20. A Novel Approach in the Treatment of Dystrophic Cardiomyopathy

Abstract

Duchenne muscular dystrophy (DMD) is the most common muscular dystrophy with a worldwide incidence of one in 3500 live male births. It is caused by the lack of dystrophin, a critical muscle protein that connects the cytoskeleton and the extracellular matrix (ECM). Cardiomyopathy develops in at least 90% of patients and alone can shorten the life expectancy of DMD patients by at least 2 years and up to 40% of DMD patients eventually die from heart failure. Recently, RNA-guided, nuclease-mediated genome editing based on type II CRISPR (clustered regularly interspaced short palindromic repeat)/Cas (CRISPR-associated) system, has been emerged to alter the genome. In this study, we hypothesize that CRISPR-mediated genome editing could offer a novel therapy for DMD-associated cardiomyopathy in live mice. Two gRNA target sites were chosen from intron 20 and 23 of mouse Dmd. Co- transfection of the two gRNA with cas9 plasmids into mouse C2C12 cells resulted in the detection of a small PCR product as predicted, indicating successful CRISPR-mediated genome editing. DNA sequencing confirmed that the transcripts from C2C12 cells treated with gRNA/cas9 were formed due to successful deletion of exons 21-23 of mouse Dmd. Moreover, we injected the adenoviral vectors carrying GFP-2A-cas9 and gRNAs systemically and locally into the newborn pups. Four weeks after adenovirus transduction, dystrophin expression was restored in the heart muscles positive for GFP. Our PCR and western blotting data demonstrated that in-frame deletion of the genomic DNA covering exon 23 restored functional dystrophin expression in the hearts of mdx mice. Immunofluorescence staining also demonstrated that β-dystroglycan, which is normally located to the sarcolemma in healthy heart muscles via interaction with dystrophin-glycoprotein complex, was also restored at the sarcolemma of GFP-positive heart muscle fibers. These data provide the proof evidence of systemic restoration of dystrophin in the hearts of live mice.