Exercise metabolism and the molecular regulation of skeletal muscle adaptation

Is lean mass quantity or quality the determinant of maximal fat oxidation capacity? The potential mediating role of cardiorespiratory fitness

BACKGROUND

Impaired fat oxidation is linked to cardiometabolic risk. Maximal fat oxidation rate (MFO) reflects metabolic flexibility and is influenced by lean mass, muscle strength, muscle quality - defined as the ratio of strength to mass - and cardiorespiratory fitness. The relationship between these factors and fat oxidation is not fully understood. The aim is to analyze the associations of lean-mass, muscle strength and quality with fat oxidation parameters in young adults, considering the mediating role of VO2max.

METHODS

A cross-sectional observational study. Eighty-one adults (50 males, 31 females; age 22.8 ± 4.4, BMI 25.70 ± 5.75, lean-mass 54.19 ± 8.78, fat-mass 18.66 ± 11.32) Body composition assessment by bioimpedance determine fat and lean-mass. Indirect calorimetry at rest and exercise was used for the calculation of fat oxidation. An incremental exercise protocol in a cycle ergometer with two consecutive phases was performed. The first to determine MFO consisted of 3 min steps of 15W increments with a cadence of 60rpm. The test was stopped when RQ ≥ 1. After 5 min rest, a phase to detect VO2max began with steps of 15W/min until exhaustion. Muscular strength was assessed by handgrip dynamometry and the standing longitudinal jump test. A strength cluster was calculated with handgrip and long jump adjusted by sex and age. Data were analyzed using multiple linear regression and mediation analyses.

RESULTS

Total lean-mass and leg lean-mass were not associated with MFO. Long jump, relativized by lean-mass and by leg lean-mass have a standardized indirect effect on MFO of 0.50, CI: 0.32-0.70, on MFO/lean-mass 0.43, CI:0.27-0.60 and MFO/leg lean-mass 0.44, CI: 0.30-0.06, which VO2max mediated, VO2max/lean-mass and VO2max/leg lean-mass, respectively (all p < 0.01). The handgrip/arm lean-mass had an indirect effect of 0.25 (CI: 0.12-0.38) on MFO/leg lean-mass, with VO2max/leg lean-mass as the mediator (p < 0.01). The Cluster/lean-mass and Cluster/Extremities lean-mass have a standardized indirect effect on MFO/lean-mass (0.34, CI: 0.20-0.48) and MFO/leg lean-mass (0.44, CI: 0.28-0.60), mediated by VO2max/lean-mass and VO2max/leg lean-mass (p < 0.01).

CONCLUSIONS

Muscular strength and quality have an indirect effect on MFO mediated by VO2max. These findings suggest the importance of muscle quality on MFO.

Mediation role of telomere length in the relationship between physical activity and PhenoAge: A population-based study

Background

The relationship between physical activity (PA), telomere length, and phenotypic age (PhenoAge) represents a pivotal area of investigation in aging research.

Methods

The study encompassed a cohort of 6200 participants aged 20 years and above, sourced from the National Health and Nutrition Examination Survey (NHANES). Physical activity (PA) levels were assessed employing the Global Physical Activity Questionnaire, while DNA samples were collected to determine telomere length, measured in base pairs. PhenoAge, an emerging aging index relying on nine distinct chemical biomarkers, was computed.

Results

Incorporating a fully adjusted model, our analysis showed significant correlations between PA engagement and PhenoAge [Low PA, β (95 % CI): 0.039(-0.071,-0.008), p = 0.021; Moderate PA, β (95 % CI): 0.058(-0.082,-0.034), p < 0.001; High PA, β (95 % CI): 0.069(-0.096,-0.042), p < 0.001]. Furthermore, a positive link emerged between elevated PA levels and telomere length, with a β (95 % CI) of 0.011(0.001, 0.022), p = 0.034. A mediation analysis was performed, demonstrating that telomere length mediated the connection between PA and PhenoAge, with a proportion mediated calculated at 3.57 %.

Conclusions

Our findings suggest that PA may play a key role in mitigating aging processes by preserving telomere length, highlighting the potential of PA as a target for interventions aimed at promoting healthy aging and longevity.

SESN2 mediates resistance training-induced improvements in exercise performance and energy metabolism in C57BL/6J mice

Long-term resistance training promotes skeletal muscle hypertrophy and boosts energy metabolism. The stress-inducible protein, SESN2 is a mediator of aerobic training benefits. However, whether SESN2 mediates resistance training to promote skeletal muscle hypertrophy and energy metabolism remains elusive. In this study, eight-week-old C57BL/6J male wild-type (WT) and SESN2-/- mice were subjected to resistance training intervention for 12 weeks. Our results revealed that SESN2 deficiency weakened the effects of resistance training on the increase of grip strength, maximum load capacity, time to exhaustion, and grid suspension time. SESN2 promoted skeletal muscle hypertrophy by inhibiting protein degradation in response to resistance training. Moreover, SESN2 ablation blocked the resistance training-induced improvements in oxygen consumption, carbon dioxide production and energy expenditure. Glycolysis and tricarboxylic acid cycle in skeletal muscle of SESN2-/- mice remain unchanged after resistance training. Furthermore, SESN2 deletion did not alter the expression of key metabolic enzymes in glycolysis and tricarboxylic acid cycle in both atrophied skeletal muscle and resistance exercise preconditioned muscle. These results imply that the SESN2 is a crucial regulator in facilitating the beneficial effects of resistance training on exercise performance, skeletal muscle mass and energy metabolism. This study contributes to the understanding of the mechanisms by which resistance training promotes skeletal muscle energy metabolism.

Protein Nutrition for Endurance Athletes: A Metabolic Focus on Promoting Recovery and Training Adaptation

The purpose of this narrative review is to provide an evidence-based update on the protein needs of endurance athletes with a focus on high-quality metabolic studies conducted on the topics of recovery and training adaptation over the past decade. We use the term 'protein needs' to delineate between the concepts of a daily protein requirement and per meal protein recommendations when devising scientific evidence-based protein guidelines for the endurance athlete to promote post-exercise recovery, enhance the adaptive response to endurance training and improve endurance performance. A habitual protein intake of 1.5 g/kg of body mass (BM)-1·day-1 is typical in male and female endurance athletes. Based on findings from a series of contemporary protein requirement studies, the evidence suggests a daily protein intake of ~ 1.8 g·kgBM-1·day-1 should be advocated for endurance athletes, with the caveat that the protein requirement may be further elevated in excess of 2.0 g·kgBM-1·day-1 during periods of carbohydrate-restricted training and on rest days. Regarding protein recommendations, the current lack of metabolic studies that determine the dose response of muscle protein synthesis to protein ingestion in relation to endurance exercise makes it difficult to present definitive guidelines on optimal per meal protein intakes for endurance athletes. Moreover, there remains no compelling evidence that co-ingesting protein with carbohydrate before or during endurance exercise confers any performance advantage, nor facilitates the resynthesis of liver or muscle glycogen stores during recovery, at least when carbohydrate recommendations are met. However, recent evidence suggests a role for protein nutrition in optimising the adaptive metabolic response to endurance training under conditions of low carbohydrate and/or energy availability that represent increasingly popular periodised strategies for endurance athletes.

Educational strategies for teaching metabolic profiles across three endurance training zones

This article explores an innovative educational approach using a metabolic board designed to enhance understanding of muscle metabolism across three endurance training zones: Z1 (light intensity), Z2 (moderate intensity), and Z3 (intense/severe intensity). The aerobic threshold marks the transition from light to moderate domains and the anaerobic threshold separates moderate from intense domains, with both thresholds adapting to training. Exercises within each training zone elicit specific adaptive responses through distinct signaling pathways, but the metabolic profile induced remains relatively constant across these intensity domains. The assembly of the metabolic board is guided by interpretative questions derived from recent incremental exercise studies. By interacting with the board, students gain clear insights into the rationale for choosing between continuous and interval exercises. This interactive tool simplifies complex physiological processes into understandable components, clarifying the relationships among motor unit types and their metabolism and principal energy sources at each intensity level. By assembling the board, students demystify muscle metabolism as a continuum of responses crucial for sustaining various exercise intensities. This integration of theoretical knowledge with practical application empowers students and professionals to make informed decisions about training prescriptions, a critical element of training periodization.NEW & NOTEWORTHY Our pedagogical tool offers a unique and enriching learning experience. By active construction of a metabolic board using real data, focused on a predominance of a specific muscle fiber type and its metabolic characteristics across three ranges of exercise intensity domains, the tool promotes deep learning for sports science professionals.

Targeting intramyocellular lipids to improve aging muscle function

Decline of skeletal muscle function in old age is a significant contributor to reduced quality of life, risk of injury, comorbidity and disability and even mortality. While this loss of muscle function has traditionally been attributed to sarcopenia (loss of muscle mass), it is now generally appreciated that factors other than mass play a significant role in age-related muscle weakness. One such factor gaining increased attention is the ectopic accumulation of lipids in skeletal muscle, in particular, intramyocellular lipids (IMCLs). It has been appreciated for some time that metabolic flexibility of several tissues/organs declines with age and may be related to accumulation of IMCLs in a "vicious cycle" whereby blunted metabolic flexibility promotes accumulation of IMCLs, which leases to lipotoxicity, which can then further impair metabolic flexibility. The standard interventions for addressing lipid accumulation and muscle weakness remain diet (caloric restriction) and exercise. However, long-term compliance with both interventions in older adults is low, and in the case of caloric restriction, may be inappropriate for many older adults. Accordingly, it is important, from a public health standpoint, to pursue potential pharmacological strategies for improving muscle function. Because of the success of incretin-analog drugs in addressing obesity, these medications may potentially reduce IMCLs in aging muscles and thus improve metabolic flexibility and improve muscle health. A contrasting potential pharmacological strategy for addressing these issues might be to enhance energy provision to stimulate metabolism by increasing NAD + availability, which is known to decline with age and has been linked to reduced metabolic flexibility. In this narrative review, we present information related to IMCL accumulation and metabolic flexibility in old age and how the two major lifestyle interventions, caloric restriction and exercise, can affect these factors. Finally, we discuss the potential benefits and risks of select pharmacologic interventions in older adults.

Skeletal Muscle as a Mediator of Interorgan Crosstalk During Exercise: Implications for Aging and Obesity

Physical exercise is critical for preventing and managing chronic conditions, such as cardiovascular disease, type 2 diabetes, hypertension, and sarcopenia. Regular physical activity significantly reduces cardiovascular and all-cause mortality. Exercise also enhances metabolic health by promoting muscle growth, mitochondrial biogenesis, and improved nutrient storage while preventing age-related muscle dysfunction. Key metabolic benefits include increased glucose uptake, enhanced fat oxidation, and the release of exercise-induced molecules called myokines, which mediate interorgan communication and improve overall metabolic function. These myokines and other exercise-induced signaling molecules hold promise as therapeutic targets for aging and obesity-related conditions.

Resistance Exercise as a Safe Modality for Quality of Life Improvement in Patients with Coronary Artery Diseases: A Review

Individuals with cardiovascular diseases (CVD) tend to have decreasing cardiorespiratory fitness (CRF), muscle strength, and quality of life (QoL). Because of its multiple benefits, participation in an exercise-based cardiac rehabilitation (CR) program was highly recommended for CVD patients. Currently, there is a trend of increasing the use of resistance exercises (RE) in CR and treatment of CVD, including coronary artery disease (CAD), peripheral arterial disease, and stroke. The application of RE in CVD patients also raises concerns for physicians due to adverse events related to cardiovascular responses. Therefore, this review aimed to explore the effect of RE on cardiovascular responses, cardiovascular risk factors, muscle strength, CRF, and the QoL, including its safety in CAD patients. Articles published in the last ten years were searched using PubMed, Science Direct, Research Gate, and Google Scholar databases using relevant keywords. Studies found that the administration of RE in CAD patients was proven safe when prescribed properly. Some literature showed that RE affected CVD risk factors by improving blood pressure, blood sugar, lipid profile, and body composition. In addition, systemic vascular resistance change led to vasodilatation and reduced blood pressure. Fatal and non-fatal myocardial infarction and mortality also decreased after progressive RE. High-intensity RE was proven to be better at increasing muscle strength compared to low-intensity because it produced a greater increase in the number of myofibrils and neural adaptation. Subsequently, aerobic exercise (AE) combined with RE caused a better increase in CRF. An increase in muscle strength and CRF, as well as diminished symptoms and controlled risk factors obtained from RE administration, increased QoL. To conclude, RE was a safe modality for QoL improvement in CAD patients through controlling risk factors and improving muscle strength and CRF.

Integrated miRNA-mRNA Profiling of C2C12 Myoblasts Indicates Regulatory Interactions Involved in Proliferation and Differentiation

Myogenesis is a complex biological process regulated by multiple factors. This study systematically revealed the dynamic changes of gene expression and its regulatory network in C2C12 myoblasts during proliferation and differentiation stages by integrating transcriptome and miRNA-omics data. The analysis results showed that in the early stage of proliferation, gene expression showed significant fluctuations, and key cell cycle and DNA replication-related genes were closely associated with specific miRNAs (miR-486a-5p, miR-486b-5p, and miR-351-5p), suggesting that these miRNAs play an important role in regulating cell proliferation. In the differentiation stage, the activation of key myogenic transcription factors and signaling pathways, such as MAPK and PI3K-Akt, synergizes with miRNA regulation to promote the myogenic program. In addition, we found that genes such as IGF1 and Dio2 were continuously upregulated during differentiation, and IGF1 might be regulated by multiple miRNAs during this process. This study provides key molecular insights for a deeper understanding of muscle development and regeneration.

Molecular mechanisms of UCP1-independent thermogenesis: the role of futile cycles in energy dissipation

Adipose tissue thermogenesis has emerged as a prominent research focus for the treatment of metabolic diseases, particularly through mitochondrial uncoupling, which oxidizes nutrients to produce heat rather than synthesizing ATP. Uncoupling protein 1 (UCP1) has garnered significant attention as a core protein mediating non-shivering thermogenesis(NST). However, recent studies indicate that energy dissipation can also occur via UCP1-independent thermogenesis, partially driven by futile metabolic cycles. These cycles involve ATP depletion coupled with reversible energy reactions, resulting in futile energy expenditure. Unlike classical UCP1-mediated thermogenesis, futile cycling is not confined to brown and beige adipose tissue, suggesting a broader range of therapeutic targets. These findings open new avenues for targeting these pathways to enhance metabolic health. This review explores the characteristics and distinctions of the primary metabolic organs (adipose tissue, liver, and skeletal muscle) involved in the futile cycles of thermogenesis. It further elaborates on the cellular and molecular mechanisms underlying calcium, creatine, and lipid cycling, emphasizing their strengths, limitations, and roles beyond thermogenesis.

The effect of paraspinal muscle morphology on the development of osteoporotic lumbar vertebral fractures

BackgroundVertebral compression fractures associated with osteoporosis reduce daily living activities. The primary risk factor for osteoporotic vertebral fractures (OVCFs) is the severity of osteoporosis, defined as low bone mineral density (BMD) in both peripheral and central regions. In addition to BMD, sarcopenia is also thought to affect OVCFs by reducing paraspinal muscle mass and strength.ObjectiveWe aimed to evaluate the association between vertebral compression fractures and paraspinal/psoas muscle characteristics, including muscle mass and fatty degeneration, using quantitative MRI measurements.MethodsWe retrospectively enrolled 77 patients aged ≥60 years who were diagnosed with acute OVCF between January 2019 and August 2023. The control group consisted of age- and sex-matched patients with osteoporosis (BMD > -2.5) who were followed up without fractures for at least six months. Demographic characteristics, relative total cross-sectional area (rTCSA) and relative functional CSA (rFCSA) of the multifidus (MF), erector spinae (ES), and psoas major (PS) were measured at the L4-5 and L5-S levels on MRI.ResultsThe TCSA and rTCSA of the multifidus (MF) and erector spinae (ES) muscles at both the L4-5 and L5-S1 levels did not show significant differences between the control and OVCF groups. (all p value > 0.05) The mean FCSAL4-5 of the MF 8.97 ± 2.81, ES 16.73 ± 6.49, the mean FCSAL5-1 of the MF 9.43 ± 3.27, ES 10.76 ± 5.79 in the fracture group, while the mean FCSAL4-5 of the MF 11.39 ± 2.6, ES 19.35 ± 4.04, the mean FCSAL5-1 of the MF 13.42 ± 2.56, ES 14.11 ± 4.6 in the non-fracture group. (PMFL4-5 < 0.001, PMFL5-1 < 0.001, PESL4-5 = 0.003, PESL5-1 < 0.001) The mean TCSA of the psoas muscle was significantly higher in the fracture group (17.65 ± 6.21) than in the control group (15.9 ± 4.14) (p = 0.042). Despite the significantly larger total psoas muscle mass in the fracture group, the rFCSA of the psoas muscle was lower in the fracture group (0.81 ± 0.27) compared to the control group (0.89 ± 0.25) (p = 0.046).ConclusionsThe study shows that the functional muscle mass of the paraspinal muscles is significantly lower in patients with osteoporotic vertebral compression fractures (OVCF) as compared to those without fractures. Quantitative measurement of the functional capacity of the paraspinal muscles using MRI can effectively predict the risk of OVCF and enable early intervention and adopt preventive measures to reduce the incidence of these fractures.

Identification of a resistance-exercise-specific signalling pathway that drives skeletal muscle growth

Endurance and resistance exercise lead to distinct functional adaptations: the former increases aerobic capacity and the latter increases muscle mass. However, the signalling pathways that drive these adaptations are not well understood. Here we identify phosphorylation events that are differentially regulated by endurance and resistance exercise. Using a model of unilateral exercise in male participants and deep phosphoproteomic analyses, we find that a prolonged activation of a signalling pathway involving MKK3b/6, p38, MK2 and mTORC1 occurs specifically in response to resistance exercise. Follow-up studies in both male and female participants reveal that the resistance-exercise-induced activation of MKK3b is highly correlated with the induction of protein synthesis (R = 0.87). Additionally, we show that in mice, genetic activation of MKK3b is sufficient to induce signalling through p38, MK2 and mTORC1, along with an increase in protein synthesis and muscle fibre size. Overall, we identify core components of a signalling pathway that drives the growth-promoting effects of resistance exercise.

Gut microbiome and blood biomarkers reveal differential responses to aerobic and anaerobic exercise in collegiate men of diverse training backgrounds

The gut microbiome influences physiological responses to exercise by modulating inflammatory markers and metabolite production. Athletes typically exhibit greater microbial diversity, which may be associated with improved performance, but the mechanisms linking different exercise modalities to the gut microbiome are not fully understood. In this study, blood and stool samples were collected from endurance athletes, strength athletes, and non-athletic controls performing two maximal exercise tests (the anaerobic Wingate test and the aerobic Bruce Treadmill Test) to integrate serum biomarker data with gut bacterial metagenomic profiles. While most biochemical markers showed similar post-exercise trends across groups, SPARC (secreted protein acidic and rich in cysteine) and adiponectin levels showed modality-specific responses. Strength-trained participants showed unique microbiome-biomarker associations after the Wingate test. In addition, baseline enrichment of certain bacterial taxa, including Clostridium phoceensis and Catenibacterium spp., correlated with reduced Bruce Treadmill test response in strength-trained individuals. These findings, while requiring further validation, indicate the complex interplay between exercise type, training background, and the gut microbiome, and suggest that specific microbial species may help shape recovery and adaptation.

Viral agents in neuromuscular pathology

In recent years, viral infections have been increasingly identified as major players in neuromuscular pathologies. This chapter presents an overview of the evidence and future directions for virus-induced neuromuscular disorders. Information is integrated on the global burden of these diseases related to epidemiology, clinical features, diagnosis, treatment, and preventive strategies was integrated. Responsible viruses include enteroviruses, flaviviruses, herpesviruses, and emerging pathogens such as SARS-CoV-2. It represents a broad spectrum of neuromuscular disorders, including Guillain-Barré syndrome, viral myositis, and critical illness neuropathy/myopathy. The book chapter discusses different diagnostic approaches, therapy strategies, and rehabilitation methods, in addition to early intervention and preventive measures. This has led to new insights into novel therapies, unmet research needs, and future perspectives on viral neuromuscular disorders. This chapter demonstrates that supporting both clinical care and patient management with clinical research entails a profound understanding of the difficult interactions between the viruses concerned and the neuromuscular system.

Reevaluating the energy cost in locomotion: quadrupedal vs. bipedal walking in humans

This study examines the energy expenditure and physiological responses associated with short-term quadrupedal locomotion compared to bipedal walking in humans. It aims to support evolutionary theory and explore quadrupedal locomotion's potential for enhancing fitness and health. In a randomized crossover design, 12 participants performed quadrupedal and bipedal walking on a treadmill at identical speeds. Physiological responses, including energy expenditure, carbohydrate oxidation rates, respiratory rate, and heart rate, were measured during both forms of locomotion. Quadrupedal walking significantly increased total energy expenditure by 4.15 Kcal/min [95% CI, 3.11 - 5.19 Kcal/min], due to a rise in carbohydrate oxidation of 1.70 g/min [95% CI, 1.02 - 2.24 g/min]. It also increased respiratory and heart rates, indicating higher metabolic demands. The exercise mainly activated upper limb muscles and the gluteus maximus in the lower limbs. Ten minutes of quadrupedal walking at the same speed as bipedal walking resulted in a 254.48% increase in energy consumption. This simple form of locomotion offers a strategy for enhancing physical activity, and supports the idea that energy optimization influenced the evolution of efficient bipedal locomotion.

Physical training reduces cell senescence and associated insulin resistance in skeletal muscle

BACKGROUND

Cell senescence (CS) is a key aging process that leads to irreversible cell cycle arrest and an altered secretory phenotype. In skeletal muscle (SkM), the accumulation of senescent cells contributes to sarcopenia. Despite exercise being a known intervention for maintaining SkM function and metabolic health, its effects on CS remain poorly understood.

OBJECTIVES

This study aimed to investigate the impact of exercise on CS in human SkM by analyzing muscle biopsies from young, normal-weight individuals and middle-aged individuals with obesity, both before and after exercise intervention.

METHODS

Muscle biopsies were collected from both groups before and after an exercise intervention. CS markers, insulin sensitivity (measured with euglycemic clamp), and satellite cell markers were analyzed. Additionally, in vitro experiments were conducted to evaluate the effects of cellular senescence on human satellite cells, focusing on key regulatory genes and insulin signaling.

RESULTS

Individuals with obesity showed significantly elevated CS markers, along with reduced expression of GLUT4 and PAX7, indicating impaired insulin action and regenerative potential. Exercise improved insulin sensitivity, reduced CS markers, and activated satellite cell response in both groups. In vitro experiments revealed that senescence downregulated key regulatory genes in satellite cells and impaired insulin signaling by reducing the Insulin Receptor β-subunit.

CONCLUSIONS

These findings highlight the role of CS in regulating insulin sensitivity in SkM and underscore the therapeutic potential of exercise in mitigating age- and obesity-related muscle dysfunction. Targeting CS through exercise or senolytic agents could offer a promising strategy for improving metabolic health and combating sarcopenia, particularly in at-risk populations.

Evaluation of the toxicity potential of exercise and atorvastatin/metformin combination therapy on STZ-diabetic rats

Exercise is recommended for individuals with diabetes, and metformin and atorvastatin are commonly prescribed to diabetic patients. However, these two drugs have potential effects that may lead to toxicity in the skeletal muscle system. Therefore, the effects and potential interactions of combining these two drugs on skeletal muscle performance and structure were investigated in vivo in an experimental diabetes model. Male Wistar rats were divided into six groups: a sedentary control group (N) and five treatment groups-exercise (C), diabetes (D), diabetes with metformin (MET), diabetes with atorvastatin (ATO), and diabetes with metformin and atorvastatin (MET + ATO). In the diabetes model experimentally created with streptozotocin (STZ; 45 mg/kg, i.p.) and metformin (300 mg/kg/day), atorvastatin (10 mg/kg/day) was administered to drug groups by gavage during the 4-week study period. The rats were allowed to run (at moderate level) for 30 min, 5 days a week, on the treadmill. At the end of the study, blood samples and gastrocnemius muscle tissues of the rats were obtained under ketamine anesthesia (100 mg/kg; i.p). The effects of combining exercise and medication on skeletal muscle were assessed by examining the levels of significant biomarkers including PGC-1α, UCP-3, and MyHCs, as well as analyzing oxidative stress/antioxidant capacity parameters in muscle tissue samples. Additionally, relevant biochemical indicators were determined in serum samples. The quantity and morphology of mitochondria in muscle tissue were assessed using transmission electron microscopy. It was observed in the study that some toxic effects associated with the use of drugs alone were reduced by combination therapy. It is thought that this study will contribute to the literature in the evaluation of the effects of drugs and their combined use in Type 1 diabetes under exercise conditions.

Skeletal muscle-specific Bambi deletion induces hypertrophy and oxidative switching coupling with adipocyte thermogenesis against metabolic disorders

Skeletal muscle plays a significant role in both local and systemic energy metabolism. The current investigation aims to explore the role of the Bambi gene in skeletal muscle, focusing on its implications for muscle hypertrophy and systemic metabolism. We hypothesize that skeletal muscle-specific deletion of Bambi induces muscle hypertrophy, improves metabolic performance, and activates thermogenic adipocytes via the reprogramming of progenitor of iWAT, offering potential therapeutic strategies for metabolic syndromes. Leveraging the Chromatin immunoprecipitation (ChIP)-seq and bioinformatics analysis, Bambi gene is shown to be a direct target of HIF2α, which is further confirmed by ChIP-qPCR and promoter luciferase assay. Skeletal muscle-specific Bambi deletion led to significant muscle hypertrophy and improved metabolic parameters, even under high-fat diet conditions. This deletion induced metabolic reprogramming of stromal vascular fractions (SVFs) into thermogenic adipocytes, contributing to systemic metabolic improvements, potentially through the secretory factor. Notably, mice with skeletal muscle-specific Bambi deletion demonstrate resistance to high-fat diet-induced metabolic disorders, highlighting a potential therapeutic pathway for metabolic syndrome management. Thus, skeletal muscle-specific deletion of Bambi triggers muscle growth, enhances metabolic performance, and activates thermogenic adipocytes. These findings suggest Bambi as a novel therapeutic target for metabolic syndromes, providing new insights into the interaction between muscle hypertrophy and systemic metabolic improvement. The study underscores the potential of manipulating muscle physiology to regulate whole-body metabolism, offering a novel perspective on treating metabolic disorders.

Fiber Type-Specific Adaptations to Exercise Training in Human Skeletal Muscle: Lessons From Proteome Analyses and Future Directions

Skeletal muscle is a key determinant of sports performance. It is a highly specialized, yet complex and heterogeneous tissue, comprising multiple cell types. Muscle fibers are the main functional cell type responsible for converting energy into mechanical work. They exhibit a remarkable ability to adapt in response to stressors, such as exercise training. But while it is recognized that human skeletal muscle fibers have distinct contractile and metabolic features, classified as slow/oxidative (type 1) or fast/glycolytic (type 2a/x), less attention has been directed to the adaptability of the different fiber types. Methodological advancements in mass spectrometry-based proteomics allow researchers to quantify thousands of proteins with only a small amount of muscle tissue-even in a single muscle fiber. By exploiting this technology, studies are emerging highlighting that muscle fiber subpopulations adapt differently to exercise training. This review provides a contemporary perspective on the fiber type-specific adaptability to exercise training in humans. A key aim of our review is to facilitate further advancements within exercise physiology by harnessing mass spectrometry proteomics.

Constitutively active mTORC1 signaling modifies the skeletal muscle metabolome and lipidome response to exercise

A chronic increase in the Mammalian Target of Rapamycin Complex 1 (mTORC1) signaling is implicated in reduced longevity, altered metabolism, and mitochondrial dysfunction. Abnormal mTORC1 signaling may also be involved in the etiology of sarcopenia. To better understand the role of mTORC1 signaling in the regulation of muscle metabolism, we developed an inducible muscle-specific knockout model of DEP domain-containing 5 protein (DEPDC5 mKO), which results in constitutively active mTORC1 signaling. We hypothesized that constitutively active mTORC1 signaling in skeletal muscle would alter the metabolomic and lipidomic response to an acute bout of exercise. Wild-type (WT) and DEPDC5 muscle-specific knockout (KO) mice were studied at rest and following a 1 h bout of treadmill exercise. Acute exercise induced an increased reliance on glycolytic and pentose phosphate pathway (PPP) metabolites in the muscle of mice with hyperactive mTORC1. Lipidomic analysis showed an increase in triglycerides (TGs) in KO mice. Although exercise had a pronounced effect on muscle metabolism, the genotype effect was larger, indicating that constitutively active mTORC1 signaling exerts a dominant influence on metabolic and lipidomic regulation. We conclude that increased mTORC1 signaling shifts muscle metabolism toward greater reliance on nonoxidative energy sources in response to exercise. Understanding the mechanisms responsible for these effects may lead to the development of strategies for restoring proper mTORC1 signaling in conditions such as aging and sarcopenia.NEW & NOTEWORTHY This study demonstrates that hyperactive mTORC1 alters the muscle metabolomic and lipidomic response to exercise, with genotype having a larger effect than exercise. Knockout mice exhibited an increase in reliance on glycolysis and pentose phosphate pathway and an increase in triglyceride turnover. Wild-type mice primarily showed an increase in utilization of TCA cycle and lipid metabolism intermediates.

Impact of 24-week concurrent training on bone parameters and plasma levels of osteoglycin and sclerostin in young, sedentary adults: secondary analyses from the ACTIBATE randomized controlled trial

OBJECTIVE

To examine the effects of 24-week moderate (MOD-EX) and vigorous-intensity concurrent training (VIG-EX) on bone parameters and plasma levels of osteoglycin and sclerostin and their interplay with body composition and cardiometabolic risk factors in young, sedentary men and women.

DESIGN

Secondary study from the ACTIBATE randomized controlled trial (ClinicalTrials.gov ID: NCT02365129).

METHODS

This study was performed at the Sport and Health University Research Institute and the Virgen de las Nieves University Hospital of the University of Granada. Bone parameters were measured by dual-energy X-ray absorptiometry, and osteoglycin and sclerostin levels, by enzyme-linked immunosorbent assay.

RESULTS

145 young sedentary adults were assigned to a control (CON, n = 54), a MOD-EX (n = 48), or a VIG-EX (n = 43). 106 participants were included in the per-protocol analyses (CON, n = 42; MOD-EX, n = 33; and VIG-EX, n = 31). After 24 weeks of concurrent training, we observed no differences in changes in bone parameters (all P time × group ≥ .300), osteoglycin (P time × group = .250), and sclerostin levels (P time × group = .489). Moreover, we found no correlations between osteoglycin and sclerostin levels with body composition (all P ≥ .639) and cardiometabolic risk factors (all P ≥ .119).

CONCLUSION

24 weeks of concurrent training did not alter bone parameters, and plasma levels of osteoglycin and sclerostin in young, sedentary adults. Moreover, osteoglycin and sclerostin are not related with bone parameters and cardiometabolic risk factors in this population. These findings suggest that longer concurrent training interventions may be needed to enhance bone parameters in young, sedentary adults.

Effects of Time-Restricted Fasting-Nicotinamide Mononucleotide Combination on Exercise Capacity via Mitochondrial Activation and Gut Microbiota Modulation

BACKGROUND/OBJECTIVES

Athletic performance matters for athletes and fitness enthusiasts. Scientific dietary intervention may boost athletic performance alongside training. Intermittent fasting, like time-restricted fasting (TF), may enhance metabolic health. NAD+ supplement nicotinamide mononucleotide (NMN) improves mitochondrial activity. Both potentially boost athletic performance. However, whether TF combined with NMN treatment can further enhance athletic ability is unclear.

METHODS

Healthy Kunming mice were utilized to test the effects of NMN and TF on the athletic performance of mice. To simulate the in vivo state and further verify the role of TF and NMN, low glucose combined with NMN was used to intervene in C2C12 cells. The exercise capacity of mice was evaluated through motor behavior experiments. At the same time, blood gas analysis and kit tests were used to assess oxygen uptake capacity and post-exercise oxidative stress levels. Muscle development and mitochondrial function were examined through gene expression, protein analysis, and enzyme activity tests, and the distribution of intestinal microbiota and short-chain fatty acid content were also analyzed.

RESULTS

The results show that TF combined with NMN improved mitochondrial dynamics and biosynthesis, mitochondrial respiratory function, and oxidative metabolism. Then, the intervention enhanced mice's endurance, limb strength, motor coordination, and balance and reduced oxidative damage after exercise. Moreover, TF combined with NMN significantly increased the gut microbiota diversity and upregulated Ruminococcus, Roseburia, and Akkermansia in intestinal bacteria and short-chain fatty acids, which are associated with athletic performance.

CONCLUSION

TF combined with NMN enhanced mitochondrial function, improved energy metabolism, modulated the gut microbiota and short-chain fatty acids, and affected muscle fiber transformation, ultimately leading to an overall improvement in exercise performance. These findings provide a theoretical framework for expanding the application of NMN and TF in kinesiology.

Development and characterization of an Sf-1-Flp mouse model

The use of genetically engineered tools, including combinations of Cre-LoxP and Flp-FRT systems, enables the interrogation of complex biology. Steroidogenic factor-1 (SF-1) is expressed in the ventromedial hypothalamic nucleus (VMH). Development of genetic tools, such as mice expressing Flp recombinase (Flp) in SF-1 neurons (Sf-1-Flp), will be useful for future studies that unravel the complex physiology regulated by the VMH. Here, we developed and characterized Sf-1-Flp mice and demonstrated their utility. The Flp sequence was inserted into the Sf-1 locus with P2A. This insertion did not affect Sf-1 mRNA expression levels and Sf-1-Flp mice do not have any visible phenotypes. They are fertile and metabolically comparable to wild-type littermate mice. Optogenetic stimulation using adeno-associated virus (AAV) carrying Flp-dependent channelrhodopsin-2 (ChR2) increased blood glucose and skeletal muscle PGC-1α in Sf-1-Flp mice. This was similar to SF-1 neuronal activation using Sf-1-BAC-Cre and AAV carrying Cre-dependent ChR2. Finally, we generated Sf-1-Flp mice that lack β2-adrenergic receptors (Adrb2) only in skeletal muscle with a combination of Cre/LoxP technology (Sf-1-Flp:SKMΔAdrb2). Optogenetic stimulation of SF-1 neurons failed to increase skeletal muscle PGC-1α in Sf-1-Flp:SKMΔAdrb2 mice, suggesting that Adrb2 in skeletal muscle is required for augmented skeletal muscle PGC-1α by SF-1 neuronal activation. Our data demonstrate that Sf-1-Flp mice are useful for interrogating complex physiology.

Phosphoproteomics Uncovers Exercise Intensity-Specific Skeletal Muscle Signaling Networks Underlying High-Intensity Interval Training in Healthy Male Participants

BACKGROUND

In response to exercise, protein kinases and signaling networks are engaged to blunt homeostatic threats generated by acute contraction-induced increases in skeletal muscle energy and oxygen demand, as well as serving roles in the adaptive response to chronic exercise training to blunt future disruptions to homeostasis. High-intensity interval training (HIIT) is a time-efficient exercise modality that induces superior or similar health-promoting skeletal muscle and whole-body adaptations compared with prolonged, moderate-intensity continuous training (MICT). However, the skeletal muscle signaling pathways underlying HIIT's exercise intensity-specific adaptive responses are unknown.

OBJECTIVE

We mapped human muscle kinases, substrates, and signaling pathways activated/deactivated by an acute bout of HIIT versus work-matched MICT.

METHODS

In a randomized crossover trial design (Australian New Zealand Clinical Trials Registry number ACTRN12619000819123; prospectively registered 6 June 2019), ten healthy male participants (age 25.4 ± 3.2 years; BMI 23.5 ± 1.6 kg/m2;V ˙ O 2 max 37.9 ± 5.2 ml/kg/min, mean values ± SD) completed a single bout of HIIT and MICT cycling separated by ≥ 10 days and matched for total work (67.9 ± 10.2 kJ) and duration (10 min). Mass spectrometry-based phosphoproteomic analysis of muscle biopsy samples collected before, during (5 min), and immediately following (10 min) each exercise bout, to map acute temporal signaling responses to HIIT and MICT, identified and quantified 14,931 total phosphopeptides, corresponding to 8509 phosphorylation sites.

RESULTS

Bioinformatic analyses uncovered exercise intensity-specific signaling networks, including > 1000 differentially phosphorylated sites (± 1.5-fold change; adjusted P < 0.05; ≥ 3 participants) after 5 min and 10 min HIIT and/or MICT relative to rest. After 5 and 10 min, 92 and 348 sites were differentially phosphorylated by HIIT, respectively, versus MICT. Plasma lactate concentrations throughout HIIT were higher than MICT (P < 0.05), and correlation analyses identified > 3000 phosphosites significantly correlated with lactate (q < 0.05) including top functional phosphosites underlying metabolic regulation.

CONCLUSIONS

Collectively, this first global map of the work-matched HIIT versus MICT signaling networks has revealed rapid exercise intensity-specific regulation of kinases, substrates, and pathways in human skeletal muscle that may contribute to HIIT's skeletal muscle adaptations and health-promoting effects.  Preprint: The preprint version of this work is available on medRxiv, https://doi.org/10:1101/2024.07.11.24310302 .

Vitamin B6 status is related to disease severity and modulated by endurance exercise in individuals with multiple sclerosis: a secondary analysis of a randomized controlled trial

BACKGROUND

Low circulating concentrations of B vitamins are linked to various chronic and neurodegenerative diseases. Notably, pyridoxal 5'-phosphate (vitamin B6) deficiency is linked to altered inflammatory responses and cellular immune function, both critical in multiple sclerosis (MS). Nevertheless, most MS research has focused on folate (vitamin B9) and vitamin B12, leaving other B vitamins understudied.

OBJECTIVES

This secondary analysis investigated B-vitamin serum concentrations and related metabolites across MS phenotypes (primary progressive MS, relapsing-remitting MS, and secondary progressive MS) and disease severity levels. Additionally, the impact of endurance exercise on B-vitamin concentrations was investigated.

METHODS

In total, 106 individuals with MS participated in a randomized controlled trial, including different endurance exercise conditions. Serum B-vitamin concentrations were analyzed in 99 participants before and after 3 wk of intervention. Before analysis, participants were dichotomized to 1 of the 2 disability groups based on their expanded disability status scale (EDSS) score: EDSS≥4.5 (n = 47, EDSS: 5.86 ± 0.56) and EDSS<4 (n = 52, EDSS: 3.59 ± 0.83).

RESULTS

Higher EDSS scores were associated with lower pyridoxal 5'-phosphate (vitamin B-6) concentrations (rs: -0.32; 95% CI: -0.49, -0.12; P = 0.011), with the EDSS≥4.5 group also showing lower baseline pyridoxal 5'-phosphate (vitamin B6) concentrations (β: -0.18; 95% CI: -0.30, -0.07; P = 0.007) than the EDSS<4 group. Significant time × EDSS group interactions were evident for pyridoxal 5'-phosphate (vitamin B6; β: 0.05; 95% CI: 0.02, 0.08; P = 0.011), pyridoxal (vitamin B6; β: 0.05; 95% CI: 0.02, 0.09; P = 0.005), and riboflavin (vitamin B2; β: 0.06; 95% CI: 0.02, 0.09; P = 0.008), showing increases in these vitamers in the EDSS≥4.5 group postexercise. N1-Methylnicotinamide (vitamin B3; β: -0.11; 95% CI: -0.15, -0.06; P < 0.001) decreased in both groups over time.

CONCLUSIONS

Disease severity is associated with distinct B-vitamin profiles in individuals with MS, although endurance exercise appears to modify specific B-vitamin concentrations. This trial was registered at clinicaltrials.gov as NCT04356248.

Development of the MetFlex Index™: associations between cardiometabolic risk factors and fitness using a novel approach with blood lactate

Introduction

Cardiometabolic health is declining in the U.S. and anticipated to worsen over the next 30 years. Measurements of cardiometabolic health include blood metabolite profiles. One such metabolite is blood lactate. Lactate assessment is common in critical care and performance settings but less frequently used for the general population. The delayed onset of lactate accumulation during exercise may be an indicator of cardiometabolic health. Assessing lactate during a submaximal exercise test may assist in describing cardiometabolic health status in terms of metabolic fitness and metabolic flexibility.

Objectives

To introduce the MetFlex Index™ (MFI), a novel, scalable exercise-based and marker of cardiometabolic health, and to characterize its associations with routinely assessed cardiometabolic health risk factors.

Methods

Participants completed a submaximal test on a commercial stationary cycle following assessments of body composition, anthropometrics, vital signs, and a blood draw. Lactate was collected at each stage and the 1st and 2nd lactate thresholds were described. The MFI was calculated by using the power, in Watts, attained at the 1st lactate threshold relative to the participant's Body Mass Index (BMI).

Results

Data were collected on 827 participants (43 ± 13 years, 67% male, 72% overweight or obese). MFI peaked in the 30-39 year old cohort and decreased in subsequent decades. MFI was negatively associated with most markers of anthropometry, body composition, blood pressure, and was not associated with most blood metabolites.

Discussion

The MetFlex Index™ is a novel exercise-based approach using blood lactate to characterize skeletal muscle metabolism and is associated with several cardiometabolic health indices.

Predicting VO2max Using Lung Function and Three-Dimensional (3D) Allometry Provides New Insights into the Allometric Cascade (M0.75)

BACKGROUND

Using directly measured cardiorespiratory fitness (i.e. VO2max) in epidemiological/population studies is rare due to practicality issues. As such, predicting VO2max is an attractive alternative. Most equations that predict VO2max adopt additive rather than multiplicative models despite evidence that the latter provides superior fits and more biologically interpretable models. Furthermore, incorporating some but not all confounding variables may lead to inflated mass exponents (∝ M0.75) as in the allometric cascade.

OBJECTIVE

Hence, the purpose of the current study was to develop multiplicative, allometric models to predict VO2max incorporating most well-known, but some less well-known confounding variables (FVC, forced vital capacity; FEV1, forced expiratory volume in 1 s) that might provide a more dimensionally valid model (∝ M2/3) originally proposed by Astrand and Rodahl.

METHODS

We adopted the following three-dimensional multiplicative allometric model for VO2max (l⋅min-1) = Mk1·HTk2·WCk3·exp(a + b·age + c·age2 + d·%fat)·ε, (M, body mass; HT, height; WC, waist circumference; %fat, percentage body fat). Model comparisons (goodness-of-fit) between the allometric and equivalent additive models was assessed using the Akaike information criterion plus residual diagnostics. Note that the intercept term 'a' was allowed to vary for categorical fixed factors such as sex and physical inactivity.

RESULTS

Analyses revealed that significant predictors of VO2max were physical inactivity, M, WC, age2, %fat, plus FVC, FEV1. The body-mass exponent was k1 = 0.695 (M0.695), approximately∝M2/3. However, the calculated effect-sizes identified age2 and physical inactivity, not mass, as the strongest predictors of VO2max. The quality-of-fit of the allometric models were superior to equivalent additive models.

CONCLUSIONS

Results provide compelling evidence that multiplicative allometric models incorporating FVC and FEV1 are dimensionally and theoretically superior at predicting VO2max(l⋅min-1) compared with additive models. If FVC and FEV1 are unavailable, a satisfactory model was obtained simply by using HT as a surrogate.

Nutritional Strategies to Improve Post-exercise Recovery and Subsequent Exercise Performance: A Narrative Review

Post-exercise recovery strategies influence the body's ability to restore physiological homeostasis, replenish energy stores, repair muscle damage, and promote desired adaptations, which improve exercise performance. This narrative review examines the impact of nutritional strategies commonly used for enhancing recovery and subsequent exercise performance, particularly when athletes face short recovery periods. Carbohydrate ingestion is essential for glycogen replenishment, especially within the initial hours post-exercise, with its impact dependent on the types, timing, and amount. Protein is essential for accelerating muscle recovery and achieving a positive nitrogen balance, depending on the type and dosage. The co-ingestion of carbohydrates with proteins or fats is explored for its role in maximizing glycogen resynthesis and muscle repair, with evidence supporting the addition of protein to suboptimal carbohydrate intake for enhanced recovery. Moreover, this review addresses the potential benefits of creatine and caffeine co-ingestion for accelerating glycogen synthesis and improving subsequent performance. Hydration strategies, including the use of milk-based beverages and electrolyte solutions, are also discussed, emphasizing their importance in maintaining fluid balance and optimizing recovery. This review also highlights the emerging role of micronutrients such as omega-3 fatty acids, antioxidants, and sodium bicarbonate in reducing muscle damage and improving acid-base balance. Evidence supports the tailored use of these nutritional strategies, particularly for athletes managing tight competition/training schedules. Future research should focus on refining individualized approaches for recovery and investigating the impact of novel supplements on subsequent performance.

Autophagy in adult stem cell homeostasis, aging, and disease therapy

Autophagy is a crucial cellular process that facilitates the degradation of damaged organelles and protein aggregates, and the recycling of cellular components for the energy production and macromolecule synthesis. It plays an indispensable role in maintaining cellular homeostasis. Over recent decades, research has increasingly focused on the role of autophagy in regulating adult stem cells (SCs). Studies suggest that autophagy modulates various cellular processes and states of adult SCs, including quiescence, proliferation, self-renewal, and differentiation. The primary role of autophagy in these contexts is to sustain homeostasis, withstand stressors, and supply energy. Notably, the dysfunction of adult SCs during aging is correlated with a decline in autophagic activity, suggesting that autophagy is also involved in SC- and aging-associated disorders. Given the diverse cellular processes mediated by autophagy and the intricate mechanisms governing adult SCs, further research is essential to elucidate both universal and cell type-specific regulatory pathways of autophagy. This review discusses the role of autophagy in regulating adult SCs during quiescence, proliferation, self-renewal, and differentiation. Additionally, it summarizes the relationship between SC aging and autophagy, providing therapeutical insights into treating and ameliorating aging-associated diseases and cancers, and ultimately promoting longevity.

Mitophagy-mediated S1P facilitates muscle adaptive responses to endurance exercise through SPHK1-S1PR1/S1PR2 in slow-twitch myofibers

Endurance exercise triggers adaptive responses especially in slow-twitch myofibers of skeletal muscles, leading to the remodeling of myofiber structure and the mitochondrial network. However, molecular mechanisms underlying these adaptive responses, with a focus on the fiber type-specific perspective, remains largely unknown. In this study we analyzed the alterations of transcriptomics and metabolomics in distinct skeletal myofibers in response to endurance exercise. We determined that genes associated with sphingolipid metabolism, namely those encoding SPHK1, S1PR1, and S1PR2, are enriched in slow-twitch but not fast-twitch myofibers from both mouse and human skeletal muscles, and found that the SPHK1-S1PR pathway is essential for adaptive responses of slow-twitch to endurance exercise. Importantly, we demonstrate that endurance exercise causes the accumulation of ceramides on stressed mitochondria, and the mitophagic degradation of ceramides results in an increase of the sphingosine-1-phosphate (S1P) level. The elevated S1P thereby facilitates mitochondrial adaptation and enhances endurance capacity via the SPHK1-S1PR1/S1PR2 axis in slow-twitch muscles. Moreover, administration of S1P improves endurance performance in muscle atrophy mice by emulating these adaptive responses. Our findings reveal that the SPHK1-S1P-S1PR1/S1PR2 axis through mitophagic degradation of ceramides in slow-twitch myofibers is the central mediator to endurance exercise and highlight a potential therapeutic target for ameliorating muscle atrophy diseases.Abbreviations CQ: chloroquine; DMD: Duchenne muscular dystrophy; EDL: extensor digitorum longus; FCCP: carbonyl cyanide p-trifluoromethoxyphenyl hydrazone; FUNDC1: FUN14 domain containing 1; GTEx: genotype-tissue expression; MYH: myosin heavy chain; mtDNA: mitochondrial DNA; PPARGC1A/PGC-1α: peroxisome proliferator activated receptor, gamma, coactivator 1 alpha; RG: red gastrocnemius; S1P: sphingosine-1-phosphate; S1PR: sphingosine-1-phosphate receptor; Sol: soleus; SPHK1: sphingosine kinase 1; TA: tibialis anterior; WG: white gastrocnemius.

Unaltered maximal power and submaximal performance correlates with an oxidative vastus lateralis proteome phenotype during tapering in male cyclists

Little is known on how a short-term reduction of training volume changes muscle proteome and physiological parameters. We investigated the impact of halving training volume during regular training of cyclists on physiological parameters in relation to vastus lateralis protein profiles and fiber percentage ratios. Fifteen male cyclists (age: 30.1 ± 9.6 yrs.; VO2max: 59.4 ± 4.4 mL∙kg-1∙min-1; weekly training volume: 8.7 ± 2.3 h) participated in an 11-week training intervention. During 2 weeks after a shared training programme for 9 weeks, a control group continued training and a taper group reduced training volume by 50%. No end-point differences were found for peak power output, maximal oxygen uptake, or peak and mean power in a sprint test (p > 0.05), although in the taper group, muscle proteins involved in mitochondrial aerobic respiration increased whereas those involved in translation, protein catabolism, and actin organization decreased, without between-group differences in type I/type II fiber percentage ratios. Tapering did not decrease power at the first (LT1) and second lactate threshold (LT2) compared to t0, whereas power increased in the control group (LT1: 216 ± 28 W vs. 238 ± 11 W, p = 0.042, LT2: 290 ± 42 W vs. 318 ± 13 W, p = 0.005). Our data indicate that transient 50% training volume reductions may be beneficial for oxidative metabolism in muscle.

Acute treadmill exercise induces mitochondrial unfolded protein response in skeletal muscle of male rats

Mitochondria are often referred to as the energy centers of the cell and are recognized as key players in signal transduction, sensing, and responding to internal and external stimuli. Under stress conditions, the mitochondrial unfolded protein response (UPRmt), a conserved mitochondrial quality control mechanism, is activated to maintain mitochondrial and cellular homeostasis. As a physiological stimulus, exercise-induced mitochondrial perturbations trigger UPRmt, coordinating mitochondria-to-nucleus communication and initiating a transcriptional program to restore mitochondrial function. The aim of this study was to evaluate the UPRmt signaling response to acute exercise in skeletal muscle. Male rats were subjected to acute treadmill exercise at 25 m/min for 60 min on a 0 % grade. Plantaris muscles were collected from both sedentary and exercise groups at various times: immediately (0), and at 1, 3, 6, 12, and 24 h post-exercise. Reactive oxygen species (ROS) production was assessed using hydrogen peroxide assay and dihydroethidium staining. Additionally, the mRNA and protein expression of UPRmt markers were measured using ELISA and real-time PCR. Mitochondrial activity was assessed using succinate dehydrogenase (SDH) and cytochrome c oxidase (COX) staining. Our results demonstrated that acute exercise increased ROS production and upregulated UPRmt markers at both gene and protein levels. Moreover, skeletal muscle exhibited an increase in mitochondrial activity in response to exercise, as indicated by SDH and COX staining. These findings suggest that acute treadmill exercise is sufficient to induce ROS production, activate UPRmt signaling, and enhance mitochondrial activity in skeletal muscle, expanding our understanding of mitochondrial adaptations to exercise.

Exercise and tissue fibrosis: recent advances in therapeutic potential and molecular mechanisms

Tissue fibrosis represents an aberrant repair process, occurring because of prolonged injury, sustained inflammatory response, or metabolic disorders. It is characterized by an excessive accumulation of extracellular matrix (ECM), resulting in tissue hardening, structural remodeling, and loss of function. This pathological phenomenon is a common feature in the end stage of numerous chronic diseases. Despite the advent of novel therapeutic modalities, including antifibrotic agents, these have only modest efficacy in reversing established fibrosis and are associated with adverse effects. In recent years, a growing body of research has demonstrated that exercise has significant benefits and potential in the treatment of tissue fibrosis. The anti-fibrotic effects of exercise are mediated by multiple mechanisms, including direct inhibition of fibroblast activation, reduction in the expression of pro-fibrotic factors such as transforming growth factor-β (TGF-β) and slowing of collagen deposition. Furthermore, exercise has been demonstrated to assist in maintaining the dynamic equilibrium of tissue repair, thereby indirectly reducing tissue damage and fibrosis. It can also help maintain the dynamic balance of tissue repair by improving metabolic disorders, exerting anti-inflammatory and antioxidant effects, regulating cellular autophagy, restoring mitochondrial function, activating stem cell activity, and reducing cell apoptosis, thereby indirectly alleviating tissue. This paper presents a review of the therapeutic potential of exercise and its underlying mechanisms for the treatment of a range of tissue fibrosis, including cardiac, pulmonary, renal, hepatic, and skeletal muscle. It offers a valuable reference point for non-pharmacological intervention strategies for the comprehensive treatment of fibrotic diseases.

Baicalin Promotes Skeletal Muscle Fiber Remodeling by Activating the p38MAPK/PGC-1α Signaling Pathway

Skeletal muscle is the major tissue for metabolic activity in the body and performs a variety of physiological functions. Among these, muscle fiber types are decisive in muscle function and meat quality. Numerous studies have shown that natural products can affect the development of skeletal muscle, regulate the formation of muscle fibers, and impact muscle function under physiological or pathological conditions. Baicalin, a natural flavonoid compound mainly derived from the dried roots of Scutellaria baicalensis, has been reported to affect glucose metabolism and insulin resistance in skeletal muscle. However, the role of baicalin in the conversion of skeletal muscle fiber types and its underlying mechanisms remain unclear. This study aimed to explore the effects of baicalin on skeletal muscle fiber conversion in vitro and in vivo. The in vitro experiment used C2C12 cells as a model, with a baicalin treatment concentration of 125 μM; the in vivo experiment used C57BL/6J mice and weaned piglets as the models. The results showed that baicalin could participate in the remodeling of skeletal muscle fibers, promoting the conversion from glycolytic fibers to oxidative fibers in mice and pigs. This was evidenced by increased protein and mRNA expression levels of genes related to oxidative fibers, upregulated SDH enzyme activity, and mitochondrial complex expression in vivo and in vitro, while the protein and mRNA expression levels of genes related to glycolytic fibers were decreased, and LDH enzyme activity was downregulated. Mechanistic studies revealed that baicalin, as a small molecule, could target and bind to the p38 MAPK protein, increase its expression and phosphorylation levels, and activate the p38 MAPK/PGC-1α signaling pathway. Collectively, these data showed that baicalin induced a shift in skeletal muscle fiber composition from glycolytic to oxidative myofibers by activating the p38 MAPK/PGC-1α signaling pathway, thereby affecting the meat quality.

Plasma metabolomics dataset of race-walking athletes illuminating systemic metabolic reaction of exercise

This study investigates the metabolic changes induced by endurance exercise, specifically race walking, in a cohort of 19 athletes. Blood samples were collected at four time points: pre-exercise (REST), immediately post-exercise (STAT), 3 hours into recovery (REC3), and 22 hours post-exercise (REC22). A total of 859 metabolites were identified through the untargeted method, and 465 metabolites and 411 lipids were identified through the targeted methods. Rigorous quality control measures were implemented throughout the study to ensure data reliability. The comprehensive dataset, which is publicly available on the Metabolomics Workbench website, offers valuable insights into the systemic metabolic shifts triggered by endurance exercise. This resource may prove instrumental in uncovering biomarkers associated with athletic performance, providing a foundation for future research in exercise physiology and metabolic health.

Myokines as potential mediators of changes in glucose homeostasis and muscle mass after bariatric surgery

Myokines are bioactive peptides released by skeletal muscle. Myokines exert auto-, para-, or endocrine effects, enabling them to regulate many aspects of metabolism in various tissues. However, the contribution of myokines to the dramatic changes in glucose homeostasis and muscle mass induced by bariatric surgery has not been established. Our review highlights that myokines such as brain-derived neurotrophic factor (BDNF), meteorin-like protein (Metrnl), secreted protein acidic and rich in cysteine (SPARC), apelin (APLN) and myostatin (MSTN) may mediate changes in glucose homeostasis and muscle mass after bariatric surgery. Our review also identifies myonectin as an interesting candidate for future studies, as this myokine may regulate lipid metabolism and muscle mass after bariatric surgery. These myokines may provide novel therapeutic targets and biomarkers for obesity, type 2 diabetes and sarcopenia.

Flexible Fiber Sensors for Real-Time Monitoring of Redox Signaling Molecules in Exercise-Mimicking Engineered Skeletal Muscle

Real-time monitoring of reactive oxygen and nitrogen species (RONS) in skeletal muscle provides crucial insights into the cause-and-effect relationships between physical activity and health benefits. However, the dynamic production of exercise-induced RONS remains poorly explored, due to the lack of sensing tools that can conform to soft skeletal muscle while monitor RONS release during exercise. Here we introduce dual flexible sensors via twisting carbon nanotubes into helical bundles of fibers and subsequent assembling electrochemical sensing components. These flexible sensors exhibit low bending stiffness, excellent H2O2 and NO sensing abilities, outstanding biocompatibility and compliance with engineered skeletal muscle tissue. This allows real-time and simultaneous monitoring of H2O2 and NO release from engineered skeletal muscle in response to different exercise-mimicking stretches, which reveals that warm-up activities before high-intensity exercise may enhance adaptive responses by down-regulating H2O2 and up-regulating NO production. The proposed sensing strategy demonstrates great versatility in monitoring multiple biomarkers of soft tissue and organs.

Effect of different Lys/Met ratios in a low-protein diet on the meat quality of Tibetan sheep: A transcriptomics- and metabolomics-based analysis

This study integrated the the effects of dietary Lys/Met ratio in a low protein diet on the meat quality in Tibetan sheep. A total of 90 weaned Tibetan sheep, 2 months old with initial weight of 15.37 ± 0.92 kg were randomly divided into 3 treatments, which were supplemented with Lys/Met ratio at 3 (LP-H), 2 (LP-M), and 1 (LP-L) in the basal diet (10 % crude protein), respectively. After slaughter (150 days of age), the growth performances and meat quality of longissimus dorsi muscle were evaluated. The LP-L group showed significantly higher final body weight compared to the LP-M group (P < 0.05). Serum albumin and total protein levels were significantly higher in the LP-L group than in the LP-H group (P < 0.05). Furthermore, meat from the LP-L group had significantly higher protein, calcium, and vitamin E content compared to the LP-M group (P < 0.05). Transcriptomic analysis revealed 3,479 differentially expressed genes enriched in pathways related to muscle growth, energy metabolism, and signaling transduction. Metabolomic analysis identified 771 differential metabolites, significantly enriched in ABC transporters, beta-alanine metabolism, and taste transduction pathways. Integrated analysis highlighted the upregulation of the ABCD4 gene and L-valine metabolite in the LP-L group, contributing to improved phenotypic traits. These findings provide molecular insights into the regulatory mechanisms underlying the effects of dietary Lys/Met ratios on Tibetan sheep meat quality and offer a basis for developing nutritional strategies to enhance premium meat production.

The effect of exercise and physical activity on skeletal muscle epigenetics and metabolic adaptations

Physical activity (PA) and exercise elicit adaptations and physiological responses in skeletal muscle, which are advantageous for preserving health and minimizing chronic illnesses. The complicated atmosphere of the exercise response can be attributed to hereditary and environmental variables. The primary cause of these adaptations and physiological responses is the transcriptional reactions that follow exercise, whether endurance- (ET) or resistance- training (RT). As a result, the essential metabolic and regulatory pathways and myogenic genes associated with skeletal muscle alter in response to acute and chronic exercise. Epigenetics is the study of the relationship between genetics and the environment. Exercise evokes signaling pathways that strongly alter myofiber metabolism and skeletal muscle physiological and contractile properties. Epigenetic modifications have recently come to light as essential regulators of exercise adaptations. Research has shown various epigenetic markers linked to PA and exercise. The most critical epigenetic alterations in gene transcription identified are DNA methylation and histone modifications, which are associated with the transcriptional response of skeletal muscle to exercise and facilitate the modification to exercise. Other changes in the epigenetic markers are starting to emerge as essential processes for gene transcription, including acetylation as a new epigenetic modification, mediated changes by methylation, phosphorylation, and micro-RNA (miRNA). This review briefly introduces PA and exercise and associated benefits, provides a summary of epigenetic modifications, and a fundamental review of skeletal muscle physiology. The objectives of this review are 1) to discuss exercise-induced adaptations related to epigenetics and 2) to examine the interaction between exercise metabolism and epigenetics.

Circulating microRNAs and physical activity: Impact in diabetes

The term "ci-miRNAs," or "circulating microRNAs," refers to extracellular microRNAs (miRNAs) that exist outside of cells and can be detected in various bodily fluids, including blood, saliva, urine, and breast milk. These ci-miRNAs play a role in regulating gene expression and are mainly recognized for their functions beyond the cell, serving as signaling molecules in the blood. Researchers have thoroughly investigated the roles of these circulating miRNAs in various diseases. The capacity to detect and quantify ci-miRNAs in bodily fluids suggests their potential as biomarkers for monitoring several health conditions, including cancer, heart disease, brain disorders, and metabolic disorders, where fluctuations in miRNA levels may correlate with different physiological and pathological states. Current methods enable researchers to identify and measure miRNAs in these fluids, facilitating the exploration of their roles in health maintenance and disease resistance. Although research on ci-miRNAs is ongoing, recent studies focus on uncovering their significance, assessing their viability as biomarkers, and clarifying their functions. However, our understanding of how various types, intensities, and durations of exercise influence the levels of these miRNAs in the bloodstream is still limited. This section seeks to provide an overview of the changes in ci-miRNAs in response to exercise.

Development and Characterization of a Sf-1-Flp Mouse Model

The use of genetically engineered tools, including combinations of Cre-LoxP and Flp-FRT systems, enable the interrogation of complex biology. Steroidogenic factor-1 (SF-1) is expressed in the ventromedial hypothalamic nucleus (VMH). Development of genetic tools, such as mice expressing Flp recombinase (Flp) in SF-1 neurons (Sf-1-Flp), will be useful for future studies that unravel the complex physiology regulated by the VMH. Here, we developed and characterized Sf-1-Flp mice and demonstrated its utility. Flp sequence was inserted into Sf-1 locus with P2A. This insertion did not affect Sf-1 mRNA expression levels and Sf-1-Flp mice do not have any visible phenotypes. They are fertile and metabolically comparable to wild-type littermate mice. Optogenetic stimulation using adeno-associated virus (AAV)-bearing Flp-dependent channelrhodopsin-2 (ChR2) increased blood glucose and skeletal muscle PGC-1α in Sf-1-Flp mice. This was similar to SF-1 neuronal activation using Sf-1-BAC-Cre and AAV-bearing Cre-dependent ChR2. Finally, we generated Sf-1-Flp mice that lack β2-adrenergic receptors (Adrβ2) only in skeletal muscle with a combination of Cre/LoxP technology (Sf-1-Flp::SKMΔAdrβ2). Optogenetic stimulation of SF-1 neurons failed to increase skeletal muscle PGC-1α in Sf-1-Flp::SKMΔAdrβ2 mice, suggesting that Adrβ2 in skeletal muscle is required for augmented skeletal muscle PGC-1α by SF-1 neuronal activation. Our data demonstrate that Sf-1-Flp mice are useful for interrogating complex physiology.

Energy metabolism in health and diseases

Energy metabolism is indispensable for sustaining physiological functions in living organisms and assumes a pivotal role across physiological and pathological conditions. This review provides an extensive overview of advancements in energy metabolism research, elucidating critical pathways such as glycolysis, oxidative phosphorylation, fatty acid metabolism, and amino acid metabolism, along with their intricate regulatory mechanisms. The homeostatic balance of these processes is crucial; however, in pathological states such as neurodegenerative diseases, autoimmune disorders, and cancer, extensive metabolic reprogramming occurs, resulting in impaired glucose metabolism and mitochondrial dysfunction, which accelerate disease progression. Recent investigations into key regulatory pathways, including mechanistic target of rapamycin, sirtuins, and adenosine monophosphate-activated protein kinase, have considerably deepened our understanding of metabolic dysregulation and opened new avenues for therapeutic innovation. Emerging technologies, such as fluorescent probes, nano-biomaterials, and metabolomic analyses, promise substantial improvements in diagnostic precision. This review critically examines recent advancements and ongoing challenges in metabolism research, emphasizing its potential for precision diagnostics and personalized therapeutic interventions. Future studies should prioritize unraveling the regulatory mechanisms of energy metabolism and the dynamics of intercellular energy interactions. Integrating cutting-edge gene-editing technologies and multi-omics approaches, the development of multi-target pharmaceuticals in synergy with existing therapies such as immunotherapy and dietary interventions could enhance therapeutic efficacy. Personalized metabolic analysis is indispensable for crafting tailored treatment protocols, ultimately providing more accurate medical solutions for patients. This review aims to deepen the understanding and improve the application of energy metabolism to drive innovative diagnostic and therapeutic strategies.

Effects of Physical Exercise on Cardiometabolic Health in Individuals with Autism Spectrum Disorder: A Systematic Review

BACKGROUND/OBJECTIVES

Individuals with autism spectrum disorder (ASD) are at increased risk of developing cardiometabolic diseases. Although physical exercise (PE) has emerged in the literature as an important modulator for reducing such risk, evidence remains unclear. This systematic review aimed to investigate the effects of PE on cardiometabolic health in individuals with ASD.

METHODS

A systematic review was carried out according to the PRISMA guidelines, from their inception until 18 July 2023, in the following electronic databases: Scopus, Medline, and Web of Science. Studies were included if they focused on ASD patients undergoing physical exercise, assessing cardiometabolic risk, exercise tolerance, and QoL. The following were excluded: non-exercise interventions, additional therapies, non-English studies, and reviews. The methodological quality of the included studies was assessed through the Downs and Black scale.

RESULTS

A total of four studies (149 participants) were included in this review, with the average methodological quality being rated as "fair". Interventions had mixed effects on cardiometabolic health. The BMI (↓2.8 kg/m2), waist circumference (↓1.86 cm), and lipid profiles improved in some cases. VO2max and HRbaseline showed moderate gains. Secondary outcomes included enhanced endurance, strength, and calorie expenditure, especially in mild ASD. Autistic traits and quality of life improved post-intervention, with better results in the experimental groups.

CONCLUSIONS

This review indicates that aerobic and functional training improves cardiometabolic health, autistic traits, and QoL in individuals with ASD, particularly in mild cases. Further research is needed to explore the impact of ASD severity on these outcomes.

Diurnal variation in skeletal muscle mitochondrial function dictates time-of-day-dependent exercise capacity

Exercise impinges on almost all physiological processes at an organismal level and is a potent intervention to treat various diseases. Exercise performance is well established to display diurnal rhythm, peaking during the late active phase. However, the underlying molecular/metabolic factors and mitochondrial energetics that possibly dictate time-of-day exercise capacity remain unknown. Here, we have unraveled the importance of diurnal variation in mitochondrial functions as a determinant of skeletal muscle exercise performance. Our results show that exercise-induced muscle metabolome and mitochondrial energetics are distinct at ZT3 and ZT15. Importantly, we have elucidated key diurnal differences in mitochondrial functions that are well correlated with disparate time-of-day-dependent exercise capacity. Providing causal mechanistic evidence, we illustrate that loss of Sirtuin4 (SIRT4), a well-known mitochondrial regulator, abrogates mitochondrial diurnal variation and consequently abolishes time-of-day-dependent muscle output. Therefore, our findings unequivocally demonstrate the pivotal role of baseline skeletal muscle mitochondrial functions in dictating diurnal exercise capacity.

The association between the lifestyle risk score and metabolically healthy and unhealthy obesity phenotype in Iranian women with overweight and obesity: a cross-sectional study

Background

The evidence shows that all women with obesity do not develop metabolic complications thus, they may be metabolically healthy. The lifestyle factors in combination may influence obesity phenotypes including metabolically healthy and unhealthy obesity. While previous studies examined associations between single lifestyle factors and obesity phenotype, no previous study has examined associations between lifestyle risk score (LRS) and obesity phenotypes. This study for the first time created the LRS which is a combination of lifestyle factors and investigated the LRS in relation to various obesity phenotypes among women with overweight and obesity.

Methods

This cross-sectional study analyzed 278 women referred to health centers of the Tehran University of Medical Sciences. A multistage sampling method was used to recruit the participants. The LRS was created based on diet, physical activity (PA), sleep, obesity, and sociodemographic characteristics. A binary logistic regression analysis was used to evaluate the association between obesity phenotypes and LRS.

Results

Women with higher LRS had higher body mass index (BMI) and high-sensitivity C-reactive protein (hs-CRP) while had lower high-density lipoprotein cholesterol (HDL-C), PA, education levels, sleep quality, vegetables, grains and legumes intake. Furthermore, women with higher LRS were more likely to experience metabolically unhealthy obesity (MUO).

Conclusion

This study found significant associations between higher LRS and an increased likelihood of MUO. Further prospective studies are needed to advance our understanding of the relationship between lifestyle and obesity.

Endurance exercise remodels skeletal muscle by suppressing Ythdf1-mediated myostatin expression

Exercise can improve health via skeletal muscle remodeling. Elucidating the underlying mechanism may lead to new therapeutics for aging-related loss of skeletal muscle mass. Here, we show that endurance exercise suppresses expression of YT521-B homology domain family (Ythdf1) in skeletal muscle, which recognizes the N6-methyladenosine (m6A). Ythdf1 deletion phenocopies endurance exercise-induced muscle hypertrophy in mice increases muscle mitochondria content and type I fiber specification. At the molecular level, Ythdf1 recognizes and promotes the translation of m6A-modified Mstn mRNA, which encodes a muscle growth inhibitor, Myostatin. Loss of Ythdf1 leads to hyperactivation of skeletal muscle stem cells (MuSCs), also called satellite cells (SCs), enhancing muscle growth and injury-induced regeneration. Our data reveal Ythdf1 as a key regulator of skeletal muscle homeostasis, provide insights into the mechanism by which endurance exercise promotes skeletal muscle remodeling and highlight potential strategies to prevent aging-related muscle degeneration.

Differential Regulation of miRNA and Protein Profiles in Human Plasma-Derived Extracellular Vesicles via Continuous Aerobic and High-Intensity Interval Training

Both continuous aerobic training (CAT) and high-intensity interval training (HIIT) are recommended to promote health and prevent diseases. Exercise-induced circulating extracellular vesicles (EX-EVs) have been suggested to play essential roles in mediating organ crosstalk, but corresponding molecular mechanisms remain unclear. To assess and compare the systemic effects of CAT and HIIT, five healthy male volunteers were assigned to HIIT and CAT, with a 7-day interval between sessions. Plasma EVs were collected at rest or immediately after each training section, prior to proteomics and miRNA profile analysis. We found that the differentially expressed (DE) miRNAs in EX-EVs were largely involved in the regulation of transcriptional factors, while most of the DE proteins in EX-EVs were identified as non-secreted proteins. Both CAT and HIIT play common roles in neuronal signal transduction, autophagy, and cell fate regulation. Specifically, CAT showed distinct roles in cognitive function and substrate metabolism, while HIIT was more associated with organ growth, cardiac muscle function, and insulin signaling pathways. Interestingly, the miR-379 cluster within EX-EVs was specifically regulated by HIIT, involving several biological functions, including neuroactive ligand-receptor interaction. Furthermore, EX-EVs likely originate from various tissues, including metabolic tissues, the immune system, and the nervous system. Our study provides molecular insights into the effects of CAT and HIIT, shedding light on the roles of EX-EVs in mediating organ crosstalk and health promotion.

Kdm2a inhibition in skeletal muscle improves metabolic flexibility in obesity

Skeletal muscle is a critical organ in maintaining homoeostasis against metabolic stress, and histone post-translational modifications are pivotal in those processes. However, the intricate nature of histone methylation in skeletal muscle and its impact on metabolic homoeostasis have yet to be elucidated. Here, we report that mitochondria-rich slow-twitch myofibers are characterized by significantly higher levels of H3K36me2 along with repressed expression of Kdm2a, an enzyme that specifically catalyses H3K36me2 demethylation. Deletion or inhibition of Kdm2a shifts fuel use from glucose under cold challenge to lipids under obese conditions by increasing the proportion of mitochondria-rich slow-twitch myofibers. This protects mice against cold insults and high-fat-diet-induced obesity and insulin resistance. Mechanistically, Kdm2a deficiency leads to a marked increase in H3K36me2 levels, which then promotes the recruitment of Mrg15 to the Esrrg locus to process its precursor messenger RNA splicing, thereby reshaping skeletal muscle metabolic profiles to induce slow-twitch myofiber transition. Collectively, our data support the role of Kdm2a as a viable target against metabolic stress.

Exercise and exerkines: Mechanisms and roles in anti-aging and disease prevention

Aging is a complex biological process characterized by increased inflammation and susceptibility to various age-related diseases, including cognitive decline, osteoporosis, and type 2 diabetes. Exercise has been shown to modulate mitochondrial function, immune responses, and inflammatory pathways, thereby attenuating aging through the regulation of exerkines secreted by diverse tissues and organs. These bioactive molecules, which include hepatokines, myokines, adipokines, osteokines, and neurokines, act both locally and systemically to exert protective effects against the detrimental aspects of aging. This review provides a comprehensive summary of different forms of exercise for older adults and the multifaceted role of exercise in anti-aging, focusing on the biological functions and sources of these exerkines. We further explore how exerkines combat aging-related diseases, such as type 2 diabetes and osteoporosis. By stimulating the secretion of these exerkines, exercise supports healthy longevity by promoting tissue homeostasis and metabolic balance. Additionally, the integration of exercise-induced exerkines into therapeutic strategies represents a promising approach to mitigating age-related pathologies at the molecular level. As our understanding deepens, it may pave the way for personalized interventions leveraging physical activity to enhance healthspan and improve quality of life.

Exercise-induced methylation of the Serhl2 promoter and implication for lipid metabolism in rat skeletal muscle

OBJECTIVES

Environmental factors such as physical activity induce epigenetic modifications, with exercise-responsive DNA methylation changes occurring in skeletal muscle. To determine the skeletal muscle DNA methylation signature of endurance swim training, we used whole-genome methylated DNA immunoprecipitation (MeDIP) sequencing.

METHODS

We utilized endurance-trained rats, cultured L6 myotubes, and human skeletal muscle cells, employing MeDIP sequencing, gene silencing, and palmitate oxidation assays. Additional methods included promoter luciferase assays, fluorescence microscopy, and RNA/DNA analysis to investigate exercise-induced molecular changes.

RESULTS

Gene set enrichment analysis (GSEA) of differentially methylated promoter regions identified an enrichment of four gene sets, including those linked to lipid metabolic processes, with hypermethylated or hypomethylated promoter regions in skeletal muscle of exercise-trained rats. Bisulfite sequencing confirmed hypomethylation of CpGs in the Serhl2 (Serine Hydrolase Like 2) transcription start site in exercise-trained rats. Serhl2 gene expression was upregulated in both exercise-trained rats and an "exercise-in-a-dish" model of L6 myotubes subjected to electrical pulse stimulation (EPS). Serhl2 promoter activity was regulated by methylation and EPS. A Nr4a binding motif in the Serhl2 promoter, when deleted, reduced promoter activity and sensitivity to methylation in L6 myotubes. Silencing Serhl2 in L6 myotubes reduced intracellular lipid oxidation and triacylglycerol synthesis in response to EPS.

CONCLUSIONS

Exercise-training enhances intracellular lipid metabolism and phenotypic changes in skeletal muscle through epigenomic modifications on Serhl2. Hypomethylation of the Serhl2 promoter influences Nr4a transcription factor binding, promoter activity, and gene expression, linking exercise-induced epigenomic regulation of Serhl2 to lipid oxidation and triacylglycerol synthesis.