Skeletal muscle hypertrophy and atrophy signaling pathways

ER stress in skeletal muscle remodeling and myopathies

Skeletal muscle is a highly plastic tissue in the human body that undergoes extensive adaptation in response to environmental cues, such as physical activity, metabolic perturbation, and disease conditions. The endoplasmic reticulum (ER) plays a pivotal role in protein folding and calcium homeostasis in many mammalian cell types, including skeletal muscle. However, overload of misfolded or unfolded proteins in the ER lumen cause stress, which results in the activation of a signaling network called the unfolded protein response (UPR). The UPR is initiated by three ER transmembrane sensors: protein kinase R-like endoplasmic reticulum kinase, inositol-requiring protein 1α, and activating transcription factor 6. The UPR restores ER homeostasis through modulating the rate of protein synthesis and augmenting the gene expression of many ER chaperones and regulatory proteins. However, chronic heightened ER stress can also lead to many pathological consequences including cell death. Accumulating evidence suggests that ER stress-induced UPR pathways play pivotal roles in the regulation of skeletal muscle mass and metabolic function in multiple conditions. They have also been found to be activated in skeletal muscle under catabolic states, degenerative muscle disorders, and various types of myopathies. In this article, we have discussed the recent advancements toward understanding the role and mechanisms through which ER stress and individual arms of the UPR regulate skeletal muscle physiology and pathology.

Muscle wasting in the presence of disease, why is it so variable?

Skeletal muscle wasting is a common clinical feature of many chronic diseases and also occurs in response to single acute events. The accompanying loss of strength can lead to significant disability, increased care needs and have profound negative effects on quality of life. As muscle is the most abundant source of amino acids in the body, it appears to function as a buffer for fuel and substrates that can be used to repair damage elsewhere and to feed the immune system. In essence, the fundamentals of muscle wasting are simple: less muscle is made than is broken down. However, although well-described mechanisms modulate muscle protein turnover, significant individual differences in the amount of muscle lost in the presence of a given severity of disease complicate the understanding of underlying mechanisms and suggest that individuals have different sensitivities to signals for muscle loss. Furthermore, the rate at which muscle protein is turned over under normal conditions means that clinically significant muscle loss can occur with changes in the rate of protein synthesis and/or breakdown that are too small to be measurable. Consequently, the changes in expression of factors regulating muscle turnover required to cause a decline in muscle mass are small and, except in cases of rapid wasting, there is no consistent pattern of change in the expression of factors that regulate muscle mass. MicroRNAs are fine tuners of cell phenotype and are therefore ideally suited to cause the subtle changes in proteome required to tilt the balance between synthesis and degradation in a way that causes clinically significant wasting. Herein we present a model in which muscle loss as a consequence of disease in non-muscle tissue is modulated by a set of microRNAs, the muscle expression of which is associated with severity of disease in the non-muscle tissue. These microRNAs alter fundamental biological processes including the synthesis of ribosomes and mitochondria leading to reduced protein synthesis and increased protein breakdown, thereby freeing amino acids from the muscle. We argue that the variability in muscle loss observed in the human population arises from at least two sources. The first is from pre-existing or disease-induced variation in the expression of microRNAs controlling the sensitivity of muscle to the atrophic signal and the second is from the expression of microRNAs from imprinted loci (i.e. only expressed from the maternally or paternally inherited allele) and may control the rate of myonuclear recruitment. In the absence of disease, these factors do not correlate with muscle mass, since there is no challenge to the established balance. However, in the presence of such a challenge, these microRNAs determine the rate of decline for a given disease severity. Together these mechanisms provide novel insight into the loss of muscle mass and its variation in the human population. The involvement of imprinted loci also suggests that genes that regulate early development also contribute to the ability of individuals to resist muscle loss in response to disease.

Adipocytes suppress differentiation of muscle cells in a co-culture system

The development of adipose tissue in skeletal muscle is important for improving meat quality. However, it is still unclear how adipocytes grow in the proximity of muscle fibers. We hypothesized that adipocytes would suppress muscle cell growth so as to grow dominantly within muscle. In this study, we investigated the effect of adipocytes on the differentiation of muscle cells in a co-culture system. The fusion index of C2C12 myoblasts co-cultured with 3T3-L1 adipocytes was significantly lower than that of the control. The expression of myogenin and myosin heavy chain in C2C12 muscle cells co-cultured with 3T3-L1 adipocytes was significantly lower than in the control. Furthermore, the expression of Atrogin-1 and MuRF-1 was higher in C2C12 muscle cells co-cultured with 3T3-L1 adipocytes than the control. These results suggest that 3T3-L1 adipocytes suppress the differentiation of C2C12 myoblasts. In addition, 3T3-L1 adipocytes induced the expression and secretion of IL-6 in C2C12 muscle cells. The fusion index and myotube diameter were higher in C2C12 muscle cells co-cultured with 3T3-L1 cells in medium containing IL-6-neutralizing antibody than the control. Taken together, there is a possibility that adipocyte-induced IL-6 expression in muscle cells could be involved in the inhibition of muscle cell differentiation via autocrine.

Do neurogenic and cancer-induced muscle atrophy follow common or divergent paths?

Skeletal muscle is a dynamic tissue capable of responding to a large variety of physiological stimuli by adjusting muscle fiber size, metabolism and function. However, in pathological conditions such as cancer and neural disorders, this finely regulated homeostasis is impaired leading to severe muscle wasting, reduced muscle fiber size (atrophy), and impaired function. These disease features develop due to enhanced protein breakdown, which relies on two major degradation systems: the ubiquitin-proteasome and the autophagy-lysosome. These systems are independently regulated by different signalling pathways, which in physiological conditions, determine protein and organelle turnover. However, alterations in one or both systems, as it happens in several disorders, leads to enhanced protein breakdown and muscle atrophy. Although this is a common feature in the different types of muscle atrophy, the relative contribution of each of these systems is still under debate. Here, we will briefly describe the regulation and the activity of the ubiquitin-proteasome and the autophagy-lysosome systems during muscle wasting. We will then discuss what we know regarding how these pathways are involved in cancer induced and in neurogenic muscle atrophy, highlighting common and divergent paths. It is now clear that there is no one unifying common mechanism that can be applied to all models of muscle loss. Detailed understanding of the pathways and proteolysis mechanisms involved in each model will hopefully help the development of drugs to counteract muscle wasting in specific conditions.

Pyropia yezoensis Protein Prevents Dexamethasone-Induced Myotube Atrophy in C2C12 Myotubes

Glucocorticoids (GCs), which are endocrine hormones released under stress conditions, can cause skeletal muscle atrophy. This study investigated whether Pyropia yezoensis crude protein (PYCP) inhibits synthetic GCs dexamethasone (DEX)-induced myotube atrophy associated with proteolytic systems. Mouse skeletal muscle C2C12 myotubes were treated with DEX in the presence or absence of PYCP. DEX exposure (100 μM) for 24 h significantly decreased myotube diameter and myogenin expression, which were all increased by treatment with 20 and 40 μg/mL PYCP. Additionally, PYCP significantly reduced the nuclear expression of the forkhead box transcription factors, FoxO1 and FoxO3a, and ubiquitin-proteasome pathway activation. Further mechanistic research revealed that PYCP inhibited the autophagy-lysosome pathway in DEX-induced C2C12 myotubes. These findings indicate that PYCP prevents DEX-induced myotube atrophy through the regulation of FoxO transcription factors, followed by the inhibition of the ubiquitin-proteasome and autophagy-lysosome pathways. Therefore, we suggest that inhibiting these two proteolytic processes with FoxO transcription factors is a promising strategy for preventing DEX-related myotube atrophy.

RAGE in the pathophysiology of skeletal muscle

Emerging evidence suggests that the signalling of the Receptor for Advanced Glycation End products (RAGE) is critical for skeletal muscle physiology controlling both the activity of muscle precursors during skeletal muscle development and the correct time of muscle regeneration after acute injury. On the other hand, the aberrant re-expression/activity of RAGE in adult skeletal muscle is a hallmark of muscle wasting that occurs in response to ageing, genetic disorders, inflammatory conditions, cancer, and metabolic alterations. In this review, we discuss the mechanisms of action and the ligands of RAGE involved in myoblast differentiation, muscle regeneration, and muscle pathological conditions. We highlight potential therapeutic strategies for targeting RAGE to improve skeletal muscle function.

Effects of Strength Training on the Physiological Determinants of Middle- and Long-Distance Running Performance: A Systematic Review

Background

Middle- and long-distance running performance is constrained by several important aerobic and anaerobic parameters. The efficacy of strength training (ST) for distance runners has received considerable attention in the literature. However, to date, the results of these studies have not been fully synthesized in a review on the topic.

Objectives

This systematic review aimed to provide a comprehensive critical commentary on the current literature that has examined the effects of ST modalities on the physiological determinants and performance of middle- and long-distance runners, and offer recommendations for best practice.

Methods

Electronic databases were searched using a variety of key words relating to ST exercise and distance running. This search was supplemented with citation tracking. To be eligible for inclusion, a study was required to meet the following criteria: participants were middle- or long-distance runners with ≥ 6 months experience, a ST intervention (heavy resistance training, explosive resistance training, or plyometric training) lasting ≥ 4 weeks was applied, a running only control group was used, data on one or more physiological variables was reported. Two independent assessors deemed that 24 studies fully met the criteria for inclusion. Methodological rigor was assessed for each study using the PEDro scale.

Results

PEDro scores revealed internal validity of 4, 5, or 6 for the studies reviewed. Running economy (RE) was measured in 20 of the studies and generally showed improvements (2–8%) compared to a control group, although this was not always the case. Time trial (TT) performance (1.5–10 km) and anaerobic speed qualities also tended to improve following ST. Other parameters [maximal oxygen uptake (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{{2{ \hbox{max} }}}$$\end{document}V˙O2max), velocity at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{{2{ \hbox{max} }}}$$\end{document}V˙O2max, blood lactate, body composition] were typically unaffected by ST.

Conclusion

Whilst there was good evidence that ST improves RE, TT, and sprint performance, this was not a consistent finding across all works that were reviewed. Several important methodological differences and limitations are highlighted, which may explain the discrepancies in findings and should be considered in future investigations in this area. Importantly for the distance runner, measures relating to body composition are not negatively impacted by a ST intervention. The addition of two to three ST sessions per week, which include a variety of ST modalities are likely to provide benefits to the performance of middle- and long-distance runners.

Partial Compared with Full Range of Motion Resistance Training for Muscle Hypertrophy: A Brief Review and an Identification of Potential Mechanisms

Newmire, DE and Willoughby, DS. Partial compared to full range of motion resistance training for muscle hypertrophy: A brief review and an identification of potential mechanisms. J Strength Cond Res 32(9): 2661-2673, 2018-Resistance training promotes skeletal muscle hypertrophy; there are specific recommendations of intensity, volume, and duration that appear to facilitate hypertrophy the greatest. However, currently, there is not a definitive consensus on optimal range of motion. It appears that the partial range of motion (pROM) mode of exercise may have some similar benefit on muscle hypertrophy as the conventional full range of motion (fROM). Because of the dynamic and multiplanar movement pattern of a multijoint resistance exercise, there may be variation in human force-length and strength-curve theories, which may influence optimal muscle force production at differing portions of a fROM. This suggests specific muscle groups may potentially be optimally recruited during a specific portion of the exercise. The majority of previous research has primarily focused on strength outcomes opposed to muscle hypertrophy. The purpose of this brief review is to highlight the limited and relative pROM literature on muscle hypertrophy and some potential pROM mechanisms that require investigation to assess any plausible relationships. Some potential mechanisms and outcomes of interest are muscle time under tension, muscle activation, and nonuniform hypertrophy. This mode of resistance exercise requires further evaluation on hypertrophic responses; if proven efficacious, it may be employed to those in rehabilitative environments and those that seek more specific regional, local hypertrophic responses such as physique competitors.

Maternal Selenium Supplementation Enhanced Skeletal Muscle Development Through Increasing Protein Synthesis and SelW mRNA Levels of their Offspring

The present study aimed to investigate the influence of maternal selenium supplementation on the skeletal muscle development of the offspring. A total of 720 Ross 308 broiler breeders at 24-week-old were allocated into 3 treatments with 6 replicates of 40 hens each and fed with 0 mg/kg-(group Se/C), 0.5 mg/kg organic-(group Se/O), and 0.5 mg/kg inorganic-(group Se/I) selenium, respectively for 8 weeks. The male offspring from each nutritional treatment were divided and housed into 8 cages of 12 birds each and fed with a commercial diet supplemented with selenium from Na₂SeO₃ at 0.15 mg/kg. Results showed that Se/O group had the highest selenium deposition (P < 0.05) in the egg yolk and albumen. Furthermore, maternal selenium supplementation promoted breast muscle yield; increased serum insulin and IGF-I concentration; upregulated AKT, mammalian target of rapamycin (mTOR), P70S6K, Myf5, MyoD, MyoG, and SelW mRNA levels; and improved the phosphorylation of AKT at Serine 473 residue, mTOR at Serine 2448 residue, and FOXO at Serine 256 residue in skeletal muscles of the offspring. In contrast, the hens' diet supplemented with selenium could result in reduction of uric acid level in serum and downregulation of Atrogin-1 and MuRF1 mRNA levels in the skeletal muscle of the offspring. Additionally, no significant effect on the skeletal muscle development post-hatch was observed between organic and inorganic selenium supplementation. In conclusion, maternal organic selenium supplementation improved selenium deposition in egg; however, no significant effect has been detected on the breast muscle development of the offspring of broiler breeder compared with inorganic selenium supplementation.

Carbohydrate restriction: Friend or foe of resistance-based exercise performance?

It is commonly accepted that adequate carbohydrate availability is necessary for optimal endurance performance. However, for strength- and physique-based athletes, sports nutrition research and recommendations have focused on protein ingestion, with far less attention given to carbohydrates. Varying resistance exercise protocols, such as differences in intensity, volume, and intraset rest prescriptions between strength-training and physique-training goals elicit different metabolic responses, which may necessitate different carbohydrate needs. The results of several acute and chronic training studies suggest that although severe carbohydrate restriction may not impair strength adaptations during a resistance training program, consuming an adequate amount of carbohydrate in the days leading up to testing may enhance maximal strength and strength-endurance performance. Although several molecular studies demonstrate no additive increases in postexercise mammalian target of rapamycin 1 phosphorylation with carbohydrate and protein compared with protein ingestion alone, the effects of chronic resistance training with carbohydrate restriction on muscle hypertrophy are conflicting and require further research to determine a minimal carbohydrate threshold necessary to optimize muscle hypertrophy. This review summarizes the current knowledge regarding carbohydrate availability and resistance training outcomes and poses new research questions that will better help guide carbohydrate recommendations for strength and physique athletes. In addition, given that success in physique sports is based on subjective appearance, and not objective physical performance, we also review the effects of subchronic carbohydrate ingestion during contest preparation on aesthetic appearance.

Role of altered proteostasis network in chronic hypobaric hypoxia induced skeletal muscle atrophy

Background

High altitude associated hypobaric hypoxia is one of the cellular and environmental perturbation that alters proteostasis network and push the healthy cell towards loss of muscle mass. The present study has elucidated the robust proteostasis network and signaling mechanism for skeletal muscle atrophy under chronic hypobaric hypoxia (CHH).

Methods

Male Sprague Dawley rats were exposed to simulated hypoxia equivalent to a pressure of 282 torr for different durations (1, 3, 7 and 14 days). After CHH exposure, skeletal muscle tissue was excised from the hind limb of rats for biochemical analysis.

Results

Chronic hypobaric hypoxia caused a substantial increase in protein oxidation and exhibited a greater activation of ER chaperones, glucose-regulated protein-78 (GRP-78) and protein disulphide isomerase (PDI) till 14d of CHH. Presence of oxidized proteins triggered the proteolytic systems, 20S proteasome and calpain pathway which were accompanied by a marked increase in [Ca²⁺]. Upregulated Akt pathway was observed upto 07d of CHH which was also linked with enhanced glycogen synthase kinase-3β (GSk-3β) expression, a negative regulator of Akt. Muscle-derived cytokines, tumor necrosis factor-α (TNF-α), interferon-ϒ (IFN-©) and interleukin-1β (IL-1β) levels significantly increased from 07d onwards. CHH exposure also upregulated the expression of nuclear factor kappa-B (NF-κB) and E3 ligase, muscle atrophy F-box-1 (Mafbx-1/Atrogin-1) and MuRF-1 (muscle ring finger-1) on 07d and 14d. Further, severe hypoxia also lead to increase expression of ER-associated degradation (ERAD) CHOP/ GADD153, Ub-proteasome and apoptosis pathway.

Conclusions

The disrupted proteostasis network was tightly coupled to degradative pathways, altered anabolic signaling, inflammation, and apoptosis under chronic hypoxia. Severe and prolonged hypoxia exposure affected the protein homeostasis which overwhelms the muscular system and tends towards skeletal muscle atrophy.

Hypoxia impairs adaptation of skeletal muscle protein turnover- and AMPK signaling during fasting-induced muscle atrophy

BACKGROUND

Hypoxemia in humans may occur during high altitude mountaineering and in patients suffering from ventilatory insufficiencies such as cardiovascular- or respiratory disease including Chronic Obstructive Pulmonary Disease (COPD). In these conditions, hypoxemia has been correlated to reduced appetite and decreased food intake. Since hypoxemia and reduced food intake intersect in various physiological and pathological conditions and both induce loss of muscle mass, we investigated whether hypoxia aggravates fasting-induced skeletal muscle atrophy and evaluated underlying protein turnover signaling.

METHODS

Mice were kept under hypoxic (8% oxygen) or normoxic conditions (21% oxygen), or were pair-fed to the hypoxia group for 12 days. Following an additional 24 hours of fasting, muscle weight and protein turnover signaling were assessed in the gastrocnemius muscle by RT-qPCR and Western blotting.

RESULTS

Loss of gastrocnemius muscle mass in response to fasting in the hypoxic group was increased compared to the normoxic group, but not to the pair-fed normoxic control group. Conversely, the fasting-induced increase in poly-ubiquitin conjugation, and expression of the ubiquitin 26S-proteasome E3 ligases, autophagy-lysosomal degradation-related mRNA transcripts and proteins, and markers of the integrated stress response (ISR), were attenuated in the hypoxia group compared to the pair-fed group. Mammalian target of rapamycin complex 1 (mTORC1) downstream signaling was reduced by fasting under normoxic conditions, but sustained under hypoxic conditions. Activation of AMP-activated protein kinase (AMPK) / tuberous sclerosis complex 2 (TSC2) signaling by fasting was absent, in line with retained mTORC1 activity under hypoxic conditions. Similarly, hypoxia suppressed AMPK-mediated glucocorticoid receptor (GR) signaling following fasting, which corresponded with blunted proteolytic signaling responses.

CONCLUSIONS

Hypoxia aggravates fasting-induced muscle wasting, and suppresses AMPK and ISR activation. Altered AMPK-mediated regulation of mTORC1 and GR may underlie aberrant protein turnover signaling and affect muscle atrophy responses in hypoxic skeletal muscle.

Pyropia yezoensis Protein Supplementation Prevents Dexamethasone-Induced Muscle Atrophy in C57BL/6 Mice

We investigated the protective effects of Pyropia yezoensis crude protein (PYCP) against dexamethasone (DEX)-induced myotube atrophy and its underlying mechanisms. DEX (3 mg/kg body weight, intraperitoneal injection) and PYCP (150 and 300 mg/kg body weight, oral) were administrated to mice for 18 days, and the effects of PYCP on DEX-induced muscle atrophy were evaluated. Body weight, calf thickness, and gastrocnemius and tibialis anterior muscle weight were significantly decreased by DEX administration (p < 0.05), while PYCP supplementation effectively prevented the DEX-induced decrease in body weight, calf thickness, and muscle weight. PYCP supplementation also attenuated the DEX-induced increase in serum glucose, creatine kinase, and lactate dehydrogenase levels. Additionally, PYCP supplementation reversed DEX-induced muscle atrophy via the regulation of the insulin-like growth factor-I/protein kinase B/rapamycin-sensitive mTOR complex I/forkhead box O signaling pathway. The mechanistic investigation revealed that PYCP inhibited the ubiquitin-proteasome and autophagy-lysosome pathways in DEX-administrated C57BL/6 mice. These findings demonstrated that PYCP increased protein synthesis and decreased protein breakdown to prevent muscle atrophy. Therefore, PYCP supplementation appears to be useful for preventing muscle atrophy.

Can Plasma Rich in Growth Factors Be Safe for Parental Use? A Safety Study in the Canine Model

Low invasiveness is the main goal of modern surgery. The use of platelet-rich plasma (PRP) is known to be effective in a variety of applications, such as oral, maxillofacial, orthopedic, dermatologic and cosmetic surgeries. However, a potential ergogenic and carcinogenic effect of PRP derivatives by means of the insulin-like growth factor-1 (IGF-1) pathway has been suggested. Because of this notion, the purpose of this study is to assess the effect of a commercially available PRP-derivative intramuscular injection in the lumbar muscular tissue (local effect) and to determine the IGF-1 blood concentration (systemic effect) on healthy beagle dogs. Local effect was evaluated by computed tomography (CT) scan and echography, and systemic effect was calculated by blood testing on days 0, 14, 28, 42 and 56. No statistically significant changes were observed; thus, PRGF could be considered safe when using therapeutic doses.

Release of pro-inflammatory cytokines from muscle and bone causes tenocyte death in a novel rotator cuff in vitro explant culture model

PURPOSE

Tendinopathy is a significant clinical problem thought to be associated with altered mechanical loading. Explant culture models allow researchers to alter mechanical loading in a controlled in vitro environment while maintaining tenocytes in their native matrix. However, current models do not accurately represent commonly injured tendons, ignoring contributions of associated musculature and bone, as well as regional collagen structure. This study details the characterization of amouse rotator cuff explant culture model, including bone, tendon, and muscle (BTM).

MATERIALS AND METHODS

Following harvest, BTM explants were maintained in stress-deprived culture for one week and tendon was then assessed for changes in cell viability, metabolism, matrix structure and content.

RESULTS

Matrix turnover occurred throughout culture as manifested in both gene expression and biosynthesis, but this did not translate to net changes in total collagen or sulfated glycosaminoglycan content. Furthermore, tendon structure was not significantly altered throughout culture. However, we found significant cell death in BTM tendons after 3 days in culture, which we hypothesize is cytokine-induced. Using a targeted multiplex assay, we found high levels of pro-inflammatory cytokines released to the culture medium from muscle and bone, levels that did cause cell deathin tendon-alone controls.

CONCLUSIONS

Overall, this model presents an innovative approach to understandingrotator cuff injury and tenocyte mechanobiology in a clinically-relevant tendon structure. Our model can be a powerful tool to investigate how mechanical and biological stimuli can alter normal tendon health and lead to tendon degeneration, and may provide a testbed for therapeutics for tendon repair.

Effects of food availability on growth performance and immune-related gene expression of juvenile olive flounder (Paralichthys olivaceus)

Unfavorable environmental conditions and inappropriate culture practices have increased the vulnerability of cultured fish to disease infection. Up to date many studies have aimed to determine a feeding regimen to maximize productivity; however, very little information on immune responses of cultured fish in response to underfeeding or overfeeding is available. Therefore, a preliminary study was conducted to evaluate effects of graded feeding levels (i.e., food availability) on growth performance and immune-related gene expression of juvenile olive flounder (Paralichthys olivaceus). Six different feeding rates including 1, 4, 7, 10, 13, and 16% body weight per day (BW/d) were randomly assigned to three replicate tanks stocking 150 fish (average initial body weight: 0.27 ± 0.02 g; mean ± SD) per tank. A feeding trial lasted for two weeks. Based on the results of the weight gain, nutrient gain, and whole-body compositions and energy content, the feeding rate of 10%, 13%, and 16% BW/d resulted in high nutritional status, whereas the feeding rate of 1% and 4% BW/d resulted in low nutritional status. Intermediate nutritional status was observed at the feeding rate of 7% BW/d. In the given rearing conditions the optimum feeding rate resulting in the maximum growth was estimated to be 11.9% BW/d based on the quadratic broken-line regression model, chosen as the best-fit model among the tested models. Expression of immune-related genes including IL-8 and IgM was significantly down-regulated in the flounder fed at 1% BW/d in comparison to those fed at 7% BW/d. Interestingly, expression of these genes in the flounder fed at 10%, 13%, and 16% BW/d was relatively down-regulated in comparison to that of the flounder fed at 7% BW/d. Although no statistical difference was detected, overall response patterns of other immune-related genes, including TLR3, polymeric Ig receptor, lysozyme C-type, GPx, SOD, and Trx followed what IL-8 and IgM exhibited in response to the various feeding rates. Given the current challenges in aquaculture of the flounder our findings suggest to prohibit underfeeding or overfeeding (i.e., ad-libitum feeding) when culturing the young flounder.

Effects of ursolic acid on sub-lesional muscle pathology in a contusion model of spinal cord injury

Spinal Cord Injury (SCI) results in severe sub-lesional muscle atrophy and fiber type transformation from slow oxidative to fast glycolytic, both contributing to functional deficits and maladaptive metabolic profiles. Therapeutic countermeasures have had limited success and muscle-related pathology remains a clinical priority. mTOR signaling is known to play a critical role in skeletal muscle growth and metabolism, and signal integration of anabolic and catabolic pathways. Recent studies show that the natural compound ursolic acid (UA) enhances mTOR signaling intermediates, independently inhibiting atrophy and inducing hypertrophy. Here, we examine the effects of UA treatment on sub-lesional muscle mTOR signaling, catabolic genes, and functional deficits following severe SCI in mice. We observe that UA treatment significantly attenuates SCI induced decreases in activated forms of mTOR, and signaling intermediates PI3K, AKT, and S6K, and the upregulation of catabolic genes including FOXO1, MAFbx, MURF-1, and PSMD11. In addition, UA treatment improves SCI induced deficits in body and sub-lesional muscle mass, as well as functional outcomes related to muscle function, motor coordination, and strength. These findings provide evidence that UA treatment may be a potential therapeutic strategy to improve muscle-specific pathological consequences of SCI.

Integrated analysis of mRNA and miRNA expression profiles reveals muscle growth differences between adult female and male Chinese concave-eared frogs (Odorrana tormota)

The Chinese concave-eared torrent frog (Odorrana tormota) is the first known non-mammalian vertebrate that can communicate using ultrasound. In this species, females are approximately four times as large as males, in which the female growth rate is obviously higher than that of male. Until now, the molecular mechanisms underlying muscle growth development differences between male and female frogs have not been reported. Here, we integrated mRNA and miRNA expression profiles to reveal growth differences in the hindlimb muscles of 2-year-old frogs. Among 569 differentially expressed genes (DEGs), 69 were associated with muscle growth and regeneration. Fifty-one up-regulated genes in females were potentially involved in promoting muscle growth and regeneration, whereas 18 up-regulated genes in males may lead to muscle growth inhibition and fast-twitch muscle fiber contraction. 244 DEGs were enriched in mTOR and other protein synthesis signaling pathways, and protein degradation pathways, including lysosomal protease, calpain, caspase, and ubiquitin-proteasome system pathways. It may interpret why female muscles grow faster than males. Based on expression differences of genes involved in glycolysis and oxidative metabolism, we speculated that the proportion of slow muscle fiber was higher and that of fast muscle fiber was lower in female compared with male muscle. Additionally, 767 miRNAs were identified, including 217 new miRNAs, and 6248 miRNA-negatively regulated mRNAs were predicted. The miRNA target genes were enriched in pathways related to muscle growth, protein synthesis, and degradation. Thus, in addition to the identified mRNA differential expressions, miRNAs may play other important roles in the differential regulation of hindlimb muscle growth between female and male O. tormota.

Decreased muscle strength is associated with proinflammatory cytokines but not testosterone levels in men with diabetes

The aim of this study was to compare muscle strength in male subjects with type 2 diabetes mellitus (DM2) with and without low plasma testosterone levels and assess the relationship between muscle strength, testosterone levels, and proinflammatory cytokines. Males (75) aged between 18 and 65 years were divided into 3 groups: control group that did not have diabetes and had a normal testosterone plasma level (>250 ng/dL), DnormalTT group that had DM2 with normal testosterone levels, and the DlowTT group that had DM2 and low plasma testosterone levels (<250 ng/dL). The age (means±SD) of the groups was 48.4±10, 52.6±7, and 54.6±7 years, respectively. Isokinetic concentric and isometric torque of knee flexors and extensors were analyzed by an isokinetic dynamometer. Plasma testosterone and proinflammatory cytokine levels were determined by chemiluminescence and ELISA, respectively. Glycemic control was analyzed by glycated hemoglobin (HbA1C). In general, concentric and isometric torques were lower and tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-1β plasma levels were higher in the groups with diabetes than in controls. There was no correlation between testosterone level and knee torques or proinflammatory cytokines. Concentric and isometric knee flexion and extension torque were negatively correlated with TNF-α, IL-6, and HbA1C. IL-6 and TNF-α were positively correlated with HbA1C. The results of this study demonstrated that muscle strength was not associated with testosterone levels in men with DM2. Low muscle strength was associated with inflammatory markers and poor glycemic control.

Transcriptome analysis reveals candidate genes involved in splay leg syndrome in piglets

Splay leg is frequently observed in newborn piglets and leads to economic loss as well as welfare concerns. However, the etiology and pathogenesis of splay leg syndrome in piglets are still poorly understood. The aims of this paper were to characterize changes in the transcriptome of splay leg piglets and identify candidate genes responsible for this disease. We chose three splay leg piglets and their healthy full sibs, and constructed six RNA libraries using skeletal muscle samples from both groups and identified the differentially expressed genes between the two groups using RNA-seq. A total of 555 differentially expressed genes were identified, of which 216 were up-regulated and 339 genes were down-regulated in the splay leg group relative to the healthy group. In addition, 321 significantly enriched GO terms and 12 significantly enriched KEGG pathways were identified. FBXO32 is one of the ten most differentially expressed genes in our experiment, and it is regulated by the significantly enriched pathway (PI3K-Akt). The overexpression of FBXO32 which leads to the process of muscle atrophy might be responsible for congenital splay leg in piglets. The result of this study could help improve understanding of the molecular mechanism of congenital splay leg syndrome.

Targeted ablation of p38α MAPK suppresses denervation-induced muscle atrophy

The loss of skeletal muscle mass is a major cause of falls and fractures in the elderly, leading to compromised independence and a decrease in the quality of life. However, only a few therapeutic interventions leading to marginal clinical benefits in patients with this condition are currently available. Therefore, the demand to further understand the pathology of muscle atrophy and establish a treatment modality for patients with muscle atrophy is significant. p38α mitogen-activated protein kinase (p38α MAPK) is a ubiquitous signaling molecule that is implicated in various cellular functions, including cell proliferation, differentiation, and senescence. In the present study, we generated a mutant line in which p38α MAPK is specifically abrogated in muscle tissues. Compared with the control mice, these mutant mice are significantly resistant to denervation-induced muscle atrophy, suggesting that p38α MAPK positively regulates muscle atrophy. We also identified CAMK2B as a potential downstream target of p38α MAPK and found that the pharmacological inhibition of CAMK2B activity suppresses denervation-induced muscle atrophy. Altogether, our findings identify p38α MAPK as a novel regulator of muscle atrophy and suggest that the suppression of intracellular signaling mediated by p38α MAPK serves as a potential target for the treatment of muscle atrophy.

Chemotherapy-induced muscle wasting: association with NF-κB and cancer cachexia

A compounding feature of greater than 50% of all cancers is the high incidence of the cachexia syndrome, a complex metabolic disorder characterized by extreme weight loss due mainly to the gross depletion of skeletal muscle tissue. Although studies into the cause of cancer cachexia has spanned over multiple decades, little is known about the effects of various cancer treatments themselves on cachexia. For example, chemotherapy agents induce side effects such as nausea and anorexia, but these symptoms do not fully account for the changes seen with cancer cachexia. In this study we examine the effects of chemotherapeutic compounds, specifically, cisplatin in the colon-26 adenocarcinoma model of cancer cachexia. We find that although cisplatin is able to reduce tumor burden as expected, muscle wasting in mice nevertheless persists. Strikingly, cisplatin alone was seen to regulate muscle atrophy, which was independent of the commonly implicated ubiquitin proteasome system. Finally, we show that cisplatin is able to induce NF-κB activity in both mouse muscles and myotube cultures, suggesting that an additional side effect of cancer treatment is the regulation of muscle wasting that may be mediated through activation of the NF-κB signaling pathway.

The Association of Diet and Exercise With Body Composition in Pediatric Crohn's Disease

BACKGROUND

In pediatric Crohn's disease, fat mass improves over time with treatment, but lean mass deficits persist. This observational study of the associations of physical activity and dietary intake with lean mass and muscle strength in children with Crohn's disease was ancillary to a previously reported randomized clinical trial of an intervention to improve bone health.

METHODS

In this study, 138 participants were followed at baseline and at 6, 12, and 24 months with evaluation of lean and fat mass using DXA, muscle strength (peak torque), Crohn's characteristics, dietary intake, time in moderate to vigorous physical activity (MVPA), and serum insulin-like growth factor-1 (IGF-1) and tumor necrosis factor-alpha (TNF-α). Race- and sex-specific Z-scores for leg lean mass and whole body fat mass were generated. Quasi least square regression evaluated determinants of changes in body composition and muscle strength.

RESULTS

Leg lean mass and muscle strength were positively associated with time in MVPA (P < 0.05) and negatively associated with increasing clinical disease activity (P < 0.05). Both leg lean mass and strength were positively associated with IGF-1 Z-score (P ≤ 0.03) but negatively associated with serum TNF-α (P ≤ 0.04). Neither lean mass nor muscle strength was associated with caloric or protein intake.

CONCLUSIONS

Persistence of lean mass deficits was related to ongoing Crohn's disease activity but improved with greater time spent in moderate to vigorous physical activity. Future trials are needed to evaluate the efficacy of physical activity in improving lean mass in pediatric Crohn's disease.

Pulsed electromagnetic fields alleviate streptozotocin‑induced diabetic muscle atrophy

Diabetic muscle atrophy causes a reduction of skeletal muscle size and strength, which affects normal daily activities. However, pulsed electromagnetic fields (PEMFs) can retard the atrophy of type II fibers (ActRIIB) in denervated muscles. Therefore, the purpose of the present study was to determine whether PEMFs can alleviate streptozotocin (STZ)‑induced diabetic muscle atrophy. To do this, 40 Sprague‑Dawley (SD) rats were randomly divided into four groups (n=10 per group): The normal control group (NC; nondiabetic rats without treatment); the diabetic mellitus group (DM; STZ‑induced rats without treatment); the diabetic insulin‑treated group (DT; diabetic rats on insulin treatment, 6‑8 U/d twice a day for 6 weeks) as a positive control; and the diabetic PEMFs therapy group (DP; diabetic rats with PEMFs exposure treatment, 15 Hz, 1.46 mT, 30 min/day for 6 weeks). Body weight, muscle strength, muscle mass and serum insulin level were significantly increased in the DP group compared with the DM group. PEMFs also decreased the blood glucose level and altered the activity of metabolic enzymes. PEMFs significantly increased the cross‑sectional area of muscle fiber. In addition, PEMFs significantly activated protein kinase B (Akt) and mammalian target of rapamycin (mTOR), and inhibited the activity of myostatin (MSTN), ActRIIB and forkhead box protein O1 (FoxO1) compared with the DM group. Thus indicating that the Akt/mTOR and Akt/FoxO1 signaling pathways may be involved in the promotion of STZ‑induced diabetic muscle atrophy by PEMFs. The results of the present study suggested that PEMFs stimulation may alleviate diabetic muscle atrophy in the STZ model, and that this is associated with alterations in multiple signaling pathways in which MSTN may be an integral factor. MSTN‑associated signaling pathways may provide therapeutic targets to attenuate severe diabetic muscle wasting.

The Glycoproteomics-MS for Studying Glycosylation in Cardiac Hypertrophy and Heart Failure

With recent advancements of analytical techniques and mass spectrometric instrumentations, proteomics has been widely exploited to study the regulation of protein expression associated with disease states. Many proteins may undergo abnormal change in response to the stimulants, leading to regulation of posttranslationally modified proteins. In this review, the physiological and pathological roles of protein glycosylation in cardiac hypertrophy is discussed, and how the signal pathways regulate heart function and leading to heart failure. The analytical methods for analysis of protein glycosylation, including glycans, glycosite, occupancy, and heterogeneity is emphasized. The rationale on glycoproteins as disease biomarkers is also discussed. The authors also propose potential research in this field and challenges in the diagnosis and treatment of this disease.

Therapeutic Benefit of Autophagy Modulation in Pompe Disease

The complexity of the pathogenic cascade in lysosomal storage disorders suggests that combination therapy will be needed to target various aspects of pathogenesis. The standard of care for Pompe disease (glycogen storage disease type II), a deficiency of lysosomal acid alpha glucosidase, is enzyme replacement therapy (ERT). Many patients have poor outcomes due to limited efficacy of the drug in clearing muscle glycogen stores. The resistance to therapy is linked to massive autophagic buildup in the diseased muscle. We have explored two strategies to address the problem. Genetic suppression of autophagy in muscle of knockout mice resulted in the removal of autophagic buildup, increase in muscle force, decrease in glycogen level, and near-complete clearance of lysosomal glycogen following ERT. However, this approach leads to accumulation of ubiquitinated proteins, oxidative stress, and exacerbation of muscle atrophy. Another approach involves AAV-mediated TSC knockdown in knockout muscle leading to upregulation of mTOR, inhibition of autophagy, reversal of atrophy, and efficient cellular clearance on ERT. Importantly, this approach reveals the possibility of reversing already established autophagic buildup, rather than preventing its development.

Pulmonary inflammation-induced loss and subsequent recovery of skeletal muscle mass require functional poly-ubiquitin conjugation

BACKGROUND

Pulmonary inflammation in response to respiratory infections can evoke muscle wasting. Increased activity of the ubiquitin (Ub)-proteasome system (UPS) and the autophagy lysosome pathway (ALP) have been implicated in inflammation-induced muscle atrophy. Since poly-Ub conjugation is required for UPS-mediated proteolysis and has been implicated in the ALP, we assessed the effect of impaired ubiquitin conjugation on muscle atrophy and recovery following pulmonary inflammation, and compared activation and suppression of these proteolytic systems to protein synthesis regulation.

METHODS

Pulmonary inflammation was induced in mice by an intratracheal instillation of LPS. Proteolysis (UPS and ALP) and synthesis signaling were examined in gastrocnemius muscle homogenates. Ub-conjugation-dependency of muscle atrophy and recovery was addressed using Ub-K48R (K48R) mice with attenuated poly-ubiquitin conjugation, and compared to UBWT control mice.

RESULTS

Pulmonary inflammation caused a decrease in skeletal muscle mass which was accompanied by a rapid increase in expression of UPS and ALP constituents and reduction in protein synthesis signaling acutely after LPS. Muscle atrophy was attenuated in K48R mice, while ALP and protein synthesis signaling were not affected. Muscle mass recovery starting 72 h post LPS, correlated with reduced expression of UPS and ALP constituents and restoration of protein synthesis signaling. K48R mice however displayed impaired recovery of muscle mass.

CONCLUSION

Pulmonary inflammation-induced muscle atrophy is in part attributable to UPS-mediated proteolysis, as activation of ALP- and suppression of protein synthesis signaling occur independently of poly-Ub conjugation during muscle atrophy. Recovery of muscle mass following pulmonary inflammation involves inverse regulation of proteolysis and protein synthesis signaling, and requires a functional poly-Ub conjugation.

Climatic modulation of neurotransmitter release in amphibian neuromuscular junctions: role of dynorphin-A

Amphibian neuromuscular junctions (NMJs) become relatively more silent during the dry winter season in Australia. During the dry, calcium sensitivity is reduced, whereas calcium dependence remains unchanged. Endogenous opioid peptides play an important role in the regulation of the physiological functions of active and dormant vertebrates. Previous findings suggest that dynorphin-A is more potent than other opiates in decreasing evoked neurotransmission in amphibian NMJs. Dynorphin-A has been shown not to alter the amplitude or the frequency of miniature quantal neurotransmitter release. In the present study, we report that dynorphin-A exerted a more pronounced inhibitory effect on evoked neurotransmitter release during the dry (hibernating period) when compared with the wet (active period) season. Dynorphin-A increased the frequency and decreased the amplitude of miniature neurotransmitter release only at relatively high concentration during the dry season. In the present study, we propose that dynorphin-A suppresses evoked neurotransmitter release and thus contraction of skeletal muscles, while allowing subthreshold activation of the NMJ by miniature neurotransmission, thus preventing any significant neuromuscular remodeling. The inhibitory effect of dynorphin-A on evoked transmitter release is reduced by increasing the extracellular calcium concentration.

Can muscle protein metabolism be specifically targeted by nutritional support and exercise training in chronic obstructive pulmonary disease?

Chronic obstructive pulmonary disease (COPD) associates with several extra-pulmonary effects. Muscle dysfunction and wasting is one of the most prominent extra-pulmonary effects and contributes to exercise limitation and health related quality of life (HRQoL), morbidity as well as mortality. The loss of muscle mass is characterised by an impaired balance between protein synthesis (anabolism) and protein breakdown (catabolism) which relates to nutritional disturbances, muscle disuse and the presence of a systemic inflammation, among other factors. Current approaches to reverse skeletal muscle dysfunction and wasting attain only modest improvements. The development of new therapeutic strategies aiming at improving skeletal muscle dysfunction and wasting are needed. This requires a better understanding of the underlying molecular pathways responsible for these abnormalities. In this review we update recent research on protein metabolism, nutritional depletion as well as physical (in)activity in relation to muscle wasting and dysfunction in patients with COPD. We also discuss the role of nutritional supplementation and exercise training as strategies to re-establish the disrupted balance of protein metabolism in the muscle of patients with COPD. Future areas of research and clinical practice directions are also addressed.

Regulation and function of avian selenogenome

BACKGROUND

Selenium (Se) is an essential micronutrient required by avian species. Dietary Se/vitamin E deficiency induces three classical diseases in chicks: exudative diathesis, nutritional pancreatic atrophy, and nutritional muscular dystrophy.

SCOPE OF REVIEW

This review is to summarize and analyze the evolution, regulation, and function of avian selenogenome and selenoproteome and their relationship with the three classical Se/vitamin E deficiency diseases.

MAJOR CONCLUSIONS

There are 24 selenoproteins confirmed in chicks, with two avian-specific members (SELENOU and SELENOP2) and two missing mammalian members (GPX6 and SELENOV). There are two forms of SELENOP containing 1 or 13 selenocysteine residues. In addition, a Gallus gallus gene was conjectured to be the counterpart of the human SEPHS2. Expression of selenoprotein genes in the liver, pancreas, and muscle of chicks seemed to be highly responsive to dietary Se changes. Pathogeneses of the Se/vitamin E deficient diseases in the chicks were likely produced by missing functions of selected selenoproteins in regulating cellular and tissue redox balance and inhibiting oxidative/reductive stress-induced cell death.

GENERAL SIGNIFICANCE

Gene knockout models, similar to those of rodents, will help characterize the precise functions of avian selenoproteins and their comparisons with those of mammalian species.

miR-424-5p reduces ribosomal RNA and protein synthesis in muscle wasting

BACKGROUND

A loss of muscle mass occurs as a consequence of a range of chronic and acute diseases as well as in older age. This wasting results from an imbalance of protein synthesis and degradation with a reduction in synthesis and resistance to anabolic stimulation often reported features. Ribosomes are required for protein synthesis, so changes in the control of ribosome synthesis are potential contributors to muscle wasting. MicroRNAs (miRNAs) are known regulators of muscle phenotype and have been shown to modulate components of the protein synthetic pathway. One miRNA that is predicted to target a number of components of protein synthetic pathway is miR-424-5p, which is elevated in the quadriceps of patients with chronic obstructive pulmonary disease (COPD).

METHODS

Targets of miR-424-5p were identified by Argonaute2 pull down, and the effects of the miRNA on RNA and protein expression were determined by quantitative polymerase chain reaction and western blotting in muscle cells in vitro. Protein synthesis was determined by puromycin incorporation in vitro. The miRNA was over-expressed in the tibialis anterior muscle of mice by electroporation and the effects quantified. Finally, quadriceps expression of the miRNA was determined by quantitative polymerase chain reaction in patients with COPD and intensive care unit (ICU)-acquired weakness and in patients undergoing aortic surgery as well as in individuals from the Hertfordshire Sarcopenia Study.

RESULTS

Pull-down assays showed that miR-424-5p bound to messenger RNAs encoding proteins associated with muscle protein synthesis. The most highly enriched messenger RNAs encoded proteins required for the Pol I RNA pre-initiation complex required for ribosomal RNA (rRNA) transcription, (PolR1A and upstream binding transcription factor). In vitro, miR-424-5p reduced the expression of these RNAs, reduced rRNA levels, and inhibited protein synthesis. In mice, over-expression of miR-322 (rodent miR-424 orthologue) caused fibre atrophy and reduced upstream binding transcription factor expression and rRNA levels. In humans, elevated miR-424-5p associated with markers of disease severity in COPD (FEV₁ %), in patients undergoing aortic surgery (LVEF%), and in patients with ICU-acquired weakness (days in ICU). In patients undergoing aortic surgery, preoperative miR-424-5p expression in skeletal muscle was associated with muscle loss over the following 7 days.

CONCLUSIONS

These data suggest that miR-424-5p regulates rRNA synthesis by inhibiting Pol I pre-initiation complex formation. Increased miR-424-5p expression in patients with conditions associated with muscle wasting is likely to contribute to the inhibition of protein synthesis and loss of muscle mass.

Use of growth hormone, IGF-I, and insulin for anabolic purpose: Pharmacological basis, methods of detection, and adverse effects

Hormones with anabolic properties such as growth hormone (GH), insulin-like growth factor-1 (IGF-I), and insulin are commonly abused among professional and recreational athletes to enhance physical ability. Performance enhancing drugs (PEDs) such as these are also commonly used by recreational athletes to improve body aesthetics. The perception of increased muscle mass due to supraphysiologic hormone supplementation, or doping, is widespread among PED users despite a paucity of evidence-based data in humans. Even still, athletes will continue to abuse PEDs in hopes of replicating anecdotal results. It is important to educate the general public and potential treating physicians of the risks of PED use, including the dangers of polypharmacy and substance dependence. It will also be important for the research community to address the common challenges associated with studying PED use such as the ethical considerations of PED administration, the general reticence of the PED-using community to volunteer information, and the constant need to improve or create new detection methods as athletes continually attempt to circumvent current methods. This review highlights the anabolic mechanisms and suggestive data implicating GH, IGF-I, and insulin for use as PEDs, the specific detection methods with cutoff ranges that may be utilized to diagnose abuse of each substance, and their respective side effects.

Extracellular polysaccharides purified from Aureobasidium pullulans SM‑2001 (Polycan) inhibit dexamethasone‑induced muscle atrophy in mice

The present study assessed the beneficial skeletal muscle‑preserving effects of extracellular polysaccharides from Aureobasidium pullulans SM‑2001 (Polycan) (EAP) on dexamethasone (DEXA)‑induced catabolic muscle atrophy in mice. To investigate whether EAP prevented catabolic DEXA‑induced muscle atrophy, and to examine its mechanisms of action, EAP (100, 200 and 400 mg/kg) was administered orally, once a day for 24 days. EAP treatment was initiated 2 weeks prior to DEXA treatment (1 mg/kg, once a day for 10 days) in mice. Body weight alterations, serum biochemistry, calf thickness, calf muscle strength, gastrocnemius muscle thickness and weight, gastrocnemius muscle antioxidant defense parameters, gastrocnemius muscle mRNA expression, histology and histomorphometry were subsequently assessed. After 24 days, DEXA control mice exhibited muscle atrophy according to all criteria indices. However, these muscle atrophy symptoms were significantly inhibited by oral treatment with all three doses of EAP. Regarding possible mechanisms of action, EAP exhibited favorable ameliorating effects on DEXA‑induced catabolic muscle atrophy via antioxidant and anti‑inflammatory effects; these effects were mediated by modulation of the expression of genes involved in muscle protein synthesis (AKT serine/threonine kinase 1, phosphatidylinositol 3‑kinase, adenosine A1 receptor and transient receptor potential cation channel subfamily V member 4) and degradation (atrogin‑1, muscle RING‑finger protein‑1, myostatin and sirtuin 1). Therefore, these results indicated that EAP may be helpful in improving muscle atrophies of various etiologies. EAP at 400 mg/kg exhibited favorable muscle protective effects against DEXA‑induced catabolic muscle atrophy, comparable with the effects of oxymetholone (50 mg/kg), which has been used to treat various muscle disorders.

Muscle-protective effects of Schisandrae Fructus extracts in old mice after chronic forced exercise

ETHNOPHARMACOLOGICAL RELEVANCE

Schisandrae Fructus (SF), the dried fruit of Schisandra chinensis (Turcz.) Baill., is a well-known traditional herb used in Asia for enhancing physical work capacity as well as providing anti-stress and anti-inflammatory effects. Extracts of SF (SFe) have also been reported to increase skeletal muscle mass and inhibit muscle atrophy.

AIM OF THE STUDY

We examined whether SFe had muscle-protective effects in old mice after chronic forced exercises, and, if so, relevant mechanisms.

MATERIALS AND METHODS

Ten-month-old aged male mice were divided into six groups. One group received no forced swimming after oral administration of distilled water (Intact); the other groups received forced swimming after administration of distilled water (SW), oxymetholone (OXY), or SFe at 500, 250 and 125mg/kg (SFe500, SFe250, and SFe125, respectively). Forced swimming was conducted for 2min at 30min after oral administration; the treatment was repeated for 28 days. Muscle thickness, weight, lean proportion, and strength were examined. The sampled muscles were subjected to histopathological and biochemical analyses. Plasma was examined by biochemical analyses.

RESULTS

The thicknesses of the calf muscle and the sampled gastrocnemius and soleus, protein proportion and muscle strength increased significantly in the SW group versus Intact, and they were further increased in the SFe and OXY groups versus SW. The forced swimming in the SW group upregulated mRNA expression related to protein synthesis (Akt1, PI3K) and muscle growth (A1R, TRPV4), while it downregulated mRNAs related to protein degradation (atrogin-1, MuRF1) and muscle growth inhibitor (myostatin, SIRT1). The detected upregulation and downregulation were enhanced in the SFe groups. In addition, the SFe administration inhibited lipid peroxidation and reactive oxygen species, and accelerated activities of endogenous anti-oxidants and anti-oxidant enzymes. Plasma biochemistry showed decreases in creatine, creatine kinase and LDH in the SFe groups versus SW, suggesting muscle-protective effects of SFe. In the SFe groups versus SW, histopathological analyses revealed an increase in myofibre diameter, and immunohistochemistry showed increases in myofibres immunoreactive for ATPase and decreases in myofibres for apoptosis markers (caspase-3, PARP) and oxidative stress markers (NT, 4HNE, iNOS).

CONCLUSIONS

Oral administration of SFe, especially SFe500, enhanced exercise-induced adaptive muscle strengthening in aged mice after forced swimming through anti-apoptotic and anti-oxidant effects, mediated via modulation of gene expression related to muscle synthesis or degradation. These results suggest that SFe may be helpful in improvement various muscle disorders as an adjuvant therapy to exercise-based remedies.

Insulin treatment reverses the increase in atrogin-1 expression in atrophied skeletal muscles of diabetic rats with acute joint inflammation

Background

The aim of this study was to evaluate the changes in biomarkers of skeletal muscle proteolysis (atrogin-1, muscle RING finger-1 protein [MuRF-1]) and inflammation (nuclear factor kappa-B) in skeletal muscles of rats under two catabolic conditions, diabetes mellitus (DM) and acute joint inflammation, and the effects of insulin therapy.

Materials and methods

Male Wistar rats were divided into groups without diabetes – normal (N), saline (NS), or ι-carrageenan (NCa) injection into the tibiotarsal joint – and groups with diabetes – diabetes (D), plus insulin (DI), saline (DS), or ι-carrageenan (DCa) injection into the tibiotarsal joint, or ι-carrageenan injection and treatment with insulin (DCaI). Three days after ι-carrageenan injection (17 days after diabetes induction), tibialis anterior (TA) and soleus (SO) skeletal muscles were used for analysis.

Results

DM alone caused a significant decrease in the mass of TA and SO muscles, even with low levels of atrogenes (atrogin-1, MuRF-1), which could be interpreted as an adaptive mechanism to spare muscle proteins under this catabolic condition. The loss of muscle mass was exacerbated when ι-carrageenan was administered in the joints of diabetic rats, in association with increased expression of atrogin-1, MuRF-1, and nuclear factor kappa-B. Treatment with insulin prevented the increase in atrogin-1 (TA, SO) and the loss of muscle mass (SO) in diabetic-carrageenan rats; in comparison with TA, SO muscle was more responsive to the anabolic actions of insulin.

Conclusion

Acute joint inflammation overcame the adaptive mechanism in diabetic rats to prevent excessive loss of muscle mass, worsening the catabolic state. The treatment of diabetic-carrageenan rats with insulin prevented the loss of skeletal muscle mass mainly via atrogin-1 inhibition. Under the condition of DM and inflammation, muscles with the prevalence of slow-twitch, type 1 fibers were more responsive to insulin treatment, recovering the ability to grow.

Beta-2 Adrenergic Receptor Genotype Influences Power Output in Healthy Subjects

Kelley, EF, Johnson, BD, and Snyder, EM. Beta-2 adrenergic receptor genotype influences power output in healthy subjects. J Strength Cond Res 31(8): 2053-2059, 2017-The purpose of this study was to determine the effects of ADRB2 genotypes on muscle function (absolute power and relative power) in healthy subjects. We performed genotyping of the ADRB2 (amino acid 16) and high-intensity, steady-state exercise on 77 healthy subjects (AA = 18, AG = 25, GG = 34). There were no differences between genotype groups in age, height, weight, or body mass index (BMI) (age = 28.9 ± 5.7 years, 27.9 ± 5.7 years, 29.2 ± 5.9 years, height = 170.7 ± 8.6 cm, 174.9 ± 8.7 cm, 173.4 ± 9.6 cm, weight = 68.5 ± 13.0 kg, 75.0 ± 12.9 kg, 74.4 ± 12.9 kg, and BMI = 23.4 ± 3.9, 24.4 ± 2.9, 24.7 ± 3.4, for AA, AG, and GG, respectively). The genotype groups differed significantly in watts, and watts/V[Combining Dot Above]O2 with heavy exercise (watts = 186.3 ± 54.6, 237.8 ± 54.4, 219.4 ± 79.5, watts/V[Combining Dot Above]O2 = 0.08 ± 0.006, 0.09 ± 0.005, 0.08 ± 0.006). There was a trend toward significance (p = 0.058) for W·kg (2.7 ± 0.4, 3.2 ± 0.5, 2.9 ± 0.8, for AA, AG, and GG, respectively). These data suggest that genetic variation of the ADRB2 may influence relative strength in healthy subjects and may become an important genetic determinant of muscular strength and functional capacity in patients with diseases that result in a loss of muscle strength.

The role of mechanobiology in progression of rotator cuff muscle atrophy and degeneration

Rotator cuff (RC) muscles undergo several detrimental changes following mechanical unloading resulting from RC tendon tear. In this review, we highlight the pathological causes and consequences of mechanical alterations at the whole muscle, muscle fiber, and muscle resident cell level as they relate to RC disease progression. In brief, the altered mechanical loads associated with RC tear lead to architectural, structural, and compositional changes at the whole-muscle and muscle fiber level. At the cellular level, these changes equate to direct disruption of mechanobiological signaling, which is exacerbated by mechanically regulated biophysical and biochemical changes to the cellular and extra-cellular environment (also known as the stem cell "niche"). Together, these data have important implications for both pre-clinical models and clinical practice. In pre-clinical models, it is important to recapitulate both the atrophic and degenerative muscle loss found in humans using clinically relevant modes of injury. Clinically, understanding the mechanics and underlying biology of the muscle will impact both surgical decision-making and rehabilitation protocols, as interventions that may be good for atrophic muscle will have a detrimental effect on degenerating muscle, and vice versa. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:546-556, 2018.

Select Skeletal Muscle mRNAs Related to Exercise Adaptation Are Minimally Affected by Different Pre-exercise Meals that Differ in Macronutrient Profile

Background: Substantial research has been done on the impact of carbohydrate and fat availability on endurance exercise adaptation, though its role in the acute adaptive response to resistance exercise has yet to be fully characterized. Purpose: We aimed to assess the effects of a pre-resistance exercise isocaloric mixed meal containing different amounts of carbohydrates and fat, on post-resistance exercise gene expression associated with muscle adaptation. Methods: Thirteen young (age 21.2 ± 1.6 year), recreationally trained (VO_2max 51.3 ± 4.8 ml/kg/min) men undertook an aerobic exercise session of 90-min continuous cycling (70% VO_2max) in the morning with pre- and post-exercise protein ingestion (10 and 15 g casein in a 500 ml beverage pre- and post-exercise, respectively). Subjects then rested for 2 h and were provided with a meal consisting of either 3207 kJ; 52 g protein; 51 g fat; and 23 g carbohydrate (FAT) or 3124 kJ; 53 g protein; 9 g fat; and 109 g carbohydrate (CHO). Two hours after the meal, subjects completed 5 × 8 repetitions (80% 1-RM) for both bilateral leg press and leg extension directly followed by 25 g of whey protein (500 ml beverage). Muscle biopsies were obtained from the vastus lateralis at baseline (morning) and 1 and 3 h post-resistance exercise (afternoon) to determine intramuscular mRNA response. Results: Muscle glycogen levels were significantly decreased post-resistance exercise, without any differences between conditions. Plasma free fatty acids increased significantly after the mixed meal in the FAT condition, while glucose and insulin were higher in the CHO condition. However, PDK4 mRNA quantity was significantly higher in the FAT condition at 3 h post-resistance exercise compared to CHO. HBEGF, INSIG1, MAFbx, MURF1, SIRT1, and myostatin responded solely as a result of exercise without any differences between the CHO and FAT group. FOXO3A, IGF-1, PGC-1α, and VCP expression levels remained unchanged over the course of the day. Conclusion: We conclude that mRNA quantity associated with muscle adaptation after resistance exercise is not affected by a difference in pre-exercise nutrient availability. PDK4 was differentially expressed between CHO and FAT groups, suggesting a potential shift toward fat oxidation and reduced glucose oxidation in the FAT group.

The Drosophila junctophilin gene is functionally equivalent to its four mammalian counterparts and is a modifier of a Huntingtin poly-Q expansion and the Notch pathway

Members of the Junctophilin (JPH) protein family have emerged as key actors in all excitable cells, with crucial implications for human pathophysiology. In mammals, this family consists of four members (JPH1-JPH4) that are differentially expressed throughout excitable cells. The analysis of knockout mice lacking JPH subtypes has demonstrated their essential contribution to physiological functions in skeletal and cardiac muscles and in neurons. Moreover, mutations in the human JPH2 gene are associated with hypertrophic and dilated cardiomyopathies; mutations in JPH3 are responsible for the neurodegenerative Huntington's disease-like-2 (HDL2), whereas JPH1 acts as a genetic modifier in Charcot–Marie–Tooth 2K peripheral neuropathy. Drosophila melanogaster has a single junctophilin (jp) gene, as is the case in all invertebrates, which might retain equivalent functions of the four homologous JPH genes present in mammalian genomes. Therefore, owing to the lack of putatively redundant genes, a jpDrosophila model could provide an excellent platform to model the Junctophilin-related diseases, to discover the ancestral functions of the JPH proteins and to reveal new pathways. By up- and downregulation of Jp in a tissue-specific manner in Drosophila, we show that altering its levels of expression produces a phenotypic spectrum characterized by muscular deficits, dilated cardiomyopathy and neuronal alterations. Importantly, our study has demonstrated that Jp modifies the neuronal degeneration in a Drosophila model of Huntington's disease, and it has allowed us to uncover an unsuspected functional relationship with the Notch pathway. Therefore, this Drosophila model has revealed new aspects of Junctophilin function that can be relevant for the disease mechanisms of their human counterparts.

Summary: This work reveals that the Drosophila Junctophilin protein has similar functions to its mammalian homologues and uncovers new interactions of potential biomedical interest with Huntingtin and Notch signalling.

Loss of imprinting mutations define both distinct and overlapping roles for misexpression of IGF2 and of H19 lncRNA

Imprinted genes occur in discrete clusters that are coordinately regulated by shared DNA elements called Imprinting Control Regions. H19 and Igf2 are linked imprinted genes that play critical roles in development. Loss of imprinting (LOI) at the IGF2/H19 locus on the maternal chromosome is associated with the developmental disorder Beckwith Wiedemann Syndrome (BWS) and with several cancers. Here we use comprehensive genetic and genomic analyses to follow muscle development in a mouse model of BWS to dissect the separate and shared roles for misexpression of Igf2 and H19 in the disease phenotype. We show that LOI results in defects in muscle differentiation and hypertrophy and identify primary downstream targets: Igf2 overexpression results in over-activation of MAPK signaling while loss of H19 lncRNA prevents normal down regulation of p53 activity and therefore results in reduced AKT/mTOR signaling. Moreover, we demonstrate instances where H19 and Igf2 misexpression work separately, cooperatively, and antagonistically to establish the developmental phenotype. This study thus identifies new biochemical roles for the H19 lncRNA and underscores that LOI phenotypes are multigenic so that complex interactions will contribute to disease outcomes.

Breathlessness and inflammation: potential relationships and implications

PURPOSE OF REVIEW

Breathlessness and chronic inflammation both span a wide range of disease contexts and hold prognostic significance. The possibility of a causal relationship between the two has been hypothesized. The aims of this article are to review the intersections between breathlessness and inflammation in the literature, describe potential mechanisms connecting the two phenomena, and discuss the potential clinical implications of a causal relationship.

RECENT FINDINGS

There is a very limited literature exploring the relationship between systemic inflammation and breathlessness in chronic obstructive pulmonary disease, heart failure, and cancer. One large study in cancer patients is suggestive of a weak association between self-reported breathlessness and inflammation. Studies exploring the relationship between inflammation and Medical Research Council Dyspnoea grade in chronic obstructive pulmonary disease patients have produced inconsistent findings. Although a causal relationship has not yet been proven, there is evidence to support the existence of potential mechanisms mediating a relationship. This evidence points to a role for the skeletal muscle and stress hormone systems.

SUMMARY

There is much progress to be made in this area. Interventional studies, evaluating the impact of anti-inflammatory interventions on breathlessness, are needed to help determine whether a causal relationship exists. If proven, this relationship might have important implications for both the treatment and impact of breathlessness.

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

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.

The Role of IGF-1 Signaling in Skeletal Muscle Atrophy

Insulin-like growth factor 1 (IGF-1) is a key anabolic growth factor stimulating phosphatidylinositol 3-kinase (PI3K)/Akt signaling which is well known for regulating muscle hypertrophy. However, the role of IGF-1 in muscle atrophy is less clear. This review provides an overview of the mechanisms via which IGF-1 signaling is implicated in several conditions of muscle atrophy and via which mechanisms protein turnover is altered. IGF-1/PI3K/Akt signaling stimulates the rate of protein synthesis via p70S6Kinase and p90 ribosomal S6 kinase and negatively regulates protein degradation, predominantly by its inhibiting effect on proteasomal and lysosomal protein degradation. Caspase-dependent protein degradation is also attenuated by IGF/PI3K/Akt signaling, whereas evidence for an effect on calpain-dependent protein degradation is inconclusive. IGF-1/PI3K/Akt signaling reduces during denervation-, unloading-, and joint immobilization-induced muscle atrophy, whereas IGF-1/PI3K/Akt signaling seems unaltered during aging-associated muscle atrophy. During denervation and aging, IGF-1 overexpression or injection counteracts denervation- and aging-associated muscle atrophy, despite enhanced anabolic resistance with regard to IGF-1 signaling with aging. It remains unclear whether pharmacological stimulation of IGF-1/PI3K/Akt signaling attenuates immobilization- or unloading-induced muscle atrophy. Exploration of the possibilities to interfere with IGF-1/PI3K/Akt signaling reveals that microRNAs targeting IGF-1 signaling components are promising targets to counterbalance muscle atrophy. Overall, the findings summarized in this review show that in disuse conditions, but not with aging, IGF-1/PI3K/Akt signaling is attenuated and that in some conditions stimulation of this pathway may alleviate skeletal muscle atrophy.

A new perspective on managing the onset of puberty and early reproductive performance in ewe lambs: a review

Global changes in industry and society have led us to reassess the numerous factors that combine to influence the time of onset of puberty and the efficiency of reproduction in young sheep. Age and weight have long been considered the dominant factors that influence the onset of puberty and, for many years, it has been accepted that these relationships are mediated by the hormone, leptin, produced by body fat. However, recent studies showing that muscle mass also plays a role have challenged this dogma and also presented new options for our understanding of metabolic inputs into the brain control of reproduction. Moreover, the possibility that an improvement in meat production will simultaneously advance puberty is exciting from an industry perspective. An industry goal of strong reproductive performance in the first year of life is becoming possible and, with it, a major step upwards in the lifetime reproductive performance of ewes. The concept of early puberty is not well accepted by producers for a variety of reasons, but the new data show clear industry benefits, so the next challenge is to change that perception and encourage producers to manage young ewes so they produce their first lamb at 1 year of age.