AN ESTROGEN-RECEPTOR PATHWAY REGULATES THE TELOGEN-ANAGEN HAIR FOLLICLE TRANSITION AND INFLUENCES EPIDERMAL-CELL PROLIFERATION

The hair follicle is a cyclic, self renewing epidermal structure which is thought to be controlled by signals from the dermal papilla, a spe cialized cluster of mesenchymal cells within the dermis, Topical treat ments with 17-beta-estradiol to the clipped dorsal skin of mice arrest ed hair follicles in telogen and produced a profound and prolonged inh ibition of hair growth while treatment with the biologically inactive stereoisomer, 17-alpha-estradiol, did not inhibit hair growth, Topical treatments with ICI 182,780, a pure estrogen receptor antagonist, cau sed the hair follicles to exit telogen and enter anagen, thereby initi ating hair growth, Immunohistochemical staining for the estrogen recep tor in skin revealed intense and specific staining of the nuclei of th e cells of the dermal papilla, The expression of the estrogen receptor in the dermal papilla was hair cycle-dependent with the highest Level s of expression associated with the telogen follicle, 17-beta-Estradio l-treated epidermis demonstrated a similar number of 5-bromo-2'-deoxyu ridine (BrdUrd) S-phase cells as the control epidermis above telogen f ollicles; however, the number of BrdUrd S-phase basal cells in the con trol epidermis varied according to the phase of the cycle of the under lying hair follicles and ranged from 2.6% above telogen follicles to 7 .0% above early anagen follicles, These findings indicate an estrogen receptor pathway within the dermal papilla regulates the telogen-anage n follicle transition and suggest that diffusible factors associated w ith the anagen follicle influence cell proliferation in the epidermis.