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

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Myotonic dystrophy type 1 (DM1) is a chronic disease characterized by RNA toxicity due to expanded CUG-repeats (CUGexp).
• Nuclear accumulation of CUGexp sequesters splicing factors, particularly from the Muscleblind-like (Mbnl) family, leading to splicing dysregulation.
• Developing effective oligonucleotide therapies for DM1 requires reliable biomarkers to measure target engagement and therapeutic efficacy.

Purpose of the Study:

• To investigate the utility of targeted RNA sequencing as a biomarker for assessing therapeutic interventions in DM1.
• To correlate changes in alternative splicing patterns with disease progression and therapeutic response in DM1 mouse models.

Main Methods:

• Analysis of muscle transcriptomes in mouse models of DM1, including those with CUGexp expression or Mbnl gene deletion.
• Selection and targeted RNA sequencing of 35 dysregulated exons identified in DM1 models.
• Monitoring of CUGexp RNA levels, splicing index, and myotonia following antisense oligonucleotide treatment.

Main Results:

• Both CUGexp expression and Mbnl gene deletion induced similar alternative splicing dysregulation.
• A composite index derived from 35 dysregulated splice events showed a graded response to varying levels of Mbnl or CUGexp.
• Antisense oligonucleotide treatment rapidly reduced CUGexp RNA, corrected the splicing index, and subsequently alleviated myotonia.

Conclusions:

• Targeted splice sequencing serves as a sensitive and reliable method for assessing therapeutic impact in DM1.
• This approach can monitor target engagement and downstream effects of oligonucleotide therapies.
• The findings support the use of splicing biomarkers in the development of DM1 therapeutics.