Methoxychlor stimulates estrogen-responsive messenger ribonucleic acids in mouse uterus through a non-estrogen receptor (non-ER) alpha and non-ER beta mechanism

Estrogenic endocrine disruptors: Molecular mechanisms of action

A comprehensive summary of more than 450 estrogenic chemicals including estrogenic endocrine disruptors is provided here to understand the complex and profound impact of estrogen action. First, estrogenic chemicals are categorized by structure as well as their applications, usage and effects. Second, estrogenic signaling is examined by the molecular mechanism based on the receptors, signaling pathways, crosstalk/bypassing and autocrine/paracrine/homeostatic networks involved in the signaling. Third, evaluation of estrogen action is discussed by focusing on the technologies and protocols of the assays for assessing estrogenicity. Understanding the molecular mechanisms of estrogen action is important to assess the action of endocrine disruptors and will be used for risk management based on pathway-based toxicity testing.

Perinatal exposure to methoxychlor enhances adult cognitive responses and hippocampal neurogenesis in mice

During perinatal life, sex steroids, such as estradiol, have marked effects on the development and function of the nervous system. Environmental estrogens or xenoestrogens are man-made chemicals, which animal and human population encounter in the environment and which are able to disrupt the functioning of the endocrine system. Scientific interest in the effects of exposure to xenoestrogens has focused more on fertility and reproductive behaviors, while the effects on cognitive behaviors have received less attention. Therefore, the present study explored whether the organochlorine insecticide Methoxychlor (MXC), with known xenoestrogens properties, administered during the perinatal period (from gestational day 11 to postnatal day 8) to pregnant-lactating females, at an environmentally relevant dose (20 µg/kg (body weight)/day), would also affect learning and memory functions depending on the hippocampus of male and female offspring mice in adulthood. When tested in adulthood, MXC perinatal exposure led to an increase in anxiety-like behavior and in short-term spatial working memory in both sexes. Emotional learning was also assessed using a contextual fear paradigm and MXC treated male and female mice showed an enhanced freezing behavior compared to controls. These results were correlated with an increased survival of adult generated cells in the adult hippocampus. In conclusion, our results show that perinatal exposure to an environmentally relevant dose of MXC has an organizational effect on hippocampus-dependent memory and emotional behaviors.

Low concentrations of o,p'-DDT inhibit gene expression and prostaglandin synthesis by estrogen receptor-independent mechanism in rat ovarian cells

o,p'-DDT is an infamous xenoestrogen as well as a ubiquitous and persistent pollutant. Biomonitoring studies show that women have been internally exposed to o,p'-DDT at range of 0.3-500 ng/g (8.46×10(-10) M-1.41×10(-6) M) in blood and other tissues. However, very limited studies have investigated the biological effects and mechanism(s) of o,p'-DDT at levels equal to or lower than current exposure levels in human. In this study, using primary cultures of rat ovarian granulosa cells, we determined that very low doses of o,p'-DDT (10(-12)-10(-8) M) suppressed the expression of ovarian genes and production of prostaglandin E2 (PGE2). In vivo experiments consistently demonstrated that o,p'-DDT at 0.5-1 mg/kg inhibited the gene expression and PGE2 levels in rat ovary. The surprising results from the receptor inhibitors studies showed that these inhibitory effects were exerted independently of either classical estrogen receptors (ERs) or G protein-coupled receptor 30 (GPR30). Instead, o,p'-DDT altered gene expression or hormone action via inhibiting the activation of protein kinase A (PKA), rather than protein kinase C (PKC). We further revealed that o,p'-DDT directly interfered with the PKA catalytic subunit. Our novel findings support the hypothesis that exposure to low concentrations of o,p'-DDT alters gene expression and hormone synthesis through signaling mediators beyond receptor binding, and imply that the current exposure levels of o,p'-DDT observed in the population likely poses a health risk to female reproduction.

Methoxychlor inhibits growth and induces atresia through the aryl hydrocarbon receptor pathway in mouse ovarian antral follicles

Methoxychlor (MXC) is an organochlorine pesticide used against pests that attack crops, vegetables, and livestock. MXC inhibits growth and induces atresia (death) of mouse ovarian antral follicles in vitro. Since several studies indicate that many chemicals act through the aryl hydrocarbon receptor (AHR) pathway, the current study tested the hypothesis that MXC binds to the AHR to inhibit growth and induce atresia of antral follicles. The data indicate that MXC binds to AHR. Further, a relatively high dose of MXC (100μg/ml) inhibits growth and induces atresia in both wild-type (WT) and AHR null (AHRKO) follicles, whereas a lower dose of MXC (10μg/ml) inhibits growth and induces atresia in WT, but not in AHRKO follicles. These data indicate that AHR deletion partially protects antral follicles from MXC induced slow growth and atresia. Collectively, these data show that MXC may act through the AHR pathway to inhibit follicle growth and induce atresia in antral follicles of the ovary.

Developmental programming: impact of fetal exposure to endocrine-disrupting chemicals on gonadotropin-releasing hormone and estrogen receptor mRNA in sheep hypothalamus

Bisphenol-A (BPA) and methoxychlor (MXC), two endocrine-disrupting chemicals (EDCs) with estrogenic and antiandrogenic effects, disrupt the reproductive system. BPA has profound effects on luteinizing hormone (LH) surge amplitude, and MXC has profound effects on on LH surge timing in sheep. The neural mechanisms involved in the differential disruption of the LH surge by these two EDCs remain to be elucidated. We tested the hypothesis that the differential effects of BPA and MXC on LH surge system involved changes in hypothalamic gonadotropin-releasing hormone (GnRH) and estrogen receptors (ESR), ESR1 and ESR2, mRNA expression. Pregnant sheep were given daily injections of cottonseed oil (controls), MXC, or BPA (5mg/kg/day) from day 30 to 90 of gestation (term 147d). Offspring from these animals were euthanized as adults, during the late follicular phase following synchronization of estrus with prostaglandin F(2alpha), just before the expected onset of preovulatory LH surge and changes in mRNA expression of hypothalamic GnRH, ESR1, and ESR2 quantified following in situ hybridization. GnRH mRNA expression was significantly lower in both groups of EDC-treated females compared to controls. ESR1 expression was increased in prenatal BPA- but not MXC-treated females in medial preoptic area relative to controls. In contrast, ESR2 expression was reduced in the medial preoptic area of both EDC-treated groups. Differences in expression of ESR1/ESR2 receptors may contribute to the differential effects of BPA and MXC on the LH surge system. These findings provide support that prenatal exposure to EDCs alters the neural developmental trajectory leading to long-term reproductive consequences in the adult female.

Gene expression analysis of estrogenic compounds in the liver of common carp (Cyprinus carpio) using a custom cDNA microarray

Exposure to a variety of compounds with estrogenic activity has been shown to interfere with normal developmental and reproductive processes in various vertebrate species. The aim of this study was to determine the transcriptional profile of the natural estrogen, 17 beta-estradiol, and three synthetic estrogenic compounds (4-nonylphenol, bisphenol A, ethinylestradiol) in the liver of common carp, using a custom cDNA microarray. For that purpose, fish were aqueously exposed to three concentrations of each chemical for 24 or 96 h. Microarray analysis revealed that a total of 185 different gene transcripts were differentially expressed following exposure to at least one of the estrogen(-like) concentrations. We were able to identify a common set of 28 gene fragments, whose expression was significantly modified in the same way by the three xenoestrogens and 17 beta-estradiol. Although several of these gene expression effects corroborated past literature data, we also discovered some novel target genes of (xeno)estrogen exposure, providing interesting insights into the molecular basis of estrogenic effects. In addition, each of the four compounds induced gene expression changes that were not, or only partially, shared by the other chemicals, suggesting that not all chemicals with estrogenic activity act alike. These results demonstrate the potential of our custom Cyprinus carpio microarray to detect common estrogen-like activity as well as to identify unique compound-associated effects of (estrogenic) endocrine disruptors in fish.

Stimulation of transactivation of the largemouth bass estrogen receptors alpha, beta-a, and beta-b by methoxychlor and its mono- and bis-demethylated metabolites in HepG2 cells

The purpose of this study was to determine the mechanisms by which the pesticide, methoxychlor (MXC), acts as an environmental endocrine disruptor through interaction with the three largemouth bass (Micropterus salmoides) estrogen receptors (ERs) alpha, betaa, and betab. MXC is a less-environmentally persistent analog of DDT that behaves as a weak estrogen. Using transient transfection assays in HepG2 cells, we have previously shown that each receptor is responsive to the endogenous ligand 17beta-estradiol (E(2)) in a dose-dependent manner. The parent compound, MXC, showed dose-dependent stimulation of transcriptional activation through all three ERs. In addition to the parent molecule, each of the metabolites was also estrogenic with all three ERs. The order of potency for ERalpha and ERbetab was HPTE>OH-MXC>MXC, while the opposite order was seen for ERbetaa. HepG2 cells did not substantially metabolize MXC to the active metabolites, thus the activity of MXC was not due to metabolism. When examining the effects of increasing concentrations of MXC at a fixed concentration of E(2), all three ERs show increased activity compared to that with E(2) alone, showing that the effects of MXC and E(2) are additive. However, when this experiment was repeated with increasing concentrations of HPTE at a fixed concentration of E(2), the activity of ERalpha was decreased, that of ERbetab was increased, while that of ERbetaa was unaffected compared to E(2) alone. These experiments suggest that HPTE functions as an E(2) antagonist with ERalpha, an E(2) agonist with ERbetab and does not perturb E(2) stimulation of ERbetaa. While it is clear the ERbeta subtypes are the products of different genes (due to a gene duplication in teleosts) the differences in their responses to MXC and its metabolites indicate that their functions diverge, both in their in vivo molecular response to E(2), as well as in their interaction with endocrine disrupting compounds found in the wild.

Increased level of cellular Bip critically determines estrogenic potency for a xenoestrogen kepone in the mouse uterus

Xenoestrogen mimics estrogen-like activities primarily based on alterations of gene expression and interactions with estrogen receptor (ER)-alpha and -beta. However, the requirement for large concentrations to induce estrogenic phenotypes and low affinity for ERs has challenged the notion that prevailing xenoestrogens are significant health hazards. Here in this study, we show that under certain conditions, exposure of xenoestrogen could be potentially harmful in respect to enhanced uterine estrogenicity. Previously, we have demonstrated that estradiol-17beta up-regulates uterine Bip, a stress-related endoplasmic reticulum protein, via an ER-independent mechanism in mice. Moreover, this protein essentially involves in estradiol-17beta-mediated uterine growth response and ERalpha-dependent gene transcription. Here, we demonstrate that among three tested xenoestrogens, only kepone (>15-30 mg/kg) exerts sustained inductive response for uterine Bip expression. Interestingly, this kepone-induced Bip strongly correlates with ERalpha-dependent growth and gene expressional responses in the mouse uterus. Furthermore, these effects were strongly suppressed after knockdown of uterine Bip, via the adenovirus approach. Although kepone at 7.5 mg/kg was not effective, it was strongly stimulatory by the adenovirus-driven forced expression of uterine Bip. In contrast, the control green fluorescence protein virus was not effective in the aforementioned responses. Furthermore, the induction of uterine Bip by stress-related signals also revealed the onset of uterine growth in mice when exposed to a sublethal dose of kepone. Collectively, studies provide novel molecular evidence that Bip acts as a critical regulator to amplify estrogenic potency for a weak xenoestrogen kepone.

The endocrine-disrupting compound, nonylphenol, inhibits neurotrophin-dependent neurite outgrowth

Endocrine-disrupting compounds (EDCs) may interfere with neuronal development due to high levels of accumulation in biological tissue and potentially aberrant steroid signaling. Treatment of dissociated embryonic Xenopus spinal cord neurons with the EDC, nonylphenol (NP), did not alter cell survival or neurite outgrowth but inhibited neurotrophin-induced neurite outgrowth, effects that were recapitulated by treatment with comparable concentrations of 17 beta-estradiol (E2) and beta-estradiol 6-(O-carboxy-methyl)oxime: BSA (E2-BSA), but not a synthetic androgen. Effects of NP were not inhibited by the nuclear estrogen receptor antagonist, ICI 182,780, but were inhibited by the G protein antagonist, pertussis toxin. Nerve growth factor (NGF)-induced neurite outgrowth in Xenopus neurons was shown to require MAPK signaling. NP did not affect TrkA expression, MAPK signaling, or phosphatidylinositol 3' kinase-Akt-glycogen synthase kinase 3 beta (PI3K-Akt-GSK3 beta) signaling in Xenopus. The ability of NP to inhibit NGF-induced neurite outgrowth without altering survival was recapitulated in the rat pheochromocytoma (PC12) cell line. As with Xenopus neurons, the inhibitory actions of NP in PC12 cells were not antagonized by ICI 182,780 and did not involve alterations in signaling along either the MAPK or PI3K-Akt-GSK3 beta pathways. NP did significantly inhibit the ability of NGF to increase protein kinase A activity in this cell line. These data have important implications with respect to potentially deleterious effects of NP exposure during early neural development and highlight the fact that bioaccumulation of EDCs, such as NP, may elicit very disparate effects along divergent signaling pathways than those that arise from the actions of physiological levels of endogenous estrogens.

RNAi-mediated silencing of estrogen receptor {alpha} in the ventromedial nucleus of hypothalamus abolishes female sexual behaviors

Estrogen receptor alpha (ERalpha) plays a major role in the regulation of neuroendocrine functions and behaviors by estrogens. Although the generation of ERalpha knockout mice advanced our knowledge of ERalpha functions, gene deletion using this method is global and potentially confounded by developmental consequences. To achieve a site-specific knockdown of ERalpha in the normally developed adult brain, we have generated an adeno-associated virus vector expressing a small hairpin RNA targeting ERalpha. After bilateral injection of this vector into the hypothalamic ventromedial nucleus in ovariectomized female mice, expression levels of ERalpha as well as the estrogen-inducible progesterone receptor were profoundly reduced despite the continued presence of this receptor elsewhere in the brain. Functionally, silencing of ERalpha in the ventromedial nucleus abolished female proceptive and receptive sexual behaviors while enhancing rejection behavior. These results provide evidence that adeno-associated virus-mediated long-term knockdown of genes can be used to delineate their effects on complex behaviors in discrete brain regions.

Methoxychlor induces atresia of antral follicles in ERalpha-overexpressing mice

Methoxychlor (MXC) is a pesticide that is known to bind to estrogen receptor alpha (ERalpha) and to induce atresia of antral ovarian follicles. Although studies have shown that MXC is toxic to the ovary, we hypothesize that perturbation to the estrogen-signaling system (i.e., increase or decrease in estrogen sensitivity) might alter ovarian responsiveness to MXC. Thus, we examined whether ERalpha overexpression alters the ability of MXC to increase follicle atresia. To do so, we employed a transgenic mouse model in which ERalpha can be inducibly overexpressed in animal tissues (ERalpha overexpressors). We dosed female controls and ERalpha overexpressors with sesame oil (vehicle control) or MXC (32 and 64 mg/kg/day) for 20 days. After dosing, the ovaries were collected for histological evaluation of follicle numbers and follicle atresia, while blood was collected for measurements of hormones. Estrous cycles were determined in all animals to ensure that all were terminated during estrus. Although there were no significant effects of MXC on the numbers of primordial, primary, and preantral follicles in both controls and ERalpha overexpressors, there was an effect on antral follicles. Specifically, our data indicate that 32 and 64 mg/kg MXC increased the percentage of atretic follicles compared to vehicle in both control and ERalpha overexpressor groups. Moreover, there was a clear trend toward greater sensitivity to 64 mg/kg MXC in ERalpha-overexpressing mice compared to control animals. Specifically, at the 64-mg/kg MXC dose, ERalpha-overexpressing mice had a significantly higher percentage of atretic follicles compared to control animals (controls = 21.5 +/- 3%, n = 5; ERalpha overexpressors = 37 +/- 23%, n = 9, p < or = 0.05 vs. controls). After 20 days of dosing, there were no differences in estradiol levels between controls and ERalpha-overexpressing mice in all treatment groups. Follicle-stimulating hormone (FSH) levels were similar in sesame oil-treated control mice and control mice treated with 32 mg/kg MXC, while control mice treated with 64 mg/kg MXC had significantly lower levels of FSH compared to sesame oil-treated controls (sesame oil = 4.31 +/- 0.7, MXC [64 mg/kg/day] = 1.89 +/- 0.4, n = 3, p < or = 0.02 vs. sesame oil). ERalpha-overexpressing mice treated with sesame oil, 32 or 64 mg/kg MXC, had similar FSH levels. Thus, we observed an increased percentage of atretic antral follicles in ERalpha-overexpressing mice treated with MXC compared to control mice treated with the same compound, suggesting that the ERalpha-signaling pathway plays an important role in MXC-induced atresia. The trend toward greater sensitivity to MXC in ERalpha-overexpressing mice compared to control animals cannot be explained by alterations in estradiol and/or FSH levels.

Pesticide exposure: the hormonal function of the female reproductive system disrupted?

Some pesticides may interfere with the female hormonal function, which may lead to negative effects on the reproductive system through disruption of the hormonal balance necessary for proper functioning. Previous studies primarily focused on interference with the estrogen and/or androgen receptor, but the hormonal function may be disrupted in many more ways through pesticide exposure. The aim of this review is to give an overview of the various ways in which pesticides may disrupt the hormonal function of the female reproductive system and in particular the ovarian cycle. Disruption can occur in all stages of hormonal regulation: 1. hormone synthesis; 2. hormone release and storage; 3. hormone transport and clearance; 4. hormone receptor recognition and binding; 5. hormone postreceptor activation; 6. the thyroid function; and 7. the central nervous system. These mechanisms are described for effects of pesticide exposure in vitro and on experimental animals in vivo. For the latter, potential effects of endocrine disrupting pesticides on the female reproductive system, i.e. modulation of hormone concentrations, ovarian cycle irregularities, and impaired fertility, are also reviewed. In epidemiological studies, exposure to pesticides has been associated with menstrual cycle disturbances, reduced fertility, prolonged time-to-pregnancy, spontaneous abortion, stillbirths, and developmental defects, which may or may not be due to disruption of the female hormonal function. Because pesticides comprise a large number of distinct substances with dissimilar structures and diverse toxicity, it is most likely that several of the above-mentioned mechanisms are involved in the pathophysiological pathways explaining the role of pesticide exposure in ovarian cycle disturbances, ultimately leading to fertility problems and other reproductive effects. In future research, information on the ways in which pesticides may disrupt the hormonal function as described in this review, can be used to generate specific hypotheses for studies on the effects of pesticides on the ovarian cycle, both in toxicological and epidemiological settings.

Cell-specific Localization of Oestrogen Receptor beta (ESR2) mRNA within Various Bovine Ovarian Cell Types Using In situ Hybridization

The localization of oestrogen receptor beta (ESR2) mRNA, in this article denominated as (ERbeta) mRNA, was examined using in situ hybridization in the ovaries of randomly selected cows, irrespective of the cycle stage of the animals. A 602-bp fragment of ERbeta mRNA was cloned, sequenced and digoxigenin (DIG)-labelled. Semi-quantitative evaluation showed that the scores for ERbeta mRNA were moderate to high in the follicle cells of both primordial and primary follicles, but lower in granulosa cells of secondary follicles. In vital tertiary follicles, the total ERbeta mRNA expression was low but varied between the different animals. In both obliterative and cystic atretic follicles, high to moderate ERbeta mRNA scores were noticed in the granulosa cells. The stroma cells surrounding primordial and primary follicles and the theca cells of secondary follicles showed moderate ERbeta mRNA levels, whereas the ERbeta mRNA score in theca interna and theca externa cells of vital tertiary follicles was distinctly higher. In the theca cells of atretic follicles the score was even higher. Cells of corpora hemorrhagica and corpora lutea had moderate ERbeta mRNA scores, while higher scores were seen in cells of corpora albicantia. Cells of the surface epithelium had a moderate score for ERbeta mRNA, whereas cells of the tunica albuginea and deep stroma showed high ERbeta mRNA scores. The present findings have clearly established a cell-specific localization of ERbeta mRNA in several cell types in the bovine ovary.

Xenoestrogens at picomolar to nanomolar concentrations trigger membrane estrogen receptor-alpha-mediated Ca2+ fluxes and prolactin release in GH3/B6 pituitary tumor cells

Xenoestrogens (XEs) are widespread in our environment and are known to have deleterious effects in animal (and perhaps human) populations. Acting as inappropriate estrogens, XEs are thought to interfere with endogenous estrogens such as estradiol (E2) to disrupt normal estrogenic signaling. We investigated the effects of E2 versus several XEs representing organochlorine pesticides (dieldrin, endosulfan, o',p'-dichlorodiphenylethylene), plastics manufacturing by-products/detergents (nonylphenol, bisphenol A), a phytoestrogen (coumestrol), and a synthetic estrogen (diethylstilbestrol) on the pituitary tumor cell subline GH3/B6/F10, previously selected for expression of high levels of membrane estrogen receptor-alpha. Picomolar to nanomolar concentrations of both E2 and XEs caused intracellular Ca2+ changes within 30 sec of administration. Each XE produced a unique temporal pattern of Ca2+ elevation. Removing Ca2+ from the extracellular solution abolished both spontaneous and XE-induced intracellular Ca2+ changes, as did 10 microM nifedipine. This suggests that XEs mediate their actions via voltage-dependent L-type Ca2+ channels in the plasma membrane. None of the Ca2+ fluxes came from intracellular Ca2+ stores. E2 and each XE also caused unique time- and concentration-dependent patterns of prolactin (PRL) secretion that were largely complete within 3 min of administration. PRL secretion was also blocked by nifedipine, demonstrating a correlation between Ca2+ influx and PRL secretion. These data indicate that at very low concentrations, XEs mediate membrane-initiated intracellular CCa2+ increases resulting in PRL secretion via a mechanism similar to that for E2, but with distinct patterns and potencies that could explain their abilities to disrupt endocrine functions.

Molecular cues to implantation

Successful implantation is the result of reciprocal interactions between the implantation-competent blastocyst and receptive uterus. Although various cellular aspects and molecular pathways of this dialogue have been identified, a comprehensive understanding of the implantation process is still missing. The receptive state of the uterus, which lasts for a limited period, is defined as the time when the uterine environment is conducive to blastocyst acceptance and implantation. A better understanding of the molecular signals that regulate uterine receptivity and implantation competency of the blastocyst is of clinical relevance because unraveling the nature of these signals may lead to strategies to correct implantation failure and improve pregnancy rates. Gene expression studies and genetically engineered mouse models have provided valuable clues to the implantation process with respect to specific growth factors, cytokines, lipid mediators, adhesion molecules, and transcription factors. However, a staggering amount of information from microarray experiments is also being generated at a rapid pace. If properly annotated and explored, this information will expand our knowledge regarding yet-to-be-identified unique, complementary, and/or redundant molecular pathways in implantation. It is hoped that the forthcoming information will generate new ideas and concepts for a process that is essential for maintaining procreation and solving major reproductive health issues in women.

Preimplantation mouse embryo development as a target of the pesticide methoxychlor

Effects of methoxychlor (MXC) and estradiol-17beta (E) were studied in mouse preimplantation embryos. Pregnant mice received s.c. injections of sesame oil only, 10 microg E, or 0.5 mg purified (95%) MXC on Days 2-4 of pregnancy (plug = Day 1). Another group received a single dose of 2.5 microg E on Day 2 only. Based on the average weight of pregnant females, 10 microg of estradiol was equivalent to 0.33 mg/kg of bw, 2.5 microg of estradiol was equivalent to 0.082 mg/kg of bw, and the 0.5-mg dose of MXC was equivalent to 16.5 mg/kg of bw. All embryos were collected for analyses on Day 4. MXC and both estradiol-17beta doses suppressed embryonic development to blastocyst, decreased embryo cell numbers, and caused abnormal blastocyst formation. The high estradiol-17beta dose significantly increased the percent degenerating embryos and caused a tube-locking effect, with retention of embryos in the oviduct. In contrast to estradiol-17beta, MXC at the dose used in this study did not alter tubal transport of embryos. Also in contrast to estradiol-17beta, MXC increased the percentage of nuclear fragmentation and micronuclei. In preimplantation embryos, MXC and estradiol-17beta both suppressed embryo development. MXC effects were, however, different from those of estradiol-17beta, indicating a difference in mechanism of action, possibly due to cytotoxicity and induction of apoptosis.

Lactoferrin gene expression and regulation: an overview

Lactoferrin is highly conserved among human, mouse, bovine, and porcine species. The numbers of amino acids encoded by 15 of the 17 exons in these species are identical, and in 12 locations, they have identical codon interruptions at the intron-exon splice junctions. However, lactoferrin expression is both ubiquitous and species, tissue, and cell-type specific. It is differentially regulated through multiple signaling pathways such as steroid hormone, growth factor, and kinase cascade pathways. Comparing the lactoferrin gene promoters from different species, common and different characteristics are observed. The human, mouse, bovine, porcine, and bubaline (African antelope) promoters all contain a noncanonical TATA box with an adjacent Sp1 site. Both human and mouse have multiple steroid hormone response elements, while none are found in the other species studied, suggesting that the lactoferrin gene is differentially regulated among different species by steroid hormones. Several transcription factors have been identified that are crucial for the expression of the lactoferrin gene during differentiation of the myeloid cells and in estrogen and epidermal growth factor regulation. This article provides an overview on lactoferrin expression and regulation in different species.

Methoxychlor stimulates the mouse lactoferrin gene promoter through a GC-rich element

The lactoferrin gene in the mouse uterus is a target gene for natural estrogens and xenoestrogens. One of the xenoestrogens is methyoxychlor, an insecticide that displays both estrogenic and antiandrogenic activities. Recently, methyoxychlor was found to stimulate lactoferrin gene expression in the uterus of an estrogen receptor null mouse. The present study is designed to uncover the methoxychlor response region in the mouse lactoferrin gene promoter. A series of different lengths of the mouse lactoferrin gene 5' flanking region were linked to a chloramphenicol acetyltransferase (CAT) reporter construct and transfected into human endometrial carcinoma HEC-1B cells, an estrogen receptor null cell line, in order to examine the methoxychlor response. The transfected cells were treated with methoxychlor or the metabolite of methoxychlor, HPTE, and the CAT reporter activities were measured. Constructs that contain a mouse lactoferrin 5' region longer than 100 bp were activated more than twofold by both methoxychlor and HPTE. The activation of the CAT reporter by the chemicals was dose dependent and reached saturation. Additional deletion mutants within the 100-bp region were tested, and a GC-rich sequence (GC-II) that we have previously characterized as an epidermal growth factor (EGF) response element was identified to be the region for the methoxychlor response. GC-II binds Sp1, Sp3, and IKLF transcription factors, collaborates with the AP1/CREB binding element, and confers the EGF response. Whether the effect of methoxychlor requires the AP1/CREB binding element has yet to be established; however, the present finding provides an alternative signaling pathway for the xenoestrogens.

A novel mechanism for endocrine-disrupting effects of polychlorinated biphenyls: direct effects on gonadotropin-releasing hormone neurones

Polychlorinated biphenyls (PCBs) cause abnormal development and physiology of the reproductive system. We hypothesized that these effects may be mediated, at least in part, by neuroendocrine cells in the hypothalamus that integrate inputs to and outputs from the central nervous system and reproductive systems. The effects of two PCB mixtures, Aroclor 1221 and Aroclor 1254, were tested on the hypothalamic GT1-7 cells, which synthesize and secrete the key hypothalamic hormone, gonadotropin-releasing hormone (GnRH). GT1-7 cells were treated for 24 h in dose-response experiments and GnRH gene expression and release were quantified. Aroclor 1221 was stimulatory to GnRH gene expression, particularly at post-transcriptional levels (GnRH cytoplasmic mRNA), and increased GnRH peptide levels, suggesting a post-translational regulation of GnRH biosynthesis. It also caused a qualitative increase in GT1-7 neurite outgrowth and cell confluency. Aroclor 1254 had very different effects from Aroclor 1221. It inhibited GnRH nuclear mRNA levels at high dosages, and stimulated GnRH mRNA at low doses, suggesting a post-transcriptional mechanism of regulation. Aroclor 1254 did not alter GnRH peptide levels. Qualitatively, Aroclor 1254 caused a retraction of GT1-7 cell processes and neurotoxicity at high dosages. In order to gauge the involvement of the oestrogen receptor in these responses, the oestrogen receptor antagonist, ICI 182,780 (ICI) was coadministered in other studies with the PCBs. While effects of Aroclor 1221 on GnRH gene expression were not blocked by ICI, its effects on GnRH peptide levels were blocked by ICI, indicating that some but not all of the effects of Aroclor 1221 are mediated by the classical oestrogen receptor alpha and/or beta. The inhibitory effects of Aroclor 1254 on GnRH gene expression were not prevented by ICI, although ICI itself had stimulatory effects on GnRH gene expression that were blocked by cotreatment with Aroclor 1254. These results demonstrate a novel mechanism for effects of the two PCBs directly on GnRH gene expression, and indicate a hypothalamic level for endocrine disruption by these environmental toxicants.

Uterine responsiveness to estradiol and DNA methylation are altered by fetal exposure to diethylstilbestrol and methoxychlor in CD-1 mice: effects of low versus high doses

We examined the effects on female CD-1 mice of fetal exposure to low doses of the drug diethylstilbestrol (DES) (0.1 microg/kg/day) and the insecticide methoxychlor (MXC) (10 microg/kg/day) as well as 1000-fold higher doses: 100 microg/kg/day DES and 10,000 microg/kg/day MXC. Pregnant females were administered these chemicals on gestation days 12-18. At 7-8 months of age, female offspring were ovariectomized and implanted for 7 days with a Silastic capsule containing estradiol. Relative to controls, females exposed to the 0.1 microg DES dose showed significantly heavier uteri, while females exposed to the 100 microg DES dose showed significantly lighter uteri. Females exposed prenatally to the 10 microg/kg dose of MXC had significantly heavier uteri relative to females exposed to the 10,000 microg/kg dose of MXC, but neither group differed significantly from controls. Liver weight for females exposed to both doses of DES was significantly greater than controls. Using a microarray approach to analyze DNA methylation, an increase in ribosomal DNA (rDNA) methylation was observed. Sequence data and Southern analysis indicate an increase in 18S rDNA and 45S pre-rDNA methylation in uterine samples exposed prenatally to low and high doses of DES. We thus found opposite effects of fetal exposure to a low and a high dose of DES on the uterine response to estradiol (inverted-U dose-response relationship). In contrast, there was a monotonic dose-response relationship found for prenatal DES exposure on both liver weight and ribosomal DNA hypermethylation.

Enhancing effects of beta-estradiol 3-benzoate but not methoxychlor on the promotion/progression stage of chemically-induced mammary carcinogenesis in ovariectomized rats

Modifying effects of beta-estradiol 3-benzoate (EB) and methoxychlor (MXC), a pesticide which possesses weak estrogenic activity, on 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary carcinogenesis were investigated in ovariectomized or intact female Sprague-Dawley rats. Twenty-eight weeks after a single DMBA (100 mg / kg body weight) initiation, when the incidence of mammary tumor-bearing rats had reached 75%, a number of the animals were subjected to ovariectomy in order to obtain 3 groups: i) tumor-bearing, ovariectomized group; ii) tumor-bearing, intact group; iii) no-tumor, ovariectomized group. Subsequently animals of each group were subjected to subcutaneous implantation of 0.5 mg EB or given diet containing 1000 ppm MXC for 13 weeks. Although the incidences, multiplicities and volumes of the palpable tumors gradually decreased after ovariectomy, EB treatment stimulated tumor growth in the tumor-bearing, ovariectomized group thereafter. A similar effect of EB treatment was also observed in the no-tumor, ovariectomized group. However, MXC did not show any effect in the tumor-bearing, or no-tumor ovariectomized groups, except that the multiplicity of tumors was significantly decreased by MXC treatment in the tumor-bearing, intact group. The results of our study suggest that MXC has no promotion / progression effect, but rather possesses a weak inhibitory effect, whereas the strongly estrogenic substance EB clearly enhanced DMBA-induced mammary tumorigenesis.

Estrogen-binding sites and their functional capacity in estrogen receptor double knockout mouse brain

Early studies found estrogen-binding sites in the ER knockout (ERalphaKO) mouse brain, suggesting a splice variant of ERalpha or another ER. The discovery of ERbeta suggested that binding was due to ERbeta, although questions about an ERgamma remained. To test this hypothesis, ERbetaKO mice were generated and crossed with ERalphaKO mice, and ERalpha/betaKO animals were used for in vivo binding studies with [(125)I]estrogen. The results revealed nuclear binding sites in the ERalpha/betaKO hypothalamus and amygdala. As the binding resembled the distribution of ERalpha, we evaluated the presence of ERalpha splicing variants. A nonphysiological splice variant of ERalpha was identified in ERalpha/betaKO brain and uterus, but was absent in wild-type mice. ERalpha immunoreactivity was also detected in regions of ERalpha/betaKO brain where residual binding was seen. To ascertain the functionality of the variant, the regulation of PR was assessed in brain. The results revealed that E2 significantly increased PR expression, an indication that the variant can regulate gene transcription. These data demonstrate the presence and functionality of an ERalpha variant in ERalpha/betaKO brain and suggest that the residual binding and regulation of PR in ERalpha/betaKO brain can be accounted for by the variant.

The pesticide methoxychlor disrupts the fusion of myoblasts into myotubes in skeletal muscle cell culture

We studied the effect of the estrogenic pesticide methoxychlor (MXC) on skeletal muscle development using C2C12 muscle cell culture. Various concentrations of MXC or beta-estradiol (E) were added to the culture media. MXC (100 microM) disrupted myoblast fusion into myotubes, but 10 microM MXC or 10 microM E had no effect. Correlated with the diminished size of the myotubes, the clustering of acetylcholine receptors (AChRs) was inhibited by 100 microM MXC, but not by 10 microM MXC or 10 microM E. However, since clusters of AChR receptors did form, the postsynaptic clustering mechanism remained intact. Since E did not disrupt myoblast fusion into myotubes or the clustering of AChRs, we conclude that the abnormality induced by MXC is mediated by a mechanism of action that is independent of E. We believe this to be the first demonstration that MXC induces abnormal effects in the process of muscle development in skeletal muscle cell culture.

Effects of currently used pesticides in assays for estrogenicity, androgenicity, and aromatase activity in vitro

Twenty-four pesticides were tested for interactions with the estrogen receptor (ER) and the androgen receptor (AR) in transactivation assays. Estrogen-like effects on MCF-7 cell proliferation and effects on CYP19 aromatase activity in human placental microsomes were also investigated. Pesticides (endosulfan, methiocarb, methomyl, pirimicarb, propamocarb, deltamethrin, fenpropathrin, dimethoate, chlorpyriphos, dichlorvos, tolchlofos-methyl, vinclozolin, iprodion, fenarimol, prochloraz, fosetyl-aluminum, chlorothalonil, daminozid, paclobutrazol, chlormequat chlorid, and ethephon) were selected according to their frequent use in Danish greenhouses. In addition, the metabolite mercaptodimethur sulfoxide, the herbicide tribenuron-methyl, and the organochlorine dieldrin, were included. Several of the pesticides, dieldrin, endosulfan, methiocarb, and fenarimol, acted both as estrogen agonists and androgen antagonists. Prochloraz reacted as both an estrogen and an androgen antagonist. Furthermore, fenarimol and prochloraz were potent aromatase inhibitors while endosulfan was a weak inhibitor. Hence, these three pesticides possess at least three different ways to potentially disturb sex hormone actions. In addition, chlorpyrifos, deltamethrin, tolclofos-methyl, and tribenuron-methyl induced weak responses in one or both estrogenicity assays. Upon cotreatment with 17beta-estradiol, the response was potentiated by endosulfan in the proliferation assay and by pirimicarb, propamocarb, and daminozid in the ER transactivation assay. Vinclozolin reacted as a potent AR antagonist and dichlorvos as a very weak one. Methomyl, pirimicarb, propamocarb, and iprodion weakly stimulated aromatase activity. Although the potencies of the pesticides to react as hormone agonists or antagonists are low compared to the natural ligands, the integrated response in the organism might be amplified by the ability of the pesticides to act via several mechanism and the frequent simultaneous exposure to several pesticides.

Contrasting phenotypes in reproductive tissues of female estrogen receptor null mice

The estrogen receptor (ER) exists in two known forms, ERalpha and ERbeta, and acts as a ligand-inducible transcription factor to fulfill critical roles in reproductive physiology. Although in vitro studies suggest the ERs may play redundant roles, a dissimilar tissue distribution indicates otherwise. Therefore, to gain insight into the role of each ER form, individual lines of mice lacking each respective receptor, as well as mice lacking both ER forms, were generated. alphaERKO and betaERKO female mice possess a normally developed reproductive tract and maintain expression of the opposite ER. The alphaERKO female is infertile and exhibits a hypoplastic uterus that is refractory to estrogens. The ovaries of the alphaERKO female are consistently polycystic and lack indications of spontaneous ovulation. In contrast, the betaERKO female exhibits a hormonally responsive uterus and grossly normal ovaries, but is subfertile in terms of the frequency and size of litters. Immature females of both ERKO lines successfully ovulate viable ova when superovulated with exogenous gonadotropins, yet the average yield of ooctyes is reduced. Mice lacking both known ER forms (alphabetaERKO) are infertile, possess the expected reproductive tract structures, but exhibit a remarkably distinct ovarian phenotype characterized by postnatal loss of oocytes and redifferentiation of the remaining somatic cells to Sertoli-like cells. This "sex-reversal" in the alphabetaERKO ovary is accompanied by the ectopic expression of testis-specific genes, for example, Sox9 and sulfatedglycoprotein-2.

Estrogen receptor-alpha knockout mice exhibit resistance to the developmental effects of neonatal diethylstilbestrol exposure on the female reproductive tract

Data indicate that estrogen-dependent and -independent pathways are involved in the teratogenic/carcinogenic syndrome that follows developmental exposure to 17beta-estradiol or diethylstilbestrol (DES), a synthetic estrogen. However, the exact role and extent to which each pathway contributes to the resulting pathology remain unknown. We employed the alphaERKO mouse, which lacks estrogen receptor-alpha (ERalpha), to discern the role of ERalpha and estrogen signaling in mediating the effects of neonatal DES exposure. The alphaERKO provides the potential to expose DES actions mediated by the second known ER, ERbeta, and those that are ER-independent. Wild-type and alphaERKO females were treated with vehicle or DES (2 microg/pup/day for Days 1-5) and terminated after 5 days and 2, 4, 8, 12, and 20 months for biochemical and histomorphological analyses. Assays for uterine expression of the genes Hoxa10, Hoxa11, and Wnt7a shortly after treatment indicated significant decreases in DES-treated wild-type but no effect in the alphaERKO. In contrast, the DES effect on uterine expression of Wnt4 and Wnt5a was preserved in both genotypes, suggesting a developmental role for ERbeta. Adult alphaERKO mice exhibited complete resistance to the chronic effects of neonatal DES exposure exhibited in treated wild-type animals, including atrophy, decreased weight, smooth muscle disorganization, and epithelial squamous metaplasia in the uterus; proliferative lesions of the oviduct; and persistent vaginal cornification. Therefore, the lack of DES effects on gene expression and tissue differentiation in the alphaERKO provides unequivocal evidence of an obligatory role for ERalpha in mediating the detrimental actions of neonatal DES exposure in the murine reproductive tract.

Neuroendocrine and behavioral implications of endocrine disrupting chemicals in quail

Studies in our laboratory have focused on endocrine, neuroendocrine, and behavioral components of reproduction in the Japanese quail. These studies considered various stages in the life cycle, including embryonic development, sexual maturation, adult reproductive function, and aging. A major focus of our research has been the role of neuroendocrine systems that appear to synchronize both endocrine and behavioral responses. These studies provide the basis for our more recent research on the impact of endocrine disrupting chemicals (EDCs) on reproductive function in the Japanese quail. These endocrine active chemicals include pesticides, herbicides, industrial products, and plant phytoestrogens. Many of these chemicals appear to mimic vertebrate steroids, often by interacting with steroid receptors. However, most EDCs have relatively weak biological activity compared to native steroid hormones. Therefore, it becomes important to understand the mode and mechanism of action of classes of these chemicals and sensitive stages in the life history of various species. Precocial birds, such as the Japanese quail, are likely to be sensitive to EDC effects during embryonic development, because sexual differentiation occurs during this period. Accordingly, adult quail may be less impacted by EDC exposure. Because there are a great many data available on normal development and reproductive function in this species, the Japanese quail provides an excellent model for examining the effects of EDCs. Thus, we have begun studies using a Japanese quail model system to study the effects of EDCs on reproductive endocrine and behavioral responses. In this review, we have two goals: first, to provide a summary of reproductive development and sexual differentiation in intact Japanese quail embryos, including ontogenetic patterns in steroid hormones in the embryonic and maturing quail. Second, we discuss some recent data from experiments in our laboratory in which EDCs have been tested in Japanese quail. The Japanese quail provides an excellent avian model for testing EDCs because this species has well-characterized reproductive endocrine and behavioral responses. Considerable research has been conducted in quail in which the effects of embryonic steroid exposure have been studied relative to reproductive behavior. Moreover, developmental processes have been studied extensively and include investigations of the reproductive axis, thyroid system, and stress and immune responses. We have conducted a number of studies, which have considered long-term neuroendocrine consequences as well as behavioral responses to steroids. Some of these studies have specifically tested the effects of embryonic steroid exposure on later reproductive function in a multigenerational context. A multigenerational exposure provides a basis for understanding potential exposure scenarios in the field. In addition, potential routes of exposure to EDCs for avian species are being considered, as well as differential effects due to stage of the life cycle at exposure to an EDC. The studies in our laboratory have used both diet and egg injection as modes of exposure for Japanese quail. In this way, birds were exposed to a specific dose of an EDC at a selected stage in development by injection. Alternatively, dietary exposure appears to be a primary route of exposure; therefore experimental exposure through the diet mimics potential field situations. Thus, experiments should consider a number of aspects of exposure when attempting to replicate field exposures to EDCs.

2-Methoxyestradiol, an endogenous estradiol metabolite, differentially inhibits granulosa and endothelial cell mitosis: a potential follicular antiangiogenic regulator

2-Methoxyestradiol (2-ME) is an estradiol metabolite with antiangiogenic and antitumor activity. It is formed by granulosa cell (GC) catechol-O-methyltransferase activity and is present in the normal follicle at high concentrations. In this unique microenvironment, it may regulate selected cell types via autocrine and/or paracrine action. To assess the possibility that 2-ME or estradiol might exert differential mitotic and/or apoptotic effects on endothelial cells and GCs, we compared their actions on primary cultures of hormone- and/or growth factor-stimulated porcine GCs (pGCs) as well as two types of endothelial cells, primary cultures of porcine endothelial cells (pECs), and a spontaneously transformed rabbit endothelial vascular cell (REVC) line. The 2-ME, but not estradiol, dose dependently suppressed tritiated thymidine ((3)H-T) incorporation into epidermal growth factor (EGF)-stimulated REVCs and EGF/insulin (INS)-stimulated pECs. In contrast, 2-ME did not attenuate incorporation in FSH/INS-stimulated pGCs. It reduced incorporation by approximately 50% in EGF/INS-stimulated pGCs, indicating that responsiveness to 2-ME in normal cells can be modulated by hormone and growth factor treatment. Estradiol was not antimitotic to pGCs. As indicated by 4',6-diamido-2-phenylindole hydrochloride nuclear staining, estradiol was nonapoptotic in either cell type, and 2-ME significantly increased apoptosis of REVCs, but not of pGCs. In a cell migration assay, REVC movement was attenuated by 2-ME, but not by estradiol. In summary, the results show that antimitotic as well as proapoptotic responses to 2-ME vary with cell type and, in the case of pGC antimitotic activity, with the regulatory microenvironment. Thus, they provide a rationale for autocrine and/or paracrine action of 2-ME at its site of production in vivo, and they strongly support the concept of 2-ME as a candidate ovarian angiogenesis inhibitor.

Estrogen receptor- and aromatase-deficient mice provide insight into the roles of estrogen within the ovary and uterus

Estrogen receptor (ER)- (alpha, beta, and both alpha and beta) and aromatase (Ar) knockout (KO) mice have been created to assess the biological effects of estrogens. This review article discusses the ovarian and uterine phenotypes of these mice. The data obtained have confirmed some older inferences about how the steroid acts, but have also revealed some unexpected aspects of estrogen action. Mol. Reprod. Dev. 59:336-346, 2001.

Estrogen receptor specificity in the regulation of skeletal growth and maturation in male mice

Androgens may regulate the male skeleton directly through a stimulation of androgen receptors or indirectly through aromatization of androgens into estrogen and, thereafter, through stimulation of estrogen receptors (ERs). The relative importance of ER subtypes in the regulation of the male skeleton was studied in ERalpha-knockout (ERKO), ERbeta-knockout (BERKO), and double ERalpha/beta-knockout (DERKO) mice. ERKO and DERKO, but not BERKO, demonstrated decreased longitudinal as well as radial skeletal growth associated with decreased serum levels of insulin-like growth factor I. Therefore, ERalpha, but not ERbeta, mediates important effects of estrogen in the skeleton of male mice during growth and maturation.