Arginine promotes myogenic differentiation and myotube formation through the elevation of cytoplasmic calcium concentration

Inhibitor of Myom3 inhibits proliferation and promotes differentiation of sheep myoblasts

Skeletal muscle quality and yield are important production traits in livestock, and improving skeletal muscle quality while increasing its yield is an important goal of economic breeding. The proliferation and differentiation process of sheep myoblasts directly affects the growth and development of their muscles, thereby affecting the yield of mutton. Myomesin 3 (Myom3), as a functional gene related to muscle growth, currently lacks research on its function in myoblasts. This study aims to investigate the effect of the Myom3 gene on the proliferation and differentiation of sheep myoblasts and its potential molecular mechanisms. The results showed that inhibitor of Myom3 in the proliferation phase of myoblasts resulted in significant downregulation of the proliferation marker gene paired box 7 (Pax7) and myogenic regulatory factors (MRFs; Myf5, Myod1, Myog, P < 0.01), a significant decrease in the EdU-positive cell rate (P < 0.05), and a significant increase in the cell apoptosis rate (P < 0.01), which inhibited the proliferation of myoblasts and promoted their apoptosis. During the differentiation phase of myoblasts, the inhibitor of Myom3 resulted in significant downregulation of the Pax7 gene, upregulation of MRFs (Myod1, Myog, P < 0.05), and a significant increase in fusion index (P < 0.05), promoting the differentiation of myoblasts. Further transcriptome sequencing revealed that differentially expressed genes in the Myom3 interference group were mainly enriched in the MAPK signaling pathway, TNF signaling pathway, and IL-17 signaling pathway. In summary, the inhibitor of Myom3 inhibits myoblast proliferation and promotes myoblast differentiation. Therefore, Myom3 has a potential regulatory effect on the growth and development of sheep muscles, and in-depth functional research can be used for molecular breeding practices in sheep.

Skeletal muscle: molecular structure, myogenesis, biological functions, and diseases

Skeletal muscle is an important motor organ with multinucleated myofibers as its smallest cellular units. Myofibers are formed after undergoing cell differentiation, cell-cell fusion, myonuclei migration, and myofibril crosslinking among other processes and undergo morphological and functional changes or lesions after being stimulated by internal or external factors. The above processes are collectively referred to as myogenesis. After myofibers mature, the function and behavior of skeletal muscle are closely related to the voluntary movement of the body. In this review, we systematically and comprehensively discuss the physiological and pathological processes associated with skeletal muscles from five perspectives: molecule basis, myogenesis, biological function, adaptive changes, and myopathy. In the molecular structure and myogenesis sections, we gave a brief overview, focusing on skeletal muscle-specific fusogens and nuclei-related behaviors including cell-cell fusion and myonuclei localization. Subsequently, we discussed the three biological functions of skeletal muscle (muscle contraction, thermogenesis, and myokines secretion) and its response to stimulation (atrophy, hypertrophy, and regeneration), and finally settled on myopathy. In general, the integration of these contents provides a holistic perspective, which helps to further elucidate the structure, characteristics, and functions of skeletal muscle.

Arginine Regulates Skeletal Muscle Fiber Type Formation via mTOR Signaling Pathway

The composition of skeletal muscle fiber types affects the quality of livestock meat and human athletic performance and health. L-arginine (Arg), a semi-essential amino acid, has been observed to promote the formation of slow-twitch muscle fibers in animal models. However, the precise molecular mechanisms are still unclear. This study investigates the role of Arg in skeletal muscle fiber composition and mitochondrial function through the mTOR signaling pathway. In vivo, 4-week C56BL/6J male mice were divided into three treatment groups and fed a basal diet supplemented with different concentrations of Arg in their drinking water. The trial lasted 7 weeks. The results show that Arg supplementation significantly improved endurance exercise performance, along with increased SDH enzyme activity and upregulated expression of the MyHC I, MyHC IIA, PGC-1α, and NRF1 genes in the gastrocnemius (GAS) and quadriceps (QUA) muscles compared to the control group. In addition, Arg activated the mTOR signaling pathway in the skeletal muscle of mice. In vitro experiments using cultured C2C12 myotubes demonstrated that Arg elevated the expression of slow-fiber genes (MyHC I and Tnnt1) as well as mitochondrial genes (PGC-1α, TFAM, MEF2C, and NRF1), whereas the effects of Arg were inhibited by the mTOR inhibitor rapamycin. In conclusion, these findings suggest that Arg modulates skeletal muscle fiber type towards slow-twitch fibers and enhances mitochondrial functions by upregulating gene expression through the mTOR signaling pathway.

Near-infrared light-triggered polypyrrole promotes C2C12 cell differentiation and inhibits TNF-α induced myotube atrophy

Treatment of skeletal muscle atrophy and strengthening the muscles remain a challenge in modern medicine. Studies have shown that photobiomodulation can inhibit skeletal muscle atrophy and aid in functional recovery. Near-infrared radiation (NIR) therapy has emerged as a complementary therapy for the treatment of skeletal muscle atrophy, but its underlying mechanism remains unclear. Polypyrrole (PPy) is an organic polymer with strong near-infrared absorption, which can generate heat from absorbed NIR. In this study, MHC immunofluorescence staining was performed on C2C12 myoblasts to investigate the differentiation of C2C12 cells after NIR-triggered PPy exposure. As TNF-α-induced C2C12 myotubes were used as a model of muscular atrophy. Giemsa staining was used to determine the myotube diameter. Western blot analysis was performed to examine the proteins involved in the differentiation and atrophy of muscle cells, as well as in the Akt/P70S6K signaling pathway. PPy triggered by NIR promoted the differentiation of C2C12 cells, inhibited C2C12 myotube atrophy caused by TNF-α, and downregulated the expression levels of Atrogin-1 and MuRF 1 protein. In addition, we determined that Akt/P70S6K signaling pathway activity plays a crucial role in the therapeutic effect of NIR-triggered polypyrrole, which was further confirmed by the administration of the Akt inhibitor GDC0068. The optimal conditions for these effects were a PPy concentration of 0.125 mg/ml and NIR exposure for 80 s. We show that the photothermal effect of PPy triggered by near-infrared light can increase the beneficial effects of NIR, promote the differentiation of C2C12 cells, and improve C2C12 myotube atrophy, laying a foundation for its future clinical use.

Neuronal and Non-Neuronal GABA in COVID-19: Relevance for Psychiatry

Infection with SARS-CoV-2, the causative agent of the COVID-19 pandemic, originated in China and quickly spread across the globe. Despite tremendous economic and healthcare devastation, research on this virus has contributed to a better understanding of numerous molecular pathways, including those involving γ-aminobutyric acid (GABA), that will positively impact medical science, including neuropsychiatry, in the post-pandemic era. SARS-CoV-2 primarily enters the host cells through the renin–angiotensin system’s component named angiotensin-converting enzyme-2 (ACE-2). Among its many functions, this protein upregulates GABA, protecting not only the central nervous system but also the endothelia, the pancreas, and the gut microbiota. SARS-CoV-2 binding to ACE-2 usurps the neuronal and non-neuronal GABAergic systems, contributing to the high comorbidity of neuropsychiatric illness with gut dysbiosis and endothelial and metabolic dysfunctions. In this perspective article, we take a closer look at the pathology emerging from the viral hijacking of non-neuronal GABA and summarize potential interventions for restoring these systems.

Virus-Induced Membrane Fusion in Neurodegenerative Disorders

A growing body of epidemiological and research data has associated neurotropic viruses with accelerated brain aging and increased risk of neurodegenerative disorders. Many viruses replicate optimally in senescent cells, as they offer a hospitable microenvironment with persistently elevated cytosolic calcium, abundant intracellular iron, and low interferon type I. As cell-cell fusion is a major driver of cellular senescence, many viruses have developed the ability to promote this phenotype by forming syncytia. Cell-cell fusion is associated with immunosuppression mediated by phosphatidylserine externalization that enable viruses to evade host defenses. In hosts, virus-induced immune dysfunction and premature cellular senescence may predispose to neurodegenerative disorders. This concept is supported by novel studies that found postinfectious cognitive dysfunction in several viral illnesses, including human immunodeficiency virus-1, herpes simplex virus-1, and SARS-CoV-2. Virus-induced pathological syncytia may provide a unified framework for conceptualizing neuronal cell cycle reentry, aneuploidy, somatic mosaicism, viral spreading of pathological Tau and elimination of viable synapses and neurons by neurotoxic astrocytes and microglia. In this narrative review, we take a closer look at cell-cell fusion and vesicular merger in the pathogenesis of neurodegenerative disorders. We present a "decentralized" information processing model that conceptualizes neurodegeneration as a systemic illness, triggered by cytoskeletal pathology. We also discuss strategies for reversing cell-cell fusion, including, TMEM16F inhibitors, calcium channel blockers, senolytics, and tubulin stabilizing agents. Finally, going beyond neurodegeneration, we examine the potential benefit of harnessing fusion as a therapeutic strategy in regenerative medicine.

l-Arginine Alleviates LPS-Induced Oxidative Stress and Apoptosis via Activating SIRT1-AKT-Nrf2 and SIRT1-FOXO3a Signaling Pathways in C2C12 Myotube Cells

l-arginine (l-Arg) has been reported to possess a wide range of functions, including anti-inflammatory, anti-oxidative, and anti-apoptosis. However, the role of l-Arg in LPS-induced muscle injury and its potential protective mechanism has not been well elucidated. This study aimed to investigate the effects of l-Arg on the LPS-induced oxidative stress and apoptosis in differentiated C2C12 myotube cells. Our results demonstrated that myotube cells treated with 0.2 mg/mL LPS significantly decreased cell viability. l-Arg treatment significantly suppressed LPS induced ROS accumulation and cell apoptosis. Furthermore, l-Arg improved antioxidant-related enzymes’ activities; increased antioxidant ability via Akt-Nrf2 signaling pathway; maintained the mitochondrial membrane potential (MMP); and enhanced FOXO3a expression, leading to a decrease in the mitochondrial-associated apoptotic proteins. In addition, l-Arg exposure dramatically increased the mRNA and protein expressions of SIRT1. The cytoprotective effect of l-Arg was restricted by the SIRT1 inhibitor EX527, which led to an increase in ROS level, apoptosis rate, and decreased cell MMP. The results also demonstrated that EX527 treatment significantly eliminated the effect of l-Arg on LPS-induced oxidative damage and mitochondria-mediated cell apoptosis. Our findings revealed that l-Arg could be used as a potential nutraceutical in reducing muscle injury via regulating SIRT1-Akt-Nrf2 and SIRT1-FOXO3a-mitochondria apoptosis signaling pathways.