Endogenous Aryl Hydrocarbon Receptor Ligand Research Articles

AhR signaling modulates Ferroptosis by regulating SLC7A11 expression

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that is pivotal in development, metabolic homeostasis, and immune responses. While recent research has highlighted AhR's significant role in modulating oxidative stress responses, its mechanistic relationship with ferroptosis—an iron-dependent, non-apoptotic cell death—remains to be fully elucidated. In our study, we discovered that AhR plays a crucial role in ferroptosis, in part by transcriptionally regulating the expression of the solute carrier family 7 member 11 (SLC7A11). Our findings indicate that both pharmacological inactivation and genetic ablation of AhR markedly enhance erastin-induced ferroptosis. This enhancement is achieved by suppressing SLC7A11, leading to increased lipid peroxidation. We also obtained evidence of post-translational modifications of SLC7A11 during ferroptosis. Additionally, we observed that indole 3-pyruvate (I3P), an endogenous ligand of AhR, protects cells from ferroptosis through an AhR-dependent mechanism. Based on these insights, we propose that AhR transcriptionally regulates the expression of SLC family genes, which in turn play a pivotal role in mediating ferroptosis. This underscores AhR's essential role in suppressing lipid oxidation and ensuring cell survival under oxidative stress.

Therapeutic effects of in vivo administration of an inhibitor of tryptophan 2,3-dioxygenase (680c91) for the treatment of fibroids: a preclinical study

ObjectiveFibroids are characterized by marked overexpression of Tryptophan 2,3 dioxygenase (TDO2). The objective of this study was to determine the effectiveness of in vivo administration of an inhibitor of TDO2 (680C91) on fibroid size and gene expression. DesignAnimal and ex vivo human study. SubjectsSCID mice bearing human fibroid xenografts treated with vehicle and TDO2 inhibitor. InterventionDaily intraperitoneal administration of 680C91 or vehicle for two months and in vitro studies with fibroid explants. Main Outcome MeasuresTumor weight and gene expression profile of xenografts and in vitro mechanistic experiments using fibroid explants. ResultsCompound 680C91 was well-tolerated with no effects on blood chemistry and body weight. Treatment of mice with 680C91 resulted in 30% reduction in the weight of fibroid xenografts after two months of treatment and as expected lower levels of kynurenine, the byproduct of tryptophan degradation and an endogenous ligand of AhR (aryl hydrocarbon receptor) in the xenografts. The expression of CYP1B1 (cytochrome P450 family 1 subfamily B member 1), TGF-β3 (transforming growth factor beta 3), FN1 (fibronectin), CDK2 (cyclin-dependent kinase 2), E2F1 (E2F transcription factor 1), IL-8 (interleukin 8) and SPARC (secreted protein acidic and cysteine rich) mRNA, were lower in the xenografts of mice treated with 680C91 as compared with vehicle controls. Similarly, the protein abundance of collagen, FN1, CYP1B1 and SPARC were lower in the xenografts of 680C91 treated mice as compared with vehicle controls. Immunohistochemical analysis of xenografts indicated decreased expression of collagen, Ki67 and E2F1 but no significant changes in cleaved caspase 3 expression in mice treated with 680C91. The levels of kynurenine in the xenografts showed a direct correlation with the tumor weight and FN1 levels. In vitro studies with fibroid explants showed a significant induction of CYP1B1, TGF-β3, FN1, CDK2, E2F1, IL8 and SPARC mRNA by tryptophan which could be blocked by co-treatment with 680C91 and the AhR antagonist CH-223191. ConclusionThe results indicate that correction of aberrant tryptophan catabolism in fibroids could be an effective treatment through its effect to reduce cell proliferation and ECM accumulation.

Kynurenine attenuates mitochondrial depolarization and neuronal cell death induced by rotenone exposure independently of AhR-mediated parkin induction in SH-SY5Y differentiated cells

Rotenone is a pesticide commonly used in agriculture that is associated with the risk of developing Parkinson’s disease (PD) by inducing mitochondrial damage. As a protective cell response to different challenges, they activate mitophagy, which involves parkin activity. Parkin is an E3 ubiquitin ligase necessary in the initial steps of mitophagy, and its overexpression protects against parkinsonian effects in different models. Recent studies have reported that the aryl hydrocarbon receptor (AHR), a ligand-dependent transcription factor, induces parkin expression. Kynurenine, an endogenous AHR ligand, promotes neuroprotection in chronic neurodegenerative disorders, such as PD, although its neuroprotective mechanism needs to be fully understood. Therefore, we evaluated whether the overexpression of parkin by AHR activation with kynurenine promotes autophagy and reduces the neurotoxicity induced by rotenone in SH-SY5Y cells differentiated to dopaminergic neurons. SH-SY5Y neurons were treated with rotenone or pretreated with kynurenine or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and parkin levels, apoptosis, mitochondrial potential membrane, and autophagy were determined. The results showed that kynurenine and TCDD treatments induced parkin expression in an AHR-dependent manner. Kynurenine pretreatment inhibited rotenone-induced neuronal apoptosis in 17%, and the loss of mitochondrial membrane potential in 30% when compare to rotenone alone, together with a decrease in autophagy. By contrast, although TCDD treatment increased parkin levels, non-neuroprotective effects were observed. The kynurenine protective activity was AHR independent, suggesting that parkin induction might not be related to this effect. On the other hand, kynurenine treatment inhibited alpha amine-3-hydroxy-5-methyl-4-isoxazol propionic acid and N-methyl-D-aspartate receptors, which are well-known excitotoxicity mediators activated by rotenone exposure.

Targeting the aryl hydrocarbon receptor (AhR) with BAY 2416964: a selective small molecule inhibitor for cancer immunotherapy

BackgroundThe metabolism of tryptophan to kynurenines (KYN) by indoleamine-2,3-dioxygenase or tryptophan-2,3-dioxygenase is a key pathway of constitutive and adaptive tumor immune resistance. The immunosuppressive effects of KYN in the tumor...

Non-Toxicological Role of Aryl Hydrocarbon Receptor in Obesity-Associated Multiple Myeloma Cell Growth and Survival.

Obesity is not only a risk factor for multiple myeloma (MM) incidence, but it is also associated with an increased risk of progression from myeloma precursors-monoclonal gammopathy of undetermined significance-and smoldering myeloma. Adipocytes in the bone marrow (BMAs) microenvironment have been shown to facilitate MM cell growth via secreted factors, but the nature of these secreted factors and their mechanism of action have not been fully elucidated. The elevated expression of aryl hydrocarbon receptor (AhR) is associated with a variety of different cancers, including MM; however, the role of AhR activity in obesity-associated MM cell growth and survival has not been explored. Indeed, this is of particular interest as it has been recently shown that bone marrow adipocytes are a source of endogenous AhR ligands. Using multiple in vitro models of tumor-adipocyte crosstalk to mimic the bone microenvironment, we identified a novel, non-toxicological role of the adipocyte-secreted factors in the suppression of AhR activity in MM cells. A panel of six MM cell lines were cultured in the presence of bone marrow adipocytes in (1) a direct co-culture, (2) a transwell co-culture, or (3) an adipocyte-conditioned media to interrogate the effects of the secreted factors on MM cell AhR activity. Nuclear localization and the transcriptional activity of the AhR, as measured by CYP1A1 and CYP1B1 gene induction, were suppressed by exposure to BMA-derived factors. Additionally, decreased AhR target gene expression was associated with worse clinical outcomes. The knockdown of AhR resulted in reduced CYP1B1 expression and increased cellular growth. This tumor-suppressing role of CYP1A1 and CYP1B1 was supported by patient data which demonstrated an association between reduced target gene expression and worse overall survival. These data demonstrated a novel mechanism by which bone marrow adipocytes promote MM progression.

Abstract 2890: Investigating dynamic IDO-Kyn-Ahr pathway induced tumor immunosuppression using imaging modality to optimize therapeutic Intervention

Abstract Despite great clinical responses in several cancers to immune checkpoint blockade (ICB) intervention, there persist many mechanisms of tumor evasion. Tryptophan catabolism by enzymes Indoleamine-2,3-dioxygenase 1 (IDO1) and tryptophan-2,3-dioxygenase 2 (TDO2) into metabolite L-Kynurenine (Kyn) has been shown to drive an immunosuppressive tumor microenvironment (TME). We have shown tumors overexpressing IDO1 recruit and activate the Treg/macrophage suppressive axis and blockade of aryl hydrocarbon receptor (AHR) activation abrogates this. Preclinical models demonstrate inhibition of IDO1 delayed tumor growth and increased T cell function. However, a phase III clinical trial in melanoma patients combining IDO1 inhibition with anti-PD-1 blockade showed no improved efficacy when compared to anti-PD-1 blockade. Kyn can act as a key signaling molecule through activation of AHR. We hypothesize that AHR engagement by kyn within the TME is highly dynamic and elevated AHR engagement must coincide with intervention to maximize therapeutic response. Using an AHR biosensor, we designed a construct with a dioxin response element (DRE) promoter that is engaged upon AHR-ligand complex, translocated to the nucleus, and drives a luciferase gene with a luminescence readout. This allows us to use an image-guided approach to track AHR bioactivity in real-time. In-vitro, we were able to validate our construct using transduced murine B16 melanoma and 4T1 breast cancer models. We treated transduced cells with endogenous AHR ligands, kynurenine, and AHR agonist (FICZ), and observed a significant dose-dependent increase in AHR reporter readout. Additionally, the AHR inhibitor (CH-223191) abrogated AHR activity and subsequent luminescence below control threshold. We implanted both DRE transduced B16 (B16-DRE) and 4T1 (4T1-DRE) intradermally and intramammary fat pad respectively. Tumors were imaged and we observed total luminescence flux corresponding to increased tumor growth. After three weeks, we assessed IDO, AHR, and HIF1a expression which all converge on the IDO-Kyn-AhR pathway using a broad panel of lymphocyte and myeloid markers from tumors and spleen. We identified high expression of IDO, AHR, and HIF1a markers in myeloid cells with an increased frequency of dendritic cells and macrophages. Future experiments will focus on using our reporter construct in the context of ICB treatment and assessing AHR activity overtime as well as sampling peripheral blood to assess the magnitude of tryptophan, kyn, and other polycyclic hydrocarbons including gut microbiome-derived indoles. The characterization of the IDO-Kyn-AhR modulation after therapeutic intervention will inform the rational design of treatment regimens to abrogate immune suppression associated with AHR activity in combination with ICB treatment. Citation Format: Mamadou Alpha Bah, Inna Serganova, Sadna Budhu, Tanya Schild, Jonathan F. Khan, Kayvan R. Keshari, Jedd D. Wolchok, Taha Merghoub. Investigating dynamic IDO-Kyn-Ahr pathway induced tumor immunosuppression using imaging modality to optimize therapeutic Intervention [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2890.

Aryl hydrocarbon receptor maintains hepatic mitochondrial homeostasis in mice

ObjectiveMitophagy removes damaged mitochondria to maintain cellular homeostasis. Aryl hydrocarbon receptor (AhR) expression in the liver plays a crucial role in supporting normal liver functions, but its impact on mitochondrial function is unclear. Here, we identified a new role of AhR in the regulation of mitophagy to control hepatic energy homeostasis. MethodsIn this study, we utilized primary hepatocytes from AhR knockout (KO) mice and AhR knockdown AML12 hepatocytes. An endogenous AhR ligand, kynurenine (Kyn), was used to activate AhR in AML12 hepatocytes. Mitochondrial function and mitophagy process were comprehensively assessed by MitoSOX and mt-Keima fluorescence imaging, Seahorse XF-based oxygen consumption rate measurement, and Mitoplate S-1 mitochondrial substrate utilization analysis. ResultsTranscriptomic analysis indicated that mitochondria-related gene sets were dysregulated in AhR KO liver. In both primary mouse hepatocytes and AML12 hepatocyte cell lines, AhR inhibition strongly suppressed mitochondrial respiration rate and substrate utilization. AhR inhibition also blunted the fasting response of several essential autophagy genes and the mitophagy process. We further identified BCL2 interacting protein 3 (BNIP3), a mitophagy receptor that senses nutrient stress, as an AhR target gene. AhR is directly recruited to the Bnip3 genomic locus, and Bnip3 transcription was enhanced by AhR endogenous ligand treatment in wild-type liver and abolished entirely in AhR KO liver. Mechanistically, overexpression of Bnip3 in AhR knockdown cells mitigated the production of mitochondrial reactive oxygen species (ROS) and restored functional mitophagy. ConclusionsAhR regulation of the mitophagy receptor BNIP3 coordinates hepatic mitochondrial function. Loss of AhR induces mitochondrial ROS production and impairs mitochondrial respiration. These findings provide new insight into how endogenous AhR governs hepatic mitochondrial homeostasis.

Indole-3-pyruvic acid alleviates rheumatoid arthritis via the aryl hydrocarbon receptor pathway.

In previous studies, we found that smoking may participate in the pathogenesis of rheumatoid arthritis (RA) via the aryl hydrocarbon receptor (AhR) pathway. However, when we conducted a subgroup analysis, the expression of AhR and CYP1A1 in healthy people was higher than that in RA patients. We considered that endogenous AhR ligands may exist in vivo that activate AhR to play a protective role. Indole-3-pyruvic acid (IPA) is a tryptophan (Trp) metabolite produced by the indole pathway and serves as a ligand of AhR. This study aimed to reveal the effect and mechanism of IPA in RA. A total of 14 patients with RA and 14 healthy volunteers were enrolled. The differential metabolites were screened with liquid chromatography-mass spectrometry (LC-MS) metabolomics technology. We also treated peripheral blood mononuclear cells (PBMCs) with IPA to evaluate the effect on the differentiation of T helper 17 (Th17) cells or regulatory T (Treg) cells. To determine whether IPA can be used to alleviate RA, we administered IPA to rats with collagen-induced arthritis (CIA). Methotrexate was used as a standard drug for CIA. When the dose reached 20 mg/kg/d, the severity of CIA was significantly reduced. In vitro experiments verified that IPA inhibited the differentiation of Th17 cells and promoted the differentiation of Treg cells, but this effect was weakened by CH223191. IPA is a protective factor for RA; it can restore the Th17/Treg cell balance through the AhR pathway, which can alleviate RA.

Induction of the hepatic aryl hydrocarbon receptor by alcohol dysregulates autophagy and phospholipid metabolism via PPP2R2D

Disturbed lipid metabolism precedes alcoholic liver injury. Whether and how AhR alters degradation of lipids, particularly phospho-/sphingo-lipids during alcohol exposure, was not explored. Here, we show that alcohol consumption in mice results in induction and activation of aryl hydrocarbon receptor (AhR) in the liver, and changes the hepatic phospho-/sphingo-lipids content. The levels of kynurenine, an endogenous AhR ligand, are elevated with increased hepatic tryptophan metabolic enzymes in alcohol-fed mice. Either alcohol or kynurenine treatment promotes AhR activation with autophagy dysregulation via AMPK. Protein Phosphatase 2 Regulatory Subunit-Bdelta (Ppp2r2d) is identified as a transcriptional target of AhR. Consequently, PPP2R2D-dependent AMPKα dephosphorylation causes autophagy inhibition and mitochondrial dysfunction. Hepatocyte-specific AhR ablation attenuates steatosis, which is associated with recovery of phospho-/sphingo-lipids content. Changes of AhR targets are corroborated using patient specimens. Overall, AhR induction by alcohol inhibits autophagy in hepatocytes through AMPKα, which is mediated by Ppp2r2d gene transactivation, revealing an AhR-dependent metabolism of phospho-/sphingo-lipids.

Activation of the kynurenine-aryl hydrocarbon receptor axis impairs the chondrogenic and chondroprotective effects of human umbilical cord-derived mesenchymal stromal cells in osteoarthritis rats.

It has been proven that intra-articular injection of mesenchymal stromal cells (MSCs) can alleviate cartilage damage in osteoarthritis (OA) by differentiating into chondrocytes and protecting inherent cartilage. However, the mechanism by which the OA articular microenvironment affects MSCs' therapeutic efficiency is yet to be fully elucidated. The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor involved in various cellular processes, such as osteogenesis and immune regulation. Tryptophan (Trp) metabolites, most of which are endogenous ligand for AHR, are abnormally increased in synovial fluid (SF) of OA and rheumatoid arthritis (RA) patients. In this study, the effects of kynurenine (KYN), one of the most important metabolites of Trp, were evaluated on the chondrogenic and chondroprotective effects of human umbilical cord-derived mesenchymal stromal cells (hUC-MSCs). hUC-MSCs were cultured in conditioned medium containing different proportions of OA/RA SF, or stimulated with KYN directly, and then, AHR activation, proliferation, and chondrogenesis of hUC-MSCs were measured. Moreover, the chondroprotective efficiency of short hairpin-AHR-UC-MSC (shAHR-UC-MSC) was determined in a rat surgical OA model (right hind joint). OA SF could activate AHR signaling in hUC-MSCs in a concentration-dependent manner and inhibit the chondrogenic differentiation and proliferation ability of hUC-MSCs. Similar results were observed in hUC-MSCs stimulated with KYN in vitro. Notably, shAHR-UC-MSC exhibited superior therapeutic efficiency in OA rat upon intra-articular injection. Taken together, this study indicates that OA articular microenvironment is not conducive to the therapeutic effect of hUC-MSCs, which is related to the activation of the AHR pathway by tryptophan metabolites, and thus impairs the chondrogenic and chondroprotective effects of hUC-MSCs. AHR might be a promising modification target for further improving the therapeutic efficacy of hUC-MSCs on treatment of cartilage-related diseases such as OA.

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

AbstractWe 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.

Sorafenib is an antagonist of the aryl hydrocarbon receptor

Sorafenib is an orally administered inhibitor of several tyrosine protein kinases. Treatment with sorafenib induces autophagy, which may suppress the growth of hepatocellular carcinoma (HCC) and other cancers. Aryl hydrocarbon receptor (AhR) is activated by xenbiotics and is involved in detoxification, but also plays other physiological roles. The following results were obtained. ITE and β-NF are endogenous and synthetic AhR ligands, respectively. One μM sorafenib can strongly suppress baseline as well as 0.5 μM ITE- and 1 μM β-NF-induced transcriptional activity of the aryl hydrocarbon response element (AHRE) in both human and mouse cells. Cytochrome p450 (CYP) 1A1 is mainly transcribed by activated AhR. Sorafenib (2−15 μM) strongly and dose-dependently suppressed baseline as well as 2 μM ITE- and 10 μM β-NF-induced CYP1A1 mRNA and protein expression. Ligand-activated AhR translocates from the cytoplasm to the nucleus. While sorafenib was found to suppress AhR activity, the drug alone was able to induce AhR translocation into the nucleus. Sorafenib’s antagonistic action on AhR was comparable to that of the known AhR antagonist CH-223191 in human liver and ovarian cell lines. In summary, we demonstrate that sorafenib is a potent AhR antagonist and likely endocrine disruptor of the AhR. Moreover, sorafenib offers potential benefit for diseases treatable through AhR suppression strategies. Further investigation is warranted into sorafenib’s AhR antagonistic behavior.

LACTOBACILLUS MURINUS ACTIVATES THE ARYL HYDROCARBON RECEPTOR TO ATTENUATE TNF-ALPHA-INDUCED PRO-INFLAMMATORY RESPONSES IN HUMAN INTESTINAL EPITHELIAL CELLS

Abstract BACKGROUND Anti-TNF-alpha therapy is an established treatment modality for inflammatory bowel disease (IBD). Yet up to 30% of patients do not respond to anti-TNF-alpha therapy (primary non-responders), and almost 50% of responders lose clinical efficacy over time (secondary non-responders). Furthermore, numerous safety concerns are associated with the long-term use of anti-TNF-alpha agents. Anti-TNF-alpha therapy safety concerns and the increased incidence of non-responders have driven the need to develop innovative strategies to treat IBD. OBJECTIVE A potential alternative to anti-TNF-alpha therapy is the use of novel probiotics capable of attenuating the damaging effects of TNF-alpha on the intestinal epithelium. We hypothesized that Lactobacillus murinus attenuates TNF-alpha induced pro-inflammatory responses and decreases barrier disruption in human intestinal epithelial cells (Caco-2) by activating the aryl hydrocarbon receptor (AhR). METHODS We used Caco-2 cells grown on Transwell inserts to model the human intestinal epithelial barrier. Transepithelial Electrical Resistance (TEER) was measured to evaluate the formation of tight junctions. Once TEER reached 500 ohms per cm2, the cells were considered to have formed tight junctions. To induce pro-inflammatory responses, Caco-2 cell monolayers were treated with increasing doses of TNF-alpha (0.1, 1 and 10 ng/ml). Caco-2 cell monolayers were also treated with L. murinus to test its ability to activate AhR. Two defined ligands for AhR were used as controls i.e., 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 6-formylindolo[3,2-b] carbazole (FICZ). Next, we pre-treated the Caco-2 cells with either L. murinus or defined AhR ligands for 12 hours. After pre-treatment, monolayers were stimulated with TNF-alpha for 24 hours. IL-8 and TEER were quantified as endpoints to determine treatment efficacy. RESULTS TNF-alpha stimulation decreased the TEER and induced the secretion of IL-8 in a dose-dependent manner thus, providing a model of intestinal inflammation. AhR was significantly activated in monolayers treated with L. murinus as well as with defined AhR ligands. Furthermore, pre-treating the cells with L. murinus or with endogenous AhR ligand attenuated the TNF-alpha induced pro-inflammatory response and decreased epithelial barrier disruption in Caco-2 cells. CONCLUSIONS These results indicate that TNF-alpha induced damage to the gut wall can be attenuated using novel probiotics such L. murinus or endogenous AhR ligand. These data suggest that AhR could be a novel drug target for treating IBD. These results also indicate that L. murinus may be a potential therapeutic to mitigate or treat IBD without the use of anti-TNF-alpha agents.

The interplay of aryl hydrocarbon receptor/WNT/CTNNB1/Notch signaling pathways regulate amyloid beta precursor mRNA/protein expression and effected the learning and memory of mice.

The amyloid beta precursor protein (APP) plays a pathophysiological role in the development of Alzheimer's disease as well as a physiological role in neuronal growth and synaptogenesis. The aryl hydrocarbon receptor (AhR)/WNT/Catenin Beta 1 (CTNNB1)/Notch signaling pathways stamp in many functions, including development and growth of neurons. However, the regulatory role of AhR-/WNT-/CTNNB1-/Notch-induced APP expression and its influence on hippocampal-dependent learning and memory deficits is not clear. Male BALB/C mice received 6-formylindolo[3,2-b]carbazole (an AhR agonist), CH223191(an AhR antagonist), DAPT (an inhibitor of Notch signaling), and XAV-939 (a WNT pathway inhibitor) at a single dose of 100μg/kg, 1, 5, and 5mg/kg of body weight, respectively, via intraperitoneal injection alone or in combination. Gene expression analyses and protein assay were performed on the 7th and 29th days. To assess the hippocampal-dependent memory, all six mice also underwent contextual fear conditioning on the 28th day after treatments. Our results showed that endogenous ligand of AhR has a regulatory effect on APP gene. Also, the interaction of AhR/WNT/CTNNB1 has a positive regulatory effect, but Notch has a negative regulatory effect on the mRNA and protein expression of APP, which have a correlation with mice's learning skills and memory.

Toxic Effects of Indoxyl Sulfate on Osteoclastogenesis and Osteoblastogenesis.

Uremic toxins, such as indoxyl sulfate (IS) and kynurenine, accumulate in the blood in the event of kidney failure and contribute to further bone damage. To maintain the homeostasis of the skeletal system, bone remodeling is a persistent process of bone formation and bone resorption that depends on a dynamic balance of osteoblasts and osteoclasts. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that regulates the toxic effects of uremic toxins. IS is an endogenous AhR ligand and is metabolized from tryptophan. In osteoclastogenesis, IS affects the expression of the osteoclast precursor nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) through AhR signaling. It is possible to increase osteoclast differentiation with short-term and low-dose IS exposure and to decrease differentiation with long-term and/or high-dose IS exposure. Coincidentally, during osteoblastogenesis, through the AhR signaling pathway, IS inhibits the phosphorylation of ERK, and p38 reduces the expression of the transcription factor 2 (Runx2), disturbing osteoblastogenesis. The AhR antagonist resveratrol has a protective effect on the IS/AhR pathway. Therefore, it is necessary to understand the multifaceted role of AhR in CKD, as knowledge of these transcription signals could provide a safe and effective method to prevent and treat CKD mineral bone disease.

Activation of Aryl Hydrocarbon Receptor by ITE Improves Cardiac Function in Mice After Myocardial Infarction.

BackgroundThe immune and inflammatory responses play a considerable role in left ventricular remodeling after myocardial infarction (MI). Binding of AhR (aryl hydrocarbon receptor) to its ligands modulates immune and inflammatory responses; however, the effects of AhR in the context of MI are unknown. Therefore, we evaluated the potential association between AhR and MI by treating mice with a nontoxic endogenous AhR ligand, ITE (2‐[1’H‐indole‐3’‐carbonyl]‐thiazole‐4‐carboxylic acid methyl ester). We hypothesized that activation of AhR by ITE in MI mice would boost regulatory T‐cell differentiation, modulate macrophage activity, and facilitate infarct healing.Methods and ResultsAcute MI was induced in C57BL/6 mice by ligation of the left anterior descending coronary artery. Then, the mice were randomized to daily intraperitoneal injection of ITE (200 µg/mouse, n=19) or vehicle (n=16) to examine the therapeutic effects of ITE during the postinfarct healing process. Echocardiographic and histopathological analyses revealed that ITE‐treated mice exhibited significantly improved systolic function (P<0.001) and reduced infarct size compared with control mice (P<0.001). In addition, we found that ITE increased regulatory T cells in the mediastinal lymph node, spleen, and infarcted myocardium, and shifted the M1/M2 macrophage balance toward the M2 phenotype in vivo, which plays vital roles in the induction and resolution of inflammation after acute MI. In vitro, ITE expanded the Foxp3+ (forkhead box protein P3‐positive) regulatory T cells and tolerogenic dendritic cell populations.ConclusionsActivation of AhR by a nontoxic endogenous ligand, ITE, improves cardiac function after MI. Post‐MI mice treated with ITE have a significantly lower risk of developing advanced left ventricular systolic dysfunction than nontreated mice. Thus, the results imply that ITE has a potential as a stimulator of cardiac repair after MI to prevent heart failure.

Impact of Bacterial Metabolites on Gut Barrier Function and Host Immunity: A Focus on Bacterial Metabolism and Its Relevance for Intestinal Inflammation.

The diverse and dynamic microbial community of the human gastrointestinal tract plays a vital role in health, with gut microbiota supporting the development and function of the gut immune barrier. Crosstalk between microbiota-gut epithelium and the gut immune system determine the individual health status, and any crosstalk disturbance may lead to chronic intestinal conditions, such as inflammatory bowel diseases (IBD) and celiac disease. Microbiota-derived metabolites are crucial mediators of host-microbial interactions. Some beneficially affect host physiology such as short-chain fatty acids (SCFAs) and secondary bile acids. Also, tryptophan catabolites determine immune responses, such as through binding to the aryl hydrocarbon receptor (AhR). AhR is abundantly present at mucosal surfaces and when activated enhances intestinal epithelial barrier function as well as regulatory immune responses. Exogenous diet-derived indoles (tryptophan) are a major source of endogenous AhR ligand precursors and together with SCFAs and secondary bile acids regulate inflammation by lowering stress in epithelium and gut immunity, and in IBD, AhR expression is downregulated together with tryptophan metabolites. Here, we present an overview of host microbiota-epithelium- gut immunity crosstalk and review how microbial-derived metabolites contribute to host immune homeostasis. Also, we discuss the therapeutic potential of bacterial catabolites for IBD and celiac disease and how essential dietary components such as dietary fibers and bacterial tryptophan catabolites may contribute to intestinal and systemic homeostasis.

Downregulation of AW112010 upon treatment with 6-formylindolo[3,2-b] carbazole protects mice from fulminant Concanavalin-induced T cell-mediated liver injury

Abstract Upregulation of long noncoding RNA (lncRNA) AW112010 has been observed in multiple inflammatory disease models. In line with implication of this lncRNA as a regulator of inflammation, it has also been shown that AW112010 expression decreases upon treatment with anti-inflammatory compounds. Since lncRNAs show abnormal expression in many inflammatory diseases and reactions, elucidating their role in such ailments is necessary. Data from our lab has shown that treatment with aryl hydrocarbon receptor (AhR) ligands induce epigenetic pathway dysregulation, so this study aimed to determine inflammatory genes dysregulated upon treatment with the endogenous AhR ligand, 6-formylindolo[3,2-b] carbazole (FICZ). A murine model of immune cell-mediated liver injury was employed by intravenously injecting 12.5 mg/kg Concanavalin A (ConA). One hour after challenge, mice were treated with 50 μg/kg FICZ via an intraperitoneal injection. Interestingly, analysis of serum collected twenty-four hours after challenge showed that FICZ was able to reduce the level of alanine transaminase (ALT) suggesting a decrease in disease severity. Single cell RNA sequencing was conducted on infiltrating liver mononuclear cells enriched via a percoll gradient. We observed a reduced percentage of T cells upon FICZ treatment and an increase in the percentage of neutrophils. Overall, we observed downregulation of AW112010 in the FICZ-treated group. Specifically, AW112010 was identified as one of the top 20 genes dysregulated in the NK cell cluster and was downregulated in the B cell, CD8+ T cell, and Kupffer cell clusters. Together, these data suggest AW112010 downregulation as a potential mechanism through which FICZ protects mice from severe liver injury.

The Aryl Hydrocarbon Receptor Attenuates Acute Cigarette Smoke-Induced Airway Neutrophilia Independent of the Dioxin Response Element.

Cigarette smoke is a prevalent respiratory toxicant that remains a leading cause of death worldwide. Cigarette smoke induces inflammation in the lungs and airways that contributes to the development of diseases such as lung cancer and chronic obstructive pulmonary disease (COPD). Due to the presence of aryl hydrocarbon receptor (AhR) ligands in cigarette smoke, activation of the AhR has been implicated in driving this inflammatory response. However, we have previously shown that the AhR suppresses cigarette smoke-induced pulmonary inflammation, but the mechanism by which the AhR achieves its anti-inflammatory function is unknown. In this study, we use the AhR antagonist CH-223191 to inhibit AhR activity in mice. After an acute (3-day) cigarette smoke exposure, AhR inhibition was associated with significantly enhanced neutrophilia in the airways in response to cigarette smoke, mimicking the phenotype of AhR-deficient mice. We then used genetically-modified mouse strains which express an AhR that can bind ligand but either cannot translocate to the nucleus or bind its cognate response element, to show that these features of the AhR pathway are not required for the AhR to suppress pulmonary neutrophilia. Finally, using the non-toxic endogenous AhR ligand FICZ, we provide proof-of-concept that activation of pulmonary AhR attenuates smoke-induced inflammation. Collectively, these results support the importance of AhR activity in mediating its anti-inflammatory function in response to cigarette smoke. Further investigation of the precise mechanisms by which the AhR exerts is protective functions may lead to the development of therapeutic agents to treat people with chronic lung diseases that have an inflammatory etiology, but for which few therapeutic options exist.

Benzo(a)pyrene induces MUC5AC expression through the AhR/mitochondrial ROS/ERK pathway in airway epithelial cells

ObjectivesBenzo(a)pyrene (BaP) is a ubiquitous air pollutants, and BaP exposure leads to a risk of respiratory diseases. The oversecretion of airway mucus and high expression of mucin 5AC (MUC5AC) are associated with common respiratory disorders caused by air pollution. We aimed to investigate the effect of BaP on MUC5AC expression, especially the mechanisms by which BaP induces MUC5AC gene expression. MethodsThe human airway epithelial cell NCI-H292 was used to test the effects of BaP on the expression of MUC5AC in vitro. MUC5AC mRNA and protein expression were assessed with real-time quantitative PCR, immunochemistry, and western blotting. A luciferase assay was conducted to detect the activity of the promoter. The total cellular ROS and mitochondrial ROS were measured by corresponding probes. Small-interfering RNAs were used for gene silencing. AhR-overexpressing cell lines were constructed by transfection with AhR overexpression lentivirus. ResultsWe found that BaP stimulation upregulated the MUC5AC mRNA and protein levels and activated the ERK pathway. Suppressing ERK with U0126 (an ERK inhibitor) or knocking down ERK with siRNA decreased BaP-induced MUC5AC expression. The luciferase activity transfected with the MUC5AC promoter and cAMP-response element (CRE) was increased after BaP treatment, whereas CREB siRNA suppressed the BaP-induced overexpression of MUC5AC. In addition, BaP increased mitochondrial ROS production, and Mito-TEMP, a mitochondrial ROS inhibitor, inhibited BaP-induced MUC5AC expression and ERK activation. BaP increased the mRNA levels of CYP1A1 and CYP1B1, while Alizarin, a CYP1s inhibitor, suppressed the effects of BaP, including the MUC5AC overexpression, ERK activation and mitochondrial ROS generation. BaP induced the translocation of aryl hydrocarbon receptor (AhR) from the cytoplasm to the nucleus. SiRNA-mediated knockdown or chemical inhibition of AhR decreased the BaP-induced expression of MUC5AC, while the overexpression of AhR significantly enhanced the BaP-induced expression of MUC5AC. ITE, an endogenous AhR ligand, also upregulated the mRNA and protein expression of MUC5AC. Furthermore, resveratrol treatment inhibited the BaP-induced MUC5AC overexpression, AhR translocation, mitochondrial ROS production and ERK pathway activation. ConclusionHere, we highlighted the crucial role of AhR/mitochondrial ROS/ERK pathway activation in BaP-induced MUC5AC overexpression and identified resveratrol as a promising drug to reduce BaP-induced MUC5AC overexpression.