F10 EXPRESSION OF PRO-OPIOMELANOCORTIN-DERIVED PEPTIDES IN HAIR FOLLICLE MELANOCYTES IS INVERSELY CORRELATED WITH PIGMENTATION LEVEL

Kauser S, Schallreuter KU, Thody AJ, Tobin DJ.  Dept. of Biomedical Sciences, University of Bradford, West Yorkshire, England.

The pro-opiomelanocortin (POMC)-derived peptides a-MSH, ACTH and b-endorphin are produced in the skin where they are thought to have also a role in melanogenesis.  It has been established that a-MSH and ACTH act via the MC1 receptor. In addition, it has been demonstrated that a-MSH can activate the 6BH₄ – tyrosinase inhibitor complex to regulate tyrosinase activity. Previously we have shown discontinuous expression of a-MSH in the human scalp anagen hair follicle whereby a-MSH was undetectable in the melanogenic zone and most proximal bulb. However, it was present through-out the entire outer root sheath containing keratinocytes and amelanotic melanocytes. Here, we extend these findings by assessing a-MSH, ACTH and b-endorphin expression in primary hair follicle melanocyte cultures (HFM) cultivated with and without artificial mitogens. Cells were derived from normal scalp and examined by both immunochemistry and immunoflourescence.

Primary cultures of HFM contained both proliferative amelanotic and non-proliferative intensely pigmented bulbar melanocytes. The expression of all three POMC peptides was strongest in cells with negligible melanin content, whereas melanogenically active bulbar melanocytes stained weakly or were negative. This study indicates for the first time that the level of POMC peptide expression in HFM is inversely proportional to the degree of melanization. Hence, POMC peptides could be down regulated in terminally differentiated HFM and a-MSH and ACTH could be directly involved in differentiation and/or survival of these cells.