Foxo Transcription Factors Induce the Atrophy-Related Ubiquitin Ligase Atrogin-1 and Cause Skeletal Muscle Atrophy

GL261 glioblastoma induces delayed body weight gain and stunted skeletal muscle growth in young mice

The survival rate for children and adolescents has increased to over 85%. However, there is limited understanding of the impact of pediatric cancers on muscle development and physiology. Given that brain tumors alone account for 26% of all pediatric cancers, this study aimed to investigate the skeletal muscle consequences of tumor growth in young mice. C2C12 myotubes were cocultured with GL261 murine glioblastoma cells to assess myotube size. GL261 cells were then injected subcutaneously into 4-wk-old male C57BL/6J mice. Animals were euthanized 28 days post-GL261 implantation. Muscle function was tested in vivo and ex vivo. Muscle protein synthesis was estimated via the SUnSET method, and gene/protein expression levels were assessed via Western blotting and qPCR. In vitro, the C2C12 cultures exposed to GL261 exhibited myotube atrophy, consistent with a disrupted anabolic/catabolic balance. In vivo, carcass, heart, and fat mass were significantly reduced in the tumor-bearing mice. Skeletal muscle growth was impeded in the GL261 hosts, along with a smaller muscle cross-sectional area (CSA). Both in vivo muscle torque and the ex vivo Extensor Digitorum Longus (EDL) muscle force were unchanged. At molecular level, the tumor hosts displayed reduced estimations of muscle protein synthesis and increased muscle protein ubiquitination, in disagreement with decreased muscle ubiquitin ligase mRNA expression. Overall, we showed that GL261 tumors impact the growth of pediatric mice by stunting skeletal muscle development, decreasing muscle mass, reducing muscle fiber size, diminishing muscle protein synthesis, and altering protein catabolism signaling.NEW & NOTEWORTHY This study shows that pediatric brain tumors stunt muscle development in young mice. GL261 glioblastoma cells caused myotube atrophy, reduced carcass, heart, and fat mass, and impeded skeletal muscle growth. Tumor-bearing mice had decreased muscle protein synthesis and increased protein ubiquitination. This is the first demonstration that GL261 tumors reduce muscle mass and fiber size, impair muscle function and innervation, and alter muscle protein turnover.

Study on the comorbid mechanisms of sarcopenia and late-life depression

The increasing global aging population has brought greater focus to age-related diseases, particularly muscle-brain comorbidities such as sarcopenia and late-life depression. Sarcopenia, defined by the gradual loss of muscle mass and function, is notably prevalent among older individuals, while late-life depression profoundly affects their mental health and overall well-being. Epidemiological evidence suggests a high co-occurrence of these two conditions, although the precise biological mechanisms linking them remain inadequately understood. This review synthesizes the existing body of literature on sarcopenia and late-life depression, examining their definitions, prevalence, clinical presentations, and available treatments. The goal is to clarify the potential connections between these comorbidities and offer a theoretical framework for the development of future preventive and therapeutic strategies.

Deubiquitinating Enzyme USP2 Alleviates Muscle Atrophy by Stabilizing PPAR-γ

Insulin resistance, a hallmark of type 2 diabetes, accelerates muscle breakdown and impairs energy metabolism. However, the role of ubiquitin specific peptidase 2 (USP2), a key regulator of insulin resistance, in sarcopenia remains unclear. Peroxisome proliferator-activated receptor γ (PPAR-γ) plays a critical role in regulating muscle atrophy. The role of deubiquitinase USP2 in mitigating muscle atrophy was investigated. Our findings revealed reduced USP2 expression in skeletal muscles of patients with type 2 diabetes. In mouse models of diabetes- and dexamethasone (DEX)-induced muscle atrophy, USP2 expression was downregulated in skeletal muscles. Usp2 knockout exacerbated muscle loss and functional impairment induced by diabetes or DEX. Moreover, skeletal muscle-specific Usp2 knockout further aggravated muscle loss and functional impairment induced by diabetes. Local injection of adeno-associated virus-Usp2 into the gastrocnemius muscles of diabetic mice increased muscle mass and improved skeletal muscle performance and endurance. It enhanced insulin sensitivity in diabetic mice, shown by lower fasting serum glucose and insulin levels and better glucose tolerance. Mechanistic analysis showed USP2 directly interacted with PPAR-γ by deubiquitinating it, stabilizing its protein levels, enhancing insulin signaling and sensitivity, and maintaining muscle mass. Loss of PPAR-γ abolishes the regulatory effects of USP2 on insulin sensitivity and muscle atrophy. MYOD1 activates USP2 transcription by binding to its promoter region. This study demonstrates the protective role of USP2 in mitigating muscle atrophy by stabilizing PPAR-γ through deubiquitination, particularly in models of diabetic and DEX-induced muscle atrophy. Targeting the USP2-PPAR-γ axis may offer promising therapeutic strategies for metabolic disorders and sarcopenia.

ARTICLE HIGHLIGHTS

The Alleviative Effect of Sodium Butyrate on Dexamethasone-Induced Skeletal Muscle Atrophy

Skeletal muscle mass is significantly negatively regulated by glucocorticoids. Following glucocorticoid administration, the balance between protein synthesis and breakdown in skeletal muscle is disrupted, shifting towards a predominance of catabolic metabolism. Short-chain fatty acids like sodium butyrate have been found to regulate inflammatory reactions and successively activate signaling pathways. The preventive benefits of sodium butyrate against dexamethasone-induced skeletal muscle atrophy and myotube atrophy models were examined in this work, and the underlying mechanism was clarified. A total of 32 6-week-old C57BL/6 inbred male mice were randomly assigned to one of four groups and treated with dexamethasone to induce muscle atrophy and sodium butyrate. We found that sodium succinate alleviated dexamethasone-induced myotube atrophy in the myotube atrophy model by lowering the gene expression of two E3 ubiquitin ligases, Atrogin-1 and MURF1, and activating the AKT/mTOR signaling pathway. Pertussis toxin reversed this effect, indicating that G protein-coupled receptors were involved in sodium butyrate's action as a mediator. Additionally, pre-treatment with sodium butyrate lowered weight and muscle mass loss in a mouse model of skeletal muscle atrophy, dramatically decreased the MURF1 gene expression and decreased the nuclear translocation of the glucocorticoid receptor. In conclusion, this study shows that sodium butyrate inhibits the expression of atrophy genes, thus preventing the breakdown of proteins and the loss of muscle mass, while also inhibiting weight loss, in animal models.

Role of GLP‑1 receptor agonists in sepsis and their therapeutic potential in sepsis‑induced muscle atrophy (Review)

Sepsis‑induced myopathy (SIM) is a common complication in intensive care units, which is often associated with adverse outcomes, primarily manifested as skeletal muscle weakness and atrophy. Currently, the management of SIM focuses on prevention strategies, as effective therapeutic options remain elusive. Glucagon‑like peptide‑1 (GLP‑1) receptor agonists (GLP‑1RAs) have garnered attention as hypoglycemic and weight‑loss agents, with an increasing body of research focusing on the extrapancreatic effects of GLP‑1. In preclinical settings, GLP‑1RAs exert protective effects against sepsis‑related multiple organ dysfunction through anti‑inflammatory and antioxidant mechanisms. Based on the existing research, we hypothesized that GLP‑1RAs may serve potential protective roles in the repair and regeneration of skeletal muscle affected by sepsis. The present review aimed to explore the relationship between GLP‑1RAs and sepsis, as well as their impact on muscle atrophy‑related myopathy. Furthermore, the potential mechanisms and therapeutic benefits of GLP‑1RAs are discussed in the context of muscle atrophy induced by sepsis.

Lambertianic Acid from Platycladus orientalis Inhibits Muscle Atrophy in Dexamethasone-Induced C2C12 Muscle Atrophy Cells

Platycladus orientalis, an evergreen tree belonging to the Cupressaceae family, has been traditionally used to treat various ailments, including fever, cough, diarrhea, diuresis, cold symptoms, and gastrointestinal disorders in folk medicine. As part of our ongoing investigation aimed at discovering bioactive natural products and elucidating their mechanisms of action from various natural sources, we investigated a methanol (MeOH) extract of P. orientalis leaves. This investigation led to the isolation and identification of a labdane-type diterpene, lambertianic acid (LA), via column chromatography and HPLC purification. The structure of LA was elucidated using LC/MS and NMR spectroscopic analyses, including HR-ESIMS, while its absolute configuration was confirmed through electronic circular dichroism (ECD) calculations. Recent studies have reported that labdane-type diterpenes exhibit diverse pharmacological activities, such as anticancer, anti-inflammatory, anti-obesity, and hypolipidemic effects. Notably, LA has been shown to modulate adipocyte metabolism via AMPK signaling; however, its role in skeletal muscle atrophy remains unexplored. Therefore, in this study, we investigated the effects of LA on dexamethasone (Dex)-induced muscle atrophy in C2C12 myotubes. Treatment with LA at concentrations of 25 µM and 50 µM significantly rescued myotube diameter and reduced the expression of atrophy-related proteins, including MuRF-1 and atrogin-1/MAFbx, without compromising cell viability at these moderate concentrations. These findings suggest that LA derived from P. orientalis exerts protective effects against skeletal muscle atrophy, highlighting its potential as a promising natural therapeutic candidate for muscle-wasting disorders.

Dnmt3a overexpression disrupts skeletal muscle homeostasis, promotes an aging-like phenotype, and reduces metabolic elasticity

Mammalian aging is reportedly driven by the loss of epigenetic information; however, its impact on skeletal muscle aging remains unclear. This study shows that aging mouse skeletal muscle exhibits increased DNA methylation, and overexpression of DNA methyltransferase 3a (Dnmt3a) induces an aging-like phenotype. Muscle-specific Dnmt3a overexpression leads to an increase in central nucleus-positive myofibers, predominantly in fast-twitch fibers, a shift toward slow-twitch fibers, elevated inflammatory and senescence markers, mitochondrial OXPHOS complex I reduction, and decreased basal autophagy. Dnmt3a overexpression resulted in reduced muscle mass and strength and impaired endurance exercise capacity with age, accompanied by an enhanced inflammatory signature. In addition, Dnmt3a overexpression reduced not only sensitivity to starvation-induced muscle atrophy but also the restorability from muscle atrophy. These findings suggest that increased DNA methylation disrupts skeletal muscle homeostasis, promotes an aging-like phenotype, and reduces muscle metabolic elasticity.

Pilot Study on the Profiling and Functional Analysis of mRNA, miRNA, and lncRNA in the Skeletal Muscle of Mongolian Horses, Xilingol Horses, and Grassland-Thoroughbreds

Muscle fibers, as the fundamental units of muscle tissue, play a crucial role in determining skeletal muscle function through their growth, development, and composition. To investigate changes in muscle fiber types and their regulatory mechanisms in Mongolian horses (MG), Xilingol horses (XL), and Grassland-Thoroughbreds (CY), we conducted histological and bioinformatic analyses on the gluteus medius muscle of these three horse breeds. Immunofluorescence analysis revealed that Grassland-Thoroughbreds had the highest proportion of fast-twitch muscle fibers at 78.63%, while Mongolian horses had the lowest proportion at 57.54%. Whole-transcriptome analysis identified 105 differentially expressed genes (DEGs) in the CY vs. MG comparison and 104 DEGs in the CY vs. XL comparison. Time-series expression profiling grouped the DEGs into eight gene sets, with three sets showing significantly up-regulated or down-regulated expression patterns (p < 0.05). Additionally, 280 differentially expressed long non-coding RNAs (DELs) were identified in CY vs. MG, and 213 DELs were identified in CY vs. XL. A total of 32 differentially expressed microRNAs (DEMIRs) were identified in CY vs. MG, while 44 DEMIRs were found in CY vs. XL. Functional enrichment analysis indicated that the DEGs were significantly enriched in essential biological processes, such as actin filament organization, muscle contraction, and protein phosphorylation. KEGG pathway analysis showed their involvement in key signaling pathways, including the mTOR signaling pathway, FoxO signaling pathway, and HIF-1 signaling pathway. Furthermore, functional variation-based analyses revealed associations between non-coding RNAs and mRNAs, with some non-coding RNAs targeting genes potentially related to muscle function regulation. These findings provide valuable insights into the molecular basis for the environmental adaptability, athletic performance, and muscle characteristics in horses, offering new perspectives for the breeding of Grassland-Thoroughbreds.

The Functions and Regulatory Mechanisms of Histone Modifications in Skeletal Muscle Development and Disease

Skeletal muscle development is a complex biological process regulated by many factors, such as transcription factors, signaling pathways, and epigenetic modifications. Histone modifications are important epigenetic regulatory factors involved in various biological processes, including skeletal muscle development, and play a crucial role in the pathogenesis of skeletal muscle diseases. Histone modification regulators affect the expression of many genes involved in skeletal muscle development and disease by adding or removing certain chemical modifications. In this review, we comprehensively summarize the functions and regulatory activities of the histone modification regulators involved in skeletal muscle development, regeneration, and disease.

Establishing a Murine Model of Muscle Changes in Chronic Nerve Compression

PURPOSE

We aimed to build upon a previously validated model of early chronic nerve compression (CNC) by evaluating changes in gross muscle weight, muscle gene expression, and muscle function, and correlating the mechanism and timing of muscle- and nerve related changes.

METHODS

Chronic nerve compression was induced by placing a Silastic tube around the sciatic nerve with the contralateral limb as control. At 6, 8, and 12 weeks of compression, gait analysis, muscle force measurements, and electrodiagnostics (EDX) were performed, and the sciatic nerve, tibialis anterior (TA), extensor digitorum longus (EDL), and gastrocnemius were harvested. Muscle weight (MW), cross-sectional area (CSA), g-ratio, axon area, and axon density were measured. Reverse transcripton polymerase chain reaction of TA+EDL muscle was performed. Genes assayed included atrogenes (Foxo-3, Atrogin-1, and MuRF1), markers of myogenesis (MyoD and MyoG), fatty acid synthase, type-I collagen (Col1a1), and inflammatory markers (tumor necrosis factor-α and interleukin-1β).

RESULTS

At 6 weeks, we observed a maximum 30.8% decrease in nerve conduction speed. G-ratio was increased 14.4% at 8 weeks, and at all time points, we observed a 25%-26% decrease in axon area. At 12 weeks, we observed a 10.4% decrease in TA+EDL MW, and at 8 weeks, CSA was reduced 13.9%. At 8 weeks, expression of atrogenes was increased 2-3-fold implying ongoing atrophy. MyoD/MyoG expression was reduced 0.3 times, and fatty acid synthase, type-1 collagen, and inflammatory marker expression was increased 1.3-, 1.4-, and >2-fold, respectively. There were no clinically important differences in gait analysis or muscle force measurement between compressed and control limbs at any time-point.

CONCLUSIONS

The murine model of muscle changes in CNC demonstrates reduced nerve conduction speed, demyelination, and a shift in axon size consistent with early CNC. Changes in MW, CSA, and gene expression occur in the absence of significant differences in muscle function.

CLINICAL RELEVANCE

These findings establish a mouse model of early muscle changes in CNC that can be used to investigate interventions to reduce or delay muscle changes in compression neuropathies.

Biomarkers of Skeletal Muscle Atrophy Based on Atrogenes Evaluation: A Systematic Review and Meta-Analysis Study

Muscle atrophy leads to decreased muscle mass, weakness, inactivity, and increased mortality. E3 ubiquitin ligases, key regulators of protein degradation via the ubiquitin-proteasome system, play a critical role in atrophic mechanisms. This meta-analysis followed Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, and its objective was to evaluate the association between E3 ligases Muscle Atrophy F-box (MAFbx)/Atrogin-1 (Fbxo32) and Muscle RING-finger protein 1 (MuRF-1) (TRIM63) E3 ligase mRNA levels, reductions in skeletal muscle CSA measures, and atrophy conditions. We examined papers published on PubMed®, Scopus, and Web of Science that studied E3 ligase gene expression signatures for Fbxo32 (MAFbx/Atrogin-1) and Trim63 (MuRF1) in different types of muscle atrophy and hypertrophy murine models. Twenty-nine studies selected by two independent raters were analyzed. Standardized mean differences (SMDs)/effect sizes (ESs) and 95% confidence intervals (CIs) were calculated for the outcomes using fixed-effects models. We found that 6- and 4.8-fold upregulation, respectively, of Fbxo32 and Trim63 was sufficient to reduce the ES to -3.89 (95% CI: -4.45 to -3.32) for the muscle fiber cross-sectional area and the development of skeletal muscle atrophy. I² and Q test statistics did not indicate heterogeneous data. There was a low probability of bias after both the funnel plot and Egger's test analyses. These results were sustained independently of the atrophic model and muscle type. Therefore, the magnitude of the increase in muscle Fbxo32 and Trim63 mRNA is a feasible, reliable molecular marker for skeletal muscle atrophy in mice. The next step for the Ubiquitin-proteasome system (UPS) field involves elucidating the targets of E3 ligases, paving the way for diagnostic and treatment applications in humans.

Statin-Associated muscle symptoms and vitamin D supplementation

PURPOSE OF REVIEW

Statin medications play a pivotal role in the primary and secondary prevention and management of cardiovascular disease due to their potent lipid-lowering and anti-inflammatory effects. Nevertheless, the clinical application of statins is often hampered by statin-associated muscle symptoms (SAMS), which deter patient adherence and treatment efficacy considerably. SAMS currently affects 10-20% of statin users, thus understanding potential mitigation strategies is crucial. This review focuses on the role of vitamin D in mitigating SAMS, given the growing interest in vitamin D deficiency as a potentially modifiable risk factor.

RECENT FINDINGS

Despite observational suggestions linking vitamin D deficiency to heightened SAMS risk, recent studies have yielded conflicting results on the role of vitamin D supplementation in preventing SAMS. Some studies report an improvement in statin tolerance following vitamin D repletion. However, recent large-scale clinical trials, particularly the Vitamin D and Omega-3 trial (VITAL) report no significant benefit of vitamin D supplementation in preventing SAMS or reducing statin discontinuation rates, regardless of baseline vitamin D levels.

SUMMARY

Observational data provides evidence for the use of vitamin D supplementation in SAMS management, however conflicting evidence in recent clinical trials do not support its routine use for preventing or treating SAMS. To explore alternative strategies in improving statin tolerance and adherence, this discourse aims to elucidate the current understanding the complex mechanisms underlying SAMS, the influence of serum vitamin D levels, and the implications for clinical management.

Low-Carbohydrate Diet Exacerbates Denervation-Induced Atrophy of Rat Skeletal Muscle Under the Condition of Identical Protein Intake

BACKGROUND

While decreased protein intake is associated with muscle mass loss, it is unclear whether a decrease in carbohydrate intake adversely affects muscle atrophy independently of protein intake. Herein, we examined whether a low-carbohydrate (low-CHO) diet exacerbates denervation-induced muscle atrophy under conditions of identical protein intake.

METHODS

On day one of the experiment, male Wistar rats underwent unilateral denervation. The contralateral leg was used as the control. After denervation, rats were divided into two dietary groups: high-carbohydrate (high-CHO) and low-CHO. Each group was fed a high-CHO (70% carbohydrate) or low-CHO (20% carbohydrate) diet over 7 days. Total protein and energy intakes in both groups were matched by pair feeding. Rats were provided with deuterium oxide (D2O) tracer over the last 3 days of dietary intervention to quantify myofibrillar (muscle) protein synthesis (MPS).

RESULTS

Denervation reduced wet weight of the gastrocnemius muscle compared to the contralateral control (p < 0.05). Reductions in gastrocnemius muscle weight were greater in the low-CHO group (-34%) than the high-CHO group (-28%) (p < 0.05). Although denervation decreased MPS compared to the contralateral control (p < 0.05), no dietary effect on MPS was observed. Denervation resulted in increased mRNA and protein expression of Atrogin-1, a ubiquitin E3 ligase, compared to that in the contralateral control (p < 0.05). Increases in Atrogin-1 gene and protein expression due to denervation were greater in the low-CHO group than in the high-CHO group (p < 0.05).

CONCLUSIONS

We conclude that a low-CHO diet may exacerbate denervation-induced atrophy in fast-twitch-dominant muscles compared to a high-CHO diet, even when the same protein intake is maintained. Although blunted MPS contributed to muscle atrophy due to denervation, exacerbation of muscle atrophy by the low-CHO diet was not accompanied by explanatory changes in MPS. The effect of the low-CHO diet might be related to promotion of muscle-specific ubiquitin E3 ligase gene expression.

Astragaloside IV Improves Muscle Atrophy by Modulating the Activity of UPS and ALP via Suppressing Oxidative Stress and Inflammation in Denervated Mice

Peripheral nerve injury is common clinically and can lead to neuronal degeneration and atrophy and fibrosis of the target muscle. The molecular mechanisms of muscle atrophy induced by denervation are complex and not fully understood. Inflammation and oxidative stress play an important triggering role in denervated muscle atrophy. Astragaloside IV (ASIV), a monomeric compound purified from astragalus membranaceus, has antioxidant and anti-inflammatory properties. The aim of this study was to investigate the effect of ASIV on denervated muscle atrophy and its molecular mechanism, so as to provide a new potential therapeutic target for the prevention and treatment of denervated muscle atrophy. In this study, an ICR mouse model of muscle atrophy was generated through sciatic nerve dissection. We found that ASIV significantly inhibited the reduction of tibialis anterior muscle mass and muscle fiber cross-sectional area in denervated mice, reducing ROS and oxidative stress-related protein levels. Furthermore, ASIV inhibits the increase in inflammation-associated proteins and infiltration of inflammatory cells, protecting the denervated microvessels in skeletal muscle. We also found that ASIV reduced the expression levels of MAFbx, MuRF1 and FoxO3a, while decreasing the expression levels of autophagy-related proteins, it inhibited the activation of ubiquitin-proteasome and autophagy-lysosome hydrolysis systems and the slow-to-fast myofiber shift. Our results show that ASIV inhibits oxidative stress and inflammatory responses in skeletal muscle due to denervation, inhibits mitophagy and proteolysis, improves microvascular circulation and reverses the transition of muscle fiber types; Therefore, the process of skeletal muscle atrophy caused by denervation can be effectively delayed.

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.

Genetic variation in the RETN promoter, accompanied by latent sarcopenic obesity, led to insulin resistance in a Japanese cohort: the Toon Genome Study

AIMS/HYPOTHESIS

Resistin, inducing insulin resistance, is elevated in the sera of individuals with the G-A haplotype at c.-420 C>G (rs1862513) and c.-358 G>A (rs3219175). This haplotype is associated with visceral obesity and low grip strength. To elucidate the hidden relationship between the G-A haplotype and insulin resistance, integration of specific phenotypes defined by body composition and 75 g OGTT would be a promising strategy.

METHODS

The 803 Japanese participants (average age: 62 years), attending annual medical checkups, were evaluated every 5 years. Participants were categorised by skeletal muscle mass, visceral fat score and OGTT results. Hierarchical clustering was performed using body composition and glucose metabolism parameters. Whole blood cells from participants homozygous for the G-A or C-G haplotype (n=25 and 33, respectively), matched for age, sex and BMI, using propensity score matching, were used for RNA-seq, pathway analysis and RT-PCR.

RESULTS

Multivariate analysis showed that individuals with the G-A haplotype, when accompanied by latent skeletal muscle loss and visceral obesity (latent sarcopenic obesity), presented a pronounced deterioration in insulin resistance over a 5 year period. Cluster 2, identified using hierarchical clustering, was characterised by low skeletal muscle mass, visceral obesity and insulin resistance. This cluster, with the G-A haplotype, demonstrated deterioration in insulin resistance. RNA-seq and RT-PCR revealed altered expression of mitophagy-related genes in whole blood cells of the G-A homozygotes.

CONCLUSIONS/INTERPRETATION

The G-A haplotype, accompanied by latent low skeletal muscle mass and visceral obesity, led to the deterioration of insulin resistance over a 5 year period in this cohort, possibly through the altered expression of mitophagy-related genes.

Nestin Regulates Autophagy-Dependent Ferroptosis Mediated Skeletal Muscle Atrophy by Ubiquitinating MAP 1LC3B

BACKGROUND

Programmed cell death plays a critical role in skeletal muscle atrophy. Ferroptosis, an iron-dependent form of programmed cell death driven by lipid peroxidation, has been implicated in various diseases, but its role in skeletal muscle atrophy remains unclear.

METHODS

Ferroptosis in skeletal muscle atrophy was investigated using two models: dexamethasone (Dex)-induced atrophy (n = 6 independent cell cultures per group) and simulated microgravity (n = 6 mice per group). Conditional Nestin knockout (KO) mice were generated using CRISPR/Cas9 (n = 6-8 mice per group), with wild-type (WT) controls (n = 6-8). Phenotypic analyses included histopathology (HE staining), functional assessments (muscle strength, weight analysis, treadmill), and dystrophy evaluation (dystrophin staining). Molecular analyses involved flow cytometry, ELISA, transmission electron microscopy, PI staining, and IP/MS to delineate Nestin-regulated ferroptosis pathways in skeletal muscle atrophy.

RESULTS

Ferroptosis was significantly activated in both atrophy models, with a 2.5-fold increase in lipid peroxidation (p < 0.01), a 2-fold accumulation of Fe2+ (p < 0.01) and a 50% reduction in Nestin expression (p < 0.001). Nestin KO mice exhibited exacerbated muscle atrophy, showing a 40% decrease in muscle weight (p < 0.01) and a 30% reduction in muscle strength (p < 0.05) compared to WT mice. Nestin overexpression mitigated Dex-induced ferroptosis, reducing lipid peroxidation by 40%, decreasing Fe2+ accumulation by 50% (p < 0.01), and improving muscle function by 30% (p < 0.05). Mechanistically, Nestin interacted with MAP 1LC3B (LC3B) to catalyse LC3B polyubiquitination at lysine-51, reducing LC3B availability for autophagy and inhibiting autophagy flux by 60% (p < 0.01), leading to a 50% reduction in ferroptosis (p < 0.001).

CONCLUSIONS

Our study identifies Nestin as a critical regulator of ferroptosis-autophagy crosstalk in skeletal muscle atrophy. Targeting Nestin-LC3B ubiquitination may offer novel therapeutic strategies for preventing muscle wasting in diseases such as cachexia and sarcopenia.

Upregulation of FAM129B protects against glucocorticoid-induced skeletal muscle atrophy via regulating long non-coding RNA NEAT1

Skeletal muscle atrophy, manifested by a reduction in muscle size and quantity, is primarily attributed to excessive protein catabolism. FAM129B, an antioxidant protein, has been previously implicated in muscle growth and development in cattle. Aim of this study is to elucidate the role of FAM129B in muscle atrophy. FAM129B was consistently down-regulated in muscle atrophy models in vitro and in vivo and in human steroid-treated gluteus muscles. FAM129B depletion resulted in myotubes atrophy with reduced diameter, increased MuRF-1 and Atrogin-1. Conversely, FAM129B overexpression ameliorated muscle atrophy by increasing myotube diameter and reducing Atrogin-1 and MuRF-1. Mice overexpressing FAM129B exhibited resistance to muscle atrophy, evidenced by increased grip strength, increased tibial anterior weight, increased myofiber cross-sectional area and decreased MuRF-1 and Atrogin-1. RNA sequencing revealed NEAT1 as a downstream gene of FAM129B. Mechanistically, FAM129B was found to influence the stability of NEAT1 by directly binding to it. The enhanced stability of NEAT1 subsequently led to increased FoxO1 expression and subsequent protein degradation. Our study has provided evidence that the upregulation of FAM129B rescues the glucocorticoid-induced skeletal muscle atrophy, suggesting that FAM129B may be a potential target for alleviating skeletal muscle atrophy.

Resistance but not endurance training suppresses glucocorticoid-induced leucine zipper (GILZ) expression in human skeletal muscle

PURPOSE

Within human skeletal muscle, statin treatment leads to elevated levels of the glucocorticoid-induced leucine zipper (GILZ). Further, GILZ mediates the muscle-related side effects of statins. Physical exercise leads to GILZ suppression, in a mechanosensitive manner. Given that statin treatment is rarely tolerated by habitually exercising individuals due to statin-associated muscle symptoms (SAMS), it appears that the opposing regulation of GILZ facilitates this detrimental interaction of two key measures of cardiovascular prevention, specifically for exercise modalities with high muscle strain. Similarly, opposing regulation of atrophy associated genes (atrogenes) may be a further mechanism. If confirmed, these results might have implications for the exercise prescription of statin-users.

METHODS

A systematic search of the Gene Expression Omnibus (GEO) repository for studies reporting the acute effects of either endurance (END), conventional resistance (RT), or eccentric resistance training (ECC) was conducted. GILZ, as well as the expression of pivotal atrogenes (e.g., muscle atrophy F-box, cathepsin L, etc.) were quantified.

RESULTS

15 studies with 204 participants (22 females; 182 males) were included. RT resulted in the highest GILZ suppression, significantly differing from the expressional change after END ( - 0.46 ± 1.11 vs.  - 0.07 ± 1.08), but not from ECC ( - 0.46 ± 1.11 vs. - 0.46 ± 0.95). Similar results were seen for various atrogenes.

CONCLUSION

Our results strengthen the assumption that mechanical loading can be considered a key mediator of exercise-induced changes in GILZ and atrogene expression.

Mechanism of Qigu capsule as a treatment for sarcopenia based on network pharmacology and experimental validation

OBJECTIVE

To explore the potential molecular mechanism of Qigu capsule (，QGC) in the treatment of sarcopenia through network pharmacology and to verify it experimentally.

METHODS

The active compounds of QGC and common targets between QGC and sarcopenia were screened from databases. Then the herbs-compounds-targets network, and protein-protein interaction (PPI) network was constructed. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were performed by R software. Next, we used a dexamethasone-induced sarcopenia mouse model to evaluate the anti-sarcopenic mechanism of QGC.

RESULTS

A total of 57 common targets of QGC and sarcopenia were obtained. Based on the enrichment analysis of GO and KEGG, we took the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway as a key target to explore the mechanism of QGC on sarcopenia. Animal experiments showed that QGC could increase muscle strength and inhibit muscle fiber atrophy. In the model group, the expression of muscle ring finger-1 and Atrogin-1 were increased, while myosin heavy chain was decreased, QGC treatment reversed these changes. Moreover, compared with the model group, the expressions of p-PI3K, p-Akt, p-mammalian target of rapamycin and p-Forkhead box O3 in the QGC group were all upregulated.

CONCLUSION

QGC exerts an anti-sarcopenic effect by activating PI3K/Akt signaling pathway to regulate skeletal muscle protein metabolism.

Preliminary Evidence Suggests That a 12-Week Treatment with Tirzepatide Plus Low-Energy Ketogenic Therapy Is More Effective than Its Combination with a Low-Calorie Diet in Preserving Fat-Free Mass, Muscle Strength, and Resting Metabolic Rate in Patients with Obesity

Background: Tirzepatide (TZP), a unimolecular dual agonist targeting glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 receptors, is a promising weight loss agent in obesity. The preservation of metabolically active fat-free mass (FFM), muscle strength (MS), and resting metabolic rate (RMR) is essential for optimizing fat mass (FM) reduction. Although TZP is typically combined with a low-calorie diet (LCD), its impact on FFM is uncertain, and studies on MS and RMR are lacking. Evidence suggests that Low-Energy Ketogenic Therapy (LEKT) may reduce FM while preserving FFM, MS, and RMR. Therefore, this study aimed to compare the effects of an LEKT and an LCD, both combined with TZP, on body weight (BW), FM, FFM, MS, and RMR in patients with obesity. Methods: We prospectively compared the effects of TZP combined with either an LCD or LEKT in 60 patients with obesity (n = 30 per group) over 12 weeks. BW, FM, FFM, MS, and RMR were measured at baseline and after 12 weeks. Clinical parameters, an assessment of dietary compliance, and side effects were also evaluated. Results: At 12-week follow-up, both groups showed a significant BW reduction from baseline (TZP+LEKT, p = 0.0289; TZP+LCD, p = 0.0278), with no significant intergroup difference (p = 0.665). Similarly, FM decreased significantly in both cohorts (TZP+LEKT, p < 0.001; TZP+LCD, p = 0.0185), with the TZP+LEKT group achieving a greater FM loss (p = 0.042). However, the TZP+LCD group exhibited significant declines from baseline in FFM (p = 0.0284), MS (p = 0.0341), and RMR (p < 0.001), whereas we did not observe any significant changes in FFM (p = 0.487), MS (p = 0.691), and RMR (p = 0.263) in the TZP+LEKT group. Intergroup direct comparisons confirmed that the TZP+LCD group experienced significantly greater reductions in FFM (p = 0.0388), MS (p = 0.046), and RMR (p = 0.019). Conclusions: Based on the findings of these preliminary data, we are able to support the hypothesis that TZP+LEKT seems to be superior to TZP+LCD in promoting FM reduction while preserving FFM, MS, and RMR in patients with obesity.

Zebrafish genetic model of neuromuscular degeneration associated with Atrogin-1 expression

The degenerative loss of muscle associated with aging leading to muscular atrophy is called sarcopenia. Currently, practicing regular physical exercise is the only efficient way to delay sarcopenia onset. Identification of therapeutic targets to alleviate the symptoms of aging requires in vivo model organisms of accelerated muscle degeneration and atrophy. The zebrafish undergoes aging, with hallmarks including mitochondrial dysfunction, telomere shortening, and accumulation of senescent cells. However, zebrafish age slowly, and no specific zebrafish models of accelerated muscle atrophy associated with molecular events of aging are currently available. We have developed a new genetic tool to efficiently accelerate muscle-fiber degeneration and muscle-tissue atrophy in zebrafish larvae and adults. We used a gain-of-function strategy with a molecule that has been shown to be necessary and sufficient to induce muscle atrophy and a sarcopenia phenotype in mammals: Atrogin-1 (also named Fbxo32). We report the generation, validation, and characterization of a zebrafish genetic model of accelerated neuromuscular atrophy, the atrofish. We demonstrated that Atrogin-1 expression specifically in skeletal muscle tissue induces a muscle atrophic phenotype associated with locomotion dysfunction in both larvae and adult fish. We identified degradation of the myosin light chain as an event occurring prior to muscle-fiber degeneration. Biological processes associated with muscle aging such as proteolysis, inflammation, stress response, extracellular matrix (ECM) remodeling, and apoptosis are upregulated in the atrofish. Surprisingly, we observed a strong correlation between muscle-fiber degeneration and reduced numbers of neuromuscular junctions in the peripheral nervous system, as well as neuronal cell bodies in the spinal cord, suggesting that muscle atrophy could underly a neurodegenerative phenotype in the central nervous system. Finally, while atrofish larvae can recover locomotive functions, adult atrofish have impaired regenerative capacities, as is observed in mammals during muscle aging. In the future, the atrofish could serve as a platform for testing molecules aimed at treating or alleviating the symptoms of muscle aging, thereby opening new therapeutic avenues in the fight against sarcopenia.

Streptozotocin-induced hyperglycemia unmasks cardiotoxicity induced by doxorubicin

Late-onset cardiotoxicity induced by anthracyclines occurs years to decades after completion of anti-cancer therapy and is associated with increased morbi-mortality of cancer survivors. Chemotherapy at the time of treatment probably causes cardiac damages for which the juvenile heart compensate. Co-morbidities happening in the adulthood such as type 1 diabetes (DT1), affect the heart and thus can unmask chemotherapy induced cardiotoxicity. To prove our hypothesis, we induced hyperglycemia [Streptozotocin treatment (STZ), 50 mg/kg/day for 5 days] in 11 weeks old mice who previously received doxorubicin treatment (Dox, 3 mg/kg) when they were six-weeks old. Interestingly, streptozotocin-induced hyperglycemia in Dox-pretreated mice (Dox-STZ) induced a higher mortality (p < 0.05) and more severe cardiac dysfunction (p < 0.0001) when compared with mice receiving Dox or STZ alone. Apoptosis evaluated by caspase 3 protein expression and Bax/Bcl2 genes expression was higher in Dox-STZ mice compared to STZ or Dox alone. While Dox and STZ independently induced capillary rarefaction, cardiomyocytes atrophy was only induced by STZ. Furthermore, Sirius-red staining of cardiac sections showed higher fibrosis levels (p < 0.0001) in Dox-STZ compared to Dox or STZ alone. All together, these results demonstrate that STZ precipitates and unmask cardiac dysfunction in previously treated Dox animals.

Dehydroandrographolide succinate attenuates dexamethasone-induced skeletal muscle atrophy by regulating Akt/GSK3β and MuRF-1 pathways

Andrographis paniculata (AGPA) is known for its wide-ranging biological activities, including antiviral, antipyretic, and anticancer properties. However, its effects on muscle atrophy have not been well understood. This study investigates the impact of andrographolide (AD) and dehydroandrographolide succinate (DAS), key components of AGPA, on skeletal muscle atrophy using in vitro and in vivo models. We employed dexamethasone (DEX)-treated mice and C2C12 myotubes as models of skeletal muscle atrophy. While DAS and AD did not reverse the DEX-induced reduction in body weight, both compounds significantly restored grip strength in DEX-treated mice. Notably, DAS treatment, but not AD, markedly improved running speed, endurance time, and distance. Both DAS and AD enhanced lean muscle mass in the whole body, tibialis anterior (TA), and gastrocnemius (GS) muscles, as well as increased TA thickness, with DAS demonstrating superior efficacy compared to AD. In C2C12 myotubes treated with DEX, DAS and AD increased ATP production and myotube diameter. Mechanistically, both compounds upregulated phosphorylation of Akt and GSK3β and downregulated MuRF-1 expression. These results indicate that DAS and AD mitigate muscle atrophy via the Akt/GSK3β and MuRF-1 pathways, with DAS showing greater anti-atrophy efficiency. Thus, DAS emerges as a promising therapeutic candidate for the prevention of skeletal muscle atrophy.

Mechanisms, assessment, and exercise interventions for skeletal muscle dysfunction post-chemotherapy in breast cancer: from inflammation factors to clinical practice

Chemotherapy remains a central component of breast cancer treatment, significantly improving patient survival rates. However, its toxic side effects, along with cancer-related paraneoplastic syndromes, can lead to the loss of skeletal muscle mass and function, impairing physical abilities and increasing the risk of complications during treatment. Chemotherapeutic agents directly impact skeletal muscle cells by promoting protein degradation, inhibiting protein synthesis, and triggering systemic inflammation, all of which contribute to muscle atrophy. Additionally, these drugs can interfere with the proliferation and differentiation of stem cells, such as satellite cells, disrupting muscle regeneration and repair while inducing abnormal differentiation of intermuscular tissue, thereby worsening muscle wasting. These effects not only reduce the effectiveness of chemotherapy but also negatively affect patients' quality of life and disease prognosis. Recent studies have emphasized the role of exercise as an effective non-pharmacological strategy for preventing muscle loss and preserving muscle mass in cancer patients. This review examines the clinical manifestations of muscle dysfunction following breast cancer chemotherapy, the potential mechanisms underlying these changes, and the evidence supporting exercise as a therapeutic approach for improving muscle function.

Rebastinib inhibits FoxO1 activity and reduces dexamethasone-induced atrophy and its-related gene expression in cultured myotubes

FoxO1, a transcription factor, is upregulated in skeletal muscle during atrophy and inactivation of FoxO1 is a potential strategy to prevent muscle loss. This study identified Rebastinib as a potent suppressor of FoxO1 activity among protein kinase inhibitors. To determine whether Rebastinib inhibits atrophy-related ubiquitin ligases gene expression and mitigates atrophy in mouse skeletal muscle-derived cells, we investigated its protective effects of the compound against dexamethasone (DEX)-induced muscle atrophy using C2C12 myotubes. Rebastinib inhibited the DEX-induced upregulation of atrogin-1 and MuRF-1 mRNA, and atrogin-1 protein. Rebastinib also suppressed protein degradation and increased myotube diameter in DEX-treated C2C12 myotubes. Additionally, Rebastinib ameliorated the DEX- and cachexia-induced reduction in contractile force generation. Although the precise mechanisms underlying the action of Rebastinib against muscle atrophy and its efficacy in vivo remains to be elucidated, this compound shows great potential as a therapeutic agent for muscle atrophy.

The role of Forkhead box O in diabetes mellitus

Forkhead box O (FOXO) proteins are transcription factors that are involved in many physiological processes, including diabetes mellitus, which is a complex, multifactorial metabolic disorder. FOXO proteins are emerging as pivotal regulators in the progression of diabetes mellitus, mainly by inhibiting insulin or insulin-like growth factor, but little is known about their roles in diabetes mellitus. Although no targeted therapy exists to slow the development of diabetes and diabetes-related complications, several recent advances have clarified the molecular mechanisms underlying the disease. This review summarizes findings about FOXO proteins and diabetes mellitus, and sheds new light on the roles of FOXO proteins in diabetes mellitus.

Aerobic plus resistance exercise attenuates skeletal muscle atrophy induced by dexamethasone through the HDAC4/FoxO3a pathway

This study aimed to investigate the underlying mechanisms by which physical exercise mitigates muscle atrophy induced by Dexamethasone (Dex). A muscle atrophy model was established in the mouse C2C12 cell line and 8-week-old mice treated with Dex, with subsequent verification of phenotype and atrogene expression. The potential benefits of combined aerobic and resistance exercise in mitigating muscle atrophy were then examined. To elucidate the involvement of Histone deacetylase 4 (HDAC4) in the protective effects of exercise against muscle loss, a combination of RT-PCR, Western blotting, immunoprecipitation, and immunofluorescence staining techniques were employed. The upregulation of HDAC4 was observed following Dex-induced muscle atrophy in vitro and in vivo. Inhibition of HDAC4 in C2C12 cells resulted in an increase in myotube diameter and fusion index, along with a decrease in the expression of Atrogin-1 and MuRF1. Treatment with Tasquinimod, an HDAC4 inhibitor, effectively prevented muscle wasting and dysfunction in mice induced by Dex. After a 6-week exercise intervention, the Dex-Exercise group exhibited significant improvements in body fat level, hyperinsulinemia, muscle mass and function in comparison to the Dex-Sedentary group. Mechanistically, we discovered that HDAC4 bound to and deacetylated Forkhead box protein O 3a (FoxO3a) within the nucleus, leading to decreased phosphorylation of FoxO3a at Ser 253. This interaction subsequently facilitated the expression of downstream atrogene Atrogin-1 and MuRF1, resulting in muscle atrophy. Conversely, exercise was found to potentially mitigate muscle atrophy by inhibiting the HDAC4/FoxO3a pathway. These findings suggest that HDAC4 may be a potential therapeutic target for exercise to combat Dex-induced muscle atrophy.

Maintaining myoprotein and redox homeostasis via an orally recharged nanoparticulate supplement potentiates sarcopenia treatment

Sarcopenia is a progressive skeletal muscle disorder characterized by the accelerated loss of muscle mass and function, with no promising pharmacotherapies. Understanding the imbalance of myoprotein homeostasis within myotubes, which causes sarcopenia, may facilitate the development of novel treatments for clinical use. In this study, we found a strong correlation between low serum selenium levels and muscle function in elderly patients with sarcopenia. We hypothesized that supplementation with selenium might be beneficial for the management of sarcopenia. To verify this hypothesis, we developed diselenide-bridged mesoporous silica nanoparticles (Se-Se-MSNs) with ROS-responsive degradation and release to supplement selenium. Se-Se-MSNs outperformed free selenocysteine in alleviating sarcopenia in both dexamethasone (Dex)- and denervation-induced mouse models. Subsequently, Se-Se-MSNs were loaded with leucine (Leu@Se-Se-MSNs), another nutritional supplement used in sarcopenia management. Oral administration of Leu@Se-Se-MSNs restored myoprotein homeostasis by enhancing mTOR/S6K signaling and inactivating Akt/FoxO3a/MuRF1 signaling, thus exerting optimal therapeutic effects against sarcopenia and exhibiting a more favorable in vivo safety profile. This study provides a proof of concept for treating sarcopenia by maintaining myoprotein and redox homeostasis simultaneously and offers valuable insights into the development of multifunctional nanoparticle-based supplements for sarcopenia management.

Microbiota protect against frailty and loss of skeletal muscle, and maintain inflammatory tone during aging in mice

Chronic low-level inflammation or "inflammaging" is hypothesized to contribute to sarcopenia and frailty. Resident microbiota are thought to promote inflammaging, frailty, and loss of skeletal muscle mass. We tested immunity and frailty in male C57BL6/N germ-free (GF), specific pathogen-free (SPF) mice, and mice that were born germ-free and colonized (COL) with an SPF microbiota. Male and female GF mice had lower systemic cellular inflammation indicated by lower blood Ly6Chigh monocytes across their lifespan. Male GF mice had lower body mass, but relative to body mass, GF mice had smaller hindlimb muscles and smaller muscle fibers compared with SPF mice across the lifespan. Male and female GF mice had increased frailty at 18 mo or older. Colonization of female GF mice increased blood Ly6Chigh monocytes but did not affect frailty at 18 mo or older. Colonization of male GF mice increased blood Ly6Chigh monocytes, skeletal muscle size, myofiber fiber size, and decreased frailty at 18 mo or older. Transcriptomic analysis of the tibialis anterior muscle revealed a microbiota-muscle axis with over 550 differentially expressed genes in COL male mice at 18 mo or older. Colonized male mice had transcripts indicative of lower tumor necrosis factor (TNF)-α signaling via nuclear factor κB (NF-κB). Our findings show that microbiota can increase systemic cellular immunity while decreasing muscle inflammation, thereby protecting against muscle loss and frailty. We also found sex differences in the role of microbiota regulating frailty. We propose that microbiota components protect against lower muscle mass and frailty across the lifespan in mice.NEW & NOTEWORTHY Germ-free mice had increased frailty, lower muscle mass, and lower circulating inflammatory monocytes. Therefore, lower systemic inflammation coincided with worse frailty and muscle loss. Microbial colonization decreased frailty, restored muscle mass, and increased circulating inflammatory monocytes while lowering transcripts in inflammatory TNF and NF-κB pathways within muscle. Hence, microbiota can increase circulating inflammation but decrease muscle inflammation to protect against frailty. This microbiota-muscle axis should be investigated for therapeutic potential in muscle wasting and sarcopenia.

Effects of 12-week whole-body vibration training versus resistance training in older people with sarcopenia

Sarcopenia is a syndrome commonly found in older people. The aim of this study was to evaluate the effects of whole-body vibration training (WBVT) and resistance training (RT) on body composition, muscle strength, physical performance and blood biomarkers in older people with sarcopenia. We conducted a 12-week, 3-times-weekly assessor-blinded, randomized controlled trial of 27 older people with sarcopenia aged ≥ 65 years. Subjects were randomized into WBVT group (n = 14) and RT group (n = 13). The primary outcome was knee extension strength (KES). Secondary outcomes were body composition [body weight, body mass index (BMI), percentage of body fat (PBF), and appendicular skeletal muscle mass index (ASMI)], muscle strength [handgrip strength (HS)], physical performance [gait speed (GS), 5-time chair stand test (5CST), and short physical performance battery (SPPB)], blood biomarkers (inflammatory factors, hormones, growth factors, and muscle injury biomarker), and quality of life questionnaire [medical outcomes study short-form 36 (SF-36)]. After 12-week intervention, in the WBVT group, we observed significant improvements in body composition (weight, BMI, PBF and ASMI), muscle strength (KES), physical performance (GS, SPPB and 5CST), blood biomarkers [insulin-like growth factor 1 (IGF-1), growth hormone, follistatin (FST) and creatine kinase (CK)] and quality of life. In the RT group, we observed significant improvements in body composition (weight, BMI and PBF), muscle strength (KES), physical performance (GS and SPPB), blood biomarkers (growth hormone, FST and CK) and quality of life. Between-group comparisons were only significant for KES (P = 0.007) and the role-physical (RP) dimension of the SF-36 (P = 0.007). WBVT and RT both improved the physical condition of older people with sarcopenia. RT excelled in muscle strength, but WBVT offered an alternative for those with restrictions. WBVT's low risk and flexibility suited diverse conditions, providing a new rehabilitation option for patients with sarcopenia.

Resistance exercise training in older men reduces ATF4-activated and senescence-associated mRNAs in skeletal muscle

Sarcopenia increases the risk of frailty, morbidity, and mortality in older adults. Resistance exercise training improves muscle size and function; however, the response to exercise training is variable in older adults. The objective of our study was to determine both the age-independent and age-dependent changes to the transcriptome following progressive resistance exercise training. Skeletal muscle biopsies were obtained before and after 12 weeks of resistance exercise training in 8 young (24 ± 3.3 years) and 10 older (72 ± 4.9 years) men. RNA was extracted from each biopsy and prepared for analysis via RNA sequencing. We performed differential mRNA expression, gene ontology, and gene set enrichment analyses. We report that when comparing post-training vs pre-training 226 mRNAs and 959 mRNAs were differentially expressed in the skeletal muscle of young and older men, respectively. Additionally, 94 mRNAs increased, and 17 mRNAs decreased in both young and old, indicating limited overlap in response to resistance exercise training. Furthermore, the differential gene expression was larger in older skeletal muscle. Finally, we report three novel findings: 1) resistance exercise training decreased the abundance of ATF4-activated and senescence-associated skeletal muscle mRNAs in older men; 2) resistance exercise-induced increases in lean mass correlate with increased mRNAs encoding mitochondrial proteins; and 3) increases in muscle strength following resistance exercise positively correlate with increased mRNAs involved in translation, rRNA processing, and polyamine metabolism. We conclude that resistance exercise training elicits a differential gene expression response in young and old skeletal muscle, including reduced ATF-4 activated and senescence-associated gene expression.

The Protective Effects of Perch Essence Against Muscle Atrophy in Cancer Cachexia and Cisplatin Treatment

Muscle atrophy, through several pathways including increased protein catabolism, leads to adverse effects in cachexia induced by cancer and chemotherapy. Perch essence (PE) is a perch extract rich in branched-chain amino acids and peptides. The present study initially investigated the effects of PE supplementation on muscle atrophy in a mouse model of cancer cachexia induced by C26 cancer cells and compared these effects with those of tryptone. Compared with the tumor-only group, we found that PE supplementation significantly improved body weight, muscle mass, maximum limb grip strength (MLGS), and myosin heavy chain expression in the muscles of tumor-bearing mice. PE also significantly inhibited the expression of factors related to protein degradation, oxidative stress, and inflammation, while enhancing the expression of antioxidant enzymes in tumor-bearing mice. These effects of PE were associated with an increased expression of phosphorylated Akt and forkhead box protein O1, along with a reduced expression of phosphorylated nuclear factor-κB p65 in the muscles of tumor-bearing mice. Furthermore, PE similarly increased MLGS and attenuated muscle atrophy in mice exposed to cisplatin by inhibiting protein degradation. All the therapeutic effects of PE supplementation mentioned above were generally greater than those of tryptone supplementation. These results suggest the potential of PE in protecting against muscle atrophy induced by tumors or chemotherapy.

Iron homeostasis and ferroptosis in muscle diseases and disorders: mechanisms and therapeutic prospects

The muscular system plays a critical role in the human body by governing skeletal movement, cardiovascular function, and the activities of digestive organs. Additionally, muscle tissues serve an endocrine function by secreting myogenic cytokines, thereby regulating metabolism throughout the entire body. Maintaining muscle function requires iron homeostasis. Recent studies suggest that disruptions in iron metabolism and ferroptosis, a form of iron-dependent cell death, are essential contributors to the progression of a wide range of muscle diseases and disorders, including sarcopenia, cardiomyopathy, and amyotrophic lateral sclerosis. Thus, a comprehensive overview of the mechanisms regulating iron metabolism and ferroptosis in these conditions is crucial for identifying potential therapeutic targets and developing new strategies for disease treatment and/or prevention. This review aims to summarize recent advances in understanding the molecular mechanisms underlying ferroptosis in the context of muscle injury, as well as associated muscle diseases and disorders. Moreover, we discuss potential targets within the ferroptosis pathway and possible strategies for managing muscle disorders. Finally, we shed new light on current limitations and future prospects for therapeutic interventions targeting ferroptosis.

Atrophic C2C12 Myotubes Activate Inflammatory Response of Macrophages In Vitro

BACKGROUND

Skeletal muscle wasting is commonly observed in aging, immobility, and chronic diseases. In pathological conditions, the impairment of skeletal muscle and immune system often occurs simultaneously. Recent studies have highlighted the initiative role of skeletal muscle in interactions with immune cells. However, the impact of skeletal muscle wasting on macrophage inflammatory responses remains poorly understood.

METHODS

To investigate the effect of atrophic myotubes on the inflammatory response of macrophages, we established two in vitro models to induce myotube atrophy: one induced by D-galactose and the other by starvation. Conditioned medium (CM) from normal and atrophic myotubes were collected and administered to bone marrow-derived macrophages (BMDMs) from mice. Subsequently, lipopolysaccharide (LPS) stimulation was applied, and the expression of inflammatory cytokines was measured via RT-qPCR.

RESULTS

Both D-galactose and starvation treatments reduced myotube diameter and upregulated muscle atrophy-related gene expression. CM from both atrophic myotubes models augmented the gene expression of pro-inflammatory factors in BMDMs following LPS stimulation, including Il6, Il1b, and Nfkb1. Notably, CM from starvation-induced atrophic myotubes also enhanced Il12b, Tnf, and Nos2 expression in BMDMs after stimulation, a response not observed in D-galactose-induced atrophic myotubes.

CONCLUSIONS

These findings suggest that CM from atrophic myotubes enhanced the expression of LPS-induced pro-inflammatory mediators in macrophages.

Impact of physical activity on physical function, mitochondrial energetics, ROS production, and Ca2+ handling across the adult lifespan in men

Aging-related muscle atrophy and weakness contribute to loss of mobility, falls, and disability. Mitochondrial dysfunction is widely considered a key contributing mechanism to muscle aging. However, mounting evidence positions physical activity as a confounding factor, making unclear whether muscle mitochondria accumulate bona fide defects with aging. To disentangle aging from physical activity-related mitochondrial adaptations, we functionally profiled skeletal muscle mitochondria in 51 inactive and 88 active men aged 20-93. Physical activity status confers partial protection against age-related decline in physical performance. Mitochondrial respiration remains unaltered in active participants, indicating that aging per se does not alter mitochondrial respiratory capacity. Mitochondrial reactive oxygen species (ROS) production is unaffected by aging and higher in active participants. In contrast, mitochondrial calcium retention capacity decreases with aging regardless of physical activity and correlates with muscle mass, performance, and the stress-responsive metabokine/mitokine growth differentiation factor 15 (GDF15). Targeting mitochondrial calcium handling may hold promise for treating aging-related muscle impairments.

Epigenetic factors and inflammaging: FOXO3A as a potential biomarker of sarcopenia and upregulation of DNMT3A and SIRT3 in older adults

Background

Epigenetic factors influence inflammaging and geriatric disorders such as sarcopenia and frailty. It is necessary to develop a biomarker/panel of biomarkers for fast and easy diagnostics. Currently, hard-to-access equipment is required to diagnose sarcopenia. The development of a biomarker/panel of biomarkers will prevent many older adults from being excluded from the diagnostic process.

Methods

In this study, we analyzed selected gene expression profiles, namely, SIRT1, SIRT3, SIRT6, DNMT3A, FOXO1, FOXO3A, and ELAVL1, in whole blood. The study included 168 subjects divided into five groups: patients hospitalized at the Geriatrics Clinic and Polyclinic with sarcopenia, frailty syndrome, or without those disorders (geriatric control), and non-hospitalized healthy controls (HC) aged 25 to 30 years and over 50 years.

Results

We revealed a lower mRNA level of FOXO3A (p<0.001) in sarcopenic patients compared to the geriatric controls. Furthermore, we detected upregulation of DNMT3A (p=0.003) and SIRT3 (p=0.015) in HC over 50 years old compared to HC aged 25 to 30 years. Interestingly, we observed 2 cluster formations during the gene expression correlation analysis (SIRT1, SIRT3, DNMT3A, and FOXO1, ELAVL1). We also noted correlations of clinical parameters with mRNA levels in the sarcopenic patients group, such as vitamin D level with SIRT1 (r=0.64, p=0.010), creatine kinase with SIRT3 (r=-0.58, p=0.032) and DNMT3A (r=-0.59, p=0.026), creatinine with DNMT3A (r=0.57, p=0.026), erythrocyte sedimentation rate (ESR) with FOXO3A (r=0.69, p=0.004), and lactate dehydrogenase (LDH) with FOXO3A (r=-0.86, p=0.007). In the frailty syndrome group, we noted a correlation of appendicular skeletal muscle mass (ASMM) with ELAVL1 (r=0.59, p=0.026) mRNA level. In the geriatric controls, we observed a correlation of serum iron with FOXO3A mRNA level (r=-0.79, p=0.036).

Conclusions

Our study revealed FOXO3A as a potential biomarker of sarcopenia. Furthermore, we observed a high expression of epigenetic factors (DNMT3A and SIRT3) in older adults.

GL261 glioblastoma induces delayed body weight gain and stunted skeletal muscle growth in young mice

Introduction

The survival rate for children and adolescents has increased to over 85%. However, there is limited understanding of the impact of pediatric cancers on muscle development and physiology. Given that brain tumors alone account for 26% of all pediatric cancers, this study aimed to investigate the skeletal muscle consequences of tumor growth in young mice.

Methods

C2C12 myotubes were co-cultured with GL261 murine glioblastoma cells to assess myotube size. GL261 cells were then injected subcutaneously into 4-week-old male C57BL/6J mice. Animals were euthanized 28 days post-GL261 implantation. Muscle function was tested in vivo and ex vivo . Muscle protein synthesis was measured via the SUnSET method, and gene/protein expression levels were assessed via Western blotting and qPCR.

Results

In vitro , the C2C12 cultures exposed to GL261 exhibited myotube atrophy, consistent with a disrupted anabolic/catabolic balance. In vivo , carcass, heart, and fat mass were significantly reduced in the tumor-bearing mice. Skeletal muscle growth was impeded in the GL261 hosts, along with smaller muscle CSA. Both in vivo muscle torque and the ex vivo EDL muscle force were unchanged. At molecular level, the tumor hosts displayed reduced muscle protein synthesis and increased muscle protein ubiquitination, in disagreement with decreased muscle ubiquitin ligase mRNA expression.

Conclusions

Overall, we showed that GL261 tumors impact the growth of pediatric mice by stunting skeletal muscle development, decreasing muscle mass, reducing muscle fiber size, diminishing muscle protein synthesis, and altering protein catabolism signaling.

Deciphering molecular crosstalk mechanisms between skeletal muscle atrophy and KRAS-mutant pancreatic cancer: a literature review

Background and Objective

Cachexia-induced skeletal muscle atrophy is a critical manifestation in Kirsten rat sarcoma viral oncogene homologue (KRAS)-mutant pancreatic cancer (PC) patients, predominantly characterized by a shift in metabolic equilibrium towards catabolism that accelerates protein degradation in myofibers and leads to muscle atrophy. This metabolic reprogramming not only supports tumor growth but also precipitates energy depletion in skeletal muscle tissues. Exploring these mechanisms reveals potential therapeutic targets in the metabolic and proteolytic pathways associated with KRAS-mutant PC.

Methods

A comprehensive search for literature was conducted in PubMed, Web of Science, Google Scholar and other search engines up to May 21st, 2024. Studies on PC models and patients were included.

Key Content and Findings

The crosstalk between KRAS-mutant PC and skeletal muscle atrophy can be categorized into four principal domains: (I) KRAS-driven metabolic reprogramming in cancer cells leads to the depletion of muscle energy reserves, thereby influencing the reallocation of myofiber energy towards fueling cancer cell; (II) KRAS-mutant cancer cells rely on nutrient-scavenging pathways, resulting in altered cytokine profiles, increased ubiquitin mRNA expression and autophagy-lysosome pathway, which facilitate myotube degradation and inhibit muscle regeneration, thereby disrupting muscular homeostasis and causing a one-way nutrient flux; (III) tumor-induced oxidative stress inflicts damage on myotubes, highlighting the detrimental effects of reactive oxygen species on muscle structure; (IV) KRAS-mutant cancer cells remodulate immune cell dynamics within the tumor environment, thereby reshaping host immunity. Together, these findings illuminate the intricate interplay between KRAS-mutant PC and skeletal muscle atrophy, mapping the pathophysiological framework that is crucial for understanding sarcopenia and related disorders.

Conclusions

This comprehensive analysis advances our understanding of the complex etiology of cancer cachexia and stimulates the development of targeted therapeutic strategies.

GDF15 Neutralization Ameliorates Muscle Atrophy and Exercise Intolerance in a Mouse Model of Mitochondrial Myopathy

BACKGROUND

Primary mitochondrial myopathies (PMMs) are disorders caused by mutations in genes encoding mitochondrial proteins and proteins involved in mitochondrial function. PMMs are characterized by loss of muscle mass and strength as well as impaired exercise capacity. Growth/Differentiation Factor 15 (GDF15) was reported to be highly elevated in PMMs and cancer cachexia. Previous studies have shown that GDF15 neutralization is effective in improving skeletal muscle mass and function in cancer cachexia. It remains to be determined if the inhibition of GDF15 could be beneficial for PMMs. The purpose of the present study is to assess whether treatment with a GDF15 neutralizing antibody can alleviate muscle atrophy and physical performance impairment in a mouse model of PMM.

METHODS

The effects of GDF15 neutralization on PMM were assessed using PolgD257A/D257A (POLG) mice. These mice express a proofreading-deficient version of the mitochondrial DNA polymerase gamma, leading to an increased rate of mutations in mitochondrial DNA (mtDNA). These animals display increased circulating GDF15 levels, reduced muscle mass and function, exercise intolerance, and premature aging. Starting at 9 months of age, the mice were treated with an anti-GDF15 antibody (mAB2) once per week for 12 weeks. Body weight, food intake, body composition, and muscle mass were assessed. Muscle function and exercise capacity were evaluated using in vivo concentric max force stimulation assays, forced treadmill running and voluntary home-cage wheel running. Mechanistic investigations were performed via muscle histology, bulk transcriptomic analysis, RT-qPCR and western blotting.

RESULTS

Anti-GDF15 antibody treatment ameliorated the metabolic phenotypes of the POLG animals, improving body weight (+13% ± 8%, p < 0.0001), lean mass (+13% ± 15%, p < 0.001) and muscle mass (+35% ± 24%, p < 0.001). Additionally, the treatment improved skeletal muscle max force production (+35% ± 43%, p < 0.001) and exercise performance, including treadmill (+40% ± 29%, p < 0.05) and voluntary wheel running (+320% ± 19%, p < 0.05). Mechanistically, the beneficial effects of GDF15 neutralization are linked to the reversal of the transcriptional dysregulation in genes involved in autophagy and proteasome signalling. The treatment also appears to dampen glucocorticoid signalling by suppressing circulating corticosterone levels in the POLG animals.

CONCLUSIONS

Our findings highlight the potential of GDF15 neutralization with a monoclonal antibody as a therapeutic avenue to enhance physical performance and mitigate adverse clinical outcomes in patients with PMM.

Pharmacological reduction of lipid hydroperoxides as a potential modulator of sarcopenia

We previously reported that elevated expression of phospholipid hydroperoxide glutathione peroxidase 4, an enzyme that regulates membrane lipid hydroperoxides, can mitigate sarcopenia in mice. However, it is still unknown whether a pharmacological intervention designed to modulate lipid hydroperoxides might be an effective strategy to reduce sarcopenia in aged mice. Here we asked whether a newly developed compound, CMD-35647 (CMD), can reduce muscle atrophy induced by sciatic nerve transection. We treated mice daily with vehicle or CMD (15 mg/kg, i.p. injection) starting 1 day prior to denervation. CMD treatment reduced hydroperoxide generation and blunted muscle atrophy by over 17% in denervated muscle. To test whether CMD can reduce ageing-induced muscle atrophy and weakness, we treated mice with either vehicle or CMD (15 mg/kg, i.p. injection) 3 days per week for 8 months, starting at 18 months of age until 26 months of age. We measured muscle mass, functional status of neuromuscular junctions, muscle contractile function and mitochondrial function in control and CMD-treated 26-month-old female mice. Treatment with CMD conferred protection against muscle atrophy in both tibialis anterior and extensor digitorum longus that was associated with maintenance of fibre size of MHC 2b and 2x fibres. Mitochondrial respiration was also protected in CMD-treated mice. We also found that muscle force generation was protected with CMD treatment despite denervation in ∼25% of the muscle fibres. Overall, this study shows that pharmacological interventions designed to reduce lipid hydroperoxides might be effective for preventing sarcopenia. KEY POINTS: Sarcopenia in aged mice is associated with muscle loss, contractile dysfunction, denervation, and reduced mitochondrial respiration. CMD-35647 is a pharmocological compound that can neutralize lipid hydroperoxides. 8 month treatment of CMD-35647 mitigated muscle atrophy in tibialis anterior and extensor digitorum longus. 8 month treatment of CMD-35647 improved muscle function in aged mice independent of the neuromuscular junction. Aged mice treated with CMD-35647 had greater respiration in red gastrocnemius muscle when compared to vehicle treated mice.

Transcriptional regulation of autophagy in skeletal muscle stem cells

Muscle stem cells (MuSCs) are essential for the regenerative capabilities of skeletal muscles. MuSCs are maintained in a quiescent state, but, when activated, can undergo proliferation and differentiation into myocytes, which fuse and mature to generate muscle fibers. The maintenance of MuSC quiescence and MuSC activation are processes that are tightly regulated by autophagy, a conserved degradation system that removes unessential or dysfunctional cellular components via lysosomes. Both the upregulation and downregulation of autophagy have been linked to impaired muscle regeneration, causing myopathies such as cancer cachexia, sarcopenia and Duchenne muscular dystrophy. In this Review, we highlight the importance of autophagy in regulating MuSC activity during muscle regeneration. Additionally, we summarize recent studies that link the transcriptional dysregulation of autophagy to muscle atrophy, emphasizing the dominant roles that transcription factors play in myogenic programs. Deciphering and understanding the roles of these transcription factors in the regulation of autophagy during myogenesis could advance the development of regenerative medicine.

The Effects of Vitamin D on Muscle Strength Are Influenced by Testosterone Levels

BACKGROUND

Although the role of vitamin D receptor (VDR) in muscle mass and strength is well established, the effects of vitamin D (VD) on muscle remain controversial due to various factors. Herein, the influence of sex on the effects of VD on muscle function and the underlying reasons was explored.

METHODS

Male and female Sod1 gene knockout (SKO) mice, serving as a model for skeletal muscle atrophy, were treated with the VD active analogue calcipotriol, and RNA sequencing was employed to investigate this potential signalling pathway. The National Health and Nutrition Examination Survey (NHANES) database was utilized to explore whether testosterone affects the correlation between VD and grip strength in human participants. Experiments involving C2C12 cells and castrated male mice subjected to immobilization were conducted to demonstrate the enhancing effects of testosterone on VD function.

RESULTS

In male SKO mice, Vdr expression in the gastrocnemius muscle was positively correlated with grip strength (R2 = 0.4689, p < 0.001), whereas no such correlation was identified in female mice. At 28 weeks of age, both male and female SKO mice exhibited significantly reduced grip strength compared to Sod1 wild-type (SWT) mice, and calcipotriol restored grip strength in male SKO mice (SWT-veh: 0.0716 ± 0.0006, SWT-cal: 0.0686 ± 0.0010, SKO-veh: 0.0601 ± 0.0010, SKO-cal: 0.0703 ± 0.0007; p < 0.05). Calcipotriol increased muscle protein synthesis and mitochondrial biogenesis while decreasing inflammation and atrogenes in gastrocnemius muscle of male SKO mice. However, the effect of calcipotriol on muscle was not significant in female SKO mice. Compared to wild-type mice, both male and female SKO mice exhibited reduced levels of 1,25(OH)2D3 due to ROS-induced hepatic CYP3A4 overexpression, thereby excluding the influence of baseline VD levels. The serum 25(OH)D3 and testosterone interactively affect grip strength in adults (p < 0.05). Using C2C12 cells differentiated into myotubes, testosterone significantly enhanced the inducing effects of VD on VDR, androgen receptor (AR), P-AKT, PGC1α, Beclin1 and LC3B. Calcipotriol improved grip strength in sham-operated mice but had a negligible effect on grip strength in castrated mice. However, a significant improvement in grip strength was observed in castrated mice following testosterone restoration (p < 0.05).

CONCLUSIONS

This study demonstrates the existence of sex heterogeneity in the effects of VD on muscle and that testosterone enhances the strength and molecular responses to VD. These findings underscore the importance of considering testosterone levels when utilizing VD to enhance muscle strength.

Muscle fiber types switched during the development of experimental autoimmune myasthenia gravis via the PI3K/Akt signaling pathway

As one of the largest organs of our human body, skeletal muscle has good research prospects in myasthenia gravis (MG), the symptoms of which include systemic skeletal muscle weakness. Skeletal muscle is composed of two types of muscle fibers. Different fiber subtypes can be converted into each other; however, the underlying mechanism is not yet clear. In this paper, we firstly established an experimental autoimmune myasthenia gravis (EAMG) rat model and found that the skeletal muscle fibers of the EAMG group were atrophied, with a change in the proportion of fiber subtypes, which switched from type IIa to type I in the EAMG group at the peak stage, as verified by histological and molecular analyses. Second-generation sequencing results predicted that the PI3K-Akt signaling pathway might be involved in the switch, and the mRNA expression levels of the PI3K-Akt pathway-related genesNr4a1, IL2rb, Col1A1 and Ddit4 were significantly different. In conclusion, this study indicates that the switch of muscle fiber subtypes in MG via the PI3K-Akt signaling pathway may be a potential target for the treatment of MG-related skeletal muscle atrophy in the future.

Transcriptomic Profiling Reveals Differences in Slow-Twitch and Fast-Twitch Muscles of a Cigarette Smoke-Exposed Rat Model

BACKGROUND

Cigarette smoking is known to affect muscle function and exercise capacity, including muscle fatigue resistance. Most studies showed diminished cross-sectional area and fibre type shifting in slow-twitch muscles such as the soleus, while effects on fast-twitch muscles were seldom reported and the differential responses between muscle types in response to exposure to cigarette smoke (CS) were largely unknown. This study aimed to elucidate the histomorphological, biochemical and transcriptomic changes induced by CS on both slow-twitch and fast-twitch muscles.

METHOD

Male Sprague-Dawley rats were randomly divided into two groups: sham air (SA) and CS. The rats were exposed to CS for 8 weeks using an exposure chamber system to mimic smoking conditions. Histomorphological analyses on muscle fibre type and cross-sectional area were determined in soleus and extensor digitorum longus (EDL). Transcriptomic profiles were investigated for identifying differentially expressed genes (DEGs) and potential mechanistic pathways involved. Inflammatory responses in terms of the macrophage population and the level of inflammatory cytokines were measured. Markers for muscle-specific proteolysis were also examined.

RESULT

Soleus muscle, but not in EDL, exhibited a significant increase in Type IIa fibres (SA: 9.0 ± 3.3%; CS: 19.8 ± 2.4%, p = 0.002) and decrease in Type I fibres (SA: 90.1 ± 3.6%; CS: 77.9 ± 3.3%, p = 0.003) after CS exposure. RNA sequencing revealed 165 identified DEGs in soleus including upregulation of 'Cd68', 'Ccl2' and 'Ucp2' as well as downregulation of 'Ucp3', etc. Pathways enrichment analysis revealed that the upregulated pathways in soleus were related to immune system and cellular response, while the downregulated pathways were related to oxidative metabolism. Only 10 DEGs were identified in EDL with less enriched pathways. The soleus also showed elevated pro-inflammatory cytokines, and the total macrophage marker CD68 was significantly higher in soleus of CS compared to the SA group (CD68+/no. of fibre: SA = 60.3 ± 39.3%; CS = 106.5 ± 27.2%, p = 0.0039), while the two groups in EDL muscle showed no significant difference. The expression of E3 ubiquitin ligase atrogin-1 associated with muscle degradation pathways was 1.63-fold higher in the soleus after CS, while no significant differences were observed in the EDL.

CONCLUSION

The CS-induced inflammatory responses on soleus muscle are likely mediated via targeting mitochondrial-related signalling, resulting in mitochondrial dysfunction and impaired oxidative capacity. The presumably less active mitochondrial-related signalling in EDL renders it less susceptible to changes towards CS, accounting for differential impacts between muscle types.

Aptamer-Conjugated Exosomes Ameliorate Diabetes-Induced Muscle Atrophy by Enhancing SIRT1/FoxO1/3a-Mediated Mitochondrial Function

BACKGROUND

Muscle atrophy is associated with Type 2 diabetes mellitus, which reduces the quality of life and lacks effective treatment strategies. Previously, it was determined that human umbilical cord mesenchymal stromal cell (hucMSC)-derived exosomes (EXOs) ameliorate diabetes-induced muscle atrophy. However, the systemic application of EXOs is less selective for diseased tissues, which reduces their efficacy and safety associated with their nonspecific biological distribution in vivo. Therefore, improving exosomal targeting is imperative. In this study, a skeletal muscle-specific aptamer (Apt) was used to explore the effects of Apt-functionalized EXOs derived from hucMSCs in diabetes-associated muscle atrophy and its specific mechanisms.

METHODS

Diabetic db/db mice and C2C12 myotubes were used to explore the effects of MSC-EXOs or Apt-EXOs in alleviating muscle atrophy. Grip strength, muscle weight and muscle fibre cross-sectional area (CSA) were used to evaluate skeletal muscle strength and muscle mass. Western blot analysis of muscle atrophy signalling, including MuRF1 and Atrogin 1 and the mitochondrial complex and Seahorse analysis were performed to investigate the underlying mechanisms of MSC-EXOs or Apt-EXOs on muscle atrophy.

RESULTS

MSC-EXOs increased grip strength (p = 0.0002) and muscle mass (p = 0.0044 for tibialis anterior (TA) muscle, p = 0.002 for soleus (SO) muscle) in db/db mice. It also increased the CSA of muscle fibres (p = 0.0011 for all fibres, p = 0.0036 for slow muscle fibres and p = 0.0089 for fast muscle fibres) and the percentage of slow-to-fast muscle fibres (p = 0.0109). However, Atrogin 1 (p = 0.0455) and MuRF1 expression (p = 0.0168) was reduced. MSC-EXOs activated SIRT1/FoxO1/3a signalling and enhanced mitochondrial function in db/db mice and C2C12 myotubes. SIRT1 knockdown decreased the beneficial antiatrophic effects of MSC-EXOs. Additionally, Apt conjugation increased the effect of MSC-EXOs on muscle atrophy and myofiber-type transition (p = 0.0133 for grip strength, p = 0.0124 for TA muscle weight, p = 0.0008 for SO muscle weight, p < 0.0001 for CSA of all muscle fibres, p = 0.0198 for CSA of slow muscle fibres, p = 0.0213 for CSA of fast muscle fibres, p = 0.011 for percentage of slow-fast muscle fibres, p = 0.0141 for Atrogin 1 expression and p = 0.005 for MuRF1 expression).

CONCLUSIONS

The results suggest that hucMSC-derived exosomes ameliorate diabetes-associated muscle atrophy by enhancing SIRT1/FoxO1/3a-mediated mitochondrial function and that Apt conjugation strengthens the effects of MSC-EXOs on muscle atrophy. These findings demonstrate the therapeutic potential of muscle-targeted MSC-EXOs for the treatment of muscle atrophy.

Gut dysbiosis in primary sarcopenia: potential mechanisms and implications for novel microbiome-based therapeutic strategies

Primary sarcopenia is characterized by a progressive loss of skeletal muscle mass, strength, and physical function that occurs with aging. Despite the related adverse or even serious health outcomes, no medications are currently available for treating primary sarcopenia. Here, we discuss recent advancements in understanding the mechanistic role of gut microbiota-muscle cross-talk in primary sarcopenia, and the therapeutic implications. The mechanistic insights encompass a causal role of gut dysbiosis in primary sarcopenia, potentially mediated through gut microbiota-derived bioactive metabolites, such as short-chain fatty acids (SCFAs), secondary bile acids, and their associated signaling pathways, which may be translated into the development of new microbiome-based treatment and diagnostic approaches. Furthermore, we identify challenges that need addressing in future studies to facilitate the translation into potential novel treatment and differential diagnosis for older individuals with sarcopenia.

Activation of the 26S Proteasome to Reduce Proteotoxic Stress and Improve the Efficacy of PROTACs

The 26S proteasome degrades the majority of cellular proteins and affects all aspects of cellular life. Therefore, the 26S proteasome abundance, proper assembly, and activity in different life contexts need to be precisely controlled. Impaired proteasome activity is considered a causative factor in several serious disorders. Recent advances in proteasome biology have revealed that the proteasome can be activated by different factors or small molecules. Thus, activated ubiquitin-dependent proteasome degradation has effects such as extending the lifespan in different models, preventing the accumulation of protein aggregates, and reducing their negative impact on cells. Increased 26S proteasome-mediated degradation reduces proteotoxic stress and can potentially improve the efficacy of engineered degraders, such as PROTACs, particularly in situations characterized by proteasome malfunction. Here, emerging ideas and recent insights into the pharmacological activation of the proteasome at the transcriptional and posttranslational levels are summarized.

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.

Glucosamine inhibits myoblast proliferation and differentiation, and stimulates myotube atrophy through distinct signal pathways

Glucosamine (GlcN) is one of the dietary supplements used in the treatment of osteoarthritis. Endogenously, GlcN is synthesized from glucose through the hexosamine pathway. In addition to ameliorating arthritis, several biological functions of GlcN have been reported, including insulin resistance in skeletal muscle. However, the regulatory role of GlcN in skeletal muscle development is not clear. We therefore investigated the effect of GlcN on myoblast proliferation, differentiation, and myotube development and their underlying mechanisms in C2C12 cells. Myoblast proliferation was measured by MTT assay. The expressions of MyoD, myogenin (MyoG), and myosin heavy chain (MyHC) were identified as determinants of myoblast differentiation. Expressions of atrogin-1 and muscle RING-finger protein-1 (MuRF-1) were identified as markers of myotube atrophy. The results show that treatment with GlcN significantly reduced myoblast proliferation and phosphorylation of Stat3 and S6K. These findings suggest that GlcN can inhibit growth of myoblasts through inhibiting phosphorylation of Stat3 and S6K. In addition, GlcN significantly suppressed the expression of MyoD, MyoG, and MyHC, as well as myotube formation. Pretreatment of C2C12 myoblast cells with ER stress inhibitors significantly blocked GlcN-inhibited MyHC expression and myotube formation. It can be concluded that GlcN suppressed myogenic differentiation via a pathway that involved ER stress. Moreover, GlcN decreased myotube diameter and expression of MyHC, as well as increased MuRF-1 in C2C12 myotubes. Meanwhile, GlcN also reduced the expressions of phosphorylated Akt and mTOR were stimulated after GlcN treatment in C2C12 myotubes. Thus, GlcN induced skeletal muscle atrophy by inhibiting the protein synthesis pathway. Chronic GlcN infusion also caused skeletal muscle atrophy in mice. In conclusion, GlcN regulated important stages of skeletal muscle development through different signaling pathways.