Cellular and molecular regulation of muscle regeneration

Mechanisms of muscle repair after peripheral nerve injury by electrical stimulation combined with blood flow restriction training

This review elucidates the impact of electrical stimulation (ES) and blood flow restriction (BFR) training on muscle function. ES induces a transformation in muscle fibers type by rearranging myosin heavy chain isoform patterns. Additionally, it influences muscle protein synthesis and degradation through specific signaling pathways such as protein kinase B/mechanistic target of rapamycin (Akt/mTOR), as well as via autophagy and the ubiquitin-proteasome system, thereby effectively maintaining muscle mass. BFR, on the other hand, restricts muscle blood flow, leading to metabolic products accumulation and localized hypoxia, which not only promotes the recruitment of fast-twitch fibers but also activates the mTOR signaling pathway, enhancing muscle protein synthesis. The combination of ES and BFR synergistically facilitates muscle protein synthesis through the mTOR pathway, thereby accelerating the recovery of muscle function following peripheral nerve injury.

Circular RNAs and host genes act synergistically in regulating cellular processes and functions in skeletal myogenesis

Circular RNAs (circRNAs) are post-transcriptional regulators generated from backsplicing of pre-mRNAs of host genes. A major circRNA regulatory mechanism involves microRNA (miRNA) sequestering, relieving miRNA-blocked mRNAs for translation and functions. To investigate possible circRNA-host gene relationship, skeletal myogenesis is chosen as a study model for its developmental importance and for readily available muscle tissues from farm animals for studies at different myogenic stages. This review aims to provide an integrated interpretations on methodologies, regulatory mechanisms and possible host gene-circRNA synergistic functional relationships in skeletal myogenesis, focusing on myoblast differentiation and proliferation, core drivers of muscle formation in myogenesis, while other myogenic processes that play supportive roles in the structure, maintenance and function of muscle tissues are also briefly discussed. On literature review,thirty-two circRNAs derived from thirty-one host genes involved in various myogenic stages are identified; twenty-two (68.6 %) of these circRNAs regulate myogenesis by sequestering miRNAs to engage PI3K/AKT and other signaling pathways while four (12.5 %) are translated into proteins for functions. In circRNA-host gene relationship,ten (32.3 %) host genes are shown to regulate myogenesis,nine (29.0 %) are specific to skeletal muscle functions,and twelve (38.8 %) are linked to skeletal muscle disorders.Our analysis of skeletal myogenesis suggests that circRNAs and host genes act synergistically to regulate cellular functions. Such circRNA-host gene functional synergism may also be found in other major cellular processes. CircRNAs may have evolved later than miRNAs to counteract the suppressive effects of miRNAs and to augment host gene functions to further fine-tune gene regulation.

Immunomodulatory role of the stem cell circadian clock in muscle repair

Circadian rhythms orchestrate physiological processes such as metabolism, immune function, and tissue regeneration, aligning them with the optimal time of day (TOD). This study identifies an interplay between the circadian clock within muscle stem cells (SCs) and their capacity to modulate the immune microenvironment during muscle regeneration. We reveal that the SC clock triggers TOD-dependent inflammatory gene transcription after injury, particularly genes related to neutrophil activity and chemotaxis. These responses are driven by cytosolic regeneration of the signaling metabolite nicotinamide adenine dinucleotide (oxidized form) (NAD+), as enhancing cytosolic NAD+ regeneration in SCs is sufficient to induce inflammatory responses that influence muscle regeneration. Mononuclear single-cell sequencing of the regenerating muscle niche further implicates the cytokine CCL2 in mediating SC-neutrophil cross-talk in a TOD-dependent manner. Our findings highlight the intersection between SC metabolic shifts and immune responses within the muscle microenvironment, dictated by circadian rhythms, and underscore the potential for targeting circadian and metabolic pathways to enhance tissue regeneration.

Exploring the potential regulation of DUOX in thyroid hormone‑autophagy signaling via IGF‑1 in the skeletal muscle (Review)

Dual oxidases (DUOX) are enzymes that have the main function in producing reactive oxygen species (ROS) in various tissues. DUOX also play an important role in the synthesis of H2O2, which is essential for the production of thyroid hormone. Thyroid hormones can influence the process of muscle development through direct stimulation of ROS, 5' AMP-activated protein kinase (AMPK) and mTOR and indirect effect autophagy and the insulin-like growth factor 1 (IGF-1) pathway. IGF-1 signaling controls autophagy in two ways: Inhibiting autophagy through activation of the PI3K/AKT/mTOR/MAPK pathway and promoting mitophagy through the nuclear factor erythroid 2-related factor 2-binding receptor Bcl2/adenovirus E1B 19 kDa protein-interacting protein 3. Thyroid hormone deficiency caused by the absence of DUOX should be considered because it might have a significant effect on the growth of skeletal muscle. The effect of DUOX regulation on thyroid hormone autophagy via IGF-1 in skeletal muscle has not been well investigated. The present review discussed the regulatory interactions between DUOX, thyroid hormone, IGF-1 and autophagy, which can influence skeletal muscle development.

The Roles of myomiRs in the Pathogenesis of Sarcopenia: From Literature to In Silico Analysis

Senile sarcopenia is a condition of age-associated muscular disorder and is a significant health issue around the world. In the current review, we curated the information from the NCBI, PubMed, and Google Scholar literature and explored the non-genetic and genetic causes of senile sarcopenia. Interestingly, the myomiRs such as miR-1, miR-206, miR-133a, miR-133b, miR-208b, and miR-499 are skeletal muscle's critical structural and functional regulators. However, very scattered information is available regarding the roles of myomiRs in different skeletal muscle phenotypes through a diverse list of known target genes. Therefore, these pieces of information must be organized to focus on the conserved target genes and comparable effects of the myomiRs in regulating senile sarcopenia. Hence, in the present review, the roles of pathogenetic factors in regulating senile sarcopenia were highlighted. The literature was further curated for the roles of myomiRs such as hsa-miR-1-3p/206, hsa-miR-27-3p, hsa-miR-146-5p, and hsa-miR-499-5p and their target genes. Additionally, we used different bioinformatics tools and predicted target genes of the myomiRs and found the most critical target genes, shared pathways, and their standard functions in regulating muscle structure and functions. The information gathered in the current review will help the researchers to explore their possible therapeutic potential, especially the use of the myomiRs for the treatment of senile sarcopenia.

MEF2A promoter methylation negatively regulates mRNA transcription and affects myoblast physiological function in cattle

This study investigates the regulatory effects of methylation in the promoter region of the bovine MEF2A gene on its transcription levels and the impact on bovine myoblasts. Transcription levels and promoter methylation status of MEF2A in the same tissues of calves and adult cattle were assessed using qRT-PCR and BSP methods. The results indicated that MEF2A expression levels in calves were significantly lower than those in adult cattle (P < 0.05), while the methylation rate of MEF2A was significantly higher in calves (P < 0.05), suggesting a correlation between high methylation levels and reduced gene expression. Subsequently, MEF2A overexpression and interference vectors were transfected into bovine myoblasts to examine the effects of altered MEF2A expression on its promoter methylation status. The findings revealed that MEF2A overexpression significantly reduced the methylation rate (P < 0.01), whereas MEF2A interference increased the methylation rate (P < 0.01), aligning with the expression trends of DNMT1. Furthermore, bovine myoblasts were treated with varying concentrations of the methylation inhibitor 5-Aza-dC to evaluate changes in MEF2A promoter methylation and mRNA levels. The effects on cell cycle progression, apoptosis, and other growth parameters were assessed using flow cytometry, ELISA, and qRT-PCR. Results showed that a concentration of 1 μM 5-Aza-dC effectively reduced MEF2A promoter methylation and significantly upregulated MEF2A expression, leading to accelerated cell cycle progression and increased secretion levels of GH and INS, all differences being statistically significant (P < 0.01). Additionally, 1 μM of 5-Aza-dC promoted apoptosis, with qRT-PCR results for relevant genes supporting this finding. In conclusion, methylation of the MEF2A promoter negatively regulates its mRNA transcription levels, thereby impacting the growth and development of Guanling cattle myoblasts. These results provide valuable insights for the genetic improvement of cattle through marker-assisted selection.

Liposome-Enabled Nanomaterials for Muscle Regeneration

Muscle regeneration is a vital biological process that is crucial for maintaining muscle function and integrity, particularly for the treatment of muscle diseases such as sarcopenia and muscular dystrophy. Generally, muscular tissues can self-repair and regenerate under various conditions, including acute or chronic injuries, aging, and genetic mutation. However, regeneration becomes challenging beyond a certain threshold, particularly in severe muscle injuries or progressive diseases. In recent years, liposome-based nanotechnologies have shown potential as promising therapeutic strategies for muscle regeneration. Liposomes offer an adaptable platform for targeted drug delivery due to their cell membrane-like structure and excellent biocompatibility. They can enhance drug solubility, stability, and targeted delivery while minimizing systemic side effects by different mechanisms. This review summarizes recent advancements, discusses current applications and mechanisms, and highlights challenges and future directions for possible clinical translation of liposome-based nanomaterials in the treatment of muscle diseases. It is hoped this review offers new insights into the development of liposome-enabled nanomedicine to address current limitations.

CRISPR/Cas9-Targeted Myostatin Deletion Improves the Myogenic Differentiation Parameters for Muscle-Derived Stem Cells in Mice

Skeletal muscle plays a pivotal role in physical activity, protein storage and energy utilization. Skeletal muscle wasting due to immobilization, aging, muscular dystrophy and cancer cachexia has negative impacts on the quality of life. The deletion of myostatin, a growth and differentiation factor-8 (GDF-8) augments muscle mass through hyperplasia and hypertrophy of muscle fibers. The present study examines the impact of myostatin deletion using CRISPR/Cas9 editing on the myogenic differentiation (MD) of C2C12 muscle stem cells. A total of five myostatin loci were targeted using guided RNAs that had been previously cloned into a vector. The clones were transfected in C2C12 cells via electroporation. The cell viability and MD of myostatin-edited clones (Mstn-/-) were compared with C2C12 (Mstn+/+) using a series of assays, including MTT, sulforhodamine B, immunocytochemistry, morphometric analysis and RT-qPCR. The clones sequenced showed evidence of nucleotides deletion in Mstn-/- cells. Mstn-/- cells demonstrated a normal physiological performance and lack of cytotoxicity. Myostatin depletion promoted the myogenic commitment as evidenced by upregulated MyoD and myogenin expression. The number of MyoD-positive cells was increased in the differentiated Mstn-/- clones. The Mstn-/- editing upregulates both mTOR and MyH expression, as well as increasing the size of myotubes. The differentiation of Mstn-/- cells upregulates ActRIIb; in contrast, it downregulates decorin expression. The data provide evidence of successful CRISPR/Cas9-mediated myostatin deletion. In addition, targeting myostatin could be a beneficial therapeutic strategy to promote MD and to restore muscle loss. In conclusion, the data suggest that myostatin editing using CRISPR/Cas9 could be a potential therapeutic manipulation to improve the regenerative capacity of muscle stem cells before in vivo application.

Withaferin A Attenuates Muscle Cachexia Induced by Angiotensin II Through Regulating Pathways Activated by Angiotensin II

Cachexia is a multifactorial syndrome characterized by severe muscle wasting and is a debilitating condition frequently associated with cancer. Previous studies from our group revealed that withaferin A (WFA), a steroidal lactone, mitigated muscle cachexia induced by ovarian tumors in NSG mice. However, it remains unclear whether WFA's protective effects are direct or secondary to its antitumor properties. We developed a cachectic model through continuous angiotensin II (Ang II) infusion in C57BL/6 mice to address this issue. Ang II infusion resulted in profound muscle atrophy, evidenced by significant reductions in grip strength and in the TA, GA, and GF muscle mass. Molecular analyses indicated elevated expression of inflammatory cytokines (TNFα, IL-6, MIP-2, IL-18, IL-1β), NLRP3 inflammasome, and genes associated with the UPS (MuRF1, MAFBx) and autophagy pathways (Bacl1, LC3B), along with suppression of anti-inflammatory heme oxygenase-1 (HO-1) and myogenic regulators (Pax7, Myod1). Strikingly, WFA treatment reversed these pathological changes, restoring muscle mass, strength, and molecular markers to near-normal levels. These findings demonstrate that WFA exerts direct anti-cachectic effects by targeting key inflammatory and atrophic pathways in skeletal muscle, highlighting its potential as a novel therapeutic agent for cachexia management.

Skeletal muscle stem cells modulate niche function in Duchenne muscular dystrophy mouse through YY1-CCL5 axis

Adult skeletal muscle stem cells (MuSCs) are indispensable for muscle regeneration and tightly regulated by macrophages (MPs) and fibro-adipogenic progenitors (FAPs) in their niche. Deregulated MuSC/MP/FAP interactions and the ensuing inflammation and fibrosis are hallmarks of dystrophic muscle. Here we demonstrate intrinsic deletion of transcription factor Yin Yang 1 (YY1) in MuSCs exacerbates dystrophic pathologies by altering composition and heterogeneity of MPs and FAPs. Further analysis reveals YY1 loss induces expression of immune genes in MuSCs, including C-C motif chemokine ligand 5 (Ccl5). Augmented CCL5 secretion promotes MP recruitment via CCL5/C-C chemokine receptor 5 (CCR5) crosstalk, which subsequently hinders FAP clearance through elevated Transforming growth factor-β1 (TGFβ1). Maraviroc-mediated pharmacological blockade of the CCL5/CCR5 axis effectively mitigates muscle dystrophy and improves muscle performance. Lastly, we demonstrate YY1 represses Ccl5 transcription by binding to its enhancer thus facilitating promoter-enhancer looping. Altogether, our study demonstrates the critical role of MuSCs in actively shaping their niche and provides novel insight into the therapeutic intervention of muscle dystrophy.

Current Methodologies for Inducing Aligned Myofibers in Tissue Constructs for Skeletal Muscle Tissue Regeneration

Significance: Volumetric muscle loss (VML) results in the loss of large amounts of tissue that inhibits muscle regeneration. Existing therapies, such as autologous muscle transfer and physical therapy, are incapable of returning full function and force production to injured muscle. Recent Advances: Skeletal muscle tissue constructs may provide an alternative to existing therapies currently used to treat VML. Unlike autologous muscle transplants, muscle constructs can be cultured in vitro and are not reliant on intact muscle tissue. Skeletal muscle constructs can be generated from small muscle biopsies and could be used to generate skeletal muscle tissue constructs to replace injured tissues. Critical Issues: To serve as effective therapies, muscle constructs must be capable of generating contractile forces that can assist the function of host skeletal muscle. The contractile force of native muscle arises in part as a consequence of the highly aligned, bundled architecture of myofibers. Attempts to induce similar alignment include applications of tension/strain across hydrogels, inducing aligned architectures within scaffolds, casting tissues in straited molds, and 3D printing. While all these methods have demonstrated efficacy toward inducing myofiber alignment, the extent of myofiber alignment, tissue formation, and force production varies. This manusript critically reviews the advantages and limitations of these methods and specifically discusses their ability to impart mechanical and architectural cues to induce alignment within tissue constructs. Future Directions: As tissue-synthesizing techniques continue to improve, muscle constructs must include more cell types than simply myoblasts, such as the addition of neuronal and endothelial cells. Higher-level tissue organization is critical to the success of these constructs. Many of these technologies have yet to be implanted into host tissue to understand engraftment and how they can contribute to traumatic injury, and as such continued collaboration between surgeons and tissue engineers is necessary to ultimately result in clinical translation.

Cytotoxic T-Lymphocyte-Associated Protein 4 Fused to a Modified Fragment of IgG1 Reduces Muscle Fiber Damage in a Model of Duchenne Muscular Dystrophy by Attenuating Proinflammatory Gene Expression in Myeloid Lineage Cells

Duchenne muscular dystrophy (DMD) is a lethal, muscle-wasting, genetic disease that is greatly amplified by an immune response to the diseased muscles. The mdx mouse model of DMD was used to test whether the pathology can be reduced by treatments with a cytotoxic T-lymphocyte-associated protein 4 fused to a modified fragment of IgG1 (CTLA4-Ig) fusion protein that blocks costimulatory signals required for activation of T cells. CTLA4-Ig treatments reduced mdx sarcolemma lesions and reduced the numbers of activated T cells, macrophages, and antigen-presenting cells in mdx muscle and reduced macrophage invasion into muscle fibers. In vitro data showed that CTLA4-Ig acts directly on bone marrow cells and macrophages to modify their function and gene expression. CTLA4-Ig treatments of mdx bone marrow cells diminished their mobility and chemotactic response to chemokine ligand-2. Treating mdx macrophages with CTLA4-Ig reduced their cytolysis of muscle cells in vitro. RNA-sequencing analysis of mdx macrophages showed that CTLA4-Ig reduced expression of genes associated with leukocyte chemotaxis, migration, and extravasation; >90% of those affected genes were tumor necrosis factor-α target genes. Comparison of mdx and wild-type macrophages by RNA sequencing showed that 46% of the genes down-regulated by CTLA4-Ig were genes up-regulated in macrophages by the presence of muscular dystrophy in mice. These findings show that CTLA4-Ig is a promising immunotherapeutic for DMD, and many of its beneficial effects may result from direct actions on macrophages that modify their expression of proinflammatory genes.

Rapamycin improves satellite cells' autophagy and muscle regeneration during hypercapnia

Both CO2 retention, or hypercapnia, and skeletal muscle dysfunction predict higher mortality in critically ill patients. Mechanistically, muscle injury and reduced myogenesis contribute to critical illness myopathy, and while hypercapnia causes muscle wasting, no research has been conducted on hypercapnia-driven dysfunctional myogenesis in vivo. Autophagy flux regulates myogenesis by supporting skeletal muscle stem cell - satellite cell - activation, and previous data suggest that hypercapnia inhibits autophagy. We tested whether hypercapnia worsens satellite cell autophagy flux and myogenic potential and if autophagy induction reverses these deficits. Satellite cell transplantation and lineage-tracing experiments showed that hypercapnia undermined satellite cells' activation, replication, and myogenic capacity. Bulk and single-cell sequencing analyses indicated that hypercapnia disrupts autophagy, senescence, and other satellite cell programs. Autophagy activation was reduced in hypercapnic cultured myoblasts, and autophagy genetic knockdown phenocopied these changes in vitro. Rapamycin stimulation led to AMPK activation and downregulation of the mTOR pathway, which are both associated with accelerated autophagy flux and cell replication. Moreover, hypercapnic mice receiving rapamycin showed improved satellite cell autophagy flux, activation, replication rate, and posttransplantation myogenic capacity. In conclusion, we have shown that hypercapnia interferes with satellite cell activation, autophagy flux, and myogenesis, and systemic rapamycin administration improves these outcomes.

Adapting cytoskeleton-mitochondria patterning with myocyte differentiation by promyogenic PRR33

Coordinated cytoskeleton-mitochondria organization during myogenesis is crucial for muscle development and function. Our understanding of the underlying regulatory mechanisms remains inadequate. Here, we identified a novel muscle-enriched protein, PRR33, which is upregulated during myogenesis and acts as a promyogenic factor. Depletion of Prr33 in C2C12 represses myoblast differentiation. Genetic deletion of Prr33 in mice reduces myofiber size and decreases muscle strength. The Prr33 mutant mice also exhibit impaired myogenesis and defects in muscle regeneration in response to injury. Interactome and transcriptome analyses reveal that PRR33 regulates cytoskeleton and mitochondrial function. Remarkably, PRR33 interacts with DESMIN, a key regulator of cytoskeleton-mitochondria organization in muscle cells. Abrogation of PRR33 in myocytes substantially abolishes the interaction of DESMIN filaments with mitochondria, leading to abnormal intracellular accumulation of DESMIN and mitochondrial disorganization/dysfunction in myofibers. Together, our findings demonstrate that PRR33 and DESMIN constitute an important regulatory module coordinating mitochondrial organization with muscle differentiation.

Neuromuscular Regeneration of Volumetric Muscle Loss Injury in Response to Agrin-Functionalized Tissue Engineered Muscle Grafts and Rehabilitative Exercise

Neuromuscular deficits compound the loss of contractile tissue in volumetric muscle loss (VML). Two avenues for promoting recovery are neuromuscular junction (NMJ)-promoting substrates (e.g., agrin) and endurance exercise. Although mechanical stimulation enhances agrin-induced NMJ formation, the two modalities have yet to be evaluated combinatorially. It is hypothesized that the implantation of human myogenic progenitor-seeded tissue-engineered muscle grafts (hTEMGs) in combination with agrin treatment and/or exercise will enhance neuromuscular recovery after VML. The hTEMGs alone transplant into VML defects promote significant regeneration with minimal scarring. A sex-appropriate, low-intensity continuous running exercise paradigm increases acetylcholine receptor (AChR) cluster density in male mice twofold relative to hTEMG alone after 7 weeks of treadmill training (p < 0.05). To further promote neuromuscular recovery, agrin is incorporated into the scaffolds via covalent tethering. In vitro, agrin increases the proliferation of hMPs, and trends toward greater myogenic maturity and AChR clustering. Upon transplantation, both hTEMGs + agrin and hTEMGs + exercise induce near 100% recovery of muscle mass and increase twitch and tetanic force output (p > 0.05). However, agrin treatment in combination with exercise produces no additional benefit. These data highlight the unprecedented regenerative potential of using hTEMGs together with either agrin or exercise supplementation to treat VML injuries.

Effects of Alnus japonica Hot Water Extract and Oregonin on Muscle Loss and Muscle Atrophy in C2C12 Murine Skeletal Muscle Cells

Background/Objectives: Sarcopenia is characterized by the loss of muscle mass and function, increases in mortality rate, and risk of comorbidities in the elderly. This study evaluated the effects of Alnus japonica hot water extract (AJHW) and its active compound, oregonin, on muscle atrophy and apoptosis in vitro. Methods: AJHW underwent phytochemical analysis. C2C12 cells were subjected to H2O2 and dexamethasone to induce oxidative stress and muscle loss, after which AJHW and oregonin were administered to assess their impacts on cell viability, apoptosis, muscle protein synthesis stimulation, and muscle protein degradation inhibition. Cell viability was assessed via an MTT assay, and apoptosis was analyzed by measuring Bcl-2, Bax, cleaved caspase-3, and cleaved PARP through Western blotting. Western blotting and RT-PCR were utilized to analyze MyoD, Myogenin, Atrogin-1, and MuRF1 protein and gene expression in a muscle atrophy model, as well as the Akt/mTOR and FoxO3α pathways. Results: AJHW was confirmed to contain oregonin, an active compound. AJHW and oregonin significantly increased cell viability and reduced apoptosis by upregulating Bcl-2 and downregulating Bax, cleaved caspase-3, and cleaved PARP. They significantly enhanced muscle protein synthesis through the upregulation of MyoD and Myogenin, while diminishing muscle degradation by downregulating Atrogin-1 and MuRF1. The activation of the Akt/mTOR pathway and inhibition of the FoxO3α pathway were also observed. Conclusions: AJHW and oregonin effectively prevented muscle cell apoptosis, promoted muscle protein synthesis, and inhibited muscle protein degradation in vitro. These results suggest that AJHW and oregonin could serve as therapeutic agents to prevent and treat sarcopenia.

Biophysics of ACL Injuries

Anterior Cruciate Ligament (ACL) injuries rank among the most prevalent and severe types of injuries, significantly impacting both athletes and non-athletes alike. These injuries not only result in immediate physical impairment, such as intense pain, substantial swelling, and a marked loss of mobility, but also carry long-term health consequences that can alter a person's quality of life. Chronic pain, persistent instability, and an increased risk of developing osteoarthritis are among the lasting effects that can follow an ACL injury. An in-depth understanding of the biophysics behind ACL injuries is paramount for devising effective prevention and treatment protocols. Biophysics, which combines principles from physics with biological systems, provides crucial insights into the mechanical and structural integrity of the ACL and its susceptibility to injury under various conditions. This systematic review aims to collate and synthesize the current knowledge surrounding the biophysical mechanisms that underlie ACL injuries.

The miR-6240 target gene Igf2bp3 promotes myoblast fusion by enhancing myomaker mRNA stability

BACKGROUND

Myoblast fusion plays a crucial role in myogenesis. Insulin-like growth factor 2 mRNA-binding protein 3 (IGF2BP3) functions as an RNA N6-methyladenosine reader and exerts important roles in various biological processes. While our prior study suggested Igf2bp3 contributes to myogenesis, its molecular regulatory mechanism is largely unclear.

METHODS

Real-time quantitative polymerase chain reaction (RT-qPCR) and western blot were used for gene expression analysis. siRNA and CRISPRi technologies were conducted to knockdown the expression of Igf2bp3. CRISPR/Cas9 technology was performed to knockout Igf2bp3. The Igf2bp3 overexpression vector was designed using the pcDNA3.1(+) vector. Immunofluorescence detection was employed for subcellular localization and cell differentiation analysis. Cell Counting Kit-8 (CCK-8) and 5-ethynyl-2'-deoxyuridine (EdU) assays were conducted for cell proliferation and fusion detection. The dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay were utilized for regulatory mechanism analysis of Igf2bp3.

RESULTS

The overexpression of Igf2bp3 enhances myoblast fusion while knockdown of Igf2bp3 blocks the formation of myotubes. miR-6240 promotes myoblast proliferation while preventing myoblast differentiation and fusion by targeting the 3' untranslated rgion (UTR) of Igf2bp3. Notably, the impacts of miR-6240 mimics on myoblast proliferation, differentiation, and fusion can be effectively counteracted by the overexpression of Igf2bp3. Moreover, our findings elucidate a direct interaction between Igf2bp3 and the myoblast fusion factor myomaker (Mymk). Igf2bp3 binds to Mymk to enhance its mRNA stability. This interaction results in increased expression of Mymk and heightened myoblast fusion.

CONCLUSIONS

Our study unveils Igf2bp3 as a novel post-transcriptional regulator of myoblast fusion through the miR-6240/Mymk axis, significantly contributing to our understanding of skeletal muscle development.

Mechanisms of muscle cells alterations and regeneration decline during aging

Skeletal muscles are essential for locomotion and body metabolism regulation. As muscles age, they lose strength, elasticity, and metabolic capability, leading to ineffective motion and metabolic derangement. Both cellular and extracellular alterations significantly influence muscle aging. Satellite cells (SCs), the primary muscle stem cells responsible for muscle regeneration, become exhausted, resulting in diminished population and functionality during aging. This decline in SC function impairs intercellular interactions as well as extracellular matrix production, further hindering muscle regeneration. Other muscle-resident cells, such as fibro-adipogenic progenitors (FAPs), pericytes, and immune cells, also deteriorate with age, reducing local growth factor activities and responsiveness to stress or injury. Systemic signaling, including hormonal changes, contributes to muscle cellular catabolism and disrupts muscle homeostasis. Collectively, these cellular and environmental components interact, disrupting muscle homeostasis and regeneration in advancing age. Understanding these complex interactions offers insights into potential regenerative strategies to mitigate age-related muscle degeneration.

Spatio-temporal expression of Sox2+ progenitor cells regulates the regeneration of rat submandibular gland

OBJECTIVE

Sox2 plays crucial roles in tissues homeostasis and regeneration. However, there are lack of a comprehensive examination of Sox2 expression and its functional role in submandibular gland regeneration. Therefore, we aimed to elucidate the impact of Sox2 on submandibular gland regeneration.

MATERIALS AND METHODS

A Sprague-Dawley rat submandibular gland duct ligation/de-ligation regeneration model was conducted in this study. Sox2-shRNA vectors were retro-ductally administered into the submandibular gland to establish a stable Sox2 knockdown model. Conventional histopathological and molecular biological methods were used to investigate phenotypic changes.

RESULTS

The submandibular gland normalized completely 28 days after ligature removal (following 7 days of duct ligation). AQP5 expression gradually increased after ligation removal until returning to normal levels. In submandibular gland regeneration, Sox2 re-expressed and co-expressed with AQP5+ acinar cells, and Sox2 expression peaked on day 14, recovered to normal on day 28, reproducing the developmental pattern. Sox2 knockdown hindered gland regeneration and induced irreversible fibrosis. The AQP5 expression was significantly lower than the contemporaneous solely ligated group, while the blue collagen deposition and the Vimentin expression increased prominently. The expression of CD68, IL-1β, TNF-α and IL-17A increased significantly, and epithelial cells in the Sox2 knockdown group expressed higher levels of IL-17A.

CONCLUSIONS

These findings highlight Sox2 as a crucial regulator of the acinar cell lineage. Sox2+ progenitor cells are pivotal for acinar cell maintenance, which is indispensable for submandibular gland regeneration. Collectively, our findings may help develop targeted interventions for enhancing tissue repair and preventing irreversible fibrosis in salivary gland disorders.

miR-136-5p/FZD4 axis is critical for Wnt signaling-mediated myogenesis and skeletal muscle regeneration

Skeletal muscle can undergo a regenerative process in response to injury or disease to maintain muscle quality and function. Myogenesis depends on the proliferation and differentiation of myoblasts, and miRNAs can maintain the balance between them by precisely regulating many key factors in the myogenic network. Here, we found that miR-136-5p was significantly upregulated during the proliferation and differentiation of C2C12 cells. We demonstrate that miR-136-5p acts as a myogenic negative regulator during the development of mouse C2C12 myoblasts. In terms of mechanism, miR-136-5p inhibits the formation of β-catenin/LEF/TCF DNA-binding factor transcriptional regulatory complex by targeting FZD4, a gating protein in the Wnt signaling pathway, thereby enhancing downstream myogenic factors and finally promoting myoblast proliferation and differentiation. In addition, in BaCl2-induced muscle injury mouse model, miR-136-5p knockdown accelerated the regeneration of skeletal muscle after injury, and further led to the improvement of gastrocnemius muscle mass and muscle fiber diameter, while being suppressed by shFZD4 lentivirus infection. In summary, these results demonstrate the essential role of miR-136-5p/FZD4 axis in skeletal muscle regeneration. Given the conservation of miR-136-5p among species, miR-136-5p may be a new target for treating human skeletal muscle injury and improving the production of animal meat products.

Theabrownin/whey protein isolate complex coacervate strengthens C2C12 cell proliferation via modulation of energy metabolism and mitochondrial apoptosis

Theabrownin (TB)-whey protein isolate (WPI) complex coacervates (TW) were firstly prepared to investigate the regulatory effects on skeletal muscle. The binding of TB to WPI reached saturation with the strongest electrostatic interaction at the ratio of 10:1. The formation of TW was driven by electrostatic interactions with the aid of hydrogen bonding and hydrophobic interactions, and the digestion behavior of TW was investigated based on in vitro gastrointestinal and CaCO2 cell models. The regulatory effect of TW on muscle cells was investigated by C2C12 cell assay. Cell cycle analysis showed that TW promoted the transition of skeletal muscle cells from proliferative state to differentiated state. Immunofluorescence and gene expression revealed that TW positively regulated myogenic regulatory factors, contributing to myofiber formation. Moreover, TW activated the intracellular TCA cycling and oxidative phosphorylation, providing energy for skeletal muscle regeneration and repair. Mechanistically, TW inhibited the release of cytochrome C from mitochondria to cytoplasm through the Bcl-2/Cytochrome C/Cleaved-Caspase-3 pathway, exhibiting a protective effect on skeletal muscle cells. In the future, the molecular mechanism of TW enhancing skeletal muscle function should be validated through aging animal models and clinical trials and expand its therapeutic application for muscle health in functional food and dietary supplements.

From Food Supplements to Functional Foods: Emerging Perspectives on Post-Exercise Recovery Nutrition

Effective post-exercise recovery is vital for optimizing athletic performance, focusing on muscle repair, glycogen replenishment, rehydration, and inflammation management. This review explores the evolving trend from traditional supplements, such as protein, carbohydrates, creatine, and branched-chain amino acids (BCAAs), toward functional foods rich in bioactive compounds. Evidence highlights the benefits of functional foods like tart cherry juice (anthocyanins), turmeric-seasoned foods, and sources of omega-3 fatty acids, including fish, flaxseeds, chia seeds, and walnuts, for mitigating oxidative stress and inflammation. Additionally, probiotics and prebiotics support gut health and immune function, which are integral to effective recovery. Personalized nutrition, informed by genetic and metabolic profiling, is examined as a promising approach to tailor recovery strategies. A systematic search across PubMed, Web of Science, and Google Scholar (2000-2024) identified studies with high empirical rigor and relevance to recovery outcomes. Findings underscore the need for further research into nutrient interactions, dosage optimization, and long-term effects on athletic performance. Integrating functional foods with personalized nutrition presents a comprehensive framework for enhanced recovery, greater resilience to physical stress, and sustained performance in athletes.

C60 Fullerene Reduces the Development of Post-Traumatic Dysfunction in Rat Soleus Muscle

Traumatic skeletal muscle injury is a complex pathology caused by high-energy trauma to muscle tissue. Previously, a positive effect was established when C60 fullerene was administered against the background of muscle ischemia, mechanical muscle injury, and other muscle dysfunctions, which probably protected the muscle tissue from damage caused by oxidative stress. Using tensiometry and biochemical analysis, the biomechanical parameters of skeletal muscle contraction and biochemical indices of the blood of rats 15 days after traumatic injury of the soleus muscle caused by myocyte destruction by compression were studied. The intraperitoneal administration of C60 fullerene aqueous solution (C60FAS) in a daily dose of 1 mg/kg improved its contractile function by 28-40 ± 2% and the values of the investigated biochemical indices of the animals' blood by 15-34 ± 2% relative to the trauma group. The obtained results indicate the potential ability of C60 fullerenes, as powerful antioxidants, to reduce the development of post-traumatic dysfunction of the soleus muscle.

Effects of Diet Supplemented With Hydrolyzable Tannin on the Growth Performance, Antioxidant Capacity, and Muscle Nutritional Quality of Juvenile Mastacembelus armatus

In this study, four groups of diet were prepared, with eel commercial diet without hydrolyzable tannin (HT) as the control group (H0), and the other three groups were fed with diet containing 0.05% (H1), 0.1% (H2), and 0.2% (H3) doses of HT to juvenile Mastacembelus armatus with an initial body weight of (0.40 ± 0.005) g. Juvenile fish in all groups were fed continuously for 60 days. Growth indices, hepatopancreatic antioxidant enzymes, biochemical indices (including total superoxide dismutase [T-SOD], catalase [CAT], malondialdehyde [MDA], total antioxidant capacity [T-AOC], alanine aminotransferase [ALT], aspartate aminotransferase [AST], alkaline phosphatase [AKP], and triglyceride [TG]), the content of muscle amino acids and fatty acids, stomach and intestine enzyme activities (pepsin, amylase, lipase), and genes expressions were evaluated. The results showed that 0.1% HT significantly improved the growth performance, hepatopancreatic antioxidant capacity, as well as muscle quality and lipase activity of juvenile M. armatus. In summary, the optimal addition level of HT in the diet of juvenile M. armatus is 0.1%, which helps to improve aquaculture efficiency and improve the muscle quality of M. armatus. However, the long-term effects of feeding HT on M. armatus and its physiological reaction mechanism need to be further explored.

Effect of NR1D1 on the proliferation and differentiation of yak skeletal muscle satellite cells

The severe conditions at high altitudes, where yaks inhabit, contribute to delayed muscular growth and compromised tenderness of their muscle tissue. Myosatellite cells are responsible for the growth and regeneration of skeletal muscle after birth and have the potential to proliferate and differentiate, its development is closely related to meat quality, and the nuclear receptor gene NR1D1 is involved in muscle formation and skeletal muscle regulation. Therefore, in order to understand the effect of NR1D1 on muscle satellite cells, we identified the mRNA expression levels of marker genes specifically expressed in muscle satellite cells at different stages to determine the type of cells isolated. Eventually, we successfully constructed a primary cell line of yak muscle satellite cells. Then we constructed NR1D1 overexpression vector and interference RNA, and introduced them into isolated yak skeletal muscle satellite cells. We performed qPCR, CCK8, and fluorescence-specific to detect the expression of genes or abundance of proteins as markers of cell proliferation and differentiation. Compared with those in the control group, the expression levels of proliferation marker genes KI-67, CYCLIND1, and CYCLINA were significantly inhibited after NR1D1 overexpression, which was also supported by the CCK-8 test, whereas differentiation marker genes MYOD, MYOG, and MYF5 were significantly inhibited. Fluorescence-specific staining showed that KI-67 protein abundance and the number of microfilaments both decreased, while the opposite trend was observed after NR1D1 interference. In conclusion, we confirmed that NR1D1 inhibited the proliferation and differentiation of yak skeletal muscle satellite cells, which provides a theoretical basis for further research on the effect of NR1D1 on improving meat quality traits and meat production performance of yaks.

Simulated altitude is medicine: intermittent exposure to hypobaric hypoxia and cold accelerates injured skeletal muscle recovery

Muscle injuries are the leading cause of sports casualties. Because of its high plasticity, skeletal muscle can respond to different stimuli to maintain and improve functionality. Intermittent hypobaric hypoxia (IHH) improves muscle oxygen delivery and utilization. Hypobaria coexists with cold in the biosphere, opening the possibility to consider the combined use of both environmental factors to achieve beneficial physiological adjustments. We studied the effects of IHH and cold exposure, separately and simultaneously, on muscle regeneration. Adult male rats were surgically injured in one gastrocnemius and randomly assigned to the following groups: (1) CTRL: passive recovery; (2) COLD: intermittently exposed to cold (4°C); (3) HYPO: submitted to IHH (4500 m); (4) COHY: exposed to intermittent simultaneous cold and hypoxia. Animals were subjected to these interventions for 4 h/day for 9 or 21 days. COLD and COHY rats showed faster muscle regeneration than CTRL, evidenced after 9 days at histological (dMHC-positive and centrally nucleated fibre reduction) and functional levels after 21 days. HYPO rats showed a full recovery from injury (at histological and functional levels) after 9 days, while COLD and COHY needed more time to induce a total functional recovery. IHH can be postulated as an anti-fibrotic treatment since it reduces collagen I deposition. The increase in the pSer473Akt/total Akt ratio observed after 9 days in COLD, HYPO and COHY, together with the increase in the pThr172AMPKα/total AMPKα ratio observed in the gastrocnemius of HYPO, provides clues to the molecular mechanisms involved in the improved muscle regeneration. KEY POINTS: Only intermittent hypobaric exposure accelerated muscle recovery as early as 9 days following injury at histological and functional levels. Injured muscles from animals treated with intermittent (4 h/day) cold, hypobaric hypoxia or a simultaneous combination of both stimuli regenerated histological structure and recovered muscle function 21 days after injury. The combination of cold and hypoxia showed a blunting effect as compared to hypoxia alone in the time course of the muscle recovery. The increased expression of the phosphorylated forms of Akt observed in all experimental groups could participate in the molecular cascade of events leading to a faster regeneration. The elevated levels of phosphorylated AMPKα in the HYPO group could play a key role in the modulation of the inflammatory response during the first steps of the muscle regeneration process.

Spiny mice are primed but fail to regenerate volumetric skeletal muscle loss injuries

BACKGROUND

In recent years, the African spiny mouse Acomys cahirinus has been shown to regenerate a remarkable array of severe internal and external injuries in the absence of a fibrotic response, including the ability to regenerate full-thickness skin excisions, ear punches, severe kidney injuries, and complete transection of the spinal cord. While skeletal muscle is highly regenerative in adult mammals, Acomys displays superior muscle regeneration properties compared with standard laboratory mice following several injuries, including serial cardiotoxin injections of skeletal muscle and volumetric muscle loss (VML) of the panniculus carnosus muscle following full-thickness excision injuries. VML is an extreme muscle injury defined as the irrecoverable ablation of muscle mass, most commonly resulting from combat injuries or surgical debridement. Barriers to the treatment of VML injury include early and prolonged inflammatory responses that promote fibrotic repair and the loss of structural and mechanical cues that promote muscle regeneration. While the regeneration of the panniculus carnosus in Acomys is impressive, its direct relevance to the study of VML in patients is less clear as this muscle has largely been lost in humans, and, while striated, is not a true skeletal muscle. We therefore sought to test the ability of Acomys to regenerate a skeletal muscle more commonly used in VML injury models.

METHODS

We performed two different VML injuries of the Acomys tibialis anterior muscle and compared the regenerative response to a standard laboratory mouse strain, Mus C57BL6/J.

RESULTS

Neither Acomys nor Mus recovered lost muscle mass or myofiber number within three months following VML injury, and Acomys also failed to recover force production better than Mus. In contrast, Acomys continued to express eMHC within the injured area even three months following injury, whereas Mus ceased expressing eMHC less than one-month post-injury, suggesting that Acomys muscle was primed, but failed, to regenerate.

CONCLUSIONS

While the panniculus carnosus muscle in Acomys regenerates following VML injury in the context of full-thickness skin excision, this regenerative ability does not translate to regenerative repair of a skeletal muscle.

Synaptic-like coupling of macrophages to myofibers regulates muscle repair

Peripheral injury responses essential for muscle repair and nociception require complex interactions of target tissues, immune cells and primary sensory neurons. Nociceptors and myofibers both react robustly to signals generated from circulating immune cells, which promote repair, growth, and regeneration of muscle while simultaneously modulating peripheral sensitization. Here, we found that macrophages form a synaptic-like contact with myofibers to hasten repair after acute incision injury and to facilitate regeneration after major muscle damage. Transient chemogenetic activation of macrophages enhanced calcium dependent membrane repair, induced muscle calcium waves in vivo , elicited low level electrical activity in the muscles and enhanced myonuclear accretion. Under severe injury, macrophage activation could also modulate pain-like behaviors. This study identifies a novel mechanism by which synaptic-like functions of macrophages impacts muscle repair after tissue damage.

Suppressing PDGFRβ Signaling Enhances Myocyte Fusion to Promote Skeletal Muscle Regeneration

Muscle cell fusion is critical for forming and maintaining multinucleated myotubes during skeletal muscle development and regeneration. However, the molecular mechanisms directing cell-cell fusion are not fully understood. Here, we identify platelet-derived growth factor receptor beta (PDGFRβ) signaling as a key modulator of myocyte fusion in adult muscle cells. Our findings demonstrate that genetic deletion of Pdgfrβ enhances muscle regeneration and increases myofiber size, whereas PDGFRβ activation impairs muscle repair. Inhibition of PDGFRβ activity promotes myonuclear accretion in both mouse and human myotubes, whereas PDGFRβ activation stalls myotube development by preventing cell spreading to limit fusion potential. Transcriptomics analysis show that PDGFRβ signaling cooperates with TGFβ signaling to direct myocyte size and fusion. Mechanistically, PDGFRβ signaling requires STAT1 activation, and blocking STAT1 phosphorylation enhances myofiber repair and size during regeneration. Collectively, PDGFRβ signaling acts as a regenerative checkpoint and represents a potential clinical target to rapidly boost skeletal muscle repair.

Exogenous hydrogen sulfide enhances myogenic differentiation of C2C12 myoblasts under high palmitate stress

Skeletal muscle atrophy was one of main complications of type 2 diabetes mellitus. Hydrogen sulfide (H2S) is involved in various physiological functions, such as anti-hypertension and anti-oxidant. Skeletal muscle atrophy caused by type 2 diabetes could lead to the regeneration of muscle fibers. Wnt signaling pathway plays a crucial important role in this process. H2S maybe regulate the Wnt signaling pathway to alleviate skeletal muscle atrophy, however, this role has not been clarified. The aim of this study is to investigate the potential regulatory role of H2S in the Wnt signaling pathway. C2C12 myoblasts treated with 500 μmol palmitate as an in vitro model. Western blot was used to detect the levels of CSE, PKM1, β-catenin, MuRF1, MYOG, MYF6 and MYOD1. In addition, MuRF1 was mutated at Cys44 and MuRF1 S-sulfhydration was detected by biotin switch assay. The interaction between PKM1 and MuRF1 was assessed via Co-immunoprecipitation. Differentiation of C2C12 myoblasts was evaluated using LAMININ staining. These data showed the levels of CSE, β-catenin, PKM1, MYOG, MYF6 and MYOD1 were decreased in pal group, compared with control and pal + NaHS groups. MuRF1 Cys44 mutants increased the protein levels of β-catenin, MYOG, MYF6 and MYOD1 in pal group. Our results suggest that H2S regulates the S-sulfhydration levels of MuRF1 at Cys44, influencing the ubiquitination levels of PKM1 and ultimately promoting myoblast differentiation.

CLIC5 promotes myoblast differentiation and skeletal muscle regeneration via the BGN-mediated canonical Wnt/β-catenin signaling pathway

Myoblast differentiation plays a vital role in skeletal muscle regeneration. However, the protein-coding genes controlling this process remain incompletely understood. Here, we showed that chloride intracellular channel 5 (CLIC5) exerts a critical role in mediating myogenesis and skeletal muscle regeneration. Deletion of CLIC5 in skeletal muscle leads to reduced muscle weight and decreases the number and differentiation potential of satellite cells. In vitro, CLIC5 consistently inhibits myoblast proliferation while promoting myotube formation. CLIC5 promotes myogenic differentiation by activating the canonical Wnt/β-catenin signaling pathway in a biglycan (BGN)-dependent manner. CLIC5 deletion impairs muscle regeneration. Paired box gene 7 (Pax7) expression and the activity of BGN-mediated canonical Wnt/β-catenin signaling are reduced in CLIC5-deficient mice. Conversely, increasing CLIC5 levels in skeletal muscles enhances muscle regeneration capacity. In conclusion, our findings underscore CLIC5 as a pivotal regulator of myogenesis and skeletal muscle regeneration, functioning through interaction with BGN to activate the canonical Wnt/β-catenin signaling pathway.

Granular Hydrogels Improve Myogenic Invasion and Repair after Volumetric Muscle Loss

Skeletal muscle injuries including volumetric muscle loss (VML) lead to excessive tissue scarring and permanent functional disability. Despite its high prevalence, there is currently no effective treatment for VML. Bioengineering interventions such as biomaterials that fill the VML defect to support cell and tissue growth are a promising therapeutic strategy. However, traditional biomaterials developed for this purpose lack the pore features needed to support cell infiltration. The present study investigates for the first time, the impact of granular hydrogels on muscle repair - hypothesizing that their flowability will permit conformable filling of the defect site and their inherent porosity will support the invasion of native myogenic cells, leading to effective muscle repair. Small and large microparticle fragments are prepared from photocurable hyaluronic acid polymer via extrusion fragmentation and facile size sorting. In assembled granular hydrogels, particle size and degree of packing significantly influence pore features, rheological behavior, and injectability. Using a mouse model of VML, it is demonstrated that, in contrast to bulk hydrogels, granular hydrogels support early-stage (satellite cell invasion) and late-stage (myofiber regeneration) muscle repair processes. Together, these results highlight the promising potential of injectable and porous granular hydrogels in supporting endogenous repair after severe muscle injury.

Bioactive Nb2C MXene-Functionalized Hydrogel with Microenvironment Remodeling and Enhanced Neurogenesis to Promote Skeletal Muscle Regeneration and Functional Restoration

The complete structure-functional repair of volumetric muscle loss (VML) remains a giant challenge and biomedical hydrogels to remodel microenvironment and enhance neurogenesis have appeared to be a promising direction. However, the current hydrogels for VML repair hardly achieve these two goals simultaneously due to their insufficient functionality and the challenge in high-cost of bioactive factors. In this study, a facile strategy using Nb2C MXene-functionalized hydrogel (OPTN) as a bioactive scaffold is proposed to promote VML repair with skeletal muscle regeneration and functional restoration. In vitro experiments show that OPTN scaffold can effectively scavenge reactive oxygen species (ROS), guide macrophages polarization toward M2 phenotype, and resist bacterial infection, providing a favorable microenvironment for myoblasts proliferation as well as the endothelial cells proliferation, migration, and tube formation. More importantly, OPTN scaffold with electroactive feature remarkably boosts myoblasts differentiation and mesenchymal stem cells neural differentiation. Animal experiments further confirm that OPTN scaffold can achieve a prominent structure-functional VML repair by attenuating ROS levels, alleviating inflammation, reducing fibrosis, and facilitating angiogenesis, newborn myotube formation, and neurogenesis. Collectively, this study provides a highly promising and effective strategy for the structure-functional VML repair through designing bioactive multifunctional hydrogel with microenvironment remodeling and enhanced neurogenesis.

In ovo betaine injection improves breast muscle growth in newly hatched goslings through FXR/IGF-2 pathway

Betaine has been shown to enhance growth performance and increase breast muscle yield in ducks and broilers through various mechanisms, including the modification of DNA methylation. However, the impact of in ovo betaine injection on muscle growth in newly hatched goslings remains unclear. In this study, fifty eggs were injected with saline or betaine at 7.5 mg/egg prior to incubation, and the subsequent effects on breast muscle growth in the newly hatched goslings were investigated. Betaine significantly increased (P < 0.05) the hatch weight, breast muscle weight, and breast muscle index, accompanied by an augmentation in muscle bundle cross-sectional area. Concurrently, betaine significantly upregulated (P < 0.05) the expression levels of myogenic regulatory factors, including myogenin (MyoG) and paired box 7 (Pax7) both mRNA and protein, while downregulating (P < 0.05) the mRNA and protein levels of myostatin (MSTN). Histological analysis revealed a higher abundance of proliferating cell nuclear antigen (PCNA) and Pax7 immune-positive cells in the breast muscle of the betaine group, consistent with elevated PCNA and Pax7 mRNA and protein levels. Additionally, significantly increased (P < 0.05) contents of insulin-like growth factor 1 (IGF-1) and insulin-like growth factor 2 (IGF-2) were observed in the breast muscle of the betaine group, so was mRNA expression of IGF-1, IGF-2, and insulin-like growth factor 1 receptor (IGF-1R). Betaine also significantly in8creased (P < 0.05) global DNA methylation of the breast muscle, accompanied by enhanced mRNA and protein levels of methionine cycle and DNA methylation-related enzymes, Interestingly, the promoter regions of IGF-1, IGF-2, and IGF-1R genes were significantly hypomethylated (P < 0.05). Moreover, in ovo betaine injection significantly upregulated (P < 0.05) the protein level of farnesoid X receptor (FXR) in breast muscle and FXR binding to the promoter of IGF-2 gene. These findings suggest that in ovo betaine injection promotes breast muscle growth during embryonic development in goslings through the FXR-mediated IGF-2 pathway, ultimately improving hatch weight and breast muscle weight.

Hotspots and trends in satellite cell research in muscle regeneration: A bibliometric visualization and analysis from 2010 to 2023

Background

The incidence of muscle atrophy or sports injuries is increasing with time and population aging, thereby attracting considerable attention to muscle generation research. Muscle satellite cells, which play an important role in this process, lack comprehensive literature regarding their use for muscle regeneration. Hence, this study aimed to analyze the hotspots and trends in satellite cell research from 2010 to 2023, providing a reference for muscle regeneration research.

Methods

Studies on satellite cells' role in muscle regeneration from 2010 to 2023 were retrieved from the Web of Science Core Collection. Using CiteSpace and VOSviewer, we analyzed annual publications, authors and co-citing authors, countries and institutions, journals and co-citing journals, co-citing references, and keywords.

Results

From 2010 to 2023, 1468 papers were retrieved, indicating an overall increasing trend in the number of annual publications related to satellite cells in muscle regeneration. The United States had the highest number of publications, while the Institut National de la Santé et de la Recherche Médicale was the institution with the most publications. Among journals, " PloS One" had the highest number of published papers, and "Cell" emerged as the most co-cited journal. A total of 7425 authors were involved, with Michael A. Rudnicki being the author with the highest number of publications and the most co-cited author. The most cited reference was "Satellite cells and the muscle stem cell niche." Among keywords, "satellite cells" was the most common, with "heterogeneity" having the highest centrality. Frontier themes included "Duchenne muscular dystrophy," "skeletal muscle," "in-vivo," "muscle regeneration," "mice," "muscle atrophy," "muscle fibers," "inflammation," " mesenchymal stem cells," and "satellite cell."

Conclusion

This study presents the current status and trends in satellite cell research on muscle regeneration from 2010 to 2023 using bibliometric analyses, providing valuable insights into numerous future research directions.

ADAR1 Promotes Myogenic Proliferation and Differentiation of Goat Skeletal Muscle Satellite Cells

As one of the most important economic traits for domestic animal husbandry, skeletal muscle is regulated by an intricate molecular network. Adenosine deaminase acting on RNA (ADAR1) involves various physiological processes and diseases, such as innate immunity and the development of lung adenocarcinoma, breast cancer, gastric cancer, etc. However, its role in skeletal muscle growth requires further clarification. Here, we explored the functions of ADAR1 in the myogenic process of goat skeletal muscle satellite cells (MuSCs). The ADAR1 transcripts were noticeably enriched in goat visceral tissues compared to skeletal muscle. Additionally, its levels in slow oxidative muscles like the psoas major and minor muscles were higher than in the fast oxidative glycolytic and fast glycolytic muscles. Among the two common isoforms from ADAR1, p110 is more abundant than p150. Moreover, overexpressing ADAR1 enhanced the proliferation and myogenic differentiation of MuSCs. The mRNA-seq performed on MuSCs' knockdown of ADAR1 obtained 146 differentially expressed genes (DEGs), 87 upregulated and 59 downregulated. These DEGs were concentrated in muscle development and process pathways, such as the MAPK and cAMP signaling pathways. Furthermore, many DEGs as the key nodes defined by protein-protein interaction networks (PPI), including STAT3, MYH3/8, TGFβ2, and ACTN4, were closely related to the myogenic process. Finally, RNA immunoprecipitation combined with qPCR (RIP-qPCR) showed that ADAR1 binds to PAX7 and MyoD mRNA. This study indicates that ADAR1 promotes the myogenic development of goat MuSCs, which provides a useful scientific reference for further exploring the ADAR1-related regulatory networks underlying mammal skeletal muscle growth.

IGF2BP1-mediated the stability and protein translation of FGFR1 mRNA regulates myogenesis through the ERK signaling pathway

N6-methyladenosine (m6A) is the most prevalent post-transcriptional modification of RNAs and plays a key regulatory role in various biological processes. As a member of the insulin-like growth factor 2 mRNA-binding proteins (IGF2BPs) family, IGF2BP1 has recently demonstrated its ability to specifically bind m6A-modified sites within mRNAs and effectively regulate their mRNA stability. However, the precise roles of IGF2BP1 in mammalian skeletal muscle development, along with its downstream mRNA targets during myogenesis, have yet to be fully elucidated. Here, we observed that IGF2BP1 expression significantly decreased during myogenic differentiation. Knockdown of IGF2BP1 significantly inhibited myoblast proliferation while promoted myogenic differentiation. In contrast, IGF2BP1 overexpression robustly stimulated myoblast proliferation but suppressed their differentiation. Combined analysis of high-throughput sequencing and RNA stability assays revealed that IGF2BP1 can enhance fibroblast growth factor receptor 1 (FGFR1) mRNA stability and promote its translation in an m6A-dependent manner, thereby regulating its expression level and the Extracellular Signal-Regulated Kinase (ERK) pathway. Additionally, knockdown of FGFR1 rescued the phenotypic changes (namely increased cell proliferation and suppressed differentiation) induced by IGF2BP1 overexpression via attenuating ERK signaling. Taken together, our findings suggest that IGF2BP1 maintains the stability and translation of FGFR1 mRNA in an m6A-dependent manner, thereby inhibiting skeletal myogenesis through activation of the ERK signaling pathway. This study further enriches the understanding of the molecular mechanisms by which RNA methylation regulates myogenesis, providing valuable insights into the role of IGF2BP1-mediated post-transcriptional regulation in muscle development.

Congenital myopathies: pathophysiological mechanisms and promising therapies

Congenital myopathies (CMs) are a kind of non-progressive or slow-progressive muscle diseases caused by genetic mutations, which are currently defined and categorized mainly according to their clinicopathological features. CMs exhibit pleiotropy and genetic heterogeneity. Currently, supportive treatment and pharmacological remission are the mainstay of treatment, with no cure available. Some adeno-associated viruses show promising prospects in the treatment of MTM1 and BIN1-associated myopathies; however, such gene-level therapeutic interventions target only specific mutation types and are not generalizable. Thus, it is particularly crucial to identify the specific causative genes. Here, we outline the pathogenic mechanisms based on the classification of causative genes: excitation-contraction coupling and triadic assembly (RYR1, MTM1, DNM2, BIN1), actin-myosin interaction and production of myofibril forces (NEB, ACTA1, TNNT1, TPM2, TPM3), as well as other biological processes. Furthermore, we provide a comprehensive overview of recent therapeutic advancements and potential treatment modalities of CMs. Despite ongoing research endeavors, targeted strategies and collaboration are imperative to address diagnostic uncertainties and explore potential treatments.

The immunology of sickness metabolism

Everyone knows that an infection can make you feel sick. Although we perceive infection-induced changes in metabolism as a pathology, they are a part of a carefully regulated process that depends on tissue-specific interactions between the immune system and organs involved in the regulation of systemic homeostasis. Immune-mediated changes in homeostatic parameters lead to altered production and uptake of nutrients in circulation, which modifies the metabolic rate of key organs. This is what we experience as being sick. The purpose of sickness metabolism is to generate a metabolic environment in which the body is optimally able to fight infection while denying vital nutrients for the replication of pathogens. Sickness metabolism depends on tissue-specific immune cells, which mediate responses tailored to the nature and magnitude of the threat. As an infection increases in severity, so do the number and type of immune cells involved and the level to which organs are affected, which dictates the degree to which we feel sick. Interestingly, many alterations associated with metabolic disease appear to overlap with immune-mediated changes observed following infection. Targeting processes involving tissue-specific interactions between activated immune cells and metabolic organs therefore holds great potential for treating both people with severe infection and those with metabolic disease. In this review, we will discuss how the immune system communicates in situ with organs involved in the regulation of homeostasis and how this communication is impacted by infection.

Tissue Engineered 3D Constructs for Volumetric Muscle Loss

Severe injuries to skeletal muscles, including cases of volumetric muscle loss (VML), are linked to substantial tissue damage, resulting in functional impairment and lasting disability. While skeletal muscle can regenerate following minor damage, extensive tissue loss in VML disrupts the natural regenerative capacity of the affected muscle tissue. Existing clinical approaches for VML, such as soft-tissue reconstruction and advanced bracing methods, need to be revised to restore tissue function and are associated with limitations in tissue availability and donor-site complications. Advancements in tissue engineering (TE), particularly in scaffold design and the delivery of cells and growth factors, show promising potential for regenerating damaged skeletal muscle tissue and restoring function. This article provides a brief overview of the pathophysiology of VML and critiques the shortcomings of current treatments. The subsequent section focuses on the criteria for designing TE scaffolds, offering insights into various natural and synthetic biomaterials and cell types for effectively regenerating skeletal muscle. We also review multiple TE strategies involving both acellular and cellular scaffolds to encourage the development and maturation of muscle tissue and facilitate integration, vascularization, and innervation. Finally, the article explores technical challenges hindering successful translation into clinical applications.

Sexual dimorphisms in skeletal muscle: current concepts and research horizons

The complex compositional and functional nature of skeletal muscle makes this organ an essential topic of study for biomedical researchers and clinicians. An additional layer of complexity is added with the consideration of sex as a biological variable. Recent research advances have revealed sexual dimorphisms in developmental biology, muscle homeostasis, adaptive responses, and disorders relating to skeletal muscle. Many of the observed sex differences have hormonal and molecular mechanistic underpinnings, whereas others have yet to be elucidated. Future research is needed to investigate the mechanisms dictating sex-based differences in the various aspects of skeletal muscle. As such, it is necessary that skeletal muscle biologists ensure that both female and male subjects are represented in biomedical and clinical studies to facilitate the successful testing and development of therapeutics for all patients.

Tumor Necrosis Factor-Alpha Modulates Expression of Genes Involved in Cytokines and Chemokine Pathways in Proliferative Myoblast Cells

Skeletal muscle regeneration after injury is a complex process involving inflammatory signaling and myoblast activation. Pro-inflammatory cytokines like tumor necrosis factor-alpha (TNF-α) are key mediators, but their effects on gene expression in proliferating myoblasts are unclear. We performed the RNA sequencing of TNF-α treated C2C12 myoblasts to elucidate the signaling pathways and gene networks regulated by TNF-α during myoblast proliferation. The TNF-α (10 ng/mL) treatment of C2C12 cells led to 958 differentially expressed genes compared to the controls. Pathway analysis revealed significant regulation of TNF-α signaling, along with the chemokine and IL-17 pathways. Key upregulated genes included cytokines (e.g., IL-6), chemokines (e.g., CCL7), and matrix metalloproteinases (MMPs). TNF-α increased myogenic factor 5 (Myf5) but decreased MyoD protein levels and stimulated the release of MMP-9, MMP-10, and MMP-13. TNF-α also upregulates versican and myostatin mRNA. Overall, our study demonstrates the TNF-α modulation of distinct gene expression patterns and signaling pathways that likely contribute to enhanced myoblast proliferation while suppressing premature differentiation after muscle injury. Elucidating the mechanisms involved in skeletal muscle regeneration can aid in the development of regeneration-enhancing therapeutics.

Matrix mechanics regulates muscle regeneration by modulating kinesin-1 activity

Sarcopenia, a prevalent muscle disease characterized by muscle mass and strength reduction, is associated with impaired skeletal muscle regeneration. However, the influence of the biomechanical properties of sarcopenic skeletal muscle on the efficiency of the myogenic program remains unclear. Herein, we established a mouse model of sarcopenia and observed a reduction in stiffness within the sarcopenic skeletal muscle in vivo. To investigate whether the biomechanical properties of skeletal muscle directly impact the myogenic program, we established an in vitro system to explore the intrinsic mechanism involving matrix stiffness control of myogenic differentiation. Our findings identify the microtubule motor protein, kinesin-1, as a mechano-transduction hub that senses and responds to matrix stiffness, crucial for myogenic differentiation and muscle regeneration. Specifically, kinesin-1 activity is positively regulated by stiff matrices, facilitating its role in transporting mitochondria and enhancing translocation of the glucose transporter GLUT4 to the cell surface for glucose uptake. Conversely, the softer matrices significantly suppress kinesin-1 activity, leading to the accumulation of mitochondria around nuclei and hindering glucose uptake by inhibiting GLUT4 membrane translocation, consequently impairing myogenic differentiation. The insights gained from the in-vitro system highlight the mechano-transduction significance of kinesin-1 motor proteins in myogenic differentiation. Furthermore, our study confirms that enhancing kinesin-1 activity in the sarcopenic mouse model restores satellite cell expansion, myogenic differentiation, and muscle regeneration. Taken together, our findings provide a potential target for improving muscle regeneration in sarcopenia.

Dual inhibition of P38 MAPK and JNK pathways preserves stemness markers and alleviates premature activation of muscle stem cells during isolation

BACKGROUND

Adult skeletal muscle contains resident muscle stem cells (MuSC) with high myogenic and engraftment potentials, making them suitable for cell therapy and regenerative medicine approaches. However, purification process of MuSC remains a major hurdle to their use in the clinic. Indeed, muscle tissue enzymatic dissociation triggers a massive activation of stress signaling pathways, among which P38 and JNK MAPK, associated with a premature loss of MuSC quiescence. While the role of these pathways in the myogenic progression of MuSC is well established, the extent to which their dissociation-induced activation affects the functionality of these cells remains unexplored.

METHODS

We assessed the effect of P38 and JNK MAPK induction on stemness marker expression and MuSC activation state during isolation by pharmacological approaches. MuSC functionality was evaluated by in vitro assays and in vivo transplantation experiments. We performed a comparative analysis of the transcriptome of human MuSC purified with pharmacological inhibitors of P38 and JNK MAPK (SB202190 and SP600125, respectively) versus available RNAseq resources.

RESULTS

We monitored PAX7 protein levels in murine MuSC during muscle dissociation and demonstrated a two-step decline partly dependent on P38 and JNK MAPK activities. We showed that simultaneous inhibition of these pathways throughout the MuSC isolation process preserves the expression of stemness markers and limits their premature activation, leading to improved survival and amplification in vitro as well as increased engraftment in vivo. Through a comparative RNAseq analysis of freshly isolated human MuSC, we provide evidence that our findings in murine MuSC could be relevant to human MuSC. Based on these findings, we implemented a purification strategy, significantly improving the recovery yields of human MuSC.

CONCLUSION

Our study highlights the pharmacological limitation of P38 and JNK MAPK activities as a suitable strategy to qualitatively and quantitatively ameliorate human MuSC purification process, which could be of great interest for cell-based therapies.

A standardized herbal combination of Astragalus membranaceus and Paeonia japonica promotes skeletal muscle hypertrophy in a treadmill exercise mouse model

Background

Maintaining a normal range of muscle mass and function is crucial not only for sustaining a healthy life but also for preventing various disorders. Numerous nutritional or natural resources are being explored for their potential muscle hypertrophic properties.

Aim

We aimed to evaluate the muscle hypertrophic effects of APX, a 1:1 mixture of Astragalus membranaceus and Paeonia japonica. In addition to the myotube differentiation cell assay, we utilized a weighted exercise-based animal model and evaluated changes in muscle hypertrophy using dual-energy X-ray absorptiometry (DXA) and histological analysis.

Results

The 8-week treadmill exercise led to notable decreases in body weight and fat mass but an increase in muscle mass compared to the control group. Administration of APX significantly accelerated muscle mass gain (p < 0.05) without altering body weight or fat mass compared to the exercise-only group. This muscle hypertrophic effect of APX was consistent with the histologic size of muscle fibers in the gastrocnemius (p > 0.05) and rectus femoris (p < 0.05), as well as the regulation of myogenic transcription factors (MyoD and myogenin), respectively. Furthermore, APX demonstrated a similar action to insulin-like growth factor 1, influencing the proliferation of C2C12 myoblast cells (p < 0.01) and their differentiation into myotubes (p < 0.05) compared to the control group.

Conclusion

The present study provides experimental evidence that APX has muscle hypertrophic effects, and its underlying mechanisms would involve the modulation of MyoD and myogenin.

С60 fullerene protective effect against the rat muscle soleus trauma

Muscle trauma is one of the most common body injuries. Severe consequences of muscle trauma are ischemic injuries of the extremities. It is known that the intensification of free radical processes takes place in almost most acute diseases and conditions, including muscle trauma. C60 fullerene (C60) with powerful antioxidant properties can be considered a potential nanoagent for developing an effective therapy for skeletal muscle trauma. Here the water-soluble C60 was prepared and its structural organization has been studied by the atomic force microscopy and dynamic light scattering techniques. The selective biomechanical parameters of muscle soleus contraction and biochemical indicators of blood in rats were evaluated after intramuscular injection of C60 1 h before the muscle trauma initiation. Analysis of the force muscle response after C60 injection (1 mg kg-1 dose) showed its protective effect against ischemia and mechanical injury at the level of 30 ± 2 % and 17 ± 1 %, accordingly, relative to the pathology group. Analysis of biomechanical parameters that are responsible for correcting precise positioning confirmed the effectiveness of C60 at a level of more than 50 ± 3 % relative to the pathology group. Moreover, a decrease in the biochemical indicators of blood by about 33 ± 2 % and 10 ± 1 % in ischemia and mechanical injury, correspondingly, relative to the pathology group occurs. The results obtained demonstrate the ability of C60 to correct the functional activity of damaged skeletal muscle.

The Wound Environment Agent-based Model (WEABM): a digital twin platform for characterization and complex therapeutic discovery for volumetric muscle loss

Volumetric Muscle Loss (VML) injuries are characterized by significant loss of muscle mass, usually due to trauma or surgical resection, often with a residual open wound in clinical settings and subsequent loss of limb function due to the replacement of the lost muscle mass with non-functional scar. Being able to regrow functional muscle in VML injuries is a complex control problem that needs to override robust, evolutionarily conserved healing processes aimed at rapidly closing the defect in lieu of restoration of function. We propose that discovering and implementing this complex control can be accomplished by the development of a Medical Digital Twin of VML. Digital Twins (DTs) are the subject of a recent report from the National Academies of Science, Engineering and Medicine (NASEM), which provides guidance as to the definition, capabilities and research challenges associated with the development and implementation of DTs. Specifically, DTs are defined as dynamic computational models that can be personalized to an individual real world "twin" and are connected to that twin via an ongoing data link. DTs can be used to provide control on the real-world twin that is, by the ongoing data connection, adaptive. We have developed an anatomic scale cell-level agent-based model of VML termed the Wound Environment Agent Based Model (WEABM) that can serve as the computational specification for a DT of VML. Simulations of the WEABM provided fundamental insights into the biology of VML, and we used the WEABM in our previously developed pipeline for simulation-based Deep Reinforcement Learning (DRL) to train an artificial intelligence (AI) to implement a robust generalizable control policy aimed at increasing the healing of VML with functional muscle. The insights into VML obtained include: 1) a competition between fibrosis and myogenesis due to spatial constraints on available edges of intact myofibrils to initiate the myoblast differentiation process, 2) the need to biologically "close" the wound from atmospheric/environmental exposure, which represents an ongoing inflammatory stimulus that promotes fibrosis and 3) that selective, multimodal and adaptive local mediator-level control can shift the trajectory of healing away from a highly evolutionarily beneficial imperative to close the wound via fibrosis. Control discovery with the WEABM identified the following design principles: 1) multimodal adaptive tissue-level mediator control to mitigate pro-inflammation as well as the pro-fibrotic aspects of compensatory anti-inflammation, 2) tissue-level mediator manipulation to promote myogenesis, 3) the use of an engineered extracellular matrix (ECM) to functionally close the wound and 4) the administration of an anti-fibrotic agent focused on the collagen-producing function of fibroblasts and myofibroblasts. The WEABM-trained DRL AI integrates these control modalities and provides design specifications for a potential device that can implement the required wound sensing and intervention delivery capabilities needed. The proposed cyber-physical system integrates the control AI with a physical sense-and-actuate device that meets the tenets of DTs put forth in the NASEM report and can serve as an example schema for the future development of Medical DTs.

Three-dimensional imaging studies in mice identify cellular dynamics of skeletal muscle regeneration

The function of many organs, including skeletal muscle, depends on their three-dimensional structure. Muscle regeneration therefore requires not only reestablishment of myofibers but also restoration of tissue architecture. Resident muscle stem cells (SCs) are essential for regeneration, but how SCs regenerate muscle architecture is largely unknown. We address this problem using genetic labeling of mouse SCs and whole-mount imaging to reconstruct, in three dimensions, muscle regeneration. Unexpectedly, we found that myofibers form via two distinct phases of fusion and the residual basement membrane of necrotic myofibers is critical for promoting fusion and orienting regenerated myofibers. Furthermore, the centralized myonuclei characteristic of regenerated myofibers are associated with myofibrillogenesis and endure months post injury. Finally, we elucidate two cellular mechanisms for the formation of branched myofibers, a pathology characteristic of diseased muscle. We provide a synthesis of the cellular events of regeneration and show that these differ from those used during development.

Identification and functional analysis of circpdlim5a generated from pdlim5a gene splicing in the skeletal muscle of Japanese flounder (Paralichthys olivaceus)

Circular RNAs (circRNAs) are non-coding RNAs with endogenous regulatory functions, including regulating skeletal muscle development. However, its role in the development of skeletal muscle in Japanese flounder (Paralichthys olivaceus) is not clear. Therefore we screened a candidate circpdlim5a, which is derived from the gene pdlim5a, from the skeletal muscle transcriptome of Japanese flounder. We characterized circpdlim5a, which was more stable compared to the linear RNA pdlim5a. Distributional characterization of circpdlim5a showed that circpdlim5a was predominantly distributed in the nucleus and was highly expressed in the skeletal muscle of adult Japanese flounder (24 months). When we further studied the circpdlim5a function, we found that it inhibited the expression of proliferation and differentiation genes according to the over-expression experiment of circpdlim5a in myoblasts. We concluded that circpdlim5a may inhibit the proliferation and differentiation of myoblasts and thereby inhibit skeletal muscle development in Japanese flounder. This experiment provides information for the study of circRNAs by identifying circpdlim5a and exploring its function, and offers clues for molecular breeding from an epigenetic perspective.