O#20   b-Endorphin and the regulation of human epidermal and hair follicle melanocytes

S. Kauser, K.U. Schallreuter, A.J. Thody, C. Gummer1, D.J. Tobin. Dept of Biomedical Sciences, University of Bradford, West Yorkshire and 1Procter & Gamble Ltd., Surrey, England.

b-Endorphin, a-MSH and ACTH are enzymatically cleaved from the precursor protein pro-opiomelanocortin (POMC). These peptides are synthesized in the skin where they are involved in multiple regulatory functions including immunomodulation, neurotransmission and melanogenesis. a-MSH and ACTH stimulate melanogenesis in melanocytes via the activation of the MC-1 receptor. b-Endorphin acts predominately via µ-opiate receptors. To date a functional role for b-endorphin in the regulation of human epidermal melanocytes (EM) and hair follicle melanocytes (HFM) has not been demonstrated. Thus, this study was designed to examine the involvement of b-endorphin/µ-opiate receptor system in HFM and EM biology. The expression of b-endorphin and µ-opiate receptor was assessed in gp100-positive melanocytes in situ and in vitro using double immunofluorescence. Additionally, POMC and µ-opiate receptor mRNA expression was examined by RT-PCR. The potential melanogenic, dendritogenic and mitogenic effects of b-endorphin were investigated in EM and HFM cultures after stimulation for 72 hours. This study showed that both b-endorphin and µ-opiate receptor were strongly expressed in situ in gp100-positive EM and in all gp100-positive melanocytes located predominately in the hair bulb melanogenic zone. By contrast, expression of the µ-opiate receptor was restricted to a sub-population of less melanogenic hair bulb melanocytes. Variable expression for both b-endorphin and µ-opiate receptor was evident in gp100-positive EM in vitro. For HFM, in vitro expression of b-endorphin and µ-opiate receptor protein was strongest in proliferating/differentiating cells containing negligible melanin. POMC and µ-opiate receptor mRNA expression was demonstrated in both EM and HFM cultures. Functional studies indicated that b-endorphin significantly increased melanogenesis, proliferation and dendricity in EM and HFM. To our knowledge, this is the first demonstration of prominent b-endorphin expression in EM and hair bulb melanocytes and that b-endorphin has potent melanogenic, mitogenic and dendritogenic effects in these cells. This suggests an important role for b-endorphin in the maintenance of melanogenesis associated with anagen hair growth and epidermal pigmentation. Alterations in b-endorphin homeostasis within the hair follicle pigmentary unit may contribute to the onset of hair graying and also may be involved in pathology of the epidermal melanin unit.