Summary by Florian Barthélémy

Publication

Clinical and Translational Medicine; First published: 16 February 2025

Muscle-specific gene editing improves molecular and phenotypic defects in a mouse model of myotonic dystrophy type 1

Mariapaola Izzo et al., 2025

https://pubmed.ncbi.nlm.nih.gov/39956955/

Summary

This paper describes a new AAV delivery method triggering a muscle-specific gene editing of the abnormal accumulation of CTG-repeat in DMPK, correcting the pathophysiology of a mouse model of myotonic dystrophy type 1 (DM1).

The authors used a humanised mouse model carrying a human DMPK genomic region from a DM1 patient to assess the delivery and optimization of a CRISPR/Cas9 gene editing to remove the CTG-expansion in the DMPK gene. Specifically, they used a myotropic adeno-associated virus to first assess the technique in a patient cell line, which exhibited a pronounced reduction in foci per nucleus alongside a concomitant decrease in the mutated DMPK transcript in both myoblasts and myotubes of the treated DM1 patient cells. This rescue was complemented by an increase in the normal transcript isoforms of SERCA1 and INSR, both of which are known to exhibit alternative splicing in DM1-affected cells. Subsequently, an extensive analysis of the edited cells was performed, with no identified off-target effects and a greater accuracy of on-target genomic cuts, particularly within differentiated cells.

In their in vivo investigations, the authors initially demonstrated that MyoAAV 2A exhibited a superior editing efficiency compared to AAV9 when administered systematically in DMSXL hemizygous mice. Continuing with the foremost, authors compared the effects of MyoAAV–U6-34/589 or MyoAAV–U6-C3/384, combined with MyoAAV–CK8–Cas9 at P5 or P24. While the sgRNA 34/589 showed better rescue overall, with clear decrease of foci accumulation (within skeletal muscles and the heart) particularly at p24, the heart also showed improvement of alternative splicing at P5 and P24. No apparent toxicity was demonstrated at both ages, but differences were shown in other parameters: body weight rescue (superior at P24), grip strength (slightly improved in the forelimbs of males treated at 5 weeks), and body composition (improved at P5).

Overall, the treatment resulted in substantial amelioration of both molecular alterations and phenotypic defects in the heart and skeletal muscle of the treated animals. This research represents an important preclinical step in developing a gene therapy for DM1 patients. The accurate evaluation of CRISPR/Cas9-mediated phenotypic recovery in vivo is crucial for advancing this treatment towards clinical applications.

About the author

Dr Mariapaola Izzo obtained her Ph.D. in molecular medicine from Sapienza University of Rome in 2019. Her passion for neuromuscular research blossomed during her postdoctoral period at the CNR's Institute of Biochemistry and Cell Biology in Rome, under the insightful guidance of Dr. Germana Falcone and Dr. Beatrice Cardinali. Her research focused on investigating the mechanisms, molecular pathways, genes, and cell types that contribute to histopathological tissue alterations, with a specific focus on myotonic dystrophy type 1 (DM1).

About the reviewer:

Dr Barthélémy earned his Ph.D. in human pathology, specialising in human genetics, under the mentorship of Dr. Marc Bartoli at the Marseille Medical School in France in 2013. His research trajectory continued to evolve as he joined Dr. Carrie Miceli's team at the Center for Duchenne Muscular Dystrophy (CDMD) at UCLA, initially as a postdoctoral scientist and currently as an associate project scientist, Dr. Barthélémy employs a multidisciplinary approach, utilising molecular and cell biology, immunology, microscopy, biochemistry, genomics, and bioengineering techniques. These methodologies are instrumental in developing innovative tools to characterise the molecular and mechanical properties of tissues and cells derived from patients with rare diseases and developing therapeutic strategies such as exon skipping. His translational research endeavors aim to advance personalised medicine approaches for Duchenne muscular dystrophy (DMD) and other related conditions.