Molecular regulation of skeletal muscle mass and the contribution of nitric oxide: A review

Exercise Improves Respiratory Function, Body Fluid and Nitric Oxide in Hemodialysis Patients

Emerging evidence suggests that resistance training (RT) can mitigate respiratory muscle weakness in hemodialysis (HD) patients. However, the underlying mechanisms responsible for these beneficial effects remain unclear. The purpose of this study was to assess the impact of periodized RT on respiratory muscle strength and its relationship with handgrip strength (HGS), fat-free mass (FFM), nitric oxide (NO), and interdialytic weight gain (IWG) in HD patients. Thirty-three patients were randomly assigned to two groups: control (CTL; n=18) and RT (n=15). The RT group did not perform any additional exercise training specific to the respiratory tract. Maximal inspiratory (MIP) and expiratory (MEP) pressures, peak expiratory flow (PEF), HGS, FFM, NO, and IWG were measured before and after the intervention period. Participants in the RT group engaged in a 24-week RT program, three times per week. RT resulted in significant improvements in MIP, MEP, PEF, as well as enhancements in HGS, FFM, NO, and IWG (p<0.05). Notably, inverse correlations were observed between MIP (r=-0.37, p=0.03) and PEF (r=-0.4, p=0.02) with IWG. Thus, the amelioration of HGS and FFM coincided with a reduction in respiratory muscle weakness among HD patients. Decreased IWG and increased circulating NO are plausible mechanisms contributing to these improvements.

Bezafibrate attenuates immobilization-induced muscle atrophy in mice

Muscle atrophy due to fragility fractures or frailty worsens not only activity of daily living and healthy life expectancy, but decreases life expectancy. Although several therapeutic agents for muscle atrophy have been investigated, none is yet in clinical use. Here we report that bezafibrate, a drug used to treat hyperlipidemia, can reduce immobilization-induced muscle atrophy in mice. Specifically, we used a drug repositioning approach to screen 144 drugs already utilized clinically for their ability to inhibit serum starvation-induced elevation of Atrogin-1, a factor related to muscle atrophy, in myotubes in vitro. Two candidates were selected, and here we demonstrate that one of them, bezafibrate, significantly reduced muscle atrophy in an in vivo model of muscle atrophy induced by leg immobilization. In gastrocnemius muscle, immobilization reduced muscle weight by an average of ~ 17.2%, and bezafibrate treatment prevented ~ 40.5% of that atrophy. In vitro, bezafibrate significantly inhibited expression of the inflammatory cytokine Tnfa in lipopolysaccharide-stimulated RAW264.7 cells, a murine macrophage line. Finally, we show that expression of Tnfa and IL-1b is induced in gastrocnemius muscle in the leg immobilization model, an activity significantly antagonized by bezafibrate administration in vivo. We conclude that bezafibrate could serve as a therapeutic agent for immobilization-induced muscle atrophy.

Effects of 12-Week Combined Strength and Endurance Circuit Training Program on Insulin Sensitivity and Retinol-Binding Protein 4 in Women with Insulin-Resistance and Overweight or Mild Obesity: A Randomized Controlled Trial

Background

Circuit training is an exercise mode, that may include both endurance and resistance components. There are premises that a combination of these two modalities brings additional benefits, particularly in improving insulin sensitivity. The retinol-binding protein 4 (RBP4) may inhibit signaling from insulin metabolic pathways in skeletal muscles, thus developing insulin resistance. This study aimed to evaluate whether moderate intensity circuit training combining strength and endurance exercise induces changes in tissue insulin sensitivity, carbohydrate and lipid metabolism, and serum RBP4 levels in insulin-resistant women.

Methods

In this clinical controlled trial women diagnosed with insulin-resistance were randomly divided into two groups. The training group (T) performed circuit training combining strength (50%-80%1RM) and endurance (50%-75%HRR) exercise on five weight and two cardio machines, for 33 minutes, three times per week, for 3 months. Women from the control non-training group (NT) did not change their previous physical activity. At the beginning of the study and after the intervention period, a one-repetition maximum, body mass, and composition, resting heart rate (HR), blood pressure, glucose, insulin, blood lipids, thyroid-stimulating hormone (TSH), insulin-like growth factor-1 (IGF-1), RBP4, and insulin resistance (HOMA-IR) were measured. The results of 27 patients were analyzed using a two-way repeated measures ANOVA.

Results

Significant differences in the pattern of change over time between the groups for resting HR (p < 0.010) and total lean mass (p < 0.039) were found. No differences in HOMA-IR, and RBP4 were observed post-study compared to pre-study in the T group. A significant correlation between RBP4 and TSH concentration was found.

Conclusion

Twelve-week circuit training combining strength and endurance exercise has minor effects on HOMA-IR, glucose and lipid metabolism, IGF-1, TSH, and RBP4. Although moderate-intensity circuit training is considered safe, its effectiveness in patients with overweight and mild obesity may be insufficient to reduce insulin resistance.

Trial Registration

ClinicalTrials.gov: NCT04528693, registered August 23, 2020.

Effect of dietary arginine supplementation on protein synthesis, meat quality and flavor in growing lambs

This study aimed to assess the effect of dietary arginine supplementation on protein synthesis, meat quality and flavor in lambs. Eighteen Dorper (♂) × Small Tailed Han sheep (♀) crossed ewe lambs of similar weight (27.29 ± 2.02 kg; aged 3 months) were assigned to two groups, the control group was fed the basal diet (Con group), and the arginine group (Arg group) was supplemented with 1% l-arginine based on the Con group for 90 d. The results suggested that dietary arginine significantly increased final body weight, loin eye muscle area, muscle fiber diameter, cross-sectional area (P < 0.050), and decreased shear force value and cooking loss (P < 0.050), as well as altered the composition and contents of volatile flavor compounds in lambs. Importantly, the total protein (TP) content, alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (AKP) activities in serum, branched-chain aminotransferase (BCAT), AST, ALT activities and neuronal nitric oxide synthase (nNOS) gene expression and content were elevated (P < 0.050), while content of urea nitrogen (BUN) in serum and 3-methylhistidine (3-MH) were decreased in arginine fed lambs (P < 0.050). In addition, arginine triggered muscle protein synthesis through protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway, while minimized protein degradation by regulating gene expression of myogenin (MyoG), myostatin (MSTN), muscle atrophy F-box (MAFbx) and forkhead box O3 family (FoxO3) (P < 0.050). Taken together, this study suggested that arginine can be used to improve protein deposition and meat quality in lamb production.

Endurance training changes the expression of miR-1 and miR-133 and predicted genes in slow and fast twitch muscles

PURPOSE OF THE RESEARCH

Endurance training can modify signaling and gene expression pathways that play a pivotal role in determining the phenotype of the fibers. The present study aimed to investigate the effects of endurance training on the expression of some myomiRs and related genes in slow and fast twitch muscles.

METHODS

Twenty healthy male adult Wistar rats (281 ± 14 g) were randomized to either control (n = 10) or treated (n = 10). The treated group performed an endurance program for eight weeks (running on a treadmill for eight weeks, 50 min, 23 m/min). After the end of the training protocol, the slow (soleus) and fast (EDL) twitch muscles were removed to assess the miR-1, miR-133 expression, and hdac4, mef2c genes, and protein by real-time PCR and western blot, respectively.

RESULTS

The soleus muscle miR-1 expression and mef2c gene in the treated group were significantly lower compared control (p = 0.0001). In contrast, miR-133 and hdac4 gene expression of the soleus muscle of the treated group increased significantly (p = 0001), and the EDL miR-133 and mef2c expression of the treated group increased in the compared control group (p = 0.0001). The EDL MEF2c protein expression in the treated group significantly decreased compared to the control group, although the expression of EDL HDAC4 protein significantly increased (p = 0.0001).

CONCLUSIONS

Endurance training changes the expression of the miR-1, miR-133, and their predicted genes in slow and fast twitch muscles. Also, the rate of HDAC4 and MEF2c protein synthesis, which are upstream and downstream of these myomiRs, was affected by endurance training.

Chronic Stress Induces Type 2b Skeletal Muscle Atrophy via the Inhibition of mTORC1 Signaling in Mice

Chronic stress induces psychological and physiological changes that may have negative sequelae for health and well-being. In this study, the skeletal muscles of male C57BL/6 mice subjected to repetitive water-immersion restraint stress to model chronic stress were examined. In chronically stressed mice, serum corticosterone levels significantly increased, whereas thymus volume and bone mineral density decreased. Further, body weight, skeletal muscle mass, and grip strength were significantly decreased. Histochemical analysis of the soleus muscles revealed a significant decrease in the cross-sectional area of type 2b muscle fibers. Although type 2a fibers also tended to decrease, chronic stress had no impact on type 1 muscle fibers. Chronic stress increased the expression of REDD1, FoxO1, FoxO3, KLF15, Atrogin1, and FKBP5, but did not affect the expression of myostatin or myogenin. In contrast, chronic stress resulted in a decrease in p-S6 and p-4E-BP1 levels in the soleus muscle. Taken together, these results indicate that chronic stress promotes muscle atrophy by inhibiting mammalian targets of rapamycin complex 1 activity due to the upregulation of its inhibitor, REDD1.

Effects of hydroxyurea on skeletal muscle energetics and force production in a sickle cell disease murine model

Hydroxyurea (HU) is commonly used as a treatment for patients with sickle cell disease (SCD) to enhance fetal hemoglobin production. This increased production is expected to reduce anemia (which depresses oxygen transport) and abnormal Hb content alleviating clinical symptoms such as vaso-occlusive crisis and acute chest syndrome. The effects of HU on skeletal muscle bioenergetics in vivo are still unknown. Due to the beneficial effects of HU upon oxygen delivery, improved skeletal muscle energetics and function in response to a HU treatment have been hypothesized. Muscle energetics and function were analyzed during a standardized rest-exercise-recovery protocol, using ³¹P-magnetic resonance spectroscopy in Townes SCD mice. Measurements were performed in three groups of mice: one group of 2-mo-old mice (SCD_2m, n = 8), another one of 4-mo-old mice (SCD_4m, n = 8), and a last group of 4-mo-old mice that have been treated from 2 mo of age with HU at 50 mg/kg/day (SCD_4m-HU, n = 8). As compared with SCD_2m mice, SCD_4m mice were heavier and displayed a lower acidosis. As lower specific forces were developed by SCD_4m compared with SCD_2m, greater force-normalized phosphocreatine consumption and oxidative and nonoxidative costs of contraction were also reported. HU-treated mice (SCD_4m-HU) displayed a significantly higher specific force production as compared with untreated mice (SCD_4m), whereas muscle energetics was unchanged. Overall, our results support a beneficial effect of HU on muscle function.NEW & NOTEWORTHY Our results highlighted that force production decreases between 2 and 4 mo of age in SCD mice thereby indicating a decrease of muscle function during this period. Of interest, HU treatment seemed to blunt the observed age effect given that SCD_4m-HU mice displayed a higher specific force production as compared with SCD_4m mice. In that respect, HU treatment would help to maintain a higher capacity of force production during aging in SCD.

L-Arginine/nitric oxide regulates skeletal muscle development via muscle fibre-specific nitric oxide/mTOR pathway in chickens

L-Arginine (L-Arg), the precursor of nitric oxide (NO), plays an important role in muscle function. Fast-twitch glycolytic fibres are more susceptible to age-related atrophy than slow-twitch oxidative fibres. The effect of L-Arg/NO on protein metabolism of fast- and slow-twitch muscle fibres was evaluated in chickens. In Exp. 1, 48 chicks at 1 day old were divided into 4 groups of 12 birds and subjected to 4 treatments: basal diet without supplementation or supplemented with 1% L-Arg, and water supplemented with or without L-nitro-arginine methyl ester (L-NAME, 18.5 mM). In Exp. 2, 48 chicks were divided into 4 groups of 12 birds fed with the basal diet and subjected to the following treatments: tap water (control), tap water supplemented with L-NAME (18.5 mM), or molsidomine (MS, 0.1 mM), or 18.5 mM L-NAME + 0.1 mM MS (NAMS). The regulatory effect of L-Arg/NO was further investigated in vitro with myoblasts obtained from chicken embryo pectoralis major (PM) and biceps femoris (BF). In vivo, dietary L-Arg supplementation increased breast (+14.94%, P < 0.05) and thigh muscle mass (+23.40%, P < 0.05); whereas, MS treatment had no detectable influence. However, L-NAME treatment blocked the beneficial influence of L-Arg on muscle development. L-Arg decreased (P < 0.05) protein synthesis rate, phosphorylated mTOR and ribosomal protein S6 kinase beta-1 (p70S6K) levels in breast muscle, which was recovered by L-NAME treatment. In vitro, L-Arg or sodium nitroprusside (SNP) reduced protein synthesis rate, suppressed phosphorylated mTOR/p70S6K and decreased atrogin-1 and muscle RING finger 1 (MuRF1) in myoblasts from PM muscle (P < 0.05). L-NAME abolished the inhibitory effect of L-Arg on protein synthesis and the mTOR/p70S6K pathway. However, myoblasts from BF muscle showed the weak influence. Moreover, blocking the mTOR/p70S6K pathway with rapamycin suppressed protein synthesis of the 2 types of myoblasts; whereas, the protein expression of atrogin-1 and MuRF1 levels were restricted only in myoblasts from PM muscle. In conclusion, L-Arg/NO/mTOR/p70S6K pathway enhances protein accumulation and muscle development in fast-twitch glycolytic muscle in chickens. L-Arg/NO regulates protein turnover in a muscle fibre specific way, which highlights the potential clinical application in fast-twitch glycolytic muscle fibres.

Endothelial cells are an important source of BDNF in rat skeletal muscle

BDNF (brain-derived neurotrophic factor) is present in skeletal muscle, controlling muscular metabolism, strength and regeneration processes. However, there is no consensus on BDNF cellular source. Furthermore, while endothelial tissue expresses BDNF in large amount, whether endothelial cells inside muscle expressed BDNF has never been explored. The aim of the present study was to provide a comprehensive analysis of BDNF localization in rat skeletal muscle. Cellular localization of BDNF and activated Tropomyosin-related kinase B (TrkB) receptors was studied by immunohistochemical analysis on soleus (SOL) and gastrocnemius (GAS). BDNF and activated TrkB levels were also measured in muscle homogenates using Western blot analysis and/or Elisa tests. The results revealed BDNF immunostaining in all cell types examined with a prominent staining in endothelial cells and a stronger staining in type II than type I muscular fibers. Endothelial cells but not other cells displayed easily detectable activated TrkB receptor expression. Levels of BDNF and activated TrkB receptors were higher in SOL than GAS. In conclusion, endothelial cells are an important and still unexplored source of BDNF present in skeletal muscle. Endothelial BDNF expression likely explains why oxidative muscle exhibits higher BDNF levels than glycolytic muscle despite higher the BDNF expression by type II fibers.

The expanding roles of neuronal nitric oxide synthase (NOS1)

The nitric oxide synthases (NOS; EC 1.14.13.39) use L-arginine as a substrate to produce nitric oxide (NO) as a by-product in the tissue microenvironment. NOS1 represents the predominant NO-producing enzyme highly enriched in the brain and known to mediate multiple functions, ranging from learning and memory development to maintaining synaptic plasticity and neuronal development, Alzheimer's disease (AD), psychiatric disorders and behavioral deficits. However, accumulating evidence indicate both canonical and non-canonical roles of NOS1-derived NO in several other tissues and chronic diseases. A better understanding of NOS1-derived NO signaling, and identification and characterization of NO-metabolites in non-neuronal tissues could become useful in diagnosis and prognosis of diseases associated with NOS1 expression. Continued investigation on the roles of NOS1, therefore, will synthesize new knowledge and aid in the discovery of small molecules which could be used to titrate the activities of NOS1-derived NO signaling and NO-metabolites. Here, we address the significance of NOS1 and its byproduct NO in modifying pathophysiological events, which could be beneficial in understanding both the disease mechanisms and therapeutics.

Identification of the circRNA-miRNA-mRNA Regulatory Network in Bladder Cancer by Bioinformatics Analysis

In recent years, increasing evidence shows that circular RNA (circRNA) disorder is closely related to tumorigenesis and cancer progression. However, the regulatory functions of most circRNAs in bladder cancer (BCa) remain unclear. This study was aimed at exploring the molecular regulatory mechanism of circRNAs in BCa. We obtained four datasets of circRNA, microRNA (miRNA), and messenger (mRNA) expression profiles from the Gene Expression Omnibus and The Cancer Genome Atlas microarray databases and identified 434, 367, and 4799/4841 differentially expressed circRNAs, miRNAs, and mRNAs, respectively. With these differentially expressed RNAs, we established a circRNA-miRNA-mRNA targeted interaction network. A total of 18, 24, and 51 central circRNAs, miRNAs, and mRNAs were identified, respectively. Among them, the top 10 mRNAs that had high connectivity with other circRNAs and miRNAs were regarded as hub genes. We detected the expression levels of these 10 mRNAs in 16 pairs of BCa tissues and adjacent normal tissues through quantitative real-time polymerase chain reaction. The differentially expressed mRNAs and central mRNAs were enriched in the processes and pathways that are associated with the growth, differentiation, proliferation, and apoptosis of tumor cells. The outstanding genes (CDCA4, GATA6, LATS2, RHOB, ZBTB4, and ZFPM2) also interacted with numerous drugs, indicating their potency as biomarkers and drug targets. The findings of this study provide a deep understanding of the circRNA-related competitive endogenous RNA regulatory mechanism in BCa pathogenesis.

Evaluating the role of nitric oxide in myogenesis in vitro

Skeletal muscle injury activates satellite cells to proliferate as myoblasts and migrate, differentiate and fuse with existing fibres at the site of injury. Nitric oxide (NO), a free radical produced by NO synthase, is elevated and supports healing after in vivo injury. NOS-independent elevation of NO levels in vitro is possible via donors such as molsidomine (SIN-1). We hypothesized that alterations in NO levels may directly influence myogenic processes critical for skeletal muscle wound healing. This study aimed to clarify the role of NO in myoblast proliferation, migration and differentiation. Baseline NO levels were established in vitro, whereafter NO levels were manipulated during myogenesis using l-NAME (NOS inhibitor) or SIN-1. Baseline NO levels generated by myoblasts in proliferation media did not change 1 h after stimulation. Addition of a pro-proliferative dose of HGF slightly elevated NO levels 1 h post-stimulation, whereas cell numbers assessed 24 h later increased significantly; l-NAME reduced the HGF-driven increase in NO and proliferation, reducing wound closure over 16 h. In differentiation media, NO levels increased significantly within 24 h, returning to baseline over several days. Regular addition of l-NAME to differentiating cells significantly reduced NO levels and fusion. SIN-1 increased NO levels in a dose-dependent manner, reaching maximal levels 16 h post-treatment. SIN-1, added at 0, 2 and 4 days, significantly increased myofiber area (26 ± 1.8% vs 18.6 ± 3.4% in control at 5 day, p < 0.0001), without affecting proliferation or migration. In conclusion, this study demonstrates that, during skeletal muscle regeneration, increased NO specifically stimulates myoblast differentiation.

Genetically Encoded Biosensors to Monitor Intracellular Reactive Oxygen and Nitrogen Species and Glutathione Redox Potential in Skeletal Muscle Cells

Reactive oxygen and nitrogen species (RONS) play an important role in the pathophysiology of skeletal muscle and are involved in the regulation of intracellular signaling pathways, which drive metabolism, regeneration, and adaptation in skeletal muscle. However, the molecular mechanisms underlying these processes are unknown or partially uncovered. We implemented a combination of methodological approaches that are funded for the use of genetically encoded biosensors associated with quantitative fluorescence microscopy imaging to study redox biology in skeletal muscle. Therefore, it was possible to detect and monitor RONS and glutathione redox potential with high specificity and spatio-temporal resolution in two models, isolated skeletal muscle fibers and C2C12 myoblasts/myotubes. Biosensors HyPer3 and roGFP2-Orp1 were examined for the detection of cytosolic hydrogen peroxide; HyPer-mito and HyPer-nuc for the detection of mitochondrial and nuclear hydrogen peroxide; Mito-Grx1-roGFP2 and cyto-Grx1-roGFP2 were used for registration of the glutathione redox potential in mitochondria and cytosol. G-geNOp was proven to detect cytosolic nitric oxide. The fluorescence emitted by the biosensors is affected by pH, and this might have masked the results; therefore, environmental CO₂ must be controlled to avoid pH fluctuations. In conclusion, genetically encoded biosensors and quantitative fluorescence microscopy provide a robust methodology to investigate the pathophysiological processes associated with the redox biology of skeletal muscle.

Febuxostat reduces muscle wasting in tumor-bearing mice with LM8 osteosarcoma cells via inhibition of reactive oxygen species generation

Cachexic condition due to malignant tumors has been a challenging problem. The aim of this study is to analyze effects of febuxostat on both in vitro and in vivo models of the wasting of skeletal muscles, due to LM8 osteosarcoma cells. C2C12 myotubes were incubated in the conditioned medium of LM8. Febuxostat was added at a concentration of 3 µM and 30 µM, and ROS, diameter of myotubes, and expression of atrogin-1 were analyzed. Furthermore, an in vivo study was performed by subcutaneous injection of LM8 on C3H mice. Febuxostat was administered in the drinking water at 5 µg/ml, and 25 µg/ml. In addition, tumor-bearing mice without febuxostat (group TB) and control mice (group C) were established. At 4 weeks, body weight, wet weights of the gastrocnemius muscles, XO activity, 8-OHdG, and expression of TNF-α and IL-6 were evaluated. ROS generation, atrophy of myotubes, and upregulation of atrogin-1 were clearly observed in C2C12 myotubes following incubation in the conditioned medium. These pathological conditions were significantly inhibited by febuxostat administration. Furthermore, mice in group TB showed significant loss of body weight and muscle weight in which XO activity, 8-OHdG, and expression of IL-6 were significantly increased compared to those in group C. Febuxostat administration not only significantly improved the body weight and muscleweight, but also reduced markers of oxidative stress and pro-inflammatory cytokines. Febuxostat did not show anti-tumor effects. Febuxostat, which is clinically used for treatment of hyperuricemia, is effective against the wasting of the skeletal muscles induced by LM8 osteosarcoma cells.

α-Hydroxyisocaproic Acid Decreases Protein Synthesis but Attenuates TNFα/IFNγ Co-Exposure-Induced Protein Degradation and Myotube Atrophy via Suppression of iNOS and IL-6 in Murine C2C12 Myotube

There is ongoing debate as to whether or not α-hydroxyisocaproic acid (HICA) positively regulates skeletal muscle protein synthesis resulting in the gain or maintenance of skeletal muscle. We investigated the effects of HICA on mouse C2C12 myotubes under normal conditions and during cachexia induced by co-exposure to TNFα and IFNγ. The phosphorylation of AMPK or ERK1/2 was significantly altered 30 min after HICA treatment under normal conditions. The basal protein synthesis rates measured by a deuterium-labeling method were significantly lowered by the HICA treatment under normal and cachexic conditions. Conversely, myotube atrophy induced by TNFα/IFNγ co-exposure was significantly improved by the HICA pretreatment, and this improvement was accompanied by the inhibition of iNOS expression and IL-6 production. Moreover, HICA also suppressed the TNFα/IFNγ co-exposure-induced secretion of 3-methylhistidine. These results demonstrated that HICA decreases basal protein synthesis under normal or cachexic conditions; however, HICA might attenuate skeletal muscle atrophy via maintaining a low level of protein degradation under cachexic conditions.

Large-scale sequencing of flatfish genomes provides insights into the polyphyletic origin of their specialized body plan

The evolutionary and genetic origins of the specialized body plan of flatfish are largely unclear. We analyzed the genomes of 11 flatfish species representing 9 of the 14 Pleuronectiforme families and conclude that Pleuronectoidei and Psettodoidei do not form a monophyletic group, suggesting independent origins from different percoid ancestors. Genomic and transcriptomic data indicate that genes related to WNT and retinoic acid pathways, hampered musculature and reduced lipids might have functioned in the evolution of the specialized body plan of Pleuronectoidei. Evolution of Psettodoidei involved similar but not identical genes. Our work provides valuable resources and insights for understanding the genetic origins of the unusual body plan of flatfishes.

Effects of dynamic and isometric resistance training protocols on metabolic profile in hemodialysis patients: a randomized controlled trial

The aim of this study was to compare the effect of dynamic (DRT) and isometric (IRT) resistance training on glycemic homeostasis, lipid profile, and nitric oxide (NO) in hemodialysis (HD) patients. Patients were randomly distributed into 3 groups: control (n = 65), DRT (n = 65), and IRT (n = 67). Patients assessed before and after the intervention period were tested for fasting blood glucose, glycated hemoglobin, oral glucose tolerance test, insulin resistance, lipid profile, leptin, insulin, adiponectin, C-reactive protein, and NO . Patients underwent to strength and body composition assessments. Subjects allocated in both DRT and IRT groups took part in a 24-week resistance training program, 3 times per week. Each training session was approximately 1 hour before dialysis and consisted of 3 sets of 8-12 repetitions at low intensity. Total workload was higher in the DRT as compared with the IRT. This heightened workload related to better glycemic homeostasis in HD patients as measured by regulation of insulin, adiponectin, and leptin, while improveing triglycerides, free-fat mass, and muscle strength. Additionally, NO levels were increased in the DRT group. NO was significantly correlated with glucose intolerance (r = -0.42, p = 0.0155) and workload (r = 0.46, p = 0.0022). The IRT group only improved strength (p < 0.05). Twenty-four weeks of DRT improved glycemic homeostasis, lipid profile, and NO in HD patients. Although IRT seems to play an important role in increasing strength, DRT might be a better choice to promote metabolic adjustments in HD patients. Clinical trial: http://www.ensaiosclinicos.gov.br/rg/RBR-3gpg5w. Novelty: DRT might be a better choice for metabolic improvements in patients with chronic kidney disease (CKD). Exercise-training might treat metabolic imbalance in CKD patients.

Master Regulators of Muscle Atrophy: Role of Costamere Components

The loss of muscle mass and force characterizes muscle atrophy in several different conditions, which share the expression of atrogenes and the activation of their transcriptional regulators. However, attempts to antagonize muscle atrophy development in different experimental contexts by targeting contributors to the atrogene pathway showed partial effects in most cases. Other master regulators might independently contribute to muscle atrophy, as suggested by our recent evidence about the co-requirement of the muscle-specific chaperone protein melusin to inhibit unloading muscle atrophy development. Furthermore, melusin and other muscle mass regulators, such as nNOS, belong to costameres, the macromolecular complexes that connect sarcolemma to myofibrils and to the extracellular matrix, in correspondence with specific sarcomeric sites. Costameres sense a mechanical load and transduce it both as lateral force and biochemical signals. Recent evidence further broadens this classic view, by revealing the crucial participation of costameres in a sarcolemmal “signaling hub” integrating mechanical and humoral stimuli, where mechanical signals are coupled with insulin and/or insulin-like growth factor stimulation to regulate muscle mass. Therefore, this review aims to enucleate available evidence concerning the early involvement of costamere components and additional putative master regulators in the development of major types of muscle atrophy.

Loss of melusin is a novel, neuronal NO synthase/FoxO3-independent master switch of unloading-induced muscle atrophy

BACKGROUND

Unloading/disuse induces skeletal muscle atrophy in bedridden patients and aged people, who cannot prevent it by means of exercise. Because interventions against known atrophy initiators, such as oxidative stress and neuronal NO synthase (nNOS) redistribution, are only partially effective, we investigated the involvement of melusin, a muscle-specific integrin-associated protein and a recognized regulator of protein kinases and mechanotransduction in cardiomyocytes.

METHODS

Muscle atrophy was induced in the rat soleus by tail suspension and in the human vastus lateralis by bed rest. Melusin expression was investigated at the protein and transcript level and after treatment of tail-suspended rats with atrophy initiator inhibitors. Myofiber size, sarcolemmal nNOS activity, FoxO3 myonuclear localization, and myofiber carbonylation of the unloaded rat soleus were studied after in vivo melusin replacement by cDNA electroporation, and muscle force, myofiber size, and atrogene expression after adeno-associated virus infection. In vivo interference of exogenous melusin with dominant-negative kinases and other atrophy attenuators (Grp94 cDNA; 7-nitroindazole) on size of unloaded rat myofibers was also explored.

RESULTS

Unloading/disuse reduced muscle melusin protein levels to about 50%, already after 6 h in the tail-suspended rat (P < 0.001), and to about 35% after 8 day bed rest in humans (P < 0.05). In the unloaded rat, melusin loss occurred despite of the maintenance of β1D integrin levels and was not abolished by treatments inhibiting mitochondrial oxidative stress, or nNOS activity and redistribution. Expression of exogenous melusin by cDNA transfection attenuated atrophy of 7 day unloaded rat myofibers (-31%), compared with controls (-48%, P = 0.001), without hampering the decrease in sarcolemmal nNOS activity and the increase in myonuclear FoxO3 and carbonylated myofibers. Infection with melusin-expressing adeno-associated virus ameliorated contractile properties of 7 day unloaded muscles (P ≤ 0.05) and relieved myofiber atrophy (-33%) by reducing Atrogin-1 and MurF-1 transcripts (P ≤ 0.002), despite of a two-fold increase in FoxO3 protein levels (P = 0.03). Atrophy attenuation by exogenous melusin did not result from rescue of Akt, ERK, or focal adhesion kinase activity, because it persisted after co-transfection with dominant-negative kinase forms (P < 0.01). Conversely, melusin cDNA transfection, combined with 7-nitroindazole treatment or with cDNA transfection of the nNOS-interacting chaperone Grp94, abolished 7 day unloaded myofiber atrophy.

CONCLUSIONS

Disuse/unloading-induced loss of melusin is an early event in muscle atrophy which occurs independently from mitochondrial oxidative stress, nNOS redistribution, and FoxO3 activation. Only preservation of melusin levels and sarcolemmal nNOS localization fully prevented muscle mass loss, demonstrating that both of them act as independent, but complementary, master switches of muscle disuse atrophy.

Response of Resistance Exercise-Induced Muscle Protein Synthesis and Skeletal Muscle Hypertrophy Are Not Enhanced After Disuse Muscle Atrophy in Rat

Skeletal muscle disuse rapidly decreases muscle mass. Resistance training (RT) is believed as the most effective way to gain muscle mass via an increase in mTORC1 activity and muscle protein synthesis (MPS). However, it remains unclear whether muscle atrophy by disuse alters the mTORC1 activation and MPS response to an acute resistance exercise (RE) and chronic RT-mediated skeletal muscle hypertrophy. This study investigated the influence of disuse muscle atrophy on the response of mTORC1 activation and MPS to an acute RE. We also evaluated whether disuse muscle atrophy affects the response of RT-induced muscle mass gain. Thirty male Sprague-Dawley rats were randomly divided into control (CON) or hindlimb suspension (HS) groups. A 14-day HS via the tail was used as the model for gastrocnemius muscle disuse in the HS group. Unilateral lower limb muscle contraction using by percutaneous electrical stimulation was used to mimic the stimuli of RE. Ten bouts of RE were performed in 3-week as chronic RT. Our results showed that MPS and mTORC1 activity was unchanged after HS at basal state. However, the ribosomal RNA (rRNA) level was reduced in HS rats compared to that in CON rats at basal state. MPS and rRNA increased in both HS and CON rats in response to acute RE to the same extent. However, the level of mTORC1 activation in response to an acute RE was significantly higher in HS than that in the CON group at 12 h after exercise, even though no difference was observed at 3 h after exercise. The 10-bout RT significantly increased gastrocnemius muscle mass in both CON and HS rats. The response of muscle hypertrophy did not differ between the groups. Therefore, MPS in response to acute RE and muscle hypertrophy in response to chronic RT were unaltered after disuse muscle atrophy.

Effects of dietary sea buckthorn pomace supplementation on skeletal muscle mass and meat quality in lambs

The aim of the present trial was to evaluate the effects of dietary sea buckthorn pomace (SBP) supplementation on muscle mass, meat nutritional value and quality of lambs. The results showed that dietary 16% SBP supplementation increased muscle mass and altered muscle fiber size distribution. Both nutritional compositions, including crude protein, moisture and ash, and lamb meat quality, including pH, color and cooking loss were not affected by SBP supplementation. Importantly, crude fat content was elevated, and shear force was decreased in Longissimus thoracis (LT) when lambs were fed the SBP containing diet. Moreover, the total antioxidative capacity in LT and the HDL content in serum were elevated in SBP feed lambs. Dietary SBP supplementation increased the Akt/mTOR signaling activity, and downregulated myostatin expression. Taken together, these data suggested that SBP could be used as a feed ingredient for lamb meat production by increasing muscle mass and improving tenderness, water holding capacity and antioxidative capacity of resulting meat.