The skin is the largest organ in the human body and serves as a barrier that protects the body from external stimuli. These functions are gradually lost with aging. Therefore, it is important to maintain the skin functions. In recent years, there have been reports of peptides derived from natural proteins having physiological activity, but there are few reports on the physiological activity of peptides derived from keratin, a protein that constitutes the epidermis. Therefore, we investigated keratide^®, a peptide derived from waterfowl feather keratin, to clarify its bioactivity.
We examined the physiological effects of keratide^® using keratinocyte cell lines. We found that keratide^® improves oxidative stress tolerance via induction of glutathione, and induces expression of filaggrin and involucrin, which enhance skin moisturizing and barrier function. Furthermore, experiments with inhibitors revealed that the expression of filaggrin and involucrin is mediated by the ERK MAPK pathway and the TGF-β pathway. 
These results indicate that keratide®, as a bioactive peptide, induces epidermal keratinocytes to tolerate oxidative stress and induces proteins that contribute to skin moisture retention, suggesting that keratide® is pharmacologically useful.