Hair growth control by innate immunocytes: Perifollicular macrophages revisited

The role of innate immunocytes such as mast cells, γδ T cells, NK cells and macrophages (MACs) in hair growth control under physiological and pathological conditions has recently begun to be re‐explored. Here, we revisit the role of resident perifollicular macrophages (pfMACs) located in the hair follicle (HF) mesenchyme (CTS). Substantial, stringently timed fluctuations in the number and localization of pfMACs were first observed long ago during murine HF morphogenesis and cycling. This already suggested some involvement of these innate immunocytes, with a recognized role in tissue remodelling and in hair growth control. The relatively recent demonstration of a Wnt signalling‐driven crosstalk between these immunocytes and HF epithelial stem cells in telogen HFs, which promotes anagen induction, has reinvigorated interest in the role that pfMAC plays in hair biology. Besides the apoptosis‐associated secretion of stem cell–activating Wnts and the differential secretion of HF‐targeting growth factors such as FGF‐5 and FGF5s from pfMACs, we also explore how MAC polarization, and thus function, may be influenced by the local metabolic and immune environment. Moreover, we examine how pfMACs may contribute to hair cycle–associated angiogenesis, vascular remodelling, HF immune privilege and immunopathology. On this basis, we discuss why targeting pfMACs may be relevant in the management of hair growth disorders. Finally, we argue that studying pfMACs offers an excellent, clinically relevant model system for characterizing and experimentally manipulating MAC interactions with an easily accessible mammalian, continuously remodelled (mini‐)organ under both physiological and pathological conditions.     

Hair cycle-dependent changes in adrenergic skin innervation, and hair growth modulation by adrenergic drugs

Skin nerves may exert "trophic" functions during hair follicle development, growth, and/or cycling. Here, we demonstrate hair cycle-related plasticity in the sympathetic innervation of skin and hair follicle in C57BL/6 mice. Compared with telogen skin, the number of nerve fibers containing norepinephrine or immunoreactive for tyrosine hydroxylase increased during the early growth phase of the hair cycle (anagen) in dermis and subcutis. The number of these fibers declined again during late anagen. beta2-adrenoreceptor-positive keratinocytes were transiently detectable in the noncycling hair follicle epithelium, especially in the isthmus and bulge region, but only during early anagen. In early anagen skin organ culture, the beta2-adrenoreceptor agonist isoproterenol promoted hair cycle progression from anagen III to anagen IV. The observed hair cycle-dependent changes in adrenergic skin innervation on the one hand, and hair growth modulation by isoproterenol, accompanied by changes in beta2-adrenoreceptor expression of selected regions of the hair follicle epithelium on the other, further support the concept that bi-directional interactions between the hair follicle and its innervation play a part in hair growth control. This invites one to systematically explore the neuropharmacologic manipulation of follicular neuroepithelial interactions as a novel therapeutic strategy for managing hair growth disorders.     

Hair cycle control by leptin as a new anagen inducer

Our purpose is to clarify the physiological role of leptin in hair cycle as leptin reportedly causes activation of Stat3, which is indispensable for hair cycling. While hair follicles in dorsal skin of 5‐week‐old C57/BL6 mice had progressed to late anagen phase, those in dorsal skin of 5‐week‐old leptin receptor deficient db/db mice remained in the first telogen and later entered the anagen at postnatal day 40, indicating that deficiency in leptin receptor signalling delayed the second hair cycle progression. Next, we shaved dorsal hairs on wild‐type mice at postnatal 7 weeks and injected skin with mouse leptin or a mock. After 20 days, although mock injection showed no effect, hair growth occurred around leptin injection area. Human leptin fragment (aa22–56) had similar effects. Although the hair cycle of ob/ob mice was similar to that of wild‐type mice, injection of mouse leptin on ob/ob mice at postnatal 7 weeks induced anagen transition. Immunohistochemically, leptin is expressed in hair follicles from catagen to early anagen in wild‐type mice, suggesting that leptin is an anagen inducer in vivo. Phosphorylation of Erk, Jak2 and Stat3 in human keratinocytes was stimulated by leptin and leptin fragment. In addition, RT‐PCR and ELISA showed that the production of leptin by human dermal papilla cells increased under hypoxic condition, suggesting that hypoxia in catagen/telogen phase promotes leptin production, preparing for entry into the next anagen. In conclusion, leptin, a well‐known adipokine, acts as an anagen inducer and represents a new player in hair biology.     

Hair Fibrous Protein Compositions in Some Hereditary Hair Abnormalities Determined by Two-Dimensional Polyacrylamide Gel Electrophoresis

S-carboxymethylated (SCM) fibrous proteins (FPs) from the scalp hairs of the three different hereditary hair abnormalities (trichorrhexis invaginata in Netherton's syndrome, pili trianguli et canaliculi in uncombable hair syndrome, and fine hair in anhidrotic ectodermal dysplasia) were analyzed by two-dimensional polyacrylamide gel electrophoresis. Comparison of the SCM FP compositions of the three hair abnormalities with that of the normal revealed that the SCM FP compositions of these three abnormal hairs were all electrophoretically different from each other and that of the normal.     

Effects of Transforming Growth Factor β1 in the Hair Cycle

Hair follicle growth is thought to be regulated by a complex interplay of stimulatory and inhibitory signals. From among such signals, we examined the effects of transforming growth factor β1 (TGFβ1) on the murine hair growth cycle. Quantitation of TGFβ1 per wet tissue weight was performed at different stages of the hair cycle. TGFβ1 was extracted with 10 mM HCl, and its level was measured with ELISA. The level of TGFβ1 did not change markedly during the hair cycle. Immunohistochemical observations revealed that hair follicle cells and epidermal cells were negative for TGFβ1 at all stages of the hair cycle. Mast cells in the dermis were positive throughout the cycle. To confirm whether TGFβ1 inhibits the proliferation of hair follicles, we injected it subcutaneously. TGFβ1 inhibited the proliferation of hair follicles. Our observations suggest that TGFβ1 is at least partly responsible for regulating hair follicles as a negative growth factor.     

The size and form of the medulla of human scalp hair is regulated by the hair cycle and cross-sectional size of the hair shaft

Hairs were sampled from long-haired Caucasian females, and cross-sectional measurements were performed using a rotating profile method at fixed humidity (100%). The effect of the hair cycle on medullation was investigated by examining medulla size and form along the lengths of anagen and telogen terminal hairs and also from a composite model of the entire medulla, as produced from a full cycle's growth, by amalgamating the results from the anagen and telogen hairs. The effect of hair shaft cross-sectional size on medullation has been investigated by controlling any effect of the hair cycle on terminal hairs and by use of the maximal medulla size in short, fine (vellous) hairs from the same subjects. All terminal hairs were medullated for the majority of their lengths. The presence and size of the medulla, in terminal hairs, was profoundly affected by the hair cycle. It was largest early in anagen, where the medulla minor axis, major axis and cross-sectional area represented about 26%, 23% and 7% of the corresponding whole hair shaft parameters (at 100% humidity). The medulla was virtually absent towards the end of anagen. The shape of the medulla cross-section was less elliptical than that of the whole hair shaft and was close to circular. There was no significant change in medulla shape through anagen. The form of the medulla was also affected by the hair cycle; approximately, it was continuous for the first 50% of anagen, discontinuous for the next 25% and virtually absent or absent for the final 25%. The maximal size of the medulla, as occurred in early anagen, was markedly associated with the cross-sectional size of the whole hair shaft, both within terminal hairs and between all scalp hairs. The medulla was large in terminal hairs and small or absent in very small hairs. The proportion of the whole hair shaft occupied by the medulla increased with increase in hair size and reached a maximum in terminal hairs, in which the medulla minor axis represented about 30% of the whole hair shaft minor axis. Furthermore, this proportion was constant in the terminal hairs and was not related to whole hair shaft size. Such maximal proportional medullation might represent a defining feature of terminal hairs. Variation in size of the medulla is not the cause of the previously reported cycle-dependent change in cross-sectional size of the whole hair shaft of terminal hairs.     

甲状旁腺激素对小鼠毛发周期和毛发生长的影响

以C57BL6小鼠作为动物模型,观察甲状旁腺激素(PTH)的多肽片段PTH(7～34)和PTH(1～34)对毛发周期和毛发生长的影响。用松香/蜡混合物拔毛法诱导C57BL6小鼠毛发由休止期进入生长期,拔毛同时腹腔注射PTH(7～34),持续19天,观察毛发周期的变化。结果,PTH(7～34)组小鼠在拔毛后第5天毛发进入生长期,比对照组提前24h左右;至第19天,对照组小鼠多数毛发进入退行期或休止期,而PTH(7～34)组仍有大部分毛发维持在生长期。C57BL6乳鼠触须毛囊体外培养结果,加PTH(7～34)10-6mol/L浓度组和10-7mol/L浓度组毛干生长速度显著比对照组加快(P<0.01);而PTH(1～34)10-9mol/L浓度组毛干生长明显慢于对照组(P<0.01)。提示PTH的不同片段对毛发生长有不同影响,PTH(7～34)可延长毛发生长期,促进小鼠毛发生长,而PTH(1～34)则对毛发生长有抑制作用。     

Proliferating Activity of the Hair Follicular Melanocytes at the Early and Anagen III Stages in the Hair Growth Cycle: Detection by Immunocytochemistry for Bromodeoxyuridine Combined with DOPA Reaction Cytochemistry

In order to demonstrate the existence of proliferating activity in hair follicular melanocytes during the early and anagen III stages, immunocytochemistry for bromodeoxyuridine (BrdU) incorporated in the nuclei of the melanocytes for 1 hr was undertaken at the light and electron microscopic levels in combination with DOPA reaction cytochemistry. Light microscopically, about 30% of the nuclei of the DOPA reaction positive melanocytes at the anagen III stage of the hair growth cycle were labeled by anti-BrdU antibody. These melanocytes were observed in about one hundred hair follicles. Electron microscopically, the nuclei of a few undifferentiated melanocytes at the anagen II stage were labeled by anti-BrdU antibody-affiliated secondary antibody-gold particles. At the anagen III stage, localization of the immunogold particles in the DNA replication domains of the nuclei of the undifferentiated and redifferentiating melanocytes covered the patterns of the early, middle, and late S-phase. These findings suggest that the hair follicular melanocytes begin proliferation at the anagen II stage and that the melanocytes proliferate actively at the anagen III stage to repopulate the hair matrix during subsequent hair growth.     

活血补肾合剂对C57BL/6小鼠毛发生长的影响

目的从微观结构方面探讨活血补肾合剂促进小鼠毛发生长的机理.方法用C57BL/6小鼠建立动物模型,对120只小鼠以松香/蜡混合物(1:1)拔毛,诱导其毛发由休止期进入生长期,并随机分为4个组,即实验组、对照组、模型组和空白组.从造模后第一天开始灌药,每天观察各组皮肤色泽变化,并分别于造模后第4、11、17天每组处死10只小鼠,观察拔毛部位的毛囊和血管情况.结果活血补肾合剂第4天时显示出促进血管新生(P＜0.05),在第11天时表现出促进毛囊新生(P＜0.05),第17天表现出促进毛囊成熟的作用(P＜0.05).结论活血补肾合剂可能是通过促进血管新生,改善局部血液循环达到促进毛发生长的目的.     

E- and P-cadherin expression during murine hair follicle morphogenesis and cycling

The role of adhesion molecules in the control of hair follicle (HF) morphogenesis, regression and cycling is still rather enigmatic. Since the adhesion molecules E- and P-cadherin (Ecad and Pcad) are functionally important, e.g. during embryonic pattern formation, we have studied their expression patterns during neonatal HF morphogenesis and cycling in C57/BL6 mice by immunohistology and semi-quantitative RT-PCR. The expression of both cadherins was strikingly hair cycle-dependent and restricted to distinct anatomical HF compartments. During HF morphogenesis, hair bud keratinocytes displayed strong Ecad and Pcad immunoreactivity (IR). While neonatal epidermis showed Ecad IR in all epidermal layers, Pcad IR was restricted to the basal layer. During later stages of HF morphogenesis and during anagen IV-VI of the adolescent murine hair cycle, the outer root sheath showed strong E- and Pcad IR. Instead, the outermost portion of the hair matrix and the inner root sheath displayed isolated Ecad IR, while the innermost portion of the hair matrix exhibited isolated Pcad IR. During telogen, all epidermal and follicular keratinocytes showed strong Ecad IR. This is in contrast to Pcad, whose IR was stringently restricted to matrix and secondary hair germ keratinocytes which are in closest proximity to the dermal papilla. These findings suggest that isolated or combined E- and/or Pcad expression is involved in follicular pattern formation by segregating HF keratinocytes into functionally distinct subpopulations; most notably, isolated Pcad expression may segregate those hair matrix keratinocytes into one functional epithelial tissue unit, which is particularly susceptible to growth control by dermal papilla-derived morphogens. The next challenge is to define which secreted agents implicated in hair growth control modulate these follicular cadherin expression patterns, and to define how these basic parameters of HF topobiology are altered during common hair growth disorders.     

Hair growth inhibition by psychoemotional stress: a mouse model for neural mechanisms in hair growth control

Stress has long been discussed controversially as a cause of hair loss. However, solid proof of stress-induced hair growth inhibition had long been missing. If psychoemotional stress can affect hair growth, this must be mediated via definable neurorendocrine and/or neuroimmunological signaling pathways. Revisiting and up-dating relevant background data on neural mechanisms of hair growth control, we sketch essentials of hair follicle (HF) neurobiology and discuss the modulation of murine hair growth by neuropeptides, neurotransmitters, neurotrophins, and mast cells. Exploiting an established mouse model for stress, we summarize recent evidence that sonic stress triggers a cascade of molecular events including plasticity of the peptidergic peri- and interfollicular innervation and neuroimmune crosstalk. Substance P (SP) and NGF (nerve growth factor) are recruited as key mediators of stress-induced hair growth-inhibitory effects. These effects include perifollicular neurogenic inflammation, HF keratinocyte apoptosis, inhibition of proliferation within the HF epithelium, and premature HF regression (catagen induction). Intriguingly, most of these effects can be abrogated by treatment of stressed mice with SP-receptor neurokinin-1 receptor (NK-1) antagonists or NGF-neutralizing antibodies - as well as, surprisingly, by topical minoxidil. Thus there is now solid in vivo-evidence for the existence of a defined brain- HF axis. This axis can be utilized by psychoemotional and other stressors to prematurely terminate hair growth. Stress-induced hair growth inhibition can therefore serve as a highly instructive model for exploring the brain-skin connection and provides a unique experimental model for dissecting general principles of skin neuroendocrinology and neuroimmunology well beyond the HF.     

Dynamic changes in nerve growth factor and substance P in the murine hair cycle induced by depilation

Increasing evidence suggests that various neurotrophins and neuropeptides play an important role in the progression of hair follicle cycling. Among them, nerve growth factor (NGF) and substance P (SP) have attracted special interest recently. However, the interaction between these factors during hair cycling has not yet been systematically studied. We therefore investigated the mutual relationships between NGF and SP and the mechanism by which the anagen stage of the hair cycle is initiated. Fluctuations in numbers of SP-positive nerve fibers and variations in amounts of SP, NGF, and another neurotrophic factor, glial cell-derived neurotrophic factor, in skin in the C57BL/6 mouse depilation-induced hair cycle model, together with the spatiotemporal expression patterns of each of these factors, were followed simultaneously by enzyme-linked immunosorbent assay and immunohistochemistry. The main finding was that a surge in NGF expression and a rapid increase in NGF content in skin is an initial event within 1 day after depilation, followed by elevation of SP content and numbers of SP-containing fibers 2 days after the increase in NGF. Our findings suggest that a rapid and abundant increase in NGF plays a key role in the induction and progression of anagen hair cycling through keratinocyte growth promotion. NGF may also induce plastic changes such as sprouting and hyperplasia in dermal nerve fibers and enhance their SP production. Elevated levels of SP in skin may additionally contribute to the progression of consecutive anagen hair cycles.     

中药黄芪、女贞子、人参促毛发生长的在体研究

目的:以C57BL/6小鼠为动物模型,探讨中药黄芪、女贞子、人参混合煎剂促进C57BL/6小鼠毛发生长的可能机制。方法:中药组小鼠给予中药混合煎剂口饲,对照组给予等量生理盐水,观察小鼠背部皮肤颜色变化和毛发生长情况。同时在光镜下观察小鼠毛囊组织学变化及毛囊内细胞的凋亡的状况。结果:中药组小鼠饲饮中药煎剂后背部皮肤颜色由粉红色变为黑色比对照组提前了1d,背部皮肤颜色由黑色变为灰黑色比对照组延长了1.5d。组织学上,拔毛后第18天对照组小鼠毛囊处于退行中晚期,而中药组仍为生长Ⅵ期和退行早期毛囊。中药组小鼠毛囊内凋亡细胞数量比对照组减少(P<0.001)。结论:黄芪、女贞子、人参混合煎剂促毛发生长作用可能与抑制退行期毛囊内细胞凋亡,诱导和延长C57BL小鼠毛发的生长期有关。