Abstract P1125: Development Of A Multicellular Sinoatrial Node Organoid For Modeling Robust Pacemaking And Conduction

Abstract

The prevalence and healthcare burden of sinoatrial (SA) node dysfunction have been continuously increasing due to the growth in the elderly population, emphasizing the need for more detailed studies of SA node functions to enable effective therapy for treating and preventing SA node dysfunction. However, current SA node or pacemaker models are limited to isolated single cell-type cells or cell clusters, leaving a gap in the ability to model autonomous cardiac contraction. In contrast, the SA node is a natural organoid with elaborate insulated architecture and heterogeneous cellular composition. Furthermore, current single cell-type pacemakers have worsened heart rhythm stability during one-month in vivo integration, limiting their application as clinically viable biological pacemakers that can generate robust pacemaking and conduction. To address the current limitations of SA node models, we developed a three-dimensional multicellular SA node organoid by reproducing the human SA node's multicellular tissue structure and fail-safe mechanisms. First, inspired by the SA node's partial electrical insulation, we structurally isolated a group of cardiomyocytes with a single exit pathway that allowed for electrical connection to neighboring cardiomyocytes. We found that the geometrically isolated cardiomyocytes successfully activated neighboring quiescent cardiomyocytes without any pacemaker-related gene expression, and they maintained the rhythm for three months. Second, the overexpression of HCN4, a key pacemaker channel, in these isolated cardiomyocytes further improved heart rhythm variability down to the millisecond level, suggesting the interplay between pacemaker gene expression and nodal architecture for long-term, high-fidelity pacing. Finally, we successfully fabricated and integrated the SA node organoid into our 3D pacemaker organoid-myocardium platform, and the integrated organoid dominated rhythm control in 3D cardiac muscle constructs for 30 days. These studies will help define if tissue-level architecture and multicellular compositions mediate SA node's robust pacemaking and conduction and may reveal a high-fidelity tissue-level biological pacemaker as a novel therapeutic strategy for SA node dysfunctions.