Systemic deletion of <i>DMD</i> exon 51 rescues clinically severe Duchenne muscular dystrophy in a pig model lacking <i>DMD</i> exon 52

Abstract

Duchenne muscular dystrophy (DMD) is a fatal X-linked disease caused by mutations in the <i>DMD</i> gene, leading to complete absence of dystrophin and progressive degeneration of skeletal musculature and myocardium. In DMD patients and in a corresponding pig model with a deletion of <i>DMD</i> exon 52 (<i>DMD</i>Δ52), expression of an internally shortened dystrophin can be achieved by skipping of <i>DMD</i> exon 51 to reframe the transcript. To predict the best possible outcome of this strategy, we generated <i>DMD</i>Δ51-52 pigs, additionally representing a model for Becker muscular dystrophy (BMD). <i>DMD</i>Δ51-52 skeletal muscle and myocardium samples stained positive for dystrophin and did not show the characteristic dystrophic alterations observed in <i>DMD</i>Δ52 pigs. Western blot analysis confirmed the presence of dystrophin in the skeletal muscle and myocardium of <i>DMD</i>Δ51-52 pigs and its absence in <i>DMD</i>Δ52 pigs. The proteome profile of skeletal muscle, which showed a large number of abundance alterations in <i>DMD</i>Δ52 vs. wild-type (WT) samples, was normalized in <i>DMD</i>Δ51-52 samples. Cardiac function at age 3.5 mo was significantly reduced in <i>DMD</i>Δ52 pigs (mean left ventricular ejection fraction 58.8% vs. 70.3% in WT) but completely rescued in <i>DMD</i>Δ51-52 pigs (72.3%), in line with normalization of the myocardial proteome profile. Our findings indicate that ubiquitous deletion of <i>DMD</i> exon 51 in <i>DMD</i>Δ52 pigs largely rescues the rapidly progressing, severe muscular dystrophy and the reduced cardiac function of this model. Long-term follow-up studies of <i>DMD</i>Δ51-52 pigs will show if they develop symptoms of the milder BMD.