The Aryl Hydrocarbon Receptor and Its Ligands Inhibit Myofibroblast Formation and Activation: Implications for Thyroid Eye Disease

The Aryl Hydrocarbon Receptor: A Crucial Mediator in Ocular Disease Pathogenesis and Therapeutic Targeting

The aryl hydrocarbon receptor (AHR) is a pivotal nuclear receptor involved in mediating cellular responses to a wide range of environmental pollutants and endogenous ligands. AHR plays a central role in regulating essential physiological processes, including xenobiotic metabolism, immune response modulation, cell cycle control, tumorigenesis, and developmental events. Recent studies have identified AHR as a critical mediator and a potential therapeutic target in the pathogenesis of ocular diseases. This review provides a thorough analysis of the various functions of AHR signalling in the ocular environment, with a specific emphasis on its effects on the retina, retinal pigment epithelium (RPE), choroid, and cornea. We provide a detailed discussion on the molecular mechanisms through which AHR integrates environmental and endogenous signals, influencing the development and progression of age-related macular degeneration (AMD), retinitis pigmentosa, uveitis, and other major ocular disorders. Furthermore, we evaluate the therapeutic potential of modulating AHR activity through novel ligands and agonists as a strategy for treating eye diseases. Understanding the molecular mechanisms of AHR in ocular tissues may facilitate the development of AHR-targeted therapies, which is crucial for addressing the pressing clinical demand for novel treatment strategies in ocular diseases.

Tumor suppressive activity of AHR in environmental arsenic-induced carcinogenesis

The aryl hydrocarbon receptor (AHR) is a highly conserved pleiotropic transcription factor that senses environmental pollutants, microbial products, and endogenous ligands. The transcriptional targets of AHR include phase I and phase II detoxification enzymes, as well as numerous signaling molecules that affect a wide spectrum of biological and biochemical processes in a manner of cellular context-dependent. In this review, we systematically assess the latest discoveries of AHR in carcinogenesis with an emphasis on its tumor suppressor-like property that represses the expression of genes in oncogenic signaling pathways. Additionally, we outline recent progress in our studies on the interaction among AHR, TGFb and NRF2 in cellular responses to arsenic and malignant transformation. Our findings indicate that AHR antagonized TGFb and NRF2, suggesting that AHR could serve as a potential tumor suppressor in arsenic-induced carcinogenesis. Notably, while AHR can exhibit both oncogenic and tumor-suppressive properties in cancer development and the generation of the cancer stem-like cells (CSCs), the tumor suppressor-like effect of AHR warrants further extensive exploration for the prevention and clinical treatment of cancers.

RNA aptamers with specific binding affinity to CD40 (CD40Apt) represents a promising antagonist of the CD40-CD40L signaling for thyroid-associated ophthalmopathy (TAO) treatment in mouse

Thyroid-associated ophthalmopathy (TAO) is the most common autoimmune inflammatory diseases of the orbit. The CD40-CD40L pathway has been regarded as a potential molecular mechanism contributing to the development and progression of TAO, and RNA aptamers with specific binding affinity to CD40 (CD40Apt) represents a promising inhibitor of the CD40-CD40L signaling in TAO treatment. In this study, CD40Apt was confirmed to specifically recognize mouse CD40-positive ortibtal fibroblast. Mouse orbital fibroblasts were isolated from TAO mice model orbital tissues and validated. In TGF-β-induced orbital fibroblast activation model in vitro, CD40Apt administration inhibited TGF-β-induced cell viability, decreased TGF-β-induced α-SMA, Collagen I, Timp-1, and vimentin levels, and suppressed TGF-β-induced phosphorylation of Erk, p38, JNK, and NF-κB. In TAO mice model in vivo, CD40Apt caused no significant differences to the body weight of mice; furthermore, CD40Apt improved the eyelid broadening, ameliorated inflammatory infiltration and the hyperplasia in orbital muscle and adipose tissues in model mice. Concerning orbital fibroblast activation, CD40Apt reduced the levels of CD40, collagen I, TGF-β, and α-SMA in orbital muscle and adipose tissues of model mice. Finally, CD40Apt administration significantly suppressed Erk, p38, JNK, and NF-κB phosphorylation. In conclusion, CD40Apt, specifically binds to CD40 proteins in their natural state on the cell surface with high affinity, could suppress mouse orbital fibroblast activation, therefore improving TAO in mice model through the CD40 and downstream signaling pathways. CD40Apt represents a promising antagonist of the CD40-CD40L signaling for TAO treatment.

AhR and Wnt/β-Catenin Signaling Pathways and Their Interplay

As evolutionarily conserved signaling cascades, AhR and Wnt signaling pathways play a critical role in the control over numerous vital embryonic and somatic processes. AhR performs many endogenous functions by integrating its signaling pathway into organ homeostasis and into the maintenance of crucial cellular functions and biological processes. The Wnt signaling pathway regulates cell proliferation, differentiation, and many other phenomena, and this regulation is important for embryonic development and the dynamic balance of adult tissues. AhR and Wnt are the main signaling pathways participating in the control of cell fate and function. They occupy a central position in a variety of processes linked with development and various pathological conditions. Given the importance of these two signaling cascades, it would be interesting to elucidate the biological implications of their interaction. Functional connections between AhR and Wnt signals take place in cases of crosstalk or interplay, about which quite a lot of information has been accumulated in recent years. This review is focused on recent studies about the mutual interactions of key mediators of AhR and Wnt/β-catenin signaling pathways and on the assessment of the complexity of the crosstalk between the AhR signaling cascade and the canonical Wnt pathway.

Thinking inside the box: Current insights into targeting orbital tissue remodeling and inflammation in thyroid eye disease

Thyroid eye disease (TED) is an autoimmune disorder that manifests in the orbit. In TED, the connective tissue behind the eye becomes inflamed and remodels with increased fat accumulation and/or increased muscle and scar tissue. As orbital tissue expands, patients develop edema, exophthalmos, diplopia, and optic neuropathy. In severe cases vision loss may occur secondary to corneal scarring from exposure or optic nerve compression. Currently there is no cure for TED, and treatments are limited. A major breakthrough in TED therapy occurred with the FDA approval of teprotumumab, a monoclonal insulin-like growth factor 1 receptor (IGF1R) blocking antibody. Yet, teprotumumab therapy has limitations, including cost, infusion method of drug delivery, variable response, and relapse. We describe approaches to target orbital fibroblasts and the complex pathophysiology that underlies tissue remodeling and inflammation driving TED. Further advances in the elucidation of the mechanisms of TED may lead to prophylaxis based upon early biomarkers as well as lead to more convenient, less expensive therapies.

More than Meets the Eye: The Aryl Hydrocarbon Receptor is an Environmental Sensor, Physiological Regulator and a Therapeutic Target in Ocular Disease

The aryl hydrocarbon receptor (AHR) is a ligand activated transcription factor originally identified as an environmental sensor of xenobiotic chemicals. However, studies have revealed that the AHR regulates crucial aspects of cell growth and metabolism, development and the immune system. The importance of the AHR and AHR signaling in eye development, toxicology and disease is now being uncovered. The AHR is expressed in many ocular tissues including the retina, choroid, cornea and the orbit. A significant role for the AHR in age-related macular degeneration (AMD), autoimmune uveitis, and other ocular diseases has been identified. Ligands for the AHR are structurally diverse organic molecules from exogenous and endogenous sources. Natural AHR ligands include metabolites of tryptophan and byproducts of the microbiome. Xenobiotic AHR ligands include persistent environmental pollutants such as dioxins, benzo (a) pyrene [B (a) P] and polychlorinated biphenyls (PCBs). Pharmaceutical agents including the proton pump inhibitors, esomeprazole and lansoprazole, and the immunosuppressive drug, leflunomide, activate the AHR. In this review, we highlight the role of the AHR in the eye and discuss how AHR signaling is involved in responding to endogenous and environmental stimuli. We also present the emerging concept that the AHR is a promising therapeutic target for eye disease.

Aryl Hydrocarbon Receptor Mechanisms Affecting Chronic Kidney Disease

The aryl hydrocarbon receptor (AHR) is a basic helix-loop-helix transcription factor that binds diverse endogenous and xenobiotic ligands, which regulate AHR stability, transcriptional activity, and cell signaling. AHR activity is strongly implicated throughout the course of chronic kidney disease (CKD). Many diverse organic molecules bind and activate AHR and these ligands are reported to either promote glomerular and tubular damage or protect against kidney injury. AHR crosstalk with estrogen, peroxisome proliferator-activated receptor-γ, and NF-κB pathways may contribute to the diversity of AHR responses during the various forms and stages of CKD. The roles of AHR in kidney fibrosis, metabolism and the renin angiotensin system are described to offer insight into CKD pathogenesis and therapies.

IL-11 Is Elevated and Drives the Profibrotic Phenotype Transition of Orbital Fibroblasts in Thyroid-Associated Ophthalmopathy

Orbital fibrosis is a hallmark of tissue remodeling in thyroid-associated ophthalmopathy (TAO). Previous studies have shown that interleukin (IL)-11 plays a pivotal profibrotic role in various inflammatory and autoimmune diseases. However, the expression pattern of IL-11 in patients with TAO and whether IL-11 is mechanistically linked with pathological fibrosis remains unknown. In this study, we investigated IL-11 levels in the serum and orbital connective tissue of patients with TAO, and evaluated the correlation of these levels with the patient's clinical activity score. We also evaluated the expression pattern of IL-11Rα in orbital connective tissue. Furthermore, we elucidated the regulatory factors, profibrotic function, and downstream signaling pathways for IL-11 in TAO using in vitro studies. IL-11 levels in serum and orbital connective tissues were increased in patients with TAO, as compared with healthy controls. In addition, both levels were positively correlated with disease activity. Single-cell RNA sequencing of orbital connective tissue indicated that IL-11Rα was dominantly expressed in orbital fibroblasts (OFs). RNA sequencing of paired unstimulated and transforming growth factor (TGF)-β1-stimulated samples demonstrated that upregulation of IL-11 expression defined the dominant transcriptional response. IL-11 signaling was also confirmed to be downstream of TGF-β1 and IL-1β. Therefore, we deduced that IL-11 protein is secreted in an autocrine loop in TAO. We also indicated that IL-11 mediated the profibrotic phenotype switch by inducing the expression of myofibroblast differentiation markers, including α-smooth muscle actin and collagen type I α1, which could be abrogated by an anti-IL-11 neutralizing antibody. Furthermore, we revealed that extracellular regulated protein kinase may be a crucial factor in the pro-fibrotic, translationally specific signaling activity of IL-11. These data demonstrate that IL-11 plays a crucial role in orbital fibroblast phenotype switching and may be a potential therapeutic target candidate for the treatment of TAO.

Therapeutic Effect of α-MSH in Primary Cultured Orbital Fibroblasts Obtained from Patients with Thyroid Eye Disease

Inflammation, hyaluronan production, and adipogenesis are the main pathological events leading to thyroid eye disease (TED). α-Melanocytemelanocyte-stimulating hormone (α-MSH) is a well-known tridecapeptidetreatment for several inflammatory disorders including sepsis syndrome, acute respiratory distress syndrome, rheumatoid arthritis, and encephalitis. Here, we investigated the effect of α-MSH treatment on TED. The 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and Lactate Dehydrogenase (LDH) assays were performed to analyze the effect of α-MSH on cell viability and it's toxicity. Using primary cultures of orbital fibroblasts from TED patients and non-TED as control, we examined the effects of α-MSH on proinflammatory cytokine production induced by interleukin (IL)-1β, further analyzed by real-time reverse transcription-polymerase chain reaction (qPCR) and western blotting. Immunofluorescence staining assay and qPCR were performed to examine proopiomelanocortin (POMC) expression, the upstream neuropeptide of α-MSH in TED patients and non-TED control. Treatment with non-cytotoxic concentrations of α-MSH resulted in the dose-dependent inhibition of mRNA and protein levels (p < 0.05) for IL-1β-induced inflammatory cytokines: IL-6, IL-8, MCP-1, ICAM-1, and COX-2. The expression of POMC mRNA and protein were significantly higher in TED patients compared to non-TED control (p < 0.05). Our data show significant inhibitory effects of α-MSH on inflammation, POMC production in orbital fibroblasts. At present, this is the first in vitro preclinical evidence of α-MSH therapeutic effect on TED. These findings indicate that POMC and α-MSH may play a role in the immune regulation of TED and can be a potential therapeutic target.

TGF-β Physiology as a Novel Therapeutic Target Regarding Autoimmune Thyroid Diseases: Where Do We Stand and What to Expect

Transforming growth factor beta (TGF-β), as a master regulator of immune response, is deeply implicated in the complex pathophysiology and development of autoimmune thyroid diseases. Based on the close interplay between thyroid autoimmunity and TGF-β, scientific interest was shifted to the understanding of the possible role of this molecule regarding the diagnosis, prognosis, and therapy of these diseases. The main aim of this review is to present research data about possible treatment options based on the role of TGF-β in thyroid autoimmunity. Suggested TGF-β-mediated therapeutic strategies regarding autoimmune thyroid diseases include either the enhancement of its immunosuppressive role or inhibition of its facilitatory role in thyroid autoimmunity. For example, the application of hr-TGF-β can be used to bolster the inhibitory role of TGF-β regarding the development of thyroid diseases, whereas anti-TGF-β antibodies and similar molecules could impede its immune-promoting effects by blocking different levels of TGF-β biosynthesis and activation pathways. In conclusion, TGF-β could evolve to a promising, novel therapeutic tool for thyroid autoimmunity.

Serum Krebs von den Lungen-6 and lung ultrasound B lines as potential diagnostic and prognostic factors for rheumatoid arthritis-associated interstitial lung disease

INTRODUCTION

Rheumatoid arthritis (RA)-associated interstitial lung disease (ILD) (RA-ILD) is a serious systemic RA manifestation with high mortality that needs proper, accurate, and sensitive assessment tools.

OBJECTIVES

Firstly, evaluate serum Krebs von den Lungen-6 (KL-6) levels and lung ultrasound B lines (LUS B lines) score in RA-ILD correlating them with the severity of ILD assessed by high-resolution computed tomography (HRCT) and pulmonary function tests (PFTs). Secondly, determine cut-off values for LUS and KL-6 in RA-ILD assessment and outcome prediction.

METHODS

A case-control study included seventy-five RA-ILD patients with an equal number of matched RA patients without ILD. Clinical assessment includes DAS-28 and PFTs, laboratory assessment of serum KL-6 by latex-enhanced immunoturbidimetric assay, and radiological evaluation of ILD using semiquantitative CT grade and LUS B lines.

RESULTS

RA-ILD patients had significantly higher serum KL6 compared to those without ILD (1025.5 ± 419.6 vs. 237.5 ± 51.9, p ≤ 0.001). Serum KL6 was positively correlated with HRCT and LUS scores (r = 0.93, r = 0.97, respectively) with negative correlation with FVC% and FEV1% (r = - 0.93, r = - 0.91, respectively). LUS was positively correlated with KL6 and HRCT (r = 0.97, r = 0.944, respectively) while, negatively correlated with PFTs. Cut-off values of KL6 and LUS were 277.5 U/ml and < 5.5, with AUC 0.878 and 1, sensitivity 86.7% and 100%, and specificity 88% and 100%, respectively.

CONCLUSIONS

The non-invasive, radiation-free LUS with a score < 5.5 combined with serum KL6 could be helpful for RA-ILD assessment correlating with HRCT and disease severity. Serum KL6 combined with LUS is important new and potential prognostic factor predicting poor outcomes in RA-ILD. Further large-scale, multi-center, and prospective studies are needed to confirm these findings.

KEY POINTS

• Combination of the non-invasive, radiation-free LUS with a score < 5.5 and serum KL6 levels of 277.5 U/ml is recommended as prognostic tools for RA-ILD. • Easily obtainable tests such as serum KL-6, inflammatory markers, and LUS are sensitive for assessing RA-ILD and the risk of poor outcomes in patients with RA-ILD. • RA-ILD patients with higher KL6 levels, higher LUS scores had a poor prognosis with short survival. • LUS B lines could be used as the first imaging tool for the evaluation of RA-ILD decreasing the risk of HRCT radiation exposure in asymptomatic or mild RA-ILD patients.

Kynurenine promotes the cytotoxicity of NK cells through aryl hydrocarbon receptor in early pregnancy

During early pregnancy, decidual NK (dNK) cells play indispensable roles in many processes including the decidualization, the implantation, and the maintenance of immune tolerance. Abnormal cytotoxic activity of NK cells can cause recurrent spontaneous abortion (RSA), while the regulatory mechanism of NK cytotoxicity remains to be unclear. In this study, we found that kynurenine in decidua and villus was in a comparable level between patients with RSA and normal pregnancy women. However, the aryl hydrocarbon receptor (AhR) in decidual NK cells was significantly increased in RSA. Compared with AhR^- NK cells, cytotoxic activity-related molecules (NKP30, NKP46, NKG2D, perforin, granzyme B and IFN-γ) was highly expressed in both AhR⁺ peripheral and decidual NK cells, and kynurenine stimulation promoted the expression of killer receptors and the cytoplasmic granules in an AhR-dependent manner. Stimulation with TNF-α, IL-β and LPS upregulated the AhR expression in dNK cells in vitro. These results indicate that kyn/AhR signal enhances the cytotoxicity of NK cells, and increased expression of AhR may be an induction factor of RSA.

The Aryl Hydrocarbon Receptor: A Mediator and Potential Therapeutic Target for Ocular and Non-Ocular Neurodegenerative Diseases

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor, which senses environmental, dietary or metabolic signals to mount a transcriptional response, vital in health and disease. As environmental stimuli and metabolic products have been shown to impact the central nervous system (CNS), a burgeoning area of research has been on the role of the AHR in ocular and non-ocular neurodegenerative diseases. Herein, we summarize our current knowledge, of AHR-controlled cellular processes and their impact on regulating pathobiology of select ocular and neurodegenerative diseases. We catalogue animal models generated to study the role of the AHR in tissue homeostasis and disease pathogenesis. Finally, we discuss the potential of targeting the AHR pathway as a therapeutic strategy, in the context of the maladies of the eye and brain.

The aryl hydrocarbon receptor: An environmental effector in the pathogenesis of fibrosis

The aryl hydrocarbon receptor (AhR) is a highly conserved transcription factor that can be activated by small molecules provided by dietary, plant, or microbial metabolites, and environmental pollutants. AhR is expressed in many cell types and engages in crosstalk with other signaling pathways, and therefore provides a molecular pathway that integrates environmental cues and metabolic processes. Fibrosis, which is defined as an aberrant extracellular matrix formation, is a reparative process in the terminal stage of chronic diseases. Both environmental and internal factors have been shown to participate in the pathogenesis of fibrosis; however, the underlying mechanisms still remain elusive. In this review, the potential role of AhR in the process of fibrosis, as well as potential opportunities and challenges in the development of AhR targeting therapeutics, are summarized.

Aryl hydrocarbon receptor signaling activation in systemic sclerosis attenuates collagen production and is a potential antifibrotic target

Systemic sclerosis (SSc) is a systemic autoimmune disease that often leads to fibrosis of multiple organs, and there are no effective treatments. Aryl hydrocarbon receptor (AhR) is a highly evolutionarily conserved transcription factor activated by endogenous and exogenous ligands and that regulate cell proliferation, tumorigenesis and immune balance. Recently, it have reported AhR signaling may participate in fibrosis process, usually consider as a negative regulator of TGF-β. However, the detailed relationship between AhR and SSc has not been reported yet. Here we firstly found that AhR and CYP1A1 downregulated in SSc fibroblast(n = 6). The AhR ligand-Ficz negatively regulates TGF-β1, COL1A1 and α-SMA expression, also enhances the MMP-1 expression via the AhR signaling activation. Conversely the AhR antagonist CH223191 could inhibit this effect. Furthermore, the antifibrosis effect of AhR signaling activation was also confirmed in bleomycin induced scleroderma mouse model. In conclusion, AhR signaling activation balances the extracellular matrix (ECM) composition and deposition, which may provide a new sight to the pathogenesis of SSc and AhR signaling activation may be a potential therapy for SSc.

A highly simulated scar model developed by grafting human thin split-thickness skin on back of nude mouse: The remodeling process, histological characteristics of scars

A predictive scar animal model is needed in order to study the mechanism and assess the therapies before its use in humans. However, due to the differences in wound healing patterns and regeneration ability, none of the existing models can fully simulate the characteristics of human scar. The aim of this study was to build a model that recapitulated the developing process and outcomes of human hypertrophic scar (HS). Nude mice were grafted with thin split-thickness human skins. The dynamic changes and final outcomes of the grafts were investigated. The results showed that human skin grafts survived and underwent progressive scarring remodeling in morphology and histology. Scar related markers (α-SMA, CD34, Collage I, TGF-β1) were positive in immunohistology. Protein expressions in TGF-β1/Smad2/3 pathway were increased in accordance with HS during the development process by western blotting. It was finally proved that scar reconstructed by this model matches a real-world human HS. This is a stable, easy to reproduce model for studying the scar formation process and its properties.

The aryl hydrocarbon receptor pathway controls matrix metalloproteinase-1 and collagen levels in human orbital fibroblasts

Thyroid eye disease (TED) affects 25–50% of patients with Graves’ Disease. In TED, collagen accumulation leads to an expansion of the extracellular matrix (ECM) which causes destructive tissue remodeling. The purpose of this study was to investigate the therapeutic potential of activating the aryl hydrocarbon receptor (AHR) to limit ECM accumulation in vitro. The ability of AHR to control expression of matrix metalloproteinase-1 (MMP1) was analyzed. MMP1 degrades collagen to prevent excessive ECM. Human orbital fibroblasts (OFs) were treated with the pro-scarring cytokine, transforming growth factor beta (TGFβ) to induce collagen production. The AHR ligand, 6-formylindolo[3,2b]carbazole (FICZ) was used to activate the AHR pathway in OFs. MMP1 protein and mRNA levels were analyzed by immunosorbent assay, Western blotting and quantitative PCR. MMP1 activity was detected using collagen zymography. AHR and its transcriptional binding partner, ARNT were depleted using siRNA to determine their role in activating expression of MMP1. FICZ induced MMP1 mRNA, protein expression and activity. MMP1 expression led to a reduction in collagen 1A1 levels. Furthermore, FICZ-induced MMP1 expression required both AHR and ARNT, demonstrating that the AHR-ARNT transcriptional complex is necessary for expression of MMP1 in OFs. These data show that activation of the AHR by FICZ increases MMP1 expression while leading to a decrease in collagen levels. Taken together, these studies suggest that AHR activation could be a promising target to block excessive collagen accumulation and destructive tissue remodeling that occurs in fibrotic diseases such as TED.

TSHR Signaling Stimulates Proliferation Through PI3K/Akt and Induction of miR-146a and miR-155 in Thyroid Eye Disease Orbital Fibroblasts

Purpose

To investigate the molecular pathways that drive thyroid stimulating hormone receptor (TSHR)–induced cellular proliferation in orbital fibroblasts (OFs) from thyroid eye disease (TED) patients.

Methods

Orbital fibroblasts from TED and non-TED patients were treated with TSH and changes in gene expression and proliferation were measured. To determine the role of TSHR, TSHR-specific siRNA was used to deplete TSHR levels. Proliferation was measured by bromodeoxyuridine (BrdU) incorporation. PI3K/Akt activation was analyzed by Western blot. The PI3K inhibitor LY294002 was used to investigate PI3K/Akt signaling in OF proliferation. Expression of TSHR, inflammatory cytokines, proliferation related genes and miR-146a and miR-155 were measured by qPCR.

Results

Orbital fibroblasts from TED patients proliferate significantly more than non-TED OFs in response to TSH. TSH-induced proliferation was dependent upon TSHR expression and required the PI3K/Akt signaling cascade. TSHR activation stimulated miR-146a and miR-155 expression. TED OFs produced significantly more miR-146a and miR-155 than non-TED OFs. MiR-146a and miR-155 targets, ZNRF3 and PTEN, which both limit cell proliferation, were decreased in TSH treated OFs.

Conclusions

These data reveal that TSHR signaling in TED OFs stimulates proliferation directly through PI3K/Akt signaling and indirectly through induction of miR-146a and miR-155. MiR-146a and miR-155 enhance TED OF proliferation by reducing expression of target genes that normally block cell proliferation. TSHR-dependent expression of miR-146a and miR-155 may explain part of the fibroproliferative pathology observed in TED.

Exposure to Heptachlorodibenzo-p-dioxin (HpCDD) Regulates microRNA Expression in Human Lung Fibroblasts

OBJECTIVE

Benzo(ghi)perylene (BghiP) and 1,2,3,4,6,7,8-Heptachlorodibenzo-p-dioxin (HpCDD) were elevated in serum from personnel deployed to sites with open burn pits. Here, we investigated the ability of BghiP and HpCDD to regulate microRNA (miRNA) expression through the aryl hydrocarbon receptor (AHR).

METHODS

Human lung fibroblasts (HLFs) were exposed to BghiP and HpCDD. AHR activity was measured by reporter assay and gene expression. Deployment related miRNA were measured by quantitative polymerase chain reaction. AHR expression was depleted using siRNA.

RESULTS

BghiP displayed weak AHR agonist activity. HpCDD induced AHR activity in a dose-dependent manner. Let-7d-5p, miR-103-3p, miR-107, and miR-144-3p levels were significantly altered by HpCDD. AHR knockdown attenuated these effects.

CONCLUSIONS

These studies reveal that miRNAs previously identified in sera from personnel deployed to sites with open burn pits are altered by HpCDD exposure in HLFs.

Targeting Aryl hydrocarbon receptor for next-generation immunotherapies: Selective modulators (SAhRMs) versus rapidly metabolized ligands (RMAhRLs)

Aryl Hydrocarbon Receptor (AhR) constitutes a major network hub of genomic and non-genomic signaling pathways, connecting host's immune cells to environmental factors. It shapes innate and adaptive immune processes to environmental stimuli with species-, cell- and tissue-type dependent specificity. Although an ever increasing number of studies has thrust AhR into the limelight as attractive target for the development of next-generation immunotherapies, concerns exist on potential safety issues associated with small molecule modulation of the receptor. Selective AhR modulators (SAhRMs) and rapidly metabolized AhR ligands (RMAhRLs) are two classes of receptor agonists that are emerging as interesting lead compounds to bypass AhR-related toxicity in favor of therapeutic effects. In this article, we discuss SAhRMs and RMAhRLs reported in literature, covering concepts underlying their definitions, specific binding modes, structure-activity relationships and AhR-mediated functions.

Proton pump inhibitors attenuate myofibroblast formation associated with thyroid eye disease through the aryl hydrocarbon receptor

Thyroid eye disease (TED) can lead to scar formation and tissue remodeling in the orbital space. In severe cases, the scarring process leads to sight-threatening pathophysiology. There is no known effective way to prevent scar formation in TED patients, or to reverse scarring once it occurs. In this study, we show that the proton pump inhibitors (PPIs), esomeprazole and lansoprazole, can prevent transforming growth factor beta (TGFβ)-mediated differentiation of TED orbital fibroblasts to myofibroblasts, a critical step in scar formation. Both PPIs prevent TGFβ-induced increases in alpha-smooth muscle actin (αSMA), calponin, and collagen production and reduce TED orbital fibroblast cell proliferation and migration. Esomeprazole and lansoprazole exert these effects through an aryl hydrocarbon receptor (AHR)-dependent pathway that includes reducing β-catenin/Wnt signaling. We conclude that PPIs are potentially useful therapies for preventing or treating TED by reducing the myofibroblast accumulation that occurs in the disease.

Discovery of Novel Small Molecules that Block Myofibroblast Formation: Implications for Capsular Contracture Treatment

Capsular contracture is a devastating complication that occurs in patients undergoing implant-based breast reconstruction. Ionizing radiation drives and exacerbates capsular contracture in part by activating cytokines, including transforming growth factor-beta (TGF-β). TGF-β promotes myofibroblast differentiation and proliferation, leading to excessive contractile scar formation. Therefore, targeting the TGF-β pathway may attenuate capsular contracture.

METHODS

A 20,000 small molecule library was screened for anti-TGF-β activity. Structurally diverse anti-TGF-β agents were identified and then tested on primary human capsular fibroblasts. Fibroblasts were irradiated or not, and then treated with both TGF-β and candidate molecules. Resulting cells were then analyzed for myofibroblast activity using myofibroblast markers including alpha-smooth muscle actin, collagen I, Thy1, and periostin, using Western Blot, quantitative real-time polymerase chain reaction, and immunofluorescence.

RESULTS

Human capsular fibroblasts treated with TGF-β showed a significant increase in alpha-smooth muscle actin, collagen I, and periostin levels (protein and/or mRNA). Interestingly, fibroblasts treated with latent TGF-β and 10 Gy radiation also showed significantly increased levels of myofibroblast markers. Cells that were treated with the novel small molecules showed a significant reduction in myofibroblast activation, even in the presence of radiation.

CONCLUSIONS

Several novel small molecules with anti-TGF-β activity can effectively prevent human capsular fibroblast to myofibroblast differentiation in vitro, even in the presence of radiation. These results highlight novel therapeutic options that may be utilized in the future to prevent radiation-induced capsular contracture.

Mechanisms of lung disease development in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disorder that causes joint inflammation and damage. Extra-articular manifestations occur in many patients and can include lung involvement in the form of airway or parenchymal inflammation and fibrosis. Although the pathophysiology of articular RA has been extensively investigated, the mechanisms causing airway and parenchymal lung disease are not well defined. Infections, cigarette-smoking, mucosal dysbiosis, host genetics and premature senescence are all potentially important contributors to the development of lung disease in patients with RA. RA-associated lung disease (which can predate the onset of articular disease by many years) probably originates from chronic airway and alveolar epithelial injury that occurs in an individual with a genetic background that permits the development of autoimmunity, leading to chronic inflammation and subsequent airway and lung parenchymal remodelling and fibrosis. Further investigations into the specific mechanisms by which lung disease develops in RA will be crucial for the development of effective therapies. Identifying mechanisms by which environmental and host factors cooperate in the induction of autoimmunity in the lung might also help to establish the order of early events in RA.

Negative association between serum aryl hydrocarbon receptor concentrations and β-cell function in patients with no history of diabetes undergoing coronary angiography

BACKGROUND

The aim of the present study was to investigate the association between serum aryl hydrocarbon receptor (AhR) levels and insulin resistance and β-cell function in patients undergoing coronary angiography with no history of diabetes.

METHODS

Patients with no history of diabetes who had undergone coronary angiography underwent an oral glucose tolerance test (OGTT) 2-4 weeks after discharge from hospital; blood samples were collected for measurements of glucose, insulin, and AhR. Patients' glucose regulation status was determined on the basis of the OGTT. Insulin resistance was assessed using the homeostasis model assessment of insulin resistance (HOMA-IR). β-Cell function was assessed using the insulinogenic index (IGI).

RESULTS

The study included 473 patients (mean (±SD) age 61 ±12 years, 81.8% male, mean body mass index 26.1 ±3.6 kg/m² ). Overall, mean serum AhR concentrations were 25.1 ±12.2 pg/mL. Patients with normal glucose tolerance had a lower serum AhR concentrations than patients with prediabetes or newly diagnosed diabetes (23.4 ±10.8 vs 26.2 ±13.2 and 26.9 ±12.3 pg/mL, respectively; P = 0.029). Linear regression analysis revealed that serum AhR concentrations were not associated with HOMA-IR, but were negatively associated with IGI after adjustment for several confounders, including HOMA-IR (β = -0.162; 95% confidence interval - 0.302, -0.022; P = 0.023).

CONCLUSIONS

In patients with no history of diabetes, serum AhR concentrations were negatively associated with β-cell function, independent of several confounders, including insulin resistance.

Tryptophan metabolites kynurenine and serotonin regulate fibroblast activation and fibrosis

Fibrosis is a pathological form of aberrant tissue repair, the complications of which account for nearly half of all deaths in the industrialized world. All tissues are susceptible to fibrosis under particular pathological sets of conditions. Though each type of fibrosis has characteristics and hallmarks specific to that particular condition, there appear to be common factors underlying fibrotic diseases. One of these ubiquitous factors is the paradigm of the activated myofibroblast in the promotion of fibrotic phenotypes. Recent research has implicated metabolic byproducts of the amino acid tryptophan, namely serotonin and kynurenines, in the pathology or potential pharmacologic therapy of fibrosis, in part through their effects on development of myofibroblast phenotypes. Here, we review literature underlying what is known mechanistically about the effects of these compounds and their respective pathways on fibrosis. Pharmacologic administration of kynurenine improves scarring outcomes in vivo likely not only through its well-characterized immunosuppressive properties but also via its demonstrated antagonism of fibroblast activation and of collagen deposition. In contrast, serotonin directly promotes activation of fibroblasts via activation of canonical TGF-β signaling, and overstimulation with serotonin leads to fibrotic outcomes in vivo. Recently discovered feedback inhibition between serotonin and kynurenine pathways also reveals more information about the cellular physiology of tryptophan metabolism and may also underlie possible paradigms for anti-fibrotic therapy. Together, understanding of the effects of tryptophan metabolism on modulation of fibrosis may lead to the development of new therapeutic avenues for treatment through exploitation of these effects.

The tryptophan derivative 6-formylindolo[3,2-b]carbazole, FICZ, a dynamic mediator of endogenous aryl hydrocarbon receptor signaling, balances cell growth and differentiation

The aryl hydrocarbon receptor (AHR) is not essential to survival, but does act as a key regulator of many normal physiological events. The role of this receptor in toxicological processes has been studied extensively, primarily employing the high-affinity ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, regulation of physiological responses by endogenous AHR ligands remains to be elucidated. Here, we review developments in this field, with a focus on 6-formylindolo[3,2-b]carbazole (FICZ), the endogenous ligand with the highest affinity to the receptor reported to date. The binding of FICZ to different isoforms of the AHR seems to be evolutionarily well conserved and there is a feedback loop that controls AHR activity through metabolic degradation of FICZ via the highly inducible cytochrome P450 1A1. Several investigations provide strong evidence that FICZ plays a critical role in normal physiological processes and can ameliorate immune diseases with remarkable efficiency. Low levels of FICZ are pro-inflammatory, providing resistance to pathogenic bacteria, stimulating the anti-tumor functions, and promoting the differentiation of cancer cells by repressing genes in cancer stem cells. In contrast, at high concentrations FICZ behaves in a manner similar to TCDD, exhibiting toxicity toward fish and bird embryos, immune suppression, and activation of cancer progression. The findings are indicative of a dual role for endogenously activated AHR in barrier tissues, aiding clearance of infections and suppressing immunity to terminate a vicious cycle that might otherwise lead to disease. There is not much support for the AHR ligand-specific immune responses proposed, the differences between FICZ and TCDD in this context appear to be explained by the rapid metabolism of FICZ.

Chemistry and Properties of Indolocarbazoles

The indolocarbazoles are an important class of nitrogen heterocycles which has evolved significantly in recent years, with numerous studies focusing on their diverse biological effects, or targeting new materials with potential applications in organic electronics. This review aims at providing a broad survey of the chemistry and properties of indolocarbazoles from an interdisciplinary point of view, with particular emphasis on practical synthetic aspects, as well as certain topics which have not been previously accounted for in detail, such as the occurrence, formation, biological activities, and metabolism of indolo[3,2- b]carbazoles. The literature of the past decade forms the basis of the text, which is further supplemented with older key references.

In Vitro Characterization of Variable Porosity Wound Dressing With Anti-Scar Properties

Introduction: New options are needed to improve wound healing while preventing excessive scar formation. Temporary primary dressings are important options in topical wound management that allow the natural healing process. Methods: We evaluated a novel primary dressing consisting of a biosynthetic, variable porosity, matrix-containing gelatin and Aloe Vera extract and a derivative dressing coated with the anti-scarring agent salinomycin for their ability to promote cell growth, reduce myofibroblast formation, and regulate cytokine production. In addition, salinomycin-coated primary dressings were tested for antimicrobial activity. Results: Both primary wound dressings permitted cell growth and attenuated TGFβ-induced scar-forming myofibroblast formation. The primary wound dressings also reduced IL-6 production by 50%, IL-8 by 20%, MCP-1 by 75%, and GRO by 60% in human mesenchymal stem cells treated with TGFβ. Salinomycin coating of the dressing showed antimicrobial activity by preventing Staphylococcus aureus growth. Conclusions: Both primary wound dressings support the growth of human fibroblasts and stem cells, as well as reduce inflammatory cytokine production, demonstrating their potential to serve as temporary wound dressings.

Tryptophan photo-product FICZ upregulates AHR/MEK/ERK-mediated MMP1 expression: Implications in anti-fibrotic phototherapy

BACKGROUND

Scleroderma is caused by aberrant transforming growth factor-ß signaling. The degradation of extracellular matrix proteins is regulated by matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs). Ultraviolet (UV) radiation has been a therapy for scleroderma. 6-Formylindolo[3,2-b]carbazole (FICZ), an endogenous aryl hydrocarbon receptor (AHR) ligand, is a tryptophan metabolite generated by UV exposure. Nonetheless, whether FICZ regulates MMPs and TIMPs has not been investigated.

OBJECTIVE

To elucidate the regulatory roles of FICZ in the expression of MMPs and TIMPs in normal human dermal fibroblasts (NHDFs).

METHODS

Quantitative real-time polymerase chain reaction was performed to determine the expression of MMPs or TIMPs in the NHDFs treated with FICZ or UVB. The MMPs levels were measured by enzyme-linked immunosorbent assay. The actions of FICZ on MMPs were analyzed using AHR-knockdown NHDFs or selective inhibitors of mitogen-activated protein kinases (MAPKs). Microtubule-associated protein kinase (MEK) and extracellular signal-regulated kinase (ERK) phosphorylation was examined by western blotting.

RESULTS

UVB increased the mRNA and protein levels of MMP1 and MMP3 in NHDFs, while FICZ upregulated those of MMP1, but not MMP3. The effects of FICZ on TIMPs were negligible. FICZ increased MMP1 expression in an AHR-dependent manner. The FICZ-induced MMP1 upregulation was ameliorated with MEK/ERK inhibitors, whereas the effects of UVB were canceled with c-Jun N-terminal kinase (JNK) and p38-MAPK as well as MEK/ERK inhibitors. FICZ-induced ERK phosphorylation is dependent on AHR.

CONCLUSION

FICZ contributes to the UV-mediated anti-fibrotic effects via the AHR/MEK/ERK signal pathway in NHDFs. FICZ is a potential therapeutic agent for scleroderma.

An endogenous tryptophan photo-product, FICZ, is potentially involved in photo-aging by reducing TGF-β-regulated collagen homeostasis

BACKGROUND

Persistent ultraviolet (UV) radiation in the form of sunlight causes photo-aging of the skin by reducing the production of type I collagen, the major constituent of the extracellular matrix of the dermis. Transforming growth factor (TGF)-β transforms dermal fibroblasts into α2-smooth muscle actin (ACTA2)-expressing myofibroblasts. Myofibroblasts produce a precursor form of type I collagen, type I procollagen (collagen I), consisting of pro-alpha1 (produced by the COL1A1 gene) and pro-alpha2 chains (produced by the COL1A2 gene). Smad2/3 is a key downstream molecule of TGF-β signaling. The mechanisms through which UV inhibits collagen I synthesis are not fully understood. 6-Formylindolo[3,2-b]carbazole (FICZ) is an endogenous tryptophan photo-metabolite generated by UV irradiation. FICZ is well known as a high-affinity ligand for aryl hydrocarbon receptor (AHR). However, the physiological roles of FICZ in photo-aging have yet to be addressed.

OBJECTIVE

To evaluate the effects of FICZ on the TGF-β-mediated ACTA2 and collagen I expression in normal human dermal fibroblasts (NHDFs).

METHODS

Quantitative real-time polymerase chain reaction and western blot analysis were performed to determine the expression of ACTA2, COL1A1, and COL1A2 in NHDFs with or without FICZ and TGF-β. The phosphorylated Smad2/3 (pSmad2/3) protein levels in cytoplasmic or nuclear portions were investigated by western blot analysis. Immunofluorescence staining was conducted to evaluate pSmad2/3 localization, and F-actin staining with phalloidin was performed to visualize actin polymerization in myofibroblasts. The actions of FICZ on the TGF-β-mediated collagen I expression and nuclear translocation of pSmad2/3 were analyzed in the presence of selective AHR antagonists or in AHR-knockdown NHDFs.

RESULTS

We found that FICZ significantly inhibited the TGF-β-induced upregulation of mRNA and protein levels of ACTA2 and collagen I and actin polymerization in myofibroblasts. FICZ did not disturb the phosphorylation of Smad2/3. Notably, FICZ reduced the expression of pSmad2/3 in the nucleus, while it increased that in the cytoplasm, suggesting that it inhibits the nuclear translocation of pSmad2/3 induced by TGF-β. The inhibitory actions of FICZ on the TGF-β-mediated collagen I expression and nuclear translocation of pSmad2/3 were independent of AHR signaling. Another endogenous AHR agonist, kynurenine, also inhibited the TGF-β-mediated ACTA2 and collagen I upregulation in NHDFs in an AHR-independent manner; however, its effects were insignificant in comparison with those of FICZ.

CONCLUSIONS

These findings suggest that the endogenous photo-product FICZ may be a key chromophore that involves in photo-aging. Downregulation of FICZ signaling is thus a potential strategy to protect against photo-aging.

Aryl hydrocarbon receptor (AHR): "pioneer member" of the basic-helix/loop/helix per-Arnt-sim (bHLH/PAS) family of "sensors" of foreign and endogenous signals

The basic-helix/loop/helix per-Arnt-sim (bHLH/PAS) family comprises many transcription factors, found throughout all three kingdoms of life; bHLH/PAS members "sense" innumerable intracellular and extracellular "signals" - including endogenous compounds, foreign chemicals, gas molecules, redox potential, photons (light), gravity, heat, and osmotic pressure. These signals then initiate downstream signaling pathways involved in responding to that signal. The term "PAS", abbreviation for "per-Arnt-sim" was first coined in 1991. Although the mouse Arnt gene was not identified until 1991, evidence of its co-transcriptional binding partner, aryl hydrocarbon receptor (AHR), was first reported in 1974 as a "sensor" of foreign chemicals, up-regulating cytochrome P450 family 1 (CYP1) and other enzyme activities that usually metabolize the signaling chemical. Within a few years, AHR was proposed also to participate in inflammation. The mouse [Ah] locus was shown (1973-1989) to be relevant to chemical carcinogenesis, mutagenesis, toxicity and teratogenesis, the mouse Ahr gene was cloned in 1992, and the first Ahr(-/-) knockout mouse line was reported in 1995. After thousands of studies from the early 1970s to present day, we now realize that AHR participates in dozens of signaling pathways involved in critical-life processes, affecting virtually every organ and cell-type in the animal, including many invertebrates.