Comments' abstract Signalling from the sympathetic nervous system of mice when subjected to stress leads to the depletion of a stem-cell population in their hair follicles. This discovery sheds light on why stress turns hair premaurely grey.
Figure 1 | Melanocyte stem cells and stress. Melanocyte stem cells (MeSCs) are located in the bulge of the hair follicle, which is innervated by neurons of the sympathetic nervous system that release the neurotransmitter molecule noradrenaline. The follicle cycles through three phases: regeneration (anagen), degeneration (catagen) and rest (telogen). a, Under normal conditions, MeSCs migrate away from the bulge (red arrows) and differentiate into melanocytes during anagen. Melanocytes synthesize pigments that add colour to the regenerating hair. During catagen and telogen, they begin to die and migrate out of the niche (not shown). However, plentiful MeSCs remain to replace the melanocytes in the next anagen phase. b, Zhang et al.1 show that stressful stimuli activate the sympathetic nervous system, increasing noradrenaline release in hair follicles. Noradrenaline causes complete conversion of MeSCs into melanocytes, which migrate out of the niche in catagen and telogen. The hair follicle is depleted of MeSCs that would have differentiated to replace these melanocytes. Without any pigment cells to colour the hair in the next anagen phase, it begins to look grey or white.
Title：Hyperactivation of sympathetic nerves drives depletion of melanocyte stem cells
Abstract Empirical and anecdotal evidence has associated stress with accelerated hair greying (formation of unpigmented hairs), but so far there has been little scientific validation of this link. Here we report that, in mice, acute stress leads to hair greying through the fast depletion of melanocyte stem cells. Using a combination of adrenalectomy, denervation, chemogenetics, cell ablation and knockout of the adrenergic receptor specifically in melanocyte stem cells, we find that the stress-induced loss of melanocyte stem cells is independent of immune attack or adrenal stress hormones. Instead, hair greying results from activation of the sympathetic nerves that innervate the melanocyte stem-cell niche. Under conditions of stress, the activation of these sympathetic nerves leads to burst release of the neurotransmitter noradrenaline (also known as norepinephrine). This causes quiescent melanocyte stem cells to proliferate rapidly, and is followed by their differentiation, migration and permanent depletion from the niche. Transient suppression of the proliferation of melanocyte stem cells prevents stress-induced hair greying. Our study demonstrates that neuronal activity that is induced by acute stress can drive a rapid and permanent loss of somatic stem cells, and illustrates an example in which the maintenance of somatic stem cells is directly influenced by the overall physiological state of the organism.
a, Black-coated C57BL/6J mice were subjected to different stress models. CUS, chronic unpredictable stress.
b, Hair greying after injection of mice with RTX or saline. Right, quantification of the area of skin covered by white hairs (n = 10 mice for each condition, two-tailed unpaired t-test).
c, Liquid chromatography with tandem mass spectrometry (LC–MS/MS) was used to quantify the concentration of serum stress hormones (corticosterone and noradrenaline) after injection of RTX alone or in combination with buprenorphine (bup) (n = 6 mice for each condition, one-way analysis of variance (ANOVA) with Tukey’s multiple comparisons test).
d, Injection of RTX with buprenorphine blocks formation of white hairs (n = 6 mice for each condition, two-tailed unpaired t-test).
e, Top, experimental design (black arrow, RTX injection; red arrows, collection of skin samples). Bottom, immunofluorescent staining for TRP2 (a marker of the melanocyte lineage) in the hair follicle (HF) of control (ctrl, saline-injected) and RTX injected mice (n = 30 hair follicles throughout the skin from 6 mice for each condition, two-way ANOVA with Benjamini–Hochberg correction). Yellow boxes denote the upper region of the hair follicle, where MeSCs reside. Enlarged views are shown to the right, and the number of MeSCs for each condition is quantified. Arrowheads denote MeSCs. Ana, anagen; cata, catagen; telo, telogen; diff. Mcs, differentiated melanocytes. Scale bars, 50 μm. All data are mean ± s.d.
b, Injection of RTX into TyrcreERT2;Adrb2fl/fl (MeSC-specific Adrb2 conditional knockout (cKO)) mice does not trigger hair greying (n = 6 mice for each condition, two-tailed unpaired t-test). NA, noradrenaline.
c, Formation of white hairs at sites of noradrenaline injection (n = 10 injected sites from 8 mice for each condition). For quantifications, see Extended Data Fig. 4e. Yellow dashed circles denote intradermal injection sites.
d, Formation of white hairs after RTX injection in adrenalectomized mice (ADX) (n = 6 mice for each
condition, two-tailed unpaired t-test). All data are mean ± s.d.
Fig. 3 | Hyperactivation of the sympathetic nervous system depletes MeSCs.
a, Sympathetic nerves innervate MeSC niches. White arrowhead on the immunofluorescent staining indicates the close proximity of nerve endings to MeSCs (n = 6 mice for each condition).
b, Left, immunofluorescent staining of sympathetic ganglia for tyrosine hydroxylase (TH; green) and FOS (red) from mice injected with saline, RTX and RTX with buprenorphine. Right, quantification of FOS+ cells in sympathetic ganglia (SG) (n = 6 ganglia from 3 mice for each condition, one-way ANOVA with Tukey’s multiple comparisons test).
c, Injection of 6-hydroxydopamine (6-OHDA) blocks loss of MeSCs and induction of white hairs by RTX (n = 30 hair follicles from 6 mice for each condition, two-tailed unpaired t-test). SN abla, sympathetic nerve ablation. See also Extended Data Fig. 5d.
d, Left, schematic of sympathetic nerve activation using a Gq-DREADD system. Right, immunofluorescent staining for TH (green) and TRP2 (red) from THcreERT2;CAG-LSL-Gq-DREADD mice treated with saline or CNO (n = 30 hair follicles from 6 mice for each condition, two-tailed unpaired t-test).
e, Mosaic activation of sympathetic nerves in THcreERT2;CAG-LSL-Gq-DREADD;RosamT/mG mice. Bar graphs quantify the number of MeSCs in hair follicles innervated by DREADD-negative sympathetic nerves (without DREADD) versus DREADD-positive sympathetic nerves (with DREADD; marked by membrane GFP expression) (n = 30 hair follicles for each condition from 4 mice, two-tailed unpaired t-test). Scale bars, 50 μm. All data are mean ± s.d.
Fig. 4 | Noradrenaline drives MeSCs out of quiescence.
a, Possible mechanisms by which noradrenaline depletes MeSCs.
b, Left, immunofluorescent staining for phosphorylated histone H3 (pHH3, green) and TRP2 (red) one day after injection of RTX or noradrenaline. White arrowheads indicate the proliferative MeSCs. Right, quantification of pHH3+ MeSCs (n = 30 hair follicles from 5 mice for each condition, one-way ANOVA with Tukey’s multiple comparisons test).
c, Time course of MeSC behaviour after treatment with RTX in TyrcreERT2;RosamT/mG mice. White arrowheads mark MeSCs (n = 30 hair follicles from 3 mice for each time point, one-way ANOVA with Tukey’s multiple comparisons test). TAM, tamoxifen.
d, Fontana-Masson melanin staining five days after injection of saline or RTX (n = 6 mice for each condition). Blue arrowheads indicate ectopic pigments.
e, Model summarizing steps of stress induced MeSC depletion. Scale bars, 50 μm. All data are mean ± s.d.
a, Experimental workflow. FACS was performed in cells at telogen.
b, GO enrichment analysis of significantly dysregulated genes in stressed MeSCs (n = 2 biologically independent samples for each condition, Fisher’s exact test).
c, Heat map of signature gene expression for genes that are related to the proliferation of MeSCs (n = 2 biologically independent samples for each condition).
d, qRT–PCR of genes that are related to MeSC proliferation and differentiation in cultured primary human melanocytes treated with noradrenaline (n = 6 samples from 3 independent donors, two-way ANOVA with Benjamini–Hochberg correction).
e, Top, immunofluorescent staining for TRP2 (red) from mice five days after treatment with RTX, RTX with CDK inhibitors (AT7519 or flavopiridol (flavo)) or RTX with MeSC-specific overexpression of P27 (P27 OE). Bottom, quantification of MeSCs (n = 30 hair follicles from 6 mice for each condition, one-way ANOVA with Tukey’s multiple comparisons test).
f, Topical treatment with AT7519, flavopiridol or MeSCspecific P27 overexpression inhibits RTX-induced hair greying (n = 6 mice for each condition, one-way ANOVA with Tukey’s multiple comparisons test).
g, Model summarizing the main findings of the study. Under strong external stressors, activated sympathetic nerves secrete noradrenaline that binds to ADRB2 on MeSCs. Noradrenaline–ADRB2 signalling drives rapid proliferation of MeSCs, followed by their ectopic differentiation and exhaustion. Scale bars, 50 μm. All data are mean ± s.d.