Therapeutic Strategies for Duchenne Muscular Dystrophy: An Update

Neuromuscular disorders encompass a heterogeneous group of conditions that impair the function of muscles, motor neurons, peripheral nerves, and neuromuscular junctions. Being the most common and most severe type of muscular dystrophy, Duchenne muscular dystrophy (DMD), is caused by mutations in the X-linked dystrophin gene. Loss of dystrophin protein leads to recurrent myofiber damage, chronic inflammation, progressive fibrosis, and dysfunction of muscle stem cells. Over the last few years, there has been considerable development of diagnosis and therapeutics for DMD, but current treatments do not cure the disease. Here, we review the current status of DMD pathogenesis and therapy, focusing on mutational spectrum, diagnosis tools, clinical trials, and therapeutic approaches including dystrophin restoration, gene therapy, and myogenic cell transplantation. Furthermore, we present the clinical potential of advanced strategies combining gene editing, cell-based therapy with tissue engineering for the treatment of muscular dystrophy.

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Autophagy in the heart is enhanced and independent of disease progression in mus musculus dystrophinopathy models

JRSM Cardiovascular Disease ◽

10.1177/2048004019879581 ◽

2019 ◽

Vol 8 ◽

pp. 204800401987958

Author(s):

HR Spaulding ◽

C Ballmann ◽

JC Quindry ◽

MB Hudson ◽

JT Selsby

Keyword(s):

Skeletal Muscle ◽

Duchenne Muscular Dystrophy ◽

Muscular Dystrophy ◽

Disease Progression ◽

Gene Mutations ◽

Dystrophin Gene ◽

Mdx Mice ◽

Dystrophin Deficiency ◽

Muscle Wasting Disease ◽

Dystrophin Protein

Background Duchenne muscular dystrophy is a muscle wasting disease caused by dystrophin gene mutations resulting in dysfunctional dystrophin protein. Autophagy, a proteolytic process, is impaired in dystrophic skeletal muscle though little is known about the effect of dystrophin deficiency on autophagy in cardiac muscle. We hypothesized that with disease progression autophagy would become increasingly dysfunctional based upon indirect autophagic markers. Methods Markers of autophagy were measured by western blot in 7-week-old and 17-month-old control (C57) and dystrophic (mdx) hearts. Results Counter to our hypothesis, markers of autophagy were similar between groups. Given these surprising results, two independent experiments were conducted using 14-month-old mdx mice or 10-month-old mdx/Utrn± mice, a more severe model of Duchenne muscular dystrophy. Data from these animals suggest increased autophagosome degradation. Conclusion Together these data suggest that autophagy is not impaired in the dystrophic myocardium as it is in dystrophic skeletal muscle and that disease progression and related injury is independent of autophagic dysfunction.

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The Interplay of Mitophagy and Inflammation in Duchenne Muscular Dystrophy

Life ◽

10.3390/life11070648 ◽

2021 ◽

Vol 11 (7) ◽

pp. 648

Author(s):

Andrea L. Reid ◽

Matthew S. Alexander

Keyword(s):

Duchenne Muscular Dystrophy ◽

Muscular Dystrophy ◽

Mitochondrial Dysfunction ◽

Disease Onset ◽

Exon Skipping ◽

Dystrophin Gene ◽

Muscle Disease ◽

Mitochondrial Morphology ◽

Gene Therapies ◽

Dystrophin Protein

Duchenne muscular dystrophy (DMD) is an X-linked neuromuscular disease caused by a pathogenic disruption of the DYSTROPHIN gene that results in non-functional dystrophin protein. DMD patients experience loss of ambulation, cardiac arrhythmia, metabolic syndrome, and respiratory failure. At the molecular level, the lack of dystrophin in the muscle results in myofiber death, fibrotic infiltration, and mitochondrial dysfunction. There is no cure for DMD, although dystrophin-replacement gene therapies and exon-skipping approaches are being pursued in clinical trials. Mitochondrial dysfunction is one of the first cellular changes seen in DMD myofibers, occurring prior to muscle disease onset and progresses with disease severity. This is seen by reduced mitochondrial function, abnormal mitochondrial morphology and impaired mitophagy (degradation of damaged mitochondria). Dysfunctional mitochondria release high levels of reactive oxygen species (ROS), which can activate pro-inflammatory pathways such as IL-1β and IL-6. Impaired mitophagy in DMD results in increased inflammation and further aggravates disease pathology, evidenced by increased muscle damage and increased fibrosis. This review will focus on the critical interplay between mitophagy and inflammation in Duchenne muscular dystrophy as a pathological mechanism, as well as describe both candidate and established therapeutic targets that regulate these pathways.

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Duchenne Muscular Dystrophy - Family in a Crisis

Journal of Medicine ◽

10.3329/jom.v10i3.2015 ◽

1970 ◽

pp. 36-39

Author(s):

M Robed Amin ◽

Chowdhury Chironjib Borua ◽

Kaji Shafiqul Alam ◽

Fazle Rabbi Chowdhury ◽

Rabiul Jahan Sarkar ◽

...

Keyword(s):

Duchenne Muscular Dystrophy ◽

Muscular Dystrophy ◽

Case Series ◽

Dystrophin Gene ◽

Muscle Disease ◽

Motor Neuron Diseases ◽

Muscle Diseases ◽

Progressive Muscle Weakness ◽

Recessive Disorders ◽

Dystrophin Protein

Progressive muscular weakness with deformity leading to crippled states develop due to musculoskeletal and neurological disorders. Sometimes it is difficult to differentiate between primary muscle disease and neurological disease. But there is some classical presentation of muscle diseases which have its own entity and thus can be clinically differentiated from neurological disorder especially spinal cord and motor neuron diseases. Muscular dystrophy is one of those disorder with distinct clinical features. Muscular dystrophy refers to a group of genetic, hereditary muscle diseases that cause progressive muscle weakness. Most types of MD are multi-system disorders with manifestations in body systems including skeletal system, the heart, gastrointestinal and nervous systems, endocrine glands, skin, eyes and other organs. Duchenne muscular dystrophy (DMD), is inherited in an X-linked recessive pattern, meaning that the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes, and is thus considered sex-linked. Males are therefore affected by X-linked recessive disorders much more often than females. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons. Duchenne muscular dystrophy and Backers muscular dystrophy are caused by mutations of the gene for the dystrophin protein and lead to an overabundance of the enzyme creatine kinase. The dystrophin gene is the largest gene in humans. In this case series a family with three brothers suffering from Duchenne muscular dystrophy is described and review with literature was done. Â doi:10.3329/jom.v10i3.2015 J Medicine 2009; 10 (Supplement 1): 36-39

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The Duchenne muscular dystrophy gene and cancer

Cellular Oncology ◽

10.1007/s13402-020-00572-y ◽

2020 ◽

Author(s):

Leanne Jones ◽

Michael Naidoo ◽

Lee R. Machado ◽

Karen Anthony

Keyword(s):

Duchenne Muscular Dystrophy ◽

Muscular Dystrophy ◽

Muscle Protein ◽

Neuromuscular Disorders ◽

Becker Muscular Dystrophy ◽

Gene Products ◽

Large Gene ◽

Cancer Types ◽

And Function ◽

Dystrophin Protein

Abstract Background Mutation of the Duchenne muscular dystrophy (DMD) gene causes Duchenne and Becker muscular dystrophy, degenerative neuromuscular disorders that primarily affect voluntary muscles. However, increasing evidence implicates DMD in the development of all major cancer types. DMD is a large gene with 79 exons that codes for the essential muscle protein dystrophin. Alternative promotor usage drives the production of several additional dystrophin protein products with roles that extend beyond skeletal muscle. The importance and function(s) of these gene products outside of muscle are not well understood. Conclusions We highlight a clear role for DMD in the pathogenesis of several cancers, including sarcomas, leukaemia’s, lymphomas, nervous system tumours, melanomas and various carcinomas. We note that the normal balance of DMD gene products is often disrupted in cancer. The short dystrophin protein Dp71 is, for example, typically maintained in cancer whilst the full-length Dp427 gene product, a likely tumour suppressor, is frequently inactivated in cancer due to a recurrent loss of 5’ exons. Therefore, the ratio of short and long gene products may be important in tumorigenesis. In this review, we summarise the tumours in which DMD is implicated and provide a hypothesis for possible mechanisms of tumorigenesis, although the question of cause or effect may remain. We hope to stimulate further study into the potential role of DMD gene products in cancer and the development of novel therapeutics that target DMD.

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Reparative dysfunction during muscle regeneration in Duchenne muscular dystrophy: therapeutic approaches to modulating the muscle environment and muscle stem cells

10.32469/10355/76151 ◽

2019 ◽

Author(s):

◽

Michael Everette Nance

Keyword(s):

Skeletal Muscle ◽

Stem Cells ◽

Duchenne Muscular Dystrophy ◽

Muscular Dystrophy ◽

Muscle Regeneration ◽

Genetic Mutation ◽

Critical Determinant ◽

Muscle Stem Cells ◽

Dystrophin Protein

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Duchenne muscular dystrophy (DMD) is a lethal muscular dystrophy resulting from functional loss of the dystrophin protein, a critical sub-sarcolemmal protein involved in membrane stability. While reparative dysfunction is thought to be a critical determinant of disease progression in humans, regeneration is not significantly impaired in the murine muscular dystrophy (mdx) model. Furthermore, it is not well understood if reparative dysfunction is related to inherent defects in stem cells or chronic alterations in the muscle environment due to disease related remodeling. To address these observed discrepancies, we adapted a whole muscle transplant model to study the in vivo regeneration of intact pieces of skeletal muscle from normal and dystrophic dogs (cDMD), a physiological and clinically relevant model to humans. Regeneration in cDMD muscle grafts was significantly attenuated compared to normal and predisposed to the development of skeletal muscle tumors. We used an adeno-associated virus (AAV) expressing a micro-dystrophin protein to specifically rescue the muscle environment by preventing fiber damage while retaining dystrophin-null SCs. AAV.micro-dystrophin rescued the environment by improving fibrosis, stiffness, and fiber orientation, which significantly improved early muscle regeneration but not late regeneration (2 greater than and less than 4 months post-transplant) via enhancing muscle stem cells differentiation. We next developed Cre- and CRISPR-cas9 gene editing strategies to test the ability of AAV serotype 9 to transduce and treat the genetic mutation in muscle stem cells. We observed efficient SC transduction when used as a single vector expressing Cre. Dual-vector CRISPR-cas9 SC transduction was inefficient and likely related to the requirement for two vectors, promoter usage, and mechanistic differences between Cre-recombination and CRISPR genome editing.

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Single-cut genome editing restores dystrophin expression in a new mouse model of muscular dystrophy

Science Translational Medicine ◽

10.1126/scitranslmed.aan8081 ◽

2017 ◽

Vol 9 (418) ◽

pp. eaan8081 ◽

Cited By ~ 82

Author(s):

Leonela Amoasii ◽

Chengzu Long ◽

Hui Li ◽

Alex A. Mireault ◽

John M. Shelton ◽

...

Keyword(s):

Muscular Dystrophy ◽

Mouse Model ◽

Genome Editing ◽

Neuromuscular Disorders ◽

Dystrophin Gene ◽

Muscle Disease ◽

Systemic Delivery ◽

Specific Expression ◽

Reading Frame ◽

Dystrophin Protein

Duchenne muscular dystrophy (DMD) is a severe, progressive muscle disease caused by mutations in the dystrophin gene. The majority of DMD mutations are deletions that prematurely terminate the dystrophin protein. Deletions of exon 50 of the dystrophin gene are among the most common single exon deletions causing DMD. Such mutations can be corrected by skipping exon 51, thereby restoring the dystrophin reading frame. Using clustered regularly interspaced short palindromic repeats/CRISPR-associated 9 (CRISPR/Cas9), we generated a DMD mouse model by deleting exon 50. These ΔEx50 mice displayed severe muscle dysfunction, which was corrected by systemic delivery of adeno-associated virus encoding CRISPR/Cas9 genome editing components. We optimized the method for dystrophin reading frame correction using a single guide RNA that created reframing mutations and allowed skipping of exon 51. In conjunction with muscle-specific expression of Cas9, this approach restored up to 90% of dystrophin protein expression throughout skeletal muscles and the heart of ΔEx50 mice. This method of permanently bypassing DMD mutations using a single cut in genomic DNA represents a step toward clinical correction of DMD mutations and potentially those of other neuromuscular disorders.

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Innovative Therapeutic Approaches for Duchenne Muscular Dystrophy

Journal of Clinical Medicine ◽

10.3390/jcm10040820 ◽

2021 ◽

Vol 10 (4) ◽

pp. 820

Author(s):

Fernanda Fortunato ◽

Rachele Rossi ◽

Maria Sofia Falzarano ◽

Alessandra Ferlini

Keyword(s):

Duchenne Muscular Dystrophy ◽

Muscular Dystrophy ◽

Dystrophin Gene ◽

Orphan Drugs ◽

Therapeutic Approaches ◽

Anchoring Protein ◽

Cardiac Muscles ◽

Dystrophin Protein ◽

The Brain

Duchenne muscular dystrophy (DMD) is the most common childhood muscular dystrophy affecting ~1:5000 live male births. Following the identification of pathogenic variations in the dystrophin gene in 1986, the underlining genotype/phenotype correlations emerged and the role of the dystrophin protein was elucidated in skeletal, smooth, and cardiac muscles, as well as in the brain. When the dystrophin protein is absent or quantitatively or qualitatively modified, the muscle cannot sustain the stress of repeated contractions. Dystrophin acts as a bridging and anchoring protein between the sarcomere and the sarcolemma, and its absence or reduction leads to severe muscle damage that eventually cannot be repaired, with its ultimate substitution by connective tissue and fat. The advances of an understanding of the molecular pathways affected in DMD have led to the development of many therapeutic strategies that tackle different aspects of disease etiopathogenesis, which have recently led to the first successful approved orphan drugs for this condition. The therapeutic advances in this field have progressed exponentially, with second-generation drugs now entering in clinical trials as gene therapy, potentially providing a further effective approach to the condition.

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Inflammation in Duchenne Muscular Dystrophy–Exploring the Role of Neutrophils in Muscle Damage and Regeneration

Biomedicines ◽

10.3390/biomedicines9101366 ◽

2021 ◽

Vol 9 (10) ◽

pp. 1366

Author(s):

Ankita Tulangekar ◽

Tamar E. Sztal

Keyword(s):

Duchenne Muscular Dystrophy ◽

Muscular Dystrophy ◽

Muscle Damage ◽

Tissue Injury ◽

Dystrophin Gene ◽

Neuromuscular Disorder ◽

Muscle Membrane ◽

Dystrophin Protein ◽

Pro Inflammatory Cytokines

Duchenne muscular dystrophy (DMD) is a severe and progressive, X-linked, neuromuscular disorder caused by mutations in the dystrophin gene. In DMD, the lack of functional dystrophin protein makes the muscle membrane fragile, leaving the muscle fibers prone to damage during contraction. Muscle degeneration in DMD patients is closely associated with a prolonged inflammatory response, and while this is important to stimulate regeneration, inflammation is also thought to exacerbate muscle damage. Neutrophils are one of the first immune cells to be recruited to the damaged muscle and are the first line of defense during tissue injury or infection. Neutrophils can promote inflammation by releasing pro-inflammatory cytokines and compounds, including myeloperoxidase (MPO) and neutrophil elastase (NE), that lead to oxidative stress and are thought to have a role in prolonging inflammation in DMD. In this review, we provide an overview of the roles of the innate immune response, with particular focus on mechanisms used by neutrophils to exacerbate muscle damage and impair regeneration in DMD.

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Muscle-specific CRISPR/Cas9 dystrophin gene editing ameliorates pathophysiology in a mouse model for Duchenne muscular dystrophy

Nature Communications ◽

10.1038/ncomms14454 ◽

2017 ◽

Vol 8 (1) ◽

Cited By ~ 170

Author(s):

Niclas E. Bengtsson ◽

John K. Hall ◽

Guy L. Odom ◽

Michael P. Phelps ◽

Colin R. Andrus ◽

...

Keyword(s):

Duchenne Muscular Dystrophy ◽

Muscular Dystrophy ◽

Gene Editing ◽

Neuromuscular Disorders ◽

Dystrophin Gene ◽

Gene Replacement ◽

Great Promise ◽

Specific Gene ◽

Gene Correction ◽

Guide Rna

Abstract Gene replacement therapies utilizing adeno-associated viral (AAV) vectors hold great promise for treating Duchenne muscular dystrophy (DMD). A related approach uses AAV vectors to edit specific regions of the DMD gene using CRISPR/Cas9. Here we develop multiple approaches for editing the mutation in dystrophic mdx 4cv mice using single and dual AAV vector delivery of a muscle-specific Cas9 cassette together with single-guide RNA cassettes and, in one approach, a dystrophin homology region to fully correct the mutation. Muscle-restricted Cas9 expression enables direct editing of the mutation, multi-exon deletion or complete gene correction via homologous recombination in myogenic cells. Treated muscles express dystrophin in up to 70% of the myogenic area and increased force generation following intramuscular delivery. Furthermore, systemic administration of the vectors results in widespread expression of dystrophin in both skeletal and cardiac muscles. Our results demonstrate that AAV-mediated muscle-specific gene editing has significant potential for therapy of neuromuscular disorders.

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