Abstract 16713: Defining the Tbx5-Dependent miRNA Regulatory Networks of Atrial Fibrillation

Abstract

Atrial fibrillation (AF) is the most commonly diagnosed arrhythmic disorder, characterized by random electrical activity in the heart. Complications of AF include stroke and heart failure, which makes understanding the molecular mechanism underlying this conduction defect imperative. The Tbx5 locus has been implicated by genome wide association studies (GWAS) to have an increased risk for AF. Our lab has previously demonstrated the absence of this transcription factor leads to spontaneous and sustained AF, which corroborates the importance of Tbx5 in the maintenance of cardiac rhythm. While Tbx5 is known to drive the network for cardiac rhythm, the downstream regulatory components need to be further characterized, including the downstream miRNAs. The components involved in cardiac rhythm are dose sensitive, therefore small perturbations in gene expression can lead to arrhythmias. Maintaining stable levels of gene expression can be regulated with miRNAs, which provide a negative feedback in dose sensitive pathways. Tbx5 -deficient mice developed spontaneous, sustained AF; in order to further interrogate the TBX5-dependent pathway that led to AF, we transcriptionally profiled small RNAs from the left atrium of Tbx5 -deficient mice. The most downregulated TBX5-dependent miRNA was miR10b. In concordance with previous publications, our miR10b mimic and inhibitor experiments in HL-1 cardiomyocytes demonstrate that miR10b negatively regulates Tbx5 expression. Therefore, we hypothesized that miR10b was crucial in the maintenance of atrial rhythm. Cellular electrophysiology studies with the overexpression of miR10b in HL-1 cardiomyocytes led to the elongation of atrial action potentials, similar to the phenotype we saw in the Tbx5 -deficient atrial tissue. Using whole mouse electrophysiology, we found that the mir10b removal in the hearts leads to increased AF susceptibility. Thus, providing evidence that mirR10b is crucial for the maintenance of normal cardiac conduction. In order to identify other miRNAs essential for cardiac conduction, we examined the other TBX5-dependent miRNAs in a high-throughput calcium screen. Further defining the miRNAs can provide a better understanding of the regulatory mechanisms crucial for cardiac conduction.