Exercise and myocyte enhancer factor 2 regulation in human skeletal muscle

High-intensity training on CREB activation for improving brain health: a narrative review of possible molecular talks

Although physical exercise has obvious benefits in brain physiology, the molecular biomarkers induced by exercise protocols are inconclusive. Evidence indicates that exercise interventions are effective in shaping brain physiology. However, the potential mediator for improving brain functions is uncertain. CREB is one of the potential targets of exercise that triggers various molecular cross-talk to improve neurogenesis, long-term potentiation, and synaptogenesis. Therefore, CREB may be situated on the causal path between maintaining brain health and exercising. To support this, studies have shown that exercise-mediated CREB phosphorylation improves cognitive functions and memory. In addition, among the protocols of exercise (types, duration, and frequency), the intensity has been reported to be the most effective in triggering CREB-mediated molecular signaling. For example, HIT increases the synthesis of CREB, which may not only induce brain physiology but also induce brain pathology by higher activation of its downstream targets, such as BDNF. Therefore, this review aims to understand the effects of HIT on CREB function and how HIT can mediate the CREB-induced molecular cross-talk for maintaining brain health.

Epigenetic regulation is involved in reversal of obesity

Epigenetic processes play a crucial role in mediating the impact of environmental energetic challenges, from overconsumption to starvation. Over-nutrition of energy-dense foods and sedentary lifestyles contribute to the development of obesity, characterized by excessive fat storage and impaired metabolic signaling, stemming from disrupted brain signaling. Conversely, dieting and physical activity facilitate body weight rebalancing and trigger adaptive neural responses. These adaptations involve the upregulation of neurogenesis, synaptic plasticity and optimized brain function and energy homeostasis, balanced hormone signaling, normal metabolism, and reduced inflammation. The transition of the brain from a maladaptive to an adaptive state is partially guided by epigenetic mechanisms. While epigenetic mechanisms underlying obesity-related brain changes have been described, their role in mediating the reversal of maladaptation/obesity through lifestyle interventions remains less explored. This review focuses on elucidating epigenetic mechanisms involved in hypothalamic adaptations induced by lifestyle interventions. Given that lifestyle interventions are widely prescribed and accessible approaches for weight loss and maintenance, it is our challenge to uncover epigenetic mechanisms moderating these hypothalamic-functional beneficial changes.

Role of the histone deacetylase family in lipid metabolism: Structural specificity and functional diversity

Lipids play crucial roles in signal transduction. Lipid metabolism is associated with several transcriptional regulators, including peroxisome proliferator activated receptor γ, sterol regulatory element-binding protein 1, and acetyl-CoA carboxylase. In recent years, increasing evidence has suggested that members of the histone deacetylase (HDAC) family play key roles in lipid metabolism. However, the mechanisms by which each member of this family regulates lipid metabolism remain unclear. This review discusses the latest research on the roles played by HDACs in fat metabolism. The role of HDACs in obesity, diabetes, and atherosclerosis has also been discussed. In addition, the interaction of HDACs with the gut microbiome and circadian rhythm has been reviewed, and the future development trend in HDACs has been predicted, which may potentiate therapeutic application of targeted HDACs in related metabolic diseases.

Exercise performance and health: Role of GLUT4

The glucose transporter GLUT4 is integral for optimal skeletal muscle performance during exercise, as well as for metabolic health. Physiological regulation of GLUT4 translocation during exercise and increased GLUT4 expression following exercise involves multiple, redundant signalling pathways. These include effects of reactive oxygen species (ROS). ROS contribute to GLUT4 translocation that increases skeletal muscle glucose uptake during exercise and stimulate signalling pathways that increase GLUT4 expression. Conversely, ROS can also inhibit GLUT4 translocation and expression in metabolic disease states. The opposing roles of ROS in GLUT4 regulation are ultimately linked to the metabolic state of skeletal muscle and the intricate mechanisms involved give insights into pathways critical for exercise performance and implicated in metabolic health and disease.

Histone deacetylase inhibition enhances extracellular vesicles from muscle to promote osteogenesis via miR-873-3p

Regular physical activity is widely recognized for reducing the risk of various disorders, with skeletal muscles playing a key role by releasing biomolecules that benefit multiple organs and tissues. However, many individuals, particularly the elderly and those with clinical conditions, are unable to engage in physical exercise, necessitating alternative strategies to stimulate muscle cells to secrete beneficial biomolecules. Histone acetylation and deacetylation significantly influence exercise-induced gene expression, suggesting that targeting histone deacetylases (HDACs) could mimic some exercise responses. In this study, we explored the effects of the HDAC inhibitor Trichostatin A (TSA) on human skeletal muscle myoblasts (HSMMs). Our findings showed that TSA-induced hyperacetylation enhanced myotube fusion and increased the secretion of extracellular vesicles (EVs) enriched with miR-873-3p. These TSA-EVs promoted osteogenic differentiation in human bone marrow mesenchymal stem cells (hBMSCs) by targeting H2 calponin (CNN2). In vivo, systemic administration of TSA-EVs to osteoporosis mice resulted in significant improvements in bone mass. Moreover, TSA-EVs mimicked the osteogenic benefits of exercise-induced EVs, suggesting that HDAC inhibition can replicate exercise-induced bone health benefits. These results demonstrate the potential of TSA-induced muscle-derived EVs as a therapeutic strategy to enhance bone formation and prevent osteoporosis, particularly for individuals unable to exercise. Given the FDA-approved status of various HDAC inhibitors, this approach holds significant promise for rapid clinical translation in osteoporosis treatment.

The effects of exercise on epigenetic modifications: focus on DNA methylation, histone modifications and non-coding RNAs

Physical activity on a regular basis has been shown to bolster the overall wellness of an individual; research is now revealing that these changes are accompanied by epigenetic modifications. Regular exercise has been proven to make intervention plans more successful and prolong adherence to them. When it comes to epigenetic changes, there are four primary components. This includes changes to the DNA, histones, expression of particular non-coding RNAs and DNA methylation. External triggers, such as physical activity, can lead to modifications in the epigenetic components, resulting in changes in the transcription process. This report pays attention to the current knowledge that pertains to the epigenetic alterations that occur after exercise, the genes affected and the resulting characteristics.

Class IIa HDACs inhibit cell death pathways and protect muscle integrity in response to lipotoxicity

Lipotoxicity, the accumulation of lipids in non-adipose tissues, alters the metabolic transcriptome and mitochondrial metabolism in skeletal muscle. The mechanisms involved remain poorly understood. Here we show that lipotoxicity increased histone deacetylase 4 (HDAC4) and histone deacetylase 5 (HDAC5), which reduced the expression of metabolic genes and oxidative metabolism in skeletal muscle, resulting in increased non-oxidative glucose metabolism. This metabolic reprogramming was also associated with impaired apoptosis and ferroptosis responses, and preserved muscle cell viability in response to lipotoxicity. Mechanistically, increased HDAC4 and 5 decreased acetylation of p53 at K120, a modification required for transcriptional activation of apoptosis. Redox drivers of ferroptosis derived from oxidative metabolism were also reduced. The relevance of this pathway was demonstrated by overexpression of loss-of-function HDAC4 and HDAC5 mutants in skeletal muscle of obese db/db mice, which enhanced oxidative metabolic capacity, increased apoptosis and ferroptosis and reduced muscle mass. This study identifies HDAC4 and HDAC5 as repressors of skeletal muscle oxidative metabolism, which is linked to inhibition of cell death pathways and preservation of muscle integrity in response to lipotoxicity.

Research progress in the role and mechanism of Leucine in regulating animal growth and development

Leucine, a branched-chain amino acid, is essential in regulating animal growth and development. Recent research has uncovered the mechanisms underlying Leucine's anabolic effects on muscle and other tissues, including its ability to stimulate protein synthesis by activating the mTORC1 signaling pathway. The co-ingestion of carbohydrates and essential amino acids enhances Leucine's anabolic effects. Moreover, Leucine has been shown to benefit lipid metabolism, and insulin sensitivity, making it a promising strategy for preventing and treating metabolic diseases, including type 2 diabetes and obesity. While emerging evidence indicates that epigenetic mechanisms may mediate Leucine's effects on growth and development, more research is needed to elucidate its mechanisms of action fully. Specific studies have demonstrated that Leucine promotes muscle growth and metabolic health in animals and humans, making it a promising therapeutic agent. However, it is essential to note that Leucine supplementation may cause digestive issues or interact with certain medications, and More study is required to determine definitively optimal dosages. Therefore, it is important to understand how Leucine interacts with other nutrients, dietary factors, and lifestyle habits to maximize its benefits. Overall, Leucine's importance in human nutrition is far-reaching, and its potential to prevent muscle loss and enhance athletic performance warrants further investigation.

Transient changes to metabolic homeostasis initiate mitochondrial adaptation to endurance exercise

Endurance exercise is well established to increase mitochondrial content and function in skeletal muscle, a process termed mitochondrial biogenesis. Current understanding is that exercise initiates skeletal muscle mitochondrial remodeling via modulation of cellular nutrient, energetic and contractile stress pathways. These subtle changes in the cellular milieu are sensed by numerous transduction pathways that serve to initiate and coordinate an increase in mitochondrial gene transcription and translation. The result of these acute signaling events is the promotion of growth and assembly of mitochondria, coupled to a greater capacity for aerobic ATP provision in skeletal muscle. The aim of this review is to highlight the acute metabolic events induced by endurance exercise and the subsequent molecular pathways that sense this transient change in cellular homeostasis to drive mitochondrial adaptation and remodeling.

Histone deacetylase functions and therapeutic implications for adult skeletal muscle metabolism

Skeletal muscle is a highly adaptive organ that sustains continuous metabolic changes in response to different functional demands. Healthy skeletal muscle can adjust fuel utilization to the intensity of muscle activity, the availability of nutrients and the intrinsic characteristics of muscle fibers. This property is defined as metabolic flexibility. Importantly, impaired metabolic flexibility has been associated with, and likely contributes to the onset and progression of numerous pathologies, including sarcopenia and type 2 diabetes. Numerous studies involving genetic and pharmacological manipulations of histone deacetylases (HDACs) in vitro and in vivo have elucidated their multiple functions in regulating adult skeletal muscle metabolism and adaptation. Here, we briefly review HDAC classification and skeletal muscle metabolism in physiological conditions and upon metabolic stimuli. We then discuss HDAC functions in regulating skeletal muscle metabolism at baseline and following exercise. Finally, we give an overview of the literature regarding the activity of HDACs in skeletal muscle aging and their potential as therapeutic targets for the treatment of insulin resistance.

No dynamic changes in the expression of genes related to the epigenetic mechanism during acute exercise

Physical exercise results in structural remodeling in tissues and modifies cellular metabolism. Changes in gene expression lie at the root of these adaptations. Epigenetic changes are one of the factors responsible for such exercise-related alterations. One-hour acute exercise will change DNMT1, HDAC1, and JHDM1D transcriptions in PBMC. This study examined changes in the expression of genes responsible for epigenetic modifications (HDAC1, DNMT1, and JHDM1D) during and after an incremental exercise test on a treadmill and a 30-min recovery. Blood samples from 9 highly trained triathletes were tested. Examination of the transcripts showed no significant changes. Correlations between transcript results and biochemical indices revealed a significant (p = 0.007) relationship between JHDM1D mRNA and the number of monocytes at peak exercise intensity (exhaustion), while there was no significant (p = 0.053) correlation at rest. There are no rapid changes in the mRNA levels of the genes studied in blood cells in competitive athletes during acute exercise and recovery. Due to the small group of subjects studied, more extensive research is needed to verify correlations between transcription and biochemical variables.

PGC-1α and MEF2 Regulate the Transcription of the Carnitine Transporter OCTN2 Gene in C2C12 Cells and in Mouse Skeletal Muscle

OCTN2 (SLC22A5) is a carnitine transporter whose main function is the active transport of carnitine into cells. In skeletal muscle and other organs, the regulation of the SLC22A5 gene transcription has been shown to depend on the nuclear transcription factor PPAR-α. Due to the observation that the muscle OCTN2 mRNA level is maintained in PPAR-α knock-out mice and that PGC-1α overexpression in C2C12 myoblasts increases OCTN2 mRNA expression, we suspected additional regulatory pathways for SLC22A5 gene transcription. Indeed, we detected several binding sites of the myocyte-enhancing factor MEF2 in the upstream region of the SLC22A5 gene, and MEF2C/MEF2D stimulated the activity of the OCTN2 promoter in gene reporter assays. This stimulation was increased by PGC-1α and was blunted for a SLC22A5 promoter fragment with a mutated MEF2 binding site. Further, we demonstrated the specific binding of MEF2 to the SLC22A5 gene promoter, and a supershift of the MEF2/DNA complex in electrophoretic mobility shift assays. In immunoprecipitation experiments, we could demonstrate the interaction between PGC-1α and MEF2. In addition, SB203580, a specific inhibitor of p38 MAPK, blocked and interferon-γ stimulated the transcriptional activity of the SLC22A5 gene promoter. Finally, mice with muscle-specific overexpression of OCTN2 showed an increase in OCTN2 mRNA and protein expression in skeletal muscle. In conclusion, we detected and characterized a second stimulatory pathway of SLC22A5 gene transcription in skeletal muscle, which involves the nuclear transcription factor MEF2 and co-stimulation by PGC-1α and which is controlled by the p38 MAPK signaling cascade.

Post-translational Modifications: The Signals at the Intersection of Exercise, Glucose Uptake, and Insulin Sensitivity

Diabetes is a global epidemic, of which type 2 diabetes makes up the majority of cases. Nonetheless, for some individuals, type 2 diabetes is eminently preventable and treatable via lifestyle interventions. Glucose uptake into skeletal muscle increases during and in recovery from exercise, with exercise effective at controlling glucose homeostasis in individuals with type 2 diabetes. Furthermore, acute and chronic exercise sensitizes skeletal muscle to insulin. A complex network of signals converge and interact to regulate glucose metabolism and insulin sensitivity in response to exercise. Numerous forms of post-translational modifications (eg, phosphorylation, ubiquitination, acetylation, ribosylation, and more) are regulated by exercise. Here we review the current state of the art of the role of post-translational modifications in transducing exercise-induced signals to modulate glucose uptake and insulin sensitivity within skeletal muscle. Furthermore, we consider emerging evidence for noncanonical signaling in the control of glucose homeostasis and the potential for regulation by exercise. While exercise is clearly an effective intervention to reduce glycemia and improve insulin sensitivity, the insulin- and exercise-sensitive signaling networks orchestrating this biology are not fully clarified. Elucidation of the complex proteome-wide interactions between post-translational modifications and the associated functional implications will identify mechanisms by which exercise regulates glucose homeostasis and insulin sensitivity. In doing so, this knowledge should illuminate novel therapeutic targets to enhance insulin sensitivity for the clinical management of type 2 diabetes.

High-intensity interval training improves fat oxidation during submaximal exercise in active young men

This study aimed to examine the effects of four-weeks high-intensity interval training (HIIT) on fat oxidation responses during submaximal exercise in active young men. For this purpose, 20 active young men (who participated in the exercise three times per week) were divided into two groups, including a training group (age: 19.3±0.48 years, V̇O2peak 2.9±0.35 l/min, n=10) and a control group (age: 19.7±0.67 years, V̇O2peak 2.7±0.26 l/min, n=10). The training group performed high-intensity interval training for three sessions per week. Specifically, each session included 8-11 intensive cycling efforts comprising of 60 s duration. A 75 s low pedalling rate (30 W) was used as an active recovery between the intervals. Furthermore, a V̇O2peak test was performed prior to, at the end of two weeks and after the training period. Also, a 60 min constant cycling protocol was performed at ~60% V̇O2peak, in addition to the V̇O2peak test, before and after the training protocol. To assess plasma free fatty acids and glucose, blood samples were taken during a 60-min aerobic exercise prior to and following the training period. An increase (17.8%) in V̇O2peak was observed for the HIIT group after the training period compared to the control group (P<0.05). The HIIT group performed the 60 min sub-maximal exercise test at a lower percentage of V̇O2peak, and decreases in the respiratory exchange ratio were greater in the HIIT group than in the control group (P<0.05). Compared to the pre-test values and control group results, the HIIT group used less carbohydrate and more lipid oxidation during submaximal exercise (P<0.05). The present study’s results indicate that short-term low volume HIIT can increase aerobic capacity and fat oxidation during submaximal exercise.

The epigenetic landscape of exercise in cardiac health and disease

With the rising incidence of cardiovascular diseases, the concomitant mortality and morbidity impose huge burdens on quality of life and societal costs. It is generally accepted that physical inactivity is one of the major risk factors for cardiac disease and that exercise benefits the heart in both physiological and pathologic conditions. However, the molecular mechanisms governing the cardioprotective effects exerted by exercise remain incompletely understood. Most recently, an increasing number of studies indicate the involvement of epigenetic modifications in the promotion of cardiac health and prevention of cardiac disease. Exercise and other lifestyle factors extensively induce epigenetic modifications, including DNA/RNA methylation, histone post-translational modifications, and non-coding RNAs in multiple tissues, which may contribute to their positive effects in human health and diseases. In addition, several studies have shown that maternal or paternal exercise prevents age-associated or high-fat diet-induced metabolic dysfunction in the offspring, reinforcing the importance of epigenetics in mediating the beneficial effects of exercise. It has been shown that exercise can directly modify cardiac epigenetics to promote cardiac health and protect the heart against various pathological processes, or it can modify epigenetics in other tissues, which reduces the risk of cardiac disease and affords cardioprotection through exerkines. An in-depth understanding of the epigenetic landscape of cardioprotective response to exercise will provide new therapeutic targets for cardiac diseases. This review, therefore, aimed to acquaint the cardiac community with the rapidly advancing and evolving field of exercise and epigenetics.

Role of genes related to performance and reproduction of Thoroughbreds in training and breeding - A review

Thoroughbreds have been selected for speed and stamina since the 1700s. This selection resulted in structural and functional system-wide adaptations that enhanced physiological characteristics for outstanding speed of 61-71 kph (38-44 mph) between 1,000 and 3,200 m (5 furlongs - 2 miles). At present, horseracing is still an economically important industrial sector, therefore intensive research is underway to explore genes that allow the utilisation of genetic abilities and are significant in breeding and training. This study aims to provide an overview of genetic research and its applicability related to Thoroughbreds.

Building-up fit muscles for the future: Transgenerational programming of skeletal muscle through physical exercise

'Special issue - In Utero and Early Life Programming of Aging and Disease'. Skeletal muscle (SM) adaptations to physical exercise (PE) have been extensively studied due, not only to the relevance of its in situ plasticity, but also to the SM endocrine-like effects in noncontractile tissues, such as brain, liver or adipocytes. Regular PE has been considered a pleiotropic nonpharmacological strategy to prevent and counteract the deleterious consequences of several metabolic, cardiovascular, oncological and neurodegenerative disorders. Additionally, PE performed by parents seems to have a direct impact in the offspring through the transgenerational programming of different tissues, such as SM. In fact, SM offspring programming mechanisms seems to be orchestrated, at least in part, by epigenetic machinery conditioning transcriptional or post-transcriptional processes. Ultimately, PE performed in the early in life is also a critical window of opportunity to positively modulate the juvenile and adult phenotype. Parental PE has a positive impact in several health-related offspring outcomes, such as SM metabolism, differentiation, morphology and ultimately in offspring exercise volition and endurance. Also, early-life PE counteracts conceptional-related adverse effects and induces long-lasting healthy benefits throughout adulthood. Additionally, epigenetics mechanisms seem to play a key role in the PE-induced SM adaptations. Despite the undoubtedly positive role of parental and early-life PE on SM phenotype, a strong research effort is still needed to better understand the mechanisms that positively regulate PE-induced SM programming.

Exercise and health: historical perspectives and new insights

Since ancient times, the health benefits of regular physical activity/exercise have been recognized and the classic studies of Morris and Paffenbarger provided the epidemiological evidence in support of such an association. Cardiorespiratory fitness, often measured by maximal oxygen uptake, and habitual physical activity levels are inversely related to mortality. Thus, studies exploring the biological bases of the health benefits of exercise have largely focused on the cardiovascular system and skeletal muscle (mass and metabolism), although there is increasing evidence that multiple tissues and organ systems are influenced by regular exercise. Communication between contracting skeletal muscle and multiple organs has been implicated in exercise benefits, as indeed has other interorgan "cross-talk." The application of molecular biology techniques and "omics" approaches to questions in exercise biology has opened new lines of investigation to better understand the beneficial effects of exercise and, in so doing, inform the optimization of exercise regimens and the identification of novel therapeutic strategies to enhance health and well-being.

Mitochondrial network remodeling: an important feature of myogenesis and skeletal muscle regeneration

The remodeling of the mitochondrial network is a critical process in maintaining cellular homeostasis and is intimately related to mitochondrial function. The interplay between the formation of new mitochondria (biogenesis) and the removal of damaged mitochondria (mitophagy) provide a means for the repopulation of the mitochondrial network. Additionally, mitochondrial fission and fusion serve as a bridge between biogenesis and mitophagy. In recent years, the importance of these processes has been characterised in multiple tissue- and cell-types, and under various conditions. In skeletal muscle, the robust remodeling of the mitochondrial network is observed, particularly after injury where large portions of the tissue/cell structures are damaged. The significance of mitochondrial remodeling in regulating skeletal muscle regeneration has been widely studied, with alterations in mitochondrial remodeling processes leading to incomplete regeneration and impaired skeletal muscle function. Needless to say, important questions related to mitochondrial remodeling and skeletal muscle regeneration still remain unanswered and require further investigation. Therefore, this review will discuss the known molecular mechanisms of mitochondrial network remodeling, as well as integrate these mechanisms and discuss their relevance in myogenesis and regenerating skeletal muscle.

Exercise, CaMKII, and type 2 diabetes

Individuals who exercise regularly are protected from type 2 diabetes and other metabolic syndromes, in part by enhanced gene transcription and induction of many signaling pathways crucial in correcting impaired metabolic pathways associated with a sedentary lifestyle. Exercise activates Calmodulin-dependent protein kinase (CaMK)II, resulting in increased mitochondrial oxidative capacity and glucose transport. CaMKII regulates many health beneficial cellular functions in individuals who exercise compared with those who do not exercise. The role of exercise in the regulation of carbohydrate, lipid metabolism, and insulin signaling pathways are explained at the onset. Followed by the role of exercise in the regulation of glucose transporter (GLUT)4 expression and mitochondrial biogenesis are explained. Next, the main functions of Calmodulin-dependent protein kinase and the mechanism to activate it are illustrated, finally, an overview of the role of CaMKII in regulating GLUT4 expression, mitochondrial biogenesis, and histone modification are discussed.

Plantar Mechanical Stimulation Maintains Slow Myosin Expression in Disused Rat Soleus Muscle via NO-Dependent Signaling

It was observed that gravitational unloading during space missions and simulated microgravity in ground-based studies leads to both transformation of slow-twitch muscle fibers into fast-twitch fibers and to the elimination of support afferentation, leading to the "switching-off" of postural muscle motor units electrical activity. In recent years, plantar mechanical stimulation (PMS) has been found to maintain the neuromuscular activity of the hindlimb muscles. Nitric oxide (NO) was shown to be one of the mediators of muscle fiber activity, which can also promote slow-type myosin expression. We hypothesized that applying PMS during rat hindlimb unloading would lead to NO production upregulation and prevention of the unloading-induced slow-to-fast fiber-type shift in rat soleus muscles. To test this hypothesis, Wistar rats were hindlimb suspended and subjected to daily PMS, and one group of PMS-subjected animals was also treated with nitric oxide synthase inhibitor (L-NAME). We discovered that PMS led to sustained NO level in soleus muscles of the suspended animals, and NOS inhibitor administration blocked this effect, as well as the positive effects of PMS on myosin I and IIa mRNA transcription and slow-to-fast fiber-type ratio during rat hindlimb unloading. The results of the study indicate that NOS activity is necessary for the PMS-mediated prevention of slow-to-fast fiber-type shift and myosin I and IIa mRNA transcription decreases during rat hindlimb unloading.

Histone deacetylase 5 regulates interleukin 6 secretion and insulin action in skeletal muscle

OBJECTIVE

Physical exercise training is associated with increased glucose uptake in skeletal muscle and improved glycemic control. HDAC5, a class IIa histone deacetylase, has been shown to regulate transcription of the insulin-responsive glucose transporter GLUT4 in cultured muscle cells. In this study, we analyzed the contribution of HDAC5 to the transcriptional network in muscle and the beneficial effect of muscle contraction and regular exercise on glucose metabolism.

METHODS

HDAC5 knockout mice (KO) and wild-type (WT) littermates were trained for 8 weeks on treadmills, metabolically phenotyped, and compared to sedentary controls. Hdac5-deficient skeletal muscle and cultured Hdac5-knockdown (KD) C2C12 myotubes were utilized for studies of gene expression and glucose metabolism. Chromatin immunoprecipitation (ChIP) studies were conducted to analyze Il6 promoter activity using H3K9ac and HDAC5 antibodies.

RESULTS

Global transcriptome analysis of Hdac5 KO gastrocnemius muscle demonstrated activation of the IL-6 signaling pathway. Accordingly, knockdown of Hdac5 in C2C12 myotubes led to higher expression and secretion of IL-6 with enhanced insulin-stimulated activation of AKT that was reversed by Il6 knockdown. Moreover, Hdac5-deficient myotubes exhibited enhanced glucose uptake, glycogen synthesis, and elevated expression levels of the glucose transporter GLUT4. Transcription of Il6 was further enhanced by electrical pulse stimulation in Hdac5-deficient C2C12 myotubes. ChIP identified a ∼1 kb fragment of the Il6 promoter that interacts with HDAC5 and demonstrated increased activation-associated histone marker AcH3K9 in Hdac5-deficient muscle cells. Exercise intervention of HDAC5 KO mice resulted in improved systemic glucose tolerance as compared to WT controls.

CONCLUSIONS

We identified HDAC5 as a negative epigenetic regulator of IL-6 synthesis and release in skeletal muscle. HDAC5 may exert beneficial effects through two different mechanisms, transcriptional control of genes required for glucose disposal and utilization, and HDAC5-dependent IL-6 signaling cross-talk to improve glucose uptake in muscle in response to exercise.

Exercise and GLUT4

The glucose transporter GLUT4 is critical for skeletal muscle glucose uptake in response to insulin and muscle contraction/exercise. Exercise increases GLUT4 translocation to the sarcolemma and t-tubule and, over the longer term, total GLUT4 protein content. Here, we review key aspects of GLUT4 biology in relation to exercise, with a focus on exercise-induced GLUT4 translocation, postexercise metabolism and muscle insulin sensitivity, and exercise effects on GLUT4 expression.

The role of MAP-kinase p38 in the m. soleus slow myosin mRNA transcription regulation during short-term functional unloading

The unloading of postural muscles leads to the changes in myosins heavy chains isoforms (MyHCs) mRNAs transcription pattern, that cause severe alterations of muscle functioning. Several transcription factors such as NFATc1 and TEAD1 upregulate slow MyHC mRNA transcription, and p38 MAP kinase can phosphorylate NFAT and TEAD1, causing their inactivation. However, the role p38 MAP kinase plays in MyHCs mRNAs transcription regulation in postural soleus muscle during unloading remains unclear. We aimed to investigate whether pharmacological inhibition of p38 MAPK during rat soleus unloading would prevent the unloading-induced slow-type MyHC mRNA transcription decrease by affecting calcineurin/NFATc1 or TEAD1 signaling. Male Wistar rats were randomly assigned to three groups: cage control (C), 3-day hindlimb suspended group (3HS) and 3-day hindlimb suspended group with the daily oral supplementation of 10 mg/kg p38 MAPK inhibitor VX-745 (3HS + VX-745). 3 days of hindlimb suspension caused the significant decreases of slow MyHC and slow-tonic myh7b mRNAs transcription as well as the decrease of NFATc1-dependent MCIP1.4 mRNA transcription in rat soleus muscles compared to the cage control. P38 MAP-kinase inhibition during hindlimb suspension completely prevented slow MyHC mRNA content decrease and partially prevented slow-tonic myh7b and MCIP1.4 mRNAs transcription decreases compared to the 3HS group. We also observed NFATc1 and TEAD1 myonuclear contents increases in the 3HS + VX-745 group compared to both 3HS and C groups (p < 0.05). Therefore, we found that p38 inhibition counteracts the unloading-induced slow MyHC mRNA transcription downregulation and leads to the activation of calcineurin/NFAT signaling cascade in unloaded rat soleus muscles.

p38 MAPK in Glucose Metabolism of Skeletal Muscle: Beneficial or Harmful?

Skeletal muscles respond to environmental and physiological changes by varying their size, fiber type, and metabolic properties. P38 mitogen-activated protein kinase (MAPK) is one of several signaling pathways that drive the metabolic adaptation of skeletal muscle to exercise. p38 MAPK also participates in the development of pathological traits resulting from excessive caloric intake and obesity that cause metabolic syndrome and type 2 diabetes (T2D). Whereas p38 MAPK increases insulin-independent glucose uptake and oxidative metabolism in muscles during exercise, it contrastingly mediates insulin resistance and glucose intolerance during metabolic syndrome development. This article provides an overview of the apparent contradicting roles of p38 MAPK in the adaptation of skeletal muscles to exercise and to pathological conditions leading to glucose intolerance and T2D. Here, we focus on the involvement of p38 MAPK in glucose metabolism of skeletal muscle, and discuss the possibility of targeting this pathway to prevent the development of T2D.

Exercise adaptations: molecular mechanisms and potential targets for therapeutic benefit

Exercise is fundamental for good health, whereas physical inactivity underpins many chronic diseases of modern society. It is well appreciated that regular exercise improves metabolism and the metabolic phenotype in a number of tissues. The phenotypic alterations observed in skeletal muscle are partly mediated by transcriptional responses that occur following each individual bout of exercise. This adaptive response increases oxidative capacity and influences the function of myokines and extracellular vesicles that signal to other tissues. Our understanding of the epigenetic and transcriptional mechanisms that mediate the skeletal muscle gene expression response to exercise as well as of their upstream signalling pathways has advanced substantially in the past 10 years. With this knowledge also comes the opportunity to design new therapeutic strategies based on the biology of exercise for a variety of chronic conditions where regular exercise might be a challenge. This Review provides an overview of the beneficial adaptive responses to exercise and details the molecular mechanisms involved. The possibility of designing therapeutic interventions based on these molecular mechanisms is addressed, using relevant examples that have exploited this approach.

Glucose transporters in adipose tissue, liver, and skeletal muscle in metabolic health and disease

A family of facilitative glucose transporters (GLUTs) is involved in regulating tissue-specific glucose uptake and metabolism in the liver, skeletal muscle, and adipose tissue to ensure homeostatic control of blood glucose levels. Reduced glucose transport activity results in aberrant use of energy substrates and is associated with insulin resistance and type 2 diabetes. It is well established that GLUT2, the main regulator of hepatic hexose flux, and GLUT4, the workhorse in insulin- and contraction-stimulated glucose uptake in skeletal muscle, are critical contributors in the control of whole-body glycemia. However, the molecular mechanism how insulin controls glucose transport across membranes and its relation to impaired glycemic control in type 2 diabetes remains not sufficiently understood. An array of circulating metabolites and hormone-like molecules and potential supplementary glucose transporters play roles in fine-tuning glucose flux between the different organs in response to an altered energy demand.

Transcriptional cofactor Vgll2 is required for functional adaptations of skeletal muscle induced by chronic overload

Skeletal muscle is composed of heterogeneous populations of myofibers classified as slow- and fast-twitch fibers. Myofiber size and composition are drastically changed in response to physiological demands. We previously showed that transcriptional cofactor vestigial-like (Vgll) 2 is a pivotal regulator of slow muscle gene programming under sedentary conditions. However, whether Vgll2 is required for skeletal muscle adaptations after chronic overload is unclear. Therefore, we investigated the role of Vgll2 in chronic overload-inducing skeletal muscle adaptations using synergist ablation (SA) on plantaris. We found that Vgll2 is an essential regulator of the switch towards a slow-contractile phenotype and oxidative metabolism during chronic overload. Mice lacking Vgll2 exhibited limited fiber type transition and downregulation of genes related to lactate metabolism and their regulator peroxisome proliferator-activated receptor gamma coactivator 1α1, after SA, was augmented in Vgll2-deficient mice compared with in wild-type mice. Mechanistically, increased muscle usage elevated Vgll2 levels and promoted the interaction between Vgll2 and its transcription partners such as TEA domain1 (TEAD1), MEF2c, and NFATc1. Calcium ionophore treatment promoted nuclear translocation of Vgll2 and increased TEAD-dependent MYH7 promotor activity in a Vgll2-dependent manner. Taken together, these data demonstrate that Vgll2 plays an important role for functional adaptation of skeletal muscle to chronic overload.

Thirty sweet years of GLUT4

A pivotal metabolic function of insulin is the stimulation of glucose uptake into muscle and adipose tissues. The discovery of the insulin-responsive glucose transporter type 4 (GLUT4) protein in 1988 inspired its molecular cloning in the following year. It also spurred numerous cellular mechanistic studies laying the foundations for how insulin regulates glucose uptake by muscle and fat cells. Here, we reflect on the importance of the GLUT4 discovery and chronicle additional key findings made in the past 30 years. That exocytosis of a multispanning membrane protein regulates cellular glucose transport illuminated a novel adaptation of the secretory pathway, which is to transiently modulate the protein composition of the cellular plasma membrane. GLUT4 controls glucose transport into fat and muscle tissues in response to insulin and also into muscle during exercise. Thus, investigation of regulated GLUT4 trafficking provides a major means by which to map the essential signaling components that transmit the effects of insulin and exercise. Manipulation of the expression of GLUT4 or GLUT4-regulating molecules in mice has revealed the impact of glucose uptake on whole-body metabolism. Remaining gaps in our understanding of GLUT4 function and regulation are highlighted here, along with opportunities for future discoveries and for the development of therapeutic approaches to manage metabolic disease.

Histone deacetylase activity mediates thermal plasticity in zebrafish (Danio rerio)

Regulatory mechanisms underlying thermal plasticity determine its evolution and potential to confer resilience to climate change. Here we show that class I and II histone deacetylases (HDAC) mediated thermal plasticity globally by shifting metabolomic profiles of cold acclimated zebrafish (Danio rerio) away from warm acclimated animals. HDAC activity promoted swimming performance, but reduced slow and fast myosin heavy chain content in cardiac and skeletal muscle. HDAC increased sarco-endoplasmic reticulum ATPase activity in cold-acclimated fish but not in warm-acclimated animals, and it promoted cardiac function (heart rate and relative stroke volume) in cold but not in warm-acclimated animals. HDAC are an evolutionarily ancient group of proteins, and our data show that they mediate the capacity for thermal plasticity, although the actual manifestation of plasticity is likely to be determined by interactions with other regulators such as AMP-activated protein kinase and thyroid hormone.

Histone deacetylases in cardiovascular and metabolic diseases

Histone deacetylases (HDACs) regulate gene transcription by catalyzing the removal of acetyl groups from key lysine residues in nucleosomal histones and via the recruitment of other epigenetic regulators to DNA promoter/enhancer regions. Over the past two decades, HDACs have been implicated in multiple processes pertinent to cardiovascular and metabolic diseases, including cardiac hypertrophy and remodeling, fibrosis, calcium handling, inflammation and energy metabolism. The development of small molecule HDAC inhibitors and genetically modified loss- and gain-of-function mouse models has allowed interrogation of the roles of specific HDAC isoforms in these processes. Isoform-selective HDAC inhibitors may prove to be powerful therapeutic agents for the treatment of cardiovascular diseases, obesity and diabetes.

Principles of Exercise Prescription, and How They Influence Exercise-Induced Changes of Transcription Factors and Other Regulators of Mitochondrial Biogenesis

Physical inactivity represents the fourth leading risk factor for mortality, and it has been linked with a series of chronic disorders, the treatment of which absorbs ~ 85% of healthcare costs in developed countries. Conversely, physical activity promotes many health benefits; endurance exercise in particular represents a powerful stimulus to induce mitochondrial biogenesis, and it is routinely used to prevent and treat chronic metabolic disorders linked with sub-optimal mitochondrial characteristics. Given the importance of maintaining a healthy mitochondrial pool, it is vital to better characterize how manipulating the endurance exercise dose affects cellular mechanisms of exercise-induced mitochondrial biogenesis. Herein, we propose a definition of mitochondrial biogenesis and the techniques available to assess it, and we emphasize the importance of standardizing biopsy timing and the determination of relative exercise intensity when comparing different studies. We report an intensity-dependent regulation of exercise-induced increases in nuclear peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) protein content, nuclear phosphorylation of p53 (serine 15), and PGC-1α messenger RNA (mRNA), as well as training-induced increases in PGC-1α and p53 protein content. Despite evidence that PGC-1α protein content plateaus within a few exercise sessions, we demonstrate that greater training volumes induce further increases in PGC-1α (and p53) protein content, and that short-term reductions in training volume decrease the content of both proteins, suggesting training volume is still a factor affecting training-induced mitochondrial biogenesis. Finally, training-induced changes in mitochondrial transcription factor A (TFAM) protein content are regulated in a training volume-dependent manner and have been linked with training-induced changes in mitochondrial content.

Exercise and GLUT4 in human subcutaneous adipose tissue

To examine the effect of acute and chronic exercise on adipose tissue GLUT4 expression, a total of 20 healthy, male subjects performed one of two studies. Ten subjects performed cycle ergometer exercise for 60 min at 73 ± 2% VO2 peak and abdominal adipose tissue samples were obtained immediately before and after exercise and after 3 h of recovery. Another 10 subjects completed 10 days of exercise training, comprising a combination of six sessions of 60 min at 75% VO2 peak and four sessions of 6 × 5 min at 90% VO2 peak, separated by 3 min at 40% VO2 peak. Abdominal adipose tissue and vastus lateralis muscle samples were obtained before training and 24 h after the last training session. A single bout of exercise did not change adipose tissue GLUT4 mRNA; however, there was a small, but significant, reduction in adipose tissue GLUT4 protein expression 3 h after exercise. There were no changes in adipose tissue GLUT4 or COX-IV expression following exercise training. In contrast, skeletal muscle GLUT4 and COX-IV were increased by 47% and 44%, respectively following exercise training. The exercise training-induced increase in GLUT4 expression was similar in both type I and type IIa single muscle fibers. Our results indicate that neither a single exercise bout, nor 10 days of exercise training, increased adipose tissue GLUT4, in contrast with the increases observed in skeletal muscle GLUT4 expression.

The effects of obesity on skeletal muscle contractile function

Obesity can cause a decline in contractile function of skeletal muscle, thereby reducing mobility and promoting obesity-associated health risks. We reviewed the literature to establish the current state-of-knowledge of how obesity affects skeletal muscle contraction and relaxation. At a cellular level, the dominant effects of obesity are disrupted calcium signalling and 5'-adenosine monophosphate-activated protein kinase (AMPK) activity. As a result, there is a shift from slow to fast muscle fibre types. Decreased AMPK activity promotes the class II histone deacetylase (HDAC)-mediated inhibition of the myocyte enhancer factor 2 (MEF2). MEF2 promotes slow fibre type expression, and its activity is stimulated by the calcium-dependent phosphatase calcineurin. Obesity-induced attenuation of calcium signalling via its effects on calcineurin, as well as on adiponectin and actinin affects excitation-contraction coupling and excitation-transcription coupling in the myocyte. These molecular changes affect muscle contractile function and phenotype, and thereby in vivo and in vitro muscle performance. In vivo, obesity can increase the absolute force and power produced by increasing the demand on weight-supporting muscle. However, when normalised to body mass, muscle performance of obese individuals is reduced. Isolated muscle preparations show that obesity often leads to a decrease in force produced per muscle cross-sectional area, and power produced per muscle mass. Obesity and ageing have similar physiological consequences. The synergistic effects of obesity and ageing on muscle function may exacerbate morbidity and mortality. Important future research directions include determining: the relationship between time course of weight gain and changes in muscle function; the relative effects of weight gain and high-fat diet feeding per se; the effects of obesity on muscle function during ageing; and if the effects of obesity on muscle function are reversible.

DNA methylation in the pathogenesis of type 2 diabetes in humans

Background

Type 2 diabetes (T2D) is a multifactorial, polygenic disease caused by impaired insulin secretion and insulin resistance. Genome-wide association studies (GWAS) were expected to resolve a large part of the genetic component of diabetes; yet, the single nucleotide polymorphisms identified by GWAS explain less than 20% of the estimated heritability for T2D. There was subsequently a need to look elsewhere to find disease-causing factors. Mechanisms mediating the interaction between environmental factors and the genome, such as epigenetics, may be of particular importance in the pathogenesis of T2D.

Scope of Review

This review summarizes knowledge of the impact of epigenetics on the pathogenesis of T2D in humans. In particular, the review will focus on alterations in DNA methylation in four human tissues of importance for the disease; pancreatic islets, skeletal muscle, adipose tissue, and the liver. Case–control studies and studies examining the impact of non-genetic and genetic risk factors on DNA methylation in humans will be considered. These studies identified epigenetic changes in tissues from subjects with T2D versus non-diabetic controls. They also demonstrate that non-genetic factors associated with T2D such as age, obesity, energy rich diets, physical activity and the intrauterine environment impact the epigenome in humans. Additionally, interactions between genetics and epigenetics seem to influence the pathogenesis of T2D.

Conclusions

Overall, previous studies by our group and others support a key role for epigenetics in the growing incidence of T2D.

AMPK in skeletal muscle function and metabolism

Skeletal muscle possesses a remarkable ability to adapt to various physiologic conditions. AMPK is a sensor of intracellular energy status that maintains energy stores by fine-tuning anabolic and catabolic pathways. AMPK’s role as an energy sensor is particularly critical in tissues displaying highly changeable energy turnover. Due to the drastic changes in energy demand that occur between the resting and exercising state, skeletal muscle is one such tissue. Here, we review the complex regulation of AMPK in skeletal muscle and its consequences on metabolism (e.g., substrate uptake, oxidation, and storage as well as mitochondrial function of skeletal muscle fibers). We focus on the role of AMPK in skeletal muscle during exercise and in exercise recovery. We also address adaptations to exercise training, including skeletal muscle plasticity, highlighting novel concepts and future perspectives that need to be investigated. Furthermore, we discuss the possible role of AMPK as a therapeutic target as well as different AMPK activators and their potential for future drug development.—Kjøbsted, R., Hingst, J. R., Fentz, J., Foretz, M., Sanz, M.-N., Pehmøller, C., Shum, M., Marette, A., Mounier, R., Treebak, J. T., Wojtaszewski, J. F. P., Viollet, B., Lantier, L. AMPK in skeletal muscle function and metabolism.

The role of MEF2 transcription factors in dehydration and anoxia survival in Rana sylvatica skeletal muscle

The wood frog (Rana sylvatica) can endure freezing of up to 65% of total body water during winter. When frozen, wood frogs enter a dormant state characterized by a cessation of vital functions (i.e., no heartbeat, blood circulation, breathing, brain activity, or movement). Wood frogs utilize various behavioural and biochemical adaptations to survive extreme freezing and component anoxia and dehydration stresses, including a global suppression of metabolic functions and gene expression. The stress-responsive myocyte enhancer factor-2 (MEF2) transcription factor family regulates the selective expression of genes involved in glucose transport, protein quality control, and phosphagen homeostasis. This study examined the role of MEF2A and MEF2C proteins as well as select downstream targets (glucose transporter-4, calreticulin, and muscle and brain creatine kinase isozymes) in 40% dehydration and 24 h anoxia exposure at the transcriptional, translational, and post-translational levels using qRT-PCR, immunoblotting, and subcellular localization. Mef2a/c transcript levels remained constant during dehydration and anoxia. Total, cytoplasmic, and nuclear MEF2A/C and phospho-MEF2A/C protein levels remained constant during dehydration, whereas a decrease in total MEF2C levels was observed during rehydration. Total and phospho-MEF2A levels remained constant during anoxia, whereas total MEF2C levels decreased during 24 h anoxia and P-MEF2C levels increased during 4 h anoxia. In contrast, cytoplasmic MEF2A levels and nuclear phospho-MEF2A/C levels were upregulated during anoxia. MEF2 downstream targets remained constant during dehydration and anoxia, with the exception of glut4 which was upregulated during anoxia. These results suggest that the upregulated MEF2 response reported in wood frogs during freezing may in part stem from their cellular responses to surviving prolonged anoxia, rather than dehydration, leading to an increase in GLUT4 expression which may have an important role during anoxia survival.

The evolution of metabolic regulation in animals

Energy metabolism is determined by a suite of regulatory mechanism, and their increasing complexity over evolutionary time provides the key to understanding the emergence of different metabolic phenotypes. Energy metabolism is at the core of biological processes because all organisms must maintain energy balance against thermodynamic gradients. Energy metabolism is regulated by a bewildering array of interacting molecular mechanisms, and much of what is known about metabolic regulation comes from the medical literature. However, ecology and evolutionary research would gain considerably by incorporating regulatory mechanisms more explicitly in research on topics such as the evolution of endothermy, metabolic plasticity, and energy balance. The purpose of this brief review is to summarise the main regulatory pathways of energy metabolism in animals and their evolutionary origins to make these complex interactions more accessible to researchers from a broad range of backgrounds. Some of the principal regulators of energy balance, such as the AMP-stimulated protein kinase, have an ancient prokaryotic origin. Most regulatory pathways (e.g. thyroid hormone, insulin, adipokines), however, are eukaryotic in origin and diversified substantially in metazoans and vertebrates. Diversification in vertebrates is at least partly due to genome duplications early in this lineage. The interaction between regulatory mechanisms permitted an increasingly sophisticated fine-tuning of energy balance and metabolism. Hence, regulatory complexity increased over evolutionary time, and taxa differ in their potential range of metabolic phenotypes. Choice of model organism therefore becomes important, and bacteria or even invertebrates are not good models for more derived vertebrates. Different metabolic phenotypes and their evolution, such as endothermy and metabolic plasticity, should be interpreted against this regulatory background.

Exercise and the Skeletal Muscle Epigenome

An acute bout of exercise is sufficient to induce changes in skeletal muscle gene expression that are ultimately responsible for the adaptive responses to exercise. Although much research has described the intracellular signaling responses to exercise that are linked to transcriptional regulation, the epigenetic mechanisms involved are only just emerging. This review will provide an overview of epigenetic mechanisms and what is known in the context of exercise. Additionally, we will explore potential interactions between metabolism during exercise and epigenetic regulation, which serves as a framework for potential areas for future research. Finally, we will consider emerging opportunities to pharmacologically manipulate epigenetic regulators and mechanisms to induce aspects of the skeletal muscle exercise adaptive response for therapeutic intervention in various disease states.

Exercise-induced GLUT4 transcription via inactivation of HDAC4/5 in mouse skeletal muscle in an AMPKα2-dependent manner

Abnormal glucose metabolism induces various metabolic disorders such as insulin resistance and type 2 diabetes. Regular exercise improved glucose uptake and enhanced glucose oxidation by increasing GLUT4 transcription in skeletal muscle. However, the regulatory mechanisms of GLUT4 transcription in response to exercise are poorly understood. AMPK is a sensor of exercise and upstream kinase of class II HDACs that act as transcriptional repressors. We used 6-week treadmill exercise or one single-bout exercise wild type or AMPKα2^-/- C57BL/6J mice to explore how HDACs regulate GLUT4 transcription and the underlying molecular mechanisms mediated by AMPK in the physiologic process of exercise. We demonstrate that regular physical exercise significantly enhanced GLUT4 transcription by inactivating HDAC4/5 in skeletal muscle by ChIP experiment. HDAC4 coordinately regulated with HDAC5 represses transcriptional activity of GLUT4 promoter in C2C12 myotubes by Luciferase assay. If either HDAC4 or HDAC5 is silenced via RNAi technology, the functional compensation by the other will occur. In addition, a single-bout of exercise decreased HDAC4/5 activity in skeletal muscle of wild type but not in AMPKα2^-/- mice, suggesting an AMPKα2-dependent manner. Those findings provide new insight into the mechanisms responsible for AMPKα2-dependent regulation of GLUT4 transcription after exercise.

Histone deacetylase activity modulates exercise-induced skeletal muscle plasticity in zebrafish (Danio rerio)

Aerobic exercise has a positive impact on animals by enhancing skeletal muscle function and locomotor performance. Responses of skeletal muscle to exercise involve changes in energy metabolism, calcium handling, and the composition of contractile protein isoforms, which together influence contractile properties. Histone deacetylases (HDAC) can cause short-term changes in gene expression and may thereby mediate plasticity in contractile properties of skeletal muscle in response to exercise. The aim of this project was to determine (in zebrafish, Danio rerio) the traits that mediate interindividual differences in sustained and sprint performance and to determine whether inhibiting class I and II HDACs mediates exercise-induced changes in these traits. High sustained performers had greater aerobic metabolic capacity [citrate synthase (CS) activity], calcium handling capacity [sarco/endoplasmic reticulum ATPase (SERCA) activity], and slow contractile protein concentration [slow myosin heavy chain (MHC)] compared with low performers. High sprint performers had lower CS activity and slow MHC concentrations compared with low performers, but there were no significant differences in lactate dehydrogenase activity or fast MHC concentrations. Four weeks of aerobic exercise training increased sustained performance, CS activity, SERCA activity, and slow MHC concentration. Inhibiting class I and II HDACs increased slow MHC concentration in untrained fish but not in trained fish. However, inhibiting HDACs reduced SERCA activity, which was paralleled by a reduction in sustained and sprint performance. The regulation of muscle phenotypes by HDACs could be a mechanism underlying the adaptation of sustained locomotor performance to different environmental conditions, and may therefore be of therapeutic and ecological significance.

Scriptaid enhances skeletal muscle insulin action and cardiac function in obese mice

AIM

To determine the effect of Scriptaid, a compound that can replicate aspects of the exercise adaptive response through disruption of the class IIa histone deacetylase (HDAC) corepressor complex, on muscle insulin action in obesity.

MATERIALS AND METHODS

Diet-induced obese mice were administered Scriptaid (1 mg/kg) via daily intraperitoneal injection for 4 weeks. Whole-body and skeletal muscle metabolic phenotyping of mice was performed, in addition to echocardiography, to assess cardiac morphology and function.

RESULTS

Scriptaid treatment had no effect on body weight or composition, but did increase energy expenditure, supported by increased lipid oxidation, while food intake was also increased. Scriptaid enhanced the expression of oxidative genes and proteins, increased fatty acid oxidation and reduced triglycerides and diacylglycerides in skeletal muscle. Furthermore, ex vivo insulin-stimulated glucose uptake by skeletal muscle was enhanced. Surprisingly, heart weight was reduced in Scriptaid-treated mice and was associated with enhanced expression of genes involved in oxidative metabolism in the heart. Scriptaid also improved indices of both diastolic and systolic cardiac function.

CONCLUSION

These data show that pharmacological targeting of the class IIa HDAC corepressor complex with Scriptaid could be used to enhance muscle insulin action and cardiac function in obesity.

Metabolism of ketone bodies during exercise and training: physiological basis for exogenous supplementation

Optimising training and performance through nutrition strategies is central to supporting elite sportspeople, much of which has focused on manipulating the relative intake of carbohydrate and fat and their contributions as fuels for energy provision. The ketone bodies, namely acetoacetate, acetone and β-hydroxybutyrate (βHB), are produced in the liver during conditions of reduced carbohydrate availability and serve as an alternative fuel source for peripheral tissues including brain, heart and skeletal muscle. Ketone bodies are oxidised as a fuel source during exercise, are markedly elevated during the post-exercise recovery period, and the ability to utilise ketone bodies is higher in exercise-trained skeletal muscle. The metabolic actions of ketone bodies can alter fuel selection through attenuating glucose utilisation in peripheral tissues, anti-lipolytic effects on adipose tissue, and attenuation of proteolysis in skeletal muscle. Moreover, ketone bodies can act as signalling metabolites, with βHB acting as an inhibitor of histone deacetylases, an important regulator of the adaptive response to exercise in skeletal muscle. Recent development of ketone esters facilitates acute ingestion of βHB that results in nutritional ketosis without necessitating restrictive dietary practices. Initial reports suggest this strategy alters the metabolic response to exercise and improves exercise performance, while other lines of evidence suggest roles in recovery from exercise. The present review focuses on the physiology of ketone bodies during and after exercise and in response to training, with specific interest in exploring the physiological basis for exogenous ketone supplementation and potential benefits for performance and recovery in athletes.

Epigenetic regulation of skeletal muscle metabolism

Normal skeletal muscle metabolism is essential for whole body metabolic homoeostasis and disruptions in muscle metabolism are associated with a number of chronic diseases. Transcriptional control of metabolic enzyme expression is a major regulatory mechanism for muscle metabolic processes. Substantial evidence is emerging that highlights the importance of epigenetic mechanisms in this process. This review will examine the importance of epigenetics in the regulation of muscle metabolism, with a particular emphasis on DNA methylation and histone acetylation as epigenetic control points. The emerging cross-talk between metabolism and epigenetics in the context of health and disease will also be examined. The concept of inheritance of skeletal muscle metabolic phenotypes will be discussed, in addition to emerging epigenetic therapies that could be used to alter muscle metabolism in chronic disease states.

Sprint-interval but not continuous exercise increases PGC-1α protein content and p53 phosphorylation in nuclear fractions of human skeletal muscle

Sprint interval training has been reported to induce similar or greater mitochondrial adaptations to continuous training. However, there is limited knowledge about the effects of different exercise types on the early molecular events regulating mitochondrial biogenesis. Therefore, we compared the effects of continuous and sprint interval exercise on key regulatory proteins linked to mitochondrial biogenesis in subcellular fractions of human skeletal muscle. Nineteen men, performed either 24 min of moderate-intensity continuous cycling at 63% of W_Peak (CE), or 4 × 30-s “all-out” cycling sprints (SIE). Muscle samples (vastus lateralis) were collected pre-, immediately (+0 h) and 3 (+3 h) hours post-exercise. Nuclear p53 and PHF20 protein content increased at +0 h, with no difference between groups. Nuclear p53 phosphorylation and PGC-1α protein content increased at +0 h after SIE, but not CE. We demonstrate an exercise-induced increase in nuclear p53 protein content, an event that may relate to greater p53 stability - as also suggested by increased PHF20 protein content. Increased nuclear p53 phosphorylation and PGC-1α protein content immediately following SIE but not CE suggests these may represent important early molecular events in the exercise-induced response to exercise, and that SIE is a time-efficient and possibly superior option than CE to promote these adaptations.