in a membrane receptor-dependent manner

Stress hyperglycemia is commonly observed in patients suffering from ischemic heart disease. It not only worsens cardiovascular prognosis but also attenuates the efficacies of various cardioprotective agents. This study aimed to investigate the protective effect of melatonin against myocardial ischemia-reperfusion (MI/R) injury in acute hyperglycemic state with a focus on Notch1/Hes1/Akt signaling and intracellular thioredoxin (Trx) system. Sprague Dawley rats were subjected to MI/R surgery and high-glucose (HG, 500 g/L) infusion (4 mL/kg/h) to induce temporary hyperglycemia. Rats were treated with or without melatonin (10 mg/kg/d) during the operation. Furthermore, HG (33 mmol/L)-incubated H9c2 cardiomyoblasts were treated in the presence or absence of luzindole (a competitive melatonin receptor antagonist), DAPT (a γ-secretase inhibitor), LY294002 (a PI3-kinase/Akt inhibitor), or thioredoxin-interacting protein (Txnip) adenoviral vectors. We found that acute hyperglycemia aggravated MI/R injury by suppressing Notch1/Hes1/Akt signaling and intracellular Trx activity. Melatonin treatment effectively ameliorated MI/R injury by reducing infarct size, myocardial apoptosis, and oxidative stress. Moreover, melatonin also markedly enhanced Notch1/Hes1/Akt signaling and rescued intracellular Trx system by upregulating Notch1, N1ICD, Hes1, and p-Akt expressions, increasing Trx activity, and downregulating Txnip expression. However, these effects were blunted by luzindole, DAPT, or LY294002. Additionally, Txnip overexpression not only decreased Trx activity, but also attenuated the cytoprotective effect of melatonin. We conclude that impaired Notch1 signaling aggravates MI/R injury in acute hyperglycemic state. Melatonin rescues Trx system by reducing Txnip expression via Notch1/Hes1/Akt signaling in a membrane receptor-dependent manner. Its role as a prophylactic/therapeutic drug deserves further clinical study.

Thioredoxin superfamily and its effects on cardiac physiology and pathology

A precise control of oxidation/reduction of protein thiols is essential for intact cardiac physiology. Irreversible oxidative modifications have been proposed to play a role in the pathogenesis of cardiovascular diseases. An imbalance of redox homeostasis with diminution of antioxidant capacities predisposes the heart to oxidant injury. There is growing interest in endoplasmic reticulum (ER) stress in the cardiovascular field, since perturbation of redox homeostasis in the ER is sufficient to cause ER stress. Because a number of human diseases are related to altered redox homeostasis and defects in protein folding, many research efforts have been devoted in recent years to understanding the structure and enzymatic properties of the thioredoxin superfamily. The thioredoxin superfamily has been well documented as thiol oxidoreductases to exert a role in various cell signaling pathways. The redox properties of the thioredoxin motif account for the different functions of several members of the thioredoxin superfamily. While thioredoxin and glutaredoxin primarily act as antioxidants by reducing protein disulfides and mixed disulfide, another member of the superfamily, protein disulfide isomerase (PDI), can act as an oxidant by forming intrachain disulfide bonds that contribute to proper protein folding. Increasing evidence suggests a pivotal role of PDI in the survival pathway that promotes cardiomyocyte survival and leads to more favorable cardiac remodeling. Thus, the thiol redox state is important for cellular redox signaling and survival pathway in the heart. This review summarizes the key features of major members of the thioredoxin superfamily directly involved in cardiac physiology and pathology.

Thioredoxin-mediated redox regulation of resistance to endocrine therapy in breast cancer

Resistance to endocrine therapy in breast carcinogenesis due to the redox regulation of the signal transduction system by reactive oxygen species (ROS) is the subject of this review article. Both antiestrogens and aromatase inhibitors are thought to prevent cancer through modulating the estrogen receptor function, but other mechanisms cannot be ruled out as these compounds also block metabolism and redox cycling of estrogen and are free radical scavengers. Endocrine therapeutic agents, such as, tamoxifen and other antiestrogens, and the aromatase inhibitor, exemestane, are capable of producing ROS. Aggressive breast cancer cells have high oxidative stress and chronic treatment with exemestane, fulvestrant or tamoxifen may add additional ROS stress. Breast cancer cells receiving long-term antiestrogen treatment appear to adapt to this increased persistent level of ROS. This, in turn, may lead to the disruption of reversible redox signaling that involves redox-sensitive phosphatases, protein kinases, such as, ERK and AKT, and transcription factors, such as, AP-1, NRF-1 and NF-κB. Thioredoxin modulates the expression of estrogen responsive genes through modulating the production of H2O2 in breast cancer cells. Overexpressing thioredoxine reductase 2 and reducing oxidized thioredoxin restores tamoxifen sensitivity to previously resistant breast cancer cells. In summary, it appears that resistance to endocrine therapy may be mediated, in part, by ROS-mediated dysregulation of both estrogen-dependent and estrogen-independent redox-sensitive signaling pathways. Further studies are needed to define the mechanism of action of thioredoxin modifiers, and their effect on the redox regulation that contributes to restoring the antiestrogen-mediated signal transduction system and growth inhibitory action.

Plasma thioredoxin levels during post-cardiac arrest syndrome: relationship with severity and outcome

Introduction

Despite experimental evidence, clinical demonstration of acute state of oxidative stress and inflammation during post-cardiac arrest syndrome is lacking. Plasma level of thioredoxin (TRX), a redox-active protein induced under conditions of oxidative stress and inflammation, is increased in various critical care conditions. We determined plasma TRX concentrations after cardiac arrest and assessed relationships with severity and outcome.

Methods

Retrospective study of consecutive patients admitted to a single academic intensive care unit (ICU) for out-of-hospital cardiac arrest (between July 2006 and March 2008). Plasma levels of TRX were measured at admission, day (D) 1, 2 and 3.

Results

Of 176 patients included, median TRX values measured in ICU survivors and non-survivors were, respectively: 22 ng/mL (7.8 to 77) vs. 72.4 (21.9 to 117.9) at admission (P < 0.001); 5.9 (3.5 to 25.5) vs. 23.2 (5.8 to 81.4) at D1 (P = 0.003); 10.8 (3.6 to 50.8) vs. 11.7 (4.5 to 66.4) at D2 (P = 0.22); and 16.7 (5.3 to 68.3) vs. 17 (4.3 to 62.9) at D3 (P = 0.96). Patients dying within 24 hours had significantly (P < 0.001) higher TRX levels (118.6 ng/mL (94.8 to 280)) than those who died after 24 hours or survived (50.8 (13.9 to 95.7) and 22 (7.8 to 77)). The area under the ROC curve to predict early death was 0.84 (0.76 to 0.91).

TRX levels on admission were significantly correlated with 'low-flow' duration (P = 0.003), sequential organ failure assessment (SOFA) score (P < 0.001), and blood lactate concentration (P < 0.001), but not with 'no-flow' duration or simplified acute physiology score (SAPS) II score. TRX levels and admission arterial pO² correlated negatively (r = -0.17, P = 0.03). Finally, cardiac arrest with cardiac etiology exhibited lower levels of TRX than in cases of extra-cardiac cause (46 ng/mL (11 to 104) vs. 68 (42 to 137), P = 0.01).

Conclusions

Our data show for the first time that TRX levels were elevated early following cardiac arrest, suggestive of oxidative stress and inflammation occurring with this condition. Highest values were found in the most severe patients. TRX could be a useful tool for further exploration and comprehension of post-cardiac arrest syndrome.

The disulfide proteome and other reactive cysteine proteomes: analysis and functional significance

Ten years ago, proteomics techniques designed for large-scale investigations of redox-sensitive proteins started to emerge. The proteomes, defined as sets of proteins containing reactive cysteines that undergo oxidative post-translational modifications, have had a particular impact on research concerning the redox regulation of cellular processes. These proteomes, which are hereafter termed "disulfide proteomes," have been studied in nearly all kingdoms of life, including animals, plants, fungi, and bacteria. Disulfide proteomics has been applied to the identification of proteins modified by reactive oxygen and nitrogen species under stress conditions. Other studies involving disulfide proteomics have addressed the functions of thioredoxins and glutaredoxins. Hence, there is a steadily growing number of proteins containing reactive cysteines, which are probable targets for redox regulation. The disulfide proteomes have provided evidence that entire pathways, such as glycolysis, the tricarboxylic acid cycle, and the Calvin-Benson cycle, are controlled by mechanisms involving changes in the cysteine redox state of each enzyme implicated. Synthesis and degradation of proteins are processes highly represented in disulfide proteomes and additional biochemical data have established some mechanisms for their redox regulation. Thus, combined with biochemistry and genetics, disulfide proteomics has a significant potential to contribute to new discoveries on redox regulation and signaling.

Thioredoxin increases exocytosis by denitrosylating N-ethylmaleimide-sensitive factor

Exocytosis involves membrane fusion between granules and the plasma membrane. Nitric oxide (NO) inhibits exocytosis by chemically modifying N-ethylmaleimide-sensitive factor (NSF), a key component of the exocytic machinery. However, cells recover the ability to release messenger molecules within hours of exposure to NO through unknown mechanisms. We now identify thioredoxin (TRX1) as a denitrosylase that reverses NO inhibition of exocytosis. Endogenously synthesized NO increases S-nitrosylated NSF levels, but S-nitrosylated NSF levels decrease within 3 h after exposure to NO. We found that NO increases the interaction between TRX1 and NSF, and endogenous TRX1 removes NO from S-nitrosylated NSF. Knockdown of TRX1 increases the level of S-nitrosylated NSF, prolongs the inhibition of exocytosis, and suppresses leukocyte adhesion. Taken together, these data show that TRX1 promotes exocytosis by denitrosylating NSF. Our findings suggest that TRX1 might regulate exocytosis in a variety of physiological settings, such as vascular inflammation, thrombosis, and insulin release.

Thioredoxin 1 negatively regulates angiotensin II-induced cardiac hypertrophy through upregulation of miR-98/let-7

RATIONALE

Thioredoxin (Trx)1 inhibits pathological cardiac hypertrophy. MicroRNAs (miRNAs) are small noncoding RNAs that downregulate posttranscriptional expression of target molecules.

OBJECTIVES

We investigated the role of miRNAs in mediating the antihypertrophic effect of Trx1 on angiotensin II (Ang II)-induced cardiac hypertrophy.

METHODS AND RESULTS

Microarray analyses of mature rodent microRNAs and quantitative RT-PCR/Northern blot analyses showed that Trx1 upregulates members of the let-7 family, including miR-98, in the heart and the cardiomyocytes therein. Adenovirus-mediated expression of miR-98 in cardiomyocytes reduced cell size both at baseline and in response to Ang II. Knockdown of miR-98, and of other members of the let-7 family, augmented Ang II-induced cardiac hypertrophy, and attenuated Trx1-mediated inhibition of Ang II-induced cardiac hypertrophy, suggesting that endogenous miR-98/let-7 mediates the antihypertrophic effect of Trx1. Cyclin D2 is one of the predicted targets of miR-98. Ang II significantly upregulated cyclin D2, which in turn plays an essential role in mediating Ang II-induced cardiac hypertrophy, whereas overexpression of Trx1 inhibited Ang II-induced upregulation of cyclin D2. miR-98 decreased both expression of cyclin D2 and the activity of a cyclin D2 3'UTR luciferase reporter, suggesting that both Trx1 and miR-98 negatively regulate cyclin D2. Overexpression of cyclin D2 attenuated the suppression of Ang II-induced cardiac hypertrophy by miR-98, suggesting that the antihypertrophic actions of miR-98 are mediated in part by downregulation of cyclin D2.

CONCLUSIONS

These results suggest that Trx1 upregulates expression of the let-7 family, including miR-98, which in turn inhibits cardiac hypertrophy, in part through downregulation of cyclin D2.

Thioredoxin-1 gene therapy enhances angiogenic signaling and reduces ventricular remodeling in infarcted myocardium of diabetic rats

BACKGROUND

The present study evaluated the reversal of diabetes-mediated impairment of angiogenesis in a myocardial infarction model of type 1 diabetic rats by intramyocardial administration of an adenoviral vector encoding thioredoxin-1 (Ad.Trx1). Various studies have linked diabetes-mediated impairment of angiogenesis to dysfunctional antioxidant systems in which thioredoxin-1 plays a central role.

METHODS AND RESULTS

Ad.Trx1 was administered intramyocardially in nondiabetic and diabetic rats immediately after myocardial infarction. Ad.LacZ was similarly administered to the respective control groups. The hearts were excised for molecular and immunohistochemical analysis at predetermined time points. Myocardial function was measured by echocardiography 30 days after the intervention. The Ad.Trx1-administered group exhibited reduced fibrosis, oxidative stress, and cardiomyocyte and endothelial cell apoptosis compared with the diabetic myocardial infarction group, along with increased capillary and arteriolar density. Western blot and immunohistochemical analysis demonstrated myocardial overexpression of thioredoxin-1, heme oxygenase-1, vascular endothelial growth factor, and p38 mitogen-activated protein kinase-beta, as well as decreased phosphorylated JNK and p38 mitogen-activated protein kinase-alpha, in the Ad.Trx1-treated diabetic group. Conversely, we observed a significant reduction in the expression of vascular endothelial growth factor in nondiabetic and diabetic animals treated with tin protoporphyrin (SnPP, a heme oxygenase-1 enzyme inhibitor), even after Ad.Trx1 therapy. Echocardiographic analysis after 4 weeks of myocardial infarction revealed significant improvement in myocardial functional parameters such as ejection fraction, fractional shortening, and E/A ratio in the Ad.Trx1-administered group compared with the diabetic myocardial infarction group.

CONCLUSIONS

This study demonstrates for the first time that impairment of angiogenesis and myocardial dysfunction can be regulated by Ad.Trx1 gene therapy in streptozotocin-induced diabetic rats subjected to infarction.

Redox regulation of cell survival by the thioredoxin superfamily: an implication of redox gene therapy in the heart

Reactive oxygen species (ROS) are the key mediators of pathogenesis in cardiovascular diseases. Members of the thioredoxin superfamily take an active part in scavenging reactive oxygen species, thus playing an essential role in maintaining the intracellular redox status. The alteration in the expression levels of thioredoxin family members and related molecules constitute effective biomarkers in various diseases, including cardiovascular complications that involve oxidative stress. Thioredoxin, glutaredoxin, peroxiredoxin, and glutathione peroxidase, along with their isoforms, are involved in interaction with the members of metabolic and signaling pathways, thus making them attractive targets for clinical intervention. Studies with cells and transgenic animals have supported this notion and raised the hope for possible gene therapy as modern genetic medicine. Of all the molecules, thioredoxins, glutaredoxins, and peroxiredoxins are emphasized, because a growing body of evidence reveals their essential and regulatory role in several steps of redox regulation. In this review, we discuss some pertinent observations regarding their distribution, structure, functions, and interactions with the several survival- and death-signaling pathways, especially in the myocardium.

Different extent of cardiac malfunction and resistance to oxidative stress in heterozygous and homozygous manganese-dependent superoxide dismutase-mutant mice

AIMS

The mitochondrially expressed manganese-dependent superoxide dismutase (MnSOD, SOD2) is an essential antioxidative enzyme that is necessary for normal heart function. In this study, we investigated the heart function of mice that were exposed to increased oxidative stress for time periods of up to 6 months due to decreased MnSOD activity caused by heterozygous deletion of the MnSOD gene.

METHODS AND RESULTS

We generated a mouse strain in which the gene encoding MnSOD was exchanged against a cassette containing the SOD cDNA under the control of the tetracycline response element. After breeding with mice carrying the tetracycline receptor, compound mice express MnSOD depending on the presence of tetracycline. Without tetracycline receptor the MnSOD gene is fully inactivated, and animals show an MnSOD-deficient phenotype. Using echocardiographic recordings, we found an impairment of left ventricular functions: MnSOD+/- mice displayed a decrease in fraction shortening and ejection fraction and an increase in left ventricular internal diameter in systole. Furthermore, MnSOD+/- mice developed heart hypertrophy with accompanying fibrosis and necrosis revealed by immunhistochemical analysis. Although we did not find an increase in apoptosis in MnSOD+/- hearts under normal conditions, we observed an increase of the number of apoptotic cells and vascular senescence after treatment with doxorubicin.

CONCLUSION

Our study demonstrates that lifelong reduction of MnSOD activity has a negative effect on normal heart function. This animal model presents a valuable tool to investigate the mechanism of heart pathology reported in patients bearing different polymorphic variants of the MnSOD gene and to develop new therapeutic strategies through manipulation of the antioxidative defence system.

Cardiac hypertrophy is associated with altered thioredoxin and ASK-1 signaling in a mouse model of menopause

Oxidative stress is implicated in menopause-associated hypertension and cardiovascular disease. The role of antioxidants in this process is unclear. We questioned whether the downregulation of thioredoxin (TRX) is associated with oxidative stress and the development of hypertension and target-organ damage (cardiac hypertrophy) in a menopause model. TRX is an endogenous antioxidant that also interacts with signaling molecules, such as apoptosis signal-regulated kinase 1 (ASK-1), independently of its antioxidant function. Aged female wild-type (WT) and follitropin receptor knockout (FORKO) mice (20-24 wk), with hormonal imbalances, were studied. Mice were infused with ANG II (400 ng x kg(-1) x min(-1); 14 days). Systolic blood pressure was increased by ANG II in WT (166+/-8 vs. 121+/-5 mmHg) and FORKO (176+/-7 vs. 115+/-5 mmHg; P<0.0001; n=9/group) mice. In ANG II-infused FORKO mice, cardiac mass was increased by 42% (P<0.001). This was associated with increased collagen content and augmented ERK1/2 phosphorylation (2-fold). Cardiac TRX expression and activity were decreased by ANG II in FORKO but not in WT (P<0.01) mice. ASK-1 expression, cleaved caspase III content, and Bax/Bcl-2 content were increased in ANG II-infused FORKO (P<0.05). ANG II had no effect on cardiac NAD(P)H oxidase activity or on O(2)(*-) levels in WT or FORKO. Cardiac ANG II type 1 receptor expression was similar in FORKO and WT. These findings indicate that in female FORKO, ANG II-induced cardiac hypertrophy and fibrosis are associated with the TRX downregulation and upregulation of ASK-1/caspase signaling. Our data suggest that in a model of menopause, protective actions of TRX may be blunted, which could contribute to cardiac remodeling independently of oxidative stress and hypertension.

Redox compartmentalization in eukaryotic cells

Diverse functions of eukaryotic cells are optimized by organization of compatible chemistries into distinct compartments defined by the structures of lipid-containing membranes, multiprotein complexes and oligomeric structures of saccharides and nucleic acids. This structural and chemical organization is coordinated, in part, through cysteine residues of proteins which undergo reversible oxidation-reduction and serve as chemical/structural transducing elements. The central thiol/disulfide redox couples, thioredoxin-1, thioredoxin-2, GSH/GSSG and cysteine/cystine (Cys/CySS), are not in equilibrium with each other and are maintained at distinct, non-equilibrium potentials in mitochondria, nuclei, the secretory pathway and the extracellular space. Mitochondria contain the most reducing compartment, have the highest rates of electron transfer and are highly sensitive to oxidation. Nuclei also have more reduced redox potentials but are relatively resistant to oxidation. The secretory pathway contains oxidative systems which introduce disulfides into proteins for export. The cytoplasm contains few metabolic oxidases and this maintains an environment for redox signaling dependent upon NADPH oxidases and NO synthases. Extracellular compartments are maintained at stable oxidizing potentials. Controlled changes in cytoplasmic GSH/GSSG redox potential are associated with functional state, varying with proliferation, differentiation and apoptosis. Variation in extracellular Cys/CySS redox potential is also associated with proliferation, cell adhesion and apoptosis. Thus, cellular redox biology is inseparable from redox compartmentalization. Further elucidation of the redox control networks within compartments will improve the mechanistic understanding of cell functions and their disruption in disease.