Exercise and skeletal muscle gene expression

Effect of Mechanical Loading of Senescent Myoblasts on Their Myogenic Lineage Progression and Survival

BACKGROUND

During aging, muscle cell apoptosis increases and myogenesis gradually declines. The impaired myogenic and survival potential of the aged skeletal muscle can be ameliorated by its mechanical loading. However, the molecular responses of aged muscle cells to mechanical loading remain unclear. This study examined the effect of mechanical loading of aged, proliferating, and differentiated myoblasts on the gene expression and signaling responses associated with their myogenic lineage progression and survival.

METHODS

Control and aged C2C12 cells were cultured on elastic membranes and underwent passive stretching for 12 h at a low frequency (0.25 Hz) and different elongations, varying the strain on days 0 and 10 of myoblast differentiation. Activation of ERK1/2 and Akt, and the expression of focal adhesion kinase (FAK) and key myogenic regulatory factors (MRFs), MyoD and Myogenin, were determined by immunoblotting of the cell lysates derived from stretched and non-stretched myoblasts. Changes in the expression levels of the MRFs, muscle growth, atrophy, and pro-apoptotic factors in response to mechanical loading of the aged and control cells were quantified by real-time qRT-PCR.

RESULTS

Mechanical stretching applied on myoblasts resulted in the upregulation of FAK both in proliferating (day 0) and differentiated (day 10) cells, as well as in increased phosphorylation of ERK1/2 in both control and aged cells. Moreover, Akt activation and the expression of early differentiation factor MyoD increased significantly after stretching only in the control myoblasts, while the late differentiation factor Myogenin was upregulated in both the control and aged myoblasts. At the transcriptional level, mechanical loading of the proliferating myoblasts led to an increased expression of IGF-1 isoforms and MRFs, and to downregulation of muscle atrophy factors mainly in control cells, as well as in the upregulation of pro-apoptotic factors both in control and aged cells. In differentiated cells, mechanical loading resulted in an increased expression of the IGF-1Ea isoform and Myogenin, and in the downregulation of atrophy and pro-apoptotic factors in both the control and aged cells.

CONCLUSIONS

This study revealed a diminished beneficial effect of mechanical loading on the myogenic and survival ability of the senescent muscle cells compared with the controls, with a low strain (2%) loading being most effective in upregulating myogenic/anabolic factors and downregulating atrophy and pro-apoptotic genes mainly in the aged myotubes.

Association of muscle fiber composition with health and exercise-related traits in athletes and untrained subjects

Skeletal muscle is a heterogenous and metabolically active tissue, the composition of which is associated with multiple traits. The aim of the study was to determine whether there are additional health and exercise-related traits associated with muscle fiber composition in athletes and non-athletes. This study recruited 164 Russian participants (51 endurance and 48 power athletes; 65 controls). Vastus lateralis muscle fiber composition was assessed by immunohistochemistry. Slow-twitch muscle fiber percentage (STMF%) was significantly greater in endurance than power athletes and non-athletes, and in non-athlete females than males. STMF% was positively associated with athletes' training frequency, non-athletes' and endurance athletes' age, endurance athletes' competition level and chest depth, and power athletes' training age. STMF% was negatively associated with diastolic blood pressure in power athletes and with systolic blood pressure and reaction time in non-athletes. In all participants, STMF% was positively associated with age, tolerance to long distance exercise, chest depth and fracture incidence, and negatively with systolic blood pressure and resting heart rate. Age, sex and training frequency explained 10.6% and 13.2% of the variance in STMF% in endurance and power athletes, respectively. This is one of the most comprehensive studies involving athletes and untrained subjects and provides novel information concerning associations of increased STMF percentage with lower resting heart rate, better tolerance to long distances, faster reaction time and larger chest depth. On the other hand, the increased percentage of fast-twitch muscle fibers was associated with rare fracture incidence.

The Prospective Study of Epigenetic Regulatory Profiles in Sport and Exercise Monitored Through Chromosome Conformation Signatures

The integration of genetic and environmental factors that regulate the gene expression patterns associated with exercise adaptation is mediated by epigenetic mechanisms. The organisation of the human genome within three-dimensional space, known as chromosome conformation, has recently been shown as a dynamic epigenetic regulator of gene expression, facilitating the interaction of distal genomic regions due to tight and regulated packaging of chromosomes in the cell nucleus. Technological advances in the study of chromosome conformation mean a new class of biomarker-the chromosome conformation signature (CCS)-can identify chromosomal interactions across several genomic loci as a collective marker of an epigenomic state. Investigative use of CCSs in biological and medical research shows promise in identifying the likelihood that a disease state is present or absent, as well as an ability to prospectively stratify individuals according to their likely response to medical intervention. The association of CCSs with gene expression patterns suggests that there are likely to be CCSs that respond, or regulate the response, to exercise and related stimuli. The present review provides a contextual background to CCS research and a theoretical framework discussing the potential uses of this novel epigenomic biomarker within sport and exercise science and medicine.

Comparison of the Effects of Endurance Training on Alternate Days and on Consecutive 4 Days Each Week for 8 Weeks on the Abundance of PGC-1α, CaMKII, NRF-1, mtTFA, and COXIV Proteins in Rat Skeletal Muscle

Qiu, J, Huang, L, Davie, AJ, and Zhou, S. Comparison of the effects of endurance training on alternate days and on consecutive 4 days each week for 8 weeks on the abundance of PGC-1α, CaMKII, NRF-1, mtTFA, and COXIV proteins in rat skeletal muscle. J Strength Cond Res 33(11): 3136-3144, 2019-The aim of this study was to compare the effects of 2 training protocols, training on alternate days (A) or on consecutive 4 days followed by 3 days of rest in each week (C) for 8 weeks, on selected proteins involved in the biogenesis and function of mitochondria in skeletal muscle. Eighty male Sprague Dawley rats were randomly allocated into 10 groups (n = 8 each), including Pre and Post control groups and A or C training groups with 8, 16, 24, and 32 training sessions, respectively. The vastus lateralis and soleus muscle samples were obtained 24 hours after the last training session, or at rest for the controls. The abundance of the proteins for PGC-1α, CaMKII, NRF-1, mtTFA, and COXIV was analyzed by Western blotting. Analysis of the results with 2-way ANOVA showed no significant effect and interaction (training protocol by duration) in abundance of the proteins by the 2 protocols. However, fold changes normalized to control showed significant increases COXIV of the soleus muscle at most time points in both A and C training as indicated by Kruskal-Wallis H tests. There were significant correlations found between the abundance of the measured proteins of the vastus lateralis. The findings suggest that the 2 training protocols with the same intensity and total volume of work would not make a significant difference in respect of the changes in the targeted proteins. Alternative regulatory factors and the responses in different types of muscles to the training programs need to be examined in future research.

The activity of satellite cells and myonuclei following 8 weeks of strength training in young men with suppressed testosterone levels

AIM

To investigate how suppression of endogenous testosterone during an 8-week strength training period influences the activity of satellite cells and myonuclei.

METHODS

Twenty-two moderately trained young men participated in this randomized, placebo-controlled, and double-blinded intervention study. The participants were randomized to treatment with a GnRH analogue, goserelin (n = 12), which suppresses testosterone or placebo (n = 10) for 12 weeks. The strength training period of 8 weeks started after 4 weeks of treatment and included exercises for all major muscles. Biopsies were obtained from the mid-portion of the vastus lateralis muscle.

RESULTS

Testosterone resting level in goserelin was 10-20 times lower compared with placebo, and the training-induced increase in the level of testosterone was abolished in goserelin. Training increased satellite cells number in type II fibres by 20% in placebo and by 52% in goserelin (P < 0.01), whereas the myonuclear number significantly increased by 12% in type II fibres in placebo and remained unchanged in goserelin (P < 0.05). No changes in satellite cells and myonuclei were seen in type I fibres in either group. Data from the microarray analysis indicated that low testosterone affects the bone morphogenetic proteins signalling, which might regulate proliferation vs. differentiation of satellite cells.

CONCLUSION

Eight weeks of strength training enhances the myonuclear number in type II fibres, and this is largely blocked by the suppression of testosterone. The data indicate that low testosterone levels could reduce the differentiation of satellite cells to myonuclei via the bone morphogenetic proteins signalling pathway, resulting in reduced increases in lean leg mass.

Skeletal muscle wasting with disuse atrophy is multi-dimensional: the response and interaction of myonuclei, satellite cells and signaling pathways

Maintenance of skeletal muscle is essential for health and survival. There are marked losses of skeletal muscle mass as well as strength and physiological function under conditions of low mechanical load, such as space flight, as well as ground based models such as bed rest, immobilization, disuse, and various animal models. Disuse atrophy is caused by mechanical unloading of muscle and this leads to reduced muscle mass without fiber attrition. Skeletal muscle stem cells (satellite cells) and myonuclei are integrally involved in skeletal muscle responses to environmental changes that induce atrophy. Myonuclear domain size is influenced differently in fast and slow twitch muscle, but also by different models of muscle wasting, a factor that is not yet understood. Although the myonuclear domain is 3-dimensional this is rarely considered. Apoptosis as a mechanism for myonuclear loss with atrophy is controversial, whereas cell death of satellite cells has not been considered. Molecular signals such as myostatin/SMAD pathway, MAFbx, and MuRF1 E3 ligases of the ubiquitin proteasome pathway and IGF1-AKT-mTOR pathway are 3 distinctly different contributors to skeletal muscle protein adaptation to disuse. Molecular signaling pathways activated in muscle fibers by disuse are rarely considered within satellite cells themselves despite similar exposure to unloading or low mechanical load. These molecular pathways interact with each other during atrophy and also when various interventions are applied that could alleviate atrophy. Re-applying mechanical load is an obvious method to restore muscle mass, however how nutrient supplementation (e.g., amino acids) may further enhance recovery (or reduce atrophy despite unloading or ageing) is currently of great interest. Satellite cells are particularly responsive to myostatin and to growth factors. Recently, the hibernating squirrel has been identified as an innovative model to study resistance to atrophy.

Management of limited joint mobility in diabetic patients

Several rheumatologic manifestations are more pronounced in subjects with diabetes, ie, frozen shoulder, rotator cuff tears, Dupuytren's contracture, trigger finger, cheiroarthropathy in the upper limb, and Achilles tendinopathy and plantar fasciitis in the lower limb. These conditions can limit the range of motion of the affected joint, thereby impairing function and ability to perform activities of daily living. This review provides a short description of diabetes-related joint diseases, the specific pathogenetic mechanisms involved, and the role of inflammation, overuse, and genetics, each of which activates a complex sequence of biochemical alterations. Diabetes is a causative factor in tendon diseases and amplifies the damage induced by other agents as well. According to an accepted hypothesis, damaged joint tissue in diabetes is caused by an excess of advanced glycation end products, which forms covalent cross-links within collagen fibers and alters their structure and function. Moreover, they interact with a variety of cell surface receptors, activating a number of effects, including pro-oxidant and proinflammatory events. Adiposity and advanced age, commonly associated with type 2 diabetes mellitus, are further pathogenetic factors. Prevention and strict control of this metabolic disorder is essential, because it has been demonstrated that limited joint motion is related to duration of the disease and hyperglycemia. Several treatments are used in clinical practice, but their mechanisms of action are not completely understood, and their efficacy is also debated.

Resistance exercise training influences skeletal muscle immune activation: a microarray analysis

The primary aim of this investigation was to evaluate the effect of training on the immune activation in skeletal muscle in response to an acute bout of resistance exercise (RE). Seven young healthy men and women underwent a 12-wk supervised progressive unilateral arm RE training program. One week after the last training session, subjects performed an acute bout of bilateral RE in which the trained and the untrained arm exercised at the same relative intensity. Muscle biopsies were obtained 4 h postexercise from the biceps brachii of both arms and assessed for global transcriptom using Affymetrix U133 plus 2.0 microarrays. Significantly regulated biological processes and gene groups were analyzed using a logistic regression-based method following differential (trained vs. untrained) gene expression testing via an intensity-based Bayesian moderated t-test. The results from the present study suggest that training blunts the transcriptional upregulation of immune activation by minimizing expression of genes involved in monocyte recruitment and enhancing gene expression involved in macrophage anti-inflammatory polarization. Additionally, our data suggest that training blunts the transcriptional upregulation of the stress response and the downregulation of glucose metabolism, mitochondrial structure, and oxidative phosphorylation, and it enhances the transcriptional upregulation of the extracellular matrix and cytoskeleton development and organization and the downregulation of gene transcription and muscle contraction. This study provides novel insight into the molecular processes involved in the adaptive response of skeletal muscle following RE training and the cellular and molecular events implicating the protective role of training on muscle stress and damage inflicted by acute mechanical loading.

Combined approach to counteract experimental cancer cachexia: eicosapentaenoic acid and training exercise

BACKGROUND: Cancer cachexia is a syndrome characterized by loss of skeletal muscle protein, depletion of lipid stores, anorexia, weakness, and perturbations of the hormonal homeostasis. Despite several therapeutic approaches described in the past, effective interventions countering cancer cachexia are still lacking. METHODS: The present work was aimed to verify the ability of eicosapentaenoic acid (EPA) to prevent the muscle depletion in Lewis lung carcinoma-bearing mice and to test the ability of endurance exercise training to increase the EPA effect. RESULTS: EPA alone did not prevent the muscle loss induced by tumor growth while the combination with exercise induced a partial rescue of muscle strength and mass. Moreover, the association of EPA and exercise reduced the dramatic PAX-7 accumulation and stimulated the increase of PCG-1 protein. CONCLUSIONS: Overall, the present data suggest that exercise is an effective tool that should be added for combined therapeutic approaches against cancer cachexia. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s13539-011-0028-4) contains supplementary material, which is available to authorized users.

Exercise, sex, menstrual cycle phase, and 17beta-estradiol influence metabolism-related genes in human skeletal muscle

Higher fat and lower carbohydrate and amino acid oxidation are observed in women compared with men during endurance exercise. We hypothesized that the observed sex difference is due to estrogen and that menstrual cycle phase or supplementation of men with 17beta-estradiol (E(2)) would coordinately influence the mRNA content of genes involved in lipid and/or carbohydrate metabolism in skeletal muscle. Twelve men and twelve women had muscle biopsies taken before and immediately after 90 min of cycling at 65% peak oxygen consumption (Vo(2peak)). Women were studied in the midfollicular (Fol) and midluteal (Lut) phases, and men were studied after 8 days of E(2) or placebo supplementation. Targeted RT-PCR was used to compare mRNA content for genes involved in transcriptional regulation and lipid, carbohydrate, and amino acid metabolism. Sex was the greatest predictor of substrate metabolism gene content. Sex affected the mRNA content of FATm, FABPc, SREBP-1c, mtGPAT, PPARdelta, PPARalpha, CPTI, TFP-alpha, GLUT4, HKII, PFK, and BCOADK (P < 0.05). E(2) administration significantly (P < 0.05) affected the mRNA content of PGC-1alpha, PPARalpha, PPARdelta, TFP-alpha, CPTI, SREBP-1c, mtGPAT, GLUT4, GS-1, and AST. Acute exercise increased the mRNA abundance for PGC-1alpha, HSL, FABPc, CPTI, GLUT4, HKII, and AST (P < 0.05). Menstrual cycle had a small effect on PPARdelta, GP, and glycogenin mRNA content. Overall, women have greater mRNA content for several genes involved in lipid metabolism, which is partially due to an effect of E(2).

Ca2+/calmodulin-dependent transcriptional pathways: potential mediators of skeletal muscle growth and development

The loss of muscle mass with age and disuse has a significant impact on the physiological and social well-being of the aged; this is an increasingly important problem as the population becomes skewed towards older age. Exercise has psychological benefits but it also impacts on muscle protein synthesis and degradation, increasing muscle tissue volume in both young and older individuals. Skeletal muscle hypertrophy involves an increase in muscle mass and cross-sectional area and associated increased myofibrillar protein content. Attempts to understand the molecular mechanisms that underlie muscle growth, development and maintenance, have focused on characterising the molecular pathways that initiate, maintain and regenerate skeletal muscle. Such understanding may aid in improving targeted interventional therapies for age-related muscle loss and muscle wasting associated with diseases. Two major routes through which skeletal muscle development and growth are regulated are insulin-like growth factor I (IGF-I) and Ca(2+)/calmodulin-dependent transcriptional pathways. Many reviews have focused on understanding the signalling pathways of IGF-I and its receptor, which govern skeletal muscle hypertrophy. However, alternative molecular signalling pathways such as the Ca(2+)/calmodulin-dependent transcriptional pathways should also be considered as potential mediators of muscle growth. These latter pathways have received relatively little attention and the purpose herein is to highlight the progress being made in the understanding of these pathways and associated molecules: calmodulin, calmodulin kinases (CaMKs), calcineurin and nuclear factor of activated T-cell (NFAT), which are involved in skeletal muscle regulation. We describe: (1) how conformational changes in the Ca(2+) sensor calmodulin result in the exposure of binding pockets for the target proteins (CaMKs and calcineurin). (2) How Calmodulin consequently activates either the Ca(2+)/calmodulin-dependent kinases pathways (via CaMKs) or calmodulin-dependent serine/threonine phosphatases (via calcineurin). (3) How calmodulin kinases alter transcription in the nucleus through the phosphorylation, deactivation and translocation of histone deacetylase 4 (HDAC4) from the nucleus to the cytoplasm. (4) How calcineurin transmits signals to the nucleus through the dephosphorylation and translocation of NFAT from the cytoplasm to the nucleus.

Suppression of testosterone does not blunt mRNA expression of myoD, myogenin, IGF, myostatin or androgen receptor post strength training in humans

We hypothesized that suppression of endogenous testosterone blunts mRNA expression post strength training (ST). Twenty-two young men were randomized for treatment with the GnRH analogue goserelin (3.6 mg every 4 weeks) or placebo for a period of 12 weeks. The ST period of 8 weeks started at week 4. Strength test, blood sampling, muscle biopsies, and whole-body dual-energy X-ray absorptiometry (DXA) scan were performed at weeks 4 and 12. Muscle biopsies were taken during the final ST session (pre, post 4 h, and post 24 h). Resting serum testosterone decreased significantly (P < 0.01) in the goserelin group from 22.6 +/- 1.6 (mean +/- s.e.m.) to 2.0 +/- 0.1 nmol l(-1) (week 4), whereas it remained unchanged in the placebo group. An acute increase of serum testosterone was observed during the final ST session in the placebo group (P < 0.05), whereas a decreased response was observed in the goserelin group (P < 0.05). mRNA expression of IGF-IE(bc) and myogenin increased, while expression of myostatin decreased (P < 0.01); however, no differences were observed between the groups. Muscle strength and muscle mass showed a tendency to increase more in the placebo group than in the goserelin group (P = 0.05). In conclusion, despite blocked acute responses of testosterone and 10- to 20-fold lower resting levels in the goserelin group, ST resulted in a similar mRNA expression of myoD, myogenin, IGF-IE(abc), myostatin and androgen receptor as observed in the placebo group. Therefore, in the present study, the molecular events were the same, despite divergent muscle hypertrophy and strength gains.

Satellite cell numbers in young and older men 24 hours after eccentric exercise

We tested the hypothesis that the expansion of satellite cell numbers, 24 h after maximal eccentric knee extensor exercise, is blunted in older men. Muscle biopsies were obtained from the vastus lateralis of 10 young (23-35 years) and 9 older (60-75 years) men. Satellite cells were identified immunohistochemically using an antibody to neural cell adhesion molecule. After 92 maximal eccentric contractions, the mean number of satellite cells per muscle fiber increased to a greater extent among the young men (141%; P < 0.001) than older men (51%; P = 0.002) from preexercise levels. Similar results were obtained when satellite cells were expressed as a proportion of all sublaminar nuclei. We conclude that a single bout of maximal eccentric exercise increases satellite cell numbers in both age groups, with a significantly greater response among the young men. These data suggest that age-related changes in satellite cell recruitment may contribute to muscle regeneration deficits among the elderly.

Serum creatine kinase activity varies with ovulatory status in regularly exercising, premenopausal women

BACKGROUND/AIMS

The clinical complications associated with an unopposed estrogen environment and luteal phase defects observed in exercising women prompted the examination of the relationship of exercise and endogenous ovarian steroids with serum creatine kinase (CK) activity.

METHODS

Subjects (n = 34) were classified into three groups according to their exercise and menstrual status, sedentary and exercising ovulatory groups (SedOvul, ExOvul), and an exercising amenorrheic group (ExAmen). Daily urine samples were collected to assess urinary ovarian steroid exposure and menstrual status. Serum CK activity was assayed in each menstrual cycle of all subjects.

RESULTS

Exercise increased serum CK activity in all exercising subjects (p < 0.01), but the increase was greater in amenorrheic women compared to ovulatory women (SedOvul: 33.0 +/- 3.4; ExOvul: 43.7 +/- 4.1; ExAmen: 54.4 +/- 3.6, p < 0.05). When the ovulatory women were further divided into those with normal steroid production (ExOvul subgroup) and those with a suppressed progesterone luteal phase environment (ExLPD), both the ExOvul (51.9 +/- 5.4 IU/l) subgroup and ExAmen group had higher serum CK activity (p < 0.05) than the ExLPD (36.6 +/- 5.2 IU/l) subjects or the sedentary controls.

CONCLUSIONS

These data demonstrate the complex association between ovarian hormone status and the normal serum CK response to regular mechanical stress imposed by chronic exercise training.

Prevention of hyperglycemia in Zucker diabetic fatty rats by exercise training: effects on gene expression in insulin-sensitive tissues determined by high-density oligonucleotide microarray analysis

Exercise training (ET) causes metabolic improvement in the prediabetic and diabetic states. However, only little information exists on the changes to ET at the transcriptional level in insulin-sensitive tissues. We have investigated the gene expression changes in skeletal muscle, liver, fat, and pancreatic islets after ET in male Zucker diabetic fatty (ZDF) rats. Eighteen ZDF rats (7 weeks old) were divided in a control and ET group. Exercise was performed using a motorized treadmill (20 m/min 1 hour daily for 6 days a week). Blood glucose, weight, and food intake were measured weekly. After 5 weeks, blood samples, soleus muscle, liver, visceral fat (epididymal fat pads), and islet tissue were collected. Gene expression was quantified with Affymetrix RG-U34A array (16 chips). Exercise training ameliorates the development of hyperglycemia and reduces plasma free fatty acid and the level of glucagon-insulin ratio (P < .05). In skeletal muscle, the expression of 302 genes increased, whereas that of 119 genes decreased. These changes involved genes related to skeletal muscle plasticity, Ca(2+) signals, energy metabolism (eg, glucose transporter 1, phosphorylase kinase), and other signaling pathways as well as genes with unknown functions (expressed sequence tags). In the liver, expression of 148 genes increased, whereas that of 199 genes decreased. These were primarily genes involved in lipogenesis and detoxification. Genes coding for transcription factors were changed in parallel in skeletal muscle and liver tissue. Training did not markedly influence the gene expression in islets. In conclusion, ET changes the expression of multiple genes in the soleus muscle and liver tissue and counteracts the development of diabetes, indicating that ET-induced changes in gene transcription may play an important role en the prevention of diabetes.

Exercise-related novel gene is involved in myoblast differentiation

In this study we tried to identify new genes or proteins in skeletal muscle induced by exercise. We analyzed alterations of protein expression in mouse gastrocnemius muscles induced by swim-exercise using two dimensional gel electrophoresis and mass spectrometry. Nine spots were significantly altered between control and swim groups. One of the four protein spots whose expression was decreased was identified as functionally unknown "expressed sequence AI854635" gene. The AI854635 gene has C2H2 type zinc finger motif, and is considered to be a transcription factor. The mRNA of AI854635 gene was expressed in skeletal muscle, brain, kidney, and thymus. To elucidate the function of the AI854635 gene we analyzed mRNA expression levels during C2C12 myoblast differentiation. C2C12 myoblast began to form myotube around 20 h after the initiation of differentiation. The mRNA expression levels of AI854635 gene was significantly induced around 6 h and increased till 48 h, indicating a pivotal role in myoblast differentiation. Although the significance of decreased expression of AI854635 gene induced by swim-exercise is not clear, we found that this gene is involved in myoblast differentiation.

Signaling satellite-cell activation in skeletal muscle: markers, models, stretch, and potential alternate pathways

Activation of skeletal muscle satellite cells, defined as entry to the cell cycle from a quiescent state, is essential for normal growth and for regeneration of tissue damaged by injury or disease. This review focuses on early events of activation by signaling through nitric oxide and hepatocyte growth factor, and by mechanical stimuli. The impact of various model systems used to study activation and the regulation of satellite-cell quiescence are placed in the context of activation events in other tissues, concluding with a speculative model of alternate pathways signaling satellite-cell activation.

The effect of chronic physical exercise on succinic dehydrogenase activity in the heart muscle of old rats

Succinic dehydrogenase (SDH) activity, preferentially evidenced by cytochemical methods, has been measured by computer-assisted morphometry in the heart muscle of old sedentary and age-matched animals chronically undergone physical exercise (20 min, twice a day, 5 days a week). The area of the SDH-positive mitochondria (MA) and the overall area of the cytochemical precipitates due to SDH activity (PA) were semiautomatically measured and the ratios PA/MA as well as MA/overall myocardial tissue area analysed (MA/TA) were the parameters taken into account. No significant difference was found between the two groups investigated as regards PA/MA, whereas the MA/TA value is significantly increased in the animals undergone physical training. The present findings document that chronic physical exercise significantly increases the overall mitochondrial area involved in energy provision in the old myocardial tissue. Considering that myocardial function highly relies on mitochondrial metabolism, our results support a beneficial effect of chronic physical exercise on the old heart muscle.

Alterations in the expression of mRNAs and proteins that code for species relevant to eIF2B activity after an acute bout of resistance exercise

The focus of the study described herein was to examine the relative expression levels of mRNAs and proteins relevant to the regulation of translational initation, and hence protein synthesis, in the time course after an acute bout of resistance exercise in male Sprague-Dawley rats. Significant increases in the relative abundance of the mRNAs coding for the epsilon (33%) and gamma (26%) subunits of eukaryotic initiation factor (eIF) 2B were observed 48 h after the exercise bout. Furthermore, the mRNA coding for the delta subunit of eIF2B was also significantly increased, both 24 h (46%) and 48 h (44%) postexercise. There was a relative decrease in three eIF2Bϵ kinase mRNAs, namely sequences coding for glycogen synthase kinase 3β (49%), casein kinase I (48%), and casein kinase II (42%) 48 h into the recovery period. Additionally, there was a significant decrease in expression of the mRNAs coding for eIF2α (28% 24 h postexercise) and one of its regulatory kinases, double-stranded RNA-activated protein kinase (33% 48 h postexercise). Finally, an increase in eIF2B total protein (124%) was observed within 3 h postexercise. These results suggest that there may be rapid translational regulation of mRNAs coding for species relevant to translational initiation after an acute bout of resistance exercise. Furthermore, transcription of these mRNAs is altered further into the recovery period, and this might play a role in protein synthetic capacity on subsequent bouts of resistance exercise.

Regulatory gene expression in skeletal muscle of highly endurance-trained humans

AIM AND BACKGROUND

Changes in regulatory and structural gene expression provide the molecular basis for the adaptation of human skeletal muscle to endurance exercise.

HYPOTHESIS

The steady-state levels of multiple mRNAs mainly involved in regulatory functions differ between highly endurance-trained and untrained subjects in a muscle heavily recruited during the exercise.

METHODS

Biopsies from musculus vastus lateralis of seven untrained (UT) subjects [maximal oxygen consumption (VO2max) = 39 mL kg-1 min-1] and seven trained (T) professional cyclists (VO2max = 72 mL kg-1 min-1) were analysed for the contents of 597 different mRNAs using commercially available cDNA arrays (Clontech no. 7740-1). Intra-individual expression profiles were compared by least-square linear regression analysis. Differences in gene expression between the two groups were tested for statistical significance using L1 regression analysis combined with the sign test on all permutations of scatter plots of log raw values from UT vs. T subjects.

RESULTS

Transcripts for 144 of 597 genes were sufficiently abundant to be analysed quantitatively. The expression profiles of the T group had a better intragroup correlation (R2) than those of the UT group (0.78 vs. 0.65, P < 0.05). An intergroup (T vs. UT) correlation of expression profiles gave an R2 of 0.71. Statistical analysis at a false discovery rate of 5% identified differential expression of nine cell-regulatory genes between T and UT. The mRNA levels of eight genes, including two DNA repair enzymes, transcription factors, signal transducers, a glycolytic enzyme and a factor involved in steroid hormone metabolism were increased in T vs. UT. Conversely, the mRNA of the tumour suppressor APC was downregulated with endurance training. Selective reverse-transcriptase polymerase chain reaction experiments confirmed the signal estimates from the array analysis.

CONCLUSIONS

The repetitive impact of the complex exercise stimuli in professional cyclists attenuated the interindividual differences in regulatory gene expression in skeletal muscle. Long-term nuclear reprogramming of regulatory gene expression seems to be characteristic of human musculus vastus lateralis in a highly endurance-trained steady state.

Tetracycline-inducible system for regulation of skeletal muscle-specific gene expression in transgenic mice

Tightly regulated control of over-expression is often necessary to study one aspect or time point of gene function and, in transgenesis, may help to avoid lethal effects and complications caused by ubiquitous over-expression. We have utilized the benefits of an optimized tet-on system and a modified muscle creatine kinase (MCK) promoter to generate a skeletal muscle-specific, doxycycline (Dox) controlled over-expression system in transgenic mice. A DNA construct was generated in which the codon optimized reverse tetracycline transactivator (rtTA) was placed under control of a skeletal muscle-specific version of the mouse MCK promoter. Transgenic mice containing this construct expressed rtTA almost exclusively in skeletal muscles. These mice were crossed to a second transgenic line containing a bi-directional promoter centered on a tet responder element driving both a luciferase reporter gene and a tagged gene of interest; in this case the calpain inhibitor calpastatin. Compound hemizygous mice showed high level, Dox dependent muscle-specific luciferase activity often exceeding 10,000-fold over non-muscle tissues of the same mouse. Western and immunocytochemical analysis demonstrated similar Dox dependent muscle-specific induction of the tagged calpastatin protein. These findings demonstrate the effectiveness and flexibility of the tet-on system to provide a tightly regulated over-expression system in adult skeletal muscle. The MCKrtTA transgenic lines can be combined with other transgenic responder lines for skeletal muscle-specific over-expression of any target gene of interest.