Studies On The Mechanisms For Abnormal Hair Cycle And Cyclic Alopecia Caused By Msx2 Deficiency

Objects: To explore the molecular mechanisms of Msx2 in regulating hair follicle stem cells(HFSCs)and their niche which impact the hair cycle.Methods:1.We identified the dynamic expression profile of Msx2 in hair follicles from different hair cycles through the RNAscope(?) technique.2.We constructed Msx2 knockout(Msx2-KO)mice to observe their hair cycle and phenotype differences.3.By immunofluorescence and HE staining detection methods,the differences in the skin and hair follicles were examined between wide type and Msx2-KO mice.4.Isolation of HFSCs from dorsal skins in telogen were prepared by FACSs.Then,transcriptome analysis was performed using RNA sequencing technology to further reveal the target genes and signaling pathways of Msx2 in regulating hair cycle.5.In order to explore the potential role of Msx2 in regulating exogen stage,immunofluorescence and other detection methods were used to detect the expression of related molecules.Results:1.In anagen,Msx2 was primarily expressed in hair matrix cells and inner root sheath.Msx2 expression was mainly restricted to hair germ in telogen hair,also in inner bulge in wide type mice.2.During the hair cycle,Msx2 deficiency shortens anagen phase,but prolongs telogen and initiation of hair follicle regeneration.Meanwhile,Msx2-deficient mice exhibited cyclic alopecia.3.Msx2-KO hair follicles were able to generate a new bulge but failed to anchor the old one during hair growth.In addition,histology of hair follicles in young Msx2-KO mice were similar to that of aged wide type mice.4.RNA sequencing results underscored the most notable changes in extracellular matrix(ECM)molecules between control and Msx2-KO mice.Moreover,Msx2-deficient hair presented ectopic expression of K10 in HFSC compartment,and resulted in a shift towards a quiescent state of HFSC characterized by downregulation of TGF-β and WNT/β-catenin pathways,as well as the fate switch into the epidermal keratinocytes.5.In exogen,several cell adhesion molecules(POSTN,FBLN-1,ANGPTL2,and COLVI)in Msx2-deficient mice were significantly reduced within the bulge area,which may lead to the loss of club hair adhesion,or impact the signals released to the new growing hair,resulting in the precocious entry of exogen and hair loss,eventually.Conclusion:Msx2 plays an important role in maintaining HFSCs activation,proliferation and epidermal differentiation.Additionally,Msx2 is required to maintain the club hair.Impaired ECM deposition around HFSC niche is probably a potential mechanism for hair loss in Msx2-KO skin.