Human skeletal muscle fibre type variations correlate with PPAR alpha, PPAR delta and PGC-1 alpha mRNA

Identification of genes related to growth traits from transcriptome profiles of duck breast muscle tissue

The growth and development of duck skeletal muscle is an important economic trait that is genetically regulated. The internal mechanism underlying the regulation of skeletal muscle growth and development in ducks remains unclear. The purpose of this study was to identify candidate genes related to the growth of duck skeletal muscle. RNA-sequencing technology was used to compare the transcriptome of duck breast muscles in an F2 population with the high breast muscle rate (HB) and the low breast muscle rate (LB). A total of 14,522 genes were confirmed to be expressed in the breast muscle, and 173 differentially expressed genes (DEGs) were identified between the HB and LB groups. Functional analysis showed that these DEGs were mainly involved in biological processes and pathways of fat metabolism and muscle growth, especially the FABP3 and MYL4 involved in the PPAR signaling pathway and cardiac muscle contraction pathway. These findings deepened our understanding of the molecular mechanisms involved in muscle growth in ducks and provided a theoretical basis for improving duck production and breeding of ducks.

Slow or fast: Implications of myofibre type and associated differences for manifestation of neuromuscular disorders

Many neuromuscular disorders can have a differential impact on a specific myofibre type, forming the central premise of this review. The many different skeletal muscles in mammals contain a spectrum of slow- to fast-twitch myofibres with varying levels of protein isoforms that determine their distinctive contractile, metabolic, and other properties. The variations in functional properties across the range of classic 'slow' to 'fast' myofibres are outlined, combined with exemplars of the predominantly slow-twitch soleus and fast-twitch extensor digitorum longus muscles, species comparisons, and techniques used to study these properties. Other intrinsic and extrinsic differences are discussed in the context of slow and fast myofibres. These include inherent susceptibility to damage, myonecrosis, and regeneration, plus extrinsic nerves, extracellular matrix, and vasculature, examined in the context of growth, ageing, metabolic syndrome, and sexual dimorphism. These many differences emphasise the importance of carefully considering the influence of myofibre-type composition on manifestation of various neuromuscular disorders across the lifespan for both sexes. Equally, understanding the different responses of slow and fast myofibres due to intrinsic and extrinsic factors can provide deep insight into the precise molecular mechanisms that initiate and exacerbate various neuromuscular disorders. This focus on the influence of different myofibre types is of fundamental importance to enhance translation for clinical management and therapies for many skeletal muscle disorders.

AAV1.NT-3 gene therapy prevents age-related sarcopenia

Sarcopenia is progressive loss of muscle mass and strength, occurring during normal aging with significant consequences on the quality of life for elderly. Neurotrophin 3 (NT-3) is an important autocrine factor supporting Schwann cell survival and differentiation and stimulating axon regeneration and myelination. NT-3 is involved in the maintenance of neuromuscular junction (NMJ) integrity, restoration of impaired radial growth of muscle fibers through activation of the Akt/mTOR pathway. We tested the efficacy of NT-3 gene transfer therapy in wild type (WT)-aged C57BL/6 mice, a model for natural aging and sarcopenia, via intramuscular injection 1 × 1011 vg AAV1.tMCK.NT-3, at 18 months of age. The treatment efficacy was assessed at 6 months post-injection using run to exhaustion and rotarod tests, in vivo muscle contractility assay, and histopathological studies of the peripheral nervous system, including NMJ connectivity and muscle. AAV1.NT-3 gene therapy in WT-aged C57BL/6 mice resulted in functional and in vivo muscle physiology improvements, supported by quantitative histology from muscle, peripheral nerves and NMJ. Hindlimb and forelimb muscles in the untreated cohort showed the presence of a muscle- and sex-dependent remodeling and fiber size decrease with aging, which was normalized toward values obtained from 10 months old WT mice with treatment. The molecular studies assessing the NT-3 effect on the oxidative state of distal hindlimb muscles, accompanied by western blot analyses for mTORC1 activation were in accordance with the histological findings. Considering the cost and quality of life to the individual, we believe our study has important implications for management of age-related sarcopenia.

Anatomical variations of the flexor carpi ulnaris in the fetal period

Introduction: The Flexor Carpi Ulnaris (FCU) is a part of the palmar the forearm muscle group and one of the most important muscles for upper limb functioning - is responsible for flexion and adduc­tion of the hand at the radio-carpal joint. There are clinically significant but rare anatomical variations of FCU. The variability of the FCU has not been described up to now, and no typology of the muscle based on its more variable terminal attachment has been created. Aim of the study: Determination of FCU muscle typology based on available fetal material. Material and methods: A total of 114 human fetuses (53 female, 61 male) between 117 and 197 days of fetal life were eligible for the study. Preparations were carried out using classical anatomical techniques based on a previously published procedure. Thanks to that significant anthropometric landmarks were vis­ible for the gathering of metric measurements. Metric measurements were taken and statistically analysed using R-Project software. Results: A new typology was created based on variable muscle insertions. Additionally, the presence of an atypically located, additional, separated muscle belly was described. A comparison of measurements of the left upper limb in relation to the right upper limb showed significant differences for forearm length to the anthropometric point of the stylion radiale, limb length, total FCU length and FCU length which means that the left limb is longer than the right limb. A comparison of FCU insertion types between left and right upper limb showed there’s no significant difference between counts of each type. Conclusion: The FCU is a muscle that is easy to palpate and may therefore act as a topographical marker for healthcare professionals. Knowledge of its variability is not only of theoretical importance but also has clinical sig­nificance. The current publication demonstrates presence of variability in FCU terminal attachment. Certainly, this topic requires further research and continued work on a detailed understanding of forearm anatomy in the fetal period.

Cutting edge concepts: Does bilirubin enhance exercise performance?

Exercise performance is dependent on many factors, such as muscular strength and endurance, cardiovascular capacity, liver health, and metabolic flexibility. Recent studies show that plasma levels of bilirubin, which has classically been viewed as a liver dysfunction biomarker, are elevated by exercise training and that elite athletes may have significantly higher levels. Other studies have shown higher plasma bilirubin levels in athletes and active individuals compared to general, sedentary populations. The reason for these adaptions is unclear, but it could be related to bilirubin's antioxidant properties in response to a large number of reactive oxygen species (ROS) that originates from mitochondria during exercise. However, the mechanisms of these are unknown. Current research has re-defined bilirubin as a metabolic hormone that interacts with nuclear receptors to drive gene transcription, which reduces body weight. Bilirubin has been shown to reduce adiposity and improve the cardiovascular system, which might be related to the adaption of bilirubin increasing during exercise. No studies have directly tested if elevating bilirubin levels can influence athletic performance. However, based on the mechanisms proposed in the present review, this seems plausible and an area to consider for future studies. Here, we discuss the importance of bilirubin and exercise and how the combination might improve metabolic health outcomes and possibly athletic performance.

Muscle mitochondrial catalase expression prevents neuromuscular junction disruption, atrophy, and weakness in a mouse model of accelerated sarcopenia

BACKGROUND

Oxidative stress and damage are associated with a number of ageing phenotypes, including age-related loss of muscle mass and reduced contractile function (sarcopenia). Our group and others have reported loss of neuromuscular junction (NMJ) integrity and increased denervation as initiating factors in sarcopenia, leading to mitochondrial dysfunction, generation of reactive oxygen species and peroxides, and loss of muscle mass and weakness. Previous studies from our laboratory show that denervation-induced skeletal muscle mitochondrial peroxide generation is highly correlated to muscle atrophy. Here, we directly test the impact of scavenging muscle mitochondrial hydrogen peroxide on the structure and function of the NMJ and muscle mass and function in a mouse model of denervation-induced muscle atrophy CuZnSOD (Sod1^-/- mice, Sod1KO).

METHODS

Whole-body Sod1KO mice were crossed to mice with increased expression of human catalase (MCAT) targeted specifically to mitochondria in skeletal muscle (mMCAT mice) to determine the impact of reduced hydrogen peroxide levels on key targets of sarcopenia, including mitochondrial function, NMJ structure and function, and indices of muscle mass and function.

RESULTS

Female adult (~12-month-old) Sod1KO mice show a number of sarcopenia-related phenotypes in skeletal muscle including reduced mitochondrial oxygen consumption and elevated reactive oxygen species generation, fragmentation, and loss of innervated NMJs (P < 0.05), a 30% reduction in muscle mass (P < 0.05), a 36% loss of force generation (P < 0.05), and a loss of exercise capacity (305 vs. 709 m in wild-type mice, P < 0.05). Muscle from Sod1KO mice also shows a 35% reduction in sarco(endo)plasmic reticulum ATPase activity (P < 0.05), changes in the amount of calcium-regulating proteins, and altered fibre-type composition. In contrast, increased catalase expression in the mMCAT × Sod1KO mice completely prevents the mitochondrial and NMJ-related phenotypes and maintains muscle mass and force generation. The reduction in exercise capacity is also partially inhibited (~35%, P < 0.05), and the loss of fibre cross-sectional area is inhibited by ~50% (P < 0.05).

CONCLUSIONS

Together, these striking findings suggest that scavenging of mitochondrial peroxide generation by mMCAT expression efficiently prevents mitochondrial dysfunction and NMJ disruption associated with denervation-induced atrophy and weakness, supporting mitochondrial H₂ O₂ as an important effector of NMJ alterations that lead to phenotypes associated with sarcopenia.

Systemic delivery of AAVrh74.tMCK.hCAPN3 rescues the phenotype in a mouse model for LGMD2A/R1

Limb girdle muscular dystrophy (LGMD) 2A/R1, caused by mutations in the CAPN3 gene and CAPN3 loss of function, is known to play a role in disease pathogenicity. In this study, AAVrh74.tMCK.CAPN3 was delivered systemically to two different age groups of CAPN3 knockout (KO) mice; each group included two treatment cohorts receiving low (1.17 × 10¹⁴ vg/kg) and high (2.35 × 10¹⁴ vg/kg) doses of the vector and untreated controls. Treatment efficacy was tested 20 weeks after gene delivery using functional (treadmill), physiological (in vivo muscle contractility assay), and histopathological outcomes. AAV.CAPN3 gene therapy resulted in significant, robust improvements in functional outcomes and muscle physiology at low and high doses in both age groups. Histological analyses of skeletal muscle showed remodeling of muscle, a switch to fatigue-resistant oxidative fibers in females, and fiber size increases in both sexes. Safety studies revealed no organ tissue abnormalities; specifically, there was no histopathological evidence of cardiotoxicity. These results show that CAPN3 gene replacement therapy improved the phenotype in the CAPN3 KO mouse model at both doses independent of age at the time of vector administration. The improvements were supported by an absence of cardiotoxicity, showing the efficacy and safety of the AAV.CAPN3 vector as a potential gene therapy for LGMDR1.

Ketogenic diet feeding improves aerobic metabolism property in extensor digitorum longus muscle of sedentary male rats

Recent studies of the ketogenic diet, an extremely high-fat diet with extremely low carbohydrates, suggest that it changes the energy metabolism properties of skeletal muscle. However, ketogenic diet effects on muscle metabolic characteristics are diverse and sometimes countervailing. Furthermore, ketogenic diet effects on skeletal muscle performance are unknown. After male Wistar rats (8 weeks of age) were assigned randomly to a control group (CON) and a ketogenic diet group (KD), they were fed for 4 weeks respectively with a control diet (10% fat, 10% protein, 80% carbohydrate) and a ketogenic diet (90% fat, 10% protein, 0% carbohydrate). After the 4-week feeding period, the extensor digitorum longus (EDL) muscle was evaluated ex vivo for twitch force, tetanic force, and fatigue. We also analyzed the myosin heavy chain composition, protein expression of metabolic enzymes and regulatory factors, and citrate synthase activity. No significant difference was found between CON and KD in twitch or tetanic forces or muscle fatigue. However, the KD citrate synthase activity and the protein expression of Sema3A, citrate synthase, succinate dehydrogenase, cytochrome c oxidase subunit 4, and 3-hydroxyacyl-CoA dehydrogenase were significantly higher than those of CON. Moreover, a myosin heavy chain shift occurred from type IIb to IIx in KD. These results demonstrated that the 4-week ketogenic diet improves skeletal muscle aerobic capacity without obstructing muscle contractile function in sedentary male rats and suggest involvement of Sema3A in the myosin heavy chain shift of EDL muscle.

Physical fitness status modulates the inflammatory proteins in peripheral blood and circulating monocytes: role of PPAR-gamma

The aim of this study was to analyze the metabolic and molecular profile according to physical fitness status (Low or High VO_2max) and its impacts on peripheral and cellular inflammatory responses in healthy men. First (Phase I), inflammatory profile (TNF-α, IL-6, IL-10) was analyzed at baseline and post-acute exercise sessions performed at low (< 60% VO_2max) and high (> 90% VO_2max) intensities considering the individual endotoxin concentrations. Next (Phase II), monocyte cell cultures were treated with LPS alone or associated with Rosiglitazone (PPAR-γ agonist drug) to analyze cytokine production and gene expression. Monocyte subsets were also evaluated by flow cytometry. A positive relationship was observed between LPS concentrations and oxygen uptake (VO_2max) (r = 0.368; p = 0.007); however, in the post-exercise an inverse correlation was found between LPS variation (Δ%) and VO_2max (r = -0.385; p = 0.004). With the low-intensity exercise session, there was inverse correlation between LPS and IL-6 concentrations post-exercise (r = -0.505; p = 0.046) and a positive correlation with IL-10 in the recovery (1 h post) (r = 0.567; p = 0.011), whereas with the high-intensity exercise an inverse correlation was observed with IL-6 at pre-exercise (r = -0.621; p = 0.013) and recovery (r = -0.574; p = 0.016). When monocyte cells were treated with LPS, High VO_2max individuals showed higher PPAR-γ gene expression whereas Low VO_2max individuals displayed higher IL-10 production. Additionally, higher TLR-4, IKK1, and PGC-1α gene expression were observed in the High VO_2max group than Low VO_2max individuals. In conclusion, even with elevated endotoxemia, individuals with High VO_2max exhibited higher IL-6 concentration in peripheral blood post-acute aerobic exercise and lower IL-10 concentration during recovery (1 h post-exercise). The anti-inflammatory effects linked with exercise training and physical fitness status may be explained by a greater gene expression of IKK1, TLR-4, and PGC-1α, displaying an extremely efficient cellular framework for the PPAR-γ responses.

Chronic exercise provides renal-protective effects with upregulation of fatty acid oxidation in the kidney of high fructose-fed rats

Excessive fructose intake causes metabolic syndrome and lipid accumulation in the kidney and leads to renal dysfunction and damage. Exercise (Ex) improves lipids regulation, but the mechanisms are unclarified in the kidney. In the present study, male Sprague-Dawley rats were allocated to groups fed with control or high-fructose (HFr) diet. Part of rats in each group underwent aerobic treadmill Ex for 12 wk. Drug treatment was performed as the fenofibrate gavage during the last 4 wk on HFr diet-fed rats. Renal function, histological changes, and expression of regulators involved in fatty acid (FA) metabolism were assessed. In CON diet-fed groups, Ex did not affect renal function or histology and significantly increased renal expression of FA β-oxidation regulators including acyl-CoA dehydrogenases (CADs), acyl-CoA oxidase, peroxisome proliferator-activated receptor (PPAR)-α, and PPAR-γ coactivator (PGC)-1α and lipogenic factors including acetyl-CoA carboxylase (ACCα), FA synthase (FAS), and sterol regulatory element-binding protein 1c. HFr caused albuminuria, lipid accumulation, and renal pathohistological changes, which were attenuated by Ex but not by fenofibrate. HFr decreased renal expression of medium- and short-chain CADs and PPAR-α and increased renal expression of ACCα, FAS, and sterol regulatory element-binding protein 1c. Ex increased expression of CADs, carnitine palmitoyltransferase type I, acyl-CoA oxidase, PPAR-α, and PGC-1α and decreased renal expression of ACCα and FAS in HFr diet-fed rats. The Ex-induced FA metabolism alteration was similar to that in the fenofibrate-treated group. In conclusion, the present study indicates that Ex enhanced renal FA metabolism, which might protect the kidney in lipid dysregulation diseases.

Impact of exercise training status on the fiber type-specific abundance of proteins regulating intramuscular lipid metabolism

Endurance training enhances the capacity for fat oxidation during exercise due to increased utilization of intramuscular lipid (IMCL). This study quantitatively investigated the impact of exercise training status on muscle fiber type-specific abundance of regulatory proteins involved in IMCL utilization. Endurance-trained [n = 7 subjects, peak oxygen consumption (V̇o_2peak) 62.6 ± 4.1 (SD) mL·min^-1·kg^-1] and non-endurance-trained (n = 8 subjects, V̇o_2peak 44.9 ± 5.3 mL·min^-1·kg^-1) young men completed an incremental exercise test to determine maximal fat oxidation (MFO) and maximal oxygen uptake. Fiber type-specific IMCL content and protein abundance were assessed with immunofluorescence microscopy and immunoblot analysis of pooled single muscle fibers and whole muscle. Endurance-trained individuals displayed a higher MFO rate (0.45 ± 0.15 vs. 0.19 ± 0.07 g/min, P < 0.05), a greater proportion of type I muscle fibers, and higher IMCL content compared with untrained individuals (P < 0.05). Adipose triglyceride lipase, hormone-sensitive lipase, perilipin 2, perilipin 5, and hydroxyacyl-coenzyme A dehydrogenase abundances were ~2-3-fold higher in type I muscle fibers compared with type IIa fibers (P < 0.05). Correspondingly, these lipid proteins and oxidative enzymes were higher in endurance-trained individuals when assessed in whole muscle. MFO rate was strongly related to the proportion of type I fibers (R = 0.81, P < 0.01). The abundance of proteins involved in the regulation of IMCL storage and oxidation is highly muscle fiber type specific. The increased capacity for fat oxidation in endurance-trained individuals corresponded with increased IMCL content and elevated abundance of lipolytic and oxidative enzymes in combination with a greater proportion of type I muscle fibers.NEW & NOTEWORTHY We have utilized contemporary techniques to compare the fiber type-specific characteristics of skeletal muscle from endurance-trained athletes and untrained individuals. We show that type I muscle fibers have a coordinated upregulation of proteins controlling intramuscular lipid storage, mobilization, and oxidation. Furthermore, the enhanced capacity for intramuscular lipid storage and utilization in endurance-trained individuals is related to the increased expression of lipid regulatory proteins combined with a greater proportion of type I muscle fibers.

Activity-Based Physical Rehabilitation with Adjuvant Testosterone to Promote Neuromuscular Recovery after Spinal Cord Injury

Neuromuscular impairment and reduced musculoskeletal integrity are hallmarks of spinal cord injury (SCI) that hinder locomotor recovery. These impairments are precipitated by the neurological insult and resulting disuse, which has stimulated interest in activity-based physical rehabilitation therapies (ABTs) that promote neuromuscular plasticity after SCI. However, ABT efficacy declines as SCI severity increases. Additionally, many men with SCI exhibit low testosterone, which may exacerbate neuromusculoskeletal impairment. Incorporating testosterone adjuvant to ABTs may improve musculoskeletal recovery and neuroplasticity because androgens attenuate muscle loss and the slow-to-fast muscle fiber-type transition after SCI, in a manner independent from mechanical strain, and promote motoneuron survival. These neuromusculoskeletal benefits are promising, although testosterone alone produces only limited functional improvement in rodent SCI models. In this review, we discuss the (1) molecular deficits underlying muscle loss after SCI; (2) independent influences of testosterone and locomotor training on neuromuscular function and musculoskeletal integrity post-SCI; (3) hormonal and molecular mechanisms underlying the therapeutic efficacy of these strategies; and (4) evidence supporting a multimodal strategy involving ABT with adjuvant testosterone, as a potential means to promote more comprehensive neuromusculoskeletal recovery than either strategy alone.

An aPPARent Functional Consequence in Skeletal Muscle Physiology via Peroxisome Proliferator-Activated Receptors

Skeletal muscle comprises 30–40% of the total body mass and plays a central role in energy homeostasis in the body. The deregulation of energy homeostasis is a common underlying characteristic of metabolic syndrome. Over the past decades, peroxisome proliferator-activated receptors (PPARs) have been shown to play critical regulatory roles in skeletal muscle. The three family members of PPAR have overlapping roles that contribute to the myriad of processes in skeletal muscle. This review aims to provide an overview of the functions of different PPAR members in energy homeostasis as well as during skeletal muscle metabolic disorders, with a particular focus on human and relevant mouse model studies.

The carnitine status does not affect the contractile and metabolic phenotype of skeletal muscle in pigs

Background

Recently, supplementation of L-carnitine to obese rats was found to improve the carnitine status and to counteract an obesity-induced muscle fiber transition from type I to type II. However, it has not been resolved if the change of muscle fiber distribution induced in obese rats and the restoration of the "normal" muscle fiber distribution, which is found in lean rats, in obese rats by supplemental L-carnitine is causally linked with the carnitine status. In the present study we hypothesized that fiber type distribution in skeletal muscle is dependent on carnitine status.

Methods

To test this, an experiment with 48 piglets which were randomly allocated to four groups (n = 12) was performed. All piglets were given orally either 60 mg sodium bicarbonate/kg body weight (group CON), 20 mg L-carnitine and 60 mg sodium bicarbonate/kg body weight (group CARN), 30 mg pivalate (dissolved in sodium bicarbonate)/kg body weight (group PIV) or 20 mg L-carnitine and 30 mg pivalate/kg body weight (group CARN + PIV) each day for a period of 4 weeks.

Results

Concentrations of total carnitine in plasma, liver and longissimus dorsi and biceps femoris muscles were 2.0-2.7 fold higher in group CARN than in group CON, whereas these concentrations were 1.9-2.5-fold lower in group PIV than in group CON. The concentrations of total carnitine in these tissues did not statistically differ between group CARN + PIV and group CON. Fiber type distribution of longissimus dorsi and biceps femoris muscles, mRNA and protein levels of molecular regulators of fiber distribution in longissimus dorsi and biceps femoris muscles and mRNA levels of genes reflecting the metabolic phenotype of longissimus dorsi and biceps femoris muscles did not differ between groups.

Conclusion

Changes in the systemic carnitine status and the muscle carnitine concentration induced by either supplementing L-carnitine or administering pivalate have no impact on the contractile and metabolic phenotype of skeletal muscles in pigs.

Transcriptomic analysis of chicken Myozenin 3 regulation reveals its potential role in cell proliferation

Embryonic muscle development and fibre type differentiation has always been a topic of great importance due to its impact on both human health and farm animal financial values. Myozenin3 (Myoz3) is an important candidate gene that may regulate these processes. In the current study, we knocked down and overexpressed Myoz3 in chicken embryonic fibroblasts (CEFs) and chicken myoblasts, then utilized RNA-seq technology to screen genes, pathways and biological processes associated with Myoz3. Multiple differentially expressed genes were identified, including MYH10, MYLK2, NFAM1, MYL4, MYL9, PDZLIM1; those can in turn regulate each other and influence the development of muscle fibres. Gene ontology (GO) terms including some involved in positive regulation of cell proliferation were enriched. We further validated our results by testing the activity of cells by cell counting kit-8(CCK-8) and confirmed that under the condition of Myoz3 overexpression, the proliferation rate of CEFs and myoblasts was significantly upregulated, in addition, expression level of fast muscle specific gene was also significantly upregulated in myoblasts. Pathway enrichment analysis revealed that the PPAR (Peroxisome Proliferator-Activated Receptor) pathway was enriched, suggesting the possibility that Myoz3 regulates muscle fibre development and differentiation through the PPAR pathway. Our results provide valuable evidence regarding the regulatory functions of Myoz3 in embryonic cells by screening multiple candidate genes, biological processes and pathways associated with Myoz3.

Exercise training reverses inflammation and muscle wasting after tobacco smoke exposure

Long-term cigarette smoking induces inflammatory processes in the pulmonary system that are suggested to "spill over" into systemic inflammation. Regular exercise has been shown to have anti-inflammatory properties. The aim of the study was to investigate the effects of therapeutic exercise on inflammation and muscle wasting in smoke-exposed mice. C57BL/6J mice ( n = 30) were separated into three groups to receive either 1) no specific treatment (control group), 2) 8-mo exposure to cigarette smoke [smoke-exposed (SE) group], or 3) 8 mo of cigarette smoke combined with exercise training during the last 2 mo (SEex group). The inflammatory status was analyzed by quantifying levels of various plasma proteins using multiplex ELISA and detection of lymphocyte surface markers by flow cytometry. Muscle tissue was analyzed by histological techniques and measurements of RNA/protein expression. SE led to decreased maximal O₂ uptake (V̇o_2max) and maximal running speed ( V_max), which was reversed by exercise ( P < 0.05). Expression of ICAM-1, VCAM-1, and CD62L on T cells increased and was reversed by exercise ( P < 0.05). Similarly, SE induced an increase of various inflammatory cytokines, which were downregulated by exercise. In muscle, exercise improved the structure, oxidative capacity, and metabolism by reducing ubiquitin proteasome system activation, stimulating insulin-like growth factor 1 expression, and the SE-induced inhibition of mammalian target of rapamycin signaling pathway ( P < 0.05). Exercise training reverses smoke-induced decline in exercise capacity, systemic inflammation, and muscle wasting by addressing immune-regulating, anabolic, and metabolic pathways.

Peroxisome proliferator-activated receptor gamma co-activator 1 gene Gly482Ser polymorphism is associated with the response of low-density lipoprotein cholesterol concentrations to exercise training in elderly Japanese

Muscle peroxisome proliferator-activated receptor gamma co-activator 1 (PGC-1)α gene expression is influenced by the Gly482Ser gene polymorphism, which is a candidate genetic risk factor for diabetes mellitus and obesity. This study investigated the effects of PGC-1 gene Gly482Ser polymorphisms on alterations in glucose and lipid metabolism induced by exercise training. A 12-week intervention study was performed for 119 participants who were more than 65 years of age and completed exercise training at lactate threshold intensity. Total cholesterol and low-density lipoprotein cholesterol were significantly reduced in Gly/Gly but not in Gly/Ser and Ser/Ser participants after exercise. The Gly/Gly genotype of the PGC-1 gene Gly482Ser polymorphism influences the effects of moderate-intensity exercise training on low-density lipoprotein cholesterol and total cholesterol concentrations in older people.

Skeletal muscle mitochondrial mass is linked to lipid and metabolic profile in individuals with spinal cord injury

PURPOSE

Changes in metabolism and body composition after spinal cord injury (SCI) predispose individuals to obesity, type II diabetes, and cardiovascular disease. A link between lean mass and skeletal muscle mitochondrial mass has been reported but it is unknown how skeletal muscle mitochondrial mass and activity impact metabolic health. This study examined the relationship between skeletal muscle mitochondrial mass, activity and metabolic profile in individuals with chronic SCI.

METHODS

Twenty-two men with motor complete SCI participated in the study. Citrate synthase (CS) and complex III (CIII) activity was measured in vastus lateralis biopsies. Metabolic profile was assessed by intravenous glucose tolerance test, basal metabolic rate (BMR), maximum oxygen uptake (VO₂ peak) and blood lipid profile.

RESULTS

Skeletal muscle CS activity was negatively related to the cholesterol:high density lipoprotein cholesterol (HDL-C) ratio and triglycerides (r = -0.60, p = 0.009; r = -0.64, p = 0.004, respectively). CS activity was positively related to insulin sensitivity and BMR (r = 0.67, p = 0.006; r = 0.64, p = 0.005, respectively). Similar relationships were found for CIII and metabolic profile, but not CIII normalized to CS. Many of the relationships between CS and metabolism remained significant when age, level of injury, or time since injury were accounted for. They also remained significant when CS activity was normalized to total lean mass.

CONCLUSIONS

These results suggest that an increase in skeletal muscle mitochondrial mass is associated with improved metabolic health independent of age, level of injury, or time since injury in individuals with chronic SCI. This highlights the importance of maintaining and improving mitochondrial health in individuals with SCI.

Relationship between PPARα mRNA expression and mitochondrial respiratory function and ultrastructure of the skeletal muscle of patients with COPD

Peripheral muscle dysfunction is an important complication in patients with chronic obstructive pulmonary disease (COPD). The objective of this study was to explore the relationship between the levels of peroxisome proliferator-activated receptor α (PPARα) mRNA expression and the respiratory function and ultrastructure of mitochondria in the vastus lateralis of patients with COPD. Vastus lateralis biopsies were performed on 14 patients with COPD and 6 control subjects with normal lung function. PPARα mRNA levels in the muscle tissue were detected by real-time PCR. A Clark oxygen electrode was used to assess mitochondrial respiratory function. Mitochondrial number, fractional area in skeletal muscle cross-sections, and Z-line width were observed via transmission electron microscopy. The PPARα mRNA expression was significantly lower in COPD patients with low body mass index (BMIL) than in both COPD patients with normal body mass index (BMIN) and controls. Mitochondrial respiratory function (assessed by respiratory control ratio) was impaired in COPD patients, particularly in BMIL. Compared with that in the control group, mitochondrial number and fractional area were lower in the BMIL group, but were maintained in the BMIN group. Further, the Z-line became narrow in the BMIL group. PPARα mRNA expression was positively related to mitochondrial respiratory function and volume density. In COPD patients with BMIN, mitochondria volume density was maintained, while respiratory function decreased, whereas both volume density and respiratory function decreased in COPD patients with BMIL. PPARα mRNA expression levels are associated with decreased mitochondrial respiratory function and volume density, which may contribute to muscle dysfunction in COPD patients.

Exercise-induced modification of the skeletal muscle transcriptome in Arabian horses

It has been found that Arabian and Thoroughbred horses differ in muscle fiber structure and thus in physiological changes occurring in muscles during exercise. The aim of the present study was to identify the global gene expression modifications that occur in skeletal muscle following a training regime to prepare for flat racing. Whole transcriptomes of muscle (gluteus medius) were compared between three time points of tissue collection: T0 (untrained horses), T1 (horses after intense gallop phase), and T2 (horses at the end of racing season), 23 samples in total. The numerous groups of exercise-regulated differentially expressed genes (DEGs) were related to muscle cell structure and signaling and included insulin-like growth factor 1 receptor ( IGF1R), insulin receptor ( INSR), transforming growth factor beta receptors 1 and 2 ( TGFBR1, TGFBR2), vascular endothelial growth factor B ( VEGFB); epidermal growth factor ( EGF), hepatocyte growth factor ( HGF), and vascular endothelial growth factor D ( FIGF). In Arabian horses, exercise modified the expression of genes belonging to the PPAR signaling pathway (e.g., PPARA, PPARD, and PLIN2), calcium signaling pathway, and pathways associated with metabolic processes (e.g., oxidative phosphorylation, fatty acid metabolism, glycolysis/gluconeogenesis, and citrate cycle). According to detected gene expression modifications, our results suggested that in Arabian horses, exercise switches energy generation toward fatty acid utilization and enhances glycogen transport and calcium signaling. The use of the RNA-Seq approach in analyzing the skeletal muscle transcriptome allowed for the proposal of a panel of new candidate genes potentially related to body homeostasis maintenance and racing performance in Arabian horses.

Effects of Testosterone and Evoked Resistance Exercise after Spinal Cord Injury (TEREX-SCI): study protocol for a randomised controlled trial

INTRODUCTION

Individuals with spinal cord injury (SCI) are at a lifelong risk of obesity and chronic metabolic disorders including insulin resistance and dyslipidemia. Within a few weeks of injury, there is a significant decline in whole body fat-free mass, particularly lower extremity skeletal muscle mass, and subsequent increase in fat mass (FM). This is accompanied by a decrease in anabolic hormones including testosterone. Testosterone replacement therapy (TRT) has been shown to increase skeletal muscle mass and improve metabolic profile. Additionally, resistance training (RT) has been shown to increase lean mass and reduce metabolic disturbances in SCI and other clinical populations.

METHODS AND ANALYSIS

26 individuals with chronic, motor complete SCI between 18 and 50 years old were randomly assigned to a RT+TRT group (n=13) or a TRT group (n=13). 22 participants completed the initial 16-week training phase of the study and 4 participants withdrew. 12 participants of the 22 completed 16 weeks of detraining. The TRT was provided via transdermal testosterone patches (4-6 mg/day). The RT+TRT group had 16 weeks of supervised unilateral progressive RT using surface neuromuscular electrical stimulation with ankle weights. This study will investigate the effects of evoked RT+TRT or TRT alone on body composition (muscle cross-sectional area, visceral adipose tissue, %FM) and metabolic profile (glucose and lipid metabolism) in individuals with motor complete SCI. Findings from this study may help in designing exercise therapies to alleviate the deterioration in body composition after SCI and decrease the incidence of metabolic disorders in this clinical population.

ETHICS AND DISSEMINATION

The study is currently approved by the McGuire VA Medical Center and Virginia Commonwealth University. All participants read and signed approved consent forms. Results will be submitted to peer-reviewed journals and presented at national and international conferences.

TRIAL REGISTRATION NUMBER

Pre-result, NCT01652040.

Overexpression of PGC-1α increases peroxisomal activity and mitochondrial fatty acid oxidation in human primary myotubes

Peroxisomes are indispensable organelles for lipid metabolism in humans, and their biogenesis has been assumed to be under regulation by peroxisome proliferator-activated receptors (PPARs). However, recent studies in hepatocytes suggest that the mitochondrial proliferator PGC-1α (peroxisome proliferator-activated receptor gamma coactivator-1α) also acts as an upstream transcriptional regulator for enhancing peroxisomal abundance and associated activity. It is unknown whether the regulatory mechanism(s) for enhancing peroxisomal function is through the same node as mitochondrial biogenesis in human skeletal muscle (HSkM) and whether fatty acid oxidation (FAO) is affected. Primary myotubes from vastus lateralis biopsies from lean donors (BMI = 24.0 ± 0.6 kg/m²; n = 6) were exposed to adenovirus encoding human PGC-1α or GFP control. Peroxisomal biogenesis proteins (peroxins) and genes (PEXs) responsible for proliferation and functions were assessed by Western blotting and real-time qRT-PCR, respectively. [1-¹⁴C]palmitic acid and [1-¹⁴C]lignoceric acid (exclusive peroxisomal-specific substrate) were used to assess mitochondrial oxidation of peroxisomal-derived metabolites. After overexpression of PGC-1α, 1) peroxisomal membrane protein 70 kDa (PMP70), PEX19, and mitochondrial citrate synthetase protein content were significantly elevated (P < 0.05), 2) PGC-1α, PMP70, key PEXs, and peroxisomal β-oxidation mRNA expression levels were significantly upregulated (P < 0.05), and 3) a concomitant increase in lignoceric acid oxidation by both peroxisomal and mitochondrial activity was observed (P < 0.05). These novel findings demonstrate that, in addition to the proliferative effect on mitochondria, PGC-1α can induce peroxisomal activity and accompanying elevations in long-chain and very-long-chain fatty acid oxidation by a peroxisomal-mitochondrial functional cooperation, as observed in HSkM cells.

Muscle fiber-type conversion in the transgenic pigs with overexpression of PGC1α gene in muscle

The peroxisome proliferator-activated receptor gamma, co-activator 1 alpha(PGC1α) effectively induced the biosynthesis of the mitochondria and the energy metabolism, and also regulated the muscle fiber-type shift. Overexpression of PGC1α gene in mice led to higher oxidative muscle fiber composition in muscle. However, no researches about the significant differences of muscle fiber phenotype in pigs after PGC1α overexpression had been reported. The composition of muscle fiber-types which were distinguished by four myosin heavy chain(MYHC) isoforms, can significantly affect the muscle functions. In our study, we generated the transgenic pigs to investigate the effect of overexpression of PGC1α gene on muscle fiber-type conversion. The results showed that the number of oxidative muscle fiber(type1 muscle fiber) was increased and the number of glycolytic muscle fiber(type2b muscle fiber) was decreased in the transgenic pigs. Furthermore, we found that PGC1α overexpression up-regulated the expression of MYHC1 and MYHC2a and down-regulated the expression of MYHC2b.The analysis of genes expression demonstrated the main differentially expressed genes were MSTN, Myog and FOXO1. In conclusion, the overexpression of PGC1α gene can promote the glycolytic muscle fiber transform to the oxidative muscle fiber in pigs.

Skeletal muscle fiber type: using insights from muscle developmental biology to dissect targets for susceptibility and resistance to muscle disease

Skeletal muscle fibers are classified into fiber types, in particular, slow twitch versus fast twitch. Muscle fiber types are generally defined by the particular myosin heavy chain isoforms that they express, but many other components contribute to a fiber's physiological characteristics. Skeletal muscle fiber type can have a profound impact on muscle diseases, including certain muscular dystrophies and sarcopenia, the aging-induced loss of muscle mass and strength. These findings suggest that some muscle diseases may be treated by shifting fiber type characteristics either from slow to fast, or fast to slow phenotypes, depending on the disease. Recent studies have begun to address which components of muscle fiber types mediate their susceptibility or resistance to muscle disease. However, for many diseases it remains largely unclear why certain fiber types are affected. A substantial body of work has revealed molecular pathways that regulate muscle fiber type plasticity and early developmental muscle fiber identity. For instance, recent studies have revealed many factors that regulate muscle fiber type through modulating the activity of the muscle regulatory transcription factor MYOD1. Future studies of muscle fiber type development in animal models will continue to enhance our understanding of factors and pathways that may provide therapeutic targets to treat muscle diseases. WIREs Dev Biol 2016, 5:518-534. doi: 10.1002/wdev.230 For further resources related to this article, please visit the WIREs website.

PPARδ preserves a high resistance to fatigue in the mouse medial gastrocnemius after spinal cord transection

INTRODUCTION

Skeletal muscle oxidative capacity decreases and fatigability increases after spinal cord injury. Transcription factor peroxisome proliferator-activated receptor δ (PPARδ) promotes a more oxidative phenotype.

METHODS

We asked whether PPARδ overexpression could ameliorate these deficits in the medial gastrocnemius of spinal cord transected (ST) adult mice.

RESULTS

Time-to-peak tension and half-relaxation times were longer in PPARδ-Con and PPARδ-ST compared with littermate wild-type (WT) controls. Fatigue index was 50% higher in PPARδ-Con than WT-Con and 70% higher in the PPARδ-ST than WT-ST. There was an overall higher percent of darkly stained fibers for succinate dehydrogenase in both PPARδ groups.

CONCLUSIONS

The results indicate a conversion toward slower, more oxidative, and less fatigable muscle properties with overexpression of PPARδ. Importantly, the elevated fatigue resistance was maintained after ST, suggesting that enhanced PPARδ expression, and possibly small molecule agonists, could ameliorate the increased fatigability routinely observed in chronically paralyzed muscles.

MicroRNA-208b progressively declines after spinal cord injury in humans and is inversely related to myostatin expression

The effects of long-term physical inactivity on the expression of microRNAs involved in the regulation of skeletal muscle mass in humans are largely unknown. MicroRNAs are short, noncoding RNAs that fine-tune target expression through mRNA degradation or by inhibiting protein translation. Intronic to the slow, type I, muscle fiber type genes MYH7 and MYH7b, microRNA-208b and microRNA-499-5p are thought to fine-tune the expression of genes important for muscle growth, such as myostatin. Spinal cord injured humans are characterized by both skeletal muscle atrophy and transformation toward fast-twitch, type II fibers. We determined the expression of microRNA-208b, microRNA-499-5p, and myostatin in human skeletal muscle after complete cervical spinal cord injury. We also determined whether these microRNAs altered myostatin expression in rodent skeletal muscle. A progressive decline in skeletal muscle microRNA-208b and microRNA-499-5p expression occurred in humans during the first year after spinal cord injury and with long-standing spinal cord injury. Expression of myostatin was inversely correlated with microRNA-208b and microRNA-499-5p in human skeletal muscle after spinal cord injury. Overexpression of microRNA-208b in intact mouse skeletal muscle decreased myostatin expression, whereas microRNA-499-5p was without effect. In conclusion, we provide evidence for an inverse relationship between expression of microRNA-208b and its previously validated target myostatin in humans with severe skeletal muscle atrophy. Moreover, we provide direct evidence that microRNA-208b overexpression decreases myostatin gene expression in intact rodent muscle. Our results implicate that microRNA-208b modulates myostatin expression and this may play a role in the regulation of skeletal muscle mass following spinal cord injury.

Exercise training in chronic heart failure: improving skeletal muscle O2 transport and utilization

Chronic heart failure (CHF) impairs critical structural and functional components of the O2 transport pathway resulting in exercise intolerance and, consequently, reduced quality of life. In contrast, exercise training is capable of combating many of the CHF-induced impairments and enhancing the matching between skeletal muscle O2 delivery and utilization (Q̇mO2 and V̇mO2 , respectively). The Q̇mO2 /V̇mO2 ratio determines the microvascular O2 partial pressure (PmvO2 ), which represents the ultimate force driving blood-myocyte O2 flux (see Fig. 1). Improvements in perfusive and diffusive O2 conductances are essential to support faster rates of oxidative phosphorylation (reflected as faster V̇mO2 kinetics during transitions in metabolic demand) and reduce the reliance on anaerobic glycolysis and utilization of finite energy sources (thus lowering the magnitude of the O2 deficit) in trained CHF muscle. These adaptations contribute to attenuated muscle metabolic perturbations (e.g., changes in [PCr], [Cr], [ADP], and pH) and improved physical capacity (i.e., elevated critical power and maximal V̇mO2 ). Preservation of such plasticity in response to exercise training is crucial considering the dominant role of skeletal muscle dysfunction in the pathophysiology and increased morbidity/mortality of the CHF patient. This brief review focuses on the mechanistic bases for improved Q̇mO2 /V̇mO2 matching (and enhanced PmvO2 ) with exercise training in CHF with both preserved and reduced ejection fraction (HFpEF and HFrEF, respectively). Specifically, O2 convection within the skeletal muscle microcirculation, O2 diffusion from the red blood cell to the mitochondria, and muscle metabolic control are particularly susceptive to exercise training adaptations in CHF. Alternatives to traditional whole body endurance exercise training programs such as small muscle mass and inspiratory muscle training, pharmacological treatment (e.g., sildenafil and pentoxifylline), and dietary nitrate supplementation are also presented in light of their therapeutic potential. Adaptations within the skeletal muscle O2 transport and utilization system underlie improvements in physical capacity and quality of life in CHF and thus take center stage in the therapeutic management of these patients.

Pathogenesis of the limb manifestations and exercise limitations in peripheral artery disease

Patients with peripheral artery disease have a marked reduction in exercise performance and daily ambulatory activity irrespective of their limb symptoms of classic or atypical claudication. This review will evaluate the multiple pathophysiologic mechanisms underlying the exercise impairment in peripheral artery disease based on an evaluation of the current literature and research performed by the authors. Peripheral artery disease results in atherosclerotic obstructions in the major conduit arteries supplying the lower extremities. This arterial disease process impairs the supply of oxygen and metabolic substrates needed to match the metabolic demand generated by active skeletal muscle during walking exercise. However, the hemodynamic impairment associated with the occlusive disease process does not fully account for the reduced exercise impairment, indicating that additional pathophysiologic mechanisms contribute to the limb manifestations. These mechanisms include a cascade of pathophysiological responses during exercise-induced ischemia and reperfusion at rest that are associated with endothelial dysfunction, oxidant stress, inflammation, and muscle metabolic abnormalities that provide opportunities for targeted therapeutic interventions to address the complex pathophysiology of the exercise impairment in peripheral artery disease.

Time course of cigarette smoke-induced changes of systemic inflammation and muscle structure

It has become more evident that long-term cigarette smoking (LTCS) has an important extrapulmonary toxicity. The aim of the study was to investigate the time-dependent effects of cigarette smoke exposure on exercise capacity, markers of systemic inflammation, and skeletal muscle structure. c57bl/6j-mice were either exposed to mainstream cigarette smoke for 6 h/day, 5 days/wk [smoke-exposed (SE) group] or assigned to the control, unexposed group (Con group). SE group mice were exposed for 8, 16, 24, and 32 wk to smoke and unexposed Con mice were used as age-matched controls. Exercise capacity was investigated by spiroergometry. Systemic inflammatory status was analyzed by flow cytometry and multiplexed fluorescent immunoassay. For analysis of muscle tissue, histological techniques and microarray analysis were used. Mice of the SE group exhibited a lower increase of body mass and a decrease of V̇o2 max (P < 0.05). An increase of lymphocyte CD62, ICAM, and VCAM expression was found in SE mice (P < 0.05). A biphasic trend of protein up- and downregulation was observed in markers of systemic inflammation, tissue deterioration, and allergic reactions such as C-reactive protein (CRP), eotaxin, haptoglobin, macrophage colony-stimulating factor-1 (M-CSF-1), and macrophage inflammatory protein-1γ (MIP-1γ). Thereby, the expression of several chemotactic proteins in plasma correlated with their expression in muscle. A time-dependent decrease of muscle mass, oxidative type-I fibers, and muscle cross-sectional area was found (P < 0.05). Microarray analysis revealed a SE-induced upregulation of several pathways of metabolic processes and tissue degradation. Taken together it was found that the loss of exercise capacity and systemic inflammation are early events of SE, which might induce muscular atrophy and loss of oxidative muscle capacity.

Peroxisome proliferator-activated receptor β/δ: a master regulator of metabolic pathways in skeletal muscle

Skeletal muscle is considered to be a major site of energy expenditure and thus is important in regulating events affecting metabolic disorders. Over the years, both in vitro and in vivo approaches have established the role of peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) in fatty acid metabolism and energy expenditure in skeletal muscles. Pharmacological activation of PPARβ/δ by specific ligands regulates the expression of genes involved in lipid use, triglyceride hydrolysis, fatty acid oxidation, energy expenditure, and lipid efflux in muscles, in turn resulting in decreased body fat mass and enhanced insulin sensitivity. Both the lipid-lowering and the anti-diabetic effects exerted by the induction of PPARβ/δ result in the amelioration of symptoms of metabolic disorders. This review summarizes the action of PPARβ/δ activation in energy metabolism in skeletal muscles and also highlights the unexplored pathways in which it might have potential effects in the context of muscular disorders. Numerous preclinical studies have identified PPARβ/δ as a probable potential target for therapeutic interventions. Although PPARβ/δ agonists have not yet reached the market, several are presently being investigated in clinical trials.

The single nucleotide polymorphism Gly482Ser in the PGC-1α gene impairs exercise-induced slow-twitch muscle fibre transformation in humans

PGC-1α (peroxisome proliferator-activated receptor γ co-activator 1α) is an important regulator of mitochondrial biogenesis and a master regulator of enzymes involved in oxidative phosphorylation. Recent evidence demonstrated that the Gly482Ser single nucleotide polymorphism (SNP) in the PGC-1α gene affects insulin sensitivity, blood lipid metabolism and binding to myocyte enhancer factor 2 (MEF2). Individuals carrying this SNP were shown to have a reduced cardiorespiratory fitness and a higher risk to develop type 2 diabetes. Here, we investigated the responses of untrained men with the Gly482Ser SNP to a 10 week programme of endurance training (cycling, 3 x 60 min/week, heart rate at 70-90% VO_2peak). Quantitative data from analysis of biopsies from vastus lateralis muscle revealed that the SNP group, in contrast to the control group, lacked a training-induced increase in content of slow contracting oxidative fibres. Capillary supply, mitochondrial density, mitochondrial enzyme activities and intramyocellular lipid content increased similarly in both groups. These results indicate that the impaired binding of MEF2 to PGC-1α in humans with this SNP impedes exercise-induced fast-to-slow muscle fibre transformation.

Impact of oxidative stress on exercising skeletal muscle

It is well established that muscle contractions during exercise lead to elevated levels of reactive oxygen species (ROS) in skeletal muscle. These highly reactive molecules have many deleterious effects, such as a reduction of force generation and increased muscle atrophy. Since the discovery of exercise-induced oxidative stress several decades ago, evidence has accumulated that ROS produced during exercise also have positive effects by influencing cellular processes that lead to increased expression of antioxidants. These molecules are particularly elevated in regularly exercising muscle to prevent the negative effects of ROS by neutralizing the free radicals. In addition, ROS also seem to be involved in the exercise-induced adaptation of the muscle phenotype. This review provides an overview of the evidences to date on the effects of ROS in exercising muscle. These aspects include the sources of ROS, their positive and negative cellular effects, the role of antioxidants, and the present evidence on ROS-dependent adaptations of muscle cells in response to physical exercise.

Carbohydrate restricted recovery from long term endurance exercise does not affect gene responses involved in mitochondrial biogenesis in highly trained athletes

The aim was to determine if the metabolic adaptations, particularly PGC-1α and downstream metabolic genes were affected by restricting CHO following an endurance exercise bout in trained endurance athletes. A second aim was to compare baseline expression level of these genes to untrained. Elite endurance athletes (VO2max 66 ± 2 mL·kg(-1)·min(-1), n = 15) completed 4 h cycling at ~56% VO2max. During the first 4 h recovery subjects were provided with either CHO or only H2O and thereafter both groups received CHO. Muscle biopsies were collected before, after, and 4 and 24 h after exercise. Also, resting biopsies were collected from untrained subjects (n = 8). Exercise decreased glycogen by 67.7 ± 4.0% (from 699 ± 26.1 to 239 ± 29.5 mmol·kg(-1)·dw(-1)) with no difference between groups. Whereas 4 h of recovery with CHO partly replenished glycogen, the H2O group remained at post exercise level; nevertheless, the gene expression was not different between groups. Glycogen and most gene expression levels returned to baseline by 24 h in both CHO and H2O. Baseline mRNA expression of NRF-1, COX-IV, GLUT4 and PPAR-α gene targets were higher in trained compared to untrained. Additionally, the proportion of type I muscle fibers positively correlated with baseline mRNA for PGC-1α, TFAM, NRF-1, COX-IV, PPAR-α, and GLUT4 for both trained and untrained. CHO restriction during recovery from glycogen depleting exercise does not improve the mRNA response of markers of mitochondrial biogenesis. Further, baseline gene expression of key metabolic pathways is higher in trained than untrained.

Physiological functions of peroxisome proliferator-activated receptor β

The peroxisome proliferator-activated receptors, PPARα, PPARβ, and PPARγ, are a family of transcription factors activated by a diversity of molecules including fatty acids and fatty acid metabolites. PPARs regulate the transcription of a large variety of genes implicated in metabolism, inflammation, proliferation, and differentiation in different cell types. These transcriptional regulations involve both direct transactivation and interaction with other transcriptional regulatory pathways. The functions of PPARα and PPARγ have been extensively documented mainly because these isoforms are activated by molecules clinically used as hypolipidemic and antidiabetic compounds. The physiological functions of PPARβ remained for a while less investigated, but the finding that specific synthetic agonists exert beneficial actions in obese subjects uplifted the studies aimed to elucidate the roles of this PPAR isoform. Intensive work based on pharmacological and genetic approaches and on the use of both in vitro and in vivo models has considerably improved our knowledge on the physiological roles of PPARβ in various cell types. This review will summarize the accumulated evidence for the implication of PPARβ in the regulation of development, metabolism, and inflammation in several tissues, including skeletal muscle, heart, skin, and intestine. Some of these findings indicate that pharmacological activation of PPARβ could be envisioned as a therapeutic option for the correction of metabolic disorders and a variety of inflammatory conditions. However, other experimental data suggesting that activation of PPARβ could result in serious adverse effects, such as carcinogenesis and psoriasis, raise concerns about the clinical use of potent PPARβ agonists.

Irisin and FNDC5: effects of 12-week strength training, and relations to muscle phenotype and body mass composition in untrained women

PURPOSE

To investigate the effects of strength training on abundances of irisin-related biomarkers in skeletal muscle and blood of untrained young women, and their associations with body mass composition, muscle phenotype and levels of thyroid hormones.

METHODS

Eighteen untrained women performed 12 weeks of progressive whole-body heavy strength training, with measurement of strength, body composition, expression of irisin-related genes (FNDC5 and PGC1α) in two different skeletal muscles, and levels of serum-irisin and -thyroid hormones, before and after the training intervention.

RESULTS

The strength training intervention did not result in changes in serum-irisin or muscle FNDC5 expression, despite considerable effects on strength, lean body mass (LBM) and skeletal muscle phenotype. Our data indicate that training affects irisin biology in a LBM-dependent manner. However, no association was found between steady-state serum-irisin or training-associated changes in serum-irisin and alterations in body composition. FNDC5 expression was higher in m.Biceps brachii than in m.Vastus lateralis, with individual expression levels being closely correlated, suggesting a systemic mode of transcriptional regulation. In pre-biopsies, FNDC5 expression was correlated with proportions of aerobic muscle fibers, a relationship that disappeared in post-biopsies. No association was found between serum-thyroid hormones and FNDC5 expression or serum-irisin.

CONCLUSION

No evidence was found for an effect of strength training on irisin biology in untrained women, though indications were found for a complex interrelationship between irisin, body mass composition and muscle phenotype. FNDC5 expression was closely associated with muscle fiber composition in untrained muscle.

From gene engineering to gene modulation and manipulation: can we prevent or detect gene doping in sports?

During the last 2 decades, progress in deciphering the human gene map as well as the discovery of specific defective genes encoding particular proteins in some serious human diseases have resulted in attempts to treat sick patients with gene therapy. There has been considerable focus on human recombinant proteins which were gene-engineered and produced in vitro (insulin, growth hormone, insulin-like growth factor-1, erythropoietin). Unfortunately, these substances and methods also became improper tools for unscrupulous athletes. Biomedical research has focused on the possible direct insertion of gene material into the body, in order to replace some defective genes in vivo and/or to promote long-lasting endogenous synthesis of deficient proteins. Theoretically, diabetes, anaemia, muscular dystrophies, immune deficiency, cardiovascular diseases and numerous other illnesses could benefit from such innovative biomedical research, though much work remains to be done. Considering recent findings linking specific genotypes and physical performance, it is tempting to submit the young athletic population to genetic screening or, alternatively, to artificial gene expression modulation. Much research is already being conducted in order to achieve a safe transfer of genetic material to humans. This is of critical importance since uncontrolled production of the specifically coded protein, with serious secondary adverse effects (polycythaemia, acute cardiovascular problems, cancer, etc.), could occur. Other unpredictable reactions (immunogenicity of vectors or DNA-vector complex, autoimmune anaemia, production of wild genetic material) also remain possible at the individual level. Some new substances (myostatin blockers or anti-myostatin antibodies), although not gene material, might represent a useful and well-tolerated treatment to prevent progression of muscular dystrophies. Similarly, other molecules, in the roles of gene or metabolic activators [5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside (AICAR), GW1516], might concomitantly improve endurance exercise capacity in ischaemic conditions but also in normal conditions. Undoubtedly, some athletes will attempt to take advantage of these new molecules to increase strength or endurance. Antidoping laboratories are improving detection methods. These are based both on direct identification of new substances or their metabolites and on indirect evaluation of changes in gene, protein or metabolite patterns (genomics, proteomics or metabolomics).

Molecular mechanisms of muscle plasticity with exercise

The skeletal muscle phenotype is subject to considerable malleability depending on use. Low-intensity endurance type exercise leads to qualitative changes of muscle tissue characterized mainly by an increase in structures supporting oxygen delivery and consumption. High-load strength-type exercise leads to growth of muscle fibers dominated by an increase in contractile proteins. In low-intensity exercise, stress-induced signaling leads to transcriptional upregulation of a multitude of genes with Ca(2+) signaling and the energy status of the muscle cells sensed through AMPK being major input determinants. Several parallel signaling pathways converge on the transcriptional co-activator PGC-1α, perceived as being the coordinator of much of the transcriptional and posttranscriptional processes. High-load training is dominated by a translational upregulation controlled by mTOR mainly influenced by an insulin/growth factor-dependent signaling cascade as well as mechanical and nutritional cues. Exercise-induced muscle growth is further supported by DNA recruitment through activation and incorporation of satellite cells. Crucial nodes of strength and endurance exercise signaling networks are shared making these training modes interdependent. Robustness of exercise-related signaling is the consequence of signaling being multiple parallel with feed-back and feed-forward control over single and multiple signaling levels. We currently have a good descriptive understanding of the molecular mechanisms controlling muscle phenotypic plasticity. We lack understanding of the precise interactions among partners of signaling networks and accordingly models to predict signaling outcome of entire networks. A major current challenge is to verify and apply available knowledge gained in model systems to predict human phenotypic plasticity.

Insulin, IGF-I, and muscle MAPK pathway responses after sustained exercise and their contribution to growth and lipid metabolism regulation in gilthead sea bream

Herein, we studied whether sustained exercise positively affects growth of gilthead sea bream by alterations in a) plasma concentrations of insulin and IGF-I, b) signaling pathways in muscle, or c) regulation of lipid metabolism. Specifically, we evaluated the effects of moderated swimming (1.5 body lengths per second; BL/s) on the circulating concentrations of insulin and IGF-I, morphometric parameters, and expression of genes related to lipid metabolism in gilthead sea bream (80-90 g BW). Exercise increased the specific growth rate (P < 0.05) and reduced the hepatosomatic index (P = 0.006). Plasma IGF-I concentrations increased in exercised fish (P = 0.037), suggesting a role for this endocrine factor in the control of muscular growth and metabolic homeostasis during swimming. The observed decrease in plasma insulin concentrations (P = 0.016) could favor the mobilization of tissue reserves in exercised fish. In this sense, the increase in liver fatty acid content (P = 0.041) and the changes in expression of peroxisome proliferator-activated receptors PPARα (P = 0.017) and PPARγ (P = 0.033) indicated a hepatic lipid mobilization. Concentration of glycogen in both white and red muscles was decreased (P = 0.021 and P = 0.017, respectively) in exercised (n = 12) relative to control (n = 12) gilthead sea bream, whereas concentrations of glucose (P = 0.016) and lactate (P = 0.0007) were decreased only in red muscle, indicating the use of these substrates. No changes in the glucose transporter and in lipoprotein lipase mRNA expression were found in any of the tissues studied. Exercised sea bream had decreased content of PPARβ mRNA in white and red muscle relative to control sea bream expression (P = 0.001 and P = 0.049, respectively). Mitogen-activated protein kinase phosphorylation was significantly down-regulated in both white and red muscles of exercised sea bream (P = 0.0374 and P = 0.0371, respectively). Tumor necrosis factor-α expression of white muscle was down-regulated in exercised gilthead sea bream (P = 0.045). Collectively, these results contribute to the knowledge base about hormonal regulation of growth and lipid metabolism in exercised gilthead sea bream.

Are cultured human myotubes far from home?

Satellite cells can be isolated from skeletal muscle biopsies, activated to proliferating myoblasts and differentiated into multinuclear myotubes in culture. These cell cultures represent a model system for intact human skeletal muscle and can be modulated ex vivo. The advantages of this system are that the most relevant genetic background is available for the investigation of human disease (as opposed to rodent cell cultures), the extracellular environment can be precisely controlled and the cells are not immortalized, thereby offering the possibility of studying innate characteristics of the donor. Limitations in differentiation status (fiber type) of the cells and energy metabolism can be improved by proper treatment, such as electrical pulse stimulation to mimic exercise. This review focuses on the way that human myotubes can be employed as a tool for studying metabolism in skeletal muscles, with special attention to changes in muscle energy metabolism in obesity and type 2 diabetes.

microRNAs regulate adipocyte differentiation

The number of adipocytes is relevant to the extent of differentiation from pluripotent stem cells into pre-adipocytes, whereas the size of adipocytes relates to the extent of differentiation from pre-adipocytes into mature fat cells and the accumulation of triglyceride. Investigation of the molecular regulatory mechanism of adipocyte differentiation is not only essential for understanding the physiological processes of adipogenesis, but it is also important for identifying new biomarkers and therapeutic targets for some metabolic diseases, such as obesity and diabetes. microRNAs (miRNAs) appear to play important roles in adipocyte differentiation. During adipogenesis, miRNAs can accelerate or inhibit adipocyte differentiation by acting on transcription factors, regulating signalling pathways related to adipogenesis, or blocking the mitotic clonal expansion stage, thus regulating adipocyte development. The regulatory role of some miRNAs varies in different species or different cells. In this review, the biological characteristics of miRNA and the adipocyte differentiation process are concisely discussed. Recent advances in our understanding of the role of miRNAs in adipocytes development or adipogenesis are discussed.

Muscle development and obesity: Is there a relationship?

The formation of skeletal muscle from the epithelial somites involves a series of events triggered by temporally and spatially discrete signals resulting in the generation of muscle fibers which vary in their contractile and metabolic nature. The fiber type composition of muscles varies between individuals and it has now been found that there are differences in fiber type proportions between lean and obese animals and humans. Amongst the possible causes of obesity, it has been suggested that inappropriate prenatal environments may 'program' the fetus and may lead to increased risks for disease in adult life. The characteristics of muscle are both heritable and plastic, giving the tissue some ability to adapt to signals and stimuli both pre and postnatally. Given that muscle is a site of fatty acid oxidation and carbohydrate metabolism and that its development can be changed by prenatal events, it is interesting to examine the possible relationship between muscle development and the risk of obesity.

Muscle fiber type-dependent differences in the regulation of protein synthesis

This study examined fiber type-dependent differences in the regulation of protein synthesis in individual muscle fibers found within the same whole muscle. Specifically, the in vivo SUrface SEnsing of Translation (SUnSET) methodology was used to measure protein synthesis in type 1, 2A, 2X and 2B fibers of the mouse plantaris muscle, in response to food deprivation (FD), and mechanical overload induced by synergist ablation (SA). The results show that 48 h of FD induced a greater decrease in protein synthesis in type 2X and 2B fibers compared to type 1 and 2A fibers. Type 2X and 2B fibers also had the largest FD-induced decrease in total S6 protein and Ser^240/244 S6 phosphorylation, respectively. Moreover, only type 2X and 2B fibers displayed a FD-induced decrease in cross-sectional area (CSA). Ten days of SA also induced fiber type-dependent responses, with type 2B fibers having the smallest SA-induced increases in protein synthesis, CSA and Ser^240/244 S6 phosphorylation, but the largest increase in total S6 protein. Embryonic myosin heavy chain (MHC^Emb) positive fibers were also found in SA muscles and the protein synthesis rates, levels of S6 Ser^240/244 phosphorylation, and total S6 protein content, were 3.6-, 6.1- and 2.9-fold greater than that found in fibers from control muscles, respectively. Overall, these results reveal differential responses in the regulation of protein synthesis and fiber size between fiber types found within the same whole muscle. Moreover, these findings demonstrate that changes found at the whole muscle level do not necessarily reflect changes in individual fiber types.

Influence of chronic and acute spinal cord injury on skeletal muscle Na+-K+-ATPase and phospholemman expression in humans

Na(+)-K(+)-ATPase is an integral membrane protein crucial for the maintenance of ion homeostasis and skeletal muscle contractibility. Skeletal muscle Na(+)-K(+)-ATPase content displays remarkable plasticity in response to long-term increase in physiological demand, such as exercise training. However, the adaptations in Na(+)-K(+)-ATPase function in response to a suddenly decreased and/or habitually low level of physical activity, especially after a spinal cord injury (SCI), are incompletely known. We tested the hypothesis that skeletal muscle content of Na(+)-K(+)-ATPase and the associated regulatory proteins from the FXYD family is altered in SCI patients in a manner dependent on the severity of the spinal cord lesion and postinjury level of physical activity. Three different groups were studied: 1) six subjects with chronic complete cervical SCI, 2) seven subjects with acute, complete cervical SCI, and 3) six subjects with acute, incomplete cervical SCI. The individuals in groups 2 and 3 were studied at months 1, 3, and 12 postinjury, whereas individuals with chronic SCI were compared with an able-bodied control group. Chronic complete SCI was associated with a marked decrease in [(3)H]ouabain binding site concentration in skeletal muscle as well as reduced protein content of the α(1)-, α(2)-, and β(1)-subunit of the Na(+)-K(+)-ATPase. In line with this finding, expression of the Na(+)-K(+)-ATPase α(1)- and α(2)-subunits progressively decreased during the first year after complete but not after incomplete SCI. The expression of the regulatory protein phospholemman (PLM or FXYD1) was attenuated after complete, but not incomplete, cervical SCI. In contrast, FXYD5 was substantially upregulated in patients with complete SCI. In conclusion, the severity of the spinal cord lesion and the level of postinjury physical activity in patients with SCI are important factors controlling the expression of Na(+)-K(+)-ATPase and its regulatory proteins PLM and FXYD5.

The effect of continuous and interval exercise on PGC-1α and PDK4 mRNA in type I and type II fibres of human skeletal muscle

AIM

Differences in fibre-type recruitment during exercise may induce a heterogenic response in fibre-type gene expression. We have investigated the effect of two different exercise protocols on the fibre-type-specific expression of master genes involved in oxidative metabolism [proliferator-activated receptor-γ coactivator-1α (PGC-1α) and Pyruvate dehydrogenase kinase 4 (PDK4)].

METHODS

Untrained subjects (n = 7) completed 90-min cycling either at a constant intensity [continuous exercise (CE): approximately 60% of VO(2max) ] or as interval exercise (IE: approximately 120/20% VO(2max) , duty cycle 12/18s). Muscle samples were taken before (pre) and 3 h after (post) exercise. Single fibres were isolated from freeze-dried muscle and characterized as type I or type II. The cDNA from two fibres of the same type was pooled and mRNA analysed with reverse transcription quantitative real-time PCR.

RESULTS

Continuous exercise and IE elicited a small increase in blood lactate (<2.5 mM) and moderate glycogen depletion (<40%) without difference between exercise modes. The mRNA of PGC-1α and PDK4 increased 5- to 8-fold in both fibre types after exercise, and the relative increase was negatively correlated with the basal level. However, the mRNA of PGC-1α and PDK4 was not different between type I and II fibres neither pre nor post, and there was no difference in the exercise-induced response between fibre types or exercise modes.

CONCLUSION

We conclude that the mRNA of PGC-1α and PDK4 increases markedly in both fibre types after prolonged exercise without difference between CE and IE. The similar response between fibre types may relate to that subjects were sedentary and that the metabolic stress was low.

PGC-1α induces mitochondrial and myokine transcriptional programs and lipid droplet and glycogen accumulation in cultured human skeletal muscle cells

The transcriptional coactivator peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α) is a chief activator of mitochondrial and metabolic programs and protects against atrophy in skeletal muscle (skm). Here we tested whether PGC-1α overexpression could restructure the transcriptome and metabolism of primary cultured human skm cells, which display a phenotype that resembles the atrophic phenotype. An oligonucleotide microarray analysis was used to reveal the effects of PGC-1α on the whole transcriptome. Fifty-three different genes showed altered expression in response to PGC-1α: 42 upregulated and 11 downregulated. The main gene ontologies (GO) associated with the upregulated genes were mitochondrial components and processes and this was linked with an increase in COX activity, an indicator of mitochondrial content. Furthermore, PGC-1α enhanced mitochondrial oxidation of palmitate and lactate to CO₂, but not glucose oxidation. The other most significantly associated GOs for the upregulated genes were chemotaxis and cytokine activity, and several cytokines, including IL-8/CXCL8, CXCL6, CCL5 and CCL8, were within the most highly induced genes. Indeed, PGC-1α highly increased IL-8 cell protein content. The most upregulated gene was PVALB, which is related to calcium signaling. Potential metabolic regulators of fatty acid and glucose storage were among mainly regulated genes. The mRNA and protein level of FITM1/FIT1, which enhances the formation of lipid droplets, was raised by PGC-1α, while in oleate-incubated cells PGC-1α increased the number of smaller lipid droplets and modestly triglyceride levels, compared to controls. CALM1, the calcium-modulated δ subunit of phosphorylase kinase, was downregulated by PGC-1α, while glycogen phosphorylase was inactivated and glycogen storage was increased by PGC-1α. In conclusion, of the metabolic transcriptome deficiencies of cultured skm cells, PGC-1α rescued the expression of genes encoding mitochondrial proteins and FITM1. Several myokine genes, including IL-8 and CCL5, which are known to be constitutively expressed in human skm cells, were induced by PGC-1α.