Ultraviolet-irradiated endothelial cells secrete stem cell factor and induce epidermal pigmentation.

Ultraviolet (UV)-associated hyperpigmented skins are characterized with increased vasculature underlying pigmentation, suggestive of the possible biological role of endothelial cells in the regulation of skin pigmentation during UV irradiation. In this study, we showed that UV-irradiated endothelial cells significantly increased the pigmentation of melanocytes through epithelial-mesenchymal crosstalk. The stimulatory effect of endothelial cells was further demonstrated using ex vivo human skin. RNA sequence analysis and enzyme-linked immunosorbent assay showed that endothelial cells secrete more stem cell factor (SCF) upon UV irradiation than non-irradiated cells. The increased pigmentation elicited by endothelial cells was abrogated following inhibition of SCF/c-KIT signaling. Together these results suggest that endothelial cells are activated upon UV exposure to release melanogenic factors such as SCF, which contributes to the development of skin hyperpigmentation during chronic sun exposure.