transforming-growth-factor-beta and Muscular-Atrophy

Transforming growth factor-beta (TGF-β) is part of a family of molecules that is present in many body tissues and performs many different functions. Evidence has been obtained from mice and human cancer patients with bony metastases and non-metastatic disease, as well as pediatric burn patients, that inflammation leads to bone resorption and release of TGF-β from the bone matrix with paracrine effects on muscle protein balance, possibly mediated by the generation of reactive oxygen species. Whether immobilization, which confounds the etiology of bone resorption in burn injury, also leads to the release of TGF-β from bone contributing to muscle wasting in other conditions is unclear. The use of anti-resorptive therapy in both metastatic cancer patients and pediatric burn patients has been successful in the prevention of muscle wasting, thereby creating an additional therapeutic niche for this class of drugs. The liberation of TGF-β may be one way in which bone helps to control muscle mass, but further investigation will be necessary to assess whether the rate of bone resorption is the determining factor for the release of TGF-β. Moreover, whether different resorptive conditions, such as immobilization and hyperparathyroidism, also involve TGF-β release in the pathogenesis of muscle wasting needs to be investigated.

Topics: Animals; Bone Resorption; Humans; Muscle Proteins; Muscular Atrophy; Reactive Oxygen Species; Transforming Growth Factor beta

Aging is broadly defined as the functional decline that occurs in all body systems. The accumulation of senescent cells is considered a hallmark of aging and thought to contribute to the aging pathologies. Transforming growth factor-β (TGF-β) is a pleiotropic cytokine that regulates a myriad of cellular processes and has important roles in embryonic development, physiological tissue homeostasis, and various pathological conditions. TGF-β exerts potent growth inhibitory activities in various cell types, and multiple growth regulatory mechanisms have reportedly been linked to the phenotypes of cellular senescence and stem cell aging in previous studies. In addition, accumulated evidence has indicated a multifaceted association between TGF-β signaling and aging-associated disorders, including Alzheimer's disease, muscle atrophy, and obesity. The findings regarding these diseases suggest that the impairment of TGF-β signaling in certain cell types and the upregulation of TGF-β ligands contribute to cell degeneration, tissue fibrosis, inflammation, decreased regeneration capacity, and metabolic malfunction. While the biological roles of TGF-β depend highly on cell types and cellular contexts, aging-associated changes are an important additional context which warrants further investigation to better understand the involvement in various diseases and develop therapeutic options. The present review summarizes the relationships between TGF-β signaling and cellular senescence, stem cell aging, and aging-related diseases.

Topics: Aging; Alzheimer Disease; Cell Proliferation; Cellular Senescence; Fibrosis; Hematopoietic Stem Cells; Homeostasis; Inflammation; Ligands; Mesenchymal Stem Cells; Muscular Atrophy; Obesity; Signal Transduction; Stem Cells; Transforming Growth Factor beta

To provide an overview and describe the mode of action of miRNAs recently implicated in muscle atrophy, and discuss the challenges to explore their potential as putative therapeutic targets in cachexia.. Recent work showed differentially expressed miRNAs in skeletal muscle of patients with cachexia-associated diseases. Studies using experimental models revealed miRNA regulation of the anabolic IGF-1 and catabolic TGF- β/myostatin pathways, and downstream protein synthesis and proteolysis signaling in control of muscle mass.. Cachexia is a complex metabolic condition associated with progressive body weight loss, wasting of skeletal muscle mass and decrease in muscle strength. MiRNAs play a central role in post-transcriptional gene regulation by targeting mRNAs, thereby coordinating and fine-tuning many cellular processes. MiRNA expression profiling studies of muscle biopsies have revealed differentially expressed miRNAs in patients with low muscle mass or cachexia. Evaluation in experimental models has revealed muscle atrophy, inhibition of protein synthesis and activation of proteolysis in response to modulation of specific miRNAs, termed 'atromiRs' in this review. These exciting findings call for further studies aimed at exploring the conservation of differentially expressed miRNAs across diseases accompanied by cachexia, identification of miRNA clusters and targets involved in muscle atrophy, and probing whether these miRNAs might be potential therapeutic targets for cachexia.

Topics: Animals; Cachexia; Gene Expression Regulation; Humans; Insulin-Like Growth Factor I; MicroRNAs; Muscle, Skeletal; Muscular Atrophy; Myostatin; Signal Transduction; Transforming Growth Factor beta

The transforming growth factor beta (TGFβ) superfamily comprises a large number of secreted proteins that regulate various fundamental biological processes underlying embryonic development and the postnatal regulation of many cell types and organs. Sequence similarities define two ligand subfamilies: the TGFβ/activin subfamily and the bone morphogenetic protein (BMP) subfamily. The discovery that myostatin, a member of the TGFβ/activin subfamily, negatively controls muscle mass attracted attention to this pathway. However, recent findings of a positive role for BMP-mediated signaling in muscle have challenged the model of how the TGFβ network regulates skeletal muscle phenotype. This review illustrates how this complex network integrates crosstalk among members of the TGFβ superfamily and downstream signaling elements to regulate muscle in health and disease.

Topics: Activin Receptors; Activins; Animals; Autophagy; Bone Morphogenetic Protein Receptors; Bone Morphogenetic Proteins; Humans; Hypertrophy; Mice, Knockout; Mice, Transgenic; Models, Biological; Muscle, Skeletal; Muscular Atrophy; Muscular Diseases; Protein Isoforms; Receptors, Transforming Growth Factor beta; Signal Transduction; Transforming Growth Factor beta

There are a variety of pathophysiologic conditions that are known to induce skeletal muscle atrophy. However, muscle wasting can occur through multiple distinct signaling pathways with differential sensitivity between selective skeletal muscle fiber subtypes. This review summarizes some of the underlying molecular mechanisms responsible for fiber-specific muscle mass regulation.. Peroxisome proliferator-activated receptor gamma coactivator 1-alpha protects slow-twitch oxidative fibers from denervation/immobilization (disuse)-induced muscle atrophies. Nutrient-related muscle atrophies, such as those induced by cancer cachexia, sepsis, chronic heart failure, or diabetes, are largely restricted to fast-twitch glycolytic fibers, of which the underlying mechanism is usually related to abnormality of protein degradation, including proteasomal and lysosomal pathways. In contrast, nuclear factor kappaB activation apparently serves a dual function by inducing both fast-twitch fiber atrophy and slow-twitch fiber degeneration.. Fast-twitch glycolytic fibers are more vulnerable than slow-twitch oxidative fibers under a variety of atrophic conditions related to signaling transduction of Forkhead box O family, autophagy inhibition, transforming growth factor beta family, and nuclear factor-kappaB. The resistance of oxidative fibers may result from the protection of peroxisome proliferator-activated receptor gamma coactivator 1-alpha.

Topics: Animals; Cachexia; Chronic Disease; Diabetes Mellitus; Disease Models, Animal; Forkhead Box Protein O1; Forkhead Transcription Factors; Glycolysis; Heart Diseases; Humans; Muscle Fibers, Fast-Twitch; Muscle Fibers, Slow-Twitch; Muscular Atrophy; Muscular Diseases; NF-kappa B; Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; Sepsis; Signal Transduction; Transcription Factors; Transforming Growth Factor beta

To discuss the mechanisms of muscle loss during cachexia.. Cachexia can be defined as a wasting of lean body mass that cannot be reversed nutrionally, indicating a dysregulation in the pathways maintaining body composition. In skeletal muscle, during cachexia, there is an upregulation of protein degradation. A search for transcriptional markers of muscle atrophy led to the discovery of the E3 ubiquitin ligases MuRF1 and MAFbx (also called Atrogin-1). These genes are upregulated in multiple models of atrophy and cachexia. They target particular protein substrates for degradation via the ubiquitin/proteasome pathway. The insulin-like growth factor-1 can block the transcriptional upregulation of MuRF1 and MAFbx via the phosphatidylinositol-3 kinase/Akt/Foxo pathway. MuRF1's substrates include several components of the sarcomeric thick filament, including myosin heavy chain. Thus, by blocking MuRF1, insulin-like growth factor-1 prevents the breakdown of the thick filament, particularly myosin heavy chain, which is asymmetrically lost in settings of cortisol-linked skeletal muscle atrophy. Insulin-like growth factor-1/phosphatidylinositol-3 kinase/Akt signaling also dominantly inhibits the effects of myostatin, which is a member of the transforming growth factor-[beta] family of proteins. Deletion or inhibition of myostatin causes a significant increase in skeletal muscle size. Recently, myostatin has been shown to act both by inhibiting gene activation associated with differentiation, even when applied to postdifferentiated myotubes, and by blocking the phosphatidylinositol-3 kinase/Akt pathway.. These findings will help to define strategies to treat cachexia.

Topics: Cachexia; Forkhead Box Protein O1; Forkhead Transcription Factors; Gene Expression Regulation; Hydrocortisone; Muscle Proteins; Muscle, Skeletal; Muscular Atrophy; Myosin Heavy Chains; Organ Size; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; Signal Transduction; Transforming Growth Factor beta; Ubiquitin-Protein Ligases

To describe the most relevant recent observations concerning the molecular mechanisms behind myostatin-induced muscle wasting.. The main theme of this review is to summarize the biology and function of myostatin. Myostatin is a secreted growth factor that negatively regulates muscle growth. While inactivation of myostatin leads to muscle growth in vivo, excess levels of myostatin induces cachectic-like muscle wasting. Molecular analyses reveal that excess levels of myostatin induce Atrogin-1 expression by reducing Akt phosphorylation and thereby increasing FoxO1 activity. Recent findings have further speculated that myostatin may also play a role in cardiac cachexia.. As myostatin is a potent inducer of muscle wasting, antagonists to myostatin have been speculated to have great therapeutic value in alleviating muscle wasting. Indeed, myostatin peptide antagonists and antibodies have shown great promise in containing muscle loss in animal models of muscle wasting. Given the beneficial effects of myostatin antagonists in animal models, clinical trials are underway with myostatin antibodies, peptibodies and soluble receptor. Therefore, this review article on the role of myostatin in muscle wasting is highly relevant to current themes in muscle biology.

Topics: Animals; Antibodies, Monoclonal; Cachexia; Cell Size; Gene Expression Regulation; Humans; Muscle Development; Muscular Atrophy; Muscular Diseases; Myostatin; Transforming Growth Factor beta

In addition to gene correction therapy and cell transplantation techniques, multidisciplinary approaches to drug discovery and development offer promising therapeutic strategies for intractable genetic muscular disorders including muscular dystrophy. Inhibition of the production and activity of myostatin, a potent growth factor that determines skeletal muscle size, is a novel strategy for the treatment of muscle-wasting disorders such as muscular dystrophy, cachexia and sarcopenia. Myostatin blockers include myostatin-blocking antibodies, myostatin propeptide, follistatin and follistatin-related proteins, soluble myostatin receptors, small interfering RNA and small chemical inhibitors. This review describes the discovery and development of myostatin inhibitors.

Topics: Amino Acid Sequence; Animals; Antibodies; Drug Design; Follistatin; Genetic Therapy; Humans; Models, Molecular; Molecular Sequence Data; Muscle, Skeletal; Muscular Atrophy; Myostatin; Peptides; Protein Conformation; RNA Interference; Signal Transduction; Transforming Growth Factor beta

Skeletal muscle mass can be markedly reduced through a process called atrophy, as a consequence of many diseases or critical physiological and environmental situations. Atrophy is characterised by loss of contractile proteins and reduction of fiber volume. Although in the last decade the molecular aspects underlying muscle atrophy have received increased attention, the fine mechanisms controlling muscle degeneration are still incomplete. In this study we applied meta-analysis on gene expression signatures pertaining to different types of muscle atrophy for the identification of novel key regulatory signals implicated in these degenerative processes.. We found a general down-regulation of genes involved in energy production and carbohydrate metabolism and up-regulation of genes for protein degradation and catabolism. Six functional pathways occupy central positions in the molecular network obtained by the integration of atrophy transcriptome and molecular interaction data. They are TGF-beta pathway, apoptosis, membrane trafficking/cytoskeleton organization, NFKB pathways, inflammation and reorganization of the extracellular matrix. Protein degradation pathway is evident only in the network specific for muscle short-term response to atrophy. TGF-beta pathway plays a central role with proteins SMAD3/4, MYC, MAX and CDKN1A in the general network, and JUN, MYC, GNB2L1/RACK1 in the short-term muscle response network.. Our study offers a general overview of the molecular pathways and cellular processes regulating the establishment and maintenance of atrophic state in skeletal muscle, showing also how the different pathways are interconnected. This analysis identifies novel key factors that could be further investigated as potential targets for the development of therapeutic treatments. We suggest that the transcription factors SMAD3/4, GNB2L1/RACK1, MYC, MAX and JUN, whose functions have been extensively studied in tumours but only marginally in muscle, appear instead to play important roles in regulating muscle response to atrophy.

Topics: Animals; Apoptosis; Binding Sites; Down-Regulation; Extracellular Matrix; Gene Expression Profiling; Gene Expression Regulation; Gene Regulatory Networks; Humans; Mice; Muscle Proteins; Muscle, Skeletal; Muscular Atrophy; Rats; Transcription Factors; Transforming Growth Factor beta; Up-Regulation

A decade has passed since myostatin was first identified as a negative regulator of muscle growth. Since then, studies in both humans and animals have demonstrated that decreasing the levels of this growth factor or inhibiting its function can dramatically increase muscle size, and a number of therapeutic applications of myostatin inhibition to the treatment of myopathies and muscle atrophy have been proposed. As such treatments would be likely to also stimulate muscle growth in healthy individuals, there is a growing concern among anti-doping authorities that myostatin inhibitors may be among the next generation of ergogenic pharmaceuticals or even in the vanguard of "gene doping" technology. While the ability to stimulate muscle growth through myostatin inhibition is well documented, a growing body of evidence suggests such increases may not translate into an improvement in athletic performance. This article briefly reviews the function of this potent regulator of muscle development and explores the potential therapeutic uses, and potential ergogenic abuses, of myostatin manipulation.

Topics: Athletic Performance; Doping in Sports; Humans; Muscle, Skeletal; Muscular Atrophy; Myostatin; Sports; Transforming Growth Factor beta

Although the boundaries of skeletal muscle size are fundamentally determined by genetics, this dynamic tissue also demonstrates great plasticity in response to environmental and hormonal factors. Recent work indicates that contractile activity, nutrients, growth factors, and cytokines all contribute to determining muscle mass. Muscle responds not only to endocrine hormones but also to the autocrine production of growth factors and cytokines. Skeletal muscle synthesizes anabolic growth factors such as insulin-like growth factor (IGF)-I and potentially inhibitory cytokines such as interleukin (IL)-6, tumor necrosis factor (TNF)-alpha, and myostatin. These self-regulating inputs in turn influence muscle metabolism, including the use of nutrients such as glucose and amino acids. These changes are principally achieved by altering the activity of the protein kinase known as protein kinase B or Akt. Akt plays a central role in integrating anabolic and catabolic responses by transducing growth factor and cytokine signals via changes in the phosphorylation of its numerous substrates. Activation of Akt stimulates muscle hypertrophy and antagonizes the loss of muscle protein. Here we review the many signals that funnel through Akt to alter muscle mass.

Topics: Adenosine Triphosphate; Animals; Autocrine Communication; Cell Proliferation; Cell Size; Cytokines; Humans; Hypertrophy; Insulin-Like Growth Factor I; Intercellular Signaling Peptides and Proteins; Muscle Contraction; Muscle, Skeletal; Muscular Atrophy; Myostatin; NF-kappa B; Paracrine Communication; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; Signal Transduction; Transforming Growth Factor beta

Myostatin, which was cloned in 1997, is a potent inhibitor of skeletal muscle growth and member of the tumour growth factor-beta family. Disruption of the myostatin gene in mice induces a dramatic increase in muscle mass, caused by a combination of hypertrophy and hyperplasia. Natural mutations occurring in cattle were also associated with a significant increase in muscle mass and, recently, an inactivating myostatin mutation associated with the same phenotype was identified in humans. Studies into the molecular basis of this antimyogenic influence led to the conclusion that myostatin inhibits myoblast proliferation and differentiation through a classical tumour growth factor-beta pathway involving the activin receptor ActRIIB and Smads 2 and 3. Approaches that induce myostatin depletion or inactivation have led to a significant improvement in muscle regeneration processes, especially in degenerative diseases, through stimulation of satellite cell proliferation and differentiation. These promising data open the way to new therapeutic approaches in muscle diseases through targeting of the myostatin pathway.

Topics: Animals; Gene Expression Regulation; Humans; Muscular Atrophy; Myostatin; Transforming Growth Factor beta

There is now a large body of evidence that weight loss in older persons not only increases mortality, but also increases the incidence of hip fracture, functional deterioration and institutionalization. Weight loss is a central component of frailty. There is evidence that it is not only muscle, but also fat loss that leads to these deleterious effects. The reasons why fat loss can be harmful in older persons are reviewed. There are four major causes of weight loss in older persons viz. anorexia, sarcopenia, cachexia and dehydration. This review concentrates on the major causes of anorexia and sarcopenia. In particular, the emergence of new medications such as selective androgen receptor molecules, antimyostatin analogues, megestrol acetate (nanocrystal formulation), and ghrelin agonists are reviewed. The potential role of anabolic steroids is also discussed.

Topics: Adipose Tissue; Aged; Aged, 80 and over; Aging; Anabolic Agents; Anorexia; Appetite Stimulants; Feeding Behavior; Frail Elderly; Humans; Megestrol Acetate; Muscular Atrophy; Myostatin; Receptors, Androgen; Receptors, Ghrelin; Transforming Growth Factor beta; Weight Loss

The presence of sufficient skeletal muscle is of paramount importance for body function. Cachexia can be defined as a wasting syndrome describing the progressive loss of both adipose and skeletal muscle tissue in concert with severe injury, chronic or end-stage malignant and infectious diseases. Generally, cachexia predisposes to poor prognosis, co-morbidities and death. One signaling pathway possibly involved in muscle atrophy and cachexia is the myostatin cascade. This transforming growth factor-beta superfamily member myostatin is a strong candidate for regulating muscle mass, and is shown to inhibit muscle growth in different in vivo mammalian models. Overall, the modulation of the myostatin pathway seems interesting from the perspective of both pathology and sports medicine. Hence, myostatin signaling components and post-translational modulators are possible targets of pharmacological and other treatments against muscle loss, thus potentially contributing to the understanding and mitigation of muscle atrophies associated with inactivity, senescence and disease.

Topics: Animals; Cachexia; Humans; Muscle, Skeletal; Muscular Atrophy; Myostatin; Signal Transduction; Transforming Growth Factor beta

Many situations cause muscle atrophy. When severe, muscle atrophy is associated with an increase in morbidity and mortality. This loss of muscle mass is thought to be due to an imbalance between catabolic and anabolic pathways, resulting in an increase of muscle protein proteolysis and in a decrease in protein synthesis. Changes in muscle levels of muscle growth factors are thought to play a major role in this imbalance. Despite recent better understanding of the metabolic and molecular derangements leading to muscle wasting, therapy of muscle atrophy still has a poor success rate.. The recent demonstration that changes in local growth factors, such as insulin-like growth factor-I and myostatin, occur during muscle atrophy has stimulated research interest to prevent muscle mass loss by delivering these growth factors or their inhibitors into the muscle. During the last few years, several advances in the field of muscle gene transfer, using electroporation or recombinant adeno-associated viral vectors, have opened novel therapeutic ways to deliver growth factors able to counteract the loss of muscle mass.. Preventing decrease of insulin-like growth factor-I muscle, or inhibiting myostatin action by local genes over-expression, may provide a clinically relevant avenue for the preservation, attenuation or reversal of disease-related muscle loss.

Topics: Animals; Gene Expression Regulation; Genetic Therapy; Growth Substances; Humans; Insulin-Like Growth Factor I; Muscle Proteins; Muscular Atrophy; Myostatin; Transforming Growth Factor beta

Myostatin and the insulin-like growth factors (IGF-I and -II) play inhibitory and stimulatory roles, respectively, in the development and regulation of skeletal muscle mass. The findings of Sun et al. in this issue shed light on the potential regulation and actions of this yin-and-yang system in uremic sarcopenia and the salutary effects of exercise.

Topics: Animals; Humans; Muscular Atrophy; Myostatin; Somatomedins; Transforming Growth Factor beta; Uremia

This review looks at new therapeutic developments for the increasingly recognized problem of sarcopenia. Increased adiposity and reduced lean body mass characterize ageing men. The potential therapeutic role of the growth hormone/insulin-like growth factor axis, androgen modulators and myostatin inhibition are discussed.

Topics: Aged; Aging; Androgens; Exercise; Growth Hormone; Hormones; Humans; Insulin-Like Growth Factor I; Male; Middle Aged; Muscular Atrophy; Myostatin; Transforming Growth Factor beta; Treatment Outcome

This review describes the major hormonal factors that determine the balance between human skeletal muscle anabolism and catabolism in health and disease, with specific reference to age-related muscle loss (sarcopenia). The molecular mechanisms associated with muscle hypertrophy are described, and the central role of the satellite cell highlighted. The biological dynamics of satellite cells, varying between states of quiescence, proliferation and differentiation are strongly influenced by local endocrine factors. The molecular mechanisms of muscle atrophy are examined focussing on the causes of sarcopenia and associations with systemic medical disorders. In addition, evidence is provided that the mechanisms of atrophy and hypertrophy are unlikely to be simple opposites. Novel endocrine mechanisms underpinning mechano-transduction include IGF-I subtypes that may differentiate between endocrine and mechanical signals; their interaction with classical endocrine factors is an active area of translational research. Recently acquired knowledge on the mechanism of anabolic effects of androgens is also reviewed. The increasingly recognised role of myostatin, a negative regulator of muscle function, is described, as well as its potential as a therapeutic target. Strategies to counter age-related sarcopenia thus represent an exciting field of future investigation.

Topics: Adaptation, Physiological; Adult; Aged; Aging; Androgens; Clinical Trials as Topic; Female; Hormones; Humans; Male; Middle Aged; Muscle, Skeletal; Muscular Atrophy; Myostatin; Transforming Growth Factor beta

Skeletal muscles become atrophied by muscular disorders such as muscular dystrophy, wasting and even aging. In addition to muscle atrophy, progressive muscle damage, inflammation and replacement of muscle fibers with fibrous and fatty tissues are observed in muscular dystrophy. Neuronal innervation is required for skeletal muscle, and muscles become atrophic when motor neurons are affected by neurodegenerative disorders such as amyotrophic lateral sclerosis. Restoring muscle mass and function lost by diseases such as muscular dystrophy and neurodegenerative disorders is important. There are three rational therapies for muscular dystrophy and related diseases: gene therapy, cell therapy and drug therapy. Gene therapies to replace the defective genes have been tried with various degrees of effectiveness. Multiple myogenic stem cells including satellite cells, bone marrow cells, muscle side population cells, muscle-derived stem cells and mesoangioblast have been characterized. Cell therapies using these stem cells are one of the promising therapies for neuromuscular diseases causing muscle atrophy. As pharmacological drug therapies, increasing skeletal muscle mass by myostatin inhibition is quite promising and will be applied clinically in the near future.

Topics: Amyotrophic Lateral Sclerosis; Animals; Cell Differentiation; Cell Division; Drug Design; Genetic Therapy; Guanine Nucleotide Exchange Factors; Humans; Muscle, Skeletal; Muscular Atrophy; Mutation; Myostatin; Neuromuscular Diseases; Signal Transduction; Stem Cell Transplantation; Superoxide Dismutase; Superoxide Dismutase-1; Transforming Growth Factor beta

Regulation of muscle size is essential for proper development and homeostasis of adult musculature. This regulation is mediated in large part by signal transduction pathways that promote the synthesis or breakdown of skeletal muscle. PI(3)K/Akt, myostatin and NF-kappaB represent three such pathways that will be the focus of this review.. Recent reports solidify the requirement of the PI(3)K/Akt pathway in the regulation of muscle hypertrophy. In response to IGF-1, Akt activates downstream effectors, mTOR and p70S6K to stimulate protein synthesis thereby increasing the cytoplasmic compartment in muscle fibers. Tsc2 was also identified as a novel Akt target, whose phosphorylation and inactivation by Akt may lead to an increase in cell size. The mechanisms by which myostatin functions in muscle wasting was recently explored using in-vitro assays of myogenesis. Myostatin was found to repress myogenesis by inhibiting the synthesis and activity of MyoD. Paradoxically, myostatin expression is itself regulated by MyoD binding to the myostatin promoter. The NF-kappaB transcription factor also functions as a negative regulator of myogenesis by inhibiting MyoD. Chronic activation of NF-kappaB has been associated with muscle wasting, but the mechanisms by which this regulation occurs remain for the most part unknown.. Recent cell culture and animal studies have provided insight on the mechanisms by which Akt, myostatin, and NF-kappaB signaling pathways regulate muscle size. Clinical intervention to boost Akt signaling or modulate myostatin and NF-kappaB activities may prove useful in diseases associated with chronic muscle wasting.

Topics: Animals; Humans; Muscle, Skeletal; Muscular Atrophy; Myostatin; NF-kappa B; Protein Kinases; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Signal Transduction; Somatomedins; TOR Serine-Threonine Kinases; Transforming Growth Factor beta

Topics: Adult; Aged; Aged, 80 and over; Aging; Alleles; Exons; Female; Humans; Italy; Male; Middle Aged; Muscle Weakness; Muscular Atrophy; Mutation, Missense; Myostatin; Polymorphism, Genetic; Prevalence; Transforming Growth Factor beta

Skeletal muscle dysfunction is a clinically important complication of pulmonary arterial hypertension (PAH). Growth/differentiation factor 15 (GDF-15), a prognostic marker in PAH, has been associated with muscle loss in other conditions. We aimed to define the associations of GDF-15 and muscle wasting in PAH, to assess its utility as a biomarker of muscle loss and to investigate its downstream signalling pathway as a therapeutic target.. GDF-15 levels and measures of muscle size and strength were analysed in the monocrotaline (MCT) rat, Sugen/hypoxia mouse and in 30 patients with PAH. In C2C12 myotubes the downstream targets of GDF-15 were identified. The pathway elucidated was then antagonised in vivo.. Circulating GDF-15 levels correlated with tibialis anterior (TA) muscle fibre diameter in the MCT rat (Pearson r=-0.61, p=0.003). In patients with PAH, plasma GDF-15 levels of <564 pg/L predicted those with preserved muscle strength with a sensitivity and specificity of ≥80%. In vitro GDF-15 stimulated an increase in phosphorylation of TGFβ-activated kinase 1 (TAK1). Antagonising TAK1, with 5(Z)-7-oxozeaenol, in vitro and in vivo led to an increase in fibre diameter and a reduction in mRNA expression of atrogin-1 in both C2C12 cells and in the TA of animals who continued to grow. Circulating GDF-15 levels were also reduced in those animals which responded to treatment.. Circulating GDF-15 is a biomarker of muscle loss in PAH that is responsive to treatment. TAK1 inhibition shows promise as a method by which muscle atrophy may be directly prevented in PAH.. NCT01847716; Results.

Topics: Adult; Animals; Biomarkers; Blotting, Western; Enzyme-Linked Immunosorbent Assay; Female; Growth Differentiation Factor 15; Humans; Hypertension, Pulmonary; Immunohistochemistry; Male; MAP Kinase Kinase Kinases; Mice; Middle Aged; Muscle, Skeletal; Muscular Atrophy; Rats; Rats, Sprague-Dawley; Real-Time Polymerase Chain Reaction; Signal Transduction; Transforming Growth Factor beta

After anterior cruciate ligament (ACL) reconstruction, there is significant atrophy of the quadriceps muscles that can limit full recovery and place athletes at risk for recurrent injuries with return to play. The cause of this muscle atrophy is not fully understood.. Circulating levels of proatrophy, proinflammatory, and cartilage turnover cytokines and biomarkers would increase after ACL reconstruction.. Descriptive laboratory study.. Patients (N = 18; mean age, 28 ± 2.4 years) underwent surgical reconstruction of the ACL after a noncontact athletic injury. Circulating levels of biomarkers were measured along with Short Form-12, International Knee Documentation Committee, and objective knee strength measures preoperatively and at 6 postoperative visits. Differences were tested using repeated-measures 1-way analysis of variance.. Myostatin, TGF-β, and C-reactive protein levels were significantly increased in the early postoperative period and returned to baseline. Cartilage oligomeric matrix protein levels decreased immediately after surgery and then returned to baseline. CCL2, CCL3, CCL4, CCL5, EGF, FGF-2, IGF-1, IL-10, IL-1α, IL-1β, IL-1ra, IL-6, myoglobin, and TNF-α were not different over the course of the study.. An increase in potent atrophy-inducing cytokines and corresponding changes in knee strength and functional scores were observed after ACL reconstruction.. Although further studies are necessary, the therapeutic inhibition of myostatin may help prevent the muscle atrophy that occurs after ACL reconstruction and provide an accelerated return of patients to sport.

Topics: Adolescent; Adult; Anterior Cruciate Ligament Injuries; Anterior Cruciate Ligament Reconstruction; Biomarkers; C-Reactive Protein; Cartilage Oligomeric Matrix Protein; Chondrogenesis; Cytokines; Extracellular Matrix Proteins; Female; Follow-Up Studies; Glycoproteins; Humans; Inflammation; Insulin-Like Growth Factor I; Knee Injuries; Male; Matrilin Proteins; Middle Aged; Muscular Atrophy; Myostatin; Postoperative Complications; Postoperative Period; Preoperative Period; Transforming Growth Factor beta; Treatment Outcome; Young Adult

Skeletal muscle atrophy occurs as a consequence of injury, illness, surgery, and muscle disuse, impacting appreciably on health care costs and patient quality of life, particularly in the absence of appropriate rehabilitation. The molecular mechanisms that regulate muscle mass during atrophy and rehabilitation in humans have not been elucidated, despite several robust candidate pathways being identified. Here, we induced skeletal muscle atrophy in healthy volunteers using two weeks of limb immobilization, and then stimulated the restoration of muscle mass with six weeks of supervised exercise rehabilitation. We determined muscle mass and function and performed targeted gene expression analysis at prescribed time points during immobilization and rehabilitation. For the first time, we have identified novel changes in gene expression following immobilization-induced atrophy and during a program of rehabilitative exercise that restored muscle mass and function. Furthermore, we have shown that exercise performed immediately following immobilization induces profound changes in the expression of a number of genes in favor of the restoration of muscle mass, within 24 h. This information will be of considerable importance to our understanding of how immobilization and contraction stimulate muscle atrophy and hypertrophy, respectively, and to the development of novel therapeutic strategies aimed at maintaining or restoring muscle mass.

Topics: Adolescent; Adult; Calpain; Cysteine Endopeptidases; Exercise; Gene Expression Profiling; Gene Expression Regulation; Humans; I-kappa B Kinase; Immobilization; Insulin-Like Growth Factor I; Isometric Contraction; Male; Multienzyme Complexes; Muscle, Skeletal; Muscular Atrophy; Muscular Disorders, Atrophic; Myostatin; Organ Size; Proteasome Endopeptidase Complex; Protein Serine-Threonine Kinases; RNA, Messenger; Signal Transduction; Time Factors; Transforming Growth Factor beta; Ubiquitin

Topics: Animals; Cachexia; Early Growth Response Transcription Factors; Humans; Kruppel-Like Transcription Factors; Mice; Muscle, Skeletal; Muscular Atrophy; Pancreatic Neoplasms; Transforming Growth Factor beta

We investigated the protective effect of losartan, an angiotensin II type 1 receptor blocker, on soleus muscle atrophy. Age-matched male and female Wistar rats were subjected to hindlimb unloading, and the soleus muscle was removed on days 1 and 7 for analysis. Females showed greater reductions in relative weight and myofiber cross-sectional area of the soleus muscle than males on day 7 post-hindlimb unloading. Losartan partially protected females against muscle atrophy. Activation of the canonical TGF-β signaling pathway, assessed via Smad2/3 phosphorylation, was lower in females following losartan treatment and associated with lower levels of protein ubiquitination after 1 (myofibril) and 7 (cytosol) days of unloading. However, no effect was observed in non-canonical TGF-β signaling (p44/p42 and p38 MAPK phosphorylation) in males or females during unloading. Our results suggest that losartan provides partial protection against hindlimb unloading-induced soleus muscle atrophy in female rats, possibly associated with decreased canonical TGF-β signaling.

Topics: Animals; Female; Hindlimb; Hindlimb Suspension; Losartan; Male; Muscle, Skeletal; Muscular Atrophy; Rats; Rats, Wistar; Signal Transduction; Transforming Growth Factor beta

Skeletal muscle mass is negatively regulated by several TGF-β superfamily members. Myostatin (MSTN) is the most prominent negative regulator of muscle mass. Recent studies show that in addition to MSTN, GDF11, which shares a high sequence identity with MSTN, induces muscle atrophy in vitro and in vivo at supraphysiological levels, whereas controversy regarding its roles exists. Furthermore, higher circulating GDF11 levels associate with frailty in humans. On the other hand, little is known about the effect of pathophysiological levels of GDF11 on muscle atrophy. Here we seek to determine whether pathophysiological levels of GDF11 are sufficient to activate Smad2/Smad3 signaling and induce muscle atrophy using human iPSC-derived myocytes (hiPSC myocytes). We first show that incubating hiPSC myocytes with pathophysiological concentrations of GDF11 significantly reduces myocyte diameters. We next demonstrate that pathophysiological levels of GDF11 are sufficient to activate Smad2/3 signaling. Finally, we show that pathophysiological levels of GDF11 are capable of inducing the expression of Atrogin-1, an atrophy-promoting E3 ubiquitin ligase and that FOXO1 blockage reverses the GDF11-induced Atrogin-1 expression and atrophic phenotype. Collectively, our results suggest that GDF11 induces skeletal muscle atrophy at the pathophysiological levels through the GDF11-FOXO1 axis.

Topics: Bone Morphogenetic Proteins; Growth Differentiation Factors; Humans; Induced Pluripotent Stem Cells; Muscle Cells; Muscle, Skeletal; Muscular Atrophy; Myostatin; Smad2 Protein; Smad3 Protein; Transforming Growth Factor beta; Ubiquitin-Protein Ligases

The absence of dystrophin in Duchenne muscular dystrophy disrupts the dystrophin-associated glycoprotein complex resulting in skeletal muscle fiber fragility and atrophy, associated with fibrosis as well as microtubule and neuromuscular junction disorganization. The specific, non-conventional cytoplasmic histone deacetylase 6 (HDAC6) was recently shown to regulate acetylcholine receptor distribution and muscle atrophy. Here, we report that administration of the HDAC6 selective inhibitor tubastatin A to the Duchenne muscular dystrophy, mdx mouse model increases muscle strength, improves microtubule, neuromuscular junction, and dystrophin-associated glycoprotein complex organization, and reduces muscle atrophy and fibrosis. Interestingly, we found that the beneficial effects of HDAC6 inhibition involve the downregulation of transforming growth factor beta signaling. By increasing Smad3 acetylation in the cytoplasm, HDAC6 inhibition reduces Smad2/3 phosphorylation, nuclear translocation, and transcriptional activity. These findings provide in vivo evidence that Smad3 is a new target of HDAC6 and implicate HDAC6 as a potential therapeutic target in Duchenne muscular dystrophy.

Topics: Acetylation; Animals; Dystrophin; Fibrosis; Glycoproteins; Histone Deacetylase 6; Histone Deacetylase Inhibitors; Mice; Mice, Inbred mdx; Muscle, Skeletal; Muscular Atrophy; Muscular Dystrophy, Duchenne; Phenotype; Transforming Growth Factor beta

Topics: Activating Transcription Factor 4; Animals; Hibernation; Mice; Muscle, Skeletal; Muscular Atrophy; Signal Transduction; Transforming Growth Factor beta; Ursidae

Maslinic acid (MA) is a pentacyclic triterpene abundant in olive peels. MA reportedly increases skeletal muscle mass and strength in older adults; however, the underlying mechanism is unknown. This study aimed to investigate the effects of MA on denervated muscle atrophy and strength and to explore the underlying molecular mechanism. Mice were fed either a control diet or a 0.27% MA diet. One week after intervention, the sciatic nerves of both legs were cut to induce muscle atrophy. Mice were examined 14 days after denervation. MA prevented the denervation-induced reduction in gastrocnemius muscle mass and skeletal muscle strength. Microarray gene expression profiling in gastrocnemius muscle demonstrated several potential mechanisms for muscle maintenance. Gene set enrichment analysis (GSEA) revealed different enriched biological processes, such as myogenesis, PI3/AKT/mTOR signaling, TNFα signaling via NF-κB, and TGF-β signaling in MA-treated mice. In addition, qPCR data showed that MA induced

Topics: Animals; Gene Expression Profiling; Humans; Male; Mice; Mice, Inbred ICR; Muscle Denervation; Muscle Development; Muscle Strength; Muscle, Skeletal; Muscular Atrophy; Muscular Diseases; NF-kappa B; Olea; Sciatic Nerve; Signal Transduction; Transforming Growth Factor beta; Triterpenes; Tumor Necrosis Factor-alpha

Muscle atrophy arises from a multiplicity of physio-pathological situations and has very detrimental consequences for the whole body. Although knowledge of muscle atrophy mechanisms keeps growing, there is still no proven treatment to date. This study aimed at identifying new drivers for muscle atrophy resistance. We selected an innovative approach that compares muscle transcriptome between an original model of natural resistance to muscle atrophy, the hibernating brown bear, and a classical model of induced atrophy, the unloaded mouse. Using RNA sequencing, we identified 4415 differentially expressed genes, including 1746 up- and 2369 down-regulated genes, in bear muscles between the active versus hibernating period. We focused on the Transforming Growth Factor (TGF)-β and the Bone Morphogenetic Protein (BMP) pathways, respectively, involved in muscle mass loss and maintenance. TGF-β- and BMP-related genes were overall down- and up-regulated in the non-atrophied muscles of the hibernating bear, respectively, and the opposite occurred for the atrophied muscles of the unloaded mouse. This was further substantiated at the protein level. Our data suggest TGF-β/BMP balance is crucial for muscle mass maintenance during long-term physical inactivity in the hibernating bear. Thus, concurrent activation of the BMP pathway may potentiate TGF-β inhibiting therapies already targeted to prevent muscle atrophy.

Topics: Animals; Bone Morphogenetic Proteins; Disease Models, Animal; Female; Gene Expression Profiling; Gene Expression Regulation; Gene Regulatory Networks; Hibernation; Hindlimb Suspension; Male; Mice; Mice, Inbred C57BL; Muscular Atrophy; Quadriceps Muscle; RNA-Seq; Signal Transduction; Time Factors; Transcriptome; Transforming Growth Factor beta; Ursidae

Topics: Growth Differentiation Factor 15; Humans; Hypertension, Pulmonary; Muscle, Skeletal; Muscular Atrophy; Transforming Growth Factor beta

Promoter-associated long non-coding RNAs (lncRNAs) regulate the expression of adjacent genes; however, precise roles of these lncRNAs in skeletal muscle remain largely unknown. Here, we characterize a promoter-associated lncRNA,

Topics: Animals; Cell Cycle; Cell Differentiation; Cell Line; DEAD-box RNA Helicases; Gene Expression Regulation, Developmental; Humans; Mice, Inbred C57BL; Models, Biological; Muscle Development; Muscle, Skeletal; Muscular Atrophy; Myoblasts; MyoD Protein; Myogenin; p300-CBP Transcription Factors; Promoter Regions, Genetic; Protein Binding; RNA, Long Noncoding; Transforming Growth Factor beta

The transforming growth factor type-beta (TGF-β) induces skeletal muscle atrophy characterised by a decrease in the fibre's diameter and levels of myosin heavy chain (MHC), also as an increase of MuRF-1 expression. In addition, TGF-β induces muscle atrophy by a mechanism dependent on reactive oxygen species (ROS). TGF-β signals by activating both canonical Smad-dependent, and non-canonical signalling pathways such as ERK1/2, JNK1/2, and p38 MAPKs. However, the participation of canonical and non-canonical signalling pathways in the TGF-β atrophic effect on skeletal muscle is unknown. We evaluate the impact of Smad and MAPK signalling pathways on the TGF-β-induced atrophic effect in C2C12 myotubes. The results indicate that TGF-β activates Smad2/3, ERK1/2 and JNK1/2, but not p38 in myotubes. The pharmacological inhibition of Smad3, ERK1/2 and JNK1/2 activation completely abolished the atrophic effect of TGF-β. Finally, the inhibition of these canonical and non-canonical pathways did not decrease the ROS increment, while the inhibition of ROS production entirely abolished the phosphorylation of Smad3, ERK1/2 and JNK1/2. These results suggest that TGF-β requires Smad3, ERK1/2 and JNK1/2 activation to produce skeletal muscle atrophy. Moreover, the induction of ROS by TGF-β is an upstream event to canonical and non-canonical pathways.

Topics: Humans; Mitogen-Activated Protein Kinases; Muscle, Skeletal; Muscular Atrophy; Phosphorylation; Signal Transduction; Smad2 Protein; Smad3 Protein; Transforming Growth Factor beta

Myoblast fusion is critical for muscle growth, regeneration, and repair. We previously reported that the enzyme peptidyl-prolyl cis-trans isomerase NIMA interacting 1 (Pin1) is involved in osteoclast fusion. The objective of this study was to investigate the possibility that Pin1 also inhibits myoblast fusion. Here, we show the increased number of nuclei in the Pin1

Topics: Animals; Cell Fusion; Cell Line; Extracellular Signal-Regulated MAP Kinases; Gene Expression Regulation; Male; Mice, Inbred C57BL; Muscle, Skeletal; Muscular Atrophy; Myoblasts; Myostatin; NIMA-Interacting Peptidylprolyl Isomerase; Phosphorylation; Protein Binding; Serine; Signal Transduction; Smad3 Protein; Transforming Growth Factor beta

The aim of this work was to investigate the effects of electrical stimulation (ES) of denervated muscles of rat in neuromuscular performance, muscle atrophy, and fibrosis formation.. Wistar rats were divided into normal (N), 7- or 15-day denervation (D7d and D15d), D7d or D15d plus ES (DES7d and DES15d, respectively). Sciatic nerves were crushed causing muscle denervation. Two hundred muscle contractions were electrically induced daily by surface electrodes, considering muscle chronaxie. Sciatic functional index was used to determine neuromuscular performance during walking. The muscle fiber cross-sectional area and percentage of connective tissue were assessed by light microscopy. Molecular markers of extracellular matrix production and remodeling were evaluated. Metalloproteinase (MMP) activity was assessed by zymography, and TWEAK, Fn14, myostatin, and transforming growth factor (TGF)-β gene expressions were determined by real-time PCR.. Electrical stimulation impaired natural recovery of walking at 15 days. In addition, ES induced fibrosis and accentuated muscle atrophy in denervated muscles. Although ES reduced the accumulation of TWEAK and myostatin expressions, it up-regulated Fn14 and TGF-β in a time-dependent manner. Electrical stimulation also increased the activity of MMP-2 compared to the other groups (P < 0.05).. Electrical stimulation applied to denervated muscles induced muscle fibrosis and atrophy, as well as loss of performance. The TWEAK/Fn14 system, TGF-beta/myostatin pathway, and MMP activity seem to be involved in these deleterious changes.

Topics: Animals; Apoptosis Regulatory Proteins; Chronaxy; Cytokine TWEAK; Down-Regulation; Electric Stimulation; Fibrosis; Matrix Metalloproteinase 2; Membrane Proteins; Models, Animal; Muscle Denervation; Muscle, Skeletal; Muscular Atrophy; Myostatin; Rats, Wistar; Receptors, Tumor Necrosis Factor; Transforming Growth Factor beta; Tumor Necrosis Factors; TWEAK Receptor; Up-Regulation

The pathological endpoint of congenital and senile myopathies is chronic muscle degeneration characterized by the atrophy of contractile elements, accompanied by fibrosis and fatty infiltration of the interstitium. Tenotomy is the release of preload that causes abrupt shortening of the muscle and models atrophy and fibrosis without prominent inflammatory response. Fibrosis in the skeletal muscle is known to be triggered by transforming growth factor (TGF)-β, which is activated by inflammatory events. As these were lacking, tenotomy provided an opportunity to investigate transcriptional events on a background without inflammation. An unbiased look at the transcriptome of tenotomy-immobilized soleus muscle revealed that the majority of the transcriptional changes took place in the first 4 wk. Regarding atrophy, proteasomal and lysosomal pathways were actively involved in accompanying cathepsins and calpains in the breakdown of the macromolecular contractile machinery. The transcriptome provided clear-cut evidence for the upregulation of collagens and several extracellular matrix components that define fibrotic remodeling of the skeletal muscle architecture as well as activation of the fibro-adipogenic precursors. Concomitantly, Sfrp2, a Wnt antagonist as well as a procollagen processor, accompanied fibrosis in skeletal muscle with an expression that was stringently confined to the slow-twitch fibers. An interpreted mechanistic scenario construed the kinetic events initiated through the abnormal shortening of the muscle fibers as enough to trigger the resident latent TGF-β in the extracellular matrix, leading to the activation of fibroadipogenic precursors. As in the heart, Sfrp2 shows itself to be a therapeutic target for the prevention of irreversible fibrosis in degenerative skeletal muscle conditions.

Topics: Animals; Fibrosis; Lysosomes; Male; Membrane Proteins; Muscle Fibers, Skeletal; Muscular Atrophy; Muscular Diseases; Proteasome Endopeptidase Complex; Rats; Rats, Sprague-Dawley; Tenotomy; Transforming Growth Factor beta; Up-Regulation

Rotator cuff tears represent a large burden of muscle-tendon injuries in our aging population. While small tears can be repaired surgically with good outcomes, critical size tears are marked by muscle atrophy, fibrosis, and fatty infiltration, which can lead to failed repair, frequent re-injury, and chronic disability. Previous animal studies have indicated that Transforming Growth Factor-β (TGF-β) signaling may play an important role in the development of these muscle pathologies after injury. Here, we demonstrated that inhibition of TGF-β1 signaling with the small molecule inhibitor SB431542 in a mouse model of massive rotator cuff tear results in decreased fibrosis, fatty infiltration, and muscle weight loss. These observed phenotypic changes were accompanied by decreased fibrotic, adipogenic, and atrophy-related gene expression in the injured muscle of mice treated with SB431542. We further demonstrated that treatment with SB431542 reduces the number of fibro/adipogenic progenitor (FAP) cells-an important cellular origin of rotator cuff muscle fibrosis and fatty infiltration, in injured muscle by promoting apoptosis of FAPs. Together, these data indicate that the TGF-β pathway is a critical regulator of the degenerative muscle changes seen after massive rotator cuff tears. TGF-β promotes rotator cuff muscle fibrosis and fatty infiltration by preventing FAP apoptosis. TGF-β regulated FAP apoptosis may serve as an important target pathway in the future development of novel therapeutics to improve muscle outcomes following rotator cuff tear.

Topics: Adipose Tissue; Animals; Apoptosis; Benzamides; Dioxoles; Disease Models, Animal; Female; Fibrosis; Gene Expression Regulation; Mice; Muscular Atrophy; Rotator Cuff; Rotator Cuff Injuries; Signal Transduction; Stem Cells; Transforming Growth Factor beta

Transforming growth factor type beta 1 (TGF-β1) produces skeletal muscle atrophy. Angiotensin-(1-7) (Ang-(1-7)), through the Mas receptor, prevents the skeletal muscle atrophy induced by sepsis, immobilization, or angiotensin II (Ang-II). However, the effect of Ang-(1-7) on muscle wasting induced by TGF-β1 is unknown.. To evaluate whether Ang-(1-7)/Mas receptor axis could prevent the skeletal muscle atrophy induced by TGF-β1.. This study assessed the atrophic effect of TGF-β1 in C2C12 myotubes and mice in absence or presence of Ang-(1-7), and the receptor participation using A779, an antagonist of the Mas receptor. The levels of myosin heavy chain (MHC), polyubiquitination, and MuRF-1 were detected by western blot. Myotube diameter was also evaluated. In vivo analysis included the muscle strength, fibre diameter, MHC and MuRF-1 levels by western blot, and ROS levels by DCF probe detection.. The results showed that Ang-(1-7) prevented the increase in MuRF-1 and polyubiquitined protein levels, the decrease of MHC levels, the myotubes/fibre diameter diminution, and the increased production of reactive oxygen species (ROS) induced by TGF-β1. Utilizing A779 inhibited the anti-atrophic effect of Ang-(1-7).. The preventive effect of Ang-(1-7) on skeletal muscle atrophy induced by TGF-β1 is produced through inhibition of ROS production and proteasomal degradation of MHC.

Topics: Angiotensin I; Animals; Cell Line; Mice, Inbred C57BL; Muscle Fibers, Skeletal; Muscle Proteins; Muscle, Skeletal; Muscular Atrophy; Myosin Heavy Chains; Myosins; Peptide Fragments; Polyubiquitin; Proteasome Endopeptidase Complex; Proto-Oncogene Mas; Proto-Oncogene Proteins; Reactive Oxygen Species; Receptors, G-Protein-Coupled; Transforming Growth Factor beta; Tripartite Motif Proteins; Ubiquitin; Ubiquitin-Protein Ligases; Ubiquitination

The phenotype and severity of cancer cachexia differ among tumor types and metastatic site in individual patients. In this study, we evaluated if differences in tumor microenvironment would affect the development of cancer cachexia in a murine model, and demonstrated that body weight, adipose tissue and gastrocnemius muscle decreased in tumor-bearing mice. Interestingly, a reduction in heart weight was observed in the intraperitoneal tumor group but not in the subcutaneous group. We evaluated 23 circulating cytokines and members of the TGF-β family, and found that levels of IL-6, TNF-α and activin A increased in both groups of tumor-bearing mice. Eotaxin and G-CSF levels in the intraperitoneal tumor group were higher than in the subcutaneous group. Atrogin 1 and MuRF1 mRNA expressions in the gastrocnemius muscle increased significantly in both groups of tumor-bearing mice, however, in the myocardium, expression of these mRNAs increased in the intraperitoneal group but not in subcutaneous group. Based on these results, we believe that differences in microenvironment where tumor cells develop can affect the progression and phenotype of cancer cachexia through alterations in various circulating factors derived from the tumor microenvironment.

Topics: Activins; Animals; Cachexia; Cell Line, Tumor; Disease Models, Animal; Interleukin-6; Male; Mice; Mice, Inbred BALB C; Muscle Proteins; Muscle, Skeletal; Muscular Atrophy; Myocardium; RNA, Messenger; SKP Cullin F-Box Protein Ligases; Transforming Growth Factor beta; Tripartite Motif Proteins; Tumor Microenvironment; Tumor Necrosis Factor-alpha; Ubiquitin-Protein Ligases

Cancer cachexia is a debilitating condition characterized by a combination of anorexia, muscle wasting, weight loss, and malnutrition. This condition affects an overwhelming majority of patients with pancreatic cancer and is a primary cause of cancer-related death. However, few, if any, effective therapies exist for both treatment and prevention of this syndrome. In order to develop novel therapeutic strategies for pancreatic cancer cachexia, appropriate animal models are necessary. In this study, we developed and validated a syngeneic, metastatic, murine model of pancreatic cancer cachexia. Using our model, we investigated the ability of transforming growth factor beta (TGF-β) blockade to mitigate the metabolic changes associated with cachexia. We found that TGF-β inhibition using the anti-TGF-β antibody 1D11.16.8 significantly improved overall mortality, weight loss, fat mass, lean body mass, bone mineral density, and skeletal muscle proteolysis in mice harboring advanced pancreatic cancer. Other immunotherapeutic strategies we employed were not effective. Collectively, we validated a simplified but useful model of pancreatic cancer cachexia to investigate immunologic treatment strategies. In addition, we showed that TGF-β inhibition can decrease the metabolic changes associated with cancer cachexia and improve overall survival.

Topics: Animals; Antibodies; Body Composition; Cachexia; Cell Line, Tumor; Disease Models, Animal; Immunotherapy; Male; Mice; Mice, Inbred C57BL; Muscular Atrophy; Neoplasm Metastasis; Pancreatic Neoplasms; Survival Analysis; Transforming Growth Factor beta

The purpose of our study was to compare two acquired muscle atrophies and the use of myostatin inhibition for their treatment. Myostatin naturally inhibits skeletal muscle growth by binding to ActRIIB, a receptor on the cell surface of myofibers. Because blocking myostatin in an adult wild-type mouse induces profound muscle hypertrophy, we applied a soluble ActRIIB receptor to models of disuse (limb immobilization) and denervation (sciatic nerve resection) atrophy. We found that treatment of immobilized mice with ActRIIB prevented the loss of muscle mass observed in placebo-treated mice. Our results suggest that this protection from disuse atrophy is regulated by serum and glucocorticoid-induced kinase (SGK) rather than by Akt. Denervation atrophy, however, was not protected by ActRIIB treatment, yet resulted in an upregulation of the pro-growth factors Akt, SGK and components of the mTOR pathway. We then treated the denervated mice with the mTOR inhibitor rapamycin and found that, despite a reduction in mTOR activation, there is no alteration of the atrophy phenotype. Additionally, rapamycin prevented the denervation-induced upregulation of the mTORC2 substrates Akt and SGK. Thus, our studies show that denervation atrophy is not only independent from Akt, SGK and mTOR activation but also has a different underlying pathophysiological mechanism than disuse atrophy.

Topics: Activin Receptors, Type II; Animals; Autophagy; Biomarkers; Enzyme Activation; Male; Mice; Muscle Denervation; Muscular Atrophy; Myostatin; Phenotype; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins c-akt; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Transforming Growth Factor beta; Up-Regulation

The expression of secreted protein acidic and rich in cysteine (SPARC) in skeletal muscle decreases with age. Here, we examined the role of SPARC in skeletal muscle by reducing its expression.. SPARC expression was suppressed by introducing short interfering RNA (siRNA) into mouse tibialis anterior muscle. Myofiber diameter, atrogin1, and muscle RING-finger protein 1 (MuRF1) expression, and tumor necrosis factor-α (TNFα) and transforming growth factor-β (TGFβ) signaling were then analyzed.. Reduced SPARC expression caused decreases in the diameter of myofibers, especially fast-type ones, accompanied by upregulation of atrogin1, but not MuRF1, at 10 days after siRNA transfection. The expression of TNFα and TGFβ and the phosphorylation status of p38 were not affected by SPARC knockdown, whereas Smad3 phosphorylation was increased at 2 days after siRNA transfection.. The loss of SPARC not only upregulates atrogin1 expression but also enhances TGFβ signaling, which may in turn cause muscle atrophy.

Topics: Animals; Male; Mice; Mice, Inbred C57BL; Muscle Fibers, Skeletal; Muscle Proteins; Muscular Atrophy; Osteonectin; Phosphorylation; RNA, Small Interfering; Signal Transduction; SKP Cullin F-Box Protein Ligases; Transfection; Transforming Growth Factor beta; Tripartite Motif Proteins; Tumor Necrosis Factor-alpha; Ubiquitin-Protein Ligases; Up-Regulation

Transforming growth factor-β (TGF-β) is a proinflammatory cytokine that regulates the response of many tissues following injury. Previous studies in our lab have shown that treating muscles with TGF-β results in a dramatic accumulation of type I collagen, substantial fiber atrophy, and a marked decrease in force production. Because TGF-β promotes atrophy and fibrosis, our objective was to investigate whether the inhibition of TGF-β after injury would enhance the recovery of muscle following injury. We hypothesized that inhibiting TGF-β after contraction-induced injury would improve the functional recovery of muscles by preventing muscle fiber atrophy and weakness, and by limiting the accumulation of fibrotic scar tissue. To test this hypothesis, we induced an injury using a series of in situ lengthening contractions to extensor digitorum longus muscles of mice treated with either a bioneutralizing antibody against TGF-β or a sham antibody. Compared with controls, muscles from mice receiving TGF-β inhibitor showed a greater recovery in force 3 days and 7 days after injury but had a decrease in force compared with controls at the 21-day time point. The early enhancement in force in the TGF-β inhibitor group was associated with an initial improvement in tissue morphology, but, at 21 days, while the control group was fully recovered, the TGF-β inhibitor group displayed an irregular extracellular matrix and an increase in atrogin-1 gene expression. These results indicate that the inhibition of TGF-β promotes the early recovery of muscle function but is detrimental overall to full muscle recovery following moderate to severe muscle injuries.

Topics: Animals; Extracellular Matrix; Fibrosis; Mice; Mice, Inbred C57BL; Muscle Contraction; Muscle Fibers, Skeletal; Muscle Proteins; Muscle Weakness; Muscle, Skeletal; Muscular Atrophy; Recovery of Function; SKP Cullin F-Box Protein Ligases; Transforming Growth Factor beta

Anabolic/androgenic steroids (AAS) are drugs that enhance muscle mass, and are often illegally utilized in athletes to improve their performances. Recent data suggest that the increased risk for amyotrophic lateral sclerosis (ALS) in male soccer and football players could be linked to AAS abuse. ALS is a motor neuron disease mainly occurring in sporadic (sALS) forms, but some familial forms (fALS) exist and have been linked to mutations in different genes. Some of these, in their wild type (wt) form, have been proposed as risk factors for sALS, i.e. superoxide dismutase 1 (SOD1) gene, whose mutations are causative of about 20% of fALS. Notably, SOD1 toxicity might occur both in motor neurons and in muscle cells. Using gastrocnemius muscles of mice overexpressing human mutant SOD1 (mutSOD1) at different disease stages, we found that the expression of a selected set of genes associated to muscle atrophy, MyoD, myogenin, atrogin-1, and transforming growth factor (TGF)β1, is up-regulated already at the presymptomatic stage. Atrogin-1 gene expression was increased also in mice overexpressing human wtSOD1. Similar alterations were found in axotomized mouse muscles and in cultured ALS myoblast models. In these ALS models, we then evaluated the pharmacological effects of the synthetic AAS nandrolone on the expression of the genes modified in ALS muscle. Nandrolone administration had no effects on MyoD, myogenin, and atrogin-1 expression, but it significantly increased TGFβ1 expression at disease onset. Altogether, these data suggest that, in fALS, muscle gene expression is altered at early stages, and AAS may exacerbate some of the alterations induced by SOD1 possibly acting as a contributing factor also in sALS.

Topics: Amyotrophic Lateral Sclerosis; Anabolic Agents; Androgens; Animals; Cells, Cultured; Disease Models, Animal; Gene Expression; Humans; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Motor Neurons; Muscle Proteins; Muscle, Skeletal; Muscular Atrophy; Mutation; Myoblasts; MyoD Protein; Myogenin; Nandrolone; SKP Cullin F-Box Protein Ligases; Superoxide Dismutase; Superoxide Dismutase-1; Transforming Growth Factor beta; Up-Regulation

Transforming growth factor-beta (TGF-β) is a well-known regulator of fibrosis and inflammation in many tissues. During embryonic development, TGF-β signaling induces expression of the transcription factor scleraxis, which promotes fibroblast proliferation and collagen synthesis in tendons. In skeletal muscle, TGF-β has been shown to induce atrophy and fibrosis, but the effect of TGF-β on muscle contractility and the expression of scleraxis and atrogin-1, an important regulator of muscle atrophy, were not known.. We treated muscles from mice with TGF-β and measured force production, scleraxis, procollagen Iα2, and atrogin-1 protein levels.. TGF-β decreased muscle fiber size and dramatically reduced maximum isometric force production. TGF-β also induced scleraxis expression in muscle fibroblasts, and increased procollagen Iα2 and atrogin-1 levels in muscles.. These results provide new insight into the effect of TGF-β on muscle contractility and the molecular mechanisms behind TGF-β-mediated muscle atrophy and fibrosis.

Topics: Animals; Basic Helix-Loop-Helix Transcription Factors; Collagen Type I; Fibrosis; Gene Expression Regulation; Green Fluorescent Proteins; In Vitro Techniques; Mice; Mice, Transgenic; Muscle Contraction; Muscle Proteins; Muscular Atrophy; SKP Cullin F-Box Protein Ligases; Transforming Growth Factor beta

Topics: Aged; Cross-Sectional Studies; Female; Gene Expression Regulation; Humans; Inflammation; Male; Middle Aged; Muscular Atrophy; Myostatin; Phenotype; Pulmonary Disease, Chronic Obstructive; Quadriceps Muscle; RNA, Messenger; Transforming Growth Factor beta

Loss of muscle mass occurs in a variety of diseases, including cancer, chronic heart failure, aquired immunodeficiency syndrome, diabetes, and renal failure, often aggravating pathological progression. Preventing muscle wasting by promoting muscle growth has been proposed as a possible therapeutic approach. Myostatin is an important negative modulator of muscle growth during myogenesis, and myostatin inhibitors are attractive drug targets. However, the role of the myostatin pathway in adulthood and the transcription factors involved in the signaling are unclear. Moreover, recent results confirm that other transforming growth factor-beta (TGF-beta) members control muscle mass. Using genetic tools, we perturbed this pathway in adult myofibers, in vivo, to characterize the downstream targets and their ability to control muscle mass. Smad2 and Smad3 are the transcription factors downstream of myostatin/TGF-beta and induce an atrophy program that is muscle RING-finger protein 1 (MuRF1) independent. Furthermore, Smad2/3 inhibition promotes muscle hypertrophy independent of satellite cells but partially dependent of mammalian target of rapamycin (mTOR) signaling. Thus myostatin and Akt pathways cross-talk at different levels. These findings point to myostatin inhibitors as good drugs to promote muscle growth during rehabilitation, especially when they are combined with IGF-1-Akt activators.

Topics: Age Factors; Animals; Carrier Proteins; Cell Differentiation; Cells, Cultured; Disease Models, Animal; Hypertrophy; Male; Mice; Mice, Transgenic; Muscle Denervation; Muscle Development; Muscle Proteins; Muscle, Skeletal; Muscular Atrophy; Mutation; Myostatin; Phosphorylation; Phosphotransferases (Alcohol Group Acceptor); Protein Serine-Threonine Kinases; Proto-Oncogene Proteins c-akt; Receptor, Transforming Growth Factor-beta Type I; Receptor, Transforming Growth Factor-beta Type II; Receptors, Transforming Growth Factor beta; RNA Interference; RNA, Small Interfering; Sciatic Nerve; Signal Transduction; Smad2 Protein; Smad3 Protein; TOR Serine-Threonine Kinases; Transfection; Transforming Growth Factor beta; Tripartite Motif Proteins; Ubiquitin-Protein Ligases

Three complete cDNAs for the first myostatin-like gene identified in a crustacean species were cloned from the land crab, Gecarcinus lateralis. Sequence analysis demonstrates a high degree of conservation with myostatin orthologs from vertebrates. The furin cleavage site is identical to that of human myostatin, and all nine cysteines critical to the structure/function of mature myostatin peptides are conserved. Message levels for transcripts encoding the complete crustacean preproprotein were highest in skeletal muscle and heart. Lower levels of expression were observed in nervous tissue, gill, gonad, and hepatopancreas. This expansive distribution is similar to that observed for teleost myostatin, vertebrate GDF-11, and amphioxus GDF8/11, and indicates a potentially broad functional repertoire for the land crab ortholog. In addition to one cDNA encoding a complete preproprotein, two cDNAs encoding C-terminal truncated proteins lacking a mature peptide domain were identified. Expression of these truncated splice variants was restricted to skeletal muscle and heart. Myostatin is a potent negative regulator of muscle mass in mammals, and strong expression of this TGF-beta factor in skeletal muscle during intermolt indicates that a myostatin-like gene product could regulate muscle mass in crustaceans when growth is physically restricted by a calcified exoskeleton.

Topics: Alternative Splicing; Animals; Bone Morphogenetic Proteins; Brachyura; Cloning, Molecular; DNA, Complementary; Gene Expression Profiling; Gene Expression Regulation; Growth Differentiation Factors; Humans; Muscle, Skeletal; Muscular Atrophy; Myostatin; RNA, Messenger; Tissue Distribution; Transforming Growth Factor beta

Myostatin belongs to the transforming growth factor-beta superfamily and negatively regulates skeletal muscle mass. Its deletion induces muscle overgrowth, while, on the contrary, its overexpression or systemic administration cause muscle atrophy. The present study was aimed at investigating whether muscle depletion as occurring in an experimental model of cancer cachexia, the rat bearing the Yoshida AH-130 hepatoma, is associated with modulations of myostatin signalling and whether the cytokine tumour necrosis factor-alpha may be relevant in this regard.. Protein levels of myostatin, follistatin (myostatin endogenous inhibitor) and the activin receptor type IIB have been evaluated in the gastrocnemius of tumour-bearing rats by Western blotting. Circulating myostatin and follistatin in tumour hosts were evaluated by immunoprecipitation, while the DNA-binding activity of the SMAD transcription factors was determined by electrophoretic-mobility shift assay.. In day 4 tumour hosts muscle myostatin levels were comparable to controls, yet follistatin was reduced, and SMAD DNA-binding activity was enhanced. At day 7, both myostatin and follistatin increased in tumour bearers, while SMAD DNA-binding activity was unchanged. To investigate whether tumour necrosis factor-alpha contributed to induce such changes, rats were administered pentoxifylline, an inhibitor of tumour necrosis factor-alpha synthesis that partially corrects muscle depletion in tumour-bearing rats. The drug reduced both myostatin expression and SMAD DNA-binding activity in day 4 tumour hosts and up-regulated follistatin at day 7.. These observations suggest that myostatin pathway should be regarded as a potential therapeutic target in cancer cachexia.

Topics: Analysis of Variance; Animals; Blotting, Western; Cachexia; Disease Models, Animal; Male; Muscle, Skeletal; Muscular Atrophy; Myostatin; Rats; Rats, Wistar; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction; Transforming Growth Factor beta; Tumor Necrosis Factor-alpha

Myostatin is a negative regulator of myogenesis, and inactivation of myostatin leads to muscle growth. Here we have used modified RNA oligonucleotides targeting the myostatin mRNA and examined the therapeutic potential in normal and cancer cachexia mouse models. We found that the RNA oligonucleotides could suppress the myostatin expression in vivo, leading to the increase in muscle growth both in normal and cachectic mice. We also established that the effect of myostatin inhibition caused by the RNA oligonucleotides may be through the MyoD pathway, as evidenced by a significant upregulation of MyoD expression. Taken together, these results demonstrate the feasibility using antisense strategy for the treatment of muscle wasting conditions.

Topics: Adenosine Triphosphatases; Administration, Oral; Animals; Base Sequence; Biomarkers; Blotting, Western; Cachexia; Female; Genetic Therapy; Injections, Intraperitoneal; Injections, Intravenous; Mice; Mice, Inbred BALB C; Models, Animal; Molecular Sequence Data; Muscle, Skeletal; Muscular Atrophy; MyoD Protein; Myostatin; Neoplasm Transplantation; Reverse Transcriptase Polymerase Chain Reaction; RNA, Antisense; RNA, Messenger; Transforming Growth Factor beta

Cachexia is a debilitating syndrome characterized by body weight loss, muscle wasting, and anemia. Muscle wasting results from an altered balance between protein synthesis and degradation rates. Reactive oxygen species are indicated as crucial players in the onset of muscle protein hypercatabolism by upregulating elements of the ubiquitin-proteasome pathway. The present study has been aimed at evaluating comparatively the involvement of oxidative stress in the pathogenesis of skeletal muscle wasting in two different experimental models: rats rendered hyperglycemic by treatment with streptozotocin and rats bearing the Yoshida AH-130 ascites hepatoma. For this purpose, both tumor bearers and diabetic animals have been treated with dehydroepiandrosterone (DHEA), a multifunctional steroid endowed with multitargeted antioxidant properties. We show that diabetic rats and AH-130 rats share several features, hypoinsulinemia, occurrence of oxidative stress, and positive response to DHEA administration, although the extent of the effects of DHEA largely differs between diabetic animals and tumor-bearing rats. The hypercatabolism, evaluated in terms of proteasome activity and expression of atrogin-1 and MuRF1, is activated in AH-130 rats, whereas it is lacking in streptozotocin-treated rats. Moreover, we demonstrate that the role of oxidative stress can interfere with muscle wasting through different mechanisms, not necessarily involving NF-kappaB activation. In conclusion, the present results show that, although skeletal muscle wasting occurs in both diabetic rats and tumor-host rats, the underlying mechanisms are different. Moreover, despite oxidative stress being detectable in both experimental models, its contribution to muscle wasting is not comparable.

Topics: Animals; Dehydroepiandrosterone; Diabetes Mellitus, Experimental; DNA; Male; Muscular Atrophy; MyoD Protein; Myostatin; Neoplasms, Experimental; NF-kappa B; Oxidative Stress; Proto-Oncogene Proteins c-jun; Rats; Rats, Wistar; Streptozocin; Transforming Growth Factor beta

Spinal cord injury reduces the rate of skeletal muscle protein synthesis and increases protein breakdown, resulting in rapid muscle loss. The purpose of this study was to determine whether long-term paraplegia would eventually result in a downregulation of muscle mRNA and protein expression associated with both protein synthesis and breakdown. After 10 weeks of spinal cord transection, soleus muscle from 12 rats (6 sham-control, 6 paraplegic) was studied for mRNAs and proteins associated with protein synthesis and breakdown using real-time polymerase chain reaction and immunoblotting techniques. Protein kinase B (PKB/Akt), ribosomal S6 kinase 1 (S6K1), and myogenin mRNA were downregulated, whereas muscle ring finger 1 (MuRF1) and phospho-forkhead transcription factor 4 (FoxO4) protein were increased in paraplegic rats. We conclude that gene and protein expression of pathways associated with protein synthesis are reduced, whereas some markers of protein breakdown remain elevated following chronic paraplegia. Clinical interventions designed to increase muscle protein synthesis may be helpful in preventing excessive muscle loss during long-term paraplegia.

Topics: Animals; Body Weight; Forkhead Transcription Factors; Insulin-Like Growth Factor I; Male; Muscle Proteins; Muscle, Skeletal; Muscular Atrophy; Myogenin; Myostatin; Nerve Tissue Proteins; Paraplegia; Protein Kinases; Proto-Oncogene Proteins c-akt; Rats; Rats, Sprague-Dawley; Ribosomal Protein S6 Kinases; RNA, Messenger; SKP Cullin F-Box Protein Ligases; Spinal Cord Injuries; TOR Serine-Threonine Kinases; Transforming Growth Factor beta; Tripartite Motif Proteins; Ubiquitin-Protein Ligases

Age-related skeletal muscle sarcopenia is linked with increases in falls, fractures, and death and therefore has important socioeconomic consequences. The molecular mechanisms controlling age-related muscle loss in humans are not well understood, but are likely to involve multiple signaling pathways. This study investigated the regulation of several genes and proteins involved in the activation of key signaling pathways promoting muscle hypertrophy, including GH/STAT5, IGF-1/Akt/GSK-3beta/4E-BP1, and muscle atrophy, including TNFalpha/SOCS-3 and Akt/FKHR/atrogene, in muscle biopsies from 13 young (20 +/- 0.2 years) and 16 older (70 +/- 0.3 years) males. In the older males compared to the young subjects, muscle fiber cross-sectional area was reduced by 40-45% in the type II muscle fibers. TNFalpha and SOCS-3 were increased by 2.8 and 1.5 fold, respectively. Growth hormone receptor protein (GHR) and IGF-1 mRNA were decreased by 45%. Total Akt, but not phosphorylated Akt, was increased by 2.5 fold, which corresponded to a 30% reduction in the efficiency of Akt phosphorylation in the older subjects. Phosphorylated and total GSK-3beta were increased by 1.5 and 1.8 fold, respectively, while 4E-BP1 levels were not changed. Nuclear FKHR and FKHRL1 were decreased by 73 and 50%, respectively, with no changes in their atrophy target genes, atrogin-1 and MuRF1. Myostatin mRNA and protein levels were significantly elevated by 2 and 1.4 fold. Human sarcopenia may be linked to a reduction in the activity or sensitivity of anabolic signaling proteins such as GHR, IGF-1, and Akt. TNFalpha, SOCS-3, and myostatin are potential candidates influencing this anabolic perturbation.

Topics: Adult; Aged; Aging; Biopsy; Humans; Male; Models, Biological; Muscle, Skeletal; Muscular Atrophy; Myostatin; Oncogene Protein v-akt; Phosphorylation; Suppressor of Cytokine Signaling 3 Protein; Suppressor of Cytokine Signaling Proteins; Transforming Growth Factor beta; Tumor Necrosis Factor-alpha; Up-Regulation

Preferential atrophy of Type-II muscle fibres occurs in several clinical situations, including cachexia, muscle disuse, chronic glucocorticoid treatment, remote neoplasia, and sometimes as an aspect of recent-denervation. For the patient, the Type-II atrophy itself might be unfavourable (as a glucocorticoid side-effect) or favourable (survivalistic via the muscle-alanine liver-gluconeogenesis pathway in starvation). The cellular mechanisms underlying Type-II fibre atrophy are unclear. Myostatin (Mstn) is physiologically a negative regulator of muscle mass and strength. In this study we evaluated a possible role of Mstn in Type-II fibre atrophy in human muscle. Mstn and Mstn precursor protein (MstnPP) were studied in 10-muscle biopsies containing Type-II fibre atrophy and in 17 disease and normal control muscle biopsies. When comparison was made with normal control fibres, we found the following: 1) by immunocytochemistry, diffusely increased Mstn/MstnPP in the atrophic Type-II muscle fibres; 2) by immunoblots, Mstn/MstnPP increased individually; 3) by RT-PCR, no increase in MstnPP mRNA. In conclusion, our results a) suggest that Mstn/ /MstnPP might play a role in the pathogenic cascade of Type-II muscle fibre atrophy; b) broaden our previously-described associations of Mstn in human muscle pathology, and c) could possibly lead to clinical prevention when Type-II muscle fibre atrophy is unfavourable, for instance in glucocorticoid therapy.

Topics: Adenosine Triphosphatases; Adult; Aged; Aged, 80 and over; Biomarkers; Biopsy; Glucocorticoids; Humans; Immunohistochemistry; Middle Aged; Muscle Fibers, Fast-Twitch; Muscle, Skeletal; Muscular Atrophy; Myostatin; Protein Precursors; RNA, Messenger; Transforming Growth Factor beta; Up-Regulation

Insulin-like growth factor (IGF)-I increases muscle mass while myostatin inhibits its development. Muscle wasting is common in patients with uremic cachexia and may be due to imbalance of this regulation. We had proposed a central mechanism involving leptin and melanocortin signaling in the pathogenesis of uremic cachexia since agouti-related peptide (AgRP), a melanocortin-4 receptor antagonist, reduced uremic cachexia. Here we found that injection of AgRP into the cerebral ventricles resulted in a gain of body mass and improved metabolic rate regulation in a mouse model of uremic cachexia. These salutary effects occurred independent of increased protein and calorie intake. Myostatin mRNA and protein concentrations were increased while those of IGF-I were decreased in the skeletal muscle of uremic mice. AgRP treatment partially corrected these uremia-induced changes. Suppressor of cytokine signaling-2 gene expression (SOCS2) was significantly increased in uremic animals and AgRP reduced this expression. We suggest that AgRP improves uremic cachexia and muscle wasting by a peripheral mechanism involving the balance between myostatin and IGF-I.

Topics: Agouti-Related Protein; Animals; Appetite Regulation; Cachexia; Chronic Disease; Gene Expression; Humans; Insulin-Like Growth Factor I; Leptin; Male; Melanocortins; Mice; Mice, Inbred C57BL; Muscular Atrophy; Myostatin; Nephrectomy; RNA, Messenger; Signal Transduction; Suppressor of Cytokine Signaling 3 Protein; Suppressor of Cytokine Signaling Proteins; Transforming Growth Factor beta; Uremia

Glucocorticoids mediate muscle atrophy in many catabolic states. Myostatin expression, a negative regulator of muscle growth, is increased by glucocorticoids and myostatin overexpression is associated with lower muscle mass. This suggests that myostatin is required for the catabolic effects of glucocorticoids. We therefore investigated whether myostatin gene disruption could prevent muscle atrophy caused by glucocorticoids. Male myostatin knockout (KO) and wild-type mice were subjected to dexamethasone treatment (1 mg/kg.d for 10 d or 5 mg/kg.d for 4 d). In wild-type mice, daily administration of low-dose dexamethasone for 10 d resulted in muscle atrophy (tibialis anterior: -15%; gastrocnemius: -13%; P < 0.01) due to 15% decrease in the muscle fiber cross-sectional area (1621 +/- 31 vs. 1918 +/- 64 microm(2), P < 0.01). In KO mice, there was no reduction of muscle mass nor fiber cross-sectional area after dexamethasone treatment. Muscle atrophy after 4 d of high-dose dexamethasone was associated with increased mRNA of enzymes involved in proteolytic pathways (atrogin-1, muscle ring finger 1, and cathepsin L) and increased chymotrypsin-like proteasomal activity. In contrast, the mRNA of these enzymes and the proteasomal activity were not significantly affected by dexamethasone in KO mice. Muscle IGF-I mRNA was paradoxically decreased in KO mice (-35%, P < 0.05); this was associated with a potentially compensatory increase of IGF-II expression in both saline and dexamethasone-treated KO mice (2-fold, P < 0.01). In conclusion, our results show that myostatin deletion prevents muscle atrophy in glucocorticoid-treated mice, by blunting the glucocorticoid-induced enhanced proteolysis, and suggest an important role of myostatin in muscle atrophy caused by glucocorticoids.

Topics: Animals; Body Weight; Dexamethasone; Gene Deletion; Gene Expression Regulation, Enzymologic; Glucocorticoids; Insulin-Like Growth Factor I; Male; Mice; Mice, Inbred Strains; Mice, Knockout; Muscle Fibers, Skeletal; Muscle, Skeletal; Muscular Atrophy; Myofibrils; Myostatin; Organ Size; Peptide Hydrolases; Proteasome Endopeptidase Complex; Transforming Growth Factor beta; Ubiquitin

Stretching is widely used in rehabilitation and sports activities to improve joint range-of-motion and flexibility in humans, but the effect of stretching on the gene expression of skeletal muscle is poorly understood. We evaluated the effect of short bouts of passive stretching of rat soleus muscle on myo-D, myostatin, and atrogin-1 gene expressions. Six groups of animals were submitted to a single session of stretching (10 stretches of 1 minute with 30 seconds of rest between them, performed manually) and were evaluated immediately (I), and 8, 24, 48, 72, and 168 hours after the session. To evaluate the effect of repetitive sessions of stretching on the soleus muscle over 1 week, three groups of animals received a single session per day of stretching and the muscle was evaluated immediately after 2, 3, and 7 sessions. The mRNA levels of myo-D, myostatin, and atrogin-1 were determined by real-time polymerase chain reaction. A single session of stretching increased the mRNA levels of myo-D (after 24 h), myostatin (I, and 168 h later), and atrogin-1 (after 48 h). Repeated daily session of stretching over 1 week increased myostatin (after 7 sessions) and atrogin-1 expression (after 2, 3, and 7 sessions). Thus, short bouts of passive stretching are able to increase the gene expression of factors associated with muscle growth (myo-D), negative regulation of muscle mass (myostatin), and atrophy (atrogin-1), indicating muscle remodeling through different pathways.

Topics: Animals; Cell Enlargement; Gene Expression Regulation; Male; Muscle Fibers, Skeletal; Muscle Proteins; Muscle Stretching Exercises; Muscle, Skeletal; Muscular Atrophy; MyoD Protein; Myostatin; Physical Conditioning, Animal; Range of Motion, Articular; Rats; Rats, Wistar; Regeneration; RNA, Messenger; SKP Cullin F-Box Protein Ligases; Transforming Growth Factor beta; Up-Regulation

Myostatin is a strong inhibitor of skeletal muscle growth. The purpose of this study was to investigate myostatin expression profiles during denervation-induced muscle atrophy in order to understand the relationship between myostatin expression and muscle atrophy. We constructed a sciatic nerve crush model, undertook morphometric analyses of rat gastrocnemius muscle to evaluate the degree of muscle atrophy, and utilized a real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis to measure myostatin mRNA and protein expression levels, respectively, in the gastrocnemius at different time-points after nerve injury. Muscle atrophy changed in a parabola-like manner from day 1 to day 28 after nerve injury, with a maximum value at day 14. During this time, myostatin expression changed in the reverse manner, with myostatin mRNA or protein expression gradually increasing from days 1-14, and then gradually declining to day 28, when the normal level was reached. Statistical analyses further provided evidence for a significant negative linear correlation between myostatin expression and muscle atrophy within a 28-day period after nerve injury. Our study thus describes the expression pattern of myostatin in response to a specific type of muscle atrophy and raises the possibility of developing myostatin as a therapeutic target for future clinical applications.

Topics: Animals; Muscle, Skeletal; Muscular Atrophy; Myostatin; Nerve Crush; Rats; Rats, Sprague-Dawley; RNA, Messenger; Sciatic Nerve; Sciatic Neuropathy; Transforming Growth Factor beta; Walking

Myostatin is a master regulator of myogenesis and early postnatal skeletal muscle growth. However, myostatin has been also involved in several forms of muscle wasting in adulthood, suggesting a functional role for myostatin in the regulation of skeletal muscle mass in adult. In the present study, localized ectopic expression of myostatin was achieved by gene electrotransfer of a myostatin expression vector into the tibialis anterior muscle of adult Sprague Dawley male rats. The corresponding empty vector was electrotransfected in contralateral muscle. Ectopic myostatin mRNA was abundantly present in muscles electrotransfected with myostatin expression vector, whereas it was undetectable in contralateral muscles. Overexpression of myostatin elicited a significant decrease in muscle mass (10 and 20% reduction 7 and 14 d after gene electrotransfer, respectively), muscle fiber cross-sectional area (15 and 30% reduction 7 and 14 d after gene electrotransfer, respectively), and muscle protein content (20% reduction). No decrease in fiber number was observed. Overexpression of myostatin markedly decreased the expression of muscle structural genes (myosin heavy chain IIb, troponin I, and desmin) and the expression of myogenic transcription factors (MyoD and myogenin). Incidentally, mRNA level of caveolin-3 and peroxisome proliferator activated receptor gamma coactivator-1alpha was also significantly decreased 14 d after myostatin gene electrotransfer. To conclude, our study demonstrates that myostatin-induced muscle atrophy elicits the down-regulation of muscle-specific gene expression. Our observations support an important role for myostatin in muscle atrophy in physiological and physiopathological situations where myostatin expression is induced.

Topics: Animals; Caveolin 3; Gene Expression Regulation; Genetic Vectors; Immunoblotting; Male; Muscle Development; Muscle Fibers, Skeletal; Muscle, Skeletal; Muscular Atrophy; MyoD Protein; Myogenin; Myostatin; Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; RNA-Binding Proteins; RNA, Messenger; Time Factors; Transcription Factors; Transforming Growth Factor beta

Myostatin, a member of the transforming growth factor-beta (TGF-beta) superfamily, has been identified as a negative regulator of skeletal muscle mass. To provide more data on the role of myostatin in denervation-induced muscle atrophy, we examined the time-dependent changes in myostatin mRNA and protein as well as Smad2 and phospho-Smad2 protein levels in the denervated gastrocnemius muscle of mice after sciatic neurectomy, using quantitative real-time RT-PCR and Western blotting, respectively. We conducted morphometric analyses to measure the wet weight ratio of the denervated muscle (the operated side/contralateral nonoperated side) and the cross-sectional area of muscle fibers, and observed the morphology of denervated muscle. The experimental results showed that in the early stage of denervation, the levels of myostatin mRNA and protein in the denervated gastrocnemius muscle increased instantly, reaching a peak at day 3 and day 7 after sciatic neurectomy, respectively, when compared with the normal values. In addition, the phospho-Smad2 protein was observed to have a similar expression profile to that of the myostatin mRNA. The present study perhaps opens a new window into myostatin modulation in muscle atrophy due to denervation.

Topics: Animals; Blotting, Western; DNA Primers; Gene Expression Regulation; Male; Mice; Mice, Inbred ICR; Models, Animal; Muscle Denervation; Muscle, Skeletal; Muscular Atrophy; Myostatin; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Sciatic Nerve; Sciatic Neuropathy; Smad2 Protein; Time Factors; Transforming Growth Factor beta

Foxo-1, a member of the Foxo forkhead type transcription factors, is markedly upregulated in skeletal muscle in energy-deprived states such as fasting, cancer and severe diabetes. In this study, we target the Foxo-1 mRNA in a mouse skeletal myoblast cell line C2C12 and in vivo models of normal and cancer cachexia mice by a Foxo-1 specific RNA oligonucleotide. Our results demonstrate that the RNA oligonucleotide can reduce the expression of Foxo-1 in cells and in normal and cachectic mice, leading to an increase in skeletal muscle mass of the mice. In search for the possible downstream target genes of Foxo-1, we show that when Foxo-1 expression is blocked both in cells and in mice, the level of MyoD, a myogenic factor, is increased while a muscle negative regulator GDF-8 or myostatin is suppressed. Taken together, these results show that Foxo-1 pays a critical role in development of muscle atrophy, and suggest that Foxo-1 is a potential molecular target for treatment of muscle wasting conditions.

Topics: Animals; Cachexia; Cell Line, Tumor; Female; Forkhead Box Protein O1; Forkhead Transcription Factors; Gene Expression Regulation; Mice; Mice, Inbred BALB C; Muscle, Skeletal; Muscular Atrophy; Myoblasts; MyoD Protein; Myostatin; Neoplasms; Oligoribonucleotides, Antisense; Transforming Growth Factor beta

The FASEB summer research conference on Skeletal Muscle Satellite and Stem Cells, organized by Thomas Rando, Giulio Cossu and Jeffrey Chamberlain, was held in Indian Wells, California, in July. An international array of researchers gathered to share numerous new insights into the cellular and molecular regulation of stem cells and satellite cells in skeletal muscle biology. The conference is unique in that it brings together investigators from diverse backgrounds, who work on the growth and repair of skeletal muscle in humans and model systems, in health and disease.

Topics: Animals; Cell Communication; Cell Differentiation; Cell Proliferation; Humans; Muscle Development; Muscle, Skeletal; Muscular Atrophy; Muscular Diseases; Myostatin; Receptors, Notch; Regeneration; Satellite Cells, Skeletal Muscle; Signal Transduction; Transcription Factors; Transforming Growth Factor beta; Wnt Proteins

This study tested the hypothesis that an isometric resistance training paradigm targeting the medial gastrocnemius of adult rodents is effective in preventing muscle atrophy during the early stages of hindlimb unloading by maintaining normal activation of the insulin receptor substrate-1 (IRS-1)/phosphoinositide-3 kinase (PI3K)/Akt signaling pathway. This pathway has been shown to simultaneously create an anabolic response while inhibiting processes upregulating catabolic processes involving expression of key enzymes in the ubiquitination of proteins for degradation. The findings show that during the 5 days of unloading 1) absolute medial gastrocnemius muscle weight reduction occurred by approximately 20%, but muscle weight corrected to body weight was not different from normal weight-bearing controls (P < 0.05); 2) normalized myofibril fraction concentration and content were decreased; and 3) a robust isometric training program, known to induce a hypertrophy response, failed to maintain the myofibril protein content. This response occurred despite fully blunting the increases in the mRNA for of atrogin-1, MURF-1, and myostatin, e.g., sensitive gene markers of an activated catabolic state. Analyses of the IRS-1/PI3K/Akt markers indicated that abundance of IRS-1 and phosphorylation state of Akt and p70S6 kinase were decreased relative to normal control rats, and the resistance training failed to maintain these signaling markers at normal regulatory level. Our findings suggest that to fully prevent muscle atrophy responses affecting the myofibril system during unloading, the volume of mechanical stress must be augmented sufficiently to maintain optimal activity of the IRS-1/PI3K/Akt pathway to provide an effective anabolic stimulus on the muscle.

Topics: Animals; Disease Models, Animal; Electric Stimulation; Exercise Therapy; Female; Hindlimb Suspension; Insulin Receptor Substrate Proteins; Muscle Proteins; Muscle, Skeletal; Muscular Atrophy; Myofibrils; Myostatin; Organ Size; Phosphoproteins; Phosphorylation; Physical Conditioning, Animal; Proto-Oncogene Proteins c-akt; Rats; Rats, Sprague-Dawley; RNA, Messenger; Sciatic Nerve; Signal Transduction; SKP Cullin F-Box Protein Ligases; Transforming Growth Factor beta; Tripartite Motif Proteins; Ubiquitin-Protein Ligases

Myostatin, a member of the transforming growth factor-beta (TGF-beta) superfamily, has been identified as an inhibitor of skeletal muscle mass. To have an insight into the expression pattern of myostatin and its potential role in skeletal muscle atrophy induced by denervation, we used an animal model of peripheral nerve resection to examine the time-dependent changes in myostatin mRNA and protein levels in the denervated gastrocnemius muscle of rats after sciatic neurectomy by the aid of quantitative real-time RT-PCR and Western blotting, respectively. We also conducted morphometric analyses to measure the wet weight ratio of the denervated muscle (the operated side/contralateral non-operated side) and the cross sectional area of muscle fibers and to observe muscle morphology. The experimental results showed that myostatin mRNA and protein levels in rat gastrocnemius muscle persistently elevated after denervation, despite a fluctuation of myostatin mRNA level at day 3 after denervation, reached their respective peaks at day 28 after denervation, and then depressed slightly until day 56 after denervation. Furthermore, a significant negative linear correlation was found between myostatin abundance and muscle atrophy degree, suggesting that myostatin might probably play an important role in denervation-induced muscle atrophy. Our present study perhaps provides a new window into myostatin regulation in association with a specific type of muscle atrophy.

Topics: Animals; Disease Models, Animal; Down-Regulation; Female; Gene Expression Regulation; Male; Muscle Denervation; Muscle Fibers, Skeletal; Muscle, Skeletal; Muscular Atrophy; Myostatin; Rats; Rats, Sprague-Dawley; RNA, Messenger; Sciatic Neuropathy; Time Factors; Transforming Growth Factor beta; Up-Regulation

Amyotrophic lateral sclerosis (ALS) is an incurable neurodegenerative disease leading to motor neuron cell death, but recent studies suggest that non-neuronal cells may contribute to the pathological mechanisms involved. Myostatin is a negative regulator of muscle growth whose function can be inhibited using neutralizing antibodies. In this study, we used transgenic mouse and rat models of ALS to test whether treatment with anti-myostatin antibody slows muscle atrophy, motor neuron loss, or disease onset and progression. Significant increases in muscle mass and strength were observed in myostatin-antibody-treated SOD1(G93A) mice and rats prior to disease onset and during early-stage disease. By late stage disease, only diaphragm muscle remained significantly different in treated animals in comparison to untreated controls. Myostatin inhibition did not delay disease onset nor extend survival in either the SOD1(G93A) mouse or rat. Together, these results indicate that inhibition of myostatin does not protect against the onset and progression of motor neuron degenerative disease. However, the preservation of skeletal muscle during early-stage disease and improved diaphragm morphology and function maintained through late stage disease suggest that anti-myostatin therapy may promote some improved muscle function in ALS.

Topics: Age of Onset; Amyotrophic Lateral Sclerosis; Animals; Animals, Genetically Modified; Antibodies; Cell Death; Diaphragm; Disease Models, Animal; Female; Growth Inhibitors; Humans; Male; Mice; Mice, Knockout; Motor Neurons; Muscle Weakness; Muscle, Skeletal; Muscular Atrophy; Myostatin; Organ Size; Rats; Recovery of Function; Superoxide Dismutase; Superoxide Dismutase-1; Survival Rate; Transforming Growth Factor beta; Treatment Outcome

Resistance to growth hormone (GH)-induced insulin-like growth factor-1 (IGF-1) gene expression contributes to uremic muscle wasting. Since exercise stimulates muscle IGF-1 expression independent of GH, we tested whether work overload (WO) could increase skeletal muscle IGF-1 expression in uremia and thus bypass the defective GH action. Furthermore, to provide insight into the mechanism of uremic wasting and the response to exercise we examined myostatin expression. Unilateral plantaris muscle WO was initiated in uremic and pairfed (PF) normal rats by ablation of a gastrocnemius tendon and adjoining part of this muscle with the contralateral plantaris as a control. Some rats were GH treated for 7 days. WO led to similar gains in plantaris weight in both groups and corrected the uremic muscle atrophy. GH increased plantaris IGF-1 mRNA >twofold in PF rats but the response in uremia was severely attenuated. WO increased the IGF-1 mRNA levels significantly in both uremic and PF groups, albeit less brisk in uremia; however, after 7 days IGF-1 mRNA levels were elevated similarly, >2-fold, in both groups. In the atrophied uremic plantaris muscle basal myostatin mRNA levels were increased significantly and normalized after an increase in WO suggesting a myostatin role in the wasting process. In the hypertrophied uremic left ventricle the basal myostatin mRNA levels were reduced and likely favor the cardiac hypertrophy. Together the findings provide insight into the mechanisms of skeletal muscle wasting in uremia and the hypertrophic response to exercise, and suggest that alterations in the balance between IGF-1 and myostatin play an important role in these processes.

Topics: Animals; Blood Urea Nitrogen; Body Weight; Creatinine; Drug Resistance; Gene Expression; Growth Hormone; Heart; Hypertrophy; Hypertrophy, Left Ventricular; Insulin-Like Growth Factor I; Kidney Failure, Chronic; Male; Muscle, Skeletal; Muscular Atrophy; Myostatin; Physical Conditioning, Animal; Rats; Rats, Sprague-Dawley; RNA, Messenger; Transforming Growth Factor beta; Uremia

Excess glucocorticoids (GCs) cause muscle atrophy. Glucocorticoid-induced muscle atrophy is associated with increased intramuscular myostatin expression. Myostatin is a negative regulator of skeletal muscle mass. Glutamine prevents GC-induced muscle atrophy. We hypothesized that glutamine effect on reversal of GC-induced muscle atrophy is mediated in part by suppression of myostatin. We administered daily to male Sprague-Dawley rats dexamethasone, dexamethasone plus glutamine, saline or saline plus glutamine, all pair-fed. Animals were killed on day 5. Body weight and weights of gastrocnemius muscles were measured. Myostatin expression was measured by Northern and Western blots, and was compared with glyceraldehyde-3-phosphate dehydrogenase. Myoblast C2C12 cells were exposed to dexamethasone, or dexamethasone and glutamine, and their myostatin messenger RNA and protein expression compared with glyceraldehyde-3-phosphate dehydrogenase. Myostatin promoter activity was measured by luciferase activity of transfected C2C12 cells, grown in medium including dexamethasone, or dexamethasone plus glutamine. Rats that received dexamethasone showed significant body and muscle weight loss accompanied by an increase in intramuscular myostatin expression, compared with their saline-treated controls. Pair-fed rats given dexamethasone plus glutamine had significantly less reduction in body and muscle weights and lower myostatin expression when compared with those treated with dexamethasone alone. In C2C12 myoblast cells, addition of glutamine to dexamethasone prevented the hyperexpression of myostatin induced by dexamethasone. Myostatin promoter activity increased in cells exposed to dexamethasone, but this increase was partially blocked by addition of the glutamine. Administration of glutamine partially prevents GC-induced myostatin expression and muscle atrophy, providing a potential mechanism for the prevention of muscle atrophy induced by glucocorticoids.

Topics: Animals; Body Weight; Cell Line; Dexamethasone; Drug Antagonism; Glucocorticoids; Glutamine; Male; Muscle, Skeletal; Muscular Atrophy; Myostatin; Organ Size; Promoter Regions, Genetic; Rats; Rats, Sprague-Dawley; RNA, Messenger; Transforming Growth Factor beta

Sarcopenia is a progressive age-related loss of skeletal muscle mass and strength. Parabiotic experiments show that circulating factors positively influence the proliferation and regenerative capacity of satellite cells in aged mice. In addition, we believe that negative regulators of muscle mass also serve to balance the signals that influence satellite cell activation and regeneration capacity with ageing. Myostatin, a negative regulator of pre- and postnatal myogenesis, inhibits satellite cell activation and muscle regeneration postnatally. To investigate the role of myostatin during age-related sarcopenia, we examined muscle mass and regeneration in young and old myostatin-null mice. Young myostatin-null muscle fibers were characterized by massive hypertrophy and hyperplasia and an increase in type IIB fibers, resulting in a more glycolytic muscle. With ageing, wild-type muscle became increasingly oxidative and fiber atrophy was prominent. In contrast no fiber type switching was observed and atrophy was minimal in aged myostatin-null muscle. The effect of ageing on satellite cell numbers appeared minimal, however, satellite cell activation declined significantly in both wild-type and myostatin-null muscles. In young mice, lack of myostatin resulted in increased satellite cell number and activation compared to wild-type, suggesting a greater propensity to undergo myogenesis, a difference maintained in the aged mice. In addition, muscle regeneration of myostatin-null muscle following notexin injury was accelerated and fiber hypertrophy and type were recovered with regeneration, unlike in wild-type muscle. In conclusion, a lack of myostatin appears to reduce age-related sarcopenia and loss of muscle regenerative capacity.

Topics: Aging; Animals; Cell Shape; Elapid Venoms; Humans; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Muscle Development; Muscle, Skeletal; Muscular Atrophy; Myostatin; Regeneration; Satellite Cells, Skeletal Muscle; Transforming Growth Factor beta

Caveolin-3, the muscle-specific isoform of caveolins, plays important roles in signal transduction. Dominant-negative mutations of the caveolin-3 gene cause autosomal dominant limb-girdle muscular dystrophy 1C (LGMD1C) with loss of caveolin-3. However, identification of the precise molecular mechanism leading to muscular atrophy in caveolin-3-deficient muscle has remained elusive. Myostatin, a member of the muscle-specific TGF-beta superfamily, negatively regulates skeletal muscle volume. Here we report that caveolin-3 inhibited myostatin signaling by suppressing activation of its type I receptor; this was followed by hypophosphorylation of an intracellular effector, Mad homolog 2 (Smad2), and decreased downstream transcriptional activity. Loss of caveolin-3 in P104L mutant caveolin-3 transgenic mice caused muscular atrophy with increase in phosphorylated Smad2 (p-Smad2) as well as p21 (also known as Cdkn1a), a myostatin target gene. Introduction of the myostatin prodomain, an inhibitor of myostatin, by genetic crossing or intraperitoneal administration of the soluble type II myostatin receptor, another inhibitor, ameliorated muscular atrophy of the mutant caveolin-3 transgenic mice with suppression of p-Smad2 and p21 levels. These findings suggest that caveolin-3 normally suppresses the myostatin-mediated signal, thereby preventing muscular atrophy, and that hyperactivation of myostatin signaling participates in the pathogenesis of muscular atrophy in a mouse model of LGMD1C. Myostatin inhibition may be a promising therapy for LGMD1C patients.

Topics: Animals; Caveolin 3; Cell Line; Chlorocebus aethiops; Female; Humans; Male; Mice; Mice, Knockout; Muscle Strength; Muscular Atrophy; Mutation; Myostatin; Phosphorylation; Protein Binding; Recombinant Fusion Proteins; Signal Transduction; Smad2 Protein; Transcription, Genetic; Transforming Growth Factor beta; Transgenes

Skeletal muscle wasting is a common symptom in the adrenal insufficiency such as Addison's disease. Although it has been suspected that several cytokines and/or growth factors are responsible for the manifestation of the symptom, the precise mechanisms underlying the phenomenon have so far been poorly understood. Myostatin is predominantly expressed in skeletal muscles and involved in the regulation of skeletal muscle mass. Recently, several reports indicated that myostatin is secreted into the circulation and the increased levels of circulating myostatin is associated with the induction of skeletal muscle wasting in adult animals. We, therefore, hypothesized that the increased levels of circulating myostatin may account for the development of skeletal muscle wasting in adrenal insufficiency. To test the validity of this hypothesis, we compared the serum levels of myostatin in normal with those in bilaterally adrenalectomized (ADX) rats, a model of Addison's disease, by Western blot analysis. The active form of myostatin (13 kDa) was barely detectable in the sera collected either 1 month or 2 month after adrenalectomy, but present at conspicuously detectable levels in those obtained 3 month after the operation, while the total amounts of myostatin proteins (sum of the precursor and the active forms) remained constant at all the time points examined post-operatively. These results are consistent with the hypothesis that the increased serum levels of active form of myostatin protein, induced yet unknown post-translational control mechanisms may be responsible, at least in part, for the muscle wasting associated with the adrenal insufficiency syndromes.

Topics: Adrenal Insufficiency; Adrenalectomy; Analysis of Variance; Animals; Blotting, Western; Chromatography, Ion Exchange; DNA Primers; Muscle, Skeletal; Muscular Atrophy; Myosin Heavy Chains; Myostatin; Rats; Reverse Transcriptase Polymerase Chain Reaction; Transforming Growth Factor beta

Maintenance hemodialysis patients often display evidence for protein-energy malnutrition, inflammation, and sarcopenia. We therefore investigated whether sedentary maintenance hemodialysis patients have decreased skeletal muscle mRNA levels and muscle and serum protein concentrations of certain growth factors.. Fifty-one clinically stable maintenance hemodialysis patients (32 men and 19 women), and 21 normal adults (16 men and five women) of similar age, gender mix, racial/ethnic backgrounds, serum albumin, body composition, and level of sedentary activity were studied. Individuals underwent biopsy of the right vastus lateralis muscle, and real-time polymerase chain reaction (PCR) amplification of mRNAs for insulin-like growth factor-I (IGF-I), IGF-II, IGF-I receptor (IGF-IR), IGF-IIR, and myostatin (44 patients) was performed. Serum and muscle IGF-I and IGF-II, serum proinflammatory cytokines, and leg muscle strength, power, and fatigability were measured.. Maintenance hemodialysis patients displayed significantly reduced mRNA levels for IGF-IEa mRNA (P < 0.05), IGF-II (P < 0.001), and IGF-IR (P < 0.001), and no difference in mRNAs for IGF-IEc, IGF-IIR, or myostatin as compared to normal controls. Muscle mRNA levels, in general, followed the same pattern in male and female maintenance hemodialysis patients considered separately. In the maintenance hemodialysis patients, muscle IGF-I protein, serum IGF-II and tumor necrosis factor-alpha (TNF-alpha) were each increased, whereas serum C-reactive protein (CRP) and interleukin-6 (IL-6) were normal. Muscle strength and power, but not fatigability, were reduced in the maintenance hemodialysis patients.. In sedentary, clinically stable maintenance hemodialysis patients as compared to sedentary normal individuals, the mRNA levels for IGF-IEa, IGF-II, and the IGF-I receptor are decreased in vastus lateralis muscle. Protein levels for muscle IGF-I and serum IGF-II are increased.

Topics: Adult; Female; Humans; Insulin-Like Growth Factor I; Insulin-Like Growth Factor II; Kidney Failure, Chronic; Life Style; Male; Middle Aged; Motor Activity; Muscle, Skeletal; Muscular Atrophy; Myostatin; Receptor, IGF Type 1; Receptor, IGF Type 2; Renal Dialysis; RNA, Messenger; Transforming Growth Factor beta

Topics: Apoptosis; Humans; Mitogen-Activated Protein Kinases; Muscle, Skeletal; Muscular Atrophy; Muscular Diseases; Quadriplegia; Transforming Growth Factor beta; Ubiquitin

Acute quadriplegic myopathy (AQM; also called "critical illness myopathy") shows acute muscle wasting and weakness and is experienced by some patients with severe systemic illness, often associated with administration of corticosteroids and/or neuroblocking agents. Key aspects of AQM include muscle atrophy and myofilament loss. Although these features are shared with neurogenic atrophy, myogenic atrophy in AQM appears mechanistically distinct from neurogenic atrophy. Using muscle biopsies from AQM, neurogenic atrophy, and normal controls, we show that both myogenic and neurogenic atrophy share induction of myofiber-specific ubiquitin/proteosome pathways (eg, atrogin-1). However, AQM patient muscle showed a specific strong induction of transforming growth factor (TGF)-beta/MAPK pathways. Atrophic AQM myofibers showed coexpression of TGF-beta receptors, p38 MAPK, c-jun, and c-myc, including phosphorylated active forms, and these same fibers showed apoptotic features. Our data suggest a model of AQM pathogenesis in which stress stimuli (sepsis, corticosteroids, pH imbalance, osmotic imbalance) converge on the TGF-beta pathway in myofibers. The acute stimulation of the TGF-beta/MAPK pathway, coupled with the inactivity-induced atrogin-1/proteosome pathway, leads to the acute muscle loss seen in AQM patients.

Topics: Acute Disease; Aged; Gene Expression Profiling; Humans; Immunoblotting; Immunohistochemistry; In Situ Nick-End Labeling; Microscopy, Electron; Middle Aged; Mitogen-Activated Protein Kinases; Muscle, Skeletal; Muscular Atrophy; Muscular Diseases; Oligonucleotide Array Sequence Analysis; Quadriplegia; Reverse Transcriptase Polymerase Chain Reaction; Transforming Growth Factor beta; Ubiquitin

Proliferation and differentiation of satellite cells are critical in the regeneration of atrophied muscle following immobilization and aging. We hypothesized that impaired satellite cell function is responsible for the atrophy of skeletal muscle also seen in cirrhosis. Myostatin and insulin-like growth factor 1 (IGF1) have been identified to be positive and negative regulators, respectively, of satellite cell function. Using a rat model of cirrhosis [portacaval anastamosis (PCA)] and sham-operated controls, we examined the expression of myostatin, its receptor activinR2b, and its downstream messenger cyclin-dependent kinase inhibitor p21 (CDKI p21) as well as IGF1 and its receptor in the gastrocnemius muscle. Expression of PCNA, a marker of proliferation, and myogenic regulatory factors (myoD, myf5, and myogenin), markers of differentiation of satellite cells, were also measured. Real- time PCR for mRNA and Western blot assay for protein quantification were performed. PCA rats had lower body weight and gastrocnemius weight compared with sham animals (P < 0.05). PCNA and myogenic regulatory factors were lower in PCA rats (P < 0.05). Myostatin, activinR2b, and CDKI p21 were higher in the PCA animals (P < 0.05). The expression of IGF1 and its receptor was lower in liver and skeletal muscle of PCA animals (P < 0.05). These data suggest that skeletal muscle atrophy seen in the portacaval shunted rats is a consequence of impaired satellite cell proliferation and differentiation mediated, in part, by higher myostatin and lower IGF1 expression.

Topics: Animals; Antibodies, Monoclonal; Blotting, Western; Body Weight; Cell Differentiation; DNA Primers; Insulin-Like Growth Factor I; Liver Cirrhosis, Experimental; Male; Muscle Proteins; Muscular Atrophy; Myogenic Regulatory Factors; Myosin Heavy Chains; Myostatin; Organ Size; Portacaval Shunt, Surgical; Proteasome Endopeptidase Complex; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; Satellite Cells, Skeletal Muscle; Transforming Growth Factor beta; Ubiquitin

The mechanisms by which excessive glucocorticoids cause muscular atrophy remain unclear. We previously demonstrated that dexamethasone increases the expression of myostatin, a negative regulator of skeletal muscle mass, in vitro. In the present study, we tested the hypothesis that dexamethasone-induced muscle loss is associated with increased myostatin expression in vivo. Daily administration (60, 600, 1,200 micro g/kg body wt) of dexamethasone for 5 days resulted in rapid, dose-dependent loss of body weight (-4.0, -13.4, -17.2%, respectively, P < 0.05 for each comparison), and muscle atrophy (6.3, 15.0, 16.6% below controls, respectively). These changes were associated with dose-dependent, marked induction of intramuscular myostatin mRNA (66.3, 450, 527.6% increase above controls, P < 0.05 for each comparison) and protein expression (0.0, 260.5, 318.4% increase above controls, P < 0.05). We found that the effect of dexamethasone on body weight and muscle loss and upregulation of intramuscular myostatin expression was time dependent. When dexamethasone treatment (600 micro g. kg-1. day-1) was extended from 5 to 10 days, the rate of body weight loss was markedly reduced to approximately 2% within this extended period. The concentrations of intramuscular myosin heavy chain type II in dexamethasone-treated rats were significantly lower (-43% after 5-day treatment, -14% after 10-day treatment) than their respective corresponding controls. The intramuscular myostatin concentration in rats treated with dexamethasone for 10 days returned to basal level. Concurrent treatment with RU-486 blocked dexamethasone-induced myostatin expression and significantly attenuated body loss and muscle atrophy. We propose that dexamethasone-induced muscle loss is mediated, at least in part, by the upregulation of myostatin expression through a glucocorticoid receptor-mediated pathway.

Topics: Animals; Body Weight; Dexamethasone; Gene Expression Regulation; Glucocorticoids; Kinetics; Male; Mifepristone; Muscle, Skeletal; Muscular Atrophy; Myostatin; Organ Size; Rats; Rats, Sprague-Dawley; Receptors, Glucocorticoid; RNA, Messenger; Transforming Growth Factor beta

Changes in myostatin content and localization in mouse skeletal muscles were investigated during aging, hindlimb suspension (HS) and reloading after HS. During aging, the content of myostatin among solubilized proteins in gastrocnemius and plantaris muscles (Gast/Plant) was initially low and increased until their wet weight/body weight ratio reached a peak. It remained unchanged with further aging, although gradual atrophy of the muscles was seen to occur. Also, the myostatin content did not change significantly during HS (up to 14 days) in both Gast/Plant and soleus muscles, though the muscles showed morphological signs of atrophy. However, reloading for 2 days after a 14-day HS caused significant decreases in the myostatin content in both of these muscles. Immunohistochemical observations showed the sarcoplasmic existence of myostatin, the amount of which appeared to decrease after reloading. The results suggest that myostatin plays a part in the processes of muscular growth and loading-induced hypertrophy, but is not involved in either aging-related or unloading-induced muscular atrophy.

Topics: Aging; Animals; Hindlimb Suspension; Immunohistochemistry; Male; Mice; Mice, Inbred C57BL; Muscle, Skeletal; Muscular Atrophy; Myostatin; Transforming Growth Factor beta; Weight-Bearing

Human disuse muscle atrophy frequently accompanies orthopedic injury, arthritis, or bed rest, and recovery is often incomplete despite current rehabilitation programs. We have studied the vastus lateralis muscle in 12 patients with chronic disuse atrophy associated with chronic osteoarthritis of the hip both preoperatively and after total hip arthroplasty. Semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) demonstrated an increase in the level of expression of myostatin, insulin-like growth factor-1 (IGF-1) and leukemia inhibitory factor (LIF) mRNAs compared to healthy control muscle. In all patients there was a significant correlation preoperatively between increasing myostatin mRNA expression and reduction in type 2A and 2B fiber area. In the 8 female patients there was a significant correlation between increased myostatin mRNA expression and the atrophy factor calculated for 2A and 2B fiber types preoperatively. We hypothesize that a complex interaction occurs between muscle growth regulating factors in the genesis of muscle wasting. Our results indicate that myostatin is a muscle-wasting factor contributing to type 2B and 2A atrophy. Other muscle growth factors, such as IGF-1 and LIF, may be upregulated in a counterregulatory fashion or may be involved in the fiber type switching seen in disuse muscle wasting.

Topics: Adult; Aged; Chronic Disease; Female; Gene Expression; Growth Inhibitors; Humans; Immobilization; Insulin-Like Growth Factor I; Interleukin-6; Leukemia Inhibitory Factor; Lymphokines; Male; Middle Aged; Muscle, Skeletal; Muscular Atrophy; Myostatin; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Transforming Growth Factor beta

To determine whether polymorphic variation in the myostatin gene differentially influences the maintenance of muscle strength in older adults, and to find supportive evidence in a cohort of older women.. Correlation study of polymorphic variation in a cohort of older women.. Representatively sampled older female population living in the eastern half of Baltimore, Maryland.. Participants were 286 women, age 70 to 79. Of these, 81.1% were Caucasian, 18.8% were African American, and 0.2% were Asian or Hispanic.. Overall strength was measured with a dynamometer and defined as the sum of the strongest measures of hip, knee, and grip strength on the dominant side.. We identified or confirmed six myostatin polymorphic variants in the Women's Health and Aging Study II population. Of the polymorphisms, K153R is the most common, with an allele frequency of 0.19 in African Americans. Unadjusted mean strength by genotype suggested lower muscle strength in those African-American women with the R genotype compared with those with the K genotype (K/K: 72.50 +/- 13.9 kg (n = 39) vs K/R: 67.14 +/- 11.4 kg (n = 13) vs R/R: 63.1 +/- 11.3 kg (n = 3)). After adjustment for race in a linear regression model, the R genotype remained associated with lower strength levels (P = .04). Statistical significance decreased when body mass index and race were both added to the model (P = .09).. Recognizing that small sample size in the study of genes of modest effect are unlikely to yield significant differences, these data suggest an association of the R153 allele with lower strength in high-functioning older women, which should be studied further in a larger cohort.

Topics: Aged; Baltimore; Black People; Female; Gene Frequency; Genetic Predisposition to Disease; Humans; Linear Models; Muscle, Skeletal; Muscular Atrophy; Myostatin; Polymorphism, Single-Stranded Conformational; Transforming Growth Factor beta; White People

Myostatin is a newly described member of the TGF-beta superfamily acting as a secreted negative regulator of skeletal muscle mass in several species, but whose mode of action remains largely unknown. In the present work, we followed the myostatin mRNA and protein levels in rat soleus and extensor digitorum longus (EDL) muscles regenerating in vivo from notexin-induced necrosis, and the myostatin transcript levels in two different in vitro myogenic differentiation models: i.e. in mouse BC3H1 and C2Cl2 cultured cells. The in vivo regenerating rat skeletal muscles showed a characteristic time-dependent expression of myostatin mRNA. After notexin injection, the transcript levels dropped below the detection limit on day 1 in soleus and close to the detection limit on day 3 in EDL, then increased to a maximum on day 7 in soleus and after 28 days finally reached the control values in both types of muscles. In contrast, the myostatin protein levels increased dramatically on the first days of regeneration in both muscles, i.e. at the time when its transcript level was low. Later on the myostatin protein level gradually declined to normal in soleus while in EDL it stayed high some days longer and decreased to normal on days 21-28. In vitro proliferating myoblasts produced low level of myostatin mRNA, which increased upon induction of differentiation suggesting that functional innervation is no prerequisite for myostatin expression. Myostatin production in vitro seems not to be dependent on myocyte fusion either, since it is observed in differentiated BC3H1 cells, which are defective in myofiber formation.

Topics: Animals; Cells, Cultured; Culture Media; Elapid Venoms; Gene Expression Regulation, Developmental; Male; Models, Biological; Muscle Development; Muscle Fibers, Skeletal; Muscle, Skeletal; Muscular Atrophy; Myostatin; Rats; Rats, Wistar; Regeneration; RNA, Messenger; Time Factors; Transcription, Genetic; Transforming Growth Factor beta

It has been hypothesized that myostatin, a newly identified member of the transforming growth factor-beta (TGF-beta) family of proteins, acts as a negative regulator of skeletal muscle growth. Because bed rest induced muscle atrophy results from a decreased rate of muscle protein synthesis, we hypothesized that circulating levels of myostatin would be increased following prolonged bed rest. Twelve men (age, 35.8 +/- 4.6 yr; height, 175.7 +/- 2.3 cm; weight, 74.8 +/- 3.5 kg; mean +/- SE) were confined to bed for 25 days at 6 degrees head-down tilt while receiving triiodothyronine (T3; 50 micrograms/day) to accelerate protein loss. Total lean body and appendicular skeletal muscle mass were determined by dual energy x-ray absorptiometry (DEXA) before and after the bed rest period. Plasma myostatin-immunoreactive protein was measured in blood samples obtained after an overnight fast 5 days prior to, and on the 25th day of bed rest. Lean body mass decreased an average 2.2 kg (p < 0.0001). Appendicular skeletal muscle accounted for a majority of the lean body mass loss. On day 25 of bed rest, plasma myostatin-immunoreactive protein was 12% higher (p = 0.01) than measured at baseline. These data support the idea that myostatin regulates muscle growth in humans and that it may be a novel target for interventions aiming to reduce space flight induced muscle atrophy.

Topics: Adult; Bed Rest; Body Composition; Head-Down Tilt; Humans; Male; Muscle, Skeletal; Muscular Atrophy; Myostatin; Thyrotropin; Thyroxine; Transforming Growth Factor beta; Triiodothyronine; Weightlessness Simulation

Masticatory muscle myositis (MMM) is presumed to be an immunologically mediated canine myopathy but is of unknown origin. Severe atrophy and degeneration of masticatory muscle fibres, infiltration of eosinophilic granulocytes, and proliferation of the fibrous interstitial tissue are the hallmarks of MMM. Transforming growth factor-beta (TGF-beta) is a multifunctional regulatory peptide controlling myogenesis, inflammation and tissue repair. We investigated immunocytochemically the expression of TGF-beta 1 and latent transforming growth factor-beta binding protein (LTBP), a TGF-beta modulator protein, in cases of MMM. The study demonstrated the presence of TGF-beta and LTBP in muscle fibres. infiltrating leucocytes and extracellular matrix in MMM, and suggested that TGF-beta and LTBP play a role in muscle tissue repair, inflammation and fibrogenesis in MMM.

Topics: Animals; Dogs; Female; Immunohistochemistry; Male; Masticatory Muscles; Muscle Fibers, Skeletal; Muscular Atrophy; Myositis; Transforming Growth Factor beta