AhR-deficient Mice 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.

Activation of the aryl hydrocarbon receptor improves allergen-specific immunotherapy of murine allergic airway inflammation: a novel adjuvant option?

Allergen-specific immunotherapy (AIT) is able to restore immune tolerance to allergens in allergic patients. However, some patients do not or only poorly respond to current treatment protocols. Therefore, there is a need for deeper mechanistic insights and further improvement of treatment strategies. The relevance of the aryl hydrocarbon receptor (AhR), a ligand-dependent transcription factor, has been investigated in several inflammatory diseases, including allergic asthma. However, its potential role in AIT still needs to be addressed. A murine model of AIT in ovalbumin-induced allergic airway inflammation was performed in AhR-deficient (AhR-/-) and wild-type mice. Furthermore, AIT was combined with the application of the high-affinity AhR agonist 10-chloro-7H-benzimidazo[2,1-a]benzo[de]iso-quinolin-7-one (10-Cl-BBQ) as an adjuvant to investigate the effects of AhR activation on therapeutic outcome. Although AhR-/- mice suffer stronger allergic responses than wild-type mice, experimental AIT is comparably effective in both. Nevertheless, combining AIT with the administration of 10-Cl-BBQ improved therapeutic effects by an AhR-dependent mechanism, resulting in decreased cell counts in the bronchoalveolar fluid, decreased pulmonary Th2 and Th17 cell levels, and lower sIgE levels. This study demonstrates that the success of AIT is not dependent on the AhR. However, targeting the AhR during AIT can help to dampen inflammation and improve tolerogenic vaccination. Therefore, AhR ligands might represent promising candidates as immunomodulators to enhance the efficacy of AIT.

Dysregulation of stress erythropoiesis and enhanced susceptibility to Salmonella Typhimurium infection in AhR-deficient mice.

By acting as an environmental sensor, the ligand-induced transcription factor aryl hydrocarbon receptor (AhR) regulates acute innate and adaptive immune responses against pathogens. Here, we analyzed the function of AhR in a model for chronic systemic infection with attenuated Salmonella Typhimurium (STM). WT and AhR-deficient mice were infected with the attenuated STM strain TAS2010 and analyzed for bacterial burden, host defense functions and inflammatory stress erythropoiesis. AhR-deficient mice were highly susceptible to TAS2010 infection compared with WT mice demonstrated by reduced bacterial clearance and increased mortality. STM infection resulted in macrocytic anemia and enhanced splenomegaly along with destruction of the splenic architecture in AhR-deficient mice. In addition, AhR-deficient mice displayed a major expansion of splenic immature red blood cells, indicative of infection-induced stress erythropoiesis. Elevated serum levels of erythropoietin and interleukin-6 upon infection as well as increased numbers of splenic stress erythroid progenitors already in steady state probably drive this effect and might cause the alterations in splenic immune cell compartments, thereby preventing an effective host defense against STM in AhR-deficient mice. AhR-deficient mice fail to clear chronic TAS2010 infection due to enhanced stress erythropoiesis in the spleen and accompanying destruction of the splenic architecture.

Tumor formation at ileocecal junction associated with interleukin-1β upregulation in aryl hydrocarbon receptor-deficient mouse.

Aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor. We previously reported spontaneous ileocecal tumorigenesis in AhR-deficient mice after the age of 10 weeks, which originated in the confined area between ileum and cecum. This study aimed to investigate the underlying mechanism that causes tumor development at this particular location. To observe mucosal architecture in detail, tissues of ileocecal region were stained with methylene blue. Gene expression profile in the ileocecal tissue was compared with cecum. Immunohistochemical analysis was performed with ileocecal tissues using antibodies against ileum-specific Reg3β or cecum-specific Pitx2. In AhR+/+ mice and AhR+/- mice, that do not develop lesions, methylene blue staining revealed the gradually changing shape and arrangement of villi from ileum to cecum. It was also observed in AhR-deficient mice before developing lesions. Microarray-based analysis revealed abundant antimicrobial genes, such as Reg3, in the ileocecal tissue while FGFR2 and Pitx2 were specific to cecum. Immunohistochemical analysis of AhR-deficient mice indicated that lesions originated from the ileocecal junction, a boundary area between different epithelial types. Site-specific gene expression analysis revealed higher expression of IL-1β at the ileocecal junction compared with the ileum or cecum of 9-11-week-old AhR-deficient mice. These findings indicate that AhR plays a vital function in the ileocecal junction. Regulating AhR activity can potentially manage the stability of ileocecal tissue possessing cancer-prone characteristics. This investigation contributes to understanding homeostasis in different epithelial transitional tissues, frequently associated with pathological states.

Nutrition impact on ILC3 maintenance and function centers on a cell-intrinsic CD71-iron axis.

Iron metabolism is pivotal for cell fitness in the mammalian host; however, its role in group 3 innate lymphoid cells (ILC3s) is unknown. Here we show that transferrin receptor CD71 (encoded by Tfrc)-mediated iron metabolism cell-intrinsically controls ILC3 proliferation and host protection against Citrobacter rodentium infection and metabolically affects mitochondrial respiration by switching of oxidative phosphorylation toward glycolysis. Iron deprivation or Tfrc ablation in ILC3s reduces the expression and/or activity of the aryl hydrocarbon receptor (Ahr), a key ILC3 regulator. Genetic ablation or activation of Ahr in ILC3s leads to CD71 upregulation or downregulation, respectively, suggesting Ahr-mediated suppression of CD71. Mechanistically, Ahr directly binds to the Tfrc promoter to inhibit transcription. Iron overload partially restores the defective ILC3 compartment in the small intestine of Ahr-deficient mice, consistent with the compensatory upregulation of CD71. These data collectively demonstrate an under-appreciated role of the Ahr-CD71-iron axis in the regulation of ILC3 maintenance and function.

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”.

The aryl hydrocarbon receptor contributes to tissue adaptation of intestinal eosinophils in mice.

Eosinophils are potent sources of inflammatory and toxic mediators, yet they reside in large numbers in the healthy intestine without causing tissue damage. We show here that intestinal eosinophils were specifically adapted to their environment and underwent substantial transcriptomic changes. Intestinal eosinophils upregulated genes relating to the immune response, cell-cell communication, extracellular matrix remodeling, and the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor with broad functions in intestinal homeostasis. Eosinophils from AHR-deficient mice failed to fully express the intestinal gene expression program, including extracellular matrix organization and cell junction pathways. AHR-deficient eosinophils were functionally impaired in the adhesion to and degradation of extracellular matrix, were more prone to degranulation, and had an extended life span. Lack of AHR in eosinophils had wider effects on the intestinal immune system, affecting the T cell compartment in nave and helminth-infected mice. Our study demonstrates that the response to environmental triggers via AHR partially shapes tissue adaptation of eosinophils in the small intestine.

Differential Regulation of the Asthmatic Phenotype by the Aryl Hydrocarbon Receptor.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that regulates the metabolism of xenobiotics. There is growing evidence that the AhR is implicated in physiological processes such proliferation, differentiation, and immune responses. Recently, a role of the AhR in regulating allergic asthma has been suggested, but whether the AhR also regulates other type of asthma, particularly occupational/irritant-induced asthma, remains unknown. Using AhR-deficient (Ahr−/−) mice, we compared the function of the AhR in the response to ovalbumin (OVA; allergic asthma) vs. chlorine (Cl2; irritant-induced asthma) exposure. Lung inflammation and airway hyperresponsiveness were assessed 24h after exposure to Cl2 or OVA challenge in Ahr−/− and heterozygous (Ahr+/−) mice. After OVA challenge, absence of AhR was associated with significantly enhanced eosinophilia and lymphocyte influx into the airways of Ahr−/− mice. There were also increased levels of interleukin-4 (IL-4) and IL-5 in the airways. However, OVA-induced airway hyperresponsiveness was not affected. In the irritant-induced asthma model caused by exposure to Cl2, the AhR did not regulate the inflammatory response. However, absence of AhR reduced Cl2-induced airway hyperresponsiveness. Collectively, these results support a differential role for the AhR in regulating asthma outcomes in response to diverse etiological agents.

AHR in the intestinal microenvironment: safeguarding barrier function.

Mammalian aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor that belongs to the basic helix-loop-helix (bHLH)-PAS family of transcription factors, which are evolutionarily conserved environmental sensors. In the absence of ligands, AHR resides in the cytoplasm in a complex with molecular chaperones such as HSP90, XAP2 and p23. Upon ligand binding, AHR translocates into the nuclear compartment, where it dimerizes with its partner protein, AHR nuclear translocator (ARNT), an obligatory partner for the DNA-binding and functional activity. Historically, AHR had mostly been considered as a key intermediary for the detrimental effects of environmental pollutants on the body. However, following the discovery of AHR-mediated functions in various immune cells, as well as the emergence of non-toxic 'natural' AHR ligands, this view slowly began to change, and the study of AHR-deficient mice revealed a plethora of important beneficial functions linked to AHR activation. This Review focuses on regulation of the AHR pathway and the barrier-protective roles AHR has in haematopoietic, as well as non-haematopoietic, cells within the intestinal microenvironment. It covers the nature of AHR ligands and feedback regulation of the AHR pathway, outlining the currently known physiological functions in immune, epithelial, endothelial and neuronal cells of the intestine.

The aryl hydrocarbon receptor regulates expression of mucosal trafficking receptor GPR15.

GPR15 is a chemoattractant receptor that facilitates colon homing of regulatory and effector CD4+ T cells in health and colitis. The molecular mechanisms that control GPR15 expression are not fully known. Here we report the presence of two highly conserved aryl hydrocarbon receptor (AHR) binding sequences in a 3′ enhancer of GPR15, leading us to investigate AHR function in regulating GPR15 expression. Using luciferase reporter assays, we show that AHR activation increased GPR15 expression and requires both the AHR binding sites. Consistent with a transcriptional regulatory role, treatment with AHR agonists induce GPR15 expression on human CD4+ T cells. Using AHR-deficient mice, we demonstrate that the lack of AHR signaling drastically reduces GPR15 expression on effector/memory and Foxp3+ CD4+ T cells. In mixed bone marrow chimeras of AHR-deficient and wildtype cells, GPR15 expression was similarly diminished on AHR-deficient CD4+ effector/memory and regulatory T cells in the colon and small intestine. Furthermore, administration of AHR agonists upregulated GPR15 expression on CD4+ effector/memory T cells and increased their homing capability, especially to the colon. Collectively, our studies reveal a novel function of the AHR in regulation of GPR15 expression and increased colon trafficking of CD4+ T cells expressing GPR15.

Aryl hydrocarbon receptor deficiency causes the development of chronic obstructive pulmonary disease through the integration of multiple pathogenic mechanisms.

Emphysema, a component of chronic obstructive pulmonary disease (COPD), is characterized by irreversible alveolar destruction that results in a progressive decline in lung function. This alveolar destruction is caused by cigarette smoke, the most important risk factor for COPD. Only 15%-20% of smokers develop COPD, suggesting that unknown factors contribute to disease pathogenesis. We postulate that the aryl hydrocarbon receptor (AHR), a receptor/transcription factor highly expressed in the lungs, may be a new susceptibility factor whose expression protects against COPD. Here, we report that Ahr-deficient mice chronically exposed to cigarette smoke develop airspace enlargement concomitant with a decline in lung function. Chronic cigarette smoke exposure also increased cleaved caspase-3, lowered SOD2 expression, and altered MMP9 and TIMP-1 levels in Ahr-deficient mice. We also show that people with COPD have reduced expression of pulmonary and systemic AHR, with systemic AHR mRNA levels positively correlating with lung function. Systemic AHR was also lower in never-smokers with COPD. Thus, AHR expression protects against the development of COPD by controlling interrelated mechanisms involved in the pathogenesis of this disease. This study identifies the AHR as a new, central player in the homeostatic maintenance of lung health, providing a foundation for the AHR as a novel therapeutic target and/or predictive biomarker in chronic lung disease.

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.

CYP1A1 Enzymatic Activity Influences Skin Inflammation Via Regulation of the AHR Pathway

The AHR is an environmental sensor and transcription factor activated by a variety of man-made and natural ligands, which has recently emerged as a critical regulator of homeostasis at barrier organs such as the skin. Activation of the AHR pathway downmodulates skin inflammatory responses in animal models and psoriasis clinical samples. In this study, we identify CYP1A1 enzymatic activity as a critical regulator of beneficial AHR signaling in the context of skin inflammation. Mice constitutively expressing Cyp1a1 displayed increased CYP1A1 enzymatic activity in the skin, which resulted in exacerbated immune cell activation and skin pathology, mirroring that observed in Ahr-deficient mice. Inhibition of CYP1A1 enzymatic activity ameliorated the skin immunopathology by restoring beneficial AHR signaling. Importantly, patients with psoriasis displayed reduced activation of the AHR pathway and increased CYP1A1 enzymatic activity compared with healthy donors, suggesting that dysregulation of the AHR/CYP1A1 axis may play a role in inflammatory skin disease. Thus, modulation of CYP1A1 activity may represent a promising alternative strategy to harness the anti-inflammatory effect exerted by activation of the AHR pathway in the skin.

Dietary AhR Ligands Regulate AhRR Expression in Intestinal Immune Cells and Intestinal Microbiota Composition

A diet rich in vegetables and fruit is generally considered healthy because of a high content of phytochemicals, vitamins, and fiber. The phytochemical indole-3-carbinol (I3C), a derivative of glucobrassicin, is sold as a dietary supplement promising diverse health benefits. I3C metabolites act as ligands of the aryl hydrocarbon receptor (AhR), an important sensor for environmental polyaromatic chemicals. Here, we investigated how dietary AhR ligand supplementation influences AhR target gene expression and intestinal microbiota composition. For this, we used AhR repressor (AhRR)-reporter mice as a tool to study AhR activation in the intestine following dietary I3C-supplementation in comparison with AhR ligand-deprived diets, including a high fat diet. AhRR expression in intestinal immune cells was mainly driven by dietary AhR ligands and was independent of microbial metabolites. A lack of dietary AhR ligands caused enhanced susceptibility to dextran sodium sulfate (DSS)-induced colitis and correlated with the expansion of Enterobacteriaceae, whereas Clostridiales, Muribaculaceae, and Rikenellaceae were strongly reduced. I3C supplementation largely reverted this effect. Comparison of I3C-induced changes in microbiota composition using wild-type (WT), AhRR-deficient, and AhR-deficient mice revealed both AhR-dependent and -independent alterations in the microbiome. Overall, our study demonstrates that dietary AhR ligand supplementation has a profound influence on Ahrr expression in intestinal immune cells as well as microbiota composition.

AHR Signaling Dampens Inflammatory Signature in Neonatal Skin γδ T Cells.

Background Aryl hydrocarbon receptor (AHR)-deficient mice do not support the expansion of dendritic epidermal T cells (DETC), a resident immune cell population in the murine epidermis, which immigrates from the fetal thymus to the skin around birth. Material and Methods In order to identify the gene expression changes underlying the DETC disappearance in AHR-deficient mice, we analyzed microarray RNA-profiles of DETC, sorted from the skin of two-week-old AHR-deficient mice and their heterozygous littermates. In vitro studies were done for verification, and IL-10, AHR repressor (AHRR), and c-Kit deficient mice analyzed for DETC frequency. Results We identified 434 annotated differentially expressed genes. Gene set enrichment analysis demonstrated that the expression of genes related to proliferation, ion homeostasis and morphology differed between the two mouse genotypes. Importantly, with 1767 pathways the cluster-group “inflammation” contained the majority of AHR-dependently regulated pathways. The most abundant cluster of differentially expressed genes was “inflammation.” DETC of AHR-deficient mice were inflammatory active and had altered calcium and F-actin levels. Extending the study to the AHRR, an enigmatic modulator of AHR-activity, we found approximately 50% less DETC in AHRR-deficient mice than in wild-type-littermates. Conclusion AHR-signaling in DETC dampens their inflammatory default potential and supports their homeostasis in the skin.

The Dual Function of Aryl Hydrocarbon Receptor in Bladder Carcinogenesis.

Although Aryl hydrocarbon receptor (AhR) may be critical to several types of cancers, the function of AhR for carcinogenesis of bladder cancer (BC) is still inconclusive. We, therefore, sought to examine the involvement of AhR in bladder carcinogenesis. We examined the AhR expression of human BC and N-butyl-N-(4-hydroxybutyl)-induced bladder carcinogenesis in AhR-deficient mice. There was a significantly higher expression of AhR in non-muscle-invasive BC compared to normal tissue and muscle-invasive BC (MIBC). The incidence of MIBC in AhR-deficient mice (87.5%) was significantly higher than wild-type mice (9.5%, p<0.01). In cell invasion assay, the induction of AhR signaling resulted in attenuation of BC cell invasiveness and proliferation. These results suggest that AhR may be essential for the initiation of carcinogenesis and attenuated the invasion of BC cells; this signaling may have a dual function in bladder carcinogenesis.

Aryl Hydrocarbon Receptor Contributes to the Transcriptional Program of IL-10-Producing Regulatory B Cells

SummaryRegulatory B cells (Bregs) play a critical role in the control of autoimmunity and inflammation. IL-10 production is the hallmark for the identification of Bregs. However, the molecular determinants that regulate the transcription of IL-10 and control the Breg developmental program remain unknown. Here, we demonstrate that aryl hydrocarbon receptor (AhR) regulates the differentiation and function of IL-10-producing CD19+CD21hiCD24hiBregs and limits their differentiation into B cells that contribute to inflammation. Chromatin profiling and transcriptome analyses show that loss of AhR in B cells reduces expression of IL-10 by skewing the differentiation of CD19+CD21hiCD24hiB cells into a pro-inflammatory program, under Breg-inducing conditions. B cell AhR-deficient mice develop exacerbated arthritis, show significant reductions in IL-10-producing Bregs and regulatory T cells, and show an increase in T helper (Th) 1 and Th17 cells compared with B cell AhR-sufficient mice. Thus, we identify AhR as a relevant contributor to the transcriptional regulation of Breg differentiation.

NPD-0414-2 and NPD-0414-24, Two Chemical Entities Designed as Aryl Hydrocarbon Receptor (AhR) Ligands, Inhibit Gut Inflammatory Signals.

Defects in counterregulatory mechanisms contribute to amplify the detrimental inflammatory response leading to the pathologic process occurring in the gut of patients with Crohn’s disease (CD) and ulcerative colitis (UC), the major inflammatory bowel diseases (IBDs), in human beings. One such mechanism involves aryl hydrocarbon receptor (AhR), a transcription factor activated by natural and synthetic ligands, which induces the production of interleukin (IL)-22 and down-regulates inflammatory signals. In IBD, AhR expression is down-regulated and its activation by natural ligands promotes clinical and endoscopic benefit. Since the use of AhR natural ligands can associate with serious adverse events, we developed new chemical ligands of AhR and assessed their regulatory effects. Among these derivatives, we selected the compounds NPD-0414-2 and NPD-0414-24, as they displayed the more pronounced capacity to induce IL-22. Peripheral blood mononuclear cells and lamina propria mononuclear cells (LPMC) were isolated from CD and UC patients. Cells were treated in vitro with Ficz, AhR ligands, and AhR antagonist and then cytokines’ expression was evaluated by real-time PCR and flow cytometry. After the induction of TNBS colitis, Ficz and AhR ligands were injected intra-peritoneally to wild type and AhR knock-out mice. After 4 days, mice were sacrificed and colonic tissues were collected for histologic examination and real-time PCR analysis. Treatment of IBD LPMC with NPD-0414-2 and NPD-0414-24 reduced IFN-γ and increased IL-22 transcripts, and these effects were abrogated by CH223191, a specific inhibitor of AhR interaction with its ligands. Mice given NPD-0414-2 and NPD-0414-24 developed a significantly less severe form of TNBS colitis and exhibited reduced expression of IFN-γ and increased expression of IL-22. The therapeutic effect of NPD-0414-2 and NPD-0414-24 on the ongoing colitis was abrogated in AhR-deficient mice. Collectively, these data show that NPD-0414-2 and NPD-0414-24 exert Ahr-dependent regulatory effects in the gut.

Aryl hydrocarbon receptor acts as a tumor suppressor in a syngeneic MC38 colon carcinoma tumor model.

Background: Aryl hydrocarbon receptor (AHR), commonly known as an environmental sensor involved in the metabolism and elimination of xenobiotic substances, is also an important modulator in the development and functioning of the immune system. AHR expression is varied in the T cell subsets with the highest expression in T-helper 17 and T regulatory cells. It has been reported that AHR can act as a tumor promoter or a tumor suppressor, depending on the tumor type.Methods: In an effort to understand the role played by AHR in tumor growth, the MC38 syngeneic colon carcinoma tumor model was used on C57BL/6 or ahr knockout (KO, -/-) mice with or without AHR antagonist (CH223191) treatment. Tumor sizes were measured, and biomarkers were quantified in tumor microenvironment and draining lymph nodes using flow cytometry. Enzyme-linked immunosorbent assay was used to determine the amount of cytokines in tumors.Results: In ahr deficient mice, MC38 tumors progress more rapidly than in wild-type mice, accompanied by an increase in tumor-associated macrophages and M2 macrophages and a decrease in CD8a positive cytotoxic lymphocytes. Analysis of cytokines in the tumor microenvironment reveals a pro-inflammatory phenotype. Similar changes were observed by pharmacologic blockade of the receptor using CH223191.Conclusion: AHR acts as a tumor suppressor in mice implanted with MC38 colon carcinoma cells as evidenced by either a blockade or deficiency of AHR.

The impact of irradiance on UVB-induced cutaneous immunosuppression: Implications on administering most efficient phototherapy

BackgroundUltraviolet B (UVB) is commonly used for treating dermatologic conditions. Recently, high irradiance UVB (HIUVB) has been suggested to be more effective for treating skin conditions as compared to its low irradiance (LI) counterpart. The biological impact of UVB radiation emitted at different irradiance on cutaneous immunity remains obscure. ObjectiveThis study aimed to explore the impacts of UVB radiation administered at equivalent fluence (mJ/cm2) but different irradiance (mW/cm2) on cutaneous immune response. MethodsCultured bone marrow derived dendritic cell (BMDC) were treated with equivalent fluence of UVB radiation with HIUVB or LIUVB. The phenotypic and functional alterations of BMDCs were documented. Animal models were used to validate the in vitro results in vivo and explore the mechanisms involved. ResultsAfter equivalent fluence of UVB radiation, the HIUVB treated BMDC showed significantly lower MHCII and CD86 expressions, reduced capacity to stimulate T cell proliferation, and enhanced activation of aryl hydrocarbon receptor (AhR)-activated genes as compared to control while their LIUVB treated counterpart showed no significant change. Using animal model, the HIUVB induced significantly higher immune suppressive effect in mice as compared to their LIUVB counterpart after equivalent fluence of UVB treatment. The superior immune suppressive effect of HIUVB over LIUVB radiation was not observed when similar experiments were performed using AhR-deficient mice. ConclusionWe propose irradiance played an important role modulating UVB-induced cutaneous immune suppression. Future works on UVB phototherapy, both clinical and research, should incorporate this important parameter into consideration.