Abstract P1168: Hippo Signaling Interacts With Tgfb Pathway To Regulate Pacemaker Cell State And Fibrosis In The Sinoatrial Node

Abstract

Rhythmic heartbeats are initiated by electrical impulses from pacemaker cells (PCs) within the sinoatrial node (SAN). Fibroblasts provide structure support for PCs in the SAN, yet excessive fibrosis causes cardiac diseases and arrhythmias. Here we found that Hippo signaling cell-autonomously controls the cell state of PCs and non-cell-autonomously regulates the proliferation of fibroblasts in the SAN. Conditional knockout of Hippo signaling kinases Lats1 and Lats2 in PCs of adult mice ( Lats1/2 CKO) leads to SAN fibrosis and cardiac arrhythmias. RNAscope and immunostaining data indicated significantly increased Tgfβ1 and pSmad3 (Tgfβ signaling effector) in the SANs of Lats1/2 CKO compared to controls. Treatment with Tgfβ receptor inhibitor significantly reduced fibroblasts proliferation in Lats1/2 CKO, suggesting that Lats1/2 deletion caused fibrosis is partially mediated through Tgfβ signaling. Single-cell (sc)-multi-omics data (paired scRNA-seq and scATAC-seq) from control and Lats1/2 CKO SANs indicated that among three subtypes of PCs (PC1-PC3, classification based on their transcriptomic profile and chromatin accessibility), PC3 had the most upregulation of Yap (Hippo signaling effector) target genes in response to Lats1/2 deletion. Notably, Lats1/2 CKO PC3 was featured by highly increased expression of the smooth muscle genes, suggesting a smooth-muscle-like cell state change in PC3 after Lats1/2 deletion. Moreover, compared to controls, smooth-muscle-like PCs of Lats1/2 CKO had increased expression of Tgfβ ligands and Smad2/3, as well as Yap/Smad co-activation of smooth-muscle genes. In response to these changes in the smooth-muscle-like PCs of Lats1/2 CKO, fibroblasts exhibited increased expression of Tgfβ receptors. These PCs state changes and PC-fibroblasts communications likely lead to increased fibrosis and arrhythmias in Lats1/2 CKO. Taken together, our findings suggest that the Hippo signaling crosstalk with Tgfβ pathway regulates PC state and PC-fibroblasts communication.