Obesity and diabetes are known risk factors for the development of physical disability among older adults. With the number of seniors with these conditions rising worldwide, the prevention and treatment of physical disability in these persons has become a major public health challenge. Sarcopenia, the progressive loss of muscle mass and strength, has been identified as a common pathway associated with the initial onset and progression of physical disability among older adults. A growing body of evidence suggests that metabolic dysregulation associated with obesity and diabetes accelerates the progression of sarcopenia, and subsequently functional decline in older adults. The focus of this brief review is on the contributions of obesity and diabetes in accelerating sarcopenia and functional decline among older adults. We also briefly discuss the underexplored interaction between obesity and diabetes that may further accelerate sarcopenia and place obese older adults with diabetes at particularly high risk of disability. Finally, we review findings from studies that have specifically tested the efficacy of lifestyle-based interventions in maintaining the functional status of older persons with obesity and/or diabetes.
Physical Function; Obesity; Diabetes; Aging
Accumulating evidence suggests that both dietary restriction and exercise (DR + E) should be incorporated in weight loss interventions to treat obese, older adults. However, more information is needed on the effects to lower extremity tissue composition—an important consideration for preserving mobility in older adults.
Twenty-seven sedentary women (body mass index: 36.3±5.4kg/m2; age: 63.6±5.6 yrs) were randomly assigned to 6 months of DR + E or a health education control group. Thigh and calf muscle, subcutaneous adipose tissue (SAT), and intermuscular adipose tissue (IMAT) size were determined using magnetic resonance imaging. Physical function was measured using a long-distance corridor walk and knee extension strength.
Compared with control, DR + E significantly reduced body mass (-6.6±3.7kg vs control: -0.05±3.5kg; p < .01). Thigh and calf muscle volumes responded similarly between groups. Within the DR + E group, adipose tissue was reduced more in the thigh than in the calf (p < .04). Knee extension strength was unaltered by DR + E, but a trend toward increased walking speed was observed in the DR + E group (p = .09). Post hoc analyses showed that reductions in SAT and IMAT within the calf, but not the thigh, were associated with faster walking speed achieved with DR + E (SAT: r = -0.62; p = .01; IMAT: r = -0.62; p = .01).
DR + E preserved lower extremity muscle size and function and reduced regional lower extremity adipose tissue. Although the magnitude of reduction in adipose tissue was greater in the thigh than the calf region, post hoc analyses demonstrated that reductions in calf SAT and IMAT were associated with positive adaptations in physical function.
Body composition; Weight loss; Obesity; Aging; Disability.
Sarcopenia, the age-related loss of muscle mass and function, imposes a dramatic burden on individuals and society. The development of preventive and therapeutic strategies against sarcopenia is therefore perceived as an urgent need by health professionals and has instigated intensive research on the pathophysiology of this syndrome. The pathogenesis of sarcopenia is multifaceted and encompasses lifestyle habits, systemic factors (e.g., chronic inflammation and hormonal alterations), local environment perturbations (e.g., vascular dysfunction), and intramuscular specific processes. In this scenario, derangements in skeletal myocyte mitochondrial function are recognized as major factors contributing to the age-dependent muscle degeneration. In this review, we summarize prominent findings and controversial issues on the contribution of specific mitochondrial processes – including oxidative stress, quality control mechanisms and apoptotic signaling – on the development of sarcopenia. Extramuscular alterations accompanying the aging process with a potential impact on myocyte mitochondrial function are also discussed. We conclude with presenting methodological and safety considerations for the design of clinical trials targeting mitochondrial dysfunction to treat sarcopenia. Special emphasis is placed on the importance of monitoring the effects of an intervention on muscle mitochondrial function and identifying the optimal target population for the trial.
mitophagy; vascular dysfunction; fusion and fission; apoptosis; biomarkers
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
This commentary offers a discussion of the need to consider behavioral interventions such as physical exercise as integral components of personalized medicine.
We discuss the concept of personalized medicine and review existing evidence of variability in response to exercise training.
We argue that increased understanding is needed regarding sources of variability in exercise responsiveness, and that such understanding should lead to more tailored, often multi-modal interventions.
Studies of personalized medicine to date have primarily investigated heterogeneity in drug responsiveness; we believe it is time to begin considering preventive strategies such as exercise within a broader scope of personalized care.
Personalized Medicine; Physical Activity; Non-responder; Genomics; Phenomics
Background and aims
Aging is associated with significant losses of skeletal muscle mass and function. Numerous biochemical molecules have been implicated in the development of these age-related changes, however evidence from human models is sparse. Assessment of transcript expression is useful as it requires minimal tissue and may potentially be used in clinical trials. This study aimed to compare mRNA expression of proteolytic genes in skeletal muscle of young (18–35 yrs) and older (55–75 yrs) men.
Muscle tissue was obtained from young (n=14, 21.35±1.03 yrs) and older (n=13, 63.85±1.83 yrs) men using percutaneous biopsy, and transcript expression was quantified using real-time polymerase chain reaction. Lower limb muscle mass was assessed using DEXA while concentric peak torque (PT) and power were assessed via isokinetic dynamometer. When age-related differences in mRNA expression were observed, Pearson correlation coefficients were obtained to examine the relationship of transcripts to muscle mass and function.
Older muscle contained significantly more transcript for Forkhead Box O 1 (FoxO1, p=0.001), Inhibitor of DNA binding 1 (ID1, p=0.009), and Inhibitor of DNA Binding 3 (ID3, p=0.043) than young muscle. FoxO1 was significantly correlated with lean mass (R=−0.44, p=0.023) and PT (R=−0.40, p=0.046) while ID3 was significantly correlated with PT (R=−0.58, p=0.001) and power (R=−0.65, p<0.001). Moreover, ID1 was significantly correlated with all assessed measures of muscle function - mass (R=−0.39, p=0.046), PT (R=−0.53, p=0.005), and power (R=−0.520, p=0.005).
These data suggest that FoxO1, ID1, and ID3 are potentially useful as clinical biomarkers of age-related muscle atrophy and dysfunction.
Aging; atrophy; peak torque; proteolysis; RNA; sarcopenia
The objective of this study is to evaluate the effects of blood flow restriction (BFR) on muscle oxygenation during low-intensity resistance exercise as well as postexercise expression of molecules related to physiological angiogenesis.
Using a randomized cross-over design, six apparently healthy young adults (22 ± 1 yr) performed 120 unilateral knee extensions at 40% of 1 repetition maximum with and without BFR (CNTRL). Near-infrared spectroscopy was used to measure oxygenation of the vastus lateralis during exercise. Serum and muscle expression of Post–Resistance vascular endothelial growth factor (VEGF) were determined preexercise, 4 h postexercise, and 24 h postexercise. Transcript (mRNA) expression of VEGF and other angiogenic genes was also determined.
BFR increased muscle hemoglobin (Hb) concentrations during exercise (14.4 ± 1.6 vs. 0.9 ± 1.6, P = 0.002), driven largely by an increase in deoxygenated Hb (11.0 ± 2.5 vs. 0.5 ± 1.1, P = 0.030). BFR also increased (P < 0.05) transcript expression of VEGF, VEGF-R2, hypoxia-inducible factor 1 alpha, inducible nitric oxide synthase (NOS), and neuronal NOS. The most dramatic change in response to BFR was an increase in VEGF mRNA at 4 h postexercise (4.1 ± 0.6 vs. 0.6 ± 0.2-fold change, P = 0.028). Compared with control, transcript expression of endothelial NOS, serum VEGF, or muscle protein expression of VEGF was not altered in response to BFR (P > 0.05).
Acute BFR increases postexercise expression of mRNA related to skeletal muscle angiogenesis, plausibly in response to changes in muscle Hb concentrations.
BFR; KAATSU; SKELETAL MUSCLE; RESISTANCE EXERCISE; NIRS; VEGF; NOS
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
The present study evaluated the effects of creatine monohydrate (CrM) consumption post-exercise on body composition and muscle strength in middle to older males following a 12-week resistance training program.
In a double-blind, randomized trial, 20 males aged between 55 and 70 years were randomly assigned to consume either CrM-carbohydrate (CHO) [20 g days−1 CrM + 5 g days−1 CHO × 7 days, then 0.1 g kg−1 CrM + 5 g CHO on training days (average dosage of ~8.8 g)] or placebo CHO (20 g days−1 CHO × 7 days, then 5 g CHO on training days) while participating in a high intensity resistance training program [3 sets × 10 repetitions at 75 % of 1 repetition maximum (1RM)], 3 days weeks−1 for 12 weeks. Following the initial 7-day “loading” phase, participants were instructed to ingest their supplement within 60 min post-exercise. Body composition and muscle strength measurements, blood collection and vastus lateralis muscle biopsy were completed at 0, 4, 8 and 12 weeks of the supplement and resistance training program.
A significant time effect was observed for 1RM bench press (p = 0.016), leg press (p = 0.012), body mass (p = 0.03), fat-free mass (p = 0.005) and total myofibrillar protein (p = 0.005). A trend for larger muscle fiber cross-sectional area in the type II fibers compared to type I fibers was observed following the 12-week resistance training (p = 0.08). No supplement interaction effects were observed.
Post-exercise ingestion of creatine monohydrate does not provide greater enhancement of body composition and muscle strength compared to resistance training alone in middle to older males.
Supplementation; Aging; Muscle; Hypertrophy; Creatine; Supplementation
The lower extremities are important to performing physical activities of daily life. This study investigated lower extremity tissue composition, i.e. muscle and fat volumes, in young and older adults and the relative importance of individual tissue compartments to the physical function of older adults. A total of 43 older (age 78.3 ± 5.6 yr) and 20 younger (age 23.8 ± 3.9 yr) healthy men and women participated in the study. Older participants were further classified as either high- (HF) or low-functioning (LF) according to the Short Physical Performance Battery (SPPB). Magnetic resonance images were used to determine the volumes of skeletal muscle, subcutaneous fat (SAT), and intermuscular fat (IMAT) in the thigh (femoral) and calf (tibiofibular) regions. After adjusting for the sex of participants, younger participants had more femoral muscle mass than older adults (p < 0.001 for between group differences) as well as less femoral IMAT (p = 0.008) and tibiofibular IMAT (p < 0.001). Femoral muscle was the only tissue compartment demonstrating a significant difference between the two older groups, with HF participants having 31% more femoral muscle mass than LF participants (mean difference = 103.0 ± 34.0 cm3; p = 0.011). In subsequent multiple regression models including tissue compartments and demographic confounders, femoral muscle was the primary compartment associated with both SPPB score (r2 = 0.264, p= 0.001) and 4-meter gait speed (r2 = 0.187, p= 0.007). These data suggest that aging affects all lower extremity compartments, but femoral muscle mass is the major compartment associated with physical function in older adults.
Aging; Sarcopenia; Older Adults; Disability; SPPB; IMAT
The early 21st century has witnessed a steady push by scientists, industry leaders, and government officials to make medicine more personalized. To date, the concept of personalized medicine has referred largely to the field of pharmacogenomics. In contrast, relatively few data exist regarding the application of preventive strategies such as physical exercise in the context of personalized medicine. Within this review, we highlight the extant literature and propose five strategies for scientists that may propel the exercise and sports science fields toward this global goal. Notably, these approaches are in addition to methods to maintain adherence to training – a well-known factor in determining exercise responsiveness. Briefly, these strategies include (1) evaluating participant responses to training at the individual as well as group level; (2) identifying sources of variability in responsiveness to training; (3) optimizing exercise dosing strategies to maximize benefits while minimizing barriers to participation; (4) evaluating the efficacy of multimodal interventions for relevant population subgroups; and (5) increasing the clinical relevance of study populations and outcomes in exercise trials. We look forward to seeing these strategies considered in trials of preventive health interventions such as exercise. Extensive future research in this area is needed for the vision of exercise as a personalized form of medicine to become a reality.
Resistance exercise (RE) stimulates growth hormone (GH) secretion in a load-dependent manner, with heavier loads producing larger GH responses. However, new research demonstrates that low-load RE performed with blood flow restriction (BFR) produces potent GH responses that are similar to or exceed those produced following high-load RE. We hypothesized that low-load RE with vascular restriction would attenuate the known age-related reduction in GH response to RE.
In a randomized crossover design, ten young (28±7.8 years) and ten older (67.4±4.6 years) men performed bilateral knee extension RE with low-load [20% of one-repetition maximum (1RM)] with BFR and high-load (80% 1RM) without BFR. GH and lactate were measured every 10 minutes throughout a 150-minute testing session (30 minutes prior to and 120 minutes following completion of the exercise); IGF-I was measured at baseline and 60 minutes post-exercise.
Area under the GH curve indicated that both age groups responded similarly to each exercise condition. However, young men had a significantly greater maximal GH response to low-load RE with BFR than the high-load condition without BFR. Additionally, younger men had greater maximal GH concentrations to low-load RE with BFR than older men (p=0.02). The GH responses were marginally correlated to lactate concentration (r=0.13, p=0.002) and IGF-I levels were unchanged with RE.
GH responses to low-load RE with vascular restriction are slightly higher than high-load RE without vascular restriction in young men. However, low-load RE with vascular restriction did not attenuate the known age-related reduction in GH response with exercise. These data suggest that while low-load RE with vascular restriction is as effective for inducing a GH response than traditionally-based high-load RE, there is a more potent response in young men.
KAATSU; Blood flow restriction; muscle; growth hormone; vascular; hypoxia; ischemia; endocrine
The prevalence and significance of low normal and abnormal ankle brachial index (ABI) values in a community‐dwelling population of sedentary, older individuals is unknown. We describe the prevalence of categories of definite peripheral artery disease (PAD), borderline ABI, low normal ABI, and no PAD and their association with lower‐extremity functional performance in the LIFE Study population.
Methods and Results
Participants age 70 to 89 in the LIFE Study underwent baseline measurement of the ABI, 400‐m walk, and 4‐m walking velocity. Participants were classified as follows: definite PAD (ABI <0.90), borderline PAD (ABI 0.90 to 0.99), low normal ABI (ABI 1.00 to 1.09), and no PAD (ABI 1.10 to 1.40). Of 1566 participants, 220 (14%) had definite PAD, 250 (16%) had borderline PAD, 509 (33%) had low normal ABI, and 587 (37%) had no PAD. Among those with definite PAD, 65% were asymptomatic. Adjusting for age, sex, race, body mass index, smoking, and comorbidities, lower ABI was associated with longer mean 400‐m walk time: (definite PAD=533 seconds; borderline PAD=514 seconds; low normal ABI=503 seconds; and no PAD=498 seconds [P<0.001]). Among asymptomatic participants with and without PAD, lower ABI values were also associated with longer 400‐m walk time (P<0.001) and slower walking velocity (P=0.042).
Among older community‐dwelling men and women, 14% had PAD and 49% had borderline or low normal ABI values. Lower ABI values were associated with greater functional impairment, suggesting that lower extremity atherosclerosis may be a common preventable cause of functional limitations in older people.
Clinical Trial Registration
URL: http://clinicaltrials.gov/ Unique identifier: NCT01072500.
aging; exercise; peripheral vascular disease
We sought to identify novel pharmacogenomic markers for HDL-C response to atenolol in participants with mild to moderate hypertension. We genotyped 768 hypertensive participants from the Pharmacogenomic Evaluation of Antihypertensive Responses (PEAR) study on the Illumina HumanCVD Beadchip. During PEAR, participants were randomized to receive atenolol or hydrochlorothiazide. Blood pressure and cholesterol levels were evaluated at baseline and after treatment. This study focused on participants treated with atenolol monotherapy. Association with atenolol induced HDL-C change was evaluated in 232 whites and 152 African Americans using linear regression. No SNPs achieved a Bonferroni corrected P-value. However, we identified 13 regions with consistent association across whites and African Americans. The most interesting of these regions were seven with prior associations with HDL-C, other metabolic traits, or functional implications in the lipid pathway: GALNT2, FTO, ABCB1, LRP5, STARD3NL, ESR1, and LIPC. Examples are rs2144300 in GALNT2 in whites (P=2.29x10-4, β=-1.85 mg/dL) and rs12595985 in FTO in African Americans (P=2.90x10-4, β=4.52 mg/dL), both with consistent regional association (P<0.05) in the other race group. Additionally, baseline GALNT2 expression differed by rs2144300 genotype in whites (P=0.0279). In conclusion, we identified multiple gene regions associated with atenolol induced HDL-C change that were consistent across race groups, several with functional implications or prior associations with HDL-C.
Age-related loss of muscle mass and strength (sarcopenia) leads to a decline in physical function and frailty in the elderly. Among the many proposed underlying causes of sarcopenia, mitochondrial dysfunction is inherent in a variety of aged tissues. The intent of this study was to examine the effect of aging on key groups of regulatory proteins involved in mitochondrial biogenesis and how this relates to physical performance in two groups of sedentary elderly participants, classified as high- and low-functioning based on the Short Physical Performance Battery test. Muscle mass was decreased by 38% and 30% in low-functioning elderly (LFE) participants when compared to young and high-functioning elderly (HFE) participants, respectively, and positively correlated to physical performance. Mitochondrial respiration in permeabilized muscle fibers was reduced (41%) in the LFE group when compared to the young, and this was associated with a 30% decline in COX activity. Levels of key metabolic regulators, SIRT3 and PGC-1α were significantly reduced (50%) in both groups of elderly participants when compared to young. Similarly, the fusion protein OPA1 was lower in muscle from elderly subjects, however no changes were detected in Mfn2, Drp1 or Fis1 among the groups. In contrast, protein import machinery (PIM) components Tom22 and cHsp70 were increased in the LFE group when compared to the young. This study suggests that aging in skeletal muscle is associated with impaired mitochondrial function and altered biogenesis pathways, and that this may contribute to muscle atrophy and the decline in muscle performance observed in the elderly population.
aging; sarcopenia; mitochondria; skeletal muscle; PGC-1α
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
Preclinical studies strongly suggest that accelerated apoptosis in skeletal myocytes may be involved in the pathogenesis of sarcopenia. However, evidence in humans is sparse. In the present study, we investigated whether apoptotic signaling in the skeletal muscle was associated with indices of muscle mass and function in older persons.
Community-dwelling older adults were categorized into high-functioning (HF) or low-functioning (LF) groups according to their short physical performance battery (SPPB) summary score. Participants underwent an isokinetic knee extensor strength test and 3-dimensional magnetic resonance imaging of the thigh. Vastus lateralis muscle samples were obtained by percutaneous needle biopsy and assayed for the expression of a set of apoptotic signaling proteins. Age, sex, number of comorbid conditions and medications as well as knee extensor strength were not different between groups. HF participants displayed greater thigh muscle volume compared with LF persons. Multivariate partial least squares (PLS) regressions showed significant correlations between caspase-dependent apoptotic signaling proteins and the muscular percentage of thigh volume (R2 = 0.78; Q2 = 0.61) as well as gait speed (R2 = 0.81; Q2 = 0.56). Significant variables in the PLS model of percent muscle volume were active caspase-8, cleaved caspase-3, cytosolic cytochrome c and mitochondrial Bak. The regression model of gait speed was mainly described by cleaved caspase-3 and mitochondrial Bax and Bak. PLS predictive apoptotic variables did not differ between functional groups. No correlation was determined between apoptotic signaling proteins and muscle strength or quality (strength per unit volume).
Data from this exploratory study show for the first time that apoptotic signaling is correlated with indices of muscle mass and function in a cohort of community-dwelling older persons. Future larger-scale studies are needed to corroborate these preliminary findings and determine if down-regulation of apoptotic signaling in skeletal myocytes will provide improvements in the muscle mass and functional status of older persons.
A primary focus of longevity research is to identify prognostic risk factors that can be mediated by early treatment efforts. To date, much of this work has focused on understanding the biological processes that may contribute to aging process and age-related disease conditions. Although such processes are undoubtedly important, no current biological intervention aimed at increasing health and lifespan exists. Interestingly, a close relationship between mobility performance and the aging process has been documented in older adults. For example, recent studies have identified functional status, as assessed by walking speed, as a strong predictor of major health outcomes, including mortality, in older adults. This paper aims to describe the relationship between the comorbidities related to decreased health and lifespan and mobility function in obese, older adults. Concurrently, lifestyle interventions, including diet and exercise, are described as a means to improve mobility function and thereby limit the functional limitations associated with increased mortality.
Objective. To determine if supplementation of protein and amino acids (PAA) decreases skeletal muscle expression of atrophy-related genes, muscle mass, and strength during immobilization in humans. Methods. Twenty males wore a lower-limb immobilization boot for 28 days and consumed either a PAA supplement (28 g protein) or carbohydrate placebo (28 g maltodextrose), while consuming their normal daily diet. Testing sessions included dietary analysis, lower-leg girth and body composition measurements, strength testing, and gastrocnemius muscle biopsies. Muscle was analyzed for mRNA expression of markers in the ubiquitin and calpain systems, myostatin, TNF-α, and NF-κB. Results. All genes of interest increased over time (P < .05), but there was no difference between groups. Lower-leg girth decreased over time (P = 0.02); however, there were no significant changes in body composition or strength. Conclusion. Short-term lower-limb disuse, despite the absence of significant muscle atrophy, is associated with increases in skeletal muscle gene expression of several proteolysis-related genes. These changes do not appear to be altered by oral PAA supplementation.
Nuclear factor kappa B (NF-κB) is a critical signaling molecule of disuse-induced skeletal muscle atrophy. However, few studies have carefully investigated whether similar pathways are modulated with physical activity and age.
The present study examined lean mass, maximal force production, and skeletal muscle NF-κB signaling in 41 men categorized as sedentary (OS, N = 13, 63.85 ± 6.59 year), physically active (OA, N = 14, 60.71 ± 5.54 year), or young and sedentary (YS, N = 14, 21.35 ± 3.84 year). Muscle tissue from the vastus lateralis was assayed for messenger RNA (mRNA) expression of the β subunit of IkB kinase (IKKβ), cytosolic protein content of phosphorylated inhibitor of kappa B alpha (pIKBα), and nuclear content of NF-κB subunits p50 and p65.
When compared with YS, OS demonstrated age-related muscle atrophy and reduced isokinetic knee extension torque. Physical activity in older individuals preserved maximal isokinetic knee extension torque. OS muscle contained 50% more pIKBα than OA and 61% more pIKBα than YS. Furthermore, nuclear p65 was significantly elevated in OS compared with YS. OS muscle did not differ from either of the other two groups for nuclear p50 or for mRNA expression of IKKβ.
These results indicate that skeletal muscle content of nuclear-bound p65 is elevated by age in humans. The elevation in nuclear-bound p65 appears to be at least partially due to significant increases in pIKBα. A sedentary lifestyle appears to play some role in increased IKBα; however, further research is needed to identify downstream effects of this increase.
Sarcopenia; Atrophy; Strength; Proteolysis