Aging-associated Cardiac Dysfunction Research Articles

Tet2-mediated clonal hematopoiesis in non-conditioned mice accelerates age-associated cardiac dysfunction.

Tet2-mediated clonal hematopoiesis in non-conditioned mice accelerates age-associated cardiac dysfunction.

Modulating sialylation as therapeutic approach for preventing age-associated cardiac dysfunction

Abstract Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): Ministry of Health Voltage-gated sodium channel Nav1.5 plays a pivotal role in the proper functioning of cardiac muscle cells. Sialylation, a post-translational modification involving the addition of negatively charged sialic acid moieties, is essential for Nav1.5 functionality. Altered sialylation has been observed in various cardiovascular diseases, including Chagas disease and congenital disorders of glycosylation affecting the heart. Furthermore, sialylation status has been shown to change during human adult life, impacting brain and muscle structural properties. Cardiac arrhythmias increase in prevalence with age, contributing to higher morbidity and mortality in older people. Using an aging mouse model, we observed a decline in cardiac sialic acid levels and NaV1.5 associated with the aging process. In compelling in vitro experiments on HEK293 cells and induced pluripotent stem cell-derived cardiomyocytes, diminished external sialic acid induces Nav1.5 channel internalization, activating endocytic pathways and leading to proteasome-mediated degradation. Intriguingly, proteomic analysis revealed that introducing a specific sialic acid precursor increased membrane protein trafficking, restoring Nav1.5 protein levels and the sodium current. Electrophysiological experiments demonstrated functional recovery and highlighted the rapid response, observable within just 2 hours of sialic acid stimulation. In summary, this study provides novel insights into the complex relationship between sialic acid and NaV1.5 channel trafficking, offering new perspectives and promising therapeutic strategies to prevent cardiac dysfunction in elderly.Modulating sialylation on NaV1.5 channelOur project goal

Combined Endurance and Resistance Exercise Mitigates Age-Associated Cardiac Dysfunction.

Aging is associated with a decline in cardiac function. Exercise has been shown to effectively reduce the risks of cardiovascular diseases. Here whether a combination of endurance and resistance exercises can improve cardiac function in aged mice during late life is investigated. Through transcriptome analysis, several signaling pathways activated in the hearts of 22-month-old mice after combined exercise, including cardiac muscle contraction, mitophagy, and longevity regulation are identified. Combined exercise training mitigated age-associated pathological cardiac hypertrophy, reduced oxidative stress, cardiac senescence, and enhanced cardiac function. Upstream stimulatory factor 2 (Usf2) is upregulated in the aged mouse hearts with combined exercise compared to sedentary mice. In the human cardiomyocytes senescent model, overexpression of Usf2 led to anti-senescence effects, while knockdown of Usf2 exacerbated cellular senescence. The results suggest that a combination of endurance and resistance exercises, such as swimming and resistance running, can mitigate age-related pathological cardiac remodeling and cardiac dysfunction in late life. These cardioprotective effects are likely due to the activation of Usf2 and its anti-senescence effect. Therefore, Usf2 can potentially be a novel therapeutic target for mitigating age-related cardiac dysfunction.

Abstract 12226: Aging Impairs the Neuro-Vascular Interface in the Heart

Aging is a major risk factor for impaired cardiovascular function. The aging heart is characterized by vascular dysfunction, increased hypertrophy, fibrosis and electrophysiological alterations. However, the interaction between the different age-associated changes in cardiac remodelling is poorly define. Since vessels are aligned with nerves, and this interplay is critical for tissue homeostasis, we investigated whether an impairment of the neuro-vascular interface may contribute to age-associated pathologies in the heart. We show that aging reduces sympathetic and sensory nerve fibers, which both align to arteries and arterioles. Aging induced a dysregulation of vascular-derived neuro-regulatory genes, especially the axon repellent factor Sema3A, which was augmented by 2.4±0.1-fold in old heart endothelial cells. Consistently, endothelial Sema3a overexpression reduced axon density in vivo, thus mimicking the observed aged heart phenotype. Since cellular senescence was induced at the same time point when nerve density declined (16 months of age) and senescence endothelial cells showed a higher expression of Sema3a, we hypothesized that endothelial senescence may contribute to cardiac denervation. Indeed, supernatants of senescent endothelial cells reduced neurite outgrowth in vitro in a Sema3A-dependent manner. In vivo studies further confirmed that endothelial-specific induction of senescence by overexpression of Progerin induced left ventricular denervation and induced Sema3a expression. By contrast, the pharmacological removal of senescent cells by the senolytic drugs dasatinib and quercetin rescued age-induced denervation and prevented the age-induced induction of endothelial Sema3a expression. Functional studies additionally demonstrated that endothelial senescence reduced heart rate variability, while senolytics preserved heart rate variability, restored age-associated declines in sympathetic and parasympathetic activity and reduced age-associated increase in arrhythmias. These data suggest that senescence-associated regulation of neuro-regulatory genes in endothelial cells is associated with reduced nerve density and, thereby, contributes to age-associated cardiac dysfunction.

Aging impairs the neurovascular interface in the heart.

Aging is a major risk factor for impaired cardiovascular health. Because the aging myocardium is characterized by microcirculatory dysfunction, and because nerves align with vessels, we assessed the impact of aging on the cardiac neurovascular interface. We report that aging reduces nerve density in the ventricle and dysregulates vascular-derived neuroregulatory genes. Aging down-regulates microRNA 145 (miR-145) and derepresses the neurorepulsive factor semaphorin-3A. miR-145 deletion, which increased Sema3a expression or endothelial Sema3a overexpression, reduced axon density, mimicking the aged-heart phenotype. Removal of senescent cells, which accumulated with chronological age in parallel to the decline in nerve density, rescued age-induced denervation, reversed Sema3a expression, preserved heart rate patterns, and reduced electrical instability. These data suggest that senescence-mediated regulation of nerve density contributes to age-associated cardiac dysfunction.

Reduce, Reuse, Recycle, Run ! : 4 Rs to improve cardiac health in advanced age.

During the aging process damaged/dysfunctional proteins and organelles accumulate and contribute to organ dysfunction. Luckily, there is a conserved intracellular process to reuse and recycle these dysregulated cellular components termed macroautophagy (autophagy). Unfortunately, strong evidence indicates autophagy is compromised with aging, protein quality control is jeopardized, and resultant proteotoxicity can contribute significantly to age-associated organ dysfunction. Are there interventions that can re-establish autophagic flux that is otherwise impaired with aging? With particular regard to the heart, here we review evidence that caloric-restriction, the polyamine spermidine, and the mTOR inhibitor rapamycin, even when initiated late-in-life, restore cardiomyocyte autophagy to an extent that lessens age-associated cardiac dysfunction. Cho et al. provide a physiological intervention to this list i.e., regular physical exercise initiated late-in-life boosts cardiomyocyte autophagic flux and rejuvenates cardiac function in male mice. While this study provides strong evidence for a mechanism whereby heightened physical activity can lead to improved heart health in the context of aging, (i) only male mice were studied; (ii) the intensity of exercise-training might not be suitable for all; and (iii) mice with aging-associated comorbidities were not investigated. Nonetheless, Cho et al. provide robust evidence that a low-cost and simple behavioral intervention initiated late-in-life improves cardiomyocyte autophagic flux and rejuvenates cardiac function.

Abstract 13208: Deletion of the Type I Interleukin-1 Receptor Prevents the Development of Cardiomyopathy Associated With Aging in Mice

Background: Aging is associated with metabolic and structural changes causing heart failure with preserved ejection fraction (HFpEF). Interleukin-1 (IL-1) is a pro-inflammatory cytokine involved in aging-related inflammation. We sought to determine whether IL-1 mediates aging-related changes in the heart as seen in HFpEF. Hypothesis: We hypothesize that mice with genetic deletion of IL-1RI, not responsive to IL-1β, would be protected from age-associated cardiac dysfunction. Methods: We studied age-matched young (4-month-old), middle-aged (14-month-old) and old (23-month-old) wild-type (WT) C57BL/6J and IL-1 receptor type I deficient (IL1RI-KO) male mice. Echocardiography was used to left ventricular (LV) dimensions and systolic/diastolic function, and a pressure-transducer was used to measure the LV end-diastolic pressure. Picrosirius red stain was used to assess for myocardial interstitial fibrosis (MIF) at pathology. Results: WT and IL-1RIKO mice showed a normal cardiac phenotype at young age, without any differences in between the two groups. With aging, the WT mice developed LV concentric hypertrophy (as measured by a significant increase in LV mass [+42%, P<0.01] and relative wall thickness [+34%, P<0.01]), whereas the aging IL-1RI-KO mice did not (Figure 1a,b). With aging the WT mice also developed diastolic dysfunction (as measured by a significant increase in isovolumetric relaxation time [+148%, P<0.01] and a significantly higher LV end diastolic pressure [+174%, P<0.01]), whereas the aging IL1RI-KO did not (Figure 1c,d). With aging WT mice showed a significant increase in MIF (+124%, P<0.01) at cardiac pathology, whereas the aging IL-1RI-KO did not (Figure 1e). Conclusions: Genetically-modified mice lacking the IL-1RI receptor, not responsive to IL-1, are protected from aging-related LV hypertrophy, fibrosis and diastolic dysfunction. These data support a central role of IL-1 in the pathophysiology of aging-related HFpEF.

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.

Role of FoxO transcription factors in aging-associated cardiovascular diseases.

Aging constitutes a major risk factor toward the development of cardiovascular diseases (CVDs). The aging heart undergoes several changes at the molecular, cellular and physiological levels, which diminishes its contractile function and weakens stress tolerance. Further, old age increases the exposure to risk factors such as hypertension, diabetes and hypercholesterolemia. Notably, research in the past decades have identified FoxO subfamily of the forkhead transcription factors as key players in regulating diverse cellular processes linked to cardiac aging and diseases. In the present chapter, we discuss the important role of FoxO in the development of various aging-associated cardiovascular complications such as cardiac hypertrophy, cardiac fibrosis, heart failure, vascular dysfunction, atherosclerosis, hypertension and myocardial ischemia. Besides, we will also discuss the role of FoxO in cardiometabolic alterations, autophagy and proteasomal degradation, which are implicated in aging-associated cardiac dysfunction.

Late‐In‐Life Treadmill‐Training Improves Autophagy, Protein Clearance, and Contractile Function in Mouse Hearts

Evidence exists that a progressive decline of the cellular quality control mechanism called macroautophagy occurs during the process of primary aging. This leads to the accumulation of protein aggregates (i.e., proteotoxicity) that would otherwise be transported to and degraded in the lysosome. Post‐mitotic cells like cardiomyocytes rely heavily on macroautophagy because of their inability to clear defective proteins via cell division. While voluntary wheel running improves cardiac autophagy, lessens cardiac proteotoxicity, and attenuates myocardial dysfunction in mice with desmin‐related cardiomyopathy (Bhuiyan et al., JCI, 2013), the ability for a physiological intervention to improve these indexes in aged mice is unknown. We hypothesized that late‐in‐life exercise training improves autophagy, protein aggregate clearance, and function that is otherwise dysregulated in hearts from old vs adult mice. As expected, 24‐month old male C57Bl6 mice (old) exhibited repressed autophagosome formation in the heart, myocardial protein aggregate accumulation, systolic and diastolic dysfunction, and reduced exercise capacity vs. 6‐month old (adult) mice (all p< 0.05; n=10 per group) Separate cohorts of 21 month old mice completed a 10‐week progressive resistance / duration treadmill‐running program (old‐ETR) that improved (all p<0.05): (i) body composition; (ii) maximal workload capacity; and (iii) soleus muscle citrate synthase activity vs. age‐matched sedentary mice (old‐SED). Of note, (iv) mRNA and protein expression of autophagy markers indicated trafficking of the autophagosome to the lysosome increased, (v) protein aggregate clearance improved, and (vi) contractile function was enhanced (all p<0.05), in hearts from old‐ETR vs. old‐SED mice. Dietary maneuvers (e.g., caloric restriction, nutraceutical supplementation) and pharmacological interventions (e.g., rapamycin) are reported to elevate myocardial autophagy and mitigate / reverse age‐associated cardiac dysfunction. Here we show the first evidence that a physiological intervention i.e., late‐in‐life exercise training, improves autophagic flux, protein aggregate clearance, and contractile function in hearts from aged mice.Support or Funding InformationKL [APS STRIDE, UU Undergraduate Research Program (UROP)], JMC (UU Research Fellowship), SKP (AHA 17POST33670663), CR (APS UGRF, UROP), LT (UROP), SB (NIDDK R01‐DK‐098646‐01A1, R01‐DK‐099110, AHA 16GRNT30990018), JDS (AHA16GRNT31050004, NIH RO3AGO52848, NIHRO1HL141540).

Tet2-mediated clonal hematopoiesis in nonconditioned mice accelerates age-associated cardiac dysfunction.

Clonal hematopoiesis of indeterminate potential is prevalent in elderly individuals and associated with increased risks of all-cause mortality and cardiovascular disease. However, mouse models to study the dynamics of clonal hematopoiesis and its consequences on the cardiovascular system under homeostatic conditions are lacking. We developed a model of clonal hematopoiesis using adoptive transfer of unfractionated ten-eleven translocation 2-mutant (Tet2-mutant) bone marrow cells into nonirradiated mice. Consistent with age-related clonal hematopoiesis observed in humans, these mice displayed a progressive expansion of Tet2-deficient cells in multiple hematopoietic stem and progenitor cell fractions and blood cell lineages. The expansion of the Tet2-mutant fraction was also observed in bone marrow-derived CCR2+ myeloid cell populations within the heart, but there was a negligible impact on the yolk sac-derived CCR2- cardiac-resident macrophage population. Transcriptome profiling revealed an enhanced inflammatory signature in the donor-derived macrophages isolated from the heart. Mice receiving Tet2-deficient bone marrow cells spontaneously developed age-related cardiac dysfunction characterized by greater hypertrophy and fibrosis. Altogether, we show that Tet2-mediated hematopoiesis contributes to cardiac dysfunction in a nonconditioned setting that faithfully models human clonal hematopoiesis in unperturbed bone marrow. Our data support clinical findings that clonal hematopoiesis per se may contribute to diminished health span.

Zeaxanthin Isolated from Dunaliella salina Microalgae Ameliorates Age Associated Cardiac Dysfunction in Rats through Stimulation of Retinoid Receptors.

Retinoids are essential during early cardiovascular morphogenesis. However, recent studies showed their important role in cardiac remodeling in rats with hypertension and following myocardial infarction. The present study aimed to investigate the effect of zeaxanthin heneicosylate (ZH); a carotenoid ester isolated from Dunaliella salina microalgae, on cardiac dysfunction ensuing d-galactose injection in rats. Rats injected with d-GAL (200 mg/kg; I.P) for 8 weeks were orally treated with ZH (250 μg/kg) for 28 consecutive days. Results showed that d-GAL injection caused dramatic electrocardiographic changes as well as marked elevation in serum levels of homocysteine, creatinine kinase isoenzyme and lactate dehydrogenase. A reduction in the cardiac contents of glucose transporter-4 and superoxide dismutase along with the elevation of inducible nitric oxide synthetase and interleukin-6 was also noticed. Oral administration of ZH significantly improved the above mentioned cardiac aging manifestations; this was further emphasized through histopathological examinations. The effect of ZH is mediated through the interaction with retinoid receptor alpha (RAR-α) as evidenced through a significant elevation of RAR-α expression in cardiac tissue following the lead of an in silico molecular docking study. In conclusion, zeaxanthin heneicosylate isolated from D. salina ameliorated age-associated cardiac dysfunction in rats through the activation of retinoid receptors.

Protective and therapeutic potentials of Dunaliella salina on aging-associated cardiac dysfunction in rats

Objective: To investigate the possible protective and/or therapeutic potentials of Dunaliella salina (D. salina) biomass, its carotenoid and polar fractions on cardiac dysfunction associated with D-galactose (D-GAL) induced aging in rats. Methods: Aging associated cardiac dysfunction was induced in rats by injection of D-GAL (200 mg/kg; i.p) for 8 weeks. D-GAL injected rats were treated with two regimens; protective regimen where D. salina biomass (250 mg/kg), its carotenoid (250 μg/kg) and polar (250 μg/kg) fractions were given orally for two weeks concurrently with D-GAL injection as well as treatment regimen where the three treatments were given orally for 28 consecutive days after D-GAL injection. Results: D-GAL injection for 8 weeks was accompanied with dramatic electrocardiographic changes as well as profound elevation in serum levels of homocysteine, creatinine kinase isoenzyme and lactate dehydrogenase in addition to the reduction of the cardiac content of glucose trasporter 4. D-GAL also induced reduction in cardiac superoxide dismutase activity and elevation of inducible nitric oxide synthetase and interleukin-6. On the other hand, oral administration of D. salina carotenoid fraction as well as the total biomass significantly attenuated the D-GAL-induced disturbances in the above mentioned parameters where the protective regimen appeared more successful in controlling the manifestations of cardiac dysfunction. The histopathological examination further emphasized the promising results. Besides, the HPLC analysis of the carotenoid fraction of D. salina revealed the presence of 2.31% β -carotene. Conclusions: D. salina carotenoid fraction as well as the total biomass ameliorate D-GAL-induced aging associated cardiac dysfunction which is attributed to the potent antioxidant activity of β -carotene.

Amalaki rasayana, a traditional Indian drug enhances cardiac mitochondrial and contractile functions and improves cardiac function in rats with hypertrophy

We evaluated the cardioprotective effect of Amalaki Rasayana (AR), a rejuvenating Ayurvedic drug prepared from Phyllanthusemblica fruits in the reversal of remodeling changes in pressure overload left ventricular cardiac hypertrophy (LVH) and age-associated cardiac dysfunction in male Wistar rats. Six groups (aging groups) of 3 months old animals were given either AR or ghee and honey (GH) orally; seventh group was untreated. Ascending aorta was constricted using titanium clips in 3 months old rats (N = 24; AC groups) and after 6 months, AR or GH was given for further 12 months to two groups; one group was untreated. Histology, gene and protein expression analysis were done in heart tissues. Chemical composition of AR was analyzed by HPLC, HPTLC and LC-MS. AR intake improved (P < 0.05) cardiac function in aging rats and decreased LVH (P < 0.05) in AC rats as well as increased (P < 0.05) fatigue time in treadmill exercise in both groups. In heart tissues of AR administered rats of both the groups, SERCA2, CaM, Myh11, antioxidant, autophagy, oxidative phosphorylation and TCA cycle proteins were up regulated. ADRB1/2 and pCREB expression were increased; pAMPK, NF-kB were decreased. AR has thus a beneficial effect on myocardial energetics, muscle contractile function and exercise tolerance capacity.

Heart‐Specific Overexpression of FOXO Ameliorates Performance Decline through Enhanced UPS Processing in Aging Drosophila

Heart performance declines with age. Reduced protein quality control due to decreased function of the ubiquitin/proteasome system (UPS) and autophagy is a likely contributor to age‐associated cardiac dysfunction. The transcription factor FOXO has been shown to be involved in the regulation of genes involved in both as well as a host of other processes. Here, the effect of overexpression (OE) of dFOXO was investigated in Drosophila melanogaster, a rapidly aging model in which the tissue‐specific UAS‐GAL4 expression system is often exploited. This system permitted different extents of heart‐restricted dFOXO OE. Excessive dFOXO doses proved fatal while mild levels appeared cardioprotective, ameliorating functional decline as determined by high‐speed video microscopy and motion analysis of aging hearts. OE of dFOXO in all muscle was previously shown to increase lifespan, likely caused by systemic expression of autophagy related proteins and reduced ubiquitin content. Similarly, in this study dFOXO‐mediated improvement in heart function with age was also accompanied by a significant decrease in ubiquitinated myocardial proteins as determined by quantitative western blot. However, microarray data suggested that this reduction was caused by increased expression of genes associated with UPS rather than autophagy, indicating FOXO may perform its function differently in the heart than in other striated muscles. FOXO gene candidates from the transcriptomic analysis will be probed to pinpoint how mild FOXO OE halts the natural decline in heart performance in Drosophila.

Overexpression of Foxo in the Heart Ameliorates Performance Decline through Enhanced UPS Processing in Aging Drosophila

Heart performance declines with age. A likely contributor to age-associated cardiac dysfunction is reduced protein quality control due to decreased function of the ubiquitin/proteasome system (UPS) and the autophagy lysosomal pathway (ALP). The transcription factor, FOXO, has been shown to be involved in the regulation of genes related to both of these interrelated pathways as well as a host of other cellular processes. Here, we investigated the effects of cardiac-restricted overexpression of dFOXO in Drosophila melanogaster, an ideal model for aging studies, exploiting the tissue-specific UAS-GAL4 expression system. Using high-speed video microscopy and motion analysis and atomic force microscopy, we showed that with age, mild heart-specific overexpression of dFOXO significantly attenuated senescence-associated cardiac functional decline and stiffening, respectively. We also determined that differing amounts of heart-specific dFOXO overexpression elicited disparate effects, the strongest driver proving fatal. Overexpression of dFOXO in all Drosophila muscle has been shown to increase lifespan, likely owing to systemic expression of autophagy related proteins and reduced ubiquitin content. Similarly, we found that dFOXO-mediated improvement in heart function with age was also accompanied by a significant decrease in ubiquitinated myocardial proteins as determined by quantitative western blot analysis. However, microarray data suggested that this reduction was caused by increased expression of genes associated with the UPS rather than autophagy, indicating that FOXO may perform its function differently in the heart than in other striated muscles. Because FOXO transcriptionally regulates genes associated with many facets of cellular life, we have established a list of specific targets that dFOXO may affect when its expression is increased to attenuate cardiac dysfunction with age. We will systematically investigate these candidates to pinpoint how mild FOXO overexpression ameliorates the natural decline in heart performance in Drosophila.

Deficiency of insulin-like growth factor 1 reduces sensitivity to aging-associated cardiomyocyte dysfunction.

Circulating insulin-like growth factor-1 (IGF-1) levels are linked to cardiac performance and lifespan. However, the role of IGF-1 levels in aging-associated cardiac dysfunction has not been defined. This study was designed to evaluate the impact of severe liver IGF-1 deficiency (LID) on aging-induced cardiomyocyte contractile and intracellular Ca(++) dysfunction. Cardiomyocytes were isolated from young (2- to 4-month-old) and old (24- to 26-month-old) male C57BL/6 and LID mice. Cardiomyocyte contractile and intracellular Ca(++) transient properties were evaluated, including peak shortening (PS), maximal velocity of shortening/relengthening (+/-dL/dt), time-to-PS (TPS), time-to-90% relengthening (TR(90)), electrically stimulated change in fura-fluorescence intensity (DeltaFFI), and intracellular Ca(++) decay rate. Aged C57BL/6 myocytes displayed reduced PS, +/-dL/dt and DeltaFFI as well as prolonged TR(90) and intracellular Ca(++) decay. IGF-1 deficiency decreased +/-dL/dt, and prolonged TR(90) with little change in other mechanical indices. Interestingly, LID dampened aging-induced changes in cardiomyocyte function. Aging and IGF-1 deficiency both contributed to whole-body glucose intolerance. Aging downregulated expression of Akt, Klotho, and pAMPK, whereas it upregulated p53 expression, the effects of which were cancelled by IGF-1 deficiency. Aging and IGF-1 deficiency significantly reduced expression of the transcriptional factor Foxo3a without an overt effect on the mammalian target of rapamycin (mTOR) level. Collectively, these data depicted that IGF-1 deficiency may reduce the cardiomyocyte sensitivity to aging-induced mechanical dysfunction. Our data suggest that regulation of Akt, p53, adenosine monophosphate-activated protein kinase (AMPK) phosphorylation, and Klotho may play a role, at least in part, in IGF-1 deficiency-induced "desensitization" of cardiac aging.

Metallothionein antagonizes aging‐induced cardiac contractile dysfunction: role of PTP1B, insulin receptor tyrosine phosphorylation and Akt

Aging is often accompanied by reduced insulin sensitivity and cardiac dysfunction. However, the causal relationship between the two remains poorly understood. This study was designed to determine the impact of cardiac-specific overexpression of antioxidant metallothionein (MT) on aging-associated cardiac dysfunction and impaired insulin signaling. Contractile and intracellular Ca(2+) properties were evaluated in left ventricular myocytes including peak shortening (PS), maximal velocity of shortening/relengthening (+/- dL/dt), time-to-PS (TPS), time-to-90% relengthening (TR(90)), fura-2 fluorescence intensity change (DeltaFFI) and intracellular Ca(2+) decay rate. Expression of insulin receptor, protein-tyrosine phosphatase 1B (PTP1B), phosphorylation of insulin receptor (Tyr1146) and Akt were evaluated by Western blot analysis. Aged wild-type FVB and MT transgenic mice (26-28 months old) displayed glucose intolerance and hyperinsulinemia. Cardiomyocytes from aged FVB mice exhibited prolonged TR(90) and intracellular Ca(2+) decay associated with normal PS, +/- dL/dt, TPS and DeltaFFI compared with those from young (2-3 months old) mice. Western blot analysis revealed reduced Akt expression and insulin (5 mU g(-1))-stimulated Akt phosphorylation, elevated PTP1B expression and diminished basal insulin receptor tyrosine phosphorylation associated with comparable insulin receptor expression in aged FVB mouse hearts. All of these aging-related defects in cardiac contractile function and insulin signaling (although not hyperinsulinemia and glucose intolerance) were significantly attenuated or ablated by MT transgene. These data indicate that enhanced antioxidant defense is beneficial for aging-induced cardiac contractile dysfunction and alteration in insulin signaling.