Skeletal Muscle Contractile Activity Research Articles

General physiological patterns (principles) of classes

Systematic physical culture or sports cause adaptation (specific adaptation) of the body to physical stress. Such adaptation is based on the morphological, metabolic and functional changes that occur as a result of training in various organs and tissues, the improvement of the nervous, hormonal and autonomic cellular regulation of functions. All these changes determine the training effects. They are manifested in the improvement of various body functions that ensure the implementation of this (trained) muscular activity, and, as a result, in an increase in the level of physical fitness (training) of the student, in the growth of sports results. The second effect is evidenced by a decrease in functional shifts in the activity of various leading organs and systems of the body when performing a standard non-maximal load. So, when performing the same load in a trained person compared to an untrained person or in the same person after a certain period of training, there are smaller functional changes (in heart rate, pulmonary ventilation, the amount and level of contractile activity of skeletal muscles, body temperature, lactate concentration, catecholamines and other hormones in the blood, sympathetic nervous activity, etc.), as well as a decrease in energy expenditure during this exercise (for example, a decrease in O2 consumption). The latter phenomenon manifests itself most noticeably in those types of muscular activity, the performance of which is associated with the mastery and improvement of complex coordination of movements, for example, in swimming.

Effects of Physical Exercise on Metabolic Diseases

Physical activity and diabetes have been linked, as it plays an important role in preventing the progression of peripheral neuropathy, and their impact is primarily on the development of muscle strength and the ability to replace the function of nerve fibers with impaired disabilities. It seems that any form of exercise added to a balanced lifestyle significantly improves the quality of the subject with diabetes (type 2 diabetes). The small differences between aerobic and endurance training as a benefit for type 2 diabetes do not promote a certain form of exercise. In conclusion, the effects of regular exercise are recognized as an effective way to improve the condition of the disease. The basis of exercise therapy is simply the ability of skeletal muscle contractile activity to increase insulin sensitivity and promote blood glucose absorption and stabilization. Thus, regular participation in aerobic structure, endurance, or competing exercise had generally favorable effects on glycemic control, body composition, endothelial function, physical work capacity, and self-reported well-being.

Roles of ATP and SERCA in the Regulation of Calcium Turnover in Unloaded Skeletal Muscles: Current View and Future Directions.

A decrease in skeletal muscle contractile activity or its complete cessation (muscle unloading or disuse) leads to muscle fibers’ atrophy and to alterations in muscle performance. These changes negatively affect the quality of life of people who, for one reason or another, are forced to face a limitation of physical activity. One of the key regulatory events leading to the muscle disuse-induced changes is an impairment of calcium homeostasis, which leads to the excessive accumulation of calcium ions in the sarcoplasm. This review aimed to analyze the triggering mechanisms of calcium homeostasis impairment (including those associated with the accumulation of high-energy phosphates) under various types of muscle unloading. Here we proposed a hypothesis about the regulatory mechanisms of SERCA and IP3 receptors activity during muscle unloading, and about the contribution of these mechanisms to the excessive calcium ion myoplasmic accumulation and gene transcription regulation via excitation–transcription coupling.

Real Time and Repeated Measurement of Skeletal Muscle Growth in Individual Live Zebrafish Subjected to Altered Electrical Activity

A number of methods can be used to visualize individual cells throughout the body of live embryonic, larval or juvenile zebrafish. We show that live fish with fluorescently-marked plasma membranes can be scanned in a confocal laser scanning microscope in order to determine the volume of muscle tissue and the number of muscle fibers present. Efficient approaches for the measurement of cell number and size in live animals over time are described and validated against more arduous segmentation methods. Methods are described that permit the control of muscle electrical, and thus contractile, activity. Loss of skeletal muscle contractile activity greatly reduced muscle growth. In larvae, a protocol is described that allows reintroduction of patterned electrical-evoked contractile activity. The described methods minimize the effect of inter-individual variability and will permit analysis of the effect of electrical, genetic, drug, or environmental stimuli on a variety of cellular and physiological growth parameters in the context of the living organism. Long-term follow-up of the measured effects of a defined early-life intervention on individuals can subsequently be performed.

Disuse-induced skeletal muscle atrophy in disease and nondisease states in humans: mechanisms, prevention, and recovery strategies.

Decreased skeletal muscle contractile activity (disuse) or unloading leads to muscle mass loss, also known as muscle atrophy. The balance between muscle protein synthesis (MPS) and muscle protein breakdown (MPB) is the primary determinant of skeletal muscle mass. A reduced mechanical load on skeletal muscle is one of the main external factors leading to muscle atrophy. However, endocrine and inflammatory factors can act synergistically in catabolic states, amplifying the atrophy process and accelerating its progression. In addition, older individuals display aging-induced anabolic resistance, which can predispose this population to more pronounced effects when exposed to periods of reduced physical activity or mechanical unloading. Different cellular mechanisms contribute to the regulation of muscle protein balance during skeletal muscle atrophy. This review summarizes the effects of muscle disuse on muscle protein balance and the molecular mechanisms involved in muscle atrophy in the absence or presence of disease. Finally, a discussion of the current literature describing efficient strategies to prevent or improve the recovery from muscle atrophy is also presented.

Less Sitting for Preventing Type 2 Diabetes.

The findings reported by Li et al. (1) in this issue of Diabetes Care are a welcome contribution to the body of evidence informing type 2 diabetes prevention. They focus on sedentary behavior (put simply, too much sitting), which has adverse health consequences that are distinct from those of too little exercise (2). These new findings, from a prospective study with long-term follow-up of 475,502 adults with 18,619 type 2 diabetes cases, represent strong evidence pointing to causality in the relationships of sedentary behavior with the development of type 2 diabetes. To this end, the study by Li et al. has strengths of method and analytical approach, employing measures of both physical activity and sedentary behavior as exposures, and examining their interrelationships as predictors of the diagnosis of type 2 diabetes over an 11-year median follow-up interval. Importantly, their analyses used iso-temporal substitution methods, which allow statistical estimation of the benefits of reallocating time in one behavior for time in another behavior. Although iso-temporal substitution has previously been used to model the putative impacts of substituting physical activity for sedentary time, such evidence has come predominantly from cross-sectional studies (3). Sedentary behaviors—primarily television (TV) viewing and other screen use, time sitting in cars, and desk-based working—occupy the largest proportion of adults’ waking hours. Over the past 10 years, sedentary time, characterized by a sitting posture in the absence of skeletal muscle contractile activity (4,5), has increased by ∼1 h/day (6). The coronavirus disease 2019 pandemic has further exacerbated the pervasiveness of prolonged periods of time spent sitting in people’s lives (7). The widespread implementation of infection-risk mitigation strategies has seen daily time spent sitting increase by a staggering 3 h/day (8). Because sedentary behavior displaces time spent engaging in …

Transcription factor EB and TFE3: new metabolic coordinators mediating adaptive responses to exercise in skeletal muscle?

In response to the increased energy demands of contractions, skeletal muscle adapts remarkably well through acutely regulating metabolic pathways to maintain energy balance and in the longer term by regulating metabolic reprogramming, such as remodeling and expanding the mitochondrial network. This long-term adaptive response involves modulation of gene expression at least partly through the regulation of specific transcription factors and transcriptional coactivators. The AMPK-peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α) pathway has long been known to orchestrate contraction-mediated adaptive responses, although AMPK- and PGC1α-independent pathways have also been proposed. Transcription factor EB (TFEB) and TFE3, known as important regulators of lysosomal biogenesis and autophagic processes, have emerged as new metabolic coordinators. The activity of TFEB/TFE3 is regulated through posttranslational modifications (i.e., phosphorylation) and spatial organization. Under nutrient and energy stress, TFEB and TFE3 are dephosphorylated and translocate to the nucleus, where they activate transcription of their target genes. It has recently been reported that exercise promotes nuclear translocation and activation of TFEB/TFE3 in mouse skeletal muscle through the Ca2+-stimulated protein phosphatase calcineurin. Skeletal muscle-specific ablation of TFEB exhibits impaired glucose homeostasis and mitochondrial biogenesis with reduced metabolic flexibility during exercise, and global TFE3 depletion results in diminished endurance and abolished exercise-induced metabolic benefits. Transcriptomic analysis of the muscle-specific TFEB-null mice has demonstrated that TFEB regulates the expression of genes involved in glucose metabolism and mitochondrial homeostasis. This review aims to summarize and discuss emerging roles for TFEB/TFE3 in metabolic and adaptive responses to exercise and contractile activity in skeletal muscle.

2-Cys peroxiredoxin oxidation in response to hydrogen peroxide and contractile activity in skeletal muscle: A novel insight into exercise-induced redox signalling?

Skeletal muscle generates superoxide during contractions which is rapidly converted to H2O2. This molecule has been proposed to activate signalling pathways and transcription factors that regulate key adaptive responses to exercise but the concentration of H2O2 required to oxidise and activate key signalling proteins in vitro is much higher than the intracellular concentration in muscle fibers following exercise. We hypothesised that Peroxiredoxins (Prx), which reacts with H2O2 at the low intracellular concentrations found in muscle, would be rapidly oxidised in contracting muscle and hence potentially transmit oxidising equivalents to downstream signalling proteins as a method for their oxidation and activation. The aim of this study was to characterise the effects of muscle contractile activity on the oxidation of Prx1, 2 and 3 and determine if these were affected by aging. Prx1, 2 and 3 were all rapidly and reversibly oxidised following treatment with low micromolar concentrations of H2O2 in C2C12 myotubes and also in isolated mature flexor digitalis brevis fibers from adult mice following a protocol of repeated isometric contractions. Significant oxidation of Prx2 was seen within 1 min (i.e. after 12 contractions), whereas significant oxidation was seen after 2 min for Prx1 and 3. In muscle fibers from old mice, Prx2 oxidation was significantly attenuated following contractile activity. Thus we show for the first time that Prx are rapidly and reversibly oxidised in response to contractile activity in skeletal muscle and hypothesise that these proteins act as effectors of muscle redox signalling pathways which are key to adaptations to exercise that are attenuated during aging.

Enhancement of mouse diaphragm contractility in the presence of antagonists of GABAA and GABAB receptors.

What is the central question of this study? Do GABA receptors play any role at the neuromuscular junction? What is the main finding and its importance? In the presence of either ionotropic or metabotropic GABA receptor antagonists, diaphragm muscle force production elicited by stimulating the motor nerve at ≥50Hz was increased. Our data indicate the presence of GABAergic signalling at the neuromuscular junction. Despite the signalling role of GABA in the brain and spinal cord, the role of this molecule in the peripheral nervous system and, in particular, at the neuromuscular junction remains practically unexplored. In the present work, the force of mouse diaphragm contractions was measured in the presence of blockers of metabotropic GABAB receptors (CGP55845) and ionotropic GABAA receptors (picrotoxin) with various patterns of indirect and direct stimulation of muscle by trains of 40 pulses delivered at 10, 20, 50 and 70Hz. It was found that neither blocker affected the diaphragm contractility caused by indirect stimulation through the motor nerve at 10 and 20Hz. However, when the stimulation frequency was increased to 50 or 70Hz, the force of subsequent contractions in the train (when compared with the amplitude of contraction in response to the first pulse) was increased by both CGP55845 and picrotoxin. With direct stimulation of the diaphragm, no significant changes in the contraction force were detected at any frequency used. The results obtained support the following conclusions: (i) pharmacological inhibition of GABA receptors increases the contractile activity of skeletal muscle; and (ii) frequency-dependent enhancement of GABA receptor activation takes place in the region of the neuromuscular junction.

Oxidation of Peroxiredoxins in Response to Hydrogen Peroxide and Contractile Activity in Skeletal Muscle

Skeletal muscle responds to exercise and other environmental changes by modifying the expression and activity of genes involved in regulation of muscle structure, mass and energy metabolism. These responses are attenuated during ageing contributing to reduced muscle mass and function. Exercise generates reactive oxygen species, including hydrogen peroxide (H2O2) which is a key signalling molecule involved in cell responses to stress. A possible mechanism by which increased H2O2 leads to modified gene expression is by reaction of H2O2 with peroxiredoxins (PRX) leading to their oxidation and the formation of disulphide bridges resulting in dimerisation. PRX can then transmit oxidising equivalents to other less reactive proteins by disulphide exchange as part of a redox relay culminating in the activation of specific transcription factors and increased transcription of target genes.This study investigated the oxidation of PRX in the response of muscle to contractile activity and how this pathway was disrupted during ageing. Dimerisation (used as a marker of oxidation) of each PRX was analysed using non‐reducing SDS‐PAGE and western blot analysis. In C2C12 cells PRX1, PRX2 and PRX3 were all found to have increased dimerisation in response to acute treatment with low doses (2.5 and 25μM) of H2O2 in a dose‐dependent manner. A higher dose of H2O2 (250μM) caused all PRXs tested to revert to the monomeric form, consistent with the formation of hyper‐oxidised forms of PRX that are unable to form disulphide bridges. This was confirmed using an antibody specific to hyper‐oxidised PRX.PRX oxidation in response to contractile activity was examined in muscle fibres isolated from the flexor digitalis brevis of adult (6–8 months) or old (26 months) C57BL/6J mice with contractions induced by electrical field stimulation. In fibres from adult mice dimerisation of PRX2 was observed to increase significantly following 2 minutes (28% increase, p<0.05) and 15 minutes of contractions (34% increase, p<0.05), indicating significantly increased PRX2 oxidation. PRX3 dimerisation was significantly increased after 15 minutes of contractions (96% increase, p<0.05) whilst dimerisation of PRX1 remained unchanged. In muscle fibres isolated from old mice there were no significant changes in dimerisation of any of the PRX tested following contractile activity.Contractile activity induced rapid oxidation of PRX2 and PRX3 in skeletal muscle and this process was dysregulated in muscle from old mice. Defects in the regulation of PRX can lead to disruption of downstream signalling pathways and may be responsible for the loss of muscle adaptation to exercise. An understanding of how redox signals are transmitted in muscle following exercise and how they are changed in ageing may help indicate approaches designed to maintain muscle strength in older people.Support or Funding InformationSupported by the UK Medical Research Council (MRC).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Возможности стабилометрической диагностики нарушений функции равновесия

The aim of this study was to develop an automated system for differential diagnosis of various types of ataxias method of computer stabilography using the principle of vector analysis statokinesigram and create predictive mathematical models on the basis of the mathematical method of analysis of tree classifications. In this study, 217 people were included, including 196 patients and 21 healthy subjects. Patients with labyrinth, cerebellar and sensitive ataxia were studied. Additional parameters of vector analysis of stabilographic information allow fully and comprehensively characterize the dynamic process of maintaining a person's vertical posture. The analysis of stabilograms was reduced, basically, to the study of their amplitude-frequency characteristics by means of various methods of statistical processing, including spectral analysis. Analysis of the frequency of oscillations made it possible to identify slow (respiratory, cardiac) and fast waves, which characterize the contractile activity of skeletal muscles. In the course of the study it was revealed that the artificial division of the movement of the human body into oscillations in the frontal and sagittal planes led the researcher away from understanding the essence of the process of movement of the human body while maintaining a static equilibrium. An adequate method of predicting the type of ataxia based on the data of stabilographic information for performing automated computer differential diagnosis of various ataxia types, as well as screening the normal equilibrium function, is the compilation of mathematical models of „classification trees“.

Hypothermia Decreases O2 Cost for Ex Vivo Contraction in Mouse Skeletal Muscle.

Evidence suggests that the energy efficiency of key ATPases involved in skeletal muscle contractile activity is improved in a hypothermic condition. However, it is unclear how a decrease in temperature affects skeletal muscle O2 consumption (mVO2) induced by muscle contraction. Isolated mouse extensor digitorum longus (EDL) muscles were incubated in a temperature-controlled (37°C or 25°C) bath that included an O2 probe. EDL muscles from one limb were subjected to the measurement of resting mVO2, and the contralateral EDL muscles were used for the measurement of mVO2 with electrically stimulated contraction. For the resting protocol, muscles were suspended at resting tension for 15 min with continuous O2 recordings. For the contraction protocol, EDL muscles underwent 10 electrically stimulated isometric contractions with continuous O2 recordings for 15 min. The rate of O2 disappearance was quantified as micromoles of O2 per minute and normalized to the wet weight of the muscle. Resting mVO2 was greater at 37°C than at 25°C, consistent with the idea that lower temperature reduces basal metabolic rate. Electrically stimulated contraction robustly increased mVO2 at both 37°C and 25°C, which was sustained for ~3 min postcontraction. During that period, mVO2 was elevated approximately fivefold at both 37°C and 25°C. Greater contraction-induced mVO2 at 37°C compared with 25°C occurred despite lower force generated at 37°C than at 25°C. Together, O2 cost for muscle contraction (force-time integral per O2 consumed) was greater at 37°C than at 25°C. Levels of high-energy phosphates were consistent with greater energy demand at 37°C compared with 25°C. In conclusion, these results indicate that muscle contraction that occurs at subnormal temperature requires less O2 than at 37°C.

A mitochondrial-targeted antioxidant improves myofilament Ca2+ sensitivity during prolonged low frequency force depression at low PO2.

Skeletal muscle contractile activity is associated with an enhanced reactive oxygen species (ROS) generation. At very low PO2, ROS generation by mitochondria can be elevated in intact cells. An elevated intracellular oxidant activity may affect muscle force development and recovery from fatigue. We treated intact single muscle fibres with a mitochondrial antioxidant and stimulated the fibres to contract at a low extracellular PO2 that is similar to the intracellular PO2 that is observed during moderate to intense exercise in vivo. The mitochondrial antioxidant prevented a sustained decrease in the myofibrillar Ca2+ sensitivity and improved muscle submaximal force development after fatigue at low extracellular PO2. Skeletal muscle can develop a prolonged low frequency-stimulation force depression (PLFFD) following fatigue-inducing contractions. Increased levels of reactive oxygen species (ROS) have been implicated in the development of PLFFD. During exercise the skeletal muscle intracellular PO2 decreases to relatively low levels, and can be further decreased when there is an impairment in O2 diffusion or availability, such as in certain chronic diseases and during exercise at high altitude. Since ROS generation by mitochondria is elevated at very low PO2 in cells, we tested the hypothesis that treatment of muscle fibres with a mitochondrial-targeted antioxidant at a very low, near hypoxic, PO2 can attenuate PLFFD. We treated intact single fibres from mice with the mitochondrial-specific antioxidant SS31, and measured force development and intracellular [Ca2+ ] 30min after fatigue at an extracellular PO2 of ∼5Torr. After 30min following the end of the fatiguing contractions, fibres treated with SS31 showed significantly less impairment in force development compared to untreated fibres at submaximal frequencies of stimulation. The cytosolic peak [Ca2+ ] transients (peak [Ca2+ ]c ) were equally decreased in both groups compared to pre-fatigue values. The combined force and peak [Ca2+ ]c data demonstrated that myofibrillar Ca2+ sensitivity was diminished in the untreated fibres 30min after fatigue compared to pre-fatigue values, but Ca2+ sensitivity was unaltered in the SS31 treated fibres. These results demonstrate that at a very low PO2, treatment of skeletal muscle fibres with a mitochondrial antioxidant prevents a decrease in the myofibrillar Ca2+ sensitivity, which alleviates the fatigue induced PLFFD.

Розвиток утоми muscle soleus у результаті його тривалої активації при розвитку ішемічної контрактури

У роботі досліджували процес розвитку м’язової втоми при ішемічних патологіях. Аналіз проводився визначенням сили на початку та в кінці поодиноких тетанічних скорочень і різниці між цими величинами. Результати досліджень показали, що при розвитку ішемічних контрактур відбувається значне пригнічення скоротливої активності скелетних м’язів. Установлено, що порушення скоротливої здатності скелетних м’язів виникає внаслідок нехолінергічних ефектів цієї патології.

Immunometabolic Responses to Concurrent Training: The Effects of Exercise Order in Recreational Weightlifters.

Inoue, DS, Panissa, VLG, Monteiro, PA, Gerosa-Neto, J, Rossi, FE, Antunes, BMM, Franchini, E, Cholewa, JM, Gobbo, LA, and Lira, FS. Immunometabolic responses to concurrent training: the effects of exercise order in recreational weightlifters. J Strength Cond Res 30(7): 1960-1967, 2016-The relationship between immunometabolic response and performance is not well understood. This study evaluated the influence of concurrent strength and high-intensity aerobic sequence of exercise order between sessions on strength performance, metabolic, and inflammatory response. Eleven recreational weightlifters underwent the following 2 randomized sessions: (a) strength-aerobic exercise order (SA) and (b) aerobic-strength exercise order (AS). Blood samples were collected before (Pre) and immediately after the first exercise (Post-1) and the second exercise (Post-2) of each session. The SA condition presented a higher number of repetitions (SA: 54 ± 15 vs. AS: 43 ± 12) and total volume (SA: 7,265 ± 2,323 vs. AS: 5,794 ± 1846 kg) than the AS condition (both p = 0.001). Glucose was higher in Pre when compared with post-1 in both orders (p ≤ 0.05); changes in lactate were time-dependent in the different orders (p ≤ 0.05); however, AS post-2 lactate was lower when compared with SA post-2 (p ≤ 0.05). Interleukin-6 levels showed time-dependent changes for both exercise orders (p ≤ 0.05). Tumor necrosis factor alpha (TNF-α) level was increased only in AS post-1 (AS: pre = 21.91 ± 35.47, post-1 = 26.99 ± 47.69 pg·ml vs. SA: pre = 25.74 ± 43.64, post-1 = 29.74 ± 46.05 pg·ml, p ≤ 0.05). These results suggest that concurrent training order exhibits different immunometabolic responses and, at least in part, can be associated with the acute decline in strength performance induced by concurrent exercise. Our results point to a possible role of TNF-α (post-1 AS condition) as a trigger to restore the energy demand by providing substrates to help maintain contractile activity in skeletal muscle.

Neuromuscular interaction is required for neurotrophins-mediated locomotor recovery following treadmill training in rat spinal cord injury.

Recent results have shown that exercise training promotes the recovery of injured rat distal spinal cords, but are still unclear about the function of skeletal muscle in this process. Herein, rats with incomplete thoracic (T10) spinal cord injuries (SCI) with a dual spinal lesion model were subjected to four weeks of treadmill training and then were treated with complete spinal transection at T8. We found that treadmill training allowed the retention of hind limb motor function after incomplete SCI, even with a heavy load after complete spinal transection. Moreover, treadmill training alleviated the secondary injury in distal lumbar spinal motor neurons, and enhanced BDNF/TrkB expression in the lumbar spinal cord. To discover the influence of skeletal muscle contractile activity on motor function and gene expression, we adopted botulinum toxin A (BTX-A) to block the neuromuscular activity of the rat gastrocnemius muscle. BTX-A treatment inhibited the effects of treadmill training on motor function and BDNF/TrKB expression. These results indicated that treadmill training through the skeletal muscle-motor nerve-spinal cord retrograde pathway regulated neuralplasticity in the mammalian central nervous system, which induced the expression of related neurotrophins and promoted motor function recovery.

Cellular mechanisms underlying oxidative stress in human exercise

A relative increase in oxidation of lipids, proteins and DNA has been recognised to occur in the circulation and tissues of exercising humans and animals since the late 1970s and throughout the ensuing 40 years a great deal of work has been undertaken to elucidate the potential source(s) of this exercise-induced “oxidative stress”. Specific aspects of physical exercise (e.g. contractile activity, relative hypoxia, hyperaemia) may theoretically induce increased generation of reactive oxygen species in a number of potential tissues, but data strongly indicate that contractile activity of skeletal muscle predominates as the source of oxidants and contributes to local oxidation and that of extracellular biomaterials. Taken together with the relatively large mass of muscle compared with other tissues and cells it appears that muscle fibres are the major contributor to the relative increase in whole body “oxidative stress” during some forms of exercise. The sub-cellular sources of this increased oxidation have also been the subject of considerable research with early studies predominantly indicating that muscle mitochondria were the likely increased source of oxidants, such as hydrogen peroxide, but assessments of the relative concentrations of hydrogen peroxide in skeletal muscle fibres at rest and during contractile activity do not support this possibility. In contrast, several recent studies have identified NADPH oxidase enzymes in skeletal muscle that appear to play a signalling role in physiological responses exercise and together with xanthine oxidase enzymes may contribute to the relative increase in whole body oxidation. A fuller understanding of the relative roles of these sources and the function(s) of the species generated appears increasingly important in attempts to harness the beneficial effects of exercise for maintenance of health in aging and a variety of chronic conditions.

An electrochemical biosensor based on gold microspheres and nanoporous gold for real-time detection of superoxide anion in skeletal muscle tissue.

Superoxide anion (SOA) as a member of reactive oxygen species (ROS) group is involved in various physiological and pathological states. For instance, generation of SOA is known to increase with skeletal muscle contractile activity and fatigue. It is therefore important to selectively detect and accurately quantify the release of SOA within both physiological and pathological levels. We report fabrication and characterization of a cytochrome-c functionalized SOA biosensor built on commercially available miniaturized screen-printed electrodes made of gold microspheres. The device was first tested and calibrated in a xanthine/xanthine oxidase (XOD) system and then employed to detect SOA release from C2C12 myoblasts and myotubes upon stimulation with PMA.

PGC-1α modulates denervation-induced mitophagy in skeletal muscle.

BackgroundAlterations in skeletal muscle contractile activity necessitate an efficient remodeling mechanism. In particular, mitochondrial turnover is essential for tissue homeostasis during muscle adaptations to chronic use and disuse. While mitochondrial biogenesis appears to be largely governed by the transcriptional co-activator peroxisome proliferator co-activator 1 alpha (PGC-1α), selective mitochondrial autophagy (mitophagy) is thought to mediate organelle degradation. However, whether PGC-1α plays a direct role in autophagy is currently unclear.MethodsTo investigate the role of the co-activator in autophagy and mitophagy during skeletal muscle remodeling, PGC-1α knockout (KO) and overexpressing (Tg) animals were unilaterally denervated, a common model of chronic muscle disuse.ResultsAnimals lacking PGC-1α exhibited diminished mitochondrial density alongside myopathic characteristics reminiscent of autophagy-deficient muscle. Denervation promoted an induction in autophagy and lysosomal protein expression in wild-type (WT) animals, which was partially attenuated in KO animals, resulting in reduced autophagy and mitophagy flux. PGC-1α overexpression led to an increase in lysosomal capacity as well as indicators of autophagy flux but exhibited reduced localization of LC3II and p62 to mitochondria, compared to WT animals. A correlation was observed between the levels of the autophagy-lysosome master regulator transcription factor EB (TFEB) and PGC-1α in muscle, supporting their coordinated regulation.ConclusionsOur investigation has uncovered a regulatory role for PGC-1α in mitochondrial turnover, not only through biogenesis but also via degradation using the autophagy-lysosome machinery. This implies a PGC-1α-mediated cross-talk between these two opposing processes, working to ensure mitochondrial homeostasis during muscle adaptation to chronic disuse.Electronic supplementary materialThe online version of this article (doi:10.1186/s13395-015-0033-y) contains supplementary material, which is available to authorized users.

O-GlcNAcylation, contractile protein modifications and calcium affinity in skeletal muscle.

O-GlcNAcylation, a generally undermined atypical protein glycosylation process, is involved in a dynamic and highly regulated interplay with phosphorylation. Akin to phosphorylation, O-GlcNAcylation is also involved in the physiopathology of several acquired diseases, such as muscle insulin resistance or muscle atrophy. Recent data underline that the interplay between phosphorylation and O-GlcNAcylation acts as a modulator of skeletal muscle contractile activity. In particular, the O-GlcNAcylation level of the phosphoprotein myosin light chain 2 seems to be crucial in the modulation of the calcium activation properties, and should be responsible for changes in calcium properties observed in functional atrophy. Moreover, since several key structural proteins are O-GlcNAc-modified, and because of the localization of the enzymes involved in the O-GlcNAcylation/de-O-GlcNAcylation process to the nodal Z disk, a role of O-GlcNAcylation in the modulation of the sarcomeric structure should be considered.