Background: Despite in-depth knowledge of the molecular mechanisms controlling embryonic heart development, little is known about the signals governing postnatal maturation of the human heart. Methods: Single nucleus RNA-sequencing (snRNA-seq) of 54,140 nuclei from 9 human donors was used to profile transcriptional changes in diverse cardiac cell types during maturation from fetal stages to adulthood. Bulk RNA-sequencing and the assay for transposase-accessible chromatin using sequencing (ATAC-seq) were used to further validate transcriptional changes and to profile alterations in the chromatin accessibility landscape in purified cardiomyocyte nuclei from 21 human donors. Functional validation studies of sex steroids implicated in cardiac maturation were performed in human pluripotent stem cell-derived cardiac organoids and mice. Results: Our data identify the progesterone receptor as a key mediator of sex-dependent transcriptional programs during cardiomyocyte maturation. Functional validation studies in human cardiac organoids and mice demonstrate the progesterone receptor drives sex-specific metabolic programs and maturation of cardiac contractile properties. Conclusions: These data provide a blueprint for understanding human heart maturation in both sexes and reveal an important role for the progesterone receptor in human heart development.

SummaryAdrenomedullary chromaffin cells are catecholamine (CA)-producing cells originating from trunk neural crest (NC) via sympathoadrenal progenitors (SAPs). We generated NC and SAPs from human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) in vitro via BMP2/FGF2 exposure, ascertained by qPCR and immunoexpression of SOX10, ASCL1, TFAP2α, and PHOX2B, and by fluorescence-activated cell sorting selection for p75NTR and GD2, and confirmed their trunk-like HOX gene expression. We showed that continuing BMP4 and curtailing FGF2 in vitro, augmented with corticosteroid mimetic, induced these cells to upregulate the chromaffin cell-specific marker PNMT and other CA synthesis and storage markers, and we demonstrated noradrenaline and adrenaline by Faglu and high-performance liquid chromatography. We showed these human cells' SAP-like property of migration and differentiation into cells expressing chromaffin cell markers by implanting them into avian embryos in vivo and in chorio-allantoic membrane grafts. These cells have the potential for investigating differentiation of human chromaffin cells and for modeling diseases involving this cell type.