Exercise-induced skeletal muscle remodeling and metabolic adaptation: redox signaling and role of autophagy

Mechanical Loading Modulates AMPK and mTOR Signaling in Muscle Cells

Skeletal muscle adaptation to exercise involves various phenotypic changes that enhance the metabolic and contractile functions. One key regulator of these adaptive responses is the activation of AMPK, which is influenced by exercise intensity. However, the mechanistic understanding of AMPK activation during exercise remains incomplete. In this study, we utilized an in vitro model to investigate the effects of mechanical loading on AMPK activation and its interaction with the mTOR signaling pathway. Proteomic analysis of muscle cells subjected to static loading (SL) revealed distinct quantitative protein alterations associated with RNA metabolism, with 10% SL inducing the most pronounced response compared to lower intensities of 5% and 2% as well as the control. Additionally, 10% SL suppressed RNA and protein synthesis while activating AMPK and inhibiting the mTOR pathway. We also found that SRSF2, necessary for pre-mRNA splicing, is regulated by AMPK and mTOR signaling, which, in turn, is regulated in an intensity-dependent manner by SL with the highest expression in 2% SL. Further examination showed that the ADP/ATP ratio was increased after 10% SL compared to the control and that SL induced changes in mitochondrial biogenesis. Furthermore, Seahorse assay results indicate that 10% SL enhances mitochondrial respiration. These findings provide novel insights into the cellular responses to mechanical loading and shed light on the intricate AMPK-mTOR regulatory network in muscle cells.

Secondary mitochondrial dysfunction across the spectrum of hereditary and acquired muscle disorders

Mitochondria form a dynamic network within skeletal muscle. This network is not only responsible for producing adenosine triphosphate (ATP) through oxidative phosphorylation, but also responds through fission, fusion and mitophagy to various factors, such as increased energy demands, oxidative stress, inflammation, and calcium dysregulation. Mitochondrial dysfunction in skeletal muscle not only occurs in primary mitochondrial myopathies, but also other hereditary and acquired myopathies. As such, this review attempts to highlight the clinical and histopathologic aspects of mitochondrial dysfunction seen in hereditary and acquired myopathies, as well as discuss potential mechanisms leading to mitochondrial dysfunction and therapies to restore mitochondrial function.

The potential therapeutic role of curcumin in osteoporosis treatment: based on multiple signaling pathways

Osteoporosis is a common chronic metabolic bone disease caused by disturbances in normal bone metabolism and an imbalance between osteoblasts and osteoclasts. Osteoporosis is characterized by a decrease in bone mass and bone density, leading to increased bone fragility. Osteoporosis is usually treated with medications and surgical methods, but these methods often produce certain side effects. Therefore, the use of traditional herbal ingredients for the treatment of osteoporosis has become a focus of attention and a hot topic in recent years. Curcumin, widely distributed among herbs such as turmeric, tulip, and curcuma longa, contains phenolic, terpenoid, and flavonoid components. Modern pharmacological studies have confirmed that curcumin has a variety of functions including antioxidant and anti-inflammatory properties. In addition, curcumin positively regulates the differentiation and promotes the proliferation of osteoblasts, which play a crucial role in bone formation. Multiple studies have shown that curcumin is effective in the treatment of osteoporosis as it interacts with a variety of signaling pathway targets, thereby interfering with the formation of osteoblasts and osteoclasts and regulating the development of osteoporosis. This review summarized the key signaling pathways and their mechanisms of action of curcumin in the prevention and treatment of osteoporosis and analyzed their characteristics and their relationship with osteoporosis and curcumin. This not only proves the medicinal value of curcumin as a traditional herbal ingredient but also further elucidates the molecular mechanism of curcumin's anti-osteoporosis effect, providing new perspectives for the prevention and treatment of osteoporosis through multiple pathways.

Muscle Organoid and Assembloid Systems

Skeletal muscle is one of the most complex and largest tissues that perform important processes in the body, including performing voluntary movements and maintaining body temperature. Disruption of muscle homeostasis results in the development of several disorders, including diabetes and sarcopenia. To study the developmental and regenerative dynamics of skeletal muscle and the mechanism behind muscle diseases, it is important to model skeletal muscle and diseases in vitro. Since skeletal muscle has a complex structure and interaction with other tissues and cells that are required to perform their function, conventional 2D cultures are not sufficient to model the skeletal muscle with their interactions. Advances in the field of organoids and assembloids will enable the establishment of more complex and realistic tissue or disease models which cannot be fully recapitulated in conventional 2D culture systems for use in several areas, including disease research, regenerative, and tissue biology. To overcome these limitations, 3D organoid systems and assembloid systems are promising because of their success in recapitulating the complex structural organization, function, and cellular interactions of skeletal muscle.

The interplay of exercise and polyphenols in cancer treatment: A focus on oxidative stress and antioxidant mechanisms

Exercise has been demonstrated to induce an elevated production of free radicals, leading to the onset of oxidative stress. Numerous studies highlight the positive impacts of aerobic exercise, primarily attributed to the increase in overall antioxidant capacity. The evidence suggests that engaging in aerobic exercise contributes to a reduction in the likelihood of advanced cancer and mortality. Oxidative stress occurs when there is an imbalance between the generation of free radicals and the collective antioxidant defense system, encompassing both enzymatic and nonenzymatic antioxidants. Typically, oxidative stress triggers the formation of reactive oxygen or nitrogen species, instigating or advancing various issues in cancers and other diseases. The pro-oxidant-antioxidant balance serves as a direct measure of this imbalance in oxidative stress. Polyphenols contain a variety of bioactive compounds, including flavonoids, flavanols, and phenolic acids, conferring antioxidant properties. Previous research highlights the potential of polyphenols as antioxidants, with documented effects on reducing cancer risk by influencing processes such as proliferation, angiogenesis, and metastasis. This is primarily attributed to their recognized antioxidant capabilities. Considering the extensive array of signaling pathways associated with exercise and polyphenols, this overview will specifically focus on oxidative stress, the antioxidant efficacy of polyphenols and exercise, and their intricate interplay in cancer treatment.

Relationships between endurance exercise training-induced muscle fiber-type shifting and autophagy in slow- and fast-twitch skeletal muscles of mice

PURPOSE

Endurance exercise induces muscle fiber-type shifting and autophagy; however, the potential role of autophagy in muscle fiber-type transformation remains unclear. This study examined the relationship between muscle fiber-type shifting and autophagy in the soleus (SOL) and extensor digitorum longus (EDL) muscles, which are metabolically discrete muscles.

METHODS

Male C57BL/6J mice were randomly assigned to sedentary control (CON) and exercise (EXE) groups. After 1 week of acclimation to treadmill running, the mice in the EXE group ran at 12-15 m/min, 60 min/day, 5 days/week for 6 weeks. All mice were sacrificed 90 min after the last exercise session, and the targeted tissues were rapidly dissected. The right side of the tissues was used for western blot analysis, whereas the left side was subjected to immunohistochemical analysis.

RESULTS

Endurance exercise resulted in muscle fiber-type shifting (from type IIa to type I) and autophagy (an increase in LC3-II) in the SOL muscle. However, muscle fiber-type transformation and autophagy were not correlated in the SOL and EDL muscles. Interestingly, in contrast to the canonical autophagy signaling pathways, our study showed that exercise-induced autophagy concurs with enhanced anabolic (increased p-AKTSer473/AKT and p-mTOR/mTORSer2448 ratios) and suppressed catabolic (reduced p-AMPKThr172/AMPK ratio) states.

CONCLUSION

Our findings demonstrate that chronic endurance exercise-induced muscle fiber-type transformation and autophagy occur in a muscle-specific manner (e.g., SOL). More importantly, our study suggests that endurance training-induced SOL muscle fiber-type transition may underlie metabolic modulations caused by the AMPK and AKT/mTOR signaling pathways rather than autophagy.

circUSP13 facilitates the fast-to-slow myofiber shift via the MAPK/ERK signaling pathway in goat skeletal muscles

Understanding how skeletal muscle fiber proportions are regulated is essential for understanding muscle function and improving the quality of mutton. While circular RNA (circRNA) has a critical function in myofiber type transformation, the specific mechanisms are not yet fully understood. Prior evidence indicates that circular ubiquitin-specific peptidase 13 (circUSP13) can promote myoblast differentiation by acting as a ceRNA, but its potential role in myofiber switching is still unknown. Herein, we found that circUSP13 enhanced slow myosin heavy chain (MyHC-slow) and suppressed MyHC-fast expression in goat primary myoblasts (GPMs). Meanwhile, circUSP13 evidently enhanced the remodeling of the mitochondrial network while inhibiting the autophagy of GPMs. We obtained fast-dominated myofibers, via treatment with rotenone, and further demonstrated the positive role of circUSP13 in the fast-to-slow transition. Mechanistically, activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway significantly impaired the slow-to-fast shift in fully differentiated myotubes, which was restored by circUSP13 or IGF1 overexpression. In conclusion, circUSP13 promoted the fast-to-slow myofiber type transition through MAPK/ERK signaling in goat skeletal muscle. These findings provide novel insights into the role of circUSP13 in myofiber type transition and contribute to a better understanding of the genetic mechanisms underlying meat quality.

Molecular insights into the lipid-carbohydrates metabolism switch under the endurance effort in Arabian horses

BACKGROUND

Recent studies have shown that in Arabian horse muscle, long-term exercise-induced expression of genes related to fatty acid degradation and the downregulation of genes belonging to the glycolysis/gluconeogenesis and insulin signalling pathways. Long-lasting physical exertion may trigger the metabolism to switch the main energy source from carbohydrates to lipids due to higher caloric content.

OBJECTIVES

To describe the metabolism adaptation at the whole transcriptome of blood to endurance effort in Arabian horses.

STUDY DESIGN

In vivo experiment.

METHODS

Venous blood samples from 10 Arabian horses were taken before and after a 120 km long endurance ride to isolate the RNA and perform the high-throughput NGS transcriptome sequencing.

RESULTS

The results, including KEGG (Kyoto Encyclopaedia of Genes and Genomes) and GO (Gene Ontology) analyses, allowed us to describe the most significantly upregulated-ARV1, DGAT2, LIPE, APOA2, MOGAT1, MOGAT2, GYS1, GYS2 and downregulated-ACACA, ACACB, FADS1, FADS2 genes involved in carbohydrate and lipid metabolism. Also, the increased expression of RAF1, KRAS and NRAS genes involved in the Insulin pathway and PI3K-Akt was shown.

MAIN LIMITATIONS

Limited sample size, Arabians used for endurance racing were not compared to Arabians from other equestrian disciplines.

CONCLUSIONS

This general insight into the processes described supports the thesis of the lipid-carbohydrates metabolism switch in endurance Arabian horses and provides the basis for further research.

The physiologic benefits of optimizing cardiorespiratory fitness and physical activity - From the cell to systems level in a post-pandemic world

Cardiovascular (CV) disease (CVD) is a leading cause of premature death and hospitalization which places a significant strain on health services and economies around the World. Evidence from decades of empirical and observational research demonstrates clear associations between physical activity (PA) and cardiorespiratory fitness (CRF) which can offset the risk of mortality and increase life expectancy and the quality of life in patients. Whilst well documented, the narrative of increased CRF remained pertinent during the coronavirus disease 2019 (COVID-19) pandemic, where individuals with lower levels of CRF had more than double the risk of dying from COVID-19 compared to those with a moderate or high CRF. The need to better understand the mechanisms associated with COVID-19 and those that continue to be affected with persistent symptoms following infection (Long COVID), and CV health is key if we are to be able to effectively target the use of CRF and PA to improve the lives of those suffering its afflictions. Whilst there is a long way to go to optimise PA and CRF for improved health at a population level, particularly in a post-pandemic world, increasing the understanding using a cellular-to-systems approach, we hope to provide further insight into the benefits of engaging in PA.

New Insights into Antioxidant Peptides: An Overview of Efficient Screening, Evaluation Models, Molecular Mechanisms, and Applications

Antioxidant peptides are currently a hotspot in food science, pharmaceuticals, and cosmetics. In different fields, the screening, activity evaluation, mechanisms, and applications of antioxidant peptides are the pivotal areas of research. Among these topics, the efficient screening of antioxidant peptides stands at the forefront of cutting-edge research. To this end, efficient screening with novel technologies has significantly accelerated the research process, gradually replacing the traditional approach. After the novel antioxidant peptides are screened and identified, a time-consuming activity evaluation is another indispensable procedure, especially in in vivo models. Cellular and rodent models have been widely used for activity evaluation, whilst non-rodent models provide an efficient solution, even with the potential for high-throughput screening. Meanwhile, further research of molecular mechanisms can elucidate the essence underlying the activity, which is related to several signaling pathways, including Keap1-Nrf2/ARE, mitochondria-dependent apoptosis, TGF-β/SMAD, AMPK/SIRT1/PGC-1α, PI3K/Akt/mTOR, and NF-κB. Last but not least, antioxidant peptides have broad applications in food manufacture, therapy, and the cosmetics industry, which requires a systematic review. This review introduces novel technologies for the efficient screening of antioxidant peptides, categorized with a new vision. A wide range of activity evaluation assays, encompassing cellular models, as well as rodent and non-rodent models, are provided in a comprehensive manner. In addition, recent advances in molecular mechanisms are analyzed with specific cases. Finally, the applications of antioxidant peptides in food production, therapy, and cosmetics are systematically reviewed.

Major Depressive Disorder and Gut Microbiota: Role of Physical Exercise

Major depressive disorder (MDD) has a high prevalence and is a major contributor to the global burden of disease. This psychiatric disorder results from a complex interaction between environmental and genetic factors. In recent years, the role of the gut microbiota in brain health has received particular attention, and compelling evidence has shown that patients suffering from depression have gut dysbiosis. Several studies have reported that gut dysbiosis-induced inflammation may cause and/or contribute to the development of depression through dysregulation of the gut-brain axis. Indeed, as a consequence of gut dysbiosis, neuroinflammatory alterations caused by microglial activation together with impairments in neuroplasticity may contribute to the development of depressive symptoms. The modulation of the gut microbiota has been recognized as a potential therapeutic strategy for the management of MMD. In this regard, physical exercise has been shown to positively change microbiota composition and diversity, and this can underlie, at least in part, its antidepressant effects. Given this, the present review will explore the relationship between physical exercise, gut microbiota and depression, with an emphasis on the potential of physical exercise as a non-invasive strategy for modulating the gut microbiota and, through this, regulating the gut-brain axis and alleviating MDD-related symptoms.

Therapeutic Myogenesis Induced by Ultrasound Exposure in a Volumetric Skeletal Muscle Loss Injury Model

BACKGROUND

Low-intensity pulsed ultrasound (LIPUS) irradiation has been shown to induce various responses in different cells. It has been shown that LIPUS activates extracellular signal-regulated kinase 1/2 (ERK1/2) through integrin.

PURPOSE

To study the effects of LIPUS on myogenic regulatory factors and other related myogenesis elements in a volumetric skeletal muscle loss injury model.

STUDY DESIGN

Controlled laboratory study.

METHODS

C57BL/6J mice were subjected to full-thickness muscle defect injury of the quadriceps and treated with direct application of LIPUS 20 min/d or non-LIPUS treatment (control) for 3, 7, and 14 days. LIPUS was also applied to C2C12 cells in culture in the presence of low and high doses of lipopolysaccharides. The expression levels of myogenic regulatory factors and the expression levels of myokine-related and angiogenic-related proteins of the control and LIPUS groups were analyzed.

RESULTS

Muscle volume in the injury site was restored at day 14 with LIPUS treatment. Paired-box protein 7, myogenic factor 5, myogenin, and desmin expressions were significantly different between control and LIPUS groups at days 7 and 14. Myokine and angiogenic cytokine-related factors were significantly increased in the LIPUS group at day 3 and decreased with no significant difference between the groups by day 14. LIPUS induced different responses of myogenic regulatory factors in C2C12 cells with low and high doses of lipopolysaccharides. LIPUS promoted myogenesis through short-lived increase in interleukin-6 and heme oxygenase 1, together with activation of ERK1/2.

CONCLUSION

LIPUS had a constant effect on the variables of tissue damage, from macrotrauma to microtrauma, leading to efficient muscle regeneration.

CLINICAL RELEVANCE

The focus of therapeutic strategies with LIPUS has been not only for microvascular regeneration but also for skeletal muscle and related local tissue recovery from acute or chronic damage.

Intermittent fasting associated with aerobic exercise improves oxidative parameters and causes muscle damage without compromising the performance of Wistar rats

OBJECTIVES

The aim of this study was to` investigate the effects of intermittent fasting (IF) and the possible association with aerobic exercise on performance, oxidative, biochemical, and somatic parameters of Wistar rats.

METHODS

Forty rats were randomized into the following groups: sedentary (SC) and trained (TC) controls, sedentary intermittent fasting (SIF), and trained intermittent fasting (TIF). The rats were subjected to IF for 15 h every day and aerobic exercise lasting 30 min, five times a week, at a speed of 15 m/min for 4 wk. Performance tests were performed at the beginning and end of the protocol. Glucose and insulin tolerance, somatic parameters, lipidogram, leptin, insulin, malondialdehyde, antioxidant capacity, C-reactive protein, alpha acid glycoprotein, creatine kinase, lactate dehydrogenase, and muscle histology were analyzed.

RESULTS

The trained groups had similar performance and significantly improved performance at the end of the experiment. TIF showed lower body weight (-16 g), lean mass (22.49%), homeostatic model assessment for insulin resistance (29%), and lactate dehydrogenase (48%), and higher malondialdehyde (53%) and antioxidant capacity (75%) than the TC group. The SIF and TIF groups showed a fiber area reduction and positivity marking for tumor necrosis factor-α in the muscles.

CONCLUSION

Although IF associated with aerobic exercise improved antioxidant capacity caused damage to muscle fibers and lean mass loss, it did not change the performance of the rats.

Discordant skeletal muscle gene and protein responses to exercise

The ability of skeletal muscle to adapt to repeated contractile stimuli is one of the most intriguing aspects of physiology. The molecular bases underpinning these adaptations involve increased protein activity and/or expression, mediated by an array of pre- and post-transcriptional processes, as well as translational and post-translational control. A longstanding dogma assumes a direct relationship between exercise-induced increases in mRNA levels and subsequent changes in the abundance of the proteins they encode. Drawing on the results of recent studies, we dissect and question the common assumption of a direct relationship between changes in the skeletal muscle transcriptome and proteome induced by repeated muscle contractions (e.g., exercise).

Crosstalk between autophagy and insulin resistance: evidence from different tissues

Insulin is a critical hormone that promotes energy storage in various tissues, as well as anabolic functions. Insulin resistance significantly reduces these responses, resulting in pathological conditions, such as obesity and type 2 diabetes mellitus (T2DM). The management of insulin resistance requires better knowledge of its pathophysiological mechanisms to prevent secondary complications, such as cardiovascular diseases (CVDs). Recent evidence regarding the etiological mechanisms behind insulin resistance emphasizes the role of energy imbalance and neurohormonal dysregulation, both of which are closely regulated by autophagy. Autophagy is a conserved process that maintains homeostasis in cells. Accordingly, autophagy abnormalities have been linked to a variety of metabolic disorders, including insulin resistance, T2DM, obesity, and CVDs. Thus, there may be a link between autophagy and insulin resistance. Therefore, the interaction between autophagy and insulin function will be examined in this review, particularly in insulin-responsive tissues, such as adipose tissue, liver, and skeletal muscle.

Voluntary wheel running mitigates disease in an Orai1 gain-of-function mouse model of tubular aggregate myopathy

Tubular aggregate myopathy (TAM) is an inherited skeletal muscle disease associated with progressive muscle weakness, cramps, and myalgia. Tubular aggregates (TAs) are regular arrays of highly ordered and densely packed SR straight-tubes in muscle biopsies; the extensive presence of TAs represent a key histopathological hallmark of this disease in TAM patients. TAM is caused by gain-of-function mutations in proteins that coordinate store-operated Ca2+ entry (SOCE): STIM1 Ca2+ sensor proteins in the sarcoplasmic reticulum (SR) and Ca2+-permeable ORAI1 channels in the surface membrane. We have previously shown that voluntary wheel running (VWR) prevents formation of TAs in aging mice. Here, we assessed the therapeutic potential of endurance exercise (in the form of VWR) in mitigating the functional and structural alterations in a knock-in mouse model of TAM (Orai1G100S/+ or GS mice) based on a gain-of-function mutation in the ORAI1 pore. WT and GS mice were singly-housed for six months (from two to eight months of age) with either free-spinning or locked low profile wheels. Six months of VWR exercise significantly increased soleus peak tetanic specific force production, normalized FDB fiber Ca2+ store content, and markedly reduced TAs in EDL muscle from GS mice. Six months of VWR exercise normalized the expression of mitochondrial proteins found to be altered in soleus muscle of sedentary GS mice in conjunction with a signature of increased protein translation and biosynthetic processes. Parallel proteomic analyses of EDL muscles from sedentary WT and GS mice revealed changes in a tight network of pathways involved in formation of supramolecular complexes, which were also normalized following six months of VWR. In summary, sustained voluntary endurance exercise improved slow twitch muscle function, reduced the presence of TAs in fast twitch muscle, and normalized the muscle proteome of GS mice consistent with protective adaptions in proteostasis, mitochondrial structure/function, and formation of supramolecular complexes.

Mitochondrial dysfunction and skeletal muscle atrophy: Causes, mechanisms, and treatment strategies

Skeletal muscle, which accounts for approximately 40% of total body weight, is one of the most dynamic and plastic tissues in the human body and plays a vital role in movement, posture and force production. More than just a component of the locomotor system, skeletal muscle functions as an endocrine organ capable of producing and secreting hundreds of bioactive molecules. Therefore, maintaining healthy skeletal muscles is crucial for supporting overall body health. Various pathological conditions, such as prolonged immobilization, cachexia, aging, drug-induced toxicity, and cardiovascular diseases (CVDs), can disrupt the balance between muscle protein synthesis and degradation, leading to skeletal muscle atrophy. Mitochondrial dysfunction is a major contributing mechanism to skeletal muscle atrophy, as it plays crucial roles in various biological processes, including energy production, metabolic flexibility, maintenance of redox homeostasis, and regulation of apoptosis. In this review, we critically examine recent knowledge regarding the causes of muscle atrophy (disuse, cachexia, aging, etc.) and its contribution to CVDs. Additionally, we highlight the mitochondrial signaling pathways involvement to skeletal muscle atrophy, such as the ubiquitin-proteasome system, autophagy and mitophagy, mitochondrial fission-fusion, and mitochondrial biogenesis. Furthermore, we discuss current strategies, including exercise, mitochondria-targeted antioxidants, in vivo transfection of PGC-1α, and the potential use of mitochondrial transplantation as a possible therapeutic approach.

Mitochondrial Properties in Skeletal Muscle Fiber

Mitochondria are the primary source of energy production and are implicated in a wide range of biological processes in most eukaryotic cells. Skeletal muscle heavily relies on mitochondria for energy supplements. In addition to being a powerhouse, mitochondria evoke many functions in skeletal muscle, including regulating calcium and reactive oxygen species levels. A healthy mitochondria population is necessary for the preservation of skeletal muscle homeostasis, while mitochondria dysregulation is linked to numerous myopathies. In this review, we summarize the recent studies on mitochondria function and quality control in skeletal muscle, focusing mainly on in vivo studies of rodents and human subjects. With an emphasis on the interplay between mitochondrial functions concerning the muscle fiber type-specific phenotypes, we also discuss the effect of aging and exercise on the remodeling of skeletal muscle and mitochondria properties.

A Combination of Soy Isoflavone and L-Carnitine Improves Running Endurance in Mice

The present study aimed to investigate the effect of APIC, a mixture containing soy isoflavone and L-carnitine on running endurance. Male C57BL/6 mice were orally administered APIC for 8 weeks. The APIC group exhibited a significant increase in treadmill running time until exhaustion compared to the control group. The respiratory exchange ratio in the APIC group was lower, indicating an enhancement in fatty acid oxidative metabolism. Furthermore, APIC supplementation increased the proportion of oxidative myofibers. Biochemical parameters associated with endurance capacity were also affected by APIC, as evidenced by increased muscle ATP levels and decreased levels of muscle triglycerides and blood lactate. qPCR and immunoblot analysis of C2C12 myotubes and gastrocnemius muscles indicated that APIC treatment stimulated AMPK signaling, mitochondrial biogenesis, and fatty acid metabolism. Additionally, treatment with APIC led to an increased oxygen consumption rate in C2C12 myotubes. Collectively, these findings suggest that APIC supplementation enhances mitochondrial biogenesis, promotes a switch from glycolytic to oxidative fiber types, and improves fatty acid metabolism through the activation of the AMPK signaling pathway in murine skeletal muscle. Ultimately, these effects contribute to the enhancement of running endurance.

Thyroid Hormone Regulates the Lipid Content of Muscle Fibers, Thus Affecting Physical Exercise Performance

Skeletal muscle (SkM) lipid composition plays an essential role in physiological muscle maintenance and exercise performance. Thyroid hormones (THs) regulate muscle formation and fuel energy utilization by modulating carbohydrates and lipid and protein metabolism. The best-known effects of THs in SkM include the promotion of mitochondrial biogenesis, the fiber-type switch from oxidative to glycolytic fibers, and enhanced angiogenesis. To assess the role of THs on the lipidic composition of SkM fibers, we performed lipidomic analyses of SkM cells and tissues, glucose tolerance experiments, and exercise performance tests. Our data demonstrated that TH treatment induces remodeling of the lipid profile and changes the proportion of fatty acids in SkM. In brief, THs significantly reduced the ratio of stearic/oleic acid in the muscle similar to what is induced by physical activity. The increased proportion of unsaturated fatty acids was linked to an improvement in insulin sensitivity and endurance exercise. These findings point to THs as critical endocrine factors affecting exercise performance and indicate that homeostatic maintenance of TH signals, by improving cell permeability and receptor stability at the cell membrane, is crucial for muscle physiology.

Endurance Exercise-Induced Fgf21 Promotes Skeletal Muscle Fiber Conversion through TGF-β1 and p38 MAPK Signaling Pathway

Fgf21 has been identified as playing a regulatory role in muscle growth and function. Although the mechanisms through which endurance training regulates skeletal muscle have been widely studied, the contribution of Fgf21 remains poorly understood. Here, muscle size and function were measured, and markers of fiber type were evaluated using immunohistochemistry, immunoblots, or qPCR in endurance-exercise-trained wild-type and Fgf21 KO mice. We also investigated Fgf21-induced fiber conversion in C2C12 cells, which were incubated with lentivirus and/or pathway inhibitors. We found that endurance exercise training enhanced the Fgf21 levels of liver and GAS muscle and exercise capacity and decreased the distribution of skeletal muscle fiber size, and fast-twitch fibers were observed converting to slow-twitch fibers in the GAS muscle of mice. Fgf21 promoted the markers of fiber-type transition and eMyHC-positive myotubes by inhibiting the TGF-β1 signaling axis and activating the p38 MAPK signaling pathway without apparent crosstalk. Our findings suggest that the transformation and function of skeletal muscle fiber types in response to endurance training could be mediated by Fgf21 and its downstream signaling pathways. Our results illuminate the mechanisms of Fgf21 in endurance-exercise-induced fiber-type conversion and suggest a potential use of Fgf21 in improving muscle health and combating fatigue.

Muscle Architecture Adaptations to Static Stretching Training: A Systematic Review with Meta-Analysis

BACKGROUND

Long-term stretching of human skeletal muscles increases joint range of motion through altered stretch perception and decreased resistance to stretch. There is also some evidence that stretching induces changes in muscle morphology. However, research is limited and inconclusive.

OBJECTIVE

To examine the effect of static stretching training on muscle architecture (i.e., fascicle length and fascicle angle, muscle thickness and cross-sectional area) in healthy participants.

DESIGN

Systematic review and meta-analysis.

METHODS

PubMed Central, Web of Science, Scopus, and SPORTDiscus were searched. Randomized controlled trials and controlled trials without randomization were included. No restrictions on language or date of publication were applied. Risk of bias was assessed using Cochrane RoB2 and ROBINS-I tools. Subgroup analyses and random-effects meta-regressions were also performed using total stretching volume and intensity as covariates. Quality of evidence was determined by GRADE analysis.

RESULTS

From the 2946 records retrieved, 19 studies were included in the systematic review and meta-analysis (n = 467 participants). Risk of bias was low in 83.9% of all criteria. Confidence in cumulative evidence was high. Stretching training induces trivial increases in fascicle length at rest (SMD = 0.17; 95% CI 0.01-0.33; p = 0.042) and small increases in fascicle length during stretching (SMD = 0.39; 95% CI 0.05 to 0.74; p = 0.026). No increases were observed in fascicle angle or muscle thickness (p = 0.30 and p = 0.18, respectively). Subgroup analyses showed that fascicle length increased when high stretching volumes were used (p < 0.004), while no changes were found for low stretching volumes (p = 0.60; subgroup difference: p = 0.025). High stretching intensities induced fascicle length increases (p < 0.006), while low stretching intensities did not have an effect (p = 0.72; subgroup difference: p = 0.042). Also, high intensity stretching resulted in increased muscle thickness (p = 0.021). Meta-regression analyses showed that longitudinal fascicle growth was positively associated with stretching volume (p < 0.02) and intensity (p < 0.04).

CONCLUSIONS

Static stretching training increases fascicle length at rest and during stretching in healthy participants. High, but not low, stretching volumes and intensities induce longitudinal fascicle growth, while high stretching intensities result in increased muscle thickness.

REGISTRATION

PROSPERO, registration number: CRD42021289884.

Exercise improves homeostasis of the intestinal epithelium by activation of apelin receptor-AMP-activated protein kinase signalling

Intestinal remodelling is dynamically regulated by energy metabolism. Exercise is beneficial for gut health, but the specific mechanisms remain poorly understood. Intestine-specific apelin receptor (APJ) knockdown (KD) and wild-type male mice were randomly divided into two subgroups, with/without exercise, to obtain four groups: WT, WT with exercise, APJ KD and APJ KD with exercise. Animals in the exercise groups were subjected to daily treadmill exercise for 3 weeks. Duodenum was collected at 48 h after the last bout of exercise. AMP-activated protein kinase (AMPK) α1 KD and wild-type mice were also utilized for investigating the mediatory role of AMPK on exercise-induced duodenal epithelial development. AMPK and peroxisome proliferator-activated receptor γ coactivator-1 α were upregulated by exercise via APJ activation in the intestinal duodenum. Correspondingly, exercise induced permissive histone modifications in the PR domain containing 16 (PRDM16) promoter to activate its expression, which was dependent on APJ activation. In agreement, exercise elevated the expression of mitochondrial oxidative markers. The expression of intestinal epithelial markers was downregulated due to AMPK deficiency, and AMPK signalling facilitated epithelial renewal. These data demonstrate that exercise-induced activation of the APJ-AMPK axis facilitates the homeostasis of the intestinal duodenal epithelium. KEY POINTS: Apelin receptor (APJ) signalling is required for improved epithelial homeostasis of the small intestine in response to exercise. Exercise intervention activates PRDM16 through inducing histone modifications, enhanced mitochondrial biogenesis and fatty acid metabolism in duodenum. The morphological development of duodenal villus and crypt is enhanced by the muscle-derived exerkine apelin through the APJ-AMP-activated protein kinase axis.

Dynamic of irisin secretion change after moderate-intensity chronic physical exercise on obese female

OBJECTIVES

Exercise is one of the beneficial mediators for the regulation and prevention of obesity through the role of irisin, so it potentially enhances metabolism health. This study aims to investigate the dynamic of irisin secrecy change after chronic exercise in obese females.

METHODS

Thirty-one female adolescents aged 20-22 years enrolled in the study and were given interventions aerobic, resistance, and a combination of aerobic and resistance training. The exercises were performed at moderate-intensity, for 35-40 min per session, and three times a week for four weeks. The measurement of irisin level, IGF-1 level, and bio-anthropometry was carried out before and after the four weeks of exercise. The bio-anthropometry measurement was carried out using seca mBCA 514, while the measurement of insulin-like growth factor 1 (IGF-1) and irisin was completed using an enzyme-linked immunosorbent assay (ELISA). The obtained data were analyzed using a one-way ANOVA test with 5 % significance.

RESULTS

Our results indicated higher dynamic of irisin and IGF-1 increases in the group with a combination of aerobic and resistance training exercises than the other two groups with a different exercise. Further, we also observed different dynamics of irisin and IGF-1 level increase (p<0.05). Besides, the irisin was also correlated with the IGF-1 and bio-anthropometric parameters (p<0.05).

CONCLUSIONS

The combination of aerobic and resistance training exercises is considered as the alternative for enhancing the dynamic of irisin and IGF-1 increase. Thus, it can be used to prevent and regulate obesity.

Cadmium exposure impairs skeletal muscle function by altering lipid signature and inducing inflammation in C57BL/6J mice

Cadmium (Cd) is a well-known environmental pollutant with high toxicity. Despite a variety of studies have demonstrated that Cd exposure induces multiple organ damages in humans, there is still a lack of knowledge of Cd induced skeletal muscle impairment. Exercise is a non-invasive, effective intervention to improve human health and combat diseases. In this study, we aimed to evaluate the toxic effects of Cd exposure on skeletal muscle function and explore the possibility of exercise for attenuating skeletal muscle toxicity of chronic Cd exposure. C57BL/6J mice were exposed to Cd via drinking water containing CdCl₂ 10 mg/dL for 8 weeks while a moderate exercise was daily induced by a motorized treadmill to mice. It was found that Cd exposure significantly reduced the ratio of gastrocnemius and body weight, decreased mouse exercise capacity, weakened muscle strength, promoted lipid accumulation and up-regulated pro-apoptotic genes in the skeletal muscle. Non-targeted lipidomics analysis indicated that Cd exposure disturbed lipid metabolism, altered lipid signatures and elevated pro-inflammatory lipid species in the skeletal muscle. Moreover, Cd exposure evoked an intense inflammatory response in the skeletal muscle by up-regulating pro-inflammatory cytokine production such as Eotaxin (CCL11), TNF-α, IL-1β, IL-6, RANTES (CCL5) and so on. Notably, treadmill exercise effectively protected against Cd induced skeletal muscle impairment indicated by the effects of inhibiting lipid metabolism disturbance, suppressing pro-inflammatory cytokine production and preserving skeletal muscle function. These results demonstrated that environment relevant Cd exposure impairs skeletal muscle function and exercise effectively antagonizes the Cd toxicity in the skeletal muscle and preserves skeletal muscle function. This study provided the novel evidence for unraveling Cd toxicity on the skeletal muscle function and highlighted the possibility of considering exercise as a countermeasure for Cd induced skeletal muscle impairment at population level.

The Potential Modulatory Effects of Exercise on Skeletal Muscle Redox Status in Chronic Kidney Disease

Chronic Kidney Disease (CKD) is a global health burden with high mortality and health costs. CKD patients exhibit lower cardiorespiratory and muscular fitness, strongly associated with morbidity/mortality, which is exacerbated when they reach the need for renal replacement therapies (RRT). Muscle wasting in CKD has been associated with an inflammatory/oxidative status affecting the resident cells' microenvironment, decreasing repair capacity and leading to atrophy. Exercise may help counteracting such effects; however, the molecular mechanisms remain uncertain. Thus, trying to pinpoint and understand these mechanisms is of particular interest. This review will start with a general background about myogenesis, followed by an overview of the impact of redox imbalance as a mechanism of muscle wasting in CKD, with focus on the modulatory effect of exercise on the skeletal muscle microenvironment.

Cholesterol: An Important Determinant of Muscle Atrophy in Astronauts

Since cholesterol is not routinely measured in astronauts before and after their return from space, there is no data on the role of blood cholesterol level in muscle atrophy and microgravity. Since the first moon landing, aerospace medicine became outdated and has not pushed boundaries like its rocket engineering counterpart. Since the 2019 astronaut twin study, there has yet to be another scientific breakthrough for aerospace medicine. Microgravity-induced muscle atrophy is the most known consequence of spaceflight. Yet, so far, there is no therapeutic solution to prevent it or any real efforts in understanding it on a cellular or molecular level. The most obvious reason to this unprecedented level of research is due to the small cohort of astronauts. With the establishment of private space industries and exponential recruitment of astronauts, there is more reason to push forward spaceflight-related health guidelines and ensure the safety of the brave humans who risk their lives for the progression of mankind. Spaceflight is considered the most challenging job and the failure to prevent injury or harm should be considered reckless negligence by the institutions that actively prevented sophistication of aerospace medicine. In this critical review, role of cholesterol is analyzed across the NASA-established parameters of microgravity-induced muscle atrophy with a focus on potential therapeutic targets for research.

Specification of skeletal muscle fiber-type is determined by the calcineurin/NFATc1 signaling pathway during muscle regeneration

Skeletal muscle fiber type specification is changeable during muscle regeneration following cardiotoxin (CTX) injection; however, the mechanism of muscle fiber shift in regenerating muscle fibers remains unclear. Furthermore, it is unclear as to which factors determine skeletal muscle fiber types in regenerating muscle fibers. Previous studies showed that CTX-induced muscle damage resulted in a temporary hypoxic condition, indicating that hypoxia-inducible factor (HIF)-1α may be involved in muscle fiber type transition. Stabilization of HIF-1α has been shown to result in muscle fiber type transition toward slow-twitch phenotype through the calcineurin/nuclear factor activated T cell 1 (NFATc1) signaling pathway. Therefore, the aim of the present study was to determine whether the calcineurin/NFATc1 pathway is a key mediator of skeletal muscle fiber type transition during muscle regeneration. We found that CTX-induced muscle damage resulted in transient ischemia and HIF-1α expression in skeletal muscle. Additionally, it shifted the muscle fiber type proportion toward a slow-twitch phenotype in the soleus muscle (37.5% in the control muscle vs. 61.3% in the damaged muscle; p < 0.01) three weeks after muscle damage. Moreover, the NFATc1 protein levels increased in damaged muscle, and blockage of the calcineurin/NFATc1 signaling pathway by tacrolimus (FK-506) treatment substantially decreased the number of slow-twitch muscle fibers in the soleus muscle. This study demonstrated that CTX-induced muscle injury results in transient ischemia in hind limb muscle and stabilizes HIF-1α. Moreover, muscle damage increased oxidative phenotype muscle fibers through the calcineurin/NFATc1 signaling pathway during muscle regeneration.

Does resistance exercise lifting velocity change with different rest intervals?

BACKGROUND

In this study, we examined the sex difference of the effect of rest intervals on lifting velocity during resistance exercise.

METHODS

Twenty-two trained subjects (11 men and 11 women) were included. Each protocol consisted of 3 sets of 10 repetitions at 70% of 1- repetition maximum (1RM) with rest intervals of 90 s (R90), 150 s (R150), and 240 s (R240) in a crossover design. The exercise did parallel squats with free weights. The measurement items are lifting velocity (mean velocity) in each repetition and blood lactate concentration after exercise.

RESULTS

There was a significant interaction between changes in the average velocity of 10 repetition in each set (AV<inf>10rep</inf>) and sex in each protocol, indicating that AV<inf>10rep</inf> during squat exercise has decreased in men but not in women in each protocol (P=0.002-0.03).

CONCLUSIONS

Our results suggested that short rest intervals will not recover lifting velocity between short rest intervals until the next set at men, while women will be able to recover even with short rest intervals.

Endogenous and Exogenous Antioxidants in Skeletal Muscle Fatigue Development during Exercise

Muscle fatigue is defined as a decrease in maximal force or power generated in response to contractile activity, and it is a risk factor for the development of musculoskeletal injuries. One of the many stressors imposed on skeletal muscle through exercise is the increased production of reactive oxygen species (ROS) and reactive nitrogen species (RNS), which intensifies as a function of exercise intensity and duration. Exposure to ROS/RNS can affect Na⁺/K⁺-ATPase activity, intramyofibrillar calcium turnover and sensitivity, and actin-myosin kinetics to reduce muscle force production. On the other hand, low ROS/RNS concentrations can likely upregulate an array of cellular adaptative responses related to mitochondrial biogenesis, glucose transport and muscle hypertrophy. Consequently, growing evidence suggests that exogenous antioxidant supplementation might hamper exercise-engendering upregulation in the signaling pathways of mitogen-activated protein kinases (MAPKs), peroxisome-proliferator activated co-activator 1α (PGC-1α), or mammalian target of rapamycin (mTOR). Ultimately, both high (exercise-induced) and low (antioxidant intervention) ROS concentrations can trigger beneficial responses as long as they do not override the threshold range for redox balance. The mechanisms underlying the two faces of ROS/RNS in exercise, as well as the role of antioxidants in muscle fatigue, are presented in detail in this review.

High-intensity circuit training change serum myostatin but not myogenin in adolescents' soccer players: a quasi-experimental study

BACKGROUND

Skeletal muscle contractions due to exercise lead to the secretion of many proteins and proteoglycan peptides called myokines. Myostatin (MSTN) and Myogenin (MyoG) are two of the most important skeletal muscle growth regulatory factors related to myoblast differentiation and muscle hypertrophy. The present study aims at investigating the effects over eight weeks of high-intensity circuit training (HICT) on serum MyoG and MSTN in male soccer players.

METHOD

The present study is a quasi-experimental study on 21 male soccer players (Experimental group: n = 11, Control group: n = 10) (ages 15.0 ± 3.4 years, body mass 55.7 ± 7.8 kg, height 173.3 ± 8.0 cm, Body mass index 18.4 ± 1.9 kg m^-2, maximum oxygen uptake 61.89 ± 3.01 ml kg^-1 and the peak height velocity 14.5 ± 0.3 years). Participants were randomly divided into two groups: training group and a control group. The first resting blood samples were obtained in the morning-fasting state, and the second blood samples were obtained after the maximum aerobic test at pre- and post-HICT.

RESULTS

There were non-significant differences in resting serum values of MyoG (p = 0.309, p > 0.05) but significant differences in resting serum values of MSTN between the training and control groups after eight weeks of HICT (p = 0.003, p < 0.05). No significant differences were observed between groups in the acute response of serum values of MyoG (p = 0.413, p < 0.05) and MSTN (p = 0.465, p < 0.05) to the maximum aerobic test after eight weeks of HICT.

CONCLUSION

These results suggest that eight weeks of HICT can decrease the resting serum values of MSTN but not change the resting serum values of MyoG in male adolescent soccer players. Also, eight weeks of HICT does not affect the acute response of MSTN and MyoG after a maximum aerobic test.

Cutting edge concepts: Does bilirubin enhance exercise performance?

Exercise performance is dependent on many factors, such as muscular strength and endurance, cardiovascular capacity, liver health, and metabolic flexibility. Recent studies show that plasma levels of bilirubin, which has classically been viewed as a liver dysfunction biomarker, are elevated by exercise training and that elite athletes may have significantly higher levels. Other studies have shown higher plasma bilirubin levels in athletes and active individuals compared to general, sedentary populations. The reason for these adaptions is unclear, but it could be related to bilirubin's antioxidant properties in response to a large number of reactive oxygen species (ROS) that originates from mitochondria during exercise. However, the mechanisms of these are unknown. Current research has re-defined bilirubin as a metabolic hormone that interacts with nuclear receptors to drive gene transcription, which reduces body weight. Bilirubin has been shown to reduce adiposity and improve the cardiovascular system, which might be related to the adaption of bilirubin increasing during exercise. No studies have directly tested if elevating bilirubin levels can influence athletic performance. However, based on the mechanisms proposed in the present review, this seems plausible and an area to consider for future studies. Here, we discuss the importance of bilirubin and exercise and how the combination might improve metabolic health outcomes and possibly athletic performance.

Bavachin and Corylifol A Improve Muscle Atrophy by Enhancing Mitochondria Quality Control in Type 2 Diabetic Mice

Type 2 diabetes reduces muscle mass and function. Chronic inflammation and mitochondrial dysfunction play critical roles in muscle atrophy pathogenesis. Here, we investigated the effects of bavachin and corylifol A from Psoralea corylifolia L. seeds on muscle atrophy in dexamethasone-treated mice and in db/db mice. Bavachin and corylifol A enhanced muscle strength and muscle mass in dexamethasone-treated mice. In diabetic mice, they enhanced muscle strength and cross-sectional areas. Bavachin and corylifol A suppressed inflammatory cytokine (interleukin-6 and tumor necrosis factor-α) expression levels by downregulating nuclear factor-κB phosphorylation. They decreased the muscle atrophic factor (myostatin, atrogin-1, and muscle RING finger-1) expression levels. They activated the AKT synthetic signaling pathway and induced a switch from fast-type glycolytic fibers (type 2B) to slow-type oxidative fibers (types I and 2A). They increased mitochondrial biogenesis and dynamic factor (optic atrophy-1, mitofusin-1/2, fission, mitochondrial 1, and dynamin 1-like) expression levels via the AMP-activated protein kinase-peroxisome proliferator-activated receptor gamma coactivator 1-alpha signaling pathway. They also improved mitochondrial quality by upregulating the mitophagy factor (p62, parkin, PTEN-induced kinase-1, and BCL2-interacting protein-3) expression levels. Therefore, bavachin and corylifol A exert potential therapeutic effects on muscle atrophy by suppressing inflammation and improving mitochondrial function.

Yunpi Heluo decoction reduces ectopic deposition of lipids by regulating the SIRT1-FoxO1 autophagy pathway in diabetic rats

CONTEXT

Yunpi Heluo (YPHL) decoction is a Chinese herbal formula with particular advantages for treating type 2 diabetes. Yet, its exact mechanism of action is not fully understood.

OBJECTIVE

To examine the therapeutic effect of YPHL on ectopic lipid deposition (EDL) in Zucker diabetic fatty (ZDF) rats and the underlying mechanism.

MATERIALS AND METHODS

The ZDF Rats were randomized into five groups, including model, YPHL (200 mg/kg/d for 10 weeks), SIRT1-overexpression (injected with HBAAV2/9-r-SIRT1-3'-flag-GFP), NC (injected with HBAAV2/9-CMV-GFP as blank control) and control group. Pancreatic β-cells obtained from high-lipid-high-glucose fed rats were treated with YPHL (10 mg/mL) for 48 h. Lipid deposition and autophagosomes were analyzed by transmission electron microscopy. Intracellular H₂O₂ and ROS concentrations were measured by flow cytometry. SIRT1, FOXO1, LC3 and P62 mRNA and protein levels were analyzed using qRT-PCR and Western blots.

RESULTS

Compared with the model group, blood glucose levels in YPHL and si-SIRT1 groups were reduced by 19.3% and 27.9%, respectively. In high-lipid-high-glucose cells treated with YPHL, lipid droplets were reduced and decrease in apoptosis rate (38.6%), H₂O₂ (31.2%) and ROS (44.5%) levels were observed. After YPHL intervention or SIRT1 overexpression, LC3 and p62 expression increased. Protein expression of SIRT1 and LC3 in model, si-SIRT1, si-NC and si-SIRT1 + YPHL groups was lower than those in control group, while FoxO1 expression was increased. All of these protein level alterations were reversed in the si-NC + YPHL group.

DISCUSSION AND CONCLUSIONS

YPHL reduced EDL by regulating the SIRT1-FoxO1 autophagy pathway in diabetic rats, which could lead to future perspectives for the treatment of diabetes.

Limonium tetragonum Promotes Running Endurance in Mice through Mitochondrial Biogenesis and Oxidative Fiber Formation

The purpose of this study was to examine whether Limonium tetragonum, cultivated in a smart-farming system with LED lamps, could increase exercise capacity in mice. C57BL/6 male mice were orally administered vehicle or Limonium tetragonum water extract (LTE), either 30 or 100 mg/kg, and were subjected to moderate intensity treadmill exercise for 4 weeks. Running distance markedly increased in the LTE group (100 mg/kg) by 80 ± 4% compared to the vehicle group, which was accompanied by a higher proportion of oxidative fibers (6 ± 6% vs. 10 ± 4%). Mitochondrial DNA content and gene expressions related to mitochondrial biogenesis were significantly increased in LTE-supplemented gastrocnemius muscles. At the molecular level, the expression of PGC-1α, a master regulator of fast-to-slow fiber-type transition, was increased downstream of the PKA/CREB signaling pathway. LTE induction of the PKA/CREB signaling pathway was also observed in C2C12 cells, which was effectively suppressed by PKA inhibitors H89 and Rp-cAMP. Altogether, these findings indicate that LTE treatment enhanced endurance exercise capacity via an improvement in mitochondrial biosynthesis and the increases in the formation of oxidative slow-twitch fibers. Future study is warranted to validate the exercise-enhancing effect of LTE in the human.

SESN2 prevents the slow-to-fast myofiber shift in denervated atrophy via AMPK/PGC-1α pathway

BACKGROUND

Sestrin2 (SESN2), a stress-inducible protein, has been reported to protect against denervated muscle atrophy through unfolded protein response and mitophagy, while its role in myofiber type transition remains unknown.

METHODS

A mouse sciatic nerve transection model was created to evaluate denervated muscle atrophy. Myofiber type transition was confirmed by western blot, fluorescence staining, ATP quantification, and metabolic enzyme activity analysis. Adeno-associated virus (AAV) was adopted to achieve SESN2 knockdown and overexpression in gastrocnemius. AMPK/PGC-1α signal was detected by western blot and activated with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR). C2C12 myotubes with rotenone treatment were adopted for in vitro experiments.

RESULTS

SESN2 was found to be upregulated in denervated skeletal muscles and rotenone-treated C2C12 cells. Knockdown of SESN2 aggravated muscle atrophy and accelerated myofiber type transition from slow-twitch to fast-twitch. Moreover, AMPK/PGC-1α signaling was proven to be activated by SESN2 after denervation, which further induced the expression of hypoxia-inducible factor HIF2α. Exogenous activation of AMPK/PGC-1α signaling could counteract the addition of slow-to-fast myofiber shift caused by SESN2 knockdown and lead to the retainment of muscle mass after denervation.

CONCLUSION

Collectively, the present study indicates that SESN2 prevents myofiber type transition from slow-twitch to fast-twitch and preserves muscle mass in denervated atrophy via AMPK/PGC-1α signaling. These findings contribute to a better understanding of the pathogenesis of muscle atrophy and provide novel insights into the role of SESN2 in myofiber type transition.

Insight Into the Metabolic Adaptations of Electrically Pulse-Stimulated Human Myotubes Using Global Analysis of the Transcriptome and Proteome

Electrical pulse stimulation (EPS) has proven to be a useful tool to interrogate cell-specific responses to muscle contraction. In the present study, we aimed to uncover networks of signaling pathways and regulatory molecules responsible for the metabolic effects of exercise in human skeletal muscle cells exposed to chronic EPS. Differentiated myotubes from young male subjects were exposed to EPS protocol 1 (i.e. 2 ms, 10 V, and 0.1 Hz for 24 h), whereas myotubes from middle-aged women and men were exposed to protocol 2 (i.e. 2 ms, 30 V, and 1 Hz for 48 h). Fuel handling as well as the transcriptome, cellular proteome, and secreted proteins of EPS-treated myotubes from young male subjects were analyzed using a combination of high-throughput RNA sequencing, high-resolution liquid chromatography-tandem mass spectrometry, oxidation assay, and immunoblotting. The data showed that oxidative metabolism was enhanced in EPS-exposed myotubes from young male subjects. Moreover, a total of 81 differentially regulated proteins and 952 differentially expressed genes (DEGs) were observed in these cells after EPS protocol 1. We also found 61 overlapping genes while comparing the DEGs to mRNA expression in myotubes from the middle-aged group exposed to protocol 2, assessed by microarray. Gene ontology (GO) analysis indicated that significantly regulated proteins and genes were enriched in biological processes related to glycolytic pathways, positive regulation of fatty acid oxidation, and oxidative phosphorylation, as well as muscle contraction, autophagy/mitophagy, and oxidative stress. Additionally, proteomic identification of secreted proteins revealed extracellular levels of 137 proteins were changed in myotubes from young male subjects exposed to EPS protocol 1. Selected putative myokines were measured using ELISA or multiplex assay to validate the results. Collectively, our data provides new insight into the transcriptome, proteome and secreted proteins alterations following in vitro exercise and is a valuable resource for understanding the molecular mechanisms and regulatory molecules mediating the beneficial metabolic effects of exercise.

Ranolazine Counteracts Strength Impairment and Oxidative Stress in Aged Sarcopenic Mice

Sarcopenia is defined as the loss of muscle mass associated with reduced strength leading to poor quality of life in elderly people. The decline of skeletal muscle performance is characterized by bioenergetic impairment and severe oxidative stress, and does not always strictly correlate with muscle mass loss. We chose to investigate the ability of the metabolic modulator Ranolazine to counteract skeletal muscle dysfunctions that occur with aging. For this purpose, we treated aged C57BL/6 mice with Ranolazine/vehicle for 14 days and collected the tibialis anterior and gastrocnemius muscles for histological and gene expression analyses, respectively. We found that Ranolazine treatment significantly increased the muscle strength of aged mice. At the histological level, we found an increase in centrally nucleated fibers associated with an up-regulation of genes encoding MyoD, Periostin and Osteopontin, thus suggesting a remodeling of the muscle even in the absence of physical exercise. Notably, these beneficial effects of Ranolazine were also accompanied by an up-regulation of antioxidant and mitochondrial genes as well as of NADH-dehydrogenase activity, together with a more efficient protection from oxidative damage in the skeletal muscle. These data indicate that the protection of muscle from oxidative stress by Ranolazine might represent a valuable approach to increase skeletal muscle strength in elderly populations.

Characterization of Redox Environment and Tryptophan Catabolism through Kynurenine Pathway in Military Divers’ and Swimmers’ Serum Samples

Endurance and resistance exercises, alone or in combination, induce metabolic changes that affect tryptophan (Trp) catabolism. The kynurenine pathway (KP) is the main route of Trp degradation, and it is modulated by the inflammatory and redox environments. Previous studies have shown that KP metabolites work as myokines that mediate the positive systemic effects related to exercise. However, it is poorly understood how different exercise modalities and intensities impact the KP. The aim of this study was to characterize the effect of two different exercise modalities, military diving and swimming, on the KP and the redox environment. A total of 34 healthy men from the Mexican Navy were included in the study, 20 divers and 14 swimmers, who started and stayed in military training consistently during the six months of the study; 12 Mexican men without fitness training were used as the control group. Physical fitness was determined at the beginning and after 6 months of training; criteria included body composition; serum levels of Trp, kynurenine (KYN), kynurenic acid (KYNA) and 3-hydroxykynurenine (3-HK); the glutathione ratio (GSH/GSSG); and malondialdehyde (MDA).. Results showed a significant loss of body fat in both the diver and swimmer groups. Compared with the control group, divers showed a decrease in Trp and 3-HK levels, but no changes were observed in the KYN/Trp, KYNA/Trp or 3-HK/Trp ratios, while swimmers showed a decrease in KYN levels and an increase in the KYNA and 3-HK levels. Additionally, divers showed a decrease in the GSH/GSSG ratio and an increase in MDA levels, in contrast to the swimmers, who showed a decrease in MDA levels and an increase in GSH/GSSG levels. Our findings suggest a differential shift in the KP and redox environment induced by diving and swimming. Swimming promotes an antioxidant environment and a peripheral overactivation of the KP.

Activation of AMPK/miR-181b Axis Alleviates Endothelial Dysfunction and Vascular Inflammation in Diabetic Mice

Hyperglycemia in diabetes mellitus impairs endothelial function and disrupts microRNA (miRNA) profiles in vasculature, increasing the risk of diabetes-associated complications, including coronary artery disease, diabetic retinopathy, and diabetic nephropathy. miR-181b was previously reported to be an anti-inflammatory mediator in vasculature against atherosclerosis. The current study aimed to investigate whether miR-181b ameliorates diabetes-associated endothelial dysfunction, and to identify potential molecular mechanisms and upstream inducer of miR-181b. We found that miR-181b level was decreased in renal arteries of diabetic patients and in advanced glycation end products (AGEs)-treated renal arteries of non-diabetic patients. Transfection of miR-181b mimics improved endothelium-dependent vasodilation in aortas of high fat diet (HFD)/streptozotocin (STZ)-induced diabetic mice, accompanied by suppression of superoxide overproduction and vascular inflammation markers. AMPK activator-induced AMPK activation upregulated miR-181b level in human umbilical vein endothelial cells (HUVECs). Chronic exercise, potentially through increased blood flow, activated AMPK/miR-181b axis in aortas of diabetic mice. Exposure to laminar shear stress upregulated miR-181b expression in HUVECs. Overall, our findings highlight a critical role of AMPK/miR-181b axis and extend the benefits of chronic exercise in counteracting diabetes-associated endothelial dysfunction.

Endurance exercise attenuates juvenile irradiation-induced skeletal muscle functional decline and mitochondrial stress

BACKGROUND

Radiotherapy is commonly used to treat childhood cancers and can have adverse effects on muscle function, but the underlying mechanisms have yet to be fully elucidated. We hypothesized that endurance exercise following radiation treatment would improve skeletal muscle function.

METHODS

We utilized the Small Animal Radiation Research Platform (SARRP) to irradiate juvenile male mice with a clinically relevant fractionated dose of 3× (every other day over 5 days) 8.2 Gy X-ray irradiation locally from the knee to footpad region of the right hindlimb. Mice were then singly housed for 1 month in cages equipped with either locked or free-spinning voluntary running wheels. Ex vivo muscle contractile function, RT-qPCR analyses, resting cytosolic and sarcoplasmic reticulum (SR) store Ca2+ levels, mitochondrial reactive oxygen species levels (MitoSOX), and immunohistochemical and biochemical analyses of muscle samples were conducted to assess the muscle pathology and the relative therapeutic impact of voluntary wheel running (VWR).

RESULTS

Irradiation reduced fast-twitch extensor digitorum longus (EDL) muscle-specific force by 27% compared to that of non-irradiated mice, while VWR post-irradiation improved muscle-specific force by 37%. Radiation treatment similarly reduced slow-twitch soleus muscle-specific force by 14% compared to that of non-irradiated mice, while VWR post-irradiation improved specific force by 18%. We assessed intracellular Ca2+ regulation, oxidative stress, and mitochondrial homeostasis as potential mechanisms of radiation-induced pathology and exercise-mediated rescue. We found a significant reduction in resting cytosolic Ca2+ concentration following irradiation in sedentary mice. Intriguingly, however, SR Ca2+ store content was increased in myofibers from irradiated mice post-VWR compared to mice that remained sedentary. We observed a 73% elevation in the overall protein oxidization in muscle post-irradiation, while VWR reduced protein nitrosylation by 35% and mitochondrial reactive oxygen species (ROS) production by 50%. Finally, we found that VWR significantly increased the expression of PGC1α at both the transcript and protein levels, consistent with an exercise-dependent increase in mitochondrial biogenesis.

CONCLUSIONS

Juvenile irradiation stunted muscle development, disrupted proper Ca2+ handling, damaged mitochondria, and increased oxidative and nitrosative stress, paralleling significant deficits in muscle force production. Exercise mitigated aberrant Ca2+ handling, mitochondrial homeostasis, and increased oxidative and nitrosative stress in a manner that correlated with improved skeletal muscle function after radiation.

Positive Aspects of Oxidative Stress at Different Levels of the Human Body: A Review

Oxidative stress is the subject of numerous studies, most of them focusing on the negative effects exerted at both molecular and cellular levels, ignoring the possible benefits of free radicals. More and more people admit to having heard of the term "oxidative stress", but few of them understand the meaning of it. We summarized and analyzed the published literature data in order to emphasize the importance and adaptation mechanisms of basal oxidative stress. This review aims to provide an overview of the mechanisms underlying the positive effects of oxidative stress, highlighting these effects, as well as the risks for the population consuming higher doses than the recommended daily intake of antioxidants. The biological dose-response curve in oxidative stress is unpredictable as reactive species are clearly responsible for cellular degradation, whereas antioxidant therapies can alleviate senescence by maintaining redox balance; nevertheless, excessive doses of the latter can modify the redox balance of the cell, leading to a negative outcome. It can be stated that the presence of oxidative status or oxidative stress is a physiological condition with well-defined roles, yet these have been insufficiently researched and explored. The involvement of reactive oxygen species in the pathophysiology of some associated diseases is well-known and the involvement of antioxidant therapies in the processes of senescence, apoptosis, autophagy, and the maintenance of cellular homeostasis cannot be denied. All data in this review support the idea that oxidative stress is an undesirable phenomenon in high and long-term concentrations, but regular exposure is consistent with the hormetic theory.

Exploratory Systematic Review and Meta-Analysis of Panax Genus Plant Ingestion Evaluation in Exercise Endurance

Background: Many studies that use food containing Panax genus plants (PGPs) have been conducted but most of them have not mentioned the effective compounds ginsenosides and their composition. Therefore, we conducted a systematic review and meta-analysis of time to exhaustion as an index of exercise endurance with ingestion of PGPs or ginsenosides to reveal their effects. Methods: We performed a systematic review with a comprehensive and structured literature search using seven literature databases, four clinical trial databases, and three general web search engines during 15–22 March 2021. A random-effects model was applied to calculate the standardized mean difference (SMD) and 95% confidence interval (CI) as the difference between the mean in the treatment and placebo groups. We evaluated the risk of bias of individual studies along with the risk of bias tool in the Cochrane handbook. This study was funded by Maruzen Pharmaceuticals Co., Ltd. (Hiroshima, Japan). The protocol for this study was registered with the UMIN-CTR (No. UMIN000043341). Results: Five studies met the inclusion criteria. The number of total participants was 90, with 59 in the ingestion-PGPs group and 64 in the control group, because three studies were crossover-design trials. We found that ingestion of PGPs or ginsenosides significantly improved exercise endurance (SMD [95% CI]: 0.58 [0.22–0.95], I² = 0%). It was suggested that ginsenoside Rg₁ (Rg₁) and PGPs extract containing Rg₁ were significantly effective in improving exercise endurance (SMD [95% CI]: 0.70 [0.14–1.27], I² = 30%) by additional analysis. Conclusions: This systematic review suggests that the ingestion of PGPs or ginsenosides, especially Rg₁, is effective in improving exercise endurance in healthy adults. However, further high-quality randomized controlled trials are required because imprecision and publication bias cannot be ignored in this systematic review.

The exercise-instrumental music program and irisin levels in younger non-professional athletes

A passive lifestyle and lack of exercise are triggering factors in increasing metabolic syndrome, whereas metabolic syndrome is associated with increased morbidity and mortality. This study aimed to analyse an exercise-based non-pharmacological approach combined with instrumental music to the plasma levels of irisin. The study employed a randomised pretest-posttest-only group design recruiting 30 male participants. The individuals aged between 19-21 years, body mass index (BMI) 18.5-24.9 kg/m2, normal blood pressure, normal resting heart rate (RHR), VO2max 40-50 ml/kg bodyweight/min, normal haemoglobin (Hb). The subjects were randomly divided into three groups, MIE (n=10, moderate-intensity exercise), MIEM (n=10, moderate-intensity exercise + instrumental music), and HIE (n=10, high-intensity exercise). Blood sampling was collected from pre- and 5 min post-exercise treatment. ELISA method was used to measure the circulating irisin levels. The non-parametric Kruskal-Wallis test, Mann Whitney test and Spearman correlation were chosen to analyse the data. The results showed that there is no significant difference in pre-exercise irisin levels (ng/ml) in MIE (1.58±0.89), MIEM (1.77±3.12), and HIE (1.65±0.88) with a P-value of 0.098. Importantly, the alteration of irisin levels post-exercise program revealed that the level of this peptide (ng/ml) is higher in HIE (7.28±5.11) compared to MIE (1.95±1.85) and MIEM (4.16±3.40) with a P-value of 0.019. The plasma levels of irisin significantly correlate to energy expenditure (r=0.353, P≤0.01), plasma peroxisome proliferator-activated receptor gamma coactivator-1α (r=0.597, P≤0.001), and high-density lipoprotein (r=0.513, P≤0.01). In summary, increased irisin secretion may directly contribute to the gradual alteration of energy expenditure and correlate to physical exercise intensity-related musical treatment.

Comprehensive Transcriptome Profiling of NAFLD- and NASH-Induced Skeletal Muscle Dysfunction

Nonalcoholic fatty liver disease (NAFLD), characterized by extensive triglyceride accumulation in hepatocytes, may progress to nonalcoholic steatohepatitis (NASH) with liver fibrosis and inflammation and increase the risk of cirrhosis, cancer, and death. It has been reported that physical exercise is effective in ameliorating NAFLD and NASH, while skeletal muscle dysfunctions, including lipid deposition and weakness, are accompanied with NAFLD and NASH. However, the molecular characteristics and alterations in skeletal muscle in the progress of NAFLD and NASH remain unclear. In the present study, we provide a comprehensive analysis on the similarity and heterogeneity of quadriceps muscle in NAFLD and NASH mice models by RNA sequencing. Importantly, Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway functional enrichment analysis revealed that NAFLD and NASH led to impaired glucose and lipid metabolism and deteriorated functionality in skeletal muscle. Besides this, we identified that myokines possibly mediate the crosstalk between muscles and other metabolic organs in pathological conditions. Overall, our analysis revealed a comprehensive understanding of the molecular signature of skeletal muscles in NAFLD and NASH, thus providing a basis for physical exercise as an intervention against liver diseases.

Gynostemma pentaphyllum extract and Gypenoside L enhance skeletal muscle differentiation and mitochondrial metabolism by activating the PGC-1α pathway in C2C12 myotubes

BACKGROUND/OBJECTIVES

Peroxisome proliferator-activated receptor-gamma co-activator-1α (PGC-1α) has a central role in regulating muscle differentiation and mitochondrial metabolism. PGC-1α stimulates muscle growth and muscle fiber remodeling, concomitantly regulating lactate and lipid metabolism and promoting oxidative metabolism. Gynostemma pentaphyllum (Thumb.) has been widely employed as a traditional herbal medicine and possesses antioxidant, anti-obesity, anti-inflammatory, hypolipemic, hypoglycemic, and anticancer properties. We investigated whether G. pentaphyllum extract (GPE) and its active compound, gypenoside L (GL), affect muscle differentiation and mitochondrial metabolism via activation of the PGC-1α pathway in murine C2C12 myoblast cells.

MATERIALS/METHODS

C2C12 cells were treated with GPE and GL, and quantitative reverse transcription polymerase chain reaction and western blot were used to analyze the mRNA and protein expression levels. Myh1 was determined using immunocytochemistry. Mitochondrial reactive oxygen species generation was measured using the 2′7′-dichlorofluorescein diacetate assay.

RESULTS

GPE and GL promoted the differentiation of myoblasts into myotubes and elevated mRNA and protein expression levels of Myh1 (type IIx). GPE and GL also significantly increased the mRNA expression levels of the PGC-1α gene (Ppargc1a), lactate metabolism-regulatory genes (Esrra and Mct1), adipocyte-browning gene fibronectin type III domain-containing 5 gene (Fndc5), glycogen synthase gene (Gys), and lipid metabolism gene carnitine palmitoyltransferase 1b gene (Cpt1b). Moreover, GPE and GL induced the phosphorylation of AMP-activated protein kinase, p38, sirtuin1, and deacetylated PGC-1α. We also observed that treatment with GPE and GL significantly stimulated the expression of genes associated with the anti-oxidative stress response, such as Ucp2, Ucp3, Nrf2, and Sod2.

CONCLUSIONS

The results indicated that GPE and GL enhance exercise performance by promoting myotube differentiation and mitochondrial metabolism through the upregulation of PGC-1α in C2C12 skeletal muscle.

High-Intensity Interval Training Improves Physical Function, Prevents Muscle Loss, and Modulates Macrophage-Mediated Inflammation in Skeletal Muscle of Cerebral Ischemic Mice

Although skeletal muscle is the main effector organ largely accounting for disability after stroke, considerably less attention is paid to the secondary abnormalities of stroke-related skeletal muscle loss. It is necessary to explore the mechanism of muscle atrophy after stroke and further develop effective rehabilitation strategy. Here, we evaluated the effects of high-intensity interval (HIIT) versus moderate-intensity aerobic training (MOD) on physical function, muscle mass, and stroke-related gene expression profile of skeletal muscle. After the model of middle cerebral artery occlusion (MCAO) was successfully made, the blood lactate threshold corresponding speed (S_LT) and maximum speed (S_max) were measured. Different intensity training protocols (MOD < S_LT; S_LT < HIIT < S_max) were carried out for 3 weeks beginning at 7 days after MCAO in the MOD and HIIT groups, respectively. We found that both HIIT and MOD prevented stroke-related gastrocnemius muscle mass loss in MCAO mice. HIIT was more beneficial than MOD for improvements in muscle strength, motor coordination, walking competency, and cardiorespiratory fitness. Furthermore, HIIT was superior to MOD in terms of reducing lipid accumulation, levels of IL-1β and IL-6 in paretic gastrocnemius, and improving peripheral blood CD4+/CD8+ T cell ratio, level of IL-10. Additionally, RNA-seq analysis revealed that the differentially expressed genes among HIIT, MOD, and MCAO groups were highly associated with signaling pathways involved in inflammatory response, more specifically the I-kappaB kinase/NF-kappaB signaling. Following the outcome, we further investigated the infiltrating immune cells abundant in paretic muscles. The results showed that HIIT modulated macrophage activation by downregulating CD86+ (M1 type) macrophages and upregulating CD163+ (M2 type) macrophages via inhibiting the TLR4/MyD88/NFκB signaling pathway and exerting an anti-inflammatory effect in paretic skeletal muscle. It is expected that these data will provide novel insights into the mechanisms and potential targets underlying muscle wasting in stroke.

Oxidative Stress, Mitochondrial Function and Adaptation to Exercise: New Perspectives in Nutrition

Cells have the ability to adapt to stressful environments as a part of their evolution. Physical exercise induces an increase of a demand for energy that must be met by mitochondria as the main (ATP) provider. However, this process leads to the increase of free radicals and the so-called reactive oxygen species (ROS), which are necessary for the maintenance of cell signaling and homeostasis. In addition, mitochondrial biogenesis is influenced by exercise in continuous crosstalk between the mitochondria and the nuclear genome. Excessive workloads may induce severe mitochondrial stress, resulting in oxidative damage. In this regard, the objective of this work was to provide a general overview of the molecular mechanisms involved in mitochondrial adaptation during exercise and to understand if some nutrients such as antioxidants may be implicated in blunt adaptation and/or an impact on the performance of exercise by different means.

Exercise training in heart transplantation

Heart transplantation remains the gold standard in the treatment of end-stage heart failure (HF). Heart transplantation patients present lower exercise capacity due to cardiovascular and musculoskeletal alterations leading thus to poor quality of life and reduction in the ability of daily self-service. Impaired vascular function and diastolic dysfunction cause lower cardiac output while decreased skeletal muscle oxidative fibers, enzymes and capillarity cause arteriovenous oxygen difference, leading thus to decreased peak oxygen uptake in heart transplant recipients. Exercise training improves exercise capacity, cardiac and vascular endothelial function in heart transplant recipients. Pre-rehabilitation regular aerobic or combined exercise is beneficial for patients with end-stage HF awaiting heart transplantation in order to maintain a higher fitness level and reduce complications afterwards like intensive care unit acquired weakness or cardiac cachexia. All hospitalized patients after heart transplantation should be referred to early mobilization of skeletal muscles through kinesiotherapy of the upper and lower limbs and respiratory physiotherapy in order to prevent infections of the respiratory system prior to hospital discharge. Moreover, all heart transplant recipients after hospital discharge who have not already participated in an early cardiac rehabilitation program should be referred to a rehabilitation center by their health care provider. Although high intensity interval training seems to have more benefits than moderate intensity continuous training, especially in stable transplant patients, individualized training based on the abilities and needs of each patient still remains the most appropriate approach. Cardiac rehabilitation appears to be safe in heart transplant patients. However, long-term follow-up data is incomplete and, therefore, further high quality and adequately-powered studies are needed to demonstrate the long-term benefits of exercise training in this population.

Treadmill running prevents atrophy differently in fast- versus slow-twitch muscles in a rat model of rheumatoid arthritis

To investigate the effects of treadmill running on two different types of skeletal muscle, we established a rat model of collagen-induced arthritis (CIA). The skeletal muscles studied were the extensor digitorum longus (EDL), which is rich in fast-twitch muscle fibers, and the soleus, which is rich in slow-twitch muscle fibers. The histological and transcriptional changes in these muscles at 14 and 44 days after immunosensitization were compared between rats that were forced to exercise (CIA ex group) and free-reared CIA rats (CIA no group). Change in protein expression was examined on day 14 after a single bout of treadmill running. Treadmill running had different effects on the relative muscle weight and total and fiber cross-sectional areas in each muscle type. In the soleus, it prevented muscle atrophy. Transcriptional analysis revealed increased eukaryotic translation initiation factor 4E (Eif4e) expression on day 14 and increased Atrogin-1 and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) expression on day 44 in the soleus in the CIA ex group, suggesting an interaction between muscle type and exercise. A single bout of treadmill running increased the level of Eif4e and p70S6K and decreased that of Atrogin-1 in the soleus on day 14. Treadmill running prevented muscle atrophy in the soleus in a rat model of rheumatoid arthritis via activation of mitochondrial function, as evidenced by increased PGC-1α expression.