P5.50 Is the murine hair follicle both a melatonin target and source?

H. Kobayashi^{1, 2}, T.W. Dunlop³, B. Tychsen¹, F. Conrad¹, T. Ito¹, N. Ito¹, S. Aiba², C. Carlberg³, R. Paus¹

¹Department of Dermatology, University of Hamburg, Hamburg, Germany ²Tohoku University School of Medicine, Sendai, Japan ³Department of Biochemistry, University of Kuopio, Kuopio, Finland

The aim of this study was to investigate whether the murine hair follicles in situ are indeed peripheral melatonin targets (i.e. express melatonin membrane receptors (MT1, MT2) and/or a mediator of nuclear melatonin signaling, the orphan nuclear receptor RORalpha and its target p21^WAF/CIP1), and whether it may actually serve as an extrapineal source of melatonin. Immunohistochemical examination of melatonin, MT1, RORalpha, and p21^WAF/CIP1 on c57BL/6 mouse hair follicle, and semi-quantitive RT-PCR for MT1 and MT2, and quantitive real time PCR for MT1, MT2 and RORalpha on mouse skin cDNA has been studied. Short term-mouse skin organ culture stimulated with melatonin was studied to examine the effect of melatonin on keratinocyte apoptosis. Murine hair follicle keratinocytes expresses melatonin-like immunoreactivity (IR) as well as IR for MT1, RORalpha and p21^WAF/CIP1, each of which changed substantially in a hair cycle-dependent manner: Melatonin-like IR was strongest in outer root sheath keratinocytes and dermal papilla fibroblasts in mid anagen follicles in situ; MT1-like IR was most prominent in hair follicle epithelium, while it was only weak in the dermal papilla, RORalpha-like IR was most strongly expressed in dermal papilla fibroblasts in mid anagen. Both semi-quantitive RT-PCR for MT1 and MT2, and quantitive real time PCR for MT1, MT2 and RORalpha revealed that all three genes are transcribed in normal mouse skin in a hair cycle-dependent manner. Functionally, melatonin (0.01 to 1 nM) significantly inhibited the constitutional level of hair follicle keratinocyte apoptosis in short term-mouse skin organ culture. In conclusion, we here provide evidence that normal murine hair follicles are prominent targets for melatonin bioregulation, and may even operate as extrapineal sources of melatonin synthesis (the latter is currently being double-checked e.p. by mass spectrometry).