Influence of cardiac-specific overexpression of insulin-like growth factor 1 on lifespan and aging-associated changes in cardiac intracellular Ca2+ homeostasis, protein damage and apoptotic protein expression

Exploratory bibliometric analysis and text mining to reveal research trends in cardiac aging

Objectives

We conducted a text mining analysis of 40 years of literature on cardiac aging from PubMed to investigate the current understanding on cardiac aging and its mechanisms. This study aimed to embody what most researchers consider cardiac aging to be.

Methods

We used multiple text mining and machine learning tools to extract important information from a large amount of text.

Results

Analysis revealed that the terms most frequently associated with cardiac aging include "diastolic," "hypertrophy," "fibrosis," "apoptosis," "mitochondrial," "oxidative," and "autophagy." These terms suggest that cardiac aging is characterized by mitochondrial dysfunction, oxidative stress, and impairment of autophagy, especially mitophagy. We also revealed an increase in the frequency of occurrence of "autophagy" in recent years, suggesting that research on autophagy has made a breakthrough in the field of cardiac aging. Additionally, the frequency of occurrence of "mitophagy" has increased significantly since 2019, suggesting that mitophagy is an important factor in cardiac aging.

Conclusions

Cardiac aging is a complex process that involves mitochondrial dysfunction, oxidative stress, and impairment of autophagy, especially mitophagy. Further research is warranted to elucidate the mechanisms of cardiac aging and develop strategies to mitigate its detrimental effects.

Age-Related Hormones Changes and Its Impact on Health Status and Lifespan

The increase in life expectancy is accompanied with an increased consultation of age-related pathologies including endocrine disorders. Two main areas are focusing the attention of medical and social research in older population: the diagnosis and care of this heterogeneous population, and the interventional measures potentially useful to mitigate age-related functional declines and to increase health and quality of lifespan. Thus, better understanding the physiopathology of aging and establishing accurate diagnostic and personalized approaches are a priority and currently an unmet need of the medical community. The endocrine system plays a major role in survival and lifespan through regulating vital processes such as energy consumption and optimizing the stress response among others. The aim of this paper is to review the physiological evolution of the main hormonal functions in aging and its clinical translation to improve our approach to the aging patient.

Role of a small GTPase Cdc42 in aging and age-related diseases

A small GTPase, Cdc42 is evolutionarily one of the most ancient members of the Rho family, which is ubiquitously expressed and involved in a wide range of fundamental cellular functions. The crucial role of Cdc42 includes regulation of the actin cytoskeleton, cell polarity, morphology and migration, endocytosis and exocytosis, cell cycle, and proliferation in many different cell types. Many studies have provided compelling yet contradicting evidence that Cdc42 dysregulation plays an important role in cellular and tissue aging. Furthermore, Cdc42 is a critical factor in the development and progression of aging-related pathologies, such as neurodegenerative and cardiovascular disorders, diabetes type 2, and aging-related disorders of the joints and bones, and the inhibition of the Cdc42 demonstrates potentially significant therapeutic and anti-aging effects in animal models of aging and disease. However, regulation of Cdc42 expression and activity is very complex and depends on many factors, such as the origin and complexity of the tissues, hormonal status, etc. Therefore, this review is focused on current advances in understanding the underlying cellular and molecular mechanisms associated with Cdc42 activity and regulation of senescence in different cell types since they may provide a foundation for novel therapeutic strategies and targeted drugs to reverse the aging process and treat aging-associated disorders.

Role of apoptosis repressor with caspase recruitment domain (ARC) in cell death and cardiovascular disease

Apoptosis repressor with caspase recruitment domain (ARC) is a highly effective and multifunctional inhibitor of apoptosis that is mainly expressed in postmitotic cells such as cardiomyocytes and skeletal muscle cells. ARC contains a C-terminal region rich in proline and glutamic acid residues and an N-terminal caspase recruitment domain (CARD). The CARD is originally described as a protein-binding motif that interacts with caspase through a CARD-CARD interaction. Initially, the inhibitory effect of ARC was only found in apoptosis, however, it was later found that ARC also played a regulatory role in other types of cell death. As a powerful cardioprotective factor, ARC can protect the heart by inhibiting the death of cardiomyocytes in various ways. ARC can reduce the cardiomyocyte apoptotic response to various stresses and injuries, including extrinsic apoptosis induced by death receptor ligands, cellular Ca²⁺ homeostasis and the dysregulation of endoplasmic reticulum (ER) stress, oxidative stress and hypoxia. In addition, changes in ARC transcription and translation levels in the heart can cause a series of physiological and pathological changes, and ARC can also perform corresponding functions through interactions with other molecules. Although there has been much research on ARC, the functional redundancy among proteins shows that ARC still has much research value. This review summarizes the molecular characteristics of ARC, its roles in the various death modes in cardiomyocytes and the roles of ARC in cardiac pathophysiology. This article also describes the potential therapeutic effect and research prospects of ARC.

Protein Biomarkers and Risk of Atrial Fibrillation: The FHS

BACKGROUND

Identification of protein biomarkers associated with incident atrial fibrillation (AF) may improve the understanding of the pathophysiology, risk prediction, and development of new therapeutics for AF. We examined the associations between 85 protein biomarkers and incident AF.

METHODS

We included participants ≥50 years of age from the FHS (Framingham Heart Study) Offspring and Third Generation cohorts, who had 85 fasting plasma proteins measured using Luminex xMAP platform. Hazard ratios (per 1 SD increment of rank-normalized biomarker [hazard ratio]) and 95% CIs for incident AF were calculated using Cox regression models adjusted for age, sex, height, weight, current smoking, systolic blood pressure, diastolic blood pressure, hypertension treatment, diabetes mellitus, valvular heart disease, prevalent myocardial infarction, and prevalent heart failure. We used the false discovery rate to account for multiple testing.

RESULTS

The study sample comprised 3378 participants (54% women) with mean (SD) age of 61.5 (8.4) years. In total, 401 developed AF over a mean follow-up of 12.3±3.8 years. We observed lower hazard of incident AF associated with higher mean levels of IGF1 (insulin-like growth factor 1; hazard ratio per 1 SD increment in protein level, 0.84 [95% CI, 0.76-0.93]), and higher hazard of incident AF associated with higher mean levels of both IGFBP1 (insulin-like growth factor-binding protein 1; hazard ratio, 1.24 [95% CI, 1.1-1.39]) and NT-proBNP (N-terminal pro-B-type natriuretic peptide; hazard ratio, 1.73 [95% CI, 1.52-1.96]).

CONCLUSIONS

Decreased levels of IGF1 and increased levels of IGFBP1 and NT-proBNP were associated with higher risk of incident AF.

Effects of IGF-1 on the Cardiovascular System

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Cardiovascular (CV) diseases are the most common health problems worldwide, with a permanent increase in incidence. Growing evidence underlines that insulin-like growth factor 1 (IGF-1) is a very important hormone responsible for normal CV system physiology. IGF-1 is an anabolic growth hormone, responsible for cell growth, differentiation, proliferation, and survival. Despite systemic effects, IGF-1 exerts a wide array of influences in the CV system affecting metabolic homeostasis, vasorelaxation, cardiac contractility and hypertrophy, autophagy, apoptosis, and antioxidative processes. The vasodilatory effect of IGF-1, is achieved through the regulation of the activity of endothelial nitric oxide synthase (eNOS) and, at least partly, through enhancing inducible NOS (iNOS) activity. Also, IGF-1 stimulates vascular relaxation through regulation of sodium/potassiumadenosine- triphosphatase. Numerous animal studies provided evidence of diverse influences of IGF-1 in the CV system such as vasorelaxation, anti-apoptotic and prosurvival effects. Human studies indicate that low serum levels of free or total IGF-1 contribute to an increased risk of CV and cerebrovascular disease. Large human trials aiming at finding clinical efficacy and outcome of IGF-1-related therapy are of great interest.

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We look forward to the development of new IGF 1 therapies with minor side effects. In this review, we discuss the latest literature data regarding the function of IGF-1 in the CV system in the physiological and pathophysiological conditions.

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.

Cardiac-specific overexpression of metallothionein attenuates L-NAME-induced myocardial contractile anomalies and apoptosis

Hypertension contributes to the high cardiac morbidity and mortality. Although oxidative stress plays an essential role in hypertensive heart diseases, the mechanism remains elusive. Transgenic mice with cardiac overexpression of metallothionein, a heavy metal‐binding scavenger, were challenged with N^G‐nitro‐L‐arginine methyl ester (L‐NAME) for 14 days prior to measurement of myocardial contractile and intracellular Ca²⁺ anomalies as well as cell signalling mechanisms using Western blot and immunofluorescence analysis. L‐NAME challenge elicited hypertension, macrophage infiltration, oxidative stress, inflammation and cardiac dysfunction manifested as increased proinflammatory macrophage marker F4/80, interleukin‐1β (IL‐1β), intracellular O2- production, LV end systolic and diastolic diameters as well as depressed fractional shortening. L‐NAME treatment reduced mitochondrial membrane potential (MMP), impaired cardiomyocyte contractile and intracellular Ca²⁺ properties as evidenced by suppressed peak shortening, maximal velocity of shortening/relengthening, rise in intracellular Ca²⁺, along with elevated baseline and peak intracellular Ca²⁺. These unfavourable mechanical changes and decreased MMP (except blood pressure and macrophage infiltration) were alleviated by overexpression of metallothionein. Furthermore, the apoptosis markers including BAD, Bax, Caspase 9, Caspase 12 and cleaved Caspase 3 were up‐regulated while the anti‐apoptotic marker Bcl‐2 was decreased by L‐NAME treatment. Metallothionein transgene reversed L‐NAME‐induced changes in Bax, Bcl‐2, BAD phosphorylation, Caspase 9, Caspase 12 and cleaved Caspase 3. Our results suggest that metallothionein protects against L‐NAME‐induced myocardial contractile anomalies in part through inhibition of apoptosis.

Growth signaling and longevity in mouse models

Reduction of insulin/insulin-like growth factor 1 (IGF1) signaling (IIS) extends the lifespan of various species. So far, several longevity mouse models have been developed containing mutations related to growth signaling deficiency by targeting growth hormone (GH), IGF1, IGF1 receptor, insulin receptor, and insulin receptor substrate. In addition, p70 ribosomal protein S6 kinase 1 (S6K1) knockout leads to lifespan extension. S6K1 encodes an important kinase in the regulation of cell growth. S6K1 is regulated by mechanistic target of rapamycin (mTOR) complex 1. The v-myc myelocytomatosis viral oncogene homolog (MYC)-deficient mice also exhibits a longevity phenotype. The gene expression profiles of these mice models have been measured to identify their longevity mechanisms. Here, we summarize our knowledge of long-lived mouse models related to growth and discuss phenotypic characteristics, including organ-specific gene expression patterns.

Relation of IGF-1 and IGFBP-3 with prevalent and incident atrial fibrillation in a population-based study

BACKGROUND

Insulin-like growth factor 1 (IGF-1) and its main binding protein insulin-like growth factor binding protein 3 (IGFBP-3) have been related to several cardiovascular diseases. The relation with atrial fibrillation (AF) is largely unknown.

OBJECTIVE

The objective of this study was to investigate the association of IGF-1 and IGFBP-3 levels with prevalent and incident AF in a large population-based study.

METHODS

Data from the Study of Health in Pomerania (SHIP) were collected. At presentation, a medical examination, standardized electrocardiographic assessment, and measurements of serum IGF-1 and IGFBP-3 levels were performed. Incident AF was assessed in individuals without AF at baseline (SHIP-1) who developed AF during follow-up (SHIP-2; after a mean of 5.2 years).

RESULTS

Of 3160 participants, 66 (2.1%) exhibited AF at baseline. IGF-1 levels and IGF-1/IGFBP-3 ratios were significantly lower in individuals with AF than in those without AF (IGF-1: 104.2 ± 41.6 ng/mL vs 142.9 ± 53.5 ng/mL, P < .001 and IGF-1/IGFBP-3: 0.031 ± (0.009 ng/mL vs 0.036 ± 0.010 ng/mL, P = .006, respectively). Multivariable-adjusted logistic regression models showed that a low IGF-1/IGFBP-3 ratio was associated with prevalent AF (odds ratios 0.67; 95% confidence interval 0.48-0.94; P = .021). Of 1817 individuals without AF at baseline, 27 (1.5%) developed AF during follow-up. In these participants, IGF-1 levels, but not IGF-1/IGFBP-3 ratios, were significantly lower (IGF-1: 113.3 ± 38.6 ng/mL vs 147.2 ± 51.6 ng/mL, P = .013 and IGF-1/IGFBP-3: 0.033 ± 0.008 ng/mL vs 0.036 ± 0.010 ng/mL, P = .176).

CONCLUSION

Low IGF-1/IGFBP-3 ratios are associated with a higher prevalence of AF. There seems to be a similar impact in incident AF.

Ablation of toll-like receptor 4 attenuates aging-induced myocardial remodeling and contractile dysfunction through NCoRI-HDAC1-mediated regulation of autophagy

Aging is usually accompanied with overt structural and functional changes as well as suppressed autophagy in the heart although the precise regulatory mechanisms are somewhat unknown. Here we evaluated the role of the innate proinflammatory mediator toll-like receptor 4 (TLR4) in cardiac aging and the underlying mechanism with a focus on autophagy. Cardiac geometry and function were monitored in young or old wild-type (WT) and TLR4 knockout (TLR4^-/-) mice using echocardiography, IonOptix® edge-detection and fura-2 techniques. Levels of autophagy and mitophagy, nuclear receptor corepressor 1 (NCoR1) and histone deacetylase I (HDAC1) were examined using western blot. Transmission electronic microscopy (TEM) was employed to monitor myocardial ultrastructure. Our results revealed that TLR4 ablation alleviated advanced aging (24 months)-induced changes in myocardial remodeling (increased heart weight, chamber size, cardiomyocyte cross-sectional area), contractile function and intracellular Ca²⁺ handling as well as autophagy and mitophagy [Beclin-1, Atg5, LC3B, PTEN-induced putative kinase 1 (PINK1), Parkin and p62]. Aging downregulated levels of NCoR1 and HDAC1 as well as their interaction, the effects were significantly attenuated or negated by TLR4 ablation. Advanced aging disturbed myocardial ultrastructure as evidenced by loss of myofilament alignment and swollen mitochondria, which was obliterated by TLR4 ablation. Moreover, aging suppressed autophagy (GFP-LC3B puncta) in neonatal mouse cardiomyocytes, the effect of which was negated by the TLR4 inhibitor CLI-095. Inhibition of HDCA1 using apicidin cancelled off CLI095-induced beneficial response of GFP-LC3B puncta against aging. Our data collectively indicate a role for TLR4-mediated autophagy in cardiac remodeling and contractile dysfunction in aging through a HDAC1-NCoR1-dependent mechanism.

A Reassessment of Genes Modulating Aging in Mice Using Demographic Measurements of the Rate of Aging

Many studies have reported genetic interventions that have an effect on mouse life span; however, it is crucial to discriminate between manipulations of aging and aging-independent causes of life extension. Here, we used the Gompertz equation to determine whether previously reported aging-related mouse genes statistically affect the demographic rate of aging. Of 30 genetic manipulations previously reported to extend life span, for only two we found evidence of retarding demographic aging: Cisd2 and hMTH1. Of 24 genetic manipulations reported to shorten life span and induce premature aging features, we found evidence of five accelerating demographic aging: Casp2, Fn1, IKK-β, JunD, and Stub1. Overall, our reassessment found that only 15% of the genetic manipulations analyzed significantly affected the demographic rate of aging as predicted, suggesting that a relatively small proportion of interventions affecting longevity do so by regulating the rate of aging. By contrast, genetic manipulations affecting longevity tend to impact on aging-independent mortality. Our meta-analysis of multiple mouse longevity studies also reveals substantial variation in the controls used across experiments, suggesting that a short life span of controls is a potential source of bias. Overall, the present work leads to a reassessment of genes affecting the aging process in mice, with broad implications for our understanding of the genetics of mammalian aging and which genes may be more promising targets for drug discovery.

Akt2 ablation prolongs life span and improves myocardial contractile function with adaptive cardiac remodeling: role of Sirt1-mediated autophagy regulation

Aging is accompanied with unfavorable geometric and functional changes in the heart involving dysregulation of Akt and autophagy. This study examined the impact of Akt2 ablation on life span and cardiac aging as well as the mechanisms involved with a focus on autophagy and mitochondrial integrity. Cardiac geometry, contractile, and intracellular Ca2+ properties were evaluated using echocardiography, IonOptix® edge-detection and fura-2 techniques. Levels of Sirt1, mitochondrial integrity, autophagy, and mitophagy markers were evaluated using Western blot. Our results revealed that Akt2 ablation prolonged life span (by 9.1%) and alleviated aging (24 months)-induced unfavorable changes in myocardial function and intracellular Ca2+ handling (SERCA2a oxidation) albeit with more pronounced cardiac hypertrophy (58.1%, 47.8%, and 14.5% rises in heart weight, wall thickness, and cardiomyocyte cross-sectional area). Aging downregulated levels of Sirt1, increased phosphorylation of Akt, and the nuclear transcriptional factor Foxo1, as well as facilitated acetylation of Foxo1, the effects of which (except Sirt1 and Foxo1 acetylation) were significantly attenuated or negated by Akt2 ablation. Advanced aging disturbed autophagy, mitophagy, and mitochondrial integrity as evidenced by increased p62, decreased levels of beclin-1, Atg7, LC3B, BNIP3, PTEN-induced putative kinase 1 (PINK1), Parkin, UCP-2, PGC-1α, and aconitase activity, the effects of which were reversed by Akt2 ablation. Aging-induced cardiomyocyte contractile dysfunction and loss of mitophagy were improved by rapamycin and the Sirt1 activator SRT1720. Activation of Akt using insulin or Parkin deficiency prevented SRT1720-induced beneficial effects against aging. In conclusion, our data indicate that Akt2 ablation protects against cardiac aging through restored Foxo1-related autophagy and mitochondrial integrity.

GH and ageing: Pitfalls and new insights

The interrelationships of growth hormone (GH) actions and aging are complex and incompletely understood. The very pronounced age-related decline in GH secretion together with benefits of GH therapy in individuals with congenital or adult GH deficiency (GHD) prompted interest in GH as an anti-aging agent. However, the benefits of treatment of normal elderly subjects with GH appear to be marginal and counterbalanced by worrisome side effects. In laboratory mice, genetic GH deficiency or resistance leads to a remarkable extension of longevity accompanied by signs of delayed and/or slower aging. Mechanisms believed to contribute to extended longevity of GH-related mutants include improved anti-oxidant defenses, enhanced insulin sensitivity and reduced insulin levels, reduced inflammation and cell senescence, major shifts in mitochondrial function and energy metabolism, and greater stress resistance. Negative association of the somatotropic signaling and GH/insulin-like growth factor 1 (IGF-1)-dependent traits with longevity has also been shown in other mammalian species. In humans, syndromes of GH resistance or deficiency have no consistent effect on longevity, but can provide striking protection from cancer, diabetes and atherosclerosis. More subtle alterations in various steps of GH and IGF-1 signaling are associated with reduced old-age mortality, particularly in women and with improved chances of attaining extremes of lifespan. Epidemiological studies raise a possibility that the relationship of IGF-1 and perhaps also GH levels with human healthy aging and longevity may be biphasic. However, the impact of somatotropic signaling on neoplastic disease is difficult to separate from its impact on aging, and IGF-1 levels exhibit opposite associations with different chronic, age-related diseases.

Different Mechanisms of Longevity in Long-Lived Mouse and Caenorhabditis elegans Mutants Revealed by Statistical Analysis of Mortality Rates

Mouse and Caenorhabditis elegans mutants with altered life spans are being used to investigate the aging process and how genes determine life span. The survival of a population can be modeled by the Gompertz function, which comprises two parameters. One of these parameters ("G") describes the rate at which mortality accelerates with age and is often described as the "rate of aging." The other parameter ("A") may correspond to the organism's baseline vulnerability to deleterious effects of disease and the environment. We show that, in mice, life-span-extending mutations systematically fail to affect the age-dependent acceleration of mortality (G), but instead affect only baseline vulnerability (A). This remains true even when comparing strains maintained under identical environmental conditions. In contrast, life-span-extending mutations in C. elegans were associated with decreases in G These observations on mortality rate kinetics suggest that the mechanisms of aging in mammals might fundamentally differ from those in nematodes.

Antioxidant metallothionein alleviates endoplasmic reticulum stress-induced myocardial apoptosis and contractile dysfunction

AIMS

Endoplasmic reticulum (ER) stress exerts myocardial oxidative stress, apoptosis, and contractile anomalies, although the precise interplay between ER stress and apoptosis remains elusive. This study was designed to examine the impact of the cysteine-rich free radical scavenger metallothionein on ER stress-induced myocardial contractile defect and underlying mechanisms.

METHODS AND RESULTS

Wild-type friendly virus B and transgenic mice with cardiac-specific overexpression of metallothionein were challenged with the ER stress inducer tunicamycin (1 mg/kg, intraperitoneal, 48 h) prior to the assessment of myocardial function, oxidative stress, and apoptosis. Our results revealed that tunicamycin promoted cardiac remodeling (enlarged left ventricular end systolic/diastolic diameters with little changes in left ventricular wall thickness), suppressed fractional shortening and cardiomyocyte contractile function, elevated resting Ca(2+), decreased stimulated Ca(2+) release, prolonged intracellular Ca(2+) clearance, and downregulated sarco(endo)plasmic reticulum Ca(2+)-ATPase levels, the effects of which were negated by metallothionein. Treatment with tunicamycin caused cardiomyocyte mitochondrial injury, as evidenced by decreased mitochondrial membrane potential (∆Ѱm, assessed by JC-1 staining), the effect of which was negated by the antioxidant. Moreover, tunicamycin challenge dramatically facilitated myocardial apoptosis as manifested by increased Bax, caspase 9, and caspase 12 protein levels, as well as elevated caspase 3 activity. Interestingly, metallothionein transgene significantly alleviated tunicamycin-induced myocardial apoptosis.

CONCLUSION

Taken together, our data favor a beneficial effect of metallothionein against ER stress-induced cardiac dysfunction possibly associated with attenuation of myocardial apoptosis.

Effect of Age, Estrogen Status, and Late-Life GPER Activation on Cardiac Structure and Function in the Fischer344×Brown Norway Female Rat

Age-associated changes in cardiac structure and function, together with estrogen loss, contribute to the progression of heart failure with preserved ejection fraction in older women. To investigate the effects of aging and estrogen loss on the development of its precursor, asymptomatic left ventricular diastolic dysfunction, echocardiograms were performed in 10 middle-aged (20 months) and 30 old-aged (30 months) female Fischer344×Brown-Norway rats, 4 and 8 weeks after ovariectomy (OVX) and sham procedures (gonads left intact). The cardioprotective potential of administering chronic G1, the selective agonist to the new G-protein-coupled estrogen receptor (GPER), was further evaluated in old rats (Old-OVX+G1) versus age-matched, vehicle-treated OVX and gonadal intact rats. Advanced age and estrogen loss led to decreases in myocardial relaxation and elevations in filling pressure, in part, due to reductions in phosphorylated phospholamban and increases in cardiac collagen deposition. Eight weeks of G-protein-coupled estrogen receptor activation in Old-OVX+G1 rats reversed the adverse effects of age and estrogen loss on myocardial relaxation through increases in sarcoplasmic reticulum Ca²⁺ ATPase expression and reductions in interstitial fibrosis. These findings may explain the preponderance of heart failure with preserved ejection fraction in older postmenopausal women and provide a promising, late-life therapeutic target to reverse or halt the progression of left ventricular diastolic dysfunction.

Neuroendocrine Regulation of Growth Hormone Secretion

This article reviews the main findings that emerged in the intervening years since the previous volume on hormonal control of growth in the section on the endocrine system of the Handbook of Physiology concerning the intra- and extrahypothalamic neuronal networks connecting growth hormone releasing hormone (GHRH) and somatostatin hypophysiotropic neurons and the integration between regulators of food intake/metabolism and GH release. Among these findings, the discovery of ghrelin still raises many unanswered questions. One important event was the application of deconvolution analysis to the pulsatile patterns of GH secretion in different mammalian species, including Man, according to gender, hormonal environment and ageing. Concerning this last phenomenon, a great body of evidence now supports the role of an attenuation of the GHRH/GH/Insulin-like growth factor-1 (IGF-1) axis in the control of mammalian aging.

Protective actions of melatonin and growth hormone on the aged cardiovascular system

Epidemiological studies indicate that certain aspects of lifestyle and genetics act as risk factors for a variety of cardiovascular disorders, including coronary disease, hypertension, heart failure and stroke. Aging, however, appears to be the major contributor for morbidity and mortality of the impaired cardiovascular system. Growth hormone (GH) and melatonin seem to prevent cardiac aging, as they contribute to the recovery of several physiological parameters affected by age. These hormones exhibit antioxidant properties and decrease oxidative stress and apoptosis. This paper summarizes a set of studies related to the potential role that therapy with GH and melatonin may play in the protection of the altered cardiac function due to aging, with a focus on experiments performed in our laboratory using the senescence-accelerated mouse as an aging model. In general, we observed significantly increased inflammation, oxidative stress and apoptosis markers in hearts from senescence-accelerated prone 10-month-old animals compared to 2-month-old controls, while anti-inflammatory and antiapoptotic markers as well as endothelial nitric oxide synthase were decreased. Senescence-accelerated resistant animals showed no significant changes with age. GH or melatonin treatment prevented the age-dependent cardiac alterations observed in the senescence-accelerated prone group. Combined administration of GH plus melatonin reduced the age-related changes in senescence-accelerated prone hearts in an additive fashion that was different to that displayed when administered alone. GH and melatonin may be potential agents for counteracting oxidative stress, apoptosis and inflammation in the aging heart.

The insulin-like growth factor I system: physiological and pathophysiological implication in cardiovascular diseases associated with metabolic syndrome

Metabolic syndrome is a cluster of risk factors including obesity, dyslipidemia, hypertension, and insulin resistance. A number of theories have been speculated for the pathogenesis of metabolic syndrome including impaired glucose and lipid metabolism, lipotoxicity, oxidative stress, interrupted neurohormonal regulation and compromised intracellular Ca(2+) handling. Recent evidence has revealed that adults with severe growth hormone (GH) and insulin-like growth factor I (IGF-1) deficiency such as Laron syndrome display increased risk of stroke and cardiovascular diseases. IGF-1 signaling may regulate contractility, metabolism, hypertrophy, apoptosis, autophagy, stem cell regeneration and senescence in the heart to maintain cardiac homeostasis. An inverse relationship between plasma IGF-1 levels and prevalence of metabolic syndrome as well as associated cardiovascular complications has been identified, suggesting the clinical promises of IGF-1 analogues or IGF-1 receptor activation in the management of metabolic and cardiovascular diseases. However, the underlying pathophysiological mechanisms between IGF-1 and metabolic syndrome are still poorly understood. This mini-review will discuss the role of IGF-1 signaling cascade in the prevalence of metabolic syndrome in particular the susceptibility to overnutrition and sedentary life style-induced obesity, dyslipidemia, insulin resistance and other features of metabolic syndrome. Special attention will be dedicated in IGF-1-associated changes in cardiac responses in various metabolic syndrome components such as insulin resistance, obesity, hypertension and dyslipidemia. The potential risk of IGF-1 and IGF-1R stimulation such as tumorigenesis is discussed. Therapeutic promises of IGF-1 and IGF-1 analogues including mecasermin, mecasermin rinfabate and PEGylated IGF-1 will be discussed.

MnSOD overexpression reduces fibrosis and pro-apoptotic signaling in the aging mouse heart

Contractility of the heart is impaired with advancing age via mechanical remodeling, as myocytes are lost through apoptosis and collagenous fibers accumulate. Exercise training confers protection against fibrosis and apoptosis in the aging heart, but the mechanisms remain poorly understood. We recently reported that exercise training elevates Mn isoform of superoxide dismutase (MnSOD) in the aging heart, concomitant with reduction in oxidative stress and fibrosis. Here, we tested the hypothesis that overexpression of MnSOD would be causal in protection against fibrosis and apoptosis in the aging heart. Hearts were extracted from young (8 months) wild-type, young mice overexpressing the Sod2 (MnSOD) gene, old (28 months) wild-type, and old transgenic mice. Left ventricle MnSOD protein levels were elevated in young mice overexpressing the Sod2 (MnSOD) gene and old transgenic mice. MnSODTg mice exhibited lower oxidative stress (total hydroperoxides, 4-hydroxynonenal, and 8-isoprostane) in the old group. Age-related cardiac remodeling and fibrosis was mitigated in MnSOD Tg mice with reductions in extramyocyte space (-65%), collagen-I, and transforming growth factor-β. Pro-apoptotic markers Bax (-38%) and caspase-3 cleavage (-41%) were reduced and apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive nuclei, DNA laddering) was mitigated in MnSOD Tg hearts compared with old wild-type. We conclude that MnSOD elevation is indeed protective against oxidative stress, fibrosis, and apoptosis in the aging heart.

Mitochondrial aldehyde dehydrogenase 2 accentuates aging-induced cardiac remodeling and contractile dysfunction: role of AMPK, Sirt1, and mitochondrial function

Cardiac aging is associated with compromised myocardial function and morphology although the underlying mechanism remains elusive. Aldehyde dehydrogenase 2 (ALDH2), an essential mitochondrial enzyme governing cardiac function, displays polymorphism in humans. This study was designed to examine the role of ALDH2 in aging-induced myocardial anomalies. Myocardial mechanical and intracellular Ca(2+) properties were examined in young (4-5 months) and old (26-28 months) wild-type and ALDH2 transgenic mice. Cardiac histology, mitochondrial integrity, O2(-) generation, apoptosis, and signaling cascades, including AMPK activation and Sirt1 level were evaluated. Myocardial function and intracellular Ca(2+) handling were compromised with advanced aging; the effects were accentuated by ALDH2. Hematoxylin and eosin and Masson trichrome staining revealed cardiac hypertrophy and interstitial fibrosis associated with greater left-ventricular mass and wall thickness in aged mice. ALDH2 accentuated aging-induced cardiac hypertrophy but not fibrosis. Aging promoted O2(-) release, apoptosis, and mitochondrial injury (mitochondrial membrane potential, levels of UCP-2 and PGC-1α), and the effects were also exacerbated by ALDH2. Aging dampened AMPK phosphorylation and Sirt1, the effects of which were exaggerated by ALDH2. Treatment with the ALDH2 activator Alda-1 accentuated aging-induced O2(-) generation and mechanical dysfunction in cardiomyocytes, the effects of which were mitigated by cotreatment with activators of AMPK and Sirt1, AICAR, resveratrol, and SRT1720. Examination of human longevity revealed a positive correlation between life span and ALDH2 gene mutation. Taken together, our data revealed that ALDH2 enzyme may accentuate myocardial remodeling and contractile dysfunction in aging, possibly through AMPK/Sirt1-mediated mitochondrial injury.

Insulin-like growth factor I, insulin-like growth factor binding protein 3, and atrial fibrillation in the elderly

BACKGROUND

Insulin-like growth factor I (IGF-I) and insulin-like growth factor binding protein 3 (IGFBP-3) are involved in oxidative stress and atherosclerosis; however, the relationship between the IGF-I system and atrial fibrillation (AF) is not known. The objective of this analysis was to assess, the relationship between IGF-I and IGFBP-3 serum levels and AF among elderly participants.

METHODS

In this cross-sectional study, 719 participants (mean age [SD] years: 78.2 [6.8]; 31.8% men) were evaluated during an outpatient geriatric assessment. AF was determined by electrocardiogram or medical record. Participants were classified into two groups: Participants with AF (n = 91) or without AF (n = 628). IGF-I and IGFBP-3 serum levels were determined by enzyme linked immunosorbent assay.

RESULTS

After adjusting for age and sex, the mean IGF-I and IGFBP-3 serum levels were significantly lower among AF participants than among non-AF participants (mean IGF-I ng/mL [SD] = 133.8 [66.6] vs 157.9 [80.0], p = .02; mean IGFBP-3 ng/mL [SD] = 3,653 [1,393] vs 4,151 [1,583], p = .03, respectively). After adjusting for confounding factors (age, gender, beta blocker medication, heart rate, hypertension, stroke, and chronic heart failure), low IGF-I serum level (OR [95% CI] = 0.66 [0.49-0.87]) and low IGFBP-3 serum level (0.71 [0.54-0.93]) remained independent determinants of AF.

CONCLUSIONS

Low IGF-I and low IGFBP-3 serum levels were independently associated with AF in this elderly population. This result should be confirmed in a longitudinal study to evaluate whether IGF-I and/or IGFBP-3 serum levels are predictive of incident AF.

Growth properties of cardiac stem cells are a novel biomarker of patients' outcome after coronary bypass surgery

BACKGROUND

The efficacy of bypass surgery in patients with ischemic cardiomyopathy is not easily predictable; preoperative clinical conditions may be similar, but the outcome may differ significantly. We hypothesized that the growth reserve of cardiac stem cells (CSCs) and circulating cytokines promoting CSC activation are critical determinants of ventricular remodeling in this patient population.

METHODS AND RESULTS

To document the growth kinetics of CSCs, population-doubling time, telomere length, telomerase activity, and insulin-like growth factor-1 receptor expression were measured in CSCs isolated from 38 patients undergoing bypass surgery. Additionally, the blood levels of insulin-like growth factor-1, hepatocyte growth factor, and vascular endothelial growth factor were evaluated. The variables of CSC growth were expressed as a function of the changes in wall thickness, chamber diameter and volume, ventricular mass-to-chamber volume ratio, and ejection fraction, before and 12 months after surgery. A high correlation was found between indices of CSC function and cardiac anatomy. Negative ventricular remodeling was not observed if CSCs retained a significant growth reserve. The high concentration of insulin-like growth factor-1 systemically pointed to the insulin-like growth factor-1-insulin-like growth factor-1 receptor system as a major player in the adaptive response of the myocardium. hepatocyte growth factor, a mediator of CSC migration, was also high in these patients preoperatively, as was vascular endothelial growth factor, possibly reflecting the vascular growth needed before bypass surgery. Conversely, a decline in CSC growth was coupled with wall thinning, chamber dilation, and depressed ejection fraction.

CONCLUSIONS

The telomere-telomerase axis, population-doubling time, and insulin-like growth factor-1 receptor expression in CSCs, together with a high circulating level of insulin-like growth factor-1, represent a novel biomarker able to predict the evolution of ischemic cardiomyopathy following revascularization.

Innate regeneration in the aging heart: healing from within

The concept of the heart as a terminally differentiated organ incapable of replacing damaged myocytes has been at the center of cardiovascular research and therapeutic development for the past 50 years. The progressive decline in myocyte number as a function of age and the formation of scarred tissue after myocardial infarction have been interpreted as irrefutable proofs of the postmitotic characteristic of the heart. However, emerging evidence supports a more dynamic view of the heart in which cell death and renewal are vital components of the remodeling process that governs cardiac homeostasis, aging, and disease. The identification of dividing myocytes in the adult and senescent heart raises the important question concerning the origin of these newly formed cells. In vitro and in vivo findings strongly suggest that replicating myocytes derive from lineage determination of resident primitive cells, supporting the notion that cardiomyogenesis is controlled by activation and differentiation of a stem cell compartment. It is the current view that the myocardium is an organ permissive of tissue regeneration mediated by exogenous and endogenous progenitor cells.

Mice producing reduced levels of insulin-like growth factor type 1 display an increase in maximum, but not mean, life span

Reduced signaling through the IGF type 1 (IGF-1) receptor increases life span in multiple invertebrate organisms. Studies on mammalian longevity suggest that reducing levels of IGF-1 may also increase life span. However, the data are conflicting and complicated by the physiology of the mammalian neuroendocrine system. We have performed life-span analysis on mice homozygous for an insertion in the Igf1 gene. These mice produce reduced levels of IGF-1 and display a phenotype consistent with a significant decrease in IGF-1. Life-span analysis was carried out at three independent locations. Although the life-span data varied between sites, the maximum life span of the IGF-1-deficient mice was significantly increased and age-specific mortality rates were reduced in the IGF-1-deficient mice; however, mean life span did not differ except at one site, where mean life span was increased in female IGF-1-deficient animals. Early life mortality was noted in one cohort of IGF-1-deficient mice. The results are consistent with a significant role for IGF-1 in the modulation of life span but contrast with the published life-span data for the hypopituitary Ames and Snell dwarf mice and growth hormone receptor null mice, indicating that a reduction in IGF-1 alone is insufficient to increase both mean and maximal life span in mice.

Decreased levels of proapoptotic factors and increased key regulators of mitochondrial biogenesis constitute new potential beneficial features of long-lived growth hormone receptor gene-disrupted mice

Decreased somatotrophic signaling is among the most important mechanisms associated with extended longevity. Mice homozygous for the targeted disruption of the growth hormone (GH) receptor gene (GH receptor knockout; GHRKO) are obese and dwarf, are characterized by a reduced weight and body size, undetectable levels of GH receptor, high concentration of serum GH, and greatly reduced plasma levels of insulin and insulin-like growth factor-I, and are remarkably long lived. Recent results suggest new features of GHRKO mice that may positively affect longevity-decreased levels of proapoptotic factors and increased levels of key regulators of mitochondrial biogenesis. The alterations in levels of the proapoptotic factors and key regulators of mitochondrial biogenesis were not further improved by two other potential life-extending interventions-calorie restriction and visceral fat removal. This may attribute the primary role to GH resistance in the regulation of apoptosis and mitochondrial biogenesis in GHRKO mice in terms of increased life span.

Variations in the protein level of Omi/HtrA2 in the heart of aged rats may contribute to the increased susceptibility of cardiomyocytes to ischemia/reperfusion injury and cell death : Omi/HtrA2 and aged heart injury

Survival after acute myocardial infarction is decreased in elderly patients. The enhanced rates of apoptosis in the aging heart exacerbate myocardial ischemia/reperfusion (MI/R) injury. We have recently demonstrated that the X-linked inhibitor of apoptosis protein (XIAP), the most potent endogenous inhibitor of apoptosis, was decreased in aging rats' hearts. XIAP was balanced by two mitochondria proteins, Omi/HtrA2 and Smac/DIABLO. However, the implicative role of XIAP, Omi/HtrA2, and Smac/DIABLO to aging-related MI/R injury has not been previously investigated. In our study, male aging rats (20-24 months) or young adult rats (4-6 months) were subjected to 30 min of myocardial ischemia followed by reperfusion. MI/R-induced cardiac injury was enhanced in aging rats, as evidenced by aggravated cardiac dysfunction, enlarged infarct size, and increased myocardial apoptosis (TUNEL and caspase-3 activity). Then, the XIAP, Omi/HtrA2, and Smac/DIABLO protein and mRNA expression was detected. XIAP protein and mRNA expression was decreased in both aging hearts and aging hearts subjected to MI/R. Meanwhile, myocardial XIAP protein expression was correlated to cardiac function after MI/R. However, Omi/HtrA2, but not Smac/DIABLO, expression was increased in aging hearts. Moreover, the translocation of Omi/HtrA2 from mitochondria to cytosol was increased in both aging hearts and aging hearts subjected to MI/R. Treatment with ucf-101 (a novel and specific Omi/HtrA2 inhibitor) attenuated XIAP degradation and caspase-3 activity and exerted cardioprotective effects. Taken together, these results demonstrated that increased expression and leakage of Omi/HtrA2 enhanced MI/R injury in aging hearts via degrading XIAP and promoting myocardial apoptosis.

Insulin/IGF-1 signaling, including class II/III PI3Ks, β-arrestin and SGK-1, is required in C. elegans to maintain pharyngeal muscle performance during starvation

In C. elegans, pharyngeal pumping is regulated by the presence of bacteria. In response to food deprivation, the pumping rate rapidly declines by about 50–60%, but then recovers gradually to baseline levels on food after 24 hr. We used this system to study the role of insulin/IGF-1 signaling (IIS) in the recovery of pharyngeal pumping during starvation. Mutant strains with reduced function in the insulin/IGF-1 receptor, DAF-2, various insulins (INS-1 and INS-18), and molecules that regulate insulin release (UNC-64 and NCA-1; NCA-2) failed to recover normal pumping rates after food deprivation. Similarly, reduction or loss of function in downstream signaling molecules (e.g., ARR-1, AKT-1, and SGK-1) and effectors (e.g., CCA-1 and UNC-68) impaired pumping recovery. Pharmacological studies with kinase and metabolic inhibitors implicated class II/III phosphatidylinositol 3-kinases (PI3Ks) and glucose metabolism in the recovery response. Interestingly, both over- and under-activity in IIS was associated with poorer recovery kinetics. Taken together, the data suggest that optimum levels of IIS are required to maintain high levels of pharyngeal pumping during starvation. This work may ultimately provide insights into the connections between IIS, nutritional status and sarcopenia, a hallmark feature of aging in muscle.

Somatotropic signaling: trade-offs between growth, reproductive development, and longevity

Growth hormone (GH) is a key determinant of postnatal growth and plays an important role in the control of metabolism and body composition. Surprisingly, deficiency in GH signaling delays aging and remarkably extends longevity in laboratory mice. In GH-deficient and GH-resistant animals, the "healthspan" is also extended with delays in cognitive decline and in the onset of age-related disease. The role of hormones homologous to insulin-like growth factor (IGF, an important mediator of GH actions) in the control of aging and lifespan is evolutionarily conserved from worms to mammals with some homologies extending to unicellular yeast. The combination of reduced GH, IGF-I, and insulin signaling likely contributes to extended longevity in GH or GH receptor-deficient organisms. Diminutive body size and reduced fecundity of GH-deficient and GH-resistant mice can be viewed as trade-offs for extended longevity. Mechanisms responsible for delayed aging of GH-related mutants include enhanced stress resistance and xenobiotic metabolism, reduced inflammation, improved insulin signaling, and various metabolic adjustments. Pathological excess of GH reduces life expectancy in men as well as in mice, and GH resistance or deficiency provides protection from major age-related diseases, including diabetes and cancer, in both species. However, there is yet no evidence of increased longevity in GH-resistant or GH-deficient humans, possibly due to non-age-related deaths. Results obtained in GH-related mutant mice provide striking examples of mutations of a single gene delaying aging, reducing age-related disease, and extending lifespan in a mammal and providing novel experimental systems for the study of mechanisms of aging.

Human conditions of insulin-like growth factor-I (IGF-I) deficiency

Insulin-like growth factor I (IGF-I) is a polypeptide hormone produced mainly by the liver in response to the endocrine GH stimulus, but it is also secreted by multiple tissues for autocrine/paracrine purposes. IGF-I is partly responsible for systemic GH activities although it possesses a wide number of own properties (anabolic, antioxidant, anti-inflammatory and cytoprotective actions). IGF-I is a closely regulated hormone. Consequently, its logical therapeutical applications seems to be limited to restore physiological circulating levels in order to recover the clinical consequences of IGF-I deficiency, conditions where, despite continuous discrepancies, IGF-I treatment has never been related to oncogenesis. Currently the best characterized conditions of IGF-I deficiency are Laron Syndrome, in children; liver cirrhosis, in adults; aging including age-related-cardiovascular and neurological diseases; and more recently, intrauterine growth restriction. The aim of this review is to summarize the increasing list of roles of IGF-I, both in physiological and pathological conditions, underlying that its potential therapeutical options seem to be limited to those proven states of local or systemic IGF-I deficiency as a replacement treatment, rather than increasing its level upper the normal range.

The emerging role of IGF-1 deficiency in cardiovascular aging: recent advances

This review focuses on cardiovascular protective effects of insulin-like growth factor (IGF)-1, provides a landscape of molecular mechanisms involved in cardiovascular alterations in patients and animal models with congenital and adult-onset IGF-1 deficiency, and explores the link between age-related IGF-1 deficiency and the molecular, cellular, and functional changes that occur in the cardiovascular system during aging. Microvascular protection conferred by endocrine and paracrine IGF-1 signaling, its implications for the pathophysiology of cardiac failure and vascular cognitive impairment, and the role of impaired cellular stress resistance in cardiovascular aging considered here are based on emerging knowledge of the effects of IGF-1 on Nrf2-driven antioxidant response.

Normal lactational environment restores cardiomyocyte number after uteroplacental insufficiency: implications for the preterm neonate

A reduced complement of cardiomyocytes in early life can adversely affect life-long cardiac functional reserve. In the present study, using a cross-fostering approach in rats, we examined the contributions of the prenatal and postnatal environments in the programming of cardiomyocyte growth. Rat dams underwent either bilateral uterine vessel ligation (Restricted) or sham surgery (Control) on day 18 of gestation. One day after birth, Control and Restricted pups were cross-fostered onto Control (normal lactation) or Restricted (impaired lactation due to impaired mammary gland formation) mothers. In male offspring, genes involved in cardiomyocyte differentiation, proliferation, hypertrophy and apoptosis were examined at gestational day 20 and postnatal days 1 and 7 to assess effects on cardiomyocyte growth. At postnatal day 7 cardiomyocyte number was determined stereologically. Offspring were examined at age 6 mo for evidence of hypertension and pathological cardiac gene expression. There was an increase in Igf1 and Igf2 mRNA expression in hearts of Restricted pups at gestational day 20. At postnatal day 7, Agtr1a and Agtr1b mRNA expression as well as Bcl2 and Cmyc were elevated in all hearts from offspring that were prenatally or postnatally growth restricted. There was a significant reduction (-29%) in cardiomyocyte number in the Restricted-on-Restricted group. Importantly, this deficit was prevented by optimization of postnatal nutrition (in the Restricted-on-Control group). At 6 mo, blood pressure was significantly elevated in the Restricted-on-Restricted group, but there was no difference in expression of the cardiac hypertrophy, remodeling or angiogenic genes across groups. In conclusion, the findings reveal a critical developmental window, when cardiomyocytes are still proliferating, whereby improved neonatal nutrition has the capacity to restore cardiomyocyte number to normal levels. These findings are of particular relevance to the preterm infant who is born at a time when cardiomyocytes are immature and still dividing.

Insulin-like growth factor I (IGF-1) deficiency ameliorates sex difference in cardiac contractile function and intracellular Ca(2+) homeostasis

Sex difference in cardiac contractile function exists which may contribute to the different prevalence in cardiovascular diseases between genders. However, the precise mechanisms of action behind sex difference in cardiac function are still elusive. Given that sex difference exists in insulin-like growth factor I (IGF-1) cascade, this study is designed to evaluate the impact of severe liver IGF-1 deficiency (LID) on sex difference in cardiac function. Echocardiographic, cardiomyocyte contractile and intracellular Ca(2+) properties were evaluated including ventricular geometry, fractional shortening, peak shortening, maximal velocity of shortening/relengthening (±dL/dt), time-to-peak shortening (TPS), time-to-90% relengthening (TR(90)), fura-fluorescence intensity (FFI) and intracellular Ca(2+) clearance. Female C57 mice exhibited significantly higher plasma IGF-1 levels than their male counterpart. LID mice possessed comparably low IGF-1 levels in both sexes. Female C57 and LID mice displayed lower body, heart and liver weights compared to male counterparts. Echocardiographic analysis revealed larger LV mass in female C57 but not LID mice without sex difference in other cardiac geometric indices. Myocytes from female C57 mice exhibited reduced peak shortening, ±dL/dt, longer TPS, TR(90) and intracellular Ca(2+) clearance compared with males. Interestingly, this sex difference was greatly attenuated or abolished by IGF-1 deficiency. Female C57 mice displayed significantly decreased mRNA and protein levels of Na(+)-Ca(2+) exchanger, SERCA2a and phosphorylated phospholamban as well as SERCA activity compared with male C57 mice. These sex differences in Ca(2+) regulatory proteins were abolished or overtly attenuated by IGF-1 deficiency. In summary, our data suggested that IGF-1 deficiency may significantly attenuated or mitigate the sex difference in cardiomyocyte contractile function associated with intracellular Ca(2+) regulation.

Chronic Akt activation accentuates aging-induced cardiac hypertrophy and myocardial contractile dysfunction: role of autophagy

Aging is often accompanied with geometric and functional changes in the heart, although the underlying mechanisms remain unclear. Recent evidence has described a potential role of Akt and autophagy in aging-associated organ deterioration. This study was to examine the impact of cardiac-specific Akt activation on aging-induced cardiac geometric and functional changes and underlying mechanisms involved. Cardiac geometry, contractile and intracellular Ca(2+) properties were evaluated using echocardiography, edge-detection and fura-2 techniques. Level of insulin signaling and autophagy was evaluated by western blot. Our results revealed cardiac hypertrophy (enlarged chamber size, wall thickness, myocyte cross-sectional area), fibrosis, decreased cardiac contractility, prolonged relengthening along with compromised intracellular Ca(2+) release and clearance in aged (24-26 month-old) mice compared with young (3-4 month-old) mice, the effects of which were accentuated by chronic Akt activation. Aging enhanced Akt and mTOR phosphorylation while reducing that of PTEN, AMPK and ACC with a more pronounced response in Akt transgenic mice. GSK3β phosphorylation and eNOS levels were unaffected by aging or Akt overexpression. Levels of beclin-1, Atg5 and LC3-II-to-LC3-I ratio were decreased in aged hearts, the effect of which with the exception of Atg 5 was exacerbated by Akt overactivation. Levels of p62 were significantly enhanced in aged mice with a more pronounced increase in Akt mice. Neither aging nor Akt altered β-glucuronidase activity and cathepsin B although aging reduced LAMP1 level. In addition, rapamycin reduced aging-induced cardiomyocyte contractile and intracellular Ca(2+) dysfunction while Akt activation suppressed autophagy in young but not aged cardiomyocytes. In conclusion, our data suggest that Akt may accentuate aging-induced cardiac geometric and contractile defects through a loss of autophagic regulation.

Potent Long-Term Cardioprotective Effects of Single Low-Dose Insulin-Like Growth Factor-1 Treatment Postmyocardial Infarction

Background—

Insulin-like growth factor-1 (IGF-1) is recognized as an important regulator of cardiac structure and cardiomyocyte homeostasis. The prosurvival and antiapoptotic effects of IGF-1 have been investigated in vitro and in rodent models of myocardial infarction (MI). However, the clinical application of IGF-1 has been hampered by dose-dependent side effects both acutely and during chronic administration. We hypothesized that single, low-dose IGF-1 (LD-IGF-1) administered locally and early in the reperfusion phase after acute MI in a large animal model would avoid significant side effects but would have prosurvival effects that would manifest in long-term structural and functional improvement after MI treatment.

Methods and Results—

Forty-four female Landrace pigs underwent intracoronary administration of LD-IGF-1 or saline 2 hours into the reperfusion phase of acute left anterior descending artery occlusion MI. In the area of infarction, IGF-1 receptor and signaling responses were activated at 30 minutes and cardiomyocyte cell death attenuated at 24 hours after LD-IGF-1 but not saline treatment. Hemodynamic and structural studies using pressure-volume loop, CT, and triphenyltetrazolium chloride analysis 2 months post-MI confirmed a marked reduction in infarct size, attenuation of wall thinning, and augmentation of wall motion in the LD-IGF-1-treated but not in the saline-treated animals. These regional structural benefits were associated with global reductions in left ventricular volumes and significant improvement in left ventricular systolic and diastolic function.

Conclusions—

One-time LD-IGF-1 effects potent acute myocardial salvage in a preclinical model of left anterior descending artery occlusive MI, extending to long-term benefits in MI size, wall structure, and function and underscoring its potential as an adjunctive therapeutic agent.

Mice as a mammalian model for research on the genetics of aging

Mice are an ideal mammalian model for studying the genetics of aging: considerable resources are available, the generation time is short, and the environment can be easily controlled, an important consideration when performing mapping studies to identify genes that influence lifespan and age-related diseases. In this review we highlight some salient contributions of the mouse in aging research: lifespan intervention studies in the Interventions Testing Program of the National Institute on Aging; identification of the genetic underpinnings of the effects of calorie restriction on lifespan; the Aging Phenome Project at the Jackson Laboratory, which has submitted multiple large, freely available phenotyping datasets to the Mouse Phenome Database; insights from spontaneous and engineered mouse mutants; and complex traits analyses identifying quantitative trait loci that affect lifespan. We also show that genomewide association peaks for lifespan in humans and lifespan quantitative loci for mice map to homologous locations in the genome. Thus, the vast bioinformatic and genetic resources of the mouse can be used to screen candidate genes identified in both mouse and human mapping studies, followed by functional testing, often not possible in humans, to determine their influence on aging.

Modulation of beta-adrenergic receptor signaling in heart failure and longevity: targeting adenylyl cyclase type 5

Despite remarkable advances in therapy, heart failure remains a leading cause of morbidity and mortality. Although enhanced beta-adrenergic receptor stimulation is part of normal physiologic adaptation to either the increase in physiologic demand or decrease in cardiac function, chronic beta-adrenergic stimulation has been associated with increased mortality and morbidity in both animal models and humans. For example, overexpression of cardiac Gsalpha or beta-adrenergic receptors in transgenic mice results in enhanced cardiac function in young animals, but with prolonged overstimulation of this pathway, cardiomyopathy develops in these mice as they age. Similarly, chronic sympathomimetic amine therapy increases morbidity and mortality in patients with heart failure. Conversely, the use of beta-blockade has proven to be of benefit and is currently part of the standard of care for heart failure. It is conceivable that interrupting distal mechanisms in the beta-adrenergic receptor-G protein-adenylyl cyclase pathway may also provide targets for future therapeutic modalities for heart failure. Interestingly, there are two major isoforms of adenylyl cyclase (AC) in the heart (type 5 and type 6), which may exert opposite effects on the heart, i.e., cardiac overexpression of AC6 appears to be protective, whereas disruption of type 5 AC prolongs longevity and protects against cardiac stress. The goal of this review is to summarize the paradigm shift in the treatment of heart failure over the past 50 years from administering sympathomimetic amine agonists to administering beta-adrenergic receptor antagonists, and to explore the basis for a novel therapy of inhibiting type 5 AC.

Decreased expression level of apoptosis-related genes and/or proteins in skeletal muscles, but not in hearts, of growth hormone receptor knockout mice

The long-lived growth hormone (GH) receptor knockout (GHRKO; KO) mice are GH-resistant due to targeted disruption of the GH receptor (Ghr) gene. Apoptosis is a physiological process in which cells play an active role in their own death and is a normal component of the development and health of multicellular organisms. Aging is associated with the progressive loss of strength of skeletal and heart muscles. Calorie restriction (CR) is a well-known experimental model to delay aging and increase lifespan. The aim of the study was to examine the expression of the following apoptosis-related genes: caspase-3, caspase-9, caspase-8, bax, bcl-2, Smac/DIABLO, p53 and cytochrome c1 (cyc1) in the skeletal muscles and hearts of female normal and GHRKO mice, fed ad libitum or subjected to 40% CR for six months, starting at two months of age. Moreover, skeletal muscle caspase-3, caspase-9, caspase-8, bax, bcl-2, Smac/DIABLO, Apaf-1, bad, phospho-bad (pbad), phospho-p53 and cytochrome c (cyc) protein expression levels were assessed. Expression of caspase-3, caspase-9, bax and Smac/DIABLO genes and proteins was decreased in GHRKO's skeletal muscles. The Apaf-1 protein expression also was diminished in this tissue. In contrast, bcl-2 and pbad protein levels were increased in skeletal muscles in knockouts. No changes were demonstrated for the examined genes' expression in GHRKO's hearts except for the increased level of cyc1 mRNA. CR did not alter the expression of the examined genes and proteins in skeletal muscles of knockouts versus normal (N) mice. In heart homogenates, CR increased caspase-3 mRNA level as compared with ad libitum mice. Decreased expression of certain proapoptotic genes and/or proteins may constitute the potential mechanism of prolonged longevity in GHRKO mice, protecting these animals from aging; this potential beneficial mechanism is not affected by CR.

Comparative endocrinology of aging and longevity regulation

Hormones regulate growth, development, metabolism, and other complex processes in multicellular animals. For many years it has been suggested that hormones may also influence the rate of the aging process. Aging is a multifactorial process that causes biological systems to break down and cease to function in adult organisms as time passes, eventually leading to death. The exact underlying causes of the aging process remain a topic for debate, and clues that may shed light on these causes are eagerly sought after. In the last two decades, gene mutations that result in delayed aging and extended longevity have been discovered, and many of the affected genes have been components of endocrine signaling pathways. In this review we summarize the current knowledge on the roles of endocrine signaling in the regulation of aging and longevity in various animals. We begin by discussing the notion that conserved systems, including endocrine signaling pathways, "regulate" the aging process. Findings from the major model organisms: worms, flies, and rodents, are then outlined. Unique lessons from studies of non-traditional models: bees, salmon, and naked mole rats, are also discussed. Finally, we summarize the endocrinology of aging in humans, including changes in hormone levels with age, and the involvement of hormones in aging-related diseases. The most well studied and widely conserved endocrine pathway that affects aging is the insulin/insulin-like growth factor system. Mutations in genes of this pathway increase the lifespan of worms, flies, and mice. Population genetic evidence also suggests this pathway's involvement in human aging. Other hormones including steroids have been linked to aging only in a subset of the models studied. Because of the value of comparative studies, it is suggested that the aging field could benefit from adoption of additional model organisms.

Longevity and lifespan control in mammals: lessons from the mouse

Aging, which affects all organ systems, is one of the most complex phenotypes. Recent discoveries in long-lived mutant mice have revealed molecular mechanisms of longevity in mammals which may contribute to our understanding of why humans age. These mutations include naturally occurring spontaneous mutations, and those of mice genetically modified by modern genomic technologies. It is generally believed that the most fundamental mechanisms of aging are evolutionarily conserved across species. The following types of longevity mechanisms have been intensively studied: suppression of the somatotropic (growth hormone/insulin-like growth factor 1) axis, decreased metabolism and increased resistance of oxidative stress, reduced insulin secretion and increased insulin sensitivity, and delayed reproductive maturation and reduced fertility. In addition, many of the mutations have a sex-dependent effect on lifespan, and when present in different genetic backgrounds, the effects of the same gene mutation can vary considerably. The present review discusses these phenotypic variations as well as describing the known longevity genes in long-lived mutant mice and the molecular mechanisms specifying longevity. We anticipate that these mouse studies will ultimately provide clues about how to delay the aging and prolong lifespan, and help to develop therapies for healthier human aging.

Cardiac overexpression of insulin-like growth factor 1 attenuates chronic alcohol intake-induced myocardial contractile dysfunction but not hypertrophy: Roles of Akt, mTOR, GSK3beta, and PTEN

Chronic alcohol intake leads to the development of alcoholic cardiomyopathy manifested by cardiac hypertrophy and contractile dysfunction. This study was designed to examine the effects of transgenic overexpression of insulin-like growth factor 1 (IGF-1) on alcohol-induced cardiac contractile dysfunction. Wild-type FVB and cardiac-specific IGF-1 mice were placed on a 4% alcohol or control diet for 16weeks. Cardiac geometry and mechanical function were evaluated by echocardiography and cardiomyocyte and intracellular Ca(2+) properties. Histological analyses for cardiac fibrosis and apoptosis were evaluated by Masson trichrome staining and TUNEL assay, respectively. Expression and phosphorylation of Cu/Zn superoxide dismutase (SOD1), Ca(2+) handling proteins, and key signaling molecules for survival including Akt, mTOR, GSK3beta, Foxo3a, and the negative regulator of Akt, phosphatase and tensin homolog on chromosome 10 (PTEN), as well as mitochondrial proteins UCP-2 and PGC1alpha, were evaluated by Western blot analysis. Chronic alcohol intake led to cardiac hypertrophy, interstitial fibrosis, reduced mitochondrial number, compromised cardiac contractile function and intracellular Ca(2+) handling, decreased SOD1 expression, elevated superoxide production, and overt apoptosis, all of which, with the exception of cardiac hypertrophy, were abrogated by the IGF-1 transgene. Immunoblotting data showed reduced phosphorylation of Akt, mTOR, GSK3beta, and Foxo3a; upregulated Foxo3a and PTEN; and dampened SERCA2a, PGC1alpha, and UCP-2 after alcohol intake. All these alcohol-induced changes in survival and mitochondrial proteins were alleviated by IGF-1. Taken together, these data favor a beneficial role for IGF-1 in alcohol-induced myocardial contractile dysfunction independent of cardiac hypertrophy.

Smaller cardiac cell size and reduced extra-cellular collagen might be beneficial for hearts of Ames dwarf mice

PURPOSE

To test the hypothesis that cardiac morphologic differences between Ames dwarf and wild-type littermates might correlate with the increased longevity observed in the Ames dwarf mice.

METHODS

Hearts removed from young adult (5-7 mo) and old (24-28 mo) Ames dwarf and wild-type littermates underwent histological and morphometric analysis. Measurements of cell size, nuclear size, and collagen content were made using computerized color deconvolution and particle analysis methodology.

RESULTS

In the young mice at six months of age, mean cardiomyocyte area was 46% less in Ames dwarf than in wild-type mice (p<0.0001). Cardiomyocyte size increased with age by about 52% in the wild-type mice and 44% in the Ames dwarf mice (p<0.001). There was no difference in nuclear size of the cardiomyocytes between the young adult wild-type and Ames dwarf mice. There was an age-associated increase in the cardiomyocyte nuclear size by approximately 50% in both the Ames and wild-type mice (p<0.001). The older Ames dwarf mice had slightly larger cardiomyocyte nuclei compared to wild-type (2%, p<0.05). The collagen content of the hearts in young adult Ames dwarf mice was estimated to be 57% less compared to wild-type littermates (p<0.05). Although collagen content of both Ames dwarf and wild-type mouse hearts increased with age, there was no significant difference at 24 months.

CONCLUSIONS

In wild-type and Ames dwarf mice, nuclear size, cardiomyocyte size, and collagen content increased with advancing age. While cardiomyocyte size was much reduced in young and old Ames dwarf mice compared with wild-type, collagen content was reduced only in the young adult mice. Taken together, these findings suggest that Ames dwarf mice may receive some longevity benefit from the reduced cardiomyocyte cell size and a period of reduced collagen content in the heart during adulthood.

AMP-activated protein kinase deficiency exacerbates aging-induced myocardial contractile dysfunction

Aging is associated with myocardial dysfunction although the underlying mechanism is unclear. AMPK, a key cellular fuel sensor for energy metabolism, is compromised with aging. This study examined the role of AMPK deficiency in aging-associated myocardial dysfunction. Young or old wild-type (WT) and transgenic mice with overexpression of a mutant AMPK alpha(2) subunit (kinase dead, KD) were used. AMPK alpha isoform activity, myocardial function and morphology were examined. DCF and JC-1 fluorescence probes were employed to quantify reactive oxygen species (ROS) and mitochondrial membrane potential (DeltaPsim), respectively. KD mice displayed significantly reduced alpha(2) but not alpha(1) AMPK isoform activity at both ages with a greater effect at old age. Aging itself decreased alpha(1) isoform activity. Cardiomyocyte contractile function, intracellular Ca(2+) handling, and SERCA2a levels were compromised with aging, the effects of which were exacerbated by AMPK deficiency. H&E staining revealed cardiomyocyte hypertrophy with aging, which was more pronounced in KD mice. TEM micrographs displayed severe disruption of mitochondrial ultrastructure characterized by swollen, irregular shape and disrupted cristae in aged KD compared with WT mice. Aging enhanced ROS production and reduced DeltaPsim, the effects of which were accentuated by AMPK deficiency. Immunoblotting data depicted unchanged Akt phosphorylation and a significant decrease in mitochondrial biogenesis cofactor PGC-1alpha in aged groups. AMPK deficiency but not aging decreased the phosphorylation of ACC and eNOS. Expression of membrane Glut4 and HSP90 was decreased in aged KD mice. Moreover, treatment of the AMPK activator metformin attenuated aging-induced cardiomyocyte contractile defects. Collectively, our data suggest a role for AMPK deficiency in aging-induced cardiac dysfunction possibly through disrupted mitochondrial function and ROS production.

Activation of proteasome by insulin-like growth factor-I may enhance clearance of oxidized proteins in the brain

The insulin-like growth factor type 1 (IGF-I) plays an important role in neuronal physiology. Reduced IGF-I levels are observed during aging and this decrease may be important to age-related changes in the brain. We studied the effects of IGF-I on total protein oxidation in brain tissues and in cell cultures. Our results indicate that in frontal cortex the level of oxidized proteins is significantly reduced in transgenic mice designed to overproduce IGF-I compared with wild-type animals. The frontal cortex of IGF-I-overproducing mice exhibited high chymotrypsin-like activity of the 20S and 26S proteasomes. The proteasome can also be activated in response to IGF-I in cell cultures. Kinetic studies revealed peak activation of the proteasome within 15 min following IGF-I stimulation. The effects of IGF-I on proteasome were not observed in R(-) cells lacking the IGF-I receptor. Experiments using specific kinase inhibitors suggested that activation of proteasome by IGF-I involves phosphatidyl inositol 3-kinase and mammalian target of rapamycin signaling. IGF-I also attenuated the increase in protein carbonyl content induced by proteasome inhibition. Thus, appropriate levels of IGF-I may be important for the elimination of oxidized proteins in the brain in a process mediated by activation of the proteasome.