Redox modulation of muscle mass and function

Paternal exercise induces antioxidant defenses by α-Klotho/Keap1 pathways in the skeletal muscle of offspring exposed to a high fat-diet without changing telomere length

Although previous studies demonstrated that the ancestral lifestyle can enhance the metabolic health of offspring exposed to an obesogenic diet, the specific connections between these positive effects in redox state and telomere length are unknown. We investigated the impact of paternal resistance training (RT) on stress-responsive signaling and the pathways involved in telomere homeostasis in skeletal muscle. This investigation encompassed both the fathers and first-generation litter exposed to a long-term standard diet (24 weeks) and high fat diet (HFD). Wistar rats were randomized into sedentary or trained fathers (8 weeks of resistance training). The offspring were obtained by mating with sedentary females. Upon weaning, male offspring were divided into four groups: offspring of sedentary or trained fathers exposed to either a control diet or HFD. The gastrocnemius was prepared for reverse transcription-quantitative polymerase chain reaction, immunoblotting, ELISA, and electron paramagnetic resonance spectroscopy. RT upregulated shelterin mRNA levels and antioxidant protein, preserving muscle telomere in fathers. Conversely, HFD induced a disturbance in the redox balance, which may have contributed to the offspring telomere shortening from sedentary fathers. Preconceptional paternal RT downregulates Kelch-like ECH-associated protein 1 (Keap1) mRNA levels in the skeletal muscle of progeny exposed to HFD, driving an increase in Glutathione reductase mRNA levels, Sod1 and Catalase protein levels to mitigate ROS production. Also, paternal exercise upregulates α-Klotho protein levels, mediating antioxidative responses without altering shelterin mRNA levels and telomere length. We provide the first in-depth analysis that the offspring's redox state seems to be directly associated with the beneficial effects of paternal exercise.

Skeletal muscle reactive oxygen species and microvascular endothelial function in age-related hypertension: a study protocol using a microdialysis technique

Increased reactive oxygen species (ROS) generation and microvascular endothelial disruptions occur with natural ageing, but often transpire before the detection of cardiometabolic conditions including hypertension. Age-related increases in blood pressure are driven by complex systemic changes with poorly understood integrated mechanisms. The deconditioning experienced by ageing skeletal muscle from mid-life is associated with reduced microvascular blood flow and increased peripheral resistance, suggesting that vasodilatory decrements in the muscle may precede the age-related increases in blood pressure. Structural and functional changes within the vascular and skeletal muscle systems with advancing age can influence redox homeostasis, and vice versa, further compounding microvascular endothelial dysfunction. Therefore, comparisons between the microvascular environments of healthy and hypertensive cohorts can provide insights into the changes that occur during significant periods of functional decline. This comprehensive study protocol describes a microdialysis technique to assess the interactions of microvascular health and functional changes in the muscle, which currently cannot be otherwise addressed. Here, we detail an experimental protocol to simultaneously detect skeletal muscle ROS (H2O2 and indirect O2 -), determine nutritive blood flow and assess microvascular endothelial function in response to acetylcholine stimulation. We expect that healthy middle-aged individuals should not have increased ROS generation in the muscle at rest, compared to their hypertensive or older counterparts, but may exhibit perturbed microvascular function. The described technique allows for intricate exploration of microvascular physiology that will provide a critically novel insight into benchmarking potential age-related mechanisms involved in the development of age-related hypertension, and aid in early identification and prevention. KEY POINTS: Increased reactive oxygen species (ROS) production and microvascular endothelial dysfunction precede the onset of age-related cardiometabolic and vascular conditions such as hypertension. The profound structural and functional changes that occur within the vasculature and in skeletal muscle from middle age prompt a need to mechanistically explore the microvascular environment in healthy and hypertensive individuals. Using a novel microdialysis technique, we detail an experimental protocol to simultaneously detect skeletal muscle ROS (H2O2 and indirect O2 -), determine nutritive blood flow and assess microvascular endothelial function in response to acetylcholine stimulation. With this technique and study protocol, we can reveal functional insights into potential perturbations in ROS generation at rest and the microvascular endothelium, which play important roles in the development of age-related hypertension.

Single-nucleus transcriptomics reveals subsets of degenerative myonuclei after rotator cuff tear-induced muscle atrophy

Rotator cuff tear (RCT) is the primary cause of shoulder pain and disability and frequently trigger muscle degeneration characterised by muscle atrophy, fatty infiltration and fibrosis. Single-nucleus RNA sequencing (snRNA-seq) was used to reveal the transcriptional changes in the supraspinatus muscle after RCT. Supraspinatus muscles were obtained from patients with habitual shoulder dislocation (n = 3) and RCT (n = 3). In response to the RCT, trajectory analysis showed progression from normal myonuclei to ANKRD1+ myonuclei, which captured atrophy-and fatty infiltration-related regulons (KLF5, KLF10, FOSL1 and BHLHE40). Transcriptomic alterations in fibro/adipogenic progenitors (FAPs) and muscle satellite cells (MuSCs) have also been studied. By predicting cell-cell interactions, we observed communication alterations between myofibers and muscle-resident cells following RCT. Our findings reveal the plasticity of muscle cells in response to RCT and offer valuable insights into the molecular mechanisms and potential therapeutic targets of RCT.

Role of Irisin in exercise training-regulated endoplasmic reticulum stress, autophagy and myogenesis in the skeletal muscle after myocardial infarction

Patients with heart failure (HF) are often accompanied by skeletal muscle abnormalities, which can lead to exercise intolerance and compromise daily activities. Irisin, an exercise training (ET) -induced myokine, regulates energy metabolism and skeletal muscle homeostasis. However, the precise role of Irisin in the benefits of ET on inhibiting skeletal muscle atrophy, particularly on endoplasmic reticulum (ER) stress, autophagy, and myogenesis following myocardial infarction (MI) remains unclear. In this study, we investigated the expression of Irisin protein in wild-type mice with MI, and assessed its role in the beneficial effects of ET using an Fndc5 knockout mice. Our findings revealed that MI reduced muscle fiber cross-sectional area (CSA), while downregulating the expression of Irisin, PGC-1α and SOD1. Concurrently, MI elevated the levels of ER stress and apoptosis, and inhibited autophagy in skeletal muscle. Conversely, ET mitigated ER stress and apoptosis in the skeletal muscle of infarcted mice. Notably, Fndc5 knockout worsened MI-induced ER stress and apoptosis, suppressed autophagy and myogenesis, and abrogated the beneficial effects of ET. In conclusion, our findings highlight the role of Irisin in the ET-mediated alleviation of skeletal muscle abnormalities. This study provides valuable insights into MI-induced muscle abnormalities and enhances our understanding of exercise rehabilitation mechanisms in clinical MI patients.

Bacterioruberin extract from Haloarchaea Haloferax marinum: Component identification, antioxidant activity and anti-atrophy effect in LPS-treated C2C12 myotubes

Carotenoids are natural pigments utilized as colourants and antioxidants across food, pharmaceutical and cosmetic industries. They exist in carbon chain lengths of C30, C40, C45 and C50, with C40 variants being the most common. Bacterioruberin (BR) and its derivatives are part of the less common C50 carotenoid group, synthesized primarily by halophilic archaea. This study analysed the compositional characteristics of BR extract (BRE) isolated from 'Haloferax marinum' MBLA0078, a halophilic archaeon isolated from seawater near Yeoungheungdo Island in the Republic of Korea, and investigated its antioxidant activity and protective effect on lipopolysaccharide (LPS)-induced C2C12 myotube atrophy. The main components of BRE included all-trans-BR, monoanhydrobacterioruberin, 2-isopentenyl-3,4-dehydrorhodopin and all-trans-bisanhydrobacterioruberin. BRE exhibited higher antioxidant activity and DNA nicking protection activity than other well-known C40 carotenoids, such as β-carotene, lycopene and astaxanthin. In C2C12 myotubes, LPS treatment led to a reduction in myotube diameter and number, as well as the hypertranscription of the muscle-specific ubiquitin ligase MAFbx and MuRF1. BRE mitigated these changes by activating the Akt/mTOR pathway. Furthermore, BRE abolished the elevated cellular reactive oxygen species levels and the inflammation response induced by LPS. This study demonstrated that 'Hfx. marinum' is an excellent source of natural microbial C50 carotenoids with strong antioxidant capacity and may offer potential protective effects against muscle atrophy.

Mitochondria as Nutritional Targets to Maintain Muscle Health and Physical Function During Ageing

The age-related loss of skeletal muscle mass and physical function leads to a loss of independence and an increased reliance on health-care. Mitochondria are crucial in the aetiology of sarcopenia and have been identified as key targets for interventions that can attenuate declines in physical capacity. Exercise training is a primary intervention that reduces many of the deleterious effects of ageing in skeletal muscle quality and function. However, habitual levels of physical activity decline with age, making it necessary to implement adjunct treatments to maintain skeletal muscle mitochondrial health and physical function. This review provides an overview of the effects of ageing and exercise training on human skeletal muscle mitochondria and considers several supplements that have plausible mechanistic underpinning to improve physical function in ageing through their interactions with mitochondria. Several supplements, including MitoQ, urolithin A, omega-3 polyunsaturated fatty acids (n3-PUFAs), and a combination of glycine and N-acetylcysteine (GlyNAC) can improve physical function in older individuals through a variety of inter-dependent mechanisms including increases in mitochondrial biogenesis and energetics, decreases in mitochondrial reactive oxygen species emission and oxidative damage, and improvements in mitochondrial quality control. While there is evidence that some nicotinamide adenine dinucleotide precursors can improve physical function in older individuals, such an outcome seems unrelated to and independent of changes in skeletal muscle mitochondrial function. Future research should investigate the safety and efficacy of compounds that can improve skeletal muscle health in preclinical models through mechanisms involving mitochondria, such as mitochondrial-derived peptides and mitochondrial uncouplers, with a view to extending the human health-span.

The role of TGF-β signaling in muscle atrophy, sarcopenia and cancer cachexia

Skeletal muscle, comprising a significant proportion (40 to 50 percent) of total body weight in humans, plays a critical role in maintaining normal physiological conditions. Muscle atrophy occurs when the rate of protein degradation exceeds protein synthesis. Sarcopenia refers to age-related muscle atrophy, while cachexia represents a more complex form of muscle wasting associated with various diseases such as cancer, heart failure, and AIDS. Recent research has highlighted the involvement of signaling pathways, including IGF1-Akt-mTOR, MuRF1-MAFbx, and FOXO, in regulating the delicate balance between muscle protein synthesis and breakdown. Myostatin, a member of the TGF-β superfamily, negatively regulates muscle growth and promotes muscle atrophy by activating Smad2 and Smad3. It also interacts with other signaling pathways in cachexia and sarcopenia. Inhibition of myostatin has emerged as a promising therapeutic approach for sarcopenia and cachexia. Additionally, other TGF-β family members, such as TGF-β1, activin A, and GDF11, have been implicated in the regulation of skeletal muscle mass. Furthermore, myostatin cooperates with these family members to impair muscle differentiation and contribute to muscle loss. This review provides an overview of the significance of myostatin and other TGF-β signaling pathway members in muscular dystrophy, sarcopenia, and cachexia. It also discusses potential novel therapeutic strategies targeting myostatin and TGF-β signaling for the treatment of muscle atrophy.

5'-Cytimidine Monophosphate Ameliorates H2O2-Induced Muscular Atrophy in C2C12 Myotubes by Activating IRS-1/Akt/S6K Pathway

Age-related muscle atrophy (sarcopenia), characterized by reduced skeletal muscle mass and muscle strength, is becoming increasingly prevalent worldwide, which is especially true for older people, and can seriously damage health and quality of life in older adults. This study aims to investigate the beneficial effects of 5'-cytimidine monophosphate (CMP) on H2O2-induced muscular atrophy in C2C12 myotubes. C2C12 myotubes were treated with H2O2 in the presence and absence of CMP and the changes in the anti-oxidation, mitochondrial functions, and expression of sarcopenia-related proteins were observed. Immunofluorescence analysis showed that CMP significantly increased the diameter of myotubes. We found that CMP could increase the activity of antioxidant enzymes and improve mitochondrial dysfunction, as well as reduce inflammatory cytokine levels associated with sarcopenia. RNA-seq analysis showed that CMP could relieve insulin resistance and promote protein digestion and absorption. Western blot analysis further confirmed that CMP could promote the activation of the IRS-1/Akt/S6K signaling pathway and decrease the expression of MuRF1 and Atrogin-1, which are important markers of muscle atrophy. The above results suggest that CMP protects myotubes from H2O2-induced atrophy and that its potential mechanism is associated with activating the IRS-1/Akt/S6K pathway to promote protein synthesis by improving mitochondrial dysfunction and insulin resistance. These results indicate that CMP can improve aging-related sarcopenia.

Handelin alleviates cachexia- and aging-induced skeletal muscle atrophy by improving protein homeostasis and inhibiting inflammation

BACKGROUND

Handelin is a bioactive compound from Chrysanthemum indicum L. that improves motor function and muscle integrity during aging in Caenorhabditis elegans. This study aimed to further evaluate the protective effects and molecular mechanisms of handelin in a mouse muscle atrophy model induced by cachexia and aging.

METHODS

A tumour necrosis factor (TNF)-α-induced atrophy model was used to examine handelin activity in cultured C2C12 myotubes in vitro. Lipopolysaccharide (LPS)-treated 8-week-old model mice and 23-month-old (aged) mice were used to examine the therapeutic effects of handelin on cachexia- and aging-induced muscle atrophy, respectively, in vivo. Protein and mRNA expressions were analysed by Western blotting, ELISA and quantitative PCR, respectively. Skeletal muscle mass was measured by histological analysis.

RESULTS

Handelin treatment resulted in an upregulation of protein levels of early (MyoD and myogenin) and late (myosin heavy chain, MyHC) differentiation markers in C2C12 myotubes (P < 0.05), and enhanced mitochondrial respiratory (P < 0.05). In TNF-α-induced myotube atrophy model, handelin maintained MyHC protein levels, increased insulin-like growth factor (Igf1) mRNA expression and phosphorylated protein kinase B protein levels (P < 0.05). Handelin also reduced atrogin-1 expression, inhibited nuclear factor-κB activation and reduced mRNA levels of interleukin (Il)6, Il1b and chemokine ligand 1 (Cxcl1) (P < 0.05). In LPS-treated mice, handelin increased body weight (P < 0.05), the weight (P < 0.01) and cross-sectional area (CSA) of the soleus muscle (P < 0.0001) and improved motor function (P < 0.05). In aged mice, handelin slightly increased the weight of the tibialis anterior muscle (P = 0.06) and CSA of the tibialis anterior and gastrocnemius muscles (P < 0.0001). In the tibialis anterior muscle of aged mice, handelin upregulated mRNA levels of Igf1 (P < 0.01), anti-inflammatory cytokine Il10 (P < 0.01), mitochondrial biogenesis genes (P < 0.05) and antioxidant-related enzymes (P < 0.05) and strengthened Sod and Cat enzyme activity (P < 0.05). Handelin also reduced lipid peroxidation and protein carbonylation, downregulated mRNA levels of Fbxo32, Mstn, Cxcl1, Il1b and Tnf (P < 0.05), and decreased IL-1β levels in serum (P < 0.05). Knockdown of Hsp70 or using an Hsp70 inhibitor abolished the ameliorating effects of handelin on myotube atrophy.

CONCLUSIONS

Handelin ameliorated cachexia- and aging-induced skeletal muscle atrophy in vitro and in vivo, by maintaining homeostasis of protein synthesis and degradation, possibly by inhibiting inflammation. Handelin is a potentially promising drug candidate for the treatment of muscle wasting.

In vivo cytosolic H2O2 changes and Ca2+ homeostasis in mouse skeletal muscle

Hydrogen peroxide (H2O2) and calcium ions (Ca2+) are functional regulators of skeletal muscle contraction and metabolism. Although H2O2 is one of the activators of the type-1 ryanodine receptor (RyR1) in the Ca2+ release channel, the interdependence between H2O2 and Ca2+ dynamics remains unclear. This study tested the following hypotheses using an in vivo model of mouse tibialis anterior (TA) skeletal muscle. 1) Under resting conditions, elevated cytosolic H2O2 concentration ([H2O2]cyto) leads to a concentration-dependent increase in cytosolic Ca2+ concentration ([Ca2+]cyto) through its effect on RyR1; and 2) in hypoxia (cardiac arrest) and muscle contractions (electrical stimulation), increased [H2O2]cyto induces Ca2+ accumulation. Cytosolic H2O2 (HyPer7) and Ca2+ (Fura-2) dynamics were resolved by TA bioimaging in young C57BL/6J male mice under four conditions: 1) elevated exogenous H2O2; 2) cardiac arrest; 3) twitch (1 Hz, 60 s) contractions; and 4) tetanic (30 s) contractions. Exogenous H2O2 (0.1-100 mM) induced a concentration-dependent increase in [H2O2]cyto (+55% at 0.1 mM; +280% at 100 mM) and an increase in [Ca2+]cyto (+3% at 1.0 mM; +8% at 10 mM). This increase in [Ca2+]cyto was inhibited by pharmacological inhibition of RyR1 by dantrolene. Cardiac arrest-induced hypoxia increased [H2O2]cyto (+33%) and [Ca2+]cyto (+20%) 50 min postcardiac arrest. Compared with the exogenous 1.0 mM H2O2 condition, [H2O2]cyto after tetanic muscle contractions rose less than one-tenth as much, whereas [Ca2+]cyto was 4.7-fold higher. In conclusion, substantial increases in [H2O2]cyto levels evoke only modest Ca2+ accumulation via their effect on the sarcoplasmic reticulum RyR1. On the other hand, contrary to hypoxia secondary to cardiac arrest, increases in [H2O2]cyto from muscle contractions are small, indicating that H2O2 generation is unlikely to be a primary factor driving the significant Ca2+ accumulation after, especially tetanic, muscle contractions.NEW & NOTEWORTHY We developed an in vivo mouse myocyte H2O2 imaging model during exogenous H2O2 loading, ischemic hypoxia induced by cardiac arrest, and muscle contractions. In this study, the interrelationship between cytosolic H2O2 levels and Ca2+ homeostasis during muscle contraction and hypoxic conditions was revealed. These results contribute to the elucidation of the mechanisms of muscle fatigue and exercise adaptation.

Selenium deficiency-induced high concentration of reactive oxygen species restricts hypertrophic growth of skeletal muscle in juvenile zebrafish by suppressing TORC1-mediated protein synthesis

Se deficiency causes impaired growth of fish skeletal muscle due to the retarded hypertrophy of muscle fibres. However, the inner mechanisms remain unclear. According to our previous researches, we infer this phenomenon is associated with Se deficiency-induced high concentration of reactive oxygen species (ROS), which could suppress the target of rapamycin complex 1 (TORC1) pathway-mediated protein synthesis by inhibiting protein kinase B (Akt), an upstream protein of TORC1. To test this hypothesis, juvenile zebrafish (45 d post-fertilisation) were fed a basal Se-adequate diet or a basal Se-deficient diet or them supplemented with an antioxidant (DL-α-tocopherol acetate, designed as VE) or a TOR activator (MHY1485) for 30 d. Zebrafish fed Se-deficient diets exhibited a clear Se-deficient status in skeletal muscle, which was not influenced by dietary VE and MHY1485. Se deficiency significantly elevated ROS concentrations, inhibited Akt activity and TORC1 pathway, suppressed protein synthesis in skeletal muscle, and impaired hypertrophy of skeletal muscle fibres. However, these negative effects of Se deficiency were partly (except that on ROS concentration) alleviated by dietary MHY1485 and completely alleviated by dietary VE. These data strongly support our speculation that Se deficiency-induced high concentration of ROS exerts a clear inhibiting effect on TORC1 pathway-mediated protein synthesis by regulating Akt activity, thereby restricting the hypertrophy of skeletal muscle fibres in fish. Our findings provide a mechanistic explanation for Se deficiency-caused retardation of fish skeletal muscle growth, contributing to a better understanding of the nutritional necessity and regulatory mechanisms of Se in fish muscle physiology.

The adaptive antioxidant response during fasting-induced muscle atrophy is oppositely regulated by ZEB1 and ZEB2

Reactive oxygen species (ROS) serve important homeostatic functions but must be constantly neutralized by an adaptive antioxidant response to prevent supraphysiological levels of ROS from causing oxidative damage to cellular components. Here, we report that the cellular plasticity transcription factors ZEB1 and ZEB2 modulate in opposing directions the adaptive antioxidant response to fasting in skeletal muscle. Using transgenic mice in which Zeb1 or Zeb2 were specifically deleted in skeletal myofibers, we show that in fasted mice, the deletion of Zeb1, but not Zeb2, increased ROS production and that the adaptive antioxidant response to fasting essentially requires ZEB1 and is inhibited by ZEB2. ZEB1 expression increased in fasted muscles and protected them from atrophy; conversely, ZEB2 expression in muscles decreased during fasting and exacerbated muscle atrophy. In fasted muscles, ZEB1 reduces mitochondrial damage and increases mitochondrial respiratory activity; meanwhile, ZEB2 did the opposite. Treatment of fasting mice with Zeb1-deficient myofibers with the antioxidant triterpenoid 1[2-cyano-3,12-dioxool-eana-1,9(11)-dien-28-oyl] trifluoro-ethylamide (CDDO-TFEA) completely reversed their altered phenotype to that observed in fasted control mice. These results set ZEB factors as potential therapeutic targets to modulate the adaptive antioxidant response in physiopathological conditions and diseases caused by redox imbalance.

Redox Profile of Skeletal Muscles: Implications for Research Design and Interpretation

Mammalian skeletal muscles contain varying proportions of Type I and II fibers, which feature different structural, metabolic and functional properties. According to these properties, skeletal muscles are labeled as 'red' or 'white', 'oxidative' or 'glycolytic', 'slow-twitch' or 'fast-twitch', respectively. Redox processes (i.e., redox signaling and oxidative stress) are increasingly recognized as a fundamental part of skeletal muscle metabolism at rest, during and after exercise. The aim of the present review was to investigate the potential redox differences between slow- (composed mainly of Type I fibers) and fast-twitch (composed mainly of Type IIa and IIb fibers) muscles at rest and after a training protocol. Slow-twitch muscles were almost exclusively represented in the literature by the soleus muscle, whereas a wide variety of fast-twitch muscles were used. Based on our analysis, we argue that slow-twitch muscles exhibit higher antioxidant enzyme activity compared to fast-twitch muscles in both pre- and post-exercise training. This is also the case between heads or regions of fast-twitch muscles that belong to different subcategories, namely Type IIa (oxidative) versus Type IIb (glycolytic), in favor of the former. No safe conclusion could be drawn regarding the mRNA levels of antioxidant enzymes either pre- or post-training. Moreover, slow-twitch skeletal muscles presented higher glutathione and thiol content as well as higher lipid peroxidation levels compared to fast-twitch. Finally, mitochondrial hydrogen peroxide production was higher in fast-twitch muscles compared to slow-twitch muscles at rest. This redox heterogeneity between different muscle types may have ramifications in the analysis of muscle function and health and should be taken into account when designing exercise studies using specific muscle groups (e.g., on an isokinetic dynamometer) or isolated muscle fibers (e.g., electrical stimulation) and may deliver a plausible explanation for the conflicting results about the ergogenic potential of antioxidant supplements.

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.

Inter-individual variability in redox and performance responses after antioxidant supplementation: A randomized double blind crossover study

AIM

We aimed to investigate the inter-individual variability in redox and physiological responses of antioxidant-deficient subjects after antioxidant supplementation.

METHODS

Two hundred individuals were sorted by plasma vitamin C levels. A low vitamin C group (n = 22) and a control group (n = 22) were compared in terms of oxidative stress and performance. Subsequently, the low vitamin C group received for 30 days vitamin C (1 g) or placebo, in randomized, double-blind, crossover fashion, and the effects were examined through a mixed-effects model, while individual responses were calculated.

RESULTS

The low vitamin C group exhibited lower vitamin C (-25 μmol/L; 95%CI[-31.7, -18.3]; p < 0.001), higher F2 -isoprostanes (+17.1 pg/mL; 95%CI[6.5, 27.7]; p = 0.002), impaired VO2max (-8.2 mL/kg/min; 95%CI[-12.8, -3.6]; p < 0.001) and lower isometric peak torque (-41.5 Nm; 95%CI[-61.8, -21.2]; p < 0.001) compared to the control group. Regarding antioxidant supplementation, a significant treatment effect was found in vitamin C (+11.6 μmol/L; 95%CI[6.8, 17.1], p < 0.001), F2 -isoprostanes (-13.7 pg/mL; 95%CI[-18.9, -8.4], p < 0.001), VO2max (+5.4 mL/kg/min; 95%CI[2.7, 8.2], p = 0.001) and isometric peak torque (+18.7; 95%CI[11.8, 25.7 Nm], p < 0.001). The standard deviation for individual responses (SDir) was greater than the smallest worthwhile change (SWC) for all variables indicating meaningful inter-individual variability. When a minimal clinically important difference (MCID) was set, inter-individual variability remained for VO2max , but not for isometric peak torque.

CONCLUSION

The proportion of response was generally high after supplementation (82.9%-95.3%); however, a few participants did not benefit from the treatment. This underlines the potential need for personalized nutritional interventions in an exercise physiology context.

Ageing of skeletal muscle extracellular matrix and mitochondria: finding a potential link

Aim: To discuss the progress of extracellular matrix (ECM) characteristics, mitochondrial homeostasis, and their potential crosstalk in the pathogenesis of sarcopenia, a geriatric syndrome characterized by a generalized and progressive reduction in muscle mass, strength, and physical performance.Methods: This review focuses on the anatomy and physiology of skeletal muscle, alterations of ECM and mitochondria during ageing, and the role of the interplay between ECM and mitochondria in the pathogenesis of sarcopenia.Results: Emerging evidence points to a clear interplay between mitochondria and ECM in various tissues and organs. Under the ageing process, the ECM undergoes changes in composition and physical properties that may mediate mitochondrial changes via the systematic metabolism, ROS, SPARC pathway, and AMPK/PGC-1α signalling, which in turn exacerbate muscle degeneration. However, the precise effects of such crosstalk on the pathobiology of ageing, particularly in skeletal muscle, have not yet been fully understood.Conclusion: The changes in skeletal muscle ECM and mitochondria are partially responsible for the worsened muscle function during the ageing process. A deeper understanding of their alterations and interactions in sarcopenic patients can help prevent sarcopenia and improve its prognoses.

Exercise and Exercise Mimetics for the Treatment of Musculoskeletal Disorders

PURPOSE OF REVIEW

The incidence of musculoskeletal disorders affecting bones, joints, and muscles is dramatically increasing in parallel with the increased longevity of the worldwide population, severely impacting on the individual's quality of life and on the healthcare costs. Inactivity and sedentary lifestyle are nowadays considered the main drivers of age-associated musculoskeletal disorders and exercise may counteract such alterations also in other bone- and muscle-centered disorders. This review aims at clarifying the potential use of exercise training to improve musculoskeletal health.

RECENT FINDINGS

Both the skeletal muscle and the bone are involved in a complex crosstalk determining, in part through tissue-specific and inflammatory/immune released factors, the occurrence of musculoskeletal disorders. Exercise is able to modulate the levels of those molecules and several associated molecular pathways. Evidence from preclinical and clinical trials supports the adoption of exercise and the future use of exercise mimicking drugs will optimize the care of individuals with musculoskeletal disorders.

Skeletal muscle oxidative stress and inflammation in aging: Focus on antioxidant and anti-inflammatory therapy

With aging, the progressive loss of skeletal muscle will have negative effect on multiple physiological parameters, such as exercise, respiration, thermoregulation, and metabolic homeostasis. Accumulating evidence reveals that oxidative stress and inflammation are the main pathological characteristics of skeletal muscle during aging. Here, we focus on aging-related sarcopenia, summarize the relationship between aging and sarcopenia, and elaborate on aging-mediated oxidative stress and oxidative damage in skeletal muscle and its critical role in the occurrence and development of sarcopenia. In addition, we discuss the production of excessive reactive oxygen species in aging skeletal muscle, which reduces the ability of skeletal muscle satellite cells to participate in muscle regeneration, and analyze the potential molecular mechanism of ROS-mediated mitochondrial dysfunction in aging skeletal muscle. Furthermore, we have also paid extensive attention to the possibility and potential regulatory pathways of skeletal muscle aging and oxidative stress mediate inflammation. Finally, in response to the abnormal activity of oxidative stress and inflammation during aging, we summarize several potential antioxidant and anti-inflammatory strategies for the treatment of sarcopenia, which may provide beneficial help for improving sarcopenia during aging.

Circulating Sestrins and Force Velocity Profiling in Older Adults with Type 2 Diabetes

ABSTRACTType 2 diabetes mellitus (T2DM) in old age affects the musculoskeletal system causing loss of muscle mass, strength, and physical function. Stress-inducible proteins named sestrins are potential novel biomarkers of muscle function due to their ability to suppress oxidative stress and prevent muscle degeneration. Our aim was to determine the association between different force-velocity (F-V) profiles with body composition, physical performance, and glucose control in older adults with T2DM. We also intended to determine the potential utility of sestrin 1 (Sesn1) and 2 (Sesn2) as biomarkers of physical functionality. Fifty-nine participants (69-79 years) were classified in 3 groups according to their F-V profile based on the leg press exercise: nondeficit (N_DEF= 40.7%), force deficit (F_DEF= 28.8%), and velocity deficit (V_DEF= 30.5%). Both V_DEF and F_DEF groups showed lower muscle power than N_DEF (Cohen's d 0.87 and 0.75 for effect size, respectively). Serum Sesn2 levels, maximal dynamic strength, arms and legs fat-free mass were reduced in F_DEF compared to the N_DEF group (p < 0.05), whereas glycated hemoglobin (HbA1c) and fasting glucose levels were similar among groups. ROC analysis revealed the distinction between the N_DEF and F_DEF group based on Sesn2 concentrations (<0.72 ng/mL), suggesting their potential use as functional biomarkers for early intervention through exercise. Older adults with T2DM show different F-V profiles, related to low levels of Sesn2, impaired body composition and physical performance, and may be taken into consideration to target exercise training in this specific population.

Defining roles of specific reactive oxygen species (ROS) in cell biology and physiology

'Reactive oxygen species' (ROS) is a generic term that defines a wide variety of oxidant molecules with vastly different properties and biological functions that range from signalling to causing cell damage. Consequently, the description of oxidants needs to be chemically precise to translate research on their biological effects into therapeutic benefit in redox medicine. This Expert Recommendation article pinpoints key issues associated with identifying the physiological roles of oxidants, focusing on H₂O₂ and O₂^.-. The generic term ROS should not be used to describe specific molecular agents. We also advocate for greater precision in measurement of H₂O₂, O₂^.- and other oxidants, along with more specific identification of their signalling targets. Future work should also consider inter-organellar communication and the interactions of redox-sensitive signalling targets within organs and whole organisms, including the contribution of environmental exposures. To achieve these goals, development of tools that enable site-specific and real-time detection and quantification of individual oxidants in cells and model organisms are needed. We also stress that physiological O₂ levels should be maintained in cell culture to better mimic in vivo redox reactions associated with specific cell types. Use of precise definitions and analytical tools will help harmonize research among the many scientific disciplines working on the common goal of understanding redox biology.

Cardiovasomobility: an integrative understanding of how disuse impacts cardiovascular and skeletal muscle health

Cardiovasomobility is a novel concept that encompasses the integration of cardiovascular and skeletal muscle function in health and disease with critical modification by physical activity, or lack thereof. Compelling evidence indicates that physical activity improves health while a sedentary, or inactive, lifestyle accelerates cardiovascular and skeletal muscle dysfunction and hastens disease progression. Identifying causative factors for vascular and skeletal muscle dysfunction, especially in humans, has proven difficult due to the limitations associated with cross-sectional investigations. Therefore, experimental models of physical inactivity and disuse, which mimic hospitalization, injury, and illness, provide important insight into the mechanisms and consequences of vascular and skeletal muscle dysfunction. This review provides an overview of the experimental models of disuse and inactivity and focuses on the integrated responses of the vasculature and skeletal muscle in response to disuse/inactivity. The time course and magnitude of dysfunction evoked by various models of disuse/inactivity are discussed in detail, and evidence in support of the critical roles of mitochondrial function and oxidative stress are presented. Lastly, strategies aimed at preserving vascular and skeletal muscle dysfunction during disuse/inactivity are reviewed. Within the context of cardiovasomobility, experimental manipulation of physical activity provides valuable insight into the mechanisms responsible for vascular and skeletal muscle dysfunction that limit mobility, degrade quality of life, and hasten the onset of disease.

Interaction between the Effects of Sustained Swimming Activity and Dietary Macronutrient Proportions on the Redox Status of Gilthead Sea Bream Juveniles (Sparus aurata L.)

The combination of physical exercise and a balanced diet presents substantial health benefits and could improve fish production. However, the redox balance can be affected by training regimen, dietary macronutrient ratio and their interaction. In this study, we conjointly evaluated the effects of physical activity (by voluntary swimming (VS) or sustained swimming as exercise (Ex)) and diet composition (by high-protein (HP) or high-lipid (HE) commercial diets) after 6 weeks on oxidative stress status in liver, white muscle and red muscle of gilthead sea bream juveniles. The HE diet increased the biochemical redox markers’ thiobarbituric acid reactive substances (TBARS), advanced oxidation protein products (AOPP) and reduced thiols (-SH) in the different tissues. Exercise increased AOPP and -SH levels in liver but reduced TBARS levels in white muscle. Regarding the expression of oxidative stress, chaperones and apoptosis-related genes, the VSHE group showed the highest values and the VSHP the lowest, whereas the application of sustained swimming partially equalized those differences. Diet composition modulated the enzyme activity, prioritizing the superoxide dismutase and catalase in the HE-fed groups and the glutathione-related enzymes in the HP groups. Exercise also altered enzyme activity, but in a tissue-dependent manner. Overall, the redox balance in gilthead sea bream juveniles can be affected by diet composition and sustained swimming. However, the response will partly depend on the interaction between these factors and the tissue studied. Therefore, the combination of an adequate diet and sustained exercise could be used in fish production to improve the physiological redox status.

Silibinin Alleviates Muscle Atrophy Caused by Oxidative Stress Induced by Cisplatin through ERK/FoxO and JNK/FoxO Pathways

Cisplatin (DDP), a widely used chemotherapeutic drug in cancer treatment, causes oxidative stress, resulting in cancer cachexia and skeletal muscle atrophy. This study investigated the effects and activity of silibinin (SLI) in reducing DDP-induced oxidative stress and skeletal muscle atrophy in vivo and in vitro. SLI alleviated weight loss, food intake, muscle wasting, adipose tissue depletion, and organ weight reduction induced by DDP and improved the reduction of grip force caused by DDP. SLI can attenuated the increase in reactive oxygen species (ROS) levels, the decrease in Nrf2 expression, the decrease in the fiber cross-sectional area, and changes in fiber type induced by DDP. SLI regulated the ERK/FoxO and JNK/FoxO pathways by downregulating the abnormal increase in ROS and Nrf2 expression in DDP-treated skeletal muscle and C2C12 myotube cells. Further, SLI inhibited the upregulation of MAFbx and Mstn, the downregulation of MyHC and MyoG, the increase in protein degradation, and the decrease of protein synthesis. The protective effects of SLI were reversed by cotreatment with JNK agonists and ERK inhibitors. These results suggest that SLI can reduce DDP-induced skeletal muscle atrophy by reducing oxidative stress and regulating ERK/FoxO and JNK/FoxO pathways.

Mitophagy reporter mouse analysis reveals increased mitophagy activity in disuse-induced muscle atrophy

Muscle disuse induces atrophy through increased reactive oxygen species (ROS) released from damaged mitochondria. Mitophagy, the autophagic degradation of mitochondria, is associated with increased ROS production. However, the mitophagy activity status during disuse-induced muscle atrophy has been a subject of debate. Here, we developed a new mitophagy reporter mouse line to examine how disuse affected mitophagy activity in skeletal muscles. Mice expressing tandem mCherry-EGFP proteins on mitochondria were then used to monitor the dynamics of mitophagy activity. The reporter mice demonstrated enhanced mitophagy activity and increased ROS production in atrophic soleus muscles following a 14-day hindlimb immobilization. Results also showed an increased expression of multiple mitophagy genes, including Bnip3, Bnip3l, and Park2. Our findings thus conclude that disuse enhances mitophagy activity and ROS production in atrophic skeletal muscles and suggests that mitophagy is a potential therapeutic target for disuse-induced muscle atrophy.

Redox Signaling and Sarcopenia: Searching for the Primary Suspect

Sarcopenia, the age-related decline in muscle mass and function, derives from multiple etiological mechanisms. Accumulative research suggests that reactive oxygen species (ROS) generation plays a critical role in the development of this pathophysiological disorder. In this communication, we review the various signaling pathways that control muscle metabolic and functional integrity such as protein turnover, cell death and regeneration, inflammation, organismic damage, and metabolic functions. Although no single pathway can be identified as the most crucial factor that causes sarcopenia, age-associated dysregulation of redox signaling appears to underlie many deteriorations at physiological, subcellular, and molecular levels. Furthermore, discord of mitochondrial homeostasis with aging affects most observed problems and requires our attention. The search for the primary suspect of the fundamental mechanism for sarcopenia will likely take more intense research for the secret of this health hazard to the elderly to be unlocked.

Selenium Status Affects Hypertrophic Growth of Skeletal Muscle in Growing Zebrafish by Mediating Protein Turnover

BACKGROUND

Selenium (Se) status is closely related to skeletal muscle physiological status. However, its influence on skeletal muscle growth has not been well studied.

OBJECTIVES

This study aimed to analyze the impacts of overall Se status (deficient, adequate, and high) on skeletal muscle growth using a growing zebrafish model.

METHODS

Zebrafish (1.5-mo-old) were fed graded levels of Se (deficient: 0.10 mg Se/kg; marginally deficient: 0.22 mg Se/kg; adequate: 0.34 mg Se/kg; high: 0.44, 0.57, and 0.69 mg Se/kg) as Se-enriched yeast for 30 d. Zebrafish growth, and Se accumulation, selenoenzyme activity, selenotranscriptome profiles, and oxidative status in the whole body, and selenotranscriptome profiles, histological characteristics, biochemicals, and gene and protein expression profiles related to muscle growth in the skeletal muscle were analyzed by model fitting and/or 1-factor ANOVA.

RESULTS

Se status biomarkers within the whole body and skeletal muscle indicated that 0.34 mg Se/kg was adequate for growing zebrafish. For biomarkers related to skeletal muscle growth, compared with 0.34 mg Se/kg, 0.10 mg Se/kg decreased the white muscle cross-sectional area (WMCSA) and the mean diameter of white muscle fibers (MDWMF) by 14.4%-15.1%, inhibited protein kinase B-target of rapamycin complex 1 signaling by 63.7%-68.5%, and stimulated the autophagy-lysosome pathway by 1.07 times and the ubiquitin-proteasome pathway (UPP) by 96.0% (P < 0.05), whereas 0.22 mg Se/kg only decreased the WMCSA by 7.8% (P < 0.05); furthermore, 0.44 mg Se/kg had no clear effects on skeletal muscle biomarkers, whereas 0.57-0.69 mg Se/kg decreased the WMCSA and MDWMF by 6.3%-25.9% and 5.1%-21.3%, respectively, and stimulated the UPP by 2.23 times (P < 0.05).

CONCLUSIONS

A level of 0.34 mg Se/kg is adequate for the growth of zebrafish skeletal muscle, whereas ≤0.10 and ≥0.57 mg Se/kg are too low or too high, respectively, for maintaining efficient protein accretion and normal hypertrophic growth.

Exercise-Stimulated ROS Sensitive Signaling Pathways in Skeletal Muscle

Physical exercise represents a major challenge to whole-body homeostasis, provoking acute and adaptative responses at the cellular and systemic levels. Different sources of reactive oxygen species (ROS) have been described in skeletal muscle (e.g., NADPH oxidases, xanthine oxidase, and mitochondria) and are closely related to the physiological changes induced by physical exercise through the modulation of several signaling pathways. Many signaling pathways that are regulated by exercise-induced ROS generation, such as adenosine monophosphate-activated protein kinase (AMPK), mitogen activated protein kinase (MAPK), nuclear respiratory factor2 (NRF2), and PGC-1α are involved in skeletal muscle responses to physical exercise, such as increased glucose uptake, mitochondriogenesis, and hypertrophy, among others. Most of these adaptations are blunted by antioxidants, revealing the crucial role played by ROS during and after physical exercise. When ROS generation is either insufficient or exacerbated, ROS-mediated signaling is disrupted, as well as physical exercise adaptations. Thus, an understanding the limit between "ROS that can promote beneficial effects" and "ROS that can promote harmful effects" is a challenging question in exercise biology. The identification of new mediators that cause reductive stress and thereby disrupt exercise-stimulated ROS signaling is a trending on this topic and are covered in this current review.

Redox-related biomarkers in physical exercise

Research in redox biology of exercise has made considerable advances in the last 70 years. Since the seminal study of George Pake's group calculating the content of free radicals in skeletal muscle in resting conditions in 1954, many discoveries have been made in the field. The first section of this review is devoted to highlight the main research findings and fundamental changes in the exercise redox biology discipline. It includes: i) the first steps in free radical research, ii) the relation between exercise and oxidative damage, iii) the redox regulation of muscle fatigue, iv) the sources of free radicals during muscle contractions, and v) the role of reactive oxygen species as regulators of gene transcription and adaptations in skeletal muscle.

In the second section of the manuscript, we review the available biomarkers for assessing health, performance, recovery during exercise training and overtraining in the sport population. Among the set of biomarkers that could be determined in exercise studies we deepen on the four categories of redox biomarkers: i) oxidants, ii) antioxidants, iii) oxidation products (markers of oxidative damage), and iv) measurements of the redox balance (markers of oxidative stress). The main drawbacks, strengths, weaknesses, and methodological considerations of every biomarker are also discussed.

Oxidative eustress: On constant alert for redox homeostasis

In the open metabolic system, redox-related signaling requires continuous monitoring and fine-tuning of the steady-state redox set point. The ongoing oxidative metabolism is a persistent challenge, denoted as oxidative eustress, which operates within a physiological range that has been called the 'Homeodynamic Space', the 'Goldilocks Zone' or the 'Golden Mean'. Spatiotemporal control of redox signaling is achieved by compartmentalized generation and removal of oxidants. The cellular landscape of H₂O₂, the major redox signaling molecule, is characterized by orders-of-magnitude concentration differences between organelles. This concentration pattern is mirrored by the pattern of oxidatively modified proteins, exemplified by S-glutathionylated proteins. The review presents the conceptual background for short-term (non-transcriptional) and longer-term (transcriptional/translational) homeostatic mechanisms of stress and stress responses. The redox set point is a variable moving target value, modulated by circadian rhythm and by external influence, summarily denoted as exposome, which includes nutrition and lifestyle factors. Emerging fields of cell-specific and tissue-specific redox regulation in physiological settings are briefly presented, including new insight into the role of oxidative eustress in embryonal development and lifespan, skeletal muscle and exercise, sleep-wake rhythm, and the function of the nervous system with aspects leading to psychobiology.

Master Regulators of Muscle Atrophy: Role of Costamere Components

The loss of muscle mass and force characterizes muscle atrophy in several different conditions, which share the expression of atrogenes and the activation of their transcriptional regulators. However, attempts to antagonize muscle atrophy development in different experimental contexts by targeting contributors to the atrogene pathway showed partial effects in most cases. Other master regulators might independently contribute to muscle atrophy, as suggested by our recent evidence about the co-requirement of the muscle-specific chaperone protein melusin to inhibit unloading muscle atrophy development. Furthermore, melusin and other muscle mass regulators, such as nNOS, belong to costameres, the macromolecular complexes that connect sarcolemma to myofibrils and to the extracellular matrix, in correspondence with specific sarcomeric sites. Costameres sense a mechanical load and transduce it both as lateral force and biochemical signals. Recent evidence further broadens this classic view, by revealing the crucial participation of costameres in a sarcolemmal “signaling hub” integrating mechanical and humoral stimuli, where mechanical signals are coupled with insulin and/or insulin-like growth factor stimulation to regulate muscle mass. Therefore, this review aims to enucleate available evidence concerning the early involvement of costamere components and additional putative master regulators in the development of major types of muscle atrophy.

Silencing COX-2 blocks PDK1/TRAF4-induced AKT activation to inhibit fibrogenesis during skeletal muscle atrophy

Skeletal muscle atrophy with high prevalence can induce weakness and fatigability and place huge burden on both health and quality of life. During skeletal muscle degeneration, excessive fibroblasts and extracellular matrix (ECM) accumulated to replace and impair the resident muscle fiber and led to loss of muscle mass. Cyclooxygenase-2 (COX-2), the rate-limiting enzyme in synthesis of prostaglandin, has been identified as a positive regulator in pathophysiological process like inflammation and oxidative stress. In our study, we found injured muscles of human subjects and mouse model overexpressed COX-2 compared to the non-damaged region and COX-2 was also upregulated in fibroblasts following TGF-β stimulation. Then we detected the effect of selective COX-2 inhibitor celecoxib on fibrogenesis. Celecoxib mediated anti-fibrotic effect by inhibiting fibroblast differentiation, proliferation and migration as well as inactivating TGF-β-dependent signaling pathway, non-canonical TGF-β pathways and suppressing generation of reactive oxygen species (ROS) and oxidative stress. In vivo pharmacological inhibition of COX-2 by celecoxib decreased tissue fibrosis and increased skeletal muscle fiber preservation reflected by less ECM formation and myofibroblast accumulation with decreased p-ERK1/2, p-Smad2/3, TGF-βR1, VEGF, NOX2 and NOX4 expression. Expression profiling further found that celecoxib could suppress PDK1 expression. The interaction between COX-2 and PDK1/AKT signaling remained unclear, here we found that COX-2 could bind to PDK1/AKT to form compound. Knockdown of COX-2 in fibroblasts by pharmacological inactivation or by siRNA restrained PDK1 expression and AKT phosphorylation induced by TGF-β treatment. Besides, si-COX-2 prevented TGF-β-induced K63-ubiquitination of AKT by blocking the interaction between AKT and E3 ubiquitin ligase TRAF4. In summary, we found blocking COX-2 inhibited fibrogenesis after muscle atrophy induced by injury and suppressed AKT signaling pathway by inhibiting upstream PDK1 expression and preventing the recruitment of TRAF4 to AKT, indicating that COX-2/PDK1/AKT signaling pathway promised to be target for treating muscle atrophy in the future.