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Background Cachectic patients with chronic obstructive pulmonary disease (COPD) may benefit from nutritional support. This double-blind, randomized, controlled trial evaluated the safety and efficacy of targeted medical nutrition (TMN) vs. an isocaloric comparator in pre-cachectic and cachectic patients with COPD.Methods Patients aged >= 50 years with moderate-to-severe COPD and involuntary weight loss or low body mass index (1618 kg/m(2)) were randomized 1: 1 to receive TMN (similar to 230 kcal; 2 g omega-3 fatty acids; 10 mu g 25-hydroxy-vitamin D3) or isocaloric comparator twice daily for 12 weeks (ClinicalTrials.gov Identifier: NCT02442908). Primary safety endpoints comprised adverse events and changes in vital signs, laboratory parameters, and concomitant medications. Secondary efficacy endpoints included changes in weight, body composition, exercise tolerance, metabolic biomarkers, and systemic inflammation.Results Forty-five patients were randomized to receive TMN (n = 22; mean 69.2 years) or isocaloric comparator (n = 23; mean 69.7 years). TMN was well tolerated. Adverse events were similar in number and type in both groups. Compliance to both products was good (TMN, 79%; comparator, 77%). Both groups gained weight, but the TMN group gained comparatively more fat mass (P = 0.0013). Reductions in systolic blood pressure (P = 0.0418) and secondary endpoints of triglycerides (P = 0.0217) and exercise-induced fatigue (P = 0.0223) and dyspnoea (P = 0.0382), and increases in high-density lipoprotein cholesterol (P = 0.0254), were observed in the TMN vs. the comparator group by week 12.Conclusions Targeted medical nutrition containing high-dose omega-3 fatty acids, vitamin D, and high-quality protein is well tolerated with a good safety profile and has positive effects on blood pressure and blood lipids and on exercise-induced fatigue and dyspnoea. Therefore, this TMN could be clinically beneficial in the nutritional and metabolic support of precachectic and cachectic patients with COPD.

Background: Sarcopenia, or the loss of muscle mass and strength, is known to increase the risk for falls and (hip) fractures in older people. The objective of this study was to assess the skeletal muscle fiber characteristics in elderly female hip fracture patients.Method: Percutaneous needle biopsies were collected from the vastus lateralis muscle in 15 healthy young women (20 +/- 0.4 years), 15 healthy elderly women (79 +/- 1.7 years), and 15 elderly women with a fall-related hip fracture (82 +/- 1.5 years). Immunohistochemical analyses were performed to assess Type I and Type II muscle fiber size, and myonuclear and satellite cell content.Results: Type II muscle fiber size was significantly different between all groups (p

BackgroundCachectic patients with chronic obstructive pulmonary disease (COPD) may benefit from nutritional support. This double-blind, randomized, controlled trial evaluated the safety and efficacy of targeted medical nutrition (TMN) vs. an isocaloric comparator in pre-cachectic and cachectic patients with COPD.MethodsPatients aged ≥50 years with moderate-to-severe COPD and involuntary weight loss or low body mass index (16–18 kg/m2) were randomized 1:1 to receive TMN (~230 kcal; 2 g omega-3 fatty acids; 10 μg 25-hydroxy-vitamin D3) or isocaloric comparator twice daily for 12 weeks (ClinicalTrials.gov Identifier: NCT02442908). Primary safety endpoints comprised adverse events and changes in vital signs, laboratory parameters, and concomitant medications. Secondary efficacy endpoints included changes in weight, body composition, exercise tolerance, metabolic biomarkers, and systemic inflammation.ResultsForty-five patients were randomized to receive TMN (n = 22; mean 69.2 years) or isocaloric comparator (n = 23; mean 69.7 years). TMN was well tolerated. Adverse events were similar in number and type in both groups. Compliance to both products was good (TMN, 79%; comparator, 77%). Both groups gained weight, but the TMN group gained comparatively more fat mass (P = 0.0013). Reductions in systolic blood pressure (P = 0.0418) and secondary endpoints of triglycerides (P = 0.0217) and exercise-induced fatigue (P = 0.0223) and dyspnoea (P = 0.0382), and increases in high-density lipoprotein cholesterol (P = 0.0254), were observed in the TMN vs. the comparator group by week 12.ConclusionsTargeted medical nutrition containing high-dose omega-3 fatty acids, vitamin D, and high-quality protein is well tolerated with a good safety profile and has positive effects on blood pressure and blood lipids and on exercise-induced fatigue and dyspnoea. Therefore, this TMN could be clinically beneficial in the nutritional and metabolic support of pre-cachectic and cachectic patients with COPD.

The aim of this study was to examine the temporal relationship between intramyocellular lipid (IMCL) content and the expression of genes associated with IMCL turnover, fat metabolism, and inflammation during recovery from an acute bout of resistance type exercise in old versus young men. Seven healthy young (23 2 years, 77.2 +/- 2.9 kg) and seven healthy older (72 +/- 1 years, 79.3 +/- 4.9 kg) males performed a single bout of resistance exercise involving 6 sets of 10 repetitions of leg press and 6 sets of 10 repetitions of leg extension at 75% one-repetition maximum (1-RM). Muscle biopsy samples were obtained before and 12, 24 and 48 h after the completion of exercise and analysed for IMCL content and the expression of 48 genes. The subjects refrained from further heavy physical exercise and consumed a standardized diet for the entire experimental period. The IMCL content was similar to 2-fold higher at baseline and 12 h post-exercise in old compared with young individuals. However, no differences between groups were apparent after 48 h of recovery. There was higher expression of genes involved in fatty acid synthesis (FASN and PPAR gamma) during the first 24 h of recovery. Differential responses to exercise were observed between groups for a number of genes indicating increased inflammatory response (IL6, IkBalpha, CREB1) and impaired fat metabolism and TCA cycle (LPL, ACAT1, SUCLGI) in older compared With younger individuals. A singe bout of resistance type exercise leads to molecular changes in skeletal muscle favouring reduced lipid oxidation, increased lipogenesis, and exaggerated inflammation during post-exercise recovery in the older compared with younger individuals, which may be indicative of a blunted response of IMCL turnover with ageing. (C) 2017 Published by Elsevier Inc.

Muscle weakness and exercise intolerance negatively affect the quality of life of patients with mitochondrial myopathy. Short-term dietary nitrate supplementation has been shown to improve exercise performance and reduce oxygen cost of exercise in healthy humans and trained athletes. We investigated whether 1 wk of dietary inorganic nitrate supplementation decreases the oxygen cost of exercise and improves mitochondrial function in patients with mitochondrial myopathy. Ten patients with mitochondrial myopathy (40 ± 5 yr, maximal whole body oxygen uptake = 21.2 ± 3.2 ml·min−1·kg body wt−1, maximal work load = 122 ± 26 W) received 8.5 mg·kg body wt−1·day−1inorganic nitrate (~7 mmol) for 8 days. Whole body oxygen consumption at 50% of the maximal work load, in vivo skeletal muscle oxidative capacity (evaluated from postexercise phosphocreatine recovery using31P-magnetic resonance spectroscopy), and ex vivo mitochondrial oxidative capacity in permeabilized skinned muscle fibers (measured with high-resolution respirometry) were determined before and after nitrate supplementation. Despite a sixfold increase in plasma nitrate levels, nitrate supplementation did not affect whole body oxygen cost during submaximal exercise. Additionally, no beneficial effects of nitrate were found on in vivo or ex vivo muscle mitochondrial oxidative capacity. This is the first time that the therapeutic potential of dietary nitrate for patients with mitochondrial myopathy was evaluated. We conclude that 1 wk of dietary nitrate supplementation does not reduce oxygen cost of exercise or improve mitochondrial function in the group of patients tested.

Since the pioneering studies conducted in the 1960s in which glycogen status was investigated using the muscle biopsy technique, sports scientists have developed a sophisticated appreciation of the role of glycogen in cellular adaptation and exercise performance, as well as sites of storage of this important metabolic fuel. While sports nutrition guidelines have evolved during the past decade to incorporate sport-specific and periodized manipulation of carbohydrate (CHO) availability, athletes attempt to maximize muscle glycogen synthesis between important workouts or competitive events so that fuel stores closely match the demands of the prescribed exercise. Therefore, it is important to understand the factors that enhance or impair this biphasic process. In the early postexercise period (0-4 h), glycogen depletion provides a strong drive for its own resynthesis, with the provision of CHO (similar to 1 g/kg body mass) optimizing this process. During the later phase of recovery (4-24 h), CHO intake should meet the anticipated fuel needs of the training/competition, with the type, form, and pattern of intake being less important than total intake. Dietary strategies that can enhance glycogen synthesis from suboptimal amounts of CHO or energy intake are of practical interest to many athletes; in this scenario, the coingestion of protein with CHO can assist glycogen storage. Future research should identify other factors that enhance the rate of synthesis of glycogen storage in a limited time frame, improve glycogen storage from a limited CHO intake, or increase muscle glycogen supercompensation.

Purpose of review The review is an update on recent research investigating the role of skeletal muscle stem cells (also known as satellite cells) during muscle fiber regeneration and growth in animal and human skeletal muscle, with an emphasis on their role in age-related sarcopenia. Recent findings Studies indicate clear impairments in satellite cell function with aging, resulting in an impaired muscle fiber regenerative response. The autophagy-mediated switch to an irreversible presenescent state of geriatric satellite cells appears to play a key role in age-related impaired satellite cell function. In addition, inadequate muscle fiber vascularization may be a crucial factor underlying impaired regulation of satellite cells in older adults. Controversy remains on the actual contribution of satellite cells to the development of sarcopenia in later life, this clearly requires further research. Nevertheless, exercise training remains to be a potent intervention strategy, mediated through satellite cells or not, to counteract the ill effects of sarcopenia. Summary Although important strides are made investigating the importance of satellite cells in the development and/ or treatment of sarcopenia, the idea that satellite cell function is a therapeutic target to treat sarcopenia remains controversial.

Purpose of reviewThe review is an update on recent research investigating the role of skeletal muscle stem cells (also known as satellite cells) during muscle fiber regeneration and growth in animal and human skeletal muscle, with an emphasis on their role in age-related sarcopenia.Recent findingsStudies indicate clear impairments in satellite cell function with aging, resulting in an impaired muscle fiber regenerative response. The autophagy-mediated switch to an irreversible presenescent state of geriatric satellite cells appears to play a key role in age-related impaired satellite cell function. In addition, inadequate muscle fiber vascularization may be a crucial factor underlying impaired regulation of satellite cells in older adults. Controversy remains on the actual contribution of satellite cells to the development of sarcopenia in later life, this clearly requires further research. Nevertheless, exercise training remains to be a potent intervention strategy, mediated through satellite cells or not, to counteract the ill effects of sarcopenia.SummaryAlthough important strides are made investigating the importance of satellite cells in the development and/ or treatment of sarcopenia, the idea that satellite cell function is a therapeutic target to treat sarcopenia remains controversial.

Background Adequate muscle fibre perfusion is critical for the maintenance of muscle mass; it is essential in the rapid delivery of oxygen, nutrients and growth factors to the muscle, stimulating muscle fibre growth. Muscle fibre capillarization is known to decrease substantially with advancing age. However, whether (relative) low muscle fibre capillarization negatively impacts the muscle hypertrophic response following resistance exercise training in older adults is unknown. Methods Twenty-two healthy older men (711years) performed 24weeks of progressive resistance type exercise training. To assess the change in muscle fibre characteristics, percutaneous biopsies from the vastus lateralis muscle were taken before and following 12 and 24weeks of the intervention programme. A comparison was made between participants who had a relatively low type II muscle fibre capillary-to-fibre perimeter exchange index (CFPE; LOW group) and high type II muscle fibre CFPE (HIGH group) at baseline. Type I and type II muscle fibre size, satellite cell, capillary content and distance between satellite cells to the nearest capillary were determined by immunohistochemistry. Results Overall, type II muscle fibre size (from 5150 +/- 234 to 6719 +/- 446 mu m(2), P Conclusions Type II muscle fibre capillarization at baseline may be a critical factor for allowing muscle fibre hypertrophy to occur during prolonged resistance exercise training in older men.

Diurnal oscillations in energy metabolism are linked to the activity of biological clocks and contribute to whole-body glucose homeostasis. Postprandially, skeletal muscle takes up approximately 80% of circulatory glucose and hence is a key organ in maintenance of glucose homeostasis. Dysregulation of molecular clock components in skeletal muscle disrupts whole-body glucose homeostasis. Next to light-dark cycles, nonphotic cues such as nutrient intake and physical activity are also potent cues to (re)set (dys)regulated clocks. Physical exercise is one of the most potent ways to improve myocellular insulin sensitivity. Given the role of the biological clock in glucose homeostasis and the power of exercise to improve insulin sensitivity, one can hypothesize that there might be an optimal time for exercise to maximally improve insulin sensitivity and glucose homeostasis. In this review, we aim to summarize the available information related to the interaction of diurnal rhythm, glucose homeostasis, and physical exercise as a nonphotic cue to correct dysregulation of human glucose metabolism.

IntroductionWe investigated the effects of a supervised progressive sprint interval training (SIT) and moderate-intensity continuous training (MICT) on adipocyte morphology and adipose tissue metabolism and function; we also tested whether the responses were similar regardless of baseline glucose tolerance and sex.Research design and methods26 insulin-resistant (IR) and 28 healthy participants were randomized into 2-week-long SIT (4–6×30 s at maximum effort) and MICT (40–60 min at 60% of maximal aerobic capacity (VO2peak)). Insulin-stimulated glucose uptake and fasting-free fatty acid uptake in visceral adipose tissue (VAT), abdominal and femoral subcutaneous adipose tissues (SATs) were quantified with positron emission tomography. Abdominal SAT biopsies were collected to determine adipocyte morphology, gene expression markers of lipolysis, glucose and lipid metabolism and inflammation.ResultsTraining increased glucose uptake in VAT (p2peak and VAT glucose uptake in the IR group, whereas MICT reduced VAT fatty acid uptake more than SIT.ConclusionsShort-term training improves adipose tissue metabolism both in healthy and IR participants independently of the sex. Adipose tissue angiogenesis and gene expression was only significantly affected in IR participants.

Supplemental digital content is available in the text., Purpose This study aimed to assess the effect of dietary protein ingestion on intramuscular connective tissue protein synthesis rates during overnight recovery from a single bout of resistance exercise. Methods Thirty-six healthy, young males were randomly assigned to one of three treatments. One group ingested 30 g intrinsically L-[1-13C]-phenylalanine-labeled casein protein before sleep (PRO, n = 12). The other two groups performed a bout of resistance exercise in the evening and ingested either placebo (EX, n = 12) or 30 g intrinsically L-[1-13C]-phenylalanine-labeled casein protein before sleep (EX + PRO, n = 12). Continuous intravenous infusions of L-[ring-2H5]-phenylalanine and L-[1-13C]-leucine were applied, and blood and muscle tissue samples were collected to assess connective tissue protein synthesis rates and dietary protein-derived amino acid incorporation in the connective tissue protein fraction. Results Resistance exercise resulted in higher connective tissue protein synthesis rates when compared with rest (0.086 ± 0.017%·h−1 [EX] and 0.080 ± 0.019%·h−1 [EX + PRO] vs 0.059 ± 0.016%·h−1 [PRO]; P < 0.05). Postexercise casein protein ingestion did not result in higher connective tissue protein synthesis rates when compared with postexercise placebo ingestion (P = 1.00). Dietary protein-derived amino acids were incorporated into the connective tissue protein fraction at rest, and to a greater extent during recovery from exercise (P = 0.002). Conclusion Resistance exercise increases intramuscular connective tissue protein synthesis rates during overnight sleep, with no further effect of postexercise protein ingestion. However, dietary protein-derived amino acids are being used as precursors to support de novo connective tissue protein synthesis.

Nemaline myopathy (NM) caused by mutations in the gene encoding nebulin (NEB) accounts for at least 50% of all NM cases worldwide, representing a significant disease burden. Most NEB-NM patients have autosomal recessive disease due to a compound heterozygous genotype. Of the few murine models developed for NEB-NM, most are Neb knockout models rather than harbouring Neb mutations. Additionally, some models have a very severe phenotype that limits their application for evaluating disease progression and potential therapies. No existing murine models possess compound heterozygous Neb mutations that reflect the genotype and resulting phenotype present in most patients. We aimed to develop a murine model that more closely matched the underlying genetics of NEB-NM, which could assist elucidation of the pathogenetic mechanisms underlying the disease. Here, we have characterised a mouse strain with compound heterozygous Neb mutations; one missense (p.Tyr2303His), affecting a conserved actin-binding site and one nonsense mutation (p.Tyr935*), introducing a premature stop codon early in the protein. Our studies reveal that this compound heterozygous model, NebY2303H, Y935X, has striking skeletal muscle pathology including nemaline bodies. In vitro whole muscle and single myofibre physiology studies also demonstrate functional perturbations. However, no reduction in lifespan was noted. Therefore, NebY2303H,Y935X mice recapitulate human NEB-NM and are a much needed addition to the NEB-NM mouse model collection. The moderate phenotype also makes this an appropriate model for studying NEB-NM pathogenesis, and could potentially be suitable for testing therapeutic applications.

BACKGROUND: Insulin resistance results from impaired skeletal muscle glucose transport/phosphorylation, linked to augmented lipid availability. Despite greater intramuscular lipids, athletes are highly insulin sensitive, which could result from higher rates of insulin-stimulated glycogen synthesis or glucose transport/phosphorylation and oxidation. Thus, we examined the time course of muscle glycogen and glucose-6-phosphate concentrations during low and high systemic lipid availability. METHODS: Eight endurance-trained and 9 sedentary humans (VO(2) peak: 56 ± 2 vs. 33 ± 2 mL/kg/min, P < 0.05) underwent 6-hour hyperinsulinemic-isoglycemic clamp tests with infusions of triglycerides or saline in a randomized crossover design. Glycogen and glucose-6-phosphate concentrations were monitored in vastus lateralis muscles using (13)C/(31)P magnetic resonance spectroscopy. RESULTS: Athletes displayed a 25% greater (P < 0.05) insulin-stimulated glucose disposal rate (Rd) than sedentary participants. During Intralipid infusion, insulin sensitivity remained higher in the athletes (ΔRd: 25 ± 3 vs. 17 ± 3 μmol/kg/min, P < 0.05), supported by higher glucose transporter type 4 protein expression than in sedentary humans. Compared to saline infusion, AUC of glucose-6-phosphate remained unchanged during Intralipid infusion in athletes (1.6 ± 0.2 mmol/L vs. 1.4 ± 0.2 [mmol/L] × h, P = n.s.) but tended to decrease by 36% in sedentary humans (1.7 ± 0.4 vs. 1.1 ± 0.1 [mmol/L] × h, P < 0.059). This drop was accompanied by a 72% higher rate of net glycogen synthesis in the athletes upon Intralipid infusion (47 ± 9 vs. 13 ± 3 μmol/kg/min, P < 0.05). CONCLUSION: Athletes feature higher skeletal muscle glucose disposal and glycogen synthesis during increased lipid availability, which primarily results from maintained insulin-stimulated glucose transport with increased myocellular glucose-6-phosphate levels for subsequent glycogen synthesis. TRIAL REGISTRATION: ClinicalTrials.gov NCT01229059. FUNDING: German Federal Ministry of Health (BMG).

We aimed to evaluate the effect of multi-ingredient nutritional supplementation, with and without exercise training, on cognitive function in healthy older men. Forty-nine sedentary men [age: 73 ± 6 years (mean ± SD); body mass index: 28.5 ± 3.6 kg/m2] were randomized to consume a supplement (SUPP n = 25; 1500 mg n-3 polyunsaturated fatty acids, 30 g whey protein, 2.5 g creatine, 500 IU vitamin D, and 400 mg calcium) or control beverage (CON n = 24; 22 g maltodextrin) twice daily for 20 weeks consisting of Phase 1: SUPP/CON followed by Phase 2: 12-week resistance exercise training plus high-intensity interval training, while continuing to consume the study beverages (SUPP/CON + EX). At baseline, 6 weeks, and 19 weeks we assessed cognitive function [Montréal Cognitive Assessment (MOCA)], memory [word recall during the Rey Auditory Verbal Learning Test (RAVLT)], executive functions (working memory inhibition control), and nutrient bioavailability. We did not observe changes to any aspect of cognitive function after Phase 1; however, significant improvements in the following cognitive function outcomes were detected following Phase 2: MOCA scores increased (6 weeks: 23.5 ± 3.3 vs. 19 weeks: 24.4 ± 2.5, p = 0.013); number of words recalled during the RAVLT increased (6 weeks: 6.6 ± 3.6 vs. 19 weeks: 7.6 ± 3.8, p = 0.047); and reaction time improved (6 weeks: 567 ± 49 ms vs. 19 weeks: 551 ± 51 ms, p = 0.002). Although between-group differences in these outcomes were not significant, we observed within-group improvements in composite cognitive function scores over the course of the entire study only in the SUPP group (Δ = 0.58 ± 0.62, p = 0.004) but not in the CON group (Δ = 0.31 ± 0.61, p = 0.06). We observed a progressive increase in n-3 index, and a concomitant decrease in the ratio of arachidonic acid (ARA) to eicosapentaenoic acid (EPA) within erythrocyte plasma membranes, in the SUPP group only. At week 19, n-3 index (r = 0.49, p = 0.02) and the ARA:EPA ratio (r = -0.44, p = 0.03) were significantly correlated with composite cognitive function scores. Our results show that 12 weeks of RET + HIIT resulted in improved MOCA scores, word recall, and reaction time during an executive functions task; and suggest that a multi-ingredient supplement combined with this exercise training program may improve composite cognitive function scores in older men possibly via supplementation-mediated alterations to n-3 PUFA bioavailability. Clinical Trial Registration: http://www.ClinicalTrials.gov, identifier NCT02281331.

Context The mechanisms responsible for dietary fat-induced insulin resistance of skeletal muscle and its microvasculature are only partially understood. Objective To determine the impact of high-fat overfeeding on postprandial glucose fluxes, muscle insulin signaling, and muscle microvascular endothelial nitric oxide synthase (eNOS) content and activation. Design Fifteen non-obese volunteers consumed a high-fat (64%) high-energy (+47%) diet for 7 days. Experiments were performed before and after the diet. Stable isotope tracers were used to determine glucose fluxes in response to carbohydrate plus protein ingestion. Muscle insulin signaling was determined as well as the content and activation state of muscle microvascular eNOS. Results High-fat overfeeding impaired postprandial glycemic control as demonstrated by higher concentrations of glucose (+11%; P = 0.004) and insulin (+19%; P = 0.035). Carbohydrate plus protein ingestion suppressed endogenous glucose production to a similar extent before and after the diet. Conversely, high-fat overfeeding reduced whole-body glucose clearance (–16%; P = 0.021) and peripheral insulin sensitivity (–26%; P = 0.006). This occurred despite only minor alterations in skeletal muscle insulin signaling. High-fat overfeeding reduced eNOS content in terminal arterioles (P = 0.017) and abolished the increase in eNOS Ser1177 phosphorylation that was seen after carbohydrate plus protein ingestion. Conclusion High-fat overfeeding impaired whole-body glycemic control due to reduced glucose clearance, not elevated endogenous glucose production. The finding that high-fat overfeeding abolished insulin-mediated eNOS Ser1177 phosphorylation in the terminal arterioles suggests that impairments in the vasodilatory capacity of the skeletal muscle microvasculature may contribute to early dietary fat-induced impairments in glycemic control.

Since the discovery of AMP-activated protein kinase (AMPK) as a central regulator of energy homeostasis, many exciting insights into its structure, regulation and physiological roles have been revealed. While exercise, caloric restriction, metformin and many natural products increase AMPK activity and exert a multitude of health benefits, developing direct activators of AMPK to elicit beneficial effects has been challenging. However, in recent years, direct AMPK activators have been identified and tested in preclinical models, and a small number have entered clinical trials. Despite these advances, which disease(s) represent the best indications for therapeutic AMPK activation and the long-term safety of such approaches remain to be established.

Introduction: Quadriceps dysfunction is important in chronic obstructive pulmonary disease (COPD), with an associated increased proportion of type II fibers. Investigation of protein synthesis and degradation has yielded conflicting results, possibly due to study of whole biopsy samples, whereas signalling may be fiber-specific. Our objective was to develop a method for fiber-specific gene expression analysis. Methods: 12 COPD and 6 healthy subjects underwent quadriceps biopsy. Cryosections were immunostained for type II fibers, which were separated using laser capture microdissection (LCM). Whole muscle and different fiber populations were subject to quantitative polymerase chain reaction (qPCR). Results: Muscle-RING-finger-protein-1(MURF-1) and Atrogin-1 were lower in type II fibers of COPD versus healthy subjects (P=0.02 and P=0.03, respectively), but differences were not apparent in whole muscle or type I fibers. Discussion: We describe a novel method for studying fiber-specific gene expression in optimum-cutting-temperature (OCT) compound-embedded muscle specimens. LCM offers a more sensitive way to identify molecular changes in COPD muscle. This article is protected by copyright. All rights reserved.

Key points Skeletal muscle hypertrophy is one of the main outcomes from resistance training (RT), but how it is modulated throughout training is still unknown. We show that changes in myofibrillar protein synthesis (MyoPS) after an initial resistance exercise (RE) bout in the first week of RT (T1) were greater than those seen post-RE at the third (T2) and tenth week (T3) of RT, with values being similar at T2 and T3. Muscle damage (Z-band streaming) was the highest during post-RE recovery at T1, lower at T2 and minimal at T3. When muscle damage was the highest, so was the integrated MyoPS (at T1), but neither were related to hypertrophy; however, integrated MyoPS at T2 and T3 were correlated with hypertrophy. We conclude that muscle hypertrophy is the result of accumulated intermittent increases in MyoPS mainly after a progressive attenuation of muscle damage. AbstractSkeletal muscle hypertrophy is one of the main outcomes of resistance training (RT), but how hypertrophy is modulated and the mechanisms regulating it are still unknown. To investigate how muscle hypertrophy is modulated through RT, we measured day-to-day integrated myofibrillar protein synthesis (MyoPS) using deuterium oxide and assessed muscle damage at the beginning (T1), at 3weeks (T2) and at 10weeks of RT (T3). Ten young men (27(1)years, mean (SEM)) had muscle biopsies (vastus lateralis) taken to measure integrated MyoPS and muscle damage (Z-band streaming and indirect parameters) before, and 24h and 48h post resistance exercise (post-RE) at T1, T2 and T3. Fibre cross-sectional area (fCSA) was evaluated using biopsies at T1, T2 and T3. Increases in fCSA were observed only at T3 (P=0.017). Changes in MyoPS post-RE at T1, T2 and T3 were greater at T1 (P

Stem cells maintain homeostasis in all regenerating tissues during the lifespan of an organism. Thus, age-related functional decline of such tissues is likely to be at least partially explained by molecular events occurring in the stem cell compartment. Some of these events involve epigenetic changes, which may dictate how an aging genome can lead to differential gene expression programs. Recent technological advances have made it now possible to assess the genome-wide distribution of an ever-increasing number of epigenetic marks. As a result, the hypothesis that there may be a causal role for an altered epigenome contributing to the functional decline of cells, tissues, and organs in aging organisms can now be explored. In this paper, we review recent developments in the field of epigenetic regulation of stem cells, and how this may contribute to aging.

International audience; Purpose: This study aimed at investigating the mechanisms involved in the force reduction induced by two electrical stimulation (ES) protocols that were designed to activate motor units differently. Methods: The triceps surae of 11 healthy subjects (8 men; age, similar to 28 yr) was activated using ES applied over the tibial nerve. Two ES protocols (conventional [CONV]: 20 Hz, 0.05 ms vs wide-pulse high-frequency [WPHF]: 80 Hz, 1 ms) were performed and involved 40 trains (6 s on-6 s off) delivered at an intensity (I-ES) evoking 20% of maximal voluntary contraction. To analyze the mechanical properties of the motor units activated at I-ES, force-frequency relation was evoked before and after each protocol. H-reflex and M-wave responses evoked by the last stimulation pulse were also assessed during each ES protocol. Electromyographic responses (Sigma EMG) were recorded after each train to analyze the behavior of the motor units activated at I-ES. Metabolic variables, including relative concentrations of phosphocreatine and inorganic phosphate as well as intracellular pH, were assessed using P-31-MR spectroscopy during each protocol. Results: Larger H-reflex amplitudes were observed during WPHF as compared with CONV, whereas opposite findings were observed for M-wave amplitudes. Despite this difference, both the force reduction (-26%) and metabolic changes were similar between the two protocols. The CONV protocol induced a rightward shift of the force-frequency relation, whereas a significant reduction of the Sigma EMG evoked at I-ES was observed only for the WPHF. Conclusions: These results suggest that a decreased number of active motor units mainly contributed to WPHF-induced force decrease, whereas intracellular processes were most likely involved in the force reduction occurring during CONV stimulation.

BACKGROUND: Physical inactivity contributes to muscle wasting and reductions in mitochondrial oxidative phenotype (OXPHEN), reducing physical performance and quality of life during aging and in chronic disease. Previously, it was shown that inactivation of glycogen synthase kinase (GSK)-3β stimulates muscle protein accretion, myogenesis, and mitochondrial biogenesis. Additionally, GSK-3β is inactivated during recovery of disuse-induced muscle atrophy. AIM: Therefore, we hypothesize that GSK-3 inhibition is required for reloading-induced recovery of skeletal muscle mass and OXPHEN. METHODS: Wild-type (WT) and whole-body constitutively active (C.A.) Ser21/9 GSK-3α/β knock-in mice were subjected to a 14-day hind-limb suspension/14-day reloading protocol. Soleus muscle mass, fiber cross-sectional area (CSA), OXPHEN (abundance of sub-units of oxidative phosphorylation (OXPHOS) complexes and fiber-type composition), as well as expression levels of their main regulators (respectively protein synthesis/degradation, myogenesis and peroxisome proliferator-activated receptor-γ co-activator-1α (PGC-1α) signaling) were monitored. RESULTS: Subtle but consistent differences suggesting suppression of protein turnover signaling and decreased expression of several OXPHOS sub-units and PGC-1α signaling constituents were observed at baseline in C.A. GSK-3 versus WT mice. Although soleus mass recovery during reloading occurred more rapidly in C.A. GSK-3 mice, this was not accompanied by a parallel increased CSA. The OXPHEN response to reloading was not distinct between C.A. GSK-3 and WT mice. No consistent or significant differences in reloading-induced changes in the regulatory steps of protein turnover, myogenesis or muscle OXPHEN were observed in C.A. GSK-3 compared to WT muscle. CONCLUSION: This study indicates that GSK-3 inactivation is dispensable for reloading-induced recovery of muscle mass and OXPHEN. ispartof: BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR BASIS OF DISEASE vol:1866 issue:6 ispartof: location:Netherlands status: published

Introduction Ageing is associated with an attenuated hypertrophic response to resistance training and periods of training interruptions. Hence, elderly would benefit from the ‘muscle memory’ effects of resistance training on muscle strength and mass during detraining and retraining. As the underlying mechanisms are not yet clear, this study investigated the role of myonuclei during training, detraining and retraining by using PCM1 labelling in muscle cross-sections of six older men. Methods Knee extension strength and power were measured in 30 older men and 10 controls before and after 12 weeks resistance training and after detraining and retraining of similar length. In a subset, muscle biopsies from the vastus lateralis were taken for analysis of fibre size, fibre type distribution, Pax7+ satellite cell number and myonuclear domain size. Results Resistance training increased knee extension strength and power parameters (+10 to +36%, p < .001) and decreased the frequency of type IIax fibres by half (from 20 to 10%, p = .034). Detraining resulted in a modest loss of strength and power (−5 to −15%, p ≤ .004) and a trend towards a fibre-type specific decrease in type II fibre cross-sectional area (−17%, p = .087), type II satellite cell number (−30%, p = .054) and type II myonuclear number (−12%, p = .084). Less than eight weeks of retraining were needed to reach the post-training level of one-repetition maximum strength. Twelve weeks of retraining were associated with type II fibre hypertrophy (+29%, p = .050), which also promoted an increase in the number of satellite cells (+72%, p = .036) and myonuclei (+13%, p = .048) in type II fibres. Changes in the type II fibre cross-sectional area were positively correlated with changes in the myonuclear number (Pearson's r between 0.40 and 0.73), resulting in a stable myonuclear domain. Conclusion Gained strength and power and fibre type changes were partially preserved following 12 weeks of detraining, allowing for a fast recovery of the 1RM performance following retraining. Myonuclear number tended to follow individual changes in type II fibre size, which is in support of the myonuclear domain theory., Experimental Gerontology, 133

International audience

Introduction: Although resistance type exercise training (RT) effectively increases muscle mass and strength in older individuals, it remains unclear whether gains in muscle mass and strength are maintained without continued supervised training. We assessed the capacity of older individuals to maintain muscle mass and strength gains one year after partaking in a successful RT program.Methods: Fifty-three healthy older adults performed a 24-wk supervised RT program. Upon the cessation of the training program, participants were not provided with any advice or incentives to continue exercise training. One year after completion of the training program, all participants were contacted and invited back to the laboratory to assess anthropometrics, body composition (DXA), quadriceps muscle cross-sectional area (CSA) (CT-scan), muscle strength (1RM knee extension/leg press), and muscle fiber characteristics (muscle biopsy). Following primary analyses on all participants that responded to the invitation (n = 35), participants were divided into two groups: individuals who had continued to perform exercise training on an individual basis (EXER group; n = 16) and individuals who had not continued to perform any regular exercise (STOP group; n = 19) after completing the RT program.Results: The initial increases in quadriceps CSA ( + 506 +/- 209 and +584 +/- 287 mm(2)) and knee extension strength ( + 32 +/- 12 vs +34 +/- 10 kg) after the 24-wk RT program did not differ between the STOP and EXER group (all P > 0.05). One year after discontinuation of the RT program, participants had lost muscle mass (P 0.05), yet remained higher compared with values before the RT program (P Conclusion: Though prolonged RT can effectively increase muscle mass and strength in the older population, muscle mass gains are lost and muscle strength gains are only partly preserved within one year if the supervised exercise program is not continued.

This study aims to identify a genetic predisposition score from a set of candidate gene variants that predicts the response to a one-year exercise intervention. 200 participants (aged 60-83 years) were randomly assigned to a fitness (FIT), whole-body vibration (WBV) and control group. Participants in the exercise (FIT and WBV) groups performed a one-year intervention program. Whole-body skeletal muscle mass (SMM) and isometric knee extension strength (PTIM60) were measured before and after the intervention. A set of 170 muscle-related single nucleotide polymorphisms (SNPs) were genotyped. Stepwise regression analysis was applied to select significantly contributing SNPs for baseline and relative change parameters. A data-driven genetic predisposition score (GPS) was calculated by adding up predisposing alleles for each of the phenotypes. GPS was calculated based on 4 to 8 SNPs which were significantly related to the corresponding phenotypes. These SNPs belong to genes that are involved in myoblast differentiation, muscle and bone growth, myofiber contraction, cytokines and DNA methylation. GPS was related to baseline PTIM60 and relative changes of SMM and PTIM60 in the exercise groups, explaining the variance of the corresponding parameter by 3.2%, 14% and 27%, respectively. Adding one increasing allele in the GPS increased baseline PTIM60 by 4.73 Nm, and exercise-induced relative changes of SMM and PTIM60 by 1.78% and 3.86% respectively. The identified genetic predisposition scores were positively related to baseline knee extension strength and muscle adaptations to exercise in healthy elderly. These findings provide supportive genetic explanations for high and low responders in exercise-induced muscle adaptations. ispartof: EXPERIMENTAL GERONTOLOGY vol:111 pages:17-26 ispartof: location:England status: published

Background Recent advanced applications of the functional electrical stimulation (FES) mostly used closed-loop control strategies based on mathematical models to improve the performance of the FES systems. In most of them, the pulse amplitude was used as an input control. However, in controlling the muscle force, the most popular force model developed by Ding et al. does not take into account the pulse amplitude effect. The purpose of this study was to include the pulse amplitude in the existing Ding et al. model based on the recruitment curve function. Methods Quadriceps femoris muscles of eight healthy subjects were tested. Forces responses to stimulation trains with different pulse amplitudes (30–100 mA) and frequencies (20–80 Hz) were recorded and analyzed. Then, specific model parameter values were identified by fitting the measured forces for one train (50 Hz, 100 mA). The obtained model parameters were then used to identify the recruitment curve parameter values by fitting the force responses for different pulse amplitudes at the same frequency train. Finally, the extended model was used to predict force responses for a range of stimulation pulse amplitudes and frequencies. Results The experimental results indicated that our adapted model accurately predicts the force-pulse amplitude relationship with an excellent agreement between measured and predicted forces ( R 2 =0.998, RMSE = 6.6 N). Conclusions This model could be used to predict the pulse amplitude effect and to design control strategies for controlling the muscle force in order to obtain precise movements during FES sessions using intensity modulation.

Human myogenic precursor cells have been isolated and expanded from a number of skeletal muscles, but alternative donor biopsy sites must be sought after in diseases where muscle damage is widespread. Biopsy sites must be relatively accessible, and the biopsied muscle dispensable. Here, we aimed to histologically characterize the cremaster muscle with regard number of satellite cells and regenerative fibres, and to isolate and characterize human cremaster muscle-derived stem/precursor cells in adult male donors with the objective of characterizing this muscle as a novel source of myogenic precursor cells. Cremaster muscle biopsies (or adjacent non-muscle tissue for negative controls; N = 19) were taken from male patients undergoing routine surgery for urogenital pathology. Myosphere cultures were derived and tested for their in vitro and in vivo myogenic differentiation and muscle regeneration capacities. Cremaster-derived myogenic precursor cells were maintained by myosphere culture and efficiently differentiated to myotubes in adhesion culture. Upon transplantation to an immunocompromised mouse model of cardiotoxin-induced acute muscle damage, human cremaster-derived myogenic precursor cells survived to the transplants and contributed to muscle regeneration. These precursors are a good candidate for cell therapy approaches of skeletal muscle. Due to their location and developmental origin, we propose that they might be best suited for regeneration of the rhabdosphincter in patients undergoing stress urinary incontinence after radical prostatectomy. We thank patients and medical personnel for their generous involvement in the study. We also acknowledge the help of Biodonostia Animal and Experimental Operations Facility. This work was supported by grants from Ministerio de Economía y Competitividad (RTC-2015-3750-1) and Instituto de Salud Carlos III (PI13/02172, PI16/01430) to A.I., co-funded by the European Union (ERDF/ESF, ‘Investing in your future’). N.N.-G. received a studentship from the Department of Education, University and Research of the Basque Government (PRE2013-1-1168). A.L.M. was funded by grants from FIS (PI17/01841 and PI14/00436), CIBERNED and the Basque Government (2015/11038, RIS3 2017222021 and BIO16/ER/022). M.F.L.-C. was supported by the Servicio Andaluz de Salud from the Consejería de Salud de la Junta de Andalucía, grant PI 0222-2014, co-funded by the European Union (ERDF/ESF). I.M.A was funded by grants from Ministerio de Economia y Competitividad (PEJ-2014-P-01215 and FJCI-2016-28121). Sí

Objective Intramyocellular lipid (IMCL) storage negatively associates with insulin resistance, albeit not in endurance-trained athletes. We investigated the putative contribution of lipid droplet (LD) morphology and subcellular localization to the so-called athlete's paradox. Methods We performed quantitative immunofluorescent confocal imaging of muscle biopsy sections from endurance Trained, Lean sedentary, Obese, and Type 2 diabetes (T2DM) participants (n = 8/group). T2DM patients and Trained individuals were matched for IMCL content. Furthermore we performed this analysis in biopsies of T2DM patients before and after a 12-week exercise program (n = 8). Results We found marked differences in lipid storage morphology between trained subjects and T2DM: the latter group mainly store lipid in larger LDs in the subsarcolemmal (SS) region of type II fibers, whereas Trained store lipid in a higher number of LDs in the intramyofibrillar (IMF) region of type I fibers. In addition, a twelve-week combined endurance and strength exercise program resulted in a LD phenotype shift in T2DM patients partly towards an ‘athlete-like’ phenotype, accompanied by improved insulin sensitivity. Proteins involved in LD turnover were also more abundant in Trained than in T2DM and partly changed in an ‘athlete-like’ fashion in T2DM patients upon exercise training. Conclusions Our findings provide a physiological explanation for the athlete's paradox and reveal LD morphology and distribution as a major determinant of skeletal muscle insulin sensitivity., Highlights • Distinct lipid droplet morphology and distribution underlies the athletes' paradox. • Muscle lipid storage occurs in a fiber type specific manner. • Exercise training shifts LD morphology towards an athletes' phenotype.

Stretching exercises are known for reduction of musculoskeletal stiffness and elongation of electromechanical delay (EMD). However, computing a change in stiffness by means of time delays, detected between onset of electromyographic (EMG), mechanomyographic (MMG) and force signals, can reveal changes in subcomponents (Delta tEMG-MMG and Delta tMMG-FORCE) of EMD after stretching. In our study, the effect of stretching was investigated while quadriceps femoris (QF) muscle performed isometric contractions. The EMG, MMG, and Force signals were recorded from rectus femoris (RF) and vastus medialis (VM) during five voluntarily isometric contractions at 15 degrees, 30 degrees, and 45 degrees of knee flexion angle, while the leg was positioned on a custom-made device. Subjects in both intervention and control groups underwent same recording procedure before and after stretching. No difference between the baseline repeated contractions (before stretching) was ensured by ANOVA for repeated measures while a difference between PRE and POST was analyzed and concluded based on the effect size results. The EMD did not change; however, subcomponents (Delta tEMG-MMG and Delta tMMG-FORCE) showed differences within RF and VM muscles after stretching. The 30 degrees knee flexion angle appears to be a position where isometric contraction intensity needs to be carefully monitored during rehabilitation period.

Sarcopenia is the age-related loss of skeletal muscle mass, strength, and function. It is associated with regenerative difficulties by satellite cells, adult muscle stem cells, and alteration of oxidative management, mainly the increase in superoxide anions (O2•−). We aimed to investigate the relation between regenerative deficit in elderly and increase in O2•− production along with mitochondrial alterations. Myoblasts and myotubes from skeletal muscle of young and elderly healthy subjects (27.8 ± 6 and 72.4 ± 6.5 years old) were measured: (1) superoxide dismutase activity and protein content, (2) mitochondrial O2•− production levels, (3) O2•− production variability, and (4) mitochondrial bioenergetic profile. Compared to young myoblasts, elderly myoblasts displayed decreased SOD2 protein expression, elevated mitochondrial O2•− baseline levels, and decreased oxidative phosphorylation and glycolysis. Additionally, elderly versus young myotubes showed elevated mitochondrial O2•− levels when stressed with N-acetyl cysteine or high glucose and higher glycolysis despite showing comparable oxidative phosphorylation levels. Altogether, the elderly may have less metabolic plasticity due to the impaired mitochondrial function caused by O2•−. However, the increased energy demand related to the differentiation process appears to activate compensatory mechanisms for the partial mitochondrial dysfunction.

Background Whey and micellar casein are high-quality dairy proteins that can stimulate postprandial muscle protein synthesis rates. How whey and casein compare with milk protein in their capacity to stimulate postprandial myofibrillar (MyoPS) and mitochondrial (MitoPS) protein synthesis rates during postexercise recovery is currently unknown. Objective The objective of this study was to compare postprandial MyoPS and MitoPS rates after protein-carbohydrate co-ingestion with milk protein, whey, or micellar casein during recovery from a single bout of concurrent resistance- and endurance-type exercise in young healthy men. Methods In a randomized, double-blind, parallel-group design, 48 healthy, young, recreationally active men (mean ± SEM age: 23 ± 0.3 y) received a primed continuous infusion of L-[ring-13C6]-phenylalanine and L-[ring-3,5-2H2]-tyrosine and ingested 45 g carbohydrate with 0 g protein (CHO), 20 g milk protein (MILK), 20 g whey protein (WHEY), or 20 g micellar casein protein (CASEIN) after a sequential bout of resistance- and endurance-type exercise (i.e., concurrent exercise). Blood and muscle biopsies were collected over 360 min during recovery from exercise to assess MyoPS and MitoPS rates and signaling through mammalian target of rapamycin complex 1 (mTORC1). Results Despite temporal differences in postprandial plasma leucine concentrations between treatments (P

Skeletal muscle wasting is a common clinical feature of many chronic diseases and also occurs in response to single acute events. The accompanying loss of strength can lead to significant disability, increased care needs and have profound negative effects on quality of life. As muscle is the most abundant source of amino acids in the body, it appears to function as a buffer for fuel and substrates that can be used to repair damage elsewhere and to feed the immune system. In essence, the fundamentals of muscle wasting are simple: less muscle is made than is broken down. However, although well‐described mechanisms modulate muscle protein turnover, significant individual differences in the amount of muscle lost in the presence of a given severity of disease complicate the understanding of underlying mechanisms and suggest that individuals have different sensitivities to signals for muscle loss. Furthermore, the rate at which muscle protein is turned over under normal conditions means that clinically significant muscle loss can occur with changes in the rate of protein synthesis and/or breakdown that are too small to be measurable. Consequently, the changes in expression of factors regulating muscle turnover required to cause a decline in muscle mass are small and, except in cases of rapid wasting, there is no consistent pattern of change in the expression of factors that regulate muscle mass. MicroRNAs are fine tuners of cell phenotype and are therefore ideally suited to cause the subtle changes in proteome required to tilt the balance between synthesis and degradation in a way that causes clinically significant wasting. Herein we present a model in which muscle loss as a consequence of disease in non‐muscle tissue is modulated by a set of microRNAs, the muscle expression of which is associated with severity of disease in the non‐muscle tissue. These microRNAs alter fundamental biological processes including the synthesis of ribosomes and mitochondria leading to reduced protein synthesis and increased protein breakdown, thereby freeing amino acids from the muscle. We argue that the variability in muscle loss observed in the human population arises from at least two sources. The first is from pre‐existing or disease‐induced variation in the expression of microRNAs controlling the sensitivity of muscle to the atrophic signal and the second is from the expression of microRNAs from imprinted loci (i.e. only expressed from the maternally or paternally inherited allele) and may control the rate of myonuclear recruitment. In the absence of disease, these factors do not correlate with muscle mass, since there is no challenge to the established balance. However, in the presence of such a challenge, these microRNAs determine the rate of decline for a given disease severity. Together these mechanisms provide novel insight into the loss of muscle mass and its variation in the human population. The involvement of imprinted loci also suggests that genes that regulate early development also contribute to the ability of individuals to resist muscle loss in response to disease.

International audience; Modifications of the interactions between endoplasmic reticulum (ER) and mitochondria, defined as mitochondria-associated membranes (MAMs), were recently shown to be involved in the control of hepatic insulin action and glucose homeostasis, but with conflicting results. Whereas skeletal muscle is the primary site of insulin-mediated glucose uptake and the main target for alterations in insulin-resistant states, the relevance of MAM integrity in muscle insulin resistance is unknown. Deciphering the importance of MAMs on muscle insulin signaling could help to clarify this controversy. Here, we show in skeletal muscle of different mice models of obesity and type 2 diabetes (T2D) a marked disruption of ER-mitochondria interactions as an early event preceding mitochondrial dysfunction and insulin resistance. Furthermore, in human myotubes, palmitate-induced insulin resistance is associated with a reduction of structural and functional ER-mitochondria interactions. Importantly, experimental increase of ER-mitochondria contacts in human myotubes prevents palmitate-induced alterations of insulin signaling and action, whereas disruption of MAM integrity alters the action of the hormone. Lastly, we found an association between altered insulin signaling and ER-mitochondria interactions in human myotubes from obese subjects with or without T2D compared with healthy lean subjects. Collectively, our data reveal a new role of MAM integrity in insulin action of skeletal muscle and highlight MAM disruption as an essential subcellular alteration associated with muscle insulin resistance in mice and humans. Therefore, reduced ER-mitochondria coupling could be a common alteration of several insulin-sensitive tissues playing a key role in altered glucose homeostasis in the context of obesity and T2D.

The majority of fat in the human body is stored as triacylglycerols in white adipose tissue. In the obese state, adipose tissue mass expands and excess lipids are stored in non-adipose tissues, such as skeletal muscle. Lipids are stored in skeletal muscle in the form of small lipid droplets. Although originally viewed as dull organelles that simply store lipids as a consequence of lipid overflow from adipose tissue, lipid droplets are now recognized as key components in the cell that exert a variety of relevant functions in multiple tissues (including muscle). Here, we review the effect of diet and exercise interventions on myocellular lipid droplets and their putative role in insulin sensitivity from a human perspective. We also provide an overview of lipid droplet biology and identify gaps for future research.

The majority of fat in the human body is stored as triacylglycerols in white adipose tissue. In the obese state, adipose tissue mass expands and excess lipids are stored in non-adipose tissues, such as skeletal muscle. Lipids are stored in skeletal muscle in the form of small lipid droplets. Although originally viewed as dull organelles that simply store lipids as a consequence of lipid overflow from adipose tissue, lipid droplets are now recognized as key components in the cell that exert a variety of relevant functions in multiple tissues (including muscle). Here, we review the effect of diet and exercise interventions on myocellular lipid droplets and their putative role in insulin sensitivity from a human perspective. We also provide an overview of lipid droplet biology and identify gaps for future research.

Intramyocellular lipid (IMCL) hampers insulin sensitivity, albeit not in endurance-trained athletes (Trained). Compared to type 2 diabetes mellitus (T2DM) patients, Trained subjects have high levels of perilipin 5 (PLIN5). In the present study, we tested whether the fraction of PLIN5-coated lipid droplets (LDs) is a determinant of skeletal muscle insulin sensitivity and contributes to the athlete's paradox. Muscle biopsies were taken from eight Trained, Lean sedentary, Obese and T2DM subjects. Trained, Obese and T2DM subjects were matched for total IMCL content. Confocal images were analysed for lipid area fraction, LD size and number and PLIN5+ and PLIN5- LDs were measured. A stepwise linear regression was performed to identify factors explaining observed variance in glucose infusion rate (GIR). Trained and T2DM subjects stored IMCL differently; Trained subjects had a higher number of LDs compared to T2DM subjects (0.0370.004m(-2)vs. 0.0230.003m(-2), P=0.024) that were non-significantly smaller (0.270.01m(2)vs. 0.320.02m(2), P=0.197, Trained vs. T2DM). Even though total PLIN5 protein content was almost double in Trained vs. T2DM subjects (1.650.21AU vs. 0.89 +/- 0.09AU, P=0.004), PLIN5 coating did not affect LD number or size significantly. Of the observed variance in GIR, the largest fraction by far (70.2%) was explained by maximal oxygen uptake. Adding PLIN5 protein content or PLIN5+ LDs increased the explained variance in GIR (74.7% and 80.7% for PLIN5 protein content and PLIN5+ LDs, respectively). Thus, the putative relationship between PLIN5 and insulin sensitivity is at best indirect and is apparent only in conjunction with maximal oxygen uptake. Hence, PLIN5 abundance cannot be causally linked to the athlete's paradox.

Aim: Muscle fibre hypertrophy is accompanied by an increase in myonuclear number, an increase in myonuclear domain size or both. It has been suggested that increases in myonuclear domain size precede myonuclear accretion and subsequent muscle fibre hypertrophy during prolonged exercise training. In this study, we assessed the changes in muscle fibre size, myonuclear and satellite cell content throughout 12 weeks of resistance-type exercise training in young men.Methods: Twenty-two young men (23 +/- 1 year) were assigned to a progressive, 12-weeks resistance-type exercise training programme (3 sessions per week). Muscle biopsies from the vastus lateralis muscle were taken before and after 2, 4, 8 and 12 weeks of exercise training. Muscle fibre size, myonuclear content, myonuclear domain size and satellite cell content were assessed by immunohistochemistry.Results: Type I and type II muscle fibre size increased gradually throughout the 12 weeks of training (type I: 18 +/- 5%, type II: 41 +/- 6%, P Conclusion: Increases in myonuclear domain size do not appear to drive myonuclear accretion and muscle fibre hypertrophy during prolonged resistance-type exercise training in vivo in humans.

Aims/hypothesis Dissipating energy via mitochondrial uncoupling has been suggested to contribute to enhanced insulin sensitivity. We hypothesised that skeletal muscle mitochondria of endurance-trained athletes have increased sensitivity for fatty acid (FA)-induced uncoupling, which is driven by the mitochondrial protein adenine nucleotide translocase 1 (ANT1). Methods Capacity for FA-induced uncoupling was measured in endurance-trained male athletes (T) and sedentary young men (UT) in an observational study and also in isolated skeletal muscle mitochondria from Zucker diabetic fatty (ZDF) rats and C2C12 myotubes following small interfering RNA (siRNA)-mediated gene silencing of ANT1. Thus, fuelled by glutamate/succinate (fibres) or pyruvate (mitochondria and myotubes) and in the presence of oligomycin to block ATP synthesis, increasing levels of oleate (fibres) or palmitate (mitochondria and myotubes) were automatically titrated while respiration was monitored. Insulin sensitivity was measured by hyperinsulinaemic–euglycaemic clamp in humans and via insulin-stimulated glucose uptake in myotubes. Results Skeletal muscle from the T group displayed increased sensitivity to FA-induced uncoupling (p = 0.011) compared with muscle from the UT group, and this was associated with elevated insulin sensitivity (p = 0.034). ANT1 expression was increased in T (p = 0.013). Mitochondria from ZDF rats displayed decreased sensitivity for FA-induced uncoupling (p = 0.008). This difference disappeared in the presence of the adenine nucleotide translocator inhibitor carboxyatractyloside. Partial knockdown of ANT1 in C2C12 myotubes decreased sensitivity to the FA-induced uncoupling (p = 0.008) and insulin-stimulated glucose uptake (p = 0.025) compared with controls. Conclusions/interpretation Increased sensitivity to FA-induced uncoupling is associated with enhanced insulin sensitivity and is affected by ANT1 activity in skeletal muscle. FA-induced mitochondrial uncoupling may help to preserve insulin sensitivity in the face of a high supply of FAs. Trial registration www.trialregister.nl NTR2002

Despite their classic bean-shaped depiction, mitochondria have very different aspects in each cell type. From long filamentous structures to punctuated small round organelles. These shapes can dynamically change in response to nutrients and in situations of metabolic disease. However, why do mitochondria adapt different shapes and how is this determined? In this review, we will aim to understand different visions on how metabolic cues influence mitochondrial shape and vice-versa. This response can be dramatically different between tissues and cells, as illustrated by a large array of genetically engineered mouse models reported to date. We will use these models to understand the role of different mitochondrial dynamicserelated proteins and processes.

Background Due to the post-mitotic nature of myonuclei, postnatal myogenesis is essential for skeletal muscle growth, repair, and regeneration. This process is facilitated by satellite cells through proliferation, differentiation, and subsequent fusion with a pre-existing muscle fiber (i.e., myonuclear accretion). Current knowledge of myogenesis is primarily based on the in vitro formation of syncytia from myoblasts, which represents aspects of developmental myogenesis, but may incompletely portray postnatal myogenesis. Therefore, we aimed to develop an in vitro model that better reflects postnatal myogenesis, to study the cell intrinsic and extrinsic processes and signaling involved in the regulation of postnatal myogenesis. Methods Proliferating C2C12 myoblasts were trypsinized and co-cultured for 3 days with 5 days differentiated C2C12 myotubes. Postnatal myonuclear accretion was visually assessed by live cell time-lapse imaging and cell tracing by cell labeling with Vybrant® DiD and DiO. Furthermore, a Cre/LoxP-based cell system was developed to semi-quantitatively assess in vitro postnatal myonuclear accretion by the conditional expression of luciferase upon myoblast–myotube fusion. Luciferase activity was assessed luminometrically and corrected for total protein content. Results Live cell time-lapse imaging, staining-based cell tracing, and recombination-dependent luciferase activity, showed the occurrence of postnatal myonuclear accretion in vitro. Treatment of co-cultures with the myogenic factor IGF-I (p

Mesenchymal stem/stromal cells (MSCs) represent a promising adult progenitor cell source for tissue repair and regeneration. Their mysterious identityin situhas gradually been unveiled by the accumulating evidence indicating an association between adult multipotent stem/progenitor cells and vascular/perivascular niches. Using immunohistochemistry and fluorescence-activated cell sorting, we and other groups have prospectively identified and purified subpopulations of multipotent precursor cells associated with the blood vessels within multiple human organs. The three precursor subsets, myogenic endothelial cells (MECs), pericytes (PCs), and adventitial cells (ACs), are located, respectively, in the three structural tiers of typical blood vessels: intima, media, and adventitia. MECs, PCs, and ACs have been extensively characterized in prior studies and are currently under investigation for their therapeutic potentials in preclinical animal models. In this review, we will briefly discuss the identification, isolation, and characterization of these human blood-vessel-derived stem cells (hBVSCs) and summarize the current status of regenerative applications of hBVSC subsets.

Background Though it is well appreciated that insulin plays an important role in the regulation of muscle protein metabolism, there is much discrepancy in the literature on the capacity of exogenous insulin administration to increase muscle protein synthesis rates in vivo in humans. Objective To assess whether exogenous insulin administration increases muscle protein synthesis rates in young and older adults. Design A systematic review of clinical trials was performed and the presence or absence of an increase in muscle protein synthesis rate was reported for each individual study arm. In a stepwise manner, multiple models were constructed that excluded study arms based on the following conditions: model 1, concurrent hyperaminoacidemia; model 2, insulin-induced hypoaminoacidemia; model 3, supraphysiological insulin concentrations; and model 4, older, more insulin resistant, subjects. Conclusions From the presented data in the current systematic review, we conclude that: i) exogenous insulin and amino acid administration effectively increase muscle protein synthesis, but this effect is attributed to the hyperaminoacidemia; ii) exogenous insulin administered systemically induces hypoaminoacidemia which obviates any insulin-stimulatory effect on muscle protein synthesis; iii) exogenous insulin resulting in supraphysiological insulin levels exceeding 50¿000¿pmol/l may effectively augment muscle protein synthesis; iv) exogenous insulin may have a diminished effect on muscle protein synthesis in older adults due to age-related anabolic resistance; and v) exogenous insulin administered systemically does not increase muscle protein synthesis in healthy, young adults.