Chronic ultraviolet radiation modulates epidermal differentiation as it up‐regulates transglutaminase 1 and its substrates

Abstract

Ultraviolet radiation (UVR) stimulates cellular mitosis, which leads to epidermal hyperplasia. On the basis of hypothesis that chronic UVR may modulate differentiation as well as epidermal hyperplasia, we evaluated the modulation of markers of epidermal differentiation, such as transglutaminase 1 (TGase 1), filaggrin and loricrin, by chronic UVR in vivo. Total TGase activities assay or in situ TGase activities were measured in human and mouse skin. TGase 1 expression was identified by immunohistochemical staining in human skin. In the human, the pre-auricular skin of face was used for samples of chronic UVR, and the post-auricular skin was selected as non-UVR control. The changes of filaggrin and loricrin were identified by western immunoblots. In human and mouse epidermis, chronic UVR induced the increase of in situ TGase activities or total TGase activities as it up-regulated TGase 1 expression in the epidermis. As the substrates of TGase 1, chronic UVR induced the up-regulation of filaggrin and loricrin in mouse epidermis as well. At the same time, chronic UVR induced the marked epidermal hyperplasia in human and mouse skin. Chronic UVR stimulates epidermal differentiation as it up-regulates TGase 1 and its substrates. The modified epidermal differentiation is balanced with epidermal hyperplasia, leading to the maintenance of epidermal homeostasis in the UV-irradiated epidermis.