Influence of long-term caloric restriction on myocardial and cardiomyocyte contractile function and autophagy in mice

Ablation of Akt2 rescues chronic caloric restriction-provoked myocardial remodeling and dysfunction through a CDK1-mediated regulation of mitophagy

Chronic caloric restriction triggers unfavorable alterations in cardiac function albeit responsible scenarios remain unclear. This work evaluated the possible involvement of Akt2 in caloric restriction-evoked cardiac geometric and functional changes and responsible processes focusing on autophagy and mitophagy. Akt2 knockout and WT mice were subjected to caloric restriction for 30 weeks prior to assessment of myocardial homeostasis. Caloric restriction compromised echocardiographic parameters (decreased LV wall thickness, LVEDD, stroke volume, cardiac output, ejection fraction, fractional shortening, and LV mass), cardiomyocyte contractile and intracellular Ca2+ capacity, myocardial atrophy, interstitial fibrosis and mitochondrial injury associated with elevated blood glucocorticoids, autophagy (LC3B, p62, Atg7, Beclin-1), and mitophagy (Pink1, Parkin, TOM20), dampened cardiac ATP levels, mitochondrial protein PGC1α and UCP2, anti-apoptotic protein Bcl2, intracellular Ca2+ governing components Na+-Ca2+ exchanger, phosphorylation of SERCA2a, mTOR (Ser2481) and ULK1 (Ser757), and upregulated Bax, phospholamban, phosphorylation of Akt2, AMPK, and ULK1 (Ser555), the responses except autophagy markers (Beclin-1, Atg7), phosphorylation of AMPK, mTOR and ULK1 were negated by Akt2 ablation. Levels of CDK1 and DRP1 phosphorylation were overtly upregulated with caloric restriction, the response was reversed by Akt2 knockout. Caloric restriction-evoked changes in cardiac remodeling and cardiomyocyte function were alleviated by glucocorticoid receptor antagonism, Parkin ablation and Mdivi-1. In vitro experiment indicated that serum deprivation or glucocorticoids evoked GFP-LC3B accumulation and cardiomyocyte dysfunction, which was negated by inhibition of Akt2, CDK1 or DRP1, whereas mitophagy induction reversed Akt2 ablation-evoked cardioprotection. These observations favor a protective role of Akt2 ablation in sustained caloric restriction-evoked cardiac pathological changes via correction of glucocorticoid-induced mitophagy defect in a CDK1-DRP1-dependent manner.

Risks and Benefits of Intermittent Fasting for the Aging Cardiovascular System

Population aging and the associated increase in cardiovascular disease rates pose serious threats to global public health. Different forms of fasting have become an increasingly attractive strategy to directly address aging and potentially limit or delay the onset of cardiovascular diseases. A growing number of experimental studies and clinical trials indicate that the amount and timing of food intake as well as the daily time window during which food is consumed, are crucial determinants of cardiovascular health. Indeed, intermittent fasting counteracts the molecular hallmarks of cardiovascular aging and promotes different aspects of cardiometabolic health, including blood pressure and glycemic control, as well as body weight reduction. In this report, we summarize current evidence from randomized clinical trials of intermittent fasting on body weight and composition as well as cardiovascular and metabolic risk factors. Moreover, we critically discuss the preventive and therapeutic potential of intermittent fasting, but also possible detrimental effects in the context of cardiovascular aging and related disease. We delve into the physiological mechanisms through which intermittent fasting might improve cardiovascular health, and raise important factors to consider in the design of clinical trials on the efficacy of intermittent fasting to reduce major adverse cardiovascular events among aged individuals at high risk of cardiovascular disease. We conclude that despite growing evidence and interest among the lay and scientific communities in the cardiovascular health-improving effects of intermittent fasting, further research efforts and appropriate caution are warranted before broadly implementing intermittent fasting regimens, especially in elderly persons.

The role of autophagy in the progression of HIV infected cardiomyopathy

Although highly active antiretroviral therapy (HAART) has changed infection with human immunodeficiency virus (HIV) from a diagnosis with imminent mortality to a chronic illness, HIV positive patients who do not develop acquired immunodeficiency syndrome (AIDs) still suffer from a high rate of cardiac dysfunction and fibrosis. Regardless of viral load and CD count, HIV-associated cardiomyopathy (HIVAC) still causes a high rate of mortality and morbidity amongst HIV patients. While this is a well characterized clinical phenomena, the molecular mechanism of HIVAC is not well understood. In this review, we consolidate, analyze, and discuss current research on the intersection between autophagy and HIVAC. Multiple studies have linked dysregulation in various regulators and functional components of autophagy to HIV infection regardless of mode of viral entry, i.e., coronary, cardiac chamber, or pericardial space. HIV proteins, including negative regulatory factor (Nef), glycoprotein 120 (gp120), and transactivator (Tat), have been shown to interact with type II microtubule-associated protein-1 β light chain (LC3-II), Rubiquitin, SQSTM1/p62, Rab7, autophagy-specific gene 7 (ATG7), and lysosomal-associated membrane protein 1 (LAMP1), all molecules critical to normal autophagy. HIV infection can also induce dysregulation of mitochondrial bioenergetics by altering production and equilibrium of adenosine triphosphate (ATP), mitochondrial reactive oxygen species (ROS), and calcium. These changes alter mitochondrial mass and morphology, which normally trigger autophagy to clear away dysfunctional organelles. However, with HIV infection also triggering autophagy dysfunction, these abnormal mitochondria accumulate and contribute to myocardial dysfunction. Likewise, use of HAART, azidothymidine and Abacavir, have been shown to induce cardiac dysfunction and fibrosis by inducing abnormal autophagy during antiretroviral therapy. Conversely, studies have shown that increasing autophagy can reduce the accumulation of dysfunctional mitochondria and restore cardiomyocyte function. Interestingly, Rapamycin, a mammalian target of rapamycin (mTOR) inhibitor, has also been shown to reduce HIV-induced cytotoxicity by regulating autophagy-related proteins, making it a non-antiviral agent with the potential to treat HIVAC. In this review, we synthesize these findings to provide a better understanding of the role autophagy plays in HIVAC and discuss the potential pharmacologic targets unveiled by this research.

Crosstalk between autophagy and insulin resistance: evidence from different tissues

Insulin is a critical hormone that promotes energy storage in various tissues, as well as anabolic functions. Insulin resistance significantly reduces these responses, resulting in pathological conditions, such as obesity and type 2 diabetes mellitus (T2DM). The management of insulin resistance requires better knowledge of its pathophysiological mechanisms to prevent secondary complications, such as cardiovascular diseases (CVDs). Recent evidence regarding the etiological mechanisms behind insulin resistance emphasizes the role of energy imbalance and neurohormonal dysregulation, both of which are closely regulated by autophagy. Autophagy is a conserved process that maintains homeostasis in cells. Accordingly, autophagy abnormalities have been linked to a variety of metabolic disorders, including insulin resistance, T2DM, obesity, and CVDs. Thus, there may be a link between autophagy and insulin resistance. Therefore, the interaction between autophagy and insulin function will be examined in this review, particularly in insulin-responsive tissues, such as adipose tissue, liver, and skeletal muscle.

Targeting the biology of aging with mTOR inhibitors

Inhibition of the protein kinase mechanistic target of rapamycin (mTOR) with the Food and Drug Administration (FDA)-approved therapeutic rapamycin promotes health and longevity in diverse model organisms. More recently, specific inhibition of mTORC1 to treat aging-related conditions has become the goal of basic and translational scientists, clinicians and biotechnology companies. Here, we review the effects of rapamycin on the longevity and survival of both wild-type mice and mouse models of human diseases. We discuss recent clinical trials that have explored whether existing mTOR inhibitors can safely prevent, delay or treat multiple diseases of aging. Finally, we discuss how new molecules may provide routes to the safer and more selective inhibition of mTOR complex 1 (mTORC1) in the decade ahead. We conclude by discussing what work remains to be done and the questions that will need to be addressed to make mTOR inhibitors part of the standard of care for diseases of aging.

The Effect of Diet on the Cardiac Circadian Clock in Mice: A Systematic Review

Circadian rhythms play important roles in regulating physiological and behavioral processes. These are adjusted by environmental cues, such as diet, which acts by synchronizing or attenuating the circadian rhythms of peripheral clocks, such as the liver, intestine, pancreas, white and brown adipose tissue, lungs, kidneys, as well as the heart. Some studies point to the influence of diet composition, feeding timing, and dietary restriction on metabolic homeostasis and circadian rhythms at various levels. Therefore, this systematic review aimed to discuss studies addressing the effect of diet on the heart clock in animal models and, additionally, the chronodisruption of the clock and its relation to the development of cardiovascular disorders in the last 15 years. A search was conducted in the PubMed, Scopus, and Embase databases. The PRISMA guide was used to construct the article. Nineteen studies met all inclusion and exclusion criteria. In summary, these studies have linked the circadian clock to cardiovascular health and suggested that maintaining a robust circadian system may reduce the risks of cardiometabolic and cardiovascular diseases. The effect of time-of-day-dependent eating on the modulation of circadian rhythms of the cardiac clock and energy homeostasis is notable, among its deleterious effects predominantly in the sleep (light) phase and/or at the end of the active phase.

Effects of caloric overload before caloric restriction in the murine heart

The beneficial effects of caloric restriction (CR) against cardiac aging and for prevention of cardiovascular diseases are numerous. However, to our knowledge, there is no scientific evidence about how a high-calorie diet (HCD) background influences the mechanisms underlying CR in whole heart tissue (WHT) in experimental murine models. In the current study, CR-treated mice with different alimentary backgrounds were subjected to transthoracic echocardiographic measurements. WHT was then analyzed to determine cardiac energetics, telomerase activity, the expression of energy-sensing networks, tissue-specific adiponectin, and cardiac precursor/cardiac stem cell markers. Animals with a balanced diet consumption before CR presented marked cardiac remodeling with improved ejection fraction (EF) and fractional shortening (FS), enhanced OXPHOS complex I, III, and IV, and CKMT2 enzymatic activity. Mice fed an HCD before CR presented moderate changes in cardiac geometry with diminished EF and FS values, but improved OXPHOS complex IV and CKMT2 activity. Differences in cardiac remodeling, left ventricular systolic/diastolic performance, and mitochondrial energetics, found in the CR-treated mice with contrasting alimentary backgrounds, were corroborated by inconsistencies in the expression of mitochondrial-biogenesis-related markers and associated regulatory networks. In particular, disruption of eNOS and AMPK -PGC-1α-mTOR-related axes. The impact of a past habit of caloric overload on the effects of CR in the WHT is a scarcely explored subject that requires deeper study in combination with analyses of other tissues and organs at higher levels of organization within the organ system. Such research will eventually lead to the development of preventative and therapeutic strategies to promote health and longevity.

Autophagy, Oxidative Stress and Cancer Development

Simple Summary

Autophagy, as an important cellular repair mechanism, is important for the prevention of several diseases, including metabolic and neurologic disorders, and cancer. Hence, dysfunctional autophagy has been linked to these diseases, and in recent years researchers have tried to outline therapeutic targets in autophagy-related pathways as a treatment. With this review of the literature, we want to give an overview about the connection between oxidative stress, autophagy and cancer.

Abstract

Autophagy is an important cellular repair mechanism, aiming at sequestering misfolded and dysfunctional proteins and damaged cell organelles. Dysfunctions in the autophagy process have been linked to several diseases, like infectious and neurodegenerative diseases, type II diabetes mellitus and cancer. Living organisms are constantly subjected to some degree of oxidative stress, mainly induced by reactive oxygen and nitrogen species. It has been shown that autophagy is readily induced by reactive oxygen species (ROS) upon nutrient deprivation. In recent years, research has increasingly focused on outlining novel therapeutic targets related to the autophagy process. With this review of the literature, we want to give an overview about the link between autophagy, oxidative stress and carcinogenesis.

Energy metabolism homeostasis in cardiovascular diseases

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in the general population. Energy metabolism disturbance is one of the early abnormalities in CVDs, such as coronary heart disease, diabetic cardiomyopathy, and heart failure. To explore the role of myocardial energy homeostasis disturbance in CVDs, it is important to understand myocardial metabolism in the normal heart and their function in the complex pathophysiology of CVDs. In this article, we summarized lipid metabolism/lipotoxicity and glucose metabolism/insulin resistance in the heart, focused on the metabolic regulation during neonatal and ageing heart, proposed potential metabolic mechanisms for cardiac regeneration and degeneration. We provided an overview of emerging molecular network among cardiac proliferation, regeneration, and metabolic disturbance. These novel targets promise a new era for the treatment of CVDs.

Age-related defects in autophagy alter the secretion of paracrine factors from bone marrow mononuclear cells

Bone marrow mononuclear cell therapy improves cardiac repair after myocardial infarction (MI), in-part through signaling to resident cardiac cells, such as fibroblasts, which regulate scar formation. The efficacy of cell therapy declines with age, as aging of both donor and recipient cells decreases repair responses. Autophagy regulates the microenvironment by both extracellular vesicle (EV)-dependent and independent secretion pathways. We hypothesized that age-related autophagy changes in bone marrow cells (BMCs) alter paracrine signaling, contributing to lower cell therapy efficacy. Here, we demonstrate that young Sca-1+ BMCs exhibited a higher LC3II/LC3I ratio compared to old Sca-1+ BMCs, which was accentuated when BMCs were cultured under hypoxia. To examine the effect on paracrine signaling, old cardiac fibroblasts were cultured with conditioned medium (CM) from young and old Sca-1+ BMCs. Young, but not old CM, enhanced fibroblast proliferation, migration, and differentiation, plus reduced senescence. These beneficial effects were lost when autophagy or EV secretion in BMCs was blocked pharmacologically, or by siRNA knockdown of Atg7. Therefore, both EV-dependent and -independent paracrine signaling from young BMCs is responsible for paracrine stimulation of old cardiac fibroblasts. In vivo, bone marrow chimerism of old mice with young BMCs increased the number of LC3b+ cells in the heart compared to old mice reconstituted with old BMCs. These data suggest that the deterioration of autophagy with aging negatively impacts the paracrine effects of BMCs, and provide mechanistic insight into the age-related decline in cell therapy efficacy that could be targeted to improve the function of old donor cells.

Obesity cardiomyopathy: evidence, mechanisms, and therapeutic implications

The prevalence of heart failure is on the rise and imposes a major health threat, in part, due to the rapidly increased prevalence of overweight and obesity. To this point, epidemiological, clinical, and experimental evidence supports the existence of a unique disease entity termed “obesity cardiomyopathy,” which develops independent of hypertension, coronary heart disease, and other heart diseases. Our contemporary review evaluates the evidence for this pathological condition, examines putative responsible mechanisms, and discusses therapeutic options for this disorder. Clinical findings have consolidated the presence of left ventricular dysfunction in obesity. Experimental investigations have uncovered pathophysiological changes in myocardial structure and function in genetically predisposed and diet-induced obesity. Indeed, contemporary evidence consolidates a wide array of cellular and molecular mechanisms underlying the etiology of obesity cardiomyopathy including adipose tissue dysfunction, systemic inflammation, metabolic disturbances (insulin resistance, abnormal glucose transport, spillover of free fatty acids, lipotoxicity, and amino acid derangement), altered intracellular especially mitochondrial Ca²⁺ homeostasis, oxidative stress, autophagy/mitophagy defect, myocardial fibrosis, dampened coronary flow reserve, coronary microvascular disease (microangiopathy), and endothelial impairment. Given the important role of obesity in the increased risk of heart failure, especially that with preserved systolic function and the recent rises in COVID-19-associated cardiovascular mortality, this review should provide compelling evidence for the presence of obesity cardiomyopathy, independent of various comorbid conditions, underlying mechanisms, and offer new insights into potential therapeutic approaches (pharmacological and lifestyle modification) for the clinical management of obesity cardiomyopathy.

Cardioprotective effects of severe calorie restriction from birth in adult ovariectomized rats

AIMS

Menopause is a female condition induced by a reduction of ovarian hormone and is related to an increase in cardiovascular diseases in women. We have shown that severe calorie restriction (SCR) from birth reduces the cardiometabolic risk in adult male Wistar rats. In this study, we investigated the effects of SCR from birth to adulthood on cardiovascular function of ovariectomized rats.

MAIN METHODS

From birth to adulthood, rats were daily fed ad libitum (control group - C) or with 50% of the amount consumed by the control group (calorie-restricted group - R). At 90 days, half of the rats in each group underwent bilateral ovariectomy (OVX), totaling 4 groups: C-Sham, C-OVX, R-Sham, R-OVX. Systolic blood pressure (SBP), heart rate (HR) and, double product (DP) index were recorded by tail-cuff plethysmography. Cardiac function was analyzed by the Langendorff technique and cardiomyocyte diameter was accessed by histologic analysis. Additionally, cardiac SERCA2 content and redox status were evaluated.

KEY FINDINGS

C-OVX rats exhibited reduced cardiac function and cardiac non-enzymatic total antioxidant capacity (TAC). R-Sham animals showed reduced SBP, DP, HR, improved cardiac function, reduced cardiac protein carbonyl derivatives and increased TAC, catalase, and superoxide dismutase activities. R-OVX rats maintained reduced SBP, DP, HR, and increased contractility and relaxation indexes. R-Sham and R-OVX rats exhibited preserved heart mass and reduced cardiomyocyte diameter. Cardiac SERCA2 content did not differ between the groups.

SIGNIFICANCE

Taken together, our findings show cardioprotective effects of SCR from birth in adult ovariectomized rats.

Adiponectin, Leptin and Cardiovascular Disorders

The landmark discoveries of leptin and adiponectin firmly established adipose tissue as a sophisticated and highly active endocrine organ, opening a new era of investigating adipose-mediated tissue crosstalk. Both obesity-associated hyperleptinemia and hypoadiponectinemia are important biomarkers to predict cardiovascular outcomes, suggesting a crucial role for adiponectin and leptin in obesity-associated cardiovascular disorders. Normal physiological levels of adiponectin and leptin are indeed essential to maintain proper cardiovascular function. Insufficient adiponectin and leptin signaling results in cardiovascular dysfunction. However, a paradox of high levels of both leptin and adiponectin is emerging in the pathogenesis of cardiovascular disorders. Here, we (1) summarize the recent progress in the field of adiponectin and leptin and its association with cardiovascular disorders, (2) further discuss the underlying mechanisms for this new paradox of leptin and adiponectin action, and (3) explore the possible application of partial leptin reduction, in addition to increasing the adiponectin/leptin ratio as a means to prevent or reverse cardiovascular disorders.

Mitochondrial quality control mechanisms as molecular targets in cardiac ageing

Cardiovascular disease is the leading cause of morbidity and mortality worldwide. Advancing age is a major risk factor for developing cardiovascular disease because of the lifelong exposure to cardiovascular risk factors and specific alterations affecting the heart and the vasculature during ageing. Indeed, the ageing heart is characterized by structural and functional changes that are caused by alterations in fundamental cardiomyocyte functions. In particular, the myocardium is heavily dependent on mitochondrial oxidative metabolism and is especially susceptible to mitochondrial dysfunction. Indeed, primary alterations in mitochondrial function, which are subsequently amplified by defective quality control mechanisms, are considered to be major contributing factors to cardiac senescence. In this Review, we discuss the mechanisms linking defective mitochondrial quality control mechanisms (that is, proteostasis, biogenesis, dynamics, and autophagy) to organelle dysfunction in the context of cardiac ageing. We also illustrate relevant molecular pathways that might be exploited for the prevention and treatment of age-related heart dysfunction.

Perfluorooctanoic acid-induced toxicities in chicken embryo primary cardiomyocytes: Roles of PPAR alpha and Wnt5a/Frizzled2

Perfluorooctanoic acid (PFOA) is a widespread persistent organic pollutant and may induce developmental toxicities, including developmental cardiotoxicity. To explore the potential mechanism of developmental cardiotoxicity induced by PFOA exposure, chicken embryo primary cardiomyocytes were extracted either from chicken embryos pretreated with PFOA (2 mg/kg), or from untreated embryos and then directly exposed cells to PFOA (1, 10, 30 or 100 μg/ml) in culture. Additionally, peroxisome proliferator activated receptor alpha (PPAR alpha) silencing lentivirus was applied to the embryos on embryonic day (ED2). Cell viability was measured with CCK-8 kit, morphology was assessed with hematoxylin and eosin staining, and intracellular Ca²⁺ concentrations were determined with Fluo-4 AM probe. Western blotting was utilized to confirm PPAR alpha silencing efficiency and the protein abundance of Wnt5a and Frizzled2. The results indicated that both PFOA pretreatment and direct exposure decreased primary cardiomyocyte viability, altered cell morphology and increased intracellular Ca²⁺ concentrations. While l-carnitine co-treatment effectively abolished such changes, PPAR alpha silencing only abolished most of the changes in PFOA pretreatment group, but not in cells directly exposed to relatively high doses of PFOA. The protein abundance of Wnt5a and Frizzled2 was increased by PFOA pretreatment, while direct exposure to PFOA increased Frizzled2 abundance but decreased Wnt5a abundance. PPAR alpha silencing resulted in over 50% decrease of PPAR alpha expression level, which abolished the Wnt5a/Frizzled2 expression alterations following PFOA exposure. In conclusion, PFOA-induced primary cardiomyocyte toxicity is associated with PPAR alpha and Wnt5a/Frizzled2, in which PPAR alpha seems to play regulatory roles towards Wnt5a/Frizzled2.

The Role of Heme Oxygenase 1 in the Protective Effect of Caloric Restriction against Diabetic Cardiomyopathy

Type 2 diabetes mellitus (DM2) leads to cardiomyopathy characterized by cardiomyocyte hypertrophy, followed by mitochondrial dysfunction and interstitial fibrosis, all of which are exacerbated by angiotensin II (AT). SIRT1 and its transcriptional coactivator target PGC-1α (peroxisome proliferator-activated receptor-γ coactivator), and heme oxygenase-1 (HO-1) modulates mitochondrial biogenesis and antioxidant protection. We have previously shown the beneficial effect of caloric restriction (CR) on diabetic cardiomyopathy through intracellular signaling pathways involving the SIRT1–PGC-1α axis. In the current study, we examined the role of HO-1 in diabetic cardiomyopathy in mice subjected to CR. Methods: Cardiomyopathy was induced in obese diabetic (db/db) mice by AT infusion. Mice were either fed ad libitum or subjected to CR. In an in vitro study, the reactive oxygen species (ROS) level was determined in cardiomyocytes exposed to different glucose levels (7.5–33 mM). We examined the effects of Sn(tin)-mesoporphyrin (SnMP), which is an inhibitor of HO activity, the HO-1 inducer cobalt protoporphyrin (CoPP), and the SIRT1 inhibitor (EX-527) on diabetic cardiomyopathy. Results: Diabetic mice had low levels of HO-1 and elevated levels of the oxidative marker malondialdehyde (MDA). CR attenuated left ventricular hypertrophy (LVH), increased HO-1 levels, and decreased MDA levels. SnMP abolished the protective effects of CR and caused pronounced LVH and cardiac metabolic dysfunction represented by suppressed levels of adiponectin, SIRT1, PPARγ, PGC-1α, and increased MDA. High glucose (33 mM) increased ROS in cultured cardiomyocytes, while SnMP reduced SIRT1, PGC-1α levels, and HO activity. Similarly, SIRT1 inhibition led to a reduction in PGC-1α and HO-1 levels. CoPP increased HO-1 protein levels and activity, SIRT1, and PGC-1α levels, and decreased ROS production, suggesting a positive feedback between SIRT1 and HO-1. Conclusion: These results establish a link between SIRT1, PGC-1α, and HO-1 signaling that leads to the attenuation of ROS production and diabetic cardiomyopathy. CoPP mimicked the beneficial effect of CR, while SnMP increased oxidative stress, aggravating cardiac hypertrophy. The data suggest that increasing HO-1 levels constitutes a novel therapeutic approach to protect the diabetic heart. Brief Summary: CR attenuates cardiomyopathy, and increases HO-1, SIRT activity, and PGC-1α protein levels in diabetic mice. High glucose reduces adiponectin, SIRT1, PGC1-1α, and HO-1 levels in cardiomyocytes, resulting in oxidative stress. The pharmacological activation of HO-1 activity mimics the effect of CR, while SnMP increased oxidative stress and cardiac hypertrophy. These data suggest the critical role of HO-1 in protecting the diabetic heart.

The effect of fasting or calorie restriction on autophagy induction: A review of the literature

Autophagy is a lysosomal degradation process and protective housekeeping mechanism to eliminate damaged organelles, long-lived misfolded proteins and invading pathogens. Autophagy functions to recycle building blocks and energy for cellular renovation and homeostasis, allowing cells to adapt to stress. Modulation of autophagy is a potential therapeutic target for a diverse range of diseases, including metabolic conditions, neurodegenerative diseases, cancers and infectious diseases. Traditionally, food deprivation and calorie restriction (CR) have been considered to slow aging and increase longevity. Since autophagy inhibition attenuates the anti-aging effects of CR, it has been proposed that autophagy plays a substantive role in CR-mediated longevity. Among several stress stimuli inducers of autophagy, fasting and CR are the most potent non-genetic autophagy stimulators, and lack the undesirable side effects associated with alternative interventions. Despite the importance of autophagy, the evidence connecting fasting or CR with autophagy promotion has not previously been reviewed. Therefore, our objective was to weigh the evidence relating the effect of CR or fasting on autophagy promotion. We conclude that both fasting and CR have a role in the upregulation of autophagy, the evidence overwhelmingly suggesting that autophagy is induced in a wide variety of tissues and organs in response to food deprivation.

Impact of Nutrition on Cardiovascular Function

The metabolic sources of energy for myocardial contractility include mainly free fatty acids (FFA) for 95%, and in lesser amounts for 5% from glucose and minimal contributions from other substrates such lactate, ketones, and amino acids. However, myocardial efficiency is influenced by metabolic condition, overload, and ischemia. During cardiac stress, cardiomyocytes increase glucose oxidation and reduce FFA oxidation. In patients with ischemic coronary disease and heart failure, the low oxygen availability limits myocardial reliance on FFA and glucose utilization must increase. Although glucose uptake is fundamental to cardiomyocyte function, an excessive intracellular glucose level is detrimental. Insulin plays a fundamental role in maintaining myocardial efficiency and in reducing glycemia and inflammation; this is particularly evident in obese and type-2 diabetic patients. An excess of F availability increase fat deposition within cardiomyocytes and reduces glucose oxidation. In patients with high body mass index, a restricted diet or starvation have positive effects on cardiac metabolism and function while, in patients with low body mass index, restrictive diets, or starvation have a deleterious effect. Thus, weight loss in obese patients has positive impacts on ventricular mass and function, whereas, in underweight heart failure patients, such weight reduction adds to the risk of heart damage, predisposing to cachexia. Nutrition plays an essential role in the evolution of cardiovascular disease and should be taken into account. An energy-restricted diet improves myocardial efficiency but can represent a potential risk of heart damage, particularly in patients affected by cardiovascular disease. Micronutrient integration has a marginal effect on cardiovascular efficiency.

Fasting/Refeeding Cycles Prevent Myocardial Dysfunction and Morphology Damage in the Spontaneously Hypertensive Rats

Background

Caloric restriction is known to impair the cardiac function and morphology in hypertrophied hearts of spontaneously hypertensive rats (SHR); however, the influence of fasting/refeeding (RF) is unknown.

Objective

To investigate the fasting/refeeding approach on myocardial remodeling and function. In addition, the current study was designed to bring information regarding the mechanisms underlying the participation of Ca²⁺ handling and β-adrenergic system.

Methods

Sixty-day-old male SHR rats were submitted to food ad libitum (C), 50% food restriction (R₅₀) or RF cycles for 90 days. Cardiac remodeling was assessed by ultrastructure analysis and isolated papillary muscle function. The level of significance considered was 5% (α = 0.05).

Results

The RF rats presented lower cardiac atrophy than R₅₀ in relation to C rats. The C rats increased weight gain, R₅₀ maintained their initial body weight and RF rats increased and decreased weight during RF. The RF did not cause functional impairment because the isotonic and isometric parameters showed similar behavior to those of C. The isotonic and isometric cardiac parameters were significantly elevated in RF rats compared to R₅₀ rats. In addition, the R₅₀ rats had cardiac damage in relation to C for isotonic and isometric variables. While the R₅₀ rats showed focal changes in many muscle fibers, the RF rats displayed mild alterations, such as loss or disorganization of myofibrils.

Conclusion

Fasting/refeeding promotes cardiac beneficial effects and attenuates myocardial injury caused by caloric restriction in SHR rats, contributing to reduce the cardiovascular risk profile and morphological injuries. Furthermore, RF promotes mild improvement in Ca²⁺ handling and β-adrenergic system.

Regulation of diabetic cardiomyopathy by caloric restriction is mediated by intracellular signaling pathways involving 'SIRT1 and PGC-1α'

Background

Metabolic disorders such as obesity, insulin resistance and type 2 diabetes mellitus (DM2) are all linked to diabetic cardiomyopathy that lead to heart failure. Cardiomyopathy is initially characterized by cardiomyocyte hypertrophy, followed by mitochondrial dysfunction and fibrosis, both of which are aggravated by angiotensin. Caloric restriction (CR) is cardioprotective in animal models of heart disease through its catabolic activity and activation of the expression of adaptive genes. We hypothesized that in the diabetic heart; this effect involves antioxidant defenses and is mediated by SIRT1 and the transcriptional coactivator PGC-1α (Peroxisome proliferator-activated receptor-γ coactivator).

Methods

Obese Leptin resistant (db/db) mice characterized by DM2 were treated with angiotensin II (AT) for 4 weeks to enhance the development of cardiomyopathy. Mice were concomitantly either on a CR diet or fed ad libitum. Cardiomyocytes were exposed to high levels of glucose and were treated with EX-527 (SIRT1 inhibitor). Cardiac structure and function, gene and protein expression and oxidative stress parameters were analyzed.

Results

AT treated db/db mice developed cardiomyopathy manifested by elevated levels of serum glucose, cholesterol and cardiac hypertrophy. Leukocyte infiltration, fibrosis and an increase in an inflammatory marker (TNFα) and natriuretic peptides (ANP, BNP) gene expression were also observed. Oxidative stress was manifested by low SOD and PGC-1α levels and an increase in ROS and MDA. DM2 resulted in ERK1/2 activation. CR attenuated all these deleterious perturbations and prevented the development of cardiomyopathy. ERK1/2 phosphorylation was reduced in CR mice (p = 0.008). Concomitantly CR prevented the reduction in SIRT activity and PGC-1α (p < 0.04). Inhibition of SIRT1 activity in cardiomyocytes led to a marked reduction in both SIRT1 and PGC-1α. ROS levels were significantly (p < 0.03) increased by glucose and SIRT1 inhibition.

Conclusion

In the current study we present evidence of the cardioprotective effects of CR operating through SIRT1 and PGC-1 α, thereby decreasing oxidative stress, fibrosis and inflammation. Our results suggest that increasing SIRT1 and PGC-1α levels offer new therapeutic approaches for the protection of the diabetic heart.

Targeting autophagy in obesity: from pathophysiology to management

Obesity poses a severe threat to human health, including the increased prevalence of hypertension, insulin resistance, diabetes mellitus, cancer, inflammation, sleep apnoea and other chronic diseases. Current therapies focus mainly on suppressing caloric intake, but the efficacy of this approach remains poor. A better understanding of the pathophysiology of obesity will be essential for the management of obesity and its complications. Knowledge gained over the past three decades regarding the aetiological mechanisms underpinning obesity has provided a framework that emphasizes energy imbalance and neurohormonal dysregulation, which are tightly regulated by autophagy. Accordingly, there is an emerging interest in the role of autophagy, a conserved homeostatic process for cellular quality control through the disposal and recycling of cellular components, in the maintenance of cellular homeostasis and organ function by selectively ridding cells of potentially toxic proteins, lipids and organelles. Indeed, defects in autophagy homeostasis are implicated in metabolic disorders, including obesity, insulin resistance, diabetes mellitus and atherosclerosis. In this Review, the alterations in autophagy that occur in response to nutrient stress, and how these changes alter the course of obesogenesis and obesity-related complications, are discussed. The potential of pharmacological modulation of autophagy for the management of obesity is also addressed.

Mechanisms of Cardiac Repair and Regeneration

Cardiovascular regenerative therapies are pursued on both basic and translational levels. Although efficacy and value of cell therapy for myocardial regeneration can be debated, there is a consensus that profound deficits in mechanistic understanding limit advances, optimization, and implementation. In collaboration with the TACTICS (Transnational Alliance for Regenerative Therapies in Cardiovascular Syndromes), this review overviews several pivotal aspects of biological processes impinging on cardiac maintenance, repair, and regeneration. The goal of summarizing current mechanistic understanding is to prompt innovative directions for fundamental studies delineating cellular reparative and regenerative processes. Empowering myocardial regenerative interventions, whether dependent on endogenous processes or exogenously delivered repair agents, ultimately depends on mastering mechanisms and novel strategies that take advantage of rather than being limited by inherent myocardial biology.

Opposing effects on cardiac function by calorie restriction in different-aged mice

Calorie restriction (CR) increases average and maximum lifespan and exhibits an apparent beneficial impact on age‐related diseases. Several studies have shown that CR initiated either in middle or old age could improve ischemic tolerance and rejuvenate the aging heart; however, the data are not uniform when initiated in young. The accurate time to initiate CR providing maximum benefits for cardiac remodeling and function during aging remains unclear. Thus, whether a similar degree of CR initiated in mice of different ages could exert a similar effect on myocardial protection was investigated in this study. C57BL/6 mice were subjected to a calorically restricted diet (40% less than the ad libitum diet) for 3 months initiated in 3, 12, and 19 months. It was found that CR significantly reversed the aging phenotypes of middle‐aged and old mice including cardiac remodeling (cardiomyocyte hypertrophy and cardiac fibrosis), inflammation, mitochondrial damage, telomere shortening, as well as senescence‐associated markers but accelerated in young mice. Furthermore, whole‐genome microarray demonstrated that the AMP‐activated protein kinase (AMPK)–Forkhead box subgroup ‘O’ (FOXO) pathway might be a major contributor to contrasting regulation by CR initiated in different ages; thus, increased autophagy was seen in middle‐aged and old mice but decreased in young mice. Together, the findings demonstrated promising myocardial protection by 40% CR should be initiated in middle or old age that may have vital implications for the practical nutritional regimen.

Short-term moderate diet restriction in adulthood can reverse oxidative, cardiovascular and metabolic alterations induced by postnatal overfeeding in mice

We aimed to determine whether moderate diet restriction could restore cardiac, oxidative and metabolic alterations induced by postnatal overfeeding (PNOF). Litters of C57BL/6 male mice were either maintained at 9 (normal litter, NL), or reduced to 3 (small litter, SL) in order to induce PNOF. At 6 months, half of the NL and SL mice were subjected to 20% calorie-restriction (CR: NLCR, SLCR) for one month, while the other half continued to eat ad libitum (AL: NLAL, SLAL). Six-month old SL mice presented overweight, fat accumulation, hyperleptinemia, glucose intolerance, insulin resistance, increased cardiac ROS production and decreased left ventricular ejection fraction (LVEF). After CR, SL mice body weight was normalized; however, their fat mass and leptinemia were not decreased, glucose metabolism was improved and LVEF was increased. In SL mice, CR increased the cardiac mitochondrial respiratory rate and decreased cardiac ROS production. Hearts from SLCR mice showed better recovery and smaller postischemic infarct size. Intriguingly, no difference was observed between NLAL and NLCR mice for most of the parameters investigated. Short-term moderate CR not only normalized body weight in SL mice but also improved metabolic programming and reversed oxidative and cardiac dysfunction induced by PNOF.

Autophagy in cardiac metabolic control: Novel mechanisms for cardiovascular disorders

As an extensively studied quality control system, autophagy is responsible for clearance of dysfunctional organelles and damaged marcomolecules in cells. In addition to its biological recycling function, autophagy plays a significant role in the pathogenesis of metabolic syndromes such as obesity and diabetes. In particular, metabolic disorders contribute to cardiovascular disease development. As energy required to maintain cardiac cells functional is immense, disturbances in the balance between anabolic and catabolic metabolism possibly contribute to cardiovascular disorders. Therefore, an urgent need to expand our knowledge on the role of autophagy on the metabolic regulation of hearts emerges. In this review, the potential relationship between autophagic activity and cardiac metabolism is explored and we also discuss how dysregulated autophagy leads to severe cardiac disorders from the perspective of metabolic control.

Inhibition of the Mechanistic Target of Rapamycin (mTOR)-Rapamycin and Beyond

Rapamycin is a Food and Drug Administration (FDA)-approved immunosuppressant and anticancer agent discovered in the soil of Easter Island in the early 1970s. Rapamycin is a potent and selective inhibitor of the mechanistic target of rapamycin (mTOR) protein kinase, which acts as a central integrator of nutrient signaling pathways. During the last decade, genetic and pharmaceutical inhibition of mTOR pathway signaling has been found to promote longevity in yeast, worms, flies, and mice. In this article, we will discuss the molecular biology underlying the effects of rapamycin and its physiological effects, evidence for rapamycin as an antiaging compound, mechanisms by which rapamycin may extend life span, and the potential limitations of rapamycin as an antiaging molecule. Finally, we will discuss possible strategies that may allow us to inhibit mTOR signaling safely while minimizing side effects, and reap the health, social, and economic benefits from slowing the aging process.

Severe Calorie Restriction Reduces Cardiometabolic Risk Factors and Protects Rat Hearts from Ischemia/Reperfusion Injury

Background and Aims: Recent studies have proposed that if a severe caloric restriction (SCR) is initiated at the earliest period of postnatal life, it can lead to beneficial cardiac adaptations later on. We investigated the effects of SCR in Wistar rats from birth to adult age on risk factors for cardiac diseases (CD), as well as cardiac function, redox status, and HSP72 content in response to ischemia/reperfusion (I/R) injury.

Methods and Results: From birth to the age of 3 months, CR50 rats were fed 50% of the food that the ad libitum group (AL) was fed. Food intake was assessed daily and body weight were assessed weekly. In the last week of the SCR protocol, systolic blood pressure and heart rate were measured and the double product index was calculated. Also, oral glucose and intraperitoneal insulin tolerance tests were performed. Thereafter, rats were decapitated, visceral fat was weighed, and blood and hearts were harvested for biochemical, functional, tissue redox status, and western blot analyzes. Compared to AL, CR50 rats had reduced the main risk factors for CD. Moreover, the FR50 rats showed increased cardiac function both at baseline conditions (45% > AL rats) and during the post-ischemic period (60% > AL rats) which may be explained by a decreased cardiac oxidative stress and increased HSP72 content.

Conclusion: SCR from birth to adult age reduced risk factors for CD, increased basal cardiac function and protected hearts from the I/R, possibly by a mechanism involving ROS.

Derailed Proteostasis as a Determinant of Cardiac Aging

Age comprises the single most important risk factor for cardiac disease development. The incidence and prevalence of cardiac diseases, which represents the main cause of death worldwide, will increase even more because of the aging population. A hallmark of aging is that it is accompanied by a gradual derailment of proteostasis (eg, the homeostasis of protein synthesis, folding, assembly, trafficking, function, and degradation). Loss of proteostasis is highly relevant to cardiomyocytes, because they are postmitotic cells and therefore not constantly replenished by proliferation. The derailment of proteostasis during aging is thus an important factor that preconditions for the development of age-related cardiac diseases, such as atrial fibrillation. In turn, frailty of proteostasis in aging cardiomyocytes is exemplified by its accelerated derailment in multiple cardiac diseases. Here, we review 2 major components of the proteostasis network, the stress-responsive and protein degradation pathways, in healthy and aged cardiomyocytes. Furthermore, we discuss the relation between derailment of proteostasis and age-related cardiac diseases, including atrial fibrillation. Finally, we introduce novel therapeutic targets that might possibly attenuate cardiac aging and thus limit cardiac disease progression.

Long-Lived αMUPA Mice Show Attenuation of Cardiac Aging and Leptin-Dependent Cardioprotection

αMUPA transgenic mice spontaneously consume less food compared with their wild type (WT) ancestors due to endogenously increased levels of the satiety hormone leptin. αMUPA mice share many benefits with mice under caloric restriction (CR) including an extended life span. To understand mechanisms linked to cardiac aging, we explored the response of αMUPA hearts to ischemic conditions at the age of 6, 18, or 24 months. Mice were subjected to myocardial infarction (MI) in vivo and to ischemia/reperfusion ex vivo. Compared to WT mice, αMUPA showed functional and histological advantages under all experimental conditions. At 24 months, none of the WT mice survived the first ischemic day while αMUPA mice demonstrated 50% survival after 7 ischemic days. Leptin, an adipokine decreasing under CR, was consistently ~60% higher in αMUPA sera at baseline. Leptin levels gradually increased in both genotypes 24h post MI but were doubled in αMUPA. Pretreatment with leptin neutralizing antibodies or with inhibitors of leptin signaling (AG-490 and Wortmannin) abrogated the αMUPA benefits. The antibodies also reduced phosphorylation of the leptin signaling components STAT3 and AKT specifically in the αMUPA myocardium. αMUPA mice did not show elevation in adiponectin, an adipokine previously implicated in CR-induced cardioprotection. WT mice treated for short-term CR exhibited cardioprotection similar to that of αMUPA, however, along with increased adiponectin at baseline. Collectively, the results demonstrate a life-long increased ischemic tolerance in αMUPA mice, indicating the attenuation of cardiac aging. αMUPA cardioprotection is mediated through endogenous leptin, suggesting a protective pathway distinct from that elicited under CR.

Staying young at heart: autophagy and adaptation to cardiac aging

Aging is a predominant risk factor for developing cardiovascular disease. Therefore, the cellular processes that contribute to aging are attractive targets for therapeutic interventions that can delay or prevent the development of age-related diseases. Our understanding of the underlying mechanisms that contribute to the decline in cell and tissue functions with age has greatly advanced over the past decade. Classical hallmarks of aging cells include increased levels of reactive oxygen species, DNA damage, accumulation of dysfunctional organelles, oxidized proteins and lipids. These all contribute to a progressive decline in the normal physiological function of the cell and to the onset of age-related conditions. A major cause of the aging process is progressive loss of cellular quality control. Autophagy is an important quality control pathway and is necessary to maintain cardiac homeostasis and to adapt to stress. A reduction in autophagy has been observed in a number of aging models and there is compelling evidence that enhanced autophagy delays aging and extends life span. Enhancing autophagy counteracts age-associated accumulation of protein aggregates and damaged organelles in cells. In this review, we discuss the functional role of autophagy in maintaining homeostasis in the heart, and how a decline is associated with accelerated cardiac aging. We also evaluate therapeutic approaches being researched in an effort to maintain a healthy young heart.

Quality control systems in cardiac aging

Cardiac aging is an intrinsic process that results in impaired cardiac function, along with cellular and molecular changes. These degenerative changes are intimately associated with quality control mechanisms. This review provides a general overview of the clinical and cellular changes which manifest in cardiac aging, and the quality control mechanisms involved in maintaining homeostasis and retarding aging. These mechanisms include autophagy, ubiquitin-mediated turnover, apoptosis, mitochondrial quality control and cardiac matrix homeostasis. Finally, we discuss aging interventions that have been observed to impact cardiac health outcomes. These include caloric restriction, rapamycin, resveratrol, GDF11, mitochondrial antioxidants and cardiolipin-targeted therapeutics. A greater understanding of the quality control mechanisms that promote cardiac homeostasis will help to understand the benefits of these interventions, and hopefully lead to further improved therapeutic modalities.

Deficiency in adiponectin exaggerates cigarette smoking exposure-induced cardiac contractile dysfunction: Role of autophagy

Second hand smoke is an independent risk factor for cardiovascular disease. Adiponectin (APN), an adipose-derived adipokine, has been shown to offer cardioprotective effect through an AMPK-dependent manner. This study was designed to evaluate the impact of adiponectin deficiency on second hand smoke-induced cardiac pathology and underlying mechanisms using a mouse model of side-stream smoke exposure. Adult wild-type (WT) and adiponectin knockout (APNKO) mice were placed in a chamber exposed to cigarette smoke for 1 hour daily for 40 days. Echocardiographic, cardiomyocyte function, and intracellular Ca2+ handling were evaluated. Autophagy and apoptosis were examined using western blot. 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA) staining was used to evaluate reactive oxygen species (ROS) generation. Masson trichrome staining was employed to measure interstitial fibrosis. Our data revealed that adiponectin deficiency provoked smoke exposure-induced cardiomyopathy (compromised fractional shortening, disrupted cardiomyocyte function and intracellular Ca2+ homeostasis, apoptosis and ROS generation). In addition, these detrimental effects of side-stream smoke were accompanied by defective autophagolysosome formation, the effect of which was exacerbated by adiponectin deficiency. Blocking autophagolysosome formation using bafilomycin A1 (BafA1) negated the cardioprotective effect of rapamycin against smoke extract. Induction of autophagy using rapamycin and AMPKα activation using AICAR rescued against smoke extract-induced myopathic anomalies in APNKO mice. Our data suggest that adiponectin serves as an indispensable cardioprotective factor against side-stream smoke exposure-induced myopathic changes possibly through facilitating autophagolysosome formation.

Cardioprotective Signature of Short-Term Caloric Restriction

Objective

To understand the molecular pathways underlying the cardiac preconditioning effect of short-term caloric restriction (CR).

Background

Lifelong CR has been suggested to reduce the incidence of cardiovascular disease through a variety of mechanisms. However, prolonged adherence to a CR life-style is difficult. Here we reveal the pathways that are modulated by short-term CR, which are associated with protection of the mouse heart from ischemia.

Methods

Male 10-12 wk old C57bl/6 mice were randomly assigned to an ad libitum (AL) diet with free access to regular chow, or CR, receiving 30% less food for 7 days (d), prior to myocardial infarction (MI) via permanent coronary ligation. At d8, the left ventricles (LV) of AL and CR mice were collected for Western blot, mRNA and microRNA (miR) analyses to identify cardioprotective gene expression signatures. In separate groups, infarct size, cardiac hemodynamics and protein abundance of caspase 3 was measured at d2 post-MI.

Results

This short-term model of CR was associated with cardio-protection, as evidenced by decreased infarct size (18.5±2.4% vs. 26.6±1.7%, N=10/group; P=0.01). mRNA and miR profiles pre-MI (N=5/group) identified genes modulated by short-term CR to be associated with circadian clock, oxidative stress, immune function, apoptosis, metabolism, angiogenesis, cytoskeleton and extracellular matrix (ECM). Western blots pre-MI revealed CR-associated increases in phosphorylated Akt and GSK3ß, reduced levels of phosphorylated AMPK and mitochondrial related proteins PGC-1α, cytochrome C and cyclooxygenase (COX) IV, with no differences in the levels of phosphorylated eNOS or MAPK (ERK1/2; p38). CR regimen was also associated with reduced protein abundance of cleaved caspase 3 in the infarcted heart and improved cardiac function.

Impact of caloric restriction on myocardial ischaemia/reperfusion injury and new therapeutic options to mimic its effects

Caloric restriction (CR) is the most reliable intervention to extend lifespan and prevent age-related disorders in various species from yeast to rodents. Short- and long-term CR confers cardio protection against ischaemia/reperfusion injury in young and even in aged rodents. A few human trials suggest that CR has the potential to mediate improvement of cardiac or vascular function and induce retardation of cardiac senescence also in humans. The underlying mechanisms are diverse and have not yet been clearly defined. Among the known mediators for the benefits of CR are NO, the AMP-activated PK, sirtuins and adiponectin. Mitochondria, which play a central role in such complex processes within the cell as apoptosis, ATP-production or oxidative stress, are centrally involved in many aspects of CR-induced protection against ischaemic injury. Here, we discuss the relevant literature regarding the protection against myocardial ischaemia/reperfusion injury conferred by CR. Furthermore, we will discuss drug targets to mimic CR and the possible role of calorie restriction in preserving cardiovascular function in humans.

Aging and cardiovascular diseases: the role of gene-diet interactions

In the study of longevity, increasing importance is being placed on the concept of healthy aging rather than considering the total number of years lived. Although the concept of healthy lifespan needs to be defined better, we know that cardiovascular diseases (CVDs) are the main age-related diseases. Thus, controlling risk factors will contribute to reducing their incidence, leading to healthy lifespan. CVDs are complex diseases influenced by numerous genetic and environmental factors. Numerous gene variants that are associated with a greater or lesser risk of the different types of CVD and of intermediate phenotypes (i.e., hypercholesterolemia, hypertension, diabetes) have been successfully identified. However, despite the close link between aging and CVD, studies analyzing the genes related to human longevity have not obtained consistent results and there has been little coincidence in the genes identified in both fields. The APOE gene stands out as an exception, given that it has been identified as being relevant in CVD and longevity. This review analyzes the genomic and epigenomic factors that may contribute to this, ranging from identifying longevity genes in model organisms to the importance of gene-diet interactions (outstanding among which is the case of the TCF7L2 gene).

RETRACTED: Akt2 knockout alleviates prolonged caloric restriction-induced change in cardiac contractile function through regulation of autophagy

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). At the request of the University of Wyoming, this article has been retracted. Although an investigation report from Air Force Medical University found no evidence of misconduct, the University of Wyoming’s institutional investigation of the work authored by Dr. Jun Ren found evidence of data irregularities in Figures 2, 3, and 4 that affect the reported results and conclusions. All authors have been notified of the retraction of this article.

Inhibition of AMPK accentuates prolonged caloric restriction-induced change in cardiac contractile function through disruption of compensatory autophagy

Prolonged caloric restriction often results in alteration in heart geometry and function although the underlying mechanism remains poorly defined. Autophagy, a conserved pathway for bulk degradation of intracellular proteins and organelles, preserves energy and nutrient in the face of caloric insufficiency. This study was designed to examine the role of AMPK in prolonged caloric restriction-induced change in cardiac homeostasis and the underlying mechanism(s) involved with a focus on autophagy. Wild-type (WT) and AMPK kinase dead (KD) mice were caloric restricted (by 40%) for 30 weeks. Echocardiographic, cardiomyocyte contractile and intracellular Ca²⁺ properties, autophagy and autophagy regulatory proteins were evaluated. Caloric restriction compromised echocardiographic indices (decreased ventricular mass, left ventricular diameters, and cardiac output), cardiomyocyte contractile and intracellular Ca²⁺ properties associated with upregulated autophagy (Beclin-1, Atg5 and LC3BII-to-LC3BI ratio), increased autophagy adaptor protein p62, elevated phosphorylation of AMPK and TSC1/2, depressed phosphorylation of mTOR and ULK1. Although AMPK inhibition did not affect cardiac mechanical function, autophagy and autophagy signaling proteins, it significantly accentuated caloric restriction-induced changes in myocardial contractile function and intracellular Ca²⁺ handling. Interestingly, AMPK inhibition reversed caloric restriction-induced changes in autophagy and autophagy signaling. AMPK inhibition led to dampened levels of Beclin-1, Atg 5 and LC3B ratio along with suppressed phosphorylation of AMPK and TSC1/2 as well as elevated phosphorylation of mTOR and ULK1. Taken together, these data suggest an indispensible role for AMPK in the maintenance of cardiac homeostasis under prolonged caloric restriction-induced pathological changes possibly through autophagy regulation. This article is part of a Special Issue entitled: Autophagy and protein quality control in cardiometabolic diseases.

The interplay between autophagy and mitochondrial dysfunction in oxidative stress-induced cardiac aging and pathology

Aging is accompanied by a progressive increase in the incidence and prevalence of cardiovascular disease (CVD). Prolonged exposure to cardiovascular risk factors, together with intrinsic age-dependent declines in cardiac functionality, increases the vulnerability of the heart to both endogenous and exogenous stressors, ultimately enhancing the susceptibility to developing CVD in late life. Both increased levels of oxidative damage and the accumulation of dysfunctional mitochondria have been observed in a wide range of cardiac diseases, which may therefore represent a common ground upon which many aspects of CVD develop. In this review, we summarize the current knowledge on the mechanisms whereby oxidative stress arising from mitochondrial dysfunction is involved in the process of cardiac aging and in the pathogenesis of CVD highly prevalent in late life (e.g., heart failure and ischemic heart disease). Special emphasis is placed on recent evidence about the role played by alterations in cellular quality control systems, in particular autophagy/mitophagy and mitochondrial dynamics (fusion and fission), and their interconnections in the context of age-related CVD. Cardioprotective interventions acting through the modulation of mitochondrial autophagy (calorie restriction, calorie restriction mimetics, and the gasotransmitter hydrogen sulfide) are also presented. This article is part of a Special Issue entitled "Protein Quality Control, the Ubiquitin Proteasome System, and Autophagy".

Autophagy and leucine promote chronological longevity and respiration proficiency during calorie restriction in yeast

We have previously shown that autophagy is required for chronological longevity in the budding yeast Saccharomyces cerevisiae. Here we examine the requirements for autophagy during extension of chronological life span (CLS) by calorie restriction (CR). We find that autophagy is upregulated by two CR interventions that extend CLS: water wash CR and low glucose CR. Autophagy is required for full extension of CLS during water wash CR under all growth conditions tested. In contrast, autophagy was not uniformly required for full extension of CLS during low glucose CR, depending on the atg allele and strain genetic background. Leucine status influenced CLS during CR. Eliminating the leucine requirement in yeast strains or adding supplemental leucine to growth media extended CLS during CR. In addition, we observed that both water wash and low glucose CR promote mitochondrial respiration proficiency during aging of autophagy-deficient yeast. In general, the extension of CLS by water wash or low glucose CR was inversely related to respiration deficiency in autophagy-deficient cells. Also, autophagy is required for full extension of CLS under non-CR conditions in buffered media, suggesting that extension of CLS during CR is not solely due to reduced medium acidity. Thus, our findings show that autophagy is: (1) induced by CR, (2) required for full extension of CLS by CR in most cases (depending on atg allele, strain, and leucine availability) and, (3) promotes mitochondrial respiration proficiency during aging under CR conditions.

Nutritional models of foetal programming and nutrigenomic and epigenomic dysregulations of fatty acid metabolism in the liver and heart

Barker's concept of 'foetal programming' proposes that intrauterine growth restriction (IUGR) predicts complex metabolic diseases through relationships that may be further modified by the postnatal environment. Dietary restriction and deficit in methyl donors, folate, vitamin B12, and choline are used as experimental conditions of foetal programming as they lead to IUGR and decreased birth weight. Overfeeding and deficit in methyl donors increase central fat mass and lead to a dramatic increase of plasma free fatty acids (FFA) in offspring. Conversely, supplementing the mothers under protein restriction with folic acid reverses metabolic and epigenomic phenotypes of offspring. High-fat diet or methyl donor deficiency (MDD) during pregnancy and lactation produce liver steatosis and myocardium hypertrophy that result from increased import of FFA and impaired fatty acid β-oxidation, respectively. The underlying molecular mechanisms show dysregulations related with similar decreased expression and activity of sirtuin 1 (SIRT1) and hyperacetylation of peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α). High-fat diet and overfeeding impair AMPK-dependent phosphorylation of PGC-1α, while MDD decreases PGC-1α methylation through decreased expression of PRMT1 and cellular level of S-adenosyl methionine. The visceral manifestations of metabolic syndrome are under the influence of endoplasmic reticulum (ER) stress in overnourished animal models. These mechanisms should also deserve attention in the foetal programming effects of MDD since vitamin B12 influences ER stress through impaired SIRT1 deacetylation of HSF1. Taken together, similarities and synergies of high-fat diet and MDD suggest, therefore, considering their consecutive or contemporary influence in the mechanisms of complex metabolic diseases.

Effects of severe caloric restriction from birth on the hearts of adult rats

There has been increasing evidence suggesting that a severe caloric restriction (SCR) (above 40%) has beneficial effects on the hearts of rats. However, most of the reports have focused on the effects of SCR that started in adulthood. We investigated the consequences of SCR on the hearts of rats subjected to SCR since birth (CR50). From birth to the age of 3 months, CR50 rats were fed 50% of the food that the ad libitum group (AL) was fed. Thereafter, a maximal aerobic test was performed to indirectly evaluate global cardiovascular function. Indices of contractility (+dT/dt) and relaxation (−dT/dt) were analyzed in isolated heart preparation, and cardiomyocyte diameter, number, density, and myocardium collagen content were obtained through histologic analysis. Ventricular myocytes were isolated, using standard methods to evaluate phosphorylated AKT levels, and Ca2+ handling was evaluated with a combination of Western blot analysis, intracellular Ca2+ imaging, and confocal microscopy. CR50 rats exhibited increased aerobic performance and cardiac function, as shown by the increase in ±dT/dt. Despite the smaller cardiomyocyte diameter, CR50 rats had an increased heart−body weight ratio, increased cardiomyocyte density and number, and similar levels of myocardium collagen content, compared with AL rats. AKT was hyperphosphorylated in cardiomyocytes from CR50 rats, and there were no significant differences in Ca2+ transient and SERCA2 levels in cardiomyocytes between CR50 and AL rats. Collectively, these observations reveal the beneficial effects of a 50% caloric restriction on the hearts of adult rats restricted since birth, which might involve cardiomyocyte AKT signaling.

Rapalogs and mTOR inhibitors as anti-aging therapeutics

Rapamycin, an inhibitor of mechanistic target of rapamycin (mTOR), has the strongest experimental support to date as a potential anti-aging therapeutic in mammals. Unlike many other compounds that have been claimed to influence longevity, rapamycin has been repeatedly tested in long-lived, genetically heterogeneous mice, in which it extends both mean and maximum life spans. However, the mechanism that accounts for these effects is far from clear, and a growing list of side effects make it doubtful that rapamycin would ultimately be beneficial in humans. This Review discusses the prospects for developing newer, safer anti-aging therapies based on analogs of rapamycin (termed rapalogs) or other approaches targeting mTOR signaling.

Cardiac dysfunction and oxidative stress in the metabolic syndrome: an update on antioxidant therapies

The metabolic syndrome (MetS) is a cluster of risk factors including obesity, insulin resistance, dyslipidemia, elevated blood pressure and glucose intolerance. The MetS increases the risk for cardiovascular disease (CVD) and type 2 diabetes. Each component of the MetS causes cardiac dysfunction and their combination carries additional risk. The mechanisms underlying cardiac dysfunction in the MetS are complex and might include lipid accumulation, increased fibrosis and stiffness, altered calcium homeostasis, abnormal autophagy, altered substrate utilization, mitochondrial dysfunction and increased oxidative stress. Mitochondrial and extra-mitochondrial sources of reactive oxygen species (ROS) and reduced antioxidant defense mechanisms characterize the myocardium of humans and animals with the MetS. The mechanisms for increased cardiac oxidative stress in the MetS are not fully understood but include increased fatty acid oxidation, mitochondrial dysfunction and enhanced NADPH oxidase activity. Therapies aimed to reduce oxidative stress and enhance antioxidant defense have been employed to reduce cardiac dysfunction in the MetS in animals. In contrast, large scale clinical trials using antioxidants therapies for the treatment of CVD have been disappointing because of the lack of efficacy and undesired side effects. The focus of this review is to summarize the current knowledge about the mechanisms underlying cardiac dysfunction in the MetS with a special interest in the role of oxidative stress. Finally, we will update the reader on the results obtained with natural antioxidant and mitochondria-targeted antioxidant therapies for the treatment of CVD in the MetS.

Chronic caloric restriction preserves mitochondrial function in senescence without increasing mitochondrial biogenesis

Caloric restriction (CR) mitigates many detrimental effects of aging and prolongs life span. CR has been suggested to increase mitochondrial biogenesis, thereby attenuating age-related declines in mitochondrial function, a concept that is challenged by recent studies. Here we show that lifelong CR in mice prevents age-related loss of mitochondrial oxidative capacity and efficiency, measured in isolated mitochondria and permeabilized muscle fibers. We find that these beneficial effects of CR occur without increasing mitochondrial abundance. Whole-genome expression profiling and large-scale proteomic surveys revealed expression patterns inconsistent with increased mitochondrial biogenesis, which is further supported by lower mitochondrial protein synthesis with CR. We find that CR decreases oxidant emission, increases antioxidant scavenging, and minimizes oxidative damage to DNA and protein. These results demonstrate that CR preserves mitochondrial function by protecting the integrity and function of existing cellular components rather than by increasing mitochondrial biogenesis.