Overexpression of a non-muscle RBFOX2 isoform triggers cardiac conduction defects in myotonic dystrophy
Myotonic dystrophy type 1 (DM1) is a multisystemic genetic disorder caused by a CTG trinucleotide repeat expansion in the 3' untranslated region of DMPK gene. Heart dysfunctions occur in nearly 80% of DM1 patients and are the second leading cause of DM1-related deaths. Despite these figures, the mechanisms underlying cardiac-based DM1 phenotypes are unknown. Herein, we report that upregulation of a non-muscle splice isoform of RNA binding protein RBFOX2 in DM1 heart tissue--due to altered splicing factor and microRNA activities--induces cardiac conduction defects in DM1 individuals. Mice engineered to express the non-muscle RBFOX2 isoform in heart via tetracycline-inducible transgenesis, or CRISPR/Cas9-mediated genome editing, reproduced DM1-related cardiac-conduction delay and spontaneous episodes of arrhythmia. Further, by integrating RNA binding with cardiac transcriptome datasets from both DM1 patients and mice expressing the non-muscle RBFOX2 isoform, we identified RBFOX2-driven splicing defects in the voltage-gated sodium and potassium channels, which can alter their electrophysiological properties. Thus, our results uncover a trans-dominant role for an aberrantly expressed RBFOX2 isoform in DM1 cardiac pathogenesis.