Mechanisms of protein balance in skeletal muscle

Transcriptome-derived evidence reveals the regulatory network in the skeletal muscle of the fast-growth mstnb-/- male tilapia

Myostatin (Mstn) negatively regulates muscle growth and Mstn deficiency induced "double-skeletal muscle" development in vertebrates, including tilapias. In this study, we performed a transcriptomic analysis of skeletal muscle from both wild-type and mstnb-/- males to investigate the molecular mechanisms underlying skeletal muscle hypertrophy in mstnb-/- mutants. We identified 4697 differentially expressed genes (DEGs), 113 differentially expressed long non-coding RNAs (DE lncRNAs), 211 differentially expressed circular RNAs (DE circRNAs), and 98 differentially expressed microRNAs (DE miRNAs). The DEGs were significantly enriched in proteasome and ubiquitin-mediated proteolysis pathways. Cis- and trans-targeting genes of DE lncRNAs were also notably enriched in the above two pathways. The putative host genes of DE circRNAs linked to myofibrils, contractile fibers, and so on. Additionally, DE miRNAs were associated with ubiquitin-mediated proteolysis and key signaling pathways, including AMPK, FoxO, and mTOR. Furthermore, the core competing endogenous RNA (ceRNA) network was constructed comprising 31 DEGs, 37 DE miRNAs, 14 DE circRNAs, and 45 DE lncRNAs. The key roles of ubiquitin-proteasome system were highlighted in the ceRNA network. Taken together, this study provides a novel perspective on muscle mass increase in Mstn mutants through the repression of protein degradation and facilitates our understanding of the molecular mechanisms of skeletal muscle hypertrophy in fish.

Sinapine suppresses ROS-induced C2C12 myoblast cell death through MAPK and autophagy pathways

Oxidative stress in skeletal muscle can lead to muscle atrophy through reactive oxygen species (ROS)-induced damage and cell death. tert-Butyl hydroperoxide (TBHP), an exogenous ROS generator, induces oxidative stress and cell death in various cells. Sinapine from cruciferous plants possesses beneficial effects, but its role in protecting skeletal muscle cells against ROS-induced cell death remains unclear. This study demonstrates that sinapine pretreatment significantly reduced TBHP-induced cell death and ROS accumulation in a dose-dependent manner. TBHP activated mitogen-activated protein kinase (MAPK) pathways including Akt, p38, and JNK, and triggered autophagy. Sinapine suppressed the phosphorylation of Akt, MEK3/6, p38, MEK4, and JNK, and modulated key autophagy markers. Notably, the co-treatment of MAPK inhibitors attenuated TBHP-induced cell death and LC3B-II accumulation. These findings suggest that sinapine is a promising phytochemical for mitigating oxidative stress-mediated muscle injury, offering potential therapeutic strategies for maintaining skeletal muscle homeostasis and addressing muscle-related pathologies.

Embryonic Leucine Promotes Early Postnatal Growth via mTOR Signalling in Japanese Quails

Nutritional cues during embryonic development can alter developmental trajectories and affect postnatal growth. However, the specific mechanisms by which nutrients influence avian growth remain largely unknown. Amino acids can directly interact with the nutrient-sensing pathways, such as the insulin-like growth factor 1 (IGF-1)/mechanistic target of rapamycin (mTOR) pathways, which are known to regulate growth. We examined the effects of embryonic leucine on gene expression and phenotypic growth in Japanese quails by injecting 2.5 mg leucine or saline (control) into Japanese quail eggs on the tenth day of incubation and incubating them under standard conditions. The treatment groups had similar hatching success and size at hatching. However, between 3 and 7 days post-hatching, quails treated with embryonic leucine showed increased growth in body mass and wing, tarsus, head, and intestinal lengths, lasting up to 21 days. The hepatic expression of IGF1, IGF1R, mTOR, and RPS6K1 was upregulated in leucine-treated quails, while the expression of FOXO1 remained unaffected. In conclusion, a subtle increase in embryonic leucine may induce developmental programming effects in Japanese quail by interacting with the IGF-1/mTOR nutrient-sensing pathway to promote growth. This study highlights the role of embryonic amino acids as crucial nutrients for enhancing growth. It provides valuable insight into nutrient intervention strategies during embryonic development to potentially improve poultry growth performance.

Myokines: A central point in managing redox homeostasis and quality of life

Redox homeostasis is a crucial phenomenon that is obligatory for maintaining the healthy status of cells. However, the loss of redox homeostasis may lead to numerous diseases that ultimately result in a compromised quality of life. Skeletal muscle is an endocrine organ that secretes hundreds of myokines. Myokines are peptides and cytokines produced and released by muscle fibers. Skeletal muscle secreted myokines act as a robust modulator for regulating cellular metabolism and redox homeostasis which play a prime role in managing and improving metabolic function in multiple organs. Further, the secretory myokines maintain redox homeostasis not only in muscles but also in other organs of the body via stabilizing oxidants and antioxidant levels. Myokines are also engaged in maintaining mitochondrial dynamics as mitochondria is a central point for the generation of reactive oxygen species (ROS). Ergo, myokines also act as a central player in communicating signals to other organs, including the pancreas, gut, liver, bone, adipose tissue, brain, and skin via their autocrine, paracrine, or endocrine effects. The present review provides a comprehensive overview of skeletal muscle-secreted myokines in managing redox homeostasis and quality of life. Additionally, probable strategies will be discussed that provide a solution for a better quality of life.

Oxidative stress and metabolism meet epigenetic modulation in physical exercise

Physical exercise is established as an important factor of health and generally is recommended for its positive effects on several tissues, organs, and systems. These positive effects come from metabolic adaptations that also include oxidative eustress, in which physical activity increases ROS production and antioxidant mechanisms, although this depends on the intensity of the exercise. Muscle metabolism through mechanisms such as aerobic and anaerobic glycolysis, tricarboxylic acid cycle, and oxidative lipid metabolism can produce metabolites and co-factors which directly impact the epigenetic machinery. In this review, we clearly reinforce the evidence that exercise regulates several epigenetic mechanisms and explain how these mechanisms can be regulated by metabolic products and co-factors produced during exercise. In fact, recent evidence has demonstrated the importance of epigenetics in the gene expression changes implicated in metabolic adaptation after exercise. Importantly, intermediates of the metabolism generated by continuous, acute, moderate, or strenuous exercise control the activity of epigenetic enzymes, therefore turning on or turning off the gene expression of specific programs which can lead to physiological adaptations after exercise.

Lactate administration induces skeletal muscle synthesis by influencing Akt/mTOR and MuRF1 in non-trained mice but not in trained mice

The perception regarding lactate has changed over the past decades, and some of its physiological roles have gradually been revealed. However, the effects of exogenous lactate on skeletal muscle synthesis remain unclear. This study aimed to confirm the effects of a 5-week lactate administration and post-exercise lactate administration on skeletal muscle synthesis. Thirty-two Institute of Cancer Research mice were randomly assigned to non-trained + placebo, non-trained + lactate, trained + placebo, and trained + lactate groups. Furthermore, 3 g/kg of lactate or an equivalent volume of saline was immediately administered after exercise training (maximum oxygen uptake: 70%). Lactate administration and/or exercise training was performed 5 days/week for 5 weeks. After the experimental period, it was observed that lactate administration tended to elevate skeletal muscle weight, increased protein kinase B (p < 0.05) and mammalian target of rapamycin (p < 0.05) mRNA levels, and decreased muscle ring-finger protein-1 expression (p < 0.05). Lactate administration after exercise training significantly enhanced plantaris muscle weight; however, it had no additional effects on most signaling factors. This study demonstrated that a 5-week lactate administration could stimulate skeletal muscle synthesis, and lactate administration after exercise training may provide additional effects, such as increasing skeletal muscle.

Deliberation on debilitating condition of cancer cachexia: Skeletal muscle wasting

BACKGROUND

Cancer cachexia is a debilitating syndrome associated with marked body loss because of muscular atrophy and fat loss. There are several mechanisms contributing to the pathogenesis of cachexia. The presence of the tumor releases cytokines from inflammatory and immune cells, which play a significant role in activating and deactivating certain pathways associated with protein, carbohydrate, and lipid metabolism. This review focuses on various cascades involving an imbalance between protein synthesis and degradation in the skeletal muscles.

OBJECTIVES

This study aimed to elucidate the mechanisms involved in skeletal muscle wasting phenomenon over the last few years.

METHODS

This article briefly overviews different pathways responsible for muscle atrophy in cancer cachexia. Studies published up to April 2023 were included. Important findings and study contributions were chosen and compiled using several databases including PubMed, Google Scholar, Science Direct, and ClinicalTrials.gov using relevant keywords.

RESULTS

Cancer cachexia is a complex disease involving multiple factors resulting in atrophy of skeletal muscles. Systemic inflammation, altered energy balance and carbohydrate metabolism, altered lipid and protein metabolism, and adipose tissue browning are some of the major culprits in cancer cachexia. Increased protein degradation and decreased protein synthesis lead to muscle atrophy. Changes in signaling pathway like ubiquitin-proteasome, autophagy, mTOR, AMPK, and IGF-1 also lead to muscle wasting. Physical exercise, nutritional supplementation, steroids, myostatin inhibitors, and interventions targeting on inflammation have been investigated to treat cancer cachexia. Some therapy showed positive results in preclinical and clinical settings, although more research on the efficacy and safety of the treatment should be done.

CONCLUSION

Muscle atrophy in cancer cachexia is the result of multiple complex mechanisms; as a result, a lot more research has been done to describe the pathophysiology of the disease. Targeted therapy and multimodal interventions can improve clinical outcomes for patients.

Unravelling the Role of Cancer Cell-Derived Extracellular Vesicles in Muscle Atrophy, Lipolysis, and Cancer-Associated Cachexia

Cancer-associated cachexia is a metabolic syndrome that causes significant reduction in whole-body weight due to excessive loss of muscle mass accompanied by loss of fat mass. Reduced food intake and several metabolic abnormalities, such as increased energy expenditure, excessive catabolism, and inflammation, are known to drive cachexia. It is well documented that cancer cells secrete EVs in abundance which can be easily taken up by the recipient cell. The cargo biomolecules carried by the EVs have the potential to alter the signalling pathways and function of the recipient cells. EV cargo includes proteins, nucleic acids, lipids, and metabolites. Tumour-secreted EVs have been found to alter the metabolic and biological functions of adipose and muscle tissue, which aids in the development of the cachexia phenotype. To date, no medical intervention or FDA-approved drug exists that can completely reverse cachexia. Therefore, understanding how cancer-derived EVs contribute to the onset and progression of cancer-associated cachexia may help with the identification of new biomarkers as well as provide access to novel treatment alternatives. The goal of this review article is to discuss the most recent research on cancer-derived EVs and their function in cellular crosstalk that promotes catabolism in muscle and adipose tissue during cancer-induced cachexia.

Skeletal muscle wasting after burn is regulated by a decrease in anabolic signaling in the early flow phase

Following burns a sustained catabolic stress response is activated, resulting in skeletal muscle wasting. A better understanding of the underlying mechanisms of postburn skeletal muscle wasting is essential for the development of preventive and/or therapeutic strategies. Six weeks old female rats underwent a sham, 10% or 40% total body surface area scald burn. Ten days post-injury, severely burned animals gained significantly less weight compared to sham treated and minor burned animals, reflected in a significantly lower ratio of muscle to total body weight for Soleus (SOL) and Extensor Digitorum Longus (EDL) in the severely burned group. Postburn, total fiber number was significantly lower in EDL, while in SOL the amount of type1 fibers significantly increased and type2 fibers significantly decreased. No signs of mitochondrial dysfunction (COX/SDH) or apoptosis (caspase-3) were found. In SOL and EDL, eEF2 and pAKT expression was significantly lower after severe burn. MURF1,2,3 and Atrogin-1 was significantly higher in SOL, whilst in EDL MURF1,2,3 was significantly lower postburn. In both muscles, FOXO3A was significantly lower postburn. This study identified postburn changes in muscle anthropomorphology and proteins involved in pathways regulating protein synthesis and breakdown, with more pronounced catabolic effects in SOL.

A novel method for visualizing in-vivo rates of protein degradation provides insight into how TRIM28 regulates muscle size

Skeletal muscle size is controlled by the balance between protein synthesis and protein degradation. Given the essential role of skeletal muscle in maintaining a high quality of life, understanding the mechanisms that modulate this balance are of critical importance. Previously, we demonstrated that muscle-specific knockout of TRIM28 reduces muscle size and function and in the current study, we discovered that this effect is associated with an increase in protein degradation and a dramatic reduction in the expression of Mettl21c. Importantly, we also determined that overexpression of Mettl21c is sufficient to induce hypertrophy in both control and TRIM28 knockout muscles. Moreover, we developed a simple pulse-chase biorthogonal non-canonical amino acid tagging technique that enabled us to visualize the in vivo rate of protein degradation, and with this technique were able to conclude that the hypertrophic effect of Mettl21c is due, at least in part, to an inhibition of protein degradation.

Skeletal muscle gene expression dysregulation in long-term spaceflights and aging is clock-dependent

The circadian clock regulates cellular and molecular processes in mammals across all tissues including skeletal muscle, one of the largest organs in the human body. Dysregulated circadian rhythms are characteristic of aging and crewed spaceflight, associated with, for example, musculoskeletal atrophy. Molecular insights into spaceflight-related alterations of circadian regulation in skeletal muscle are still missing. Here, we investigated potential functional consequences of clock disruptions on skeletal muscle using published omics datasets obtained from spaceflights and other clock-altering, external (fasting and exercise), or internal (aging) conditions on Earth. Our analysis identified alterations of the clock network and skeletal muscle-associated pathways, as a result of spaceflight duration in mice, which resembles aging-related gene expression changes observed in humans on Earth (e.g., ATF4 downregulation, associated with muscle atrophy). Furthermore, according to our results, external factors such as exercise or fasting lead to molecular changes in the core-clock network, which may compensate for the circadian disruption observed during spaceflights. Thus, maintaining circadian functioning is crucial to ameliorate unphysiological alterations and musculoskeletal atrophy reported among astronauts.

Pathophysiological Aspects of Muscle Atrophy and Osteopenia Induced by Chronic Constriction Injury (CCI) of the Sciatic Nerve in Rats

Skeletal muscle atrophy is a condition characterized by a loss of muscle mass and muscle strength caused by an imbalance between protein synthesis and protein degradation. Muscle atrophy is often associated with a loss of bone mass manifesting as osteoporosis. The aim of this study was to evaluate if chronic constriction injury (CCI) of the sciatic nerve in rats can be a valid model to study muscle atrophy and consequent osteoporosis. Body weight and body composition were assessed weekly. Magnetic resonance imaging (MRI) was performed on day zero before ligation and day 28 before sacrifice. Catabolic markers were assessed via Western blot and Quantitative Real-time PCR. After the sacrifice, a morphological analysis of the gastrocnemius muscle and Micro-Computed Tomography (Micro-CT) on the tibia bone were performed. Rats that underwent CCI had a lower body weight increase on day 28 compared to the naive group of rats (p < 0.001). Increases in lean body mass and fat mass were also significantly lower in the CCI group (p < 0.001). The weight of skeletal muscles was found to be significantly lower in the ipsilateral hindlimb compared to that of contralateral muscles; furthermore, the cross-sectional area of muscle fibers decreased significantly in the ipsilateral gastrocnemius. The CCI of the sciatic nerve induced a statistically significant increase in autophagic and UPS (Ubiquitin Proteasome System) markers and a statistically significant increase in Pax-7 (Paired Box-7) expression. Micro-CT showed a statistically significant decrease in the bone parameters of the ipsilateral tibial bone. Chronic nerve constriction appeared to be a valid model for inducing the condition of muscle atrophy, also causing changes in bone microstructure and leading to osteoporosis. Therefore, sciatic nerve constriction could be a valid approach to study muscle-bone crosstalk and to identify new strategies to prevent osteosarcopenia.

Molecular mechanisms of post-burn muscle wasting and the therapeutic potential of physical exercise

After a severe burn injury, a systemic stress response activates metabolic and inflammatory derangements that, among other, leads to muscle mass loss (muscle wasting). These negative effects on skeletal muscle continue for several months or years and are aggravated by short-term and long-term disuse. The dynamic balance between muscle protein synthesis and muscle protein breakdown (proteolysis) is regulated by complex signalling pathways that leads to an overall negative protein balance in skeletal muscle after a burn injury. Research concerning these molecular mechanisms is still scarce and inconclusive, understanding of which, if any, molecular mechanisms contribute to muscle wasting is of fundamental importance in designing of therapeutic interventions for burn patients as well. This review not only summarizes our present knowledge of the molecular mechanisms that underpin muscle protein balance but also summarizes the effects of exercise on muscle wasting post-burn as promising strategy to counteract the detrimental effects on skeletal muscle. Future research focusing on the pathways causing post-burn muscle wasting and the different effects of exercise on them is needed to confirm this hypothesis and to lay the foundation of therapeutic strategies.

Mannan Oligosaccharides Promoted Skeletal Muscle Hypertrophy through the Gut Microbiome and Microbial Metabolites in Mice

Mannan oligosaccharides (MOSs) have been implicated in the animal growth rate, health indices, and lipid oxidative stability. MOSs have been indicated to maintain intestinal health and anti-inflammatory effects via modulation of gut microbiota. Furthermore, the role of MOSs in modulating skeletal muscle function is largely unknown. Here, this study aimed to investigate the effects of MOS supplementation on muscle function and muscle mass in mice. Additionally, the possible underlying mechanisms, including the contributions of gut microbiota and microbial metabolites, were explored. In our study, 3-week-old C57BL/6J male mice (body weight of approximately 10.7 ± 1.1 g) were given pure water or pure water with 1% MOS. To study the effect of MOSs on gut-microbiota-derived metabolites, serum metabolic profiles were analyzed through untargeted metabolomic profiling. Moreover, we detected the downstream signals of differential metabolites, and decanoic acid (DA) was selected as our target spot. Then, DA was used to treat C2C12 cells, and we found that DA promotes C2C12 cell differentiation via the GPR84 and PI3K/AKT signaling pathways. In conclusion, these results showed that MOS supplementation improves muscle function and muscle mass. Additionally, gut microbiome and microbial metabolites were regulated by MOSs, and DA may be one of the most important links between the gut microbiome and skeletal muscle function regulation.

Bone-Muscle Crosstalk: Musculoskeletal Complications of Chemotherapy

PURPOSE OF REVIEW

Chemotherapy drugs combat tumor cells and reduce metastasis. However, a significant side effect of some chemotherapy strategies is loss of skeletal muscle and bone. In cancer patients, maintenance of lean tissue is a positive prognostic indicator of outcomes and helps to minimize the toxicity associated with chemotherapy. Bone-muscle crosstalk plays an important role in the function of the musculoskeletal system and this review will focus on recent findings in preclinical and clinical studies that shed light on chemotherapy-induced bone-muscle crosstalk.

RECENT FINDINGS

Chemotherapy-induced loss of bone and skeletal muscle are important clinical problems. Bone antiresorptive drugs prevent skeletal muscle weakness in preclinical models. Chemotherapy-induced loss of bone can cause muscle weakness through both changes in endocrine signaling and mechanical loading between muscle and bone. Chemotherapy-induced changes to bone-muscle crosstalk have implications for treatment strategies and patient quality of life. Recent findings have begun to determine the role of chemotherapy in bone-muscle crosstalk and this review summarizes the most relevant clinical and preclinical studies.

Loss of REDD1 prevents chemotherapy-induced muscle atrophy and weakness in mice

BACKGROUND

Chemotherapy is an essential treatment to combat solid tumours and mitigate metastasis. Chemotherapy causes side effects including muscle wasting and weakness. Regulated in Development and DNA Damage Response 1 (REDD1) is a stress-response protein that represses the mechanistic target of rapamycin (mTOR) in complex 1 (mTORC1), and its expression is increased in models of muscle wasting. The aim of this study was to determine if deletion of REDD1 is sufficient to attenuate chemotherapy-induced muscle wasting and weakness in mice.

METHODS

C2C12 myotubes were treated with carboplatin, and changes in myotube diameter were measured. Protein synthesis was measured by puromycin incorporation, and REDD1 mRNA and protein expression were analysed in myotubes treated with carboplatin. Markers of mTORC1 signalling were measured by western blot. REDD1 global knockout mice and wild-type mice were treated with a single dose of carboplatin and euthanized 7 days later. Body weight, hindlimb muscle weights, forelimb grip strength, and extensor digitorum longus whole muscle contractility were measured in all groups. Thirty minutes prior to euthanasia, mice were injected with puromycin to measure puromycin incorporation in skeletal muscle.

RESULTS

C2C12 myotube diameter was decreased at 24 (P = 0.0002) and 48 h (P < 0.0001) after carboplatin treatment. Puromycin incorporation was decreased in myotubes treated with carboplatin for 24 (P = 0.0068) and 48 h (P = 0.0008). REDD1 mRNA and protein expression were increased with carboplatin treatment (P = 0.0267 and P = 0.0015, respectively), and this was accompanied by decreased phosphorylation of Akt T³⁰⁸ (P < 0.0001) and S⁴⁷³ (P = 0.0006), p70S6K T³⁸⁹ (P = 0.0002), and 4E-binding protein 1 S⁶⁵ (P = 0.0341), all markers of mTORC1 activity. REDD1 mRNA expression was increased in muscles from mice treated with carboplatin (P = 0.0295). Loss of REDD1 reduced carboplatin-induced body weight loss (P = 0.0013) and prevented muscle atrophy in mice. REDD1 deletion prevented carboplatin-induced decrease of protein synthesis (P = 0.7626) and prevented muscle weakness.

CONCLUSIONS

Carboplatin caused loss of body weight, muscle atrophy, muscle weakness, and inhibition of protein synthesis. Loss of REDD1 attenuates muscle atrophy and weakness in mice treated with carboplatin. Our study illustrates the importance of REDD1 in the regulation of muscle mass with chemotherapy treatment and may be an attractive therapeutic target to combat cachexia.

Leucine-Rich Diet Improved Muscle Function in Cachectic Walker 256 Tumour-Bearing Wistar Rats

Skeletal muscle atrophy occurs in several pathological conditions, such as cancer, especially during cancer-induced cachexia. This condition is associated with increased morbidity and poor treatment response, decreased quality of life, and increased mortality in cancer patients. A leucine-rich diet could be used as a coadjutant therapy to prevent muscle atrophy in patients suffering from cancer cachexia. Besides muscle atrophy, muscle function loss is even more important to patient quality of life. Therefore, this study aimed to investigate the potential beneficial effects of leucine supplementation on whole-body functional/movement properties, as well as some markers of muscle breakdown and inflammatory status. Adult Wistar rats were randomly distributed into four experimental groups. Two groups were fed with a control diet (18% protein): Control (C) and Walker 256 tumour-bearing (W), and two other groups were fed with a leucine-rich diet (18% protein + 3% leucine): Leucine Control (L) and Leucine Walker 256 tumour-bearing (LW). A functional analysis (walking, behaviour, and strength tests) was performed before and after tumour inoculation. Cachexia parameters such as body weight loss, muscle and fat mass, pro-inflammatory cytokine profile, and molecular and morphological aspects of skeletal muscle were also determined. As expected, Walker 256 tumour growth led to muscle function decline, cachexia manifestation symptoms, muscle fibre cross-section area reduction, and classical muscle protein degradation pathway activation, with upregulation of FoxO1, MuRF-1, and 20S proteins. On the other hand, despite having no effect on the walking test, inflammation status or muscle oxidative capacity, the leucine-rich diet improved muscle strength and behaviour performance, maintained body weight, fat and muscle mass and decreased some protein degradation markers in Walker 256 tumour-bearing rats. Indeed, a leucine-rich diet alone could not completely revert cachexia but could potentially diminish muscle protein degradation, leading to better muscle functional performance in cancer cachexia.

Gintonin-enriched fraction improves sarcopenia by maintaining immune homeostasis in 20- to 24-month-old C57BL/6J mice

Background

Gintonin-enriched fraction (GEF) is a new non-saponin component glycolipoprotein isolated from ginseng root. This study examined the effect of GEF on age-related sarcopenia in old C57BL/6J mice.

Methods

Young (3–6 months) and old (20–24 months) C57BL/6J mice received oral GEF (50 mg/kg/day or 150 mg/kg/day) daily for 5 weeks. During the oral administration period, body weight and grip strength were measured weekly. After sacrifice, muscles from the hindlimb were excised and used for hematoxylin and eosin staining and western blotting to determine the effects of GEF on sarcopenia. The thymus was photographed to compare size, and flow cytometry was performed to examine the effect of GEF on immune homeostasis in the thymus and spleen. Blood samples were collected, and the concentrations of pro-inflammatory cytokines and IGF-1 were measured.

Results

GEF caused a significant increase in muscle strength, mass, and fiber size in old mice. GEF restored age-related disruption of immune homeostasis by maintaining T cell compartments and regulating inflammatory biomarkers. Thus, GEF reduced common low-grade chronic inflammatory parameters, which are the main cause of muscle loss.

Conclusion

GEF maintained immune homeostasis and inhibited markers of chronic inflammation, resulting in anti-sarcopenia effects in aged C57BL/6J mice. Thus, GEF is a potential therapeutic agent that slows sarcopenia in the elderly.

2-D08 treatment regulates C2C12 myoblast proliferation and differentiation via the Erk1/2 and proteasome signaling pathways

SUMOylation is one of the post-translational modifications that involves the covalent attachment of the small ubiquitin-like modifier (SUMO) to the substrate. SUMOylation regulates multiple biological processes, including myoblast proliferation, differentiation, and apoptosis. 2-D08 is a synthetically available flavone, which acts as a potent cell-permeable SUMOylation inhibitor. Its mechanism of action involves preventing the transfer of SUMO from the E2 thioester to the substrate without influencing SUMO-activating enzyme E1 (SAE-1/2) or E2 Ubc9-SUMO thioester formation. However, both the effects and mechanisms of 2-D08 on C2C12 myoblast cells remain unclear. In the present study, we found that treatment with 2-D08 inhibits C2C12 cell proliferation and differentiation. We confirmed that 2-D08 significantly hampers the viability of C2C12 cells. Additionally, it inhibited myogenic differentiation, decreasing myosin heavy chain (MHC), MyoD, and myogenin expression. Furthermore, we confirmed that 2-D08-mediated anti-myogenic effects impair myoblast differentiation and myotube formation, reducing the number of MHC-positive C2C12 cells. In addition, we found that 2-D08 induces the activation of ErK1/2 and the degradation of MyoD and myogenin in C2C12 cells. Taken together, these results indicated that 2-D08 treatment results in the deregulated proliferation and differentiation of myoblasts. However, further research is needed to investigate the long-term effects of 2-D08 on skeletal muscles.

β2-adrenergic receptor agonist counteracts skeletal muscle atrophy and oxidative stress in uremic mice

In patients with chronic kidney disease, skeletal muscle dysfunction is associated with mortality. Uremic sarcopenia is caused by ageing, malnutrition, and chronic inflammation, but the molecular mechanism and potential therapeutics have not been fully elucidated yet. We hypothesize that accumulated uremic toxins might exert a direct deteriorative effect on skeletal muscle and explore the pharmacological treatment in experimental animal and culture cell models. The mice intraperitoneally injected with indoxyl sulfate (IS) after unilateral nephrectomy displayed an elevation of IS concentration in skeletal muscle and a reduction of instantaneous muscle strength, along with the predominant loss of fast-twitch myofibers and intramuscular reactive oxygen species (ROS) generation. The addition of IS in the culture media decreased the size of fully differentiated mouse C2C12 myotubes as well. ROS accumulation and mitochondrial dysfunction were also noted. Next, the effect of the β2-adrenergic receptor (β2-AR) agonist, clenbuterol, was evaluated as a potential treatment for uremic sarcopenia. In mice injected with IS, clenbuterol treatment increased the muscle mass and restored the tissue ROS level but failed to improve muscle weakness. In C2C12 myotubes stimulated with IS, although β2-AR activation also attenuated myotube size reduction and ROS accumulation as did other anti-oxidant reagents, it failed to augment the mitochondrial membrane potential. In conclusion, IS provokes muscular strength loss (uremic dynapenia), ROS generation, and mitochondrial impairment. Although the β2-AR agonist can increase the muscular mass with ROS reduction, development of therapeutic interventions for restoring skeletal muscle function is still awaited.

Prospect of early vascular tone and satellite cell modulations on white striping muscle myopathy

Polyphasic myodegeneration potentially causes severe physiological and metabolic disorders in the breast muscle of fast-growing broiler chickens. To date, the etiology of recent muscle myopathies, such as the white striping (WS) phenotype, is still unknown. White striping–affected breast meats compromise the water holding capacity and predispose muscle to poor vascular tone, leading to the deterioration of meat qualities. Herein, this review article provides insight on the complexities around chicken breast myopathies: (i) the etiologies of WS occurrence in chicken; (ii) the metabolic changes that occur in WS defect in pectoralis major; and (iii) the interactions between breast muscle physiology and vascular tone. It also addressed the effects of nutritional supplements on muscle myopathies on chicken breast meats. Moreover, the review explored breast muscle biology focusing on the early preparation of satellite and vascular cells in fast-growth chicken breeds. Transcriptomics and histological analyses revealed poor vascularity in breast muscle of fast growth chickens. Thus, we suggest in ovo feeding of nutrients promoting vascularization and satellite cells replenishment as a potential strategy to enhance endothelium-derived nitric oxide availability to promote vascularization in the pectoralis major muscle region.

What skeletal muscle has to say in amyotrophic lateral sclerosis: Implications for therapy

Amyotrophic lateral sclerosis (ALS) is an adult onset disorder characterized by progressive neuromuscular junction (NMJ) dismantling and degeneration of motor neurons leading to atrophy and paralysis of voluntary muscles responsible for motion and breathing. Except for a minority of patients harbouring genetic mutations, the origin of most ALS cases remains elusive. Peripheral tissues, and particularly skeletal muscle, have lately demonstrated an active contribution to disease pathology attracting a growing interest for these tissues as therapeutic targets in ALS. In this sense, molecular mechanisms essential for cell and tissue homeostasis have been shown to be deregulated in the disease. These include muscle metabolism and mitochondrial activity, RNA processing, tissue-resident stem cell function responsible for muscle regeneration, and proteostasis that regulates muscle mass in adulthood. This review aims to compile scientific evidence that demonstrates the role of skeletal muscle in ALS pathology and serves as reference for development of novel therapeutic strategies targeting this tissue to delay disease onset and progression. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.6/issuetoc.

Effectiveness of non-pharmacological interventions on the management of sarcopenic obesity: A systematic review and meta-analysis

BACKGROUND

Sarcopenic obesity is a combination of both sarcopenia and obesity, which potentiate each other and maximize the negative influences of each, such as physical disability, morbidity, or even mortality.

OBJECTIVES

To describe the criteria used to identify people with sarcopenic obesity and the components of the non-pharmacological interventions used to manage it, and to evaluate the effectiveness of those interventions.

METHODS

Randomized controlled trials (RCTs) in Cochrane Library, Scopus, EMBASE, PscyINFO, CINAHL and PubMed were searched. The risk of bias was examined using the Cochrane risk of bias tool. The template for intervention description and replication (TIDieR) checklist was used to summarize the intervention components. Meta-analyses were conducted using random-effect models to pool estimates of the effects of the non-pharmacological interventions on body composition, BMI, grip strength, and gait speed.

RESULTS

Sixteen papers (12 RCTs) with 863 participants were included. Diverse diagnostic criteria were used in the studies. Four categories of interventions were used: exercise (aerobic exercises, resistance exercises and exercise machines), nutritional interventions (supplements or dietary control), combined intervention and electrical acupuncture. Intervention durations varied from 8 to 28 weeks. Meta-analyses revealed that exercise with or without nutritional interventions had significant effects on grip strength (exercise: mean difference (MD): 1.63 kg, 95% confidence interval (CI): 0.94, 2.32, P< 0.00001; exercise + nutrition: MD: 1.24 kg, 95% CI: 0.48, 1.99, P = 0.001) and gait speed (exercise: MD: 0.13 m/s, 95% CI: 0.08, 0.18, P < 0.00001, I2 = 0%; exercise + nutrition: MD: 0.04 m/s, 95% CI: 0.02, 0.06, P = 0.0002). Exercise had significant effects on reducing the percentage of body fat (PBF) compared to usual care (MD: -1.08%, 95% CI: -1.99, -0.17, P = 0.02), while exercise combined with nutritional interventions showed no superiority over exercise solely on decreasing PBF (P = 0.49). Exercise combined with nutritional interventions had significant effects on increasing appendicular skeletal muscle mass (MD: 0.43 kg, 95% CI: 0.20, 0.66, P = 0.0003). Low-caloric high-protein diets showed no superiority over low-caloric low-protein diets in increasing fat-free mass. Subgroup analyses showed that using different formulas to estimate the skeletal muscle mass index may lead to significant differences in determining the effects of exercise on grip strength.

CONCLUSION

The diagnostic criteria for sarcopenic obesity used in future studies should refer to the latest consensus definition. Exercise tended to be the most effective method of improving grip strength and physical performance (e.g. gait speed). The combined effects of exercise and nutritional interventions on muscle mass and muscle strength require further exploration.

REV-ERBα activates the mTOR signalling pathway and promotes myotubes differentiation

BACKGROUND INFORMATION

Mammalian target of rapamycin (mTOR) complex 1 (mTORC1) is a master regulator of cell and whole-body energy homoeostasis. REV-ERBα is a nuclear receptor that plays an important role in metabolism. While mTORC1 activation is necessary for muscle differentiation, the role of REV-ERBα is less clear.

RESULTS

We studied the effect of REV-ERBα overexpression and silencing as well as mTORC1 activation and inhibition on the differentiation of C2C12 myoblasts to myotubes. mTOR, myogenin and REV-ERBα were induced during differentiation of myoblasts into myotubes. REV-ERBα was found to activate mTORC1 during the differentiation process even in the absence of the differentiation medium. This activation was presumably through the downregulation of the expression of TSC1, an mTORC1 inhibitor.

CONCLUSION

Herein we show that REV-ERBα promotes myoblasts differentiation via the activation of the mTORC1 signalling pathway.

SIGNIFICANCE

REV-ERBα modulation can activate mTORC1 signalling and promote myoblasts differentiation.

Aberrant Protein Turn-Over Associated With Myofibrillar Disorganization in FHL1 Knockout Mice

Mutations in the FHL1 gene, and FHL1 protein deletion, are associated with rare hereditary myopathies and cardiomyopathies. FHL1-null mice develop age-dependent myopathy and increased autophagic activity. However, the molecular pathway involved in contractile function and increased autophagic activity in the FHL1-null mouse has not yet been fully elucidated. In this study, FHL1 protein was knocked out in mice using Transcription Activator-like Effector Nucleases (TALENs) and the IRS1-FOXO1/mTOR signaling pathway was investigated in skeletal muscles and heart. TALEN constructs caused targeted mutations in 30% of newborn mice; these mutations caused a deletion of 1–13 base pairs which blocked synthesis of the full-length FHL1 protein. Furthermore, 2.5-month old FHL1-null male mice were not prone to global muscular fatigue when compared with WT littermates, but histological analysis and ultrastructural analysis by transmission electron microscopy confirmed the presence of myofibrillar disorganization and the accumulation of autophagosome or autolysosome-like structures in FHL1-null mice. Moreover, autophagy and mitophagy were both activated in FHL1 KO mice and the degradation of autophagic lysosomes was impeded. Enhanced autophagic activity in FHL1 KO mice was induced by FOXO1 up-regulation and protein synthesis was increased via mTOR. The cytoskeletal proteins, MYBPC2 and LDB3, were involved in the formation of pathological changes in FHL1 KO mice. Markers of early differentiation (MEF2C and MYOD1) and terminal differentiation (total MYH) were both up-regulated in tibialis anterior (TA) muscles in FHL1 KO mice. The number of type I and type II fibers increased in FHL1-null TA muscles, but the number of type| | b, and type | | d fibers were both reduced in FHL1-null TA muscles. The results obtained from the heart were consistent with those from the skeletal muscle and indicated autophagic activation by FOXO1 and an increase in protein synthesis via mTOR also occurred in the heart tissue of FHL1 knockout mice. In conclusion, aberrant protein turn-over associated with myofibrillar disorganization in FHL1 knockout mice. the up-regulation of FOXO1 was associated with enhanced autophagic activity and pathological changes in the muscle fibers of FHL1 KO mice. These results indicated that autophagy activated by FOXO1 is a promising therapeutic target for hereditary myopathies and cardiomyopathies induced by FHL1.

α-Ketoglutarate prevents skeletal muscle protein degradation and muscle atrophy through PHD3/ADRB2 pathway

Skeletal muscle atrophy due to excessive protein degradation is the main cause for muscle dysfunction, fatigue, and weakening of athletic ability. Endurance exercise is effective to attenuate muscle atrophy, but the underlying mechanism has not been fully investigated. α-Ketoglutarate (AKG) is a key intermediate of tricarboxylic acid cycle, which is generated during endurance exercise. Here, we demonstrated that AKG effectively attenuated corticosterone-induced protein degradation and rescued the muscle atrophy and dysfunction in a Duchenne muscular dystrophy mouse model. Interestingly, AKG also inhibited the expression of proline hydroxylase 3 (PHD3), one of the important oxidoreductases expressed under hypoxic conditions. Subsequently, we identified the β2 adrenergic receptor (ADRB2) as a downstream target for PHD3. We found AKG inhibited PHD3/ADRB2 interaction and therefore increased the stability of ADRB2. In addition, combining pharmacologic and genetic approaches, we showed that AKG rescues skeletal muscle atrophy and protein degradation through a PHD3/ADRB2 mediated mechanism. Taken together, these data reveal a mechanism for inhibitory effects of AKG on muscle atrophy and protein degradation. These findings not only provide a molecular basis for the potential use of exercise-generated metabolite AKG in muscle atrophy treatment, but also identify PHD3 as a potential target for the development of therapies for muscle wasting.-Cai, X., Yuan, Y., Liao, Z., Xing, K., Zhu, C., Xu, Y., Yu, L., Wang, L., Wang, S., Zhu, X., Gao, P., Zhang, Y., Jiang, Q., Xu, P., Shu, G. α-Ketoglutarate prevents skeletal muscle protein degradation and muscle atrophy through PHD3/ADRB2 pathway.

Hyperammonemia and proteostasis in cirrhosis

PURPOSE OF REVIEW

Skeletal muscle loss or sarcopenia is a frequent complication of cirrhosis that adversely affects clinical outcomes. As skeletal muscle is the largest store of proteins in the body, proteostasis or protein homeostasis is required for maintenance of muscle mass. This review will focus on disordered skeletal muscle proteostasis in liver disease.

RECENT FINDINGS

Increased skeletal muscle uptake of ammonia initiates responses that result in disordered proteostasis including impaired protein synthesis and increased autophagy. The cellular response to the stress of hyperammonemia (hyperammonemic stress response, HASR) involves the coordinated action of diverse signaling pathways targeting the molecular mechanisms of regulation of protein synthesis. Transcriptional upregulation of myostatin, a TGFβ superfamily member, results in impaired mTORC1 signaling. Phosphorylation of the eukaryotic translation initiation factor 2α (eIF2α) also relates to decreased global protein synthesis rates and mTORC1 signaling. Ammonia also causes mitochondrial and bioenergetic dysfunction because of cataplerosis of α-ketoglutarate. Lowering ammonia, targeting components of HASR and regulating cellular amino acid levels can potentially restore proteostasis.

SUMMARY

Signaling via myostatin and eIF2α phosphorylation causes decreases in protein synthesis and mTORC1 activity with a parallel mitochondrial dysfunction and increased autophagy contributing to proteostasis perturbations during skeletal muscle hyperammonemia of liver disease.

Role of nerve-muscle interactions and reactive oxygen species in regulation of muscle proteostasis with ageing

Skeletal muscle ageing is characterised by atrophy, a deficit in specific force generation, increased susceptibility to injury, and incomplete recovery after severe damage. The hypothesis that increased generation of reactive oxygen species (ROS) in vivo plays a key role in the ageing process has been extensively studied, but remains controversial. Skeletal muscle generates ROS at rest and during exercise. ROS can cause oxidative damage particularly to proteins. Indeed, products of oxidative damage accumulate in skeletal muscle during ageing and the ability of muscle cells to respond to increased ROS becomes defective. The aim of this review is to examine the evidence that ROS manipulation in peripheral nerves and/or muscle modifies mechanisms of proteostasis in skeletal muscle and plays a key role in initiating sarcopenia.

Reduced skeletal muscle fiber size following caloric restriction is associated with calpain-mediated proteolysis and attenuation of IGF-1 signaling

Caloric restriction decreases skeletal muscle mass in mammals, principally due to a reduction in fiber size. The effect of suboptimal nutrient intake on skeletal muscle metabolic properties in neonatal calves was examined. The longissimus muscle (LM) was collected after a control (CON) or caloric restricted (CR) diet was cosnumed for 8 wk and muscle fiber size, gene expression, and metabolic signal transduction activity were measured. Results revealed that CR animals had smaller (P < 0.05) LM fiber cross-sectional area than CON, as expected. Western blot analysis detected equivalent amounts of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α) but reduced (P < 0.05) amounts of the splice-variant, PGC1α-4 in CR LM. Expression of IGF-1, a PGC1α-4 target gene, was 40% less (P < 0.05) in CR than CON. Downstream mediators of autocrine IGF-1 signaling also are attenuated in CR by comparison with CON. The amount of phosphorylated AKT1 was less (P < 0.05) in CR than CON. The ratio of p4EBP1^T37/46 to total 4EBP1, a downstream mediator of AKT1, did not differ between CON and CR. By contrast, protein lysates from CR LM contained less (P < 0.05) total glycogen synthase kinase-3β (GSK3β) and phosphorylated GSK3β than CON LM, suggesting blunted protein synthesis. Smaller CR LM fiber size associates with increased (P < 0.05) calpain 1 (CAPN1) activity coupled with lower (P < 0.05) expression of calpastatin, the endogenous inhibitor of CAPN1. Atrogin-1 and MuRF expression and autophagy components were unaffected by CR. Thus CR suppresses the hypertrophic PGC1α-4/IGF-1/AKT1 pathway while promoting activation of the calpain system.