Minoxidil activates β-catenin pathway in human dermal papilla cells: a possible explanation for its anagen...

It is believed that the length of the actively growing phase of the anagen hair cycle mainly contributes to hair length. Recent studies showed that maintenance of β-catenin activity in the dermal papilla cells (DPCs) enables hair follicles to keep actively growing. Topical minoxidil treatment promotes hair growth in men with androgenetic alopecia, suggesting that minoxidil may prolong the actively growing phase of the anagen hair cycle.

To investigate whether minoxidil prolongs the anagen hair cycle in mice and, if so, to investigate whether minoxidil activates β-catenin pathway in human DPCs.

Dorsal skins of C57BL/6 mice were depilated to synchronize the hair cycle. After 10 days, 3% minoxidil were topically applied daily for 10 days. Sections of back skins were stained with hematoxylin and eosin. Hair follicles were graded and hair cycle score (HCS) was calculated. Cultured human DPCs were transiently transfected with the β-catenin responsive TCF reporter plasmid (pTopflash) and corresponding negative control reporter (pFopflash) to assess the activity of β-catenin signaling by minoxidil. Immunofluorescence staining and immunoblot were performed to examine the expression and localization of β-catenin in the presence or absence of minoxidil. Phosphorylation of GSK3β, PKA and PKB were also examined by immunoblot after minoxidil treatment. RT-PCR analysis and immunoblot were employed to investigate the expression of β-catenin pathway targets in DPCs, such as Axin2, Lef-1, and EP2.

Modest extension of anagen phase thereby delay of catagen progression was observed by application of minoxidil in mice. Minoxidil stimulated the transcriptional activity of pTopflash but not pFopflash. Nuclear accumulation of β-catenin was also observed after minoxidil treatment. Immunoblot further showed that minoxidil treatment increases the phosphorylation of GSK3β, PKA and PKB. Moreover, minoxidil induced Axin2, Lef-1, and EP2 expression.

Our results strongly suggest that minoxidil extends the anagen phase by activating β-catenin activity in the DPCs.