Characterizing Age-related Changes in Intact Mitochondrial Proteoforms in Murine Hearts using Quantitative Top-Down Proteomics

Cardiovascular diseases (CVDs) are the leading cause of death worldwide, and the prevalence of CVDs increases markedly with age. Due to the high energetic demand, the heart is highly sensitive to mitochondrial dysfunction. The complexity of the cardiac mitochondrial proteome hinders the development of effective strategies that target mitochondrial dysfunction in CVDs. Mammalian mitochondria are composed of over 1000 proteins, most of which can undergo post-translational protein modifications (PTMs). Top-down proteomics is a powerful technique for characterizing and quantifying all protein sequence variations and PTMs. However, there are still knowledge gaps in the study of age-related mitochondrial proteoform changes using this technique. In this study, we used top-down proteomics to identify intact mitochondrial proteoforms in young and old hearts and determined changes in protein abundance and PTMs in cardiac aging.

METHODS

Intact mitochondria were isolated from the hearts of young (4-month-old) and old (24-25-month-old) mice. The mitochondria were lysed, and mitochondrial lysates were subjected to denaturation, reduction, and alkylation. For quantitative top-down analysis, there were 12 runs in total arising from 3 biological replicates in two conditions, with technical duplicates for each sample. The collected top-down datasets were deconvoluted and quantified, and then the proteoforms were identified.

RESULTS

From a total of 12 LC-MS/MS runs, we identified 134 unique mitochondrial proteins in the different sub-mitochondrial compartments (OMM, IMS, IMM, matrix). 823 unique proteoforms in different mass ranges were identified. Compared to cardiac mitochondria of young mice, 7 proteoforms exhibited increased abundance and 13 proteoforms exhibited decreased abundance in cardiac mitochondria of old mice. Our analysis also detected PTMs of mitochondrial proteoforms, including N-terminal acetylation, lysine succinylation, lysine acetylation, oxidation, and phosphorylation.

CONCLUSION

By combining mitochondrial protein enrichment using mitochondrial fractionation with quantitative top-down analysis using ultrahigh-pressure liquid chromatography (UPLC)-MS and label-free quantitation, we successfully identified and quantified intact proteoforms in the complex mitochondrial proteome. Using this approach, we detected age-related changes in abundance and PTMs of mitochondrial proteoforms in the heart.

Remodeling of the Cardiac Extracellular Matrix Proteome During Chronological and Pathological Aging

Impaired extracellular matrix (ECM) remodeling is a hallmark of many chronic inflammatory disorders that can lead to cellular dysfunction, aging, and disease progression. The ECM of the aged heart and its effects on cardiac cells during chronological and pathological aging are poorly understood across species. For this purpose, we first used mass spectrometry-based proteomics to quantitatively characterize age-related remodeling of the left ventricle (LV) of mice and humans during chronological and pathological (Hutchinson-Gilford progeria syndrome (HGPS)) aging. Of the approximately 300 ECM and ECM-associated proteins quantified (named as Matrisome), we identified 13 proteins that were increased during aging, including lactadherin (MFGE8), collagen VI α6 (COL6A6), vitronectin (VTN) and immunoglobulin heavy constant mu (IGHM), whereas fibulin-5 (FBLN5) was decreased in most of the data sets analyzed. We show that lactadherin accumulates with age in large cardiac blood vessels and when immobilized, triggers phosphorylation of several phosphosites of GSK3B, MAPK isoforms 1, 3, and 14, and MTOR kinases in aortic endothelial cells (ECs). In addition, immobilized lactadherin increased the expression of pro-inflammatory markers associated with an aging phenotype. These results extend our knowledge of the LV proteome remodeling induced by chronological and pathological aging in different species (mouse and human). The lactadherin-triggered changes in the proteome and phosphoproteome of ECs suggest a straight link between ECM component remodeling and the aging process of ECs, which may provide an additional layer to prevent cardiac aging.

Unraveling the role of galectin-3 in cardiac pathology and physiology

Galectin-3 (Gal-3) is a carbohydrate-binding protein with multiple functions. Gal-3 regulates cell growth, proliferation, and apoptosis by orchestrating cell-cell and cell-matrix interactions. It is implicated in the development and progression of cardiovascular disease, and its expression is increased in patients with heart failure. In atherosclerosis, Gal-3 promotes monocyte recruitment to the arterial wall boosting inflammation and atheroma. In acute myocardial infarction (AMI), the expression of Gal-3 increases in infarcted and remote zones from the beginning of AMI, and plays a critical role in macrophage infiltration, differentiation to M1 phenotype, inflammation and interstitial fibrosis through collagen synthesis. Genetic deficiency of Gal-3 delays wound healing, impairs cardiac remodeling and function after AMI. On the contrary, Gal-3 deficiency shows opposite results with improved remodeling and function in other cardiomyopathies and in hypertension. Pharmacologic inhibition with non-selective inhibitors is also protective in cardiac disease. Finally, we recently showed that Gal-3 participates in normal aging. However, genetic absence of Gal-3 in aged mice exacerbates pathological hypertrophy and increases fibrosis, as opposed to reduced fibrosis shown in cardiac disease. Despite some gaps in understanding its precise mechanisms of action, Gal-3 represents a potential therapeutic target for the treatment of cardiovascular diseases and the management of cardiac aging. In this review, we summarize the current knowledge regarding the role of Gal-3 in the pathophysiology of heart failure, atherosclerosis, hypertension, myocarditis, and ischemic heart disease. Furthermore, we describe the physiological role of Gal-3 in cardiac aging.

Circulating Total Extracellular Vesicles Cargo Are Associated with Age-Related Oxidative Stress and Susceptibility to Cardiovascular Diseases: Exploratory Results from Microarray Data

Aging is a risk factor for many non-communicable diseases such as cardiovascular and neurodegenerative diseases. Extracellular vesicles and particles (EVP) carry microRNAs that may play a role in age-related diseases and may induce oxidative stress. We hypothesized that aging could impact EVP miRNA and impair redox homeostasis, contributing to chronic age-related diseases. Our aims were to investigate the microRNA profiles of circulating total EVPs from aged and young adult animals and to evaluate the pro- and antioxidant machinery in circulating total EVPs. Plasma from 3- and 21-month-old male Wistar rats were collected, and total EVPs were isolated. MicroRNA isolation and microarray expression analysis were performed on EVPs to determine the predicted regulation of targeted mRNAs. Thirty-one mature microRNAs in circulating EVPs were impacted by age and were predicted to target molecules in canonical pathways directly related to cardiovascular diseases and oxidative status. Circulating total EVPs from aged rats had significantly higher NADPH oxidase levels and myeloperoxidase activity, whereas catalase activity was significantly reduced in EVPs from aged animals. Our data shows that circulating total EVP cargo-specifically microRNAs and oxidative enzymes-are involved in redox imbalance in the aging process and can potentially drive cardiovascular aging and, consequently, cardiac disease.

Bibliometric analysis of trends in cardiac aging research over the past 20 years

BACKGROUND

In recent years, many studies have addressed cardiac aging and related diseases. This study aims to understand the research trend of cardiac aging and find new hot issues.

METHODS

We searched the web of science core collection database for articles published between 2003 and 2022 on the topic of "cardiac aging." Complete information including keywords, publication year, journal title, country, organization, and author were extracted for analysis. The VOS viewer software was used to generate network maps of keywords, countries, institutions, and author relationships for visual network analysis.

RESULTS

A total of 1002 papers were analyzed in the study. Overall, the number of annual publications on cardiac aging has increased since 2009, and new hot topics are emerging. The top 3 countries with the most publications were the United States (471 articles), China (209 articles) and Italy (101 articles). The University of Washington published the most papers (35 articles). The cluster analysis with author as the keyword found that the connections among different scholars are scattered and clustered in a small range. Network analysis based on keyword co-occurrence and year of publication identified relevant features and trends in cardiac aging research. According to the results of cluster analysis, all the articles are divided into 4 topics: "mechanisms of cardiac aging", "prevention and treatment of cardiac aging", "characteristics of cardiac aging", and "others." In recent years, the mechanism and treatment of cardiac aging have attracted the most attention. In both studies, animal models are used more often than in human populations. Mitochondrial dysfunction, autophagy and mitochondrial autophagy are hotspots in current research.

CONCLUSION

In this study, bibliometric analysis was used to analyze the research trend of cardiac aging in the past 20 years. The mechanism and treatment of cardiac aging are the most concerned contents. Mitochondrial dysfunction, autophagy and mitophagy are the focus of future research on cardiac aging.

Mitral Valve Repair in Advanced Age Groups: Does Cardiac Age Differ from Chronological Age?

OBJECTIVE

Advanced age is a risk factor in cardiac surgery contributing significantly to a worse outcome. The reasons are frailty and multimorbidity. In this study, we asked: Is there an aging of the heart which differs from chronological age?

METHODS

Propensity score matching was performed between 115 seniors ≥ 80 years and 345 juniors < 80 years. After the patients were found to be comparable in terms of cardiac and noncardiac disease and risk profiles, they were further analyzed for cardiac parameters. In addition, the seniors and juniors were compared in terms of cardiac health and postoperative outcome. Furthermore, the patients were subdivided into several age groups (<60 years, 60-69 years, 70-79 years, and >80 years) and compared regarding outcome.

RESULTS

The seniors demonstrated significantly lower tricuspid annular plane systolic excursion (TAPSE), significantly more frequent diastolic dysfunction, significantly higher plasma levels of NT-proBNP, and significantly larger left ventricular end-diastolic and end-systolic diameters and left atrial diameters (p < 0.001, respectively). Furthermore, in-hospital mortality and most postoperative complications were significantly higher in seniors compared with juniors. While old cardiac healthy patients showed better outcome than old cardiac aged patients, the outcome from young cardiac aged patients was better than old cardiac aged patients. The outcome and survival deteriorated with increasing life decades.

CONCLUSIONS

The elderly suffer significantly more from cardiac deterioration, i.e., cardiac aging, and show higher multimorbidity. Mortality risk is significantly higher and they suffer more often from a complicated postoperative course compared to younger patients. Further approaches to prevention and treatment of cardiac aging are needed to address the needs of an aging society.

The mTOR signaling pathway in cardiac aging

The mammalian target of rapamycin (mTOR) is one of the most important signaling pathways that regulate nutrient sensing, cell growth, metabolism, and aging. The mTOR pathway, particularly mTOR complex 1 (mTORC1), has been shown to control aging, lifespan, and healthspan through the regulation of protein synthesis, autophagy, mitochondrial function, and metabolic health. The mTOR pathway also plays critical roles in the heart, from cardiac development, growth and maturation, and maintenance of cardiac homeostasis. Hyperactivation of mTORC1 signaling is well documented in aging and many age-related pathologies, including age-related cardiac dysfunction and heart failure. Suppression of mTORC1 by calorie restriction or rapamycin not only extends lifespan but also restores youthful phenotypes in the heart. In this article, we review model organisms of cardiac aging and highlight recent advances in the impact of the mTORC1 pathway on organismal and cardiac aging, particularly in Drosophila and mice. We focus on the downstream signaling pathways S6 kinase and 4EBP1, which regulates protein synthesis, as well as ULK1 and its related pathway that regulates autophagy. The interaction with mTOR complex 2 (mTORC2) and its potential role in cardiac aging are also discussed.

WGCNA and molecular docking identify hub genes for cardiac aging

Background

Cardiac aging and ageing-related cardiovascular diseases remain increase medical and social burden. Discovering the molecular mechanisms associated with cardiac aging is expected to provide new perspectives for delaying aging and related disease treatment.

Methods

The samples in GEO database were divided into older group and younger group based on age. Age-associated differentially expressed genes (DEGs) were identified by limma package. Gene modules significantly associated with age were mined using weighted gene co-expression network analysis (WGCNA). Protein-protein interaction networks (PPI) networks were developed using genes within modules, and topological analysis on the networks was performed to identify hub genes in cardiac aging. Pearson correlation was used to analyze the association among hub genes and immune and immune-related pathways. Molecular docking of hub genes and the anti-aging drug Sirolimus was performed to explore the potential role of hub genes in treating cardiac aging.

Results

We found a generally negative correlation between age and immunity, with a significant negative correlation between age and b_cell_receptor_signaling_pathway, fc_gamma_r_mediated_phagocytosis, chemokine signaling pathway, t-cell receptor signaling pathway, toll_like_receptor_signaling_pathway, and jak_stat_signaling_pathway, respectively. Finally, 10 cardiac aging-related hub genes including LCP2, PTPRC, RAC2, CD48, CD68, CCR2, CCL2, IL10, CCL5 and IGF1 were identified. 10-hub genes were closely associated with age and immune-related pathways. There was a strong binding interaction between Sirolimus-CCR2. CCR2 may be a key target for Sirolimus in the treatment of cardiac aging.

Conclusion

The 10 hub genes may be potential therapeutic targets for cardiac aging, and our study provided new ideas for the treatment of cardiac aging.

Common electrocardiogram measures are not associated with telomere length

AIMS

Aging is accompanied by telomere shortening. Increased telomere shortening is considered a marker of premature aging. Cardiac aging results in the development of cardiac pathologies. Electrocardiogram (ECG) measures reflect cardiac excitation, conduction, and repolarization. ECG measures also prolong with aging and are associated with cardiac pathologies including atrial fibrillation. As premature prolongation of ECG measures is observed, we hypothesized that such prolongation may be associated with telomere length.

METHODS AND RESULTS

We studied the large, community-based KORA F4 Study. Of 3,080 participants enrolled between 2006 and 2007 with detailed information on demographic, anthropometric, clinical, and ECG characteristics, 2,575 presented with available data on leukocyte telomere length. Telomere length was determined by real-time quantitative PCR and expressed relative to a single copy gene. We fitted multivariable adjusted linear regression models to associate the ECG measures RR-interval, PR-interval, QRS-duration, and heart rate corrected QTc with telomere length. In our cohort, the mean age was 54.9±12.9 years and 46.6% were men. Increased age was associated with shorter telomere length (p<0.01), and men had shorter telomere length than women (p<0.05). In unadjusted models, heart rate (p=0.023), PR-interval (p<0.01), and QTc-interval (p<0.01) were significantly associated with shorter telomere length. However, no significant associations remained after accounting for age, sex, and covariates.

CONCLUSIONS

ECG measures are age-dependent, but not associated with shortened telomere length as a marker of biological aging. Further research is warranted to clarify if shortened telomeres are associated with clinical cardiac pathologies including atrial fibrillation.

Rejuvenating the Aging Heart by Enhancing the Expression of the Cisd2 Prolongevity Gene

Aging is the major risk factor for cardiovascular disease, which is the leading cause of mortality worldwide among aging populations. Cisd2 is a prolongevity gene that mediates lifespan in mammals. Previously, our investigations revealed that a persistently high level of Cisd2 expression in mice is able to prevent age-associated cardiac dysfunction. This study was designed to apply a genetic approach that induces cardiac-specific Cisd2 overexpression (Cisd2 icOE) at a late-life stage, namely a time point immediately preceding the onset of old age, and evaluate the translational potential of this approach. Several discoveries are pinpointed. Firstly, Cisd2 is downregulated in the aging heart. This decrease in Cisd2 leads to cardiac dysfunction and impairs electromechanical performance. Intriguingly, Cisd2 icOE prevents an exacerbation of age-associated electromechanical dysfunction. Secondly, Cisd2 icOE ameliorates cardiac fibrosis and improves the integrity of the intercalated discs, thereby reversing various structural abnormalities. Finally, Cisd2 icOE reverses the transcriptomic profile of the aging heart, changing it from an older-age pattern to a younger pattern. Intriguingly, Cisd2 icOE modulates a number of aging-related pathways, namely the sirtuin signaling, autophagy, and senescence pathways, to bring about rejuvenation of the heart as it enters old age. Our findings highlight Cisd2 as a novel molecular target for developing therapies targeting cardiac aging.

Effects of Aging on Cardiac Oxidative Stress and Transcriptional Changes in Pathways of Reactive Oxygen Species Generation and Clearance

Background Age-related heart diseases are significant contributors to increased morbidity and mortality. Emerging evidence indicates that mitochondria within cardiomyocytes contribute to age-related increased reactive oxygen species (ROS) generation that plays an essential role in aging-associated cardiac diseases. Methods and Results The present study investigated differences between ROS production in cardiomyocytes isolated from adult (6 months) and aged (24 months) Fischer 344 rats, and in cardiac tissue of adult (18-65 years) and elderly (>65 years) patients with preserved cardiac function. Superoxide dismutase inhibitable ferricytochrome c reduction assay (1.32±0.63 versus 0.76±0.31 nMol/mg per minute; P=0.001) superoxide and H2O2 production, measured as dichlorofluorescein diacetate fluorescence (1646±428 versus 699±329, P=0.04), were significantly higher in the aged versus adult cardiomyocytes. Similarity in age-related alteration between rats and humans was identified in mitochondrial-electron transport chain-complex-I-associated increased oxidative-stress by MitoSOX fluorescence (53.66±18.58 versus 22.81±12.60; P=0.03) and in 4-HNE adduct levels (187.54±54.8 versus 47.83±16.7 ng/mg protein, P=0.0063), indicative of increased peroxidation in the elderly. These differences correlated with changes in functional enrichment of genes regulating ROS homeostasis pathways in aged human and rat hearts. Functional merged collective network and pathway enrichment analysis revealed common genes prioritized in human and rat aging-associated networks that underlay enriched functional terms of mitochondrial complex I and common pathways in the aging human and rat heart. Conclusions Aging sensitizes mitochondrial and extramitochondrial mechanisms of ROS buildup within the heart. Network analysis of the transcriptome highlights the critical elements involved with aging-related ROS homeostasis pathways common in rat and human hearts as targets.

Genetic associations for two biological age measures point to distinct aging phenotypes

Biological age measures outperform chronological age in predicting various aging outcomes, yet little is known regarding genetic predisposition. We performed genome-wide association scans of two age-adjusted biological age measures (PhenoAgeAcceleration and BioAgeAcceleration), estimated from clinical biochemistry markers (Levine et al., 2018; Levine, 2013) in European-descent participants from UK Biobank. The strongest signals were found in the APOE gene, tagged by the two major protein-coding SNPs, PhenoAgeAccel-rs429358 (APOE e4 determinant) (p = 1.50 × 10-72 ); BioAgeAccel-rs7412 (APOE e2 determinant) (p = 3.16 × 10-60 ). Interestingly, we observed inverse APOE e2 and e4 associations and unique pathway enrichments when comparing the two biological age measures. Genes associated with BioAgeAccel were enriched in lipid related pathways, while genes associated with PhenoAgeAccel showed enrichment for immune system, cell function, and carbohydrate homeostasis pathways, suggesting the two measures capture different aging domains. Our study reaffirms that aging patterns are heterogeneous across individuals, and the manner in which a person ages may be partly attributed to genetic predisposition.

Altered Glycosylation in the Aging Heart

Cardiovascular disease is one of the leading causes of death in developed countries. Because the incidence increases exponentially in the aging population, aging is a major risk factor for cardiovascular disease. Cardiac hypertrophy, fibrosis and inflammation are typical hallmarks of the aged heart. The molecular mechanisms, however, are poorly understood. Because glycosylation is one of the most common post-translational protein modifications and can affect biological properties and functions of proteins, we here provide the first analysis of the cardiac glycoproteome of mice at different ages. Western blot as well as MALDI-TOF based glycome analysis suggest that high-mannose N-glycans increase with age. In agreement, we found an age-related regulation of GMPPB, the enzyme, which facilitates the supply of the sugar-donor GDP-mannose. Glycoprotein pull-downs from heart lysates of young, middle-aged and old mice in combination with quantitative mass spectrometry bolster widespread alterations of the cardiac glycoproteome. Major hits are glycoproteins related to the extracellular matrix and Ca²⁺-binding proteins of the endoplasmic reticulum. We propose that changes in the heart glycoproteome likely contribute to the age-related functional decline of the cardiovascular system.

Metabolic Complications in Cardiac Aging

Aging is a process that can be accompanied by molecular and cellular alterations that compromise cardiac function. Although other metabolic disorders with increased prevalence in aged populations, such as diabetes mellitus, dyslipidemia, and hypertension, are associated with cardiovascular complications; aging-related cardiomyopathy has some unique features. Healthy hearts oxidize fatty acids, glucose, lactate, ketone bodies, and amino acids for producing energy. Under physiological conditions, cardiac mitochondria use fatty acids and carbohydrate mainly to generate ATP, 70% of which is derived from fatty acid oxidation (FAO). However, relative contribution of nutrients in ATP synthesis is altered in the aging heart with glucose oxidation increasing at the expense of FAO. Cardiac aging is also associated with impairment of mitochondrial abundance and function, resulting in accumulation of reactive oxygen species (ROS) and activation of oxidant signaling that eventually leads to further mitochondrial damage and aggravation of cardiac function. This review summarizes the main components of pathophysiology of cardiac aging, which pertain to cardiac metabolism, mitochondrial function, and systemic metabolic changes that affect cardiac function.

The nuclear sirtuin SIRT6 protects the heart from developing aging-associated myocyte senescence and cardiac hypertrophy

Sirtuins have been shown to regulate the aging process. We have previously demonstrated that Sirt6 blocks the pressure overload-induced cardiac hypertrophy in mice. Here, we show that Sirt6 can also mitigate aging-induced cardiomyocyte senescence and cardiac hypertrophy. We found that aging is associated with altered Sirt6 activity along with development of cardiac hypertrophy and fibrosis. Compared to young mice (4-months), the hearts of aged mice (24-months) showed increased levels of mitochondrial DNA damage, shortened telomere length, and increased accumulation of 8-oxo-dG adducts, which are hallmarks of aging. The aged hearts also showed reduced levels of NAD⁺ and altered levels of mitochondrial fusion-fission proteins. Similar characteristics were observed in the hearts of Sirt6 deficient mice. Additionally, we found that doxorubicin (Dox) induced cardiomyocyte senescence, as measured by expression of p16^INK4a, p53, and β-galactosidase, was associated with loss of Sirt6. However, Sirt6 overexpression protected cardiomyocytes from developing Dox-induced senescence. Further, compared to wild-type mice, the hearts of Sirt6.Tg mice showed reduced expression of aging markers, and the development of aging-associated cardiac hypertrophy and fibrosis. Our data suggest that Sirt6 is a critical anti-aging molecule that regulates various cellular processes associated with aging and protects the heart from developing aging-induced cardiac hypertrophy and fibrosis.

Deficiency of telomere-associated repressor activator protein 1 precipitates cardiac aging in mice via p53/PPARα signaling

Background: Telomere shortening and dysfunction may cause metabolic disorders, tissue damage and age-dependent pathologies. However, little is known about the association of telomere-associated protein Rap1 with mitochondrial energy metabolism and cardiac aging. Methods: Echocardiography was performed to detect cardiac structure and function in Rap1^+/+ and Rap1^-/- mice at different ages (3 months, 12 months and 20 months). Telomere length, DNA damage, cardiac senescence and cardiomyocyte size were analyzed using the real-time PCR, Western blotting, senescence associated β-galactosidase assay and wheat germ agglutinin staining, respectively. Western blotting was also used to determine the level of cardiac fatty acid metabolism related key enzymes in mouse and human myocardium. Chromatin immunoprecipitation assay was used to verify the direct link between p53 and PPARα. The p53 inhibitor, Pifithrin-α and PPARα activator WY14643 were utilized to identify the effects of Rap1/p53/PPARα signaling pathway. Results: Telomere was shortened concomitant with extensive DNA damage in aged Rap1^-/- mouse hearts, evidenced by reduced T/S ratios and increased nuclear γH2AX. Meanwhile, the aging-associated phenotypes were pronounced as reflected by altered mitochondrial ultrastructure, enhanced senescence, cardiac hypertrophy and dysfunction. Mechanistically, acetylated p53 and nuclear p53 was enhanced in the Rap1^-/- mouse hearts, concomitant with reduced PPARα. Importantly, p53 directly binds to the promoter of PPARα in mouse hearts and suppresses the transcription of PPARα. In addition, aged Rap1^-/- mice exhibited reduced cardiac fatty acid metabolism. Pifithrin-α alleviated cardiac aging and enhanced fatty acid metabolism in the aged Rap1^-/- mice. Activating PPARα with WY14643 in primarily cultured Rap1^-/- cardiomyocytes restored maximal oxygen consumption rates. Reduced Rap1 expression and impaired p53/PPARα signaling also presented in aged human myocardium. Conclusion: In summary, Rap1 may link telomere biology to fatty acid metabolism and aging-related cardiac pathologies via modulating the p53/PPARα signaling pathway, which could represent a therapeutic target in preventing/attenuating cardiac aging.

TOR Signaling Pathway in Cardiac Aging and Heart Failure

Mechanistic Target of Rapamycin (mTOR) signaling is a key regulator of cellular metabolism, integrating nutrient sensing with cell growth. Over the past two decades, studies on the mTOR pathway have revealed that mTOR complex 1 controls life span, health span, and aging by modulating key cellular processes such as protein synthesis, autophagy, and mitochondrial function, mainly through its downstream substrates. Thus, the mTOR pathway regulates both physiological and pathological processes in the heart from embryonic cardiovascular development to maintenance of cardiac homeostasis in postnatal life. In this regard, the dysregulation of mTOR signaling has been linked to many age-related pathologies, including heart failure and age-related cardiac dysfunction. In this review, we highlight recent advances of the impact of mTOR complex 1 pathway and its regulators on aging and, more specifically, cardiac aging and heart failure.

Potassium channel Shaker play a protective role against cardiac aging in Drosophila

Potassium channels, which are the most diverse group of the ion channel family, play an important role in the repolarization of cardiomyocytes. Recent studies showed that potassium channels, such as KCNQ and HERG/eag, play an important role in regulating adult heart function through shaping the action potential and maintaining the rhythm of cardiac contraction. The potassium channel protein Shaker is the first voltage-gated potassium channel found in Drosophila to maintain the electrical excitability of neurons and muscle cells, but its role in adult cardiac function is still unclear. In this study, Drosophila was used as a model to study the role of Shaker channel in the maintenance of cardiac function under stress and aging. The incidence of heart failure was observed in shaker mutant after external electrical pacing, which simulates cardiac stress. Additionally, The cardiac-specific driver hand4.2 Gal4 was used to specifically knock down the expression of the potassium channel shaker in Drosophila. The cardiac parameter was analyzed at 1, 3, 5 weeks of age on cardiac specific knockdown of shaker using Drosophila adult cardiac physiological assay. The results showed that the mutation of shaker gene seriously affect the cardiac function under stress, demonstrated by significant increase in heart failure rate under electrical stimulation. In addition, cardiac specific knockdown of shaker increased the incidence of arrhythmias in Drosophila at the age of 5 weeks. Cardiac-specific knockdown of shaker reduces life span. Therefore, the results of this study suggest a vital role of the potassium channel shaker in maintaining normal cardiac function during aging.

p300 in Cardiac Development and Accelerated Cardiac Aging

The heart is the first functional organ that develops during embryonic development. While a heartbeat indicates life, cessation of a heartbeat signals the end of life. Heart disease, due either to congenital defects or to acquired dysfunctions in adulthood, remains the leading cause of death worldwide. Epigenetics plays a key role in both embryonic heart development and heart disease in adults. Stress-induced vascular injury activates pathways involved in pathogenesis of accelerated cardiac aging that includes cellular dysfunction, pathological cardiac hypertrophy, diabetic cardiomyopathy, cardiac matrix remodeling, cardiac dysfunction and heart failure. Acetyltransferase p300 (p300), a major epigenetic regulator, plays a pivotal role in heart development during embryogenesis, as deficiency or abnormal expression of p300 leads to embryonic death at early gestation periods due to deformation of the heart and neural tube. Acetyltransferase p300 controls heart development through histone acetylation-mediated chromatin remodeling and transcriptional regulation of genes required for cardiac development. In adult hearts, p300 is differentially expressed in different chambers and epigenetically controls cardiac gene expression. Deregulation of p300, in response to prohypertrophic and profibrogenic stress signals, is associated with increased recruitment of p300 to several genes including transcription factors, increased acetylation of specific lysines in histones and transcription factors, altered chromatin organization, and increased hypertrophic and fibrogenic gene expression. Cardiac hypertrophy and myocardial fibrogenesis are common pathological manifestations of several stress-induced accelerated cardiac aging-related pathologies, including high blood pressure-induced or environmentally induced cardiac hypertrophy, myocardial infarction, diabetes-induced cardiomyopathy, and heart failure. Numerous studies using cellular and animal models clearly indicate that pharmacologic or genetic normalization of p300 activity has the potential to prevent or halt the progression of cardiac aging pathologies. Based on these preclinical studies, development of safe, non-toxic, small molecule inhibitors/epidrugs targeting p300 is an ideal approach to control accelerated cardiac aging-related deaths worldwide.

Sex differences in the aging human heart: decreased sirtuins, pro-inflammatory shift and reduced anti-oxidative defense

Aging is associated with increased inflammation and alterations in mitochondrial biogenesis, which promote the development of cardiovascular diseases. Emerging evidence suggests a role for sirtuins, which are NAD⁺-dependent deacetylases, in the regulation of cardiovascular inflammation and mitochondrial biogenesis. Sirtuins are regulated by sex or sex hormones and are decreased during aging in animal models. We hypothesized that age-related alterations in cardiac Sirt1 and Sirt3 occur in the human heart and examined whether these changes are associated with a decrease in anti-oxidative defense, inflammatory state and mitochondrial biogenesis. Using human ventricular tissue from young (17-40 years old) and old (50-68 years old) individuals, we found significantly lower Sirt1 and Sirt3 expression in old female hearts than in young female hearts. Additionally, lower expression of the anti-oxidative protein SOD2 was observed in old female hearts than in young female hearts. Aging in female hearts was associated with a significant increase in the number of cardiac macrophages and pro-inflammatory cytokines, as well as NF-kB upregulation, indicating a pro-inflammatory shift. Aging-associated pathways in the male hearts were different, and no changes in Sirt1 and Sirt3 or cardiovascular inflammation were observed. In conclusion, the present study revealed a female sex-specific downregulation of Sirt1 and Sirt3 in aged hearts, as well as a decline in mitochondrial anti-oxidative defense and a pro-inflammatory shift in old female hearts but not in male hearts.

TASK-1 and TASK-3 channels modulate pressure overload-induced cardiac remodeling and dysfunction

Tandem pore domain acid-sensitive K⁺ (TASK) channels are present in cardiac tissue; however, their contribution to cardiac pathophysiology is not well understood. Here, we investigate the role of TASK-1 and TASK-3 in the pathogenesis of cardiac dysfunction using both human tissue and mouse models of genetic TASK channel loss of function. Compared with normal human cardiac tissue, TASK-1 gene expression is reduced in association with either cardiac hypertrophy alone or combined cardiac hypertrophy and heart failure. In a pressure overload cardiomyopathy model, TASK-1 global knockout (TASK-1 KO) mice have both reduced cardiac hypertrophy and preserved cardiac function compared with wild-type mice. In contrast to the TASK-1 KO mouse pressure overload response, TASK-3 global knockout (TASK-3 KO) mice develop cardiac hypertrophy and a delayed onset of cardiac dysfunction compared with wild-type mice. The cardioprotective effects observed in TASK-1 KO mice are associated with pressure overload-induced augmentation of AKT phosphorylation and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) expression, with consequent augmentation of cardiac energetics and fatty acid oxidation. The protective effects of TASK-1 loss of function are associated with an enhancement of physiologic hypertrophic signaling and preserved metabolic functions. These findings may provide a rationale for TASK-1 channel inhibition in the treatment of cardiac dysfunction.NEW & NOTEWORTHY The role of tandem pore domain acid-sensitive K⁺ (TASK) channels in cardiac function is not well understood. This study demonstrates that TASK channel gene expression is associated with the onset of human cardiac hypertrophy and heart failure. TASK-1 and TASK-3 strongly affect the development of pressure overload cardiomyopathies in genetic models of TASK-1 and TASK-3 loss of function. The effects of TASK-1 loss of function were associated with enhanced AKT phosphorylation and expression of peroxisome proliferator-activated receptor-γ coactivator-1 (PGC-1) transcription factor. These data suggest that TASK channels influence the development of cardiac hypertrophy and dysfunction in response to injury.

NLRP3 inflammasome suppression improves longevity and prevents cardiac aging in male mice

While NLRP3‐inflammasome has been implicated in cardiovascular diseases, its role in physiological cardiac aging is largely unknown. During aging, many alterations occur in the organism, which are associated with progressive impairment of metabolic pathways related to insulin resistance, autophagy dysfunction, and inflammation. Here, we investigated the molecular mechanisms through which NLRP3 inhibition may attenuate cardiac aging. Ablation of NLRP3‐inflammasome protected mice from age‐related increased insulin sensitivity, reduced IGF‐1 and leptin/adiponectin ratio levels, and reduced cardiac damage with protection of the prolongation of the age‐dependent PR interval, which is associated with atrial fibrillation by cardiovascular aging and reduced telomere shortening. Furthermore, old NLRP3 KO mice showed an inhibition of the PI3K/AKT/mTOR pathway and autophagy improvement, compared with old wild mice and preserved Nampt‐mediated NAD⁺ levels with increased SIRT1 protein expression. These findings suggest that suppression of NLRP3 prevented many age‐associated changes in the heart, preserved cardiac function of aged mice and increased lifespan.

Fully Automated, Quality-Controlled Cardiac Analysis From CMR: Validation and Large-Scale Application to Characterize Cardiac Function

Objectives

This study sought to develop a fully automated framework for cardiac function analysis from cardiac magnetic resonance (CMR), including comprehensive quality control (QC) algorithms to detect erroneous output.

Background

Analysis of cine CMR imaging using deep learning (DL) algorithms could automate ventricular function assessment. However, variable image quality, variability in phenotypes of disease, and unavoidable weaknesses in training of DL algorithms currently prevent their use in clinical practice.

Methods

The framework consists of a pre-analysis DL image QC, followed by a DL algorithm for biventricular segmentation in long-axis and short-axis views, myocardial feature-tracking (FT), and a post-analysis QC to detect erroneous results. The study validated the framework in healthy subjects and cardiac patients by comparison against manual analysis (n = 100) and evaluation of the QC steps’ ability to detect erroneous results (n = 700). Next, this method was used to obtain reference values for cardiac function metrics from the UK Biobank.

Results

Automated analysis correlated highly with manual analysis for left and right ventricular volumes (all r > 0.95), strain (circumferential r = 0.89, longitudinal r > 0.89), and filling and ejection rates (all r ≥ 0.93). There was no significant bias for cardiac volumes and filling and ejection rates, except for right ventricular end-systolic volume (bias +1.80 ml; p = 0.01). The bias for FT strain was <1.3%. The sensitivity of detection of erroneous output was 95% for volume-derived parameters and 93% for FT strain. Finally, reference values were automatically derived from 2,029 CMR exams in healthy subjects.

Conclusions

The study demonstrates a DL-based framework for automated, quality-controlled characterization of cardiac function from cine CMR, without the need for direct clinician oversight.

Role of c-Kit in Myocardial Regeneration and Aging

c-Kit, a type III receptor tyrosine kinase (RTK), is involved in multiple intracellular signaling whereby it is mainly considered a stem cell factor receptor, which participates in vital functions of the mammalian body, including the human. Furthermore, c-kit is a necessary yet not sufficient marker to detect and isolate several types of tissue-specific adult stem cells. Accordingly, c-kit was initially used as a marker to identify and enrich for adult cardiac stem/progenitor cells (CSCs) that were proven to be clonogenic, self-renewing and multipotent, being able to differentiate into cardiomyocytes, endothelial cells and smooth muscle cells in vitro as well as in vivo after myocardial injury. Afterwards it was demonstrated that c-kit expression labels a heterogenous cardiac cell population, which is mainly composed by endothelial cells while only a very small fraction represents CSCs. Furthermore, c-kit as a signaling molecule is expressed at different levels in this heterogenous c-kit labeled cardiac cell pool, whereby c-kit low expressers are enriched for CSCs while c-kit high expressers are endothelial and mast cells. This heterogeneity in cell composition and expression levels has been neglected in recent genetic fate map studies focusing on c-kit, which have claimed that c-kit identifies cells with robust endothelial differentiation potential but with minimal if not negligible myogenic commitment potential. However, modification of c-kit gene for Cre Recombinase expression in these Cre/Lox genetic fate map mouse models produced a detrimental c-kit haploinsufficiency that prevents efficient labeling of true CSCs on one hand while affecting the regenerative potential of these cells on the other. Interestingly, c-kit haploinsufficiency in c-kit-deficient mice causes a worsening myocardial repair after injury and accelerates cardiac aging. Therefore, these studies have further demonstrated that adult c-kit-labeled CSCs are robustly myogenic and that the adult myocardium relies on c-kit expression to regenerate after injury and to counteract aging effects on cardiac structure and function.

New Insights in Cardiac β-Adrenergic Signaling During Heart Failure and Aging

Heart failure (HF) has become increasingly common within the elderly population, decreasing their survival and overall quality of life. In fact, despite the improvements in treatment, many elderly people suffer from cardiac dysfunction (HF, valvular diseases, arrhythmias or hypertension-induced cardiac hypertrophy) that are much more common in an older fragile heart. Since β-adrenergic receptor (β-AR) signaling is abnormal in failing as well as aged hearts, this pathway is an effective diagnostic and therapeutic target. Both HF and aging are characterized by activation/hyperactivity of various neurohormonal pathways, the most important of which is the sympathetic nervous system (SNS). SNS hyperactivity is initially a compensatory mechanism to stimulate contractility and maintain cardiac output. Unfortunately, this chronic stimulation becomes detrimental and causes decreased cardiac function as well as reduced inotropic reserve due to a decrease in cardiac β-ARs responsiveness. Therapies which (e.g., β-blockers and physical activity) restore β-ARs responsiveness can ameliorate cardiac performance and outcomes during HF, particularly in older patients. In this review, we will discuss physiological β-adrenergic signaling and its alterations in both HF and aging as well as the potential clinical application of targeting β-adrenergic signaling in these disease processes.

New Insights in Cardiac β-Adrenergic Signaling During Heart Failure and Aging

Heart failure (HF) has become increasingly common within the elderly population, decreasing their survival and overall quality of life. In fact, despite the improvements in treatment, many elderly people suffer from cardiac dysfunction (HF, valvular diseases, arrhythmias or hypertension-induced cardiac hypertrophy) that are much more common in an older fragile heart. Since β-adrenergic receptor (β-AR) signaling is abnormal in failing as well as aged hearts, this pathway is an effective diagnostic and therapeutic target. Both HF and aging are characterized by activation/hyperactivity of various neurohormonal pathways, the most important of which is the sympathetic nervous system (SNS). SNS hyperactivity is initially a compensatory mechanism to stimulate contractility and maintain cardiac output. Unfortunately, this chronic stimulation becomes detrimental and causes decreased cardiac function as well as reduced inotropic reserve due to a decrease in cardiac β-ARs responsiveness. Therapies which (e.g., β-blockers and physical activity) restore β-ARs responsiveness can ameliorate cardiac performance and outcomes during HF, particularly in older patients. In this review, we will discuss physiological β-adrenergic signaling and its alterations in both HF and aging as well as the potential clinical application of targeting β-adrenergic signaling in these disease processes.

Increasing autophagy and blocking Nrf2 suppress laminopathy-induced age-dependent cardiac dysfunction and shortened lifespan

Mutations in the human LMNA gene cause a collection of diseases known as laminopathies. These include myocardial diseases that exhibit age-dependent penetrance of dysrhythmias and heart failure. The LMNA gene encodes A-type lamins, intermediate filaments that support nuclear structure and organize the genome. Mechanisms by which mutant lamins cause age-dependent heart defects are not well understood. To address this issue, we modeled human disease-causing mutations in the Drosophila melanogaster Lamin C gene and expressed mutant Lamin C exclusively in the heart. This resulted in progressive cardiac dysfunction, loss of adipose tissue homeostasis, and a shortened adult lifespan. Within cardiac cells, mutant Lamin C aggregated in the cytoplasm, the CncC(Nrf2)/Keap1 redox sensing pathway was activated, mitochondria exhibited abnormal morphology, and the autophagy cargo receptor Ref2(P)/p62 was upregulated. Genetic analyses demonstrated that simultaneous over-expression of the autophagy kinase Atg1 gene and an RNAi against CncC eliminated the cytoplasmic protein aggregates, restored cardiac function, and lengthened lifespan. These data suggest that simultaneously increasing rates of autophagy and blocking the Nrf2/Keap1 pathway are a potential therapeutic strategy for cardiac laminopathies.

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.

Role of circulating factors in cardiac aging

Worldwide increase in life expectancy is a major contributor to the epidemic of chronic degenerative diseases. Aging, indeed, simultaneously affects multiple organ systems, and it has been hypothesized that systemic alterations in regulators of tissue physiology may regulate this process. Cardiac aging itself is a major risk factor for cardiovascular diseases and, because of the intimate relationship with the brain, may contribute to increase the risk of neurodegenerative disorders. Blood-borne factors may play a major role in this complex and still elusive process. A number of studies, mainly based on the revival of parabiosis, a surgical technique very popular during the 70s of the 20th century to study the effect of a shared circulation in two animals, have indeed shown the potential that humoral factors can control the aging process in different tissues. In this article we review the role of circulating factors in cardiovascular aging. A better understanding of these mechanisms may provide new insights in the aging process and provide novel therapeutic opportunities for chronic age-related disorders.

Modest overexpression of FOXO maintains cardiac proteostasis and ameliorates age-associated functional decline

Heart performance declines with age. Impaired protein quality control (PQC), due to reduced ubiquitin‐proteasome system (UPS) activity, autophagic function, and/or chaperone‐mediated protein refolding, contributes to cardiac deterioration. The transcription factor FOXO participates in regulating genes involved in PQC, senescence, and numerous other processes. Here, a comprehensive approach, involving molecular genetics, novel assays to probe insect cardiac physiology, and bioinformatics, was utilized to investigate the influence of heart‐restricted manipulation of dFOXO expression in the rapidly aging Drosophila melanogaster model. Modest dFOXO overexpression was cardioprotective, ameliorating nonpathological functional decline with age. This was accompanied by increased expression of genes associated predominantly with the UPS, relative to other PQC components, which was validated by a significant decrease in ubiquitinated proteins. RNAi knockdown of UPS candidates accordingly compromised myocardial physiology in young flies. Conversely, excessive dFOXO overexpression or suppression proved detrimental to heart function and/or organismal development. This study highlights D. melanogaster as a model of cardiac aging and FOXO as a tightly regulated mediator of proteostasis and heart performance over time.

Exercise, Nrf2 and Antioxidant Signaling in Cardiac Aging

Aging is represented by a progressive decline in cellular functions. The age-related deformities in cardiac behaviors are the loss of cardiac myocytes through apoptosis or programmed cell death. Oxidative stress (OS) and its deleterious consequence contribute to age-related mechanical remodeling, reduced regenerative capacity, and apoptosis in cardiac tissue. The pathogenesis of OS in the elderly can predispose the heart to other cardiac complications such as atherosclerosis, hypertension, ischemic heart disease, cardiac myopathy, and so on. At the molecular level, oxidant-induced activation of Nrf2 (Nuclear erythroid-2-p45-related factor-2), a transcription factor, regulates several genes containing AREs (Antioxidant Response Element) and bring the respective translates to counteract the reactive radicals and establish homeostasis. Myriad of Nrf2 gene knockout studies in various organs such as lung, liver, kidney, brain, etc. have shown that dysregulation of Nrf2 severely affects the oxidant/ROS sensitivity and predispose the system to several pathological changes with aberrant cellular lesions. On the other hand, its gain of function chemical interventions exhibited oxidant stress resistance and cytoprotection. However, thus far, only a few investigations have shown the potential role of Nrf2 and its non-pharmacological induction in cardiac aging. Therefore, here we review the involvement of Nrf2 signaling along with its responses and ramifications on the cascade of OS under acute exercise stress (AES), moderate exercise training (MET), and endurance exercise stress (EES) conditions in the aging heart.

Rapamycin transiently induces mitochondrial remodeling to reprogram energy metabolism in old hearts

Rapamycin, an inhibitor of mTOR signaling, has been shown to reverse diastolic dysfunction in old mice in 10 weeks, highlighting its therapeutic potential for a poorly treatable condition. However, the mechanisms and temporal regulation of its cardiac benefits remain unclear. We show that improved diastolic function in old mice begins at 2-4 weeks, progressing over the course of 10-week treatment. While TORC1-mediated S6 phosphorylation and TORC2 mediated AKT and PKCα phosphorylation are inhibited throughout the course of treatment, rapamycin inhibits ULK phosphorylation and induces autophagy during just the first week of treatment, returning to baseline at two weeks and after. Concordantly, markers of mitochondrial biogenesis increase over the first two weeks of treatment and return to control levels thereafter. This transient induction of autophagy and mitochondrial biogenesis suggests that damaged mitochondria are replaced by newly synthesized ones to rejuvenate mitochondrial homeostasis. This remodeling is shown to rapidly reverse the age-related reduction in fatty acid oxidation to restore a more youthful substrate utilization and energetic profile in old isolated perfused hearts, and modulates the myocardial metabolomein vivo. This study demonstrates the differential and dynamic mechanisms following rapamycin treatment and highlights the importance of understanding the temporal regulation of rapamycin effects.

Fatiguing exercise initiated later in life reduces incidence of fibrillation and improves sleep quality in Drosophila

As the human body ages, the risk of heart disease and stroke greatly increases. While there is evidence that lifelong exercise is beneficial to the heart's health, the effects of beginning exercise later in life remain unclear. This study aimed to investigate whether exercise training started later in life is beneficial to cardiac aging in Drosophila. We examined 4-week-old wild-type virgin female flies that were exposed to exercise periods of either 1.5, 2.0, or 2.5 h per day, 5 days a week for 2 weeks. Using M-mode traces to analyze cardiac function by looking at parameters including heart rate, rhythmicity, systolic and diastolic diameter, and interval and fractional shortening, we found that cardiac function declined with age, shown by an increase in the number of fibrillation events and a decrease in fractional shortening. About 2.0 and 2.5 h of exercise per day displayed a reduced incidence of fibrillation events, and only physical exercise lasting 2.5-h period increased fractional shortening and total sleep time in Drosophila. These data suggested that training exercise needs to be performed for longer duration to exert physiological benefits for the aging heart. Additionally, climbing ability to assess the exercise-induced muscle fatigue was also measured. We found that 2.0 and 2.5 h of exercise caused exercise-induced fatigue, and fatiguing exercise is beneficial for cardiac and healthy aging overall. This study provides a basis for further study in humans on the impact of beginning an exercise regimen later in life on cardiac health.

Advanced glycation end-products accelerate the cardiac aging process through the receptor for advanced glycation end-products/transforming growth factor-β-Smad signaling pathway in cardiac fibroblasts

AIMS

The current study was carried out to evaluate the effect of advanced glycation end-products (AGE) on cardiac aging and to explore its underlying mechanisms.

METHODS

Neonatal rat cardiac fibroblasts were cultured and divided into four groups: control; AGE; AGE + receptor for AGE antibody and AGE + SB431542 (transforming growth factor-β [TGF-β]/Smad signaling pathway inhibitor, 10 μmol/L) group. After being cultured for 48 h, the cells were harvested and the senescence-associated beta-galactosidase expression was analyzed. Then the level of p16, TGF-β, Smad/p-smad and matrix metalloproteinases-2 was evaluated by western blot.

RESULTS

Significantly increased senescence-associated beta-galactosidase activity as well as p16 level was observed in the AGE group. Furthermore, AGE also significantly increased the TGF-β1, p-smad2/3 and metalloproteinases-2 expression in cardiac fibroblasts (all P < 0.01). Meanwhile, either pretreatment with receptor for AGE-Ab or SB431542 significantly inhibited the upregulated cardiac senescence (beta-galactosidase activity and P16) and fibrosis-associated (TGF-β1, p-smad2/3 and metalloproteinases-2) markers induced by AGE.

CONCLUSIONS

Taken together, all these results suggested that AGE are an important factor for cardiac aging and fibrosis, whereas the receptor for AGE and TGF-β/Smad signaling pathway might be involved in the AGE-induced cardiac aging process.

Altered proteome turnover and remodeling by short-term caloric restriction or rapamycin rejuvenate the aging heart

Chronic caloric restriction (CR) and rapamycin inhibit the mechanistic target of rapamycin (mTOR) signaling, thereby regulating metabolism and suppressing protein synthesis. Caloric restriction or rapamycin extends murine lifespan and ameliorates many aging-associated disorders; however, the beneficial effects of shorter treatment on cardiac aging are not as well understood. Using a recently developed deuterated-leucine labeling method, we investigated the effect of short-term (10 weeks) CR or rapamycin on the proteomics turnover and remodeling of the aging mouse heart. Functionally, we observed that short-term CR and rapamycin both reversed the pre-existing age-dependent cardiac hypertrophy and diastolic dysfunction. There was no significant change in the cardiac global proteome (823 proteins) turnover with age, with a median half-life 9.1 days in the 5-month-old hearts and 8.8 days in the 27-month-old hearts. However, proteome half-lives of old hearts significantly increased after short-term CR (30%) or rapamycin (12%). This was accompanied by attenuation of age-dependent protein oxidative damage and ubiquitination. Quantitative proteomics and pathway analysis revealed an age-dependent decreased abundance of proteins involved in mitochondrial function, electron transport chain, citric acid cycle, and fatty acid metabolism as well as increased abundance of proteins involved in glycolysis and oxidative stress response. This age-dependent cardiac proteome remodeling was significantly reversed by short-term CR or rapamycin, demonstrating a concordance with the beneficial effect on cardiac physiology. The metabolic shift induced by rapamycin was confirmed by metabolomic analysis.

Effects of long-term atorvastatin treatment on cardiac aging

A number of studies have reported that atorvastatin (AVT) may have an important role in the delay of cardiac aging. However, the mechanism by which AVT affects cardiac aging has not been established. In this study, a series of experiments were performed to investigate the effects of AVT treatment on the cardiovascular system and the associated mechanism. Wistar rats were administered AVT or saline for 4 months. Age-related changes in the hearts were measured at the end of the experiment. The results showed that compared with young rats, the aged rats had significant changes indicative of myocardial aging, including increased blood lipid 1evelss, increased body weight, cardiac hypertrophy, larger myocardial cells, irregular muscle fibers, fewer deeply stained nuclei, smaller intercellular spaces, a larger number of apoptotic cells and increased levels of lipofuscin in myocardial tissue. However, long-term AVT treatment was able to significantly delay or even reverse these aging-related changes. In addition, these effects showed a certain dose-dependence. In general, long-term AVT treatment reduces blood lipids, inhibits cardiac hypertrophy, suppresses cardiomyocyte apoptosis and lowers the level of oxidative stress to protect the heart from aging.

MicroRNA-22 increases senescence and activates cardiac fibroblasts in the aging heart

MicroRNAs (miRs) are small non- coding RNA molecules controlling a plethora of biological processes such as development, cellular survival and senescence. We here determined miRs differentially regulated during cardiac postnatal development and aging. Cardiac function, morphology and miR expression profiles were determined in neonatal, 4 weeks, 6 months and 19 months old normotensive male healthy C57/Bl6N mice. MiR-22 was most prominently upregulated during cardiac aging. Cardiac expression of its bioinformatically predicted target mimecan (osteoglycin, OGN) was gradually decreased with advanced age. Luciferase reporter assays validated mimecan as a bona fide miR-22 target. Both, miR-22 and its target mimecan were co- expressed in cardiac fibroblasts and smooth muscle cells. Functionally, miR-22 overexpression induced cellular senescence and promoted migratory activity of cardiac fibroblasts. Small interference RNA-mediated silencing of mimecan in cardiac fibroblasts mimicked the miR-22-mediated effects. Rescue experiments revealed that the effects of miR-22 on cardiac fibroblasts were only partially mediated by mimecan. In conclusion, miR-22 upregulation in the aging heart contributed at least partly to accelerated cardiac fibroblast senescence and increased migratory activity. Our results suggest an involvement of miR-22 in age-associated cardiac changes, such as cardiac fibrosis.

Low glial angiotensinogen improves body habitus, diastolic function, and exercise tolerance in aging male rats

OBJECTIVES

Long-term systemic blockade of the renin-angiotensin system (RAS) with either an angiotensin (Ang) II type 1 receptor antagonist or an angiotensin-converting enzyme inhibitor attenuates age-related cardiac remodeling and oxidative damage, and improves myocardial relaxation. However, the role of the brain RAS in mediating the development of diastolic dysfunction during aging is not known. We hypothesized that low brain RAS protects against the development of age-related diastolic dysfunction and left ventricular remodeling.

METHODS

Sixty-week-old transgenic male ASrAOGEN rats (n =9), with normal circulating Ang II and functionally low brain Ang II, because of a GFAP promoter-linked angiotensinogen antisense targeted to glia, and age-matched and sex-matched Hannover Sprague-Dawley (SD; n= 9) rats, with normal levels of both circulating and brain Ang II, underwent echocardiograms to evaluate cardiac structure and function. Postmortem hearts were further compared for histological, molecular, and biochemical changes consistent with cardiac aging.

RESULTS

ASrAOGEN rats showed preserved systolic and diastolic function at mid-life and this was associated with a lower, more favorable ratio of the phospholamban-SERCA2 ratio, reduced incidence of histological changes in the left ventricle, and increased cardiac Ang-(1-7) when compared with the in-vivo functional, and ex-vivo structural and biochemical indices from age-matched SD rats. Moreover, ASrAOGEN rats had lower percent body fat and a superior exercise tolerance when compared with SD rats of the same age.

CONCLUSION

Our data indicate that the central RAS plays a role in the maintenance of diastolic function and exercise tolerance in mid-life and this may be related to effects on body habitus.

Matrix metalloproteinase-28 deletion amplifies inflammatory and extracellular matrix responses to cardiac aging

To determine if matrix metalloproteinase (MMP)-28 mediates cardiac aging, wild-type (WT) and MMP-28-/- young (7 ± 1 months, n = 9 each) and old (20 ± 2 months, n = 7 each) female mice were evaluated. MMP-28 expression in the left ventricle (LV) increased 42% in old WT mice compared to young controls (p < 0.05). By Doppler echocardiography, LV function declined at 20 ± 2 months of age for both groups. However, dobutamine stress responses were similar, indicating that cardiac reserve was maintained. Plasma proteomic profiling revealed that macrophage inflammatory protein (MIP)-1 α, MIP-1β and MMP-9 plasma levels did not change in WT old mice but were significantly elevated in MMP-28-/- old mice (all p < 0.05), suggestive of a higher inflammatory status when MMP-28 is deleted. RT2-PCR gene array and immunoblotting analyses demonstrated that MIP-1α and MMP-9 gene and protein levels in the LV were also higher in MMP-28-/- old mice (all p < 0.05). Macrophage numbers in the LV increased similarly in WT and MMP-28-/- old mice, compared to respective young controls (both p < 0.05). Collagen content was not different among the WT and MMP-28-/- young and old mice. In conclusion, LV inflammation increases with age, and MMP-28 deletion further elevates inflammation and extracellular matrix responses, without altering macrophage numbers or collagen content.