Skeletal muscle hypertrophy and regeneration: interplay between the myogenic regulatory factors (MRFs) and insulin-like growth factors (IGFs) pathways

Effects of photobiomodulation and deep water running in patients with chronic non-specific low back pain: a randomized controlled trial

Photobiomodulation therapy (PBM) is often used to treat musculoskeletal disorders such as chronic non-specific low back pain (NSCLBP) as it can have positive effects on biomarkers-creatine kinase (CK) and serum cortisol levels-related to stress caused by physical exercise, such as deep water running (DWR) or by pain. The aim of this study was to evaluate the effects of the combination of PBM and aquatic exercise (DWR) on the intensity of pain, disability, 6-min walk test adapted (6WTA), and on cortisol and creatine kinase (CK) levels in a population with NSCLBP. The participants were allocated into three groups: TG_PBM (Photobiomodulation and Training Group), TG_PLA (Placebo Photobiomodulation and Training Group), and the G_PBM (Photobiomodulation Group). Information regarding anthropometric data, blood pressure, and heart rate were collected, and the questionnaires were applied: IPAQ-Short Form, Oswestry Disability Index, and the Visual Analog Scale for Pain. The submaximal exercise test (6WTA) was performed. Blood was collected for analysis of cortisol and CK levels. The training sessions were performed twice a week, for 4 weeks. In the intragroup comparisons, there were statistically significant changes in the TG_PBM and G_PBM groups in the outcomes pain intensity, disability (reductions in both groups), and in cortisol (increased in the TG_PBM and reduced in the G_PBM); in the TG_PLA group, there was a statistically significant reduction only in the outcome of pain intensity. In the intergroup comparison, in the comparison between TG_PBM and TG_PLA, there was a statistically significant difference in the level of cortisol, as well as in the comparison between TG_PBM and G_PBM, in which there was a statistically significant difference for this same outcome (cortisol) and for the 6WTA outcome. The effects of the combination of PBM and aquatic exercise have positive effects on reducing pain intensity, disability, and cortisol levels, but its effects on other variables (6WTA and CK) are too small to be considered significant. Trial registration number: NCT03465228-April 3, 2019; retrospectively registered (ClinicalTrials.gov).

Muscle Stem Cell Function Is Impaired in β2-Adrenoceptor Knockout Mice

Knockout (ko) mice for the β2 adrenoceptor (Adrβ2) have impaired skeletal muscle regeneration, suggesting that this receptor is important for muscle stem cell (satellite cell) function. Here, we investigated the role of Adrβ2 in the function of satellite cells from β2ko mice in the context of muscle regeneration, through in vivo and in vitro experiments. Immunohistochemical analysis showed a significant reduction in the number of self-renewed Pax7⁺ satellite cells, proliferating Pax7⁺/MyoD⁺ myogenic precursor cells, and regenerating eMHC⁺ myofibers in regenerating muscle of β2ko mice at 30, 3, and 10 days post-injury, respectively. Quiescent satellite cells were isolated by fluorescence-activated cell sorting, and cell cycle entry was assessed by EdU incorporation. The results demonstrated a lower number of proliferating Pax7⁺/EdU⁺ satellite cells from β2ko mice. There was an increase in the gene expression of the cell cycle inhibitor Cdkn1a and Notch pathway components and the activation of Notch signaling in proliferating myoblasts from β2ko mice. There was a decrease in the number of myogenin-positive nuclei in myofibers maintained in differentiation media, and a lower fusion index in differentiating myoblasts from β2ko mice. Furthermore, the gene expression of Wnt/β-catenin signaling components, the expression of nuclear β-catenin and the activation of Wnt/β-catenin signaling decreased in differentiating myoblasts from β2ko mice. These results indicate that Adrβ2 plays a crucial role in satellite cell self-renewal, as well as in myoblast proliferation and differentiation by regulating Notch and Wnt/β-catenin signaling, respectively.

Beneficial impact of dietary methyl methionine sulfonium chloride and/or L-carnitine supplementation on growth performance, feed efficiency, and serum biochemical parameters in broiler chicken: role of IGF-1 and MSTN genes

The purpose of this study was to examine the effect of dietary supplementation with methyl methionine sulfonium chloride (MMSC), and L-carnitine (L-CAR) alone or in combination on the growth performance of broilers through their impact on the expression of IGF-1 and MSTN genes associated with growth in broilers. One-day-old female Ross 308 broiler chicks were allocated into four groups, each of which received a broiler starter diet and water daily ad libitum. The control group (group 1) was given drinking water without any additives. Group 2 received 0.25 g L-carnitine per liter of drinking water, group 3 received 0.25 g MMSC per liter of drinking water, and group 4 received 0.25 g of both L-carnitine and MMSC per liter of drinking water. Birds were given a starter diet to 21 days after which they received a broiler grower diet to 35 days when the experiment ended. There were five replicate groups of 12 birds per treatment. Body weights and feed intake were recorded weekly. Compared to the control group of birds, supplementation with MMSC either alone or in combination with L-carnitine resulted in an increase in growth rate or feed utilization efficiency; L-carnitine by itself had no effect. MMSC supplementation, again either alone or in combination with L-carnitine, increased jejunal and ileal villi height, increased serum total proteins and globulins, downregulated myostatin (MSTN) mRNA, and upregulated insulin growth factor-1 (IGF-1) mRNA expression. Supplementation with L-carnitine alone showed none of these effects. We conclude that MMSC supplementation improved growth performance through the upregulation of IGF-1 mRNA expression and downregulation of MSTN mRNA expression.

Effects of photobiomodulation therapy on regulation of myogenic regulatory factor mRNA expression in vivo: A systematic review

Non-invasive promotion of myogenic regulatory factors (MRFs), through photobiomodulation therapy (PBMT), may be a viable method of facilitating skeletal muscle regeneration post-injury, given the importance of MRF in skeletal muscle regeneration. The aim of this systematic review was to collate current evidence, identifying key themes and changes in expression of MRF in in vivo models. Web of Science, PubMed, Scopus and Cochrane databases were systematically searched and identified 1459 studies, of which 10 met the inclusion criteria. Myogenic determination factor was most consistently regulated in response to PBMT treatment, and the expression of remaining MRFs was heterogenous. All studies exhibited a high risk of bias, primarily due to lack of blinding in PBMT application and MRF analysis. Our review suggests that the current evidence base for MRF expression from PBMT is highly variable. Future research should focus on developing a robust methodology for determining the effect of laser therapy on MRF expression, as well as long-term assessment of skeletal muscle regeneration.

Neuregulin 1 Drives Morphological and Phenotypical Changes in C2C12 Myotubes: Towards De Novo Formation of Intrafusal Fibres In Vitro

Muscle spindles are sensory organs that detect and mediate both static and dynamic muscle stretch and monitor muscle position, through a specialised cell population, termed intrafusal fibres. It is these fibres that provide a key contribution to proprioception and muscle spindle dysfunction is associated with multiple neuromuscular diseases, aging and nerve injuries. To date, there are few publications focussed on de novo generation and characterisation of intrafusal muscle fibres in vitro. To this end, current models of skeletal muscle focus on extrafusal fibres and lack an appreciation for the afferent functions of the muscle spindle. The goal of this study was to produce and define intrafusal bag and chain myotubes from differentiated C2C12 myoblasts, utilising the addition of the developmentally associated protein, Neuregulin 1 (Nrg-1). Intrafusal bag myotubes have a fusiform shape and were assigned using statistical morphological parameters. The model was further validated using immunofluorescent microscopy and western blot analysis, directed against an extensive list of putative intrafusal specific markers, as identified in vivo. The addition of Nrg-1 treatment resulted in a 5-fold increase in intrafusal bag myotubes (as assessed by morphology) and increased protein and gene expression of the intrafusal specific transcription factor, Egr3. Surprisingly, Nrg-1 treated myotubes had significantly reduced gene and protein expression of many intrafusal specific markers and showed no specificity towards intrafusal bag morphology. Another novel finding highlights a proliferative effect for Nrg-1 during the serum starvation-initiated differentiation phase, leading to increased nuclei counts, paired with less myotube area per myonuclei. Therefore, despite no clear collective evidence for specific intrafusal development, Nrg-1 treated myotubes share two inherent characteristics of intrafusal fibres, which contain increased satellite cell numbers and smaller myonuclear domains compared with their extrafusal neighbours. This research represents a minimalistic, monocellular C2C12 model for progression towards de novo intrafusal skeletal muscle generation, with the most extensive characterisation to date. Integration of intrafusal myotubes, characteristic of native, in vivo intrafusal skeletal muscle into future biomimetic tissue engineered models could provide platforms for developmental or disease state studies, pre-clinical screening, or clinical applications.

Amino Acids and IGF1 Regulation of Fish Muscle Growth Revealed by Transcriptome and microRNAome Integrative Analyses of Pacu (Piaractus mesopotamicus) Myotubes

Amino acids (AA) and IGF1 have been demonstrated to play essential roles in protein synthesis and fish muscle growth. The myoblast cell culture is useful for studying muscle regulation, and omics data have contributed enormously to understanding its molecular biology. However, to our knowledge, no study has performed the large-scale sequencing of fish-cultured muscle cells stimulated with pro-growth signals. In this work, we obtained the transcriptome and microRNAome of pacu (Piaractus mesopotamicus)-cultured myotubes treated with AA or IGF1. We identified 1228 and 534 genes differentially expressed by AA and IGF1. An enrichment analysis showed that AA treatment induced chromosomal changes, mitosis, and muscle differentiation, while IGF1 modulated IGF/PI3K signaling, metabolic alteration, and matrix structure. In addition, potential molecular markers were similarly modulated by both treatments. Muscle-miRNAs (miR-1, -133, -206 and -499) were up-regulated, especially in AA samples, and we identified molecular networks with omics integration. Two pairs of genes and miRNAs demonstrated a high-level relationship, and involvement in myogenesis and muscle growth: marcksb and miR-29b in AA, and mmp14b and miR-338-5p in IGF1. Our work helps to elucidate fish muscle physiology and metabolism, highlights potential molecular markers, and creates a perspective for improvements in aquaculture and in in vitro meat production.

Regulation of Myostatin on the Growth and Development of Skeletal Muscle

Myostatin (MSTN), a member of the transforming growth factor-β superfamily, can negatively regulate the growth and development of skeletal muscle by autocrine or paracrine signaling. Mutation of the myostatin gene under artificial or natural conditions can lead to a significant increase in muscle quality and produce a double-muscle phenotype. Here, we review the similarities and differences between myostatin and other members of the transforming growth factor-β superfamily and the mechanisms of myostatin self-regulation. In addition, we focus extensively on the regulation of myostatin functions involved in myogenic differentiation, myofiber type conversion, and skeletal muscle protein synthesis and degradation. Also, we summarize the induction of reactive oxygen species generation and oxidative stress by myostatin in skeletal muscle. This review of recent insights into the function of myostatin will provide reference information for future studies of myostatin-regulated skeletal muscle formation and may have relevance to agricultural fields of study.

MiR-22-3p Inhibits Proliferation and Promotes Differentiation of Skeletal Muscle Cells by Targeting IGFBP3 in Hu Sheep

The growth and development of skeletal muscle require a series of regulatory factors. MiRNA is a non-coding RNA with a length of about 22 nt, which can inhibit the expression of mRNA and plays an important role in the growth and development of muscle cells. The role of miR-22-3p in C2C12 cells and porcine skeletal muscle has been reported, but it has not been verified in Hu sheep skeletal muscle. Through qPCR, CCK-8, EdU and cell cycle studies, we found that overexpression of miR-22-3p inhibited proliferation of skeletal muscle cells (p < 0.01). The results of qPCR and immunofluorescence showed that overexpression of miR-22-3p promoted differentiation of skeletal muscle cells (p < 0.01), while the results of inhibiting the expression of miR-22-3p were the opposite. These results suggested that miR-22-3p functions in growth and development of sheep skeletal muscle cells. Bioinformatic analysis with mirDIP, miRTargets, and RNAhybrid software suggested IGFBP3 was the target of miR-22-3p, which was confirmed by dual-luciferase reporter system assay. IGFBP3 is highly expressed in sheep skeletal muscle cells. Overexpression of IGFBP3 was found to promote proliferation of skeletal muscle cells indicated by qPCR, CCK-8, EdU, and cell cycle studies (p < 0.01). The results of qPCR and immunofluorescence experiments proved that overexpression of IGFBP3 inhibited differentiation of skeletal muscle cells (p < 0.01), while the results of interfering IGFBP3 with siRNA were the opposite. These results indicate that miR-22-3p is involved in proliferation and differentiation of skeletal muscle cells by targeting IGFBP3.

Aging, Osteo-Sarcopenia, and Musculoskeletal Mechano-Transduction

The decline in the mass and function of bone and muscle is an inevitable consequence of healthy aging with early onset and accelerated decline in those with chronic disease. Termed osteo-sarcopenia, this condition predisposes the decreased activity, falls, low-energy fractures, and increased risk of co-morbid disease that leads to musculoskeletal frailty. The biology of osteo-sarcopenia is most understood in the context of systemic neuro-endocrine and immune/inflammatory alterations that drive inflammation, oxidative stress, reduced autophagy, and cellular senescence in the bone and muscle. Here we integrate these concepts to our growing understanding of how bone and muscle senses, responds and adapts to mechanical load. We propose that age-related alterations in cytoskeletal mechanics alter load-sensing and mechano-transduction in bone osteocytes and muscle fibers which underscores osteo-sarcopenia. Lastly, we examine the evidence for exercise as an effective countermeasure to osteo-sarcopenia.

L-Arginine Supplementation for Nulliparous Sows during the Last Third of Gestation

We evaluated the effects of L-arginine supplementation during the last third of gestation on molecular mechanisms related to skeletal muscle development of piglets and litter traits at birth. Twenty-three nulliparous sows averaging 205.37 ± 11.50 kg of body weight were randomly assigned to the following experimental treatments: control (CON), where pregnant sows were fed diets to meet their nutritional requirements; arginine (ARG), where sows where fed CON + 1.0% L-arginine. Skeletal muscle from piglets born from sows from ARG group had greater mRNA expression of MYOD (p = 0.043) and MYOG (p ≤ 0.01), and tended to present greater mRNA expression (p = 0.06) of IGF-2 gene compared to those born from CON sows. However, there were no differences (p > 0.05) in the histomorphometric variables of fetuses' skeletal muscle. The total weight of born piglets, total weight of born alive piglets, piglet weight at birth, coefficient of variation of birth weight, and the incidence of intrauterine growth restriction (IUGR) piglets did not differ between groups. No stillborn piglets (p < 0.01) were verified in the ARG sows compared to CON group. The blood levels of estradiol (p = 0.035) and urea (p = 0.03) were higher in ARG sows compared to those from the CON group. In summary, our data show that arginine supplementation of nulliparous sows at late gestation enhance mRNA expression of key myogenic regulatory factors, which likely contribute to improve animal growth rates in later stages of development.

Aerobic exercise and resistance exercise alleviate skeletal muscle atrophy through IGF-1/IGF-1R-PI3K/Akt pathway in mice with myocardial infarction

OBJECTIVES

Myocardial infarction (MI)-induced heart failure (HF) is commonly accompanied with profound effects on skeletal muscle. With the process of MI-induced HF, perturbations in skeletal muscle contribute to muscle atrophy. Exercise is viewed as a feasible strategy to prevent muscle atrophy. The aims of this study were to investigate whether exercise could alleviate MI-induced skeletal muscle atrophy via insulin-like growth factor 1 (IGF-1) pathway in mice.

MATERIALS AND METHODS

Male C57/BL6 mice were used to establish the MI model and divided into three groups: sedentary MI group, MI with aerobic exercise group and MI with resistance exercise group, sham-operated group was used as control. Exercise-trained animals were subjected to four-weeks of aerobic exercise (AE) or resistance exercise (RE). Cardiac function, muscle weight, myofiber size, levels of IGF-1 signaling and proteins related to myogenesis, protein synthesis and degradation and cell apoptosis in gastrocnemius muscle were detected. And H₂O₂-treated C2C12 cells were intervened with recombinant human IGF-1, IGF-1R inhibitor NVP-AEW541 and PI3K inhibitor LY294002 to explore the mechanism. Results：Exercises up-regulated the IGF-1/IGF-1R-phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling, increased the expressions of Pax7, myogenic regulatory factors (MRFs) and protein synthesis, reduced protein degradation and cell apoptosis in MI-mice. In vitro, IGF-1 up-regulated the levels of Pax7 and MRFs, mTOR and P70S6K, reduced MuRF1, MAFbx and inhibited cell apoptosis via IGF-1R-PI3K/Akt pathway.

CONCLUSION

AE and RE, safely and effectively, alleviate skeletal muscle atrophy by regulating the levels of myogenesis, protein degradation and cells apoptosis in mice with MI via activating IGF-1/IGF-1R-PI3K/Akt pathway.

Does the combination of resistance training and a nutritional intervention have a synergic effect on muscle mass, strength, and physical function in older adults? A systematic review and meta-analysis

BACKGROUND

Health-promoting interventions are important for preventing frailty and sarcopenia in older adults. However, there is limited evidence that nutritional interventions yield additional effects when combined with resistance training. This systematic review and meta-analysis aimed to compare the effectiveness of nutritional interventions with resistance training and that of resistance training alone.

METHODS

Randomized controlled trials published in peer-reviewed journals prior to July 2020 were retrieved from databases and other sources. The articles were screened according to the inclusion and exclusion criteria. The methodological quality of the included studies was assessed using Cochrane's risk of bias tool 2. A meta-analysis was performed using the RevMan 5.4 program and STATA 16 program.

RESULTS

A total of 22 studies were included in the meta-analysis. The results of the meta-analysis showed no significant differences between groups in muscle mass, muscle strength, or physical functional performance. In the subgroup analysis regarding the types of nutritional interventions, creatine showed significant effects on lean body mass (n = 4, MD 2.61, 95% CI 0.51 to 4.72). Regarding the other subgroup analyses, there were no significant differences in appendicular skeletal muscle mass (p = .43), hand grip strength (p = .73), knee extension strength (p = .09), chair stand test results (p = .31), or timed up-and-go test results (p = .31). In the meta-regression, moderators such as the mean age of subjects and duration of interventions were not associated with outcome variables.

CONCLUSIONS

This meta-analysis showed that nutritional interventions with resistance training have no additional effect on body composition, muscle strength, or physical function. Only creatine showed synergistic effects with resistance training on muscle mass.

TRIAL REGISTRATION

CRD42021224843 .

Response to Electrostimulation Is Impaired in Muscle Cells from Patients with Chronic Obstructive Pulmonary Disease

Among the comorbidities associated with chronic obstructive pulmonary disease (COPD), skeletal muscle weakness and atrophy are known to affect patient survival rate. In addition to muscle deconditioning, various systemic and intrinsic factors have been implicated in COPD muscle dysfunction but an impaired COPD muscle adaptation to contraction has never been extensively studied. We submitted cultured myotubes from nine healthy subjects and nine patients with COPD to an endurance-type protocol of electrical pulse stimulation (EPS). EPS induced a decrease in the diameter, covered surface and expression of MHC1 in COPD myotubes. Although the expression of protein degradation markers was not affected, expression of the protein synthesis marker mTOR was not induced in COPD compared to healthy myotubes after EPS. The expression of the differentiation markers p16INK4a and p21 was impaired, while expression of Myf5 and MyoD tended to be affected in COPD muscle cells in response to EPS. The expression of mitochondrial biogenesis markers PGC1α and MFN2 was affected and expression of TFAM and COX1 tended to be reduced in COPD compared to healthy myotubes upon EPS. Lipid peroxidation was increased and the expression of the antioxidant enzymes SOD2 and GPx4 was affected in COPD compared to healthy myotubes in response to EPS. Thus, we provide evidence of an impaired response of COPD muscle cells to contraction, which might be involved in the muscle weakness observed in patients with COPD.

The dominant-negative mitochondrial calcium uniporter subunit MCUb drives macrophage polarization during skeletal muscle regeneration

[Figure: see text].

Effects of hyperoxia and hypoxia on the proliferation of C2C12 myoblasts

Hyperoxic conditions are known to accelerate skeletal muscle regeneration after injuries. In the early phase of regeneration, macrophages invade the injured area and subsequently secrete various growth factors, which regulate myoblast proliferation and differentiation. Although hyperoxic conditions accelerate muscle regeneration, it is unknown whether this effect is indirectly mediated by macrophages. Here, using C2C12 cells, we show that not only hyperoxia but also hypoxia enhance myoblast proliferation directly, without accelerating differentiation into myotubes. Under hyperoxic conditions (95% O₂ + 5% CO₂), the cell membrane was damaged because of lipid oxidization, and a disrupted cytoskeletal structure, resulting in suppressed cell proliferation. However, a culture medium containing vitamin C (VC), an antioxidant, prevented this lipid oxidization and cytoskeletal disruption, resulting in enhanced proliferation in response to hyperoxia exposure of ≤4 h/day. In contrast, exposure to hypoxic conditions (95% N₂ + 5% CO₂) for ≤8 h/day enhanced cell proliferation. Hyperoxia did not promote cell differentiation into myotubes, regardless of whether the culture medium contained VC. Similarly, hypoxia did not accelerate cell differentiation. These results suggest that regardless of hyperoxia or hypoxia, changes in oxygen tension can enhance cell proliferation directly, but do not influence differentiation efficiency in C2C12 cells. Moreover, excess oxidative stress abrogated the enhancement of myoblast proliferation induced by hyperoxia. This research will contribute to basic data for applying the effects of hyperoxia or hypoxia to muscle regeneration therapy.

A Coupled Mechanobiological Model of Muscle Regeneration In Cerebral Palsy

Cerebral palsy is a neuromusculoskeletal disorder associated with muscle weakness, altered muscle architecture, and progressive musculoskeletal symptoms that worsen with age. Pathological changes at the level of the whole muscle have been shown; however, it is unclear why this progression of muscle impairment occurs at the cellular level. The process of muscle regeneration is complex, and the interactions between cells in the muscle milieu should be considered in the context of cerebral palsy. In this work, we built a coupled mechanobiological model of muscle damage and regeneration to explore the process of muscle regeneration in typical and cerebral palsy conditions, and whether a reduced number of satellite cells in the cerebral palsy muscle environment could cause the muscle regeneration cycle to lead to progressive degeneration of muscle. The coupled model consisted of a finite element model of a muscle fiber bundle undergoing eccentric contraction, and an agent-based model of muscle regeneration incorporating satellite cells, inflammatory cells, muscle fibers, extracellular matrix, fibroblasts, and secreted cytokines. Our coupled model simulated damage from eccentric contraction followed by 28 days of regeneration within the muscle. We simulated cyclic damage and regeneration for both cerebral palsy and typically developing muscle milieus. Here we show the nonlinear effects of altered satellite cell numbers on muscle regeneration, where muscle repair is relatively insensitive to satellite cell concentration above a threshold, but relatively sensitive below that threshold. With the coupled model, we show that the fiber bundle geometry undergoes atrophy and fibrosis with too few satellite cells and excess extracellular matrix, representative of the progression of cerebral palsy in muscle. This work uses in silico modeling to demonstrate how muscle degeneration in cerebral palsy may arise from the process of cellular regeneration and a reduced number of satellite cells.

Molecular cloning, expression, and functional features of IGF1 splice variants in sheep

Insulin-like growth factor 1 (IGF1), also known as somatomedin C, is essential for the regulation of animal growth and development. In many species, the IGF1 gene can be alternatively spliced into multiple transcripts, encoding different pre-pro-IGF1 proteins. However, the exact alternative splicing patterns of IGF1 and the sequence information of different splice variants in sheep are still unclear. In this study, four splice variants (class 1-Ea, class 1-Eb, class 2-Ea, and class 2-Eb) were obtained, but no IGF1 Ec, similar to that found in other species, was discovered. Bioinformatics analysis showed that the four splice variants shared the same mature peptide (70 amino acids) and possessed distinct signal peptides and E peptides. Tissue expression analysis indicated that the four splice variants were broadly expressed in all tested tissues and were most abundantly expressed in the liver. In most tissues and stages, the expression of class 1-Ea was highest, and the expression of other splice variants was low. Overall, levels of the four IGF1 splice variants at the fetal and lamb stages were higher than those at the adult stage. Overexpression of the four splice variants significantly increased fibroblast proliferation and inhibited apoptosis (P < 0.05). In contrast, silencing IGF1 Ea or IGF1 Eb with siRNA significantly inhibited proliferation and promoted apoptosis (P < 0.05). Among the four splice variants, class 1-Ea had a more evident effect on cell proliferation and apoptosis. In summary, the four ovine IGF1 splice variants have different structures and expression patterns and might have different biological functions.

Circular PPP1R13B RNA Promotes Chicken Skeletal Muscle Satellite Cell Proliferation and Differentiation via Targeting miR-9-5p

Skeletal muscle plays important roles in animal locomotion, metabolism, and meat production in farm animals. Current studies showed that non-coding RNAs, especially the circular RNA (circRNA) play an indispensable role in skeletal muscle development. Our previous study revealed that several differentially expressed circRNAs among fast muscle growing broilers (FMGB) and slow muscle growing layers (SMGL) may regulate muscle development in the chicken. In this study, a novel differentially expressed circPPP1R13B was identified. Molecular mechanism analysis indicated that circPPP1R13B targets miR-9-5p and negatively regulates the expression of miR-9-5p, which was previously reported to be an inhibitor of skeletal muscle development. In addition, circPPP1R13B positively regulated the expression of miR-9-5p target gene insulin like growth factor 2 mRNA binding protein 3 (IGF2BP3) and further activated the downstream insulin like growth factors (IGF)/phosphatidylinositol 3-kinase (PI3K)/AKT serine/threonine kinase (AKT) signaling pathway. The results also showed that the knockdown of circPPP1R13B inhibits chicken skeletal muscle satellite cells (SMSCs) proliferation and differentiation, and the overexpression of circPPP1R13B promotes the proliferation and differentiation of chicken SMSCs. Furthermore, the overexpression of circPPP1R13B could block the inhibitory effect of miR-9-5p on chicken SMSC proliferation and differentiation. In summary, our results suggested that circPPP1R13B promotes chicken SMSC proliferation and differentiation by targeting miR-9-5p and activating IGF/PI3K/AKT signaling pathway.

Comprehensive analysis of lncRNAs involved in skeletal muscle development in ZBED6-knockout Bama pigs

BACKGROUND

The mutation of insulin-like growth factor 2 (IGF2 mutation) that a single-nucleotide substitution (G→A) in the third intron of IGF2 abrogates the interaction with zinc finger BED-type containing 6 (ZBED6) and leads to increased muscle mass in pigs. IGF2 mutation knock-in (IGF2 KI) and ZBED6 knockout (ZBED6 KO) lead to changes in IGF2 expression and increase muscle mass in mice and pigs. Long noncoding RNAs (lncRNAs) may participate in numerous biological processes, including skeletal muscle development. However, the role of the ZBED6-lncRNA axis in skeletal muscle development is poorly characterized.

RESULTS

In this study, we assembled transcriptomes using RNA-seq data published in previous studies by our group and identified 11,408 known lncRNAs and 2269 potential lncRNAs in seven tissues, heart, longissimus dorsi, gastrocnemius muscle, liver, spleen, lung and kidney, of ZBED6 KO (lean mass model) and WT Bama pigs. ZBED6 affected the expression of 1570 lncRNAs (differentially expressed lncRNAs [DE-lncRNAs]; log2-fold change ≥ 1, nominal p-value ≤ 0.05) in the seven examined tissues. The expressed lncRNAs (FPKM > 0.1) exhibited tissue-specific patterns in WT pigs. Specifically, 3410 lncRNAs were expressed exclusively in only one tissue. Potential functions of lncRNAs were indirectly predicted by searching their target cis- and trans-regulated protein-coding genes. LncRNAs with tissue-specific expression influence numerous genes related to tissue functions. Weighted gene coexpression network analysis (WGCNA) of 1570 DE-lncRNAs between WT and ZBED6 KO pigs was used to define the following six lncRNA modules specific to different tissues: skeletal muscle, heart, lung, spleen, kidney and liver modules. Furthermore, by conjoint analysis of longissimus dorsi data (tissue-specific expression, muscle module and DE-lncRNAs) and ChIP-PCR revealed NONSUSG002145.1 (adjusted p-values = 0.044), which is coexpressed with the IGF2 gene and binding with ZBED6, may play important roles in ZBED6 KO pig skeletal muscle development.

CONCLUSIONS

These findings indicate that the identified lncRNAs may play essential roles in tissue function and regulate the mechanism of ZBED6 action in skeletal muscle development in pigs. To our knowledge, this is the first study describing lncRNAs in ZBED6 KO pigs. These results may open new research directions leading to a better understanding of the global functions of ZBED6 and of lncRNA functions in skeletal muscle development in pigs.

Creating stem cell-derived neuromuscular junctions in vitro

Recent development of novel therapies has improved mobility and quality of life for people suffering from inheritable neuromuscular disorders. Despite this progress, the majority of neuromuscular disorders are still incurable, in part due to a lack of predictive models of neuromuscular junction (NMJ) breakdown. Improvement of predictive models of a human NMJ would be transformative in terms of expanding our understanding of the mechanisms that underpin development, maintenance, and disease, and as a testbed with which to evaluate novel therapeutics. Induced pluripotent stem cells (iPSCs) are emerging as a clinically relevant and non‐invasive cell source to create human NMJs to study synaptic development and maturation, as well as disease modeling and drug discovery. This review will highlight the recent advances and remaining challenges to generating an NMJ capable of eliciting contraction of stem cell‐derived skeletal muscle in vitro. We explore the advantages and shortcomings of traditional NMJ culturing platforms, as well as the pioneering technologies and novel, biomimetic culturing systems currently in use to guide development and maturation of the neuromuscular synapse and extracellular microenvironment. Then, we will explore how this NMJ‐in‐a‐dish can be used to study normal assembly and function of the efferent portion of the neuromuscular arc, and how neuromuscular disease‐causing mutations disrupt structure, signaling, and function.

An insight on the impact of teleost whole genome duplication on the regulation of the molecular networks controlling skeletal muscle growth

Fish muscle growth is a complex process regulated by multiple pathways, resulting on the net accumulation of proteins and the activation of myogenic progenitor cells. Around 350–320 million years ago, teleost fish went through a specific whole genome duplication (WGD) that expanded the existent gene repertoire. Duplicated genes can be retained by different molecular mechanisms such as subfunctionalization, neofunctionalization or redundancy, each one with different functional implications. While the great majority of ohnolog genes have been identified in the teleost genomes, the effect of gene duplication in the fish physiology is still not well characterized. In the present study we studied the effect of WGD on the transcription of the duplicated components controlling muscle growth. We compared the expression of lineage-specific ohnologs related to myogenesis and protein balance in the fast-skeletal muscle of pacus (Piaractus mesopotamicus—Ostariophysi) and Nile tilapias (Oreochromis niloticus—Acanthopterygii) fasted for 4 days and refed for 3 days. We studied the expression of 20 ohnologs and found that in the great majority of cases, duplicated genes had similar expression profiles in response to fasting and refeeding, indicating that their functions during growth have been conserved during the period after the WGD. Our results suggest that redundancy might play a more important role in the retention of ohnologs of regulatory pathways than initially thought. Also, comparison to non-duplicated orthologs showed that it might not be uncommon for the duplicated genes to gain or loss new regulatory elements simultaneously. Overall, several of duplicated ohnologs have similar transcription profiles in response to pro-growth signals suggesting that evolution tends to conserve ohnolog regulation during muscle development and that in the majority of ohnologs related to muscle growth their functions might be very similar.

Characterization of MRF genes and their tissue distributions and analysis of the effects of starvation and refeeding on the expression of these genes in Acipenser dabryanus muscle

The purpose of the study was to clone the sequences of myogenic regulatory factors in Acipenser dabryanus and explore the changes in their expression during starvation and refeeding in A. dabryanus muscle. One hundred twenty fish (60.532 ± 0.284 g) were randomly assigned to four groups (fasted for 0, 3, 7 or 14 d and then refed for 14 d). Our predictions showed that the coding sequences of myod1, myf5, myog and myf6 in A. dabryanus encoded 275, 248, 248 and 243 amino acids, respectively, and the expression of the four genes was the highest in muscle. During fasting, the expression of myod1 in muscle was significantly decreased in the 14 d group. The expressions of myf5 and myf6 were increased significantly at first and then decreased with prolonged starvation time. The expression of myog in the 14 d group was significantly decreased compared with other groups (P < 0.05). During refeeding, the highest values of myod1 and myf6 expression were found in the 3 d group (P < 0.05).The expressions of myf5 and myog in 0 d and 3 d group were significantly higher than those in 7 d and 14 d group (P < 0.05). These results indicate that myogenic regulatory factors (MRFs) play important roles in muscle growth and development in A. dabryanus. The inhibition of long-term starvation (14 d) on the expression of myogenic regulatory factors is probably one of the reasons why it can not achieve full compensation for growth.

Genome-wide DNA methylation profiles provide insight into epigenetic regulation of red and white muscle development in Chinese perch Siniperca chuatsi

Fish skeletal muscles are composed of spatially well-separated fiber types, namely, red and white muscles with different physiological functions and metabolism. To compare the DNA methylation profiles of the two types of muscle tissues and identify potential candidate genes for the muscle growth and development under epigenetic regulation, genome-wide DNA methylation of the red and white muscle in Chinese perch Siniperca chuatsi were comparatively analyzed using bisulfate sequencing methods. An average of 0.9 billion 150-bp paired-end reads were obtained, of which 86% were uniquely mapped to the genome. Methylation mostly occurred at CG sites at a ratio of 94.43% in the red muscle and 93.16% in the white muscle. The mean methylation levels at C-sites were 5.95% in red muscle and 5.83% in white muscle, whereas the mean methylation levels of CG, CHG, and CHH were 73.23%, 0.62%, and 0.67% in red muscle, and 71.01%, 0.62%, and 0.67% in white muscle, respectively. A total of 4192 differentially methylated genes (DMGs) were identified significantly enriched in cell signaling pathways related to skeletal muscle differentiation and growth. Various muscle-related genes, including myosin gene isoforms and regulatory factors, are differentially methylated in the promoter region between the red and white muscles. Further analysis of the transcriptional expression of these genes showed that the muscle regulatory factors (myf5, myog, pax3, pax7, and twitst2) and myosin genes (myh10, myh16, myo18a, myo7a, myo9a, and myl3) were differentially expressed between the two kinds of muscles, consistent with the DNA methylation analysis results. ELISA assays confirmed that the level of 5mC in red muscle was significantly higher than in white muscle (P < 0.05). The RT-qPCR assays revealed that the expression levels of the three DNA methylation transferase (dnmt) subtypes, dnmt1, dnmt3ab, and dnmt3bb1, were significantly higher in red muscle than in white muscle. The higher DNA methylation levels in the red muscle may result from higher DNA methylation transferase expression in the red muscles. Thus, this study might provide a theoretical foundation to better understand epigenetic regulation in the growth and development of red and white muscles in animals, at least in Chinese perch fish.

Low-Dose Acrolein, an Endogenous and Exogenous Toxic Molecule, Inhibits Glucose Transport via an Inhibition of Akt-Regulated GLUT4 Signaling in Skeletal Muscle Cells

Urinary acrolein adduct levels have been reported to be increased in both habitual smokers and type-2 diabetic patients. The impairment of glucose transport in skeletal muscles is a major factor responsible for glucose uptake reduction in type-2 diabetic patients. The effect of acrolein on glucose metabolism in skeletal muscle remains unclear. Here, we investigated whether acrolein affects muscular glucose metabolism in vitro and glucose tolerance in vivo. Exposure of mice to acrolein (2.5 and 5 mg/kg/day) for 4 weeks substantially increased fasting blood glucose and impaired glucose tolerance. The glucose transporter-4 (GLUT4) protein expression was significantly decreased in soleus muscles of acrolein-treated mice. The glucose uptake was significantly decreased in differentiated C2C12 myotubes treated with a non-cytotoxic dose of acrolein (1 μM) for 24 and 72 h. Acrolein (0.5–2 μM) also significantly decreased the GLUT4 expression in myotubes. Acrolein suppressed the phosphorylation of glucose metabolic signals IRS1, Akt, mTOR, p70S6K, and GSK3α/β. Over-expression of constitutive activation of Akt reversed the inhibitory effects of acrolein on GLUT4 protein expression and glucose uptake in myotubes. These results suggest that acrolein at doses relevant to human exposure dysregulates glucose metabolism in skeletal muscle cells and impairs glucose tolerance in mice.

Stimulation of myogenesis by ascorbic acid and capsaicin

Myogenesis is a complex process regulated by several factors. This study evaluated the functional interaction between vitamin C and a high dose of capsaicin (a potential endoplasmic reticulum (ER) stress inducer) on myogenesis. After the induction of differentiation, treatment with ascorbic acid or ascorbic acid phosphate (AsAp) alone had minimal effects on myogenesis in C2C12 cells. However, treatment with capsaicin (300 μM) in undifferentiated C2C12 cells increased the expression levels of genes related to ER stress as well as oxidative stress. Myogenesis was effectively enhanced in C2C12 cells treated with a combination of capsaicin (300 μM) for one day before differentiation stimulation and AsAp for four days post-differentiation; subsequently, thick and long myotubes formed, and the expression levels of myosin heavy chain (MYH) 1/2 and Myh1, Myh4, and Myh7 increased. Considering that mild ER stress stimulates myogenesis, AsAp may elicit myogenesis through the alleviation of oxidative stress-induced negative effects in capsaicin-pretreated cells. The enhanced expression of Myh1 and Myh4 coincided with the expression of Col1a1, a type I collagen, suggesting that the fine-tuning of the myogenic cell microenvironment is responsible for efficient myogenesis. Our results indicate that vitamin C is a potential stimulator of myogenesis in cells, depending on the cell context.

Programmed death-1 promotes contused skeletal muscle regeneration by regulating Treg cells and macrophages

Immune cells are involved in skeletal muscle regeneration. The mechanism by which Treg cells are involved in the regeneration of injured skeletal muscle is still unclear. The purpose of this study was to explore the role of programmed death-1 in contused skeletal muscle regeneration, and to clarify the regulation of programmed death-1 on Treg cell generation and macrophage polarization, in order to deepen our understanding of the relationship between the immune system and injured skeletal muscle regeneration. The results show that programmed death-1 knockdown reduced the number of Treg cells and impaired contused skeletal muscle regeneration compared with those of wild-type mice. The number of pro-inflammatory macrophages in the contused skeletal muscle of programmed death-1 knockout mice increased, and the expression of pro-inflammatory factors and oxidative stress factors increased, while the number of anti-inflammatory macrophages and the expression of anti-inflammatory factors, antioxidant stress factors, and muscle regeneration-related factors decreased. These results suggest that programmed death-1 can promote contused skeletal muscle regeneration by regulating Treg cell generation and macrophage polarization.

Activation of IGF-1 pathway and suppression of atrophy related genes are involved in Epimedium extract (icariin) promoted C2C12 myotube hypertrophy

The regenerative effect of Epimedium and its major bioactive flavonoid icariin (ICA) have been documented in traditional medicine, but their effect on sarcopenia has not been evaluated. The aim of this study was to investigate the effects of Epimedium extract (EE) on skeletal muscle as represented by differentiated C2C12 cells. Here we demonstrated that EE and ICA stimulated C2C12 myotube hypertrophy by activating several, including IGF-1 signal pathways. C2C12 myotube hypertrophy was demonstrated by enlarged myotube and increased myosin heavy chains (MyHCs). In similar to IGF-1, EE/ICA activated key components of the IGF-1 signal pathway, including IGF-1 receptor. Pre-treatment with IGF-1 signal pathway specific inhibitors such as picropodophyllin, LY294002, and rapamycin attenuated EE induced myotube hypertrophy and MyHC isoform overexpression. In a different way, EE induced MHyC-S overexpression can be blocked by AMPK, but not by mTOR inhibitor. On the level of transcription, EE suppressed myostatin and MRF4 expression, but did not suppress atrogenes MAFbx and MuRF1 like IGF-1 did. Differential regulation of MyHC isoform and atrogenes is probably due to inequivalent AKT and AMPK phosphorylation induced by EE and IGF-1. These findings suggest that EE/ICA stimulates pathways partially overlapping with IGF-1 signaling pathway to promote myotube hypertrophy.

A novel lncRNA promotes myogenesis of bovine skeletal muscle satellite cells via PFN1-RhoA/Rac1

Myogenesis, the process of skeletal muscle formation, is a highly coordinated multistep biological process. Accumulating evidence suggests that long non-coding RNAs (lncRNAs) are emerging as a gatekeeper in myogenesis. Up to now, most studies on muscle development-related lncRNAs are mainly focussed on humans and mice. In this study, a novel muscle highly expressed lncRNA, named lnc23, localized in nucleus, was found differentially expressed in different stages of embryonic development and myogenic differentiation. The knockdown and over-expression experiments showed that lnc23 positively regulated the myogenic differentiation of bovine skeletal muscle satellite cells. Then, TMT 10-plex labelling quantitative proteomics was performed to screen the potentially regulatory proteins of lnc23. Results indicated that lnc23 was involved in the key processes of myogenic differentiation such as cell fusion, further demonstrated that down-regulation of lnc23 may inhibit myogenic differentiation by reducing signal transduction and cell fusion among cells. Furthermore, RNA pulldown/LC-MS and RIP experiment illustrated that PFN1 was a binding protein of lnc23. Further, we also found that lnc23 positively regulated the protein expression of RhoA and Rac1, and PFN1 may negatively regulate myogenic differentiation and the expression of its interacting proteins RhoA and Rac1. Hence, we support that lnc23 may reduce the inhibiting effect of PFN1 on RhoA and Rac1 by binding to PFN1, thereby promoting myogenic differentiation. In short, the novel identified lnc23 promotes myogenesis of bovine skeletal muscle satellite cells via PFN1-RhoA/Rac1.

Dietary isoleucine improved flesh quality, muscle antioxidant capacity, and muscle growth associated with AKT/TOR/S6K1 and AKT/FOXO3a signaling in hybrid bagrid catfish (Pelteobagrus vachelli♀ × Leiocassis longirostris♂)

BACKGROUND

Muscle is the complex and heterogeneous tissue, which comprises the primary edible part of the trunk of fish and mammals. Previous studies have shown that dietary isoleucine (Ile) exerts beneficial effects on growth in aquatic animals. However, there were limited studies regarding the benefits of Ile on fish muscle and their effects on flesh quality and muscle growth. Thus, this study was conducted to explore whether dietary Ile had affected flesh quality and muscle growth in hybrid bagrid catfish (Pelteobagrus vachelli♀ × Leiocassis longirostris♂).

METHODS

A total of 630 hybrid fish, with an initial average body weight of 33.11 ± 0.09 g, were randomly allotted into seven experimental groups with three replicates each, and respectively fed seven diets with 5.0, 7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 g Ile/kg diets for 8 weeks.

RESULTS

In the present study, we demonstrated that Ile significantly: (1) increased muscle protein and lipid contents and the frequency distribution of myofibers with ≤ 20 μm and ≥ 50 μm of diameter; (2) improved pH value, shear force, cathepsin B and L activities, hydroxyproline content, resilience, cohesiveness, and decreased cooking loss, lactate content, hardness, springiness, gumminess, and chewiness; (3) decreased reactive oxygen species (ROS), malondialdehyde (MDA), and protein carbonyl (PC) contents, GCLC and Keap1 mRNA levels, and up-regulated CuZnSOD, CAT, GPX1a, GST, and Nrf2 mRNA levels; (4) up-regulated the insulin-like growth factor 1, 2 (IGF-1, IGF-2), insulin-like growth factor 1 receptor (IGF-1R), proliferating cell nuclear antigen (PCNA), Myf5, Myod, Myog, Mrf4, and MyHC mRNA levels, and decreased MSTN mRNA level; (5) increased muscle protein deposition by activating AKT-TOR-S6K1 and AKT-FOXO3a signaling pathways.

CONCLUSION

These results revealed that dietary Ile improved flesh quality, which might be due to increasing nutritional content, physicochemical, texture parameters, and antioxidant ability; promoting muscle growth by affecting myocytes hyperplasia and hypertrophy, and muscle protein deposition associated with protein synthesis and degradation signaling pathways. Finally, the quadratic regression analysis of chewiness, ROS, and protein contents against dietary Ile levels suggested that the optimal dietary Ile levels for hybrid bagrid catfish was estimated to be 14.19, 12.36, and 12.78 g/kg diet, corresponding to 36.59, 31.87, and 32.96 g/kg dietary protein, respectively.

IGF2 deficiency causes mitochondrial defects in skeletal muscle

Exercise training improves muscle fitness in many aspects, including induction of mitochondrial biogenesis and maintenance of mitochondrial dynamics. The insulin-like growth factors were recently proposed as key regulators of myogenic factors to regulate muscle development. The present study aimed to investigate the physical exercise impact on insulin-like growth factor 2 (IGF2) and analyzed its functions on skeletal muscle cells in vitro. Using online databases, we stated that IGF2 was relatively highly expressed in skeletal muscle cells and increased after exercise training. Then, IGF2 deficiency in myotubes from C2C12 and primary skeletal muscle cells (PMSCs) led to impaired mitochondrial function, reduced mitochondria-related protein content, and decreased mitochondrial biogenesis. Furthermore, we explored the possible regulatory pathway and found that mitochondrial regulation in skeletal muscle cells might occur through IGF2-Sirtuin 1 (SIRT1)-peroxisome proliferator-activated receptor-γ co-activator-1α (PGC1α) signaling pathway. Therefore, the present study first demonstrated the relationship between IGF2 and mitochondria in skeletal muscle.

Firearms-related skeletal muscle trauma: pathophysiology and novel approaches for regeneration

One major cause of traumatic injury is firearm-related wounds (i.e., ballistic trauma), common in both civilian and military populations, which is increasing in prevalence and has serious long-term health and socioeconomic consequences worldwide. Common primary injuries of ballistic trauma include soft-tissue damage and loss, haemorrhage, bone fracture, and pain. The majority of injuries are of musculoskeletal origin and located in the extremities, such that skeletal muscle offers a major therapeutic target to aid recovery and return to normal daily activities. However, the underlying pathophysiology of skeletal muscle ballistic trauma remains poorly understood, with limited evidence-based treatment options. As such, this review will address the topic of firearm-related skeletal muscle injury and regeneration. We first introduce trauma ballistics and the immediate injury of skeletal muscle, followed by detailed coverage of the underlying biological mechanisms involved in regulating skeletal muscle dysfunction following injury, with a specific focus on the processes of muscle regeneration, muscle wasting and vascular impairments. Finally, we evaluate novel approaches for minimising muscle damage and enhancing muscle regeneration after ballistic trauma, which may have important relevance for primary care in victims of violence.

Interactions between Growth of Muscle and Stature: Mechanisms Involved and Their Nutritional Sensitivity to Dietary Protein: The Protein-Stat Revisited

Childhood growth and its sensitivity to dietary protein is reviewed within a Protein-Stat model of growth regulation. The coordination of growth of muscle and stature is a combination of genetic programming, and of two-way mechanical interactions involving the mechanotransduction of muscle growth through stretching by bone length growth, the core Protein-Stat feature, and the strengthening of bone through muscle contraction via the mechanostat. Thus, growth in bone length is the initiating event and this is always observed. Endocrine and cellular mechanisms of growth in stature are reviewed in terms of the growth hormone-insulin like growth factor-1 (GH-IGF-1) and thyroid axes and the sex hormones, which together mediate endochondral ossification in the growth plate and bone lengthening. Cellular mechanisms of muscle growth during development are then reviewed identifying (a) the difficulties posed by the need to maintain its ultrastructure during myofibre hypertrophy within the extracellular matrix and the concept of muscle as concentric "bags" allowing growth to be conceived as bag enlargement and filling, (b) the cellular and molecular mechanisms involved in the mechanotransduction of satellite and mesenchymal stromal cells, to enable both connective tissue remodelling and provision of new myonuclei to aid myofibre hypertrophy and (c) the implications of myofibre hypertrophy for protein turnover within the myonuclear domain. Experimental data from rodent and avian animal models illustrate likely changes in DNA domain size and protein turnover during developmental and stretch-induced muscle growth and between different muscle fibre types. Growth of muscle in male rats during adulthood suggests that "bag enlargement" is achieved mainly through the action of mesenchymal stromal cells. Current understanding of the nutritional regulation of protein deposition in muscle, deriving from experimental studies in animals and human adults, is reviewed, identifying regulation by amino acids, insulin and myofibre volume changes acting to increase both ribosomal capacity and efficiency of muscle protein synthesis via the mechanistic target of rapamycin complex 1 (mTORC1) and the phenomenon of a "bag-full" inhibitory signal has been identified in human skeletal muscle. The final section deals with the nutritional sensitivity of growth of muscle and stature to dietary protein in children. Growth in length/height as a function of dietary protein intake is described in the context of the breastfed child as the normative growth model, and the "Early Protein Hypothesis" linking high protein intakes in infancy to later adiposity. The extensive paediatric studies on serum IGF-1 and child growth are reviewed but their clinical relevance is of limited value for understanding growth regulation; a role in energy metabolism and homeostasis, acting with insulin to mediate adiposity, is probably more important. Information on the influence of dietary protein on muscle mass per se as opposed to lean body mass is limited but suggests that increased protein intake in children is unable to promote muscle growth in excess of that linked to genotypic growth in length/height. One possible exception is milk protein intake, which cohort and cross-cultural studies suggest can increase height and associated muscle growth, although such effects have yet to be demonstrated by randomised controlled trials.

Regenerative medicine for skeletal muscle loss: a review of current tissue engineering approaches

Skeletal muscle is capable of regeneration following minor damage, more significant volumetric muscle loss (VML) however results in permanent functional impairment. Current multimodal treatment methodologies yield variable functional recovery, with reconstructive surgical approaches restricted by limited donor tissue and significant donor morbidity. Tissue-engineered skeletal muscle constructs promise the potential to revolutionise the treatment of VML through the regeneration of functional skeletal muscle. Herein, we review the current status of tissue engineering approaches to VML; firstly the design of biocompatible tissue scaffolds, including recent developments with electroconductive materials. Secondly, we review the progenitor cell populations used to seed scaffolds and their relative merits. Thirdly we review in vitro methods of scaffold functional maturation including the use of three-dimensional bioprinting and bioreactors. Finally, we discuss the technical, regulatory and ethical barriers to clinical translation of this technology. Despite significant advances in areas, such as electroactive scaffolds and three-dimensional bioprinting, along with several promising in vivo studies, there remain multiple technical hurdles before translation into clinically impactful therapies can be achieved. Novel strategies for graft vascularisation, and in vitro functional maturation will be of particular importance in order to develop tissue-engineered constructs capable of significant clinical impact.

Molecular Mechanisms Regulating Muscle Plasticity in Fish

Growth rates in fish are largely dependent on genetic and environmental factors, of which the latter can be highly variable throughout development. For this reason, muscle growth in fish is particularly dynamic as muscle structure and function can be altered by environmental conditions, a concept referred to as muscle plasticity. Myogenic regulatory factors (MRFs) like Myogenin, MyoD, and Pax7 control the myogenic mechanisms regulating quiescent muscle cell maintenance, proliferation, and differentiation, critical processes central for muscle plasticity. This review focuses on recent advancements in molecular mechanisms involving microRNAs (miRNAs) and DNA methylation that regulate the expression and activity of MRFs in fish. Findings provide overwhelming support that these mechanisms are significant regulators of muscle plasticity, particularly in response to environmental factors like temperature and nutritional challenges. Genetic variation in DNA methylation and miRNA expression also correlate with variation in body weight and growth, suggesting that genetic markers related to these mechanisms may be useful for genomic selection strategies. Collectively, this knowledge improves the understanding of mechanisms regulating muscle plasticity and can contribute to the development of husbandry and breeding strategies that improve growth performance and the ability of the fish to respond to environmental challenges.

Effect of Photobiomodulation in Lipopolysaccharide-Treated Myoblasts

Objective: To evaluate the effect of photobiomodulation (PBM) on cell viability, synthesis of nitric oxide (NO), and interleukin (IL)-6 inflammatory cytokine production in myoblasts cultured in the presence of lipopolysaccharides (LPSs). Methods: C2C12 myoblasts were treated with LPS and PBM using different parameters (wavelength: 780 nm; beam spot: 0.04 cm²; power output: 10 or 40 mW; energy density: 5 or 20 J/cm²; and 20-sec exposure time). Nonirradiated cells were used to the control group. Results: An increase in cell viability was found in both LPS groups in comparison with the control. PBM with the higher power output (40 mW) induced a reduction in cell viability. PBM also modulated the synthesis of NO in the myoblasts, but did not alter the expression of IL-6. Conclusions: Based on these findings, PBM is capable of modulating the cell viability and the production of NO in LPS-treated myoblasts and it is, therefore, a possible tool for the treatment of muscle injury caused by infection.

Downregulated miR-204 Promotes Skeletal Muscle Regeneration

Skeletal muscle is the most abundant and a highly plastic tissue of the mammals, especially when it comes to regenerate after trauma, but there is limited information about the mechanism of muscle repair and its regeneration. In the present study, we found that miR-204 is downregulated after skeletal muscle injury. In vitro experiments showed that over-expression of miR-204 by transfecting with miR-204 mimics suppressed C2C12 cell proliferation, migration, and blocked subsequent differentiation, whereas inhibition of miR-204 by transfecting with miR-204 inhibitor showed the converse effects. Furthermore, through the dual luciferase reporter system, we demonstrated that miR-204 can target the 3'UTR regions of Pax7, IGF1, and Mef2c and inhibit their expression. Taken together, our results suggest that Pax7, IGF1, and Mef2c are the target genes of miR-204 in the process of myoblasts proliferation, cell migration, and differentiation, respectively, and may contribute to mouse skeletal muscle regeneration. Our results may provide new ideas and references for the skeletal muscle study and may also provide therapeutic strategies of skeletal muscle injury.

Effects of photobiomodulation and swimming on gene expression in rats with the tibialis anterior muscle injury

The aim of the present study was to evaluate the effects of photobiomodulation (low-level laser therapy (LLLT)) and aquatic exercise on the expression of genes related to muscle regeneration in rats. Wistar rats were divided into five groups: control group (n = 15), non-treated injury group (n = 15), injury+LLLT group (n = 15), injury+aquatic exercise group (n = 15), and injury+LLLT+aquatic exercise group (n = 15). Cryoinjury was performed on the belly of the tibialis anterior (TA) muscle. LLLT was performed daily with an AlGaAs laser (830 nm; beam spot of 0.0324 cm², output power of 100 mW, energy density of 180 J/cm², and 58-s exposure time). Animals were euthanized at 7, 14, and 21 days. The TA muscles were removed for gene expression analysis of TGF-β, Myogenin, and MyoD. The results were statistically analyzed at a significance level of 5%. The cryoinjury increased the expression of genes related to muscle regeneration-MyoD, Myogenin, and TGF-β-compared to the control group (p < 0.05); the photobiomodulation increased the expression of these genes at day 7 (p < 0.05), decreasing until day 21; and the aquatic exercise increases the expression of the three genes over time. When the two treatments were combined, the expression of the analyzed genes also increased over time. In summary, the results of our study suggest that photobiomodulation (LLLT), when applied alone in cryoinjury, is able to increase the gene expression of MyoD, Myogenin, and TGF-β at the acute phase, while when combined with aquatic exercises, there is an increase in expression of these genes specially at the long-term treatment.

siRNA knockdown of alanine aminopeptidase impairs myoblast proliferation and differentiation

A large number of intracellular proteins are degraded by the ubiquitin-proteasome system, one of the major protein degradation pathways. It produces peptides of several different sizes through protein degradation, and these peptides are rapidly degraded into free amino acids by various intracellular aminopeptidases. Previously, we reported that the activity of proteasomes and aminopeptidases in the proteolysis pathway are necessary for myoblast proliferation and differentiation. However, the detailed function of intracellular aminopeptidases in myoblast proliferation and differentiation has not yet been elucidated. In this study, we focused on alanine aminopeptidase (APN) and investigated the function of APN in C2C12 myoblast proliferation and differentiation. In myoblasts and myotubes, APN was mainly localized in the cell membrane as well as expressed at low levels in the cytoplasm and nucleus. The reduction of the APN enzymatic activity impaired the cell cycle progression in C2C12 myoblasts. In addition, apoptosis was induced after APN-knockdown. Finally, myogenic differentiation was also delayed in the APN-suppressed myoblasts. These findings indicate that APN is required for myoblast proliferation and differentiation.

Genome-wide identification and analysis of long noncoding RNAs in longissimus muscle tissue from Kazakh cattle and Xinjiang brown cattle

Objective

In recent years, lncRNAs have been identified in many species, and some of them have been shown to play important roles in muscle development and myogenesis. However, the differences in lncRNAs between Kazakh cattle and Xinjiang brown cattle remain undefined; therefore, we aimed to confirm whether lncRNAs are differentially expressed in the longissimus dorsi between these two types of cattle and whether differentially expressed lncRNAs regulate muscle differentiation.

Methods

We used RNA-seq technology to identify lncRNAs in longissimus muscles from these cattle. The expression of lncRNAs were analyzed using StringTie (1.3.1) in terms of the FPKM values of the encoding genes. The differential expression of the transcripts in the two samples were analyzed using the DESeq R software package. The resulting FDR was controlled by the Benjamini and Hochberg's approach. KOBAS software was utilized to measure the expression of different genes in KEGG pathways. We randomly selected eight lncRNA genes and validated them by RT-qPCR.

Results

We found that 182 lncRNA transcripts, including 102 upregulated and 80 downregulated transcripts, were differentially expressed between Kazakh cattle and Xinjiang brown cattle. The results of RT-qPCR were consistent with the sequencing results. Enrichment analysis and functional annotation of the target genes revealed that the differentially expressed lncRNAs were associated with the MAPK, Ras and PI3k/Akt signaling pathways. We also constructed a lncRNA/mRNA coexpression network for the PI3k/Akt signaling pathway.

Conclusion

Our study provides insights into cattle muscle-associated lncRNAs and will contribute to a more thorough understanding of the molecular mechanism underlying muscle growth and development in cattle.

The Role of Incubation Conditions in the Onset of Avian Myopathies

White striping, wooden breast, and spaghetti muscle have become common myopathies in broilers worldwide. Several research reports have indicated that the origin of these lesions is metabolic disorders. These failures in normal metabolism can start very early in life, and suboptimal incubation conditions may trigger some of the key alterations on muscle metabolism. Incubation conditions affect the development of muscle and can be associated with the onset of myopathies. A series of experiments conducted with broilers, turkeys, and ducks are discussed to overview primary information showing the main changes in breast muscle histomorphology, metabolism, and physiology caused by suboptimal incubation conditions. These modifications may be associated with current myopathies. Those effects of incubation on myopathy occurrence and severity have also been confirmed at slaughter age. The impact of egg storage, temperature profiles, oxygen concentrations, and time of hatch have been evaluated. The effects have been observed in diverse species, genetic lines, and both genders. Histological and muscle evaluations have detected that myopathies could be induced by extended hypoxia and high temperatures, and those effects depend on the genetic line. Thus, these modifications in muscle metabolic responses may make hatchlings more susceptible to develop myopathies during grow out due to thermal stress, high-density diets, and fast growth rates.

Increased expression of IGF-1Ec with increasing colonic polyp dysplasia and colorectal cancer

PURPOSE

IGF-1Ec is an isoform of Insulin-like growth factor 1 (IGF-1) and has recently been identified to be overexpressed in cancers including prostate and neuroendocrine tumours. The aim of this paper is to investigate the expression of IGF-1Ec in colorectal cancer and polyps compared to normal colon tissues and its association with recurrent disease using semi-quantitative immunohistochemistry.

METHODS

Immunohistochemistry for IGF-1Ec expression was performed for colorectal cancer, colorectal polyps and normal colonic tissues. The quantification of IGF-1Ec expression was performed with the use of Image J software and the IHC profiler plugin. Following ethics approval from the National Research Ethics Service (Reference 11/LO/1521), clinical information including recurrent disease on follow-up was collected for patients with colorectal cancer.

RESULTS

Immunohistochemistry was performed in 16 patients with colorectal cancer and 11 patients with colonic polyps and compared to normal colon tissues and prostate adenocarcinoma (positive control) tissues. Significantly increased expression of IGF-1Ec was demonstrated in colorectal cancer (p < 0.001) and colorectal polyps (p < 0.05) compared to normal colonic tissues. Colonic adenomas with high-grade dysplasia had significantly higher expression of IGF-1Ec compared to low-grade dysplastic adenomas (p < 0.001). Colorectal cancers without lymph node metastases at the time of presentation had significantly higher IGF-1Ec expression compared to lymph node-positive disease (p < 0.05). No correlation with recurrent disease was identified with IGF-1Ec expression.

CONCLUSION

IGF-1Ec is significantly overexpressed in colorectal cancer and polyps compared to normal colon tissues offering a potential target to improve colonoscopic identification of colorectal polyps and cancer and intraoperative identification of colorectal tumours.

The Temporomandibular Joint: A Critical Review of Life-Support Functions, Development, Articular Surfaces, Biomechanics and Degeneration

The temporomandibular joint is a highly conserved articulation because it promotes survival and propagation via the essential functions of mastication, communication, and routine mating success (dentofacial esthetics). The temporomandibular joint is a unique secondary joint formed between the endochondral temporal bone and the mandibular secondary condylar cartilage via Indian hedgehog and bone morphogenetic protein signaling that is closely related to ear development. A dynamic epigenetic environment is provided by Spry1 and Spry2 genetic induction of the lateral pterygoid and temporalis muscles. Mechanical loading of the condylar periosteum during fetal development produces a superficial layer of fibrocartilage that separates from the condyle to form the interposed temporomandibular joint disc. The articular surfaces of the condyle and fossa are dynamically modified periosteum that has healing and regenerative capability. This unique tissue is composed of a superficial fibrous layer (synovial surface) with an underlying proliferative (cambium) layer that produces a cushioning layer of fibrocartilage which subsequently forms bone. Prior to occlusion of the first primary (deciduous) molars at about 16 months, facial development is dominated by primary genetic mechanisms. After achieving posterior functional occlusion, biomechanics enhances temporomandibular joint maturation, and assumes control of facial growth, development and adaptation. Concurrently, hypothalamus control of musculoskeletal physiology shifts from insulin-like growth factor IGF2 to IGF1, which affects bone via muscular loading (biomechanics). Three layers of temporomandibular joint fibrocartilage are resistant to heavy functional loading, but parafunctional clenching may result in degeneration that is first manifest as trabecular sclerosis of the mandibular condyle.

Preserved Capacity for Adaptations in Strength and Muscle Regulatory Factors in Elderly in Response to Resistance Exercise Training and Deconditioning

Aging is related to an inevitable loss of muscle mass and strength. The mechanisms behind age-related loss of muscle tissue are not fully understood but may, among other things, be induced by age-related differences in myogenic regulatory factors. Resistance exercise training and deconditioning offers a model to investigate differences in myogenic regulatory factors that may be important for age-related loss of muscle mass and strength. Nine elderly (82 ± 7 years old) and nine young, healthy persons (22 ± 2 years old) participated in the study. Exercise consisted of six weeks of resistance training of the quadriceps muscle followed by eight weeks of deconditioning. Muscle biopsy samples before and after training and during the deconditioning period were analyzed for MyoD, myogenin, insulin-like growth-factor I receptor, activin receptor IIB, smad2, porin, and citrate synthase. Muscle strength improved with resistance training by 78% (95.0 ± 22.0 kg) in the elderly to a similar extent as in the young participants (83.5%; 178.2 ± 44.2 kg) and returned to baseline in both groups after eight weeks of deconditioning. No difference was seen in expression of muscle regulatory factors between elderly and young in response to exercise training and deconditioning. In conclusion, the capacity to gain muscle strength with resistance exercise training in elderly was not impaired, highlighting this as a potent tool to combat age-related loss of muscle function, possibly due to preserved regulation of myogenic factors in elderly compared with young muscle.

Stimulating Factors and Origins of Precursor Cells in Traumatic Heterotopic Ossification Around the Temporomandibular Joint in Mice

The contributing factors and the origins of precursor cells in traumatic heterotopic ossification around the temporomandibular joint (THO-TMJ), which causes obvious restriction of mouth opening and maxillofacial malformation, remain unclear. In this study, our findings demonstrated that injured chondrocytes in the condylar cartilage, but not osteoblasts in the injured subchondral bone, played definite roles in the development of THO-TMJ in mice. Injured condylar chondrocytes without articular disc reserves might secrete growth factors, such as IGF1 and TGFβ2, that stimulate precursor cells, such as endothelial cells and muscle-derived cells, to differentiate into chondrocytes or osteoblasts and induce THO-TMJ. Preserved articular discs can alleviate the pressure on the injured cartilage and inhibit the development of THO-TMJ by inhibiting the secretion of these growth factors from injured chondrocytes. However, the exact molecular relationships among trauma, the injured condylar cartilage, growth factors such as TGFβ2, and pressure need to be explored in detail in the future.

[Anti-diabetic effect of ethanol extract of Cyclolepis genistoides D. Don (Palo azul), made in Paraguay]

Extract of Cyclolepis genistoides D. Don (vernacular name Palo azul; Palo) are traditionally consumed in the Republic of Paraguay in South America for the treatment of diabetes and kidney disease, and is sold in Japan as dietary supplement. This study aimed to elucidate the mechanism of anti-diabetes activity of Palo, especially focused on insulin resistance. Palo promoted adipocytes differentiation and regulated adipokine profiles in 3T3-L1 adipocytes by modulation of PPARγ, a major regulator of adipose differentiation. Human adipocyte showed almost similar profile with 3T3-L1 against Palo treatment. Furthermore, Palo treatment (250 or 1000 mg/kg) was performed with C57BL/6J mice for 14 weeks, being fed high-fat-diet (HFD60) simultaneously. Palo 250 mg/kg exhibited a tendency to decrease subcutaneous adipose volume along with increase of PPARγ and its target, adiponectin mRNA expression. In addition, as the other insulin targeted cell, effect on muscle differentiation was examined. Palo increased differentiation of C2C12 mouse muscle myoblasts by increase of IGF-1, myogenin, and myosine heavy chain (MHC) as well as 5'-AMP-activated protein kinase (AMPK) activation. Palo subsequently promoted myotube formation under differentiation condition. From the above, it was clarified that Palo acts variously on the differentiation and maturation of both adipocytes and muscle cells, and from the viewpoint of the regulatory mechanism for adipocytes, PPARγ-inducing action was shown to be a mechanism that acts across species.

Isolation and Culture of Quiescent Skeletal Muscle Satellite Cells

It has been shown that freshly isolated satellite cells from adult muscle constitute a stem cell-like population that exhibits more efficient engraftment and self-renewal activity in regenerating muscle than myoblast. Thus, purification of pure populations of quiescent satellite cells from adult skeletal muscle is highly necessary, not only for understanding the biology of satellite cells and myoblasts but also for improving cell-based therapies for muscle regeneration. This chapter describes a basic protocol used in our laboratory to isolate quiescent muscle satellite cells from adult skeletal muscle by enzymatic dissociation followed by a sequential magnetic-activated cell sorting (MACS). This method is cheap and fast providing and alternative procedure to other purification methods that require fluorescence-activated cell sorting (FACS) machines. Freshly isolated quiescent satellite cells purified by this method can be used in a broad range of experiments including cell transplantation for satellite cell self-renewal experiments or cell therapies.

Functions of Vertebrate Ferlins

Ferlins are multiple-C2-domain proteins involved in Ca²⁺-triggered membrane dynamics within the secretory, endocytic and lysosomal pathways. In bony vertebrates there are six ferlin genes encoding, in humans, dysferlin, otoferlin, myoferlin, Fer1L5 and 6 and the long noncoding RNA Fer1L4. Mutations in DYSF (dysferlin) can cause a range of muscle diseases with various clinical manifestations collectively known as dysferlinopathies, including limb-girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi myopathy. A mutation in MYOF (myoferlin) was linked to a muscular dystrophy accompanied by cardiomyopathy. Mutations in OTOF (otoferlin) can be the cause of nonsyndromic deafness DFNB9. Dysregulated expression of any human ferlin may be associated with development of cancer. This review provides a detailed description of functions of the vertebrate ferlins with a focus on muscle ferlins and discusses the mechanisms leading to disease development.

Blockade of IGF2R improves muscle regeneration and ameliorates Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a debilitating fatal X-linked muscle disorder. Recent findings indicate that IGFs play a central role in skeletal muscle regeneration and development. Among IGFs, insulinlike growth factor 2 (IGF2) is a key regulator of cell growth, survival, migration and differentiation. The type 2 IGF receptor (IGF2R) modulates circulating and tissue levels of IGF2 by targeting it to lysosomes for degradation. We found that IGF2R and the store-operated Ca2+ channel CD20 share a common hydrophobic binding motif that stabilizes their association. Silencing CD20 decreased myoblast differentiation, whereas blockade of IGF2R increased proliferation and differentiation in myoblasts via the calmodulin/calcineurin/NFAT pathway. Remarkably, anti-IGF2R induced CD20 phosphorylation, leading to the activation of sarcoplasmic/endoplasmic reticulum Ca2+ -ATPase (SERCA) and removal of intracellular Ca2+ . Interestingly, we found that IGF2R expression was increased in dystrophic skeletal muscle of human DMD patients and mdx mice. Blockade of IGF2R by neutralizing antibodies stimulated muscle regeneration, induced force recovery and normalized capillary architecture in dystrophic mdx mice representing an encouraging starting point for the development of new biological therapies for DMD.

Involvement of ST6Gal I-mediated α2,6 sialylation in myoblast proliferation and differentiation

Myogenesis is a physiological process which involves the proliferation of myoblasts and their differentiation into multinucleated myotubes, which constitute the future muscle fibers. Commitment of myoblasts to differentiation is regulated by the balance between the myogenic factors Pax7 and MyoD. The formation of myotubes requires the presence of glycans, especially N‐glycans, on the cell surface. We examined here the involvement of α2,6 sialylation during murine myoblastic C2C12 cell differentiation by generating a st6gal1‐knockdown C2C12 cell line; these cells exhibit reduced proliferative potential and precocious differentiation due to the low expression of Pax7. The earlier fusion of st6gal1‐knockdown cells leads to a high fusion index and a drop in reserve cells (Pax7⁺/MyoD⁻). In st6gal1‐knockdown cells, the Notch pathway is inactivated; consequently, Pax7 expression is virtually abolished, leading to impairment of the proliferation rate. All these results indicate that the decrease in α2,6 sialylation of N‐glycans favors the differentiation of most cells and provokes a significant loss of reserve cells.