Fibroblasts are the main dermal cell type and are essential for the architecture and function of human skin. Important differences have been described between fibroblasts localized in distinct dermal layers, and these cells are also known to perform varied functions. However, this phenomenon has not been analyzed comprehensively yet. Here we have used single-cell RNA sequencing to analyze >15,000 cells from a sun-protected area in young and old donors. Our results define four main fibroblast subpopulations that can be spatially localized and functionally distinguished. Importantly, intrinsic aging reduces this fibroblast priming, generates distinct expression patterns of skin aging-associated genes, and substantially reduces the interactions of dermal fibroblasts with other skin cell types. Our work thus provides comprehensive evidence for a functional specialization of human dermal fibroblasts and suggests that the age-related loss of fibroblast priming contributes to human skin aging.
