Deletion Of Aryl Hydrocarbon Receptor Research Articles

Beyond transcription, aryl hydrocarbon receptor plays a protective role in periodontitis by interacting with CaMKII.

The aryl hydrocarbon receptor (AhR) has been studied as an intracellular pattern recognition receptor that can identify bacterial pigments. To identify a potential therapeutic target for periodontitis, we investigated the expression of AhR in periodontitis and its role in the pathogenesis of periodontitis. First, we analyzed AhR expression in a single-cell dataset from human periodontal tissue. Quantitative polymerase chain reaction (qPCR), immunofluorescence, and immunohistochemistry were used to verify the AhR level. Later, we determined the phenotypes of ligature-induced periodontitis in myeloid-specific AhR-deficient mice (Lyz2-Cre+/- AhRfx/fx), after which RNA sequencing (RNA-seq), qPCR, Western blot, immunofluorescence, and immunohistochemistry were used to investigate the impacts of AhR on periodontitis and its mechanism. Finally, we determined the therapeutic effect of AhR agonist 6-Formylindolo[3,2-b]carbazole (FICZ) administration on murine periodontitis and verified the effects of FICZ on macrophage polarization in vitro. AhR expression was enhanced in macrophages from periodontitis patients. Deletion of AhR from macrophages aggravated ligature-induced periodontitis and promoted the inflammatory response. Calcium/calmodulin-stimulated protein kinase II (CaMKII) phosphorylation was accelerated in AhR-deficient macrophages. Inhibiting CaMKII phosphorylation ameliorated periodontitis in Lyz2-Cre+/- AhRfx/fx mice. FICZ treatment blocked alveolar bone loss and relieved periodontal inflammation. FICZ diminished M1 macrophage polarization and promoted M2 macrophage polarization upon M1 macrophage induction. AhR played a protective role in the pathogenesis of periodontitis by orchestrating macrophage polarization via interacting with the CaMKII signaling pathway.

Abstract 2649: A new role for the aryl hydrocarbon receptor (AhR) as a proximal mediator of immune checkpoints (PD-L1/2 and IDO1) in non-small cell lung cancer: Insights into an interferon-induced, LncRNA-and JAK/STAT-mediated signaling pathway

Abstract Non-small cell lung cancer (NSCLC) is the second most common cancer and accounts for ~127,000 deaths/year in the U.S. Its current ~30% five-year survival rate is an improvement from a decade ago thanks in part to the introduction of immune checkpoint inhibitors including PD1- and PD-L1-specific monoclonal antibodies. While PD-1/PD-L1-targeted immunotherapy is effective in many cases, not all patients respond and complete remissions still only occur in a minority of patients. Therefore, a greater understanding of immune checkpoint regulation in human NSCLC is needed. Here, we investigated a novel role for the aryl hydrocarbon receptor (AhR), an environmental carcinogen receptor previously associated with smoking-induced lung cancers, in the regulation of immune checkpoints PD-L1, PD-L2, and IDO1. Computational analyses of existing databases for protein-protein interactions linked to the AhR signaling pathway suggested crosstalk between the AhR, type I and type II Interferon (IFN), and JAK/STAT signaling pathways. AhR deletion from human lung A549 adenocarcinoma cells significantly reduced expression of JAK2, STAT1, STAT2, and the JAK/STAT signaling targets IRF1 and IRF9. Type II IFNγ significantly increased expression of those genes as well as the immune checkpoints IDO1, PD-L1, and PD-L2 in an AhR-dependent fashion. Interestingly, AhR deletion also eliminated IFNγ-mediated induction of a recently described long non-coding RNA, INCR1, which is encoded across the CD274/CD273 locus, and which facilitates JAK2, CD274/PD-L1, and IDO1 translation. Concomitantly, AhR knockout increased baseline expression of an RNA-binding protein, HNRNPH1, known to sequester JAK2 and CD274 mRNA thereby reducing IDO, PD-L1 and PD-L2 expression. Similarly, the AhR was shown to regulate Type I IFNα-mediated induction of STAT1, STAT2, CD274/PD-L1, and CD273/PD-L2. The data indicate that IFN induction of key immune checkpoints in lung adenocarcinoma cells is dependent on the AhR through its control of a conventional JAK/STAT pathway and an unconventional lncRNA (INCR1) and RNA-binding protein (HNRNPH1) pathway. Citation Format: Brian Lara, Megan Snyder, Zhongyan Wang, Jocelyn Fimbres, Eric Yang, David H. Sherr. A new role for the aryl hydrocarbon receptor (AhR) as a proximal mediator of immune checkpoints (PD-L1/2 and IDO1) in non-small cell lung cancer: Insights into an interferon-induced, LncRNA-and JAK/STAT-mediated signaling pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2649.

Deletion of AhR attenuates fear memory leaving other types of memory intact

The aryl hydrocarbon receptor (AhR), a classic “environmental sensor”, has been found to play an important role in cognitive and emotional function. Recent studies showed AhR deletion led to an attenuated fear memory, providing a potential target against fear memory, whether it is the consequence of attenuated sense of fear or memory ability deficit or both is unclear. Here this study aims to work this out. The freezing time in contextual fear conditioning (CFC) reduced significantly in AhR knockout mice, indicating an attenuated fear memory. Hot plate test and acoustic startle reflex showed that AhR knockout did not change the pain threshold and hearing, excluded the possibility of sensory impairments. Results from NORT, MWM and SBT showed that deletion of AhR had little effects on other types of memory. But the anxiety-like behaviors reduced both in naïve or suffered (tested after CFC) AhR knockout mice, showing that AhR-deficient mice have a reduced basal and stressful emotional response. The basal low-frequency to high-frequency (LF/HF) ratio of the AhR knockout mice was significantly lower than that of the control group, indicating lower sympathetic excitability in the basal state, suggesting a low level of basal stress in the knockout mice. Before and after CFC, the LF/HF ratio of AhR-KO mice tended to be significantly lower than that of WT mice, and their heart rate was significantly lower; and the AhR-KO mice also has a decreased serum corticosterone level after CFC, suggesting a reduced stress response in AhR knockout mice. Altogether, the basal stress level and stress response were significant reduced in AhR knockout mice, which might contribute to the attenuated fear memory with little impairment on other types of memory, suggesting AhR as a “psychologic sensor” additional to “environmental sensor”.

Tumor-Suppressive Functions of the Aryl Hydrocarbon Receptor (AhR) and AhR as a Therapeutic Target in Cancer.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor involved in regulating a wide range of biological responses. A diverse array of xenobiotics and endogenous small molecules bind to the receptor and drive unique phenotypic responses. Due in part to its role in mediating toxic responses to environmental pollutants, AhR activation has not been traditionally viewed as a viable therapeutic approach. Nonetheless, the expression and activation of AhR can inhibit the proliferation, migration, and survival of cancer cells, and many clinically approved drugs transcriptionally activate AhR. Identification of novel select modulators of AhR-regulated transcription that promote tumor suppression is an active area of investigation. The development of AhR-targeted anticancer agents requires a thorough understanding of the molecular mechanisms driving tumor suppression. Here, we summarized the tumor-suppressive mechanisms regulated by AhR with an emphasis on the endogenous functions of the receptor in opposing carcinogenesis. In multiple different cancer models, the deletion of AhR promotes increased tumorigenesis, but a precise understanding of the molecular cues and the genetic targets of AhR involved in this process is lacking. The intent of this review was to synthesize the evidence supporting AhR-dependent tumor suppression and distill insights for development of AhR-targeted cancer therapeutics.

Microglial aryl hydrocarbon receptor enhances phagocytic function via SYK and promotes remyelination in the cuprizone mouse model of demyelination

Multiple sclerosis (MS) is an inflammatory-mediated demyelinating disease of the central nervous system (CNS). Although studies have demonstrated that microglia facilitate remyelination in demyelinating diseases, the underlying mechanisms are still not fully characterized. We found that aryl hydrocarbon receptor (AhR), an environment sensor, was upregulated within the corpus callosum in the cuprizone model of CNS demyelination, and upregulated AhR was mainly confined to microglia. Deletion of AhR in adult microglia inhibited efficient remyelination. Transcriptome analysis using RNA-seq revealed that AhR-deficient microglia displayed impaired gene expression signatures associated with lysosome and phagocytotic pathways. Furthermore, AhR-deficient microglia showed impaired clearance of myelin debris and defected phagocytic capacity. Further investigation of target genes of AhR revealed that spleen tyrosine kinase (SYK) is the downstream effector of AhR and mediated the phagocytic capacity of microglia. Additionally, AhR deficiency in microglia aggravated CNS inflammation during demyelination. Altogether, our study highlights an essential role for AhR in microglial phagocytic function and suggests the therapeutic potential of AhR in demyelinating diseases.Graphical

Aryl Hydrocarbon Receptor (AhR) Signaling in Colonic Cells and Tumors.

The aryl hydrocarbon receptor (AhR) is overexpressed in many tumor types and exhibits tumor-specific tumor promoter and tumor suppressor-like activity. In colon cancer, most but not all studies suggest that the AhR exhibits tumor suppressor activity which is enhanced by AhR ligands acting as agonists. Our studies investigated the role of the AhR in colon tumorigenesis using wild-type and AhR-knockout mice, the inflammation model of colon tumorigenesis using mice treated with azoxymethane (AOM)/dextran sodium sulfate (DSS) and APCS580/+; KrasG12D/+ mice all of which form intestinal tumors. The effects of tissue-specific AhR loss in the intestine of the tumor-forming mice on colonic stem cells, organoid-initiating capacity, colon tumor formation and mechanisms of AhR-mediated effects were investigated. Loss of AhR enhanced stem cell and tumor growth and in the AOM/DSS model AhR-dependent suppression of FOXM1 and downstream genes was important for AhR-dependent anticancer activity. Furthermore, the effectiveness of interleukin-22 (IL22) in colonic epithelial cells was also dependent on AhR expression. IL22 induced phosphorylation of STAT3, inhibited colonic organoid growth, promoted colonic cell proliferation in vivo and enhanced DNA repair in AOM/DSS-induced tumors. In this mouse model, the AhR suppressed SOCS3 expression and enhanced IL22-mediated activation of STAT3, whereas the loss of the AhR increased levels of SOCS3 which in turn inhibited IL22-induced STAT3 activation. In the APCS580/+; KrasG12D/+ mouse model, the loss of the AhR enhanced Wnt signaling and colon carcinogenesis. Results in both mouse models of colon carcinogenesis were complemented by single cell transcriptomics on colonic intestinal crypts which also showed that AhR deletion promoted expression of FOXM1-regulated genes in multiple colonic cell subtypes. These results support the role of the AhR as a tumor suppressor-like gene in the colon.

Modulation of Aryl Hydrocarbon Receptor Expression Alleviated Neuropathic Pain in a Chronic Constriction Nerve Injury Animal Model.

Neuropathic pain is well known to occur after damage to the somatosensory system. Aryl hydrocarbon receptor (AhR) has neuroprotective effects when the central nervous system is subjected to internal and external stimulations. However, the exact mechanism by which AhR regulates neuropathic pain is poorly understood. Nerve explant culture and the chronic constrictive nerve injury (CCI) model in wild or AhR-knockout mice were used in this study. In the nerve explant culture, the ovoid number increased in the AhR−/− condition and was decreased by omeprazole (AhR agonist) in a dose-dependent manner. Increased nerve degeneration and the associated inflammation response appeared in the AhR−/− condition, and these changes were attenuated by omeprazole. High expression of AhR in the injured nerve was noted after CCI. Deletion of AhR aggravated nerve damages and this was restored by omeprazole. Deletion of AhR increased NGF expression and reduced axon number in the paw skin, but this was attenuated by omeprazole. A highly expressed inflammation reaction over the dorsal spinal cord, somatosensory cortex, and hippocampus was noted in the AhR-deleted animals. Administration of omeprazole attenuated not only the inflammatory response, but also the amplitude of somatosensory evoked potential. Deletion of AhR further aggravated the neurobehavior compared with the wild type, but such behavior was attenuated by omeprazole. Chronic constrictive nerve injury augmented AhR expression of the injured nerve, and AhR deletion worsened the damage, while AhR agonist omeprazole counteracted such changes. AhR agonists could be potential candidates for neuropathic pain treatment.

The aryl hydrocarbon receptor instructs the immunomodulatory profile of a subset of Clec4a4+ eosinophils unique to the small intestine

C-type lectin domain family 4, member a4 (Clec4a4) is a C-type lectin inhibitory receptor specific for glycans thought to be exclusively expressed on murine CD8α− conventional dendritic cells. Using newly generated Clec4a4-mCherry knock-in mice, we identify a subset of Clec4a4-expressing eosinophils uniquely localized in the small intestine lamina propria. Clec4a4+ eosinophils evinced an immunomodulatory signature, whereas Clec4a4− eosinophils manifested a proinflammatory profile. Clec4a4+ eosinophils expressed high levels of aryl hydrocarbon receptor (Ahr), which drove the expression of Clec4a4 as well as other immunomodulatory features, such as PD-L1. The abundance of Clec4a4+ eosinophils was dependent on dietary AHR ligands, increased with aging, and declined in inflammatory conditions. Mice lacking AHR in eosinophils expanded innate lymphoid cells of type 2 and cleared Nippostrongylus brasiliensis infection more effectively than did wild-type mice. These results highlight the heterogeneity of eosinophils in response to tissue cues and identify a unique AHR-dependent subset of eosinophils in the small intestine with an immunomodulatory profile.

Aryl hydrocarbon receptor (AhR) activation contributes to high-fat diet-induced vascular dysfunction.

Metabolic and vascular dysfunction are common features of obesity. Aryl hydrocarbon receptor (AhR) regulates lipid metabolism and vascular homeostasis, but whether vascular AhR are activated in obesity or have a protective and/or harmful effects on vascular function in obesity are unknown. Our study addresses whether AhR activation contributes to obesity-associated vascular dysfunction and the mechanisms involved in these AhR effects. Male AhR KO (Ahr-/- ) and WT mice were fed either control or a HF (high-fat) diet for 10 weeks. Metabolic and inflammatory parameters were measured in serum and adipose tissue. Vascular reactivity (isometric force) was evaluated using a myography. Endothelial NOS (eNOS) and AhR protein expression was determined by western blot, Cyp1A1 and Nos3 gene expression by RT-PCR and.NO production was quantified by DAF fluorescence. HF diet increased total serum HDL and LDL, as well as vascular AhR protein expression and proinflammatory cytokines in the adipose tissue. HF diet decreased endothelium-dependent vasodilation. AhR deletion protected mice from HF diet-induced dyslipidaemia, weight gain and inflammatory processes. HF diet-induced endothelial dysfunction was attenuated in Ahr-/- mice. Vessels from Ahr-/- mice exhibited a greater NO reserve. In cultured endothelial cells, lysophosphatidylcholine (LPC) a major component of LDL and oxidized LDL [oxLDL]) reduced Nos3 gene expression and NO production. Antagonism of the AhR inhibited LPC effects on endothelial cells and induced decreased endothelium-dependent vasodilation. AhR deletion attenuates HF diet-induced dyslipidaemia and vascular dysfunction by improving eNOS/NO signalling. Targeting AhRs may prevent obesity-associated vascular dysfunction.

Epithelial Aryl Hydrocarbon Receptor Protects From Mucus Production by Inhibiting ROS-Triggered NLRP3 Inflammasome in Asthma.

BackgroundDespite long-standing recognition in the significance of mucus overproduction in asthma, its etiology remains poorly understood. Muc5ac is a secretory mucin that has been associated with reduced pulmonary function and asthma exacerbations.ObjectivesWe sought to investigate the immunological pathway that controls Muc5ac expression and allergic airway inflammation in asthma.MethodsCockroach allergen-induced Muc5ac expression and aryl hydrocarbon receptor (AhR) signaling activation was examined in the human bronchial epithelial cells (HBECs) and mouse model of asthma. AhR regulation of Muc5ac expression, mitochondrial ROS (Mito-ROS) generation, and NLRP3 inflammasome was determined by AhR knockdown, the antagonist CH223191, and AhR-/- mice. The role of NLRP3 inflammasome in Muc5ac expression and airway inflammation was also investigated.ResultsCockroach allergen induced Muc5ac overexpression in HBECs and airways of asthma mouse model. Increased expression of AhR and its downstream genes CYP1A1 and CYP1B1 was also observed. Mice with AhR deletion showed increased allergic airway inflammation and MUC5AC expression. Moreover, cockroach allergen induced epithelial NLRP3 inflammasome activation (e.g., NLRP3, Caspase-1, and IL-1β), which was enhanced by AhR knockdown or the antagonist CH223191. Furthermore, AhR deletion in HBECs led to enhanced ROS generation, particularly Mito-ROS, and inhibition of ROS or Mito-ROS subsequently suppressed the inflammasome activation. Importantly, inhibition of the inflammasome with MCC950, a NLRP3-specifc inhibitor, attenuated allergic airway inflammation and Muc5ac expression. IL-1β generated by the activated inflammasomes mediated cockroach allergen-induced Muc5ac expression in HBECs.ConclusionsThese results reveal a previously unidentified functional axis of AhR-ROS-NLRP3 inflammasome in regulating Muc5ac expression and airway inflammation.

Genetic deletion of aryl hydrocarbon receptor activates cardiac NLRP3-inflammasome and suppresses apoptosis in mice with acute myocardial infarction

Abstract Background and purpose There is great interest in understanding the role of immune cells in the inflammatory mechanisms associated with acute myocardial infarction (AMI). Resident cardiac immune cells are activated by damage-associated molecular patterns interacting with specific pattern recognition receptors (PRRs), triggering inflammatory responses. Activated immune cells and fibroblasts then promote prohypertrophic and profibrotic signalling, which induces cardiac hypertrophy, fibrosis and remodelling after AMI. Nucleotide-binding domain leucine-rich repeat-containing proteins (NLRs) are PRRs that have emerged as key therapeutic targets in cardiovascular disease. NLRP3 assembles the inflammasome, which serves as molecular signalling platform to activate caspase-1 and regulate maturation of the potent proinflammatory cytokine IL-1β. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor of the basic Helix-Loop-Helix-PER-ARNT-SIM superfamily that mediates responses against environmental pollutants. Beyond its role in metabolising exogenous toxins as part of an adaptive chemical response, there is growing evidence that AhR is activated by endogenous ligands under physiological conditions. AhR has been proposed as a negative regulator of NLRP3-inflammasome activation. Here we studied the effects of defective AhR signalling on apoptosis, NLRP3-inflammasome activation and survival in a mouse model of AMI. Methods and results AMI was induced in 8–10-weeks-old AhR+/+ and AhR−/− mice by ligation of the left anterior descending coronary artery. Immunofluorescence analysis revealed that the number of TUNEL-positive nuclei and the expression of the apoptotic effector cleaved caspase-3 was higher in hearts from infarcted AhR+/+ mice than from sham-operated AhR+/+ mice 24 h after surgery. A similar analysis in AhR−/− mice revealed the absence of apoptotic markers after AMI. Gene analysis showed that cardiac levels of Nlrp3, apoptosis-associated speck-like protein (Asc) and Il1b were all significantly higher in AhR−/− mice than in AhR+/+ mice 24 h after AMI. Finally, survival analysis showed that 25% of AhR+/+ mice died 72 h after AMI surgery whereas the mortality in AhR−/− mice was 100%. Conclusion Our results show that loss of AhR inhibits cardiac apoptosis and increases NLRP3-mediated inflammation 24 h after AMI, highlighting a possible role for this nuclear receptor in cardiac remodelling post-AMI. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund

The Aryl Hydrocarbon Receptor Modulates Murine Hematopoietic Stem Cell Homeostasis and Influences Lineage-Biased Stem and Progenitor Cells.

The core function of hematopoietic stem and progenitor cells (HSPCs) is to provide lifelong production of all lineages of the blood and immune cells. The mechanisms that modulate HSPC homeostasis and lineage biasing are not fully understood. Growing evidence implicates the aryl hydrocarbon receptor (AHR), an environment-sensing transcription factor, as a regulator of hematopoiesis. AHR ligands modulate the frequency of mature hematopoietic cells in the bone marrow and periphery, while HSPCs from mice lacking AHR (AHR KO) have increased proliferation. Yet, whether AHR modulates HSPC lineage potential and directs differentiation toward specific lineage-biased progenitors is not well understood. This study revealed that AHR KO mice have an increased proportion of myeloid-biased HSCs and myeloid-biased multipotent progenitor (MPP3) cells. Utilizing inducible AHR knockout mice (iAHR KO), it was discovered that acute deletion of AHR doubled the number of MPP3 cells and altered the composition of downstream lineage-committed progenitors, such as increased frequency of pregranulocyte/premonocyte committed progenitors. Furthermore, in vivo antagonism of the AHR led to a 2.5-fold increase in the number of MPP3 cells and promoted myeloid-biased differentiation. Using hematopoietic-specific conditional AHR knockout mice (AHRVav1) revealed that increased frequency of myeloid-biased HSCs and myeloid-biased progenitors is driven by AHR signaling that is intrinsic to the hematopoietic compartment. These findings demonstrate that the AHR plays a pivotal role in regulating steady-state hematopoiesis, influencing HSPC homeostasis and lineage potential. In addition, the data presented provide potential insight into how deliberate modulation of AHR signaling could help with the treatment of a broad range of diseases that require the hematopoietic compartment.

Depletion of AhR Ligands in Diet Worsens Inflammatory Conditions in Mice with Chronic DSS‐Induced Colitis

The aryl hydrocarbon receptor (AhR) is an important transcription factor that regulates xenobiotic metabolism and is vital for maintaining immune cell populations, proliferation, and motility in the gastrointestinal (GI) tract. Recent studies have shown that deletion of AhR from mouse intestinal epithelial cells worsens experimental colitis, while activation of AhR by its agonists protects against acuteinflammation. AhR is activated by a variety of ligands including indole-3-carbinole (I3C) derived from cruciferous vegetables, such as broccoli and brussels sprouts. Whether AhR ligands derived from the diet impact chronic intestinal inflammation and/or cause gut microbiota alterations has not yet been investigated. Methods C57BL/6 mice (7-9 wk, M) were fed either standard chow diet or purified diet (depleted of AhR ligands, referred to as -I3C diet) or the purified diet supplemented with 200 ppm of I3C (+I3C diet). Along with the diet, the mice were given either water or treated with 5 cycles of 2.5% dextran sulfate sodium (DSS) alternating weekly with water to induce chronic colitis. Total RNA was extracted from mouse colonic mucosal scrapings and amplified using Real Time qRT-PCR. Myeloperoxidase (MPO) assay and histological analysis was used to assess inflammation. 16S sequencing was performed on DNA extracted from cecal contents for microbiota analysis (Zymo). Results : Depletion of AhR ligands in the diet increased severity of DSS induced colitis as evidenced by: i) a significant decrease in the colon length and an increase in colon weight to length ratio in chronic DSS mice fed the purified -I3C diet vs +I3C diet; ii) an increase in myeloperoxidase activity and increased histological scores in chronic DSS mice fed the -I3C diet vs DSS mice fed +I3C diet; iii) a significant decrease in mRNA expression of pro-inflammatory cytokines, TNF-α, IL-1β, CCl20, and CXCl2 in the colon of DSS mice fed +I3C diet compared with -I3C diet; iv) a significant decrease in tight junction (occludin and ZO-1) and adherens junction (E-cadherin) protein levels in chronic DSS mice fed -I3C diet and this decrease was attenuated by supplementation of I3C. The different diets modulated gut microbiota under basal and in chronic colitis conditions. -I3C diet alone led to the emergence of the pathobiont, Parvibacter caecicola (phylum Actinobacterium) which was not detected in either the chow or +I3C diet. Chronic DSS and -I3C diet induced major alterations in phylum Firmicutes (with less abundance of Clostridia and an increase of Erysipeltrichia), and an increase in abundance of Bacteroides thetaoitaomicron (phylumActinobacterium). Interestingly, these changes in microbiota composition in DSS groups were reversed with I3C supplementation to diet. Conclusions Depletion of AhR ligands in the diet worsens colitis and induces dysbiosis. These results highlight the importance of diet in shaping gut microbiota and underscore the significance of potential nutritional strategies to alleviate colitis.

Effect of diet and intestinal AhR expression on fecal microbiome and metabolomic profiles

BackgroundDiet, loss of aryl hydrocarbon receptor (AhR) expression and their modification of the gut microbiota community composition and its metabolites affect the development of colorectal cancer (CRC). However, the concordance between fecal microbiota composition and the fecal metabolome is poorly understood. Mice with specific AhR deletion (AhRKO) in intestinal epithelial cell and their wild-type littermates were fed a low-fat diet or a high-fat diet. Shifts in the fecal microbiome and metabolome associated with diet and loss of AhR expression were assessed. Microbiome and metabolome data were integrated to identify specific microbial taxa that contributed to the observed metabolite shifts.ResultsOur analysis shows that diet has a more pronounced effect on mouse fecal microbiota composition than the impact of the loss of AhR. In contrast, metabolomic analysis showed that the loss of AhR in intestinal epithelial cells had a more pronounced effect on metabolite profile compared to diet. Integration analysis of microbiome and metabolome identified unclassified Clostridiales, unclassified Desulfovibrionaceae, and Akkermansia as key contributors to the synthesis and/or utilization of tryptophan metabolites.ConclusionsAkkermansia are likely to contribute to the synthesis and/or degradation of tryptophan metabolites. Our study highlights the use of multi-omic analysis to investigate the relationship between the microbiome and metabolome and identifies possible taxa that can be targeted to manipulate the microbiome for CRC treatment.

Loss of aryl hydrocarbon receptor potentiates FoxM1 signaling to enhance self-renewal of colonic stem and progenitor cells.

The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor that senses xenobiotics, diet, and gut microbial-derived metabolites, is increasingly recognized as a key regulator of intestinal biology. However, its effects on the function of colonic stem and progenitor cells remain largely unexplored. Here, we observed that inducible deletion of AhR in Lgr5+ stem cells increases the percentage of colonic stem cells and enhances organoid initiating capacity and growth of sorted stem and progenitor cells, while AhR activation has the opposite effect. Moreover, intestinal-specific AhR knockout increases basal stem cell and crypt injury-induced cell proliferation and promotes colon tumorigenesis in a preclinical colitis-associated tumor model by upregulating FoxM1 signaling. Mechanistically, AhR transcriptionally suppresses FoxM1 expression. Activation of AhR in human organoids recapitulates phenotypes observed in mice, such as reduction in the percentage of colonic stem cells, promotion of stem cell differentiation, and attenuation of FoxM1 signaling. These findings indicate that the AhR-FoxM1 axis, at least in part, mediates colonic stem/progenitor cell behavior.

Effects of high-fat diet and intestinal aryl hydrocarbon receptor deletion on colon carcinogenesis.

Consumption of a high-fat diet has been associated with an increased risk of developing colorectal cancer (CRC). However, the effects of the interaction between dietary fat content and the aryl hydrocarbon receptor (AhR) on colorectal carcinogenesis remain unclear. Mainly known for its role in xenobiotic metabolism, AhR has been identified as an important regulator for maintaining intestinal epithelial homeostasis. Although previous research using whole body AhR knockout mice has revealed an increased incidence of colon and cecal tumors, the unique role of AhR activity in intestinal epithelial cells (IECs) and modifying effects of fat content in the diet at different stages of sporadic CRC development are yet to be elucidated. In the present study, we have examined the effects of a high-fat diet on IEC-specific AhR knockout mice in a model of sporadic CRC. Although loss of AhR activity in IECs significantly induced the development of premalignant lesions, in a separate experiment, no significant changes in colon mass incidence were observed. Moreover, consumption of a high-fat diet promoted cell proliferation in crypts at the premalignant colon cancer lesion stage and colon mass multiplicity as well as β-catenin expression and nuclear localization in actively proliferating cells in colon masses. Our data demonstrate the modifying effects of high-fat diet and AhR deletion in IECs on tumor initiation and progression.NEW & NOTEWORTHY Through the use of an intestinal-specific aryl hydrocarbon receptor (AhR) knockout mouse model, this study demonstrates that the expression of AhR in intestinal epithelial cells is required to reduce the formation of premalignant colon cancer lesions. Furthermore, consumption of a high-fat diet and the loss of AhR in intestinal epithelial cells influences the development of colorectal cancer at various stages.

Aryl hydrocarbon receptor activation alleviates dextran sodium sulfate-induced colitis through enhancing the differentiation of goblet cells

BackgroundThe intestinal inflammation induces disruption of the intestinal barrier function and leads to bacteria invasion. Accumulating evidences revealed that the aryl hydrocarbon receptor (AhR) plays a vital role in maintaining the intestinal barrier function. However, the precise mechanism remains to be unclear. MethodsAdult C57BL/6J mice were randomly divided into three groups: Sham, DSS and DSS + 6-formylindolo (3, 2-b) carbazole (FICZ)group. The colons and epithelial cell were harvested for histological examination, pro-inflammatory cytokines detection, bacterial load analysis, immunohistochemistry and Muc2 protein analysis. Under physiological condition, AhRKO model and FICZ treatment were used to evaluate the roles of AhR in the differentiation of goblet cells and the expression of Muc2 in mice. In vitro, we used HT29 mol to research the signaling pathway. ResultsAhR activation by FICZ could increase the Muc2 expression and the number of goblet cells and reduce bacterial infiltration to ameliorate DSS-induced Colitis. Under physiological conditions, the treatment of FICZ promote the differentiation of goblet cell and the expression of Muc2 and inhibit the notch-signaling. Genetic deletion of AhR led to the loss of goblet cells and the decrease of Muc2 expression and enhance the notch-signaling. In HT29 cells, the differentiation of goblet cell meditated by AhR can be abolished by the inhibitor of AhR, pErk1/2 and knocking-down AhR. ConclusionFICZ promoted the differentiation of goblet cell through AhR-pErk1/2 signaling pathway and ameliorate DSS-induced Colitis.

AhR Deletion Promotes Aberrant Morphogenesis and Synaptic Activity of Adult-Generated Granule Neurons and Impairs Hippocampus-Dependent Memory

Newborn granule cells are continuously produced in the subgranular zone of dentate gyrus throughout life. Once these cells mature, they integrate into pre-existing circuits modulating hippocampus-dependent memory. Subsequently, mechanisms controlling generation and maturation of newborn cells are essential for proper hippocampal function. Therefore, we have studied the role of aryl hydrocarbon receptor (AhR), a ligand-activated bHLH-PAS transcription factor, in hippocampus-dependent memory and granule neuronal morphology and function using genetic loss-of-function approaches based on constitutive and inducible-nestin AhR-/- mice. The results presented here show that the impaired hippocampus-dependent memory in AhR absence is not due to its effects on neurogenesis but to aberrant dendritic arborization and an increased spine density, albeit with a lower number of mature mushrooms spines in newborn granule cells, a finding that is associated with an immature electrophysiological phenotype. Together, our data strongly suggest that AhR plays a pivotal role in the regulation of hippocampal function, by controlling hippocampal granule neuron morphology and synaptic maturation.

Aryl-hydrocarbon receptor-driven responses of innate lymphocytes

Abstract Innate Lymphoid Cells (ILCs) play significant roles during immune responses to infection at barrier sites and in the control of tissue damage and repair. In addition, ILCs have been involved in several pathologies, including exacerbated inflammation and carcinogenesis. However, understanding the contribution of distinct ILC subsets and modules of their regulation in both homeostasis and disease, is still incomplete. The Aryl-hydrocarbon Receptor (AhR) is a ligand-induced transcription factor that binds various exo- and endogenous polycyclic hydrocarbons and induces transcription of numerous target genes involved in development, cell differentiation and immune response. Here, we show that subsets of NKp46-expressing ILCs, including natural killer (NK) cells and helper ILC1, express AhR and respond to stimulation with AhR ligands. Exposure of NK cells to the tryptophan degradation product kynurenine, an endogenous AhR ligand, induced changes in global gene expression and primed NK cells for enhanced effector responses, including cytokine secretion and migration. In the context of diet-induced chronic liver damage, NK cells accumulated in the liver in an AhR-dependent manner. Conditional AhR deletion abolished NK cell accumulation, which correlated with reduced liver damage. In contrast to NK cells, liver resident helper ILC1 required AhR for the development and/or maintenance. In conclusion, the AhR is expressed by ILC1 subsets and differentially affects their development and effector responses. This might impact ILC1-driven responses in the context of chronic liver damage and could be of significance for liver tissue regeneration.

Aryl hydrocarbon receptor inhibition promotes hematolymphoid development from human pluripotent stem cells

AbstractThe aryl hydrocarbon receptor (AHR) plays an important physiological role in hematopoiesis. AHR is highly expressed in hematopoietic stem and progenitor cells (HSPCs) and inhibition of AHR results in a marked expansion of human umbilical cord blood–derived HSPCs following cytokine stimulation. It is unknown whether AHR also contributes earlier in human hematopoietic development. To model hematopoiesis, human embryonic stem cells (hESCs) were allowed to differentiate in defined conditions in the presence of the AHR antagonist StemReginin-1 (SR-1) or the AHR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). We demonstrate a significant increase in CD34+CD31+ hematoendothelial cells in SR-1–treated hESCs, as well as a twofold expansion of CD34+CD45+ hematopoietic progenitor cells. Hematopoietic progenitor cells were also significantly increased by SR-1 as quantified by standard hematopoietic colony-forming assays. Using a clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9)-engineered hESC-RUNX1c-tdTomato reporter cell line with AHR deletion, we further demonstrate a marked enhancement of hematopoietic differentiation relative to wild-type hESCs. We also evaluated whether AHR antagonism could promote innate lymphoid cell differentiation from hESCs. SR-1 increased conventional natural killer (cNK) cell differentiation, whereas TCDD treatment blocked cNK development and supported group 3 innate lymphoid cell (ILC3) differentiation. Collectively, these results demonstrate that AHR regulates early human hematolymphoid cell development and may be targeted to enhance production of specific cell populations derived from human pluripotent stem cells.