Dermal fibrosis in male pattern hair loss: a suggestive implication of mast cells

The Biology and Genomics of Human Hair Follicles: A Focus on Androgenetic Alopecia

Androgenetic alopecia is a highly prevalent condition mainly affecting men. This complex trait is related to aging and genetics; however, multiple other factors, for example, lifestyle, are also involved. Despite its prevalence, the underlying biology of androgenetic alopecia remains elusive, and thus advances in its treatment have been hindered. Herein, we review the functional anatomy of hair follicles and the cell signaling events that play a role in follicle cycling. We also discuss the pathology of androgenetic alopecia and the known molecular mechanisms underlying this condition. Additionally, we describe studies comparing the transcriptional differences in hair follicles between balding and non-balding scalp regions. Given the genetic contribution, we also discuss the most significant risk variants found to be associated with androgenetic alopecia. A more comprehensive understanding of this pathology may be generated through using multi-omics approaches.

Association between angiotensin-converting enzyme gene insertion deletion polymorphism and androgenetic alopecia susceptibility among Egyptian patients: A preliminary case-controlled study

BACKGROUND

Androgenetic alopecia (AGA) is a prevalent condition with a complex etiopathogenesis. Angiotensin-converting enzyme (ACE) gene located on the chromosome 17q23 contains an insertion (I) and deletion (D) polymorphism in the intron 16. This gene polymorphism plays a role in multiple inflammatory disorders. However, there are no studies investigating its association with AGA susceptibility.

OBJECTIVES

In this work, we aimed at exploring the association of ACE gene I/D polymorphism in AGA susceptibility in a group of Egyptian patients.

METHODS

This study included 100 AGA patients, and 100 apparently healthy controls. The ACE gene I/D polymorphism was analyzed by polymerase chain reaction.

RESULTS

The DD, ID genotypes, and D allele showed higher frequent distribution among studied AGA patients than controls (p < 0.05 each). Positive family history and ACE gene I/D polymorphism were considered AGA susceptibility predictors in both uni- and multivariable analyses [p < 0.05 each (OR (95% CI)] on applying logistic regression analysis for risk factors prediction.

CONCLUSIONS

This study highlights the possible contribution of the suspected genetic polymorphism as a susceptibility indicator for AGA development in the examined group of patients.

Conflicting Reports Regarding the Histopathological Features of Androgenic Alopecia: Are Biopsy Location, Hair Diameter Diversity, and Relative Hair Follicle Miniaturization Partly to Blame?

Despite decades of study, debate persists over the role of inflammation, fibrosis, and prostaglandins in the histopathology of androgenic alopecia (AGA). This brief review proposes that inconsistent findings across histological studies are a consequence of three inadequately controlled variables: 1) biopsy location, 2) hair diameter diversity (HDD), and 3) relative hair follicle miniaturization (HFM) within and across subjects. We suggest new methodological considerations to improve AGA histopathological research, as well as a novel classification system to quantify HFM by its stages. Finally, we hypothesize a dynamic relationship between inflammation, fibrosis, and prostaglandin activity dependent on relative HFM.

A hypothetical pathogenesis model for androgenic alopecia: clarifying the dihydrotestosterone paradox and rate-limiting recovery factors

Androgenic alopecia, also known as pattern hair loss, is a chronic progressive condition that affects 80% of men and 50% of women throughout a lifetime. But despite its prevalence and extensive study, a coherent pathology model describing androgenic alopecia's precursors, biological step-processes, and physiological responses does not yet exist. While consensus is that androgenic alopecia is genetic and androgen-mediated by dihydrotestosterone, questions remain regarding dihydrotestosterone's exact role in androgenic alopecia onset. What causes dihydrotestosterone to increase in androgenic alopecia-prone tissues? By which mechanisms does dihydrotestosterone miniaturize androgenic alopecia-prone hair follicles? Why is dihydrotestosterone also associated with hair growth in secondary body and facial hair? Why does castration (which decreases androgen production by 95%) stop pattern hair loss, but not fully reverse it? Is there a relationship between dihydrotestosterone and tissue remodeling observed alongside androgenic alopecia onset? We review evidence supporting and challenging dihydrotestosterone's causal relationship with androgenic alopecia, then propose an evidence-based pathogenesis model that attempts to answer the above questions, account for additionally-suspected androgenic alopecia mediators, identify rate-limiting recovery factors, and elucidate better treatment targets. The hypothesis argues that: (1) chronic scalp tension transmitted from the galea aponeurotica induces an inflammatory response in androgenic alopecia-prone tissues; (2) dihydrotestosterone increases in androgenic alopecia-prone tissues as part of this inflammatory response; and (3) dihydrotestosterone does not directly miniaturize hair follicles. Rather, dihydrotestosterone is a co-mediator of tissue dermal sheath thickening, perifollicular fibrosis, and calcification - three chronic, progressive conditions concomitant with androgenic alopecia progression. These conditions remodel androgenic alopecia-prone tissues - restricting follicle growth space, oxygen, and nutrient supply - leading to the slow, persistent hair follicle miniaturization characterized in androgenic alopecia. If true, this hypothetical model explains the mechanisms by which dihydrotestosterone miniaturizes androgenic alopecia-prone hair follicles, describes a rationale for androgenic alopecia progression and patterning, makes sense of dihydrotestosterone's paradoxical role in hair loss and hair growth, and identifies targets to further improve androgenic alopecia recovery rates: fibrosis, calcification, and chronic scalp tension.

Study of gene expression alteration in male androgenetic alopecia: evidence of predominant molecular signalling pathways

BACKGROUND

Male androgenetic alopecia (AGA) is the most common form of hair loss in men. It is characterized by a distinct pattern of progressive hair loss starting from the frontal area and the vertex of the scalp. Although several genetic risk loci have been identified, relevant genes for AGA remain to be defined.

OBJECTIVES

To identify biomarkers associated with AGA.

METHODS

Molecular biomarkers associated with premature AGA were identified through gene expression analysis using cDNA generated from scalp vertex biopsies of hairless or bald men with premature AGA, and healthy volunteers.

RESULTS

This monocentric study reveals that genes encoding mast cell granule enzymes, inflammatory mediators and immunoglobulin-associated immune mediators were significantly overexpressed in AGA. In contrast, underexpressed genes appear to be associated with the Wnt/β-catenin and bone morphogenic protein/transforming growth factor-β signalling pathways. Although involvement of these pathways in hair follicle regeneration is well described, functional interpretation of the transcriptomic data highlights different events that account for their inhibition. In particular, one of these events depends on the dysregulated expression of proopiomelanocortin, as confirmed by polymerase chain reaction and immunohistochemistry. In addition, lower expression of CYP27B1 in patients with AGA supports the notion that changes in vitamin D metabolism contributes to hair loss.

CONCLUSIONS

This study provides compelling evidence for distinct molecular events contributing to alopecia that may pave the way for new therapeutic approaches.

Scalp dermatoscopic findings in androgenetic alopecia and their relations with disease severity

Background

Clinicians are searching for new methods to diagnose and predict the course of androgenetic alopecia noninvasively.

Objective

Our aim is to evaluate trichoscopic findings and their relations with disease severity in androgenetic alopecia.

Methods

The videodermatoscopic findings of 143 female and 63 male patients with androgenetic alopecia were compared with each other, with those of healthy subjects (n=100), and with those of patients with other nonscarring alopecias (n=208). Mann-Whitney U-test, χ² analyses, and logistic regression analysis were used for statistical analysis.

Results

No statistically significant relation was found between trichoscopic findings and severity in male androgenetic alopecia (MAGA) on the basis of the modified Hamilton Norwood scale (among 7 degrees); however, multihair follicular unit and perifollicular pigmentation were related to low severity whereas white dots, honeycomb pattern pigmentation, and brown dots were related to high severity. On the other hand, according to the Ludwig classification, arborizing red lines were related to low severity and brown dots were related to high severity, whereas there was no difference in stages between the Ebling and Olsen classifications in female androgenetic alopecia (FAGA). In the characteristic trichoscopic findings in this study, perifollicular pigmentation was found as a normal feature of the scalp, whereas multihair follicular unit and honeycomb pigment pattern, which were previously considered as normal features, were observed to be related to androgenetic alopecia.

Conclusion

No relation was found between MAGA severity and trichoscopic findings, as well as between FAGA severity according to different disease severity classifications and trichoscopic findings.

Inhibitory effect of tianeptine on catagen induction in alopecia areata-like lesions induced by ultrasonic wave stress in mice

BACKGROUND

Alopecia areata (AA) is characterized by rapid and complete hair loss in one or multiple areas of the scalp. Stress is an important triggering factor in AA.

AIM

To identify the inhibitory effect of tianeptine on catagen induction in C57BL/6 mice with AA-like lesions induced by ultrasonic wave stress (UWS).

METHODS

The mice were divided into four groups. Group 1 received oral tianeptine before and after UWS; group 2 received oral tianeptine only after UWS; group 3 was given UWS treatment only; and group 4 (negative control group) was not given any treatment. Phototrichigraphy and dermatoscopy were used for assessment. Histological analysis was performed using haematoxylin and eosin, toluidine blue, Masson trichrome and Verhoeff-van Gieson stains. Immunohistochemical analysis was also performed. The level of apoptosis and expression of neuropeptides in the skin were assessed by terminal deoxynucleotidyl transferase dUTP nick end labelling and immunofluorescence assays.

RESULTS

Mice in group 1 had an increased rate of hair growth and greater hair-shaft thickness compared with mice in groups 2 and 3. In addition, mice in group 1 had a higher number of anagen hair follicles, increased synthesis of collagen and elastic fibres, decreased mast-cell degranulation, reduction in cell apoptosis in hair follicles, and recovery of vitamin D receptor expression. Expression of neuropeptides (substance P, calcitonin gene-related peptide) was not altered.

CONCLUSIONS

Tianeptine might play a role in suppressing catagen induction in a stress-induced AA mouse model.

Alopecia in IL-10-deficient mouse pups is c-kit-dependent and can be triggered by iron deficiency

Hair loss (alopecia) can result from a variety of metabolic, endocrine, immunologic, and environmental causes. This investigation was undertaken to determine the mechanisms underlying the sporadic development of alopecia in litters from C57BL/6 interleukin-10-deficient (Il10(-/-)) mice. All pups in affected litters demonstrated alopecia by postnatal days 17-19, with hair loss from their trunks but not from their head, base of tail, or feet. Histopathology revealed distorted hair follicles containing broken hair shafts and prominent dermal infiltrates containing increased numbers of activated mast cells. Hair re-growth began soon after weaning, suggesting that the alopecia was triggered by factors transmitted during lactation. Milk from Il10(-/-) dams induced macrophage secretion of pro-inflammatory cytokines in vitro regardless of whether or not their pups developed alopecia. Feeding dams a diet containing 3-6 ppm iron increased the percentage of litters with alopecia to 100% for pups with mast cells, with 0% alopecia in mast cell-deficient pups. When dams were fed a diet containing 131 ppm iron, significantly lower haemoglobin and hematocrit values were observed in pups from litters with alopecia (71%; 5 of 7 litters) compared to litters without alopecia. Genetic or pharmacologic inhibition of c-kit that resulted in depletion of mast cells in pups prevented hair loss in at-risk litters. These studies demonstrate that maternal iron-restricted diets enhance the incidence of alopecia in IL-10-deficient mouse pups and suggest mast cells as potential effector cells. Further studies are indicated to further explore the mechanisms involved and to determine how mast cells may contribute to alopecia in humans.