Keratin 17 as a marker of UVB-induced stress in human epidermis and modulation by Vitis vinifera extract

Human epidermis responds to ultraviolet (UV)B-induced damage by tolerating it, restoring it, or undergoing programmed cell death when the damage is massive. Recently, compounds rich in polyphenols, such as Vitis vinifera L. leaf extract (VVLe), have attracted a lot of interest for skin protection. We investigated the effect of VVLe pre-treatment (1 h) in a 2D model of HaCaT cells and in 3D organotypic cultures of normal human skin exposed to a single UVB dose to study the immediate specific events 1 h and the response orchestrated in the epidermal layer 24 h after irradiation, respectively. In both models, transmission electron microscopy analysis was carried out. The expression of the inducible keratin K17, the activation of both pSTAT3 and Nuclear Factor (NF)-κB signalling pathways, and the epidermal distribution of Toll-Like Receptor (TLR) 4 were assessed by immunofluorescence in the 2D and 3D model. In 3D organotypic cultures, thanks to the preservation of a multi-layered structure, the epidermal distribution of the differentiation biomarkers K10 and K14 as well as of K16 was analysed by immunofluorescence, while the release of interleukin (IL)-8 was evaluated by ELISA. In skin bioptic fragments, cytotoxicity and genotoxicity were investigated by LDH assay and Alkaline Comet assay, respectively, and then compared to cell proliferation. The epidermal distribution of the histone γ-H2AX, indicating the fragmented DNA, was analysed by immunofluorescence. In both experimental models, VVLe tuned UVB-induced K17 expression to a different extent in HaCaT cells and in the skin. In HaCaT cells, pSTAT3 activation was induced by UVB and reverted by VVLe pre-treatment. TLR4 expression was triggered by UVB in both models, but VVLe pre-treatment abolished this event only in HaCaT cells. NF-κB immunostaining increased both in the nucleus and in the cytoplasm only in HaCaT cells after UVB irradiation. In all irradiated skin samples, VVLe pre-treatment was not able to revert the inhibition of epidermal proliferation, K16 expression, and IL-8 secretion. The effectiveness of VVLe in contrasting the irradiation-induced genotoxicity still remains unclear. In conclusion, our study clearly shows that K17 is a robust marker induced in keratinocytes upon UVB stimulation and that this event can be reverted by a pre-treatment with VVLe. On the whole, these observations represent a novelty in the scenario of the complex relationships between the effects exerted by UVB rays on human skin and significantly improve the knowledge regarding the modulation of the early epidermal response induced by a single exposure to UVB in the presence of VVLe.