Key result
Inducible expression of pathogenic CUGexp RNA in mouse hearts reproduced DM1-associated cardiac conduction defects, supraventricular arrhythmias, and alternative splicing defects, all of which were reversible upon cessation of RNA expression.
Why the study?
Cardiac involvement affects 50% of individuals with DM1 and causes 25% of disease-related deaths, driven by pathogenic expanded CUG repeat RNA.
This inducible mouse model demonstrates that the cardiac electrophysiological and molecular defects of myotonic dystrophy type 1 are reversible upon cessation of toxic CUGexp RNA expression, highlighting a potential therapeutic strategy.
Reversibility of DM1 cardiac defects by CUGexp suppression in mice; leaves open translation to human therapy.
Myotonic dystrophy type 1 (DM1) is caused by a CTG repeat expansion in the DMPK gene. Expression of pathogenic expanded CUG repeat (CUGexp) RNA causes multisystemic disease by perturbing the functions of RNA-binding proteins, resulting in expression of fetal protein isoforms in adult tissues. Cardiac involvement affects 50% of individuals with DM1 and causes 25% of disease-related deaths. We developed a transgenic mouse model for tetracycline-inducible and heart-specific expression of human DMPK mRNA containing 960 CUG repeats. CUGexp RNA is expressed in atria and ventricles and induced mice exhibit electrophysiological and molecular features of DM1 disease, including cardiac conduction delays, supraventricular arrhythmias, nuclear RNA foci with Muscleblind protein colocalization, and alternative splicing defects. Importantly, these phenotypes were rescued upon loss of CUGexp RNA expression. Transcriptome analysis revealed gene expression and alternative splicing changes in ion transport genes that are associated with inherited cardiac conduction diseases, including a subset of genes involved in calcium handling. Consistent with RNA-Seq results, calcium-handling defects were identified in atrial cardiomyocytes isolated from mice expressing CUGexp RNA. These results identify potential tissue-specific mechanisms contributing to cardiac pathogenesis in DM1 and demonstrate the utility of reversible phenotypes in our model to facilitate development of targeted therapeutic approaches.
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Rao et al. (2021) studied Myotonic dystrophy type 1 (DM1) cardiac disease. Doxycycline-induced expression of CUGexp RNA vs. MHCrtTA +dox control mice was evaluated on Cardiac conduction intervals (QRS and QTc) and atrial arrhythmias. Inducible expression of pathogenic CUGexp RNA in mouse hearts reproduced DM1-associated cardiac conduction defects, supraventricular arrhythmias, and alternative splicing defects, all of which were reversible upon cessation of RNA expression.
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