Genome-wide association studies in the Japanese population identified genetic loci and target gene associated with epidermal turnover.

The epidermis is an essential organ for life by retaining water and as a protective barrier. The epidermis is maintained through metabolism, in which basal cells produced from epidermal stem cells differentiate into spinous cells, granular cells and corneocytes, and are finally shed from the epidermal surface. This is epidermal turnover, and with aging, there is a decline in epidermis function. Other factors that may affect epidermal turnover include ultraviolet damage and genetic factors. These genetic factors are of particular interest as little is known. Although recent skin-focused genome-wide association studies (GWAS) have been conducted, the genetic regions associated with epidermal turnover are almost uninvestigated. Therefore, we conducted a GWAS on epidermal turnover in the Japanese population, using the corneocyte area, which correlates to the rate of epidermal turnover, as an indicator. As a result, rs2278431 (p = 1.29 × 10-7 ) in 19q13.2 was associated with corneocyte size. Furthermore, eQTL analysis suggested that rs2278431 was related to the SPINT2 gene. In addition, SPINT2 knockdown studies using epidermal keratinocytes revealed that SPINT2 is involved in keratinocyte proliferation and in corneocyte size regulation in reconstructed epidermis. These results suggest that rs2278431 is involved in the expression of SPINT2 and affects epidermal turnover.