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The independent domestication of local wild boar populations in Asia and Europe about 10,000 years ago led to distinct European and Asian pig breeds, each with very different phenotypic characteristics. During the Industrial Revolution, Chinese breeds were imported to Europe to improve commercial traits in European breeds. Here we demonstrate the presence of introgressed Asian haplotypes in European domestic pigs and selection signatures on some loci in these regions, using whole genome sequence data. The introgression signatures are widespread and the Asian haplotypes are rarely fixed. The Asian introgressed haplotypes are associated with regions harbouring genes involved in meat quality, development and fertility. We identify Asian-derived non-synonymous mutations in the AHR gene that associate with increased litter size in multiple European commercial lines. These findings demonstrate that increased fertility was an important breeding goal for early nineteenth century pig farmers, and that Asian variants of genes related to this trait were preferentially selected during the development of modern European pig breeds. Domestication of wild boar populations has led to phenotypically distinct European and Asian pig breeds. Here, the authors show that Asian haplotypes that have introgressed into European pig breeds harbour genes that control economically important traits such as meat quality, development and fertility.

[b]Introduction and objective[/b]. Despite the restrictive legal regulations related to the reduction of dioxins emission, their concentration in the environment is still too high. Mainly, this is related to the illegal utilisation of electronic equipment and combustion of wastes, and also to intensified activity and maintenance of ships, especially in developing countries. The most important remaining source in Europe is the metal industry. Studies on the mechanism of impact of dioxins are still being carried out. This review points at new possibilities for limiting the molecular mechanisms of dioxins activity, inter alia, through the application of high doses of tocopherol and acetylsalicylic acid while treating dioxins intoxication. [b]Brief description of the state of knowledge. [/b]Apart from the knowledge of dioxins affinity to the aryl hydrocarbon receptor (AhR), the multi-stage radical-form actions and the pro-inflammatory mechanism associated with cyclooxygenase-II enzyme (COX-2) are under intense investigation at the moment. Due to the high affinity of dioxins to animals adipose tissue and their ability to accumulate in it, they can enter the food chain. Furthermore, high dioxin doses can cause poisoning manifested as advanced clinical symptoms, whereas in smaller doses, when cumulated, can cause metabolic changes which are often difficult to associate with their presence. Recently, some serious food contaminations by dioxins have been demonstrated. Sea fish and products from contaminated aqueducts still constitute potential sources of dioxins pollution. [b]Conclusion.[/b] According to recent studies, dioxins are present in different concentrations in the environment and cause specific and long-time effects. These effects could be limited by the use of tocopherol and acetylsalicylic acid.

Quercetin is a flavonoid with a wide range of pharmacological activities, including anticancer, antioxidant, and anti-inflammatory effects. Since it is a nutrient that can be consumed with a regular diet, quercetin has recently garnered interest. Quercetin acts as a phytochemical ligand for the aryl hydrocarbon receptor (AhR). Cleft lip and palate are among the most frequently diagnosed congenital diseases, and exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) during pregnancy induces cleft palate via AhR. In this study, we investigated the preventive effect of quercetin intake on the TCDD-induced cleft palate and its mechanism of action. The in vivo results suggest that quercetin intake by pregnant mice can prevent cleft palate in fetal mice. In vitro, the addition of TCDD induced a reduction in cell migration and the proliferation of mouse embryonic palatal mesenchymal cells, which was mitigated by the addition of quercetin. The addition of quercetin did not alter the mRNA expression levels of the AhR repressor but significantly suppressed mRNA expression of CYP1A1. In addition, the binding of AhR to a xenobiotic responsive element was inhibited by quercetin, based on a chemically activated luciferase expression assay. In conclusion, our results suggest that quercetin reduces the development of TCDD-induced cleft palate by inhibiting CYP1A1 through AhR.

The dioxin/aryl hydrocarbon receptor functions as a ligand-activated transcription factor regulating transcription of a battery of genes encoding primarily drug-metabolizing enzymes. Expression of a constitutively active mutant of the aryl hydrocarbon receptor (CA-AhR) in transgenic mice results in development of stomach tumours, correlating with increased mortality. We have used suppression subtractive hybridization techniques followed by macroarray analysis to elucidate which genes are differentially expressed during this process. In the glandular stomach of CA-AhR mice, we observed decreased mRNA expression of osteopontin (OPN), a noncollagenous protein of bone matrix that is also involved in several important functions including regulation of cytokine production, macrophage accumulation, cell motility and adhesion. Downregulated expression of OPN during tumour development was confirmed by RT–PCR and RNA blot analysis. Immunohistochemical analysis showed that this decrease was confined to the corpus region, correlating with the restricted localization of the tumours. Decreased OPN mRNA expression was also observed in other organs of CA-AhR mice. Taken together, these results show that OPN is negatively regulated by the dioxin receptor, and that downregulation of its expression correlates with development of stomach tumours in mice expressing a constitutively active mutant of dioxin receptor.

Adaptation in response to changes in internal as well as external environment is imperative to sustenance of life. Modulation of gene expression is a critical component of this adaptive response and is mediated by activation of various transcription factors. Individual signaling pathways have been well characterized for many transcription factor systems. Aryl hydrocarbon receptor (AHR) is a transcription factor that is activated by a variety of structurally diverse ligands, including the environmental contaminant dioxin, the cigarette smoke constituent benzo[a]pyrene and the therapeutically prescribed drug omeprazole. Prior to activation, AHR is primarily located in a cytoplasmic complex with chaperone and co-chaperone proteins. Ligand-binding is believed to initiate a conformational change that leads to nuclear translocation, dissociation from the chaperones and heterodimerization with AHR-nuclear translocator (ARNT). AHR-ARNT heterodimer recognizes and binds to a consensus DNA sequence (TNGCGTG), commonly referred to as a dioxin response element (DRE), to drive transcription of target genes. Phase I and II xenobiotic metabolism enzymes have been the well-characterized targets of AHR-mediated transactivation. This sequence of coordinate events has been described as the classical pathway of AHR activity. Different lines of evidence suggest that AHR serves physiologically relevant functions, though the details have not been elucidated. The goal of this research project was to identify previously uncharacterized targets of AHR-mediated gene regulation and to investigate the hypothesis that AHR functions through mechanisms that are independent of DNA-binding. The advances in performing genome-wide transcriptional profiling at the time of commencement of this project, encouraged the use of DNA-microarray technology for identifying new target genes. Epiregulin, a potent mitogen belonging to the epidermal growth factor family, was discovered to be regulated by AHR in immortalized murine hepatocytes. The fact that a number of AHR ligands have been associated with carcinogenesis signifies that the induction of growth factors like epiregulin might be a potential mechanism for AHR-mediated tumor enhancement. The next phase of this project led to the identification of the constitutive androstane receptor (CAR), another receptor involved in drug metabolism, as an in vivo target of AHR activation. This association between AHR-CAR highlights the possibility of crosstalk between AHR and other pathways. Exposure to divergent stimuli leads to simultaneous activation of multiple signaling pathways. This suggests that it is essential to study the networking of various pathways to be able to predict the biological outcomes. The third phase of this project focuses on the ability of AHR to modulate the inflammatory pathway and on the involved mechanism. AHR activation can repress the acute-phase response (APR) gene expression, implicated in disorders like septic shock and Alzheimer’s, partly by antagonizing NF-κB mediated gene regulation through a non-classical mechanism not involving DRE. Serum amyloid family members, C-reactive protein and haptoglobin were found to be repressed by AHR, signifying that AHR regulates multiple members of the APR. Thus, this research has led to the identification of multiple AHR-regulated genes. It also presents a model to study AHR-mediated gene repression, an aspect that has therapeutic potential.

Immune checkpoint inhibitors represent some of the most important cancer treatments developed in the last 20 y. However, existing immunotherapy approaches benefit only a minority of patients. Here, we provide evidence that the aryl hydrocarbon receptor (AhR) is a central player in the regulation of multiple immune checkpoints in oral squamous cell carcinoma (OSCC). Orthotopic transplant of mouse OSCC cells from which the AhR has been deleted (MOC1AhR-KO) results, within 1 wk, in the growth of small tumors that are then completely rejected within 2 wk, concomitant with an increase in activated T cells in tumor-draining lymph nodes (tdLNs) and T cell signaling within the tumor. By 2 wk, AhR⁺ control cells (MOC1Cas9), but not MOC1AhR-KO cells up-regulate exhaustion pathways in the tumor-infiltrating T cells and expression of checkpoint molecules on CD4⁺ T cells (PD-1, CTLA4, Lag3, and CD39) and macrophages, dendritic cells, and Ly6G⁺ myeloid cells (PD-L1 and CD39) in tdLNs. Notably, MOC1AhR-KO cell transplant renders mice 100% immune to later challenge with wild-type tumors. Analysis of altered signaling pathways within MOC1AhR-KO cells shows that the AhR controls baseline and IFNγ-induced Ido and PD-L1 expression, the latter of which occurs through direct transcriptional control. These observations 1) confirm the importance of malignant cell AhR in suppression of tumor immunity, 2) demonstrate the involvement of the AhR in IFNγ control of PD-L1 and IDO expression in the cancer context, and 3) suggest that the AhR is a viable target for modulation of multiple immune checkpoints.

The environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) causes hepatic toxicity associated with prominent lipid accumulation in humans. Here, the authors report that the lysosomal copper transporter SLC46A3 is induced by TCDD and underlies the hepatic lipid accumulation in mice, potentially via effects on mitochondrial function. SLC46A3 was localized to the lysosome where it modulated intracellular copper levels. Forced expression of hepatic SLC46A3 resulted in decreased mitochondrial membrane potential and abnormal mitochondria morphology consistent with lower copper levels. SLC46A3 expression increased hepatic lipid accumulation similar to the known effects of TCDD exposure in mice and humans. The TCDD-induced hepatic triglyceride accumulation was significantly decreased in Slc46a3 −/− mice and was more pronounced when these mice were fed a high-fat diet, as compared to wild-type mice. These data are consistent with a model where lysosomal SLC46A3 induction by TCDD leads to cytosolic copper deficiency resulting in mitochondrial dysfunction leading to lower lipid catabolism, thus linking copper status to mitochondrial function, lipid metabolism and TCDD-induced liver toxicity. The environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) causes hepatic toxicity associated with prominent lipid accumulation in humans. Here, the authors report that the lysosomal copper transporter SLC46A3 is induced by TCDD and underlies the hepatic lipid accumulation in mice, potentially via effects on mitochondrial function.

Although an immunoregulatory role of aryl hydrocarbon receptor (Ahr) has been demonstrated in T cells and macrophages, little is known about its function in dendritic cells (DC). Here, we show that lipopolysaccharide (LPS) and CpG stimulate Ahr expression in bone marrow-derived dendritic cells (BMDC). Furthermore, we found that Ahr is required to induce indoleamine 2,3-dioxygenase (IDO) expression, an immunosuppressive enzyme that catabolizes tryptophan into kynurenine (Kyn) and other metabolites in DC. In the presence of LPS or CpG, Ahr-deficient (Ahr -/- ) mature BMDC induced immune responses characterized by reduced Kyn and IL-10 production compared with results observed with tolerogenic mature WT BMDC. In a coculture system with LPS- or CpG-stimulated BMDC and naive T cells, Ahr -/- BMDC inhibited naive T-cell differentiation into regulatory T (Treg) cells, which likely facilitated Th17 cell development and promoted naive T-cell proliferation. Addition of synthetic L-Kyn to the coculture system skewed the differentiation of naive T cells to Treg cells rather than Th17 cells. Taken together, our results demonstrate a previously unknown negatively regulatory role for Ahr in DC-mediated immunogenesis in the presence of LPS or CpG, which, in turn, alters the Kyn-dependent generation of Treg cells and Th17 cells from naive T cells.

Smoking is a major risk factor for osteoporosis and fracture, but the mechanism through which smoke causes bone loss remains unclear. Here, we show that the smoke toxins benzo(a)pyrene (BaP) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) interact with the aryl hydrocarbon receptor (Ahr) to induce osteoclastic bone resorption through the activation of cytochrome P450 1a/1b (Cyp1) enzymes. BaP and TCDD enhanced osteoclast formation in bone marrow cell cultures and gavage with BaP stimulated bone resorption and osteoclastogenesis in vivo. The osteoclastogenesis triggered by BaP or RANK-L was reduced in Ahr-/- cells, consistent with the high bone mass noted in Ahr-/- male mice. The receptor activator of NF-κB ligand (RANK-L) also failed to induce the expression of Cyp1 enzymes in Ahr-/- cells. Furthermore, the osteoclastogenesis induced by TCDD was lower in Cyp1a1/1a2-/- and Cyp1a1/1a2/1b1-/- cultures, indicating that Ahr was upstream of the Cyp enzymes. Likewise, the pharmacological inhibition of the Cyp1 enzymes with tetramethylsilane or proadifen reduced osteoclastogenesis. Finally, deletion of the Cyp1a1, Cyp1a2, and Cyp1b1 in triple knockout mice resulted in reduced bone resorption and recapitulated the high bone mass phenotype of Ahr-/- mice. Overall, the data identify the Ahr and Cyp1 enzymes not only in the pathophysiology of smoke-induced osteoporosis, but also as potential targets for selective modulation by new therapeutics.

Altered systemic levels of 6-formylindolo[3,2-b]carbazole (FICZ), an enigmatic endogenous ligand for the aryl hydrocarbon receptor (AHR), may explain adverse physiological responses evoked by small natural and anthropogenic molecules as well as by oxidative stress and light. We demonstrate here that several different chemical compounds can inhibit the metabolism of FICZ, thereby disrupting the autoregulatory feedback control of cytochrome P4501 systems and other proteins whose expression is regulated by AHR. FICZ is both the most tightly bound endogenous agonist for the AHR and an ideal substrate for cytochrome CYP1A1/1A2 and 1B1, thereby also participating in an autoregulatory loop that keeps its own steady-state concentration low. At very low concentrations FICZ influences circadian rhythms, responses to UV light, homeostasis associated with pro- and anti-inflammatory processes, and genomic stability. Here, we demonstrate that, if its metabolic clearance is compromised, femtomolar background levels of this compound in cell-culture medium are sufficient to up-regulate CYP1A1 mRNA and enzyme activity. The oxidants UVB irradiation and hydrogen peroxide and the model AHR antagonist 3'-methoxy-4'-nitroflavone all inhibited induction of CYP1A1 enzyme activity by FICZ or 2,3,7,8-tetrachlorodibenzo-p-dioxin, thereby subsequently elevating intracellular levels of FICZ and activating AHR. Taken together, these findings support an indirect mechanism of AHR activation, indicating that AHR activation by molecules with low affinity actually may reflect inhibition of FICZ metabolism and raising questions about the reported promiscuity of the AHR. Accordingly, we propose that prolonged induction of AHR activity through inhibition of CYP1 disturbs feedback regulation of FICZ levels, with potential detrimental consequences.