RESUMO
Objective@#To identify the time window during which the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway plays a key role in telogen-to-anagen transition of hair follicles, and to explore whether the pathway specifically promotes the proliferation of hair follicle stem cells (HFSCs) .@*Methods@#Totally, 36 newborn ICR mice were randomly and equally divided into 3 groups: RAPA-P19 group intraperitoneally injected with 5 mg·kg-1·d-1 sirolimus on days 19-24 after birth, RAPA-P21 group intraperitoneally injected with 5 mg·kg-1·d-1 sirolimus on days 21-24 after birth, and control group intraperitoneally injected with the same volume of solvent on days 19-24 after birth. Four mice were sacrificed in each group on days 22, 23 and 24 separately. Skin tissues were resected from the back, and hematoxylin-eosin staining of the skin tissues were performed followed by observation of hair follicle morphology to evaluate whether murine hair follicles progressed into the anagen phase on day 24. Immunofluorescence costaining was conducted to determine the expression and localization of mTORC1 downstream molecular marker pS6 and cell proliferation marker Ki67 on days 22 and 23.@*Results@#On day 24, hematoxylin-eosin staining showed anagen hair follicles in the control group and RAPA-P21 group, but telogen hair follicles in the RAPA-P19 group. On days 22 and 23, immunofluorescence costaining revealed positive staining for both pS6 and Ki67 in HFSCs in the control group, negative staining for both pS6 and Ki67 in the RAPA-P19 group, negative staining for pS6 and positive staining for Ki67 in the RAPA-P21 group. On day 23, epidermal cells and sebaceous gland cells in the upper hair follicle bulge were stained positively for Ki67 in all the 3 groups.@*Conclusion@#mTORC1 signaling specifically promotes the proliferation of HFSCs during telogen-to-anagen transition, but not affects proliferation of other cells in hair follicles.
RESUMO
To detemine the expression pattern of mTOR complex subunits Raptor and Rictor in the hair follicles of mice at different hair follicle stages, and to explore its significance. Methods: Immunostaining of Ki-67, a proliferative marker, was used to determine the precise hair follicle stages of mouse dorsal skin at different postnatal time points. Real-time PCR was used to detect the mRNA expression of Raptor and Rictor in mouse dorsal skin at 43 days after birth (P43, early telogen), 56 days after birth (P56, mid-telogen), 69 days after birth (P69, late telogen) and 74 days after birth (P74, early anagen). The expression intensity and localization of Raptor and Rictor at different stages of hair cycle were tested by co-immumostaining. Results: Ki-67 immunostaining showed that the time points (P43, P56, P69, P74) and hair follicle stages (early telogen, mid-telogen, late telogen, early anagen) of the dorsal skin were consistent with each other. The results of real-time PCR and immunostaining were consistent, showing that the expression of Raptor and Rictor did not changed in the early-, mid-, late telogen, and early anagen. However, Raptor was specifically expressed in the bulge where hair follicle stem cells (HFSCs) are residing in, and Rictor was mainly detected in inner root sheath (IRS) cells. Conclusion: The expression of Raptor and Rictor does not altered in the hair follicles at different hair follicle stages, but Raptor and Rictor are specifically expressed in the HFSCs and IRS cells, respectively, indicating that Raptor might be a molecular marker for HFSCs, and Rictor might be involved in the maintenance of IRS and formation of hair shaft.