KERATINOCYTES AND FIBROBLASTS IN A HUMAN SKIN EQUIVALENT MODEL ENHANCE MELANOCYTE SURVIVAL AND MELANIN SYNTHESIS AFTER ULTRAVIOLET-IRRADIATION

To investigate paracrine effects of fibroblasts and keratinocytes on m elanocyte behavior after ultraviolet (UV) irradiation, we compared an in vitro skin equivalent model with melanocyte cultures. Human melanoc ytes were maintained alone in monolayer cultures or on dermal equivale nts with or without keratinocytes and were irradiated daily with solar -simulated light. After seven daily UV irradiations, monolayer melanoc ytes displayed dose-dependent increases in cellular damage. In contras t, melanocytes on dermal equivalents survived strikingly better. Moreo ver, UV-irradiated skin equivalent melanocytes became highly dendritic as compared with sham-irradiated cells, closely mimicking their morph ology in UV-irradiated skin. In addition, in skin equivalents melanocy tes migrated from the center to the periphery of the keratinocyte laye r after UV irradiation. Melanin production per culture, as measured by C-14-dihydroxyphenylalanine incorporation, was consistently higher in skin equivalent melanocytes than in monolayer melanocytes from the sa me donor, and it was highest in melanocytes from skin equivalents cont aining both keratinocytes and fibroblasts. Our data strongly suggest t hat fibroblasts and keratinocytes modulate melanocyte function in skin . The skin equivalent is a valuable model for investigating paracrine effects on melanocytes after UV irradiation.