Development of alopecia areata is associated with higher central and peripheral hypothalamic-pituitary-adrenal tone in the skin graft induced C3H/HeJ mouse model

Increasing GSH-Px Activity and Activating Wnt Pathway Promote Fine Wool Growth in FGF5-Edited Sheep

Fibroblast growth factor 5 (FGF5) plays key roles in promoting the transition from the anagen to catagen during the hair follicle cycle. The sheep serves as an excellent model for studying hair growth and is frequently utilized in various research processes related to human skin diseases. We used the CRISPR/Cas9 system to generate four FGF5-edited Dorper sheep and only low levels of FGF5 were detected in the edited sheep. The density of fine wool in GE sheep was markedly increased, and the proportion of fine wool with a diameter of 14.4-20.0 μm was significantly higher. The proliferation signal in the skin of gene-edited (GE) sheep was stronger than in wild-type (WT) sheep. FGF5 editing decreased cortisol concentration in the skin, further activated the activity of antioxidant enzymes such as Glutathione peroxidase (GSH-Px), and regulated the expression of Wnt signaling pathways containing Wnt agonists (Rspondins, Rspos) and antagonists (Notum) in hair regeneration. We suggest that FGF5 not only mediates the activation of antioxidant pathways by cortisol, which constitutes a highly coordinated microenvironment in hair follicle cells, but also influences key signals of the Wnt pathway to regulate secondary hair follicle (SHF) development. Overall, our findings here demonstrate that FGF5 plays a significant role in regulating SHF growth in sheep and potentially serves as a molecular marker of fine wool growth in sheep breeding.

Dissecting hair breakage in alopecia areata: the central role of dysregulated cysteine homeostasis

In the initial stages of Alopecia Areata (AA), the predominance of hair breakage or exclamation mark hairs serves as vital indicators of disease activity. These signs are non-invasive and are commonly employed in dermatoscopic examinations. Despite their clinical salience, the underlying etiology precipitating this hair breakage remains largely uncharted territory. Our exhaustive review of the existing literature points to a pivotal role for cysteine-a key amino acid central to hair growth-in these mechanisms. This review will probe and deliberate upon the implications of aberrant cysteine metabolism in the pathogenesis of AA. It will examine the potential intersections of cysteine metabolism with autophagy, ferroptosis, immunity, and psychiatric manifestations associated with AA. Such exploration could illuminate new facets of the disease's pathophysiology, potentially paving the way for innovative therapeutic strategies.

Psychological Stress-Induced Pathogenesis of Alopecia Areata: Autoimmune and Apoptotic Pathways

Alopecia areata (AA) is an autoimmune dermatological disease with multifactorial etiology and is characterized by reversible hair loss in patches. AA may be closely related to emotional stress and influenced by psychological factors as part of its pathophysiology; however, its etiology remains predominantly unknown. This review aimed to elucidate the association between AA occurrence and the neuropeptide substance P (SP) and corticotropin-releasing hormone (CRH), which are secreted during emotional stress, and have been understood to initiate and advance the etiopathogenesis of AA. Therefore, this review aimed to explain how SP and CRH initiate and contribute to the etiopathogenesis of AA. To assess the etiopathogenesis of AA, we conducted a literature search on PubMed and ClinicalTrials.gov. Overall, several authors described interactions between the hair follicles (HFs) and the stress-associated signaling substances, including SP and CRH, in the etiology of AA; this was attributed to the understanding in that AA can occur without the loss of HFs, similar to that observed in hereditary hair loss with age. Most studies demonstrated that the collapse of "immune privilege" plays a crucial role in the development and exacerbation of the AA; nonetheless, a few studies indicated that substances unrelated to autoimmunity may also cause apoptosis in keratocytes, leading to the development of AA. We investigated both the autoimmune and apoptotic pathways within the etiology of AA and assessed the potential interactions between the key substances of both pathways to evaluate potential therapeutic targets for the treatment of AA. Clinical trials of marketed/unreviewed intervention drugs for AA were also reviewed to determine their corresponding target pathways.

Baricitinib for the Treatment of Alopecia Areata

Alopecia areata (AA) is a relapsing, chronic, immune-mediated disease characterized by nonscarring, inflammatory hair loss that can affect any hair-bearing site. AA clinical presentation is heterogeneous. Its pathogenesis involves immune and genetic factors and several pro-inflammatory cytokines involved in AA pathogenesis, including interleukin-15 and interferon-γ, as well as Th2 cytokines, such as IL-4/IL-13, that signal through Janus kinase (JAK) pathway. AA treatment aims to stop its progression and reverse hair loss, and JAK inhibition has been shown to stop hair loss and reverse alopecia and has exhibited promising results in treating AA in clinical trials. Baricitinib, an oral, reversible, selective JAK1/JAK2 inhibitor, was shown to be superior to placebo on hair growth after 36 weeks of treatment in adults with severe AA in a phase 2 trial and recently in two phase 3 trials (BRAVE-AA1 and BRAVE-AA2). In both studies, the most common adverse events were upper respiratory tract infections, urinary tract infection, acne, headache, and elevated creatine kinase levels. On the basis of these trial results, baricitinib was recently approved by the European Medicines Agency (EMA) and US Food and Drug Administration (FDA) for the treatment of adults with severe AA. Nevertheless, longer trials are needed to determine the long-term efficacy and safety of baricitinib in AA. Current trials are ongoing and are planned to remain randomized and blinded for up to 200 weeks.

Increased Risk of Suicide Attempt in Patients with Alopecia Areata: A Nationwide Population-Based Cohort Study

BACKGROUND

There is growing evidence that patients with alopecia areata (AA) have an increased risk of developing psychiatric comorbidities. However, the relationship between AA and suicidal behaviors remains unclear.

OBJECTIVE

The objective of this study was to investigate the association between AA and suicidal behaviors.

METHODS

Participants were recruited from the National Health Insurance Research Database in Taiwan, including 10,515 patients with AA and 10,5150 matched controls, to assess the risk of suicide attempts. A Cox regression model was used for all analyses.

RESULTS

Compared with the controls, an increased risk of suicide attempts was observed in patients with AA, with an adjusted hazard ratio of 6.28 (95% confidence interval, 4.47-8.81). Suicide risk remained significantly elevated in AA patients when stratified by underlying psychiatric disorders. The mean age of initial suicidal behaviors was also lower in patients with AA.

CONCLUSIONS

Patients with AA had a significantly higher incidence of suicidal attempts than controls, regardless of concurrent psychiatric illness. Further studies are needed to elucidate the pathophysiology of the association between AA and suicidality. In addition, dermatologists should be aware of the increased suicidality of patients with AA.

A Study of Correlation of Alopecia Areata and Metabolic Syndrome in Northwest Indian Population: A Case-Control Study

Context

Alopecia areata (AA) is the most common cause of inflammatory, nonscarring hair loss, involving hair-bearing areas of the body. The etiology of AA still remains uncertain; however, genetic, environmental, and autoimmunity play a role. Newer theories such as oxidative theory, HPA axis activation, and finally, the role of increased inflammatory cytokines such as interleukin 1 (IL1), tumor necrosis factor-alpha, interferon-gamma, IL-2 IL-4, and MIF are suggested to contribute to both AA and metabolic syndrome (MS).

Aims

Assessment of the degree of association of MS (NCEP ATP III criteria) in clinically diagnosed cases of AA and compare to that of controls.

Materials and Methods

Similar age/sex-matched AA patients and controls (106 in each group) were taken. Anthropometric measurements, blood-sugar estimation, lipid-profile estimation in venous blood sample, and blood-pressure measurement were done.

Results

Prevalence of MS was almost similar among cases of AA 9/106 (8.47%) as well as healthy controls 8/106 (7.54%), and the difference was not statistically significant (P = 1). Among all components of MS, waist circumference (WC) (central obesity) was the most common parameter (100% cases). In controls, high systolic blood pressure (SBP) was the most common parameter (77.78% controls). AA is associated with a higher level of SBP, diastolic blood pressure (DBP), WC although nonsignificant, and low level of high-density lipoprotein cholesterol which was the only significant association.

Conclusion

Insignificant correlation between occurrence of MS and evidence of insulin resistance (IR) in AA was observed in this study population. However, some of the observations in the present study may raise awareness in susceptible individuals that lifestyle changes and regular screening in AA can reduce the risk of cardiovascular diseases and other co-existing autoimmune inflammatory condition-IR, dyslipidemia, and hypertension.

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

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

Advancing Regenerative Cellular Therapies in Non-Scarring Alopecia

Alopecia or baldness is a common diagnosis in clinical practice. Alopecia can be scarring or non-scarring, diffuse or patchy. The most prevalent type of alopecia is non-scarring alopecia, with the majority of cases being androgenetic alopecia (AGA) or alopecia areata (AA). AGA is traditionally treated with minoxidil and finasteride, while AA is treated with immune modulators; however, both treatments have significant downsides. These drawbacks compel us to explore regenerative therapies that are relatively devoid of adverse effects. A thorough literature review was conducted to explore the existing proven and experimental regenerative treatment modalities in non-scarring alopecia. Multiple treatment options compelled us to classify them into growth factor-rich and stem cell-rich. The growth factor-rich group included platelet-rich plasma, stem cell-conditioned medium, exosomes and placental extract whereas adult stem cells (adipose-derived stem cell-nano fat and stromal vascular fraction; bone marrow stem cell and hair follicle stem cells) and perinatal stem cells (umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs), Wharton jelly-derived MSCs (WJ-MSCs), amniotic fluid-derived MSCs (AF-MSCs), and placental MSCs) were grouped into the stem cell-rich group. Because of its regenerative and proliferative capabilities, MSC lies at the heart of regenerative cellular treatment for hair restoration. A literature review revealed that both adult and perinatal MSCs are successful as a mesotherapy for hair regrowth. However, there is a lack of standardization in terms of preparation, dose, and route of administration. To better understand the source and mode of action of regenerative cellular therapies in hair restoration, we have proposed the "À La Mode Classification". In addition, available evidence-based cellular treatments for hair regrowth have been thoroughly described.

Psychological Aspects of Hair Disorders: Consideration for Dermatologists, Cosmetologists, Aesthetic, and Plastic Surgeons

Hair loss disorders may cause considerable distress to patients. Although many do not pose a significant medical risk, the sociocultural importance of hair is substantial. Often the extent of hair loss does not correlate to the impact on psychosocial function, thus necessitating an individualized approach. Hair loss disorders are interrelated with mental health and at times exert significant psychological percussions, and therefore, providers should address both medical and psychological aspects of treatment. This review contains a discussion of the impact on quality of life of common hair loss disorders and the psychological approaches that providers may utilize to improve care. The incorporation of psychodermatology and psychotrichology in dermatology and psychiatry residency programs is of vital importance. Dermatology and psychiatry liaison clinics may prove useful in the treatment of these patients.

Narrow-band UVB combined with compound clobetasol propionate can improve the therapeutic effect in hand eczema patients

OBJECTIVE

To explore the therapeutic effect of narrow-band UVB combined with compound clobetasol propionate on hand eczema patients.

METHODS

From June 2017 to June 2020, 102 patients with hand eczema in our hospital were recruited for this study and divided into group A (GA) and group B (GB). The 50 patients in GA were treated with narrow-band UVB irradiation only, and the 52 patients in GB were treated with compound clobetasol propionate in addition to the treatment administered to GA. The patients' general data and therapeutic effects were observed in both groups. The adverse reactions were also observed during the treatment. The severity index scores (EASI) of the pruritus and eczema areas of the skin lesions were observed before and after the therapy. The IFN-γ and IL-4 levels in the serum were tested using ELISA. After the therapy, the quality of life and any recurrences within 3 months were observed in both groups.

RESULTS

There were no differences in the baseline data between the two groups (P>0.05). The curative effect in GB was better than it was in GA (P<0.05). The incidence of adverse reactions in GB was significantly lower than the incidence in GA (P<0.05). After the therapy, the EASI scores of the pruritus and eczema areas of the skin lesions in GB were significantly lower than they were in GA (P<0.05). After the therapy, the patients' serum IFN-γ and IL-4 levels in GB were significantly better than they were in GA. After the therapy, the quality of life of the patients in GB was significantly higher than it was in in GA (P<0.05). After 3 months of therapy, the recurrence rate in GB was significantly lower than it was in GA (P<0.05).

CONCLUSION

Narrow-band UVB combined with compound clobetasol propionate is effective at treating patients with hand eczema, as it can effectively improve their clinical symptoms and is very safe.

Clinical and biological impact of the exposome on the skin

The skin exposome is defined as the totality of environmental exposures over the life course that can induce or modify various skin conditions. Here, we review the impact on the skin of solar exposure, air pollution, hormones, nutrition and psychological factors. Photoageing, photocarcinogenesis and pigmentary changes are well-established consequences of chronic exposure of the skin to solar radiation. Exposure to traffic-related air pollution contributes to skin ageing. Particulate matter and nitrogen dioxide cause skin pigmentation/lentigines, while ozone causes wrinkles and has an impact on atopic eczema. Human skin is a major target of hormones, and they exhibit a wide range of biological activities on the skin. Hormones decline with advancing age influencing skin ageing. Nutrition has an impact on numerous biochemical processes, including oxidation, inflammation and glycation, which may result in clinical effects, including modification of the course of skin ageing and photoageing. Stress and lack of sleep are known to contribute to a pro-inflammatory state, which, in turn, affects the integrity of extracellular matrix proteins, in particular collagen. Hormone dysregulation, malnutrition and stress may contribute to inflammatory skin disorders, such as atopic dermatitis, psoriasis, acne and rosacea.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Mouse Models of Alopecia Areata: C3H/HeJ Mice Versus the Humanized AA Mouse Model

The C3H/HeJ model has long dominated basic alopecia areata (AA) in vivo research and has been used as proof-of-principle that Jak inhibitors are suitable agents for AA management in vivo. However, its histologic features are not typical of human AA, and it is questionable whether it is sufficiently clinically predictive for evaluating the therapeutic effects of candidate AA agents. Instead, the humanized mouse model of AA has been used to functionally demonstrate the role of key immune cells in AA pathogenesis and to discover human-specific pharmacologic targets in AA management. Therefore, we advocate the use of both models in future preclinical AA research.

Exploring the anti-stress effects of imatinib and tetrabenazine in cold-water immersion-induced acute stress in mice

The aim of the present study was to explore the ameliorative role of imatinib and tetrabenazine in acute stress-induced behavioural and biochemical changes in mice. Cold-water immersion (5 min duration) was employed to induce acute stress and the resulting changes in the locomotor activity, exploratory behaviour, motor activity and social behaviour were assessed using the actophotometer, the hole board, the open field and the social interaction tests. The biochemical alterations were assessed by measuring the plasma corticosterone levels using ELISA kit. Cold-water immersion-induced acute stress diminished the locomotor activity, exploratory behaviour, motor activity and social behaviour along with increase in the plasma corticosterone levels. Administration of imatinib (50 and 100 mg/kg, i.p.), a tyrosine kinase inhibitor, significantly attenuated the cold-water immersion-induced behavioural alterations with normalization of the plasma corticosterone levels in a dose-dependent manner. Moreover, administration of tetrabenazine (1 and 2 mg/kg, i.p.), a vesicular monoamine transporter 2 (VMAT2) inhibitor, also abolished the acute stress-induced behavioural and biochemical changes in a dose-dependent manner. The beneficial effects of imatinib and tetrabenazine in normalizing acute stress-induced biochemical and behavioural changes make them promising therapeutic agents in the treatment of acute stress-related problems.

Local secretion of stress hormones increases in alopecia areata lesions after treatment with UVA-1 phototherapy

Alopecia areata (AA) is an autoimmune disease of the hair follicle. Keratinocytes of the hair follicle generate an immunosuppressive environment by the local secretion of hormones of the hypothalamic-pituitary-adrenal axis of the skin (skin HPA analog). Our objective was to measure the local production of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), and α-melanocyte-stimulating hormone (α-MSH) in the scalp tissue of patients with AA before and after ultraviolet A1 (UVA-1) phototherapy to determine their role in the pathogenesis of AA and the effect of UVA-1 on the AA hormonal environment. This was a retrospective and descriptive study of skin samples from 22 patients with AA before and after UVA-1 treatment. We compared the changes in the local hormonal environment by measuring CRH, ACTH, type 2 melanocortin receptor (ACTH receptor) and α-MSH with immunohistochemical stains. The positivity of MSH was significantly higher (P = .037) in the post-treatment samples compared with the baseline value. ACTH was significantly higher in intensity (P = .032) in the post-treatment samples compared with the initial value. CRH was significantly higher in intensity (P = .013) in baseline samples compared with the final biopsies. The positivity of the ACTH receptor MC2R was not different between the two groups (P = .626). In AA, an interruption in the signalling of CRH could decrease the local concentration of ACTH and MSH, and consequently, the immunosuppressive effect of these hormones. This phenomenon is normalized in the skin treated with UVA-1. A defective signalling system in the cutaneous HPA axis may be involved in the pathogenesis of AA.

A "hair-raising" history of alopecia areata

A 3500-year-old papyrus from ancient Egypt provides a list of treatments for many diseases including "bite hair loss," most likely alopecia areata (AA). The treatment of AA remained largely unchanged for over 1500 years. In 30 CE, Celsus described AA presenting as scalp alopecia in spots or the "windings of a snake" and suggested treatment with caustic compounds and scarification. The first "modern" description of AA came in 1813, though treatment still largely employed caustic agents. From the mid-19th century onwards, various hypotheses of AA development were put forward including infectious microbes (1843), nerve defects (1858), physical trauma and psychological stress (1881), focal inflammation (1891), diseased teeth (1902), toxins (1912) and endocrine disorders (1913). The 1950s brought new treatment developments with the first use of corticosteroid compounds (1952), and the first suggestion that AA was an autoimmune disease (1958). Research progressively shifted towards identifying hair follicle-specific autoantibodies (1995). The potential role of lymphocytes in AA was made implicit with immunohistological studies (1980s). However, studies confirming their functional role were not published until the development of rodent models (1990s). Genetic studies, particularly genome-wide association studies, have now come to the forefront and open up a new era of AA investigation (2000s). Today, AA research is actively focused on genetics, the microbiome, dietary modulators, the role of atopy, immune cell types in AA pathogenesis, primary antigenic targets, mechanisms by which immune cells influence hair growth, and of course the development of new treatments based on these discoveries.

Protective effects of human umbilical cord blood‑derived mesenchymal stem cells against dexamethasone‑induced apoptotic cell death in hair follicles

Alopecia is a common and distressing condition, and developing new therapeutic agents to prevent hair loss is important. Human umbilical cord blood‑derived mesenchymal stem cells (hUCB‑MSCs) have been studied intensively in regenerative medicine. However, the therapeutic potential of these cells against hair loss and hair organ damage remains unclear, and the effects of hUCB‑MSC transplantation on hair loss require evaluation. The current study aimed to investigate the effects of hUCB‑MSCs on hair regression in vivo and restoration of anagen conduction on hair growth in vitro. The effects of hUCB‑MSCs were explored in mouse catagen induction models using a topical treatment of 0.1% dexamethasone to induce hair regression. Dexamethasone was also used to simulate a stress environment in vitro. The results demonstrated that hUCB‑MSCs significantly prevented hair regression induced by dexamethasone topical stimulation in vivo. Additionally, hUCB‑MSCs significantly increased the proliferation of human dermal papilla cells (hDPCs) and HaCaT cells, which are key constituent cells of the hair follicle. Stimulation of vascular endothelial growth factor secretion and decreased expression of DKK‑1 by hUCB‑MSCs were also observed in hDPCs. Restoration of cell viability by hUCB‑MSCs suggested that these cells exerted a protective effect on glucocorticoid stress‑associated hair loss. In addition, anti‑apoptotic effects and regulation of the autophagic flux recovery were observed in HaCaT cells. The results of the present study indicated that hUCB‑MSCs may have the capacity to protect hair follicular dermal papilla cells and keratinocytes, thus preventing hair loss. Additionally, the protective effects of hUCB‑MSCs may be resistant to dysregulation of autophagy under harmful stress.

What's New in the Pathophysiology of Alopecia Areata? The Possible Contribution of Skin and Gut Microbiome in the Pathogenesis of Alopecia - Big Opportunities, Big Challenges, and Novel Perspectives

The term “microbiome” defines the collective genome of all commensal, symbiotic, and pathogenic microbes living in the human body. The composition of microbiota in the gut and skin is influenced by many factors such as the stage of life, nutrition, lifestyle, and gender. In the past few years, several scientific papers have demonstrated an implication of microbiota in many immune-mediated diseases, for example, diabetes, ulcerative colitis, and multiple sclerosis. The alterations in the proportion of gut microbiota have emerged as potential immunomodulators with the capacity to induce physiologic as well as pathologic immune responses against the human body, causing inflammation and destruction of tissues or organs. The microbiota influences the differentiation of adaptive immune cells not only in the gut but also in the skin. Alopecia areata (AA) is a dermatologic disorder which causes hair loss in most cases resistant to treatment. There are some clinical and experimental evidences indicating that AA is the demonstration of autoimmune attack against hair follicles. The factors that may implicate such an autoimmunity in AA still remain unknown. Despite more and more evidences demonstrate that human microbiome plays a key role in human health and diseases, to the best of our knowledge, no study has been conducted to analyze an implication of microbiome in the pathogenesis of AA. Undoubtedly, there is a need to performing a study which might explain the involvement of gut and skin microbiota in the unclear pathogenesis of AA and lead to alternative treatment options for numerous patients suffering from current treatment limitations.

Alopecia areata: a review of disease pathogenesis

BACKGROUND

Alopecia areata is a disorder that results in nonscarring hair loss. The psychological impact can be significant, leading to feelings of depression and social isolation. Objectives In this article, we seek to review the pathophysiological mechanisms proposed in recent years in a narrative fashion.

METHODS

We searched MEDLINE and Scopus for articles related to alopecia areata, with a particular emphasis on its pathogenesis.

RESULTS

The main theory of alopecia areata pathogenesis is that it is an autoimmune phenomenon resulting from a disruption in hair follicle immune privilege. What causes this breakdown is an issue of debate. Some believe that a stressed hair follicle environment triggers antigen presentation, while others blame a dysregulation in the central immune system entangling the follicles. Evidence for the latter theory is provided by animal studies, as well investigations around the AIRE gene. Different immune-cell lines including plasmacytoid dendritic cells, natural killer cells and T cells, along with key molecules such as interferon-γ, interleukin-15, MICA and NKG2D, have been identified as contributing to the autoimmune process.

CONCLUSIONS

Alopecia areata remains incurable, although it has been studied for years. Available treatment options at best are beneficial for milder cases, and the rate of relapse is high. Understanding the exact mechanisms of hair loss in alopecia areata is therefore of utmost importance to help identify potential therapeutic targets.

Involvement of the central hypothalamic-pituitary-adrenal axis in hair growth and melanogenesis among different mouse strains

Stress has been demonstrated to play an important role in hair follicle function and the pathogenesis of some hair disorders. The central hypothalamic-pituitary-adrenal (HPA) axis is activated by stress stimuli, synthesizes and releases various components and eventually induces the pathogenesis and recurrence of peripheral diseases. Our aim is to compare the different responses under exposure of stress in hair follicle function among different mouse strains, and to detect the involvement of the central HPA axis after stress in hair follicle growth and melanogenesis. In this study, we exposed different mouse strains (C57BL/6, CBA/J, C3H/HeN, BALB/c and ICR) to a 21-day chronic restraint stress protocol and selected C57BL/6, CBA/J and BALB/c mice for further study because of their significant behavioral alterations. Then, we evaluated and compared the different responses and sensitivity to chronic restraint stress in hair follicle function and central HPA axis among the selected strains. The results showed that expression of POMC, CRF and GR mRNA and protein and serum levels of corticosterone were inhibited in response to stress. These findings suggested that chronic restraint stress may inhibit hair follicle growth and melanogenesis via regulating the key elements of the central HPA axis. In addition, the results revealed different mouse strains exhibit different responses in the central HPA axis and hair follicle after stress exposure. C57BL/6 might be the most sensitive strain among the three strains tested as well as an appropriate strain to study possible pathophysiological mechanisms by which the nervous system influences skin function and screen dermatological drugs suitable for psychotherapy. We believe the current study will provide some useful information for researchers who are interested in the bidirectional communication between the nervous and skin systems and the management of stress-induced cutaneous diseases.

Genetic analysis of interleukin 18 gene polymorphisms in alopecia areata

BACKGROUND

Alopecia areata (AA), which appears as nonscarring hair shedding on any hair-bearing area, is a common organ-specific autoimmune condition. Cytokines have important roles in the development of AA. Interleukin (IL) 18 is a significant proinflammatory cytokine that was found higher in the patients with AA. We aimed to investigate whether the IL-18 (rs187238 and rs1946518) single nucleotide polymorphisms (SNPs) may be associated with AA and/or clinical outcome of patients with AA in Turkish population.

METHODS

Genotyping of rs187238 and rs1946518 SNPs were detected using sequence-specific primer-polymerase chain reaction (SSP-PCR) method in 200 patients with AA and 200 control subjects.

RESULTS

The genotype distribution of rs1946518 (-607C>A) SNP was found to be statistically significantly different among patients with AA and controls (P = .0008). Distribution of CC+CA genotypes and frequency of -607/allele C of rs1946518 SNP were higher in patients with AA (P = .001, P = .001, respectively). The genotype distribution of rs187238 (-137G>C) SNP was found to be statistically significantly different among patients with AA and control subjects (P = .0014). Distribution of GG genotype and frequency of -137/allele G of rs187238 SNP were higher in patients with AA (P = .0003, P = .001, respectively).

CONCLUSION

The rs1946518 (-607C>A) and rs187238 (-137G>C) polymorphisms were found associated with alopecia areata disease. The study suggests that IL-18 rs187238 and rs1946518 SNPs may be the cause of the AA susceptibility.

Alopecia Areata: Review of Epidemiology, Clinical Features, Pathogenesis, and New Treatment Options

Alopecia areata (AA) is a complex autoimmune condition that causes nonscarring hair loss. It typically presents with sharply demarcated round patches of hair loss and may present at any age. In this article, we review the epidemiology, clinical features, pathogenesis, and new treatment options of AA, with a focus on the immunologic mechanism underlying the treatment. While traditional treatment options such as corticosteroids are moderately effective, a better understanding of the disease pathogenesis may lead to the development of new treatments that are more directed and effective against AA. Sources were gathered from PubMed, Embase, and the Cochrane database using the keywords: alopecia, alopecia areata, hair loss, trichoscopy, treatments, pathogenesis, and epidemiology.

11β-Hydroxysteroid Dehydrogenase Type 1 Inhibition Attenuates the Adverse Effects of Glucocorticoids on Dermal Papilla Cells

PURPOSE

Glucocorticoids, stress-related hormones, inhibit hair growth. Intracellular glucocorticoid availability is regulated by 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). 11β-HSD1 was recently detected in keratinocytes and fibroblasts. However, the expression of 11β-HSD1 in human hair follicles remains unknown. We aimed to examine 11β-HSD1 expression in human dermal papilla cells (DPCs) and to investigate whether modulation of 11β-HSD1 activity can regulate the negative effects of glucocorticoids on DPCs.

MATERIALS AND METHODS

11β-HSD1 expression in normal human scalp skin was examined by immunohistochemistry. 11β-HSD1 protein was detected in Western blots of human DPCs. Cultured human DPCs were treated with cortisol with or without a selective 11β-HSD1 inhibitor and subsequently stained for Ki-67 antibody. Expression levels of 11β-HSD1, Wnt5a, alkaline phosphatase (ALP), and vascular endothelial growth factor (VEGF) were analyzed by Western blotting.

RESULTS

11β-HSD1 was detected in dermal papilla in human scalp skin by immunohistochemistry. Human DPCs expressed 11β-HSD1 protein in vitro. Furthermore, cortisol stimulated the expression of 11β-HSD1 in DPCs. Glucocorticoids decreased cellular proliferation and the expression of Wnt5a, ALP, and VEGF in DPCs. A specific 11β-HSD1 inhibitor significantly attenuated the anti-proliferative effects of cortisol and reversed the cortisol-induced suppression of Wnt5a, ALP, and VEGF expression in DPCs.

CONCLUSION

Our data demonstrated the expression of 11β-HSD1 in human DPCs and revealed that inhibition of 11β-HSD1 activity can partially prevent the negative effect of glucocorticoids on DPCs, suggesting the possible application of 11β-HSD1 inhibitors for stress-related hair loss.

Exposure to Zearalenone During Early Pregnancy Causes Estrogenic Multitoxic Effects in Mice

Although zearalenone (ZEN; Sigma Chemicals, St Louis, Missouri) is a well-known mycotoxin with estrogenic activity, the toxic effects of ZEN during pregnancy are unknown. This study compared the effects of daily subcutaneous injections of ZEN (2, 4, or 8 mg/kg) with those of 17β-estradiol (E2; [Sigma Chemicals] 0.8, 1.6, or 3.2 μg/kg) in mice. Injections were administered on gestational days (GDs) 1 to 5, the period including implantation which is sensitive to hormonal balance. The effects of ZEN or E2 were evaluated by comparing the number of live fetuses, their weight, and absorbed conceptuses on GD 18, with those in vehicle-treated controls. In addition, implantation, embryos in the oviducts and those in uteri without implantation sites were investigated on GD 5. In mice treated with the highest dose of ZEN or E2, decidual responses and plasma progesterone concentrations were measured on GDs 5 and 6, respectively, and delayed implantation was investigated on GDs 9 and 14. The results showed that treatment with ZEN, in a manner similar to that seen for E2, led to obstruction of essential processes for establishing and maintaining pregnancy, such as embryo migration from oviducts to uteri, the decidual response, and activation of luteal function. Zearalenone also induced delayed implantation and loss of conceptuses and at low doses caused a retarded growth of the fetuses after normal implantation. It was therefore concluded that ZEN causes multiple estrogenic toxic actions when administered during early pregnancy in mice.

The gender differences in the inhibitory action of UVB-induced melanocyte activation by the administration of tranexamic acid

BACKGROUND

Tranexamic acid has an inhibitory action on ultraviolet (UV) B-induced melanocyte activation. This study examined the sex differences in the inhibitory action of tranexamic acid on UVB-induced melanocyte activation.

METHODS

We irradiated the eye and ear of male and female mice with UVB at a dose of 1.0 kJ/m(2) using a 20SE sunlamp. We orally administered tranexamic acid (750 mg/kg/day) at 30 min before UVB exposure.

RESULTS

Tranexamic acid inhibited the UVB-induced epidermal melanocyte activation, and the effect was more remarkable under UVB eye irradiation than under UVB ear irradiation. Furthermore, the melanocyte activity suppression effect was stronger in female mice than in male mice. Following the administration of tranexamic acid, the female displayed increased blood levels of β-endorphin and μ-opioid receptor and estradiol receptor β expression in comparison with the male. Furthermore, the effect of melanocyte activity suppression in the female mice was decreased by the administration of tamoxifen (antagonist of estrogen receptor) or naltrexone (antagonist of μ-opioid receptor).

CONCLUSIONS

These results suggest that the suppression by tranexamic acid of the UVB-induced melanocyte activation (UVB sensitivity) is stronger in female mice than in male mice and that female hormones and β-endorphin play an important role in this sex difference.

Chronic stress suppresses the expression of cutaneous hypothalamic-pituitary-adrenocortical axis elements and melanogenesis

Chronic stress can affect skin function, and some skin diseases might be triggered or aggravated by stress. Stress can activate the central hypothalamic–pituitary–adrenocortical (HPA) axis, which causes glucocorticoid levels to increase. The skin has HPA axis elements that react to environmental stressors to regulate skin functions, such as melanogenesis. This study explores the mechanism whereby chronic stress affects skin pigmentation, focusing on the HPA axis, and investigates the role of glucocorticoids in this pathway. We exposed C57BL/6 male mice to two types of chronic stress, chronic restraint stress (CRS) and chronic unpredictable mild stress (CUMS). Mice subjected to either stress condition showed reduced melanogenesis. Interestingly, CRS and CUMS triggered reductions in the mRNA expression levels of key factors involved in the HPA axis in the skin. In mice administered corticosterone, decreased melanin synthesis and reduced expression of HPA axis elements were observed. The reduced expression of HPA axis elements and melanogenesis in the skin of stressed mice were reversed by RU486 (a glucocorticoid receptor antagonist) treatment. Glucocorticoids had no significant inhibitory effect on melanogenesis in vitro. These results suggest that, high levels of serum corticosterone induced by chronic stress can reduce the expression of elements of the skin HPA axis by glucocorticoid-dependent negative feedback. These activities can eventually result in decreased skin pigmentation. Our findings raise the possibility that chronic stress could be a risk factor for depigmentation by disrupting the cutaneous HPA axis and should prompt dermatologists to exercise more caution when using glucocorticoids for treatment.

An overview of alopecias

Hair loss is a topic of enormous public interest and understanding the pathophysiology and treatment of various alopecias will likely make a large impact on patients' lives. The investigation of alopecias also provides important insight in the basic sciences; for instance, the abundance of stem cell populations and regenerative cycles that characterize a hair follicle render it an excellent model for the study of stem cell biology. This review seeks to provide a concise summary of the major alopecias with regard to presentation and management, and correlate these to recent advances in relevant research on pathogenesis.

Key role of CRF in the skin stress response system

The discovery of corticotropin-releasing factor (CRF) or CRH defining the upper regulatory arm of the hypothalamic-pituitary-adrenal (HPA) axis, along with the identification of the corresponding receptors (CRFRs 1 and 2), represents a milestone in our understanding of central mechanisms regulating body and local homeostasis. We focused on the CRF-led signaling systems in the skin and offer a model for regulation of peripheral homeostasis based on the interaction of CRF and the structurally related urocortins with corresponding receptors and the resulting direct or indirect phenotypic effects that include regulation of epidermal barrier function, skin immune, pigmentary, adnexal, and dermal functions necessary to maintain local and systemic homeostasis. The regulatory modes of action include the classical CRF-led cutaneous equivalent of the central HPA axis, the expression and function of CRF and related peptides, and the stimulation of pro-opiomelanocortin peptides or cytokines. The key regulatory role is assigned to the CRFR-1α receptor, with other isoforms having modulatory effects. CRF can be released from sensory nerves and immune cells in response to emotional and environmental stressors. The expression sequence of peptides includes urocortin/CRF→pro-opiomelanocortin→ACTH, MSH, and β-endorphin. Expression of these peptides and of CRFR-1α is environmentally regulated, and their dysfunction can lead to skin and systemic diseases. Environmentally stressed skin can activate both the central and local HPA axis through either sensory nerves or humoral factors to turn on homeostatic responses counteracting cutaneous and systemic environmental damage. CRF and CRFR-1 may constitute novel targets through the use of specific agonists or antagonists, especially for therapy of skin diseases that worsen with stress, such as atopic dermatitis and psoriasis.

Total glucosides of paeony capsule plus compound glycyrrhizin tablets for the treatment of severe alopecia areata in children: a randomized controlled trial

Total glucosides of paeony capsule (TGPC) and compound glycyrrhizin tablets (CGT) are plant extracts of glycosides. We conducted this study to examine the efficacy and safety of TGPC plus CGT for severe alopecia areata in children. 117 subjects were randomly allocated into TGPC plus CGT group or CGT group. For consecutive 12 months, subjects were given oral TGPC and CGT or oral CGT alone. The outcome measures included score of alopecia areata severity, effective rate, and adverse events observed in the 3rd, 6th, and 12th month. We found that the scores of alopecia areata severity of both groups were significantly reduced, and the scores of treatment group were lower than those of control group; for effective rate, there was no statistical difference between the two groups in the 3rd month, while in the 6th and 12th months the treatment group was superior compared with control group; the incidence rate of adverse events between the two groups was not statistically different, and no severe adverse events were observed. In conclusion, TGPC plus CGT appears effective and safe for severe alopecia areata in children.

Recent advances in the pathogenesis of autoimmune hair loss disease alopecia areata

Alopecia areata is considered to be a cell-mediated autoimmune disease, in which autoreactive cytotoxic T cells recognize melanocyte-associated proteins such as tyrosinase. This review discusses recent advances in the understanding of the pathogenesis of alopecia areata, focusing on immunobiology and hormonal aspects of hair follicles (HFs). The HF is a unique “miniorgan” with its own immune and hormonal microenvironment. The immunosuppressive milieu of the anagen hair bulb modulated by immunosuppressive factors is known as “hair follicle immune privilege.” The collapse of the hair follicle immune privilege leads to autoimmune reactions against hair follicle autoantigens. Alopecia areata is sometimes triggered by viral infections such as influenza that causes excess production of interferons (IFN). IFN-γ is one of the key factors that lead to the collapse of immune privilege. This paper reviews the interactions between the endocrine and immune systems and hair follicles in the pathogenesis of alopecia areata.

What causes alopecia areata?

The pathobiology of alopecia areata (AA), one of the most frequent autoimmune diseases and a major unsolved clinical problem, has intrigued dermatologists, hair biologists and immunologists for decades. Simultaneously, both affected patients and the physicians who take care of them are increasingly frustrated that there is still no fully satisfactory treatment. Much of this frustration results from the fact that the pathobiology of AA remains unclear, and no single AA pathogenesis concept can claim to be universally accepted. In fact, some investigators still harbour doubts whether this even is an autoimmune disease, and the relative importance of CD8(+) T cells, CD4(+) T cells and NKGD2(+) NK or NKT cells and the exact role of genetic factors in AA pathogenesis remain bones of contention. Also, is AA one disease, a spectrum of distinct disease entities or only a response pattern of normal hair follicles to immunologically mediated damage? During the past decade, substantial progress has been made in basic AA-related research, in the development of new models for translationally relevant AA research and in the identification of new therapeutic agents and targets for future AA management. This calls for a re-evaluation and public debate of currently prevalent AA pathobiology concepts. The present Controversies feature takes on this challenge, hoping to attract more skin biologists, immunologists and professional autoimmunity experts to this biologically fascinating and clinically important model disease.

Examining the relationship between alopecia areata, androgenetic alopecia, and emotional intelligence

BACKGROUND

Emotional stress has been associated with the development of alopecia areata (AA) and androgenetic alopecia (AGA). Emotional intelligence (EI), a component of general intelligence, is thought to govern the recognition, expression, and control of stress and other emotions. People with low EI are unable to adequately control stress in everyday life.

OBJECTIVE

To investigate EI differences between AA and AGA patients and a control population.

METHODS

Thirty-five AGA patients and 42 AA patients, with patchy (n  =  28), ophiasis (n  =  5), totalis (n  =  5), and universalis (n  =  4) distribution of hair loss, completed a 133-item Emotional Quotient-Inventory (EQ-I ) psychometric assessment. Scores were compared between AA, AGA, and 77 control subjects obtained from the North American normative population sample on which the psychometric instrument was normed.

RESULTS

Statistically significant differences were found in EI between AA patients and controls with the EQ-I Stress Tolerance scale (p  =  .005). AGA patients also differed significantly from the controls but to a lesser degree compared toAA patients. In overall EI, there were no apparent differences between AGA and AA patients.

CONCLUSIONS

AA and AGA patients exhibit a mild depressive reaction to their condition, with AA patients demonstrating a significantly stronger deficiency in coping with stress than AGA patients. The data support a psychosomatic contribution to AA. Referral of patients for EI assessment and psychosocial counseling could help reduce stress.

Development of autoimmune hair loss disease alopecia areata is associated with cardiac dysfunction in C3H/HeJ mice

Alopecia areata (AA) is a chronic autoimmune hair loss disease that affects several million men, women and children worldwide. Previous studies have suggested a link between autoimmunity, stress hormones, and increased cardiovascular disease risk. In the current study, histology, immunohistology, quantitative PCR (qPCR) and ELISAs were used to assess heart health in the C3H/HeJ mouse model for AA and heart tissue response to adrenocorticotropic hormone (ACTH) exposure. Mice with AA exhibited both atrial and ventricular hypertrophy, and increased collagen deposition compared to normal-haired littermates. QPCR revealed significant increases in Il18 (4.6-fold), IL18 receptor-1 (Il18r1; 2.8-fold) and IL18 binding protein (Il18bp; 5.2-fold) in AA hearts. Time course studies revealed a trend towards decreased Il18 in acute AA compared to controls while Il18r1, Il18bp and Casp1 showed similar trends to those of chronic AA affected mice. Immunohistochemistry showed localization of IL18 in chronic AA mouse atria. ELISA indicated cardiac troponin-I (cTnI) was elevated in the serum and significantly increased in AA heart tissue. Cultures of heart atria revealed differential gene expression between AA and control mice in response to ACTH. ACTH treatment induced significant increase in cTnI release into the culture medium in a dose-dependent manner for both AA and control mice. In conclusion, murine AA is associated with structural, biochemical, and gene expression changes consistent with cardiac hypertrophy in response to ACTH exposure.

Psychotrichology: psychosomatic aspects of hair diseases

Hair growth and hair disorders with changes in hair density or quality not only influence an individual's appearance but also often lead to an enormous emotional burden with low self-confidence, impaired quality of life, and even psychological disorders. Psychosomatic hair diseases cover a wide spectrum of specific psycho-dermatological disease patterns. This review provides an overview and classification of psychosomatic hair diseases based on primary and secondary disorders. Somatoform disorders are among the primary psychiatric diseases, especially body dysmorphic disorder in which patients have an exaggerated and excessive preoccupation of normal and physiological hair loss. Self-inflicted skin diseases as trichotillomania, often with an impairment of impulse control, also belong to this group. Secondary/reactive psychosocial disorders may occur in congenital and acquired hair disorders. These may be accompanied by feelings of disfigurement, depressive and anxiety disorders including social avoidance. Furthermore, psychosomatic comorbidity could complicate coping with hair loss. Psychosomatic therapy and coping are based on an early and accurate differential diagnostic approach to psychosomatic disorders. Psychotrichological disorders need to be treated promptly with psychosomatic basic care, improvement of coping strategies, behavior therapy, depth psychology, and/or appropriate psychopharmacotherapy with antidepressants or anxiolytics.

The basic science of hair biology: what are the causal mechanisms for the disordered hair follicle?

A hair disorder can be difficult to define, but patients are typically motivated to seek treatment when their hair growth patterns are significantly different from their cultural group or when growth patterns change significantly. The causes of hair disorders are many and varied, but fundamentally the disorder is a consequence of aberrant alterations of normal hair biology. The potential trigger factors for hair disorders can be attributed to inflammation, genetics, the environment, or hormones, of which the relative contributions vary for different diagnoses, between individuals, and over time. This article discusses the causal mechanisms for the disordered hair follicle.

Insulin resistance is increased in alopecia areata patients

Increased insulin resistance (IR) has been found in androgenetic alopecia in several studies. However, IR has not been investigated in alopecia areata (AA). We aimed to investigate IR in AA patients and the controls. Anthropometric and demographic data were obtained from 51 AA patients and 36 controls. We measured insulin, c-peptide and blood glucose and HOMA-IR. Demographic characteristics of the two groups were similar. AA group had higher insulin [12.5 ± 7.01 vs. 8.3 ± 3.9 µIU/mL, p = 0.001], c-peptide [2.7 ± 1.07 vs. 2. ± 0.6 ng/mL, p = 0.007] and HOMA-IR levels [2.8 ± 1.6 vs. 1.9 ± 0.9, p = .004] than the controls. Patient and control groups were also similar regarding lipid profiles. In this study, we found increased IR in AA patients for the first time in literature. Increased inflammatory cytokines and hypothalamic-pituitary-adrenal axis activation may be responsible for this finding. Further studies with larger sample sizes may give additional information for IR in AA.

Psychiatric comorbidities in patients with alopecia areata in Taiwan: a case-control study

BACKGROUND

Alopecia areata (AA) may be related to stress and has been reported to be associated with psychiatric disorders. Nevertheless, a nationwide study of the relationship between AA and comorbid psychiatric diseases has not been conducted, and the effect of onset age has rarely been reported.

OBJECTIVES

To analyse the associations between AA and various psychiatric disorders using a nationwide database in Taiwan.

METHODS

Data were obtained from the National Health Insurance Research Database of Taiwan from 2000 to 2009. In total, 5117 patients with AA and 20 468 age- and gender-matched controls were enrolled.

RESULTS

Patients with AA tended to have more coexisting anxiety and less comorbid schizophrenia. Differences in ages of onset revealed differences in comorbidities. An increased risk of depression [odds ratio (OR) 2·23; 95% confidence interval (CI) 1·09-4·54] was found in patients with AA aged < 20years. An increased rate of anxiety (OR 1·43; CI 1·15-1·77) was observed with AA onset between the ages of 20 and 39years. The highest odds of obsessive-compulsive disorder (OR 3·00; CI 1·11-8·12) and anxiety (OR 2·05; CI 1·56-2·68) were observed in patients with AA aged 40-59years. Moreover, about 50% of psychiatric disorders occurred earlier than AA.

CONCLUSIONS

AA is related to various psychiatric disorders. Onset age of AA is an important factor in the association with different comorbid psychiatric diseases. In addition to cosmetic impact, which may bring about anxiety or depression, stress neuroendocrine immunology may play an important role in the pathogenesis of both AA and psychiatric disorders.

Anti-stress effects of cilnidipine and nimodipine in immobilization subjected mice

The present study was designed to investigate the ameliorative role of cilnidipine and nimodipine in immobilization stress-induced behavioral alterations and memory defects in the mice. Acute stress was induced by immobilizing the mice for 150 min and stress-induced behavioral changes were assessed using actophotometer, hole board, open field and social interaction tests. The learning and memory was evaluated using elevated plus maze tests and biochemically, the corticosterone levels were measured in the blood serum. Acute immobilization stress resulted in decrease in locomotor activity, frequency of head dips and rearings in hole board; line crossing and rearing in the open field; increase in avoidance in social behavior along with development of memory deficits assessed by an increased transfer latency time and elevation of the corticosterone levels. Administration of cilnidipine (10 mg/kg), an L and N-type dual calcium channel blocker, and nimodipine (10 mg/kg), an L-type calcium channel blocker, significantly attenuated the immobilized stress-induced behavioral changes and restored memory deficits along with normalization of the corticosterone levels. Cilnidipine and nimodipine produced comparable beneficial effects in restoring immobilization stress subjected mice. It may be concluded that cilnidipine and nimodipine mediated attenuation of corticosterone release by blockage of calcium channels (both L and N-type) on the HPA-axis is responsible for beneficial effects in restoration of behavioral alterations and memory deficits in immobilization-induced acute stress in mice.

Etiopathogenesis of alopecia areata: Why do our patients get it?

Alopecia areata (AA) is a nonscarring, inflammatory skin disease that results in patchy hair loss. AA is unpredictable in its onset, severity, and duration making it potentially very stressful for affected individuals. Currently, the treatment options for AA are limited and the efficacy of these treatments varies from patient to patient. The exact etiology of AA is unknown. This article provides some insights into the etiopathogenesis of AA and why some people develop it. The current knowledge on the pathogenesis of AA is summarized and some of the recent hypotheses and studies on AA are presented to allow for a fuller understanding of the possible biological mechanisms of AA.