Effects of RGD-fused silk fibroin in a solution format on the proliferation and gene expression of epidermal keratinocytes

In cutaneous wound healing, it is important to stimulate the functions of skin cells such as keratinocytes and fibroblasts. In this study, we investigated the effects of transgenic silk fibroin (SF) fused with the cell-adhesive Arg-Gly-Asp (RGD) peptide (RGD-SF) on behavior of normal human epidermal keratinocytes. RGD-SFs were added to the culture medium to stimulate keratinocyte proliferation. In addition, immunostaining and DNA microarrays revealed that keratinocytes treated with RGD-SF showed distributed dash-like vinculin (a focal adhesion protein) and increased expression of genes related to cell migration in cutaneous wound healing, such as serine protease inhibitor clade E member 1 and matrix metalloproteinase 9. Although RGD-SF in solution was unable to permeate the stratum corneum of a normal human three-dimensional epidermal model, the transgenic SF reached keratinocytes in the epidermal layer when administered to an epidermal model with immature stratum corneum. The results of this study suggest the potential of RGD-SF in a solution format as an active component in the treatment of skin with a damaged stratum corneum, such as chapped skin.