UC San Diego

The heart, which is the first organ to develop, is highly dependent on its form to function. Disruption of cardiac structures contributing to this form can lead to a wide range of adult/congenital heart diseases and possible fetal demise. However, how diverse cardiovascular cell types spatially interact and organize into complex morphological communities/structures that are critical for heart function remains to be fully illuminated. Here, we interrogate the interactive cellular mechanisms that direct the morphogenesis and remodeling of heterogeneous cellular communities during the construction of the human heart by providing a high-resolution spatial and single-cell transcriptomic human cardiovascular cell atlas. We integrated high-throughput multiplexed fluorescent in situ hybridization (MERFISH) spatial transcriptomics with corresponding single-cell RNA-seq and spatially mapped 27 major cardiac cell types that could be further refined into specialized cellular subtypes and states including previously uncharacterized cell populations. These major cell types were spatially organized into unique cellular communities that compose of combinations of specific cardiac cell types and correspond to distinct anatomic cardiac structures. Detailed examination of the cardiac ventricles revealed an unexpected cellular heterogeneity and organization of the ventricular wall, which was composed of at least three regional cellular communities corresponding to outer-compact, mid, and inner-trabecular layers. Analysis of these communities uncovered thousands of cellular interactions among 11 cell types within the left ventricular wall, including a Semaphorin-Plexin mediated cardiomyocyte-cardiac fibroblast-endothelial multi-cellular interaction that coordinates the precise allocation of migrating ERBB2/4+PLEXINA2/4+ cardiomyocyte subtypes during the critical cardiac developmental process of ventricular compaction. These identified morphogenetic events could be recapitulated in a human pluripotent stem cell (hPSC) cardiac organoid system thus confirming the role of Semaphorin-Plexin during human ventricular wall morphogenesis. Our findings provide the foundations for analyzing the morphogenesis of the critical structures comprising the heart and serves as a guide to improve the construction of complex structures during cardiovascular development and generate hPSC-derived cardiac tissues composed of multiple cardiac cell-types for the study of human cardiovascular development, tissue replacement therapy and disease modeling.