Metabolic control of mitophagy

Mitochondrial dysfunction is a major hallmark of ageing and related chronic disorders. Controlled removal of damaged mitochondria by the autophagic machinery, a process known as mitophagy, is vital for mitochondrial homeostasis and cell survival. The central role of mitochondria in cellular metabolism places mitochondrial removal at the interface of key metabolic pathways affecting the biosynthesis or catabolism of acetyl-coenzyme A, nicotinamide adenine dinucleotide, polyamines, as well as fatty acids and amino acids. Molecular switches that integrate the metabolic status of the cell, like AMP-dependent protein kinase, protein kinase A, mechanistic target of rapamycin and sirtuins, have also emerged as important regulators of mitophagy. In this review, we discuss how metabolic regulation intersects with mitophagy. We place special emphasis on the metabolic regulatory circuits that may be therapeutically targeted to delay ageing and mitochondria-associated chronic diseases. Moreover, we identify outstanding knowledge gaps, such as the ill-defined distinction between basal and damage-induced mitophagy, which must be resolved to boost progress in this area.

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.

Loss of lysosomal acid lipase results in mitochondrial dysfunction and fiber switch in skeletal muscles of mice

OBJECTIVE

Lysosomal acid lipase (LAL) is the only enzyme known to hydrolyze cholesteryl esters (CE) and triacylglycerols in lysosomes at an acidic pH. Despite the importance of lysosomal hydrolysis in skeletal muscle (SM), research in this area is limited. We hypothesized that LAL may play an important role in SM development, function, and metabolism as a result of lipid and/or carbohydrate metabolism disruptions.

RESULTS

Mice with systemic LAL deficiency (Lal-/-) had markedly lower SM mass, cross-sectional area, and Feret diameter despite unchanged proteolysis or protein synthesis markers in all SM examined. In addition, Lal-/- SM showed increased total cholesterol and CE concentrations, especially during fasting and maturation. Regardless of increased glucose uptake, expression of the slow oxidative fiber marker MYH7 was markedly increased in Lal-/-SM, indicating a fiber switch from glycolytic, fast-twitch fibers to oxidative, slow-twitch fibers. Proteomic analysis of the oxidative and glycolytic parts of the SM confirmed the transition between fast- and slow-twitch fibers, consistent with the decreased Lal-/- muscle size due to the "fiber paradox". Decreased oxidative capacity and ATP concentration were associated with reduced mitochondrial function of Lal-/- SM, particularly affecting oxidative phosphorylation, despite unchanged structure and number of mitochondria. Impairment in muscle function was reflected by increased exhaustion in the treadmill peak effort test in vivo.

CONCLUSION

We conclude that whole-body loss of LAL is associated with a profound remodeling of the muscular phenotype, manifested by fiber type switch and a decline in muscle mass, most likely due to dysfunctional mitochondria and impaired energy metabolism, at least in mice.

Hallmarks of cardiovascular ageing

Normal circulatory function is a key determinant of disease-free life expectancy (healthspan). Indeed, pathologies affecting the cardiovascular system, which are growing in prevalence, are the leading cause of global morbidity, disability and mortality, whereas the maintenance of cardiovascular health is necessary to promote both organismal healthspan and lifespan. Therefore, cardiovascular ageing might precede or even underlie body-wide, age-related health deterioration. In this Review, we posit that eight molecular hallmarks are common denominators in cardiovascular ageing, namely disabled macroautophagy, loss of proteostasis, genomic instability (in particular, clonal haematopoiesis of indeterminate potential), epigenetic alterations, mitochondrial dysfunction, cell senescence, dysregulated neurohormonal signalling and inflammation. We also propose a hierarchical order that distinguishes primary (upstream) from antagonistic and integrative (downstream) hallmarks of cardiovascular ageing. Finally, we discuss how targeting each of the eight hallmarks might be therapeutically exploited to attenuate residual cardiovascular risk in older individuals.

The impact of moderate endurance exercise on cardiac telomeres and cardiovascular remodeling in obese rats

Introduction

Hypercaloric nutrition and physical inactivity cause obesity, a potential driver of myocardial apoptosis and senescence that may accelerate cardiac aging. Although physical activity reduces mortality, its impact on myocardial aging is insufficiently understood. Here we investigated the effects of a hypercaloric high-fat diet (HFD) and regular exercise training on cardiac cells telomeres and histomorphometric indices of cardiac aging.

Methods

Ninety-six 4-months old female Sprague-Dawley rats were fed for 10 months normal (ND) or a HFD diet. Half of the animals in each group performed 30 min treadmill-running sessions on 5 consecutive days per week. At study end, cardiomyocyte cross-sectional area (CSA), interstitial collagen content, vascular density, apoptotic and senescent cells, relative telomere length (RTL), and expression of telomerase-reverse transcriptase (Tert) as marker of telomere-related senescence and apoptosis were analyzed.

Results

Compared to ND, the HFD group developed obesity, higher CSA, lower capillary density and tended to have more apoptotic cardiomyocytes and interstitials cells. Myocardial RTL and the expression of Terf-1 and Terf-2 were comparable in sedentary HFD and ND animals. In the HFD group, regular moderate endurance exercise improved myocardial vascularization, but had no effect on CSA or apoptosis. Notably, the combination of exercise and HFD increased senescence when compared to sedentary ND or HFD, and reduced RTL when compared to exercise ND animals. Exercising HFD animals also showed a trend toward higher Tert expression compared to all other groups. In addition, exercise reduced Terf-1 expression regardless of diet.

Conclusion

HFD-induced obesity showed no effects on myocardial telomeres and induced only mild morphologic alterations. Summarized, long-term moderate endurance exercise partially reverses HFD-induced effects but may even trigger cardiac remodeling in the context of obesity.

Transcriptomic and proteomic profiling of human diabetic heart disease

 

Studies in animal models demonstrated the capability of type 2 diabetes (T2D) to induce cardiac dysfunction in the absence of vascular disease. However, whether and how T2D also impairs structure and function in human hearts remains poorly understood. Here, we performed transcriptional and proteomic profiling of left ventricular samples of 8 subjects with T2D, preserved EF (63,5%) and no history of ischemic heart disease (= diabetic cardiomyopathy; DbCM), 7 subjects with T2D, reduced EF (26,9%) and ischemic heart disease (= diabetic heart failure; DbHF), and 15 non-diabetic individuals with normal EF (64,7%) serving as controls. Among 1168 proteins identified by LC-MS/MS, 146 proteins were differentially regulated in DbHF, but only 66 in DbCM. Pathway analysis revealed downregulation of energy metabolic proteins, but upregulation of proteins involved in oxidative stress and inflammatory response. In DbCM, pathways of structural remodeling, cardiomyocyte proliferation, and mechanotransduction were upregulated. Bulk RNA sequencing revealed 1795 differentially regulated genes in DbHF, and 527 in DbCM, with only 128 genes being commonly regulated. DbHF, but not DbCM, could be clearly discriminated from controls by hierarchical clustering. While inflammation/immunity were major regulated pathways in DbHF, extracellular matrix remodeling and cellular growth were the most regulated pathways in DbCM. Thus, the differential regulation of biological pathways in DbCM versus DbHF suggests the existence of two distinct disease entities rather than DbHF being an advanced disease stage of DbCM.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Austrian Diabetes Society

Acetylation and phosphorylation changes to cardiac proteins in experimental HFpEF due to metabolic risk reveal targets for treatment

AIMS

Despite the high prevalence of heart failure with preserved ejection fraction (HFpEF), the pathomechanisms remain elusive and specific therapy is lacking. Disease-causing factors include metabolic risk, notably obesity. However, proteomic changes in HFpEF are poorly understood, hampering therapeutic strategies. We sought to elucidate how metabolic syndrome affects cardiac protein expression, phosphorylation and acetylation in the Zucker diabetic fatty/Spontaneously hypertensive heart failure F1 (ZSF1) rat HFpEF model, and to evaluate changes regarding their potential for treatment.

MAIN METHODS

ZSF1 obese and lean rats were fed a Purina diet up to the onset of HFpEF in the obese animals. We quantified the proteome, phosphoproteome and acetylome of ZSF1 obese versus lean heart tissues by mass spectrometry and singled out targets for site-specific evaluation.

KEY FINDINGS

The acetylome of ZSF1 obese versus lean hearts was more severely altered (21 % of proteins changed) than the phosphoproteome (9 %) or proteome (3 %). Proteomic alterations, confirmed by immunoblotting, indicated low-grade systemic inflammation and endothelial remodeling in obese hearts, but low nitric oxide-dependent oxidative/nitrosative stress. Altered acetylation in ZSF1 obese hearts mainly affected pathways important for metabolism, energy production and mechanical function, including hypo-acetylation of mechanical proteins but hyper-acetylation of proteins regulating fatty acid metabolism. Hypo-acetylation and hypo-phosphorylation of elastic titin in ZSF1 obese hearts could explain myocardial stiffening.

SIGNIFICANCE

Cardiometabolic syndrome alters posttranslational modifications, notably acetylation, in experimental HFpEF. Pathway changes implicate a HFpEF signature of low-grade inflammation, endothelial dysfunction, metabolic and mechanical impairment, and suggest titin stiffness and mitochondrial metabolism as promising therapeutic targets.

Cardiac PI3K p110α attenuation delays aging and extends lifespan

Phosphoinositide 3-kinase (PI3K) is a key component of the insulin signaling pathway that controls cellular me-tabolism and growth. Loss-of-function mutations in PI3K signaling and other downstream effectors of the insulin signaling pathway extend the lifespan of various model organisms. However, the pro-longevity effect appears to be sex-specific and young mice with reduced PI3K signaling have increased risk of cardiac disease. Hence, it remains elusive as to whether PI3K inhibition is a valid strategy to delay aging and extend healthspan in humans. We recently demonstrated that reduced PI3K activity in cardiomyocytes delays cardiac growth, causing subnormal contractility and cardiopulmonary functional capacity, as well as increased risk of mortality at young age. In stark contrast, in aged mice, experi-mental attenuation of PI3K signaling reduced the age-dependent decline in cardiac function and extended maximal lifespan, suggesting a biphasic effect of PI3K on cardiac health and survival. The cardiac anti-aging effects of reduced PI3K activity coincided with enhanced oxida-tive phosphorylation and required increased autophagic flux. In humans, explanted failing hearts showed in-creased PI3K signaling, as indicated by increased phos-phorylation of the serine/threonine-protein kinase AKT. Hence, late-life cardiac-specific targeting of PI3K might have a therapeutic potential in cardiac aging and related diseases.

Spermidine overrides INSR (insulin receptor)-IGF1R (insulin-like growth factor 1 receptor)-mediated inhibition of autophagy in the aging heart

Although attenuated IGF1R (insulin-like growth factor 1 receptor) signaling has long been viewed to promote longevity in model organisms, adverse effects on the heart have been the subject of major concern. We observed that IGF1R is overexpressed in cardiac tissues from patients with end-stage non-ischemic heart failure, coupled to the activation of the IGF1R downstream effector AKT/protein kinase B and inhibition of ULK1 (unc-51 like autophagy activating kinase 1). Transgenic overexpression of human IGF1R in cardiomyocytes from mice initially induces physiological cardiac hypertrophy and superior function, but later in life confers a negative impact on cardiac health, causing macroautophagy/autophagy inhibition as well as impaired oxidative phosphorylation, thus reducing life expectancy. Treatment with the autophagy inducer and caloric restriction mimetic spermidine ameliorates most of these IGF1R-induced cardiotoxic effects in vivo. Moreover, inhibition of IGF1R signaling by means of a dominant-negative phosphoinositide 3-kinase (PI3K) mutant induces cardioprotective autophagy, restores myocardial bioenergetics and improves late-life survival. Hence, our results demonstrate that IGF1R exerts a dual biphasic impact on cardiac health, and that autophagy mediates the late-life geroprotective effects of IGF1R inhibition in the heart.

miR-1183 Is a Key Marker of Remodeling upon Stretch and Tachycardia in Human Myocardium

Many cardiac insults causing atrial remodeling are linked to either stretch or tachycardia, but a comparative characterization of their effects on early remodeling events in human myocardium is lacking. Here, we applied isometric stretch or sustained tachycardia at 2.5 Hz in human atrial trabeculae for 6 h followed by microarray gene expression profiling. Among largely independent expression patterns, we found a small common fraction with the microRNA miR-1183 as the highest up-regulated transcript (up to 4-fold). Both, acute stretch and tachycardia induced down-regulation of the predicted miR-1183 target genes ADAM20 and PLA2G7. Furthermore, miR-1183 was also significantly up-regulated in chronically remodeled atrial samples from patients with persistent atrial fibrillation (3-fold up-regulation versus sinus rhythm samples), and in ventricular myocardium from dilative cardiomyopathy hearts (2-fold up-regulation) as compared to non-failing controls. In sum, although stretch and tachycardia show distinct transcriptomic signatures in human atrial myocardium, both cardiac insults consistently regulate the expression of miR-1183 and its downstream targets in acute and chronic remodeling. Thus, elevated expression of miR-1183 might serve as a tissue biomarker for atrial remodeling and might be of potential functional significance in cardiac disease.

Fine-Tuning Cardiac Insulin-Like Growth Factor 1 Receptor Signaling to Promote Health and Longevity

BACKGROUND

The insulin-like growth factor 1 (IGF1) pathway is a key regulator of cellular metabolism and aging. Although its inhibition promotes longevity across species, the effect of attenuated IGF1 signaling on cardiac aging remains controversial.

METHODS

We performed a lifelong study to assess cardiac health and lifespan in 2 cardiomyocyte-specific transgenic mouse models with enhanced versus reduced IGF1 receptor (IGF1R) signaling. Male mice with human IGF1R overexpression or dominant negative phosphoinositide 3-kinase mutation were examined at different life stages by echocardiography, invasive hemodynamics, and treadmill coupled to indirect calorimetry. In vitro assays included cardiac histology, mitochondrial respiration, ATP synthesis, autophagic flux, and targeted metabolome profiling, and immunoblots of key IGF1R downstream targets in mouse and human explanted failing and nonfailing hearts, as well.

RESULTS

Young mice with increased IGF1R signaling exhibited superior cardiac function that progressively declined with aging in an accelerated fashion compared with wild-type animals, resulting in heart failure and a reduced lifespan. In contrast, mice with low cardiac IGF1R signaling exhibited inferior cardiac function early in life, but superior cardiac performance during aging, and increased maximum lifespan, as well. Mechanistically, the late-life detrimental effects of IGF1R activation correlated with suppressed autophagic flux and impaired oxidative phosphorylation in the heart. Low IGF1R activity consistently improved myocardial bioenergetics and function of the aging heart in an autophagy-dependent manner. In humans, failing hearts, but not those with compensated hypertrophy, displayed exaggerated IGF1R expression and signaling activity.

CONCLUSIONS

Our findings indicate that the relationship between IGF1R signaling and cardiac health is not linear, but rather biphasic. Hence, pharmacological inhibitors of the IGF1 pathway, albeit unsuitable for young individuals, might be worth considering in older adults.

Basal oxidation of conserved cysteines modulates cardiac titin stiffness and dynamics

Titin, as the main protein responsible for the passive stiffness of the sarcomere, plays a key role in diastolic function and is a determinant factor in the etiology of heart disease. Titin stiffness depends on unfolding and folding transitions of immunoglobulin-like (Ig) domains of the I-band, and recent studies have shown that oxidative modifications of cryptic cysteines belonging to these Ig domains modulate their mechanical properties in vitro. However, the relevance of this mode of titin mechanical modulation in vivo remains largely unknown. Here, we describe the high evolutionary conservation of titin mechanical cysteines and show that they are remarkably oxidized in murine cardiac tissue. Mass spectrometry analyses indicate a similar landscape of basal oxidation in murine and human myocardium. Monte Carlo simulations illustrate how disulfides and S-thiolations on these cysteines increase the dynamics of the protein at physiological forces, while enabling load- and isoform-dependent regulation of titin stiffness. Our results demonstrate the role of conserved cysteines in the modulation of titin mechanical properties in vivo and point to potential redox-based pathomechanisms in heart disease.

NAD+ and Vascular Dysfunction: From Mechanisms to Therapeutic Opportunities

Nicotinamide adenine dinucleotide (NAD+) is an essential and pleiotropic coenzyme involved not only in cellular energy metabolism, but also in cell signaling, epigenetic regulation, and post-translational protein modifications. Vascular disease risk factors are associated with aberrant NAD+ metabolism. Conversely, the therapeutic increase of NAD+ levels through the administration of NAD+ precursors or inhibitors of NAD+-consuming enzymes reduces chronic low-grade inflammation, reactivates autophagy and mitochondrial biogenesis, and enhances oxidative metabolism in vascular cells of humans and rodents with vascular pathologies. As such, NAD+ has emerged as a potential target for combatting age-related cardiovascular and cerebrovascular disorders. This review discusses NAD+-regulated mechanisms critical for vascular health and summarizes new advances in NAD+ research directly related to vascular aging and disease, including hypertension, atherosclerosis, coronary artery disease, and aortic aneurysms. Finally, we enumerate challenges and opportunities for NAD+ repletion therapy while anticipating the future of this exciting research field, which will have a major impact on vascular medicine.

Effects of Atrial Fibrillation on the Human Ventricle

RATIONALE

Atrial fibrillation (AF) and heart failure often coexist, but their interaction is poorly understood. Clinical data indicate that the arrhythmic component of AF may contribute to left ventricular (LV) dysfunction.

OBJECTIVE

This study investigates the effects and molecular mechanisms of AF on the human LV.

METHODS AND RESULTS

Ventricular myocardium from patients with aortic stenosis and preserved LV function with sinus rhythm or rate-controlled AF was studied. LV myocardium from patients with sinus rhythm and patients with AF showed no differences in fibrosis. In functional studies, systolic Ca2+ transient amplitude of LV cardiomyocytes was reduced in patients with AF, while diastolic Ca2+ levels and Ca2+ transient kinetics were not statistically different. These results were confirmed in LV cardiomyocytes from nonfailing donors with sinus rhythm or AF. Moreover, normofrequent AF was simulated in vitro using arrhythmic or rhythmic pacing (both at 60 bpm). After 24 hours of AF-simulation, human LV cardiomyocytes from nonfailing donors showed an impaired Ca2+ transient amplitude. For a standardized investigation of AF-simulation, human iPSC-cardiomyocytes were tested. Seven days of AF-simulation caused reduced systolic Ca2+ transient amplitude and sarcoplasmic reticulum Ca2+ load likely because of an increased diastolic sarcoplasmic reticulum Ca2+ leak. Moreover, cytosolic Na+ concentration was elevated and action potential duration was prolonged after AF-simulation. We detected an increased late Na+ current as a potential trigger for the detrimentally altered Ca2+/Na+-interplay. Mechanistically, reactive oxygen species were higher in the LV of patients with AF. CaMKII (Ca2+/calmodulin-dependent protein kinase IIδc) was found to be more oxidized at Met281/282 in the LV of patients with AF leading to an increased CaMKII activity and consequent increased RyR2 phosphorylation. CaMKII inhibition and ROS scavenging ameliorated impaired systolic Ca2+ handling after AF-simulation.

CONCLUSIONS

AF causes distinct functional and molecular remodeling of the human LV. This translational study provides the first mechanistic characterization and the potential negative impact of AF in the absence of tachycardia on the human ventricle.

Effects of Short Term Adiponectin Receptor Agonism on Cardiac Function and Energetics in Diabetic db/db Mice

Objective

Impaired cardiac efficiency is a hallmark of diabetic cardiomyopathy in models of type 2 diabetes. Adiponectin receptor 1 (AdipoR1) deficiency impairs cardiac efficiency in non-diabetic mice, suggesting that hypoadiponectinemia in type 2 diabetes may contribute to impaired cardiac efficiency due to compromised AdipoR1 signaling. Thus, we investigated whether targeting cardiac adiponectin receptors may improve cardiac function and energetics, and attenuate diabetic cardiomyopathy in type 2 diabetic mice.

Methods

A non-selective adiponectin receptor agonist, AdipoRon, and vehicle were injected intraperitoneally into Eight-week-old db/db or C57BLKS/J mice for 10 days. Cardiac morphology and function were evaluated by echocardiography and working heart perfusions.

Results

Based on echocardiography, AdipoRon treatment did not alter ejection fraction, left ventricular diameters or left ventricular wall thickness in db/db mice compared to vehicle-treated mice. In isolated working hearts, an impairment in cardiac output and efficiency in db/db mice was not improved by AdipoRon. Mitochondrial respiratory capacity, respiration in the presence of oligomycin, and 4-hydroxynonenal levels were similar among all groups. However, AdipoRon induced a marked shift in the substrate oxidation pattern in db/db mice towards increased reliance on glucose utilization. In parallel, the diabetes-associated increase in serum triglyceride levels in vehicle-treated db/db mice was blunted by AdipoRon treatment, while an increase in myocardial triglycerides in vehicle-treated db/db mice was not altered by AdipoRon treatment.

Conclusion

AdipoRon treatment shifts myocardial substrate preference towards increased glucose utilization, likely by decreasing fatty acid delivery to the heart, but was not sufficient to improve cardiac output and efficiency in db/db mice.

Spermidine supplementation influences mitochondrial number and morphology in the heart of aged mice

Aging is associated with cardiac hypertrophy and progressive decline in heart function. One of the hallmarks of cellular aging is the dysfunction of mitochondria. These organelles occupy around 1/4 to 1/3 of the cardiomyocyte volume. During cardiac aging, the removal of defective or dysfunctional mitochondria by mitophagy as well as the dynamic equilibrium between mitochondrial fusion and fission is distorted. Here, we hypothesized that these changes affect the number of mitochondria and alter their three-dimensional (3D) characteristics in aged mouse hearts. The polyamine spermidine stimulates both mitophagy and mitochondrial biogenesis, and these are associated with improved cardiac function and prolonged lifespan. Therefore, we speculated that oral spermidine administration normalizes the number of mitochondria and their 3D morphology in aged myocardium. Young (4-months old) and old (24-months old) mice, treated or not treated with spermidine, were used in this study (n = 10 each). The number of mitochondria in the left ventricles was estimated by design-based stereology using the Euler-Poincaré characteristic based on a disector at the transmission electron microscopic level. The 3D morphology of mitochondria was investigated by 3D reconstruction (using manual contour drawing) from electron microscopic z-stacks obtained by focused ion beam scanning electron microscopy. The volume of the left ventricle and cardiomyocytes were significantly increased in aged mice with or without spermidine treatment. Although the number of mitochondria was similar in young and old control mice, it was significantly increased in aged mice treated with spermidine. The interfibrillar mitochondria from old mice exhibited a lower degree of organization and a greater variation in shape and size compared to young animals. The mitochondrial alignment along the myofibrils in the spermidine-treated mice appeared more regular than in control aged mice, however, old mitochondria from animals fed spermidine also showed a greater diversity of shape and size than young mitochondria. In conclusion, mitochondria of the aged mouse left ventricle exhibited changes in number and 3D ultrastructure that is likely the structural correlate of dysfunctional mitochondrial dynamics. Spermidine treatment reduced, at least in part, these morphological changes, indicating a beneficial effect on cardiac mitochondrial alterations associated with aging.

NAD+ Metabolism in Cardiac Health, Aging, and Disease

Nicotinamide adenine dinucleotide (NAD⁺) is a central metabolite involved in energy and redox homeostasis as well as in DNA repair and protein deacetylation reactions. Pharmacological or genetic inhibition of NAD⁺-degrading enzymes, external supplementation of NAD⁺ precursors, and transgenic overexpression of NAD⁺-generating enzymes have wide positive effects on metabolic health and age-associated diseases. NAD⁺ pools tend to decline with normal aging, obesity, and hypertension, which are all major risk factors for cardiovascular disease, and NAD⁺ replenishment extends healthspan, avoids metabolic syndrome, and reduces blood pressure in preclinical models. In addition, experimental elevation of NAD⁺ improves atherosclerosis, ischemic, diabetic, arrhythmogenic, hypertrophic, or dilated cardiomyopathies, as well as different modalities of heart failure. Here, we critically discuss cardiomyocyte-specific circuitries of NAD⁺ metabolism, comparatively evaluate distinct NAD⁺ precursors for their preclinical efficacy, and raise outstanding questions on the optimal design of clinical trials in which NAD⁺ replenishment or supraphysiological NAD⁺ elevations are assessed for the prevention or treatment of major cardiac diseases. We surmise that patients with hitherto intractable cardiac diseases such as heart failure with preserved ejection fraction may profit from the administration of NAD⁺ precursors. The development of such NAD⁺-centered treatments will rely on technological and conceptual progress on the fine regulation of NAD⁺ metabolism.

Autophagy-related gene 5 (Atg5) is required for maintaining subcellular calcium homeostasis during acute cardiac stress

Background

Autophagy exerts protective effects during cardiac stress inflicted by β-adrenergic stimulation and pressure overload. Contrarily, deletion of the cardiac-specific Atg5 gene contributes to left ventricular hypertrophy and contractile dysfunction, resulting in dilated cardiomyopathy. Heart failure is characterized by perturbations of excitation-contraction coupling (ECC) underlying alterations in intracellular calcium signaling.

Purpose

In this study, we aimed to understand whether loss of basal autophagy due to Atg5 deletion specifically in cardiomyocytes contributes directly to disturbances in subcellular calcium cycling.

Methods

Cardiac-specific Atg5−/− and Atg5+/+ mice were used to isolate ventricular cardiomyocytes, which were loaded with 8 μM Ca2+ indicator Fluo4/AM. Isolated cells were electrically stimulated and subjected to elevated workload by increasing pacing frequencies from 1 to 4 Hz. Cytosolic and nuclear calcium transients (CaTs) were recorded in line-scan mode using a laser scanning confocal microscope. Pharmacological inhibition of autophagic flux was performed by an intraperitoneal injection of 40 mg/kg leupeptin to Atg5+/+ mice.

Results

At baseline (1 Hz) stimulation the amplitude and kinetics of calcium transients were comparable between Atg5−/− and Atg5+/+ cells. However, after progressive increase of the pacing rate from 1 Hz to 4 Hz, Atg5−/− cardiomyocytes displayed reduced cytoplasmic and nuclear CaT amplitude, but increased nuclear time-averaged CaTs compared to controls. Such increase in nuclear calcium load stimulates Ca2+-dependent transcriptional activity, and likely involves CaMKII-mediated pro-hypertrophic gene program thus contributing to cardiac remodelling. In addition, we observed increased occurrence of arrhythmic events in Atg5−/− hearts at high pacing frequency, indicative of intracellular calcium overload and disturbed ECC. Acute pharmacological autophagy inhibition failed to elicit direct changes in time-averaged CaTs in the cytoplasm and nucleoplasm, suggesting that loss of Atg5-dependent autophagy seems to induce adverse cardiac remodelling that involves increased CaMKII activity due to the imbalances in nuclear Ca2+ levels.

Conclusion

Specific loss of ATG5 protein impairs calcium cycling during acute stress exposure by reducing CaT amplitudes, promoting arrhythmia, and increasing nuclear calcium load, which may induce hypertrophic gene expression. Further work is needed to identify key components mediating autophagy-related cardioprotection to develop strategies against cardiac remodeling and its progression to heart failure.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Austrian Science Fund (FWF)

Effects of atrial fibrillation on ventricular remodeling in the human heart

 

Atrial fibrillation (AF) is often found in patients with heart failure (HF). Clinical data indicated that the arrhythmic component of AF alone could contribute to left-ventricular (LV) dysfunction. However, the effects of non-tachycardic AF with arrhythmic excitation of the human LV, are unknown.

We investigated human LV myocardium from patients with sinus rhythm (SR) or normofrequent AF (mean EF>50%, matched clinical data, derived from septal resections during AVR). In histological analysis we detected no difference between SR (n=17 patients) and AF patients (n=18) regarding the amount and distribution of fibrosis. We isolated human LV cardiomyocytes (CM) and studied cellular Ca-handling (Fura-2). Systolic Ca-transient amplitude of LV CM was reduced in patients suffering from AF (n=8 AF patients vs. 11 SR), while diastolic Ca-levels and Ca-transient kinetics were not significantly changed. These results were confirmed in LV CM from non-failing donors (NF) with AF (n=4 AF patients vs. 8 SR). For the standardized investigation of a normofrequent arrhythmia, we simulated AF in vitro by using arrhythmic (60 bpm, 40% beat-to-beat variability) or rhythmic (60 bpm) field stimulation. Human LV CM from NF SR patients (n=8) showed an impaired Ca-transient amplitude after 24h arrhythmic culture pacing without changes in diastolic Ca and Ca-transient kinetics. For studying a model suitable for more standardized chronic pacing, we utilized human iPSC cardiomyocytes (iPSC-CM) from healthy donors (n=6). After 7 days, arrhythmically paced iPSC-CM exhibited a reduced systolic Ca-transient amplitude, a trend towards a prolonged Ca-elimination time and a reduced sarcoplasmic reticulum Ca-load. Confocal line-scans of arrhythmically paced cells (Fluo-4 AM) showed an increased diastolic Ca-leak from the sarcoplasmic reticulum, possibly underlying the reduced Ca-load. Coupled with the Ca changes, cytosolic Na was elevated after arrhythmia. We found an increased late INa, which could explain the detrimentally altered Ca/Na-interplay. Accordingly, Patch-clamp experiments revealed a prolonged action potential duration after arrhythmia. We further elucidated the underlying mechanisms of this electrophysiological remodeling by showing that oxidative stress (H2O2, LPO) is increased in the LV of patients suffering from AF (n=6 AF patients vs. 6 SR), which was associated with an enhanced NOX2/-4 activity. Consecutively, Ca2+/calmodulin-dependent protein kinase IIδ (CaMKII) was found to be more oxidized (CaMKII-Met281/282) in the LV of AF patients (n=7 AF patients vs. 7 SR) leading to an increased CaMKII activity, which adversely regulated EC-coupling protein phosphorylation including RyR2 hyperphosphorylation.

Normofrequent arrhythmia/AF impairs human ventricular EC-coupling via increased oxidative stress and enhanced CaMKII. Thus, this translational study provides the first mechanistic characterization and the potential negative impact of isolated AF on the human LV.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): Else Kröner-Fresenius-Stiftung (EKFS) and Deutsche Gesellschaft für Innere Medizin

Altered spatio-specific CaMKII activation in autophagy deficient mice

Background

Autophagy is linked to preventing the development of cardiac hypertrophy and failure. While aberrant activation of Ca2+/calmodulin-dependent kinase II (CaMKII) promotes myocardial remodeling, the role of autophagy in maintaining cardiac Ca2+ homeostasis and regulating CaMKII signaling is unknown.

Objective

To test whether loss of autophagy promotes subcellular alterations in CaMKII activation in early myocardial remodelling, and whether compromised in vivo cardiac function parallels those changes.

Methods

Young (10–15 weeks) cardiomyocyte-specific autophagy protein 5-deficient mice (Atg5−/−) mice and their littermate controls (Atg5+/+) underwent comprehensive in vivo phenotyping using echocardiography, exercise tolerance and hemodynamic stress testing. In vitro assessment included gravimetry, qPCR of hypertrophy marker genes and cellular and nuclear dimensions of isolated ventricular myocytes. CaMKII activation was studied by immunocytochemistry in cardiomyocytes upon exposure to basal (1Hz) or high (4Hz) pacing frequency. Autophosphorylated CaMKII (pT286) signal was evaluated in different subcellular spaces (i.e. cytoplasm, nucleoplasm and nuclear envelope).

Results

Before symptomatic cardiac dysfunction occurred, Atg5−/− mice showed compromised cardiac reserve in response to β-adrenergic stimulation (dp/dt max: 9475±126 vs 7364±496 mmHg/s, N=4–5; p=0.041), despite similar maximum heart rate. Consequently, effort intolerance (distance run: 251±22 vs 152±13 m, N=8; p=0.03) and maximal oxygen consumption (2093±66 vs 1763±131 ml/h/kg, N=8; p=0.04) were reduced during treadmill exercise tolerance testing. Increased heart-to-body weight ratio (8.1±0.5 vs 10.2±0.8 N=9; p=0.017) was associated with elevated mRNA expression of hypertrophy marker NppB (278% of Atg5+/+, N=5; p=0.016) in Atg5−/− mice, which showed enlarged cardiomyocytes and nuclei, as width-to-length ratio.

Because Atg5−/− cardiomyocytes exhibit elevated nuclear Ca2+ levels at high pacing frequency, we now measured subcellular CaMKII activation under the same experimental conditions. Interestingly, at 1Hz, p-CaMKII was increased specifically at the nuclear envelope (154% of Atg5+/+, N=5 mice, 153–159 cells; p=0.029), but not in the cytoplasm or nucleoplasm. Increasing pacing frequency to 4Hz did not alter p-CaMKII levels in Atg5+/+ cells. However, p-CaMKII was increased by ∼30% and ∼20% in the cytoplasm and nucleoplasm of Atg5−/− cells respectively (N=5 mice, 153–155 cells).

Conclusion

Loss of ATG5-dependent autophagy causes cardiac hypertrophy and impaired cardiac reserve upon acute stress, which involves CaMKII activation, likely through the imbalance of nuclear Ca2+ load. Although, selective increase in p-CaMKII at the nuclear envelope in Atg5−/− mice may temporarily protect from nuclear Ca2+ overload, excessive CaMKII activation in the cytoplasm and the nucleoplasm upon increased workload, likely drives hypertrophic signalling toward heart failure in autophagy-defective mice.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Austrian Science Fund (FWF)

Targeting Cardiovascular Risk Factors Through Dietary Adaptations and Caloric Restriction Mimetics

The average human life expectancy continues to rise globally and so does the prevalence and absolute burden of cardiovascular disease. Dietary restriction promotes longevity and improves various cardiovascular risk factors, including hypertension, obesity, diabetes mellitus, and metabolic syndrome. However, low adherence to caloric restriction renders this stringent dietary intervention challenging to adopt as a standard practice for cardiovascular disease prevention. Hence, alternative eating patterns and strategies that recapitulate the salutary benefits of caloric restriction are under intense investigation. Here, we first provide an overview of alternative interventions, including intermittent fasting, alternate-day fasting and the Mediterranean diet, along with their cardiometabolic effects in animal models and humans. We then present emerging pharmacological alternatives, including spermidine, NAD+ precursors, resveratrol, and metformin, as promising caloric restriction mimetics, and briefly touch on the mechanisms underpinning their cardiometabolic and health-promoting effects. We conclude that implementation of feasible dietary approaches holds the promise to attenuate the burden of cardiovascular disease and facilitate healthy aging in humans.

The effects of long-term moderate exercise and Western-type diet on oxidative/nitrosative stress, serum lipids and cytokines in female Sprague Dawley rats

Purpose

Regular exercise reduces obesity and the risk of cardiovascular disease. However, health-promoting benefits of physical activity are commonly associated with increased inflammation and oxidative stress. Here, we tested whether constant moderate exercise is able to prevent or attenuate the oxidative/nitrosative stress, inflammation, and serum lipids in lean and obese rats.

Methods

Four-month-old female Sprague Dawley rats received standard or a high-fat diet. Animals were subjected to a physical activity protocol, consisting of 30 min forced treadmill exercise for 5 consecutive days per week during 10 months. Baseline and sedentary (non-exercised) rats were used as controls. Lipids, oxidized low-density lipoprotein cholesterol, nitric oxide metabolites, and pro- and anti-inflammatory markers were measured in blood collected upon euthanasia.

Results

At variance to young baseline control rats, 14-month-old animals fed normal diet had increased plasma lipid levels, including total cholesterol and triglycerides, which were further elevated in rats that consumed a high-fat diet. While treadmill exercise did not lower the amount of serum lipids in standard diet group, forced physical activity reduced non-high-density lipoprotein cholesterol in response to high-fat diet feeding. Exercised rats fed standard diet or high-fat diet had lower abundancy of nitric oxide metabolites, which coincided with increased levels of oxidized low-density lipoprotein cholesterol. Accordingly, the amount of nitric oxide metabolites correlated inversely with oxidized low-density lipoprotein cholesterol and homo-arginine. Exercise significantly reduced inflammatory cytokines in high-fat diet fed rats only.

Conclusion

Our study suggests that regular exercise alters the equilibrium between oxidative and anti-oxidative compounds and reduces pro-inflammatory cytokines.

Nicotinamide for the treatment of heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is a highly prevalent and intractable form of cardiac decompensation commonly associated with diastolic dysfunction. Here, we show that diastolic dysfunction in patients with HFpEF is associated with a cardiac deficit in nicotinamide adenine dinucleotide (NAD⁺). Elevating NAD⁺ by oral supplementation of its precursor, nicotinamide, improved diastolic dysfunction induced by aging (in 2-year-old C57BL/6J mice), hypertension (in Dahl salt-sensitive rats), or cardiometabolic syndrome (in ZSF1 obese rats). This effect was mediated partly through alleviated systemic comorbidities and enhanced myocardial bioenergetics. Simultaneously, nicotinamide directly improved cardiomyocyte passive stiffness and calcium-dependent active relaxation through increased deacetylation of titin and the sarcoplasmic reticulum calcium adenosine triphosphatase 2a, respectively. In a long-term human cohort study, high dietary intake of naturally occurring NAD⁺ precursors was associated with lower blood pressure and reduced risk of cardiac mortality. Collectively, these results suggest NAD⁺ precursors, and especially nicotinamide, as potential therapeutic agents to treat diastolic dysfunction and HFpEF in humans.

Editorial of Special Issue "Sirtuins in Health and Disease"

The discovery and characterization of sirtuins as NAD+-dependent deacylases have transformed our understanding of post-translational protein regulation [...].

Dietary spermidine improves cognitive function

Decreased cognitive performance is a hallmark of brain aging, but the underlying mechanisms and potential therapeutic avenues remain poorly understood. Recent studies have revealed health-protective and lifespan-extending effects of dietary spermidine, a natural autophagy-promoting polyamine. Here, we show that dietary spermidine passes the blood-brain barrier in mice and increases hippocampal eIF5A hypusination and mitochondrial function. Spermidine feeding in aged mice affects behavior in homecage environment tasks, improves spatial learning, and increases hippocampal respiratory competence. In a Drosophila aging model, spermidine boosts mitochondrial respiratory capacity, an effect that requires the autophagy regulator Atg7 and the mitophagy mediators Parkin and Pink1. Neuron-specific Pink1 knockdown abolishes spermidine-induced improvement of olfactory associative learning. This suggests that the maintenance of mitochondrial and autophagic function is essential for enhanced cognition by spermidine feeding. Finally, we show large-scale prospective data linking higher dietary spermidine intake with a reduced risk for cognitive impairment in humans.

Loss of autophagy protein ATG5 impairs cardiac capacity in mice and humans through diminishing mitochondrial abundance and disrupting Ca2+ cycling

Aims

Autophagy protects against the development of cardiac hypertrophy and failure. While aberrant Ca²⁺ handling promotes myocardial remodelling and contributes to contractile dysfunction, the role of autophagy in maintaining Ca²⁺ homeostasis remains elusive. Here, we examined whether Atg5 deficiency-mediated autophagy promotes early changes in subcellular Ca²⁺ handling in ventricular cardiomyocytes, and whether those alterations associate with compromised cardiac reserve capacity, which commonly precedes the onset of heart failure.

Methods and results

RT–qPCR and immunoblotting demonstrated reduced Atg5 gene and protein expression and decreased abundancy of autophagy markers in hypertrophied and failing human hearts. The function of ATG5 was examined using cardiomyocyte-specific Atg5-knockout mice (Atg5^−/−). Before manifesting cardiac dysfunction, Atg5^−/− mice showed compromised cardiac reserve in response to β-adrenergic stimulation. Consequently, effort intolerance and maximal oxygen consumption were reduced during treadmill-based exercise tolerance testing. Mechanistically, cellular imaging revealed that Atg5 deprivation did not alter spatial and functional organization of intracellular Ca²⁺ stores or affect Ca²⁺ cycling in response to slow pacing or upon acute isoprenaline administration. However, high-frequency stimulation exposed stunted amplitude of Ca²⁺ transients, augmented nucleoplasmic Ca²⁺ load, and increased CaMKII activity, especially in the nuclear region of hypertrophied Atg5^−/− cardiomyocytes. These changes in Ca²⁺ cycling were recapitulated in hypertrophied human cardiomyocytes. Finally, ultrastructural analysis revealed accumulation of mitochondria with reduced volume and size distribution, meanwhile functional measurements showed impaired redox balance in Atg5^−/− cardiomyocytes, implying energetic unsustainability due to overcompensation of single mitochondria, particularly under increased workload.

Conclusion

Loss of cardiac Atg5-dependent autophagy reduces mitochondrial abundance and causes subtle alterations in subcellular Ca²⁺ cycling upon increased workload in mice. Autophagy-related impairment of Ca²⁺ handling is progressively worsened by β-adrenergic signalling in ventricular cardiomyocytes, thereby leading to energetic exhaustion and compromised cardiac reserve.

Mass Spectrometry-Based Redox and Protein Profiling of Failing Human Hearts

Oxidative stress contributes to detrimental functional decline of the myocardium, leading to the impairment of the antioxidative defense, dysregulation of redox signaling, and protein damage. In order to precisely dissect the changes of the myocardial redox state correlated with oxidative stress and heart failure, we subjected left-ventricular tissue specimens collected from control or failing human hearts to comprehensive mass spectrometry-based redox and quantitative proteomics, as well as glutathione status analyses. As a result, we report that failing hearts have lower glutathione to glutathione disulfide ratios and increased oxidation of a number of different proteins, including constituents of the contractile machinery as well as glycolytic enzymes. Furthermore, quantitative proteomics of failing hearts revealed a higher abundance of proteins responsible for extracellular matrix remodeling and reduced abundance of several ion transporters, corroborating contractile impairment. Similar effects were recapitulated by an in vitro cell culture model under a controlled oxygen atmosphere. Together, this study provides to our knowledge the most comprehensive report integrating analyses of protein abundance and global and peptide-level redox state in end-stage failing human hearts as well as oxygen-dependent redox and global proteome profiles of cultured human cardiomyocytes.

MIR1183 as a new tissue biomarker with triggered acute response and upregulation in chronic atrial and ventricular remodeling

Background and purpose

Cardiac remodeling can be caused by a variety of insults linked to either stretch or tachycardia as a triggering mechanism. We aimed to investigate similarities and differences of the transcriptomic profiles in response to either acute stretch or tachycardia in isolated human atrial myocardium. In addition, we tested the highest acutely regulated target for its chronic regulation in human tissue with atrial or ventricular cardiac remodeling.

Methods

For acute trigger testing we applied either stretch (high pre- and afterload) or sustained tachycardia (2.5 Hz) for 6 hours in isolated atrial human trabeculae from cardiac surgery patients (all in sinus rhythm, SR). We performed gene expression profiling by RNA microarrays (n=5 per group) as a remodeling readout. For chronic regulation we performed qPCR of selected genes of interest in right atrial appendage tissue obtained from cardiac surgery patients with persistent atrial fibrillation compared to control patients with SR (n=6 per group), and also in ventricular tissue samples from failing hearts (from transplanted dilative cardiomyopathy patients) or non-failing control hearts (from multi-organ donors denied for transplantation), n=6 per group.

Results

The expression patterns of stretch and tachycardia were largely independent with 1305 transcripts regulated solely by stretch and 1837 transcripts by tachycardia with p<0.05. In contrast, the fraction of commonly regulated genes was small (65 transcripts with p<0.05). However, this fraction contained the strongest upregulated transcript, the microRNA precursor gene MIR1183, which was similarly upregulated by both triggers (4.1fold in stretch and 2.7fold in tachycardia, both p<0.05). MIR1183 also showed upregulation in two important chronic remodeling settings: In atrial samples with persistent atrial fibrillation in comparison to sinus rhythm, it was 2.8fold upregulated, and in ventricular samples from dilative cardiomyopathy hearts it was 1.6fold upregulated (p<0.05 for both). A functional role of MIR1183 in remodeling was also suggested by significant downregulation of its predicted downstream target genes ADAM20 and PLA2G7. Our ongoing research aims to confirm upregulation also in the circulating expression levels of the mature form of MIR1183 in human plasma samples in a cohort of atrial fibrillation patients with diseased atria, these findings will also be presented at scientific sessions.

Conclusion

Stretch and tachycardia show distinct transcriptomic signatures in human atrial trabeculae but share the strongest upregulated gene MIR1183 and consistent regulation of its downstream targets. This is present in an acute as well as chronic remodeling setting. Expression levels of MIR1183 might serve as a biomarker for atrial remodeling and to some extend ventricular remodeling and have potential functional significance in cardiac disease.

Funding Acknowledgement

Type of funding source: Public Institution(s). Main funding source(s): Medical University of Graz

Atrial fibrillation impairs ventricular function by altering excitation-contraction coupling in the human heart

 

Atrial fibrillation (AF) often co-exists in patients with heart failure (HF). Recent clinical evidence suggests that the arrhythmic component of AF alone may contribute to ventricular dysfunction. However, the pathophysiological effects of a non-tachycardic AF on the human ventricle are unknown. To investigate the effects of normofrequent AF on the human ventricle we investigated ventricular myocardium from patients with preserved ejection fraction with sinus rhythm (SR) or AF in the absence of HF (compensated hypertrophy, EF>50%, matched clinical characteristics). In histological analysis we detected no difference between SR (n=9) vs. AF (n=6) regarding the amount and distribution of fibrosis. For functional investigation, Ca-handling was studied (Fura-2 AM). While systolic Ca-transient amplitude was in trend reduced in isolated human ventricular AF cardiomyocytes, we found a significantly prolonged Ca-elimination time (n=17–22 cells/4 pat.). Using caffeine application, a decreased SR Ca-load in AF was detected, which may be explained by a significant decrease in SERCA2a activity (ksys-kCaff, n=10–12/4 pat.). Patch-clamp experiments revealed a prolonged action potential duration in AF cardiomyocytes (n=5/15 cells).

For the standardized evaluation of the mechanisms of persistent normofrequent arrhythmia, we simulated AF in vitro by using arrhythmic (1 Hz, 40% R-R-variability) or rhythmic (1 Hz) field stimulation. We performed contractility experiments using in-toto isolated human ventricular trabeculae from explanted human hearts. After 8h of pacing, arrhythmically stimulated human trabeculae showed a significantly reduced systolic force, an increase in diastolic tension and a prolonged relaxation (n=11–12 trabeculae/11 pat.). For studying the cellular effects of persistent normofrequent arrhythmia in a model suitable for chronic pacing (up to 7 days), we utilized human iPSC cardiomyocytes (iPSC-CM) from healthy donors (n=6). After 7 days, arrhythmic paced iPSC-CM showed a significantly reduced systolic Ca-transient amplitude, a prolonged Ca-elimination time (n=35/45 cells) as well as a reduced SR Ca-load and a trend towards a lower SERCA2a activity compared to control (n=11 cells). Confocal line-scans (Fluo-4 AM) showed an increased diastolic SR Ca-release, which might also explain the reduced SR Ca-content (n=45/35 cells). Moreover, in irregularly paced iPSC-CM we found significant increased levels of cytosolic Na (n=69 cells each) and in patch-clamp experiments a significantly prolonged action potential duration (n=14/11 cells/3 diff.).

This study demonstrates that a normofrequent arrhythmic ventricular excitation as it occurs in AF impairs human ventricular myocardial function by altering cardiomyocyte excitation-contraction coupling. Thus, this study provides the first translational mechanistic characterization and the potential negative impact of isolated AF in the absence of tachycardia on the human ventricle.

Funding Acknowledgement

Type of funding source: None

CaMKIIδC Drives Early Adaptive Ca2+ Change and Late Eccentric Cardiac Hypertrophy

Supplemental Digital Content is available in the text.

CaMKII (Ca²⁺-Calmodulin dependent protein kinase) δC activation is implicated in pathological progression of heart failure (HF) and CaMKIIδC transgenic mice rapidly develop HF and arrhythmias. However, little is known about early spatio-temporal Ca²⁺ handling and CaMKII activation in hypertrophy and HF.

The role of stretch, tachycardia and sodium-calcium exchanger in induction of early cardiac remodelling

Stretch and tachycardia are common triggers for cardiac remodelling in various conditions, but a comparative characterization of their role in the excitation‐transcription coupling (ETC) and early regulation of gene expression and structural changes is lacking. Here, we show that stretch and tachycardia directly induced hypertrophy of neonatal rat cardiac myocytes and also of non‐myocytes. Both triggers induced similar patterns of hypertrophy but had largely distinct gene expression profiles. ACTA1 served as good hypertrophy marker upon stretch, while RCAN1 was found increased in response to tachycardia in a rate‐dependent fashion. Mechanistically, several calcium‐handling proteins, including the sodium‐calcium exchanger (NCX), contributed to ETC. Phosphorylation of the calcium/calmodulin‐dependent protein kinase II (CaMKII) was elevated and occurred downstream of NCX activation upon tachycardia, but not stretch. Microarray profiling revealed that stretch and tachycardia regulated around 33% and 20% genes in a NCX‐dependent manner, respectively. In conclusion, our data show that hypertrophy induction by stretch and tachycardia is associated with different gene expression profiles with a significant contribution of the NCX.

Spermidine supplementation and voluntary activity differentially affect obesity-related structural changes in the mouse lung

Obesity is associated with lung function impairment and respiratory diseases; however, the underlying pathophysiological mechanisms are still elusive, and therapeutic options are limited. This study examined the effects of prolonged excess fat intake on lung mechanics and microstructure and tested spermidine supplementation and physical activity as intervention strategies. C57BL/6N mice fed control diet (10% fat) or high-fat diet (HFD; 60% fat) were left untreated or were supplemented with 3 mM spermidine, had access to running wheels for voluntary activity, or a combination of both. After 30 wk, lung mechanics was assessed, and left lungs were analyzed by design-based stereology. HFD exerted minor effects on lung mechanics and resulted in higher body weight and elevated lung, air, and septal volumes. The number of alveoli was higher in HFD-fed animals. This was accompanied by an increase in epithelial, but not endothelial, surface area. Moreover, air-blood barrier and endothelium were significantly thicker. Neither treatment affected HFD-related body weights. Spermidine lowered lung volumes as well as endothelial and air-blood barrier thicknesses toward control levels and substantially increased the endothelial surface area under HFD. Activity resulted in decreased volumes of lung, septa, and septal compartments but did not affect vascular changes in HFD-fed mice. The combination treatment showed no additive effect. In conclusion, excess fat consumption induced alveolar capillary remodeling indicative of impaired perfusion and gas diffusion. Spermidine alleviated obesity-related endothelial alterations, indicating a beneficial effect, whereas physical activity reduced lung volumes apparently by other, possibly systemic effects.

Autophagy in cardiovascular health and disease

Autophagy is a cellular housekeeping and quality control mechanism that is essential for homeostasis and survival. By virtue of this role, any perturbations to the flow of this process in cardiac or vascular cells can elicit harmful effects on the cardiovascular system, and subsequently affect whole organismal health. In this chapter, we summarize the preclinical evidence supporting the role of autophagy in sustaining cardiovascular health during homeostasis and disease. Furthermore, we discuss how autophagy activation by dietary, genetic and pharmaceutical interventions can be exploited to counteract common cardiovascular disorders, including atherosclerosis, coronary artery disease, diabetic cardiomyopathy, arrhythmia, chemotherapy-induced cardiotoxicity and heart failure.

N-acetylaspartate availability is essential for juvenile survival on fat-free diet and determines metabolic health

N-acetylaspartate (NAA) is synthesized by aspartate N-acetyltransferase (gene: Nat8l) from acetyl-coenzyme A and aspartate. In the brain, NAA is considered an important energy metabolite for lipid synthesis. However, the role of NAA in peripheral tissues remained elusive. Therefore, we characterized the metabolic phenotype of knockout (ko) and adipose tissue-specific (ako) Nat8l-ko mice as well as NAA-supplemented mice on various diets. We identified an important role of NAA availability in the brain during adolescence, as 75% of Nat8l-ko mice died on fat-free diet (FFD) after weaning but could be rescued by NAA supplementation. In adult life, NAA deficiency promotes a beneficial metabolic phenotype, as Nat8l-ko and Nat8l-ako mice showed reduced body weight, increased energy expenditure, and improved glucose tolerance on chow, high-fat, and FFDs. Furthermore, Nat8l-deficient adipocytes exhibited increased mitochondrial respiration, ATP synthesis, and an induction of browning. Conversely, NAA-treated wild-type mice showed reduced adipocyte respiration and lipolysis and increased de novo lipogenesis, culminating in reduced energy expenditure, glucose tolerance, and insulin sensitivity. Mechanistically, our data point to a possible role of NAA as modulator of pancreatic insulin secretion and suggest NAA as a critical energy metabolite for adipocyte and whole-body energy homeostasis.-Hofer, D. C., Zirkovits, G., Pelzmann, H. J., Huber, K., Pessentheiner, A. R., Xia, W., Uno, K., Miyazaki, T., Kon, K., Tsuneki, H., Pendl, T., Al Zoughbi, W., Madreiter-Sokolowski, C. T., Trausinger, G., Abdellatif, M., Schoiswohl, G., Schreiber, R., Eisenberg, T., Magnes, C., Sedej, S., Eckhardt, M., Sasahara, M., Sasaoka, T., Nitta, A., Hoefler, G., Graier, W. F., Kratky, D., Auwerx, J., Bogner-Strauss, J. G. N-acetylaspartate availability is essential for juvenile survival on fat-free diet and determines metabolic health.

Autophagy in Cardiovascular Aging

Cardiovascular diseases are the most prominent maladies in aging societies. Indeed, aging promotes the structural and functional declines of both the heart and the blood circulation system. In this review, we revise the contribution of known longevity pathways to cardiovascular health and delineate the possibilities to interfere with them. In particular, we evaluate autophagy, the intracellular catabolic recycling system associated with life- and health-span extension. We present genetic models, pharmacological interventions, and dietary strategies that block, reduce, or enhance autophagy upon age-related cardiovascular deterioration. Caloric restriction or caloric restriction mimetics like metformin, spermidine, and rapamycin (all of which trigger autophagy) are among the most promising cardioprotective interventions during aging. We conclude that autophagy is a fundamental process to ensure cardiac and vascular health during aging and outline its putative therapeutic importance.

The flavonoid 4,4'-dimethoxychalcone promotes autophagy-dependent longevity across species

Ageing constitutes the most important risk factor for all major chronic ailments, including malignant, cardiovascular and neurodegenerative diseases. However, behavioural and pharmacological interventions with feasible potential to promote health upon ageing remain rare. Here we report the identification of the flavonoid 4,4'-dimethoxychalcone (DMC) as a natural compound with anti-ageing properties. External DMC administration extends the lifespan of yeast, worms and flies, decelerates senescence of human cell cultures, and protects mice from prolonged myocardial ischaemia. Concomitantly, DMC induces autophagy, which is essential for its cytoprotective effects from yeast to mice. This pro-autophagic response induces a conserved systemic change in metabolism, operates independently of TORC1 signalling and depends on specific GATA transcription factors. Notably, we identify DMC in the plant Angelica keiskei koidzumi, to which longevity- and health-promoting effects are ascribed in Asian traditional medicine. In summary, we have identified and mechanistically characterised the conserved longevity-promoting effects of a natural anti-ageing drug.

Cardioprotection by spermidine does not depend on structural characteristics of the myocardial microcirculation in aged mice

AIMS

Ageing is associated with cardiovascular disease and reduced cardiac function. This cardiac functional decline is accompanied by cardiac remodeling and alterations in cardiomyocyte composition. Recently, it was shown that the natural polyamine spermidine preserves cardiac function and cardiomyocyte composition in old mice. As cardiac function critically relies on blood supply, we tested whether spermidine has also beneficial effects on ageing-associated changes of the myocardial microcirculation.

METHODS

Using transmission electron microscopy, the left ventricular capillaries of young (4-months old) and aged (24-months old) C57BL/6J male mice were investigated by stereology. Aged mice were subdivided into an untreated group and a group that was fed spermidine late in life for 6 months. Specifically, total volume, surface area and length of capillaries as well as endothelial thickness were estimated. Additionally, the total length of precapillary arterioles was assessed. The protein level of VEGF-A was measured using Western blot.

RESULTS

Ageing was associated with whole heart and left ventricular hypertrophy. All total capillary-related values (including volume, surface area and length) were significantly higher in 24-month-old mice compared with 4-month-old mice. Moreover, VEGF-A expression was significantly enhanced in aged mice. The mean thickness of the endothelium was not different, but the mean area of myocardium supplied by capillaries was smaller in old mice. Spermidine treatment had no significant effect on the ageing-associated structural changes or VEGF-A expression.

CONCLUSIONS

In conclusion, in the left ventricles of aged mice the growth of capillaries and arterioles supplying cardiomyocytes were in proportion to whole organ hypertrophy. Spermidine had no effect on quantitative characteristics of capillaries or arterioles, suggesting that the beneficial effects of spermidine on the ageing heart do not depend on the quantitative structural characteristics of the microcirculation which does not exclude potential functional differences between the groups.

Suppression of Arrhythmia by Enhancing Mitochondrial Ca2+ Uptake in Catecholaminergic Ventricular Tachycardia Models

Cardiovascular disease-related deaths frequently arise from arrhythmias, but treatment options are limited due to perilous side effects of commonly used antiarrhythmic drugs. Cardiac rhythmicity strongly depends on cardiomyocyte Ca2+ handling and prevalent cardiac diseases are causally associated with perturbations in intracellular Ca2+ handling. Therefore, intracellular Ca2+ transporters are lead candidate structures for novel and safer antiarrhythmic therapies. Mitochondria and mitochondrial Ca2+ transport proteins are important regulators of cardiac Ca2+ handling. Here we evaluated the potential of pharmacological activation of mitochondrial Ca2+ uptake for the treatment of cardiac arrhythmia. To this aim,we tested substances that enhance mitochondrial Ca2+ uptake for their ability to suppress arrhythmia in a murine model for ryanodine receptor 2 (RyR2)-mediated catecholaminergic polymorphic ventricular tachycardia (CPVT) in vitro and in vivo and in induced pluripotent stem cell-derived cardiomyocytes from a CPVT patient. In freshly isolated cardiomyocytes of RyR2R4496C/WT mice efsevin, a synthetic agonist of the voltage-dependent anion channel 2 (VDAC2) in the outer mitochondrial membrane, prevented the formation of diastolic Ca2+ waves and spontaneous action potentials. The antiarrhythmic effect of efsevin was abolished by blockade of the mitochondrial Ca2+ uniporter (MCU), but could be reproduced using the natural MCU activator kaempferol. Both mitochondrial Ca2+ uptake enhancers (MiCUps), efsevin and kaempferol, significantly reduced episodes of stress-induced ventricular tachycardia in RyR2R4496C/WT mice in vivo and abolished diastolic, arrhythmogenic Ca2+ events in human iPSC-derived cardiomyocytes.

Cold-Induced Thermogenesis Depends on ATGL-Mediated Lipolysis in Cardiac Muscle, but Not Brown Adipose Tissue

Fatty acids (FAs) activate and fuel UCP1-mediated non-shivering thermogenesis (NST) in brown adipose tissue (BAT). Release of FAs from intracellular fat stores by adipose triglyceride lipase (ATGL) is considered a key step in NST. Accordingly, the severe cold intolerance of global ATGL knockout (AKO) mice has been attributed to defective BAT lipolysis. Here we show that this conclusion is incorrect. We demonstrate that although the BAT-specific loss of ATGL impairs BAT lipolysis and alters BAT morphology, it does not compromise the β₃-adrenergic thermogenic response or cold-induced NST. Instead, NST depends on nutrient supply or lipolysis in white adipose tissue during fasting, suggesting that circulating energy substrates are sufficient to fuel NST. Cold intolerance in AKO mice is not caused by BAT dysfunction as previously suspected but by severe cardiomyopathy. We conclude that functional NST requires adequate substrate supply and cardiac function, but does not depend on ATGL-mediated lipolysis in BAT.