Aryl hydrocarbon receptor expression in serum, peripheral blood mononuclear cells, and skin lesions of patients with atopic dermatitis and its correlation with disease severity

Genome-wide identification of dysregulated alternative splicing and RNA-binding proteins involved in atopic dermatitis

Objectives: We explored the role and molecular mechanisms of RNA-binding proteins (RBPs) and their regulated alternative splicing events (RASEs) in the pathogenesis of atopic dermatitis (AD). Methods: We downloaded RNA-seq data (GSE121212) from 10 healthy control skin samples (healthy, Ctrl), 10 non-lesional skin samples with AD damage (non-lesional, NL), and 10 lesional skin samples with AD damage (lesional, LS). We performed the analysis of differentially expressed genes (DEGs), differentially expressed RBPs (DE-RBPs), alternative splicing (AS), functional enrichment, the co-expression of RBPs and RASEs, and quantitative polymerase chain reaction (qPCR). Results: We identified 60 DE-RBP genes by intersecting 2141 RBP genes from existing reports with overall 2697 DEGs. Most of the DE-RBP genes were found to be upregulated in the AD LS group and related to immune and apoptosis pathways. We observed different ASEs and RASEs among the healthy, AD NL, and AD LS groups. In particular, alt3p and alt5p were the main ASEs and RASEs in AD NL and AD LS groups, compared to the healthy group. Furthermore, we constructed co-expression networks of DE-RBPs and RAS, with particular enrichment in biological pathways including cytoskeleton organization, inflammation, and immunity. Subsequently, we selected seven genes that are commonly present in these three pathways to assess their expression levels in the peripheral blood mononuclear cells (PBMCs) from both healthy individuals and AD patients. The results demonstrated the upregulation of four genes (IFI16, S100A9, PKM, and ENO1) in the PBMCs of AD patients, which is highly consistent with DE-RBP genes analysis. Finally, we selected four RAS genes regulated by RBPs that were related to immune pathways and examined their RASEs in PBMCs from both AD patients and healthy controls. The results revealed an increased percentage of RASEs in the DDX60 gene in AD, which is highly consistent with AS analysis. Conclusion: Dysregulated RBPs and their associated RASEs may have a significant regulatory role in the development of AD and could be potential therapeutic targets in the future.

Benvitimod Inhibits IL-4- and IL-13-Induced Tight Junction Impairment by Activating AHR/ARNT Pathway and Inhibiting STAT6 Phosphorylation in Human Keratinocytes

Tight junctions are involved in skin barrier functions. In this study, the expression of CLDN1, CLDN4, and OCLN was found to decrease in skin lesions of atopic dermatitis by bioinformatics analysis. Immunohistochemistry staining in skin specimens from 12 patients with atopic dermatitis and 12 healthy controls also showed decreased CLDN1, CLDN4, and OCLN expression in atopic dermatitis lesions. In vitro studies showed that IL-4 and IL-13 downregulated CLDN1, CLDN4, and OCLN expression in HaCaT cells as well as CLDN4 and OCLN expression in human primary keratinocytes. This effect, which was mediated through the Jak-signal transducer and activator of transcription 6 signaling pathway, increased paracellular flux of 4-kDa dextran. Benvitimod, a new drug for atopic dermatitis, upregulated CLDN4 and OCLN through the aryl hydrocarbon receptor/aryl hydrocarbon receptor nuclear translocator pathway. Benvitimod induced nuclear translocation of NRF2 and reduced production of ROS in keratinocytes, thus inhibiting IL-4-/IL-13-induced CLDN1 downregulation and signal transducer and activator of transcription 6 phosphorylation. These results indicate that T helper 2 cytokines are involved in tight junction impairment, and benvitimod can inhibit these effects.

Aryl hydrocarbon receptor and IL-13 signaling crosstalk in human keratinocytes and atopic dermatitis

Introduction

Atopic dermatitis (AD) is an allergic skin disease mediated by skin barrier impairment and IL-13-driven immune response. Activation of the aryl hydrocarbon receptor (AHR) has shown promise in early clinical trials for AD; however, the mechanism by which AHR partially ameliorates AD is not well known.

Methods

Gene expression data from human biopsies were analyzed, and compared to gene expression from RNA-sequencing in our in-vitro HaCaT cell model system. Western blot, ELISA qRT-PCR were used to further explore the relationship between AHR and IL-13 signaling in HaCaT cells.

Results

The AHR target gene CYP1A1 was decreased in lesional skin compared with healthy control skin (p = 4.30 × 10-9). Single-cell RNA sequencing (scRNAseq) demonstrated increased AHR expression (p < 1.0 × 10-4) and decreased CYP1A1 expression in lesional AD keratinocytes compared with healthy control keratinocytes (p < 0.001). Activation of AHR by AHR agonists in HaCaT cells reversed IL-13-dependent gene expression of several key genes in AD pathogenesis, most notably the eosinophil chemoattractant CCL26 (eotaxin-3). Differentially expressed genes in keratinocytes of patients with AD substantially overlapped with genes regulated by AHR agonists from HaCaT cells by RNAseq, but in reverse direction. Mechanistically, there was evidence for direct transcriptional effects of AHR; AHR binding motifs were identified in the differentially expressed genes from lesional AD keratinocytes compared to control keratinocytes, and AHR activation did not modify IL-13-dependent signal transducer and activator of transcription 6 (STAT6) translocation to the nucleus.

Discussion

Together, these data suggest that the AHR pathway is dysregulated in AD and that AHR modulates IL-13 downstream signaling in keratinocytes through genome-wide, transcriptional regulatory effects.

Anti-PD-L1 therapy altered inflammation but not survival in a lethal murine hepatitis virus-1 pneumonia model

Introduction

Because prior immune checkpoint inhibitor (ICI) therapy in cancer patients presenting with COVID-19 may affect outcomes, we investigated the beta-coronavirus, murine hepatitis virus (MHV)-1, in a lethal pneumonia model in the absence (Study 1) or presence of prior programmed cell death ligand-1 (PD-L1) antibody (PD-L1mAb) treatment (Study 2).

Methods

In Study 1, animals were inoculated intratracheally with MHV-1 or vehicle and evaluated at day 2, 5, and 10 after infection. In Study 2, uninfected or MHV-1-infected animals were pretreated intraperitoneally with control or PD-L1-blocking antibodies (PD-L1mAb) and evaluated at day 2 and 5 after infection. Each study examined survival, physiologic and histologic parameters, viral titers, lung immunophenotypes, and mediator production.

Results

Study 1 results recapitulated the pathogenesis of COVID-19 and revealed increased cell surface expression of checkpoint molecules (PD-L1, PD-1), higher expression of the immune activation marker angiotensin converting enzyme (ACE), but reduced detection of the MHV-1 receptor CD66a on immune cells in the lung, liver, and spleen. In addition to reduced detection of PD-L1 on all immune cells assayed, PD-L1 blockade was associated with increased cell surface expression of PD-1 and ACE, decreased cell surface detection of CD66a, and improved oxygen saturation despite reduced blood glucose levels and increased signs of tissue hypoxia. In the lung, PD-L1mAb promoted S100A9 but inhibited ACE2 production concomitantly with pAKT activation and reduced FOXO1 levels. PD-L1mAb promoted interferon-γ but inhibited IL-5 and granulocyte-macrophage colony-stimulating factor (GM-CSF) production, contributing to reduced bronchoalveolar lavage levels of eosinophils and neutrophils. In the liver, PD-L1mAb increased viral clearance in association with increased macrophage and lymphocyte recruitment and liver injury. PD-L1mAb increased the production of virally induced mediators of injury, angiogenesis, and neuronal activity that may play role in COVID-19 and ICI-related neurotoxicity. PD-L1mAb did not affect survival in this murine model.

Discussion

In Study 1 and Study 2, ACE was upregulated and CD66a and ACE2 were downregulated by either MHV-1 or PD-L1mAb. CD66a is not only the MHV-1 receptor but also an identified immune checkpoint and a negative regulator of ACE. Crosstalk between CD66a and PD-L1 or ACE/ACE2 may provide insight into ICI therapies. These networks may also play role in the increased production of S100A9 and neurological mediators in response to MHV-1 and/or PD-L1mAb, which warrant further study. Overall, these findings support observational data suggesting that prior ICI treatment does not alter survival in patients presenting with COVID-19.

Unbalanced Aryl Hydrocarbon Receptor Expression in Peripheral and Lesional T Cell Subsets of Atopic Dermatitis

Background and Objective

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor, which is involved in the pathogenesis of a variety of skin diseases such as atopic dermatitis (AD). In this study, we aimed to study the AhR-expressing cells in T helper 17 (Th17), T helper 22 (Th22), regulatory T cells (Treg) and B cells in peripheral blood and in AD skin lesions.

Methods

Twenty AD patients defined according to the Chinese criteria of atopic dermatitis and eighteen healthy subjects were included in our study. The AhR-expressing Th17, Th22, Treg and total B cells in peripheral blood were measured by flow cytometry. The AhR+ Th17 cells and AhR+ Th22 cells in AD skin lesions were measured by immunofluorescence. The mRNA of AhR, interleukin (IL)-22, IL-17A, IL-10, Foxp3, RORγT and TGF-β in peripheral blood mononuclear cells (PBMCs) was measured by real-time quantitative polymerase chain reaction.

Results

The expression of AhR in peripheral CD4+ T cells, Th22 cells, Treg cells and total B cells was significantly increased in AD. AhR+IL-17A+ and AhR+IL-22+ lymphocytes were also increased in AD skin lesions. The mRNA levels of AhR, IL-22 and IL-17A in PBMCs in AD patients were significantly higher. AhR mRNA levels in PBMCs positively correlated with peripheral basophil count, peripheral eosinophil count and mRNA levels of IL-22.

Conclusion

AhR was highly expressed in subpopulations of CD4+ T cells in peripheral blood and skin lesions of AD, suggesting that AhR might contribute to the pathogenesis of AD.

Plasma aryl hydrocarbon receptor associated with epicardial adipose tissue in men: a cross-sectional study

BACKGROUND

Epicardial adipose tissue (EAT) is a type of ectopic fat with endocrine and paracrine functions. Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that responds to environmental stimuli. AhR expression is associated with obesity. In this cross-sectional study, we aimed to determine the relationship between circulating AhR concentrations and EAT.

METHODS

A total of 30 men with obesity and 23 age-matched men as healthy controls were enrolled. Plasma AhR concentrations were determined at fasting. The EAT thickness was measured on the free wall of the right ventricle from the basal short-axis plane by magnetic resonance imaging.

RESULTS

The participants with obesity had a higher plasma AhR level than the controls (81.0 ± 24.5 vs. 65.1 ± 16.4 pg/mL, P = 0.010). The plasma AhR level was positively correlated with EAT thickness (correlation coefficient = 0.380, P = 0.005). After adjusting for fasting glucose levels, plasma AhR levels were still significantly associated with EAT thickness (95% CI 0.458‒5.357, P = 0.021) but not with body mass index (P = 0.168).

CONCLUSION

Plasma AhR concentrations were positively correlated with EAT thickness on the free wall of the right ventricle in men. Further investigations are needed to evaluate the causal effects and underlying mechanisms between AhR and EAT.

Association between AHR Expression and Immune Dysregulation in Pancreatic Ductal Adenocarcinoma: Insights from Comprehensive Immune Profiling of Peripheral Blood Mononuclear Cells

Pancreatic cancer, particularly pancreatic ductal adenocarcinoma (PDAC), has an immune suppressive environment that allows tumour cells to evade the immune system. The aryl-hydrocarbon receptor (AHR) is a transcription factor that can be activated by certain exo/endo ligands, including kynurenine (KYN) and other tryptophan metabolites. Once activated, AHR regulates the expression of various genes involved in immune responses and inflammation. Previous studies have shown that AHR activation in PDAC can have both pro-tumorigenic and anti-tumorigenic effects, depending on the context. It can promote tumour growth and immune evasion by suppressing anti-tumour immune responses or induce anti-tumour effects by enhancing immune cell function. In this study involving 30 PDAC patients and 30 healthy individuals, peripheral blood samples were analysed. PDAC patients were categorized into Low (12 patients) and High/Medium (18 patients) AHR groups based on gene expression in peripheral blood mononuclear cells (PBMCs). The Low AHR group showed distinct immune characteristics, including increased levels of immune-suppressive proteins such as PDL1, as well as alterations in lymphocyte and monocyte subtypes. Functional assays demonstrated changes in phagocytosis, nitric oxide production, and the expression of cytokines IL-1, IL-6, and IL-10. These findings indicate that AHR's expression level has a crucial role in immune dysregulation in PDAC and could be a potential target for early diagnostics and personalised therapeutics.

Bacterial Metabolites and Inflammatory Skin Diseases

The microbiome and gut-skin axis are popular areas of interest in recent years concerning inflammatory skin diseases. While many bacterial species have been associated with commensalism of both the skin and gastrointestinal tract in certain disease states, less is known about specific bacterial metabolites that regulate host pathways and contribute to inflammation. Some of these metabolites include short chain fatty acids, amine, and tryptophan derivatives, and more that when dysregulated, have deleterious effects on cutaneous disease burden. This review aims to summarize the knowledge of wealth surrounding bacterial metabolites of the skin and gut and their role in immune homeostasis in inflammatory skin diseases such as atopic dermatitis, psoriasis, and hidradenitis suppurativa.

Environmental Air Pollutants Affecting Skin Functions with Systemic Implications

The increase in air pollution worldwide represents an environmental risk factor that has global implications for the health of humans worldwide. The skin of billions of people is exposed to a mixture of harmful air pollutants, which can affect its physiology and are responsible for cutaneous damage. Some polycyclic aromatic hydrocarbons are photoreactive and could be activated by ultraviolet radiation (UVR). Therefore, such UVR exposure would enhance their deleterious effects on the skin. Air pollution also affects vitamin D synthesis by reducing UVB radiation, which is essential for the production of vitamin D3, tachysterol, and lumisterol derivatives. Ambient air pollutants, photopollution, blue-light pollution, and cigarette smoke compromise cutaneous structural integrity, can interact with human skin microbiota, and trigger or exacerbate a range of skin diseases through various mechanisms. Generally, air pollution elicits an oxidative stress response on the skin that can activate the inflammatory responses. The aryl hydrocarbon receptor (AhR) can act as a sensor for small molecules such as air pollutants and plays a crucial role in responses to (photo)pollution. On the other hand, targeting AhR/Nrf2 is emerging as a novel treatment option for air pollutants that induce or exacerbate inflammatory skin diseases. Therefore, AhR with downstream regulatory pathways would represent a crucial signaling system regulating the skin phenotype in a Yin and Yang fashion defined by the chemical nature of the activating factor and the cellular and tissue context.

The role of short-chain fatty acids in inflammatory skin diseases

Short-chain fatty acids (SCFAs) are metabolites of gut microbes that can modulate the host inflammatory response, and contribute to health and homeostasis. Since the introduction of the gut-skin axis concept, the link between SCFAs and inflammatory skin diseases has attracted considerable attention. In this review, we have summarized the literature on the role of SCFAs in skin inflammation, and the correlation between SCFAs and inflammatory skin diseases, especially atopic dermatitis, urticaria, and psoriasis. Studies show that SCFAs are signaling factors in the gut-skin axis and can alleviate skin inflammation. The information presented in this review provides new insights into the molecular mechanisms driving gut-skin axis regulation, along with possible pathways that can be targeted for the treatment and prevention of inflammatory skin diseases.

Aryl Hydrocarbon Receptor/nuclear factor E2-related factor 2 (AHR/NRF2) Signaling: A Novel Therapeutic Target for Atopic Dermatitis

Aryl hydrocarbon receptor (AHR)/nuclear factor-erythroid 2-related factor 2 (NRF2) modulation are emerging as novel targets in the treatment of atopic dermatitis and other inflammatory skin disorders. Agonist activation of this pathway has downstream effects on epidermal barrier function, immunomodulation, oxidative stress reduction, and cutaneous microbiome modulation. Tapinarof, a dual agonist of the AHR/NRF2 signaling pathway, has shown promise in phase 2 trials for atopic dermatitis. In this review, we summarize current knowledge of the AHR/NRF2 pathway and implications in skin disease process. We also review the therapeutic potential of current AHR agonists and propose future directions to address knowledge gaps.

Cutaneous Effects of In Utero and Lactational Exposure of C57BL/6J Mice to 2,3,7,8-Tetrachlorodibenzo-p-dioxin

To determine the cutaneous effects of in utero and lactational exposure to the AHR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), pregnant C57BL/6J mice were exposed by gavage to a vehicle or 5 μg TCDD/kg body weight at embryonic day 12 and epidermal barrier formation and function were studied in their offspring from postnatal day 1 (P1) through adulthood. TCDD-exposed pups were born with acanthosis. This effect was AHR-dependent and subsided by P6 with no evidence of subsequent inflammatory dermatitis. The challenge of adult mice with MC903 showed similar inflammatory responses in control and treated animals, indicating no long-term immunosuppression to this chemical. Chloracne-like sebaceous gland hypoplasia and cyst formation were observed in TCDD-exposed P21 mice, with concomitant microbiome dysbiosis. These effects were reversed by P35. CYP1A1 and CYP1B1 expression in the skin was increased in the exposed mice until P21, then declined. Both CYP proteins co-localized with LRIG1-expressing progenitor cells at the infundibulum. CYP1B1 protein also co-localized with a second stem cell niche in the isthmus. These results indicate that this exposure to TCDD causes a chloracne-like effect without inflammation. Transient activation of the AhR, due to the shorter half-life of TCDD in mice, likely contributes to the reversibility of these effects.

A New Insight into the Potential Role of Tryptophan-Derived AhR Ligands in Skin Physiological and Pathological Processes

The aryl hydrocarbon receptor (AhR) plays a crucial role in environmental responses and xenobiotic metabolism, as it controls the transcription profiles of several genes in a ligand-specific and cell-type-specific manner. Various barrier tissues, including skin, display the expression of AhR. Recent studies revealed multiple roles of AhR in skin physiology and disease, including melanogenesis, inflammation and cancer. Tryptophan metabolites are distinguished among the groups of natural and synthetic AhR ligands, and these include kynurenine, kynurenic acid and 6-formylindolo[3,2-b]carbazole (FICZ). Tryptophan derivatives can affect and regulate a variety of signaling pathways. Thus, the interest in how these substances influence physiological and pathological processes in the skin is expanding rapidly. The widespread presence of these substances and potential continuous exposure of the skin to their biological effects indicate the important role of AhR and its ligands in the prevention, pathogenesis and progression of skin diseases. In this review, we summarize the current knowledge of AhR in skin physiology. Moreover, we discuss the role of AhR in skin pathological processes, including inflammatory skin diseases, pigmentation disorders and cancer. Finally, the impact of FICZ, kynurenic acid, and kynurenine on physiological and pathological processes in the skin is considered. However, the mechanisms of how AhR regulates skin function require further investigation.

A double-blind, randomized, placebo- and positive-controlled phase III trial of 1% benvitimod cream in mild-to-moderate plaque psoriasis

Background

Benvitimod cream, a novel synthetic small molecule, was effective in treating mild-to-moderate plaque psoriasis. We conducted a phase III clinical trial to assess the efficacy and safety of benvitimod cream in patients with mild-to-moderate plaque psoriasis.

Methods

We randomly assigned 686 patients (2:1:1) to receive 1% benvitimod cream, 0.005% calcipotriol ointment or placebo twice a day for 12 weeks. The primary efficacy end points were the percentage of patients with a 75% or greater reduction from baseline in the psoriasis area and severity index (PASI 75) score and with a score of 0 or 1 in static physician's global assessment (sPGA) at week 12.

Results

The results showed that 50.4% of patients in the benvitimod group achieved PASI 75, which was significantly higher than that in the calcipotriol (38.5%, P < 0.05) and placebo (13.9%, P < 0.05) groups. The proportion of patients achieving an sPGA score 0 or 1 was 66.3% in the benvitimod group and 63.9% in the calcipotriol group, which were both significantly higher than that in the placebo group (34%, P < 0.05). In the long-term follow-up study, 50.8% of patients experienced recurrence. After retreatment with 1% benvitimod, 73.3% of patients achieved an sPGA score of 0 or 1 again at week 52. Adverse events included application site irritation, follicular papules, and contact dermatitis. No systemic adverse reactions were reported.

Conclusion

During this 12-week study, benvitimod cream was demonstrated with high effectiveness and safety in patients with mild-to-moderate plaque psoriasis.

Trial Registration

Chinese Clinical Trial Registry (ChiCTR), ChiCTR-TRC-13003259; http://www.chictr.org.cn/showprojen.aspx?proj=6300.

The show must go on: an update on clinical experiences and clinical studies on novel pharmaceutical developments for the treatment of atopic dermatitis

PURPOSE OF REVIEW

This review reports on published clinical studies (full publications) with novel therapeutic agents on the treatment of atopic dermatitis with a focus on the last 2 years.

RECENT FINDINGS

Atopic dermatitis is a T-cell driven complex inflammatory skin disease. The secretion of cytokines involving not only particularly Th2 but also Th17 and Th22 cell subsets provides a broad spectrum of potential therapeutical targets. A couple of studies on atopic dermatitis with new therapeutical antibodies that target not only the Th2 cytokines IL-4, IL-13, IL- 31 but also additional targets, such as TSLP, IL-22 or IL-33, and innovative small molecules binding to the histamine-4 receptor, the phosphodiesterase-4, the aryl hydrocarbon receptor or downstream molecules like Janus kinases have recently been published with promising results on symptoms and signs of atopic dermatitis.

SUMMARY

Applications of newly developed drugs in clinical studies or already in daily practice show a substantial progress in the treatment of moderately to severely affected patients with atopic dermatitis not responsive to standard topical treatments with corticosteroids or topical calcineurin inhibitors alone. Moreover, novel treatment approaches generate new knowledge about (anti)inflammatory effects of immune modulations in atopic dermatitis and the heterogeneity of patient subgroups, which may stimulate further innovations in this field.

Single-cell transcriptomics reveals the alteration of peripheral blood mononuclear cells driven by sepsis

Background

Sepsis is a serious systemic inflammatory response syndrome caused by infection, with an extremely high mortality rate. Peripheral blood mononuclear cells (PBMCs) played a key role in the immune response against infection, whose components and functions were altered radically in Sepsis. Here, we wondered to characterize the alteration of PBMCs in sepsis at the single-cell transcriptional level.

Methods

We isolated PBMCs from seven septic patients and four donors. Based on BD Rhapsody, PBMCs were generated by single-cell RNA sequencing, and cell types were clustered and named by unsupervised clustering and annotation analysis.

Results

PBMCs were profiled for 6 kinds of cell types, the biological properties of T cell and monocytes were shown in a detailed manner. We noticed that monocytes could be clustered into 6 subsets, with great heterogeneity in the alteration of composition, gene profile, and signaling pathways driven by sepsis. Moreover, the expression of representative genes was high associated with septic clinical indicators in clusters of monocytes, such as NEAT1.

Conclusions

Although the study was preliminary, we revealed sepsis-specific alteration of PBMCs and associated pathways. These results give a panoramic picture of PBMCs in composition, genes profiles, and pathway signatures that are driven by sepsis, which offers a unique perspective to understand disease progression or treatment in clinical practice.