transforming-growth-factor-beta and Muscular-Diseases

Post-natal skeletal muscle is a highly plastic tissue that has the capacity to regenerate rapidly following injury, and to undergo significant modification in tissue mass (i.e. atrophy/hypertrophy) in response to global metabolic changes. These processes are reliant largely on soluble factors that directly modulate muscle regeneration and mass. However, skeletal muscle function also depends on an adequate blood supply. Thus muscle regeneration and changes in muscle mass, particularly hypertrophy, also demand rapid changes in the microvasculature. Recent evidence clearly demonstrates a critical role for soluble growth factors in the tight regulation of angiogenic expansion of the muscle microvasculature. Furthermore, exogenous modulation of these factors has the capacity to impact directly on angiogenesis and thus, indirectly, on muscle regeneration, growth and performance. This chapter reviews recent developments in understanding the role of growth factors in modulating the skeletal muscle microvasculature, and the potential therapeutic applications of exogenous angiogenic and anti-angiogenic mediators in promoting effective growth and regeneration, and ameliorating certain diseases, of skeletal muscle.

Topics: Adult; Hedgehog Proteins; Humans; Intercellular Signaling Peptides and Proteins; Microvessels; Muscle, Skeletal; Muscular Diseases; Neovascularization, Physiologic; Regeneration; Transforming Growth Factor beta; Vascular Endothelial Growth Factor A

The purpose of this study is to discuss the involvement of bone and morphogenetic proteins (BMPs) in the control of muscle mass.. The transforming growth factor-beta (TGFβ) superfamily comprises a large number of secreted proteins that regulate a variety of fundamental biological processes. Sequence similarities define two ligand subfamilies: the TGFβ/Activin subfamily and the BMP subfamily. Within the members of TGFβ subfamily, myostatin emerged as the most critical ligand that affects muscle size and function. Indeed, mutations that inactivate Myostatin lead to important muscle growth in animals and humans. However, recent findings have increased the complexity of the TGFβ superfamily. Indeed, two independent groups have shown that BMP pathway, acting through Smad1/5/8, is the fundamental hypertrophic signal and dominates Myostatin signalling. Moreover, BMP-Smad1/5/8 negatively regulates a novel ubiquitin ligase, named MUSA1 that is required for muscle loss. This article reviews the rapid progress made in the last year regarding the signalling downstream TGFβ superfamily and its involvement in the homeostasis of adult muscle fibres.. The recent insights gained into the interplay of TGFβ and BMP signalling in muscle have challenged our pre-existing ideas of how the adult skeletal muscle phenotype is regulated in health and disease.

Topics: Activins; Animals; Bone Morphogenetic Proteins; Humans; Muscle, Skeletal; Muscular Diseases; 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

Skeletal muscle fibrosis can be a devastating clinical problem that arises from many causes, including primary skeletal muscle tissue diseases, as seen in the muscular dystrophies, or it can be secondary to events that include trauma to muscle or brain injury. The cellular source of activated fibroblasts (myofibroblasts) may include resident fibroblasts, adult muscle stem cells, or inflammatory or perivascular cells, depending on the model studied. Even though it is likely that there is no single source for all myofibroblasts, a common mechanism for the production of fibrosis is via the transforming growth factor-β/phosphorylated Smad3 pathway. This pathway and its downstream targets thus provide loci for antifibrotic therapies, as do methods for blocking the transdifferentiation of progenitors into activated fibroblasts. A structural model for the extracellular collagen network of skeletal muscle is needed so that measurements of collagen content, morphology, and gene expression can be related to mechanical properties. Approaches used to study fibrosis in tissues, such as lung, kidney, and liver, need to be applied to studies of skeletal muscle to identify ways to prevent or even cure the devastating maladies of skeletal muscle.

Topics: Animals; Cell Transdifferentiation; Collagen; Extracellular Matrix; Extracellular Matrix Proteins; Fibrosis; Humans; Muscle, Skeletal; Muscular Diseases; Myofibroblasts; Myostatin; Smad3 Protein; Transforming Growth Factor beta; Wnt Signaling Pathway

Modifiers of TGFβ signaling have been investigated as treatment options for several types of muscle diseases. The purpose of this review is to focus on the most recent studies that have used this treatment strategy for pathological muscle disorders. We also review the recent insight into the mechanistic processes by which TGFβ signaling contributes to these pathologies by promoting fibrosis formation.. Recent research has shed light on the role of TGFβ signaling in the regulation of microRNAs associated with fibrosis formation. Inhibition of TGFβ signaling by Losartan treatment greatly improved the phenotype of myopathies associated with laminin-α2-deficient congenital muscular dystrophy. Caveolin 3 deficiency was also ameliorated by the use of several different types of TGFβ signaling inhibitors. Use of Losartan had dramatically beneficial effects on sarcopenic muscle by improving the regeneration after injury. Pharmacological manipulation to increase muscle mass is an emerging trend in obesity treatment research. New advances in the use of potent myostatin inhibitors have made this an attractive approach for future studies.. An increasing number of skeletal myopathies are demonstrating favorable responses to alterations of the TGFβ signaling pathway. However, future research is needed to fully understand the downstream molecular signature associated with this pathway in order to develop more specific targeted therapies.

Topics: Animals; Caveolin 3; Disease Models, Animal; Fibrosis; Humans; Losartan; MicroRNAs; Muscle, Skeletal; Muscular Diseases; Muscular Dystrophies; Sarcopenia; Signal Transduction; Transforming Growth Factor beta

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

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

Topics: Adipose Tissue; Agriculture; Animals; Brain; Cattle; Evolution, Molecular; Fishes; Heart; Humans; Mice; Muscular Diseases; Myostatin; Sheep; Transforming Growth Factor beta

Wasting, or cachexia, is a significant, debilitating, and potentially life-threatening complication of HIV infection. It is associated with reduced strength and functional ability, reduced ability to withstand opportunistic infections, and increased risk of mortality. Although the incidence of HIV-associated wasting may have declined since the introduction of highly active antiretroviral therapy (HAART), it continues to be a concern in this patient population.. This paper reviews available data on the etiology and clinical impact of HIV-associated wasting, the role of the growth hormone/insulin-like growth factor-I axis in the pathophysiology of this condition, and the rationale for its treatment with recombinant human growth hormone (rhGH).. MEDLINE was searched for articles published in English through August 2007 using the terms HIV, wasting (and related terms), and growth hormone. Preference was given to clinical studies (including randomized clinical studies), meta-analyses, and guidelines. Review articles were evaluated and the bibliographies examined for additional relevant articles. The analysis was restricted to studies conducted in developed countries.. Alterations in the growth hormone/insulin like growth factor-I axis have been observed in patients with HIV-associated wasting, including elevated levels of the former and reduced levels of insulin-like growth factor I. In randomized, placebo-controlled studies, rhGH significantly improved lean body mass by approximately 3 kg compared with placebo (P < 0.001) and total body weight by approximately 3 kg (P < 0.001), and was associated with significant improvements in physical endurance and quality of life (P < 0.001). Common adverse events with rhGH therapy include blood glucose elevations, arthralgia (36.4%), myalgia (30.4%), and peripheral edema (26.1%), but these usually respond to dose reduction or drug discontinuation.. Physicians should be alert to the possibility of wasting in HIV-infected patients receiving HAART and should consider treatment to improve patients' stamina and quality of life. The evidence supports a role for rhGH in the treatment of patients with HIV-associated wasting. Regular blood glucose monitoring is advised when treating wasting with rhGH.

Topics: Adolescent; Adult; Antiretroviral Therapy, Highly Active; Body Composition; Cachexia; Child; Cytokines; Energy Metabolism; Growth Hormone; HIV Infections; HIV Wasting Syndrome; Human Growth Hormone; Humans; Insulin-Like Growth Factor I; Muscular Diseases; Myostatin; Proteins; Recombinant Proteins; Risk Factors; Signal Transduction; Testosterone; Transforming Growth Factor beta

Skeletal muscle is the largest organ in the human body, and plays an important role in body movement and metabolism. Skeletal muscle mass is lost in genetic disorders such as muscular dystrophy, muscle wasting and ageing. Chemicals and proteins that restore muscle mass and function are potential drugs that can improve human health and could be used in the clinic. Myostatin is a muscle-specific member of the transforming growth factor (TGF)-beta superfamily that plays an essential role in the negative regulation of muscle growth. Inhibition of myostatin activity is a promising therapeutic method for restoring muscle mass and strength. Potential inhibitors of myostatin include follistatin domain-containing proteins, myostatin propeptide, myostatin antibodies and chemical compounds. These inhibitors could be beneficial for the development of clinical drugs for the treatment of muscular disorders. Bone morphogenetic protein (BMP) plays a significant role in the development of neuromuscular architecture and its proper functions. Modulation of BMP activity could be beneficial for muscle function in muscular disorders. This review will describe the current progress in therapy for muscular disorders, emphasising the importance of myostatin as a drug target.

Topics: Animals; Bone Morphogenetic Proteins; Follistatin; Humans; Models, Biological; Muscle, Skeletal; Muscles; Muscular Diseases; Muscular Dystrophies; Myosarcoma; Myostatin; Protein Structure, Tertiary; Transforming Growth Factor beta

The transforming growth factor-beta (TGF-beta) superfamily includes TGF-betas, activin, myostatin and bone morphogenetic proteins. Misregulation of the activity of TGF-beta family members is involved in pathogenesis of cancer, muscular dystrophy, obesity and bone and tooth remodeling. Natural inhibitors for the TGF-beta superfamily regulate fine-tuning of activity of TGF-beta family in vivo. In addition to natural inhibitors for the TGF-beta family, soluble forms of receptors for the TGF-beta family, blocking monoclonal antibodies and small chemical TGF-beta inhibitors have been developed. In this review, we summarize recent advances in our understanding of inhibitors for the TGF-beta superfamily and their medical applications.

Topics: Animals; Bone Morphogenetic Proteins; Humans; Muscular Diseases; Myostatin; Neoplasms; Protein Binding; Transforming Growth Factor beta

Skeletal muscle possesses the ability to both respond and adapt to changing environmental stimuli, leading to a set of metabolic and morphological adaptations, which allow it to better meet the energy demands of sustained physical activity. Great progress has been achieved over the past years by means of innovative molecular techniques, which has led to the discovery of new growth factors and the identification of molecular mechanisms involved in the regulation of muscle development. These findings provide new starting points to understand the molecular mechanisms involved in the adaptation of skeletal muscle to exercise training. One of these new identified growth factors is myostatin, a member of the transforming growth factor-beta family of proteins that has been demonstrated to play a fundamental role in the regulation of skeletal muscle growth during embryogenesis. Blocking of the myostatin signalling transduction pathway by specific inhibitors and genetic manipulations has been shown to result in a dramatic increase of skeletal muscle mass. This review focuses on the importance of myostatin in mediating skeletal muscle homeostasis in response to training as well as during the progress of myogenic disease, like atrophy or dystrophy. Manipulations of myostatin signalling may be useful for agriculture applications, treatment of muscle diseases, inhibition of muscle atrophy and last but not least as life style drugs in antiaging therapies or manipulations of the muscle to fat ratio. Drugs with the ability to modulate myostatin signalling may have the potential to enhance physical performance in athletes and therefore they probably represent a new class of doping substances.

Topics: Animals; Cattle; Doping in Sports; Homeostasis; Humans; Muscle, Skeletal; Muscular Diseases; Myostatin; Phenotype; Physical Endurance; Signal Transduction; Sports; Transforming Growth Factor beta

Myostatin is a secreted protein that negatively regulates skeletal muscle mass determining both muscle fiber number and size. The myostatin pathway is conserved and regulates muscle mass in a number of animal species ranging from fish to humans. Inhibition of myostatin using a variety of therapeutic approaches can increase muscle mass in a number of animal models of human disease, including muscular dystrophy.

Topics: Animals; Humans; Muscular Diseases; Myostatin; Signal Transduction; Transforming Growth Factor beta

Myostatin is a member of the TGF-beta superfamily of secreted growth factors. A lack of functional myostatin or inhibition of the normal myostatin function results in an increased muscling phenotype and, conversely, the systemic administration of myostatin results in muscle wasting. Thus, myostatin is well established as a negative regulator of skeletal muscle mass. Myostatin binds to cell-surface receptors to inhibit both the proliferation and differentiation of myoblasts. Moreover, it functions to regulate both embryonic and post-natal musculature. Thus, potential antagonists to myostatin, whether targeting myostatin synthesis, secretion or receptor binding, show great promise as therapies against muscle-wasting diseases. This review provides an expert opinion on the biology and potential of myostatin antagonists in the treatment of muscle-wasting disorders.

Topics: Animals; Growth Inhibitors; Humans; Muscular Diseases; Myostatin; Technology, Pharmaceutical; Transforming Growth Factor beta

Myostatin is an endogenous, negative regulator of muscle growth. Selective inhibition of myostatin may have broad clinical utility by improving regeneration in diverse and burdensome muscle disorders. An understanding of this potential is relevant because inhibitors of myostatin have recently entered clinical trials.. This article reviews the structure and function of myostatin, the effect of inhibiting myostatin in models of disease, and potential therapeutic approaches to blocking myostatin pharmacologically. The possibility that a myostatin inhibitor will promote muscle regeneration in human disease, as seen in animal models, is suggested by the observation that loss of myostatin results in muscle hypertrophy in a human subject.. Multiple approaches to inhibiting myostatin are suggested by the recent elucidation of its signaling pathway. An inhibitor of myostatin may be the first drug specifically designed to enhance muscle growth and regeneration.

Topics: Animals; Cell Differentiation; Follistatin; Follistatin-Related Proteins; Humans; Muscle, Skeletal; Muscular Diseases; Myostatin; Regeneration; Transforming Growth Factor beta; Vesicular Transport Proteins

This review discusses recent developments in myostatin research, focusing on the basic actions of myostatin on skeletal muscle, the identification of key regulatory elements of the myostatin pathway, and the promise of myostatin as a therapeutic target in muscle-related disorders.. In addition to a well-characterized role in muscle development, recent research advances have solidified the importance of myostatin in adult muscle, although questions remain. A number of possible regulatory proteins for myostatin have been identified, showing a complex picture of myostatin regulation that requires clarification. The identification of an antimyostatin monoclonal antibody (JA16) shows the promise of myostatin as a target for muscle-wasting disorders; the antibody has already been shown to increase muscle mass in healthy older mice and muscle function in postnatal mdx mice.. Since its discovery in 1997, myostatin has quickly been established as a key regulator of skeletal muscle mass. Recent developments strengthen the idea that myostatin will be an important therapeutic target for muscle-wasting-related disorders, and as more details of myostatin regulation and its mechanisms of action are clarified, myostatin will continue to dominate the skeletal muscle development and muscle-wasting literature.

Topics: Animals; Antibodies, Monoclonal; Gene Expression; Humans; Muscle, Skeletal; Muscular Diseases; Myostatin; Regeneration; Transcription, Genetic; Transforming Growth Factor beta

Myostatin is a secreted protein that acts as a negative regulator of skeletal muscle mass. During embryogenesis, myostatin is expressed by cells in the myotome and in developing skeletal muscle and acts to regulate the final number of muscle fibers that are formed. During adult life, myostatin protein is produced by skeletal muscle, circulates in the blood, and acts to limit muscle fiber growth. The existence of circulating tissue-specific growth inhibitors of this type was hypothesized over 40 years ago to explain how sizes of individual tissues are controlled. Skeletal muscle appears to be the first example of a tissue whose size is controlled by this type of regulatory mechanism, and myostatin appears to be the first example of the long-sought chalone.

Topics: Animals; Muscle, Skeletal; Muscular Diseases; Myostatin; Signal Transduction; Transforming Growth Factor beta

The development of new biological approaches based on cell and gene therapies, in combination with tissue engineering, may create innovative ways to treat various tissues of the musculoskeletal system. It is vital for practicing orthopaedic surgeons to understand the terminology, fundamental concepts, and current research in this burgeoning field so that they may practice their discipline in its fullest form. Such techniques, coupled with advances in cell biology and polymer chemistry, are resulting in novel approaches to treating musculoskeletal disorders in which surgeons, who have traditionally used the tools of excision and reconstruction to treat patients, may now serve as surgical gardeners who create microenvironments that are conducive for tissue regeneration. Gene therapy and tissue engineering applications for bone healing, articular disorders, and skeletal muscle diseases and injuries are currently being explored. This review is intended to update readers on the principles and current advances in muscle-based gene therapy and tissue engineering for the musculoskeletal system.

Topics: Animals; Bone Diseases; Bone Morphogenetic Protein 2; Bone Morphogenetic Proteins; Cell Transplantation; Forecasting; Genetic Therapy; Genetic Vectors; Humans; Injections, Intra-Articular; Joint Diseases; Muscle, Skeletal; Muscular Diseases; Muscular Dystrophies; Recombinant Fusion Proteins; Recombinant Proteins; Stem Cell Transplantation; Stem Cells; Tissue Engineering; Transforming Growth Factor beta; Wound Healing

Volumetric muscle loss (VML) overwhelms the innate regenerative capacity of mammalian skeletal muscle (SkM), leading to numerous disabilities and reduced quality of life. Immune cells are critical responders to muscle injury and guide tissue resident stem cell– and progenitor-mediated myogenic repair. However, how immune cell infiltration and intercellular communication networks with muscle stem cells are altered following VML and drive pathological outcomes remains underexplored. Herein, we contrast the cellular and molecular mechanisms of VML injuries that result in the fibrotic degeneration or regeneration of SkM. Following degenerative VML injuries, we observed the heightened infiltration of natural killer (NK) cells as well as the persistence of neutrophils beyond 2 wk postinjury. Functional validation of NK cells revealed an antagonistic role in neutrophil accumulation in part via inducing apoptosis and CCR1-mediated chemotaxis. The persistent infiltration of neutrophils in degenerative VML injuries was found to contribute to impairments in muscle stem cell regenerative function, which was also attenuated by transforming growth factor beta 1 (TGFβ1). Blocking TGFβ signaling reduced neutrophil accumulation and fibrosis and improved muscle-specific force. Collectively, these results enhance our understanding of immune cell–stem cell cross talk that drives regenerative dysfunction and provide further insight into possible avenues for fibrotic therapy exploration.

Topics: Animals; Fibrosis; Killer Cells, Natural; Mice; Muscle, Skeletal; Muscular Diseases; Neutrophil Infiltration; Neutrophils; Regeneration; Satellite Cells, Skeletal Muscle; Transforming Growth Factor beta

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

Fibrosis has also been recorded as a prominent pathological feature within wooden breast (WB) myopathy of broiler chickens. This study was conducted to evaluate the accumulation of fibril collagen, deposition of the extracellular matrix (ECM) components, and the underlying mechanism mediating the pathogenic fibrotic process in the pectoralis major (PM) muscle of WB-affected birds. Broiler chickens were categorized into the control and WB groups based on the evaluation of myopathic lesions. Results indicated that the total content and area of collagen in cross-sections of the PM muscle, as well as the augmented expression of collagen-I and fibronectin in the ECM, were greatly increased in birds with WB. Wooden breast myopathy upregulated expressions of transforming growth factor-beta (TGF-β) and the phosphorylation of Smad 2 and 3, thereby activating TGF-β-mediated Smad signaling pathway, which further enhanced the transcription of profibrotic mediators. In addition, regulators involved in collagen biosynthesis and cross-linking including prolyl 4-hydroxylase, lysyl oxidase, lysyl hydroxylase, and decorin were increased in the WB muscle. Finally, the expressions of both matrix metalloproteinases (MMP) and tissue inhibitor of metalloproteinases (TIMP) were increased in the WB muscle, which might be related with reduced ECM remodeling. Overall, WB myopathy induces severe fibrosis by enhancing ECM deposition and collagen cross-linking in the PM muscle of broiler chickens, possibly via the activation of TGF-β signaling and the dysregulation of the MMP and TIMP system.

Topics: Animals; Chickens; Fibrosis; Muscular Diseases; Pectoralis Muscles; Poultry Diseases; Signal Transduction; Transforming Growth Factor beta

Cancer-induced skeletal muscle defects show sex-specific differences in severity with men performing poorly compared to women. Hormones and sex chromosomal differences are suggested to mediate these differences, but the functional skeletal muscle markers to document these differences are unknown. We show that the myogenic microRNA miR-486 is a marker of sex-specific differences in cancer-induced skeletal muscle defects. Cancer-induced loss of circulating miR-486 was more severe in men with bladder, lung, and pancreatic cancers compared to women with the same cancer types. In a syngeneic model of pancreatic cancer, circulating and skeletal muscle loss of miR-486 was more severe in male mice compared to female mice. Estradiol (E2) and the clinically used selective estrogen receptor modulator toremifene increased miR-486 in undifferentiated and differentiated myoblast cell line C2C12 and E2-inducible expression correlated with direct binding of estrogen receptor alpha (ERα) to the regulatory region of the miR-486 gene. E2 and toremifene reduced the actions of cytokines such as myostatin, transforming growth factor β, and tumor necrosis factor α, which mediate cancer-induced skeletal muscle wasting. E2- and toremifene-treated C2C12 myoblast/myotube cells contained elevated levels of active protein kinase B (AKT) with a corresponding decrease in the levels of its negative regulator PTEN, which is a target of miR-486. We propose an ERα:E2-miR-486-AKT signaling axis, which reduces the deleterious effects of cancer-induced cytokines/chemokines on skeletal muscle mass and/or function.

Topics: Animals; Cell Differentiation; Cell Line, Tumor; Estradiol; Female; Gene Expression Regulation, Neoplastic; Humans; Male; Mice; Mice, Inbred C57BL; MicroRNAs; Muscle, Skeletal; Muscular Diseases; Myostatin; Neoplasms; Sex Factors; Signal Transduction; Toremifene; Transforming Growth Factor beta; Tumor Necrosis Factor-alpha

Partial bladder outlet obstruction (pBOO) results in bladder fibrosis that is initiated by an inflammatory cascade and the decompensation after smooth muscle hypertrophy. We have been using an animal model to develop the hypothesis that mesenchymal stem cells (MSCs) are able to mitigate this cytokine cascade and prevent bladder deterioration. We hypothesized that intraperitoneal administration of MSCs can produce the same effects as intravenously administered cells but may require higher dosing. Intraperitoneal treatment will provide insights into the mechanisms of action and may offer advantages over intravenous administration, as it will permit allow higher doses and potentially reduce systemic exposure. Rats underwent a surgical induction of pBOO and instillation of either 1 × 10

Topics: Animals; Female; Fibrosis; Gene Expression Regulation; Hypertrophy; Hypoxia-Inducible Factor 1, alpha Subunit; Inflammation; Injections, Intraperitoneal; Mesenchymal Stem Cell Transplantation; Muscle, Smooth; Muscular Diseases; Random Allocation; Rats; Rats, Sprague-Dawley; Smad2 Protein; Transcription Factors; Transforming Growth Factor beta; Urinary Bladder Neck Obstruction; Urodynamics

Transforming growth factor beta (TGF-β)-Smad2/3 is the major signaling pathway of fibrosis, which is characterized by the excessive production and accumulation of extracellular matrix (ECM) components, including collagen. Although the ECM is an essential component of skeletal muscle, fibrosis may be harmful to muscle function. On the other hand, our previous studies have shown that levels of angiotensin II, which acts upstream of TGF-β-Smad2/3 signaling, is increased in mice with myocardial infarction (MI). In this study, we found higher skeletal muscle fibrosis in MI mice compared with control mice, and we investigated the mechanisms involved therein. Moreover, we administered an inhibitor based on the above mechanism and investigated its preventive effects on skeletal muscle fibrosis.. Male C57BL/6 J mice with MI were created, and sham-operated mice were used as controls. The time course of skeletal muscle fibrosis post-MI was analyzed by picrosirius-red staining (days 1, 3, 7, and 14). Mice were then divided into 3 groups: sham + vehicle (Sham + Veh), MI + Veh, and MI + lisinopril (an angiotensin-converting enzyme [ACE] inhibitor, 20 mg/kg body weight/day in drinking water; MI + Lis). Lis or Veh was administered from immediately after the surgery to 14 days postsurgery.. Skeletal muscle fibrosis was significantly increased in MI mice compared with sham mice from 3 to 14 days postsurgery. Although mortality was lower in the MI + Lis mice than the MI + Veh mice, there was no difference in cardiac function between the 2 groups at 14 days. Skeletal muscle fibrosis and hydroxyproline (a key marker of collagen content) were significantly increased in MI + Veh mice compared with the Sham + Veh mice. Consistent with these results, protein expression of TGF-β and phosphorylated Smad2/3 in the skeletal muscle during the early time points after surgery (days 1-7 postsurgery) and blood angiotensin II at 14 days postsurgery was increased in MI mice compared with sham mice. These impairments were improved in MI + Lis mice, without any effects on spontaneous physical activity, muscle strength, muscle weight, and blood pressure.. ACE inhibitor administration prevents increased skeletal muscle fibrosis during the early phase after MI. Our findings indicate a new therapeutic target for ameliorating skeletal muscle abnormalities in heart diseases.

Topics: Angiotensin II; Angiotensin-Converting Enzyme Inhibitors; Animals; Collagen; Fibrosis; Lisinopril; Male; Mice; Mice, Inbred C57BL; Muscle, Skeletal; Muscular Diseases; Myocardial Infarction; Smad Proteins; Transforming Growth Factor beta

Skeletal muscle injuries are the most common type of injury occurring in sports, and investigating skeletal muscle regeneration as well as understanding the related processes is an important aspect of the sports medicine field. The process of regeneration appears to be complex and precisely orchestrated, involving fibro-adipogenic progenitors (FAPs) which are a muscle-resident stem cell population that appears to play a major role in abnormal development of fibrotic tissue or intermuscular adipose tissue (IMAT). Our present study aims to investigate whether muscle resting or endurance exercise following muscle injury may change the behavior of FAPs and subsequently impact the development of fatty infiltrations and fibrosis, two hallmarks of regeneration failure.. We used the validated glycerol muscle injury model to mimic abnormal muscle regenerative conditions in mice. We challenged this specific regeneration model with hindlimb unloading or endurance exercise and, in a second set of experiments, we treated mice with decorin, a TGF-β inhibitor.. In this study, we demonstrated that: i) muscle resting just after injury leads to inhibition of IMAT development, ii) TNF-α mediated FAP apoptosis might be perturbed in this specific glycerol model of muscle injury, leading to IMAT development, and iii) treatment with the TGF-β inhibitor decorin decreases IMAT development and might restores FAP apoptosis.. In addition to the potential clinical relevance of decorin treatment in situations involving muscle plasticity and regeneration, this study also demonstrates that a period of muscle resting is necessary following muscle injury to achieve efficient muscle regeneration which is associated with a reduction in fatty infiltration. Unreasonably early resumption of exercise brings no gain to regeneration, further highlighting that this resting period is necessary.

Topics: Adipose Tissue; Animals; Apoptosis; Decorin; Female; Glycerol; Mice; Mice, Inbred C57BL; Muscle, Skeletal; Muscular Diseases; Physical Conditioning, Animal; Receptor, Platelet-Derived Growth Factor alpha; Stem Cells; Transforming Growth Factor beta

Skeletal muscle and brown adipose tissue (BAT) are functionally linked, as exercise increases browning via secretion of myokines. It is unknown whether BAT affects muscle function. Here, we find that loss of the transcription factor IRF4 in BAT (BATI4KO) reduces exercise capacity, mitochondrial function, ribosomal protein synthesis, and mTOR signaling in muscle and causes tubular aggregate formation. Loss of IRF4 induces myogenic gene expression in BAT, including the secreted factor myostatin, a known inhibitor of muscle function. Reducing myostatin via neutralizing antibodies or soluble receptor rescues the exercise capacity of BATI4KO mice. In addition, overexpression of IRF4 in brown adipocytes reduces serum myostatin and increases exercise capacity in muscle. Finally, mice housed at thermoneutrality have reduced IRF4 in BAT, lower exercise capacity, and elevated serum myostatin; these abnormalities are corrected by excising BAT. Collectively, our data point to an unsuspected level of BAT-muscle crosstalk driven by IRF4 and myostatin.

Topics: Adipocytes, Brown; Adipose Tissue, Brown; Animals; Antibodies, Neutralizing; Energy Metabolism; Gene Expression Regulation; Interferon Regulatory Factors; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Microscopy, Electron; Mitochondria; Muscular Diseases; Myostatin; Oxygen Consumption; Physical Conditioning, Animal; Quadriceps Muscle; Thermosensing; Transforming Growth Factor beta

The transforming growth factor-β (TGF-β) network of ligands and intracellular signaling proteins is a subject of intense interest within the field of skeletal muscle biology. To define the relative contribution of endogenous TGF-β proteins to the negative regulation of muscle mass via their activation of the Smad2/3 signaling axis, we used local injection of adeno-associated viral vectors (AAVs) encoding ligand-specific antagonists into the tibialis anterior (TA) muscles of C57BL/6 mice. Eight weeks after AAV injection, inhibition of activin A and activin B signaling produced moderate (∼20%), but significant, increases in TA mass, indicating that endogenous activins repress muscle growth. Inhibiting myostatin induced a more profound increase in muscle mass (∼45%), demonstrating a more prominent role for this ligand as a negative regulator of adult muscle mass. Remarkably, codelivery of activin and myostatin inhibitors induced a synergistic response, resulting in muscle mass increasing by as much as 150%. Transcription and protein analysis indicated that this substantial hypertrophy was associated with both the complete inhibition of the Smad2/3 pathway and activation of the parallel bone morphogenetic protein (BMP)/Smad1/5 axis (recently identified as a positive regulator of muscle mass). Analyses indicated that hypertrophy was primarily driven by an increase in protein synthesis, but a reduction in ubiquitin-dependent protein degradation pathways was also observed. In models of muscular dystrophy and cancer cachexia, combined inhibition of activins and myostatin increased mass or prevented muscle wasting, respectively, highlighting the potential therapeutic advantages of specifically targeting multiple Smad2/3-activating ligands in skeletal muscle.

Topics: Activins; Animals; Dependovirus; Gene Targeting; Genetic Vectors; Male; Mice; Muscle Proteins; Muscle, Skeletal; Muscular Diseases; Organ Size; Signal Transduction; Smad Proteins; Transforming Growth Factor beta

Endoplasmic reticulum (ER) and oxidative stress are two related phenomena that have important metabolic consequences. As many skeletal muscle diseases are triggered by oxidative stress, we explored the chain of events linking a hyperoxidized ER (which causes ER and oxidative stress) with skeletal muscle dysfunction. An unbiased exon expression array showed that the combined genetic modulation of the two master ER redox proteins, selenoprotein N (SEPN1) and endoplasmic oxidoreductin 1 (ERO1), led to an SEPN1-related myopathic phenotype due to excessive signalling of transforming growth factor (TGF)-beta. The increased TGF-beta activity in the genetic mutants was caused by accelerated turnover of the ER localized (anti-oxidant) ascorbic acid that affected collagen deposition in the extracellular matrix. In a mouse mutant of SEPN1, which is dependent on exogenous ascorbic acid, a limited intake of ascorbic acid revealed a myopathic phenotype as a consequence of an altered TGF-beta signalling. Indeed, systemic antagonism of TGF-beta re-established skeletal muscle function in SEPN1 mutant mice. In conclusion, this study sheds new light on the molecular mechanism of SEPN1-related myopathies and indicates that the TGF-beta/ERO1/ascorbic acid axis offers potential for their treatment.

Topics: Animals; Antioxidants; Ascorbic Acid; Endoplasmic Reticulum; Gene Expression Profiling; Glycoproteins; Histocytochemistry; Mice; Mice, Transgenic; Microarray Analysis; Microscopy, Electron; Muscle Proteins; Muscle, Skeletal; Muscular Diseases; Mutant Proteins; Oxidative Stress; Oxidoreductases; Selenoproteins; Signal Transduction; Transforming Growth Factor beta

Sulforaphane (SFN), an activator of NF-E2-related factor 2 (Nrf2), has been found to have an antifibrotic effect on liver and lung. However, its effects on dystrophic muscle fibrosis remain unknown. This work was undertaken to evaluate the effects of SFN-mediated activation of Nrf2 on dystrophic muscle fibrosis. Male mdx mice (age 3 mo) were treated with SFN by gavage (2 mg/kg body wt per day) for 3 mo. Experimental results demonstrated that SFN remarkably attenuated skeletal and cardiac muscle fibrosis as indicated by reduced Sirius Red staining and immunostaining of the extracellular matrix. Moreover, SFN significantly inhibited the transforming growth factor-β (TGF-β)/Smad signaling pathway and suppressed profibrogenic gene and protein expressions such as those of α-smooth muscle actin (α-SMA), fibronectin, collagen I, plasminogen activator inhibitor-1 (PAI-1), and tissue inhibitor metalloproteinase-1 (TIMP-1) in an Nrf2-dependent manner. Furthermore, SFN significantly decreased the expression of inflammatory cytokines CD45, TNF-α, and IL-6 in mdx mice. In conclusion, these results show that SFN can attenuate dystrophic muscle fibrosis by Nrf2-mediated inhibition of the TGF-β/Smad signaling pathway, which indicates that Nrf2 may represent a new target for dystrophic muscle fibrosis.

Topics: Actins; Animals; Collagen Type I; Fibronectins; Fibrosis; Interleukin-6; Isothiocyanates; Leukocyte Common Antigens; Male; Mice; Mice, Inbred C57BL; Mice, Inbred mdx; Muscle, Skeletal; Muscular Diseases; NF-E2-Related Factor 2; Plasminogen Activator Inhibitor 1; Signal Transduction; Smad Proteins; Sulfoxides; Tissue Inhibitor of Metalloproteinase-1; Transforming Growth Factor beta; Tumor Necrosis Factor-alpha

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

We have identified integrin beta 6 (Itgb6) as a transcript highly enriched in skeletal muscle. This finding is unexpected because Itgb6 is typically associated with epithelial expression domains in normal tissue. Further we find that ITGB6 protein expression in muscle is post-transcriptionally regulated. Uninjured muscle expresses Itgb6 RNA but no ITGB6 protein is detectable. Muscle injury induces ITGB6 protein accumulation rapidly post-injury in myofibers adjacent to the site of injury. As regeneration of the injured muscle tissue progresses ITGB6 protein is found in newly formed fibers up to at least 15 days post-injury.

Topics: Animals; Gene Expression Profiling; Gene Expression Regulation; Immunohistochemistry; Integrin beta Chains; Male; Mice; Muscle, Skeletal; Muscular Diseases; RNA Processing, Post-Transcriptional; RNA, Messenger; Signal Transduction; Transforming Growth Factor beta

Recently, adipose tissue-derived stem cells (ASCs) were emerged as an alternative, abundant, and easily accessible source of stem cell therapy. Previous studies revealed losartan (an angiotensin II type I receptor blocker) treatment promoted the healing of skeletal muscle by attenuation of the TGF-β signaling pathway, which inhibits muscle differentiation. Therefore, we hypothesized that a combined therapy using ASCs and losartan might dramatically improve the muscle remodeling after muscle injury. To determine the combined effect of losartan with ASC transplantation, we created a muscle laceration mouse model. EGFP-labeled ASCs were locally transplanted to the injured gastrocnemius muscle after muscle laceration. The dramatic muscle regeneration and the remarkably inhibited muscular fibrosis were observed by combined treatment. Transplanted ASCs fused with the injured or differentiating myofibers. Myotube formation was also enhanced by ASC(+) satellite coculture and losartan treatment. Thus, the present study indicated that ASC transplantation effect for skeletal muscle injury can be dramatically improved by losartan treatment inducing better niche.

Topics: Adipose Tissue; Animals; Coculture Techniques; Fibrosis; Immunoblotting; Losartan; Male; Mice; Mice, Inbred C57BL; Muscle, Skeletal; Muscular Diseases; Reverse Transcriptase Polymerase Chain Reaction; Satellite Cells, Skeletal Muscle; Stem Cell Niche; Transforming Growth Factor beta

Inhibition of the myostatin signaling pathway is emerging as a promising therapeutic means to treat muscle wasting and degenerative disorders. Activin type IIB receptor (ActRIIB) is the putative myostatin receptor, and a soluble activin receptor (ActRIIB-Fc) has been demonstrated to potently inhibit a subset of transforming growth factor (TGF)-β family members including myostatin. To determine reliable and valid biomarkers for ActRIIB-Fc treatment, we assessed gene expression profiles for quadriceps muscles from mice treated with ActRIIB-Fc compared with mice genetically lacking myostatin and control mice. Expression of 134 genes was significantly altered in mice treated with ActRIIB-Fc over a 2-wk period relative to control mice (fold change > 1.5, P < 0.001), whereas the number of significantly altered genes in mice treated for 2 days was 38, demonstrating a time-dependent response to ActRIIB-Fc in overall muscle gene expression. The number of significantly altered genes in Mstn(-/-) mice relative to control mice was substantially higher (360), but for most of these genes the expression levels in the 2-wk treated mice were closer to the levels in the Mstn(-/-) mice than in control mice (P < 10⁻³⁰). Expression levels of 30 selected genes were further validated with quantitative real-time polymerase chain reaction (qPCR), and a correlation of ≥ 0.89 was observed between the fold changes from the microarray analysis and the qPCR analysis. These data suggest that treatment with ActRIIB-Fc results in overlapping but distinct gene expression signatures compared with myostatin genetic mutation. Differentially expressed genes identified in this study can be used as potential biomarkers for ActRIIB-Fc treatment, which is currently in clinical trials as a therapeutic agent for muscle wasting and degenerative disorders.

Topics: Activin Receptors, Type II; Animals; Biomarkers; Female; Gene Expression; Gene Expression Profiling; Mice; Mice, Inbred C57BL; Mice, Knockout; Microarray Analysis; Muscle, Skeletal; Muscular Diseases; Myostatin; Quadriceps Muscle; Transforming Growth Factor beta

TGF-beta regulates many aspects of cellular performance relevant to tissue morphogenesis and homeostasis. Postnatal perturbation of TGF-beta signaling contributes to the pathogenesis of many disease states, as recently exemplified through the study of Marfan syndrome (MFS), including aortic aneurysm and skeletal muscle myopathy. Heterogeneity in the regulation and consequences of TGF-beta signaling, amplified in the context of disease, has engendered confusion and controversy regarding its utility as a therapeutic target. Three studies recently published in the JCI, including one in this issue, underscore the complexity of this subject. Heydemann and colleagues implicate dimorphic variation in latent TGF-beta-binding protein 4 (LTBP4), a regulator of TGF-beta bioavailability and activation, as a modifier of muscular dystrophy in gamma-sarcoglycan-deficient mice. In contrast to experience with ascending aortic aneurysm in MFS, Wang and colleagues show that systemic abrogation of TGF-beta signaling worsens (rather than attenuates) Ang II-induced abdominal aortic aneurysm progression in mice. Tieu and colleagues define alterations in the regulation of vascular inflammation in the pathogenesis of Ang II-induced aneurysm and dissection in mice, which may help shed some light on this apparent paradox.

Topics: Animals; Aortic Aneurysm; Child; Disease Models, Animal; Humans; Latent TGF-beta Binding Proteins; Male; Marfan Syndrome; Mice; Muscle Fibers, Skeletal; Muscle, Skeletal; Muscular Diseases; Muscular Dystrophies; Signal Transduction; Transforming Growth Factor beta

Loss of skeletal muscle mass is a poorly understood complication of end-stage liver disease (ESLD). Based on recent stem cell literature, we hypothesized that the potent negative regulator of muscle mass, myostatin, could play a role in the muscle loss associated with ESLD. In this preliminary investigation, we measured myostatin levels in patients undergoing liver transplant evaluation, using a novel enzyme-linked immunosensitivity assay. Myostatin levels were significantly elevated in patients with ESLD compared with healthy controls. These data suggest that myostatin deserves further investigation as a target for therapies designed to preserve muscle mass in patients with ESLD.

Topics: Enzyme-Linked Immunosorbent Assay; Female; Humans; Liver Failure; Liver Transplantation; Male; Malnutrition; Middle Aged; Muscular Diseases; Myostatin; Prothrombin Time; Reverse Transcriptase Polymerase Chain Reaction; Transforming Growth Factor beta; Wasting Syndrome

Myostatin is a secreted protein that normally acts to limit skeletal muscle growth. As a result, there is considerable interest in developing agents capable of blocking myostatin activity, as such agents could have widespread applications for the treatment of muscle degenerative and wasting conditions. Myostatin normally exists in an inactive state in which the mature C-terminal portion of the molecule is bound non-covalently to its N-terminal propeptide. We previously showed that this latent complex can be activated in vitro by cleavage of the propeptide with members of the bone morphogenetic protein-1/tolloid (BMP-1/TLD) family of metalloproteases. Here, I show that mice engineered to carry a germline point mutation rendering the propeptide protease-resistant exhibit increases in muscle mass approaching those seen in mice completely lacking myostatin. Mice homozygous for the point mutation have increased muscling even though their circulating levels of myostatin protein are dramatically increased, consistent with an inability of myostatin to be activated from its latent state. Furthermore, I show that a loss-of-function mutation in Tll2, which encodes one member of this protease family, has a small, but significant, effect on muscle mass, implying that its function is likely redundant with those of other family members. These findings provide genetic support for the hypothesis that proteolytic cleavage of the propeptide by BMP-1/TLD proteases plays a critical role in the activation of latent myostatin in vivo and suggest that targeting the activities of these proteases may be an effective therapeutic strategy for enhancing muscle growth in clinical settings of muscle loss and degeneration.

Topics: Animals; Bone Morphogenetic Protein 1; Bone Morphogenetic Proteins; Metalloendopeptidases; Mice; Muscle, Skeletal; Muscular Diseases; Myostatin; Peptide Hydrolases; Point Mutation; Protein Precursors; Tolloid-Like Metalloproteinases; Transforming Growth Factor beta

Skeletal muscle fibrosis is a major pathological hallmark of chronic myopathies in which myofibers are replaced by progressive deposition of collagen and other extracellular matrix proteins produced by muscle fibroblasts. Recent studies have shown that in the absence of the endogenous muscle growth regulator myostatin, regeneration of muscle is enhanced, and muscle fibrosis is correspondingly reduced. We now demonstrate that myostatin not only regulates the growth of myocytes but also directly regulates muscle fibroblasts. Our results show that myostatin stimulates the proliferation of muscle fibroblasts and the production of extracellular matrix proteins both in vitro and in vivo. Further, muscle fibroblasts express myostatin and its putative receptor activin receptor IIB. Proliferation of muscle fibroblasts, induced by myostatin, involves the activation of Smad, p38 MAPK and Akt pathways. These results expand our understanding of the function of myostatin in muscle tissue and provide a potential target for anti-fibrotic therapies.

Topics: Activin Receptors, Type II; Animals; Cell Line; Cell Proliferation; Collagen; Fibroblasts; Fibrosis; Mice; Mice, Knockout; Muscle Fibers, Skeletal; Muscle, Skeletal; Muscular Diseases; Myostatin; p38 Mitogen-Activated Protein Kinases; Proto-Oncogene Proteins c-akt; Regeneration; Signal Transduction; Smad Proteins; Transforming Growth Factor beta

To characterize muscle and nerve pathology in Dunnigan familial partial lipodystrophy (FPLD).. We used conventional histology, immunohistochemistry, messenger RNA (mRNA) expression, gene sequencing, and clinical studies of 13 patients with neuromuscular involvement.. The clinical findings consisted of muscle hypertrophy (12/13), severe myalgias (9/13), and multiple nerve entrapment syndromes (8/13). Skeletal muscle histology demonstrated marked Type 1 and 2 muscle fiber hypertrophy and nonspecific myopathic changes, whereas numerous paranodal myelin swellings (tomacula) were found in sural nerve biopsies. We found that myostatin mRNA expression was reduced in patients with FPLD vs controls. We sequenced the myostatin gene in our subjects, but found no mutations. We then investigated whether or not SMAD, the intracellular mediator of myostatin signaling, might be impaired in patients with FPLD. We found that in FPLD muscle, a large number of SMAD molecules adhered to the nuclear membrane and were not found within the nucleus, compared with normal muscle or muscle from a patient with a non-FPLD lamin A/C disease.. The myopathy and neuropathy associated with Dunnigan familial partial lipodystrophy are distinct from other lamin A/C disorders. We hypothesize that the lipodystrophy-associated mutation interferes with SMAD signaling, linking this type of lipodystrophy to the phenotypically similar myostatin deficiency.

Topics: Adult; Female; Humans; Lipodystrophy, Familial Partial; Male; Muscle, Skeletal; Muscular Diseases; Myostatin; Peripheral Nervous System Diseases; Smad Proteins; Sural Nerve; Transforming Growth Factor beta

Recent studies have shown that myostatin, first identified as a negative regulator of skeletal muscle growth, may also be involved in the formation of fibrosis within skeletal muscle. In this study, we further explored the potential role of myostatin in skeletal muscle fibrosis, as well as its interaction with both transforming growth factor-beta1 and decorin. We discovered that myostatin stimulated fibroblast proliferation in vitro and induced its differentiation into myofibroblasts. We further found that transforming growth factor-beta1 stimulated myostatin expression, and conversely, myostatin stimulated transforming growth factor-beta1 secretion in C2C12 myoblasts. Decorin, a small leucine-rich proteoglycan, was found to neutralize the effects of myostatin in both fibroblasts and myoblasts. Moreover, decorin up-regulated the expression of follistatin, an antagonist of myostatin. The results of in vivo experiments showed that myostatin knock-out mice developed significantly less fibrosis and displayed better skeletal muscle regeneration when compared with wild-type mice at 2 and 4 weeks following gastrocnemius muscle laceration injury. In wild-type mice, we found that transforming growth factor-beta1 and myostatin co-localize in myofibers in the early stages of injury. Recombinant myostatin protein stimulated myofibers to express transforming growth factor-beta1 in skeletal muscles at early time points following injection. In summary, these findings define a fibrogenic property of myostatin and suggest the existence of co-regulatory relationships between transforming growth factor-beta1, myostatin, and decorin.

Topics: Animals; Cell Differentiation; Cell Proliferation; Decorin; Extracellular Matrix Proteins; Female; Fibroblasts; Fibrosis; Follistatin; Mice; Muscle Fibers, Skeletal; Muscle, Skeletal; Muscular Diseases; Myoblasts; Myostatin; NIH 3T3 Cells; Proteoglycans; Recombinant Proteins; Transforming Growth Factor beta; Transforming Growth Factor beta1

The demonstration that myostatin may negatively regulate muscle mass in adult individuals has raised the possibility of targeting the myostatin pathway to increase muscle growth in a variety of muscle-degenerative and -wasting conditions. To gain further insight into the possible role of myostatin in primary muscle diseases, the authors investigated the expression of muscle myostatin in children with congenital fiber type 1 disproportion, in others with neurogenic muscular atrophy, in others with myotonia congenita, in others with infantile glycogenosis type II, in others with Prader-Willi syndrome, and in 4 age-matched controls. No differences in the pattern of myostatin expression were found in any case, even in those patients with prominent muscular atrophy or hypertrophy. These findings suggest that muscle alterations that can be observed in primary muscle diseases do not depend on changes in myostatin expression.

Topics: Child; Child, Preschool; Female; Gene Expression; Humans; Infant; Male; Muscle, Skeletal; Muscular Diseases; Myostatin; RNA, Messenger; Transforming Growth Factor beta

Myostatin is a potent inhibitor of myogenesis; thus differential expression might be expected across individuals varying in responsiveness to myogenic stimuli. We hypothesized that myostatin would be differentially regulated across humans with markedly different hypertrophic responses to resistance training (RT; 16 wk). Targets were assessed in muscle biopsies at baseline (T1) and 24 h after the first (T2) and last (T3) loading bouts in previously untrained subjects statistically clustered based on mean myofiber hypertrophy as extreme (Xtr; n = 17, 2,475 microm(2)), modest (n = 32, 1,111 microm(2)), and nonresponders (n = 17, -16 microm(2)). We assessed protein levels of latent full-length myostatin protein complex and its propeptide; mRNA levels of myostatin, cyclin D1, p21(cip1), p27(kip1), and activin receptor IIB; and serum myostatin protein concentration. Total RNA concentration increased by T3 in nonresponders (37%) and modest responders (40%), while it increased acutely (T2) only in Xtr (26%), remaining elevated at T3 (40%). Myostatin mRNA decreased at T2 (-44%) and remained suppressed at T3 (-52%), but not differentially across clusters. Cyclin D1 mRNA increased robustly by T2 (38%) and T3 (74%). The increase at T2 was driven by Xtr (62%, P < 0.005), and Xtr had the largest elevation at T3 (82%, P < 0.001). No effects were found for other target transcripts. Myostatin protein complex increased 44% by T3 (P < 0.001), but not differentially by cluster. Myostatin protein complex propeptide and circulating myostatin were not influenced by RT or cluster. Overall, we found no compelling evidence that myostatin is differentially regulated in humans demonstrating robust RT-mediated myofiber hypertrophy vs. those more resistant to growth.

Topics: Activin Receptors, Type II; Adult; Aged; Cluster Analysis; Cyclin D; Cyclin-Dependent Kinase Inhibitor p21; Cyclin-Dependent Kinase Inhibitor p27; Cyclins; Down-Regulation; Exercise; Female; Humans; Hypertrophy; Intracellular Signaling Peptides and Proteins; Male; Middle Aged; Muscle Contraction; Muscle Fibers, Skeletal; Muscle, Skeletal; Muscular Diseases; Myostatin; RNA, Messenger; Time Factors; 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

Topics: Cluster Analysis; Down-Regulation; Exercise; Humans; Hypertrophy; Muscle Contraction; Muscle Fibers, Skeletal; Muscle, Skeletal; Muscular Diseases; Myostatin; Reproducibility of Results; Research Design; RNA, Messenger; RNA, Ribosomal, 18S; Time Factors; Transforming Growth Factor beta

Topics: Animals; Disease Models, Animal; Humans; Hypertrophy; Mice; Models, Biological; Muscular Diseases; Myostatin; 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

The osteoinductive potential of growth factors leads not only to a stimulated bone formation in bony tissue but also in extra skeletal tissue. This potential depends on the dosage and potentially on the application method and may limit the clinical use. The aim of the present study was to investigate the potential of IGF-I, TGF-beta1 and BMP-2 released from a newly developed application systems of orthopaedic implants to induce ectopic bone formation in muscles. This bioactive coating showed a stimulating effect on fracture healing in several experimental studies before. Titanium discs were coated on one side with the drug carrier poly(d,l-lactide) (PDLLA), with the carrier plus IGF-I and TGF-beta1 or with the carrier plus BMP-2. The discs were implanted in the Musculus cleidomastoideus of sheep and followed up for 3 months. X-rays were taken after the operation and the day of sacrifice. The muscles plus implant were harvested and prepared for histology. Neither the radiology nor the histology revealed any signs of ectopic ossification in the implant/muscle interface or in a distance to the plate in any group. An influence of the locally applied growth factor, however, was seen in the formation of a soft tissue capsule. Histomorphometric analysis revealed a significantly larger capsule area over the growth factor coated side in comparison to the uncoated side or the pure titanium plate, indicating an effect of the applied growth factors on cells, however, not resulting in osteoinduction in muscle. The result showed that the local and controlled release of growth factors from PDLLA coated implants does not induce ectopic bone formation in sheep muscle and could be used in orthopaedic surgery to increase healing without the risk of ectopic bone formation in the surrounding soft tissue.

Topics: Animals; Bone and Bones; Bone Morphogenetic Protein 2; Bone Morphogenetic Proteins; Choristoma; Coated Materials, Biocompatible; Excipients; Female; Insulin-Like Growth Factor I; Muscle, Skeletal; Muscular Diseases; Osteogenesis; Polyesters; Prostheses and Implants; Radiography; Sheep; Titanium; Transforming Growth Factor beta; Transforming Growth Factor beta1

Topics: Female; Gene Expression; Humans; Hypertrophy; Male; Muscle, Skeletal; Muscular Diseases; Mutation; Myostatin; Polymorphism, Genetic; Sports; Substance-Related Disorders; Transforming Growth Factor beta

Topics: DNA Mutational Analysis; Female; Humans; Hypertrophy; Infant, Newborn; Male; Muscle, Skeletal; Muscular Diseases; Mutation; Myostatin; Pedigree; Phenotype; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Transforming Growth Factor beta; Ultrasonography

Double muscling is a partially recessive trait present in some beef breeds. It shows a high frequency in some breeds, while in others the frequency is low, and double-muscled individuals are rare. The double muscling is caused by an allelic series of mutations that cause a loss of function of the myostatin gene ( GDF8). We describe here a new mutation in the myostatin gene in Marchigiana breed, a typical beef breed of Central Italy, in which rare double-muscling individuals have been described. A PCR product of the third exon was sequenced in subjects phenotypically showing double muscling, and a G > T transversion was discovered that introduces a premature stop codon. The variant found adds to the large series of mutations present in cattle, and particularly to the only two causative of double muscling in the third exon. A PCR-RFLP test is described for the rapid and effective identification of both heterozygous and homozygous subjects. It was applied to a larger survey carried on the same and also in two other beef breeds, Chianina and Romagnola. Further individuals carrying the new variant were found in Marchigiana, but none in the other breeds. The results may be important for a better comprehension of the role of myostatin in muscular development, for commercial use and for the inference of phylogeny of this gene.

Topics: Animals; Cattle; Codon, Nonsense; DNA Primers; Italy; Muscular Diseases; Myostatin; Polymorphism, Restriction Fragment Length; Sequence Analysis, DNA; Transforming Growth Factor beta

Decades of selective breeding have yielded lines of poultry with substantial myofiber hyperplasia, vet little is known about what genes have been altered during the course of selection. Myostatin is a strong negative regulator of muscle mass in mice and cattle and could have been one of many genetic factors contributing to increased myofiber deposition in growth-selected lines of poultry. To test this hypothesis, the sequence and expression patterns of myostatin were analyzed in growth-selected lines of chickens and quail. The sequence of broiler myostatin cDNA, amplified via reverse transcription (RT)-PCR from embryonic muscle RNA, contained no missense mutations in the coding sequence when compared to that of White Leghorn layers, although two silent single nucleotide polymorphisms (SNP) were found. Northern analysis of myostatin transcripts from embryonic pectoralis and quadriceps showed no significant differences in expression levels between broiler and layer muscle RNA. However, levels of myostatin transcripts were greatly reduced in muscles of posthatch chicks compared to embryonic muscle. Myostatin protein was also present in broiler and layer embryonic muscle at similar levels. No significant polymorphisms or differences in RNA expression levels were found in embryonic muscles of divergently selected lines of Japanese quail. These results indicate that intense artificial selection in these growth-selected lines of poultry has neither silenced the expression of myostatin nor created null alleles via mutation in the lines analyzed.

Topics: Animal Husbandry; Animals; Base Sequence; Chickens; DNA Primers; DNA, Complementary; Gene Expression Regulation; Molecular Sequence Data; Muscle, Skeletal; Muscular Diseases; Myostatin; Reverse Transcriptase Polymerase Chain Reaction; Selection, Genetic; Transforming Growth Factor beta

Chronic tendon lesions are degenerative conditions and may represent a failure to repair or remodel the extracellular matrix after repeated micro-injury. Since TGF-beta is strongly associated with tissue repair, we investigated the expression of TGF-beta isoforms (beta1, beta2 and beta3) and their 2 signalling receptors (TGF-betaRI and TGF-betaRII) in normal and pathological Achilles tendons. In all tissues, all 3 TGF-beta isoforms and the 2 receptors were present at sites of blood vessels. Cells in the matrix showed no staining for TGF-beta1 or beta3, while TGF-beta2 was associated with cells throughout the normal cadaver tendon. Tissue from tendons with pathological lesions showed an increase in cell numbers and percentage TGF-beta2 expression. TGF-betaRII showed a wide distribution in cells throughout the tissue sections. As with TGF-beta2, there was an increase in the number of cells expressing TGF-betaRII in pathological tissue. TGF-betaRI was restricted to blood vessels and was absent from the fibrillar matrix. We conclude that despite the presence and upregulation of TGF-beta2, TGF-beta signalling is not propagated due to the lack of TGF-betaRI. This might explain why chronic tendon lesions fail to resolve and suggests that the addition of exogenous TGF-beta will have little effect on chronic tendinopathy.

Topics: Achilles Tendon; Adult; Aged; Aged, 80 and over; Chronic Disease; Humans; Immunoenzyme Techniques; Male; Middle Aged; Muscular Diseases; Protein Isoforms; Receptors, Transforming Growth Factor beta; Transforming Growth Factor beta

The formation of restrictive adhesions around the musculotendinous unit after injury is one of the most vexing processes faced by the surgeon. In flexor tendons it has been shown that the synovial tissue is the source of aggressive fibroblasts which contribute to this process. Using a rabbit model, we have examined the effects of treating the synovial sheath with the antimetabolite 5-fluorouracil (5-FU) for five minutes. Inflammatory, proliferative and molecular markers were compared in the response of the treated and control tendons to injury. Compared with a control group we found that the proliferative and inflammatory responses were significantly reduced (p < 0.001) in the treated tendons. Not only was there a reduction in the cellular and cytokine response, but there also was a significant (p < 0.001) reduction in the level of activity of the known pro-scarring agent, transforming growth factor beta 1 (TGF-beta1). These pilot studies indicate that the formation of restrictive adhesions may be modulated using a simple single-touch technique in the hope of producing a better return of function.

Topics: Animals; Cell Count; Disease Models, Animal; Fibroblasts; Fluorouracil; Hindlimb; Immunosuppressive Agents; Macrophages; Male; Microscopy, Electron; Muscular Diseases; Pilot Projects; Proliferating Cell Nuclear Antigen; Rabbits; Random Allocation; Statistics, Nonparametric; Synovial Membrane; Tendon Injuries; Tendons; Tissue Adhesions; Transforming Growth Factor beta; Transforming Growth Factor beta1; Vascular Cell Adhesion Molecule-1; Wound Healing

The transforming growth factor betas (TGF-betas) are multifunctional growth factors that act on both fibroblasts and myosatellite cells. In rodent models of muscle diseases, high levels of TGF-beta2 are expressed by myogenic cells. We have examined whether the expression of TGF-beta2 is also elevated in diseased human muscles. The disorders examined were Duchenne muscular dystrophy, myotonic dystrophy, myotubular myopathy, spinal muscular atrophy, and amyotrophic lateral sclerosis. The levels of TGF-beta2 immunoreactivity were elevated in atrophic, necrotic, and regenerating fibers and in fibers with central nuclei or cytoplasmic masses, irrespective of whether fibrosis was present. We therefore suggest that TGF-beta2 is important for muscle repair and that the presence of a TGF-beta within a muscle only leads to fibrosis if certain other factors are present.

Topics: Amyotrophic Lateral Sclerosis; Animals; Biopsy; Case-Control Studies; Desmin; Humans; Immunohistochemistry; Microscopy, Immunoelectron; Muscle, Skeletal; Muscular Atrophy, Spinal; Muscular Diseases; Muscular Dystrophies; Rats; Species Specificity; Transforming Growth Factor beta