Dietary sphingolipids improve skin barrier functions via the upregulation of ceramide synthases in the epidermis

Sphingolipids are ubiquitous in eukaryotic organisms and are significant components in foods. It has been reported that treatment with sphingolipids prevents colon cancer, improves skin barrier function and suppresses inflammatory responses. However, the mechanisms for those effects of dietary sphingolipids are not well understood. In this study, to investigate the effects of dietary glucosylceramide (GluCer) and sphingomyelin (SM) on skin function, we characterized the recovery of skin barrier function and the change in sphingolipid metabolism-related enzymes in the epidermis using a special Mg-deficient diet-induced atopic dermatitis-like skin and tape-stripping damaged skin murine models. Our results show that dietary GluCer and SM accelerate the recoveries of damaged skin barrier functions. Correspondingly, dietary sphingolipids significantly upregulated the expression of ceramide synthases 3 and 4 in the epidermis of the atopic dermatitis-like skin model (P < 0.05). In the case of cultured cells, the expression of ceramide synthases 2-4 in normal human foreskin keratinocytes was significantly upregulated by treatment with 0.001-0.1 μm sphingoid bases (sphinganine, sphingosine and trans-4,cis-8-sphingadienine) (P < 0.05). These results suggest that the effects of dietary sphingolipids might be due to the activation of ceramide synthesis in the skin, rather than the direct reutilization of dietary sphingolipids. Our findings provide a novel insight into the mechanisms of the skin barrier improving effect and a more comprehensive understanding of dietary sphingolipids.