Innate lymphoid cells (ILC)-22 protect the intestinal mucosa from infections by secreting interleukin-22 (IL-22). They include NKp46+ and Lymphoid Tissues inducer (LTi)-like subsets. Both express the aryl-hydrocarbon receptor (AHR), a sensor for environmental, dietary and endogenous aromatic compounds. We show that AHR-/- mice have a marked ILC22 deficit, resulting in diminished IL-22 secretion and inadequate protection against intestinal bacterial infections. AHR-/- mice also lack post-natally-imprinted cryptopatches (CP) and isolated lymphoid follicles (ILF), but not embryonically-imprinted Peyer's Patches (PP). AHR induces Notch, which is required for NKp46+ILC, while LTi-like ILC, CP and ILF are partially dependent on Notch signaling. These results establish that AHR is essential for ILC22 and post-natal intestinal lymphoid tissues and reveal heterogeneity of ILC22 subsets in their developmental requirements and their impact on the generation of intestinal lymphoid tissues.

The aryl hydrocarbon receptor (AHR) plays a central role in 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) hepatotoxicity, regulation of xenobiotic metabolism, and hepatovascular development. Each of these processes appears to be dependent on binding of the AHR to dioxin-responsive elements (DREs) within the genome. The Cyp1a1 and Cyp1a2 loci represent linked genes thought to play important roles in AHR biology. In the mouse, 8 DREs are located in the 14-kb intergenic region between the Cyp1a1 and Cyp1a2 genes. Seven of these DREs, collectively known as the DRE cluster (DREC), are located 1.4 kb upstream of the Cyp1a1 transcriptional start site and 12.6 kb upstream of the Cyp1a2 start site. To investigate the role of the DREC in each aspect of AHR biology, we generated a DREC-deficient mouse model through homologous recombination. Using this mouse model, we demonstrate that the DREC controls the adaptive up-regulation of both Cyp1a1 and Cyp1a2 genes in vivo. Using selected aspects of acute hepatic injury as endpoints, we also demonstrate that DREC null mice are more sensitive to dioxin-induced hepatotoxicity than WT mice. The results of parallel toxicologic studies using individual Cyp1a1 and Cyp1a2 null mice support the observation that up-regulation of these P450s is not the cause of many aspects of dioxin hepatotoxicity. Finally, we observed normal closure of the ductus venosus (DV) in DREC null mice. Given the 100% penetrance of patent DV in Ahr null mice, these results indicate that Cyp1a1 and Cyp1a2 do not play a dominant role in AHR-mediated vascular development.AHR ͉ Cyp1a1 ͉ Cyp1a2 ͉ cytochrome P450 ͉ DRE

The aryl hydrocarbon receptor (AHR) is a transcription factor that responds to diverse ligands and plays a critical role in toxicology, immune function, and cardiovascular physiology. The structural basis of the AHR for ligand promiscuity and preferences is critical for understanding AHR function. Based on the structure of a closely related protein HIF2α, we modeled the AHR ligand binding domain (LBD) bound to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and benzo(a)pyrene (BaP) and identified residues that control ligand preferences by shape and H-bond potential. Mutations to these residues, particularly Q377 and G298, resulted in robust and opposite changes in the potency of TCDD and BaP and up to a 20-fold change in the ratio of TCDD/BaP efficacy. The model also revealed a flexible "belt" structure; molecular dynamic (MD) simulation suggested that the "belt" and several other structural elements in the AHR-LBD are more flexible than HIF2α and likely contribute to ligand promiscuity. Molecular docking of TCDD congeners to a model of human AHR-LBD ranks their binding affinity similar to experimental ranking of their toxicity. Our study reveals key structural basis for prediction of toxicity and understanding the AHR signaling through diverse ligands.

Objective To determine the role of the aryl hydrocarbon receptor (AHR) in colitis-associated colorectal tumorigenesis. Summary Background Data Colorectal cancer (CRC) is the third most commonly diagnosed cancer in both men and women in United States. Chronic intestinal inflammation increases the risk for the development of CRC. We questioned the involvement of AHR, a transcriptional regulator for intestinal innate immunity and inflammation, in the colitis-associated tumorigenesis. Methods We used a mouse model for chemically-induced colorectal tumorigenesis by treatment of azoxymethane (AOM) and sodium dextran sulfate (DSS). We examined the role of AHR using Ahr-deletion mouse model and I3C treatment. Tumor incidence, number and location were visually counted. Tumor multiplicities were evaluated and compared using GraphPad Prism software (version 6, LaJolla, CA). Results In Ahr null mice, the tumor incidence was 32% increased and the mean tumor number was approximately 3 time increased compared to WT mice (7 v 2.4, P<0.05). The tumor number was 92% decreased by treatment of I3C in WT mice, while the chemopreventive effect of I3C was not observed in Ahr null mice (P<0.05). Conclusions We found that the AHR may play a protective role in colitis-associated colorectal tumorigenesis. This work supports the application of AHR agonists such as I3C as a chemopreventive therapy for CRC in human patient.