Development of a lip vermilion epithelium reconstruction model using keratinocytes from skin and oral mucosa

Lip vermilion is unique and can be distinguished from the adjacent skin and oral mucosa. However, because of the lack of appropriate evaluation tools, skin and/or oral mucosa substitutes such as in vitro vermilion epithelial models have been used for lip product testing. We aimed to develop and characterize a lip vermilion epithelium reconstruction model (LVERM) using skin and oral keratinocytes. LVERM was manufactured by co-culturing primary skin and oral keratinocytes, using a device that allowed the separation of cell seeding, and created an intercalated cell-free zone, referred to as the vermilion part. After removing the device, LVERM construction was completed in 8 days, in a submerged condition. Subsequently, they were placed in an air-liquid interface for 7 days. To determine the epithelial characteristics of LVERM, keratin 2e (KRT2) and small proline-rich protein 3 (SPRR3) expression patterns were examined. The in vivo expression profiles of KRT2 and SPRR3 genes in vermilion were also examined. We found that a continuous multi-layered epithelium was generated in the LVERM that exhibited ortho- and para-keratinization in the skin and oral mucosa parts, respectively. Although an intermediate keratinization pattern was observed in the vermilion part, KRT2 and SPRR3 were co-expressed in the suprabasal layer, consistent with the expression pattern of a single vermilion epithelial model. Clustering analysis revealed that KRT2 and SPRR3 gene expression in vermilion was location-dependent within the sample. Therefore, LVERM can be used as an evaluation tool for lip products and has great importance in innovative approaches for cosmetic testing.