Activation of the aryl hydrocarbon receptor dampens the severity of inflammatory skin conditions

GWAS meta-analysis of psoriasis identifies new susceptibility alleles impacting disease mechanisms and therapeutic targets

Psoriasis is a common, debilitating immune-mediated skin disease. Genetic studies have identified biological mechanisms of psoriasis risk, including those targeted by effective therapies. However, the genetic liability to psoriasis is not fully explained by variation at robustly identified risk loci. To move towards a saturation map of psoriasis susceptibility we meta-analysed 18 GWAS comprising 36,466 cases and 458,078 controls and identified 109 distinct psoriasis susceptibility loci, including 45 that have not been previously reported. These include susceptibility variants at loci in which the therapeutic targets IL17RA and AHR are encoded, and deleterious coding variants supporting potential new drug targets (including in STAP2, CPVL and POU2F3). We conducted a transcriptome-wide association study to identify regulatory effects of psoriasis susceptibility variants and cross-referenced these against single cell expression profiles in psoriasis-affected skin, highlighting roles for the transcriptional regulation of haematopoietic cell development and epigenetic modulation of interferon signalling in psoriasis pathobiology.

Ligand Activation of the Aryl Hydrocarbon Receptor Upregulates Epidermal Uridine Diphosphate Glucose Ceramide Glucosyltransferase and Glucosylceramides

Ligand activation of the aryl hydrocarbon receptor (AHR) accelerates keratinocyte differentiation and the formation of the epidermal permeability barrier. Several classes of lipids, including ceramides, are critical to the epidermal permeability barrier. In normal human epidermal keratinocytes, the AHR ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin, increased RNA levels of ceramide metabolism and transport genes: uridine diphosphate glucose ceramide glucosyltransferase (UGCG), ABCA12, GBA1, and SMPD1. Levels of abundant skin ceramides were also increased by 2,3,7,8-tetrachlorodibenzo-p-dioxin. These included the metabolites synthesized by UGCG, glucosylceramides, and acyl glucosylceramides. Chromatin immunoprecipitation-sequence analysis and luciferase reporter assays identified UGCG as a direct AHR target. The AHR antagonist, GNF351, inhibited the 2,3,7,8-tetrachlorodibenzo-p-dioxin-mediated RNA and transcriptional increases. Tapinarof, an AHR ligand approved for the treatment of psoriasis, increased UGCG RNA, protein, and its lipid metabolites hexosylceramides as well as increased the RNA expression of ABCA12, GBA1, and SMPD1. In Ahr-null mice, Ugcg RNA and hexosylceramides were lower than those in the wild type. These results indicate that the AHR regulates the expression of UGCG, a ceramide-metabolizing enzyme required for ceramide trafficking, keratinocyte differentiation, and epidermal permeability barrier formation.

Dynamic relationship between the aryl hydrocarbon receptor and long noncoding RNA balances cellular and toxicological responses

The aryl hydrocarbon receptor (AhR) is a cytosolic transcription factor activated by endogenous ligands and xenobiotic chemicals. Once the AhR is activated, it translocates to the nucleus, dimerizes with the AhR nuclear translator (ARNT) and binds to xenobiotic response elements (XRE) to promote gene transcription, notably the cytochrome P450 CYP1A1. The AhR not only mediates the toxic effects of environmental chemicals, but also has numerous putative physiological functions. This dichotomy in AhR biology may be related to reciprocal regulation of long non-coding RNA (lncRNA). lncRNA are defined as transcripts more than 200 nucleotides in length that do not encode a protein but are implicated in many physiological processes such as cell differentiation, cell proliferation, and apoptosis. lncRNA are also linked to disease pathogenesis, particularly the development of cancer. Recent studies have revealed that AhR activation by environmental chemicals affects the expression and function of lncRNA. In this article, we provide an overview of AhR signaling pathways activated by diverse ligands and highlight key differences in the putative biological versus toxicological response of AhR activation. We also detail the functions of lncRNA and provide current data on their regulation by the AhR. Finally, we outline how overlap in function between AhR and lncRNA may be one way in which AhR can be both a regulator of endogenous functions but also a mediator of toxicological responses to environmental chemicals. Overall, more research is still needed to fully understand the dynamic interplay between the AhR and lncRNA.

Impact of Gut Bacterial Metabolites on Psoriasis and Psoriatic Arthritis: Current Status and Future Perspectives

There is growing evidence that supports a role of gut dysbiosis in the pathogenesis of psoriasis (Pso). Thus, probiotic supplementation and fecal microbiota transplantation may serve as promising preventive and therapeutic strategies for patients with Pso. One of the basic mechanisms through which the gut microbiota interacts with the host is through bacteria-derived metabolites, usually intermediate or end products produced by microbial metabolism. In this study, we provide an up-to-date review of the most recent literature on microbial-derived metabolites and highlight their roles in the immune system, with a special focus on Pso and one of its most common comorbidities, psoriatic arthritis.

IL17A Blockade with Ixekizumab Suppresses MuvB Signaling in Clinical Psoriasis

Unbiased informatics approaches have the potential to generate insights into uncharacterized signaling pathways in human disease. In this study, we generated longitudinal transcriptomic profiles of plaque psoriasis lesions from patients enrolled in a clinical trial of the anti-IL17A antibody ixekizumab (IXE). This dataset was then computed against a curated matrix of over 700 million data points derived from published psoriasis and signaling node perturbation transcriptomic and chromatin immunoprecipitation-sequencing datasets. We observed substantive enrichment within both psoriasis-induced and IXE-repressed gene sets of transcriptional targets of members of the MuvB complex, a master regulator of the mitotic cell cycle. These gene sets were similarly enriched for pathways involved in the regulation of the G2/M transition of the cell cycle. Moreover, transcriptional targets for MuvB nodes were strongly enriched within IXE-repressed genes whose expression levels correlated strongly with the extent and severity of the psoriatic disease. In models of human keratinocyte proliferation, genes encoding MuvB nodes were transcriptionally repressed by IXE, and depletion of MuvB nodes reduced cell proliferation. Finally, we made the expression and regulatory networks that supported this study available as a freely accessible, cloud-based hypothesis generation platform. Our study positions inhibition of MuvB signaling as an important determinant of the therapeutic impact of IXE in psoriasis.

Unleashing nature's potential and limitations: Exploring molecular targeted pathways and safe alternatives for the treatment of multiple sclerosis (Review)

Driven by the limitations and obstacles of the available approaches and medications for multiple sclerosis (MS) that still cannot treat the disease, but only aid in accelerating the recovery from its attacks, the use of naturally occurring molecules as a potentially safe and effective treatment for MS is being explored in model organisms. MS is a devastating disease involving the brain and spinal cord, and its symptoms vary widely. Multiple molecular pathways are involved in the pathogenesis of the disease. The present review showcases the recent advancements in harnessing nature's resources to combat MS. By deciphering the molecular pathways involved in the pathogenesis of the disease, a wealth of potential therapeutic agents is uncovered that may revolutionize the treatment of MS. Thus, a new hope can be envisioned in the future, aiming at paving the way toward identifying novel safe alternatives to improve the lives of patients with MS.

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.

Successful secukinumab therapy in plaque psoriasis is associated with altered gut microbiota and related functional changes

Introduction

The role of gut microbiome dysbiosis in the pathogenesis of psoriasis has gained increasing attention in recent years. Secukinumab, targeting interleukin (IL)-17, has a promising efficacy in psoriasis treatment. However, it remains unclear the gut microbiota alteration and related functional changes caused by successful secukinumab therapy in psoriatic patients.

Methods

In our study, we compared the fecal microbiome profile between psoriatic patients after secukinumab successful treatment (AT) and the other two groups, psoriatic patients without therapy (BT) and healthy people (H), respectively, by using next-generation sequencing targeting 16S ribosomal RNA. Then, shotgun metagenomic sequencing was first used to characterize bacterial gut microbial communities and related functional changes in the AT group.

Results

We found that the diversity and structure of the microbial community in the AT group were significantly changed compared to those in the BT group and the H group. The AT group showed a microbiota profile characterized by increased proportions of the phylum Firmicute, families Ruminococcaceae, and a reduction in the phylum Bacteroidota (elevated F/B ratio). To detect functional alteration, we discovered that secukinumab treatment may construct a more stable homeostasis of the gut microbiome with functional alteration. There were different KEGG pathways, such as the downregulated cardiovascular diseases pathway and the upregulated infectious diseases in the AT group. By metagenomic analysis, the metabolic functional pathway was changed after secukinumab therapy.

Discussion

It seems that gut microbiota investigation during biologic drug treatment is useful for predicting the efficacy and risks of drug treatment in disease.

Manuka honey activates the aryl hydrocarbon receptor: Implications for skin inflammation

Manuka honey (MH) is a complex nutritional material with antimicrobial, antioxidant and anti-inflammatory activity. We have previously shown that MH down regulates IL-4-induced CCL26 expression in immortalized keratinocytes. As MH contains potential ligands of the Aryl Hydrocarbon Receptor (AHR), a key regulator of skin homeostasis, we hypothesize that this effect is mediated via AHR activation. Here, we treated HaCaT cell lines, either stable transfected with an empty vector (EV-HaCaT) or in which AHR had been stable silenced (AHR-silenced HaCaT); or primary normal human epithelial keratinocytes (NHEK) with 2% MH for 24 h. This induced a 15.4-fold upregulation of CYP1A1 in EV-HaCaTs, which was significantly reduced in AHR-silenced cells. Pre-treatment with the AHR antagonist CH223191 completely abrogated this effect. Similar findings were observed in NHEK. In vivo treatment of the Cyp1a1Cre x R26ReYFP reporter mice strain's skin with pure MH significantly induced CYP1A1 expression compared with Vaseline. Treatment of HaCaT with 2% MH significantly decreased baseline CYP1 enzymatic activity at 3 and 6 h but increased it after 12 h, suggesting that MH may activate the AHR both through direct and indirect means. Importantly, MH downregulation of IL-4-induced CCL26 mRNA and protein was abrogated in AHR-silenced HaCaTs and by pre-treatment with CH223191. Finally, MH significantly upregulated FLG expression in NHEK in an AHR-dependent manner. In conclusion, MH activates AHR, both in vitro and in vivo, thereby providing a mechanism of its IL4-induced CCL26 downregulation and upregulation of FLG expression. These results have potential clinical implications for atopic diseases and beyond.

6-Formylindolo[3,2-b]carbazole Protects Against Angiotensin II-Induced Cellular Hypertrophy through the Induction of Cytochrome P450 1A1 and Its Associated 19(S)-HETE Metabolite In Vitro

Aryl hydrocarbon receptor (AhR) is a multifunctional receptor that regulates cytochrome P450 1A1 (CYP1A1), an arachidonic acid (AA) metabolizing enzyme producing 19-hydroxyeicosatetraenoic acid (HETE). 6-formylindolo[3,2-b]carbazole (FICZ) demonstrates great affinity toward the AhR. Recently, we have shown that 19(S)-HETE is preferentially cardioprotective. This study investigates the role of FICZ on AhR and cytochrome P450 (CYP) 1A1-mediated AA metabolism and whether it attenuates angiotensin (Ang) II-induced cardiac hypertrophy. Adult human ventricular cardiomyocytes cell line treated with FICZ in the presence and absence of Ang II 10 μM. Protein levels of AhR and CYPs were determined by Western blot analysis and the mRNA expression of cardiac hypertrophic markers and CYPs were determined by real-time polymerase chain reaction. CYP1A1 enzyme activity and proteasomal degradation were determined by 7-ethoxyresorufin O-deethylase and proteasome 20S activity assays, respectively. Liquid chromatography tandem mass spectrometry was used to measure AA metabolites. Our results show that Ang II-induced cardiac hypertrophy modulates AA metabolites in an enantioselective manner, and that FICZ activates AhR in a time-dependent manner, inhibits AhR proteasomal degradation, induces CYP1A1, increases the concentration of 19(S)-HETE, and attenuates Ang II-induced cardiac hypertrophy by inhibiting the hypertrophic markers and decreasing cell surface area through midchain-HETE-dependent mechanism. In conclusion, the results demonstrate the ability of FICZ to protect against Ang II-induced cardiac hypertrophy by increasing the concentration of 19(S)-HETE through AhR regulated enzyme induction and inhibition of midchain-HETEs metabolites. SIGNIFICANCE STATEMENT: This study shows that 6-formylindolo[3,2-b]carbazole attenuate angiotensin II-induced cellular hypertrophy. The novel findings of our investigation are in characterizing the aryl hydrocarbon receptor involvement and the enantioselective differences in arachidonic acid metabolism in cardiac hypertrophy, which opens a new pathway to tackle and eventually treat heart failure.

Immune regulation through tryptophan metabolism

Amino acids are fundamental units of molecular components that are essential for sustaining life; however, their metabolism is closely interconnected to the control systems of cell function. Tryptophan (Trp) is an essential amino acid catabolized by complex metabolic pathways. Several of the resulting Trp metabolites are bioactive and play central roles in physiology and pathophysiology. Additionally, various physiological functions of Trp metabolites are mutually regulated by the gut microbiota and intestine to coordinately maintain intestinal homeostasis and symbiosis under steady state conditions and during the immune response to pathogens and xenotoxins. Cancer and inflammatory diseases are associated with dysbiosis- and host-related aberrant Trp metabolism and inactivation of the aryl hydrocarbon receptor (AHR), which is a receptor of several Trp metabolites. In this review, we focus on the mechanisms through which Trp metabolism converges to AHR activation for the modulation of immune function and restoration of tissue homeostasis and how these processes can be targeted using therapeutic approaches for cancer and inflammatory and autoimmune diseases.

Navigating the landscape of psoriasis therapy: novel targeted pathways and emerging trends

INTRODUCTION

Psoriasis is a chronic, inflammatory, non-communicable skin disorder that affects a patient's social and emotional well-being. It is characterized by hyperproliferation of keratinocytes, irregular shedding of skin cells, and abnormal invasion of inflammatory mediators. The treatment strategy is designed based on the severity of the disease condition starting from topical, phototherapy, systemic, and biologics. In recent years, extensive research into the underlying mechanisms of psoriasis has led to significant advancement in treatment options from small molecules to biologics.

AREA COVERED

This review focuses on intracellular and molecular mechanisms such as AhR, A3AR, RIP1, CGRP, and S1P that serve as novel pharmacological targets for psoriasis. Moreover, new molecules are approved or are under clinical investigation to interfere with these target mechanisms.

EXPERT OPINION

A detailed understanding of signaling pathways provides potential targets and molecular mechanisms for the inflammatory cascade in psoriasis. This has led to the development of small molecules targeting specific pathways. Further, the combination of nanotechnology can assist in dose reduction leading to reduced adverse effects in the management of psoriasis.

Ethyl Caffeate Can Inhibit Aryl Hydrocarbon Receptor (AhR) Signaling and AhR-Mediated Potentiation of Mast Cell Activation

Ethyl caffeate (EC) is a natural phenolic compound that is present in several medicinal plants used to treat inflammatory disorders. However, its anti-inflammatory mechanisms are not fully understood. Here, we report that EC inhibits aryl hydrocarbon receptor (AhR) signaling and that this is associated with its anti-allergic activity. EC inhibited AhR activation, induced by the AhR ligands FICZ and DHNA in AhR signaling-reporter cells and mouse bone marrow-derived mast cells (BMMCs), as assessed by AhR target gene expressions such as CYP1A1. EC also inhibited the FICZ-induced downregulation of AhR expression and DHNA-induced IL-6 production in BMMCs. Furthermore, the pretreatment of mice with orally administered EC inhibited DHNA-induced CYP1A1 expression in the intestine. Notably, both EC and CH-223191, a well-established AhR antagonist, inhibited IgE-mediated degranulation in BMMCs grown in a cell culture medium containing significant amounts of AhR ligands. Furthermore, oral administration of EC or CH-223191 to mice inhibited the PCA reaction associated with the suppression of constitutive CYP1A1 expression within the skin. Collectively, EC inhibited AhR signaling and AhR-mediated potentiation of mast cell activation due to the intrinsic AhR activity in both the culture medium and normal mouse skin. Given the AhR control of inflammation, these findings suggest a novel mechanism for the anti-inflammatory activity of EC.

The aryl hydrocarbon receptor regulates epidermal differentiation through transient activation of TFAP2A

The aryl hydrocarbon receptor (AHR) is an evolutionary conserved environmental sensor identified as indispensable regulator of epithelial homeostasis and barrier organ function. Molecular signaling cascade and target genes upon AHR activation and their contribution to cell and tissue function are however not fully understood. Multi-omics analyses using human skin keratinocytes revealed that, upon ligand activation, AHR binds open chromatin to induce expression of transcription factors (TFs), e.g., Transcription Factor AP-2α (TFAP2A), as a swift response to environmental stimuli. The terminal differentiation program including upregulation of barrier genes, filaggrin and keratins, was mediated by TFAP2A as a secondary response to AHR activation. The role of AHR-TFAP2A axis in controlling keratinocyte terminal differentiation for proper barrier formation was further confirmed using CRISPR/Cas9 in human epidermal equivalents. Overall, the study provides novel insights into the molecular mechanism behind AHR-mediated barrier function and potential novel targets for the treatment of skin barrier diseases.

Heterogeneous effects of S100 proteins during cell interactions between immune cells and stromal cells from synovium or skin

Cell interactions represent an important mechanism involved in the pathogenesis of chronic inflammation. The key S100 proteins A8 and A9 have been studied in several models of chronic inflammatory diseases with highly heterogeneous conclusions. In this context, the aim of this study was to determine the role of cell interactions on S100 protein production and their effect on cytokine production during cell interactions, between immune and stromal cells from synovium or skin. Peripheral blood mononuclear cells (PBMC) were cultured alone or with synoviocytes or skin fibroblasts, with or without phytohemagglutinin, exogenous A8, A9, A8/A9 proteins or anti-A8/A9 antibody. Production of IL-6, IL-1β, IL-17, TNF, A8, A9, and A8/A9 was measured by ELISA. Cell interactions with synoviocytes had no effect on A8, A9, or A8/A9 secretion, while cell interactions with skin fibroblasts decreased A8 production. This highlights the importance of stromal cell origin. The addition of S100 proteins in co-cultures with synoviocytes did not increase the production of IL-6, IL-17, or IL-1β, except for an increase of IL-6 secretion with A8. The presence of anti-S100A8/A9 antibody did not show obvious effects. Low concentration or absence of serum in the culture medium decreased the production of IL-17, IL-6, and IL-1β but despite these conditions, the addition of S100 proteins did not increase cytokine secretion. In conclusion, the role of A8/A9 in cell interactions during chronic inflammation appears complex and heterogeneous, depending on multiple factors, notably the origin of stromal cells that can affect their secretion.

Homeostatic activation of aryl hydrocarbon receptor by dietary ligands dampens cutaneous allergic responses by controlling Langerhans cells migration

Dietary compounds can affect the development of inflammatory responses at distant sites. However, the mechanisms involved remain incompletely understood. Here, we addressed the influence on allergic responses of dietary agonists of aryl hydrocarbon receptor (AhR). In cutaneous papain-induced allergy, we found that lack of dietary AhR ligands exacerbates allergic responses. This phenomenon was tissue-specific as airway allergy was unaffected by the diet. In addition, lack of dietary AhR ligands worsened asthma-like allergy in a model of 'atopic march.' Mice deprived of dietary AhR ligands displayed impaired Langerhans cell migration, leading to exaggerated T cell responses. Mechanistically, dietary AhR ligands regulated the inflammatory profile of epidermal cells, without affecting barrier function. In particular, we evidenced TGF-β hyperproduction in the skin of mice deprived of dietary AhR ligands, explaining Langerhans cell retention. Our work identifies an essential role for homeostatic activation of AhR by dietary ligands in the dampening of cutaneous allergic responses and uncovers the importance of the gut-skin axis in the development of allergic diseases.

Targeting the aryl hydrocarbon receptor by gut phenolic metabolites: A strategy towards gut inflammation

The Aryl Hydrocarbon Receptor (AHR) is a ligand-dependent transcription factor able to control complex transcriptional processes in several cell types, which has been correlated with various diseases, including inflammatory bowel diseases (IBD). Numerous studies have described different compounds as ligands of this receptor, like xenobiotics, natural compounds, and several host-derived metabolites. Dietary (poly)phenols have been studied regarding their pleiotropic activities (e.g., neuroprotective and anti-inflammatory), but their AHR modulatory capabilities have also been considered. However, dietary (poly)phenols are submitted to extensive metabolism in the gut (e.g., gut microbiota). Thus, the resulting gut phenolic metabolites could be key players modulating AHR since they are the ones that reach the cells and may exert effects on the AHR throughout the gut and other organs. This review aims at a comprehensive search for the most abundant gut phenolic metabolites detected and quantified in humans to understand how many have been described as AHR modulators and what could be their impact on inflammatory gut processes. Even though several phenolic compounds have been studied regarding their anti-inflammatory capacities, only 1 gut phenolic metabolite, described as AHR modulator, has been evaluated on intestinal inflammatory models. Searching for AHR ligands could be a novel strategy against IBD.

Gram-positive anaerobic cocci guard skin homeostasis by regulating host-defense mechanisms

In atopic dermatitis (AD), chronic skin inflammation is associated with skin barrier defects and skin microbiome dysbiosis including a lower abundance of Gram-positive anaerobic cocci (GPACs). We here report that, through secreted soluble factors, GPAC rapidly and directly induced epidermal host-defense molecules in cultured human keratinocytes and indirectly via immune-cell activation and cytokines derived thereof. Host-derived antimicrobial peptides known to limit the growth of Staphylococcus aureus-a skin pathogen involved in AD pathology-were strongly upregulated by GPAC-induced signaling through aryl hydrocarbon receptor (AHR)-independent mechanisms, with a concomitant AHR-dependent induction of epidermal differentiation genes and control of pro-inflammatory gene expression in organotypic human epidermis. By these modes of operandi, GPAC may act as an "alarm signal" and protect the skin from pathogenic colonization and infection in the event of skin barrier disruption. Fostering growth or survival of GPAC may be starting point for microbiome-targeted therapeutics in AD.

Machine learning study: from the toxicity studies to tetrahydrocannabinol effects on Parkinson's disease

Aim: Investigating molecules having toxicity and chemical similarity to find hit molecules. Methods: The machine learning (ML) model was developed to predict the arylhydrocarbon receptor (AHR) activity of anti-Parkinson's and US FDA-approved drugs. The ML algorithm was a support vector machine, and the dataset was Tox21. Results: The ML model predicted apomorphine in anti-Parkinson's drugs and 73 molecules in FDA-approved drugs as active. The authors were curious if there is any molecule like apomorphine in these 73 molecules. A fingerprint similarity analysis of these molecules was conducted and found tetrahydrocannabinol (THC). Molecular docking studies of THC for dopamine receptor 1 (affinity = -8.2 kcal/mol) were performed. Conclusion: THC may affect dopamine receptors directly and could be useful for Parkinson's disease.

Assessment of cytochrome P450 1A1 gene polymorphism and vitamin A serum level in psoriasis vulgaris

Psoriasis is characterized by cutaneous hyperproliferation, secondary to immune system dysregulation. Vitamin A regulates the immune response and sustains epithelial tissue hemostasis. The CYP1A1 gene, has many biological actions, including vitamin A metabolism. To evaluate CYP1A1 gene polymorphism and serum vitamin A level in patients with psoriasis vulgaris, a case-control study involving two groups was conducted: group 1 (45 patients with psoriasis vulgaris) served as the cased group and group 2 (45 healthy participants who were sex and age matched) acted as the control group. CYP1A1 (rs1048943) gene polymorphism and vitamin A serum level were assessed by TaqMan allelic discrimination (PCR) and ELISA, respectively. AG genotype was present only in cases (22.2%), while AA genotype was present in all controls (P=.001). Vitamin A levels were lower in cases than in controls (32.0 ± 7.41 vs. 46.2 ± 15.7 μg/ml, respectively) (P<.001). AG genotype was associated with a lower vitamin A level (P=.001). The detected genotype difference between psoriasis patients and controls, which was associated with a lower serum vitamin A level and was also lower in more severe cases, suggests a role of the CYP1A1 gene and vitamin A in disease pathogenesis and prognosis.

Updated view of tars for psoriasis: what have we learned over the last decade?

Tars are one of the most effective, unknown, and oldest therapies for psoriasis. They include coal tar (CT) and biomass-derived products. These treatments, particularly the CT, have proven to be cost-effective with long remission times compared to other systemic or topical treatments. However, they have hardly evolved in recent years, as they are not well-embraced by clinicians or patients because of concerns regarding cosmesis and safety. This review summarizes current knowledge about the chemical characterization, mechanism of action, toxicity, and clinical studies supporting the use of tars for psoriasis over the last decade. Trends within these above aspects are reviewed, and avenues of research are identified. CT is rich in polycyclic aromatic hydrocarbons, whereas biomass-derived tars are rich in phenols. While the activation of the aryl hydrocarbon receptor is involved in the antipsoriatic effect of CT, the mechanism of action of biomass-derived products remains to be elucidated. No conclusive evidence exists about the risk of cancer in psoriasis patients under CT treatment. Large, randomized, double-blind, controlled clinical trials are necessary to promote the inclusion of tars as part of modern therapies for psoriasis.

Increased sensitivity to chemically induced colitis in mice harboring a DNA-binding deficient aryl hydrocarbon receptor

The aryl hydrocarbon receptor (AHR), a transcription factor best known for mediating toxic responses of environmental pollutants, also integrates metabolic signals to promote anti-inflammatory responses, intestinal homeostasis, and maintain barrier integrity. AHR regulates its target genes through direct DNA-binding to aryl hydrocarbon response elements (AHREs) but also through tethering to other transcription factors in a DNA-binding independent manner. However, it is not known if AHR's anti-inflammatory role in the gut requires its ability to bind to AHREs. To test this, we determined the sensitivity of Ahrdbd/dbd mice, a genetically modified mouse line that express an AHR protein incapable of binding to AHREs, to dextran sulfate sodium (DSS)-induced colitis. Ahrdbd/dbd mice exhibited more severe symptoms of intestinal inflammation than Ahr+/+ mice. None of the Ahrdbd/dbd mice survived after the 5-day DSS followed by 7-day washout period. By day 6, the Ahrdbd/dbd mice had severe body weight loss, shortening of the colon, higher disease index scores, enlarged spleens, and increased expression of several inflammation genes, including interleukin 1b (Il-1b), Il-6, Il-17, C-x-c motif chemokine ligand 1 (Cxcl1), Cxcl2, Prostaglandin-endoperoxide synthase (Ptgs2), and lipocalin-2. Our findings show that AHR's DNA-binding domain and ability to bind to AHREs are required to reduce inflammation, maintain a healthy intestinal environment, and protect against DSS-induced colitis.

Lead optimization of aryl hydrocarbon receptor ligands for treatment of inflammatory skin disorders

Therapeutic aryl hydrocarbon receptor (AHR) modulating agents gained attention in dermatology as non-steroidal anti-inflammatory drugs that improve skin barrier properties. By exploiting AHR's known ligand promiscuity, we generated novel AHR modulating agents by lead optimization of a selective AHR modulator (SAhRM; SGA360). Twenty-two newly synthesized compounds were screened yielding two novel derivatives, SGA360f and SGA388, in which agonist activity led to enhanced keratinocyte terminal differentiation. SGA388 showed the highest agonist activity with potent normalization of keratinocyte hyperproliferation, restored expression of skin barrier proteins and dampening of chemokine expression by keratinocytes upon Th2-mediated inflammation in vitro. The topical application of SGA360f and SGA388 reduced acute skin inflammation in vivo by reducing cyclooxygenase levels, resulting in less neutrophilic dermal infiltrates. The minimal induction of cytochrome P450 enzyme activity, lack of cellular toxicity and mutagenicity classifies SGA360f and SGA388 as novel potential therapeutic AHR ligands and illustrates the potential of medicinal chemistry to fine-tune AHR signaling for the development of targeted therapies in dermatology and beyond.

SCD1 Sustains Homeostasis of Bulge Niche via Maintaining Hemidesmosomes in Basal Keratinocytes

Niche for stem cells profoundly influences their maintenance and fate during tissue homeostasis and pathological disorders; however, the underlying mechanisms and tissue-specific features remain poorly understood. Here, it is reported that fatty acid desaturation catabolized by stearoyl-coenzyme A desaturase 1 (SCD1) regulates hair follicle stem cells (HFSCs) and hair growth by maintaining the bulge, niche for HFSCs. Scd1 deletion in mice results in abnormal hair growth, an effect exerted directly on keratin K14+ keratinocytes rather than on HFSCs. Mechanistically, Scd1 deficiency impairs the level of integrin α6β4 complex and thus the assembly of hemidesmosomes (HDs). The disruption of HDs allows the aberrant activation of focal adhesion kinase and PI3K in K14+ keratinocytes and subsequently their differentiation and proliferation. The overgrowth of basal keratinocytes results in downward extension of the outer root sheath and interruption of bulge formation. Then, inhibition of PI3K signaling in Scd1-/- mice normalizes the bulge, HFSCs, and hair growth. Additionally, supplementation of oleic acid to Scd1-/- mice reestablishes HDs and the homeostasis of bulge niche, and restores hair growth. Thus, SCD1 is critical in regulating hair growth through stabilizing HDs in basal keratinocytes and thus sustaining bulge for HFSC residence and periodic activity.

The intestine: A highly dynamic microenvironment for IgA plasma cells

To achieve longevity, IgA plasma cells require a sophisticated anatomical microenvironment that provides cytokines, cell-cell contacts, and nutrients as well as metabolites. The intestinal epithelium harbors cells with distinct functions and represents an important defense line. Anti-microbial peptide-producing paneth cells, mucus-secreting goblet cells and antigen-transporting microfold (M) cells cooperate to build a protective barrier against pathogens. In addition, intestinal epithelial cells are instrumental in the transcytosis of IgA to the gut lumen, and support plasma cell survival by producing the cytokines APRIL and BAFF. Moreover, nutrients are sensed through specialized receptors such as the aryl hydrocarbon receptor (AhR) by both, intestinal epithelial cells and immune cells. However, the intestinal epithelium is highly dynamic with a high cellular turn-over rate and exposure to changing microbiota and nutritional factors. In this review, we discuss the spatial interplay of the intestinal epithelium with plasma cells and its potential contribution to IgA plasma cell generation, homing, and longevity. Moreover, we describe the impact of nutritional AhR ligands on intestinal epithelial cell-IgA plasma cell interaction. Finally, we introduce spatial transcriptomics as a new technology to address open questions in intestinal IgA plasma cell biology.

Aryl hydrocarbon receptor: The master regulator of immune responses in allergic diseases

The aryl hydrocarbon receptor (AhR) is a widely studied ligand-activated cytosolic transcriptional factor that has been associated with the initiation and progression of various diseases, including autoimmune diseases, cancers, metabolic syndromes, and allergies. Generally, AhR responds and binds to environmental toxins/ligands, dietary ligands, and allergens to regulate toxicological, biological, cellular responses. In a canonical signaling manner, activation of AhR is responsible for the increase in cytochrome P450 enzymes which help individuals to degrade and metabolize these environmental toxins and ligands. However, canonical signaling cannot be applied to all the effects mediated by AhR. Recent findings indicate that activation of AhR signaling also interacts with some non-canonical factors like Kruppel-like-factor-6 (KLF6) or estrogen-receptor-alpha (Erα) to affect the expression of downstream genes. Meanwhile, enormous research has been conducted to evaluate the effect of AhR signaling on innate and adaptive immunity. It has been shown that AhR exerts numerous effects on mast cells, B cells, macrophages, antigen-presenting cells (APCs), Th1/Th2 cell balance, Th17, and regulatory T cells, thus, playing a significant role in allergens-induced diseases. This review discussed how AhR mediates immune responses in allergic diseases. Meanwhile, we believe that understanding the role of AhR in immune responses will enhance our knowledge of AhR-mediated immune regulation in allergic diseases. Also, it will help researchers to understand the role of AhR in regulating immune responses in autoimmune diseases, cancers, metabolic syndromes, and infectious diseases.

Particulate matter 2.5 induces the skin barrier dysfunction and cutaneous inflammation via AhR- and T helper 17 cell-related genes in human skin tissue as identified via transcriptome analysis

Particulate matter (PM2.5) is an environmental pollutant causing skin inflammatory diseases via epidermal barrier damage. However, the mechanism and related gene expression induced by PM2.5 remains unclear. Our aim was to determine the effect of PM2.5 on human skin tissue ex vivo, and elucidate the mechanism of T helper 17 cell-related inflammatory cytokine and skin barrier function. We verified the expression levels of gene in PM2.5-treated human skin tissue using Quantseq (3' mRNA-Seq), and Gene Ontology (GO) terms and protein-protein interaction (PPI) networks were performed. The PM2.5 treatment significantly enhanced the expression of Th 1, 2, 17 and 22 cell-related genes (cut-off value: │1.2 │ > fold change and p < 0.05). Most of all, Th17 cell-related genes are upregulated and those genes are associated with skin epidermal barrier function and Aryl hydrocarbon receptor (AhR), a xenobiotic receptor, pathway. In human keratinocyte cell lines, AhR-regulated genes (e.g. AhRR, CYP1A1, IL6 and IL36G), Th17 cell-related genes (e.g. IL17C) and epidermal barrier-related genes (e.g. SPRR2A and KRT71) are significantly increased after PM2.5. In the protein level, the secretion of IL-6 and IL-36G was increased in human skin tissue following PM2.5 treatment, and the expression of SPRR2A and KRT71 was significantly increased. PM2.5 exposure could ruin the skin epidermal barrier function via AhR- and Th17 cell-related inflammatory pathway.

Tapinarof for the treatment of psoriasis

Although topical drugs are the mainstay of treatment for patients with mild-to-moderate psoriasis, the developments observed in this field in the last two decades have been limited. The most commonly used drugs are still vitamin D analogues and corticosteroids, both with several limitations. The aryl hydrocarbon receptor (AhR) plays a role in the pathogenesis of psoriasis, and tapinarof, a novel, first-in-class, small molecule topical therapeutic AhR-modulating agent has been recently approved by the FDA for the topical treatment of plaque psoriasis in adults. Two large, 12-week, phase III trials, PSOARING 1 and 2, showed that 35.4%-40.2% of patients in the tapinarof 1% cream arm achieved the primary endpoint (Physician's Global Assessment [PGA] score of 0 or 1 and a decrease of ≥2-5 points at week 12) compared with 6.0%-6.3% for vehicle arm, respectively. The most common adverse effects were folliculitis, contact dermatitis, headache and pruritus. In the open label, 40-week, extension trial, PSOARING 3, the efficacy and safety results were similar, with 40.9% of patients achieving a PGA = 0 at least one time during the trial and 58.2% of patients with PGA≥2 achieved PGA = 0/1 at least once during the trial, without tachyphylaxis. There were no new safety signals, with most frequent adverse events being folliculitis, contact dermatitis, and upper respiratory tract infection. Tapinarof 1% cream has shown to be effective and to have a favorable safety profile in the treatment of psoriatic patients, representing an alternative to the current therapeutic options, increasing our armamentarium in the topical treatment of psoriasis.

Multi-omics integration reveals a core network involved in host defence and hyperkeratinization in psoriasis

OBJECTIVES

The precise pathogenesis of psoriasis remains incompletely explored. We aimed to better understand the underlying mechanisms of psoriasis, using a systems biology approach based on transcriptomics and microbiome profiling.

METHODS

We collected the skin tissue biopsies and swabs in both lesional and non-lesional skin of 13 patients with psoriasis, 15 patients with psoriatic arthritis and healthy skin from 12 patients with ankylosing spondylitis. To study the similarities and differences in the molecular profiles between these three conditions, and the associations between the host defence and microbiota composition, we performed high-throughput RNA-sequencing to quantify the gene expression profile in tissues. The metagenomic composition of 16S on local skin sites was quantified by clustering amplicon sequences and counted into operational taxonomic units. We further analysed associations between the transcriptome and microbiome profiling.

RESULTS

We found that lesional and non-lesional samples were remarkably different in terms of their transcriptome profiles. The functional annotation of differentially expressed genes showed a major enrichment in neutrophil activation. By using co-expression gene networks, we identified a gene module that was associated with local psoriasis severity at the site of biopsy. From this module, we found a 'core' set of genes that was functionally involved in neutrophil activation, epidermal cell differentiation and response to bacteria. Skin microbiome analysis revealed that the abundances of Enhydrobacter, Micrococcus and Leptotrichia were significantly correlated with the genes in core network.

CONCLUSIONS

We identified a core gene network that associated with local disease severity and microbiome composition, involved in the inflammation and hyperkeratinization in psoriatic skin.

Effects of ambient PM2.5 on development of psoriasiform inflammation through KRT17-dependent activation of AKT/mTOR/HIF-1α pathway

Exposure to fine particulate matter (PM2.5) has significant effects on human skin health, mainly disrupting skin homeostasis and accelerating aging. To date, the effects of PM2.5 on psoriasis (PSO) have not been elucidated. An ambient particulate matter exposed and well characterized imiquimod (IMQ)-induced psoriasis mouse model was established. Thirty male C57BL/6 mice aged 8 weeks were randomly divided into three groups: filtered air (FA) group (Control group), PSO+ FA group and PSO + PM2.5 group. A KRT17 knockdown (KRT17-KD) mouse model was simultaneously established by subcutaneously injecting KRT17-KD lentivirus. Forty male C57BL/6 mice were randomly divided into four groups: PSO + FA + KRT17-RNAi negative control lentivirus (KRT17-NC) group, PSO+ FA+ KRT17-KD group, PSO + PM2.5 + KRT17-NC group and PSO + PM2.5 + KRT17-KD group. PM2.5 exposure continued for 8 weeks. Psoriasis was induced by topically applying IMQ on the dorsal skin of the mice for 6 days during week 8. Morphometric and histological analyses were performed to investigate the changes in psoriatic lesions. Differentially expressed genes and enriched pathways were explored using bioinformatics analysis and showed that KRT17 gene and the vascular endothelial growth factor receptor signaling pathway were associated with psoriasis. HaCaT cells were stimulated with interleukin-17A and infected with KRT17-KD lentivirus to establish an in vitro KRT17 knockdown psoriasis cell model. Notably, PM2.5 exposure increased the expression of KRT17 protein and activated AKT/mTOR/HIF-1α signaling pathway in vivo. Moreover, specific agonist of AKT (740Y-P) reversed the decreased neovascularization induced by KRT17 knockdown through AKT/mTOR/HIF-1α signaling pathway in vitro. Consequently, PM2.5 exposure could promote the development and progression of psoriasis through KRT17-dependent activation of AKT/mTOR/HIF-1α signaling pathway.

Type II alveolar epithelial cell aryl hydrocarbon receptor protects against allergic airway inflammation through controlling cell autophagy

RATIONALE

Aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, has been considered as an important regulator for immune diseases. We have previously shown that AhR protects against allergic airway inflammation. The underlying mechanism, however, remains undetermined.

OBJECTIVES

We sought to determine whether AhR specifically in type II alveolar epithelial cells (AT2) modulates allergic airway inflammation and its underlying mechanisms.

METHODS

The role of AhR in AT2 cells in airway inflammation was investigated in a mouse model of asthma with AhR conditional knockout mice in AT2 cells (Sftpc-Cre;AhRf/f ). The effect of AhR on allergen-induced autophagy was examined by both in vivo and in vitro analyses. The involvement of autophagy in airway inflammation was analyzed by using autophagy inhibitor chloroquine. The AhR-regulated gene profiling in AT2 cells was also investigated by RNA sequencing (RNA-seq) analysis.

RESULTS

Sftpc-Cre;AhRf/f mice showed exacerbation of allergen-induced airway hyperresponsiveness and airway inflammation with elevated Th2 cytokines in bronchoalveolar lavage fluid (BALF). Notably, an increased allergen-induced autophagy was observed in the lung tissues of Sftpc-Cre;AhRf/f mice when compared with wild-type mice. Further analyses suggested a functional axis of AhR-TGF-β1 that is critical in driving allergic airway inflammation through regulating allergen-induced cellular autophagy. Furthermore, inhibition of autophagy with autophagy inhibitor chloroquine significantly suppressed cockroach allergen-induced airway inflammation, Th2 cytokines in BALFs, and expression of autophagy-related genes LC3 and Atg5 in the lung tissues. In addition, RNA-seq analysis suggests that autophagy is one of the major pathways and that CALCOCO2/NDP52 and S1009 are major autophagy-associated genes in AT2 cells that may contribute to the AhR-mediated cockroach allergen-induced airway inflammation and, subsequently, allergic asthma.

CONCLUSION

These results suggest that AhR in AT2 cells functions as a protective mechanism against allergic airway inflammation through controlling cell autophagy.

Effects of Air Pollution on Cellular Senescence and Skin Aging

The human skin is exposed daily to different environmental factors such as air pollutants and ultraviolet (UV) light. Air pollution is considered a harmful environmental risk to human skin and is known to promote aging and inflammation of this tissue, leading to the onset of skin disorders and to the appearance of wrinkles and pigmentation issues. Besides this, components of air pollution can interact synergistically with ultraviolet light and increase the impact of damage to the skin. However, little is known about the modulation of air pollution on cellular senescence in skin cells and how this can contribute to skin aging. In this review, we are summarizing the current state of knowledge about air pollution components, their involvement in the processes of cellular senescence and skin aging, as well as the current therapeutic and cosmetic interventions proposed to prevent or mitigate the effects of air pollution in the skin.

Human-β-defensin-3 attenuates atopic dermatitis-like inflammation through autophagy activation and the aryl hydrocarbon receptor signaling pathway

Human β-defensin-3 (hBD-3) exhibits antimicrobial and immunomodulatory activities; however, its contribution to autophagy regulation remains unclear, and the role of autophagy in the regulation of the epidermal barrier in atopic dermatitis (AD) is poorly understood. Here, keratinocyte autophagy was restrained in the skin lesions of patients with AD and murine models of AD. Interestingly, hBD-3 alleviated the IL-4– and IL-13–mediated impairment of the tight junction (TJ) barrier through keratinocyte autophagy activation, which involved aryl hydrocarbon receptor (AhR) signaling. While autophagy deficiency impaired the epidermal barrier and exacerbated inflammation, hBD-3 attenuated skin inflammation and enhanced the TJ barrier in AD. Importantly, hBD-3–mediated improvement of the TJ barrier was abolished in autophagy-deficient AD mice and in AhR-suppressed AD mice, suggesting a role for hBD-3–mediated autophagy in the regulation of the epidermal barrier and inflammation in AD. Thus, autophagy contributes to the pathogenesis of AD, and hBD-3 could be used for therapeutic purposes.

Molecular and cellular regulation of psoriatic inflammation

This review highlights the molecular and cellular mechanisms underlying psoriatic inflammation with an emphasis on recent developments which may impact on treatment approaches for this chronic disease. We consider both the skin and the musculoskeletal compartment and how different manifestations of psoriatic inflammation are linked. This review brings a focus to the importance of inflammatory feedback loops that exist in the initiation and chronic stages of the condition, and how close interaction between the epidermis and both innate and adaptive immune compartments drives psoriatic inflammation. Furthermore, we highlight work done on biomarkers to predict the outcome of therapy as well as the transition from psoriasis to psoriatic arthritis.

Aryl Hydrocarbon Receptor in Oxidative Stress as a Double Agent and Its Biological and Therapeutic Significance

The aryl hydrocarbon receptor (AhR) has long been implicated in the induction of a battery of genes involved in the metabolism of xenobiotics and endogenous compounds. AhR is a ligand-activated transcription factor necessary for the launch of transcriptional responses important in health and disease. In past decades, evidence has accumulated that AhR is associated with the cellular response to oxidative stress, and this property of AhR must be taken into account during investigations into a mechanism of action of xenobiotics that is able to activate AhR or that is susceptible to metabolic activation by enzymes encoded by the genes that are under the control of AhR. In this review, we examine various mechanisms by which AhR takes part in the oxidative-stress response, including antioxidant and prooxidant enzymes and cytochrome P450. We also show that AhR, as a participant in the redox balance and as a modulator of redox signals, is being increasingly studied as a target for a new class of therapeutic compounds and as an explanation for the pathogenesis of some disorders.

Indoleamine 2,3-dioxygenase 1 activation in mature cDC1 promotes tolerogenic education of inflammatory cDC2 via metabolic communication

Conventional dendritic cells (cDCs), cDC1 and cDC2, act both to initiate immunity and maintain self-tolerance. The tryptophan metabolic enzyme indoleamine 2,3-dioxygenase 1 (IDO1) is used by cDCs in maintaining tolerance, but its role in different subsets remains unclear. At homeostasis, only mature CCR7⁺ cDC1 expressed IDO1 that was dependent on IRF8. Lipopolysaccharide treatment induced maturation and IDO1-dependent tolerogenic activity in isolated immature cDC1, but not isolated cDC2. However, both human and mouse cDC2 could induce IDO1 and acquire tolerogenic function when co-cultured with mature cDC1 through the action of cDC1-derived l-kynurenine. Accordingly, cDC1-specific inactivation of IDO1 in vivo exacerbated disease in experimental autoimmune encephalomyelitis. This study identifies a previously unrecognized metabolic communication in which IDO1-expressing cDC1 cells extend their immunoregulatory capacity to the cDC2 subset through their production of tryptophan metabolite l-kynurenine. This metabolic axis represents a potential therapeutic target in treating autoimmune demyelinating diseases.

Lung Epithelial CYP1 Activity Regulates Aryl Hydrocarbon Receptor Dependent Allergic Airway Inflammation

The lung epithelial barrier serves as a guardian towards environmental insults and responds to allergen encounter with a cascade of immune reactions that can possibly lead to inflammation. Whether the environmental sensor aryl hydrocarbon receptor (AhR) together with its downstream targets cytochrome P450 (CYP1) family members contribute to the regulation of allergic airway inflammation remains unexplored. By employing knockout mice for AhR and for single CYP1 family members, we found that AhR^-/- and CYP1B1^-/- but not CYP1A1^-/- or CYP1A2^-/- animals display enhanced allergic airway inflammation compared to WT. Expression analysis, immunofluorescence staining of murine and human lung sections and bone marrow chimeras suggest an important role of CYP1B1 in non-hematopoietic lung epithelial cells to prevent exacerbation of allergic airway inflammation. Transcriptional analysis of murine and human lung epithelial cells indicates a functional link of AhR to barrier protection/inflammatory mediator signaling upon allergen challenge. In contrast, CYP1B1 deficiency leads to enhanced expression and activity of CYP1A1 in lung epithelial cells and to an increased availability of the AhR ligand kynurenic acid following allergen challenge. Thus, differential CYP1 family member expression and signaling via the AhR in epithelial cells represents an immunoregulatory layer protecting the lung from exacerbation of allergic airway inflammation.

Aryl hydrocarbon receptor-targeted therapy for CD4+ T cell-mediated idiopathic pneumonia syndrome in mice

We previously demonstrated that interferon γ (IFN-γ) derived from donor T cells co-opts the indoleamine 2,3-dioxygenase 1 (IDO1) → aryl hydrocarbon receptor (AHR) axis to suppress idiopathic pneumonia syndrome (IPS). Here we report that the dysregulated expression of AP-1 family genes in Ahr-/- lung epithelial cells exacerbated IPS in allogeneic bone marrow transplantation settings. AHR repressed transcription of Jund by preventing STAT1 from binding to its promoter. As a consequence, decreased interleukin-6 impaired the differentiation of CD4+ T cells toward Th17 cells. IFN-γ- and IDO1-independent induction of Ahr expression indicated that the AHR agonist might be a better therapeutic target for IPS than the IDO1 activator. We developed a novel synthetic AHR agonist (referred to here as PB502) that potently inhibits Jund expression. PB502 was highly effective at inducing AHR activation and ameliorating IPS. Notably, PB502 was by far superior to the endogenous AHR ligand, L-kynurenine, in promoting the differentiation of both mouse and human FoxP3+ regulatory CD4+ T cells. Our results suggest that the IDO1-AHR axis in lung epithelial cells is associated with IPS repression. A specific AHR agonist may exhibit therapeutic activity against inflammatory and autoimmune diseases by promoting regulatory T-cell differentiation.

Aryl Hydrocarbon Receptors: Evidence of Therapeutic Targets in Chronic Inflammatory Skin Diseases

The aryl hydrocarbon receptor (AhR), a ligand-dependent transcription factor, is important for xenobiotic metabolism and binds to various endogenous and exogenous ligands present in the skin. AhR is known to be associated with diseases in various organs; however, its functions in chronic inflammatory skin diseases, such as atopic dermatitis (AD) and psoriasis (PS), have recently been elucidated. Here, we discuss the molecular mechanisms of AhR related to chronic inflammatory skin diseases, such as AD and PS, and the mechanisms of action of AhR on the skin immune system. The importance of AhR molecular biological pathways, clinical features in animal models, and AhR ligands in skin diseases need to be investigated. In conclusion, the therapeutic effects of AhR ligands are demonstrated based on the relationship between AhR and skin diseases. Nevertheless, further studies are required to elucidate the detailed roles of AhR in chronic inflammatory skin diseases.

Rosmarinus officinalis L. Leaf Extracts and Their Metabolites Inhibit the Aryl Hydrocarbon Receptor (AhR) Activation In Vitro and in Human Keratinocytes: Potential Impact on Inflammatory Skin Diseases and Skin Cancer

Aryl hydrocarbon receptor (AhR) activation by environmental agents and microbial metabolites is potentially implicated in a series of skin diseases. Hence, it would be very important to identify natural compounds that could inhibit the AhR activation by ligands of microbial origin as 6-formylindolo[3,2-b]carbazole (FICZ), indirubin (IND) and pityriazepin (PZ) or the prototype ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Five different dry Rosmarinus officinalis L. extracts (ROEs) were assayed for their activities as antagonists of AhR ligand binding with guinea pig cytosol in the presence of [³H]TCDD. The methanolic ROE was further assayed towards CYP1A1 mRNA induction using RT-PCR in human keratinocytes against TCDD, FICZ, PZ, and IND. The isolated metabolites, carnosic acid, carnosol, 7-O-methyl-epi-rosmanol, 4′,7-O-dimethylapigenin, and betulinic acid, were assayed for their agonist and antagonist activity in the presence and absence of TCDD using the gel retardation assay (GRA). All assayed ROE extracts showed similar dose-dependent activities with almost complete inhibition of AhR activation by TCDD at 100 ppm. The methanol ROE at 10 ppm showed 99%, 50%, 90%, and 85% inhibition against TCDD, FICZ, IND, and PZ, respectively, in human keratinocytes. Most assayed metabolites exhibited dose-dependent antagonist activity. ROEs inhibit AhR activation by TCDD and by the Malassezia metabolites FICZ, PZ, and IND. Hence, ROE could be useful for the prevention or treatment of skin diseases mediated by activation of AhR.

Cell-intrinsic Aryl Hydrocarbon Receptor signalling is required for the resolution of injury-induced colonic stem cells

The aryl hydrocarbon receptor (AHR) is an environmental sensor that integrates microbial and dietary cues to influence physiological processes within the intestinal microenvironment, protecting against colitis and colitis-associated colorectal cancer development. Rapid tissue regeneration upon injury is important for the reinstatement of barrier integrity and its dysregulation promotes malignant transformation. Here we show that AHR is important for the termination of the regenerative response and the reacquisition of mature epithelial cell identity post injury in vivo and in organoid cultures in vitro. Using an integrative multi-omics approach in colon organoids, we show that AHR is required for timely termination of the regenerative response through direct regulation of transcription factors involved in epithelial cell differentiation as well as restriction of chromatin accessibility to regeneration-associated Yap/Tead transcriptional targets. Safeguarding a regulated regenerative response places AHR at a pivotal position in the delicate balance between controlled regeneration and malignant transformation.

Rapid intestinal regeneration after injury is critical to maintain barrier integrity and homeostasis, but must be tightly controlled to prevent tumorigenesis. Here they show that the aryl hydrocarbon receptor is required to terminate the regenerative response after wound healing.

S100A8 (rs3806232) gene polymorphism and S100A8 serum level in psoriasis vulgaris patients: A preliminary study

BACKGROUND

S100A8 single nucleotide polymorphism (SNP) and S100A8 blood level are related to many inflammatory disorders with no available conclusion in psoriasis.

AIM

to evaluate the possible role of S100A8 in psoriasis pathogenesis through analyzing its S100A8 (rs3806232) gene polymorphism and S100A8 serum level in psoriasis vulgaris patients, in addition to correlate the detected results with severity psoriasis in those patients.

METHODS

This case-control study was conducted on 50 patients having psoriasis vulgaris, and 26 controls. Severity of psoriasis was evaluated using psoriasis area and severity index (PASI) score. S100A8 serum level and S100A8 (rs3806232) SNP were evaluated by ELISA and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) respectively.

RESULTS

Serum S100A8 level was significantly higher in psoriatic patients than controls and was positively correlated with PASI score (r=0.826, p<0.001). S100A8 (rs3806232) AA genotype and A allele were significantly increased among psoriasis patients than controls (p<0.001) increasing risk of psoriasis development by about 5, 12 and 6 times than AG, GG and G allele. AA genotype was significantly associated with psoriasis severity (p=0.005), and high S100A8 serum levels (P= 0.018).

CONCLUSIONS

Circulating S100A8 could associated with disease severity and have an active role in psoriasis pathogenesis. S100A8 (rs3806232) SNP (AA genotype and A allele) might contribute to development and severity of psoriasis in the Egyptian population.

UVB-mediated DNA damage induces matrix metalloproteinases to promote photoaging in an AhR- and SP1-dependent manner

It is currently thought that UVB radiation drives photoaging of the skin primarily by generating ROS. In this model, ROS purportedly activates activator protein-1 to upregulate MMPs 1, 3, and 9, which then degrade collagen and other extracellular matrix components to produce wrinkles. However, these MMPs are expressed at relatively low levels and correlate poorly with wrinkles, suggesting that another mechanism distinct from ROS and MMP1/3/9 may be more directly associated with photoaging. Here we show that MMP2, which degrades type IV collagen, is abundantly expressed in human skin, increases with age in sun-exposed skin, and correlates robustly with aryl hydrocarbon receptor (AhR), a transcription factor directly activated by UV-generated photometabolites. Through mechanistic studies with HaCaT human immortalized keratinocytes, we found that AhR, specificity protein 1 (SP1), and other pathways associated with DNA damage are required for the induction of both MMP2 and MMP11 (another MMP implicated in photoaging), but not MMP1/3. Last, we found that topical treatment with AhR antagonists vitamin B₁₂ and folic acid ameliorated UVB-induced wrinkle formation in mice while dampening MMP2 expression in the skin. These results directly implicate DNA damage in photoaging and reveal AhR as a potential target for preventing wrinkles.

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.

6-Formylindolo[3,2-b]carbazole, a Potent Ligand for the Aryl Hydrocarbon Receptor Produced Both Endogenously and by Microorganisms, can Either Promote or Restrain Inflammatory Responses

The aryl hydrocarbon receptor (AHR) binds major physiological modifiers of the immune system. The endogenous 6-formylindolo[3,2-b]carbazole (FICZ), which binds with higher affinity than any other compound yet tested, including TCDD, plays a well-documented role in maintaining the homeostasis of the intestines and skin. The effects of transient activation of AHR by FICZ differ from those associated with continuous stimulation and, depending on the dose, include either differentiation into T helper 17 cells that express proinflammatory cytokines or into regulatory T cells or macrophages with anti-inflammatory properties. Moreover, in experimental models of human diseases high doses stimulate the production of immunosuppressive cytokines and suppress pathogenic autoimmunity. In our earlier studies we characterized the formation of FICZ from tryptophan via the precursor molecules indole-3-pyruvate and indole-3-acetaldehyde. In the gut formation of these precursor molecules is catalyzed by microbial aromatic-amino-acid transaminase ArAT. Interestingly, tryptophan can also be converted into indole-3-pyruvate by the amino-acid catabolizing enzyme interleukin-4 induced gene 1 (IL4I1), which is secreted by host immune cells. By thus generating derivatives of tryptophan that activate AHR, IL4I1 may have a role to play in anti-inflammatory responses, as well as in a tumor escape mechanism that reduces survival in cancer patients. The realization that FICZ can be produced from tryptophan by sunlight, by enzymes expressed in our cells (IL4I1), and by microorganisms as well makes it highly likely that this compound is ubiquitous in humans. A diurnal oscillation in the level of FICZ that depends on the production by the fluctuating number of microbes might influence not only intestinal and dermal immunity locally, but also systemic immunity.

Targeting AhR as a Novel Therapeutic Modality against Inflammatory Diseases

For decades, activation of Aryl Hydrocarbon Receptor (AhR) was excluded from consideration as a therapeutic approach due to the potential toxic effects of AhR ligands and the induction of the cytochrome P450 enzyme, Cyp1a1, following AhR activation. However, it is now understood that AhR activation not only serves as an environmental sensor that regulates the effects of environmental toxins, but also as a key immunomodulator where ligands induce a variety of cellular and epigenetic mechanisms to attenuate inflammation. Thus, the emergence of further in-depth research into diverse groups of compounds capable of activating this receptor has prompted reconsideration of its use therapeutically. The aim of this review is to summarize the body of research surrounding AhR and its role in regulating inflammation. Specifically, evidence supporting the potential of targeting this receptor to modulate the immune response in inflammatory and autoimmune diseases will be highlighted. Additionally, the opportunities and challenges of developing AhR-based therapies to suppress inflammation will be discussed.

Role of Aryl Hydrocarbon Receptor Activation in Inflammatory Chronic Skin Diseases

Aryl Hydrocarbon Receptor (AhR) is an evolutionary transcription factor which acts as a crucial sensor of different exogenous and endogenous molecules Recent data indicate that AhR is implicated in several physiological processes such as cell physiology, host defense, proliferation and differentiation of immune cells, and detoxification. Moreover, AhR involvement has been reported in the development and maintenance of several pathological conditions. In recent years, an increasing number of studies have accumulated highlighting the regulatory role of AhR in the physiology of the skin. However, there is evidence of both beneficial and harmful effects of AHR signaling. At present, most of the evidence concerns inflammatory skin diseases, in particular atopic dermatitis, psoriasis, acne, and hidradenitis suppurativa. This review exam-ines the role of AhR in skin homeostasis and the therapeutic implication of its pharmacological modulation in these cutaneous inflammatory diseases.