Localized Topical Melatonin Therapy Promotes Hair Regrowth in C57BL/6 Mice in Association with Wnt/β-Catenin Pathway Activation

Melatonin, a methoxyindole synthesized by the pineal gland, is secreted in response to photoperiodic cues relayed from the retina through an endogenous circadian oscillator within the suprachiasmatic nucleus. Consequently, melatonin secretion regulates the circadian rhythm. Melatonin has been reported to have antioxidant, photoprotective, anti-inflammatory, anticancer, and wound-healing properties. It has also been reported to promote hair growth, although the underlying mechanisms remain unclear. In this study, we explored the potential molecular mechanisms of melatonin-induced hair growth by using an in vivo C57BL/6 mouse model. We observed morphological changes in the dorsal area and changes in the hair cycle and anagen induction were observed through hematoxylin–eosin staining. The molecular mechanisms were explored using Western blotting and immunofluorescence assay. Our findings indicate that topical melatonin promotes anagen entry and hair regrowth in C57BL/6 mice, accompanied by the modulation of Wnt/β-catenin-related signaling proteins. The decrease in grayscale value, increase in hair length and skin thickness and histological change in hair follicles in the melatonin-treated group indicated hair regrowth in the dorsal skin of mice. Moreover, the expression of the Wnt/β-catenin pathway was remarkably regulated. These findings further our understanding of the molecular mechanisms underlying topical melatonin-induced hair growth.