Pitx2 modulates a Tbx5 -dependent gene regulatory network to maintain atrial rhythm

Abstract

Cardiac rhythm is extremely robust, generating 2 billion contraction cycles during the average human life span. Transcriptional control of cardiac rhythm is poorly understood. We found that removal of the transcription factor gene Tbx5 from the adult mouse caused primary spontaneous and sustained atrial fibrillation (AF). Atrial cardiomyocytes from the Tbx5-mutant mice exhibited action potential abnormalities, including spontaneous depolarizations, which were rescued by chelating free calcium. We identified a multitiered transcriptional network that linked seven previously defined AF risk loci: TBX5 directly activated PITX2, and TBX5 and PITX2 antagonistically regulated membrane effector genes Scn5a, Gja1, Ryr2, Dsp, and Atp2a2. In addition, reduced Tbx5 dose by adult-specific haploinsufficiency caused decreased target gene expression, myocardial automaticity, and AF inducibility, which were all rescued by Pitx2 haploinsufficiency in mice. These results defined a transcriptional architecture for atrial rhythm control organized as an incoherent feed-forward loop, driven by TBX5 and modulated by PITX2. TBX5/PITX2 interplay provides tight control of atrial rhythm effector gene expression, and perturbation of the co-regulated network caused AF susceptibility. This work provides a model for the molecular mechanisms underpinning the genetic implication of multiple AF genome-wide association studies loci and will contribute to future efforts to stratify patients for AF risk by genotype.

A Comprehensive TALEN-Based Knockout Library for Generating Human-Induced Pluripotent Stem Cell–Based Models for Cardiovascular Diseases

“…The directed differentiation protocol yielded cultures enriched (70%–85%) in cTnT (+) beating iPSC-CMs in both WT and TBX5-KO iPSC lines at day 15 post-differentiation (Online Figure VII) that displayed a typical sarcomeric morphology (Figure 4b). As HOS is associated with electrophysiological abnormalities, 26,28 we next characterized the action potential (APs) of the isogenic iPSC-CMs. Both TBX5-KO and WT iPSC-CMs displayed typical AP morphologies, including ventricular-, atrial-, and nodal-like subtypes (Figure 4d and Online Table V).…”

Association of atrial fibrillation susceptibility genes, atrial fibrillation phenotypes and response to catheter ablation: a gene-based analysis of GWAS data

“…In addition, both ZFHX3 and PITX2 impact on other downstream genes such as TBX5, NKX2.5, KCNQ1 and SCN1B that play critical roles in cardiac electrophysiology and AF [20]. Of those, TBX5 modulation has very recently been found to profoundly alter cardiac channel gene expression and to cause primary, spontaneous AF in mice [22]. …”

Multi-ethnic genome-wide association study for atrial fibrillation

“…22–24 A transcriptional co-regulatory network governed by transcription factors encoded by TBX5 and PITX2 has been shown to be critical for atrial development. 25 …”