Abstract 14227: A Pitx2-microRNA Pathway Functions in Inhibiting Susceptibility to Atrial Fibrillation
Background: Atrial fibrillation (AF) is the most common adult arrhythmia, but the molecular mechanisms underlying AF remain poorly understood. Genome wide association studies uncovered a major AF susceptibility locus on human chromosome 4q25 in close proximity to the Pitx2 homeobox gene. Pitx2, a target of the left-sided Nodal signaling pathway that initiates early in cardiac development, represses the sinoatrial node (SAN) program and pacemaker activity on the left side. To address the mechanisms underlying this repressive activity, we hypothesize that Pitx2 regulates microRNAs (miRs) to repress the SAN genetic program. microRNAs (miRs) are small non-coding RNAs that regulate gene expression post-transcriptionally.
Methods and Results: Using miR-microarray and chromatin immuno-precipitation (ChIP) sequencing, we discovered that Pitx2 positively regulates miR-17-92 and miR-106b-25. Intra-cardiac electrical stimulation reveals that loss of miR-17-92 and miR-106b-25 increases susceptibility to AF, exhibiting much higher incidence and significantly longer duration of pacing-inducible AF compared with controls. Electrocardiogram telemetry reveals that mice with miR-17-92 cardiac-specific inactivation and miR-106b-25 heterozygosity develop SAN dysfunction, a risk factor for AF in humans. The cardiac structure and function are normal in miR compound mutants, as examined by echocardiography, haematoxylin eosin staining, wheat germ agglutinin staining and Masson’s trichrome staining. Importantly, miR-17-92 and miR-106b-25 directly repress genes such as Shox2 and Tbx3 that are required for SAN development, as determined by in situ hybridization, real time PCR and luciferase assays. Furthermore we evaluated the spontaneous calcium (Ca) release events in isolated atrial myocytes and found significantly increased Ca spark frequency in miR compound mutants compared with controls.
Conclusion: Our findings unveil a Pitx2-miR pathway inhibits AF susceptibility, potentially through mechanisms including limiting the SAN genetic program to the right-sided pacemaker region, and regulating atrial calcium handling.
- © 2013 by American Heart Association, Inc.