Single muscle fiber contractile properties in adults with muscular dystrophy treated with MYO-029

Prevalence of Sarcopenic Obesity in Various Comorbidities, Diagnostic Markers, and Therapeutic Approaches: A Review

The coexistence of sarcopenia and obesity characterizes sarcopenic obesity. In this condition, there is an imbalance between lean and fat mass amounts. It is a prevalent issue that is gaining prevalence among the elderly population. To evaluate the condition, allied health professionals may employ non-invasive diagnostic techniques, such as gait speed, skeletal muscle mass, and muscle strength. Nevertheless, early diagnosis and treatment of pathology are essential for preventing debilitating effects and providing the highest quality of care. This article reviews the prevalence of sarcopenic obesity in numerous medical conditions, such as cancer, arthritis, postoperative cases, diabetes mellitus, obesity, and metabolic syndrome. In addition, this paper aims to examine the available evidence regarding the prevalence of sarcopenic obesity in other conditions along with their diagnostic markers and therapeutic approaches.

Effect of Chinese herbal medicines on the overall survival of patients with muscular dystrophies in Taiwan

ETHNOPHARMACOLOGICAL RELEVANCE

Muscular dystrophies are a rare, severe, and genetically inherited group of disorders characterized by progressive loss of muscle fibers, leading to muscle weakness. The current treatment plan for muscular dystrophies includes the use of steroids to slow muscle deterioration by dampening the inflammatory response.

AIM OF THE STUDY

Chinese herbal medicine (CHM) has been offered as an adjunctive therapy in Taiwan's medical healthcare plan, making it possible to track CHM usage in patients with muscular dystrophic disease. Therefore, we explored the long-term effects of CHM use on the overall mortality of patients with muscular dystrophies.

MATERIALS AND METHODS

A total of 581 patients with muscular dystrophies were identified from the database of Registry for Catastrophic Illness Patients in Taiwan. Among them, 80 and 201 patients were CHM users and non-CHM users, respectively. Student's t-test, chi-squared test, Cox proportional hazard model, and Kaplan-Meier curve (log-rank test) were used for evaluation. Association rules and network analyses were performed to explore the combination of CHMs used in muscular dystrophies.

RESULTS

Compared to non-CHM users, there were more female patients, more comorbidities, including chronic pulmonary disease and peptic ulcer disease in the CHM user group. Patients with prednisolone usage exhibited a lower risk of overall mortality than those who did not, after adjusting for age, sex, use of CHM, and comorbidities. CHM users showed a lower risk of overall mortality after adjusting for age, sex, prednisolone use, and comorbidities. The cumulative incidence of the overall survival was significantly higher in CHM users. Association rule and network analysis showed that one main CHM cluster was commonly used to treat patients with muscular dystrophies in Taiwan. The cluster includes Yin-Qiao-San, Ban-Xia-Bai-Zhu-Tian-Ma-Tang, Zhi-Ke (Citrus aurantium L.), Yu-Xing-Cao (Houttuynia cordata Thunb.), Che-Qian-Zi (Plantago asiatica L.), and Da-Huang (Rheum palmatum L.).

CONCLUSIONS

Our data suggest that adjunctive therapy with CHM may help to reduce the overall mortality among patients with muscular dystrophies. The identification of the CHM cluster allows us to narrow down the key active compounds and may enable future therapeutic developments and clinical trial designs to improve overall survival in these patients.

Principles of the activin receptor signaling pathway and its inhibition

This review captures the anabolic and stimulatory effects observed with inhibition of the transforming growth factor β superfamily in muscle, blood, and bone. New medicinal substances that rectify activin, myostatin, and growth differentiation factor 11 signaling give hope to the many whose lives are affected by deterioration of these tissues. The review first covers the origin, structure, and common pathway of activins, myostatin, and growth differentiation factor 11 along with the pharmacodynamics of the new class of molecules designed to oppose the activin receptor signaling pathway. Current terminology surrounding this new class of molecules is inconsistent and does not infer functionality. Adopting inhibitors of the activin receptor signaling pathway (IASPs) as a generic term is proposed because it encapsulates the molecular mechanisms along the pathway trajectory. To conclude, a pragmatic classification of IASPs is presented that integrates functionality and side effects based on the data available from animals and humans. This provides researchers and clinicians with a tool to tailor IASPs therapy according to the need of projects or patients and with respect to side effects.

Novel insights into the complex architecture of osteoporosis molecular genetics

Osteoporosis is a prevalent osteodegenerative disease and silent killer linked to a decrease in bone mass and decline of bone microarchitecture, due to impaired bone matrix mineralization, raising the risk of fracture. Nevertheless, the process of bone matrix mineralization is still an unsolved mystery. Osteoporosis is a polygenic disorder associated with genetic and environmental risk factors; however, the majority of genes associated with osteoporosis remain largely unknown. Several signaling pathways regulate bone mass; therefore, dysregulation of a single signaling pathway leads to metabolic bone disease owing to high or low bone mass. Parathyroid hormone, core-binding factor α-1 (Cbfa1), Wnt/β-catenin, the receptor activator of the nuclear factor kappa-B (NF-κB) ligand (RANKL), myostatin, and osteogenic exercise signaling pathways play pivotal roles in the regulation of bone mass. The myostatin signaling pathway increases bone resorption by activating the RANKL signaling pathway, whereas osteogenic exercise inhibits myostatin and sclerostin while inducing irisin that consequentially activates the Cbfa1 and Wnt/β-catenin bone formation pathways. The aims of this review are to summarize what is known about osteoporosis-related signaling pathways; define the role of these pathways in osteoporosis drug discovery; focus light on the link between bone, muscle, pancreas, and adipose integrative physiology and osteoporosis; and underline the emerging role of osteogenic exercise in the prevention of, and care for, osteoporosis, obesity, and diabetes.

Mechanisms Underlying Metabolic Syndrome-Related Sarcopenia and Possible Therapeutic Measures

Although there are several reviews that report the interrelationship between sarcopenia and obesity and insulin resistance, the relation between sarcopenia and the other signs that compose the metabolic syndrome (MetS) has not been extensively revised. Here, we review the mechanisms underlying MetS-related sarcopenia and discuss the possible therapeutic measures proposed. A vicious cycle between the loss of muscle and the accumulation of intramuscular fat might be associated with MetS via a complex interplay of factors including nutritional intake, physical activity, body fat, oxidative stress, proinflammatory cytokines, insulin resistance, hormonal changes, and mitochondrial dysfunction. The enormous differences in lipid storage capacities between the two genders and elevated amounts of endogenous fat having lipotoxic effects that lead to the loss of muscle mass are discussed. The important repercussions of MetS-related sarcopenia on other illnesses that lead to increased disability, morbidity, and mortality are also addressed. Additional research is needed to better understand the pathophysiology of MetS-related sarcopenia and its consequences. Although there is currently no consensus on the treatment, lifestyle changes including diet and power exercise seem to be the best options.

Phenotypes of Obesity: How it Impacts Management

PURPOSE OF REVIEW

The worldwide prevalence of obesity is increasing. Obesity is strongly associated with many chronic health conditions that have been shown to improve with weight loss. However, counseling patients on weight loss can be challenging. Identifying specific aspects of weight management may personalize the conversation about weight loss and better address the individual patient's health goals and perceived barriers to change.

RECENT FINDINGS

Physical and behavioral phenotypes are being identified to better tailor treatment recommendations, given lack of efficacy of currently available interventions. The current review provides a summary of the evidence behind the management of several recognized clinical phenotypes, to include body fat distribution (e.g., central obesity), muscle mass (e.g., sarcopenic obesity of the elderly), and problematic eating behaviors (e.g., cravings). Identifying specific aspects of weight management may personalize the conversation about weight loss and better address the individual patient's health goals and perceived barriers to change.

Human growth hormone stabilizes walking and improves strength in a patient with dominantly inherited calpainopathy

The aim was to investigate if daily low-dose treatment with recombinant human growth hormone (somatropine) can stabilize or improve muscle strength and walking capability in a patient with dominantly inherited calpainopathy. The patient was treated with daily injections of somatropine, except for a 6-month pause, over a period of 4.5 years. Efficacy was assessed by repeated muscle dynamometry tests and 6-minute walk tests (6MWT). Strength improved in most muscle groups on treatment, deteriorated in the 6-month off treatment, and improved again when treatment was resumed. The 6MWT stabilized during the initial 18-month treatment period, then deteriorated in the 6 months off treatment and improved to pre-trial levels when treatment was resumed. The findings suggest that supplementation with somatropine, within physiological ranges, may improve muscle strength and stabilize walking capability in a patient with calpainopathy. This finding calls for testing of somatropine supplementation in muscular dystrophies in a randomized study.

Immune-mediated pathology in Duchenne muscular dystrophy

Immunological and inflammatory processes downstream of dystrophin deficiency as well as metabolic abnormalities, defective autophagy, and loss of regenerative capacity all contribute to muscle pathology in Duchenne muscular dystrophy (DMD). These downstream cascades offer potential avenues for pharmacological intervention. Modulating the inflammatory response and inducing immunological tolerance to de novo dystrophin expression will be critical to the success of dystrophin-replacement therapies. This Review focuses on the role of the inflammatory response in DMD pathogenesis and opportunities for clinical intervention.

Biology of frailty: Modulation of ageing genes and its importance to prevent age-associated loss of function

Frailty is associated with loss of functional reserve as well as with the prediction of adverse events in the old population. The traditional criteria of frailty are based on five physical determinations described in the Cardiovascular Health Study. We propose that biological and genetic markers of frailty should be used to increase the predictive capacity of the established clinical indeces. In recent times, research for biological markers of frailty has gained impetus. Finding a biological markers with diagnostic and prognostic capacity would be a major milestone to identify frailty risk, and also pre-frailty status. In the first section of the manuscript, we review the available biomarkers that help to monitor and prevent the evolution and the efficacy of interventions to delay the onset of frailty and to prevent its progression to incapacity. We also discuss the contribution of genetics to frailty. There are scientific bases that support that genetics influences frailty, although environmental factors probably will have the highest contribution. We review the known SNPs of the genes associated with frailty and classify them, taking into account the pathway in which they are involved. We also highlight the importance of longevity genes and their possible relation with frailty, citing centenarians who reach a very old age as an example of successful ageing. Finally, the reversibility of frailty is discussed. It can potentially be treated with nutritional or pharmacological interventions. However, physical exercise seems to be the most effective strategy to treat and prevent frailty. The last section of the manuscript is devoted to explaining the recommendations on the appropriate design of an exercise protocol to maximize its beneficial effects in a population of frail individuals.

Mitochondrial impairment induced by postnatal ActRIIB blockade does not alter function and energy status in exercising mouse glycolytic muscle in vivo

Because it leads to a rapid and massive muscle hypertrophy, postnatal blockade of the activin type IIB receptor (ActRIIB) is a promising therapeutic strategy for counteracting muscle wasting. However, the functional consequences remain very poorly documented in vivo. Here, we have investigated the impact of 8-wk ActRIIB blockade with soluble receptor (sActRIIB-Fc) on gastrocnemius muscle anatomy, energy metabolism, and force-generating capacity in wild-type mice, using totally noninvasive magnetic resonance imaging (MRI) and dynamic(31)P-MRS. Compared with vehicle (PBS) control, sActRIIB-Fc treatment resulted in a dramatic increase in body weight (+29%) and muscle volume (+58%) calculated from hindlimb MR imaging, but did not alter fiber type distribution determined via myosin heavy chain isoform analysis. In resting muscle, sActRIIB-Fc treatment induced acidosis and PCr depletion, thereby suggesting reduced tissue oxygenation. During an in vivo fatiguing exercise (6-min repeated maximal isometric contraction electrically induced at 1.7 Hz), maximal and total absolute forces were larger in sActRIIB-Fc treated animals (+26 and +12%, respectively), whereas specific force and fatigue resistance were lower (-30 and -37%, respectively). Treatment with sActRIIB-Fc further decreased the maximal rate of oxidative ATP synthesis (-42%) and the oxidative capacity (-34%), but did not alter the bioenergetics status in contracting muscle. Our findings demonstrate in vivo that sActRIIB-Fc treatment increases absolute force-generating capacity and reduces mitochondrial function in glycolytic gastrocnemius muscle, but this reduction does not compromise energy status during sustained activity. Overall, these data support the clinical interest of postnatal ActRIIB blockade.

Emerging drugs affecting skeletal muscle function and mitochondrial biogenesis - Potential implications for sports drug testing programs

RATIONALE

A plethora of compounds potentially leading to drug candidates that affect skeletal muscle function and, more specifically, mitochondrial biogenesis, has been under (pre)clinical investigation for rare as well as more common diseases. Some of these compounds could be the object of misuse by athletes aiming at artificial and/or illicit and drug-facilitated performance enhancement, necessitating preventive and proactive anti-doping measures.

METHODS

Early warnings and the continuous retrieval and dissemination of information are crucial for sports drug testing laboratories as well as anti-doping authorities, as they assist in preparation of efficient doping control analytical strategies for potential future threats arising from new therapeutic developments. Scientific literature represents the main source of information, which yielded the herein discussed substances and therapeutic targets, which might become relevant for doping controls in the future. Where available, mass spectrometric data are presented, supporting the development of analytical strategies and characterization of compounds possibly identified in human sports drug testing samples.

RESULTS & CONCLUSIONS

Focusing on skeletal muscle and mitochondrial biogenesis, numerous substances exhibiting agonistic or antagonistic actions on different cellular 'control centers' resulting in increased skeletal muscle mass, enhanced performance (as determined with laboratory animal models), and/or elevated amounts of mitochondria have been described. Substances of interest include agonists for REV-ERBα (e.g. SR9009, SR9011, SR10067, GSK4112), sirtuin 1 (e.g. SRT1720, SRT2104), adenosine monophosphate-activated protein kinase (AMPK, e.g. AICAR), peroxisome proliferator-activated receptor (PPAR)δ (e.g. GW1516, GW0742, L165041), and inhibitory/antagonistic agents targeting the methionine-folate cycle (MOTS-c), the general control non-derepressible 5 (GCN5) acetyl transferase (e.g. CPTH2, MB-3), myostatin (e.g. MYO-029), the myostatin receptor (bimagrumab), and myostatin receptor ligands (e.g. sotatercept, ACE-031). In addition, potentially relevant drug targets were identified, e.g. with the sarcoplasmic transmembrane peptide myoregulin and the nuclear receptor corepressor 1 (NCOR-1). The antagonism of these has shown to result in substantially enhanced physical performance in animals, necessitating the monitoring of strategies such as RNA interference regarding these substances. Most drug candidates are of lower molecular mass and comprise non-natural compositions, facts which suggest approaches for their qualitative identification in doping control samples by mass spectrometry. Electrospray ionization/collision-induced dissociation mass spectra of representatives of the aforementioned substances and selected in vitro derived phase-I metabolites support this assumption, and test methods for a subset of these have been recently established. Expanding the knowledge on analytical data will further facilitate the identification of such analytes and related compounds in confiscated material as well as sports drug testing specimens.

Selective Retinoic Acid Receptor γ Agonists Promote Repair of Injured Skeletal Muscle in Mouse

Retinoic acid signaling regulates several biological events, including myogenesis. We previously found that retinoic acid receptor γ (RARγ) agonist blocks heterotopic ossification, a pathological bone formation that mostly occurs in the skeletal muscle. Interestingly, RARγ agonist also weakened deterioration of muscle architecture adjacent to the heterotopic ossification lesion, suggesting that RARγ agonist may oppose skeletal muscle damage. To test this hypothesis, we generated a critical defect in the tibialis anterior muscle of 7-week-old mice with a cautery, treated them with RARγ agonist or vehicle corn oil, and examined the effects of RARγ agonist on muscle repair. The muscle defects were partially repaired with newly regenerating muscle cells, but also filled with adipose and fibrous scar tissue in both RARγ-treated and control groups. The fibrous or adipose area was smaller in RARγ agonist-treated mice than in the control. In addition, muscle repair was remarkably delayed in RARγ-null mice in both critical defect and cardiotoxin injury models. Furthermore, we found a rapid increase in retinoid signaling in lacerated muscle, as monitored by retinoid signaling reporter mice. Together, our results indicate that endogenous RARγ signaling is involved in muscle repair and that selective RARγ agonists may be beneficial to promote repair in various types of muscle injuries.

Muscle hypertrophy induced by myostatin inhibition accelerates degeneration in dysferlinopathy

Myostatin is a secreted signaling molecule that normally acts to limit muscle growth. As a result, there is extensive effort directed at developing drugs capable of targeting myostatin to treat patients with muscle loss. One potential concern with this therapeutic approach in patients with muscle degenerative diseases like muscular dystrophy is that inducing hypertrophy may increase stress on dystrophic fibers, thereby accelerating disease progression. To investigate this possibility, we examined the effect of blocking the myostatin pathway in dysferlin-deficient (Dysf^−/−) mice, in which membrane repair is compromised, either by transgenic expression of follistatin in skeletal muscle or by systemic administration of the soluble form of the activin type IIB receptor (ACVR2B/Fc). Here, we show that myostatin inhibition by follistatin transgene expression in Dysf^−/− mice results in early improvement in histopathology but ultimately exacerbates muscle degeneration; this effect was not observed in dystrophin-deficient (mdx) mice, suggesting that accelerated degeneration induced by follistatin transgene expression is specific to mice lacking dysferlin. Dysf^−/− mice injected with ACVR2B/Fc showed significant increases in muscle mass and amelioration of fibrotic changes normally seen in 8-month-old Dysf^−/− mice. Despite these potentially beneficial effects, ACVR2B/Fc treatment caused increases in serum CK levels in some Dysf^−/− mice, indicating possible muscle damage induced by hypertrophy. These findings suggest that depending on the disease context, inducing muscle hypertrophy by myostatin blockade may have detrimental effects, which need to be weighed against the potential gains in muscle growth and decreased fibrosis.

Measurement of Maximum Isometric Force Generated by Permeabilized Skeletal Muscle Fibers

Analysis of the contractile properties of chemically skinned, or permeabilized, skeletal muscle fibers offers a powerful means by which to assess muscle function at the level of the single muscle cell. Single muscle fiber studies are useful in both basic science and clinical studies. For basic studies, single muscle fiber contractility measurements allow investigation of fundamental mechanisms of force production, and analysis of muscle function in the context of genetic manipulations. Clinically, single muscle fiber studies provide useful insight into the impact of injury and disease on muscle function, and may be used to guide the understanding of muscular pathologies. In this video article we outline the steps required to prepare and isolate an individual skeletal muscle fiber segment, attach it to force-measuring apparatus, activate it to produce maximum isometric force, and estimate its cross-sectional area for the purpose of normalizing the force produced.

Combination Antisense Treatment for Destructive Exon Skipping of Myostatin and Open Reading Frame Rescue of Dystrophin in Neonatal mdx Mice

The fatal X-linked Duchenne muscular dystrophy (DMD), characterized by progressive muscle wasting and muscle weakness, is caused by mutations within the DMD gene. The use of antisense oligonucleotides (AOs) modulating pre-mRNA splicing to restore the disrupted dystrophin reading frame, subsequently generating a shortened but functional protein has emerged as a potential strategy in DMD treatment. AO therapy has recently been applied to induce out-of-frame exon skipping of myostatin pre-mRNA, knocking-down expression of myostatin protein, and such an approach is suggested to enhance muscle hypertrophy/hyperplasia and to reduce muscle necrosis. Within this study, we investigated dual exon skipping of dystrophin and myostatin pre-mRNAs using phosphorodiamidate morpholino oligomers conjugated with an arginine-rich peptide (B-PMOs). Intraperitoneal administration of B-PMOs was performed in neonatal mdx males on the day of birth, and at weeks 3 and 6. At week 9, we observed in treated mice (as compared to age-matched, saline-injected controls) normalization of muscle mass, a recovery in dystrophin expression, and a decrease in muscle necrosis, particularly in the diaphragm. Our data provide a proof of concept for antisense therapy combining dystrophin restoration and myostatin inhibition for the treatment of DMD.

Integrated therapies for osteoporosis and sarcopenia: from signaling pathways to clinical trials

Sarcopenia and osteoporosis are two sides of the same coin. They represent different aspects of the same age-related process of musculoskeletal atrophy and together culminate in falls, fractures, deconditioning, and increased mortality in older individuals. However, the current therapeutic approach to the prevention of minimal trauma fracture is unilateral and focuses solely on bone. In theory, an integrated approach that recognizes the interaction between muscle and bone could break the vicious cycle of their combined involution and more effectively minimize falls/fractures. In this review, signaling pathways and cross-talk mechanisms that integrate bone/muscle, and the emergence of novel therapies that exploit these pathways to target osteoporosis/sarcopenia will be discussed. In broad terms, these agents act on nuclear receptors (e.g., VDR, AR) or transmembrane receptors (e.g., activins, GH/IGF-1) expressed in muscle and bone, and seek to alter biologic responses to musculoskeletal aging, loading, and injury. Challenges in the development of these dual bone-muscle therapies, early clinical trials examining their safety/efficacy, and novel targets that hold promise in the reversal of musculoskeletal aging will be discussed.

Fibronectin-based scaffold domain proteins that bind myostatin: a patent evaluation of WO2014043344

Muscular dystrophies (MD) are commonly characterized by progressive loss of muscle mass and function. It is hypothesized that therapeutic blockade of the TGF-β ligand myostatin, a negative regulator of muscle mass, will stimulate muscle growth and restore muscle function. Although many anti-myostatin targets are currently being pursued in the clinical setting, the efficacies of the tested molecules have shown mixed results. The patent WO2014043344 describes a novel approach for myostatin inhibition using a modified fibronectin type III domain that could potentially be used to treat MD and other muscle-related pathologies.

Utilization of microscale silicon cantilevers to assess cellular contractile function in vitro

The development of more predictive and biologically relevant in vitro assays is predicated on the advancement of versatile cell culture systems which facilitate the functional assessment of the seeded cells. To that end, microscale cantilever technology offers a platform with which to measure the contractile functionality of a range of cell types, including skeletal, cardiac, and smooth muscle cells, through assessment of contraction induced substrate bending. Application of multiplexed cantilever arrays provides the means to develop moderate to high-throughput protocols for assessing drug efficacy and toxicity, disease phenotype and progression, as well as neuromuscular and other cell-cell interactions. This manuscript provides the details for fabricating reliable cantilever arrays for this purpose, and the methods required to successfully culture cells on these surfaces. Further description is provided on the steps necessary to perform functional analysis of contractile cell types maintained on such arrays using a novel laser and photo-detector system. The representative data provided highlights the precision and reproducible nature of the analysis of contractile function possible using this system, as well as the wide range of studies to which such technology can be applied. Successful widespread adoption of this system could provide investigators with the means to perform rapid, low cost functional studies in vitro, leading to more accurate predictions of tissue performance, disease development and response to novel therapeutic treatment.

Therapies for musculoskeletal disease: can we treat two birds with one stone?

Musculoskeletal diseases are highly prevalent with staggering annual health care costs across the globe. The combined wasting of muscle (sarcopenia) and bone (osteoporosis)-both in normal aging and pathologic states-can lead to vastly compounded risk for fracture in patients. Until now, our therapeutic approach to the prevention of such fractures has focused solely on bone, but our increasing understanding of the interconnected biology of muscle and bone has begun to shift our treatment paradigm for musculoskeletal disease. Targeting pathways that centrally regulate both bone and muscle (eg, GH/IGF-1, sex steroids, etc.) and newly emerging pathways that might facilitate communication between these 2 tissues (eg, activin/myostatin) might allow a greater therapeutic benefit and/or previously unanticipated means by which to treat these frail patients and prevent fracture. In this review, we will discuss a number of therapies currently under development that aim to treat musculoskeletal disease in precisely such a holistic fashion.

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.

Exercise is the real polypill

The concept of a "polypill" is receiving growing attention to prevent cardiovascular disease. Yet similar if not overall higher benefits are achievable with regular exercise, a drug-free intervention for which our genome has been haped over evolution. Compared with drugs, exercise is available at low cost and relatively free of adverse effects. We summarize epidemiological evidence on the preventive/therapeutic benefits of exercise and on the main biological mediators involved.

Association of the K153R polymorphism in the myostatin gene and extreme longevity

The myostatin (MSTN) gene is a candidate to influence extreme longevity owing to its role in modulating muscle mass and sarcopenia and especially in inhibiting the main nutrient-sensing pathway involved in longevity, i.e. mammalian target of rapamycin. We compared allele/genotype distributions of the exonic MSTN variants K153R (rs1805086), E164K (rs35781413), I225T and P198A, in Spanish centenarians (cases, n = 156; 132 women, age range 100-111 years) and younger adults (controls, n = 384; 167 women, age <50 years). No subject of either group carried a mutant allele of the E164K, I225T or P198A variation. The frequency of the variant R allele was significantly higher in centenarians (7.1%) than in controls (2.7%) (P = 0.001). The odds ratio of being a centenarian if the subject had the R allele was 3.48 (95% confidence interval 1.67-7.28, P = 0.001), compared to the control group, after adjusting for sex. The results were replicated in an Italian cohort (centenarians, n = 79 (40 women), age range 100-104 years; younger controls, n = 316 (155 women), age <50 years), where a higher frequency of the R allele in centenarians (7.6%) compared to controls (3.0%) (P = 0.004) was independently confirmed. Although more research is needed, the variant allele of the MSTN K153R polymorphism could be among the genetic contributors associated with exceptional longevity.

Myostatin--the holy grail for muscle, bone, and fat?

Myostatin, a member of the transforming growth factor beta (TGF-β) superfamily, was first described in 1997. Since then, myostatin has gained growing attention because of the discovery that myostatin inhibition leads to muscle mass accrual. Myostatin not only plays a key role in muscle homeostasis, but also affects fat and bone. This review will focus on the impact of myostatin and its inhibition on muscle mass/function, adipose tissue and bone density/geometry in humans. Although existing data are sparse, myostatin inhibition leads to increased lean mass and 1 study found a decrease in fat mass and increase in bone formation. In addition, myostatin levels are increased in sarcopenia, cachexia and bed rest whereas they are increased after resistance training, suggesting physiological regulatory of myostatin. Increased myostatin levels have also been found in obesity and levels decrease after weight loss from caloric restriction. Knowledge on the relationship of myostatin with bone is largely based on animal data where elevated myostatin levels lead to decreased BMD and myostatin inhibition improved BMD. In summary, myostatin appears to be a key factor in the integrated physiology of muscle, fat, and bone. It is unclear whether myostatin directly affects fat and bone, or indirectly via muscle. Whether via direct or indirect effects, myostatin inhibition appears to increase muscle and bone mass and decrease fat tissue-a combination that truly appears to be a holy grail. However, at this time, human data for both efficacy and safety are extremely limited. Moreover, whether increased muscle mass also leads to improved function remains to be determined. Ultimately potential beneficial effects of myostatin inhibition will need to be determined based on hard outcomes such as falls and fractures.

Sarcopenic obesity: how do we treat it?

PURPOSE OF REVIEW

The increasing prevalence of sarcopenic obesity in older adults has heightened interest in identifying the most effective treatment. This review highlights recent progress in the management, with an emphasis on lifestyle interventions and pharmacologic therapy aimed at reversing sarcopenic obesity.

RECENT FINDINGS

Whereas weight loss and exercise independently reverse sarcopenic obesity, they act synergistically in combination to improve body composition and physical function, beyond which is observed with either intervention alone. Optimizing protein intake appears to have beneficial effects on net muscle protein accretion in older adults. Myostatin inhibition is associated with favorable changes in body composition in animal studies, although experience in humans is relatively limited. Testosterone and growth hormone offer improvements in body composition, but the benefits must be weighed against potential risks of therapy. GHRH-analog therapy shows promise, but further studies are needed in older adults.

SUMMARY

At present, lifestyle interventions incorporating both diet-induced weight loss and regular exercise appear to be the optimal treatment for sarcopenic obesity. Maintenance of adequate protein intake is also advisable. Ongoing studies will determine whether pharmacologic therapy such as myostatin inhibitors or GHRH analogs have a role in the treatment of sarcopenic obesity.

The methyltransferase SMYD3 mediates the recruitment of transcriptional cofactors at the myostatin and c-Met genes and regulates skeletal muscle atrophy

Elucidating the epigenetic mechanisms underlying muscle mass determination and skeletal muscle wasting holds the potential of identifying molecular pathways that constitute possible drug targets. Here, we report that the methyltransferase SMYD3 modulates myostatin and c-Met transcription in primary skeletal muscle cells and C2C12 myogenic cells. SMYD3 targets the myostatin and c-Met genes and participates in the recruitment of the bromodomain protein BRD4 to their regulatory regions through protein-protein interaction. By recruiting BRD4, SMYD3 favors chromatin engagement of the pause-release factor p-TEFb (positive transcription elongation factor) and elongation of Ser2-phosphorylated RNA polymerase II (PolIISer2P). Reducing SMYD3 decreases myostatin and c-Met transcription, thus protecting from glucocorticoid-induced myotube atrophy. Supporting functional relevance of the SMYD3/BRD4 interaction, BRD4 pharmacological blockade by the small molecule JQ1 prevents dexamethasone-induced myostatin and atrogene up-regulation and spares myotube atrophy. Importantly, in a mouse model of dexamethasone-induced skeletal muscle atrophy, SMYD3 depletion prevents muscle loss and fiber size decrease. These findings reveal a mechanistic link between SMYD3/BRD4-dependent transcriptional regulation, muscle mass determination, and skeletal muscle atrophy and further encourage testing of small molecules targeting specific epigenetic regulators in animal models of muscle wasting.

Genes and the ageing muscle: a review on genetic association studies

Western populations are living longer. Ageing decline in muscle mass and strength (i.e. sarcopenia) is becoming a growing public health problem, as it contributes to the decreased capacity for independent living. It is thus important to determine those genetic factors that interact with ageing and thus modulate functional capacity and skeletal muscle phenotypes in older people. It would be also clinically relevant to identify 'unfavourable' genotypes associated with accelerated sarcopenia. In this review, we summarized published information on the potential associations between some genetic polymorphisms and muscle phenotypes in older people. A special emphasis was placed on those candidate polymorphisms that have been more extensively studied, i.e. angiotensin-converting enzyme (ACE) gene I/D, α-actinin-3 (ACTN3) R577X, and myostatin (MSTN) K153R, among others. Although previous heritability studies have indicated that there is an important genetic contribution to individual variability in muscle phenotypes among old people, published data on specific gene variants are controversial. The ACTN3 R577X polymorphism could influence muscle function in old women, yet there is controversy with regards to which allele (R or X) might play a 'favourable' role. Though more research is needed, up-to-date MSTN genotype is possibly the strongest candidate to explain variance among muscle phenotypes in the elderly. Future studies should take into account the association between muscle phenotypes in this population and complex gene-gene and gene-environment interactions.

Genes, physical fitness and ageing

Persons aged 80 years and older are the fastest growing segment of the population. As more individuals live longer, we should try to understand the mechanisms involved in healthy ageing and preserving functional independence in later life. In elderly people, functional independence is directly dependent on physical fitness, and ageing is inevitably associated with the declining functions of systems and organs (heart, lungs, blood vessels, skeletal muscles) that determine physical fitness. Thus, age-related diminished physical fitness contributes to the development of sarcopenia, frailty or disability, all of which severely deteriorate independent living and thus quality of life. Ageing is a complex process involving many variables that interact with one another, including - besides lifestyle factors or chronic diseases - genetics. Thus, several studies have examined the contribution of genetic endowment to a decline in physical fitness and subsequent loss of independence in later life. In this review, we compile information, including data from heritability, candidate-gene association, linkage and genome-wide association studies, on genetic factors that could influence physical fitness in the elderly.

Myostatin: genetic variants, therapy and gene doping

Since its discovery, myostatin (MSTN) has been at the forefront of muscle therapy research because intrinsic mutations or inhibition of this protein, by either pharmacological or genetic means, result in muscle hypertrophy and hyperplasia. In addition to muscle growth, MSTN inhibition potentially disturbs connective tissue, leads to strength modulation, facilitates myoblast transplantation, promotes tissue regeneration, induces adipose tissue thermogenesis and increases muscle oxidative phenotype. It is also known that current advances in gene therapy have an impact on sports because of the illicit use of such methods. However, the adverse effects of these methods, their impact on athletic performance in humans and the means of detecting gene doping are as yet unknown. The aim of the present review is to discuss biosynthesis, genetic variants, pharmacological/genetic manipulation, doping and athletic performance in relation to the MSTN pathway. As will be concluded from the manuscript, MSTN emerges as a promising molecule for combating muscle wasting diseases and for triggering wide-ranging discussion in view of its possible use in gene doping.

Myostatin as a therapeutic target in Amyotrophic lateral sclerosis

Amyotrophic Lateral Sclerosis is a devastating neurological disease that is inevitably fatal after 3-5years duration. Treatment options are minimal and as such new therapeutic modalities are required. In this review, we discuss the role of the myostatin pathway as a modulator of skeletal muscle mass and therapeutic approaches using biological based therapies. Both monoclonal antibodies to myostatin and a soluble receptor decoy to its high affinity receptor have been used in clinical trials of neuromuscular diseases and while there have been efficacy signals with the latter approach there have also been safety issues. Our approach is to target the high affinity receptor-binding site on myostatin and to develop a next generation set of therapeutic reagents built on a novel protein scaffold. This is the natural single domain VNAR found in sharks which is extremely versatile and has the ability to develop products with superior properties compared to existing therapeutics.

TGF-β signaling in Duchenne muscular dystrophy

The TGF-β protein family consists of secreted multifunctional cytokines that control diverse processes, such as cell growth and differentiation. Aberrant expression and downstream signaling of these growth factors have been associated with multiple diseases, including muscle wasting disorders, such as Duchenne muscular dystrophy. In this review we discuss recent advances in understanding the role of TGF-β family members during normal skeletal muscle biology/regeneration and their role in muscle pathology, with a special focus on Duchenne muscular dystrophy. In addition, we will highlight progress in the development of potential therapeutics for Duchenne muscular dystrophy based on intervention of TGF-β signaling.

Decreased specific force and power production of muscle fibers from myostatin-deficient mice are associated with a suppression of protein degradation

Myostatin (MSTN) is a member of the transforming growth factor-β superfamily of cytokines and is a negative regulator of skeletal muscle mass. Compared with MSTN(+/+) mice, the extensor digitorum longus muscles of MSTN(-/-) mice exhibit hypertrophy, hyperplasia, and greater maximum isometric force production (F(o)), but decreased specific maximum isometric force (sF(o); F(o) normalized by muscle cross-sectional area). The reason for the reduction in sF(o) was not known. Studies in myotubes indicate that inhibiting myostatin may increase muscle mass by decreasing the expression of the E3 ubiquitin ligase atrogin-1, which could impact the force-generating capacity and size of muscle fibers. To gain a greater understanding of the influence of myostatin on muscle contractility, we determined the impact of myostatin deficiency on the contractility of permeabilized muscle fibers and on the levels of atrogin-1 and ubiquitinated myosin heavy chain in whole muscle. We hypothesized that single fibers from MSTN(-/-) mice have a greater F(o), but no difference in sF(o), and a decrease in atrogin-1 and ubiquitin-tagged myosin heavy chain levels. The results indicated that fibers from MSTN(-/-) mice have a greater cross-sectional area, but do not have a greater F(o) and have a sF(o) that is significantly lower than fibers from MSTN(+/+) mice. The extensor digitorum longus muscles from MSTN(-/-) mice also have reduced levels of atrogin-1 and ubiquitinated myosin heavy chain. These findings suggest that myostatin inhibition in otherwise healthy muscle increases the size of muscle fibers and decreases atrogin-1 levels, but does not increase the force production of individual muscle fibers.

Dual exon skipping in myostatin and dystrophin for Duchenne muscular dystrophy

Background

Myostatin is a potent muscle growth inhibitor that belongs to the Transforming Growth Factor-β (TGF-β) family. Mutations leading to non functional myostatin have been associated with hypermuscularity in several organisms. By contrast, Duchenne muscular dystrophy (DMD) is characterized by a loss of muscle fibers and impaired regeneration. In this study, we aim to knockdown myostatin by means of exon skipping, a technique which has been successfully applied to reframe the genetic defect of dystrophin gene in DMD patients.

Methods

We targeted myostatin exon 2 using antisense oligonucleotides (AON) in healthy and DMD-derived myotubes cultures. We assessed the exon skipping level, transcriptional expression of myostatin and its target genes, and combined myostatin and several dystrophin AONs. These AONs were also applied in the mdx mice models via intramuscular injections.

Results

Myostatin AON induced exon 2 skipping in cell cultures and to a lower extent in the mdx mice. It was accompanied by decrease in myostatin mRNA and enhanced MYOG and MYF5 expression. Furthermore, combination of myostatin and dystrophin AONs induced simultaneous skipping of both genes.

Conclusions

We conclude that two AONs can be used to target two different genes, MSTN and DMD, in a straightforward manner. Targeting multiple ligands of TGF-beta family will be more promising as adjuvant therapies for DMD.

Endurance exercise training in myostatin null mice

The growth factor myostatin (Mstn) is a negative regulator of skeletal muscle mass. Mstn(-/-) muscles are hypertrophied, stronger, and more glycolytic than Mstn(+/+) muscles, suggesting that they might not perform endurance exercise as well as Mstn(+/+) mice. Indeed, it has previously been shown that treadmill exercise training reduces triceps weight in Mstn(-/-) mice. To analyze the response of Mstn(-/-) muscle to endurance exercise in detail, we carried out endurance training over 4 weeks to examine muscle mass, histology, and oxidative enzyme activity. We found that muscle mass was reduced with training in several muscles from both genotypes, with no evidence of muscle damage. Citrate synthase activity was increased with training in control and mutant mice. Non-trained Mstn(-/-) mice did, however, have lower maximal exercise capacity compared with Mstn(+/+) mice. These results show that Mstn(-/-) muscle retains the metabolic plasticity necessary to adapt normally to endurance training.

Administration of a soluble activin type IIB receptor promotes skeletal muscle growth independent of fiber type

This is the first report that inhibition of negative regulators of skeletal muscle by a soluble form of activin type IIB receptor (ACE-031) increases muscle mass independent of fiber-type expression. This finding is distinct from the effects of selective pharmacological inhibition of myostatin (GDF-8), which predominantly targets type II fibers. In our study 8-wk-old C57BL/6 mice were treated with ACE-031 or vehicle control for 28 days. By the end of treatment, mean body weight of the ACE-031 group was 16% greater than that of the control group, and wet weights of soleus, plantaris, gastrocnemius, and extensor digitorum longus muscles increased by 33, 44, 46 and 26%, respectively (P<0.05). Soleus fiber-type distribution was unchanged with ACE-031 administration, and mean fiber cross-sectional area increased by 22 and 28% (P<0.05) in type I and II fibers, respectively. In the plantaris, a predominantly type II fiber muscle, mean fiber cross-sectional area increased by 57% with ACE-031 treatment. Analysis of myosin heavy chain (MHC) isoform transcripts by real-time PCR indicated no change in transcript levels in the soleus, but a decline in MHC I and IIa in the plantaris. In contrast, electrophoretic separation of total soleus and plantaris protein indicated that there was no change in the proportion of MHC isoforms in either muscle. Thus these data provide optimism that ACE-031 may be a viable therapeutic in the treatment of musculoskeletal diseases. Future studies should be undertaken to confirm that the observed effects are not age dependent or due to the relatively short study duration.

Molecular, cellular and physiological investigation of myostatin propeptide-mediated muscle growth in adult mice

Inhibition of myostatin signalling or its biological activity has recently emerged as a potential remedial approach against muscle wasting and degenerative diseases such as muscular dystrophies. In the present study we systemically administered a recombinant AAV8 vector expressing a mutated myostatin propeptide (AAV8ProMyo) to healthy mice in order to assess its impact on the histological, cellular and physiological properties of the skeletal muscle, exploiting the fact that myostatin is naturally inhibited by its own propeptide. We report that a single intravenous administration of AAV8ProMyo leads to increases in muscle mass of tibialis anterior, extensor digitorum longus and gastrocnemius muscles 8 weeks post-injection and tibialis anterior, gastrocnemius and rectus femoris muscles 17 weeks post-injection. Moreover, treatment resulted in muscle fibre hypertrophy but not hyperplasia, with IIB myofibres responding to the greatest extent following propeptide-induced myostatin inhibition. Additionally, myofibre nuclear:cytoplasmic ratio was decreased in the AAV8ProMyo treated animals. Importantly, the hypertrophic EDL muscle 8 weeks after AAV8ProMyo treatment did not show the dramatic decrease in specific force displayed by the germline myostatin null mice.