Background: Significant therapeutic advancements have been made in Duchenne Muscular Dystrophy. Becker Muscular Dystrophy (BMD), however, is understudied and underserved. This discordance is explained in part, by the absence of a BMD mouse model: generation of such a model which would enable a greater understanding of disease pathophysiology and de-risk potential therapeutics before first-in-human trials.
Objectives: To fill this void, we used CRISPR-Cas9 to create genomic deletion of dystrophin exons 45-47, the most common BMD mutation, to generate bmx (Becker muscular dystrophy, X-linked) mice.
Results: Bmx mice show impaired motor function, including reduced grip strength and in vivo isometric torque. Histologically, Bmx muscles show increased myofiber size variability, centrally localized nuclei, inflammatory/necrotic foci, and collagen staining. Immunofluorescence and capillary western immunoassay (Wes) show reduced dystrophin protein levels in bmx skeletal and cardiac muscles; interestingly, dystrophin mRNA levels remain unchanged. Related to this, bmx muscles show elevated expression of NF-kB-regulated dystrophin-targeting miRNAs. Higher levels of NF-kB regulated inflammatory genes and inflammatory miRNAs, as well as genes indicative of fibrosis are also observed.
Conclusions: Collectively, our data demonstrate that bmx mice recapitulate the BMD disease phenotype and can serve as a useful tool to the muscular dystrophy research community. Moving forward, this model can be utilized for in-depth characterization of BMD disease progression, to identify biomarkers and therapeutic targets, and to perform preclinical drug studies aimed at identifying a first treatment for BMD patients.