The Expression and Function of Aquaporins in the Epidermis

The aquaporins (AQPs) are a family of water cannel proteins with at least 13 known members (AQP0 AQP12) in human tissues. Of the 13 members of AQP, AQP3, AQP7, AQP9 and AQP10 were known to facilitate permeation of small solutes such as glycerol and urea as well as water. The distributions of AQP family in the tissues are quite di#erent one another and the expression of each AQP is thought to be strictly regulated in a cell type specific manner. In human epidermis, AQP 3 was expressed from basal to granular layers, while AQP 9 was only detected in granular layer. Incubation of cultured human keratinocytes in sorbitol-added hypertonic medium increased AQP 3, but not AQP 9, expression at both mRNA and protein levels, indicating that osmotic stress up- regulates AQP3 expression in keratinocytes. In addition, expression studies for AQP3 revealed that retinoic acid is a regulatory factor for AQP3 expression in keratinocytes. With regard to the function of AQP3 in skin, impair- ments in the hydration, elasticity and barrier recovery of skin in AQP3 knockout mice indicated that AQP3 plays important roles in skin physiology. The activities in the field of AQP research would provide new insights for the novel cosmetics.