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Molecular Basis of Exercise-Induced Skeletal Muscle Mitochondrial Biogenesis: Historical Advances, Current Knowledge, and Future Challenges
Abstract
We provide an overview of groundbreaking studies that laid the foundation for our current understanding of exercise-induced mitochondrial biogenesis and its contribution to human skeletal muscle fitness. We highlight the mechanisms by which skeletal muscle responds to the acute perturbations in cellular energy homeostasis evoked by a single bout of endurance-based exercise and the adaptations resulting from the repeated demands of exercise training that ultimately promote mitochondrial biogenesis through hormetic feedback loops. Despite intense research efforts to elucidate the cellular mechanisms underpinning mitochondrial biogenesis in skeletal muscle, translating this basic knowledge into improved metabolic health at the population level remains a future challenge. E xercise represents a major challenge to multiple whole-body homeostatic functions. In an effort to overcome this challenge, numerous responses take place at the cellular and systemic levels that operate to blunt the homeostatic threats generated by exercise-induced increases in muscle energy turnover and oxygen demand (Hawley et al. 2014). The capacity of skeletal muscle to adapt to repeated bouts of activity such that physical capacity is enhanced is termed exercise training. When considering endurance based exercise (e.g., sustained activities that are .10 min duration and performed at 60%-90% of maximal oxygen uptake [VO 2max ] including sprint-interval training), the goals of such exercise are to induce an array of physiological and metabolic adaptations that enable an individual to increase the rate of energy production from both aerobic pathways, maintain tighter metabolic control (i.e., match adenosine triphosphate (ATP) production with ATP hy-drolysis), minimize cellular perturbations, increase efficiency of motion, and improve the capacity of the trained musculature to resist
... Skeletal muscle oxidative capacity is a key component related to human health and physical performance (Holloszy, 1967;Hood et al., 2011;Perry & Hawley, 2018). During exercise, enhanced muscle oxidative capacity minimizes disruption to cellular homeostasis through the cell's ability to match ATP production with ATP hydrolysis (Perry & Hawley, 2018). ...
... Skeletal muscle oxidative capacity is a key component related to human health and physical performance (Holloszy, 1967;Hood et al., 2011;Perry & Hawley, 2018). During exercise, enhanced muscle oxidative capacity minimizes disruption to cellular homeostasis through the cell's ability to match ATP production with ATP hydrolysis (Perry & Hawley, 2018). Historically, muscle oxidative capacity has been assessed with invasive procedures involving a small biopsy of muscle tissue (Granata et al., 2018;Perry & Hawley, 2018) or costly in vivo technology (e.g., magnetic resonance spectroscopy) to quantify the recovery rate of phosphocreatine following exercise (Chance et al., 2006). ...
... During exercise, enhanced muscle oxidative capacity minimizes disruption to cellular homeostasis through the cell's ability to match ATP production with ATP hydrolysis (Perry & Hawley, 2018). Historically, muscle oxidative capacity has been assessed with invasive procedures involving a small biopsy of muscle tissue (Granata et al., 2018;Perry & Hawley, 2018) or costly in vivo technology (e.g., magnetic resonance spectroscopy) to quantify the recovery rate of phosphocreatine following exercise (Chance et al., 2006). In the past decade, muscle oxidative capacity in vivo has also been evaluated through the use of muscle oxygen uptake (mV O 2 ) kinetics using an inexpensive and portable near-infrared spectroscopy (NIRS) system (Adami et al., 2017;Motobe et al., 2004;Ryan et al., 2012). ...
New findings:
What is the central question of this study? In vivo muscle oxidative capacity has been evaluated through the mV̇O2 kinetics following single joint exercise using NIRS system. Here, we demonstrated its utility following running exercise. What is the main finding and its importance? We demonstrated that time constant of mV̇O2 kinetics in gastrocnemius following moderate running exercise presents good to excellent reliability. In addition, it was well correlated with parameters of aerobic fitness, such as maximal speed of the incremental test, ventilatory threshold and pulmonary V̇O2 on-kinetics. Therefore, NIRS-derived muscle oxidative capacity together with other physiological measurements may allow a concomitant local and systemic analysis of the components of the oxidative system.
Abstract:
NIRS-derived muscle oxygen uptake (mV̇O2 ) kinetics following single-joint exercise has been used to assess muscle oxidative capacity. However, little evidence is available on the use of this technique following whole-body exercises. Therefore, this study aimed to assess the reliability of the NIRS-derived mV̇O2 kinetics following running exercise and to investigate the relationship between the time constant of mV̇O2 off-kinetics (τmV̇O2 ) with parameters of aerobic fitness. After an incremental test to determine V̇O2 max, first (VT1 ) and second (VT2 ) ventilatory thresholds, and maximal speed (Smax), thirteen males (age = 21 ± 4 years; V̇O2 max = 55.9 ± 3.4 mlꞏkg-1ꞏmin-1) performed three sets (two in the first day and one on a subsequent day) of two repetitions of 6-min running exercise at 90%VT1 . The pulmonary V̇O2 on-kinetics (pV̇O2 ) and mV̇O2 off-kinetics in gastrocnemius were assessed. τmV̇O2 presented no systematic change and satisfactory reliability (SEM and ICC of 4.21 s and 0.49 for between transitions; and 2.65 s and 0.74 averaging τmV̇O2 within each time-set), with no difference (p > 0.3) between the within- (SEM = 2.92 s) and between-day variability (SEM = 2.78 s and 2.19 s between first vs. third set, and second vs. third set, respectively). τmV̇O2 (28.5 ± 4.17 s) correlated significantly (p < 0.05) with Smax (r = -0.66), VT1 (r = -0.64) and time constant of the pV̇O2 on-kinetics (r = 0.69). These findings indicate that NIRS-derived mV̇O2 kinetics in the gastrocnemius following moderate running exercise is a useful and reliable method to assess muscle oxidative capacity. This article is protected by copyright. All rights reserved.
... Horses have been identified as a suitable model for studying gene expression in skeletal muscle related to exercise ability [7][8][9][10][11], which is rare for livestock. The present study is similar to a prior report of muscle activity and associated genes in humans [12][13][14][15]. Skeletal muscles have different physiological characteristics depending on their role, which is related to the composition of muscle fibers according to the main purpose of the muscle in question. ...
... As a result of previous studies of equine exercise capacity, the classification, properties, and related genes of skeletal muscle tissue are well characterized. These prior studies demonstrated a large number of exercise-induced changes, with increased expression of genes associated with oxidative phosphorylation and mitochondrial function in skeletal muscle of individuals endurance-exercised continuously for long periods of time [8,11,15,27]. These results have been verified by molecular biology studies [8,9,15]. ...
... These prior studies demonstrated a large number of exercise-induced changes, with increased expression of genes associated with oxidative phosphorylation and mitochondrial function in skeletal muscle of individuals endurance-exercised continuously for long periods of time [8,11,15,27]. These results have been verified by molecular biology studies [8,9,15]. ...
Horses have been studied for exercise function rather than food production, unlike most livestock. Therefore, the role and characteristics of tissue landscapes are critically understudied, except for certain muscles used in exercise-related studies. In the present study, we compared RNA-Seq data from 18 Jeju horse skeletal muscles to identify differentially expressed genes (DEGs) between tissues that have similar functions and to characterize these differences. We identified DEGs between different muscles using pairwise differential expression (DE) analyses of tissue transcriptome expression data and classified the samples using the expression values of those genes. Each tissue was largely classified into two groups and their subgroups by k-means clustering, and the DEGs identified in comparison between each group were analyzed by functional/pathway level using gene set enrichment analysis and gene level, confirming the expression of significant genes. As a result of the analysis, the differences in metabolic properties like glycolysis, oxidative phosphorylation, and exercise adaptation of the groups were detected. The results demonstrated that the biochemical and anatomical features of a wide range of muscle tissues in horses could be determined through transcriptome expression analysis, and provided proof-of-concept data demonstrating that RNA-Seq analysis can be used to classify and study in-depth differences between tissues with similar properties.
... The goals of endurance exercise training are to induce an array of physiological and metabolic adaptations that enable an individual to increase the rate of energy production from both aerobic and oxygen-independent pathways, maintain tighter metabolic control (i.e., match ATP production with ATP hydrolysis), minimize cellular perturbations, increase efficiency of motion, and improve the capacity of the trained musculature to resist fatigue (Hawley 2002). The mechanisms and metabolic signals by which active muscle senses homeostatic perturbations and then translates them into improved function has been a topic of intense research for several decades (for review, see Perry and Hawley 2017). It is now accepted that a variety of cellular disruptions takes place at the onset of exercise, including (but not limited to) increased cytoplasmic free [Ca 2+ ], increased free AMP (AMPf) and an increased ADP/ATP ratio, reduced creatine phosphate and glycogen levels, increased FA concentrations and reactive oxygen/nitrogen species (ROS/RNS), acidosis and altered redox state, including [NAD/NADH] Perry and Hawley 2017). ...
... The mechanisms and metabolic signals by which active muscle senses homeostatic perturbations and then translates them into improved function has been a topic of intense research for several decades (for review, see Perry and Hawley 2017). It is now accepted that a variety of cellular disruptions takes place at the onset of exercise, including (but not limited to) increased cytoplasmic free [Ca 2+ ], increased free AMP (AMPf) and an increased ADP/ATP ratio, reduced creatine phosphate and glycogen levels, increased FA concentrations and reactive oxygen/nitrogen species (ROS/RNS), acidosis and altered redox state, including [NAD/NADH] Perry and Hawley 2017). Within the context of metabolic homeostasis, an array of regulatory networks is stimulated that sustain rates of ATP synthesis over time through the activation of rate-limiting enzymes controlling carbohydrate and fat catabolism. ...
... A key component of improved "muscle fitness" following exercise training is biogenesis of mitochondria in skeletal muscle. A comprehensive discussion of this topic is beyond the scope of this chapter and the reader is referred to recent reviews (Hood et al. 2016;Perry and Hawley 2017). In brief, the molecular bases of skeletal muscle adaptations to an endurance exercise stimulus requires increased expression and/or activity of key mitochondrial proteins mediated by an array of intra-cellular signaling events, pre-and post-transcriptional processes, regulation of translation and protein expression, and modulation of protein (enzyme) activities and/or intracellular localization. ...
The world is faced with an epidemic of metabolic diseases such as obesity and type 2 diabetes. This is due to changes in dietary habits and the decrease in physical activity. Exercise is usually part of the prescription, the first line of defense, to prevent or treat metabolic disorders. However, we are still learning how and why exercise provides metabolic benefits in human health. This open access volume focuses on the cellular and molecular pathways that link exercise, muscle biology, hormones and metabolism. This will include novel “myokines” that might act as new therapeutic agents in the future.
... It is well known that exercise is one of the main stimuli for PGC-1α activation. Thus, according to the literature a single bout of exercise can activate calcium/calmodulin-dependent protein kinase (CaMK), p38 mitogen-activated protein kinase (p38 MAPK), cyclic adenosine monophosphate (cAMP), and phosphorylate AMP activated protein kinase (AMPK), which are the molecular signals responsible for the increase in PGC-1α expression (Bonen, 2009;Lira et al., 2010;Perry and Hawley, 2018;Memme et al., 2021). Our results are in accordance with the literature and demonstrate that a single bout of exercise increases the expression and/or content of PGC-1α (Wright et al., 2007;Ikeda et al., 2008;Seebacher and Glanville, 2010;Fujimoto et al., 2011;Shute et al., 2018) and NRF-1 (Murakami et al., 1998;Seebacher and Glanville, 2010;Daussin et al., 2012). ...
... The results of these seminal studies provided evidence that whole-body aerobic capacity could be limited not only by "central" cardiorespiratory factors (i.e., oxygen delivery/transport system) but also by "local" factors, including skeletal muscle mitochondrial content. The increase in mitochondrial content is known as mitochondrial biogenesis (Perry & Hawley, 2018). ...
Skeletal muscle is a key metabolic tissue that has been purported to be affected by omega-3 (n-3) polyunsaturated fatty acids (PUFAs). Although the mechanisms remain unclear, recent evidence has shown that these benefits may in part be mediated by the capacity of n-3 PUFAs to be incorporated into skeletal muscle membranes including mitochondrial membranes, potentially altering mitochondrial biosynthesis and dynamics. The following chapter will address current evidence from in vitro, animal, and human studies regarding the effects of n-3 PUFAs on skeletal muscle mitochondrial biogenesis and dynamics.
... Ainda não existe consenso entre pesquisadores como esse mecanismo acontece, mas já existem evidencias que a expressão de PGC-1α na fibra muscular esta diminuída de forma basal, mas está aumentado após sessão de exercício de resistência aeróbica tanto de forma aguda como crônica (Hood et al., 2016). Essa relação da resposta ao exercício de resistência aeróbica na indução na expressão de PGC-1α no musculo esquelético está relacionada com a quantidade de fibras musculares oxidativas (Perry & Hawley, 2018). ...
RESUMO Introdução: O estímulo metabólico do exercício físico pode impulsionar direta ou indiretamente a indução da biogênese mitocondrial via PGC-1 α. Objetivo: evidenciar ação do exercício físico como estimulador do PGC-1 α, o maestro chave responsável pela cascata de sinalização da biogénese mitocondrial, através de uma revisão bibliográfica. Métodos e resultados: Para atingir este objetivo, este estudo utilizou artigos originais retirados das bases de dados online MEDLINE (Pubmed), Scopus e Scielo, descrevendo as palavras-chave, "mitocôndria", "biogénese", "exercício físico. As referências escolhidas foram selecionadas de forma específica para a temática proposta. Todos os artigos utilizados e publicados foram revisados por pares limitados ao período de 2012 a 2022 e somente em língua inglesa. Conclusão: o exercício estimula a homeostase energéticas, estimulando o complexo Ca+2/calmodulina, proteína quinase 5'-AMP-ativada (AMPK) juntamente com a Sirtuina 1 (SIRT 1), levando a regulação do PGC-1 α, que por sua vez, estimula proteínas especificas na replicação ou na transcrição do RNA mitocondrial. ABSTRACT Introduction: The metabolic stimulus of physical exercise can directly or indirectly drive together with other regulators such as miRNAs, epigenetic marks, and nutritional strategies drive the induction of mitochondrial biogenesis via PGC-1 α.
... Митохондрии являются древнейшими органеллами клетки, участвующими в ее жизненно важных функциях, в том числе производстве энергии, обмене веществ, клеточном дыхании, продукции активных форм кислорода, пролиферации и гибели [2]. Необходимость удовлетворять метаболические и энергетические потребности клетки делает митохондрии динамичными: они способны к модификации формы и размера, в ходе чего могут изменяться масса и число органелл в клетке [2,9]. Объем митохондрий может составлять до 20-25% от общего объема клетки. ...
Mitochondria play a key role in the vital functions of the cell, i.e., energy production, metabolism, respiration, generation of reactive oxygen species, cell division and death. Impairment of these mitochondrial functions is associated with emergence of various diseases. Their amounts and membrane potential are important indices of the mitochondrial condition. To assess these parameters, various fluorochrome-labeled probes are used, which are detectable by flow cytometry. The opportunity of using fluorescent mitochondrial dyes, together with labeled monoclonal antibodies, opens up new prospects for studying the metabolic parameters in various immune cells. The aim of the present study was to assess the mitochondrial state in CD4+T lymphocytes by flow cytometry. To search for the differences in mitochondrial indexes, a group of HIV-infected patients receiving antiretroviral therapy (n = 21) and healthy volunteers (n = 23) were compared. Mononuclear cells isolated from peripheral blood were under the study. Using flow cytometry and commercial mitochondria-selective dyes MitoTracker Green and MitoTracker Orange, we determined, respectively, the mitochondrial mass and membrane charge in the total CD4+T lymphocyte pool, as well as in the naive and memory cell subsets. It has been shown that the mitochondrial mass and charge in naive CD4+T lymphocytes are lower than in memory cells, both in HIV-infected and uninfected subjects. Moreover, we have established that the HIV-infected patients have an increased mitochondrial mass in total CD4+T lymphocyte pool and in their memory cell subset, as compared with healthy donors. That increase, however, was not accompanied by the higher membrane charge. Thus, the analysis of mitochondrial mass and membrane potential using flow cytometry and MitoTracker Green/MitoTracker Orange dyes is relatively easy, fast, and informative for preliminary assessment of the mitochondrial state.
... In response to different external stimuli, cellular signalling transduction pathways are used to coordinate transcriptional, translational and post-translational processes that increase mitochondrial biogenesis and respiration. Exposure to lower temperatures in brown/beige fat or physical activity in skeletal muscle exemplifies potent signals that stimulate mitochondrial biogenesis and respiratory adaption [56][57][58] . Cold promotes secretion of catecholamines that activate cAMP signalling to stimulate mitochondrial biogenesis 42 , which involves the activity of energy-sensing pathways centred at mTor 59 and AMPK 60 . ...
Mitochondrial energetic adaptations encompass a plethora of conserved processes that maintain cell and organismal fitness and survival in the changing environment by adjusting the respiratory capacity of mitochondria. These mitochondrial responses are governed by general principles of regulatory biology exemplified by changes in gene expression, protein translation, protein complex formation, transmembrane transport, enzymatic activities and metabolite levels. These changes can promote mitochondrial biogenesis and membrane dynamics that in turn support mitochondrial respiration. The main regulatory components of mitochondrial energetic adaptation include: the transcription coactivator peroxisome proliferator-activated receptor-γ (PPARγ) coactivator 1α (PGC1α) and associated transcription factors; mTOR and endoplasmic reticulum stress signalling; TOM70-dependent mitochondrial protein import; the cristae remodelling factors, including mitochondrial contact site and cristae organizing system (MICOS) and OPA1; lipid remodelling; and the assembly and metabolite-dependent regulation of respiratory complexes. These adaptive molecular and structural mechanisms increase respiration to maintain basic processes specific to cell types and tissues. Failure to execute these regulatory responses causes cell damage and inflammation or senescence, compromising cell survival and the ability to adapt to energetically demanding conditions. Thus, mitochondrial adaptive cellular processes are important for physiological responses, including to nutrient availability, temperature and physical activity, and their failure leads to diseases associated with mitochondrial dysfunction such as metabolic and age-associated diseases and cancer.
... It is well known that exercise is one of the main stimuli for PGC-1α activation. Thus, according to the literature a single bout of exercise can activate calcium/calmodulin-dependent protein kinase (CaMK), p38 mitogen-activated protein kinase (p38 MAPK), cyclic adenosine monophosphate (cAMP), and phosphorylate AMP activated protein kinase (AMPK), which are the molecular signals responsible for the increase in PGC-1α expression (Bonen, 2009;Lira et al., 2010;Perry and Hawley, 2018;Memme et al., 2021). Our results are in accordance with the literature and demonstrate that a single bout of exercise increases the expression and/or content of PGC-1α (Wright et al., 2007;Ikeda et al., 2008;Seebacher and Glanville, 2010;Fujimoto et al., 2011;Shute et al., 2018) and NRF-1 (Murakami et al., 1998;Seebacher and Glanville, 2010;Daussin et al., 2012). ...
Compelling evidence has demonstrated the effect of melatonin on exhaustive exercise tolerance and its modulatory role in muscle energy substrates at the end of exercise. In line with this, PGC-1α and NRF-1 also seem to act on physical exercise tolerance and metabolic recovery after exercise. However, the literature still lacks reports on these proteins after exercise until exhaustion for animals treated with melatonin. Thus, the aim of the current study was to determine the effects of acute melatonin administration on muscle PGC-1α and NRF-1, and its modulatory role in glycogen and triglyceride contents in rats subjected to exhaustive swimming exercise at an intensity corresponding to the anaerobic lactacidemic threshold (iLAn). In a randomized controlled trial design, thirty-nine Wistar rats were allocated into four groups: control (CG = 10), rats treated with melatonin (MG = 9), rats submitted to exercise (EXG = 10), and rats treated with melatonin and submitted to exercise (MEXG = 10). Forty-eight hours after the graded exercise test, the animals received melatonin (10 mg/kg) or vehicles 30 min prior to time to exhaustion test in the iLAn (tlim). Three hours after tlim the animals were euthanized, followed by muscle collection for specific analyses: soleus muscles for immunofluorescence, gluteus maximus, red and white gastrocnemius for the assessment of glycogen and triglyceride contents, and liver for the measurement of glycogen content. Student t-test for independent samples, two-way ANOVA, and Newman keuls post hoc test were used. MEXG swam 120.3% more than animals treated with vehicle (EXG; p < 0.01). PGC-1α and NRF-1 were higher in MEXG with respect to the CG (p < 0.05); however, only PGC-1α was higher for MEXG when compared to EXG. Melatonin reduced the triglyceride content in gluteus maximus, red and white gastrocnemius (F = 6.66, F = 4.51, and F = 6.02, p < 0.05). The glycogen content in red gastrocnemius was higher in MEXG than in CG (p = 0.01), but not in EXG (p > 0.05). In conclusion, melatonin was found to enhance exercise tolerance, potentiate exercise-mediated increases in PGC-1α, decrease muscle triglyceride content and increase muscle glycogen 3 h after exhaustive exercise, rapidly providing a better cellular metabolic environment for future efforts.
... These previous studies suggest that lactate production in the skeletal muscle during exercise may be important for exercise-induced mitochondrial biogenesis. Mitochondrial biogenesis is induced by the activation of important kinases, such as AMP-activated protein kinase (AMPK), Ca 2+ /calmodulin-dependent protein kinase (CaMK) II, and p38 mitogen-activated protein kinase (MAPK) 21 . An increase in lactate production volume during exercise may reflect the activations of signaling molecules involved with mitochondrial biogenesis, yet the relationship between lactate production volume and their activations requires further elucidation. ...
Lactate production is an important clue for understanding metabolic and signal responses to exercise but its measurement is difficult. Therefore, this study aimed (1) to develop a method of calculating lactate production volume during exercise based on blood lactate concentration and compare the effects between endurance exercise training (EX) and PGC-1α overexpression (OE), (2) to elucidate which proteins and enzymes contribute to changes in lactate production due to EX and muscle PGC-1α OE, and (3) to elucidate the relationship between lactate production volume and signaling phosphorylations involved in mitochondrial biogenesis. EX and PGC-1α OE decreased muscle lactate production volume at the absolute same-intensity exercise, but only PGC-1α OE increased lactate production volume at the relative same-intensity exercise. Multiple linear regression revealed that phosphofructokinase, monocarboxylate transporter (MCT)1, MCT4, and citrate synthase equally contribute to the lactate production volume at high-intensity exercise within physiological adaptations, such as EX, not PGC-1α OE. We found that an exercise intensity-dependent increase in the lactate production volume was associated with a decrease in glycogen concentration and an increase in P-AMPK/T-AMPK. This suggested that the calculated lactate production volume was appropriate and reflected metabolic and signal responses but further modifications are needed for the translation to humans.
... В настоящей работе мы установили, что по сравнению со здоровыми донорами у ВИЧ/ВГС коинфицированных пациентов со стандартным и дискордантным ответом на АРВТ значительно увеличена масса митохондрий в CD4+ Т-лимфоцитах. Известно, что повышение массы органелл может происходить в физиологических условиях, например, в мышечной ткани как адаптивная реакция клеток к высокому расходу энергии при физической нагрузке [21]. Вместе с тем было показано, что у ВИЧ-инфицированных больных увеличение массы митохондрий в CD8+ Т-лимфоцитах является негативным фактором, связанным с повышенной чувствительностью клеток к спонтанному и Fas-индуцированному апоптозу [10]. ...
Objective: to assess mitochondrial parameters in CD4+ T-cells of HIV/HCV coinfected patients with a discordant and standard response of the immune system to antiretroviral therapy. Materials and methods. HIV/HCV coinfected patients with discordant (n=21) and standard (n=20) response to treatment were examined. The control group comprised of 23 uninfected volunteers. In CD4+ T-cells, PGC-1a content, mitochondrial mass, and mitochondrial membrane potential were determined with flow cytometry. Results. In CD4+ T-cells of HIV/HCV coinfected subjects with standard and discordant response to treatment, mitochondrial membrane potential was similar to that of uninfected donors. Compared with healthy controls, HIV/HCV coinfected patients had increased organelles’ mass and PGC-1a expression in CD4+ T-cells. In contrast to healthy individuals, HIV/HCV coinfected subjects had no correlation between mitochondrial mass and PGC-1a content in CD4+ T-lymphocytes. Conclusion. In CD4+ T-cells of HIV/HCV coinfected patients with discordant and standard response to antiretroviral therapy, up-regulation of mitochondrial mass is not associated with energy production. In HIV/HCV coinfection, there is no relationship between the mitochondrial mass and mitochondrial biogenesis regulator.
... However, as mitochondria are the main energy-producing organelles in the cell, it could also be argued that it is counterintuitive to decrease its density when the cell is facing an increased energy demand, such as during increased ribosome biogenesis and cytosolic protein synthesis after resistance exercise. Moreover, several proteins needed for mitochondrial biogenesis are encoded in nuclear DNA and synthesized by cytosolic ribosomes before they can be imported into the mitochondria (Jornayvaz and Shulman, 2010;Perry and Hawley, 2018). Again, it would be counterintuitive to decrease ribosome density when there is an increased demand for nuclear-encoded proteins needed for mitochondrial biogenesis. ...
Skeletal muscle adaptations to resistance and endurance training include increased ribosome and mitochondrial biogenesis, respectively. Such adaptations are believed to contribute to the notable increases in hypertrophy and aerobic capacity observed with each exercise mode. Data from multiple studies suggest the existence of a competition between ribosome and mitochondrial biogenesis, in which the first adaptation is prioritized with resistance training while the latter is prioritized with endurance training. In addition, reports have shown an interference effect when both exercise modes are performed concurrently. This prioritization/interference may be due to the interplay between the 5’ AMP-activated protein kinase (AMPK) and mechanistic target of rapamycin complex 1 (mTORC1) signaling cascades and/or the high skeletal muscle energy requirements for the synthesis and maintenance of cellular organelles. Negative associations between ribosomal DNA and mitochondrial DNA copy number in human blood cells also provide evidence of potential competition in skeletal muscle. However, several lines of evidence suggest that ribosome and mitochondrial biogenesis can occur simultaneously in response to different types of exercise and that the AMPK-mTORC1 interaction is more complex than initially thought. The purpose of this review is to provide in-depth discussions of these topics. We discuss whether a curious competition between mitochondrial and ribosome biogenesis exists and show the available evidence both in favor and against it. Finally, we provide future research avenues in this area of exercise physiology.
... This umbrella term can include exercise and sport. Studies that perform repeated bodily movements, often in the context of exercise, confer increases in mitochondrial biogenesis, but our data demonstrated that wheel running, in general, lowered expression of mitochondrial content in the soleus and EDL 65,66 . Our findings of lowered mitochondrial content in CKD are consistent with other animal models of CKD that showed reduced mitochondrial content and altered mitochondrial complex activity 10,63,67,68 . ...
Chronic kidney disease (CKD) leads to musculoskeletal impairments that are impacted by muscle metabolism. We tested the hypothesis that 10-weeks of voluntary wheel running can improve skeletal muscle mitochondria activity and function in a rat model of CKD. Groups included (n = 12–14/group): (1) normal littermates (NL); (2) CKD, and; (3) CKD-10 weeks of voluntary wheel running (CKD-W). At 35-weeks old the following assays were performed in the soleus and extensor digitorum longus (EDL): targeted metabolomics, mitochondrial respiration, and protein expression. Amino acid-related compounds were reduced in CKD muscle and not restored by physical activity. Mitochondrial respiration in the CKD soleus was increased compared to NL, but not impacted by physical activity. The EDL respiration was not different between NL and CKD, but increased in CKD-wheel rats compared to CKD and NL groups. Our results demonstrate that the soleus may be more susceptible to CKD-induced changes of mitochondrial complex content and respiration, while in the EDL, these alterations were in response the physiological load induced by mild physical activity. Future studies should focus on therapies to improve mitochondrial function in both types of muscle to determine if such treatments can improve the ability to adapt to physical activity in CKD.
... exercise session on mitochondrial biogenesis (Granata et al., 2016;Holloszy, 1967;Hood, 2001;Little et al., 2011;Perry & Hawley, 2018;Russell et al., 2014) -which has been defined as "the making of new components of the mitochondrial reticulum" (Miller & Hamilton, 2012). This is a result of the coordinated expression of the nuclear and the mitochondrial genomes (Hood, 2001). ...
Aim:
Exercise is able to increase both muscle protein synthesis and mitochondrial biogenesis. However, acidosis, which can occur in pathological states as well as during high-intensity exercise, can decrease mitochondrial function, whilst its impact on muscle protein synthesis is disputed. Thus, the aim of this study was to determine the effect of a mild physiological decrease in pH, by administration of ammonium chloride, on myofibrillar and mitochondrial protein synthesis, as well as associated molecular signaling events.
Methods:
Male Wistar rats were given either a placebo or ammonium chloride prior to a short interval training session. Rats were killed before exercise, immediately after exercise, or 3 h after exercise.
Results:
Myofibrillar (p = 0.036) fractional protein synthesis rates was increased immediately after exercise in the soleus muscle of the placebo group, but this effect was absent in the ammonium chloride group. However, in the gastrocnemius muscle NH4 Cl increased myofibrillar (p = 0.044) and mitochondrial protein synthesis (0 h after exercise p = 0.01; 3 h after exercise p = 0.003). This was accompanied by some small differences in protein phosphorylation and mRNA expression.
Conclusion:
This study found ammonium chloride administration immediately prior to a single session of exercise in rats had differing effects on mitochondrial and myofibrillar protein synthesis rates in soleus (type I) and gastrocnemius (type II) muscle in rats.
... In a neuronal context, mitochondria play as platforms in sensing adverse effects of stress and ameliorate the cellular activities, neuronal morphology, and cell survival [10]. Besides, it has been accepted that adaptation to exercise leads to increased mitochondrial function and biogenesis, and eventually improved antioxidant state [11,12]. Collectively, mitochondrial activities seem to be a candidate for evaluating physical activity and its possible effects on the neuronal tissue [13]. ...
Evidence has validated the prophylactic effects of exercising on different aspects of health. On the opposite side, immobilization may lead to various destructive effects causing neurodegeneration. Here, we investigated the association between exercising and mitochondrial quality for preventing the destructive effects of restraint stress in different rat brain regions. Twenty-four male Wistar rats, were randomized into four groups (n = 6), exercise, stress, exercise + stress, and control. The exercise procedure consisted of running on a rodent treadmill for 8 weeks, and rats in the stress group were immobilized for 6 h. Rats were then euthanized by decapitation and tricarboxylic acid (TCA) cycle enzyme activity, antioxidant levels, and mitochondrial biogenesis factors were assessed in the frontal, hippocampus, parietal and temporal regions using spectrophotometer and western blot technique. Based on our results, increased activity of TCA cycle enzymes in the exercised and exercise-stressed groups was detected, except for malate dehydrogenase which was decreased in exercise-stressed group, and fumarase that did not change. Furthermore, the level of antioxidant agents (superoxide dismutase and reduced glutathione), mitochondrial biogenesis factors (peroxisome proliferator-activated receptor gamma coactivator 1-alpha and mitochondrial transcription factor A), and dynamics markers (Mitofusin 2, dynamic related protein 1, PTEN induced putative kinase-1, and parkin) increased in both mentioned groups. Interestingly our results also revealed that the majority of the mitochondrial factors increased in the frontal and parietal lobes, which may be in relation with the location of motor and sensory areas. Exercise can be used as a prophylactic approach against bioenergetics and mitochondrial dysfunction.
... Traditionally, exercise training adaptations in metabolic proteins are thought to be initiated by contraction-induced mechanical stress and challenges in energy (for example, changes to the AMP to ATP ratio), redox (for example, the NAD to NADH ratio), oxidative stress and ionic homeostasis (for example, Ca 2+ flux) leading to increased transcription of exercise-responsive lipid metabolic genes [84][85][86][87][88] . Such signalling pathways are not substantially affected by high fat intake, suggesting other potentially overlapping mechanisms. ...
Both the consumption of a diet rich in fatty acids and exercise training result in similar adaptations in several skeletal muscle proteins. These adaptations are involved in fatty acid uptake and activation within the myocyte, the mitochondrial import of fatty acids and further metabolism of fatty acids by β-oxidation. Fatty acid availability is repeatedly increased postprandially during the day, particularly during high dietary fat intake and also increases during, and after, aerobic exercise. As such, fatty acids are possible signalling candidates that regulate transcription of target genes encoding proteins involved in muscle lipid metabolism. The mechanism of signalling might be direct or indirect targeting of peroxisome proliferator-activated receptors by fatty acid ligands, by fatty acid-induced NAD+-stimulated activation of sirtuin 1 and/or fatty acid-mediated activation of AMP-activated protein kinase. Lactate might also have a role in lipid metabolic adaptations. Obesity is characterized by impairments in fatty acid oxidation capacity, and individuals with obesity show some rigidity in increasing fatty acid oxidation in response to high fat intake. However, individuals with obesity retain improvements in fatty acid oxidation capacity in response to exercise training, thereby highlighting exercise training as a potential method to improve lipid metabolic flexibility in obesity.
... Endurance exercise triggers transient and repeated increases in mRNA expression that drive changes in muscle protein content and ultimately result in training-induced adaptations. Thus, after an exercise session, changes in mRNA expressions occur on a minutes-hours timescale, whereas changes in protein content normally develops over days to weeks [33]. We observed little difference in the measured mRNA expressions between rested muscle (i.e., before SIT sessions) in the untrained and the trained state (see Figures S2-S6), which would imply that the changes in mRNA expression observed after SIT sessions typically returned to baseline before the next SIT session. ...
Sprint interval training (SIT) has emerged as a time-efficient training regimen for young individuals. Here, we studied whether SIT is effective also in elderly individuals and whether the training response was affected by treatment with the antioxidants vitamin C and E. Recreationally active elderly (mean age 65) men received either vitamin C (1 g/day) and vitamin E (235 mg/day) or placebo. Training consisted of nine SIT sessions (three sessions/week for three weeks of 4-6 repetitions of 30-s all-out cycling sprints) interposed by 4 min rest. Vastus lateralis muscle biopsies were taken before, 1 h after, and 24 h after the first and last SIT sessions. At the end of the three weeks of training, SIT-induced changes in relative mRNA expression of reactive oxygen/nitrogen species (ROS)-and mitochondria-related proteins, inflammatory mediators, and the sarcoplasmic reticulum Ca 2+ channel, the ryanodine receptor 1 (RyR1), were blunted in the vitamin treated group. Western blots frequently showed a major (>50%) decrease in the full-length expression of RyR1 24 h after SIT sessions; in the trained state, vitamin treatment seemed to provide protection against this severe RyR1 modification. Power at exhaustion during an incremental cycling test was increased by~5% at the end of the training period, whereas maximal oxygen uptake remained unchanged; vitamin treatment did not affect these measures. In conclusion, treatment with the antioxidants vitamin C and E blunts SIT-induced cellular signaling in skeletal muscle of elderly individuals, while the present training
... The mechanisms by which these homeostatic perturbations are sensed and then translated into improved function remain unresolved. Nonetheless, one common theory is these homeostatic perturbations in response to exercise will then initiate transcriptional programmes essential to increase the abundance of specific proteins and to ultimately improve cellular function [42][43][44]. In support of this, there is emerging evidence that in vivo lactate production from glycolysis upregulates genes associated with mitochondrial biogenesis [45,46]. ...
Prescribing the frequency, duration, or volume of training is simple as these factors can be altered by manipulating the number of exercise sessions per week, the duration of each session, or the total work performed in a given time frame (e.g., per week). However, prescribing exercise intensity is complex and controversy exists regarding the reliability and validity of the methods used to determine and prescribe intensity. This controversy arises from the absence of an agreed framework for assessing the construct validity of different methods used to determine exercise intensity. In this review, we have evaluated the construct validity of different methods for prescribing exercise intensity based on their ability to provoke homeostatic disturbances (e.g., changes in oxygen uptake kinetics and blood lactate) consistent with the moderate, heavy, and severe domains of exercise. Methods for prescribing exercise intensity include a percentage of anchor measurements, such as maximal oxygen uptake (\({\dot{\text{V}}\text{O}}_{{{\text{2max}}}}\)), peak oxygen uptake (\({\dot{\text{V}}\text{O}}_{{{\text{2peak}}}}\)), maximum heart rate (HRmax), and maximum work rate (i.e., power or velocity—\({\dot{\text{W}}}_{{\max}}\) or \({\dot{\text{V}}}_{{\max}}\), respectively), derived from a graded exercise test (GXT). However, despite their common use, it is apparent that prescribing exercise intensity based on a fixed percentage of these maximal anchors has little merit for eliciting distinct or domain-specific homeostatic perturbations. Some have advocated using submaximal anchors, including the ventilatory threshold (VT), the gas exchange threshold (GET), the respiratory compensation point (RCP), the first and second lactate threshold (LT1 and LT2), the maximal lactate steady state (MLSS), critical power (CP), and critical speed (CS). There is some evidence to support the validity of LT1, GET, and VT to delineate the moderate and heavy domains of exercise. However, there is little evidence to support the validity of most commonly used methods, with exception of CP and CS, to delineate the heavy and severe domains of exercise. As acute responses to exercise are not always predictive of chronic adaptations, training studies are required to verify whether different methods to prescribe exercise will affect adaptations to training. Better ways to prescribe exercise intensity should help sport scientists, researchers, clinicians, and coaches to design more effective training programs to achieve greater improvements in health and athletic performance.
... The beneficial effects of endurance exercise training on skeletal muscle mitochondrial biogenesis and mitochondrial function have been well characterized (Baar et al., 2002;Dohm et al., 1973;Hood, 2009;Perry and Hawley, 2018). Likewise, endurance exercise has been shown to promote myogenesis and myonuclear accretion (Hawke, 2005;Shefer et al., 2010;Smith et al., 2001). ...
Mitochondrial dysfunction has been implicated in various pathologies, including muscular dystrophies. During muscle regeneration, resident stem cells, also known as muscle satellite cells (MuSCs), undergo myogenic differentiation to form de novo myofibers or fuse to existing syncytia. Leveraging this cell-cell fusion process, we postulated that mitochondria stemming from MuSCs could be transferred to myofibers during muscle regeneration to remodel the mitochondrial network and restore bioenergetic function. Here, we report that dystrophic MuSCs manifest significant mitochondrial dysfunction and fuse with existing dystrophic myofibers to propagate mitochondrial dysfunction during muscle repair. We demonstrate that by transplanting healthy donor MuSCs into dystrophic host muscle, the mitochondrial network (reticulum) and bioenergetic function can be rejuvenated. Conversely, when bioenergetically-compromised donor MuSCs are transplanted, improvements in mitochondrial organization and bioenergetic function were ablated in the dystrophic recipient. Overall, these data reveal a unique role of muscle stem cells as an essential regulator of myofiber mitochondrial homeostasis and a potential therapeutic target against mitochondrial myopathies.
... Mitochondrial contents in skeletal muscle can be stimulated by mitochondrial biogenesis (Yan et al., 2012;Perry and Hawley, 2018), which is regulated by multiple signaling pathways, including peroxisome proliferator-activated receptorγ coactivator 1α (PGC-1α). PGC-1α is stimulated by several kinases, including CREB and extracellular signal-regulated protein kinases 1/2 (ERK1/2). ...
Mouse olfactory receptor 544 (Olfr544) is ectopically expressed in varied extra-nasal organs with tissue specific functions. Here, we investigated the functionality of Olfr544 in skeletal muscle cells and tissue. The expression of Olfr544 is confirmed by RT-PCR and qPCR in skeletal muscle cells and mouse skeletal muscle assessed by RT-PCR and qPCR. Olfr544 activation by its ligand, azelaic acid (AzA, 50 μM), induced mitochondrial biogenesis and autophagy in cultured skeletal myotubes by induction of cyclic adenosine monophosphate-response element binding protein (CREB)-peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α)-extracellular signal-regulated kinase-1/2 (ERK1/2) signaling axis. The silencing Olfr544 gene expression abrogated these effects of AzA in cultured myotubes. Similarly, in mice, the acute subcutaneous injection of AzA induced the CREB-PGC-1α-ERK1/2 pathways in mouse skeletal muscle, but these activations were negated in those of Olfr544 knockout mice. These demonstrate that the induction of mitochondrial biogenesis in skeletal muscle by AzA is Olfr544-dependent. Oral administration of AzA to high-fat-diet fed obese mice for 6 weeks increased mitochondrial DNA content in the skeletal muscle as well. Collectively, these findings demonstrate that Olfr544 activation by AzA regulates mitochondrial biogenesis in skeletal muscle. Intake of AzA or food containing AzA may help to improve skeletal muscle function.
... Additionally, although acute exercise studies involve non-blinded participants, these studies are relatively short (e.g. measurements collected at baseline and three hours-postacute exercise (Egan and Zierath, 2013;Perry and Hawley, 2017)) and may not provide enough time for behavioral-environmental differences (i.e., factors contributing to VDWS) to emerge between EX and CON. To our knowledge, only one acute exercise study has utilized the SD IR , highlighting acute exercise as a feasible model for exploring the existence and magnitude of VDTRUE. ...
Calculating the standard deviation of individual responses (SDIR) is recommended for estimating the magnitude of individual differences in training responsiveness in parallel‐arm exercise randomized controlled trials (RCTs). The purpose of this review article is to discuss potential limitations of parallel‐arm exercise RCTs that may confound/complicate the interpretation of the SDIR. To provide context for this discussion, we define the sources of variation that contribute to variability in the observed responses to exercise training and review the assumptions that underlie the interpretation of SDIR as a reflection of true individual differences in training responsiveness. This review also contains two novel analyses: (1) we demonstrate differences in variability in changes in diet and physical activity habits across an intervention period in both exercise and control groups, and (2) we examined participant dropout data from six RCTs and found that significantly (P < 0.001) more participants in control groups (12.8%) dropped out due to dissatisfaction with group assignment compared to exercise groups (3.4%). These novel analyses raise the possibility that the magnitude of within‐subject variability may not be equal between exercise and control groups. Overall, this review highlights that potential limitations of parallel‐arm exercise RCTs can violate the underlying assumptions of the SDIR and suggests that these limitations should be considered when interpreting the SDIR as an estimate of true individual differences in training responsiveness. Our review provides a critical appraisal of the SDIR approach, which is a statistical method for estimating individual variability in individual responses to exercise training. In our review, we discuss the assumptions and limitations that limit the application of this approach for exercise randomized controlled trials.
... The definition of mitochondrial biogenesis is sometimes too general. In the present review, we will consider mitochondrial biogenesis as recently defined by Perry and Hawley [73]: "an expansion of total muscle mitochondrial volume." This process requires a complex coordination of the transcription of the nuclear and the mitochondrial genome to assemble functional multisubunit respiratory chain proteins [52]. ...
Skeletal muscles require the proper production and distribution of energy to sustain their work. To ensure this requirement is met, mitochondria form large networks within skeletal muscle cells, and during exercise, they can enhance their functions. In the present review, we discuss recent findings on exercise-induced mitochondrial adaptations. We emphasize the importance of mitochondrial biogenesis, morphological changes, and increases in respiratory supercomplex formation as mechanisms triggered by exercise that may increase the function of skeletal muscles. Finally, we highlight the possible effects of nutraceutical compounds on mitochondrial performance during exercise and outline the use of exercise as a therapeutic tool in noncommunicable disease prevention. The resulting picture shows that the modulation of mitochondrial activity by exercise is not only fundamental for physical performance but also a key point for whole-organism well-being.
... Interestingly, the mitochondrial transcription factor A (TFAM, beta = 0.045, p = 0.0026) was also upregulated (beta = 0.045, p = 0.0026). This is consistent with the notion that exercise stimulates the activity of peroxisome proliferator-activated receptor gamma co-activator-1 alpha (PGC-1α), which in turn stimulates the transcription of TFAM (Perry and Hawley, 2018). TFAM binds to specific mtDNA sites and promotes the transcription and replication of mtDNA, which ultimately results in mitochondrial biogenesis (Bengtsson et al., 2001). ...
Muscle strength declines with aging and increasing physical activity is the only intervention known to attenuate this decline. In order to adequately investigate both preventive and therapeutic interventions against sarcopenia, a better understanding of the biological changes that are induced by physical activity in skeletal muscle is required. To determine the effect of physical activity on the skeletal muscle proteome, we utilized liquid-chromatography mass spectrometry to obtain quantitative proteomics data on human skeletal muscle biopsies from 60 well-characterized healthy individuals (20–87 years) who reported heterogeneous levels of physical activity (not active, active, moderately active, and highly active). Over 4,000 proteins were quantified, and higher self-reported physical activity was associated with substantial overrepresentation of proteins associated with mitochondria, TCA cycle, structural and contractile muscle, and genome maintenance. Conversely, proteins related to the spliceosome, transcription regulation, immune function, and apoptosis, DNA damage, and senescence were underrepresented with higher self-reported activity. These differences in observed protein expression were related to different levels of physical activity in daily life and not intense competitive exercise. In most instances, differences in protein levels were directly opposite to those reported in the literature observed with aging. These data suggest that being physically active in daily life has strong and biologically detectable beneficial effects on muscle.
Antioxidants in sports exercise training remain a debated research topic. Plant-derived polyphenol supplements are frequently used by athletes to reduce the negative effects of exercise-induced oxidative stress, accelerate the recovery of muscular function, and enhance performance. These processes can be efficiently modulated by antioxidant supplementation. The existing literature has failed to provide unequivocal evidence that dietary polyphenols should be promoted specifically among athletes. This narrative review summarizes the current knowledge regarding polyphenols’ bioavailability, their role in exercise-induced oxidative stress, antioxidant status, and supplementation strategies in athletes. Overall, we draw attention to the paucity of available evidence suggesting that most antioxidant substances are beneficial to athletes. Additional research is necessary to reveal more fully their impact on exercise-induced oxidative stress and athletes’ antioxidant status, as well as optimal dosing methods.
Acute exercise increases liver gluconeogenesis to supply glucose to working muscle. Concurrently, elevated liver lipid breakdown fuels the high energetic cost of gluconeogenesis. This functional coupling between liver gluconeogenesis and lipid oxidation has been proposed to underlie the ability of regular exercise to enhance liver mitochondrial oxidative metabolism and decrease liver steatosis in individuals with non-alcoholic fatty liver disease. Herein we tested whether repeated bouts of increased hepatic gluconeogenesis are necessary for exercise training to lower liver lipids. Experiments used diet-induced obese mice lacking hepatic phosphoenolpyruvate carboxykinase 1 (KO) to inhibit gluconeogenesis and wild type (WT) littermates. ² H/ ¹³ C metabolic flux analysis quantified glucose and mitochondrial oxidative fluxes in untrained mice at rest and during acute exercise. Circulating and tissue metabolite levels were determined during sedentary conditions, acute exercise, and refeeding post-exercise. Mice also underwent six weeks of treadmill running protocols to define hepatic and extrahepatic adaptations to exercise training. Untrained KO mice were unable to maintain euglycemia during acute exercise resulting from an inability to increase gluconeogenesis. Liver triacylglycerides were elevated following acute exercise and circulating β-hydroxybutyrate was higher during post-exercise refeeding in untrained KO mice. In contrast, exercise training prevented liver triacylglyceride accumulation in KO mice. This was accompanied by pronounced increases in indices of skeletal muscle mitochondrial oxidative metabolism in KO mice. Together, these results show that hepatic gluconeogenesis is dispensable for exercise training to reduce liver lipids. This may be due to responses in ketone body metabolism and/or metabolic adaptations in skeletal muscle to exercise.
Caffeine is one of the most widely used substances as recreational drug for performance-enhancement in sport, underpinned by a strong evidence base. Although the effects of caffeine are widely investigated within the scope of performance physiology, the molecular effects of caffeine within skeletal muscle remain unclear. Evidence from in vitro and in vivo models suggest that caffeine regulates the glucose metabolism in the skeletal muscle. Moreover, caffeine seems to stimulate CaMKII, PPARδ/β, AMPK and PGC1α, classical markers of exercise-adaptations, including mitochondrial biogenesis and mitochondrial content. This review summarizes evidence to suggest caffeine-effects within skeletal muscle fibers, focusing on the putative role of caffeine on mitochondrial biogenesis to explore whether caffeine supplementation might be a strategy to enhance mitochondrial biogenesis.
Physical inactivity and disuse lead to a decrease in the functionality of skeletal muscles (oxidative capacity, insulin sensitivity, and performance), which is associated with a change in mitochondrial density. In contrast, aerobic exercise training is effective for maintaining/increasing skeletal muscle mitochondrial density and functionality. The review considers the effect of increasing and decreasing physical activity on the mitochondrial density of human skeletal muscles, as well as the main mechanisms responsible for these changes. It is discussed that the content of mitochondrial proteins can be regulated by changing the content of their mRNAs, changes in the rate of synthesis specific for mitochondrial proteins, as well as changes in the rate of degradation, transport, import, and stability of mitochondrial proteins. It has been shown that the mechanisms of regulation of the mitochondrial proteins content under various interventions are significantly different. At the same time, their contribution to the change in the content of mitochondrial proteins is characterized clearly insufficiently, which emphasizes the relevance of further research in this area.
High-intensity interval training (HIIT) generates profound metabolic adaptations in skeletal muscle. These responses mirror performance improvements but follow a non-linear pattern comprised of an initial fast phase followed by a gradual plateau effect. The complete time-dependent molecular sequelae that regulates this plateau effect remains unknown. We hypothesize that the plateau effect during HIIT is restricted to specific pathways with communal upstream transcriptional regulation. To investigate this, eleven healthy men performed nine sessions of HIIT (10x4 minutes of cycling at 91 % of HR max ) over a 3-week period. Before and 3h after the 1 st and 9 th exercise bout, skeletal muscle biopsies were obtained, and RNA sequencing performed. Almost 2,000 genes across 84 pathways were differentially expressed in response to a single HIIT session. The overall transcriptional response to acute exercise was strikingly similar at 3 weeks, 83 % (n=1650) of the genes regulated after the 1 st bout of exercise were similarly regulated by the 9 th bout, albeit with a smaller effect size, and the response attenuated to on average 70 % of the 1 st bout. The attenuation differed substantially between pathways and was very pronounced for glycolysis and cellular adhesion but more preserved for MAPK and VEGF-A signalling. The attenuation was driven by a combination of changes in steady-state expression and specific transcriptional regulation. Given that the exercise intensity was progressively increased, and that the attenuation was pathway specific, we suggest that moderation of muscular adaptation after a period of training stems from targeted regulation rather than a diminished exercise stimulus.
Aim:
The maintenance of healthy and functional mitochondria is the result of a complex mitochondrial turnover and herein quality-control program which includes both mitochondrial biogenesis and autophagy of mitochondria. The aim of this study was to examine the effect of an intensified training load on skeletal muscle mitochondrial quality control in relation to changes in mitochondrial oxidative capacity, maximal oxygen consumption and performance in highly trained endurance athletes.
Methods:
27 elite endurance athletes performed high intensity interval exercise followed by moderate intensity continuous exercise 3 days per week for 4 weeks in addition to their usual volume of training. Mitochondrial oxidative capacity, abundance of mitochondrial proteins, markers of autophagy and antioxidant capacity of skeletal muscle were assessed in skeletal muscle biopsies before and after the intensified training period.
Results:
The intensified training period increased several autophagy markers suggesting an increased turnover of mitochondrial and cytosolic proteins. In permeabilized muscle fibers, mitochondrial respiration was ~20 % lower after training although some markers of mitochondrial density increased by 5-50%, indicative of a reduced mitochondrial quality by the intensified training intervention. The antioxidative proteins UCP3, ANT1, and SOD2 were increased after training, whereas we found an inactivation of aconitase. In agreement with the lower aconitase activity, the amount of mitochondrial LON protease that selectively degrades oxidized aconitase, was doubled.
Conclusion:
Together, this suggests that mitochondrial respiratory function is impaired during the initial recovery from a period of intensified endurance training while mitochondrial quality control is slightly activated in highly trained skeletal muscle.
Exercise training can induce robust changes in mitochondria that are beneficial for a range of metabolic health outcomes. However, a recent study suggests there might be an upper limit to the amount of high-intensity training that can be tolerated before disruptions to mitochondrial function and whole-body metabolic homeostasis occur.
Adult human brains consume a disproportionate amount of energy substrates (2–3% of body weight; 20–25% of total glucose and oxygen). Adenosine triphosphate (ATP) is a universal energy currency in brains and is produced by oxidative phosphorylation (OXPHOS) using ATP synthase, a nano-rotor powered by the proton gradient generated from proton-coupled electron transfer (PCET) in the multi-complex electron transport chain (ETC). ETC catalysis rates are reduced in brains from humans with neurodegenerative diseases (NDDs). Declines of ETC function in NDDs may result from combinations of nitrative stress (NS)–oxidative stress (OS) damage; mitochondrial and/or nuclear genomic mutations of ETC/OXPHOS genes; epigenetic modifications of ETC/OXPHOS genes; or defects in importation or assembly of ETC/OXPHOS proteins or complexes, respectively; or alterations in mitochondrial dynamics (fusion, fission, mitophagy). Substantial free energy is gained by direct O2-mediated oxidation of NADH. Traditional ETC mechanisms require separation between O2 and electrons flowing from NADH/FADH2 through the ETC. Quantum tunneling of electrons and much larger protons may facilitate this separation. Neuronal death may be viewed as a local increase in entropy requiring constant energy input to avoid. The ATP requirement of the brain may partially be used for avoidance of local entropy increase. Mitochondrial therapeutics seeks to correct deficiencies in ETC and OXPHOS.
New findings:
Blood flow restricted (BFR) exercise represents an approach to potentially augment the adaptive response to training and improve performance in endurance trained individuals. When combined with low-load resistance exercise, low- and moderate-intensity endurance exercise, and sprint interval exercise, BFR can provide an augmented acute stimulus for angiogenesis and mitochondrial biogenesis. These augmented acute responses can translate to enhanced capillary supply and mitochondrial function, and subsequent endurance-type performance, although this may depend on the nature of the exercise stimulus. There is a requirement to clarify whether BFR-training interventions can be utilised by high-performance endurance athletes within their structured training programme.
Abstract:
A key objective of an endurance athlete's training programme is to optimise the underlying physiological determinants of performance. Training-induced adaptations are governed by physiological and metabolic stressors which initiate transcriptional and translational signalling cascades to increase the abundance and/or function of proteins to improve physiological function. One important consideration is that training adaptations are reduced as training status increases, which is reflected at the molecular level as a blunting of the acute signalling response to exercise. This review examines blood-flow-restricted (BFR) exercise as a strategy for augmenting exercise-induced stressors and subsequent molecular signalling responses to enhance the physiological characteristics of the endurance athlete. Focus is placed on the processes of capillary growth and mitochondrial biogenesis. Recent evidence supports that BFR exercise presents an intensified training stimulus beyond that of performing the same exercise alone. We suggest this has the potential to induce enhanced physiological adaptations, including increases in capillary supply and mitochondrial function, which can contribute to improving endurance-exercise performance. There is, however, a lack of consensus as to the potency of BFR-training which is invariably due to the different modes, intensities, and durations of exercise and BFR methods. Further studies are needed to confirm its potential in the endurance-trained athlete. This article is protected by copyright. All rights reserved.
Purpose
To examine the relationship between changes in nuclear factor erythroid 2-related factor 2 (Nrf2) expression and markers of mitochondrial biogenesis in acutely and chronically exercised human skeletal muscle.
Methods
The impact of acute submaximal endurance (END) and supramaximal interval (Tabata) cycling on the upregulation of Nrf2 (and its downstream targets), nuclear respiratory factor-1 (NRF-1) and mitochondrial transcription factor A (TFAM) mRNA expression was examined in healthy young males (n = 10). The relationship between changes in citrate synthase (CS) maximal activity and the protein content of Nrf2, heme oxygenase 1 (HO-1), NRF-1, and TFAM was also investigated following 4 weeks of Tabata in a separate group of males (n = 21).
Results
Nrf2, NRF-1, and HO-1 mRNA expression increased after acute exercise (p < 0.05), whereas the increase in superoxide dismutase 2 (SOD2) mRNA expression approached significance (p = 0.08). Four weeks of Tabata increased CS activity and Nrf2, NRF-1, and TFAM protein content (p < 0.05), but decreased HO-1 protein content (p < 0.05). Training-induced changes in Nrf2 protein were strongly correlated with NRF-1 (r = 0.63, p < 0.01). When comparing protein content changes between individuals with the largest (HI: + 23%) and smallest (LO: − 1%) observed changes in CS activity (n = 8 each), increases in Nrf2 and TFAM protein content were apparent in the HI group only (p < 0.02) with medium-to-large effect sizes for between-group differences in changes in Nrf2 (ηp²=0.15) and TFAM (ηp² = 0.12) protein content.
Conclusion
Altogether, our findings support a potential role for Nrf2 in exercise-induced mitochondrial biogenesis in human skeletal muscle.
The chronic use of Dexamethasone (Dex) induced hyperglycemia and insulin resistance. On the other hand, physical exercise attenuates the symptoms induced by Dex in many physiological systems. However, the effect of the exercise on the changes in gastric motility induced by dexamethasone remains unknown. We hypothesized that low-intensity aerobic exercise modulates the metabolic effects induced by Dex-treatment by modifying the gastrointestinal function and feeding behavior in rats. Male rats were distributed into the following groups: Control (Ctrl), Dex (1.0 mg/kg, i.p.), Exercise (Ctrl + Exercise 5%) and (Dex1.0 + Exercise 5%). The exercise protocol was swimming for 5 consecutive days. We assessed the murinometric and nutritional indices, food intake, blood glucose by (ipGTT) and the gastric emptying rate of a liquid test meal were assessed in all rats. We observed a significant decrease (p < .05) in the gastric emptying in Dex1.0 group in relation to Ctrl group. The exercise prevented decrease in the gastric emptying (p < .05) in Dex1.0 + EX5% group when compared with Dex1.0 groups. The Dex1.0 group induced a significantly increase (p < .05) in glycaemia vs Ctrl group. The hyperglycemia was improving (p < .05) in the Dex1.0 + Ex5% compared with Dex1.0 groups. We observed a positive correlation (p < .05, and r = 0.7065) between gastric retention vs glycaemia in the Dex1.0 groups. The Dex1.0 reduced (p < .05) the body weight and altered body composition, promoting hypophagia. IL-6 increased (p < .05) at gastric fundus in Ex5% compared with Ctrl groups. In conclusion, the use of Dex1.0 decreases gastric emptying, promotes hyperglycemia and modifies feeding behavior. The low-intensity exercise prevents hyperglycemia, thus improving gastric dysmotility without improving the anthropometric parameters.
Despite its widespread acceptance as the “master regulator” of mitochondrial biogenesis (i.e., the expansion of the mitochondrial reticulum), peroxisome proliferator-activated receptor (PPAR) gamma coactivator-1 alpha (PGC-1α) appears to be dispensable for the training-induced augmentation of skeletal muscle mitochondrial content and respiratory function. In fact, a number of regulatory proteins have emerged as important players in skeletal muscle mitochondrial biogenesis and many of these proteins share key attributes with PGC-1α. In an effort to move past the simplistic notion of a “master regulator” of mitochondrial biogenesis, we highlight the regulatory mechanisms by which nuclear factor erythroid 2-related factor 2 (Nrf2), estrogen-related receptor gamma (ERRγ), PPARβ, and leucine-rich pentatricopeptide repeat-containing protein (LRP130) may contribute to the control of skeletal muscle mitochondrial biogenesis. We also present evidence supporting/refuting the ability of sulforaphane, quercetin, and epicatechin to promote skeletal muscle mitochondrial biogenesis and their potential to augment mitochondrial training adaptations. Targeted activation of specific pathways by these compounds may allow for greater mechanistic insight into the molecular pathways controlling mitochondrial biogenesis in human skeletal muscle. Dietary activation of mitochondrial biogenesis may also be useful in clinical populations with basal reductions in mitochondrial protein content, enzyme activities, and/or respiratory function as well as individuals who exhibit a blunted skeletal muscle responsiveness to contractile activity.
Novelty The existence of redundant pathways leading to mitochondrial biogenesis refutes the simplistic notion of a “master regulator” of mitochondrial biogenesis. Dietary activation of specific pathways may provide greater mechanistic insight into the exercise-induced mitochondrial biogenesis in human skeletal muscle.
Mitochondrial function have over the years been recognized as an important factor involved in health, disease, longevity and age-related disease progression. In this chapter, we discuss the relationship between exercise and the mitochondria and their role in the prevention, treatment, and risk assessment for cardiovascular diseases. Physical activity and mitochondrial function influence the whole body and have been proven to be important in cardiovascular health. The exact molecular mechanism(s) by which exercise and physical activity impact mitochondria function are an ongoing and increasing field of research. In this chapter, we will also discuss the basic functions and morphology of the mitochondria, with special reference to the heart and skeletal muscle tissue, and how it is affected by physical activity. Mitochondrial aspects such as disorders, dysfunction, replication, transcription, biogenesis, epigenetics, and mitochondrial therapeutics are also reviewed.
The present review highlights the idea that antioxidant supplementation can be optimized when tailored to the precise antioxidant status of each individual. A novel methodologic approach involving personalized nutrition, the mechanisms by which antioxidant status regulates human metabolism and performance, and similarities between antioxidants and other nutritional supplements are described. The usefulness of higher-level phenotypes for data-driven personalized treatments is also explained. We conclude that personally tailored antioxidant interventions based on specific antioxidant inadequacies or deficiencies could result in improved exercise performance accompanied by consistent alterations in redox profile.
Interval exercise typically involves repeated bouts of relatively intense exercise interspersed by short periods of recovery. A common classification scheme subdivides this method into high-intensity interval training (HIIT; ‘near maximal’ efforts) and sprint interval training (SIT; ‘supramaximal’ efforts). Both forms of interval training induce the classic physiological adaptations characteristic of moderate-intensity continuous training (MICT) such as increased aerobic capacity (VO2max) and mitochondrial content. This brief review considers the role of exercise intensity in mediating physiological adaptations to training, with a focus on the capacity for aerobic energy metabolism. With respect to skeletal muscle adaptations, cellular stress and the resultant metabolic signals for mitochondrial biogenesis depend largely on exercise intensity, with limited work suggesting that increases in mitochondrial content are superior after HIIT compared to MICT, at least when matched-work comparisons are made within the same individual. It is well established that SIT increases mitochondrial content to a similar extent as MICT despite a reduced exercise volume. At the whole-body level, VO2max is generally increased more by HIIT than MICT for a given training volume, whereas SIT and MICT similarly improve VO2max despite differences in training volume. There is less evidence available regarding the role of exercise intensity in mediating changes in skeletal muscle capillary density, maximum stroke volume and cardiac output, and blood volume. Furthermore, the interactions between intensity and duration and frequency have not been thoroughly explored. While interval training is clearly a potent stimulus for physiological remodelling in humans, the integrative response to this type of exercise warrants further attention, especially in comparison to traditional endurance training. This article is protected by copyright. All rights reserved
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.-Granata, C., Oliveira, R. S. F., Little, J. P., Renner, K., Bishop, D. J. 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 increases skeletal muscle expression of metabolic proteins improving the oxidative capacity. Adaptations in skeletal muscle by pharmacologically induced activation of 5'AMP-activated protein kinase (AMPK) are dependent on the AMPKα2 subunit. We hypothesized that exercise training-induced increases in exercise capacity and expression of metabolic proteins as well as acute exercise-induced gene regulation would be compromised in AMPKα1 and -α2 muscle-specific double knockout (mdKO) mice. An acute bout of exercise increased skeletal muscle mRNA content of cytochrome C oxidase subunit I, glucose transporter 4 and VEGF in an AMPK-dependent manner, while cluster of differentiation 36 and fatty acid transport protein 1 mRNA content increased similarly in AMPKα wild type (WT) and mdKO mice. During four weeks of voluntary running wheel exercise training, the AMPKα mdKO mice ran less than WT. Maximal running speed was lower in AMPKα mdKO than WT mice, but increased similarly in both genotypes with exercise training. Exercise training increased quadriceps protein content of ubiquinol-cytochrome-C reductase core protein 1 (UQCRC1), cytochrome C, hexokinase II, plasma membrane fatty acid binding protein and citrate synthase activity more in AMPKα WT than mdKO muscle. However, analysis of a subgroup of mice matched for running distance revealed that only UQCRC1 protein content increased more in WT than mdKO mice with exercise training. Thus, AMPKα1 and -α2 subunits are important for acute exercise-induced mRNA responses of some genes and may be involved in regulating basal metabolic protein expression, but seem to be less important in exercise training-induced adaptations in metabolic proteins.
Proteins of the peroxisome proliferator-activated receptor γ (PPARγ) coactivator 1 (PGC-1) family of transcriptional coactivators coordinate physiological adaptations in many tissues, usually in response to demands for higher nutrient and energy supply. Of the founding members of the family, PGC-1α (also known as PPARGC1A) is the most highly regulated gene, using multiple promoters and alternative splicing to produce a growing number of coactivator variants. PGC-1α promoters are selectively active in distinct tissues in response to specific stimuli. To date, more than ten novel PGC-1α isoforms have been reported to be expressed from a novel promoter (PGC-1α-b, PGC-1α-c), to undergo alternative splicing (NT-PGC-1α) or both (PGC-1α2, PGC-1α3, PGC-1α4). The resulting proteins display differential regulation and tissue distribution and, most importantly, exert specific biological functions. In this review we discuss the structural and functional characteristics of the novel PGC-1α isoforms, aiming to provide an integrative view of this constantly expanding system of transcriptional coactivators.
Physical exercise increases the cellular production of reactive oxygen species (ROS) in muscle, liver, and other organs. This is unlikely due to increased mitochondrial production but rather to extra-mitochondrial sources such as NADPH oxidase or xanthine oxidase. We have reported a xanthine oxidase mediated increase in ROS production in many experimental models from isolated cells to humans. Originally, ROS were considered as detrimental and thus as a likely cause of cell damage associated with exhaustion. In the last decade, evidence showing that ROSact as signals has been gathered and thus the idea that antioxidant supplementation in exercise is always recommendable has proved incorrect. In fact, we proposed that exercise itself can be considered as an antioxidant because training increases the expression of classical antioxidant enzymes such as superoxide dismutase and glutathione peroxidase and, in general, lowering the endogenous antioxidant enzymes by administration of antioxidant supplements may not be a good strategy when training. Antioxidant enzymes are not the only ones to be activated by training. Mitochondriogenesis is an important process activated in exercise. Many redox-sensitive enzymes are involved in this process. Important signaling molecules like MAP Kinases, NF-κB, PGC-1α, p53, Heat Shock Factor, and others modulate muscle adaptation to exercise. Interventions aimed at modifying the production of ROS in exercise must be performed with care as they may be detrimental in that they may lower useful adaptations to exercise.
Copyright © 2015. Published by Elsevier Inc.
An acute bout of exercise activates downstream signaling cascades that ultimately result in mitochondrial biogenesis. In addition to inducing mitochondrial synthesis, exercise also triggers the removal of damaged cellular material via autophagy, and of dysfunctional mitochondria through mitophagy. Here we investigated the necessity of p53 for the changes that transpire within the muscle upon an imposed metabolic and physiological challenge such as a bout of endurance exercise. We randomly assigned wildtype, (WT) and p53 knockout (KO) mice to control, acute exercise (90mins at 15m/min, AE) and AE + 3hr recovery (AER) group, and measured downstream alterations in markers of mitochondrial biogenesis, autophagy and mitophagy. In the absence of p53, activation of p38MAPK upon exercise was abolished, whereas CAMKII and AMPK only displayed an attenuated enhancement in the AER group compared to WT mice. The translocation of PGC-1α to the nucleus was diminished and only observed in the AER group, and the subsequent increase in mRNA transcripts related to mitochondrial biogenesis with exercise and recovery was absent in the p53 KO animals. Whole muscle autophagic and lysosomal markers did not respond to exercise irrespective of the genotype of the exercised mice, with the exception of increased ubiquitination observed in KO mice with exercise. Markers of mitophagy were elevated in response to AE and AER conditions in both WT and p53 KO runners. The data suggest that p53 is important for the exercise-induced activation of mitochondrial synthesis, and is integral in regulating autophagy during control conditions, but not in response to exercise.
The major tumour suppressor protein, p53, is one of the most well-studied proteins in cell biology. Often referred to as the Guardian of the Genome, the list of known functions of p53 include regulatory roles in cell cycle arrest, apoptosis, angiogenesis, DNA repair and cell senescence. More recently, p53 has been implicated as a key molecular player regulating substrate metabolism and exercise-induced mitochondrial biogenesis in skeletal muscle. In this context, the study of p53 therefore has obvious implications for both human health and performance, given that impaired mitochondrial content and function is associated with the pathology of many metabolic disorders such as ageing, type 2 diabetes, obesity and cancer, as well as reduced exercise performance. Studies on p53 knockout (KO) mice collectively demonstrate that ablation of p53 content reduces intermyofibrillar (IMF) and subsarcolemmal (SS) mitochondrial yield, reduces cytochrome c oxidase (COX) activity and peroxisome proliferator-activated receptor gamma co-activator 1-α protein content whilst also reducing mitochondrial respiration and increasing reactive oxygen species production during state 3 respiration in IMF mitochondria. Additionally, p53 KO mice exhibit marked reductions in exercise capacity (in the magnitude of 50 %) during fatiguing swimming, treadmill running and electrical stimulation protocols. p53 may regulate contractile-induced increases in mitochondrial content via modulating mitochondrial transcription factor A (Tfam) content and/or activity, given that p53 KO mice display reduced skeletal muscle mitochondrial DNA, Tfam messenger RNA and protein levels. Furthermore, upon muscle contraction, p53 is phosphorylated on serine 15 and subsequently translocates to the mitochondria where it forms a complex with Tfam to modulate expression of mitochondrial-encoded subunits of the COX complex. In human skeletal muscle, the exercise-induced phosphorylation of p53(Ser15) is enhanced in conditions of reduced carbohydrate availability in association with enhanced upstream signalling through 5'adenosine monophosphate-activated protein kinase but not p38 mitogen-activated protein kinase. In this way, undertaking regular exercise in carbohydrate restricted states may therefore be a practical approach to achieve the physiological benefits of consistent p53 signalling. Although our knowledge of p53 in exercise metabolism has advanced considerably, much of our current understanding of p53 regulation and associated targets is derived from various non-muscle cells and tissues. As such, many fundamental questions remain unanswered in contracting skeletal muscle. Detailed studies concerning the time-course of p53 activation (including additional post-translational modifications and subsequent subcellular translocation), as well as the effects of exercise modality (endurance versus resistance), intensity, duration, fibre type, age, training status and nutrient availability, must now be performed so that we can optimise exercise prescription guidelines to strategically target p53 signalling. The emerging role of p53 in skeletal muscle metabolism therefore represents a novel and exciting research area for exercise and muscle physiologists.
Repeated bouts of episodic myofibrillar contraction associated with exercise training are potent stimuli for physiological adaptation. However, the time course of adaptation and the continuity between alterations in mRNA expression and protein content are not well described in human skeletal muscle. Eight healthy, sedentary males cycled for 60 min at 80% of peak oxygen consumption (VO2peak) each day for fourteen consecutive days, resulting in an increase in VO2peak of 17.5±3.8%. Skeletal muscle biopsies were taken at baseline, and on the morning following (+16 h after exercise) the first, third, seventh, tenth and fourteenth training sessions. Markers of mitochondrial adaptation (Cyt c and COXIV expression, and citrate synthase activity) were increased within the first week of training, but the mtDNA/nDNA ratio was unchanged by two weeks of training. Accumulation of PGC-1α and ERRα protein during training suggests a regulatory role for these factors in adaptations of mitochondrial and metabolic gene expression. A subset of genes were transiently increased after one training session, but returned to baseline levels thereafter, which is supportive of the concept of transcriptional capacity being particularly sensitive to the onset of a new level of contractile activity. Thus, gene-specific temporal patterns of induction of mRNA expression and protein content are described. Our results illustrate the phenomenology of skeletal muscle plasticity and support the notion that transcript level adjustments, coupled to accumulation of encoded protein, underlie the modulation of skeletal muscle metabolism and phenotype by regular exercise.
Muscle activation as well as changes in peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1a) following high-intensity interval exercise (HIIE) were examined in young healthy men (n = 8; age, 21.962.2 yrs; VO 2 peak, 53.166.4 ml/min/kg; peak work rate, 317623.5 watts). On each of 3 visits HIIE was performed on a cycle ergometer at a target intensity of 73, 100, or 133% of peak work rate. Muscle biopsies were taken at rest and three hours after each exercise condition. Total work was not different between conditions (,730 kJ) while average power output (73%, 237621; 100%, 323626; 133%, 384635 watts) and EMG derived muscle activation (73%, 12626605; 100%, 20896737; 133%, 302961206 total integrated EMG per interval) increased in an intensity dependent fashion. PGC-1a mRNA was elevated after all three conditions (p,0.05), with a greater increase observed following the 100% condition (,9 fold, p,0.05) compared to both the 73 and 133% conditions (,4 fold). When expressed relative to muscle activation, the increase in PGC-1a mRNA for the 133% condition was less than that for the 73 and 100% conditions (p,0.05). SIRT1 mRNA was also elevated after all three conditions (,1.4 fold, p,0.05), with no difference between conditions. These findings suggest that intensity-dependent increases in PGC-1a mRNA following submaximal exercise are largely due to increases in muscle recruitment. As well, the blunted response of PGC-1a mRNA expression following supramaximal exercise may indicate that signalling mediated activation of PGC-1a may also be blunted. We also indentify that increases in PDK4, SIRT1, and RIP140 mRNA following acute exercise are dissociated from exercise intensity and muscle activation, while increases in EGR1 are augmented with supramaximal HIIE (p,0.05).
While a paucity of information exists regarding post-transcriptional mechanisms influencing mitochondrial biogenesis, in resting muscle the stability of peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α) mRNA has been linked to mitochondrial content. Therefore, in the current study we have examined if exercise promotes mRNA accumulation through the induction of proteins affiliated with mRNA stabilization (HuR) or conversely by decreasing the expression of mRNA destabilizing proteins (AUF1 and CUG-BP1). A single bout of exercise increased (P<0.05) the mRNA content of the transcriptional co-activator PGC-1α ~3.5 fold without affecting mRNA content for HuR, CUG-BP1 or AUF1. One week of treadmill exercise training did not alter markers of mitochondrial content, the mRNA stabilizing protein HuR, or the mRNA destabilizing protein AUF1. In contrast, the mRNA destabilizing protein CUG-BP1 increased ~40%. Four weeks of treadmill training increased the content of subunits of the electron transport chain ~50%, suggesting induction of mitochondrial biogenesis. Expression levels for HuR and CUG-BP1 were not altered with chronic training; however AUF1 expression was increased post-training. Specifically, training increased (P<0.05) total muscle expression of two of the four AUF1 isoforms ~50% (AUF1(p37), AUF1(p40)). Interestingly, these two isoforms were not detected in isolated nuclei; however, a large band representing the other two isoforms (AUF1(p42), AUF1(p45)) was present in nuclei and increased ~35% following chronic training. Altogether the current data provides evidence that mitochondrial biogenesis occurs in the presence of increased CUG-BP1 and AUF1 following, suggesting that reductions in known mRNA destabilizing proteins likely does not contribute to exercise-induced mitochondrial biogenesis.
The peroxisome proliferator-activated receptor (PPAR)-gamma coactivator-1 (PGC-1) can induce mitochondria biogenesis and has been implicated in the development of oxidative type I muscle fibers. The PPAR isoforms alpha, beta/delta, and gamma control the transcription of genes involved in fatty acid and glucose metabolism. As endurance training increases skeletal muscle mitochondria and type I fiber content and fatty acid oxidative capacity, our aim was to determine whether these increases could be mediated by possible effects on PGC-1 or PPAR-alpha, -beta/delta, and -gamma. Seven healthy men performed 6 weeks of endurance training and the expression levels of PGG-1 and PPA-R-alpha, -beta/delta, and -gamma mRNA as well as the fiber type distribution of the PGC-1 and PPAR-alpha proteins were measured in biopsies from their vastus lateralis muscle. PGC-1 and PPAR-a mRNA expression increased by 2.7- and 2.2-fold (P < 0.01), respectively, after endurance training. PGC-1 expression was 2.2- and 6-fold greater in the type IIa than in the type I and IIx fibers, respectively. It increased by 2.8-fold in the type IIa fibers and by 1.5-fold in both the type I and IIx fibers after endurance training (P < 0.015). PPAR-alpha was 1.9-fold greater in type I than in the II fibers and increased by 3.0-fold and 1.5-fold in these respective fibers after endurance training (P < 0.001). The increases in PGC-1 and PPAR-alpha levels reported in this study may play an important role in the changes in muscle mitochondria content, oxidative phenotype, and sensitivity to insulin known to be induced by endurance training.
Peroxisome proliferator-activated receptor a (PPARa) plays a key role in the transcriptional control of genes encoding mitochondrial fatty acid b-oxidation (FAO) enzymes. In this study we sought to determine whether the recently identified PPAR gamma coactivator 1 (PGC-1) is capable of coactivating PPARa in the transcriptional control of genes encoding FAO enzymes. Mammalian cell cotransfection experiments demon- strated that PGC-1 enhanced PPARa-mediated transcriptional activation of reporter plasmids containing PPARa target elements. PGC-1 also enhanced the transactivation activity of a PPARa-Gal4 DNA binding domain fusion protein. Retroviral vector-mediated expression studies performed in 3T3-L1 cells demonstrated that PPARa and PGC-1 cooperatively induced the expression of PPARa target genes and increased cellular palmitate oxidation rates. Glutathione S-transferase "pulldown" studies revealed that in contrast to the previously reported ligand-independent interaction with PPARg, PGC-1 binds PPARa in a ligand-influenced manner. Protein-protein interaction studies and mammalian cell hybrid experiments demonstrated that the PGC-1-PPARa interaction involves an LXXLL domain in PGC-1 and the PPARa AF2 region, consistent with the observed ligand influence. Last, the PGC-1 transactivation domain was mapped to within the NH2-terminal 120 amino acids of the PGC-1 molecule, a region distinct from the PPARa interacting domains. These results identify PGC-1 as a coactivator of PPARa in the transcriptional control of mitochondrial FAO capacity, define separable PPARa interaction and transactivation domains within the PGC-1 molecule, and demonstrate that certain features of the PPARa-PGC-1 interaction are distinct from that of PPARg-PGC-1.
Spatially indirect radiative recombinations (type II) have been studied in InAlAs–InP heterostructures grown by gas source molecular beam epitaxy with emphasis on the direct (InAlAs grown on InP) or inverse (InP on InAlAs) interface composition profile. Based on the results of their injection-dependent energy, lifetime and polarization, a new transition scheme is proposed: type II transitions have a low injection limit between 1.27 and 1.28 eV, a long lifetime (τ>1 μs) and strongly shift towards higher energy when increasing the injection. The type II recombination is polarized, the direction of maximum intensity being correlated with the expected interface structure. Lower energy transitions (E ⩽ 1.2 eV) indicate the presence of a well transition material at the interface: they should be better labeled as mixed type I–II. Previously published results are also reconsidered and seem to fit well within this model. © 1998 American Institute of Physics.
The aim of this study was to evaluate the changes in aerobic and anaerobic metabolism produced by a newly devised short training
programme. Five young male volunteers trained daily for 2 weeks on a cycle ergometer. Sessions consisted of 15-s all-out repetitions
with 45-s rest periods, plus 30-s all-out repetitions with 12-min rest periods. The number of repetitions was gradually increased
up to a maximum of seven. Biopsy samples of the vastus lateralis muscle were taken before and after training. Performance
changes were evaluated by two tests, a 30-s all-out test and a maximal progressive test. Significant increases in phosphocreatine
(31%) and glycogen (32%) were found at the end of training. In addition, a significant increase was observed in the muscle
activity of creatine kinase (44%), phosphofructokinase (106%), lactate dehydrogenase (45%), 3-hydroxy-acyl-CoA dehydrogenase
(60%) and citrate synthase (38%). After training, performance of the 30-s all-out test did not increase significantly, while
in the maximal progressive test, the maximum oxygen consumption increased from mean (SD) 57.3 (2.6) ml · min−1 · kg−1 to 63.8 (3.0) ml · min−1 · kg−1, and the maximum load from 300 (11) W to 330 (21) W; all changes were significant. In conclusion, this new protocol, which
utilises short durations, high loads and long recovery periods, seems to be an effective programme for improving the enzymatic
activities of the energetic pathways in a short period of time.
The mRNA of the nuclear coactivator peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) increases during prolonged exercise and is influenced by carbohydrate availability. It is unknown if the increases in mRNA reflect the PGC-1alpha protein or if glycogen stores are an important regulator. Seven male subjects [23 +/- 1.3 yr old, maximum oxygen uptake (Vo(2 max)) 48.4 +/- 0.8 ml.kg(-1).min(-1)] exercised to exhaustion ( approximately 2 h) at 65% Vo(2 max) followed by ingestion of either a high-carbohydrate (HC) or low-carbohydrate (LC) diet (7 or 2.9 g.kg(-1).day(-1), respectively) for 52 h of recovery. Glycogen remained depressed in LC (P < 0.05) while returning to resting levels by 24 h in HC. PGC-1alpha mRNA increased both at exhaustion (3-fold) and 2 h later (6.2-fold) (P < 0.05) but returned to rest levels by 24 h. PGC-1alpha protein increased (P < 0.05) 23% at exhaustion and remained elevated for at least 24 h (P < 0.05). While there was no direct treatment effect (HC vs. LC) for PGC-1alpha mRNA or protein, there was a linear relationship between the changes in glycogen and those in PGC-1alpha protein during exercise and recovery (r = -0.68, P < 0.05). In contrast, PGC-1beta did not increase with exercise but rather decreased (P < 0.05) below rest level at 24 and 52 h, and the decrease was greater (P < 0.05) in LC. PGC-1alpha protein content increased in prolonged exercise and remained upregulated for 24 h, but this could not have been predicted by the changes in mRNA. The beta-isoform declined rather than increasing, and this was greater when glycogen was not resynthesized to rest levels.
Endurance exercise is known to induce metabolic adaptations in skeletal muscle via activation of the transcriptional co-activator peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α). PGC-1α regulates mitochondrial biogenesis via regulating transcription of nuclear-encoded mitochondrial genes. Recently, PGC-1α has been shown to reside in mitochondria; however, the physiological consequences of mitochondrial PGC-1α remain unknown. We sought to delineate if an acute bout of endurance exercise can mediate an increase in mitochondrial PGC-1α content where it may co-activate mitochondrial transcription factor A to promote mtDNA transcription. C57Bl/6J mice (n = 12/group; ♀ = ♂) were randomly assigned to sedentary (SED), forced-endurance (END) exercise (15 m/min for 90 min), or forced endurance +3 h of recovery (END+3h) group. The END group was sacrificed immediately after exercise, whereas the SED and END+3h groups were euthanized 3 h after acute exercise. Acute exercise coordinately increased the mRNA expression of nuclear and mitochondrial DNA-encoded mitochondrial transcripts. Nuclear and mitochondrial abundance of PGC-1α in END and END+3h groups was significantly higher versus SED mice. In mitochondria, PGC-1α is in a complex with mitochondrial transcription factor A at mtDNA D-loop, and this interaction was positively modulated by exercise, similar to the increased binding of PGC-1α at the NRF-1 promoter. We conclude that in response to acute altered energy demands, PGC-1α re-localizes into nuclear and mitochondrial compartments where it functions as a transcriptional co-activator for both nuclear and mitochondrial DNA transcription factors. These results suggest that PGC-1α may dynamically facilitate nuclear-mitochondrial DNA cross-talk to promote net mitochondrial biogenesis.
The observation that muscular exercise is associated with oxidative stress in humans was first reported over 30 years ago. Since this initial report, numerous studies have confirmed that prolonged or high-intensity exercise results in oxidative damage to macromolecules in both blood and skeletal muscle. Although the primary tissue(s) responsible for reactive oxygen species (ROS) production during exercise remains a topic of debate, compelling evidence indicates that muscular activity promotes oxidant production in contracting skeletal muscle fibers. Mitochondria, NADPH oxidase, PLA₂-dependent processes, and xanthine oxidase have all been postulated to contribute to contraction-induced ROS production in muscle but the primary site of contraction-induced ROS production in muscle fibers remains unclear. Nonetheless, contraction-induced ROS generation has been shown to play an important physiological function in the regulation of both muscle force production and contraction-induced adaptive responses of muscle fibers to exercise training. Although knowledge in the field of exercise and oxidative stress has grown markedly during the past 30 years, this area continues to expand and there is much more to be learned about the role of ROS as signaling molecules in skeletal muscle.
Exercise training induces mitochondrial biogenesis, but the time course of molecular sequelae that accompany repetitive training stimuli remains to be determined in human skeletal muscle. Therefore, throughout a seven-session, high-intensity interval training period that increased (12%), we examined the time course of responses of (a) mitochondrial biogenesis and fusion and fission proteins, and (b) selected transcriptional and mitochondrial mRNAs and proteins in human muscle. Muscle biopsies were obtained 4 and 24 h after the 1st, 3rd, 5th and 7th training session. PGC-1α mRNA was increased >10-fold 4 h after the 1st session and returned to control within 24 h. This 'saw-tooth' pattern continued until the 7th bout, with smaller increases after each bout. In contrast, PGC-1α protein was increased 24 h after the 1st bout (23%) and plateaued at +30-40% between the 3rd and 7th bout. Increases in PGC-1β mRNA and protein were more delayed and smaller, and did not persist. Distinct patterns of increases were observed in peroxisome proliferator-activated receptor (PPAR) α and γ protein (1 session), PPAR β/δ mRNA and protein (5 sessions) and nuclear respiratory factor-2 protein (3 sessions) while no changes occurred in mitochondrial transcription factor A protein. Citrate synthase (CS) and β-HAD mRNA were rapidly increased (1 session), followed 2 sessions later (session 3) by increases in CS and β-HAD activities, and mitochondrial DNA. Changes in COX-IV mRNA (session 3) and protein (session 5) were more delayed. Training also increased mitochondrial fission proteins (fission protein-1, >2-fold; dynamin-related protein-1, 47%) and the fusion protein mitofusin-1 (35%) but not mitofusin-2. This study has provided the following novel information: (a) the training-induced increases in transcriptional and mitochondrial proteins appear to result from the cumulative effects of transient bursts in their mRNAs, (b) training-induced mitochondrial biogenesis appears to involve re-modelling in addition to increased mitochondrial content, and (c) the 'transcriptional capacity' of human muscle is extremely sensitive, being activated by one training bout.
AMP-activated protein kinase (AMPK) β subunits (β1 and β2) provide scaffolds for binding α and γ subunits and contain a carbohydrate-binding module important for regulating enzyme activity. We generated C57Bl/6 mice with germline deletion of AMPK β2 (β2 KO) and examined AMPK expression and activity, exercise capacity, metabolic control during muscle contractions, aminoimidazole carboxamide ribonucleotide (AICAR) sensitivity, and susceptibility to obesity-induced insulin resistance. We find that β2 KO mice are viable and breed normally. β2 KO mice had a reduction in skeletal muscle AMPK α1 and α2 expression despite up-regulation of the β1 isoform. Heart AMPK α2 expression was also reduced but this did not affect resting AMPK α1 or α2 activities. AMPK α1 and α2 activities were not changed in liver, fat, or hypothalamus. AICAR-stimulated glucose uptake but not fatty acid oxidation was impaired in β2 KO mice. During treadmill running β2 KO mice had reduced maximal and endurance exercise capacity, which was associated with lower muscle and heart AMPK activity and reduced levels of muscle and liver glycogen. Reductions in exercise capacity of β2 KO mice were not due to lower muscle mitochondrial content or defects in contraction-stimulated glucose uptake or fatty acid oxidation. When challenged with a high-fat diet β2 KO mice gained more weight and were more susceptible to the development of hyperinsulinemia and glucose intolerance. In summary these data show that deletion of AMPK β2 reduces AMPK activity in skeletal muscle resulting in impaired exercise capacity and the worsening of diet-induced obesity and glucose intolerance.
Repeated bouts of exercise promote the biogenesis of mitochondria by multiple steps in the gene expression patterning. The role of mRNA stability in controlling the expression of mitochondrial proteins is relatively unexplored. To induce mitochondrial biogenesis, we chronically stimulated (10 Hz; 3 or 6 h/day) rat muscle for 7 days. Chronic contractile activity (CCA) increased the protein expression of PGC-1alpha, c-myc, and mitochondrial transcription factor A (Tfam) by 1.6-, 1.7- and 2.0-fold, respectively. To determine mRNA stability, we incubated total RNA with cytosolic extracts using an in vitro cell-free system. We found that the intrinsic mRNA half-lives (t(1/2)) were variable within control muscle. Peroxisome proliferator-activated receptor-gamma, coactivator-1alpha (PGC-1alpha) and Tfam mRNAs decayed more rapidly (t(1/2) = 22.7 and 31.4 min) than c-myc mRNA (t(1/2) = 99.7 min). Furthermore, CCA resulted in a differential response in degradation kinetics. After CCA, PGC-1alpha and Tfam mRNA half-lives decreased by 48% and 44%, respectively, whereas c-myc mRNA half-life was unchanged. CCA induced an elevation of both the cytosolic RNA-stabilizing human antigen R (HuR) and destabilizing AUF1 (total) by 2.4- and 1.8-fold, respectively. Increases in the p37(AUF1), p40(AUF1), and p45(AUF1) isoforms were most evident. Thus these data indicate that CCA results in accelerated turnover rates of mRNAs encoding important mitochondrial biogenesis regulators in skeletal muscle. This adaptation is likely beneficial in permitting more rapid phenotypic plasticity in response to subsequent contractile activity.
Skeletal muscle contraction increases intracellular ATP turnover, calcium flux, and mechanical stress, initiating signal transduction pathways that modulate peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha)-dependent transcriptional programmes. The purpose of this study was to determine if the intensity of exercise regulates PGC-1alpha expression in human skeletal muscle, coincident with activation of signalling cascades known to regulate PGC-1alpha transcription. Eight sedentary males expended 400 kcal (1674 kj) during a single bout of cycle ergometer exercise on two separate occasions at either 40% (LO) or 80% (HI) of . Skeletal muscle biopsies from the m. vastus lateralis were taken at rest and at +0, +3 and +19 h after exercise. Energy expenditure during exercise was similar between trials, but the high intensity bout was shorter in duration (LO, 69.9 +/- 4.0 min; HI, 36.0 +/- 2.2 min, P < 0.05) and had a higher rate of glycogen utilization (P < 0.05). PGC-1alpha mRNA abundance increased in an intensity-dependent manner +3 h after exercise (LO, 3.8-fold; HI, 10.2-fold, P < 0.05). AMP-activated protein kinase (AMPK) (2.8-fold, P < 0.05) and calcium/calmodulin-dependent protein kinase II (CaMKII) phosphorylation (84%, P < 0.05) increased immediately after HI but not LO. p38 mitogen-activated protein kinase (MAPK) phosphorylation increased after both trials (2.0-fold, P < 0.05), but phosphorylation of the downstream transcription factor, activating transcription factor-2 (ATF-2), increased only after HI (2.4-fold, P < 0.05). Cyclic-AMP response element binding protein (CREB) phosphorylation was elevated at +3 h after both trials (80%, P < 0.05) and class IIa histone deacetylase (HDAC) phosphorylation increased only after HI (2.0-fold, P < 0.05). In conclusion, exercise intensity regulates PGC-1alpha mRNA abundance in human skeletal muscle in response to a single bout of exercise. This effect is mediated by differential activation of multiple signalling pathways, with ATF-2 and HDAC phosphorylation proposed as key intensity-dependent mediators.
Peroxisome proliferator-activated receptor gamma coactivator (PGC-1alpha) is a transcriptional coactivator that plays a key role in coordinating mitochondrial biogenesis. Recent evidence has linked p38 MAPK and AMPK with activation of PGC-1alpha. It was recently shown in rodent skeletal muscle that acute endurance exercise causes a shift in the subcellular localization of PGC-1alpha from the cytosol to the nucleus, allowing PGC-1alpha to coactivate transcription factors and increase mitochondrial gene expression, but human data are limited and equivocal in this regard. Our purpose was to examine p38 MAPK and AMPK activation, and PGC-1alpha protein content in whole muscle, cytosolic, and nuclear fractions of human skeletal muscle following an acute bout of endurance exercise. Eight trained men (29 +/- 3 yr; Vo(2peak) = 55 +/- 2 ml.kg(-1).min(-1)) cycled for 90 min at approximately 65% of Vo(2peak) and needle biopsy samples (vastus lateralis) were obtained before and immediately after exercise. At rest, the majority of PGC-1alpha was detected in cytosolic compared with the nuclear fractions. In response to exercise, nuclear PGC-1alpha protein increased by 54% (P < 0.05), yet whole muscle PGC-1alpha protein was unchanged compared with rest. Whole muscle and cytosolic p38 MAPK phosphorylation increased several-fold immediately after exercise compared with rest (P < 0.05). Acetyl CoA carboxylase (ACC) phosphorylation, a marker of AMPK activation, was increased by approximately 5-fold in cytosolic fractions following exercise (P < 0.05). These data provide evidence that, in human skeletal muscle, activation of cytosolic p38 MAPK and AMPK may be potential signals that lead to increased nuclear abundance and activation of PGC-1alpha in response to an acute bout of endurance exercise.
Acute exercise initiates rapid cellular signals, leading to the subsequent activation of proteins that increase gene transcription. The result is a higher level of mRNA expression, often observed during the recovery period following exercise. These molecules are translated into precursor proteins for import into preexisting mitochondria. Once inside the organelle, the protein is processed to its mature form and either activates mitochondrial DNA gene expression, serves as a single subunit enzyme, or is incorporated into multi-subunit complexes of the respiratory chain devoted to electron transport and substrate oxidation. The result of this exercise-induced sequence of events is the expansion of the mitochondrial network within muscle cells and the capacity for aerobic ATP provision. An understanding of the molecular processes involved in this complex pathway of organelle synthesis is important for therapeutic purposes, and is a primary research undertaking in laboratories involved in the study of mitochondrial biogenesis. This pathway in muscle becomes impaired with chronic inactivity and aging, which leads to a reduced muscle aerobic capacity and an increased tendency for mitochondrially mediated apoptosis, a situation that can contribute to muscle atrophy. The resumption, or adoption, of an active lifestyle can ameliorate this metabolic dysfunction, improve endurance, and help maintain muscle mass.
High-intensity aerobic interval training (HIIT) is a compromise between time-consuming moderate-intensity training and sprint-interval training requiring all-out efforts. However, there are few data regarding the ability of HIIT to increase the capacities of fat and carbohydrate oxidation in skeletal muscle. Using untrained recreationally active individuals, we investigated skeletal muscle and whole-body metabolic adaptations that occurred following 6 weeks of HIIT (~1 h of 10 x 4 min intervals at ~90% of peak oxygen consumption (VO2 peak), separated by 2 min rest, 3 d.week-1). A VO2 peak test, a test to exhaustion (TE) at 90% of pre-training VO2 peak, and a 1 h cycle at 60% of pre-training VO2 peak were performed pre- and post-HIIT. Muscle biopsies were sampled during the TE at rest, after 5 min, and at exhaustion. Training power output increased by 21%, and VO2 peak increased by 9% following HIIT. Muscle adaptations at rest included the following: (i) increased cytochrome c oxidase IV content (18%) and maximal activities of the mitochondrial enzymes citrate synthase (26%), beta-hydroxyacyl-CoA dehydrogenase (29%), aspartate-amino transferase (26%), and pyruvate dehydrogenase (PDH; 21%); (ii) increased FAT/CD36, FABPpm, GLUT 4, and MCT 1 and 4 transport proteins (14%-30%); and (iii) increased glycogen content (59%). Major adaptations during exercise included the following: (i) reduced glycogenolysis, lactate accumulation, and substrate phosphorylation (0-5 min of TE); (ii) unchanged PDH activation (carbohydrate oxidation; 0-5 min of TE); (iii) ~2-fold greater time during the TE; and (iv) increased fat oxidation at 60% of pre-training VO2 peak. This study demonstrated that 18 h of repeated high-intensity exercise sessions over 6 weeks (3 d.week-1) is a powerful method to increase whole-body and skeletal muscle capacities to oxidize fat and carbohydrate in previously untrained individuals.
We determined the effects of a cycle training program in which selected sessions were performed with low muscle glycogen content on training capacity and subsequent endurance performance, whole body substrate oxidation during submaximal exercise, and several mitochondrial enzymes and signaling proteins with putative roles in promoting training adaptation. Seven endurance-trained cyclists/triathletes trained daily (High) alternating between 100-min steady-state aerobic rides (AT) one day, followed by a high-intensity interval training session (HIT; 8 x 5 min at maximum self-selected effort) the next day. Another seven subjects trained twice every second day (Low), first undertaking AT, then 1-2 h later, the HIT. These training schedules were maintained for 3 wk. Forty-eight hours before and after the first and last training sessions, all subjects completed a 60-min steady-state ride (60SS) followed by a 60-min performance trial. Muscle biopsies were taken before and after 60SS, and rates of substrate oxidation were determined throughout this ride. Resting muscle glycogen concentration (412 +/- 51 vs. 577 +/- 34 micromol/g dry wt), rates of whole body fat oxidation during 60SS (1,261 +/- 247 vs. 1,698 +/- 174 micromol.kg(-1).60 min(-1)), the maximal activities of citrate synthase (45 +/- 2 vs. 54 +/- 1 mmol.kg dry wt(-1).min(-1)), and beta-hydroxyacyl-CoA-dehydrogenase (18 +/- 2 vs. 23 +/- 2 mmol.kg dry wt(-1).min(-1)) along with the total protein content of cytochrome c oxidase subunit IV were increased only in Low (all P < 0.05). Mitochondrial DNA content and peroxisome proliferator-activated receptor-gamma coactivator-1alpha protein levels were unchanged in both groups after training. Cycling performance improved by approximately 10% in both Low and High. We conclude that compared with training daily, training twice every second day compromised high-intensity training capacity. While selected markers of training adaptation were enhanced with twice a day training, the performance of a 1-h time trial undertaken after a 60-min steady-state ride was similar after once daily or twice every second day training programs.
Skeletal muscle is a tissue with a low mitochondrial content under basal conditions, but it is responsive to acute increases in contractile activity patterns (i.e. exercise) which initiate the signalling of a compensatory response, leading to the biogenesis of mitochondria and improved organelle function. Exercise also promotes the degradation of poorly functioning mitochondria (i.e. mitophagy), thereby accelerating mitochondrial turnover, and preserving a pool of healthy organelles. In contrast, muscle disuse, as well as the aging process, are associated with reduced mitochondrial quality and quantity in muscle. This has strong negative implications for whole-body metabolic health and the preservation of muscle mass. A number of traditional, as well as novel regulatory pathways exist in muscle that control both biogenesis and mitophagy. Interestingly, although the ablation of single regulatory transcription factorswithin these pathways often leads to a reduction in the basal mitochondrial content of muscle, this can invariably be overcome with exercise, signifying that exercise activates a multitude of pathways which can respond to restore mitochondrial health. This knowledge, along with growing realization that pharmacological agents can also promote mitochondrial health independently of exercise, leads to an optimistic outlook in which the maintenance of mitochondrial and whole-body metabolic health can be achieved by taking advantage of the broad benefits of exercise, along with the potential specificity of drug action. © 2016 The Author(s). Published by Portland Press Limited on behalf of the Biochemical Society.
The health-promoting benefits of exercise have been recognized for centuries, yet the molecular and cellular mechanisms for the acute and chronic adaptive response to a variety of physical activities remain incompletely described. This Perspective will take a forward view to highlight emerging questions and frontiers in the ever-changing landscape of exercise biology. The biology of exercise is complex, highly variable, and involves a myriad of adaptive responses in multiple organ systems. Given the multitude of changes that occur in each organ during exercise, future researchers will need to integrate tissue-specific responses with large-scale omics to resolve the integrated biology of exercise. The ultimate goal will be to understand how these system-wide, tissue-specific exercise-induced changes lead to measurable physiological outcomes at the whole-body level to improve health and well-being.
Copyright © 2015 Elsevier Inc. All rights reserved.
The beneficial effects of physical activity (PA) are well documented, yet the mechanisms by which PA prevents disease and improves health outcomes are poorly understood. To identify major gaps in knowledge and potential strategies for catalyzing progress in the field, the NIH convened a workshop in late October 2014 entitled "Understanding the Cellular and Molecular Mechanisms of Physical Activity-Induced Health Benefits." Presentations and discussions emphasized the challenges imposed by the integrative and intermittent nature of PA, the tremendous discovery potential of applying "-omics" technologies to understand interorgan crosstalk and biological networking systems during PA, and the need to establish an infrastructure of clinical trial sites with sufficient expertise to incorporate mechanistic outcome measures into adequately sized human PA trials. Identification of the mechanisms that underlie the link between PA and improved health holds extraordinary promise for discovery of novel therapeutic targets and development of personalized exercise medicine.
Copyright © 2015 Elsevier Inc. All rights reserved.
Regular exercise leads to systemic metabolic benefits which require the remodeling of energy resources in skeletal muscle. During acute exercise the increase in energy demands initiate mitochondrial biogenesis, orchestrated by the transcriptional co-activator PGC-1α. Much less is known about the degradation of mitochondria following exercise, although new evidence implicates a cellular recycling mechanism, autophagy/mitophagy, in exercise-induced adaptations. How mitophagy is activated, and what role PGC-1α plays in this process during exercise, has yet to be evaluated. Thus, we investigated autophagy/mitophagy in muscle immediately following an acute bout of exercise (Ex), or 90 min following exercise (Ex+R) in wild type (WT) and in PGC-1α knockout animals (KO). Deletion of PGC-1α resulted in a 40% decrease in mitochondrial content, as well as a 25% decline in running performance which was accompanied by severe acidosis in KO animals, indicating metabolic distress. Ex induced significant increases in gene transcripts of various mitochondrial (e.g COXIV, Tfam) and autophagy-related genes (e.g. p62, LC3) only in WT, but not in KO animals. Exercise also resulted in enhanced targeting of mitochondria for mitophagy, as well as increased autophagy and mitophagy flux in WT animals. This effect was attenuated in absence of PGC-1α. We also identified NPC1, a transmembrane protein involved in lysosomal lipid trafficking, as a target of PGC-1α that is induced with exercise. These results suggest that mitochondrial turnover is increased following exercise, and that this effect is at least in part co-ordinated by PGC-1α.
Copyright © 2015, American Journal of Physiology - Cell Physiology.
Exercise represents a major challenge to whole-body homeostasis provoking widespread perturbations in numerous cells, tissues, and organs that are caused by or are a response to the increased metabolic activity of contracting skeletal muscles. To meet this challenge, multiple integrated and often redundant responses operate to blunt the homeostatic threats generated by exercise-induced increases in muscle energy and oxygen demand. The application of molecular techniques to exercise biology has provided greater understanding of the multiplicity and complexity of cellular networks involved in exercise responses, and recent discoveries offer perspectives on the mechanisms by which muscle "communicates" with other organs and mediates the beneficial effects of exercise on health and performance.
Mitochondrial biogenesis in skeletal muscle results from the cumulative effect of transient increases in mRNA transcripts encoding mitochondrial proteins in response to repeated exercise sessions. This process requires the coordinated expression of both nuclear and mitochondrial (mt) DNA genomes and is regulated, for the most part, by the peroxisome proliferator-activated receptor γ coactivator 1α. Several other exercise-inducible proteins also play important roles in promoting an endurance phenotype, including AMP-activated protein kinase, p38 mitogen-activated protein kinase and tumour suppressor protein p53. Commencing endurance-based exercise with low muscle glycogen availability results in greater activation of many of these signalling proteins compared with when the same exercise is undertaken with normal glycogen concentration, suggesting that nutrient availability is a potent signal that can modulate the acute cellular responses to a single bout of exercise. When exercise sessions are repeated in the face of low glycogen availability (i.e. chronic training), the phenotypic adaptations resulting from such interventions are also augmented.
High-intensity interval training (HIIT) performed in an "all-out" manner (e.g., repeated Wingate Tests) is a time-efficient strategy to induce skeletal muscle remodelling towards a more oxidative phenotype. A fundamental question that remains unclear, however, is whether the intermittent or "pulsed" nature of the stimulus is critical to the adaptive response. In Study 1, we examined whether the activation of signalling cascades linked to mitochondrial biogenesis was dependent on the manner in which an acute high-intensity exercise stimulus was applied. Subjects performed either 4 x 30 s Wingate Tests interspersed with 4 min of rest (INT), or a bout of continuous exercise (CONT) that was matched for total work (67 ± 7 kJ) and which required ~4 min to complete as fast as possible. Both protocols elicited similar increases in markers of AMPK and p38 MAPK activation, and PGC-1α mRNA expression (main effects for time, P≤0.05). In Study 2, we determined whether 6 wk of the CONT protocol (3 d/wk) would increase skeletal muscle mitochondrial content similar to what we have previously reported after 6 wk of INT. Despite similar acute signalling responses to the CONT and INT protocols, training with CONT did not increase the maximal activity or protein content of a range of mitochondrial markers. However, peak oxygen uptake (VO2peak) was higher after CONT training (45.7 ± 5.4 to 48.3 ± 6.5 mL·kg-1·min-1; p < 0.05) and 250 kJ time trial performance was improved (26:32 ± 4:48 to 23:55 ± 4:16 min:sec, p < 0.001) in our recreationally-active participants. We conclude that the intermittent nature of the stimulus is important for maximizing skeletal muscle adaptations to low-volume, all-out HIIT. Despite the lack of skeletal muscle mitochondrial adaptations, our data show that a training program based on a brief bout of high-intensity exercise, which lasted <10 minutes per session including warm-up, and performed 3x/wk for 6 week, improved VO2peak in young healthy subjects.
The sections in this article are:
ABSTRACT Background: Human skeletal muscle fibers are the red, white, and intermediate fibers. They differ in their mitochondrial structure and enzyme activity. Scanning electron microscopy (SEM) was used on specially prepared specimens to determine the distinctive features of mitochondria and sarcoplasmic reticulum (SR) in each fiber type.Methods
Specimens of human limb muscles were glutaraldehyde fixed, frozen, fractured, and macerated by the aldehyde-osmium-DMSO-osmium procedure to expose large areas of mitochondria and SR. Osmium-hydrazine-impregnated tissues were examined without metal coating by ultra-high-resolution SEM.ResultsIn white fibers, paired long, thin mitochondria encircled myofibrils at the I-band level. In red fibers, the paired rows of stubby mitochondria at the I-band level were often connected across the A-band to the next row of mitochondria by a slender mitochondrial stalk. Intermediate fiber mitochondria resembled those in red fibers but were longer and thinner. Intermyofibrillar mitochondrial columns were most common in red fibers. All three muscle types had T-tubules along the A-I junction level, and small periodic terminal cisternae formed triads or dyads. Sarcotubules from terminal cisternae formed continuous three-dimensional networks at the I-band level, but intermittent straight sarcotubules, narrow two-dimensional networks, and some axial tubules traversed the A-band. The subsarcolemmal space had continuous two-dimensional SR at the H-band level and a coarse SR network at the I-band. These two SR networks were connected by single A-band sarcotubules.Conclusions
Mitochondrial shape and configuration were distinctive for each human skeletal muscle fiber type, but the SR was similar in all muscles examined. © 1997 Wiley-Liss, Inc.
Muscle biopsies were taken from the middle part of the vastus lateralis muscle of 9 men, who were not regularly involved in endurance training (M, average
[(V)\dot]\textO\text2 \dot V_{{\text{O}}_{\text{2}} }
max=61.3 ml/minkg), 3 sedentary women (W,
[(V)\dot]\textO\text2 \dot V_{{\text{O}}_{\text{2}} }
max=43.7 ml/minkg) and 5 well trained orienteers (TO,
[(V)\dot]\textO\text2 \dot V_{{\text{O}}_{\text{2}} }
max=76.1 ml/minkg). Morphometric analysis of 60 electron micrographs per biopsy gave the following significant differneces:
1.
The volume density of central mitochondria was 1.47-fold higher in TO than in M, and 1.44-fold higher in M than in W.
2.
The volume density of peripheric mitochondria was 3.22 times higher in TO compared to M.
3.
The ratio of the central mitochondrial volume to the volume of myofibrils was 1.54-fold higher in TO compared to M, while the respective ratio was 1.49 for M compared to W.
4.
The surface of the central mitochondria was 1.28-fold higher in TO than in M and 1.35-fold higher in M than in M.
5.
The surface of mitochondrial cristae was higher by a factor of 1.62 in TO compared to M and 1.35 in M compared to W.
6.
The central mitochondria were larger in TO compared to M by a factor of 1.12.
7.
The volume density of intracellular lipid (triglyceride droplets), was 2.5-fold higher in TO than in M.
There were highly significant correlations between
[(V)\dot]\textO\text2 \dot V_{{\text{O}}_{\text{2}} }
max and volume density of central mitochondria (r=0.82), surface of mitochondrial cristae (r=0.80) and the ratio of mitochondrial volume to myofibrillar volume (r=0.78).
No quantitative changes could be observed in mitochondrial fine structure. Neither volume density of sarcoplasma nor volume and surface density of the tubular system showed any difference as a function of training and sex.
It is postulated that
a)
an individual's maximum oxygen intake is limited not only by the capacity of the oxygen transport system but also by the oxidative capacity of mitochondria in the skeletal muscles, and
b)
the skeletal muscle of trained athletes contains a much higher quantity of intracellular lipids (triglyceride droplets) as a substrate directly available for energy production.
The dielectric constants in mixed oxides ZrO <sub> 2 </sub> +Y <sub> 2 </sub> O <sub> 3 </sub>, Ta <sub> 2 </sub> O <sub> 5 </sub> +TiO <sub> 2 </sub>, Ta <sub> 2 </sub> O <sub> 5 </sub> +Y <sub> 2 </sub> O <sub> 3 </sub>, and ZrO <sub> 2 </sub> +SiO <sub> 2 </sub> are examined in the context of the oxide additivity rule for molecular polarizability. The experimentally observed concentration dependence of the dielectric constant can be satisfactorily explained by taking account of effective molecular polarizability and molecular volume changes. The simple rule thus enables predictive study of the dielectric constant of oxide alloys. © 2001 American Institute of Physics.
The pyridine nucleotides, NAD(+) and NADH, are coenzymes that provide oxidoreductive power for the generation of ATP by mitochondria. In skeletal muscle, exercise perturbs the levels of NAD(+), NADH, and consequently, the NAD(+)/NADH ratio, and initial research in this area focused on the contribution of redox control to ATP production. More recently, numerous signaling pathways that are sensitive to perturbations in NAD(+)(H) have come to the fore, as has an appreciation for the potential importance of compartmentation of NAD(+)(H) metabolism and its subsequent effects on various signaling pathways. These pathways, which include the sirtuin (SIRT) proteins SIRT1 and SIRT3, the poly(ADP-ribose) polymerase (PARP) proteins PARP1 and PARP2, and COOH-terminal binding protein (CtBP), are of particular interest because they potentially link changes in cellular redox state to both immediate, metabolic-related changes and transcriptional adaptations to exercise. In this review, we discuss what is known, and not known, about the contribution of NAD(+)(H) metabolism and these aforementioned proteins to mitochondrial adaptations to acute and chronic endurance exercise.
Adaptive thermogenesis is an important component of energy homeostasis and a metabolic defense against obesity. We have cloned a novel transcriptional coactivator of nuclear receptors, termed PGC-1, from a brown fat cDNA library. PGC-1 mRNA expression is dramatically elevated upon cold exposure of mice in both brown fat and skeletal muscle, key thermogenic tissues. PGC-1 greatly increases the transcriptional activity of PPARgamma and the thyroid hormone receptor on the uncoupling protein (UCP-1) promoter. Ectopic expression of PGC-1 in white adipose cells activates expression of UCP-1 and key mitochondrial enzymes of the respiratory chain, and increases the cellular content of mitochondrial DNA. These results indicate that PGC-1 plays a key role in linking nuclear receptors to the transcriptional program of adaptive thermogenesis.
Receptor interacting protein 1 (RIP140) has recently been demonstrated to be a key player in the regulation of skeletal muscle mitochondrial content. We have shown that β-guanadinopropionic acid (β-GPA) feeding reduces RIP140 protein content and mRNA levels concomitant with increases in mitochondrial content (Williams DB, Sutherland LN, Bomhof MR, Basaraba SA, Thrush AB, Dyck DJ, Field CJ, Wright DC. Am J Physiol Endocrinol Metab 296: E1400-E1408, 2009). Since β-GPA feeding reduces high-energy phosphate levels and activates AMPK, alterations reminiscent of exercise, we hypothesized that exercise training would reduce RIP140 protein content. We further postulated that an acute bout of exercise, or interventions known to induce the expression of mitochondrial enzymes or genes involved in mitochondrial biogenesis, would result in decreases in nuclear RIP140 content. Two weeks of daily swim training increased markers of mitochondrial content in rat skeletal muscle independent of reductions in RIP140 protein. Similarly, high-intensity exercise training in humans failed to reduce RIP140 content despite increasing skeletal muscle mitochondrial enzymes. We found that 6 wk of daily 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) injections had no effect on RIP140 protein content in rat skeletal muscle while RIP140 content from LKB1 knockout mice was unaltered despite reductions in mitochondria. An acute bout of exercise, AICAR treatment, and epinephrine injections increased the mRNA levels of PGC-1α, COXIV, and lipin1 independent of decreases in nuclear RIP140 protein. Surprisingly these interventions increased RIP140 mRNA expression. In conclusion our results demonstrate that decreases in RIP140 protein content are not required for exercise and AMPK-dependent increases in skeletal muscle mitochondrial content, nor do acute perturbations alter the cellular localization of RIP140 in parallel with the induction of genes involved in mitochondrial biogenesis.
Evidence exists that mitochondrial content and/or function is reduced in muscle of aging individuals. The purposes of this study were to investigate the contribution of outer membrane protein import and assembly processes to this decline and to determine whether the assembly process could adapt to chronic contractile activity (CCA). Tom40 assembly into the translocases of the outer membrane (TOM complex) was measured in subsarcolemmal mitochondria obtained from young (6 mo old) and aged (36 mo old) Fischer 344 x Brown Norway animals. While the initial import of Tom40 did not differ between young and aged animals, its subsequent assembly into the final approximately 380 kDa complex was 2.2-fold higher (P < 0.05) in mitochondria from aged compared with young animals. This was associated with a higher abundance of Tom22, a protein vital for the assembly process. CCA induced a greater initial import and subsequent assembly of Tom40 in mitochondria from young animals, resulting in a CCA-induced 75% increase (P < 0.05) in Tom40 within mitochondria. This effect of CCA was attenuated in mitochondria from old animals. These data suggest that the import and assembly of proteins into the outer membrane do not contribute to reduced mitochondrial content or function in aged animals. Indeed, the greater assembly rate in mitochondria from aged animals may be a compensatory mechanism attempting to offset any decrements in mitochondrial content or function within aged muscle. Our data also indicate the potential of CCA to contribute to increased mitochondrial biogenesis in muscle through changes in the outer membrane import and assembly pathway.