P-33   HUMAN HAIR GREYING IS LINKED TO A SPECIFIC DEPLETION OF HAIR FOLLICLE MELANOCYTES AFFECTING BOTH THE BULB AND THE OUTER ROOT SHEATH

S. Commo*, O. Gaillard, BA Bernard, L’Oreal Advanced Research, Hair Biology Group, Centre de Recherche C. Zviak, 92110 Clichy, France.

Although hair greying is a very common phenomenon characterised by loss of pigment in the hair shaft, the events that cause and control natural hair whitening with age in human are still unclear. In an attempt to identify clues in this process, human hair melanocytes were immunohistochemically characterized as a function of hair shaft pigmentation. Loss of hair shaft melanins was found associated with a decrease in both bulb melanin content and bulb melanocyte population. Although a few melanocytes were present in the bulb of grey hair, they still expressed tyrosinase and TRP-1, synthesised and transferred melanins to cortical keratinocytes as evidenced by the presence of melanin granules. In white hair bulb, no melanocyte can be detected either with pMel- 17 or vimentin labelling. If pigmented hair follicles are known to contain inactive melanocytes in the outer root sheath, grey and white hairs were also found to contain some of those amelanotic melanocytes. Their population however was decreased as compared to pigmented hair follicles, ranging from small to null. This depletion of melanocyte in the different areas of white hairs was detected throughout the hair cycle, namely at telogen and early anagen stages. On the opposite, the infundibulum and sebaceous gland of both pigmented and white hairs showed similar distribution of melanocytes. Furthermore, other distinct cell populations located in ORS, namely putative stem cells, Merckel cells and Langerhans cell, were equivalently identified in pigmented and white hairs. Thus, reduction in melanin content of the shaft appears as a consequence of an overall and specific depletion of bulb and outer root sheath melanocytes of human hair.