New Insights in Photoaging Process Revealed by In Vitro Reconstructed Skin Models

Abstract

Photoaging, clinically characterized by wrinkles, sagging, and age spots, mostly results from chronic impacts of solar ultraviolet (UV) rays affecting the whole skin, from surface to deep dermis. Three-dimensional (3-D) organotypic skin models represent useful in vitro tools to better understand the early UV-induced biological events. Such systems not only allow to reproduce in vitro well-known biomarkers for sunburn reaction but also to identify new key biological alterations induced by UVA exposure and involved in dermal photoaging process. Based upon new scientific proofs of the harmful role of chronic suberythemal UV exposures, the effects of exposures to nonextreme daily UV spectrum, mimicking more realistic everyday life conditions, have revealed a true biological impact upon skin with a strong oxidative stress and a major contribution of UVA rays. More recent data have demonstrated the damaging effects of long UVA wavelengths (UVA1), although less energetic than UVB or UVA2. UVA1 exposure could actually induce the production of reactive oxygen species (ROS) and DNA lesions but also impair several major biological functions and pathways in both epidermis and dermis. These data are in line with recent in vivo data, altogether strongly supporting the need for an adequate UVA1 photoprotection. Finally, the development of a full-thickness pigmented skin model allows to prove the role of dermal fibroblasts on the pigmentary function, showing that the photoaging of dermal fibroblasts can stimulate skin pigmentation. A link between photoaging-induced dermal alterations and pigmentary changes could then be established thanks to an appropriate in vitro skin model.