ABSTRACT: Aging is characterized by a gradual decline in function, partly due to molecular damage that accumulates over time. Human skin is highly susceptible to both chronological aging and environmental damage in the form of UV photoaging. This results in detrimental structural and physiological changes with age. In this study we sought to comprehensively address both chronological and photoaging at the single-cell level, and to explore genetic and environmental factors, revealing their influences on the aging process. We included samples from young, middle-aged, and old individuals, and with these samples, we compared chronological aging and photoaging. Utilizing single-cell RNA sequencing, we created a comprehensive human skin cell atlas, that offers insights into the cellular composition and functions. We investigated the renewal ability of epidermis stem cells as they age and extended the study to fibroblasts, hair follicles, and endothelial cells. Examining the genetic landscape of aging in keratinocytes, we identified two distinct "gene modules" with altered gene expression during aging. Furthermore, we uncovered that skin aging involves interactions between epidermal keratinocytes and dermal fibroblasts, as well as extensive communication of keratinocytes with various other skin cell types as revealed through ligand-receptor pairs. Interactions, such as COL17A1-A1b1complex, highlighted a direct link between keratinocytes and fibroblast stimulation for collagen production. Most importantly, A key gene, MYO1, associated with skin aging was identified, leading to the development of an innovative mRNA treatment aimed at promoting skin rejuvenation by targeting this gene. Experimental results demonstrated that the mRNA treatment reduces basal stem cell senescence, increases basal stem cell proliferation, and enhances collagen production in fibroblasts via keratinocyte-fibroblast communication. The MYO1-targeted treatment is validated as an effective strategy for reversing skin aging by targeting cellular mechanisms.
