Systemic AAV Micro-dystrophin Gene Therapy for Duchenne Muscular Dystrophy

AAV-mediated inner ear gene delivery triggers mild host immune responses in the mammalian inner ear

Hearing loss is a common disability affecting the world's population. Currently, its treatment options are limited. Adeno-associated virus (AAV)-mediated inner ear gene therapy has shown great promise as a treatment for hereditary hearing loss. However, the host immune responses to AAV-mediated gene therapy in the mammalian inner ear is not well understood. In this study, two serotypes of AAV vectors were injected individually into the mouse inner ear to evaluate the host innate and adaptive immune responses up to 1 month after inner ear gene delivery. Our results suggest that the host innate and adaptive immune responses to AAV-mediated inner ear gene delivery are limited and mild, which is favorable for its clinical translation.

Single-cut gene therapy in a one-step generated rhesus monkey model of Duchenne muscular dystrophy

Progress in Duchenne muscular dystrophy (DMD) treatment is hindered by the lack of animal models that closely replicate human pathology and enable the evaluation of therapy efficacy and safety based on these models. To address this need, we optimize the generation of nonhuman primate DMD models, reducing the development time from 6 to 7 years to under 1 year, enabling the rapid generation of DMD monkey models. These models closely mimic human DMD pathology and motor dysfunction, making them suitable for testing gene therapies. Using these models, we develop a single-cut gene therapy strategy that can be directly applied to humans. This treatment restores dystrophin expression, improves pathological features, and enhances motor abilities in DMD monkeys, with effects lasting at least 1.5 years. In conclusion, we achieve the rapid generation of DMD monkey models and demonstrate that our gene therapy approach is effective and holds significant potential for clinical application.

The road toward AAV-mediated gene therapy of Duchenne muscular dystrophy

Forty years after the dystrophin gene was cloned, significant progress has been made in developing gene therapy approaches for Duchenne muscular dystrophy (DMD). The disorder has presented numerous challenges, including the enormous size of the gene (2.2 MB), the need to target muscles body wide, and immunogenic issues against both vectors and dystrophin. Among human genetic disorders, DMD is relatively common, and the genetics are complicated since one-third of all cases arise from a spontaneous new mutation, resulting in thousands of independent lesions throughout the locus. Many approaches have been pursued in the goal of finding an effective therapy, including exon skipping, nonsense codon suppression, upregulation of surrogate genes, gene replacement, and gene editing. Here, we focus specifically on methods using AAV vectors, as these approaches have been tested in numerous clinical trials and are able to target muscles systemically. We discuss early advances to understand the structure of dystrophin, which are crucial for the design of effective DMD gene therapies. Included is a summary of efforts to deliver micro-, mini-, and full-length dystrophins to muscles. Finally, we review current approaches to adapt gene editing to the enormous DMD gene with prospects for improved therapies using all these methods.

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.

Research Status and Applications of Adeno-Associated Virus

Adeno-associated virus (AAV) has emerged as a powerful and effective tool for the delivery of exogenous genes into various cells or tissues. To improve the gene delivery efficiency, as well as the safety and specificity of AAV's cell-targeting capabilities, extensive investigations have been conducted into its molecular biological characteristics, including capsid structure, cellular tropism, and the mechanisms underlying its entry, replication, DNA packaging, and capsid assembly. Significant differences exist between human and non-human primate AAVs regarding tissue targeting and transduction efficiency. These differences are primarily attributed to the amino acid sequences of AAV capsid proteins, the structural characteristics of these proteins, and the interactions of AAV with surface factors on host cells, such as cell surface receptors, signaling molecules, and associated proteins. This review primarily focuses on several key aspects of AAV, including its genome, coat proteins and their structures, genome replication, virus assembly, and the role of helper viruses. Additionally, it examines the utilization of recombinant adeno-associated viruses (rAAV), detailing their production methods, mechanisms of cell entry and trafficking, and various serotypes. The review further interprets the role of rAAV by analyzing its current applications in research and therapy.

Preclinical development of genome editing to treat Duchenne muscular dystrophy by exon skipping

Duchenne muscular dystrophy (DMD) is caused by loss-of-function mutations to the gene encoding dystrophin. Restoring the reading frame of dystrophin by removing internal out-of-frame exons may address symptoms of DMD. Therefore, the principle of exon skipping has been at the center stage in drug development for Duchenne muscular dystrophy (DMD) over the past two decades. Antisense oligonucleotides (AONs) have proven effective in modulating splicing sites for exon skipping, resulting in the FDA approval of several drugs using this technique in recent years. However, due to the temporary nature of AON, researchers are actively exploring genome editing as a potential long-term, single-administration treatment. The advancements in genome-editing technology over the last decade have boosted this transition. While no clinical trials for exon skipping in DMD via genome editing have been conducted as of this writing, preclinical studies show encouraging results. This review describes the preclinical landscape of genome editing for exon skipping in DMD treatment. Along with highlighting the adaptability of genome editing in exon skipping, this review also describes delivery challenges and outlines future research directions that could set a new stage for enhanced therapeutic development in DMD.

Systemic delivery of AAV5, AAV8, and AAV9 packaging a C5-12-microdystrophin-FLAG expression cassette in non-human primates

Safely achieving therapeutic expression levels with adeno-associated virus (AAV) gene therapy is a significant challenge for treating the large muscle mass in humans. Non-human primates (NHPs) provide a more accurate assessment of the feasibility of achieving an effective and safe dose than rodents. Here, we compared a single systemic administration of AAV5, AAV8, or AAV9 in NHPs, each packaging the C5-12-microdystrophin-FLAG expression cassette. At 1 month post-dose, we compared tissue vector genomes, mRNA, and microdystrophin-FLAG protein levels by meso-scale discovery-enzyme-linked immunosorbent assay, liquid chromatography-mass spectrometry, and immunofluorescence. The C5-12 promoter was highly selective for heart and skeletal muscles, when compared to off-target tissues such as peripheral blood mononuclear cells, lung, liver, and kidney. AAV8 led to higher levels of microdystrophin-FLAG mRNA and protein in the cardiac ventricles and skeletal muscles when compared to AAV5 or AAV9. The AAV8-microdystrophin-FLAG led to ∼20% of wild-type NHP dystrophin protein expression levels and was located on the sarcolemma of ∼40% of skeletal muscles fibers and ∼15% of left ventricular cardiomyocytes. Hematology, serum chemistry, and pathology were unremarkable. Thus, a systemic dose of ∼1.18 × 1014 vector genomes/kg AAV8 is predicted to be safe and efficacious for treating Duchenne muscular dystrophy (DMD) but has significant room for improvement.

Transcriptional adaptation upregulates utrophin in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a muscle-degenerating disease caused by mutations in the DMD gene, which encodes the dystrophin protein1,2. Utrophin (UTRN), the genetic and functional paralogue of DMD, is upregulated in some DMD patients3-5. To further investigate this UTRN upregulation, we first developed an inducible messenger RNA (mRNA) degradation system for DMD by introducing a premature termination codon (PTC) in one of its alternatively spliced exons. Inclusion of the PTC-containing exon triggers DMD mutant mRNA decay and UTRN upregulation. Notably, blocking nonsense-mediated mRNA decay results in the reversal of UTRN upregulation, whereas overexpressing DMD does not. Furthermore, overexpressing DMDPTC minigenes in wild-type cells causes UTRN upregulation, as does a wild-type DMD minigene containing a self-cleaving ribozyme. To place these findings in a therapeutic context, we used splice-switching antisense oligonucleotides (ASOs) to induce the skipping of out-of-frame exons of DMD, aiming to introduce PTCs. We found that these ASOs cause UTRN upregulation. In addition, when using an ASO to restore the DMD reading frame in myotubes derived from a DMDΔE52 patient, an actual DMD treatment, UTRN upregulation was reduced. Altogether, these results indicate that an mRNA decay-based mechanism called transcriptional adaptation6-8 plays a key role in UTRN upregulation in DMDPTC patients, and they highlight an unexplored therapeutic application of ASOs, as well as ribozymes, in inducing genetic compensation via transcriptional adaptation.

A brief guide for gene delivery to the brain using adeno-associated viral vectors

The advent of recombinant adeno-associated viral (rAAV) vector-mediated gene delivery has accelerated the comprehensive analysis and manipulation of the nervous system owing to its ability to regulate gene expression in a spatiotemporal manner, thereby facilitating the study of brain physiology and the investigation of the pathophysiology of neurological disorders. Here, we provide a concise guide to stereotaxic gene delivery into the mouse brain using rAAV vectors. Key considerations for designing a customized rAAV vector are discussed, along with an overview of the surgical procedures of intracranial stereotaxic injection. This article aims to assist neuroscientists in establishing experimental setups for genetic manipulation in the mouse brain.

Superparamagnetic nanoparticles as potential drug delivery systems for the treatment of Duchenne muscular dystrophy

This study aims to use superparamagnetic iron oxide nanoparticles (SPIONs), specifically magnetite (Fe3O4), to deliver deflazacort (DFZ) and ibuprofen (IBU) to Duchenne muscular dystrophy-affected (DMD) mouse muscles using an external magnetic field. The SPIONs are synthesized by the co-precipitation method, and their surfaces are functionalized with L-cysteine to anchor the drugs, considering that the cysteine on the surface of the SPIONs in the solid state dimerizes to form the cystine molecule, creating the Fe3O4-(Cys)2-DFZ and Fe3O4-(Cys)2-IBU systems for in vivo tests. The Fe3O4 nanoparticles (NPs) were characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), and magnetic measurements. The results show that the SPIONs have an average crystallite size of about 8 nm in the solid state and a hydrodynamic size of about 120 nm, which is suitable for biological applications in aqueous dispersion. The nanoparticles exhibit superparamagnetic behavior at room temperature and spherical-close morphology. In addition, vibrational modes characteristic of the functional groups of the molecules anchored to the surface of the SPIONs are identified. Data from blood tests of mdx mice after seven consecutive days of treatment with nanoparticles confirm the non-toxic nature of the system and show an improvement in DMD, with normal levels of liver and kidney enzymes and a decrease in creatine kinase protein.

Adeno-Associated Virus Vectors: Principles, Practices, and Prospects in Gene Therapy

Gene therapy offers promising potential as an efficacious and long-lasting therapeutic option for genetic conditions, by correcting defective mutations using engineered vectors to deliver genetic material to host cells. Among these vectors, adeno-associated viruses (AAVs) stand out for their efficiency, versatility, and safety, making them one of the leading platforms in gene therapy. The enormous potential of AAVs has been demonstrated through their use in over 225 clinical trials and the FDA's approval of six AAV-based gene therapy products, positioning these vectors at the forefront of the field. This review highlights the evolution and current applications of AAVs in gene therapy, focusing on their clinical successes, ongoing developments, and the manufacturing processes required for the rapid commercial growth anticipated in the AAV therapy market. It also discusses the broader implications of these advancements for future therapeutic strategies targeting more complex and multi-systemic conditions and biological processes such as aging. Finally, we explore some of the major challenges currently confronting the field.

The latest developments in synthetic approaches to Duchenne muscular dystrophy

INTRODUCTION

Duchenne muscular dystrophy (DMD) is a rare X-linked genetic disorder caused by mutations in the dystrophin gene, leading to an almost complete absence of dystrophin, which is essential for muscle cell structure and function. This resulting muscle deterioration and fibrosis, eventually causes respiratory failure and cardiomyopathy. While there is currently no cure, existing therapies aim to prolong survival and alleviate symptoms.

AREAS COVERED

This paper reviews current and emerging therapies for DMD, focusing on their safety and efficacy. Although corticosteroids remain the standard treatment, newly approved drugs such as exon-skipping therapies, vamorolone, delandistrogene moxeparvovec, and givinostat provide new treatment options. Additionally, future therapies, including gene therapy, stem cell treatments, and anti-fibrotic agents, show promise for clinical application.

EXPERT OPINION

Advancements in DMD treatments have expanded patient options. While gene therapy offers potential for correcting the genetic defect and alleviating symptoms, corticosteroids remain the most cost-effective and well-researched treatment. This is partly due to the lack of compelling long-term safety and efficacy data for gene therapies. The accelerated FDA review process has enabled faster approval of new medications; however many have provided minimal clinical benefit to patients. Despite these challenges, continued drug development and innovative research offer hope to patients.

Biological biomarkers in muscle diseases relevant for follow-up and evaluation of treatment

Muscle diseases cover a diverse group of disorders that, in most cases, are hereditary. The rarity of the individual muscle diseases provides a challenge for researchers when wanting to establish natural history of the conditions and when trying to develop diagnostic tools, therapies, and outcome measures to evaluate disease progression. With emerging molecular therapies in many genetic muscle diseases, as well as biological therapies for the immune-mediated diseases, biological biomarkers play an important role in both drug development and evaluation. In this review, we focus on the role of biological biomarkers in muscle diseases and discuss their utility as surrogate end points in therapeutic trials. We categorize these as either (i) disease unspecific markers; (ii) markers of specific pathways that may be used for more than one disease; or (iii) disease-specific markers. We also propose that evaluation of specific therapeutic interventions benefits from biological markers that match the intervention.

Gene therapy for genetic diseases: challenges and future directions

Genetic diseases constitute the majority of rare human diseases, resulting from abnormalities in an individual's genetic composition. Traditional treatments offer limited relief for these challenging conditions. In contrast, the rapid advancement of gene therapy presents significant advantages by directly addressing the underlying causes of genetic diseases, thereby providing the potential for precision treatment and the possibility of curing these disorders. This review aims to delineate the mechanisms and outcomes of current gene therapy approaches in clinical applications across various genetic diseases affecting different body systems. Additionally, genetic muscular disorders will be examined as a case study to investigate innovative strategies of novel therapeutic approaches, including gene replacement, gene suppression, gene supplementation, and gene editing, along with their associated advantages and limitations at both clinical and preclinical levels. Finally, this review emphasizes the existing challenges of gene therapy, such as vector packaging limitations, immunotoxicity, therapy specificity, and the subcellular localization and immunogenicity of therapeutic cargos, while discussing potential optimization directions for future research. Achieving delivery specificity, as well as long-term effectiveness and safety, will be crucial for the future development of gene therapies targeting genetic diseases.

Hydroxyapatite nanoparticle mediated delivery of full length dystrophin gene as a potential therapeutic for the treatment of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a severe genetic disorder characterized by progressive muscle degeneration, primarily affecting young males. In this study, we investigated arginine-modified hydroxyapatite nanoparticles (R-HAp) as a novel non-viral vector for DMD gene therapy, particularly for delivering the large 18.8 kb dystrophin gene. Addressing the limitations of traditional adeno-associated viral vectors, R-HAp demonstrated efficient binding and delivery of the dystrophin plasmid to DMD patient-derived skeletal muscle cells. Using confocal imaging and RT-PCR analysis, our results showed effective gene delivery and expression in both mouse myotubes and patient-derived cells, with sustained expression evident up to 5 days post transfection. The patient-derived myotubes also showed dystrophin protein production 7 days post transfection. These findings suggest R-HAp nanoparticles as a promising and cost-effective alternative for DMD treatment, highlighting their potential for overcoming current gene therapy challenges.

Delivery of genetic medicines for muscular dystrophies

Muscular dystrophies are a group of heterogenic disorders characterized by progressive muscle weakness, the most common of them being Duchenne muscular dystrophy (DMD). Muscular dystrophies are caused by mutations in over 50 distinct genes, and many of them are caused by different genetic mechanisms. Currently, none of these diseases have a cure. However, in recent years, significant progress has been made to correct the underlying genetic cause. The clinical development of adeno-associated viral vector-based therapies has simultaneously produced excitement and disappointment in the research community due to the moderate effect, making it clear that new methods of muscle delivery have to be created. Herein, we review the main characteristics of major muscular dystrophies and outline various muscle-targeted delivery methods being explored for genetic medicines.

Myoblast-derived ADAMTS-like 2 promotes skeletal muscle regeneration after injury

Skeletal muscle regeneration and functional recovery after minor injuries requires the activation of muscle-resident myogenic muscle stem cells (i.e. satellite cells) and their subsequent differentiation into myoblasts, myocytes, and ultimately myofibers. We recently identified secreted ADAMTS-like 2 (ADAMTSL2) as a pro-myogenic regulator of muscle development, where it promoted myoblast differentiation. Since myoblast differentiation is a key process in skeletal muscle regeneration, we here examined the role of ADAMTSL2 during muscle regeneration after BaCl2 injury. Specifically, we found that muscle regeneration was delayed after ablation of ADAMTSL2 in myogenic precursor cells and accelerated following injection of pro-myogenic ADAMTSL2 protein domains. Mechanistically, ADAMTSL2 regulated the number of committed myoblasts, which are the precursors for myocytes and regenerating myofibers. Collectively, our data support a role for myoblast-derived ADAMTSL2 as a positive regulator of muscle regeneration and provide a proof-of-concept for potential therapeutic applications.

Striking Cardioprotective Effects of an Adiponectin Receptor Agonist in an Aged Mouse Model of Duchenne Muscular Dystrophy

Adiponectin (ApN) is a hormone with potent effects on various tissues. We previously demonstrated its ability to counteract Duchenne muscular dystrophy (DMD), a severe muscle disorder. However, its therapeutic use is limited. AdipoRon, an orally active ApN mimic, offers a promising alternative. While cardiomyopathy is the primary cause of mortality in DMD, the effects of ApN or AdipoRon on dystrophic hearts have not been investigated. Our recent findings demonstrated the significant protective effects of AdipoRon on dystrophic skeletal muscle. In this study, we investigated whether AdipoRon effects could be extended to dystrophic hearts. As cardiomyopathy develops late in mdx mice (DMD mouse model), 14-month-old mdx mice were orally treated for two months with AdipoRon at a dose of 50 mg/kg/day and then compared with untreated mdx and wild-type (WT) controls. Echocardiography revealed cardiac dysfunction and ventricular hypertrophy in mdx mice, which were fully reversed in AdipoRon-treated mice. AdipoRon also reduced markers of cardiac inflammation, oxidative stress, hypertrophy, and fibrosis while enhancing mitochondrial biogenesis via ApN receptor-1 and CAMKK2/AMPK pathways. Remarkably, treated mice also showed improved skeletal muscle strength and endurance. By offering protection to both cardiac and skeletal muscles, AdipoRon holds potential as a comprehensive therapeutic strategy for better managing DMD.

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.

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.

Cardiomyopathy: pathogenesis and therapeutic interventions

Cardiomyopathy is a group of disease characterized by structural and functional damage to the myocardium. The etiologies of cardiomyopathies are diverse, spanning from genetic mutations impacting fundamental myocardial functions to systemic disorders that result in widespread cardiac damage. Many specific gene mutations cause primary cardiomyopathy. Environmental factors and metabolic disorders may also lead to the occurrence of cardiomyopathy. This review provides an in-depth analysis of the current understanding of the pathogenesis of various cardiomyopathies, highlighting the molecular and cellular mechanisms that contribute to their development and progression. The current therapeutic interventions for cardiomyopathies range from pharmacological interventions to mechanical support and heart transplantation. Gene therapy and cell therapy, propelled by ongoing advancements in overarching strategies and methodologies, has also emerged as a pivotal clinical intervention for a variety of diseases. The increasing number of causal gene of cardiomyopathies have been identified in recent studies. Therefore, gene therapy targeting causal genes holds promise in offering therapeutic advantages to individuals diagnosed with cardiomyopathies. Acting as a more precise approach to gene therapy, they are gradually emerging as a substitute for traditional gene therapy. This article reviews pathogenesis and therapeutic interventions for different cardiomyopathies.

Histone modifications in Duchenne muscular dystrophy: pathogenesis insights and therapeutic implications

Duchenne muscular dystrophy (DMD) is a commonly encountered genetic ailment marked by loss-of-function mutations in the Dystrophin gene, ultimately resulting in progressive debilitation of skeletal muscle. The investigation into the pathogenesis of DMD has increasingly converged on the role of histone modifications within the broader context of epigenetic regulation. These modifications, including histone acetylation, methylation and phosphorylation, are catalysed by specific enzymes and play a critical role in gene expression. This article provides an overview of the histone modifications occurring in DMD and analyses the research progress and potential of different types of histone modifications in DMD due to changes in cellular signalling for muscle regeneration, to provide new insights into diagnostic and therapeutic options for DMD.

Developing Advanced Chimeric Cell Therapy for Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy (DMD) is a lethal, X-linked disorder leading to muscle degeneration and premature death due to cardiopulmonary complications. Currently, there is no cure for DMD. We previously confirmed the efficacy of human Dystrophin-Expressing Chimeric (DEC) cells created via the fusion of myoblasts from normal and DMD-affected donors. The current study aimed to optimize the development of DEC therapy via the polyethylene glycol (PEG)-mediated fusion protocol of human myoblasts derived from normal, unrelated donors. The optimization of cell fusion assessed different factors influencing fusion efficacy, including myoblast passage number, the efficacy of PKH myoblast staining, the ratio of the single-stained myoblasts in the MIX, and PEG administration time. Additionally, the effect of PEG fusion procedure on cell viability was assessed. A correlation was found between the number of cells used for PKH staining and staining efficacy. Furthermore, the ratio of single-stained myoblasts in the MIX and PEG administration time correlated with fusion efficacy. There was no correlation found between the myoblast passage number and fusion efficacy. This study successfully optimized the myoblast fusion protocol for creation of human DEC cells, introducing DEC as a new Advanced Therapy Medicinal Product (ATMP) for DMD patients.

Deletion of exons 45 to 55 in the DMD gene: from the therapeutic perspective to the in vitro model

BACKGROUND

Gene editing therapies in development for correcting out-of-frame DMD mutations in Duchenne muscular dystrophy aim to replicate benign spontaneous deletions. Deletion of 45-55 DMD exons (del45-55) was described in asymptomatic subjects, but recently serious skeletal and cardiac complications have been reported. Uncovering why a single mutation like del45-55 is able to induce diverse phenotypes and grades of severity may impact the strategies of emerging therapies. Cellular models are essential for this purpose, but their availability is compromised by scarce muscle biopsies.

METHODS

We introduced, as a proof-of-concept, using CRISPR-Cas9 edition, a del45-55 mimicking the intronic breakpoints harboured by a subset of patients of this form of dystrophinopathy (designing specific gRNAs), into a Duchenne patient's cell line. The edited cell line was characterized evaluating the dystrophin expression and the myogenic status.

RESULTS

Dystrophin expression was restored, and the myogenic defects were ameliorated in the edited myoblasts harbouring a specific del45-55. Besides confirming the potential of CRISPR-Cas9 to create tailored mutations (despite the low cleavage efficiency of our gRNAs) as a useful approach to generate in vitro models, we also generated an immortalized myoblast line derived from a patient with a specific del45-55.

CONCLUSIONS

Overall, we provide helpful resources to deepen into unknown factors responsible for DMD-pathophysiology.

Pig models for translational Duchenne muscular dystrophy research

Duchenne muscular dystrophy (DMD) is caused by mutations in the X-linked DMD gene, resulting in the absence of dystrophin, progressive muscle degeneration, and heart failure. Genetically tailored pig models resembling human DMD mutations recapitulate the biochemical, clinical, and pathological hallmarks of DMD with an accelerated disease progression compared to human patients. DMD pigs have been used to evaluate therapeutic concepts such as gene editing to reframe a disrupted DMD reading frame or the delivery of artificial chromosome vectors carrying the complete DMD gene. Moreover, DMD pigs have been instrumental in validating new diagnostic modalities such as multispectral optoacoustic tomography (MSOT) for non-invasive monitoring of disease progression. DMD pigs may thus help to bridge the gap between proof-of-concept studies in cellular or rodent models and clinical studies in patients.

Protein overexpression by adeno-associated virus-based gene therapy products in cardiomyocytes induces endoplasmic reticulum stress and myocardial degeneration in mice

Gene therapy (GT) products created using adeno-associated virus (AAV) vectors tend to exhibit toxicity via immune reactions, but other mechanisms of toxicity remain incompletely understood. We examined the cardiotoxicity of an overexpressed transgenic protein. Male C57BL/6J mice were treated with a single intravenous dose of product X, an AAV-based GT product, at 2.6 × 1013 vg/kg. Necropsies were performed at 24 h, 7 days, and 14 days after dosing. Pathological examination and gene expression analysis were performed on the heart. Histopathologically, hypertrophy and vacuolar degeneration of cardiomyocytes and fibrosis were observed 14 days after dosing. Immunohistochemistry for endoplasmic reticulum (ER) stress-related proteins revealed increased positive reactions for glucose-regulated protein 78 and C/EBPR homologous protein in cardiomyocytes 7 days after dosing, without histopathological abnormalities. Fourteen days after dosing, some cardiomyocytes showed positivity for PKR-like endoplasmic reticulum kinase and activating transcription factor 4 expression. Ultrastructurally, increases in the ER and cytosol were observed in cardiomyocytes 7 days after dosing, along with an increase in the number of Golgi apparatus compartments 14 days after dosing. The tissue concentration of the transgene product protein increased 7 days after dosing. Gene expression analysis showed upregulation of ER stress-related genes 7 days after dosing, suggesting activation of the PKR-like ER kinase pathway of the unfolded protein reaction (UPR). Thus, the cardiotoxicity induced by product X was considered to involve cell damage caused by the overexpression of the product protein accompanied by UPR. Marked UPR activation may also cause toxicity of AAV-based GT products.

High mobility group box 1 (HMGB1) is a potential disease biomarker in cell and mouse models of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a progressive muscle wasting disorder affecting 1:3500 male births and is associated with myofiber degeneration, regeneration, and inflammation. Glucocorticoid treatments have been the standard of care due to immunomodulatory/immunosuppressive properties but novel genetic approaches, including exon skipping and gene replacement therapy, are currently being developed. The identification of additional biomarkers to assess DMD-related inflammatory responses and the potential efficacy of these therapeutic approaches are thus of critical importance. The current study uses RNA sequencing of skeletal muscle from two mdx mouse models to identify high mobility group box 1 (HMGB1) as a candidate biomarker potentially contributing to DMD-related inflammation. HMGB1 protein content was increased in a human iPSC-derived skeletal myocyte model of DMD and microdystrophin treatment decreased HMGB1 back to control levels. In vivo, HMGB1 protein levels were increased in vehicle treated B10-mdx skeletal muscle compared to B10-WT and significantly decreased in B10-mdx animals treated with adeno-associated virus (AAV)-microdystrophin. However, HMGB1 protein levels were not increased in D2-mdx skeletal muscle compared to D2-WT, demonstrating a strain-specific difference in DMD-related immunopathology.

An engineered AAV targeting integrin alpha V beta 6 presents improved myotropism across species

Current adeno-associated virus (AAV) gene therapy using nature-derived AAVs is limited by non-optimal tissue targeting. In the treatment of muscular diseases (MD), high doses are often required but can lead to severe adverse effects. Here, we rationally design an AAV capsid that specifically targets skeletal muscle to lower treatment doses. We computationally integrate binding motifs of human integrin alphaV beta6, a skeletal muscle receptor, into a liver-detargeting capsid. Designed AAVs show higher productivity and superior muscle transduction compared to their parent. One variant, LICA1, demonstrates comparable muscle transduction to other myotropic AAVs with reduced liver targeting. LICA1's myotropic properties are observed across species, including non-human primate. Consequently, LICA1, but not AAV9, effectively delivers therapeutic transgenes and improved muscle functionality in two mouse MD models (male mice) at a low dose (5E12 vg/kg). These results underline the potential of our design method for AAV engineering and LICA1 variant for MD gene therapy.

Current developments of gene therapy in human diseases

Gene therapy has witnessed substantial advancements in recent years, becoming a constructive tactic for treating various human diseases. This review presents a comprehensive overview of these developments, with a focus on their diverse applications in different disease contexts. It explores the evolution of gene delivery systems, encompassing viral (like adeno-associated virus; AAV) and nonviral approaches, and evaluates their inherent strengths and limitations. Moreover, the review delves into the progress made in targeting specific tissues and cell types, spanning the eye, liver, muscles, and central nervous system, among others, using these gene technologies. This targeted approach is crucial in addressing a broad spectrum of genetic disorders, such as inherited lysosomal storage diseases, neurodegenerative disorders, and cardiovascular diseases. Recent clinical trials and successful outcomes in gene therapy, particularly those involving AAV and the clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated proteins, are highlighted, illuminating the transformative potentials of this approach in disease treatment. The review summarizes the current status of gene therapy, its prospects, and its capacity to significantly ameliorate patient outcomes and quality of life. By offering comprehensive analysis, this review provides invaluable insights for researchers, clinicians, and stakeholders, enriching the ongoing discourse on the trajectory of disease treatment.

Imaging of adeno-associated viral capsids for purposes of gene editing using CEST NMR/MRI

PURPOSE

Gene therapy using adeno-associated virus (AAV) vector-mediated gene delivery has undergone substantial growth in recent years with promising results in both preclinical and clinical studies, as well as emerging regulatory approval. However, the inability to quantify the efficacy of gene therapy from cellular delivery of gene-editing technology to specific functional outcomes is an obstacle for efficient development of gene therapy treatments. Building on prior works that used the CEST reporter gene lysine rich protein, we hypothesized that AAV viral capsids may generate endogenous CEST contrast from an abundance of surface lysine residues.

METHODS

NMR experiments were performed on isolated solutions of AAV serotypes 1-9 on a Bruker 800-MHz vertical scanner. In vitro experiments were performed for testing of CEST-NMR contrast of AAV2 capsids under varying pH, density, biological transduction stage, and across multiple serotypes and mixed biological media. Reverse transcriptase-polymerase chain reaction was used to quantify virus concentration. Subsequent experiments at 7 T optimized CEST saturation schemes for AAV contrast detection and detected AAV2 particles encapsulated in a biocompatible hydrogel administered in the hind limb of mice.

RESULTS

CEST-NMR experiments revealed CEST contrast up to 52% for AAV2 viral capsids between 0.6 and 0.8 ppm. CEST contrast generated by AAV2 demonstrated high levels of CEST contrast across a variety of chemical environments, concentrations, and saturation schemes. AAV2 CEST contrast displayed significant positive correlations with capsid density (R2 > 0.99, p < 0.001), pH (R2 = 0.97, p = 0.01), and viral titer per cell count (R2 = 0.92, p < 0.001). Transition to a preclinical field strength yielded up to 11.8% CEST contrast following optimization of saturation parameters. In vivo detection revealed statistically significant molecular contrast between viral and empty hydrogels using both mean values (4.67 ± 0.75% AAV2 vs. 3.47 ± 0.87% empty hydrogel, p = 0.02) and quantile analysis.

CONCLUSION

AAV2 viral capsids exhibit strong capacity as an endogenous CEST contrast agent and can potentially be used for monitoring and evaluation of AAV vector-mediated gene therapy protocols.

Exome sequencing revealed variants in SGCA and SIL1 genes underlying limb girdle muscular dystrophy and Marinesco-Sjögren syndrome patients

BACKGROUND

Inherited neuromuscular (NMD) and neurodegenerative diseases (NDD) belong to two distinct categories that disturb different components of the nervous system, leading to a variety of different symptoms and clinical manifestations. Both NMD and NDD are a heterogeneous group of genetic conditions. Genetic variations in the SGCA and SIL1 genes have been implicated in causing Limb Girdle Muscular Dystrophy (LGMD), a type of neuromuscular disorder, and Marinesco-Sjögren Syndrome (MSS) which is a neurodegenerative disorder.

METHODS

In the present study, we have investigated four patients presenting LGMD and five patients with MSS features. After collecting detailed clinical and family history, necessary laboratory investigations, including estimation of a skeletal muscle marker enzyme serum creatine kinase (CK), nerve conduction study (NCS), electromyography (EMG), echocardiography (Echo), Magnetic resonance imaging (MRI -brain), CT-brain and X-rays were performed. Whole exome followed by Sanger sequencing was employed to search for the disease-causing variants.

RESULTS

Physical examination in LGMD patients revealed poor muscle tone and facing difficulty in straightening up from the floor. Clinical history revealed frequent falls and strenuousness in climbing stairs. They started toe-walking in early childhood. Laboratory investigations confirmed elevated CK levels and abnormal NCS and EMG. The MSS patients showed abnormalities in gate and jerking movement, abnormal speech, and strabismus with cataract. MRI-brain showed cerebral atrophy in some MSS patients with elevated CK levels. Whole exome sequencing revealed a nonsense variant [c.C574T, p.(Arg192*)] in the SGCA gene and a frameshift [c.936dupG, p.(Leu313AlaFs*39)] in the SIL1 gene in LGMD and MSS patients, respectively.

CONCLUSION

Our study emphasizes the significance of integrating clinical and genetic analyses for precise diagnosis and tailored management strategies in inherited NMD and NDD disorders. To the best of our knowledge, this is the first study documenting SGCA and SIL1 recurrent variants in subcontinent populations with few rare clinical features. The recurrent mutations expanding the global understanding of the mutation's geographic and ethnic distribution and contributing valuable epidemiological data. The study will facilitate genetic counseling for families experiencing similar clinical features, both within Pakistani populations and in other regions.

Exploring lipin1 as a promising therapeutic target for the treatment of Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is a progressive and devastating muscle disease, resulting from the absence of dystrophin. This leads to cell membrane instability, susceptibility to contraction-induced muscle damage, subsequent muscle degeneration, and eventually disability and early death of patients. Currently, there is no cure for DMD. Our recent studies identified that lipin1 plays a critical role in maintaining myofiber stability and integrity. However, lipin1 gene expression levels are dramatically reduced in the skeletal muscles of DMD patients and mdx mice.

METHODS

To identify whether increased lipin1 expression could prevent dystrophic pathology, we employed unique muscle-specific mdx:lipin1 transgenic (mdx:lipin1Tg/0) mice in which lipin1 was restored in the dystrophic muscle of mdx mice, intramuscular gene delivery, as well as cell culture system.

RESULTS

We found that increased lipin1 expression suppressed muscle degeneration and inflammation, reduced fibrosis, strengthened membrane integrity, and resulted in improved muscle contractile and lengthening force, and muscle performance in mdx:lipin1Tg/0 compared to mdx mice. To confirm the role of lipin1 in dystrophic muscle, we then administered AAV1-lipin1 via intramuscular injection in mdx mice. Consistently, lipin1 restoration inhibited myofiber necroptosis and lessened muscle degeneration. Using a cell culture system, we further found that differentiated primary mdx myoblasts had elevated expression levels of necroptotic markers and medium creatine kinase (CK), which could be a result of sarcolemmal damage. Most importantly, increased lipin1 expression levels in differentiated myoblasts from mdx:lipin1Tg/0 mice substantially inhibited the elevation of necroptotic markers and medium CK levels.

CONCLUSIONS

Overall, our data suggest that lipin1 is a promising therapeutic target for the treatment of dystrophic muscles.

Molecular and Biochemical Therapeutic Strategies for Duchenne Muscular Dystrophy

Significant progress has been achieved in understanding Duchenne muscular dystrophy (DMD) mechanisms and developing treatments to slow disease progression. This review article thoroughly assesses primary and secondary DMD therapies, focusing on innovative modalities. The primary therapy addresses the genetic abnormality causing DMD, specifically the absence or reduced expression of dystrophin. Gene replacement therapies, such as exon skipping, readthrough, and gene editing technologies, show promise in restoring dystrophin expression. Adeno-associated viruses (AAVs), a recent advancement in viral vector-based gene therapies, have shown encouraging results in preclinical and clinical studies. Secondary therapies aim to maintain muscle function and improve quality of life by mitigating DMD symptoms and complications. Glucocorticoid drugs like prednisone and deflazacort have proven effective in slowing disease progression and delaying loss of ambulation. Supportive treatments targeting calcium dysregulation, histone deacetylase, and redox imbalance are also crucial for preserving overall health and function. Additionally, the review includes a detailed table of ongoing and approved clinical trials for DMD, exploring various therapeutic approaches such as gene therapies, exon skipping drugs, utrophin modulators, anti-inflammatory agents, and novel compounds. This highlights the dynamic research field and ongoing efforts to develop effective DMD treatments.

Elasticity and Thermal Stability are Key Determinants of Hearing Rescue by Mini-Protocadherin-15 Proteins

Protocadherin-15 is a core protein component of inner-ear hair-cell tip links pulling on transduction channels essential for hearing and balance. Protocadherin-15 defects can result in non-syndromic deafness or Usher syndrome type 1F (USH1F) with hearing loss, balance deficits, and progressive blindness. Three rationally engineered shortened versions of protocadherin-15 (mini-PCDH15s) amenable for gene therapy have been used to rescue function in USH1F mouse models. Two can successfully or partially rescue hearing, while another one fails. Here we show that despite varying levels of hearing rescue, all three mini-PCDH15 versions can rescue hair-cell mechanotransduction. Negative-stain electron microscopy shows that all three versions form dimers like the wild-type protein, while crystal structures of some engineered fragments show that these can properly fold and bind calcium ions essential for function. In contrast, simulations predict distinct elasticities and nano differential scanning fluorimetry shows differences in melting temperature measurements. Our data suggest that elasticity and thermal stability are key determinants of sustained hearing rescue by mini-PCDH15s.

Nanodysferlins support membrane repair and binding to TRIM72/MG53 but do not localize to t-tubules or stabilize Ca2+ signaling

Mutations in the DYSF gene, encoding the protein dysferlin, lead to several forms of muscular dystrophy. In healthy skeletal muscle, dysferlin concentrates in the transverse tubules and is involved in repairing the sarcolemma and stabilizing Ca2+ signaling after membrane disruption. The DYSF gene encodes 7-8 C2 domains, several Fer and Dysf domains, and a C-terminal transmembrane sequence. Because its coding sequence is too large to package in adeno-associated virus, the full-length sequence is not amenable to current gene delivery methods. Thus, we have examined smaller versions of dysferlin, termed "nanodysferlins," designed to eliminate several C2 domains, specifically C2 domains D, E, and F; B, D, and E; and B, D, E, and F. We also generated a variant by replacing eight amino acids in C2G in the nanodysferlin missing domains D through F. We electroporated dysferlin-null A/J mouse myofibers with Venus fusion constructs of these variants, or as untagged nanodysferlins together with GFP, to mark transfected fibers We found that, although these nanodysferlins failed to concentrate in transverse tubules, three of them supported membrane repair after laser wounding while all four bound the membrane repair protein, TRIM72/MG53, similar to WT dysferlin. By contrast, they failed to suppress Ca2+ waves after myofibers were injured by mild hypoosmotic shock. Our results suggest that the internal C2 domains of dysferlin are required for normal t-tubule localization and Ca2+ signaling and that membrane repair does not require these C2 domains.

A Novel CRISPR-Cas9 Strategy to Target DYSTROPHIN Mutations Downstream of Exon 44 in Patient-Specific DMD iPSCs

Mutations in the DMD gene cause fatal Duchenne Muscular Dystrophy (DMD). An attractive therapeutic approach is autologous cell transplantation utilizing myogenic progenitors derived from induced pluripotent stem cells (iPSCs). Given that a significant number of DMD mutations occur between exons 45 and 55, we developed a gene knock-in approach to correct any mutations downstream of exon 44. We applied this approach to two DMD patient-specific iPSC lines carrying mutations in exons 45 and 51 and confirmed mini-DYSTROPHIN (mini-DYS) protein expression in corrected myotubes by western blot and immunofluorescence staining. Transplantation of gene-edited DMD iPSC-derived myogenic progenitors into NSG/mdx4Cv mice produced donor-derived myofibers, as shown by the dual expression of human DYSTROPHIN and LAMIN A/C. These findings further provide proof-of-concept for the use of programmable nucleases for the development of autologous iPSC-based therapy for muscular dystrophies.

Physiological stress improves stem cell modeling of dystrophic cardiomyopathy

Heart failure contributes to Duchenne muscular dystrophy (DMD), which arises from mutations that ablate dystrophin, rendering the plasma membrane prone to disruption. Cardiomyocyte membrane breakdown in patients with DMD yields a serum injury profile similar to other types of myocardial injury with the release of creatine kinase and troponin isoforms. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are highly useful but can be improved. We generated hiPSC-CMs from a patient with DMD and subjected these cells to equibiaxial mechanical strain to mimic in vivo stress. Compared to healthy cells, DMD hiPSC-CMs demonstrated greater susceptibility to equibiaxial strain after 2 h at 10% strain. We generated an aptamer-based profile of proteins released from hiPSC-CMs both at rest and subjected to strain and identified a strong correlation in the mechanical stress-induced proteome from hiPSC-CMs and serum from patients with DMD. We exposed hiPSC-CMs to recombinant annexin A6, a protein resealing agent, and found reduced biomarker release in DMD and control hiPSC-CMs subjected to strain. Thus, the application of mechanical strain to hiPSC-CMs produces a model that reflects an in vivo injury profile, providing a platform to assess pharmacologic intervention.

Functional abilities, respiratory and cardiac function in a large cohort of adults with Duchenne muscular dystrophy treated with glucocorticoids

BACKGROUND AND PURPOSE

The transition to adult services, and subsequent glucocorticoid management, is critical in adults with Duchenne muscular dystrophy. This study aims (1) to describe treatment, functional abilities, respiratory and cardiac status during transition to adulthood and adult stages; and (2) to explore the association between glucocorticoid treatment after loss of ambulation (LOA) and late-stage clinical outcomes.

METHODS

This was a retrospective single-centre study on individuals with Duchenne muscular dystrophy (≥16 years old) between 1986 and 2022. Logistic regression, Cox proportional hazards models and survival analyses were conducted utilizing data from clinical records.

RESULTS

In all, 112 individuals were included. Mean age was 23.4 ± 5.2 years and mean follow-up was 18.5 ± 5.5 years. At last assessment, 47.2% were on glucocorticoids; the mean dose of prednisone was 0.38 ± 0.13 mg/kg/day and of deflazacort 0.43 ± 0.16 mg/kg/day. At age 16 years, motor function limitations included using a manual wheelchair (89.7%), standing (87.9%), transferring from a wheelchair (86.2%) and turning in bed (53.4%); 77.5% had a peak cough flow <270 L/min, 53.3% a forced vital capacity percentage of predicted <50% and 40.3% a left ventricular ejection fraction <50%. Glucocorticoids after LOA reduced the risk and delayed the time to difficulties balancing in the wheelchair, loss of hand to mouth function, forced vital capacity percentage of predicted <30% and forced vital capacity <1 L and were associated with lower frequency of left ventricular ejection fraction <50%, without differences between prednisone and deflazacort. Glucocorticoid dose did not differ by functional, respiratory or cardiac status.

CONCLUSION

Glucocorticoids after LOA preserve late-stage functional abilities, respiratory and cardiac function. It is suggested using functional abilities, respiratory and cardiac status at transition stages for adult services planning.

Long-term clinical follow-up of a family with Becker muscular dystrophy associated with a large deletion in the DMD gene

Duchenne muscular dystrophy is a neuromuscular disease caused by DMD gene mutations that result in an absence of functional dystrophin protein. Patients with Duchenne experience progressive muscle weakness, are typically wheelchair dependent by their early teens, and develop respiratory and cardiac complications that lead to death in their twenties or thirties. Becker muscular dystrophy is also caused by DMD gene mutations, but symptoms are less severe and progression is slower compared with Duchenne. We describe a case study of a patient with Becker muscular dystrophy who was still ambulant at age 61 years and had a milder phenotype than Duchenne, despite 46% of his DMD gene being missing. His affected relatives had similarly mild phenotypes and clinical courses. These data guided the understanding of the criticality of various regions of dystrophin and informed the development of micro-dystrophin constructs to compensate for the absence of functional dystrophin in Duchenne.

Gene-based therapies for neuromuscular disorders

Neuromuscular diseases (NMD) include a broad group of medical conditions with both acquired and genetic causes. In recent years, important advances have been made in the treatment of genetically caused NMD, and most of these advances are due to the implementation of therapies aimed at gene regulation. Among these therapies, gene replacement, small interfering RNA (siRNA), and antisense antinucleotides are the most promising approaches. More importantly, some of these therapies have already gained regulatory approval or are in the final stages of approval. The review focuses on motor neuron diseases, neuropathies, and Duchenne muscular dystrophy, summarizing the most recent developments in gene-based therapies for these 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 β-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.

Potential limitations of microdystrophin gene therapy for Duchenne muscular dystrophy

Clinical trials delivering high doses of adeno-associated viruses (AAVs) expressing truncated dystrophin molecules (microdystrophins) are underway for Duchenne muscular dystrophy (DMD). We examined the efficiency and efficacy of this strategy with 4 microdystrophin constructs (3 in clinical trials and a variant of the largest clinical construct), in a severe mouse model of DMD, using AAV doses comparable with those in clinical trials. We achieved high levels of microdystrophin expression in striated muscles with cardiac expression approximately 10-fold higher than that observed in skeletal muscle. Significant, albeit incomplete, correction of skeletal muscle disease was observed. Surprisingly, a lethal acceleration of cardiac disease occurred with 2 of the microdystrophins. The detrimental cardiac effect appears to be caused by variable competition (dependent on microdystrophin design and expression level) between microdystrophin and utrophin at the cardiomyocyte membrane. There may also be a contribution from an overloading of protein degradation. The significance of these observations for patients currently being treated with AAV-microdystrophin therapies is unclear since the levels of expression being achieved in the DMD hearts are unknown. However, these findings suggest that microdystrophin treatments need to avoid excessively high levels of expression in the heart and that cardiac function should be carefully monitored in these patients.

Comparative in vivo characterization of newly discovered myotropic adeno-associated vectors

BACKGROUND

Adeno-associated virus (AAV)-based gene therapy is a promising strategy to treat muscle diseases. However, this strategy is currently confronted with challenges, including a lack of transduction efficiency across the entire muscular system and toxicity resulting from off-target tissue effects. Recently, novel myotropic AAVs named MyoAAVs and AAVMYOs have been discovered using a directed evolution approach, all separately demonstrating enhanced muscle transduction efficiency and liver de-targeting effects. However, these newly discovered AAV variants have not yet been compared.

METHODS

In this study, we performed a comparative analysis of these various AAV9-derived vectors under the same experimental conditions following different injection time points in two distinct mouse strains.

RESULTS

We highlight differences in transduction efficiency between AAV9, AAVMYO, MyoAAV2A and MyoAAV4A that depend on age at injection, doses and mouse genetic background. In addition, specific AAV serotypes appeared more potent to transduce skeletal muscles including diaphragm and/or to de-target heart or liver.

CONCLUSIONS

Our study provides guidance for researchers aiming to establish proof-of-concept approaches for preventive or curative perspectives in mouse models, to ultimately lead to future clinical trials for muscle disorders.

Population longitudinal analysis of Gait Profile Score and North Star Ambulatory Assessment in children with Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a rare X-linked recessive disorder characterized by loss-of-function mutations in the gene encoding dystrophin. These mutations lead to progressive functional deterioration including muscle weakness, respiratory insufficiency, and musculoskeletal deformities. Three-dimensional gait analysis (3DGA) has been used as a tool to analyze gait pathology through the quantification of altered joint kinematics, kinetics, and muscle activity patterns. Among 3DGA indices, the Gait Profile Score (GPS), has been used as a sensitive overall measure to detect clinically relevant changes in gait patterns in children with DMD. To enhance our understanding of the clinical translation of 3DGA, we report here the development of a population nonlinear mixed-effect model that jointly describes the disease progression of the 3DGA index, GPS, and the functional endpoint, North Star Ambulatory Assessment (NSAA). The final model consists of a quadratic structure for GPS progression and a linear structure for GPS-NSAA correlation. Our model was able to capture the improvement in function in GPS and NSAA in younger subjects, as well as the decline of function in older subjects. Furthermore, the model predicted NSAA (CFB) at 1 year reasonably well for DMD subjects ≤7 years old at baseline. The model tended to slightly underpredict the decline in NSAA after 1 year for those >7 years old at baseline, but the prediction summary statistics were well maintained within the standard deviation of observed data. Quantitative models such as this may help answer clinically relevant questions to facilitate the development of novel therapies in DMD.

Unnatural Amino Acid-Based Ionic Liquid Enables Oral Treatment of Nonsense Mutation Disease in Mice

This investigation addresses the challenge of suboptimal unnatural amino acid (UAA) utilization in the site-specific suppression of nonsense mutations through genetic code expansion, which is crucial for protein restoration and precise property tailoring. A facile and economical oral liquid formulation is developed by converting UAAs into ionic liquids, significantly enhancing their bioavailability and tissue accumulation. Empirical data reveal a 10-fold increase in bioavailability and up to a 13-fold rise in focal tissue accumulation, alongside marked improvements in UAA incorporation efficiency. A 4-week oral administration in mdx mice, a model for Duchenne muscular dystrophy (DMD), demonstrates the formulation's unprecedented therapeutic potential, with up to 40% dystrophin expression restoration and 75% recovery of normal fiber functions, surpassing existing treatments and exhibiting substantial long-term safety. This study presents a potent oral dosage form that dramatically improves UAA incorporation into target proteins in vivo, offering a significant advance in the treatment of nonsense mutation-mediated disorders and holding considerable promise for clinical translation.

The BALB/c.mdx62 mouse exhibits a dystrophic muscle pathology and is a model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a devastating monogenic skeletal muscle-wasting disorder. Although many pharmacological and genetic interventions have been reported in preclinical studies, few have progressed to clinical trials with meaningful benefit. Identifying therapeutic potential can be limited by availability of suitable preclinical mouse models. More rigorous testing across models with varied background strains and mutations can identify treatments for clinical success. Here, we report the generation of a DMD mouse model with a CRISPR-induced deletion within exon 62 of the dystrophin gene (Dmd) and the first generated in BALB/c mice. Analysis of mice at 3, 6 and 12 months of age confirmed loss of expression of the dystrophin protein isoform Dp427 and resultant dystrophic pathology in limb muscles and the diaphragm, with evidence of centrally nucleated fibers, increased inflammatory markers and fibrosis, progressive decline in muscle function, and compromised trabecular bone development. The BALB/c.mdx62 mouse is a novel model of DMD with associated variations in the immune response and muscle phenotype, compared with those of existing models. It represents an important addition to the preclinical model toolbox for developing therapeutic strategies.

A review on mechanistic insights into structure and function of dystrophin protein in pathophysiology and therapeutic targeting of Duchenne muscular dystrophy

Duchenne Muscular Dystrophy (DMD) is an X-linked recessive genetic disorder characterized by progressive and severe muscle weakening and degeneration. Among the various forms of muscular dystrophy, it stands out as one of the most common and impactful, predominantly affecting boys. The condition arises due to mutations in the dystrophin gene, a key player in maintaining the structure and function of muscle fibers. The manuscript explores the structural features of dystrophin protein and their pivotal roles in DMD. We present an in-depth analysis of promising therapeutic approaches targeting dystrophin and their implications for the therapeutic management of DMD. Several therapies aiming to restore dystrophin protein or address secondary pathology have obtained regulatory approval, and many others are ongoing clinical development. Notably, recent advancements in genetic approaches have demonstrated the potential to restore partially functional dystrophin forms. The review also provides a comprehensive overview of the status of clinical trials for major therapeutic genetic approaches for DMD. In addition, we have summarized the ongoing therapeutic approaches and advanced mechanisms of action for dystrophin restoration and the challenges associated with DMD therapeutics.

Cell-mediated exon skipping normalizes dystrophin expression and muscle function in a new mouse model of Duchenne Muscular Dystrophy

Cell therapy for muscular dystrophy has met with limited success, mainly due to the poor engraftment of donor cells, especially in fibrotic muscle at an advanced stage of the disease. We developed a cell-mediated exon skipping that exploits the multinucleated nature of myofibers to achieve cross-correction of resident, dystrophic nuclei by the U7 small nuclear RNA engineered to skip exon 51 of the dystrophin gene. We observed that co-culture of genetically corrected human DMD myogenic cells (but not of WT cells) with their dystrophic counterparts at a ratio of either 1:10 or 1:30 leads to dystrophin production at a level several folds higher than what predicted by simple dilution. This is due to diffusion of U7 snRNA to neighbouring dystrophic resident nuclei. When transplanted into NSG-mdx-Δ51mice carrying a mutation of exon 51, genetically corrected human myogenic cells produce dystrophin at much higher level than WT cells, well in the therapeutic range, and lead to force recovery even with an engraftment of only 3-5%. This level of dystrophin production is an important step towards clinical efficacy for cell therapy.