The Role Of Foxp1 Gene In Hair Follicle Cycling

Skin epidermis has been considered to be a good model to explore the function of adult stem cells, since keratinocytes are easily accessible and are one of the few adult stem cell types that can be separated and propagated in vitro. Hair follicle morphogenesis begins at E12.5, coming into being hair placode and hair peg, up to a complete hair follicle structure, with that hair follicles periodically undergo cycles of growth(anagen), regression(catagen) and rest(telogen) throughout life.A number of previous studies have demonstrated an enrichment of Foxp1 in hair follicle stem cells. We investigated the wide expression of Foxp1 in hair follicle cell populatins by IHC and observed periodically nuclear/cytoplasmic shuttling of Foxp1 during hair cycling.To address the role of Foxp1 in hair cycling, we inactivated it in hair cells by keratin 14(K14) promoter-driven Cre mice. Usually, the length of telogen, anagen and catagen is relatively stable during each hair cycle. Interestingly, premature and accelerated hair regeneration was detected in the Foxp1-cKO mice. And more, slight hair shedding and shorter hair shaft were observed in the Foxp1-cKO mice since the first anagen.Given that skin tissues are frequently exposed to oxidative stress, such as UV light, we hypothesized that Foxp1 was involved in the ROS-related regulation of hair cycling. With FACS analysis, we detected an increase of cellular ROS from anagen to catagen in HF-SCs. More over, pro-oxidant TPA and anti-oxidant NAC would promote or attenuate the T-A transition, respectively. Thus, we speculated the cellular ROS played a key role in the phase transition of hair cycling.We observed a comparable level of cellular ROS at telogen both in WT and cKO mice, but an decreased ROS level at anagen and catagen in the cKO mice. Accordingly, the proliferation of hair follicle stem cells(HFSCs) evidently increased in the cKO mice compared to WT controls. Meanwhile, the relative expression level of p19 ARF and the phosphorylation level of p53 decreased in cKO mice. We speculated that Foxp1 regulated HFSC proliferation partially through p53-dependent oxidative stress responsive pathway.We found that the post translational modification(phosphorylation and acetylation), transcriptional activity and nuclear/cytoplasmic shuttling of Foxp1 were all affected by oxidative stress stimulation. Point mutation analysis revealed that the phosphorylation at S468 was responsible for the nuclear/cytoplasmic shuttling of Foxp1 in responsive to ROS stress. In addition, we found Trx1 is a potential transcriptional target for Foxp1. In vitro, the transcriptional activity of Foxp1 was slightly inhibited by Trx1. Reciprocally, Foxp1 partially rescued the ability of Trx1 to suppress cellular ROS. These findings suggested that Foxp1 regulated ROS level, partially through its interaction with Trx1.In summary, we indentified an extensive expression of Foxp1 in hair follicle cells. Loss of Foxp1 resulted premature exhaustion of HFSCs, coupled with shortened anagen duration, shorter hair shaft and decreased ROS levels. The post translational modification, transcriptional activity and nuclear/cytoplasmic shuttling of Foxp1 were responsive to oxidative stress. Foxp1 regulated the proliferation of HFSCs through the interaction of ROS signaling. Our research shed new light into the molecular mechanisms controlling anagen duration and presented novel therapeutic targets for hair-related diseases.