It has been shown in vitro that melanocyte proliferation and function in palmoplantar skin is regulated by mesenchymal factors derived from fibroblasts. In this study, we investigated in vivo the influence of mesenchymal-epithelial interactions in human tissue-engineered
skin substitutes reconstructed from palmar- and nonpalmoplantar-derived fibroblasts. Tissue-engineered dermo-epidermal analogs based on
collagen type I hydrogels were populated with either human palmar or nonpalmoplantar fibroblasts and seeded with human nonpalmoplantar-derived melanocytes and keratinocytes. These
skin substitutes were transplanted onto full-thickness skin
wounds of immunoincompetent rats. Four weeks after
transplantation the development of skin color was measured and grafts were excised and analyzed with regard to epidermal characteristics, in particular melanocyte number and function.
Skin substitutes containing palmar-derived fibroblasts in comparison to nonpalmoplantar-derived fibroblasts showed (a) a significantly lighter pigmentation; (b) a reduced amount of epidermal
melanin granules; and (c) a distinct melanosome expression. However, the number of melanocytes in the basal layer remained similar in both
transplantation groups. These findings demonstrate that human palmar fibroblasts regulate the function of melanocytes in human pigmented dermo-epidermal
skin substitutes after
transplantation, whereas the number of melanocytes remains constant. This underscores the influence of site-specific stromal cells and their importance when constructing
skin substitutes for clinical application.