Nrf2 enhances myocardial clearance of toxic ubiquitinated proteins

Sulforaphane regulates AngII-induced podocyte oxidative stress injury through the Nrf2-Keap1/ho-1/ROS pathway

OBJECTIVE

This study aimed to investigate the therapeutic effects of sulforaphane and the role of the Nrf2-Keap1/HO-1/ROS pathway in AngII-induced oxidative stress in podocyte injury.

METHODS

Mouse mpc5 podocytes were divided into four groups: control (Con), AngII, AngII + sulforaphane (AngII + SFN), and control + sulforaphane (Con + SFN). Western blotting was used to detect protein expression of Nrf2-Keap1, antioxidant enzyme HO-1, and apoptosis-related proteins. ROS levels were measured using a ROS assay kit, and cell survival and viability were assayed using the CCK-8 kit. Molecular interactions between Nrf2 and sulforaphane were analyzed computationally.

RESULTS

Compared with the Con group, podocytes treated with AngII alone exhibited inhibited proliferation, reduced cell viability, lower Bcl-2 expression, and higher cleaved caspase 3 expression. In the presence of sulforaphane, AngII group showed a mild inhibition on podocyte proliferation but did not induce the aforementioned changes in Bcl-2 and cleaved caspase 3 expression. Similarly, compared to the Con group, AngII treatment alone had lower Nrf2 expression and higher Keap1 expression in podocytes, accompanied by a significant decrease in ROS content. However, in the presence of sulforaphane, AngII failed to induce increases in Nrf2 and a decrease in Keap1 expression, as well as ROS levels. Furthermore, cells treated with sulforaphane exhibited higher HO-1 levels than control cells, and co-incubation with AngII did not alter HO-1 levels. Computational modeling revealed hydrophobic interactions between sulforaphane and the amino acid LYS-462 of Nrf2, as well as hydrogen bonding with amino acid HIS-465. The binding score between sulforaphane and Nrf2 was -4.7.

CONCLUSION

Sulforaphane alleviated AngII-induced podocyte oxidative stress injury via the Nrf2-Keap1/HO-1/ROS pathway, providing new insights into therapeutic compounds for mitigating chronic kidney disease.

Naturally-derived modulators of the Nrf2 pathway and their roles in the intervention of diseases

Cumulative evidence has verified that persistent oxidative stress is involved in the development of various chronic diseases, including pulmonary, neurodegenerative, kidney, cardiovascular, and liver disease, as well as cancer. Nuclear factor erythroid 2-related factor 2 (Nrf2) is pivotal role in regulating cellular oxidative stress and inflammatory reactions, making it a focal point for disease prevention and treatment strategies. Natural products are essential resources for discovering leading molecules for new drug research and development. In this review, we comprehensively outlined the progression of the knowledge on the Nrf2 pathway, Nrf2 activators in clinical trials, the naturally-derived Nrf2 modulators (particularly from 2014-present), as well as their effects on the pathogenesis of chronic diseases.

Inhibition of ubiquitin-specific protease 7 ameliorates ferroptosis-mediated myocardial infarction by contrasting oxidative stress: An in vitro and in vivo analysis

BACKGROUND

Our prior research determined that USP7 exacerbates myocardial injury. Additionally, existing studies indicate a strong connection between USP7 and ferroptosis. However, the influence of USP7 on ferroptosis-mediated myocardial infarction (MI) remains unclear. Given these findings, we are particularly interested in USP7's regulatory role in ferroptosis-mediated MI and its underlying mechanisms.

METHODS

In this study, we established MI models and lentivirus-transfected groups to inhibit USP7 expression both in vivo and in vitro. Cardiac function was detected with Echocardiography. TTC and HE staining were employed to assess myocardial alterations. The expression of ferroptosis markers (PTGS2, ACSL4, GPX4) were analyzed by RT-qPCR and Western blotting. Flow cytometry and ELISA were used for measuring Fe2+, lipid ROS, GSH, and GSSG levels. TEM and Prussian blue staining were used to observe mitochondrial alterations and iron deposition. RT-qPCR, Western blotting, and immunofluorescence were conducted to analyze Keap1, Nrf2, and nuclear Nrf2 expression in vitro and in vivo.

RESULTS

In the MI model group, USP7 expression significantly increased, worsening ferroptosis-mediated MI. Conversely, in the USP7-inhibited group, activation of the Keap1-Nrf2 signaling pathway improved ferroptosis-mediated MI outcomes. In vitro, the MI model exhibited a marked decline in cardiomyocyte viability and notable mitochondrial damage. However, these issues improved in the USP7-inhibited groups. In vivo, USP7 intensified MI and iron deposition within the MI model group, with decreased values of LVEF, LVFS, SV, LVAWd, and LVPWs, all of which showed improvement in the USP7-inhibited group, except for LVPWd and LVPWs, which showed no significant variation. Importantly, both the in vitro and in vivo experiments revealed analogous results: a reduction in Keap1 expression and an increase in both Nrf2 and nuclear Nrf2 post USP7 inhibition. Additionally, GPX4 expression decreased while PTGS2 and ACSL4 expressions increased. Notably, concentrations of Fe2+, lipid ROS, GSH, and GSSG significantly decreased.

CONCLUSION

In vitro and in vivo studies have found that inhibition of USP7 attenuates iron deposition and suppresses oxidative stress, resulting in amelioration of ferroptosis-induced MI.

Building an Understanding of Proteostasis in Reproductive Cells: The Impact of Reactive Carbonyl Species on Protein Fate

Significance: Stringent regulation of protein homeostasis pathways, under both physiological and pathological conditions, is necessary for the maintenance of proteome fidelity and optimal cell functioning. However, when challenged by endogenous or exogenous stressors, these proteostasis pathways can become dysregulated with detrimental consequences for protein fate, cell survival, and overall organism health. Most notably, there are numerous somatic pathologies associated with a loss of proteostatic regulation, including neurodegenerative disorders, type 2 diabetes, and some cancers. Recent Advances: Lipid oxidation-derived reactive carbonyl species (RCS), such as 4-hydroxynonenal (4HNE) and malondialdehyde, are relatively underappreciated purveyors of proteostatic dysregulation, which elicit their effects via the nonenzymatic post-translational modification of proteins. Emerging evidence suggests that a subset of germline proteins can serve as substrates for 4HNE modification. Among these, prevalent targets include succinate dehydrogenase, heat shock protein A2 and A-kinase anchor protein 4, all of which are intrinsically associated with fertility. Critical Issues: Despite growing knowledge in this field, the RCS adductomes of spermatozoa and oocytes are yet to be comprehensively investigated. Furthermore, the manner by which RCS-mediated adduction impacts protein fate and drives cellular responses, such as protein aggregation, requires further examination in the germline. Given that RCS-protein adduction has been attributed a role in infertility, there has been sparked research investment into strategies to prevent lipid peroxidation in germ cells. Future Directions: An increased depth of knowledge regarding the mechanisms and substrates of RCS-mediated protein modification in reproductive cells may reveal important targets for the development of novel therapies to improve fertility and pregnancy outcomes for future generations.

Aucubin alleviates doxorubicin-induced cardiotoxicity through crosstalk between NRF2 and HIPK2 mediating autophagy and apoptosis

BACKGROUND

Doxorubicin (DOX) is widely used for the treatment of a variety of cancers. However, its clinical application is limited by dose-dependent cardiotoxicity. Recent findings demonstrated that autophagy inhibition and apoptosis of cardiomyocytes induced by oxidative stress dominate the pathophysiology of DOX-induced cardiotoxicity (DIC), however, there are no potential molecules targeting on these.

PURPOSE

This study aimed to explore whether aucubin (AU) acting on inimitable crosstalk between NRF2 and HIPK2 mediated the autophagy, oxidative stress, and apoptosis in DIC, and provide a new and alternative strategy for the treatment of DIC.

METHODS AND RESULTS

We first demonstrated the protection of AU on cardiac structure and function in DIC mice manifested by increased EF and FS values, decreased serum CK-MB and LDH contents and well-aligned cardiac tissue in HE staining. Furthermore, AU alleviated DOX-induced myocardial oxidative stress, mitochondrial damage, apoptosis, and autophagy flux dysregulation in mice, as measured by decreased ROS, 8-OHdG, and TUNEL-positive cells in myocardial tissue, increased SOD and decreased MDA in serum, aligned mitochondria with reduced vacuoles, and increased autophagosomes. In vitro, AU alleviated DOX-induced oxidative stress, autophagy inhibition, and apoptosis by promoting NRF2 and HIPK2 expression. We also identified crosstalk between NRF2 and HIPK2 in DIC as documented by overexpression of NRF2 or HIPK2 reversed cellular oxidative stress, autophagy blocking, and apoptosis aggravated by HIPK2 or NRF2 siRNA, respectively. Simultaneously, AU promoted the expression and nuclear localization of NRF2 protein, which was reversed by HIPK2 siRNA, and AU raised the expression of HIPK2 protein as well, which was reversed by NRF2 siRNA. Crucially, AU did not affect the antitumor activity of DOX against MCF-7 and HepG2 cells, which made up for the shortcomings of previous anti-DIC drugs.

CONCLUSION

These collective results innovatively documented that AU regulated the unique crosstalk between NRF2 and HIPK2 to coordinate oxidative stress, autophagy, and apoptosis against DIC without compromising the anti-tumor effect of DOX in vitro.

LuQi formula attenuates Cardiomyocyte ferroptosis via activating Nrf2/GPX4 signaling axis in heart failure

BACKGROUND

The terminal stage of all cardiovascular diseases typically culminates in heart failure (HF), with no effective intervention available to halt its progression. LuQi formula (LQF) has been employed in clinical for numerous years to significantly ameliorate cardiac function in HF patients. Nevertheless, the underlying mechanism of LQF's efficacy remains inadequately comprehended. Cardiomyocyte ferroptosis has served as a pathogenic mechanism in HF. The goal of the current experiment was to ascertain whether LQF ameliorates HF by preventing cardiomyocyte ferroptosis and to elucidate the intrinsic mechanism involved.

PURPOSE

This research objective is to investigate the impact and underlying mechanism of LQF attenuating cardiomyocyte ferroptosis in heart failure.

METHODS

Transverse aortic constriction (TAC) was performed to construct the HF mouse model. Neonatal rat cardiomyocytes (NRCMs) were subjected to in vitro experiments. High-performance liquid chromatography (HPLC) identified the bioactive compounds in LQF. Transcriptomic and quantitative proteomic analyses revealed the potential targets of LQF anti-HF. Specifically, histological staining evaluated cardiac hypertrophy and fibrosis. Transmission electron microscopy (TEM) observed mitochondrial morphology. The content of Fe2+, ROS, MDA, GSH, and GSSH was detected using kits. Molecular docking evaluated the binding activities between essential active ingredients of LQF and critical proteins of cardiomyocyte ferroptosis. Mechanistically, the expression levels of Nrf2, Keap1, HO-1, SLC7A11, and GPX4 were evaluated using qPCR, Western blot (WB), or immunohistochemical staining.

RESULTS

The primary nine active ingredients in LQF were detected. Transcriptomic and proteomic analyses demonstrated that LQF may ameliorate HF by preventing cardiomyocyte ferroptosis. Histomorphometric analyses revealed that LQF attenuates myocardial hypertrophy and fibrosis. TEM revealed that LQF diminished mitochondrial shrinkage and increased membrane density in myocardial tissue. Additionally, LQF diminished reactive oxygen species (ROS) generation in cardiomyocytes and suppressed cardiomyocyte ferroptosis. Furthermore, the molecular docking technique revealed that the primary active ingredients of LQF had suitable binding activities with Nrf2, GPX4, and SLC7A11. Western analysis further verified that LQF activated the Nrf2/GPX4 signaling axis. decreased SLC7A11 and HO-1 expression.

CONCLUSIONS

These results demonstrated that LQF prevents cardiomyocyte ferroptosis via activating Nrf2/GPX4 signaling axis and suppressing SLC7A11 and HO-1 expression. Concurrently, it contributed to elucidating the intrinsic mechanism of LQF and provided a scientific rationale for its development as a novel cardiovascular therapeutic drug.

Nrf2 prevents diabetic cardiomyopathy via antioxidant effect and normalization of glucose and lipid metabolism in the heart

Metabolic disorders and oxidative stress are the main causes of diabetic cardiomyopathy. Activation of nuclear factor erythroid 2-related factor 2 (Nrf2) exerts a powerful antioxidant effect and prevents the progression of diabetic cardiomyopathy. However, the mechanism of its cardiac protection and direct action on cardiomyocytes are not well understood. Here, we investigated in a cardiomyocyte-restricted Nrf2 transgenic mice (Nrf2-TG) the direct effect of Nrf2 on cardiomyocytes in DCM and its mechanism. In this study, cardiomyocyte-restricted Nrf2 transgenic mice (Nrf2-TG) were used to directly observe whether cardiomyocyte-specific overexpression of Nrf2 can prevent diabetic cardiomyopathy and correct glucose and lipid metabolism disorders in the heart. Compared to wild-type mice, Nrf2-TG mice showed resistance to diabetic cardiomyopathy in a streptozotocin-induced type 1 diabetes mouse model. This was primarily manifested as improved echocardiography results as well as reduced myocardial fibrosis, cardiac inflammation, and oxidative stress. These results showed that Nrf2 can directly act on cardiomyocytes to exert a cardioprotective role. Mechanistically, the cardioprotective effects of Nrf2 depend on its antioxidation activity, partially through improving glucose and lipid metabolism by directly targeting lipid metabolic pathway of AMPK/Sirt1/PGC-1α activation via upstream genes of sestrin2 and LKB1, and indirectly enabling AKT/GSK-3β/HK-Ⅱ activity via AMPK mediated p70S6K inhibition.

Metal profiling in coronary ischemia-reperfusion injury: Implications for KEAP1/NRF2 regulated redox signaling

Coronary ischemia-reperfusion (IR) injury results from a blockage of blood supply to the heart followed by restoration of perfusion, leading to oxidative stress induced pathological processes. Nuclear factor erythroid 2-related factor 2 (NRF2), a master antioxidant transcription factor, plays a key role in regulating redox signaling. Over the past decades, the field of metallomics has provided novel insights into the mechanism of pro-oxidant and antioxidant pathological processes. Both redox-active (e.g. Fe and Cu) and redox-inert (e.g. Zn and Mg) metals play unique roles in establishing redox balance under IR injury. Notably, Zn protects against oxidative stress in coronary IR injury by serving as a cofactor of antioxidant enzymes such as superoxide dismutase [Cu-Zn] (SOD1) and proteins such as metallothionein (MT) and KEAP1/NRF2 mediated antioxidant defenses. An increase in labile Zn2+ inhibits proteasomal degradation and ubiquitination of NRF2 by modifying KEAP1 and glycogen synthase kinase 3β (GSK3β) conformations. Fe and Cu catalyse the formation of reactive oxygen species via the Fenton reaction and also serve as cofactors of antioxidant enzymes and can activate NRF2 antioxidant signaling. We review the evidence that Zn and redox-active metals Fe and Cu affect redox signaling in coronary cells during IR and the mechanisms by which oxidative stress influences cellular metal content. In view of the unique double-edged characteristics of metals, we aim to bridge the role of metals and NRF2 regulated redox signaling to antioxidant defenses in IR injury, with a long-term aim of informing the design and application of novel therapeutics.

The Potential of Cylindromatosis (CYLD) as a Therapeutic Target in Oxidative Stress-Associated Pathologies: A Comprehensive Evaluation

Oxidative stress (OS) arises as a consequence of an imbalance between the formation of reactive oxygen species (ROS) and the capacity of antioxidant defense mechanisms to neutralize them. Excessive ROS production can lead to the damage of critical biomolecules, such as lipids, proteins, and DNA, ultimately contributing to the onset and progression of a multitude of diseases, including atherosclerosis, chronic obstructive pulmonary disease, Alzheimer's disease, and cancer. Cylindromatosis (CYLD), initially identified as a gene linked to familial cylindromatosis, has a well-established and increasingly well-characterized function in tumor inhibition and anti-inflammatory processes. Nevertheless, burgeoning evidence suggests that CYLD, as a conserved deubiquitination enzyme, also plays a pivotal role in various key signaling pathways and is implicated in the pathogenesis of numerous diseases driven by oxidative stress. In this review, we systematically examine the current research on the function and pathogenesis of CYLD in diseases instigated by oxidative stress. Therapeutic interventions targeting CYLD may hold significant promise for the treatment and management of oxidative stress-induced human diseases.

Insights into the Molecular Mechanisms of NRF2 in Kidney Injury and Diseases

Redox is a constant phenomenon in organisms. From the signaling pathway transduction to the oxidative stress during the inflammation and disease process, all are related to reduction-oxidation (redox). Nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor targeting many antioxidant genes. In non-stressed conditions, NRF2 maintains the hemostasis of redox with housekeeping work. It expresses constitutively with basal activity, maintained by Kelch-like-ECH-associated protein 1 (KEAP1)-associated ubiquitination and degradation. When encountering stress, it can be up-regulated by several mechanisms to exert its anti-oxidative ability in diseases or inflammatory processes to protect tissues and organs from further damage. From acute kidney injury to chronic kidney diseases, such as diabetic nephropathy or glomerular disease, many results of studies have suggested that, as a master of regulating redox, NRF2 is a therapeutic option. It was not until the early termination of the clinical phase 3 trial of diabetic nephropathy due to heart failure as an unexpected side effect that we renewed our understanding of NRF2. NRF2 is not just a simple antioxidant capacity but has pleiotropic activities, harmful or helpful, depending on the conditions and backgrounds.

Induction of Cardiac Pathology: Endogenous versus Exogenous Nrf2 Upregulation

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a master regulator of the endogenous antioxidant response to reactive oxygen species as well as a controller of Phase II detoxification in response to xenobiotics. This amenity to specific external manipulation exploits the binding affinity of Nrf2 for its constitutive repressor and degradation facilitator Kelch-like erythroid cell-derived protein with CNC homology-associated protein 1 (Keap1). Derived from both natural and synthesized origins, these compounds have been extensively tested without definitive beneficial results. Unfortunately, multiple terminated trials have shown a negative side to Nrf2 with regard to cardiac pathologies while animal-based studies have demonstrated cardiomyocyte hypertrophy and heart failure after chronic Nrf2 upregulation. Putatively based on autophagic control of Nrf2 activity-modulating upstream factors, new evidence of miRNA involvement has added complexity to this mechanism. What follows is an extensive survey of Nrf2-regulating exogenous compounds that may promote cardiomyopathy, clinical trial evidence, and a comparison to exercise-induced factors that also upregulate Nrf2 while preventing cardiac pathologies.

Diabetes-induced chronic heart failure is due to defects in calcium transporting and regulatory contractile proteins: cellular and molecular evidence

Heart failure (HF) is a major deteriorating disease of the myocardium due to weak myocardial muscles. As such, the heart is unable to pump blood efficiently around the body to meet its constant demand. HF is a major global health problem with more than 7 million deaths annually worldwide, with some patients dying suddenly due to sudden cardiac death (SCD). There are several risk factors which are associated with HF and SCD which can negatively affect the heart synergistically. One major risk factor is diabetes mellitus (DM) which can cause an elevation in blood glucose level or hyperglycaemia (HG) which, in turn, has an insulting effect on the myocardium. This review attempted to explain the subcellular, cellular and molecular mechanisms and to a lesser extent, the genetic factors associated with the development of diabetes- induced cardiomyopathy due to the HG which can subsequently lead to chronic heart failure (CHF) and SCD. The study first explained the structure and function of the myocardium and then focussed mainly on the excitation-contraction coupling (ECC) processes highlighting the defects of calcium transporting (SERCA, NCX, RyR and connexin) and contractile regulatory (myosin, actin, titin and troponin) proteins. The study also highlighted new therapies and those under development, as well as preventative strategies to either treat or prevent diabetic cardiomyopathy (DCM). It is postulated that prevention is better than cure.

The Interplay between Autophagy and Redox Signaling in Cardiovascular Diseases

Reactive oxygen and nitrogen species produced at low levels under normal cellular metabolism act as important signal molecules. However, at increased production, they cause damage associated with oxidative stress, which can lead to the development of many diseases, such as cardiovascular, metabolic, neurodegenerative, diabetes, and cancer. The defense systems used to maintain normal redox homeostasis plays an important role in cellular responses to oxidative stress. The key players here are Nrf2-regulated redox signaling and autophagy. A tight interface has been described between these two processes under stress conditions and their role in oxidative stress-induced diseases progression. In this review, we focus on the role of Nrf2 as a key player in redox regulation in cell response to oxidative stress. We also summarize the current knowledge about the autophagy regulation and the role of redox signaling in this process. In line with the focus of our review, we describe in more detail information about the interplay between Nrf2 and autophagy pathways in myocardium and the role of these processes in cardiovascular disease development.

Pak2 Regulation of Nrf2 Serves as a Novel Signaling Nexus Linking ER Stress Response and Oxidative Stress in the Heart

Endoplasmic Reticulum (ER) stress and oxidative stress have been highly implicated in the pathogenesis of cardiac hypertrophy and heart failure (HF). However, the mechanisms involved in the interplay between these processes in the heart are not fully understood. The present study sought to determine a causative link between Pak2-dependent UPR activation and oxidative stress via Nrf2 regulation under pathological ER stress. We report that sustained ER stress and Pak2 deletion in cardiomyocytes enhance Nrf2 expression. Conversely, AAV9 mediated Pak2 delivery in the heart leads to a significant decrease in Nrf2 levels. Pak2 overexpression enhances the XBP1-Hrd1 UPR axis and ameliorates tunicamycin induced cardiac apoptosis and dysfunction in mice. We found that Pak2 deletion and altered proteostasis render Nrf2 detrimental by switching from its antioxidant role to renin-angiotensin aldosterone system (RAAS) gene regulator. Mechanistically, Pak2 mediated Hrd1 expression targets Nrf2 for ubiquitination and degradation thus preventing its aberrant activation. Moreover, we find a significant increase in Nrf2 with a decrease in Pak2 in human myocardium of dilated heart disease. Using human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs), we find that Pak2 is able to ameliorate Nrf2 induced RAAS activation under ER stress. These findings demonstrate that Pak2 is a novel Nrf2 regulator in the stressed heart. Activation of XBP1-Hrd1 is attributed to prevent ER stress-induced Nrf2 RAAS component upregulation. This mechanism explains the functional dichotomy of Nrf2 in the stressed heart. Thus, Pak2 regulation of Nrf2 homeostasis may present as a potential therapeutic route to alleviate detrimental ER stress and heart failure.

Involvement of Oxidative Stress in the Development of Subcellular Defects and Heart Disease

It is now well known that oxidative stress promotes lipid peroxidation, protein oxidation, activation of proteases, fragmentation of DNA and alteration in gene expression for producing myocardial cell damage, whereas its actions for the induction of fibrosis, necrosis and apoptosis are considered to result in the loss of cardiomyocytes in different types of heart disease. The present article is focused on the discussion concerning the generation and implications of oxidative stress from various sources such as defective mitochondrial electron transport and enzymatic reactions mainly due to the activation of NADPH oxidase, nitric oxide synthase and monoamine oxidase in diseased myocardium. Oxidative stress has been reported to promote excessive entry of Ca²⁺ due to increased permeability of the sarcolemmal membrane as well as depressions of Na⁺-K⁺ ATPase and Na⁺-Ca²⁺ exchange systems, which are considered to increase the intracellular of Ca²⁺. In addition, marked changes in the ryanodine receptors and Ca²⁺-pump ATPase have been shown to cause Ca²⁺-release and depress Ca²⁺ accumulation in the sarcoplasmic reticulum as a consequence of oxidative stress. Such alterations in sarcolemma and sarcoplasmic reticulum are considered to cause Ca²⁺-handling abnormalities, which are associated with mitochondrial Ca²⁺-overload and loss of myofibrillar Ca²⁺-sensitivity due to oxidative stress. Information regarding the direct effects of different oxyradicals and oxidants on subcellular organelles has also been outlined to show the mechanisms by which oxidative stress may induce Ca²⁺-handling abnormalities. These observations support the view that oxidative stress plays an important role in the genesis of subcellular defects and cardiac dysfunction in heart disease.

Notoginsenoside R1 Protects Against High Glucose-Induced Cell Injury Through AMPK/Nrf2 and Downstream HO-1 Signaling

Notoginsenoside R1 (NGR1), the primary bioactive compound found in Panax notoginseng, is believed to have antihypertrophic and antiapoptotic properties, and has long been used to prevent and treat cardiovascular diseases. However, its potential role in prevention of diabetic cardiomyopathy remains unclear. The present study aimed to investigate the mechanism of NGR1 action in high glucose-induced cell injury. H9c2 cardiomyocytes were cultured in a high-glucose medium as an in-vitro model, and apoptotic cells were visualized using TUNEL staining. Expression of Nrf2 and HO-1 was measured using Western blotting or reverse transcription-quantitative PCR (RT-qPCR). The Nrf2 small interfering (si) RNA was transfected into cardiomyocytes using Opti-MEM containing Lipofectamine^® RNAiMAX. NGR1 protected H9c2 cardiomyocytes from cell death, apoptosis and hypertrophy induced by high glucose concentration. Expression of auricular natriuretic peptide and brain natriuretic peptide was remarkably reduced in NGR1-treated H9C2 cells. Western blot analysis showed that high glucose concentration markedly inhibited AMPK, Nrf2 and HO-1, and this could be reversed by NGR1 treatment. However, the cardioprotective effect of NGR1 was attenuated by compound C, which reverses Nrf2 and HO-1 expression levels, suggesting that AMPK upregulates Nrf2 and HO-1 gene expression, protein synthesis and secretion. Transfection of H9C2 cells with Nrf2 siRNA markedly reduced the cardioprotective effect of NGR1 via reduced expression of HO-1. These results indicated that NGR1 attenuated high glucose-induced cell injury via AMPK/Nrf2 signaling and its downstream target, the HO-1 pathway. We conclude that the cardioprotective effects of NGR1 result from upregulation of AMPK/Nrf2 signaling and HO-1 expression in cardiomyocytes. Our findings suggest that NGR1 treatment might provide a novel therapy for diabetic cardiomyopathy.

Inflammation and Oxidative Stress in Chronic Kidney Disease and Dialysis Patients

Significance: Chronic kidney disease (CKD) can be regarded as a burden of lifestyle disease that shares common underpinning features and risk factors with the aging process; it is a complex constituted by several adverse components, including chronic inflammation, oxidative stress, early vascular aging, and cellular senescence. Recent Advances: A systemic approach to tackle CKD, based on mitigating the associated inflammatory, cell stress, and damage processes, has the potential to attenuate the effects of CKD, but it also preempts the development and progression of associated morbidities. In effect, this will enhance health span and compress the period of morbidity. Pharmacological, nutritional, and potentially lifestyle-based interventions are promising therapeutic avenues to achieve such a goal. Critical Issues: In the present review, currents concepts of inflammation and oxidative damage as key patho-mechanisms in CKD are addressed. In particular, potential beneficial but also adverse effects of different systemic interventions in patients with CKD are discussed. Future Directions: Senotherapeutics, the nuclear factor erythroid 2-related factor 2-kelch-like ECH-associated protein 1 (NRF2-KEAP1) signaling pathway, the endocrine klotho axis, inhibitors of the sodium-glucose cotransporter 2 (SGLT2), and live bio-therapeutics have the potential to reduce the burden of CKD and improve quality of life, as well as morbidity and mortality, in this fragile high-risk patient group. Antioxid. Redox Signal. 35, 1426-1448.

Loss of PKA regulatory subunit 1α aggravates cardiomyocyte necrosis and myocardial ischemia/reperfusion injury

Reperfusion therapy, the standard treatment for acute myocardial infarction, can trigger necrotic death of cardiomyocytes and provoke ischemia/reperfusion (I/R) injury. However, signaling pathways that regulate cardiomyocyte necrosis remain largely unknown. Our recent genome-wide RNAi screen has identified a potential necrosis suppressor gene PRKAR1A, which encodes PKA regulatory subunit 1α (R1α). R1α is primarily known for regulating PKA activity by sequestering PKA catalytic subunits in the absence of cAMP. Here, we showed that depletion of R1α augmented cardiomyocyte necrosis in vitro and in vivo, resulting in exaggerated myocardial I/R injury and contractile dysfunction. Mechanistically, R1α loss downregulated the Nrf2 antioxidant transcription factor and aggravated oxidative stress following I/R. Degradation of the endogenous Nrf2 inhibitor Keap1 through p62-dependent selective autophagy was blocked by R1α depletion. Phosphorylation of p62 at Ser349 by mammalian target of rapamycin complex 1 (mTORC1), a critical step in p62-Keap1 interaction, was induced by I/R, but diminished by R1α loss. Activation of PKA by forskolin or isoproterenol almost completely abolished hydrogen-peroxide-induced p62 phosphorylation. In conclusion, R1α loss induces unrestrained PKA activation and impairs the mTORC1-p62-Keap1-Nrf2 antioxidant defense system, leading to aggravated oxidative stress, necrosis, and myocardial I/R injury. Our findings uncover a novel role of PKA in oxidative stress and necrosis, which may be exploited to develop new cardioprotective therapies.

Protective Role of Polyphenols in Heart Failure: Molecular Targets and Cellular Mechanisms Underlying Their Therapeutic Potential

Heart failure (HF) is a leading cause of death in the United States, with a 5-year mortality rate of 50% despite modern pharmacological therapies. Plant-based diets are comprised of a diverse polyphenol profile, which lends to their association with reduced cardiovascular disease risk. Whether a polyphenol-rich diet can slow the progression of or reverse HF in humans is not known. To date, in vitro and in vivo studies have reported on the protective role of polyphenols in HF. In this review, we will discuss the major mechanisms by which polyphenols mitigate HF in vitro and in vivo, including (1) reduced cardiac inflammation and oxidative stress, (2) reduced mitochondrial dysfunction, (3) improved Ca²⁺ homeostasis, (4) increased survival signaling, and (5) increased sirtuin 1 activity.

Stimulation of Sigma-1 Receptor Protects against Cardiac Fibrosis by Alleviating IRE1 Pathway and Autophagy Impairment

Sigma-1 receptor (Sig1R), a chaperone in the endoplasmic reticulum (ER) membrane, has been implicated in cardiac hypertrophy; however, its role in cardiac fibroblast activation has not been established. This study investigated the possible association between Sig1R and this activation by subjecting mice to sham, transverse aortic constriction (TAC), and TAC plus fluvoxamine (an agonist of Sig1R) treatments. Cardiac function and fibrosis were evaluated four weeks later by echocardiography and histological staining. In an in vitro study, neonatal rat cardiac fibroblasts were treated with fluvoxamine or NE-100 (an antagonist of Sig1R) in the presence or absence of transforming growth factor beta1 (TGF-β1). Fibrotic markers, ER stress pathways, and autophagy were then investigated by qPCR, western blotting, immunofluorescence, confocal microscopy, and transmission electron microscopy. Fluvoxamine treatment reduced cardiac fibrosis, preserved cardiac function, and attenuated cardiac fibroblast activation. Inhibition of the IRE1/XBP1 pathway, a branch of ER stress, by a specific inhibitor of IRE1 endonuclease activity, attenuated the pathological process. Fluvoxamine stimulation of Sig1R restored autophagic flux in cardiac fibroblasts, indicating that Sig1R appears to play a protective role in the activation of cardiac fibroblasts by inhibiting the IRE1 pathway and restoring autophagic flux. Sig1R may therefore represent a therapeutic target for cardiac fibrosis.

Autophagy Inhibition Enables Nrf2 to Exaggerate the Progression of Diabetic Cardiomyopathy in Mice

Nuclear factor-erythroid factor 2-related factor 2 (Nrf2) may either ameliorate or worsen diabetic cardiomyopathy. However, the underlying mechanisms are poorly understood. Herein we report a novel mechanism of Nrf2-mediated myocardial damage in type 1 diabetes (T1D). Global Nrf2 knockout (Nrf2KO) hardly affected the onset of cardiac dysfunction induced by T1D but slowed down its progression in mice independent of sex. In addition, Nrf2KO inhibited cardiac pathological remodeling, apoptosis, and oxidative stress associated with both onset and advancement of cardiac dysfunction in T1D. Such Nrf2-mediated progression of diabetic cardiomyopathy was confirmed by a cardiomyocyte-restricted (CR) Nrf2 transgenic approach in mice. Moreover, cardiac autophagy inhibition via CR knockout of autophagy-related 5 gene (CR-Atg5KO) led to early onset and accelerated development of cardiomyopathy in T1D, and CR-Atg5KO-induced adverse phenotypes were rescued by additional Nrf2KO. Mechanistically, chronic T1D leads to glucolipotoxicity inhibiting autolysosome efflux, which in turn intensifies Nrf2-driven transcription to fuel lipid peroxidation while inactivating Nrf2-mediated antioxidant defense and impairing Nrf2-coordinated iron metabolism, thereby leading to ferroptosis in cardiomyocytes. These results demonstrate that diabetes over time causes autophagy deficiency, which turns off Nrf2-mediated defense while switching on an Nrf2-operated pathological program toward ferroptosis in cardiomyocytes, thereby worsening the progression of diabetic cardiomyopathy.

Cellular Protein Quality Control in Diabetic Cardiomyopathy: From Bench to Bedside

Heart failure is a serious comorbidity and the most common cause of mortality in diabetes patients. Diabetic cardiomyopathy (DCM) features impaired cellular structure and function, culminating in heart failure; however, there is a dearth of specific clinical therapy for treating DCM. Protein homeostasis is pivotal for the maintenance of cellular viability under physiological and pathological conditions, particularly in the irreplaceable cardiomyocytes; therefore, it is tightly regulated by a protein quality control (PQC) system. Three evolutionarily conserved molecular processes, the unfolded protein response (UPR), the ubiquitin-proteasome system (UPS), and autophagy, enhance protein turnover and preserve protein homeostasis by suppressing protein translation, degrading misfolded or unfolded proteins in cytosol or organelles, disposing of damaged and toxic proteins, recycling essential amino acids, and eliminating insoluble protein aggregates. In response to increased cellular protein demand under pathological insults, including the diabetic condition, a coordinated PQC system retains cardiac protein homeostasis and heart performance, on the contrary, inappropriate PQC function exaggerates cardiac proteotoxicity with subsequent heart dysfunction. Further investigation of the PQC mechanisms in diabetes propels a more comprehensive understanding of the molecular pathogenesis of DCM and opens new prospective treatment strategies for heart disease and heart failure in diabetes patients. In this review, the function and regulation of cardiac PQC machinery in diabetes mellitus, and the therapeutic potential for the diabetic heart are discussed.

Proteotoxic Stress and Cell Death in Cancer Cells

To maintain proteostasis, cells must integrate information and activities that supervise protein synthesis, protein folding, conformational stability, and also protein degradation. Extrinsic and intrinsic conditions can both impact normal proteostasis, causing the appearance of proteotoxic stress. Initially, proteotoxic stress elicits adaptive responses aimed at restoring proteostasis, allowing cells to survive the stress condition. However, if the proteostasis restoration fails, a permanent and sustained proteotoxic stress can be deleterious, and cell death ensues. Many cancer cells convive with high levels of proteotoxic stress, and this condition could be exploited from a therapeutic perspective. Understanding the cell death pathways engaged by proteotoxic stress is instrumental to better hijack the proliferative fate of cancer cells.

Sulforaphane suppresses obesity-related glomerulopathy-induced damage by enhancing autophagy via Nrf2

AIMS

Obesity-related glomerulopathy (ORG) is characterized by glomerulomegaly with or without focal and segmental glomerulosclerosis lesions. Isothiocyanate sulforaphane (SFN) can protect kidneys from ORG-related damages. In this study, we investigated the effects of SFN as a preventive therapy or intervention for ORG to reveal its mechanism of action.

MAIN METHODS

We established a mouse obesity model with preventive SFN or N-acetylcysteine treatment for 2 months. Thereafter, we used nuclear factor erythroid 2-related factor 2-deficient (Nrf2^-/-) and wild type mice in our ORG model with SFN treatment. Finally, we generated a corresponding mouse podocyte model in vitro. The body weight, wet weight of perirenal-and peritesticular fat, and urinary albumin/creatinine ratio were assessed. We used periodic acid-Schiff staining and electron microscopy to assess the function of the kidneys and podocytes. In addition, we evaluated the expression of Nrf2 and podocyte-specific proteins by western blotting.

KEY FINDINGS

Treatment with SFN reduced body weight, organ-associated fat weight, and urinary albumin/creatinine ratio in both the preventive treatment and disease intervention regimens. SFN treated mice exhibited higher expression levels of podocyte-specific proteins and better podocyte function. However, treatment with SFN did not affect these parameters in obese Nrf2^-/- mice. Light chain 3 of microtubule-associated protein 1-II and metallothionein had higher expression in the wild type than in the Nrf2^-/- mice.

SIGNIFICANCE

Treatment with SFN limited ORG-induced damage by enhancing podocyte autophagy via Nrf2.

The Dark Side of Nrf2 in the Heart

Nuclear factor-erythroid factor 2-related factor 2 (Nrf2) is a critical transcription factor that regulates the expression of over 1000 genes in the cell under normal and stressed conditions. These transcripts can be categorized into different groups with distinct functions, including antioxidative defense, detoxification, inflammatory responses, transcription factors, proteasomal and autophagic degradation, and metabolism. Nevertheless, Nrf2 has been historically considered as a crucial regulator of antioxidant defense to protect against various insult-induced organ damage and has evolved as a promising drug target for the treatment of human diseases, such as heart failure. However, burgeoning evidence has revealed a detrimental role of Nrf2 in cardiac pathological remodeling and dysfunction toward heart failure. In this mini-review, we outline recent advances in structural features of Nrf2 and regulation of Nrf2 activity and discuss the emerging dark side of Nrf2 in the heart as well as the potential mechanisms of Nrf2-mediated myocardial damage and dysfunction.

CYLD exaggerates pressure overload-induced cardiomyopathy via suppressing autolysosome efflux in cardiomyocytes

Deubiquitinating enzymes (DUBs) appear to be a new class of regulators of cardiac homeostasis and disease. However, DUB-mediated signaling in the heart is not well understood. Herein we report a novel mechanism by which cylindromatosis (CYLD), a DUB mediates cardiac pathological remodeling and dysfunction. Cardiomyocyte-restricted (CR) overexpression of CYLD (CR-CYLD) did not cause gross health issues and hardly affected cardiac function up to age of one year in both female and male mice at physiological conditions. However, CR-CYLD overexpression exacerbated pressure overload (PO)-induced cardiac dysfunction associated with suppressed cardiac hypertrophy and increased myocardial apoptosis in mice independent of the gender. At the molecular level, CR-CYLD overexpression enhanced PO-induced increases in poly-ubiquitinated proteins marked by lysine (K)48-linked ubiquitin chains and autophagic vacuoles containing undegraded contents while suppressing autophagic flux. Augmentation of cardiac autophagy via CR-ATG7 overexpression protected against PO-induced cardiac pathological remodeling and dysfunction in both female and male mice. Intriguingly, CR-CYLD overexpression switched the CR-ATG7 overexpression-dependent cardiac protection into myocardial damage and dysfunction associated with increased accumulation of autophagic vacuoles containing undegraded contents in the heart. Genetic manipulation of Cyld in combination with pharmacological modulation of autophagic functional status revealed that CYLD suppressed autolysosomal degradation and promoted cell death in cardiomyocytes. In addition, Cyld gene gain- and/or loss-of-function approaches in vitro and in vivo demonstrated that CYLD mediated cardiomyocyte death associated with impaired reactivation of mechanistic target of rapamycin complex 1 (mTORC1) and upregulated Ras genes from rat brain 7 (Rab7), two key components for autolysosomal degradation. These results demonstrate that CYLD serves as a novel mediator of cardiac pathological remodeling and dysfunction by suppressing autolysosome efflux in cardiomyocytes. Mechanistically, it is most likely that CYLD suppresses autolysosome efflux via impairing mTORC1 reactivation and interrupting Rab7 release from autolysosomes in cardiomyocytes.

Altered C10 domain in cardiac myosin binding protein-C results in hypertrophic cardiomyopathy

AIMS

A 25-base pair deletion in the cardiac myosin binding protein-C (cMyBP-C) gene (MYBPC3), proposed to skip exon 33, modifies the C10 domain (cMyBP-CΔC10mut) and is associated with hypertrophic cardiomyopathy (HCM) and heart failure, affecting approximately 100 million South Asians. However, the molecular mechanisms underlying the pathogenicity of cMyBP-CΔC10mutin vivo are unknown. We hypothesized that expression of cMyBP-CΔC10mut exerts a poison polypeptide effect leading to improper assembly of cardiac sarcomeres and the development of HCM.

METHODS AND RESULTS

To determine whether expression of cMyBP-CΔC10mut is sufficient to cause HCM and contractile dysfunction in vivo, we generated transgenic (TG) mice having cardiac-specific protein expression of cMyBP-CΔC10mut at approximately half the level of endogenous cMyBP-C. At 12 weeks of age, significant hypertrophy was observed in TG mice expressing cMyBP-CΔC10mut (heart weight/body weight ratio: 4.43 ± 0.11 mg/g non-transgenic (NTG) vs. 5.34 ± 0.25 mg/g cMyBP-CΔC10mut, P < 0.05). Furthermore, haematoxylin and eosin, Masson's trichrome staining, as well as second-harmonic generation imaging revealed the presence of significant fibrosis and a greater relative nuclear area in cMyBP-CΔC10mut hearts compared with NTG controls. M-mode echocardiography analysis revealed hypercontractile hearts (EF: 53.4%±2.9% NTG vs. 66.4% ± 4.7% cMyBP-CΔC10mut; P < 0.05) and early diastolic dysfunction (E/E': 28.7 ± 3.7 NTG vs. 46.3 ± 8.4 cMyBP-CΔC10mut; P < 0.05), indicating the presence of an HCM phenotype. To assess whether these changes manifested at the myofilament level, contractile function of single skinned cardiomyocytes was measured. Preserved maximum force generation and increased Ca2+-sensitivity of force generation were observed in cardiomyocytes from cMyBP-CΔC10mut mice compared with NTG controls (EC50: 3.6 ± 0.02 µM NTG vs. 2.90 ± 0.01 µM cMyBP-CΔC10mut; P < 0.0001).

CONCLUSION

Expression of cMyBP-C protein with a modified C10 domain is sufficient to cause contractile dysfunction and HCM in vivo.

Nrf2 deficiency aggravates Angiotensin II-induced cardiac injury by increasing hypertrophy and enhancing IL-6/STAT3-dependent inflammation

BACKGROUND

NF-E2-related factor 2 (Nrf2) is a transcription factor playing cytoprotective effects in various pathological processes including oxidative stress and cardiac hypertrophy. Despite being a potential therapeutic target to treat several cardiomyopathies, the signaling underlying Nrf2-dependent cardioprotective action remains largely uncharacterized.

AIM

This study aimed to explore the signaling mediating the role of Nrf2 in the development of hypertensive cardiac pathogenesis by analyzing the response to Angiotensin II (Ang II) in the presence or absence of Nrf2 expression, both in vivo and in vitro.

RESULTS

Our results indicated that Nrf2 deficiency exacerbated cardiac damage triggered by Ang II infusion. Mechanistically, our study shows that Ang II-triggered hypertrophy and inflammation is exacerbated in the absence of Nrf2 expression and points to the involvement of the IL-6/STAT3 signaling pathway in this event. Indeed, our results show that IL-6 abundance triggered by Ang II is increased in the absence of Nrf2 and demonstrate the requirement of IL-6 in STAT3 activation and cardiac inflammation induced by Ang II.

CONCLUSION

Our results show that Nrf2 is important for the protection of the heart against Ang II-induced cardiac hypertrophy and inflammation by mechanisms involving the regulation of IL-6/STAT3-dependent signaling.

The KEAP1-NRF2 System: a Thiol-Based Sensor-Effector Apparatus for Maintaining Redox Homeostasis

The Kelch-like ECH-associated protein 1-NF-E2-related factor 2 (KEAP1-NRF2) system forms the major node of cellular and organismal defense against oxidative and electrophilic stresses of both exogenous and endogenous origins. KEAP1 acts as a cysteine thiol-rich sensor of redox insults, whereas NRF2 is a transcription factor that robustly transduces chemical signals to regulate a battery of cytoprotective genes. KEAP1 represses NRF2 activity under quiescent conditions, whereas NRF2 is liberated from KEAP1-mediated repression on exposure to stresses. The rapid inducibility of a response based on a derepression mechanism is an important feature of the KEAP1-NRF2 system. Recent studies have unveiled the complexities of the functional contributions of the KEAP1-NRF2 system and defined its broader involvement in biological processes, including cell proliferation and differentiation, as well as cytoprotection. In this review, we describe historical milestones in the initial characterization of the KEAP1-NRF2 system and provide a comprehensive overview of the molecular mechanisms governing the functions of KEAP1 and NRF2, as well as their roles in physiology and pathology. We also refer to the clinical significance of the KEAP1-NRF2 system as an important prophylactic and therapeutic target for various diseases, particularly aging-related disorders. We believe that controlled harnessing of the KEAP1-NRF2 system is a key to healthy aging and well-being in humans.

Sulforaphane prevents angiotensin II-induced cardiomyopathy by activation of Nrf2 via stimulating the Akt/GSK-3ß/Fyn pathway

Aims

Activation of nuclear factor erythroid 2-related factor 2 (Nrf2) by sulforaphane (SFN) protects from, and deletion of the Nrf2 gene exaggerates, diabetic cardiomyopathy. Angiotensin II (Ang II) plays a critical role in the development of diabetic cardiomyopathy. Therefore, whether SFN prevents Ang II-induced cardiomyopathy through activation of Nrf2 was examined using wild-type, global deletion of Nrf2 gene (Nrf2-KO) and cardiomyocyte-specific overexpression of Nrf2 gene (Nrf2-TG) mice.

Methods and results

Administration of a subpressor dose of Ang II to wild-type mice induced cardiac oxidative stress, inflammation, remodeling and dysfunction, all of which could be prevented by SFN treatment with Nrf2 up-regulation and activation. Nrf2-KO mice are susceptible, and Nrf2-TG mice are resistant, respectively, to Ang II-induced cardiomyopathy. Meanwhile, the ability of SFN to protect against Ang II-induced cardiac damage was lost in Nrf2-KO mice. Up-regulation and activation of Nrf2 by SFN is accompanied by activation of Akt, inhibition of glycogen synthase kinase (GSK)-3β, and accumulation of Fyn in nuclei. In vitro up-regulation of Nrf2 by SFN was abolished and nuclear Fyn accumulation was increased when cardiac cells were exposed to a PI3K inhibitor or GSK-3β-specific activator.

Conclusion

These results suggest that Nrf2 plays a central role in the prevention of Ang II-induced cardiomyopathy, and SFN prevents Ang II-induced cardiomyopathy partially via the Akt/GSK-3β/Fyn-mediated Nrf2 activation.

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Sulforaphane (SFN) can prevent angiotensin II (AngII) -induced cardiomyopathy.

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SFN prevents AngII-induced cardiomyopathy via up-regulating and activating Nrf2.

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Cardiac overexpression of Nrf2 prevents Ang II-induced cardiomyopathy.

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Up-regulation and activation of Nrf2 by SFN is achieved through the Akt/GSK-3β/Fyn pathway.

Molecular Alterations in a Mouse Cardiac Model of Friedreich Ataxia: An Impaired Nrf2 Response Mediated via Upregulation of Keap1 and Activation of the Gsk3β Axis

Nuclear factor-erythroid 2-related factor-2 (Nrf2) is a master regulator of the antioxidant response. However, studies in models of Friedreich ataxia, a neurodegenerative and cardiodegenerative disease associated with oxidative stress, reported decreased Nrf2 expression attributable to unknown mechanisms. Using a mouse conditional frataxin knockout (KO) model in the heart and skeletal muscle, we examined the Nrf2 pathway in these tissues. Frataxin KO results in fatal cardiomyopathy, whereas skeletal muscle was asymptomatic. In the KO heart, protein oxidation and a decreased glutathione/oxidized glutathione ratio were observed, but the opposite was found in skeletal muscle. Decreased total and nuclear Nrf2 and increased levels of its inhibitor, Kelch-like ECH-associated protein 1, were evident in the KO heart, but not in skeletal muscle. Moreover, a mechanism involving activation of the nuclear Nrf2 export/degradation machinery via glycogen synthase kinase-3β (Gsk3β) signaling was demonstrated in the KO heart. This process involved the following: i) increased Gsk3β activation, ii) β-transducin repeat containing E3 ubiquitin protein ligase nuclear accumulation, and iii) Fyn phosphorylation. A corresponding decrease in Nrf2-DNA-binding activity and a general decrease in Nrf2-target mRNA were observed in KO hearts. Paradoxically, protein levels of some Nrf2 antioxidant targets were significantly increased in KO mice. Collectively, cardiac frataxin deficiency reduces Nrf2 levels via two potential mechanisms: increased levels of cytosolic Kelch-like ECH-associated protein 1 and activation of Gsk3β signaling, which decreases nuclear Nrf2. These findings are in contrast to the frataxin-deficient skeletal muscle, where Nrf2 was not decreased.

Intermittent hypoxia-induced cardiomyopathy and its prevention by Nrf2 and metallothionein

The mechanism for intermittent hypoxia (IH)-induced cardiomyopathy remains obscure. We reported the prevention of acute and chronic IH-induced cardiac damage by selective cardiac overexpression of metallothionein (MT). Herein we defined that MT-mediated protection from IH-cardiomyopathy is via activation of nuclear factor erythroid 2-related factor 2 (Nrf2), a critical redox-balance controller in the body. For this, mice were exposed to IH for 3 days (acute) or 4 or 8 weeks (chronic). Cardiac Nrf2 and MT expression in response to IH were significantly increased acutely yet decreased chronically. Interestingly, cardiac overexpression (Nrf2-TG) or global deletion of the Nrf2 gene (Nrf2-KO) made mice highly resistant or highly susceptible, respectively, to IH-induced cardiomyopathy and MT expression. Mechanistically, 4-week IH exposure significantly decreased cardiac Nrf2 binding to the MT gene promoter, and thus, depressed both MT transcription and translation in WT mice but not Nrf2-TG mice. Likewise, cardiac MT overexpression prevented chronic IH-induced cardiomyopathy and down-regulation of Nrf2 likely via activation of a PI3K/Akt/GSK-3β/Fyn-dependent signaling pathway. These results reveal an integrated relationship between cardiac Nrf2 and MT expression in response to IH -- acute compensatory up-regulation followed by chronic down-regulation and cardiomyopathy. Cardiac overexpression of either Nrf2 or MT offered cardioprotection from IH via complicated PI3K/Akt/GSK3B/Fyn signaling. Potential therapeutics may target either Nrf2 or MT to prevent chronic IH-induced cardiomyopathy.

Neferine modulates IGF-1R/Nrf2 signaling in doxorubicin treated H9c2 cardiomyoblasts

Doxorubicin (DOX) induced cardiotoxicity is a major problem during chemotherapy of cancers. DOX-mediated suppression of type 1 IGF receptor (IGF-1R) signaling leads to cardiac dysfunction. Neferine, a bisbezylisoquinoline alkaloid from the seed embryos of Nelumbo nucifera Gaertn possesses a distinct range of pharmacological properties. Herewith, the present study attempts to elucidate the protective role of neferine against DOX induced toxicity in H9c2 rat cardiomyoblast cell line model. DOX-treated H9c2 cells significantly increased mitochondrial superoxide generation, depleted cellular antioxidant status, suppressed the activation of IGF-1R signaling via PI3K/Akt/mTOR and induced autophagy by the activation of ULK1, Beclin1, Atg7, and LC3B. Neferine pre-treatment activated IGF-1R signaling, improved cellular antioxidant pool, increased the expression of down-stream targets of IGF-1R, such as PI3K/Akt/mTOR, inhibited mitochondrial superoxide generation and autophagy significantly with the induction of Nrf2 translocation and expressions of HO1 and SOD1. Our study suggests the use of neferine for amelioration of DOX-mediated cardiotoxicity.

Responses to reductive stress in the cardiovascular system

There is a growing appreciation that reductive stress represents a disturbance in the redox state that is harmful to biological systems. On a cellular level, the presence of increased reducing equivalents and the lack of beneficial fluxes of reactive oxygen species can prevent growth factor-mediated signaling, promote mitochondrial dysfunction, increase apoptosis, and decrease cell survival. In this review, we highlight the importance of redox balance in maintaining cardiovascular homeostasis and consider the tenuous balance between oxidative and reductive stress. We explain the role of reductive stress in models of protein aggregation-induced cardiomyopathies, such as those caused by mutations in αB-crystallin. In addition, we discuss the role of NADPH oxidases in models of heart failure and ischemia-reperfusion to illustrate how oxidants may mediate the adaptive responses to injury. NADPH oxidase 4, a hydrogen peroxide generator, also has a major role in promoting vascular homeostasis through its regulation of vascular tone, angiogenic responses, and effects on atherogenesis. In contrast, the lack of antioxidant enzymes that reduce hydrogen peroxide, such as glutathione peroxidase 1, promotes vascular remodeling and is deleterious to endothelial function. Thus, we consider the role of oxidants as necessary signals to promote adaptive responses, such as the activation of Nrf2 and eNOS, and the stabilization of Hif1. In addition, we discuss the adaptive metabolic reprogramming in hypoxia that lead to a reductive state, and the subsequent cellular redistribution of reducing equivalents from NADH to other metabolites. Finally, we discuss the paradoxical ability of excess reducing equivalents to stimulate oxidative stress and promote injury.

Sodium Sulfide Attenuates Ischemic-Induced Heart Failure by Enhancing Proteasomal Function in an Nrf2-Dependent Manner

BACKGROUND

Therapeutic strategies aimed at increasing hydrogen sulfide (H2S) levels exert cytoprotective effects in various models of cardiovascular injury. However, the underlying mechanism(s) responsible for this protection remain to be fully elucidated. Nuclear factor E2-related factor 2 (Nrf2) is a cellular target of H2S and facilitator of H2S-mediated cardioprotection after acute myocardial infarction. Here, we tested the hypothesis that Nrf2 mediates the cardioprotective effects of H2S therapy in the setting of heart failure.

METHODS AND RESULTS

Mice (12 weeks of age) deficient in Nrf2 (Nrf2 KO; C57BL/6J background) and wild-type littermates were subjected to ischemic-induced heart failure. Wild-type mice treated with H2S in the form of sodium sulfide (Na2S) displayed enhanced Nrf2 signaling, improved left ventricular function, and less cardiac hypertrophy after the induction of heart failure. In contrast, Na2S therapy failed to provide protection against heart failure in Nrf2 KO mice. Studies aimed at evaluating the underlying cardioprotective mechanisms found that Na2S increased the expression of proteasome subunits, resulting in an increased proteasome activity and a reduction in the accumulation of damaged proteins. In contrast, Na2S therapy failed to enhance the proteasome and failed to attenuate the accumulation of damaged proteins in Nrf2 KO mice. Additionally, Na2S failed to improve cardiac function when the proteasome was inhibited.

CONCLUSIONS

These findings indicate that Na2S therapy enhances proteasomal activity and function during the development of heart failure in an Nrf2-dependent manner and that this enhancement leads to attenuation in cardiac dysfunction.

Nitrite Therapy Ameliorates Myocardial Dysfunction via H2S and Nuclear Factor-Erythroid 2-Related Factor 2 (Nrf2)-Dependent Signaling in Chronic Heart Failure

BACKGROUND

Bioavailability of nitric oxide (NO) and hydrogen sulfide (H2S) is reduced in heart failure (HF). Recent studies suggest cross-talk between NO and H2S signaling. We previously reported that sodium nitrite (NaNO2) ameliorates myocardial ischemia-reperfusion injury and HF. Nuclear factor-erythroid-2-related factor 2 (Nrf2) regulates the antioxidant proteins expression and is upregulated by H2S. We examined the NaNO2 effects on endogenous H2S bioavailability and Nrf2 activation in mice subjected to ischemia-induced chronic heart failure (CHF).

METHODS AND RESULTS

Mice underwent 60 minutes of left coronary artery occlusion and 4 weeks of reperfusion. NaNO2 (165 μg/kgic) or vehicle was administered at reperfusion and then in drinking water (100 mg/L) for 4 weeks. Left ventricular (LV), ejection fraction (EF), LV end diastolic (LVEDD) and systolic dimensions (LVESD) were determined at baseline and at 4 weeks of reperfusion. Myocardial tissue was analyzed for oxidative stress and respective gene/protein-related assays. We found that NaNO2 therapy preserved LVEF, LVEDD and LVSD at 4 weeks during ischemia-induced HF. Myocardial malondialdehyde and protein carbonyl content were significantly reduced in NaNO2-treated mice as compared to vehicle, suggesting a reduction in oxidative stress. NaNO2 therapy markedly increased expression of Cu,Zn-superoxide dismutase, catalase, and glutathione peroxidase during 4 weeks of reperfusion. Furthermore, NaNO2 upregulated the activity of Nrf2, as well as H2S-producing enzymes, and ultimately increased H2S bioavailability in ischemia-induced CHF in mice as compared with vehicle.

CONCLUSIONS

Our results demonstrate that NaNO2 therapy significantly improves LV function via increasing H2S bioavailability, Nrf2 activation, and antioxidant defenses.

Bixin protects mice against ventilation-induced lung injury in an NRF2-dependent manner

Mechanical ventilation (MV) is a therapeutic intervention widely used in the clinic to assist patients that have difficulty breathing due to lung edema, trauma, or general anesthesia. However, MV causes ventilator-induced lung injury (VILI), a condition characterized by increased permeability of the alveolar-capillary barrier that results in edema, hemorrhage, and neutrophil infiltration, leading to exacerbated lung inflammation and oxidative stress. This study explored the feasibility of using bixin, a canonical NRF2 inducer identified during the current study, to ameliorate lung damage in a murine VILI model. In vitro, bixin was found to activate the NRF2 signaling pathway through blockage of ubiquitylation and degradation of NRF2 in a KEAP1-C151 dependent manner; intraperitoneal (IP) injection of bixin led to pulmonary upregulation of the NRF2 response in vivo. Remarkably, IP administration of bixin restored normal lung morphology and attenuated inflammatory response and oxidative DNA damage following MV. This observed beneficial effect of bixin derived from induction of the NRF2 cytoprotective response since it was only observed in Nrf2^+/+ but not in Nrf2^−/− mice. This is the first study providing proof-of-concept that NRF2 activators can be developed into pharmacological agents for clinical use to prevent patients from lung injury during MV treatment.

Nuclear factor erythroid-2 related factor 2 (Nrf2)-mediated protein quality control in cardiomyocytes

Protein quality control (PQC) acts to minimize the level and toxicity of malfolded proteins in the cell. It is performed by an elaborate network of molecular chaperones and targeted protein degradation pathways. PQC monitors and maintains protein homeostasis or proteostasis in the cells. Whilst chaperones may actively promote refolding of malfolded proteins, the malfolded proteins which cannot be correctly refolded are degraded by the ubiquitin proteasome system (UPS) and the autophagic-lysosome pathway (ALP). The UPS degrades individual misfolded protein molecules, whereas the ALP removes large and less soluble protein aggregates and organelles. Emerging evidence indicates that dysregulated and inadequate PQC play an important role in the pathogenesis of not only classic conformational disease but more common forms of cardiac pathology such as cardiac pathological hypertrophy and heart failure. Nuclear factor erythroid 2-related factor 2 (Nrf2), a master transcription factor of cellular defense, appears to regulate the USP and the ALP by directly controlling the expression of UPS- and ALP- related genes. This article highlights an emerging role of Nrf2 in the regulation of intracellular PQC as well as its potential involvement in cardiac pathology.

CDDO and Its Role in Chronic Diseases

There has been a continued interest in translational research focused on both natural products and manipulation of functional groups on these compounds to create novel derivatives with higher desired activities. Oleanolic acid, a component of traditional Chinese medicine used in hepatitis therapy, was modified by chemical processes to form 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO). This modification increased anti-inflammatory activity significantly and additional functional groups on the CDDO backbone have shown promise in treating conditions ranging from kidney disease to obesity to diabetes. CDDO's therapeutic effect is due to its upregulation of the master antioxidant transcription factor Nuclear factor erythroid 2-related factor 2 (Nrf2) through conformational change of Nrf2-repressing, Kelch-like erythroid cell-derived protein with CNC homology-associated protein 1 (Keap1) and multiple animal and human studies have verified subsequent activation of Nrf2-controlled antioxidant genes via upstream Antioxidant Response Element (ARE) regions. At the present time, positive results have been obtained in the laboratory and clinical trials with CDDO derivatives treating conditions such as lung injury, inflammation and chronic kidney disease. However, clinical trials for cancer and cardiovascular disease have not shown equally positive results and further exploration of CDDO and its derivatives is needed to put these shortcomings into context for the purpose of future therapeutic modalities.

Nrf2-Mediated Cardiac Maladaptive Remodeling and Dysfunction in a Setting of Autophagy Insufficiency

Nuclear factor erythroid-2-related factor 2 (Nrf2) appears to exert either a protective or detrimental effect on the heart; however, the underlying mechanism remains poorly understood. Herein, we uncovered a novel mechanism for turning off the Nrf2-mediated cardioprotection and switching on Nrf2-mediated cardiac dysfunction. In a murine model of pressure overload-induced cardiac remodeling and dysfunction via transverse aortic arch constriction, knockout of Nrf2 enhanced myocardial necrosis and death rate during an initial stage of cardiac adaptation when myocardial autophagy function is intact. However, knockout of Nrf2 turned out to be cardioprotective throughout the later stage of cardiac maladaptive remodeling when myocardial autophagy function became insufficient. Transverse aortic arch constriction -induced activation of Nrf2 was dramatically enhanced in the heart with impaired autophagy, which is induced by cardiomyocyte-specific knockout of autophagy-related gene (Atg)5. Notably, Nrf2 activation coincided with the upregulation of angiotensinogen (Agt) only in the autophagy-impaired heart after transverse aortic arch constriction. Agt5 and Nrf2 gene loss-of-function approaches in combination with Jak2 and Fyn kinase inhibitors revealed that suppression of autophagy inactivated Jak2 and Fyn and nuclear translocation of Fyn, while enhancing nuclear translocation of Nrf2 and Nrf2-driven Agt expression in cardiomyocytes. Taken together, these results indicate that the pathophysiological consequences of Nrf2 activation are closely linked with the functional integrity of myocardial autophagy during cardiac remodeling. When autophagy is intact, Nrf2 is required for cardiac adaptive responses; however, autophagy impairment most likely turns off Fyn-operated Nrf2 nuclear export thus activating Nrf2-driven Agt transcription, which exacerbates cardiac maladaptation leading to dysfunction.

KEAP1-NRF2 signalling and autophagy in protection against oxidative and reductive proteotoxicity

Maintaining cellular redox status to allow cell signalling to occur requires modulation of both the controlled production of oxidants and the thiol-reducing networks to allow specific regulatory post-translational modification of protein thiols. The oxidative stress hypothesis captured the concept that overproduction of oxidants can be proteotoxic, but failed to predict the recent finding that hyperactivation of the KEAP1-NRF2 system also leads to proteotoxicity. Furthermore, sustained activation of thiol redox networks by KEAP1-NRF2 induces a reductive stress, by decreasing the lifetime of necessary oxidative post-translational modifications required for normal metabolism or cell signalling. In this context, it is now becoming clear why antioxidants or hyperactivation of antioxidant pathways with electrophilic therapeutics can be deleterious. Furthermore, it suggests that the autophagy-lysosomal pathway is particularly important in protecting the cell against redox-stress-induced proteotoxicity, since it can degrade redox-damaged proteins without causing aberrant changes to the redox network needed for metabolism or signalling. In this context, it is important to understand: (i) how NRF2-mediated redox signalling, or (ii) the autophagy-mediated antioxidant/reductant pathways sense cellular damage in the context of cellular pathogenesis. Recent studies indicate that the modification of protein thiols plays an important role in the regulation of both the KEAP1-NRF2 and autophagy pathways. In the present review, we discuss evidence demonstrating that the KEAP1-NRF2 pathway and autophagy act in concert to combat the deleterious effects of proteotoxicity. These findings are discussed with a special emphasis on their impact on cardiovascular disease and neurodegeneration.

Identifying panaxynol, a natural activator of nuclear factor erythroid-2 related factor 2 (Nrf2) from American ginseng as a suppressor of inflamed macrophage-induced cardiomyocyte hypertrophy

ETHNOPHARMACOLOGICAL RELEVANCE

American ginseng is capable of ameliorating cardiac dysfunction and activating Nrf2, a master regulator of antioxidant defense, in the heart. This study was designed to isolate compounds from American ginseng and to determine those responsible for the Nrf2-mediated resolution of inflamed macrophage-induced cardiomyocyte hypertrophy.

MATERIALS AND METHODS

A standardized crude extract of American ginseng was supplied by the National Research Council of Canada, Institute for National Measurement Standards. A bioassay-based fractionization of American ginseng was performed to identify the putative substances which could activate Nrf2-mediated suppression of pro-inflammatory cytokine expression in macrophages and macrophage-mediated pro-hypertrophic growth in cardiomyocytes.

RESULTS

A hexane fraction of an anti-inflammatory crude extract of American ginseng was found to be most effective in suppressing the inflammatory responses in macrophages. Preparative, reverse-phase HPLC and a comparative analysis by analytical scale LC-UV/MS revealed the hexane fraction contains predominantly C17 polyacetylenes and linolenic acid. Panaxynol, one of the major polyacetylenes, was found to be a potent Nrf2 activator. Panaxynol posttranscriptionally activated Nrf2 by inhibiting Kelch-like ECH-associated protein (Keap) 1-mediated degradation without affecting the binding of Keap1 and Nrf2. Moreover, panaxynol suppressed a selected set of cytokine expression via the activation of Nrf2 while minimally regulating nuclear factor-kappa B (NF-κB)-mediated cytokine expression in macrophages. It also dramatically inhibited the inflamed macrophage-mediated cardiomyocyte death and hypertrophy by activating Nrf2 in macrophages.

CONCLUSIONS

These results demonstrate that American ginseng-derived panaxynol is a specific Nrf2 activator and panaxynol-activated Nrf2 signaling is at least partly responsible for American ginseng-induced health benefit in the heart.

Deubiquitinating enzyme CYLD mediates pressure overload-induced cardiac maladaptive remodeling and dysfunction via downregulating Nrf2

Ubiquitin proteasome system (UPS) consists of ubiquitin, ubiquitin-activating enzymes (E1s), ubiquitin-conjugating enzymes (E2s), ubiquitin ligases (E3s), proteasomes, and deubiquitinating enzymes (DUBs). Ubiquitin, E1s, several E2s, E3s, and proteasomes play an important role in the regulation of cardiac homeostasis and dysfunction; however, less is known about the role of DUBs in the heart. Here, we uncovered a crucial role of cyclindromatosis (CYLD), a DUB, in mediating cardiac maladaptive remodeling and dysfunction. CYLD expression was dramatically upregulated in the cardiomyocytes of hypertrophic and failing human and murine hearts. Knockout of CYLD improved survival rate and alleviated cardiac hypertrophy, fibrosis, apoptosis, oxidative stress, and dysfunction in mice that were subjected to sustained pressure overload induced by transverse aortic constriction. Deep sequencing and gene array analyses revealed that the most dramatically changed genes are those involving in the free radical scavenging pathway and cardiovascular disease, including fos, jun, myc, and nuclear factor erythroid-2 related factor 2 (Nrf2) in the heart. Moreover, knockdown of CYLD enhanced mitogen-activated protein kinase (MAPK) ERK- and p38-mediated expression of c-jun, c-fos, and c-myc, which govern Nrf2 expression in cardiomyocytes. The CYLD deficiency-induced suppression of reactive oxygen species (ROS) formation, death and hypertrophy in cardiomyocytes was blocked by additional knockdown of Nrf2. Taken together, our findings demonstrate for the first time that CYLD mediates cardiac maladaptive remodeling and dysfunction, most likely via enhancing myocardial oxidative stress in response to pressure overload. At the molecular level, CYLD interrupts the ERK- and p38-/AP-1 and c-Myc pathways to suppress Nrf2-operated antioxidative capacity, thereby enhancing oxidative stress in the heart.