Corticosterone inhibits GAS6 to govern hair follicle stem-cell quiescence

Abstract

Chronic, sustained exposure to stressors can profoundly affect tissue homeostasis, although the mechanisms by which these changes occur are largely unknown. Here we report that the stress hormone corticosterone-which is derived from the adrenal gland and is the rodent equivalent of cortisol in humans-regulates hair follicle stem cell (HFSC) quiescence and hair growth in mice. In the absence of systemic corticosterone, HFSCs enter substantially more rounds of the regeneration cycle throughout life. Conversely, under chronic stress, increased levels of corticosterone prolong HFSC quiescence and maintain hair follicles in an extended resting phase. Mechanistically, corticosterone acts on the dermal papillae to suppress the expression of Gas6, a gene that encodes the secreted factor growth arrest specific 6. Restoring Gas6 expression overcomes the stress-induced inhibition of HFSC activation and hair growth. Our work identifies corticosterone as a systemic inhibitor of HFSC activity through its effect on the niche, and demonstrates that the removal of such inhibition drives HFSCs into frequent regeneration cycles, with no observable defects in the long-term.

Extended Data Fig. 1 |. Hair cycle progression in ADX mice over time.

a, Hair cycle with immunohistochemical analyses (PCAD) in sham and ADX mice. b, Hair cycle progression in sham males and ADX males. c, Schematic depicting HFSCs in anagen and telogen. The upper ORS of anagen HFs contributes to the new bulge and hair germ (HG) of the following telogen HFs. See Ref^, for details. d, The ORS length in the zigzag hairs of sham (P113) and ADX mice (P65) during late anagen. Brackets: the ORS length below the bulge. e, The hair shaft length of each hair subtype in sham and ADX mice after anagen. f, H&E staining at P65 of sham and ADX skin. g, Immunohistochemical analyses (Sox9 and CD34) in telogen (telo), late anagen (AnaV), and mid-catgen (CatV) HFs. Yellow dashed lines: bulge; white dashed lines: HG (telo), HF (AnaV, CatV); solid line: DP. h, Immunocolocalization (EdU and CD34) in infundibulum (IF), junctional zone (JZ), sebaceous gland (SG), mid ORS (ORS^mid), lower ORS (ORS^low), and matrix (Mx) of late anagen (AnaVI) HFs. Dashed lines: HF. i, H&E staining in the late anagen skin of sham and ADX mice with quantification of the epidermal thickness (E) (left). Immunocolocalization (EdU and DAPI) in interfollicular epidermis (IFE) and dermis (right). Dashed lines: the boundary between epidermis and dermis. j, Representative hair re-growth status of sham and ADX mice from P60 to P549. k, Telogen duration of sham and ADX mice. l, H&E staining of young sham, aged sham, and aged ADX mice with quantification of HF number per mm. Yellow dashed lines: bulge; White dashed lines: HG, Solid lines: DP. Telo, telogen; Ana, anagen; Cat, Catagen. Scale bars, 50 μm (a,d,f,g,h,i,l), 1 mm (e). Data are mean±s.e.m. *P < 0.05, ****P < 0.0001, NS, not significant. Exact P values see source data files. Statistics, sample sizes, and numbers of replications are in Methods, ‘Statistics and Reproducibility’.

Extended Data Fig. 2 |. Corticosterone restores normal hair cycle progression in ADX mice.

a, H&E staining of 21-month-old sham and ADX skin. b, Morphology of each hair subtype from skin of 18-month-old sham and ADX mice. c, Immunohistochemical analyses (CD34 and PCAD) of telogen HF in sham and ADX skin at 22 months old showing normal HF morphology and comparable stem cell numbers. Quantification of the number of bulge and hair germ cells per HF left). Quantification of % of HFSCs in epithelial fraction by FACS (right). d, Hormones from the adrenal gland and plasma levels of corticosterone in P45 sham and ADX animals. e, Plasma levels of norepinephrine and epinephrine measured by LC-MS/MS at P45 (10 days after surgery) in sham and ADX mice. f, Experimental design to test if supplying corticosterone rescues ADX phenotypes (left). Hair cycle progression of sham fed with vehicle (sham+Veh) or ADX fed with corticosterone (ADX+CORT) (right). g, Plasma corticosterone levels at P62 in C57BL/6 mice after a week’s feeding with vehicle or corticosterone. h, Experimental design for 3 days of corticosterone feeding (top). Quantification shows % of hair re-growth of the back skin at P38 (bottom). i, Hair cycle progression of C57BL/6 male mice fed with vehicle or corticosterone. Corticosterone feeding prolonged telogen as long as corticosterone was provided to the mice (both male and female). j, Body weight in C57BL/6 mice fed with vehicle or corticosterone from P83 to P118. k, H&E staining in the skin of vehicle and corticosterone-fed mice (left). Quantification of the thickness of dermis (middle) and dermal adipose layer (right). D, dermis; A, adipose layer. l, Immunohistochemical analysis (active caspase 3 (aCAS3) and PCAD) in vehicle- and corticosterone-fed mice. Dashed lines: epidermis and HFs. m, Experimental design to test effect of corticosterone withdrawal (left). Hair cycle progression of C57BL/6 mice after completion of 3 weeks of vehicle or corticosterone feeding (right). Veh, vehicle; CORT, corticosterone. Scale bars, 50 μm (a,b,c,k,l). Data are mean±s.e.m. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001, NS, not significant. Exact P values see source data files. Statistics, sample sizes, and numbers of replications are in Methods, ‘Statistics and Reproducibility’.

Extended Data Fig. 3 |. Removal of the adrenal glands in stressed or aged mice leads to hair follicle regeneration.

a, Plasma corticosterone levels at P62 in non-stressed control and stressed mice. b, c, H&E staining (b) and immunohistochemical analyses (active caspase3 (aCAS3) and PCAD) (c) in control and stressed mice. Dashed lines, epidermis and HFs. d, Stressed sham (sham+Stress) and stressed ADX (ADX+Stress) mice were monitored for hair coat recovery. Quantification shows % of back skin covered by newly regenerated hairs. e, Plasma levels of corticosterone in young mice (P46, P77, and P98) and aged mice (P427 and P581). f, Sham and ADX operations were performed on aged mice (P521). The mice were shaved and monitored for hair coat recovery from P521 to P574. Scale bars, 50 μm (b,c). Data are mean±s.e.m. *P < 0.05, **P < 0.01, ****P < 0.0001. Exact P values see source data files. Statistics, sample sizes, and numbers of replications are in Methods, ‘Statistics and Reproducibility’.

Extended Data Fig. 4.. GR depletion in different cell types in the skin.

a, K15-CrePGR depletes GR efficiently in HFSCs (top). Immunohistochemical analysis (GR and CD140a) of telogen HF in control and K15-CrePGR;GRfl/fl skin (bottom). b, Hair cycle progression of control and K15-CrePGR;GRfl/fl mice. c, Pdgfra-CreER depletes GR efficiently in the dermis. Immunohistochemical analyses (GR and PCAD) of telogen HF in control and Pdgfra-CreER;GRfl/fl skin. d, Premature HFSC activation in Pdgfra-CreER;GRfl/fl as revealed by EdU incorporation. Immunocolocalization (EdU and CD34) in control and Pdgfra-CreER;GRfl/fl HFs after tamoxifen administration. e, Comparison of EdU localization in bulge and upper outer root sheath (ORS) in late anagen (AnaV) of control (P124) and Pdgfra-CreER;GRfl/fl mice (P73). f, Representative hair regeneration status of control and Pdgfra-CreER;GRfl/fl mice from P73 to P205 with the quantification of the hair cycle numbers. g, Immunocolocalization (EdU and CD34) in infundibulum (IF), junctional zone (JZ), sebaceous gland (SG), mid ORS (ORS^mid), lower ORS (ORS^low), and matrix (Mx) of late anagen (AnaVI) HFs in control and Pdgfra-CreER;GRfl/fl mice during late anagen with quantifications. h, H&E staining in the late anagen skin of control and Pdgfra-CreER;GRfl/fl with quantification of the thickness of epidermis (E) (top). Immunocolocalization (EdU and DAPI) in interfollicular epidermis (IFE) and dermis in control and Pdgfra-CreER;GRfl/fl mice (bottom). Scale bars, 50 μm (a,c,d,e,g,h). Yellow dashed lines, bulge (a,c,d,e); white dashed lines, hair germ (a,c,d), the rest of hair follicles (e,g), or the boundary between epidermis and dermis (h); solid white line, dermal papilla (DP) (a,c,d). Data are mean±s.e.m. **P < 0.01, ***P < 0.001, ****P < 0.0001, NS, not significant. Exact P values see source data files. Statistics, sample sizes, and numbers of replications are in Methods, ‘Statistics and Reproducibility’.

Extended Data Fig. 5.. Corticosterone acts on dermal papilla.

a, qRT-PCR of GR from dermal papilla (DP) and dermal fibroblasts (DF). b, Immunohistochemical analyses (YFP and DAPI) of anagen Sox2-CreER;R26-lsl-YFP skin. Arrowhead: an anagen guard hair follicle with YFP^+ve DP cells (left). Quantification of the percentage of YFP^+ve and YFP^−ve DP in Sox2-CreER;R26-lsl-YFP. Only guard hair follicles have YFP^+ve DP (right). c, Immunohistochemical analyses (GR and DAPI) of control and Sox2-CreER;GRfl/fl skin. Dashed lines: epidermis and hair follicles; solid line: DP. Arrowhead: DP of Sox2-CreER;GRfl/fl guard hairs. d, Representative hair regeneration status of control and Sox2-CreER; GR fl/fl mice from P45 to P160. Quantification showing the hair cycle numbers for guard hairs and other hairs in control and Sox2-CreER; GR fl/fl mice. e, Comparison of the hair bulb diameter in late anagen (AnaV) control (P120) and Sox2-CreER;GRfl/fl skin (P67). Yellow lines: hair bulb diameter. Arrowhead denotes minor hyper-thickening of Sox2-CreER; GR fl/fl hair follicle around the ORS, likely because the dermis has not expanded to accommodate the extra proliferation from HFSCs. f, Immunocolocalization of phospho-Histone H3 (pHH3) and CD34 in bulge and upper ORS, middle ORS (ORS^mid), lower ORS (ORS^low), and matrix (Mx) of late anagen (AnaV) guard HFs in control and Sox2-CreER;GRfl/fl mice. White arrowhead denotes thickened region in Sox2-CreER; GR fl/fl hair follicle, likely due to excessive proliferation from HFSCs. Yellow dashed lines, bulge; white dashed lines, the rest of hair follicles. g, Hair shaft length of guard hairs in control and Sox2-CreER;GRfl/fl mice after anagen. Scale bars, 50 μm (b,c,e,f), 1 mm (d,g). Data are mean±s.e.m. ****P < 0.0001, NS, not significant. Exact P values see source data files. Statistics, sample sizes, and numbers of replications are in Methods, ‘Statistics and Reproducibility’.

Extended Data Fig. 6 |. Differential gene expression in HFSCs of control, ADX, and dermal GR knockout mice.

a, Sample clustering based on Pearson’s correlation of transcriptomes in sham, ADX, and ADX+CORT, as well as control and Pdgfra-CreER;GRfl/fl HFSCs. b, Principal component analysis (PCA) comparing the transcriptome of sham, ADX, ADX+CORT, control, and Pdgfra-CreER;GRfl/fl HFSCs. c, Heat map of log2 fold change of gene expression of 121 common genes among ADX (versus sham), Pdgfra-CreER;GRfl/fl (versus control), and ADX+CORT (versus ADX). Cell cycle-related genes are noted in orange. d, (Left) heat map of log2 fold change of gene expression of transcription factors (Foxc1, Lhx2, Foxp1, Nfatc1), key signalling factors (Fgf18), or downstream readout of key signalling factors (Id1 for BMP pathway, Axin2 for WNT pathway, Gli1 for SHH pathway) known to regulate HFSC quiescence. (Right) heat map of log2 fold change of gene expression of 7 core genes related to cell cycle machineries and cytokinesis. e, f, qRT-PCR of genes related to cell cycle machineries and cytokinesis from telogen HFSCs of sham and ADX mice (e) and control and Pdgfra-CreER;GRfl/fl mice (f). Data are mean±s.e.m. *P < 0.05, **P < 0.01, ***P < 0.001. Exact P values see source data files. Statistics, sample sizes, and numbers of replications are in Methods, ‘Statistics and Reproducibility’.

Extended Data Fig. 7 |. The expression of cell cycle-related genes in HFSCs.

a, b, qRT-PCR of genes related to cell cycle machineries and cytokinesis using telogen HFSCs from vehicle and corticosterone-fed mice (a) and control and stressed mice (b). c, d, qRT-PCR of genes related to cell cycle machineries and cytokinesis in telogen epidermis from sham and ADX mice (c) and vehicle and corticosterone fed mice (d). e, Experimental workflow of the differentially expressed genes (DEGs, > 1.5 fold, adjusted P < 0.05) from DP cells of sham and ADX mice, as well as control and Pdgfra-CreER;GRfl/fl mice. f, g, Immunohistochemical analysis (PCAD) of skin samples from sham and ADX (f) or control and Pdgfra-CreER GR fl/fl (g) used in RNAseq experiments to validate hair cycle (all telogen). Dashed lines, epidermis and HFs. h, FACS strategies for isolating DP cells for RNAseq^, (top). The expression levels of cell type-specific signature genes (DP, fibroblasts, HFSCs, and mast cells) in FACS-purified DP cells (bottom). TPM, transcripts per million. i, Sample clustering based on Pearson’s correlation of transcriptomes in sham and ADX (left), as well as control and Pdgfra-CreER;GRfl/fl DPs (right). j, heatmaps of the differentially expressed genes (DEGs, > 1.5 fold, adjusted P < 0.05) from FACS-purified DP cells of sham and ADX mice (left) or control and Pdgfra-CreER;GRfl/fl mice (right). Scale bars, 50 μm (f,g). Data are mean±s.e.m. *P < 0.05, **P < 0.01, ***P < 0.001, NS, not significant. Exact P values see source data files. Statistics, sample sizes, and numbers of replications are in Methods, ‘Statistics and Reproducibility’.

Extended Data Fig. 8 |. Transcriptome analysis and secretome analysis identified GAS6 as a secreted factor suppressed by systemic corticosterone in the DP.

a, Secretome analysis identifying common secreted factors from DEGs (> 1.5 fold, adjusted P < 0.05) in ADX and Pdgfra-CreER;GRfl/fl DP cells identified by RNAseq. b,c, Expression levels of shared differentially expressed secreted factors as transcripts per million (TPM), in the DP cells of ADX (b) and Pdgfra-CreER GR fl/fl mice (c). d, Negative control and Gas6 mRNA expression by in situ hybridization in late anagen (AnaV) and mid catagen (CatV) skin of sham and ADX mice. Quantification Gas6 mRNA in the DP. Dashed lines, HF; solid lines, DP. e, Representative image of negative control and Axl mRNA expression by in situ hybridization in telogen skin. Yellow dashed lines: bulge; white dashed lines: hair germ (top). qRT-PCR of Axl, Tgfbr1, Bmpr1a, Nfatc1 and PPIB from HFSCs and epidermal stem cells (EpSCs) of control mice (P83) (bottom). f, Representative images of negative control and Axl mRNA expression by in situ hybridization in late anagen skin. Yellow dashed lines: bulge; white dashed lines: epidermis and HFs. g, The expression levels as TPM of TAM receptors (Tyro3, Axl, and Mertk) in HFSCs. h, Schematic of the GAS6-AXL receptor tyrosine kinase pathway. R428 is a selective inhibitor of AXL tyrosine kinase activity (left). Colony formation assays of cultured HFSCs in R428 or GAS6 with R428 with quantifications (right). Scale bars, 50 μm (d,e,f). Data are mean±s.e.m. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001, NS, not significant. Exact P values see source data files. Statistics, sample sizes, and numbers of replications are in Methods, ‘Statistics and Reproducibility’.

Extended Data Fig. 9 |. Analyses of skin changes upon Gas6 overexpression or AXL inhibitor treatment.

a, Immunohistochemical analysis (GFP and PCAD) of PBS-injected 2^nd telogen skin and AAV-GFP injected 2^nd telogen skin. Dashed lines, epidermis and HFs; solid lines: DP. b, qRT-PCR of Gas6 from dermal fibroblasts of PBS-injected 2^nd telogen skin (control) and AAV-Gas6 injected 2^nd telogen skin. c, Precocious HFSC activation in mice injected with AAV-Gas6 shown by EdU incorporation. Immunocolocalization (EdU and CD34) in control and AAV-Gas6 injected skin after AAV injection (D3 to D9). d, Comparison of EdU and CD34 localization in bulge and upper outer root sheath (ORS) in late anagen (AnaV, control: D50 after injection; Gas6: D17 after injection). e, H&E staining of late anagen (AnaVI) skin (control: D53 after injection; Gas6: D20 after injection). Quantification of the ORS length in the zigzag hairs of control and AAV-Gas6 injected mice during late anagen. Brackets: the ORS length below the bulge. f, Immunocolocalization (EdU and CD34) in infundibulum (IF), junctional zone (JZ), sebaceous gland (SG), mid ORS (ORS^mid), lower ORS (ORS^low), and matrix (Mx) of late anagen (AnaVI) HFs in control and AAV-Gas6 injected mice with quantifications. Dashed lines, HFs. g, H&E staining in the late anagen skin of control and AAV-Gas6 injected mice with quantification of the thickness of epidermis (E) (top). Immunocolocalization (EdU and DAPI) in interfollicular epidermis (IFE) and dermis in control and AAV-Gas6 injected mice with quantifications (bottom). h, qRT-PCR of genes related to HFSC proliferation in HFSCs of 2^nd telogen skin. i, Hair cycle progression of sham and ADX mice treated with ethanol topically, or ADX mice treated with R428 in ethanol. j, qRT-PCR of genes related to cell cycle machineries and cytokinesis from HFSCs of sham, ADX mice treated with ethanol topically, or ADX mice treated for 7 days with R428 (in ethanol) topically. Yellow dashed lines: bulge (c,d); white dashed lines: hair germ (c), the rest of the HF (d,f), or the boundary of epidermis and dermis (g); solid white line: DP (c). EtOH, ethonal. Scale bars, 50 μm (a,c,d,e,f,g). Data are mean±s.e.m. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001, NS, not significant. Exact P values see source data files. Statistics, sample sizes, and numbers of replications are in Methods, ‘Statistics and Reproducibility’.

Extended Data Fig. 10 |. Interactions between systemic corticosterone and local BMP signalling.

a, In situ hybridization of negative control and Gas6 mRNA expression in different conditions, including P49 (early telogen) of sham, P80 (late telogen) of sham, P49 of ADX alone, P49 of AAV-Noggin injection in sham mice (Noggin in sham), and P49 of AAV-Noggin injection in ADX mice (Noggin in ADX). Quantifications show in situ signal intensities in DP. Model denotes how changes in corticosterone and BMP signalling influence Gas6 levels in DP. b, qRT-PCR of Gas6 from DP of P49 (early telogen) and P80 (late telogen) of sham, and P49 of ADX, AAV-Noggin in sham, and AAV-Noggin in ADX mice. c, Hair cycle progression in sham, ADX, AAV-Noggin injection in sham, and AAV-Noggin injection in ADX with quantifications. Dashed circles: AAV-Noggin injection areas. d, Control and Pdgfra-CreER;GRfl/fl mice were subjected to chronic unpredictable stress from P55. Quantification shows % of hair re-growth at P107. e, qRT-PCR of Gas6 from DP cells of control (P83) and stressed mice (P83) (left), and vehicle (P83) and corticosterone-fed mice (P83) (right). f, In situ hybridization of Gas6 in vehicle (P83, late telogen) and corticosterone-fed mice (P83) with quantification of in situ signals in DP. g, Model for corticosterone regulation of telogen length. In normal conditions, corticosterone levels remain constant, but BMP levels naturally decrease as telogen progresses, until a point is reached at which Gas6 levels are sufficiently elevated to drive HFSCs out of quiescence. This dynamic can be altered by changing either the corticosterone level or the BMP level. If corticosterone levels drop, the sum of inhibitory cues on Gas6 drops below a critical threshold sooner in telogen, leading to elevated Gas6 levels and precocious anagen entry. In the case of stress, age, or corticosterone feeding, elevated corticosterone levels reduce Gas6 levels to below the critical threshold, leading to an extended telogen. Dashed lines, HFs; solid lines, DP. Scale bars, 50 μm (a,f). Data are mean±s.e.m. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001, NS, not significant. Exact P values see source data files. Statistics, sample sizes, and numbers of replications are in Methods, ‘Statistics and Reproducibility’.

Fig. 1 |. Removal of adrenal glands activates HFSCs.

a, Sham and ADX mice were shaved and monitored for hair coat recovery. Quantifications show % of back skin covered by regrown hairs. b, EdU and PCAD staining in sham and ADX hair follicles (HFs) (P49 to P58) with quantifications. Yellow dashed lines: bulge; white dashed lines: hair germ or hair bulb (HB); solid lines: dermal papilla (DP). c, EdU and CD34 staining in late anagen (AnaV: sham, P110; ADX, P62) and catagen (CatV: sham, P122; ADX, P74). Yellow dashed lines: bulge (Bu); white dashed lines: rest of HF. ORS^up (upper outer root sheath) d, Hair cycle length. e, Hair cycle numbers of sham and ADX mice from P60 to P513 (see also Extended Data Fig. 1). f, Representative hair re-growth status of 22-month-old sham and ADX mice. Telo, telogen; Ana, anagen; Cat, Catagen. Scale bars, 50 μm (b,c). Data are mean±s.e.m. **P < 0.01, ***P < 0.001, ****P < 0.0001, NS, not significant. Exact P values see source data files. Statistics, sample sizes, and numbers of replications are in Methods, ‘Statistics and Reproducibility’.

Fig. 2 |. Adrenal gland-derived corticosterone regulates HFSC quiescence.

a, Plasma corticosterone levels in different mice 2 weeks after feeding corticosterone (CORT) or vehicle (Veh). b, Hair cycle progression and H&E staining of sham+Veh, ADX+Veh, and ADX+CORT mice. Scale bar, 50 μm. c, Hair cycle progression of C57BL/6 mice fed with vehicle or corticosterone. d, Hair cycle progression in C57BL/6 mice subjected to chronic unpredictable stress and non-stressed control. Data are mean±s.e.m. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. Exact P values see source data files. Statistics, sample sizes, and numbers of replications are in Methods, ‘Statistics and Reproducibility’.

Fig. 3 |. Corticosterone acts on dermal papilla (DP) to regulate HFSC quiescence.

a, Pdgfra-CreER depletes GR efficiently in DP and dermal fibroblasts (DF). b, Hair cycle progression of control and Pdgfra-CreER;GRfl/fl mice. c, Immunohistochemical analyses (YFP and PCAD) of Sox2-CreER;R26-lsl-YFP skin showing YFP in DP of guard HFs but not zigzag HFs. d, H&E staining of control and Sox2-CreER;GRfl/fl skin (arrowhead: an anagen guard HF surrounded by telogen HFs). e, Surface view (side and top) showing accelerated anagen only in the guard hairs in Sox2-CreER;GRfl/fl mice (shaved at P45; imaged at P67). f, RNAseq workflow. g, GO enrichment analysis of 121 shared differentially expressed genes in HFSCs comparing sham vs. ADX, ADX vs. ADX+CORT, and control vs. Pdgfra-CreER;GRfl/fl (see also Extended Data Fig. 6). Scale bars, 50 μm (c,d), 1 mm (e). Data are mean±s.e.m. **P < 0.01, ****P < 0.0001. Exact P values see source data files. Statistics, sample sizes, and numbers of replications are in Methods, ‘Statistics and Reproducibility’.

Fig. 4 |. Gas6 overexpression counteracts the inhibitory effect of corticosterone.

a, Negative control and Gas6 expression visualized by in situ hybridization in early telogen of sham, ADX, and ADX+CORT. Quantification shows Gas6 signals in DP. Bold dashed lines, bulge; thin dashed lines, hair germ; solid lines, DP. b, Cultured HFSCs in the presence or absence of GAS6. c, Intradermal injection of AAV-Gas6 but not AAV-GFP induces anagen in injection sites. Dashed circles: AAV injection areas. d, AAV-mediated expression of GFP or Gas6 in mice subjected to chronic unpredictable stress or corticosterone feeding. e, Model summarizing main findings. When corticosterone levels drop, elevated Gas6 expression promotes HFSC activation and anagen entry. Conversely, when corticosterone levels are elevated, Gas6 expression is inhibited, HFSCs stay in prolonged quiescence. Scale bar, 50 μm (a,c). Data are mean±s.e.m. *P < 0.05, ****P < 0.0001. Exact P values see source data files. Statistics, sample sizes, and numbers of replications are in Methods, ‘Statistics and Reproducibility’.