Skeletal Muscle Plasticity In Response Research Articles

The molecular athlete: exercise physiology from mechanisms to medals.

Human skeletal muscle demonstrates remarkable plasticity, adapting to numerous external stimuli including the habitual level of contractile loading. Accordingly, muscle function and exercise capacity encompass a broad spectrum, from inactive individuals with low levels of endurance and strength to elite athletes who produce prodigious performances underpinned by pleiotropic training-induced muscular adaptations. Our current understanding of the signal integration, interpretation, and output coordination of the cellular and molecular mechanisms that govern muscle plasticity across this continuum is incomplete. As such, training methods and their application to elite athletes largely rely on a "trial-and-error" approach, with the experience and practices of successful coaches and athletes often providing the bases for "post hoc" scientific enquiry and research. This review provides a synopsis of the morphological and functional changes along with the molecular mechanisms underlying exercise adaptation to endurance- and resistance-based training. These traits are placed in the context of innate genetic and interindividual differences in exercise capacity and performance, with special consideration given to aging athletes. Collectively, we provide a comprehensive overview of skeletal muscle plasticity in response to different modes of exercise and how such adaptations translate from "molecules to medals."

RNA-Sequencing Muscle Plasticity to Resistance Exercise Training and Disuse in Youth and Older Age

Maintenance of skeletal muscle mass and function is critical to health and wellbeing throughout the lifespan. However, disuse through reduced physical activity (e.g., sedentarism), immobilisation, bed rest or microgravity has significant adverse effects on skeletal muscle health. Conversely, resistance exercise training (RET) induces positive muscle mass and strength adaptations. Several studies have employed microarray technology to understand the transcriptional basis of muscle atrophy and hypertrophy after disuse and RET, respectively, to devise fully effective therapeutic interventions. More recently, rapidly falling costs have seen RNA-sequencing (RNA-seq) increasingly applied in exploring muscle adaptations to RET and disuse. The aim of this review is to summarise the transcriptional responses to RET or disuse measured via RNA-seq in young and older adults. We also highlight analytical considerations to maximise the utility of RNA-seq in the context of skeletal muscle research. The limited number of muscle transcriptional signatures obtained thus far with RNA-seq are generally consistent with those obtained with microarrays. However, RNA-seq may provide additional molecular insight, particularly when combined with data-driven approaches such as correlation network analyses. In this context, it is essential to consider the most appropriate study design parameters as well as bioinformatic and statistical approaches. This will facilitate the use of RNA-seq to better understand the transcriptional regulators of skeletal muscle plasticity in response to increased or decreased use.

In vivo Measurement of Knee Extensor Muscle Function in Mice.

Skeletal muscle plasticity in response to countless conditions and stimuli mediates concurrent functional adaptation, both negative and positive. In the clinic and the research laboratory, maximal muscular strength is widely measured longitudinally in humans, with knee extensor musculature the most reported functional outcome. Pathology of the knee extensor muscle complex is well documented in aging, orthopedic injury, disease, and disuse; knee extensor strength is closely related to functional capacity and injury risk, underscoring the importance of reliable measurement of knee extensor strength. Repeatable, in vivo assessment of knee extensor strength in pre-clinical rodent studies offers valuable functional endpoints for studies exploring osteoarthritis or knee injury. We report an in vivo and non-invasive protocol to repeatedly measure isometric peak tetanic torque of the knee extensors in mice across time. We demonstrate consistency using this novel method to measure knee extensor strength with repeated assessment in multiple mice producing similar results.

β2-Adrenergic Signaling Modulates Mitochondrial Function and Morphology in Skeletal Muscle in Response to Aerobic Exercise.

The molecular mechanisms underlying skeletal muscle mitochondrial adaptations induced by aerobic exercise (AE) are not fully understood. We have previously shown that AE induces mitochondrial adaptations in cardiac muscle, mediated by sympathetic stimulation. Since direct sympathetic innervation of neuromuscular junctions influences skeletal muscle homeostasis, we tested the hypothesis that β2-adrenergic receptor (β2-AR)-mediated sympathetic activation induces mitochondrial adaptations to AE in skeletal muscle. Male FVB mice were subjected to a single bout of AE on a treadmill (80% Vmax, 60 min) under β2-AR blockade with ICI 118,551 (ICI) or vehicle, and parameters of mitochondrial function and morphology/dynamics were evaluated. An acute bout of AE significantly increased maximal mitochondrial respiration in tibialis anterior (TA) isolated fiber bundles, which was prevented by β2-AR blockade. This increased mitochondrial function after AE was accompanied by a change in mitochondrial morphology towards fusion, associated with increased Mfn1 protein expression and activity. β2-AR blockade fully prevented the increase in Mfn1 activity and reduced mitochondrial elongation. To determine the mechanisms involved in mitochondrial modulation by β2-AR activation in skeletal muscle during AE, we used C2C12 myotubes, treated with the non-selective β-AR agonist isoproterenol (ISO) in the presence of the specific β2-AR antagonist ICI or during protein kinase A (PKA) and Gαi protein blockade. Our in vitro data show that β-AR activation significantly increases mitochondrial respiration in myotubes, and this response was dependent on β2-AR activation through a Gαs-PKA signaling cascade. In conclusion, we provide evidence for AE-induced β2-AR activation as a major mechanism leading to alterations in mitochondria function and morphology/dynamics. β2-AR signaling is thus a key-signaling pathway that contributes to skeletal muscle plasticity in response to exercise.

The Effects of Acute and Chronic Exercise on Skeletal Muscle Proteome.

Skeletal muscle plasticity and its adaptation to exercise is a topic that is widely discussed and investigated due to its primary role in the field of exercise performance and health promotion. Repetitive muscle contraction through exercise stimuli leads to improved cardiovascular output and the regulation of endothelial dysfunction and metabolic disorders such as insulin resistance and obesity. Considerable improvements in proteomic tools and data analysis have broth some new perspectives in the study of the molecular mechanisms underlying skeletal muscle adaptation in response to physical activity. In this sense, this review updates the main relevant studies concerning muscle proteome adaptation to acute and chronic exercise, from aerobic to resistance training, as well as the proteomic profile of natural inbred high running capacity animal models. Also, some promising prospects in the muscle secretome field are presented, in order to better understand the role of physical activity in the release of extracellular microvesicles and myokines activity. Thus, the present review aims to update the fast-growing exercise-proteomic scenario, leading to some new perspectives about the molecular events under skeletal muscle plasticity in response to physical activity. J. Cell. Physiol. 232: 257-269, 2017. © 2016 Wiley Periodicals, Inc.

Assessing the regulation of skeletal muscle plasticity in response to protein ingestion and resistance exercise: recent developments.

The main purpose of this review is to discuss novel methodological advances in the assessment of muscle protein synthesis (MPS) in response to protein feeding and resistance exercise. In the past 20 years, there has been a shift from application of the nitrogen balance methods toward the infusion of stable isotopic tracers to assess rates of MPS in response to a range of perturbations. Although this approach has enabled MPS to be assessed with a greater temporal resolution and precision, the method limits the capture of MPS to relatively short-duration infusions of approximately 3-12 h. Recent refinement of analytical methods to assess long-term MPS responses have now provided a platform for studying the impact of exercise and nutrition on muscle anabolism with an extended temporal resolution from hours to days or even weeks. Finally, novel insights into cellular signaling processes may help delineate the molecular mechanisms that govern skeletal muscle plasticity in response to exercise and feeding. Future work should focus on the impact of novel exercise and nutritional interventions on MPS in an extended postexercise adaptive period, that is, days. The findings of such investigations will help test the long-term efficacy of interventions to enhance skeletal muscle protein reconditioning and hypertrophy.

Autophagy is essential to support skeletal muscle plasticity in response to endurance exercise.

Physical exercise is a stress that can substantially modulate cellular signaling mechanisms to promote morphological and metabolic adaptations. Skeletal muscle protein and organelle turnover is dependent on two major cellular pathways: Forkhead box class O proteins (FOXO) transcription factors that regulate two main proteolytic systems, the ubiquitin-proteasome, and the autophagy-lysosome systems, including mitochondrial autophagy, and the MTORC1 signaling associated with protein translation and autophagy inhibition. In recent years, it has been well documented that both acute and chronic endurance exercise can affect the autophagy pathway. Importantly, substantial efforts have been made to better understand discrepancies in the literature on its modulation during exercise. A single bout of endurance exercise increases autophagic flux when the duration is long enough, and this response is dependent on nutritional status, since autophagic flux markers and mRNA coding for actors involved in mitophagy are more abundant in the fasted state. In contrast, strength and resistance exercises preferentially raise ubiquitin-proteasome system activity and involve several protein synthesis factors, such as the recently characterized DAGK for mechanistic target of rapamycin activation. In this review, we discuss recent progress on the impact of acute and chronic exercise on cell component turnover systems, with particular focus on autophagy, which until now has been relatively overlooked in skeletal muscle. We especially highlight the most recent studies on the factors that can impact its modulation, including the mode of exercise and the nutritional status, and also discuss the current limitations in the literature to encourage further works on this topic.

Last Word on Point:Counterpoint: Satellite cell addition is/is not obligatory for skeletal muscle hypertrophy

To the Editor : The authors of the Point:Counterpoint debate ([1][1], [2][2]) collectively thank our colleagues for their thoughtful responses to the topic “Satellite cell addition is/is not obligatory for skeletal muscle hypertrophy.” While the goal of our initial position piece and rebuttal

Point:Counterpoint: Satellite cell addition is/is not obligatory for skeletal muscle hypertrophy

Myofiber size is dynamically regulated, increasing and decreasing depending on muscle use. Hypertrophy is defined by increases in myofiber cross-sectional area and mass as well as myofibrillar protein content. Myofibers contain many hundreds of nuclei, each of which has a nuclear domain. A nuclear

Substrate depletion in different types of muscle and in liver during prolonged running.

Substrate depletion in different types of muscle and in liver during prolonged running.

Glycogen depletion pattern in human skeletal muscle fibers after heavy exercise.

Glycogen depletion pattern in human skeletal muscle fibers after heavy exercise.

Diet, muscle glycogen, and endurance performance.

Diet, muscle glycogen, and endurance performance.

Effect of exercise on skeletal muscle. II. Contractile properties.

Effect of exercise on skeletal muscle. II. Contractile properties.