The single-cell atlas of the heart reveals an unexpected erythrocyte-like cardiomyocyte

BACKGROUND: Single-cell RNA sequencing (scRNA-seq) is widely used in cancer research and organ development since its powerful ability to analyze cellular heterogeneity. However, its application in cardiomyocytes is rare mainly because the cardiomyocytes are too large and fragile to withstand traditional single-cell approaches. METHODS: Through designing the isolation procedure of neonatal mouse cardiac cells, we perform scRNA-seq with samples from 27 neonatal mice. Individual cell transcriptomes were subsequently clustered based on transcriptional profiles of highly variable genes. Then these clusters were used as the basis for between-cluster differential gene expression analyses and between-cluster interaction analyses. At last, we analyzed the intersection of these clusters with genetic and pharmacologic data. RESULTS: We provide detailed cellular atlases of the heart at single-cell resolution across four different stages after birth. We have luckily obtained tens of thousands of cardiomyocytes, to our knowledge, the most extensive reference framework so far. Moreover, we have discovered unexpected erythrocytes-like cardiomyocyte-terminal cardiomyocytes, comprising more than a third of all the cardiomyocytes. Only a few genes are highly expressed in these cardiomyocytes. They are highly differentiated cardiomyocytes that function as contraction pump. In addition, we have identified two cardiomyocyte-like conducting cells, lending support to the theory that the sinoatrial node pacemaker cells are specialized cardiomyocytes. Furthermore, we provide a substantial blueprint for comprehensive interactions between cardiomyocytes and other cardiac cells. We linked specific cell types to adverse drug reactions and congenital heart diseases and analyzed the roles of cell subtypes in adverse drug reactions and cardiac diseases. CONCLUSIONS: This mouse cardiac cell atlas improves our understanding of the heart and provides a valuable reference in response to varying physiological conditions and diseases. We collected ~50000 single cells from the entire hearts of neonatal C57BL/6 mice (Day1, Day2, Day4, and Day6 after birth) and performed single-cell RNA-seq sequencing.