Acute loading and aging effects on myostatin pathway biomarkers in human skeletal muscle after three sequential bouts of resistance exercise

Skeletal muscle myostatin mRNA expression is upregulated in aged human adults with excess adiposity but is not associated with insulin resistance and ageing

Myostatin negatively regulates skeletal muscle growth and appears upregulated in human obesity and associated with insulin resistance. However, observations are confounded by ageing, and the mechanisms responsible are unknown. The aim of this study was to delineate between the effects of excess adiposity, insulin resistance and ageing on myostatin mRNA expression in human skeletal muscle and to investigate causative factors using in vitro models. An in vivo cross-sectional analysis of human skeletal muscle was undertaken to isolate effects of excess adiposity and ageing per se on myostatin expression. In vitro studies employed human primary myotubes to investigate the potential involvement of cross-talk between subcutaneous adipose tissue (SAT) and skeletal muscle, and lipid-induced insulin resistance. Skeletal muscle myostatin mRNA expression was greater in aged adults with excess adiposity than age-matched adults with normal adiposity (2.0-fold higher; P < 0.05) and occurred concurrently with altered expression of genes involved in the maintenance of muscle mass but did not differ between younger and aged adults with normal adiposity. Neither chronic exposure to obese SAT secretome nor acute elevation of fatty acid availability (which induced insulin resistance) replicated the obesity-mediated upregulation of myostatin mRNA expression in vitro. In conclusion, skeletal muscle myostatin mRNA expression is uniquely upregulated in aged adults with excess adiposity and insulin resistance but not by ageing alone. This does not appear to be mediated by the SAT secretome or by lipid-induced insulin resistance. Thus, factors intrinsic to skeletal muscle may be responsible for the obesity-mediated upregulation of myostatin, and future work to establish causality is required.

Paraspinal muscles in individuals undergoing surgery for lumbar spine pathology lack a myogenic response to an acute bout of resistance exercise

Background

Lumbar spine pathology (LSP) is a common source of low back or leg pain, and paraspinal muscle in these patients demonstrates fatty and fibrotic infiltration, and cellular degeneration that do not reverse with exercise-based rehabilitation. However, it is unclear of this lack of response is due to insufficient exercise stimulus, or an inability to mount a growth response. The purpose of this study was to compare paraspinal muscle gene expression between individuals with LSP who do and do not undergo an acute bout of resistance exercise.

Methods

Paraspinal muscle biopsies were obtained from 64 individuals with LSP undergoing spinal surgery. Eight participants performed an acute bout of machine-based lumbar extension resistance exercise preoperatively. Gene expression for 42 genes associated with adipogenic/metabolic, atrophic, fibrogenic, inflammatory, and myogenic pathways was measured, and differential expression between exercised and non-exercised groups was evaluated for (a) the full cohort, and (b) an age, gender, acuity, and etiology matched sub-cohort. Principal components analyses were used to identify gene expression clustering across clinical phenotypes.

Results

The exercised cohort demonstrated upregulation of inflammatory gene IL1B, inhibition of extracellular matrix components (increased MMP3&9, decreased TIMP1&3, COL1A1) and metabolic/adipogenic genes (FABP4, PPARD, WNT10B), and downregulation of myogenic (MYOD, ANKRD2B) and atrophic (FOXO3) genes compared to the non-exercised cohort, with similar patterns in the matched sub-analysis. There were no clinical phenotypes significantly associated with gene expression profiles.

Conclusion

An acute bout of moderate-high intensity resistance exercise did not result in upregulation of myogenic genes in individuals with LSP. The response was characterized by mixed metabolic and fibrotic gene expression, upregulation of inflammation, and downregulation of myogenesis.

Mechanisms of mechanical overload-induced skeletal muscle hypertrophy: current understanding and future directions

Mechanisms underlying mechanical overload-induced skeletal muscle hypertrophy have been extensively researched since the landmark report by Morpurgo (1897) of "work-induced hypertrophy" in dogs that were treadmill trained. Much of the preclinical rodent and human resistance training research to date supports that involved mechanisms include enhanced mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling, an expansion in translational capacity through ribosome biogenesis, increased satellite cell abundance and myonuclear accretion, and postexercise elevations in muscle protein synthesis rates. However, several lines of past and emerging evidence suggest that additional mechanisms that feed into or are independent of these processes are also involved. This review first provides a historical account of how mechanistic research into skeletal muscle hypertrophy has progressed. A comprehensive list of mechanisms associated with skeletal muscle hypertrophy is then outlined, and areas of disagreement involving these mechanisms are presented. Finally, future research directions involving many of the discussed mechanisms are proposed.

Highlighting the idea of exerkines in the management of cancer patients with cachexia: novel insights and a critical review

BACKGROUND

Exerkines are all peptides, metabolites, and nucleic acids released into the bloodstream during and after physical exercise. Exerkines liberated from skeletal muscle (myokines), the heart (cardiokines), liver (hepatokines), white adipose tissue (adipokines), brown adipose tissue (batokines), and neurons (neurokines) may benefit health and wellbeing. Cancer-related cachexia is a highly prevalent disorder characterized by weight loss with specific skeletal muscle and adipose tissue loss. Many studies have sought to provide exercise strategies for managing cachexia, focusing on musculoskeletal tissue changes. Therefore, understanding the responses of musculoskeletal and other tissue exerkines to acute and chronic exercise may provide novel insight and recommendations for physical training to counteract cancer-related cachexia.

METHODS

For the purpose of conducting this study review, we made efforts to gather relevant studies and thoroughly discuss them to create a comprehensive overview. To achieve this, we conducted searches using appropriate keywords in various databases. Studies that were deemed irrelevant to the current research, not available in English, or lacking full-text access were excluded. Nevertheless, it is important to acknowledge the limited amount of research conducted in this specific field.

RESULTS

In order to obtain a comprehensive understanding of the findings, we prioritized human studies in order to obtain results that closely align with the scope of the present study. However, in instances where human studies were limited or additional analysis was required to draw more robust conclusions, we also incorporated animal studies. Finally, 295 studies, discussed in this review.

CONCLUSION

Our understanding of the underlying physiological mechanisms related to the significance of investigating exerkines in cancer cachexia is currently quite basic. Nonetheless, this demonstrated that resistance and aerobic exercise can contribute to the reduction and control of the disease in individuals with cancer cachexia, as well as in survivors, by inducing changes in exerkines.

Transcriptional time course after rotator cuff repair in 6 month old female rabbits

Introduction: Rotator cuff tears are prevalent in the population above the age of 60. The disease progression leads to muscle atrophy, fibrosis, and fatty infiltration, which is not improved upon with surgical repair, highlighting the need to better understand the underlying biology impairing more favorable outcomes. Methods: In this study, we collected supraspinatus muscle tissue from 6 month old female rabbits who had undergone unilateral tenotomy for 8 weeks at 1, 2, 4, or 8 weeks post-repair (n = 4/group). RNA sequencing and enrichment analyses were performed to identify a transcriptional timeline of rotator cuff muscle adaptations and related morphological sequelae. Results: There were differentially expressed (DE) genes at 1 (819 up/210 down), 2 (776/120), and 4 (63/27) weeks post-repair, with none at 8 week post-repair. Of the time points with DE genes, there were 1092 unique DE genes and 442 shared genes, highlighting that there are changing processes in the muscle at each time point. Broadly, 1-week post-repair differentially expressed genes were significantly enriched in pathways of metabolism and energetic activity, binding, and regulation. Many were also significantly enriched at 2 weeks, with the addition of NIF/NF-kappaB signaling, transcription in response to hypoxia, and mRNA stability alongside many additional pathways. There was also a shift in transcriptional activity at 4 weeks post-repair with significantly enriched pathways for lipids, hormones, apoptosis, and cytokine activity, despite an overall decrease in the number of differentially expressed genes. At 8 weeks post-repair there were no DE genes when compared to control. These transcriptional profiles were correlated with the histological findings of increased fat, degeneration, and fibrosis. Specifically, correlated gene sets were enriched for fatty acid metabolism, TGF-B-related, and other pathways. Discussion: This study identifies the timeline of transcriptional changes in muscle after RC repair, which by itself, does not induce a growth/regenerative response as desired. Instead, it is predominately related to metabolism/energetics changes at 1 week post-repair, unclear or asynchronous transcriptional diversity at 2 weeks post-repair, increased adipogenesis at 4 weeks post-repair, and a low transcriptional steady state or a dysregulated stress response at 8 weeks post-repair.

Different Resistance Exercise Loading Paradigms Similarly Affect Skeletal Muscle Gene Expression Patterns of Myostatin-Related Targets and mTORC1 Signaling Markers

Although transcriptome profiling has been used in several resistance training studies, the associated analytical approaches seldom provide in-depth information on individual genes linked to skeletal muscle hypertrophy. Therefore, a secondary analysis was performed herein on a muscle transcriptomic dataset we previously published involving trained college-aged men (n = 11) performing two resistance exercise bouts in a randomized and crossover fashion. The lower-load bout (30 Fail) consisted of 8 sets of lower body exercises to volitional fatigue using 30% one-repetition maximum (1 RM) loads, whereas the higher-load bout (80 Fail) consisted of the same exercises using 80% 1 RM loads. Vastus lateralis muscle biopsies were collected prior to (PRE), 3 h, and 6 h after each exercise bout, and 58 genes associated with skeletal muscle hypertrophy were manually interrogated from our prior microarray data. Select targets were further interrogated for associated protein expression and phosphorylation induced-signaling events. Although none of the 58 gene targets demonstrated significant bout x time interactions, ~57% (32 genes) showed a significant main effect of time from PRE to 3 h (15↑ and 17↓, p < 0.01), and ~26% (17 genes) showed a significant main effect of time from PRE to 6 h (8↑ and 9↓, p < 0.01). Notably, genes associated with the myostatin (9 genes) and mammalian target of rapamycin complex 1 (mTORC1) (9 genes) signaling pathways were most represented. Compared to mTORC1 signaling mRNAs, more MSTN signaling-related mRNAs (7 of 9) were altered post-exercise, regardless of the bout, and RHEB was the only mTORC1-associated mRNA that was upregulated following exercise. Phosphorylated (phospho-) p70S6K (Thr389) (p = 0.001; PRE to 3 h) and follistatin protein levels (p = 0.021; PRE to 6 h) increased post-exercise, regardless of the bout, whereas phospho-AKT (Thr389), phospho-mTOR (Ser2448), and myostatin protein levels remained unaltered. These data continue to suggest that performing resistance exercise to volitional fatigue, regardless of load selection, elicits similar transient mRNA and signaling responses in skeletal muscle. Moreover, these data provide further evidence that the transcriptional regulation of myostatin signaling is an involved mechanism in response to resistance exercise.

Organotypic cultures as aging associated disease models

Aging remains a primary risk factor for a host of diseases, including leading causes of death. Aging and associated diseases are inherently multifactorial, with numerous contributing factors and phenotypes at the molecular, cellular, tissue, and organismal scales. Despite the complexity of aging phenomena, models currently used in aging research possess limitations. Frequently used in vivo models often have important physiological differences, age at different rates, or are genetically engineered to match late disease phenotypes rather than early causes. Conversely, routinely used in vitro models lack the complex tissue-scale and systemic cues that are disrupted in aging. To fill in gaps between in vivo and traditional in vitro models, researchers have increasingly been turning to organotypic models, which provide increased physiological relevance with the accessibility and control of in vitro context. While powerful tools, the development of these models is a field of its own, and many aging researchers may be unaware of recent progress in organotypic models, or hesitant to include these models in their own work. In this review, we describe recent progress in tissue engineering applied to organotypic models, highlighting examples explicitly linked to aging and associated disease, as well as examples of models that are relevant to aging. We specifically highlight progress made in skin, gut, and skeletal muscle, and describe how recently demonstrated models have been used for aging studies or similar phenotypes. Throughout, this review emphasizes the accessibility of these models and aims to provide a resource for researchers seeking to leverage these powerful tools.

Association of Myostatin Gene Polymorphisms with Strength and Muscle Mass in Athletes: A Systematic Review and Meta-Analysis of the MSTN rs1805086 Mutation

Polymorphism (rs1805086), c.458A>G, p.Lys(K)153Arg(R), (K153R) of the myostatin gene (MSTN) has been associated with a skeletal muscle phenotype (hypertrophic response in muscles due to strength training). However, there are not enough reliable data to demonstrate whether MSTN rs1805086 K and R allelic variants are valid genetic factors that can affect the strength phenotype of athletes' skeletal muscles. The aim is to conduct a systematic review and meta-analysis of the association of MSTN rs1805086 polymorphism with the strength phenotype of athletes. This study analyzed 71 research articles on MSTN and performed a meta-analysis of MSTN K153R rs1805086 polymorphism in strength-oriented athletes and a control (non-athletes) group. It was found that athletes in the strength-oriented athlete group had a higher frequency of the R minor variant than that in the control group (OR = 2.02, P = 0.05). Thus, the obtained results convincingly demonstrate that there is an association between the studied polymorphism and strength phenotype of athletes; therefore, further studies on this association are scientifically warranted.

Gene expression changes in vastus lateralis muscle after different strength training regimes during rehabilitation following anterior cruciate ligament reconstruction

Impaired muscle regeneration has repeatedly been described after anterior cruciate ligament reconstruction (ACL-R). The results of recent studies provided some evidence for negative alterations in knee extensor muscles after ACL-R causing persisting strength deficits in spite of the regain of muscle mass. Accordingly, we observed that 12 weeks of concentric/eccentric quadriceps strength training with eccentric overload (CON/ECC⁺) induced a significantly greater hypertrophy of the atrophied quadriceps muscle after ACL-R than conventional concentric/eccentric quadriceps strength training (CON/ECC). However, strength deficits persisted and there was an unexpected increase in the proportion of slow type I fibers instead of the expected shift towards a faster muscle phenotype after CON/ECC⁺. In order to shed further light on muscle recovery after ACL-R, the steady-state levels of 84 marker mRNAs were analyzed in biopsies obtained from the vastus lateralis muscle of 31 subjects before and after 12 weeks of CON/ECC⁺ (n = 18) or CON/ECC strength training (n = 13) during rehabilitation after ACL-R using a custom RT² Profiler PCR array. Significant (p < 0.05) changes were detected in the expression of 26 mRNAs, several of them involved in muscle wasting/atrophy. A different pattern with regard to the strength training mode was observed for 16 mRNAs, indicating an enhanced hypertrophic stimulus, mechanical sensing or fast contractility after CON/ECC⁺. The effects of the type of autograft (quadriceps, QUAD, n = 19, or semitendinosus tendon, SEMI, n = 12) were reflected in the lower expression of 6 mRNAs involved in skeletal muscle hypertrophy or contractility in QUAD. In conclusion, the greater hypertrophic stimulus and mechanical stress induced by CON/ECC⁺ and a beginning shift towards a faster muscle phenotype after CON/ECC⁺ might be indicated by significant gene expression changes as well as still ongoing muscle wasting processes and a negative impact of QUAD autograft.

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.

Role of exercise-induced hepatokines in metabolic disorders

The health-promoting effects of physical activity to prevent and treat metabolic disorders are numerous. However, the underlying molecular mechanisms are not yet completely deciphered. In recent years, studies have referred to the liver as an endocrine organ, since it releases specific proteins called hepatokines. Some of these hepatokines are involved in whole body metabolic homeostasis and are theorized to participate in the development of metabolic disease. In this regard, the present review describes the role of Fibroblast Growth Factor 21, Fetuin-A, Angiopoietin-like protein 4, and Follistatin in metabolic disease and their production in response to acute exercise. Also, we discuss the potential role of hepatokines in mediating the beneficial effects of regular exercise and the future challenges to the discovery of new exercise-induced hepatokines.

Physical Activity and Bone Health: What Is the Role of Immune System? A Narrative Review of the Third Way

Bone tissue can be seen as a physiological hub of several stimuli of different origin (e.g., dietary, endocrine, nervous, immune, skeletal muscle traction, biomechanical load). Their integration, at the bone level, results in: (i) changes in mineral and protein composition and microarchitecture and, consequently, in shape and strength; (ii) modulation of calcium and phosphorous release into the bloodstream, (iii) expression and release of hormones and mediators able to communicate the current bone status to the rest of the body. Different stimuli are able to act on either one or, as usual, more levels. Physical activity is the key stimulus for bone metabolism acting in two ways: through the biomechanical load which resolves into a direct stimulation of the segment(s) involved and through an indirect load mediated by muscle traction onto the bone, which is the main physiological stimulus for bone formation, and the endocrine stimulation which causes homeostatic adaptation. The third way, in which physical activity is able to modify bone functions, passes through the immune system. It is known that immune function is modulated by physical activity; however, two recent insights have shed new light on this modulation. The first relies on the discovery of inflammasomes, receptors/sensors of the innate immunity that regulate caspase-1 activation and are, hence, the tissue triggers of inflammation in response to infections and/or stressors. The second relies on the ability of certain tissues, and particularly skeletal muscle and adipose tissue, to synthesize and secrete mediators (namely, myokines and adipokines) able to affect, profoundly, the immune function. Physical activity is known to act on both these mechanisms and, hence, its effects on bone are also mediated by the immune system activation. Indeed, that immune system and bone are tightly connected and inflammation is pivotal in determining the bone metabolic status is well-known. The aim of this narrative review is to give a complete view of the exercise-dependent immune system-mediated effects on bone metabolism and function.

Physiology of Activins/Follistatins: Associations With Metabolic and Anthropometric Variables and Response to Exercise

CONTEXT

Clinical trials are evaluating the efficacy of inhibitors of the myostatin pathway in neuromuscular and metabolic diseases. Activins and follistatins are major regulators of the myostatin pathway, but their physiology in relation to metabolic and anthropometric variables and in response to exercise remains to be fully elucidated in humans.

OBJECTIVE

We investigated whether concentrations of circulating activin A, activin B, follistatin, and follistatin-like 3 (FSTL3) are associated with anthropometric and metabolic variables and whether they are affected by exercise.

DESIGN

Activin A, activin B, follistatin, and FSTL3 were measured in (1) 80 subjects divided according to age (young vs old) and fitness status (active vs sedentary) before and after exercise at 70% maximal oxygen consumption (VO2max), followed by 90% of VO2max until exhaustion; and (2) 23 subjects [9 healthy and 14 with metabolic syndrome (MetS)] who completed four sessions: no exercise, high-intensity interval exercise, continuous moderate-intensity exercise, and resistance exercise for up to 45 minutes.

RESULTS

At baseline, follistatin and FSTL3 concentrations were positively associated with age, fat percentage, and body mass index (P < 0.001). Follistatin was positively associated with serum cholesterol (P = 0.005), low-density lipoprotein cholesterol (P = 0.01), triglycerides (P = 0.033), and blood pressure (P = 0.019), whereas activin A and activin B were higher in physically active participants (P = 0.056 and 0.029, respectively). All exercise types increased the levels of all hormones ∼10% to 21% (P = 0.034 for activin B, P < 0.001 for the others) independent of the presence of MetS.

CONCLUSION

Concentrations of circulating activins and follistatins are associated with metabolic parameters and increase after 45 minutes of exercise.

Role of serum myostatin in the association between hyperinsulinemia and muscle atrophy in Japanese obese patients

AIMS

The protein myostatin is a member of the transforming growth factor β superfamily. This is mainly expressed in skeletal muscle and negatively regulates skeletal muscle growth. The present study aimed to elucidate the associations among circulating myostatin level, skeletal muscle mass, and metabolic profiles in Japanese obese patients.

METHODS

Japanese obese outpatients (n = 74) were enrolled. We measured clinical parameters, quantified serum myostatin levels, and examined their associations in a cross-sectional manner.

RESULTS

Both total skeletal muscle mass and serum myostatin level were higher in males than in females. Among 74 patients, serum myostatin level was positively correlated with skeletal muscle mass and serum immunoreactive insulin (IRI) level [correlation coefficient (r) = 0.294, P = 0.011; r = 0.262, P = 0.024, respectively]. Furthermore, multivariate linear regression analysis revealed that serum myostatin level was positively correlated with IRI after adjusting for gender and skeletal muscle mass (β-coefficient = 0.230, P = 0.029, R² = 0.236).

CONCLUSIONS

In obese patients, serum myostatin level was elevated in conjunction with an increase in IRI level independent of skeletal muscle mass. This may imply possible novel pathological implications of serum myostatin in muscle mass and metabolism in obese patients with hyperinsulinemia.

Physiological Differences Between Low Versus High Skeletal Muscle Hypertrophic Responders to Resistance Exercise Training: Current Perspectives and Future Research Directions

Numerous reports suggest there are low and high skeletal muscle hypertrophic responders following weeks to months of structured resistance exercise training (referred to as low and high responders herein). Specifically, divergent alterations in muscle fiber cross sectional area (fCSA), vastus lateralis thickness, and whole body lean tissue mass have been shown to occur in high versus low responders. Differential responses in ribosome biogenesis and subsequent protein synthetic rates during training seemingly explain some of this individual variation in humans, and mechanistic in vitro and rodent studies provide further evidence that ribosome biogenesis is critical for muscle hypertrophy. High responders may experience a greater increase in satellite cell proliferation during training versus low responders. This phenomenon could serve to maintain an adequate myonuclear domain size or assist in extracellular remodeling to support myofiber growth. High responders may also express a muscle microRNA profile during training that enhances insulin-like growth factor-1 (IGF-1) mRNA expression, although more studies are needed to better validate this mechanism. Higher intramuscular androgen receptor protein content has been reported in high versus low responders following training, and this mechanism may enhance the hypertrophic effects of testosterone during training. While high responders likely possess “good genetics,” such evidence has been confined to single gene candidates which typically share marginal variance with hypertrophic outcomes following training (e.g., different myostatin and IGF-1 alleles). Limited evidence also suggests pre-training muscle fiber type composition and self-reported dietary habits (e.g., calorie and protein intake) do not differ between high versus low responders. Only a handful of studies have examined muscle biomarkers that are differentially expressed between low versus high responders. Thus, other molecular and physiological variables which could potentially affect the skeletal muscle hypertrophic response to resistance exercise training are also discussed including rDNA copy number, extracellular matrix and connective tissue properties, the inflammatory response to training, and mitochondrial as well as vascular characteristics.

Effects of elastic band exercises on physical ability and muscular topography of elderlyfemales

[Purpose] This study examined the effects of band exercise types on the physical ability and muscular topography for elderly females. [Subjects and Methods] Twenty-six females older than 65 years were divided into the dynamic band exercise (DBE; n=13) group and the Static band exercise (SBE; n=13) group. Each participant performed 12 weeks of elastic band exercises. Physical abilities were measured by leg extension power, sitting trunk flexion, closed eyes foot balance, and time to get up. Changes in muscle topography were evaluated with Moire measurement equipment for the chest, abdomen, and lumbar region. All results were compared before and after 12 weeks of exercise. [Results] Changes in physical ability were significantly increased in both groups. The scores for the muscular topography of the chest, abdomen, lumbar region, and all body parts was significantly improved in both groups for closed eyes foot balance. There were more improvements in the DBE group. [Conclusion] Two types of static and dynamic elastic band exercises effectively changed the physical fitness and muscle topography of elderly females. Therefore, to increase the effects of exercise, dynamic band exercises are considered useful. Because band exercises are simple, they can be used to maintain the health of elderly people.

Effect of eccentric action velocity on expression of genes related to myostatin signaling pathway in human skeletal muscle

The aim of this study was to investigate the effects of an acute bout of eccentric actions, performed at fast velocity (210º^.s^-1) and at slow velocity (20º^.s^-1), on the gene expression of regulatory components of the myostatin (MSTN) signalling pathway. Participants performed an acute bout of eccentric actions at either a slow or a fast velocity. Muscle biopsy samples were taken before, immediately after, and 2 h after the exercise bout. The gene expression of the components of the MSTN pathway was assessed by real-time PCR. No change was observed in MSTN, ACTRIIB, GASP-1 or FOXO-3a gene expression after either slow or fast eccentric actions (p > 0.05). However, the MSTN inhibitors follistatin (FST), FST-like-3 (FSTL3) and SMAD-7 were significantly increased 2 h after both eccentric actions (p < 0.05). No significant difference between bouts was found before, immediately after, or 2 h after the eccentric actions (slow and fast velocities, p > 0.05). The current findings indicate that a bout of eccentric actions activates the expression of MSTN inhibitors. However, no difference was observed in MSTN inhibitors’ gene expression when comparing slow and fast eccentric actions. It is possible that the greater time under tension induced by slow eccentric (SE) actions might compensate the effect of the greater velocity of fast eccentric (FE) actions. Additional studies are required to address the effect of eccentric action (EA) velocities on the pathways related to muscle hypertrophy.

The Effects of Fortetropin Supplementation on Body Composition, Strength, and Power in Humans and Mechanism of Action in a Rodent Model

OBJECTIVE

The purpose of this study was to investigate the effects of Fortetropin on skeletal muscle growth and strength in resistance-trained individuals and to investigate the anabolic and catabolic signaling effects using human and rodent models.

METHODS

In the rodent model, male Wistar rats (250 g) were gavage fed with either 1.2 ml of tap water control (CTL) or 0.26 g Fortetropin for 8 days. Then rats participated in a unilateral plantarflexion exercise bout. Nonexercised and exercised limbs were harvested at 180 minutes following and analyzed for gene and protein expression relative to mammalian target of rapamycin (mTOR) and ubiquitin signaling. For the human model, 45 (of whom 37 completed the study), resistance-trained college-aged males were divided equally into 3 groups receiving a placebo macronutrient matched control, 6.6 or 19.8 g of Fortetropin supplementation during 12 weeks of resistance training. Lean mass, muscle thickness, and lower and upper body strength were measured before and after 12 weeks of training.

RESULTS

The human study results indicated a Group × Time effect (p ≤ 0.05) for lean mass in which the 6.6 g (+1.7 kg) and 19.8 g (+1.68 kg) but not placebo (+0.6 kg) groups increased lean mass. Similarly, there was a Group × Time effect for muscle thickness (p ≤ 0.05), which increased in the experimental groups only. All groups increased equally in bench press and leg press strength. In the rodent model, a main effect for exercise (p ≤ 0.05) in which the control plus exercise but not Fortetropin plus exercise increased both ubiquitin monomer protein expression and polyubiquitination. mTOR signaling was elevated to a greater extent in the Fortetropin exercising conditions as indicated by greater phosphorylation status of 4EBP1, rp6, and p70S6K for both exercising conditions.

CONCLUSIONS

Fortetropin supplementation increases lean body mass (LBM) and decreases markers of protein breakdown while simultaneously increasing mTOR signaling.

Testosterone and trenbolone enanthate increase mature myostatin protein expression despite increasing skeletal muscle hypertrophy and satellite cell number in rodent muscle

The androgen-induced alterations in adult rodent skeletal muscle fibre cross-sectional area (fCSA), satellite cell content and myostatin (Mstn) were examined in 10-month-old Fisher 344 rats (n = 41) assigned to Sham surgery, orchiectomy (ORX), ORX + testosterone (TEST; 7.0 mg week^-1 ) or ORX + trenbolone (TREN; 1.0 mg week^-1 ). After 29 days, animals were euthanised and the levator ani/bulbocavernosus (LABC) muscle complex was harvested for analyses. LABC muscle fCSA was 102% and 94% higher in ORX + TEST and ORX + TREN compared to ORX (p < .001). ORX + TEST and ORX + TREN increased satellite cell numbers by 181% and 178% compared to ORX, respectively (p < .01), with no differences between conditions for myonuclear number per muscle fibre (p = .948). Mstn protein was increased 159% and 169% in the ORX + TEST and ORX + TREN compared to ORX (p < .01). pan-SMAD2/3 protein was ~30-50% greater in ORX compared to SHAM (p = .006), ORX + TEST (p = .037) and ORX + TREN (p = .043), although there were no between-treatment effects regarding phosphorylated SMAD2/3. Mstn, ActrIIb and Mighty mRNAs were lower in ORX, ORX + TEST and ORX + TREN compared to SHAM (p < .05). Testosterone and trenbolone administration increased muscle fCSA and satellite cell number without increasing myonuclei number, and increased Mstn protein levels. Several genes and signalling proteins related to myostatin signalling were differentially regulated by ORX or androgen therapy.

A single 60-min bout of peristaltic pulse external pneumatic compression transiently upregulates phosphorylated ribosomal protein s6

We investigated whether a single 60-min bout of whole leg, peristaltic pulse external pneumatic compression (EPC) altered select growth factor-related mRNAs and/or various phospho(p)-proteins related to cell growth, proliferation, inflammation and apoptosis signalling (e.g. Akt-mTOR, Jak-Stat). Ten participants (8 males, 2 females; aged 22·2 ± 0·4 years) reported to the laboratory 4 h post-prandial, and vastus lateralis muscle biopsies were obtained prior to (PRE), 1 h and 4 h post-EPC treatment. mRNA expression was analysed using real-time RT-PCR and phosphophorylated and cleaved proteins were analysed using an antibody array. No changes in selected growth factor-related mRNAs were observed following EPC. All p-proteins significantly altered by EPC decreased, except for p-rps6 (Ser235/236) which increased 31% 1 h post-EPC compared to PRE levels (P = 0·016). Notable decreases also included p-BAD (Ser112; -28%, P = 0·004) at 4 h post-EPC compared to PRE levels. In summary, an acute bout of EPC transiently upregulates p-rps6 as well as affecting other markers in the Akt-mTOR signalling cascade. Future research should characterize whether chronic EPC application promotes alterations in lower-limb musculature and/or enhances exercise-induced training adaptations.

Changes in Serum Levels of Myokines and Wnt-Antagonists after an Ultramarathon Race

BACKGROUND

Regular physical activities have a positive effect on the muscular skeletal system but overstrenuous exercise may be different. Transiently suppressed bone formation and increased bone resorption after participation in a 246-km ultradistance race has been demonstrated.

PURPOSE

The aim of this study was to analyze effects of the Spartathlon race on novel musculoskeletal markers.

METHODS

Venous blood samples were obtained before and immediately after the race from 19 participants of the Spartathlon. From 9 runners who were available 3 days after the start blood was drawn for a third time. Serum levels of myostatin, an inhibitor of myogenic differentiation, and its opponent follistatin as well as sclerostin and dickkopf-1, both of them inhibitors of the wnt signaling pathway, and markers of bone turnover were determined.

RESULTS

Serum levels of myostatin were significantly higher after the race. Serum follistatin only showed a transient increase. Sclerostin levels did not significantly differ before and after the race, whereas dickkopf-1 levels were significantly decreased. At follow-up a decrement of sclerostin and dickkopf-1 levels was seen. Serum cathepsin K levels did not change.

CONCLUSION

The increase of serum levels of myostatin appears to reflect muscle catabolic processes induced by overstrenuous exercise. After the short-term uncoupling of bone turnover participation in an ultradistance race seems to initiate a long-term positive effect on bone indicated by the low-level inhibition of the Wnt/β-catenin signaling pathway.

The Effect of Rate of Weight Reduction on Serum Myostatin and Follistatin Concentrations in Competitive Wrestlers

Purpose:

To evaluate anthropometric measures and serum markers of myostatin-pathway activity after different weight-reduction protocols in wrestlers.

Methods:

Subjects were randomly assigned to a gradual-weight-reduction (GWR) or rapid-weight-reduction (RWR) group. Food logs were collected for the duration of the study. Anthropometric measurements and serum samples were collected after an 8-h fast at baseline and after the weight-reduction intervention. Subjects reduced body mass by 4%. The GWR group restricted calories over 12 d, while the RWR group restricted calories over 2 d. A series of 2 × 5 repeated-measures (RM) ANOVAs was conducted to examine differences in nutrient consumption, while separate 2 × 2 RM ANOVAs were conducted to examine differences in anthropometric measures and serum markers. When applicable, Tukey post hoc comparisons were conducted. Significance for all tests was set at P < .05.

Results:

There were no between-groups differences for any anthropometric measure (P > .05). Subjects in both groups experienced a significant reduction in body mass, fat mass, lean mass, and percent body fat (P < .05). There were no between-groups differences in serum markers of myostatin-pathway activity (P > .05), but subjects in the RWR condition experienced a significant increase in serum myostatin (P < .01), a decrease in follistatin (P < .01), and an increase in myostatin-to-follistatin ratio (P < .001).

Conclusion:

Although there were no between-groups differences for any outcome variables, the serum myostatin-to-follistatin ratio was significantly increased in the RWR group, possibly signaling the early stages of skeletal-muscle catabolism.

SMAD3 negatively regulates serum irisin and skeletal muscle FNDC5 and peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α) during exercise

Beige adipose cells are a distinct and inducible type of thermogenic fat cell that express the mitochondrial uncoupling protein-1 and thus represent a powerful target for treating obesity. Mice lacking the TGF-β effector protein SMAD3 are protected against diet-induced obesity because of browning of their white adipose tissue (WAT), leading to increased whole body energy expenditure. However, the role SMAD3 plays in WAT browning is not clearly understood. Irisin is an exercise-induced skeletal muscle hormone that induces WAT browning similar to that observed in SMAD3-deficient mice. Together, these observations suggested that SMAD3 may negatively regulate irisin production and/or secretion from skeletal muscle. To address this question, we used wild-type and SMAD3 knock-out (Smad3(-/-)) mice subjected to an exercise regime and C2C12 myotubes treated with TGF-β, a TGF-β receptor 1 pharmacological inhibitor, adenovirus expressing constitutively active SMAD3, or siRNA against SMAD3. We find that in Smad3(-/-) mice, exercise increases serum irisin and skeletal muscle FNDC5 (irisin precursor) and its upstream activator peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α) to a greater extent than in wild-type mice. In C2C12 myotubes, TGF-β suppresses FNDC5 and PGC-1α mRNA and protein levels via SMAD3 and promotes SMAD3 binding to the FNDC5 and PGC-1α promoters. These data establish that SMAD3 suppresses FNDC5 and PGC-1α in skeletal muscle cells. These findings shed light on the poorly understood regulation of irisin/FNDC5 by demonstrating a novel association between irisin and SMAD3 signaling in skeletal muscle.

L-leucine, beta-hydroxy-beta-methylbutyric acid (HMB) and creatine monohydrate prevent myostatin-induced Akirin-1/Mighty mRNA down-regulation and myotube atrophy

Background

The purpose of this study was to examine if L-leucine (Leu), β-hydroxy-β-methylbutyrate (HMB), or creatine monohydrate (Crea) prevented potential atrophic effects of myostatin (MSTN) on differentiated C2C12 myotubes.

Methods

After four days of differentiation, myotubes were treated with MSTN (10 ng/ml) for two additional days and four treatment groups were studied: 1) 3x per day 10 mM Leu, 2) 3x per day 10 mM HMB, 3) 3x per day 10 mM Crea, 4) DM only. Myotubes treated with DM without MSTN were analyzed as the control condition (DM/CTL). Following treatment, cells were analyzed for total protein, DNA content, RNA content, muscle protein synthesis (MPS, SUnSET method), and fiber diameter. Separate batch treatments were analyzed for mRNA expression patterns of myostatin-related genes (Akirin-1/Mighty, Notch-1, Ski, MyoD) as well as atrogenes (MuRF-1, and MAFbx/Atrogin-1).

Results

MSTN decreased fiber diameter approximately 30% compared to DM/CTL myotubes (p < 0.001). Leu, HMB and Crea prevented MSTN-induced atrophy. MSTN did not decrease MPS levels compared to DM/CTL myotubes, but MSTN treatment decreased the mRNA expression of Akirin-1/Mighty by 27% (p < 0.001) and MyoD by 26% (p < 0.01) compared to DM/CTL myotubes. shRNA experiments confirmed that Mighty mRNA knockdown reduced myotube size, linking MSTN treatment to atrophy independent of MPS. Remarkably, MSTN + Leu and MSTN + HMB myotubes had similar Akirin-1/Mighty and MyoD mRNA levels compared to DM/CTL myotubes. Furthermore, MSTN + Crea myotubes exhibited a 36% (p < 0.05) and 86% (p < 0.001) increase in Akirin-1/Mighty mRNA compared to DM/CTL and MSTN-only treated myotubes, respectively.

Conclusions

Leu, HMB and Crea may reduce MSTN-induced muscle fiber atrophy by influencing Akirin-1/Mighty mRNA expression patterns. Future studies are needed to examine if Leu, HMB and Crea independently or synergistically affect Akirin-1/Mighty expression, and how Akirin-1/Mighty expression mechanistically relates to skeletal muscle hypertrophy in vivo.

Effects of (-)-epicatechin on molecular modulators of skeletal muscle growth and differentiation

Sarcopenia is a notable and debilitating age-associated condition. Flavonoids are known for their healthy effects and limited toxicity. The flavanol (-)-epicatechin (Epi) enhances exercise capacity in mice, and Epi-rich cocoa improves skeletal muscle structure in heart failure patients. (-)-Epicatechin may thus hold promise as treatment for sarcopenia. We examined changes in protein levels of molecular modulators of growth and differentiation in young vs. old, human and mouse skeletal muscle. We report the effects of Epi in mice and the results of an initial proof-of-concept trial in humans, where muscle strength and levels of modulators of muscle growth were measured. In mice, myostatin and senescence-associated β-galactosidase levels increase with aging, while those of follistatin and Myf5 decrease. (-)-Epicatechin decreases myostatin and β-galactosidase and increases levels of markers of muscle growth. In humans, myostatin and β-galactosidase increase with aging while follistatin, MyoD and myogenin decrease. Treatment for 7 days with (-)-epicatechin increases hand grip strength and the ratio of plasma follistatin/myostatin. In conclusion, aging has deleterious effects on modulators of muscle growth/differentiation, and the consumption of modest amounts of the flavanol (-)-epicatechin can partially reverse these changes. This flavanol warrants its comprehensive evaluation for the treatment of sarcopenia.

Inhibition of myostatin signaling through Notch activation following acute resistance exercise

Myostatin is a TGFβ family member and negative regulator of muscle size. Due to the complexity of the molecular pathway between myostatin mRNA/protein and changes in transcription, it has been difficult to understand whether myostatin plays a role in resistance exercise-induced skeletal muscle hypertrophy. To circumvent this problem, we determined the expression of a unique myostatin target gene, Mighty, following resistance exercise. Mighty mRNA increased by 6 h (82.9 ± 24.21%) and remained high out to 48 h (56.5 ± 19.67%) after resistance exercise. Further examination of the soleus, plantaris and tibialis anterior muscles showed that the change in Mighty mRNA at 6 h correlated with the increase in muscle size associated with this protocol (R(2) = 0.9996). The increase in Mighty mRNA occurred both independent of Smad2 phosphorylation and in spite of an increase in myostatin mRNA (341.8 ± 147.14% at 3 h). The myostatin inhibitor SKI remained unchanged. However, activated Notch, another potential inhibitor of TGFβ signaling, increased immediately following resistance exercise (83 ± 11.2%) and stayed elevated out to 6 h (78 ± 16.6%). Electroportion of the Notch intracellular domain into the tibialis anterior resulted in an increase in Mighty mRNA (63 ± 13.4%) that was equivalent to the canonical Notch target HES-1 (94.4 ± 7.32%). These data suggest that acute resistance exercise decreases myostatin signaling through the activation of the TGFβ inhibitor Notch resulting in a decrease in myostatin transcriptional activity that correlates well with muscle hypertrophy.

Effects of the activin A-myostatin-follistatin system on aging bone and muscle progenitor cells

The activin A-myostatin-follistatin system is thought to play an important role in the regulation of muscle and bone mass throughout growth, development, and aging; however, the effects of these ligands on progenitor cell proliferation and differentiation in muscle and bone are not well understood. In addition, age-associated changes in the relative expression of these factors in musculoskeletal tissues have not been described. We therefore examined changes in protein levels of activin A, follistatin, and myostatin (GDF-8) in both muscle and bone with age in C57BL6 mice using ELISA. We then investigated the effects of activin A, myostatin and follistatin on the proliferation and differentiation of primary myoblasts and mouse bone marrow stromal cells (BMSCs) in vitro. Myostatin levels and the myostatin:follistatin ratio increased with age in the primarily slow-twitch mouse soleus muscle, whereas the pattern was reversed with age in the fast-twitch extensor digitorum longus muscle. Myostatin levels and the myostatin:follistatin ratio increased significantly (+75%) in mouse bone marrow with age, as did activin A levels (+17%). Follistatin increased the proliferation of primary myoblasts from both young and aged mice, whereas myostatin increased proliferation of younger myoblasts but decreased proliferation of older myoblasts. Myostatin reduced proliferation of both young and aged BMSCs in a dose-dependent fashion, and activin A increased mineralization in both young and aged BMSCs. Together these data suggest that aging in mice is accompanied by changes in the expression of activin A and myostatin, as well as changes in the response of bone and muscle progenitor cells to these factors. Myostatin appears to play a particularly important role in the impaired proliferative capacity of muscle and bone progenitor cells from aged mice.

A mesenchymal stromal cell gene signature for donor age

Human aging is associated with loss of function and regenerative capacity. Human bone marrow derived mesenchymal stromal cells (hMSCs) are involved in tissue regeneration, evidenced by their capacity to differentiate into several lineages and therefore are considered the golden standard for cell-based regeneration therapy. Tissue maintenance and regeneration is dependent on stem cells and declines with age and aging is thought to influence therapeutic efficacy, therefore, more insight in the process of aging of hMSCs is of high interest. We, therefore, hypothesized that hMSCs might reflect signs of aging. In order to find markers for donor age, early passage hMSCs were isolated from bone marrow of 61 donors, with ages varying from 17–84, and clinical parameters, in vitro characteristics and microarray analysis were assessed. Although clinical parameters and in vitro performance did not yield reliable markers for aging since large donor variations were present, genome-wide microarray analysis resulted in a considerable list of genes correlating with human age. By comparing the transcriptional profile of aging in human with the one from rat, we discovered follistatin as a common marker for aging in both species. The gene signature presented here could be a useful tool for drug testing to rejuvenate hMSCs or for the selection of more potent, hMSCs for cell-based therapy.

Resistance training induced increase in muscle fiber size in young and older men

Muscle strength and mass decline in sedentary individuals with aging. The present study investigated the effects of both age and 21 weeks of progressive hypertrophic resistance training (RT) on skeletal muscle size and strength, and on myostatin and myogenin mRNA expression in 21 previously untrained young men (26.0 ± 4.3 years) and 18 older men (61.2 ± 4.1 years) and age-matched controls. Vastus lateralis muscle biopsies were taken before and after RT. Type I and type II muscle fiber cross-sectional areas increased more in young men than in older men after RT (P < 0.05). Concentric leg extension increased (P < 0.05) more after 10.5 weeks in young men compared to older men, but after 21 weeks no statistical differences existed. The daily energy and protein intake were greater (P < 0.001) in young subjects. Both myostatin and myogenin mRNA expression increased in older when compared with young men after RT (P < 0.05). In conclusion, after RT, muscle fiber size increased less in older compared to young men. This was associated with lower protein and energy intake and increases in myostatin gene expression in older when compared to young men.

The effect of physiological stimuli on sarcopenia; impact of Notch and Wnt signaling on impaired aged skeletal muscle repair

The age-related loss of skeletal muscle mass and function that is associated with sarcopenia can result in ultimate consequences such as decreased quality of life. The causes of sarcopenia are multifactorial and include environmental and biological factors. The purpose of this review is to synthesize what the literature reveals in regards to the cellular regulation of sarcopenia, including impaired muscle regenerative capacity in the aged, and to discuss if physiological stimuli have the potential to slow the loss of myogenic potential that is associated with sarcopenia. In addition, this review article will discuss the effect of aging on Notch and Wnt signaling, and whether physiological stimuli have the ability to restore Notch and Wnt signaling resulting in rejuvenated aged muscle repair. The intention of this summary is to bring awareness to the benefits of consistent physiological stimulus (exercise) to combating sarcopenia as well as proclaiming the usefulness of contraction-induced injury models to studying the effects of local and systemic influences on aged myogenic capability.

Effects of pre-exercise feeding on serum hormone concentrations and biomarkers of myostatin and ubiquitin proteasome pathway activity

PURPOSE

The aim of the study was to examine the acute effects of pre-exercise ingestion of protein, carbohydrate, and a non-caloric placebo on serum concentrations of insulin and cortisol, and the intramuscular gene expression of myostatin- and ubiquitin proteasome pathway (UPP)-related genes following a bout of resistance exercise.

METHODS

Ten untrained college-aged men participated in three resistance exercise sessions (3 × 10 at 80 % 1RM for bilateral hack squat, leg press, and leg extension) in a cross-over fashion, which were randomly preceded by protein, carbohydrate, or placebo ingestion 30 min prior to training. Pre-supplement/pre-exercise, 2 h and 6 h post-exercise muscle biopsies were obtained during each session and analyzed for mRNA fold changes in myostatin (MSTN), activin IIB, follistatin-like 3 (FSTL3), SMAD specific E3 ubiquitin protein ligase 1 (SMURF1), forkhead box O3, F-box protein 32 (FBXO32), and Muscle RING-finger protein-1, with beta-actin serving as the housekeeping gene. Gene expression of all genes was analyzed using real-time PCR.

RESULTS

Acute feeding appeared to have no significant effect on myostatin or UPP biomarkers. However, resistance exercise resulted in a significant downregulation of MSTN and FBXO32 mRNA expression and a significant upregulation in FSTL3 and SMURF1 mRNA expression (p < 0.05).

CONCLUSIONS

An acute bout of resistance exercise results in acute post-exercise alterations in intramuscular mRNA expression of myostatin and UPP markers suggestive of skeletal muscle growth. However, carbohydrate and protein feeding surrounding resistance exercise appear to have little influence on the acute expression of these markers.