Cardiac organoids reveal mechanisms of human cardiogenesis

Self-organisation and coordinated morphogenesis of multiple cardiac lineages is essential for the development and function of the heart. However, the absence of a human in vitro model that mimics the basic lineage architecture of the heart hinders research into developmental mechanisms and congenital defects. Here, we describe the establishment of a reliable, lineage-controlled and high-throughput cardiac organoid platform. We show that cardiac mesoderm derived from human pluripotent stem cells robustly self-organises and differentiates into cardiomyocytes forming a cavity. Co-differentiation of cardiomyocytes and endothelial cells from cardiac mesoderm within these structures is required to form a separate endothelial layer. As in vivo, the epicardium engulfs these cardiac organoids, migrates into the cardiomyocyte layer and differentiates. Thus, the cardiac organoid platform represents a powerful resource for the quantitative and mechanistic analysis of early human cardiogenesis that is otherwise inaccessible. Overall design: Human pluripotent stem cells were differentiated into 2D cardiomyocytes, 2D endothelial cells, 3D assembled CM structures, 2D and 3D epicardial cells and 3D cardiac organoids consisting of 1) mainly cardiomyocytes or 2) cardiomyocytes and endothelial cells. 2D Human cardiac microvascular endothelial cells were used as a control endothelial cell population.