Myostatin Inhibitors: Panacea or Predicament for Musculoskeletal Disorders?

Sarcopenic obesity and osteoporosis: Research progress and hot spots

Sarcopenic obesity (SO) and osteoporosis (OP) are associated with aging and obesity. The pathogenesis of SO is complex, including glucolipid and skeletal muscle metabolic disorders caused by inflammation, insulin resistance, and other factors. Growing evidence links muscle damage to bone loss. Muscle-lipid metabolism disorders of SO disrupt the balance between bone formation and bone resorption, increasing the risk of OP. Conversely, bones also play a role in fat and muscle metabolism. In the context of aging and obesity, the comprehensive review focuses on the effects of mechanical stimulation, mesenchymal stem cells (MSCs), chronic inflammation, myokines, and adipokines on musculoskeletal, at the same time, the impact of osteokines on muscle-lipid metabolism were also analyzed. So far, exercise combined with diet therapy is the most effective strategy for increasing musculoskeletal mass. A holistic treatment of musculoskeletal diseases is still in the preliminary exploration stage. Therefore, this article aims to improve the understanding of musculoskeletal -fat interactions in SO and OP, explores targets that can provide holistic treatment for SO combined with OP, and discusses current limitations and challenges. We hope to provide relevant ideas for developing specific therapies and improving disease prognosis in the future.

Fermented Yak-Kong using Bifidobacterium animalis derived from Korean infant intestine effectively relieves muscle atrophy in an aging mouse model

Yak-Kong (YK) is a small black soybean widely cultivated in Korea. It is considered to have excellent health functionality, as it has been reported to have better antioxidant efficacy than conventional black or yellow soybeans. Since YK has been described as good for the muscle health of the elderly in old oriental medicine books, this study sought to investigate the effect of fermented YK with Bifidobacterium animalis subsp. lactis LDTM 8102 (FYK) on muscle atrophy. In C2C12 mouse myoblasts, FYK elevated the expression of MyoD, total MHC, phosphorylated AKT, and PGC1α. In addition, two kinds of in vivo studies were conducted using both an induced and normal aging mouse model. The behavioral test results showed that in the induced aging mouse model, FYK intake alleviated age-related muscle weakness and loss of exercise performance. In addition, FYK alleviated muscle mass decrease and improved the expression of biomarkers including total MHC, myf6, phosphorylated AKT, PGC1α, and Tfam, which are related to myoblast differentiation, muscle protein synthesis, and mitochondrial generation in the muscle. In the normal aging model, FYK consumption did not increase muscle mass, but did upregulate the expression levels of biomarkers related to myoblast differentiation, muscle hypertrophy, and muscle function. Furthermore, it mitigated age-related declines in skeletal muscle force production and functional limitation by enhancing exercise performance and grip strength. Taken together, the results suggest that FYK has the potential to be a new functional food material that can alleviate the loss of muscle mass and strength caused by aging and prevent sarcopenia.

Role of Myostatin in Rheumatoid Arthritis: A Review of the Clinical Impact

Rheumatoid arthritis (RA) is a chronic inflammatory disease that affects synovial joints and that frequently involves extra-articular organs. A multiplicity of interleukins (IL) participates in the pathogenesis of RA, including IL-6, IL-1β, transforming growth factor-beta (TGF-β), and tumor necrosis factor (TNF)-α; immune cells such as monocytes, T and B lymphocytes, and macrophages; and auto-antibodies, mainly rheumatoid factor and anti-citrullinated protein antibodies (ACPAs). Skeletal muscle is also involved in RA, with many patients developing muscle wasting and sarcopenia. Several mechanisms are involved in the myopenia observed in RA, and one of them includes the effects of some interleukins and myokines on myocytes. Myostatin is a myokine member of the TGF-β superfamily; the overproduction of myostatin acts as a negative regulator of growth and differentiates the muscle fibers, limiting their number and size. Recent studies have identified abnormalities in the serum myostatin levels of RA patients, and these have been found to be associated with muscle wasting and other manifestations of severe RA. This review analyzes recent information regarding the relationship between myostatin levels and clinical manifestations of RA and the relevance of myostatin as a therapeutic target for future research.

Skeletal Muscle Injury in Chronic Kidney Disease-From Histologic Changes to Molecular Mechanisms and to Novel Therapies

Chronic kidney disease (CKD) is associated with significant reductions in lean body mass and in the mass of various tissues, including skeletal muscle, which causes fatigue and contributes to high mortality rates. In CKD, the cellular protein turnover is imbalanced, with protein degradation outweighing protein synthesis, leading to a loss of protein and cell mass, which impairs tissue function. As CKD itself, skeletal muscle wasting, or sarcopenia, can have various origins and causes, and both CKD and sarcopenia share common risk factors, such as diabetes, obesity, and age. While these pathologies together with reduced physical performance and malnutrition contribute to muscle loss, they cannot explain all features of CKD-associated sarcopenia. Metabolic acidosis, systemic inflammation, insulin resistance and the accumulation of uremic toxins have been identified as additional factors that occur in CKD and that can contribute to sarcopenia. Here, we discuss the elevation of systemic phosphate levels, also called hyperphosphatemia, and the imbalance in the endocrine regulators of phosphate metabolism as another CKD-associated pathology that can directly and indirectly harm skeletal muscle tissue. To identify causes, affected cell types, and the mechanisms of sarcopenia and thereby novel targets for therapeutic interventions, it is important to first characterize the precise pathologic changes on molecular, cellular, and histologic levels, and to do so in CKD patients as well as in animal models of CKD, which we describe here in detail. We also discuss the currently known pathomechanisms and therapeutic approaches of CKD-associated sarcopenia, as well as the effects of hyperphosphatemia and the novel drug targets it could provide to protect skeletal muscle in CKD.

Population longitudinal analysis of Gait Profile Score and North Star Ambulatory Assessment in children with Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a rare X-linked recessive disorder characterized by loss-of-function mutations in the gene encoding dystrophin. These mutations lead to progressive functional deterioration including muscle weakness, respiratory insufficiency, and musculoskeletal deformities. Three-dimensional gait analysis (3DGA) has been used as a tool to analyze gait pathology through the quantification of altered joint kinematics, kinetics, and muscle activity patterns. Among 3DGA indices, the Gait Profile Score (GPS), has been used as a sensitive overall measure to detect clinically relevant changes in gait patterns in children with DMD. To enhance our understanding of the clinical translation of 3DGA, we report here the development of a population nonlinear mixed-effect model that jointly describes the disease progression of the 3DGA index, GPS, and the functional endpoint, North Star Ambulatory Assessment (NSAA). The final model consists of a quadratic structure for GPS progression and a linear structure for GPS-NSAA correlation. Our model was able to capture the improvement in function in GPS and NSAA in younger subjects, as well as the decline of function in older subjects. Furthermore, the model predicted NSAA (CFB) at 1 year reasonably well for DMD subjects ≤7 years old at baseline. The model tended to slightly underpredict the decline in NSAA after 1 year for those >7 years old at baseline, but the prediction summary statistics were well maintained within the standard deviation of observed data. Quantitative models such as this may help answer clinically relevant questions to facilitate the development of novel therapies in DMD.

Targeting Molecular Mechanisms of Obesity- and Type 2 Diabetes Mellitus-Induced Skeletal Muscle Atrophy with Nerve Growth Factor

Skeletal muscle plays a critical role in metabolic diseases, such as obesity and type 2 diabetes mellitus (T2DM). Muscle atrophy, characterized by a decrease in muscle mass and function, occurs due to an imbalance between the rates of muscle protein synthesis and degradation. This study aimed to investigate the molecular mechanisms that lead to muscle atrophy in obese and T2DM mouse models. Additionally, the effect of nerve growth factor (NGF) on the protein synthesis and degradation pathways was examined. Male mice were divided into three groups: a control group that was fed a standard chow diet, and two experimental groups that were fed a Western diet. After 8 weeks, the diabetic group was injected with streptozotocin to induce T2DM. Each group was then further divided into NGF-treated or non-treated control group. In the gastrocnemius muscles of the Western diet group, increased expressions of myostatin, autophagy markers, and ubiquitin ligases were observed. Skeletal muscle tissue morphology indicated signs of muscle atrophy in both obese and diabetic mice. The NGF-treated group showed a prominent decrease in the protein levels of myostatin and autophagy markers. Furthermore, the NGF-treated group showed an increased Cyclin D1 level. Western diet-induced obesity and T2DM may be linked to muscle atrophy through upregulation of myostatin and subsequent increase in the ubiquitin and autophagy systems. Moreover, NGF treatment may improve muscle protein synthesis and cell cycling.

Advances in sarcopenia: mechanisms, therapeutic targets, and intervention strategies

Sarcopenia is a multifactorial condition characterized by loss of muscle mass. It poses significant health risks in older adults worldwide. Both pharmacological and non-pharmacological approaches are reported to address this disease. Certain dietary patterns, such as adequate energy intake and essential amino acids, have shown positive outcomes in preserving muscle function. Various medications, including myostatin inhibitors, growth hormones, and activin type II receptor inhibitors, have been evaluated for their effectiveness in managing sarcopenia. However, it is important to consider the variable efficacy and potential side effects associated with these treatments. There are currently no drugs approved by the Food and Drug Administration for sarcopenia. The ongoing research aims to develop more effective strategies in the future. Our review of research on disease mechanisms and drug development will be a valuable contribution to future research endeavors.

Synergistically Acting on Myostatin and Agrin Pathways Increases Neuromuscular Junction Stability and Endurance in Old Mice

Sarcopenia is the primary cause of impaired motor performance in the elderly. The current prevailing approach to counteract such condition is increasing the muscle mass through inhibition of the myostatin system: however, this strategy only moderately improves muscular strength, not being able to sustain the innervation of the hypertrophic muscle per se, leading to a progressive worsening of motor performances. Thus, we proposed the administration of ActR-Fc-nLG3, a protein that combines the soluble activin receptor, a strong myostatin inhibitor, with the C-terminal agrin nLG3 domain. This compound has the potential of reinforcing neuro-muscular stability to the hypertrophic muscle. We previously demonstrated an enhancement of motor endurance and ACh receptor aggregation in young mice after ActR-Fc-nLG3 administration. Now we extended these observations by demonstrating that also in aged (2 years-old) mice, long-term administration of ActR-Fc-nLG3 increases in a sustained way both motor endurance and muscle strength, compared with ActR-Fc, a myostatin inhibitor, alone. Histological data demonstrate that the administration of this biological improves neuromuscular stability and fiber innervation maintenance, preventing muscle fiber atrophy and inducing only moderate hypertrophy. Moreover, at the postsynaptic site we observe an increased folding in the soleplate, a likely anatomical substrate for improved neurotransmission efficiency in the NMJ, that may lead to enhanced motor endurance. We suggest that ActR-Fc-nLG3 may become a valid option for treating sarcopenia and possibly other disorders of striatal muscles.

Licochalcone A and B enhance muscle proliferation and differentiation by regulating Myostatin

BACKGROUND

Myostatin (MSTN) inhibition has demonstrated promise for the treatment of diseases associated with muscle loss. In a previous study, we discovered that Glycyrrhiza uralensis (G. uralensis) crude water extract (CWE) inhibits MSTN expression while promoting myogenesis. Furthermore, three specific compounds of G. uralensis, namely liquiritigenin, tetrahydroxymethoxychalcone, and Licochalcone B (Lic B), were found to promote myoblast proliferation and differentiation, as well as accelerate the regeneration of injured muscle tissue.

PURPOSE

The purpose of this study was to build on our previous findings on G. uralensis and demonstrate the potential of its two components, Licochalcone A (Lic A) and Lic B, in muscle mass regulation (by inhibiting MSTN), aging and muscle formation.

METHODS

G. uralensis, Lic A, and Lic B were evaluated thoroughly using in silico, in vitro and in vivo approaches. In silico analyses included molecular docking, and dynamics simulations of these compounds with MSTN. Protein-protein docking was carried out for MSTN, as well as for the docked complex of MSTN-Lic with its receptor, activin type IIB receptor (ACVRIIB). Subsequent in vitro studies used C2C12 cell lines and primary mouse muscle stem cells to acess the cell proliferation and differentiation of normal and aged cells, levels of MSTN, Atrogin 1, and MuRF1, and plasma MSTN concentrations, employing techniques such as western blotting, immunohistochemistry, immunocytochemistry, cell proliferation and differentiation assays, and real-time RT-PCR. Furthermore, in vivo experiments using mouse models focused on measuring muscle fiber diameters.

RESULTS

CWE of G. uralensis and two of its components, namely Lic A and B, promote myoblast proliferation and differentiation by inhibiting MSTN and reducing Atrogin1 and MuRF1 expressions and MSTN protein concentration in serum. In silico interaction analysis revealed that Lic A (binding energy -6.9 Kcal/mol) and B (binding energy -5.9 Kcal/mol) bind to MSTN and reduce binding between it and ACVRIIB, thereby inhibiting downstream signaling. The experimental analysis, which involved both in vitro and in vivo studies, demonstrated that the levels of MSTN, Atrogin 1, and MuRF1 were decreased when G. uralensis CWE, Lic A, or Lic B were administered into mice or treated in the mouse primary muscle satellite cells (MSCs) and C2C12 myoblasts. The diameters of muscle fibers increased in orally treated mice, and the differentiation and proliferation of C2C12 cells were enhanced. G. uralensis CWE, Lic A, and Lic B also promoted cell proliferation in aged cells, suggesting that they may have anti-muslce aging properties. They also reduced the expression and phosphorylation of SMAD2 and SMAD3 (MSTN downstream effectors), adding to the evidence that MSTN is inhibited.

CONCLUSION

These findings suggest that CWE and its active constituents Lic A and Lic B have anti-mauscle aging potential. They also have the potential to be used as natural inhibitors of MSTN and as therapeutic options for disorders associated with muscle atrophy.

Mitochondrial involvement in sarcopenia

Sarcopenia lowers the quality-of-life for millions of people across the world, as accelerated loss of skeletal muscle mass and function contributes to both age- and disease-related frailty. Physical activity remains the only proven therapy for sarcopenia to date, but alternatives are much sought after to manage this progressive muscle disorder in individuals who are unable to exercise. Mitochondria have been widely implicated in the etiology of sarcopenia and are increasingly suggested as attractive therapeutic targets to help restore the perturbed balance between protein synthesis and breakdown that underpins skeletal muscle atrophy. Reviewing current literature, we note that mitochondrial bioenergetic changes in sarcopenia are generally interpreted as intrinsic dysfunction that renders muscle cells incapable of making sufficient ATP to fuel protein synthesis. Based on the reported mitochondrial effects of therapeutic interventions, however, we argue that the observed bioenergetic changes may instead reflect an adaptation to pathologically decreased energy expenditure in sarcopenic muscle. Discrimination between these mechanistic possibilities will be crucial for improving the management of sarcopenia.

Myostatin and CXCL11 promote nervous tissue macrophages to maintain osteoarthritis pain

Pain is the most debilitating symptom of knee osteoarthritis (OA) that can even persist after total knee replacement. The severity and duration of pain do not correlate well with joint tissue alterations, suggesting other mechanisms may drive pain persistence in OA. Previous work identified that macrophages accumulate in the dorsal root ganglia (DRG) containing the somas of sensory neurons innervating the injured knee joint in a mouse OA model and acquire a M1-like phenotype to maintain pain. Here we aimed to unravel the mechanisms that govern DRG macrophage accumulation and programming. The accumulation of F4/80+iNOS+ (M1-like) DRG macrophages was detectable at day 3 after mono-iodoacetate (MIA)-induced OA in the mouse. Depletion of macrophages prior to induction of OA resolved pain-like behaviors by day 7 without affecting the initial development of pain-like behaviors. Analysis of DRG transcript identified CXCL11 and myostatin. CXCL11 and myostatin were increased at 3 weeks post OA induction, with CXCL11 expression partially localized in satellite glial cells and myostatin in sensory neurons. Blocking CXCL11 or myostatin prevented the persistence of OA pain, without affecting the initiation of pain. CXCL11 neutralization reduced the number of total and F4/80+iNOS+ DRG macrophages, whilst myostatin inhibition diminished the programming of F4/80+iNOS+ DRG macrophages. Intrathecal injection of recombinant CXCL11 did not induce pain-associated behaviors. In contrast, intrathecal myostatin increased the number of F4/80+iNOS+ DRG macrophages concurrent with the development of mechanical hypersensitivity that was prevented by macrophages depletion or CXCL11 blockade. Finally, myostatin inhibition during established OA, resolved pain and F4/80+iNOS+ macrophage accumulation in the DRG. In conclusion, DRG macrophages maintain OA pain, but are not required for the induction of OA pain. Myostatin is a key ligand in neuro-immune communication that drives the persistence of pain in OA through nervous tissue macrophages and represent a novel therapeutic target for the treatment of OA pain.

Frailty in end-stage liver disease: Understanding pathophysiology, tools for assessment, and strategies for management

Frailty and sarcopenia are frequently observed in patients with end-stage liver disease. Frailty is a complex condition that arises from deteriorations across various physiological systems, including the musculoskeletal, cardiovascular, and immune systems, resulting in a reduced ability of the body to withstand stressors. This condition is associated with declined resilience and increased vulnerability to negative outcomes, including disability, hospitalization, and mortality. In cirrhotic patients, frailty is influenced by multiple factors, such as hyperammonemia, hormonal imbalance, malnutrition, ascites, hepatic encephalopathy, and alcohol intake. Assessing frailty is crucial in predicting morbidity and mortality in cirrhotic patients. It can aid in making critical decisions regarding patients' eligibility for critical care and transplantation. This, in turn, can guide the development of an individualized treatment plan for each patient with cirrhosis, with a focus on prioritizing exercise, proper nutrition, and appropriate treatment of hepatic complications as the primary lines of treatment. In this review, we aim to explore the topic of frailty in liver diseases, with a particular emphasis on pathophysiology, clinical assessment, and discuss strategies for preventing frailty through effective treatment of hepatic complications. Furthermore, we explore novel assessment and management strategies that have emerged in recent years, including the use of wearable technology and telemedicine.

Myostatin inhibitory peptides in sports drug testing

Across species, skeletal muscle mass is negatively regulated by the TGF-β cytokine myostatin (MSTN). Inhibitors of this growth factor and its signaling pathways are therefore not only promising therapeutics for muscular diseases but also potential performance-enhancing agents in sports. Within this study, protein precipitation and liquid chromatography high-resolution tandem mass spectrometry (LC-HRMS/MS) were employed to develop a detection method for six novel MSTN inhibitory peptides derived from the regulatory MSTN propeptide and the natural MSTN inhibitor follistatin (FST) from doping control serum samples. The approach was comprehensively characterized and found to allow for a specific detection down to concentrations of 3-9 ng/mL. Moreover, several potential metabolites of the drug candidates referred to as DF-3, DF-25, and Peptide 7 were identified as valuable complementary analytical targets for doping control analytical assays. Overall, the acquired data pave the way for an implementation of MSTN inhibitory peptides into routine sports drug testing. Even though no drug candidate has obtained clinical approval yet, a proactive development of detection assays is of utmost importance to deter athletes from misusing such compounds, which are readily available for research purposes and on the black market.

Ginsenoside Rg5 promotes muscle regeneration via p38MAPK and Akt/mTOR signaling

Background

Skeletal muscles play a key role in physical activity and energy metabolism. The loss of skeletal muscle mass can cause problems related to metabolism and physical activity. Studies are being conducted to prevent such diseases by increasing the mass and regeneration capacity of muscles. Ginsenoside Rg5 has been reported to exhibit a broad range of pharmacological activities. However, studies on the effects of Rg5 on muscle differentiation and growth are scarce.

Methods

To investigate the effects of Rg5 on myogenesis, C2C12 myoblasts were induced to differentiate with Rg5, followed by immunoblotting, immunostaining, and qRT-PCR for myogenic markers and promyogenic signaling (p38MAPK). Immunoprecipitation confirmed that Rg5 increased the interaction between MyoD and E2A via p38MAPK. To investigate the effects of Rg5 on prevention of muscle mass loss, C2C12 myotubes were treated with dexamethasone to induce muscle atrophy. Immunoblotting, immunostaining, and qRT-PCR were performed for myogenic markers, Akt/mTOR signaling for protein synthesis, and atrophy-related genes (Atrogin-1 and MuRF1).

Results

Rg5 promoted C2C12 myoblast differentiation through phosphorylation of p38MAPK and MyoD/E2A heterodimerization. Furthermore, Rg5 stimulated C2C12 myotube hypertrophy via phosphorylation of Akt/mTOR. Phosphorylation of Akt induces FoxO3a phosphorylation, which reduces the expression of Atrogin-1 and MuRF1.

Conclusion

This study provides an understanding of how Rg5 promotes myogenesis and hypertrophy and prevents dexamethasone-induced muscle atrophy. The study is the first, to the best of our knowledge, to show that Rg5 promotes muscle regeneration and to suggest that Rg5 can be used for therapeutic intervention of muscle weakness and atrophy, including cancer cachexia.

Systematic Myostatin Expression Screening Platform for Identification and Evaluation of Myogenesis-Related Phytogenic in Pigs

Skeletal muscle growth in livestock impacts meat quantity and quality. Concerns arise because certain feed additives, like beta-agonists, may affect food safety. Skeletal muscle is a specialized tissue consisting of nondividing and multinucleated muscle fibers. Myostatin (MSTN), a protein specific to skeletal muscle, is secreted and functions as a negative regulator of muscle mass by inhibiting the proliferation and differentiation of myoblasts. To enhance livestock muscle growth, phytogenic feed additives could be an alternative as they inhibit MSTN activity. The objective of this study was to establish a systematic screening platform using MSTN activity to evaluate phytogenics, providing scientific evidence of their assessment and potency. In this study, we established a screening platform to monitor myostatin promoter activity in rat L8 myoblasts. Extract of Glycyrrhiza uralensis (GUE), an oriental herbal medicine, was identified through this screening platform, and the active fractions of GUE were identified using a process-scale liquid column chromatography system. For in vivo study, GUE as a feed additive was investigated in growth-finishing pigs. The results showed that GUE significantly increased body weight, carcass weight, and lean content in pigs. Microbiota analysis indicated that GUE did not affect the composition of gut microbiota in pigs. In summary, this established rodent myoblast screening platform was used to identify a myogenesis-related phytogenic, GUE, and further demonstrated that the active fractions and compounds inhibited MSTN expression. These findings suggest a novel application for GUE in growth performance enhancement through modulation of MSTN expression. Moreover, this well-established screening platform holds significant potential for identifying and assessing a diverse range of phytogenics that contribute to the process of myogenesis.

Cancer Cachexia: Underlying Mechanisms and Potential Therapeutic Interventions

Cancer cachexia, a multifactorial metabolic syndrome developed during malignant tumor growth, is characterized by an accelerated loss of body weight accompanied by the depletion of skeletal muscle mass. This debilitating condition is associated with muscle degradation, impaired immune function, reduced functional capacity, compromised quality of life, and diminished survival in cancer patients. Despite the lack of the known capability of fully reversing or ameliorating this condition, ongoing research is shedding light on promising preclinical approaches that target the disrupted mechanisms in the pathophysiology of cancer cachexia. This comprehensive review delves into critical aspects of cancer cachexia, including its underlying pathophysiological mechanisms, preclinical models for studying the progression of cancer cachexia, methods for clinical assessment, relevant biomarkers, and potential therapeutic strategies. These discussions collectively aim to contribute to the evolving foundation for effective, multifaceted counteractive strategies against this challenging condition.

Silver electroceutical technology to treat sarcopenia

While the world is rapidly transforming into a superaging society, pharmaceutical approaches to treat sarcopenia have hitherto not been successful due to their insufficient efficacy and failure to specifically target skeletal muscle cells (skMCs). Although electrical stimulation (ES) is emerging as an alternative intervention, its efficacy toward treating sarcopenia remains unexplored. In this study, we demonstrate a silver electroceutical technology with the potential to treat sarcopenia. First, we developed a high-throughput ES screening platform that can simultaneously stimulate 15 independent conditions, while utilizing only a small number of human-derived primary aged/young skMCs (hAskMC/hYskMC). The in vitro screening showed that specific ES conditions induced hypertrophy and rejuvenation in hAskMCs, and the optimal ES frequency in hAskMCs was different from that in hYskMCs. When applied to aged mice in vivo, specific ES conditions improved the prevalence and thickness of Type IIA fibers, along with biomechanical attributes, toward a younger skMC phenotype. This study is expected to pave the way toward an electroceutical treatment for sarcopenia with minimal side effects and help realize personalized bioelectronic medicine.

Serum Myostatin among Excessive Drinkers

Myostatin acts as a negative regulator of muscle growth. Its effect on fat mass is subject to debate. Among alcoholics, there is a high prevalence of muscle atrophy, and increased fat deposition has been also described in these patients. Myostatin could be involved in these alterations, but its relationships with body composition have been scarcely studied in alcoholic patients. To analyze the behavior of myostatin among alcoholics and its relationship with alcohol intake, liver function, and body composition. We investigated serum myostatin in 59 male patients and 18 controls. Patients were all heavy drinkers admitted with organic complications related to excessive ethanol ingestion. Densitometry analysis was used to assess body composition in 46 patients. Handgrip was assessed in 51 patients. Patients showed lower myostatin values than controls (Z = 3.80; p < 0.001). There was a significant relationship between myostatin and fat at the right leg (ρ = 0.32; p = 0.028), left leg (ρ = 0.32; p = 0.028), trunk (ρ = 0.31, p = 0.038), total fat proport ion (ρ = 0.33, p = 0.026), and gynecoid fat distribution (ρ = 0.40, p = 0.006) but not with lean mass (total lean ρ = 0.07; p = 0.63; trunk lean ρ = 0.03; p = 0.85; lower limbs ρ = 0.08; p = 0.58; upper limbs ρ = 0.04 p = 0.82; android ρ = 0.02; p = 0.88, or gynoid lean mass ρ = 0.20; p = 0.19). In total, 80.43% of patients showed at least one criterion of osteosarcopenic adiposity (OSA). Myostatin was related to OSA obesity. We also observed higher myostatin values among patients with body mass index > 30 kg/m². Serum myostatin was lower among excessive drinkers, and it was related to increased fat deposition among these patients but not to lean mass, handgrip, or bone mineral density.

Induction of ATF4-Regulated Atrogenes Is Uncoupled from Muscle Atrophy during Disuse in Halofuginone-Treated Mice and in Hibernating Brown Bears

Activating transcription factor 4 (ATF4) is involved in muscle atrophy through the overexpression of some atrogenes. However, it also controls the transcription of genes involved in muscle homeostasis maintenance. Here, we explored the effect of ATF4 activation by the pharmacological molecule halofuginone during hindlimb suspension (HS)-induced muscle atrophy. Firstly, we reported that periodic activation of ATF4-regulated atrogenes (Gadd45a, Cdkn1a, and Eif4ebp1) by halofuginone was not associated with muscle atrophy in healthy mice. Secondly, halofuginone-treated mice even showed reduced atrophy during HS, although the induction of the ATF4 pathway was identical to that in untreated HS mice. We further showed that halofuginone inhibited transforming growth factor-β (TGF-β) signalling, while promoting bone morphogenetic protein (BMP) signalling in healthy mice and slightly preserved protein synthesis during HS. Finally, ATF4-regulated atrogenes were also induced in the atrophy-resistant muscles of hibernating brown bears, in which we previously also reported concurrent TGF-β inhibition and BMP activation. Overall, we show that ATF4-induced atrogenes can be uncoupled from muscle atrophy. In addition, our data also indicate that halofuginone can control the TGF-β/BMP balance towards muscle mass maintenance. Whether halofuginone-induced BMP signalling can counteract the effect of ATF4-induced atrogenes needs to be further investigated and may open a new avenue to fight muscle atrophy. Finally, our study opens the way for further studies to identify well-tolerated chemical compounds in humans that are able to fine-tune the TGF-β/BMP balance and could be used to preserve muscle mass during catabolic situations.

Skeletal Muscle Complications in Chronic Kidney Disease

PURPOSE OF REVIEW

To provide an overview of the recent literature investigating the pathophysiology of skeletal muscle changes, interventions for skeletal muscle, and effects of exercise in chronic kidney disease (CKD).

RECENT FINDINGS

There are multiple CKD-related changes that negatively impact muscle size and function. However, the variability in the assessment of muscle size, in particular, hinders the ability to truly understand the impact it may have in CKD. Exercise interventions to improve muscle size and function demonstrate inconsistent responses that warrant further investigation to optimize exercise prescription. Despite progress in the field, there are many gaps in the knowledge of the pathophysiology of sarcopenia of CKD. Identifying these gaps will help in the design of interventions that can be tested to target muscle loss and its consequences such as impaired mobility, falls, and poor quality of life in patients with CKD.

The Effects of Dietary Supplements, Nutraceutical Agents, and Physical Exercise on Myostatin Levels: Hope or Hype?

Myostatin, a secreted growth factor belonging to the transforming growth factor β (TGF-β) family, performs a role in hindering muscle growth by inhibiting protein kinase B (Akt) phosphorylation and the associated activation of hypertrophy pathways (e.g., IGF-1/PI3K/Akt/mTOR pathway). In addition to pharmacological agents, some supplements and nutraceutical agents have demonstrated modulatory effects on myostatin levels; however, the clinical magnitude must be appraised with skepticism before translating the mechanistic effects into muscle hypertrophy outcomes. Here, we review the effects of dietary supplements, nutraceutical agents, and physical exercise on myostatin levels, addressing the promise and pitfalls of relevant randomized clinical trials (RCTs) to draw clinical conclusions. RCTs involving both clinical and sports populations were considered, along with wasting muscle disorders (e.g., sarcopenia) and resistance training-induced muscle hypertrophy, irrespective of disease status. Animal models were considered only to expand the mechanisms of action, and observational data were consulted to elucidate potential cutoff values. Collectively, the effects of dietary supplements, nutraceutical agents, and physical exercise on myostatin mRNA expression in skeletal muscle and serum myostatin levels are not uniform, and there may be reductions, increases, or neutral effects. Large amounts of research using resistance protocols shows that supplements or functional foods do not clearly outperform placebo for modulating myostatin levels. Thus, despite some biological hope in using supplements or certain functional foods to decrease myostatin levels, caution must be exercised not to propagate the hope of the food supplement market, select health professionals, and laypeople.

Insight into the role of myokines and myogenic regulatory factors under hypobaric hypoxia induced skeletal muscle loss

Aim: The present study aimed to analyze the role of myokines and the regeneration capacity of skeletal muscle during chronic hypobaric hypoxia (HH).Method: Male SD rats were exposed to HH for 1d, 3d, and 7d.Results: Exposure to HH enhanced the levels of decorin, irisin, IL-6 and IL-15 till 3 days of hypoxia and on 7 day of exposure, no significant changes were observed in relation to control. A significant upregulation in myostatin, AMPK, SMAD3, SMAD4, FOXO-1, MURF-1 expression was observed with prolonged HH exposure as compared to normoxic control. Further, myogenesis-related markers, PAX-7, Cyclin D1, and MYOG were downregulated during chronic HH exposure in comparison to control. Energy metabolism regulators such as SIRT1, PGC-1α, and GLUT-4, were also increased on 1d HH exposure that showed a declining trend on chronic HH exposure.Conclusion: These results indicated the impairment in the levels of myokines and myogenesis during prolonged hypoxia. Chronic HH exposure enhanced the levels of myostatin and reduced the regeneration or repair capacity of the skeletal muscles. Myokine levels could be a predictive biomarker for evaluating skeletal muscle performance and loss at high altitudes.

Molecular Mechanisms of Inflammation in Sarcopenia: Diagnosis and Therapeutic Update

Sarcopenia is generally an age-related condition that directly impacts the quality of life. It is also related to chronic diseases such as metabolic dysfunction associated with diabetes and obesity. This means that everyone will be vulnerable to sarcopenia at some point in their life. Research to find the precise molecular mechanisms implicated in this condition can increase knowledge for the better prevention, diagnosis, and treatment of sarcopenia. Our work gathered the most recent research regarding inflammation in sarcopenia and new therapeutic agents proposed to target its consequences in pyroptosis and cellular senescence. Finally, we compared dual X-ray absorptiometry (DXA), magnetic resonance imaging (MRI), and ultrasound (US) as imaging techniques to diagnose and follow up on sarcopenia, indicating their respective advantages and disadvantages. Our goal is for the scientific evidence presented here to help guide future research to understand the molecular mechanisms involved in sarcopenia, new treatment strategies, and their translation into clinical practice.

Effects of Muscles on Bone Metabolism—with a Focus on Myokines

Skeletal muscles and bones, the largest tissues in the body of a non-obese person, comprise the musculoskeletal system, which allows mobility and protects internal organs. Although muscles and bones are closely related throughout life, observations during development and aging and in human and animal disuse models have revealed the synchronization of tissue mass such that muscle phenotype changes precede alterations in bone mineral density and strength. This review discussed that mechanical forces, which have been the traditional research focus, are not the only mechanism by which muscle-derived signals may affect bone metabolism and emphasized the significance of skeletal muscles as an endocrine organ that secretes bone-regulatory factors. Consequently, both mechanical and biochemical aspects should be considered to fully understand muscle–bone crosstalk. This review also suggested that specific myokines could be ideal therapeutic targets for osteoporosis to both increase bone formation and reduce bone resorption; moreover, these myokines could also be potential circulating biomarkers to predict musculoskeletal health.

Myostatin and its Regulation: A Comprehensive Review of Myostatin Inhibiting Strategies

Myostatin (MSTN) is a well-reported negative regulator of muscle growth and a member of the transforming growth factor (TGF) family. MSTN has important functions in skeletal muscle (SM), and its crucial involvement in several disorders has made it an important therapeutic target. Several strategies based on the use of natural compounds to inhibitory peptides are being used to inhibit the activity of MSTN. This review delivers an overview of the current state of knowledge about SM and myogenesis with particular emphasis on the structural characteristics and regulatory functions of MSTN during myogenesis and its involvements in various muscle related disorders. In addition, we review the diverse approaches used to inhibit the activity of MSTN, especially in silico approaches to the screening of natural compounds and the design of novel short peptides derived from proteins that typically interact with MSTN.

Randomized Phase 2 Study of ACE-083 in Patients With Charcot-Marie-Tooth Disease

BACKGROUND AND OBJECTIVES

The goal of this work was to determine whether locally acting ACE-083 is safe and well tolerated and increases muscle volume, motor function, and quality of life (QoL) in adults with Charcot-Marie-Tooth disease (CMT) type 1.

METHODS

This phase 2 study enrolled adults with CMT1 or CMTX (N = 63). Part 1 was open label and evaluated the safety and tolerability of different dose levels of ACE-083 for use in part 2. Part 2 was a randomized, placebo-controlled, 6-month study of 240 mg/muscle ACE-083 injected bilaterally into the tibialis anterior muscle, followed by a 6-month, open-label extension in which all patients received ACE-083. Pharmacodynamic endpoints included total muscle volume (TMV; primary endpoint), contractile muscle volume (CMV), and fat fraction. Additional secondary endpoints included 6-minute walk test, 10-m walk/run, muscle strength, and QoL. Safety was assessed with treatment-emergent adverse events (TEAEs) and clinical laboratory tests.

RESULTS

In part 1 (n = 18), ACE-083 was generally safe and well tolerated at all dose levels, with no serious adverse events, TEAEs of grade 3 or greater, or death reported. In part 2 (n = 45 enrolled, n = 44 treated), there was significantly greater change in TMV with ACE-083 compared with placebo (least-squares mean difference 13.5%; p = 0.0096). There was significant difference between ACE-083 and placebo for CMV and change in ankle dorsiflexion strength. Fat fraction and all other functional outcomes were not significantly improved by ACE-083. Moderate to mild injection-site reactions were the most common TEAEs.

DISCUSSION

Despite significantly increased TMV and CMV, patients with CMT receiving ACE-083 in tibialis anterior muscles did not demonstrate greater functional improvement compared with those receiving placebo.

TRIAL REGISTRATION INFORMATION

Clinical Trials Registration: NCT03124459.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that intramuscular ACE-083 is safe and well tolerated and increases total muscle volume after 6 months of treatment in adults with CMT1 or CMTX.

MIF1 and MIF2 Myostatin Peptide Inhibitors as Potent Muscle Mass Regulators

The use of peptides as drugs has progressed over time and continues to evolve as treatment paradigms change and new drugs are developed. Myostatin (MSTN) inhibition therapy has shown great promise for the treatment of muscle wasting diseases. Here, we report the MSTN-derived novel peptides MIF1 (10-mer) and MIF2 (10-mer) not only enhance myogenesis by inhibiting MSTN and inducing myogenic-related markers but also reduce adipogenic proliferation and differentiation by suppressing the expression of adipogenic markers. MIF1 and MIF2 were designed based on in silico interaction studies between MSTN and its receptor, activin type IIB receptor (ACVRIIB), and fibromodulin (FMOD). Of the different modifications of MIF1 and MIF2 examined, _Ac-MIF1 and _Ac-MIF2-_NH2 significantly enhanced cell proliferation and differentiation as compared with non-modified peptides. Mice pretreated with _Ac-MIF1 or _Ac-MIF2-_NH2 prior to cardiotoxin-induced muscle injury showed more muscle regeneration than non-pretreated controls, which was attributed to the induction of myogenic genes and reduced MSTN expression. These findings imply that _Ac-MIF1 and _Ac-MIF2-_NH2 might be valuable therapeutic agents for the treatment of muscle-related diseases.

The Evolution of Complex Muscle Cell In Vitro Models to Study Pathomechanisms and Drug Development of Neuromuscular Disease

Many neuromuscular disease entities possess a significant disease burden and therapeutic options remain limited. Innovative human preclinical models may help to uncover relevant disease mechanisms and enhance the translation of therapeutic findings to strengthen neuromuscular disease precision medicine. By concentrating on idiopathic inflammatory muscle disorders, we summarize the recent evolution of the novel in vitro models to study disease mechanisms and therapeutic strategies. A particular focus is laid on the integration and simulation of multicellular interactions of muscle tissue in disease phenotypes in vitro. Finally, the requirements of a neuromuscular disease drug development workflow are discussed with a particular emphasis on cell sources, co-culture systems (including organoids), functionality, and throughput.

Myostatin/Activin Receptor Ligands in Muscle and the Development Status of Attenuating Drugs

Muscle wasting disease indications are among the most debilitating and often deadly noncommunicable disease states. As a comorbidity, muscle wasting is associated with different neuromuscular diseases and myopathies, cancer, heart failure, chronic pulmonary and renal diseases, peripheral neuropathies, inflammatory disorders, and, of course, musculoskeletal injuries. Current treatment strategies are relatively ineffective and can at best only limit the rate of muscle degeneration. This includes nutritional supplementation and appetite stimulants as well as immunosuppressants capable of exacerbating muscle loss. Arguably, the most promising treatments in development attempt to disrupt myostatin and activin receptor signaling because these circulating factors are potent inhibitors of muscle growth and regulators of muscle progenitor cell differentiation. Indeed, several studies demonstrated the clinical potential of "inhibiting the inhibitors," increasing muscle cell protein synthesis, decreasing degradation, enhancing mitochondrial biogenesis, and preserving muscle function. Such changes can prevent muscle wasting in various disease animal models yet many drugs targeting this pathway failed during clinical trials, some from serious treatment-related adverse events and off-target interactions. More often, however, failures resulted from the inability to improve muscle function despite preserving muscle mass. Drugs still in development include antibodies and gene therapeutics, all with different targets and thus, safety, efficacy, and proposed use profiles. Each is unique in design and, if successful, could revolutionize the treatment of both acute and chronic muscle wasting. They could also be used in combination with other developing therapeutics for related muscle pathologies or even metabolic diseases.

The Role of Lifestyle Intervention, in Addition to Drugs, for Diabetic Kidney Disease with Sarcopenic Obesity

Diabetic kidney disease is the leading cause of end-stage renal disease in developing and developed countries. The growing prevalence and clinical challenges of sarcopenic obesity have been associated with the frailty and disability of diabetic kidney disease. It has been reported that insulin resistance, chronic inflammation, enhanced oxidative stress and lipotoxicity contribute to the pathophysiology of muscle loss and visceral fat accumulation. Sarcopenic obesity, which is diagnosed with dual-energy X-ray absorptiometry, is associated with worse outcomes in kidney disease. Growing evidence indicates that adherence to healthy lifestyles, including low protein diet, proper carbohydrate control, vitamin D supplement, and regular physical training, has been shown to improve clinical prognosis. Based on the higher risk of sarcopenic-obesity-related renal function decline, it has led to the exploration and investigation of the pathophysiology, clinical aspects, and novel approach of these controversial issues in daily practice.

Clinical Significance of Serum Zinc Levels on the Development of Sarcopenia in Cirrhotic Patients

BACKGROUND/AIM

Sarcopenia increases the mortality in patients with cirrhosis. Approximately 60% of zinc is accumulated in skeletal muscle. We aimed to determine the role of subclinical zinc deficiency on sarcopenia development in patients with cirrhosis.

PATIENTS AND METHODS

We enrolled 151 patients with cirrhosis and divided them into the group with normal serum zinc levels (Group N: 80-130 μg/dl; n=38) and group with subclinical zinc deficiency (Group D: <80 μg/dl; n=113). The risk factors for sarcopenia were then investigated.

RESULTS

Group D had more sarcopenia cases than Group N (31.0% vs. 13.2%). In group D, HGS exhibited a weakly positive but significant correlation with serum zinc levels (R=0.287, p=0.00212), serum zinc levels negatively correlated with both ammonia and myostatin levels (R=-0.254, p=0.0078; R=-0.33, p<0.01), and low zinc levels were independently associated with sarcopenia development.

CONCLUSION

Patients with cirrhosis showing subclinical zinc deficiency have a significantly higher risk of developing sarcopenia.

Adeno-associated virus-mediated expression of an inactive CaMKIIβ mutant enhances muscle mass and strength in mice

A concurrent reduction in muscle mass and strength is frequently observed in numerous conditions, including neuromuscular disease, ageing, and muscle inactivity due to limb immobilization or prolonged bed rest. Thus, identifying the molecular mechanisms that control skeletal muscle mass and strength is fundamental for developing interventions aimed at counteracting muscle loss (muscle atrophy). It was recently reported that muscle atrophy induced by denervation of motor nerves was associated with increased expression of Ca2+/calmodulin-dependent protein serine/threonine kinase II β (CaMKIIβ) in muscle. In addition, treatment with KN-93 phosphate, which inhibits CaMKII-family kinases, partly suppressed denervation-induced muscle atrophy. Therefore, to test a possible role for CaMKIIβ in muscle mass regulation, we generated and injected recombinant adeno-associated virus (AAV) vectors encoding wild-type (AAV-WT), inactive (AAV-K43 M), or constitutively active (AAV-T287D) CaMKIIβ into the left hindlimb tibialis anterior muscle of mice at three months of age. Although AAV-WT infection induced expression of exogenous CaMKIIβ in the hindlimb muscle, no significant changes in muscle mass and strength were observed. By contrast, AAV-K43 M or AAV-T287D infection induced exogenous expression of the corresponding mutants and significantly increased or decreased the muscle mass and strength of the infected hind limb, respectively. Together, these findings demonstrate the potential of CaMKIIβ as a novel therapeutic target for enhancing muscle mass and strength.

Therapeutic approaches to preserve the musculature in Duchenne Muscular Dystrophy: The importance of the secondary therapies

Muscular dystrophies (MDs) are heterogeneous diseases, characterized by primary wasting of skeletal muscle, which in severe cases, such as Duchenne Muscular Dystrophy (DMD), leads to wheelchair dependency, respiratory failure, and premature death. Research is ongoing to develop efficacious therapies, particularly for DMD. Most of the efforts, currently focusing on correcting or restoring the primary defect of MDs, are based on gene-addition, exon-skipping, stop codon read-through, and genome-editing. Although promising, most of them revealed several practical limitations. Shared knowledge in the field is that, in order to be really successful, any therapeutic approach has to rely on spared functional muscle tissue, restricting the number of patients eligible for clinical trials to the youngest and less compromised individuals. In line with this, many therapeutic strategies aim to preserve muscle tissue and function. This Review outlines the most interesting and recent studies addressing the secondary outcomes of DMD and how to better deliver the therapeutic agents. In the future, the effective treatment of DMD will likely require combinations of therapies addressing both the primary genetic defect and its consequences.

Irisin Serum Levels and Skeletal Muscle Assessment in a Cohort of Charcot-Marie-Tooth Patients

BACKGROUND

Charcot-Marie-Tooth (CMT) indicates a group of inherited polyneuropathies whose clinical phenotypes primarily include progressive distal weakness and muscle atrophy. Compelling evidence showed that the exercise-mimetic myokine irisin protects against muscle wasting in an autocrine manner, thus possibly preventing the onset of musculoskeletal atrophy. Therefore, we sought to determine if irisin serum levels correlate with biochemical and muscle parameters in a cohort of CMT patients.

METHODS

This cohort study included individuals (N=20) diagnosed with CMT disease. Irisin and biochemical markers were quantified in sera. Skeletal muscle mass (SMM) was evaluated by bioelectric impedance analysis, muscle strength by handgrip, and muscle quality was derived from muscle strength and muscle mass ratio.

RESULTS

CMT patients (m/f, 12/8) had lower irisin levels than age and sex matched healthy subjects (N=20) (6.51 ± 2.26 vs 9.34 ± 3.23 μg/ml; p=0.003). SMM in CMT patients was always lower compared to SMM reference values reported in healthy Caucasian population matched for age and sex. Almost the totality of CMT patients (19/20) showed low muscle quality and therefore patients were evaluated on the basis of muscle strength. Irisin was lower in presence of pathological compared to normal muscle strength (5.56 ± 1.26 vs 7.67 ± 2.72 μg/ml; p=0.03), and directly correlated with the marker of bone formation P1PN (r= 0.669; 95%CI 0.295 to 0.865; p=0.002), but inversely correlated with Vitamin D (r=-0.526; 95%CI -0,791 to -0,095; p=0.017). Surprisingly, in women, irisin levels were higher than in men (7.31 ± 2.53 vs 5.31 ± 1.02 μg/ml, p=0.05), and correlated with both muscle strength (r=0.759; 95%CI 0.329 to 0.929; p=0.004) and muscle quality (r=0.797; 95%CI 0.337 to 0.950; p=0.006).

CONCLUSION

Our data demonstrate lower irisin levels in CMT patients compared to healthy subjects. Moreover, among patients, we observed, significantly higher irisin levels in women than in men, despite the higher SMM in the latter. Future studies are necessary to establish whether, in this clinical contest, irisin could represent a marker of the loss of muscle mass and strength and/or bone loss.

Therapeutic Implications of miRNAs for Muscle-Wasting Conditions

MicroRNAs (miRNAs) are small, non-coding RNA molecules that are mainly involved in translational repression by binding to specific messenger RNAs. Recently, miRNAs have emerged as biomarkers, relevant for a multitude of pathophysiological conditions, and cells can selectively sort miRNAs into extracellular vesicles for paracrine and endocrine effects. In the overall context of muscle-wasting conditions, a multitude of miRNAs has been implied as being responsible for the typical dysregulation of anabolic and catabolic pathways. In general, chronic muscle disorders are associated with the main characteristic of a substantial loss in muscle mass. Muscular dystrophies (MDs) are a group of genetic diseases that cause muscle weakness and degeneration. Typically, MDs are caused by mutations in those genes responsible for upholding the integrity of muscle structure and function. Recently, the dysregulation of miRNA levels in such pathological conditions has been reported. This revelation is imperative for both MDs and other muscle-wasting conditions, such as sarcopenia and cancer cachexia. The expression levels of miRNAs have immense potential for use as potential diagnostic, prognostic and therapeutic biomarkers. Understanding the role of miRNAs in muscle-wasting conditions may lead to the development of novel strategies for the improvement of patient management.

Advances in research on pharmacotherapy of sarcopenia

Sarcopenia is a comprehensive degenerative disease with the progressive loss of skeletal muscle mass with age, accompanied by the loss of muscle strength and muscle dysfunction. As a new type of senile syndrome, sarcopenia seriously threatens the health of the elderly. The first-line treatment for sarcopenia is exercise and nutritional supplements. However, pharmacotherapy will provide more reliable and sustainable interventions in geriatric medicine. Clinical trials of new drugs targeting multiple molecules are ongoing. This article focuses on the latest progress in pharmacotherapeutic approaches of sarcopenia in recent years by comprehensively reviewing the clinical outcomes of the existing and emerging pharmacotherapies as well as the molecular mechanisms underlying their therapeutic benefits and side effects.

Receptor-Mediated Muscle Homeostasis as a Target for Sarcopenia Therapeutics

Sarcopenia is a disease characterized by age-related decline of skeletal muscle mass and function. The molecular mechanisms of the pathophysiology of sarcopenia form a complex network due to the involvement of multiple interconnected signaling pathways. Therefore, signaling receptors are major targets in pharmacological strategies in general. To provide a rationale for pharmacological interventions for sarcopenia, we herein describe several druggable signaling receptors based on their role in skeletal muscle homeostasis and changes in their activity with aging. A brief overview is presented of the efficacy of corresponding drug candidates under clinical trials. Strategies targeting the androgen receptor, vitamin D receptor, Insulin-like growth factor-1 receptor, and ghrelin receptor primarily focus on promoting anabolic action using natural ligands or mimetics. Strategies involving activin receptors and angiotensin receptors focus on inhibiting catabolic action. This review may help to select specific targets or combinations of targets in the future.

Therapeutic aspects of cell signaling and communication in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a devastating chromosome X-linked disease that manifests predominantly in progressive skeletal muscle wasting and dysfunctions in the heart and diaphragm. Approximately 1/5000 boys and 1/50,000,000 girls suffer from DMD, and to date, the disease is incurable and leads to premature death. This phenotypic severity is due to mutations in the DMD gene, which result in the absence of functional dystrophin protein. Initially, dystrophin was thought to be a force transducer; however, it is now considered an essential component of the dystrophin-associated protein complex (DAPC), viewed as a multicomponent mechanical scaffold and a signal transduction hub. Modulating signal pathway activation or gene expression through epigenetic modifications has emerged at the forefront of therapeutic approaches as either an adjunct or stand-alone strategy. In this review, we propose a broader perspective by considering DMD to be a disease that affects myofibers and muscle stem (satellite) cells, as well as a disorder in which abrogated communication between different cell types occurs. We believe that by taking this systemic view, we can achieve safe and holistic treatments that can restore correct signal transmission and gene expression in diseased DMD tissues.

Targeting the Activin Receptor Signaling to Counteract the Multi-Systemic Complications of Cancer and Its Treatments

Muscle wasting, i.e., cachexia, frequently occurs in cancer and associates with poor prognosis and increased morbidity and mortality. Anticancer treatments have also been shown to contribute to sustainment or exacerbation of cachexia, thus affecting quality of life and overall survival in cancer patients. Pre-clinical studies have shown that blocking activin receptor type 2 (ACVR2) or its ligands and their downstream signaling can preserve muscle mass in rodents bearing experimental cancers, as well as in chemotherapy-treated animals. In tumor-bearing mice, the prevention of skeletal and respiratory muscle wasting was also associated with improved survival. However, the definitive proof that improved survival directly results from muscle preservation following blockade of ACVR2 signaling is still lacking, especially considering that concurrent beneficial effects in organs other than skeletal muscle have also been described in the presence of cancer or following chemotherapy treatments paired with counteraction of ACVR2 signaling. Hence, here, we aim to provide an up-to-date literature review on the multifaceted anti-cachectic effects of ACVR2 blockade in preclinical models of cancer, as well as in combination with anticancer treatments.

Novel myostatin-specific antibody enhances muscle strength in muscle disease models

Myostatin, a member of the transforming growth factor-β superfamily, is an attractive target for muscle disease therapy because of its role as a negative regulator of muscle growth and strength. Here, we describe a novel antibody therapeutic approach that maximizes the potential of myostatin-targeted therapy. We generated an antibody, GYM329, that specifically binds the latent form of myostatin and inhibits its activation. Additionally, via "sweeping antibody technology", GYM329 reduces or "sweeps" myostatin in the muscle and plasma. Compared with conventional anti-myostatin agents, GYM329 and its surrogate antibody exhibit superior muscle strength-improvement effects in three different mouse disease models. We also demonstrate that the superior efficacy of GYM329 is due to its myostatin specificity and sweeping capability. Furthermore, we show that a GYM329 surrogate increases muscle mass in normal cynomolgus monkeys without any obvious toxicity. Our findings indicate the potential of GYM329 to improve muscle strength in patients with muscular disorders.

The Failed Clinical Story of Myostatin Inhibitors against Duchenne Muscular Dystrophy: Exploring the Biology behind the Battle

Myostatin inhibition therapy has held much promise for the treatment of muscle wasting disorders. This is particularly true for the fatal myopathy, Duchenne Muscular Dystrophy (DMD). Following on from promising pre-clinical data in dystrophin-deficient mice and dogs, several clinical trials were initiated in DMD patients using different modality myostatin inhibition therapies. All failed to show modification of disease course as dictated by the primary and secondary outcome measures selected: the myostatin inhibition story, thus far, is a failed clinical story. These trials have recently been extensively reviewed and reasons why pre-clinical data collected in animal models have failed to translate into clinical benefit to patients have been purported. However, the biological mechanisms underlying translational failure need to be examined to ensure future myostatin inhibitor development endeavors do not meet with the same fate. Here, we explore the biology which could explain the failed translation of myostatin inhibitors in the treatment of DMD.