Transient mouse models for the preclinical evaluation of therapeutic dystrophin exon skipping strategies

Antisense oligomer (AO)-mediated splicing manipulation can remove specific exons during transcript processing, to by-pass DMD-causing dystrophin gene lesions and generate shorter, partially functional BMD-like dystrophin isoforms, and is showing promise as a therapy for DMD. Dystrophin gene structure in mildly affected and asymptomatic BMD patients indicates templates for a number of functional dystrophins, however, in-frame deletions in some regions of the dystrophin gene, particularly 5 of exon 55 are rare and the consequences of exon exclusion in this region are not known. The mdx mouse is a widely used dystrophinopathy model and has a nonsense mutation in dystrophin exon 23. AO induced- excision of this exon from the mRNA removes the mutation without disrupting the reading frame, resulting in functional dystrophin expression and amelioration of the phenotype. We now report that systemic administration of AO combinations to wild-type mice can remove dystrophin exons to generate DMD- and BMD- like dystrophin isoforms for functional evaluation. Assessment of contractile properties of the muscle reveals that some in-frame exon combinations confer near normal function, while others result in muscle susceptible to contraction-induced damage. Furthermore, we show that concurrent administration of prednisolone and AOs improves dystrophin exon skipping and muscle function