Effect of swimming on myostatin expression in white and red gastrocnemius muscle and in cardiac muscle of rats

Swimming in cold water increases the browning process by diminishing the Myostatin pathway

BACKGROUND

Brown adipose tissue (BAT) is a thermogenic tissue that uncouples oxidative phosphorylation from ATP synthesis and increases energy expenditure via non-shivering thermogenesis in mammals. Cold exposure and exercise have been shown to increase BAT and browning of white adipose tissue (WAT) in mice. This study aimed to determine whether there is an additive effect of exercise during cold exposure on markers related to browning of adipose tissue. in Wistar rats.

METHODS

Twenty-four male Wistar rats were randomly divided into three groups: Control (C, 25˚C), Swimming in Neutral (SN, 30˚C) water, and Swimming in Cold (SC, 15˚C) water. Swimming included intervals of 2-3 min, 1 min rest, until exhausted, three days a week for six weeks, with a training load of 3-6% body weight. After the experimental protocol, interscapular BAT and inguinal subcutaneous white adipose tissue (WAT) were excised, weighed, and processed for beiging marker gene expression.

RESULTS

SN and SC resulted in lower body weight gain, associated with reduced WAT and BAT volume and increased BAT number with greater effects observed in SC. Myostatin protein expression was lower in BAT, WAT, soleus muscle, and serum NC and SC compared to the C group. Expression of the interferon regulatory factor-4 (IRF4) gene in both BAT and WAT tissues was significantly greater in the SC than in the C. Expression of the PGC-1α in BAT was significantly increased in the SC compared to C and increased in WAT in NC and SC. Expression of the UCP1 in BAT and WAT increased in the SC group compared to other groups.

CONCLUSION

The findings demonstrate that six weeks of swimming training in cold water promotes additive effects of the expression of genes and proteins involved in the browning process of adipose tissue in Wistar rats. Myostatin inhibition may possess a regulator effect on the PGC-1α - UCP1 pathway that mediates adipose tissue browning.

Myostatin and the Heart

Myostatin (growth differentiation factor 8) is a member of the transforming growth factor-β superfamily. It is secreted mostly by skeletal muscles, although small amounts of myostatin are produced by the myocardium and the adipose tissue as well. Myostatin binds to activin IIB membrane receptors to activate the downstream intracellular canonical Smad2/Smad3 pathway, and additionally acts on non-Smad (non-canonical) pathways. Studies on transgenic animals have shown that overexpression of myostatin reduces the heart mass, whereas removal of myostatin has an opposite effect. In this review, we summarize the potential diagnostic and prognostic value of this protein in heart-related conditions. First, in myostatin-null mice the left ventricular internal diameters along with the diastolic and systolic volumes are larger than the respective values in wild-type mice. Myostatin is potentially secreted as part of a negative feedback loop that reduces the effects of the release of growth-promoting factors and energy reprogramming in response to hypertrophic stimuli. On the other hand, both human and animal data indicate that myostatin is involved in the development of the cardiac cachexia and heart fibrosis in the course of chronic heart failure. The understanding of the role of myostatin in such conditions might initiate a development of targeted therapies based on myostatin signaling inhibition.

Exaggerated blood pressure response to static exercise in hindlimb ischemia-reperfusion

Peripheral artery disease (PAD) reduces the blood flow supply in the affected limbs as one of the significant cardiovascular concerns. Revascularization surgery in the femoral artery plays a central role in treating PAD. Exercise is also a rehabilitation strategy suggested for PAD patients to improve vascular functions. However, the effects of limb ischemia-reperfusion (IR), one of the most predominant complications in revascularization surgery, on exercise-induced arterial blood pressure (BP) response are poorly understood. In the present study, we determined 1) the blood flow status in the hindlimb muscles of rats (plantar muscle, red and white portions of gastrocnemius) with different time points of the hindlimb IR; and 2) the BP response to static muscle contraction in rats at different time points after the blood flow reperfusion procedure. Results of this study indicated that, compared with the Sham group, the blood flow in the hindlimb muscles evaluated by Evans blue concentration was significantly reduced at 6 h of femoral artery occlusion (FAO 6 h) (vs. sham control, p < 0.05). The decreased blood flow was gradually recovered after the blood flow reperfusion for 18 (IR 18 h), 66 (IR 66 h), and 114 (IR 114 h) hours (p < 0.05 vs. FAO 6 h for all IR groups). The response of mean arterial pressure was 20 ± 4 mmHg in Sham rats (n = 7); 32 ± 10 mmHg in IR 18 h rats (n = 10); 27 ± 7 mmHg in IR 66 h rats (n = 13); 26 ± 4 mmHg in IR 114 h rats (n = 9) (p < 0.05 vs. Sham for all groups). No significant difference was observed in the peak-developed tension during muscle contraction among all the groups (p > 0.05). In conclusion, static exercise-induced BP response is exaggerated following IR. Whereas the BP response is not statistically significant but tends to decrease with a prolonged IR time, the exaggerated BP response remains through time points from post-IR 18 h-114 h.

Regenerating Urethral Striated Muscle by CRISPRi/dCas9-KRAB-Mediated Myostatin Silencing for Obesity-Associated Stress Urinary Incontinence

Overweight females are prone to obesity-associated stress urinary incontinence (OA-SUI), and there are no definitive medical therapies for this common urologic condition. This study was designed to test the hypothesis that regenerative therapy to restore urethral striated muscle (stM) and pelvic floor muscles might represent a valuable therapeutic approach. For the in vitro experiment, single-guide RNAs targeting myostatin (MSTN) were used for CRISPRi/dCas9-Kruppel associated box (KRAB)-mediated gene silencing. For the in vivo experiment, a total of 14 female lean ZUC-Leprfa 186 and 14 fatty ZUC-Leprfa 185 rats were used as control and CRISPRi-MSTN treated groups, respectively. The results indicated that lentivirus-mediated expression of MSTN CRISPRi/dCas9-KRAB caused sustained downregulation of MSTN in rat L6 myoblast cells and significantly enhanced myogenesis in vitro. In vivo, the urethral sphincter injection of lentiviral-MSTN sgRNA and lentiviral-dCas9-KRAB significantly increased the leak point pressure, the thickness of the stM layer, the ratio of stM to smooth muscle, and the number of neuromuscular junctions. Downregulation of MSTN with CRISPRi/dCas9-KRAB-mediated gene silencing significantly enhanced myogenesis in vitro and in vivo. It also improved urethral continence in the OA-SUI rat model.

Effect of different muscle contraction mode on the expression of Myostatin, IGF-1, and PGC-1 alpha family members in human Vastus Lateralis muscle

Muscle contraction stimulates a transient change of myogenic factors, partly related to the mode of contractions. Here, we assessed the response of IGF-1Ea, IGF-1Eb, IGF-1Ec, PGC1α-1, PGC1α-4, and myostatin to the eccentric Vs. the concentric contraction in human skeletal muscle. Ten healthy males were performed an acute eccentric and concentric exercise bout (n = 5 per group). For each contraction type, participants performed 12 sets of 10 repetitions knee extension by the dominant leg. Baseline and post-exercise muscle biopsy were taken 4 weeks before and immediately after experimental sessions from Vastus Lateralis muscle. Genes expression was measured by real-time PCR technique. There was a significant increase in PGC1α-1, PGC1α-4, IGF-1Ea and, IGF-1Eb mRNA after concentric contraction (p ≤ 0.05), while the PGC1α-4 and IGF-1Ec significantly increased after eccentric contraction (p ≤ 0.05). It is intriguing to highlight that; no significant differences between groups were evident for changes in any variables following exercise bouts (p ≥ 0.05). Our results found that concentric and eccentric contractions presented different responses in PGC1α-1, IGF-1Ea, IGF-1Eb, and IGF-1Ec mRNA. However, a similar significant increase in mRNA content was observed in PGC1α-4. Further, no apparent differences could be found between the response of genes to eccentric and concentric contraction.

Beyond the Big Five: Investigating Myostatin Structure, Polymorphism and Expression in Camelus dromedarius

Myostatin, a negative regulator of skeletal muscle mass in animals, has been shown to play a role in determining muscular hypertrophy in several livestock species, and a high degree of polymorphism has been previously reported for this gene in humans and cattle. In this study, we provide a characterization of the myostatin gene in the dromedary (Camelus dromedarius) at the genomic, transcript and protein level. The gene was found to share high structural and sequence similarity with other mammals, notably Old World camelids. 3D modeling highlighted several non-conservative SNP variants compared to the bovine, as well as putative functional variants involved in the stability of the myostatin dimer. NGS data for nine dromedaries from various countries revealed 66 novel SNPs, all of them falling either upstream or downstream the coding region. The analysis also confirmed the presence of three previously described SNPs in intron 1, predicted here to alter both splicing and transcription factor binding sites (TFBS), thus possibly impacting myostatin processing and/or regulation. Several putative TFBS were identified in the myostatin upstream region, some of them belonging to the myogenic regulatory factor family. Patterns of SNP distribution across countries, as suggested by Bayesian clustering of the nine dromedaries using the 69 SNPs, pointed to weak geographic differentiation, in line with known recurrent gene flow at ancient trading centers along caravan routes. Myostatin expression was investigated in a set of 8 skeletal muscles, both at transcript and protein level, via Digital Droplet PCR and Western Blotting, respectively. No significant differences were observed at the transcript level, while, at the protein level, the only significant differences concerned the promyostatin dimer (75 kDa), in four pair-wise comparisons, all involving the tensor fasciae latae muscle. Beside the mentioned band at 75 kDa, additional bands were observed at around 40 and 25 kDa, corresponding to the promyostatin monomer and the active C-terminal myostatin dimer, respectively. Their weaker intensity suggests that the unprocessed myostatin dimers could act as important reservoirs of slowly available myostatin forms. Under this assumption, the sequential cleavage steps may contribute additional layers of control within an already complex regulatory framework.

Blood Flow Restriction During Futsal Training Increases Muscle Activation and Strength

The aim of this study was to investigate the effect of leg blood flow restriction (BFR) applied during a 3-a-side futsal game on strength-related parameters. Twelve male futsal players were randomly assigned into two groups (n = 6 for each group) during 10 training sessions either with or without leg BFR. Prior to and post-training sessions, participants completed a series of tests to assess anabolic hormones and leg strength. Pneumatic cuffs were initially inflated to 110% of leg systolic blood pressure and further increased by 10% after every two completed sessions. In comparison with baseline, the resting post-training levels of myostatin (p = 0.002) and IGF-1/MSTN ratio (p = 0.006) in the BFR group changed, whereas no change in the acute level of IGF-1 and myostatin after exercise was observed. Peak torque of knee extension and flexion increased in both groups (p < 0.05). A trend of increased neural activation of all heads of the quadriceps was observed in both groups, however, it was statistically significant only for rectus femoris in BFR (p = 0.02). These findings indicated that the addition of BFR to normal futsal training might induce greater neuromuscular benefits by increasing muscle activation and augmenting the hormonal response.

Platelet releasate promotes skeletal myogenesis by increasing muscle stem cell commitment to differentiation and accelerates muscle regeneration following acute injury

AIM

The use of platelets as biomaterials has gained intense research interest. However, the mechanisms regarding platelet-mediated skeletal myogenesis remain to be established. The aim of this study was to determine the role of platelet releasate in skeletal myogenesis and muscle stem cell fate in vitro and ex vivo respectively.

METHODS

We analysed the effect of platelet releasate on proliferation and differentiation of C2C12 myoblasts by means of cell proliferation assays, immunohistochemistry, gene expression and cell bioenergetics. We expanded in vitro findings on single muscle fibres by determining the effect of platelet releasate on murine skeletal muscle stem cells using protein expression profiles for key myogenic regulatory factors.

RESULTS

TRAP6 and collagen used for releasate preparation had a more pronounced effect on myoblast proliferation vs thrombin and sonicated platelets (P < 0.05). In addition, platelet concentration positively correlated with myoblast proliferation. Platelet releasate increased myoblast and muscle stem cell proliferation in a dose-dependent manner, which was mitigated by VEGFR and PDGFR inhibition. Inhibition of VEGFR and PDGFR ablated MyoD expression on proliferating muscle stem cells, compromising their commitment to differentiation in muscle fibres (P < 0.001). Platelet releasate was detrimental to myoblast fusion and affected differentiation of myoblasts in a temporal manner. Most importantly, we show that platelet releasate promotes skeletal myogenesis through the PDGF/VEGF-Cyclin D1-MyoD-Scrib-Myogenin axis and accelerates skeletal muscle regeneration after acute injury.

CONCLUSION

This study provides novel mechanistic insights on the role of platelet releasate in skeletal myogenesis and set the physiological basis for exploiting platelets as biomaterials in regenerative medicine.

Effect of high-fat mixed lipid diet and swimming on fibre types in skeletal muscles of rats with colon tumours

Skeletal muscle fibre types, whose characteristics are determined by myosin heavy chain (MyHC) isoforms, can adapt to changed physiological demands with changed MyHC isoform expression resulting in the fibre type transitions. The endurance training is known to induce fastto- slow transitions and has beneficial effect in carcinogenesis, whereas the effect of an excessive fat intake and its interaction with the effect of swimming are less conclusive. Therefore, we studied the effect of high-fat mixed lipid (HFML) diet and long-term (21-week) swimming on fibre type transitions and their average diameters by immunohistochemical demonstration of MyHC isoforms in slow soleus (SOL), fast extensor digitorum longus (EDL), and mixed gastrocnemius medialis and lateralis (GM, GL) muscles, divided to deep and superficial portions (GMd, GMs, GLd, GLs), of sedentary and swimming Wistar rats with experimentally (dimethylhydrazine) induced colon tumours and fed either with HFML or low-fat corn oil (LFCO) diet. HFML diet induced only a trend for fast-to-slow transitions in SOL and in the opposite direction in GMd. Swimming triggered significant transitions in unexpected slow-to-fast direction in SOL, whereas in GMs the transitions had tendency to proceed in the expected fast-toslow direction. The average diameters of fibre types were mostly unaffected. Hence, it can be concluded that if present, the effects of HFML diet and swimming on fibre type transitions were counteractive and muscle-specific implying that each muscle possesses its own adaptive range of response to changed physiological conditions.

Effect of carcinogen 1,2-dimethylhydrazine treatment on fiber types in skeletal muscles of male Wistar rats

The cancerogen 1,2-dimethylhydrazine (DMH), widely used in the experimental animal model of carcinogenesis, affects various organs, but its effect on muscle fibers is unknown. To evaluate the effect of 15-week DMH treatment on the fiber size and myosin heavy chain (MyHC) isoforms, which substantially determine fiber types and their contractile characteristics, pure and hybrid fiber types were immunohistochemically determined according to the MyHC isoform expression in soleus, extensor digitorum longus, gastrocnemius medialis and lateralis muscles of DMH-treated and control male Wistar rats. Whereas the size of fibers was mostly unaffected, the MyHC isoform expression was partially affected in both gastrocnemius samples, but not in the soleus and extensor digitorum longus of DMH-treated rats. The lower proportions of hybrid fiber types and especially that of type 1/2x in most gastrocnemius samples of DMH-treated rats resulted in a shift towards a single MyHC isoform expression, but the extent and pattern of the MyHC isoform shift varied across the different gastrocnemius samples. Such variable response to DMH treatment across muscles indicates that each muscle possesses its own adaptive range. These findings are essential for an accurate evaluation of skeletal muscle characteristics in DMH animal model.

Serum reference value of two potential doping candidates-myostatin and insulin-like growth factor-I in the healthy young male

Background

Myostatin negatively regulates muscle growth, and its inhibition by suitable proteins can increase muscle bulk and exercise performance. However, the reference values of serum myostatin in athletes performing strength training are still lacking.

Methods

A cross-sectional study recruiting28 male collegiate athletes performing strength training and 29 age-matched normal controls was conducted.

The serum concentration of myostatin and insulin-like growth factor 1 (IGF-1), grip strength, and body composition were the main outcome measures. We used regression models to analyze the correlation between serum markers and the physiological parameters. The athlete group had greater height, weight, body mass index (BMI), fat mass percentage, fat-free mass, muscle mass, waist girth, grip strength, and estimated daily energy expenditure.

Results

The IGF-1 concentration was higher in the athlete group (324 ± 80 vs. 263 ± 134 ng/ml), but the myostatin levels did not differ (12.1 ± 3.7 vs. 12.4 ± 3.5 ng/ml). The reference value for IGF-1 among the healthy young males was 293 ± 114 ng/ml, correlated with age and height; the value for myostatin was 12.3 ± 3.6 ng/ml, correlated negatively with BMI, fat mass percentage, and waist girth after adjustment for age.

Conclusion

Myostatin level is negatively related to fat percentage, and serum IGF-1 is positively related to height. The reference values could provide a basis for future doping-related study.

The effect of eight weeks resistance and aerobic training on myostatin and follistatin expression in cardiac muscle of rats

Introduction: The clinical studies have shown that the myostatin gene expression and its serum density occur more frequently in heart patients than in healthy individuals. The purpose of this study is to investigate the influence of 8-week resistance and aerobic exercise on the myostatin and follistatin gene expression of myocardium muscle of healthy male Wistar rats.

Methods: In this experimental study, 20 five-week-old adult Wistar rats (250 ± 26.5 g) were divided into three groups: healthy control group (n = 6), resistance exercise group (n = 7), and aerobic exercise group (n = 7). The resistance and aerobic exercise plan consisted of 8 weeks and 3 sessions per week. The resistance exercise group performed climbing a one-meter 26-stair ladder with a slope of 85 degrees for 3 sets of 5 repetitions per session. The aerobic exercise group performed running at a speed of 12 meters per minute for 30 minutes during the first sessions gradually increasing up to a speed of 30 meters per minute for 60 minutes during the final sessions (equivalent to 70% to 80% of maximum oxygen consumption). The differences between the groups were evaluated using a one-way analysis of variance (ANOVA) test. When appropriate, LSD post-hoc test was used. The significance level for the study was less than 0.05.

Results: The results of this study shows that after 8 weeks of exercise, there is no significant difference between myostatin mRNA gene expression levels of the heart muscle among the three groups of control, resistance exercise, and aerobic exercise (P = 0.172, F = 1.953). However, the mean differences between follistatin mRNA levels of the heart muscle among the three groups of control, resistance exercise, and aerobic exercise are statistically significant (F = 38.022, P = 0.001). Furthermore, the ratio of follistatin to myostatin mRNA gene expression of the heart muscle (P = 0.001, F = 10.288) shows significant difference among the three groups.

Conclusion: Our results indicate that the resistance and aerobic exercise could cause a decrease in myostatin and an increase in follistatin levels, thus preventing many muscular physiological disorders such as arthritis and muscle weakness.

Delay in post-ovariectomy estrogen replacement negates estrogen-induced augmentation of post-exercise muscle satellite cell proliferation

This study examined the effects of a delay in post-ovariectomy replacement of 17β-estradiol (estrogen) on the post-exercise proliferation of muscle satellite cells. Nine-week-old, ovariectomized, female Sprague-Dawley rats (n = 64) were distributed among 8 groups based on estrogen status (0.25 mg estrogen pellet or sham), exercise status (90 min run at 17 m·min(-1) and a grade of -13.5° or unexercised), and estrogen replacement ("proximal", estrogen replacement within 2 weeks; or "delayed", estrogen replacement at 11 weeks following ovariectomy). Significant increases in satellite cells were found in the soleus and white gastrocnemius muscle (immunofluorescent colocalization of nuclei with Pax7) 72 h following eccentric exercise (p < 0.05) in all exercised groups. Proximal E2 replacement resulted in a further augmentation of muscle satellite cells in exercised rats (p < 0.05) relative to the delayed estrogen replacement group. Expression of PI3K was unaltered and phosphorylation of Akt relative to total Akt increased following estrogen supplementation and exercise. Exercise alone did not alter the expression levels of Akt. An 11 week delay in post-ovariectomy estrogen replacement negated the augmenting influence seen with proximal (2 week delay) post-ovariectomy estrogen replacement on post-exercise muscle satellite cell proliferation. This effect appears to be independent of the PI3K-Akt signaling pathway.

Alleviating exercise-induced muscular stress using neat and processed bee pollen: oxidative markers, mitochondrial enzymes, and myostatin expression in rats

BACKGROUND

The current study was designed to investigate the influence of monofloral Indian mustard bee pollen (MIMBP) and processed monofloral Indian mustard bee pollen (PMIMBP) supplementation on chronic swimming exercise-induced oxidative stress implications in the gastrocnemius muscle of Wistar rats.

METHODS

MIMBP was processed with an edible lipid-surfactant mixture (Captex 355:Tween 80) to increase the extraction of polyphenols and flavonoid aglycones as analyzed by UV spectroscopy and high performance liquid chromatography-photo diode array. Wistar rats in different groups were fed with MIMBP or PMIMBP supplements at a dose of 100 mg/kg, 200 mg/kg and 300 mg/kg individually, while being subjected to chronic swimming exercise for 4 weeks (5 d/wk). Various biochemical [superoxide dismutase (SOD), glutathione (GSH), malonaldehyde (MDA), nitric oxide (NO), and total protein content], mitochondrial (Complex I, II, III, and IV enzyme activity), and molecular (myostatin mRNA expression) parameters were monitored in the gastrocnemius muscle of each group.

RESULTS

Administration of both MIMBP (300 mg/kg) and PMIMBP (100 mg/kg, 200 mg/kg, and 300 mg/kg) wielded an antioxidant effect by significantly improving SOD, GSH, MDA, NO, and total protein levels. Further MIMBP (300 mg/kg) and PMIMBP (200 mg/kg and 300 mg/kg) significantly improved impaired mitochondrial Complex I, II, III, and IV enzyme activity. Significant down-regulation of myostatin mRNA expression by MIMBP (300 mg/kg) and PMIMBP (200 mg/kg and 300 mg/kg) indicates a muscle protectant role in oxidative stress conditions.

CONCLUSION

The study establishes the antioxidant, mitochondrial upregulatory, and myostatin inhibitory effects of both MIMBP and PMIMBP in exercise-induced oxidative stress conditions, suggesting their usefulness in effective management of exercise-induced muscular stress. Further, processing of MIMBP with an edible lipid-surfactant mixture was found to improve the therapeutic efficiency of pollen.

Phenotypic flexibility of skeletal muscle and heart masses and expression of myostatin and tolloid-like proteinases in migrating passerine birds

Migrant birds require large flight muscles and hearts to enhance aerobic capacity and support sustained flight. A potential mechanism for increasing muscle and heart masses during migration in birds is the muscle growth inhibitor myostatin and its metalloproteinase activators, tolloid-like proteinases (TLL-1 and TLL-2). We hypothesized that myostatin, TLL-1 and TLL-2 are downregulated during migration in pectoralis and hearts of migratory passerines to promote hypertrophy. We measured seasonal variation of tissue masses, mRNA expression of myostatin, TLL-1, and TLL-2, and myostatin protein levels in pectoralis muscle and heart for yellow warblers (Setophaga petechia), warbling vireos (Vireo gilvus), and yellow-rumped warblers (Setophaga coronata). Pectoralis mass was greatest in spring for warbling vireos and yellow warblers, but was stable between spring and fall for yellow-rumped warblers. Heart mass was higher in spring than in fall for yellow-rumped warblers, lowest in fall for warbling vireos, and seasonally stable for yellow warblers. Pectoralis and heart mRNA expression of myostatin and the TLLs did not differ significantly for any of the three species, offering little support for our hypothesis for a prominent role for myostatin in regulating migration-induced variation in pectoralis and heart masses. In contrast, pectoralis myostatin protein levels were lowest in spring for all three species, consistent with our hypothesis. Myostatin protein levels in heart, however, were seasonally stable for warbling vireos and yellow warblers, and increased in spring relative to fall for yellow-rumped warblers. These data offer mixed support for our hypothesis for the pectoralis, but suggest that myostatin is not a prominent regulator of migration-induced heart hypertrophy. Moreover, the different seasonal patterns for pectoralis mRNA and protein expression suggest that post-transcriptional modification of myostatin may contribute to pectoralis mass regulation during migration.

Endurance training prevents TWEAK but not myostatin-mediated cardiac remodelling in cancer cachexia

Strategies to prevent tumour burden-induced cardiac remodelling that might progress to heart failure are necessary to improve patients' health outcomes and tolerability to cancer therapies. Exercise has been suggested as a measure to prevent cardiac damage; however, its effectiveness on regulating cardiac remodelling secondary to cancer was never addressed. Using an animal model of mammary tumorigenesis, we studied the impact of 35weeks of endurance training on heart, focusing on the signalling pathways modulated by pro-inflammatory and wasting cytokines. The cardiac fibrosis and myofiber disorganization induced by tumour burden was paralleled by the increase of myostatin and TWEAK with the activation of signalling pathways involving Smad-3, NF-κB, TRAF-6 and atrogin-1. The activation of Akt/mTOR was observed in heart from rats with tumours, for which contributed the extracellular matrix. Endurance training prevented the increase of serum and cardiac TWEAK promoted by cancer, as well as the activation of NF-κB, TRAF6, atrogin-1 and p70S6K in heart. Data highlight the impact of exercise in the modulation of signalling pathways activated by wasting cytokines and the resulting outcomes on heart adaptation. Future studies focused on the cellular pathways underlying cardiac remodelling will assist in the development of exercise programs targeting cancer-related cardiac alterations.

Aerobic exercise training prevents heart failure-induced skeletal muscle atrophy by anti-catabolic, but not anabolic actions

Background

Heart failure (HF) is associated with cachexia and consequent exercise intolerance. Given the beneficial effects of aerobic exercise training (ET) in HF, the aim of this study was to determine if the ET performed during the transition from cardiac dysfunction to HF would alter the expression of anabolic and catabolic factors, thus preventing skeletal muscle wasting.

Methods and Results

We employed ascending aortic stenosis (AS) inducing HF in Wistar male rats. Controls were sham-operated animals. At 18 weeks after surgery, rats with cardiac dysfunction were randomized to 10 weeks of aerobic ET (AS-ET) or to an untrained group (AS-UN). At 28 weeks, the AS-UN group presented HF signs in conjunction with high TNF-α serum levels; soleus and plantaris muscle atrophy; and an increase in the expression of TNF-α, NFκB (p65), MAFbx, MuRF1, FoxO1, and myostatin catabolic factors. However, in the AS-ET group, the deterioration of cardiac function was prevented, as well as muscle wasting, and the atrophy promoters were decreased. Interestingly, changes in anabolic factor expression (IGF-I, AKT, and mTOR) were not observed. Nevertheless, in the plantaris muscle, ET maintained high PGC1α levels.

Conclusions

Thus, the ET capability to attenuate cardiac function during the transition from cardiac dysfunction to HF was accompanied by a prevention of skeletal muscle atrophy that did not occur via an increase in anabolic factors, but through anti-catabolic activity, presumably caused by PGC1α action. These findings indicate the therapeutic potential of aerobic ET to block HF-induced muscle atrophy by counteracting the increased catabolic state.

Oestrogen-dependent satellite cell activation and proliferation following a running exercise occurs via the PI3K signalling pathway and not IGF-1

AIM

The purpose of this study was to determine whether 17β-estradiol (E2) enhances the activation, proliferation and differentiation of muscle satellite cells (SC) following eccentric exercise either via insulin-like growth factor-1 (IGF-1) or through phosphatidylinositol 3-kinase (PI3K) signalling.

METHODS

This study used 64, 9-week-old, ovariectomized Sprague-Dawley rats that were divided into eight treatments groups based on oestrogen status (0.25 mg oestrogen pellet or sham), exercise status (90 min run @ 17 m min(-1), -13.5° or unexercised) and PI3K signalling inhibition (0.7 mg wortmannin kg(-1) body weight or DMSO control).

RESULTS

Significant increases in total SCs were found in both soleus and white gastrocnemius muscles (immunofluorescent co-localization of Pax7(+) nuclei) 72 h following eccentric exercise (P < 0.05). Oestrogen supplementation caused a further enhancement in total SCs in exercised rats (P < 0.05). In animals where the PI3K pathway was inhibited, regardless of oestrogen or exercise status, there was no significant enhancement of SC number in both the soleus or white gastrocnemius muscles. Interestingly, oestrogen supplementation lowered muscle levels of IGF-1 with this effect being most prominent in the soleus muscle. While IGF-1 was increased following exercise (P < 0.05), oestrogen supplementation abrogated this increase back to sedentary levels.

CONCLUSION

These data suggest that the increase in SC population following exercise in oestrogen-supplemented females may be mediated via PI3K pathway signalling and not IGF-1.

Effect of physical training on liver expression of activin A and follistatin in a nonalcoholic fatty liver disease model in rats

Nonalcoholic fatty liver disease (NAFLD) is characterized by fat accumulation in the liver and is associated with obesity and insulin resistance. Activin A is a member of the transforming growth factor beta (TGF)-β superfamily and inhibits hepatocyte growth. Follistatin antagonizes the biological actions of activin. Exercise is an important therapeutic strategy to reduce the metabolic effects of obesity. We evaluated the pattern of activin A and follistatin liver expression in obese rats subjected to swimming exercise. Control rats (C) and high-fat (HF) diet-fed rats were randomly assigned to a swimming training group (C-Swim and HF-Swim) or a sedentary group (C-Sed and HF-Sed). Activin βA subunit mRNA expression was significantly higher in HF-Swim than in HF-Sed rats. Follistatin mRNA expression was significantly lower in C-Swim and HF-Swim than in either C-Sed or HF-Sed animals. There was no evidence of steatosis or inflammation in C rats. In contrast, in HF animals the severity of steatosis ranged from grade 1 to grade 3. The extent of liver parenchyma damage was less in HF-Swim animals, with the severity of steatosis ranging from grade 0 to grade 1. These data showed that exercise may reduce the deleterious effects of a high-fat diet on the liver, suggesting that the local expression of activin-follistatin may be involved.

Supplement with Cystoseira canariensis promotes an increase of resistance to the maximum load in the grastrocnemius muscle of female rats

Was evaluated the maximum load supported by the grastrocnemius muscle of female rats after the ministering of Cystoseira canariensis, either associated or not to swimming. Twenty-eight young Wistar female rats were used, divided into 4 groups: control (C, n=7); supplement (S, n=7); supplement and swimming (SSw, n=7); swimming (Sw, n=7). Each one pertaining to the groups S and SSw received 20 mg of myostatin inhibitor per day. The swimming consisted in an aerobe protocol, three times in a week, during eight weeks. The right grastrocnemius muscle of each animal was removed and a tension test was performed in an Emic testing machine. The results (Mean±SEM) were evaluated through ANOVA and Tukey test (p<0.05). A significant difference for maximum load (in N) was verified among the groups C (35.41±1.06) and S (39.98±1.15); Sw (27.94±2.19) and S (39.98±1.15); Sw (27.94±2.19) and SSw (37.78±1.28). In relation to the stretching at the maximum limit (in x10-3m) at the maximum load, the group SSw obtained a value (20.68±1.19) significantly greater than the groups C (17.15±1.11), S and Sw (16.11±1.60). There was a significant difference for body weight gain among the groups treated with supplement and supplement associated to the swimming, with smaller values for this last. The myostatin inhibitor either, associated or not to the swimming, promotes an increase of resistance to the maximum load in the tension test in grastrocnemius muscle of young female rats.

Expression of myostatin, myostatin receptors and follistatin in diabetic rats submitted to exercise

Myostatin (MSTN) has been implicated in metabolic adaptation to physiological stimuli, such as physical exercise, which is linked to improved glucose homeostasis. The aim of the present study was to evaluate the influence of exercise on the expression of MSTN, MSTN receptors (ActRIIB and ALK4) and follistatin (FS) in the muscle and fat of streptozotocin-induced diabetic rats. Control and diabetic rats were randomly assigned to a swimming training group (EC and ED, respectively) and a sedentary group (SC and SD, respectively). Exercising animals swam for 45 min at 0900 and 1700 hours, 5 day/week, for 4 weeks. The mRNA expression of MSTN, ActRIIB, ALK4 and FS mRNA was quantified by real-time reverse transcription-polymerase chain reaction. Expression of MSTN and FS mRNA increased in the muscle and subcutaneous fat of SD compared with SC rats. Expression of ActRIIB mRNA was increased in the muscle, mesenteric fat and brown adipose tissue (BAT) of SD compared with SC rats, whereas ALK4 mRNA expression was only increased in the BAT of SD compared with SC rats. After training, MSTN and ActRIIB expression was lower in the BAT of EC compared with SC rats. Expression of MSTN mRNA increased in the mesenteric fat of ED compared with SD rats, whereas FS mRNA expression decreased in the muscle, mesenteric and subcutaneous fat and BAT. Lower ALK4 mRNA expression was noted in the BAT of ED compared with SD rats. These results indicate that MSTN, its receptors and FS expression change in both the muscle and fat of diabetic rats and that the expression of these factors can be modulated by exercise in diabetes.

The central role of myostatin in skeletal muscle and whole body homeostasis

Myostatin is a powerful negative regulator of skeletal muscle mass in mammalian species. It plays a key role in skeletal muscle homeostasis and has now been well described since its discovery. Myostatin is capable of inducing muscle atrophy via its inhibition of myoblast proliferation, increasing ubiquitin-proteasomal activity and downregulating activity of the IGF-Akt pathway. These well-recognized effects are seen in multiple atrophy causing situations, including injury, diseases such as cachexia, disuse and space flight, demonstrating the importance of the myostatin signalling mechanism. Based on this central role, significant work has been pursued to inhibit myostatin's actions in vivo. Importantly, several new studies have uncovered roles for myostatin distinct from skeletal muscle size. Myostatin has been suggested to play a role in cardiomyocyte homeostasis, glucose metabolism and adipocyte proliferation, all of which are examined in detail below. Based on these effects, myostatin inhibition has potential to be widely utilized in many Western diseases such as chronic obstructive pulmonary disease, type II diabetes and obesity. However, if myostatin inhibitors are to successfully translate from bench-top to bedside in the near future, awareness must be raised on these non-traditional effects of myostatin away from skeletal muscle. Indeed, further research into these novel areas is required.

Expression and function of myostatin in obesity, diabetes, and exercise adaptation

Myostatin is a member of the transforming growth factor-β/bone morphogenetic protein (TGF-β/BMP) superfamily of secreted factors that functions as a potent inhibitor of skeletal muscle growth. Moreover, considerable evidence has accumulated that myostatin also regulates metabolism and that its inhibition can significantly attenuate the progression of obesity and diabetes. Although at least part of these effects on metabolism can be attributable to myostatin's influence over skeletal muscle growth and therefore on the total volume of metabolically active lean body mass, there is mounting evidence that myostatin affects the growth and metabolic state of other tissues, including the adipose and the liver. In addition, recent work has explored the role of myostatin in substrate mobilization, uptake, and/or utilization of muscle independent of its effects on body composition. Finally, the effects of both endurance and resistance exercise on myostatin expression, as well as the potential role of myostatin in the beneficial metabolic adaptations occurring in response to exercise, have also begun to be delineated in greater detail. The purpose of this review was to summarize the work to date on the expression and function of myostatin in obesity, diabetes, and exercise adaptation.

Differential synthesis and action of TGFß superfamily ligands in mouse and rat islets

Members of the TGFß superfamily, including activins and TGFß, modulate glucose-stimulated insulin secretion (GSIS) in vitro using rat islets while genetic manipulations that reduce TGFß superfamily signaling in vivo in mice produced hypoplastic islets and/or hyperglycemia. Moreover, deletion of Fstl3, an antagonist of activin and myostatin, resulted in enlarged islets and ß-cell hyperplasia. These studies suggest that endogenous TGFß superfamily ligands regulate ß-cell generation and/or function. To test this hypothesis, we examined endogenous TGFß ligand synthesis and action in isolated rat and mouse islets. We found that activin A, TGFß1, and myostatin treatment enhanced rat islet GSIS but none of the ligands tested enhanced GSIS in mouse islets. However, follistatin inhibited GSIS, consistent with a role for endogenous TGFß superfamily ligands in regulating insulin secretion. Endogenous expression of TGFß superfamily members was different in rat and mouse islets with myostatin being highly expressed in mouse islets and not detectable in rats. These results indicate that TGFß superfamily members directly regulate islet function in a species-specific manner while the ligands produced by islets differ between mice and rats. The lack of in vitro actions of ligands on mouse islets may be mechanical or result from species-specific actions of these ligands.

Migration- and exercise-induced changes to flight muscle size in migratory birds and association with IGF1 and myostatin mRNA expression

Seasonal adjustments to muscle size in migratory birds may result from preparatory physiological changes or responses to changed workloads. The mechanisms controlling these changes in size are poorly understood. We investigated some potential mediators of flight muscle size (myostatin and insulin-like growth factor, IGF1) in pectoralis muscles of wild wintering or migrating white-throated sparrows (Zonotrichia albicollis), captive white-throated sparrows that were photoperiod manipulated to be in a `wintering' or `migratory' (Zugunruhe) state, and captive European starlings (Sturnus vulgaris) that were either exercised for 2 weeks in a wind tunnel or untrained. Flight muscle size increased in photo-stimulated `migrants' and in exercised starlings. Acute exercise but not long-term training caused increased expression of IGF1, but neither caused a change in expression of myostatin or its metalloprotease activator TLL1. Photo-stimulated `migrant' sparrows demonstrated increased expression of both myostatin and IGF1, but wild sparrows exhibited no significant seasonal changes in expression of either myostatin or IGF1. Additionally, in both study species we describe several splice variants of myostatin that are shared with distantly related bird species. We demonstrate that their expression patterns are not different from those of the typical myostatin, suggesting that they have no functional importance and may be mistakes of the splicing machinery. We conclude that IGF1 is likely to be an important mediator of muscle phenotypic flexibility during acute exercise and during endogenous, seasonal preparation for migration. The role of myostatin is less clear, but its paradoxical increase in photo-stimulated `migrants' may indicate a role in seasonal adjustments of protein turnover.

Mitochondrial biogenesis and PGC-1α deacetylation by chronic treadmill exercise: differential response in cardiac and skeletal muscle

Posttranslational modifications of the transcriptional coactivator PGC-1α by the deacetylase SIRT1 and the kinase AMPK are involved in exercise-induced mitochondrial biogenesis in skeletal muscle. However, similar investigations have not been performed in the left ventricle (LV). Here, we tested whether treadmill training (12 weeks) modifies PGC-1α and mitochondrial biogenesis in gastrocnemius muscle and LV of C57BL/6 J wild-type mice and IL-6-deficient mice with a reported impairment in muscular AMPK activation similarly. Physical activity lowered the plasma insulin and glucose in both mouse strains, suggesting improved insulin sensitivity. The gastrocnemius muscle of IL-6-deficient mice showed reduced mitochondrial respiration and enzyme activity, which was partially normalized after training. Chronic exercise enhanced the mitochondrial biogenesis in gastrocnemius muscle as indicated by increased mRNA or protein expression of primary mitochondrial transcripts, higher mtDNA content and increased citrate synthase activity. Parallel to these changes, we observed AMPK activation, SIRT1 induction and PGC-1α deacetylation. Chronic treadmill training resulted in a mild cardiac hypertrophy in both mouse strains. However, none of these changes observed in skeletal muscle were detected in the LV (both mouse strains) with the exception of AMPK activation and a mildly increased succinate-dependent respiration. Thus, chronic endurance training induces a sustained mitochondrial biogenic response in mouse gastrocnemius muscle but not in the LV. Although AMPK activation occurs in both muscular organs, the absence of SIRT1-dependent PGC-1α deacetylation may be responsible for this significant difference. AMPK activation by IL-6 appears to be dispensable for the mitochondrial biogenic responses to chronic treadmill exercise.

Post-exercise changes in myostatin and actRIIB expression in obese insulin-resistant rats

We evaluated the expression of MSTN and ActRIIB mRNA in muscle and adipose tissue in diet-induced obesity and insulin resistance in rats subjected to exercise. There was no difference in the expression of MSTN between exercised and sedentary high-fat fed rats in muscle after swimming training. The expression of ActRIIB mRNA in muscle was not significantly different among the groups. In BAT, MSTN mRNA expression was higher in exercised high-fat fed group (EHF) compared with sedentary high-fat fed group (SHF). ActRIIB mRNA expression in BAT was higher in EHF compared with SHF. In mesenteric fat, MSTN mRNA was lower in EHF compared with SHF and ActRIIB mRNA was lower in EHF compared with SHF. In conclusion, the results demonstrate that the expression of MSTN and ActRIIB mRNA changes in both adipose tissue and skeletal muscle in diet-induced obese and exercised rats and suggest the participation of MSTN in energy homeostasis.

Myostatin from the heart: local and systemic actions in cardiac failure and muscle wasting

A significant proportion of heart failure patients develop skeletal muscle wasting and cardiac cachexia, which is associated with a very poor prognosis. Recently, myostatin, a cytokine from the transforming growth factor-β (TGF-β) family and a known strong inhibitor of skeletal muscle growth, has been identified as a direct mediator of skeletal muscle atrophy in mice with heart failure. Myostatin is mainly expressed in skeletal muscle, although basal expression is also detectable in heart and adipose tissue. During pathological loading of the heart, the myocardium produces and secretes myostatin into the circulation where it inhibits skeletal muscle growth. Thus, genetic elimination of myostatin from the heart reduces skeletal muscle atrophy in mice with heart failure, whereas transgenic overexpression of myostatin in the heart is capable of inducing muscle wasting. In addition to its endocrine action on skeletal muscle, cardiac myostatin production also modestly inhibits cardiomyocyte growth under certain circumstances, as well as induces cardiac fibrosis and alterations in ventricular function. Interestingly, heart failure patients show elevated myostatin levels in their serum. To therapeutically influence skeletal muscle wasting, direct inhibition of myostatin was shown to positively impact skeletal muscle mass in heart failure, suggesting a promising strategy for the treatment of cardiac cachexia in the future.

Myostatin decreases with aerobic exercise and associates with insulin resistance

PURPOSE

There is mounting evidence that skeletal muscle produces and secretes biologically active proteins or "myokines" that facilitate metabolic cross talk between organ systems. The increased expression of myostatin, a secreted anabolic inhibitor of muscle growth and development, has been associated with obesity and insulin resistance. Despite these intriguing findings, there have been few studies linking myostatin and insulin resistance.

METHODS

To explore this relationship in more detail, we quantified myostatin protein in muscle and plasma from 10 insulin-resistant, middle-aged (53.1 ± 5.5 yr) men before and after 6 months of moderate aerobic exercise training (1200 kcal·wk−¹ at 40%-55% VO2peak). To establish a cause-effect relationship, we also injected C57/Bl6 male mice with high physiological levels of recombinant myostatin protein.

RESULTS

Myostatin protein levels were shown to decrease in muscle (37%, P = 0.042, n = 10) and matching plasma samples (from 28.7 ng·mL−¹ pretraining to 22.8 ng·mL−¹ posttraining, P = 0.003, n = 9) with aerobic exercise. Furthermore, the strong correlation between plasma myostatin levels and insulin sensitivity (R² = 0.82, P < 0.001, n = 9) suggested a cause-effect relationship that was subsequently confirmed by inducing insulin resistance in myostatin-injected mice. A modest increase (44%) in plasma myostatin levels was also associated with significant reductions in the insulin-stimulated phosphorylation of Akt (Thr308) in both muscle and liver of myostatin-treated animals.

CONCLUSIONS

These findings indicate that both muscle and plasma myostatin protein levels are regulated by aerobic exercise and, furthermore, that myostatin is in the causal pathway of acquired insulin resistance with physical inactivity.

Subsarcolemmal and intermyofibrillar mitochondria proteome differences disclose functional specializations in skeletal muscle

Skeletal muscle is a highly specialized tissue that contains two distinct mitochondria subpopulations, the subsarcolemmal (SS) and the intermyofibrillar (IMF) mitochondria. Although it is established that these mitochondrial subpopulations differ functionally in several ways, limited information exists about the proteomic differences underlying these functional differences. Therefore, the objective of this study was to biochemically characterize the SS and IMF mitochondria isolated from rat red gastrocnemius skeletal muscle. We separated the two mitochondrial subpopulations from skeletal muscle using a refined method that provides an excellent division of these unique mitochondrial subpopulations. Using proteomics of mitochondria and its subfractions (intermembrane space, matrix and inner membrane), a total of 325 distinct proteins were identified, most of which belong to the functional clusters of oxidative phosphorylation, metabolism and signal transduction. Although more gel spots were observed in SS mitochondria, 38 of the identified proteins were differentially expressed between the SS and IMF subpopulations. Compared to the SS mitochondrial, IMF mitochondria expressed a higher level of proteins associated with oxidative phosphorylation. This observation, coupled with the finding of a higher respiratory chain complex activity in IMF mitochondria, suggests a specialization of IMF mitochondria toward energy production for contractile activity.

Myostatin expression is increased by food deprivation in a muscle-specific manner and contributes to muscle atrophy during prolonged food deprivation in mice

During food deprivation (FD), skeletal muscle protein is broken down to produce amino acids for hepatic gluconeogenesis to maintain blood glucose levels. However, it is unclear what role, if any, the secreted antigrowth factor myostatin (MSTN) plays in the muscle atrophy induced by FD. We therefore examined expression and function of MSTN in FD in mice. Two days of FD significantly decreased muscle mass and protein content and increased mRNA levels of ubiquitin ligases MuRF-1 and atrogin-1 in fast-twitch tibialis anterior (TA) muscle but not slow-twitch soleus (Sol) muscle, while 2 days of refeeding returned these to fed values in TA. MSTN mRNA levels were significantly increased approximately threefold by 2 days, but not 1 day, of FD and returned to fed levels with 2 days of refeeding in TA but were not significantly affected by FD or refeeding in Sol. TA mass decreased to a similar amount after 1 day of FD in wild-type mice and mice null for the MSTN gene but was decreased to a greater amount in wild-type than MSTN-null mice by 2 days of FD. In addition, blood glucose levels decreased and corticosterone levels increased to a greater extent in MSTN-null mice after 2 days of FD, but surprisingly muscle MuRF-1 and atrogin-1 mRNA levels were not affected by the lack of MSTN during FD. Similarly, changes in hepatic enzyme expression in response to FD were identical between wild-type and MSTN-null mice. Our data are consistent with the hypothesis that MSTN is dispensable for the initial atrophy occurring in response to FD but attenuates the decrease in fast-twitch muscle mass during prolonged FD.

Exercise does not influence myostatin and follistatin messenger RNA expression in young women

We evaluated changes in myostatin, follistatin, and MyoD messenger RNA (mRNA) gene expression using eccentric exercise (EE) and concentric exercise (CE) as probes to better understand the mechanisms of muscle hypertrophy in young women. Twelve women performed single-leg maximal eccentric (n = 6, 25 +/- 1 years, 59 +/- 7 kg) or concentric (n = 6, 24 +/- 1 years, 65 +/- 7 kg) isokinetic knee extension exercise for 7 sessions. Muscle biopsies were taken from the vastus lateralis at baseline, 8 hours after the first exercise session, and 8 hours after the seventh exercise session. In the EE group, there were no changes in myostatin and follistatin (p > or = 0.17); however, MyoD expression increased after 1 exercise bout (p = 0.02). In the CE group, there were no changes in myostatin, follistatin, or MyoD mRNA gene expression (p > or = 0.07). Differences between the EE and CE groups were not significant (p > or = 0.05). These data suggest that a single bout or multiple bouts of maximal EE or CE may not significantly alter myostatin or follistatin mRNA gene expression in young women. However, MyoD mRNA expression seems to increase only after EE.

Myostatin is upregulated following stress in an Erk-dependent manner and negatively regulates cardiomyocyte growth in culture and in a mouse model

Myostatin is well established as a negative regulator of skeletal muscle growth, but its role in the heart is controversial. Our goal in this study was to characterize myostatin regulation following cardiomyocyte stress and to examine the role of myostatin in the regulation of cardiomyocyte size. Neonatal cardiomyocytes were cultured and stressed with phenylephrine. Adenovirus was used to overexpress myostatin or dominant negative myostatin in culture. Adeno-associated virus was used to overexpress myostatin or dominant negative myostatin in mice. Myostatin is upregulated following cardiomyocyte stress in an Erk-dependent manner that is associated with increased nuclear translocation and DNA binding activity of MEF-2. Myostatin overexpression leads to decreased and myostatin inhibition to increased cardiac growth both in vitro and in vivo due to modulation of Akt and NFAT3 pathways. Myostatin is a negative regulator of cardiac growth, and further studies are warranted to investigate the role of myostatin in the healthy and failing heart.

Regulation of slow and fast muscle myofibrillogenesis by Wnt/beta-catenin and myostatin signaling

Deviation from proper muscle development or homeostasis results in various myopathic conditions. Employing genetic as well as chemical intervention, we provide evidence that a tight regulation of Wnt/β-catenin signaling is essential for muscle fiber growth and maintenance. In zebrafish embryos, gain-of-Wnt/β-catenin function results in unscheduled muscle progenitor proliferation, leading to slow and fast muscle hypertrophy accompanied by fast muscle degeneration. The effects of Wnt/β-catenin signaling on fast muscle hypertrophy were rescued by misexpression of Myostatin or p21^CIP/WAF, establishing an in vivo regulation of myofibrillogenesis by Wnt/β-catenin signaling and Myostatin. Epistatic analyses suggest a possible genetic interaction between Wnt/β-catenin and Myostatin in regulation of slow and fast twitch muscle myofibrillogenesis.

Histomorphometric analysis of the response of rat skeletal muscle to swimming, immobilization and rehabilitation

The objective of the present study was to determine to what extent, if any, swimming training applied before immobilization in a cast interferes with the rehabilitation process in rat muscles. Female Wistar rats, mean weight 260.52 +/- 16.26 g, were divided into 4 groups of 6 rats each: control, 6 weeks under baseline conditions; trained, swimming training for 6 weeks; trained-immobilized, swimming training for 6 weeks and then immobilized for 1 week; trained-immobilized-rehabilitated, swimming training for 6 weeks, immobilized for 1 week and then remobilized with swimming for 2 weeks. The animals were then sacrificed and the soleus and tibialis anterior muscles were dissected, frozen in liquid nitrogen and processed histochemically (H&E and mATPase). Data were analyzed statistically by the mixed effects linear model (P < 0.05). Cytoarchitectural changes such as degenerative characteristics in the immobilized group and regenerative characteristics such as centralized nucleus, fiber size variation and cell fragmentation in the groups submitted to swimming were more significant in the soleus muscle. The diameters of the lesser soleus type 1 and type 2A fibers were significantly reduced in the trained-immobilized group compared to the trained group (P < 0.001). In the tibialis anterior, there was an increase in the number of type 2B fibers and a reduction in type 2A fibers when trained-immobilized rats were compared to trained rats (P < 0.001). In trained-immobilized-rehabilitated rats, there was a reduction in type 2B fibers and an increase in type 2A fibers compared to trained-immobilized rats (P < 0.009). We concluded that swimming training did not minimize the deleterious effects of immobilization on the muscles studied and that remobilization did not favor tissue re-adaptation.

Impact of exercise training on myostatin expression in the myocardium and skeletal muscle in a chronic heart failure model

AIMS

In late-stage chronic heart failure (CHF), elevated cytokines and cachexia are often observed. Several studies have shown that exercise training exerts beneficial effects on skeletal muscle in this setting. Furthermore, it has been shown that the expression of myostatin, a key regulator of skeletal muscle mass, is increased in a variety of cachectic states. This study aimed to investigate the expression of myostatin in CHF, the influence of exercise training on myostatin levels, and regulation of myostatin by tumour necrosis factor-alpha (TNF-alpha).

METHODS AND RESULTS

In an animal model of CHF (LAD-ligation model), protein expression of myostatin was elevated 2.4-fold in the skeletal muscle and more than four-times in the myocardium, compared with control (Co). Exercise training on a treadmill over 4 weeks led to a significant reduction in myostatin protein expression in the skeletal muscle and the myocardium of CHF animals, with values returning to baseline levels. In differentiated C2C12 cells, TNF-alpha induced the expression of myostatin through a p38MAPK-dependent pathway involving nuclear factor kappa-B (NF-kappaB). The increased TNF-alpha mRNA levels in the skeletal muscle of CHF animals correlated significantly with myostatin expression.

CONCLUSION

These alterations in myostatin expression in the skeletal and heart muscle following exercise training could help to explain the beneficial anti-catabolic effects of exercise training in CHF.

Presence, actions, and regulation of myostatin in rat uterus and myometrial cells

Myostatin, a member of the TGF-beta superfamily of proteins, is known to suppress skeletal muscle mass and myocyte proliferation. The muscular component of the uterus is the myometrium, a tissue that regulates its mass in response to different physiological conditions under the influence of sex steroids. Recently, our laboratory reported effects of activin-A, another TGF-beta family member, on signalling and proliferation of rat uterine explants and human myometrial cell lines in culture. Here, we explore the expression, actions, and regulation of myostatin in uterine smooth muscle. Myostatin mRNA was demonstrated to be expressed in a myometrial cell line, pregnant human myometrial 1 cell line (PHM1). Functional assays showed that myostatin induced phosphorylation of Smad-2 and reduced proliferation of PHM1 number in a time and dose-dependent manner. Furthermore, myostatin activated smad-2 specific signalling pathways in rat uterine explants. To expand on our in vitro findings, we found that myostatin is expressed in rat uterus and determined that myostatin mRNA expression varies as a function of the phase of the estrous cycle. Uterine levels of myostatin peaked during late estrus and were the lowest at proestrus. Ovariectomy increased myostatin expression; estrogen treatment strongly decreased myostatin levels, whereas progesterone weakly decreased myostatin expression. In conclusion, myometrial cells are myostatin sensitive, myostatin mRNA levels are modulated in vivo in rats during the estrous cycle, and in response to steroid deprivation and replacement.

Protein synthesis and the expression of growth-related genes are altered by running in human vastus lateralis and soleus muscles

Recent evidence suggests aerobic exercise may help preserve soleus muscle mass during unloading. The purpose of this investigation was to examine the muscle-specific metabolic response to running as it relates to muscle growth. Mixed-muscle protein synthesis [fractional synthetic rate (FSR)] and gene expression (GE) were examined in the vastus lateralis (VL) and soleus (SOL) muscles from eight men (26 +/- 2 yr; Vo(2max) 63 +/- 2 ml.kg(-1).min(-1)) before and after a 45-min level-grade treadmill run at 77 +/- 1% intensity. Muscle glycogen utilization was similar between muscles. Resting FSR was similar between the VL (0.080 +/- 0.007 %/h) and SOL (0.086 +/- 0.008 %/h) and was higher (P < 0.05) 24 h postexercise compared with rest for both muscles. The absolute change in FSR was not different between muscles (0.030 +/- 0.007 vs. 0.037 +/- 0.012 %/h for VL and SOL). At baseline, myostatin GE was approximately twofold higher (P < 0.05) in SOL compared with VL, while no other muscle-specific differences in GE were present. After running, myostatin GE was suppressed (P < 0.05) in both muscles at 4 h and was higher (P < 0.05) than baseline at 24 h for VL only. Muscle regulatory factor 4 mRNA was elevated (P < 0.05) at 4 h in both SOL and VL; MyoD and peroxisome-proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) were higher (P < 0.05) at 4 h, and forkhead box [FOXO]3A was higher at 24 h in SOL only, while muscle-RING-finger protein-1 (MuRF-1) was higher (P < 0.05) at 4 h in VL only. Myogenin and atrogin-1 GE were unaltered. The similar increases between muscles in FSR support running as part of the exercise countermeasure to preserve soleus mass during unloading. The subtle differences in GE suggest a potential mechanism for muscle-specific adaptations to chronic run training.

Clinical, agricultural, and evolutionary biology of myostatin: a comparative review

The discovery of myostatin and our introduction to the "Mighty Mouse" over a decade ago spurred both basic and applied research and impacted popular culture as well. The myostatin-null genotype produces "double muscling" in mice and livestock and was recently described in a child. The field's rapid growth is by no means surprising considering the potential benefits of enhancing muscle growth in clinical and agricultural settings. Indeed, several recent studies suggest that blocking myostatin's inhibitory effects could improve the clinical treatment of several muscle growth disorders, whereas comparative studies suggest that these actions are at least partly conserved. Thus, neutralizing myostatin's effects could also have agricultural significance. Extrapolating between studies that use different vertebrate models, particularly fish and mammals, is somewhat confusing because whole genome duplication events have resulted in the production and retention of up to four unique myostatin genes in some fish species. Such comparisons, however, suggest that myostatin's actions may not be limited to skeletal muscle per se, but may additionally influence other tissues including cardiac muscle, adipocytes, and the brain. Thus, therapeutic intervention in the clinic or on the farm must consider the potential of alternative side effects that could impact these or other tissues. In addition, the presence of multiple and actively diversifying myostatin genes in most fish species provides a unique opportunity to study adaptive molecular evolution. It may also provide insight into myostatin's nonmuscle actions as results from these and other comparative studies gain visibility in biomedical fields.

Real-time polymerase chain reaction, in situ hybridization and immunohistochemical localization of insulin-like growth factor-I and myostatin during development of Dicentrarchus labrax (Pisces: Osteichthyes)

The distribution of insulin-like growth factor-I (IGF-I) and myostatin (MSTN) was investigated in sea bass (Dicentrarchus labrax) by real-time polymerase chain reaction (PCR), in situ hybridization (ISH) and immunohistochemistry. Real-time PCR indicated that IGF-I mRNA increased from the second day post-hatching and that this trend became significant from day 4. ISH confirmed a strong IGF-I mRNA expression from the first week post-hatching, with the most abundant expression being detected in the liver of larvae and adults. Real-time PCR also showed that the level of MSTN mRNA increased significantly from day 25. The expression of MSTN mRNA was higher in muscle and almost absent in other anatomical regions in both larvae and adults. Interestingly, the lateral muscle showed a quantitative differential expression of IGF-I and MSTN mRNAs in red and white muscle, depending on the developmental stage examined. IGF-I immunoreactivity was detected in developing intestine at hatching and in skeletal muscle, skin and yolk sac. MSTN immunostaining was evident in several tissues and organs in both larvae and adults. Both IGF-I and MSTN proteins were detected in the liver from day 4 post-hatching and, subsequently, in the kidney and heart muscle from day 10. Our results suggest, on the basis of a combined methodological approach, that IGF-I and MSTN are involved in the regulation of somatic growth in the sea bass.

Time course of proteolytic, cytokine, and myostatin gene expression after acute exercise in human skeletal muscle

The aim of this study was to examine the time course induction of select proteolytic [muscle ring finger-1 (MuRF-1), atrogin-1, forkhead box 3A (FOXO3A), calpain-1, calpain-2], myostatin, and cytokine (IL -6, -8, -15, and TNF-α) mRNA after an acute bout of resistance (RE) or run (RUN) exercise. Six experienced RE (25 ± 4 yr, 74 ± 14 kg, 1.71 ± 0.11 m) and RUN (25 ± 4 yr, 72 ± 5 kg, 1.81 ± 0.07 m) subjects had muscle biopsies from the vastus lateralis (RE) or gastrocnemius (RUN) before, immediately after, and 1, 2, 4, 8, 12, and 24 h postexercise. RE increased ( P < 0.05) mRNA expression of MuRF-1 early (3.5-fold, 1–4 h), followed by a decrease in atrogin-1 (3.3-fold) and FOXO3A (1.7-fold) 8–12 h postexercise. Myostatin mRNA decreased (6.3-fold; P < 0.05) from 1 to 24 h postexercise, whereas IL-6, IL-8, and TNF-α mRNA were elevated 2–12 h. RUN increased ( P < 0.05) MuRF-1 (3.6-fold), atrogin-1 (1.6-fold), and FOXO3A (1.9-fold) 1–4 h postexercise. Myostatin was suppressed (3.6-fold; P < 0.05) 8–12 h post-RUN. The cytokines exhibited a biphasic response, with immediate elevation ( P < 0.05) of IL-6, IL-8, and TNF-α, followed by a second elevation ( P < 0.05) 2–24 h postexercise. In general, the timing of the gene induction indicated early elevation of proteolytic genes, followed by prolonged elevation of cytokines and suppression of myostatin. These data provide basic information for the timing of human muscle biopsy samples for gene expression studies involving exercise. Furthermore, this information suggests a greater induction of proteolytic genes following RUN compared with RE.

Myostatin shows a specific expression pattern in pig skeletal and extraocular muscles during pre- and post-natal growth

Myogenesis is driven by an extraordinary array of cellular signals that follow a common expression pattern among different animal phyla. Myostatin (mstn) is a secreted growth factor that plays a pivotal role in skeletal muscle mass regulation. The aim of the present study was to investigate mstn expression in a large mammal (the pig) in order to ascertain whether distinct expression changes of this factor might be linked to the fiber-type composition of the muscle examined and/or to specific developmental stages. To assess the expression pattern of mstn in relation to myogenic proliferative (Pax7 and MyoD) and differentiative (myogenin) markers, we evaluated muscles with different myosin heavy-chain compositions sampled during pre- and post-natal development and on myogenic cells isolated from the same muscles. Skeletal muscles showed higher levels of mRNA for mstn and all other genes examined during fetal development than after birth. The wide distribution of mstn was also confirmed by immunohistochemistry experiments supporting evidence for cytoplasmic staining in early fetal periods as well as the localization in type 1 fibers at the end of the gestation period. Extraocular muscles, in contrast, did not exhibit decreasing mRNA levels for mstn or other genes even in adult samples and expressed higher levels of both mstn mRNA and protein compared with skeletal muscles. Experiments carried out on myogenic cells showed that mstn mRNA levels decreased when myoblasts entered the differentiation program and that cells isolated at early post-natal stages maintained a high level of Pax7 expression. Our results showed that mstn had a specific expression pattern whose variations depended on the muscle type examined, thus supporting the hypothesis that at birth, porcine myogenic cells continue to be influenced by hyperplastic/proliferative mechanisms.