Single-cell RNA sequencing profiles age-related transcriptional landscapes in human hair follicle cells.

Hair loss and graying, the earliest visible signs of skin aging, are driven by the functional decline of hair follicle stem cells and their niches. To elucidate the transcriptional mechanisms involved in scalp aging, we conducted a comprehensive analysis of human scalp samples using single-cell RNA sequencing and spatial transcriptomic technologies. Our study profiled the transcriptomes of 57,181 cells from scalp samples obtained from four young, six middle-aged, and one elderly individual. The integrated bioinformatic pipeline included cell clustering, spatial deconvolution, pseudotime trajectory, as well as cell-type specific gene expression, and intercellular communication analysis. An additional 92 volunteers were included, comprising 90 (37 young, 27 middle-aged, and 26 elderly) for trichoscopic examination, one young individual for senescence-associated β-galactosidase (SA-β-gal) staining, and one elderly individual for both MKI67 immunofluorescence and SA-β-gal staining. This approach led to several key findings: we identified three subtypes of mitotic keratinocytes that localized in the interfollicular epidermis (IFE), outer root sheath (ORS), and hair matrix, with pseudotime trajectory further confirming their transitional stage. Furthermore, in middle-aged scalps, we observed activated activator protein 1 (AP-1) transcription factor complex in keratinocytes, upregulated DCT gene in melanocytes, and decreased bone morphogenetic protein (BMP) and noncanonical wingless/integrated (ncWNT) signaling in dermal papilla (DP)-keratinocytes cross-talk. Due to the insufficient sample size and under-representation of elderly samples, transcriptional features associated with late aging, sex, and scalp regions were not completely captured. Nevertheless, our study provides valuable cell-resolved transcriptional insights into hair follicle aging and may support the development of future regenerative therapies.