• Animals
• Muscle, Skeletal/physiopathology
• Muscle, Skeletal/physiology
• Walking/physiology
• Mice, Inbred mdx
• Mice
• Humans
• Muscular Dystrophy, Duchenne/physiopathology
• Muscle Contraction/physiology
• Male
• Gait/physiology

• National Institutes of Health

• Dog
• Duchenne
• Dystrophin
• Dystrophy
• HMB
• Muscle

• Animals
• Dogs
• Valerates/pharmacology
• Valerates/administration & dosage
• Valerates/therapeutic use
• Pilot Projects
• Muscular Dystrophy, Duchenne/drug therapy
• Muscular Dystrophy, Duchenne/metabolism
• Male
• Amino Acids/metabolism
• Disease Models, Animal
• Cross-Over Studies
• Muscle, Skeletal/metabolism
• Muscle, Skeletal/drug effects

• Contraction
• Dystrophin
• L-type voltage-gated calcium channel
• Obstructed defecation syndrome
• Proteomics
• Smooth muscle

• Humans
• Constipation/physiopathology
• Constipation/metabolism
• Proteomics/methods
• Female
• Rectum/pathology
• Male
• Defecation
• Dystrophin/metabolism
• Adult
• Middle Aged
• Calcium Channels, L-Type/metabolism
• Muscle Contraction
• Myocytes, Smooth Muscle/metabolism
• Myocytes, Smooth Muscle/pathology
• Case-Control Studies
• Syndrome
• Muscle, Smooth/metabolism
• Muscle, Smooth/physiopathology
• Muscle, Smooth/pathology
• Down-Regulation
• Calcium/metabolism
• Hemorrhoids/metabolism
• Hemorrhoids/physiopathology
• Hemorrhoids/pathology
• Computational Biology

• Animals
• Male
• Female
• Mice, Inbred C57BL
• Regeneration
• Muscle, Skeletal/metabolism
• Muscle, Skeletal/pathology
• Muscle, Skeletal/physiopathology
• Muscle, Skeletal/injuries
• Mice
• Adipose Tissue/metabolism
• Fibrosis
• Disease Models, Animal
• Sex Characteristics
• Species Specificity
• Glycerol/metabolism
• Glycerol/toxicity
• Mice, 129 Strain

• R01 AR079449 NIAMS NIH HHS
• R01 HL171050 NHLBI NIH HHS
• T32HD043730 National Institute of Child Health and Human Development
• R01AR079449 NIAMS NIH HHS
• R01HL171050 NHLBI NIH HHS
• National Institute of Arthritis and Musculoskeletal and Skin Diseases
• National Heart, Lung, and Blood Institute

• Duchenne muscular dystrophy
• disease-causing variant
• hypertrophic feline muscular dystrophy
• nonsense

• Dog
• Muscular dystrophy
• Myopathy
• Whole genome sequencing

• Animals
• Dogs
• Humans
• Muscular Dystrophy, Duchenne/pathology
• Dystrophin/genetics
• Dystrophin/metabolism
• Exons/genetics
• Phenotype
• Muscle, Skeletal/pathology
• Introns

• K01 OD027058 NIH HHS
• P50 HD105351 NICHD NIH HHS
• R01 AR064300 NIAMS NIH HHS

ASP0367, or bocidelpar sulfate, is an orally administered small molecule that potently and selectively modulates peroxisome proliferator–activated receptor δ (PPARδ) to address mitochondrial dysfunction occurring in diseases including primary mitochondrial myopathy and Duchenne muscular dystrophy. The objectives of this first‐in‐human trial were to evaluate the safety/tolerability, pharmacokinetics, and pharmacodynamics of ASP0367 in healthy participants.

In this double‐blind phase 1 study, adult participants were randomized to single or multiple ascending oral doses of ASP0367 or placebo. The study duration was 1 and 14 days, respectively. Pharmacokinetic parameters under fed conditions were also evaluated.

A total of 64 (single‐dose cohort) and 37 (multiple‐dose cohort) participants were included in the study. After single doses of 1 to 120 mg, ASP0367 was rapidly absorbed, with median time to maximum plasma concentration (t_max) of 1.50 to 2.24 hours under fasting conditions; ASP0367 concentrations declined in a multiphasic manner after reaching maximum plasma concentration. Under fed conditions, t_max was delayed 1.7 hours. After multiple once‐daily doses, mean half‐life of ASP0367 10 to 75 mg ranged from 14.1 to 17.5 hours; steady state was reached after 4 days. Negligible accumulation was observed after repeated dosing. No participants receiving ASP0367 discontinued treatment, and all treatment‐emergent adverse events were mild to moderate in severity; none were considered drug‐related. No clinically significant changes were observed on laboratory or electrocardiographic evaluation. Treatment‐ and dose‐dependent upregulation of six PPARδ target genes was observed with single and multiple doses of ASP0367.

ASP0367, or bocidelpar sulfate, was well tolerated; rapid absorption, roughly dose‐proportional bioavailability, and effects on PPARδ target genes were demonstrated in healthy adult participants.

• Duchenne muscular dystrophy
• PPARδ agonist
• mitochondrial disease
• mitochondrial myopathy
• peroxisome proliferator-activated receptors

• Canine
• Gene mutation
• Genetics
• Myopathy
• Sarcoglycanopathy

• Duchenne muscular dystrophy (DMD)
• Golden retriever muscular dystrophy (GRMD)
• Peak expiratory flow
• Pulmonary function test
• Respiratory inductance plethysmography
• Spirometry

• Animals
• Diaphragm/physiopathology
• Disease Models, Animal
• Dog Diseases/physiopathology
• Dogs
• Exhalation
• Muscular Dystrophy, Animal/physiopathology
• Muscular Dystrophy, Duchenne/physiopathology
• Peak Expiratory Flow Rate
• Respiratory Function Tests

• U24 NS059696 NINDS NIH HHS

Neuromuscular diseases (NMDs) are a heterogeneous group of acquired or inherited rare disorders caused by injury or dysfunction of the anterior horn cells of the spinal cord (lower motor neurons), peripheral nerves, neuromuscular junctions, or skeletal muscles leading to muscle weakness and waste. Unfortunately, most of them entail serious or even fatal consequences. The prevalence rates among NMDs range between 1 and 10 per 100,000 population, but their rarity and diversity pose difficulties for healthcare and research. Some molecular hallmarks are being explored to elucidate the mechanisms triggering disease, to set the path for further advances. In fact, in the present review we outline the metabolic alterations of NMDs, mainly focusing on the role of mitochondria. The aim of the review is to discuss the mechanisms underlying energy production, oxidative stress generation, cell signaling, autophagy, and inflammation triggered or conditioned by the mitochondria. Briefly, increased levels of inflammation have been linked to reactive oxygen species (ROS) accumulation, which is key in mitochondrial genomic instability and mitochondrial respiratory chain (MRC) dysfunction. ROS burst, impaired autophagy, and increased inflammation are observed in many NMDs. Increasing knowledge of the etiology of NMDs will help to develop better diagnosis and treatments, eventually reducing the health and economic burden of NMDs for patients and healthcare systems.

• damage-associated molecular patterns (DAMPs)
• mitochondrial respiratory chain (MRC)
• mitophagy
• neuromuscular diseases (NMDs)
• oxidative stress
• reactive oxygen species (ROS)

• Disease modelling
• Muscular dystrophy
• Neuromuscular disease
• Rare disease
• Translational research

• Animals
• Biomedical Research
• Disease Models, Animal
• Humans
• Mice
• Muscle, Skeletal/pathology
• Neuromuscular Diseases/pathology
• Translational Research, Biomedical
• Zebrafish

• Disease pathology
• Mouse models
• Muscular dystrophy

• Animals
• Disease Models, Animal
• Gene Targeting
• Mice
• Muscular Dystrophies/pathology
• Muscular Dystrophies/therapy

Duchenne muscular dystrophy (DMD) is caused by mutations in the DMD gene that abolish the expression of dystrophin protein. Dogs with the genetic homologue, golden retriever muscular dystrophy dog (GRMD), have a splice site mutation that leads to skipping of exon 7 and a stop codon in the DMD transcript. Gene editing via homology-directed repair (HDR) has been used in the mdx mouse model of DMD but not in GRMD. In this study, we used clustered regularly interspaced short palindromic repeats (CRISPR) and transcription activator-like effector nucleases (TALEN) to restore dystrophin expression via HDR in myoblasts/myotubes and later via intramuscular injection of GRMD dogs. In vitro, DNA and RNA were successfully corrected but dystrophin protein was not translated. With intramuscular injection of two different guide arms, sgRNA A and B, there was mRNA expression and Sanger sequencing confirmed inclusion of exon 7 for all treatments. On Western blot analysis, protein expression of up to 6% of normal levels was seen in two dogs injected with sgRNA B and up to 16% of normal in one dog treated with sgRNA A. TALEN did not restore any dystrophin expression. While there were no adverse effects, clear benefits were not seen on histopathologic analysis, immunofluorescence microscopy, and force measurements. Based on these results, methods must be modified to increase the efficiency of HDR-mediated gene repair and protein expression.

Duchenne muscular dystrophy (DMD) is an X-linked genetic disease characterized by progressive muscle wasting and weakness and premature death. Glucocorticoids (e.g. prednisolone) remain the only drugs with a favorable impact on DMD patients, but not without side effects. We have demonstrated that glycine preserves muscle in various wasting models. Since glycine effectively suppresses the activity of pro-inflammatory macrophages, we investigated the potential of glycine treatment to ameliorate the dystrophic pathology. Dystrophic mdx and dystrophin-utrophin null (dko) mice were treated with glycine or L-alanine (amino acid control) for up to 15 weeks and voluntary running distance (a quality of life marker and strong correlate of lifespan in dko mice) and muscle morphology were assessed. Glycine increased voluntary running distance in mdx mice by 90% (P < 0.05) after 2 weeks and by 60% (P < 0.01) in dko mice co-treated with prednisolone over an 8 week treatment period. Glycine treatment attenuated fibrotic deposition in the diaphragm by 28% (P < 0.05) after 10 weeks in mdx mice and by 22% (P < 0.02) after 14 weeks in dko mice. Glycine treatment augmented the prednisolone-induced reduction in fibrosis in diaphragm muscles of dko mice (23%, P < 0.05) after 8 weeks. Our findings provide strong evidence that glycine supplementation may be a safe, simple and effective adjuvant for improving the efficacy of prednisolone treatment and improving the quality of life for DMD patients.

Duchenne muscular dystrophy (DMD) is an X‐linked disease that causes progressive muscle weakness. Affected boys typically die from respiratory or cardiac failure. Golden retriever muscular dystrophy (GRMD) is genetically homologous with DMD and causes analogous skeletal and cardiac muscle disease. Previous studies have detailed features of GRMD cardiomyopathy in mostly young dogs. Cardiac disease is not well characterized in adult GRMD dogs, and cardiac magnetic resonance (CMR) imaging studies have not been completed.

We evaluated echocardiography and CMR in 24 adult GRMD dogs at different ages. Left ventricular systolic and diastolic functions, wall thickness, and myocardial strain were assessed with echocardiography. Features evaluated with CMR included left ventricular function, chamber size, myocardial mass, and late gadolinium enhancement. Our results largely paralleled those of DMD cardiomyopathy. Ejection fraction and fractional shortening correlated well with age, with systolic dysfunction occurring at ≈30 to 45 months. Circumferential strain was more sensitive than ejection fraction in early disease detection. Evidence of left ventricular chamber dilatation provided proof of dilated cardiomyopathy. Late gadolinium enhancement imaging showed DMD‐like left ventricular lateral wall lesions and earlier involvement of the anterior septum. Multiple functional indexes were graded objectively and added, with and without late gadolinium enhancement, to give cardiac and cardiomyopathy scores of disease severity. Consistent with DMD, there was parallel skeletal muscle involvement, as tibiotarsal joint flexion torque declined in tandem with cardiac function.

This study established parallels of progressive cardiomyopathy between dystrophic dogs and boys, further validating GRMD as a model of DMD cardiac disease.

• Duchenne muscular dystrophy
• cardiac imaging
• cardiomyopathy
• golden retriever muscular dystrophy
• natural history

• 3D models
• Becker muscular dystrophy
• Duchenne muscular dystrophy
• cellular differentiation
• iPSC models

Metabolic dysfunction in Duchenne muscular dystrophy (DMD) is characterized by reduced glycolytic and oxidative enzymes, decreased and abnormal mitochondria, decreased ATP, and increased oxidative stress. We analyzed glucose metabolism as a potential disease biomarker in the genetically homologous golden retriever muscular dystrophy (GRMD) dog with molecular, biochemical, and in vivo imaging.

Pelvic limb skeletal muscle and left ventricle tissue from the heart were analyzed by mRNA profiling, qPCR, western blotting, and immunofluorescence microscopy for the primary glucose transporter (GLUT4). Physiologic glucose handling was measured by fasting glucose tolerance test (GTT), insulin levels, and skeletal and cardiac positron emission tomography/X-ray computed tomography (PET/CT) using the glucose analog 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG).

MRNA profiles showed decreased GLUT4 in the cranial sartorius (CS), vastus lateralis (VL), and long digital extensor (LDE) of GRMD vs. normal dogs. QPCR confirmed GLUT4 downregulation but increased hexokinase-1. GLUT4 protein levels were not different in the CS, VL, or left ventricle but increased in the LDE of GRMD vs. normal. Microscopy revealed diffuse membrane expression of GLUT4 in GRMD skeletal but not cardiac muscle. GTT showed higher basal glucose and insulin in GRMD but rapid tissue glucose uptake at 5 min post-dextrose injection in GRMD vs. normal/carrier dogs. PET/ CT with [¹⁸F]FDG and simultaneous insulin stimulation showed a significant increase (p = 0.03) in mean standard uptake values (SUV) in GRMD skeletal muscle but not pelvic fat at 5 min post-[¹⁸F]FDG /insulin injection. Conversely, mean cardiac SUV was lower in GRMD than carrier/normal (p < 0.01).

Altered glucose metabolism in skeletal and cardiac muscle of GRMD dogs can be monitored with molecular, biochemical, and in vivo imaging studies and potentially utilized as a biomarker for disease progression and therapeutic response.

The online version of this article (10.1007/s11307-018-1174-2) contains supplementary material, which is available to authorized users.

• Biomarkers
• DMD
• Dog
• Dystrophin
• GLUT4
• GRMD
• Glucose
• Insulin
• Metabolism
• PET/CT

• Animals
• Disease Models, Animal
• Dogs
• Dystrophin/genetics
• Gene Editing
• Genetic Therapy/veterinary
• Humans
• Male
• Mice
• Muscular Dystrophy, Duchenne/genetics
• Muscular Dystrophy, Duchenne/therapy

• DMD
• GRMD
• imaging biomarkers
• machine learning
• texture analysis

Duchenne muscular dystrophy (DMD) is one of the most common and severe forms of muscular dystrophy. Oxidative myofibre content, muscle vasculature architecture and exercise tolerance are impaired in DMD. Several studies have demonstrated that nutrient supplements ameliorate dystrophic features, thereby enhancing muscle performance. Here, we report that dietary supplementation with a specific branched-chain amino acid-enriched mixture (BCAAem) increased the abundance of oxidative muscle fibres associated with increased muscle endurance in dystrophic mdx mice. Amelioration of the fatigue index in BCAAem-treated mdx mice was caused by a cascade of events in the muscle tissue, which were promoted by endothelial nitric oxide synthase (eNOS) activation and vascular endothelial growth factor (VEGF) expression. VEGF induction led to recruitment of bone marrow (BM)-derived endothelial progenitors (EPs), which increased the capillary density of dystrophic skeletal muscle. Functionally, BCAAem mitigated the dystrophic phenotype of mdx mice without inducing dystrophin protein expression or replacing the dystrophin-associated glycoprotein (DAG) complex in the membrane, which is typically lost in DMD. BCAAem supplementation could be an effective adjuvant strategy in DMD treatment.

Among diseases affecting skeletal muscle, muscular dystrophy is one of the most devastating and complex disorders. The term ‘muscular dystrophy’ refers to a heterogeneous group of genetic diseases associated with a primary muscle defect that leads to progressive muscle wasting and consequent loss of muscle function. Muscular dystrophies are accompanied by numerous clinical complications and abnormalities in other tissues that cause extreme discomfort in everyday life. The fact that muscular dystrophy often takes its toll on babies and small children, and that many patients die at a young age, adds to the cruel character of the disease. Clinicians all over the world are facing the same problem: they have no therapy to offer except for symptom-relieving interventions. Patients, their families, but also clinicians, are in urgent need of an effective cure. Despite advances in genetics, increased understanding of molecular mechanisms underlying muscle disease, despite a sweeping range of successful preclinical strategies and relative progress of their implementation in the clinic, therapy for patients is currently out of reach. Only a greater comprehension of disease mechanisms, new preclinical studies, development of novel technologies, and tight collaboration between scientists and physicians can help improve clinical treatment. Fortunately, inventiveness in research is rapidly extending the limits and setting new standards for treatment design. This review provides a synopsis of muscular dystrophy and considers the steps of preclinical and clinical research that are taking the muscular dystrophy community towards the fundamental goal of combating the traumatic disease.

• animal models
• cell therapy
• clinical trials
• extracellular matrix
• gene therapy
• genome editing
• muscular dystrophy
• skeletal muscle

Duchenne muscular dystrophy (DMD) causes progressive disability in 1 of every 5,000 boys due to the lack of functional dystrophin protein. Despite much advancement in knowledge about DMD disease presentation and progression—attributable in part to studies using mouse and canine models of the disease–current DMD treatments are not equally effective in all patients. There remains, therefore, a need for translational animal models in which novel treatment targets can be identified and evaluated. Golden Retriever muscular dystrophy (GRMD) is a phenotypically and genetically homologous animal model of DMD. As with DMD, speed of disease progression in GRMD varies substantially. However, unlike DMD, all GRMD dogs possess the same causal mutation; therefore genetic modifiers of phenotypic variation are relatively easier to identify. Furthermore, the GRMD dogs used in this study reside within the same colony, reducing the confounding effects of environment on phenotypic variation. To detect modifiers of disease progression, we developed gene expression profiles using RNA sequencing for 9 dogs: 6 GRMD dogs (3 with faster-progressing and 3 with slower-progressing disease, based on quantitative, objective biomarkers) and 3 control dogs from the same colony. All dogs were evaluated at 2 time points: early disease onset (3 months of age) and the point at which GRMD stabilizes (6 months of age) using quantitative, objective biomarkers identified as robust against the effects of relatedness/inbreeding. Across all comparisons, the most differentially expressed genes fell into 3 categories: myogenesis/muscle regeneration, metabolism, and inflammation. Our findings are largely in concordance with DMD and mouse model studies, reinforcing the utility of GRMD as a translational model. Novel findings include the strong up-regulation of chitinase 3-like 1 (CHI3L1) in faster-progressing GRMD dogs, suggesting previously unexplored mechanisms underlie progression speed in GRMD and DMD. In summary, our findings support the utility of RNA sequencing for evaluating potential biomarkers of GRMD progression speed, and are valuable for identifying new avenues of exploration in DMD research.

• corticotrophin-releasing factor
• diaphragm
• interleukin-6
• mdx
• monoclonal
• urocortin 2

• Animals
• Autoantibodies/administration & dosage
• Corticotropin-Releasing Hormone/administration & dosage
• Diaphragm/drug effects
• Diaphragm/physiology
• Drug Therapy, Combination
• Male
• Mice
• Mice, Inbred C57BL
• Mice, Inbred mdx
• Muscle Contraction/drug effects
• Muscle Contraction/physiology
• Muscular Dystrophy, Animal/drug therapy
• Muscular Dystrophy, Animal/physiopathology
• Organ Culture Techniques
• Random Allocation
• Receptors, Interleukin-6/administration & dosage
• Treatment Outcome
• Urocortins/administration & dosage

• fatty acid oxidation
• histone acetylation
• mitochondrial biogenesis
• muscular dystrophy

The mouse is one of the most widely used animal models to study neuromuscular diseases and test new therapeutic strategies. However, findings from successful pre-clinical studies using mouse models frequently fail to translate to humans due to various factors. Differences in muscle function between the two species could be crucial but often have been overlooked. The purpose of this study was to evaluate and compare muscle excursions in walking between mice and humans.

Recently published musculoskeletal models of the mouse hindlimb and human lower limb were used to simulate muscle-tendon dynamics during mouse and human walking, a key daily activity. Muscle fiber length changes (fiber excursions) of 25 muscle homologs in the two species were calculated from these simulations and then compared. To understand potential causes of differences in fiber excursions in walking, joint excursions and muscle moment arms were also compared across one gait cycle.

Most muscles (19 out of 25 muscles) of the mouse hindlimb had much smaller fiber excursions as compared to human lower limb muscles during walking. For these muscles, fiber excursions in mice were only 48 ± 19% of those in humans. The differences in fiber excursion between the two species were primarily due to the reduced joint excursions and smaller muscle moment arms in mice as compared to humans.

Since progressive neuromuscular diseases, such as Duchenne muscular dystrophy, are known to be accelerated by damage accumulated from active muscle lengthening, these results suggest that biomechanical differences in muscle function during walking between mice and humans may impede the translations of knowledge gained from mouse models to humans. This knowledge would add a fresh perspective on how pre-clinical studies on mice might be better designed to improve translation to human clinical trials.

The online version of this article (10.1186/s13395-017-0143-9) contains supplementary material, which is available to authorized users.

• Biomechanics
• Duchenne muscular dystrophy
• Mice
• Muscle fiber excursion
• Musculoskeletal simulation
• Neuromuscular diseases
• Walking gait

• AMPK
• Duchenne
• dystrophin
• golden retriever muscular dystrophy
• metabolism
• muscle
• phenotype

• Animal models
• Duchenne muscular dystrophy (DMD)
• Golden retriever muscular dystrophy (GRMD)
• Preclinical studies

• Animals
• Disease Models, Animal
• Dogs/genetics
• Dystrophin/genetics
• Dystrophin/metabolism
• Muscular Dystrophy, Duchenne/drug therapy
• Muscular Dystrophy, Duchenne/etiology
• Muscular Dystrophy, Duchenne/genetics
• Muscular Dystrophy, Duchenne/pathology

• Antioxidant
• Duchenne Muscular Dystrophy (DMD)
• Ileum
• Intestine
• Myenteric plexus
• Smooth muscle

Duchenne muscular dystrophy (DMD) is caused by mutations in the DMD gene, which codes for the dystrophin protein. While progress has been made in defining the molecular basis and pathogenesis of DMD, major gaps remain in understanding mechanisms that contribute to the marked delay in cardiac compared to skeletal muscle dysfunction.

To address this question, we analyzed cardiac and skeletal muscle tissue microarrays from golden retriever muscular dystrophy (GRMD) dogs, a genetically and clinically homologous model for DMD. A total of 15 dogs, 3 each GRMD and controls at 6 and 12 months plus 3 older (47–93 months) GRMD dogs, were assessed.

GRMD dogs exhibited tissue- and age-specific transcriptional profiles and enriched functions in skeletal but not cardiac muscle, consistent with a “metabolic crisis” seen with DMD microarray studies. Most notably, dozens of energy production-associated molecules, including all of the TCA cycle enzymes and multiple electron transport components, were down regulated. Glycolytic and glycolysis shunt pathway-associated enzymes, such as those of the anabolic pentose phosphate pathway, were also altered, in keeping with gene expression in other forms of muscle atrophy. On the other hand, GRMD cardiac muscle genes were enriched in nucleotide metabolism and pathways that are critical for neuromuscular junction maintenance, synaptic function and conduction.

These findings suggest differential metabolic dysfunction may contribute to distinct pathological phenotypes in skeletal and cardiac muscle.

The online version of this article (doi:10.1186/s12920-017-0257-2) contains supplementary material, which is available to authorized users.

• BDNF
• Cardiac
• Duchenne
• Dystrophin
• Metabolism
• Muscular dystrophy

A large number of human diseases are caused by chronic tissue injury with fibrosis potentially leading to organ failure. There is a need for more effective anti-fibrotic therapies. Congenital muscular dystrophy type 1A (MDC1A) is a devastating form of muscular dystrophy caused by laminin α2 chain-deficiency. It is characterized with early inflammation and build-up of fibrotic lesions, both in patients and MDC1A mouse models (e.g. dy^3K/dy^3K). Despite the enormous impact of inflammation on tissue remodelling in disease, the inflammatory response in MDC1A has been poorly described. Consequently, a comprehensive understanding of secondary mechanisms (impaired regeneration, enhanced fibrosis) leading to deterioration of muscle phenotype in MDC1A is missing. We have monitored inflammatory processes in dy^3K/dy^3K muscle and created mice deficient in laminin α2 chain and osteopontin or galectin-3, two pro-inflammatory and pro-fibrotic molecules drastically increased in dystrophic muscle. Surprisingly, deletion of osteopontin worsened the phenotype of dy^3K/dy^3K mice and loss of galectin-3 did not reduce muscle pathology. Our results indicate that osteopontin could even be a beneficial immunomodulator in MDC1A. This knowledge is essential for the design of future therapeutic interventions for muscular dystrophies that aim at targeting inflammation, especially that osteopontin inhibition has been suggested for Duchenne muscular dystrophy therapy.

• cryosectioning
• dystrophy
• histopathology
• mdx
• muscle
• necropsy

• Animals
• Cryoultramicrotomy
• Disease Models, Animal
• Histological Techniques/methods
• Humans
• Mice
• Mice, Inbred mdx
• Muscle, Skeletal/pathology
• Muscular Dystrophy, Animal/pathology
• Muscular Dystrophy, Duchenne/pathology
• Pathology

• MR/K015168/1 Medical Research Council

• Cell differentiation
• Hindlimb suspension
• Nucleoproteins
• Rat
• rpS6

• Duchenne muscular dystrophy
• NF-κB
• TGF-β
• calcium
• corticosteroids
• fibrosis
• myostatin
• oxidative stress
• phosphodiesterase inhibitors
• therapeutics

• Biomarker
• Creatine kinase
• Duchenne muscular dystrophy
• Golden retriever muscular dystrophy
• Six-minute walk test

What is the central question of this study?

What is the functional relevance of OPN isoform expression in muscle pathology?

Although osteopontin (OPN) is an important mediator of muscle remodelling in health and disease, functional differences in human spliced OPN variants in the muscle microenvironment have not been characterized. We thus sought to define the pro‐inflammatory activities of human OPN isoforms (OPN‐a, OPN‐b and OPN‐c) on cells present in regenerating muscle. OPN transcripts were quantified in normal and dystrophic human and dog muscle. Human macrophages and myoblasts were stimulated with recombinant human OPN protein isoforms, and cytokine mRNA and protein induction was assayed. OPN isoforms were greatly increased in dystrophic human (OPN‐a > OPN‐b > OPN‐c) and dog muscle (OPN‐a = OPN‐c). In healthy human muscle, mechanical loading also upregulated OPN‐a expression (eightfold; P < 0.01), but did not significantly upregulate OPN‐c expression (twofold; P > 0.05). In vitro, OPN‐a displayed the most pronounced pro‐inflammatory activity among isoforms, acting on both macrophages and myoblasts. In vitro and in vivo data revealed that OPN‐a upregulated tenascin‐C (TNC), a known Toll‐like receptor 4 (TLR4) agonist. Inhibition of TLR4 signalling attenuated OPN‐mediated macrophage cytokine production. In summary, OPN‐a is the most abundant and functionally active human spliced isoform in the skeletal muscle microenvironment. Here, OPN‐a promotes pro‐inflammatory signalling in both macrophages and myoblasts, possibly through induction of TNC–TLR4 signalling. Together, our findings suggest that specific targeting of OPN‐a and/or TNC signalling in the damaged muscle microenvironment may be of therapeutic relevance.

• Duchenne muscular dystrophy
• OPN-a
• TNC
• muscle inflammation
• osteopontin
• skeletal muscle

• animal model(s)
• lésion musculaire
• modèle animal
• muscle damage
• muscle physiology
• muscle squelettique
• physiologie musculaire
• physiotherapy
• physiothérapie
• skeletal muscle

• Duchenne muscular dystrophy
• Gait analysis
• Kinetics
• Outcome measure
• corticosteroids

• Duchenne muscular dystrophy
• clinical trial networks
• drug delivery
• dystrophin
• exon skipping
• outcome measures

• K01 AR066077 NIAMS NIH HHS

• Duchenne muscular dystrophy (DMD)
• canine X-linked muscular dystrophy (CXMD)
• exon skipping
• golden reliever muscular dystrophy (GRMD)
• hypertrophic feline muscular dystrophy (HFMD)
• porcine (pig) model