Vitamin D and the Epidermis

The document from 18 years ago discussed the role of Vitamin D3 and its active metabolite, 1,25 dihydroxyvitamin D3 (1,25(OH)2D3), in the epidermis. It highlighted that epidermal cells, or keratinocytes, not only produce Vitamin D3 but also 1,25(OH)2D3, and contain 1,25(OH)2D3 receptors. These cells respond to 1,25(OH)2D3 with changes in proliferation and differentiation, processes that are modulated by calcium. The document also noted that a calcium gradient exists in the epidermis, which is an important regulator of proliferation and differentiation. Animals unable to produce 1,25(OH)2D3 showed difficulties in restoring this gradient and abnormalities in terminal differentiation of the epidermis. Additionally, animals lacking the vitamin D receptor (VDR) showed abnormalities in epidermal differentiation and hair follicle cycling. This suggests that the epidermis is not only a source of Vitamin D, but also a source and target for its biologically active metabolite 1,25(OH)2D3, and can be regulated by the VDR in a ligand-independent manner.