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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.

This month in Med, the description of an unusually severely affected DMD patient suffering from a large deletion in the dystrophin gene confirms that absence of utrophin worsens the dystrophy and supports the concept that utrophin upregulation ameliorates the pathology. This study may guide the development of dystrophin-based gene therapies., Competing Interests: Declarations of interest The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Skeletal muscle has an extraordinary capacity to regenerate after injury and trauma. The muscle repair mechanism is a complex process orchestrated by multiple steps. In neuromuscular disorders such as Duchenne muscular dystrophy (DMD), the pathological consequences of the lack of dystrophin and the loss of the dystrophin-associated protein complex are dramatic, with a progressive cascade of events, such as continual influx of inflammation, repeated cycles of degeneration and impaired regeneration. Thus, muscle regeneration is a hallmark of the disease and careful monitoring of regenerative processes with robust markers should provide useful information to the field. Since decades, several indices of regeneration such as centronucleation and fibre size have been commonly used. In the present review, we discuss the impaired regenerative process in DMD, the common and new indices of regeneration and their associated methodologies. We notably highlight the regenerative marker embryonic myosin as a robust indicator of muscle regeneration. We also describe new quantitative methodologies offering the possibility of using a panel of translational regenerative biomarkers to obtain a more complete view of the regeneration processes. Upregulation of utrophin, an autosomal and functional paralogue of dystrophin, is one of the most promising therapeutic strategies as it targets the primary cause of the disease and is applicable to all DMD patients regardless their genetic defects. As utrophin is a regeneration associated protein increased in dystrophic muscle, we discuss the correlation of utrophin levels after drug treatment with regeneration markers. The recent advances in technologies and complementary markers of muscle regeneration described in this review, provide an unprecedented opportunity to develop more robust utrophin DMD based strategies for all DMD patients., Competing Interests: None

Duchenne muscular dystrophy (DMD) is a lethal neuromuscular disorder caused by loss of dystrophin. Several therapeutic modalities are currently in clinical trials but none will achieve maximum functional rescue and full disease correction. Therefore, we explored the potential of combining the benefits of dystrophin with increases of utrophin, an autosomal paralogue of dystrophin. Utrophin and dystrophin can be co-expressed and co-localized at the same muscle membrane. Wild-type (wt) levels of dystrophin are not significantly affected by a moderate increase of utrophin whereas higher levels of utrophin reduce wt dystrophin, suggesting a finite number of actin binding sites at the sarcolemma. Thus, utrophin upregulation strategies may be applied to the more mildly affected Becker patients with lower dystrophin levels. Whereas increased dystrophin in wt animals does not offer functional improvement, overexpression of utrophin in wt mice results in a significant supra-functional benefit over wt. These findings highlight an additive benefit of the combined therapy and potential new unique roles of utrophin. Finally, we show a 30% restoration of wt dystrophin levels, using exon-skipping, together with increased utrophin levels restores dystrophic muscle function to wt levels offering greater therapeutic benefit than either single approach alone. Thus, this combination therapy results in additive functional benefit and paves the way for potential future combinations of dystrophin- and utrophin-based strategies., (© The Author(s) 2019. Published by Oxford University Press.)

Duchenne muscular dystrophy (DMD) is a lethal, X-linked muscle-wasting disease caused by lack of the cytoskeletal protein dystrophin. Constitutive utrophin expression, a structural and functional paralogue of dystrophin, can successfully prevent the dystrophic pathology in the dystrophin-deficient mdx mouse model. In dystrophic muscles, utrophin is increased as part of the repair process and localized at the sarcolemma of regenerating myofibers. The presence of developmental myosin such as embryonic myosin (MyHC-emb) and neonatal represents a useful marker of muscle regeneration and a meaningful indicator of muscle damage, which correlates with the clinical severity of milder Becker muscular dystrophy and DMD patients. In the present study, we demonstrate that MyHC-emb is a robust marker of regeneration at different ages and in different skeletal muscles. We also evaluate the correlation between utrophin, dystrophin and MyHC-emb in wild-type (wt) and regenerating dystrophic muscles. Restoration of dystrophin significantly reduced MyHC-emb levels. Similarly, overexpression of utrophin in the transgenic mdx-Fiona mice reduced the number of MyHC-emb positive fibers to wt level, prevented the regenerative process and rescued the muscle function. In contrast, the absence of utrophin in the dystrophin-deficient double-knockout mice resulted in a higher MyHC-emb content and in a more severe dystrophic pathophysiology than in mdx mice. These data illustrate the importance of monitoring utrophin and MyHC-emb levels in the preclinical evaluation of therapies and provide translational support for the use of developmental myosin as a disease biomarker in DMD clinical trials.

Duchenne muscular dystrophy (DMD) is an X-linked muscle-wasting disease caused by mutations in the dystrophin gene. DMD boys are wheelchair-bound around 12 years and generally survive into their twenties. There is currently no effective treatment except palliative care, although personalized treatments such as exon skipping, stop codon read-through, and viral-based gene therapies are making progress. Patients present with skeletal muscle pathology, but most also show cardiomyopathy by the age of 10. A systemic therapeutic approach is needed that treats the heart and skeletal muscle defects in all patients. The dystrophin-related protein utrophin has been shown to compensate for the lack of dystrophin in the mildly affected BL10/ mdx mouse. The purpose of this investigation was to demonstrate that AAV9-mediated micro-utrophin transgene delivery can not only functionally replace dystrophin in the heart, but also attenuate the skeletal muscle phenotype in severely affected D2/ mdx mice. The data presented here show that utrophin can indeed alleviate the pathology in skeletal and cardiac muscle in D2/ mdx mice. These results endorse the view that utrophin modulation has the potential to increase the quality life of all DMD patients whatever their mutation.

Background: Duchenne muscular dystrophy (DMD) is a lethal X-linked muscle wasting disorder caused by the absence of dystrophin, a large cytoskeletal muscle protein. Increasing the levels of the dystrophin-related-protein utrophin is a highly promising therapy for DMD and has been shown to improve pathology in dystrophin-deficient mice. One contributing factor to muscle wasting in DMD is mitochondrial pathology that contributes to oxidative stress and propagates muscle damage. The purpose of this study was to assess whether utrophin could attenuate mitochondria pathology and oxidative stress., Methods: Skeletal muscles from wildtype C57BL/10, dystrophin-deficient mdx, dystrophin/utrophin double knockout (dko) and dystrophin-deficient mdx/utrophin over-expressing mdx-Fiona transgenic mice were assessed for markers of mitochondrial damage., Results: Using transmission electron microscopy, we show that high levels of utrophin ameliorate the aberrant structure and localisation of mitochondria in mdx mice whereas absence of utrophin worsened these features in dko mice. Elevated utrophin also reverts markers of protein oxidation and oxidative stress, elevated in mdx and dko mice, to wildtype levels. These changes were observed independently of a shift in oxidative phenotype., Conclusion: These findings show that utrophin levels influence mitochondrial pathology and oxidative stress. While utrophin deficiency worsens the pathology, utrophin over-expression in dystrophic muscle benefits mitochondria and attenuates the downstream pathology associated with aberrant mitochondrial function.

Despite promising therapeutic avenues, there is currently no effective treatment for Duchenne muscular dystrophy (DMD), a lethal monogenic disorder caused by the loss of the large cytoskeletal protein, dystrophin. A highly promising approach to therapy, applicable to all DMD patients irrespective to their genetic defect, is to modulate utrophin, a functional paralogue of dystrophin, able to compensate for the primary defects of DMD restoring sarcolemmal stability. One of the major difficulties in assessing the effectiveness of therapeutic strategies is to define appropriate outcome measures. In the present study, we utilised an aptamer based proteomics approach to profile 1,310 proteins in plasma of wild-type, mdx and Fiona (mdx overexpressing utrophin) mice. Comparison of the C57 and mdx sera revealed 83 proteins with statistically significant >2 fold changes in dystrophic serum abundance. A large majority of previously described biomarkers (ANP32B, THBS4, CAMK2A/B/D, CYCS, CAPNI) were normalised towards wild-type levels in Fiona animals. This work also identified potential mdx markers specific to increased utrophin (DUS3, TPI1) and highlights novel mdx biomarkers (GITR, MYBPC1, HSP60, SIRT2, SMAD3, CNTN1). We define a panel of putative protein mdx biomarkers to evaluate utrophin based strategies which may help to accelerate their translation to the clinic.

Collagen IV is a major component of basement membranes (BMs). The α1(IV) chain, encoded by the COL4A1 gene, is expressed ubiquitously and associates with the α2(IV) chain to form the α1α1α2(IV) heterotrimer. Several COL4A1 mutations affecting a conformational domain containing integrin-binding sites are responsible for the systemic syndrome of hereditary angiopathy, nephropathy, aneurysms, and cramps (HANAC). To analyze the pathophysiology of HANAC, Col4a1 mutant mice bearing the p.Gly498Val mutation were generated. Analysis of the skeletal muscles of Col4a1 G498V mutant animals showed morphologic characteristics of a muscular dystrophy phenotype with myofiber atrophy, centronucleation, focal inflammatory infiltrates, and fibrosis. Abnormal ultrastructural aspects of muscle BMs was associated with reduced extracellular secretion of the mutant α1α1α2(IV) trimer. In addition to muscular dystrophic features, endothelial cell defects of the muscle capillaries were observed, with intracytoplasmic accumulation of the mutant α1α1α2(IV) molecules, endoplasmic reticulum cisternae dilation, and up-regulation of endoplasmic reticulum stress markers. Induction of the unfolded protein response in Col4a1 mutant muscle tissue resulted in an excess of apoptosis in endothelial cells. HANAC mutant animals also presented with a muscular functional impairment and increased serum creatine kinase levels reflecting altered muscle fiber sarcolemma. This extensive description of the muscular phenotype of the Col4a1 HANAC murine model suggests a potential contribution of primary endothelial cell defects, together with muscle BM alterations, to the development of COL4A1-related myopathy., (Copyright © 2017 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)