Systemic deletion of exon 51 rescues clinically severe Duchenne muscular dystrophy in a pig model lacking exon 52.

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