O26 Spatial transcriptomic analysis of healthy human skin reveals fundamental differences between individuals at the extremes of the pigmentary spectrum

Abstract Introduction and aims The steady-state transcriptome of healthy human skin is poorly understood at the single-cell level. Furthermore, differences in the transcriptional profile of skin of differing pigmentation remains unexplored. Our aim was to use spatial transcriptomics to compare single-cell gene expression profiles of healthy, photoprotected skin from lightly and darkly pigmented young individuals. Methods Skin punch biopsies were collected from the photoprotected buttock of young (22–29 years) participants of Fitzpatrick skin type I–II (n = 4) and type V–VI (n = 4). Spatial transcriptomic data were generated from cryosections using the Xenium In Situ platform (10X Genomics) and Prime 5K panel (5001 genes). Differentially expressed genes were identified and analysed using Ingenuity Pathway Analysis (Qiagen). Results Comparative analysis of photoprotected buttock skin identified 7 genes upregulated in lighter skin and 151 genes upregulated in darker skin. In lighter skin, upregulated genes were primarily associated with pathways linked to inflammation and sensory modulation, lipid metabolism and skin barrier function, oxidative stress regulation, and vitamin D metabolism. Spatially, these genes predominantly localized to melanocytes and differentiated keratinocytes. In darker skin, upregulated genes were mainly expressed in keratinocytes, melanocytes, Langerhans cells, and epidermal resident T cells, and were linked to epidermal turnover, modulation of inflammation, and epidermal structural integrity. Pathway analysis revealed that both lighter and darker skin exhibited activation of inflammatory pathways. Darker skin showed specific activation of pathways related to cancer development, extracellular matrix remodelling, tissue development, and metabolic regulation. In contrast, lighter skin demonstrated activation of pathways associated with anticancer mechanisms, and metabolic and mitochondrial dysfunction. Conclusions Our findings suggest that photoprotected (i.e. steady-state) darker skin has a more active transcriptome compared with lighter skin, particularly in pathways relating to epidermal turnover and structural integrity. These fundamental differences may underscore the observed structural and functional differences between skin of differing pigmentation.