Mitochondrial proteome remodelling in pressure overload-induced heart failure: the role of mitochondrial oxidative stress

lncRNA Gm20257 alleviates pathological cardiac hypertrophy by modulating the PGC-1α-mitochondrial complex IV axis

Pathological cardiac hypertrophy, a major contributor to heart failure, is closely linked to mitochondrial function. The roles of long noncoding RNAs (lncRNAs), which regulate mitochondrial function, remain largely unexplored in this context. Herein, a previously unknown lncRNA, Gm20257, was identified. It markedly increased under hypertrophic stress in vivo and in vitro. The suppression of Gm20257 by using small interfering RNAs significantly induced cardiomyocyte hypertrophy. Conversely, the overexpression of Gm20257 through plasmid transfection or adeno-associated viral vector-9 mitigated angiotensin II-induced hypertrophic phenotypes in neonatal mouse ventricular cells or alleviated cardiac hypertrophy in a mouse TAC model respectively, thus restoring cardiac function. Importantly, Gm20257 restored mitochondrial complex IV level and enhanced mitochondrial function. Bioinformatics prediction showed that Gm20257 had a high binding score with peroxisome proliferator-activated receptor coactivator-1 (PGC-1α), which could increase mitochondrial complex IV. Subsequently, Western blot analysis results revealed that Gm20257 substantially affected the expression of PGC-1α. Further analyses through RNA immunoprecipitation and immunoblotting following RNA pull-down indicated that PGC-1α was a direct downstream target of Gm20257. This interaction was demonstrated to rescue the reduction of mitochondrial complex IV induced by hypertrophic stress and promote the generation of mitochondrial ATP. These findings suggest that Gm20257 improves mitochondrial function through the PGC-1α-mitochondrial complex IV axis, offering a novel approach for attenuating pathological cardiac hypertrophy.

Mechanical stress induced mitochondrial dysfunction in cardiovascular diseases: Novel mechanisms and therapeutic targets

Cardiovascular diseases (CVDs) are the leading cause of mortality worldwide. Others and our studies have shown that mechanical stresses (forces) including shear stress and cyclic stretch, occur in various pathological conditions, play significant roles in the development and progression of CVDs. Mitochondria regulate the physiological processes of cardiac and vascular cells mainly through adenosine triphosphate (ATP) production, calcium flux and redox control while promote cell death through electron transport complex (ETC) related cellular stress response. Mounting evidence reveal that mechanical stress-induced mitochondrial dysfunction plays a vital role in the pathogenesis of many CVDs including heart failure and atherosclerosis. This review summarized mitochondrial functions in cardiovascular system under physiological mechanical stress and mitochondrial dysfunction under pathological mechanical stress in CVDs (graphical abstract). The study of mitochondrial dysfunction under mechanical stress can further our understanding of the underlying mechanisms, identify potential therapeutic targets, and aid the development of novel treatments of CVDs.

Myocardial proteome changes in aortic stenosis rats subjected to long-term aerobic exercise

The effects of exercise training (ET) on the heart of aortic stenosis (AS) rats are controversial and the mechanisms involved in alterations induced by ET have been poorly clarified. In this study, we analyzed the myocardial proteome to identify proteins modulated by moderate-intensity aerobic ET in rats with chronic supravalvular AS. Wistar rats were divided into four groups: sedentary control (C-Sed), exercised control (C-Ex), sedentary aortic stenosis (AS-Sed), and exercised AS (AS-Ex). ET consisted of five treadmill running sessions per week for 16 weeks. Statistical analysis was performed by ANOVA or Kruskal-Wallis and Goodman tests. Results were discussed at a significance level of 5%. At the end of the experiment, AS-Ex rats had higher functional capacity, lower blood lactate concentration, and better cardiac structural and left ventricular (LV) functional parameters than the AS-Sed. Myocardial proteome analysis showed that AS-Sed had higher relative protein abundance related to the glycolytic pathway, oxidative stress, and inflammation, and lower relative protein abundance related to beta-oxidation than C-Sed. AS-Ex had higher abundance of one protein related to mitochondrial biogenesis and lower relative protein abundance associated with oxidative stress and inflammation than AS-Sed. Proteomic data were validated for proteins related to lipid and glycolytic metabolism. Chronic pressure overload changes the abundance of myocardial proteins that are mainly involved in lipid and glycolytic energy metabolism in rats. Moderate-intensity aerobic training attenuates changes in proteins related to oxidative stress and inflammation and increases the COX4I1 protein, related to mitochondrial biogenesis. Protein changes are combined with improved functional capacity, cardiac remodeling, and LV function in AS rats.

Mitochondrial Targeted Interventions for Aging

Changes in mitochondrial function play a critical role in the basic biology of aging and age-related disease. Mitochondria are typically thought of in the context of ATP production and oxidant production. However, it is clear that the mitochondria sit at a nexus of cell signaling where they affect metabolite, redox, and energy status, which influence many factors that contribute to the biology of aging, including stress responses, proteostasis, epigenetics, and inflammation. This has led to growing interest in identifying mitochondrial targeted interventions to delay or reverse age-related decline in function and promote healthy aging. In this review, we discuss the diverse roles of mitochondria in the cell. We then highlight some of the most promising strategies and compounds to target aging mitochondria in preclinical testing. Finally, we review the strategies and compounds that have advanced to clinical trials to test their ability to improve health in older adults.

Advances in the molecular mechanisms of statins in regulating endothelial nitric oxide bioavailability: Interlocking biology between eNOS activity and L-arginine metabolism

Statins, inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A, are widely used to treat hypercholesterolemia. In addition, statins have been suggested to reduce the risk of cardiovascular events owing to their pleiotropic effects on the vascular system, including vasodilation, anti-inflammation, anti-coagulation, anti-oxidation, and inhibition of vascular smooth muscle cell proliferation. The major beneficial effect of statins in maintaining vascular homeostasis is the induction of nitric oxide (NO) bioavailability by activating endothelial NO synthase (eNOS) in endothelial cells. The mechanisms underlying the increased NO bioavailability and eNOS activation by statins have been well-established in various fields, including transcriptional and post-transcriptional regulation, kinase-dependent phosphorylation and protein-protein interactions. However, the mechanism by which statins affect the metabolism of L-arginine, a precursor of NO biosynthesis, has rarely been discussed. Autophagy, which is crucial for energy homeostasis, regulates endothelial functions, including NO production and angiogenesis, and is a potential therapeutic target for cardiovascular diseases. In this review, in addition to summarizing the molecular mechanisms underlying increased NO bioavailability and eNOS activation by statins, we also discuss the effects of statins on the metabolism of L-arginine.

Significance of quantitative analyses of the impact of heterogeneity in mitochondrial content and shape on cell differentiation

Mitochondria, classically known as the powerhouse of cells, are unique double membrane-bound multifaceted organelles carrying a genome. Mitochondrial content varies between cell types and precisely doubles within cells during each proliferating cycle. Mitochondrial content also increases to a variable degree during cell differentiation triggered after exit from the proliferating cycle. The mitochondrial content is primarily maintained by the regulation of mitochondrial biogenesis, while damaged mitochondria are eliminated from the cells by mitophagy. In any cell with a given mitochondrial content, the steady-state mitochondrial number and shape are determined by a balance between mitochondrial fission and fusion processes. The increase in mitochondrial content and alteration in mitochondrial fission and fusion are causatively linked with the process of differentiation. Here, we critically review the quantitative aspects in the detection methods of mitochondrial content and shape. Thereafter, we quantitatively link these mitochondrial properties in differentiating cells and highlight the implications of such quantitative link on stem cell functionality. Finally, we discuss an example of cell size regulation predicted from quantitative analysis of mitochondrial shape and content. To highlight the significance of quantitative analyses of these mitochondrial properties, we propose three independent rationale based hypotheses and the relevant experimental designs to test them.

Health position paper and redox perspectives on reactive oxygen species as signals and targets of cardioprotection

The present review summarizes the beneficial and detrimental roles of reactive oxygen species in myocardial ischemia/reperfusion injury and cardioprotection. In the first part, the continued need for cardioprotection beyond that by rapid reperfusion of acute myocardial infarction is emphasized. Then, pathomechanisms of myocardial ischemia/reperfusion to the myocardium and the coronary circulation and the different modes of cell death in myocardial infarction are characterized. Different mechanical and pharmacological interventions to protect the ischemic/reperfused myocardium in elective percutaneous coronary interventions and coronary artery bypass grafting, in acute myocardial infarction and in cardiotoxicity from cancer therapy are detailed. The second part keeps the focus on ROS providing a comprehensive overview of molecular and cellular mechanisms involved in ischemia/reperfusion injury. Starting from mitochondria as the main sources and targets of ROS in ischemic/reperfused myocardium, a complex network of cellular and extracellular processes is discussed, including relationships with Ca2+ homeostasis, thiol group redox balance, hydrogen sulfide modulation, cross-talk with NAPDH oxidases, exosomes, cytokines and growth factors. While mechanistic insights are needed to improve our current therapeutic approaches, advancements in knowledge of ROS-mediated processes indicate that detrimental facets of oxidative stress are opposed by ROS requirement for physiological and protective reactions. This inevitable contrast is likely to underlie unsuccessful clinical trials and limits the development of novel cardioprotective interventions simply based upon ROS removal.

Fatty acid metabolism disorders and potential therapeutic traditional Chinese medicines in cardiovascular diseases

Cardiovascular diseases are currently the primary cause of mortality in the whole world. Growing evidence indicated that the disturbances in cardiac fatty acid metabolism are crucial contributors in the development of cardiovascular diseases. The abnormal cardiac fatty acid metabolism usually leads to energy deficit, oxidative stress, excessive apoptosis, and inflammation. Targeting fatty acid metabolism has been regarded as a novel approach to the treatment of cardiovascular diseases. However, there are currently no specific drugs that regulate fatty acid metabolism to treat cardiovascular diseases. Many traditional Chinese medicines have been widely used to treat cardiovascular diseases in clinics. And modern studies have shown that they exert a cardioprotective effect by regulating the expression of key proteins involved in fatty acid metabolism, such as peroxisome proliferator-activated receptor α and carnitine palmitoyl transferase 1. Hence, we systematically reviewed the relationship between fatty acid metabolism disorders and four types of cardiovascular diseases including heart failure, coronary artery disease, cardiac hypertrophy, and diabetic cardiomyopathy. In addition, 18 extracts and eight monomer components from traditional Chinese medicines showed cardioprotective effects by restoring cardiac fatty acid metabolism. This work aims to provide a reference for the finding of novel cardioprotective agents targeting fatty acid metabolism.

Reactive oxygen species, toxicity, oxidative stress, and antioxidants: chronic diseases and aging

A physiological level of oxygen/nitrogen free radicals and non-radical reactive species (collectively known as ROS/RNS) is termed oxidative eustress or "good stress" and is characterized by low to mild levels of oxidants involved in the regulation of various biochemical transformations such as carboxylation, hydroxylation, peroxidation, or modulation of signal transduction pathways such as Nuclear factor-κB (NF-κB), Mitogen-activated protein kinase (MAPK) cascade, phosphoinositide-3-kinase, nuclear factor erythroid 2-related factor 2 (Nrf2) and other processes. Increased levels of ROS/RNS, generated from both endogenous (mitochondria, NADPH oxidases) and/or exogenous sources (radiation, certain drugs, foods, cigarette smoking, pollution) result in a harmful condition termed oxidative stress ("bad stress"). Although it is widely accepted, that many chronic diseases are multifactorial in origin, they share oxidative stress as a common denominator. Here we review the importance of oxidative stress and the mechanisms through which oxidative stress contributes to the pathological states of an organism. Attention is focused on the chemistry of ROS and RNS (e.g. superoxide radical, hydrogen peroxide, hydroxyl radicals, peroxyl radicals, nitric oxide, peroxynitrite), and their role in oxidative damage of DNA, proteins, and membrane lipids. Quantitative and qualitative assessment of oxidative stress biomarkers is also discussed. Oxidative stress contributes to the pathology of cancer, cardiovascular diseases, diabetes, neurological disorders (Alzheimer's and Parkinson's diseases, Down syndrome), psychiatric diseases (depression, schizophrenia, bipolar disorder), renal disease, lung disease (chronic pulmonary obstruction, lung cancer), and aging. The concerted action of antioxidants to ameliorate the harmful effect of oxidative stress is achieved by antioxidant enzymes (Superoxide dismutases-SODs, catalase, glutathione peroxidase-GPx), and small molecular weight antioxidants (vitamins C and E, flavonoids, carotenoids, melatonin, ergothioneine, and others). Perhaps one of the most effective low molecular weight antioxidants is vitamin E, the first line of defense against the peroxidation of lipids. A promising approach appears to be the use of certain antioxidants (e.g. flavonoids), showing weak prooxidant properties that may boost cellular antioxidant systems and thus act as preventive anticancer agents. Redox metal-based enzyme mimetic compounds as potential pharmaceutical interventions and sirtuins as promising therapeutic targets for age-related diseases and anti-aging strategies are discussed.

Improving mitochondrial function in preclinical models of heart failure: therapeutic targets for future clinical therapies?

INTRODUCTION

Heart failure is a complex clinical syndrome resulting from the unsuccessful compensation of symptoms of myocardial damage. Mitochondrial dysfunction is a process that occurs because of an attempt to adapt to the disruption of metabolic and energetic pathways occurring in the myocardium. This, in turn, leads to further dysfunction in cardiomyocyte processes. Currently, many therapeutic strategies have been implemented to improve mitochondrial function, but their effectiveness varies widely.

AREAS COVERED

This review focuses on new models of therapeutic strategies targeting mitochondrial function in the treatment of heart failure.

EXPERT OPINION

Therapeutic strategies targeting mitochondria appear to be a valuable option for treating heart failure. Currently, the greatest challenge is to develop new research models that could restore the disrupted metabolic processes in mitochondria as comprehensively as possible. Only the development of therapies that focus on improving as many dysregulated mitochondrial processes as possible in patients with heart failure will be able to bring the expected clinical improvement, along with inhibition of disease progression. Combined strategies involving the reduction of the effects of oxidative stress and mitochondrial dysfunction, appear to be a promising possibility for developing new therapies for a complex and multifactorial disease such as heart failure.

Mechanism of fibroblast growth factor 21 in cardiac remodeling

Cardiac remodeling is a basic pathological process that enables the progression of multiple cardiac diseases to heart failure. Fibroblast growth factor 21 is considered a regulator in maintaining energy homeostasis and shows a positive role in preventing damage caused by cardiac diseases. This review mainly summarizes the effects and related mechanisms of fibroblast growth factor 21 on pathological processes associated with cardiac remodeling, based on a variety of cells of myocardial tissue. The possibility of Fibroblast growth factor 21 as a promising treatment for the cardiac remodeling process will also be discussed.

Mitochondrial calcium and reactive oxygen species in cardiovascular disease

Cardiomyocytes are one of the most mitochondria-rich cell types in the body, with ∼30-40% of the cell volume being composed of mitochondria. Mitochondria are well established as the primary site of adenosine triphosphate (ATP) generation in a beating cardiomyocyte, generating up to 90% of its ATP. Mitochondria have many functions in the cell, which could contribute to susceptibility to and development of cardiovascular disease (CVD). Mitochondria are key players in cell metabolism, ATP production, reactive oxygen species (ROS) production, and cell death. Mitochondrial calcium (Ca2+) plays a critical role in many of these pathways, and thus the dynamics of mitochondrial Ca2+ are important in regulating mitochondrial processes. Alterations in these varied and in many cases interrelated functions play an important role in CVD. This review will focus on the interrelationship of mitochondrial energetics, Ca2+, and ROS and their roles in CVD. Recent insights into the regulation and dysregulation of these pathways have led to some novel therapeutic approaches.

Mitochondrial Oxidative Stress Mediates Bradyarrhythmia in Leigh Syndrome Mitochondrial Disease Mice

Mitochondrial oxidative stress has been implicated in aging and several cardiovascular diseases, including heart failure and cardiomyopathy, ventricular tachycardia, and atrial fibrillation. The role of mitochondrial oxidative stress in bradyarrhythmia is less clear. Mice with a germline deletion of Ndufs4 subunit respiratory complex I develop severe mitochondrial encephalomyopathy resembling Leigh Syndrome (LS). Several types of cardiac bradyarrhythmia are present in LS mice, including a frequent sinus node dysfunction and episodic atrioventricular (AV) block. Treatment with the mitochondrial antioxidant Mitotempo or mitochondrial protective peptide SS31 significantly ameliorated the bradyarrhythmia and extended the lifespan of LS mice. Using an ex vivo Langendorff perfused heart with live confocal imaging of mitochondrial and total cellular reactive oxygen species (ROS), we showed increased ROS in the LS heart, which was potentiated by ischemia-reperfusion. A simultaneous ECG recording showed a sinus node dysfunction and AV block concurrent with the severity of the oxidative stress. Treatment with Mitotempo abolished ROS and restored the sinus rhythm. Our study reveals robust evidence of the direct mechanistic roles of mitochondrial and total ROS in bradyarrhythmia in the setting of LS mitochondrial cardiomyopathy. Our study also supports the potential clinical application of mitochondrial-targeted antioxidants or SS31 for the treatment of LS patients.

Targeting Mitochondrial Metabolism to Save the Failing Heart

Despite considerable progress in treating cardiac disorders, the prevalence of heart failure (HF) keeps growing, making it a global medical and economic burden. HF is characterized by profound metabolic remodeling, which mostly occurs in the mitochondria. Although it is well established that the failing heart is energy-deficient, the role of mitochondria in the pathophysiology of HF extends beyond the energetic aspects. Changes in substrate oxidation, tricarboxylic acid cycle and the respiratory chain have emerged as key players in regulating myocardial energy homeostasis, Ca²⁺ handling, oxidative stress and inflammation. This work aims to highlight metabolic alterations in the mitochondria and their far-reaching effects on the pathophysiology of HF. Based on this knowledge, we will also discuss potential metabolic approaches to improve cardiac function.

Cardiac Metabolism in Heart Failure and Implications for Uremic Cardiomyopathy

Chronic kidney disease is associated with an increased risk for the development and progression of cardiovascular disorders including hypertension, dyslipidemia, and coronary artery disease. Chronic kidney disease may also affect the myocardium through complex systemic changes, resulting in structural remodeling such as hypertrophy and fibrosis, as well as impairments in both diastolic and systolic function. These cardiac changes in the setting of chronic kidney disease define a specific cardiomyopathic phenotype known as uremic cardiomyopathy. Cardiac function is tightly linked to its metabolism, and research over the past 3 decades has revealed significant metabolic remodeling in the myocardium during the development of heart failure. Because the concept of uremic cardiomyopathy has only been recognized in recent years, there are limited data on metabolism in the uremic heart. Nonetheless, recent findings suggest overlapping mechanisms with heart failure. This work reviews key features of metabolic remodeling in the failing heart in the general population and extends this to patients with chronic kidney disease. The knowledge of similarities and differences in cardiac metabolism between heart failure and uremic cardiomyopathy may help identify new targets for mechanistic and therapeutic research on uremic cardiomyopathy.

Atrioventricular node dysfunction in pressure overload-induced heart failure—Involvement of the immune system and transcriptomic remodelling

Heart failure is associated with atrioventricular (AV) node dysfunction, and AV node dysfunction in the setting of heart failure is associated with an increased risk of mortality and heart failure hospitalisation. This study aims to understand the causes of AV node dysfunction in heart failure by studying changes in the whole nodal transcriptome. The mouse transverse aortic constriction model of pressure overload-induced heart failure was studied; functional changes were assessed using electrocardiography and echocardiography and the transcriptome of the AV node was quantified using RNAseq. Heart failure was associated with a significant increase in the PR interval, indicating a slowing of AV node conduction and AV node dysfunction, and significant changes in 3,077 transcripts (5.6% of the transcriptome). Many systems were affected: transcripts supporting AV node conduction were downregulated and there were changes in transcripts identified by GWAS as determinants of the PR interval. In addition, there was evidence of remodelling of the sarcomere, a shift from fatty acid to glucose metabolism, remodelling of the extracellular matrix, and remodelling of the transcription and translation machinery. There was evidence of the causes of this widespread remodelling of the AV node: evidence of dysregulation of multiple intracellular signalling pathways, dysregulation of 109 protein kinases and 148 transcription factors, and an immune response with a proliferation of neutrophils, monocytes, macrophages and B lymphocytes and a dysregulation of 40 cytokines. In conclusion, inflammation and a widespread transcriptional remodelling of the AV node underlies AV node dysfunction in heart failure.

Roles of autophagy in angiotensin II-induced cardiomyocyte apoptosis

Autophagy is a self-degradation process of cytoplasmic components and occurs in the failing heart. Angiotensin II plays a critical role in the progression of heart failure and induces autophagy. We investigated the mechanism underlying angiotensin II-enhanced autophagy and examined the role of autophagy in angiotensin II-induced cardiomyocyte injury. Neonatal rat cardiomyocytes were treated with angiotensin II (1-100 nmol/L). Angiotensin II dose-dependently increased autophagy indicators of microtubule-associated protein 1 light chain (LC) 3-II and monodansylcadaverine-labelled vesicles. It also enhanced the intracellular production of reactive oxygen species (ROS), assessed by H2DCFDA, an intracellular ROS indicator. NADPH oxidase- and mitochondria-derived ROS production was increased by angiotensin II, while angiotensin II-induced LC3-II expression was suppressed by inhibitors of these sources of ROS. Confocal microscopy revealed that superoxide-producing mitochondria colocalized with lysosomes after the angiotensin II stimulation. Myocyte apoptosis was assessed by nuclear staining with DAPI and caspase-3 activity. A 6-h stimulation with angiotensin II did not affect myocyte apoptosis, while a co-treatment with 3-methyl-adenine (3MA), an autophagy inhibitor, augmented apoptosis. These results indicate that autophagy suppressed apoptosis because it removed damaged mitochondria in the early stages of the angiotensin II stimulation. A longer angiotensin II stimulation for 24 h induced apoptosis and propidium iodide-positive lethal myocytes, while the co-treatment with 3MA did not lead to further increases. In conclusion, angiotensin II-induced autophagy removes ROS-producing mitochondria. Autophagy is a beneficial phenomenon against myocyte apoptosis in the early phase, but its benefit was limited in the late phase of angiotensin II stimulation.

Mitophagy: A Potential Target for Pressure Overload-Induced Cardiac Remodelling

The pathological mechanisms underlying cardiac remodelling and cardiac dysfunction caused by pressure overload are poorly understood. Mitochondrial damage and functional dysfunction, including mitochondrial bioenergetic disorder, oxidative stress, and mtDNA damage, contribute to heart injury caused by pressure overload. Mitophagy, an important regulator of mitochondrial homeostasis and function, is triggered by mitochondrial damage and participates in the pathological process of cardiovascular diseases. Recent studies indicate that mitophagy plays a critical role in the pressure overload model, but evidence on the causal relationship between mitophagy abnormality and pressure overload-induced heart injury is inconclusive. This review summarises the mechanism, role, and regulation of mitophagy in the pressure overload model. It also pays special attention to active compounds that may regulate mitophagy in pressure overload, which provide clues for possible clinical applications.

The effects of nicotinamide adenine dinucleotide in cardiovascular diseases: Molecular mechanisms, roles and therapeutic potential

Recently, cardiovascular diseases (CVDs) were identified as the leading cause of mortality, imposing a heavy burden on health care systems and the social economy. Nicotinamide adenine dinucleotide (NAD⁺), as a pivotal co-substrate for a range of different enzymes, is involved in many signal transduction pathways activated in CVDs. Emerging evidence has shown that NAD⁺ can exert remediating effects on CVDs by regulating metabolism, maintaining redox homeostasis and modulating the immune response. In fact, NAD⁺ might delay ageing through sirtuin and non-sirtuin pathways and thus contribute to interventions for age-related diseases such as CVDs. Considering that robust clinical studies of NAD⁺ are ongoing, we discuss current challenges and the future translational potential of NAD⁺ based on existing studies and our understanding. Despite some remaining gaps in its clinical application, NAD⁺ has been shown to have broad prospects and pan-effects, making it a suitable prophylactic drug for CVDs.

Accelerated Cardiac Aging in Patients With Congenital Heart Disease

An increasing number of patients with congenital heart disease (CHD) survive into adulthood but develop long-term complications including heart failure (HF). Cellular senescence, classically defined as stable cell cycle arrest, is implicated in biological processes such as embryogenesis, wound healing, and aging. Senescent cells have a complex senescence-associated secretory phenotype (SASP), involving a range of pro-inflammatory factors with important paracrine and autocrine effects on cell and tissue biology. While senescence has been mainly considered as a cause of diseases in the adulthood, it may be also implicated in some of the poor outcomes seen in patients with complex CHD. We propose that patients with CHD suffer from multiple repeated stress from an early stage of the life, which wear out homeostatic mechanisms and cause premature cardiac aging, with this term referring to the time-related irreversible deterioration of the organ physiological functions and integrity. In this review article, we gathered evidence from the literature indicating that growing up with CHD leads to abnormal inflammatory response, loss of proteostasis, and precocious age in cardiac cells. Novel research on this topic may inspire new therapies preventing HF in adult CHD patients.

Physiological Systems in Promoting Frailty

Frailty is a complex syndrome affecting a growing sector of the global population as medical developments have advanced human mortality rates across the world. Our current understanding of frailty is derived from studies conducted in the laboratory as well as the clinic, which have generated largely phenotypic information. Far fewer studies have uncovered biological underpinnings driving the onset and progression of frailty, but the stage is set to advance the field with preclinical and clinical assessment tools, multiomics approaches together with physiological and biochemical methodologies. In this article, we provide comprehensive coverage of topics regarding frailty assessment, preclinical models, interventions, and challenges as well as clinical frameworks and prevalence. We also identify central biological mechanisms that may be at play including mitochondrial dysfunction, epigenetic alterations, and oxidative stress that in turn, affect metabolism, stress responses, and endocrine and neuromuscular systems. We review the role of metabolic syndrome, insulin resistance and visceral obesity, focusing on glucose homeostasis, adenosine monophosphate-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), and nicotinamide adenine dinucleotide (NAD⁺ ) as critical players influencing the age-related loss of health. We further focus on how immunometabolic dysfunction associates with oxidative stress in promoting sarcopenia, a key contributor to slowness, weakness, and fatigue. We explore the biological mechanisms involved in stem cell exhaustion that affect regeneration and may contribute to the frailty-associated decline in resilience and adaptation to stress. Together, an overview of the interplay of aging biology with genetic, lifestyle, and environmental factors that contribute to frailty, as well as potential therapeutic targets to lower risk and slow the progression of ongoing disease is covered. © 2022 American Physiological Society. Compr Physiol 12:1-46, 2022.

Abdominal Ischemia-Reperfusion Induced Cardiac Dysfunction Can Be Prevented by MitoTEMPO

BACKGROUND

Cardiac dysfunction is secondary to acute mesenteric ischemia (AMI) and abdominal aortic aneurysms (AAA). The underlying cause of distant organ damage in the heart is the formation of oxidative stress caused by ischemia-reperfusion. In this study, we investigated the possible protective effects of a novel mitochondria-targeted antioxidant MitoTEMPO on contractile dysfunction and structural defects of the rat papillary muscle caused by abdominal ischemia-reperfusion (AIR).

METHODS AND RESULTS

In the experiments, adult Wistar-Albino rats were used and animals were divided randomly into 3 groups; sham-operated group (SHAM), an IR group that had aortic cross-clamping for 1 h followed by 2 h reperfusion, and a third group that received protective 0.7 mg/kg/day MitoTEMPO injection for 28-day before IR. As a result, it was observed that MitoTEMPO injection had a protective effect on the mechanical activities and structural properties of the papillary muscle impaired by AIR. Our study also showed that AIR disrupted the contractile function of the papillary muscle for each stimulation frequency and post-potentiation responses tested. This is common for each measured and calculated mechanical parameter and MitoTEMPO injection showed its protective effects.

CONCLUSION

Consequently, calcium homeostasis seems to be impaired by AIR, and MitoTEMPO may exert its protective effect through energy metabolism by directly targeting the mitochondria.

The cardiac-enriched microprotein mitolamban regulates mitochondrial respiratory complex assembly and function in mice

Microproteins are a growing class of versatile small proteins previously overlooked by standard gene annotation methods due to their small size. Here we characterize mitolamban as a cardiac-enriched inner mitochondrial membrane–localized microprotein, which interacts with complex III of the electron transport chain and contributes to complex III assembly and function. Mitolamban gene deletion in mice leads to a reduction in complex III activity and metabolic perturbations in the heart that are consistent with complex III deficiency, as well as altered complex III assembly into respiratory supercomplexes. These findings define a functional role for mitolamban in the heart and highlight the importance of microproteins in regulating mitochondrial function and cardiomyocyte biology.

Emerging evidence indicates that a subset of RNA molecules annotated as noncoding contain short open reading frames that code for small functional proteins called microproteins, which have largely been overlooked due to their small size. To search for cardiac-expressed microproteins, we used a comparative genomics approach and identified mitolamban (Mtlbn) as a highly conserved 47-amino acid transmembrane protein that is abundantly expressed in the heart. Mtlbn localizes specifically to the inner mitochondrial membrane where it interacts with subunits of complex III of the electron transport chain and with mitochondrial respiratory supercomplexes. Genetic deletion of Mtlbn in mice altered complex III assembly dynamics and reduced complex III activity. Unbiased metabolomic analysis of heart tissue from Mtlbn knockout mice further revealed an altered metabolite profile consistent with deficiencies in complex III activity. Cardiac-specific Mtlbn overexpression in transgenic (TG) mice induced cardiomyopathy with histological, biochemical, and ultrastructural pathologic features that contributed to premature death. Metabolomic analysis and biochemical studies indicated that hearts from Mtlbn TG mice exhibited increased oxidative stress and mitochondrial dysfunction. These findings reveal Mtlbn as a cardiac-expressed inner mitochondrial membrane microprotein that contributes to mitochondrial electron transport chain activity through direct association with complex III and the regulation of its assembly and function.

Enhanced oxidative stress mediates pathological autophagy and necroptosis in cardiac myocytes in pressure overload induced heart failure in rats

In cardiac myocytes in vitro, hydrogen peroxide induces autophagic cell death and necroptosis. Oxidative stress, myocyte autophagy and necroptosis coexist in heart failure (HF). In this study, we tested the hypothesis that excessive oxidative stress mediates pathological autophagy and necroptosis in myocytes in pressure overload-induced HF. HF was produced by chronic pressure overload induced by abdominal aortic constriction (AAC) in rats. Rats with AAC or sham operation were randomised to orally receive an antioxidant N-acetylcysteine (NAC) or placebo for 4 weeks. Echocardiography was performed for the assessments of left ventricular (LV) structure and function. AAC rats exhibited decreased LV fractional shortening (FS) at 4 weeks after surgery. NAC treatment attenuated decreased LV FS in AAC rats. In AAC rats, myocardial level of 8-hydroxydeoxyguanosine assessed by immunohistochemical staining, indicative of oxidative stress, was increased, LC3 II protein, a marker of autophagy, Beclin1 protein and Atg4b, Atg5, Atg7 and Atg12 mRNA expression were markedly increased, RIP1, RIP3 and MLKL expression, indicative of necroptosis, was increased, and all of the alterations in AAC rats were prevented by the NAC treatment. NAC treatment also attenuated myocyte cross-sectional area and myocardial fibrosis in AAC rats. In conclusion, NAC treatment prevented the increases in oxidative stress, myocyte autophagy and necroptosis and the decrease in LV systolic function in pressure overload-induced HF. These findings suggest that enhanced oxidative stress mediates pathological autophagy and necroptosis in myocytes, leading to LV systolic dysfunction, and antioxidants may be of value to prevent HF through the inhibition of excessive autophagy and necroptosis.

Heart Metabolism in Sepsis-Induced Cardiomyopathy-Unusual Metabolic Dysfunction of the Heart

Due to the need for continuous work, the heart uses up to 8% of the total energy expenditure. Due to the relatively low adenosine triphosphate (ATP) storage capacity, the heart's work is dependent on its production. This is possible due to the metabolic flexibility of the heart, which allows it to use numerous substrates as a source of energy. Under normal conditions, a healthy heart obtains approximately 95% of its ATP by oxidative phosphorylation in the mitochondria. The primary source of energy is fatty acid oxidation, the rest of the energy comes from the oxidation of pyruvate. A failed heart is characterised by a disturbance in these proportions, with the contribution of individual components as a source of energy depending on the aetiology and stage of heart failure. A unique form of cardiac dysfunction is sepsis-induced cardiomyopathy, characterised by a significant reduction in energy production and impairment of cardiac oxidation of both fatty acids and glucose. Metabolic disorders appear to contribute to the pathogenesis of cardiac dysfunction and therefore are a promising target for future therapies. However, as many aspects of the metabolism of the failing heart remain unexplained, this issue requires further research.

Upregulation of COX-2 and PGE2 Induced by TNF-α Mediated Through TNFR1/MitoROS/PKCα/P38 MAPK, JNK1/2/FoxO1 Cascade in Human Cardiac Fibroblasts

Purpose

Tumor necrosis factor-α (TNF-α) has been shown to exert as a pathogenic factor in cardiac fibrosis and heart failure which were associated with the up-regulation of cyclooxygenase (COX)-2/prostaglandin E₂ (PGE₂) axis. However, whether TNF-α-induced COX-2/PGE₂ upregulation mediated through ROS-dependent cascade remains elusive in human cardiac fibroblasts (HCFs). This study aims to address the underlying mechanisms of TNF-α-induced COX-2/PGE₂ expression.

Methods

Here, we used TNF receptor neutralizing antibody (TNFR nAb), pharmacologic inhibitors, and siRNAs to dissect the involvement of signaling components examined by Western blot and ELISA in TNF-α-mediated responses in HCFs. MitoSOX Red was used to measure mitoROS generation. Isolation of subcellular fractions was performed to determine membrane translocation of PKCα. Promoter luciferase assay and chromatin immunoprecipitation (ChIP) assay were used to determine the role of transcription factor.

Results

We found that TNF-α time- and concentration-dependently upregulated COX-2 protein and mRNA expression as well as PGE₂ synthesis which was attenuated by TNFR1 nAb, the inhibitor of mitochondrial ROS scavenger (MitoTEMPO), protein kinase C [(PKC)α, Gö6976], p38 MAPK [p38 inhibitor VIII, (p38i VIII)], JNK1/2 (SP600125), or forkhead box protein O1 [(FoxO1), AS1842856], and transfection with their respective siRNAs in HCFs. TNF-α-stimulated PKCα phosphorylation was inhibited by TNFR1 nAb, MitoTEMPO, or Gö6976. TNF-α stimulated phosphorylation of p38 MAPK and JNK1/2 was attenuated by TNFR1 nAb, MitoTEMPO, Gö6976, and their inhibitors p38i VIII and SP600125. Moreover, TNF-α-triggered FoxO1 phosphorylation was abolished by AS1842856, TNFR1 nAb, and its upstream inhibitors MitoTEMPO, Gö6976, p38i VIII, and SP600125. Phosphorylation of FoxO1 could enhance its interaction with the COX-2 promoter element revealed by ChIP assay, which was attenuated by AS1842856.

Conclusion

Our results suggested that TNF-α-induced COX-2/PGE₂ upregulation is mediated through TNFR1-dependent MitoROS/PKCα/p38 MAPK and JNK1/2 cascade to activate FoxO1 binding with the COX-2 promoter in HCFs.

Cardiomyopathic mutations in essential light chain reveal mechanisms regulating the super relaxed state of myosin

In this study, we assessed the super relaxed (SRX) state of myosin and sarcomeric protein phosphorylation in two pathological models of cardiomyopathy and in a near-physiological model of cardiac hypertrophy. The cardiomyopathy models differ in disease progression and severity and express the hypertrophic (HCM-A57G) or restrictive (RCM-E143K) mutations in the human ventricular myosin essential light chain (ELC), which is encoded by the MYL3 gene. Their effects were compared with near-physiological heart remodeling, represented by the N-terminally truncated ELC (Δ43 ELC mice), and with nonmutated human ventricular WT-ELC mice. The HCM-A57G and RCM-E143K mutations had antagonistic effects on the ATP-dependent myosin energetic states, with HCM-A57G cross-bridges fostering the disordered relaxed (DRX) state and the RCM-E143K model favoring the energy-conserving SRX state. The HCM-A57G model promoted the switch from the SRX to DRX state and showed an ∼40% increase in myosin regulatory light chain (RLC) phosphorylation compared with the RLC of normal WT-ELC myocardium. On the contrary, the RCM-E143K–associated stabilization of the SRX state was accompanied by an approximately twofold lower level of myosin RLC phosphorylation compared with the RLC of WT-ELC. Upregulation of RLC phosphorylation was also observed in Δ43 versus WT-ELC hearts, and the Δ43 myosin favored the energy-saving SRX conformation. The two disease variants also differently affected the duration of force transients, with shorter (HCM-A57G) or longer (RCM-E143K) transients measured in electrically stimulated papillary muscles from these pathological models, while no changes were displayed by Δ43 fibers. We propose that the N terminus of ELC (N-ELC), which is missing in the hearts of Δ43 mice, works as an energetic switch promoting the SRX-to-DRX transition and contributing to the regulation of myosin RLC phosphorylation in full-length ELC mice by facilitating or sterically blocking RLC phosphorylation in HCM-A57G and RCM-E143K hearts, respectively.

Mitochondrial abnormalities: a hub in metabolic syndrome-related cardiac dysfunction caused by oxidative stress

Metabolic syndrome (MetS) refers to a group of cardiovascular risk elements comprising insulin resistance, obesity, dyslipidemia, increased glucose intolerance, and increased blood pressure. Individually, all the MetS components can lead to cardiac dysfunction, while their combination generates additional risks of morbidity and mortality. Growing evidence suggests that oxidative stress, a dominant event in cellular damage and impairment, plays an indispensable role in cardiac dysfunction in MetS. Oxidative stress can not only disrupt mitochondrial activity through inducing oxidative damage to mitochondrial DNA, RNA, lipids, and proteins but can also impair cardiomyocyte contractile function via mitochondria-related oxidative modifications of proteins central to excitation-contraction coupling. Furthermore, excessive reactive oxygen species (ROS) generation can lead to the activation of several mitochondria apoptotic signaling pathways, release of cytochrome c, and eventual induction of myocardial apoptosis. This review will focus on such processes of mitochondrial abnormalities in oxidative stress induced cardiac dysfunction in MetS.

The lncRNA Caren antagonizes heart failure by inactivating DNA damage response and activating mitochondrial biogenesis

In the past decade, many long noncoding RNAs (lncRNAs) have been identified and their in vitro functions defined, although in some cases their functions in vivo remain less clear. Moreover, unlike nuclear lncRNAs, the roles of cytoplasmic lncRNAs are less defined. Here, using a gene trapping approach in mouse embryonic stem cells, we identify Caren (short for cardiomyocyte-enriched noncoding transcript), a cytoplasmic lncRNA abundantly expressed in cardiomyocytes. Caren maintains cardiac function under pathological stress by inactivating the ataxia telangiectasia mutated (ATM)-DNA damage response (DDR) pathway and activating mitochondrial bioenergetics. The presence of Caren transcripts does not alter expression of nearby (cis) genes but rather decreases translation of an mRNA transcribed from a distant gene encoding histidine triad nucleotide-binding protein 1 (Hint1), which activates the ATM-DDR pathway and reduces mitochondrial respiratory capacity in cardiomyocytes. Therefore, the cytoplasmic lncRNA Caren functions in cardioprotection by regulating translation of a distant gene and maintaining cardiomyocyte homeostasis.

Hypertrophy-Reduced Autophagy Causes Cardiac Dysfunction by Directly Impacting Cardiomyocyte Contractility

Cardiac remodeling and contractile dysfunction are leading causes in hypertrophy-associated heart failure (HF), increasing with a population's rising age. A hallmark of aged and diseased hearts is the accumulation of modified proteins caused by an impaired autophagy-lysosomal-pathway. Although, autophagy inducer rapamycin has been described to exert cardioprotective effects, it remains to be shown whether these effects can be attributed to improved cardiomyocyte autophagy and contractility. In vivo hypertrophy was induced by transverse aortic constriction (TAC), with mice receiving daily rapamycin injections beginning six weeks after surgery for four weeks. Echocardiographic analysis demonstrated TAC-induced HF and protein analyses showed abundance of modified proteins in TAC-hearts after 10 weeks, both reduced by rapamycin. In vitro, cardiomyocyte hypertrophy was mimicked by endothelin 1 (ET-1) and autophagy manipulated by silencing Atg5 in neonatal cardiomyocytes. ET-1 and siAtg5 decreased Atg5-Atg12 and LC3-II, increased natriuretic peptides, and decreased amplitude and early phase of contraction in cardiomyocytes, the latter two evaluated using ImageJ macro Myocyter recently developed by us. ET-1 further decreased cell contractility in control but not in siAtg5 cells. In conclusion, ET-1 decreased autophagy and cardiomyocyte contractility, in line with siAtg5-treated cells and the results of TAC-mice demonstrating a crucial role for autophagy in cardiomyocyte contractility and cardiac performance.

Role of Warburg Effect in Cardiovascular Diseases: A Potential Treatment Option

Background:

Under normal conditions, the heart obtains ATP through the oxidation of fatty acids, glucose, and ketones. While fatty acids are the main source of energy in the heart, under certain conditions, the main source of energy shifts to glucose where pyruvate converts into lactate, to meet the energy demand. The Warburg effect is the energy shift from oxidative phosphorylation to glycolysis in the presence of oxygen. This effect is observed in tumors as well as in diseases, including cardiovascular diseases. If glycolysis is more dominant than glucose oxidation, the two pathways uncouple, contributing to the severity of the heart condition. Recently, several studies have documented changes in metabolism in several cardiovascular diseases; however, the specific mechanisms remain unclear.

Methods:

This literature review was conducted by an electronic database of Pub Med, Google Scholar, and Scopus published until 2020. Relevant papers are selected based on inclusion and exclusion criteria.

Results:

A total of 162 potentially relevant articles after the title and abstract screening were screened for full-text. Finally, 135 papers were included for the review article.

Discussion:

This review discusses the effects of alterations in glucose metabolism, particularly the Warburg effect, on cardiovascular diseases, including heart failure, atrial fibrillation, and cardiac hypertrophy.

Conclusion:

Reversing the Warburg effect could become a potential treatment option for cardiovascular diseases.

Regulation of miRNAs by Natural Antioxidants in Cardiovascular Diseases: Focus on SIRT1 and eNOS

Cardiovascular diseases (CVDs) are the most common cause of morbidity and mortality worldwide. The potential benefits of natural antioxidants derived from supplemental nutrients against CVDs are well known. Remarkably, natural antioxidants exert cardioprotective effects by reducing oxidative stress, increasing vasodilation, and normalizing endothelial dysfunction. Recently, considerable evidence has highlighted an important role played by the synergistic interaction between endothelial nitric oxide synthase (eNOS) and sirtuin 1 (SIRT1) in the maintenance of endothelial function. To provide a new perspective on the role of natural antioxidants against CVDs, we focused on microRNAs (miRNAs), which are important posttranscriptional modulators in human diseases. Several miRNAs are regulated via the consumption of natural antioxidants and are related to the regulation of oxidative stress by targeting eNOS and/or SIRT1. In this review, we have discussed the specific molecular regulation of eNOS/SIRT1-related endothelial dysfunction and its contribution to CVD pathologies; furthermore, we selected nine different miRNAs that target the expression of eNOS and SIRT1 in CVDs. Additionally, we have summarized the alteration of miRNA expression and regulation of activities of miRNA through natural antioxidant consumption.

Preconditioning with Short-term Dietary Restriction Attenuates Cardiac Oxidative Stress and Hypertrophy Induced by Chronic Pressure Overload

Left ventricular (LV) hypertrophy and associated heart failure are becoming a more prevalent and critical public health issue with the aging of society, and are exacerbated by reactive oxygen species (ROS). Dietary restriction (DR) markedly inhibits senescent changes; however, prolonged DR is difficult. We herein investigated whether preconditioning with short-term DR attenuates chronic pressure overload-induced cardiac hypertrophy and associated oxidative stress. Male c57BL6 mice were randomly divided into an ad libitum (AL) diet or 40% restricted diet (DR preconditioning, DRPC) group for 2 weeks prior to ascending aortic constriction (AAC), and all mice were fed ad libitum after AAC surgery. Two weeks after surgery, pressure overload by AAC increased LV wall thickness in association with LV diastolic dysfunction and promoted myocyte hypertrophy and cardiac fibrosis in the AL+AAC group. Oxidative stress in cardiac tissue and mitochondria also increased in the AL+AAC group in association with increments in cardiac NADPH oxidase-derived and mitochondrial ROS production. LV hypertrophy and associated cardiac dysfunction and oxidative stress were significantly attenuated in the DRPC+AAC group. Moreover, less severe mitochondrial oxidative damage in the DRPC+AAC group was associated with the suppression of mitochondrial permeability transition and cardiac apoptosis. These results indicate that chronic pressure overload-induced cardiac hypertrophy in association with cardiac and mitochondrial oxidative damage were attenuated by preconditioning with short-term DR.

Excess sarcoplasmic reticulum-mitochondria calcium transport induced by Sphingosine-1-phosphate contributes to cardiomyocyte hypertrophy

Sphingosine-1-phosphate (S1P) has been shown to possess pro-hypertrophic properties in the heart, but the detailed molecular mechanism that underlies the pathological process is rarely explored. In the present study, we aim to explore the role of S1P-mediated intracellular Ca²⁺ signaling, with a focus on sarcoplasmic reticulum (SR)-mitochondria communication, in cardiomyocyte hypertrophy. Cultured neonatal rat ventricular myocytes (NRVMs) displayed significantly hypertrophic growth after treatment with 1 μmol/L S1P for 48 h, as indicated by the cell surface area or mRNA expressions of hypertrophic marker genes (ANP, BNP and β-MHC). Importantly, mitochondrial Ca²⁺ and reactive oxygen species (ROS) levels were dramatically elevated upon S1P stimulation, and pharmacological blockage of which abolished NRVM hypertrophy. 0.5 Hz electrical pacing induced similar cytosolic Ca²⁺ kinetics to S1P stimulation, but unaffected the peak of mitochondrial [Ca²⁺]. With interference of the expression of type 2 inositol 1,4,5-trisphosphate receptors (IP₃R2), which are unemployed in electrical paced Ca²⁺ activity but may be activated by S1P, alteration in mitochondrial Ca²⁺ as well as the hypertrophic effect in NRVMs under S1P stimulation were attenuated. The hypertrophic effect of S1P can also be abolished by pharmacological block of S1PR1 or Gi signaling. Collectively, our study highlights the mechanistic role of IP₃R2-mediated excess SR-mitochondria Ca²⁺ transport in S1P-induced cardiomyocyte hypertrophy.

The Role of Oxidative Stress in Cardiovascular Aging and Cardiovascular Diseases

Aging can be seen as process characterized by accumulation of oxidative stress induced damage. Oxidative stress derives from different endogenous and exogenous processes, all of which ultimately lead to progressive loss in tissue and organ structure and functions. The oxidative stress theory of aging expresses itself in age-related diseases. Aging is in fact a primary risk factor for many diseases and in particular for cardiovascular diseases and its derived morbidity and mortality. Here we highlight the role of oxidative stress in age-related cardiovascular aging and diseases. We take into consideration the molecular mechanisms, the structural and functional alterations, and the diseases accompanied to the cardiovascular aging process.

Redox-Resistant SERCA [Sarco(endo)plasmic Reticulum Calcium ATPase] Attenuates Oxidant-Stimulated Mitochondrial Calcium and Apoptosis in Cardiac Myocytes and Pressure Overload-Induced Myocardial Failure in Mice

BACKGROUND

SERCA [sarco(endo)plasmic reticulum calcium ATPase] is regulated by oxidative posttranslational modifications at cysteine 674 (C674). Because sarcoplasmic reticulum (SR) calcium has been shown to play a critical role in mediating mitochondrial dysfunction in response to reactive oxygen species, we hypothesized that SERCA oxidation at C674 would modulate the effects of reactive oxygen species on mitochondrial calcium and mitochondria-dependent apoptosis in cardiac myocytes.

METHODS

Adult rat ventricular myocytes expressing wild-type SERCA2b or a redox-insensitive mutant in which C674 is replaced by serine (C674S) were exposed to H2O2 (100 µmol/Lμ). Free mitochondrial calcium concentration was measured in adult rat ventricular myocytes with a genetically targeted fluorescent probe, and SR calcium content was assessed by measuring caffeine-stimulated release. Mice with heterozygous knock-in of the SERCA C674S mutation were subjected to chronic ascending aortic constriction.

RESULTS

In adult rat ventricular myocytes expressing wild-type SERCA, H2O2 caused a 25% increase in mitochondrial calcium concentration that was associated with a 50% decrease in SR calcium content, both of which were prevented by the ryanodine receptor inhibitor tetracaine. In cells expressing the C674S mutant, basal SR calcium content was decreased by 31% and the H2O2-stimulated rise in mitochondrial calcium concentration was attenuated by 40%. In wild-type cells, H2O2 caused cytochrome c release and apoptosis, both of which were prevented in C674S-expressing cells. In myocytes from SERCA knock-in mice, basal SERCA activity and SR calcium content were decreased. To test the effect of C674 oxidation on apoptosis in vivo, SERCA knock-in mice were subjected to chronic ascending aortic constriction. In wild-type mice, ascending aortic constriction caused myocyte apoptosis, LV dilation, and systolic failure, all of which were inhibited in SERCA knock-in mice.

CONCLUSIONS

Redox activation of SERCA C674 regulates basal SR calcium content, thereby mediating the pathologic reactive oxygen species-stimulated rise in mitochondrial calcium required for myocyte apoptosis and myocardial failure.

Mitochondrial Ca2+ in heart failure: Not enough or too much?

Ca²⁺ serves as a ubiquitous second messenger mediating a variety of cellular processes including electrical excitation, contraction, gene expression, secretion, cell death and others. The identification of the molecular components of the mitochondrial Ca²⁺ influx and efflux pathways has created a resurgent interest in the regulation of mitochondrial Ca²⁺ balance and its physiological and pathophysiological roles. While the pace of discovery has quickened with the availability of new cellular and animal models, many fundamental questions remain to be answered regarding the regulation and functional impact of mitochondrial Ca²⁺ in health and disease. This review highlights several experimental observations pertaining to key aspects of mitochondrial Ca²⁺ homeostasis that remain enigmatic, particularly whether mitochondrial Ca²⁺ signaling is depressed or excessive in heart failure, which will determine the optimal approach to therapeutic intervention.

Riding the tiger - physiological and pathological effects of superoxide and hydrogen peroxide generated in the mitochondrial matrix

Elevated mitochondrial matrix superoxide and/or hydrogen peroxide concentrations drive a wide range of physiological responses and pathologies. Concentrations of superoxide and hydrogen peroxide in the mitochondrial matrix are set mainly by rates of production, the activities of superoxide dismutase-2 (SOD2) and peroxiredoxin-3 (PRDX3), and by diffusion of hydrogen peroxide to the cytosol. These considerations can be used to generate criteria for assessing whether changes in matrix superoxide or hydrogen peroxide are both necessary and sufficient to drive redox signaling and pathology: is a phenotype affected by suppressing superoxide and hydrogen peroxide production; by manipulating the levels of SOD2, PRDX3 or mitochondria-targeted catalase; and by adding mitochondria-targeted SOD/catalase mimetics or mitochondria-targeted antioxidants? Is the pathology associated with variants in SOD2 and PRDX3 genes? Filtering the large literature on mitochondrial redox signaling using these criteria highlights considerable evidence that mitochondrial superoxide and hydrogen peroxide drive physiological responses involved in cellular stress management, including apoptosis, autophagy, propagation of endoplasmic reticulum stress, cellular senescence, HIF1α signaling, and immune responses. They also affect cell proliferation, migration, differentiation, and the cell cycle. Filtering the huge literature on pathologies highlights strong experimental evidence that 30-40 pathologies may be driven by mitochondrial matrix superoxide or hydrogen peroxide. These can be grouped into overlapping and interacting categories: metabolic, cardiovascular, inflammatory, and neurological diseases; cancer; ischemia/reperfusion injury; aging and its diseases; external insults, and genetic diseases. Understanding the involvement of mitochondrial matrix superoxide and hydrogen peroxide concentrations in these diseases can facilitate the rational development of appropriate therapies.

Oxidative Stress in Cardiovascular Diseases

Reactive oxygen species (ROS) are subcellular messengers in signal transductions pathways with both beneficial and deleterious roles. ROS are generated as a by-product of mitochondrial respiration or metabolism or by specific enzymes such as superoxide dismutases, glutathione peroxidase, catalase, peroxiredoxins, and myeloperoxidases. Under physiological conditions, the low levels of ROS production are equivalent to their detoxification, playing a major role in cellular signaling and function. In pathological situations, particularly atherosclerosis or hypertension, the release of ROS exceeds endogenous antioxidant capacity, leading to cell death. At cardiovascular levels, oxidative stress is highly implicated in myocardial infarction, ischemia/reperfusion, or heart failure. Here, we will first detail the physiological role of low ROS production in the heart and the vessels. Indeed, ROS are able to regulate multiple cardiovascular functions, such as cell proliferation, migration, and death. Second, we will investigate the implication of oxidative stress in cardiovascular diseases. Then, we will focus on ROS produced by NAPDH oxidase or during endothelial or mitochondrial dysfunction. Given the importance of oxidative stress at the cardiovascular level, antioxidant therapies could be a real benefit. In the last part of this review, we will detail the new therapeutic strategies potentially involved in cardiovascular protection and currently under study.

Sustained Oligomycin Sensitivity Conferring Protein Expression in Cardiomyocytes Protects Against Cardiac hypertrophy Induced by Pressure Overload via Improving Mitochondrial Function

Cardiac hypertrophy is a major risk factor for congestive heart failure, a leading cause of morbidity and mortality. Abrogating hypertrophic progression is a well-recognized therapeutic goal. Mitochondrial dysfunction is a hallmark of numerous human diseases, including cardiac hypertrophy and heart failure. F1Fo-ATP synthase catalyzes the final step of oxidative energy production in mitochondria. Oligomycin sensitivity conferring protein (OSCP), a key component of the F1Fo-ATP synthase, plays an essential role in mitochondrial energy metabolism. However, the effects of OSCP-targeted therapy on cardiac hypertrophy remain unknown. In the present study, we found that impaired cardiac expression of OSCP is concomitant with mitochondrial dysfunction in the hypertrophied heart. We used cardiac-specific, adeno-associated virus-mediated gene therapy of OSCP to treat mice subjected to pressure overload induced by transverse aortic constriction (TAC). OSCP gene therapy protected the TAC-mice from cardiac dysfunction, cardiomyocyte hypertrophy, and fibrosis. OSCP gene therapy also enhanced mitochondrial respiration capacities in TAC-mice. Consistently, OSCP gene therapy attenuated reactive oxygen species and opening of mitochondrial permeability transition pore in the hypertrophied heart. Together, adeno-associated virus type 9-mediated, cardiac-specific OSCP overexpression can protect the heart via improving mitochondrial function. This result may provide insights into a novel therapy for cardiac hypertrophy and heart failure.

Lipid in the midst of metabolic remodeling - Therapeutic implications for the failing heart

A healthy heart relies on an intact cardiac lipid metabolism. Fatty acids represent the major source for ATP production in the heart. Not less importantly, lipids are directly involved in critical processes such as cell growth, proliferation, and cell death by functioning as building blocks or signaling molecules. In the development of heart failure, perturbations in fatty acid utilization impair cardiac energetics. Furthermore, they may affect glucose and amino acid metabolism and induce the synthesis of several lipid intermediates, whose biological functions are still poorly understood. This work outlines the pivotal role of lipid metabolism in the heart and provides a lipocentric view of metabolic remodeling in heart failure. We will also critically revisit therapeutic attempts targeting cardiac lipid metabolism in heart failure and propose specific strategies for future investigations in this regard.

Late-life restoration of mitochondrial function reverses cardiac dysfunction in old mice

Diastolic dysfunction is a prominent feature of cardiac aging in both mice and humans. We show here that 8-week treatment of old mice with the mitochondrial targeted peptide SS-31 (elamipretide) can substantially reverse this deficit. SS-31 normalized the increase in proton leak and reduced mitochondrial ROS in cardiomyocytes from old mice, accompanied by reduced protein oxidation and a shift towards a more reduced protein thiol redox state in old hearts. Improved diastolic function was concordant with increased phosphorylation of cMyBP-C Ser282 but was independent of titin isoform shift. Late-life viral expression of mitochondrial-targeted catalase (mCAT) produced similar functional benefits in old mice and SS-31 did not improve cardiac function of old mCAT mice, implicating normalizing mitochondrial oxidative stress as an overlapping mechanism. These results demonstrate that pre-existing cardiac aging phenotypes can be reversed by targeting mitochondrial dysfunction and implicate mitochondrial energetics and redox signaling as therapeutic targets for cardiac aging.

Manipulation of beta-adrenergic receptor in pressure-overloaded murine hearts mimics adverse and reverse cardiac remodeling

Transverse aortic constriction (TAC) has been widely used to create pressure overload induced heart failure in mice. However, this conventional model has some limitations such as low reproducibility and long creation period of cardiac failure. In order to establish a highly reproducible cardiac failure model that mimics adverse cardiac remodeling (ACR) we combined pressure overload and beta-adrenergic receptor stimuli using isoproterenol (ISO) and explored the optimal TAC model by changing the durations of TAC and the doses of ISO. Thus we constructed a suitable model for ACR with an effective combination of 3-week TAC and subsequent one-week ISO (3 mg/kg/day) infusion. Using RNA-Seq analyses, we identified that the up-regulated genes were mainly related to fibrosis including Fbn1, C1qtnf6 and Loxl2; and that the down-regulated genes were associated with mitochondrial function including Uqcrc1, Ndufs3, and Idh2 in failing hearts of our ACR model. Next, we followed the changes in cardiac function after ceasing ISO infusion. Left ventricular function gradually recovered after cessation of ISO, suggesting cardiac reverse remodeling (CRR). Gene expression signatures of hearts, which exhibited CRR, were almost identical to that of TAC hearts without ISO. In conclusion, our new model exhibits a transition to ACR and subsequent CRR with high reproducibility. This murine model might add new insights into the experiments of heart failure technically as well as scientifically.

Inflammasomes and Proteostasis Novel Molecular Mechanisms Associated With Atrial Fibrillation

Atrial fibrillation (AF), the most common progressive and age-related cardiac arrhythmia, affects millions of people worldwide. AF is associated with common risk factors, including hypertension, diabetes mellitus, and obesity, and serious complications such as stroke and heart failure. Notably, AF is progressive in nature, and because current treatment options are mainly symptomatic, they have only a moderate effect on prevention of arrhythmia progression. Hereto, there is an urgent unmet need to develop mechanistic treatments directed at root causes of AF. Recent research findings indicate a key role for inflammasomes and derailed proteostasis as root causes of AF. Here, we elaborate on the molecular mechanisms of these 2 emerging key pathways driving the pathogenesis of AF. First the role of NLRP3 (NACHT, LRR, and PYD domains-containing protein 3) inflammasome on AF pathogenesis and cardiomyocyte remodeling is discussed. Then we highlight pathways of proteostasis derailment, including exhaustion of cardioprotective heat shock proteins, disruption of cytoskeletal proteins via histone deacetylases, and the recently discovered DNA damage-induced nicotinamide adenine dinucleotide⁺ depletion to underlie AF. Moreover, potential interactions between the inflammasomes and proteostasis pathways are discussed and possible therapeutic targets within these pathways indicated.

Glutathione peroxidase-1 overexpression reduces oxidative stress, and improves pathology and proteome remodeling in the kidneys of old mice

This study investigated the direct roles of hydrogen peroxide (H₂O₂) in kidney aging using transgenic mice overexpressing glutathione peroxidase‐1 (GPX1 TG). We demonstrated that kidneys in old mice recapitulated kidneys in elderly humans and were characterized by glomerulosclerosis, tubular atrophy, interstitial fibrosis, and loss of cortical mass. Scavenging H₂O₂ by GPX1 TG significantly reduced mitochondrial and total cellular reactive oxygen species (ROS) and mitigated oxidative damage, thus improving these pathologies. The potential mechanisms by which ROS are increased in the aged kidney include a decreased abundance of an anti‐aging hormone, Klotho, in kidney tissue, and decreased expression of nuclear respiratory factor 2 (Nrf2), a master regulator of the stress response. Decreased Klotho or Nrf2 was not improved in the kidneys of old GPX1 TG mice, even though mitochondrial morphology was better preserved. Using laser capture microdissection followed by label‐free shotgun proteomics analysis, we show that the glomerular proteome in old mice was characterized by decreased abundance of cytoskeletal proteins (critical for maintaining normal glomerular function) and heat shock proteins, leading to increased accumulation of apolipoprotein E and inflammatory molecules. Targeted proteomic analysis of kidney tubules from old mice showed decreased abundance of fatty acid oxidation enzymes and antioxidant proteins, as well as increased abundance of glycolytic enzymes and molecular chaperones. GPX1 TG partially attenuated the remodeling of glomerular and tubule proteomes in aged kidneys. In summary, mitochondria from GPX1 TG mice are protected and kidney aging is ameliorated via its antioxidant activities, independent and downstream of Nrf2 or Klotho signaling.

PGC-1α activator ZLN005 promotes maturation of cardiomyocytes derived from human embryonic stem cells

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) have great potential in biomedical applications. However, the immature state of cardiomyocytes obtained using existing protocols limits the application of hPSC-CMs. Unlike adult cardiac myocytes, hPSC-CMs generate ATP through an immature metabolic pathway—aerobic glycolysis, instead of mitochondrial oxidative phosphorylation (OXPHOS). Hence, metabolic switching is critical for functional maturation in hPSC-CMs. Peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α) is a key regulator of mitochondrial biogenesis and metabolism, which may help promote cardiac maturation during development. In this study, we investigated the effects of PGC-1α and its activator ZLN005 on the maturation of human embryonic stem cell-derived cardiomyocyte (hESC-CM). hESC-CMs were generated using a chemically defined differentiation protocol and supplemented with either ZLN005 or DMSO (control) on differentiating days 10 to 12. Biological assays were then performed around day 30. ZLN005 treatment upregulated the expressions of PGC-1α and mitochondrial function-related genes in hESC-CMs and induced more mature energy metabolism compared with the control group. In addition, ZLN005 treatment increased cell sarcomere length, improved cell calcium handling, and enhanced intercellular connectivity. These findings support an effective approach to promote hESC-CM maturation, which is critical for the application of hESC-CM in disease modeling, drug screening, and engineering cardiac tissue.

Role of reactive oxygen species in atherosclerosis: Lessons from murine genetic models

Atherosclerosis is a multifactorial chronic and inflammatory disease of medium and large arteries, and the major cause of cardiovascular morbidity and mortality worldwide. The pathogenesis of atherosclerosis involves a number of risk factors and complex events including hypercholesterolemia, endothelial dysfunction, increased permeability to low density lipoproteins (LDL) and their sequestration on extracellular matrix in the intima of lesion-prone areas. These events promote LDL modifications, particularly by oxidation, which generates acute and chronic inflammatory responses implicated in atherogenesis and lesion progression. Reactive oxygen species (ROS) (which include both free radical and non-free radical oxygen intermediates), play a key-role at each step of atherogenesis, in endothelial dysfunction, LDL oxidation, and inflammatory events involved in the initiation and development of atherosclerosis lesions. Most advanced knowledge supporting the "oxidative theory of atherosclerosis" i.e. the nature and the cellular sources of ROS and antioxidant defences, as well as the mechanisms involved in the redox balance, is based on the use of genetically engineered animals, i.e. transgenic, genetically modified, or altered for systems producing or neutralizing ROS in the vessels. This review summarizes the results obtained from animals genetically manipulated for various sources of ROS or antioxidant defences in the vascular wall, and their relevance (advance or limitation), for understanding the place and role of ROS in atherosclerosis.

Heart Plasticity in Response to Pressure- and Volume-Overload: A Review of Findings in Compensated and Decompensated Phenotypes

The adult human heart has an exceptional ability to alter its phenotype to adapt to changes in environmental demand. This response involves metabolic, mechanical, electrical, and structural alterations, and is known as cardiac plasticity. Understanding the drivers of cardiac plasticity is essential for development of therapeutic agents. This is particularly important in contemporary cardiology, which uses treatments with peripheral effects (e.g., on kidneys, adrenal glands). This review focuses on the effects of different hemodynamic loads on myocardial phenotype. We examine mechanical scenarios of pressure- and volume overload, from the initial insult, to compensated, and ultimately decompensated stage. We discuss how different hemodynamic conditions occur and are underlined by distinct phenotypic and molecular changes. We complete the review by exploring how current basic cardiac research should leverage available cardiac models to study mechanical load in its different presentations.

Mitochondrial dysfunction and oxidative stress in heart disease

Beyond their role as a cellular powerhouse, mitochondria are emerging as integral players in molecular signaling and cell fate determination through reactive oxygen species (ROS). While ROS production has historically been portrayed as an unregulated process driving oxidative stress and disease pathology, contemporary studies reveal that ROS also facilitate normal physiology. Mitochondria are especially abundant in cardiac tissue; hence, mitochondrial dysregulation and ROS production are thought to contribute significantly to cardiac pathology. Moreover, there is growing appreciation that medical therapies designed to mediate mitochondrial ROS production can be important strategies to ameliorate cardiac disease. In this review, we highlight evidence from animal models that illustrates the strong connections between mitochondrial ROS and cardiac disease, discuss advancements in the development of mitochondria-targeted antioxidant therapies, and identify challenges faced in bringing such therapies into the clinic.

Heart disease progression could be tackled by targeting signaling molecules that cause oxidative stress. Jennifer Kwong at Emory University School of Medicine in Atlanta, USA, and co-workers reviewed research into the role of mitochondria and their associated signaling molecules in the development of heart disease. Mitochondria are a major source of reactive oxygen species (ROS), signaling molecules involved in muscle contraction and calcium transfer in the heart, but they also destroy ROS to maintain a balance. Disruption to this balance can lead to elevated ROS, causing DNA and cellular damage, triggering disease. Animal trials using drugs to target mitochondrial ROS show promise in limiting heart disease progression. Further research is needed to determine whether this approach will work in humans and which specific heart problems might benefit from such therapies.