Aging is characterized by a chronic low-grade inflammation that has been found to be related to mortality risk in older persons.
The aim of the present study was to investigate whether interleukin-6 (IL-6), C-reactive protein (CRP) and Tumor Necrosis Factor-alpha (TNF-α) protein levels predict all-cause mortality in a sample of older persons living in the community.
Design and Setting
Data are from the Aging and Longevity Study in the Sirente Geographic Area (ilSIRENTE Study), a prospective cohort study that collected information on individuals aged 80 years and older living in an Italian mountain community (n=362). The main outcome was the hazard ratio of death after four years of follow-up.
Participants and measurements
Participants were classified according to the median value of the 3 inflammatory markers (IL-6: 2.08 pg/mL; TNF-α: 1.43 pg/mL and CRP: 3.08 mg/L). In addition, a composite summary score of inflammation was created.
A total of 150 deaths occurred during a 4-year follow-up. In the unadjusted model, high levels of each of the 3 markers were associated with increased mortality. After adjusting for potential confounders, high levels of IL-6 and CRP were associated with a significantly increased risk of death (HR, 2.18; 95% CI 1.29–3.69 and 2.58; 95% CI 1.52–4.40, respectively); whereas the association between TNF-α protein levels and mortality lost significance (1.26; 95% CI: 0.74 to 2.15). The composite summary score of inflammation was strongly associated with mortality, with the highest risk estimated for individuals with all three inflammatory markers above the median.
Low levels of inflammatory markers are associated with better survival in elderly, independently of age and other clinical and functional variables.
Interleukin-6; C-Reactive Protein; TNF-alpha; Mortality; Frail Elderly
Chronic pain is becoming a more common medical diagnosis and is especially prevalent in older individuals. As such, prescribed use of opioids is on the rise, even though the efficacy for pain management in older individuals is unclear.
Thus the present preclinical study assessed the effectiveness of chronic fentanyl administration to produce antinociception in aging rats (16, 20, 24 months).
Animals were tested in a thermal sensitivity procedure known to involve neural circuits implicated in chronic pain in humans. Sensitivity to heat and cold thermal stimulation was assessed during 28 days of fentanyl administration (1.0 mg/kg/day), and 28 days of withdrawal.
Fentanyl resulted in decreased thermal sensitivity to heat but not cold stimulation indicated by more time spent in the hot compartment relative to time spent in the cold or neutral compartments. Unlike previous findings using a hot-water tail withdrawal procedure, tolerance did not develop to the antinociceptive effects of fentanyl over a 28-day period of drug administration. The oldest animals were least sensitive, and the youngest animals most sensitive to the locomotor-stimulating effects of fentanyl. The effect on the antinociceptive response to fentanyl in the oldest group of rats was difficult to interpret due to profound changes in the behavior of saline-treated animals.
Overall, aging modifies the behavioral effects of opioids, a finding that may inform future studies for devising appropriate treatment strategies.
Aging; Antinociception; Chronic administration; Geriatric pharmacotherapy; Pain; Thermal sensitivity; Tolerance; Withdrawal
Recently, we showed that administration of the angiotensin-converting enzyme inhibitor enalapril to aged rats attenuated muscle strength decline and mitigated apoptosis in the gastrocnemius muscle. The aim of the present study was to investigate possible mechanisms underlying the muscle-protective effects of enalapril. We also sought to discern the effects of enalapril mediated by nitric oxide (NO) from those independent of this signaling molecule. Eighty-seven male Fischer 344 × Brown Norway rats were randomly assigned to receive enalapril (n = 23), the NO synthase (NOS) inhibitor NG-nitro-l-arginine methyl ester (l-NAME; n = 22), enalapril + l-NAME (n = 19), or placebo (n = 23) from 24 to 27 months of age. Experiments were performed on the tibialis anterior muscle. Total NOS activity and the expression of neuronal, endothelial, and inducible NOS isoforms (nNOS, eNOS, and iNOS) were determined to investigate the effects of enalapril on NO signaling. Transcript levels of tumor necrosis factor-alpha (TNF-α) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) were assessed to explore actions of enalapril on inflammation and mitochondrial biogenesis, respectively. Protein expression of energy-sensing and insulin signaling mediators, including protein kinase B (Akt-1), phosphorylated Akt-1 (pAkt-1), mammalian target of rapamycin (mTOR), AMP-activated protein kinase subunit alpha (AMPKα), phosphorylated AMPKα (pAMPKα), and the glucose transporter GLUT-4, was also determined. Finally, the generation of hydrogen peroxide (H2O2) was quantified in subsarcolemmal (SSM) and intermyofibrillar (IFM) mitochondria. Enalapril increased total NOS activity, which was prevented by l-NAME co-administration. eNOS protein content was enhanced by enalapril, but not by enalapril + l-NAME. Gene expression of iNOS was down-regulated by enalapril either alone or in combination with l-NAME. In contrast, protein levels of nNOS were unaltered by treatments. The mRNA abundance of TNF-α was reduced by enalapril relative to placebo, with no differences among any other group. PCG-1α gene expression was unaffected by enalapril and lowered by enalapril + l-NAME. No differences in protein expression of Akt-1, pAkt-1, AMPKα, pAMPKα, or GLUT-4 were detected among groups. However, mTOR protein levels were increased by enalapril compared with placebo. Finally, all treatment groups displayed reduced SSM, but not IFM H2O2 production relative to placebo. Our data indicate that enalapril induces a number of metabolic adaptations in aged skeletal muscle. These effects result from the concerted modulation of NO and angiotensin II signaling, rather than from a dichotomous action of enalapril on the two pathways. Muscle protection by enalapril administered late in life appears to be primarily mediated by mitigation of oxidative stress and pro-inflammatory signaling.
Aging; Nitric oxide synthase (NOS) isoforms; Mitochondria; mTOR; Glucose tolerance; l-NAME; Inflammation; ACE inhibitors
Sarcopenia, the age-related loss of skeletal muscle mass, is a significant public health concern that continues to grow in relevance as the population ages. Certain conditions have the strong potential to coincide with sarcopenia to accelerate the progression of muscle atrophy in older adults. Among these conditions are co-morbid diseases common to older individuals such as cancer, kidney disease, diabetes, and peripheral artery disease. Furthermore, behaviors such as poor nutrition and physical inactivity are well-known to contribute to sarcopenia development. However, we argue that these behaviors are not inherent to the development of sarcopenia but rather accelerate its progression. In the present review, we discuss how these factors affect systemic and cellular mechanisms that contribute to skeletal muscle atrophy. In addition, we describe gaps in the literature concerning the role of these factors in accelerating sarcopenia progression. Elucidating biochemical pathways related to accelerated muscle atrophy may allow for improved discovery of therapeutic treatments related to sarcopenia.
Aging; Proteolysis; Satellite Cells; HIV; COPD; Disability
Recent scientific studies have advanced the notion of chronic inflammation as a major risk factor underlying aging and age-related diseases. In this review, low-grade, unresolved, molecular inflammation is described as an underlying mechanism of aging and age-related diseases, which may serve as a bridge between normal aging and age-related pathological processes. Accumulated data strongly suggest that continuous (chronic) up-regulation of pro-inflammatory mediators (e.g., TNF-α, IL-1β, 6, COX-2, iNOS) are induced during the aging process due to an age-related redox imbalance that activates many pro-inflammatory signaling pathways, including the NF-κB signaling pathway. These pro-inflammatory molecular events are discussed in relation to their role as basic mechanisms underlying aging and age-related diseases. Further, the anti-inflammatory actions of aging-retarding caloric restriction and exercise are reviewed. Thus, the purpose of this review is to describe the molecular roles of age-related physiological functional declines and the accompanying chronic diseases associated with aging. This new view on the role of molecular inflammation as a mechanism of aging and age-related pathogenesis can provide insights into potential interventions that may affect the aging process and reduce age-related diseases, thereby promoting healthy longevity.
molecular inflammation; aging; calorie restriction; exercise; cytokines; oxidative stress; inflammatory diseases; age-related diseases; obesity; sarcopenia; dementia; atherosclerosis; cancer; osteoporosis
No proven pharmacological therapies to delay or reverse age-related diastolic dysfunction exist. We hypothesized that late-life low-dose (non-blood-pressure-lowering) angiotensin-converting enzyme inhibition vs. angiotensin II receptor blockade would be equally efficacious at mitigating diastolic dysfunction in the senescent Fischer 344 × Brown Norway rat. Enalapril (10 mg/kg/day; n = 9) initiated at 24 months of age and continued for 6 months, increased myocardial relaxation (e'), reduced Doppler-derived indices of filling pressure (E/e'), favorably lowered the ratio of phospholamban–SERCA2 and reduced oxidative stress markers, Rac1 and nitrotyrosine, in aged hearts. Treatment with losartan (15 mg/kg/day; n = 9) similarly mitigated signs of cardiac oxidative stress, but impairments in diastolic function persisted when compared with untreated rats (n = 7). Our findings favor the idea that the lusitropic benefit of low-dose angiotensin-converting enzyme inhibitor initiated late in life may be related to an antioxidant-mediated modulation of SERCA2, resulting in improved relaxation rather than via overt effects on cardiac structure or blood pressure.
Angiotensin-converting enzyme inhibitor; Angiotensin II receptor blocker; Diastolic dysfunction; Oxidative stress; SERCA2; Tissue Doppler
There are contradictory data regarding older individuals’ sensitivity to pain stimulation and opioid administration. Adult (12–16 months; n = 10) and aged (27–31 months; n = 7) male F344xBN rats were tested in a thermal sensitivity procedure where the animal chooses to remain in one of two compartments with floors maintained at various temperatures ranging from hot (45°C) through neutral (30°C) to cold (15°C). Effects of morphine were determined for three temperature comparisons (ie, hot/neutral, cold/neutral, and hot/cold). Aged rats were more sensitive to cold stimulation during baseline. Morphine produced antinociception during hot thermal stimulation, but had no effect on cold stimulation. The antinociceptive (and locomotor-altering) effects of morphine were attenuated in aged rats. These data demonstrate age-related differences in baseline thermal sensitivity and responsiveness to opioids. Based on behavioral and physiological requirements of this procedure, it is suggested that thermal sensitivity may provide a relevant animal model for the assessment of pain and antinociception.
Opioids; Chronic pain; Operant testing; Thermal preference; Animal models
To assess the association between angiotensin converting enzyme inhibitors (ACEis) and improvements in the physical function of older adults in response to chronic exercise training.
Secondary analysis of the Lifestyle Interventions and Independence for Elders Pilot (LIFE-P) study, a multisite randomized clinical trial to evaluate the effects of chronic exercise on the physical function of older adults at risk for mobility disability.
Four academic research centers within the United States.
Four hundred twenty-four individuals aged 70 to 89 with mild to moderate functional impairments categorized for this analysis as ACEi users, users of other antihypertensive drugs, or antihypertensive nonusers.
A 12-month intervention of structured physical activity (PA) or health education promoting successful aging (SA).
Change in walking speed during a 400-m test and performance on a battery of short-duration mobility tasks (Short Physical Performance Battery (SPPB)).
Physical activity significantly improved the adjusted walking speed of ACEi users (P < .001) but did not of nonusers. PA improved the adjusted SPPB score of ACEi users (P < .001) and of persons who used other antihypertensive drugs (P = .005) but not of antihypertensive nonusers (P = .91). The percentage of ACEi users deriving clinically significant benefit from exercise training for walking speed (30%) and SPPB score (48%) was dramatically higher than for nonusers (14% and 12%, respectively).
For older adults at risk for disability, exercise-derived improvements in physical function were greater for ACEi users than users of other antihypertensive drugs and antihypertensive nonusers.
aging; exercise; physical function; LIFE Study; ACE inhibitors
Caloric restriction and physical exercise have proven beneficial against age-associated changes in body composition and declining physical performance; however, little is known regarding what benefit these interventions might have when initiated late in life. The study of mimetics of diet and exercise and the combination thereof may provide additional treatments for a vulnerable elderly population; however, how and when to initiate such interventions requires consideration in developing the most safe and efficacious treatment strategies. In this review, we focus on preclinical late-life intervention studies, which assess the relationship between physical function, sarcopenia, and body composition. We provide a conceptual framework for the ever-changing definition of sarcopenia and a rationale for the use of an appropriate rodent model of this condition. We finish by providing our perspective regarding the implications of this body of work and future areas of research that may also contribute to the ultimate goal of extending healthspan.
Renin angiotensin system; Enalapril repamycin; Physical function; Body composition
In this study, we explored the mechanisms by which the angiotensin converting enzyme inhibitor (ACEI), enalapril, and the Ang II receptor blocker (ARB), losartan suppress oxidative stress and NF-κB activation-induced inflammatory responses in aged rat kidney. The experimentations were carried out utilizing aged (24-month-old) Brown Norway x Fischer 344 (F1) male rats which were randomized into 3 groups and administered enalapril (40 mg/kg), losartan (30 mg/kg) or placebo for 6 months (daily p.o.). The level of reactive species (RS), peroxynitrite (ONOO−), GSH/GSSG and lipid peroxidation were measured. The activity of the pro-inflammatory transcription factor NF-κB, and gene expression of proteins in upstream signaling cascades were measured by electro-mobility shift assay (EMSA) and Western blotting. Enalapril and losartan differentially attenuated redox imbalance and the redox-sensitive transcription factor, NF-κB pathway. Furthermore, stimulation of the NF-κB activation pathway by phosphorylation of p65 was attenuated by both compounds. Moreover, mediation of phosphorylation of p65 by phosphorylation of IκB kinase αβ (IKKαβ) and mitogen- and stress-activated protein kinase-1 (MSK1), were also inhibited by enalapril and losartan. Finally, both compounds also lowered expression of NF-κB-dependent inflammatory genes, such as cyclooxygenase-2 (COX-2),) and inducible NO synthase (iNOS). Only losartan lowered levels of 5-lipoxygenase (5-LOX). These findings indicate that enalapril and losartan differentially suppress inflammatory responses via inhibition of oxidative stress-induced NF-κB activation in aged rat kidney.
The primary purpose of the present set of studies was to provide a direct comparison of the effects of the angiotensin-converting enzyme inhibitor enalapril and the angiotensin receptor blocker losartan on body composition, physical performance, and muscle quality when administered late in life to aged rats. Overall, enalapril treatment consistently attenuated age-related increases in adiposity relative to both placebo and losartan. The maximal effect was achieved after 3 months of treatment (between 24 and 27 months of age), at a dose of 40 mg/kg and was observed in the absence of any changes in physical activity, body temperature, or food intake. In addition, the reduction in fat mass was not due to changes in pathology given that enalapril attenuated age-related increases in tumor development relative to placebo- and losartan-treated animals. Both enalapril and losartan attenuated age-related decreases in grip strength, suggesting that changes in body composition appear dissociated from improvements in physical function and may reflect a differential impact of enalapril and losartan on muscle quality. To link changes in adiposity to improvements in skeletal muscle quality, we performed gene array analyses to generate hypotheses regarding cell signaling pathways altered with enalapril treatment. Based on these results, our primary follow-up pathway was mitochondria-mediated apoptosis of myocytes. Relative to losartan- and placebo-treated rats, only enalapril decreased DNA fragmentation and caspase-dependent apoptotic signaling. These data suggest that attenuation of the severity of skeletal muscle apoptosis promoted by enalapril may represent a distinct mechanism through which this compound improves muscle strength/quality.
Age-related adiposity; Body composition; Sarcopenia; Renin–angiotensin system; Physical function; Muscle quality
To test the hypothesis that exercise increases central leptin signaling, and thus reduces dietary weight gain in an aged obese model, we assessed the effects of voluntary wheel running (WR) in 23-month-old F344×BN rats fed a 60% high-fat (HF) diet for 3 months. After 2 months on the HF diet, half of the rats were provided access to running wheels for 2 weeks while the other half remained sedentary. Following the removal of the wheels, physical performance was evaluated, and 4 weeks later leptin signaling was assessed in hypothalamus and VTA after an acute bout of WR. Introduction of a HF diet led to prolonged hyperphagia (63.9 ± 7.8 kcal/day on chow diet vs. 88.1 ± 8.2 kcal/day on high-fat diet (when food intake stabilized), p < 0.001). As little as 9 (ranging to 135) wheel revolutions per day significantly reduced caloric consumption of HF food (46.8 ± 11.2 kcal/day) to a level below that on chow diet (63.9 ± 7.8 kcal/day, p < 0.001). After 2 weeks of WR, body weight was significantly reduced (7.9 ± 2.1% compared with prerunning weight, p < 0.001), and physical performance (latency to fall from an incline plane) was significantly improved (p = 0.04). WR significantly increased both basal (p = 0.04) and leptin-stimulated (p = 0.001) STAT3 phosphorylation in the ventral tegmental area (VTA), but not in the hypothalamus. Thus, in aged dietary obese rats, the act but not the extent of voluntary WR is highly effective in reversing HF consumption, decreasing body weight, and improving physical performance. It appears to trigger a response that substitutes for the reward of highly palatable food that may be mediated by increased leptin signaling in the VTA.
Wheel running; Leptin; Aged obese rats
Pro-opiomelanocortin (POMC) neurons are identified in two brain sites, the arcuate nucleus (ARC) of the hypothalamus and nucleus of the solitary tract (NTS) in brainstem. Earlier pharmacological and POMC gene transfer studies demonstrate melanocortin activation in either site alone improves insulin sensitivity and reduces obesity. The present study, for the first time, investigated the long-term efficacy of POMC gene transfer concurrently into both sites in the regulation of energy metabolism in aged F344xBN rats bearing adult-onset obesity. Pair feeding was included to reveal food-independent POMC impact on energy expenditure. We introduced adeno-associated virus encoding either POMC or green fluorescence protein to the two brain areas in 22-month-old rats, then recorded food intake and body weight, assessed oxygen consumption, serum leptin, insulin and glucose, tested voluntary wheel running, analyzed POMC expression, and examined fat metabolism in brown and white adipose tissues. POMC mRNA was significantly increased in both the hypothalamus and NTS region at termination. Relative to pair feeding, POMC caused sustained weight reduction and additional fat loss, lowered fasting insulin and glucose, and augmented white fat hormone-sensitive lipase activity and brown fat uncoupling protein 1 level. By wheel running assessment, the POMC-animals ran twice the distance as the control or pair-fed rats. Thus, the dual-site POMC treatment ameliorated adult-onset obesity effectively, involving a moderate hypophagia lasting ~ 60 days, enhanced lipolysis and thermogenesis, and increased physical activity in the form of voluntary wheel running. The latter finding provides a clue for countering age-related decline in physical activity.
Melanocortins; voluntary wheel running; energy expenditure
There is growing concern over the increasing use of opioids to treat chronic pain in the elderly primarily because of the potential increased sensitivity to the adverse side effects. Here, we use a preclinical model (male Brown Norway X F344 rats aged 12, 18, 24, and 30 months) to describe the outcome of chronic fentanyl administration (1.0 mg/kg/day) on various physiological and behavioral measures. Continuous fentanyl administration resulted in an initial decrease in food consumption, followed by the development of tolerance to this effect over a 4-week period and a subsequent increase in food consumption during withdrawal. This change in food consumption was associated with decreases in body weight (predominantly due to a loss of fat mass) that was maintained through early withdrawal. After one month of withdrawal, only the 12-month old animals had fully regained body weight. Fentanyl administration resulted in a decrease in grip strength and an increase in locomotor activity that did not differ across age groups. There was no effect of fentanyl administration on rotarod performance. These results demonstrate that while there is a delayed recovery of body mass with age, the observed changes in behavioral responses are uniform across ages.
Locomotor activity; Rotarod; Grip strength; Body composition; Osmotic minipump
Age-dependent renal damage is influenced by genetic background and the Fisher344xBrown Norway (F344xBN) rat is resistant to glomerular injury. In vulnerable strains, a fall in renal nitric oxide synthase (NOS) contributes to age-dependent renal damage. Here, we investigated renal NOS in young (3 months) and old (30 months) male F344xBN to test the hypothesis that renal NOS is maintained in “protected” strains. We also examined if 6 months of renin-angiotensin system (RAS) blockade using angiotensin converting enzyme inhibition (ACEI) and angiotensin receptor blockade (ARB) provides further benefit in these “protected” old rats. Aging increased tubulointerstitial injury but glomerular sclerosis was minimal and NOS and superoxide dismutase abundance increased. There was no change in the NOS inhibitor, ADMA (asymmetric dimethylarginine) or its regulatory enzymes. RAS blockade with ARB protected against tubulointerstitial injury and increased nNOSα, but ACEI, which also increased nNOSα, had no protective effect on the tubulointerstitium. We conclude that the glomerular sclerosis-resistant aged male F344xBN rat maintains renal NOS, thus reinforcing our hypothesis that progressive glomerular injury is related to renal NOS deficiency. The tubulointerstitial injury seen with aging is reversed with 6 months of ARB but not ACEI and is not associated with renal NOS.
rat strain difference; renin-angiotensin system blockade; asymmetric dimethylarginine; tubulointerstitial injury; oxidative stress
Evidence from animal models and preliminary studies in humans indicate that calorie restriction (CR) delays cardiac aging and can prevent cardiovascular disease. These effects are mediated by a wide spectrum of biochemical and cellular adaptations, including redox homeostasis, mitochondrial function, inflammation, apoptosis and autophagy. Despite the beneficial effects of CR, its large-scale implementation is challenged by applicability issues as well as health concerns. However, preclinical studies indicate that specific compounds, such as resveratrol, may mimic many of the effects of CR, thus potentially obviating the need for drastic food intake reductions. Results from ongoing clinical trials will reveal whether the intriguing alternative of CR mimetics represents a safe and effective strategy to promote cardiovascular health and delay cardiac aging in humans.
Cardiovascular disease; oxidative stress; inflammation; apoptosis; autophagy; calorie restriction mimetics
Controversy exists as to whether lifelong 40% calorie restriction (CR) enhances, has no effect on, or disrupts cognitive function during aging. Here, we report the effects of CR versus ad-lib feeding on cognitive function in male Brown Norway × Fisher344 rats across a range of ages (8–38 months), using two tasks that are differentially sensitive to age-related cognitive decline: object recognition and Morris water maze (MWM). All ages performed equally in object recognition, whereas, as a group, CR rats were impaired. In contrast, there was an age-related impairment in the MWM that was attenuated by CR as measured by time in proximity with and latency to reach the platform. Distance to the platform, a more sensitive measure, was not affected by CR. Finally, CR resulted in an overall increase in physical activity, one of several behavioral confounders to consider in the interpretation of cognitive outcomes in both tasks.
Morris water maze; Object recognition; Animal models of aging; Calorie restriction
Mitochondrial dysfunction and oxidative stress are central mechanisms underlying the aging process and the pathogenesis of many age-related diseases. Selected antioxidants and specific combinations of nutritional compounds could target many biochemical pathways that affect both oxidative stress and mitochondrial function and, thereby, preserve or enhance physical performance.
In this study, we evaluated the potential anti-aging benefits of a Q-ter® based nutritional mixture (commercially known as Eufortyn®) mainly containing the following compounds: terclatrated coenzyme Q10 (Q-ter®), creatine and a standardized ginseng extract. We found that Eufortyn® supplementation significantly ameliorated the age-associated decreases in grip strength and gastrocnemius subsarcolemmal mitochondria Ca2+ retention capacity when initiated in male Fischer344 x Brown Norway rats at 21 months, but not 29 months, of age. Moreover, the increases in muscle RNA oxidation and subsarcolemmal mitochondrial protein carbonyl levels, as well as the decline of total urine antioxidant power, which develop late in life, were mitigated by Eufortyn® supplementation in rats at 29 months of age.
These data imply that Eufortyn® is efficacious in reducing oxidative damage, improving the age-related mitochondrial functional decline, and preserving physical performance when initiated in animals at early midlife (21 months). The efficacy varied, however, according to the age at which the supplementation was provided, as initiation in late middle age (29 months) was incapable of restoring grip strength and mitochondrial function. Therefore, the Eufortyn® supplementation may be particularly beneficial when initiated prior to major biological and functional declines that appear to occur with advancing age.
The purpose of this review is to describe how recent pharmacological and genetic studies have contributed to our understanding of the role of the renin–angiotensin system (RAS) in age-related sarcopenia and diastolic dysfunction. Treatment strategies are limited in the context of both of these conditions, although interventions, which include blockade of the RAS (using angiotensin-converting enzyme inhibitors and angiotensin-receptor blockers) are successful and lead to improvements in functional outcomes that are not necessarily mediated by hemodynamic effects of the drugs. Studies in animal models of sarcopenia and diastolic dysfunction point to ubiquitous effects of RAS blockade on multiple biological mechanisms, including inflammation, oxidative damage and metabolic dysregulation. Therefore, a re-evaluation of the use of these drugs in other conditions should be considered for maintaining functional independence in older individuals.
ACE inhibitors; ACE polymorphisms; aging; angiotensin-receptor blockers; diastolic dysfunction; disability; exercise capacity; renin–angiotensin system; sarcopenia
TNF-α-mediated apoptosis is enhanced in aged rodent muscles, suggesting that this pathway may be involved in sarcopenia. Interleukin-15 (IL-15), a muscle-derived anabolic cytokine, mitigates muscle wasting and apoptosis in cachectic rats. This effect is thought to occur through inhibition of TNF-α-triggered apoptosis. We investigated IL-15 signaling and the TNF-α-mediated pathway of apoptosis in the gastrocnemius muscle of Fischer344×Brown Norway rats across the ages of 8, 18, 29 and 37 months, in relation to life-long calorie restriction (CR, 40% calorie intake reduction). Aging caused loss of muscle mass and increased apoptotic DNA fragmentation, which were mitigated by CR. Protein levels of IL-15 and mRNA abundance of IL-15 receptor α-chain decreased in senescent ad libitum (AL) fed rats, but were maintained in CR rodents. Elevations of TNF-α, TNF-receptor 1, cleaved caspase-8 and -3 were observed at advanced age in AL rats. These changes were prevented or mitigated by CR. Our results indicate that aging is associated with decreased IL-15 signaling in rat gastrocnemius muscle, which may contribute to sarcopenia partly through enhanced TNF-α-mediated apoptosis. Preservation of IL-15 signaling by CR may therefore represent a further mechanism contributing to the anti-aging effect of this dietary intervention in skeletal muscle.
sarcopenia; interleukin-15; tumor necrosis factor-α; calorie restriction; apoptosis
Accelerated apoptosis in skeletal muscle is increasingly recognized as a potential mechanism contributing to the development of sarcopenia of aging and disuse muscle atrophy. Given their central role in the regulation of apoptosis, mitochondria are regarded as key players in the pathogenesis of myocyte loss during aging and other atrophying conditions. Oxidative damage to mitochondrial constituents, impaired respiration and altered mitochondrial turnover have been proposed as potential triggering events for mitochondrial apoptotic signaling. In addition, iron accumulation within mitochondria may enhance the susceptibility to apoptosis during the development of sarcopenia and possibly acute muscle atrophy, likely through exacerbation of oxidative stress. Mitochondria can induce myocyte apoptosis via both caspase-dependent and independent pathways, although the apoptogenic mediators involved may be different depending on age, muscle type and specific atrophying conditions. Despite the considerable advances made, additional research is necessary to establish a definite causal link between apoptotic signaling and the development of sarcopenia and acute atrophy. Furthermore, a translational effort is required to determine the role played by apoptosis in the pathogenesis of sarcopenia and disuse-induced muscle loss in human subjects.
Mitochondria; Iron; Sarcopenia; Muscle atrophy; Apoptosis; Caspases; Endonuclease G; Apoptosis-inducing factor
Inhibition of the TOR signalling pathway by genetic or pharmacological intervention extends lifespan in invertebrates, including yeast, nematodes and fruit flies1–5. However, whether inhibition of mTOR signalling can extend life in a mammalian species was unknown. We report here that rapamycin, an inhibitor of the mTOR pathway, extends median and maximal lifespan of both male and female mice when fed beginning at 600 days of age. Based on age at 90% mortality, rapamycin led to an increase of 14% for females and 9% for males. The effect was seen at three independent test sites in genetically heterogeneous mice, chosen to avoid genotype-specific effects on disease susceptibility. Disease patterns of rapamycin-treated mice did not differ from those of control mice. In a separate study, rapamycin fed to mice beginning at 270 days of age also increased survival in both males and females, based on an interim analysis conducted near the median survival point. Rapamycin may extend lifespan by postponing death from cancer, by retarding mechanisms of ageing, or both. These are the first results to demonstrate a role for mTOR signalling in the regulation of mammalian lifespan, as well as pharmacological extension of lifespan in both genders. These findings have implications for further development of interventions targeting mTOR for the treatment and prevention of age-related diseases.
Caloric restriction (CR) is a daily reduction of total caloric intake without a decrease in micronutrients or disproportionate reduction of any one dietary component. CR can increase lifespan reliably in a wide range of species and appears to counteract some aspects of the aging process throughout the body. The effects on the brain are less clear, but moderate CR seems to attenuate age-related cognitive decline. Thus, we determined the effects of age and CR on key synaptic proteins in the CA3 region of the hippocampus and whether these changes were correlated with differences in behavior on a hippocampal-dependent learning and memory task. We observed an overall, age-related decline in the NR1, N2A and N2B subunits of the N-methyl-D-aspartate (NMDA)-type and the GluR1 and GluR2 subunits of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA)-type ionotropic glutamate receptors. Interestingly, we found that CR initially lowers the glutamate receptor subunit levels as compared to young AL animals, and then stabilizes the levels across lifespan. Synaptophysin, a presynaptic vesicle protein, showed a similar pattern. We also found that both CR and ad libitum (AL) fed animals exhibited age-related cognitive decline on the Morris water maze task. However, AL animals declined between young and middle-age, and between middle-age and old, whereas CR rats only declined between young and middle-age. Thus, the decrease in key synaptic proteins in CA3 and cognitive decline occurring across lifespan are stabilized by CR. This age-related decrease and CR-induced stabilization are likely to affect CA3 synaptic plasticity and, as a result, hippocampal function.
Dietary Restriction; NMDA; AMPA; synapses; rat; Morris water maze
Peripheral nerves from aged animals exhibit features of degeneration, including marked fiber loss, morphological irregularities in myelinated axons and notable reduction in the expression of myelin proteins. To investigate how protein homeostatic mechanisms change with age within the peripheral nervous system, we isolated Schwann cells from the sciatic nerves of young and old rats. The responsiveness of cells from aged nerves to stress stimuli is weakened, which in part may account for the observed age-associated alterations in glial and axonal proteins in vivo. While calorie restriction (CR) is known to slow the aging process in the central nervous system, its influence on peripheral nerves has not been investigated in detail. To determine if dietary restriction is beneficial for peripheral nerve health and glial function, we studied sciatic nerves from rats of four distinct ages (8-, 18-, 29- and 38-months) kept on an ad libitum (AL) or a 40% CR diet. Age-associated reduction in the expression of the major myelin proteins and widening of the nodes of Ranvier are attenuated by the dietary intervention, which is paralleled with the maintenance of a differentiated Schwann cell phenotype. The improvements in nerve architecture with diet restriction, in part, are underlined by sustained expression of protein chaperones and markers of the autophagy-lysosomal pathway. Together, the in vitro and in vivo results suggest that there might be an age-limit by which dietary intervention needs to be initiated to elicit a beneficial response on peripheral nerve health.
peripheral nerve; Schwann cell; heat shock protein; autophagy; myelin; chaperones