PGC-1α mediates a rapid, exercise-induced downregulation of glycogenolysis in rat skeletal muscle

Exercise-Regulated Mitochondrial and Nuclear Signalling Networks in Skeletal Muscle

Exercise perturbs energy homeostasis in skeletal muscle and engages integrated cellular signalling networks to help meet the contraction-induced increases in skeletal muscle energy and oxygen demand. Investigating exercise-associated perturbations in skeletal muscle signalling networks has uncovered novel mechanisms by which exercise stimulates skeletal muscle mitochondrial biogenesis and promotes whole-body health and fitness. While acute exercise regulates a complex network of protein post-translational modifications (e.g. phosphorylation) in skeletal muscle, previous investigations of exercise signalling in human and rodent skeletal muscle have primarily focused on a select group of exercise-regulated protein kinases [i.e. 5' adenosine monophosphate-activated protein kinase (AMPK), protein kinase A (PKA), Ca2+/calmodulin-dependent protein kinase (CaMK) and mitogen-activated protein kinase (MAPK)] and only a small subset of their respective protein substrates. Recently, global mass spectrometry-based phosphoproteomic approaches have helped unravel the extensive complexity and interconnection of exercise signalling pathways and kinases beyond this select group and phosphorylation and/or translocation of exercise-regulated mitochondrial and nuclear protein substrates. This review provides an overview of recent advances in our understanding of the molecular events associated with acute endurance exercise-regulated signalling pathways and kinases in skeletal muscle with a focus on phosphorylation. We critically appraise recent evidence highlighting the involvement of mitochondrial and nuclear protein phosphorylation and/or translocation in skeletal muscle adaptive responses to an acute bout of endurance exercise that ultimately stimulate mitochondrial biogenesis and contribute to exercise's wider health and fitness benefits.

Antifatigue effect of functional cookies fortified with mushroom powder (Tricholoma Matsutake) in mice

Bakery products made by cereal and edible fungi powder have a unique flavor and health benefits, dramatically enhancing the nutritional value of the products. In this study, we investigated the antifatigue effect of a novel Tricholoma matsutake cookie (TMC) by the exhaustive swimming test. Male Kunming ICR mice were randomly divided into seven groups (each group, n = 10), fed with saline, ordinary cookies (4, 8, 16 g/kg B.W./day), and TMC (4, 8, 16 g/kg B.W./day) by gavage. After 30-day administration, the weight-loaded swimming test was carried out on the mice to evaluate the antifatigue effect of TMC. In comparison with the effect of ordinary cookies, the intake of TMC significantly prolonged the exhaustive swimming time of mice and increased the level of muscle glycogen and liver glycogen, accompanied by the reduction of lactic acid and urea nitrogen level in serum. Additionally, TMC dramatically improved the activity of superoxide dismutase and glutathione peroxidase in serum and largely decreased the level of malondialdehyde. All in all, TMC could enforce exhaustive swimming tolerance, accelerate the decomposition of sports-related metabolites such as lactic acid and urea nitrogen, and increase the activity of the antioxidant enzyme, thereby improving sports-related energy storage and relieving fatigue. Our findings broadened the application of T. matsutake in the processing of bakery products and provided the theoretical basis and technical support for the development of antifatigue products. PRACTICAL APPLICATION: In this study, we investigated the antifatigue effect of a novel Tricholoma matsutake cookie by the exhaustive swimming test. Collectively, the results of the present study suggested that the cookies fortified with T. matsutake could be considered as an antifatigue bakery product. Furthermore, our findings broadened the application of T. matsutake in the processing of bakery products and provided the theoretical basis and technical support for the development of antifatigue products.

Metabolomics of Endurance Capacity in World Tour Professional Cyclists

The study of elite athletes provides a unique opportunity to define the upper limits of human physiology and performance. Across a variety of sports, these individuals have trained to optimize the physiological parameters of their bodies in order to compete on the world stage. To characterize endurance capacity, techniques such as heart rate monitoring, indirect calorimetry, and whole blood lactate measurement have provided insight into oxygen utilization, and substrate utilization and preference, as well as total metabolic capacity. However, while these techniques enable the measurement of individual, representative variables critical for sports performance, they lack the molecular resolution that is needed to understand which metabolic adaptations are necessary to influence these metrics. Recent advancements in mass spectrometry-based analytical approaches have enabled the measurement of hundreds to thousands of metabolites in a single analysis. Here we employed targeted and untargeted metabolomics approaches to investigate whole blood responses to exercise in elite World Tour (including Tour de France) professional cyclists before and after a graded maximal physiological test. As cyclists within this group demonstrated varying blood lactate accumulation as a function of power output, which is an indicator of performance, we compared metabolic profiles with respect to lactate production to identify adaptations associated with physiological performance. We report that numerous metabolic adaptations occur within this physically elite population (n = 21 males, 28.2 ± 4.7 years old) in association with the rate of lactate accumulation during cycling. Correlation of metabolite values with lactate accumulation has revealed metabolic adaptations that occur in conjunction with improved endurance capacity. In this population, cycling induced increases in tricarboxylic acid (TCA) cycle metabolites and Coenzyme A precursors. These responses occurred proportionally to lactate accumulation, suggesting a link between enhanced mitochondrial networks and the ability to sustain higher workloads. In association with lactate accumulation, altered levels of amino acids before and after exercise point to adaptations that confer unique substrate preference for energy production or to promote more rapid recovery. Cyclists with slower lactate accumulation also have higher levels of basal oxidative stress markers, suggesting long term physiological adaptations in these individuals that support their premier competitive status in worldwide competitions.

Exercise Training-Induced PPARβ Increases PGC-1α Protein Stability and Improves Insulin-Induced Glucose Uptake in Rodent Muscles

This study aimed to investigate the long-term effects of training intervention and resting on protein expression and stability of peroxisome proliferator-activated receptor β/δ (PPARβ), peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC1α), glucose transporter type 4 (GLUT4), and mitochondrial proteins, and determine whether glucose homeostasis can be regulated through stable expression of these proteins after training. Rats swam daily for 3, 6, 9, 14, or 28 days, and then allowed to rest for 5 days post-training. Protein and mRNA levels were measured in the skeletal muscles of these rats. PPARβ was overexpressed and knocked down in myotubes in the skeletal muscle to investigate the effects of swimming training on various signaling cascades of PGC-1α transcription, insulin signaling, and glucose uptake. Exercise training (Ext) upregulated PPARβ, PGC-1α, GLUT4, and mitochondrial enzymes, including NADH-ubiquinone oxidoreductase (NUO), cytochrome c oxidase subunit I (COX1), citrate synthase (CS), and cytochrome c (Cyto C) in a time-dependent manner and promoted the protein stability of PPARβ, PGC-1α, GLUT4, NUO, CS, and Cyto C, such that they were significantly upregulated 5 days after training cessation. PPARβ overexpression increased the PGC-1α protein levels post-translation and improved insulin-induced signaling responsiveness and glucose uptake. The present results indicate that Ext promotes the protein stability of key mitochondria enzymes GLUT4, PGC-1α, and PPARβ even after Ext cessation.

Peroxisome proliferator-activated receptor gamma co-activator-1 alpha in depression and the response to electroconvulsive therapy

BACKGROUND

The transcriptional coactivator peroxisome proliferator-activated receptor-γ coactivator (PGC-1α), termed the 'master regulator of mitochondrial biogenesis', has been implicated in stress and resilience to stress-induced depressive-like behaviours in animal models. However, there has been no study conducted to date to examine PGC-1α levels in patients with depression or in response to antidepressant treatment. Our aim was to assess PGC-1α mRNA levels in blood from healthy controls and patients with depression pre-/post-electroconvulsive therapy (ECT), and to examine the relationship between blood PGC-1α mRNA levels and clinical symptoms and outcomes with ECT.

METHODS

Whole blood PGC-1α mRNA levels were analysed in samples from 67 patients with a major depressive episode and 70 healthy controls, and in patient samples following a course of ECT using quantitative real-time polymerase chain reaction (qRT-PCR). Exploratory subgroup correlational analyses were carried out to determine the relationship between PGC-1α and mood scores.

RESULTS

PGC-1α levels were lower in patients with depression compared with healthy controls (p = 0.03). This lower level was predominantly accounted for by patients with psychotic unipolar depression (p = 0.004). ECT did not alter PGC-1α levels in the depressed group as a whole, though exploratory analyses revealed a significant increase in PGC-1α in patients with psychotic unipolar depression post-ECT (p = 0.045). We found no relationship between PGC-1α mRNA levels and depression severity or the clinical response to ECT.

CONCLUSIONS

PGC-1α may represent a novel therapeutic target for the treatment of depression, and be a common link between various pathophysiological processes implicated in depression.

Training-Induced Changes in Mitochondrial Content and Respiratory Function in Human Skeletal Muscle

A sedentary lifestyle has been linked to a number of metabolic disorders that have been associated with sub-optimal mitochondrial characteristics and an increased risk of premature death. Endurance training can induce an increase in mitochondrial content and/or mitochondrial functional qualities, which are associated with improved health and well-being and longer life expectancy. It is therefore important to better define how manipulating key parameters of an endurance training intervention can influence the content and functionality of the mitochondrial pool. This review focuses on mitochondrial changes taking place following a series of exercise sessions (training-induced mitochondrial adaptations), providing an in-depth analysis of the effects of exercise intensity and training volume on changes in mitochondrial protein synthesis, mitochondrial content and mitochondrial respiratory function. We provide evidence that manipulation of different exercise training variables promotes specific and diverse mitochondrial adaptations. Specifically, we report that training volume may be a critical factor affecting changes in mitochondrial content, whereas relative exercise intensity is an important determinant of changes in mitochondrial respiratory function. As a consequence, a dissociation between training-induced changes in mitochondrial content and mitochondrial respiratory function is often observed. We also provide evidence that exercise-induced changes are not necessarily predictive of training-induced adaptations, we propose possible explanations for the above discrepancies and suggestions for future research.

The guardian of the genome p53 regulates exercise-induced mitochondrial plasticity beyond organelle biogenesis

The Guardian of the Genome p53 has been established as a potent tumour suppressor. However, culminating from seminal findings in rodents more than a decade ago, several studies have demonstrated that p53 is required to maintain basal mitochondrial function [ie, respiration and reactive oxygen species (ROS) homeostasis]. Specifically, via its role(s) as a tumour suppressor, p53 intimately surveys cellular DNA damage, in particular mitochondrial DNA (mtDNA), to ensure that the mitochondrial network is carefully monitored and cell viability is upheld, because aberrant mtDNA damage leads to apoptosis and widespread cellular perturbations. Indeed, data from rodents and humans have demonstrated that p53 forms an integral component of the exercise-induced signal transduction network regulating skeletal muscle mitochondrial remodelling. In response to exercise-induced disruptions to cellular homeostasis that have the potential to harm mtDNA (eg, contraction-stimulated ROS emissions), appropriate p53-regulated, mitochondrial turnover responses prevail to protect the genome and ultimately facilitate a shift from aerobic glycolysis to oxidative phosphorylation, adaptations critical for endurance-based exercise that are commensurate with p53's role as a tumour suppressor. Despite these observations, several discrepancies exist between rodent and human studies pinpointing p53 subcellular trafficking from nuclear-to-mitochondrial compartments following acute exercise. Such interspecies differences in p53 activity and the plausible p53-mediated adaptations to chronic exercise training will be discussed herein.

The Limits of Exercise Physiology: From Performance to Health

Many of the established positive health benefits of exercise have been documented by historical discoveries in the field of exercise physiology. These investigations often assess limits: the limits of performance, or the limits of exercise-induced health benefits. Indeed, several key findings have been informed by studying highly trained athletes, in addition to healthy or unhealthy people. Recent progress has been made in regard to skeletal muscle metabolism and personalized exercise regimes. In this perspective, we review some of the historical milestones of exercise physiology, discuss how these inform contemporary knowledge, and speculate on future questions.

Effects of skeletal muscle energy availability on protein turnover responses to exercise

Skeletal muscle adaptation to exercise training is a consequence of repeated contraction-induced increases in gene expression that lead to the accumulation of functional proteins whose role is to blunt the homeostatic perturbations generated by escalations in energetic demand and substrate turnover. The development of a specific 'exercise phenotype' is the result of new, augmented steady-state mRNA and protein levels that stem from the training stimulus (i.e. endurance or resistance based). Maintaining appropriate skeletal muscle integrity to meet the demands of training (i.e. increases in myofibrillar and/or mitochondrial protein) is regulated by cyclic phases of synthesis and breakdown, the rate and turnover largely determined by the protein's half-life. Cross-talk among several intracellular systems regulating protein synthesis, breakdown and folding is required to ensure protein equilibrium is maintained. These pathways include both proteasomal and lysosomal degradation systems (ubiquitin-mediated and autophagy, respectively) and the protein translational and folding machinery. The activities of these cellular pathways are bioenergetically expensive and are modified by intracellular energy availability (i.e. macronutrient intake) and the 'training impulse' (i.e. summation of the volume, intensity and frequency). As such, exercise-nutrient interactions can modulate signal transduction cascades that converge on these protein regulatory systems, especially in the early post-exercise recovery period. This review focuses on the regulation of muscle protein synthetic response-adaptation processes to divergent exercise stimuli and how intracellular energy availability interacts with contractile activity to impact on muscle remodelling.

Exercise-induced skeletal muscle signaling pathways and human athletic performance

Skeletal muscle is a highly malleable tissue capable of altering its phenotype in response to external stimuli including exercise. This response is determined by the mode, (endurance- versus resistance-based), volume, intensity and frequency of exercise performed with the magnitude of this response-adaptation the basis for enhanced physical work capacity. However, training-induced adaptations in skeletal muscle are variable and unpredictable between individuals. With the recent application of molecular techniques to exercise biology, there has been a greater understanding of the multiplicity and complexity of cellular networks involved in exercise responses. This review summarizes the molecular and cellular events mediating adaptation processes in skeletal muscle in response to exercise. We discuss established and novel cell signaling proteins mediating key physiological responses associated with enhanced exercise performance and the capacity for reactive oxygen and nitrogen species to modulate training adaptation responses. We also examine the molecular bases underpinning heterogeneous responses to resistance and endurance exercise and the dissociation between molecular 'markers' of training adaptation and subsequent exercise performance.

Antifatigue Activity of Liquid Cultured Tricholoma matsutake Mycelium Partially via Regulation of Antioxidant Pathway in Mouse

Tricholoma matsutake has been popular as food and biopharmaceutical materials in Asian countries for its various pharmacological activities. The present study aims to analyze the antifatigue effects on enhancing exercise performance of Tricholoma matsutake fruit body (ABM) and liquid cultured mycelia (TM) in mouse model. Two-week Tricholoma matsutake treatment significantly enhances the exercise performance in weight-loaded swimming, rotating rod, and forced running test. In TM- and ABM-treated mice, some factors were observed at 60 min after swimming compared with nontreated mice, such as the increased levels of adenosine triphosphate (ATP), antioxidative enzymes, and glycogen and the reduced levels of malondialdehyde and reactive oxygen species in muscle, liver, and/or serum. Further data obtained from western blot show that CM and ABM have strongly enhanced the activation of 5'-AMP-activated protein kinase (AMPK), and the expressions of peroxisome proliferator have activated receptor γ coactivator-1α (PGC-1α) and phosphofructokinase-1 (PFK-1) in liver. Our data suggest that both Tricholoma matsutake fruit body and liquid cultured mycelia possess antifatigue effects related to AMPK-linked antioxidative pathway. The information uncovered in our study may serve as a valuable resource for further identification and provide experimental evidence for clinical trials of Tricholoma matsutake as an effective agent against fatigue related diseases.

Training intensity modulates changes in PGC-1α and p53 protein content and mitochondrial respiration, but not markers of mitochondrial content in human skeletal muscle

Exercise training has been associated with increased mitochondrial content and respiration. However, no study to date has compared in parallel how training at different intensities affects mitochondrial respiration and markers of mitochondrial biogenesis. Twenty-nine healthy men performed 4 wk (12 cycling sessions) of either sprint interval training [SIT; 4-10 × 30-s all-out bouts at ∼200% of peak power output (WPeak)], high-intensity interval training (HIIT; 4-7 × 4-min intervals at ∼90% WPeak), or sublactate threshold continuous training (STCT; 20-36 min at ∼65% WPeak). The STCT and HIIT groups were matched for total work. Resting biopsy samples (vastus lateralis) were obtained before and after training. The maximal mitochondrial respiration in permeabilized muscle fibers increased significantly only after SIT (25%). Similarly, the protein content of peroxisome proliferator-activated receptor γ coactivator (PGC)-1α, p53, and plant homeodomain finger-containing protein 20 (PHF20) increased only after SIT (60-90%). Conversely, citrate synthase activity, and the protein content of TFAM and subunits of the electron transport system complexes remained unchanged throughout. Our findings suggest that training intensity is an important factor that regulates training-induced changes in mitochondrial respiration and that there is an apparent dissociation between training-induced changes in mitochondrial respiration and mitochondrial content. Moreover, changes in the protein content of PGC-1α, p53, and PHF20 are more strongly associated with training-induced changes in mitochondrial respiration than mitochondrial content.

MicroRNA-761 regulates mitochondrial biogenesis in mouse skeletal muscle in response to exercise

MicroRNAs (miRNAs) have been suggested to play critical roles in skeletal muscle in response to exercise. Previous study has shown that miR-761 was involved in a novel model regulating the mitochondrial network. However, its role in mitochondrial biogenesis remains poorly understood. Therefore, the current study was aimed to examine the effect of miR-761 on mitochondrial biogenesis in skeletal muscle. Real-time quantitative PCR analysis demonstrated that aberrantly expressed miR-761 is involved in exercise activity and miR-761 is decreased by exercise training compared with the sedentary control mice. miR-761 suppresses mitochondrial biogenesis of C2C12 myocytes by targeting the 3'-UTR of peroxisome proliferator-activated receptor gamma (PPARγ) coactivator-1 (PGC-1α). Overexpression of miR-761 was capable of inhibiting the protein expression levels of PGC-1α. Moreover, miR-761 overexpression suppressed the p38 MAPK signaling pathway and down-regulated the expression of phosphorylated MAPK-activated protein kinase-2 (P-MK2), a downstream kinase of p38 MAPK. The phosphorylation of activating transcription factors 2 (ATF2) that plays a functional role in linking the activation of the p38 MAPK pathway to enhanced transcription of the PGC-1α was also inhibited by the overexpression of miR-761. These findings revealed a novel regulation mechanism for miR-761 in skeletal myocytes, and contributed to a better understanding of the modulation of skeletal muscle in response to exercise.