Aryl hydrocarbon receptor antagonists promote the expansion of human hematopoietic stem cells. Boitano AE et al. Although practiced clinically for more than 40 years, the use of hematopoietic stem cell (HSC) transplants remains limited by the ability to expand these cells ex vivo. An unbiased screen with primary human HSCs identified a purine derivative, StemRegenin 1 (SR1), that promotes the ex vivo expansion of CD34+ cells. Culture of HSCs with SR1 led to a 50-fold increase in cells expressing CD34 and a 17-fold increase in cells that retain the ability to engraft immunodeficient mice. Mechanistic studies show that SR1 acts by antagonizing the aryl hydrocarbon receptor (AHR). The identification of SR1 and AHR modulation as a means to induce ex vivo HSC expansion should facilitate the clinical use of HSC therapy.
NCBI Summary:
The protein encoded by this gene is a ligand-activated helix-loop-helix transcription factor involved in the regulation of biological responses to planar aromatic hydrocarbons. This receptor has been shown to regulate xenobiotic-metabolizing enzymes such as cytochrome P450. Before ligand binding, the encoded protein is sequestered in the cytoplasm; upon ligand binding, this protein moves to the nucleus and stimulates transcription of target genes. [provided by RefSeq, Sep 2015]
General function
Receptor, DNA binding, Transcription factor
Comment
Intrinsic Function of the Aryl Hydrocarbon (Dioxin) Receptor as a Key Factor in Female Reproduction Baba T, et al .
Dioxins exert a variety of adverse effects on organisms, including teratogenesis, immunosuppression, tumor promotion, and estrogenic action. Studies using aryl hydrocarbon receptor (AhR)-deficient mice suggest that the majority of these toxic effects are mediated by the AhR. In spite of the adverse effects mediated by this receptor, the AhR gene is conserved among a number of animal species, ranging from invertebrates to vertebrates. This high degree of conservation strongly suggests that AhR possesses an important physiologic function, and a critical function is also supported by the reduced fertility observed with AhR-null female mice. We demonstrate that AhR plays a crucial role in female reproduction by regulating the expression of ovarian P450 aromatase (Cyp19), a key enzyme in estrogen synthesis. As revealed by in vitro reporter gene assay and in vivo chromatin immunoprecipitation assay, AhR cooperates with an orphan nuclear receptor, Ad4BP/SF-1, to activate Cyp19 gene transcription in ovarian granulosa cells. Administration to female mice of an AhR ligand, DMBA (9,10-dimethyl-1,2-benzanthracene), induced ovarian Cyp19 gene expression, irrespective of the intrinsic phase of the estrus cycle. In addition to elucidating a physiological function for AhR, our studies also suggest a possible mechanism for the toxic effects of exogenous AhR ligands as endocrine disruptors.
Cellular localization
Cytoplasmic, Nuclear
Comment
Induction of aryl hydrocarbon receptor in granulosa cells by endoplasmic reticulum stress contributes to pathology of polycystic ovary syndrome. Kunitomi C et al. (2021) Recent studies have uncovered the critical role of aryl hydrocarbon receptor (AHR) in various diseases, including obesity and cancer progression, independent of its previously identified role as a receptor for endocrine-disrupting chemicals (EDCs). We previously demonstrated that endoplasmic reticulum (ER) stress, a newly recognized local factor in the follicular microenvironment, is activated in granulosa cells from patients with polycystic ovary syndrome (PCOS) and a mouse model of the disease. By affecting diverse functions of granulosa cells, ER stress contributes to PCOS pathology. We hypothesized that expression of AHR and activation of its downstream signaling were upregulated by ER stress in granulosa cells, irrespective of the presence of EDCs, thereby promoting PCOS pathogenesis. In this study, we found that AHR, AHR nuclear translocator (ARNT), and AHR target gene cytochrome P450 1B1 (CYP1B1) were upregulated in the granulosa cells of PCOS patients and model mice. We examined CYP1B1 as a representative AHR target gene. AHR and ARNT were upregulated by ER stress in human granulosa-lutein cells (GLCs), resulting in an increase in the expression and activity of CYP1B1. Administration of the AHR antagonist CH223191 to PCOS mice restored estrous cycling and decreased the number of atretic antral follicles, concomitant with downregulation of AHR and CYP1B1 in granulosa cells. Taken together, our findings indicate that AHR activated by ER stress in the follicular microenvironment contributes to PCOS pathology, and that AHR represents a novel therapeutic target for PCOS.//////////////////Bisphenol A inhibits cultured mouse ovarian follicle growth partially via the aryl hydrocarbon receptor signaling pathway. Ziv-Gal A 2013 et al.
Bisphenol A (BPA) is an endocrine disruptor that inhibits growth of mouse ovarian follicles and disrupts steroidogenesis at a dose of 438?M. However, the effects of lower doses of BPA and its mechanism of action in ovarian follicles are unknown. We hypothesized that low doses of BPA inhibit follicular growth and decrease estradiol levels through the aryl hydrocarbon receptor (AHR) pathway. Antral follicles from wild-type and Ahr knock-out (AhrKO) mice were cultured for 96hours. Follicle diameters and estradiol levels then were compared in wild-type and AhrKO follicles ? BPA (0.004 - 438?M). BPA inhibited follicle growth (110 - 438?M) and decreased estradiol levels (43.8 - 438?M) in wild-type and AhrKO follicles. However, at BPA 110?M, inhibition of growth in AhrKO follicles was attenuated compared to wild-type follicles. These data suggest that BPA may inhibit follicle growth partially via the AHR pathway, whereas its effects on estradiol synthesis likely involve other mechanisms.
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Human Primordial Germ Cell Formation is Diminished by Exposure to Environmental Toxicants Acting Through the AHR Signaling Pathway. Kee K et al. Historically, effects of environmental toxicants on human development have been deduced via epidemiological studies since direct experimental analysis has not been possible. However, in recent years, the derivation of human pluripotent stem cells has provided a potential experimental system to directly probe human development. Here, we used human embryonic stem cells (hESCs) to study the effect of environmental toxicants on human germ cell development, with a focus on differentiation of the founding population of primordial germ cells (PGCs) which will go on to form the oocytes of the adult. We demonstrate that human PGC numbers are specifically reduced by exposure to polycyclic aromatic hydrocarbons (PAHs), a group of toxicants common in air pollutants released from gasoline combustion or tobacco smoke. Further, we demonstrate that the adverse effects of PAH exposure are mediated through the aromatic hydrocarbon receptor (AHR) and BAX pathway. This study demonstrates the utility of hESCs as a model system for direct examination of the molecular and genetic pathway of environmental toxicants on human germ cell development.
Aryl hydrocarbon receptor antagonists attenuate the deleterious effects of benzopyrene on isolated rat follicle development. Neal MS et al. It has been shown that benzopyrene, a key component of cigarette smoke and an aryl hydrocarbon receptor (AhR) ligand, reduced growth of isolated rat follicles in vitro. However, the mechanism underlying the induced changes in folliculogenesis is unknown. This study proposed that the reported adverse effects of benzopyrene on follicle growth are mediated through AhR activation. The objective was to investigate the effect of benzopyrene with and without AhR antagonists (resveratrol or 3',4'-dimethoxyflavone (3,4-DMF)) on follicle growth, oestradiol output, anti-M?an hormone (AMH) concentration and cell proliferation in isolated rat follicles cultured in vitro. Benzopyrene treatment significantly inhibited follicle growth and cell proliferation at concentrations of 1.5ng/ml and higher (P<0.05), an effect attenuated by co-incubation with benzopyrene and resveratrol or 3,4-DMF. A significant decrease in oestradiol (P<0.05) and AMH output (P<0.001) by cultured follicles was induced by benzopyrene treatment, an effect attenuated by co-incubation with 3,4-DMF. The results suggest that the adverse effects of benzopyrene on follicle growth, steroidogenesis and AMH output are mediated through activation of the AhR. Moreover, AhR antagonists such as resveratrol and 3,4-DMF may have therapeutic benefit in protecting the ovary against the adverse effects of AhR ligands, including benzopyrene.
Aromatic hydrocarbon receptor-driven Bax gene expression is required for premature ovarian failure caused by biohazardous environmental chemicals. Matikainen T et al. Polycyclic aromatic hydrocarbons (PAHs) are toxic chemicals released into the environment by fossil fuel combustion. Moreover, a primary route of human exposure to PAHs is tobacco smoke. Oocyte destruction and ovarian failure occur in PAH-treated mice, and cigarette smoking causes early menopause in women. In many cells, PAHs activate the aromatic hydrocarbon receptor (Ahr), a member of the Per-Arnt-Sim family of transcription factors. The Ahr is also activated by dioxin, one of the most intensively studied environmental contaminants. Here we show that an exposure of mice to PAHs induces the expression of Bax in oocytes, followed by apoptosis. Ovarian damage caused by PAHs is prevented by Ahr or Bax inactivation. Oocytes microinjected with a Bax promoter-reporter construct show Ahr-dependent transcriptional activation after PAH, but not dioxin, treatment, consistent with findings that dioxin is not cytotoxic to oocytes. This difference in the action of PAHs versus dioxin is conveyed by a single base pair flanking each Ahr response element in the Bax promoter. Oocytes in human ovarian biopsies grafted into immunodeficient mice also accumulate Bax and undergo apoptosis after PAH exposure in vivo. Thus, Ahr-driven Bax transcription is a novel and evolutionarily conserved cell-death signaling pathway responsible for environmental toxicant-induced ovarian failure.
Ovarian function
Steroid metabolism
Comment
The Effects of Chronic Lifelong Activation of the AHR Pathway by Industrial Chemical Pollutants on Female Human Reproduction. Cavallini A et al. (2016) Environmental chemicals, such as heavy metals, affect female reproductive function. A biological sensor of the signals of many toxic chemical compounds seems to be the aryl hydrocarbon receptor (AHR). Previous studies demonstrated the environmental of heavy metals in Taranto city (Italy), an area that has been influenced by anthropogenic factors such as industrial activities and waste treatments since 1986. However, the impact of these elements on female fertility in this geographic area has never been analyzed. Thus, in the present study, we evaluated the AHR pathway, sex steroid receptor pattern and apoptotic process in granulosa cells (GCs) retrieved from 30 women, born and living in Taranto, and 30 women who are living in non-contaminated areas (control group), who were undergoing in vitro fertilization (IVF) protocol. In follicular fluids (FFs) of both groups the toxic and essential heavy metals, such as chromiun (Cr), Manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd) and lead (Pb), were also analyzed. Higher levels of Cr, Fe, Zn and Pb were found in the FFs of the women from Taranto as compared to the control group, as were the levels of AHR and AHR-dependent cytochrome P450 1A1 and 1B1; while CYP19A1 expression was decreased. The anti-apoptotic process found in the GCs of women fromTaranto was associated with the highest levels of progesterone receptor membrane component 1 (PGRMC1), a novel progesterone receptor, the expression of which is subjected to AHR activated by its highest affinity ligands (e.g., dioxins) or indirectly by other environmental pollutants, such as heavy metals. In conclusion, decreased production of estradiol and decreased number of retrieved mature oocytes found in women from Taranto could be due to chronic exposure to heavy metals, in particular to Cr and Pb.//////////////////
Aryl hydrocarbon receptor (AhR)-linked inhibition of luteal cell progesterone secretion in 2,3,7,8-tetrachlorodibenzo-p-dioxin treated cells Gregoraszczuk EL,et al .
In this study, we tested firstly, the hypothesis that decrease of progesterone secretion by luteal cells under the influence of 2,3,7,8-tetrachlorodibezo-p-dioxin (TCDD) is due to influence on specific enzymatic steps in the biosynthetic pathway of steroidogenesis and secondly, involvement of aryl hydrocarbon receptor (AhR) or estradiol receptor (ER) in this process. Luteal cells isolated from mature porcine corpora lutea were cultured with 25-hydroxycholesterole (25-OH) or pregnenolone (P5) as a substrate. Additionally aminoglutethimide, the inhibitor of P540scc or trilostane the inhibitor of 3 beta-HSD was added to basal and stimulated cells. The synergistic action of TCDD with aminoglutethimide in decreasing of progesterone secretion was observed. In pregnenolone treated cells 1.6 fold decrease of progesterone secretion was observed that in both TCDD alone and together with trilostane treated cells. In the second part of experiments to show the involvement of AhR and ER in TCDD action on progesterone secretion alpha- naphtophlavone, the AhR blockers and 4-hydroxytamoxifen (4-OH-TMX), the inhibitor of ER were used. alpha-naphtophlavone, the inhibitory effect of TCDD while 4-OH-TMX had no effect on TCDD-treated cells. These experiments suggest TCDD decreased progesterone secretion by luteal cells by reduction of the activity of mitochondrial enzymes, which converts cholesterol into pregnenolone. Moreover points to AhR dependent but not ER-dependent mechanisms in TCDD action in luteal cells.
Ligand activation of the aromatic hydrocarbon receptor transcription factor drives Bax-dependent apoptosis in developing fetal ovarian germ cells.
Endocrinology. 2002 .
The Aryl Hydrocarbon Receptor Affects Mouse Ovarian Follicle Growth Via Mechanisms Involving Estradiol Regulation and Responsiveness. Barnett KR et al. The aryl hydrocarbon receptor (AHR) is a known transcription factor. Although studies indicate that Ahr deficient (AhRKO) mice have defects in female reproduction, only a few studies have examined the role of the AHR in the ovary. These studies suggested, but did not directly test, that AhRKO mice may have slower follicular growth compared to wild-type (WT) mice. Therefore, the first objective of this study was to examine whether AhRKO follicles grow slower than WT follicles and, if so, to determine whether the mechanism by which the Ahr affects follicular growth is through effects on antrum size, granulosa cell proliferation, and regulators of cell cycle progression. Since estradiol (E2) is critical for normal growth of ovarian follicles, the second objective of this study was to determine the role of the Ahr in regulating E2 production and responsiveness. Lastly, the third objective of this study was to determine whether E2 replacement restores follicular growth of AhRKO follicles to WT levels in vitro. Our results show that AhRKO follicles grow slower than WT follicles in vitro. While AhRKO and WT follicles have similar antrum sizes, AhRKO follicles have decreased granulosa cell proliferation and reduced mRNA and protein levels of cell cycle regulators compared to WT follicles. Further, AhRKO mice have lower serum and follicle-produced E2 levels, and decreased Esr1 and Esr2 mRNA levels compared to WT mice. Finally, E2 treatment of AhRKO follicles restored follicular growth to WT levels in vitro. Collectively, these findings suggest that the AHR affects follicular growth via mechanisms involving E2 regulation and responsiveness.
Daily treatment with a-naphthoflavone enhances follicular growth and ovulation rate in the rat. Barreiro KA et al. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor and the first protein involved in a variety of physiological and toxicological processes, including those of xenobiotic metabolizing enzymes. AhR has been found in the ovary of many species and seems to mediate the ovarian toxicity of many environmental contaminants, which are AhR ligands. However, the role of AhR in the ovarian function is unknown. Therefore, the aim of this work was to study the action of a-naphthoflavone (aNF), known to be an AhR antagonist, on both follicular growth and ovulation. Immature Sprague Dawley rats were daily injected intraperitoneally with aNF (0.1-80mg/kg) or vehicle for 12days, and primed with gonadotrophins (eCG/hCG) to induce follicular growth and ovulation. Ovaries were obtained 20h after hCG administration. By means of immunohistochemistry, we found that the numbers of primordial, primary and antral follicles were increased in rats treated with 80mg/kg aNF and that there were no differences with other doses. Likewise, the ovarian weight and the ovulation rate, measured by both number of oocytes within oviducts and corpora lutea in ovarian sections, were increased when the rats received either 1 or 10mg/kg daily. Although further studies are necessary to know the mechanism of action of aNF, it is possible that the different ovarian processes can be differentially responsive to the presence of different levels of aNF, and that the same or different endogenous AhR ligands can be involved in these ovarian processes in a cell type-dependent manner.
Expression regulated by
FSH, LH, Steroids
Comment
Transcriptional repression of the Ahr gene by LHCGR signaling in preovulatory granulosa cells is controlled by chromatin accessibility. Teino I 2013 et al.
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.
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Testosterone-Dependent Interaction between Androgen Receptor and Aryl Hydrocarbon Receptor Induces Liver Receptor Homolog-1 Expression in Rat Granulosa Cells. Wu Y et al. Androgens play a major role in the regulation of normal ovarian function, however, they are also involved in the development of ovarian pathologies. These contrasting effects may involve a differential response of granulosa cells to the androgens, testosterone (T) and dihydrotestosterone (DHT). To determine the molecular pathways that mediate the distinct effects of T and DHT, we studied the expression of liver receptor homolog-1 (LRH-1), a gene differentially regulated by these steroids. We found that although both T and DHT stimulate androgen receptor (AR) binding to the LRH-1 promoter, DHT prevents T mediated stimulation of LRH-1 expression. T stimulated the expression of aryl hydrocarbon receptor (AHR) and its interaction with the AR. T also promoted the recruitment of the AR/AHR complex to the LRH-1 promoter. These effects were not mimicked by DHT. We also observed that the activation of extracellular regulated kinases by T is required for AR and AHR interaction. In summary, T, but not DHT, stimulates AHR expression and the interaction between AHR and AR leading to the stimulation of LRH-1 expression. These findings could explain the distinct response of granulosa cells to T and DHT and provide a molecular mechanism by which DHT negatively affects ovarian function.
Gonadotropin and steroid regulation of steroid receptor and aryl hydrocarbon receptor messenger ribonucleic acid in macaque granulosa cells during the periovulatory interval Chaffin CL,et al .
Although steroids play a local role(s) in ovulation and luteinization of the primate follicle, the dynamics of steroid receptor expression during the 36- to 38-h periovulatory interval has yet to be elucidated. The present study examines the regulation of messenger RNAs (mRNAs) for progesterone (PR), androgen (AR), and estrogen (ER alpha, ER beta) receptors as well as the aryl hydrocarbon receptor (AhR) in macaque granulosa cells during controlled ovarian stimulation cycles before (0 h) and after (up to 36 h) administration of the ovulatory hCG bolus with or without steroid depletion and progestin replacement. All steroid receptor mRNAs were detected in granulosa cells before the ovulatory stimulus, as determined by RT-PCR. PR mRNA increased (P < 0.05) by 12 h after hCG; 24 and 36 h after hCG, levels were intermediate between 0-12 h. PR mRNA was reduced by steroid depletion throughout the periovulatory interval (P < 0.05); however, progestin replacement returned PR mRNA to control levels at 12 h. AR mRNA increased (P < 0.05) at 24 h post-hCG and remained at this level 36 h after hCG; steroid depletion did not alter AR mRNA levels. ER alpha mRNA did not change, whereas ER beta decreased 12-36 h after the ovulatory stimulus (P < 0.05). Steroid depletion reduced ER alpha mRNA 12 h after hCG, an effect partially reversible by progestin replacement, whereas ER beta mRNA was not affected by steroids. AhR mRNA was undetectable before the administration of hCG, but increased by 12 h (P < 0.05). These data demonstrate hCG-initiated, steroid-dependent (PR, ER alpha) and -independent (AR, ER beta, AhR) expression of receptor mRNAs in primate granulosa cells during the periovulatory interval. Differences in patterns of expression may relate to diverse roles for steroid hormones and AhR ligands in periovulatory events.
Aromatic hydrocarbon receptor (AhR) in the porcine theca and granulosa cells: effect of TCDD, PCB 126 and PCB 153 on the expression of AhR. Wojtowicz A et al. OBJECTIVE: In our previous papers, we demonstrated that TCDD and PCBs (both coplanar PCB 126 and non-coplanar PCB 153) caused the decreased estradiol secretion in cultured pig ovarian follicles. However, the mechanism of action is not clearly understood. Moreover, to our knowledge, the expression of AhR in pig follicular cells was not described yet. METHODS: In order to elucidate if TCDD, PCB 126, and PCB 153 can disrupt ovarian steroidogenesis via AhR-dependent mechanism, granulosa and theca cells were isolated from pig ovarian small follicles and subsequently treated with 32 pg/ml of TCDD, 100 ng/ml of PCB 153, 100 pg/ml of PCB 126 in an in vitro culture. After 3-hour exposure to the chemicals, cells were prepared for immunohistochemical analysis or collected for immunobloting, and the effects of TCDD and PCBs on the levels of AhR protein were studied. RESULTS: Under basal conditions, AhR staining showed a diffuse cytoplasmic pattern of distribution as well in granulosa and theca cells. However, immunocytochemical labeling of AhR in theca cells was less evident and only few cells displayed cytoplasmic staining. Immunoblotts prepared from granulosa and theca cell lysates detected a strong band of 120 kDa indicating AhR protein expression. The level of AhR expression detected by Western blot analysis was higher in granulosa cells than in theca cells. Intensive cytoplasmic and nuclear labeling corresponding to AhR protein in TCDD and PCB 126 treated granulosa cells was observed. In PCB 153 treated cells, the level of AhR staining was comparable with control. Western blot analysis showed a strong band in TCDD-treated grnulosa cells and only slightly differences compared with control in those exposed to PCB 126. The effect of both PCBs on immunocytochemical AhR staining in theca cells was less evident. Immunoblott analysis did not reveal any substantial differences between the control and TCDD- and PCBs-treated theca cells. CONCLUSIONS: This study has shown different AhR expression in porcine theca and granulosa cells, in respect of both its intracellular localization and cellular distribution. Both, dioxin and dioxin-like PCB activated AhRs in granulosa but not in theca cells. Differences in AhR-responsiveness of granulosa and theca cells to TCDD and dioxin-like PCB 126 are probably connected with the differences of these cells in estradiol secretion and different proliferative potential.
Regulation of Aryl Hydrocarbon Receptor Expression in Rat Granulosa Cells. Bussmann UA et al. 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 down-regulated 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 replenish 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.
Ovarian localization
Oocyte, Granulosa
Comment
Estrous cycle-dependent changes in the expression of aromatic hydrocarbon receptor (AHR) and AHR-nuclear translocator (ARNT) mRNAs in the rat ovary and liver Chaffin CL, et al .
The aromatic hydrocarbon receptor (AHR) and AHR nuclear translocator protein (ARNT) mediate the toxic effects of a wide variety of halogenated and polycyclic aromatic hydrocarbons. While it can be assumed that AHR has an endogenous function, its role in reproduction is currently undefined. The present study seeks to examine the regulation of AHR and ARNT mRNAs in liver and ovarian tissues across the rat estrous cycle. Message for hepatic AHR was increased significantly on the morning of proestrus, and decreased dramatically by the evening of proestrus; while hepatic ARNT mRNA was significantly decreased between diestrus and the morning of proestrus, and between the evening of proestrus and the morning of estrus. Ovarian AHR mRNA was unchanged from diestrus to proestrus, and was decreased on the evening of proestrus. Changes in the expression of ARNT mRNA mirrored changes in the liver. To assess interaction between the AHR- and estrogen-receptor (ER)-signaling pathways and to test the hypothesis that estrogen regulates AHR mRNA, 25-day-old female rats were injected with either 17beta-estradiol, the ER antagonist ICI 182 780, or with vehicle, and hepatic AHR mRNA was measured. Treatment with estrogen or the estrogen antagonist did not alter the abundance of AHR mRNA in the liver. These data suggest that while estrogen may not be the key regulator of AHR mRNA expression, a factor associated with the rat reproductive cycle may be important in regulating the expression of both the AHR and ARNT genes in the ovary and liver.
Characteristic expression of aryl hydrocarbon receptor repressor gene in human tissues: organ-specific distribution and variable induction patterns in mononuclear cells. Yamamoto J et al. To investigate the expression of aryl hydrocarbon receptor repressor (AhRR) and related molecules in various tissues and the effects of aromatic hydrocarbons (AHs) on their expression, we developed a reliable technique of quantification of human AhRR as well as aryl hydrocarbon receptor (AhR), AhR nuclear translocator (ARNT) and cytochrome P450 1A1 (CYP1A1) mRNA by real-time TaqMan PCR method. First, we examined the expression of these genes in human adult or fetal tissues. The levels of AhRR expression were extremely high in testis, very high in lung, ovary, spleen and pancreas from adults, whereas those were low in those from fetuses. On the other hand, CYP1A1 expression was extremely high in lung, and AhR and ARNT were ubiquitously expressed in almost all tissues. Second, we compared the expression levels of these genes in mononuclear cells (MNCs) from various sources. Comparison of the basal expression levels of these genes in MNCs demonstrated that MNCs from umbilical cord blood showed higher AhRR or CYP1A1 expression than those from adults. The induction of AhRR or CYP1A1 expression by 3-methylcholanthrene (3-MC) was observed in MNCs from adults but not from umbilical cord blood. Consequently, there existed characteristic differences in the basal levels of AhRR and CYP1A1 expression in MNCs, as well as in their inducibility by 3-MC among MNCs from various types of human bloods. These results will provide basic information for a possible application of AhRR and CYP1A1 measurements to evaluate AH exposure in vivo.
Follicle stages
Comment
Autoradiographic localization of aromatic hydrocarbon receptor (AHR) in rhesus monkey ovary. Baldridge MG et al. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most toxic congener of a large class of manmade pollutants that persist in the environment. TCDD exerts its toxic effects, in part, by binding to its receptor known as the aromatic hydrocarbon receptor (AHR). TCDD is estrogen modulatory and in some systems its receptor associates directly with estrogen receptors via co-activator molecules. TCDD inhibits steroid synthesis in human ovarian granulosa cells and AHR is found in these cells. We have previously shown that AHR is found in whole rhesus monkey ovary, but have yet to establish its location. In the present study, we set out to show that radiolabeled TCDD binds to monkey ovarian follicles and that this binding is receptor mediated. Ovaries from Macaca mulatta were sectioned on a cryostat at 10 micro m; and sections were incubated with either control vehicle, (3)H-TCDD, or (3)H-TCDD plus alpha-naphthoflavone (ANF), a known receptor-blocking agent. Here, we show for the first time specific binding of TCDD to the granulosa cells of antral follicles and other regions of the rhesus monkey ovary. Our data indicate a 60-fold increase in binding with (3)H-TCDD over that of control, and that this binding is reduced to the levels seen in controls with the addition of the competitive antagonist ANF. These findings support the hypothesis that TCDD directly affects primate ovarian function via the AHR. Am. J. Primatol. 69:1-11, 2007. (c) 2006 Wiley-Liss, Inc.
Phenotypes
PCO (polycystic ovarian syndrome)
Mutations
3 mutations
Species: mouse
Mutation name: None
type: null mutation fertility: subfertile Comment: The aryl hydrocarbon receptor, a basic helix-loop-helix transcription factor of the PAS gene family, is required for normal ovarian germ cell dynamics in the mouse Robles R, et al .
The aryl hydrocarbon receptor (AhR), so-designated based on the ability of the protein to bind with and be activated by polycyclic aromatic hydrocarbons (PAH) and related halogenated hydrocarbons, is part of an emerging family of ligand-activated transcriptional regulators that are distinct from the steroid-thyroid hormone receptor superfamily. Once bound by ligand, the AhR interacts with the AhR nuclear translocator (ARNT) protein to form the aryl hydrocarbon receptor complex (AHRC). Both subunits of the AHRC contain sequences corresponding to basic helix-loop-helix domains, a motif that is shared by a number of other dimeric transcription factors. Although the natural ligand(s) for the AhR remains to be elucidated, to date over fifteen genes, including enzymes, growth factors and other transcription factors, have been identified as potential targets for transcriptional regulation by the chemically-activated AHRC. In the ovary, PAH exposure is known to cause destruction of oocytes within immature follicles, implying that one function of the AhR is to mediate cell death signaling in the female germ line. To assess this possibility, we explored AhR expression patterns in the murine ovary, and then determined the impact of AhR-deficiency (gene knockout) on female germ cell dynamics. Immunohistochemical analysis of ovaries of wild-type female mice indicated that AhR protein was abundantly and exclusively expressed in oocytes and granulosa cells of follicles at all stages of development. Histomorphometric analysis of serial ovarian sections revealed a two-fold higher number of primordial follicles in Ahr-null versus wild-type females at day 4 postpartum. This phenotype likely results from a cell-intrinsic death defect in the developing germ line since AhR-deficiency attenuated the magnitude of oocyte apoptosis in fetal ovaries cultured without hormonal support for 72 h. We propose that the AhR, activated by an as yet unknown endogenous ligand(s), serves to regulate the size of the oocyte reserve endowed at birth by affecting germ cell death during female gametogenesis.
Species: mouse
Mutation name: None
type: null mutation fertility: subfertile Comment: Physiological role of the aryl hydrocarbon receptor in mouse ovary development Benedict JC, et al .
The aryl hydrocarbon receptor (AhR) regulates the toxicity of environmental contaminants such as 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD). As the physiological role of the AhR in the ovary is unknown, the purpose of this study was to test the hypothesis that the AhR regulates the appearance and numbers of ovarian follicles. Ovaries were harvested from AhR-deficient (AhRKO) and wild-type mice on gestational day 18 (GD 18) and postnatal days (PND) 2-3, 8, 32-35, and 53. Complete serial sections of ovaries were evaluated histologically for the presence of germ cells and follicles. On GD 18, there was no difference in the number of germ cells per ovary between AhRKO and wild-type fetuses. However, by PND 2-3, AhRKO mice had significantly more fully formed primordial follicles (AhRKO = 38,440 +/- 3632 versus wild-type = 21,120 +/- 2688) and fewer single germ cells than wild-type mice (AhRKO = 12,696 +/- 1192 vs. wild-type = 18,160 +/- 720). On PND 8 and 32-35, there was no difference in the number of follicles between AhRKO and wild-type mice but by PND 53, AhRKO mice had significantly fewer antral follicles than wild-type (AhRKO = 3416 +/- 480 vs. wild-type = 6776 +/- 1024). Taken together, these results suggest that the AhR may play a role in the formation of primordial follicles and the regulation of antral follicle numbers.
Aryl hydrocarbon receptor regulates growth, but not atresia, of mouse preantral and antral follicles Benedict JC, et al .
The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that binds various environmental contaminants. Despite our knowledge regarding the role of the AhR in mediating toxicity, little is known about the physiological role of the AhR. Previous studies indicate that the AhR may regulate folliculogenesis, because AhR-deficient (AhRKO) mice have fewer preantral and antral follicles than wild-type (WT) mice during postnatal life. Thus, the first objective of the present study was to test the hypothesis that AhR deficiency reduces the numbers of preantral and antral follicles by slowing growth and/or increasing atresia of follicles. Because alterations in follicular growth or atresia can affect the ability to ovulate, the second objective was to test whether AhR deficiency reduces the number of ovulated eggs. To test these hypotheses, follicular growth was compared in WT and AhRKO ovaries using morphometric techniques and by measuring the ability of the ovary and follicles to grow in response to eCG. Atresia was compared in WT and AhRKO ovaries using morphometric techniques, TUNEL assays, and 3'-end labeling of fragmented DNA. Ovulation was compared in WT and AhRKO mice by assessing the number of corpora lutea per ovary. The results indicate that follicular growth and ovulation were reduced in AhRKO ovaries compared to WT ovaries. The WT ovaries had a 1.5-fold increase in the number of preantral and antral follicles between Postnatal Days 32 and 45, were more responsive to eCG, and contained more corpora lutea than AhRKO ovaries. In contrast, no significant difference was observed in the incidence of atresia in WT and AhRKO ovaries. Taken together, these results suggest that the AhR may regulate growth, but not atresia, of preantral and antral follicles in the mouse ovary.
Species: mouse
Mutation name: None
type: null mutation fertility: infertile - ovarian defect Comment: The aryl hydrocarbon receptor is required for normal gonadotropin responsiveness in the mouse ovary. Barnett KR et al. The aryl hydrocarbon receptor (AHR) mediates the toxicity of a variety of environmental chemicals. Although little is known about the physiological role of the AHR, studies suggest that it plays an important role in regulating ovulation because Ahr deficient (AhRKO) mice have a reduced number of ovulations compared to wild-type (WT) mice. The reasons for the reduced ability of AhRKO mice to ovulate are unknown. Normal ovulation, however, requires estrous cyclicity, appropriate luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels, and LH and FSH responsiveness. Thus, the purpose of this study was to test the hypothesis that Ahr deletion regulates ovulation by altering cyclicity, FSH and LH levels, follicle-stimulating hormone receptor (Fshr) and luteinizing hormone receptor (Lhcgr) levels and/or gonadotropin responsiveness. The data indicate that AhRKO and WT mice have similar levels of FSH and LH, but AhRKO mice have reduced Fshr and Lhcgr mRNA levels compared to WT mice. Furthermore, AhRKO ovaries contain fewer corpora lutea compared to WT ovaries after 5 IU equine chorionic gonadotropin (eCG) treatment. Lastly, both AhRKO and WT mice ovulate a similar number of eggs in response to 5 IU human chorionic gonadotropin (hCG), but AhRKO mice ovulate fewer eggs than WT mice in response to 2.5 IU and 1.25 IU hCG. Collectively, these data indicate that AhRKO follicles have a reduced capacity to ovulate compared to WT follicles and that this is due to reduced responsiveness to gonadotropins. Thus, in addition to mediating toxicity of environmental chemicals, the Ahr is required for normal ovulation.