Sustained Increases in Cardiomyocyte Protein O-Linked ß-N-Acetylglucosamine Levels Lead to Cardiac Hypertrophy and Reduced Mitochondrial Function Without Systolic Contractile Impairment.

Background Lifestyle and metabolic diseases influence the severity and pathogenesis of cardiovascular disease through numerous mechanisms, including regulation via posttranslational modifications. A specific posttranslational modification, the addition of O-linked ß-N acetylglucosamine (O-GlcNAcylation), has been implicated in molecular mechanisms of both physiological and pathologic adaptations. The current study aimed to test the hypothesis that in cardiomyocytes, sustained protein O-GlcNAcylation contributes to cardiac adaptations, and its progression to pathophysiology. Methods and Results Using a naturally occurring dominant-negative O-GlcNAcase (dnOGA) inducible cardiomyocyte-specific overexpression transgenic mouse model, we induced dnOGA in 8- to 10-week-old mouse hearts. We examined the effects of 2-week and 24-week dnOGA overexpression, which progressed to a 1.8-fold increase in protein O-GlcNAcylation. Two-week increases in protein O-GlcNAc levels did not alter heart weight or function; however, 24-week increases in protein O-GlcNAcylation led to cardiac hypertrophy, mitochondrial dysfunction, fibrosis, and diastolic dysfunction. Interestingly, systolic function was maintained in 24-week dnOGA overexpression, despite several changes in gene expression associated with cardiovascular disease. Specifically, mRNA-sequencing analysis revealed several gene signatures, including reduction of mitochondrial oxidative phosphorylation, fatty acid, and glucose metabolism pathways, and antioxidant response pathways after 24-week dnOGA overexpression. Conclusions This study indicates that moderate increases in cardiomyocyte protein O-GlcNAcylation leads to a differential response with an initial reduction of metabolic pathways (2-week), which leads to cardiac remodeling (24-week). Moreover, the mouse model showed evidence of diastolic dysfunction consistent with a heart failure with preserved ejection fraction. These findings provide insight into the adaptive versus maladaptive responses to increased O-GlcNAcylation in heart.

Transgenic Expression of Nrf2 Induces a Pro-Reductive Stress and Adaptive Cardiac Remodeling in the Mouse.

Nuclear factor, erythroid 2 like 2 (Nfe2l2 or Nrf2), is a transcription factor that protects cells by maintaining a homeostatic redox state during stress. The constitutive expression of Nrf2 (CaNrf2-TG) was previously shown to be pathological to the heart over time. We tested a hypothesis that the cardiac-specific expression of full length Nrf2 (mNrf2-TG) would moderately increase the basal antioxidant defense, triggering a pro-reductive environment leading to adaptive cardiac remodeling. Transgenic and non-transgenic (NTG) mice at 7−8 months of age were used to analyze the myocardial transcriptome, structure, and function. Next generation sequencing (NGS) for RNA profiling and qPCR-based validation of the NGS data, myocardial redox levels, and imaging (echocardiography) were performed. Transcriptomic analysis revealed that out of 14,665 identified mRNAs, 680 were differently expressed (DEG) in TG hearts. Of 680 DEGs, 429 were upregulated and 251 were downregulated significantly (FC > 2.0, p < 0.05). Gene set enrichment analysis revealed that the top altered pathways were (a) Nrf2 signaling, (b) glutathione metabolism and (c) ROS scavenging. A comparative analysis of the glutathione redox state in the hearts demonstrated significant differences between pro-reductive vs. hyper-reductive conditions (233 ± 36.7 and 380 ± 68.7 vs. 139 ± 8.6 µM/mg protein in mNrf2-TG and CaNrf2-TG vs. NTG). Genes involved in fetal development, hypertrophy, cytoskeletal rearrangement, histone deacetylases (HDACs), and GATA transcription factors were moderately increased in mNrf2-TG compared to CaNrf2-TG. Non-invasive echocardiography analysis revealed an increase in systolic function (ejection fraction) in mNrf2-TG, suggesting an adaptation, as opposed to pathological remodeling in CaNrf2-TG mice experiencing a hyper-reductive stress, leading to reduced survival (40% at 60 weeks). The effects of excess Nrf2-driven antioxidant transcriptome revealed a pro-reductive condition in the myocardium leading to an adaptive cardiac remodeling. While pre-conditioning the myocardial redox with excess antioxidants (i.e., pro-reductive state) could be beneficial against oxidative stress, a chronic pro-reductive environment in the myocardium might transition the adaptation to pathological remodeling.

Role of exosomal microRNA signatures: An emerging factor in preeclampsia-mediated cardiovascular disease.

Preeclampsia (PE) and vascular dysfunction are major causes of maternal and neonatal morbidity and mortality. Although extensively studied, the complete understanding of the pathophysiology behind PE remains unclear. Current reports indicate that exosomes are essential mediators in PE-related cardiovascular disease (CVDs). Exosomes are synthesized from multivesicular bodies (MVB) and contain functionally active microRNAs miRNAs). These miRNAs have been shown to mediate physiological and pathological functions through autocrine, paracrine, and endocrine signaling mechanisms. The role of miRNAs in pregnant women with PE has been studied extensively. However, little is known about the effect of exosomal miRNAs (exomiR) in PE. This paper will review and discuss the existing evidence for exomiR function in PE and highlight the need for future studies to explore the role that exomiR signatures have in cardiovascular dysfunction associated with PE.

Reductive Stress: Neglected Science.

Over the past six decades, the concept of "redox" was focused on one arm of the redox spectrum: oxidative stress. In fact, a vast majority of experimental and clinical studies addressing redox mechanisms claimed "oxidative stress" as the culprit for acute or chronic disease conditions. Recent studies have documented that reactive oxygen species (ROS) are crucial signaling molecules facilitating various cellular processes. Thus, abrogation of these key ROS signaling through abundant antioxidant systems will result in detrimental effects. This Forum highlights the emerging concepts and related mechanisms of the other extreme of the redox spectrum, known as "reductive stress (RS)." The Forum including original research and review articles discusses the causes and consequences of RS in various biological and pathological conditions such as metabolism, cancer, drug resistance, cardiac hypertrophy, and microbial adaptations.

DNA damage-free iPS cells exhibit potential to yield competent cardiomyocytes.

DNA damage accrued in induced pluripotent stem cell (iPSC)-derived cardiomyocytes during in vitro culture practices lessens their therapeutic potential. We determined whether DNA-damage-free iPSCs (DdF-iPSCs) can be selected using stabilization of p53, a transcription factor that promotes apoptosis in DNA-damaged cells, and differentiated them into functionally competent DdF cardiomyocytes (DdF-CMs). p53 was activated using Nutlin-3a in iPSCs to selectively kill the DNA-damaged cells, and the stable DdF cells were cultured further and differentiated into CMs. Both DdF-iPSCs and DdF-CMs were then characterized. We observed a significant decrease in the expression of reactive oxygen species and DNA damage in DdF-iPSCs compared with control (Ctrl) iPSCs. Next-generation RNA sequencing and Ingenuity Pathway Analysis revealed improved molecular, cellular, and physiological functions in DdF-iPSCs. The differentiated DdF-CMs had a compact beating frequency between 40 and 60 beats/min accompanied by increased cell surface area. Additionally, DdF-CMs were able to retain the improved molecular, cellular, and physiological functions after differentiation from iPSCs, and, interestingly, cardiac development network was prominent compared with Ctrl-CMs. Enhanced expression of various ion channel transcripts in DdF-CMs implies DdF-CMs are of ventricular CMs and mature compared with their counterparts. Our results indicated that DdF-iPSCs could be selected through p53 stabilization using a small-molecule inhibitor and differentiated into ventricular DdF-CMs with fine-tuned molecular signatures. These iPSC-derived DdF-CMs show immense clinical potential in repairing injured myocardium.NEW & NOTEWORTHY Culture-stress-induced DNA damage in stem cells lessens their performance. A robust small-molecule-based approach, by stabilizing/activating p53, to select functionally competent DNA-damage-free cells from a heterogeneous population of cells is demonstrated. This protocol can be adopted by clinics to select DNA-damage-free cells before transplanting them to the host myocardium. The intact DNA-damage-free cells exhibited with fine-tuned molecular signatures and improved cellular functions. DNA-damage-free cardiomyocytes compared with control expressed superior cardiomyocyte functional properties, including, but not limited to, enhanced ion channel signatures. These DNA-intact cells would better engraft, survive, and, importantly, improve the cardiac function of the injured myocardium.

MitoQ regulates redox-related noncoding RNAs to preserve mitochondrial network integrity in pressure-overload heart failure.

Evidence suggests that mitochondrial network integrity is impaired in cardiomyocytes from failing hearts. While oxidative stress has been implicated in heart failure (HF)-associated mitochondrial remodeling, the effect of mitochondrial-targeted antioxidants, such as mitoquinone (MitoQ), on the mitochondrial network in a model of HF (e.g., pressure overload) has not been demonstrated. Furthermore, the mechanism of this regulation is not completely understood with an emerging role for posttranscriptional regulation via long noncoding RNAs (lncRNAs). We hypothesized that MitoQ preserves mitochondrial fusion proteins (i.e., mitofusin), likely through redox-sensitive lncRNAs, leading to improved mitochondrial network integrity in failing hearts. To test this hypothesis, 8-wk-old C57BL/6J mice were subjected to ascending aortic constriction (AAC), which caused substantial left ventricular (LV) chamber remodeling and remarkable contractile dysfunction in 1 wk. Transmission electron microscopy and immunostaining revealed defective intermitochondrial and mitochondrial-sarcoplasmic reticulum ultrastructure in AAC mice compared with sham-operated animals, which was accompanied by elevated oxidative stress and suppressed mitofusin (i.e., Mfn1 and Mfn2) expression. MitoQ (1.36 mg·day-1·mouse-1, 7 consecutive days) significantly ameliorated LV dysfunction, attenuated Mfn2 downregulation, improved interorganellar contact, and increased metabolism-related gene expression. Moreover, our data revealed that MitoQ alleviated the dysregulation of an Mfn2-associated lncRNA (i.e., Plscr4). In summary, the present study supports a unique mechanism by which MitoQ improves myocardial intermitochondrial and mitochondrial-sarcoplasmic reticulum (SR) ultrastructural remodeling in HF by maintaining Mfn2 expression via regulation by an lncRNA. These findings underscore the important role of lncRNAs in the pathogenesis of HF and the potential of targeting them for effective HF treatment.NEW & NOTEWORTHY We have shown that MitoQ improves cardiac mitochondrial network integrity and mitochondrial-SR alignment in a pressure-overload mouse heart-failure model. This may be occurring partly through preventing the dysregulation of a redox-sensitive lncRNA-microRNA pair (i.e., Plscr4-miR-214) that results in an increase in mitofusin-2 expression.

Exercise Mediated Nrf2 Signaling Protects the Myocardium From Isoproterenol-Induced Pathological Remodeling.

Although exercise derived activation of Nrf2 signaling augments myocardial antioxidant signaling, the molecular mechanisms underlying the benefits of moderate exercise training (MET) in the heart remain elusive. Here we hypothesized that exercise training stabilizes Nrf2-dependent antioxidant signaling, which then protects the myocardium from isoproterenol-induced damage. The present study assessed the effects of 6 weeks of MET on the Nrf2/antioxidant function, glutathione redox state, and injury in the myocardium of C57/BL6J mice that received isoproterenol (ISO; 50 mg/kg/day for 7 days). ISO administration significantly reduced the Nrf2 promoter activity (p < 0.05) and downregulated the expression of cardiac antioxidant genes (Gclc, Nqo1, Cat, Gsr, and Gst-µ) in the untrained (UNT) mice. Furthermore, increased oxidative stress with severe myocardial injury was evident in UNT+ISO when compared to UNT mice receiving PBS under basal condition. Of note, MET stabilized the Nrf2-promoter activity and upheld the expression of Nrf2-dependent antioxidant genes in animals receiving ISO, and attenuated the oxidative stress-induced myocardial damage. Echocardiography analysis revealed impaired diastolic ventricular function in UNT+ISO mice, but this was partially normalized in the MET animals. Interestingly, while there was a marginal reduction in ubiquitinated proteins in MET mice that received ISO, the pathological signs were attenuated along with near normal cardiac function in response to exercise training. Thus, moderate intensity exercise training conferred protection against ISO-induced myocardial injury by augmentation of Nrf2-antioxidant signaling and attenuation of isoproterenol-induced oxidative stress.

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.

Morinda citrifolia and Its Active Principle Scopoletin Mitigate Protein Aggregation and Neuronal Apoptosis through Augmenting the DJ-1/Nrf2/ARE Signaling Pathway.

Given the role of oxidative stress in PD pathogenesis and off-target side effects of currently available drugs, several natural phytochemicals seem to be promising in the management of PD. Here, we tested the hypothesis that scopoletin, an active principle obtained from Morinda citrifolia (MC), efficiently quenches oxidative stress through DJ-1/Nrf2 signaling and ameliorates rotenone-induced PD. Despite reducing oxidative stress, the administration of MC extract (MCE) has lessened protein aggregation as evident from decreased levels of nitrotyrosine and α-synuclein. In vitro studies revealed that scopoletin lessened rotenone-induced apoptosis in SH-SY5Y cells through preventing oxidative injury. Particularly, scopoletin markedly upregulated DJ-1, which then promoted the nuclear translocation of Nrf2 and transactivation of antioxidant genes. Furthermore, we found that scopoletin prevents the nuclear exportation of Nrf2 by reducing the levels of Keap1 and thereby enhancing the neuronal defense system. Overall, our findings suggest that scopoletin acts through DJ-1-mediated Nrf2 signaling to protect the brain from rotenone-induced oxidative stress and PD. Thus, we postulate that scopoletin could be a potential drug to treat PD.

Mitoquinone ameliorates pressure overload-induced cardiac fibrosis and left ventricular dysfunction in mice.

Increasing evidence indicates that mitochondrial-associated redox signaling contributes to the pathophysiology of heart failure (HF). The mitochondrial-targeted antioxidant, mitoquinone (MitoQ), is capable of modifying mitochondrial signaling and has shown beneficial effects on HF-dependent mitochondrial dysfunction. However, the potential therapeutic impact of MitoQ-based mitochondrial therapies for HF in response to pressure overload is reliant upon demonstration of improved cardiac contractile function and suppression of deleterious cardiac remodeling. Using a new (patho)physiologically relevant model of pressure overload-induced HF we tested the hypothesis that MitoQ is capable of ameliorating cardiac contractile dysfunction and suppressing fibrosis. To test this C57BL/6J mice were subjected to left ventricular (LV) pressure overload by ascending aortic constriction (AAC) followed by MitoQ treatment (2 µmol) for 7 consecutive days. Doppler echocardiography showed that AAC caused severe LV dysfunction and hypertrophic remodeling. MitoQ attenuated pressure overload-induced apoptosis, hypertrophic remodeling, fibrosis and LV dysfunction. Profibrogenic transforming growth factor-ß1 (TGF-ß1) and NADPH oxidase 4 (NOX4, a major modulator of fibrosis related redox signaling) expression increased markedly after AAC. MitoQ blunted TGF-ß1 and NOX4 upregulation and the downstream ACC-dependent fibrotic gene expressions. In addition, MitoQ prevented Nrf2 downregulation and activation of TGF-ß1-mediated profibrogenic signaling in cardiac fibroblasts (CF). Finally, MitoQ ameliorated the dysregulation of cardiac remodeling-associated long noncoding RNAs (lncRNAs) in AAC myocardium, phenylephrine-treated cardiomyocytes, and TGF-ß1-treated CF. The present study demonstrates for the first time that MitoQ improves cardiac hypertrophic remodeling, fibrosis, LV dysfunction and dysregulation of lncRNAs in pressure overload hearts, by inhibiting the interplay between TGF-ß1 and mitochondrial associated redox signaling.

Temporal partitioning of adaptive responses of the murine heart to fasting.

Recent studies suggest that the time of day at which food is consumed dramatically influences clinically-relevant cardiometabolic parameters (e.g., adiposity, insulin sensitivity, and cardiac function). Meal feeding benefits may be the result of daily periods of feeding and/or fasting, highlighting the need for improved understanding of the temporal adaptation of cardiometabolic tissues (e.g., heart) to fasting. Such studies may provide mechanistic insight regarding how time-of-day-dependent feeding/fasting cycles influence cardiac function. We hypothesized that fasting during the sleep period elicits beneficial adaptation of the heart at transcriptional, translational, and metabolic levels. To test this hypothesis, temporal adaptation was investigated in wild-type mice fasted for 24-h, or for either the 12-h light/sleep phase or the 12-h dark/awake phase. Fasting maximally induced fatty acid responsive genes (e.g., Pdk4) during the dark/active phase; transcriptional changes were mirrored at translational (e.g., PDK4) and metabolic flux (e.g., glucose/oleate oxidation) levels. Similarly, maximal repression of myocardial p-mTOR and protein synthesis rates occurred during the dark phase; both parameters remained elevated in the heart of fasted mice during the light phase. In contrast, markers of autophagy (e.g., LC3II) exhibited peak responses to fasting during the light phase. Collectively, these data show that responsiveness of the heart to fasting is temporally partitioned. Autophagy peaks during the light/sleep phase, while repression of glucose utilization and protein synthesis is maximized during the dark/active phase. We speculate that sleep phase fasting may benefit cardiac function through augmentation of protein/cellular constituent turnover.

Cardiac Aging - Benefits of Exercise, Nrf2 Activation and Antioxidant Signaling.

Cardiovascular dysfunction and heart failure associated with aging not only impairs the cardiac function but also the quality of life eventually decreasing the life expectancy of the elderly. Notably, cardiac tissue can prematurely age under certain conditions such as genetic mutation, persistent redox stress and overload, aberrant molecular signaling, DNA damage, telomere attrition, and other pathological insults. While cardiovascular-related morbidity and mortality is on the rise and remains a global health threat, there has been only little to moderate improvements in its medical management. This is due to the fact that the lifestyle changes to molecular mechanisms underlying age-related myocardial structure and functional remodeling are multifactorial and intricately operate at different levels. Along these lines, the intrinsic redox mechanisms and oxidative stress (OS) are widely studied in the myocardium. The accumulation of reactive oxygen species (ROS) with age and the resultant oxidative damage has been shown to increase the susceptibility of the myocardium to multiple complications such as atherosclerosis, hypertension, ischemic heart disease, cardiac myopathy, and heart failure. There has been growing interest in trying to enhance the mechanisms that neutralize the ROS and curtailing OS as a possible anti-aging intervention and as a treatment for age-related disorders. Natural defense system to fight against OS involves a master transcription factor named nuclear erythroid-2-p45-related factor-2 (Nrf2) that regulates several antioxidant genes. Compelling evidence exists on the Nrf2 gain of function through pharmacological interventions in counteracting the oxidative damage and affords cytoprotection in several organs including but not limited to lung, liver, kidney, brain, etc. Nevertheless, thus far, only a few studies have described the potential role of Nrf2 and its non-pharmacological induction in cardiac aging. This chapter explores the effects of various modes of exercise on Nrf2 signaling along with its responses and ramifications on the cascade of OS in the aging heart.

Genetic disruption of the cardiomyocyte circadian clock differentially influences insulin-mediated processes in the heart.

Cardiovascular physiology exhibits time-of-day-dependent oscillations, which are mediated by both extrinsic (e.g., environment/behavior) and intrinsic (e.g., circadian clock) factors. Disruption of circadian rhythms negatively affects multiple cardiometabolic parameters. Recent studies suggest that the cardiomyocyte circadian clock directly modulates responsiveness of the heart to metabolic stimuli (e.g., fatty acids) and stresses (e.g., ischemia/reperfusion). The aim of this study was to determine whether genetic disruption of the cardiomyocyte circadian clock impacts insulin-regulated pathways in the heart. Genetic disruption of the circadian clock in cardiomyocyte-specific Bmal1 knockout (CBK) and cardiomyocyte-specific Clock mutant (CCM) mice altered expression (gene and protein) of multiple insulin signaling components in the heart, including p85α and Akt. Both baseline and insulin-mediated Akt activation was augmented in CBK and CCM hearts (relative to littermate controls). However, insulin-mediated glucose utilization (both oxidative and non-oxidative) and AS160 phosphorylation were attenuated in CBK hearts, potentially secondary to decreased Inhibitor-1. Consistent with increased Akt activation in CBK hearts, mTOR signaling was persistently increased, which was associated with attenuation of autophagy, augmented rates of protein synthesis, and hypertrophy. Importantly, pharmacological inhibition of mTOR (rapamycin; 10days) normalized cardiac size in CBK mice. These data suggest that disruption of cardiomyocyte circadian clock differentially influences insulin-regulated processes, and provide new insights into potential pathologic mediators following circadian disruption.

A biphasic effect of TNF-α in regulation of the Keap1/Nrf2 pathway in cardiomyocytes.

Antagonizing TNF-α signaling attenuates chronic inflammatory disease, but is associated with adverse effects on the cardiovascular system. Therefore the impact of TNF-α on basal control of redox signaling events needs to be understand in more depth. This is particularly important for the Keap1/Nrf2 pathway in the heart and in the present study we hypothesized that inhibition of a low level of TNF-α signaling attenuates the TNF-α dependent activation of this cytoprotective pathway. HL-1 cardiomyocytes and TNF receptor1/2 (TNFR1/2) double knockout mice (DKO) were used as experimental models. TNF-α (2-5ng/ml, for 2h) evoked significant nuclear translocation of Nrf2 with increased DNA/promoter binding and transactivation of Nrf2 targets. Additionally, this was associated with a 1.5 fold increase in intracellular glutathione (GSH). Higher concentrations of TNF-α (>10-50ng/ml) were markedly suppressive of the Keap1/Nrf2 response and associated with cardiomyocyte death marked by an increase in cleavage of caspase-3 and PARP. In vivo experiments with TNFR1/2-DKO demonstrates that the expression of Nrf2-regulated proteins (NQO1, HO-1, G6PD) were significantly downregulated in hearts of the DKO when compared to WT mice indicating a weakened antioxidant system under basal conditions. Overall, these results indicate that TNF-α exposure has a bimodal effect on the Keap1/Nrf2 system and while an intense inflammatory activation suppresses expression of antioxidant proteins a low level appears to be protective.

Reductive stress linked to small HSPs, G6PD, and Nrf2 pathways in heart disease.

SIGNIFICANCE: Aerobic organisms must exist between the dueling biological metabolic processes for energy and respiration and the obligatory generation of reactive oxygen species (ROS) whose deleterious consequences can reduce survival. Wide fluctuations in harmful ROS generation are circumvented by endogenous countermeasures (i.e., enzymatic and nonenzymatic antioxidants systems) whose capacity decline with aging and are enhanced by disease states. RECENT ADVANCES: Substantial efforts on the cellular and molecular underpinnings of oxidative stress has been complemented recently by the discovery that reductive stress similarly predisposes to inheritable cardiomyopathy, firmly establishing that the biological extremes of the redox spectrum play essential roles in disease pathogenesis. CRITICAL ISSUES: Because antioxidants by nutritional or pharmacological supplement to prevent or mitigate disease states have been largely disappointing, we hypothesize that lack of efficacy of antioxidants might be related to adverse outcomes in responders at the reductive end of the redox spectrum. As emerging concepts, such as reductive, as opposed, oxidative stress are further explored, there is an urgent and critical gap for biochemical phenotyping to guide the targeted clinical applications of therapeutic interventions. FUTURE DIRECTIONS: New approaches are vitally needed for characterizing redox states with the long-term goal to noninvasively assess distinct clinical states (e.g., presymptomatic, end-stage) with the diagnostic accuracy to guide personalized medicine.

Disruption of Nrf2/ARE signaling impairs antioxidant mechanisms and promotes cell degradation pathways in aged skeletal muscle.

Age-associated decline in antioxidant potential and accumulation of reactive oxygen/nitrogen species are primary causes for multiple health problems, including muscular dystrophy and sarcopenia. The role of the nuclear erythroid-2-p45-related factor-2 (Nrf2) signaling has been implicated in antioxidant gene regulation. Here, we investigated the loss-of-function mechanisms for age-dependent regulation of Nrf2/ARE (Antioxidant Response Element) signaling in skeletal muscle (SM). Under basal physiological conditions, disruption of Nrf2 showed minimal effects on antioxidant defenses in young (2months) Nrf2-/- mice. Interestingly, mRNA and protein levels of NADH Quinone Oxidase-1 were dramatically (*P<0.001) decreased in Nrf2-/- SM when compared to WT at 2months of age, suggesting central regulation of NQO1 occurs through Nrf2. Subsequent analysis of the Nrf2-dependent transcription and translation showed that the aged mice (>24months) had a significant increase in ROS along with a decrease in glutathione (GSH) levels and impaired antioxidants in Nrf2-/- when compared to WT SM. Further, disruption of Nrf2 appears to induce oxidative stress (increased ROS, HNE-positive proteins), ubiquitination and pro-apoptotic signals in the aged SM of Nrf2-/- mice. These results indicate a direct role for Nrf2/ARE signaling on impairment of antioxidants, which contribute to muscle degradation pathways upon aging. Our findings conclude that though the loss of Nrf2 is not amenable at younger age; it could severely affect the SM defenses upon aging. Thus, Nrf2 signaling might be a potential therapeutic target to protect the SM from age-dependent accumulation of ROS by rescuing redox homeostasis to prevent age-related muscle disorders such as sarcopenia and myopathy.

Acute exercise stress activates Nrf2/ARE signaling and promotes antioxidant mechanisms in the myocardium.

Oxidative stress has been implicated in the pathogenesis of cardiovascular diseases, including myocardial hypertrophy and infarction. Although impairment of antioxidant defense mechanisms has been thought to provoke oxidative stress-induced myocardial dysfunction, it has been difficult to clearly demonstrate. Nuclear erythroid 2 p45-related factor 2 (Nrf2) is a redox-sensitive, basic leucine zipper protein that regulates the transcription of several antioxidant genes. We previously reported that sustained activation of Nrf2 upregulates transcription of a number of endogenous antioxidants in the heart. Here, we show that acute exercise stress (AES) results in activation of Nrf2/ARE (antioxidant response element) signaling and subsequent enhancement of antioxidant defense pathways in wild-type (WT) mouse hearts, while oxidative stress, along with blunted defense mechanisms, was observed in Nrf2-/- mice. We also find that AES is associated with increased trans-activation of ARE-containing genes in exercised animals when compared to age-matched sedentary WT mice. However, enhanced oxidative stress in response to AES was observed in Nrf2-/- mice due to lower basal expression and marked attenuation of the transcriptional induction of several antioxidant genes. Thus, AES induces ROS and promotes Nrf2 function, but disruption of Nrf2 increases susceptibility of the myocardium to oxidative stress. Our findings suggest the basis for a nonpharmacological approach to activate Nrf2/ARE signaling, which might be a potential therapeutic target to protect the heart from oxidative stress-induced cardiovascular complications.

Sustained activation of nuclear erythroid 2-related factor 2/antioxidant response element signaling promotes reductive stress in the human mutant protein aggregation cardiomyopathy in mice.

Inheritable missense mutations in small molecular weight heat-shock proteins (HSP) with chaperone-like properties promote self-oligomerization, protein aggregation, and pathologic states such as hypertrophic cardiomyopathy in humans. We recently described that human mutant αB-crystallin (hR120GCryAB) overexpression that caused protein aggregation cardiomyopathy (PAC) was genetically linked to dysregulation of the antioxidant system and reductive stress (RS) in mice. However, the molecular mechanism that induces RS remains only partially understood. Here we define a critical role for the regulatory nuclear erythroid 2-related factor 2 (Nrf2)-Kelch-like ECH-associated protein (Keap1) pathway--the master transcriptional controller of antioxidants, in the pathogenesis of PAC and RS. In myopathic mice, increased reactive oxygen species signaling during compensatory hypertrophy (i.e., 3 months) was associated with upregulation of key antioxidants in a manner consistent with Nrf2/antioxidant response element (ARE)-dependent transactivation. In transcription factor assays, we further demonstrate increased binding of Nrf2 to ARE during the development of cardiomyopathy. Of interest, we show that the negative regulator Keap1 was predominantly sequestrated in protein aggregates (at 6 months), suggesting that sustained nuclear translocation of activated Nrf2 may be a contributing mechanism for RS. Our findings implicate a novel pathway for therapeutic targeting and abrogating RS linked to experimental cardiomyopathy in humans. Antioxid.