Perspectives on mammalian cardiovascular aging: humans to molecules

Preconditioning, anesthetics, and perioperative medication

Activation of endogenous signal transduction pathways, by a variety of stimuli including ischemic and anesthetic pre- and post-conditioning, protects myocardium against ischemia and reperfusion injury. Experimental evidence suggests that adenosine-regulated potassium channels, cyclooxygenase-2, intracellular kinases, endothelial nitric oxide synthase, and membrane bound receptors play critical roles in signal transduction, and that intracellular signaling pathways ultimately converge on mitochondria to produce cardioprotection. Disease states, and perioperative medications such as sulfonylureas and COX-2 antagonists, could have adverse effects on cardioprotection by impairing activation of ion channels and proteins that are important in cell signaling. Insights gained from animal and clinical studies are reviewed and recommendations given for the use of perioperative anesthetics and medications.

Single histidine-substituted cardiac troponin I confers protection from age-related systolic and diastolic dysfunction

AIMS

Contractile dysfunction associated with myocardial ischaemia is a significant cause of morbidity and mortality in the elderly. Strategies to protect the aged heart from ischaemia-mediated pump failure are needed. We hypothesized that troponin I-mediated augmentation of myofilament calcium sensitivity would protect cardiac function in aged mice.

METHODS AND RESULTS

To address this, we investigated transgenic (Tg) mice expressing a histidine-substituted form of adult cardiac troponin I (cTnI A164H), which increases myofilament calcium sensitivity in a pH-dependent manner. Serial echocardiography revealed that Tg hearts showed significantly improved systolic function at 4 months, which was sustained for 2 years based on ejection fraction and velocity of circumferential fibre shortening. Age-related diastolic dysfunction was also attenuated in Tg mice as assessed by Doppler measurements of the mitral valve inflow and lateral annulus Doppler tissue imaging. During acute hypoxia, cardiac contractility significantly improved in aged Tg mice made evident by increased stroke volume, end systolic pressure, and +dP/dt compared with non-transgenic mice.

CONCLUSION

This study shows that increasing myofilament function by means of a pH-responsive histidine button engineered into cTnI results in enhanced baseline heart function in Tg mice over their lifetime, and during acute hypoxia improves survival in aged mice by maintaining cardiac contractility.

Exposure to inhaled particulate matter impairs cardiac function in senescent mice

Daily exposure to particulate matter (PM) is known to adversely affect cardiac function and is also known to be exaggerated with senescence. This study tests the hypothesis that cardiac function is uniquely altered by PM exposure in senescent mice. A mechanism for PM-induced cardiac effects is also postulated by examining the activity of nitric oxide synthase (NOS) and the generation of reactive oxygen species (ROS) in heart tissue. Echocardiography is performed in awake 18- and 28-mo-old mice at baseline and immediately following 3-h exposures to either filtered air or carbon black (CB; approximately 400 microg/m3) on 4 days. At 28 mo, left ventricular diameter at end-systole and end-diastole is significantly (P < 0.05) elevated, and fractional shortening is significantly reduced (49 +/- 3% vs. 56 +/- 3%) with CB exposure. In vivo hemodynamic measurements at 28 mo also demonstrate significant (P < 0.05) reductions in ejection fraction and increases in right ventricular and pulmonary vascular pressures following CB exposure. Functional changes at 28 mo are associated with increased ROS production as suggested by enhanced luminol activity. This elevated ROS production with aging and CB exposure is attributable to NOS uncoupling. Measurements of natriuretic peptide (atrial and brain) transcription and matrix metalloproteinase (MMP2 and MMP9) activity in heart tissue are significantly (P < 0.05) amplified with senescence and exposure to CB, pointing to increased cardiac stress and remodeling. These results demonstrate that acute PM exposure reduces cardiac contractility in senescent mice, and this decline in function is associated with increased ROS production linked to NOS uncoupling.

Cardiac dysfunction in aging conscious rats: altered cardiac cytoskeletal proteins as a potential mechanism

The objective of this study was to test the hypothesis that the mechanism mediating left ventricular (LV) dysfunction in the aging rat heart involves, in part, changes in cardiac cytoskeletal components. Our results show that there were no significant differences in heart rate, LV pressure, or LV diameter between conscious, instrumented young [5.9 +/- 0.3 mo (n = 9)] and old rats [30.6 +/- 0.1 mo (n = 10)]. However, the first derivative of LV pressure (LV dP/dt) was reduced (8,309 +/- 790 vs. 11,106 +/- 555 mmHg/s, P < 0.05) and isovolumic relaxation time (tau) was increased (8.7 +/- 0.7 vs. 6.3 +/- 0.6 ms, P < 0.05) in old vs. young rats, respectively. The differences in baseline LV function in young and old rats, which were modest, were accentuated after beta-adrenergic receptor stimulation with dobutamine (20 mug/kg), which increased LV dP/dt by 170 +/- 9% in young rats, significantly more (P < 0.05) than observed in old rats (115 +/- 5%). Volume loading in anesthetized rats demonstrated significantly impaired LV compliance in old rats, as measured by the LV end-diastolic pressure and dimension relationship. In old rat hearts, there was a significant (P < 0.05) increase in the percentage of LV collagen (2.4 +/- 0.2 vs. 1.3 +/- 0.2%), alpha-tubulin (92%), and beta-tubulin (2.3-fold), whereas intact desmin decreased by 51%. Thus the cardiomyopathy of aging in old, conscious rats may be due not only to increases in collagen but also to alterations in cytoskeletal proteins.

A low dose of dietary resveratrol partially mimics caloric restriction and retards aging parameters in mice

Resveratrol in high doses has been shown to extend lifespan in some studies in invertebrates and to prevent early mortality in mice fed a high-fat diet. We fed mice from middle age (14-months) to old age (30-months) either a control diet, a low dose of resveratrol (4.9 mg kg⁻¹ day⁻¹), or a calorie restricted (CR) diet and examined genome-wide transcriptional profiles. We report a striking transcriptional overlap of CR and resveratrol in heart, skeletal muscle and brain. Both dietary interventions inhibit gene expression profiles associated with cardiac and skeletal muscle aging, and prevent age-related cardiac dysfunction. Dietary resveratrol also mimics the effects of CR in insulin mediated glucose uptake in muscle. Gene expression profiling suggests that both CR and resveratrol may retard some aspects of aging through alterations in chromatin structure and transcription. Resveratrol, at doses that can be readily achieved in humans, fulfills the definition of a dietary compound that mimics some aspects of CR.

Aging-induced alterations in gene transcripts and functional activity of mitochondrial oxidative phosphorylation complexes in the heart

Aging is associated with progressive decline in energetic reserves compromising cardiac performance and tolerance to injury. Although deviations in mitochondrial functions have been documented in senescent heart, the molecular bases for the decline in energy metabolism are only partially understood. Here, high-throughput transcription profiles of genes coding for mitochondrial proteins in ventricles from adult (6-months) and aged (24-months) rats were compared using microarrays. Out of 614 genes encoding for mitochondrial proteins, 94 were differentially expressed with 95% downregulated in the aged. The majority of changes affected genes coding for proteins involved in oxidative phosphorylation (39), substrate metabolism (14) and tricarboxylic acid cycle (6). Compared to adult, gene expression changes in aged hearts translated into a reduced mitochondrial functional capacity, with decreased NADH-dehydrogenase and F(0)F(1) ATPase complex activities and capacity for oxygen-utilization and ATP synthesis. Expression of genes coding for transcription co-activator factors involved in the regulation of mitochondrial metabolism and biogenesis were downregulated in aged ventricles without reduction in mitochondrial density. Thus, aging induces a selective decline in activities of oxidative phosphorylation complexes I and V within a broader transcriptional downregulation of mitochondrial genes, providing a substrate for reduced energetic efficiency associated with senescence.

Age and hypertrophy related changes in contractile post-rest behavior and action potential properties in isolated rat myocytes

"Physiological" aging as well as early and progressive cardiac hypertrophy may affect action potential (AP) pattern, contractile function, and Ca(2+) handling. We hypothesize that contractile function is disturbed in hypertrophy from early stages and is differently affected in aged myocardium. In vivo function, cardiomyocyte contractile behavior and APs were compared in Wistar-Kyoto (WIS) rats and spontaneously hypertensive rats (SHR) at different ages and degrees of hypertrophy (3-4, 9-11, 20-24 months). Post-rest (PR) behavior was used to investigate the relative contribution of the sarcoplasmic reticulum (SR) and the Na/Ca exchanger (NCX) to cytosolic Ca(2+) removal. APs were recorded by whole-cell current-clamp and sarcomere shortening by video microscopy. Cyclopiazonic acid was used to suppress Ca(2+) ATPase (SERCA) function. Heart weight/body weight ratio was increased in SHR versus WIS within all age groups. Myocyte steady state (SS) shortening amplitude was reduced in young SHR versus WIS. Aging led to a significant decay of SS contractile amplitude and relengthening velocity in WIS, but the PR potentiation was maintained. In contrast, aging in SHR led to a decrease of PR potentiation, while SS contraction and relengthening velocity increased. APD(50%) was always prolonged in SHR versus WIS. With aging, APD(50%) increased in both WIS and SHR, but was still shorter in WIS. However, in old WIS the late AP portion (APD(90%)) was prolonged. Ca(2+) handling and AP properties are disturbed progressively with aging and with increasing hypertrophy. Decreased amplitude of shortening and velocity of relengthening in aged WIS may be attributed to reduced SERCA function. In SHR, an increase in SR leak and shift towards transmembraneous Ca handling via NCX may be responsible for the changes in contractile function. A prolonged APD(90%) in aged WIS may be an adaptive mechanism to preserve basal contractility. Therefore, the effects on contractile parameters and AP are different in hypertrophy and aging.

Autophagy in the heart and liver during normal aging and calorie restriction

Autophagy is a highly regulated intracellular process for the degradation of cellular constituents and essential for the maintenance of a healthy cell. We evaluated the effects of age and life-long calorie restriction on autophagy in heart and liver of young (6 months) and old (26 months) Fisher 344 rats. We observed that the occurrence of autophagic vacuoles was higher in heart than liver. The occurrence of autophagic vacuoles was not affected by age in either tissue, but was increased with calorie restriction in heart but not in liver. Next, we examined the expression of proteins involved in the formation and maturation of autophagosomes (beclin-1, LC3, Atg7, Atg9) or associated with autolysosomes and lysosomes (LAMP-1; cathepsin D). In hearts of both ad libitum-fed and calorie-restricted rats, we observed an increase in expression of beclin-1 and procathepsin D, but not mature cathepsin D, and a decrease in expression of LAMP-1 because of aging. In hearts, calorie restriction stimulated the expression of Atg7 and Atg9 and the lipidation of Atg8 (elevated LC3-II/I ratios) in aged rats. In hearts of ad libitum-fed rats, expression of Atg7 and lipidation of Atg8 were unaffected by age, while the cellular levels of Atg9 were lower in aged animals. Furthermore, we observed that the age- and diet-dependent expression levels of those proteins differed between heart and liver. In conclusion, autophagy in heart and liver did not decrease with age in ad libitum-fed rats, but was enhanced by calorie restriction in the heart. Thus, calorie restriction may mediate some of its beneficial effects by stimulating autophagy in the heart, indicating the potential for cardioprotective therapies.

Aging influences multiple indices of oxidative stress in the heart of the Fischer 344/NNia x Brown Norway/BiNia rat

We report the influence of aging on multiple markers of oxidative-nitrosative stress in the heart of adult (6-month), aged (30-month) and very aged (36-month) Fischer 344/NNiaHSd x Brown Norway/BiNia (F344/NXBN) rats. Compared to adult (6-month) hearts, indices of oxidative (superoxide anion [O2*-], 4-hydroxy-2-nonenal [4-HNE]) and nitrosative (protein nitrotyrosylation) stress were 34.1 +/- 28.1%, 186 +/- 28.1% and 94 +/- 5.8% higher, respectively, in 36-month hearts and these findings were highly correlated with increases in left ventricular wall thickness (r > 0.669; r > 0.710 and P < 0.01, respectively). Regression analysis showed that increases in cardiac oxidative-nitrosative stress with aging were significantly correlated with changes in the expression and/or regulation of proteins involved in transcriptional (NF-kappaB) activities, signaling (mitogen-activated protein kinases along with Src), apoptotic (Bcl-2, Traf-2), and cellular stress (HSPs). These results suggest that the aging F344/NXBN heart may be highly suited for unraveling the molecular events that lead to age-associated alterations in cardiac oxidative stress.

The effects of isoproterenol on abnormal electrical and contractile activity and diastolic calcium are attenuated in myocytes from aged Fischer 344 rats

We investigated whether the age-related decrease in sensitivity of the heart to catecholamines was accompanied by changes in Ca(2+) homeostasis and abnormal electrical and contractile activity caused by beta-adrenergic receptor (beta-AR) stimulation. Ventricular myocytes were isolated from young adult (3 months) and aged (24 months) male Fischer 344 rats. Unloaded cell shortening was measured in field-stimulated myocytes (2Hz, 37 degrees C); membrane currents and action potentials were measured with microelectrodes. Contractile responses to the non-selective beta-AR agonist, isoproterenol were significantly decreased in aged myocytes compared to younger myocytes and aged myocytes were less sensitive to isoproterenol. In contrast, Ca(2+) transients measured simultaneously with contractions were similar between groups. Isoproterenol increased sarcoplasmic reticulum Ca(2+) stores in both groups, but the increase was larger in aged cells. However, signs of Ca(2+) overload induced by isoproterenol were reduced with age. Diastolic Ca(2+) accumulation, contracture and the incidences of transient inward current, oscillatory afterpotentials (OAPs), aftertransients and aftercontractions induced by isoproterenol also were reduced with age. These results demonstrate that aged myocytes exhibit fewer signs of Ca(2+) overload in response to isoproterenol than young adult myocytes. These age-related changes in intracellular Ca(2+) may protect the aging heart against induction of arrhythmias initiated by OAPs.(1).

Aging and cardioprotection

Advanced age is a strong independent predictor for death, disability, and morbidity in patients with structural heart disease. With the projected increase in the elderly population and the prevalence of age-related cardiovascular disabilities worldwide, the need to understand the biology of the aging heart, the mechanisms for age-mediated cardiac vulnerability, and the development of strategies to limit myocardial dysfunction in the elderly have never been more urgent. Experimental evidence in animal models indicate attenuation in cardioprotective pathways with aging, yet limited information is available regarding age-related changes in the human heart. Human cardiac aging generates a complex phenotype, only partially replicated in animal models. Here, we summarize current understanding of the aging heart stemming from clinical and experimental studies, and we highlight targets for protection of the vulnerable senescent myocardium. Further progress mandates assessment of human tissue to dissect specific aging-associated genomic and proteomic dynamics, and their functional consequences leading to increased susceptibility of the heart to injury, a critical step toward designing novel therapeutic interventions to limit age-related myocardial dysfunction and promote healthy aging.

Local delivery of PKCepsilon-activating peptide mimics ischemic preconditioning in aged hearts through GSK-3beta but not F1-ATPase inactivation

In adult heart, selective PKCepsilon activation limits ischemia (I)-reperfusion (R) damage and mimics the protection associated with ischemic preconditioning. We sought to determine whether local delivery of PKCepsilon activator peptide psiepsilon-receptor for activated C-kinase (psiepsilon-RACK) is sufficient to produce a similarly protected phenotype in aged hearts. Langendorff-perfused hearts isolated from adult (5 mo; n = 9) and aged (24 mo; n = 9) male Fisher 344 rats were perfused with psiepsilon-RACK conjugated to Tat (500 nM) or Tat only (500 nM) for 10 min before global 31-min ischemia. Western blotting was used to measure mitochondrial targeting of PKCepsilon, PKCdelta, phospho (p)-GSK-3beta (Ser(9)) and GSK-3beta in hearts snap-frozen during I. Recovery of left ventricular developed pressure was significantly improved by psiepsilon-RACK (P < 0.01) and infarct size reduced in 24-mo rats vs. age-matched controls (60% vs. 34%; P < 0.01). Mitochondrial PKCepsilon levels were 30% greater during I with psiepsilon-RACK in aged vs. control rats (P < 0.01). Interestingly, mitochondrial GSK-3beta levels were threefold greater in aged vs. adult rats during I, and psiepsilon-RACK prevented this increase (P < 0.01). Mitochondrial p-GSK-3beta levels were also greater in aged rats after psiepsilon-RACK (P < 0.01), and subsequent inhibition of GSK-3beta with SB-216763 (3 muM) before I/R elicited protection similar to that of psiepsilon-RACK (n = 3/group). Mitochondrial proteomic analysis further identified group differences in the F(1)-ATPase beta-subunit, and coimmunoprecipitation studies revealed a novel interaction with PKCepsilon. F(1)-ATPase-PKCepsilon association was affected by psiepsilon-RACK in adult but not aged rats. Our results provide evidence, for the first time, for PKCepsilon-mediated protection in aged rat heart after I/R and suggest a central role for mitochondrial GSK-3beta but not F(1)-ATPase as a potential target of PKCepsilon to limit I/R damage with aging.

Age-related changes in echocardiographic measurements: association with variation in the estrogen receptor-alpha gene

Left ventricular (LV) mass and other LV measures have been shown to be heritable. In this study we hypothesized that functional variation in the gene coding for estrogen receptor-alpha (ESR1), known for mediating the effect of estrogens on myocardium, is associated with age-related changes in LV structure. Four genetic markers (ESR1 TA repeat; rs2077647, or +30T>C; rs2234693, or PvuII; and rs9340799, or XbaI) were genotyped in 847 unrelated individuals (488 women) from the Framingham Offspring Study, who attended 2 examination cycles 16 years apart (mean ages at first examination: 43+/-9 years; at follow-up: 59+/-9 years). ANCOVA was used to assess the association of polymorphisms and their haplotypes with cross-sectional measurements and longitudinal changes in LV mass, wall thickness, end-diastolic and end-systolic internal diameter, and fractional shortening after adjustment for factors known to influence these variables. Changes over time were detected for all of the LV measurements (P ranging from <0.0001 to 0.02), except for fractional shortening in men. The SS genotype of the ESR1 TA repeat polymorphism in the promoter region was associated with longitudinal changes in LV mass and LV wall thickness (P ranging from 0.0006 to 0.01). Moreover, the TA[S]-+30[T]-PvuII[T]-XbaI[A] haplotype (frequency: 47.5%) was associated with greater LV changes as compared with the TA[L]-+30[C]-PvuII[C]-XbaI[G] haplotype (frequency: 31.8%). Our results are consistent with the hypothesis that common ESR1 polymorphisms are significantly associated with age-related changes in LV structure. Understanding the mechanisms predisposing to unfavorable LV remodeling of the heart with advancing age may aid in the discovery of new therapeutic targets for the prevention of heart failure.

Declining into failure: the age-dependent loss of the L-type calcium channel within the sinoatrial node

BACKGROUND

The spontaneous activity of pacemaker cells in the sinoatrial (SA) node controls heart rate under normal physiological conditions. Clinical studies have shown the incidence of SA node dysfunction increases with age and occurs with peak prevalence in the elderly population. The present study investigated whether aging affected the expression of Ca(v)1.2 channels and whether these changes could affect pacemaker activity, in turn leading to age-related SA node degeneration.

METHODS AND RESULTS

The SA node region was isolated from the right atrium of guinea pigs between birth and 38 months of age. Immunofluorescence studies showed Ca(v)1.2 protein was present as punctate labeling around the outer membrane of atrial cells but was absent from the center of the SA node. The area lacking Ca(v)1.2-labeled protein progressively increased from 2.06+/-0.1 (mean+/-SEM) mm2 at 1 month to 18.72+/-2.2 mm2 at 38 months (P<0.001). Western blot provided verification that Ca(v)1.2 protein expression within the SA node declined during aging. Functional measurements showed an increased sensitivity to the L-type calcium blocker nifedipine; SA node preparations stopped beating in 100 micromol/L nifedipine at 1 day old, compared with 30 micromol/L at 1 month and 10 micromol/L at 38 months of age. Furthermore, the amplitude of extracellular potentials declined within the center and periphery of the SA node during aging.

CONCLUSIONS

The present data show Ca(v)1.2 channel protein decreases concurrently with reduced spontaneous activity of the SA node with increased age, which provides further evidence of mechanisms underlying the age-related deterioration of the cardiac pacemaker.

Cellular trafficking of phospholamban and formation of functional sarcoplasmic reticulum during myocyte differentiation

Phospholamban (PLB) associates with the Ca(2+)-ATPase in sarcoplasmic reticulum (SR) membranes to permit the modulation of contraction in response to beta-adrenergic signaling. To understand how coordinated changes in the abundance and intracellular trafficking of PLB and the Ca(2+)-ATPase contribute to the maturation of functional muscle, we measured changes in abundance, location, and turnover of endogenous and tagged proteins in myoblasts and during their differentiation. We found that PLB is constitutively expressed in both myoblasts and differentiated myotubes, whereas abundance increases of the Ca(2+)-ATPase coincide with the formation of differentiated myotubes. We observed that PLB is primarily present in highly mobile vesicular structures outside the endoplasmic reticulum, irrespective of the expression of the Ca(2+)-ATPase, indicating that PLB targeting is regulated through vesicle trafficking. Moreover, using pulse-chase methods, we observed that in myoblasts, PLB is trafficked through directed transport through the Golgi to the plasma membrane before endosome-mediated internalization. The observed trafficking of PLB to the plasma membrane suggests an important role for PLB during muscle differentiation, which is distinct from its previously recognized role in the regulation of the Ca(2+)-ATPase.

Estrogen deficiency decreases ischemic tolerance in the aged rat heart: roles of PKCδ, PKCε, Akt, and GSK3β

The mechanisms underlying the age-dependent reversal of female cardioprotection are poorly understood and complicated by findings that estrogen replacement is ineffective at reducing cardiovascular mortality in postmenopausal women. Although several protective signals have been identified in young animals, including PKC and Akt, how these signals are affected by age, estrogen deficiency, and ischemia-reperfusion (I/R) remains unknown. To determine the independent and combined effects of age and estrogen deficiency on I/R injury and downstream PKC-Akt signaling, adult and aged female F344 rats ( n = 12/age) with ovaries intact or ovariectomy (Ovx) were subjected to I/R using Langendorff perfusion (31-min global-ischemia). Changes in cytosolic (s), nuclear (n), mitochondrial (m) PKC (δ, ε) levels, and changes in total Akt and mGSK-3β phosphorylation after I/R were assessed by Western blot analysis. Senescence increased infarct size 50% in ovary-intact females ( P < 0.05), whereas no differences in LV functional recovery or estradiol levels were observed. Ovx reduced functional recovery to a greater extent in aged compared with adult rats ( P < 0.05). In aged (vs. adult), levels of m- and nPKC(-δ, -ε) were markedly decreased, whereas mGSK3β levels were increased ( P < 0.05). Ovx led to greater levels of sPKC(-δ, -ε) independent of age ( P < 0.05). I/R reduced p-Akt(Ser473) levels by 57% and increased mGSK-3β accumulation 1.77-fold ( P < 0.05) in aged, ovary-intact females. These data suggest, for the first time, that estrogen alone cannot protect the aged female myocardium from I/R damage and that age- and estrogen-dependent alterations in PKC, Akt, and GSK-3β signaling may contribute to loss of ischemic tolerance.

Pulmonary resection in the elderly

PURPOSE OF REVIEW

With increasing longevity, altered demographics of the lung cancer population, and preoperative interventions to enhance the efficacy of surgical therapy, increasing numbers of elderly people will present for anesthesia and pulmonary resection.

RECENT FINDINGS

The geriatric population often exhibits wide disparity between chronologic and physiologic senescence which is underscored by data indicating that outcome following lung resection for cancer is influenced more by tumor stage, preoperative functional status and comorbidities than age alone. Nonetheless, the normal process of cardiopulmonary aging can limit the physiological reserve necessary to compensate for perioperative stress even in otherwise healthy elderly patients. Data indicate a relatively favorable risk-benefit relationship for lung resection in the elderly given the poor prognosis for patients undergoing palliative care or chemotherapy or radiation alone. Emerging experience now suggests that minimally invasive surgical techniques for the treatment of lung cancer may parallel conventional thoracotomy in terms of oncologic efficacy while decreasing perioperative morbidity in the elderly.

SUMMARY

The combination of an aging population, recent advances in neoadjuvant therapies, data supporting the oncologic efficacy of resection, and minimally invasive surgical techniques strongly suggests that more elderly patients will be candidates for surgical management of their lung cancer, thus presenting anesthesiologists with unique challenges.

Maintaining serum response factor activity in the older heart equal to that of the young adult is associated with better cardiac response to isoproterenol stress

To understand the effect of transcription regulation in modulating cardiac aging, we sought to study the role of serum response factor (SRF), a key transcription factor in the heart that is normally increased with senescence and also in congestive heart failure. A Tet-Off gene expression system was used for cardiac-specific over-expression of a mutant SRF protein. In these binary transgenic mice, there is no age-related increase in SRF protein expression; in fact, there appeared to be a mild reduction of SRF protein (Mild-R SRF Tg). The older, middle-aged (15 mo) Mild-R SRF Tg mice appeared healthier and were better able to maintain their left ventricular systolic pressure (LVSP) in response to moderate â-adrenergic stimulation compared with age-matched Non-Tg mice, which demonstrated a negative ionotropic response. The Mild-R SRF Tg hearts had lower mRNA expression of BNP (p < 0.05), and the sodium calcium exchanger (p < 0.05), compared to Non-Tg. Mild-R SRF Tg had higher mRNA levels of SERCA2 (p < 0.05) and ryanodine receptor 2 (p < 0.05) compared to Non-Tg hearts. These findings suggest that preventing the age-associated increase in SRF is associated with better preserved intracellular calcium handling and functional response to stress; it might be advantageous for the older adult heart. This mouse model could be helpful in elucidating the molecular mechanisms underlying certain age-related changes in cardiac reserve capacity and response to stress.

Growth hormone replacement attenuates diastolic dysfunction and cardiac angiotensin II expression in senescent rats

We tested the hypothesis that long-term growth hormone (GH) replacement in aged rats would preserve diastolic function and attenuate left ventricular remodeling associated with normal aging. Male Brown Norway x F344 rats were randomized to receive twice daily injections of porcine GH (200 microg/injection, subcutaneous) or saline from 24 to 30 months of age. Adult rats (6- to 9-months old) received saline injections throughout the study. Thirty-month-old, saline-treated rats exhibited low levels of insulin-like growth factor 1 (IGF-1), impaired diastolic left ventricular filling (Doppler), increased cardiac angiotensin II (Ang II), reduced plasma Ang II, and increased cardiac collagen. GH administration in old rats restored IGF-1 and diastolic indices to values comparable to those of adults. These effects were associated with reduced cardiac Ang II and attenuations in cardiac collagen. Age-related decreases in GH and IGF-1 may contribute to the decline in diastolic function of aging, in part through alterations in renin-angiotensin system-mediated ventricular remodeling.

Calcium spark properties in ventricular myocytes are altered in aged mice

This study determined whether whole cell Ca2+ transients and unitary sarcoplasmic reticulum (SR) Ca2+ release events are constant throughout adult life or whether Ca2+ release is altered in aging ventricular myocytes. Myocytes were isolated from young adult (∼5 mo old) and aged (∼24 mo old) mice. Spontaneous Ca2+ sparks and Ca2+ transients initiated by field stimulation were detected with fluo-4. All experiments were conducted at 37°C. Ca2+ transient amplitudes were reduced, and Ca2+ transient rise times were abbreviated in aged cells stimulated at 8 Hz compared with young adult myocytes. Furthermore, the incidence and frequency of spontaneous Ca2+ sparks were markedly higher in aged myocytes compared with young adult cells. Spark amplitudes and spatial widths were similar in young adult and aged myocytes. However, spark half-rise times and half-decay times were abbreviated in aged cells compared with younger cells. Resting cytosolic Ca2+ levels and SR Ca2+ stores were assessed by rapid application of caffeine in fura-2-loaded cells. Neither resting Ca2+ levels nor SR Ca2+ content differed between young adult and aged cells. Thus increased spark frequency in aging cells was not attributable to increased SR Ca2+ stores. Furthermore, the decrease in Ca2+ transient amplitude was not due to a decrease in SR Ca2+ load. These results demonstrate that alterations in fundamental SR Ca2+ release units occur in aging ventricular myocytes and raise the possibility that alterations in Ca2+ release may reflect age-related changes in fundamental release events rather than changes in SR Ca2+ stores and diastolic Ca2+ levels.

Left ventricular morphology, global and longitudinal function in normal older individuals: A cardiac magnetic resonance study

BACKGROUND

The heart transforms structurally and functionally with age but the nature and magnitude of reported changes appear inconsistent. This study was designed to assess left ventricular (LV) morphology, global and longitudinal function in healthy older men and women using cardiac magnetic resonance (CMR).

METHODS

Ninety-five healthy subjects (age 62+/-16 years, range 22-91 years) underwent breath-hold cine CMR. LV end-diastolic volume (EDV), end-systolic volume (ESV), myocardial mass, ejection fraction (EF), mass-to-volume ratio, mean midventricular wall motion, thickness and thickening were calculated from short-axis data sets. Average mitral annular displacement was measured to assess longitudinal LV function.

RESULTS

Subjects were divided according to age (< 65 and > or = 65 years) and sex. EDV and ESV indices (corrected for body surface area) decreased whilst EF increased with age. There was no difference in LV myocardial mass index between the age groups, but midventricular wall thickness was significantly higher in older people. Mass-to-volume ratio also increased with age. In contrast to EF, mitral annular displacement declined with age. Midventricular LV wall thickness, myocardial mass index and mass-to-volume ratio were higher in men than in women but there were no differences in measures of global and longitudinal LV systolic function.

CONCLUSIONS

Due to smaller LV volumes but higher wall thickness, myocardial mass remains unchanged with age. We have found an age-related increase in EF and reduction in longitudinal LV function in apparently normal subjects. This must be borne in mind when assessing older patients with possible heart failure and normal LV systolic function. Men have higher myocardial mass than women.

Effects of Aging and Anti-Aging Caloric Restrictions on Carbonyl and Heat Shock Protein Levels and Expression

Heat shock proteins (Hsps) are induced by stressful stimuli and have been shown to protect cells and organs from such stresses both in vitro and in vivo, and play a positive role in lifespan determination. An attenuated response to stress is characteristic of senescence and no Hsp induction is observed upon exposure to stress and no protective effect of a mild stress is observed in cells from aged individuals. The artificial over-expression of Hsps, can produce a protective effect against a variety of damaging stimuli in cells from aged rats or aged humans, in whom cardiovascular disease is a major cause of morbidity in older age. Here, we show that aging significantly decreases the levels of Hsp27, Hsp60, Hsp72 and Hsc70 in right atrium and left ventricle of the rat heart, both at level of protein and of mRNA. Two different caloric restriction regimens have been found to counteract in part the decrease in the levels of Hsp expression in the aged heart tissue as well as the tendency to an increase of the levels of carbonyl in cardiac proteins. Our data suggest that cardiac Hsp levels may be a determinant of longevity in rodents, and that generation of new regimens of caloric restriction may eventually show how to improve modulation of cardiac aging.

Chronic β-agonist administration affects cardiac function of adult but not old rats, independent of β-adrenoceptor density

Although β-adrenoceptor agonists have clinical merit for attenuating the age-related loss of skeletal muscle mass and strength (sarcopenia), potential cardiac-related side effects may limit their clinical application. The aim of this study was to determine whether chronic β-agonist administration impairs cardiac function in adult or aged rats. Adult (16 mo) and aged (28 mo) Fischer 344 rats were treated with fenoterol (1.4 mg·kg−1·day−1 ip) or vehicle for 4 wk. Heart function was assessed in vitro before analyses of cardiac structure and β-adrenoceptor density. Heart mass increased 17% and 25% in fenoterol-treated adult and aged rats, respectively. The increased heart mass in aged, but not adult, rats was associated with a relative increase in collagen content. Cardiac hypertrophy in adult rats was associated with an increase in left ventricular developed pressure, a marked reduction in cardiac output, and a reduction in coronary flow per unit heart mass. In contrast, negligible differences in ventricular function were observed in fenoterol-treated aged rats. The differential effect on contractile function was not associated with age-related differences in β-adrenoceptor density but, rather, an age-related increase in downregulation after treatment. Our results show that chronic β-agonist treatment impairs cardiac function to a greater extent in adult than in aged rats. These results provide important information regarding the potential effects of chronic β-agonist use on cardiac function and the future development of safe and effective treatments for sarcopenia.

Susceptibility to hypoxia/reoxygenation of aged rat cardiomyocytes and its modulation by selenium supplementation

Since in the aged heart an increased basal production of reactive oxygen species (ROS) has been demonstrated, and the resistance to ROS attack could be ameliorated by antioxidant supplementation, we verified the protective effect of selenium, as sodium selenite (SS) or seleno methionine (SM), in cultured rat cardiomyocytes aged in vitro. In normoxia, glutathione peroxidase (GPx) activity and total antioxidant activity were higher in old than in young cardiomyocytes, suggesting the existence of a compensatory increase of antioxidant defenses. When aged cells were submitted to hypoxia/reoxygenation, GPx activity was not modified; while total antioxidant activity decreased, conjugated diene level increased. Selenium supplementation, particularly as SM, was able to increase GPx, and consequently total antioxidant activity, and to decrease conjugated diene production. The observed ability of selenium supplementation to protect aged cardiomyocytes from hypoxia/reoxygenation damage underlines the importance of an optimal selenium dietary intake, particularly in the elderly.

Age‐associated increases in oxidative stress and antioxidant enzyme activities in cardiac interfibrillar mitochondria: implications for the mitochondrial theory of aging

Mitochondrial dysfunction and the accumulation of oxidative damage to macromolecules are believed to play key roles in the aging process. Characterization of age-related changes to cardiac mitochondria has been complicated by the fact that two distinct populations of mitochondria exist in the myocardium: subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM). We investigated whether differences in hydrogen peroxide production (H2O2) and oxidative stress existed between cardiac SSM and IFM isolated from young (6 mo) and old (24 mo) male Fischer-344 rats. There was a significant increase in oxidative stress levels (4-hydroxy-2-nonenal-modified proteins, protein carbonyls, and malondialdehyde) in IFM with age. In contrast, only protein carbonyls were elevated in SSM with age. Significant age-related increases in MnSOD, GPX, and CAT activities were detected in IFM, while in SSM, MnSOD, and GPX activities increased with age and CAT activity declined. These increases in antioxidant enzyme activity likely occurred in response to increased mitochondrial production of superoxide and hydrogen peroxide. Indeed, SSM produced more H2O2 with age, while the increase in IFM was not significant, but this may be due to the higher antioxidant enzyme activity observed in IFM compared with SSM. Finally, reduced glutathione levels were significantly lower in IFM compared with SSM in both young and old rats, while glutathione reductase activity was not different with age or mitochondrial subpopulations, indicating increased consumption of glutathione. The accumulation of oxidant-induced damage in IFM may be a major contributing factor to the age-related alterations in myocardial function. Our results emphasize the importance of studying both mitochondrial populations when attempting to elucidate the contribution of mitochondrial dysfunction to myocardial aging.

Age- and sex-dependent alterations in protein kinase C (PKC) and extracellular regulated kinase 1/2 (ERK1/2) in rat myocardium

Cardiovascular morbidity and mortality increase significantly with advancing age, with proportionally higher rates occurring in aged women when compared to aged men. The signaling alterations responsible for age-related reductions in ischemic stress reserves, particularly in aged women, are poorly understood. Accordingly, we sought to determine whether alterations in the cellular location and formation of specific protein kinase C (PKC)-extracellular regulated 1/2 (ERK1/2) signaling modules (SMS) might provide insight into known age- and sex-related differences in cardiovascular disease outcomes. Cytosolic (Cyto), mitochondrial (Mito) and nuclear (Nuc) fractions were isolated from left ventricles of male (M) and female (F) adult (6 mo), castrated or aged (23 mo) F344 rats by centrifugation. Western blotting was used to assess PKC (alpha, delta, epsilon), p-ERK1/2 and p-Bad(Ser112) levels, and immunoprecipitation to assess PKC-ERK1/2 SMS. Cyto-PKCalpha levels increased with age (p<0.0001), whereas increases in cyto-PKCalpha-ERK1/2 SMS were only observed in aged F (60%; p<0.01). Mito-PKCdelta and Mito-PKCdelta-ERK1/2 SMS increased in M and F with age (p<0.0001); however increases in Cyto-PKCdelta were only observed in aged M (80% p<0.0001). It is important to note that Nuc- and Mito-PKCdelta-ERK1/2 SMS were 3.5- and 4.8-fold greater in males versus females, respectively (p<0001). Increases in Mito-PKCepsilon-ERK1/2 SMS (216%) were also specific to aged M (p<0.0001), however, Mito-p-Bad(Ser112) levels were decreased with age in both M and F. Differences in sex hormone status could not fully account for observed age-related differences in PKC. Collectively, our results provide novel evidence for age and sex-related differences in the magnitude and distribution of cardiac PKC-ERK1/2 SMS consistent with previously described pathological and protective phenotypes, respectively.

Chronic Exercise Improves Myocardial Inotropic Reserve Capacity Through α1-Adrenergic and Protein Kinase C-Dependent Effects in Senescent Rats

We have previously demonstrated that α1-adrenergic (AR)-mediated contraction is diminished in the senescent rat heart, in part due to alterations in protein kinase C (PKC) signaling. Since chronic exercise training (EX) can exert independent effects on increasing α1-AR contraction in the adult rat heart, we sought to determine whether age-related defects in α1-AR contraction could be reversed by chronic EX. We further hypothesized that improved α1-AR contraction by EX may be PKC dependent. Adult (4 months; Y) and aged (24 months; O) male F344 rats were treadmill-trained (n = 12–13/group; TR) at ∼70% of VO2max for 12 weeks or remained sedentary (YSED, YTR, OSED, OTR). Training status was verified by plantaris citrate synthase activity and left ventricular (LV) contractile responses (dP/dt) to α1-AR stimulation were assessed in Langendorff-perfused hearts using the α1-AR agonist phenylephrine (PE; 10−5 M) with and without the PKC inhibitor chelerythrine (CE; 10−6 M). α1-AR stimulation elicited greater increases in LV dP/dt in hearts isolated from OTR (4525.4 ± 224.1 mmHg/s) versus OSED (3658.9 ± 291.0 mmHg/s), while CE abolished PE-induced effects (OTR, 4069.2 ± 341.2) versus (OSED, 3608.9 ± 321.2) (p &lt;.01). Upon western blotting, phosphospecific antibodies directed at PKCε (pSer729) revealed greater levels in LV isolated from YTR versus YSED, and EX ameliorated aged-related reductions in OSED (p &lt;.001). Basal PKCε mRNA levels were also greater in YTR and OTR versus YSED (p &lt;.01). PE-induced increases in phosphor-PKCδ (pThr507) levels observed in OSED were attenuated in OTR (p &lt;.03). Chronic EX was also associated with significant reductions in PKCα (pSer657) levels following PE in OTR (p &lt;.002). The results indicate that age-related reductions in α1-AR contraction can be partially reversed by EX in the rat heart. These results further suggest that alterations in PKC levels underlie, at least in part, EX-induced improvements in α1-AR contraction.

Eplerenone, a selective aldosterone blocker, improves diastolic function in aged rats with small-to-moderate myocardial infarction

BACKGROUND

The incidence of cardiovascular diseases increases rapidly with age, and the elderly suffer higher morbidity and mortality. Aldosterone blockers have shown benefits in patients with left ventricular (LV) dysfunction and heart failure after myocardial infarction (MI). However, aldosterone blockade efficacy has not been explored in aged animals with MI. Methods and results Small-to-moderate MI was induced by coronary artery ligation in 16-month old rats, divided into 3 groups: sham-operated (control, n = 9), MI (n = 9), and MI fed a diet containing eplerenone (120 mg/kg/day, MI+Eplerenone, n = 9) given 18 days postsurgery and up to sacrifice 3 months later. At sacrifice, untreated MI rats did not show overt systolic dysfunction but they had (1) echocardiographic evidences of impaired relaxation (increase of E wave deceleration time and of isovolumic relaxation time, decrease of peak E wave velocity), (2) hemodynamically impaired LV relaxation (LV -dP/dt from 7413 +/- 720 to 4956 +/- 475 mm Hg/s, P < .05), and (3) significant increase of collagen content in LV interstitium (from 4.27 +/- 0.23 to 5.34 +/- 0.24%, P < .01) and in aorta (from 19 +/- 1 to 24 +/- 2%, P < .05). Eplerenone normalized echocardiographic and hemodynamic evidences of diastolic dysfunction, as well as myocardial interstitial collagen and aortic fibrosis (all parameters statistically different from untreated MI).

CONCLUSION

In aged rats with small to moderate MI, eplerenone normalized diastolic relaxation, possibly through a reduction of interstitial fibrosis.

Protein Kinase Cε Overexpression Alters Myofilament Properties and Composition During the Progression of Heart Failure

We report characterization of a transgenic mouse that overexpresses constitutively active protein kinase Cε in the heart and slowly develops a dilated cardiomyopathy with failure. The hemodynamic, mechanical, and biochemical properties of these hearts demonstrate a series of temporal events that mark the progression of the disease. In the 3-month transgenic (TG) animals, contractile properties and gene expression measurements are normal, but an increase in myofibrillar Ca 2+ sensitivity and thin filament protein phosphorylation is noted. At 6 months, there is a decrease in the myofibrillar Ca 2+ sensitivity, a significant increase in β-myosin heavy chain mRNA and protein, normal cardiac function, but a blunted response to an inotropic challenge. The transition at 9 months is especially interesting because age-related changes appear to contribute to the decline in function seen in the TG heart. At this point, there is a decline in baseline function and maximum tension produced by the myofibrils, which is coincident with the onset of atrial myosin light chain isoform re-expression in the ventricles. In the 12-month TG mice, there is clear hemodynamic and geometric evidence of failure. Alterations in the composition of the myofibrils persist but the phosphorylation of myosin light chain 2v is dramatically different at this age compared with all others. We interpret these data to implicate the disruption of the myofibrillar proteins and their interactions in the propagation of dilated cardiac disease.

Ageing-related changes of connexins and conduction within the sinoatrial node

Clinical studies have shown that sinoatrial node dysfunction occurs at the highest incidence in the elderly population. Guinea-pigs were studied throughout their lifespan (i.e. birth to 38 months) to investigate the possible mechanism leading to nodal dysfunction. Using immunofluorescence with confocal microscopy, Cx43 protein expression was shown at birth to be present throughout the sinoatrial node and atrial muscle, however, at one month Cx43 protein was not expressed in the centre of the sinoatrial node. Throughout the remainder of the animal's lifespan the area of tissue lacking Cx43 protein progressively increased. Western blot provided verification by quantitative analysis that Cx43 protein expression within the sinoatrial node decreased with age; however, the expression of other cardiac connexins, Cx40 and Cx45, did not differ with age. Analysis of conduction maps showing propagation of the action potential across the sinoatrial node, from the initiation point to the crista terminalis, found that the action potential conduction time taken and conduction distance increased proportionally with age; conversely the conduction velocity decreased with age. We have shown ageing induces degenerative changes in action potential conduction, contributed to by the observed loss of Cx43 protein. Our data identify Cx43 as a potential therapeutic target for quashing the age-related deterioration of the cardiac pacemaker.

Myocardial beta-1 adrenoceptor down-regulation in aging and heart failure: implications for beta-blocker use in older adults with heart failure

Heart failure is associated with increased sympathetic nervous stimulation that results in down-regulation of myocardial beta-1 receptors. The failing heart might depend more on beta-2 receptors for positive inotropic support than the normal heart. Suppression of both beta-1 and beta-2 adrenoceptors by a non-selective beta-blocker, such as carvedilol, is likely to eliminate the failing heart's much needed inotropic support, resulting in an exacerbation of symptoms. Use of a beta-1 selective blocker, such as metoprolol, on the other hand, is likely to be well tolerated. Unlike carvedilol, the use of metoprolol is associated with up-regulation of beta-1 receptors. The clinical significance of the pharmacodynamic differences between these two beta-blockers in terms of their short-term hemodynamic and long-term beneficial effects is not clearly understood. However, in clinical trials, both carvedilol and metoprolol improved left ventricular function, heart failure symptoms and survival. Both drugs are well tolerated as well. Aging itself is associated with elevated myocardial and serum norepinephrine levels, which is associated with down-regulation of beta-1 receptors. In this article, we reviewed the literature to examine the clinical implications of this dual (age- and heart failure-related) sympathetic stimulation and beta-1 receptor down-regulation on selection of beta-blockers in older adults with heart failure.

Aging, Exercise, and Cardioprotection

Myocardial ischemia-reperfusion (I-R) injury is a major contributor to the morbidity and mortality associated with coronary artery disease. The incidence of I-R events is greatest in older persons, and studies also indicate that the magnitude of myocardial I-R injury is greater in senescent individuals compared to younger adults. Regular exercise has been confirmed as a pragmatic countermeasure to protect against I-R-induced cardiac injury. Specifically, endurance exercise has been proven to provide cardioprotection against an I-R insult in both young and old animals. Proposed mechanisms to explain the cardioprotective effect of exercise include the induction of myocardial heat shock proteins (HSPs), improved cardiac antioxidant capacity, and/or elevation of other cardioprotective proteins. Of these potential mechanisms, evidence indicates that elevated myocardial levels of heat shock proteins or antioxidants can provide myocardial protection against I-R injury. At present, which of these protective mechanisms is essential for exercise-induced cardioprotection remains unclear. Understanding the molecular basis for exercise-induced cardioprotection is important in developing exercise paradigms to protect the heart during an I-R insult.

Aging increases stiffness of cardiac myocytes measured by atomic force microscopy nanoindentation

It is well established that the aging heart exhibits left ventricular (LV) diastolic dysfunction and changes in mechanical properties, which are thought to be due to alterations in the extracellular matrix. We tested the hypothesis that the mechanical properties of cardiac myocytes significantly change with aging, which could contribute to the global changes in LV diastolic dysfunction. We used atomic force microscopy (AFM), which determines cellular mechanical property changes at nanoscale resolution in myocytes, from young (4 mo) and old (30 mo) male Fischer 344 x Brown Norway F1 hybrid rats. A measure of stiffness, i.e., apparent elastic modulus, was determined by analyzing the relationship between AFM indentation force and depth with the classical infinitesimal strain theory and by modeling the AFM probe as a blunted conical indenter. This is the first study to demonstrate a significant increase (P < 0.01) in the apparent elastic modulus of single, aging cardiac myocytes (from 35.1 +/- 0.7, n = 53, to 42.5 +/- 1.0 kPa, n = 58), supporting the novel concept that the mechanism mediating LV diastolic dysfunction in aging hearts resides, in part, at the level of the myocyte.

Noninvasive quantification of regional myocardial function using Doppler-derived velocity, displacement, strain rate, and strain in healthy volunteers: effects of aging

Quantification of regional function can be performed using Doppler tissue echocardiography to evaluate myocardial velocity, tissue displacement, strain, and strain rate. Although these techniques have been validated in animal experiments and early clinical trials, there are only limited measurements in healthy populations to use as reference data. In 100 healthy volunteers, left ventricular myocardial velocity, displacement, strain, and strain rate were measured using Doppler tissue echocardiography. Measurements were obtained from basal, mid, and apical segments of walls visualized from left ventricular apical 4- and 2-chamber views. Analysis of covariance was used to examine the effects of age and wall segment position. All parameters showed a strong dependence on wall segment position. Although myocardial velocities and strain rate showed significant dependence on age, displacement and peak systolic strain measures were less affected. Like pulsed Doppler mitral inflow velocity, tissue velocity and strain rate show age-related changes.

Beta 2-agonist administration reverses muscle wasting and improves muscle function in aged rats

The beta2-adrenoceptor agonist (beta2-agonist) fenoterol has potent anabolic effects on rat skeletal muscle. We conducted an extensive dose-response study to determine the most efficacious dose of fenoterol for increasing skeletal muscle mass in adult rats and used this dose in testing the hypothesis that fenoterol may have therapeutic potential for ameliorating age-related muscle wasting and weakness. We used adult (16-month-old) rats that had completed their growth and development, and old (28-month-old) rats that exhibited characteristic muscle wasting and weakness, and treated them daily with either fenoterol (1.4 mg kg(-1), i.p), or saline vehicle, for 4 weeks. Following treatment, functional characteristics of fast-twitch extensor digitorum longus (EDL) and predominantly slow-twitch soleus muscles of the hindlimb were assessed in vitro. Untreated old rats exhibited a loss of skeletal muscle mass and a decrease in force-producing capacity, in both fast and slow muscles, compared with adult rats (P < 0.05). However, there was no age-associated decrease in skeletal muscle beta-adrenoceptor density, nor was the muscle response to chronic beta-agonist stimulation reduced with age. Thus, muscle mass and force-producing capacity of EDL and soleus muscles from old rats treated with fenoterol was equivalent to, or greater than, untreated adult rats. The increase in mass and strength was attributed to a non-selective increase in the cross-sectional area of all muscle fibre types, in both the EDL and soleus. Fenoterol treatment caused a small increase in fatiguability due to a decrease in oxidative metabolism in both EDL and soleus muscles, with some cardiac hypertrophy. Further studies are needed to fully separate the desirable effects on skeletal muscle and the undesirable effects on the heart. Nevertheless, our results demonstrate that fenoterol is a powerful anabolic agent that can restore muscle mass and strength in old rats, and provide preliminary evidence of therapeutic potential for age-related muscle wasting and weakness.

Molecular mechanisms of reduced beta-adrenergic signaling in the aged heart as revealed by genomic profiling

Myocardial aging leads to a reduction of beta-adrenergic receptor-induced metabolic and contractile responsiveness. We hypothesize that a change in the patterns of gene expression is important in these age-related events. To test this, hearts were harvested from young and aged male rats (3-4 and 20-22 mo, respectively). Total mRNA was extracted and prepared for hybridization to Affymetrix U34A GeneChips. Filtering criteria, involving fold change and a statistical significance cutoff were employed, yielding 263 probe pairs exhibiting differential signals. Of the 163 annotated genes, at least 56 (34%) were classified as signaling/cell communication. Of these 56, approximately half were directly involved in G protein-coupled receptor signaling pathways. We next determined which of these changes might be involved in anti-adrenergic activity and identified 19 potentially important gene products. Importantly, we observed a decrease in beta1-adrenergic receptor and adenylyl cyclase mRNAs, whereas the mRNA encoding beta-arrestin increased. Furthermore, the results demonstrate an increase in mRNAs encoding the adenosine A1 receptor and phospholipase D, which could increase anti-adrenergic effects. Moreover, the mRNAs encoding the muscarinic M3 receptor, nicotinic acetylcholine receptor beta3, and nicotinic acetylcholine receptor-related protein were increased as was the mRNA encoding guanylate kinase-associated protein. Interestingly, we also observed eight mRNAs whose abundance changed three- to sixfold with aging that could be considered as being compensatory. Although these results do not prove causality, they demonstrate that cardiac aging is associated with changes in the profiles of gene expression and that many of these changes may contribute to reduced adrenergic signaling.

Model of functional cardiac aging: young adult mice with mild overexpression of serum response factor

Serum response factor (SRF) is an important transcription factor that may have a role in the maintenance of cardiac structure and function. The level of SRF mRNA expression increases approximately 16% in the hearts of mice during adult aging. To model the effect of mild SRF elevation in the aging heart, transgenic mice with low levels of SRF overexpression were generated. By 6 mo of age, the transgenic mice had a 19% increase of heart-to-body weight ratio compared with nontransgenic mice. In addition, they had a 12% increase in myocyte size, a 6.7% increase in collagen deposition, and altered gene expression of a number of muscle-specific and cardiac genes. Doppler echocardiography revealed that these transgenic mice had increased left ventricular wall thickness and decreased left ventricular (LV) volumes, increased LV stiffness with 20% reduction in early diastolic LV filling (peak E), and 35% decline in peak E-to-peak A (late diastolic filling) ratio. The observed changes, especially those in the E/A ratio, are similar to those seen clinically in late life as a part of human adult myocardial aging.

Exercise improves postischemic function in aging hearts

Exercise improves cardioprotection against ischemia-reperfusion in young animals but has not been investigated in older animals, which represent the population most likely to suffer an ischemic event. Therefore, we sought to determine the effects of aging on exercise-induced cardioprotection. Young, middle-aged, and old (4, 12, and 21 mo old) male Fischer 344 rats ran 60 min at 70-75% of maximum oxygen consumption. Twenty-four hours postexercise, isolated perfused working hearts underwent 22.5 min of global ischemia and then 30 min of recovery (reperfusion). Compared with sedentary rats (n = 8-9 rats/group), recovery of function (cardiac output x systolic pressure) improved after exercise (n = 9 rats/group) by 40% at 4 mo, 78% at 12 mo, and 59% at 21 mo. Exercise increased inducible heat shock protein 70 expression 105% at 4 mo but only 27% at 12 mo and 24% at 21 mo. Catalase activity progressively increased with age (P < 0.05) and was increased by exercise at 4 mo (26%) and 21 mo (19%). Manganese superoxide dismutase activity was increased by exercise only at 21 mo (45%). No exercise-related change in any antioxidant enzyme was observed at 12 mo. We conclude that exercise can enhance cardioprotection regardless of age, but the cardioprotective protein phenotype changes with age.

Age, cell signalling and cardioprotection

For many years investigators have been researching methods of preconditioning the myocardium against ischaemia-induced damage; however, a majority of this research has been carried out in young animals and cells. Normal ageing is accompanied by changes in the human myocardium that decrease its capacity to tolerate and respond to various forms of stress. Also, the likelihood of experiencing an ischaemic stress and other cardiovascular complications increases as an individual ages; therefore, an aged population would benefit most from cardioprotective treatments. Methods currently known to provide cardioprotection (or preconditioning) include exercise, heat stress, oxidative stress, brief ischaemia, stretch and certain pharmacological interventions. It is unclear whether the aged myocardium can adapt to a preconditioning stimulus; however, many researchers have observed age-related alterations in the expression and activation of proteins key to the cardioprotective process. These proteins include heat shock protein 70 (HSP70), nitric oxide synthase (NOS), the sodium-hydrogen exchanger (NHE), and the mitogen-activated protein (MAP) kinases c-Jun N-terminal Kinase (JNK), extracellular signal-regulated kinase (ERK), and p38. Therefore, the purpose of the current review will be to outline the current knowledge of these cardioprotective agents in an aged myocardium. Interactions among the cardioprotective agents outlined herein suggest that age-related changes in the myocardium will need to be better understood before cardioprotective interventions that have been proved effective in young animals can be applied to an aged human population.

Pharmacodynamics in the elderly

An overview is given of the influence of age on the pharmacodynamics of drugs used during general and locoregional anaesthesia. For some groups of agents a distinct separation into age-related changes in the pharmacokinetics and pharmacodynamics is possible, whereas for others the literature indicates only that responses in the elderly are enhanced. I start with an overview of the influence of age on cardiovascular and neuroendocrine function and include a short account of the state-of-the-art in pharmacodynamic modelling. The physiological changes that occur with age are associated with an increased sensitivity to the effects of anaesthetic agents. For most intravenous hypnotic agents, and inhalational anaesthetic agents, the increased sensitivity with age is, at least in part, explained by altered pharmacodynamics. For opioids and local anaesthetics applied for blockade of the central nervous system, the pharmacodynamic involvement is not always clear. For neuromuscular blocking agents, pharmacodynamic involvement appears to be nearly absent in the reduced dose requirements seen with age--so that the latter appear to be caused by altered pharmacokinetics. Future studies, using pharmacokinetic-pharmacodynamic (PK-PD) mixed-effects modelling, should further explore this area to obtain clinically applicable data for improving our insight into the delivery of anaesthetics to the elderly and improving the quality of anaesthesia in this fast-growing population.

Age and anesthetic effects on murine electrocardiography

Murine models offer potential insights regarding human cardiac disease, but efficient and reliable methods for phenotype evaluation are necessary. We employed non-invasive electrocardiography (ECG) in mice, investigating statistical reliability of these parameters with respect to anesthetic and animal age. Mice (C57BL/6, 8 or 48 weeks) were anesthetized by ketamine/xylazine (K/X, 80/10 mg/kg ip) or by inhalation anesthetic (halothane, HAL; sevoflurane, SEV) and 6 lead ECGs were recorded. P wave duration and QT interval was significantly prolonged with K/X compared to HAL and SEV, indicating slowed atrial and ventricular conduction. P-R interval (atrio-ventricular conduction) was significantly increased in aged mice under all anesthetics. Heart rate was inversely correlated to QT interval and P wave duration. We also detected significant age effects with respect to optimal approaches for QT interval corrections. Power analysis showed 4-fold higher number of mice/group, were required for K/X, to achieve identical statistical sensitivity. These data demonstrate the importance of anesthetic selection for relevant and reliable ECG analysis in mice and illustrate the selective influences of anesthetics and age on cardiac conductance in this species.

Decreased efficiency of adenovirus-mediated gene transfer in aging cardiomyocytes

BACKGROUND

Aging is an independent risk factor for the development of cardiovascular disease. Clinical application of myocardial gene transfer may be best suited in the elderly. In vivo gene transfer by adenovirus is less efficient in aging myocardium.

METHODS AND RESULTS

When infected with adenovirus containing beta-galactosidase (beta-gal) and green fluorescent protein (GFP) driven by cytomegalovirus promoters in vitro, aging rat cardiac myocytes exhibit significantly lower infectivity and delayed transgene expression compared with adult controls. Abnormalities of viral internalization may be one mechanism accounting for this difference. To investigate this, we studied expression levels of the coxsackievirus and adenovirus receptor (CAR) as well as other potential integrins involved in the internalization of adenoviruses. CAR expression tended to be upregulated whereas among potential integrins, alpha(3)beta(1) was downregulated in aging cardiac myocytes. Blocking the beta(1) component of alpha(3)beta(1) further decreased infectivity, suggesting that the interaction between the penton base of the adenovirus and beta(1) maybe a crucial component of the viral entry mechanism.

CONCLUSIONS

These results suggest that it is integrin-stimulated internalization rather than the adenovirus-CAR interaction that plays a vital role in adenoviral entry. The downregulation of integrins observed in senescent cells may be a key mechanism accounting for the decrease in viral infectivity seen in these cells. These findings have implications for the gene therapy treatment of myocardial failure in the elderly.

Titin--springing back to youth?

Mutations in the muscle protein titin have been linked to dilated cardiomyopathy, a condition in which the heart chambers are enlarged and blood is ineffectively pumped, in humans and in animal models. This protein, which is a component of sarcomeres, provides essential scaffolding for other muscle proteins and acts as a spring to confer passive elasticity on the cardiomyocyte. Several titin isoforms exist, and they display varying size and degrees of elasticity. We review two interesting reports that show how variations in titin isoforms might be implicated in cardiac failure.