Histone modifications and exercise adaptations

Integrative biology of exercise

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.

A brief review of exercise, bipolar disorder, and mechanistic pathways

Despite evidence that exercise has been found to be effective in the treatment of depression, it is unclear whether these data can be extrapolated to bipolar disorder. Available evidence for bipolar disorder is scant, with no existing randomized controlled trials having tested the impact of exercise on depressive, manic or hypomanic symptomatology. Although exercise is often recommended in bipolar disorder, this is based on extrapolation from the unipolar literature, theory and clinical expertise and not empirical evidence. In addition, there are currently no available empirical data on program variables, with practical implications on frequency, intensity and type of exercise derived from unipolar depression studies. The aim of the current paper is to explore the relationship between exercise and bipolar disorder and potential mechanistic pathways. Given the high rate of medical co-morbidities experienced by people with bipolar disorder, it is possible that exercise is a potentially useful and important intervention with regard to general health benefits; however, further research is required to elucidate the impact of exercise on mood symptomology.

Physical exercise and epigenetic modulation: elucidating intricate mechanisms

Physical exercise induces several metabolic adaptations to meet increased energy requirements. Promoter DNA methylation, histone post-translational modifications, or microRNA expression are involved in the gene expression changes implicated in metabolic adaptation after exercise. Epigenetic modifications and many epigenetic enzymes are potentially dependent on changes in the levels of metabolites, such as oxygen, tricarboxylic acid cycle intermediates, 2-oxoglutarate, 2-hydroxyglutarate, and β-hydroxybutyrate, and are therefore susceptible to the changes induced by exercise in a tissue-dependent manner. Most of these changes are regulated by important epigenetic modifiers that control DNA methylation (DNA methyl transferases, and ten-eleven-translocation proteins) and post-translational modifications in histone tails controlled by histone acetyltransferases, histone deacetylases, and histone demethylases (jumonji C proteins, lysine-specific histone demethylase, etc.), among others. Developments in mass spectrometry approaches and the comprehension of the interconnections between epigenetics and metabolism further increase our understanding of underlying epigenetic mechanisms, not only of exercise, but also of disease and aging. In this article, we describe several of these substrates and signaling molecules regulated by exercise that affect some of the most important epigenetic mechanisms, which, in turn, control the gene expression involved in metabolism.

Exercise: putting action into our epigenome

Most human phenotypes are influenced by a combination of genomic and environmental factors. Engaging in regular physical exercise prevents many chronic diseases, decreases mortality risk and increases longevity. However, the mechanisms involved are poorly understood. The modulating effect of physical (aerobic and resistance) exercise on gene expression has been known for some time now and has provided us with an understanding of the biological responses to physical exercise. Emerging research data suggest that epigenetic modifications are extremely important for both development and disease in humans. In the current review, we summarise findings on the effect of exercise on epigenetic modifications and their effects on gene expression. Current research data suggest epigenetic modifications (DNA methylation and histone acetylation) and microRNAs (miRNAs) are responsive to acute aerobic and resistance exercise in brain, blood, skeletal and cardiac muscle, adipose tissue and even buccal cells. Six months of aerobic exercise alters whole-genome DNA methylation in skeletal muscle and adipose tissue and directly influences lipogenesis. Some miRNAs are related to maximal oxygen consumption (VO(2max)) and VO(2max) trainability, and are differentially expressed amongst individuals with high and low VO(2max). Remarkably, miRNA expression profiles discriminate between low and high responders to resistance exercise (miR-378, -26a, -29a and -451) and correlate to gains in lean body mass (miR-378). The emerging field of exercise epigenomics is expected to prosper and additional studies may elucidate the clinical relevance of miRNAs and epigenetic modifications, and delineate mechanisms by which exercise confers a healthier phenotype and improves performance.

Heat acclimation memory: do the kinetics of the deacclimated transcriptome predispose to rapid reacclimation and cytoprotection?

Faster reinduction of heat acclimation (AC) after its decline indicates "AC memory." Our previous results revealed involvement of epigenetic mechanisms of transcriptional regulation. We hypothesized that the decline of AC (DeAC) is a period of "dormant memory" during which many processes are alerted to enable rapid reacclimation (ReAC). Using a genomewide approach we studied the AC, DeAC, and ReAC transcriptomes, to uncover hallmark pathways linked to "molecular memory" in the cardioacclimatome. Fifty rats subjected to heat acclimation [34°C for 2d (AC2d) or 30d (AC30)], DeAC (24°C, 30 days), ReAC (34°C, 2 days), and untreated controls were used. The GeneChip Rat Gene 1.0 ST Array was employed for left ventricular (cardiac) mRNA hybridization. Three independent bioinformatic analyses showed that 1) during AC2d enrichment of DNA impair/repair-linked genes is seen, and this is the molecular on-switch of acclimation; 2) genes activated in AC30 underlie the qualitative physiological adaptations of cardiac performance; 3) particular molecular programs encompassing constitutive upregulation of p38 MAPK, Jak/Stat, and Akt pathways and targets are specifically activated during DeAC and ReAC; and 4) epigenetic markers such as linker histones (histones H1 cluster), associated with nucleosome spacing, transcriptional chromatin modifiers, poly-(ADP-ribose) polymerase-1 (PARP1) linked to chromatin compaction, and microRNAs are only altered during DeAC/ReAC. The latter are newcomers to the AC/DeAC puzzle. We suggest that these transcriptional responses maintain euchromatin and proteostasis and enable faster physiological recovery upon ReAC by rapidly reestablishing the protected acclimated cardiophenotype. We propose that the cardiac AC model can be applied to acclimation processes in general.

Understanding the acetylome: translating targeted proteomics into meaningful physiology

It is well established that exercise elicits a finely tuned adaptive response in skeletal muscle, with contraction frequency, duration, and recovery shaping skeletal muscle plasticity. Given the power of physical activity to regulate metabolic health, numerous research groups have focused on the molecular mechanisms that sense, interpret, and translate this contractile signal into postexercise adaptation. While our current understanding is that contraction-sensitive allosteric factors (e.g., Ca²⁺, AMP, NAD⁺, and acetyl-CoA) initiate signaling changes, how the muscle translates changes in these factors into the appropriate adaptive response remains poorly understood. During the past decade, systems biology approaches, utilizing “omics” screening techniques, have allowed researchers to define global processes of regulation with incredible sensitivity and specificity. As a result, physiologists are now able to study substrate flux with stable isotope tracers in combination with metabolomic approaches and to coordinate these functional changes with proteomic and transcriptomic analysis. In this review, we highlight lysine acetylation as an important posttranslational modification in skeletal muscle. We discuss the evolution of acetylation research and detail how large proteomic screens in diverse metabolic systems have led to the current hypothesis that acetylation may be a fundamental mechanism to fine-tune metabolic adaptation in skeletal muscle.

Gene expression in mdx mouse muscle in relation to age and exercise: aberrant mechanical-metabolic coupling and implications for pre-clinical studies in Duchenne muscular dystrophy

Weakness and fatigability are typical features of Duchenne muscular dystrophy patients and are aggravated in dystrophic mdx mice by chronic treadmill exercise. Mechanical activity modulates gene expression and muscle plasticity. Here, we investigated the outcome of 4 (T4, 8 weeks of age) and 12 (T12, 16 weeks of age) weeks of either exercise or cage-based activity on a large set of genes in the gastrocnemius muscle of mdx and wild-type (WT) mice using quantitative real-time PCR. Basal expression of the exercise-sensitive genes peroxisome-proliferator receptor γ coactivator 1α (Pgc-1α) and Sirtuin1 (Sirt1) was higher in mdx versus WT mice at both ages. Exercise increased Pgc-1α expression in WT mice; Pgc-1α was downregulated by T12 exercise in mdx muscles, along with Sirt1, Pparγ and the autophagy marker Bnip3. Sixteen weeks old mdx mice showed a basal overexpression of the slow Mhc1 isoform and Serca2; T12 exercise fully contrasted this basal adaptation as well as the high expression of follistatin and myogenin. Conversely, T12 exercise was ineffective in WT mice. Damage-related genes such as gp91-phox (NADPH-oxidase2), Tgfβ, Tnfα and c-Src tyrosine kinase were overexpressed in mdx muscles and not affected by exercise. Likewise, the anti-inflammatory adiponectin was lower in T12-exercised mdx muscles. Chronic exercise with minor adaptive effects in WT muscles leads to maladaptation in mdx muscles with a disequilibrium between protective and damaging signals. Increased understanding of the pathways involved in the altered mechanical-metabolic coupling may help guide appropriate physical therapies while better addressing pharmacological interventions in translational research.

Suppression of the GLUT4 adaptive response to exercise in fructose-fed rats

Exercise-induced increase in skeletal muscle GLUT4 expression is associated with hyperacetylation of histone H3 within a 350-bp DNA region surrounding the myocyte enhancer factor 2 (MEF2) element on the Glut4 promoter and increased binding of MEF2A. Previous studies have hypothesized that the increase in MEF2A binding is a result of improved accessibility of this DNA segment. Here, we investigated the impact of fructose consumption on exercise-induced GLUT4 adaptive response and directly measured the accessibility of the above segment to nucleases. Male Wistar rats (n = 30) were fed standard chow or chow + 10% fructose or maltodextrin drinks ad libitum for 13 days. In the last 6 days five animals per group performed 3 × 17-min bouts of intermittent swimming daily and five remained untrained. Triceps muscles were harvested and used to measure 1) GLUT4, pAMPK, and HDAC5 contents by Western blot, 2) accessibility of the DNA segment from intact nuclei using nuclease accessibility assays, 3) acetylation level of histone H3 and bound MEF2A by ChIP assays, and 4) glycogen content. Swim training increased GLUT4 content by ∼66% (P < 0.05) but fructose and maltodextrin feeding suppressed the adaptation. Accessibility of the DNA region to MNase and DNase I was significantly increased by swimming (∼2.75- and 5.75-fold, respectively) but was also suppressed in trained rats that consumed fructose or maltodextrin. Histone H3 acetylation and MEF2A binding paralleled the accessibility pattern. These findings indicate that both fructose and maltodextrin modulate the GLUT4 adaptive response to exercise by mechanisms involving chromatin remodeling at the Glut4 promoter.

Resistance to aerobic exercise training causes metabolic dysfunction and reveals novel exercise-regulated signaling networks

Low aerobic exercise capacity is a risk factor for diabetes and a strong predictor of mortality, yet some individuals are "exercise-resistant" and unable to improve exercise capacity through exercise training. To test the hypothesis that resistance to aerobic exercise training underlies metabolic disease risk, we used selective breeding for 15 generations to develop rat models of low and high aerobic response to training. Before exercise training, rats selected as low and high responders had similar exercise capacities. However, after 8 weeks of treadmill training, low responders failed to improve their exercise capacity, whereas high responders improved by 54%. Remarkably, low responders to aerobic training exhibited pronounced metabolic dysfunction characterized by insulin resistance and increased adiposity, demonstrating that the exercise-resistant phenotype segregates with disease risk. Low responders had impaired exercise-induced angiogenesis in muscle; however, mitochondrial capacity was intact and increased normally with exercise training, demonstrating that mitochondria are not limiting for aerobic adaptation or responsible for metabolic dysfunction in low responders. Low responders had increased stress/inflammatory signaling and altered transforming growth factor-β signaling, characterized by hyperphosphorylation of a novel exercise-regulated phosphorylation site on SMAD2. Using this powerful biological model system, we have discovered key pathways for low exercise training response that may represent novel targets for the treatment of metabolic disease.

Nuclear receptors and epigenetic signaling: novel regulators of glycogen metabolism in skeletal muscle

Glycogen is an energy storage depot for the mammalian species. This review focuses on recent developments that have identified the role of nuclear hormone receptor (NR) signaling and epigenomic control in the regulation of important genes that modulate glycogen metabolism. Specifically, new studies have revealed that the NR4A subgroup (of the NR superfamily) are strikingly sensitive to beta-adrenergic stimulation in skeletal muscle, and transgenic studies in mice have revealed the expression of these NRs affects endurance and glycogen levels in muscle. Furthermore, other studies have demonstrated that one of the NR coregulator class of enzymes that mediate chromatin remodeling, the histone methyltransferases (for example, protein arginine methyltransferase 4) regulates the expression of several genes involved in glycogen metabolism and glycogen storage diseases in skeletal muscle. Importantly, NRs and histone methyltransferases, have the potential to be pharmacologically exploited and may provide novel targets in the quest to treat disorders of glycogen storage.

Paracrine effects of IGF-1 overexpression on the functional decline due to skeletal muscle disuse: molecular and functional evaluation in hindlimb unloaded MLC/mIgf-1 transgenic mice

Slow-twitch muscles, devoted to postural maintenance, experience atrophy and weakness during muscle disuse due to bed-rest, aging or spaceflight. These conditions impair motion activities and can have survival implications. Human and animal studies demonstrate the anabolic role of IGF-1 on skeletal muscle suggesting its interest as a muscle disuse countermeasure. Thus, we tested the role of IGF-1 overexpression on skeletal muscle alteration due to hindlimb unloading (HU) by using MLC/mIgf-1 transgenic mice expressing IGF-1 under the transcriptional control of MLC promoter, selectively activated in skeletal muscle. HU produced atrophy in soleus muscle, in terms of muscle weight and fiber cross-sectional area (CSA) reduction, and up-regulation of atrophy gene MuRF1. In parallel, the disuse-induced slow-to-fast fiber transition was confirmed by an increase of the fast-type of the Myosin Heavy Chain (MHC), a decrease of PGC-1α expression and an increase of histone deacetylase-5 (HDAC5). Consistently, functional parameters such as the resting chloride conductance (gCl) together with ClC-1 chloride channel expression were increased and the contractile parameters were modified in soleus muscle of HU mice. Surprisingly, IGF-1 overexpression in HU mice was unable to counteract the loss of muscle weight and the decrease of fiber CSA. However, the expression of MuRF1 was recovered, suggesting early effects on muscle atrophy. Although the expression of PGC-1α and MHC were not improved in IGF-1-HU mice, the expression of HDAC5 was recovered. Importantly, the HU-induced increase of gCl was fully contrasted in IGF-1 transgenic mice, as well as the changes in contractile parameters. These results indicate that, even if local expression does not seem to attenuate HU-induced atrophy and slow-to-fast phenotype transition, it exerts early molecular effects on gene expression which can counteract the HU-induced modification of electrical and contractile properties. MuRF1 and HDAC5 can be attractive therapeutic targets for pharmacological countermeasures and then deserve further investigations.

Physical exercise as an epigenetic modulator: Eustress, the "positive stress" as an effector of gene expression

Physical exercise positively influences epigenetic mechanisms and improves health. Several issues remain unclear concerning the links between physical exercise and epigenetics. There is growing concern about the negative influence of excessive and persistent physical exercise on health. How an individual physically adapts to the prevailing environmental conditions might influence epigenetic mechanisms and modulate gene expression. In this article, we put forward the idea that physical exercise, especially long-term repetitive strenuous exercise, positively affects health, reduces the aging process, and decreases the incidence of cancer through induced stress and epigenetic mechanisms. We propose herein that stress may stimulate genetic adaptations through epigenetics that, in turn, modulate the link between the environment, human lifestyle factors, and genes.

Opposing HDAC4 nuclear fluxes due to phosphorylation by β-adrenergic activated protein kinase A or by activity or Epac activated CaMKII in skeletal muscle fibres

Class IIa histone deacetylases (HDACs) move between skeletal muscle fibre cytoplasm and nuclei in response to various stimuli, suppressing activity of the exclusively nuclear transcription factor Mef2. Protein kinase A (PKA) phosphorylates class IIa HDACs in cardiac muscle, resulting in HDAC nuclear accumulation, but this has not been examined in skeletal muscle. Using HDAC4-green fluorescent protein (HDAC4-GFP) expressed in isolated skeletal muscle fibres, we now show that activation of PKA by the beta-receptor agonist isoproterenol or dibutyryl (Db) cAMP causes a steady HDAC4-GFP nuclear influx. The beta-receptor blocker propranolol or PKA inhibitor Rp-cAMPS blocks the effects of isoproterenol on the nuclear influx of HDAC4-GFP, and Rp-cAMPS blocks the effects of Db cAMP. The HDAC4-GFP construct having serines 265 and 266 replaced with alanines, HDAC4 (S265/266A)-GFP, did not respond to beta-receptor or PKA activation. Immunoprecipitation results show that HDAC4-GFP is a substrate of PKA, but HDAC4 (S265/266A)-GFP is not, implicating HDAC4 serines 265/266 as the site(s) phosphorylated by PKA. During 10 Hz trains of muscle fibre electrical stimulation, the nuclear efflux rate of HDAC4-GFP, but not of HDAC4 (S265/266)-GFP, was decreased by PKA activation, directly demonstrating antagonism between the effects of fibre stimulation and beta-adrenergic activation of PKA on HDAC4 nuclear fluxes. 8-CPT, a specific activator of Epac, caused nuclear efflux of HDAC4-GFP, opposite to the effect of PKA. Db cAMP increased both phosphorylated PKA and GTP-bound Rap1. Our results demonstrate that the PKA and CaMKII pathways play important opposing roles in skeletal muscle gene expression by oppositely affecting the subcellular localization of HDAC4.

Role of physical activity in tumor patients and possible underlying mechanisms

A growing knowledge regarding the influence of exercise on adverse physiologic outcomes associated with cancer and its treatment exists. Aside from its effects on psychological behavior, quality of life, and cancer-related fatigue, physical exercise can target physical and cardio-respiratory fitness, insulin regulation and metabolic syndrome, body weight and composition, and immune function in tumor patients. The increasing number of study results for different cancer types, which prove the positive influences of physical activity in cancer patients, changed the contradictory opinions which existed until the end of the last century. Although an increasing number of studies showing the positive effects of physical activity and more specifically of endurance and resistance training in cancer patients have been published, the underlying mechanisms are mostly unknown. Thus, we summarized the current knowledge of the effects of physical activity and specific training in different tumor entities with specific respect to the possible underlying mechanisms. Especially, the association between physical activity and (1) the improvement of fatigue and the role of free radicals in this process, (2) the counterbalance of tumor-induced cachexia, (3) the improvement of the immune system for supportive tumor treatment, and (4) the possible role of epigenetic modulation against tumor and tumor treatment-dependent adverse physiologic outcomes is focused.

The corepressor NCoR1 antagonizes PGC-1α and estrogen-related receptor α in the regulation of skeletal muscle function and oxidative metabolism

Skeletal muscle exhibits a high plasticity and accordingly can quickly adapt to different physiological and pathological stimuli by changing its phenotype largely through diverse epigenetic mechanisms. The nuclear receptor corepressor 1 (NCoR1) has the ability to mediate gene repression; however, its role in regulating biological programs in skeletal muscle is still poorly understood. We therefore studied the mechanistic and functional aspects of NCoR1 function in this tissue. NCoR1 muscle-specific knockout mice exhibited a 7.2% higher peak oxygen consumption (VO(2peak)), a 11% reduction in maximal isometric force, and increased ex vivo fatigue resistance during maximal stimulation. Interestingly, global gene expression analysis revealed a high overlap between the effects of NCoR1 deletion and peroxisome proliferator-activated receptor gamma (PPARγ) coactivator 1α (PGC-1α) overexpression on oxidative metabolism in muscle. Importantly, PPARβ/δ and estrogen-related receptor α (ERRα) were identified as common targets of NCoR1 and PGC-1α with opposing effects on the transcriptional activity of these nuclear receptors. In fact, the repressive effect of NCoR1 on oxidative phosphorylation gene expression specifically antagonizes PGC-1α-mediated coactivation of ERRα. We therefore delineated the molecular mechanism by which a transcriptional network controlled by corepressor and coactivator proteins determines the metabolic properties of skeletal muscle, thus representing a potential therapeutic target for metabolic diseases.

Nutrition, epigenetics, and metabolic syndrome

SIGNIFICANCE

Epidemiological and animal studies have demonstrated a close link between maternal nutrition and chronic metabolic disease in children and adults. Compelling experimental results also indicate that adverse effects of intrauterine growth restriction on offspring can be carried forward to subsequent generations through covalent modifications of DNA and core histones.

RECENT ADVANCES

DNA methylation is catalyzed by S-adenosylmethionine-dependent DNA methyltransferases. Methylation, demethylation, acetylation, and deacetylation of histone proteins are performed by histone methyltransferase, histone demethylase, histone acetyltransferase, and histone deacetyltransferase, respectively. Histone activities are also influenced by phosphorylation, ubiquitination, ADP-ribosylation, sumoylation, and glycosylation. Metabolism of amino acids (glycine, histidine, methionine, and serine) and vitamins (B6, B12, and folate) plays a key role in provision of methyl donors for DNA and protein methylation.

CRITICAL ISSUES

Disruption of epigenetic mechanisms can result in oxidative stress, obesity, insulin resistance, diabetes, and vascular dysfunction in animals and humans. Despite a recognized role for epigenetics in fetal programming of metabolic syndrome, research on therapies is still in its infancy. Possible interventions include: 1) inhibition of DNA methylation, histone deacetylation, and microRNA expression; 2) targeting epigenetically disturbed metabolic pathways; and 3) dietary supplementation with functional amino acids, vitamins, and phytochemicals.

FUTURE DIRECTIONS

Much work is needed with animal models to understand the basic mechanisms responsible for the roles of specific nutrients in fetal and neonatal programming. Such new knowledge is crucial to design effective therapeutic strategies for preventing and treating metabolic abnormalities in offspring born to mothers with a previous experience of malnutrition.

Why do anti-inflammatory therapies fail to improve insulin sensitivity?

Chronic inflammation occurs in obese conditions in both humans and animals. It also contributes to the pathogenesis of type 2 diabetes (T2D) through insulin resistance, a status in which the body loses its ability to respond to insulin. Inflammation impairs insulin signaling through the functional inhibition of IRS-1 and PPARγ. Insulin sensitizers (such as rosiglitazone and pioglitazone) inhibit inflammation while improving insulin sensitivity. Therefore, anti-inflammatory agents have been suggested as a treatment strategy for insulin resistance. This strategy has been tested in laboratory studies and clinical trials for more than 10 years; however, no significant progress has been made in any of the model systems. This status has led us to re-evaluate the biological significance of chronic inflammation in obesity. Recent studies have consistently asserted that obesity-associated inflammation helps to maintain insulin sensitivity. Inflammation stimulates local adipose tissue remodeling and promotes systemic energy expenditure. We propose that these beneficial activities of inflammation provide an underlying mechanism for the failure of anti-inflammatory therapy in the treatment of insulin resistance. Current literature will be reviewed in this article to present evidence that supports this viewpoint.

Epigenetics and diabetic cardiomyopathy

Cardiovascular complications are a chief cause of mortality and morbidity in diabetic patients. Recent studies suggest that epigenetic changes which may arise as a consequence of environmental factors play an important role in predisposition to disease. Epigenetic mechanisms such as DNA methylation, chromatin remodeling and histone modifications regulate the gene expression in response to environmental signals. Role of epigenetics has been recognized in the pathology of diabetes, however its role in diabetic associated cardiomyopathy remains largely unexplored. In this article, we review current literature on the epigenetic mechanisms involved in diabetes and discuss recent evidence of epigenetic changes that may play an important role in pathophysiology of DCM.

Deacetylation of PGC-1α by SIRT1: importance for skeletal muscle function and exercise-induced mitochondrial biogenesis

Activation of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α)-mediated transcription is important for both the determination of mitochondrial content and the induction of mitochondrial biogenesis in skeletal muscle. SIRT1 (silent mating type information regulator 2 homolog 1) deactetylation is proposed as a potential activator of PGC-1α transcriptional activity. The current review examines the importance of SIRT1 deacetylation of PGC-1α in skeletal muscle. Models of SIRT1 overexpression and pharmacological activation are examined, but changes in SIRT1 expression and deacetylase activity following acute and chronic contractile activity will be emphasized. In addition, potential mechanisms of SIRT1 activation in skeletal muscle will be examined. The importance of the PGC-1α acetyltransferase GCN5 will also be briefly discussed. The current evidence supports the contribution of SIRT1 deacetylation of PGC-1α to exercise-induced mitochondrial biogenesis. Further research examining exercise-mediated activation of SIRT1 and the role of GCN5 in regulating PGC-1α transcriptional activity in skeletal muscle is required.

Effect of different exercise protocols on histone acetyltransferases and histone deacetylases activities in rat hippocampus

Regular and moderate exercise has been considered an interesting neuroprotective strategy. Although the mechanisms by which physical exercise alters brain function are not clear, it appears that neuroprotective properties of exercise could be related to chromatin remodeling, specifically the induction of histone acetylation through modulation of histone deacetylases (HDAC) and histone acetyltransferases (HAT) activities. The aim of the present work was to investigate the effect of exercise on HDAC and HAT activities in rat whole hippocampus at different times after treadmill. Adult male Wistar rats were assigned to non-exercised (sedentary) and exercised groups on different protocols: a single session of treadmill exercise (running for 20 min) and a chronic treadmill protocol (running once daily for 20 min, for 2 weeks). The effects of exercise on HDAC and HAT activities were measured immediately, 1 h and 18 h after the single session or the last training session of chronic treadmill exercise using specific assay kits. The single session of treadmill exercise reduced HDAC activity, increased HAT activity and increased the HAT/HDAC balance in rat hippocampus immediately and 1 h after exercise, an indicative of histone hyperacetylation status. The acetylation balance was also influenced by the circadian rhythm, since the HAT/HDAC ratio was significantly decreased in the early morning in all groups when compared to the afternoon. These data support the hypothesis that exercise neuroprotective effects may be related, at least in part, to acetylation levels through modulation of HAT and HDAC activities. We also demonstrated circadian changes in the HAT and HDAC activities and, consequently, in the acetylation levels.