Age-associated fibroblasts identified by single cell RNA-seq of human dermis disrupt fibroblastic identity as a hallmark of aging skin

Summary: Abstract Body: Skin aging is characterized by marked atrophy and loss of elasticity within the dermal connective tissue. Fibroblasts (FBs), which primarily regulate dermal components, exhibit cellular diversity. However, the alterations in FBs diversity and communication signals during aging remain poorly understood. Here we show that single-cell RNA sequencing (scRNAseq) on human dermis from healthy individuals of varying ages, clarified seven distinct FB clusters, including age-associated fibroblasts (AAF) with canonical senescent features. Immunostaining revealed the localization of seven FB subpopulations and a dramatic increase in the number of AAF with age. The putative trajectory of seven FB clusters revealed a lineage progression from stem cells to terminal differentiation states characterized by AAF. Immunostaining for AAF markers showed a significant overlap with oxidative DNA damage. Furthermore, ligand-receptor analyses indicated that AAF interact with other FB clusters through TGFβ superfamily to affect the fate of dermal mesenchymal cells. Indeed, genes enriched in papillary FB cluster from old donors showed adipogenic and chondrogenic traits compared to young. The combination of TGFβs and BMPs enhanced the commitment to adipocyte lineages and upregulated chondrocytes-related genes in isolated papillary FBs. Finally, aged human dermis showed ectopic adipogenesis and the accumulation of cartilage-related matrix protein. In summary, we identified AAF within the diverse population of dermal FBs and their function. AAF not only causes inflammation due to the cellular senescence, but also disrupts the nature of FBs and even shakes the fate of FBs to adipogenic and chondrogenic lineages in skin aging. A "loss of fibroblastic identity" can be introduced as a novel concept in the understanding of dermal skin aging. Mika Sawane¹, Tsukasa Kouno², Yoshinari Ando², Miki Kojima², Makiko Komata¹, Jay W. Shin^{2, 3}, Kentaro Kajiya¹ 1. MIRAI Technology Institute, Shiseido Co., Ltd, Yokohama, Kanagawa, Japan. 2. IMS, RIKEN, Yokohama, Kanagawa, Japan. 3. Genome Institute of Singapore, A*STAR, Singapore, Singapore. Cell Communication Networks and Stromal Biology