title: Distinct melanogenic response of human melanocytes in mono-culture, in co-culture with keratinocytes and in reconstructed epidermis, to UV exposure.
abstract: Striking differences are observed in the melanogenic response of normal human melanocytes to UVA and UVB irradiation depending on culture conditions and the presence of keratinocytes. Exposure of melanocytes co-cultured with keratinocytes to UVB irradiation triggered, already at low doses (5 mJ/cm2), an increase in melanin synthesis whereas in melanocyte mono-cultures, UVB doses up to 50 mJ/cm2 had no melanogenic effect. Unlike UVB, UVA exposure caused the same melanogenic response in both mono- and co-cultures. Removing certain keratinocyte growth factors from the co-culture medium abolished the melanogenic response to UVB, but not to UVA exposure. When integrated into the basal layer of a reconstructed human epidermis, human melanocytes similarly reacted to UVA and UVB irradiation as in vivo by increasing their production and transfer of melanin to the neighboring keratinocytes which resulted in a noticeable tanning of the reconstructed epidermis. The presence of a dense stratum corneum, known to scatter and absorb UV light, is responsible for higher minimal UVB and UVA doses required to trigger a melanogenic response in the reconstructed epidermis compared to keratinocyte-melanocyte co-cultures. Furthermore, an immediate tanning response was observed in the pigmented epidermis following UVA irradiation. From these results we conclude that: (i) keratinocytes play an important role in mediating UVB-induced pigmentation, (ii) UVA-induced pigmentation is the result of a rather direct effect on melanocytes and (iii) reconstructed pigmented epidermis is the most appropriate model to study UV-induced pigmentation in vitro.
authors.affiliation: Life Sciences Research, L'Oreal, Centre Charles Zviak, Clichy, France. cduval@recherche.loreal.com
authors.forename: C
authors.initials: C
authors.lastname: Duval
authors.forename: M
authors.initials: M
authors.lastname: Régnier
authors.forename: R
authors.initials: R
authors.lastname: Schmidt
mesh_terms: D002478:Cells, Cultured; D018920:Coculture Techniques; D004817:Epidermis / Q000378:metabolism* / Q000528:radiation effects; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism / Q000528:radiation effects*; D008543:Melanins / Q000096:biosynthesis*; D008544:Melanocytes / Q000378:metabolism / Q000528:radiation effects*; D010858:Pigmentation / Q000502:physiology; D014466:Ultraviolet Rays
chemical_list: D008543:Melanins