Androgen-dependent beard dermal papilla cells secrete autocrine growth factor(s) in response to testosterone unlike scalp cells

Immune and Non-immune Interactions in the Pathogenesis of Androgenetic Alopecia

Androgenetic alopecia (AGA), a leading cause of progressive hair loss, affects up to 50% of males aged 50 years, causing significant psychological burden. Current treatments, such as anti-androgen drugs and minoxidil, show heterogeneous effects, even with long-term application. Meanwhile, the large-scale adoption of other adjuvant therapies has been slow, partly due to insufficient mechanistic evidence. A major barrier to developing better treatment for AGA is the incomplete understanding of its pathogenesis. The predominant academic consensus is that AGA is caused by abnormal expression of androgens and their receptors in individuals with a genetic predisposition. Emerging evidence suggests the contributing role of factors such as immune responses, oxidative stress, and microbiome changes, which were not previously given due consideration. Immune-mediated inflammation and oxidative stress disrupt hair follicles' function and damage the perifollicular niche, while scalp dysbiosis influences local metabolism and destabilizes the local microenvironment. These interconnected mechanisms collectively contribute to AGA pathogenesis. These additional aspects enhance our current understanding and confound the conventional paradigm, bridging the gap in developing holistic solutions for AGA. In this review, we gather existing evidence to discuss various etiopathogenetic factors involved in AGA and their possible interconnections, aiming to lay the groundwork for the future identification of therapeutic targets and drug development. Additionally, we summarize the advantages and disadvantages of AGA research models, ranging from cells and tissues to animals, to provide a solid basis for more effective mechanistic studies.

Efficacy of topical minoxidil in enhancing beard growth in a group of transgender assigned female at birth individuals on gender affirming hormone therapy

PURPOSE

Testosterone therapy represents the cornerstone of gender affirming hormone therapy (GAHT) among t-AFAB (transgender Assigned Female At Birth) people. Minoxidil is a vasodilator drug approved for topical use for the treatment of androgenetic alopecia. The aim of the present study was to evaluate the efficacy of topical minoxidil in enhancing beard growth in a group of t-AFAB people on GAHT.

METHODS

Sixteen t-AFAB individuals with an incomplete beard development, on GAHT for at least 6 months, were enrolled. Topical minoxidil was applied to the interested facial areas. Before starting (T0), after 3 (T3) and 6 (T6) months, we evaluated facial hair growth using the Ferriman-Gallwey modified score (FGm).

RESULTS

Subjects were 26 (2.7) years old and on GAHT for 18.5 [15-54] months; using a paired match evaluation, a statistically significant facial hair growth was observed over time, in particular at T6 (median upper lip FGm 3.5 [3-4] vs 2 [1-2] at T0 and chin FGm 4 [3.25-4] vs 1 [1-2] at T0; p ≤ 0.002). Comparing the minoxidil group with a control group (n = 16) matched for age and BMI who developed a full-grown beard only with GAHT, a logistic multivariable analysis identified hirsutism before GAHT was independently positively associated with the development of a full beard [OR 15.22 (95% CI 1.46-158.82); p = 0.023].

CONCLUSIONS

This is the first study demonstrating the efficacy of topical minoxidil in enhancing facial hair growth among t-AFAB people on GAHT. Further studies will be necessary to assess whether the obtained improvements will persist after discontinuing the medication.

Three-dimensional correlative light and focused ion beam scanning electron microscopy reveals the distribution and ultrastructure of lanceolate nerve endings surrounding terminal hair follicles in human scalp skin

Lanceolate nerve endings (LNEs) surrounding hair follicles (HFs) play an important role in detecting hair deflection. Complexes of the LNEs form a palisade-like structure along the longitudinal axis of hair roots in which axons are sandwiched between two processes of terminal Schwann cells (tSCs) at the isthmus of HFs. The structure and molecular mechanism of LNEs in animal sinus hair, pelage, and human vellus hairs have been investigated. Despite the high density of HFs in human scalp skin, the LNEs in human terminal HFs have not been investigated. In this study, we aimed to reveal the distribution and ultrastructure of LNEs in terminal HFs of human scalp skin. Using light-sheet microscopy and immunostaining, the LNEs were observed at one terminal HF but not at the other terminal HFs in the same follicular unit. The ultrastructure of the LNEs of terminal HFs in human scalp skin was characterized using correlated light and electron microscopy (CLEM). Confocal laser microscopy and transmission electron microscopy of serial transverse sections of HFs revealed that LNEs were aligned adjacent to the basal lamina outside the outer root sheath (ORS), at the isthmus of terminal HFs, and adjacent to CD200-positive ORS cells in the upper bulge region. Moreover, axons with abundant mitochondria were sandwiched between tSCs. Three-dimensional CLEM, specifically confocal laser microscopy and focused ion beam scanning electron microscopy, of stained serial transverse sections revealed that LNEs were wrapped with type I and type II tSCs, with the processes protruding from the space between the Schwann cells. Moreover, the ultrastructures of LNEs at miniaturized HFs were similar to those of LNEs at terminal HFs. Preembedding immunoelectron microscopy revealed that Piezo-type mechanosensitive ion channel component 2 (Piezo2), a gated ion channel, was in axons and tSCs and adjacent to the cell membrane of axons and tSCs, suggesting that LNEs function as mechanosensors. The number of LNEs increased as the diameter of the ORS decreased, suggesting that LNEs dynamically adapt to the HF environment as terminal HFs miniaturize into vellus-like hair. These findings will provide insights for investigations of mechanosensory organs, aging, and re-innervation during wound healing.

Ethnobotany, phytochemistry, pharmacology, and conservation of the genus Calanthe R. Br. (Orchidaceae)

ETHNOPHARMACOLOGICAL RELEVANCE

The Genus Calanthe (family Orchidaceae) consists of more than 207 species distributed in both tropical and subtropical regions. In traditional medicine, Calanthe species provide remedies against various conditions such as arthritis, rheumatism, traumatic injuries, snake-bites, abdominal discomfort, nose bleeding, common colds, ulcers, chronic coughs, and others. Some species are also used as aphrodisiacs, tonics, and as pain relievers on joints and toothaches.

AIM OF THE REVIEW

This review provides comprehensive information on the herbal uses, chemical components, pharmacological activities, and conservation of Calanthe, which might be useful in the future development of potent herbal medicines and facilitate the enactment of better conservation strategies.

MATERIALS AND METHODS

Relevant information was obtained from online databases including SCI-Finder, Google Scholar, Web of Science, Science Direct, PubMed, Springer, IOP Science, and other web sources such as PubChem, The Plant List, and World Flora Online. Books, Ph.D. and MSc dissertations were used for unpublished literature. Information from Chinese literature was obtained from the CNKI database.

RESULTS

In total, 19 species of the genus Calanthe have been reported to be used in traditional medicine in different countries of Asia. A total of 265 chemical compounds from different chemical classes including, alkaloids, terpenoids, phenolic compounds and phenolic derivatives, phenanthrenes, and others, have been identified from Calanthe species. Calanquinone A isolated from C. arisanensis has been reported to exhibit antitumor activity against six malignant cell lines. Other bioactive compounds from Calanthe with pharmacological activity include phenanthrenes, phenanthrenequinones, 6'-O-β-D-apiofuranosylindican, 4H-Pyran-4one, 2, 3-dihydro-3,5 dihydroxy-6-methyl, and calanthoside. These compounds exhibit valuable biological properties such as hair restoration, anticancer activity, anti-inflammatory and antiarthritic activity, antidiabetic and hepatoprotective potency, antiplatelet aggregation action, and antibacterial and antifungal activities. Some Calanthe species, including C. ecallosa and C. yuana, are endangered in the IUCN red list. The high risk of extinction is attributed to illegal trade and unsustainable harvesting and utilization.

CONCLUSIONS

This review summarizes the herbal uses, chemical components, biological activity, and conservation of Calanthe. The pharmacological studies on this genus are limited; thus, extensive research on the toxicology, pharmaceutical standardization, and mechanism of action of the isolated bioactive compounds are needed. Since some species of Calanthe are listed as endangered, stringent guidelines on trade, collection, and sustainable utilization of medicinal orchids should be set up to facilitate the conservation of these species.

Are Beards Honest Signals of Male Dominance and Testosterone?

The male beard is one of the most visually salient and sexually dimorphic traits and a hypothesized potential marker of other traits, such as dominance, masculinity, social status, and self-confidence. However, as men can easily alter their facial hair, beards may provide unreliable information about the beard owner's characteristics. Here, we examined whether beards are honest signals of biological (testosterone levels) and psychological (self-reported dominance) traits. Young (M = 21.29, SD = 1.54) and healthy men (N = 97) participated in the study. Their beards were measured directly (using digital calipers) and by self-report. Participants provided saliva samples before and after acute exercise (to assess their testosterone and cortisol levels) and reported their dominance on a 5-item scale. The results showed that beard length (directly measured and self-reported) was not related to testosterone levels or dominance; thus, no evidence was found to support the hypothesis that beards are honest (or dishonest) signals of the beard owners' testosterone levels and dominance.

Indole Glycosides from Calanthe discolor with Proliferative Activity on Human Hair Follicle Dermal Papilla Cells

A methanol extract from the underground part of Calanthe discolor Lindl. (Orchidaceae) demonstrated significant proliferative activity on human hair follicle dermal papilla cells (HFDPC, % of control: 120.8 ± 0.2%) at 100 µg/mL against HFDPC. Through bioassay-guided separation of the extract, a new indole glycoside named 6'-O-β-D-apiofuranosylindican (1) was isolated along with six known compounds (2-7) including three indole glycosides. The stereostructure of 1 was elucidated based on its spectroscopic properties and chemical characteristics. Among the isolates, 1 (110.0 ± 1.0%), glucoindican (3, 123.9 ± 6.8%), and calanthoside (4, 158.6 ± 7.1%) showed significant proliferative activity at 100 µM. Furthermore, the active indole glycosides (1, 3, and 4) upregulated the expression of vascular endothelial growth factor (VEGF) and fibroblast growth factor-7 (FGF-7) mRNA and protein in HFDPC, which could be the mechanism of their proliferative activity.

Ent-kaurane-type diterpenoids from Isodonis Herba activate human hair follicle dermal papilla cells proliferation via the Akt/GSK-3β/β-catenin transduction pathway

A methanol extract from Isodonis Herba demonstrated significant proliferative effect on human hair follicle dermal papilla cells (HFDPC, % of control: 150.0 ± 2.0% at 20 µg/mL, p < 0.01). From the extract, 14 ent-kaurane-type diterpenoids (1-14), two abietane-type diterpenoids (15 and 16) and four triterpenoids (17-20) were isolated. Among the isolates, enmein (1, 160.9 ± 3.0% at 20 µM, p < 0.01), isodocarpin (2, 169.3 ± 4.9% at 5 µM, p < 0.01), nodosin (4, 160.5 ± 12.4% at 20 µM, p < 0.01), and oridonin (8, 165.4 ± 10.6% at 10 µM, p < 0.01) showed the proliferative effects. The principal component enmein (1) activated the expression of vascular endothelial growth factor (VEGF) mRNA, upregulated the production of VEGF and increased levels of phospho-Akt, phospho-GSK-3β, and β-catenin accumulation in HFDPC, which could be the mechanism of these activate proliferation activity.

Inhibition of Rab27a and Rab27b Has Opposite Effects on the Regulation of Hair Cycle and Hair Growth

Rab27a/b are known to play an important role in the transport of melanosomes, with their knockout causing silvery gray hair. However, the relationship between Rab27a/b and hair growth is not well known. To evaluate the role of Rab27a/b in hair cycle, we investigated the expression of Rab27a/b during hair cycling and human outer root sheath (hORS) cells. The expression of Rab27a in ORS cells was mainly detected at the anagen, whereas expression of Rab27b in ORS, and epidermal cells was strongly expressed at the telogen. Additionally, Rab27a/b were expressed in the Golgi of hORS cells. To evaluate the role of Rab27a/b in hair growth, telogen-to-anagen transition animal and vibrissae hair follicles (HFs) organ culture models were assayed using Rab27a/b siRNAs. The knockdown of Rab27a or Rab27b suppressed or promoted hair growth, respectively. These results were also confirmed in human dermal papilla cells (hDPCs) and hORS cells, showing the opposite mitogenic effects. Moreover, Rab27b knockdown increased the expression levels of various growth factors in the hDPCs and hORS cells. Overall, the opposite temporal expression patterns during hair cycling and roles for hair growth of Rab27a/b suggested that Rab27a/b might regulate the hair cycle. Therefore, our study may provide a novel solution for the development of hair loss treatment by regulating Rab27a/b levels.

The diagnosis of androgenetic alopecia in children: Considerations of pathophysiological plausibility

Androgenetic alopecia (AGA), one of the most common causes of hair loss in men and women, is an infrequent cause of alopecia in children. In AGA, patients generally start noticing hair thinning after the onset of puberty due to progressive miniaturisation of the hair follicle which leads to vellus transformation of terminal hair. However, the occurrence of prepubertal AGA has rarely been reported in the literature. The pathophysiology of AGA is tightly linked to androgen hormones; prepubertal children do not usually produce significant amounts of adrenal or gonadal androgens. When it does occur, an underlying abnormality should be suspected. Secondary causes of AGA must be excluded when evaluating a patient before the appearance of puberty. Premature puberty, polycystic ovarian syndrome and other causes of hyperandrogenism can present with hair loss in an androgenetic pattern. This article reviews the normal physiology of androgen hormones and their role in the pathophysiology of childhood AGA.

Androgens and androgen receptor action in skin and hair follicles

Beyond sexual functions, androgens exert their action in skin physiology and pathophysiology. Skin cells are able to synthesize most active androgens from gonadal or adrenal precursors and the enzymes involved in skin steroidogenesis are implicated both in normal or pathological processes. Even when the role of androgens and androgen receptor (AR) in skin pathologies has been studied for decades, their molecular mechanisms in skin disorders remain largely unknown. Here, we analyze recent studies of androgens and AR roles in several skin-related disorders, focusing in the current understanding of their molecular mechanisms in androgenetic alopecia (AGA). We review the molecular pathophysiology of type 2 5α-reductase, AR coactivators, the paracrine factors deregulated in dermal papillae (such as TGF-β, IGF 1, WNTs and DKK-1) and the crosstalk between AR and Wnt signaling in order to shed some light on new promising treatments.

Multi-therapies in androgenetic alopecia: review and clinical experiences

Androgenetic alopecia (AGA) is a genetically determined progressive hair-loss condition which represents the most common cause of hair loss in men. The use of the medical term androgenetic alopecia reflects current knowledge about the important role of androgens and genetic factors in its etiology. In addition to androgen-dependent changes in the hair cycle, sustained microscopic follicular inflammation contributes to its onset. Furthermore, Prostaglandins have been demonstrated to have the ability in modulating hair follicle cycle; in particular, PGD2 inhibits hair growth while PGE2/F2a promote growth. Due to the progressive nature of AGA, the treatment should be started early and continued indefinitely, since the benefit will not be maintained upon ceasing therapy. To date, only two therapeutic agents have been approved by the Food and Drug Administration and European Medicines Agency for the treatment of AGA: topical minoxidil and oral finasteride. Considering the many pathogenetic mechanisms involved in AGA, various treatment options are available: topical and systemic drugs may be used and the choice depends on various factors including grading of AGA, patients' pathological conditions, practicability, costs and risks. So, the treatment for AGA should be based on personalized therapy and targeted at the different pathophysiological aspects of AGA.

Androgen actions on the human hair follicle: perspectives

Androgens stimulate beard growth but suppress hair growth in androgenetic alopecia (AGA). This condition is known as 'androgen paradox'. Human pilosebaceous units possess enough enzymes to form the active androgens testosterone and dihydrotestosterone. In hair follicles, 5α-reductase type 1 and 2, androgen receptors (AR) and AR coactivators can regulate androgen sensitivity of dermal papillae (DP). To regulate hair growth, androgens stimulate production of IGF-1 as positive mediators from beard DP cells and of TGF-β1, TGF-β2, dickkopf1 and IL-6 as negative mediators from balding DP cells. In addition, androgens enhance inducible nitric oxide synthase from occipital DP cells and stem cell factor for positive regulation of hair growth in beard and negative regulation of balding DP cells. Moreover, AGA involves crosstalk between androgen and Wnt/β-catenin signalling. Finally, recent data on susceptibility genes have provided us with the impetus to investigate the molecular pathogenesis of AGA.

Androgens and hair growth

Hair's importance in human communication means that abnormalities like excess hair in hirsutism or hair loss in alopecia cause psychological distress. Androgens are the main regulator of human hair follicles, changing small vellus follicles producing tiny, virtually invisible hairs into larger intermediate and terminal follicles making bigger, pigmented hairs. The response to androgens varies with the body site as it is specific to the hair follicle itself. Normally around puberty, androgens stimulate axillary and pubic hair in both sexes, plus the beard, etc. in men, while later they may also inhibit scalp hair growth causing androgenetic alopecia. Androgens act within the follicle to alter the mesenchyme-epithelial cell interactions, changing the length of time the hair is growing, the dermal papilla size and dermal papilla cell, keratinocyte and melanocyte activity. Greater understanding of the mechanisms of androgen action in follicles should improve therapies for poorly controlled hair disorders like hirsutism and alopecia.

17beta-estradiol regulates the secretion of TGF-beta by cultured human dermal fibroblasts

Estrogen plays an important role in skin homeostasis, as demonstrated by the changes seen in the skin of post-menopausal women, changes reversed by HRT. Estrogen also has a role in wound healing, since estrogen deficiency as occurs post-menopausally and in ovariectomised animals, is associated with a reduced rate of wound healing. Estrogen appears to modulate all phases of wound healing with effects on inflammatory cells, epithelialization, angiogenesis, extracellular matrix deposition and tissue remodelling. This study was designed to investigate the effects of 17beta-estradiol on cultured human dermal fibroblasts using an in vitro wound-healing assay. The end points investigated were cell migration, proliferation, total collagen secretion and active TGF-beta1 secretion. 17beta-estradiol significantly increased the migration and proliferation of cultured dermal fibroblasts following mechanical wounding, although the secretion of total soluble collagen was not altered. An increase in TGF-beta1 was demonstrated by unwounded confluent dermal fibroblast monolayers in response to 17beta-estradiol, but paradoxically, a decrease in the secretion of TGF-beta1 was demonstrated in the mechanically wounded dermal fibroblasts. These results identify human dermal fibroblasts as estrogen target cells and provide further evidence for a role by which estrogen regulates this particular cell type as part of the wound-healing process. However, the paradoxical nature of the effect of estrogen on TGF-beta1 secretion following mechanical wounding suggests that the cellular mechanism of action is complex. A greater understanding of the cell-specific action of estrogen may help to develop therapies that will improve cutaneous wound healing in the future.

Differing responses of human follicular and nonfollicular scalp cells in an in vitro wound healing assay: effects of estrogen on vascular endothelial growth factor secretion

Improved wound healing of hairy skin may involve mesenchymal hair follicle cells with stem cell potential and enhancement by estrogen therapy. How estrogen affects follicular dermal papilla (DP) and dermal sheath (DS) cells in wound healing is unknown. Therefore, a comparison of estradiol action on DP, DS, and corresponding interfollicular dermal fibroblasts (DF) in a scratch-wound assay was performed using matching primary cultures established from female temporo-occipital scalp. All three cell types expressed mRNA transcripts and protein for estrogen receptors alpha (ERalpha) and beta (ERbeta). DF ERalpha transcripts were half that of DP and one-third of DS cells, while DF ERbeta transcripts were two-thirds of DP and DS cells. In the scratch-wound assay all three cells types migrated at similar rates, but only the rate of DF was enhanced by estradiol. Mechanical wounding increased DNA synthesis rates of all three cell types and increased the secretion of collagen by DF and DS cells. All three secreted similar basal levels of vascular endothelial growth factor (VEGF), which was increased by wounding DF and DS cells, but not DP cells. DP cells required estradiol to increase VEGF secretion; by contrast VEGF secretion was decreased by estradiol in wounded DS cells. These results highlight differences in the responses of DF, DP, and DS cells to estradiol in a scratch-wound assay, providing further support for the dichotomy of cellular functions in the hair follicle. Further understanding of the role of estrogen in cutaneous wound healing may have important implications for the management of chronic wounds and scarring.

Hormonal regulation of hair follicles exhibits a biological paradox

Hair's importance for insulation and camouflage or human communication means that hairs need to change with season, age or sexual development. Regular, regenerating hair follicle growth cycles produce new hairs which may differ in colour and/or size, e.g., beard development. Hormones of the pineal-hypothalamus-pituitary axis coordinate seasonal changes, while androgens regulate most sexual aspects with paradoxically different effects depending on body site; compare beard growth and balding! Hormones affect follicular mesenchymal-epithelial interactions altering growing time, dermal papilla size and dermal papilla cell, keratinocyte and melanocyte activity. Greater understanding of these mechanisms should improve treatments for poorly controlled hair disorders, alopecia and hirsutism.

Inhibitory autocrine factors produced by the mesenchyme-derived hair follicle dermal papilla may be a key to male pattern baldness

BACKGROUND

Androgenetic alopecia, or male pattern baldness, is a common, progressive disorder where large, terminal scalp hairs are gradually replaced by smaller hairs in precise patterns until only tiny vellus hairs remain. This balding can cause a marked reduction in the quality of life. Although these changes are driven by androgens, most molecular mechanisms are unknown, limiting available treatments. The mesenchyme-derived dermal papilla at the base of the mainly epithelial hair follicle controls the type of hair produced and is probably the site through which androgens act on follicle cells by altering the regulatory paracrine factors produced by dermal papilla cells. During changes in hair size the relationship between the hair and dermal papilla size remains constant, with alterations in both dermal papilla volume and cell number. This suggests that alterations within the dermal papilla itself play a key role in altering hair size in response to androgens. Cultured dermal papilla cells offer a useful model system to investigate this as they promote new hair growth in vivo, retain characteristics in vitro which reflect their parent follicle's response to androgens in vivo and secrete mitogenic factors for dermal papilla cells and keratinocytes.

OBJECTIVES

To investigate whether cultured dermal papilla cells from balding follicles secrete altered amounts/types of mitogenic factors for dermal papilla cells than those from larger, normal follicles. We also aimed to determine whether rodent cells would recognize mitogenic signals from human cells in vitro and whether factors produced by balding dermal papilla cells could alter the start of a new mouse hair cycle in vivo.

METHODS

Dermal papilla cells were cultured from normal, balding and almost clinically normal areas of balding scalps and their ability to produce mitogenic factors compared using both human and rat whisker dermal papilla cells as in vitro targets and mouse hair growth in vivo.

RESULTS

Normal scalp cells produced soluble factors which stimulated the growth of both human scalp and rat whisker dermal papilla cells in vitro, demonstrating dose-responsive mitogenic capability across species. Although balding cells stimulated some growth, this was much reduced and they also secreted inhibitory factor(s). Balding cell media also delayed new hair growth when injected into mice.

CONCLUSIONS

Human balding dermal papilla cells secrete inhibitory factors which affect the growth of both human and rodent dermal papilla cells and factors which delay the onset of anagen in mice in vivo. These inhibitory factor(s) probably cause the formation of smaller dermal papillae and smaller hairs in male pattern baldness. Identification of such factor(s) could lead to novel therapeutic approaches.

Perifollicular Fibrosis: Pathogenetic Role in Androgenetic Alopecia

Androgenetic alopecia (AGA) is a dihydrotestosterone (DHT)-mediated process, characterized by continuous miniaturization of androgen reactive hair follicles and accompanied by perifollicular fibrosis of follicular units in histological examination. Testosterone (T: 10(-9)-10(-7) M) treatment increased the expression of type I procollagen at mRNA and protein level. Pretreatment of finasteride (10(-8) M) inhibited the T-induced type I procollagen expression at mRNA (40.2%) and protein levels (24.9%). T treatment increased the expression of transforming growth factor-beta 1 (TGF-beta1) at protein levels by 81.9% in the human scalp dermal fibroblasts (DFs). Pretreatment of finasteride decreased the expression of TGF-beta1 protein induced by an average of T (30.4%). The type I procollagen expression after pretreatment of neutralizing TGF-beta1 antibody (10 microg/ml) was inhibited by an average of 54.3%. Our findings suggest that T-induced TGF-beta1 and type I procollagen expression may contribute to the development of perifollicular fibrosis in the AGA, and the inhibitory effects on T-induced procollagen and TGF-beta1 expression may explain another possible mechanism how finasteride works in AGA.

[Androgenetic alopecia]

Androgenetic alopecia is the most common form of hair loss in men and women. Although the clinical manifestations are different in men and women, the pathogenetic pathways leading to this type of hair loss are similar in both sexes. In short genetically predestined hair follicles show an increased sensitivity to androgens. In recent years, much new data concerning the pathophysiology, management and therapy of androgenetic alopecia has been gathered. This article gives a critical overview of these new findings and assesses their practical relevance.

Steroidogenic isoenzymes in human hair and their potential role in androgenetic alopecia

Androgenetic alopecia (AGA) is the most common type of hair loss. The relatively strong concordance of the degree of baldness in fathers and sons is not consistent with a simple Mendelian trait, and a polygenic basis is considered to be most likely. So far, the predisposing genes for AGA are unknown and we do not understand the molecular steps involved in androgen-dependent beard growth versus androgen-dependent hair loss, but AGA can be defined as a dihydrotestosterone (DHT)-dependent process with continuous miniaturization of sensitive hair follicles. The type 2 5alpha-reductase plays a central role by the intrafollicular conversion of testosterone to DHT. However, due to the increasing knowledge in this field, we now know that there are many more steroidogenic enzymes involved in the onset and development of AGA, and this article shall provide a critical overview of recent discoveries.

Animal and in vitro models for the study of hair follicles

Since the way in which the hair follicle functions is not well understood, many hair disorders are poorly controlled. A range of in vitro and in vivo models have therefore been developed to investigate the cell biological and biochemical mechanisms involved in the organization of this complex tissue. These range from cultures of a single cell type, such as those of the regulatory, mesenchyme-derived dermal papilla, through organ culture of isolated follicles to natural or genetically manipulated animal models. Each system has advantages and disadvantages for studying particular aspects of follicular function and some are potentially useful for the development of novel treatments for hair disorders.

Male androgenetic alopecia

Androgenetic alopecia (AGA) is the most common type of hair loss in men. The relative strong concordance of the degree of baldness in fathers and sons is not consistent with a smiple Mendelian trait and a polygenic basis is considered to be most likely. So far the predisposing genes for AGA are unknown and we do not understand the molecular steps involved in androgen-dependent beard growth versus androgen-dependent hair loss, but AGA can be defined as a DHT-dependent process with continuous miniaturization of sensitive hair follicles. The type 2 5aR plays a central role by the intrafollicular conversion of T to DHT. Due to the inceasing knowledge in this field, this article shall privide an critical overwiew of recent discoveries.

Primary cell culture and morphological characterization of canine dermal papilla cells and dermal fibroblasts

Skin biopsies were taken from female dogs, the primary hair follicles isolated and the dermal papilla dissected. After incubation in supplemented Amniomax complete C100 medium in 24-well culture plates, the dermal papilla cells (DPC) grew to confluence within 3 weeks. Thereafter, they were subcultivated every 7 days. Dermal fibroblast (DFB) cultures were established by explant culture of interfollicular dermis in serum-free medium, where they reached confluence in 10 days. They were subcultivated every 5 days. For immunohistochemistry, cells were grown on cover slips for 24 h, fixed and stained with antibodies against collagen IV and laminin. DPC showed an aggregative growth pattern and formation of pseudopapillae. Intensive staining for collagen IV and laminin could be observed until the sixth passage. DFB grew as branching, parallel lines and showed only weak staining for collagen IV and laminin.

Interferon Beta secreted from human hair dermal papilla cells inhibits the growth of outer root sheath cells cultured in vitro

Hair growth is tightly regulated by the epithelial-mesenchymal interaction of hair follicle cells. To investigate the molecular interaction between epithelial and mesenchymal cells of the hair follicle, the outer root sheath (ORS) cells were cultured with the dermal papilla (DP)-conditioned medium. Using the techniques of differential display reverse transcription-polymerase chain reaction (DD RT-PCR) and Northern blot analysis, we identified that an interferon-inducible gene 6-16 is regulated in the ORS cells when cultured with the DP-conditioned medium. We further studied the effect of the DP-conditioned medium and found that interferon beta, a predominant interferon secreted by the fibroblasts, is expressed by the DP cells. Moreover, the anti-interferon beta neutralized DP-conditioned medium dramatically inhibited the 6-16 mRNA expression. Interferon beta or DP-conditioned medium suppressed the growth of the in vitro cultured ORS cells, suggesting that interferon beta secreted from the DP cells negatively regulates the growth of ORS cells. Together these results reveal the potential importance of the interferon beta as a negative regulator of hair growth.

The hair follicle: a paradoxical androgen target organ

Androgens are the main regulator of normal human hair growth. After puberty, they promote transformation of vellus follicles, producing tiny, unpigmented hairs, to terminal ones, forming larger pigmented hairs, in many areas, e.g. the axilla. However, they have no apparent effect on the eyelashes, but can cause the opposite transformation on the scalp leading to the replacement of terminal hairs by vellus ones and the gradual onset of androgenetic alopecia. This paradox appears to be an unique hormonal effect. Hair follicles are mainly epithelial tissues, continuous with the epidermis, which project into the dermis. A mesenchyme-derived dermal papilla enclosed within the hair bulb at the base controls many aspects of follicle function. In the current hypothesis for androgen regulation, the dermal papilla is also considered the main site of androgen action with androgens from the blood binding to receptors in dermal papilla cells of androgen-sensitive follicles and causing an alteration of their production of paracrine factors for target cells e.g. keratinocytes. Studies of cultured dermal papilla cells from sites with different responses to androgens in vivo have confirmed the paradoxical responses. All dermal papilla cells from androgen-sensitive sites contain low capacity, high affinity androgen receptors. However, only some cells formed 5alpha-dihydrotestosterone, e.g. beard but not axillary cells, in line with hair growth in 5alpha-reductase deficiency. Incubation with androgens also stimulated the mitogenic capacity of beard cell media, but inhibited that produced by scalp cells. This suggests that the paradoxical differences are due to differential gene expression within hair follicles, presumably caused during embryogenesis.

Differences in hair follicle dermal papilla volume are due to extracellular matrix volume and cell number: implications for the control of hair follicle size and androgen responses

The size of a hair follicle is thought to be determined by the volume of its dermal papilla. The volume of the dermal papilla depends on the number of cells it contains and on the volume of the extracellular matrix. To establish which of these two variables is related to differences in hair follicle size we performed a stereologic study on 235 hair follicles from different sites, including male facial skin (beard), female facial skin, and scalp. In facial follicles there was a strong correlation between the area of the hair cortex and the volume of the dermal papilla. The area of the hair cortex also correlated with the number of cells in the dermal papilla and with the volume of dermal papilla per cell. In scalp hair follicles, where there was a smaller range of sizes, the correlations between these variables were weaker. In large male facial follicles the mean total dermal papilla volume was almost 40-fold higher than in vellus follicles from female facial skin. This difference was associated with a mean 17-fold greater number of cells in the dermal papilla and a 2.4-fold greater volume associated with each cell. Intermediate results were obtained in scalp follicles. In many regions of the skin hair follicles enlarge in response to androgens during adult life hair. Our results imply that the increase in the volume of the dermal papilla in these follicles is due to an increase in the number of cells, either through proliferation or through the migration of cells from the follicular dermal sheath, and to an increase in the amount of extracellular matrix per cell. As androgens are thought to act primarily on the dermal papilla, these changes may have a direct bearing on the mechanism of androgen-mediated alterations in hair follicle size.