Gapmer Antisense Oligonucleotides Suppress the Mutant Allele of COL6A3 and Restore Functional Protein in Ullrich Muscular Dystrophy

Dominant-negative mutations in the genes that encode the three major a chains of collagen type VI, COL6A1, COL6A2, and COL6A3, account for more than 50% of Ullrich congenital muscular dystrophy patients and nearly all Bethlem myopathy patients. Gapmer antisense oligonucleotides (AONs) are usually used for gene silencing by stimulating RNA cleavage through the recruitment of an endogenous endonuclease known as RNase H to cleave the RNA strand of a DNA-RNA duplex. In this study, we exploited the application of the allele-specific silencing approach by gapmer AON as a potential therapy for Collagen-VI-related congenital muscular dystrophy (COL6-CMD). A series of AONs were designed to selectively target an 18-nt heterozygous genomic deletion in exon 15 of COL6A3 at the mRNA and pre-mRNA level. We showed that gapmer AONs can selectively suppress the expression of mutant transcripts at both pre-mRNA and mRNA levels, and that the latter strategy had a far stronger efficiency than the former. More importantly, we found that silencing of the mutant transcripts by gapmer AONs increased the deposition of collagen VI protein into the extracellular matrix, thus restoring functional protein production. Our findings provide a clear proof of concept for AON allele-specific silencing as a therapeutic approach for COL6-CMD.