Role of TGF-β2 in the human hair cycle

Male pattern baldness is the result of premature entry into catagen due to androgens. In order to prevent hair toss, it is important to understand two critical steps, i.e., the induction mechanism of premature entry and the regression process of catagen. At the initiation, dihydrotestosterone (DHT) stimulates synthesis of transforming growth factor-beta2 (TGF-beta2) in dermal papilla cells. TGF-beta2 suppresses proliferation of epithelial cells and stimulates synthesis of certain caspases. Then TGF-beta2 triggers the intrinsic caspase network and subsequently epithelial cells are eliminated through apoptotic cell. death. TGF-beta antagonists are effective in preventing catagen-like morphological changes and in promoting elongation of hair follicles in vivo and in vitro. These lines of evidence strongly suggest the presence of a catagen cascade in mate pattern baldness, involving: (1) the conversion of testosterone to DHT by type II 5-alpha-reductase; (2) the synthesis of TGF-beta2 in dermal papilla cells; and (3) the activation of the intrinsic caspase network. These sequential events contribute to the shortening of the human hair cycle. (C) 2004 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.