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Fibrosis is the main complication of muscular dystrophies. We identified moesin, a member of the ezrin-radixin-moesin family, in dystrophic muscles of mice representing Duchenne and congenital muscular dystrophies (DMD and CMD, respectively) and dysferlinopathy, but not in the wild type. High levels of moesin were also observed in muscle biopsy specimens from DMD, Ullrich CMD, and merosin-deficient CMD patients, all of which present high levels of fibrosis. The myofibroblasts, responsible for extracellular matrix protein synthesis, and the macrophages infiltrating the dystrophic muscles were the source of moesin. Moesin-positive cells were embedded within the fibrotic areas between the myofibers adjacent to the collagen type I fibers. Radixin was also synthesized by the myofibroblasts, whereas ezrin colocalized with the myofiber membranes. In animal models and patients' muscles, part of the moesin was in its active phosphorylated form. Inhibition of fibrosis by halofuginone, an antifibrotic agent, resulted in a major decrease in moesin levels in the muscles of DMD and CMD mice. In summary, the results of this study may pave the way for exploiting moesin as a novel target for intervention in MDs, and as part of a battery of biomarkers to evaluate treatment success in preclinical studies and clinical trials.
The fascinating world of noncoding RNAs has recently come to light, thanks to the development of powerful sequencing technologies, revealing a variety of RNA molecules playing important regulatory functions in most, if not all, cellular processes. Many noncoding RNAs have been implicated in regulatory networks that are determinant for skeletal muscle differentiation and disease. In this review, we outline the noncoding RNAs involved in physiological mechanisms of myogenesis and those that appear dysregulated in muscle dystrophies, also discussing their potential use as disease biomarkers and therapeutic targets.
Major efforts have been made in the last decade to develop and improve therapies for proximal spinal muscular atrophy (SMA). The introduction of Nusinersen/Spinraza™ as an antisense oligonucleotide therapy, Onasemnogene abeparvovec/Zolgensma™ as an AAV9-based gene therapy and Risdiplam/Evrysdi™ as a small molecule modifier of pre-mRNA splicing have set new standards for interference with neurodegeneration.
Muscular dystrophies are groups of inherited progressive diseases of the muscle caused by mutations of diverse genes related to normal muscle function. Although there is no current effective treatment for these devastating diseases, various molecular strategies have been developed to restore the expressions of the associated defective proteins. In preclinical animal models, both viral and nonviral vectors have been shown to deliver recombinant versions of defective genes. Antisense oligonucleotides have been shown to modify the splicing mechanism of mesenger ribonucleic acid to produce an internally deleted but partially functional dystrophin in an experimental model of Duchenne muscular dystrophy. In addition, chemicals can induce readthrough of the premature stop codon in nonsense mutations of the dystrophin gene. On the basis of these preclinical data, several experimental clinical trials are underway that aim to demonstrate efficacy in treating these devastating diseases.
The purpose of this study was to systematically review, assess, and prioritize factors (including biological, socioeconomic, environmental, psychosocial, comorbid, and genetic) for the onset and natural progression of Muscular Dystrophy. Comprehensive review of current literature of these factors was carried out in order to provide a basis for policy makers to identify appropriate measures to mitigate the burden of disease in Canada. A three-stage approach to searching for relevant studies was conducted in multiple databases. Using variations of MeSH terms and keywords, Systematic reviews or meta-analyses published in English or French that meet the inclusion criteria were first identified, then searched for relevant observational studies. Two independent reviewers screened abstracts, then qualifying articles, conducted quality assessment, and finally extracted relevant data using the application, DistillerSR. No existing systematic reviews, meta-analyses, or non-genetic observational studies were identified that met the inclusion criteria. A number of existing systematic reviews and observational studies focused on pharmacological or therapeutic interventions, which was beyond the scope of this study. Four genetic observational studies were identified that focused on aspects of disease progression of Duchenne and Becker Muscular Dystrophy. While this systematic review found that certain genetic polymorphisms and mutations may be a factor for Duchenne or Becker Muscular Dystrophy disease progression, further investigation into other genetic factors and environmental factors is still warranted. Much of the current literature focuses on these Muscular Dystrophies, however, other types of Muscular Dystrophy and their associated risk factors have yet to be extensively studied.
Despite the expression of the mutated gene in all muscles, selective muscles are involved in genetic muscular dystrophies. Different muscular dystrophies show characteristic patterns of fatty degenerative changes by muscle imaging, even to the extent that the patterns have been used for diagnostic purposes. However, the underlying molecular mechanisms explaining the selective involvement of muscles are not known. To test the hypothesis that different muscles may express variable amounts of different isoforms of muscle genes, we applied a custom-designed exon microarray containing probes for 57 muscle-specific genes to assay the transcriptional profiles in sets of human adult lower limb skeletal muscles. Quantitative real-time PCR and whole transcriptome sequencing were used to further analyze the results. Our results demonstrate significant variations in isoform and gene expression levels in anatomically different muscles. Comparison of the known patterns of selective involvement of certain muscles in two autosomal dominant titinopathies and one autosomal dominant myosinopathy, with the isoform and gene expression results, shows a correlation between the specific muscles involved and significant differences in the level of expression of the affected gene and exons in these same muscles compared with some other selected muscles. Our results suggest that differential expression levels of muscle genes and isoforms are one determinant in the selectivity of muscle involvement in muscular dystrophies.
Autosomal recessive limb-girdle muscular dystrophies (LGMD2) include a number of disorders with heterogeneous etiology that cause predominantly weakness and wasting of the shoulder and pelvic girdle muscles. In this study, we determined the frequency of LGMD subtypes within a cohort of Czech LGMD2 patients using mutational analysis of the CAPN3, FKRP, SGCA, and ANO5 genes.
The recent availability and development of mutant and transgenic zebrafish strains that model human muscular dystrophies has created new research opportunities for therapeutic development. Not only do these models mimic many pathological aspects of human dystrophies, but their small size, large clutch sizes, rapid ex utero development, body transparency, and genetic tractability enable research approaches that would be inconceivable with mammalian model systems. Here we discuss the use of zebrafish models of muscular dystrophy to rapidly screen hundreds to thousands of bioactive compounds in order to identify novel therapeutic candidates that modulate pathologic phenotypes. We review the justification and rationale behind this unbiased approach, including how zebrafish screens have identified FDA-approved drugs that are candidates for treating Duchenne and limb girdle muscular dystrophies. Not only can these drugs be re-purposed for treating dystrophies in a fraction of the time and cost of new drug development, but their identification has revealed novel, unexpected directions for future therapy development. Phenotype-driven zebrafish drug screens are an important compliment to the more established mammalian, target-based approaches for rapidly developing and validating therapeutics for muscular dystrophies.
Muscular dystrophies are a group of genetic disorders that specifically affect skeletal muscle and are characterized by progressive muscle degeneration and weakening. To develop therapies and treatments for these diseases, a better understanding of the molecular basis of muscular dystrophies is required. Thus, identification of causative genes mutated in specific disorders and the study of relevant animal models are imperative. Zebrafish genetic models of human muscle disorders often closely resemble disease pathogenesis, and the optical clarity of zebrafish embryos and larvae enables visualization of dynamic molecular processes in vivo. As an adjunct tool, morpholino studies provide insight into the molecular function of genes and allow rapid assessment of candidate genes for human muscular dystrophies. This unique set of attributes makes the zebrafish model system particularly valuable for the study of muscle diseases. This review discusses how recent research using zebrafish has shed light on the pathological basis of muscular dystrophies, with particular focus on the muscle cell membrane and the linkage between the myofibre cytoskeleton and the extracellular matrix.
Pediatric muscular dystrophies (MDs) are a heterogeneous group of rare neuromuscular diseases characterized by progressive muscle degeneration. A neuropsychosocial approach is crucial for these patients due to associated cognitive, behavioral, and psychiatric comorbidities; however, the social cognitive domain has not been adequately addressed.
The North Star Assessment for limb-girdle type muscular dystrophies (NSAD), a clinician-reported outcome measure (ClinRO) of motor performance, was initially developed and validated for use in dysferlinopathy, an autosomal recessive form of limb-girdle muscular dystrophy (LGMD R2/2B). Recent developments in treatments for limb-girdle muscular dystrophies (LGMD) have highlighted the urgent need for disease-specific ClinROs. The purpose of this study was to understand the ability of the NSAD to quantify motor function across the broad spectrum of LGMD phenotypes.
Analysis of muscle biopsies allowed to characterize the pathophysiological changes of Duchenne and Becker muscular dystrophies (D/BMD) leading to the clinical phenotype. Muscle tissue is often investigated during interventional dose finding studies to show in situ proof of concept and pharmacodynamics effect of the tested drug. Less invasive readouts are needed to objectively monitor patients' health status, muscle quality, and response to treatment. The identification of serum biomarkers correlating with clinical function and able to anticipate functional scales is particularly needed for personalized patient management and to support drug development programs.
Albeit genetically highly heterogeneous, muscular dystrophies (MDs) share a convergent pathology leading to muscle wasting accompanied by proliferation of fibrous and fatty tissue, suggesting a common MD-pathomechanism. Here we show that mutations in muscular dystrophy genes (Dmd, Dysf, Capn3, Large) lead to the spontaneous formation of skeletal muscle-derived malignant tumors in mice, presenting as mixed rhabdomyo-, fibro-, and liposarcomas. Primary MD-gene defects and strain background strongly influence sarcoma incidence, latency, localization, and gender prevalence. Combined loss of dystrophin and dysferlin, as well as dystrophin and calpain-3, leads to accelerated tumor formation. Irrespective of the primary gene defects, all MD sarcomas share non-random genomic alterations including frequent losses of tumor suppressors (Cdkn2a, Nf1), amplification of oncogenes (Met, Jun), recurrent duplications of whole chromosomes 8 and 15, and DNA damage. Remarkably, these sarcoma-specific genetic lesions are already regularly present in skeletal muscles in aged MD mice even prior to sarcoma development. Accordingly, we show also that skeletal muscle from human muscular dystrophy patients is affected by gross genomic instability, represented by DNA double-strand breaks and age-related accumulation of aneusomies. These novel aspects of molecular pathologies common to muscular dystrophies and tumor biology will potentially influence the strategies to combat these diseases.
Muscular dystrophies and congenital myopathies arise from specific genetic mutations causing skeletal muscle weakness that reduces quality of life. Muscle health relies on resident muscle stem cells called satellite cells, which enable life-course muscle growth, maintenance, repair and regeneration. Such tuned plasticity gradually diminishes in muscle diseases, suggesting compromised satellite cell function. A central issue however, is whether the pathogenic mutation perturbs satellite cell function directly and/or indirectly via an increasingly hostile microenvironment as disease progresses. Here, we explore the effects on satellite cell function of pathogenic mutations in genes (myopathogenes) that associate with muscle disorders, to evaluate clinical and muscle pathological hallmarks that define dysfunctional satellite cells. We deploy transcriptomic analysis and comparison between muscular dystrophies and myopathies to determine the contribution of satellite cell dysfunction using literature, expression dynamics of myopathogenes and their response to the satellite cell regulator PAX7. Our multimodal approach extends current pathological classifications to define Satellite Cell-opathies: muscle disorders in which satellite cell dysfunction contributes to pathology. Primary Satellite Cell-opathies are conditions where mutations in a myopathogene directly affect satellite cell function, such as in Progressive Congenital Myopathy with Scoliosis (MYOSCO) and Carey-Fineman-Ziter Syndrome (CFZS). Primary satellite cell-opathies are generally characterised as being congenital with general hypotonia, and specific involvement of respiratory, trunk and facial muscles, although serum CK levels are usually within the normal range. Secondary Satellite Cell-opathies have mutations in myopathogenes that affect both satellite cells and muscle fibres. Such classification aids diagnosis and predicting probable disease course, as well as informing on treatment and therapeutic development.
Megaconial congenital muscular dystrophy (OMIM 602541) is characterized with early-onset hypotonia, muscle wasting, proximal weakness, cardiomyopathy, mildly elevated serum creatine kinase (CK) levels, and mild-to-moderate intellectual disability. We report two siblings in a consanguineous family admitted for psychomotor delay. Physical examination revealed proximal muscle weakness, contractures in the knee of elder sibling, diffuse mild generalized muscle atrophy, and dry skin with ichthyosis together with multiple nummular eczema in both siblings. Serum CK values were elevated up to 500 U/L. For genetic work-up, we performed whole exome sequencing (WES) after Nimblegen enrichment on the Illumina platform. The WES revealed a novel homozygous missense mutation in the Choline Kinase-Beta (CHKB) gene c.1031G>A (p.R344Q) in exon 9. Ichthyosis-like skin changes with intense pruritus and nummular eczema may lead to clinical diagnosis in cases with megaconial congenital muscular dystrophy.
Fibrosis is the main complication of muscular dystrophies. We identified collagen triple helix repeat containing 1 (Cthrc1) in skeletal and cardiac muscles of mice, representing Duchenne and congenital muscle dystrophies (DMD and CMD, respectively), and dysferlinopathy. In all of the mice, Cthrc1 was associated with high collagen type I levels; no Cthrc1 or collagen was observed in muscles of control mice. High levels of Cthrc1 were also observed in biopsy specimens from patients with DMD, in whom they were reversibly correlated with that of β-dystroglycan, whereas collagen type I levels were elevated in all patients with DMD. At the muscle sites where collagen and Cthrc1 were adjacent, collagen fibers appeared smaller, suggesting involvement of Cthrc1 in collagen turnover. Halofuginone, an inhibitor of Smad3 phosphorylation downstream of the transforming growth factor-β signaling, reduced Cthrc1 levels in skeletal and cardiac muscles of mice, representing DMD, CMD, and dysferlinopathy. The myofibroblasts infiltrating the dystrophic muscles of the murine models of DMD, CMD, and dysferlinopathy were the source of Cthrc1. Transforming growth factor-β did not affect Cthrc1 levels in the mdx fibroblasts but decreased them in the control fibroblasts, in association with increased migration of mdx fibroblasts and dystrophic muscle invasion by myofibroblasts. To our knowledge, this is the first demonstration of Cthrc1 as a marker of the severity of the disease progression in the dystrophic muscles, and as a possible target for therapy.
Duchenne and Becker muscular dystrophies (DMD/BMD) result in progressive weakness of skeletal and cardiac muscles due to the deficiency of functional dystrophin. Respiratory failure is a leading cause of mortality in DMD patients; however, improved management of the respiratory symptoms have increased patients' life expectancy, thereby also increasing the clinical relevance of heart disease. In fact, the prevalence of cardiomyopathy, which significantly contributes to mortality in DMD patients, increases with age and disease progression, so that over 95% of adult patients has cardiomyopathy signs. We here review the current literature featuring the metabolic alterations observed in the dystrophic heart of the mdx mouse, i.e., the best-studied animal model of the disease, and discuss their pathophysiological role in the DMD heart. It is well assessed that dystrophin deficiency is associated with pathological alterations of lipid metabolism, intracellular calcium levels, neuronal nitric oxide (NO) synthase localization, and NO and reactive oxygen species production. These metabolic stressors contribute to impair the function of the cardiac mitochondrial bulk, which has a relevant pathophysiological role in the development of cardiomyopathy. In fact, mitochondrial dysfunction becomes more severe as the dystrophic process progresses, thereby indicating it may be both the cause and the consequence of the dystrophic process in the DMD heart.
Limb-girdle muscular dystrophies are characterized by predominant involvement of the shoulder and pelvic girdle and trunk muscle groups. Currently, there are 31 genes implicated in the different forms of limb-girdle muscular dystrophies, which exhibit similar phenotypes and clinical overlap; therefore, advanced molecular techniques are required to achieve differential diagnosis.
Cardiac involvement in patients with muscular dystrophy associated with Lamin A/C mutations (LMNA) is characterized by atrioventricular conduction abnormalities and life-threatening cardiac arrhythmias. Little is known about cardiac involvement in patients with emerin mutation (EMD). The aim of our study was to describe and compare the prevalence and time distribution of cardiac arrhythmias at extended follow-up.
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