Intensive stress impedes hair follicle growth through triggering cell cycle arrest of hair follicle stem cells

The detrimental effects of stress on hair growth are supported by empirical and experimental evidence, but the specific impact and mechanisms remain poorly understood. Here we utilized two intensive stress paradigms, repeated resiniferatoxin (RTX) injections and physical restraint in mice, to assess the effects of intensive stress on hair follicle growth after depilation. Initially, macroscopic pictures of the mice dorsal skin and HE staining showed a substantial inhibition of depilation-induced hair growth in both telogen and anagen hair follicle growth under intensive stress induced by RTX and restraint. Mechanistically, single-cell RNA sequencing analysis of mice skin under intensive stress highlighted a significant downregulation of cell-cycle genes and upregulation of the cAMP signaling pathway in Lgr5⁺ hair follicle stem cells (HFSCs). Notably, the sympathetic nervous system was activated under intensive stress. Then, the neurotransmitter noradrenaline (NA), a secretion of the sympathetic nervous system, and 8-bromo-cAMP, a cAMP analog, were used to manifest the inhibitory effect of the sympathetic nervous system on HaCaT cell proliferation, as evidenced by the results of decreased cell activity and colony formation, downregulated expression of cyclin D1/2 and CDK4, the increased percentage of G0/G1, and decreased percentage of the S phase. Importantly, hair follicle regeneration was significantly inhibited by NA and 8-bromo-cAMP in mice. Collectively, our study suggests that intensive stress inhibits the cell cycle of hair follicle growth through the sympathetic nervous system/NA/cAMP pathway, thus providing a mechanistic insight into intensive stress-induced inhibition in hair follicle growth.