PITX2 missense coding variant expression in mice reveals direct function in atrial fibrillation

Atrial fibrillation (AF) is the most common sustained human cardiac arrhythmia and linked to a drastic increase in stroke and heart failure risk. While sequence variations in the PITX2 non-coding region are the strongest genetic signature of AF risk, the direct role of PITX2 in AF remains a topic of debate. Here, we generated a mouse model (Pitx2Pro41Ser) of a human PITX2 coding variant linked to increased AF risk in the Finnish population. The Pitx2Pro41Ser mice exhibit near-complete penetrance of pacing-induced AF, and transcriptional profiling indicates that Pitx2Pro41Ser is a loss-of-function mutation. In vivo cleavage under targets and tagmentation (CUT&Tag) reveals that PITX2 acts as a transcriptional repressor in developing left atrial cardiomyocytes independent of DNA methylation. Ectopic Pitx2 expression in postnatal right atrial cardiomyocytes via adeno-associated virus (AAV) delivery or genetic overexpression represses right atrial genes and induces a left atrial transcriptome, revealing unexpected plasticity of postnatal atrial cardiomyocytes. Strikingly, delivery of Pitx2 AAV into Pitx2Pro41Ser mice rescues AF inducibility uncovering a direct link between PITX2 activity and AF susceptibility.