Function of the myogenic regulatory factors Myf5, MyoD, Myogenin and MRF4 in skeletal muscle, satellite cells and regenerative myogenesis

Molecular cloning of TPM3 gene in qinchuan cattle and its effect on myoblast proliferation and differentiation

Tropomyosin 3 (TPM3) plays a significant role as a regulatory protein in muscle contraction, affecting the growth and development of skeletal muscles. Despite its importance, limited research has been conducted to investigate the influence of TPM3 on bovine skeletal muscle development. Therefore, this study revealed the role of TPM3 in bovine myoblast growth and development. This research involved conducting a thorough examination of the Qinchuan cattle TPM3 gene using bioinformatics tools to examine its sequence and structural characteristics. Furthermore, TPM3 expression was evaluated in various bovine tissues and cells using quantitative real-time polymerase chain reaction (qRT-PCR). The results showed that the coding region of TPM3 spans 855 bp, with the 161st base being the T base, encoding a protein with 284 amino acids and 19 phosphorylation sites. This protein demonstrated high conservation across species while displaying a predominant α-helix secondary structure despite being an unstable acidic protein. Notably, a noticeable increase in TPM3 expression was observed in the longissimus dorsi muscle and myocardium of calves and adult cattle. Expression patterns varied during different stages of myoblast differentiation. Functional studies that involved interference with TPM3 in Qinchuan cattle myoblasts revealed a very significantly decrease in S-phase cell numbers and EdU-positive staining (P < 0.01), and disrupted myotube morphology. Moreover, interference with TPM3 resulted in significantly (P < 0.05) or highly significantly (P < 0.01) decreased mRNA and protein levels of key proliferation and differentiation markers, indicating its role in the modulation of myoblast behavior. These findings suggest that TPM3 plays an essential role in bovine skeletal muscle growth by influencing myoblast proliferation and differentiation. This study provides a foundation for further exploration into the mechanisms underlying TPM3-mediated regulation of bovine muscle development and provides valuable insights that could guide future research directions as well as potential applications for livestock breeding and addressing muscle-related disorders.

Lipidomics and single-cell RNA sequencing reveal lipid and cell dynamics of porcine glycerol-injured skeletal muscle regeneration model

AIMS

Intramuscular fat (IMF) infiltration and extracellular matrix (ECM) deposition are characteristic features of muscle dysfunction, such as muscular dystrophy and severe muscle injuries. However, the underlying mechanisms of cellular origin, adipocyte formation and fibrosis in skeletal muscle are still unclear.

MAIN METHODS

Pigs were injected with 50 % glycerol (GLY) to induce skeletal muscle injury and regeneration. The acyl chain composition was analyzed by lipidomics, and the cell atlas and molecular signatures were revealed via single-cell RNA sequencing (scRNA-seq). Adipogenesis analysis was performed on fibroblast/fibro-adipogenic progenitors (FAPs) isolated from pigs.

KEY FINDINGS

The porcine GLY-injured skeletal muscle regeneration model was characterized by IMF infiltration and ECM deposition. Skeletal muscle stem cells (MuSCs) and FAP clusters were analyzed to explore the potential mechanisms of adipogenesis and fibrosis, and it was found that the TGF-β signaling pathway might be a key switch that regulates differentiation. Consistently, activation of the TGF-β signaling pathway increased SMAD2/3 phosphorylation and inhibited adipogenesis in FAPs, while inhibition of the TGF-β signaling pathway increased the expression of PPARγ and promoted adipogenesis.

SIGNIFICANCE

GLY-induced muscle injury and regeneration provides comprehensive insights for the development of therapies for human skeletal muscle dysfunction and fatty infiltration-related diseases in which the TGF-β/SMAD signaling pathway might play a primary regulatory role.

A dual-color PAX7 and MYF5 in vivo reporter to investigate muscle stem cell heterogeneity in regeneration and aging

Increasing evidence suggests that the muscle stem cell (MuSC) pool is heterogeneous. In particular, a rare subset of PAX7-positive MuSCs that has never expressed the myogenic regulatory factor MYF5 displays unique self-renewal and engraftment characteristics. However, the scarcity and limited availability of protein markers make the characterization of these cells challenging. Here, we describe the generation of StemRep reporter mice enabling the monitoring of PAX7 and MYF5 proteins based on equimolar levels of dual nuclear fluorescence. High levels of PAX7 protein and low levels of MYF5 delineate a deeply quiescent MuSC subpopulation with an increased capacity for asymmetric division and distinct dynamics of activation, proliferation, and commitment. Aging primarily reduces the MYF5Low MuSCs and skews the stem cell pool toward MYF5High cells with lower quiescence and self-renewal potential. Altogether, we establish the StemRep model as a versatile tool to study MuSC heterogeneity and broaden our understanding of mechanisms regulating MuSC quiescence and self-renewal in homeostatic, regenerating, and aged muscles.

Mitochondrial mechanisms in the pathogenesis of chronic inflammatory musculoskeletal disorders

Chronic inflammatory musculoskeletal disorders characterized by prolonged muscle inflammation, resulting in enduring pain and diminished functionality, pose significant challenges for the patients. Emerging scientific evidence points to mitochondrial malfunction as a pivotal factor contributing to these ailments. Mitochondria play a critical role in powering skeletal muscle activity, but in the context of persistent inflammation, disruptions in their quantity, configuration, and performance have been well-documented. Various disturbances, encompassing alterations in mitochondrial dynamics (such as fission and fusion), calcium regulation, oxidative stress, biogenesis, and the process of mitophagy, are believed to play a central role in the progression of these disorders. Additionally, unfolded protein responses and the accumulation of fatty acids within muscle cells may adversely affect the internal milieu, impairing the equilibrium of mitochondrial functioning. The structural discrepancies between different mitochondrial subsets namely, intramyofibrillar and subsarcolemmal mitochondria likely impact their metabolic capabilities and susceptibility to inflammatory influences. The release of signals from damaged mitochondria is known to incite inflammatory responses. Intriguingly, migrasomes and extracellular vesicles serve as vehicles for intercellular transfer of mitochondria, aiding in the removal of impaired mitochondria and regulation of inflammation. Viral infections have been implicated in inducing stress on mitochondria. Prolonged dysfunction of these vital organelles sustains oxidative harm, metabolic irregularities, and heightened cytokine release, impeding the body's ability to repair tissues. This review provides a comprehensive analysis of advancements in understanding changes in the intracellular environment, mitochondrial architecture and distribution, biogenesis, dynamics, autophagy, oxidative stress, cytokines associated with mitochondria, vesicular structures, and associated membranes in the context of chronic inflammatory musculoskeletal disorders. Strategies targeting key elements regulating mitochondrial quality exhibit promise in the restoration of mitochondrial function, alleviation of inflammation, and enhancement of overall outcomes.

The Impact of Ulmus macrocarpa Extracts on a Model of Sarcopenia-Induced C57BL/6 Mice

Aging leads to tissue and cellular changes, often driven by oxidative stress and inflammation, which contribute to age-related diseases. Our research focuses on harnessing the potent anti-inflammatory and antioxidant properties of Korean Ulmus macrocarpa Hance, a traditional herbal remedy, to address muscle loss and atrophy. We evaluated the effects of Ulmus extract on various parameters in a muscle atrophy model, including weight, exercise performance, grip strength, body composition, muscle mass, and fiber characteristics. Additionally, we conducted Western blot and RT-PCR analyses to examine muscle protein regulation, apoptosis factors, inflammation, and antioxidants. In a dexamethasone-induced muscle atrophy model, Ulmus extract administration promoted genes related to muscle formation while reducing those associated with muscle atrophy. It also mitigated inflammation and boosted muscle antioxidants, indicating a potential improvement in muscle atrophy. These findings highlight the promise of Ulmus extract for developing pharmaceuticals and supplements to combat muscle loss and atrophy, paving the way for clinical applications.

Post-natal muscle growth and protein turnover: a narrative review of current understanding

A model explaining the dietary-protein-driven post-natal skeletal muscle growth and protein turnover in the rat is updated, and the mechanisms involved are described, in this narrative review. Dietary protein controls both bone length and muscle growth, which are interrelated through mechanotransduction mechanisms with muscle growth induced both from stretching subsequent to bone length growth and from internal work against gravity. This induces satellite cell activation, myogenesis and remodelling of the extracellular matrix, establishing a growth capacity for myofibre length and cross-sectional area. Protein deposition within this capacity is enabled by adequate dietary protein and other key nutrients. After briefly reviewing the experimental animal origins of the growth model, key concepts and processes important for growth are reviewed. These include the growth in number and size of the myonuclear domain, satellite cell activity during post-natal development and the autocrine/paracrine action of IGF-1. Regulatory and signalling pathways reviewed include developmental mechanotransduction, signalling through the insulin/IGF-1-PI3K-Akt and the Ras-MAPK pathways in the myofibre and during mechanotransduction of satellite cells. Likely pathways activated by maximal-intensity muscle contractions are highlighted and the regulation of the capacity for protein synthesis in terms of ribosome assembly and the translational regulation of 5-TOPmRNA classes by mTORC1 and LARP1 are discussed. Evidence for and potential mechanisms by which volume limitation of muscle growth can occur which would limit protein deposition within the myofibre are reviewed. An understanding of how muscle growth is achieved allows better nutritional management of its growth in health and disease.

Perfusable adipose decellularized extracellular matrix biological scaffold co-recellularized with adipose-derived stem cells and L6 promotes functional skeletal muscle regeneration following volumetric muscle loss

Muscle tissue engineering is a promising therapeutic strategy for volumetric muscle loss (VML). Among them, decellularized extracellular matrix (dECM) biological scaffolds have shown certain effects in restoring muscle function. However, researchers have inconsistent or even contradictory results on whether dECM biological scaffolds can efficiently regenerate muscle fibers and restore muscle function. This suggests that therapeutic strategies based on dECM biological scaffolds need to be further optimized and developed. In this study, we used a recellularization method of perfusing adipose-derived stem cells (ASCs) and L6 into adipose dECM (adECM) through vascular pedicles. On one hand, this strategy ensures sufficient quantity and uniform distribution of seeded cells inside scaffold. On the other hand, auxiliary L6 cells addresses the issue of low myogenic differentiation efficiency of ASCs. Subsequently, the treatment of VML animal experiments showed that the combined recellularization strategy can improve muscle regeneration and angiogenesis than the single ASCs recellularization strategy, and the TA of former had greater muscle contraction strength. Further single-nucleus RNA sequencing (snRNA-seq) analysis found that L6 cells induced ASCs transform into a new subpopulation of cells highly expressing Mki67, CD34 and CDK1 genes, which had stronger ability of oriented myogenic differentiation. This study demonstrates that co-seeding ASCs and L6 cells through vascular pedicles is a promising recellularization strategy for adECM biological scaffolds, and the engineered muscle tissue constructed based on this has significant therapeutic effects on VML. Overall, this study provides a new paradigm for optimizing and developing dECM-based therapeutic strategies.

Effect of LncRNA LOC106505926 on myogenesis and Lipogenesis of porcine primary cells

BACKGROUND

Skeletal muscle development and fat deposition have important effects on meat quality. The study of regulating skeletal muscle development and fat deposition is of great significance in improving the quality of carcass and meat. In the present study, whole transcriptome sequencing (including RNA-Seq and miRNA-Seq) was performed on the longissimus dorsi muscle (LDM) of Jinfen White pigs at 1, 90, and 180 days of age.

RESULTS

The results showed that a total of 245 differentially expressed miRNAs were screened in any two comparisons, which may be involved in the regulation of myogenesis. Among them, compared with 1-day-old group, miR-22-5p was significantly up-regulated in 90-day-old group and 180-day-old group. Functional studies demonstrated that miR-22-5p inhibited the proliferation and differentiation of porcine skeletal muscle satellite cells (PSCs). Pearson correlation coefficient analysis showed that long non-coding RNA (lncRNA) LOC106505926 and CXXC5 gene had strong negative correlations with miR-22-5p. The LOC106505926 and CXXC5 were proven to promote the proliferation and differentiation of PSCs, as opposed to miR-22-5p. In terms of mechanism, LOC106505926 functions as a molecular sponge of miR-22-5p to modulate the expression of CXXC5, thereby inhibits the differentiation of PSCs. In addition, LOC106505926 regulates the differentiation of porcine preadipocytes through direct binding with FASN.

CONCLUSIONS

Collectively, our results highlight the multifaceted regulatory role of LOC106505926 in controlling skeletal muscle and adipose tissue development in pigs and provide new targets for improving the quality of livestock products by regulating skeletal muscle development and fat deposition.

The Mediator Med23 controls a transcriptional switch for muscle stem cell proliferation and differentiation in muscle regeneration

Muscle stem cells (MuSCs) contribute to a robust muscle regeneration process after injury, which is highly orchestrated by the sequential expression of multiple key transcription factors. However, it remains unclear how key transcription factors and cofactors such as the Mediator complex cooperate to regulate myogenesis. Here, we show that the Mediator Med23 is critically important for MuSC-mediated muscle regeneration. Med23 is increasingly expressed in activated/proliferating MuSCs on isolated myofibers or in response to muscle injury. Med23 deficiency reduced MuSC proliferation and enhanced its precocious differentiation, ultimately compromising muscle regeneration. Integrative analysis revealed that Med23 oppositely impacts Ternary complex factor (TCF)-targeted MuSC proliferation genes and myocardin-related transcription factor (MRTF)-targeted myogenic differentiation genes. Consistently, Med23 deficiency decreases the ETS-like transcription factor 1 (Elk1)/serum response factor (SRF) binding at proliferation gene promoters but promotes MRTF-A/SRF binding at myogenic gene promoters. Overall, our study reveals the important transcriptional control mechanism of Med23 in balancing MuSC proliferation and differentiation in muscle regeneration.

The effect of Limosilactobacillus fermentum 2i3 and 0.6% addition of humic substances on production parameters and the immune system of broilers

The widespread use of antibiotics in the poultry industry as growth promoters has led to the emergence of bacterial resistance, which poses a significant health risk to humans and animals. Substances of natural origin, such as probiotic bacteria and humic substances, can be a promising solution. The aim of this experiment was to study the effect of the administration of a probiotic strain of Limosilactobacillus fermentum 2i3 and/or a new formula of humic substances specifically designed for detoxification on the production parameters, including gene expression of myogenic growth factors and selected parameters of the immune response. We found that production parameters such as feed conversion ratio and weekly weight gain, as well as gene expression of mucin-2 and immunoglobulin A, were positively influenced mainly by the administration of L. fermentum 2i3. Similarly, the percentage of active phagocytes and their absorption capacity as well as the proportions of CD8+ and CD4+CD8+ T-lymphocyte subpopulations were significantly increased. The addition of humic substances, either alone or in combination with probiotics, significantly reduced the aforementioned parameters compared to the control. On the other hand, the relative gene expression for all myogenic growth factors was the highest in the humic group alone. Based on the results obtained, we can confirm the immunostimulating effect of L. fermentum 2i3 administered in drinking water, which also had an impact on important production parameters of broiler meat. On the other hand, in the combined group there was no expected potentiation of the positive effects on the observed parameters.

Mutant RAS-driven Secretome Causes Skeletal Muscle Defects in Breast Cancer

Cancer-induced skeletal muscle defects differ in severity between individuals with the same cancer type. Cancer subtype-specific genomic aberrations are suggested to mediate these differences, but experimental validation studies are very limited. We utilized three different breast cancer patient-derived xenograft (PDX) models to correlate cancer subtype with skeletal muscle defects. PDXs were derived from brain metastasis of triple-negative breast cancer (TNBC), estrogen receptor-positive/progesterone receptor-positive (ER+/PR+) primary breast cancer from a BRCA2-mutation carrier, and pleural effusion from an ER+/PR- breast cancer. While impaired skeletal muscle function as measured through rotarod performance and reduced levels of circulating and/or skeletal muscle miR-486 were common across all three PDXs, only TNBC-derived PDX activated phospho-p38 in skeletal muscle. To further extend these results, we generated transformed variants of human primary breast epithelial cells from healthy donors using HRASG12V or PIK3CAH1047R mutant oncogenes. Mutations in RAS oncogene or its modulators are found in approximately 37% of metastatic breast cancers, which is often associated with skeletal muscle defects. Although cells transformed with both oncogenes generated adenocarcinomas in NSG mice, only HRASG12V-derived tumors caused skeletal muscle defects affecting rotarod performance, skeletal muscle contraction force, and miR-486, Pax7, pAKT, and p53 levels in skeletal muscle. Circulating levels of the chemokine CXCL1 were elevated only in animals with tumors containing HRASG12V mutation. Because RAS pathway aberrations are found in 19% of cancers, evaluating skeletal muscle defects in the context of genomic aberrations in cancers, particularly RAS pathway mutations, may accelerate development of therapeutic modalities to overcome cancer-induced systemic effects.

SIGNIFICANCE

Mutant RAS- and PIK3CA-driven breast cancers distinctly affect the function of skeletal muscle. Therefore, research and therapeutic targeting of cancer-induced systemic effects need to take aberrant cancer genome into consideration.

Microbiota-derived 3-phenylpropionic acid promotes myotube hypertrophy by Foxo3/NAD+ signaling pathway

BACKGROUND

Gut microbiota and their metabolites play a regulatory role in skeletal muscle growth and development, which be known as gut-muscle axis. 3-phenylpropionic acid (3-PPA), a metabolite produced by colonic microorganisms from phenylalanine in the gut, presents in large quantities in the blood circulation. But few study revealed its function in skeletal muscle development.

RESULTS

Here, we demonstrated the beneficial effects of 3-PPA on muscle mass increase and myotubes hypertrophy both in vivo and vitro. Further, we discovered the 3-PPA effectively inhibited protein degradation and promoted protein acetylation in C2C12 and chick embryo primary skeletal muscle myotubes. Mechanistically, we supported that 3-PPA reduced NAD+ synthesis and subsequently suppressed tricarboxylic acid cycle and the mRNA expression of SIRT1/3, thus promoting the acetylation of total protein and Foxo3. Moreover, 3-PPA may inhibit Foxo3 activity by directly binding.

CONCLUSIONS

This study firstly revealed the effect of 3-PPA on skeletal muscle growth and development, and newly discovered the interaction between 3-PPA and Foxo3/NAD+ which mechanically promote myotubes hypertrophy. These results expand new understanding for the regulation of gut microbiota metabolites on skeletal muscle growth and development.

PHF2 regulates sarcomeric gene transcription in myogenesis

Myogenesis is regulated mainly by transcription factors known as Myogenic Regulatory Factors (MRFs), and the transcription is affected by epigenetic modifications. However, the epigenetic regulation of myogenesis is poorly understood. Here, we focused on the epigenomic modification enzyme, PHF2, which demethylates histone 3 lysine 9 dimethyl (H3K9me2) during myogenesis. Phf2 mRNA was expressed during myogenesis, and PHF2 was localized in the nuclei of myoblasts and myotubes. We generated Phf2 knockout C2C12 myoblasts using the CRISPR/Cas9 system and analyzed global transcriptional changes via RNA-sequencing. Phf2 knockout (KO) cells 2 d post differentiation were subjected to RNA sequencing. Gene ontology (GO) analysis revealed that Phf2 KO impaired the expression of the genes related to skeletal muscle fiber formation and muscle cell development. The expression levels of sarcomeric genes such as Myhs and Mybpc2 were severely reduced in Phf2 KO cells at 7 d post differentiation, and H3K9me2 modification of Mybpc2, Mef2c and Myh7 was increased in Phf2 KO cells at 4 d post differentiation. These findings suggest that PHF2 regulates sarcomeric gene expression via epigenetic modification.

Expression of intramuscular extracellular matrix proteins in vastus lateralis muscle fibres between atrophic and non-atrophic COPD

Background

Extracellular matrix (ECM) proteins are the major constituents of the muscle cell micro-environment, imparting instructive signalling, steering cell behaviour and controlling muscle regeneration. ECM remodelling is among the most affected signalling pathways in COPD and aged muscle. As a fraction of COPD patients present muscle atrophy, we questioned whether ECM composition would be altered in patients with peripheral muscle wasting (atrophic COPD) compared to those without muscle wasting (non-atrophic COPD).

Methods

A set of ECM molecules with known impact on myogenesis were quantified in vastus lateralis muscle biopsies from 29 COPD patients (forced expiratory volume in 1 s 55±12% predicted) using ELISA and real-time PCR. COPD patients were grouped to atrophic or non-atrophic based on fat-free mass index (<17 or ≥17 kg·m-2).

Results

Atrophic COPD patients presented a lower average vastus lateralis muscle fibre cross-sectional area (3872±258 μm2) compared to non-atrophic COPD (4509±198 μm2). Gene expression of ECM molecules was found significantly lower in atrophic COPD compared to non-atrophic COPD for collagen type I alpha 1 chain (COL1A1), fibronectin (FN1), tenascin C (TNC) and biglycan (BGN). In terms of protein levels, there were no significant differences between the two COPD cohorts for any of the ECM molecules tested.

Conclusions

Although atrophic COPD presented decreased contractile muscle tissue, the differences in ECM mRNA expression between atrophic and non-atrophic COPD were not translated at the protein level, potentially indicating an accumulation of long-lived ECM proteins and dysregulated proteostasis, as is typically observed during deconditioning and ageing.

The RNA-binding protein Msi2 regulates autophagy during myogenic differentiation

Skeletal muscle development is a highly ordered process orchestrated transcriptionally by the myogenic regulatory factors. However, the downstream molecular mechanisms of myogenic regulatory factor functions in myogenesis are not fully understood. Here, we identified the RNA-binding protein Musashi2 (Msi2) as a myogenin target gene and a post-transcriptional regulator of myoblast differentiation. Msi2 knockdown in murine myoblasts blocked differentiation without affecting the expression of MyoD or myogenin. Msi2 overexpression was also sufficient to promote myoblast differentiation and myocyte fusion. Msi2 loss attenuated autophagosome formation via down-regulation of the autophagic protein MAPL1LC3/ATG8 (LC3) at the early phase of myoblast differentiation. Moreover, forced activation of autophagy effectively suppressed the differentiation defects incurred by Msi2 loss. Consistent with its functions in myoblasts in vitro, mice deficient for Msi2 exhibited smaller limb skeletal muscles, poorer exercise performance, and muscle fiber-type switching in vivo. Collectively, our study demonstrates that Msi2 is a novel regulator of mammalian myogenesis and establishes a new functional link between muscular development and autophagy regulation.

Polysaccharide of Atractylodes macrocephala Koidz alleviates LPS-induced proliferation, differentiation inhibition and excessive apoptosis in chicken embryonic myogenic cells

BACKGROUND

Lipopolysaccharide (LPS) can induce systemic inflammation and affect the growth and development of poultry. As a kind of traditional Chinese medicine, polysaccharide of Atractylodes macrocephala Koidz (PAMK) can effectively improve the growth performance of animals and improve the immunity of animal bodies.

OBJECTIVES

The purpose of this study was to investigate the effects of PAMK on LPS-induced inflammatory response, proliferation, differentiation and apoptosis of chicken embryonic myogenic cells.

METHODS

We used chicken embryonic myogenic cells as a model by detecting EdU/MYHC immunofluorescence, the expression of inflammation, proliferation, differentiation-related genes and proteins and the number of apoptotic cells in the condition of adding LPS, PAMK, belnacasan (an inhibitor of Caspase1) or their combinations.

RESULTS

The results showed that LPS stimulation increased the expression of inflammatory factors, inhibited proliferation and differentiation, and excessive apoptosis in chicken embryonic myogenic cells, and PAMK alleviated these adverse effects induced by LPS. After the addition of belnacasan (inhibitor of Caspase1), apoptosis in myogenic cells was inhibited, and therefore, the number of apoptotic cells and the expression of pro-apoptotic genes Caspase1 and Caspase3 were increased. In addition, belnacasan inhibited the increased expression of inflammatory factors, inhibited proliferation, differentiation and excessive apoptosis in chicken embryonic myogenic cells induced by LPS.

CONCLUSIONS

This study provides a theoretical basis for further exploring the mechanism of action of PAMK and exogenous LPS on chicken embryonic myogenic cells and lays the foundation for the development and application of green feed additives in animal husbandry industry.

Uremia Impedes Skeletal Myocyte Myomixer Expression and Fusogenic Activity: Implication for Uremic Sarcopenia

In patients with chronic kidney disease (CKD), skeletal muscle mass and function are known to occasionally decline. However, the muscle regeneration and differentiation process in uremia has not been extensively studied. In mice with CKD induced by adenine-containing diet, the tibialis anterior muscle injured using a barium chloride injection method recovered poorly as compared to control mice. In the cultured murine skeletal myocytes, stimulation with indoxyl sulfate (IS), a representative uremic toxin, morphologically jeopardized the differentiation, which was counteracted by L-ascorbic acid (L-AsA) treatment. Transcriptome analysis of cultured myocytes identified a set of genes whose expression was down-regulated by IS stimulation but up-regulated by L-AsA treatment. Gene silencing of myomixer, one of the genes in the set, impaired myocyte fusion during differentiation. By contrast, lentiviral overexpression of myomixer compensated for a hypomorphic phenotype caused by IS treatment. The split-luciferase technique demonstrated that IS stimulation negatively affected early myofusion activity that was rescued by L-AsA treatment. Lastly, in mice with CKD compared with control mice, myomixer expression in the muscle tissue in addition to the muscle weight after the injury was reduced, both of which were restored with L-AsA treatment. Collectively, data showed that the uremic milieu impairs the expression of myomixer and impedes the myofusion process. Considering frequent musculoskeletal injuries in uremic patients, defective myocyte fusion followed by delayed muscle damage recovery could underlie their muscle loss and weakness.

Laminin as a Key Extracellular Matrix for Proliferation, Differentiation, and Maturation of Porcine Muscle Stem Cell Cultivation

Extracellular matrix (ECM) proteins play a crucial role in culturing muscle stem cells (MuSCs). However, there is a lack of extensive research on how each of these proteins influences proliferation and differentiation of MuSCs from livestock animals. Therefore, we investigated the effects of various ECM coatings-collagen, fibronectin, gelatin, and laminin-on the proliferation, differentiation, and maturation of porcine MuSCs. Porcine MuSCs, isolated from 14-day-old Berkshire piglets, were cultured on ECM-coated plates, undergoing three days of proliferation followed by three days of differentiation. MuSCs on laminin showed higher proliferation rate than others (p<0.05). There was no significant difference in the mRNA expression levels of PAX7, MYF5, and MYOD among MuSCs on laminin, collagen, and fibronectin (p>0.05). During the differentiation period, MuSCs cultured on laminin exhibited a significantly higher differentiation rate, resulting in thicker myotubes compared to those on other ECMs (p<0.05). Also, MuSCs on laminin showed higher expression of mRNA related with maturated muscle fiber such as MYH1 and MYH4 corresponding to muscle fiber type IIx and muscle fiber type IIb, respectively, compared with MuSCs on other ECM coatings (p<0.05). In summary, our comparison of ECMs revealed that laminin significantly enhances MuSC proliferation and differentiation, outperforming other ECMs. Specifically, muscle fibers cultured on laminin exhibited a more mature phenotype. These findings underscore laminin's potential to advance in vitro muscle research and cultured meat production, highlighting its role in supporting rapid cell proliferation, higher differentiation rates, and the development of mature muscle fibers.

Research progress on the biological regulatory mechanisms of selenium on skeletal muscle in broilers

As one of the indispensable trace elements for both humans and animals, selenium widely participates in multiple physiological processes and facilitates strong anti-inflammatory, antioxidant, and immune enhancing abilities. The biological functions of selenium are primarily driven by its presence in selenoproteins as a form of selenocysteine. Broilers are highly sensitive to selenium intake. Recent reports have demonstrated that selenium deficiency can adversely affect the quality of skeletal muscles and the economic value of broilers; the regulatory roles of several key selenoproteins (e.g., GPX1, GPX4, TXNRD1, TXNRD3, SelK, SelT, and SelW) have been identified. Starting from the selenium metabolism and its biological utilization in the skeletal muscle, the effect of the selenium antioxidant function on broiler meat quality is discussed in detail. The progress of research into the prevention of skeletal muscle injury by selenium and selenoproteins is also summarized. The findings emphasize the necessity of in vivo and in vitro research, and certain mechanism problems are identified, which aids their further examination. This mini-review will be helpful to provide a theoretical basis for the further study of regulatory mechanisms of selenium nutrition in edible poultry.

Integrative ATAC-seq and RNA-seq analysis of myogenic differentiation of ovine skeletal muscle satellite cell

Skeletal muscle satellite cells (SMSCs) play an important role in regulating muscle growth and regeneration. Chromatin accessibility allows physical interactions that synergistically regulate gene expression through enhancers, promoters, insulators, and chromatin binding factors. However, the chromatin accessibility altas and its regulatory role in ovine myoblast differentiation is still unclear. Therefore, ATAC-seq and RNA-seq analysis were performed on ovine SMSCs at the proliferation stage (SCG) and differentiation stage (SCD). 17,460 DARs (differential accessibility regions) and 3732 DEGs (differentially expressed genes) were identified. Based on joint analysis of ATAC-seq and RNA-seq, we revealed that PI3K-Akt, TGF-β and other signaling pathways regulated SMSCs differentiation. We identified two novel candidate genes, FZD5 and MAP2K6, which may affect the proliferation and differentiation of SMSCs. Our data identify potential cis regulatory elements of ovine SMSCs. This study can provide a reference for exploring the mechanisms of the differentiation and regeneration of SMSCs in the future.

Regulation of myogenic cell proliferation and differentiation during mammalian skeletal myogenesis

Mammalian skeletal myogenesis is a complex process that allows precise control of myogenic cells' proliferation, differentiation, and fusion to form multinucleated, contractile, and functional muscle fibers. Typically, myogenic progenitors continue growth and division until acquiring a differentiated state, which then permanently leaves the cell cycle and enters terminal differentiation. These processes have been intensively studied using the skeletal muscle developing models in vitro and in vivo, uncovering a complex cellular intrinsic network during mammalian skeletal myogenesis containing transcription factors, translation factors, extracellular matrix, metabolites, and mechano-sensors. Examining the events and how they are knitted together will better understand skeletal myogenesis's molecular basis. This review describes various regulatory mechanisms and recent advances in myogenic cell proliferation and differentiation during mammalian skeletal myogenesis. We focus on significant cell cycle regulators, myogenic factors, and chromatin regulators impacting the coordination of the cell proliferation versus differentiation decision, which will better clarify the complex signaling underlying skeletal myogenesis.

LSD1 controls a nuclear checkpoint in Wnt/β-Catenin signaling to regulate muscle stem cell self-renewal

The Wnt/β-Catenin pathway plays a key role in cell fate determination during development and in adult tissue regeneration by stem cells. These processes involve profound gene expression and epigenome remodeling and linking Wnt/β-Catenin signaling to chromatin modifications has been a challenge over the past decades. Functional studies of the lysine demethylase LSD1/KDM1A converge to indicate that this epigenetic regulator is a key regulator of cell fate, although the extracellular cues controlling LSD1 action remain largely unknown. Here we show that β-Catenin is a substrate of LSD1. Demethylation by LSD1 prevents β-Catenin degradation thereby maintaining its nuclear levels. Consistently, in absence of LSD1, β-Catenin transcriptional activity is reduced in both MuSCs and ESCs. Moreover, inactivation of LSD1 in mouse muscle stem cells and embryonic stem cells shows that LSD1 promotes mitotic spindle orientation via β-Catenin protein stabilization. Altogether, by inscribing LSD1 and β-Catenin in the same molecular cascade linking extracellular factors to gene expression, our results provide a mechanistic explanation to the similarity of action of canonical Wnt/β-Catenin signaling and LSD1 on stem cell fate.

Vitamin C regulates skeletal muscle post-injury regeneration by promoting myoblast proliferation through its direct interaction with the Pax7 protein

Previous studies have shown that vitamin C (VC), an essential vitamin for the human body, can promote the differentiation of muscle satellite cells (MuSCs) in vitro and play an important role in skeletal muscle post-injury regeneration. However, the molecular mechanism of VC regulating MuSC proliferation has not been elucidated. In this study, the role of VC in promoting MuSC proliferation and its molecular mechanism were explored using cell molecular biology and animal experiments. The results showed that VC accelerates the progress of skeletal muscle post-injury regeneration by promoting MuSC proliferation in vivo. VC can also promote skeletal muscle regeneration in the case of atrophy. Using the C2C12 myoblast murine cell line, we observed that VC also stimulated cell proliferation. In addition, after an in vitro study establishing the occurrence of a physical interaction between VC and Pax7, we observed that VC also upregulated the total and nuclear Pax7 protein levels. This mechanism increased the expression of Myf5 (Myogenic Factor 5), a Pax7 target gene. This study establishes a theoretical foundation for understanding the regulatory mechanisms underlying VC-mediated MuSC proliferation and skeletal muscle regeneration. Moreover, it develops the application of VC in animal muscle nutritional supplements and treatment of skeletal muscle-related diseases.

Temporal regulation of the Mediator complex during muscle proliferation, differentiation, regeneration, aging, and disease

Genesis of skeletal muscle relies on the differentiation and fusion of mono-nucleated muscle progenitor cells into the multi-nucleated muscle fiber syncytium. The temporally-controlled cellular and morphogenetic changes underlying this process are initiated by a series of highly coordinated transcription programs. At the core, the myogenic differentiation cascade is driven by muscle-specific transcription factors, i.e., the Myogenic Regulatory Factors (MRFs). Despite extensive knowledge on the function of individual MRFs, very little is known about how they are coordinated. Ultimately, highly specific coordination of these transcription programs is critical for their masterfully timed transitions, which in turn facilitates the intricate generation of skeletal muscle fibers from a naïve pool of progenitor cells. The Mediator complex links basal transcriptional machinery and transcription factors to regulate transcription and could be the integral component that coordinates transcription factor function during muscle differentiation, growth, and maturation. In this study, we systematically deciphered the changes in Mediator complex subunit expression in skeletal muscle development, regeneration, aging, and disease. We incorporated our in vitro and in vivo experimental results with analysis of publicly available RNA-seq and single nuclei RNA-seq datasets and uncovered the regulation of Mediator subunits in different physiological and temporal contexts. Our experimental results revealed that Mediator subunit expression during myogenesis is highly dynamic. We also discovered unique temporal patterns of Mediator expression in muscle stem cells after injury and during the early regeneration period, suggesting that Mediator subunits may have unique contributions to directing muscle stem cell fate. Although we observed few changes in Mediator subunit expression in aging muscles compared to younger muscles, we uncovered extensive heterogeneity of Mediator subunit expression in dystrophic muscle nuclei, characteristic of chronic muscle degeneration and regeneration cycles. Taken together, our study provides a glimpse of the complex regulation of Mediator subunit expression in the skeletal muscle cell lineage and serves as a springboard for mechanistic studies into the function of individual Mediator subunits in skeletal muscle.

Mitochondrial stress response and myogenic differentiation

Regeneration and repair are prerequisites for maintaining effective function of skeletal muscle under high energy demands, and myogenic differentiation is one of the key steps in the regeneration and repair process. A striking feature of the process of myogenic differentiation is the alteration of mitochondria in number and function. Mitochondrial dysfunction can activate a number of transcriptional, translational and post-translational programmes and pathways to maintain cellular homeostasis under different types and degrees of stress, either through its own signaling or through constant signaling interactions with the nucleus and cytoplasm, a process known as the mitochondrial stress responses (MSRs). It is now believed that mitochondrial dysfunction is closely associated with a variety of muscle diseases caused by reduced levels of myogenic differentiation, suggesting the possibility that MSRs are involved in messaging during myogenic differentiation. Also, MSRs may be involved in myogenesis by promoting bioenergetic remodeling and assisting myoblast survival during myogenic differentiation. In this review, we will take MSRs as an entry point to explore its concrete regulatory mechanisms during myogenic differentiation, with a perspective to provide a theoretical basis for the treatment and repair of related muscle diseases.

Possible involvement of zinc transporter ZIP13 in myogenic differentiation

Ehlers-Danlos syndrome spondylodysplastic type 3 (EDSSPD3, OMIM 612350) is an inherited recessive connective tissue disorder that is caused by loss of function of SLC39A13/ZIP13, a zinc transporter belonging to the Slc39a/ZIP family. We previously reported that patients with EDSSPD3 harboring a homozygous loss of function mutation (c.221G > A, p.G64D) in ZIP13 exon 2 (ZIP13G64D) suffer from impaired development of bone and connective tissues, and muscular hypotonia. However, whether ZIP13 participates in the early differentiation of these cell types remains unclear. In the present study, we investigated the role of ZIP13 in myogenic differentiation using a murine myoblast cell line (C2C12) as well as patient-derived induced pluripotent stem cells (iPSCs). We found that ZIP13 gene expression was upregulated by myogenic stimulation in C2C12 cells, and its knockdown disrupted myotubular differentiation. Myocytes differentiated from iPSCs derived from patients with EDSSPD3 (EDSSPD3-iPSCs) also exhibited incomplete myogenic differentiation. Such phenotypic abnormalities of EDSSPD3-iPSC-derived myocytes were corrected by genomic editing of the pathogenic ZIP13G64D mutation. Collectively, our findings suggest the possible involvement of ZIP13 in myogenic differentiation, and that EDSSPD3-iPSCs established herein may be a promising tool to study the molecular basis underlying the clinical features caused by loss of ZIP13 function.

Cornflower Extract and Its Active Components Alleviate Dexamethasone-Induced Muscle Wasting by Targeting Cannabinoid Receptors and Modulating Gut Microbiota

Sarcopenia, a decline in muscle mass and strength, can be triggered by aging or medications like glucocorticoids. This study investigated cornflower (Centaurea cyanus) water extract (CC) as a potential protective agent against DEX-induced muscle wasting in vitro and in vivo. CC and its isolated compounds mitigated oxidative stress, promoted myofiber growth, and boosted ATP production in C2C12 myotubes. Mechanistically, CC reduced protein degradation markers, increased mitochondrial content, and activated protein synthesis signaling. Docking analysis suggested cannabinoid receptors (CB) 1 and 2 as potential targets of CC compounds. Specifically, graveobioside A from CC inhibited CB1 and upregulated CB2, subsequently stimulating protein synthesis and suppressing degradation. In vivo, CC treatment attenuated DEX-induced muscle wasting, as evidenced by enhanced grip strength, exercise performance, and modulation of muscle gene expression related to differentiation, protein turnover, and exercise performance. Moreover, CC enriched gut microbial diversity, and the abundance of Clostridium sensu stricto 1 positively correlated with muscle mass. These findings suggest a multifaceted mode of action for CC: (1) direct modulation of the muscle cannabinoid receptor system favoring anabolic processes and (2) indirect modulation of muscle health through the gut microbiome. Overall, CC presents a promising therapeutic strategy for preventing and treating muscle atrophy.

Lysine Distinctively Manipulates Myogenic Regulatory Factors and Wnt/Ca2+ Pathway in Slow and Fast Muscles, and Their Satellite Cells of Postnatal Piglets

Muscle regeneration, representing an essential homeostatic process, relies mainly on the myogenic progress of resident satellite cells, and it is modulated by multiple physical and nutritional factors. Here, we investigated how myogenic differentiation-related factors and pathways respond to the first limiting amino acid lysine (Lys) in the fast and slow muscles, and their satellite cells (SCs), of swine. Thirty 28-day-old weaned piglets with similar body weights were subjected to three diet regimens: control group (d 0-28: 1.31% Lys, n = 12), Lys-deficient group (d 0-28: 0.83% Lys, n = 12), and Lys rescue group (d 0-14: 0.83% Lys; d 15-28: 1.31% Lys, n = 6). Pigs on d 15 and 29 were selectively slaughtered for muscular parameters evaluation. Satellite cells isolated from fast (semimembranosus) and slow (semitendinosus) muscles were also selected to investigate differentiation ability variations. We found Lys deficiency significantly hindered muscle development in both fast and slow muscles via the distinct manipulation of myogenic regulatory factors and the Wnt/Ca2+ pathway. In the SC model, Lys deficiency suppressed the Wnt/Ca2+ pathways and myosin heavy chain, myogenin, and myogenic regulatory factor 4 in slow muscle SCs but stimulated them in fast muscle SCs. When sufficient Lys was attained, the fast muscle-derived SCs Wnt/Ca2+ pathway (protein kinase C, calcineurin, calcium/calmodulin-dependent protein kinase II, and nuclear factor of activated T cells 1) was repressed, while the Wnt/Ca2+ pathway of its counterpart was stimulated to further the myogenic differentiation. Lys potentially manipulates the differentiation of porcine slow and fast muscle myofibers via the Wnt/Ca2+ pathway in opposite trends.

Dietary inclusion of Withania somnifera and Asparagus racemosus induces growth, activities of digestive enzymes, and transcriptional modulation of MyoD, MyoG, Myf5, and MRF4 genes in fish, Channa punctatus

The present study explores growth potential of two medicinal herbs, Withania somnifera (Ashwagandha or 'A') and Asparagus racemosus (Shatavari or 'S') after their dietary inclusion in fish, Channa punctatus (13.5 ± 2 g; 11.5 ± 1 cm). Three hundred well-acclimatized fish were distributed into 10 groups- C (Control), S1 (1% S), S2 (2% S), S3 (3% S), A1 (1% A), A2 (2% A), A3 (3% A), AS1 (1% A and S), AS2 (2% A and S), and AS3 (3% A and S), each having 10 specimens. Fish were fed with these diets for 60 days. The study was performed in triplicate. Growth indices- weight gain (WG), specific growth rate percentage (SGR%), feed intake (FI), and condition factor (CF), after 30 and 60 days, were found significantly (p < 0.05) up-regulated in all the groups, except S1, when compared to the C. A significant (p < 0.05) increase in final body weight (FBW) was noticed in all the groups, except S1, after 60 days. Relative to the control group, activities of lipase and amylase in the gut tissue were elevated in all groups, at both sampling times, with the exception of lipase in S1 at 60 days, and amylase in S1 at day 30 and day 60 and S2 at day 60. The mRNA expression of myogenic regulatory factors (MRFs) was also found to be significantly (p < 0.05) up-regulated with the highest fold changes recorded in AS3 for myoD (3.93 ± 0.91); myoG (6.71 ± 0.30); myf5 (4.40 ± 0.33); MRF4 (4.94 ± 0.21) in comparison to the C.

Skeletal muscle myostatin mRNA expression is upregulated in aged human adults with excess adiposity but is not associated with insulin resistance and ageing

Myostatin negatively regulates skeletal muscle growth and appears upregulated in human obesity and associated with insulin resistance. However, observations are confounded by ageing, and the mechanisms responsible are unknown. The aim of this study was to delineate between the effects of excess adiposity, insulin resistance and ageing on myostatin mRNA expression in human skeletal muscle and to investigate causative factors using in vitro models. An in vivo cross-sectional analysis of human skeletal muscle was undertaken to isolate effects of excess adiposity and ageing per se on myostatin expression. In vitro studies employed human primary myotubes to investigate the potential involvement of cross-talk between subcutaneous adipose tissue (SAT) and skeletal muscle, and lipid-induced insulin resistance. Skeletal muscle myostatin mRNA expression was greater in aged adults with excess adiposity than age-matched adults with normal adiposity (2.0-fold higher; P < 0.05) and occurred concurrently with altered expression of genes involved in the maintenance of muscle mass but did not differ between younger and aged adults with normal adiposity. Neither chronic exposure to obese SAT secretome nor acute elevation of fatty acid availability (which induced insulin resistance) replicated the obesity-mediated upregulation of myostatin mRNA expression in vitro. In conclusion, skeletal muscle myostatin mRNA expression is uniquely upregulated in aged adults with excess adiposity and insulin resistance but not by ageing alone. This does not appear to be mediated by the SAT secretome or by lipid-induced insulin resistance. Thus, factors intrinsic to skeletal muscle may be responsible for the obesity-mediated upregulation of myostatin, and future work to establish causality is required.

Human myofiber-enriched aging-induced lncRNA FRAIL1 promotes loss of skeletal muscle function

The loss of skeletal muscle mass during aging is a significant health concern linked to adverse outcomes in older individuals. Understanding the molecular basis of age-related muscle loss is crucial for developing strategies to combat this debilitating condition. Long noncoding RNAs (lncRNAs) are a largely uncharacterized class of biomolecules that have been implicated in cellular homeostasis and dysfunction across a many tissues and cell types. To identify lncRNAs that might contribute to skeletal muscle aging, we screened for lncRNAs whose expression was altered in vastus lateralis muscle from older compared to young adults. We identified FRAIL1 as an aging-induced lncRNA with high abundance in human skeletal muscle. In healthy young and older adults, skeletal muscle FRAIL1 was increased with age in conjunction with lower muscle function. Forced expression of FRAIL1 in mouse tibialis anterior muscle elicits a dose-dependent reduction in skeletal muscle fiber size that is independent of changes in muscle fiber type. Furthermore, this reduction in muscle size is dependent on an intact region of FRAIL1 that is highly conserved across non-human primates. Unbiased transcriptional and proteomic profiling of the effects of FRAIL1 expression in mouse skeletal muscle revealed widespread changes in mRNA and protein abundance that recapitulate age-related changes in pathways and processes that are known to be altered in aging skeletal muscle. Taken together, these findings shed light on the intricate molecular mechanisms underlying skeletal muscle aging and implicate FRAIL1 in age-related skeletal muscle phenotypes.

Immunoregulation in cancer-associated cachexia

BACKGROUND

Cancer-associated cachexia is a multi-organ disorder associated with progressive weight loss due to a variable combination of anorexia, systemic inflammation and excessive energy wasting. Considering the importance of immunoregulation in cachexia, it still lacks a complete understanding of the immunological mechanisms in cachectic progression.

AIM OF REVIEW

Our aim here is to describe the complex immunoregulatory system in cachexia. We summarize the effects and translational potential of the immune system on the development of cancer-associated cachexia and we attempt to conclude with thoughts on precise and integrated therapeutic strategies under the complex immunological context of cachexia.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review is focused on three main key concepts. First, we highlight the inflammatory factors and additional mediators that have been identified to modulate this syndrome. Second, we decipher the potential role of immune checkpoints in tissue wasting. Third, we discuss the multilayered insights in cachexia through the immunometabolic axis, immune-gut axis and immune-nerve axis.

Lactate induces C2C12 myoblasts differentiation by mediating ROS/p38 MAPK signalling pathway

Lactate serves not merely as an energy substrate for skeletal muscle but also regulates myogenic differentiation, leading to an elevation of reactive oxygen species (ROS) levels. The present study was focused on exploring the effects of lactate and ROS/p38 MAPK in promoting C2C12 myoblasts differentiation. Our results demonstrated that lactate increased C2C12 myoblasts differentiation at a range of physiological concentrations, accompanied by enhanced ROS contents. We used n-acetylcysteine (NAC, a ROS scavenger) pretreatment and found that it delayed lactate-induced C2C12 myoblast differentiation by upregulating Myf5 expression on days 5 and 7 and lowering MyoD and MyoG expression. The finding implies that lactate accompanies ROS-dependent manner to promote C2C12 myoblast differentiation. Additionally, lactate significantly increased p38 MAPK phosphorylation to promote C2C12 cell differentiation, but pretreatment with SB203580 (p38 MAPK inhibitor) reduced lactate-induced C2C12 myoblasts differentiation. whereas lactate pretreatment with NAC inhibited p38 MAPK phosphorylation in C2C12 cells, demonstrating that lactate mediated ROS and regulated the p38 MAPK signalling pathway to promote C2C12 cell differentiation. In conclusion, our results suggest that the promotion of C2C12 myoblasts differentiation by lactate is dependent on ROS and the p38 MAPK signalling pathway. These observations reveal a beneficial role for lactate in increasing myogenesis through ROS-sensitive mechanisms as well as providing new ideas regarding the positive impact of ROS in improving the function of skeletal muscle.

Molecular Regulation of Porcine Skeletal Muscle Development: Insights from Research on CDC23 Expression and Function

Cell division cycle 23 (CDC23) is a component of the tetratricopeptide repeat (TPR) subunit in the anaphase-promoting complex or cyclosome (APC/C) complex, which participates in the regulation of mitosis in eukaryotes. However, the regulatory model and mechanism by which the CDC23 gene regulates muscle production in pigs are largely unknown. In this study, we investigated the expression of CDC23 in pigs, and the results indicated that CDC23 is widely expressed in various tissues and organs. In vitro cell experiments have demonstrated that CDC23 promotes the proliferation of myoblasts, as well as significantly positively regulating the differentiation of skeletal muscle satellite cells. In addition, Gene Set Enrichment Analysis (GSEA) revealed a significant downregulation of the cell cycle pathway during the differentiation process of skeletal muscle satellite cells. The protein-protein interaction (PPI) network showed a high degree of interaction between genes related to the cell cycle pathway and CDC23. Subsequently, in differentiated myocytes induced after overexpression of CDC23, the level of CDC23 exhibited a significant negative correlation with the expression of key factors in the cell cycle pathway, suggesting that CDC23 may be involved in the inhibition of the cell cycle signaling pathway in order to promote the differentiation process. In summary, we preliminarily determined the function of CDC23 with the aim of providing new insights into molecular regulation during porcine skeletal muscle development.

LEDT and Idebenone treatment modulate autophagy and improve regenerative capacity in the dystrophic muscle through an AMPK-pathway

PURPOSE

Considering the difficulties and challenges in Duchenne muscular dystrophy (DMD) treatment, such as the adverse effects of glucocorticoids, which are the main medical prescription used by dystrophic patients, new treatment concepts for dystrophic therapy are very necessary. Thus, in this study, we explore the effects of photobiomodulation (PBM; a non-invasive therapy) and Idebenone (IDE) treatment (a potent antioxidant), applied alone or in association, in dystrophic muscle cells and the quadriceps muscle, with special focus on autophagy and regenerative pathways.

METHODS

For the in vitro studies, the dystrophic primary muscle cells received 0.5J LEDT and 0.06μM IDE; and for the in vivo studies, the dystrophic quadriceps muscle received 3J LEDT and the mdx mice were treated with 200mg/kg IDE.

RESULTS

LEDT and IDE treatment modulate autophagy by increasing autophagy markers (SQSTM1/p62, Beclin and Parkin) and signaling pathways (AMPK and TGF-β). Concomitantly, the treatments prevented muscle degeneration by reducing the number of IgG-positive fibers and the fibers with a central nucleus; decreasing the fibrotic area; up-regulating the myogenin and MCH-slow levels; and down-regulating the MyoD and MHC-fast levels.

CONCLUSION

These results suggest that LEDT and IDE treatments enhance autophagy and prevented muscle degeneration in the dystrophic muscle of the experimental model. These findings illustrate the potential efficacy of LEDT and IDE treatment as an alternative therapy focused on muscle recovery in the dystrophic patient.

Podocan promoting skeletal muscle post-injury regeneration by inhibiting TGF-β signaling pathway

Podocan, the fifth member of Small Leucine-Rich Proteoglycan (SLRP) family of extracellular matrix components, is poorly known in muscle development. Previous studies have shown that Podocan promotes C2C12 differentiation in mice. In this study, we elucidated the effect of Podocan on skeletal muscle post-injury regeneration and its underlying mechanism. Injection of Podocan protein promoted the process of mice skeletal muscle post-injury regeneration. This effect seemed to be from the acceleration of muscle satellite cell differentiation in vivo. Meanwhile, Podocan promoted myogenic differentiation in vitro by binding with TGF-β1 to inhibit the activity of the TGF-β signaling pathway. These results indicated that Podocan had the potential roles to enhance skeletal muscle post-injury regeneration. Its mechanism is likely the regulation of the expression of p-Smad2 and p-Smad4 related to the TGF-β signaling pathway by interacting with TGF-β1.

Fat infiltration in skeletal muscle: Influential triggers and regulatory mechanism

Fat infiltration in skeletal muscle (also known as myosteatosis) is now recognized as a distinct disease from sarcopenia and is directly related to declining muscle capacity. Hence, understanding the origins and regulatory mechanisms of fat infiltration is vital for maintaining skeletal muscle development and improving human health. In this article, we summarized the triggering factors such as aging, metabolic diseases and metabolic syndromes, nonmetabolic diseases, and muscle injury that all induce fat infiltration in skeletal muscle. We discussed recent advances on the cellular origins of fat infiltration and found several cell types including myogenic cells and non-myogenic cells that contribute to myosteatosis. Furthermore, we reviewed the molecular regulatory mechanism, detection methods, and intervention strategies of fat infiltration in skeletal muscle. Based on the current findings, our review will provide new insight into regulating function and lipid metabolism of skeletal muscle and treating muscle-related diseases.

Integrative cross-species analysis reveals conserved and unique signatures in fatty skeletal muscles

Fat infiltration in skeletal muscle is now recognized as a standard feature of aging and is directly related to the decline in muscle function. However, there is still a limited systematic integration and exploration of the mechanisms underlying the occurrence of myosteatosis in aging across species. Here, we re-analyzed bulk RNA-seq datasets to investigate the association between fat infiltration in skeletal muscle and aging. Our integrated analysis of single-nucleus transcriptomics in aged humans and Laiwu pigs with high intramuscular fat content, identified species-preference subclusters and revealed core gene programs associated with myosteatosis. Furthermore, we found that fibro/adipogenic progenitors (FAPs) had potential capacity of differentiating into PDE4D+/PDE7B+ preadipocytes across species. Additionally, cell-cell communication analysis revealed that FAPs may be associated with other adipogenic potential clusters via the COL4A2 and COL6A3 pathways. Our study elucidates the correlation mechanism between aging and fat infiltration in skeletal muscle, and these consensus signatures in both humans and pigs may contribute to increasing reproducibility and reliability in future studies involving in the field of muscle research.

Beneficial effects of resistance training on both mild and severe mouse dystrophic muscle function as a preclinical option for Duchenne muscular dystrophy

Mechanical overloading (OVL) resulting from the ablation of muscle agonists, a supra-physiological model of resistance training, reduces skeletal muscle fragility, i.e. the immediate maximal force drop following lengthening contractions, and increases maximal force production, in mdx mice, a murine model of Duchene muscular dystrophy (DMD). Here, we further analyzed these beneficial effects of OVL by determining whether they were blocked by cyclosporin, an inhibitor of the calcineurin pathway, and whether there were also observed in the D2-mdx mice, a more severe murine DMD model. We found that cyclosporin did not block the beneficial effect of 1-month OVL on plantaris muscle fragility in mdx mice, nor did it limit the increases in maximal force and muscle weight (an index of hypertrophy). Fragility and maximal force were also ameliorated by OVL in the plantaris muscle of D2-mdx mice. In addition, OVL increased the expression of utrophin, cytoplamic γ-actin, MyoD, and p-Akt in the D2-mdx mice, proteins playing an important role in fragility, maximal force gain and muscle growth. In conclusion, OVL reduced fragility and increased maximal force in the more frequently used mild mdx model but also in D2-mdx mice, a severe model of DMD, closer to human physiopathology. Moreover, these beneficial effects of OVL did not seem to be related to the activation of the calcineurin pathway. Thus, this preclinical study suggests that resistance training could have a potential benefit in the improvement of the quality of life of DMD patients.

Denervation alters the secretome of myofibers and thereby affects muscle stem cell lineage progression and functionality

Skeletal muscle function crucially depends on innervation while repair of skeletal muscle relies on resident muscle stem cells (MuSCs). However, it is poorly understood how innervation affects MuSC properties and thereby regeneration of skeletal muscle. Here, we report that loss of innervation causes precocious activation of MuSCs concomitant with the expression of markers of myogenic differentiation. This aberrant activation of MuSCs after loss of innervation is accompanied by profound alterations on the mRNA and protein level. Combination of muscle injury with loss of innervation results in impaired regeneration of skeletal muscle including shifts in myogenic populations concomitant with delayed maturation of regenerating myofibers. We further demonstrate that loss of innervation leads to alterations in myofibers and their secretome, which then affect MuSC behavior. In particular, we identify an increased secretion of Osteopontin and transforming growth factor beta 1 (Tgfb1) by myofibers isolated from mice which had undergone sciatic nerve transection. The altered secretome results in the upregulation of early activating transcription factors, such as Junb, and their target genes in MuSCs. However, the combination of different secreted factors from myofibers after loss of innervation is required to cause the alterations observed in MuSCs after loss of innervation. These data demonstrate that loss of innervation first affects myofibers causing alterations in their secretome which then affect MuSCs underscoring the importance of proper innervation for MuSC functionality and regeneration of skeletal muscle.

Potential nutritional strategies to prevent and reverse sarcopenia in aging process: Role of fish oil-derived ω-3 polyunsaturated fatty acids, wheat oligopeptide and their combined intervention

INTRODUCTION

Nutritional support is potentially considered an essential step to prevent muscle loss and enhance physical function in older adults.

OBJECTIVES

This study aimed to assess the role of potential nutritional strategies, i.e., fish oil-derived ω-3 polyunsaturated fatty acids (PUFAs), wheat oligopeptide and their combined intervention, in preventing and reversing sarcopenia in aging process.

METHODS

One hundred 25-month-old Sprague-Dawley rats were randomly divided into 10 groups, and 10 newly purchased 6-month-old rats were included in young control group (n = 10). Fish oil (200, 400 or 800 mg/kg body weight), wheat oligopeptide (100, 200 or 400 mg/kg body weight), fish oil + wheat oligopeptide (800 + 100, 400 + 200 or 200 + 400 mg/kg body weight) or the equal volume of solvent were administered daily by gavage for 10 weeks. The effects of these interventions on natural aging rats were evaluated.

RESULTS

All intervention groups had a significant increase in muscle mass and grip strength and reduction in perirenal fat weight when compared to the aged control group (P < 0.05). The results of biochemical parameters, magnetic resonance imaging, proteomics and western blot suggested that the combination of wheat oligopeptide and fish oil-derived ω-3 PUFA, especially group WFM 2 (400 + 200 mg/kg body weight fish oil + wheat oligopeptide), was found to be more effective against aging-associated muscle loss than single intervention. Additionally, the interventions ameliorated fatty infiltration, muscle atrophy, and congestion in the intercellular matrix, and inflammatory cell infiltration in muscle tissue. The interventions also improved oxidative stress, anabolism, hormone levels, and inflammatory levels of skeletal muscle.

CONCLUSIONS

The combination of fish oil-derived ω-3 PUFA and wheat oligopeptide was found to be a promising nutritional support to prevent and reverse sarcopenia. The potential mechanism involved the promotion of protein synthesis and muscle regeneration, as well as the enhancement of muscle strength.

Parkin is a critical player in the effects of caffeine over mitochondrial quality control pathways during skeletal muscle regeneration in mice

AIM

This study aimed to investigate the effects of caffeine on pathways associated with mitochondrial quality control and mitochondrial capacity during skeletal muscle regeneration, focusing on the role of Parkin, a key protein involved in mitophagy.

METHODS

We used in vitro C2C12 myoblast during differentiation with and without caffeine in the medium, and we evaluated several markers of mitochondrial quality control pathways and myotube growth. In vivo experiments, we used C57BL/6J (WT) and Parkintm 1Shn lineage (Parkin-/- ) mice and injured tibial anterior muscle. The mice regenerated TA muscle for 3, 10, and 21 days with or without caffeine ingestion. TA muscle was used to analyze the protein content of several markers of mitochondrial quality pathways, muscle satellite cell differentiation, and protein synthesis. Furthermore, it analyzed mtDNA, mitochondrial respiration, and myofiber growth.

RESULTS

C2C12 differentiation experiments showed that caffeine decreased Parkin content, potentially leading to increased DRP1 and PGC-1α content and altered mitochondrial population, thereby enhancing growth capacity. Using Parkin-/- mice, we found that caffeine intake during the regenerative process induces an increase in AMPKα phosphorylation and PGC-1α and TFAM content, changes that were partly Parkin-dependent. In addition, the absence of Parkin potentiates the ergogenic effect of caffeine by increasing mitochondrial capacity and myotube growth. Those effects are related to increased ATF4 content and activation of protein synthesis pathways, such as increased 4E-BP1 phosphorylation.

CONCLUSION

These findings demonstrate that caffeine ingestion changes mitochondrial quality control during skeletal muscle regeneration, and Parkin is a central player in those mechanisms.

Post-transcriptional regulation of myogenic transcription factors during muscle development and pathogenesis

The transcriptional regulation of skeletal muscle (SKM) development (myogenesis) has been documented for over 3 decades and served as a paradigm for tissue-specific cell type determination and differentiation. Myogenic stem cells (MuSC) in embryos and adult SKM are regulated by the transcription factors Pax3 and Pax7 for their stem cell characteristics, while their lineage determination and terminal differentiation are both dictated by the myogenic regulatory factors (MRF) that comprise Mrf4, Myf5, Myogenin, and MyoD. The myocyte enhancer factor Mef2c is activated by MRF during terminal differentiation and collaborates with them to promote myoblast fusion and differentiation. Recent studies have found critical regulation of these myogenic transcription factors at mRNA level, including subcellular localization, stability, and translational regulation. Therefore, the regulation of Pax3/7, MRFs and Mef2c mRNAs by RNA-binding factors and non-coding RNAs (ncRNA), including microRNAs and long non-coding RNAs (lncRNA), will be the focus of this review and the impact of this regulation on myogenesis will be further addressed. Interestingly, the stem cell characteristics of MuSC has been found to be critically regulated by ncRNAs, implying the involvement of ncRNAs in SKM homeostasis and regeneration. Current studies have further identified that some ncRNAs are implicated in the etiology of some SKM diseases and can serve as valuable tools/indicators for prediction of prognosis. The roles of ncRNAs in the MuSC biology and SKM disease etiology will also be discussed in this review.

Yap/Taz activity is associated with increased expression of phosphoglycerate dehydrogenase that supports myoblast proliferation

In skeletal muscle, the Hippo effector Yap promotes satellite cell, myoblast, and rhabdomyoblast proliferation but prevents myogenic differentiation into multinucleated muscle fibres. We previously noted that Yap drives expression of the first enzyme of the serine biosynthesis pathway, phosphoglycerate dehydrogenase (Phgdh). Here, we examined the regulation and function of Phgdh in satellite cells and myoblasts and found that Phgdh protein increased during satellite cell activation. Analysis of published data reveal that Phgdh mRNA in mouse tibialis anterior muscle was highly expressed at day 3 of regeneration after cardiotoxin injection, when markers of proliferation are also robustly expressed and in the first week of synergist-ablated muscle. Finally, siRNA-mediated knockdown of PHGDH significantly reduced myoblast numbers and the proliferation rate. Collectively, our data suggest that Phgdh is a proliferation-enhancing metabolic enzyme that is induced when quiescent satellite cells become activated.

Effect of Crude Polysaccharides from Ecklonia cava Hydrolysate on Cell Proliferation and Differentiation of Hanwoo Muscle Stem Cells for Cultured Meat Production

Ecklonia cava, a brown seaweed native to the East Asian coast, is known for its unique composition, including polysaccharides, polyphenols, and phlorotannins. Fucoidan is a sulfated polysaccharide widely used as a functional ingredient in foods. This study obtained crude polysaccharides (ECC_CPS) from E. cava celluclast enzymatic hydrolysate using ethanol precipitation. ECC_CPS increased cell viability during the proliferation of Hanwoo muscle satellite cells (HMSCs). The effect of ECC_CPS on the expression of proliferation-related markers was confirmed as MYF5 and MYOD expression significantly increased, whereas PAX7 expression was maintained. The evaluation of cell migration activity has a major impact on cell proliferation and differentiation, and the cell migration index significantly increased with ECC_CPS treatment (p < 0.01). This was related to the HGF/MET pathway and FAK pathway. Treatment with ECC_CPS promoted differentiation at the cell differentiation stage, thereby increasing the expression of differentiation markers, such as MYH2, MYH7, and MYOG (p < 0.001 or p < 0.01). Therefore, our findings imply that crude polysaccharide obtained from E. cava can be an additive ingredient that enhances the proliferation and differentiation of muscle satellite cells used in the manufacture of cultured meat products.

Selenium Nanoparticles Attenuate Cobalt Nanoparticle-Induced Skeletal Muscle Injury: A Study Based on Myoblasts and Zebrafish

Cobalt alloys have numerous applications, especially as critical components in orthopedic biomedical implants. However, recent investigations have revealed potential hazards associated with the release of nanoparticles from cobalt-based implants during implantation. This can lead to their accumulation and migration within the body, resulting in adverse reactions such as organ toxicity. Despite being a primary interface for cobalt nanoparticle (CoNP) exposure, skeletal muscle lacks comprehensive long-term impact studies. This study evaluated whether selenium nanoparticles (SeNPs) could mitigate CoNP toxicity in muscle cells and zebrafish models. CoNPs dose-dependently reduced C2C12 viability while elevating reactive oxygen species (ROS) and apoptosis. However, low-dose SeNPs attenuated these adverse effects. CoNPs downregulated myogenic genes and α-smooth muscle actin (α-SMA) expression in C2C12 cells; this effect was attenuated by SeNP cotreatment. Zebrafish studies confirmed CoNP toxicity, as it decreased locomotor performance while inducing muscle injury, ROS generation, malformations, and mortality. However, SeNPs alleviated these detrimental effects. Overall, SeNPs mitigated CoNP-mediated cytotoxicity in muscle cells and tissue through antioxidative and antiapoptotic mechanisms. This suggests that SeNP-coated implants could be developed to eliminate cobalt nanoparticle toxicity and enhance the safety of metallic implants.

Effects of Different Delivery Modes on the Expression of Vesicle Transport-Related Genes in Female Pelvic Floor Muscle Repair After Injury

A sudden rise in intra-abdominal pressure that causes the pressure in the bladder to rise during physical movement and/or activity, such as coughing, sneezing, laughing, running, or weightlifting, is known as stress urinary incontinence. This condition causes an uncontrollable overflow of urine. The study's goal was to determine whether effector molecules, specifically ADP ribosylation factor GTPase activated protein 3, might play a part in the female pelvic floor muscle's ability to heal after suffering damage during vaginal delivery. Pelvic floor muscle samples were taken from women who had at least one vaginal delivery and were enrolled in either the IU group (n = 45; issue of stress urinary incontinence) or the NL group (n = 85; no issue of stress urinary incontinence) depending on whether they had a problem with stress urinary incontinence. Vesicle transport-related genes in female pelvic floor muscle injury repair were discovered using Gene Expression Omnibus. For gene analysis and screening, RT-qPCR was employed. On the first day following injury, the expression level of ARFGAP3 mRNA increased by 2.8 times (p 0.05) and by 5 times (p 0.01) on the third day. On the first day following damage, STMN1 mRNA expression rose by 0.3 times (p 0.05). On the first day following injury, the expression level of THBS2 mRNA increased by 1.6 times (p 0.01). On the third day following the injury, the expression level of PLXNB2 mRNA increased by 1.2 times (p 0. 01), and on the fifth day following the injury, it increased by 2.5 times (p 0. 01). After pelvic floor muscle damage, the mRNA expression levels of the CSF1R, ANXA4, and EMR1 genes dropped. Between those with and without pelvic floor muscle damage, there was no statistically significant difference in the expression levels of LGARLS3, KDELR3, and KIF20A mRNA (p > 0. 05 for all). The differential expression of genes after pelvic floor muscle injury can identify the target in the process of pelvic floor muscle injury repair and regeneration.

Changes in vocal fold gene expression and histology after injection augmentation in a recurrent laryngeal nerve injury model

OBJECTIVE

To investigate changes in neuroregenerative pathways with vocal fold denervation in response to vocal fold augmentation.

METHODS

Eighteen Yorkshire crossbreed swine underwent left recurrent laryngeal nerve transection, followed by observation or augmentation with carboxymethylcellulose or calcium hydroxyapatite at two weeks. Polymerase chain reaction expression of genes regulating muscle growth (MyoD1, MyoG and FoxO1) and atrophy (FBXO32) were analysed at 4 and 12 weeks post-injection. Thyroarytenoid neuromuscular junction density was quantified using immunohistochemistry.

RESULTS

Denervated vocal folds demonstrated reduced expression of MyoD1, MyoG, FoxO1 and FBXO32, but overexpression after augmentation. Healthy vocal folds showed increased early and late MyoD1, MyoG, FoxO1 and FBXO32 expression in all animals. Neuromuscular junction density had a slower decline in augmented compared to untreated denervated vocal folds, and was significantly reduced in healthy vocal folds contralateral to augmentation.

CONCLUSION

Injection augmentation may slow neuromuscular degeneration pathways in denervated vocal folds and reduce compensatory remodelling in contralateral healthy vocal folds.

MuSCs and IPCs: roles in skeletal muscle homeostasis, aging and injury

Skeletal muscle is a highly specialized tissue composed of myofibres that performs crucial functions in movement and metabolism. In response to external stimuli and injuries, a range of stem/progenitor cells, with muscle stem cells or satellite cells (MuSCs) being the predominant cell type, are rapidly activated to repair and regenerate skeletal muscle within weeks. Under normal conditions, MuSCs remain in a quiescent state, but become proliferative and differentiate into new myofibres in response to injury. In addition to MuSCs, some interstitial progenitor cells (IPCs) such as fibro-adipogenic progenitors (FAPs), pericytes, interstitial stem cells expressing PW1 and negative for Pax7 (PICs), muscle side population cells (SPCs), CD133-positive cells and Twist2-positive cells have been identified as playing direct or indirect roles in regenerating muscle tissue. Here, we highlight the heterogeneity, molecular markers, and functional properties of these interstitial progenitor cells, and explore the role of muscle stem/progenitor cells in skeletal muscle homeostasis, aging, and muscle-related diseases. This review provides critical insights for future stem cell therapies aimed at treating muscle-related diseases.

Steamed Ginseng Berry Powder Ameliorates Skeletal Muscle Atrophy via Myogenic Effects

Sarcopenia is an age-related loss of muscle mass and function for which there is no approved pharmacological treatment. We tested direct efficacy by evaluating grip strength improvement in a sarcopenia mouse model rather than drug screening, which inhibits specific molecular mechanisms. Various physiological functions of ginseng berries are beneficial to the human body. The present study aimed to evaluate the efficacy and safety of steamed ginseng berry powder (SGBP). SGBP administration increased myotube diameter and suppressed the mRNA expression of sarcopenia-inducing molecules. SGBP also reduced the levels of inflammatory transcription factors and cytokines that are known to induce sarcopenia. Oral administration of SGBP improved muscle mass and physical performance in a mouse model of sarcopenia. In summary, our data suggest that SGBP is a novel therapeutic candidate for the amelioration of muscle weakness, including sarcopenia.