Signaling in Muscle Atrophy and Hypertrophy

Physiology ◽  
2008 ◽  
Vol 23 (3) ◽  
pp. 160-170 ◽  
Author(s):  
Marco Sandri
Keyword(s):  
Physical Activity ◽  
Protein Synthesis ◽  
Growth Factors ◽  
Muscle Atrophy ◽  
Muscle Wasting ◽  
Muscle Growth ◽  
Neuromuscular Diseases ◽  
Muscle Performance ◽  
Prevention And Treatment ◽  
Atrophy And Hypertrophy

Muscle performance is influenced by turnover of contractile proteins. Production of new myofibrils and degradation of existing proteins is a delicate balance, which, depending on the condition, can promote muscle growth or loss. Protein synthesis and protein degradation are coordinately regulated by pathways that are influenced by mechanical stress, physical activity, availability of nutrients, and growth factors. Understanding the signaling that regulates muscle mass may provide potential therapeutic targets for the prevention and treatment of muscle wasting in metabolic and neuromuscular diseases.

scholarly journals A model of muscle atrophy based on live microscopy of muscle remodelling in Drosophila metamorphosis

2016 ◽  
Vol 3 (2) ◽  
pp. 150517 ◽  
Author(s):  
Yadav Kuleesha ◽  
Wee Choo Puah ◽  
Martin Wasser
Keyword(s):  
Muscle Atrophy ◽  
Cell Biology ◽  
Muscle Wasting ◽  
Cathepsin L ◽  
Muscle Growth ◽  
Muscle Size ◽  
Abdominal Muscles ◽  
Quantitative Image ◽  
Muscle Remodelling

Genes controlling muscle size and survival play important roles in muscle wasting diseases. In Drosophila melanogaster metamorphosis, larval abdominal muscles undergo two developmental fates. While a doomed population is eliminated by cell death, another persistent group is remodelled and survives into adulthood. To identify and characterize genes involved in the development of remodelled muscles, we devised a workflow consisting of in vivo imaging, targeted gene perturbation and quantitative image analysis. We show that inhibition of TOR signalling and activation of autophagy promote developmental muscle atrophy in early, while TOR and yorkie activation are required for muscle growth in late pupation. We discovered changes in the localization of myonuclei during remodelling that involve anti-polar migration leading to central clustering followed by polar migration resulting in localization along the midline. We demonstrate that the Cathepsin L orthologue Cp1 is required for myonuclear clustering in mid, while autophagy contributes to central positioning of nuclei in late metamorphosis. In conclusion, studying muscle remodelling in metamorphosis can provide new insights into the cell biology of muscle wasting.

scholarly journals Circadian regulation of muscle growth independent of locomotor activity

2020 ◽  
Vol 117 (49) ◽  
pp. 31208-31218
Author(s):  
Jeffrey J. Kelu ◽  
Tapan G. Pipalia ◽  
Simon M. Hughes
Keyword(s):  
Physical Activity ◽  
Protein Synthesis ◽  
Circadian Clock ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Muscle Growth ◽  
Diurnal Variations ◽  
Dominant Negative ◽  
Messenger Rnas ◽  
Free Running

Muscle tissue shows diurnal variations in function, physiology, and metabolism. Whether such variations are dependent on the circadian clock per se or are secondary to circadian differences in physical activity and feeding pattern is unclear. By measuring muscle growth over 12-h periods in live prefeeding larval zebrafish, we show that muscle grows more during day than night. Expression of dominant negative CLOCK (ΔCLK), which inhibits molecular clock function, ablates circadian differences and reduces muscle growth. Inhibition of muscle contraction reduces growth in both day and night, but does not ablate the day/night difference. The circadian clock and physical activity are both required to promote higher muscle protein synthesis during the day compared to night, whereas markers of protein degradation,murfmessenger RNAs, are higher at night. Proteasomal inhibitors increase muscle growth at night, irrespective of physical activity, but have no effect during the day. Although physical activity enhances TORC1 activity, and the TORC1 inhibitor rapamycin inhibits clock-driven daytime growth, no effect on muscle growth at night was detected. Importantly, day/night differences in 1) muscle growth, 2) protein synthesis, and 3)murfexpression all persist in entrained larvae under free-running constant conditions, indicating circadian drive. Removal of circadian input by exposure to either permanent darkness or light leads to suboptimal muscle growth. We conclude that diurnal variations in muscle growth and metabolism are a circadian property that is independent of, but augmented by, physical activity, at least during development.

Muscle Atrophy Classification: The Need for a Pathway-Driven Approach

2021 ◽  
Vol 27 ◽  
Author(s):  
John Zizzo
Keyword(s):  
Physical Activity ◽  
Muscle Atrophy ◽  
Muscle Wasting ◽  
Ubiquitin Proteasome System ◽  
Specific Region ◽  
Signaling Cascades ◽  
Impaired Ability ◽  
Neurogenic Atrophy ◽  
Ubiquitin Proteasome ◽  
Underlying Mechanisms

: It is well known that muscles can waste away (atrophy) due to a lack of physical activity. Muscle wasting commonly presents with reduced muscle strength and an impaired ability to perform daily tasks. Several studies have attempted to categorize muscle atrophy into three main subgroups: physiologic, pathologic, and neurogenic atrophy. Physiologic atrophy is caused by the general underuse of skeletal muscle (e.g., bedridden). Pathologic atrophy is characterized as the loss of stimulus to a specific region (e.g. aging). Neurogenic atrophy results from damage to the nerve innervating a muscle (e.g. SMA, GBS). Mechanisms have been elucidated for many of these pathways (e.g., ubiquitin-proteasome system, NF-κB, etc.). However, many causes of muscle atrophy (e.g., burns, arthritis, etc.) operate through unelucidated signaling cascades. Therefore, this review highlights the underlying mechanisms of each subtype of muscle atrophy while emphasizing the need for additional research in properly classifying and identifying muscle atrophy.

scholarly journals Effects of a Novel Selective Androgen Receptor Modulator on Dexamethasone-Induced and Hypogonadism-Induced Muscle Atrophy

Endocrinology ◽  
2010 ◽  
Vol 151 (8) ◽  
pp. 3706-3719 ◽  
Author(s):  
Amanda Jones ◽  
Dong-Jin Hwang ◽  
Ramesh Narayanan ◽  
Duane D. Miller ◽  
James T. Dalton
Keyword(s):  
Protein Synthesis ◽  
Androgen Receptor ◽  
Muscle Atrophy ◽  
Muscle Wasting ◽  
Testosterone Propionate ◽  
Levator Ani ◽  
Ubiquitin Ligases ◽  
Selective Androgen Receptor Modulator ◽  
Receptor Modulator ◽  
Igf I

Glucocorticoids are the most widely used antiinflammatory drugs in the world. However, prolonged use of glucocorticoids results in undesirable side effects such as muscle wasting, osteoporosis, and diabetes. Skeletal muscle wasting, which currently has no approved therapy, is a debilitating condition resulting from either reduced muscle protein synthesis or increased degradation. The imbalance in protein synthesis could occur from increased expression and function of muscle-specific ubiquitin ligases, muscle atrophy F-box (MAFbx)/atrogin-1 and muscle ring finger 1 (MuRF1), or decreased function of the IGF-I and phosphatidylinositol-3 kinase/Akt kinase pathways. We examined the effects of a nonsteroidal tissue selective androgen receptor modulator (SARM) and testosterone on glucocorticoid-induced muscle atrophy and castration-induced muscle atrophy. The SARM and testosterone propionate blocked the dexamethasone-induced dephosphorylation of Akt and other proteins involved in protein synthesis, including Forkhead box O (FoxO). Dexamethasone caused a significant up-regulation in the expression of ubiquitin ligases, but testosterone propionate and SARM administration blocked this effect by phosphorylating FoxO. Castration induced rapid myopathy of the levator ani muscle, accompanied by up-regulation of MAFbx and MuRF1 and down-regulation of IGF-I, all of which was attenuated by a SARM. The results suggest that levator ani atrophy caused by hypogonadism may be the result of loss of IGF-I stimulation, whereas that caused by glucocorticoid treatment relies almost solely on up-regulation of MAFbx and MuRF1. Our studies provide the first evidence that glucocorticoid- and hypogonadism-induced muscle atrophy are mediated by distinct but overlapping mechanisms and that SARMs may provide a more effective and selective pharmacological approach to prevent glucocorticoid-induced muscle loss than steroidal androgen therapy.

scholarly journals Myostatin/Activin Receptor Ligands In Muscle And The Development Status Of Attenuating Drugs

2021 ◽  
Author(s):  
Buel D Rodgers ◽  
Christopher W Ward
Keyword(s):  
Muscle Function ◽  
Muscle Wasting ◽  
Metabolic Diseases ◽  
Muscle Growth ◽  
Neuromuscular Diseases ◽  
Treatment Strategies ◽  
Noncommunicable Disease ◽  
Cell Protein ◽  
Renal Diseases ◽  
Activin Receptor

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

scholarly journals Regulation of protein synthesis and degradation in L8 myotubes. Effects of serum, insulin and insulin-like growth factors

1989 ◽  
Vol 260 (2) ◽  
pp. 377-387 ◽  
Author(s):  
E A Gulve ◽  
J F Dice
Keyword(s):  
Protein Synthesis ◽  
Growth Factors ◽  
Protein Degradation ◽  
Small Proportion ◽  
Serum Insulin ◽  
Horse Serum ◽  
Muscle Growth ◽  
Protein Synthesis And Degradation ◽  
Synthesis And Degradation ◽  
Insulin Like Growth Factors

We have examined the regulation of protein turnover in rat skeletal myotubes from the L8 cell line. We measured protein synthesis by the rates of incorporation of radiolabelled tyrosine into protein in the presence of a flooding dose of non-radioactive tyrosine. We monitored degradation of proteins labelled with radioactive tyrosine by the release of acid-soluble radioactivity into medium containing excess nonradioactive tyrosine. Extracellular tyrosine pools and intracellular tyrosyl-tRNA equilibrate rapidly during measurements of protein synthesis, and very little reutilization of the radiolabelled tyrosine occurs during degradation measurements. Measured rates of protein synthesis and degradation are constant for several hours, and changes in myotube protein content can be accurately predicted by the measured rates of protein synthesis and degradation. Most of the myotube proteins labelled with radioactive tyrosine for 2 days are degraded, with half-lives (t1/2) of approx. 50 h. A small proportion (less than 2.5%) of the radiolabelled proteins are degraded more rapidly (t1/2 less than 10 h), and, at most, a small proportion (less than 15%) are degraded more slowly (t1/2 greater than 50 h). A variety of agents commonly added to primary muscle cell cultures or to myoblast cell lines (18% Medium 199, 1% chick-embryo extract, antibiotics and antifungal agents) had no effect on rates of protein synthesis or degradation. Horse serum, fetal bovine serum and insulin stimulate protein synthesis and inhibit the degradation of long-lived proteins without affecting the degradation of short-lived proteins. Insulin-like growth factors (IGF)-1 and -2 also stimulate protein synthesis and inhibit protein degradation. The stimulation of protein synthesis and the inhibition of protein degradation are of similar magnitude (a maximum of approx. 2-fold) and display similar sensitivities to a particular anabolic agent. Insulin stimulates protein synthesis and inhibits protein degradation only at supraphysiological doses, whereas IGF-1 and -2 are effective at physiological concentrations. These and other findings suggest that IGFs may be important regulators of skeletal muscle growth during the fetal and early neonatal periods.

scholarly journals Glucocorticoid Receptor Signaling Impairs Protein Turnover Regulation in Hypoxia-Induced Muscle Atrophy in Male Mice

Endocrinology ◽  
2017 ◽  
Vol 159 (1) ◽  
pp. 519-534 ◽  
Author(s):  
Chiel C de Theije ◽  
Annemie M W J Schols ◽  
Wouter H Lamers ◽  
Judith J M Ceelen ◽  
Rick H van Gorp ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Food Intake ◽  
Glucocorticoid Receptor ◽  
Muscle Atrophy ◽  
Muscle Wasting ◽  
26S Proteasome ◽  
Skeletal Muscle Atrophy ◽  
Chronic Obstructive ◽  
E3 Ligases ◽  
Hypoxic Conditions

Abstract Hypoxemia may contribute to muscle wasting in conditions such as chronic obstructive pulmonary disease. Muscle wasting develops when muscle proteolysis exceeds protein synthesis. Hypoxia induces skeletal muscle atrophy in mice, which can in part be attributed to reduced food intake. We hypothesized that hypoxia elevates circulating corticosterone concentrations by reduced food intake and enhances glucocorticoid receptor (GR) signaling in muscle, which causes elevated protein degradation signaling and dysregulates protein synthesis signaling during hypoxia-induced muscle atrophy. Muscle-specific GR knockout and control mice were subjected to normoxia, normobaric hypoxia (8% oxygen), or pair-feeding to the hypoxia group for 4 days. Plasma corticosterone and muscle GR signaling increased after hypoxia and pair-feeding. GR deficiency prevented muscle atrophy by pair-feeding but not by hypoxia. GR deficiency differentially affected activation of ubiquitin 26S-proteasome and autophagy proteolytic systems by pair-feeding and hypoxia. Reduced food intake suppressed mammalian target of rapamycin complex 1 (mTORC1) activity under normoxic but not hypoxic conditions, and this retained mTORC1 activity was mediated by GR. We conclude that GR signaling is required for muscle atrophy and increased expression of proteolysis-associated genes induced by decreased food intake under normoxic conditions. Under hypoxic conditions, muscle atrophy and elevated gene expression of the ubiquitin proteasomal system–associated E3 ligases Murf1 and Atrogin-1 are mostly independent of GR signaling. Furthermore, impaired inhibition of mTORC1 activity is GR-dependent in hypoxia-induced muscle atrophy.

Role of β-Adrenoceptor Signaling in Skeletal Muscle: Implications for Muscle Wasting and Disease

2008 ◽  
Vol 88 (2) ◽  
pp. 729-767 ◽  
Author(s):  
Gordon S. Lynch ◽  
James G. Ryall
Keyword(s):  
Skeletal Muscle ◽  
Muscle Wasting ◽  
Therapeutic Potential ◽  
Muscle Growth ◽  
Neuromuscular Diseases ◽  
Cardiovascular Effects ◽  
Adrenergic System ◽  
Adrenergic Signaling ◽  
Beneficial Effects ◽  
Cardiovascular Side Effects

The importance of β-adrenergic signaling in the heart has been well documented, but it is only more recently that we have begun to understand the importance of this signaling pathway in skeletal muscle. There is considerable evidence regarding the stimulation of the β-adrenergic system with β-adrenoceptor agonists (β-agonists). Although traditionally used for treating bronchospasm, it became apparent that some β-agonists could increase skeletal muscle mass and decrease body fat. These so-called “repartitioning effects” proved desirable for the livestock industry trying to improve feed efficiency and meat quality. Studying β-agonist effects on skeletal muscle has identified potential therapeutic applications for muscle wasting conditions such as sarcopenia, cancer cachexia, denervation, and neuromuscular diseases, aiming to attenuate (or potentially reverse) the muscle wasting and associated muscle weakness, and to enhance muscle growth and repair after injury. Some undesirable cardiovascular side effects of β-agonists have so far limited their therapeutic potential. This review describes the physiological significance of β-adrenergic signaling in skeletal muscle and examines the effects of β-agonists on skeletal muscle structure and function. In addition, we examine the proposed beneficial effects of β-agonist administration on skeletal muscle along with some of the less desirable cardiovascular effects. Understanding β-adrenergic signaling in skeletal muscle is important for identifying new therapeutic targets and identifying novel approaches to attenuate the muscle wasting concomitant with many diseases.

scholarly journals Myostatin from the heart: local and systemic actions in cardiac failure and muscle wasting

2011 ◽  
Vol 300 (6) ◽  
pp. H1973-H1982 ◽  
Author(s):  
Astrid Breitbart ◽  
Mannix Auger-Messier ◽  
Jeffery D. Molkentin ◽  
Joerg Heineke
Keyword(s):  
Heart Failure ◽  
Skeletal Muscle ◽  
Muscle Atrophy ◽  
Muscle Wasting ◽  
Muscle Growth ◽  
Skeletal Muscle Atrophy ◽  
Cardiac Cachexia ◽  
Heart Failure Patients ◽  
Skeletal Muscle Growth ◽  
Skeletal Muscle Wasting

A significant proportion of heart failure patients develop skeletal muscle wasting and cardiac cachexia, which is associated with a very poor prognosis. Recently, myostatin, a cytokine from the transforming growth factor-β (TGF-β) family and a known strong inhibitor of skeletal muscle growth, has been identified as a direct mediator of skeletal muscle atrophy in mice with heart failure. Myostatin is mainly expressed in skeletal muscle, although basal expression is also detectable in heart and adipose tissue. During pathological loading of the heart, the myocardium produces and secretes myostatin into the circulation where it inhibits skeletal muscle growth. Thus, genetic elimination of myostatin from the heart reduces skeletal muscle atrophy in mice with heart failure, whereas transgenic overexpression of myostatin in the heart is capable of inducing muscle wasting. In addition to its endocrine action on skeletal muscle, cardiac myostatin production also modestly inhibits cardiomyocyte growth under certain circumstances, as well as induces cardiac fibrosis and alterations in ventricular function. Interestingly, heart failure patients show elevated myostatin levels in their serum. To therapeutically influence skeletal muscle wasting, direct inhibition of myostatin was shown to positively impact skeletal muscle mass in heart failure, suggesting a promising strategy for the treatment of cardiac cachexia in the future.

scholarly journals Skeletal muscle wasting in chronic kidney disease: the emerging role of microRNAs

2019 ◽  
Vol 35 (9) ◽  
pp. 1469-1478 ◽  
Author(s):  
Kate A Robinson ◽  
Luke A Baker ◽  
Matthew P M Graham-Brown ◽  
Emma L Watson
Keyword(s):  
Skeletal Muscle ◽  
Chronic Kidney Disease ◽  
Kidney Disease ◽  
Muscle Mass ◽  
Muscle Atrophy ◽  
Muscle Wasting ◽  
Muscle Growth ◽  
Exciting Field ◽  
Skeletal Muscle Wasting ◽  
And Function

Abstract Skeletal muscle wasting is a common complication of chronic kidney disease (CKD), characterized by the loss of muscle mass, strength and function, which significantly increases the risk of morbidity and mortality in this population. Numerous complications associated with declining renal function and lifestyle activate catabolic pathways and impair muscle regeneration, resulting in substantial protein wasting. Evidence suggests that increasing skeletal muscle mass improves outcomes in CKD, making this a clinically important research focus. Despite extensive research, the pathogenesis of skeletal muscle wasting is not completely understood. It is widely recognized that microRNAs (miRNAs), a family of short non-coding RNAs, are pivotal in the regulation of skeletal muscle homoeostasis, with significant roles in regulating muscle growth, regeneration and metabolism. The abnormal expression of miRNAs in skeletal muscle during disease has been well described in cellular and animal models of muscle atrophy, and in recent years, the involvement of miRNAs in the regulation of muscle atrophy in CKD has been demonstrated. As this exciting field evolves, there is emerging evidence for the involvement of miRNAs in a beneficial crosstalk system between skeletal muscle and other organs that may potentially limit the progression of CKD. In this article, we describe the pathophysiological mechanisms of muscle wasting and explore the contribution of miRNAs to the development of muscle wasting in CKD. We also discuss advances in our understanding of miRNAs in muscle–organ crosstalk and summarize miRNA-based therapeutics currently in clinical trials.

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