The role of free radicals in the pathophysiology of muscular dystrophy

Nutritional Issues among Children with Duchenne Muscular Dystrophy-Incidence of Deficiency and Excess Body Mass

The progression of Duchenne muscular dystrophy (DMD)requires the assessment of nutritional disturbances at each stage of the disease. The purpose of this study was to assess the nutritional status in various ages of boys with DMD using screening and in-depth evaluation methods. Body composition by Dual X-ray Absorptiometry (DXA), basal metabolic rate (BMR) by indirect calorimetry, a questionnaire of nutritional status-Pediatric Nutrition Screening Tool (PNST)-and laboratory parameters were performed. In the cohort of 93 boys aged 8.54 (5.9-12.6 years), inappropriate nutritional status occurred in 41.8% of boys (underweight 11.8%, overweight 16.0%, and obesity 14.0%). In the 10-13 age group, the occurrence of overweight and underweight was the highest. Based on PNST, 15.1% of patients were at nutritional risk (≥2 points)-the most in the 14-17 age group (29%). A negative correlation was identified between PNST and z-scores of body weight, BMI, and FFMI (r Spearman = -0.49, -0.46, and -0.48, respectively; p < 0.05). There were no differences between BMR results from indirect calorimetry and calculations from the Schofield formula for any age group. In obese boys, the caloric requirement in indirect calorimetry was significantly lower than that indicated by the calculations according to the Schofield formula (p < 0.028). Inappropriate nutritional status occurred in almost half of the children with DMD. The age group in which nutritional disorders were most frequently identified was 10-13 years old. PNST could be considered a tool for screening malnutrition after testing a larger group of DMD patients.

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.

Reactive oxygen species downregulate dystroglycans in the megakaryocytes of rats with arterial hypertension

Hypertension is a multifactorial disease characterized by vascular and renal dysfunction, cardiovascular remodeling, inflammation, and fibrosis, all of which are associated with oxidative stress. We previously demonstrated cellular reactive oxygen species (ROS) imbalances may impact the structural and biochemical functions of blood cells and reported downregulation of β-dystroglycan (β-Dg) and overexpression of the epithelial sodium channel (ENaC) contribute to the pathophysiology of hypertension. In this study, we aimed to determine the expression of dystroglycans (Dg) and ENaC in platelet progenitors (megakaryocytes) and their surrounding niches. Thin sections of bone marrow from 5- and 28-week-old spontaneous hypertensive rats (SHR) were compared to age-matched normotensive rats (WKY). Cytometry and immunohistochemical assays demonstrated an oxidative environment in SHR bone marrow, characterized by high levels of myeloperoxidase and 3-nitrotyrosine and downregulation of peroxiredoxin II. In addition, transmission electron micrography and confocal microscopy revealed morphological changes in platelets and Mgks from SHR rats, including swollen mitochondria. Quantitative qRT-PCR assays confirmed downregulation of Dg mRNA and immunohistochemistry and western-blotting validated low expression of β-Dg, mainly in the phosphorylated form, in Mgks from 28-week-old SHR rats. Moreover, we observed a progressive increase in β-1 integrin expression in Mgks and extracellular matrix proteins in Mgk niches in SHR rats compared to WKY controls. These results indicate accumulation of ROS promotes oxidative stress within the bone marrow environment and detrimentally affects cellular homeostasis in hypertensive individuals.

From amino-acid to disease: the effects of oxidation on actin-myosin interactions in muscle

Actin-myosin interactions form the basis of the force-producing contraction cycle within the sarcomere, serving as the primary mechanism for muscle contraction. Post-translational modifications, such as oxidation, have a considerable impact on the mechanics of these interactions. Considering their widespread occurrence, the explicit contributions of these modifications to muscle function remain an active field of research. In this review, we aim to provide a comprehensive overview of the basic mechanics of the actin-myosin complex and elucidate the extent to which oxidation influences the contractile cycle and various mechanical characteristics of this complex at the single-molecule, myofibrillar and whole-muscle levels. We place particular focus on amino acids shown to be vulnerable to oxidation in actin, myosin, and some of their binding partners. Additionally, we highlight the differences between in vitro environments, where oxidation is controlled and limited to actin and myosin and myofibrillar or whole muscle environments, to foster a better understanding of oxidative modification in muscle. Thus, this review seeks to encompass a broad range of studies, aiming to lay out the multi layered effects of oxidation in in vitro and in vivo environments, with brief mention of clinical muscular disorders associated with oxidative stress.

Febuxostat ameliorates muscle degeneration and movement disorder of the dystrophin mutant model in Caenorhabditis elegans

Duchenne muscular dystrophy (DMD) is an inherited disorder with mutations in the dystrophin gene characterized by progressive muscle degeneration and weakness. Therapy such as administration of glucocorticoids, exon skipping of mutant genes and introduction of dystrophin mini-genes have been tried, but there is no radical therapy for DMD. In this study, we used C. elegans carrying mutations in the dys-1 gene as a model of DMD to examine the effects of febuxostat (FBX). We applied FBX to dys-1 mutant animals harboring a marker for muscle nuclei and mitochondria, and found that FBX ameliorates the muscle loss. We next used a severer model dys-1; unc-22 double mutant and found the dys-1 mutation causes a weakened muscle contraction. We applied FBX and other compounds to the double mutant animals and assayed the movement. We found that the administration of FBX in combination of uric acid has the best effects on the DMD model.

Natural Compounds That Enhance Motor Function in a Mouse Model of Muscle Fatigue

Musculoskeletal disease can be a serious condition associated with aging that may lead to fractures and a bedridden state due to decreased motor function. In addition to exercise training to increase muscle mass, increasing muscle function with the intake of functional foods is an effective treatment strategy for musculoskeletal disease. Muscle-specific SOD2-deficient mice (muscle-Sod2^-/-) show a severe disturbance in exercise in association with increased mitochondrial reactive oxygen species, as well as mitochondrial dysfunction and muscle damage. In the present study, to develop a therapeutic strategy for musculoskeletal disease, we searched for substances that enhanced motor function among functional compounds by in vivo screening using muscle-Sod2^-/- mice as a muscle fatigue model. We administered 96 compounds, including antioxidants, to muscle-Sod2^-/- mice and assessed their effects on treadmill performance. Among the administered compounds, gossypin, genistein, kaempferol, taxifolin, fumaric acid, β-hydroxy-β-methylbutyrate Ca, and astaxanthin, which are dietary functional food factors, increased forced running time in muscle-Sod2^-/- mice. In addition, troglitazone, tempol, trolox, and MnTE-2-PyP, which are antioxidants, also significantly increased the running ability of muscle-Sod2^-/- mice. These results suggest that the intake of functional foods with antioxidant activity can improve motor function. Muscle-Sod2^-/- mice, as a muscle fatigue model, are suitable for the in vivo screening of functional substances that promote improvements in exercise and muscle performance.

Intertubular morphometric and ultrastructural testes analyses in mdx mice

Duchenne Muscular Dystrophy (DMD) reproductive alterations and the influence of antioxidant treatments may aid in understanding morphometry testicular quantification. In this context, the aim of the present study was to characterize the intertubular compartment (ITC) morphometry of animal testes in mdx mice supplemented with ascorbic acid (AA). Sixteen mice were used, namely the C57BL/10 (non-dystrophic) and C57BL/10Mdx (dystrophic) lineages, distributed into the following groups: Control (C60), Dystrophic (D60), Control supplemented with AA (CS60), Dystrophic supplemented with AA (DS60). A total of 200 mg/kg of AA were administered to mice for 30 days. Subsequently, the testicles were collected, weighed, and fragmented. The obtained fragments were fixed in Karnovsky's solution (pH 7.2) and embedded in historesin for morphometric and transmission electron microscopy assessments. Leydig cells were hypertrophic in the D60 group, but was reverted by AA supplementation in the DS60 group. The DS60 group also exhibited increased intertubular volume compared to the CS60 group. The ultrastructural images identified multilamellar bodies in dystrophic animals (lipid storage) and telocyte cells (transport substances) in both control and dystrophic animals. Morphometric alterations were, therefore, noted in the intertubular compartment due to Duchenne muscular dystrophy (DMD), with AA administration capable of altering Leydig cells in this condition.

Regulation of A-to-I RNA editing and stop codon recoding to control selenoprotein expression during skeletal myogenesis

Selenoprotein N (SELENON), a selenocysteine (Sec)-containing protein with high reductive activity, maintains redox homeostasis, thereby contributing to skeletal muscle differentiation and function. Loss-of-function mutations in SELENON cause severe neuromuscular disorders. In the early-to-middle stage of myoblast differentiation, SELENON maintains redox homeostasis and modulates endoplasmic reticulum (ER) Ca2+ concentration, resulting in a gradual reduction from the middle-to-late stages due to unknown mechanisms. The present study describes post-transcriptional mechanisms that regulate SELENON expression during myoblast differentiation. Part of an Alu element in the second intron of SELENON pre-mRNA is frequently exonized during splicing, resulting in an aberrant mRNA that is degraded by nonsense-mediated mRNA decay (NMD). In the middle stage of myoblast differentiation, ADAR1-mediated A-to-I RNA editing occurs in the U1 snRNA binding site at 5' splice site, preventing Alu exonization and producing mature mRNA. In the middle-to-late stage of myoblast differentiation, the level of Sec-charged tRNASec decreases due to downregulation of essential recoding factors for Sec insertion, thereby generating a premature termination codon in SELENON mRNA, which is targeted by NMD.

Interplay between mitochondrial reactive oxygen species, oxidative stress and hypoxic adaptation in facioscapulohumeral muscular dystrophy: Metabolic stress as potential therapeutic target

Facioscapulohumeral muscular dystrophy (FSHD) is characterised by descending skeletal muscle weakness and wasting. FSHD is caused by mis-expression of the transcription factor DUX4, which is linked to oxidative stress, a condition especially detrimental to skeletal muscle with its high metabolic activity and energy demands. Oxidative damage characterises FSHD and recent work suggests metabolic dysfunction and perturbed hypoxia signalling as novel pathomechanisms. However, redox biology of FSHD remains poorly understood, and integrating the complex dynamics of DUX4-induced metabolic changes is lacking.

Here we pinpoint the kinetic involvement of altered mitochondrial ROS metabolism and impaired mitochondrial function in aetiology of oxidative stress in FSHD. Transcriptomic analysis in FSHD muscle biopsies reveals strong enrichment for pathways involved in mitochondrial complex I assembly, nitrogen metabolism, oxidative stress response and hypoxia signalling. We found elevated mitochondrial ROS (mitoROS) levels correlate with increases in steady-state mitochondrial membrane potential in FSHD myogenic cells. DUX4 triggers mitochondrial membrane polarisation prior to oxidative stress generation and apoptosis through mitoROS, and affects mitochondrial health through lipid peroxidation. We identify complex I as the primary target for DUX4-induced mitochondrial dysfunction, with strong correlation between complex I-linked respiration and cellular oxygenation/hypoxia signalling activity in environmental hypoxia. Thus, FSHD myogenesis is uniquely susceptible to hypoxia-induced oxidative stress as a consequence of metabolic mis-adaptation. Importantly, mitochondria-targeted antioxidants rescue FSHD pathology more effectively than conventional antioxidants, highlighting the central involvement of disturbed mitochondrial ROS metabolism. This work provides a pathomechanistic model by which DUX4-induced changes in oxidative metabolism impair muscle function in FSHD, amplified when metabolic adaptation to varying O₂ tension is required.

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Transcriptomics data from FSHD muscle indicates enrichment for disturbed mitochondrial pathways.

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Disturbed mitochondrial ROS metabolism correlates with mitochondrial membrane polarisation and myotube hypotrophy.

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DUX4-induced changes in mitochondrial function precede mitoROS generation and affect hypoxia signalling via complex I.

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FSHD is sensitive to environmental hypoxia, which increases ROS levels in FSHD myotubes.

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Hypotrophy in hypoxic FSHD myotubes is efficiently rescued with mitochondria-targeted antioxidants.

Effect of epicatechin on skeletal muscle

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Loss of skeletal muscle (SkM) quality is associated with different clinical conditions such as aging, diabetes, obesity, cancer and heart failure. Nutritional research has focused on identifying naturally occurring molecules that mitigate the loss of SkM quality induced by a pathology or syndrome. In this context, although few human studies have been conducted, Epicatechin (Epi) is a prime candidate that may positively affect SkM quality by its potential ability to mitigate muscle mass loss. This seems to be a consequence of its antioxidant, anti-inflammatory properties, and its stimulation of mitochondrial biogenesis to increase myogenic differentiation, as well as its modulation of key proteins involved in SkM structure, function, metabolism, and growth. In conclusion, the Epi could prevent, mitigate, delay, and even treat muscle-related disorders caused by aging and diseases, however, studies in humans are needed.

Shared and distinct mechanisms of skeletal muscle atrophy: A narrative review

Maintenance of skeletal muscle mass and function is an incredibly nuanced balance of anabolism and catabolism that can become distorted within different pathological conditions. In this paper we intend to discuss the distinct intracellular signaling events that regulate muscle protein atrophy for a given clinical occurrence. Aside from the common outcome of muscle deterioration, several conditions have at least one or more distinct mechanisms that creates unique intracellular environments that facilitate muscle loss. The subtle individuality to each of these given pathologies can provide both researchers and clinicians with specific targets of interest to further identify and increase the efficacy of medical treatments and interventions.

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.

Tetrahydrobiopterin synthesis and metabolism is impaired in dystrophin-deficient mdx mice and humans

AIM

Loss of dystrophin causes oxidative stress and affects nitric oxide synthase-mediated vascular function in striated muscle. Because tetrahydrobiopterin is an antioxidant and co-factor for nitric oxide synthase, we tested the hypothesis that tetrahydrobiopterin would be low in mdx mice and humans deficient for dystrophin.

METHODS

Tetrahydrobiopterin and its metabolites were measured at rest and in response to exercise in Duchenne and Becker muscular dystrophy patients, age-matched male controls as well as wild-type, mdx and mdx mice transgenically overexpressing skeletal muscle-specific dystrophins. Mdx mice were also supplemented with tetrahydrobiopterin and pathophysiology was assessed.

RESULTS

Duchenne muscular dystrophy patients had lower urinary dihydrobiopterin + tetrahydrobiopterin/specific gravity1.020 compared to unaffected age-matched males and Becker muscular dystrophy patients. Mdx mice had low urinary and skeletal muscle dihydrobiopterin + tetrahydrobiopterin compared to wild-type mice. Overexpression of dystrophins that localize neuronal nitric oxide synthase restored dihydrobiopterin + tetrahydrobiopterin in mdx mice to wild-type levels while utrophin overexpression did not. Mdx mice and Duchenne muscular dystrophy patients did not increase tetrahydrobiopterin during exercise and in mdx mice tetrahydrobiopterin deficiency was likely because of lower levels of sepiapterin reductase in skeletal muscle. Tetrahydrobiopterin supplementation improved skeletal muscle strength, resistance to fatiguing and injurious contractions in vivo, increased utrophin and capillary density of skeletal muscle and lowered cardiac muscle fibrosis and left ventricular wall thickness in mdx mice.

CONCLUSION

These data demonstrate that impaired tetrahydrobiopterin synthesis is associated with dystrophin loss and treatment with tetrahydrobiopterin improves striated muscle histopathology and skeletal muscle function in mdx mice.

Confounding Roles of ER Stress and the Unfolded Protein Response in Skeletal Muscle Atrophy

Skeletal muscle is an essential organ, responsible for many physiological functions such as breathing, locomotion, postural maintenance, thermoregulation, and metabolism. Interestingly, skeletal muscle is a highly plastic tissue, capable of adapting to anabolic and catabolic stimuli. Skeletal muscle contains a specialized smooth endoplasmic reticulum (ER), known as the sarcoplasmic reticulum, composed of an extensive network of tubules. In addition to the role of folding and trafficking proteins within the cell, this specialized organelle is responsible for the regulated release of calcium ions (Ca2+) into the cytoplasm to trigger a muscle contraction. Under various stimuli, such as exercise, hypoxia, imbalances in calcium levels, ER homeostasis is disturbed and the amount of misfolded and/or unfolded proteins accumulates in the ER. This accumulation of misfolded/unfolded protein causes ER stress and leads to the activation of the unfolded protein response (UPR). Interestingly, the role of the UPR in skeletal muscle has only just begun to be elucidated. Accumulating evidence suggests that ER stress and UPR markers are drastically induced in various catabolic stimuli including cachexia, denervation, nutrient deprivation, aging, and disease. Evidence indicates some of these molecules appear to be aiding the skeletal muscle in regaining homeostasis whereas others demonstrate the ability to drive the atrophy. Continued investigations into the individual molecules of this complex pathway are necessary to fully understand the mechanisms.

Decreased smooth muscle function, peristaltic activity, and gastrointestinal transit in dystrophic (mdx) mice

BACKGROUND

Duchenne muscular dystrophy (DMD) is characterized by the lack of dystrophin in skeletal, cardiac, and smooth muscle. Slow colonic transit and constipation are common in DMD patients and animal models of DMD. However, the cause of this hypocontractility and the expression of contractile proteins in smooth muscle are unknown. The aim of the study was to investigate the expression of contractile proteins in the colonic smooth muscle and the function of the colon in control and mdx mice.

METHODS

Muscle contraction was measured in muscle strips and isolated muscle cells. Peristaltic activity was measured in ex vivo preparations by spatiotemporal mapping, and gastrointestinal (GI) transit in vivo was measured by the distribution of fluorescent marker along the intestine and colon. mRNA expression of contractile proteins smoothelin, caldesmon, calponin, and tropomyosin was measured by qRT-PCR.

RESULTS

Expression of mRNA for contractile proteins was decreased in colonic smooth muscle of mdx mice compared with control. Contraction in response to acetylcholine and KCl was decreased in colonic muscle strips and in isolated muscle cells of mdx mice. Distension of ex vivo colons with Krebs buffer induced peristalsis in both control and mdx mice; however, significantly fewer full peristaltic waves were recorded in the colons of mdx mice. GI transit was also inhibited in mdx mice.

CONCLUSION AND INFERENCES

The data indicate that the lack of dystrophin causes decrease in colonic smooth muscle contractility, peristalsis, and GI transit and provides the basis for analysis of mechanisms involved in smooth muscle dysfunction in DMD.

Circulating markers of oxidative stress are associated with a muscle injury in patients with muscular dystrophy Duchenne

BACKGROUND

A small number of studies have confirmed the presence of oxidative damage in patients with Duchenne muscular dystrophy (DMD). Nevertheless, it is unknown if there a relationship of circulating markers of oxidative stress with a muscle injury.

OBJECTIVE

We evaluated if oxidative damage and anti-oxidant markers are associated with muscle damage in DMD.

METHODS

This cross-sectional study included 24 patients with DMD classified in ambulatory and non-ambulatory. Markers of muscle damage (creatine kinase [CK]), oxidative damage (malondialdehyde [MDA], and 8-isoprostane), anti-oxidant function (Thiol and mRNA of NRF2 and NF-κB) and nitric oxide (NO) were quantified in circulation.

RESULTS

Total NO, MDA, and 8-isoprostane concentrations were significantly (p < 0.05) higher, and thiol concentration was lower in non-ambulatory than ambulatory patients. A significant correlation (p < 0.05) between muscle injury (evaluated by Vignos scale) with CK (r = -0.382), NO (r = 0.444), MDA (r = 0.503), 8-isoprostanes (r = 0.435) and thiol (r = -0.430) was observed.

CONCLUSION

These findings suggest that non-ambulatory have high oxidative damage and low anti-oxidant function than ambulatory patients with DMD. Total nitric oxide and oxidative damage plasma markers increase, but the anti-oxidant marker thiol decreases with a muscle injury in boys with DMD. The findings of this study suggest that these markers could be considered as goods indicators of oxidative damage in longitudinal studies to evaluate the muscle injury during DMD progression. Additionally, these findings add new information about the pathophysiology of DMD.

The role of Nrf2 in acute and chronic muscle injury

The nuclear factor erythroid 2-related factor 2 (Nrf2) is considered as a master cytoprotective factor regulating the expression of genes encoding anti-oxidant, anti-inflammatory, and detoxifying proteins. The role of Nrf2 in the pathophysiology of skeletal muscles has been evaluated in different experimental models, however, due to inconsistent data, we aimed to investigate how Nrf2 transcriptional deficiency (Nrf2tKO) affects muscle functions both in an acute and chronic injury. The acute muscle damage was induced in mice of two genotypes-WT and Nrf2tKO mice by cardiotoxin (CTX) injection. To investigate the role of Nrf2 in chronic muscle pathology, mdx mice that share genetic, biochemical, and histopathological features with Duchenne muscular dystrophy (DMD) were crossed with mice lacking transcriptionally active Nrf2 and double knockouts (mdx/Nrf2tKO) were generated. To worsen the dystrophic phenotype, the analysis of disease pathology was also performed in aggravated conditions, by applying a long-term treadmill test. We have observed slightly increased muscle damage in Nrf2tKO mice after CTX injection. Nevertheless, transcriptional ablation of Nrf2 in mdx mice did not significantly aggravate the most deleterious, pathological hallmarks of DMD related to degeneration, inflammation, fibrotic scar formation, angiogenesis, and the number and proliferation of satellite cells in non-exercised conditions. On the other hand, upon chronic exercises, the degeneration and inflammatory infiltration of the gastrocnemius muscle, but not the diaphragm, turned to be increased in Nrf2tKOmdx in comparison to mdx mice. In conclusion, the lack of transcriptionally active Nrf2 influences moderately muscle pathology in acute CTX-induced muscle injury and chronic DMD mouse model, without affecting muscle functionality. Hence, in general, we demonstrated that the deficiency of Nrf2 transcriptional activity has no profound impact on muscle pathology in various models of muscle injury.

Redox-dependent regulation of satellite cells following aseptic muscle trauma: Implications for sports performance and nutrition

Skeletal muscle satellite cells (SCs) are indispensable for tissue regeneration, remodeling and growth. Following myotrauma, SCs are activated, and assist in tissue repair. Exercise-induced muscle damage (EIMD) is characterized by a pronounced inflammatory response and the production of reactive oxygen species (ROS). Experimental evidence suggests that SCs kinetics (the propagation from a quiescent to an activated/proliferative state) following EIMD is redox-dependent and interconnected with changes in the SCs microenvironment (niche). Animal studies have shown that following aseptic myotrauma, antioxidant and/or anti-inflammatory supplementation leads to an improved recovery and skeletal muscle regeneration through enhanced SCs kinetics, suggesting a redox-dependent molecular mechanism. Although evidence suggests that antioxidant/anti-inflammatory compounds may prevent performance deterioration and enhance recovery, there is lack of information regarding the redox-dependent regulation of SCs responses following EIMD in humans. In this review, SCs kinetics following aseptic myotrauma, as well as the intrinsic redox-sensitive molecular mechanisms responsible for SCs responses are discussed. The role of redox status on SCs function should be further investigated in the future with human clinical trials in an attempt to elucidate the molecular pathways responsible for muscle recovery and provide information for potential nutritional strategies aiming at performance recovery.

Duchenne muscular dystrophy (DMD) cardiomyocyte-secreted exosomes promote the pathogenesis of DMD-associated cardiomyopathy

Cardiomyopathy is a leading cause of early mortality in Duchenne muscular dystrophy (DMD). There is a need to gain a better understanding of the molecular pathogenesis for the development effective therapies. Exosomes (exo) are secreted vesicles and exert effects via their RNA, lipid and protein cargo. The role of exosomes in disease pathology is unknown. Exosomes derived from stem cells have demonstrated cardioprotection in the murine DMD heart. However, it is unknown how the disease status of the donor cell type influences exosome function. Here, we sought to determine the phenotypic responses of DMD cardiomyocytes (DMD-iCMs) after long-term exposure to DMD cardiac exosomes (DMD-exo). DMD-iCMs were vulnerable to stress, evidenced by production of reactive oxygen species, the mitochondrial membrane potential and cell death levels. Long-term exposure to non-affected exosomes (N-exo) was protective. By contrast, long-term exposure to DMD-exo was not protective, and the response to stress improved with inhibition of DMD-exo secretion in vitro and in vivo The microRNA (miR) cargo, but not exosome surface peptides, was implicated in the pathological effects of DMD-exo. Exosomal surface profiling revealed N-exo peptides associated with PI3K-Akt signaling. Transcriptomic profiling identified unique changes with exposure to either N- or DMD-exo. Furthermore, DMD-exo miR cargo regulated injurious pathways, including p53 and TGF-beta. The findings reveal changes in exosomal cargo between healthy and diseased states, resulting in adverse outcomes. Here, DMD-exo contained miR changes, which promoted the vulnerability of DMD-iCMs to stress. Identification of these molecular changes in exosome cargo and effectual phenotypes might shed new light on processes underlying DMD cardiomyopathy.This article has an associated First Person interview with the first author of the paper.

Cellular Stress in the Pathogenesis of Muscular Disorders-From Cause to Consequence

Cellular stress has been considered a relevant pathogenetic factor in a variety of human diseases. Due to its primary functions by means of contractility, metabolism, and protein synthesis, the muscle cell is faced with continuous changes of cellular homeostasis that require rapid and coordinated adaptive mechanisms. Hence, a prone susceptibility to cellular stress in muscle is immanent. However, studies focusing on the cellular stress response in muscular disorders are limited. While in recent years there have been emerging indications regarding a relevant role of cellular stress in the pathophysiology of several muscular disorders, the underlying mechanisms are to a great extent incompletely understood. This review aimed to summarize the available evidence regarding a deregulation of the cellular stress response in individual muscle diseases. Potential mechanisms, as well as involved pathways are critically discussed, and respective disease models are addressed. Furthermore, relevant therapeutic approaches that aim to abrogate defects of cellular stress response in muscular disorders are outlined.

Preconditioning beef cattle for long-duration transportation stress with rumen-protected methionine supplementation: A nutrigenetics study

In general, beef cattle long-distance transportation from cow-calf operations to feedlots or from feedlots to abattoirs is a common situation in the beef industry. The aim of this study was to determine the effect of rumen-protected methionine (RPM) supplementation on a proposed gene network for muscle fatigue, creatine synthesis (CKM), and reactive oxygen species (ROS) metabolism after a transportation simulation in a test track. Angus × Simmental heifers (n = 18) were stratified by body weight (408 ± 64 kg; BW) and randomly assigned to dietary treatments: 1) control diet (CTRL) or 2) control diet + 8 gr/hd/day of top-dressed rumen-protected methionine (RPM). After an adaptation period to Calan gates, animals received the mentioned dietary treatment consisting of Bermuda hay ad libitum and a soy hulls and corn gluten feed based supplement. After 45 days of supplementation, animals were loaded onto a trailer and transported for 22 hours (long-term transportation). Longissimus muscle biopsies, BW and blood samples were obtained on day 0 (Baseline), 43 (Pre-transport; PRET), and 46 (Post-transport; POST). Heifers' average daily gain did not differ between baseline and PRET. Control heifer's shrink was 10% of BW while RPM heifers shrink was 8%. Serum cortisol decreased, and glucose and creatine kinase levels increased after transportation, but no differences were observed between treatments. Messenger RNA was extracted from skeletal muscle tissue and gene expression analysis was performed by RT-qPCR. Results showed that AHCY and DNMT3A (DNA methylation), SSPN (Sarcoglycan complex), and SOD2 (Oxidative Stress-ROS) were upregulated in CTRL between baseline and PRET and, decreased between pre and POST while they remained constant for RPM. Furthermore, CKM was not affected by treatments. In conclusion, RPM supplementation may affect ROS production and enhance DNA hypermethylation, after a long-term transportation.

High prevalence of plasma lipid abnormalities in human and canine Duchenne and Becker muscular dystrophies depicts a new type of primary genetic dyslipidemia

BACKGROUND

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are allelic X-linked recessive muscle diseases caused by mutations in the DMD gene, with DMD being the more severe form. We have recently shown that increased plasma low-density lipoprotein-associated cholesterol causes severe muscle wasting in the mdx mouse, a mild DMD model, which suggested that plasma lipids may play a critical role in DMD. We have also observed that loss of dystrophin in mice causes unexpected elevations in plasma lipoprotein levels.

OBJECTIVE

The objectives of the study were to determine whether patients with DMD and BMD also present with clinically relevant plasma lipoprotein abnormalities and to mitigate the presence of confounders (medications and lifestyle) by analyzing the plasma from patients with DMD/BMD and unmedicated dogs with DMD, the most relevant model of DMD.

METHODS

Levels of low-density lipoprotein-associated cholesterol, high-density lipoprotein cholesterol, and triglycerides were analyzed in patients with DMD and BMD and female carriers. Samples from unmedicated, ambulatory dogs with DMD, unaffected carriers, and normal controls were also analyzed.

RESULTS

We report that 97% and 64% of all pediatric patients with DMD (33 of 36) and BMD (6 of 11) are dyslipidemic, along with an unusually high incidence in adult patients with BMD. All dogs with DMD showed plasma lipid abnormalities that progressively worsened with age. Most strikingly, unaffected carrier dogs also showed plasma lipid abnormalities similar to affected dogs with DMD. Dyslipidemia is likely not secondary to liver damage as unaffected carriers showed no plasma aminotransferase elevation.

CONCLUSIONS

The high incidence of plasma lipid abnormalities in dystrophin-deficient plasma may depict a new type of genetic dyslipidemia. Abnormal lipid levels in dystrophinopathic samples in the absence of muscle damage suggest a primary state of dyslipidemia. Whether dyslipidemia plays a causal role in patients with DMD warrants further investigation, which could lead to new diagnostic and therapeutic options.

Antioxidant imbalance in the erythrocytes of Myotonic dystrophy Type 1 patients

The most common form of muscular dystrophy is known as Myotonic dystrophy Type 1 (DM1) in adults. It was aimed to investigate the relationship between antioxidant imbalance and diaphragm thickness with pulmonary function test results in peripheral blood of Myotonic Dystrophy Type 1 patients. In the prospective study, 33 DM1 and 32 healthy control groups were taken after the ethics committee decision (2018-10529). Antioxidant defence system enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione reductase (GR), glutathione S-transferase (GST) and thiobarbituric acid reactive species (TBARS) levels were studied in blood samples. Also, muscular strength (MRC score), creatine kinase (CK) and diaphragm thicknesses were measured, and pulmonary function tests were performed. Among the studied parameters, TBARS levels and GPX, GR and GST activities in erythrocytes of DM1 patients showed a significant decrease in the range of 29-45% compared to the control group. MRC score, diaphragm thickness and inspiratory function test results at the end of inspiration and expiration were found lower though CK levels were higher in DM1 group. In the patient group, a positive correlation was found between antioxidant parameters (TBARS, CAT and GST) with diaphragm thicknesses and pulmonary function test though GPX showed a negative correlation with them. It was emphasized that the data obtained shows the harmful/pathogenic role of oxidative stress caused by free radicals in DM1, and also provide useful data for the treatment and processes of this disease.

Angiotensin II receptor blocker losartan exacerbates muscle damage and exhibits weak blood pressure-lowering activity in a dysferlin-null model of Limb-Girdle muscular dystrophy type 2B

There is no cure or beneficial management option for Limb-Girdle muscular dystrophy (MD) type 2B (LGMD2B). Losartan, a blood pressure (BP) lowering angiotensin II (AngII) receptor type 1 (ATR1) blocker (ARB) with unique anti-transforming growth factor-β (TGF-β) properties, can protect muscles in various types of MD such as Duchenne MD, suggesting a potential benefit for LGMD2B patients. Herein, we show in a mild, dysferlin-null mouse model of LGMD2B that losartan increased quadriceps muscle fibrosis (142%; P<0.0001). In a severe, atherogenic diet-fed model of LGMD2B recently described by our group, losartan further exacerbated dysferlin-null mouse muscle wasting in quadriceps and triceps brachii, two muscles typically affected by LGMD2B, by 40% and 51%, respectively (P<0.05). Lower TGF-β signalling was not observed with losartan, therefore plasma levels of atherogenic lipids known to aggravate LGMD2B severity were investigated. We report that losartan increased both plasma triglycerides and cholesterol concentrations in dysferlin-null mice. Other protective properties of losartan, such as increased nitric oxide release and BP lowering, were also reduced in the absence of dysferlin expression. Our data suggest that LGMD2B patients may show some resistance to the primary BP-lowering effects of losartan along with accelerated muscle wasting and dyslipidemia. Hence, we urge caution on the use of ARBs in this population as their ATR1 pathway may be dysfunctional.

An anti-RANKL treatment reduces muscle inflammation and dysfunction and strengthens bone in dystrophic mice

Duchenne muscular dystrophy (DMD) is the most severe form of muscular dystrophy which leads to progressive muscle degeneration and inflammation. The receptor activator of nuclear factor NF-κB ligand (RANKL) and its receptor (RANK), which are expressed in bone and skeletal and cardiac muscles, form a signaling network upstream from nuclear factor-kappa B (NF-κB). We thus hypothesized that prolonged silencing RANKL/RANK signaling would significantly improve DMD. We showed that RANK and RANKL protein levels were increased in the microenvironment of myofibers of 5-month-old utrophin haploinsufficient mdx (mdx/utrn+/−) mice and that a 4 mg/kg dose of anti-RANKL antibody every 3 d for 28 days is optimal and more effective than 1 mg/kg every 3 d for improving the ex vivo maximum specific force (sP0) of dystrophic EDL muscles from mdx/utrn+/− mice. This functional improvement was associated with a reduction in muscle edema, damage, and fibrosis and a marked reduction in serum CK levels. The anti-RANKL treatment inhibited the NF-κB pathway, increased the proportion of anti-inflammatory and non-cytotoxic M2 macrophages, and reduced the number of centrally-nucleated myofibers and the frequency of small myofibers, suggesting that anti-RANKL inhibits the cycle of degeneration/regeneration in dystrophic mice. A three-point bending test showed that a 28-d anti-RANKL treatment increases the mechanical properties of bone in mdx/utrn+/− dystrophic mice. In conclusion, the anti-RANKL treatment protected against skeletal muscle dysfunctions while enhancing bone mechanical properties, filling two needs with one deed in the context of muscular dystrophy.

Dynamic thiol/disulphide homeostasis in children with Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a disorder that alter the expression of the dystrophin protein. Dystrophin deficiency alters the structural integrity of the contractile apparatus/sarcolemmal integrity, leading to dystrophic changes. Dystrophin deficiency results in an increase in oxidative stress. We aimed to investigate the thiol/disulfide balance as an oxidative stress marker in children with DMD. We included 24 DMD, and 22 healthy control group subjects in the study. The total thiol, native thiol, and disulphide levels were measured and the disulphide/native thiol, disulphide/total thiol and native thiol/total thiol ratios were calculated in DMD patients and healthy subjects. The mean age distribution of the patients and the healthy control group subjects was similar. The total thiol, native thiol, and disulfide levels were lower in DMD group than the healthy controls. In conclusion, the markers and ratios were measured and calculated in the blood, and we detected that the total thiol, and native thiol levels were lower in DMD group than the healthy controls. These results indicate that dynamic thiol-disulphide homeostasis can be used as a marker of oxidative stress in clinical trials with DMD.

Demembranated skeletal and cardiac fibers produce less force with altered cross-bridge kinetics in a mouse model for limb-girdle muscular dystrophy 2i

Limb-girdle muscular dystrophy 2i (LGMD2i) is a dystroglycanopathy that compromises myofiber integrity and primarily reduces power output in limb muscles but can influence cardiac muscle as well. Previous studies of LGMD2i made use of a transgenic mouse model in which a proline-to-leucine (P448L) mutation in fukutin-related protein severely reduces glycosylation of α-dystroglycan. Muscle function is compromised in P448L mice in a manner similar to human patients with LGMD2i. In situ studies reported lower maximal twitch force and depressed force-velocity curves in medial gastrocnemius (MG) muscles from male P448L mice. Here, we measured Ca²⁺-activated force generation and cross-bridge kinetics in both demembranated MG fibers and papillary muscle strips from P448L mice. Maximal activated tension was 37% lower in MG fibers and 18% lower in papillary strips from P448L mice than controls. We also found slightly faster rates of cross-bridge recruitment and detachment in MG fibers from P448L than control mice. These increases in skeletal cross-bridge cycling could reduce the unitary force output from individual cross bridges by lowering the ratio of time spent in a force-bearing state to total cycle time. This suggests that the decreased force production in LGMD2i may be due (at least in part) to altered cross-bridge kinetics. This finding is notable, as the majority of studies germane to muscular dystrophies have focused on sarcolemma or whole muscle properties, whereas our findings suggest that the disease pathology is also influenced by potential downstream effects on cross-bridge behavior.

Neopterin/7,8-dihydroneopterin is elevated in Duchenne muscular dystrophy patients and protects mdx skeletal muscle function

NEW FINDINGS

What is the central question of this study? We examined whether the macrophage-synthesized antioxidant 7,8-dihydroneopterin was elevated in Duchenne muscular dystrophy (DMD) patients. We then examined whether 7,8-dihydroneopterin could protect dystrophic skeletal mouse muscle from eccentric contraction-induced force loss and improve recovery. What is the main finding and its importance? Urinary neopterin/creatinine and 7,8-dihydroneopterin/creatinine were elevated in DMD patients. 7,8-Dihydroneopterin attenuated eccentric contraction-induced force loss of dystrophic skeletal mouse muscle and accelerated recovery of force. These results suggest that eccentric contraction-induced force loss is mediated, in part, by an oxidative component and provides a potential protective role for 7,8-dihydroneopterin in DMD.

ABSTRACT

Macrophage infiltration is a hallmark of dystrophin-deficient muscle. We tested the hypothesis that Duchenne muscular dystrophy (DMD) patients would have elevated levels of the macrophage-synthesized pterins, neopterin and 7,8-dihydroneopterin, compared with unaffected age-matched control subjects. Urinary neopterin/creatinine and 7,8-dihydroneopterin/creatinine were elevated in DMD patients, and 7,8-dihydroneopterin/creatinine was associated with patient age and ambulation. Urinary 7,8-dihydroneopterin corrected for specific gravity was also elevated in DMD patients. Given that 7,8-dihydroneopterin is an antioxidant, we then identified a potential role for 7,8-dihydroneopterin in disease pathology. We assessed whether 7,8-dihydroneopterin could: (i) protect against isometric force loss in wild-type skeletal muscle exposed to various pro-oxidants; and (ii) protect wild-type and mdx muscle from eccentric contraction-induced force loss, which has an oxidative component. Force loss was elicited in isolated extensor digitorum longus (EDL) muscles by 10 eccentric contractions, and recovery of force after the contractions was measured in the presence of exogenous 7,8-dihydroneopterin. 7,8-Dihydroneopterin attenuated isometric force loss by wild-type EDL muscles when challenged by H₂ O₂ and HOCl, but exacerbated force loss when challenged by SIN-1 (NO^• , O₂^• , ONOO^- ). 7,8-Dihydroneopterin attenuated eccentric contraction-induced force loss in mdx muscle. Isometric force production by EDL muscles of mdx mice also recovered to a greater degree after eccentric contractions in the presence of 7,8-dihydroneopterin. The results corroborate macrophage activation in DMD patients, provide a potential protective role for 7,8-dihydroneopterin in the susceptibility of dystrophic muscle to eccentric contractions and indicate that oxidative stress contributes to eccentric contraction-induced force loss in mdx skeletal muscle.

Role of adiponectin in the metabolism of skeletal muscles in collagen VI-related myopathies

The role of adiponectin has been particularly deepened in diabetic muscles while the study of adiponectin in hereditary myopathies has been marginally investigated. Here, we report the study about adiponectin effects in Col6a1^-/- (collagen VI-null) mice. Col6a1^-/- mice show myophatic phenotype closer to that of patients with Bethlem myopathy, thus representing an excellent animal model for the study of this hereditary disease. Our findings demonstrate that Col6a1^-/- mice have decreased plasma adiponectin content and diseased myoblasts have an impaired autocrine secretion of the hormone. Moreover, Col6a1^-/- myoblasts show decreased glucose uptake and mitochondria with depolarized membrane potential and impaired functionality, as supported by decreased oxygen consumption. Exogenous addition of globular adiponectin modifies the features of Col6a1^-/- myoblasts, becoming closer to that of the healthy myoblasts. Indeed, globular adiponectin enhances glucose uptake in Col6a1^-/- myoblasts, modifies mitochondrial membrane potential, and restores oxygen consumption, turning closer to those of wild-type myoblasts. Finally, increase of plasma adiponectin level in Col6a1^-/- mice is induced by fasting, a condition that has been previously shown to lead to the amelioration of the dystrophic phenotype. Collectively, our results demonstrate that exogenous replenishment of adiponectin reverses metabolic abnormalities observed in Col6a1^-/- myoblasts. KEY MESSAGES: Col6a1^-/- mice have decreased level of plasma adiponectin. Myoblasts from Col6a1^-/- muscles have impaired local adiponectin secretion. Col6a1^-/- myoblasts reveal altered metabolic features. Addition of exogenous adiponectin ameliorates Col6a1^-/- metabolic features.

Dystrophinopathy-associated dysfunction of Krebs cycle metabolism

Duchenne muscular dystrophy is a deadly muscle-wasting disorder caused by loss of dystrophin protein. Studies suggest that metabolic alterations are important to disease pathogenesis. Because muscle accounts for ~40% of body mass, we hypothesized that dystrophy-mediated metabolic changes would be measurable in biofluids and that a metabolomic analysis of urine would provide insight into the metabolic status of dystrophic muscle. Using the mdx mouse model, we performed a large-scale metabolomic screen at 1 and 3 months. While 10% of metabolites were altered at age 1 month, 40% were changed at 3 months. Principal component analysis distinguished wild-type from mdx animals, with the greatest separation at 3 months. A critical distinguishing pathway was Krebs cycle metabolite depletion in mdx urine. Five of seven detected Krebs cycle metabolites were depleted in mdx urine, with succinate being the most robustly affected metabolite. Using selected reaction monitoring mass spectrometry, we demonstrated that muscle-specific dystrophin expression corrects mdx succinate depletion. When subjected to downhill treadmill running, wild-type and mdx mice expressing recombinant dystrophin in skeletal muscle displayed significant increases in urinary succinate levels. However, mdx succinate levels were unchanged, suggesting urinary succinate depletion may reflect an inability to upregulate the Krebs cycle following exercise. Finally, we show that supplementing the Krebs cycle in an ex vivo fatigue/recovery assay significantly impacts mdx muscle performance but has no effect on wild-type muscle. Our results suggest that global metabolic impairment is associated with mdx disease progression and that Krebs cycle deficiencies are a downstream consequence of dystrophin loss.

Acute AT1R blockade prevents isoproterenol-induced injury in mdx hearts

BACKGROUND

Duchenne muscular dystrophy (DMD) is an X-linked disease characterized by skeletal muscle degeneration and a significant cardiomyopathy secondary to cardiomyocyte damage and myocardial loss. The molecular basis of DMD lies in the absence of the protein dystrophin, which plays critical roles in mechanical membrane integrity and protein localization at the sarcolemma. A popular mouse model of DMD is the mdx mouse, which lacks dystrophin and displays mild cardiac and skeletal pathology that can be exacerbated to advance the disease state. In clinical and pre-clinical studies of DMD, angiotensin signaling pathways have emerged as therapeutic targets due to their adverse influence on muscle remodeling and oxidative stress. Here we aim to establish a physiologically relevant cardiac injury model in the mdx mouse, and determine whether acute blockade of the angiotensin II type 1 receptor (AT₁R) may be utilized for prevention of dystrophic injury.

METHODS AND RESULTS

A single IP injection of isoproterenol (Iso, 10 mg/kg) was used to induce cardiac stress and injury in mdx and wild type (C57Bl/10) mice. Mice were euthanized 8 h, 30 h, 1 week, or 1 month following the injection, and hearts were harvested for injury evaluation. At 8 and 30 h post-injury, mdx hearts showed 2.2-fold greater serum cTnI content and 3-fold more extensive injury than wild type hearts. Analysis of hearts 1 week and 1 month after injury revealed significantly higher fibrosis in mdx hearts, with a more robust and longer-lasting immune response compared to wild type hearts. In the 30-hour group, losartan treatment initiated 1 h before Iso injection protected dystrophic hearts from cardiac damage, reducing mdx acute injury area by 2.8-fold, without any significant effect on injury in wild type hearts. However, both wild type and dystrophic hearts showed a 2-fold reduction in the magnitude of the macrophage response to injury 30 h after Iso with losartan.

CONCLUSIONS

This work demonstrates that acute blockade of AT₁R has the potential for robust injury prevention in a model of Iso-induced dystrophic heart injury. In addition to selectively limiting dystrophic cardiac damage, blocking AT₁R may serve to limit the inflammatory nature of the immune response to injury in all hearts. Our findings strongly suggest that earlier adoption of angiotensin receptor blockers in DMD patients could limit myocardial damage and subsequent cardiomyopathy.

Xanthine oxidase is hyper-active in Duchenne muscular dystrophy

Generation of superoxide by xanthine oxidase can be stimulated under ischemic and aberrant calcium homeostasis. Because patients and mice with Duchenne muscular dystrophy (DMD) suffer from ischemia and excessive calcium influx, we tested the hypothesis that xanthine oxidase activity is elevated and contributes to disease pathology. Xanthine oxidase activity was measured by urinary isoxanthopterin in DMD patients at rest and in response to exercise. Urinary isoxanthopterin/creatinine was elevated compared to age-matched controls and Becker muscular dystrophy (BMD) patients. Concentrations were also increased after a six minute walk test in ambulatory patients. We also measured urinary isoxanthopterin in wildtype mice and a number of dystrophic mouse models; the DMD mouse model (mdx), mdx mice overexpressing a variety of transgenic miniaturized and chimeric skeletal muscle-specific dystrophins and utrophin and the β-sarcoglycan deficient (Scgb-/-) mouse which represents type 2E human limb-girdle muscular dystrophy. Mdx and Scgb-/-mice had greater urinary isoxanthopterin/creatinine than wildtype mice while mdx mice expressing dystrophin or utrophin linking the extracellular matrix to the actin cytoskeleton were not different than wildtype. We also measured higher levels of urinary ortho-tyrosine in humans and mice deficient for dystrophin to confirm elevated oxidative stress. Surprisingly, mdx had lower xanthine oxidase protein levels and higher mRNA in gastrocnemius muscle compared to wildtype mice, however, the enzymatic activity of skeletal muscle xanthine oxidase was elevated above wildtype and a transgenic rescued mdx mouse (DysΔMTB-mdx). Downhill treadmill running also caused significant increases in mdx urinary isoxanthopterin that was prevented with the xanthine oxidase inhibitor allopurinol. Similarly, in vitro eccentric contraction-induced force drop of mdx muscle was attenuated by the allopurinol metabolite, oxypurinol. Together, our data suggests hyper-activity of xanthine oxidase in DMD, identifies xanthine oxidase activity as a contributing factor in eccentric contraction-induced force drop of dystrophin-deficient skeletal muscle and highlights the potential of isoxanthopterin as a noninvasive biomarker in DMD.

SMYD2 glutathionylation contributes to degradation of sarcomeric proteins

Reactive oxygen species (ROS) contribute to the etiology of multiple muscle-related diseases. There is emerging evidence that cellular stress can lead to destabilization of sarcomeres, the contractile unit of muscle. However, it is incompletely understood how cellular stress induces structural destabilization of sarcomeres. Here we report that glutathionylation of SMYD2 contributes to a loss of myofibril integrity and degradation of sarcomeric proteins mediated by MMP-2 and calpain 1. We used a clickable glutathione approach in a cardiomyocyte cell line and found selective glutathionylation of SMYD2 at Cys13. Biochemical analysis demonstrated that SMYD2 upon oxidation or glutathionylation at Cys13 loses its interaction with Hsp90 and N2A, a domain of titin. Upon dissociation from SMYD2, N2A or titin is degraded by activated MMP-2, suggesting a protective role of SMYD2 in sarcomere stability. Taken together, our results support that SMYD2 glutathionylation is a novel molecular mechanism by which ROS contribute to sarcomere destabilization.

Drug Repurposing for Duchenne Muscular Dystrophy: The Monoamine Oxidase B Inhibitor Safinamide Ameliorates the Pathological Phenotype in mdx Mice and in Myogenic Cultures From DMD Patients

Oxidative stress and mitochondrial dysfunction play a crucial role in the pathophysiology of muscular dystrophies. We previously reported that the mitochondrial enzyme monoamine oxidase (MAO) is a relevant source of reactive oxygen species (ROS) not only in murine models of muscular dystrophy, in which it directly contributes to contractile impairment, but also in muscle cells from collagen VI-deficient patients. Here, we now assessed the efficacy of a novel MAO-B inhibitor, safinamide, using in vivo and in vitro models of Duchenne muscular dystrophy (DMD). Specifically, we found that administration of safinamide in 3-month-old mdx mice reduced myofiber damage and oxidative stress and improved muscle functionality. In vitro studies with myogenic cultures from mdx mice and DMD patients showed that even cultured dystrophic myoblasts were more susceptible to oxidative stress than matching cells from healthy donors. Indeed, upon exposure to the MAO substrate tyramine or to hydrogen peroxide, DMD muscle cells displayed a rise in ROS levels and a consequent mitochondrial depolarization. Remarkably, both phenotypes normalized when cultures were treated with safinamide. Given that safinamide is already in clinical use for neurological disorders, our findings could pave the way toward a promising translation into clinical trials for DMD patients as a classic case of drug repurposing.

Mitochondria-Targeted Antioxidants and Skeletal Muscle Function

One of the main sources of reactive oxygen species (ROS) in skeletal muscle is the mitochondria. Prolonged or very high ROS exposure causes oxidative damage, which can be deleterious to muscle function, and as such, there is growing interest in targeting antioxidants to the mitochondria in an effort to prevent or treat muscle dysfunction and damage associated with disease and injury. Paradoxically, however, ROS also act as important signalling molecules in controlling cellular homeostasis, and therefore caution must be taken when supplementing with antioxidants. It is possible that mitochondria-targeted antioxidants may limit oxidative stress without suppressing ROS from non-mitochondrial sources that might be important for cell signalling. Therefore, in this review, we summarise literature relating to the effect of mitochondria-targeted antioxidants on skeletal muscle function. Overall, mitochondria-targeted antioxidants appear to exert beneficial effects on mitochondrial capacity and function, insulin sensitivity and age-related declines in muscle function. However, it seems that this is dependent on the type of mitochondrial-trageted antioxidant employed, and its specific mechanism of action, rather than simply targeting to the mitochondria.

Skeletal Muscle Metabolism in Duchenne and Becker Muscular Dystrophy-Implications for Therapies

The interactions between nutrition and metabolism and skeletal muscle have long been known. Muscle is the major metabolic organ&mdash;it consumes more calories than other organs&mdash;and therefore, there is a clear need to discuss these interactions and provide some direction for future research areas regarding muscle pathologies. In addition, new experiments and manuscripts continually reveal additional highly intricate, reciprocal interactions between metabolism and muscle. These reciprocal interactions include exercise, age, sex, diet, and pathologies including atrophy, hypoxia, obesity, diabetes, and muscle myopathies. Central to this review are the metabolic changes that occur in the skeletal muscle cells of muscular dystrophy patients and mouse models. Many of these metabolic changes are pathogenic (inappropriate body mass changes, mitochondrial dysfunction, reduced adenosine triphosphate (ATP) levels, and increased Ca²⁺) and others are compensatory (increased phosphorylated AMP activated protein kinase (pAMPK), increased slow fiber numbers, and increased utrophin). Therefore, reversing or enhancing these changes with therapies will aid the patients. The multiple therapeutic targets to reverse or enhance the metabolic pathways will be discussed. Among the therapeutic targets are increasing pAMPK, utrophin, mitochondrial number and slow fiber characteristics, and inhibiting reactive oxygen species. Because new data reveals many additional intricate levels of interactions, new questions are rapidly arising. How does muscular dystrophy alter metabolism, and are the changes compensatory or pathogenic? How does metabolism affect muscular dystrophy? Of course, the most profound question is whether clinicians can therapeutically target nutrition and metabolism for muscular dystrophy patient benefit? Obtaining the answers to these questions will greatly aid patients with muscular dystrophy.

Sialic acid deficiency is associated with oxidative stress leading to muscle atrophy and weakness in GNE myopathy

Sialic acids are monosaccharides found in terminal sugar chains of cell surfaces and proteins; they have various biological functions and have been implicated in health and disease. Genetic defects of the GNE gene which encodes a critical bifunctional enzyme for sialic acid biosynthesis, lead to GNE myopathy, a disease manifesting with progressive muscle atrophy and weakness. The likely mechanism of disease is a lack of sialic acids. There remains, however, an unexplained link between hyposialylation and the muscle atrophy and weakness. In this study, we found that muscle proteins were highly modified by S-nitrosylation, and that oxidative stress-responsive genes were significantly upregulated, in hyposialylated muscles from human GNE myopathy patients and model mice. In both in vitro and in vivo models, the production of reactive oxygen species (ROS) was elevated with cellular hyposialylation, and increasing overall sialylation by extrinsic sialic acid intake reduced ROS and protein S-nitrosylation. More importantly, the antioxidant, oral N-acetylcysteine led to amelioration of the muscle atrophy and weakness in Gne mutant mice. Our data provide evidence of additional important function of sialic acids as a ROS scavenger in skeletal muscles, expanding our understanding on how sialic acid deficiency contributes to disease pathology, and identify oxidative stress as a therapeutic target in GNE myopathy.

Increased nonHDL cholesterol levels cause muscle wasting and ambulatory dysfunction in the mouse model of LGMD2B

Progressive limb and girdle muscle atrophy leading to loss of ambulation is a hallmark of dysferlinopathies, which include limb-girdle muscular dystrophy type 2B and Miyoshi myopathy. However, animal models fail to fully reproduce the disease severity observed in humans, with dysferlin-null (Dysf^-/-) mice exhibiting minor muscle damage and weakness without dramatic ambulatory dysfunction. As we have previously reported significant Dysf expression in blood vessels, we investigated the role of vascular function in development of muscle pathology by generating a Dysf-deficient mouse model with vascular disease. This was achieved by crossing Dysf^-/- mice with ApoE^-/- mice, which have high levels of nonHDL-associated cholesterol. Double-knockout Dysf^-/-ApoE^-/- mice exhibited severe ambulatory dysfunction by 11 months of age. In limb-girdle muscles, histology confirmed dramatic muscle wasting, fibrofatty replacement, and myofiber damage in Dysf^-/-ApoE^-/- mice without affecting the ratio of centrally nucleated myofibers. Although there were no major changes in ex vivo diaphragm and soleus muscle function, histological analyses revealed these muscles to be untouched by damage and remodelling. In all, these data suggest that cholesterol may be deleterious to dysferlinopathic muscle and lead to ambulatory dysfunction. Moreover, differences in plasma lipid handling between mice and humans could be a key factor affecting dysferlinopathy severity.

Increased plasma lipid levels exacerbate muscle pathology in the mdx mouse model of Duchenne muscular dystrophy

Background

Duchenne muscular dystrophy (DMD) is caused by loss of dystrophin expression and leads to severe ambulatory and cardiac function decline. However, the dystrophin-deficient mdx murine model of DMD only develops a very mild form of the disease. Our group and others have shown vascular abnormalities in animal models of MD, a likely consequence of the fact that blood vessels express the same dystrophin-associated glycoprotein complex (DGC) proteins as skeletal muscles.

Methods

To test the blood vessel contribution to muscle damage in DMD, mdx^4cv mice were given elevated lipid levels via apolipoprotein E (ApoE) gene knockout combined with normal chow or lipid-rich Western diets. Ambulatory function and heart function (via echocardiogram) were assessed at 4 and 7 months of age. After sacrifice, muscle histology and aortic staining were used to assess muscle pathology and atherosclerosis development, respectively. Plasma levels of total cholesterol, high-density lipoprotein (HDL), triglycerides, and creatine kinase (CK) were also measured.

Results

Although there was an increase in left ventricular heart volume in mdx-ApoE mice compared to that in mdx mice, parameters of heart function were not affected. Compared with wild-type and ApoE-null, only mdx-ApoE KO mice showed significant ambulatory dysfunction. Despite no significant difference in plasma CK, histological analyses revealed that elevated plasma lipids in chow- and Western diet-fed mdx-ApoE mice was associated with severe exacerbation of muscle pathology compared to mdx mice: significant increase in myofiber damage and fibrofatty replacement in the gastrocnemius and triceps brachii muscles, more reminiscent of human DMD pathology. Finally, although both ApoE and mdx-ApoE groups displayed increased plasma lipids, mdx-ApoE exhibited atherosclerotic plaque deposition equal to or less than that of ApoE mice.

Conclusions

Since others have shown that lipid abnormalities correlate with DMD severity, our data suggest that plasma lipids could be primary contributors to human DMD severity and that the notoriously mild phenotype of mdx mice might be attributable in part to their endogenously low plasma lipid profiles. Hence, DMD patients may benefit from lipid-lowering and vascular-targeted therapies.

Electronic supplementary material

The online version of this article (10.1186/s13395-017-0135-9) contains supplementary material, which is available to authorized users.

Redox Control of Skeletal Muscle Regeneration

Skeletal muscle shows high plasticity in response to external demand. Moreover, adult skeletal muscle is capable of complete regeneration after injury, due to the properties of muscle stem cells (MuSCs), the satellite cells, which follow a tightly regulated myogenic program to generate both new myofibers and new MuSCs for further needs. Although reactive oxygen species (ROS) and reactive nitrogen species (RNS) have long been associated with skeletal muscle physiology, their implication in the cell and molecular processes at work during muscle regeneration is more recent. This review focuses on redox regulation during skeletal muscle regeneration. An overview of the basics of ROS/RNS and antioxidant chemistry and biology occurring in skeletal muscle is first provided. Then, the comprehensive knowledge on redox regulation of MuSCs and their surrounding cell partners (macrophages, endothelial cells) during skeletal muscle regeneration is presented in normal muscle and in specific physiological (exercise-induced muscle damage, aging) and pathological (muscular dystrophies) contexts. Recent advances in the comprehension of these processes has led to the development of therapeutic assays using antioxidant supplementation, which result in inconsistent efficiency, underlying the need for new tools that are aimed at precisely deciphering and targeting ROS networks. This review should provide an overall insight of the redox regulation of skeletal muscle regeneration while highlighting the limits of the use of nonspecific antioxidants to improve muscle function. Antioxid. Redox Signal. 27, 276-310.

Enhanced Energetic State and Protection from Oxidative Stress in Human Myoblasts Overexpressing BMI1

The Polycomb group gene BMI1 is essential for efficient muscle regeneration in a mouse model of Duchenne muscular dystrophy, and its enhanced expression in adult skeletal muscle satellite cells ameliorates the muscle strength in this model. Here, we show that the impact of mild BMI1 overexpression observed in mouse models is translatable to human cells. In human myoblasts, BMI1 overexpression increases mitochondrial activity, leading to an enhanced energetic state with increased ATP production and concomitant protection against DNA damage both in vitro and upon xenografting in a severe dystrophic mouse model. These preclinical data in mouse models and human cells provide a strong rationale for the development of pharmacological approaches to target BMI1-mediated mitochondrial regulation and protection from DNA damage to sustain the regenerative potential of the skeletal muscle in conditions of chronic muscle wasting.

Dystrophic phenotype improvement in the diaphragm muscle of mdx mice by diacerhein

Chronic inflammation and oxidative stress are striking features of Duchenne muscular dystrophy disease. Diacerhein is an anthraquinone, which exhibits anti-inflammatory and antioxidant properties. Based on their actions, the present study evaluated the effects of diacerhein against myonecrosis, oxidative stress and inflammatory response in the diaphragm muscle of mdx mice and compared these results to current treatment widely used in DMD patients, with a main focus on the impact of prednisone. The results demonstrated that diacerhein treatment prevented muscle damage indicated by a decrease in the IgG uptake by muscle fibers, lower CK levels in serum, reduction of fibers with central nuclei with a concomitant increase in fibers with peripheral nuclei. It also had an effect on the inflammatory process, decreasing the inflammatory area, macrophage staining and TNF-α and IL-1β content. Regarding oxidative stress, diacerhein treatment was effective in reducing the ROS and lipid peroxidation in the diaphragm muscle from mdx mice. Compared to prednisone treatment, our findings demonstrated that diacerhein treatment improved the dystrophic phenotype in the diaphragm muscle of mdx mice similar to that of glucocorticoid therapy. In this respect, this work suggests that diacerhein has a potential use as an alternative drug in dystrophinopathy treatment and recommends that its anti-inflammatory and antioxidants properties in the dystrophic muscle should be better understood.

Emerging roles of ER stress and unfolded protein response pathways in skeletal muscle health and disease

Skeletal muscle is the most abundant tissue in the human body and can adapt its mass as a consequence of physical activity, metabolism, growth factors, and disease conditions. Skeletal muscle contains an extensive network of endoplasmic reticulum (ER), called sarcoplasmic reticulum, which plays an important role in the regulation of proteostasis and calcium homeostasis. In many cell types, environmental and genetic factors that disrupt ER function cause an accumulation of misfolded and unfolded proteins in the ER lumen that ultimately leads to ER stress. To alleviate the stress and restore homeostasis, the ER activates a signaling network called the unfolded protein response (UPR). The UPR has three arms, which regulate protein synthesis and expression of many ER chaperone and regulatory proteins. However, the role of individual UPR pathways in skeletal muscle has just begun to be investigated. Recent studies suggest that UPR pathways play pivotal roles in muscle stem cell homeostasis, myogenic differentiation, and regeneration of injured skeletal muscle. Moreover, markers of ER stress and the UPR are activated in skeletal muscle in diverse conditions such as exercise, denervation, starvation, high fat diet, cancer cachexia, and aging. Accumulating evidence also suggests that ER stress may have important roles in the pathogenesis of inflammatory myopathies and genetic muscle disorders. The purpose of this review article is to discuss the role and potential mechanisms by which ER stress and the individual arms of the UPR regulate skeletal muscle formation, plasticity, and function in various physiological and pathophysiological conditions.

L-carnitine protects C2C12 cells against mitochondrial superoxide overproduction and cell death

AIM

To identify and characterize the protective effect that L-carnitine exerted against an oxidative stress in C2C12 cells.

METHODS

Myoblastic C2C12 cells were treated with menadione, a vitamin K analog that engenders oxidative stress, and the protective effect of L-carnitine (a nutrient involved in fatty acid metabolism and the control of the oxidative process), was assessed by monitoring various parameters related to the oxidative stress, autophagy and cell death.

RESULTS

Associated with its physiological function, a muscle cell metabolism is highly dependent on oxygen and may produce reactive oxygen species (ROS), especially under pathological conditions. High levels of ROS are known to induce injuries in cell structure as they interact at many levels in cell function. In C2C12 cells, a treatment with menadione induced a loss of transmembrane mitochondrial potential, an increase in mitochondrial production of ROS; it also induces autophagy and was able to provoke cell death. Pre-treatment of the cells with L-carnitine reduced ROS production, diminished autophagy and protected C2C12 cells against menadione-induced deleterious effects.

CONCLUSION

In conclusion, L-carnitine limits the oxidative stress in these cells and prevents cell death.

Abnormal lipid metabolism in skeletal muscle tissue of patients with muscular dystrophy: In vitro, high-resolution NMR spectroscopy based observation in early phase of the disease

PURPOSE

Qualitative (assignment of lipid components) and quantitative (quantification of lipid components) analysis of lipid components were performed in skeletal muscle tissue of patients with muscular dystrophy in early phase of the disease as compared to control/normal subjects.

METHODS

Proton nuclear magnetic resonance (NMR) spectroscopy based experiment was performed on the lipid extract of skeletal muscle tissue of patients with muscular dystrophy in early phase of the disease and normal individuals for the analysis of lipid components [triglycerides, phospholipids, total cholesterol and unsaturated fatty acids (arachidonic, linolenic and linoleic acid)]. Specimens of muscle tissue were obtained from patients with Duchenne muscular dystrophy (DMD) [n=11; Age, Mean±SD; 9.2±1.4years; all were males], Becker muscular dystrophy (BMD) [n=12; Age, Mean±SD; 21.4±5.0years; all were males], facioscapulohumeral muscular dystrophy (FSHD) [n=11; Age, Mean±SD; 23.7±7.5years; all were males] and limb girdle muscular dystrophy-2B (LGMD-2B) [n=18; Age, Mean±SD; 24.2±4.1years; all were males]. Muscle specimens were also obtained from [n=30; Mean age±SD 23.1±6.0years; all were males] normal/control subjects.

RESULTS

Assigned lipid components in skeletal muscle tissue were triglycerides (TG), phospholipids (PL), total cholesterol (CHOL) and unsaturated fatty acids (arachidonic, linolenic and linoleic acid)]. Quantity of lipid components was observed in skeletal muscle tissue of DMD, BMD, FSHD and LGMD-2B patients as compared to control/normal subjects. TG was significantly elevated in muscle tissue of DMD, BMD and LGMD-2B patients. Increase level of CHOL was found only in muscle of DMD patients. Level of PL was found insignificant for DMD, BMD and LGMD-2B patients. Quantity of TG, PL and CHOL was unaltered in the muscle of patients with FSHD as compared to control/normal subjects. Linoleic acids were significantly reduced in muscle tissue of DMD, BMD, FSHD and LGMD-2B as compared to normal/control individuals.

CONCLUSIONS

Results clearly indicate alteration of lipid metabolism in patients with muscular dystrophy in early phase of the disease. Moreover, further evaluation is required to understand whether these changes are primary or secondary to muscular dystrophy. In future, these findings may prove an additional and improved approach for the diagnosis of different forms of muscular dystrophy.

Nutraceuticals and Their Potential to Treat Duchenne Muscular Dystrophy: Separating the Credible from the Conjecture

In recent years, complementary and alternative medicine has become increasingly popular. This trend has not escaped the Duchenne Muscular Dystrophy community with one study showing that 80% of caregivers have provided their Duchenne patients with complementary and alternative medicine in conjunction with their traditional treatments. These statistics are concerning given that many supplements are taken based on purely "anecdotal" evidence. Many nutraceuticals are thought to have anti-inflammatory or anti-oxidant effects. Given that dystrophic pathology is exacerbated by inflammation and oxidative stress these nutraceuticals could have some therapeutic benefit for Duchenne Muscular Dystrophy (DMD). This review gathers and evaluates the peer-reviewed scientific studies that have used nutraceuticals in clinical or pre-clinical trials for DMD and thus separates the credible from the conjecture.

Pharmacological therapeutics targeting the secondary defects and downstream pathology of Duchenne muscular dystrophy

INTRODUCTION

Since the identification of the dystrophin gene in 1986, a cure for Duchenne muscular dystrophy (DMD) has yet to be discovered. Presently, there are a number of genetic-based therapies in development aimed at restoration and/or repair of the primary defect. However, growing understanding of the pathophysiological consequences of dystrophin absence has revealed several promising downstream targets for the development of therapeutics.

AREAS COVERED

In this review, we discuss various strategies for DMD therapy targeting downstream consequences of dystrophin absence including loss of muscle mass, inflammation, fibrosis, calcium overload, oxidative stress, and ischemia. The rationale of each approach and the efficacy of drugs in preclinical and clinical studies are discussed.

EXPERT OPINION

For the last 30 years, effective DMD drug therapy has been limited to corticosteroids, which are associated with a number of negative side effects. Our knowledge of the consequences of dystrophin absence that contribute to DMD pathology has revealed several potential therapeutic targets. Some of these approaches may have potential to improve or slow disease progression independently or in combination with genetic-based approaches. The applicability of these pharmacological therapies to DMD patients irrespective of their genetic mutation, as well as the potential benefits even for advanced stage patients warrants their continued investigation.

Effects of muscular dystrophy, exercise and blocking activin receptor IIB ligands on the unfolded protein response and oxidative stress

Protein homeostasis in cells, proteostasis, is maintained through several integrated processes and pathways and its dysregulation may mediate pathology in many diseases including Duchenne muscular dystrophy (DMD). Oxidative stress, heat shock proteins, endoplasmic reticulum (ER) stress and its response, i.e. unfolded protein response (UPR), play key roles in proteostasis but their involvement in the pathology of DMD are largely unknown. Moreover, exercise and activin receptor IIB blocking are two strategies that may be beneficial to DMD muscle, but studies to examine their effects on these proteostasis pathways are lacking. Therefore, these pathways were examined in the muscle of mdx mice, a model of DMD, under basal conditions and in response to seven weeks of voluntary exercise and/or activin receptor IIB ligand blocking using soluble activin receptor-Fc (sAcvR2B-Fc) administration. In conjunction with reduced muscle strength, mdx muscle displayed greater levels of UPR/ER-pathway indicators including greater protein levels of IRE1α, PERK and Atf6b mRNA. Downstream to IRE1α and PERK, spliced Xbp1 mRNA and phosphorylation of eIF2α, were also increased. Most of the cytoplasmic and ER chaperones and mitochondrial UPR markers were unchanged in mdx muscle. Oxidized glutathione was greater in mdx and was associated with increases in lysine acetylated proteome and phosphorylated sirtuin 1. Exercise increased oxidative stress when performed independently or combined with sAcvR2B-Fc administration. Although neither exercise nor sAcvR2B-Fc administration imparted a clear effect on ER stress/UPR pathways or heat shock proteins, sAcvR2B-Fc administration increased protein expression levels of GRP78/BiP, a triggering factor for ER stress/UPR activation and TxNIP, a redox-regulator of ER stress-induced inflammation. In conclusion, the ER stress and UPR are increased in mdx muscle. However, these processes are not distinctly improved by voluntary exercise or blocking activin receptor IIB ligands and thus do not appear to be optimal therapeutic choices for improving proteostasis in DMD.

Going retro: Oxidative stress biomarkers in modern redox biology

The field of redox biology is inherently intertwined with oxidative stress biomarkers. Oxidative stress biomarkers have been utilized for many different objectives. Our analysis indicates that oxidative stress biomarkers have several salient applications: (1) diagnosing oxidative stress, (2) pinpointing likely redox components in a physiological or pathological process and (3) estimating the severity, progression and/or regression of a disease. On the contrary, oxidative stress biomarkers do not report on redox signaling. Alternative approaches to gain more mechanistic insights are: (1) measuring molecules that are integrated in pathways linking redox biochemistry with physiology, (2) using the exomarker approach and (3) exploiting -omics techniques. More sophisticated approaches and large trials are needed to establish oxidative stress biomarkers in the clinical setting.