New Findings in Hair Research: Influence of Prolactin, Retinoids, and Transforming Growth Factor-β on Hair Growth

Recent findings indicated that, in addition to androgens and estrogens, the hormone prolactin played a significant role in the development of androgenetic alopecia. Prolactin was shown to be expressed in a hair cycle-dependent manner in mouse skin and could induce premature catagen in murine skin organ cultures. In isolated human anagen and catagen hair follicles, prolactin and its receptor were expressed, and treatment with prolactin for 6 days resulted in premature entry into the catagen stage, increased apoptosis, and reduced proliferation of follicular keratinocytes. Contrary to previous publications, prolactin was produced locally in the hair follicle. Various growth factors influenced hair cycle regulation, with TGF-β playing a crucial role in both hair follicle morphogenesis and the hair cycle. TGF-β2 induced hair follicle formation during embryonic development, while TGF-β1 inhibited it. Both TGF-β1 and TGF-β2 had inhibitory effects on hair growth during the hair cycle and could induce catagen in human hair follicles. Retinoid-induced hair loss was partially mediated by TGF-β2, which could be significantly reduced by TGF-β antibodies. These data suggested that prolactin and TGF-β receptor antagonists should be further investigated as potential treatments for androgenetic alopecia.