Regulation Of Sirt7 On Hair Follicle Regeneration And Its Underlying Mechanism

Background:Hair follicle stem cells(HFSCs)remain in a quiescent state until activated to initiate the follicular anagen phase for hair regrowth,however,the mechanism to reactivate quiescent HFSCs is not fully understood.Sirt7 is a member of the Sirtuin family which can promote longevity and has been reported to regulate the differentiation of bone marrow mesenchymal stem cells and mediate the process of bone aging.Whether Sirt7 can be involved in regulating HFSCs to mediate hair regeneration and senescence deserves further exploration.Objective:To explore the regulation of hair regeneration by Sirt7 and its specific molecular mechanisms,and to provide new prevention and treatment strategies for clinical alopecia areata diseases such as senescenceassociated alopecia.Methods.(1)The effect of Sirt7 on hair follicle cycle in mice was analyzed by hair regeneration phenotype analysis,hair follicle HE staining and Ki67 immunofluorescence staining.(2)The effect of Sirt7 on the proliferation activity of HFSCs was clarified by ex vivo proliferation assay,while hair follicle stem cell-specific knockout Sirt7 mice were constructed for hair phenotyping to confirm the direct targeting effect of Sirt7 on hair follicle stem cells.(3)We screened Nfatc1,a target of Sirt7 to regulate the proliferative activity of hair follicle stem cells,by Western Blot,and clarified the specific mechanism of Sirt7 regulation on Nfatc1 by protein interaction assay,acetylation modification assay and protein stability assay.(4)Applying the Nfatc1 inhibitor cyclosporine A to clarify whether the delayed hair regeneration in Sirt7 knockout mice can be rescued by hair phenotype analysis,HE staining,Ki67 staining,etc.(5)The protein expression of Sirt7 and Nfatc1 in hair follicles during aging was detected by Western Blot and immunohistochemical staining,and the effects of Sirt7 knockdown and overexpression on aging-associated alopecia were observed and analyzed.Results.(1)Sirt7 overexpression could promote HFSCs activation and hair follicle conversion from quiescent phase to anagen phase in mice,thus promoting the hair regeneration.(2)Both in vivo and ex vivo proliferation experiments showed that Sirt7 could promote the proliferation of mouse HFSCs,and specific knockdown of Sirt7 in hair follicle stem cells could inhibit the activation of hair follicle stem cells,prolong the resting phase of hair follicles and delay hair regeneration.(3)Sirt7 can downregulate acetylation of Nfatc1 on K612 site by interacting with Nfatc1 and promote its degradation via PA28γ-dependent intranuclear proteasome by.(4)Cyclosporine A could lift the activation block of hair follicle stem cells in Sirt7 knockout mice and promote their hair regeneration.(5)Sirt7 expression was down-regulated and Nfatc1 accumulated in hair follicles of aged mice,and senescence-associated alopecia appeared earlier in Sirt7 knockout mice,while Sirt7 overexpression promoted hair regeneration in aged mice.Conclusion.Sirt7 can deacetylate Nfatc1 and promote its intranuclear proteasomal degradation in a PA28γ-dependent manner,and thus activate the hair follicle stem cells,promote the telogen-anagen transition of hair follicles,and regulate hair follicle regeneration and senescence.