Overexpression of the 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 disease-related deaths, yet, the underlying mechanisms remain unclear. 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 the characteristic cardiac conduction defects detected in DM1 individuals. Mice engineered to express the non-muscle RBFOX2 isoform in heart via tetracycline- inducible transgenesis, or CRISPR/Cas9 targeted genome editing, reproduced DM1- related cardiac-conduction delay and spontaneous episodes of arrhythmia. Furthermore, by integrating RNA binding with cardiac transcriptome datasets of DM1 patients, and mice expressing the non-muscle RBFOX2 isoform, we identified a core network of RBFOX2-driven splicing defects in sodium, potassium, and calcium channels that can alter their rate of ion diffusion and electrophysiological properties. Thus, our results uncover a trans-dominant role for an aberrantly expressed RBFOX2 isoform in DM1 cardiac pathogenesis. Overall design: The two set of mice, namely MHC and Rbfox2 OE were fed doxycycline containing diet for a period of 3 days, and at this point the mice were sacrificed and from harvested hearts, cardiomyocytes were isolated using the langendorff perfusion method. RNA was isolated from the cardiomyocytes using Qiagen kit, and sequenced on the Illumina HiSeq4000 platform after polyA RNA selection and library prep.