Redox signaling in cardiac physiology and pathology

N-n-Butyl Haloperidol Iodide Ameliorates Oxidative Stress in Mitochondria Induced by Hypoxia/Reoxygenation through the Mitochondrial c-Jun N-Terminal Kinase/Sab/Src/Reactive Oxygen Species Pathway in H9c2 Cells

Both c-Jun N-terminal kinase (JNK) and reactive oxygen species (ROS) play important roles in myocardial ischemia/reperfusion (I/R) injury. Our previous studies suggest that N-n-butyl haloperidol iodide (F2) exerts cardioprotection by reducing ROS production and JNK activation caused by I/R. In this study, we hypothesized that there is a JNK/Sab/Src/ROS pathway in the mitochondria in H9c2 cells following hypoxia/reoxygenation (H/R) that induces oxidative stress in the mitochondria and that F2 exerts mitochondrial protective effects during H/R injury by modulating this pathway. The results showed that H/R induced higher-level ROS in the cytoplasm on the one hand and JNK activation and translocation to the mitochondria by colocalization with Sab on the other. Moreover, H/R resulted in mitochondrial Src dephosphorylation, and subsequently, oxidative stress evidenced by the increase in ROS generation and oxidized cardiolipin in the mitochondrial membranes and by the decrease in mitochondrial superoxide dismutase activity and membrane potential. Furthermore, treatment with a JNK inhibitor or Sab small interfering RNA inhibited the mitochondrial translocation of p-JNK, decreased colocalization of p-JNK and Sab on the mitochondria, and reduced Src dephosphorylation and mitochondrial oxidative stress during H/R. In addition, Src dephosphorylation by inhibitor PP2 increased mitochondrial ROS production. F2, like inhibitors of the JNK/Sab/Src/ROS pathway, downregulated the H/R-induced mitochondrial translocation of p-JNK and the colocalization of p-JNK and Sab on the mitochondria, increased Src phosphorylation, and alleviated the above-mentioned mitochondrial oxidative stress. In conclusion, F2 could ameliorate H/R-associated oxidative stress in mitochondria in H9c2 cells through the mitochondrial JNK/Sab/Src/ROS pathway.

Enhanced Keap1-Nrf2 signaling protects the myocardium from isoproterenol-induced pathological remodeling in mice

Nuclear factor (erythroid-derived 2)-like 2 (NFE2L2/Nrf2) is an inducible transcription factor that is essential for maintenance of redox signaling in response to stress. This suggests that if Nrf2 expression response could be enhanced for a defined physiological pro-oxidant stress then it would be protective. This has important implications for the therapeutic manipulation of the Keap1/Nrf2 signaling pathway which is now gaining a lot of attention. We tested this hypothesis through the generation of Nrf2 transgene expression mouse model with and without isoproterenol-induced cardiac stress. Cardiac-specific mouse Nrf2 transgenic (mNrf2-TG) and non-transgenic (NTG) mice were subjected to isoproterenol (ISO) treatment and assessed for myocardial structure, function (echocardiography and electrocardiography), and glutathione redox state. Myocardial infarction and fibrosis along with increased inflammation leading to myocardial dysfunction was noted in NTG mice exposed to ISO, while mNrf2-TG hearts were resistant to the ISO insult. Preservation of myocardial structure and function in the mNrf2-TG mice was associated with the enhanced Nrf2 expression displayed in these hearts with an increased basal and post-treatment expression of redox modulatory genes and an overall enhanced antioxidant status. Of note, myocardium of ISO-treated TG mice displayed significantly increased stabilization of the KEAP1-NRF2 complex and enhanced release of NRF2 to the nucleus resulting in overall decreased pro-oxidant markers. Taken together, we suggest that a basal enhanced Nrf2 expression in mouse heart results in maintenance of redox homeostasis and counteracts ISO-induced oxidative stress, and suppresses pathological remodeling. These data suggest that an alternative therapeutic approach to enhance the efficacy of the Keap1-Nrf2 system is to stimulate basal expression of Nrf2.

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Isoproterenol induces oxidative/inflammatory stresses and leading to myocardial remodeling.

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Cardiac specific expression of Nrf2 augments Keap1-Nrf2 association, thereby timely responds to isoproterenol-induced stress.

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Augmented levels of Keap1-Nrf2 signaling is crucial to combat isoproterenol toxicity in the heart.

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Enhanced Nrf2-dependent antioxidant defense suppresses oxidative stress and prevents pathological cardiac remodeling.

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A controlled activation of global antioxidant signaling is vital for myocardial protection in stress conditions.

The Histone Deacetylase Inhibitor Suberoylanilide Hydroxamic Acid (SAHA) Restores Cardiomyocyte Contractility in a Rat Model of Early Diabetes

In early diabetes, hyperglycemia and the associated metabolic dysregulation promote early changes in the functional properties of cardiomyocytes, progressively leading to the appearance of the diabetic cardiomyopathy phenotype. Recently, the interplay between histone acetyltransferases (HAT) and histone deacetylases (HDAC) has emerged as a crucial factor in the development of cardiac disorders. The present study evaluates whether HDAC inhibition can prevent the development of cardiomyocyte contractile dysfunction induced by a short period of hyperglycemia, with focus on the potential underlying mechanisms. Cell contractility and calcium dynamics were measured in unloaded ventricular myocytes isolated from the heart of control and diabetic rats. Cardiomyocytes were either untreated or exposed to the pan-HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) for 90 min. Then, a fraction of each group of cells was used to evaluate the expression levels of proteins involved in the excitation-contraction coupling, and the cardiomyocyte metabolic activity, ATP content, and reactive oxygen species levels. SAHA treatment was able to counteract the initial functional derangement in cardiomyocytes by reducing cell oxidative damage. These findings suggest that early HDAC inhibition could be a promising adjuvant approach for preventing diabetes-induced cardiomyocyte oxidative damage, which triggers the pro-inflammatory signal cascade, mitochondrial damage, and ventricular dysfunction.

Nrf2 as a Potential Mediator of Cardiovascular Risk in Metabolic Diseases

Free radicals act as secondary messengers, modulating a number of important biological processes, including gene expression, ion mobilization in transport systems, protein interactions and enzymatic functions, cell growth, cell cycle, redox homeostasis, among others. In the cardiovascular system, the physiological generation of free radicals ensures the integrity and function of cardiomyocytes, endothelial cells, and adjacent smooth muscle cells. In physiological conditions, there is a balance between free radicals generation and the activity of enzymatic and non-enzymatic antioxidant systems. Redox imbalance, caused by increased free radical's production and/or reduced antioxidant defense, plays an important role in the development of cardiovascular diseases, contributing to cardiac hypertrophy and heart failure, endothelial dysfunction, hypertrophy and hypercontractility of vascular smooth muscle. Excessive production of oxidizing agents in detriment of antioxidant defenses in the cardiovascular system has been described in obesity, diabetes mellitus, hypertension, and atherosclerosis. The transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2), a major regulator of antioxidant and cellular protective genes, is primarily activated in response to oxidative stress. Under physiological conditions, Nrf2 is constitutively expressed in the cytoplasm of cells and is usually associated with Keap-1, a repressor protein. This association maintains low levels of free Nrf2. Stressors, such as free radicals, favor the translocation of Nrf2 to the cell nucleus. The accumulation of nuclear Nrf2 allows the binding of this protein to the antioxidant response element of genes that code antioxidant proteins. Although little information on the role of Nrf2 in the cardiovascular system is available, growing evidence indicates that decreased Nrf2 activity contributes to oxidative stress, favoring the pathophysiology of cardiovascular disorders found in obesity, diabetes mellitus, and atherosclerosis. The present mini-review will provide a comprehensive overview of the role of Nrf2 as a contributing factor to cardiovascular risk in metabolic diseases.

Optogenetic Monitoring of the Glutathione Redox State in Engineered Human Myocardium

Redox signaling affects all aspects of cardiac function and homeostasis. With the development of genetically encoded fluorescent redox sensors, novel tools for the optogenetic investigation of redox signaling have emerged. Here, we sought to develop a human heart muscle model for in-tissue imaging of redox alterations. For this, we made use of (1) the genetically-encoded Grx1-roGFP2 sensor, which reports changes in cellular glutathione redox status (GSH/GSSG), (2) human embryonic stem cells (HES2), and (3) the engineered heart muscle (EHM) technology. We first generated HES2 lines expressing Grx1-roGFP2 in cytosol or mitochondria compartments by TALEN-guided genomic integration. Grx1-roGFP2 sensor localization and function was verified by fluorescence imaging. Grx1-roGFP2 HES2 were then subjected to directed differentiation to obtain high purity cardiomyocyte populations. Despite being able to report glutathione redox potential from cytosol and mitochondria, we observed dysfunctional sarcomerogenesis in Grx1-roGFP2 expressing cardiomyocytes. Conversely, lentiviral transduction of Grx1-roGFP2 in already differentiated HES2-cardiomyocytes and human foreskin fibroblast was possible, without compromising cell function as determined in EHM from defined Grx1-roGFP2-expressing cardiomyocyte and fibroblast populations. Finally, cell-type specific GSH/GSSG imaging was demonstrated in EHM. Collectively, our observations suggests a crucial role for redox signaling in cardiomyocyte differentiation and provide a solution as to how this apparent limitation can be overcome to enable cell-type specific GSH/GSSG imaging in a human heart muscle context.

Proteomic Identification of Protein Glutathionylation in Cardiomyocytes

Reactive oxygen species (ROS) are important signaling molecules, but their overproduction is associated with many cardiovascular diseases, including cardiomyopathy. ROS induce various oxidative modifications, among which glutathionylation is one of the significant protein oxidations that occur under oxidative stress. Despite previous efforts, direct and site-specific identification of glutathionylated proteins in cardiomyocytes has been limited. In this report, we used a clickable glutathione approach in a HL-1 mouse cardiomyocyte cell line under exposure to hydrogen peroxide, finding 1763 glutathionylated peptides with specific Cys modification sites, which include many muscle-specific proteins. Bioinformatic and cluster analyses found 125 glutathionylated proteins, whose mutations or dysfunctions are associated with cardiomyopathy, many of which include sarcomeric structural and contractile proteins, chaperone, and other signaling or regulatory proteins. We further provide functional implication of glutathionylation for several identified proteins, including CSRP3/MLP and complex I, II, and III, by analyzing glutathionylated sites in their structures. Our report establishes a chemoselective method for direct identification of glutathionylated proteins and provides potential target proteins whose glutathionylation may contribute to muscle diseases.

Mechanisms of cardiac iron homeostasis and their importance to heart function

Heart disease is a common manifestation in conditions of iron imbalance. Normal heart function requires coupling of iron supply for oxidative phosphorylation and redox signalling with tight control of intracellular iron to below levels at which excessive ROS are generated. Iron supply to the heart is dependent on systemic iron availability which is controlled by the systemic hepcidin/ferroportin axis. Intracellular iron in cardiomyocytes is controlled in part by the iron regulatory proteins IRP1/2. This mini-review summarises current understanding of how cardiac cells regulate intracellular iron levels, and of the mechanisms linking cardiac dysfunction with iron imbalance. It also highlights a newly-recognised mechanism of intracellular iron homeostasis in cardiomyocytes, based on a cell-autonomous cardiac hepcidin/ferroportin axis. This new understanding raises pertinent questions on the interplay between systemic and local iron control in the context of heart disease, and the effects on heart function of therapies targeting the systemic hepcidin/ferroportin axis.

VEGF-A promotes angiogenesis after acute myocardial infarction through increasing ROS production and enhancing ER stress-mediated autophagy

Proangiogenesis is generally regarded as an effective approach for treating ischemic heart disease. Vascular endothelial growth factor (VEGF)-A is a strong and essential proangiogenic factor. Reactive oxygen species (ROS), endoplasmic reticulum (ER) stress, and autophagy are implicated in the process of angiogenesis. This study is designed to clarify the regulatory mechanisms underlying VEGF-A, ROS, ER stress, autophagy, and angiogenesis in acute myocardial infarction (AMI). A mouse model of AMI was successfully established by occluding the left anterior descending coronary artery. Compared with the sham-operated mice, the microvessel density, VEGF-A content, ROS production, expression of vascular endothelial cadherin, positive expression of 78 kDa glucose-regulated protein/binding immunoglobulin protein (GRP78/Bip), and LC3 puncta in CD31-positive endothelial cells of the ischemic myocardium were overtly elevated. Moreover, VEGF-A exposure predominantly increased the expression of beclin-1, autophagy-related gene (ATG) 4, ATG5, inositol-requiring enzyme-1 (IRE-1), GRP78/Bip, and LC3-II/LC3-I as well as ROS production in the human umbilical vein endothelial cells (HUVECs) in a dose and time-dependent manner. Both beclin-1 small interfering RNA and 3-methyladenine treatment predominantly mitigated VEGF-A-induced tube formation and migration of HUVECs, but they failed to elicit any notable effect on VEGF-A-increased expression of GRP78/Bip. Tauroursodeoxycholic acid not only obviously abolished VEGF-A-induced increase of IRE-1, GRP78/Bip, beclin-1 expression, and LC3-II/LC3-I, but also negated VEGF-A-induced tube formation and migration of HUVECs. Furthermore, N-acetyl- l-cysteine markedly abrogated VEGF-A-increased ROS production, IRE-1, GRP78/Bip, beclin-1 expression, and LC3-II/LC3-I in the HUVECs. Taken together, our data demonstrated that increased spontaneous production of VEGF-A may induce angiogenesis after AMI through initiating ROS-ER stress-autophagy axis in the vascular endothelial cells.

Resveratrol alleviates hypoxia/reoxygenation injury‑induced mitochondrial oxidative stress in cardiomyocytes

Resveratrol (RES) is a naturally occurring antioxidant compound found in red wine. Although it has been demonstrated to have a cardioprotective effect, the mechanism underlying this effect remains to be fully elucidated. The aim of the present study was to determine whether RES exerts a protective effect against mitochondrial oxidative stress and apoptosis in neonatal rat cardiomyocytes (NRCMs) induced by hypoxia/reoxygenation (H/R) injury. Primary cultured NRCMs were used as a model system and were divided into four experimental groups: Control, H/R, H/R + DMSO (H/R with 0.2% DMSO) and H/R + RES (H/R with 100 µM RES) groups. Mitochondrial oxidative stress was determined by measuring the alteration in the mitochondrial membrane potential (ΔΨm) of NRCMs, the release of lactate dehydrogenase (LDH) and the ratio of B-cell lymphoma 2 (Bcl-2)/Bcl-2-associated X protein (Bax) from NRCMs. Cell apoptosis was assessed by measuring cell apoptotic rates and the activity of caspase 3. In the H/R+RES group, RES significantly alleviated structural impairment, including disordered α-actin and F-actin, in the NRCMs induced by H/R injury. RES attenuated H/R injury-induced mitochondria oxidative stress. RES also attenuated H/R injury-induced cell apoptosis; it decreased the NRCM apoptotic rate from 84.25±7.41% (H/R) to 46.39±5.43% (H/R+RES) (P<0.05, n=4), rescued the decrease in the Bcl2/Bax ratio induced by H/R from 0.53±0.08-fold (H/R) to 0.86±0.06-fold (H/R+RES) (P<0.05, n=5) and alleviated the increased activity of caspase 3 induced by H/R from 1.32±0.06-fold to 1.02±0.04-fold (P<0.05, n=5). Furthermore, RES significantly attenuated the increment of LDH release induced by H/R injury in NRCMs from 1.41±0.03-fold (H/R) to 1.02±0.06-fold (H/R+RES) (P<0.01, n=4) and alleviated the depolarization of ΔΨm induced by H/R, shifting the ratio of JC-1 monomer from 62.39±1.82% (H/R) to 35.31±8.63% (H/R+RES) (P<0.05, n=4). RES alleviated the decrease in sirtuin 1 induced by H/R injury from 0.61±0.06-fold (H/R) to 1.01±0.05-fold (H/R+RES) (P<0.05, n=5). In conclusion, the present study is the first, to the best of our knowledge, to demonstrate that RES provides cardioprotection against H/R injury through decreasing mitochondria-mediated oxidative stress injury and structural impairment in NRCMs. These results provide scientific evidence for the clinical application of RES in the treatment of cardiac conditions.

Adult Cardiac Stem Cell Aging: A Reversible Stochastic Phenomenon?

Aging is by far the dominant risk factor for the development of cardiovascular diseases, whose prevalence dramatically increases with increasing age reaching epidemic proportions. In the elderly, pathologic cellular and molecular changes in cardiac tissue homeostasis and response to injury result in progressive deteriorations in the structure and function of the heart. Although the phenotypes of cardiac aging have been the subject of intense study, the recent discovery that cardiac homeostasis during mammalian lifespan is maintained and regulated by regenerative events associated with endogenous cardiac stem cell (CSC) activation has produced a crucial reconsideration of the biology of the adult and aged mammalian myocardium. The classical notion of the adult heart as a static organ, in terms of cell turnover and renewal, has now been replaced by a dynamic model in which cardiac cells continuously die and are then replaced by CSC progeny differentiation. However, CSCs are not immortal. They undergo cellular senescence characterized by increased ROS production and oxidative stress and loss of telomere/telomerase integrity in response to a variety of physiological and pathological demands with aging. Nevertheless, the old myocardium preserves an endogenous functionally competent CSC cohort which appears to be resistant to the senescent phenotype occurring with aging. The latter envisions the phenomenon of CSC ageing as a result of a stochastic and therefore reversible cell autonomous process. However, CSC aging could be a programmed cell cycle-dependent process, which affects all or most of the endogenous CSC population. The latter would infer that the loss of CSC regenerative capacity with aging is an inevitable phenomenon that cannot be rescued by stimulating their growth, which would only speed their progressive exhaustion. The resolution of these two biological views will be crucial to design and develop effective CSC-based interventions to counteract cardiac aging not only improving health span of the elderly but also extending lifespan by delaying cardiovascular disease-related deaths.

The effect of short-term coenzyme Q10 supplementation and pre-cooling strategy on cardiac damage markers in elite swimmers

Strenuous physical exercise and hyperthermia may paradoxically induce oxidative stress and adverse effects on myocardial function. The purpose of this study was to investigate the effect of 14-d coenzyme Q10 (CoQ10) supplementation and pre-cooling on serum creatine kinase-MB (CK-MB), cardiac Troponin I (cTnI), myoglobin (Mb), lactate dehydrogenase (LD), total antioxidant capacity (TAC), lipid peroxidation (LPO) and CoQ10 concentration in elite swimmers. In total, thirty-six healthy males (mean age 17 (sd 1) years) were randomly selected and divided into four groups of supplementation, supplementation with pre-cooling, pre-cooling and control. During an eighteen-session protocol in the morning and evening, subjects attended speed and endurance swimming training sessions for 5 km in each session. Blood sampling was done before (two stages) and after (two stages) administration of CoQ10 and pre-cooling. ANCOVA and repeated measurement tests with Bonferroni post hoc test were used for the statistical analysis of the data. There was no significant statistical difference among groups for the levels of CK-MB, cTnI, Mb, LD, TAC, LPO and CoQ10 at the presampling (stages 1 and 2) (P>0·05). However, pre-cooling and control groups show a significant increase in the levels of CK-MB, cTnI, Mb, LD and LPO compared with the supplementation and supplementation with pre-cooling groups in the post-sampling (stages 1 and 2) (P<0·05), except for the TAC and CoQ10. Consequently, CoQ10 supplementation prevents adverse changes of myocardial damage and oxidative stress during swimming competition phase. Meanwhile, the pre-cooling strategy individually has no desired effect on the levels of CK-MB, cTnI, Mb, LD, LPO, TAC and CoQ10.

Hydrogen peroxide constricts rat arteries by activating Na+-permeable and Ca2+-permeable cation channels

Oxidative stress is associated with many cardiovascular diseases, such as hypertension and arteriosclerosis. Oxidative stress reportedly activates the L-type voltage-gated calcium channel (VDCC_L) and elevates [Ca²⁺]_i in many cells. However, how oxidative stress activates VDCC_L under clinical setting and the consequence for arteries are unclear. Here, we examined the hypothesis that hydrogen peroxide (H₂O₂) regulates membrane potential (Em) by altering Na⁺ influx through cation channels, which consequently activates VDCC_L to induce vasoconstriction in rat mesenteric arteries. To measure the tone of the endothelium-denuded arteries, a conventional isometric organ chamber was used. Membrane currents and Em were recorded by the patch-clamp technique. [Ca²⁺]_i and [Na⁺]_i were measured with microfluorometry using Fura2-AM and SBFI-AM, respectively. We found that H₂O₂ (10 and 100 µM) increased arterial contraction, and nifedipine blocked the effects of H₂O₂ on isometric contraction. H₂O₂ increased [Ca²⁺]_i as well as [Na⁺]_i, and depolarised Em. Gd³⁺ (1 µM) blocked all these H₂O₂-induced effects including Em depolarisation and increases in [Ca²⁺]_i and [Na⁺]_i. Although both nifedipine (30 nM) and low Na⁺ bath solution completely prevented the H₂O₂-induced increase in [Na⁺], they only partly inhibited the H₂O₂-induced effects on [Ca²⁺]_i and Em. Taken together, the results suggested that H₂O₂ constricts rat arteries by causing Em depolarisation and VDCC_L activation through activating Gd³⁺-and nifedipine-sensitive, Na⁺-permeable channels as well as Gd³⁺-sensitive Ca²⁺-permeable cation channels. We suggest that unidentified Na⁺-permeable cation channels as well as Ca²⁺-permeable cation channels may function as important mediators for oxidative stress-induced vascular dysfunction.

Benefits of multiple micronutrient supplementation in heart failure: A comprehensive review

BACKGROUND

Multiple micronutrient supplementation has been suggested to have a role on health outcomes in patients with heart failure (HF), but the evidence is inconclusive.

OBJECTIVE

To elucidate the role of multiple micronutrient supplementation in heart failure we performed a comprehensive review of the literature.

METHODS AND RESULTS

The search in databases included PUBMED (until June 2018) to detect randomized controlled trials (RCTs) and meta-analyzes that investigated the impact of micronutrient supplementation in HF.

RESULTS

With more than 2357 titles and abstracts reviewed, we included only the studies suitable for the final review. Whether alone or in combination, micronutrients have been found to improve the health outcomes of patients with HF by improving symptoms, work capacity and left ventricular ejection fraction (LVEF), thus increasing the quality of life in these patients.

CONCLUSION

Future studies are needed to document the effects of multiple micronutrient associations in order to include them in nutritional guidelines to increase survival and to improve quality of life in patients with heart failure.

Targeting mitochondrial dysfunction and oxidative stress in heart failure: Challenges and opportunities

Mitochondrial dysfunction characterized by impaired bioenergetics, oxidative stress and aldehydic load is a hallmark of heart failure. Recently, different research groups have provided evidence that selective activation of mitochondrial detoxifying systems that counteract excessive accumulation of ROS, RNS and reactive aldehydes is sufficient to stop cardiac degeneration upon chronic stress, such as heart failure. Therefore, pharmacological and non-pharmacological approaches targeting mitochondria detoxification may play a critical role in the prevention or treatment of heart failure. In this review we discuss the most recent findings on the central role of mitochondrial dysfunction, oxidative stress and aldehydic load in heart failure, highlighting the most recent preclinical and clinical studies using mitochondria-targeted molecules and exercise training as effective tools against heart failure.

Protective Action of Diazoxide on Isoproterenol-Induced Hypertrophy Is Mediated by Reduction in MicroRNA-132 Expression

INTRODUCTION AND METHODS

The effects of diazoxide on cardiac hypertrophy and miR-132 expression were characterized in adult rats and in cardiomyocytes. Diazoxide effects on reactive oxygen species (ROS) production and on the cAMP-response element binding (CREB) transcription factor's abundance in cardiomyocytes were also analyzed. ROS measurements used a fluorescent dye. Western blot analysis and quantitative Reverse Transcription Polymerase Chain Reaction were used to measure phosphorylated form of CREB (pCREB) abundance and miR-132 expression, respectively.

RESULTS

Isoproterenol (ISO) induced cardiac hypertrophy, an effect that was mitigated by diazoxide. The rate of ROS production, CREB phosphorylation, and miR-132 expression increased after the addition of ISO. H2O2 increased pCREB abundance and miR-132 expression; upregulation of miR-132 was blocked by the specific inhibitor of CREB transcription, 666-15. Consistent with a role of ROS on miR-132 expression, diazoxide prevented the increase in ROS production, miR-132 expression, and pCREB abundance produced by ISO. Phosphorylation of CREB by ISO was prevented by U0126, an inhibitor of mitogen-activated protein kinase.

CONCLUSIONS

Our data first demonstrate that diazoxide mitigates hypertrophy by preventing an increase in miR-132 expression. The mechanism likely involves less ROS production leading to less phosphorylation of CREB. Our data further show that ROS enhance miR-132 transcription, and that ISO effects are probably mediated by the mitogen-activated protein kinase pathway.

SMYD2 glutathionylation contributes to degradation of sarcomeric proteins

Reactive oxygen species (ROS) contribute to the etiology of multiple muscle-related diseases. There is emerging evidence that cellular stress can lead to destabilization of sarcomeres, the contractile unit of muscle. However, it is incompletely understood how cellular stress induces structural destabilization of sarcomeres. Here we report that glutathionylation of SMYD2 contributes to a loss of myofibril integrity and degradation of sarcomeric proteins mediated by MMP-2 and calpain 1. We used a clickable glutathione approach in a cardiomyocyte cell line and found selective glutathionylation of SMYD2 at Cys13. Biochemical analysis demonstrated that SMYD2 upon oxidation or glutathionylation at Cys13 loses its interaction with Hsp90 and N2A, a domain of titin. Upon dissociation from SMYD2, N2A or titin is degraded by activated MMP-2, suggesting a protective role of SMYD2 in sarcomere stability. Taken together, our results support that SMYD2 glutathionylation is a novel molecular mechanism by which ROS contribute to sarcomere destabilization.

Arrhythmogenic Mechanisms in Heart Failure: Linking β-Adrenergic Stimulation, Stretch, and Calcium

Heart failure (HF) is associated with elevated sympathetic tone and mechanical load. Both systems activate signaling transduction pathways that increase cardiac output, but eventually become part of the disease process itself leading to further worsening of cardiac function. These alterations can adversely contribute to electrical instability, at least in part due to the modulation of Ca²⁺ handling at the level of the single cardiac myocyte. The major aim of this review is to provide a definitive overview of the links and cross talk between β-adrenergic stimulation, mechanical load, and arrhythmogenesis in the setting of HF. We will initially review the role of Ca²⁺ in the induction of both early and delayed afterdepolarizations, the role that β-adrenergic stimulation plays in the initiation of these and how the propensity for these may be altered in HF. We will then go onto reviewing the current data with regards to the link between mechanical load and afterdepolarizations, the associated mechano-sensitivity of the ryanodine receptor and other stretch activated channels that may be associated with HF-associated arrhythmias. Furthermore, we will discuss how alterations in local Ca²⁺ microdomains during the remodeling process associated the HF may contribute to the increased disposition for β-adrenergic or stretch induced arrhythmogenic triggers. Finally, the potential mechanisms linking β-adrenergic stimulation and mechanical stretch will be clarified, with the aim of finding common modalities of arrhythmogenesis that could be targeted by novel therapeutic agents in the setting of HF.

Chronic heart failure is characterized by altered mitochondrial function and structure in circulating leucocytes

Oxidative stress is currently viewed as a key factor in the genesis and progression of Heart Failure (HF). The aim of this study was to characterize the mitochondrial changes linked to oxidative stress generation in circulating peripheral blood mononuclear cells isolated from chronic HF patients (HF_PBMCs) in order to highlight the involvement of mitochondrial dysfunction in the pathophysiology of HF.

To assess the production of reactive oxygen species (ROS), mitochondrial function and ultrastructure and the mitophagic flux in circulating PBMCs we enrolled 15 patients with HF and a control group of ten healthy subjects. The HF_PBMCs showed a mitochondrial population consisting of damaged and less functional organelles responsible of higher superoxide anion production both at baseline and under in vitro stress conditions, with evidence of cellular apoptosis. Although the mitophagic flux at baseline was enhanced in HF_PBMCs at level similar to those that could be achieved in control PBMCs only under inflammatory stress conditions, the activation of mitophagy was unable to preserve a proper mitochondrial dynamics upon stress stimuli in HF.

In summary, circulating HF_PBMCs show structural and functional derangements of mitochondria with overproduction of reactive oxidant species. This mitochondrial failure sustains a leucocyte dysfunctional status in the blood that may contribute to development and persistence of stress conditions within the cardiovascular system in HF.

Cysteine-Based Redox Sensing and Its Role in Signaling by Cyclic Nucleotide-Dependent Kinases in the Cardiovascular System

Oxidant molecules are produced in biological systems and historically have been considered causal mediators of damage and disease. While oxidants may contribute to the pathogenesis of disease, evidence continues to emerge that shows these species also play important regulatory roles in health. A major mechanism of oxidant sensing and signaling involves their reaction with reactive cysteine thiols within proteins, inducing oxidative posttranslational modifications that can couple to altered function to enable homeostatic regulation. Protein kinase A and protein kinase G are regulated by oxidants in this way, and this review focuses on our molecular-level understanding of these events and their role in regulating cardiovascular physiology during health and disease.

Withaferin A inhibits apoptosis via activated Akt-mediated inhibition of oxidative stress

Withaferin A (WFA), a withanolide derived from medicinal plant Withania somnifera, possesses anti-tumorigenic and immunomodulatory activities against various cancer cells. However, the role of WFA in myocardial ischemia reperfusion (MI/R) injury remains unclear. In the present study, we determined whether WFA may regulate cardiac ischemia reperfusion injury and elucidate the underlying mechanisms. We demonstrated that WFA enhanced H9c2 cells survival ability against simulated ischemia/reperfusion (SI/R) or hydrogen peroxide (H₂O₂)-induced cell apoptosis. In addition, the enhanced oxidative stress induced by SI/R was inhibited by WFA. Among the multiple antioxidant molecules determined, antioxidants SOD2, SOD3, Prdx-1 was obviously upregulated by WFA. When Akt inhibitor IV was administrated, WFA's suppression effect on oxidative stress was obviously abolished. Additional experiments demonstrated that WFA successfully inhibited H₂O₂ induced upregulation of SOD2, SOD3, and Prdx-1, ameliorated cardiomyocyte caspase-3 activity via an Akt dependent manner. Collectively, these results support the therapeutic potential of WFA against cardiac ischemia reperfusion injury and highlight the application of WFA in cardiovascular diseases holding great promise for the future.

Tauroursodeoxycholic Acid Alleviates H2O2-Induced Oxidative Stress and Apoptosis via Suppressing Endoplasmic Reticulum Stress in Neonatal Rat Cardiomyocytes

Introduction:

We aimed to test the mechanism of protective effects of tauroursodeoxycholic acid (TUDCA) on cardiovascular disease using cultured cardiomyocytes.

Methods:

Neonatal rat cardiomyocytes (NRCMs) were isolated and cultured and then the cells were divided into 4 groups based on the treatments: control group (cells treated with culture medium), H₂O₂/thapsigargin (TG) group (cells treated with oxidative stress and endoplasmic reticulum [ER] stress inducer), TUDCA group, and H₂O₂/TG + TUDCA group. The treated NRCMs were then subjected to serial analyses including flow cytometry, enzyme-linked immunosorbent assay, and Western blotting.

Results:

Tauroursodeoxycholic acid significantly attenuated H₂O₂-induced reactive oxygen species generation and lactate dehydrogenase release and restored H₂O₂-induced reductions of glutathione and superoxide dismutase levels in NRCMs. Tauroursodeoxycholic acid also alleviated H₂O₂-induced cardiomyocytes apoptosis, as well as the Bax/Bcl2 ratio compared with that of H₂O₂ treated alone. In addition, TUDCA suppressed TG-induced ER stress as reflected by inversing cell viability and the expression levels of glucose-regulated protein 78 kDa and C/enhancer-binding protein homologous protein.

Conclusion:

Our data indicated that TUDCA-mediated inhibition on H₂O₂-induced oxidative stress and cardiomyocytes apoptosis was through suppressing ER stress, and TUDCA possesses the potential to be developed as therapeutic tool in clinical use for cardiovascular diseases.

Nox2 in regulatory T cells promotes angiotensin II-induced cardiovascular remodeling

The superoxide-generating enzyme Nox2 contributes to hypertension and cardiovascular remodeling triggered by activation of the renin-angiotensin system. Multiple Nox2-expressing cells are implicated in angiotensin II-induced (Ang II-induced) pathophysiology, but the importance of Nox2 in leukocyte subsets is poorly understood. Here, we investigated the role of Nox2 in T cells, particularly Tregs. Mice globally deficient in Nox2 displayed increased numbers of Tregs in the heart at baseline, whereas Ang II-induced effector T cell (Teff) infiltration was inhibited. To investigate the role of Treg Nox2, we generated a mouse line with CD4-targeted Nox2 deficiency (Nox2fl/flCD4Cre+). These animals showed inhibition of Ang II-induced hypertension and cardiac remodeling related to increased tissue-resident Tregs and reduction in infiltrating Teffs, including Th17 cells. The protection in Nox2fl/flCD4Cre+ mice was reversed by anti-CD25 antibody depletion of Tregs. Mechanistically, Nox2-/y Tregs showed higher in vitro suppression of Teff proliferation than WT Tregs, increased nuclear levels of FoxP3 and NF-κB, and enhanced transcription of CD25, CD39, and CD73. Adoptive transfer of Tregs confirmed that Nox2-deficient cells had greater inhibitory effects on Ang II-induced heart remodeling than WT cells. These results identify a previously unrecognized role of Nox2 in modulating suppression of Tregs, which acts to enhance hypertension and cardiac remodeling.

Anti-apoptotic effects of adipose-derived adherent stromal cells in mesenchymal stem cells exposed to oxidative stress

Adipose-derived stromal vascular fractions (SVFs) are a heterogeneous collection of cells, and their regenerative modality has been applied in various animal experiments and clinical trials. Despite the attractive advantages of SVFs in clinical interventions, the recent status of clinical studies involving the application of SVFs in many diseases has not been fully evaluated. Mesenchymal stem cells (MSCs) are multipotent stromal cells that can differentiate into a variety of cell types despite their low numbers in heart tissue. Here, we sought to determine if SVF implantation into impaired heart tissue affected endogenous MSCs in the heart. Therefore, we investigated the expression levels of proteins associated with oxidation, inflammation, and apoptosis in MSCs co-cultured with adipose-derived adherent stromal cells (ADASs) from 6 donors' SVFs under oxidative stress conditions for their roles in many physiological processes in the heart. Interestingly, p53 pathway proteins and mitogen-activated protein kinase (MAPK) signalling pathway components were up-regulated by H₂ O₂ but exhibited a downward trend in MSCs co-cultured with ADASs. These data suggest that ADASs may inhibit oxidative stress-induced apoptosis in MSCs via the p53 and MAPK pathways. Our findings also suggest that the positive effects of SVF implantation into damaged heart tissue may be attributed to the various responses of MSCs. This finding may provide new insights for the clinical application of adipose-derived SVF transplantation in cardiac diseases.

SIGNIFICANCE OF THE STUDY

We investigated the expression levels of proteins associated with oxidation, inflammation, and apoptosis in MSCs co-cultured with isolated ADASs from 6 donors' SVFs under oxidative stress conditions. Our results imply that isolated ADASs from SVFs may inhibit oxidative stress-induced cell cycle arrest and/or apoptosis in MSCs via a p53-dependent pathway. Furthermore, we identified an anti-apoptotic mechanism involving oxidative stress-induced apoptosis by adipose-derived ADASs in MSCs for the first time. Our findings suggest that the positive effects of SVF implantation into damaged heart tissue may be attributed to the various actions of MSCs.

Cardiomyopathy, oxidative stress and impaired contractility in a rheumatoid arthritis mouse model

Objectives

Patients with rheumatoid arthritis (RA) display an increased risk of heart failure independent of traditional cardiovascular risk factors. To elucidate myocardial disease in RA, we have investigated molecular and cellular remodelling of the heart in an established mouse model of RA.

Methods

The collagen antibody-induced arthritis (CAIA) RA mouse model is characterised by joint inflammation and increased inflammatory markers in the serum. We used CAIA mice in the postinflammatory phase that resembles medically controlled RA or RA in remission. Hearts were collected for cardiomyocyte isolation, biochemistry and histology analysis.

Results

Hearts from mice subjected to CAIA displayed hypertrophy (heart/body weight, mean±SD: 5.9±0.8vs 5.1±0.7 mg/g, p<0.05), fibrosis and reduced left ventricular fractional shortening compared with control. Cardiomyocytes from CAIA mice showed reduced cytosolic [Ca2+]i transient amplitudes (F/F0, mean±SD: 3.0±1.2vs 3.6±1.5, p<0.05) that was linked to reductions in sarcoplasmic reticulum (SR) Ca2+ store (F/F0, mean±SD: 3.5±1.3vs 4.4±1.3, p<0.01) measured with Ca2+ imaging. This was associated to lower fractional shortening in the cardiomyocytes from the CAIA mice (%FS, mean±SD: 3.4±2.2 vs 4.6%±2.3%, p<0.05). Ca2+ handling proteins displayed oxidation-dependent posttranslational modifications that together with an increase in superoxide dismutase expression indicate a cell environment with oxidative stress.

Conclusions

This study shows that inflammation during active RA has long-term consequences on molecular remodelling and contractile function of the heart, which further supports that rheumatology patients should be followed for development of heart failure.

Immuno-Spin Trapping-Based Detection of Oxidative Modifications in Cardiomyocytes and Coronary Endothelium in the Progression of Heart Failure in Tgαq*44 Mice

Recent studies suggest both beneficial and detrimental role of increased reactive oxygen species and oxidative stress in heart failure (HF). However, it is not clear at which stage oxidative stress and oxidative modifications occur in the endothelium in relation to cardiomyocytes in non-ischemic HF. Furthermore, most methods used to date to study oxidative stress are either non-specific or require tissue homogenization. In this study, we used immuno-spin trapping (IST) technique with fluorescent microscopy-based detection of DMPO nitrone adducts to localize and quantify oxidative modifications of the hearts from Tgαq*44 mice; a murine model of HF driven by cardiomyocyte-specific overexpression of Gαq* protein. Tgαq*44 mice and age-matched FVB controls at early, transition, and late stages of HF progression were injected with DMPO in vivo and analyzed ex vivo for DMPO nitrone adducts signals. Progressive oxidative modifications in cardiomyocytes, as evidenced by the elevation of DMPO nitrone adducts, were detected in hearts from 10- to 16-month-old, but not in 8-month-old Tgαq*44 mice, as compared with age-matched FVB mice. The DMPO nitrone adducts were detected in left and right ventricle, septum, and papillary muscle. Surprisingly, significant elevation of DMPO nitrone adducts was also present in the coronary endothelium both in large arteries and in microcirculation simultaneously, as in cardiomyocytes, starting from 10-month-old Tgαq*44 mice. On the other hand, superoxide production in heart homogenates was elevated already in 6-month-old Tgαq*44 mice and progressively increased to high levels in 14-month-old Tgαq*44 mice, while the enzymatic activity of catalase, glutathione reductase, and glutathione peroxidase was all elevated as early as in 4-month-old Tgαq*44 mice and stayed at a similar level in 14-month-old Tgαq*44. In summary, this study demonstrates that IST represents a unique method that allows to quantify oxidative modifications in cardiomyocytes and coronary endothelium in the heart. In Tgαq*44 mice with slowly developing HF, driven by cardiomyocyte-specific overexpression of Gαq* protein, an increase in superoxide production, despite compensatory activation of antioxidative mechanisms, results in the development of oxidative modifications not only in cardiomyocytes but also in coronary endothelium, at the transition phase of HF, before the end-stage disease.

Evaluation of the level of dynamic thiol/disulphide homeostasis in adolescent patients with newly diagnosed primary hypertension

BACKGROUND

Thiol/disulphide homeostasis plays a critical role in numerous intracellular enzymatic pathways including antioxidant defense and detoxification. This study was designed to investigate the impact of thiol/disulfide homeostasis in adolescent patients with recently diagnosed primary hypertension (HT) using a novel and automated method.

METHODS

Native thiol/disulphide levels were measured by a novel spectrophotometric method (Cobasc 501, Roche Diagnostics, Mannheim, Germany) in 30 patients with primary HT together with 30 healthy controls.

RESULTS

The levels of native thiol, total thiol, and native thiol/total thiol ratios were significantly lower, while the disulphide level, disulphide/native thiol, and disulphide/total thiol ratios were significantly higher in patients with primary HT compared with the control group. There were significant positive correlations between 24-h mean systolic and diastolic blood pressure and disulphide levels, disulphide/native thiol, and disulphide/total thiol ratios. A multiple linear regression model showed that a disulphide/native thiol ratio above 5 and family history of HT are independent predictors of HT.

CONCLUSIONS

Our study showed that dynamic thiol/disulphide homeostasis shifted towards disulphide formation in adolescent patients with primary HT. Understanding the role of thiol/disulfide homeostasis in primary HT might provide new therapeutic intervention strategies for patients.

Dexmedetomidine attenuates H2O2-induced neonatal rat cardiomyocytes apoptosis through mitochondria- and ER-medicated oxidative stress pathways

Dexmedetomidine (DEX), an α2 adrenoceptor agonist, has sedative and analgesic properties and myocardial protective effects. However, the mechanism underlying the protective effects of DEX on the myocardium remain unclear. The present study aimed to determine whether DEX serves an important role on cardioprotection through the endoplasmic reticulum (ER)- and mitochondria-mediated apoptosis signaling pathways. Neonatal rat cardiomyocytes (NRCMs) were cultured and divided four groups: i) Normal culture medium with 10% fetal bovine serum (control group); ii) H₂O₂ at 500 µM (H₂O₂ group); iii) DEX at 5 µM (DEX group); and iv) H₂O₂ plus DEX (H₂O₂ + DEX group). The levels of apoptosis and oxidative stress of NRCMs were investigated by ELISA, western blotting, flow cytometry and cell immunofluorescence. DEX significantly suppressed H₂O₂-induced apoptosis, and increased activity of caspases 3, 8 and 9 of NRCMs. DEX inhibited mitochondria-mediated oxidative stress and apoptosis, as evidenced by decreased levels of reactive oxygen species and lactic dehydrogenase, alleviated mitochondrial membrane potential depolarization, and increased Bcl-2-associated X protein/B-cell lymphoma 2 ratio. In addition, DEX decreased the activity of caspase 12, and the expression levels of glucose-regulated protein 78 kDa and serine/threonine-protein kinase/endoribonuclease IRE1, three major signaling molecules involved in the ER stress-mediated apoptosis pathway. Preventive treatment with DEX alleviates cardiomyocyte against H₂O₂-induced oxidative stress injury through attenuating the mitochondria- and ER-mediated apoptosis pathways.

Propofol attenuates H2O2-induced oxidative stress and apoptosis via the mitochondria- and ER-medicated pathways in neonatal rat cardiomyocytes

Previous studies have shown that propofol, an intravenous anesthetic commonly used in clinical practice, protects the myocardium from injury. Mitochondria- and endoplasmic reticulum (ER)-mediated oxidative stress and apoptosis are two important signaling pathways involved in myocardial injury and protection. The present study aimed to test the hypothesis that propofol could exert a cardio-protective effect via the above two pathways. Cultured neonatal rat cardiomyocytes were treated with culture medium (control group), H₂O₂ at 500 μM (H₂O₂ group), propofol at 50 μM (propofol group), and H₂O₂ plus propofol (H₂O₂ + propofol group), respectively. The oxidative stress, mitochondrial membrane potential (ΔΨm) and apoptosis of the cardiomyocytes were evaluated by a series of assays including ELISA, flow cytometry, immunofluorescence microscopy and Western blotting. Propofol significantly suppressed the H₂O₂-induced elevations in the activities of caspases 3, 8, 9 and 12, the ratio of Bax/Bcl-2, and cell apoptosis. Propofol also inhibited the H₂O₂-induced reactive oxygen species (ROS) generation, lactic dehydrogenase (LDH) release and mitochondrial transmembrane potential (ΔΨm) depolarization, and restored the H₂O₂-induced reductions of glutathione (GSH) and superoxide dismutase (SOD). In addition, propofol decreased the expressions of glucose-regulated protein 78 kDa (Grp78) and inositol-requiring enzyme 1α (IRE1α), two important signaling molecules in the ER-mediated apoptosis pathway. Propofol protects cardiomyocytes from H₂O₂-induced injury by inhibiting the mitochondria- and ER-mediated apoptosis signaling pathways.

Role of superoxide ion formation in hypothermia/rewarming induced contractile dysfunction in cardiomyocytes

Rewarming following accidental hypothermia is associated with circulatory collapse due primarily to impaired cardiac contractile (systolic) function. Previously, we found that reduced myofilament Ca²⁺ sensitivity underlies hypothermia/rewarming (H/R)-induced cardiac contractile dysfunction. This reduced Ca²⁺ sensitivity is associated with troponin I (cTnI) phosphorylation. We hypothesize that H/R induces reactive oxygen species (ROS) formation in cardiomyocytes, which leads to cTnI phosphorylation and reduced myofilament Ca²⁺ sensitivity. To test this hypothesis, we exposed isolated rat cardiomyocytes to a 2-h period of severe hypothermia (15 °C) followed by rewarming (35 °C) with and without antioxidant (TEMPOL) treatment. Simultaneous measurements of cytosolic Ca²⁺ ([Ca²⁺]_cyto) and contractile (sarcomere shortening) responses indicated that H/R-induced contractile dysfunction and reduced Ca²⁺ sensitivity was prevented in cardiomyocytes treated with TEMPOL. In addition, TEMPOL treatment blunted H/R-induced cTnI phosphorylation. These results support our overall hypothesis and suggest that H/R disrupts excitation-contraction coupling of the myocardium through a cascade of event triggered by excessive ROS formation during hypothermia. Antioxidant treatment may improve successful rescue of accidental hypothermia victims.

Reactive oxygen species regulate axonal regeneration through the release of exosomal NADPH oxidase 2 complexes into injured axons

Reactive oxygen species (ROS) contribute to tissue damage and remodelling mediated by the inflammatory response after injury. Here we show that ROS, which promote axonal dieback and degeneration after injury, are also required for axonal regeneration and functional recovery after spinal injury. We find that ROS production in the injured sciatic nerve and dorsal root ganglia requires CX3CR1-dependent recruitment of inflammatory cells. Next, exosomes containing functional NADPH oxidase 2 complexes are released from macrophages and incorporated into injured axons via endocytosis. Once in axonal endosomes, active NOX2 is retrogradely transported to the cell body through an importin-β1-dynein-dependent mechanism. Endosomal NOX2 oxidizes PTEN, which leads to its inactivation, thus stimulating PI3K-phosporylated (p-)Akt signalling and regenerative outgrowth. Challenging the view that ROS are exclusively involved in nerve degeneration, we propose a previously unrecognized role of ROS in mammalian axonal regeneration through a NOX2-PI3K-p-Akt signalling pathway.

Myocardial infarction-induced microRNA-enriched exosomes contribute to cardiac Nrf2 dysregulation in chronic heart failure

The imbalance between the synthesis of reactive oxygen species and their elimination by antioxidant defense systems results in macromolecular damage and disruption of cellular redox signaling, affecting cardiac structure and function, thus contributing to contractile dysfunction, myocardial hypertrophy, and fibrosis in chronic heart failure [chronic heart failure (CHF)]. The Kelch-like ECH-associated protein 1-nuclear factor erythroid 2-related factor 2 (Nrf2) pathway is an important antioxidant defense mechanism and is closely associated with oxidative stress-mediated cardiac remodeling in CHF. In the present study, we investigated the regulation of myocardial Nrf2 in the postmyocardial infarction (post-MI) state. Six weeks post-MI, Nrf2 protein was downregulated in the heart, resulting in a decrease of Nrf2-targeted antioxidant enzymes, whereas paradoxically the transcription of Nrf2 was increased, suggesting that translational inhibition of Nrf2 may contribute to the dysregulation in CHF. We therefore hypothesized that microRNAs may be involved in the translational repression of Nrf2 mRNA in the setting of CHF. Using quantitative real-time PCR analysis, we found that three microRNAs, including microRNA-27a, microRNA-28-3p, and microRNA-34a, were highly expressed in the left ventricle of infarcted hearts compared with other organs. Furthermore, in vitro analysis revealed that cultured cardiac myocytes and fibroblasts expressed these three microRNAs in response to TNF-α stimulation. These microRNAs were preferentially incorporated into exosomes and secreted into the extracellular space in which microRNA-enriched exosomes mediated intercellular communication and Nrf2 dysregulation. Taken together, these results suggest that increased local microRNAs induced by MI may contribute to oxidative stress by the inhibition of Nrf2 translation in CHF. NEW & NOTEWORTHY The results of this work provide a novel mechanism mediated by microRNA-enriched exosomes, contributing to the nuclear factor erythroid 2-related factor 2 dysregulation and subsequent oxidative stress. Importantly, these new findings will provide a promising strategy to improve the therapeutic efficacy through targeting nuclear factor erythroid 2-related factor 2-related microRNAs in the chronic heart failure state, which show potentially clinical applications.

Oxidation of Atg3 and Atg7 mediates inhibition of autophagy

Macroautophagy (autophagy) is a crucial cellular stress response for degrading defective macromolecules and organelles, as well as providing bioenergetic intermediates during hypoxia and nutrient deprivation. Here we report a thiol-dependent process that may account for impaired autophagy during aging. This is through direct oxidation of key autophagy-related (Atg) proteins Atg3 and Atg7. When inactive Atg3 and Atg7 are protected from oxidation due to stable covalent interaction with their substrate LC3. This interaction becomes transient upon activation of Atg3 and Atg7 due to transfer of LC3 to phosphatidylethanolamine (lipidation), a process crucial for functional autophagy. However, loss in covalent-bound LC3 also sensitizes the catalytic thiols of Atg3 and Atg7 to inhibitory oxidation that prevents LC3 lipidation, observed in vitro and in mouse aorta. Here findings provide a thiol-dependent process for negatively regulating autophagy that may contribute to the process of aging, as well as therapeutic targets to regulate autophagosome maturation.

A dysfunction of autophagy can be detected in aged tissues, but how this is regulated is unclear. Here, the authors show in vitro and in aged mice aorta, that inhibition of LC3 lipidation under conditions of oxidative stress causes oxidation of Atg3 and Atg7, preventing autophagosome maturation.

Physical Exercise and Its Protective Effects on Diabetic Cardiomyopathy: What Is the Evidence?

As one of the most serious complications of diabetes, diabetic cardiomyopathy (DCM) imposes a huge burden on individuals and society, and represents a major public health problem. It has long been recognized that physical exercise has important health benefits for patients with type 2 diabetes, and regular physical exercise can delay or prevent the complications of diabetes. Current studies show that physical exercise has been regarded as an importantly non-pharmacological treatment for diabetes and DCM, with high efficacy and low adverse events. It can inhibit the pathological processes of myocardial apoptosis, myocardial fibrosis, and myocardial microvascular diseases through improving myocardial metabolism, enhancing the regulation of Ca²⁺, and protecting the function of mitochondria. Eventually, it can alleviate the occurrence and development of diabetic complications. Describing the mechanisms of physical exercise on DCM may provide a new theory for alleviating, or even reversing the development of DCM, and prevent it from developing to heart failure.

Targeting Mitochondrial Calcium Handling and Reactive Oxygen Species in Heart Failure

PURPOSE OF REVIEW

In highly prevalent cardiac diseases, new therapeutic approaches are needed. Since the first description of oxidative stress in heart failure, reactive oxygen species (ROS) have been considered as attractive drug targets. Though clinical trials evaluating antioxidant vitamins as ROS-scavenging agents yielded neutral results in patients at cardiovascular risk, the knowledge of ROS as pathophysiological factors has considerably advanced in the past few years and led to novel treatment approaches. Here, we review recent new insights and current strategies in targeting mitochondrial calcium handling and ROS in heart failure.

RECENT FINDINGS

Mitochondria are an important ROS source, and more recently, drug development focused on targeting mitochondria (e.g. by SS-31 or MitoQ). Important advancement has also been made to decipher how the matching of energy supply and demand through calcium (Ca²⁺) handling impacts on mitochondrial ROS production and elimination. This opens novel opportunities to ameliorate mitochondrial dysfunction in heart failure by targeting cytosolic and mitochondrial ion transporters to improve this matching process. According to this approach, highly specific substances as the preclinical CGP-37157, as well as the clinically used ranolazine and empagliflozin, provide promising results on different levels of evidence. Furthermore, the understanding of redox signalling relays, resembled by catalyst-mediated protein oxidation, is about to change former paradigms of ROS signalling. Novel methods, as redox proteomics, allow to precisely analyse key regulatory thiol switches, which may induce adaptive or maladaptive signalling. Additionally, the generation of genetically encoded probes increased the spatial and temporal resolution of ROS imaging and opened a new methodological window to subtle, formerly obscured processes. These novel insights may broaden our understanding of why previous attempts to target oxidative stress have failed, and at the same time provide us with new targets for drug development.

NADPH Oxidase-4 Driven Cardiac Macrophage Polarization Protects Against Myocardial Infarction-Induced Remodeling

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The reactive oxygen species–generating enzyme NADPH oxidase 4 (Nox4) is up-regulated in the heart after myocardial infarction.

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Mice with cardiomyocyte-targeted overexpression of Nox4 display an increase in macrophages in the heart, with skewing of polarization toward an M2 phenotype.

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After myocardial infarction, Nox4-induced skewing of macrophage polarization toward an M2 phenotype is accompanied by a higher survival, decreased cardiac remodeling, and improved contractile function.

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The protective effects of cardiomyocyte Nox4 may, in part, involve the attenuation of cardiac matrix metalloproteinase–2 activity.

The reactive oxygen species–generating enzyme NADPH oxidase 4 (Nox4) is up-regulated in the heart after myocardial infarction (MI). Mice with cardiomyocyte-targeted Nox4 overexpression (TG) displayed increased macrophages in the heart at baseline, with skewing toward an M2 phenotype compared with wild-type controls (WT). After MI, TG mice had a higher proportion of M2 macrophages along with higher survival, decreased cardiac remodeling, and better contractile function than wild-type mice. The post-MI increase in cardiac matrix metalloproteinase–2 activity was substantially blunted in TG mice. These results indicate that cardiomyocyte Nox4 modulates macrophage polarization toward an M2 phenotype, resulting in improved post-MI survival and remodeling, likely through the attenuation of cardiac matrix metalloproteinase–2 activity.

Nox4 reprograms cardiac substrate metabolism via protein O-GlcNAcylation to enhance stress adaptation

Cardiac hypertrophic remodeling during chronic hemodynamic stress is associated with a switch in preferred energy substrate from fatty acids to glucose, usually considered to be energetically favorable. The mechanistic interrelationship between altered energy metabolism, remodeling, and function remains unclear. The ROS-generating NADPH oxidase-4 (Nox4) is upregulated in the overloaded heart, where it ameliorates adverse remodeling. Here, we show that Nox4 redirects glucose metabolism away from oxidation but increases fatty acid oxidation, thereby maintaining cardiac energetics during acute or chronic stresses. The changes in glucose and fatty acid metabolism are interlinked via a Nox4-ATF4–dependent increase in the hexosamine biosynthetic pathway, which mediates the attachment of O-linked N-acetylglucosamine (O-GlcNAcylation) to the fatty acid transporter CD36 and enhances fatty acid utilization. These data uncover a potentially novel redox pathway that regulates protein O-GlcNAcylation and reprograms cardiac substrate metabolism to favorably modify adaptation to chronic stress. Our results also suggest that increased fatty acid oxidation in the chronically stressed heart may be beneficial.

Nox4 reprograms intermediary metabolism in the heart through an ATF4-mediated enhancement of protein O-GlcNAcylation, and the resulting switch to increased fatty acid oxidation protects the overloaded heart.

2-aminoethoxydiphenyl borate provides an anti-oxidative effect and mediates cardioprotection during ischemia reperfusion in mice

Excessive levels of reactive oxygen species (ROS) and impaired Ca2+ homeostasis play central roles in the development of multiple cardiac pathologies, including cell death during ischemia-reperfusion (I/R) injury. In several organs, treatment with 2-aminoethoxydiphenyl borate (2-APB) was shown to have protective effects, generally believed to be due to Ca2+ channel inhibition. However, the mechanism of 2-APB-induced cardioprotection has not been fully investigated. Herein we investigated the protective effects of 2-APB treatment against cardiac pathogenesis and deciphered the underlying mechanisms. In neonatal rat cardiomyocytes, treatment with 2-APB was shown to prevent hydrogen peroxide (H2O2) -induced cell death by inhibiting the increase in intracellular Ca2+ levels. However, no 2-APB-sensitive channel blocker inhibited H2O2-induced cell death and a direct reaction between 2-APB and H2O2 was detected by 1H-NMR, suggesting that 2-APB chemically scavenges extracellular ROS and provides cytoprotection. In a mouse I/R model, treatment with 2-APB led to a considerable reduction in the infarct size after I/R, which was accompanied by the reduction in ROS levels and neutrophil infiltration, indicating that the anti-oxidative properties of 2-APB plays an important role in the prevention of I/R injury in vivo as well. Taken together, present results indicate that 2-APB treatment induces cardioprotection and prevents ROS-induced cardiomyocyte death, at least partially, by the direct scavenging of extracellular ROS. Therefore, administration of 2-APB may represent a promising therapeutic strategy for the treatment of ROS-related cardiac pathology including I/R injury.

Regulation of protein function by S-nitrosation and S-glutathionylation: processes and targets in cardiovascular pathophysiology

Decades of chemical, biochemical and pathophysiological research have established the relevance of post-translational protein modifications induced by processes related to oxidative stress, with critical reflections on cellular signal transduction pathways. A great deal of the so-called ‘redox regulation’ of cell function is in fact mediated through reactions promoted by reactive oxygen and nitrogen species on more or less specific aminoacid residues in proteins, at various levels within the cell machinery. Modifications involving cysteine residues have received most attention, due to the critical roles they play in determining the structure/function correlates in proteins. The peculiar reactivity of these residues results in two major classes of modifications, with incorporation of NO moieties (S-nitrosation, leading to formation of proteinS-nitrosothiols) or binding of low molecular weight thiols (S-thionylation, i.e. in particularS-glutathionylation,S-cysteinylglycinylation andS-cysteinylation). A wide array of proteins have been thus analyzed in detail as far as their susceptibility to either modification or both, and the resulting functional changes have been described in a number of experimental settings. The present review aims to provide an update of available knowledge in the field, with a special focus on the respective (sometimes competing and antagonistic) roles played by proteinS-nitrosations andS-thionylations in biochemical and cellular processes specifically pertaining to pathogenesis of cardiovascular diseases.

The role of endogenous reactive oxygen species in cardiac myocyte autophagy

Autophagy is implicated in the maintenance of cardiac homeostasis. Autophagy is activated in heart failure, in which reactive oxygen species (ROS) are increased. Exogenous ROS have been shown to induce cardiomyocyte autophagy alterations. However, little is known about the influences of physiological levels of endogenous ROS on cardiomyocyte autophagy. In the present study, we tested the hypothesis that endogenous ROS in cardiomyocytes play an important role in inducing autophagy. Cultured H9C2 cardiomyocytes or Sprague-Dawley rats were treated with the antioxidant N-acetyl-cysteine (NAC) or the superoxide dismutase mimic tempol under the basal or nutrient deprivation conditions. The autophagic flux was assessed by the lysosomal inhibitor chloroquine. In H9C2 cardiomyocytes, under a basal condition, NAC or tempol increased the ratio of LC3 II/I proteins and reduced LC3 II autophagic flux. Under nutrient deprivation, NAC increased the LC3 II/I ratio and reduced LC3 II autophagic flux. In vivo studies in rats, NAC treatment increased the LC3 II/I ratio and p-Akt protein expression in myocardium. We concluded that the antioxidants reduced autophagic flux in cardiomyocytes under the basal or nutrient deprivation conditions, suggesting that endogenous ROS promote autophagy flux under physiological conditions, and this effect is mediated, at least in part, through Akt inhibition.

Extracellular superoxide dismutase and its role in cancer

Reactive oxygen species (ROS) are increasingly recognized as critical determinants of cellular signaling and a strict balance of ROS levels must be maintained to ensure proper cellular function and survival. Notably, ROS is increased in cancer cells. The superoxide dismutase family plays an essential physiological role in mitigating deleterious effects of ROS. Due to the compartmentalization of ROS signaling, EcSOD, the only superoxide dismutase in the extracellular space, has unique characteristics and functions in cellular signal transduction. In comparison to the other two intracellular SODs, EcSOD is a relatively new comer in terms of its tumor suppressive role in cancer and the mechanisms involved are less well understood. Nevertheless, the degree of differential expression of this extracellular antioxidant in cancer versus normal cells/tissues is more pronounced and prevalent than the other SODs. A significant association of low EcSOD expression with reduced cancer patient survival further suggests that loss of extracellular redox regulation promotes a conducive microenvironment that favors cancer progression. The vast array of mechanisms reported in mediating deregulation of EcSOD expression, function, and cellular distribution also supports that loss of this extracellular antioxidant provides a selective advantage to cancer cells. Moreover, overexpression of EcSOD inhibits tumor growth and metastasis, indicating a role as a tumor suppressor. This review focuses on the current understanding of the mechanisms of deregulation and tumor suppressive function of EcSOD in cancer.

Cardiac and renal upregulation of Nox2 and NF-κB and repression of Nox4 and Nrf2 in season- and diabetes-mediated models of vascular oxidative stress in guinea-pig and rat

The superoxide-forming NADPH oxidase homologues, Nox1, Nox2, and Nox5, seem to mediate the pro-atherosclerotic vascular phenotype. The hydrogen peroxide-forming Nox4 afforded vascular protection, likely via NF-E2-related factor-2 (Nrf2) activation and/or Nox2 downregulation in transgenic mice. We hypothesized that oxidative stress in the intact vasculature involves, aside from the upregulation of the superoxide-forming Noxs, the downregulation of the Nox4/Nrf2 pathway. Guinea-pigs and rats were studied either in winter or in summer, and the streptozotocin diabetic rats in winter. Plasma nitrite, and superoxide production by isolated hearts were measured, while frozen tissues served in biochemical analyses. Summer in both species and diabetes in rats downregulated myocardial Nox4 while reciprocally upregulating Nox2 and Nox5 in guinea-pigs, and Nox2 in rats. Simultaneously, myocardial Nrf2 activity and the expression of the Nrf2-directed heme oxygenase-1 and endothelial NO synthase were reduced while activity of the nuclear factor κB (NF-κB) and the expression of NF-κB-directed inducible NO synthase and the vascular cell adhesion molecule-1 were increased. Cardiac superoxide production was increased while plasma nitrite was decreased reciprocally. Analogous disregulation of Noxs, Nrf2, and NF-κB, occurred in diabetic rat kidneys. Given the diversity of the experimental settings and the uniform pattern of the responses, we speculate that: (1) chronic vascular oxidative stress is a nonspecific (model-, species-, organ-independent) response involving the induction of Nox2 (and Nox5 in guinea-pigs) and the NF-κB pathway, and the repression of Nox4 and the Nrf2 pathway; and (2) the systems Nox2-NF-κB and Nox4-Nrf2 regulate each other negatively.

Vitamin D, reactive oxygen species and calcium signalling in ageing and disease

Vitamin D is a hormone that maintains healthy cells. It functions by regulating the low resting levels of cell signalling components such as Ca(2+) and reactive oxygen species (ROS). Its role in maintaining phenotypic stability of these signalling pathways depends on the ability of vitamin D to control the expression of those components that act to reduce the levels of both Ca(2+) and ROS. This regulatory role of vitamin D is supported by both Klotho and Nrf2. A decline in the vitamin D/Klotho/Nrf2 regulatory network may enhance the ageing process, and this is well illustrated by the age-related decline in cognition in rats that can be reversed by administering vitamin D. A deficiency in vitamin D has also been linked to two of the major diseases in man: heart disease and Alzheimer's disease (AD). In cardiac cells, this deficiency alters the Ca(2+) transients to activate the gene transcriptional events leading to cardiac hypertrophy and the failing heart. In the case of AD, it is argued that vitamin D deficiency results in the Ca(2+) landscape that initiates amyloid formation, which then elevates the resting level of Ca(2+) to drive the memory loss that progresses to neuronal cell death and dementia.This article is part of the themed issue 'Evolution brings Ca(2+) and ATP together to control life and death'.

Effects of donor age on human adipose-derived adherent stromal cells under oxidative stress conditions

Objective

Adipose-derived stromal vascular fractions (SVFs) are heterogeneous complex populations of cells with therapeutic efficacy for tissue generation and vascular stabilization. SVFs have cardiomyogenic potential, and many researchers have examined the possibility of SVF transplantation for heart disease. In cell-based therapies, donor age affects the regenerative capability, cell yield, and differentiation potential of adult tissues; however, opposing or controversial results have been found in humans. We examined whether SVF transplantation into impaired heart tissue shows differential effects according to donor age.

Methods

We investigated differences in protein expression in human umbilical vein endothelial cells (HUVECs) co-cultured with adipose-derived adherent stromal cells (ADASs) from donors of different ages [>40-year-olds (40s group) and >60-year-olds (60s group)] under oxidative stress conditions.

Results

Although co-culturing HUVECs with ADASs ameliorated inflammation due to increased oxidative stress conditions, few differences were observed between the ADASs from the 40s and 60s groups. Moreover, the Database for Annotation, Visualization, and Integrated Discovery classification tool revealed differentially expressed genes in the Kyoto Encyclopedia of Genes and Genomes pathway associated with cytokine–cytokine receptor interaction in response to ADASs.

Conclusion

Protein expression profiles were unchanged in HUVECs induced by isolated ADASs from donors of different ages under oxidative stress conditions.