Supplementary Material for: Effects of Food-Derived Collagen Peptides on the Expression of Keratin and Keratin-Associated Protein Genes in the Mouse Skin

Oral ingestion of collagen peptides (CP) has long been suggested to exert beneficial effects on the skin, but the molecular events induced by CP on the skin remain unclear. Here, we investigated the effects of oral CP administration on gene expression in hairless mouse skin and of prolyl-hydroxyproline (Pro-Hyp), a collagen-derived dipeptide, on gene expression in a coculture of mouse skin keratinocytes and fibroblasts. Using microarray analysis, we found that oral administration of CP to hairless mice for 6 weeks induced increased expression of Krtap and Krt genes in the skin. Annotation analysis using DAVID revealed that a group of the up-regulated genes, Gprc5d, Sprr2a1, Krt27 and Krtap16-7, is associated with the development of the epidermis and the hair cycle. In addition, the presence of Pro-Hyp (200 μM) induced an increase in the expression of Krtap16-7, Krtap15, Krtap14 and Krtap8-2 in keratinocytes in coculture, partially resembling the in vivo result. The Pro-Hyp-induced up-regulation of these genes was not observed when keratinocytes were cultured without fibroblasts, suggesting that the presence of fibroblasts is essential for the effects of Pro-Hyp. Our study presents new insights into the effects of CP on the skin, which might link to the hair cycle.