Gestational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin disrupts B-cell lymphopoiesis and exacerbates autoimmune disease in 24-week-old SNF1 mice

TCDD and CH223191 Alter T Cell Balance but Fail to Induce Anti-Inflammatory Response in Adult Lupus Mice

Aryl hydrocarbon receptor (AhR) responds to endogenous and exogenous ligands as a cytosolic receptor, transcription factor, and E3 ubiquitin ligase. Several studies support an anti-inflammatory effect of AhR activation. However, exposure to the AhR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) during early stages of development results in an autoimmune phenotype and exacerbates lupus. The effects of TCDD on lupus in adults with pre-existing autoimmunity have not been described. We present novel evidence that AhR stimulation by TCDD alters T cell responses but fails to impact lupus-like disease using an adult mouse model. Interestingly, AhR antagonist CH223191 also changed T cell balance in our model. We next developed a conceptual framework for identifying cellular and molecular factors that contribute to physiological outcomes in lupus and created models that describe cytokine dynamics that were fed into a system of differential equations to predict the kinetics of T follicular helper (Tfh) and regulatory T (Treg) cell populations. The model predicted that Tfh cells expanded to larger values following TCDD exposure compared with vehicle and CH223191. Following the initial elevation, both Tfh and Treg cell populations continuously decayed over time. A function based on the ratio of predicted Treg/Tfh cells showed that Treg cells exceed Tfh cells in all groups, with TCDD and CH223191 showing lower Treg/Tfh cell ratios than the vehicle and that the ratio is relatively constant over time. We conclude that AhR ligands did not induce an anti-inflammatory response to attenuate autoimmunity in adult lupus mice. This study challenges the dogma that TCDD supports an immunosuppressive phenotype.

Endocrine-disrupting chemicals and autoimmune diseases

Endocrine-disrupting chemicals (EDCs) widely exist in people's production and life which have great potential to damage human and animal health. Over the past few decades, growing attention has been paid to the impact of EDCs on human health, as well as immune system. So far, researchers have proved that EDCs (such as bisphenol A (BPA), phthalate, tetrachlorodibenzodioxin (TCDD), etc.) affect human immune function and promotes the occurrence and development of autoimmune diseases (ADs). Therefore, in order to better understand how EDCs affect ADs, we summarized the current knowledge about the impact of EDCs on ADs, and elaborated the potential mechanism of the impact of EDCs on ADs in this review.

The Aryl Hydrocarbon Receptor (AHR) as a Potential Target for the Control of Intestinal Inflammation: Insights from an Immune and Bacteria Sensor Receptor

The aryl hydrocarbon receptor (AHR) is widely expressed in immune and non-immune cells of the gut and its activation has been correlated to the outcome of inflammatory bowel diseases (IBD). In ulcerative colitis and Crohn's disease, there is an excessive chronic inflammation with massive accumulation of leukocytes in the gut, in an attempt to constrain the invasion of pathogenic microorganisms on the damaged organ. Accordingly, it is known that dietary components, xenobiotics, and some chemicals or metabolites can activate AHR and induce the modulation of inflammatory responses. In fact, the AHR triggering by specific ligands during inflammatory conditions results in decreased IFNγ, IL-6, IL-12, TNF, IL-7, and IL-17, along with reduced microbial translocation and fibrosis in the gut. Moreover, upon AHR activation, there are increased regulatory mechanisms such as IL-10, IL-22, prostaglandin E₂, and Foxp3, besides the production of anti-microbial peptides and epithelial repair. Most interestingly, commensal bacteria or their metabolites may also activate this receptor, thus contributing to the restoration of gut normobiosis and homeostasis. In line with that, Lactobacillus reuteri, Lactobacillus bulgaricus, or microbial products such as tryptophan metabolites, indole-3-pyruvic acid, urolithin A, short-chain fatty acids, dihydroxyquinoline, and others may regulate the inflammation by mechanisms dependent on AHR activation. Hence, here we discussed the potential modulatory role of AHR on intestinal inflammation, focused on the reestablishment of homeostasis through the receptor triggering by microbial metabolites. Finally, the development of AHR-based therapies derived from bacteria products could represent an important future alternative for controlling IBD.

Effects of Developmental Activation of the Aryl Hydrocarbon Receptor by 2,3,7,8-Tetrachlorodibenzo-p-dioxin on Long-term Self-renewal of Murine Hematopoietic Stem Cells

BACKGROUND

Human epidemiological and animal studies suggest that developmental exposure to contaminants that activate the aryl hydrocarbon receptor (AHR) lead to suppression of immune system function throughout life. The persistence of immune deficiency throughout life suggests that the cellular target of AHR activation is a fetal hematopoietic progenitor or stem cell.

OBJECTIVES

The aim of this study was to identify the effects of transplacental exposure to an AHR agonist on long-term self-renewal of fetal hematopoietic stem cells.

METHODS

Pregnant C57BL/6 or AHR+/- mice were exposed to the AHR agonist, 2,3,7,8-tetra-​chlorodibenzo-p-dioxin (TCDD). On day 14 of gestation, hematopoietic progenitors from wild-type or AHR-deficient fetuses were placed into in vitro T-lymphocyte differentiation cultures to identify the effects of transplacental TCDD on AHR activation in the fetus. We next analyzed the fetal hematopoietic progenitor cells for changes in reactive oxygen species (ROS). Finally, hematopoietic progenitors from fetuses exposed transplacentally to TCDD were mixed 1:1 with cells from congenic controls and used to reconstitute lethally irradiated recipients for analysis of long-term self-renewal potential.

RESULTS

Our findings suggested that the effects of TCDD on the developing hematopoietic system were mediated by direct AHR activation in the fetus. Furthermore, developmental AHR activation by TCDD increased ROS in the fetal hematopoietic stem cells, and the elevated ROS was associated with a reduced capacity of the TCDD-exposed fetal cells to compete with control cells in a mixed competitive irradiation/reconstitution assay.

CONCLUSIONS

Our findings indicate that AHR activation by TCDD in the fetus during pregnancy leads to impairment of long-term self-renewal of hematopoietic stem cells.

CITATION

Laiosa MD, Tate ER, Ahrenhoerster LS, Chen Y, Wang D. 2016. Effects of developmental activation of the aryl hydrocarbon receptor by 2,3,7,8-tetrachlorodibenzo-p-dioxin on long-term self-renewal of murine hematopoietic stem cells. Environ Health Perspect 124:957-965; http://dx.doi.org/10.1289/ehp.1509820.

The Autoimmune Ecology

Autoimmune diseases (ADs) represent a heterogeneous group of disorders that affect specific target organs or multiple organ systems. These conditions share common immunopathogenic mechanisms (i.e., the autoimmune tautology), which explain the clinical similarities they have among them as well as their familial clustering (i.e., coaggregation). As part of the autoimmune tautology, the influence of environmental exposure on the risk of developing ADs is paramount (i.e., the autoimmune ecology). In fact, environment, more than genetics, shapes immune system. Autoimmune ecology is akin to exposome, that is all the exposures - internal and external - across the lifespan, interacting with hereditary factors (both genetics and epigenetics) to favor or protect against autoimmunity and its outcomes. Herein, we provide an overview of the autoimmune ecology, focusing on the immune response to environmental agents in general, and microbiota, cigarette smoking, alcohol and coffee consumption, socioeconomic status (SES), gender and sex hormones, vitamin D, organic solvents, and vaccines in particular. Inclusion of the autoimmune ecology in disease etiology and health will improve the way personalized medicine is currently conceived and applied.

Fetal Hematopoietic Stem Cells Are the Canaries in the Coal Mine That Portend Later Life Immune Deficiency

Disorders of the blood system are a significant and growing global health concern and include a spectrum of diseases ranging from aplastic anemia and leukemias to immune suppression. This array of hematological disorders is attributed to the fact that the blood system undergoes a perpetual cycle of turn over with aged and exhausted red and white blood cells undergoing daily replacement. The foundational cells of this replenishment process are comprised of rare hematopoietic stem cells (HSCs) located in the bone marrow that possess the dual function of long-term self-renewal and multilineage differentiation. This constant turnover makes the hematopoietic system uniquely vulnerable to changes in the environment that impact multilineage differentiation, self-renewal, or both. Notably, environmental endocrine-disrupting exposures occurring during development, when HSCs are first emerging, can lead to alterations in HSC programming that impacts the blood and immune systems throughout life. In this review, we describe the process of fetal hematopoiesis and provide an overview of the intrauterine environmental and endocrine-disrupting compounds that disrupt this process. Finally, we describe research opportunities for fetal HSCs as potential sentinels of later-life blood and immune system disorders.

Histologic Features of Postnatal Development of Immune System Organs in the Sprague-Dawley Rat

The immune system of the rat undergoes substantial functional and morphological development during the postnatal period. Some aspects of this development are genetically predetermined, while other aspects depend on environmental influences. Detailed information on postnatal development is important in the interpretation of histopathologic findings in juvenile toxicology and pubertal assay studies, as well as other studies conducted in juvenile rats. Studies were conducted to provide detailed characterization of histologic features of the major functional compartments of immune system organs in male and female Sprague-Dawley rats at weekly intervals from the day of birth through postnatal day (PND) 42. Maturation of the individual immune system organs occurred across a range of ages, with histologic maturation of T-cell-related compartments typically occurring prior to maturation of B-cell-related compartments. The sequence of histologic maturation was bone marrow and thymus on PND 14, mesenteric lymph node on PND 21, Peyer's patches and bronchus-associated lymphoid tissue on PND 28, mandibular lymph node, nasopharynx-associated lymphoid tissue, and diffuse mucosal mononuclear cell population of small intestine on PND 35, and spleen on PND 42. An estimation of functional maturation can be made based on the morphological indications of maturity of each compartment of immune system organs, but histologic indications of maturity do not confirm functional immunocompetence.

Prior oral exposure to environmental immunosuppressive chemicals methoxychlor, parathion, or piperonyl butoxide aggravates allergic airway inflammation in NC/Nga mice

BACKGROUND

Immunosuppressive environmental chemicals may increase the potency of allergens and thereby play a role in the development of respiratory tract allergies, such as allergic rhinitis and asthma.

OBJECTIVES

We investigated the association between environmental immunosuppressive chemicals and the allergic airway inflammation development.

METHODS

We used a mouse model of ovalbumin (OVA)-induced allergic airway inflammation. NC/Nga mice were exposed orally to pesticides parathion (an organophosphate compound) or methoxychlor (an organochlorine compound), or to an insecticide synergist piperonyl butoxide, prior to OVA intraperitoneal sensitization and inhalation challenge. We assessed serum IgE levels, B-cell counts, cytokine production, IgE production in hilar lymph nodes, eosinophil counts, chemokine levels in bronchoalveolar lavage fluid, and cytokine gene expression in the lung.

RESULTS

Exposure to environmental immunosuppressive chemicals markedly increased serum IgE - IgE-positive B-cells, IgE and cytokines in lymph nodes - eosinophils and chemokines in BALF - IL-10a and IL-17 in the lung.

CONCLUSIONS

Allergic airway inflammation can be aggravated by prior exposure to immunosuppressive environmental chemicals.

Prenatal exposure to TCDD triggers significant modulation of microRNA expression profile in the thymus that affects consequent gene expression

Background

MicroRNAs (miRs) are a class of small RNAs that regulate gene expression. There are over 700 miRs encoded in the mouse genome and modulate most of the cellular pathways and functions by controlling gene expression. However, there is not much known about the pathophysiological role of miRs. TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), an environmental contaminant is well known to induce severe toxicity (acute and chronic) with long-term effects. Also, in utero exposure of fetus to TCDD has been shown to cause thymic atrophy and alterations in T cell differentiation. It is also relevant to understand “the fetal basis of adult disease” hypothesis, which proposes that prenatal exposure to certain forms of nutritional and environmental stress can cause increased susceptibility to clinical disorders later in life. In the current study, therefore, we investigated the effects of prenatal exposure to TCDD on miR profile in fetal thymocytes and searched for their possible role in causing thymic atrophy and alterations in the expression of apoptotic genes.

Methodology/Principal Findings

miR arrays of fetal thymocytes post exposure to TCDD and vehicle were performed. Of the 608 mouse miRs screened, 78 miRs were altered more than 1.5 fold and 28 miRs were changed more than 2 fold in fetal thymocytes post-TCDD exposure when compared to vehicle controls. We validated the expression of several of the miRs using RT-PCR. Furthermore, several of the miRs that were downregulated contained highly complementary sequence to the 3′-UTR region of AhR, CYP1A1, Fas and FasL. Also, the Ingenuity Pathway Analysis software and database was used to analyze the 78 miRs that exhibited significant expression changes and revealed that as many as 15 pathways may be affected.

Conclusions/Significance

These studies revealed that TCDD-mediated alterations in miR expression may be involved in the regulation of its toxicity including cancer, hepatic injury, apoptosis, and cellular development.

Prenatal TCDD causes persistent modulation of the postnatal immune response, and exacerbates inflammatory disease, in 36-week-old lupus-like autoimmune SNF1 mice

BACKGROUND

Prenatal exposure to the persistent environmental pollutant and model Ah receptor agonist, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), has been shown to permanently suppress postnatal cell-mediated immunity. More recently, skewing of select adult T and B cell responses toward enhanced inflammation has also been described in C57BL/6 mice after prenatal TCDD. This raises questions about adverse postnatal immune consequences of prenatal TCDD in animals genetically predisposed to inappropriate inflammatory responses.

METHODS

Lupus-prone SNF(1) mice were exposed to 0, 40, or 80 µg/kg TCDD on gestation day (gd) 12 and examined at 36 weeks-of-age for immunomodulatory effects that correlated with worsened lupus pathology.

RESULTS

Bone marrow pro- and large pre-B cells were decreased by prenatal TCDD, in both adult male and female mice, as were pre- and immature B cells. Splenic CD23(-) CD1(hi) and CD19(+) CD5(+) B cells were increased in males, as were B220(hi) B cells in females, further suggesting persistent disruption of B cell lymphopoiesis by prenatal TCDD. Female mice displayed decreased IL-10 production by ConA-activated splenocytes, while males underproduced IL-4. Autoreactive CD4(+) Vβ17a(+) spleen T cells were increased in both sexes by 80 µg/kg TCDD. Male mice but not females showed increased anti-ds DNA and cardiolipin autoantibody levels.

CONCLUSIONS

Prenatal TCDD augmented the hallmark indicators of SLE progression in the lupus-prone SNF(1) mice, including renal immune complex deposition, glomerulonephritis, and mesangial proliferation. Prenatal TCDD therefore caused persistent modulation of the postnatal immune response, and exacerbated inflammatory disease, in lupus-like autoimmune SNF(1) mice.

Prenatal TCDD in mice increases adult autoimmunity

Two immunologically different mouse strains, C57BL/6 and SNF(1), were exposed to a mid-gestation dose of TCDD. The C57BL/6 mouse has a high-affinity aryl hydrocarbon receptor (AhR) and is sensitive to TCDD. The SNF(1) mouse has a low-affinity AhR but spontaneously develops autoimmune nephritis. Autoreactive Vβ(+)CD4(+)17a and Vβ(+)CD3(+) T cells were increased at 24-weeks-of-age in offspring of C57BL/6 mice, more so in females than males. The cytokine IFN-γ was elevated in the females, while IL-10 was elevated in males. Phenotypic changes in B-lineage cells were present in bone marrow and spleen, and circulating autoantibodies were increased after prenatal TCDD. Kidneys of males showed significant anti-IgG and anti-C3 deposition, suggesting early-stage autoimmune disease. The SNF(1) offspring similarly showed increased peripheral Vβ(+) cells in the females, increased autoantibody production in both sexes, and increased IFN-γ production in females. Male SNF(1) mice had increased anti-IgG and anti-C3 deposition in kidneys. Both mouse models therefore showed clear signatures of enhanced autoimmunity after prenatal TCDD.

Dioxin toxicity, aryl hydrocarbon receptor signaling, and apoptosis-persistent pollutants affect programmed cell death

Exogenous ligands of the aryl hydrocarbon receptor (AhR) such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related substances are highly toxic pollutants ubiquitously present in the environment. They cause a variety of toxic effects to different organs and tissues. Among other effects, TCDD exposure to laboratory animals leads to thymus atrophy and immunosuppression on the one hand, and to tumor formation on the other. Apoptosis appears to be involved in both these toxic effects: AhR activation by TCDD was discussed to induce apoptosis of immune cells, leading to the depletion of thymocytes and ultimately immunosuppression. This mechanism could help to explain the highly immunotoxic actions of TCDD but it is nevertheless under debate whether this is the mode of action for immunosuppression by this class of chemical substances. In other cell types, especially liver cells, TCDD inhibits apoptosis induced by genotoxic treatment. In initiation-promotion studies, TCDD was shown to be a potent liver tumor promoter. Among other theories it was hypothesized that TCDD acts as a tumor promoter by preventing initiated cells from undergoing apoptosis. The exact mechanisms of apoptosis inhibition by TCDD are not fully understood, but both in vivo and in vitro studies consistently showed an involvement of the tumor suppressor p53 in this effect. Various strings of evidence have been established linking apoptosis to the detrimental effects of exogenous activation of the AhR. Within this article, studies elucidating the effects of TCDD and related substances on apoptosis signaling, be it inducing or repressing, is to be reviewed.