B6.3 Characteristics and potential functions of the hypothalamus-pituitary-adrenal axis (HPA)-equivalent of the human hair follicle

N. Ito, T. Ito, R. Paus

Department of Dermatology, University Hospital Hamburg-Eppendorf, University of Hamburg, Germany

Research into the neuroendocrinology of the pilosebaceous unit has recently experienced a renaissance, e.g. by the discovery that murine and human hair follicles operate as independent endocrine, paracrine and autocrine organs, which synthesize, metabolize and/or process several neurohormones in response to environmental and intracutaneous stimuli. Here, we summarize recent evidence from our lab that the epithelium of human scalp hair follicles in anagen VI not only expresses prototypic hypothalamic, pituitary and adrenal hormones (CRH, POMC, ACTH, alpha-MSH, cortisol) and their cognate receptors (CRH-R1, MC-1R, MC-2R, GR), but that these expression patterns are also functionally linked in a manner that imitates the key characteristics of the central HPA axis. We discuss the functional properties of this follicular HPA axis-equivalent in the context of our recent findings that alpha-MSH is a potent suppressor of MHC class I expression, that CRH inhibits hair matrix keratinocyte proliferation and that CRH stimulates hair follicle melanogenesis and the differentiation of mast cell precursor cells in the connective tissue sheath.