scholarly journals Characterizing the Role of HMG-CoA Reductase in Aryl Hydrocarbon Receptor-Mediated Liver Injury in C57BL/6 Mice

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Peter Dornbos ◽  
Amanda Jurgelewicz ◽  
Kelly A. Fader ◽  
Kurt Williams ◽  
Timothy R. Zacharewski ◽  
...  
Keyword(s):  
Liver Injury ◽  
Aryl Hydrocarbon Receptor ◽  
Cholesterol Biosynthesis ◽  
Competitive Inhibitor ◽  
Cholesterol Homeostasis ◽  
Hepatic Glycogen ◽  
Alcoholic Fatty Liver ◽  
Female Mice ◽  
Aryl Hydrocarbon ◽  
The Impact

Abstract The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor. The prototypical ligand of the AHR is an environmental contaminant called 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). TCDD exposure is associated with many adverse health outcomes in humans including non-alcoholic fatty liver disease (NAFLD). Previous studies suggest that AHR ligands alter cholesterol homeostasis in mice through repression of genes involved in cholesterol biosynthesis, such as Hmgcr, which encodes the rate-limiting enzyme of cholesterol biosynthesis called 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMGCR). In this study, we sought to characterize the impact of HMGCR repression in TCDD-induced liver injury. C57BL/6 mice were exposed to TCDD in the presence or absence of simvastatin, a competitive inhibitor of HMGCR. Simvastatin exposure decreased TCDD-induced hepatic lipid accumulation in both sexes, but was most prominent in females. Simvastatin and TCDD (S + T) co-treatment increased hepatic AHR-battery gene expression and liver injury in male, but not female, mice. In addition, the S + T co-treatment led to an increase in hepatic glycogen content that coincides with heavier liver in female mice. Results from this study suggest that statins, which are amongst the most prescribed pharmaceuticals, may protect from AHR-mediated steatosis, but alter glycogen metabolism and increase the risk of TCDD-elicited liver damage in a sex-specific manner.

scholarly journals Genetics-Based Approach to Identify Novel Genes Regulated by the Aryl Hydrocarbon Receptor (AHR) in Mice Liver

2021 ◽  
Author(s):  
Amanda Jurgelewicz ◽  
Peter Dornbos ◽  
Melanie Warren ◽  
Rance Nault ◽  
Anooj Arkatkar ◽  
...  
Keyword(s):  
Aryl Hydrocarbon Receptor ◽  
Metabolic Diseases ◽  
Inbred Strains ◽  
Mouse Strains ◽  
Genetic Modifiers ◽  
Novel Genes ◽  
Alcoholic Fatty Liver ◽  
Aryl Hydrocarbon ◽  
Wide Range ◽  
The Impact

Abstract The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor in the PAS superfamily of environmental sensors that is linked to several metabolic diseases, including non-alcoholic fatty liver disease (NAFLD). Much remains unknown regarding the impact of genetic variation in AHR-driven disease, as past studies have focused on a small number of inbred strains. Recently, the presence of a wide-range of interindividual variability amongst humans was reported in response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the prototypical ligand of the AHR. In this study, a panel of 14 diverse mouse strains were exposed to TCDD for 10 days to characterize the AHR-mediated response across genetic backgrounds. In this study, responses to TCDD are heavily-dependent on genetic background. While mice carry one of four Ahr alleles known to impact the affinity to AHR-ligands, we observed significant intra-allelic variability suggesting the presence of novel genetic modifiers of AHR signaling. A regression-based approach was used to scan for genes regulated by the AHR and/or associated with TCDD-induced phenotypes. The approach identified seven genes, two of which are novel, that are likely regulated by the AHR based on association with hepatic TCDD burden (p ≤ 0.05). Finally, we identified one gene, Dio1, which was associated with change in percent body fat across the diverse set of strains (p ≤ 0.05). Overall, the results in this study exemplify the power of genetics-based approaches in identifying novel genes that are putatively regulated by the AHR.

scholarly journals Immunotoxicity of Xenobiotics in Fish: A Role for the Aryl Hydrocarbon Receptor (AhR)?

2021 ◽  
Vol 22 (17) ◽  
pp. 9460
Author(s):  
Helmut Segner ◽  
Christyn Bailey ◽  
Carolina Tafalla ◽  
Jun Bo
Keyword(s):  
Immune System ◽  
Aryl Hydrocarbon Receptor ◽  
Disease Susceptibility ◽  
Immune Cell ◽  
Physiological Role ◽  
Immune Gene ◽  
Immune Systems ◽  
Aryl Hydrocarbon ◽  
The Impact

The impact of anthropogenic contaminants on the immune system of fishes is an issue of growing concern. An important xenobiotic receptor that mediates effects of chemicals, such as halogenated aromatic hydrocarbons (HAHs) and polyaromatic hydrocarbons (PAHs), is the aryl hydrocarbon receptor (AhR). Fish toxicological research has focused on the role of this receptor in xenobiotic biotransformation as well as in causing developmental, cardiac, and reproductive toxicity. However, biomedical research has unraveled an important physiological role of the AhR in the immune system, what suggests that this receptor could be involved in immunotoxic effects of environmental contaminants. The aims of the present review are to critically discuss the available knowledge on (i) the expression and possible function of the AhR in the immune systems of teleost fishes; and (ii) the impact of AhR-activating xenobiotics on the immune systems of fish at the levels of immune gene expression, immune cell proliferation and immune cell function, immune pathology, and resistance to infectious disease. The existing information indicates that the AhR is expressed in the fish immune system, but currently, we have little understanding of its physiological role. Exposure to AhR-activating contaminants results in the modulation of numerous immune structural and functional parameters of fish. Despite the diversity of fish species studied and the experimental conditions investigated, the published findings rather uniformly point to immunosuppressive actions of xenobiotic AhR ligands in fish. These effects are often associated with increased disease susceptibility. The fact that fish populations from HAH- and PAH-contaminated environments suffer immune disturbances and elevated disease susceptibility highlights that the immunotoxic effects of AhR-activating xenobiotics bear environmental relevance.

scholarly journals Microbiota tryptophan metabolism induces aryl hydrocarbon receptor activation and improves alcohol-induced liver injury

Gut ◽  
2020 ◽  
pp. gutjnl-2020-321565 ◽  
Author(s):  
Laura Wrzosek ◽  
Dragos Ciocan ◽  
Cindy Hugot ◽  
Madeleine Spatz ◽  
Margot Dupeux ◽  
...  
Keyword(s):  
Liver Disease ◽  
Liver Injury ◽  
Aryl Hydrocarbon Receptor ◽  
Intestinal Microbiota ◽  
Alcoholic Liver Disease ◽  
Receptor Activation ◽  
Liver Lesions ◽  
Knock Out ◽  
Aryl Hydrocarbon ◽  
Tryptophan Metabolites

ObjectiveChronic alcohol consumption is an important cause of liver-related deaths. Specific intestinal microbiota profiles are associated with susceptibility or resistance to alcoholic liver disease in both mice and humans. We aimed to identify the mechanisms by which targeting intestinal microbiota can improve alcohol-induced liver lesions.DesignWe used human associated mice, a mouse model of alcoholic liver disease transplanted with the intestinal microbiota of alcoholic patients and used the prebiotic, pectin, to modulate the intestinal microbiota. Based on metabolomic analyses, we focused on microbiota tryptophan metabolites, which are ligands of the aryl hydrocarbon receptor (AhR). Involvement of the AhR pathway was assessed using both a pharmacological approach and AhR-deficient mice.ResultsPectin treatment modified the microbiome and metabolome in human microbiota-associated alcohol-fed mice, leading to a specific faecal signature. High production of bacterial tryptophan metabolites was associated with an improvement of liver injury. The AhR agonist Ficz (6-formylindolo (3,2-b) carbazole) reduced liver lesions, similarly to prebiotic treatment. Conversely, inactivation of the ahr gene in alcohol-fed AhR knock-out mice abrogated the beneficial effects of the prebiotic. Importantly, patients with severe alcoholic hepatitis have low levels of bacterial tryptophan derivatives that are AhR agonists.ConclusionsImprovement of alcoholic liver disease by targeting the intestinal microbiota involves the AhR pathway, which should be considered as a new therapeutic target.

scholarly journals Aryl Hydrocarbon Receptor Activation by TCDD Modulates Expression of Extracellular Matrix Remodeling Genes during Experimental Liver Fibrosis

2016 ◽  
Vol 2016 ◽  
pp. 1-14 ◽  
Author(s):  
Cheri L. Lamb ◽  
Giovan N. Cholico ◽  
Daniel E. Perkins ◽  
Michael T. Fewkes ◽  
Julia Thom Oxford ◽  
...  
Keyword(s):  
Gene Expression ◽  
Extracellular Matrix ◽  
Liver Injury ◽  
Aryl Hydrocarbon Receptor ◽  
Receptor Activation ◽  
Matrix Remodeling ◽  
Mrna Levels ◽  
Gelatinase Activity ◽  
Ecm Remodeling ◽  
Aryl Hydrocarbon

The aryl hydrocarbon receptor (AhR) is a soluble, ligand-activated transcription factor that mediates the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Increasing evidence implicates the AhR in regulating extracellular matrix (ECM) homeostasis. We recently reported that TCDD increased necroinflammation and myofibroblast activation during liver injury elicited by carbon tetrachloride (CCl4). However, TCDD did not increase collagen deposition or exacerbate fibrosis in CCl4-treated mice, which raises the possibility that TCDD may enhance ECM turnover. The goal of this study was to determine how TCDD impacts ECM remodeling gene expression in the liver. Male C57BL/6 mice were treated for 8 weeks with 0.5 mL/kg CCl4, and TCDD (20 μg/kg) was administered during the last two weeks. Results indicate that TCDD increased mRNA levels of procollagen types I, III, IV, and VI and the collagen processing molecules HSP47 and lysyl oxidase. TCDD also increased gelatinase activity and mRNA levels of matrix metalloproteinase- (MMP-) 3, MMP-8, MMP-9, and MMP-13. Furthermore, TCDD modulated expression of genes in the plasminogen activator/plasmin system, which regulates MMP activation, and it also increased TIMP1 gene expression. These findings support the notion that AhR activation by TCDD dysregulates ECM remodeling gene expression and may facilitate ECM metabolism despite increased liver injury.

scholarly journals Endotoxin-Induced Tryptophan Degradation along the Kynurenine Pathway: The Role of Indolamine 2,3-Dioxygenase and Aryl Hydrocarbon Receptor-Mediated Immunosuppressive Effects in Endotoxin Tolerance and Cancer and Its Implications for Immunoparalysis

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Elisa Wirthgen ◽  
Andreas Hoeflich
Keyword(s):  
Aryl Hydrocarbon Receptor ◽  
Immune Escape ◽  
Endotoxin Tolerance ◽  
Kynurenine Pathway ◽  
Aryl Hydrocarbon ◽  
Tryptophan Degradation ◽  
Inflammatory Stimuli ◽  
Life Threatening ◽  
The Impact

The degradation of tryptophan (TRP) along the kynurenine pathway plays a crucial role as a neuro- and immunomodulatory mechanism in response to inflammatory stimuli, such as lipopolysaccharides (LPS). In endotoxemia or sepsis, an enhanced activation of the rate-limiting enzyme indoleamine 2,3-dioxygenase (IDO) is associated with a higher mortality risk. It is assumed that IDO induced immunosuppressive effects provoke the development of a protracted compensatory hypoinflammatory phase up to a complete paralysis of the immune system, which is characterized by an endotoxin tolerance. However, the role of IDO activation in the development of life-threatening immunoparalysis is still poorly understood. Recent reports described the impact of inflammatory IDO activation and aryl hydrocarbon receptor- (AhR-) mediated pathways on the development of LPS tolerance and immune escape of cancer cells. These immunosuppressive mechanisms offer new insights for a better understanding of the development of cellular dysfunctions in immunoparalysis. This review provides a comprehensive update of significant biological functions of TRP metabolites along the kynurenine pathway and the complex regulation of LPS-induced IDO activation. In addition, the review focuses on the role of IDO-AhR-mediated immunosuppressive pathways in endotoxin tolerance and carcinogenesis revealing the significance of enhanced IDO activity for the establishment of life-threatening immunoparalysis in sepsis.

scholarly journals Targeting the Aryl Hydrocarbon Receptor Signaling Pathway in Breast Cancer Development

2021 ◽  
Vol 12 ◽  
Author(s):  
Christoph F. A. Vogel ◽  
Gwendal Lazennec ◽  
Sarah Y. Kado ◽  
Carla Dahlem ◽  
Yi He ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Aryl Hydrocarbon Receptor ◽  
Tumor Cells ◽  
Mammary Tumor ◽  
T Antigen ◽  
Functional Restoration ◽  
Repressor Protein ◽  
Mammary Tumor Cells ◽  
Aryl Hydrocarbon ◽  
The Impact

Activation of the aryl hydrocarbon receptor (AhR) through environmental exposure to known human carcinogens including dioxins can lead to the promotion of breast cancer. While the repressor protein of the AhR (AhRR) blocks the canonical AhR pathway, the function of AhRR in the development of breast cancer is not well-known. In the current study we examined the impact of suppressing AhR activity using its dedicated repressor protein AhRR. AhRR is a putative tumor suppressor and is silenced in several cancer types, including breast, where its loss correlates with shorter patient survival. Using the AhRR transgenic mouse, we demonstrate that AhRR overexpression opposes AhR-driven and inflammation-induced growth of mammary tumors in two different murine models of breast cancer. These include a syngeneic model using E0771 mammary tumor cells as well as the Polyoma Middle T antigen (PyMT) transgenic model. Further AhRR overexpression or knockout of AhR in human breast cancer cells enhanced apoptosis induced by chemotherapeutics and inhibited the growth of mouse mammary tumor cells. This study provides the first in vivo evidence that AhRR suppresses mammary tumor development and suggests that strategies which lead to its functional restoration and expression may have therapeutic benefit.

scholarly journals Acetaminophen-Induced Liver Injury Exposes Murine IL-22 as Sex-Related Gene Product

2021 ◽  
Vol 22 (19) ◽  
pp. 10623
Author(s):  
Hendrik Stülb ◽  
Malte Bachmann ◽  
Sina Gonther ◽  
Heiko Mühl
Keyword(s):  
Liver Injury ◽  
Chromatin Immunoprecipitation ◽  
Tissue Injury ◽  
Cellular Level ◽  
Detailed Knowledge ◽  
Murine Splenocytes ◽  
Female Mice ◽  
Aryl Hydrocarbon ◽  
Inflammatory Activation ◽  
Key Parameter

Gaining detailed knowledge about sex-related immunoregulation remains a crucial prerequisite for the development of adequate disease models and therapeutic strategies enabling personalized medicine. Here, the key parameter of the production of cytokines mediating disease resolution was investigated. Among these cytokines, STAT3-activating interleukin (IL)-22 is principally associated with recovery from tissue injury. By investigating paradigmatic acetaminophen-induced liver injury, we demonstrated that IL-22 expression is enhanced in female mice. Increased female IL-22 was confirmed at a cellular level using murine splenocytes stimulated by lipopolysaccharide or αCD3/CD28 to model innate or adaptive immunoactivation. Interestingly, testosterone or dihydrotestosterone reduced IL-22 production by female but not by male splenocytes. Mechanistic studies on PMA/PHA-stimulated T-cell-lymphoma EL-4 cells verified the capability of testosterone/dihydrotestosterone to reduce IL-22 production. Moreover, we demonstrated by chromatin immunoprecipitation that testosterone impairs binding of the aryl hydrocarbon receptor to xenobiotic responsive elements within the murine IL-22 promoter. Overall, female mice undergoing acute liver injury and cultured female splenocytes upon inflammatory activation display increased IL-22. This observation is likely related to the immunosuppressive effects of androgens in males. The data presented concur with more pronounced immunological alertness demonstrable in females, which may relate to the sex-specific course of some immunological disorders.

scholarly journals Where the Aryl Hydrocarbon Receptor Meets the microRNAs: Literature Review of the Last 10 Years

2021 ◽  
Vol 8 ◽  
Author(s):  
Geonildo Rodrigo Disner ◽  
Monica Lopes-Ferreira ◽  
Carla Lima
Keyword(s):  
Immune System ◽  
Aryl Hydrocarbon Receptor ◽  
Cancer Progression ◽  
Chemical Exposure ◽  
Epigenetic Mechanisms ◽  
Mirna Regulation ◽  
Aryl Hydrocarbon ◽  
Mutual Regulation ◽  
Polycyclic Aromatic ◽  
The Impact

The aryl hydrocarbon receptor (AhR) is an environmentally responsive ligand-activated transcription factor, identified in the ‘70s for its toxic responses to halogenated polycyclic aromatic hydrocarbons, such as dioxin. Recently, AhR has been recognized as engaged in multiple physiological processes in health and diseases, particularly in the immune system, inflammatory response, tumorigenesis, and cellular differentiation by epigenetic mechanisms involving miRNAs. However, there is still scarce information about AhR-dependent miRNA regulation and miRNA-mediated epigenetic control in pathologies and therapies. In this review, we explore the mutual regulation of AhR and miRNA over the last decade of studies since many miRNAs have dioxin response elements (DRE) in their 3’ UTR, as well as AhR might contain binding sites of miRNAs. TCDD is the most used ligand to investigate the impact of AhR activation, and the immune system is one of the most sensitive of its targets. An association between TCDD-activated AhR and epigenetic mechanisms like post-transcriptional regulation by miRNAs, DNA methylation, or histone modification has already been confirmed. Besides, several studies have shown that AhR-induced miR-212/132 cluster suppresses cancers, attenuates autoimmune diseases, and has an anti-inflammatory role in different immune responses by regulating cytokine levels and immune cells. Together the ever-expanding new AhR roles and the miRNA therapeutics are a prominent segment among biopharmaceuticals. Additionally, AhR-activated miRNAs can serve as valuable biomarkers of diseases, notably cancer progression or suppression and chemical exposure. Once AhR-dependent gene expression may hinge on the ligand, cell type, and context singularity, the reviewed outcomes might help contextualize state of the art and support new trends and emerging opportunities in the field.

scholarly journals Cholesterol Homeostasis: An In Silico Investigation into How Aging Disrupts Its Key Hepatic Regulatory Mechanisms

Biology ◽  
2020 ◽  
Vol 9 (10) ◽  
pp. 314
Author(s):  
Amy Elizabeth Morgan ◽  
Mark Tomás Mc Auley
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Cholesterol Homeostasis ◽  
Enzymatic Reactions ◽  
Low Density ◽  
Acetyl Coa ◽  
Alcoholic Fatty Liver ◽  
Age Related ◽  
Intracellular Cholesterol ◽  
The Impact

The dysregulation of intracellular cholesterol homeostasis is associated with several age-related diseases, most notably cardiovascular disease (CVD). Research in this area has benefitted from using computational modelling to study the inherent complexity associated with the regulation of this system. In addition to facilitating hypothesis exploration, the utility of modelling lies in its ability to represent an array of rate limiting enzymatic reactions, together with multiple feedback loops, which collectively define the dynamics of cholesterol homeostasis. However, to date no model has specifically investigated the effects aging has on this system. This work addresses this shortcoming by explicitly focusing on the impact of aging on hepatic intracellular cholesterol homeostasis. The model was used to investigate the experimental findings that reactive oxygen species induce the total activation of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase (HMGCR). Moreover, the model explored the impact of an age-related decrease in hepatic acetyl-CoA acetyltransferase 2 (ACAT2). The model suggested that an increase in the activity of HMGCR does not have as significant an impact on cholesterol homeostasis as a decrease in hepatic ACAT2 activity. According to the model, a decrease in the activity of hepatic ACAT2 raises free cholesterol (FC) and decreases low-density lipoprotein cholesterol (LDL-C) levels. Increased acetyl CoA synthesis resulted in a reduction in the number of hepatic low-density lipoprotein receptors, and increased LDL-C, FC, and cholesterol esters. The rise in LDL-C was restricted by elevated hepatic FC accumulation. Taken together these findings have important implications for healthspan. This is because emerging clinical data suggest hepatic FC accumulation is relevant to the pathogenesis of non-alcoholic fatty liver disease (NAFLD), which is associated with an increased risk of CVD. These pathophysiological changes could, in part, help to explain the phenomenon of increased mortality associated with low levels of LDL-C which have been observed in certain studies involving the oldest old (≥85 years).

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