Ursolic Acid Restores Redox Homeostasis and Pro-inflammatory Cytokine Production in Denervation-Induced Skeletal Muscle Atrophy.

Skeletal muscle (SkM) atrophy results from metabolic disorders causing body and muscle mass loss, affecting morbidity and mortality. Increased oxidative stress, inflammation, and poor prognosis are the leading causes of involuntary weight loss. Ursolic acid (UA), known for its antioxidant and anti-inflammatory properties, can potentially reduce oxidative stress and inflammation in muscles, but its effects on muscle mass regulation are still unknown. Therefore, the present study investigated the medicinal efficacy of UA and its mode of action against the murine model of SkM atrophy over 7 days of UA supplementation. Denervation-induced SkM atrophy significantly impacts overall body weight and the weight of individual muscles (p < 0.05). However, supplementation with UA can effectively counteract these effects by promoting the synthesis of the slow-myosin heavy chain, thereby restoring body weight and myotube diameter. Moreover, UA also plays a crucial role in reducing the production levels of reactive oxygen species (ROS), lipid peroxidation (LPO), and caspase-3-like activity in atrophied muscles. UA also prevents the leakage of creatine kinase (CK) through the upregulation of superoxide dismutase (SOD) and glutathione peroxidase (GPx) expression. Furthermore, the results obtained from qRT-PCR demonstrated a significant decrease in the levels of pro-inflammatory markers, namely IL-1ß, IL-6, TNF-α, and TWEAK, up to four-fold after the third day of the UA intervention. UA also upregulated PGC-1α, Bcl2, and p-Aktser473 expression towards the regulation of redox homeostasis.

High expression of transcription factor EGR1 is associated with postoperative muscle atrophy in patients with knee osteoarthritis undergoing total knee arthroplasty.

BACKGROUND: Muscle atrophy is a typical affliction in patients affected by knee Osteoarthritis (KOA). This study aimed to examine the potential pathogenesis and biomarkers that coalesce to induce muscle atrophy, primarily through the utilization of bioinformatics analysis. METHODS: Two distinct public datasets of osteoarthritis and muscle atrophy (GSE82107 and GSE205431) were subjected to differential gene expression analysis and gene set enrichment analysis (GSEA) to probe for common differentially expressed genes (DEGs) and conduct transcription factor (TF) enrichment analysis from such genes. Venn diagrams were used to identify the target TF, followed by the construction of a protein-protein interaction (PPI) network of the common DEGs governed by the target TF. Hub genes were determined through the CytoHubba plug-in whilst their biological functions were assessed using GSEA analysis in the GTEx database. To validate the study, reverse transcriptase real-time quantitative polymerase chain reaction (qRT-PCR), enzyme-linked immunosorbent assay (ELISA), and Flow Cytometry techniques were employed. RESULTS: A total of 138 common DEGs of osteoarthritis and muscle atrophy were identified, with 16 TFs exhibiting notable expression patterns in both datasets. Venn diagram analysis identified early growth response gene-1 (EGR1) as the target TF, enriched in critical pathways such as epithelial mesenchymal transition, tumor necrosis factor-alpha signaling NF-κB, and inflammatory response. PPI analysis revealed five hub genes, including EGR1, FOS, FOSB, KLF2, and JUNB. The reliability of EGR1 was confirmed by validation testing, corroborating bioinformatics analysis trends. CONCLUSIONS: EGR1, FOS, FOSB, KLF2, and JUNB are intricately involved in muscle atrophy development. High EGR1 expression directly regulated these hub genes, significantly influencing postoperative muscle atrophy progression in KOA patients.

Muscle Atrophy and mRNA-miRNA Network Analysis of Vascular Endothelial Growth Factor (VEGF) in a Mouse Model of Denervation-Induced Disuse.

BACKGROUND: Skeletal muscle atrophy is frequently caused by the disuse of muscles. It impacts quality of life, especially in aging populations and those with chronic diseases. Understanding the molecular mechanisms underlying muscle atrophy is crucial for developing effective therapies. OBJECTIVE: To investigate the roles of vascular endothelial growth factor (VEGF) and various microRNAs (miRNAs) in muscle atrophy using a mouse model of denervation (DEN)-induced disuse, and to elucidate their interactions and regulatory functions through comprehensive network analysis. METHODS: The right sciatic nerve of C57BL/6J mice (n=6) was excised to simulate DEN, with the left serving as a sham surgery control (Sham). Following a two-week period, wet muscle weight was measured. Total RNA was extracted from the tibialis anterior muscle for microarray analysis. Significant expression changes were analyzed via Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis and miRNet for miRNAs. RESULTS: Denervated limbs showed a significant reduction in muscle weight. Over 1,000 genes displayed increased expression, while 527 showed reductions to less than half of control levels. VEGF, along with specific miRNAs such as miR-106a-5p, miR-mir20a-5p, mir93-5p and mir17-5p, occupied central regulatory nodes within the gene network. Functional analysis revealed that these molecules are involved in key biological processes including regulation of cell migration, vasculature development, and regulation of endothelial cell proliferation. The increased miRNAs were subjected to further network analysis that revealed significant regulatory interactions with target mRNAs. CONCLUSION: VEGF and miRNAs play crucial roles in the progression of skeletal muscle atrophy, offering potential targets for therapeutic interventions aimed at reducing atrophy and enhancing muscle regeneration.

High-intensity exercise alongside insulin alleviates muscle atrophy in type 1 diabetes mellitus concomitant with modulation of mitophagy-related proteins in skeletal muscle.

Background: Diabetes patients' quality of life can be severely impacted by diabetic muscle atrophy.Aim: This study aimed to explore the impact of high-intensity exercise (HIE) alongside insulin treatment on muscle atrophy in a rat model of type 1 diabetes mellitus (T1DM).Methodology: Fifty rats were allocated into five groups; Group 1, control sedentary (CS), T1DM was elicited in the rest of the groups by giving them Streptozotocin (STZ) (60 mg/kg), where group 2 (DS) remained sedentary, while groups 3,4,5 were treated with insulin after induction of diabetes. Group 4 (DI+MIE) and 5 (DI+ HIE) underwent moderate and high-intensity exercise, respectively.Results: HIE for 14 days combined with insulin treatment significantly restored muscle strength and mass with a significant modification in the mitophagy-related proteins and fibroblast growth factor 21 (FGF 21) compared to other treated groups.Conclusion: This study concluded that there is a therapeutic role for HIE with insulin against T1DM-induced muscle atrophy.

T1DM induces loss of skeletal muscle mass and strength.T1DM enhances muscle atrophy-related genes (MAFbx and MuRF1) and impairs mitochondrial function.HIE alongside insulin treatment restores muscle mass, strength, and histological architecture in T1DM-induced muscle atrophy model.HIE alongside insulin treatment over MIE moderated the mitochondrial dysfunction via modulation of the mitophagy-related mediators (BNIP3, Parkin, P62, and LC3II/LC3I) and FGF 21 expression.

Luteolin alleviates muscle atrophy, mitochondrial dysfunction and abnormal FNDC5 expression in high fat diet-induced obese rats and palmitic acid-treated C2C12 myotubes.

Obesity is associated with a series of skeletal muscle impairments and dysfunctions, which are characterized by metabolic disturbances and muscle atrophy. Luteolin is a phenolic phytochemical with broad pharmacological activities. The present study aimed to evaluate the protective effects of Luteolin on muscle function and explore the potential mechanisms in high-fat diet (HFD)-induced obese rats and palmitic acid (PA)-treated C2C12 myotubes. Male Sprague-Dawley (SD) rats were fed with a control diet or HFD and orally administrated 0.5% sodium carboxymethyl cellulose (vehicle) or Luteolin (25, 50 and 100 mg/kg, respectively) for 12 weeks. The results showed that Luteolin ameliorated HFD-induced body weight gain, glucose intolerance and hyperlipidemia. Luteolin also alleviated muscle atrophy, decreased ectopic lipid deposition and prompted muscle-fiber-type conversion in the skeletal muscle. Meanwhile, we observed an evident improvement in mitochondrial quality control and respiratory capacity, accompanied by reduced oxidative stress. Mechanistic studies indicated that AMPK/SIRT1/PGC-1α signaling pathway plays a key role in the protective effects of Luteolin on skeletal muscle in the obese states, which was further verified by using specific inhibitors of AMPK and SIRT1. Moreover, the mRNA expression levels of markers in brown adipocyte formation were significantly up-regulated post Luteolin supplementation in different adipose depots. Taken together, these results revealed that Luteolin supplementation might be a promising strategy to prevent obesity-induced loss of mass and biological dysfunctions of skeletal muscle.

Fu-Zheng-Li-Fei Recipe (FZLFR) in the treatment of Cancer Cachexia: Exploration of the Efficacy and Molecular Mechanism Based on Chemical characterization, Experimental Research and Network Pharmacology.

ETHNOPHARMACOLOGICAL RELEVANCE: FZLFR was derived from a classic traditional Chinese medicine recipe, the Shiquan-Dabu decoction. FZLFR is commonly used in clinical practice to address muscle loss and associated cancer cachexia. However, the mechanism of by which FZLFR acts in cancer cachexia remains unclear. AIM: This study aimed to assess the effects and explore the potential mechanism of action of FZLFR in treating cancer cachexia. METHODS: Cancer cachexia was induced by inoculating Lewis lung carcinoma cells into the right flank of male C57BL/6 mice. The efficacy of FZLFR was evaluated by comparing changes in body weight, tumor mass, food intake, survival time, weight, and cross-sectional area of the gastrocnemius and anterior tibial muscles. Moreover, inflammatory cytokines, such as TNF-α and IL-6, were detected by ELISA. The chemical components of FZLFR were analyzed using ultra-performance liquid chromatography-coupled with time-of-flight mass spectrometry. Network pharmacology analysis was performed to screen the core targets and potential pathways involved in FZLFR treatment of cancer cachexia. Molecular docking was used to analyze the binding ability of the core targets and key compounds. The expression levels of core targets and targets correlated with skeletal muscle atrophy were also assessed using western blotting. RESULTS: FZLFR enhanced the food intake and survival rate of mice with cancer cachexia. It also alleviated tumor-induced body weight loss, tumor growth, and muscle fiber atrophy in these mice. Additionally, it improved the weight and cross-sectional area of the gastrocnemius and anterior tibial muscles. FZLFR down-regulated the serum levels of TNF-α and IL-6. UPLC-ESI-Q-TOF-MS analysis identified 184 compounds in FZLFR. Network pharmacology analysis predicted that TNF signaling pathway, ErbB signaling pathway and VEGF signaling pathway might be essential in FZLFR action. Molecular docking showed that kaempferol, upafolin, apigenin, and luteolin might play key roles in FZLFR treatment. Moreover, FZLFR decreased MAFBx1, MURF1, NF-κB, TWEAK, MAPK8, and EGFR expression levels. FZLFR enhanced the expression of VEGFA and ESR1, as demonstrated by western blotting. CONCLUSIONS: FZLFR increased food intake and alleviated muscle atrophy in mice with cancer cachexia. The potential pharmacological mechanisms underlying its anticachexia effects include reducing inflammation, enhancing muscle vascular growth, inhibiting tumor angiogenesis, and modulating estrogen receptors.

Muscle-enriched microRNA-486-mediated regulation of muscular atrophy and exercise.

The objectives of this review were to understand the impact of microRNA-486 on myogenesis and muscle atrophy, and the change of microRNA-486 following exercise, and provide valuable information for improving muscle atrophy based on exercise intervention targeting microRNA-486. Muscle-enriched microRNAs (miRNAs), also referred to as myomiRs, control various processes in skeletal muscles, from myogenesis and muscle homeostasis to different responses to environmental stimuli such as exercise. MicroRNA-486 is a miRNA in which a stem-loop sequence is embedded within the ANKYRIN1 (ANK1) locus and is strictly conserved across mammals. MicroRNA-486 is involved in the development of muscle atrophy caused by aging, immobility, prolonged exposure to microgravity, or muscular and neuromuscular disorders. PI3K/AKT signaling is a positive pathway, as it increases muscle mass by increasing protein synthesis and decreasing protein degradation. MicroRNA-486 can activate this pathway by inhibiting phosphatase and tensin homolog (PTEN), it may also indirectly inhibit the HIPPO signaling pathway to promote cell growth. Exercises regulate microRNA-486 expression both in blood and muscle. This review focused on the recent elucidation of sarcopenia regulation by microRNA-486 and its effects on pathological states, including primary muscular disease, secondary muscular disorders, and age-related sarcopenia. Additionally, the role of exercise in regulating skeletal muscle-enriched microRNA-486 was highlighted, along with its physiological significance. Growing evidence indicates that microRNA-486 significantly impacts the development of muscle atrophy. MicroRNA-486 has great potential to become a therapeutic target for improving muscle atrophy through exercise intervention.

Fiberoptic endoscopic evaluation of swallowing (FEES) in children with spinal muscular atrophy type 1: feasibility, swallowing safety and efficacy, and dysphagia phenotype.

PURPOSE: Although dysphagia is a common symptom among patients with Spinal Muscular Atrophy Type 1 (SMA1), scant data exist on the application of Fiberoptic Endoscopic Evaluation of Swallowing (FEES) in this population. The aim was to analyze FEES feasibility, swallow safety and efficacy, dysphagia phenotype, and agreement with VideoFluoroscopic Swallow Study (VFSS) in children with symptomatic, medication-treated SMA1 and oral feeding. METHODS: 10 children with SMA1 underwent FEES. Six patients had also a VFSS. Two clinicians independently rated FEES and VFSS videos. Swallowing safety was assessed using the Penetration-Aspiration scale (PAS). Dysphagia phenotypes were defined according to the classification defined by Warnecke et al. Swallowing efficacy was evaluated with the Yale Pharyngeal Residue Severity Rating Scale (YPRSRS) in FEES, whereas pharyngeal residue was rated as present or absent in VFSS. RESULTS: FEES was performed in all children without complications. Four children tolerated bolus trials during FEES, in 4 children swallowing characteristics were inferred based on post-swallow residues, while 2 children refused to eat and only saliva management was assessed. The dysphagia phenotype of predominance of residue in the piriform sinuses was documented in 7/8 children. The PAS score was < 3 in 3 children and > 5 in one child. Swallowing efficacy was impaired in 8/8 children. VFSS showed complete agreement with FEES. CONCLUSIONS: FEES is a feasible examination in children with SMA1. Swallowing safety and efficacy are impaired in nearly all patients with strong agreement between FEES and VFSS. Dysphagia is characterized by the predominance of residue in the piriform sinus.

Hyperphosphatemia Contributes to Skeletal Muscle Atrophy in Mice.

Chronic kidney disease (CKD) is associated with various pathologic changes, including elevations in serum phosphate levels (hyperphosphatemia), vascular calcification, and skeletal muscle atrophy. Elevated phosphate can damage vascular smooth muscle cells and cause vascular calcification. Here, we determined whether high phosphate can also affect skeletal muscle cells and whether hyperphosphatemia, in the context of CKD or by itself, is associated with skeletal muscle atrophy. As models of hyperphosphatemia with CKD, we studied mice receiving an adenine-rich diet for 14 weeks and mice with deletion of Collagen 4a3 (Col4a3-/-). As models of hyperphosphatemia without CKD, we analyzed mice receiving a high-phosphate diet for three and six months as well as a genetic model for klotho deficiency (kl/kl). We found that adenine, Col4a3-/-, and kl/kl mice have reduced skeletal muscle mass and function and develop atrophy. Mice on a high-phosphate diet for six months also had lower skeletal muscle mass and function but no significant signs of atrophy, indicating less severe damage compared with the other three models. To determine the potential direct actions of phosphate on skeletal muscle, we cultured primary mouse myotubes in high phosphate concentrations, and we detected the induction of atrophy. We conclude that in experimental mouse models, hyperphosphatemia is sufficient to induce skeletal muscle atrophy and that, among various other factors, elevated phosphate levels might contribute to skeletal muscle injury in CKD.

Irisin Ameliorates Muscle Atrophy by Inhibiting the Upregulation of the Ubiquitin‒Proteasome System in Chronic Kidney Disease.

Muscle atrophy is a common complication of chronic kidney disease (CKD). Irisin, a novel muscle cytokine, protects against muscle atrophy, but its specific role in CKD-associated muscle atrophy requires further elucidation. Because the ubiquitin-proteasome system (UPS) plays an important role in CKD muscle atrophy, our study will explore whether irisin affects UPS and alleviate CKD-associated muscle atrophy. In this study, an adenine-fed mouse model of CKD and urotension II (UII)-induced C2C12 myotubes were used as in vivo and in vitro models of muscle atrophy. The results showed that renal function, mouse weight, and the cross-sectional area (CSA) of skeletal muscles were significantly improved in CKD mice treated with irisin. Moreover, irisin effectively mitigated the decreases in phosphorylated Forkhead box O 3a (p-FOXO3A) levels and increases in the levels of E3 ubiquitin ligases, such as muscle RING finger 1 (MuRF1) and muscle atrophy F-box (MAFbx/atrogin1), in both the muscles of CKD mice and UII-induced C2C12 myotubes. In addition, irisin significantly increased the expression levels of myogenic differentiation factor D (MyoD) in the muscles of CKD mice. Our study is the first to demonstrate that irisin ameliorates skeletal muscle atrophy by inhibiting UPS upregulation and improving satellite cell differentiation in CKD.

Role of mesenchymal stem cells in sepsis and their therapeutic potential in sepsis­associated myopathy (Review).

Sepsis­induced myopathy (SIM) is one of the leading causes of death in critically ill patients. SIM mainly involves the respiratory and skeletal muscles of patients, resulting in an increased risk of lung infection, aggravated respiratory failure, and prolonged mechanical ventilation and hospital stay. SIM is also an independent risk factor associated with increased mortality in critically ill patients. At present, no effective treatment for SIM has yet been established. However, mesenchymal stem cells (MSCs) have emerged as a promising therapeutic approach and have been utilized in the treatment of various clinical conditions. A significant body of basic and clinical research supports the efficacy of MSCs in managing sepsis and muscle­related diseases. This literature review aims to explore the relationship between MSCs and sepsis, as well as their impact on skeletal muscle­associated diseases. Additionally, the present review discusses the potential mechanisms and therapeutic benefits of MSCs in the context of SIM.

Astragalus membranaceus and its monomers treat peritoneal fibrosis and related muscle atrophy through the AR/TGF-ß1 pathway.

Background: To anticipate the potential molecular mechanism of Astragalus membranaceus (AM) and its monomer, Calycosin, against peritoneal fibrosis (PF) and related muscle atrophy using mRNA-seq, network pharmacology, and serum pharmacochemistry. Methods: Animal tissues were examined to evaluate a CKD-PF mice model construction. mRNA sequencing was performed to find differential targets. The core target genes of AM against PF were screened through network pharmacology analysis, and CKD-PF mice models were given high- and low-dose AM to verify common genes. Serum pharmacochemistry was conducted to clarify which components of AM can enter the blood circulation, and the selected monomer was further validated through cell experiments for the effect on PF and mesothelial mesenchymal transition (MMT) of peritoneal mesothelial cells (PMCs). Results: The CKD-PF mice models were successfully constructed. A total of 31,184 genes were detected in the blank and CKD-PF groups, and 228 transcription factors had significant differences between the groups. Combined with network pharmacology analysis, a total of 228 AM-PF-related targets were identified. Androgen receptor (AR) was the remarkable transcription factor involved in regulating transforming growth factor-ß1 (TGF-ß1). AM may be involved in regulating the AR/TGF-ß1 signaling pathway and may alleviate peritoneal dialysis-related fibrosis and muscle atrophy in CKD-PF mice. In 3% peritoneal dialysis solution-stimulated HMrSV5 cells, AR expression levels were dramatically reduced, whereas TGF-ß1/p-smads expression levels were considerably increased. Conclusion: AM could ameliorate PF and related muscle atrophy via the co-target AR and modulated AR/TGF-ß1 pathway. Calycosin, a monomer of AM, could partially reverse PMC MMT via the AR/TGF-ß1/smads pathway. This study explored the traditional Chinese medicine theory of "same treatment for different diseases," and supplied the pharmacological evidence of "AM can treat flaccidity syndrome."

A comprehensive review of animal models for cancer cachexia: Implications for translational research.

Cancer cachexia is a multifactorial syndrome characterized by progressive weight loss and a disease process that nutritional support cannot reverse. Although progress has been made in preclinical research, there is still a long way to go in translating research findings into clinical practice. One of the main reasons for this is that existing preclinical models do not fully replicate the conditions seen in clinical patients. Therefore, it is important to understand the characteristics of existing preclinical models of cancer cachexia and pay close attention to the latest developments in preclinical models. The main models of cancer cachexia used in current research are allogeneic and xenograft models, genetically engineered mouse models, chemotherapy drug-induced models, Chinese medicine spleen deficiency models, zebrafish and Drosophila models, and cellular models. This review aims to revisit and summarize the commonly used animal models of cancer cachexia by evaluating existing preclinical models, to provide tools and support for translational medicine research.

Daidzein Inhibits Muscle Atrophy by Suppressing Inflammatory Cytokine- and Muscle Atrophy-Related Gene Expression.

BACKGROUND: Sarcopenic obesity, which is associated with a poorer prognosis than that of sarcopenia alone, may be positively affected by soy isoflavones, known inhibitors of muscle atrophy. Herein, we hypothesize that these compounds may prevent sarcopenic obesity by upregulating the gut metabolites with anti-inflammatory effects. METHODS: To explore the effects of soy isoflavones on sarcopenic obesity and its mechanisms, we employed both in vivo and in vitro experiments. Mice were fed a high-fat, high-sucrose diet with or without soy isoflavone supplementation. Additionally, the mouse C2C12 myotube cells were treated with palmitic acid and daidzein in vitro. RESULTS: The isoflavone considerably reduced muscle atrophy and the expression of the muscle atrophy genes in the treated group compared to the control group (Fbxo32, p = 0.0012; Trim63, p < 0.0001; Foxo1, p < 0.0001; Tnfa, p = 0.1343). Elevated levels of daidzein were found in the muscles and feces of the experimental group compared to the control group (feces, p = 0.0122; muscle, p = 0.0020). The real-time PCR results demonstrated that the daidzein decreased the expression of the palmitate-induced inflammation and muscle atrophy genes in the C2C12 myotube cells (Tnfa, p = 0.0201; Il6, p = 0.0008; Fbxo32, p < 0.0001; Hdac4, p = 0.0002; Trim63, p = 0.0114; Foxo1, p < 0.0001). Additionally, it reduced the palmitate-induced protein expression related to the muscle atrophy in the C2C12 myotube cells (Foxo1, p = 0.0078; MuRF1, p = 0.0119). CONCLUSIONS: The daidzein suppressed inflammatory cytokine- and muscle atrophy-related gene expression in the C2C12 myotubes, thereby inhibiting muscle atrophy.

Ultrasound Evaluations of Ankle and Foot Muscles in Diabetic Peripheral Neuropathy Systematic Review with Meta-Analysis.

BACKGROUND: Diabetic peripheral neuropathy (DPN) is the prevalent microvascular complication of diabetes mellitus (DM). 30-50% of diabetics are likely to be affected by DPN. It significantly impacts the skeletal muscles, resulting in an accelerated loss of muscle mass. The objective of this systematic review was to evaluate the ankle and foot muscle changes in diabetic peripheral neuropathy using ultrasound. METHOD: A comprehensive search was conducted in Scopus, Embase, and PubMed databases, which yielded 64 studies, out of which 5 studies are included in this meta-analysis. RESULT: The meta-analysis shows that the thickness and cross-section area of the extensor digitorum brevis muscle are reduced in DPN as compared to the control group with p-value<0.004 and p-value<0.001, respectively. The thickness of MIL muscle was also smaller in DPN p-value=0.02. Similarly, the thickness and CSA of AH muscle are also reduced in DPN patients compared to the control group, with p-values of 0.21 and 0.14. CONCLUSION: Meta-analysis reveals that diabetic peripheral neuropathy (DPN) patients have reduced foot muscle thickness and cross-sectional area (CSA) compared to controls without neuropathy. This highlights the importance of ultrasound in detecting muscle atrophy early in diabetic patients since it provides objective measures beyond traditional screening with its real-time and non-invasive nature.

Neuromuscular impairment at different stages of human sarcopenia.

BACKGROUND: Degeneration of the motoneuron and neuromuscular junction (NMJ) and loss of motor units (MUs) contribute to age-related muscle wasting and weakness associated with sarcopenia. However, these features have not been comprehensively investigated in humans. This study aimed to compare neuromuscular system integrity and function at different stages of sarcopenia, with a particular focus on NMJ stability and MU properties. METHODS: We recruited 42 young individuals (Y) (aged 25.98 ± 4.6 years; 57% females) and 88 older individuals (aged 75.9 ± 4.7 years; 55% females). The older group underwent a sarcopenia screening according to the revised guidelines of the European Working Group on Sarcopenia in Older People 2. In all groups, knee extensor muscle force was evaluated by isometric dynamometry, muscle morphology by ultrasound and MU potential properties by intramuscular electromyography (iEMG). MU number estimate (iMUNE) and blood samples were obtained. Muscle biopsies were collected in a subgroup of 16 Y and 52 older participants. RESULTS: Thirty-nine older individuals were non-sarcopenic (NS), 31 pre-sarcopenic (PS) and 18 sarcopenic (S). A gradual decrease in quadriceps force, cross-sectional area and appendicular lean mass was observed across the different stages of sarcopenia (for all P < 0.0001). Handgrip force and the Short Physical Performance Battery score also showed a diminishing trend. iEMG analyses revealed elevated near fibre segment jitter in NS, PS and S compared with Y (Y vs. NS and S: P < 0.0001; Y vs. PS: P = 0.0169), suggestive of age-related impaired NMJ transmission. Increased C-terminal agrin fragment (P < 0.0001) and altered caveolin 3 protein expression were consistent with age-related NMJ instability in all the older groups. The iMUNE was lower in all older groups (P < 0.0001), confirming age-related loss of MUs. An age-related increase in MU potential complexity was also observed. These observations were accompanied by increased muscle denervation and axonal damage, evinced by the increase in neural cell adhesion molecule-positive fibres (Y vs. NS: P < 0.0001; Y vs. S: P = 0.02) and the increase in serum concentration of neurofilament light chain (P < 0.0001), respectively. Notably, most of these MU and NMJ parameters did not differ when comparing older individuals with or without sarcopenia. CONCLUSIONS: Alterations in MU properties, axonal damage, an altered innervation profile and NMJ instability are prominent features of the ageing of the neuromuscular system. These neuromuscular alterations are accompanied by muscle wasting and weakness; however, they appear to precede clinically diagnosed sarcopenia, as they are already detectable in older NS individuals.

Assessing Muscle Protein Synthesis Rates In Vivo in Humans: The Deuterated Water (2H2O) Method.

Skeletal muscle tissue is in a constant state of turnover, with muscle tissue protein synthesis and breakdown rates ranging between 1% and 2% across the day in vivo in humans. Muscle tissue remodeling is largely controlled by the up- and down-regulation of muscle tissue protein synthesis rates. Research studies generally apply stable isotope-labeled amino acids to assess muscle protein synthesis rates in vivo in humans. Following labeled amino acid administration in a laboratory setting, muscle tissue samples are collected over several hours to assess the incorporation rate of these labeled amino acids in muscle tissue protein. To allow quantification of bulk muscle protein synthesis rates over more prolonged periods, the use of deuterated water methodology has regained much interest. Ingestion of daily boluses of deuterium oxide results in 2H enrichment of the body water pool. The available 2H-atoms become incorporated into endogenously synthesized alanine primarily through transamination of pyruvate in the liver. With 2H-alanine widely available to all tissues, it becomes incorporated into de novo synthesized tissue proteins. Assessing the increase in tissue protein-bound 2H-alanine enrichment in muscle biopsy samples over time allows for the calculation of muscle protein synthesis rates over several days or even weeks. As the deuterated water method allows for the assessment of muscle tissue protein synthesis rates under free-living conditions in nonlaboratory settings, there is an increasing interest in its application. This manuscript describes the theoretical background of the deuterated water method and offers a comprehensive tutorial to correctly apply the method to determine bulk muscle protein synthesis rates in vivo in humans.

Resveratrol as a potential therapeutic agent for sarcopenic obesity: Insights from in vivoperiments.

Sarcopenic obesity (SO) is a metabolic disorder with increasing prevalence. It is characterized by a reduction in skeletal muscle mass and strength. Resveratrol (RSV) is one of the most frequently used herbs in the treatment of skeletal muscle atrophy. However, the precise mechanism of the action of RSV in SO remains unclear. The objective of this study was to examine the pharmacological mechanism of RSV in the context of SO through the lens of network pharmacology, to validate these findings through in vivo experimentation. A list of potential RSV targets was compiled by retrieving the data from multiple databases. This list was then cross-referenced with a list of potential targets related to SO. The intersections of RSV- and SO-related targets were analyzed using Venn diagrams. To identify the core genes, a protein-protein interaction (PPI) network of the intersection targets was constructed and subsequently analyzed. Molecular docking was used to predict RSV binding to its core targets. A high-fat diet was used to induce SO in mice. These findings indicated that RSV may prevent SO by acting on 11 targets. Among these, interleukin-6 (IL-6), C-reactive protein (CRP), and tumor necrosis factor (TNF) are considered core targets. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment results indicated that the anti-SO effect of RSV was predominantly linked to metabolic disease-related pathways, including those associated with nonalcoholic fatty liver disease. The anti-inflammatory effects of RSV were confirmed in vivo in an SO mouse model. This study contributes to a more comprehensive understanding of the key mechanisms of the action of RSV against SO and provides new possibilities for drug development in the pathological process of SO.

Therapeutic targeting of GDF11 in muscle atrophy: Insights and strategies.

The exploration of novel therapeutic avenues for skeletal muscle atrophy is imperative due to its significant health impact. Recent studies have spotlighted growth differentiation factor 11 (GDF11), a TGFß superfamily member, for its rejuvenating role in reversing age-related tissue dysfunction. This review synthesizes current findings on GDF11, elucidating its distinct biological functions and the ongoing debates regarding its efficacy in muscle homeostasis. By addressing discrepancies in current research outcomes and its ambiguous role due to its homological identity to myostatin, a negative regulator of muscle mass, this review aims to clarify the role of GDF11 in muscle homeostasis and its potential as a therapeutic target for muscle atrophy. Through a thorough examination of GDF11's mechanisms and effects, this review provides insights that could pave the way for innovative treatments for muscle atrophy, emphasizing the need and strategies to boost endogenous GDF11 levels for therapeutic potential.

In vitro immuno-prevention of nitration/dysfunction of myogenic stem cell activator HGF, towards developing a strategy for age-related muscle atrophy.

In response to peroxynitrite (ONOO-) generation, myogenic stem satellite cell activator HGF (hepatocyte growth factor) undergoes nitration of tyrosine residues (Y198 and Y250) predominantly on fast IIa and IIx myofibers to lose its binding to the signaling receptor c-met, thereby disturbing muscle homeostasis during aging. Here we show that rat anti-HGF monoclonal antibody (mAb) 1H41C10, which was raised in-house against a synthetic peptide FTSNPEVRnitroY198EV, a site well-conserved in mammals, functions to confer resistance to nitration dysfunction on HGF. 1H41C10 was characterized by recognizing both nitrated and non-nitrated HGF with different affinities as revealed by Western blotting, indicating that the paratope of 1H41C10 may bind to the immediate vicinity of Y198. Subsequent experiments showed that 1H41C10-bound HGF resists peroxynitrite-induced nitration of Y198. A companion mAb-1H42F4 presented similar immuno-reactivity, but did not protect Y198 nitration, and thus served as the control. Importantly, 1H41C10-HGF also withstood Y250 nitration to retain c-met binding and satellite cell activation functions in culture. The Fab region of 1H41C10 exerts resistivity to Y250 nitration possibly due to its localization in the immediate vicinity to Y250, as supported by an additional set of experiments showing that the 1H41C10-Fab confers Y250-nitration resistance which the Fc segment does not. Findings highlight the in vitro preventive impact of 1H41C10 on HGF nitration-dysfunction that strongly impairs myogenic stem cell dynamics, potentially pioneering cogent strategies for counteracting or treating age-related muscle atrophy with fibrosis (including sarcopenia and frailty) and the therapeutic application of investigational HGF drugs.