Hair growth-modulation by adrenergic drugs

The impact of perceived stress on the hair follicle: Towards solving a psychoneuroendocrine and neuroimmunological puzzle

While popular belief harbors little doubt that perceived stress can cause hair loss and premature graying, the scientific evidence for this is arguably much thinner. Here, we investigate whether these phenomena are real, and show that the cyclic growth and pigmentation of the hair follicle (HF) provides a tractable model system for dissecting how perceived stress modulates aspects of human physiology. Local production of stress-associated neurohormones and neurotrophins coalesces with neurotransmitters and neuropeptides released from HF-associated sensory and autonomic nerve endings, forming a complex local stress-response system that regulates perifollicular neurogenic inflammation, interacts with the HF microbiome and controls mitochondrial function. This local system integrates into the central stress response systems, allowing the study of systemic stress responses affecting organ function by quantifying stress mediator content of hair. Focusing on selected mediators in this "brain-HF axis" under stress conditions, we distill general principles of HF dysfunction induced by perceived stress.

Defining a Role for G-Protein Coupled Receptor/cAMP/CRE-Binding Protein Signaling in Hair Follicle Stem Cell Activation

Manipulation of adrenergic signaling has been shown experimentally and clinically to affect hair follicle growth. In this study, we provide direct evidence that canonical cAMP/CRE-binding protein signaling through adrenergic receptors can regulate hair follicle stem cell (HFSC) activation and hair cycle. We found that CRE-binding protein activation is regulated through the hair cycle and coincides with HFSC activation. Both isoproterenol and procaterol, agonists of adrenergic receptors, show the capacity to activate the hair cycle in mice. Furthermore, deletion of ADRB2 receptor, which is thought to mediate sympathetic nervous system regulation of HFSCs, was sufficient to block HFSC activation. Downstream, stimulation of adenylyl cyclase with forskolin or inhibition of phosphodiesterase to increase cAMP accumulation or direct application of cAMP was each sufficient to promote HFSC activation and accelerate initiation of hair cycle. Genetic induction of a Designer Receptors Exclusively Activated by Designer Drug allele showed that G-protein coupled receptor/GαS stimulation, specifically in HFSCs, promoted the activation of the hair cycle. Finally, we provide evidence that G-protein coupled receptor/CRE-binding protein signaling can potentially act on HFSCs by promoting glycolytic metabolism, which was previously shown to stimulate HFSC activation. Together, these data provide mechanistic insights into the role of sympathetic innervation on HFSC function.

Cigarette Smoking, Alcohol Consumption, and Risk of Alopecia Areata: A Population-Based Cohort Study in Taiwan

BACKGROUND

The effects of cigarette smoking and alcohol consumption on the risk of alopecia areata (AA) are unclear.

OBJECTIVE

The aim was to examine the association of cigarette smoking and alcohol consumption with AA.

METHODS

We collected participants from four rounds (2001, 2005, 2009, and 2013) of the Taiwan National Health Interview Survey. Incident AA cases were identified from the National Health Insurance database.

RESULTS

Of the 60,055 participants, 154 developed AA during the 647,902 person-years of follow-up. After controlling for confounders, current smokers had a higher risk of incident AA than never smokers [adjusted hazard ratio (aHR) 1.88; 95% confidence interval (CI) 1.22-2.88]. There was a trend toward an increased risk of AA with increasing numbers of years of smoking and cumulative pack-years of smoking among current smokers. The aHRs (95% CIs) of current smokers of > 5 and ≤ 15 cigarettes per day, > 10 and ≤ 20 years of smoking, ≤ 10, and > 10 and ≤ 20 pack-years of smoking were 2.03 (1.17-3.51), 2.25 (1.21-4.18), 1.86 (1.12-3.09), and 2.04 (1.04-4.01), respectively. Conversely, social and regular drinkers had significantly lower risks of AA than never drinkers [aHRs (95% CIs) 0.65 (0.43-0.98) and 0.49 (0.26-0.93), respectively].

CONCLUSION

Current smokers had an increased risk of developing AA, while alcohol consumption was associated with a decreased risk of AA.

Cell Types Promoting Goosebumps Form a Niche to Regulate Hair Follicle Stem Cells

Piloerection (goosebumps) requires concerted actions of the hair follicle, the arrector pili muscle (APM), and the sympathetic nerve, providing a model to study interactions across epithelium, mesenchyme, and nerves. Here, we show that APMs and sympathetic nerves form a dual-component niche to modulate hair follicle stem cell (HFSC) activity. Sympathetic nerves form synapse-like structures with HFSCs and regulate HFSCs through norepinephrine, whereas APMs maintain sympathetic innervation to HFSCs. Without norepinephrine signaling, HFSCs enter deep quiescence by down-regulating the cell cycle and metabolism while up-regulating quiescence regulators Foxp1 and Fgf18. During development, HFSC progeny secretes Sonic Hedgehog (SHH) to direct the formation of this APM-sympathetic nerve niche, which in turn controls hair follicle regeneration in adults. Our results reveal a reciprocal interdependence between a regenerative tissue and its niche at different stages and demonstrate sympathetic nerves can modulate stem cells through synapse-like connections and neurotransmitters to couple tissue production with demands.

Levodopa-induced skin disorders in patients with Parkinson disease: a systematic literature review approach

The use of levodopa for treatment of Parkinson's disease is a well-established clinical practice. Data about the true incidence and severity of cutaneous complications associated with the use of levodopa are largely lacking. Aim of this review was to evaluate the quality of evidence referring to the skin disorders caused by levodopa treatment for Parkinson's disease. Thirty of 1084 studies were included; 8 randomized controlled trials and 22 case reports in a total of 2749 patients. Malignant melanoma was the most frequent oral levodopa-related skin disorder followed by allergic cutaneous reactions, alopecia, vitiligo, skin hyperpigmentation, Laugier-Hunziker syndrome, Henoch-Schönlein syndrome, pseudobullous morphea and scleroderma-like illness. Naranjo scores ranged from 2 to 8. Regarding levodopa clinical trials, the most frequent skin complication was peripheral edema, followed by malignant melanoma. Although evidence is not robust, melanoma is the most frequent and possible fatal levodopa-associated skin disorder, while other skin allergic or immunological reactions are less common and reversible. Although levodopa treatment may induce melanogenesis and promote melanomagenesis, existing evidence does not support an association between levodopa therapy and induction or progression of malignant melanoma. The suggested association with melanoma may reflect the well-documented association of Parkinson's disease with melanoma rather than the exposure to the drug. Nevertheless, until a solid conclusion can be drawn, the use of levodopa in the context of malignant melanoma should be considered with caution. Well-designed prospective studies are needed to determine the cause and effect relationship between levodopa and skin disorders.

Norepinephrine Regulates Keratinocyte Proliferation to Promote the Growth of Hair Follicles

Psychological factors and stress can cause hair loss. The sympathetic-adrenal-medullary (SAM) axis has been reported to regulate the growth of hair follicles (HF). The sympathetic nerve is a component of the SAM axis, but it has not been sufficiently or convincingly linked to hair growth. In this study, we demonstrate that chemical sympathectomy via administration of the neurotoxin 6-hydroxydopamine (6-OHDA) to mice inhibited HF growth, but treatment with the β-adrenoceptor antagonist propranolol (PR) had no effect. HF length and skin thickness were greater in PR-treated and control mice than in 6-OHDA-treated mice, as evidenced by hematoxylin and eosin staining. Furthermore, we found that the reduced HF growth in sympathectomized animals was accompanied by a decreased keratinocyte proliferation. Moreover, the neurotransmitter norepinephrine (NE) was found to efficiently promote HF growth in an organotypic skin culture model. Together, these findings suggest that sympathetic nerves regulate keratinocyte behaviors to promote hair growth, providing novel insights into stress-related, chemotherapy-, and radiotherapy-induced alopecia.

Beta-2 adrenergic receptor mediated ERK activation is regulated by interaction with MAGI-3

The beta-2 adrenergic receptor (beta2AR) has a carboxyl terminus motif that can interact with PSD-95/discs-large/ZO1 homology (PDZ) domain-containing proteins. In this paper, we identified membrane-associated guanylate kinase inverted-3 (MAGI-3) as a novel binding partner of beta2AR. The carboxyl terminus of beta2AR binds with high affinity to the fifth PDZ domain of MAGI-3, with the last four amino acids (D-S-L-L) of the receptor being the key determinants of the interaction. In cells, the association of full-length beta2AR with MAGI-3 occurs constitutively and is enhanced by agonist stimulation of the receptor. Our data also demonstrated that beta2AR-stimulated extracellular signal-regulated kinase-1/2 (ERK1/2) activation was substantially retarded by MAGI-3 expression. These data suggest that MAGI-3 regulates beta2AR-mediated ERK activation through the physical interaction between beta2AR and MAGI-3.

Observation of a system of linear loops formed by re-growing hairs on rat skin

This paper details linear hair re-growth patterns observed in rats. Adult rats were shaved and observed. The first wave of hair re-growth did not distribute everywhere, but along specific craniocaudally-oriented lines. The hair-lines were 2-15 mm wide and ran from the head, through the torso to the limbs, and were symmetrical along the left and right sides of the body. The symmetric hair-lines from both sides of the body converged around the mouth, nose, and at the pubic region or ventral midline to form a system of hair-loop-lines (HLLs). The loops can be differentiated into four main patterns. The Dorsal Loop and the Lateral Dorsal Loop run along the dorsum and hindlimb. The Ventral Loop and Lateral Ventral Loop travel along the thorax, abdomen, and forelimb. These hair-lines coincide with our previously observed sympathetic-substance lines (SSLs) in the rat's skin. Histological observation indicates that rat hair follicles along the hair-lines were at anagen phase. The catecholamine histofluorescent check showed abundant sympathetic nerve fibers beneath the hair-lines. After the rats' hairs were dyed, and selected portions shaved, re-growth was only observed on the shaved portions, indicating that the linear hair growth closely correlated with the shaving. Lastly we examine the cause of the preferential re-growth and briefly discuss the purpose and physiological role of the HLL.

(Neuro-)endocrinology of epithelial hair follicle stem cells

The hair follicle is a repository of different types of somatic stem cells. However, even though the hair follicle is both a prominent target organ and a potent, non-classical site of production and/or metabolism of numerous polypetide- and steroid hormones, neuropeptides, neurotransmitters and neurotrophins, the (neuro-)endocrine controls of hair follicle epithelial stem cell (HFeSC) biology remain to be systematically explored. Focussing on HFeSCs, we attempt here to offer a "roadmap through terra incognita" by listing key open questions, by exploring endocrinologically relevant HFeSC gene profiling and mouse genomics data, and by sketching several clinically relevant pathways via which systemic and/or locally generated (neuro-)endocrine signals might impact on HFeSC. Exemplarily, we discuss, e.g. the potential roles of glucocorticoid and vitamin D receptors, the hairless gene product, thymic hormones, bone morphogenic proteins (BMPs) and their antagonists, and Skg-3 in HFeSC biology. Furthermore, we elaborate on the potential role of nerve growth factor (NGF) and substance P-dependent neurogenic inflammation in HFeSC damage, and explore how neuroendocrine signals may influence the balance between maintenance and destruction of hair follicle immune privilege, which protects these stem cells and their progeny. These considerations call for a concerted research effort to dissect the (neuro-)endocrinology of HFeSCs much more systematically than before.

Skin and hair follicle innervation in experimental models: a guide for the exact and reproducible evaluation of neuronal plasticity

The remodelling of skin innervation is an instructive example of neuronal plasticity in the peripheral nervous system. Cutaneous innervation displays dramatic plasticity during morphogenesis, adult remodelling, skin diseases and after skin nerve lesions. To recognize even subtle changes or abnormalities of cutaneous innervation under different experimental conditions, it is critically important to use a quantitative approach. Here, we introduce a simple, fast and reproducible quantitative method based on immunofluorescence histochemistry for the exact quantification of peripheral nerve fibres. Computer-generated schematic representations of cutaneous innervation in defined skin compartments are presented with the aim of standardizing reports on gene and protein expression patterns. This guide should become a useful tool when screening new mouse mutants, disease models affecting innervation or mice treated with pharmaceuticals for discrete morphologic abnormalities of skin innervation in a highly reproducible and quantifiable manner. Moreover, this method can be easily transferred to other densely innervated peripheral organs.

Neuronal Control of Skin Function: The Skin as a Neuroimmunoendocrine Organ

This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.

p75 Neurotrophin Receptor-Mediated Signaling Promotes Human Hair Follicle Regression (Catagen)

Nerve growth factor (NGF) and its apoptosis-promoting low-affinity receptor (p75NTR) regulate murine hair cycling. However, it is unknown whether human hair growth is also controlled through p75NTR, its high-affinity ligand pro-NGF, and/or the growth-promoting high-affinity NGF receptor tyrosine kinase A (TrkA). In microdissected human scalp anagen hair bulbs, mRNA for NGF, pro-NGF, p75NTR, and TrkA was transcribed. Immunohistomorphometry and in situ hybridization detected strong NGF and pro-NGF expression in terminally differentiating inner root sheath keratinocytes, whereas TrkA was co-expressed with p75NTR in basal and suprabasal outer root sheath keratinocytes. During spontaneous catagen development of organ-cultured human anagen hair follicles, p75NTR mRNA levels rose, and p75NTR and pro-NGF immunoreactivity increased dramatically in involuting compartments primarily devoid of TrkA expression. Here, TUNEL(+) apoptotic cells showed prominent p75NTR expression. Joint pro-NGF/NGF administration inhibited hair shaft elongation and accelerated catagen development in culture, which was antagonized by co-administration of p75NTR-blocking antibodies. In addition, mRNA and protein expression of transforming growth factor-beta2 increased early during spontaneous catagen development, and its neutralization blocked pro-NGF/NGF-dependent hair growth inhibition. Our findings suggest that pro-NGF/NGF interacts with transforming growth factor-beta2 and p75NTR to terminate anagen in human hair follicles, implying that p75NTR blockade may alleviate hair growth disorders characterized by excessive catagen development.

Control of Human Hair Growth by Neurotrophins: Brain-Derived Neurotrophic Factor Inhibits Hair Shaft Elongation, Induces Catagen, and Stimulates Follicular Transforming Growth Factor β2 Expression

Neurotrophins are important modulators of epithelial-mesenchymal interactions. Previously, we had shown that brain-derived neurotrophic factor (BDNF) and its high-affinity receptor tyrosine kinase B (TrkB) are prominently involved in the control of murine hair follicle cycling. We now show that BDNF and TrkB are also expressed in the human hair follicle in a manner that is both hair cycle dependent and suggestive of epithelial-mesenchymal cross-talk between BDNF-secreting dermal papilla fibroblasts of anagen hair follicles and subpopulations of TrkB+ hair follicle keratinocytes. As functional evidence for an involvement of BDNF/TrkB in human hair growth control, we show in organ-cultured human anagen hair follicles that 50 ng per mL BDNF significantly inhibit hair shaft elongation, induce premature catagen development, and inhibit keratinocyte proliferation. Quantitative real-time rtPCR analysis demonstrates upregulation of the potent catagen inducer, transforming growth factor beta2 (TGFbeta2) by BDNF, whereas catagen induction by BDNF was partially reversible through co-administration of TGFbeta-neutralizing antibody. This suggests that TrkB-mediated signaling promotes the switch between anagen and catagen at least in part via upregulation of TGFbeta2. Thus, human scalp hair follicles are both a source and target of bioregulation by BDNF, which invites to target TrkB-mediated signaling for therapeutic hair growth modulation.

Bilateral subthalamic nucleus stimulation results in reversal of alopecia in Parkinson's disease

Alopecia is a rare but important side effect of anti-parkinsonian medications. Our patient was a 72-year-old man with advanced Parkinson's disease (PD) who received levodopa and anti-cholinergic drugs and whose head had become almost completely bald. As bilateral subthalamic nucleus (STN) stimulation produced improvement in his motor symptoms, his drug dosages were reduced postoperatively. At 8 months after surgery, hair again covered his entire head. Our study presents a new aspect of the benefit of STN stimulation with regard to drug-induced non-motor symptoms in patient with PD.

Epimorphin acts to induce hair follicle anagen in C57BL/6 mice

Epimorphin is a mesenchymal morphogen that has been shown to mediate epithelial-mesenchymal signaling interactions in various organs. We now show that epimorphin functions in hair follicle morphogenesis; using a novel ex vivo organ culture assay, we define a mechanism for epimorphin signaling that may provide insight into general developmental processes. We found that epimorphin was produced by follicular mesenchymal cells and bound selectively to follicular epithelial cells, and that treatment with recombinant epimorphin could stimulate procession of hair follicles from telogen (resting stage) to anagen (growing stage). Based on analyses of epimorphin proteolytic digests that suggested a smaller peptide might be able to substitute for the full-length epimorphin molecule, we determined that pep7, a 10-amino acid peptide, was capable of inducing telogen-to-anagen transition both in the culture assay and in the mouse. That pep7 showed maximal activity only when modified with specific sulfhydryl-reactive reagents suggested that a particular structural conformation of the peptide was essential for activity; molecular dynamics studies were pursued to investigate the active peptide structure. These findings define a previously unknown morphogenic process in the hair follicle that may have applications to many other organs.

Hair loss induced by dopamine agonist: case report and review of the literature

We report the case of a female patient with Parkinson's disease who experienced hair loss that appeared after the administration of cabergoline. Her hair re-grew after decreasing the dose of cabergoline, indicating that hair loss was induced by cabergoline. In reviewing the literature, there have been reports of hair loss after administration of various dopaminergic drugs that include levodopa and all types of dopamine receptor agonists. Although the pathophysiological mechanism underlying the hair loss is unclear, hair loss may be possibly overlooked, and should be noted as a possible side effect of the dopaminergic therapy.

Inverse relationship between density of cutaneous hair and pigmented lesion count in patients with malignant melanoma

The aim of this study was to investigate whether there is an inverse relationship between the density of cutaneous hair and the number of pigmented lesions in patients with malignant melanoma, and to review the clinical and experimental findings with regard to this relationship. Cutaneous hair density and pigmented lesion counts were determined at nine sites by two physicians using specified criteria in 10 patients with a history of malignant melanoma and 22 control subjects. Study participants were Caucasian males of similar age, height and weight, and had similar occupational, ethnic, socioeconomic and sun exposure backgrounds. Statistical analysis was performed using combined data from all the sites and individual site data to determine whether an inverse relationship between cutaneous hair density and pigmented lesion counts exists. The results demonstrated statistically significant inverse relationships for the chest, upper back, upper arm and forearm in the melanoma patients, but not in the controls. For all the sites combined, both groups demonstrated statistically significant inverse relationships. The study findings are consistent with the hypothesis that some pigmented lesions may arise from the melanocytes of the hair follicle. This hypothesis may lead to new approaches to studying and treating melanoma.

Controls of hair follicle cycling

Nearly 50 years ago, Chase published a review of hair cycling in which he detailed hair growth in the mouse and integrated hair biology with the biology of his day. In this review we have used Chase as our model and tried to put the adult hair follicle growth cycle in perspective. We have tried to sketch the adult hair follicle cycle, as we know it today and what needs to be known. Above all, we hope that this work will serve as an introduction to basic biologists who are looking for a defined biological system that illustrates many of the challenges of modern biology: cell differentiation, epithelial-mesenchymal interactions, stem cell biology, pattern formation, apoptosis, cell and organ growth cycles, and pigmentation. The most important theme in studying the cycling hair follicle is that the follicle is a regenerating system. By traversing the phases of the cycle (growth, regression, resting, shedding, then growth again), the follicle demonstrates the unusual ability to completely regenerate itself. The basis for this regeneration rests in the unique follicular epithelial and mesenchymal components and their interactions. Recently, some of the molecular signals making up these interactions have been defined. They involve gene families also found in other regenerating systems such as fibroblast growth factor, transforming growth factor-beta, Wnt pathway, Sonic hedgehog, neurotrophins, and homeobox. For the immediate future, our challenge is to define the molecular basis for hair follicle growth control, to regenerate a mature hair follicle in vitro from defined populations, and to offer real solutions to our patients' problems.