Hair Cycle Control by Estrogens: Catagen Induction via Estrogen Receptor Alpha Is Checked by ER Beta Signaling

The study explored the role of estrogens in hair growth, focusing on the two estrogen receptors, ER alpha and ER beta, in murine hair cycles. It was found that both receptors are expressed throughout the hair cycle, with distinct patterns. Topical 17beta-estradiol (E2) was shown to arrest hair follicles in the telogen phase and induce premature catagen development. The ER antagonist ICI 182.780 did not induce anagen prematurely but accelerated its development in female mice. ER beta knockout mice exhibited accelerated catagen development and increased apoptotic hair follicle keratinocytes, indicating that ER beta acts as a silencer of ER alpha's catagen-promoting effects. These findings highlighted the complexity of estrogen's role in hair growth and suggested that selective ER alpha or beta antagonists/agonists could be key to effective hair growth manipulation. The study also emphasized the potential of using hair cycling responses to estrogens as a model for studying biological wave propagation.