Direct effects on proliferation, antigen expression and melanin synthesis of cultured normal human melanocytes in response to UVB and UVA light.
OBJECTIVE
Ultraviolet (UV) radiation; induces a variety of responses in the skin, including tanning and inflammation, and may also act as a carcinogen. As epidermal melanocytes are seen as the major targets of UV light, the present study was conducted to evaluate the direct effects of UVA and UVB irradiation on melanocytes in vitro.


METHODS
Normal human epidermal melanocytes (NHM) were exposed on 3 consecutive days to UVA (0.072-7.2 J/cm2) and UVB (7.2-48 mJ/cm2), respectively, and changes of morphology, cell number, melanin synthesis and antigen expression (APAAP technique) were determined 5 days after the first exposure.


RESULTS
UVA radiation caused only minimal effects on NHM by slightly inducing expression of the activation marker HMB-45 and decreasing expression of the proliferation marker Ki-67. No changes of morphology, cell number or melanin synthesis were detectable with any of the applied doses. On the other hand, UVB radiation significantly induced dendrite formation and decreased the number of NHM in a dose-dependent manner (74% of the controls at 7.2 mJ/cm2, 64% at 14.4 mJ/cm2 and 28% at 36 mJ/cm2). Significant induction of the activation marker HMB-45 was found in parallel to decreased expression of the differentiation marker K.1.2.58. UVB doses >or=9.6 mJ/cm2 also resulted in significant downregulation of the proliferation marker Ki-67, confirming the data of the cell counts, and melanin content was increased in NHM (20% over the controls, P<0.01) after applying 7.2 mJ/cm2 UVB.


CONCLUSIONS
Our results may suggest that the effect of UVB radiation in skin is due to direct activation of melanocytes, whereas skin tanning caused by UVA is mediated rather in an indirect way.
Abdel-Naser
M Badawy
MB
Department of Dermatology, University Medical Center Benjamin Franklin, the Free University of Berlin, Berlin, Germany. abdelnasermb@hotmail.com
Krasagakis
Konstantin
K
Garbe
Claus
C
Eberle
Jürgen
J
D000911:Antibodies, Monoclonal; D000941:Antigens / Q000378:metabolism; D002455:Cell Division / Q000528:radiation effects; D002478:Cells, Cultured; D000078404:Epidermal Cells; D004817:Epidermis / Q000528:radiation effects*; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008543:Melanins / Q000096:biosynthesis*; D008544:Melanocytes / Q000378:metabolism / Q000528:radiation effects*; D014466:Ultraviolet Rays
D000911:Antibodies, Monoclonal; D000941:Antigens; D008543:Melanins