Targeted splice sequencing reveals RNA toxicity and therapeutic response in myotonic dystrophy

Biomarker-driven trials hold promise for therapeutic development in chronic diseases, such as muscular dystrophy. Myotonic dystrophy type 1 (DM1) involves RNA toxicity, where transcripts containing expanded CUG-repeats (CUG(exp)) accumulate in nuclear foci and sequester splicing factors in the Muscleblind-like (Mbnl) family. Oligonucleotide therapies to mitigate RNA toxicity have emerged but reliable measures of target engagement are needed. Here we examined muscle transcriptomes in mouse models of DM1 and found that CUG(exp) expression or Mbnl gene deletion cause similar dysregulation of alternative splicing. We selected 35 dysregulated exons for further study by targeted RNA sequencing. Across a spectrum of mouse models, the individual splice events and a composite index derived from all events showed a graded response to decrements of Mbnl or increments of CUG(exp). Antisense oligonucleotides caused prompt reduction of CUG(exp) RNA and parallel correction of the splicing index, followed by subsequent elimination of myotonia. These results suggest that targeted splice sequencing may provide a sensitive and reliable way to assess therapeutic impact in DM1.

Automated summary

Biomarker-driven trials show promise in therapeutic development of chronic diseases like muscular dystrophy. RNA toxicity in myotonic dystrophy type 1 (DM1) involves expanded CUG-repeats accumulation, leading to dysregulation of alternative splicing. Targeted splice sequencing can be a sensitive and reliable way to assess therapeutic impact in DM1, as shown by prompt reduction of CUG(exp) RNA and correction of splicing index with antisense oligonucleotides.