Insights into atopic dermatitis gained from genetically defined mouse models

Melatonin treatment increases skin microbiota-derived propionic acid to alleviate atopic dermatitis

BACKGROUND

Melatonin has been reported to relieve the inflammatory symptoms and improve sleep disturbance in patients with atopic dermatitis (AD). Recent studies showed that melatonin produced beneficial effects by remodeling intestinal microbiota composition; however, whether the beneficial effects of melatonin in AD were mediated by the modulation of skin microbiota remains unclear.

OBJECTIVE

We sought to investigate the mechanism by which melatonin treatment-induced changes in the skin microbiota composition further alleviated AD.

METHODS

The changes in skin bacterial composition after melatonin treatment were detected by 16S-rRNA sequencing. Further mechanisms were explored in calcipotriol (MC903)-induced AD mice and HaCaT cells through skin microbiota transplantation, quantification detection of short-chain fatty acids, transcriptome and single-cell sequencing analysis, quantitative RT-PCR, Western blotting, and Cell Counting Kit-8 assay.

RESULTS

We demonstrated that melatonin reshaped the skin microbiota in AD mice. The transplantation of skin microbiota from melatonin-treated mice alleviated AD symptoms in mice. Skin microbiota-derived short-chain fatty acids, especially propionic acid, were increased in the skin of melatonin-treated AD mice, which further inhibited FABP5 expression to alleviate AD. Propionic acid also inhibited FABP5 expression in HaCaT cells, which was reversed by the treatment of GPR43 inhibitor GLPG0974. GLPG0974 also blocked the therapeutic effects of melatonin on AD mice.

CONCLUSIONS

Our study demonstrated that melatonin alleviates AD through the skin microbiota/propionic acid/GPR43/FABP5 axis, highlighting a novel role of melatonin as a modulator of skin microbiota to alleviate AD.

Role of LECT2 in exacerbating atopic dermatitis: insight from in vivo and in vitro models via NF-κB signaling pathway

Leukocyte cell-derived chemotaxin 2 (LECT2) is linked to various immune diseases. Previously, we reported that serum LECT2 levels correlate with disease severity in atopic dermatitis (AD) patients. To investigate the role of LECT2 in AD and elucidate its potential mechanisms, we used LECT2 to treat an AD mouse model induced by 1-Chloro-2,4-dinitrobenzene (DNCB) in LECT2 knockout (KO) and wild-type (WT) mice, and an AD cell model using TNF-α/IFN-γ-induced HaCaT cells. Inflammatory factors and barrier proteins were analyzed by histology, immunohistochemistry, RT-qPCR, ELISA, and Western Blot. Activation of the NF-κB signaling pathway was evaluated by Western Blot and immunofluorescence. In the AD mouse model, LECT2 treatment increased epidermal and dermal thickness, mast cell infiltration, and downregulated barrier proteins. Inflammatory factors were increased in skin lesions and serum. In the AD cell model, LECT2 decreased barrier protein levels and increased inflammatory factor levels, enhancing NF-κB P65 nuclear translocation. These results indicate that LECT2 exacerbates AD-like responses by dysregulating the NF-κB signaling pathway, highlighting its potential as a therapeutic target for AD management.

Exploring causal correlations between circulating cytokines and atopic dermatitis: a bidirectional two-sample Mendelian randomization study

Objectives

Numerous observational studies have reported associations between circulating cytokines and atopic dermatitis (AD); however, the causal relationships between them remain unclear. To explore the causal correlations and direction of causal effects between AD and levels of 91 circulating cytokines.

Methods

Two-sample Mendelian randomization (MR) analyses were conducted to examine the causal relationships between 91 circulating cytokines and AD using summary statistics from genome-wide association studies (GWAS). Reverse MR analyses were performed to investigate reverse causation. Pleiotropy and heterogeneity tests were conducted to assess the robustness of the findings. Additional transcriptome database and clinical peripheral blood mononuclear cells (PBMCs) samples were utilized to validate the results of MR analyses.

Results

Levels of interleukin (IL)-13, IL-18 Receptor 1, Tumor necrosis factor ligand superfamily member 14 (TNFSF14), TNF-related activation-induced cytokine (TRANCE), C-X-C motif chemokine (CXCL)11, IL-33, TNF-beta and CD5 were suggestively associated with the risk of AD (odds ratio, OR: 1.202, 95% CI: 1.018-1.422, p = 0.030; OR: 1.029, 95% CI: 1.029-1.157, p = 0.004; OR: 1.159, 95% CI: 1.018-1.320, p = 0.026; OR: 1.111, 95% CI: 1.016-1.214, p = 0.020; OR: 0.878, 95% CI: 0.783-0.984, p = 0.025; OR: 0.809, 95% CI: 0.661-0.991, p = 0.041; OR: 0.945, 95% CI: 0.896-0.997, p = 0.038; OR: 0.764, 95% CI: 0.652-0.895, p = 8.26e-04). In addition, levels of cytokines including Axin-1, CXCL5, CXCL10, Oncostatin-M (OSM), Sulfotransferase 1A1 (SULT1A1) and TNFSF14 were suggested to be consequences of AD (Beta: -0.080, p = 0.016; Beta: -0.062, p = 0.036; Beta: -0.066, p = 0.049; Beta: -0.073, p = 0.013; Beta: -0.089, p = 0.008; Beta: -0.079, p = 0.031). IL-13, IL-18R1, TNFSF14, and TRANCE were upregulated in both lesional skin biopsies and PBMCs from AD patients.

Conclusion

The study indicates that several cytokines, including IL-13, IL-18R1, TNFSF14, TRANCE, CXCL11, IL-33, TNF-beta, and CD5, are upstream of AD development, whereas a few circulating cytokines are potentially downstream in the development of AD.

Effect of Isoscopoletin on Cytokine Expression in HaCaT Keratinocytes and RBL-2H3 Basophils: Preliminary Study

Isoscopoletin is a compound derived from various plants traditionally used for the treatment of skin diseases. However, there have been no reported therapeutic effects of isoscopoletin on atopic dermatitis (AD). AD is a chronic inflammatory skin disease, and commonly used treatments have side effects; thus, there is a need to identify potential natural candidate substances. In this study, we aimed to investigate whether isoscopoletin regulates the inflammatory mediators associated with AD in TNF-α/IFN-γ-treated HaCaT cells and PMA/ionomycin treated RBL-2H3 cells. We determined the influence of isoscopoletin on cell viability through an MTT assay and investigated the production of inflammatory mediators using ELISA and RT-qPCR. Moreover, we analyzed the transcription factors that regulate inflammatory mediators using Western blots and ICC. The results showed that isoscopoletin did not affect cell viability below 40 μM in either HaCaT or RBL-2H3 cells. Isoscopoletin suppressed the production of TARC/CCL17, MDC/CCL22, MCP-1/CCL2, IL-8/CXCL8, and IL-1β in TNF-α/IFN-γ-treated HaCaT cells and IL-4 in PMA/ionomycin-treated RBL-2H3 cells. Furthermore, in TNF-α/IFN-γ-treated HaCaT cells, the phosphorylation of signaling pathways, including MAPK, NF-κB, STAT, and AKT/PKB, increased but was decreased by isoscopoletin. In PMA/ionomycin-treated RBL-2H3 cells, the activation of signaling pathways including PKC, MAPK, and AP-1 increased but was decreased by isoscopoletin. In summary, isoscopoletin reduced the production of inflammatory mediators by regulating upstream transcription factors in TNF-α/IFN-γ-treated HaCaT cells and PMA/ionomycin-treated RBL-2H3 cells. Therefore, we suggest that isoscopoletin has the potential for a therapeutic effect, particularly in skin inflammatory diseases such as AD, by targeting keratinocytes and basophils.

The Role of the Microbiota in the Pathogenesis and Treatment of Atopic Dermatitis-A Literature Review

Atopic dermatitis (AD) is a chronic inflammatory skin condition with a high prevalence worldwide. AD pathogenesis is complex and consists of immune system dysregulation and impaired skin barrier, influenced by genetic and environmental factors. The purpose of the review is to show the complex interplay between atopic dermatitis and the microbiota. Human microbiota plays an important role in AD pathogenesis and the course of the disease. Dysbiosis is an important factor contributing to the development of atopic diseases, including atopic dermatitis. The gut microbiota can influence the composition of the skin microbiota, strengthening the skin barrier and regulating the immune response via the involvement of bacterial metabolites, particularly short-chain fatty acids, in signaling pathways of the gut-skin axis. AD can be modulated by antibiotic intake, dietary adjustments, hygiene, and living conditions. One of the promising strategies for modulating the course of AD is probiotics. This review offers a summary of how the microbiota influences the development and treatment of AD, highlighting aspects that warrant additional investigation.

Exogenous drug-induced mouse models of atopic dermatitis

Atopic dermatitis (AD) is an inflammatory skin disease characterized by intense pruritus. AD is harmful to both children and adults, but its pathogenic mechanism has yet to be fully elucidated. The development of mouse models for AD has greatly contributed to its study and treatment. Among these models, the exogenous drug-induced mouse model has shown promising results and significant advantages. Until now, a large amount of AD-related research has utilized exogenous drug-induced mouse models, leading to notable advancements in research. This indicates the crucial significance of applying such models in AD research. These models exhibit diverse characteristics and are highly complex. They involve the use of various strains of mice, diverse types of inducers, and different modeling effects. However, there is currently a lack of comprehensive comparative studies on exogenous drug-induced AD mouse models, which hinders researchers' ability to choose among these models. This paper provides a comprehensive review of the features and mechanisms associated with various exogenous drug-induced mouse models, including the important role of each cytokine in AD development. It aims to assist researchers in quickly understanding models and selecting the most suitable one for further investigation.

Recent Advances in Phytochemical-Based Topical Applications for the Management of Eczema: A Review

Eczema (atopic dermatitis, AD) is a skin disease characterized by skin barrier dysfunction due to various factors, including genetics, immune system abnormalities, and environmental triggers. Application of emollients and topical drugs such as corticosteroids and calcineurin inhibitors form the mainstay of treatments for this challenging condition. This review aims to summarize the recent advances made in phytochemical-based topical applications to treat AD and the different carriers that are being used. In this review, the clinical efficacy of several plant extracts and bioactive phytochemical compounds in treating AD are discussed. The anti-atopic effects of the herbs are evident through improvements in the Scoring Atopic Dermatitis (SCORAD) index, reduced epidermal thickness, decreased transepidermal water loss, and alleviated itching and dryness in individuals affected by AD as well as in AD mouse models. Histopathological studies and serum analyses conducted in AD mouse models demonstrated a reduction in key inflammatory factors, including thymic stromal lymphopoietin (TSLP), serum immunoglobulin E (IgE), and interleukins (IL). Additionally, there was an observed upregulation of the filaggrin (FLG) gene, which regulates the proteins constituting the stratum corneum, the outermost layer of the epidermis. Carriers play a crucial role in topical drug applications, influencing dose delivery, retention, and bioavailability. This discussion delves into the efficacy of various nanocarriers, including liposomes, ethosomes, nanoemulsions, micelles, nanocrystals, solid-lipid nanoparticles, and polymeric nanoparticles. Consequently, the potential long-term side effects such as atrophy, eruptions, lymphoma, pain, and allergic reactions that are associated with current topical treatments, including emollients, topical corticosteroids, topical calcineurin inhibitors, and crisaborole, can potentially be mitigated through the use of phytochemical-based natural topical treatments.

N-benzyl-N-methyldecan-1-amine, derived from garlic, and its derivative alleviate 2,4-dinitrochlorobenzene-induced atopic dermatitis-like skin lesions in mice

Given the intricate etiology and pathogenesis of atopic dermatitis (AD), the complete cure of AD remains challenging. This study aimed to investigate if topically applying N-benzyl-N-methyldecan-1-amine (BMDA), derived from garlic, and its derivative [decyl-(4-methoxy-benzyl)-methyl-1-amine] (DMMA) could effectively alleviate AD-like skin lesions in 2,4-dinitrochlorobenzene (DNCB)-treated mice. Administering these compounds to the irritated skin of DNCB-treated mice significantly reduced swelling, rash, and excoriation severity, alongside a corresponding decrease in inflamed epidermis and dermis. Moreover, they inhibited spleen and lymph node enlargement and showed fewer infiltrated mast cells in the epidermis and dermis through toluidine-blue staining. Additionally, they led to a lower IgE titer in mouse sera as determined by ELISA, compared to vehicle treatment. Analyzing skin tissue from the mice revealed decreased transcript levels of inflammatory cytokines (TNF-α, IL-1β, and IL-6), IL-4, iNOS, and COX-2, compared to control mice. Simultaneously, the compounds impeded the activation of inflammation-related signaling molecules such as JNK, p38 MAPK, and NF-κB in the mouse skin. In summary, these findings suggest that BMDA and DMMA hold the potential to be developed as a novel treatment for healing inflammatory AD.

Establishment of an experimental model of ovalbumin-induced atopic dermatitis in canines

Introduction

A reliable standard model is required to evaluate the efficacy of new drugs for companion animals, especially dogs. Canine atopic dermatitis (cAD), also known as allergic inflammatory skin disease, is a common condition. Currently, the house dust mite animal model is used in the research of cAD; however, this model exhibits significant individual variation and is difficult to standardize. In this study, we used ovalbumin as an antigen to sensitize and stimulate dogs, thereby establishing a stable model mimicking the T-helper 2 (Th2) response seen in cAD. Our objective was to create a cAD model that could be employed to evaluate the efficacy of novel drugs and mimic the Th2 dominant allergic response observed in the pathogenesis of atopic dermatitis of dogs.

Methods

In this study, six beagles were used. Normal saline was applied to two animals, and ovalbumin to four, on their dorsal skin.

Results

The ovalbumin-treated groups exhibited clinical cAD symptoms, such as pruritus and erythema. Moreover, plasma levels of the cAD markers immunoglobulin E and CCL17 chemokine were higher in the ovalbumin-treated group than in the vehicle control group. The skin thickness of the epidermis was significantly increased in the ovalbumin-treated group, with infiltration of inflammatory cells observed in the thickened dermis region. In conclusion, treatment of canine skin with an optimal concentration of ovalbumin induced typical cAD-like symptoms, and histological and molecular analyses confirmed an enhanced Th2-related immune response.

Conclusion

Therefore, we successfully established a suitable Th2-dominant response mimicking cAD, which will facilitate targeted research of atopic dermatitis in dogs.

Regulatory T cells in allergic inflammation

Regulatory T (Treg) cells maintain immune tolerance to allergens at the environmental interfaces in the airways, skin and gut, marshalling in the process distinct immune regulatory circuits operative in the respective tissues. Treg cells are coordinately mobilized with allergic effector mechanisms in the context of a tissue-protective allergic inflammatory response against parasites, toxins and potentially harmful allergens, serving to both limit the inflammation and promote local tissue repair. Allergic diseases are associated with subverted Treg cell responses whereby a chronic allergic inflammatory environment can skew Treg cells toward pathogenic phenotypes that both perpetuate and aggravate disease. Interruption of Treg cell subversion in chronic allergic inflammatory conditions may thus provide novel therapeutic strategies by re-establishing effective immune regulation.

Atopic dermatitis: a brief review of recent advances in its management

Atopic dermatitis (AD) is a common inflammatory skin disorder characterized by recurrent eczematous lesions and intense itching. The disorder affects people of all ages and ethnicities, has a substantial psychosocial impact on patients and relatives, and is the leading cause of the global burden of skin diseases. Atopic dermatitis is associated with an increased risk of multiple comorbidities, including food allergies, asthma, allergic rhinitis, and mental health disorders. The pathophysiology is complex and involves a strong genetic predisposition, epidermal dysfunction, and T-cell-driven inflammation. Although type-2 mechanisms are dominant, there is increasing evidence that the disorder involves multiple immune pathways. Until recently, the management of AD rested mainly on the judicious use of emollients, topical steroids, and topical calcineurin inhibitors in the majority of patients, and systemic immunosuppressants were advocated in severely diseased patients. However, in the last few years, new therapeutic strategies have been designed and developed to target the various steps in the chain of molecular events that lead to the AD phenotype. This review highlights the recent advancements in the management of AD.

An inflammation-responsive double-layer microneedle patch for recurrent atopic dermatitis therapy

Seeking a potent therapeutic strategy for alleviating atopic dermatitis (AD) attack and preventing its recurrence is highly desired but remains challenging in clinical practice. Here, we propose an inflammation-responsive double-layer microneedle (IDMN) patch in situ delivering VD3 for recurrent AD therapy. IDMN comprises the backing layer part and the double-layer microneedle part, in which the inner layer is gelatin methacryloyl (GelMA) loaded with VD3 while the outer layer is composed of hyaluronic acid (HA). Introduction of the HA backing layer and outer layer around the GelMA tips can not only provide sufficient mechanical strength to penetrate into hardened AD skin with minimal invasiveness, but also exert a strong moisturizing effect after being rapidly dissolved. The inner layer of GelMA is degraded by the matrix metalloproteinase (MMP) in a dose dependent manner, which is secreted according to the disease progression of AD. The responsive degradation of GelMA tips result in corresponding release of VD3 to treat AD, triggering negative feedback against GelMA degradation. The IDMN administration on AD-bearing mice reveals efficient "curing" performances (including suppress erythema, scaling and lichenification, reduce epidermal thickness, inhibit mast cells infiltration, and down-regulate inflammatory factor secretion), which are basically realized through synergistic effect of the released VD3 and the dissolved HA molecules. Importantly, the residual tips of IDMN with VD3 are retained in the skin after the first AD relief, showing promising "warning" ability to inhibit the recurrence of AD. Hence, the developed IDMN patch is expected to be one of the excellent candidates for AD therapy and other relapsing diseases in clinical fields.

Mast cells in type 2 skin inflammation: Maintenance and function

Mast cells (MCs) are immune cells residing in tissues and playing indispensable roles in maintaining homeostasis and inflammatory states. Skin lesions associated with atopic dermatitis (AD) and type 2 skin inflammation display an increment in MCs, which have both pro- and anti-inflammatory effects. The direct and indirect activations of skin MCs by environmental factors such as Staphylococcus aureus can instigate type 2 skin inflammation in AD with poorly understood mechanisms. Furthermore, both IgE-dependent and -independent degranulation of MCs contribute to pruritus in AD. Conversely, MCs suppress type 2 skin inflammation by promoting Treg expansion through IL-2 secretion in the spleen. Moreover, skin MCs can upregulate gene expression involved in skin barrier function, thus mitigating AD-like inflammation. These functional variances of MCs in AD could stem from differences in experimental systems, their localization, and origins. In this review, we will focus on how MCs are maintained in the skin under homeostatic and inflammatory conditions, and how they are involved in the pathogenesis of type 2 skin inflammation.

Delayed type hypersensitivity reactions to various allergens may differently model inflammatory skin diseases

BACKGROUND

Treatment of inflammatory skin diseases, including atopic dermatitis (AD) and psoriasis, is undergoing transformative changes, highlighting the need to develop experimental models of skin inflammation in humans to predict treatment responses.

METHODS

We topically or intradermally administered four common sensitizers (dust mite (DM), diphencyprone (DPCP), nickel (Ni), and purified protein derivative (PPD)) to the backs of 40 healthy patients and the skin hypersensitivity response was biopsied and evaluated using immunohistochemistry, RNA-seq, and RT-PCR.

RESULTS

All agents induced strong increases in cellular infiltrates (T-cells and dendritic cells) as compared to untreated skin (p < .05), with variable T helper polarization. Overall, DPCP induced the strongest immune responses across all pathways, including innate immunity (IL-1α, IL-8), Th1 (IFNγ, CXCL10), Th2 (IL-5, CCL11), and Th17 (CAMP/LL37) products, as well as the highest regulatory tone (FOXP3, IL-34, IL-37) (FDR <0.01). Nickel induced Th17 (IL-17A), Th1 (CXCL10) and Th2 (IL-4R) immune responses to a lesser extent than DPCP (p < .05). PPD induced predominantly Th1 (IFNγ, CXCL10, STAT1) and Th17 inflammation (IL-17A) (p < .05). DM induced modulation of Th2 (IL-13, CCL17, CCL18), Th22 (IL-22), and Th17/Th22 (S100A7/9/12) pathways (p < .05). Barrier defects that characterize both AD and psoriasis were best modeled by DPCP and Ni, followed by PPD, including downregulation of terminal differentiation (FLG, FLG2, LOR, LCEs), tight junction (CLDN1/CLDN8), and lipid metabolism (FA2H, FABP7)-related markers.

CONCLUSION

Our data imply that DPCP induced the strongest immune response across all pathways, and barrier defects characteristic of AD and psoriasis.

Succinate and mitochondrial DNA trigger atopic march from atopic dermatitis to intestinal inflammation

BACKGROUND

Atopic march has long been recognized as the progression from atopic dermatitis (AD) to food allergy and asthma during infancy and childhood. However, effective blocking is hampered by the lack of specific biomarkers.

OBJECTIVES

We aimed to investigate the pathologic progression of atopic march trajectories from skin to gut.

METHODS

We built an atopic march mouse model by mechanical skin injury and percutaneous sensitization to peanut allergen. Anaphylaxis from the skin to the small intestine was then investigated by ELISA, RNA sequencing, quantitative real-time PCR, histopathologic analysis, and flow cytometry. The findings from the mice results were also verified by the serum samples of allergic pediatric patients.

RESULTS

After modeling, inflammation in the skin and small intestine manifested as a mixed type of T_H2 and T_H17. Further analysis identified elevated succinate in the circulation and expanded tuft cells with upregulated IL-25 in the small intestine, resulting in increased intestinal type 2 innate lymphoid cells and an enhanced type 2 inflammatory response. In addition, free mitochondrial DNA (mtDNA) released after tissue damage was also involved in inflammation march from injured skin to small intestine through the STING pathway. Analysis of clinical samples verified that serum concentrations of succinate and mtDNA were higher in AD allergic children than non-AD allergic children.

CONCLUSIONS

Succinate and mtDNA play key roles in skin-to-gut cross talk during the atopic march from AD to food allergy, and can be considered as biomarkers for risk assessment or targets for atopic march prevention strategies.

Combined application of dinitrofluorobenzene and ovalbumin induced AD-like dermatitis with an increase in helper T-cell cytokines and a prolonged Th2 response

BACKGROUND

The progression of acute-to-chronic atopic dermatitis is accompanied by multiple helper T-cell cytokine responses, but the mechanisms and relative importance of these changes remain unclear. There is no animal model for atopic dermatitis that recapitulates these cytokine responses.

OBJECTIVE

We sought to build a novel mouse model for atopic dermatitis (AD) that recapitulates these helper T-cell responses and some dynamic changes in cytokine responses in the progression of AD.

METHODS

Female BALB/c mice were subjected to the application of dinitrofluorobenzene (DNFB) and ovalbumin (OVA) to induce AD-like dermatitis. Skin lesions and serum were collected from mice in the acute and chronic phases to detect changes in cytokine responses and other features of AD.

RESULTS

Combined application of DNFB and OVA successfully induced AD-like dermatitis and histological changes as well as epidermal barrier dysfunction. In the acute phase of AD-like dermatitis, Th2-associated cytokines were mainly increased in serum and skin lesions. In the chronic phase of AD-like dermatitis, Th2-associated cytokines were still highly expressed, while Th1- and Th17-associated cytokines were also gradually increased. Compared with the acute phase, the JAK-STAT signaling pathway was highly expressed in the chronic phase of AD-like dermatitis.

CONCLUSION

The combined application of DNFB and OVA could be used to build a new mouse model for atopic dermatitis. This mouse model recapitulates the helper T-cell responses and some dynamic changes in cytokine responses in the progression of acute-to-chronic in human AD. The JAK-STAT signaling pathway plays a pivotal role in the chronicity of AD.

Microbiota-Independent Spontaneous Dermatitis Associated With Increased Sebaceous Lipid Production in Tmem79-Deficient Mice

TMEM79 is a predisposing gene for atopic dermatitis (AD). Tmem79-deficient mice develop spontaneous dermatitis in a biphasic pattern. The 1^st-phase dermatitis is unique, as it occurs independent of microbiota status, whereas the 2^nd-phase dermatitis is microbiota-dependent. In this study, we sought to identify key factors mediating the development of 1^st-phase dermatitis. Structural analysis showed that sebaceous gland hyperplasia started from 1^st-phase dermatitis. Longitudinal RNA-sequencing analysis revealed significant activation of fatty acid lipid-metabolism pathways in 1^st-phase dermatitis, whereas Th17-based immune response genes were highly expressed in 2^nd-phase dermatitis. Quantitative reverse transcription-polymerase chain reaction analysis revealed that genes involved in fatty acid elongation and sebocyte differentiation were upregulated in 1^st-phase dermatitis. The results of thin-layer chromatography supported these findings with an increased abundance of wax esters, cholesterol esters, and fatty alcohols in hair lipids. Further gas chromatography-tandem mass spectrometry analysis showed an increase in total fatty acid production, including that of elongated C20-24 saturated and C18-24 mono-unsaturated fatty acids. Collectively, these results suggest that aberrant production of sebaceous long-chain fatty acids is associated with microbiota-independent dermatitis. Further investigation of Tmem79-deficient mice may clarify the role of certain fatty acids in dermatitis.

An Atopic Dermatitis-Like Mouse Model by Alternate Epicutaneous Application of Dinitrofluorobenzene and an Extract of Dermatophagoides Farinae

Several studies have tried to establish mice models of atopic dermatitis (AD) through the allergen of Dermatophagoides farinae (Df). However, there are no typical skin lesions after epicutaneous application of an extract of Df (DfE) on BALB/c mice. Dinitrofluorobenzene (DNFB) is a common hapten that brings about contact dermatitis. Skin dysfunction induced by DNFB may be a way to enhance the effects of DfE on mice skin. Thus, we hypothesized that alternate epicutaneous application of DNFB and DfE could induce AD-like skin lesions on BALB/c mice. To test this hypothesis, we alternately applied the DNFB and DfE to the back skin of BALB/c mice for 8 weeks. Changes in mice skin lesions and the frequency of scratching behavior were recorded. The variation of Th1-related cytokines (interferon-γ [IFN-γ] and interleukin two [IL-2]) and Th2-related cytokines (IL-4 and IL-13) was detected in serum and lesional skin. Eventually, the BALB/c mice developed severe erythema, erosion, scarring, and excoriation on the entire back, showing a high frequency of scratching behavior. In addition, Th2 cells' dominant cytokines appeared in both serum and lesional skin. Those results indicate that alternating epicutaneous exposure to DNFB and DfE can produce AD-like models with typical clinical features and Th2-type immune responses in BALB/c mice. This model could be valuable for studying the pathogenesis of AD and developing novel therapeutic agents for it.

Narrative review on the management of moderate-severe atopic dermatitis in pediatric age of the Italian Society of Pediatric Allergology and Immunology (SIAIP), of the Italian Society of Pediatric Dermatology (SIDerP) and of the Italian Society of Pediatrics (SIP)

Currently, there are a few detailed guidelines on the overall management of children and adolescents with moderate-severe atopic dermatitis. AD ​​is a complex disease presenting with different clinical phenotypes, which require an individualized and multidisciplinary approach. Therefore, appropriate interaction between primary care pediatricians, pediatric allergists, and pediatric dermatologists is crucial to finding the best management strategy. In this manuscript, members of the Italian Society of Pediatric Allergology and Immunology (SIAIP), the Italian Society of Pediatric Dermatology (SIDerP), and the Italian Society of Pediatrics (SIP) with expertise in the management of moderate-severe atopic dermatitis have reviewed the latest scientific evidence in the field. This narrative review aims to define a pathway to appropriately managing children and adolescents with moderate-severe atopic dermatitis.

IL-33 Enhances ACE2 Expression on Epidermal Keratinocytes in Atopic Dermatitis: A Plausible Issue for SARS-CoV-2 Transmission in Inflamed Atopic Skin

Background: Interleukin-33 (IL-33) is an important cytokine in the pathophysiology of atopic dermatitis (AD) and in the progression of COVID-19. Angiotensin converting enzyme 2 (ACE2), the entry receptor for SARS-CoV-2, is expressed in epidermal keratinocytes. Whether IL-33 could regulate the expression of ACE2 mechanistically in keratinocytes warrants investigation. Objective: We questioned whether the ACE2 expression is increased in AD skin. We also questioned whether ACE2 is expressed in keratinocytes; if so, would its expression be enhanced mechanistically by IL-33. Methods: We measured and compared the expression of ACE2 in skin from patients with AD, patients with psoriasis, and healthy controls using immunohistochemistry. Flow cytometry, immunofluorescent exam, and quantitative RT-PCR were used for measuring the ACE2 expression in cultured keratinocytes treated with IL-33 and IL-17. Blocking antibodies were utilized to study the intracellular signaling pathways governing the ACE2 expression using cytokines. Results: The results showed that the ACE2 expression is increased in AD compared with that in healthy skin and psoriasis. In primary epidermal keratinocytes, ACE2 is constitutively expressed. IL-33 induces a time-dependent increase in ACE2 expression in cultured keratinocytes through quantitative PCR, flow cytometry, and immunofluorescent examinations. Furthermore, pretreatment of an ERK inhibitor, but not a STAT3 inhibitor, eliminated the increases in ACE2 by IL-33 in keratinocytes, indicating that IL-33 enhances ACE2 expression through ERK on epidermal keratinocytes. Conclusion: This is the first study to reveal that IL-33 enhances ACE2 expression on keratinocytes via ERK. Although further mechanistic studies are required, the increased ACE2 expression in IL-33 might have a biological implication on the transmission of SARS-CoV-2 in patients with AD.

Adipose-derived stem cells ameliorate atopic dermatitis by suppressing the IL-17 expression of Th17 cells in an ovalbumin-induced mouse model

Background

Mesenchymal stem cells (MSCs) have therapeutic potential for atopic dermatitis (AD) owing to their immunoregulatory effects. However, the underlying mechanisms associated with the therapeutic efficacy of MSCs on AD are diverse and related to both cell type and delivery method.

Objectives

This study investigated the therapeutic effect and mechanisms of adipose-derived stem cells (ADSCs) on AD using an ovalbumin (OVA)-induced AD mouse model.

Methods

AD mice were subcutaneously injected with mouse ADSCs, cortisone, or PBS, and the therapeutic effects were determined by gross and histological examinations and serum IgE levels. Additionally, qPCR, RNA-sequencing analyses of skin samples and co-culture of ADSCs and Th17 cells were conducted to explore the underlying therapeutic mechanisms.

Results

ADSCs treatment attenuated the AD pathology, decreased the serum IgE levels, and decreased mast cells infiltration in the skin of the model mice. Moreover, tissue levels of IL-4R and Th17-relevant products (IL-17A, CCL20, and MMP12) were suppressed in the ADSC- and cortisone-treated groups. Genomics and bioinformatics analyses demonstrated significant enrichment of inflammation-related pathways in the downregulated genes of the ADSC- and cortisone-treated groups, specifically the IL-17 signaling pathway. Co-culture experiments revealed that ADSCs significantly suppressed the proliferation of Th17 cells and the expression of proinflammatory cytokines (IL-17A and RORγT). Furthermore, expression levels of PD-L1, TGF-β, and PGE2 were significantly upregulated in co-cultured ADSCs relative to those in monocultured ADSCs.

Conclusion

ADSCs ameliorate OVA-induced AD in mice mainly by downregulating IL-17 secretion of Th17 cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02774-7.

Dendritic cell immunoreceptor drives atopic dermatitis by modulating oxidized CaMKII-involved mast cell activation

Allergens have been identified as potential triggers in patients with atopic dermatitis (AD). AD patients are highly sensitive to cockroach allergen. The underlying mechanism, however, remains undetermined. Here, we established a cockroach allergen-induced AD-like mouse model and demonstrated that repeated exposure to cockroach allergen led to aggravated mouse skin inflammation, characterized by increased type 2 immunity, type 2 innate lymphoid cells (ILC2s), and mast cells. Increased skin mast cells were also observed in AD patients. AD mice with mast cell-deficient mice (kitW-sh/W-sh) showed diminished skin inflammation, suggesting that mast cells are required in allergen-induced skin inflammation. Furthermore, dendritic cell immuno-receptor (DCIR) is up-regulated in skin mast cells of AD patients and mediates allergen binding and uptake. DCIR-/- mice or reconstituted kitW-sh/W-sh mice with DCIR-/- mast cells showed a significant reduction in AD-like inflammation. Both in vitro and in vivo analyses demonstrated that DCIR-/- mast cells had reduced IgE-mediated mast cell activation and passive cutaneous anaphylaxis. Mechanistically, DCIR regulates allergen-induced IgE-mediated mast cell ROS generation and oxidation of calmodulin kinase II (ox-CaMKII). ROS-resistant CaMKII (MM-VVδ) prevents allergen-induced mast cell activation and inflammatory mediator release. Our study reveals a previously unrecognized DCIR-ROS-CaMKII axis that controls allergen-induced mast cell activation and AD-like inflammation.

A Comprehensive Review of Therapeutic Approaches Available for the Treatment of Dermatitis

BACKGROUND

Dermatitis or eczema is a prevalent skin disorder worldwide and is also very common as a pediatric inflammatory skin disorder. Its succession gets worse with the multiple comorbidities which exhibit mechanisms that are poorly understood. Its management further becomes a challenge due to the limited effective treatment options available. However, the Novel Drug Delivery Systems (NDDS) along with new targeting strategies can easily bypass the issues associated with dermatitis management. If we compare the active constituents against phytoconstituents effective against dermatitis then phytoconstituents can be perceived to be more safe and gentle.

OBJECTIVE

Administration of NDDS of plant extract or actives displays improved absorption behavior, which helps them to permeate through lipid-rich biological membrane leading to increased bioavailability. The newer efficient discoveries related to eczema can face various exploitations. This can be intervened by the subjection of patent rights, which not only safeguard the novel works of individual(s) but also give them the opportunity to share details of their inventions with people globally.

CONCLUSION

The present review focuses on the available research about the use of nanoformulations in the topical delivery. It further elaborates the use of different animal models as the basis to characterize the different features of dermatitis. The review also highlights the recent nanoformulations which have the ability to amplify the delivery of active agents through their incorporation in transfersomes, ethosomes, niosomes or phytosomes, etc.

Hsa_circ_0004287 inhibits macrophage-mediated inflammation in an N6-methyladenosine-dependent manner in atopic dermatitis and psoriasis

BACKGROUND

Circular RNA (circRNA) was reported to involve in various diseases; however, its role in atopic dermatitis (AD) or psoriasis remains unclear.background Objective: We sought to determine the differential expression profiles of circRNAs in peripheral blood mononuclear cells (PBMCs) between healthy controls and AD patients, and explore the mechanisms underlying the effects of circRNAs on the pathogenesis of AD.

METHODS

The differential expression profiles of circRNAs were analyzed by circRNA microarray. In vitro function and mechanisms by which circRNAs regulate macrophage-mediated inflammation were detected by RT-qPCR, western blotting, RNA stability assay, immunoprecipitation, enzyme-linked immunosorbent assay (ELISA), and methylated RNA immunoprecipitation (MeRIP) assay. In vivo roles of circRNAs were determined in 2,4-dinitrochlorobenzene (DNCB)-induced dermatitis and imiquimod (IMQ)-induced psoriasis mouse model.

RESULTS

We identified a functional unknown circRNA hsa_circ_0004287 from 88750 circRNAs, which was upregulated in PBMCs of both AD and psoriasis patients, and mainly expressed by macrophages under inflammatory conditions. hsa_circ_0004287 inhibited M1 macrophage activation in vitro, and macrophage-specific overexpression of hsa_circ_0004287 alleviated skin inflammation in both AD- and psoriasis-like mice. Mechanistically, hsa_circ_0004287 reduced the stability of its host gene metastasis associated lung adenocarcinoma transcript 1 (MALAT1) by competitively binding to IGF2BP3 with MALAT1 in an N6-methyladenosine (m6A)-dependent manner. Lower levels of MALAT1 promoted the ubiquitination degradation of S100A8/S100A9, thereby impeding p38/MAPK phosphorylation and macrophage-mediated inflammation.results CONCLUSION: Hsa_circ_0004287 inhibits M1 macrophage activation in an m6A-dependent manner in AD and psoriasis, and may serve as a general therapeutic candidate for AD and psoriasis.

CONCLUSION

Advances in ameliorating inflammatory diseases and cancers by andrographolide: Pharmacokinetics, pharmacodynamics, and perspective

Andrographolide, a well-known natural lactone having a range of pharmacological actions in traditional Chinese medicine. It has long been used to cure a variety of ailments. In this review, we cover the pharmacokinetics and pharmacological activity of andrographolide which supports its further clinical application in cancers and inflammatory diseases. Growing evidence shows a good therapeutic effect in inflammatory diseases, including liver diseases, joint diseases, respiratory system diseases, nervous system diseases, heart diseases, inflammatory bowel diseases, and inflammatory skin diseases. As a result, the effects of andrographolide on immune cells and the processes that underpin them are discussed. The preclinical use of andrographolide to different organs in response to malignancies such as colorectal, liver, gastric, breast, prostate, lung, and oral cancers has also been reviewed. In addition, several clinical trials of andrographolide in inflammatory diseases and cancers have been summarized. This review highlights recent advances in ameliorating inflammatory diseases as well as cancers by andrographolide and its analogs, providing a new perspective for subsequent research of this traditional natural product.

Optimization of the extraction process of high levels of chlorogenic acid and ginsenosides from short-term hydroponic-cultured ginseng and evaluation of the extract for the prevention of atopic dermatitis

Background

Short-term hydroponic-cultured ginseng (sHCG), which is 1-year-old ginseng seedlings cultivated for 4 weeks in a hydroponic system, is a functional food item with several biological effects. However, the optimal extraction conditions for sHCG, and the bioactivity of its extracts, have not been evaluated.

Methods

Chlorogenic acid (CGA) and ginsenoside contents were evaluated in sHCG, white ginseng (WG), and red ginseng (RG) using high-performance liquid chromatography. Response surface methodology (RSM) was used to optimize the extraction conditions (temperature and ethanol concentration) to maximize the yield of dry matter, CGA, and four ginsenosides (Re, Rg₁, Rb₁, and Rd) from sHCG. The optimal extraction conditions were applied to pilot-scale production of sHCG extracts. The expression levels of tumor necrosis factor (TNF)-α/interferon (IFN)-γ-induced thymic and activation-regulated chemokines (TARC/CCL17) were measured after treatment with sHCG, WG, and RG extracts, and the effects of their bioactive compounds (CGA and four ginsenosides) on human skin keratinocytes (HaCaTs) were evaluated.

Results

CGA and four ginsenosides, which are bioactive compounds of sHCG, significantly inhibited TNF-α/IFN-γ-induced TARC/CCL17 expression. The optimal sHCG extraction conditions predicted by the RSM models were 80 °C and 60% ethanol (v/v). The sHCG extracts produced at the pilot scale under optimal conditions greatly alleviated TNF-α/IFN-γ-induced TARC/CCL17 production compared with WG and RG extracts.

Conclusions

Pesticide-free sHCG extracts, which contain high levels of CGA and the ginsenosides Re, Rg₁, Rb₁, and Rd as bioactive compounds, may have therapeutic potential for atopic diseases.

Advances in Atopic Dermatitis in 2019-2020: Endotypes from skin barrier, ethnicity, properties of antigen, cytokine profiles, microbiome, and engagement of immune cells

Key research advances in atopic dermatitis (AD) suggest the complexity of its endotypes. A comprehensive serum biomarker panel revealed at least four types of AD. Some represent classic TH2-dominant AD with filaggrin mutations commonly reported in Europeans, a simultaneously activated multipolar axes of cytokines often reported in Asians, and an intrinsic type characterized by TH2-inferiority. Innate lymphoid cells, including NK cells, NKT cells, and fibroblasts, play a role in AD development and heterogeneity. Here, we discuss the endotypes of AD from the perspective of antigen types (hapten vs. protein antigens), barrier function, and a novel set of immune cells. Endotypic stratification of AD may lead to the development of customized therapeutic strategies in the future.

Autophagy in skin barrier and immune-related skin diseases

Autophagy is a process which is highly conserved in eukaryotes to degrade or recycle cytoplasmic components through lysosomes to maintain cellular homeostasis. Recent studies have shown that autophagy also plays critical roles in cell apoptosis, inflammation, pathogen clearance, and so on under stressed conditions and thereby has been linked to a variety of human disorders. The skin is the largest organ of the body and serves as the first line of defense against environmental insult. Skin as a nutrient-poor environment requires recycling of limited resources via the autophagy machinery to maintain homeostasis. Therefore, dysregulation of autophagy has been linked to skin diseases. In this review, we describe the molecular machinery and regulation of autophagy, discuss its role in keratinocytes and skin barrier, skin immune cells, and immune-related skin diseases including autoimmune skin disorders, allergic skin diseases, infectious skin disorders, and antitumor immunity against skin tumor. Finally, we highlight the potential of autophagy as a therapeutic target for immune-related skin diseases, and delivery of autophagy-related molecules (such as inducers, inhibitors, or nucleic acid molecules) by virtue of physical materials (such as nanoparticles) or biological materials (such as peptides) to skin topically may obtain clinical benefits in immune-related skin diseases. Moreover, developing autophagy-related gene product-based biomarkers may be promising to diagnose immune-related skin diseases.

Lithospermum erythrorhizon Alleviates Atopic Dermatitis-like Skin Lesions by Restoring Immune Balance and Skin Barrier Function in 2.4-Dinitrochlorobenzene-Induced NC/Nga Mice

The incidence of atopic dermatitis (AD), a disease characterized by an abnormal immune balance and skin barrier function, has increased rapidly in developed countries. This study investigated the anti-atopic effect of Lithospermum erythrorhizon (LE) using NC/Nga mice induced by 2,4-dinitrochlorobenzene. LE reduced AD clinical symptoms, including inflammatory cell infiltration, epidermal thickness, ear thickness, and scratching behavior, in the mice. Additionally, LE reduced serum IgE and histamine levels, and restored the T helper (Th) 1/Th2 immune balance through regulation of the IgG1/IgG2a ratio. LE also reduced the levels of AD-related cytokines and chemokines, including interleukin (IL)-1β, IL-4, IL-6, tumor necrosis factor-α (TNF-α), thymic stromal lymphopoietin, thymus and activation-regulated chemokine, macrophage-derived chemokine, regulated on activation, normal T cell expressed and secreted, and monocyte chemoattractant protein-1 in the serum. Moreover, LE modulated AD-related cytokines and chemokines expressed and secreted by Th1, Th2, Th17, and Th22 cells in the dorsal skin and splenocytes. Furthermore, LE restored skin barrier function by increasing pro-filaggrin gene expression and levels of skin barrier-related proteins filaggrin, involucrin, loricrin, occludin, and zonula occludens-1. These results suggest that LE is a potential therapeutic agent that can alleviate AD by modulating Th1/Th2 immune balance and restoring skin barrier function.

Current Insights into Immunology and Novel Therapeutics of Atopic Dermatitis

Atopic dermatitis (AD) is one of the most prevalent inflammatory disease among non-fatal skin diseases, affecting up to one fifth of the population in developed countries. AD is characterized by recurrent pruritic and localized eczema with seasonal fluctuations. AD initializes the phenomenon of atopic march, during which infant AD patients are predisposed to progressive secondary allergies such as allergic rhinitis, asthma, and food allergies. The pathophysiology of AD is complex; onset of the disease is caused by several factors, including strong genetic predisposition, disrupted epidermal barrier, and immune dysregulation. AD was initially characterized by defects in the innate immune system and a vigorous skewed adaptive Th2 response to environmental agents; there are compelling evidences that the disorder involves multiple immune pathways. Symptomatic palliative treatment is the only strategy to manage the disease and restore skin integrity. Researchers are trying to more precisely define the contribution of different AD genotypes and elucidate the role of various immune axes. In this review, we have summarized the current knowledge about the roles of innate and adaptive immune responsive cells in AD. In addition, current and novel treatment strategies for the management of AD are comprehensively described, including some ongoing clinical trials and promising therapeutic agents. This information will provide an asset towards identifying personalized targets for better therapeutic outcomes.

Effects of Deacetylasperulosidic Acid on Atopic Dermatitis through Modulating Immune Balance and Skin Barrier Function in HaCaT, HMC-1, and EOL-1 Cells

The medicinal plant noni (Morinda citrifolia) is widely dispersed throughout Southeast Asia, the Caribbean, and Australia. We previously reported that fermented Noni could alleviate atopic dermatitis (AD) by recovering Th1/Th2 immune balance and enhancing skin barrier function induced by 2,4-dinitrochlorobenzene. Noni has a high deacetylasperulosidic acid (DAA) content, whose concentration further increased in fermented noni as an iridoid constituent. This study aimed to determine the anti-AD effects and mechanisms of DAA on HaCaT, HMC-1, and EOL-1 cells. DAA inhibited the gene expression and secretion of AD-related cytokines and chemokines including interleukin (IL)-1β, IL-4, IL-6, IL-8, IL-25, IL-33, thymic stromal lymphopoietin, tumor necrosis factor-alpha, monocyte chemoattractant protein-1, thymus and activation-regulated chemokine, macrophage-derived chemokine, and regulated upon activation, normal T cell expressed and secreted, in all cells, and inhibited histamine release in HMC-1 cells. DAA controlled mitogen-activated protein kinase phosphorylation levels and the translocation of nuclear factor-kappa light chain enhancer of activated B cells into the nucleus by inhibiting IκBα decomposition in all the cells. Furthermore, DAA increased the expression of proteins involved in skin barrier functions such as filaggrin and involucrin in HaCaT cells. These results confirmed that DAA could relieve AD by controlling immune balance and recovering skin barrier function.

Daily Lifestyle and Inflammatory Skin Diseases

Throughout life, it is necessary to adapt to the Earth’s environment in order to survive. A typical example of this is that the daily Earth cycle is different from the circadian rhythm in human beings; however, the ability to adapt to the Earth cycle has contributed to the development of human evolution. In addition, humans can consume and digest Earth-derived foods and use luxury materials for nutrition and enrichment of their lives, as an adaptation to the Earth’s environment. Recent studies have shown that daily lifestyles are closely related to human health; however, less attention has been paid to the fact that obesity due to excessive energy intake, smoking, and alcohol consumption contributes to the development of inflammatory skin diseases. Gluten or wheat protein, smoking and alcohol, sleep disturbance, and obesity drive the helper T (Th)1/Th2/Th17 immune response, whereas dietary fiber and omega-3 fatty acids negatively regulate inflammatory cytokine production. In this review, we have focused on daily lifestyles and the mechanisms involved in the pathogenesis of inflammatory skin diseases.

Sequestosome 1/p62 enhances chronic skin inflammation

BACKGROUND

The molecular control of inflammation and epidermal thickening in skin lesions of patients with atopic dermatitis (AD) is not known. Sequestosome 1/p62 is a multifunctional adapter protein implicated in the control of key regulators of cellular homeostasis, such as proinflammatory and mechanistic target of rapamycin signaling.

OBJECTIVE

We sought to determine whether p62 plays a role in the cutaneous and systemic manifestations of an AD-like mouse model.

METHODS

AD-like skin lesions were induced by deletion of JunB/AP-1, specifically in epidermal keratinocytes (JunB^Δep). The contribution of p62 to pathological changes was determined by inactivation of p62 in JunB^Δepp62^-/- double knockout mice.

RESULTS

Expression of p62 was elevated in skin lesions of JunB^Δep mice, resembling upregulation of p62 in AD and psoriasis. When p62 was inactivated, JunB^Δep-associated defects in the differentiation of keratinocytes, epidermal thickening, skin infiltration by mast cells and neutrophils, and the development of macroscopic skin lesions were significantly reduced. p62 inactivation had little effect on circulating cytokines, but decreased serum IgE. Signaling through mechanistic target of rapamycin and natural factor kappa B was increased in JunB^Δep but not in JunB^Δepp62^-/- double knockout skin, indicating an important role of p62 in enhancing these signaling pathways in the skin during AD-like inflammation.

CONCLUSIONS

Our results provide the first in vivo evidence for a proinflammatory role of p62 in skin and suggest that p62-dependent signaling pathways may be promising therapeutic targets to ameliorate the skin manifestations of AD and possibly psoriasis.

Translational Relevance of Mouse Models of Atopic Dermatitis

The complexity of atopic dermatitis (AD) continues to present a challenge in the appropriate selection of a mouse model because no single murine model completely recapitulates all aspects of human AD. This has been further complicated by recent evidence of the distinct AD endotypes that are dictated by unique patterns of inflammation involving Th1, Th2, Th17, and Th22 axes. A review of currently used mouse models demonstrates that while all AD mouse models consistently exhibit Th2 inflammation, only some demonstrate concomitant Th17 and/or Th22 induction. As the current understanding of the pathogenic contributions of these unique endotypes and their potential therapeutic roles expands, ongoing efforts to maximize a given mouse model’s homology with human AD necessitates a close evaluation of its distinct immunological signature.

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.

Which Way Do We Go? Complex Interactions in Atopic Dermatitis Pathogenesis

Atopic dermatitis (AD) is a common, chronic, inflammatory skin condition characterized by recurrent and pruritic skin eruptions. Multiple factors contribute to the pathogenesis of AD, including skin barrier dysfunction, microbial dysbiosis, and immune dysregulation. Interactions among these factors form a complex, multidirectional network that can reinforce atopic skin disease but can also be ameliorated by targeted therapies. This review summarizes the complex interactions among contributing factors in AD and the implications on disease development and therapeutic interventions.

Type 2 immunity in the skin and lungs

There has been extensive progress in understanding the cellular and molecular mechanisms of inflammation and immune regulation in allergic diseases of the skin and lungs during the last few years. Asthma and atopic dermatitis (AD) are typical diseases of type 2 immune responses. interleukin (IL)-25, IL-33, and thymic stromal lymphopoietin are essential cytokines of epithelial cells that are activated by allergens, pollutants, viruses, bacteria, and toxins that derive type 2 responses. Th2 cells and innate lymphoid cells (ILC) produce and secrete type 2 cytokines such as IL-4, IL-5, IL-9, and IL-13. IL-4 and IL-13 activate B cells to class-switch to IgE and also play a role in T-cell and eosinophil migration to allergic inflammatory tissues. IL-13 contributes to maturation, activation, nitric oxide production and differentiation of epithelia, production of mucus as well as smooth muscle contraction, and extracellular matrix generation. IL-4 and IL-13 open tight junction barrier and cause barrier leakiness in the skin and lungs. IL-5 acts on activation, recruitment, and survival of eosinophils. IL-9 contributes to general allergic phenotype by enhancing all of the aspects, such as IgE and eosinophilia. Type 2 ILC contribute to inflammation in AD and asthma by enhancing the activity of Th2 cells, eosinophils, and their cytokines. Currently, five biologics are licensed to suppress type 2 inflammation via IgE, IL-5 and its receptor, and IL-4 receptor alpha. Some patients with severe atopic disease have little evidence of type 2 hyperactivity and do not respond to biologics which target this pathway. Studies in responder and nonresponder patients demonstrate the complexity of these diseases. In addition, primary immune deficiency diseases related to T-cell maturation, regulatory T-cell development, and T-cell signaling, such as Omenn syndrome, severe combined immune deficiencies, immunodysregulation, polyendocrinopathy, enteropathy, X-linked syndrome, and DOCK8, STAT3, and CARD11 deficiencies, help in our understanding of the importance and redundancy of various type 2 immune components. The present review aims to highlight recent advances in type 2 immunity and discuss the cellular sources, targets, and roles of type 2 mechanisms in asthma and AD.

Protective role of Galectin-7 for skin barrier impairment in atopic dermatitis

Background

Atopic dermatitis (AD) patients have a barrier disorder in association with Th2 dominant skin inflammation. Galectin‐7 (Gal‐7), a soluble unglycosylated lectin, is highly expressed in the stratum corneum of AD patients. However, the biological significance of increased Gal‐7 expression in AD skin lesions remains unclear.

Objective

We aimed to investigate the production mechanism and functional role of Gal‐7 in AD patients and IL‐4/IL‐13–stimulated epidermal keratinocytes.

Methods

We assessed the Gal‐7 expression levels in skin lesions and sera from AD patients. Gal‐7 levels were also measured in monolayered normal human epidermal keratinocytes (NHEKs) and 3‐dimensional (3D)–reconstructed epidermis in the presence or absence of IL‐4/IL‐13 with or without Stat3, Stat6 or Gal‐7 gene silencing.

Results

Gal‐7 was highly expressed in the stratum corneum or intercellular space of AD lesional epidermis as assessed by the stratum corneum proteome analysis and immunohistochemistry. A positive correlation was noted between serum Gal‐7 level and transepidermal water loss in patients with AD. These clinical findings were corroborated by our in vitro data, which showed that IL‐4/IL‐13 facilitated the extracellular release of endogenous Gal‐7 in both monolayered NHEKs and 3D‐reconstructed epidermis. This machinery was caused by IL‐4/IL‐13–induced cell damage and inhibited by knockdown of Stat6 but not Stat3 in NHEKs. Moreover, we performed Gal‐7 knockdown experiment on 3D‐reconstructed epidermis and the result suggested that endogenous Gal‐7 serves as a protector from IL‐4/IL‐13–induced disruption of cell‐to‐cell adhesion and/or cell‐to‐extracellular matrix adhesion.

Conclusion and Clinical Relevance

Our study unveils the characteristic of Gal‐7 and its possible role as an alarmin that reflects the IL‐4/IL‐13–induced skin barrier impairment in AD.

Circadian Regulation of the Biology of Allergic Disease: Clock Disruption Can Promote Allergy

Allergic diseases such as allergic rhinitis, asthma, atopic dermatitis, and food allergy are characterized by epithelial barrier dysfunction and deregulated immune responses. Components of the circadian clock interact with critical elements of epithelial barrier function and immune responses, and regulate the biological processes on a 24-h cycle at steady state. This may represent an anticipatory defense response to day-night fluctuation of attack by noxious stimuli such as pathogens in the environment. This review will summarize clock control of epithelial barrier function and immune responses associated with allergic disease and offer novel insights and opportunities into how clock dysfunction impacts allergic disease. Importantly, perturbation of normal clock activity by genetic and environmental disturbances, such as chronic light cycle perturbations or irregular eating habits, deregulates epithelial barrier function and immune responses. This implies that the circadian clock is strongly linked to the fundamental biology of allergic disease, and that clock disruption can precipitate allergic disease by altering the epithelial barrier and immune functions. Given that contemporary lifestyles often involve chronic circadian disruptions such as shift work, we propose that lifestyle or therapeutic interventions that align the endogenous circadian clock with environmental cycles should be a part of the efforts to prevent or treat allergic disease in modern society.

ILC2s and Basophils Team Up to Orchestrate IL-33-Induced Atopic Dermatitis

In this issue, Imai et al. (2019) provide new insights into the pathophysiology of AD-like inflammation using their model (Imai et al., 2013) and ask how ILC2s and basophils contribute to the IL-33-induced AD-like inflammation. Their findings show that continuous expression of IL-33 in keratinocytes is sufficient to cause AD-like inflammation in mice, and that this occurrence is largely independent of adaptive immune cells and is mediated by basophils and ILC2s.

Anti-Inflammatory Effects of Alnus Sibirica Extract on In Vitro and In Vivo Models

Alnus sibirica extracts (ASex) have long been used in Oriental medicine to treat various conditions. To provide a scientific basis for this application and the underlying mechanism, we investigated the anti-inflammatory effects of ASex in vitro and in vivo. The in vitro model was established using human dermal fibroblasts (HDFs) treated with inflammatory stimulants (lipopolysaccharide, tumor necrosis factor-alpha, interferon-gamma). Lactate dehydrogenase and reverse transcription-polymerase chain reaction showed that ASex inhibited the increased expression of acute-phase inflammatory cytokines. The in vivo model was established by inducing skin inflammation in NC/Nga mice via the repeated application of house dust mite (HDM) ointment to the ears and back of the mice for eight weeks. HDM application increased the severity of skin lesions, eosinophil/mast cell infiltration, and serum immunoglobulin E levels, which were all significantly decreased by ASex treatment, demonstrating the same degree of protection as hydrocortisone. Overall, ASex showed excellent anti-inflammatory effects both in vitro and in vivo, suggesting its potential as an excellent candidate drug to reduce skin inflammation.

Tight junctions in the development of asthma, chronic rhinosinusitis, atopic dermatitis, eosinophilic esophagitis, and inflammatory bowel diseases

This review focuses on recent developments related to asthma, chronic rhinosinusitis, atopic dermatitis (AD), eosinophilic esophagitis, and inflammatory bowel diseases (IBD), with a particular focus on tight junctions (TJs) and their role in the pathogenetic mechanisms of these diseases. Lung, skin, and intestinal surfaces are lined by epithelial cells that interact with environmental factors and immune cells. Therefore, together with the cellular immune system, the epithelium performs a pivotal role as the first line physical barrier against external antigens. Paracellular space is almost exclusively sealed by TJs and is maintained by complex protein-protein interactions. Thus, TJ dysfunction increases paracellular permeability, resulting in enhanced flux across TJs. Epithelial TJ dysfunction also causes immune cell activation and contributes to the pathogenesis of chronic lung, skin, and intestinal inflammation. Characterization of TJ protein alteration is one of the key factors for enhancing our understanding of allergic diseases as well as IBDs. Furthermore, TJ-based epithelial disturbance can promote immune cell behaviors, such as those in dendritic cells, Th2 cells, Th17 cells, and innate lymphoid cells (ILCs), thereby offering new insights into TJ-based targets. The purpose of this review is to illustrate how TJ dysfunction can lead to the disruption of the immune homeostasis in barrier tissues and subsequent inflammation. This review also highlights the various TJ barrier dysfunctions across different organ sites, which would help to develop future drugs to target allergic diseases and IBD.

Fermented Morinda citrifolia (Noni) Alleviates DNCB-Induced Atopic Dermatitis in NC/Nga Mice through Modulating Immune Balance and Skin Barrier Function

Morinda citrifolia, a fruit generally known as "Noni", has been traditionally used in parts of East Asia to relieve inflammatory diseases. Although several studies using noni have been reported, the effect of fermented Morinda citrifolia (F.NONI) on atopic dermatitis (AD) has not been investigated. Thus, we aimed to investigate the improving effect of F.NONI treatment on AD-like skin lesions and elucidate molecular mechanisms. F.NONI was prepared by the fermentation of noni fruit with probiotics and then extracted. F.NONI was orally administrated to NC/Nga mice to evaluate its therapeutic effect on 2,4-dinitrochlorobenzene (DNCB)-induced AD. Oral administration of F.NONI significantly alleviated AD lesions and symptoms such as dermatitis scores, ear thickness, scratching behavior, epidermal thickness, and infiltration of inflammatory cells (e.g., mast cells and eosinophils). In addition, F.NONI treatment reduced the levels of histamine, IgE and IgG1/IgG2a ratio, thymus and activation regulated chemokine (TARC), and thymic stromal lymphopoietin (TSLP) in serum and beneficially modulated the expressions of Th1, Th2, Th17, and Th22-mediated cytokines in lesioned skin and splenocytes. Furthermore, the expressions of the skin barrier-related proteins including filaggrin (FLG), loricrin (LOR), involucrin (IVL), zonula occludens-1 (ZO-1), and occludin (OCC) were restored by F.NONI treatment. Taken together, these results suggest that F.NONI could be a therapeutic agent to attenuate AD-like skin lesions through modulating the immune balance and skin barrier function.

Anti-Atopic Effect of Acorn Shell Extract on Atopic Dermatitis-Like Lesions in Mice and Its Active Phytochemicals

To investigate the potential effects of acorn shells on atopic dermatitis (AD), we utilized oxazolone (OX)- or 2,4-dinitrochlorobenzene (DNCB)-induced AD-like lesion mouse models. Our research demonstrates that Acorn shell extract (ASE) improved the progression of AD-like lesions, including swelling, which were induced by oxazolone on Balb/c mouse ears. Additionally, ASE significantly decreased the ear thickness (OX: 0.42 ± 0.01 mm, OX-ASE: 0.32 ± 0.02 mm) and epidermal thickness (OX: 75.3 ± 32.6 µm, OX-ASE: 46.1 ± 13.4 µm). The continuous DNCB-induced AD mouse model in SKH-1 hairless mice demonstrated that ASE improved AD-like symptoms, including the recovery of skin barrier dysfunction, Immunoglobulin E hyperproduction (DNCB: 340.1 ± 66.8 ng/mL, DNCB-ASE: 234.8 ± 32.9 ng/mL) and an increase in epidermal thickness (DNCB: 96.4 ± 21.9 µm, DNCB-ASE: 52.4 ± 16.3 µm). In addition, we found that ASE suppressed the levels of AD-involved cytokines, such as Tumor Necrosis Factor α, IL-1β, IL-25 and IL-33 in both animal models. Furthermore, gallic acid and ellagic acid isolated from ASE suppressed β-hexosaminidase release and IL-4 expression in RBL-2H3 cells. The acorn shell and its active phytochemicals have potential as a new remedy for the improvement of atopic dermatitis and other inflammatory diseases.

Interleukin-33 in atopic dermatitis

Atopic dermatitis (AD) is characterized by pruritus, barrier disruption, and inflammationincluding type 2 cytokine production. Interleukin-33 (IL-33) is an inflammatory cytokine that is over-expressed in the keratinocytes of patients with AD. IL-33 transgenic mice, which express IL-33 specifically in keratinocytes, spontaneously develop AD-like eczema, suggesting that IL-33 is sufficient for the development of AD. IL-33 stimulates various cells, including group 2 innate lymphoid cells (ILC2s), to produce type 2 cytokines, such as IL-5 and IL-13, and IL-33-stimulated basophils activate ILC2s via IL-4. ILC2s are enriched in human AD skin lesions, and ILC2 isolated from AD lesions, are activated by IL-33, not by thymic stromal lymphopoietin (TSLP). IL-33 induces IL-31, thereby promoting pruritus and scratching behavior. Conversely, scratching the skin promotes IL-33 release from keratinocytes. IL-33 reduces the expression of filaggrin and claudin-1; it also reduces the skin barrier function. However, barrier destruction causes percutaneous exposure to allergens or IL-33 release. Thus, IL-33 is a common point of entry into the itch-scratch cycle of AD. These new findings can facilitate the development of novel therapeutic drugs targeting IL-33.

Development of a new eczema-like reconstructed skin equivalent for testing child atopic dermatitis-relieving cosmetics

OBJECTIVE

Atopic dermatitis (AD) is the most common chronic inflammatory skin disease, and it has serious effects on children's and families' quality of life. We aimed to screen and evaluate the efficacy of different formulas on relieving of atopic dermatitis clinical symptoms by developing an eczema-like reconstructed human skin equivalent in vitro.

METHOD

Some research has reported that thymic stromal lymphopoietin (TSLP) may be a potential therapeutic target for the treatment of AD. We developed an eczema-like in vitro skin equivalent by coculturing the cocktails polyinosinic-polycytidylic acid sodium salt (poly(I:C)) and lipopolysaccharides (LPS). The eczema-like skin equivalent was characterized by overexpression of TSLP and impaired skin barrier function. Three cosmetic formulas with the potential of anti-inflammation and skin barrier promotion were topically applied onto the eczema-like skin equivalent, mimicking in vivo application. The inhibitory effect on TSLP was examined by ELISA. Effects on tissue viability and skin barrier function were determined by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) method.

CONCLUSION

The results show that eczema-like skin equivalent induced by cocktails of poly(I:C) and LPS can mimic the skin characters of the atopic dermatitis. The cocktails can induce high TSLP expression, impaired cell viability, and skin barrier function. The cosmetic formulas with the potential of anti-inflammation and skin barrier promotion were evaluated to be helpful to decrease and relieve the impact of AD with the decreased TSLP and the higher tissue viability than the eczema-like skin equivalent without any cosmetic application. The eczema-like skin equivalent can be used to screen and evaluate formulas on AD relieving.