Muscular dystrophy (MD) describes generalized progressive muscular weakness due to the wasting of muscle fibers. The progression of the disease is affected by known immunological and mechanical factors, and possibly other unknown mechanisms. These dynamics have begun to be elucidated in the last two decades. This article reviews mathematical models of MD and models that could be used to study molecular and cellular components implicated in MD progression. A biological background for these processes is also presented. Molecular effectors that contribute to MD include mitochondrial bioenergetics and genetic factors; both drive cellular metabolism, communication and signaling. These molecular events leave cells vulnerable to mechanical stress which can activate an immunological cascade that weakens cells and surrounding tissues. This review article lays the foundation for a systems biology approach to study MD progression.
Histone acetyl transferases (HATs) and histone deacetylases (HDAC) control transcription during myogenesis. HDACs promote chromatin condensation, inhibiting gene transcription in muscle progenitor cells until myoblast differentiation is triggered and HDACs are released. HATs, namely CBP/p300, activate myogenic regulatory and elongation factors promoting myogenesis. HDAC inhibitors are known to improve regeneration in dystrophic muscles through follistatin upregulation. However, the potential of directly modulating HATs remains unexplored. We tested this possibility in a well-known zebrafish model of Duchenne muscular dystrophy. Interestingly, CBP/p300 transcripts were found downregulated in the absence of Dystrophin. While investigating CBP rescuing potential we observed that dystrophin-null embryos overexpressing CBP actually never show significant muscle damage, even before a first regeneration cycle could occur. We found that the pan-HDAC inhibitor trichostatin A (TSA) also prevents early muscle damage, however the single HAT CBP is as efficient even in low doses. The HAT domain of CBP is required for its full rescuing ability. Importantly, both CBP and TSA prevent early muscle damage without restoring endogenous CBP/p300 neither increasing follistatin transcripts. This suggests a new mechanism of action of epigenetic regulators protecting dystrophin-null muscle fibres from detaching, independent from the known improvement of regeneration upon damage of HDACs inhibitors. This study builds supporting evidence that epigenetic modulators may play a role in determining the severity of muscle dystrophy, controlling the ability to resist muscle damage. Determining the mode of action leading to muscle protection can potentially lead to new treatment options for muscular dystrophies in the future.
INTRODUCTION: Both genetic and infectious diseases can result in skeletal muscle degeneration, inflammation, pain, and/or weakness. Duchenne muscular dystrophy (DMD) is the most common congenital muscle disease. DMD causes progressive muscle wasting due to mutations in Dystrophin. Influenza A and B viruses are frequently associated with muscle complications, especially in children. Infections activate an immune response and immunosuppressant drugs reduce DMD symptoms. These data suggest that the immune system may contribute to muscle pathology. However, roles of the immune response in DMD and Influenza muscle complications are not well understood. Zebrafish with dmd mutations are a well-characterized model in which to study the molecular and cellular mechanisms of DMD pathology. We recently showed that zebrafish can be infected by human Influenza A virus (IAV). Thus, the zebrafish is a powerful system with which to ask questions about the etiology and mechanisms of muscle damage due to genetic and/or infectious diseases.
METHODS: We infected zebrafish with IAV and assayed muscle tissue structure, sarcolemma integrity, cell-extracellular matrix (ECM) attachment, and molecular and cellular markers of inflammation in response to IAV infection alone or in the context of DMD.
RESULTS: We find that IAV-infected zebrafish display mild muscle degeneration with sarcolemma damage and compromised ECM adhesion. An innate immune response is elicited in muscle in IAV-infected zebrafish: NFkB signaling is activated, pro-inflammatory cytokine expression is upregulated, and neutrophils localize to sites of muscle damage. IAV-infected dmd mutants display more severe muscle damage than would be expected from an additive effect of dmd mutation and IAV infection, suggesting that muscle damage caused by Dystrophin-deficiency and IAV infection is synergistic.
DISCUSSION: These data demonstrate the importance of preventing IAV infections in individuals with genetic muscle diseases. Elucidating the mechanisms of immune-mediated muscle damage will not only apply to DMD and IAV, but also to other conditions where the immune system, inflammation, and muscle tissue are known to be affected, such as autoimmune diseases, cancer, and aging.
Introduction: Duchenne Muscular Dystrophy (DMD) is a debilitating muscle wasting disorder with no cure. Safer supplements and therapies are needed to improve the severity of symptoms, as severe side effects are associated with the only effective treatment, corticosteroids. The amino acid taurine has shown promise in ameliorating dystrophic symptoms in mdx mice, an animal model of DMD, however little work is in 21-28 (d)ay animals, the period of natural peak damage.
Methods: This study compares the effect of prenatal taurine supplementation on tibialis anterior (TA) in situ contractile function, histopathological characteristics and the abundance of Ca2+-handling as well as pathologically relevant proteins in non-exercised mdx mice at 28 and 70 d.
Results: Supplementation elevated TA taurine content by 25% (p<0.05), ameliorated in situ specific force by 60% (p<0.05) and improved histological characteristics in 28 d mdx mice; however no benefit was seen in 70 d mice, where background pathology was initially stable. Age specific effects in SERCA1, calsequestrin 1 (CSQ1), CSQ2, utrophin and myogenin protein abundances were seen between both 28 and 70 d mdx and mdx taurine-supplemented mice.
Discussion: Considering these findings and that taurine is a relatively cost effective, readily accessible and side effect free dietary supplement, we propose further investigation into taurine supplementation during pregnancy in a protective capacity, reminiscent of folate in the prevention of spinal bifida.
To facilitate gene and cell therapy experiments, we created severely immune-deficient mouse models of Duchenne muscular dystrophy (DMD), limb girdle muscular dystrophy 2B (LGMD2B), and limb girdle muscular dystrophy 2D (LGMD2D) by crossing mdx4Cv, Bl/AJ, and Sgca-null mice with NRG immune-deficient mice. The resulting mdx4Cv/NRG, BlAJ/NRG, and Sgca/NRG mice demonstrated the presence of the appropriate mutant alleles at Dmd, Dysf, Sgca, Rag1, and Il2rγ by genotyping PCR. Absence of dystrophin, dysferlin, or α-sarcoglycan protein was confirmed by western blot and immunohistochemistry. We performed centronucleation, Evans blue dye, hydroxyproline, and treadmill assays on the disease model mice versus NRG controls to evaluate muscle histology and function. These studies demonstrated that the mdx4Cv/NRG and Sgca/NRG mice showed significant deficits in muscle structure and function in all the assays and were similar to each other. By contrast, the phenotype of the BlAJ/NRG mice was milder in each case. The results we observed parallel the phenotypes seen in patients with the corresponding disorders. These novel immune-deficient mouse models of DMD, LGMD2B, and LGMD2D will be useful for long-term gene and cell therapy studies involving transfer of foreign genes and cells.
Duchenne muscular dystrophy (DMD or Duchenne) is a progressive, life-limiting muscle-wasting disease that requires comprehensive, multidisciplinary care. This care, at minimum, should include neuromuscular, respiratory, cardiac, orthopedic, endocrine and rehabilitative interventions that address both the primary and secondary manifestations of the disease. The care needs of patients evolve over the cdourse of the disease and as they transition from childhood into young adulthood. In the past two decades, life expectancy has increased significantly by the use of corticosteroids and enhanced clinical management. Nevertheless, each year, patients with Duchenne muscular dystrophy are admitted to emergency departments and intensive care units where medical expertise thrives, but where expertise in rare diseases, such as Duchenne, may not. Emergency care for patients with Duchenne can be as complex as the disease process itself. While any illness or injury may occur in a person with Duchenne, some acute scenarios are much more common in the context of the disease. Making decisions about the clinical care of a person with Duchenne who presents with an acute illness can be quite difficult — in part, because of the extensive use of corticosteroids, which can lead to adrenal suppression. The life of a person with Duchenne needing emergency care may therefore depend upon the ability of the clinician on duty in the emergency department to recognize and mitigate adrenal suppression resulting from corticosteroid dependence. With this in mind, and drawing from expertise and experience with other steroid-dependent diseases, the ‘PJ Nicholoff Steroid Protocol’ was developed. The purpose of this protocol is to provide clinicians information regarding the safe management of corticosteroid during emergency situations in patients who may have accompanying adrenal suppression. The protocol explains how to recognize the signs and symptoms of acute adrenal crisis, how to prevent it with supplemental stress doses of corticosteroids, and how to taper doses after emergency care in order to prevent corticosteroid withdrawal.
Introduction: The Duchenne Regulatory Science Consortium (D-RSC) was established to develop tools to accelerate drug development for DMD. The resulting tools are anticipated to meet validity requirements outlined by qualification/endorsement pathways at both the U.S. Food and Drug Administration (FDA) and European Medicines Administration (EMA), and will be made available to the drug development community. The initial goals of the consortium include the development of a disease progression model, with the goal of creating a model that would be used to forecast changes in clinically meaningful endpoints, which would inform clinical trial protocol development and data analysis.
Methods: In April of 2016 the consortium and other experts met to formulate plans for the development of the model.
Conclusions: Here we report the results of the meeting, and discussion as to the form of the model that we plan to move forward to develop, after input from the regulatory authorities.
The new ‘Recommendation of the Committee of Ministers to member States on research on biological materials of human origin’, adopted in Europe in May 2016 is confusing and lacks specificity on the research use of biomaterials taken from persons not able to consent. It is possible to interpret the relevant clauses in a restrictive manner and doing so would hamper biobank research, by requiring researchers or biobank curators to examine individual records in detail, to check they are adhering to the Recommendation. This would be particularly problematic for muscular dystrophy and other rare disease research, the progress of which relies increasingly on the sharing of biomaterials and data internationally, as it will add complexity to the logistics of biomaterials and data sharing and introduce barriers for researchers preparing biomaterials for sharing. Such barriers are contradictory to EC policies on promoting and funding rare disease research and removing barriers to better care and treatment. Such policies work in concert with international progress in rare disease research, in particular the NIH’s Rare Diseases Clinical Research Network and Genetic and Rare Diseases Information Centre. The rare disease community has in recent years worked to create a common framework of harmonised approaches to enable the responsible, voluntary, and secure sharing of biomaterials and data. These efforts are supported by the European Commission in such moves as FP7 funding to advance rare disease research and the introduction of National Plans for rare disease; and are bolstered by similar efforts in the USA via the Clinical and Translational Science Awards Program and the NIH/NCATS Patient Registry developments. Introducing Recommendations from the Committee of Ministers, containing clauses which are incompatible to the efforts to advance rare disease research, seems counter-productive.
Background: In the absence of a curative treatment for Duchenne Muscular Dystrophy (DMD), corticosteroid therapy (prednisone, deflazacort) has been adopted as the standard of care, as it slows the progression of muscle weakness and enables longer retention of functional mobility. The ongoing development of novel pharmacological agents that target the genetic defect underlying DMD offer hope for a significant alteration in disease progression; however, substantiation of therapeutic efficacy has proved challenging. Identifying functional outcomes sensitive to the early, subtle changes in muscle function has confounded clinical trials. Additionally, the alterations in disease progression secondary to corticosteroid therapy are not well described making it difficult to ascertain the benefits of novel agents, often taken concurrently with corticosteroids.
Objective: The purpose of this study was to examine outcome responsiveness to corticosteroid therapy and age at the onset of a natural history study of ambulatory boys with DMD.
Methods: Eighty-five ambulatory boys with DMD (mean age 93 mo, range 49 to 180 mo) were recruited into this study. Fifty participants were on corticosteroid therapy, while 33 were corticosteroid naïve at the baseline assessment. Within each treatment group boys were divided in two age groups, 4 to 7 years and 8 and greater years of age. The Biodex System 3 Pro isokinetic dynamometer was used to assess muscle strength. Motor skills were assessed using the upper two dimensions (standing/walking, running & jumping) of the Gross Motor Function Measure (GMFM 88) and Timed Motor Tests (TMTs) (10-meter run, sit to stand, supine to stand, climb 4-stairs). Two way analysis of variance and Pearson correlations were used for analysis.
Results: A main effect for age was seen in select lower extremity muscle groups (hip flexors, knee extensors and ankle dorsiflexors), standing dimension skills, and all TMTs with significantly greater weakness and loss of motor skill ability seen in the older age group regardless of treatment group. Interaction effects were seen for the walking, running, and jumping dimension of the GMFM with the naïve boys scoring higher in the younger group and boys on corticosteroid therapy scoring higher in the older group. The TMT of climb 4-stairs demonstrated a significant treatment effect with the boys on corticosteroid therapy climbing stairs faster than those who were naïve, regardless of age. Examination of individual items within the upper level GMFM dimensions revealed select motor skills are more informative of disease progression than others; indicating their potential to be sensitive indicators of alterations in disease progression and intervention efficacy. Analysis of the relationship between muscle group strength and motor skill performance revealed differences in use patterns in the corticosteroid versus naïve boys.
Conclusion: Significant muscle weakness is apparent in young boys with DMD regardless of corticosteroid treatment; however, older boys on corticosteroid therapy tend to have greater retention of muscle strength and motor skill ability than those who are naive. Quantification of muscle strength via isokinetic dynamometry is feasible and sensitive to the variable rates of disease progression in lower extremity muscle groups, but possibly most informative are the subtle changes in the performance characteristics of select motor skills. Further analysis of longitudinal data from this study will explore the influence of corticosteroid therapy on muscle strength and further clarify its impact on motor performance.
The aim of this study was to determine whether prednisone and deflazacort play a different role in child behavior and perceived health related psychosocial quality of life in ambulant boys with Duchenne Muscular Dystrophy. As part of a prospective natural-history study, parents of sixty-seven ambulant boys with DMD (27 taking prednisone, 15 taking deflazacort, 25 were steroid naïve) completed the Child Behavior Checklist (CBCL) for assessment of behavioral, emotional and social problems and both parents and boys with DMD completed the PedsQL™4.0 generic core scale short form. Boys with DMD had higher rates of general behavioral problems than age-matched peers. No significant differences were found among the groups for any of the CBCL syndrome scales raw scores, including internalizing and externalizing behaviors; however, on average boys taking deflazacort demonstrated more withdrawn behaviors than those taking prednisone, while on average the boys taking prednisone demonstrated more aggressive behaviors than boys taking deflazacort. Age, internalizing and externalizing behaviors accounted for 39 and 48% of the variance in psychosocial quality of life for both parents and boys with DMD, respectively. Overall, the use of steroids was not associated with more behavioral problems in boys with DMD. As behavior played a significant role in psychosocial quality of life, comprehensive assessment and treatment of behavioral problems is crucial in this population.