A Randomized Trial of ω-3 Fatty Acid Supplementation and Circulating Lipoprotein Subclasses in Healthy Older Adults.

BACKGROUND: Omega-3 (n-3) PUFAs are recognized for triglyceride-lowering effects in people with dyslipidemia, but it remains unclear if n-3-PUFA intake influences lipoprotein profiles in older adults without hypertriglyceridemia. OBJECTIVES: The objective was to determine the effect of n-3-PUFA supplementation on plasma lipoprotein subfractions in healthy older men and women in the absence of cardiovascular disease (CVD) or hypertriglyceridemia. This was a secondary analysis and considered exploratory. METHODS: Thirty young (20-35 y old) and 54 older (65-85 y old) men and women were enrolled in the study. Fasting plasma samples were collected. After baseline sample collection, 44 older adults were randomly assigned to receive either n-3-PUFA ethyl esters (3.9 g/d) or placebo (corn oil) for 6 mo. Pre- and postintervention plasma samples were used for quantitative lipoprotein subclass analysis using high-resolution proton NMR spectroscopy. RESULTS: The number of large, least-dense LDL particles decreased 17%-18% with n-3 PUFAs compared with placebo (<1% change; P < 0.01). The number of small, dense LDL particles increased 26%-44% with n-3 PUFAs compared with placebo (∼11% decrease; P < 0.01). The cholesterol content of large HDL particles increased by 32% with n-3 PUFAs and by 2% in placebo (P < 0.01). The cholesterol content of small HDL particles decreased by 23% with n-3 PUFAs and by 2% in placebo (P < 0.01). CONCLUSIONS: Despite increasing abundance of small, dense LDL particles that are associated with CVD risk, n-3 PUFAs reduced total triglycerides, maintained HDL, reduced systolic blood pressure, and shifted the HDL particle distribution toward a favorable cardioprotective profile in healthy older adults without dyslipidemia. This study suggests potential benefits of n-3-PUFA supplementation to lipoprotein profiles in healthy older adults without dyslipidemia, which should be considered when weighing the potential health benefits against the cost and ecological impact of widespread use of n-3-PUFA supplements.This trial was registered at clinicaltrials.gov as NCT03350906.

Preserved skeletal muscle oxidative capacity in older adults despite decreased cardiorespiratory fitness with ageing.

KEY POINTS: Healthy older adults exhibit lower cardiorespiratory fitness ( V̇O2peak ) than young in the absence of any age-related difference in skeletal muscle mitochondrial capacity, suggesting central haemodynamics plays a larger role in age-related declines in V̇O2peak . Total physical activity did not differ by age, but moderate-to-vigorous physical activity was lower in older compared to young adults. Moderate-to-vigorous physical activity is associated with V̇O2peak and muscle oxidative capacity, but physical inactivity cannot entirely explain the age-related reduction in V̇O2peak . ABSTRACT: Declining fitness ( V̇O2peak ) is a hallmark of ageing and believed to arise from decreased oxygen delivery and reduced muscle oxidative capacity. Physical activity is a modifiable lifestyle factor that is critical when evaluating the effects of age on parameters of fitness and energy metabolism. The objective was to evaluate the effects of age and sex on V̇O2peak , muscle mitochondrial physiology, and physical activity in young and older adults. An additional objective was to assess the contribution of skeletal muscle oxidative capacity to age-related reductions in V̇O2peak and determine if age-related variation in V̇O2peak and muscle oxidative capacity could be explained on the basis of physical activity levels. In 23 young and 52 older men and women measurements were made of V̇O2peak , mitochondrial physiology in permeabilized muscle fibres, and free-living physical activity by accelerometry. Regression analyses were used to evaluate associations between age and V̇O2peak , mitochondrial function, and physical activity. Significant age-related reductions were observed for V̇O2peak (P < 0.001), but not muscle mitochondrial capacity. Total daily step counts did not decrease with age, but older adults showed lower moderate-to-vigorous physical activity, which was associated with V̇O2peak (R2  = 0.323, P < 0.001) and muscle oxidative capacity (R2  = 0.086, P = 0.011). After adjusting for sex and physical activity, age was negatively associated with V̇O2peak but not muscle oxidative capacity. Healthy older adults exhibit lower V̇O2peak but preserved mitochondrial capacity compared to young. Physical activity, particularly moderate-to-vigorous, is a key factor in observed age-related changes in fitness and muscle oxidative capacity, but cannot entirely explain the age-related reduction in V̇O2peak .

Methylarginine metabolites are associated with attenuated muscle protein synthesis in cancer-associated muscle wasting.

Cancer cachexia is characterized by reductions in peripheral lean muscle mass. Prior studies have primarily focused on increased protein breakdown as the driver of cancer-associated muscle wasting. Therapeutic interventions targeting catabolic pathways have, however, largely failed to preserve muscle mass in cachexia, suggesting that other mechanisms might be involved. In pursuit of novel pathways, we used untargeted metabolomics to search for metabolite signatures that may be linked with muscle atrophy. We injected 7-week-old C57/BL6 mice with LLC1 tumor cells or vehicle. After 21 days, tumor-bearing mice exhibited reduced body and muscle mass and impaired grip strength compared with controls, which was accompanied by lower synthesis rates of mixed muscle protein and the myofibrillar and sarcoplasmic muscle fractions. Reductions in protein synthesis were accompanied by mitochondrial enlargement and reduced coupling efficiency in tumor-bearing mice. To generate mechanistic insights into impaired protein synthesis, we performed untargeted metabolomic analyses of plasma and muscle and found increased concentrations of two methylarginines, asymmetric dimethylarginine (ADMA) and NG-monomethyl-l-arginine, in tumor-bearing mice compared with control mice. Compared with healthy controls, human cancer patients were also found to have higher levels of ADMA in the skeletal muscle. Treatment of C2C12 myotubes with ADMA impaired protein synthesis and reduced mitochondrial protein quality. These results suggest that increased levels of ADMA and mitochondrial changes may contribute to impaired muscle protein synthesis in cancer cachexia and could point to novel therapeutic targets by which to mitigate cancer cachexia.

Adipose tissue macrophage populations and inflammation are associated with systemic inflammation and insulin resistance in obesity.

Obesity is accompanied by numerous systemic and tissue-specific derangements, including systemic inflammation, insulin resistance, and mitochondrial abnormalities in skeletal muscle. Despite growing recognition that adipose tissue dysfunction plays a role in obesity-related disorders, the relationship between adipose tissue inflammation and other pathological features of obesity is not well-understood. We assessed macrophage populations and measured the expression of inflammatory cytokines in abdominal adipose tissue biopsies in 39 nondiabetic adults across a range of body mass indexes (BMI 20.5-45.8 kg/m2). Skeletal muscle biopsies were used to evaluate mitochondrial respiratory capacity, ATP production capacity, coupling, and reactive oxygen species production. Insulin sensitivity (SI) and ß cell responsivity were determined from test meal postprandial glucose, insulin, c-peptide, and triglyceride kinetics. We examined the relationships between adipose tissue inflammatory markers, systemic inflammatory markers, SI, and skeletal muscle mitochondrial physiology. BMI was associated with increased adipose tissue and systemic inflammation, reduced SI, and reduced skeletal muscle mitochondrial oxidative capacity. Adipose-resident macrophage numbers were positively associated with circulating inflammatory markers, including tumor necrosis factor-α (TNFα) and C-reactive protein (CRP). Local adipose tissue inflammation and circulating concentrations of TNFα and CRP were negatively associated with SI, and circulating concentrations of TNFα and CRP were also negatively associated with skeletal muscle oxidative capacity. These results demonstrate that obese humans exhibit increased adipose tissue inflammation concurrently with increased systemic inflammation, reduced insulin sensitivity, and reduced muscle oxidative capacity and suggest that adipose tissue and systemic inflammation may drive obesity-associated metabolic derangements.NEW AND NOTEWORTHY Adipose inflammation is proposed to be at the nexus of the systemic inflammation and metabolic derangements associated with obesity. The present study provides evidence to support adipose inflammation as a central feature of the pathophysiology of obesity. Adipose inflammation is associated with systemic and peripheral metabolic derangements, including increased systemic inflammation, reduced insulin sensitivity, and reduced skeletal muscle mitochondrial respiration.

The effects of normoxic endurance exercise on erythropoietin (EPO) production and the impact of selective ß1 and non-selective ß1 + ß2 adrenergic receptor blockade.

PURPOSE: Habitual endurance exercise results in increased erythropoiesis, which is primarily controlled by erythropoietin (EPO), yet studies demonstrating upregulation of EPO via a single bout of endurance exercise have been equivocal. This study compares the acute EPO response to 30 min of high versus 90 min of moderate-intensity endurance exercise and whether that response can be upregulated via selective adrenergic receptor blockade. METHODS: Using a counterbalanced, cross-over design, fifteen participants (age 28 ± 8) completed two bouts of running (30-min, high intensity vs 90-min, moderate intensity) matched for overall training stress. A separate cohort of fourteen participants (age 31 ± 6) completed three bouts of 30-min high-intensity cycling after ingesting the preferential ß1-adrenergic receptor (AR) antagonist bisoprolol, the non-preferential ß1 + ß2 antagonist nadolol or placebo. Venous blood was collected before, during, and after exercise, and serum EPO levels were determined by ELISA. RESULTS: No detectable EPO response was observed during or after high intensity running, however, in the moderate-intensity trial EPO was significantly elevated at both during-exercise timepoints (+ 6.8% ± 2.3% at 15 min and + 8.7% ± 2.2% at 60 min). No significant change in EPO was observed post-cycling or between the trials involving ßAR blockade. CONCLUSION: Neither training mode (running or cycling), nor beta-blockade significantly influenced the EPO response to 30 min of high-intensity exercise, however, 90 min of moderate-intensity running elevated EPO during exercise, returning to baseline immediately post-exercise. Identifying the optimal mode, duration and intensity required to evoke an EPO response to exercise may help tailor exercise prescriptions designed to maximize EPO response for both performance and clinical applications.

EPA and DHA elicit distinct transcriptional responses to high-fat feeding in skeletal muscle and liver.

Omega-3 polyunsaturated fatty acids (n-3 PUFAs) exert numerous beneficial biological effects and attenuate diet-induced insulin resistance in rodent models. In the present study, the independent, tissue-specific effects of two nutritionally relevant n-3 PUFAs, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), were characterized in the context of a high-fat diet (HFD). EPA and DHA supplementation (3.2% of total fat) in 6-mo-old male C57BL/6 mice fed an HFD (60% fat) partially mitigated reductions in insulin sensitivity. At 5 wk, the area above the curve below baseline glucose following an intraperitoneal insulin tolerance test was 54.5% lower in HFD than control, whereas HFD + EPA and HFD + DHA showed 27.6% and 17.1% reductions, respectively. At 10 wk, HFD increased mitochondrial oxidative capacity supported by lipid and carbohydrate-based substrates in both liver and skeletal muscle (P < 0.05), with little effect of EPA or DHA supplementation. Whole genome transcriptomic analyses revealed HFD-induced transcriptional changes indicative of inflammation and fibrosis in both liver and muscle. Gene set enrichment analyses indicated a downregulation of transcripts associated with extracellular matrix in muscle (family-wise error rate P < 0.01) and liver (P = 0.04) and in transcripts associated with inflammation in muscle (P = 0.03) in HFD + DHA compared with HFD alone. In contrast, EPA appeared to potentiate some proinflammatory effects of the HFD. In the skeletal muscle, DHA increased the expression of stress-responsive genes, whereas EPA upregulated the expression of transcripts related to cell cycle. Therefore, although both EPA and DHA supplementation during HFD partially preserve insulin signaling, they modulate distinct processes, highlighting their unique biological effects in the context of obesity.

Vigorous exercise mobilizes CD34+ hematopoietic stem cells to peripheral blood via the ß2-adrenergic receptor.

Acute dynamic exercise mobilizes CD34+ hematopoietic stem cells (HSCs) to the bloodstream, potentially serving as an economical adjuvant to boost the collection of HSCs from stem cell transplant donors. The mechanisms responsible for HSC mobilization with exercise are unknown but are likely due to hemodynamic perturbations, endogenous granulocyte-colony stimulating factor (G-CSF), and/or ß2-adrenergic receptor (ß2-AR) signaling. We characterized the temporal response of HSC mobilization and plasma G-CSF following exercise, and determined the impact of in vivo ß-AR blockade on the exercise-induced mobilization of HSCs. Healthy runners (n = 15) completed, in balanced order, two single bouts of steady state treadmill running exercise at moderate (lasting 90-min) or vigorous (lasting 30-min) intensity. A separate cohort of healthy cyclists (n = 12) completed three 30-min cycling ergometer trials at vigorous intensity after ingesting: (i) 10 mg bisoprolol (ß1-AR antagonist); (ii) 80 mg nadolol (ß1 + ß2-AR antagonist); or (iii) placebo, in balanced order with a double-blind design. Blood samples collected before, during (runners only), immediately after, and at several points during exercise recovery were used to determine circulating G-CSF levels (runners only) and enumerate CD34+ HSCs by flow cytometry (runners and cyclists). Steady state vigorous but not moderate intensity exercise mobilized HSCs, increasing the total blood CD34+ count by ∼4.15 ±â€¯1.62 Δcells/µl (+202 ±â€¯92%) compared to resting conditions. Plasma G-CSF increased in response to moderate but not vigorous exercise. Relative to placebo, nadolol and bisoprolol lowered exercising heart rate and blood pressure to comparable levels. The number of CD34+ HSCs increased with exercise after the placebo and bisoprolol trials, but not the nadolol trial, suggesting ß2-AR signaling mediated the mobilization of CD34+ cells [Placebo: 2.10 ±â€¯1.16 (207 ±â€¯69.2%), Bisoprolol 1.66 ±â€¯0.79 (+163 ±â€¯29%), Nadolol: 0.68 ±â€¯0.54 (+143 ±â€¯36%) Δcells/µL]. We conclude that the mobilization of CD34+ HSCs with exercise is not dependent on circulating G-CSF and is likely due to the combined actions of ß2-AR signaling and hemodynamic shear stress.

ß2-Adrenergic receptor signaling mediates the preferential mobilization of differentiated subsets of CD8+ T-cells, NK-cells and non-classical monocytes in response to acute exercise in humans.

Acute exercise preferentially mobilizes cytotoxic T-cells, NK-cells and non-classical monocytes to the bloodstream under the influence of hemodynamic forces and/or ß2-adrenergic receptor (ß2-AR) signaling. However, the relative contribution of these mechanisms to the redeployment of the most exercise-responsive cell types is largely unknown. We determined the lymphocyte and monocyte subtypes mobilized to blood during exercise via ß2-AR signaling whilst controlling for ß1-AR mediated reductions in hemodynamic forces. In a randomized, double blind, complete cross-over design, 14 healthy cyclists exercised for 30-minutes at +10% of blood lactate threshold after ingesting: (1) a placebo, (2) a ß1-preferential antagonist (10 mg bisoprolol), or (2) a non-preferential ß1 + ß2-antagonist (80 mg nadolol) across three trials separated by >7-days. Bisoprolol was administered to reduce hemodynamic forces (heart rate and blood pressure) during exercise to levels comparable with nadolol but without blocking ß2-ARs. The mobilization of total NK-cells, terminally differentiated (CD57+) NK-cells, central memory, effector memory and CD45RA+ effector memory CD8+ T-cells; non-classical monocytes; and γδ T-cells were significantly blunted or abrogated under nadolol compared to both bisoprolol and placebo, indicating that the exercise-induced mobilization of these cell types to the blood is largely influenced by ß2-AR signaling. Nadolol failed to inhibit the mobilization of classical monocytes, CD4+ T-cells (and their subsets) or naïve CD8+ T-cells, indicating that these cell types are mobilized with exercise independently of the ß2-AR. We conclude that the preferential mobilization of NK-cells, non-classical monocytes and differentiated subsets of CD8+ T-cells with exercise is largely dependent on catecholamine signaling through the ß2-AR. These findings provide mechanistic insights by which distinct lymphocyte and monocyte subtypes are preferentially mobilized to protect the host from anticipated injury or infection in response to an acute stress response.

Human cytomegalovirus infection and the immune response to exercise.

Human cytomegalovirus (HCMV) is a ubiquitous -herpes virus that has co-evolved with its host since the very beginning of human life. The vast majority of adults worldwide carry the virus in a latent state, which is known to have striking effects on the composition and function of both T-cells and NK-cells. While there is evidence to suggest that prior exposure to HCMV can have beneficial effects in the immune competent host, poor control of the virus may contribute to T-cell exhaustion and the early onset of immunosenescence. The interaction between HCMV and exercise has garnered a lot of recent research attention. This stemmed from observations that people with HCMV redeploy greater numbers of CD8+ T-cells in response to a single exercise bout, while NK-cell mobilization is, conversely, impaired. Moreover, athletes with latent HCMV infection may be better protected against symptoms of upper respiratory illness (URI), and it has been suggested that the host's ability to control HCMV (i.e. keeping CMV in a latent state) may connect apparent bidirectional effects of exercise volume on host immunity and infection risk. This work has set a new paradigm that immune responses to both acute and chronic exercise might be governed by the infection history of the host. In this review, we summarize current knowledge on the effects of HCMV infection on T-cells and NK-cells and synthesize the literature on HCMV and the immune response to both single exercise bouts and prolonged periods of exercise training. We also discuss potential clinical and practical applications of this work including the use of HCMV reactivation as a biomarker of immune depression in athletes, its relevance in immunosenescence and the associated immune risk profile, and the potential for exercise to augment vaccine responses and the man ufacture of immune cells for adoptive transfer immunotherapy. Although research in this area is still in its infancy, we conclude that host infection history and the ability to regulate dormant pathogens is likely to play a key role in our understanding of how the immune system responds to both acute and chronic exercise across the entire exercise volume continuum.

Acute exercise preferentially redeploys NK-cells with a highly-differentiated phenotype and augments cytotoxicity against lymphoma and multiple myeloma target cells. Part II: impact of latent cytomegalovirus infection and catecholamine sensitivity.

We showed previously that acute exercise is associated with a preferential redeployment of highly-differentiated NK-cells and increased cytotoxicity against HLA-expressing tumor cell lines during exercise recovery. In this part II study, we retrospectively analyzed these findings in the context of latent cytomegalovirus (CMV) infection and performed additional experiments to explore potential mechanisms underpinning the marked reduction in NK-cell redeployment with exercise in CMV-seropositive individuals. We show here that latent CMV infection impairs NK-cell mobilization with exercise, only when the intensity of the exercise bout exceeds the individual blood lactate threshold (BLT). This impaired mobilization is associated with increased proportions of poorly exercise-responsive NK-cell subsets (NKG2C+/KIR-, NKG2C+/NKG2A-, and NKG2C+/CD57+) and decreased NK-cell ß(2)-adrenergic receptor (AR) expression in those with CMV. As a result, NK-cell production of cyclic AMP (cAMP) in response to in vitro isoproterenol (synthetic ß-agonist) stimulation was drastically lower in those with CMV (6.0 vs. 20.3pmol/mL, p<0.001) and correlated highly with the proportion of NKG2C+/CD57+ NK-cells (R(2)=0.97). Moreover, NK-cell cytotoxic activity (NKCA) against the K562 (36.6% vs. 22.7%, p<0.05), U266 (23.6% vs. 15.9%, p<0.05), and 221.AEH (41.3% vs. 13.3%, p<0.001) cell lines was increased at baseline in those infected with CMV; however, latent CMV infection abated the post-exercise increase in NKCA as a result of decreased NK-cell mobilization. Additionally, NKCA per cell against the U266 (0.24 vs. 0.12, p<0.01), RPMI-8226 (0.17 vs. 0.11, p<0.05), and 221.AEH (0.18 vs. 0.11, p<0.05) cell lines was increased 1h post-exercise (relative to baseline) in CMV-seronegative subjects, but not in those infected with CMV. Collectively, these data indicate that latent CMV infection may compromise NK-cell mediated immunosurveillance after acute exercise due to an increased proportion of "CMV-specific" NK-cell subsets with impaired ß-adrenergic receptor signaling pathways.

Fitness level impacts salivary antimicrobial protein responses to a single bout of cycling exercise.

PURPOSE: Salivary antimicrobial proteins (sAMPs) protect the upper respiratory tract (URTI) from invading microorganisms and have been linked with URTI infection risk in athletes. While high training volume is associated with increased URTI risk, it is not known if fitness affects the sAMP response to acute exercise. This study compared the sAMP responses to various exercising workloads of highly fit experienced cyclists with those who were less fit. METHODS: Seventeen experienced cyclists (nine highly fit; eight less fit) completed three 30-min exercise trials at workloads corresponding to -5, +5 and +15 % of the individual blood lactate threshold. Saliva samples were collected pre- and post-exercise to determine the concentration and secretion of α-amylase, human neutrophil proteins 1-3 (HNP1-3) lactoferrin, LL-37, lysozyme, and salivary SIgA. RESULTS: The concentration and/or secretion of all sAMPs increased post-exercise, but only α-amylase was sensitive to exercise workload. Highly fit cyclists had lower baseline concentrations of α-amylase, HNP1-3, and lactoferrin, although secretion rates did not differ between the groups. Highly fit cyclists did, however, exhibit greater post-exercise increases in the concentration and/or secretion of a majority of measured sAMPs (percentage difference between highly fit and less fit in parentheses), including α-amylase concentration (+107 %) and secretion (+148 %), HNP1-3 concentration (+97 %) and secretion (+158 %), salivary SIgA concentration (+181 %), lactoferrin secretion (+209 %) and LL-37 secretion (+138 %). CONCLUSION: We show for the first time that fitness level is a major determinant of exercise-induced changes in sAMPs. This might be due to training-induced alterations in parasympathetic and sympathetic nervous system activation.

Metabolomic response to acute resistance exercise in healthy older adults by 1H-NMR.

BACKGROUND: The favorable health-promoting adaptations to exercise result from cumulative responses to individual bouts of physical activity. Older adults often exhibit anabolic resistance; a phenomenon whereby the anabolic responses to exercise and nutrition are attenuated in skeletal muscle. The mechanisms contributing to age-related anabolic resistance are emerging, but our understanding of how chronological age influences responsiveness to exercise is incomplete. The objective was to determine the effects of healthy aging on peripheral blood metabolomic response to a single bout of resistance exercise and whether any metabolites in circulation are predictive of anabolic response in skeletal muscle. METHODS: Thirty young (20-35 years) and 49 older (65-85 years) men and women were studied in a cross-sectional manner. Participants completed a single bout of resistance exercise consisting of eight sets of 10 repetitions of unilateral knee extension at 70% of one-repetition maximum. Blood samples were collected before exercise, immediately post exercise, and 30-, 90-, and 180-minutes into recovery. Proton nuclear magnetic resonance spectroscopy was used to profile circulating metabolites at all timepoints. Serial muscle biopsies were collected for measuring muscle protein synthesis rates. RESULTS: Our analysis revealed that one bout of resistance exercise elicits significant changes in 26 of 33 measured plasma metabolites, reflecting alterations in several biological processes. Furthermore, 12 metabolites demonstrated significant interactions between exercise and age, including organic acids, amino acids, ketones, and keto-acids, which exhibited distinct responses to exercise in young and older adults. Pre-exercise histidine and sarcosine were negatively associated with muscle protein synthesis, as was the pre/post-exercise fold change in plasma histidine. CONCLUSIONS: This study demonstrates that while many exercise-responsive metabolites change similarly in young and older adults, several demonstrate age-dependent changes even in the absence of evidence of sarcopenia or frailty. TRIAL REGISTRATION: Clinical trial registry: ClinicalTrials.gov NCT03350906.

The Influence of Aging on the Unfolded Protein Response in Human Skeletal Muscle at Rest and Following Acute Exercise.

BACKGROUND: The unfolded protein response (UPR) is a proteostatic process that is activated in response to endoplasmic reticulum stress. It is currently unclear how aging influences the chronic and adaptive UPR in human skeletal muscle. Here we determined the effect of aging on UPR activation at rest, in response to exercise, and the associations with muscle function. METHODS: Thirty young (20-35 yrs) and 50 older (65-85 yrs) individuals were enrolled. Vastus lateralis biopsies were performed at rest and 3 hrs and 48 hrs after a single bout of resistance exercise. The abundance of UPR-related transcripts and proteins were measured by RNA sequencing and Western blotting, respectively. Fractional synthetic rates (FSR) of muscle protein were determined by mass spectrometry following intravenous infusion of 13C6 phenylalanine. RESULTS: Older adults demonstrated elevated transcriptional and proteomic markers of UPR activation in resting muscle. Resting UPR gene expression was negatively associated with muscle strength and power in older adults. The UPR is similarly activated by acute resistance exercise in young and older adults and positively associated with muscle function but not the anabolic response to exercise. CONCLUSIONS: Skeletal muscle from older adults exhibits chronically activated UPR, which accompanies functional decline. The adaptive UPR is a proteostatic mechanism that is upregulated in response to exercise in young and older adults and positively associated with muscle function.

Human myofiber-enriched aging-induced lncRNA FRAIL1 promotes loss of skeletal muscle function.

The loss of skeletal muscle mass during aging is a significant health concern linked to adverse outcomes in older individuals. Understanding the molecular basis of age-related muscle loss is crucial for developing strategies to combat this debilitating condition. Long noncoding RNAs (lncRNAs) are a largely uncharacterized class of biomolecules that have been implicated in cellular homeostasis and dysfunction across a many tissues and cell types. To identify lncRNAs that might contribute to skeletal muscle aging, we screened for lncRNAs whose expression was altered in vastus lateralis muscle from older compared to young adults. We identified FRAIL1 as an aging-induced lncRNA with high abundance in human skeletal muscle. In healthy young and older adults, skeletal muscle FRAIL1 was increased with age in conjunction with lower muscle function. Forced expression of FRAIL1 in mouse tibialis anterior muscle elicits a dose-dependent reduction in skeletal muscle fiber size that is independent of changes in muscle fiber type. Furthermore, this reduction in muscle size is dependent on an intact region of FRAIL1 that is highly conserved across non-human primates. Unbiased transcriptional and proteomic profiling of the effects of FRAIL1 expression in mouse skeletal muscle revealed widespread changes in mRNA and protein abundance that recapitulate age-related changes in pathways and processes that are known to be altered in aging skeletal muscle. Taken together, these findings shed light on the intricate molecular mechanisms underlying skeletal muscle aging and implicate FRAIL1 in age-related skeletal muscle phenotypes.

The effects of age and viral serology on γδ T-cell numbers and exercise responsiveness in humans.

γδ T-cells are cytotoxic effector cells that preferentially migrate to peripheral tissues and recognize many types of antigen. We examined the effects of age and viral serology on the exercise responsiveness of γδ T-cells. Blood was collected from 17 younger (age: 23-35yrs) and 17 older (50-64yrs) healthy males matched for cytomegalovirus (CMV), Epstein-Barr virus, herpes simplex virus-1 and Parvovirus B19 serologic status before and after a single bout of cycling exercise. Older had lower numbers and proportions of γδ T-cells than younger, while CMV was associated with increased numbers and proportions of γδ T-cells in younger but not older. Exercise evoked a ∼2-fold increase in circulating γδ T-cell numbers. The magnitude of this response was 3-times greater in younger compared to older, and 1.6-times greater in younger CMV-infected compared to younger non CMV-infected. To conclude, γδ T-cell numbers and exercise responsiveness decreases with age and may contribute to impaired immunosurveillance after acute acute physical stress.

Age-associated inflammation and implications for skeletal muscle responses to exercise.

Aging is associated with profound alterations in skeletal muscle, including loss of muscle mass and function, local inflammation, altered mitochondrial physiology, and attenuated anabolic responses to exercise termed anabolic resistance. "Inflammaging," the chronic, low-grade inflammation associated with aging, may contribute to many of the age-related derangements in skeletal muscle, including its ability to respond to exercise and nutritional stimuli. Inflammation and exercise are closely intertwined in numerous ways. A single bout of muscle-damaging exercise stimulates an acute inflammatory response in the skeletal muscle that is essential for muscle repair and regeneration; however, the chronic systemic and local inflammation associated with aging may impair acute inflammatory and anabolic responses to exercise. In contrast, exercise training is anti-inflammatory, targeting many of the potential root causes of inflammaging. In this review, we discuss the interplay between inflammation and exercise in aging and highlight potential therapeutic targets for improving adaptive responses to exercise in older adults.

GADD45A is a mediator of mitochondrial loss, atrophy, and weakness in skeletal muscle.

Aging and many illnesses and injuries impair skeletal muscle mass and function, but the molecular mechanisms are not well understood. To better understand the mechanisms, we generated and studied transgenic mice with skeletal muscle-specific expression of growth arrest and DNA damage inducible α (GADD45A), a signaling protein whose expression in skeletal muscle rises during aging and a wide range of illnesses and injuries. We found that GADD45A induced several cellular changes that are characteristic of skeletal muscle atrophy, including a reduction in skeletal muscle mitochondria and oxidative capacity, selective atrophy of glycolytic muscle fibers, and paradoxical expression of oxidative myosin heavy chains despite mitochondrial loss. These cellular changes were at least partly mediated by MAP kinase kinase kinase 4, a protein kinase that is directly activated by GADD45A. By inducing these changes, GADD45A decreased the mass of muscles that are enriched in glycolytic fibers, and it impaired strength, specific force, and endurance exercise capacity. Furthermore, as predicted by data from mouse models, we found that GADD45A expression in skeletal muscle was associated with muscle weakness in humans. Collectively, these findings identify GADD45A as a mediator of mitochondrial loss, atrophy, and weakness in mouse skeletal muscle and a potential target for muscle weakness in humans.

Skeletal muscle mitochondrial dysfunction and muscle and whole body functional deficits in cancer patients with weight loss.

Reductions in skeletal muscle mass and function are often reported in patients with cancer-associated weight loss and are associated with reduced quality of life, impaired treatment tolerance, and increased mortality. Although cellular changes, including altered mitochondrial function, have been reported in animals, such changes have been incompletely characterized in humans with cancer. Whole body and skeletal muscle physical function, skeletal muscle mitochondrial function, and whole body protein turnover were assessed in eight patients with cancer-associated weight loss (10.1 ± 4.2% body weight over 6-12 mo) and 19 age-, sex-, and body mass index (BMI)-matched healthy controls to characterize skeletal muscle changes at the whole body, muscle, and cellular level. Potential pathways involved in cancer-induced alterations in metabolism and mitochondrial function were explored by interrogating skeletal muscle and plasma metabolomes. Despite similar lean mass compared with control participants, patients with cancer exhibited reduced habitual physical activity (57% fewer daily steps), cardiorespiratory fitness [22% lower V̇o2peak (mL/kg/min)] and leg strength (35% lower isokinetic knee extensor strength), and greater leg neuromuscular fatigue (36% greater decline in knee extensor torque). Concomitant with these functional declines, patients with cancer had lower mitochondrial oxidative capacity [25% lower State 3 O2 flux (pmol/s/mg tissue)] and ATP production [23% lower State 3 ATP production (pmol/s/mg tissue)] and alterations in phospholipid metabolite profiles indicative of mitochondrial abnormalities. Whole body protein turnover was unchanged. These findings demonstrate mitochondrial abnormalities concomitant with whole body and skeletal muscle functional derangements associated with human cancer, supporting future work studying the role of mitochondria in the muscle deficits associated with cancer.NEW & NOTEWORTHY To our knowledge, this is the first study to suggest that skeletal muscle mitochondrial deficits are associated with cancer-associated weight loss in humans. Mitochondrial deficits were concurrent with reductions in whole body and skeletal muscle functional capacity. Whether mitochondrial deficits are causal or secondary to cancer-associated weight loss and functional deficits remains to be determined, but this study supports further exploration of mitochondria as a driver of cancer-associated losses in muscle mass and function.

Acute responsiveness to single leg cycling in adults with obesity.

Obesity is associated with several skeletal muscle impairments which can be improved through an aerobic exercise prescription. The possibility that exercise responsiveness is diminished in people with obesity has been suggested but not well-studied. The purpose of this study was to investigate how obesity influences acute exercise responsiveness in skeletal muscle and circulating amino metabolites. Non-obese (NO; n = 19; 10F/9M; BMI = 25.1 ± 2.8 kg/m2 ) and Obese (O; n = 21; 14F/7M; BMI = 37.3 ± 4.6 kg/m2 ) adults performed 30 min of single-leg cycling at 70% of VO2 peak. 13 C6 -Phenylalanine was administered intravenously for muscle protein synthesis measurements. Serial muscle biopsies (vastus lateralis) were collected before exercise and 3.5- and 6.5-h post-exercise to measure protein synthesis and gene expression. Targeted plasma metabolomics was used to quantitate amino metabolites before and 30 and 90 min after exercise. The exercise-induced fold change in mixed muscle protein synthesis trended (p = 0.058) higher in NO (1.28 ± 0.54-fold) compared to O (0.95 ± 0.42-fold) and was inversely related to BMI (R2  = 0.140, p = 0.027). RNA sequencing revealed 331 and 280 genes that were differentially expressed after exercise in NO and O, respectively. Gene set enrichment analysis showed O had six blunted pathways related to metabolism, cell to cell communication, and protein turnover after exercise. The circulating amine response further highlighted dysregulations related to protein synthesis and metabolism in adults with obesity at the basal state and in response to the exercise bout. Collectively, these data highlight several unique pathways in individuals with obesity that resulted in a modestly blunted exercise response.

Impact of obesity on the molecular response to a single bout of exercise in a preliminary human cohort.

OBJECTIVE: The health benefits of exercise are well documented, but several exercise-response parameters are attenuated in individuals with obesity. The goal of this pilot study was to identify molecular mechanisms that may influence exercise response with obesity. METHODS: A multi-omics comparison of the transcriptome, proteome, and phosphoproteome in muscle from a preliminary cohort of lean individuals (n = 4) and individuals with obesity (n = 4) was performed, before and after a single bout of 30 minutes of unilateral cycling at 70% maximal oxygen uptake (VO2 peak). Mass spectrometry and RNA sequencing were used to interrogate the proteome, phosphoproteome, and transcriptome from muscle biopsy tissue. RESULTS: The main findings are that individuals with obesity exhibited transcriptional and proteomic signatures consistent with reduced mitochondrial function, protein synthesis, and glycogen synthesis. Furthermore, individuals with obesity demonstrated markedly different transcriptional, proteomic, and phosphoproteomic responses to exercise, particularly biosynthetic pathways of glycogen synthesis and protein synthesis. Casein kinase II subunit alpha and glycogen synthase kinase-3ß signaling was identified as exercise-response pathways that were notably altered by obesity. CONCLUSIONS: Opportunities to enhance exercise responsiveness by targeting specific molecular pathways that are disrupted in skeletal muscle from individuals with obesity await a better understanding of the precise molecular mechanisms that may limit exercise-response pathways in obesity.