Muscle type and fiber type specificity in muscle wasting

Response characteristic and potential molecular mechanism of tail resorption in Bufo gargarizans after exposure to lead and copper, alone or combined

Tail resorption during amphibian metamorphosis is one of the most dramatic processes that is obligatorily dependent on thyroid hormone (TH). Heavy metals could result in thyroid gland damages and disturb TH homeostasis. Lead (Pb) and copper (Cu) often co-exist in natural aquatic ecosystems. However, there is still little information on how tail resorption responds to alone or combined exposure to Pb and Cu. Our study investigated the effects of Pb and Cu alone or combined exposure on the morphological parameters of the tail, histological changes of thyroid gland and tail, and gene expression programs involved in cell death of the tail in Bufo gargarizans tadpoles at the climax of metamorphosis. Results demonstrated that Pb, Cu and Pb-Cu mixture exposure resulted in a significantly longer tail compared with control. Damages to notochord, muscle, skin and spinal cord of the tail were found in Pb and Cu exposure groups. The colloid area, the height of follicular cells and number of phagocytic vesicles of thyroid gland in Pb-Cu mixture exposure groups were significantly reduced. In addition, the expression levels of TH, apoptosis, autophagy, degradation of cellular components and oxidative stress-related genes in the tail were significantly altered following Pb and Cu exposure. The present work revealed the relationship between environmental pollutants and tail resorption, providing scientific basis for amphibian protection.

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.

Autophagy markers LC3 and p62 in aging lumbar motor neurons

Autophagy is a ubiquitous process through which damaged cytoplasmic structures are recycled and degraded within cells. Aging can affect autophagy regulation in different steps leading to the accumulation of damaged organelles and proteins, which can contribute to cell dysfunction and death. Motor neuron (MN) loss and sarcopenia are prominent features of neuromuscular aging. Previous studies on phrenic MNs showed increased levels of the autophagy proteins LC3 and p62 in 24 month compared to 6 month old mice, consistent with the onset of diaphragm muscle sarcopenia. In the present study, we hypothesized that aging leads to increased expression of the autophagy markers LC3 and p62 in single lumbar MNs. Expression of LC3 and p62 in lumbar MNs (spinal levels L1-L6) was assessed using immunofluorescence and confocal imaging of male and female mice at 6, 18 and 24 months of age, reflecting 100 %, 90 % and 75 % survival, respectively. A mixed linear model with animal as a random effect was used to compare relative LC3 and p62 expression in choline acetyl transferase-positive MNs across age groups. Expression of LC3 and p62 decreased in the white matter of the lumbar spinal cord with aging, with ~29 % decrease in LC3 and ~ 7 % decrease in p62 expression at 24 months of age compared to 6 months of age. There was no change in LC3 or p62 expression in the gray matter with age. LC3 expression in MNs relative to white matter increased significantly with age, with 150 % increase at 24 months of age compared to 6 months of age. Similarly, p62 expression in MNs relative to white matter increased significantly with age, with ~14 % increase at 24 months of age compared to 6 months of age. No effect of sex or MN pool was observed in LC3 and p62 expression in MNs. Overall, these data suggest autophagy impairment during elongation (increased LC3) and degradation (increased p62) phases with aging in lumbar MNs.

Sex differences in reduction of trunk muscle mass related to falls and cognitive function during the COVID-19 pandemic in older adults

AIM

This study aimed to examine the influence of the COVID-19 pandemic on physical components and activity, and its relationship to physical performance in older adults.

METHODS

Sixty-seven participants aged 75 and older (81 ± 2 years, female: 66%), who underwent medical checkups continuously from 2018 to 2022 in one clinic, were enrolled. Muscle mass was assessed by the biometrical impedance analysis method, which was adjusted by height squared. Physical, oral, and cognitive performance data were obtained from Japanese standard questionnaires at medical checkups. Values obtained in 2018 and 2019 were defined as pre-pandemic, and those in 2021 and 2022 were defined as during the pandemic.

RESULTS

Body weight, grip strength, and skeletal mass index did not change from 2018 to 2022, but trunk muscle mass index decreased significantly. A difference in the trunk muscle mass index (TMI) was observed between 2022 and 2018/2019 in men; however, a significant difference was found between 2021 and 2022 in women. Compared with the pre-pandemic period, TMI during the pandemic decreased only in men. The difference in TMI between the pre-pandemic period and during the pandemic (ΔTMI) was significantly decreased in participants with low physical activity and poor oral performance before the pandemic, and in those with falls and poor cognitive function during the pandemic only in men.

CONCLUSION

Reduction of trunk muscle mass was related to falls and poor cognitive function during the COVID-19 pandemic in older male adults. These data suggest that the difference in response to the COVID-19 pandemic between men and women necessitates different types of support for older adults. Geriatr Gerontol Int 2024; ••: ••-••.

Ubiquitination Insight from Spinal Muscular Atrophy-From Pathogenesis to Therapy: A Muscle Perspective

Spinal muscular atrophy (SMA) is one of the most frequent causes of death in childhood. The disease's molecular basis is deletion or mutations in the SMN1 gene, which produces reduced survival motor neuron protein (SMN) levels. As a result, there is spinal motor neuron degeneration and a large increase in muscle atrophy, in which the ubiquitin-proteasome system (UPS) plays a significant role. In humans, a paralogue of SMN1, SMN2 encodes the truncated protein SMNΔ7. Structural differences between SMN and SMNΔ7 affect the interaction of the proteins with UPS and decrease the stability of the truncated protein. SMN loss affects the general ubiquitination process by lowering the levels of UBA1, one of the main enzymes in the ubiquitination process. We discuss how SMN loss affects both SMN stability and the general ubiquitination process, and how the proteins involved in ubiquitination could be used as future targets for SMA treatment.

Lactate-induced metabolic remodeling and myofiber type transitions via activation of the Ca2+-NFATC1 signaling pathway

Lactate can serve as both an energy substrate and a signaling molecule, exerting diverse effects on skeletal muscle physiology. Due to the apparently positive effects, it would be interesting to consider it as a sports supplement. However, the mechanism behind these effects are yet to be comprehensively understood. In this study, we observed that lactate administration could improve the ability of antifatigue, and we further found that lactate upregulated the expression of myosin heavy chain (MYHC I) and MYHC IIa, while downregulating the expression of MYHC IIb. Besides, transcriptomics and metabolomics revealed significant changes in the metabolic profile of gastrocnemius muscle following lactate administration. Furthermore, lactate enhanced the activities of metabolic enzymes, including HK, LDHB, IDH, SDM, and MDH, and promoted the expression of lactate transport-related proteins MCT1 and CD147, thereby improving the transport and utilization of lactate in both vivo and vitro. More importantly, lactate administration increased cellular Ca2+ concentration and facilitated nuclear translocation of nuclear factor of activated T cells (NFATC1) in myotubes, whereas inhibition of NFATC1 significantly attenuated the effects of lactate treatment on NFATC1 nuclear translocation and MyHC expression. Our results elucidate the ability of lactate to induce metabolic remodeling in skeletal muscle and promote myofiber-type transitions by activating the Ca2+-NFATC1 signaling pathway. This study is useful in exploring the potential of lactate as a nutritional supplement for skeletal muscle adaptation and contributing to a mechanistic understanding of the central role of lactate in exercise physiology.

Key considerations for investigating and interpreting autophagy in skeletal muscle

Skeletal muscle plays a crucial role in generating force to facilitate movement. Skeletal muscle is a heterogenous tissue composed of diverse fibers with distinct contractile and metabolic profiles. The intricate classification of skeletal muscle fibers exists on a continuum ranging from type I (slow-twitch, oxidative) to type II (fast-twitch, glycolytic). The heterogenous distribution and characteristics of fibers within and between skeletal muscles profoundly influences cellular signaling; however, this has not been broadly discussed as it relates to macroautophagy/autophagy. The growing interest in skeletal muscle autophagy research underscores the necessity of comprehending the interplay between autophagic responses among skeletal muscles and fibers with different contractile properties, metabolic profiles, and other related signaling processes. We recommend approaching the interpretation of autophagy findings with careful consideration for two key reasons: 1) the distinct behaviors and responses of different skeletal muscles or fibers to various perturbations, and 2) the potential impact of alterations in skeletal muscle fiber type or metabolic profile on observed autophagic outcomes. This review provides an overview of the autophagic profile and response in skeletal muscles/fibers of different types and metabolic profiles. Further, this review discusses autophagic findings in various conditions and diseases that may differentially affect skeletal muscle. Finally, we provide key points of consideration to better enable researchers to fine-tune the design and interpretation of skeletal muscle autophagy experiments.Abbreviation: AKT1: AKT serine/threonine kinase 1; AMPK: AMP-activated protein kinase; ATG: autophagy related; ATG4: autophagy related 4 cysteine peptidase; ATG5: autophagy related 5; ATG7: autophagy related 7; ATG12: autophagy related 12; BECN1: beclin 1; BNIP3: BCL2 interacting protein 3; CKD: chronic kidney disease; COPD: chronic obstructive pulmonary disease; CS: citrate synthase; DIA: diaphragm; EDL: extensor digitorum longus; FOXO3/FOXO3A: forkhead box O3; GAS; gastrocnemius; GP: gastrocnemius-plantaris complex; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MAPK: mitogen-activated protein kinase; MYH: myosin heavy chain; PINK1: PTEN induced kinase 1; PLANT: plantaris; PRKN: parkin RBR E3 ubiquitin protein ligase; QUAD: quadriceps; RA: rectus abdominis; RG: red gastrocnemius; RQ: red quadriceps; SOL: soleus; SQSTM1: sequestosome 1; TA: tibialis anterior; WG: white gastrocnemius; WQ: white quadriceps; WVL: white vastus lateralis; VL: vastus lateralis; ULK1: unc-51 like autophagy activating kinase 1.

Epigenetic control of skeletal muscle atrophy

Skeletal muscular atrophy is a complex disease involving a large number of gene expression regulatory networks and various biological processes. Despite extensive research on this topic, its underlying mechanisms remain elusive, and effective therapeutic approaches are yet to be established. Recent studies have shown that epigenetics play an important role in regulating skeletal muscle atrophy, influencing the expression of numerous genes associated with this condition through the addition or removal of certain chemical modifications at the molecular level. This review article comprehensively summarizes the different types of modifications to DNA, histones, RNA, and their known regulators. We also discuss how epigenetic modifications change during the process of skeletal muscle atrophy, the molecular mechanisms by which epigenetic regulatory proteins control skeletal muscle atrophy, and assess their translational potential. The role of epigenetics on muscle stem cells is also highlighted. In addition, we propose that alternative splicing interacts with epigenetic mechanisms to regulate skeletal muscle mass, offering a novel perspective that enhances our understanding of epigenetic inheritance's role and the regulatory network governing skeletal muscle atrophy. Collectively, advancements in the understanding of epigenetic mechanisms provide invaluable insights into the study of skeletal muscle atrophy. Moreover, this knowledge paves the way for identifying new avenues for the development of more effective therapeutic strategies and pharmaceutical interventions.

Fermented Yak-Kong using Bifidobacterium animalis derived from Korean infant intestine effectively relieves muscle atrophy in an aging mouse model

Yak-Kong (YK) is a small black soybean widely cultivated in Korea. It is considered to have excellent health functionality, as it has been reported to have better antioxidant efficacy than conventional black or yellow soybeans. Since YK has been described as good for the muscle health of the elderly in old oriental medicine books, this study sought to investigate the effect of fermented YK with Bifidobacterium animalis subsp. lactis LDTM 8102 (FYK) on muscle atrophy. In C2C12 mouse myoblasts, FYK elevated the expression of MyoD, total MHC, phosphorylated AKT, and PGC1α. In addition, two kinds of in vivo studies were conducted using both an induced and normal aging mouse model. The behavioral test results showed that in the induced aging mouse model, FYK intake alleviated age-related muscle weakness and loss of exercise performance. In addition, FYK alleviated muscle mass decrease and improved the expression of biomarkers including total MHC, myf6, phosphorylated AKT, PGC1α, and Tfam, which are related to myoblast differentiation, muscle protein synthesis, and mitochondrial generation in the muscle. In the normal aging model, FYK consumption did not increase muscle mass, but did upregulate the expression levels of biomarkers related to myoblast differentiation, muscle hypertrophy, and muscle function. Furthermore, it mitigated age-related declines in skeletal muscle force production and functional limitation by enhancing exercise performance and grip strength. Taken together, the results suggest that FYK has the potential to be a new functional food material that can alleviate the loss of muscle mass and strength caused by aging and prevent sarcopenia.

Sex differences in spontaneous respiratory recovery following chronic C2 hemisection

Respiratory deficits after C2 hemisection (C2Hx) have been well documented through single-sex investigations. Although ovarian sex hormones enable enhanced respiratory recovery observed in females 2 wk post-C2Hx, it remains unknown if sex impacts spontaneous respiratory recovery at chronic time points. We conducted a longitudinal study to provide a comprehensive sex-based characterization of respiratory neuromuscular recovery for 8 wk after C2Hx. We recorded ventilation and chronic diaphragm electromyography (EMG) output in awake, behaving animals, phrenic motor output in anesthetized animals, and performed diaphragm muscle histology in chronically injured male and female rodents. Our results show that females expressed a greater recovery of tidal volume and minute ventilation compared with males during subacute and chronic time points. Eupneic diaphragm EMG amplitude during wakefulness and phrenic motor amplitude are similar between sexes at all time points after injury. Our data also suggest that females have a greater reduction in ipsilateral diaphragm EMG amplitude during spontaneous deep breaths (e.g., sighs) compared with males. Finally, we show evidence for atrophy and remodeling of the fast, fatigable fibers ipsilateral to injury in females, but not in males. To our knowledge, the data presented here represent the first study to report sex-dependent differences in spontaneous respiratory recovery and diaphragm muscle morphology following chronic C2Hx. These data highlight the need to study both sexes to inform evidence-based therapeutic interventions in respiratory recovery after spinal cord injury (SCI).NEW & NOTEWORTHY In response to chronic C2 hemisection, female rodents display increased tidal volume during eupneic breathing compared with males. Females show a greater reduction in diaphragm electromyography (EMG) amplitude during spontaneous deep breaths (e.g., sighs) and atrophy and remodeling of fast, fatigable diaphragm fibers. Given that most rehabilitative interventions occur in the subacute to chronic stages of injury, these results highlight the importance of considering sex when developing and evaluating therapeutics after spinal cord injury.

Time-dependent reduction in oxidative capacity among cultured myotubes from spinal cord injured individuals

BACKGROUND

Skeletal muscle adapts in reaction to contractile activity to efficiently utilize energy substrates, primarily glucose and free fatty acids (FA). Inactivity leads to atrophy and a change in energy utilization in individuals with spinal cord injury (SCI). The present study aimed to characterize possible inactivity-related differences in the energy metabolism between skeletal muscle cells cultured from satellite cells isolated 1- and 12-months post-SCI.

METHODS

To characterize inactivity-related disturbances in spinal cord injury, we studied skeletal muscle cells isolated from SCI subjects. Cell cultures were established from biopsy samples from musculus vastus lateralis from subjects with SCI 1 and 12 months after the injury. The myoblasts were proliferated and differentiated into myotubes before fatty acid and glucose metabolism were assessed and gene and protein expressions were measured.

RESULTS

The results showed that glucose uptake was increased, while oleic acid oxidation was reduced at 12 months compared to 1 month. mRNA expressions of PPARGC1α, the master regulator of mitochondrial biogenesis, and MYH2, a determinant of muscle fiber type, were significantly reduced at 12 months. Proteomic analysis showed reduced expression of several mitochondrial proteins.

CONCLUSION

In conclusion, skeletal muscle cells isolated from immobilized subjects 12 months compared to 1 month after SCI showed reduced fatty acid metabolism and reduced expression of mitochondrial proteins, indicating an increased loss of oxidative capacity with time after injury.

Low handgrip strength is related to elevated echogenicity in patients with chronic kidney disease: A pilot, cross-sectional and exploratory study

OBJECTIVES

Evaluate associations between triceps braqui muscle ultrasound measures (TB US) and handgrip strength (HGS), and the sensibility of TB US for low HGS in non-dialysis-dependent chronic kidney disease (nd-CKD) patients.

PARTICIPANTS AND METHODS

This pilot, cross-sectional, and exploratory study evaluated TB cross-sectional images from A-mode US and processed by FIJI-Image J to obtain muscle thickness (MT), echogenicity (EI), cross-sectional area (CSA), pennation angle (PA), and fascicle length (Lf) associating them with absolute HGS by simple and, multiple linear regression. The HGS was normalized to body mass index (BMI) and separated into low HGS (HGS/BMI≤10p according to sex and age) and adequate HGS (HGS/BMI>10p) groups. The body composition was from multifrequency bioimpedance. ROC analysis verified the TB US diagnostic accuracy to low HGS.

RESULTS

Were included 42 (21M/21F) adults with 65.5 (60-70) y median age, 47.22% in 3b CKD stage. The low HGS group (45.23%) showed a higher fat mass (FM), TB muscle medium head's PA, and EI than adequate HGS (p<0.05). In crude model, a pixels increase in EI was associated with a 0.452kgf HGS reduction (p=0.019); adjusted for sex, age, and FM, a one-unit increase in EI was associated with a 0.510kgf HGS reduction (p=0.011). The EI also showed moderate diagnostic accuracy (AUC=0.730; CI 95%=0.589; 0.919) to low HGS and a sensitivity of 86.9% (cutoff≥13.52 pixels).

CONCLUSION

In nd-CKD patients, of all measurements from US, the EI was the most associated with HGS, and the only one sensitive to low HGS diagnosis.

Bioinformatics and system biology approach to identify potential common pathogenesis for COVID-19 infection and sarcopenia

Sarcopenia is a condition characterized by age-related loss of muscle mass and strength. Increasing evidence suggests that patients with sarcopenia have higher rates of coronavirus 2019 (COVID-19) infection and poorer post-infection outcomes. However, the exact mechanism and connections between the two is unknown. In this study, we used high-throughput data from the GEO database for sarcopenia (GSE111016) and COVID-19 (GSE171110) to identify common differentially expressed genes (DEGs). We conducted GO and KEGG pathway analyses, as well as PPI network analysis on these DEGs. Using seven algorithms from the Cytoscape plug-in cytoHubba, we identified 15 common hub genes. Further analyses included enrichment, PPI interaction, TF-gene and miRNA-gene regulatory networks, gene-disease associations, and drug prediction. Additionally, we evaluated immune cell infiltration with CIBERSORT and assessed the diagnostic accuracy of hub genes for sarcopenia and COVID-19 using ROC curves. In total, we identified 66 DEGs (34 up-regulated and 32 down-regulated) and 15 hub genes associated with sarcopenia and COVID-19. GO and KEGG analyses revealed functions and pathways between the two diseases. TF-genes and TF-miRNA regulatory network suggest that FOXOC1 and hsa-mir-155-5p may be identified as key regulators, while gene-disease analysis showed strong correlations with hub genes in schizophrenia and bipolar disorder. Immune infiltration showed a correlation between the degree of immune infiltration and the level of infiltration of different immune cell subpopulations of hub genes in different datasets. The ROC curves for ALDH1L2 and KLF5 genes demonstrated their potential as diagnostic markers for both sarcopenia and COVID-19. This study suggests that sarcopenia and COVID-19 may share pathogenic pathways, and these pathways and hub genes offer new targets and strategies for early diagnosis, effective treatment, and tailored therapies for sarcopenia patients with COVID-19.

Tackling Brain and Muscle Dysfunction in Acute Respiratory Distress Syndrome Survivors: NHLBI Workshop Report

Acute respiratory distress syndrome (ARDS) is associated with long-term impairments in brain and muscle function that significantly impact the quality of life of those who survive the acute illness. The mechanisms underlying these impairments are not yet well understood, and evidence-based interventions to minimize the burden on patients remain unproved. The NHLBI of the NIH assembled a workshop in April 2023 to review the state of the science regarding ARDS-associated brain and muscle dysfunction, to identify gaps in current knowledge, and to determine priorities for future investigation. The workshop included presentations by scientific leaders across the translational science spectrum and was open to the public as well as the scientific community. This report describes the themes discussed at the workshop as well as recommendations to advance the field toward the goal of improving the health and well-being of ARDS survivors.

Type 2 diabetes mellitus related sarcopenia: a type of muscle loss distinct from sarcopenia and disuse muscle atrophy

Muscle loss is a significant health concern, particularly with the increasing trend of population aging, and sarcopenia has emerged as a common pathological process of muscle loss in the elderly. Currently, there has been significant progress in the research on sarcopenia, including in-depth analysis of the mechanisms underlying sarcopenia caused by aging and the development of corresponding diagnostic criteria, forming a relatively complete system. However, as research on sarcopenia progresses, the concept of secondary sarcopenia has also been proposed. Due to the incomplete understanding of muscle loss caused by chronic diseases, there are various limitations in epidemiological, basic, and clinical research. As a result, a comprehensive concept and diagnostic system have not yet been established, which greatly hinders the prevention and treatment of the disease. This review focuses on Type 2 Diabetes Mellitus (T2DM)-related sarcopenia, comparing its similarities and differences with sarcopenia and disuse muscle atrophy. The review show significant differences between the three muscle-related issues in terms of pathological changes, epidemiology and clinical manifestations, etiology, and preventive and therapeutic strategies. Unlike sarcopenia, T2DM-related sarcopenia is characterized by a reduction in type I fibers, and it differs from disuse muscle atrophy as well. The mechanism involving insulin resistance, inflammatory status, and oxidative stress remains unclear. Therefore, future research should further explore the etiology, disease progression, and prognosis of T2DM-related sarcopenia, and develop targeted diagnostic criteria and effective preventive and therapeutic strategies to better address the muscle-related issues faced by T2DM patients and improve their quality of life and overall health.

System-level analysis of genes mutated in muscular dystrophies reveals a functional pattern associated with muscle weakness distribution

Muscular dystrophies (MDs) are inherited genetic diseases causing weakness and degeneration of muscles. The distribution of muscle weakness differs between MDs, involving distal muscles or proximal muscles. While the mutations in most of the MD-associated genes lead to either distal or proximal onset, there are also genes whose mutations can cause both types of onsets. We hypothesized that the genes associated with different MD onsets code proteins with distinct cellular functions. To investigate this, we collected the MD-associated genes and assigned them to three onset groups: genes mutated only in distal onset dystrophies, genes mutated only in proximal onset dystrophies, and genes mutated in both types of onsets. We then systematically evaluated the cellular functions of these gene sets with computational strategies based on functional enrichment analysis and biological network analysis. Our analyses demonstrate that genes mutated in either distal or proximal onset MDs code proteins linked with two distinct sets of cellular processes. Interestingly, these two sets of cellular processes are relevant for the genes that are associated with both onsets. Moreover, the genes associated with both onsets display high centrality and connectivity in the network of muscular dystrophy genes. Our findings support the hypothesis that the proteins associated with distal or proximal onsets have distinct functional characteristics, whereas the proteins associated with both onsets are multifunctional.

Exploration of a machine learning approach for diagnosing sarcopenia among Chinese community-dwelling older adults using sEMG-based data

BACKGROUND

In the practical application of sarcopenia screening, there is a need for faster, time-saving, and community-friendly detection methods. The primary purpose of this study was to perform sarcopenia screening in community-dwelling older adults and investigate whether surface electromyogram (sEMG) from hand grip could potentially be used to detect sarcopenia using machine learning (ML) methods with reasonable features extracted from sEMG signals. The secondary aim was to provide the interpretability of the obtained ML models using a novel feature importance estimation method.

METHODS

A total of 158 community-dwelling older residents (≥ 60 years old) were recruited. After screening through the diagnostic criteria of the Asian Working Group for Sarcopenia in 2019 (AWGS 2019) and data quality check, participants were assigned to the healthy group (n = 45) and the sarcopenic group (n = 48). sEMG signals from six forearm muscles were recorded during the hand grip task at 20% maximal voluntary contraction (MVC) and 50% MVC. After filtering recorded signals, nine representative features were extracted, including six time-domain features plus three time-frequency domain features. Then, a voting classifier ensembled by a support vector machine (SVM), a random forest (RF), and a gradient boosting machine (GBM) was implemented to classify healthy versus sarcopenic participants. Finally, the SHapley Additive exPlanations (SHAP) method was utilized to investigate feature importance during classification.

RESULTS

Seven out of the nine features exhibited statistically significant differences between healthy and sarcopenic participants in both 20% and 50% MVC tests. Using these features, the voting classifier achieved 80% sensitivity and 73% accuracy through a five-fold cross-validation. Such performance was better than each of the SVM, RF, and GBM models alone. Lastly, SHAP results revealed that the wavelength (WL) and the kurtosis of continuous wavelet transform coefficients (CWT_kurtosis) had the highest feature impact scores.

CONCLUSION

This study proposed a method for community-based sarcopenia screening using sEMG signals of forearm muscles. Using a voting classifier with nine representative features, the accuracy exceeds 70% and the sensitivity exceeds 75%, indicating moderate classification performance. Interpretable results obtained from the SHAP model suggest that motor unit (MU) activation mode may be a key factor affecting sarcopenia.

Long-term stimulation by implanted pacemaker enables non-atrophic treatment of bilateral vocal fold paresis in a human-like animal model

A wide variety of treatments have been developed to improve respiratory function and quality of life in patients with bilateral vocal fold paresis (BVFP). One experimental method is the electrical activation of the posterior cricoarytenoid (PCA) muscle with a laryngeal pacemaker (LP) to open the vocal folds. We used an ovine (sheep) model of unilateral VFP to study the long-term effects of functional electrical stimulation on the PCA muscles. The left recurrent laryngeal nerve was cryo-damaged in all animals and an LP was implanted except for the controls. After a reinnervation phase of six months, animals were pooled into groups that received either no treatment, implantation of an LP only, or implantation of an LP and six months of stimulation with different duty cycles. Automated image analysis of fluorescently stained PCA cross-sections was performed to assess relevant muscle characteristics. We observed a fast-to-slow fibre type shift in response to nerve damage and stimulation, but no complete conversion to a slow-twitch-muscle. Fibre size, proportion of hybrid fibres, and intramuscular collagen content were not substantially altered by the stimulation. These results demonstrate that 30 Hz burst stimulation with duty cycles of 40% and 70% did not induce PCA atrophy or fibrosis. Thus, long-term stimulation with an LP is a promising approach for treating BVFP in humans without compromising muscle conditions.

Combined Nutrition with Exercise: Fueling the Fight Against Sarcopenia Through a Bibliometric Analysis and Review

Objective

This bibliometric analysis and review aimed to examine the current research status and trends in the combination of nutrition and exercise training for sarcopenia. Additionally, it sought to provide researchers with future research directions in this field.

Methods

Relevant publications were obtained from the Web of Science Core Collection (WoSCC) database, covering the period from January 1995 to October 2023. The collected publications were analyzed using CiteSpace, VOSviewer, Bibliometrix, and Review Manager.

Results

Out of the 2528 retrieved publications, the United States emerged as the leading contributor in terms of publication volume. The University of Texas System was identified as the most productive institution. Luc J C van Loon emerged as the most published author in this field. Analysis of keywords revealed recent hot topics and emerging areas of interest, such as "gut microbiota" and "mechanisms". Upon further evaluation, resistance training (RT) and protein supplementation were identified as the most commonly employed and effective methods.

Conclusion

RT and protein supplementation are widely recognized as effective strategies. Future research should focus on investigating the molecular aspects of sarcopenia. Moreover, the potential therapeutic role of gut microbiota in sarcopenia requires further comprehensive investigation in human subjects to establish its correlation.

The role of mitochondrial dynamics and mitophagy in skeletal muscle atrophy: from molecular mechanisms to therapeutic insights

Skeletal muscle is the largest metabolic organ of the human body. Maintaining the best quality control and functional integrity of mitochondria is essential for the health of skeletal muscle. However, mitochondrial dysfunction characterized by mitochondrial dynamic imbalance and mitophagy disruption can lead to varying degrees of muscle atrophy, but the underlying mechanism of action is still unclear. Although mitochondrial dynamics and mitophagy are two different mitochondrial quality control mechanisms, a large amount of evidence has indicated that they are interrelated and mutually regulated. The former maintains the balance of the mitochondrial network, eliminates damaged or aged mitochondria, and enables cells to survive normally. The latter degrades damaged or aged mitochondria through the lysosomal pathway, ensuring cellular functional health and metabolic homeostasis. Skeletal muscle atrophy is considered an urgent global health issue. Understanding and gaining knowledge about muscle atrophy caused by mitochondrial dysfunction, particularly focusing on mitochondrial dynamics and mitochondrial autophagy, can greatly contribute to the prevention and treatment of muscle atrophy. In this review, we critically summarize the recent research progress on mitochondrial dynamics and mitophagy in skeletal muscle atrophy, and expound on the intrinsic molecular mechanism of skeletal muscle atrophy caused by mitochondrial dynamics and mitophagy. Importantly, we emphasize the potential of targeting mitochondrial dynamics and mitophagy as therapeutic strategies for the prevention and treatment of muscle atrophy, including pharmacological treatment and exercise therapy, and summarize effective methods for the treatment of skeletal muscle atrophy.

Combination of Parenteral Amino Acid Infusion and Intermittent Loading Exercise Ameliorates Progression of Postoperative Sarcopenia in Rat Model

Postoperative sarcopenia is associated with poor outcomes in hospitalized patients. However, few studies have focused on short-term postoperative sarcopenia. Furthermore, the influence of nutritional management using amino acids (AAs) comprising a peripheral parenteral nutrition (PPN) solution and its combination with exercise (Exc) is unclear. Hence, we established a postoperative sarcopenic rat model to evaluate the effects of parenteral AA infusion combined with Exc on skeletal muscles and investigate the underlying mechanisms involved in the amelioration of muscle atrophy. Male F344 rats underwent surgery followed by hindlimb suspension (HS) for 5 days. The rats were divided into AA (-), AA (+), AA (-)-Exc, and AA (+)-Exc groups. They were continuously administered a PPN solution with or without AA at 98 kcal/kg/day. The Exc groups were subjected to intermittent loading for 1 h per day. Postoperative sarcopenic rats exhibited decreased muscle strength and mass and an upregulated ubiquitin-proteasome system, autophagy-lysosome system, and fast-twitch fiber-related genes, especially in the AA (-) group. The AA (+)-Exc group exhibited attenuated decreased muscle strength, increased gastrocnemius mass, and a suppressed upregulation of muscle atrophy- and fast-twitch fiber-related genes. Therefore, parenteral AA infusion combined with Exc may be effective in preventing postoperative sarcopenia in hospitalized patients.

Machine Learning Prediction of Tongue Pressure in Elderly Patients with Head and Neck Tumor: A Cross-Sectional Study

Background: This investigation sought to cross validate the predictors of tongue pressure recovery in elderly patients' post-treatment for head and neck tumors, leveraging advanced machine learning techniques. Methods: By employing logistic regression, support vector regression, random forest, and extreme gradient boosting, the study analyzed an array of variables including patient demographics, surgery types, dental health status, and age, drawn from comprehensive medical records and direct tongue pressure assessments. Results: Among the models, logistic regression emerged as the most effective, demonstrating an accuracy of 0.630 [95% confidence interval (CI): 0.370-0.778], F1 score of 0.688 [95% confidence interval (CI): 0.435-0.853], precision of 0.611 [95% confidence interval (CI): 0.313-0.801], recall of 0.786 [95% confidence interval (CI): 0.413-0.938] and an area under the receiver operating characteristic curve of 0.626 [95% confidence interval (CI): 0.409-0.806]. This model distinctly highlighted the significance of glossectomy (p = 0.039), the presence of functional teeth (p = 0.043), and the patient's age (p = 0.044) as pivotal factors influencing tongue pressure, setting the threshold for statistical significance at p < 0.05. Conclusions: The analysis underscored the critical role of glossectomy, the presence of functional natural teeth, and age as determinants of tongue pressure in logistics regression, with the presence of natural teeth and the tumor site located in the tongue consistently emerging as the key predictors across all computational models employed in this study.

Astaxanthin Ameliorates Skeletal Muscle Atrophy in Mice With Cancer Cachexia

Astaxanthin (AST) is a natural marine carotenoid with a variety of biological activities. This study aimed to demonstrate the possible mechanisms by which AST improves skeletal muscle atrophy in cancer cachexia. In this study, the effects of different doses of AST (30 mg/kg b.w., 60 mg/kg b.w. and 120 mg/kg b.w.) on skeletal muscle functions were explored in mice with cancer cachexia. The results showed that AST (30, 60 and 120 mg/kg b.w.) could effectively protect cachexia mice from body weight and skeletal muscle loss. AST dose-dependently ameliorated the decrease in myofibres cross-sectional area and increased the expression of myosin heavy chain (MHC). AST treatment decreased both the serum and muscle level of IL-6 but not TNF-α in C26 tumor-bearing cachexia mice. Moreover, AST alleviated skeletal muscle atrophy by decreasing the expression of two muscle-specific E3 ligases MAFBx and MuRF-1. AST improved mitochondrial function by downregulating the levels of muscle Fis1, LC3B and Bax, upregulating the levels of muscle Mfn2 and Bcl-2. In conclusion, our study show that AST might be expected to be a nutritional supplement for cancer cachexia patients.

Pathophysiological changes of muscle after ischemic stroke: a secondary consequence of stroke injury

Sufficient clinical evidence suggests that the damage caused by ischemic stroke to the body occurs not only in the acute phase but also during the recovery period, and that the latter has a greater impact on the long-term prognosis of the patient. However, current stroke studies have typically focused only on lesions in the central nervous system, ignoring secondary damage caused by this disease. Such a phenomenon arises from the slow progress of pathophysiological studies examining the central nervous system. Further, the appropriate therapeutic time window and benefits of thrombolytic therapy are still controversial, leading scholars to explore more pragmatic intervention strategies. As treatment measures targeting limb symptoms can greatly improve a patient's quality of life, they have become a critical intervention strategy. As the most vital component of the limbs, skeletal muscles have become potential points of concern. Despite this, to the best of our knowledge, there are no comprehensive reviews of pathophysiological changes and potential treatments for post-stroke skeletal muscle. The current review seeks to fill a gap in the current understanding of the pathological processes and mechanisms of muscle wasting atrophy, inflammation, neuroregeneration, mitochondrial changes, and nutritional dysregulation in stroke survivors. In addition, the challenges, as well as the optional solutions for individualized rehabilitation programs for stroke patients based on motor function are discussed.

Resistance exercise preconditioning prevents disuse muscle atrophy by inhibiting apoptosis and protein degradation via SESN2 in C57BL/6J mice

AIM

To compare the effects of different exercise preconditioning in the context of skeletal muscle atrophy and to investigate the potential involvement of Sestrin2 (SESN2), a stress-inducible protein that can be regulated by exercise, in exercise preconditioning on preventing disuse muscle atrophy.

METHODS

Eight-week-old male C57BL/6J mice were randomly assigned to sedentary groups (SD), aerobic exercise groups (AE), resistance exercise groups (RE), and combined exercise groups (CE) with or without 7 days of immobilization. The duration of the exercise intervention was 10 weeks. The effects of different exercise preconditioning to prevent muscle atrophy were analyzed by evaluating skeletal muscle function and mass. Additionally, to investigate the potential underlying mechanism of exercise-induced protection of skeletal muscle, wild-type and SESN2--/-- mice were randomly divided into sedentary group and resistance exercise preconditioning group. C2C12 cells were treated with SESN2 adenoviruses and MK2206 (an AKT inhibitor) for 48 h to elucidate the underlined mechanism.

RESULTS

RE was more effective in preserving skeletal muscle function, muscle mass and maintaining skeletal muscle protein homeostasis than AE and CE under immobilized condition. Importantly, exercise performance, muscle mass to body weight ratio, and the cross-sectional area of muscle fibers were significantly lower in SESN2-/- mice than wild-type mice after resistance exercise preconditioning. Mechanistically, the absence of SESN2 led to activation of the ubiquitin-proteasome system and induction of apoptosis. In vitro experiments showed that MK2206 treatment mitigated the regulatory effects of overexpression-SESN2 on protein hydrolysis and apoptosis.

CONCLUSION

RE was more effective than AE or CE in preventing disuse muscle atrophy. SESN2 mediated the protective effects of resistance exercise preconditioning on skeletal muscle atrophy.

Running improves muscle mass by activating autophagic flux and inhibiting ubiquitination degradation in mdx mice

BACKGROUND

Exercise therapy can improve muscle mass, strengthen muscle and cardiorespiratory function, and may be an excellent adjunctive treatment option for Duchenne muscular dystrophy.

METHODS

This article investigates the effects of 10 weeks of treadmill training on skeletal muscle in control and mdx mice. Hematoxylin and eosin (H&E) staining was used to detect the morphometry of skeletal muscle; the grip strength test, suspension test, and rotarod test were used to detect limb muscle strength of mice, and Aurora Scientific Instruments were used to detect in vivo Muscle Stimulation Measuring Maximum Force of pre-fatigue and post-fatigue. The expression levels of myogenic proteins, ubiquitination markers, autophagy pathway proteins, and the proportion of different muscle fiber types were detected.

RESULTS

The experimental results show that running exercise can significantly improve the muscle mass of mdx mice, promote muscle strength, endurance, and anti-fatigue ability, reverse the pathological state of skeletal muscle destruction in mdx mice, and promote muscle regeneration. WB experiments showed that running inhibited the ubiquitination and degradation of muscle protein in mdx mice, inhibited AKT activation, decreased phosphorylated FoxO1 and FoxO3a, and restored the suppressed autophagic flux. Running enhances muscle strength and endurance by comprehensively promoting the expression of Myh1/2/4/7 fast and slow muscle fibers in mdx mice.

CONCLUSIONS

Running can inhibit the degradation of muscle protein in mdx mice, and promote the reuse and accumulation of proteins, thereby slowing down muscle loss. Running improves skeletal muscle mass by activating autophagic flux and inhibiting ubiquitination degradation in mdx mice.

Lower limb suspension induces threshold-specific alterations of motor units properties that are reversed by active recovery

PURPOSE

This study aimed to non-invasively test the hypothesis that (a) short-term lower limb unloading would induce changes in the neural control of force production (based on motor units (MUs) properties) in the vastus lateralis muscle and (b) possible changes are reversed by active recovery (AR).

METHODS

Ten young males underwent 10 days of unilateral lower limb suspension (ULLS) followed by 21 days of AR. During ULLS, participants walked exclusively on crutches with the dominant leg suspended in a slightly flexed position (15°-20°) and with the contralateral foot raised by an elevated shoe. The AR was based on resistance exercise (leg press and leg extension) and executed at 70% of each participant's 1 repetition maximum, 3 times/week. Maximal voluntary isometric contraction (MVC) of knee extensors and MUs properties of the vastus lateralis muscle were measured at baseline, after ULLS, and after AR. MUs were identified using high-density electromyography during trapezoidal isometric contractions at 10%, 25%, and 50% of the current MVC, and individual MUs were tracked across the 3 data collection points.

RESULTS

We identified 1428 unique MUs, and 270 of them (18.9%) were accurately tracked. After ULLS, MVC decreased by 29.77%, MUs absolute recruitment/derecruitment thresholds were reduced at all contraction intensities (with changes between the 2 variables strongly correlated), while discharge rate was reduced at 10% and 25% but not at 50% MVC. Impaired MVC and MUs properties fully recovered to baseline levels after AR. Similar changes were observed in the pool of total as well as tracked MUs.

CONCLUSION

Our novel results demonstrate, non-invasively, that 10 days of ULLS affected neural control predominantly by altering the discharge rate of lower-threshold but not of higher-threshold MUs, suggesting a preferential impact of disuse on motoneurons with a lower depolarization threshold. However, after 21 days of AR, the impaired MUs properties were fully restored to baseline levels, highlighting the plasticity of the components involved in neural control.

Exercise couples mitochondrial function with skeletal muscle fiber type via ROS-mediated epigenetic modification

Skeletal muscle is a heterogeneous tissue composed of different types of muscle fibers, demonstrating substantial plasticity. Physiological or pathological stimuli can induce transitions in muscle fiber types. However, the precise regulatory mechanisms behind these transitions remains unclear. This paper reviews the classification and characteristics of muscle fibers, along with the classical mechanisms of muscle fiber type transitions. Additionally, the role of exercise-induced muscle fiber type transitions in disease intervention is reviewed. Epigenetic pathways mediate cellular adaptations and thus represent potential targets for regulating muscle fiber type transitions. This paper focuses on the mechanisms by which epigenetic modifications couple mitochondrial function and contraction characteristics. Reactive Oxygen Species (ROS) are critical signaling regulators for the health-promoting effects of exercise. Finally, we discuss the role of exercise-induced ROS in regulating epigenetic modifications and the transition of muscle fiber types.

Moderating AKT signaling with baicalein protects against weight loss by preventing muscle atrophy in a cachexia model caused by CT26 colon cancer

Cancer cachexia is a type of energy-wasting syndrome characterized by fatigue, anorexia, muscle weakness, fat loss, and systemic inflammation. Baicalein, a flavonoid with bioactive properties, has demonstrated the ability to mitigate cardiac and skeletal muscle atrophy in different experimental settings. This effect is achieved through the inhibition of muscle proteolysis, suggesting its potential in preserving skeletal muscle homeostasis. In this study, we investigated the anti-cancer cachexia effects of baicalein in the regulation of muscle and fat wasting, both in vivo and in vitro. Baicalein attenuated body weight loss, including skeletal muscle and white adipose tissue (WAT), in CT26-induced cachectic mice. Moreover, baicalein increased muscle fiber thickness and suppressed the muscle-specific ubiquitin-protease system, including F-box only protein 32 and muscle RING-finger protein-1, by activating AKT phosphorylation both in vivo and in vitro. The use of LY294002, a particular inhibitor of AKT, eliminated the observed impact of baicalein on the improvement of muscle atrophy. In conclusion, baicalein inhibits muscle proteolysis and enhances AKT phosphorylation, indicating its potential role in cancer cachexia-associated muscle atrophy.

Mitochondrial involvement in sarcopenia

Sarcopenia lowers the quality-of-life for millions of people across the world, as accelerated loss of skeletal muscle mass and function contributes to both age- and disease-related frailty. Physical activity remains the only proven therapy for sarcopenia to date, but alternatives are much sought after to manage this progressive muscle disorder in individuals who are unable to exercise. Mitochondria have been widely implicated in the etiology of sarcopenia and are increasingly suggested as attractive therapeutic targets to help restore the perturbed balance between protein synthesis and breakdown that underpins skeletal muscle atrophy. Reviewing current literature, we note that mitochondrial bioenergetic changes in sarcopenia are generally interpreted as intrinsic dysfunction that renders muscle cells incapable of making sufficient ATP to fuel protein synthesis. Based on the reported mitochondrial effects of therapeutic interventions, however, we argue that the observed bioenergetic changes may instead reflect an adaptation to pathologically decreased energy expenditure in sarcopenic muscle. Discrimination between these mechanistic possibilities will be crucial for improving the management of sarcopenia.

Deep phenotyping of post-infectious myalgic encephalomyelitis/chronic fatigue syndrome

Post-infectious myalgic encephalomyelitis/chronic fatigue syndrome (PI-ME/CFS) is a disabling disorder, yet the clinical phenotype is poorly defined, the pathophysiology is unknown, and no disease-modifying treatments are available. We used rigorous criteria to recruit PI-ME/CFS participants with matched controls to conduct deep phenotyping. Among the many physical and cognitive complaints, one defining feature of PI-ME/CFS was an alteration of effort preference, rather than physical or central fatigue, due to dysfunction of integrative brain regions potentially associated with central catechol pathway dysregulation, with consequences on autonomic functioning and physical conditioning. Immune profiling suggested chronic antigenic stimulation with increase in naïve and decrease in switched memory B-cells. Alterations in gene expression profiles of peripheral blood mononuclear cells and metabolic pathways were consistent with cellular phenotypic studies and demonstrated differences according to sex. Together these clinical abnormalities and biomarker differences provide unique insight into the underlying pathophysiology of PI-ME/CFS, which may guide future intervention.

Transcriptional programming of translation by BCL6 controls skeletal muscle proteostasis

Skeletal muscle is dynamically controlled by the balance of protein synthesis and degradation. Here we discover an unexpected function for the transcriptional repressor B cell lymphoma 6 (BCL6) in muscle proteostasis and strength in mice. Skeletal muscle-specific Bcl6 ablation in utero or in adult mice results in over 30% decreased muscle mass and force production due to reduced protein synthesis and increased autophagy, while it promotes a shift to a slower myosin heavy chain fibre profile. Ribosome profiling reveals reduced overall translation efficiency in Bcl6-ablated muscles. Mechanistically, tandem chromatin immunoprecipitation, transcriptomic and translational analyses identify direct BCL6 repression of eukaryotic translation initiation factor 4E-binding protein 1 (Eif4ebp1) and activation of insulin-like growth factor 1 (Igf1) and androgen receptor (Ar). Together, these results uncover a bifunctional role for BCL6 in the transcriptional and translational control of muscle proteostasis.

Oral glutamine supplementation relieves muscle loss in immobilized rats, altering p38MAPK and FOXO3a signaling pathways

BACKGROUND

Skeletal muscle synthesizes, stores, and releases body L-glutamine (GLN). Muscle atrophy due to disabling diseases triggers the activation of proteolytic and pro-apoptotic cell signaling, thus impairing the body's capacity to manage GLN content. This situation has a poor therapeutic prognosis.

OBJECTIVE

Evaluating if oral GLN supplementation can attenuate muscle wasting mediated by elevated plasma cortisol and activation of caspase-3, p38MAPK, and FOXO3a signaling pathways in soleus and gastrocnemius muscles of rats submitted to 14-day bilateral hindlimbs immobilization.

METHODS

Animals were randomly distributed into six groups: non-immobilized rats (Control), control orally supplemented with GLN (1 g kg-1) in solution with L-alanine (ALA: 0.61 g kg-1; GLN+ALA), control orally supplemented with dipeptide L-alanyl-L-glutamine (DIP; 1.49 g kg-1), hindlimbs immobilized rats (IMOB), IMOB orally GLN+ALA supplemented (GLN+ALA-IMOB), and IMOB orally DIP supplemented (DIP-IMOB). Plasma and muscle GLN concentration, plasma cortisol level, muscle caspase-3 activity, muscle p38MAPK and FOXO3a protein content (total and phosphorylated forms), and muscle cross-sectional area (CSA) were measured.

RESULTS

Compared to controls, IMOB rats presented: a) increased plasma cortisol levels; b) decreased plasma and muscle GLN concentration; c) increased muscle caspase-3 activity; d) increased total and phosphorylated p38MAPK protein content; e) increased FOXO3a and decreased phosphorylated FOXO3a protein content; f) reduced muscle weight and CSA befitting to atrophy. Oral supplementation with GLN+ALA and DIP was able to significantly attenuate these effects.

CONCLUSIONS

These findings attest that oral GLN supplementation in GLN+ALA solution or DIP forms attenuates rats' skeletal muscle mass wasting caused by disuse-mediated muscle atrophy.

Pathophysiological interactions between sarcopenia and type 2 diabetes: A two-way street influencing diagnosis and therapeutic options

This review will try to elucidate the interconnected pathophysiology of sarcopenia and type 2 diabetes (T2D) and will try to identify a common pathway to explain their development. To this end, the PubMed and Scopus databases were searched for articles published about the underlying pathophysiology, diagnosis and treatment of both sarcopenia and T2D. The medical subject heading (MeSH) terms 'sarcopenia' AND 'diabetes mellitus' AND ('physiopathology' OR 'diagnosis' OR 'therapeutics' OR 'aetiology' OR 'causality') were used. After screening, 32 papers were included. It was evident that sarcopenia and T2D share multiple pathophysiological mechanisms. Common changes in muscle architecture consist of a shift in myocyte composition, increased myosteatosis and a decreased capacity for muscle regeneration. Further, both diseases are linked to an imbalance in myokine and sex hormone production. Chronic low-grade inflammation and increased levels of oxidative stress are also known pathophysiological contributors. In the future, research efforts should be directed towards discovering common checkpoints in the development of T2D and sarcopenia as possible shared therapeutic targets for both diseases. Current treatment for T2D with biguanides, incretins and insulin may already convey a protective effect on the development of sarcopenia. Furthermore, attention should be given to early diagnosis of sarcopenia within the population of people with T2D, given the sizeable physical and medical burden it encompasses. A combination of simple diagnostic techniques could be used at regular diabetes check-ups to identify sarcopenia at an early stage and start lifestyle modifications and treatment as soon as possible.

Marked irregular myofiber shape is a hallmark of human skeletal muscle ageing and is reversed by heavy resistance training

BACKGROUND

Age-related loss of strength is disproportionally greater than the loss of mass, suggesting maladaptations in the neuro-myo-tendinous system. Myofibers are often misshaped in aged and diseased muscle, but systematic analyses of large sample sets are lacking. Our aim was to investigate myofiber shape in relation to age, exercise, myofiber type, species and sex.

METHODS

Vastus lateralis muscle biopsies (n = 265) from 197 males and females, covering an age span of 20-97 years, were examined. The gastrocnemius and soleus muscles of 11 + 22-month-old male C57BL/6 mice were also examined. Immunofluorescence and ATPase stainings of muscle cross-sections were used to measure myofiber cross-sectional area (CSA) and perimeter. From these, a shape factor index (SFI) was calculated in a fibre-type-specific manner (type I/II in humans; type I/IIa/IIx/IIb in mice), with higher values indicating increased deformity. Heavy resistance training (RT) was performed three times per week for 3-4 months by a subgroup (n = 59). Correlation analyses were performed comparing SFI and CSA with age, muscle mass, maximal voluntary contraction (MVC), rate of force development and specific force (MVC/muscle mass).

RESULTS

In human muscle, SFI was positively correlated with age for both type I (R2  = 0.20) and II (R2  = 0.38) myofibers. When subjects were separated into age cohorts, SFI was lower for type I (4%, P < 0.001) and II (6%, P < 0.001) myofibers in young (20-36) compared with old (60-80) and higher for type I (5%, P < 0.05) and II (14%, P < 0.001) myofibers in the oldest old (>80) compared with old. The increased SFI in old muscle was observed in myofibers of all sizes. Within all three age cohorts, type II myofiber SFI was higher than that for type I myofiber (4-13%, P < 0.001), which was also the case in mice muscles (8-9%, P < 0.001). Across age cohorts, there was no difference between males and females in SFI for either type I (P = 0.496/0.734) or II (P = 0.176/0.585) myofibers. Multiple linear regression revealed that SFI, after adjusting for age and myofiber CSA, has independent explanatory power for 8/10 indices of muscle mass and function. RT reduced SFI of type II myofibers in both young and old (3-4%, P < 0.001).

CONCLUSIONS

Here, we identify type I and II myofiber shape in humans as a hallmark of muscle ageing that independently predicts volumetric and functional assessments of muscle health. RT reverts the shape of type II myofibers, suggesting that a lack of myofiber recruitment might lead to myofiber deformity.

Caloric Restriction Rejuvenates Skeletal Muscle Growth in Heart Failure With Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is a major clinical problem, with limited treatments. HFpEF is characterized by a distinct, but poorly understood, skeletal muscle pathology, which could offer an alternative therapeutic target. In a rat model, we identified impaired myonuclear accretion as a mechanism for low myofiber growth in HFpEF following resistance exercise. Acute caloric restriction rescued skeletal muscle pathology in HFpEF, whereas cardiac therapies had no effect. Mechanisms regulating myonuclear accretion were dysregulated in patients with HFpEF. Overall, these findings may have widespread implications in HFpEF, indicating combined dietary with exercise interventions as a beneficial approach to overcome skeletal muscle pathology.

Short-Term Effects of Botulinum Toxin-A Injection on the Medial Gastrocnemius Histological Features in Ambulant Children with Cerebral Palsy: A Longitudinal Pilot Study

Botulinum toxin-A (BoNT-A) injection is known to exert beneficial effects on muscle tone, joint mobility and gait in children with cerebral palsy (CP). However, recent animal and human studies have raised the concern that BoNT-A might be harmful to muscle integrity. In CP-children, the impact of BoNT-A on muscle structure has been poorly studied, and inconsistent results have been reported. This study was aimed at determining the time course effect of a single BoNT-A administration on medial gastrocnemius (MG) morphology in CP-children. MG microbiopsies from 12 ambulant and BoNT-A-naïve CP-children (age, 3.4 (2.3) years, ranging from 2.5 to 7.8 years; seven boys and five girls; GMFCS I = 5, II = 4 and III = 3) were collected before and 3 and 6 months after BoNT-A treatment to analyze the fiber cross-sectional area (fCSA) and proportion; capillarization; and satellite cell (SC) content. Compared with the baseline, the fCSA decreased at 3 months (-14%, NS) and increased at 6 months (+13%, NS). Fiber size variability was significantly higher at 3 months (type I: +56%, p = 0.032; type IIa: +37%, p = 0.032) and 6 months (type I: +69%, p = 0.04; type IIa: +121%, p = 0.032) compared with the baseline. The higher type I proportion seen at 3 months was still present and more pronounced at 6 months (type I: +17%, p = 0.04; type IIx: -65%, p = 0.032). The capillary fiber density was reduced at 3 months (type I: -43%, NS; type II: -44%, p = 0.0320) but normalized at 6 months. There was a non-significant increase in SC/100 fibers at 3 months (+75%, NS) and 6 months (+40%, NS) compared with the baseline. These preliminary data suggest that BoNT-A induced alterations in the MG of children with CP, which were still present 6 months after BoNT-A injection but with signs of muscle recovery.

Leveraging Biomaterial Platforms to Study Aging-Related Neural and Muscular Degeneration

Aging is a complex multifactorial process that results in tissue function impairment across the whole organism. One of the common consequences of this process is the loss of muscle mass and the associated decline in muscle function, known as sarcopenia. Aging also presents with an increased risk of developing other pathological conditions such as neurodegeneration. Muscular and neuronal degeneration cause mobility issues and cognitive impairment, hence having a major impact on the quality of life of the older population. The development of novel therapies that can ameliorate the effects of aging is currently hindered by our limited knowledge of the underlying mechanisms and the use of models that fail to recapitulate the structure and composition of the cell microenvironment. The emergence of bioengineering techniques based on the use of biomimetic materials and biofabrication methods has opened the possibility of generating 3D models of muscular and nervous tissues that better mimic the native extracellular matrix. These platforms are particularly advantageous for drug testing and mechanistic studies. In this review, we discuss the developments made in the creation of 3D models of aging-related neuronal and muscular degeneration and we provide a perspective on the future directions for the field.

The MuSK-BMP pathway maintains myofiber size in slow muscle through regulation of Akt-mTOR signaling

Myofiber size regulation is critical in health, disease, and aging. MuSK (muscle-specific kinase) is a BMP (bone morphogenetic protein) co-receptor that promotes and shapes BMP signaling. MuSK is expressed at all neuromuscular junctions and is also present extrasynaptically in the mouse soleus, whose predominantly oxidative fiber composition is akin to that of human muscle. To investigate the role of the MuSK-BMP pathway in vivo, we generated mice lacking the BMP-binding MuSK Ig3 domain. These ∆Ig3-MuSK mice are viable and fertile with innervation levels comparable to wild type. In 3-month-old mice, myofibers are smaller in the slow soleus, but not in the fast tibialis anterior (TA). Transcriptomic analysis revealed soleus-selective decreases in RNA metabolism and protein synthesis pathways as well as dysregulation of IGF1-Akt-mTOR pathway components. Biochemical analysis showed that Akt-mTOR signaling is reduced in soleus but not TA. We propose that the MuSK-BMP pathway acts extrasynaptically to maintain myofiber size in slow muscle by promoting protein synthetic pathways including IGF1-Akt-mTOR signaling. These results reveal a novel mechanism for regulating myofiber size in slow muscle and introduce the MuSK-BMP pathway as a target for promoting muscle growth and combatting atrophy.

Brothers with Becker muscular dystrophy show discordance in skeletal muscle computed tomography findings: A case report

Becker muscular dystrophy is caused by DMD mutations and is characterized by progressive muscle atrophy. The wide variations observed in muscle atrophy progression in Becker muscular dystrophy are considered multifactorial, including differences in mutations and environmental factors. In this case, two brothers, aged 2 and 3 years, had the identical DMD mutation, confirming their Becker muscular dystrophy diagnosis. They began using handrails when ascending and descending stairs at the age of 16 due to progressive muscular weakness. Over an 18-year follow-up, the older brother consistently had high serum creatine kinase levels, significantly over median levels. Muscle computed tomography finings revealed that the older brother's gluteus maximus and vastus femoris cross-sectional areas were only half and one-third of the younger brother's, respectively. The mean computed tomography values of gluteus maximus and vastus femoris were significantly lower in the older brother. Our report suggests that muscle atrophy in Becker muscular dystrophy cannot be solely explained by dystrophin mutation or environmental factors.

Fiber-type traps: revisiting common misconceptions about skeletal muscle fiber types with application to motor control, biomechanics, physiology, and biology

Skeletal muscle is a highly complex tissue that is studied by scientists from a wide spectrum of disciplines, including motor control, biomechanics, exercise science, physiology, cell biology, genetics, regenerative medicine, orthopedics, and engineering. Although this diversity in perspectives has led to many important discoveries, historically, there has been limited overlap in discussions across fields. This has led to misconceptions and oversimplifications about muscle biology that can create confusion and potentially slow scientific progress across fields. The purpose of this synthesis paper is to bring together research perspectives across multiple muscle fields to identify common assumptions related to muscle fiber type that are points of concern to clarify. These assumptions include 1) classification by myosin isoform and fiber oxidative capacity is equivalent, 2) fiber cross-sectional area (CSA) is a surrogate marker for myosin isoform or oxidative capacity, and 3) muscle force-generating capacity can be inferred from myosin isoform. We address these three fiber-type traps and provide some context for how these misunderstandings can and do impact experimental design, computational modeling, and interpretations of findings, from the perspective of a range of fields. We stress the dangers of generalizing findings about "muscle fiber types" among muscles or across species or sex, and we note the importance for precise use of common terminology across the muscle fields.

Sex differences in skeletal muscle fiber types: A meta-analysis

Biopsies have been acquired from living men and women to determine proportions of Type I (slow-twitch) and II (fast-twitch) skeletal muscle fibers since the 1970s. Sex differences have been assumed but the literature has not been submitted to meta-analysis. Here, the aim was to generate effect sizes of sex differences in muscle fiber cross-sectional areas, distribution percentages, and area percentages. Data from 2875 men and 2452 women, who participated in 110 studies, were analyzed. Myofibrillar adenosine triphosphatase histochemistry was used in 71.8% of studies to classify fibers as Type I, II, IIA, and/or IIX; immunohistochemistry, immunofluorescence, or sodium dodecyl sulfate-polyacrylamide gel electrophoresis were used in 35.4% of studies to similarly classify myosin heavy chain (MHC) isoform content. Most studies involved biopsies from vastus lateralis (79.1%) in healthy individuals (92.7%) between 18 and 59 years old (80.9%). Men exhibited greater cross-sectional areas for all fiber types (g = 0.40-1.68); greater distribution percentages for Type II, MHC II, IIA, IIX fibers (g = 0.26-0.34); greater area percentages for Type II, IIA, MHC IIA, IIX fibers (g = 0.39-0.93); greater Type II/I and Type IIA/I fiber area ratios (g = 0.63, 0.94). Women exhibited greater Type I and MHC I distribution percentages (g = -0.13, -0.44); greater Type I and MHC I area percentages (g = -0.53, -0.69); greater Type I/II fiber area ratios (g = -1.24). These data, which represent the largest repository of comparative muscle fiber type data from living men and women, can inform discussions about biological sex and its impact on pathologies and sports performance (e.g., explaining sex differences in muscle strength and muscle endurance).

Therapeutic applications of ginseng for skeletal muscle-related disorder management

Skeletal muscle (SM) is the largest organ of the body and is largely responsible for the metabolism required to maintain body functions. Furthermore, the maintenance of SM is dependent on the activation of muscle satellite (stem) cells (MSCs) and the subsequent proliferation and fusion of differentiating myoblasts into mature myofibers (myogenesis). Natural compounds are being used as therapeutic options to promote SM regeneration during aging, muscle atrophy, sarcopenia, cachexia, or obesity. In particular, ginseng-derived compounds have been utilized in these contexts, though ginsenoside Rg1 is mostly used for SM mass management. These compounds primarily function by activating the Akt/mTOR signaling pathway, upregulating myogenin and MyoD to induce muscle hypertrophy, downregulating atrophic factors (atrogin1, muscle ring-finger protein-1, myostatin, and mitochondrial reactive oxygen species production), and suppressing the expressions of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in cachexia. Ginsenoside compounds are also used for obesity management, and their anti-obesity effects are attributed to peroxisome proliferator activated receptor gamma (PPARγ) inhibition, AMPK activation, glucose transporter type 4 (GLUT4) translocation, and increased phosphorylations of insulin resistance (IR), insulin receptor substrate-1 (IRS-1), and Akt. This review was undertaken to provide an overview of the use of ginseng-related compounds for the management of SM-related disorders.

The contribution of mitochondria to age-related skeletal muscle wasting: A sex-specific perspective

As people age, their skeletal muscle (SkM) experiences a decline in mitochondrial functionality and density, which leads to decreased energy production and increased generation of reactive oxygen species. This cascade of events, in turn, might determine the loss of SkM mass, strength and quality. Even though the mitochondrial processes dysregulated by aging, such as oxidative phosphorylation, mitophagy, antioxidant defenses and mtDNA transcription, are the same in both sexes, mitochondria age differently in the SkM of men and women. Indeed, the onset and magnitude of the impairment of these processes seem to be influenced by sex-specific factors. Sexual hormones play a pivotal role in the regulation of SkM mass through both genomic and non-genomic mechanisms. However, the precise mechanisms by which these hormones regulate mitochondrial plasticity in SkM are not fully understood. Although the presence of estrogen receptors in mitochondria is recognized, it remains unclear whether androgen receptors affect mitochondrial function. This comprehensive review critically dissects the current knowledge on the interplay of sex in the aging of SkM, focusing on the role of sex hormones and the corresponding signaling pathways in shaping mitochondrial plasticity. Improved knowledge on the sex dimorphism of mitochondrial aging may lead to sex-tailored interventions that target mitochondrial health, which could be effective in slowing or preventing age-related muscle loss.

Seasonal adaptation of Mangalica pigs in terms of muscle morphology and metabolism

The skeletal muscle plays an important role in maintaining body temperature, which is mediated by thermogenesis and glucose or lipid metabolism. Mangalica is a native Hungarian pig that has cold tolerance and can live in grazing environments throughout the year. We evaluated the morphological and genetic aspects of Mangalica using muscle tissues to elucidate the mechanisms underlying the tolerance to seasonal effects in grazing environments. The muscle tissues in each season were analysed using morphological evaluation and electron microscopy. The cross-sectional area of skeletal muscle cells in summer was significantly larger than that in winter. The thickness of myofibrils in summer was significantly higher than in winter. The thickness of the Z-line in winter was significantly higher than in summer. The expression of MYH4 and GLUT4 was significantly lower in winter than in summer. The result of ATPase staining indicated significantly increase the muscle fibre ratio of type 1 in winter than that in summer. These findings indicate that the muscle fibre in Mangalica shifts from fast-twitch to slow-twitch fibre, and the metabolic physiology of the muscle was adapted to the cold environment. This study demonstrates that Mangalica gained tolerance to both seasonal heat and cold stresses that are caused by significant changes in ambient temperature in a year because of changes in their muscle fibre type and metabolic function. This study may contribute to elucidating the mechanism of thermogenetic adaptation in cold and heat environments among mammals.

Lesion level-dependent systemic muscle wasting after spinal cord injury is mediated by glucocorticoid signaling in mice

An incomplete mechanistic understanding of skeletal muscle wasting early after spinal cord injury (SCI) precludes targeted molecular interventions. Here, we demonstrated systemic wasting that also affected innervated nonparalyzed (supralesional) muscles and emerged within 1 week after experimental SCI in mice. Systemic muscle wasting caused muscle weakness, affected fast type 2 myofibers preferentially, and became exacerbated after high (T3) compared with low (T9) thoracic paraplegia, indicating lesion level-dependent ("neurogenic") mechanisms. The wasting of nonparalyzed muscle and its rapid onset and severity beyond what can be explained by disuse implied unknown systemic drivers. Muscle transcriptome and biochemical analysis revealed a glucocorticoid-mediated catabolic signature early after T3 SCI. SCI-induced systemic muscle wasting was mitigated by (i) endogenous glucocorticoid ablation (adrenalectomy) and (ii) pharmacological glucocorticoid receptor (GR) blockade and was (iii) completely prevented after T3 relative to T9 SCI by genetic muscle-specific GR deletion. These results suggest that neurogenic hypercortisolism contributes to a rapid systemic and functionally relevant muscle wasting syndrome early after paraplegic SCI in mice.

From Chronodisruption to Sarcopenia: The Therapeutic Potential of Melatonin

Sarcopenia is an age-related condition that involves a progressive decline in muscle mass and function, leading to increased risk of falls, frailty, and mortality. Although the exact mechanisms are not fully understood, aging-related processes like inflammation, oxidative stress, reduced mitochondrial capacity, and cell apoptosis contribute to this decline. Disruption of the circadian system with age may initiate these pathways in skeletal muscle, preceding the onset of sarcopenia. At present, there is no pharmacological treatment for sarcopenia, only resistance exercise and proper nutrition may delay its onset. Melatonin, derived from tryptophan, emerges as an exceptional candidate for treating sarcopenia due to its chronobiotic, antioxidant, and anti-inflammatory properties. Its impact on mitochondria and organelle, where it is synthesized and crucial in aging skeletal muscle, further highlights its potential. In this review, we discuss the influence of clock genes in muscular aging, with special reference to peripheral clock genes in the skeletal muscle, as well as their relationship with melatonin, which is proposed as a potential therapy against sarcopenia.

Differences in Skeletal Muscle Fiber Characteristics Between Affected and Nonaffected Limbs in Individuals With Stroke: A Scoping Review

OBJECTIVE

The objective of this scoping review was to characterize and identify knowledge gaps about the changes in skeletal muscle fiber type proportion and cross-sectional area (CSA) after stroke.

METHODS

This scoping review followed previously proposed frameworks. A systematic search was conducted for articles examining muscle fiber type proportion and CSA in individuals with stroke in EMBASE, MEDLINE, PsycINFO, CINAHL, SPORTDiscus, and Web of Science databases from inception to December 20, 2022. Two independent authors screened and extracted the data. Results were discussed using theories proposed by the authors of the included studies.

RESULTS

Of 13 studies (115 participants), 6 (46%) were case studies or case series, 6 (46%) were cross-sectional studies, and 1 (8%) was an experimental study. Studies had small sample sizes (1-23 participants) and various muscle sampling sites (6 different muscles). All 13 studies examined muscle fiber type distributions, and 6 (46%) examined CSA. Ten (77%) studies examined differences between paretic and nonparetic muscles, and 5 (38%) compared people with stroke to people without stroke. Results from 9 of 13 studies (69%) supported a greater proportion of type II muscle fibers in the paretic limb. Of those, 4 studies (42 participants), 3 studies (17 participants), and 1 study (1 participant) saw no differences, preferential type II and type I CSA loss between limbs, respectively.

CONCLUSION

Of the limited available evidence, stroke appears to result in a shift to a higher proportion of type II muscle fibers in the paretic muscles. There are mixed results for effects on muscle fiber CSA, but there is some evidence of specific atrophy of type II muscle fibers.

IMPACT

Changes in paretic skeletal muscle fibers of individuals with stroke may explain, in part, the substantial losses in strength and power in this population. Interventions to restore type II muscle fiber size may benefit people with stroke.

Ubiquitin-proteasome pathway in skeletal muscle atrophy

Skeletal muscles underpin myriad human activities, maintaining an intricate balance between protein synthesis and degradation crucial to muscle mass preservation. Historically, disruptions in this balance-where degradation overshadows synthesis-have marked the onset of muscle atrophy, a condition diminishing life quality and, in grave instances, imperiling life itself. While multiple protein degradation pathways exist-including the autophagy-lysosome, calcium-dependent calpain, and cysteine aspartate protease systems-the ubiquitin-proteasome pathway emerges as an especially cardinal avenue for intracellular protein degradation, wielding pronounced influence over the muscle atrophy trajectory. This paper ventures a panoramic view of predominant muscle atrophy types, accentuating the ubiquitin-proteasome pathway's role therein. Furthermore, by drawing from recent scholarly advancements, we draw associations between the ubiquitin-proteasome pathway and specific pathological conditions linked to muscle atrophy. Our exploration seeks to shed light on the ubiquitin-proteasome pathway's significance in skeletal muscle dynamics, aiming to pave the way for innovative therapeutic strategies against muscle atrophy and affiliated muscle disorders.

Mass Spectrometry-Based Proteomic Technology and Its Application to Study Skeletal Muscle Cell Biology

Voluntary striated muscles are characterized by a highly complex and dynamic proteome that efficiently adapts to changed physiological demands or alters considerably during pathophysiological dysfunction. The skeletal muscle proteome has been extensively studied in relation to myogenesis, fiber type specification, muscle transitions, the effects of physical exercise, disuse atrophy, neuromuscular disorders, muscle co-morbidities and sarcopenia of old age. Since muscle tissue accounts for approximately 40% of body mass in humans, alterations in the skeletal muscle proteome have considerable influence on whole-body physiology. This review outlines the main bioanalytical avenues taken in the proteomic characterization of skeletal muscle tissues, including top-down proteomics focusing on the characterization of intact proteoforms and their post-translational modifications, bottom-up proteomics, which is a peptide-centric method concerned with the large-scale detection of proteins in complex mixtures, and subproteomics that examines the protein composition of distinct subcellular fractions. Mass spectrometric studies over the last two decades have decisively improved our general cell biological understanding of protein diversity and the heterogeneous composition of individual myofibers in skeletal muscles. This detailed proteomic knowledge can now be integrated with findings from other omics-type methodologies to establish a systems biological view of skeletal muscle function.