Regulation of NADPH oxidases in skeletal muscle

Redox signaling and skeletal muscle adaptation during aerobic exercise

Redox regulation is a fundamental physiological phenomenon related to oxygen-dependent metabolism, and skeletal muscle is mainly regarded as a primary site for oxidative phosphorylation. Several studies have revealed the importance of reactive oxygen and nitrogen species (RONS) in the signaling process relating to muscle adaptation during exercise. To date, improving knowledge of redox signaling in modulating exercise adaptation has been the subject of comprehensive work and scientific inquiry. The primary aim of this review is to elucidate the molecular and biochemical pathways aligned to RONS as activators of skeletal muscle adaptation and to further identify the interconnecting mechanisms controlling redox balance. We also discuss the RONS-mediated pathways during the muscle adaptive process, including mitochondrial biogenesis, muscle remodeling, vascular angiogenesis, neuron regeneration, and the role of exogenous antioxidants.

Reactive oxygen species promote endurance exercise-induced adaptations in skeletal muscles

The discovery that contracting skeletal muscle generates reactive oxygen species (ROS) was first reported over 40 years ago. The prevailing view in the 1980s was that exercise-induced ROS production promotes oxidation of proteins and lipids resulting in muscle damage. However, a paradigm shift occurred in the 1990s as growing research revealed that ROS are signaling molecules, capable of activating transcriptional activators/coactivators and promoting exercise-induced muscle adaptation. Growing evidence supports the notion that reduction-oxidation (redox) signaling pathways play an important role in the muscle remodeling that occurs in response to endurance exercise training. This review examines the specific role that redox signaling plays in this endurance exercise-induced skeletal muscle adaptation. We begin with a discussion of the primary sites of ROS production in contracting muscle fibers followed by a summary of the antioxidant enzymes involved in the regulation of ROS levels in the cell. We then discuss which redox-sensitive signaling pathways promote endurance exercise-induced muscle adaptation and debate the strength of the evidence supporting the notion that redox signaling plays an essential role in muscle adaptation to endurance exercise training. In hopes of stimulating future research, we highlight several important unanswered questions in this field.

Mitochondria and Reactive Oxygen Species: The Therapeutic Balance of Powers for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a genetic progressive muscle-wasting disorder that leads to rapid loss of mobility and premature death. The absence of functional dystrophin in DMD patients reduces sarcolemma stiffness and increases contraction damage, triggering a cascade of events leading to muscle cell degeneration, chronic inflammation, and deposition of fibrotic and adipose tissue. Efforts in the last decade have led to the clinical approval of novel drugs for DMD that aim to restore dystrophin function. However, combination therapies able to restore dystrophin expression and target the myriad of cellular events found impaired in dystrophic muscle are desirable. Muscles are higher energy consumers susceptible to mitochondrial defects. Mitochondria generate a significant source of reactive oxygen species (ROS), and they are, in turn, sensitive to proper redox balance. In both DMD patients and animal models there is compelling evidence that mitochondrial impairments have a key role in the failure of energy homeostasis. Here, we highlighted the main aspects of mitochondrial dysfunction and oxidative stress in DMD and discussed the recent findings linked to mitochondria/ROS-targeted molecules as a therapeutic approach. In this respect, dual targeting of both mitochondria and redox homeostasis emerges as a potential clinical option in DMD.

Blockade of angiotensin II modulates insulin-like growth factor 1-mediated skeletal muscle homeostasis in experimental steatohepatitis

Sarcopenia is associated with mortality in patients with nonalcoholic steatohepatitis (NASH). Angiotensin II receptor blocker (ARB) has been suggested to prevent sarcopenia, but reports on its effect on NASH-derived skeletal muscle atrophy in conjunction with insulin-like growth factor 1 (IGF-1)-mediated muscle homeostasis are few. Our aim was to examine the combined effect of the ARB losartan and IGF-1 replacement on skeletal muscle atrophy in a methionine-choline deficient (MCD) diet-fed murine steatohepatitis model. The MCD-fed mice developed steatohepatitis and skeletal muscle atrophy, as indicated by the reduction of psoas muscle mass and attenuation of forelimb and hindlimb grip strength. Significantly suppressed steatohepatitis and skeletal muscle atrophy was observed after single treatment with ARB or IGF-1, and these effects were augmented after combination treatment. Treatment with ARB and IGF-1 effectively inhibited ubiquitin proteasome-mediated protein degradation by reducing forkhead box protein O1 (FOXO1) and FOXO3a transcriptional activity in the skeletal muscle. Combined ARB and IGF-1 decreased the intramuscular expression of proinflammatory cytokines (i.e., TNFα, IL6, and IL1β) and increased the Trolox equivalent antioxidant capacity and antioxidant enzymes (CAT, GPX1, SOD2, and CYTB). This antioxidant effect was based on downregulation of NADPH oxidase (NOX) 2, normalization of mitochondrial biogenesis and dynamics. Moreover, ARB increased the hepatic and plasma IGF-1 levels and improved steatohepatitis, leading to enhanced skeletal muscle protein synthesis mediated by IGF-1/ AKT/ mechanistic target of rapamycin signaling. Collectively, combined ARB and IGF-1 replacement could be a promising new therapeutic target for NASH-derived skeletal muscle wasting.

Hypoxia-Inducible Factor and Oxidative Stress in Tendon Degeneration: A Molecular Perspective

Tendinopathy is a debilitating condition marked by degenerative changes in the tendons. Its complex pathophysiology involves intrinsic, extrinsic, and physiological factors. While its intrinsic and extrinsic factors have been extensively studied, the role of physiological factors, such as hypoxia and oxidative stress, remains largely unexplored. This review article delves into the contribution of hypoxia-associated genes and oxidative-stress-related factors to tendon degeneration, offering insights into potential therapeutic strategies. The unique aspect of this study lies in its pathway-based evidence, which sheds light on how these factors can be targeted to enhance overall tendon health.

Need for speed: Human fast-twitch mitochondria favor power over efficiency

OBJECTIVE

Human skeletal muscle consists of a mixture of slow- and fast-twitch fibers with distinct capacities for contraction mechanics, fermentation, and oxidative phosphorylation. While the divergence in mitochondrial volume favoring slow-twitch fibers is well established, data on the fiber type-specific intrinsic mitochondrial function and morphology are highly limited with existing data mainly being generated in animal models. This highlights the need for more human data on the topic.

METHODS

Here, we utilized THRIFTY, a rapid fiber type identification protocol to detect, sort, and pool fast- and slow-twitch fibers within 6 h of muscle biopsy sampling. Respiration of permeabilized fast- and slow-twitch fiber pools was then analyzed with high-resolution respirometry. Using standardized western blot procedures, muscle fiber pools were subsequently analyzed for control proteins and key proteins related to respiratory capacity.

RESULTS

Maximal complex I+II respiration was 25% higher in human slow-twitch fibers compared to fast-twitch fibers. However, per mitochondrial volume, the respiratory rate of mitochondria in fast-twitch fibers was approximately 50% higher for complex I+II, which was primarily mediated through elevated complex II respiration. Furthermore, the abundance of complex II protein and proteins regulating cristae structure were disproportionally elevated in mitochondria of the fast-twitch fibers. The difference in intrinsic respiratory rate was not reflected in fatty acid-or complex I respiration.

CONCLUSION

Mitochondria of human fast-twitch muscle fibers compensate for their lack of volume by substantially elevating intrinsic respiratory rate through increased reliance on complex II.

Regular exercise attenuates alcoholic myopathy in zebrafish by modulating mitochondrial homeostasis

Alcoholic myopathy is caused by chronic consumption of alcohol (ethanol) and is characterized by weakness and atrophy of skeletal muscle. Regular exercise is one of the important ways to prevent or alleviate skeletal muscle myopathy. However, the beneficial effects and the exact mechanisms underlying regular exercise on alcohol myopathy remain unclear. In this study, a model of alcoholic myopathy was established using zebrafish soaked in 0.5% ethanol. Additionally, these zebrafish were intervened to swim for 8 weeks at an exercise intensity of 30% of the absolute critical swimming speed (Ucrit), aiming to explore the beneficial effects and underlying mechanisms of regular exercise on alcoholic myopathy. This study found that regular exercise inhibited protein degradation, improved locomotion ability, and increased muscle fiber cross-sectional area (CSA) in ethanol-treated zebrafish. In addition, regular exercise increases the functional activity of mitochondrial respiratory chain (MRC) complexes and upregulates the expression levels of MRC complexes. Regular exercise can also improve oxidative stress and mitochondrial dynamics in zebrafish skeletal muscle induced by ethanol. Additionally, regular exercise can activate mitochondrial biogenesis and inhibit mitochondrial unfolded protein response (UPRmt). Together, our results suggest regular exercise is an effective intervention strategy to improve mitochondrial homeostasis to attenuate alcoholic myopathy.

From workout to molecular switches: How does skeletal muscle produce, sense, and transduce subcellular redox signals?

Skeletal muscle is crucial for maintaining human health and overall quality of life. Acute exercise introduces a multifaceted intracellular stress, with numerous post-translational modifications believed to underpin the health benefits of sustained exercise training. Reactive oxygen species (ROS) are posited to serve as second messengers, triggering cytoprotective adaptations such as the upregulation of enzymatic scavenger systems. However, a significant knowledge gap exists between the generation of oxidants in muscle and the exact mechanisms driving muscle adaptations. This review delves into the current research on subcellular redox biochemistry and its role in the physiological adaptations to exercise. We propose that the subcellular regulation of specific redox modifications is key to ensuring specificity in the intracellular response.

Sarcopenia in a type 2 diabetic state: Reviewing literature on the pathological consequences of oxidative stress and inflammation beyond the neutralizing effect of intracellular antioxidants

Sarcopenia remains one of the major pathological features of type 2 diabetes (T2D), especially in older individuals. This condition describes gradual loss of muscle mass, strength, and function that reduces the overall vitality and fitness, leading to increased hospitalizations and even fatalities to those affected. Preclinical evidence indicates that dysregulated mitochondrial dynamics, together with impaired activity of the NADPH oxidase system, are the major sources of oxidative stress that drive skeletal muscle damage in T2D. While patients with T2D also display relatively higher levels of circulating inflammatory markers in the serum, including high sensitivity-C-reactive protein, interleukin-6, and tumor necrosis factor-α that are independently linked with the deterioration of muscle function and sarcopenia in T2D. In fact, beyond reporting on the pathological consequences of both oxidative stress and inflammation, the current review highlights the importance of strengthening intracellular antioxidant systems to preserve muscle mass, strength, and function in individuals with T2D.

DNA oxidation after exercise: a systematic review and meta-analysis

Purpose: 8-Hydroxy-2'-deoxyguanosine (8-OHdG) is a byproduct of DNA oxidation resulting from free radical attacks. Paradoxically, treatment with 8-OHdG accelerates tissue healing. The aim of this study is to quantify the 8-OHdG response after a single session of exercise in both trained and untrained adults. Methods: A systematic review and meta-analysis of exercise intervention studies measuring changes in blood 8-OHdG following resistance exercise and aerobic exercise were conducted. The literature search included Web of Science, PubMed, BASE, and Scopus, with publications up to February 2023 included. Subgroup analysis of training status was also conducted. Results: Sixteen studies involving 431 participants met the eligibility criteria. Resistance exercise showed a medium effect on increasing circulating 8-OHdG levels (SMD = 0.66, p < 0.001), which was similar for both trained and untrained participants. However, studies on aerobic exercise presented mixed results. For trained participants, a small effect of aerobic exercise on increasing circulating 8-OHdG levels was observed (SMD = 0.42; p < 0.001). In contrast, for untrained participants, a large effect of decreasing circulating 8-OHdG levels was observed, mostly after long-duration aerobic exercise (SMD = -1.16; p < 0.05). Similar to resistance exercise, high-intensity aerobic exercise (5-45 min, ≥75% VO2max) significantly increased circulating 8-OHdG levels, primarily in trained participants. Conclusion: Pooled results from the studies confirm an increase in circulating 8-OHdG levels after resistance exercise. However, further studies are needed to fully confirm the circulating 8-OHdG response to aerobic exercise. Increases in 8-OHdG after high-intensity aerobic exercise are observed only in trained individuals, implicating its role in training adaptation. Systematic Review Registration: [https://Systematicreview.gov/], identifier [CRD42022324180].

Muscle-restricted Nox4 knockout partially corrects muscle contractility following spinal cord injury in mice

Spinal cord injury (SCI) results in severe atrophy of skeletal muscle in paralyzed regions, and a decrease in the force generated by muscle per unit of cross-sectional area. Oxidation of skeletal muscle ryanodine 1 receptors (RyR1) reduces contractile force due to reduced binding of calstabin 1 to RyR1 together with altered gating of RyR1. One cause of RyR1 oxidation is NADPH oxidase 4 (Nox4). We have previously shown that in rats, RyR1 was oxidized and bound less calstabin 1 at 56 days after spinal cord injury (SCI) by transection. Here, we used a conditional knock-out mouse model of Nox4 in muscle to investigate the role of Nox4 in reduced muscle specific force after SCI. Peak twitch force in control mice after SCI was reduced by 42% compared to sham-operated controls but was increased by approximately 43% in SCI Nox4 conditional KO mice compared to SCI controls although it remained less than that for sham-operated controls. Unlike what observed in rats, after SCI the expression of Nox4 was not increased in gastrocnemius muscle and binding of calstabin 1 to RyR1 was not reduced in this muscle. The results suggest a link between Nox4 expression in muscle tissue and reduction in muscle twitch force, however further studies are needed to understand the mechanistic basis for this linkage.

Effects of aerobic exercise on cardiac function and gene expression of NADPH oxidases in diaphragm muscle of rats with aortic stenosis-induced heart failure

We evaluated the influence of aerobic physical exercise (EX) on gene-encoding proteins associated with oxidative stress in diaphragm muscle of rats with aortic stenosis-induced heart failure (HF). Wistar male rats were divided into four groups: Control sedentary (C); Control exercise (C-Ex); Sedentary aortic stenosis (AS); Aortic stenosis exercise (AS-Ex). Exercised rats trained 5 times a week for 10 weeks on a treadmill. Statistical analysis was performed by ANOVA or Kruskal-Wallis test. In the final echocardiogram, animals with aortic stenosis subjected to exercise demonstrated improvement in systolic function compared to the sedentary aortic stenosis group. In diaphragm muscle, the activity of antioxidant enzymes, malondialdehyde malondialdehyde concentration, protein carbonylation, and protein expression of p65 and its inhibitor IκB did not differ between groups. Alterations in gene expression of sources that generate reactive species of oxygen were observed in AS-Ex group, which showed decreased mRNA abundance of NOX2 and NOX4 compared to the aortic stenosis group (p < 0.05). We concluded that aerobic exercise has a positive impact during heart failure, ameliorating systolic dysfunction and biomarkers of oxidative stress in diaphragm muscle of rats with aortic stenosis-induced heart failure.

Effect of RONS-Induced Intracellular Redox Homeostasis in 6-NBDG/Glucose Uptake in C2C12 Myotubes and Single Isolated Skeletal Muscle Fibres

The glucose uptake in skeletal muscle is essential to produce energy through ATP, which is needed by this organ to maintain vital functions. The impairment of glucose uptake compromises the metabolism and function of skeletal muscle and other organs and is a feature of diabetes, obesity, and ageing. There is a need for research to uncover the mechanisms involved in the impairment of glucose uptake in skeletal muscle. In this study, we adapted, developed, optimised, and validated a methodology based on the fluorescence glucose analogue 6-NBDG, combined with a quantitative fluorescence microscopy image analysis, to determine the glucose uptake in two models of skeletal muscle cells: C2C12 myotubes and single fibres isolated from muscle. It was proposed that reactive oxygen and nitrogen species (RONS) and redox homeostasis play an important role in the modulation of intracellular redox signalling pathways associated with glucose uptake. In this study, we prove that the prooxidative intracellular redox environment under oxidative eustress produced by RONS such as hydrogen peroxide and nitric oxide improves glucose uptake in skeletal muscle cells. However, when oxidation is excessive, oxidative distress occurs, and cellular viability is compromised, although there might be an increase in the glucose uptake. Based on the results of this study, the determination of 6-NBDG/glucose uptake in myotubes and skeletal muscle cells is feasible, validated, and will contribute to improve future research.

Recent advances on the molecular mechanisms of exercise-induced improvements of cognitive dysfunction

Physical exercise is of great significance for maintaining human health. Exercise can provide varying degrees of benefits to cognitive function at all stages of life cycle. Currently, with the aging of the world's population and increase of life expectancy, cognitive dysfunction has gradually become a disease of high incidence, which is accompanied by neurodegenerative diseases in elderly individuals. Patients often exhibit memory loss, aphasia and weakening of orientation once diagnosed, and are unable to have a normal life. Cognitive dysfunction largely affects the physical and mental health, reduces the quality of life, and causes a great economic burden to the society. At present, most of the interventions are aimed to maintain the current cognitive level and delay deterioration of cognition. In contrast, exercise as a nonpharmacological therapy has great advantages in its nontoxicity, low cost and universal application. The molecular mechanisms underlying the effect of exercise on cognition are complex, and studies have been extensively centered on neural plasticity, the direct target of exercise in the brain. In addition, mitochondrial stability and energy metabolism are essential for brain status. Meanwhile, the organ-brain axis responds to exercise and induces release of cytokines related to cognition. In this review, we summarize the latest evidence on the molecular mechanisms underlying the effects of exercise on cognition, and point out directions for future research.

Skeletal muscle Nox4 knockout prevents and Nox2 knockout blunts loss of maximal diaphragm force in mice with heart failure with reduced ejection fraction

Patients with heart failure with reduced ejection fraction (HFrEF) experience diaphragm weakness that contributes to the primary disease symptoms of fatigue, dyspnea, and exercise intolerance. Weakness in the diaphragm is related to excessive production of reactive oxygen species (ROS), but the exact source of ROS remains unknown. NAD(P)H Oxidases (Nox), particularly the Nox2 and 4 isoforms, are important sources of ROS within skeletal muscle that contribute to optimal cell function. There are reports of increased Nox activity in the diaphragm of patients and animal models of HFrEF, implicating these complexes as possible sources of diaphragm dysfunction in HFrEF. To investigate the role of these proteins on diaphragm weakness in HFrEF, we generated inducible skeletal muscle specific knockouts of Nox2 or Nox4 using the Cre-Lox system and assessed diaphragm function in a mouse model of HFrEF induced by myocardial infarction. Diaphragm maximal specific force measured in vitro was depressed by ∼20% with HFrEF. Skeletal muscle knockout of Nox4 provided full protection against the loss of maximal force (p < 0.01), while the knockout of Nox2 provided partial protection (7% depression, p < 0.01). Knockout of Nox2 from skeletal myofibers improved survival from 50 to 80% following myocardial infarction (p = 0.026). Our findings show an important role for skeletal muscle NAD(P)H Oxidases contributing to loss of diaphragm maximal force in HFrEF, along with systemic pathophysiological responses following myocardial infarction.

Polyphenol Supplementation and Antioxidant Status in Athletes: A Narrative Review

Antioxidants in sports exercise training remain a debated research topic. Plant-derived polyphenol supplements are frequently used by athletes to reduce the negative effects of exercise-induced oxidative stress, accelerate the recovery of muscular function, and enhance performance. These processes can be efficiently modulated by antioxidant supplementation. The existing literature has failed to provide unequivocal evidence that dietary polyphenols should be promoted specifically among athletes. This narrative review summarizes the current knowledge regarding polyphenols' bioavailability, their role in exercise-induced oxidative stress, antioxidant status, and supplementation strategies in athletes. Overall, we draw attention to the paucity of available evidence suggesting that most antioxidant substances are beneficial to athletes. Additional research is necessary to reveal more fully their impact on exercise-induced oxidative stress and athletes' antioxidant status, as well as optimal dosing methods.

Exercise Training and Skeletal Muscle Antioxidant Enzymes: An Update

The pivotal observation that muscular exercise is associated with oxidative stress in humans was first reported over 45 years ago. Soon after this landmark finding, it was discovered that contracting skeletal muscles produce oxygen radicals and other reactive species capable of oxidizing cellular biomolecules. Importantly, the failure to eliminate these oxidant molecules during exercise results in oxidation of cellular proteins and lipids. Fortuitously, muscle fibers and other cells contain endogenous antioxidant enzymes capable of eliminating oxidants. Moreover, it is now established that several modes of exercise training (e.g., resistance exercise and endurance exercise) increase the expression of numerous antioxidant enzymes that protect myocytes against exercise-induced oxidative damage. This review concisely summarizes the impact of endurance, high-intensity interval, and resistance exercise training on the activities of enzymatic antioxidants within skeletal muscles in humans and other mammals. We also discuss the evidence that exercise-induced up-regulation of cellular antioxidants reduces contraction-induced oxidative damage in skeletal muscles and has the potential to delay muscle fatigue and improve exercise performance. Finally, in hopes of stimulating further research, we also discuss gaps in our knowledge of exercise-induced changes in muscle antioxidant capacity.

Phytochemicals and modulation of exercise-induced oxidative stress: a novel overview of antioxidants

The practice of physical exercise induces a series of physiological changes in the body at different levels, either acutely or chronically. During exercise, the increase in oxygen consumption promotes the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS), which are necessary to maintain homeostasis. ROS/RNS activate cellular signaling pathways, such as the antioxidant cytoprotective systems, inflammation, and cell proliferation, which are crucial for cell survival. However, in exhaustive-extended physical exercise, workloads can exceed the endogenous antioxidant defenses, which may be related to impairment of muscle contraction, fatigue, and a decrease in athletic performance. This review addresses the role of some antioxidants from plant-derived extracts called phytochemicals that can mediate the response to oxidative stress induced by physical exercise by activating signaling pathways, such as Nrf2/Keap1/ARE, responsible for the endogenous antioxidant response and possibly having an impact on sports performance.

Advances in the study of nicotinamide adenine dinucleotide phosphate oxidase in myocardial remodeling

Myocardial remodeling is a key pathophysiological basis of heart failure, which seriously threatens human health and causes a severe economic burden worldwide. During chronic stress, the heart undergoes myocardial remodeling, mainly manifested by cardiomyocyte hypertrophy, apoptosis, interstitial fibrosis, chamber enlargement, and cardiac dysfunction. The NADPH oxidase family (NOXs) are multisubunit transmembrane enzyme complexes involved in the generation of redox signals. Studies have shown that NOXs are highly expressed in the heart and are involved in the pathological development process of myocardial remodeling, which influences the development of heart failure. This review summarizes the progress of research on the pathophysiological processes related to the regulation of myocardial remodeling by NOXs, suggesting that NOXs-dependent regulatory mechanisms of myocardial remodeling are promising new therapeutic targets for the treatment of heart failure.

Embryonic transcriptome unravels mechanisms and pathways underlying embryonic development with respect to muscle growth, egg production, and plumage formation in native and broiler chickens

Background: Muscle development, egg production, and plumage colors are different between native and broiler chickens. The study was designed to investigate why improved Aseel (PD4) is colorful, stronger, and grew slowly compared with the control broiler (CB).

Methods: A microarray was conducted using the 7th-day embryo (7EB) and 18th-day thigh muscle (18TM) of improved Aseel and broiler, respectively. Also, we have selected 24 Gallus gallus candidate reference genes from NCBI, and total RNA was isolated from the broiler, improved Aseel embryo tissues, and their expression profiles were studied by real-time quantitative PCR (qPCR). Furthermore, microarray data were validated with qPCR using improved Aseel and broiler embryo tissues.

Results: In the differential transcripts screening, all the transcripts obtained by microarray of slow and fast growth groups were screened by fold change ≥ 1 and false discovery rate (FDR) ≤ 0.05. In total, 8,069 transcripts were differentially expressed between the 7EB and 18TM of PD4 compared to the CB. A further analysis showed that a high number of transcripts are differentially regulated in the 7EB of PD4 (6,896) and fewer transcripts are differentially regulated (1,173) in the 18TM of PD4 compared to the CB. On the 7th^- and 18th-day PD4 embryos, 3,890, 3,006, 745, and 428 transcripts were up- and downregulated, respectively. The commonly up- and downregulated transcripts are 91 and 44 between the 7th- and 18th-day of embryos. In addition, the best housekeeping gene was identified. Furthermore, we validated the differentially expressed genes (DEGs) related to muscle growth, myostatin signaling and development, and fatty acid metabolism genes in PD4 and CB embryo tissues by qPCR, and the results correlated with microarray expression data.

Conclusion: Our study identified DEGs that regulate the myostatin signaling and differentiation pathway; glycolysis and gluconeogenesis; fatty acid metabolism; Jak-STAT, mTOR, and TGF-β signaling pathways; tryptophan metabolism; and PI3K-Akt signaling pathways in PD4. The results revealed that the gene expression architecture is present in the improved Aseel exhibiting embryo growth that will help improve muscle development, differentiation, egg production, protein synthesis, and plumage formation in PD4 native chickens. Our findings may be used as a model for improving the growth in Aseel as well as optimizing the growth in the broiler.

Simultaneous loss of TSC1 and DEPDC5 in skeletal and cardiac muscles produces early-onset myopathy and cardiac dysfunction associated with oxidative damage and SQSTM1/p62 accumulation

By promoting anabolism, MTORC1 is critical for muscle growth and maintenance. However, genetic MTORC1 upregulation promotes muscle aging and produces age-associated myopathy. Whether MTORC1 activation is sufficient to produce myopathy or indirectly promotes it by accelerating tissue aging is elusive. Here we examined the effects of muscular MTORC1 hyperactivation, produced by simultaneous depletion of TSC1 and DEPDC5 (CKM-TD). CKM-TD mice produced myopathy, associated with loss of skeletal muscle mass and force, as well as cardiac failure and bradypnea. These pathologies were manifested at eight weeks of age, leading to a highly penetrant fatality at around twelve weeks of age. Transcriptome analysis indicated that genes mediating proteasomal and macroautophagic/autophagic pathways were highly upregulated in CKM-TD skeletal muscle, in addition to inflammation, oxidative stress, and DNA damage signaling pathways. In CKM-TD muscle, autophagosome levels were increased, and the AMPK and ULK1 pathways were activated; in addition, autophagy induction was not completely blocked in CKM-TD myotubes. Despite the upregulation of autolysosomal markers, CKM-TD myofibers exhibited accumulation of autophagy substrates, such as SQSTM1/p62 and ubiquitinated proteins, suggesting that the autophagic activities were insufficient. Administration of a superoxide scavenger, tempol, normalized most of these molecular pathologies and subsequently restored muscle histology and force generation. However, CKM-TD autophagy alterations were not normalized by rapamycin or tempol, suggesting that they may involve non-canonical targets other than MTORC1. These results collectively indicate that the concomitant muscle deficiency of TSC1 and DEPDC5 can produce early-onset myopathy through accumulation of oxidative stress, which dysregulates myocellular homeostasis.Abbreviations: AMPK: AMP-activated protein kinase; CKM: creatine kinase, M-type; COX: cytochrome oxidase; DEPDC5: DEP domain containing 5, GATOR1 subcomplex subunit; DHE: dihydroethidium; EDL: extensor digitorum longus; EIF4EBP1: eukaryotic translation initiation factor 4E binding protein 1; GAP: GTPase-activating protein; GTN: gastrocnemius; MTORC1: mechanistic target of rapamycin kinase complex 1; PLA: plantaris; QUAD: quadriceps; RPS6KB/S6K: ribosomal protein S6 kinase beta; SDH: succinate dehydrogenase; SOL: soleus; SQSTM1: sequestosome 1; TA: tibialis anterior; TSC1: TSC complex subunit 1; ULK1: unc-51 like autophagy activating kinase 1.

Glucose 6-P Dehydrogenase—An Antioxidant Enzyme with Regulatory Functions in Skeletal Muscle during Exercise

Hypomorphic Glucose 6-P dehydrogenase (G6PD) alleles, which cause G6PD deficiency, affect around one in twenty people worldwide. The high incidence of G6PD deficiency may reflect an evolutionary adaptation to the widespread prevalence of malaria, as G6PD-deficient red blood cells (RBCs) are hostile to the malaria parasites that infect humans. Although medical interest in this enzyme deficiency has been mainly focused on RBCs, more recent evidence suggests that there are broader implications for G6PD deficiency in health, including in skeletal muscle diseases. G6PD catalyzes the rate-limiting step in the pentose phosphate pathway (PPP), which provides the precursors of nucleotide synthesis for DNA replication as well as reduced nicotinamide adenine dinucleotide phosphate (NADPH). NADPH is involved in the detoxification of cellular reactive oxygen species (ROS) and de novo lipid synthesis. An association between increased PPP activity and the stimulation of cell growth has been reported in different tissues including the skeletal muscle, liver, and kidney. PPP activity is increased in skeletal muscle during embryogenesis, denervation, ischemia, mechanical overload, the injection of myonecrotic agents, and physical exercise. In fact, the highest relative increase in the activity of skeletal muscle enzymes after one bout of exhaustive exercise is that of G6PD, suggesting that the activation of the PPP occurs in skeletal muscle to provide substrates for muscle repair. The age-associated loss in muscle mass and strength leads to a decrease in G6PD activity and protein content in skeletal muscle. G6PD overexpression in Drosophila Melanogaster and mice protects against metabolic stress, oxidative damage, and age-associated functional decline, and results in an extended median lifespan. This review discusses whether the well-known positive effects of exercise training in skeletal muscle are mediated through an increase in G6PD.

Redox signaling regulates skeletal muscle remodeling in response to exercise and prolonged inactivity

Skeletal muscle fibers are malleable and undergo rapid remodeling in response to increased contractile activity (i.e., exercise) or prolonged periods of muscle inactivity (e.g., prolonged bedrest). Exploration of the cell signaling pathways regulating these skeletal muscle adaptations reveal that redox signaling pathways play a key role in the control of muscle remodeling during both exercise and prolonged muscle inactivity. In this regard, muscular exercise results in an acute increase in the production of reactive oxygen species (ROS) in the contracting fibers; however, this contraction-induced rise in ROS production rapidly declines when contractions cease. In contrast, prolonged muscle disuse results in a chronic elevation in ROS production within the inactive fibers. This difference in the temporal pattern of ROS production in muscle during exercise and muscle inactivity stimulates divergent cell-signaling pathways that activate both genomic and nongenomic mechanisms to promote muscle remodeling. This review examines the role that redox signaling plays in skeletal muscle adaptation in response to both prolonged muscle inactivity and endurance exercise training. We begin with a summary of the sites of ROS production in muscle fibers followed by a review of the cellular antioxidants that are responsible for regulation of ROS levels in the cell. We then discuss the specific redox-sensitive signaling pathways that promote skeletal muscle adaptation in response to both prolonged muscle inactivity and exercise. To stimulate future research, we close with a discussion of unanswered questions in this exciting field.

Resistance Exercise Training Improves Metabolic and Inflammatory Control in Adipose and Muscle Tissues in Mice Fed a High-Fat Diet

This study investigates whether ladder climbing (LC), as a model of resistance exercise, can reverse whole-body and skeletal muscle deleterious metabolic and inflammatory effects of high-fat (HF) diet-induced obesity in mice. To accomplish this, Swiss mice were fed for 17 weeks either standard chow (SC) or an HF diet and then randomly assigned to remain sedentary or to undergo 8 weeks of LC training with progressive increases in resistance weight. Prior to beginning the exercise intervention, HF-fed animals displayed a 47% increase in body weight (BW) and impaired ability to clear blood glucose during an insulin tolerance test (ITT) when compared to SC animals. However, 8 weeks of LC significantly reduced BW, adipocyte size, as well as glycemia under fasting and during the ITT in HF-fed rats. LC also increased the phosphorylation of Akt_Ser473 and AMPK_Thr172 and reduced tumor necrosis factor-alpha (TNF-α) and interleukin 1 beta (IL1-β) contents in the quadriceps muscles of HF-fed mice. Additionally, LC reduced the gene expression of inflammatory markers and attenuated HF-diet-induced NADPH oxidase subunit gp91phox in skeletal muscles. LC training was effective in reducing adiposity and the content of inflammatory mediators in skeletal muscle and improved whole-body glycemic control in mice fed an HF diet.

Taurine Administration Counteracts Aging-Associated Impingement of Skeletal Muscle Regeneration by Reducing Inflammation and Oxidative Stress

Sarcopenia, which occurs during aging, is characterized by the gradual loss of skeletal muscle mass and function, resulting in a functional decline in physical abilities. Several factors contribute to the onset of sarcopenia, including reduced regenerative capacity, chronic low-grade inflammation, mitochondrial dysfunction, and increased oxidative stress, leading to the activation of catabolic pathways. Physical activity and adequate protein intake are considered effective strategies able to reduce the incidence and severity of sarcopenia by exerting beneficial effects in improving the muscular anabolic response during aging. Taurine is a non-essential amino acid that is highly expressed in mammalian tissues and, particularly, in skeletal muscle where it is involved in the regulation of biological processes and where it acts as an antioxidant and anti-inflammatory factor. Here, we evaluated whether taurine administration in old mice counteracts the physiopathological effects of aging in skeletal muscle. We showed that, in injured muscle, taurine enhances the regenerative process by downregulating the inflammatory response and preserving muscle fiber integrity. Moreover, taurine attenuates ROS production in aged muscles by maintaining a proper cellular redox balance, acting as an antioxidant molecule. Although further studies are needed to better elucidate the molecular mechanisms responsible for the beneficial effect of taurine on skeletal muscle homeostasis, these data demonstrate that taurine administration ameliorates the microenvironment allowing an efficient regenerative process and attenuation of the catabolic pathways related to the onset of sarcopenia.

Apocynin Attenuates Diabetes-Induced Skeletal Muscle Dysfunction by Mitigating ROS Generation and Boosting Antioxidant Defenses in Fast-Twitch and Slow-Twitch Muscles

In response to diabetes mellitus, skeletal muscle is negatively affected, as is evident by reduced contractile force production, increased muscle fatigability, and increased levels of oxidative stress biomarkers. Apocynin is a widely used NADPH oxidase inhibitor, with antioxidant and anti-inflammatory potential. It has been effective for amelioration of a variety of disorders, including diabetic complications. Therefore, the present study was conducted to evaluate the effects and action mechanisms of apocynin in slow- and fast-twitch diabetic rat muscles. Male Wistar rats were rendered diabetic by applying intraperitoneally a single dose of streptozotocin (45 mg/kg). Apocynin treatment (3 mg/kg/day) was administered over 8 weeks. Fasting blood glucose (FBG), insulin tolerance and body weight gain were measured. Both slow (soleus) and fast (extensor digitorum longus, EDL) skeletal muscles were used for muscle function evaluation, oxidative stress markers, and evaluating gene expression using qRT-PCR. Treatment with apocynin significantly reduced FBG levels and enhanced insulin tolerance. Apocynin also prevented muscle contractile dysfunction in EDL muscle but had no significant effect on this parameter in soleus muscles. However, in both types of muscles, apocynin mitigated the oxidative stress by decreasing ROS levels and increasing total glutathione levels and redox state. Concomitantly, apocynin also statistically enhanced Nrf-2 and GLU4 mRNA expression and downregulated NOX2, NOX4, and NF-κB mRNA. Collectively, apocynin exhibits properties myoprotective in diabetic animals. These findings indicate that apocynin predominantly acts as an antioxidant in fast-twitch and slow-twitch muscles but has differential impact on contractile function.

Circadian Clocks, Redox Homeostasis, and Exercise: Time to Connect the Dots?

Compelling research has documented how the circadian system is essential for the maintenance of several key biological processes including homeostasis, cardiovascular control, and glucose metabolism. Circadian clock disruptions, or losses of rhythmicity, have been implicated in the development of several diseases, premature ageing, and are regarded as health risks. Redox reactions involving reactive oxygen and nitrogen species (RONS) regulate several physiological functions such as cell signalling and the immune response. However, oxidative stress is associated with the pathological effects of RONS, resulting in a loss of cell signalling and damaging modifications to important molecules such as DNA. Direct connections have been established between circadian rhythms and oxidative stress on the basis that disruptions to circadian rhythms can affect redox biology, and vice versa, in a bi-directional relationship. For instance, the expression and activity of several key antioxidant enzymes (SOD, GPx, and CAT) appear to follow circadian patterns. Consequently, the ability to unravel these interactions has opened an exciting area of redox biology. Exercise exerts numerous benefits to health and, as a potent environmental cue, has the capacity to adjust disrupted circadian systems. In fact, the response to a given exercise stimulus may also exhibit circadian variation. At the same time, the relationship between exercise, RONS, and oxidative stress has also been scrutinised, whereby it is clear that exercise-induced RONS can elicit both helpful and potentially harmful health effects that are dependent on the type, intensity, and duration of exercise. To date, it appears that the emerging interface between circadian rhythmicity and oxidative stress/redox metabolism has not been explored in relation to exercise. This review aims to summarise the evidence supporting the conceptual link between the circadian clock, oxidative stress/redox homeostasis, and exercise stimuli. We believe carefully designed investigations of this nexus are required, which could be harnessed to tackle theories concerned with, for example, the existence of an optimal time to exercise to accrue physiological benefits.

Skeletal Muscle Microvascular Dysfunction in Obesity-Related Insulin Resistance: Pathophysiological Mechanisms and Therapeutic Perspectives

Obesity is a worrisomely escalating public health problem globally and one of the leading causes of morbidity and mortality from noncommunicable disease. The epidemiological link between obesity and a broad spectrum of cardiometabolic disorders has been well documented; however, the underlying pathophysiological mechanisms are only partially understood, and effective treatment options remain scarce. Given its critical role in glucose metabolism, skeletal muscle has increasingly become a focus of attention in understanding the mechanisms of impaired insulin function in obesity and the associated metabolic sequelae. We examined the current evidence on the relationship between microvascular dysfunction and insulin resistance in obesity. A growing body of evidence suggest an intimate and reciprocal relationship between skeletal muscle microvascular and glucometabolic physiology. The obesity phenotype is characterized by structural and functional changes in the skeletal muscle microcirculation which contribute to insulin dysfunction and disturbed glucose homeostasis. Several interconnected etiologic molecular mechanisms have been suggested, including endothelial dysfunction by several factors, extracellular matrix remodelling, and induction of oxidative stress and the immunoinflammatory phenotype. We further correlated currently available pharmacological agents that have deductive therapeutic relevance to the explored pathophysiological mechanisms, highlighting a potential clinical perspective in obesity treatment.

The Effect of Aerobic Exercise on the Oxidative Capacity of Skeletal Muscle Mitochondria in Mice with Impaired Glucose Tolerance

METHODS

Male C57BL/6J mice were randomly divided into six different experimental groups (8 animals/group): (1) normal group (NOR), (2) normal control group (NC), (3) normal + exercise group (NE), (4) IGT group (IGT), (5) IGT control group (IC), and (6) IGT+ exercise group (IE).The exercise group received aerobic exercise for 8 weeks. After the intervention, a blood glucose meter was used to detect the level of glucose tolerance in the mouse's abdominal cavity; a biochemical kit was used to detect serum lipid metabolism indicators, malondialdehyde, and superoxide dismutase levels; the ELISA method was used to detect serum insulin and mouse gastrocnemius homogenate LDH, PDH, SDH, and CCO levels. Western blot method was used to detect the protein expression levels of NOX4, PGC-1α, and Mfn2 in the gastrocnemius muscle of mice.

RESULTS

(1) Mice with high-fat diet for 30 weeks showed impaired glucose tolerance, insulin resistance, and lipid metabolism disorders. The level of LDH, PDH, SDH, and CCO in the gastrocnemius homogenate of mice was reduced. The expressions of NOX4 protein were significantly upregulated, while the expressions of PGC-1α and Mfn2 proteins were significantly downregulated. (2) 8-week aerobic exercise improved the disorders of glucose and lipid metabolism in IGT mice and increased homogenized LDH, PDH, SDH, and CCO levels, and the expressions of NOX4, PGC-1α, and Mfn2 proteins in the gastrocnemius muscle of mice were reversed. It is speculated that aerobic exercise can accelerate energy metabolism.

CONCLUSION

(1) C57BL/6 mice were fed high fat for 30 weeks and successfully constructed a mouse model of reduced diabetes; the mice with reduced diabetes have impaired glucose tolerance, insulin resistance, and lipid metabolism disorders; (2) 8 weeks of aerobic exercise improve glucose tolerance, reduce glucose tolerance in mice, reduce insulin resistance, improve lipid metabolism disorders, and reduce oxidative stress; (3) 8-week aerobic exercise reduces skeletal muscle NOX4 expression and increases glucose tolerance; reduces the expression of LDH, PDH, SDH, and CCO in mouse skeletal muscle; increases the expression level of mitochondrial fusion protein 2 and PGC-1α; improves glucose tolerance; reduces energy metabolism of mouse skeletal muscle; reduces oxidative stress; and reduces insulin resistance. It is speculated that aerobic exercise can accelerate energy metabolism. This process may involve two aspects: firstly, increase the expression level of oxidative metabolism enzymes and promote the tricarboxylic acid cycle; secondly, increase the expression of Mfn2 and accelerate mitochondria fission or fusion to regulate energy metabolism, thereby reducing oxidative stress and insulin resistance.

The Atrophic Effect of 1,25(OH)2 Vitamin D3 (Calcitriol) on C2C12 Myotubes Depends on Oxidative Stress

Dysfunctional mitochondrial metabolism has been linked to skeletal muscle loss in several physio-pathological states. Although it has been reported that vitamin D (VD) supports cellular redox homeostasis by maintaining normal mitochondrial functions, and VD deficiency often occurs in conditions associated with skeletal muscle loss, the efficacy of VD supplementation to overcome muscle wasting is debated. Investigations on the direct effects of VD metabolites on skeletal muscle using C2C12 myotubes have revealed an unexpected pro-atrophic activity of calcitriol (1,25VD), while its upstream metabolites cholecalciferol (VD3) and calcidiol (25VD) have anti-atrophic effects. Here, we investigated if the atrophic effects of 1,25VD on myotubes depend on its activity on mitochondrial metabolism. The impact of 1,25VD and its upstream metabolites VD3 and 25VD on mitochondria dynamics and the activity of C2C12 myotubes was evaluated by measuring mitochondrial content, architecture, metabolism, and reactive oxygen species (ROS) production. We found that 1,25VD induces atrophy through protein kinase C (PKC)-mediated ROS production, mainly of extramitochondrial origin. Consistent with this, cotreatment with the antioxidant N-acetylcysteine (NAC), but not with the mitochondria-specific antioxidant mitoTEMPO, was sufficient to blunt the atrophic activity of 1,25VD. In contrast, VD3 and 25VD have antioxidant properties, suggesting that the efficacy of VD supplementation might result from the balance between atrophic pro-oxidant (1,25VD) and protective antioxidant (VD3 and 25VD) metabolites.

Fermented Oyster Extract Attenuated Dexamethasone-Induced Muscle Atrophy by Decreasing Oxidative Stress

It is well known that oxidative stress induces muscle atrophy, which decreases with the activation of Nrf2/HO-1. Fermented oyster extracts (FO), rich in γ-aminobutyric acid (GABA) and lactate, have shown antioxidative effects. We evaluated whether FO decreased oxidative stress by upregulating Nrf2/HO-1 and whether it decreased NF-κB, leading to decreased IL-6 and TNF-α. Decreased oxidative stress led to the downregulation of Cbl-b ubiquitin ligase, which increased IGF-1 and decreased FoxO3, atrogin1, and Murf1, and eventually decreased muscle atrophy in dexamethasone (Dexa)-induced muscle atrophy animal model. For four weeks, mice were orally administered with FO, GABA, lactate, or GABA+Lactate, and then Dexa was subcutaneously injected for ten days. During Dexa injection period, FO, GABA, lactate, or GABA+Lactate were also administered, and grip strength test and muscle harvesting were performed on the day of the last Dexa injection. We compared the attenuation effect of FO with GABA, lactate, and GABA+lactate treatment. Nrf2 and HO-1 expressions were increased by Dexa but decreased by FO; SOD activity and glutathione levels were decreased by Dexa but increased by FO; NADPH oxidase activity was increased by Dexa but decreased by FO; NF-κB, IL-6, and TNF-α activities were increased by Dexa were decreased by FO; Cbl-b expression was increased by Dexa but restored by FO; IGF-1 expression was decreased by Dexa but increased by FO; FoxO3, Atrogin-1, and MuRF1 expressions were increased by Dexa but decreased by FO. The gastrocnemius thickness and weight were decreased by Dexa but increased by FO. The cross-sectional area of muscle fiber and grip strength were decreased by Dexa but increased by FO. In conclusion, FO decreased Dexa-induced oxidative stress through the upregulation of Nrf2/HO-1. Decreased oxidative stress led to decreased Cbl-b, FoxO3, atrogin1, and MuRF1, which attenuated muscle atrophy.

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.

A higher mitochondrial content is associated with greater oxidative damage, oxidative defenses, protein synthesis and ATP turnover in resting skeletal muscle

An unavoidable consequence of aerobic metabolism is the production of reactive oxygen species (ROS). Mitochondria have historically been considered the primary source of ROS; however, recent literature has highlighted the uncertainty in primary ROS production sites and it is unclear how variation in mitochondrial density influences ROS-induced damage and protein turnover. Fish skeletal muscle is composed of distinct, highly aerobic red muscle and anaerobic white muscle, offering an excellent model system in which to evaluate the relationship of tissue aerobic capacity and ROS-induced damage under baseline conditions. The present study used a suite of indices to better understand potential consequences of aerobic tissue capacity in red and white muscle of the pinfish, Lagodon rhomboides. Red muscle had a 7-fold greater mitochondrial volume density than white muscle, and more oxidative damage despite also having higher activity of the antioxidant enzymes superoxide dismutase and catalase. The dominant protein degradation system appears to be tissue dependent. Lysosomal degradation markers and autophagosome volume density were greater in white muscle, while ubiquitin expression and 20S proteasome activity were significantly greater in red muscle. However, ubiquitin ligase expression was significantly higher in white muscle. Red muscle had a more than 2-fold greater rate of translation and total ATP turnover than white muscle, results that may be due in part to the higher mitochondrial density and the associated increase in oxidative damage. Together, these results support the concept that an elevated aerobic capacity is associated with greater oxidative damage and higher costs of protein turnover.

Redox interactions of immune cells and muscle in the regulation of exercise-induced pain and analgesia: implications on the modulation of muscle nociceptor sensory neurons

The mechanistic interactions among redox status of leukocytes, muscle, and exercise in pain regulation are still poorly understood and limit targeted treatment. Exercise benefits are numerous, including the treatment of chronic pain. However, unaccustomed exercise may be reported as undesirable as it may contribute to pain. The aim of the present review is to evaluate the relationship between oxidative metabolism and acute exercise-induced pain, and as to whether improved antioxidant capacity underpins the analgesic effects of regular exercise. Preclinical and clinical studies addressing relevant topics on mechanisms by which exercise modulates the nociceptive activity and how redox status can outline pain and analgesia are discussed, in sense of translating into refined outcomes. Emerging evidence points to the role of oxidative stress-induced signaling in sensitizing nociceptor sensory neurons. In response to acute exercise, there is an increase in oxidative metabolism, and consequently, pain. Instead, regular exercise can modulate redox status in favor of antioxidant capacity and repair mechanisms, which have consequently increased resistance to oxidative stress, damage, and pain. Data indicate that acute sessions of unaccustomed prolonged and/or intense exercise increase oxidative metabolism and regulate exercise-induced pain in the post-exercise recovery period. Further, evidence demonstrates regular exercise improves antioxidant status, indicating its therapeutic utility for chronic pain disorders. An improved comprehension of the role of redox status in exercise can provide helpful insights into immune-muscle communication during pain modulatory effects of exercise and support new therapeutic efforts and rationale for the promotion of exercise.

Accumulation of lipofuscin in broiler chicken with wooden breast

Lipofuscin is one of the indicators of oxidative stress. To elucidate the role of oxidative stress in the development of wooden breast, this study investigates lipofuscin accumulation in various parts of wooden breast muscles. Sampling was performed using 46-day-old broiler chickens housed at a commercial Japanese poultry slaughterhouse. Fourteen wooden breast fillets and 13 normal breast fillets were collected in the deboning line. The samples used to measure shear force, 2-thiobarbituric acid reactive substance (TBARS), and for histological analysis were taken from the six portions of breast muscle fillets. In muscles affected by wooden breast, vacuolated muscle fibers were observed, and connective tissues appearing like perimysium were expanded with fibrosis. TBARS value and accumulation of lipofuscin were significantly higher in the wooden breast than in the normal breasts. A lot of lipofuscin granules were localized in the cytoplasm of collapsed muscle fibers of the wooden breast. The cranial portion of the wooden breast showed the highest shear force. The cranial position had a large amount of connective tissue and lipofuscin granules. The results of the present study strongly suggest that high oxidative stress, especially with a significant accumulation of lipofuscin, is associated with the development of wooden breasts.

High-Intensity Interval Training and Moderate-Intensity Continuous Training Attenuate Oxidative Damage and Promote Myokine Response in the Skeletal Muscle of ApoE KO Mice on High-Fat Diet

The purpose of this study was to investigate the effects of high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on the skeletal muscle in Apolipoprotein E knockout (ApoE KO) and wild-type (WT) C57BL/6J mice. ApoE KO mice fed with a high-fat diet were randomly allocated into: Control group without exercise (ApoE^-/- CON), HIIT group (ApoE^-/- HIIT), and MICT group (ApoE^-/- MICT). Exercise endurance, blood lipid profile, muscle antioxidative capacity, and myokine production were measured after six weeks of interventions. ApoE^-/- CON mice exhibited hyperlipidemia and increased oxidative stress, compared to the WT mice. HIIT and MICT reduced blood lipid levels, ROS production, and protein carbonyl content in the skeletal muscle, while it enhanced the GSH generation and potently promoted mRNA expression of genes involved in the production of irisin and BAIBA. Moreover, ApoE^-/- HIIT mice had significantly lower plasma HDL-C content, mRNA expression of MyHC-IIx and Vegfa165 in EDL, and ROS level; but remarkably higher mRNA expression of Hadha in the skeletal muscle than those of ApoE^-/- MICT mice. These results demonstrated that both exercise programs were effective for the ApoE KO mice by attenuating the oxidative damage and promoting the myokines response and production. In particular, HIIT was more beneficial to reduce the ROS level in the skeletal muscle.

Findings from recent studies by the Japan Aerospace Exploration Agency examining musculoskeletal atrophy in space and on Earth

The musculoskeletal system provides the body with correct posture, support, stability, and mobility. It is composed of the bones, muscles, cartilage, tendons, ligaments, joints, and other connective tissues. Without effective countermeasures, prolonged spaceflight under microgravity results in marked muscle and bone atrophy. The molecular and physiological mechanisms of this atrophy under unloaded conditions are gradually being revealed through spaceflight experiments conducted by the Japan Aerospace Exploration Agency using a variety of model organisms, including both aquatic and terrestrial animals, and terrestrial experiments conducted under the Living in Space project of the Japan Ministry of Education, Culture, Sports, Science, and Technology. Increasing our knowledge in this field will lead not only to an understanding of how to prevent muscle and bone atrophy in humans undergoing long-term space voyages but also to an understanding of countermeasures against age-related locomotive syndrome in the elderly.

Angiotensin 1-7 protects against ventilator-induced diaphragm dysfunction

Mechanical ventilation (MV) is a life‐saving instrument used to provide ventilatory support for critically ill patients and patients undergoing surgery. Unfortunately, an unintended consequence of prolonged MV is the development of inspiratory weakness due to both diaphragmatic atrophy and contractile dysfunction; this syndrome is labeled ventilator‐induced diaphragm dysfunction (VIDD). VIDD is clinically important because diaphragmatic weakness is an important contributor to problems in weaning patients from MV. Investigations into the pathogenesis of VIDD reveal that oxidative stress is essential for the rapid development of VIDD as redox disturbances in diaphragm fibers promote accelerated proteolysis. Currently, no standard treatment exists to prevent VIDD and, therefore, developing a strategy to avert VIDD is vital. Guided by evidence indicating that activation of the classical axis of the renin‐angiotensin system (RAS) in diaphragm fibers promotes oxidative stress and VIDD, we hypothesized that activation of the nonclassical RAS signaling pathway via angiotensin 1‐7 (Ang1‐7) will protect against VIDD. Using an established animal model of prolonged MV, our results disclose that infusion of Ang1‐7 protects the diaphragm against MV‐induced contractile dysfunction and fiber atrophy in both fast and slow muscle fibers. Further, Ang1‐7 shielded diaphragm fibers against MV‐induced mitochondrial damage, oxidative stress, and protease activation. Collectively, these results reveal that treatment with Ang1‐7 protects against VIDD, in part, due to diminishing oxidative stress and protease activation. These important findings provide robust evidence that Ang1‐7 has the therapeutic potential to protect against VIDD by preventing MV‐induced contractile dysfunction and atrophy of both slow and fast muscle fibers.

A necessary role of DNMT3A in endurance exercise by suppressing ALDH1L1-mediated oxidative stress

Exercise can alter the skeletal muscle DNA methylome, yet little is known about the role of the DNA methylation machinery in exercise capacity. Here, we show that DNMT3A expression in oxidative red muscle increases greatly following a bout of endurance exercise. Muscle-specific Dnmt3a knockout mice have reduced tolerance to endurance exercise, accompanied by reduction in oxidative capacity and mitochondrial respiration. Moreover, Dnmt3a-deficient muscle overproduces reactive oxygen species (ROS), the major contributors to muscle dysfunction. Mechanistically, we show that DNMT3A suppresses the Aldh1l1 transcription by binding to its promoter region, altering its epigenetic profile. Forced expression of ALDH1L1 elevates NADPH levels, which results in overproduction of ROS by the action of NADPH oxidase complex, ultimately resulting in mitochondrial defects in myotubes. Thus, inhibition of ALDH1L1 pathway can rescue oxidative stress and mitochondrial dysfunction from Dnmt3a deficiency in myotubes. Finally, we show that in vivo knockdown of Aldh1l1 largely rescues exercise intolerance in Dnmt3a-deficient mice. Together, we establish that DNMT3A in skeletal muscle plays a pivotal role in endurance exercise by controlling intracellular oxidative stress.

Mitochondrial Dysfunction Is a Common Denominator Linking Skeletal Muscle Wasting Due to Disease, Aging, and Prolonged Inactivity

Skeletal muscle is the most abundant tissue in the body and is required for numerous vital functions, including breathing and locomotion. Notably, deterioration of skeletal muscle mass is also highly correlated to mortality in patients suffering from chronic diseases (e.g., cancer). Numerous conditions can promote skeletal muscle wasting, including several chronic diseases, cancer chemotherapy, aging, and prolonged inactivity. Although the mechanisms responsible for this loss of muscle mass is multifactorial, mitochondrial dysfunction is predicted to be a major contributor to muscle wasting in various conditions. This systematic review will highlight the biochemical pathways that have been shown to link mitochondrial dysfunction to skeletal muscle wasting. Importantly, we will discuss the experimental evidence that connects mitochondrial dysfunction to muscle wasting in specific diseases (i.e., cancer and sepsis), aging, cancer chemotherapy, and prolonged muscle inactivity (e.g., limb immobilization). Finally, in hopes of stimulating future research, we conclude with a discussion of important future directions for research in the field of muscle wasting.

Beneficial Role of Exercise in the Modulation of mdx Muscle Plastic Remodeling and Oxidative Stress

Duchenne muscular dystrophy (DMD) is an X-linked recessive progressive lethal disorder caused by the lack of dystrophin, which determines myofibers mechanical instability, oxidative stress, inflammation, and susceptibility to contraction-induced injuries. Unfortunately, at present, there is no efficient therapy for DMD. Beyond several promising gene- and stem cells-based strategies under investigation, physical activity may represent a valid noninvasive therapeutic approach to slow down the progression of the pathology. However, ethical issues, the limited number of studies in humans and the lack of consistency of the investigated training interventions generate loss of consensus regarding their efficacy, leaving exercise prescription still questionable. By an accurate analysis of data about the effects of different protocol of exercise on muscles of mdx mice, the most widely-used pre-clinical model for DMD research, we found that low intensity exercise, especially in the form of low speed treadmill running, likely represents the most suitable exercise modality associated to beneficial effects on mdx muscle. This protocol of training reduces muscle oxidative stress, inflammation, and fibrosis process, and enhances muscle functionality, muscle regeneration, and hypertrophy. These conclusions can guide the design of appropriate studies on human, thereby providing new insights to translational therapeutic application of exercise to DMD patients.

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.

Skeletal muscle redox signaling in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by synovitis and the presence of serum autoantibodies. In addition, skeletal muscle weakness is a common comorbidity that contributes to inability to work and reduced quality of life. Loss in muscle mass cannot alone account for the muscle weakness induced by RA, but instead intramuscular dysfunction appears as a critical factor underlying the decreased force generating capacity for patients afflicted by arthritis. Oxidative stress and associated oxidative post-translational modifications have been shown to contribute to RA-induced muscle weakness in animal models of arthritis and patients with RA. However, it is still unclear how and which sources of reactive oxygen and nitrogen species (ROS/RNS) that are involved in the oxidative stress that drives the progression toward decreased muscle function in RA. Nevertheless, mitochondria, NADPH oxidases (NOX), nitric oxide synthases (NOS) and phospholipases (PLA) have all been associated with increased ROS/RNS production in RA-induced muscle weakness. In this review, we aim to cover potential ROS sources and underlying mechanisms of oxidative stress and loss of force production in RA. We also addressed the use of antioxidants and exercise as potential tools to counteract oxidative stress and skeletal muscle weakness.

Molecular Mechanisms of Diaphragm Myopathy in Humans With Severe Heart Failure

[Figure: see text].

Bezafibrate activation of PPAR drives disturbances in mitochondrial redox bioenergetics and decreases the viability of cells from patients with VLCAD deficiency

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is the most common inborn long-chain fatty acid oxidation (FAO) disorder. VLCAD deficiency is characterized by distinct phenotypes. The severe phenotypes are potentially life-threatening and affect the heart or liver, with a comparatively milder phenotype characterized by myopathic symptoms. There is an unmet clinical need for effective treatment options for the myopathic phenotype. The molecular mechanisms driving the gradual decrease in mitochondrial function and associated alterations of muscle fibers are unclear. The peroxisome proliferator-activated receptor (PPAR) pan-agonist bezafibrate is a potent modulator of FAO and multiple other mitochondrial functions and has been proposed as a potential medication for myopathic cases of long-chain FAO disorders. In vitro experiments have demonstrated the ability of bezafibrate to increase VLCAD expression and activity. However, the outcome of small-scale clinical trials has been controversial. We found VLCAD deficient patient fibroblasts to have an increased oxidative stress burden and deranged mitochondrial bioenergetic capacity, compared to controls. Applying heat stress under fasting conditions to bezafibrate pretreated patient cells, caused a marked further increase of mitochondrial superoxide levels. Patient cells failed to maintain levels of the essential thiol peptide antioxidant glutathione and experienced a decrease in cellular viability. Our findings indicate that chronic PPAR activation is a plausible initiator of long-term pathogenesis in VLCAD deficiency. Our findings further implicate disruption of redox homeostasis as a key pathogenic mechanism in VLCAD deficiency and support the notion that a deranged thiol metabolism might be an important pathogenic factor in VLCAD deficiency.

Inhibition of Lipopolysaccharide-Induced Inflammatory and Oxidative Responses by Trans-cinnamaldehyde in C2C12 Myoblasts

Background: Trans-cinnamaldehyde (tCA), a bioactive component found in Cinnamomum cassia, has been reported to exhibit anti-inflammatory and antioxidant effects, but its efficacy in muscle cells has yet to be found. In this study, we investigated the inhibitory effect of tCA on inflammatory and oxidative stress induced by lipopolysaccharide (LPS) in C2C12 mouse skeletal myoblasts. Methods: To investigate the anti-inflammatory and antioxidant effects of tCA in LPS-treated C2C12 cells, we measured the levels of pro-inflammatory mediator, cytokines, and reactive oxygen species (ROS). To elucidate the mechanism underlying the effect of tCA, the expression of genes involved in the expression of inflammatory and oxidative regulators was also investigated. We further evaluated the anti-inflammatory and antioxidant efficacy of tCA against LPS in the zebrafish model. Results: tCA significantly inhibited the LPS-induced release of pro-inflammatory mediators and cytokines, which was associated with decreased expression of their regulatory genes. tCA also suppressed the expression of Toll-like receptor 4 (TLR4) and myeloid differentiation factor, and attenuated the nuclear translocation of nuclear factor-kappa B (NF-κB) and the binding of LPS to TLR4 on the cell surface in LPS-treated C2C12 cells. Furthermore, tCA abolished LPS-induced generation of ROS and expression levels of ROS producing enzymes, NADPH oxidase 1 (NOX1) and NOX2. However, tCA enhanced the activation of nuclear translocation of nuclear factor-E2-related factor 2 (Nrf2) and the expression of heme oxygenase-1 (HO-1) in LPS-stimulated C2C12 myoblasts. In addition, tCA showed strong protective effects against NO and ROS production in LPS-injected zebrafish larvae. Conclusions: Our findings suggest that tCA exerts its inhibitory ability against LPS-induced inflammatory and antioxidant stress in C2C12 myoblasts by targeting the TLR4/NF-κB, which might be mediated by the NOXs and Nrf2/HO-1 pathways.

ABCG1 Attenuates Oxidative Stress Induced by H2O2 through the Inhibition of NADPH Oxidase and the Upregulation of Nrf2-Mediated Antioxidant Defense in Endothelial Cells

Summary. Oxidative stress is an important factor that is related to endothelial dysfunction. ATP-binding cassette transporter G1 (ABCG1), a regulator of intracellular cholesterol efflux, has been found to prevent endothelial activation in vessel walls. To explore the role of ABCG1 in oxidative stress production in endothelial cells, HUAECs were exposed to H₂O₂ and transfected with the specific ABCG1 siRNA or ABCG1 overexpression plasmid. The results showed that overexpression of ABCG1 by ABCG1 plasmid or liver X receptor (LXR) agonist T0901317 treatment inhibited ROS production and MDA content induced by H₂O₂ in HUAECs. Furthermore, ABCG1 upregulation blunted the activity of prooxidant NADPH oxidase and the expression of Nox4, one of the NADPH oxidase subunits. Moreover, the increased migration of Nrf2 from the cytoplasm to the nucleus and antioxidant HO-1 expression were detected in HUAECs with upregulation of ABCG1. Conversely, ABCG1 downregulation by ABCG1 siRNA increased NADPH oxidase activity and Nox4 expression and abrogated the increase at Nrf2 nuclear protein levels. In addition, intracellular cholesterol load interfered with the balance between NADPH oxidase activity and HO-1 expression. It was suggested that ABCG1 attenuated oxidative stress induced by H₂O₂ in endothelial cells, which might be involved in the balance between decreased NADPH oxidase activity and increased Nrf2/OH-1 antioxidant defense signaling via its regulation for intracellular cholesterol accumulation.

ACE2, angiotensin 1-7 and skeletal muscle: review in the era of COVID-19

Angiotensin converting enzyme-2 (ACE2) is a multifunctional transmembrane protein recently recognised as the entry receptor of the virus causing COVID-19. In the renin–angiotensin system (RAS), ACE2 cleaves angiotensin II (Ang II) into angiotensin 1-7 (Ang 1-7), which is considered to exert cellular responses to counteract the activation of the RAS primarily through a receptor, Mas, in multiple organs including skeletal muscle. Previous studies have provided abundant evidence suggesting that Ang 1-7 modulates multiple signalling pathways leading to protection from pathological muscle remodelling and muscle insulin resistance. In contrast, there is relatively little evidence to support the protective role of ACE2 in skeletal muscle. The potential contribution of endogenous ACE2 to the regulation of Ang 1-7-mediated protection of these muscle pathologies is discussed in this review. Recent studies have suggested that ACE2 protects against ageing-associated muscle wasting (sarcopenia) through its function to modulate molecules outside of the RAS. Thus, the potential association of sarcopenia with ACE2 and the associated molecules outside of RAS is also presented herein. Further, we introduce the transcriptional regulation of muscle ACE2 by drugs or exercise, and briefly discuss the potential role of ACE2 in the development of COVID-19.

Cell autonomous requirement of neurofibromin (Nf1) for postnatal muscle hypertrophic growth and metabolic homeostasis

BACKGROUND

Neurofibromatosis type 1 (NF1) is a multi-organ disease caused by mutations in neurofibromin 1 (NF1). Amongst other features, NF1 patients frequently show reduced muscle mass and strength, impairing patients' mobility and increasing the risk of fall. The role of Nf1 in muscle and the cause for the NF1-associated myopathy are mostly unknown.

METHODS

To dissect the function of Nf1 in muscle, we created muscle-specific knockout mouse models for NF1, inactivating Nf1 in the prenatal myogenic lineage either under the Lbx1 promoter or under the Myf5 promoter. Mice were analysed during prenatal and postnatal myogenesis and muscle growth.

RESULTS

Nf1^Lbx1 and Nf1^Myf5 animals showed only mild defects in prenatal myogenesis. Nf1^Lbx1 animals were perinatally lethal, while Nf1^Myf5 animals survived only up to approximately 25 weeks. A comprehensive phenotypic characterization of Nf1^Myf5 animals showed decreased postnatal growth, reduced muscle size, and fast fibre atrophy. Proteome and transcriptome analyses of muscle tissue indicated decreased protein synthesis and increased proteasomal degradation, and decreased glycolytic and increased oxidative activity in muscle tissue. High-resolution respirometry confirmed enhanced oxidative metabolism in Nf1^Myf5 muscles, which was concomitant to a fibre type shift from type 2B to type 2A and type 1. Moreover, Nf1^Myf5 muscles showed hallmarks of decreased activation of mTORC1 and increased expression of atrogenes. Remarkably, loss of Nf1 promoted a robust activation of AMPK with a gene expression profile indicative of increased fatty acid catabolism. Additionally, we observed a strong induction of genes encoding catabolic cytokines in muscle Nf1^Myf5 animals, in line with a drastic reduction of white, but not brown adipose tissue.

CONCLUSIONS

Our results demonstrate a cell autonomous role for Nf1 in myogenic cells during postnatal muscle growth required for metabolic and proteostatic homeostasis. Furthermore, Nf1 deficiency in muscle drives cross-tissue communication and mobilization of lipid reserves.