Gene regulatory mechanisms controlling cardiac rhythm and pacemaker function

Each heartbeat is initiated by specialized pacemaker cardiomyocytes in the sinus node, the heart’s primary pacemaker. Their identity and function are established and maintained by tightly regulated gene expression programs. Sinus node dysfunction and atrial arrhythmias arise when these programs are disrupted by rare coding mutations, common non-coding variation or altered three-dimensional genome organization, highlighting the importance of precise transcription factor activity, dosage and chromatin context in cardiac rhythm control.
In this thesis, we examine the gene regulatory programs that establish and maintain pacemaker cardiomyocyte identity and how their disruption leads to sinus node dysfunction and atrial arrhythmogenesis. We identify a novel cardiac syndrome associated with deletions at chromosome 4q25 that disrupt CTCF binding sites and chromatin topology, driving ectopic PITX2 expression in the sinus node. Using mouse models and human induced pluripotent stem cell-derived pacemaker cardiomyocytes, we show that PITX2 misexpression in pacemaker cardiomyocytes acts in a dosage-dependent manner to progressively impair pacemaker cardiomyocyte identity and promote sinus node dysfunction. We additionally show that altered higher-order chromatin organization at the PITX2 locus drives region-specific transcriptional changes across the atria. In parallel, we further characterize a pathogenic TBX5 gain-of-function variant that alters DNA binding and transcription factor cooperativity, reshaping atrial and sinus node gene expression, compromising sinus node function.
These findings reveal that cardiac rhythm is governed by dosage-sensitive and context-dependent gene regulatory mechanisms across developmental stages and cardiac compartments. This work advances our mechanistic understanding of sinus node function and identifies regulatory nodes as potential targets for therapeutic intervention.