Duchenne muscular dystrophy

Molecular profiling of blood plasma-derived extracellular vesicles derived from Duchenne muscular dystrophy patients through integration of FTIR spectroscopy and machine learning reveals disease signatures

PURPOSE

To identify and monitor the FTIR spectral signatures of plasma extracellular vesicles (EVs) from Duchenne Muscular Dystrophy (DMD) patients at different stages with Healthy controls using machine learning models.

MATERIALS AND METHODS

Whole blood samples were collected from the DMD (n = 30) and Healthy controls (n = 12). EVs were extracted by the Total Exosome Isolation (TEI) Method and resuspended in 1XPBS. We characterize the morphology, size, particle count, and surface markers (CD9, Alix, and Flotillin) by HR-TEM, NTA, and Western Blot analysis. The mid-IR spectra were recorded from (4000-400 cm-1) by Bruker ALPHA II FTIR spectrometer model, which was equipped with an attenuated total reflection (ATR) module. Machine learning algorithms like Principal Component Analysis (PCA) and Random Forest (RF) for dimensionality reduction and classifying the two study groups based on the FTIR spectra. The model performance was evaluated by a confusion matrix and the sensitivity, specificity, and Receiver Operating Characteristic Curve (ROC) was calculated respectively.

RESULTS

Alterations in Amide I & II (1700-1470 cm-1) and lipid (3000-2800 cm-1) regions in FTIR spectra of DMD compared with healthy controls. The PCA-RF model classified correctly the two study groups in the range of 4000-400 cm-1 with a sensitivity of 20 %, specificity of 87.50 %, accuracy of 71.43 %, precision of 33.33 %, and 5-fold cross-validation accuracy of 82 %. We analyzed the ten different spectral regions which showed statistically significant at P < 0.01 except the Ester Acyl Chain region.

CONCLUSION

Our proof-of-concept study demonstrated distinct infrared (IR) spectral signatures in plasma EVs derived from DMD. Consistent alterations in protein and lipid configurations were identified using a PCA-RF model, even with a small clinical dataset. This minimally invasive liquid biopsy method, combined with automated analysis, warrants further investigation for its potential in early diagnosis and monitoring of disease progression in DMD patients within clinical settings.

Immunologic investigations into transgene directed immune-mediated myositis following delandistrogene moxeparvovec gene therapy

Delandistrogene moxeparvovec is an rAAVrh74 vector-based gene transfer therapy that delivers a transgene encoding delandistrogene moxeparvovec micro-dystrophin, an engineered, functional form of dystrophin shown to stabilize or slow disease progression in DMD. It is approved in the US and in other select countries. Two serious adverse event cases of immune-mediated myositis (IMM) were reported in the phase Ib ENDEAVOR trial (NCT04626674). We hypothesized that immune responses to the micro-dystrophin transgene product may have mediated these IMM events. An interferon-gamma ELISpot assay was used to detect T cell responses to delandistrogene moxeparvovec micro-dystrophin peptide pools. ELISpot analysis suggested that IMM resulted from T cell-mediated responses directed against specific micro-dystrophin peptides corresponding to exons 8 and 9 (Case 1) and exon 8 (Case 2) of the DMD gene. In silico epitope mapping based on the patients' HLA-I alleles indicated greater probability for peptides derived from exons 8 and/or 9 to bind HLA-I, providing further evidence that peptides derived from corresponding micro-dystrophin regions may have higher immunogenic potential. Collectively, these data suggest that patients with DMD gene deletions involving exons 8 and/or 9 may be at increased risk of IMM following delandistrogene moxeparvovec micro-dystrophin gene therapy infusion.

Histone deacetylase 6 inhibition promotes microtubule acetylation and facilitates autophagosome-lysosome fusion in dystrophin-deficient mdx mice

AIM

Duchenne muscular dystrophy is a progressive muscle-wasting disease caused by mutations in the dystrophin gene. Despite progress in dystrophin-targeted gene therapies, it is still a fatal disease requiring novel therapeutics that can be used synergistically or alternatively to emerging gene therapy. Defective autophagy and disorganized microtubule networks contribute to dystrophic pathogenesis, yet the mechanisms by which microtubule alterations regulate autophagy remain elusive. The present study was designed to uncover possible mechanisms underpinning the role of microtubules in regulating autophagy in dystrophic mice.

METHODS

Mdx mice were also supplemented with Tubastatin A, a pharmacological inhibitor of histone deacetylase 6, and pathophysiology was assessed. Mdx mice with a genetic deletion of the Nox-2 scaffolding subunit p47phox were used to assess redox dependence on tubulin acetylation.

RESULTS

Our data show decreased acetylation of α-tubulin with enhanced histone deacetylase 6 expression. Tubastatin A increases tubulin acetylation and Q-SNARE complex formation but does not alter microtubule organization or density, indicating improved autophagosome-lysosome fusion. Tubastatin A increases the acetylation of peroxiredoxin and protects it from hyper-oxidation, hence modulating intracellular redox status in mdx mice. Tubastatin A reduces muscle damage and enhances force production. Genetic down regulation of Nox2 activity in the mdx mice promotes autophagosome maturation but not autolysosome formation.

CONCLUSION

Our data highlight that autophagy is differentially regulated by redox and acetylation in mdx mice. By improving autophagy through promoting tubulin acetylation, Tubastatin A decreases the dystrophic phenotype and improves muscle function, suggesting a great potential for clinical translation and treating dystrophic patients.

Is Duchenne gene therapy a suitable treatment despite its immunogenic class effect?

INTRODUCTION

Duchenne muscular dystrophy (DMD) is a severe X-linked disorder characterized by progressive muscle weakness and eventual death due to cardiomyopathy or respiratory complications. Currently, there is no cure for DMD, with standard treatments primarily focusing on symptom management. Using immunosuppressive measures and optimized vector designs allows for gene therapies to better address the genetic cause of the disease.

AREAS COVERED

This review evaluates the efficacy and safety of emerging DMD gene therapies as of 2024. It also discusses the potential of utrophin upregulation, gene editing, and truncated dystrophin as therapeutic strategies. It highlights safety concerns associated with these therapies, including adverse events and patient deaths. A comprehensive overview of developments covers topics such as CRISPR-Cas9 therapies, micro-dystrophin, and the potential delivery of full-length dystrophin.

EXPERT OPINION

The FDA's recent approval of delandistrogene moxeparvovec (Elevidys) underscores the promise of gene replacement therapies for DMD patients. Understanding the mechanisms behind the adverse effects and excluding patients with specific pathogenic variants may enhance the safety profiles of these therapies. CRISPR/Cas9 therapies, while promising, face significant regulatory and safety challenges that hinder their clinical application. Optimal DMD therapies should target both skeletal and cardiac muscles to be effective.

Annotating protein functions via fusing multiple biological modalities

Understanding the function of proteins is of great significance for revealing disease pathogenesis and discovering new targets. Benefiting from the explosive growth of the protein universal, deep learning has been applied to accelerate the protein annotation cycle from different biological modalities. However, most existing deep learning-based methods not only fail to effectively fuse different biological modalities, resulting in low-quality protein representations, but also suffer from the convergence of suboptimal solution caused by sparse label representations. Aiming at the above issue, we propose a multiprocedural approach for fusing heterogeneous biological modalities and annotating protein functions, i.e., MIF2GO (Multimodal Information Fusion to infer Gene Ontology terms), which sequentially fuses up to six biological modalities ranging from different biological levels in three steps, thus leading to powerful protein representations. Evaluation results on seven benchmark datasets show that the proposed method not only considerably outperforms state-of-the-art performance, but also demonstrates great robustness and generalizability across species. Besides, we also present biological insights into the associations between those modalities and protein functions. This research provides a robust framework for integrating multimodal biological data, offering a scalable solution for protein function annotation, ultimately facilitating advancements in precision medicine and the discovery of novel therapeutic strategies.

Effect of 2-Aminoethoxydiphenyl Borate on the State of Skeletal Muscles in Dystrophin-Deficient mdx Mice

OBJECTIVE

Ca2+ overload of muscle fibers is one of the factors that secondarily aggravate the development of Duchenne muscular dystrophy (DMD). The purpose of this study is to evaluate the effects of the Ca2+ channel modulator 2-aminoethoxydiphenyl borate (APB) on skeletal muscle pathology in dystrophin-deficient mdx mice.

METHODS

Mice were randomly divided into six groups: wild type (WT), WT+3 mg/kg APB, WT+10 mg/kg APB, mdx, mdx+3 mg/kg APB, mdx+10 mg/kg APB. APB was administered intraperitoneally daily for 28 days. Finally, we assessed the grip strength and hanging time of mice, the histology and ultrastructure of the quadriceps, as well as the parameters reflecting quadricep mitochondrial function.

RESULTS

3 mg/kg APB was shown to reduce creatine kinase activity in the serum, intensity of degeneration and the level of fibrosis in the quadriceps of mdx mice, and improved tissue ultrastructure. However, this effect of APB was not sufficient to improve grip strength and hanging time of mdx mice. The effect of 3 mg/kg APB may be due to improve Ca2+ homeostasis in skeletal muscles, as evidenced by a trend toward decreased Ca2+ overload of quadricep mitochondria. High dose of APB (10 mg/kg body weight) showed less pronounced effect on the pathological phenotype of mdx mice. Moreover, 10 mg/kg APB disrupted the ultrastructure of the quadriceps and caused a decrease in grip strength in WT mice.

CONCLUSIONS

APB is able to improve the phenotype in mdx mouse DMD model. However, the effect of APB is quite limited, which may be due to its multitargeting of Ca2+ channels in the membranes of muscle fibers and intracellular organelles, differentially expressed in DMD.

Model organisms for investigating the functional involvement of NRF2 in non-communicable diseases

Non-communicable chronic diseases (NCDs) are most commonly characterized by age-related loss of homeostasis and/or by cumulative exposures to environmental factors, which lead to low-grade sustained generation of reactive oxygen species (ROS), chronic inflammation and metabolic imbalance. Nuclear factor erythroid 2-like 2 (NRF2) is a basic leucine-zipper transcription factor that regulates the cellular redox homeostasis. NRF2 controls the expression of more than 250 human genes that share in their regulatory regions a cis-acting enhancer termed the antioxidant response element (ARE). The products of these genes participate in numerous functions including biotransformation and redox homeostasis, lipid and iron metabolism, inflammation, proteostasis, as well as mitochondrial dynamics and energetics. Thus, it is possible that a single pharmacological NRF2 modulator might mitigate the effect of the main hallmarks of NCDs, including oxidative, proteostatic, inflammatory and/or metabolic stress. Research on model organisms has provided tremendous knowledge of the molecular mechanisms by which NRF2 affects NCDs pathogenesis. This review is a comprehensive summary of the most commonly used model organisms of NCDs in which NRF2 has been genetically or pharmacologically modulated, paving the way for drug development to combat NCDs. We discuss the validity and use of these models and identify future challenges.

Efficient suppression of premature termination codons with alanine by engineered chimeric pyrrolysine tRNAs

Mutations that introduce premature termination codons (PTCs) within protein-coding genes are associated with incurable and severe genetic diseases. Many PTC-associated disorders are life-threatening and have no approved medical treatment options. Suppressor transfer RNAs (sup-tRNAs) with the capacity to translate PTCs represent a promising therapeutic strategy to treat these conditions; however, developing novel sup-tRNAs with high efficiency and specificity often requires extensive engineering and screening. Moreover, these efforts are not always successful at producing more efficient sup-tRNAs. Here we show that a pyrrolysine (Pyl) tRNA (tRNAPyl), which naturally translates the UAG stop codon, offers a favorable scaffold for developing sup-tRNAs that restore protein synthesis from PTC-containing genes. We created a series of rationally designed Pyl tRNAScaffold Suppressor-tRNAs (PASS-tRNAs) that are substrates of bacterial and human alanyl-tRNA synthetase. Using a PTC-containing fluorescent reporter gene, PASS-tRNAs restore protein synthesis to wild-type levels in bacterial cells. In human cells, PASS-tRNAs display robust and consistent PTC suppression in multiple reporter genes, including pathogenic mutations in the tumor suppressor gene BRCA1 associated with breast and ovarian cancer. Moreover, PTC suppression occurred with high codon specificity and no observed cellular dysregulation. Collectively, these results unveil a new class of sup-tRNAs with encouraging potential for tRNA-based therapeutic applications.

Structure and assembly of the dystrophin glycoprotein complex

The dystrophin glycoprotein complex (DGC) has a crucial role in maintaining cell membrane stability and integrity by connecting the intracellular cytoskeleton with the surrounding extracellular matrix1-3. Dysfunction of dystrophin and its associated proteins results in muscular dystrophy, a disorder characterized by progressive muscle weakness and degeneration4,5. Despite the important roles of the DGC in physiology and pathology, its structural details remain largely unknown, hindering a comprehensive understanding of its assembly and function. Here we isolated the native DGC from mouse skeletal muscle and obtained its high-resolution structure. Our findings unveil a markedly divergent structure from the previous model of DGC assembly. Specifically, on the extracellular side, β-, γ- and δ-sarcoglycans co-fold to form a specialized, extracellular tower-like structure, which has a central role in complex assembly by providing binding sites for α-sarcoglycan and dystroglycan. In the transmembrane region, sarcoglycans and sarcospan flank and stabilize the single transmembrane helix of dystroglycan, rather than forming a subcomplex as previously proposed6-8. On the intracellular side, sarcoglycans and dystroglycan engage in assembly with the dystrophin-dystrobrevin subcomplex through extensive interaction with the ZZ domain of dystrophin. Collectively, these findings enhance our understanding of the structural linkage across the cell membrane and provide a foundation for the molecular interpretation of many muscular dystrophy-related mutations.

Precision genome editing using combinatorial viral vector delivery of CRISPR-Cas9 nucleases and donor DNA constructs

Genome editing based on programmable nucleases and donor DNA constructs permits introducing specific base-pair changes and complete transgenes or live-cell reporter tags at predefined chromosomal positions. A crucial requirement for such versatile genome editing approaches is, however, the need to co-deliver in an effective, coordinated and non-cytotoxic manner all the required components into target cells. Here, adenoviral (AdV) and adeno-associated viral (AAV) vectors are investigated as delivery agents for, respectively, engineered CRISPR-Cas9 nucleases and donor DNA constructs prone to homologous recombination (HR) or homology-mediated end joining (HMEJ) processes. Specifically, canonical single-stranded and self-complementary double-stranded AAVs served as sources of ectopic HR and HMEJ substrates, whilst second- and third-generation AdVs provided for matched CRISPR-Cas9 nucleases. We report that combining single-stranded AAV delivery of HR donors with third-generation AdV transfer of CRISPR-Cas9 nucleases results in selection-free and precise whole transgene insertion in large fractions of target-cell populations (i.e. up to 93%) and disclose that programmable nuclease-induced chromosomal breaks promote AAV transduction. Finally, besides investigating relationships between distinct AAV structures and genome-editing performance endpoints, we further report that high-fidelity CRISPR-Cas9 nucleases are critical for mitigating off-target chromosomal insertion of defective AAV genomes known to be packaged in vector particles.

Molecular pathways involved in the control of contractile and metabolic properties of skeletal muscle fibers as potential therapeutic targets for Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is caused by mutations in the gene encoding dystrophin, a subsarcolemmal protein whose absence results in increased susceptibility of the muscle fiber membrane to contraction-induced injury. This results in increased calcium influx, oxidative stress, and mitochondrial dysfunction, leading to chronic inflammation, myofiber degeneration, and reduced muscle regenerative capacity. Fast glycolytic muscle fibers have been shown to be more vulnerable to mechanical stress than slow oxidative fibers in both DMD patients and DMD mouse models. Therefore, remodeling skeletal muscle toward a slower, more oxidative phenotype may represent a relevant therapeutic approach to protect dystrophic muscles from deterioration and improve the effectiveness of gene and cell-based therapies. The resistance of slow, oxidative myofibers to DMD pathology is attributed, in part, to their higher expression of Utrophin; there are, however, other characteristics of slow, oxidative fibers that might contribute to their enhanced resistance to injury, including reduced contractile speed, resistance to fatigue, increased capillary density, higher mitochondrial activity, decreased cellular energy requirements. This review focuses on signaling pathways and regulatory factors whose genetic or pharmacologic modulation has been shown to ameliorate the dystrophic pathology in preclinical models of DMD while promoting skeletal muscle fiber transition towards a slower more oxidative phenotype.

Unveiling the Future of Cardiac Care: A Review of Gene Therapy in Cardiomyopathies

For years, the treatment of many cardiomyopathies has been solely focused on symptom management. However, cardiomyopathies have a genetic substrate, and directing therapy towards the pathophysiology rather than the epiphenomenon of the disease may be a winning strategy. Gene therapy involves the insertion of genes or the modification of existing ones and their regulatory elements through strategies like gene replacement and gene editing. Recently, gene therapy for cardiac amyloidosis and Duchenne muscular dystrophy has received approval, and important clinical trials are currently evaluating gene therapy methods for rare heart diseases like Friedreich's Ataxia, Danon disease, Fabry disease, and Pompe Disease. Furthermore, favorable results have been noted in animal studies receiving gene therapy for hypertrophic, dilated, and arrhythmogenic cardiomyopathy. This review discusses gene therapy methods, ongoing clinical trials, and future goals in this area.

Treatment of giant fecalith colonic obstruction in a patient with Duchenne muscular dystrophy using endoscopic injection of hydrogen peroxide: a case report and literature review

Introduction

Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic disorder primarily affecting cardiac and skeletal muscles, with gastrointestinal obstruction being an infrequent complication.

Case report

We present a 17-year-old boy with DMD (G-to-T transversion at c.4150 in the gene encoding dystrophin protein) who developed severe colonic obstruction due to fecal impaction. Abdominal computed tomography revealed an obstructing fecalith in the left colon (length: 39.5 cm, width: 18.3 cm, height: 12.7 cm). Despite the application of initial conservative measures including fasting, enemas, and fluid resuscitation, the obstruction persisted. Therefore, we performed manual disimpaction and endoscopic injection of hydrogen peroxide, effectively alleviating the obstruction.

Discussion

This case underscores the necessity of devising stage-specific, tailored strategies for the prevention and management of gastrointestinal complications in patients with DMD.

Upper body gait deviations in children with Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy is primarily a disease of progressive muscle degeneration affecting the whole body. It is important to preserve the patients' walking ability as long as possible. Inconclusive information on Duchenne muscular dystrophy gait pattern is available for the lower body and missing for the upper body. This study aimed to objectively investigate upper body gait deviations in a group of patients with Duchenne muscular dystrophy compared to typically developing peers.

METHODS

Kinematic data of twelve boys with Duchenne muscular dystrophy that underwent three-dimensional full-body gait analysis were investigated retrospectively. Data were compared to sixteen healthy children of same age at similar walking speed. Statistical tests included the student independent t-test (with Holm-Bonferroni correction), Hedges'g for effect size, and statistical non-parametric mapping two-sample t-test (with Bonferroni correction).

FINDINGS

Duchenne muscular dystrophy compared to the healthy group: In the sagittal plane, the thorax segment was more posteriorly tilted. In addition, the relative angle between pelvis and thorax segment showed more backwards lean with increased shoulder extension. In the frontal plane, the patients walked with increased shoulder abduction and took wider strides. In the transverse plane, thorax rotation was not different between groups. Thorax range of motion was increased in all three planes.

INTERPRETATION

Including the upper body gait kinematics, especially of the trunk, adds valuable objective information on the understanding of the Duchenne muscular dystrophy gait pattern. Our findings contribute to improved understanding of full-body gait compensations in this patient group.

A Review of Muscle Relaxants in Anesthesia in Patients with Neuromuscular Disorders Including Guillain-Barré Syndrome, Myasthenia Gravis, Duchenne Muscular Dystrophy, Charcot-Marie-Tooth Disease, and Inflammatory Myopathies

Anesthesia management in neuromuscular diseases (NMDs) is a complex challenge, requiring careful preoperative evaluation, tailored treatment strategies, and vigilant perioperative monitoring. This review examines the nuances of anesthesia in patients with NMD, addressing potential complications such as intubation difficulties, respiratory failure, and adverse effects of anesthetics and neuromuscular conduction blocking agents (NMBAs). Nondepolarizing NMBAs, including steroidal agents and benzylisoquinolines, are analyzed for their role, risks, and optimal use based on procedural requirements and patient characteristics. Challenges with depolarizing agents such as succinylcholine are highlighted, emphasizing the need for careful evaluation and monitoring to reduce the risk of adverse events such as malignant hyperthermia and hyperkalemia. The review highlights the role of reversal agents, particularly sugammadex, as a safer and more effective alternative to traditional acetylcholinesterase inhibitors such as neostigmine. Sugammadex reduces the risk of complications such as prolonged paralysis and respiratory failure in patients with NMD. In addition, anesthesia considerations tailored to specific NMDs, including Guillain-Barre syndrome, myasthenia gravis, Duchenne muscular dystrophy, Charcot-Marie-Tooth disease, and inflammatory myopathies are presented, including monitoring techniques and individualized approaches. Based on the available literature and the authors' clinical experience, this review aims to discuss the role of muscle relaxants in anesthesia in patients with the aforementioned neuromuscular disorders. This document uses the latest possible articles, covering items from 1992 to 2024.

Anti-necroptotic effects of human Wharton's jelly-derived mesenchymal stem cells in skeletal muscle cell death model via secretion of GRO-α

Human mesenchymal stem cells (hMSCs) have therapeutic applications and potential for use in regenerative medicine. However, the use of hMSCs in research and clinical medicine is limited by a lack of information pertaining to their donor-specific functional attributes. In this study, we compared the characteristics of same-donor derived placenta (PL) and Wharton's jelly (WJ)-derived hMSCs, we also compared their mechanism of action in a skeletal muscle disease in vitro model. The same-donor-derived hWJ- and hPL-MSCs exhibited typical hMSC characteristics. However, GRO-α was differentially expressed in hWJ- and hPL-MSCs. hWJ-MSCs, which secreted a high amount of GRO-α, displayed a higher ability to inhibit necroptosis in skeletal muscle cells than hPL-MSCs. This demonstrates the anti-necroptotic therapeutic effect of GRO-α in the skeletal muscle cell death model. Furthermore, GRO-α also exhibited the anti-necroptotic effect in a Duchenne muscular dystrophy (DMD) mouse model. Considering their potential to inhibit necroptosis in skeletal muscle cells, hWJ-MSCs and the derived GRO-α are novel treatment options for skeletal muscle diseases such as DMD.

Effects of a Ketogenic Diet on the Assessment of Biochemical and Clinical Parameters in Duchenne Muscular Dystrophy: A Preclinical Investigation

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder characterized by progressive skeletal muscle degeneration and systemic effects, including the central nervous system (CNS). This study aimed to assess the impact of a 14-day ketogenic diet (DCet) on biochemical and clinical parameters in a DMD mouse model. Young adult mice (50 days old) were fed DCet, while control groups received a standard diet. On the 14th day, memory and behavior tests were conducted, followed by biochemical evaluations of oxidative stress, inflammatory biomarkers, body weight, feed intake, and brain-derived neurotrophic factor (BDNF) levels. mdx + DCet mice showed reduced mass (0.2 g ± 2.49) and improved memory retention (p < 0.05) compared to controls. Oxidative damage in muscle tissue and CNS decreased, along with a significant cytokine level reduction (p <0.05). The protocol led to an increase in hippocampal BDNF and mitochondrial respiratory complex activity in muscle tissue and the central nervous system (CNS), while also decreasing creatine kinase activity only in the striatum. Overall, a 14-day DCet showed protective effects by improving spatial learning and memory through reductions in oxidative stress and immune response, as well as increases in BDNF levels, consistent with our study's findings.

Systemic Treatment of Body-Wide Duchenne Muscular Dystrophy Symptoms

Duchenne muscular dystrophy (DMD) is a fatal X-linked disease that leads to premature death due to the loss of dystrophin. Current strategies predominantly focus on the therapeutic treatment of affected skeletal muscle tissue. However, certain results point to the fact that with successful treatment of skeletal muscle, DMD-exposed latent phenotypes in tissues, such as cardiac and smooth muscle, might lead to adverse effects and even death. Likewise, it is now clear that the absence of dystrophin affects the function of the nervous system, and that this phenotype is more pronounced when shorter dystrophins are absent, in addition to the full-length dystrophin that is present predominantly in the muscle. Here, I focus on the systemic aspects of DMD, highlighting the ubiquitous expression of the dystrophin gene in human tissues. Furthermore, I describe therapeutic strategies that have been tested in the clinic and point to unresolved questions regarding the function of distinct dystrophin isoforms, and the possibility of current therapeutic strategies to tackle phenotypes that relate to their absence.

Implementation of the Methyl-Seq platform to identify tissue- and sex-specific DNA methylation differences in the rat epigenome

Epigenomic annotations for the rat lag far behind those of human and mouse, despite the rat's immense utility in pharmacological and behavioral studies and the need to understand their epigenetic mechanisms. We have designed a targeted-enrichment method followed by next-generation sequencing (Methyl-Seq) to identify DNA methylation (DNAm) signatures across the rat genome. The design reflected an attempt to create a more comprehensive investigation of the rat epigenome, as it included promoters, CpG islands, and island shores of all RefSeq genes. In this study, we implemented the rat Methyl-Seq platform and tested its ability to distinguish differentially methylated regions (DMRs) among three different tissue types, three distinct brain regions, and, in the hippocampus, between males and females. These comparisons yielded DNAm differences of differing magnitudes, many of which were independently validated by bisulfite pyrosequencing, including autosomal regions that were predicted to show the least degree of difference in DNAm between males and females. Quantitative reverse transcription PCR revealed that most genes associated with the DMRs showed tissue-, brain region-, and sex-specific differences in expression. In particular, we found evidence for sex-specific DNAm and expression differences at Tubb6, Lrrn2, Tex26, and Sox5l1, all of which play important roles in neurodevelopment and have been implicated in studies examining sex differences. Our results demonstrate the utility of the rat Methyl-Seq platform and suggest the presence of DNAm differences between the male and female hippocampus. The rat Methyl-Seq has the potential to provide epigenomic insights into pharmacological and behavioral studies performed in the rat.

Review of embryo-fetal developmental toxicity studies performed for pharmaceuticals approved by FDA in 2022 and 2023

92 novel drugs were approved by the FDA in 2022-2023. 48 of these approvals were for orphan indications. Embryofetal development (EFD) studies were conducted for 79 % of approvals. Rats and rabbits were the most common species used (77 % and 62 % of studies, respectively). For the testing of biopharmaceuticals, rodents were more often used (43 % of EFD studies) than non-human primates (29 %) and rabbits (29 %). Most (75 %) biopharmaceuticals intended to treat cancer were approved without EFD studies. Amongst the 41 drugs for which both rat and rabbit EFD studies were performed, the rabbit appeared more sensitive to both maternal toxicity and developmental toxicity (61 % and 63 % of drugs, respectively). Most drugs (76 %) showed more than a 2-fold difference in the LOAEL for developmental toxicity between the rat and rabbit. EFD studies were not required for drugs with a mode of action known to pose a clear hazard for pregnancy and further EFD studies were generally not performed when clinically relevant developmental effects had already been observed in one species or in a preliminary EFD study. Many drug labels showed minor deviations from the PLLR rule: the metric used to calculate exposure margins and the presence or absence of maternal toxicity were not always specified. These omissions, however, are of little significance for the prescriber. The five reviews in this series now show compiled information on EFD studies for all small molecule pharmaceuticals approved since 2014 and for all therapeutic monoclonal antibodies approved to date.

Genomic insights into Duchene muscular dystrophy: Analysis of 1250 patients reveals 30% novel genetic patterns and 6 novel variants

Duchenne muscular dystrophy (DMD/BMD) is the most common type of muscular dystrophy, together with Becker muscular dystrophy represent more than half of all cases. DMD is a single-gene, X-linked recessive disorder that predominantly affects boys, causing progressive muscle deterioration and eventually leading to fatal cardiopulmonary complications. This study aimed to implement a cost-effective molecular diagnostic method using the SALSA MLPA Kit (probe mixes 034 and 035) to screen a large group of Egyptian DMD patients. The study included 1250 clinically diagnosed DMD males, following complete family history, pedigree analyses and an accurate clinical examination and laboratory investigations mainly considering high levels of creatine phosphokinase (>2000 U/L). We also analysed the carrier status of 100 mothers of 100 probands to gauge the inherited mutation through their patients with familial disease. The negative results of MLPA were further analysed with NGS for ten patients and the results were validated for novel missense mutations, phenotype-genotype correlations were analysed using PolyPhen2 and mutation taster. Results SALSA MLPA analysis confirmed the diagnoses in 733/1250 (58.6 %) DMD patients and the remaining of 517/1250 (41.4%) were negative. DMD patients having large deletions were 632/1250 (50.6%) while duplications occurred in 101/1250 (8%). The most common single exon deletion was 45 (50/632, 7.9%). In addition, 163 different deletion and duplication patterns were characterized among positive MLPA analyses. 30% of our studied cohort exhibited new patterns of rearragements in addition to seven cases of double deletion and duplication rearrangements identified, within nine patients. Using NGS, for small mutations detection, revealed six novel and three previously reported mutations among screened ten patients. In conclusion, our findings expand the spectrum of known DMD mutations by offering an effective diagnostic method and identifying novel point mutations through NGS analysis. We recommend using NGS to uncover uncharacterized mutations in patients who test negative with MLPA, which could contribute to the treatment of DMD.

The Innovative Role of Nuclear Receptor Interaction Protein in Orchestrating Invadosome Formation for Myoblast Fusion

BACKGROUND

Nuclear receptor interaction protein (NRIP) is versatile and engages with various proteins to execute its diverse biological function. NRIP deficiency was reported to cause small myofibre size in adult muscle regeneration, indicating a crucial role of NRIP in myoblast fusion.

METHODS

The colocalization and interaction of NRIP with actin were investigated by immunofluorescence and immunoprecipitation assay, respectively. The participation of NRIP in myoblast fusion was demonstrated by cell fusion assay and time-lapse microscopy. The NRIP mutants were generated for mechanism study in NRIP-null C2C12 (termed KO19) cells and muscle-specific NRIP knockout (NRIP cKO) mice. A GEO profile database was used to analyse NRIP expression in Duchenne muscular dystrophy (DMD) patients.

RESULTS

In this study, we found that NRIP directly and reciprocally interacted with actin both in vitro and in cells. Immunofluorescence microscopy showed that the endogenous NRIP colocalized with components of invadosome, such as actin, Tks5, and cortactin, at the tips of cells during C2C12 differentiation. The KO19 cells were generated and exhibited a significant deficit in myoblast fusion compared with wild-type C2C12 cells (3.16% vs. 33.67%, p < 0.005). Overexpressed NRIP in KO19 cells could rescue myotube formation compared with control (3.37% vs. 1.00%, p < 0.01). We further confirmed that NRIP directly participated in cell fusion by using a cell-cell fusion assay. We investigated the mechanism of invadosome formation for myoblast fusion, which depends on NRIP-actin interaction, by analysing NRIP mutants in NRIP-null cells. Loss of actin-binding of NRIP reduced invadosome (enrichment ratio, 1.00 vs. 2.54, p < 0.01) and myotube formation (21.82% vs. 35.71%, p < 0.05) in KO19 cells and forced NRIP expression in KO19 cells and muscle-specific NRIP knockout (NRIP cKO) mice increased myofibre size compared with controls (over 1500 μm2, 61.01% vs. 20.57%, p < 0.001). We also found that the NRIP mRNA level was decreased in DMD patients compared with healthy controls (18 072 vs. 28 289, p < 0.001, N = 10 for both groups).

CONCLUSIONS

NRIP is a novel actin-binding protein for invadosome formation to induce myoblast fusion.

Prevalence of Neutralizing Antibodies Against AAV Serotypes 2 and 9 in Healthy Participants from Multiple Centers Across China and Patients with DMD/BMD

To facilitate adeno-associated virus (AAV)-mediated gene therapy in China, we conducted a study on the distribution of AAV-neutralizing antibodies (NAbs) in healthy subjects and in patients with Duchenne muscular dystrophy (DMD)/Becker muscular dystrophy (BMD). A total of 352 healthy adult controls (ACs) from a national multicenter study, 100 schoolchild controls (SCs), and 281 patients with DMD/BMD from Peking Union Medical College Hospital were enrolled in this study. Cell-based inhibition assays were applied, and serum samples demonstrating 50% inhibition of infection were considered positive. The seroprevalence of AAV2 and AAV9 NAbs among the 733 participants was 86.1% and 56.3%, respectively. The AAV2 NAbs and AAV9 NAbs positivity rates in the AC, SC, and DMD/BMD groups were 97.4%/86.6%, 100.0%/17.0%, and 66.9%/32.4%, respectively. The seroprevalence of AAV NAbs gradually increased with age, especially in AAV9 NAbs. Females tended to have higher positivity rate than males. Over 85% of ACs had overlapping AAV9 and AAV2 infection. However, being positive for only AAV2 NAbs in the SC group was common, and 30.6% of patients with DMD/BMD were negative for both AAV2 and AAV9 NAbs. Our findings reveal that a significant proportion of patients with DMD/BMD were negative for AAV2 and AAV9 NAbs, which is the population that is most amenable to being treated with gene therapy.

Long-Term Survival and Myocardial Function Following Systemic Delivery of Delandistrogene Moxeparvovec in DMDMDX Rats

Delandistrogene moxeparvovec is a gene transfer therapy for Duchenne muscular dystrophy (DMD) that uses an adeno-associated viral vector to deliver a micro-dystrophin transgene to skeletal and cardiac muscle. This study evaluated the long-term survival and cardiac efficacy of delandistrogene moxeparvovec in a DMD-mutated (DMDMDX) rat model of DMD-related cardiomyopathy. DMDMDX male rats, aged 21-42 days, were injected with 1.33 × 1014 viral genomes/kilogram (vg/kg) delandistrogene moxeparvovec and followed for 12, 24, and 52 weeks. Ambulation was recorded via the Photobeam Activity System, whereas echocardiograms, cardiomyocyte contractility, calcium handling, and histological analysis of fibrosis were used to evaluate cardiac disease at 12-, 24-, and 52-weeks post-treatment. A separate cohort of rats was used to assess the impact of delandistrogene moxeparvovec on survival. Treatment with delandistrogene moxeparvovec extended median survival in DMDMDX rats to >25 months versus the 13-month median survival in saline-control-treated DMDMDX rats. Compared with saline control, delandistrogene moxeparvovec therapy elicited statistically significant improvements across cardiac parameters approaching wild-type values with additional benefits in mobility, histopathology, and fibrosis observed. Transgene expression was maintained up to >25 months and micro-dystrophin expression was broadly distributed across skeletal and cardiac muscle. Taken together, these findings demonstrate long-term cardiac efficacy and improved survival following delandistrogene moxeparvovec treatment in DMDMDX rats.

Mechanism of Genome Editing Tools and Their Application on Genetic Inheritance Disorders

In the fields of medicine and bioscience, gene editing is increasingly recognized as a promising therapeutic approach for treating pathogenic variants in humans and other living organisms. With advancements in technology and knowledge, it is now understood that most genetic defects are caused by single-base pair variants. The ability to substitute genes using genome editing tools enables scientists and doctors to cure genetic diseases and disorders. Starting with CRISPR (clustered regularly interspaced short palindromic repeats)/Cas, the technology has evolved to become more efficient and safer, leading to the development of base and prime editors. Furthermore, various approaches are used to treat genetic disorders such as hemophilia, cystic fibrosis, and Duchenne muscular dystrophy. As previously mentioned, most genetic defects leading to specific diseases are caused by single-base pair variants, which can occur at many locations in corresponding gene, potentially causing the same disease. This means that, even when using the same genome editing tool, results in terms of editing efficiency or treatment effectiveness may differ. Therefore, different approaches may need to be applied to different types of diseases. Prevalently, due to the safety of adeno-associated virus (AAV) vectors in gene therapy, most clinical trials of gene therapy are based on AAV delivery methods. However, despite their safety and nonintegration into the host genome, their limitations, such as confined capacity, dosage-dependent viral toxicity, and immunogenicity, necessitate the development of new approaches to enhance treatment effects. This review provides the structure and function of each CRISPR-based gene editing tool and focuses on introducing new approaches in gene therapy associated with improving treatment efficiency.

Muscle Pathology Associated With Cardiac Function in Duchenne Muscular Dystrophy

OBJECTIVE

To compare the progression of muscle fibrosis of various site and its relation between cardiac deterioration in Duchenne muscular dystrophy (DMD). In this study aimed to examine the associations between echocardiogram-based cardiac function indices and fibrosis of the abdominal and lower extremity muscles in patients with DMD to facilitate early detection of cardiac dysfunction and identify its predictors.

METHODS

Twenty-one patients with DMD patients were enrolled in the study. The association between cardiac dysfunction and fibrosis of the abdominal and lower extremity muscles was determined by analyzing the echocardiography and elastography. Non-parametric Spearman rank correlation coefficients were used to examine the pairwise relationships between cardiac function and muscle elasticity.

RESULTS

All patients were male and non-ambulant. Their mean age was 18.45±4.28 years. The strain ratios of the abdominal muscle and quadriceps muscles were significantly higher than those of the medial gastrocnemius. The strain ratio of the rectus abdominis muscle has a significant negative correlation with left ventricular ejection fraction. Cardiac function and valvular insufficiency were not significantly correlated with muscle strain ratio. According to the result of our study, the only skeletal muscle which showed significant correlation with cardiac dysfunction was degree abdominal muscle fibrosis.

CONCLUSION

The degree of fibrosis of respiratory muscles was also significantly associated with cardiac dysfunction; therefore, it can be used as a predictor of cardiac dysfunction in patients with DMD in clinical practice.

Multimodal three-dimensional characterization of murine skeletal muscle micro-scale elasticity, structure, and composition: Impact of dysferlinopathy, Duchenne muscular dystrophy, and age on three hind-limb muscles

Skeletal muscle tissue function is governed by the mechanical properties and organization of its components, including myofibers, extracellular matrix, and adipose tissue, which can be modified by the onset and progression of many disorders. This study used a novel combination of quantitative micro-elastography and clearing-enhanced three-dimensional (3D) microscopy to assess 3D micro-scale elasticity and micro-architecture of muscles from two muscular dystrophies: dysferlinopathy and Duchenne muscular dystrophy, using male BLA/J and mdx mice, respectively, and their wild-type (WT) controls. We examined three muscles with varying proportions of slow- and fast-twitch myofibers: the soleus (predominantly slow), extensor digitorum longus (EDL; fast), and quadriceps (mixed), from BLA/J and WTBLA/J mice aged 3, 10, and 24 months, and mdx and WTmdx mice aged 10 months. Both dysferlin deficiency and age reduced the elasticity and variability of elasticity of the soleus and quadriceps, but not EDL. Overall, the BLA/J soleus was 20% softer than WT and less mechanically heterogeneous (-14% in standard deviation of elasticity). The BLA/J quadriceps at 24 months was 72% softer than WT and less mechanically heterogeneous (-59% in standard deviation), with substantial adipose tissue accumulation. While mdx muscles did not differ quantitatively from WT, regional heterogeneity was evident in micro-scale elasticity and micro-architecture of quadriceps (e.g., 11.2 kPa in a region with marked pathology vs 3.8 kPa in a less affected area). These results demonstrate differing biomechanical changes in hind-limb muscles of two distinct muscular dystrophies, emphasizing the potential for this novel multimodal technique to identify important differences between various myopathies.

Safety and effectiveness of ataluren in patients with Duchenne muscular dystrophy: single-center experience from Saudi Arabia

OBJECTIVE

Duchenne muscular dystrophy (DMD) is a rare X-linked neurodegenerative disorder caused by mutations in the DMD gene. This study examined the efficacy and safety of ataluren, the first oral treatment for DMD with nonsense mutations (nmDMD), in patients in the Middle East.

METHODS

This retrospective longitudinal study assessed the outcomes of seven boys with nmDMD who received treatment with ataluren and follow-up at a single center since 2016.

RESULTS

The median patient age at treatment initiation was 8.04 years (range: 3.3-9.92), and the median duration of exposure was 3.95 years (interquartile range = 4.42 years). Five patients were still ambulatory at the last follow-up. Ataluren was more effective in individuals with baseline 6-min walking distance (6MWD) ≥300 m, as these patients had smaller declines in 6MWD and North Star Ambulatory Assessment scores. Pulmonary function was well preserved in all patients, with no patients having forced vital capacity <60% at their last follow-up. Six patients maintained normal cardiac function, whereas one patient developed heart failure before starting ataluren treatment.

CONCLUSIONS

Our results demonstrated both the efficacy and safety of ataluren. Early initiation of ataluren treatment delayed the loss of ambulation and cardiorespiratory milestones.

Identification of disease-specific extracellular vesicle-associated plasma protein biomarkers for Duchenne Muscular Dystrophy and Facioscapulohumeral Muscular Dystrophy

Objective

Reliable, circulating biomarkers for Duchenne, Becker and facioscapulohumeral muscular dystrophies (DBMD and FSHD) remain unvalidated. Here, we investigated the plasma extracellular vesicle (EV) proteome to identify disease-specific biomarkers that could accelerate therapy approvals.

Methods

We extracted EVs from the plasma of DBMD and FSHD patients and healthy controls using size-exclusion chromatography, conducted mass spectrometry on the extracted EV proteins, and performed comparative analysis to identify disease-specific biomarkers. We correlated the levels of these biomarkers with clinical outcome measures and confounding factors.

Results

The muscle-associated proteins PYGM, MYOM3, FLNC, MYH2 and TTN were exclusively present in DBMD EVs. PYGM, MYOM3, and TTN negatively correlated with age. PYGM and MYOM3 levels were elevated in patients without cardiomyopathy, and PYGM levels were specifically elevated in ambulatory DMD patients. On the other hand, female FSHD patients displayed significantly higher MBL2 and lower GPLD1 levels. However, male FSHD patients exhibited higher C9 and lower C4BPB levels. Additionally, desmosome proteins JUP and DSP were uniquely found in FSHD males. MBL2 positively correlated with age and C4BPB negatively correlated with FSHD severity in male patients.

Interpretation

Our findings underscore the sensitivity of analyzing circulating EV content to identify disease-specific protein biomarkers for DBMD and FSHD. Our results also emphasize the potential of EV-based biomarker discovery as a promising approach to monitor disease progression as well as effectiveness of therapies in muscular dystrophy, potentially contributing to their approval. Further research with larger cohorts is needed to validate these biomarkers and explore their clinical implications.

Research hotspots and trends for Duchenne muscular dystrophy: a machine learning bibliometric analysis from 2004 to 2023

Aims

The aim of this study was to conduct a bibliometric analysis of the relevant literature on Duchenne muscular dystrophy (DMD) to ascertain its current status, identify key areas of research and demonstrate the evolution of the field.

Methods

The analysis sourced documents from the Science Citation Index Expanded in the Web of Science core collection, utilizing CiteSpace software and an online bibliometric platform to analyze collaborative networks among authors, institutions and countries, and to map out the research landscape through journal and reference evaluations. Keyword analyses, including clustering and emergent term identification, were conducted, alongside the development of knowledge maps.

Results

The study included 9,277 documents, indicating a rising publication trend in the field. The Institut National de la Santé et de la Recherche Médicale emerged as the top publishing institution, with Francesco Muntoni as the most prolific author. The United States dominated in publication output, showcasing significant leadership. The keyword analysis highlighted 786 key emergent terms, primarily focusing on the mechanisms, diagnostics and treatment approaches in DMD.

Conclusion

The field of DMD research is experiencing robust growth, drawing keen interest globally. A thorough analysis of current research and trends is essential for advancing knowledge and therapeutic strategies in this domain.

Caregiver Global Impression Observations from EMBARK: A Phase 3 Study Evaluating Delandistrogene Moxeparvovec in Ambulatory Patients with Duchenne Muscular Dystrophy

INTRODUCTION

Duchenne muscular dystrophy (DMD) is a rare, progressive, debilitating neuromuscular disease. The early childhood onset and debilitating nature of the disease necessitate decades of caretaking for most patients. Caregivers have a critical role in evaluating patients' physical functioning and/or response to treatment. Using DMD-specific caregiver-reported scales, the impact of delandistrogene moxeparvovec gene therapy on caregivers' perceived change in patient disease status or severity was evaluated using the Caregiver Global Impression of Change and Severity (CaGI-C and CaGI-S, respectively).

METHODS

In the Phase 3 randomized, double-blind, placebo-controlled trial (EMBARK; NCT05096221), the CaGI-C at week 52 and change from baseline to week 52 in CaGI-S were evaluated in a post hoc analysis. The CaGI-C assesses caregivers' impressions of change in DMD symptoms, physical ability, ability to perform daily activities, and overall health. The CaGI-S evaluates current severity of DMD symptoms, physical ability, ability to perform activities of daily living, and overall health. Data were evaluated using multi-domain responder index (MDRI) and ordinal regression analyses.

RESULTS

MDRI analyses across all four CaGI-C items yielded a treatment difference of 1.7 (95% confidence interval [CI]: 0.90-2.5) favoring delandistrogene moxeparvovec; a treatment difference of 1.1 (95% CI 0.30-1.9) was observed for the CaGI-S favoring delandistrogene moxeparvovec. After adjusting for age, ordinal regression analysis showed a nominally significant increase in the odds of achieving a better rating for delandistrogene moxeparvovec-treated patients on all four CaGI-C items (≥ 3.8-fold increase). After adjusting for baseline severity and age, ordinal regression analysis showed a nominally significant increase in the odds of improvement on all four CaGI-S items (≥ 2.2-fold increase).

CONCLUSION

These exploratory findings captured by caregiver-reported outcomes add to the totality of evidence that supports the clinical benefits of delandistrogene moxeparvovec for patients with DMD.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov identifier, NCT05096221.

GSK3 inhibition improves skeletal muscle function and whole-body metabolism in male mouse models of Duchenne muscular dystrophy

Inhibiting glycogen synthase kinase 3 (GSK3) improves muscle function, metabolism, and bone health in many diseases and conditions; however, whether GSK3 should be targeted for Duchenne muscular dystrophy (DMD), a severe muscle wasting disorder with no cure, remains unknown. Here, we show the effects of GSK3 inhibition in male DBA/2J (D2) and C57BL/10 (C57) mdx mice. Treating D2 mdx mice with GSK3 inhibitors alone or in combination with aerobic exercise improves muscle strength, endurance, and morphology, attenuates the hypermetabolic phenotype, and enhances insulin sensitivity. GSK3 inhibition in C57 mdx mice also improves muscle fatigue resistance and increases cage ambulation. Moreover, muscle-specific GSK3 knockdown in mdx mice augments muscle force production and endurance. In both mdx strains, GSK3 inhibition increases bone mineral content and density. Overall, these improvements to muscle, metabolic, and bone health with GSK3 inhibition in mdx mice may have clinical implications for patients with DMD, where the current standard of care, glucocorticoids, delay the loss of ambulation but increase the risk for insulin resistance and osteoporosis. Along with our observation of lowered β-catenin content in DMD myoblasts, a known cellular target for GSK3, this study provides ample evidence in support of inhibiting GSK3 for this disease.

An Updated Analysis of Exon-Skipping Applicability for Duchenne Muscular Dystrophy Using the UMD-DMD Database

BACKGROUND/OBJECTIVES

Antisense oligonucleotide (ASO)-mediated exon-skipping is an effective approach to restore the disrupted reading frame of the dystrophin gene for the treatment of Duchenne muscular dystrophy (DMD). Currently, four FDA-approved ASOs can target three different exons, but these therapies are mutation-specific and only benefit a subset of patients. Understanding the broad applicability of exon-skipping approaches is essential for prioritizing the development of additional therapies with the greatest potential impact on the DMD population. This review offers an updated analysis of all theoretical exon-skipping strategies and their applicability across the patient population, with a specific focus on DMD-associated mutations documented in the UMD-DMD database. Unlike previous studies, this approach leverages the inclusion of phenotypic data for each mutation, providing a more comprehensive and clinically relevant perspective.

METHODS

The theoretical applicability of all single and double exon-skipping strategies, along with multi exon-skipping strategies targeting exons 3-9 and 45-55, was evaluated for all DMD mutations reported in the UMD-DMD database.

RESULTS

Single and double exon-skipping approaches were applicable for 92.8% of large deletions, 93.7% of small lesions, 72.4% of duplications, and 90.3% of all mutations analyzed. Exon 51 was the most relevant target and was applicable for 10.6% of all mutations and 17.2% of large deletions. Additionally, two multi-exon-skipping approaches, targeting exons 45-55 and 3-9, were relevant for 70.6% of large deletions and 19.2% of small lesions.

CONCLUSIONS

Current FDA-approved ASOs were applicable to 27% of the UMD-DMD population analyzed, leaving a significant portion of patients without access to exon-skipping therapies. The clinical translation of alternative approaches is critical to expanding the accessibility of these therapies for the DMD population.

Identification of reference microRNAs in skeletal muscle of a canine model of Duchenne muscular dystrophy

Background

Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease caused by mutations in the dystrophin gene. DE50-MD dogs are an animal model of DMD used as a final translational model for evaluation of promising treatments. MicroRNA (miR) expressions in the muscle of DE50-MD dogs represent potential biomarkers, but stable reference miRs must first be identified. The aim of this paper was to establish a panel of reference miRs for WT and DE50-MD dogs over a range of ages and muscle groups.

Methods

RNA was extracted from WT and DE50-MD dog (N=6 per genotype) vastus lateralis muscle samples collected longitudinally at 3, 6, 9, 12, 15 and 18 months of age, and from muscles collected post-mortem (N=3 per genotype; cranial tibial, semimembranosus, lateral triceps and diaphragm). 87 RNAs were quantified in a subset of 6-month-old WT and DE50-MD muscles (N=4 per genotype) using the QIAcuity miFinder panel. GeNorm, BestKeeper and Normfinder were used to identify a candidate panel of the 8 most stable small RNAs, which were then quantified in all RNA samples, alongside the commonly used reference RNA snRNA U6.

Results

The most stable miRs of this subset were used to normalise quantities of dystromiRs miR-1, miR-133a and miR-206, and fibromiR miR-214. MicroRNAs miR-191, let-7b, miR-125a and miR-15a were the most stable miRs tested, while snRNA U6 performed poorly. DystromiR expression, normalised to the geometric mean of the panel of reference miRs, was lower for miR-1 and miR-133a in DE50-MD compared to WT muscles, while miR-206 levels did not significantly differ between genotypes. FibromiR miR-214 was 2- to 4-fold higher in DE50-MD versus WT muscles.

Conclusions

A normalisation factor derived from miR-191, let-7b, miR-125a and miR-15a is suitable for normalising miR expression data from WT and DE50-MD muscle over a range of ages and muscle types.

Oral administration of plumbagin is beneficial in in vivo models of Duchenne muscular dystrophy through control of redox signaling

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disease. Recently approved molecular/gene treatments do not solve the downstream inflammation-linked pathophysiological issues such that supportive therapies are required to improve therapeutic efficacy and patients' quality of life. Over the years, a plethora of bioactive natural compounds have been used for human healthcare. Among them, plumbagin, a plant-derived analog of vitamin K3, has shown interesting potential to counteract chronic inflammation with potential therapeutic significance. In this work we evaluated the effects of plumbagin on DMD by delivering it as an oral supplement within food to dystrophic mutant of the fruit fly Drosophila melanogaster and mdx mice. In both DMD models, plumbagin show no relevant adverse effect. In terms of efficacy plumbagin improved the climbing ability of the dystrophic flies and their muscle morphology also reducing oxidative stress in muscles. In mdx mice, plumbagin enhanced the running performance on the treadmill and the muscle strength along with muscle morphology. The molecular mechanism underpinning these actions was found to be the activation of nuclear factor erythroid 2-related factor 2 pathway, the re-establishment of redox homeostasis and the reduction of inflammation thus generating a more favorable environment for skeletal muscles regeneration after damage. Our data provide evidence that food supplementation with plumbagin modulates the main, evolutionary conserved, mechanistic pathophysiological hallmarks of dystrophy, thus improving muscle function in vivo; the use of plumbagin as a therapeutic in humans should thus be explored further.

A Unified Phosphoramidite Platform for the Synthesis of Morpholino Oligonucleotides and Diverse Chimeric Backbones

Phosphorodiamidate Morpholino Oligonucleotides (PMOs) have been well established in the milieu of FDA-approved oligonucleotide-based drugs in the past decade. Given their relevance in antisense therapeutics, a DNA/RNA synthesizer-compatible modular synthesis protocol of PMOs is long awaited to explore next-generation PMO chimeras with other therapeutically proven oligonucleotide backbones. Herein, we demonstrate a streamlined 5' → 3'phosphoramidite approach for the synthesis of PMOs using tert-butyl-protected 5'-tBu-morpholino phosphoramidites, which were synthesized from 5'-OH morpholino monomers derived from commercially available ribonucleosides. 2-Cyanoethyl (CE)-protected 5'-CE-morpholino phosphoramidites were also synthesized to generate thiophosphoramidate (TMO) and phosphoramidate (MO) morpholino oligonucleotides. Full-length PMOs and TMOs in exceptional overall yields were obtained with operational simplicity and compatibility with automated DNA/RNA synthesizers utilizing controlled pore glass (CPG) as the solid support and CH3CN as the solvent. Importantly, this method has opened the possibility of designing various biologically relevant ASO design modalities, such as PMO-TMO and PMO-MO, which were inaccessible otherwise. Moreover, DNA nucleotides were also incorporated to generate PMO-psDNA and PMO-DNA using commercially available 5'-DNA phosphoramidites. The biophysical properties of all synthesized oligonucleotides were analyzed using UV melting and circular dichroism studies. The serum interaction profile and innate immune response of the PS-modified polythymidine oligonucleotides were analyzed and it was found that the mixed backbone oligonucleotides had a balanced profile compared to fully charged or neutral extremities. Overall, the synthesis is amenable to fast generation of various types of PMO chimeras for biological screening, which will expedite their therapeutic exploration and transition to clinic.

Biophysical characterization of the dystrophin C-terminal domain: Dystrophin interacts differentially with dystrobrevin isoforms

Duchenne muscular dystrophy (DMD) gene encodes dystrophin, a large multidomain protein. Its nonfunctionality leads to dystrophinopathies like DMD and Becker muscular dystrophy, for which no cure is yet available. A few therapies targeted towards specific mutations can extend the lifespan of patients, although with limited efficacy and high costs, emphasizing the need for more general treatments. Dystrophin's complex structure with poorly understood domains and the presence of multiple isoforms with varied expression patterns in different tissues pose challenges in therapeutic development. The C-terminal (CT) domain of dystrophin is less understood in terms of its structure-function, although it has been shown to perform important functional roles by interacting with another cytosolic protein, dystrobrevin. Dystrophin and dystrobrevin stabilize the sarcolemma membrane by forming a multiprotein complex called dystrophin-associated glycoprotein complex that is destabilized in DMD. Dystrobrevin has two major isoforms, alpha and beta, with tissue-specific expression patterns. Here, we characterize the CT domain of dystrophin and its interactions with the two dystrobrevin isoforms. We show that the CT domain is nonglobular and shows reversible urea denaturation as well as thermal denaturation. It interacts with dystrobrevin isoforms differentially, with differences in binding affinity and the mode of interaction. We further show that the amino acid differences in the CT region of dystrobrevin isoforms contribute to these differences. These results have implications for the stability of dystrophin-associated glycoprotein complex in different tissues and explain the differing symptoms associated with DMD patients affecting organs beyond the skeletal muscles.

Prime editing: A gene precision editing tool from inception to present

Genetic mutations significantly contribute to the onset of diseases, with over half of the cases caused by single-nucleotide mutations. Advances in gene editing technologies have enabled precise editing and correction of mutated genes, offering effective treatment methods for genetic disorders. CRISPR/Cas9, despite its power, poses risks of inducing gene mutations due to DNA double-strand breaks (DSB). The advent of base editing (BE) and prime editing (PE) has mitigated these risks by eliminating the hazards associated with DNA DSBs, allowing for more precise gene editing. This breakthrough lays a solid foundation for the clinical application of gene editing technologies. This review discusses the principles, development, and applications of PE gene editing technology in various genetic mutation-induced diseases.

Characterization of Nonclinical Drug Metabolism and Pharmacokinetic Properties of Phosphorodiamidate Morpholino Oligonucleotides, a Novel Drug Class for Duchenne Muscular Dystrophy

Eteplirsen, golodirsen, and casimersen are phosphorodiamidate morpholino oligomers (PMOs) that are approved in the United States for the treatment of patients with Duchenne muscular dystrophy (DMD) with mutations in the DMD gene that are amenable to exon 51, 53, and 45 skipping, respectively. Here we report a series of in vivo and in vitro studies characterizing the drug metabolism and pharmacokinetic (DMPK) properties of these three PMOs. Following a single intravenous dose, plasma exposure was consistent for all three PMOs in mouse, rat, and nonhuman primate (NHP), and plasma half-lives were similar for eteplirsen (2.0-4.1 h) and golodirsen (2.1-8.7 h) across species and more variable for casimersen (3.2-18.1 h). Plasma protein binding was low (<40%) for all three PMOs in mouse, rat, NHP, and human and was largely concentration independent. In the mdx mouse model of DMD, following a single intravenous injection, extensive biodistribution was observed in the target skeletal muscle tissues and the kidney for all three PMOs; consistent with the latter finding, the predominant route of elimination was renal. In vitro studies using liver microsomes showed no evidence of hepatic metabolism, and none of the PMOs were identified as inhibitors or inducers of the human cytochrome P450 enzymes or membrane drug transporters tested at clinically relevant concentrations. These findings suggest that key DMPK features are consistent for eteplirsen, golodirsen, and casimersen and provide evidence for the concept of a PMO drug class with potential application to novel exon-skipping drug candidates. SIGNIFICANCE STATEMENT: The PMOs eteplirsen, golodirsen, and casimersen share similar absorption, distribution, metabolism, and excretion and DMPK properties, which provides evidence for the concept of a PMO treatment class. A PMO drug class may support a platform approach to enhance understanding of the pharmacokinetic and pharmacodynamic behavior of these molecules. The grouping of novel agent series into platforms could be beneficial in the development of drug candidates for populations in which traditional clinical trials are not feasible.

DMD mutations in pediatric patients with phenotypes of Duchenne/Becker muscular dystrophy

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are common X-inherited neuromuscular diseases. The genetic diagnosis has been used as the diagnostic choice for DMD/BMD. The study subjects consisted of 37 patients from Southwest China. Peripheral blood was collected for the extraction of genomic DNA. DMD mutation was sequenced using the next-generation sequencing approach. The detected mutation was validated using the multiplex ligation-dependent probe amplification or Sanger sequencing methods. Variation annotation and pathogenicity prediction were performed using the online databases. Pathogenic mutations were identified 3 splicing site, 7 single nucleotide, 1 indel, 23 deletion, and 3 duplication mutations. Novel DMD variants were discovered, including two novel splicing variations (c.1890 + 1G>T; c.1923 + 1G>A), one missense mutation (c.1946G>T), one nonsense mutation (c.7441G>T), one indel mutation (INDEL EX20), and one duplication mutation (DUP EX75-78). The current study provides mutation information of DMD for the genetic diagnosis of DMD/BMD.

Safety and efficacy of viltolarsen treatment in patients with Duchenne muscular dystrophy: A retrospective study with 3-year follow-up

BACKGROUND

Duchenne muscular dystrophy (DMD) is a hereditary neuromuscular disorder characterized by severe, progressive muscle wasting. Viltolarsen, a formulation consisting of exon 53-skipping antisense oligonucleotides of the dystrophin gene, has been indicated for some patients with DMD. However, reports describing the efficacy and safety of viltolarsen treatment in patients with DMD, particularly those comparing patients receiving viltolarsen with age- and time-period-matched controls, are limited. This study aimed to confirm the safety and efficacy of viltolarsen treatment in patients with DMD.

METHODS

We retrospectively reviewed real-world data of patients with DMD aged 6-19 years who started viltolarsen treatment between July 2020 and February 2021 and compared them with age- and time-period-matched patients with DMD who did not receive viltolarsen.

RESULTS

Five patients received viltolarsen treatment for over 3 years. Three of the four patients who received viltolarsen once weekly maintained motor function, while one ambulatory patient showed remarkably slow motor function decline. Conversely, eight of nine patients who did not receive viltolarsen and one patient who underwent intermittent viltolarsen treatment showed motor function deterioration. Two patients showed significant treatment-related adverse events, namely swelling of the dorsal surface of the right hand due to extravasation of viltolarsen in one patient and axillary lymph node enlargement due to frequent intravenous infusion in another patient. None of the patients discontinued viltolarsen.

CONCLUSIONS

Viltolarsen was a safe and effective treatment for patients with DMD, and the findings highlighted the importance of once-weekly and uninterrupted viltolarsen treatment. The distinct safety and efficacy of viltolarsen require further investigation using a large number of cases and a long follow-up period.

Profound cellular defects attribute to muscular pathogenesis in the rhesus monkey model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disease caused by mutations in the DMD gene. Muscle fibers rely on the coordination of multiple cell types for repair and regenerative capacity. To elucidate the cellular and molecular changes in these cell types under pathologic conditions, we generated a rhesus monkey model for DMD that displays progressive muscle deterioration and impaired motor function, mirroring human conditions. By leveraging these DMD monkeys, we analyzed freshly isolated muscle tissues using single-cell RNA sequencing (scRNA-seq). Our analysis revealed changes in immune cell landscape, a reversion of lineage progressing directions in fibrotic fibro-adipogenic progenitors (FAPs), and TGF-β resistance in FAPs and muscle stem cells (MuSCs). Furthermore, MuSCs displayed cell-intrinsic defects, leading to differentiation deficiencies. Our study provides important insights into the pathogenesis of DMD, offering a valuable model and dataset for further exploration of the underlying mechanisms, and serves as a suitable platform for developing and evaluating therapeutic interventions.

Determination of qPCR reference genes suitable for normalizing gene expression in a novel model of Duchenne muscular dystrophy, the D2-mdx mouse

Duchenne muscular dystrophy (DMD) is a X-linked neuromuscular disorder arising from mutations in the dystrophin gene, leading to a progressive muscle wasting and disability. Currently there is no universal therapy, and there is thus a strong interest in preclinical studies for finding novel treatments. The most widely used and characterized mouse model for DMD is the C57BL/10ScSn-Dmdmdx/J (BL10-mdx), but this model exhibits mild pathology and does not replicate key features of human disease. The D2.B10-Dmdmdx/J (D2-mdx) mouse is a more recent model which seems to better mimics the complex human DMD phenotype. However, the D2-mdx mouse remains less extensively characterised than its BL10-mdx counterpart. Quantitative PCR analysis of gene expression is an important tool to monitor disease progression and evaluate therapeutic efficacy, but measurements must be normalised to stably expressed reference genes, which should ideally be determined and validated empirically. We examined gene expression in the gastrocnemius (GC), diaphragm (DIA) and heart in the D2-mdx mouse, the BL10-mdx mouse, and appropriate strain-matched wild-type controls (D2-wt and BL10-wt), from 4 to 52 weeks of age, using a large panel of candidate references (ACTB, AP3D1, CSNK2A2, GAPDH, HPRT1, PAK1IP1, RPL13A, SDHA, and in the heart, also HTATSF1 and HMBS). Data was analyzed using GeNorm, Bestkeeper, deltaCt and Normfinder algorithms to identify stable references under multiple possible scenarios. We show that CSNK2A2, AP3D1 and ACTB represent strong universal reference genes in both GC and DIA, regardless of age, muscle type, strain and genotype, while HTATSF1 and SDHA are optimal for the heart. GAPDH, HPRT1 and RPL13A were conversely revealed to be poor references, showing tissue-, age- or disease-specific changes in expression. Our results illustrate the importance of determining appropriate reference genes for specific comparative scenarios, but also reconfirm that universal panels can nevertheless be identified for normalising gene expression studies in even complex pathological states.

Lipin1 as a therapeutic target for respiratory insufficiency of duchenne muscular dystrophy

In Duchenne muscular dystrophy (DMD), diaphragm muscle dysfunction results in respiratory insufficiency which is a leading cause of death in patients. Mutations to the dystrophin gene result in myocyte membrane instability, contributing to the structural deterioration of the diaphragm muscle tissues. With previous works suggesting the importance of lipin1 for maintaining skeletal muscle membrane integrity, we explored the roles of lipin1 in the dystrophic diaphragm. We found that the protein expression levels of lipin1 were reduced by 60% in the dystrophic diaphragm. While further knockdown of lipin1 in the dystrophic diaphragm leads to increased necroptosis, restoration of lipin1 in the dystrophic diaphragm results in reduced inflammation and fibrosis, decreased myofiber death, and improved respiratory function. Our results demonstrated that lipin1 restoration improved respiratory function by enhancing membrane integrity and suggested that lipin1 could be a potential therapeutic target for preventing respiratory insufficiency and respiratory failure in DMD. Continued investigation is required to better understand the mechanisms behind these findings, and to determine the role of lipin1 in maintaining muscle membrane stability.

On RNA-programmable gene modulation as a versatile set of principles targeting muscular dystrophies

The repurposing of RNA-programmable CRISPR systems from genome editing into epigenome editing tools is gaining pace, including in research and development efforts directed at tackling human disorders. This momentum stems from the increasing knowledge regarding the epigenetic factors and networks underlying cell physiology and disease etiology and from the growing realization that genome editing principles involving chromosomal breaks generated by programmable nucleases are prone to unpredictable genetic changes and outcomes. Hence, engineered CRISPR systems are serving as versatile DNA-targeting scaffolds for heterologous and synthetic effector domains that, via locally recruiting transcription factors and chromatin remodeling complexes, seek interfering with loss-of-function and gain-of-function processes underlying recessive and dominant disorders, respectively. Here, after providing an overview about epigenetic drugs and CRISPR-Cas-based activation and interference platforms, we cover the testing of these platforms in the context of molecular therapies for muscular dystrophies. Finally, we examine attributes, obstacles, and deployment opportunities for CRISPR-based epigenetic modulating technologies.

Duchenne Muscular Dystrophy in Two Half-Brothers Due to Inherited 306 Kb Inverted Insertion of 10p15.1 into Intron 44 of the Dp427m Transcript of the DMD Gene

Duchenne muscular dystrophy (DMD) is a rare genetic disorder caused by the absence of a fully functional dystrophin protein in myocytes. In skeletal muscle, the lack of dystrophin ultimately results in muscle wasting and the replacement of myocytes with fatty or fibrous tissues. In the heart, cardiomyocytes eventually fail and cause fatal cardiomyopathy. We present a case of a male patient and his younger brother with a maternally inherited inverted insertion of approximately 306 kb of chromosome 10 in the deep intronic region between exons 44 and 45 of the DMD gene, leading to Duchenne muscular dystrophy. Chromosomal microarray, comprehensive muscular dystrophy genetic testing, and whole exome sequencing were negative. Targeted transcriptome RNA sequencing at an external lab showed no aberrant splicing. Research whole genome sequencing identified the copy number gain and insertion. Subsequent reanalysis of the RNA sequencing data showed possible aberrant splicing involving DMD exons 44-45, and research RNA sequencing revealed a fusion between the DMD gene on the minus strand of chromosome X and the PFKFB3 gene on the plus strand of chromosome 10. We demonstrate that whole genome sequencing can be valuable for identifying intronic events in the DMD gene previously undetected or not reported by traditional clinical testing.

Sirt6 Mono-ADP-Ribosylates YY1 to Promote Dystrophin Expression for Neuromuscular Transmission

The degeneration of the neuromuscular junction (NMJ) and the decline in motor function are common features of aging, but the underlying mechanisms have remained largely unclear. This study reveals that Sirt6 is reduced in aged mouse muscles. Ablation of Sirt6 in skeletal muscle causes a reduction of Dystrophin levels, resulting in premature NMJ degeneration, compromised neuromuscular transmission, and a deterioration in motor performance. Mechanistic studies show that Sirt6 negatively regulates the stability of the Dystrophin repressor YY1 (Yin Yang 1). Specifically, Sirt6 mono-ADP-ribosylates YY1, causing its disassociation from the Dystrophin promoter and allowing YY1 to bind to the SMURF2 E3 ligase, leading to its degradation. Importantly, supplementation with nicotinamide mononucleotide (NMN) enhances the mono-ADP-ribosylation of YY1 and effectively delays NMJ degeneration and the decline in motor function in elderly mice. These findings provide valuable insights into the intricate mechanisms underlying NMJ degeneration during aging. Targeting Sirt6 could be a potential therapeutic approach to mitigate the detrimental effects on NMJ degeneration and improve motor function in the elderly population.

The emerging roles of necroptosis in skeletal muscle health and disease

Necroptosis is a regulated form of cell death with implications in various physiological and pathological processes in multiple tissues. However, the relevant findings from post-mitotic tissues, such as skeletal muscle, are scarce. This review summarizes the potential contributions of necroptosis to skeletal muscle health and diseases. It first discusses the physiological roles of necroptosis in muscle regeneration and development. It then summarizes the contributions of necroptosis to the pathogenesis of multiple muscle diseases, including muscular dystrophies, inflammatory myopathies, cachexia, and neuromuscular disorders. Lastly, it unravels the gaps in our understanding and therapeutic challenges of inhibiting necroptosis as a potential intervention for muscle diseases. Specifically, the findings from the transgenic animal models and the use of pharmacological inhibitors of necroptosis are discussed with relevance to improving the structure and/or function of skeletal muscle in various diseases. Recent developments from experimental animal models and clinical data are presented to discuss the roles of necroptosis in skeletal muscle health and diseases.

Ultrasound attenuation imaging as a strategy for evaluation of early and late ambulatory functions in Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is a genetic neuromuscular disorder that leads to mobility loss and life-threatening cardiac or respiratory complications. Quantitative ultrasound (QUS) envelope statistics imaging, which characterizes fat infiltration and fibrosis in muscles, has been extensively used for DMD evaluations.

PURPOSE

Notably, changes in muscle microstructures also result in acoustic attenuation, potentially serving as another crucial imaging biomarker for DMD. Expanding upon the reference frequency method (RFM), this study contributes to the field by introducing the robust RFM (RRFM) as a novel approach for ultrasound attenuation imaging in DMD.

METHODS

The RRFM algorithm was developed using an iterative reweighted least squares technique. We conducted standard phantom measurements with a clinical ultrasound system equipped with a linear array transducer to assess the improvement in attenuation estimation bias by RRFM. Additionally, 161 DMD patients, included in both a validation dataset (n = 130) and a testing dataset (n = 31), underwent ultrasound scanning of the gastrocnemius for RRFM-based attenuation imaging. The diagnostic performances for ambulatory functions and discrimination between early and late ambulatory stages were evaluated and compared with those of QUS envelope statistics imaging (involving Nakagami distribution, homodyned K distribution, and entropy values) using the area under the receiver operating characteristic curve (AUROC).

RESULTS

The results indicated that the RRFM method more closely matched the actual attenuation properties of the phantom, reducing measurement bias by 50% compared to conventional RFM. The AUROCs for RRFM-based attenuation imaging, used to discriminate between early and late ambulatory stages, were 0.88 and 0.92 for the validation and testing datasets, respectively. These performances significantly surpassed those of QUS envelope statistics imaging (p < 0.05).

CONCLUSIONS

Ultrasound attenuation imaging employing RRFM may serve as a sensitive tool for evaluating the progression of ambulatory function deterioration, offering substantial potential for the health management and follow-up care of DMD patients.