L-04   REGULATION OF HUMAN HAIR FOLLICLE PIGMENTATION

DJ Tobin. Dept. Biomedical Sciences, University of Bradford, Bradford, England.

The field of human hair follicle pigmentation research is remarkably young when compared to the decades long focus on pigmentation in the human epidermis. Moreover, until very recently we have relied almost exclusively on the rodent coat to study the regulation of pigmentation in general. While follicular melanocytes are derived from the epidermis during hair follicle morphogenesis, these pigment cell sup-populations diverge in many important ways as they distribute to their respective distinct compartments in the integument. However, by far the most striking difference between these two principal melanocyte sub-populations, and one with significant implications for the regulation of human hair pigmentation, is the observation that the activity of the hair bulb melanocyte is under cyclical control and that melanogenesis itself is tightly coupled to the hair growth cycle. Epidermal melanogenesis, by contrast, appears to be continuous. The pigmentation of human hair fibers is affected by numerous intrinsic factors including; hair-cycle dependent changes, body distribution, racial and gender differences, variable hormone-responsiveness, genetic defects and age-associated change. Study of hair pigmentation may even be further complicated by the effects of extrinsic variables including; climate and season, infestations, pollutants, toxins, and chemical exposure. Given that melanosome biogenesis and melanogenesis involves multiple steps, it is perhaps not surprising that positive and negative regulators of hair follicle melanogenesis will involve multiple biological factors. These include growth factors, cytokines, hormones, neuropeptides and neurotransmitters, eicosanoids, cyclic nucleotides, nutrients microelements and cations/anions. These factors may act via autocrine, paracrine and endocrine mechanisms. This presentation will focus on the effect of a group of positive regulators of melanogenesis cleaved from the pro-opiomelanocortin pro-hormone including; alphaMSH and ACTH, whose melanogenic effects are mediated via the MC-1 receptor, and â endorphin, which acts predominately via µ-opiate receptors. Results obtained from our laboratory to date suggest that POMC peptides may play an important role in the regulation of human hair follicle pigmentation and suggests a particularly important role for â-endorphin in the maintenance of melanogenesis. Alterations in POMC peptide homeostasis may be involved in pathology of follicular pigmentation.