Maturation of heart valve cell populations during postnatal remodeling.

Heart valve cells mediate extracellular matrix (ECM) remodeling during postnatal valve leaflet stratification, but phenotypic and transcriptional diversity of valve cells in development is largely unknown. Single cell analysis of mouse heart valve cells was used to evaluate cell heterogeneity during postnatal ECM remodeling and leaflet morphogenesis. The transcriptomic analysis of single cells from postnatal day (P)7 and P30 murine aortic (AoV) and mitral (MV) heart valves uncovered distinct subsets of melanocytes, immune and endothelial cells present at P7 and P30. By contrast, interstitial cell populations are different from P7 to P30. P7 valve leaflets exhibit two distinct collagen- and glycosaminoglycan-expressing interstitial cell clusters, and prevalent ECM gene expression. At P30, four interstitial cell clusters are apparent with leaflet specificity and differential expression of complement factors, ECM proteins and osteogenic genes. This initial transcriptomic analysis of postnatal heart valves at single cell resolution demonstrates that subpopulations of endothelial and immune cells are relatively constant throughout postnatal development, but interstitial cell subpopulations undergo changes in gene expression and cellular functions in primordial and mature valves.