Changes in calsequestrin, TNF-α, TGF-β and MyoD levels during the progression of skeletal muscle dystrophy in mdx mice: a comparative analysis of the quadriceps, diaphragm and intrinsic laryngeal muscles

Integrating spatial transcriptomics and single-nucleus RNA-seq revealed the specific inhibitory effects of TGF-β on intramuscular fat deposition

Intramuscular fat (IMF) is a complex adipose tissue within skeletal muscle, appearing specially tissue heterogeneous, and the factors influencing its formation remain unclear. In conditions such as diabetes, aging, and muscle wasting, IMF was deposited in abnormal locations in skeletal muscle, damaged the normal physiological functions of skeletal muscle. Here, we used Longissimus dorsi muscles from pigs with different IMF contents as samples and adopted a method combining spatial transcriptome (ST) and single-nucleus RNA-seq to identify the spatial heterogeneity of IMF. ST revealed that genes involved in TGF-β signaling pathways were specifically highly enriched in IMF. In lean pigs, IMF autocrine produces more TGF-β2, while in obese pigs, IMF received more endothelial-derived TGF-β1. In vitro experiments have proven that porcine endothelial cells in a simulated high-fat environment released more TGF-β1 than TGF-β2. Moreover, under obesity mice, the addition of TGF-β after muscle injury abolished IMF production and slowed muscle repair, whereas TGF-β inhibition accelerated muscle repair. Our findings demonstrate that the TGF-β pathway specifically regulates these processes, suggesting it as a potential therapeutic target for managing muscle atrophy in obese patients and enhancing muscle repair while reducing IMF deposition.

High mobility group box 1 (HMGB1) is a potential disease biomarker in cell and mouse models of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a progressive muscle wasting disorder affecting 1:3500 male births and is associated with myofiber degeneration, regeneration, and inflammation. Glucocorticoid treatments have been the standard of care due to immunomodulatory/immunosuppressive properties but novel genetic approaches, including exon skipping and gene replacement therapy, are currently being developed. The identification of additional biomarkers to assess DMD-related inflammatory responses and the potential efficacy of these therapeutic approaches are thus of critical importance. The current study uses RNA sequencing of skeletal muscle from two mdx mouse models to identify high mobility group box 1 (HMGB1) as a candidate biomarker potentially contributing to DMD-related inflammation. HMGB1 protein content was increased in a human iPSC-derived skeletal myocyte model of DMD and microdystrophin treatment decreased HMGB1 back to control levels. In vivo, HMGB1 protein levels were increased in vehicle treated B10-mdx skeletal muscle compared to B10-WT and significantly decreased in B10-mdx animals treated with adeno-associated virus (AAV)-microdystrophin. However, HMGB1 protein levels were not increased in D2-mdx skeletal muscle compared to D2-WT, demonstrating a strain-specific difference in DMD-related immunopathology.

A fat- and sucrose-enriched diet causes metabolic alterations in mdx mice

Duchenne muscular dystrophy (DMD), a progressive muscle disease caused by the absence of functional dystrophin protein, is associated with multiple cellular, physiological, and metabolic dysfunctions. As an added complication to the primary insult, obesity/insulin resistance (O/IR) is frequently reported in patients with DMD; however, how IR impacts disease severity is unknown. We hypothesized a high-fat, high-sucrose diet (HFHSD) would induce O/IR, exacerbate disease severity, and cause metabolic alterations in dystrophic mice. To test this hypothesis, we treated 7-wk-old mdx (disease model) and C57 mice with a control diet (CD) or an HFHSD for 15 wk. The HFHSD induced insulin resistance, glucose intolerance, and hyperglycemia in C57 and mdx mice. Of note, mdx mice on CD were also insulin resistant. In addition, visceral adipose tissue weights were increased with HFHSD in C57 and mdx mice though differed by genotype. Serum creatine kinase activity and histopathological analyses using Masson's trichrome staining in the diaphragm indicated muscle damage was driven by dystrophin deficiency but was not augmented by diet. In addition, markers of inflammatory signaling, mitochondrial abundance, and autophagy were impacted by disease but not diet. Despite this, in addition to disease signatures in CD-fed mice, metabolomic and lipidomic analyses demonstrated a HFHSD caused some common changes in C57 and mdx mice and some unique signatures of O/IR within the context of dystrophin deficiency. In total, these data revealed that in mdx mice, 15 wk of HFHSD did not overtly exacerbate muscle injury but further impaired the metabolic status of dystrophic muscle.

Biomarkers for Duchenne muscular dystrophy progression: impact of age in the mdx tongue spared muscle

BACKGROUND

Duchenne muscular dystrophy (DMD) is a severe form of muscular dystrophy without an effective treatment, caused by mutations in the DMD gene, leading to the absence of dystrophin. DMD results in muscle weakness, loss of ambulation, and death at an early age. Metabolomics studies in mdx mice, the most used model for DMD, reveal changes in metabolites associated with muscle degeneration and aging. In DMD, the tongue muscles exhibit unique behavior, initially showing partial protection against inflammation but later experiencing fibrosis and loss of muscle fibers. Certain metabolites and proteins, like TNF-α and TGF-β, are potential biomarkers for dystrophic muscle characterization.

METHODS

To investigate disease progression and aging, we utilized young (1 month old) and old (21-25 months old) mdx and wild-type tongue muscles. Metabolite changes were analyzed using 1H nuclear magnetic resonance, while TNF-α and TGF-β were assessed using Western blotting to examine inflammation and fibrosis. Morphometric analysis was conducted to assess the extent of myofiber damage between groups.

RESULTS

The histological analysis of the mid-belly tongue showed no differences between groups. No differences were found between the concentrations of metabolites from wild-type or mdx whole tongues of the same age. The metabolites alanine, methionine, and 3-methylhistidine were higher, and taurine and glycerol were lower in young tongues in both wild type and mdx (p < 0.001). The metabolites glycine (p < 0.001) and glutamic acid (p = 0.0018) were different only in the mdx groups, being higher in young mdx mice. Acetic acid, phosphocreatine, isoleucine, succinic acid, creatine, and the proteins TNF-α and TGF-β had no difference in the analysis between groups (p > 0.05).

CONCLUSIONS

Surprisingly, histological, metabolite, and protein analysis reveal that the tongue of old mdx remains partially spared from the severe myonecrosis observed in other muscles. The metabolites alanine, methionine, 3-methylhistidine, taurine, and glycerol may be effective for specific assessments, although their use for disease progression monitoring should be cautious due to age-related changes in the tongue muscle. Acetic acid, phosphocreatine, isoleucine, succinate, creatine, TNF-α, and TGF-β do not vary with aging and remain constant in spared muscles, suggesting their potential as specific biomarkers for DMD progression independent of aging.

Biomarkers for Duchenne muscular dystrophy progression: impact of age in the mdx tongue spared muscle

Background: Duchenne muscular dystrophy (DMD) is a severe form of muscular dystrophy without an effective treatment, caused by mutations in the DMD gene, leading to the absence of dystrophin. DMD results in muscle weakness, loss of ambulation and death at an early age. Metabolomics studies in mdx mice, the most used model for DMD, reveal changes in metabolites associated with muscle degeneration and aging. In DMD, the tongue muscles exhibit unique behavior, initially showing partial protection against inflammation but later experiencing fibrosis and loss of muscle fibers. Certain metabolites and proteins, like TNF-α and TGF-β, are potential biomarkers for dystrophic muscle characterization. Methods: To investigate disease progression and aging, we utilized young (1-month old) and old (21-25 months old) mdx and wild-type mice. Metabolite changes were analyzed using 1-H Nuclear Magnetic Resonance, while TNF-α and TGF-β were assessed using Western blotting to examine inflammation, and fibrosis. Morphometric analysis was conducted to assess the extent of myofiber damage between groups. Results: The histological analysis of the tongue showed no differences between groups. No differences were found between the concentrations of metabolites from wild type or mdx animals of the same age. The metabolites alanine, methionine, 3-methylhistidine were higher, and taurine and glycerol were lower in young animals in both wild type and mdx (p < 0.001). The metabolites glycine (p < 0.001) and glutamic acid (p = 0.0018) were different only in the mdx groups, being higher in young mdx mice. Acetic acid, phosphocreatine, isoleucine, succinic acid, creatine and the proteins TNF-α and TGF-β had no difference in the analysis between groups (p > 0.05). Conclusions: Surprisingly, histological and protein analysis reveals that the tongue of young and old mdx animals is protected from severe myonecrosis observed in other muscles. The metabolites alanine, methionine, 3-methylhistidine, taurine, and glycerol may be effective for specific assessments, although their use for disease progression monitoring should be cautious due to age-related changes. Acetic acid, phosphocreatine, isoleucine, succinate, creatine, TNF-α, and TGF-β do not vary with aging and remain constant in spared muscles, suggesting their potential as specific biomarkers for DMD progression independent of aging.

Curcumin Administration Improves Force of mdx Dystrophic Diaphragm by Acting on Fiber-Type Composition, Myosin Nitrotyrosination and SERCA1 Protein Levels

The vegetal polyphenol curcumin displays beneficial effects against skeletal muscle derangement induced by oxidative stress, disuse or aging. Since oxidative stress and inflammation are involved in the progression of muscle dystrophy, the effects of curcumin administration were investigated in the diaphragm of mdx mice injected intraperitoneally or subcutaneously with curcumin for 4-12-24 weeks. Curcumin treatment independently of the way and duration of administration (i) ameliorated myofiber maturation index without affecting myofiber necrosis, inflammation and degree of fibrosis; (ii) counteracted the decrease in type 2X and 2B fiber percentage; (iii) increased about 30% both twitch and tetanic tensions of diaphragm strips; (iv) reduced myosin nitrotyrosination and tropomyosin oxidation; (v) acted on two opposite nNOS regulators by decreasing active AMP-Kinase and increasing SERCA1 protein levels, the latter effect being detectable also in myotube cultures from mdx satellite cells. Interestingly, increased contractility, decreased myosin nitrotyrosination and SERCA1 upregulation were also detectable in the mdx diaphragm after a 4-week administration of the NOS inhibitor 7-Nitroindazole, and were not improved further by a combined treatment. In conclusion, curcumin has beneficial effects on the dystrophic muscle, mechanistically acting for the containment of a deregulated nNOS activity.

Sarcoplasmic Reticulum Ca2+ Buffer Proteins: A Focus on the Yet-To-Be-Explored Role of Sarcalumenin in Skeletal Muscle Health and Disease

Sarcalumenin (SAR) is a luminal Ca²⁺ buffer protein with high capacity but low affinity for calcium binding found predominantly in the longitudinal sarcoplasmic reticulum (SR) of fast- and slow-twitch skeletal muscles and the heart. Together with other luminal Ca²⁺ buffer proteins, SAR plays a critical role in modulation of Ca²⁺ uptake and Ca²⁺ release during excitation-contraction coupling in muscle fibers. SAR appears to be important in a wide range of other physiological functions, such as Sarco-Endoplasmic Reticulum Calcium ATPase (SERCA) stabilization, Store-Operated-Calcium-Entry (SOCE) mechanisms, muscle fatigue resistance and muscle development. The function and structural features of SAR are very similar to those of calsequestrin (CSQ), the most abundant and well-characterized Ca²⁺ buffer protein of junctional SR. Despite the structural and functional similarity, very few targeted studies are available in the literature. The present review provides an overview of the role of SAR in skeletal muscle physiology, as well as of its possible involvement and dysfunction in muscle wasting disorders, in order to summarize the current knowledge on SAR and drive attention to this important but still underinvestigated/neglected protein.

Postdevelopmental knockout of Orai1 improves muscle pathology in a mouse model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD), an X-linked disorder caused by loss-of-function mutations in the dystrophin gene, is characterized by progressive muscle degeneration and weakness. Enhanced store-operated Ca2+ entry (SOCE), a Ca2+ influx mechanism coordinated by STIM1 sensors of luminal Ca2+ within the sarcoplasmic reticulum (SR) and Ca2+-permeable Orai1 channels in the sarcolemma, is proposed to contribute to Ca2+-mediated muscle damage in DMD. To directly determine the impact of Orai1-dependent SOCE on the dystrophic phenotype, we crossed mdx mice with tamoxifen-inducible, muscle-specific Orai1 knockout mice (mdx-Orai1 KO mice). Both constitutive and SOCE were significantly increased in flexor digitorum brevis fibers from mdx mice, while SOCE was absent in fibers from both Orai1 KO and mdx-Orai1 KO mice. Compared with WT mice, fibers from mdx mice exhibited (1) increased resting myoplasmic Ca2+ levels, (2) reduced total releasable Ca2+ store content, and (3) a prolonged rate of electrically evoked Ca2+ transient decay. These effects were partially normalized in fibers from mdx-Orai1 KO mice. Intact extensor digitorum longus muscles from mdx mice exhibited a significant reduction of maximal specific force, which was rescued in muscles from mdx-Orai1 KO mice. Finally, during exposure to consecutive eccentric contractions, muscles from mdx mice displayed a more pronounced decline in specific force compared with that of WT mice, which was also significantly attenuated by Orai1 ablation. Together, these results indicate that enhanced Orai1-dependent SOCE exacerbates the dystrophic phenotype and that Orai1 deficiency improves muscle pathology by both normalizing Ca2+ homeostasis and promoting sarcolemmal integrity/stability.

Breathing in Duchenne muscular dystrophy: Translation to therapy

Duchenne muscular dystrophy (DMD) is an X-linked neuromuscular disease caused by a deficiency in dystrophin - a structural protein which stabilizes muscle during contraction. Dystrophin deficiency adversely affects the respiratory system leading to sleep-disordered breathing, hypoventilation, and weakness of the expiratory and inspiratory musculature, which culminate in severe respiratory dysfunction. Muscle degeneration associated respiratory impairment in neuromuscular disease is a result of disruptions at multiple sites of the respiratory control network, including sensory and motor pathways. As a result of this pathology, respiratory failure is a leading cause of premature death in DMD patients. Currently available treatments for DMD respiratory insufficiency attenuate respiratory symptoms without completely reversing the underlying pathophysiology. This underscores the need to develop curative therapies to improve quality of life and longevity of DMD patients. This review summarises research findings on the pathophysiology of respiratory insufficiencies in DMD disease in humans and animal models, the clinical interventions available to ameliorate symptoms, and gene-based therapeutic strategies uncovered by preclinical animal studies. Abstract figure legend: Summary of the therapeutic strategies for respiratory insufficiency in DMD (Duchenne muscular dystrophy). Treatment options currently in clinical use only attenuate respiratory symptoms without reversing the underlying pathology of DMD-associated respiratory insufficiencies. Ongoing preclinical and clinical research is aimed at developing curative therapies that both improve quality of life and longevity of DMD patients. AAV - adeno-associated virus, PPMO - Peptide-conjugated phosphorodiamidate morpholino oligomer This article is protected by copyright. All rights reserved.

Transforming Growth Factor-Beta in Skeletal Muscle Wasting

Transforming growth factor-beta (TGF-β) is part of a family of molecules that is present in many body tissues and performs many different functions. Evidence has been obtained from mice and human cancer patients with bony metastases and non-metastatic disease, as well as pediatric burn patients, that inflammation leads to bone resorption and release of TGF-β from the bone matrix with paracrine effects on muscle protein balance, possibly mediated by the generation of reactive oxygen species. Whether immobilization, which confounds the etiology of bone resorption in burn injury, also leads to the release of TGF-β from bone contributing to muscle wasting in other conditions is unclear. The use of anti-resorptive therapy in both metastatic cancer patients and pediatric burn patients has been successful in the prevention of muscle wasting, thereby creating an additional therapeutic niche for this class of drugs. The liberation of TGF-β may be one way in which bone helps to control muscle mass, but further investigation will be necessary to assess whether the rate of bone resorption is the determining factor for the release of TGF-β. Moreover, whether different resorptive conditions, such as immobilization and hyperparathyroidism, also involve TGF-β release in the pathogenesis of muscle wasting needs to be investigated.

Ixazomib, an oral proteasome inhibitor, exhibits potential effect in dystrophin-deficient mdx mice

Dystrophin deficiency makes the sarcolemma fragile and susceptible to degeneration in Duchenne muscular dystrophy. The proteasome is a multimeric protease complex and is central to the regulation of cellular proteins. Previous studies have shown that proteasome inhibition improved pathological changes in mdx mice. Ixazomib is the first oral proteasome inhibitor used as a therapy in multiple myeloma. This study investigated the effects of ixazomib on the dystrophic muscle of mdx mice. MDX mice were treated with ixazomib (7.5 mg/kg/wk by gavage) or 0.2 mL of saline for 12 weeks. The Kondziela test was performed to measure muscle strength. The tibialis anterior (TA) and diaphragm (DIA) muscles were used for morphological analysis, and blood samples were collected for biochemical measurement. We observed maintenance of the muscle strength in the animals treated with ixazomib. Treatment with ixazomib had no toxic effect on the mdx mouse. The morphological analysis showed a reduction in the inflammatory area and fibres with central nuclei in the TA and DIA muscles and an increase in the number of fibres with a diameter of 20 µm2 in the DIA muscle after treatment with ixazomib. There was an increase in the expression of dystrophin and utrophin in the TA and DIA muscles and a reduction in the expression of osteopontin and TGF-β in the DIA muscle of mdx mice treated with ixazomib. Ixazomib was thus shown to increase the expression of dystrophin and utrophin associated with improved pathological and functional changes in the dystrophic muscles of mdx mice.

Arrhythmogenic Cardiomyopathy and Skeletal Muscle Dystrophies: Shared Histopathological Features and Pathogenic Mechanisms

Arrhythmogenic cardiomyopathy (ACM) is a heritable cardiac disease characterized by fibrotic or fibrofatty myocardial replacement, associated with an increased risk of ventricular arrhythmias and sudden cardiac death. Originally described as a disease of the right ventricle, ACM is currently recognized as a biventricular entity, due to the increasing numbers of reports of predominant left ventricular or biventricular involvement. Research over the last 20 years has significantly advanced our knowledge of the etiology and pathogenesis of ACM. Several etiopathogenetic theories have been proposed; among them, the most attractive one is the dystrophic theory, based on the observation of similar histopathological features between ACM and skeletal muscle dystrophies (SMDs), such as progressive muscular degeneration, inflammation, and tissue replacement by fatty and fibrous tissue. This review will describe the pathophysiological and molecular similarities shared by ACM with SMDs.

N-acetylcysteine Decreases Fibrosis and Increases Force-Generating Capacity of mdx Diaphragm

Respiratory muscle weakness occurs due to dystrophin deficiency in Duchenne muscular dystrophy (DMD). The mdx mouse model of DMD shows evidence of impaired respiratory muscle performance with attendant inflammation and oxidative stress. We examined the effects of N-acetylcysteine (NAC) supplementation on respiratory system performance in mdx mice. Eight-week-old male wild type (n = 10) and mdx (n = 20) mice were studied; a subset of mdx (n = 10) received 1% NAC in the drinking water for 14 days. We assessed breathing, diaphragm, and external intercostal electromyogram (EMG) activities and inspiratory pressure during ventilatory and non-ventilatory behaviours. Diaphragm muscle structure and function, cytokine concentrations, glutathione status, and mRNA expression were determined. Diaphragm force-generating capacity was impaired in mdx compared with wild type. Diaphragm muscle remodelling was observed in mdx, characterized by increased muscle fibrosis, immune cell infiltration, and central myonucleation. NAC supplementation rescued mdx diaphragm function. Collagen content and immune cell infiltration were decreased in mdx + NAC compared with mdx diaphragms. The cytokines IL-1β, IL-6 and KC/GRO were increased in mdx plasma and diaphragm compared with wild type; NAC decreased systemic IL-1β and KC/GRO concentrations in mdx mice. We reveal that NAC treatment improved mdx diaphragm force-generating capacity associated with beneficial anti-inflammatory and anti-fibrotic effects. These data support the potential use of NAC as an adjunctive therapy in human dystrophinopathies.

Photobiomodulation Therapy for Attenuating the Dystrophic Phenotype of Mdx Mice

This study analyzed photobiomodulation therapy (PBMT) effects on regenerative, antioxidative, anti-inflammatory and angiogenic markers in the dystrophic skeletal muscle of mdx mice, the experimental model of Duchenne muscular dystrophy (DMD), during the acute phase of dystrophy disease. The following groups were set up: Ctrl (control group of normal wild-type mice; C57BL/10); mdx (untreated mdx mice); mdxPred (mdx mice treated with prednisolone) and mdxLA (mdx mice treated with PBMT). The PBMT was carried out using an Aluminum Gallium Arsenide (AIGaAs; IBRAMED® laserpulse) diode, 830 nm wavelength, applied on the dystrophic quadriceps muscle. The mdxLA group showed a degenerative and regenerative area reduction simultaneously with a MyoD level increase, ROS production and inflammatory marker reduction and up-regulation in the VEGF factor. In addition, PBMT presented similar effects to prednisolone treatment in most of the parameters analyzed. In conclusion, our results indicate that PBMT in the parameters selected attenuated the dystrophic phenotype of mdx mice, improving skeletal muscle regeneration; reducing the oxidative stress and inflammatory process; and up-regulating the angiogenic marker.

Influence of β2 adrenergic receptor genotype on risk of nocturnal ventilation in patients with Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disease resulting in severe respiratory derangements. As such, DMD patients are at a high risk of nocturnal hypoventilation, thereby requiring nocturnal ventilation (NV). To this end, NV is an important clinical milestone in the management of DMD. Emerging evidence suggests that ß₂ adrenergic receptors (ADRB2) may play a role in determining respiratory function, whereby more functional ADRB2 genotype variants (e.g., Gly16) are associated with improved pulmonary function and respiratory muscle strength. These findings suggest that the more functional ADRB2 genotype may help to preserve respiratory function in patients with DMD. The purpose of this study was to identify the influence of ADRB2 genotype on the risk of NV use in DMD. Data from the CINRG Duchenne Natural History Study including 175 DMD patients (3–25 yrs) were analyzed focusing on ADRB2 genotype variants. Time-to-event analyses were used to examine differences in the age at prescription of full-time NV use between genotypes. There were no differences between genotype groups in age, height, weight, corticosteroid use, proportion of ambulatory patients, or age at loss of ambulation. DMD patients expressing the Gly16 polymorphism had a significantly (P < 0.05) lower mean age at NV prescription compared with those patients expressing the Arg16 polymorphism (21.80 ± 0.59 yrs. vs 25.91 ± 1.31 yrs., respectively). In addition, a covariate-adjusted Cox model revealed that the Gly16 variant group possessed a 6.52-fold higher risk of full-time NV use at any given age compared with the Arg16 polymorphism group. These data suggest that genetic variations in the ADRB2 gene may influence the age at which DMD patients are first prescribed NV, whereby patients with the Gly16 polymorphism are more likely to require NV assistance at an earlier age than their Arg16 counterparts.

Recovery of respiratory function in mdx mice co-treated with neutralizing interleukin-6 receptor antibodies and urocortin-2

KEY POINTS

Impaired ventilatory capacity and diaphragm muscle weakness are prominent features of Duchenne muscular dystrophy, with strong evidence of attendant systemic and muscle inflammation. We performed a 2-week intervention in young wild-type and mdx mice, consisting of either injection of saline or co-administration of a neutralizing interleukin-6 receptor antibody (xIL-6R) and urocortin-2 (Ucn2), a corticotrophin releasing factor receptor 2 agonist. We examined breathing and diaphragm muscle form and function. Breathing and diaphragm muscle functional deficits are improved following xIL-6R and Ucn2 co-treatment in mdx mice. The functional improvements were associated with a preservation of mdx diaphragm muscle myosin heavy chain IIx fibre complement. The concentration of the pro-inflammatory cytokine interleukin-1β was reduced and the concentration of the anti-inflammatory cytokine interleukin-10 was increased in mdx diaphragm following drug co-treatment. Our novel findings may have implications for the development of pharmacotherapies for the dystrophinopathies with relevance for respiratory muscle performance and breathing.

ABSTRACT

The mdx mouse model of Duchenne muscular dystrophy shows evidence of hypoventilation and pronounced diaphragm dysfunction. Six-week-old male mdx (n = 32) and wild-type (WT; n = 32) mice received either saline (0.9% w/v) or a co-administration of neutralizing interleukin-6 receptor antibodies (xIL-6R; 0.2 mg kg-1 ) and corticotrophin-releasing factor receptor 2 agonist (urocortin-2; 30 μg kg-1 ) subcutaneously over 2 weeks. Breathing and diaphragm muscle contractile function (ex vivo) were examined. Diaphragm structure was assessed using histology and immunofluorescence. Muscle cytokine concentration was determined using a multiplex assay. Minute ventilation and diaphragm muscle peak force at 100 Hz were significantly depressed in mdx compared with WT. Drug treatment completely restored ventilation in mdx mice during normoxia and significantly increased mdx diaphragm force- and power-generating capacity. The number of centrally nucleated muscle fibres and the areal density of infiltrates and collagen content were significantly increased in mdx diaphragm; all indices were unaffected by drug co-treatment. The abundance of myosin heavy chain (MyHC) type IIx fibres was significantly decreased in mdx diaphragm; drug co-treatment preserved MyHC type IIx complement in mdx muscle. Drug co-treatment increased the cross-sectional area of MyHC type I and IIx fibres in mdx diaphragm. The cytokines IL-1β, IL-6, KC/GRO and TNF-α were significantly increased in mdx diaphragm compared with WT. Drug co-treatment significantly decreased IL-1β and increased IL-10 in mdx diaphragm. Drug co-treatment had no significant effect on WT diaphragm muscle structure, cytokine concentrations or function. Recovery of breathing and diaphragm force in mdx mice was impressive in our studies, with implication for human dystrophinopathies.

Agent-based model illustrates the role of the microenvironment in regeneration in healthy and mdx skeletal muscle

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disease with no effective treatment. Multiple mechanisms are thought to contribute to muscle wasting, including increased susceptibility to contraction-induced damage, chronic inflammation, fibrosis, altered satellite stem cell (SSC) dynamics, and impaired regenerative capacity. The goals of this project were to 1) develop an agent-based model of skeletal muscle that predicts the dynamic regenerative response of muscle cells, fibroblasts, SSCs, and inflammatory cells as a result of contraction-induced injury, 2) calibrate and validate the model parameters based on comparisons with published experimental measurements, and 3) use the model to investigate how changing isolated and combined factors known to be associated with DMD (e.g., altered fibroblast or SSC behaviors) influence muscle regeneration. Our predictions revealed that the percent of injured muscle that recovered 28 days after injury was dependent on the peak SSC counts following injury. In simulations with near-full cross-sectional area recovery (healthy, 4-wk mdx, 3-mo mdx), the SSC counts correlated with the extent of initial injury; however, in simulations with impaired regeneration (9-mo mdx), the peak SSC counts were suppressed relative to initial injury. The differences in SSC counts between these groups were emergent predictions dependent on altered microenvironment factors known to be associated with DMD. Multiple cell types influenced the peak number of SSCs, but no individual parameter predicted the differences in SSC counts. This finding suggests that interventions to target the microenvironment rather than SSCs directly could be an effective method for improving regeneration in impaired muscle. NEW & NOTEWORTHY A computational model predicted that satellite stem cell (SSC) counts are correlated with muscle cross-sectional area (CSA) recovery following injury. In simulations with impaired CSA recovery, SSC counts are suppressed relative to healthy muscle. The suppressed SSC counts were an emergent model prediction, because all simulations had equal initial SSC counts. Fibroblast and anti-inflammatory macrophage counts influenced SSC counts, but no single factor was able to predict the pathological differences in SSC counts that lead to impaired regeneration.

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.

Dual Therapy Deflazacort/Doxycyclyne Is Better Than Deflazacort Monotherapy to Alleviate Cardiomyopathy in Dystrophin-Deficient mdx Mice

Cardiomyopathy related to the absence of dystrophin is an important feature in Duchenne muscular dystrophy (DMD) and in the mdx mouse. Doxycycline (DOX) could be a potential therapy for mdx skeletal muscles dystrophy. We investigated whether the corticoid deflazacort (DFZ) plus DOX could improve cardiac mdx dystrophy better than DFZ alone, later (17 months) in dystrophy. Mdx mice (8 months old) received DFZ/DOX or DFZ for 9 months. The combined therapy was greater than DFZ in reducing fibrosis (60% decrease with DFZ/DOX and 40% with DFZ alone) in the right ventricle and transforming growth factor β levels (6.8 ± 3.2 in untreated mdx mice, 2.8 ± 1.4 in combined therapy, and 4.6 ± 1.7 in DFZ; P < .05). Combined therapy more effectively ameliorated cardiac dysfunction (electrocardiogram [ECG]) than DFZ. Improvements were seen in the cardiomyopathy index (0.8 ± 0.1 in combined therapy and 1.0 ± 0.2 in DFZ), heart rate (418 ± 46 bpm in combined therapy and 457 ± 29 bpm in DFZ), QRS interval (11.3 ± 2 in combined therapy and 13.6 ± 1 in DFZ), and Q wave amplitude (-40.7 ± 21 in combined therapy and -90.9 ± 36 in DFZ). Both therapies decreased markers of inflammation (tumor necrosis factor α, nuclear factor κB, and metalloproteinase 9). DFZ/DOX improved mdx cardiomyopathy at this stage of the disease, supporting further clinical investigations.

Effect of the IL-1 Receptor Antagonist Kineret® on Disease Phenotype in mdx Mice

Duchenne muscular dystrophy (DMD) is an X-linked muscle disease caused by mutations in the dystrophin gene. The pathology of DMD manifests in patients with progressive muscle weakness, loss of ambulation and ultimately death. One of the characteristics of DMD is muscle inflammation, and dystrophin-deficient skeletal muscles produce higher levels of the pro-inflammatory cytokine interleukin 1β (IL-1β) in response to toll like receptor (TLR) stimulation compared to controls; therefore, blocking the IL-1β pathway could improve the disease phenotype in mdx mice, a mouse model of DMD. Kineret^® or IL-1Ra is a recombinant IL-1 receptor antagonist approved by the FDA for treating rheumatoid arthritis. To determine the efficacy of IL-1Ra in a DMD model, we administered subcutaneous injections of saline control or IL-1Ra (25 mg/kg/day) to mdx mice daily for 45 days beginning at 5 weeks of age. Functional and histological parameters were measured at the conclusion of the study. IL-1Ra only partially inhibited this signaling pathway in this study; however, there were still interesting observations to be noted. For example, although not significantly changed, splenocytes from the IL-1Ra-treated group secreted less IL-1β after LPS stimulation compared to control mice indicating a blunted response and incomplete inhibition of the pathway (37% decrease). In addition, normalized forelimb grip strength was significantly increased in IL-1Ra-treated mice. There were no changes in EDL muscle-specific force measurements, histological parameters, or motor coordination assessments in the dystrophic mice after IL-1Ra treatment. There was a significant 27% decrease in the movement time and total distance traveled by the IL-1Ra treated mice, correlating with previous studies examining effects of IL-1 on behavior. Our studies indicate partial blocking of IL-1β with IL-1Ra significantly altered only a few behavioral and strength related disease parameters; however, treatment with inhibitors that completely block IL-1β, pathways upstream of IL-1β production or combining various inhibitors may produce more favorable outcomes.