CISD3/MiNT is required for complex I function, mitochondrial integrity, and skeletal muscle maintenance.

Mitochondria play a central role in muscle metabolism and function. A unique family of iron-sulfur proteins, termed CDGSH Iron Sulfur Domain-containing (CISD/NEET) proteins, support mitochondrial function in skeletal muscles. The abundance of these proteins declines during aging leading to muscle degeneration. Although the function of the outer mitochondrial CISD/NEET proteins, CISD1/mitoNEET and CISD2/NAF-1, has been defined in skeletal muscle cells, the role of the inner mitochondrial CISD protein, CISD3/MiNT, is currently unknown. Here, we show that CISD3 deficiency in mice results in muscle atrophy that shares proteomic features with Duchenne muscular dystrophy. We further reveal that CISD3 deficiency impairs the function and structure of skeletal muscles, as well as their mitochondria, and that CISD3 interacts with, and donates its [2Fe-2S] clusters to, complex I respiratory chain subunit NADH Ubiquinone Oxidoreductase Core Subunit V2 (NDUFV2). Using coevolutionary and structural computational tools, we model a CISD3-NDUFV2 complex with proximal coevolving residue interactions conducive of [2Fe-2S] cluster transfer reactions, placing the clusters of the two proteins 10 to 16 Å apart. Taken together, our findings reveal that CISD3/MiNT is important for supporting the biogenesis and function of complex I, essential for muscle maintenance and function. Interventions that target CISD3 could therefore impact different muscle degeneration syndromes, aging, and related conditions.

Chimeric Cell Therapies as a Novel Approach for Duchenne Muscular Dystrophy (DMD) and Muscle Regeneration.

Chimerism-based strategies represent a pioneering concept which has led to groundbreaking advancements in regenerative medicine and transplantation. This new approach offers therapeutic potential for the treatment of various diseases, including inherited disorders. The ongoing studies on chimeric cells prompted the development of Dystrophin-Expressing Chimeric (DEC) cells which were introduced as a potential therapy for Duchenne Muscular Dystrophy (DMD). DMD is a genetic condition that leads to premature death in adolescent boys and remains incurable with current methods. DEC therapy, created via the fusion of human myoblasts derived from normal and DMD-affected donors, has proven to be safe and efficacious when tested in experimental models of DMD after systemic-intraosseous administration. These studies confirmed increased dystrophin expression, which correlated with functional and morphological improvements in DMD-affected muscles, including cardiac, respiratory, and skeletal muscles. Furthermore, the application of DEC therapy in a clinical study confirmed its long-term safety and efficacy in DMD patients. This review summarizes the development of chimeric cell technology tested in preclinical models and clinical studies, highlighting the potential of DEC therapy in muscle regeneration and repair, and introduces chimeric cell-based therapies as a promising, novel approach for muscle regeneration and the treatment of DMD and other neuromuscular disorders.

CRISPR-Based Gene Therapies: From Preclinical to Clinical Treatments.

In recent years, clustered regularly interspaced short palindromic repeats (CRISPRs) and CRISPR-associated (Cas) protein have emerged as a revolutionary gene editing tool to treat inherited disorders affecting different organ systems, such as blood and muscles. Both hematological and neuromuscular genetic disorders benefit from genome editing approaches but face different challenges in their clinical translation. The ability of CRISPR/Cas9 technologies to modify hematopoietic stem cells ex vivo has greatly accelerated the development of genetic therapies for blood disorders. In the last decade, many clinical trials were initiated and are now delivering encouraging results. The recent FDA approval of Casgevy, the first CRISPR/Cas9-based drug for severe sickle cell disease and transfusion-dependent ß-thalassemia, represents a significant milestone in the field and highlights the great potential of this technology. Similar preclinical efforts are currently expanding CRISPR therapies to other hematologic disorders such as primary immunodeficiencies. In the neuromuscular field, the versatility of CRISPR/Cas9 has been instrumental for the generation of new cellular and animal models of Duchenne muscular dystrophy (DMD), offering innovative platforms to speed up preclinical development of therapeutic solutions. Several corrective interventions have been proposed to genetically restore dystrophin production using the CRISPR toolbox and have demonstrated promising results in different DMD animal models. Although these advances represent a significant step forward to the clinical translation of CRISPR/Cas9 therapies to DMD, there are still many hurdles to overcome, such as in vivo delivery methods associated with high viral vector doses, together with safety and immunological concerns. Collectively, the results obtained in the hematological and neuromuscular fields emphasize the transformative impact of CRISPR/Cas9 for patients affected by these debilitating conditions. As each field suffers from different and specific challenges, the clinical translation of CRISPR therapies may progress differentially depending on the genetic disorder. Ongoing investigations and clinical trials will address risks and limitations of these therapies, including long-term efficacy, potential genotoxicity, and adverse immune reactions. This review provides insights into the diverse applications of CRISPR-based technologies in both preclinical and clinical settings for monogenic blood disorders and muscular dystrophy and compare advances in both fields while highlighting current trends, difficulties, and challenges to overcome.

Persistent inflammation and nutritional status in Duchenne muscular dystrophy.

BACKGROUND & AIMS: Duchenne muscular dystrophy (DMD) involves muscle fragility, sarcolemma instability, and chronic inflammation. This study aims to identify the inflammatory profile of DMD patients and evaluate associations between clinical and nutritional variables. METHODS: We performed a cross-sectional study nested in a cohort to obtain sociodemographics, illness time, use of medications, and supplement data through interviews and the patient's medical records. Then, we assessed the relationships between illness time, cytokine levels, and nutritional status. RESULTS: Forty-four male participants, aged 4.3-24.2 years, were evaluated. Concerning nutritional status, 18 participants were eutrophic. The fat mass increased and the lean mass decreased from the beginning of the first signs of DMD. Cytokines levels in DMD patients, even under corticosteroids therapy, are higher than values described in the literature on healthy subjects. The regression models demonstrated that illness time and BMI/A z-scores are associated with higher values of interleukin-6. CONCLUSIONS: A persistent inflammatory profile was observed in the patients evaluated. The data suggest that maintaining adequate nutritional status and body composition is important for determining the inflammation presented by individuals with DMD.

Barriers to diverse clinical trial participation in Duchenne muscular dystrophy: Engaging Hispanic/Latina caregivers and health professionals.

BACKGROUND: Despite the increasing availability of clinical trials in Duchenne muscular dystrophy, racial/ethnic minorities and other populations facing health disparities remain underrepresented in clinical trials evaluating products for Duchenne. We sought to understand the barriers faced by Hispanic/Latino families specifically and underrepresented groups more generally to clinical trial participation in Duchenne. METHODS: We engaged two participant groups: Hispanic/Latino caregivers of children with Duchenne in the US, including Puerto Rico, and health professionals within the broader US Duchenne community. Caregiver interviews explored attitudes towards and experiences with clinical trials, while professional interviews explored barriers to clinical trial participation among socio-demographically underrepresented families (e.g., low income, rural, racial/ethnic minority, etc.). Interviews were analyzed aggregately and using a thematic analysis approach. An advisory group was engaged throughout the course of the study to inform design, conduct, and interpretation of findings generated from interviews. RESULTS: Thirty interviews were conducted, including with 12 Hispanic/Latina caregivers and 18 professionals. We identified barriers to clinical trial participation at various stages of the enrollment process. In the initial identification of patients, barriers included lack of awareness about trials and clinical trial locations at clinics that were less likely to serve diverse patients. In the prescreening process, barriers included ineligibility, anticipated non-compliance in clinical trial protocols, and language discrimination. In screening, barriers included concerns about characteristics of the trial, as well as mistrust/lack of trust. In consent and recruitment, barriers included lack of timely decision support, logistical factors (distance, time, money), and lack of translated study materials. CONCLUSIONS: Numerous barriers hinder participation in Duchenne clinical trials for Hispanic/Latino families and other populations experiencing health disparities. Addressing these barriers necessitates interventions across multiple stages of the clinical trial enrollment process. Recommendations to enhance participation opportunities include developing clinical trial decision support tools, translating prominent clinical trials educational resources such as ClinicalTrials.gov, fostering trusting family-provider relationships, engaging families in clinical trial design, and establishing ethical guidelines for pre-screening potentially non-compliant patients.

SETDB1 modulates the TGFß response in Duchenne muscular dystrophy myotubes.

Overactivation of the transforming growth factor-ß (TGFß) signaling in Duchenne muscular dystrophy (DMD) is a major hallmark of disease progression, leading to fibrosis and muscle dysfunction. Here, we investigated the role of SETDB1 (SET domain, bifurcated 1), a histone lysine methyltransferase involved in muscle differentiation. Our data show that, following TGFß induction, SETDB1 accumulates in the nuclei of healthy myotubes while being already present in the nuclei of DMD myotubes where TGFß signaling is constitutively activated. Transcriptomics revealed that depletion of SETDB1 in DMD myotubes leads to down-regulation of TGFß target genes coding for secreted factors involved in extracellular matrix remodeling and inflammation. Consequently, SETDB1 silencing in DMD myotubes abrogates the deleterious effect of their secretome on myoblast differentiation by impairing myoblast pro-fibrotic response. Our findings indicate that SETDB1 potentiates the TGFß-driven fibrotic response in DMD muscles, providing an additional axis for therapeutic intervention.

Dmd mdx mice have defective oligodendrogenesis, delayed myelin compaction and persistent hypomyelination.

Duchenne muscular dystrophy (DMD) is caused by mutations in the DMD gene, resulting in the loss of dystrophin, a large cytosolic protein that links the cytoskeleton to extracellular matrix receptors in skeletal muscle. Aside from progressive muscle damage, many patients with DMD also have neurological deficits of unknown etiology. To investigate potential mechanisms for DMD neurological deficits, we assessed postnatal oligodendrogenesis and myelination in the Dmdmdx mouse model. In the ventricular-subventricular zone (V-SVZ) stem cell niche, we found that oligodendrocyte progenitor cell (OPC) production was deficient, with reduced OPC densities and proliferation, despite a normal stem cell niche organization. In the Dmdmdx corpus callosum, a large white matter tract adjacent to the V-SVZ, we also observed reduced OPC proliferation and fewer oligodendrocytes. Transmission electron microscopy further revealed significantly thinner myelin, an increased number of abnormal myelin structures and delayed myelin compaction, with hypomyelination persisting into adulthood. Our findings reveal alterations in oligodendrocyte development and myelination that support the hypothesis that changes in diffusion tensor imaging seen in patients with DMD reflect developmental changes in myelin architecture.

Validity of remote live stream video evaluation of the North Star Ambulatory Assessment in patients with Duchenne muscular dystrophy.

Conducting functional assessments remotely can help alleviate the burden of in-person assessment on patients with Duchenne muscular dystrophy and their caregivers. The objective of this study was to evaluate whether scores from remote functional assessment of patients with Duchenne muscular dystrophy correspond to in-person scores on the same functional assessments. Remote live stream versus in-person scores on the North Star Ambulatory Assessment (including time [seconds] to complete the 10-meter walk/run and time to rise from the floor [supine to stand]) were assessed using statistical analyses, including intraclass correlation coefficient, and Pearson, Spearman, and Bland-Altman analyses. The remote and in-clinic assessments had to occur within 2 weeks of one another to be considered for this analysis. This analysis included patients with Duchenne muscular dystrophy, aged 4 to 7 years. Participants in this analysis received delandistrogene moxeparvovec (as part of SRP-9001-101 [Study 101; NCT03375164] or SRP-9001-102 [Study 102; NCT03769116]) or were randomized to receive placebo (in Part 1 of Study 102). This study evaluates score reproducibility between live stream remote scoring versus in-person functional assessments as determined by intraclass correlation coefficient, and Pearson, Spearman, and Bland-Altman analyses. The results showed that scores from remote functional assessment of patients with Duchenne muscular dystrophy strongly correlated with those obtained in person. These findings demonstrate congruence between live stream remote and in-person functional assessment and suggest that remote assessment has the potential to reduce the burden on a family by supplementing in-clinic visits.

Gait classification for growing children with Duchenne muscular dystrophy.

Classifying gait patterns into homogeneous groups could enhance communication among healthcare providers, clinical decision making and clinical trial designs in boys with Duchenne muscular dystrophy (DMD). Sutherland's classification has been developed 40 years ago. Ever since, the state-of-the-art medical care has improved and boys with DMD are now longer ambulatory. Therefore, the gait classification requires an update. The overall aim was to develop an up-to-date, valid DMD gait classification. A total of 137 three-dimensional gait analysis sessions were collected in 30 boys with DMD, aged 4.6-17 years. Three classes were distinguished, which only partly aligned with increasing severity of gait deviations. Apart from the mildly affected pattern, two more severely affected gait patterns were found, namely the tiptoeing pattern and the flexion pattern with distinct anterior pelvic tilt and posterior trunk leaning, which showed most severe deviations at the ankle or at the proximal segments/joints, respectively. The agreement between Sutherland's and the current classification was low, suggesting that gait pathology with the current state-of-the-art medical care has changed. However, overlap between classes, especially between the two more affected classes, highlights the complexity of the continuous gait changes. Therefore, caution is required when classifying individual boys with DMD into classes.

Circadian Clock in Muscle Disease Etiology and Therapeutic Potential for Duchenne Muscular Dystrophy.

Circadian clock and clock-controlled output pathways exert temporal control in diverse aspects of skeletal muscle physiology, including the maintenance of muscle mass, structure, function, and metabolism. They have emerged as significant players in understanding muscle disease etiology and potential therapeutic avenues, particularly in Duchenne muscular dystrophy (DMD). This review examines the intricate interplay between circadian rhythms and muscle physiology, highlighting how disruptions of circadian regulation may contribute to muscle pathophysiology and the specific mechanisms linking circadian clock dysregulation with DMD. Moreover, we discuss recent advancements in chronobiological research that have shed light on the circadian control of muscle function and its relevance to DMD. Understanding clock output pathways involved in muscle mass and function offers novel insights into the pathogenesis of DMD and unveils promising avenues for therapeutic interventions. We further explore potential chronotherapeutic strategies targeting the circadian clock to ameliorate muscle degeneration which may inform drug development efforts for muscular dystrophy.

Severe cardiac and skeletal manifestations in DMD-edited microminipigs: an advanced surrogate for Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is an intractable X-linked muscular dystrophy caused by mutations in the DMD gene. While many animal models have been used to study the disease, translating findings to humans has been challenging. Microminipigs, with their pronounced physiological similarity to humans and notably compact size amongst pig models, could offer a more representative model for human diseases. Here, we accomplished precise DMD modification in microminipigs by co-injecting embryos with Cas9 protein and a single-guide RNA targeting exon 23 of DMD. The DMD-edited microminipigs exhibited pronounced clinical phenotypes, including perturbed locomotion and body-wide skeletal muscle weakness and atrophy, alongside augmented serum creatine kinase levels. Muscle weakness was observed as of one month of age, respiratory and cardiac dysfunctions emerged by the sixth month, and the maximum lifespan was 29.9 months. Histopathological evaluations confirmed dystrophin deficiency and pronounced dystrophic pathology in the skeletal and myocardial tissues, demonstrating that these animals are an unprecedented model for studying human DMD. The model stands as a distinct and crucial tool in biomedical research, offering deep understanding of disease progression and enhancing therapeutic assessments, with potential to influence forthcoming treatment approaches.

Factors Associated With Early Motor Function Trajectories in DMD After Glucocorticoid Initiation: Post Hoc Analysis of the FOR-DMD Trial.

BACKGROUND AND OBJECTIVES: Clinical trials in Duchenne muscular dystrophy (DMD) require 3-6 months of stable glucocorticoids, and the primary outcome is explored at 48-52 weeks. The factors that influence the clinical outcome assessment (COA) trajectories soon after glucocorticoid initiation are relevant for the design and analysis of clinical trials of novel drugs. We describe early COA trajectories, associated factors, and the time from glucocorticoid initiation to COA peak. METHODS: This was a prospective 18-month analysis of the Finding the Optimum Corticosteroid Regimen for Duchenne Muscular Dystrophy study. Four COAs were investigated: rise from supine velocity (RFV), 10-meter walk/run velocity (10MWRV), North Star Ambulatory Assessment (NSAA) total score, and 6-minute walk test distance (6MWT). The relationships of baseline age (4-5 vs 6-7 years), COA baseline performance, genotype, and glucocorticoid regimen (daily vs intermittent) with the COA trajectories were evaluated using linear mixed-effects models. RESULTS: One hundred ninety-six glucocorticoid-naïve boys with DMD aged 4-7 years were enrolled. The mean age at baseline was 5.9 ± 1.0 years, 66% (n = 130) were on daily regimens, 55% (n = 107) showed a 6MWT distance >330 metres; 41% (n = 78) showed RFV >0.2 rise/s; 76% (n = 149) showed 10MWRV >0.142 10m/s, and 41.0% (n = 79) showed NSAA total score >22 points. Mean COA trajectories differed by age at glucocorticoid initiation (p < 0.01 for RFV, 10MWRV, and NSAA; p < 0.05 for 6MWT) and regimen (p < 0.01 for RFV, 10MWRV, and NSAA). Boys younger than 6 years reached their peak performance 12-18 months after glucocorticoid initiation. Boys aged 6 years or older on a daily regimen peaked between months 9 and 12 and those on an intermittent regimen by 9 months. The baseline COA performance was associated with the NSAA (p < 0.01) and the 6MWT trajectory in boys younger than 6 years on a daily regimen (p < 0.01). Differences in the mean trajectories by genotype were not significant. DISCUSSION: Glucocorticoid regimen, age, duration of glucocorticoid exposure, and baseline COA performance need to be considered in the design and analysis of clinical trials in young boys with DMD.

The FDA and Gene Therapy for Duchenne Muscular Dystrophy.

This Viewpoint examines the appropriateness of FDA accelerated approval of novel gene therapies to treat boys with Duchenne muscular dystrophy following clinical trials with surrogate outcomes that did not demonstrate net benefits.

Observing the Clinical Course of Duchenne Muscular Dystrophy in Medicaid Real-World Healthcare Data.

INTRODUCTION: Duchenne muscular dystrophy (DMD) is a rare, severe progressive neuromuscular disease. Health insurance claims allow characterization of population-level real-world outcomes, based on observed healthcare resource use. An analysis of data specific to those with Medicaid insurance is presently unavailable. The objective was to describe the real-world clinical course of DMD based on claims data from Medicaid-insured individuals in the USA. METHODS: Individuals with DMD were identified from the MarketScan Multi-State Medicaid datasets (2013-2018). Diagnosis and procedure codes from healthcare claims were used to characterize the occurrence of DMD-relevant clinical observations; categories were scoliosis, cardiovascular-related, respiratory and severe respiratory-related, and neurologic/neuropsychiatric. Age-restricted analyses were conducted to focus on the ages at which DMD-relevant clinical observations were more likely to be captured, and to better understand the impact of both age and follow-up time. RESULTS: Of 2007 patients with DMD identified, median (interquartile range) age at index was 14 (9-20) years, and median follow-up was 3.1 (1.6-4.7) years. Neurologic and neuropsychiatric observations were most frequently identified, among 49.3% of the cohort; followed by cardiovascular (48.5%), respiratory (38.1%), scoliosis (36.3%), and severe respiratory (25.0%). Prevalence estimates for each category were higher when analyzed within age-restricted subgroups; and increased as follow-up time increased. CONCLUSIONS: This study is the first to use diagnosis and procedure codes from real-world Medicaid claims to document the clinical course in DMD. Findings were consistent with previously published estimates from commercially insured populations and clinical registries; and contribute to the expanding body of real-world evidence around clinical progression of patients with DMD.

"You Take This Day by Day, Come What May": A Qualitative Study of the Psychosocial Impacts of Living with Duchenne Muscular Dystrophy.

INTRODUCTION: Studies have reported health-related quality-of-life impacts of Duchenne muscular dystrophy (DMD); however, further research is needed to understand how those with DMD experience their condition and how psychosocial impacts evolve over time in response to disease progression. This qualitative study explores the social and emotional implications of key transitions, challenges and adaptations throughout the disease course from the perspective of patients and family caregivers. METHODS: Semi-structured interviews were conducted with men and boys with DMD, and/or their caregivers, in the USA. Thematic analysis was used to examine patterns in data collected across the interviews. RESULTS: Nineteen participants were included. Three major themes were identified: (1) barriers to participation are multifaceted; (2) an emotional journey shaped by 'inevitable progression;' (3) family provides critical tangible and emotional support. This study illustrates that psychosocial impacts of DMD are shaped by knowledge of the condition's natural history alongside other factors including the extent of social barriers, personal growth and adaptation, and family support. CONCLUSIONS: Findings provide insight into the strength and resilience with which individuals and their families respond to daily challenges and major clinical milestones and highlight the relative importance of loss of upper limb function as a transition in DMD affecting health-related quality-of-life.

Short developmental milestone risk assessment tool to identify Duchenne muscular dystrophy in primary care.

BACKGROUND: In patients without a family history, Duchenne muscular dystrophy (DMD) is typically diagnosed at around 4-5 years of age. It is important to diagnose DMD during infancy or toddler stage in order to have timely access to treatment, opportunities for reproductive options, prevention of potential fatal reactions to inhaled anesthetics, awareness of a child's abilities needed for good parenting, and opportunities for enrolment in clinical trials. METHOD: We aimed to develop a short risk assessment tool based on developmental milestones that may contribute to the early detection of boys with DMD in primary care. As part of the case-control 4D-DMD study (Detection by Developmental Delay in Dutch boys with DMD), data on developmental milestones, symptoms and therapies for 76 boys with DMD and 12,414 boys from a control group were extracted from the health records of youth health care services and questionnaires. Multiple imputation, diagnostic validity and pooled backward logistic regression analyses with DMD (yes/no) as the dependent variable and attainment of 26 milestones until 36 months of age (yes/no) as the independent variable were performed. Descriptive statistics on symptoms and therapies were provided. RESULTS: A tool with seven milestones assessed at specific ages between 12 and 36 months resulted in a sensitivity of 79% (95CI:67-88%), a specificity of 95.8% (95%CI:95.3-96.2), and a positive predictive value of 1:268 boys. Boys with DMD often had symptoms (e.g. 43% had calf muscle pseudohypertrophy) and were referred to therapy (e.g. 59% for physical therapy) before diagnosis. DISCUSSION: This tool followed by the examination of other DMD-related symptoms could be used by youth health care professionals during day-to-day health assessments in the general population to flag children who require further action. CONCLUSIONS: The majority of boys (79%) with DMD can be identified between 12 and 36 months of age with this tool. It increases the initial a priori risk of DMD from 1 in 5,000 to approximately 1 in 268 boys. We expect that other neuromuscular disorders and disabilities can also be found with this tool.

Identification of hub genes and therapeutic siRNAs to develop novel adjunctive therapy for Duchenne muscular dystrophy.

OBJECTIVE: Duchenne muscular dystrophy (DMD) is a devastating X-linked neuromuscular disorder caused by various defects in the dystrophin gene and still no universal therapy. This study aims to identify the hub genes unrelated to excessive immune response but responsible for DMD progression and explore therapeutic siRNAs, thereby providing a novel treatment. METHODS: Top ten hub genes for DMD were identified from GSE38417 dataset by using GEO2R and PPI networks based on Cytoscape analysis. The hub genes unrelated to excessive immune response were identified by GeneCards, and their expression was further verified in mdx and C57 mice at 2 and 4 months (M) by (RT-q) PCR and western blotting. Therapeutic siRNAs were deemed as those that could normalize the expression of the validated hub genes in transfected C2C12 cells. RESULTS: 855 up-regulated and 324 down-regulated DEGs were screened from GSE38417 dataset. Five of the top 10 hub genes were considered as the candidate genes unrelated to excessive immune response, and three of these candidates were consistently and significantly up-regulated in mdx mice at 2 M and 4 M when compared with age-matched C57 mice, including Col1a2, Fbn1 and Fn1. Furthermore, the three validated up-regulated candidate genes can be significantly down-regulated by three rational designed siRNA (p < 0.0001), respectively. CONCLUSION: COL1A2, FBN1 and FN1 may be novel biomarkers for DMD, and the siRNAs designed in our study were help to develop adjunctive therapy for Duchenne muscular dystrophy.

The glucocorticoid receptor acts locally to protect dystrophic muscle and heart during disease.

Absence of dystrophin results in muscular weakness, chronic inflammation and cardiomyopathy in Duchenne muscular dystrophy (DMD). Pharmacological corticosteroids are the DMD standard of care; however, they have harsh side effects and unclear molecular benefits. It is uncertain whether signaling by physiological corticosteroids and their receptors plays a modifying role in the natural etiology of DMD. Here, we knocked out the glucocorticoid receptor (GR, encoded by Nr3c1) specifically in myofibers and cardiomyocytes within wild-type and mdx52 mice to dissect its role in muscular dystrophy. Double-knockout mice showed significantly worse phenotypes than mdx52 littermate controls in measures of grip strength, hang time, inflammatory pathology and gene expression. In the heart, GR deletion acted additively with dystrophin loss to exacerbate cardiomyopathy, resulting in enlarged hearts, pathological gene expression and systolic dysfunction, consistent with imbalanced mineralocorticoid signaling. The results show that physiological GR functions provide a protective role during muscular dystrophy, directly contrasting its degenerative role in other disease states. These data provide new insights into corticosteroids in disease pathophysiology and establish a new model to investigate cell-autonomous roles of nuclear receptors and mechanisms of pharmacological corticosteroids.

Improved mitochondrial function in the hearts of sarcolipin-deficient dystrophin and utrophin double-knockout mice.

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disease associated with cardiomyopathy. DMD cardiomyopathy is characterized by abnormal intracellular Ca2+ homeostasis and mitochondrial dysfunction. We used dystrophin and utrophin double-knockout (mdx:utrn-/-) mice in a sarcolipin (SLN) heterozygous-knockout (sln+/-) background to examine the effect of SLN reduction on mitochondrial function in the dystrophic myocardium. Germline reduction of SLN expression in mdx:utrn-/- mice improved cardiac sarco/endoplasmic reticulum (SR) Ca2+ cycling, reduced cardiac fibrosis, and improved cardiac function. At the cellular level, reducing SLN expression prevented mitochondrial Ca2+ overload, reduced mitochondrial membrane potential loss, and improved mitochondrial function. Transmission electron microscopy of myocardial tissues and proteomic analysis of mitochondria-associated membranes showed that reducing SLN expression improved mitochondrial structure and SR-mitochondria interactions in dystrophic cardiomyocytes. These findings indicate that SLN upregulation plays a substantial role in the pathogenesis of cardiomyopathy and that reducing SLN expression has clinical implications in the treatment of DMD cardiomyopathy.