GSE195480
Systemic Delivery of an AAV9 Exon Skipping Vector Significantly Improves or Prevents Features of Duchenne Muscular Dystrophy in the Dup2 Mouse Model
Purpose: Duchenne muscular dystrophy (DMD) is typically caused by mutations that disrupt the DMD reading frame, but nonsense mutations in the 5' part of the gene lead to the utilization of an internal ribosomal entry site (IRES) in exon 5, resulting in expression of a highly functional N-truncated dystrophin. We have developed an AAV9 vector expressing U7 small nuclear RNAs targeting DMD exon 2 and tested it in a mouse model containing a duplication of exon 2, in which skipping of both exon 2 copies results in IRES-induced expression, and skipping of only one exon 2 leads to wild-type dystrophin expression. Methods: One-time intravascular injection of an AAV9 vector expressing U7 small nuclear RNAs targeting Dmd exon 2 at either P0-P1 or at 2 months of age results in efficient exon skipping and dystrophin expression, and significant protection from functional and pathologic deficits. Results: In mice treated neonatally, dystrophin immunofluorescence reached 49-85% of normal signal intensity and 76-99% dystrophin-positive fibers, with near-complete correction of dystrophic pathology, and these beneficial effects showed no significant signs of declining for at least 6 months. RNA sequencing (RNA-Seq) and Ribosome Profiling (RPF-Seq) indicated that treatment restored a 'non-dystrophic' gene expression profile by reversing the direction and magnitude of differentially expressed genes previously identified in dystrophic skeletal muscle from DMD patients. The dystrophin transcript showed clearly increased RPF reads in the treated sample, indicating that the treatment specifically increased dystrophin translation. Conclusions: The results demonstrate the robustness, durability, and safety of exon 2 skipping following delivery of scAAV9.U7snRNA.ACCA, supporting its clinical use.      Overall design: Skeletal muscle mRNA and ribosome footprinting profiles from Dmd Dup2 mice treated with an AAV9 exon skipping vector