Histomorphometric alteration and cell-type specific modulation of arylhydrocarbon receptor and estrogen receptor expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin and 17β-estradiol in mouse experimental model of endometriosis

Associations between Exposure to Organochlorine Chemicals and Endometriosis: A Systematic Review of Experimental Studies and Integration of Epidemiological Evidence

BACKGROUND

Growing epidemiological evidence suggests that organochlorine chemicals (OCCs), including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), may play a role in the pathogenesis of endometriosis.

OBJECTIVES

We aimed to systematically review the experimental evidence (in vivo and in vitro) on the associations between exposure to OCCs and endometriosis-related end points.

METHODS

A systematic review protocol was developed following the National Toxicology Program /Office of Health Assessment and Translation (NTP/OHAT) framework and managed within a web-based interface. In vivo studies designed to evaluate the impact of OCCs on the onset or progression of endometriosis and proliferation of induced endometriotic lesions were eligible. Eligible in vitro studies included single-cell and co-culture models to evaluate the proliferation, migration, and/or invasion of endometrial cells. We applied the search strings to PubMed, Web of Science, and Scopus®. A final search was performed on 24 June 2020. Assessment of risk of bias and the level of evidence and integration of preevaluated epidemiological evidence was conducted using NTP/OHAT framework Results: Out of 812 total studies, 39 met the predetermined eligibility criteria (15 in vivo, 23 in vitro, and 1 both). Most studies (n=27) tested TCDD and other dioxin-like chemicals. In vivo evidence supported TCDD's promotion of endometriosis onset and lesion growth. In vitro evidence supported TCDD's promotion of cell migration and invasion, but there was insufficient evidence for cell proliferation. In vitro evidence further supported the roles of the aryl hydrocarbon receptor and matrix metalloproteinases in mediating steroidogenic disruption and inflammatory responses. Estrogen interactions were found across studies and end points.

CONCLUSION

Based on the integration of a high level of animal evidence with a moderate level of epidemiological evidence, we concluded that TCDD was a known hazard for endometriosis in humans and the conclusion is supported by mechanistic in vitro evidence. Nonetheless, there is need for further research to fill in our gaps in understanding of the relationship between OCCs and their mixtures and endometriosis, beyond the prototypical TCDD. https://doi.org/10.1289/EHP8421.

Exposure to environmental concentrations of hexachlorobenzene induces alterations associated with endometriosis progression in a rat model

Hexachlorobenzene (HCB) is a dioxin-like compound widely distributed and is a weak ligand of the aryl hydrocarbon receptor (AhR). Endometriosis is a disease characterized by growth of endometrial tissue in ectopic sites. Our aim was to investigate the impact of HCB on the endocrine, invasion and inflammatory parameters in a rat endometriosis model surgically induced. Female rats were exposed to HCB (1, 10 and 100 mg/kg b.w.) during 30 days. Results showed that HCB increases endometriotic like-lesions (L) volume in a dose-dependent manner. In L, HCB10 increases microvessel density (immunohistochemistry) and the vascular endothelial growth factor (VEGF), cyclooxygenase-2 (COX-2) and AhR levels (Western Blot), while HCB1 enhances aromatase expression (Western Blot). In addition, in eutopic endometrium (EU), HCB10/HCB100 augments microvessel density, VEGF and MMP-9 expression, while HCB1/HCB10 increases tumor necrosis factor-α (TNF-α) content in peritoneal fluid (ELISA). Interestingly, both L and EU from HCB-treated rats exhibited higher estrogen receptor α (ERα) (immunohistochemistry) and metalloproteases (MMP)-2 and -9 levels (Western Blot), as well as lower progesterone receptor (PR) expression (immunohistochemistry) than in control rats. Environmentally relevant concentrations of HCB could contribute to abnormal changes associated with endometriosis progression and development.

Short androgen receptor poly-glutamine-promoted endometrial cancer is associated with benzo[a]pyrene-mediated aryl hydrocarbon receptor activation

The androgen receptor (AR) poly‐glutamine polymorphism (AR‐Q) was reported to play role in endometrial cancer (EMCA) development, yet controversial. Environmental factors interact with genetic variation have been reported in EMCA. Aerosol toxins, polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP), are EMCA facilitators. This report examined the interplay between AR‐Qs and BaP in EMCA. During analysing patient AR‐Q polymorphism and Aryl hydrocarbon Receptor (AhR) expressions, we found overall survival (OS) benefit is ascending with AR‐Q lengths (5‐year OS of 61.3% in Q length <20 and 88% in Q length >23). And AhR is higher expressed in short AR‐Q tumour compared to that in long AR‐Q patient. In vitro study found androgen‐response element (ARE) activity descends with AR‐Qs length (Q13 > Q25 > Q35), whereas BaP suppresses ARE activities in EMCA cells. Furthermore, AR‐Q13 (but not AR‐Q25, or ‐35) enhances BaP‐induced dioxin‐responsive element (DRE) activity. Lastly, AR‐Q13 exerts higher colony‐forming capacity than other AR‐Qs, and knock‐down AhR abolished AR‐Q13‐mediated colony numbers. This study demonstrated a possible interaction of gene (AR‐Q polymorphism) and environmental toxins (e.g. BaP) to affect cancer progression. A large‐scale epidemiology and public health survey on the interaction of environmental toxin and AR poly‐Q in EMCA is suggested.

Lupinalbin A as the most potent estrogen receptor α- and aryl hydrocarbon receptor agonist in Eriosema laurentii de Wild. (Leguminosae)

Background

Eriosema laurentii De Wild. (Leguminosae) is a plant used in Cameroon against infertility and gynecological or menopausal complaints. In our previous report, a methanol extract of its aerial parts was shown to exhibit estrogenic and aryl hydrocarbon receptor agonistic activities in vitro and to prevent menopausal symptoms in ovariectomized Wistar rats.

Methods

In order to determine the major estrogen receptor α (ERα) agonists in the extract, an activity-guided fractionation was performed using the ERα yeast screen. To check whether the ERα active fractions/compounds also accounted for the aryl hydrocarbon receptor (AhR) agonistic activity of the crude methanol extract, they were further tested on the AhR yeast screen.

Results

This study led to the identification of 2′-hydroxygenistein, lupinalbin A and genistein as major estrogenic principles of the extract. 2′-hydroxygenistein and lupinalbin A were, for the first time, also shown to possess an AhR agonistic activity, whereas genistein was not active in this assay. In addition, it was possible to deduce structure-activity relationships.

Conclusions

These results suggest that the identified compounds are the major active principles responsible for the estrogenic and AhR agonistic activities of the crude methanol extract of the aerial parts of Eriosema laurentii.

Progesterone, as well as 17β-estradiol, is important for regulating AHR battery homoeostasis in the rat uterus

Several studies indicate that the aryl hydrocarbon receptor (AHR), which plays an important role in mediating the toxicity of many industrial chemicals, plays an important role in the physiology of female reproductive tract organs. This makes it likely that the AHR and additional components of the AHR signalling pathway are under the control of female sex steroids. In a previous study, we could already demonstrate the regulation of many members of the AHR battery by 17β-estradiol (E2) in the uterus of rats. In this study, we addressed the potential role of progesterone (P4) in this context. In a comparative approach using ovariectomized rats which were treated for 3 days with either vehicle control, E2, progesterone (P4) or the combination of both hormones in addition to sham-operated animals, we could demonstrate that in addition to E2, P4 is also an important factor in regulating AHR signalling in the rat uterus. P4 has effects similar to E2 on uterine Ahr, Arnt and Arnt2 mRNA levels, resulting in a downregulation of these genes, while the E2-mediated downregulation of key AHR response genes Cyp1a1, Gsta2 and Ugt1 is completely antagonized by P4. As with E2, P4 leads to an increase in uterine AHR levels, especially in the endometrial epithelium despite the decrease in corresponding mRNA levels. This indicates a complex gene-specific regulatory network involving E2, P4 and possibly AHR itself to maintain all components of the AHR signalling cascade at the required levels during all stages of the oestrous cycle and pregnancy.

The regulation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced lung tumor promotion by estradiol in female A/J mice

Epidemiological studies indicate that women are at a higher risk developing lung cancer than men are. It is suggested that estrogen is one of the most important factors in lung cancer development in females. Additionally, cigarette smoke, and environmental pollutants, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), may play salient roles in female lung carcinogenesis. However, the mechanisms responsible for the interaction of these factors in the promotion of lung cancer are still poorly understood. The present study was designed to explore two ideas: first, the synergistic lung tumorigenic effects of 4-(methylnitrosamino)-1-(3-pyridyl)-butanol (NNK) combined with TCDD, 17β-estradiol (E2) or both through a long-term treatment experiment, and second, to identify early changes in the inflammatory and signaling pathways through short-term treatment experiments. The results indicate that A/J mice given E2 had strong effects in potentiating NNK-induced activation of MAPK signaling, NFκB, and COX-2 expression. In the long-term exposure model, E2 had a strong tumor promoting effect, whereas TCDD antagonized this effect in A/J mice. We conclude that treatment with NNK combined with either E2 or TCDD induces lung carcinogenesis and the promotion effects could be correlated with lung inflammation. E2 was shown to potentiate NNK-induced inflammation, cell proliferation, thereby leading to lung tumorigenesis.

Modified expression of aryl hydrocarbon receptor-related genes by deoxymiroestrol, a phytoestrogen, in mouse hepatocytes in primary culture

ETHNOPHARMACOLOGICAL RELEVANCE

Deoxymiroestrol (DM), a strong phytoestrogen from Pueraria candollei Wall. ex Benth. var. mirifica (family Leguminosae). This plant has long been used in traditional medicine for rejuvenation.

MATERIALS AND METHODS

The expression of aryl hydrocarbon receptor-related genes in mouse hepatocytes in primary culture was quantified by real-time RT-PCR and hepatic microsomal P450 activity was assessed by using ethoxyresorufin O-dealkylation.

RESULTS

The mRNA expression of the aryl hydrocarbon receptor (AhR), AhR nuclear translocator, and CYP1A1 was suppressed, whereas that of CYP1B1, estrogen receptor α (ERα), CYP2B9, and glutathione-S-transferase a2 (GSTa2) was increased. The effects of DM on the gene expression depended on treatment period and concentrations, and were similar to those of β-estradiol (E2). DM and E2 at pharmacological concentrations had a marked synergistic effect on CYP1A1 expression after combined treatment with a typical CYP1 inducer, β-naphthoflavone (βNF), at the level of both transcription and enzymatic activity. DM enhanced the inducible mRNA expression of CYP1A1 and CYP1B1 similar to E2. Meanwhile, the expression of ERα mRNA was not affected by βNF, which, on the contrary, completely eliminated the DM-induced mRNA expression of ERα, CYP2B9, and GSTa2.

CONCLUSION

The findings that DM modified the expression of several metabolism-related genes suggest the need for caution when using health supplements having phytoestrogenic activity.

Estrogen-independent actions of environmentally relevant AhR-agonists in human endometrial epithelial cells

The human endometrium is a cyclically regenerating organ under the influence of ovarian steroid hormones. Disturbances in this highly coordinated regulation of endometrial proliferation and differentiation may result in infertility and diseases such as endometriosis and endometrial cancer. Environmental toxins belonging to the group of polyhalogenated aromatic hydrocarbons (PAHs) are lipophilic xenobiotics, which accumulate in biological systems. PAHs have been implicated in the etiology of uterine pathologies, including infertility, endometriosis and endometrial cancer. However, suitable cellular models of the endometrium are lacking and the molecular mechanism of PAH action in the endometrium is not fully understood. In this study, we have characterized a previously established immortalized human telomerase reverse transcriptase (hTERT) endometrial epithelial cell (hTERT-EEC) model as a responsive in vitro cell model to investigate the cellular and molecular mechanisms of selected environmentally relevant PAH in human EECs. We show that dioxin-type PAHs activate the endogenous arylhydrocarbon receptor (AhR) signaling pathway in hTERT-EEC in a time-, concentration- and congener-specific manner and that the induction of AhR target genes is modulated by estrogen. Strikingly, AhR activation did not interfere with estrogenic actions in these EECs. Independent of their ability to bind to AhR, the PAHs investigated here increased cell migration by hTERT-EEC. Furthermore, we have identified several candidates by proteomic analysis, which are involved in heat shock responses and protein modification and turnover. Our data suggest that AhR-activating environmental pollutants directly alter endometrial cell stress responses and metabolism independent of estrogenic actions.

Estradiol regulates aryl hydrocarbon receptor expression in the rat uterus

Several authors have investigated the role of aryl hydrocarbon receptor (AHR) in the reproductive tract, but there are no data available whether 17beta-estradiol (E2) regulates expression of members of the AHR pathway in the uterus. We therefore examined the mRNA expression of Ahr as well as the genes of the AHR dimerization partners ARNT1 and ARNT2 and the AHR regulated genes Cyp1a1 and Gsta2 in the uterus of ovariectomized rats after administration of E2 at two different doses. The data show that Ahr mRNA expression is downregulated while AHR protein amounts increased in all uterine tissue compartments. In addition we observed a downregulation of Arnt1, Arnt2 and Cyp1a1 while Gsta2 mRNA expression is upregulated by E2 in a dose-dependent manner. These results show that members of the AHR pathway are regulated by E2 in the uterus. AHR may therefore play an important role in the mediation of uterine estrogenic effects.

Regulation of aryl hydrocarbon receptor function by selective estrogen receptor modulators

Selective estrogen receptor modulators (SERMs), such as tamoxifen (TAM), have been used extensively for the treatment and prevention of breast cancer and other pathologies associated with aberrant estrogen receptor (ER) signaling. These compounds exhibit cell-selective agonist/antagonist activities as a consequence of their ability to induce different conformational changes in ER, thereby enabling it to recruit functionally distinct transcriptional coregulators. However, the observation that SERMs can also regulate aspects of calcium signaling and apoptosis in an ER-independent manner in some systems suggests that some of the activity of drugs within this class may also arise as a consequence of their ability to interact with targets other than ER. In this study, we demonstrate that 4-hydroxy-TAM (4OHT), an active metabolite of TAM, directly binds to and modulates the transcriptional activity of the aryl hydrocarbon receptor (AHR). Of specific interest was the observation, that in the absence of ER, 4OHT can induce the expression of AHR target genes involved in estradiol metabolism, cellular proliferation, and metastasis in cellular models of breast cancer. The potential role for AHR in SERM pharmacology was further underscored by the ability of 4OHT to suppress osteoclast differentiation in vitro in part through AHR. Cumulatively, these findings provide evidence that it is necessary to reevaluate the relative roles of ER and AHR in manifesting the pharmacological actions and therapeutic efficacy of TAM and other SERMs.

Immunopathogenesis of pelvic endometriosis: role of hepatocyte growth factor, macrophages and ovarian steroids

Endometriosis, a chronic disease characterized by endometrial tissue located outside the uterine cavity is associated with chronic pelvic pain and infertility. However, an in-depth understanding of the pathophysiology of endometriosis is still elusive. It is generally believed that besides ovarian steroid hormones, the growth of endometriosis can be regulated by innate immune system in pelvic microenvironment by their interaction with endometrial cells and immune cells. We conducted a series of studies in perspectives of pelvic inflammation that is triggered primarily by bacterial endotoxin (lipopolysaccharide) and is mediated by toll-like receptor 4 and showed their involvement in the development of pelvic endometriosis. As a cellular component of innate immune system, macrophages were found to play a central role in inducing pelvic inflammatory reaction. We further report here that peritoneal macrophages retain receptors encoding for estrogen and progesterone and ovarian steroids also participate in producing an inflammatory response in pelvic cavity and are involved in the growth of endometriosis either alone or in combination with hepatocyte growth factor (HGF). As a pleiotropic growth factor, HGF retains multifunctional role ometriosis. We describe here the individual and step-wise role of HGF, macrophages and ovarian steroid hormones and their orchestrated involvement in the immunopathogenesis of pelvic endometriosis.

The role of the aryl hydrocarbon receptor in the female reproductive system

In recent years, many studies have emphasized how changes in aryl hydrocarbon receptor (AHR)-mediated gene expression result in biological effects, raising interest in this receptor as a regulator of normal biological function. This review focuses on what is known about the role of the AHR in the female reproductive system, which includes the ovaries, Fallopian tubes or oviduct, uterus and vagina. This review also focuses on the role of the AHR in reproductive outcomes such as cyclicity, senescence, and fertility. Specifically, studies using potent AHR ligands, as well as transgenic mice lacking the AHR-signaling pathway are discussed from a viewpoint of understanding the endogenous role of this ligand-activated transcription factor in the female reproductive lifespan. Based on findings highlighted in this paper, it is proposed that the AHR has a role in physiological functions including ovarian function, establishment of an optimum environment for fertilization, nourishing the embryo and maintaining pregnancy, as well as in regulating reproductive lifespan and fertility. The mechanisms by which the AHR regulates female reproduction are poorly understood, but it is anticipated that new models and the ability to generate specific gene deletions will provide powerful experimental tools for better understanding how alterations in AHR pathways result in functional changes in the female reproductive system.

Regulation of Aryl Hydrocarbon Receptor Expression in Rat Granulosa Cells1

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates most of the toxic and endocrine-disruptive actions of aromatic compounds in the ovary. Paradoxically, this receptor has been shown to play important roles in normal female reproductive function as well. Although knowledge of AHR expression regulation in the ovary is of crucial significance to understand the receptor biology and its function in reproductive physiology, there are only limited data in this area. The purpose of the present study was to establish the possible regulation that AHR might undergo in ovarian cells. Here we show that the hormones FSH and estradiol are able to reduce AHR protein and transcript levels in granulosa cells in a way that parallels the changes observed in ovarian tissue across the rat estrous cycle. These findings suggest that estradiol and FSH would be cycle-associated endogenous modulators of AHR expression. In addition, we show that in granulosa cells the receptor is rapidly downregulated via proteasomal degradation following treatment with AHR ligands. However, prolonged treatment with an agonist caused an increase in Ahr mRNA levels. These actions would constitute a regulatory mechanism that both attenuates AHR signal rapidly and replenishes the cellular receptor pool in the long term. In conclusion, our results indicate that AHR expression is regulated by classical hormones and by its own ligands in granulosa cells.

Expression of the arylhydrocarbon receptor in the peri-implantation period of the mouse uterus and the impact of dioxin on mouse implantation

The arylhydrocarbon receptor (AhR) is a nuclear transcription factor mediating toxic effects of chemicals such as dioxins. The 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a member of polyhalogenated aromatic hydrocarbons family, exerts a wide-variety of toxic effects in a tissue- and species-specific manner including the reproduction process. Recently, AhR-mediated direct effects of TCDD on a cell-specific interaction with ovarian steroids have been shown. However, information regarding the effects of TCDD on the mouse implantation is limited. We therefore examined the expression and localization of AhR in the pregnant mouse uterus from 4 to 10 days of gestation (day 4 to day 10) using immunohistochemistry to investigate the effect of TCDD on uterine tissue during the peri-implantation period. Intense AhR expression was detected in the uterine vasculature throughout the periods examined. We also found that implanted blastocysts and their surrounding luminal epithelia and decidualized stroma expressed AhR on day 5. On days 6 and 7, persistent AhR expression was found in the transitional zone between the invading embryonic tissue and decidual tissue. On days 9 to 10, placental vasculature and spongiotrophoblasts displayed AhR immunoreactivity. The administration of TCDD on day 4 decreased the number of surviving implanted embryos on day 7 in a dose-dependent manner. This effect of TCDD was inhibited by the simultaneous administration of an AhR antagonist, alpha-naphthoflavone (alpha-NF). The spatio-temporal expression of AhR during the peri-implantation phase of the mouse uterus may indicate functional roles of this orphan receptor in fetomaternal interactions as well as substantiate the risk of exposure to chemicals such as dioxins during the reproductive period.