Vitamin C Promotes Epidermal Proliferation by Promoting DNA Demethylation of Proliferation-Related Genes in Human Epidermal Equivalents

Keratinocyte differentiation is highly regulated to produce the stratified structure of the epidermis and must be balanced with cell proliferation. Our prior studies revealed that hairless mice that cannot synthesize vitamin C (VC) exhibit epidermal atrophy. VC is a cofactor for the DNA demethylation (ten-eleven translocation) enzyme, but the role of VC in DNA demethylation during keratinocyte differentiation remains unclear. In this study, we evaluated the role of VC in epigenetic regulation of epidermal proliferation and differentiation in a human epidermal equivalent model. Our findings demonstrated that intracellular VC uptake increased epidermal thickness, cell proliferation, and global levels of 5-hydroxymethylcytosine DNA. Notably, these effects of VC were attenuated by an inhibitor of the ten-eleven translocation enzyme. DNA microarray and whole-genome bisulfite sequencing analyses revealed that 12 genes related to cell proliferation were significantly upregulated by VC. Furthermore, hypomethylated DNA regions associated with these genes were revealed in the presence of VC. Collectively, our findings provide insight into how VC increases epidermal thickness by promoting keratinocyte proliferation through the DNA demethylation of proliferation-related genes. VC is a promising molecule that can be used as developing treatment for epidermal thinning, including in aging.