Aryl hydrocarbon receptor regulates growth, but not atresia, of mouse preantral and antral follicles

Dexlansoprazole is an aryl hydrocarbon receptor agonist

Dexlansoprazole, a proton pump inhibitor, is commonly used to treat gastro-esophageal reflux disease and erosive esophagitis. The activated aryl hydrocarbon receptor (AhR) functions as a transcription factor by binding to the aryl hydrocarbon response element (AHRE) of its target genes, with cytochrome P450 (CYP) 1A1 being the most well-known target. In this study, we demonstrated that dexlansoprazole stimulates AhR activity, leading to increased CYP1A1 expression. Our findings indicate that treatment with 2 μM dexlansoprazole is sufficient to induce CYP1A1 mRNA and protein expression, as well as AHRE-mediated transcriptional activity, in both human and mouse cells. Using AhR signal-deficient mutant cells and specific AhR antagonists-SR1, GNF351, and CH-223191-we confirmed that AhR is required for dexlansoprazole-induced CYP1A1 expression. Additionally, we showed that dexlansoprazole promotes AhR nuclear translocation, acting as an AhR agonist. However, due to its lower potency compared to FICZ and ITE in activating AhR, dexlansoprazole suppresses FICZ- and ITE-induced CYP1A1 expression in human liver HepG2 and ovarian granulosa HO23 cell lines, suggesting that it functions as both an AhR agonist and a modulator. This study offers valuable insights into the potential clinical side effects of dexlansoprazole.

The epoxiconazole and tebuconazole fungicides impair granulosa cells functions partly through the aryl hydrocarbon receptor (AHR) signalling with contrasted effects in obese, normo-weight and polycystic ovarian syndrome (PCOS) patients

Polycystic ovarian syndrome (PCOS), frequently associated to obesity, is the main reproductive disorder in women in age to procreate. Some evidence suggests that pesticides can result in alterations of the female reproductive system, including polycystic ovary syndrome (PCOS). Here, we detected two fungicides, Tebuconazole (Tb) and Epoxiconazole (Epox) in the soils and waters of French area. Our hypothesis is that these two triazoles could be associated to the etiology of PCOS. We used the human KGN cell line and primary human granulosa cells (hGCs) from different group of patients: normal weight non PCOS (NW), normal weight PCOS (PCOS NW), obese (obese) and obese PCOS (PCOS obese). We exposed in vitro these cells to Tb and Epox from 0 up to 10 mM for 24 and 48 h and analysed cell viability and steroidogenesis. In hGCs NW, cell viability was reduced from 12.5 µM for Tb and 75 µM for Epox. In hGCs NW, Epox decreased progesterone (Pg) and estradiol (E2) secretions and inhibited STAR, HSD3B and CYP19A1 mRNA expressions from 25 µM and increased AHR mRNA expression from 75 µM. Tb exposure also reduced steroid secretion and STAR and CYP19A1 mRNA expressions and increased AHR mRNA expression but at cytotoxic concentrations. Silencing of AHR in KGN cells reduced inhibitory effects of Tb and Epox on steroid secretion. Tb and Epox exposure decreased more steroid secretion in hGCs from obese, PCOS NW and PCOS obese groups than in NW group. Moreover, we found a higher gene expression of AHR within these three groups. Taken together, both Epox and Tb reduced steroidogenesis in hGCs through partly AHR and Tb was more cytotoxic than Epox. These triazoles alter more strongly PCOS and/or obese hGCs suggesting that human with reproductive disorders are more sensitive to triazoles exposure.

Impact of dioxins on reproductive health in female mammals

Extensive research has been conducted to investigate the toxicological impact of dioxins on mammals, revealing profound effects on the female reproductive system in both humans and animals. Dioxin exposure significantly disrupts the intricate functions of the ovary, a pivotal organ responsible for reproductive and endocrine processes. This disruption manifests as infertility, premature ovarian failure, and disturbances in sex steroid hormone levels. Comprehensive studies, encompassing accidental human exposure and experimental animal data, have raised a wealth of information with consistent yet varied conclusion influenced by experimental factors. This review begins by providing an overarching background on the ovary, emphasizing its fundamental role in reproductive health, particularly in ovarian steroidogenesis and hormone receptor regulation. Subsequently, a detailed examination of the Aryl hydrocarbon Receptor (AhR) and its role in governing ovarian function is presented. The review then outlines the sources and toxicity of dioxins, with a specific focus on AhR involvement in mediating reproductive toxicity in mammals. Within this context, the impact of dioxins, notably 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), on Folliculogenesis and Preimplantation embryos is discussed. Furthermore, the review delves into the disruptions of the female hormonal system caused by TCDD and their ramifications in endometriosis. Notably, variations in the effects of TCDD on the female reproductive and hormonal system are highlighted in relation to TCDD dose, animal species, and age. As a forward-looking perspective, questions arise regarding the potential involvement of molecular mechanisms beyond AhR in mediating the female reproductive toxicity of dioxins.

The role of the aryl hydrocarbon receptor in mediating the effects of mono(2-ethylhexyl) phthalate in mouse ovarian antral follicles†

Di(2-ethylhexyl) phthalate (DEHP) is a pervasive environmental toxicant used in the manufacturing of numerous consumer products, medical supplies, and building materials. DEHP is metabolized to mono(2-ethylhexyl) phthalate (MEHP). MEHP is an endocrine disruptor that adversely affects folliculogenesis and steroidogenesis in the ovary, but its mechanism of action is not fully understood. Thus, we tested the hypothesis that the aryl hydrocarbon receptor (AHR) plays a functional role in MEHP-mediated disruption of folliculogenesis and steroidogenesis. CD-1 mouse antral follicles were isolated and cultured with MEHP (0-400 μM) in the presence or absence of the AHR antagonist CH223191 (1 μM). MEHP treatment reduced follicle growth over a 96-h period, and this effect was partially rescued by co-culture with CH223191. MEHP exposure alone increased expression of known AHR targets, cytochrome P450 (CYP) enzymes Cyp1a1 and Cyp1b1, and this induction was blocked by CH223191. MEHP reduced media concentrations of estrone and estradiol compared to control. This effect was mitigated by co-culture with CH223191. Moreover, MEHP reduced the expression of the estrogen-sensitive genes progesterone receptor (Pgr) and luteinizing hormone/choriogonadotropin receptor (Lhcgr) and co-treatment with CH223191 blocked this effect. Collectively, these data indicate that MEHP activates the AHR to impair follicle growth and reduce estrogen production and signaling in ovarian antral follicles.

Knock-down of aryl hydrocarbon receptor (AhR) affects the lncRNA-mediated response of porcine granulosa cells (AVG-16 cell line) to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Recently, we found that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) - the most toxic dioxin - affected multiple cellular processes in AhR-knocked-down granulosa cells, including the expression of genes and the abundance of proteins. Such alterations may imply the involvement of noncoding RNAs in the remodeling of intracellular regulatory tracks. The aims of the current study were to examine the effects of TCDD on the expression of lncRNAs in AhR-knocked-down granulosa cells of pigs and to indicate potential target genes for differentially expressed lncRNAs (DELs). In the current study, the abundance of AhR protein in porcine granulosa cells was reduced by 98.9% at 24 h after AhR targeted siRNA transfection. Fifty-seven DELs were identified in the AhR-deficient cells treated with TCDD mostly after 3 h (3 h: 56, 12 h: 0, 24 h: 2) after the dioxin treatment. This number was 2.5 times higher than that of intact TCDD-treated granulosa cells. The high number of DELs identified in the early stages of the TCDD action may be associated with a rapid defensive response of cells to harmful actions of this persistent environmental pollutant. In contrast to intact TCDD-treated granulosa cells, AhR-deficient cells were characterized by a broader representation of DELs enriched in GO terms related to the immune response and regulation of transcription and cell cycle. The obtained results support the notion that TCDD may act in an AhR-independent manner. They increase our knowledge on the intracellular mechanism of TCDD action and may in the future contribute to better coping with detrimental consequences of human and animal exposure to TCDD.

Role of Hepatic Aryl Hydrocarbon Receptor in Non-Alcoholic Fatty Liver Disease

Numerous nuclear receptors including farnesoid X receptor, liver X receptor, peroxisome proliferator-activated receptors, pregnane X receptor, hepatic nuclear factors have been extensively studied within the context of non-alcoholic fatty liver disease (NAFLD). Following the first description of the Aryl hydrocarbon Receptor (AhR) in the 1970s and decades of research which unveiled its role in toxicity and pathophysiological processes, the functional significance of AhR in NAFLD has not been completely decoded. Recently, multiple research groups have utilized a plethora of in vitro and in vivo models that mimic NAFLD pathology to investigate the functional significance of AhR in fatty liver disease. This review provides a comprehensive account of studies describing both the beneficial and possible detrimental role of AhR in NAFLD. A plausible reconciliation for the paradox indicating AhR as a 'double-edged sword' in NAFLD is discussed. Finally, understanding AhR ligands and their signaling in NAFLD will facilitate us to probe AhR as a potential drug target to design innovative therapeutics against NAFLD in the near future.

Dietary phytogenic inclusion level affects production performance and expression of ovarian cytoprotective genes in laying hens

A 12-wk study was conducted to investigate the effects of a phytogenic premix (PP) inclusion level on production performance, and the expression of genes relevant for detoxification (aryl hydrocarbon receptor; AhR) and antioxidant capacity (Nuclear factor erythroid 2-related factor 2; Nrf2) in the ovaries of laying hens. The PP consisted of bioactive substances derived from ginger, lemon balm, oregano, and thyme substances (Anco FIT-Poultry). Depending on PP inclusion level (i.e., 0, 500, 750, 1,000, and 1,500 mg/kg diet) in the basal diet, 385 laying hens Hy-Line Brown, 20-wk-old were assigned into 5 treatments: CON, P500, P750, P1000, and P1500, with 7 replicates of 11 hens with ad libitum access to feed and water. Performance parameters were closely monitored on a weekly basis and analyzed in the following 3 experimental periods: 1 to 4 wk, 5 to 8 wk, and 9 to 12 wk of treatment administration (i.e., 21-24, 25-28, and 29-32 wk of layers age, respectively). At the end of the 8th and 12th wk of the experiment (i.e., 28 and 32 wk of layers age), a layer from each replicate was selected, euthanized, the ovaries sampled and stored deep frozen until gene expression analysis. Data were analyzed by ANOVA and means compared using Tukey's honest significant difference test. Polynomial contrasts tested the linear and quadratic effect of PP inclusion levels. Results revealed that PP inclusion, improved (P < 0.05) laying rate and egg mass, compared to CON. Increasing PP inclusion level enhanced laying rate and egg mass, linearly and quadratically and peaked at P1000 (P < 0.05). In the ovaries, the AhR pathway genes assessed were down-regulated (P < 0.05) mainly at P1000 and P750 treatments. In addition, PP related cytoprotective potential was demonstrated via beneficial changes seen for the majority of the Nrf2-pathway genes assessed with the P1000 displaying most significant differences from CON. Conclusively, new data highlighted beneficial cytoprotective effects of PP inclusion on layer ovaries and documented further layer performance, with the inclusion level of 1000 mg PP/kg diet being the most prominent.

The effects of polycyclic aromatic compounds (PACs) on mammalian ovarian function

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Toxicity of polycyclic aromatic compounds (PACs) is limited to a subset of PACs.

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Exposure to these compounds impact major processes necessary for ovarian function.

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PAC exposure causes follicle loss and aberrant steroid production and angiogenesis.

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PAC exposure may increase the risk for impaired fertility and ovarian pathologies.

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The study of PACs as ovarian toxicants should include additional compounds.

Polycyclic aromatic compounds (PACs) are a broad class of contaminants ubiquitously present in the environment due to natural and anthropogenic activities. With increasing industrialization and reliance on petroleum worldwide, PACs are increasingly being detected in different environmental compartments. Previous studies have shown that PACs possess endocrine disruptive properties as these compounds often interfere with hormone signaling and function. In females, the ovary is largely responsible for regulating reproductive and endocrine function and thus, serves as a primary target for PAC-mediated toxicity. Perturbations in the signaling pathways that mediate ovarian folliculogenesis, steroidogenesis and angiogenesis can lead to adverse reproductive outcomes including polycystic ovary syndrome, premature ovarian insufficiency, and infertility. To date, the impact of PACs on ovarian function has focused predominantly on polycyclic aromatic hydrocarbons like benzo(a)pyrene, 3-methylcholanthrene and 7,12-dimethylbenz[a]anthracene. However, investigation into the impact of substituted PACs including halogenated, heterocyclic, and alkylated PACs on mammalian reproduction has been largely overlooked despite the fact that these compounds are found in higher abundance in free-ranging wildlife. This review aims to discuss current literature on the effects of PACs on the ovary in mammals, with a particular focus on folliculogenesis, steroidogenesis and angiogenesis, which are key processes necessary for proper ovarian functions.

Role of aryl hydrocarbon receptor (AHR) in overall retinoid metabolism: Response comparisons to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure between wild-type and AHR knockout mice

Young adult wild-type and aryl hydrocarbon receptor knockout (AHRKO) mice of both sexes and the C57BL/6J background were exposed to 10 weekly oral doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; total dose of 200 μg/kg bw) to further characterize the observed impacts of AHR as well as TCDD on the retinoid system. Unexposed AHRKO mice harboured heavier kidneys, lighter livers and lower serum all-trans retinoic acid (ATRA) and retinol (REOH) concentrations than wild-type mice. Results from the present study also point to a role for the murine AHR in the control of circulating REOH and ATRA concentrations. In wild-type mice, TCDD elevated liver weight and reduced thymus weight, and drastically reduced the hepatic concentrations of 9-cis-4-oxo-13,14-dihydro-retinoic acid (CORA) and retinyl palmitate (REPA). In female wild-type mice, TCDD increased the hepatic concentration of ATRA as well as the renal and circulating REOH concentrations. Renal CORA concentrations were substantially diminished in wild-type male mice exclusively following TCDD-exposure, with a similar tendency in serum. In contrast, TCDD did not affect any of these toxicity or retinoid system parameters in AHRKO mice. Finally, a distinct sex difference occurred in kidney concentrations of all the analysed retinoid forms. Together, these results strengthen the evidence of a mandatory role of AHR in TCDD-induced retinoid disruption, and suggest that the previously reported accumulation of several retinoid forms in the liver of AHRKO mice is a line-specific phenomenon. Our data further support participation of AHR in the control of liver and kidney development in mice.

Diminished Ovarian Reserve Chemotherapy-Induced Mouse Model: A Tool for the Preclinical Assessment of New Therapies for Ovarian Damage

Diminished ovarian reserve (DOR) and primary ovarian insufficiency (POI) are primary factors leading to infertility. However, there is a lack of appropriate animal models of DOR usable for assessing new therapeutic strategies. In this study, we aimed to evaluate whether chemotherapy treatment in mice could reproduce features similar of that observed in women with DOR. Twenty-one Nonobese diabetic/severe combined immunodeficiency (NOD/SCID) female mice were allocated to 3 groups (n = 7/group): control, single dose of vehicle (Dimethyl Sulfoxide [DMSO]); DOR, single reduced chemotherapy dose; and POI, single standard chemotherapy dose. After 21 days, mice underwent ovarian hyperstimulation and mating. Part of the animals were harvested to analyze ovarian reserve, ovulation and fertilization rates, and morphology, apoptosis, and vascularization of the ovarian stroma. The remaining mice underwent multiple matings to assess pregnancy rates and litter sizes. The DOR and POI mice showed an impaired estrous cyclicity and a decrease in ovarian mass, number of follicles, Metaphase II (MII) oocytes, and embryos as well as in ovarian stroma vascularization. Mice in both models showed also an increase in the percentage of morphologically abnormal follicles, stromal degeneration, and apoptosis. Similar to that observed in DOR and POI patients, these impairments were less severe in DOR than in POI mice. None of the POI females were able to achieve a pregnancy. Meanwhile, DOR females achieved several consecutive pregnancies, although litter size was decreased when compared to controls. In conclusion, a mouse model which displayed most of the ovarian characteristics and fertility outcomes of women with DOR has been established using a single dose of chemotherapy.

Aryl Hydrocarbon Receptor (AHR) Ligands as Selective AHR Modulators (SAhRMs)

The aryl hydrocarbon receptor (AhR) was first identified as the intracellular protein that bound and mediated the toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) and dioxin-like compounds (DLCs). Subsequent studies show that the AhR plays an important role in maintaining cellular homeostasis and in pathophysiology, and there is increasing evidence that the AhR is an important drug target. The AhR binds structurally diverse compounds, including pharmaceuticals, phytochemicals and endogenous biochemicals, some of which may serve as endogenous ligands. Classification of DLCs and non-DLCs based on their persistence (metabolism), toxicities, binding to wild-type/mutant AhR and structural similarities have been reported. This review provides data suggesting that ligands for the AhR are selective AhR modulators (SAhRMs) that exhibit tissue/cell-specific AhR agonist and antagonist activities, and that their functional diversity is similar to selective receptor modulators that target steroid hormone and other nuclear receptors.

Ah receptor ligands and their impacts on gut resilience: structure-activity effects

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD, dioxin) and structurally related halogenated aromatics modulate gene expression and induce biochemical and toxic responses that are mediated by initial binding to the aryl hydrocarbon receptor (AhR). The AhR also binds structurally diverse compound including pharmaceuticals, endogenous biochemicals, health-promoting phytochemicals, and microbial metabolites. Many of these AhR ligands do not induce TCDD-like toxic responses and some AhR ligands such as microbial metabolites of tryptophan play a role in maintaining gut health and protecting against intestinal inflammation and cancer. Many AhR ligands exhibit tissue- and response-specific AhR agonist or antagonist activities, and act as selective AhR modulators (SAhRMs) and this SAhRM-like activity has also been observed in AhR-ligand-mediated effects in the intestine. This review summarizes studies showing that several AhR ligands including phytochemicals and TCDD protect against dextran sodium sulfate-induced intestinal inflammation. In contrast, AhR ligands such as oxazole compounds enhance intestinal inflammation suggesting that AhR-mediated gut health can be enhanced or decreased by selective AhR modulators and this needs to be considered in development of AhR ligands for therapeutic applications in treating intestinal inflammation.

Regulation of the aryl hydrocarbon receptor activity in bovine cumulus-oocyte complexes during in vitro maturation: The role of EGFR and post-EGFR ERK1/2 signaling cascade

The aryl hydrocarbon receptor (AhR) has been extensively characterized as an environmental sensor with major roles in xenobiotic-induced toxicity. Evidence is accumulating that these functions serve as adaptive mechanisms overlapping its physiological roles. We previously described a critical role of constitutive AhR activation for the correct progress of mammalian oocyte maturation but the signaling pathway through which AhR controls maturation remains unclear. The aim of this study was to investigate whether the AhR interacts with the epidermal growth factor receptor (EGFR) and p42/44 extracellular regulated kinases (ERK1/2), both key factors in the signaling network that finely regulates the oocyte maturation. As experimental model we used bovine cumulus-oocyte complexes (COCs) during in vitro maturation (IVM). Blocking ERK1/2 signaling in COCs during IVM with the specific EGFR inhibitor AG1478 or the mitogen-activated protein kinase kinase (MEK) inhibitor PD98059 downregulated the expression of the AhR-target gene Cyp1a1. Inhibition of AhR activity was associated with a reduction in the oocytes' ability to progress in meiosis resumption. In contrast, exposure to the AhR antagonist resveratrol reduced both CYP1A1 expression and the oocytes' maturation competence, without affecting ERK1/2 signaling. These findings strongly indicate the EGFR/ERKs signaling network as an upstream regulator of the AhR activation in COCs, offering a new understanding of the finely tuned physiological mechanism leading to oocyte maturation. This information may provide fresh opportunities for improving oocyte in vitro maturation, and therefore boosting the efficiency of assisted reproduction techniques in mammals.

FSH/LH-Dependent Upregulation of Ahr in Murine Granulosa Cells Is Controlled by PKA Signaling and Involves Epigenetic Regulation

The aryl hydrocarbon receptor (Ahr) is a ligand-activated transcription factor primarily known for its toxicological functions. Recent studies have established its importance in many physiological processes including female reproduction, although there is limited data about the precise mechanisms how Ahr itself is regulated during ovarian follicle maturation. This study describes the expression of Ahr in ovarian granulosa cells (GCs) of immature mice in a gonadotropin-dependent manner. We show that Ahr upregulation in vivo requires both follicle stimulating hormone (FSH) and luteinizing hormone (LH) activities. FSH alone increased Ahr mRNA, but had no effect on Ahr protein level, implicating a possible LH-dependent post-transcriptional regulation. Also, the increase in Ahr protein is specific to large antral follicles in induced follicle maturation. We show that Ahr expression in GCs of mid-phase follicular maturation is downregulated by protein kinase A (PKA) signaling and activation of Ahr promoter is regulated by chromatin remodeling.

Correlation of the Aryl Hydrocarbon Receptor with FSHR in Ovarian Cancer Patients

Expression of the aryl hydrocarbon receptor (AhR) has been described in various tumor entities from different organs. However, its role in ovarian cancer has not been thoroughly investigated. We aimed to elucidate the prognostic impact of AhR, its correlation with the follicle-stimulating hormone receptor (FSHR), and their functional role in ovarian cancer. By immunohistochemistry, AhR staining was analyzed in a subset of 156 samples of ovarian cancer patients. AhR staining was assessed in the nucleus and the cytoplasm using the semi-quantitative immunoreactive score (IRS), and the scores were grouped into high- and low-level expression. AhR expression was detected in all histological subtypes, with clear cell ovarian cancer displaying the highest staining intensity. Low cytoplasmic expression of AhR was associated with longer overall survival (median 183.46 vs. 85.07 months; p = 0.021). We found a positive correlation between AhR and FSHR (p = 0.005). Ovarian cancer patients with high cytoplasmic AhR and concurrent FSHR expression had the worst outcome (median 69.72 vs. 43.32 months; p = 0.043). Consequently, low cytoplasmic AhR expression seems to be associated with improved survival in ovarian cancer patients. Our data suggest that AhR and FSHR levels correlate with each other, and their concurrent expression was observed in ovarian cancer patients with the worst outcome. Further investigation of the interaction of both receptors and their functional role might better predict the impact of endocrine therapy in ovarian cancer.

Diminished Ovarian Reserve Chemotherapy-Induced Mouse Model: A Tool for the Preclinical Assessment of New Therapies for Ovarian Damage

Diminished ovarian reserve (DOR) and primary ovarian insufficiency (POI) are primary factors leading to infertility. However, there is a lack of appropriate animal models of DOR usable for assessing new therapeutic strategies. In this study, we aimed to evaluate whether chemotherapy treatment in mice could reproduce features similar of that observed in women with DOR. Twenty-one Nonobese diabetic/severe combined immunodeficiency (NOD/SCID) female mice were allocated to 3 groups (n = 7/group): control, single dose of vehicle (Dimethyl Sulfoxide [DMSO]); DOR, single reduced chemotherapy dose; and POI, single standard chemotherapy dose. After 21 days, mice underwent ovarian hyperstimulation and mating. Part of the animals were harvested to analyze ovarian reserve, ovulation and fertilization rates, and morphology, apoptosis, and vascularization of the ovarian stroma. The remaining mice underwent multiple matings to assess pregnancy rates and litter sizes. The DOR and POI mice showed an impaired estrous cyclicity and a decrease in ovarian mass, number of follicles, Metaphase II (MII) oocytes, and embryos as well as in ovarian stroma vascularization. Mice in both models showed also an increase in the percentage of morphologically abnormal follicles, stromal degeneration, and apoptosis. Similar to that observed in DOR and POI patients, these impairments were less severe in DOR than in POI mice. None of the POI females were able to achieve a pregnancy. Meanwhile, DOR females achieved several consecutive pregnancies, although litter size was decreased when compared to controls. In conclusion, a mouse model which displayed most of the ovarian characteristics and fertility outcomes of women with DOR has been established using a single dose of chemotherapy.

Aryl Hydrocarbon Receptor (AhR) Ligands as Selective AhR Modulators: Genomic Studies

The aryl hydrocarbon receptor (AhR) binds structurally diverse ligands that vary from the environmental toxicant 2,3,7,8-tetrachlorodibenzo-B-dioxin (TCDD) to AhR- active pharmaceuticals and health-promoting phytochemicals. There are remarkable differences in the toxicity of TCDD and related halogenated aromatics (HAs) vs. health promoting AhR ligands, and genomic analysis shows that even among the toxic HAs, there are differences in their regulation of genes and pathways. Thus, like ligands for other receptors, AhR ligands are selective AhR modulators (SAhRMs) which exhibit variable tissue-, organ- and species-specific genomic and functional activities.

Prenatal Exposure to Di(2-Ethylhexyl) Phthalate Causes Long-Term Transgenerational Effects on Female Reproduction in Mice

Di(2-ethylhexyl) phthalate (DEHP) is a plasticizer in many consumer products. Although DEHP is a known endocrine disruptor, little is known about the effects of DEHP exposure on female reproduction. Thus, this study tested the hypothesis that prenatal DEHP exposure affects follicle numbers, estrous cyclicity, and hormone levels in multiple generations of mice. Pregnant CD-1 mice were orally dosed with corn oil (vehicle control) or DEHP (20 and 200 µg/kg/d and 500 and 750 mg/kg/d) from gestational day 11 until birth. The F1 females were mated with untreated males to create the F2 generation, and the F2 females were mated with untreated males to create the F3 generation. At 1 year, ovaries, hormones, and estrous cycles were analyzed in each generation. Prenatal DEHP exposure altered estrous cyclicity (750 mg/kg/d), increased the presence of ovarian cysts (750 mg/kg/d), and decreased total follicle numbers (750 mg/kg/d) in the F1 generation. It also decreased anogenital distance (200 µg/kg/d) and altered follicle numbers (200 µg/kg/d and 500 mg/kg/d) in the F2 generation, and it altered estrous cyclicity (20 and 200 µg/kg/d and 500 and 750 mg/kg/d) and decreased folliculogenesis (200 µg/kg/d and 500 mg/kg/d) in the F3 generation. Further, prenatal DEHP increased estradiol levels (F1 and F3), decreased testosterone levels (F1, F2, and F3), decreased progesterone levels (F2), altered gonadotropin hormone levels (F1 and F3), and decreased inhibin B levels (F1 and F3). Collectively, these data show that prenatal exposure to DEHP has multigenerational and transgenerational effects on female reproduction and it may accelerate reproductive aging.

piRNA-associated proteins and retrotransposons are differentially expressed in murine testis and ovary of aryl hydrocarbon receptor deficient mice

Previous studies suggested that the aryl hydrocarbon receptor (AhR) contributes to mice reproduction and fertility. However, the mechanisms involved remain mostly unknown. Retrotransposon silencing by Piwi-interacting RNAs (piRNAs) is essential for germ cell maturation and, remarkably, AhR has been identified as a regulator of murine B1-SINE retrotransposons. Here, using littermate AhR^+/+ and AhR^−/− mice, we report that AhR regulates the general course of spermatogenesis and oogenesis by a mechanism likely to be associated with piRNA-associated proteins, piRNAs and retrotransposons. piRNA-associated proteins MVH and Miwi are upregulated in leptotene to pachytene spermatocytes with a more precocious timing in AhR^−/− than in AhR^+/+ testes. piRNAs and transcripts from B1-SINE, LINE-1 and IAP retrotransposons increased at these meiotic stages in AhR-null testes. Moreover, B1-SINE transcripts colocalize with MVH and Miwi in leptonema and pachynema spermatocytes. Unexpectedly, AhR^−/− males have increased sperm counts, higher sperm functionality and enhanced fertility than AhR^+/+ mice. In contrast, piRNA-associated proteins and B1-SINE and IAP-derived transcripts are reduced in adult AhR^−/− ovaries. Accordingly, AhR-null female mice have lower numbers of follicles when compared with AhR^+/+ mice. Thus, AhR deficiency differentially affects testis and ovary development possibly by a process involving piRNA-associated proteins, piRNAs and transposable elements.

Resveratrol supports and alpha-naphthoflavone disrupts growth of human ovarian follicles in an in vitro tissue culture model

Infertility is a global health problem with an estimated incidence of 15%. Exposure to chemicals is a potential causal factor, and there is a lack of studies examining the effects on female germ cells. Here, we have studied the impact of different aryl hydrocarbon receptor (AHR) modulators on human ovarian follicles using a human ovarian tissue culture model. Expression of AHR was analyzed in tissue samples, and effects of the selected ligands resveratrol (RSVL), 6-formylindolo(3,2-b)carbazole (FICZ), and alpha-naphthoflavone (aNF) on AHR transactivation studied in a granulosa cell tumor line. Cortical human ovarian tissue containing preantral follicles was exposed to the ligands or vehicle (dimethylsulfoxide, DMSO) for seven days in vitro. Follicle growth was assessed by counting and measuring follicles from serial tissue sections, cell death quantified using in situ Terminal deoxynucleotidyl transferase dUTP Nick-End Labeling (TUNEL) assay, and steroid hormone production measured using a newly developed ultra-performance liquid chromatography method. AHR was expressed in all donated ovarian tissue samples. FICZ induced AHR transactivation in the granulosa cell line while aNF antagonised it. Compared to DMSO control, FICZ had no effect on follicles in culture, RSVL increased the proportion of growing follicles, and aNF increased cell death, disrupted growth of secondary follicles, increased testosterone, and reduced estradiol levels. We conclude that RSVL supports and aNF disrupts growth of human ovarian follicles in culture. We further conclude that the human ovarian tissue culture model is suitable for studying effects of chemicals on follicular biology.

Changes in the expression of genes involved in the ovarian function of rats caused by daily exposure to 3-methylcholanthrene and their prevention by α-naphthoflavone

Daily exposure to low doses of 3-methylcholanthrene (3MC) during the pubertal period in rats disrupts both follicular growth and ovulation. Thus, to provide new insights into the toxicity mechanism of 3MC in the ovary, here we investigated the effect of daily exposure to 3MC on selected ovarian genes, the role of the aryl hydrocarbon receptor (AhR) and the level of epigenetic remodeling of histone post-transcriptional modifications. Immature rats were daily injected with 3MC (0.1 or 1 mg/kg) and mRNA expression of genes involved in different ovarian processes were evaluated. Of the 29 genes studied, 18 were up-regulated, five were down-regulated and six were not altered. To assess whether AhR was involved in these changes, we used the chromatin immunoprecipitation assay. 3MC increased AhR binding to promoter regions of genes involved in Notch signaling (Hes1, Jag1), activation of primordial follicles (Cdk2), cell adhesion (Icam1), stress and tumor progression (Dnajb6), apoptosis (Bax, Caspase-9) and expression of growth and transcription factors (Igf2, Sp1). Studying the trimethylation and acetylation of histone 3 (H3K4me3 and H3K9Ac, respectively) of these genes, we found that 3MC increased H3K4me3 in Cyp1a1, Jag1, Dnajb6, Igf2, Notch2, Adamts1, Bax and Caspase-9, and H3K9Ac in Cyp1a1, Jag1, Cdk2, Dnajb6, Igf2, Icam1, and Sp1. Co-treatment with α-naphthoflavone (αNF), a specific antagonist of AhR, prevented almost every 3MC-induced changes. Despite the low dose used in these experiments, daily exposure to 3MC induced changes in both gene expression and epigenomic remodeling, which may lead to premature ovarian failure.

Role of AhR in positive regulation of cell proliferation and survival

The aryl hydrocarbon receptor (AhR) is an important nuclear transcription factor that is best known for mediating toxic responses by adjusting numbers of metabolism-related enzymes, including CYP1A1 and CYP1B1. Previous findings have revealed that, in addition to negatively regulating cell proliferation and survival, AhR may also positively regulate these pathways. Here, we review these findings and summarize distinct mechanisms by which AhR promotes cell proliferation and survival, including modulation of receptor expression, growth factor signalling and apoptosis, regulating the cell cycle and promoting cytokine expression. This review will aid better understanding the role of AhR in positive regulation of cell proliferation and survival.

Loss of Fertility in the Absence of Progesterone Receptor Expression in Kisspeptin Neurons of Female Mice

Ovarian steroids, estradiol and progesterone, play central roles in regulating female reproduction by acting as both positive and negative regulators of gonadotropin-releasing hormone (GnRH) secretion in the hypothalamus. Recent studies have identified kisspeptin neurons of the hypothalamus as the target of estrogenic regulation of GnRH secretion. In this study, we aimed to determine the significance of progesterone receptor (PGR) expression in the kisspeptin neurons. To this end, the Pgr gene was selectively ablated in mouse kisspeptin neurons and the reproductive consequence assessed. The hypothalamus of the Pgr deficient female mouse expressed kisspeptin, the pituitary released LH in response to GnRH stimulation, and the ovary ovulated when stimulated with gonadotropins. However, the mutant mouse gradually lost cyclicity, was unable to generate a LH surge in response to rising estradiol, and eventually became infertile. Taken together, these results indicate that the loss of PGR impairs kisspeptin secretory machinery and therefore that PGR plays a critical role in regulating kisspeptin secretion.

The systemic and gonadal toxicity of 3-methylcholanthrene is prevented by daily administration of α-naphthoflavone

In the present study, we investigated the effect of 3-methylcholanthrene (3MC) on sexual maturity and the ability of α-naphthoflavone (αNF) to prevent this action. To this end, immature rats were daily injected intraperitoneally with 3MC (0.1 or 1mg/kg) and/or αNF (80mg/kg). Body weight, vaginal opening and estrous cycle were recorded and ovaries were obtained on the day of estrus. Ovarian weight, ovulation rate (measured by the number of oocytes within oviducts), and follicular development (determined by histology) were studied. No differences were found in body weight, ovarian weight, day of vaginal opening, or the establishment of the estrous cycle among the different groups of rats. However, animals treated with 3MC, at both doses, exhibited a lower number of primordial, primary, preantral and antral follicles than controls. Also, 3MC inhibited the ovulation rate and induced an overexpression of both the Cyp1a1 and Cyp1b1 genes, measured by chromatin immunoprecipitation assay. The daily treatment with αNF alone increased the number of follicles in most of the stages analyzed when compared with controls. Moreover, the αNF treatment prevented completely not only the 3MC-induced decrease in all types of follicles but also the 3MC-induced overexpression of Cyp enzymes and the genetic damage in bone marrow cells and oocytes. These results suggest that (i) daily exposure to 3MC during the pubertal period destroys the follicle reserve and alters the ovulation rate; (ii) the 3MC action seems to be mediated by an aryl hydrocarbon receptor-dependent mechanism; (iii) daily administration of αNF has a clear stimulatory action on the ovarian function; and (iv) αNF may prevent both the systemic and gonadal 3MC-induced toxicity.

Exposure to bisphenol A in young adult mice does not alter ovulation but does alter the fertilization ability of oocytes

Follicle growth culminates in ovulation, which allows for the expulsion of fertilizable oocytes and the formation of corpora lutea. Bisphenol A (BPA) is present in many consumer products, and it has been suggested that BPA impairs ovulation; however, the underlying mechanisms are unknown. Therefore, this study first evaluated whether BPA alters ovulation by affecting folliculogenesis, the number of corpora lutea or eggs shed to the oviduct, ovarian gonadotropin responsiveness, hormone levels, and estrous cyclicity. Because it has been suggested (but not directly confirmed) that BPA exerts toxic effects on the fertilization ability of oocytes, a second aim was to evaluate whether BPA impacts the oocyte fertilization rate using an in vitro fertilization assay and mating. The possible effects on early zygote development were also examined. Young adult female C57BL/6J mice (39 days old) were orally dosed with corn oil (vehicle) or 50 μg/kgbw/day BPA for a period encompassing the first three reproductive cycles (12-15 days). BPA exposure did not alter any parameters related to ovulation. Moreover, BPA exposure reduced the percentage of fertilized oocytes after either in vitro fertilization or mating, but it did not alter the zygotic stages. The data indicate that exposure to the reference dose of BPA does not impact ovulation but that it does influence the oocyte quality in terms of its fertilization ability.

Growth Hormone Ameliorates the Radiotherapy-Induced Ovarian Follicular Loss in Rats: Impact on Oxidative Stress, Apoptosis and IGF-1/IGF-1R Axis

Radiotherapy is one of the standard cytotoxic therapies for cancer. However, it has a profound impact on ovarian function leading to premature ovarian failure and infertility. Since none of the currently available methods for fertility preservation guarantees future fertility, the need for an effective radioprotective agent is highly intensified. The present study investigated the mechanisms of the potential radioprotective effect of growth hormone (GH) on γ irradiation-induced ovarian failure and the impact of the insulin like growth factor 1 (IGF-1) in the underlying protection. Immature female Sprague-Dawley rats were either exposed to single whole body irradiation (3.2 Gy) and/or treated with GH (1 mg/kg s.c). Experimental γ-irradiation produced an array of ovarian dysfunction that was evident by assessment of hormonal changes, follicular development, proliferation marker (PCNA), oxidative stress as well as apoptotic markers. In addition, IGF-1/IGF-1R axis expression was assessed using real-time PCR and immunolocalization techniques. Furthermore, after full maturity, fertility assessment was performed. GH significantly enhanced follicular development and restored anti-Mullerian hormone serum level as compared with the irradiated group. In addition, GH significantly ameliorated the deleterious effects of irradiation on oxidative status, PCNA and apoptosis. Interestingly, GH was shown to enhance the ovarian IGF-1 at transcription and translation levels, a property that contributes significantly to its radioprotective effect. Finally, GH regained the fertility that was lost following irradiation. In conclusion, GH showed a radioprotective effect and rescued the ovarian reserve through increasing local IGF-1 level and counteracting the oxidative stress-mediated apoptosis.

Prenatal exposure to di-(2-ethylhexyl) phthalate (DEHP) affects reproductive outcomes in female mice

This study tested the hypothesis that prenatal DEHP exposure affects female reproduction. To test this hypothesis, pregnant female CD-1 mice were orally dosed daily with tocopherol-stripped corn oil (vehicle control) or DEHP (20 μg/kg/day-750 mg/kg/day) from gestation day 11-birth. Pups were counted, weighed, and sexed at birth, ovaries were subjected to evaluations of follicle numbers on postnatal days (PNDs) 8 and 21, and fertility was evaluated at 3-9 months. The results indicate that prenatal DEHP exposure increased male-to-female ratio compared to controls. Prenatal DEHP exposure also increased preantral follicle numbers at PND 21 compared to controls. Further, 22.2% of the 20 μg/kg/day treated animals took longer than 5 days to get pregnant at 3 months and 28.6% of the 750 mg/kg/day treated animals lost some of their pups at 6 months. Thus, prenatal DEHP exposure alters F1 sex ratio, increases preantral follicle numbers, and causes some breeding abnormalities.

In vitro re-expression of the aryl hydrocarbon receptor (Ahr) in cultured Ahr-deficient mouse antral follicles partially restores the phenotype to that of cultured wild-type mouse follicles

BACKGROUND

The aryl hydrocarbon receptor (AHR) mediates the toxic effects of various endocrine disrupting chemicals. In female mice, global deletion of the Ahr (AhrKO) results in slow growth of ovarian antral follicles. No studies, however, have examined whether injection of the Ahr restores the phenotypes of cultured AhrKO ovarian antral follicles to wild-type levels.

METHODS

We developed a system to construct a recombinant adenovirus containing the Ahr to re-express the Ahr in AhrKO granulosa cells and whole antral follicles. We then compared follicle growth and levels of factors in the AHR signaling pathway (Ahr, Ahrr, Cyp1a1, and Cyp1b1) in wild-type, AhrKO, and Ahr re-expressed follicles. Further, we compared the response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in wild-type, AhrKO, and Ahr re-expressed follicles.

RESULTS

Ahr injection into AhrKO follicles partially restored their growth pattern to wild-type levels. Further, Ahr re-expressed follicles had significantly higher levels of Ahr, Ahrr, Cyp1a1, and Cyp1b1 compared to wild-type follicles. Upon TCDD treatment, only Cyp1a1 levels were significantly higher in Ahr re-expressed follicles compared to the levels in wild-type follicles.

CONCLUSION

Our system of re-expression of the Ahr partially restores follicle growth and transcript levels of factors in the AHR signaling pathway to wild-type levels.

Effects of the environmental contaminants DEHP and TCDD on estradiol synthesis and aryl hydrocarbon receptor and peroxisome proliferator-activated receptor signalling in the human granulosa cell line KGN

Environmental contaminants binding to transcription factors, such as the aryl hydrocarbon receptor (AhR) and the alpha and gamma peroxisome proliferator-activated receptors (PPARs), contribute to adverse effects on the reproductive system. Expressing both the AhR and PPARs, the human granulosa cell line KGN offers the opportunity to investigate the regulatory mechanisms involved in receptor crosstalk, independent of overriding hormonal control. The aim of the present study was to investigate the impact of two environmental contaminants, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, an AhR ligand) and di-(2-ethylhexyl) phthalate (DEHP, a PPAR ligand), on gonadotrophin sensitivity and estrogen synthesis in KGN cells. Accumulation of the DEHP metabolite mono-(2-ethylhexyl) phthalate (MEHP) in DEHP-exposed cells was measured by high-performance liquid chromatography mass spectrometry, thereby demonstrating DEHP metabolism to MEHP by KGN cells. By employing TCDD ( an AhR agonist), rosiglitazone (a PPARgamma agonist) or bezafibrate (a PPARalpha agonist), the presence of a functional AhR and PPAR cascade was confirmed in KGN cells. Cytotoxicity testing revealed no effect on KGN cell proliferation for the concentrations of TCDD and DEHP used in the current study. FSH-stimulated cells were exposed to TCDD, DEHP or a mix of both and estradiol synthesis was measured by enzyme-linked immunosorbent assay and gene expression by quantitative RT-PCR. Exposure decreased estradiol synthesis (TCDD, DEHP, mix) and reduced the mRNA expression of CYP19 aromatase (DEHP, mix) and FSHR (DEHP). DEHP induced the expression of the alpha and gamma PPARs and AhR, an effect which was inhibited by selective PPAR antagonists. Studies in the human granulosa cell line KGN show that the action of endocrine-disrupting chemicals may be due to a direct activation of AhR, for example by TCDD, and by a transactivation via PPARs, for example by DEHP, inducing subsequent transcriptional changes with a broad range of effects on granulosa cell function.

Impact of obesity on ovotoxicity induced by 7,12-dimethylbenz[a]anthracene in mice

Insulin, elevated during obesity, regulates xenobiotic biotransformation enzymes, potentially through phosphatidylinositol 3-kinase (PI3K) signaling, in extraovarian tissues. PI3K regulates oocyte viability, follicular activation, and ovarian chemical biotransformation. 7,12-Dimethylbenz[a]anthracene (DMBA), a carcinogen and ovotoxicant, destroys all stages of follicles, leading to premature ovarian failure. Obesity has been reported to promote DMBA-induced tumors, but it remains unknown whether obesity affects ovarian xenobiotic metabolism. Therefore, we investigated ovarian expression of xenobiotic metabolism genes-microsomal epoxide hydrolase (Ephx1), glutathione S-transferase (GST) class Pi (Gstp1) and class mu 1 (Gstm1), and PI3K-signaling members (protein kinase B [AKT] alpha [Akt1], beta [Akt2], and the forkhead transcription factor subfamily 3 [Foxo3])-in lean and obese female mice after DMBA exposure (1 mg/kg; intraperitoneal injection for 14 days). Relative to lean, obese mice had decreased (P < 0.05) healthy primordial and primary follicle numbers but increased (P < 0.05) secondary and preovulatory follicles numbers. Obesity increased (P < 0.05) Akt1, Akt2, Gstm1, and Ephx1 mRNA and pAKT(Ser473/Thr308), GSTM1, GSTP1, and EPHX1 protein levels. DMBA decreased (P < 0.05) ovarian weight in lean and obese mice, however, obese DMBA-treated females had a greater reduction (P < 0.05) in ovarian weight. In both lean and obese mice, DMBA decreased (P < 0.05) all stages of healthy follicle numbers, increased Gstp1 and Ephx1 mRNA as well as GSTM1, GSTP1, and EPHX1 protein levels, and decreased Akt1 and Akt2 mRNA as well as pAKT(Ser473) or pAKT(Thr308), FOXO3, and pFOXO3(Ser253) protein expression. There was an additive effect between obesity and DMBA exposure for increased Gstm1 and Ephx1 mRNA as well as GSTM1 and EPHX1 protein expression.

Transcriptional repression of the Ahr gene by LHCGR signaling in preovulatory granulosa cells is controlled by chromatin accessibility

Recent advances in establishing the role of the aryl hydrocarbon receptor (Ahr) in normophysiology have discovered its fundamental role, amongst others, in female reproduction. Considering previous studies suggesting the hormonal modulation of Ahr, we aimed to investigate whether in murine granulosa cells (GCs) the gonadotropins regulate Ahr expression and how this is mechanistically implemented. We found that the FSH-like substance--pregnant mare serum gonadotropin--led to stimulation of Ahr expression. More importantly hCG produced relatively rapid reduction of Ahr mRNA in GCs of preovulatory follicles. We show for the first time that LHCGR signaling in regulating the Ahr message involves protein kinase A pathway and is attributable to decreased transcription rate. Finally, we found that Ahr promoter accessibility was decreased by hCG, implicating chromatin remodeling in Ahr gene regulation by LH.

Insights into the protective mechanisms of tamoxifen in radiotherapy-induced ovarian follicular loss: impact on insulin-like growth factor 1

Radiotherapy is one of the most common and effective cancer treatments. However, it has a profound impact on ovarian function, leading to premature ovarian failure. With the hope of preserving fertility in cancer survivors, the need for an effective radioprotective therapy is evident. The present study investigated the mechanism of the potential radioprotective effect of tamoxifen (TAM) on γ-irradiation-induced ovarian failure on experimental rats and the impact of the IGF-1 in the underlying protective mechanisms. Female Sprague Dawley rats were either exposed to single whole-body irradiation (3.2 Gy; lethal dose [LD₂₀]) and/or treated with TAM (1 mg/kg). γ-Irradiation caused an array of ovarian dysfunction that was evident by assessment of hormonal changes, follicular development, proliferation marker (proliferating cell nuclear antigen), and oxidative stress as well as apoptotic markers. In addition, IGF-1/IGF-1 receptor axis expression was assessed using real-time RT-PCR and immunolocalization techniques. Furthermore, fertility assessment was performed. TAM significantly enhanced follicular development and restored the anti-Mullerian hormone level. Moreover, it ameliorated the deleterious effects of irradiation on oxidative stress, proliferating cell nuclear antigen expression, and apoptosis. Interestingly, TAM was shown to enhance the ovarian IGF-1 but not IGF-1 receptor, a property that contributed significantly to its radioprotective mechanisms. Finally, TAM regained the fertility that was lost after irradiation. In conclusion, TAM showed a radioprotective effect and saved the ovarian reserve and fertility through increasing anti-Mullerian hormone and the local IGF-1 level and counteracting the oxidative stress-mediated apoptosis.

Role of the aryl hydrocarbon receptor in carcinogenesis and potential as a drug target

The aryl hydrocarbon receptor (AHR) is highly expressed in multiple organs and tissues, and there is increasing evidence that the AHR plays an important role in cellular homeostasis and disease. The AHR is expressed in multiple tumor types, in cancer cell lines, and in tumors from animal models, and the function of the AHR has been determined by RNA interference, overexpression, and inhibition studies. With few exceptions, knockdown of the AHR resulted in decreased proliferation and/or invasion and migration of cancer cell lines, and in vivo studies in mice overexpressing the constitutively active AHR exhibited enhanced stomach and liver cancers, suggesting a pro-oncogenic role for the AHR. In contrast, loss of the AHR in transgenic mice that spontaneously develop colonic tumors and in carcinogen-induced liver tumors resulted in increased carcinogenesis, suggesting that the receptor may exhibit antitumorigenic activity prior to tumor formation. AHR ligands also either enhanced or inhibited tumorigenesis, and these effects were highly tumor specific, demonstrating that selective AHR modulators that exhibit agonist or antagonist activities represent an important new class of anticancer agents that can be directed against multiple tumors.

The cigarette smoke constituent benzo[a]pyrene disrupts metabolic enzyme, and apoptosis pathway member gene expression in ovarian follicles

Benzo[a]pyrene (B[a]P) is a prototypical polycyclic aromatic hydrocarbon (PAH) present in cigarette smoke. We previously showed that B[a]P adversely affects follicular development and survival. The objective of this study was to identify the key molecular pathways underlying B[a]P-induced abnormal follicular development. Isolated follicles (100-130 μm) from ovaries of F1 hybrid (C57BL/6j×CBA/Ca) mice were cultured for 8 (preantral/antral follicles) and 12 (preovulatory follicles) days in increasing concentrations of B[a]P (0 ng/mL [control] to 45 ng/mL). Expression of aryl hydrocarbon receptor (AhR), aryl hydroxylase steroidogenic enzyme, cell-cycle, and apoptotic genes were quantified. B[a]P exposure significantly (P<0.05) increased mRNA expression of Cyp1a1 in preantral/antral follicles and Cyp1b1, Bax and Hsp90ab1 in preovulatory follicles. No significant effect on mRNA expression of StAR, Cyp11a1, aromatase, Cdk4, Cdk2, Ccnd2, cIAP2, and survivin was observed. In conclusion, this study suggests that B[a]P exposure significantly affects the phase I enzymes and cell death genes during preantral/antral and preovulatory growth, and thus highlight the AhR signaling and apoptotis pathways in delayed follicle growth and decreased viability.

Knockout of the aryl hydrocarbon receptor results in distinct hepatic and renal phenotypes in rats and mice

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor which plays a role in the development of multiple tissues and is activated by a large number of ligands, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In order to examine the roles of the AHR in both normal biological development and response to environmental chemicals, an AHR knockout (AHR-KO) rat model was created and compared with an existing AHR-KO mouse. AHR-KO rats harboring either 2-bp or 29-bp deletion mutation in exon 2 of the AHR were created on the Sprague-Dawley genetic background using zinc-finger nuclease (ZFN) technology. Rats harboring either mutation type lacked expression of AHR protein in the liver. AHR-KO rats were also insensitive to thymic involution, increased hepatic weight and the induction of AHR-responsive genes (Cyp1a1, Cyp1a2, Cyp1b1, Ahrr) following acute exposure to 25 μg/kg TCDD. AHR-KO rats had lower basal expression of transcripts for these genes and also accumulated ~30-45-fold less TCDD in the liver at 7 days post-exposure. In untreated animals, AHR-KO mice, but not AHR-KO rats, had alterations in serum analytes indicative of compromised hepatic function, patent ductus venosus of the liver and persistent hyaloid arteries in the eye. AHR-KO rats, but not AHR-KO mice, displayed pathological alterations to the urinary tract: bilateral renal dilation (hydronephrosis), secondary medullary tubular and uroepithelial degenerative changes and bilateral ureter dilation (hydroureter). The present data indicate that the AHR may play significantly different roles in tissue development and homeostasis and toxicity across rodent species.

Follicle-stimulating hormone responsiveness in antral follicles from aryl hydrocarbon receptor knockout mice

BACKGROUND

Previous studies have demonstrated that pre-pubertal aryl hydrocarbon receptor knockout (AHRKO) mice have slow antral follicle growth and reduced capacity to produce estradiol compared to wild-type (WT) mice. Although previous studies have suggested that this is likely due to a reduced ability of the AHRKO follicles to respond to follicle-stimulating hormone (FSH), this possibility was not directly tested. Thus, the goal of these studies was to test the hypothesis that low FSH responsiveness is responsible for the slow growth and reduced estradiol production observed in pre-pubertal AHRKO versus WT antral follicles.

METHODS

Antral follicles from WT and AHRKO mice were cultured with varying amounts of FSH (0-15 IU/mL) for up to 7 days, and subjected to measurements of growth, FSH receptor and steroidogenic regulator expression, sex steroid hormone levels, and inhibin beta-A expression. General linear models (GLM) for repeated measures were used to compare follicle diameters over time among treatments. If the global tests from GLM were significant, Tukey's tests were used for pairwise comparisons. Remaining comparisons among groups were performed using one-way analysis of variance followed by Tukey's post hoc test.

RESULTS

The results indicate that FSH stimulated growth in both WT and AHRKO follicles, but that high levels of FSH (10-15 IU/mL) were required for AHRKO follicles to reach maximal growth, whereas lower levels of FSH (5 IU/mL) were required for WT follicles to reach maximal growth. Further, FSH stimulated expression of FSH receptor, steroidogenic factors, and inhibin beta-A as well as production of steroid hormones in both WT and AHRKO follicles, but the degree of stimulation differed between WT and AHRKO follicles. Interestingly, FSH treatment increased expression of FSH receptor, some steroidogenic regulators, inhibin beta-A, and steroid hormone production more in AHRKO follicles compared to WT follicles.

CONCLUSIONS

Collectively, these data suggest that the slow growth, but not reduced steroidogenesis in AHRKO follicles, is due to their reduced ability to respond to FSH compared to WT follicles. These data also suggest that the AHR may contribute to the ability of FSH to stimulate proper follicle growth, but it may not contribute to FSH-induced steroidogenesis.

Endocrine disruptive actions of inhaled benzo(a)pyrene on ovarian function and fetal survival in fisher F-344 adult rats

This study evaluated the effect of inhaled BaP on female reproductive function. Rats were exposed to 50, or 75 or 100 μg BaP/m(3), 4 h a day for 14 days via inhalation. Plasma E(2), P(4), LH and FSH concentrations were determined. Ovarian BaP metabolism and aryl hydrocarbon hydrolase (AHH) activity at proestrus were determined and fertility evaluations were conducted. Ovulation rate and number of pups/litter were reduced in rats exposed to 100 μg BaP/m(3) compared with other treatment and control groups. Plasma concentrations of E(2), and LH were significantly reduced at proestrus in BaP-exposed versus those of controls whereas those of P(4) were significantly reduced at diestrus I. The activity of AHH in ovarian and liver tissues and concentrations of BaP 7,8-diol and BaP 3,6-dione metabolites increased in an exposure concentration-dependent manner. These data suggest that exposure of rats to BaP prior to mating contributes to reduced ovarian function and fetal survival.

Aryl-hydrocarbon receptor activity modulates prolactin expression in the pituitary

Pituitary tumors account for 15% of intracranial neoplasms, however the extent to which environmental toxicants contribute to the proliferation and hormone expression of pituitary cells is unknown. Aryl-hydrocarbon receptor (AhR) interacting protein (AIP) loss of function mutations cause somatotrope and lactotrope adenomas in humans. AIP sequesters AhR and inhibits its transcriptional function. Because of the link between AIP and pituitary tumors, we hypothesize that exposure to dioxins, potent exogenous ligands for AhR that are persistent in the environment, may predispose to pituitary dysfunction through activation of AhR. In the present study, we examined the effect of AhR activation on proliferation and endogenous pituitary hormone expression in the GH3 rat somatolactotrope tumor cell line and the effect of loss of AhR action in knockout mice. GH3 cells respond to nM doses of the reversible AhR agonist β-naphthoflavone with a robust induction of Cyp1a1. Although mRNA levels of the anti-proliferative signaling cytokine TGFbeta1 are suppressed upon β-naphthoflavone treatment, we did not observe an alteration in cell proliferation. AhR activation with β-naphthoflavone suppresses Ahr expression and impairs expression of prolactin (PRL), but not growth hormone (GH) mRNA in GH3 cells. In mice, loss of Ahr similarly leads to a reduction in Prl mRNA at P3, while Gh is unaffected. Additionally, there is a significant reduction in pituitary hormones Lhb and Fshb in the absence of Ahr. Overall, these results demonstrate that AhR is important for pituitary hormone expression and suggest that environmental dioxins can exert endocrine disrupting effects at the pituitary.

Dioxin exposure reduces the steroidogenic capacity of mouse antral follicles mainly at the level of HSD17B1 without altering atresia

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent ovarian toxicant. Previously, we demonstrated that in vitro TCDD (1nM) exposure decreases production/secretion of the sex steroid hormones progesterone (P4), androstenedione (A4), testosterone (T), and 17β-estradiol (E2) in mouse antral follicles. The purpose of this study was to determine the mechanism by which TCDD inhibits steroidogenesis. Specifically, we examined the effects of TCDD on the steroidogenic enzymes, atresia, and the aryl hydrocarbon receptor (AHR) protein. TCDD exposure for 48h increased levels of A4, without changing HSD3B1 protein, HSD17B1 protein, estrone (E1), T or E2 levels. Further, TCDD did not alter atresia ratings compared to vehicle at 48h. TCDD, however, did down regulate the AHR protein at 48h. TCDD exposure for 96h decreased transcript levels for Cyp11a1, Cyp17a1, Hsd17b1, and Cyp19a1, but increased Hsd3b1 transcript. TCDD exposure particularly lowered both Hsd17b1 transcript and HSD17B1 protein. However, TCDD exposure did not affect levels of E1 in the media nor atresia ratings at 96h. TCDD, however, decreased levels of the proapoptotic factor Bax. Collectively, these data suggest that TCDD exposure causes a major block in the steroidogenic enzyme conversion of A4 to T and E1 to E2 and that it regulates apoptotic pathways, favoring survival over death in antral follicles. Finally, the down-regulation of the AHR protein in TCDD exposed follicles persisted at 96h, indicating that the activation and proteasomal degradation of this receptor likely plays a central role in the impaired steroidogenic capacity and altered apoptotic pathway of exposed antral follicles.

The aryl hydrocarbon receptor regulates mouse Fshr promoter activity through an e-box binding site

The aryl hydrocarbon receptor (AHR) mediates the toxicity of a variety of environmental chemicals. Apart from this, an understanding is emerging that the AHR has a fundamental role in female reproduction. Evidence suggests that AHR participates in regulation of follicle-stimulating hormone receptor (Fshr) transcript level in mouse ovary by binding to the promoter of this gene in vivo. The purpose of this study was to demonstrate the molecular interplay of the Fshr promoter involved in the transactivation by AHR in mouse granulosa cells. We found that AHR activates the Fshr promoter through the region from -209 to -99 bp. In this region, the importance of the E-box motif was revealed by site-directed mutagenesis followed by promoter analysis. By focusing on the DNA/protein interactions, we defined the fact that the intact E-box but not upstream transcription factor 1 (USF1), which is known to bind this motif, is necessary for AHR binding to mouse Fshr promoter. Furthermore, by constructing AHR mutants defective in DNA interaction, we confirmed the importance of DNA binding for AHR's ability to bind to and activate Fshr promoter. Collectively, the present study demonstrates that AHR modulates Fshr transactivation by its direct association through an E-box and not by recruitment via interaction with USFs. These observations suggest that although AHR and USF may respond to different signals, they compete on binding to the same E-box. Our data, together with that from one prior study suggesting involvement of E-box motif in AHR-mediated transcription, provide novel understanding of the way in which AHR may regulate its target genes through E-box sites.

The expression of the aryl hydrocarbon receptor in reproductive and neuroendocrine tissues during the estrous cycle in the pig

The aryl hydrocarbon receptor (AhR) has been recognized as a mediator of xenobiotic-induced toxicity. In addition, it was demonstrated that the AhR is able to influence the regulation of reproductive processes in females. The aim of this study was to examine AhR mRNA (real-time PCR) and protein (Western-blot) expression in ovarian follicles and stroma, corpora lutea (CL), oviducts, endometrium, myometrium as well as in medial basal hypothalami (MBH), and anterior (AP) and posterior (PP) pituitaries harvested during the follicular (days 17-19) and luteal (days 8-10) phase of the porcine estrous cycle. The AhR transcript and protein were found in all structures collected during both phases. AhR mRNA expression tended (p=0.06) to be higher in the CL than in follicles. The AhR protein expression in ovarian stroma was higher (p≤0.01) during the follicular than in the luteal phase. Endometrial expression of AhR mRNA was higher (p≤0.01), while AhR protein was lower (p≤0.01) during the follicular phase in comparison to the luteal phase. Within neuroendocrine tissues, AhR mRNA and protein content in hypothalamus were relatively low and did not differ (p>0.05) between phases. In contrast, higher AhR mRNA expression in AP (p≤0.001) and protein expression in PP (p≤0.01) were found during the luteal phase compared to the follicular phase. Differences in AhR expression observed in reproductive and neuroendocrine tissues during the follicular and luteal phase of the estrous cycle indicate the involvement of AhR in the regulation of reproductive function in pigs.

The ability of the aryl hydrocarbon receptor to regulate ovarian follicle growth and estradiol biosynthesis in mice depends on stage of sexual maturity

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates the toxicity of environmental chemicals and regulates many physiological functions, including processes in female reproduction. Previous studies demonstrated that Ahr deletion leads to slow ovarian follicle growth because of impaired estradiol production and reduced gonadotropin responsiveness in prepubertal mice. These studies, however, did not determine how Ahr deletion impairs estradiol production or whether the effects of Ahr deletion on follicle growth and estradiol production persist in adulthood. Thus, the present study evaluated the effect of Ahr deletion on steroid precursors in the estradiol biosynthesis pathway. Furthermore, this study evaluated follicle growth and estradiol biosynthesis in wild-type (WT) and Ahr knockout (AhrKO) antral follicles at different stages of sexual maturity. AhrKO antral follicles from prepubertal mice had slower growth, produced lower estradiol levels, and had reduced cyclin D2 (Ccnd2) expression compared to WT follicles. AhrKO follicles from adult mice, however, produced higher androgen levels and expressed higher levels of Ccnd2 compared to WT follicles. Furthermore, AhrKO follicles from adult mice had growth to that of WT follicles. These findings suggest that the AHR regulates follicle growth by altering factors involved in the estradiol biosynthesis pathway as well as key regulators of follicle growth and that this role of AHR depends on stage of sexual maturity.

Fatty acid composition and gene expression profiles are altered in aryl hydrocarbon receptor-1 mutant Caenorhabditis elegans

The aryl hydrocarbon receptor (AHR) is a eukaryotic transcription factor that plays an essential role in neuronal, immune, vascular, hepatic and hematopoietic development. In mammals, AHR induces metabolism-associated genes in response to xenobiotics. AHR is evolutionarily conserved, and the C. elegans AHR ortholog likely shares many physiologic functions with the mammalian version. While the role of AHR in development is known, the molecular basis of AHR action is less well understood. To understand the physiologic role of AHR in C. elegans, a combination of fatty acid profiling, transcriptomics, and phenotyping approaches was used. Fatty acid profiles from L4 larval stage whole animals indicated that C17isoA, C18:1n9t, C20:3n6 and C20:4n6 were significantly increased in an ahr-1 mutant compared to wild-type. Consistent with these changes, we observed a significant 5.8 fold increase in fat-7, and 1.7-1.9 fold increases in elo-5, nhr-49, and mdt-15 gene expression during the L4 stage. The ahr-1(ju145) mutant displayed deficits in growth and development including a reduced number of eggs laid, a higher proportion of dead embryos, delay in time to reach L4 stage, and movement deficits including a fewer number of body bends and a longer defecation cycle. To understand global effects of AHR-1 on transcription, microarray analysis was performed on L1 stage animals. Expression changes (324 under- and 238 over-expressed) were found in genes associated with metabolism, growth, and development. These results indicate a role for C. elegans AHR in regulating fatty acid composition and in contributing to some aspects of development. Since the transcriptional control of AHR targets may be evolutionarily conserved, these results provide a deeper understanding of the molecular actions of AHR in a model invertebrate system that may be informative for higher organisms.

Comparative contribution of the aryl hydrocarbon receptor gene to perinatal stage development and dioxin-induced toxicity between the urogenital complex and testis in the mouse

TCDD (2,3,7,8-tetrachlorodebenzo-p-dioxin) requires the presence of the aryl hydrocarbon receptor (Ahr) gene for its toxic effects, such as reproductive disorders in male offspring of maternally exposed rats and mice. To study the involvement of the Ahr gene in producing the toxic phenotype with respect to testicular development, we administered a relatively high dose of TCDD to mice with three different maternally derived Ahr genotypic traits, and then compared several Ahr-dependent alterations among male reproductive systems on Postnatal Day 14. Reduction in anogenital distance and expression of prostatic epithelial genes in the urogenital complex (UGC) were detected in Ahr(+/+) and Ahr(+/-) mice exposed to TCDD, whereas no difference was observed in Ahr(-/-) mice. In situ hybridization revealed the absence of probasin mRNA expression in the prostate epithelium, despite the obvious development of prostatic lobes in TCDD-exposed mice. In contrast to obvious prostatic dysfunction and induction of cytochrome P450 (CYP) family genes in the UGC by TCDD, no alterations in testicular functions were observed in germ cell/Sertoli cell/interstitial cell marker gene expression or CYP family induction. No histopathological changes were observed among the three genotypes and between control and TCDD-exposed mice. Therefore, mouse external genitalia and prostatic development are much more sensitive to TCDD treatment than testis. Further, the Ahr gene, analyzed in this study, does not significantly contribute to testicular function during perinatal and immature stages, and the developing mouse testis appears to be quite resistant to TCDD exposure.