Lichen planopilaris is characterized by immune privilege collapse of the hair follicle's epithelial stem cell niche

Essential Role of STAT3 Signaling in Hair Follicle Homeostasis

Dominant-negative mutations associated with signal transducer and activator of transcription 3 (STAT3) signaling, which controls epithelial proliferation in various tissues, lead to atopic dermatitis in hyper IgE syndrome. This dermatitis is thought to be attributed to defects in STAT3 signaling in type 17 helper T cell　specification. However, the role of STAT3 signaling in skin epithelial cells remains unclear. We found that STAT3 signaling in keratinocytes is required to maintain skin homeostasis by negatively controlling the expression of hair follicle-specific keratin genes. These expression patterns correlated with the onset of dermatitis, which was observed in specific pathogen-free conditions but not in germ-free conditions, suggesting the involvement of Toll-like receptor-mediated inflammatory responses. Thus, our study suggests that STAT3-dependent gene expression in keratinocytes plays a critical role in maintaining the homeostasis of skin, which is constantly exposed to microorganisms.

Clinicopathological characteristics and treatment outcomes of fibrosing alopecia in a pattern distribution: A retrospective cohort study

BACKGROUND

Fibrosing alopecia in a pattern distribution (FAPD) is a primary cicatricial alopecia considered a subtype of lichen planopilaris (LPP).

OBJECTIVE

The clinical and histopathological features, and treatment response of 24 female patients with FAPD were evaluated.

METHODS

Demographic, clinical, histopathological and treatment data of patients with FAPD were retrospectively collected.

RESULTS

Twenty-four women were included (mean age 60.7 years). The mean Lichen Planopilaris Activity Index score was 1.50, and the median Sinclair grade was 3. Twelve patients had diffuse alopecia in the centroparietal region, four had frontal accentuation and eight had vertex accentuation of hair loss. Eight had associated loss of facial hair. Predominant trichoscopic features included hair shaft diameter variability (100%), perifollicular erythema and/or scaling (95%) and loss of follicular ostia (95%). Histopathological examination revealed features of scarring alopecia with interface changes in follicular epithelia mainly targeting terminal and intermediate hairs, and less frequently, vellus hairs. Treatment with hair growth-promoting, anti-inflammatory and anti-androgen agents arrested disease progression in 14 patients and resulted in hair regrowth in two patients. Six patients had progression of their hair loss in spite of treatment.

LIMITATIONS

Referral bias to a specialist hair clinic, retrospective design and small sample size.

CONCLUSIONS

We present clinicopathological features of FAPD which can aid in the diagnosis of this insidious scarring alopecia. Our findings suggest a more favourable outcome if treatment is initiated in early stages of the disease.

An Approach to Patients with Alopecia

Alopecia is a dermatologic condition in which sudden or gradual loss of hair occurs on 1 or more areas of the body, most commonly the scalp. Hair loss can be acute or chronic in nature as a result of underlying inflammation, autoimmune processes, stressors, chemotherapy, or hairstyling practices. Alopecia can have substantial psychological consequences, having a negative impact on the quality of life in affected patients. The ability to both recognize and distinguish these condition holds great significance not only in providing adequate and timely treatment to improve outcomes but also meeting patient needs.

Hair follicle stem cells as a skin-organizing signaling center during adult homeostasis

Stem cells are the essential source of building blocks for tissue homeostasis and regeneration. Their behavior is dictated by both cell-intrinsic cues and extrinsic cues from the microenvironment, known as the stem cell niche. Interestingly, recent work began to demonstrate that hair follicle stem cells (HFSCs) are not only passive recipients of signals from the surroundings, but also actively send out signals to modulate the organization and function of their own niches. Here, we discuss recent findings, and briefly refer to the old, on the interaction of HFSCs and their niches with the emphasis on the outwards signals from HFSCs toward their niches. We also highlight recent technology advancements that further promote our understanding of HFSC niches. Taken together, the HFSCs emerge as a skin-organizing center rich in signaling output for niche remodeling during various stages of adult skin homeostasis. The intricate crosstalk between HFSCs and their niches adds important insight to skin biology that will inform clinical and bioengineering fields aiming to build complete and functional 3D organotypic cultures for skin replacement therapies.

Scalp and serum profiling of frontal fibrosing alopecia reveals scalp immune and fibrosis dysregulation with no systemic involvement

BACKGROUND

Frontal fibrosing alopecia (FFA) is a progressive, scarring alopecia of the frontotemporal scalp that poses a substantial burden on quality of life. Large-scale global profiling of FFA is lacking, preventing the development of effective therapeutics.

OBJECTIVE

To characterize FFA compared to normal and alopecia areata using broad molecular profiling and to identify biomarkers linked to disease severity.

METHODS

This cross-sectional study assessed 33,118 genes in scalp using RNA sequencing and 350 proteins in serum using OLINK high-throughput proteomics. Disease biomarkers were also correlated with clinical severity and a fibrosis gene set.

RESULTS

Genes differentially expressed in lesional FFA included markers related to Th1 (IFNγ/CXCL9/CXCL10), T-cell activation (CD2/CD3/CCL19/ICOS), fibrosis (CXCR3/FGF14/FGF22/VIM/FN1), T-regulatory (FOXP3/TGFB1/TGFB3), and Janus kinase/JAK (JAK3/STAT1/STAT4) (Fold changes [FCH]>1.5, FDR<.05 for all). Only one protein, ADM, was differentially expressed in FFA serum compared to normal (FCH>1.3, FDR<.05). Significant correlations were found between scalp biomarkers (IL-36RN/IL-25) and FFA severity, as well as between JAK/STAT and fibrosis gene-sets (r>.6; P <.05).

LIMITATIONS

This study was limited by a small sample size and predominantly female FFA patients.

CONCLUSION

Our data characterize FFA as an inflammatory condition limited to scalp, involving Th1/JAK skewing, with associated fibrosis and elevated T-regulatory markers, suggesting the potential for disease reversibility with JAK/STAT inhibition.

A Cell Membrane-Level Approach to Cicatricial Alopecia Management: Is Caveolin-1 a Viable Therapeutic Target in Frontal Fibrosing Alopecia?

Irreversible destruction of the hair follicle (HF) in primary cicatricial alopecia and its most common variant, frontal fibrosing alopecia (FFA), results from apoptosis and pathological epithelial-mesenchymal transition (EMT) of epithelial HF stem cells (eHFSCs), in conjunction with the collapse of bulge immune privilege (IP) and interferon-gamma-mediated chronic inflammation. The scaffolding protein caveolin-1 (Cav1) is a key component of specialized cell membrane microdomains (caveolae) that regulates multiple signaling events, and even though Cav1 is most prominently expressed in the bulge area of human scalp HFs, it has not been investigated in any cicatricial alopecia context. Interestingly, in mice, Cav1 is involved in the regulation of (1) key HF IP guardians (TGF-β and α-MSH signaling), (2) IP collapse inducers/markers (IFNγ, substance P and MICA), and (3) EMT. Therefore, we hypothesize that Cav1 may be an unrecognized, important player in the pathobiology of cicatricial alopecias, and particularly, in FFA, which is currently considered as the most common type of primary lymphocytic scarring alopecia in the world. We envision that localized therapeutic inhibition of Cav1 in management of FFA (by cholesterol depleting agents, i.e., cyclodextrins/statins), could inhibit and potentially reverse bulge IP collapse and pathological EMT. Moreover, manipulation of HF Cav1 expression/localization would not only be relevant for management of cicatricial alopecia, but FFA could also serve as a model disease for elucidating the role of Cav1 in other stem cell- and/or IP collapse-related pathologies.

Resident Memory T Cells in Autoimmune Skin Diseases

Tissue resident memory T cells (TRM) are a critical component of the immune system, providing the body with an immediate and highly specific response against pathogens re-infecting peripheral tissues. More recently, however, it has been demonstrated that TRM cells also form during autoimmunity. TRM mediated autoimmune diseases are particularly destructive, because unlike foreign antigens, the self-antigens are never cleared, continuously activating self-reactive TRM T cells. In this article, we will focus on how TRMs mediate disease in autoimmune skin conditions, specifically vitiligo, psoriasis, cutaneous lupus erythematosus, alopecia areata and frontal fibrosing alopecia.

Frontal Fibrosing Alopecia: A Review

Frontal fibrosing alopecia is a scarring alopecia, the prevalence of which is increasing worldwide since its first description in 1994. The reason for this emerging epidemic may be a higher exposure to an unknown trigger, although its aethiology and pathogenesis still remain enigmatic. Clinical, trichoscopic, sonographic, and histopathologic findings are allowing clinicians to understand more aspects about this type of cicatricial alopecia. Several treatments have been used in frontal fibrosing alopecia, although the 5-alpha reductase inhibitors seem to be the most promising. The aim of this report is to provide a compilation about the published data regarding frontal fibrosing alopecia in a narrative review.

Compartmentalised metabolic programmes in human anagen hair follicles: New targets to modulate epithelial stem cell behaviour, keratinocyte proliferation and hair follicle immune status?

Human scalp hair follicles (HF) preferentially engage in glycolysis followed by lactate production in the presence of oxygen (i.e. the Warburg effect). Through the spatiotemporally controlled expression of key metabolic proteins, we hypothesise that the Warburg effect and other HF metabolic programmes are compartmentalised by region in order to regulate regional cell fate and phenotypes, such as epithelial stem cell quiescence in the bulge or keratinocyte proliferation in the hair matrix. We further propose that metabolic conditions in the HF are organised in accordance with the lactate shuttle, hypothesised to occur in other tissue systems and tumours, but never before described in the HF. Specifically, we argue that lactate is produced and exported by glycolytic GLUT1+ lower outer root sheath (ORS) keratinocytes. We further propose that lactate is then utilised by neighbouring highly proliferative matrix keratinocytes to fuel oxidative metabolism via MCT1-mediated uptake. Furthermore, as lactate has been described to be immunomodulatory, its production and accumulation could enhance immune tolerance in the HF bulb. Here we delineate how to experimentally probe this hypothesis, define major open questions and present preliminary immunohistological evidence in support of metabolic compartmentalisation and lactate shuttling. Overall, we argue that basic and translational hair research needs to rediscover the importance of lactate in human HF biology, well beyond its recognised role in murine HF epithelial stem cells, and should explore how HF metabolism can be therapeutically targeted to modulate hair growth and the immunological HF microenvironment as a novel strategy for managing hair loss disorders.

Human epithelial stem cell survival within their niche requires "tonic" cannabinoid receptor 1-signalling-Lessons from the hair follicle

The endocannabinoid system (ECS) regulates multiple aspects of human epithelial physiology, including inhibition/stimulation of keratinocyte proliferation/apoptosis, respectively. Yet, how the ECS impacts on human adult epithelial stem cell (eSC) functions remains unknown. Scalp hair follicles (HFs) offer a clinically relevant, prototypic model system for studying this directly within the native human stem cell niche. Here, we show in organ-cultured human HFs that, unexpectedly, selective activation of cannabinoid receptor-1 (CB1)-mediated signalling via the MAPK (MEK/Erk 1/2) and Akt pathways significantly increases the number and proliferation of cytokeratin CK15+ or CK19+ human HF bulge eSCs in situ, and enhances CK15 promoter activity in situ. In striking contrast, CB1-stimulation promotes apoptosis in the differentiated progeny of these eSCs (CK6+ HF keratinocytes). Instead, intrafollicular CB1 gene knockdown or CB1 antagonist treatment significantly reduces human HF eSCs numbers and stimulates their apoptosis, while CB1 knockout mice exhibit a reduced bulge eSCs pool in vivo. This identifies "tonic" CB1 signalling as a required survival stimulus for adult human HF eSCs within their niche. This novel concept must be taken into account whenever the human ECS is targeted therapeutically.

Dermal Adipose Tissue Secretes HGF to Promote Human Hair Growth and Pigmentation

Hair follicles (HFs) are immersed within dermal white adipose tissue (dWAT), yet human adipocyte‒HF communication remains unexplored. Therefore, we investigated how perifollicular adipocytes affect the physiology of human anagen scalp HFs. Quantitative immunohistomorphometry, X-ray microcomputed tomography, and transmission electron microscopy showed that the number and size of perifollicular adipocytes declined during anagen‒catagen transition, whereas fluorescence-lifetime imaging revealed increased lipid oxidation in adipocytes surrounding the bulge and/or sub-bulge region. Ex vivo, dWAT tendentially promoted hair shaft production, and significantly stimulated hair matrix keratinocyte proliferation and HF pigmentation. Both dWAT pericytes and PREF1/DLK1⁺ adipocyte progenitors secreted HGF during human HF‒dWAT co-culture, for which the c-Met receptor was expressed in the hair matrix and dermal papilla. These effects were reproduced using recombinant HGF and abrogated by an HGF-neutralizing antibody. Laser-capture microdissection‒based microarray analysis of the hair matrix showed that dWAT-derived HGF upregulated keratin (K) genes (K27, K73, K75, K84, K86) and TCHH. Mechanistically, HGF stimulated Wnt/β-catenin activity in the human hair matrix (increased AXIN2, LEF1) by upregulating WNT6 and WNT10B, and inhibiting SFRP1 in the dermal papilla. Our study demonstrates that dWAT regulates human hair growth and pigmentation through HGF secretion, and thus identifies dWAT and HGF as important novel molecular and cellular targets for therapeutic intervention in human hair growth and pigmentation disorders.

Folliculitis Decalvans and Lichen Planopilaris Phenotypic Spectrum-A Series of 7 New Cases With Focus on Histopathology

BACKGROUND

Folliculitis decalvans (FD) and lichen planopilaris (LPP) are classified as neutrophilic and lymphocytic cicatricial alopecias according to the North American Hair Research Society. Recently, a clinical phenotype combining concomitant or sequential features for both was described as a FD LPP phenotypic spectrum (FDLPPPS).

OBJECTIVES

To review the most common phenotypic presentation of FDLPPPS with a main focus on histopathology.

METHODS

We reviewed retrospectively series of 7 patients with a similar phenotypic presentation with special focus on the histologic pattern. All patients presented with concomitant features for FD and LPP and recalcitrant course unresponsive to topical and systemic immunomodulatory/anti-inflammatory agents.

RESULTS

The most common clinical phenotype was that of hairless patches on the vertex with lost follicular ostia and perifollicular scale and the following diagnostic findings: (1) polytrichia; (2) positive bacterial culture for Staphylococcus in over 50% of the samples isolated from pustules and hemorrhagic crusts; (3) "mixed" histologic features for primary cicatricial alopecia including multicompound follicular structures of average 2-5 follicles (follicular packs), atrophy of the follicular epithelium, lymphohistiocytic infiltrate with granulomas, and prominent plasma cells, but absence of neutrophilic infiltrate in all cases except scarce neutrophils in one; and (4) clinical improvement with adjuvant systemic antimicrobials.

CONCLUSIONS

The FDLPPPS may be underreported and should be considered in all cases of LPP recalcitrant to treatment. Dermatologists and dermatopathologists should recognize this phenotypic spectrum to guide optimal clinical management consisting of immunomodulatory and anti-inflammatory agents along with systemic antimicrobials.

Immune privilege of skin stem cells: What do we know and what can we learn?

The skin forms a barrier that prevents dehydration and keeps us safe from pathogens. To ensure proper function, the skin possesses a myriad of stem cell populations that are essential for maintenance and repair upon damage. In order to protect, the skin is also an active immunological site, with abundant resident immune cells and strong recruitment of even more immune cells during wounding or infection. Such active and strong immunity makes the skin susceptible to a diverse spectrum of autoimmune diseases, such as vitiligo and alopecia areata. Conversely, despite constant immune surveillance, the skin is also a tissue where frequent malignancies occur, which suggests that immune evasion must also take place. Skin stem cells play a crucial role during both regeneration and tumorigenesis. How immune cells, and in particular T cells, interact with skin stem cells and the implications this crosstalk has in skin disease (both autoimmunity and cancer) is not fully understood. Uncovering the mechanisms governing immune-stem cells interactions in the skin is critical for the development of new therapeutic strategies to safeguard susceptible cells during autoimmunity and, conversely, to improve cancer immunotherapy. Here, I will discuss how distinct skin stem cell populations are attacked by, or conversely, cloaked from immune cells, and the implications their differences have in autoimmunity and cancer.

[Alopecia-keep a cool head]

Pathologists often feel discomfort when confronted with scalp biopsies, especially in the case of horizontal sectioning, which is particularly useful in the event of nonscarring alopecia. Apart from a profound knowledge of follicular anatomy, one should be capable of correlating the histologic information with the clinical features of various inflammatory scalp disorders. This review addresses the basic principles of the interpretation of scalp biopsies and discusses the most common forms of scarring and nonscarring alopecia.

Dendritic cells as predictive markers of responsiveness to hydroxychloroquine treatment in primary cicatricial alopecia patients

Primary cicatricial alopecia (PCA) encompasses a diverse group of inflammatory diseases characterized by the irreversible replacement of hair follicle structures by fibrous tissue. Although the pathogenesis of PCA remains not fully understood, the key to its understanding might be the location of dendritic cells (DCs) inflammatory infiltrate. One of the systemic therapy of choice in PCA patients is hydroxychloroquine (HCQ). We hypothesized that DCs are implicated in PCA pathogenesis and that they might constitute the biological target of HCQ treatment. For these reasons, we investigated whether DCs could affect the antimalarial responsiveness, and if DCs might be used as predictive factor of responsiveness to HCQ. In this retrospective cohort study, 65 patients diagnosed with PCA were grouped accordingly to their response to HCQ therapy. Skin biopsies had been taken before the treatment was started. Cell count was performed on immunohistochemistry by using characteristic monoclonal antibodies to specific subpopulations of DCs. In almost every second patient (47.7%), we observed remission of the disease during HCQ treatment. The number of plasmacytoid and myeloid DCs as well as Langerhans cells in lesional skin of HCQ responders was higher in comparison with HCQ nonresponders. Moreover, in a predictive model receiver operating characteristic (ROC curve) we showed that plasmacytoid DCs might be used as a predictive factor of responsiveness to HCQ. The results of this study are important as identifying biomarkers for responsiveness to a HCQ therapy will be helpful to individualize treatment and make it more effective.

Eyelash loss in frontal fibrosing alopecia: Microscopic features of two cases

BACKGROUND

To report two cases of eyelash loss in Frontal Fibrosing Alopecia, providing microscopic description of the eyelashes and possible association with Demodex folliculorum.

CASE PRESENTATION

We present two cases of postmenopausal women diagnosed with frontal fibrosing alopecia who consulted the ophthalmology department for eyelid itching and eyelash loss. On examination, there were no signs of blepharitis, but loss of lashes was observed, and the remaining eyelashes detached easily from the eyelid. The eyelashes were examined microscopically. The bulbs were small and narrow, and the caliber of the lashes was irregular, with thinner and thicker areas. The pigment distribution was irregular; there were portions with greater or lesser accumulation. In the second case, clusters of Demodex folliculorum were observed near the eyelash root.

CONCLUSION

This is the first microscopic description of eyelash loss in frontal fibrosing alopecia in the published literature. We describe small, narrow bulbs, irregular caliber of the eyelashes and irregular pigment distribution. In the second case, in which we found Demodex folliculorum infestation, there was eyelash loss even though the disease was not very advanced. We suggest that there might be an association whereby Demodex infestation might accelerate autoimmune inflammation, leading to premature eyelash loss.

Digital immunohistological dissection of immune privilege collapse in syringotropic autoimmune diseases: Implication for the pathogenesis

BACKGROUND

Syringotropic cell infiltration is a histological hallmark of some autoimmune diseases. However, its underlying mechanism remains unclear.

OBJECTIVES

To assess the immune privilege (IP) of the human sweat gland (SwG) in homeostasis and in syringotropic autoimmune diseases.

METHODS

We combined quantitative digital image microdissection with immunohistochemisty to analyze IP molecule expression in SwG of normal and diseased skin. The human skin organ culture model was used to examine the influence of proinflammatory conditions on IP in SwG.

RESULTS

In the normal subjects (n = 10), major histocompatibility complex (MHC) class І expression was significantly reduced in SwGs compared to the epidermis. In contrast, IP-guardians, macrophage migration inhibitory factor (MIF) and alpha-melanocyte stimulating hormone (α-MSH) were upregulated in SwGs. MHC class І was upregulated in whole SwGs in lupus erythematosus (LE; n = 7) and scleroderma/morphea (Scl; n = 9), whereas differential expression was noted only in the secretory portion in Sjögren's syndrome (SjS) (n = 4). MIF expression level inversely correlated with that of MHC class I in all samples tested, and downregulation of α-MSH was detected in LE SwGs alone. The severity of inflammatory changes and MIF and ⍺-MSH expression were inversely correlated in LE. CD200 expression was decreased exclusively in atrophic stage of Scl. In a human skin organ culture model, intratissue injection of interferon-gamma up-regulated MHC class I and downregulated MIF and α-MSH.

CONCLUSIONS

These findings indicate that SwGs enjoy IP. Dysregulated IP molecule expression may lead to SwG IP collapse and contribute to distinct inflammatory cell distribution in syringotropic autoimmune disorders.

Lichen planopilaris in men: a retrospective clinicopathologic study of 19 patients

BACKGROUND

Lichen planopilaris (LPP) is a scarring alopecia rarely described in men.

OBJECTIVE

To investigate the clinical and histopathologic features of LPP in men.

METHODS

We performed a retrospective cohort study of male patients with LPP seen at Mayo Clinic between 1992 and 2016.

RESULTS

Nineteen men with biopsy-confirmed LPP were included. The disease most commonly presented with diffuse (42.1%) or vertex scalp (42.1%) involvement. None of the patients had eyebrow or body hair involvement. Perifollicular erythema (94.7%) and pruritus (57.9%) were the most frequent clinical findings. Androgenetic alopecia (AGA) co-occurred in 26.3% of patients. Mucosal lichen planus was found in four patients (21.1%). Thyroid disease occurred in three patients (15.8%). Disease improvement (47.3%) occurred with combination topical and systemic therapy, topical clobetasol monotherapy, and minocycline monotherapy.

CONCLUSIONS

LPP in men has similar clinical and histologic presentations as reported in women. Nonscalp hair loss appears less likely in men with classic LPP than reported in men with frontal fibrosing alopecia, while mucosal lichen planus and thyroid disease appear to be more common in classic LPP. Men with AGA can present with new-onset concomitant LPP. Limitations included small study size, variable follow-up, and lack of standardized clinical assessment due the study's retrospective nature.

Frontal fibrosing alopecia

Frontal fibrosing alopecia (FFA) is a patterned primary cicatricial alopecia that was first described in 1994. Once rare, the incidence of FFA has increased dramatically, representing the current most common cause of cicatricial alopecia worldwide. FFA typically begins in postmenopausal women with symmetrical, progressive recession of the frontotemporal hairline together with bilateral loss of the eyebrows. FFA has a distinctive clinical phenotype, which remains a challenge. The histology is identical to lichen planopilaris (LPP), but only a small number of patients have coincidental LPP, usually of the scalp. The vast majority of patients have no evidence of lichen planus elsewhere, and the symmetry and patterned nature of the hair loss are unusual for LPP. Familial cases of FFA are reported, and gene associations have been identified in population studies; however, the pathophysiology remains controversial. Without treatment, FFA is slowly progressive, and although many treatments have been prescribed, the response is often disappointing. We review the pathogenesis, epidemiology, clinical features, histology, and treatment of FFA.

Lichen-planopilaris-like scarring pattern in a patient with alopecia and pityriasis rubra pilaris

Pityriasis rubra pilaris (PRP) is an erythematous-desquamative dermatitis that is sometimes associated with non-scarring alopecia. Despite the fact that the disease can be disfiguring, scarring alopecia has rarely been described in this disease. Here, we present a 69-year-old woman who developed an erythrodermic episode of PRP associated with telogen effluvium that left an area of persistent alopecia of the scalp and resulted in hair loss in the eyebrows. The biopsy of that area of the scalp demonstrated a scarring alopecia with lichen-planopilaris-like features. Despite this histopathology, the alopecia responded well to treatment. This finding expands the context in which lichen planopilaris features can be found and demonstrates their good prognosis under early treatment.

The biology of human hair greying

Hair greying (canities) is one of the earliest, most visible ageing-associated phenomena, whose modulation by genetic, psychoemotional, oxidative, senescence-associated, metabolic and nutritional factors has long attracted skin biologists, dermatologists, and industry. Greying is of profound psychological and commercial relevance in increasingly ageing populations. In addition, the onset and perpetuation of defective melanin production in the human anagen hair follicle pigmentary unit (HFPU) provides a superb model for interrogating the molecular mechanisms of ageing in a complex human mini-organ, and greying-associated defects in bulge melanocyte stem cells (MSCs) represent an intriguing system of neural crest-derived stem cell senescence. Here, we emphasize that human greying invariably begins with the gradual decline in melanogenesis, including reduced tyrosinase activity, defective melanosome transfer and apoptosis of HFPU melanocytes, and is thus a primary event of the anagen hair bulb, not the bulge. Eventually, the bulge MSC pool becomes depleted as well, at which stage greying becomes largely irreversible. There is still no universally accepted model of human hair greying, and the extent of genetic contributions to greying remains unclear. However, oxidative damage likely is a crucial driver of greying via its disruption of HFPU melanocyte survival, MSC maintenance, and of the enzymatic apparatus of melanogenesis itself. While neuroendocrine factors [e.g. alpha melanocyte-stimulating hormone (α-MSH), adrenocorticotropic hormone (ACTH), ß-endorphin, corticotropin-releasing hormone (CRH), thyrotropin-releasing hormone (TRH)], and micropthalmia-associated transcription factor (MITF) are well-known regulators of human hair follicle melanocytes and melanogenesis, how exactly these and other factors [e.g. thyroid hormones, hepatocyte growth factor (HGF), P-cadherin, peripheral clock activity] modulate greying requires more detailed study. Other important open questions include how HFPU melanocytes age intrinsically, how psychoemotional stress impacts this process, and how current insights into the gerontobiology of the human HFPU can best be translated into retardation or reversal of greying.

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.

Destruction of the stem cell Niche, Pathogenesis and Promising Treatment Targets for Primary Scarring Alopecias

The Primary Scarring Alopecias are characterised by the irreversible destruction and fibrosis of hair follicles, leading to permanent and often disfiguring loss of hair. The pathophysiology of these diseases is not well understood. However, follicular-fibrosis and loss of the stem-cell niche appears to be a common theme. This review explores the pathogenesis of primary scarring alopecias, asking what happens to the stem cells of the hair follicle and how they may contribute to the progression of these diseases. Bulge-resident cells are lost (leading to loss of capacity for hair growth) from the follicle either by inflammatory-mediate apoptosis or through epigenetic reprogramming to assume a mesenchymal-like identity. What proportion of bulge cells is lost to which process is unknown and probably differs depending on the individual PCA and its specific inflammatory cell infiltrate. The formation of fibroblast-like cells from follicular stem cells may also mean that the cells of the bulge have a direct role in the pathogenesis. The identification of specific cells involved in the pathogenesis of these diseases could provide unique diagnostic and therapeutic opportunities to prevent disease progression by preventing EMT and specific pro-fibrotic signals.

Frontal Fibrosing Alopecia. An Example of Disrupted Aryl Hydrocarbon Receptor-Mediated Immunological Homeostasis in the Skin?

Sun protection has been recommended by public health authorities to reduce the risk of keratinocyte and melanocyte tumors, yet some sun exposure is required for vitamin D synthesis. Frontal fibrosing alopecia (FFA) is a cicatricial alopecia that has been reported to have an association with facial photoprotection. The brief review proposes the hypothesis that FFA arises as a result of excessive facial photo-protection with a resultant disturbance in immunological homeostasis mediated via the aryl hydrocarbon receptor-kynurenine pathway axis (AHR/KP) leading to the collapse of immune privilege at the hair bulge.

Spray-Dried Rosuvastatin Nanoparticles for Promoting Hair Growth

In this research, we examined the effect of rosuvastatin calcium-loaded nanoparticles on the hair growth-promoting activity on Albino rats. Nanoparticles were prepared using 2:1 weight ratio of drug to methyl-β-cyclodextrin with 10, 20, and 30% stabilizers (phospholipid, polyvinyl pyrrolidone K30, and Compritol 888 ATO) using nanospray dryer. Subsequently, the prepared nanoparticles were evaluated for their process yield, particle size, polydispersity index, zeta potential, and in vitro drug release as well as in vivo studies. The dried nanoparticles showed process yield values up to 84% with particle size values ranging from 218 to 6258 nm, polydispersity index values ranging from 0.32 to 0.99, and zeta potential values ranging from - 6.1 to - 11.9 mV. Combination of methyl-β-cyclodextrin with 10% polyvinyl pyrrolidone K30 accomplished nanoparticles with the lowest particle size (218 nm) and polydispersity index (0.32) values. These nanoparticles had suitable process yield value (70.5%) and were able to retard drug release. The hair growth-promoting activity for the selected nanoparticles revealed the highest hair length values in Albino rats after 14 days of the hair growth study compared with non-medicated nanoparticles, nanoparticles' physical mixture, rosuvastatin solution, and marketed minoxidil preparation groups as well as the control group. The immunohistochemistry images for both selected nanoparticles and marketed minoxidil groups showed a significant increase in the diameter of hair follicle and percent area fraction of cytokeratin 19 in the outer root sheath of hair follicle compared with other tested groups. Rosuvastatin nanoparticles prepared by nanospray drying technique could be a good competitor to minoxidil for hair growth-promoting activity. Graphical abstract.

Cyclosporine or methotrexate, which one is more promising in the treatment of lichen planopilaris?; A comparative clinical trial

BACKGROUND

Lichen Planopilaris (LPP) is a primary scarring alopecia with unknown etiology and its management is a challenge for dermatologists. We aimed to compare the safety and efficacy of methotrexate and cyclosporine in LPP patients.

METHODS

In a randomized clinical trials, 33 patients were randomly allocated to receive either 15-mg oral methotrexate per week or 3-5-mg/kg/day cyclosporine for six months. During the treatment course, side effects, signs/symptoms and laboratory test were assessed periodically. Lichen planopilaris activity index (LPPAI) was measured at baseline and 2, 4, and 6 months after the intervention. Score of both photography and patient's opinion were also obtained. The collected data were analyzed in SPSS software (Ver.25.0. Armonk, NY: IBM Corp).

RESULTS

Both medications had positive effects on the signs and symptoms of LPP with a significant difference between the variables (p < 0.05), and the results showed similar efficacy at the end of 6th months of the therapy with both cyclosporine and methotrexate (p > 0.05).

CONCLUSIONS

Regarding the results of the present study, both cyclosporine and methotrexate are effective in treating refractory lichen planopilaris and we propose methotrexate as a possible earlier choice over cyclosporine. This study was registered in Iranian Registry of Clinical Trials (IRCT20190717044256N1).

Frontal fibrosing alopecia shows robust T helper 1 and Janus kinase 3 skewing

BACKGROUND

Frontal fibrosing alopecia (FFA) is a scarring alopecia with unclear pathogenesis and a progressive course. The disease has a major impact on patients' quality of life and there is a lack of effective treatment to halt disease progression.

METHODS

We profiled lesional and nonlesional scalp biopsies collected in 2017 from patients with FFA (n = 12) compared with scalp biopsies from patients with alopecia areata (AA) (n = 8) and controls (n = 8) to evaluate gene and protein expression, including the primary outcome (CXCL9). We determined significant differences between biomarkers using a two-sided Student's t-test adjusting P-values by false discovery rate.

RESULTS

Significant increases were seen in CD8+ cytotoxic T cells, CD11c+ dendritic cells, CD103+ and CD69+ tissue-resident memory T cells in FFA and AA vs. control scalp (P < 0·05), with corresponding significantly upregulated granzyme B mRNA, particularly in FFA (P < 0·01). In AA, cellular infiltrates were primarily concentrated at the bulb, while in FFA these were mainly localized at the bulge. FFA demonstrated significant upregulation of T helper 1/intereferon (IFN) (IFN-γ, CXCL9/CXCL10), the Janus kinase/signal transducers and activators of transcription (JAK-STAT) pathway (STAT1, JAK3) and fibrosis-related products (vimentin, fibronectin; P < 0·05), with no concomitant downregulation of hair keratins and the T-regulatory marker, forkhead box P3, which were decreased in AA. The stem cell markers CD200 and K15 demonstrated significantly reduced expression only in FFA (P < 0·05).

CONCLUSIONS

These data suggest that follicular damage and loss of stem cells in FFA may be mediated through immune attack in the bulge region, with secondary fibrosis and reduced but still detectable stem cells. JAK/STAT-targeting treatments may be able to prevent permanent follicular destruction and fibrosis in early disease stages.

Immune modulation of hair follicle regeneration

The mammalian hair follicle undergoes repeated bouts of regeneration orchestrated by a variety of hair follicle stem cells. The last decade has witnessed the emergence of the immune niche as a key regulator of stem cell behavior and hair follicle regeneration. Hair follicles chemotactically attract macrophages and T cells so that they are in range to regulate epithelial stem cell quiescence, proliferation and differentiation during physiologic and injured states. Disruption of this dynamic relationship leads to clinically significant forms of hair loss including scarring and non-scarring alopecias. In this review, we summarize key concepts behind immune-mediated hair regeneration, highlight gaps in the literature and discuss the therapeutic potential of exploiting this relationship for treating various immune-mediated alopecias.

Gasdermin A3-Mediated Cell Death Causes Niche Collapse and Precocious Activation of Hair Follicle Stem Cells

Hair follicles undergo recurrent growth, regression, and resting phases throughout postnatal life, which is supported by hair follicle stem cells. The niche components of hair follicle stem cells are important to maintain their quiescence and stemness. Gsdma3 gain-of-function mutations in mice cause chronic skin inflammation, aberrant hair cycle, and progressive hair loss, reminiscent of scarring alopecia in humans. However, the mechanism underlying these defects remains elusive. Here, we used a combined Cre/loxP and rtTA/TRE system to study the spatiotemporal effect of Gsdma3 overexpression on distinct hair cycle stages. We found that Gsdma3-mediated cell death affects anagen initiation, anagen progression, and catagen-telogen transition. Induced Gsdma3 expression causes bulge inner layer collapse and precocious hair follicle stem cell activation, leading to subsequent hair follicle degeneration. Although macrophages and dendritic cells are recruited to the bulge region, in vivo depletion of these cells using a neutralizing antibody does not alleviate cell death in the bulge or hair germ, indicating that macrophages are less likely to cause immediate hair follicle deletion. Our data suggest that dysregulated Gsdma3 causes bulge inner layer necrosis to induce club hair shedding and immediate anagen reentry without going through telogen morphology, which implicates a role for Gsdma3 in hair follicle stem cell niche maintenance.

Hair(y) Matters in Melanoma Biology

Melanocyte stem cells (MeSCs), one candidate for the cellular origin of melanoma, reside in the bulge region of the hair follicle (HF), an immune-privileged tissue niche with impaired tumor immunosurveillance. Surprisingly, however, primary melanoma is only very rarely associated with HFs. Here, we explore the hypothesis that this profoundly immunoinhibitory signaling environment deprives both MeSCs and melanocytes of the anagen hair matrix of proinflammatory signals required for full oncogenic transformation. Understanding the cellular and molecular mechanisms for generating a putative antimelanoma tissue habitat, namely in the bulge, could help to recreate a similar melanoma-suppressive signaling environment in melanoma high-risk individuals. We further discuss how mimicking the bulge immune privilege may be an effective melanoma prevention strategy.

Lichen Planopilaris and Low-Level Light Therapy: Four Case Reports and Review of the Literature About Low-Level Light Therapy and Lichenoid Dermatosis

Lichen planopilaris (LPP) is a cell-mediated scarring alopecia that causes inflammation of the scalp and the eventual destruction of hair follicles in affected areas. Current literature on treatment of LPP remains limited with no definitive treatment approach being recognized, although a combination of topical/intralesional steroids and orally administered hydroxychloroquine remains the most utilized option. Low-level light therapy (LLLT) is an expanding technology shown to be effective in a variety of dermatologic conditions. We report here four patients with LPP who show a dramatic response to LLLT, including a reduction of inflammation, disappearance of symptoms, and evident hair regrowth with no side effects. We review the possible role of LLLT in LPP and other lichenoid conditions.

Pathomechanisms of immune-mediated alopecia

The hair follicle (HF) is a complex mini-organ that constantly undergoes dynamic cycles of growth and regression throughout life. While proper progression of the hair cycle requires homeostatic interplay between the HF and its immune microenvironment, specific parts of the HF, such as the bulge throughout the hair cycle and the bulb in the anagen phase, maintain relative immune privilege (IP). When this IP collapses, inflammatory infiltrates that aggregate around the bulge and bulb launch an immune attack on the HF, resulting in hair loss or alopecia. Alopecia areata (AA) and primary cicatricial alopecia (PCA) are two common forms of immune-mediated alopecias, and recent advancements in understanding their disease mechanisms have accelerated the discovery of novel treatments for immune-mediated alopecias, specifically AA. In this review, we highlight the pathomechanisms involved in both AA and CA in hopes that a deeper understanding of their underlying disease pathogenesis will encourage the development of more effective treatments that can target distinct disease pathways with greater specificity while minimizing adverse effects.

Functional complexity of hair follicle stem cell niche and therapeutic targeting of niche dysfunction for hair regeneration

Stem cell activity is subject to non-cell-autonomous regulation from the local microenvironment, or niche. In adaption to varying physiological conditions and the ever-changing external environment, the stem cell niche has evolved with multifunctionality that enables stem cells to detect these changes and to communicate with remote cells/tissues to tailor their activity for organismal needs. The cyclic growth of hair follicles is powered by hair follicle stem cells (HFSCs). Using HFSCs as a model, we categorize niche cells into 3 functional modules, including signaling, sensing and message-relaying. Signaling modules, such as dermal papilla cells, immune cells and adipocytes, regulate HFSC activity through short-range cell-cell contact or paracrine effects. Macrophages capacitate the HFSC niche to sense tissue injury and mechanical cues and adipocytes seem to modulate HFSC activity in response to systemic nutritional states. Sympathetic nerves implement the message-relaying function by transmitting external light signals through an ipRGC-SCN-sympathetic circuit to facilitate hair regeneration. Hair growth can be disrupted by niche pathology, e.g. dysfunction of dermal papilla cells in androgenetic alopecia and influx of auto-reacting T cells in alopecia areata and lichen planopilaris. Understanding the functions and pathological changes of the HFSC niche can provide new insight for the treatment of hair loss.

Profiling the human hair follicle immune system in lichen planopilaris and frontal fibrosing alopecia: can macrophage polarization differentiate these two conditions microscopically?

BACKGROUND

Frontal fibrosing alopecia (FFA) is traditionally regarded as a variant of lichen planopilaris (LPP) based on histological features. Distinct clinical presentation, demographics and epidemiology suggest that differing pathogenic factors determine the final phenotype.

OBJECTIVES

To map the hair follicle immune system in LPP and FFA by systematically comparing key inflammatory markers in defined hair follicle compartments.

METHODS

Lesional scalp biopsies from LPP and FFA and healthy controls were stained with the following immunohistochemical markers: CD1a and CD209, CD4, CD8, CD56, CD68, CD123, CXCR3, forkhead box (FOX)P3, mast cell tryptase and cKit. Macrophage polarization was explored using CD206, CD163, CD86, receptor for advanced glycation end products (RAGE), interleukin (IL)-4 and IL-13 on paired lesional and nonlesional LPP and FFA samples.

RESULTS

Increased numbers of CD8⁺ , CXCR3⁺ and FOXP3⁺ T cells and CD68⁺ macrophages were identified in the distal hair follicle epithelium and perifollicular mesenchyme in both LPP and FFA compared with controls. In both LPP and FFA, total and degranulated mast cells and CD123⁺ plasmacytoid dendritic cells were increased in the perifollicular mesenchyme adjacent to the bulge and infundibulum, whereas numbers of CD1a⁺ and CD209⁺ dendritic cells were significantly reduced in the infundibulum connective tissue sheath. However, only with CD68 staining was a significant difference between LPP and FFA identified, with greater numbers of CD68⁺ cells in LPP samples. Furthermore, the identified macrophage polarization markers downregulated CD86 and upregulated CD163 and IL-4 expression in lesional LPP compared with FFA samples.

CONCLUSIONS

This comparative immunopathological analysis is the first to profile systematically the hair follicle immune system in LPP and FFA. Our analysis highlights a potential role of macrophages in disease pathobiology and suggests that macrophage polarization may differ between LPP and FFA, allowing microscopic differentiation. Linked Comment: Kinoshita-Ise. Br J Dermatol 2020; 183:419-420.