Investigating The Role of Hippo Signaling in Sinoatrial Node Development

Project Summary/Abstract Cardiac arrhythmias are one of the leading causes of cardiac-related mortalities worldwide and can arise from sinoatrial node dysfunction (SND). The sinoatrial node (SAN) is the heart's natural pacemaker and contains specialized cardiomyocytes (CMs) called pacemaker cells (PCs) that generate spontaneous action potentials to contract the cardiac chambers. Although the SAN is essential for maintaining rhythmic heartbeats, it is the least understood cardiac entity. Recent efforts in SAN research have focused on engineering a biological pacemaker to replace dysfunctional SANs. However, this requires a deep understanding of the mechanisms regulating SAN development, which is currently limited. Given the technical challenges, only a few transcription factors (TFs), such as Tbx3, Isl1, and Shox2, have been identified to regulate the SAN gene program. The fundamental Hippo signaling pathway plays critical roles in cardiac development and regeneration. Our lab recently discovered Hippo signaling as a critical regulator of adult SAN homeostasis. We effectively inhibited Hippo activity in mice by knocking out Hippo's core kinases Lats1/2 exclusively in PCs, which resulted in dysregulated calcium handling and fibrosis. Hippo signaling is also known to govern heart size by regulating CM cell state during development. Despite Hippo's critical roles in multiple cardiac contexts, its function in embryonic SAN development remains unknown. My preliminary data suggests that Hippo signaling regulates PC proliferation partially through the activation of IGF signaling, a known cardiac pro-growth signaling pathway. Additionally, my preliminary data suggests that Hippo signaling regulates SAN TF Tbx3 and calcium ion channels to influence PC function. Given my strong preliminary data, I hypothesize that Hippo signaling regulates SAN morphogenesis and function during embryonic development. To test my hypothesis, I have obtained a novel mouse model where Cre recombinase is more specific to the embryonic SAN region compared to existing Cre drivers. Using this mouse model, I will conditionally knock out Lats1/2 in the embryonic SAN. In Aim 1, I will elucidate the role of Hippo signaling in SAN morphogenesis by analyzing signaling activity, proliferation, and IGF signaling components upon Hippo inhibition. In Aim 2, I will investigate Hippo's role in regulating the SAN gene program and PC function. This project aims to elucidate how Hippo signaling regulates SAN development. The findings from this proposed study will shed light on the molecular mechanisms regulating SAN development and will discover novel insights for advancing the field in the generation of a biological pacemaker.