Constructing a Single-Cell Transcriptome Atlas of the Hair Cycle to Decipher Tissue Regeneration Dynamics in Human Skin

Abstract

The hair cycle is a valuable model for studying the process of complete tissue regeneration in adult mammals. Time-course single-cell transcriptomics offers a powerful approach for characterizing changes in cellular states and interactions during this process. However, this methodology is challenging, particularly in humans, mainly due to the unpredictability of the hair cycle stages and limited accessibility for sampling. In this study, we performed single-cell RNA sequencing on 19 individual human skin tissues containing a single hair. We generated a pseudotime of the hair cycle (i.e., a “pseudo-hair-cycle”) by statiscically analyzing gene expression across these samples to infer temporal order. The pseudo-hair-cycle delineates the continuum of gene expression changes in 16 distinct cell populations occurring throughout the entire hair cycle, which shed light on specific cellular states and interactions during various phases of the hair cycle. We identify hair follicle keratinocytes, dermal sheath fibroblasts, vascular endothelial cells, and leukocytes as being associated with tissue regeneration during the catagen phase. Thus, this study presents a valuable atlas for investigating the dynamic molecular and cellular mechanisms underlying complete tissue regeneration in humans.

Note:
Funding Information: This work was financially supported by collaborative funding from POLA Chemical Industries, Inc. to Noriko Suenobu (POLA Chemical Industries, Inc.), Satoshi Hirakawa (POLA Chemical Industries, Inc.), and H.F. H.F. gratefully acknowledges financial support from RIKEN (intramural funding), the JSPS Kakenhi (20H03706), the MEXT Kakenhi (23H04927, 23H04928) and the JST CREST (JPMJCR1926).

Declaration of Interests: J.Y., Y.S., and H.F. applied for a patent on the method of time-course gene expression analysis using samples whose time points are originally unknown. The remaining authors declare no competing interests.

Ethics Approval Statement: Full thickness human skin tissue samples without subcutaneous white adipose tissue were purchased from Biopredic International (Saint Grégoire, France) via KAC (Kyoto, Japan). Biopredic International complies strictly with the ethical rules for donation and collection of human tissues according to French Law L.1245-2 CSP.

Keywords: tissue regeneration, human hair cycle, single-cell transcriptome analysis, pseudo-time-course, catagen, lower dermal sheath fibroblast, vascular endothelial cell, leukocyte