Estrogen receptor (ER) and its messenger ribonucleic acid expression in the genital tract of female mice exposed neonatally to tamoxifen and diethylstilbestrol

New frontiers of developmental endocrinology opened by researchers connecting irreversible effects of sex hormones on developing organs

In the early 1960's, at Professor Bern's laboratory, University of California, Berkeley) in the US, Takasugi discovered ovary-independent, persistent vaginal changes in mice exposed neonatally to estrogen, which resulted in vaginal cancer later in life. Reproductive abnormalities in rodents were reported as a result of perinatal exposure to various estrogenic chemicals. Ten years later, vaginal cancers were reported in young women exposed in utero to the synthetic estrogen diethylstilbestrol (DES) and this has been called the "DES syndrome". The developing organism is particularly sensitive to developmental exposure to estrogens inducing long-term changes in various organs including the reproductive organs. The molecular mechanism underlying the persistent vaginal changes induced by perinatal estrogen exposure was partly demonstrated. Persistent phosphorylation and sustained expression of EGF-like growth factors, lead to estrogen receptor α (ESR1) activation, and then persistent vaginal epithelial cell proliferation. Agents which are weakly estrogenic by postnatal criteria may have major developmental effects, especially during a critical perinatal period. The present review outlines various studies conducted by four generations of investigators all under the influence of Prof. Bern. The studies include reports of persistent changes induced by neonatal androgen exposure, analyses of estrogen responsive genes, factors determining epithelial differentiation in the Müllerian duct, ESR and growth factor signaling, and polyovular follicles in mammals. This review is then expanded to the studies on the effects of environmental estrogens on wildlife and endocrine disruption in Daphnids.

The platelet-derived growth factor receptor alpha promoter-directed expression of cre recombinase in mouse placenta

Background

Numerous pathologies of pregnancy originate from placental dysfunction. It is essential to understand the functions of key genes in the placenta in order to discern the etiology of placental pathologies. A paucity of animal models that allow conditional and inducible expression of a target gene in the placenta is a major limitation for studying placental development and function.

Results

To study the platelet‐derived growth factor receptor alpha (PDGFRα)‐directed and tamoxifen‐induced Cre recombinase expression in the placenta, PDGFRα‐CreER mice were crossed with mT/mG dual‐fluorescent reporter mice. The expression of endogenous membrane‐localized enhanced green fluorescent protein (mEGFP) and/or dTomato in the placenta was examined to identify PDGFRα promoter‐directed Cre expression. Pregnant PDGFRα‐CreER;mT/mG mice were treated with tamoxifen at various gestational ages. Upon tamoxifen treatment, reporter protein mEGFP was observed in the junctional zone (JZ) and chorionic plate (CP). Furthermore, a single dose of tamoxifen was sufficient to induce the recombination.

Conclusions

PDGFRα‐CreER expression is restricted to the JZ and CP of mouse placentas. PDGFRα‐CreER mice provide a useful tool to conditionally knock out or overexpress a target gene in these regions of the mouse placenta.

Inducible PDGFRα‐directed Cre expression trophoblasts cells.

A single tamoxifen treatment is sufficient to induce the recombination.

Valuable tool to temporary knockout or over‐express a target gene in the placenta.

Do not require sophisticated system and suitable for ordinary laboratory setting.

Neonatal Estrogen Receptor β Is Important in the Permanent Inhibition of Epithelial Cell Proliferation in the Mouse Uterus

Estrogen receptor α (ERα) plays a pivotal role in the mouse uterine and vaginal epithelial cell proliferation stimulated by estrogen, whereas ERβ inhibits cell proliferation. ERβ mRNA is expressed in neonatal uteri and vaginae; however, its functions in neonatal tissues have not been ascertained. In this study, we investigated the ontogenic mRNA expression and localization of ERβ, and its roles in cell proliferation in neonatal uteri and vaginae of ERβ knockout (βERKO) mice. ERβ mRNA and protein were abundant in the uterine and vaginal epithelia of 2-day-old mice and decreased with age. In uterine and vaginal epithelia of 2-day-old βERKO mice, cell proliferation was greater than that in wild-type animals and in uterine epithelia of 90- and 365-day-old βERKO mice. In addition, p27 protein, known as a cyclin-dependent kinase inhibitor, was decreased in the uteri of 90- and 365-day-old βERKO mice. Inhibition of neonatal ERs by ICI 182780 (an ER antagonist) treatment stimulated cell proliferation and decreased p27 protein in the uterine luminal epithelium of 90-day-old mice but not in the vaginal epithelium. These results suggest that neonatal ERβ is important in the persistent inhibition of epithelial cell proliferation with accumulation of p27 protein in the mouse uterus. Thus, suppression of ERβ function in the uterine epithelium during the neonatal period may be responsible for a risk for proliferative disease in adults.

Tamoxifen affects glucose and lipid metabolism parameters, causes browning of subcutaneous adipose tissue and transient body composition changes in C57BL/6NTac mice

Tamoxifen is a selective estrogen receptor (ER) modulator which is widely used to generate inducible conditional transgenic mouse models. Activation of ER signaling plays an important role in the regulation of adipose tissue (AT) metabolism. We therefore tested the hypothesis that tamoxifen administration causes changes in AT biology in vivo. 12 weeks old male C57BL/6NTac mice were treated with either tamoxifen (n = 18) or vehicle (n = 18) for 5 consecutive days. Tamoxifen treatment effects on body composition, energy homeostasis, parameters of AT biology, glucose and lipid metabolism were investigated up to an age of 18 weeks. We found that tamoxifen treatment causes: I) significantly increased HbA1c, triglyceride and free fatty acid serum concentrations (p < 0.01), II) browning of subcutaneous AT and increased UCP-1 expression, III) increased AT proliferation marker Ki67 mRNA expression, IV) changes in adipocyte size distribution, and V) transient body composition changes. Tamoxifen may induce changes in body composition, whole body glucose and lipid metabolism and has significant effects on AT biology, which need to be considered when using Tamoxifen as a tool to induce conditional transgenic mouse models. Our data further suggest that tamoxifen-treated wildtype mice should be characterized in parallel to experimental transgenic models to control for tamoxifen administration effects.

Activated vitamin D3 and pro-activated vitamin D3 attenuate induction of permanent changes caused by neonatal estrogen exposure in the mouse vagina

Exposure of mice to a high dose of estrogens including diethylstilbestrol (DES) during the neonatal period modifies the developmental plan of the genital tract, which leads to various permanent changes in physiology, morphology and gene expression. These changes include development of an abnormal vaginal epithelium lined with hyperplastic mucinous cells accompanied by Tff1 gene expression in mice. Here, the influence of vitamin D on the direct effect of estrogen on the developing mouse vagina was examined. The mid-vagina of neonatal mice was cultured in a serum-free medium containing estradiol-17β (E₂) and various concentrations of 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D) ex vivo and then was transplanted under the renal capsule of ovariectomized host mice for 35 days. Exposure to E₂ alone caused the vaginal tissue to develop estrogen-independent epithelial hyperplasia and to express TFF1 mRNA, while addition of a low nanomolar amount of 1,25(OH)₂D added at the same time as E₂ to the culture medium attenuated the effects of estrogen. Expression of vitamin D receptor was also evident in the neonatal mouse vagina. Interestingly, addition of 25-hydroxyvitamin D₃, a pro-activated form of vitamin D, at the micromolar level was found to be potent in disrupting the developmental effects of E₂, while cholecalciferol was not at least at the dose examined. Correspondingly, expression of Cyp27B1, a kidney-specific 25-hydroxyvitamin D hydroxylase, was evident in the neonatal mouse vagina when examined by RT-PCR. In addition, simultaneous administration of 1,25(OH)₂D successfully attenuated DES-induced ovary-independent hyperplasia in the vagina in neonatal mice in vivo. Thus, manipulation of vitamin D influenced the harmful effects of estrogens on mouse vaginal development.

Menstrual and reproductive characteristics of women whose mothers were exposed in utero to diethylstilbestrol (DES)

BACKGROUND

In women, prenatal exposure to diethylstilbestrol (DES) is associated with adult reproductive dysfunction. The mouse model, which replicates many DES outcomes, suggests DES causes epigenetic alterations, which are transmissable to daughters of prenatally exposed animals. We report menstrual and reproductive characteristics in a unique cohort comprising daughters of women exposed prenatally to DES.

METHODS

Menstrual and reproductive outcomes and baseline characteristics were assessed by mailed questionnaire in 793 women whose mothers had documented information regarding in utero DES exposure.

RESULTS

Mean age at menarche was 12.6 years in both groups, but daughters of the exposed women attained menstrual regularization later (mean age of 16.2 years vs. 15.8 years; P = 0.05), and were more likely to report irregular menstrual periods, odds ratio (OR) = 1.54 [95% confidence interval (95% CI 1.02-2.32)]. A possible association between mothers' DES exposure and daughters' infertility was compatible with chance, age, and cohort adjusted OR = 2.19 (95% CI 0.95-5.07). We found limited evidence that daughters of the exposed had more adverse reproductive outcomes, but daughters of exposed women had fewer live births (1.6) than the unexposed (1.9) (P = 0.005).

CONCLUSIONS

The high risk of reproductive dysfunction seen in women exposed to DES in utero was not observed in their daughters, but most women in our cohort have not yet attempted to start their families, and further follow-up is needed to assess their reproductive health. Our findings of menstrual irregularity and possible infertility in third-generation women are preliminary but compatible with speculation regarding transgenerational transmission of DES-related epigenetic alterations in humans.

Persistent trefoil factor 1 expression imprinted on mouse vaginal epithelium by neonatal estrogenization

Exposure of female mice to estrogenic substances during the neonatal period induces developmental defects in the reproductive tract such as estrogen-independent persistent proliferation of the vaginal epithelium, which often leads to carcinogenesis in adulthood. In this study, several estrogen-regulated genes have been identified in the neonatal mouse vagina by DNA microarray hybridization analysis. Among the genes up-regulated in the developing vagina by a high dose of estrogen, trefoil factor 1 (TFF1), a mucin-associated gastrointestinal growth factor, showed a unique expression pattern in accordance with the irreversible changes induced by neonatal estrogenization in the vagina. Vaginal expression of TFF1 mRNA was markedly increased by estrogen in neonatal mice but not in adults, and pronouncedly intensified expression of the gastrointestinal gene was observed in the vagina of neonatally estrogenized mice even at adulthood. The specific localization of TFF1 protein in the epithelium of neonatally estrogenized vagina was confirmed by immunohistochemistry. Moreover, without any obvious alteration in the expression of gel-forming mucin genes, the lumen of the neonatally estrogenized vagina became filled with periodic-acid-Schiff-stained mucinous gel, which was possibly caused by the overexpression of TFF1. Thus, estrogen acts directly on the developing vagina in the permanent induction of TFF1 gene expression, and the gene induction does not appear to be related to hypermethylation of the cis-promoter of the TFF1 gene. TFF1 may be a useful marker for developmental estrogenization syndrome of the mouse vagina.

SEX STEROID HORMONE RECEPTORS IN THE DEVELOPING FEMALE REPRODUCTIVE TRACT OF LABORATORY RODENTS

Many chemicals released into the environment potentially disrupt the endocrine system in wildlife and humans. Some of these chemicals exhibit estrogenic activity by binding to the estrogen receptors. The developing organism is particularly sensitive to estrogenic chemicals during the critical period in which the induction of long-term changes and persistent molecular alterations in female reproductive tracts occur. Perinatal mouse and rat models can be utilized as indicators for determining the consequences of exposure to exogenous estrogenic agents, including possible xenoestrogens or environmental endocrine disruptors. Estrogen receptors (ER) and estrogen responsive genes, therefore, need to be identified in order to understand the molecular basis of estrogenic actions. Recent identifications of ER subtypes and isoforms make understanding target organ responses to these estrogenic chemicals even more difficult. Indeed, many reports suggest that these chemicals do affect the reproductive and developmental processes of female laboratory rodents that had been perinatally exposed, and that interactions between sex steroid hormone receptors occur. Much information concerning the expression of sex steroid receptors in rodents has been reported concerning the normal development of the Müllerian duct. Thus, accumulated information on the expression of ER subtypes and isoforms as well as that of progesterone and androgen receptors in laboratory rodents is herein reviewed, in addition to the presentation of our own data.

Involvement of growth factors in induction of persistent proliferation of vaginal epithelium of mice exposed neonatally to diethylstilbestrol

Neonatal treatment of female mice with natural and synthetic estrogens including diethylstilbestrol (DES) results in persistent proliferation and cornification of vaginal epithelium. In order to study the mechanism of persistent proliferation of vaginal epithelium, histological and biochemical changes were examined in the vagina of C57BL female mice exposed neonatally to 3 microg DES for 5 days. In intact control adult mice, ovariectomy induced apoptotic cell death in vaginal epithelial cells detected by in situ 3'-DNA nick end labeling method accompanied by low DNA synthesis detected by incorporation of bromodeoxyuridine. In neonatally DES-exposed adult mice, however, ovariectomy did not induce reduction of DNA synthesis and showed only a slight increase in apoptotic cells of vaginal epithelium. In neonatally DES-exposed mouse vagina, semi-quantitative reverse transcription polymerase chain reaction revealed a continuous higher expression of mRNAs encoding epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha). These results indicate that neonatal DES exposure causes the increase in expression of EGF and TGF-alpha mRNA, possibly resulting in the induction of persistent proliferation and cornification of vaginal epithelium in mice.

Involvement of keratinocyte growth factor (KGF)-KGF receptor signaling in developmental estrogenization syndrome of mouse vagina

Exposure of mice to estrogen or keratinocyte growth factor (KGF) in vivo during the neonatal period results in estrogen-independent persistent proliferation and cornification of the vaginal epithelium when the animals become adults. Here, whether and how KGF-signaling is involved in the effects of estrogen on the neonatal mouse vagina were studied with an in vitro method. Newborn mouse vaginae were cultured for 3 days in serum-free medium containing various combinations of estradiol-17beta (E2), KGF, anti-KGF antibody, KGFR inhibitory peptide and heparin, and then transplanted into ovariectomized host mice for 35 days. The vaginae cultured with 5 microg/ml E2 or 5 microg/ml KGF had a cornified thick epithelium, while the epithelium of the vehicle-treated controls stayed thin. The E2 effect was blocked by concurrent treatment with anti-KGF antibody or KGFR inhibitory peptide. KGF treatment alone at doses less than 500 ng/ml did not induce permanent vaginal changes but such changes did occur in vaginae treated with heparin plus as little as 10 ng/ml KGF. On the other hand, heparin inhibited the permanent vaginal changes induced by estrogen. These results suggest that irreversible vaginal changes are induced by the direct action of KGF on the developing vagina and that the developmental estrogenization syndrome of mouse vagina is caused by intensification of endogenous KGF/KGFR signaling by exogenous estrogen.

Ontogenic expression of estrogen receptor coactivators in the reproductive tract of female mice neonatally exposed to diethylstilbestrol

Ontogenic expression of p300, steroid receptor coactivator-1 (SRC-1), GR-interacting protein-1 (GRIP1) and p300/CBP cointegrator associate protein (p/CIP) was examined using an immunohistochemical method in the genital tract of female mice neonatally exposed to diethylstilbestrol (DES). Mice were injected with 4 microg of DES for 5 days and killed on days 10, 15 and 21; some mice were killed on day 4 after three injections. The p300 immunoreactive protein in the epithelial cells of the oviducts, uteri, and vaginae was almost constant during development independent of neonatal DES exposure, while the stromal cells exhibited a weaker reaction than that of the vehicle-treated controls on days 4 and 10. Neonatal DES exposure caused no significant changes in the SRC-1 and p/CIP expression patterns but decreased the GRIP1 expression with development in the reproductive tract. The constitutive expression of coactivators in both epithelial and stromal cells may play a role in the estrogen imprints through ER alpha systems during the period of DES treatment.

Estrogen-independent activation of erbBs signaling and estrogen receptor alpha in the mouse vagina exposed neonatally to diethylstilbestrol

Growth factors and estrogen receptor (ER) signaling cooperate to play essential roles in cell proliferation, differentiation and tumor progression in mouse reproductive organs. Treatment of neonatal mice with diethylstilbestrol (DES) induces an estrogen-independent persistent proliferation and cornification of the vaginal epithelium, which results in cancerous lesions later in life. However, the mechanisms of the estrogen-dependent and -independent pathways essentially remain unknown. We characterized the expression of epidermal growth factor (EGF)-like growth factors (EGF, transforming growth factor alpha (TGF-alpha), heparin-binding EGF-like growth factor (HB-EGF), betacellulin (BTC), amphiregulin (APR), epiregulin (EPR) and neuregulin (NRG) 1) and erbB receptors (EGF receptor (EGFR), erbB2/neu, erbB3 and erbB4) in the vaginae of mice treated either neonatally (0-4 day) or as adults (55-59 day) with estrogens. EGFR and erbB2 were activated in the vaginal epithelium of mice by estrogen treatment. This activation was also encountered in vaginae from neonatally DES-exposed mice, along with the expression of EGF, TGF-alpha, HB-EGF, BTC, APR, EPR and NRG1. Immunohistochemical analysis indicated that erbB2 was primarily expressed in vaginal epithelium. Finally, we found that serine 118 and 167 located in the AF-1 domain of ERalpha were phosphorylated in these vaginae. AG825, AG1478 or ICI 182,780 administration blocked proliferation of vaginal epithelium induced by neonatal DES exposure. Thus, signal transduction via EGFR and erbB2 could be related to the estrogen-induced vaginal changes and persistent erbBs phosphorylation and sustained expression of EGF-like growth factors, leading to ERalpha activation that may result in cancerous lesions in vaginae from neonatally DES-exposed mice later in life.

Maternal-fetal transfer of endocrine disruptors in the induction of Calbindin-D9k mRNA and protein during pregnancy in rat model

Estrogenic compounds may influence the growth, differentiation and function in many target tissues, especially in the female reproductive tract during pregnancy. The present study was designed to investigate whether CaBP-9k expression in the maternal tissues and fetal uterus is altered following maternal treatment with diethylstilbestrol (DES), 17beta-estradiol (E2), 4-tert-octylphenol (OP), nonylphenol (NP) and bisphenol A (BPA) during late pregnancy. The expression level of CaBP-9k mRNA in maternal uterus significantly increased when treated with a high dose (600 mg/kg BW per day) of OP and NP. Interestingly, the expression level of CaBP-9k mRNA in extra-embryonic membrane decreased in a dose-dependent manner, suggesting that the expression level of CaBP-9k mRNA in the fetal membrane may be differentially regulated when compared to the expression of CaBP-9k in maternal uterus. In parallel with CaBP-9k mRNA level, a high dose (600 mg/kg) of OP and BPA resulted in an increase of CaBP-9k protein in maternal uterus and low dose of OP and NP increased the expression level of CaBP-9k protein in the placenta. High doses of BPA (400 and 600 mg/kg) resulted in an increase of CaBP-9k protein in maternal uterus and placenta, indicating that these estrogenic compounds may affect both maternal uterus and placenta in the induction of CaBP-9k mRNA and/or protein. In parallel with the expression level of CaBP-9k, mRNA decreased in extra-embryonic membrane, treatment with OP (400 and 600 mg/kg) resulted in a significant decrease of CaBP-9k protein in this tissue, suggesting that both CaBP-9k mRNA and protein may be conversely regulated by OP in extra-embryonic membrane when compared to other tissues. Treatment with OP, NP, and BPA induced a significant increase of CaBP-9k mRNA in fetal uterus, indicating that maternally injected estrogenic compounds may transfer directly from placenta to fetus in the induction of fetal uterus CaBP-9k gene. Taken together, we demonstrated for the first time that maternally injected estrogenic compounds resulted in an increase of CaBP-9k mRNA and/or protein in the maternal tissues (uterus and placenta) and fetal uterus during late pregnancy, suggesting that placenta may not be a reliable barrier against these estrogenic compounds for fetal health.

Vitamin A prevents the irreversible proliferation of vaginal epithelium induced by neonatal injection of keratinocyte growth factor in mice

Exposure of female mice to estrogen during the perinatal period results in estrogen-independent persistent proliferation and cornification of the vaginal epithelium when the animals become adults. However, the occurrence of such irreversible vaginal changes is blocked by concurrent vitamin A treatment. Neonatal exposure to keratinocyte growth factor (KGF), which is a paracrine mediator of epithelial-mesenchymal interactions, also induces the persistent proliferation and cornification of the vaginal epithelium in adult mice. This study was designed to examine whether concurrent administration of vitamin A inhibits the development of the irreversible vaginal changes in mice exposed neonatally to KGF. The vaginal epithelium in ovariectomized 35-day-old mice given 5 microg of KGF for 3 days after birth possessed a significantly larger number of layers and increased thickness as compared to that in control mice. Concurrent injections of 100 IU of vitamin A acetate inhibited the occurrence of the irreversible proliferation of the vaginal epithelium. These changes were equal to the results observed when 20 micro g of estrogen with or without vitamin A acetate was administered for 5 days after birth. Unlike the case of estrogen treatment, the effect of neonatal treatment with KGF seemed to appear after a latent period, since the vaginal epithelium did not show proliferation soon after the treatment. We discuss the inhibitory effect of VA on the irreversible vaginal changes induced by neonatal KGF treatment with reference to endocrine disruption by neonatal estrogen exposure.

Effect of estrogens on ontogenetic expression of progesterone receptor in the fetal female rat reproductive tract

Ontogenetic expression of progesterone receptor (PR) and effect of estrogens on PR expression in the fetal female rat reproductive tract were investigated. To evaluate ontogenetic PR expression, female reproductive tract from untreated fetuses was examined on gestational days (GD) 15.5, 17.5, 19.5 and 21.5. To evaluate estrogen effects, pregnant rats were injected once per day with oil, 17beta-estradiol (E(2)) or diethylstilbestrol (DES) from GD 15 through 21. Female fetuses were prepared for real-time reverse-transcription polymerase chain reaction (RT-PCR) or immunohistochemistry for PR. Increase in PR mRNA expression was detected in the Müllerian duct on GD 21.5 compared to that on GDs 15.5 and 17.5 in untreated fetuses (P<0.05). Prenatal administration of E(2) or DES increased Müllerian PR mRNA levels by GD 21.5 compared with oil controls (P<0.01). To identify cell and region in which PR was expressed and up-regulated by E(2) and DES, localization was evaluated within three regions along the Müllerian duct axis which differentiate into oviduct, uterus and upper vagina in immunohistochemistry. In untreated fetuses, Müllerian epithelial PR immunoreactivity was weak on GDs 15.5 and 17.5, but then became moderate on GDs 19.5 and 21.5 in all three regions. These fetuses exhibited faint signals in Müllerian mesenchymal PR immunoreactivity during gestational monitoring. Critically, Müllerian mesenchymal PR staining became intense after E(2) exposure in all three regions by GD 21.5, but no change was observed in Müllerian epithelial PR. Similarly, DES dramatically induced Müllerian mesenchymal PR in all regions by GD 21.5, and also enhanced proximal epithelial PR. On the other hand, middle and caudal epithelial PRs were reduced by DES. These affected mesenchymal and epithelial cells by DES were ER alpha immunopositive in the Müllerian duct, except for middle Müllerian epithelium. These findings clearly demonstrate cell-specific PR localization and region-specific effect of DES on PR in the developing rat Müllerian duct, and provide fundamental information critical for investigating the tissue-specific mechanisms underlying the prenatal response to estrogen receptor agonists.

Developmental toxicity of estrogenic chemicals on rodents and other species

Antenatal sex-hormone exposure induces lesions in mouse reproductive organs, which are similar to those in humans exposed in utero to a synthetic estrogen, diethylstilbestrol. The developing organisms including rodents, fish and amphibians are particularly sensitive to exposure to estrogenic chemicals during a critical window. Exposure to estrogens during the critical period induces long-term changes in reproductive as well as non-reproductive organs, including persistent molecular alterations. The antenatal mouse model can be utilized as an indicator of possible long-term consequences of exposure to exogenous estrogenic compounds including possible environmental endocrine disruptors. Many chemicals released into the environment potentially disrupt the endocrine system in wildlife and humans, some of which exhibit estrogenic activity by binding to the estrogen receptors. Estrogen responsive genes, therefore, need to be identified to understand the molecular basis of estrogenic actions. In order to understand molecular mechanisms of estrogenic chemicals on developing organisms, we are identifying estrogen responsive genes using cDNA microarray, quantitative RT-PCR, and differential display methods, and genes related to the estrogen-independent vaginal changes in mice induced by estrogens during the critical window. In this review, discussion of our own findings related to endocrine distuptor issue will be provided.

Neonatal exposure to p-tert-octylphenol causes abnormal expression of estrogen receptor alpha and subsequent alteration of cell proliferating activity in the developing Donryu rat uterus

In the present study, we investigated immunohistochemically the time-course alterations in estrogen receptor alpha (ER) expression and cell proliferating activity in the developing uteri of Donryu rats exposed neonatally to a high dose p-tert-octylphenol (OP), an endocrine disrupting chemical (EDC). OP-treatment (sc injections of 100 mg/kg, every other day from postnatal days 1 to 15) induced an early and enhanced ER expression in the luminal epithelium compared with age-matched controls from postnatal day (PND) 10, and increased proliferating cell nuclear antigen (PCNA) positive cells up to PND21. At PND28, ER expression in the luminal epithelium of the OP-treated group was decreased, in association with decline in the luminal epithelial areas. PND14, the second week of life, is coincident with the normal time for differentiation when the luminal epithelium invaginates into the stroma to form uterine glands. OP-treatment, however, delayed and inhibited gland-formation, and suppressed ER expression in the invaginated-luminal and glandular epithelium at this time. These results indicate that ER expression in these sites is strongly linked with cell proliferating activity. In stromal cells, ER was expressed from PND6 in both groups without any PCNA positive cells, but significantly lower values were noted in the OP-treated group up to PND10. Our immunohistochemical investigation did not reveal any abnormalities in expression of the proto-oncogene c-fos, mitotic inhibitor p21, or epidermal growth factor antigen, although the apoptotic index in the luminal epithelium was slightly increased in the OP-treated group. These results demonstrate neonatal effects of a high dose of OP, already detectable at PND10, with early and enhanced ER expression, resulting in increase of cell proliferative activity in the luminal epithelium, though expression in the glandular epithelium was suppressed in relation to inhibited gland-genesis. The present study thus suggests that neonatal exposure to high doses of EDCs with estrogenic activity can induce abnormal differentiation in the developing rat uteri via abnormal ER expression and subsequent alteration of cell proliferating activity.

Characterization of diethylstilbestrol-induced hypospadias in female mice

The urethral duct and vagina are formed from the urogenital sinus (UGS) during the early neonatal period in mice. Neonatal estrogen exposure results in hypospadias, or the malpositioning of vaginal and urethral openings, with wide cleft clitoris. We sought to characterize diethylstilbestrol (DES) influence on UGS morphogenesis and hypospadias formation. Newborn (day 0) and 1-4-day-old female mice (ICR/Jcl) were given (s.c.) oil or 3.0 microg DES. Animals were killed 24 hr later; then hypospadias formation and epithelial apoptosis and proliferation within the developing UGS were assessed. DES did not alter normal UGS morphogenesis by day 1, in comparison with controls. However, hypospadias formation was observed in DES-treated mice by day 3. In these mice, the distal dorsal urethral duct appeared to fuse with and open into the lower vaginal solid cord region. Further, DES treatment produced a gradual significant increase in dorsal urethral epithelial apoptosis (P < 0.05) just prior to and during fusion and hypospadias formation. DES-induced urethral epithelial and sinus cord proliferation appeared significantly increased (P < 0.05) and unchanged, respectively, just prior to fusion. By day 5, DES-treated mice exhibited wide cleft clitoris. In addition, if DES was given on day 3 or 5, a gradual, distinct caudal shift in the vaginal-urethral junction was observed compared to mice treated on days 0-2. Although hypospadias was not induced when neonates were given DES on day 7, these mice continued to display early vaginal opening. Dose-response analysis indicated that 0.03 microg DES for 5 days is the lowest known critical dose for hypospadias induction. We have shown for the first time that DES-induced hypospadias onset may primarily be the result of changes in developing dorsal urethral epithelial cell apoptotic and proliferative activity, and that the location of DES-induced hypospadias formation is dependent on age at time of exposure.

The effect of a single neonatal treatment (hormonal imprinting) with the antihormones, tamoxifen and mifepristone on the sexual behavior of adult rats

Hormonal imprinting takes place perinatally during the first encounter between the hormone and its developing receptor. The presence of an excess of related molecules in that time provokes faulty (pathological) imprinting. In the present experiments single-neonatal treatment with 100 microg of tamoxifen completely abolished the adult male and female rats' sexual activity. Similar treatment with 100 microg of mifepristone (RU486) significantly enhanced the males sexual activity and non-significantly increased that of the females. The results demonstrate the importance of pathological imprinting during the perinatal development of sexual behavior. There are clear differences between the molecules having steroid (mifepristone) or non-steroid (tamoxifen) character, mediated through a ligand-receptor complex, and its effect in activating particular genes.

Histochemistry and cytochemistry of nuclear receptors

Receptors of steroid hormones, thyroid hormones and several kinds of vitamins have been shown to act as nuclear transcription factors and to form a nuclear receptor (NR) family. Histochemical techniques including autoradiography using radio-labeled ligands, immunohistochemistry and in situ hybridization histochemistry, have displayed that target cells of these receptors are distributed not only in the classical target organs but also widely in a variety of tissues; these techniques can demonstrate the presence of receptor proteins and mRNAs, even though they are expressed in a small cell population of tissues. On the other hand, many studies have been performed to demonstrate the interaction between NRs and nuclear and cytoplasmic proteins, and to clarify the mechanism of transcriptional regulation through NRs in artificial conditions which are created in gene transfer experiments or under cell-free conditions. Some data coincide with those obtained from histochemical techniques, however, some histochemical data do not support the results of studies in vitro. This review focuses on the following topics: histochemical methodologies to detect NRs, the distribution and function of NRs in the tissues, the intracellular and intranuclear localization of NRs, roles of gonadal steroid receptors and their ligands on developing tissues including cell communications such as mesenchymal-stromal interaction, and the interaction between other cellular components and NRs. In addition, the agreement and disagreement between the results of histochemical studies and those from the experiments in the model systems or in vitro are discussed.

Evidence that estrogens directly alter androgen-regulated prostate development

Neonatal exposure to high doses of estrogen results in permanent suppression of prostate growth and reduced sensitivity to androgens in adulthood. It is unclear whether alterations in prostate growth are due to a direct effect of estrogens on the gland or are the result of hypothalamic-pituitary-gonadal axis suppression and a subsequent reduction in androgen levels. Therefore, the aim of this study was to determine whether estrogens have a direct effect on the prostate using a defined method of culturing neonatal prostates. Newborn rat ventral prostates were microdissected and cultured in the presence of testosterone, which resulted in branching morphogenesis and ductal canalization. Solid cords of epithelium differentiated into acini lined by tall columnar epithelial cells; these acini were surrounded by stromal cells, expressing smooth muscle alpha-actin. When cultured in the presence of 17beta-estradiol or diethylstilbestrol in addition to testosterone, androgen-induced prostatic growth was reduced, and differentiation was altered. Although estrogen-treated explants were smaller than controls, quantification of epithelial, stromal, and luminal volumes using unbiased stereology revealed significant changes; the proportion of epithelial cells and lumen decreased, and the proportion of stroma increased compared with control values. Concurrent with this reduced growth rate, we observed a disturbance in the branching pattern and a reduction in ductal canalization. Specifically, stromal differentiation and organization were disrupted, so that a discontinuous smooth muscle layer was observed around the epithelial ducts, and epithelial differentiation was altered. The effects of estrogens were not accompanied by a decrease in androgen response via the androgen receptor, because immunolocalization of this receptor remained constant. These data demonstrate that high doses of estrogens are growth inhibitory and have direct effects on prostate development in vitro, which may occur in vivo in addition to indirect effects via suppression of the hypothalamic-pituitary-gonadal axis.

Tamoxifen induces endometrial and vaginal cancer in rats in the absence of endometrial hyperplasia

Tamoxifen was administered orally to neonatal rats on days 2-5 after birth and the subsequent effects on the uterus were characterized, morphometrically, over the following 12 months. Tamoxifen inhibited development of the uterus and glands in the endometrium, indicating a classical oestrogen antagonist action. Between 24 and 35 months after tamoxifen treatment there was a significant increase in the incidence (26%) of uterine adenocarcinomas and a 9% incidence of squamous cell carcinomas of the vagina/cervix in the absence of any oestrogen agonist effect in the uterus. This demonstrates that an oestrogen agonist effect is not an absolute requirement for the carcinogenic effect of tamoxifen in the reproductive tract of the rat. The unopposed oestrogen agonist effect of tamoxifen on the endometrium may not be the only factor involved in the development of endometrial cancers. It is possible that tamoxifen causes these tumours via a genotoxic mechanism similar to that seen in rat liver. However, using (32)P-post-labelling we failed to find evidence of tamoxifen-induced DNA adducts in the uterus. Tamoxifen may affect hormonal imprinting of oestrogen receptor responses in stem cells of the uterus, causing reproductive tract cancers to arise at a later time, in the same way as has been proposed for diethylstilbestrol. If these rodent data extrapolate to humans, then women who are taking tamoxifen as a chemopreventative may have an increased risk of vaginal/cervical cancer, as well as endometrial cancer.

Abnormal cell differentiation and p21 expression of endometrial epithelial cells following developmental exposure to diethylstilbestrol (DES)

Gene expression relevant to abnormal cell differentiation and altered cell cycle in endometrial epithelial cells was investigated immunohistochemically in developing mouse uteri exposed neonatally to diethylstilbestrol (DES). Female CD-1 mice were given daily s.c. injections of 2 microg of DES in corn oil or were given corn oil alone (control) at 1-5 days of age and euthanatized at 5, 6, 7, 8, 15, and 22 days of age. The endometrial epithelial cells of DES-treated mice at 5-8 days of age showed enhanced staining intensity for the estrogen receptor alpha (ER alpha), whereas the stromal cells showed decreased staining reaction; the epithelial cells showed that the protein encoded by the c-fos proto-oncogene, which plays a key role in regulating diverse estrogen-related cellular differentiation patterns, was enhanced. These cells also showed increased expression of lactoferrin, a sensitive protein marker of estrogen exposure, although the staining intensity decreased after exposure ended. The stain for p21 protein, a mitotic inhibitor which suppresses cyclin-dependent kinase activity, showed frequent positively stained cells in DES-treated mice at 5-15 days of age, whereas no accumulation of p53 protein of either wild or mutant type was detected immunohistochemically in these cells. These results indicate that suppressed cell cycle activity of endometrial epithelial cells and abnormal estrogen-related differentiation at the developmental stage following neonatal DES exposure may be caused, in part, by transient altered expression of ER alpha and expression of the p21 gene, which appears to be induced by a p53-independent mechanism.

Effect of ovarian steroid deficiency on oestrogen receptor alpha expression in bone

The mechanism by which oestrogen and hormone replacement therapy (HRT) maintain bone mass in women is still unclear. It has previously been shown that cells of osteoblast lineage in vivo, particularly osteocytes, express oestrogen receptor alpha (ERalpha). Nevertheless, it is still debatable whether oestrogen and the ovarian steroids have a direct affect on osteocytes. If they could regulate osteocyte ERalpha expression, this would be strong evidence for the involvement of these cells in the hormonal regulation of bone mass. This study therefore aimed to compare bone biopsies from women who were replete with ovarian steroids (pre-ovariectomy or post-HRT) with those from the same women when hormone-deficient (post-ovariectomy or pre-HRT) for cellular localization of ERalpha protein or mRNA expression by indirect immunofluorescence, or by in situ hybridization combined with reverse transcriptase-polymerase chain reaction (IS-RT-PCR) respectively. Image analysis showed that proportions of osteocytes positive for immunodetectable ERalpha were higher in hormone-replete than in hormone-deficient women (25+/-SEM 3 per cent, 12+/-SEM 4 per cent, respectively; n=5), with similar but non-statistically significant changes in osteoblasts. This was observed even when HRT was commenced 18 years after menopause. In contrast, grain volume/unit cell area of osteoblast mRNA signal was markedly higher when hormone-deficient (0.055+/-0.01) than when hormone-replete (0.016+/-0.004), with similar but non-significant differences in osteocytes. This preliminary study indicates up-regulation of osteocyte ERalpha protein by ovarian steroids in these patients, which is accompanied by decreased osteoblast ERalpha mRNA expression, providing further evidence for the involvement of osteocytes in the regulation of skeletal structure by ovarian steroids.

Tissue compartment-specific estrogen receptor-alpha participation in the mouse uterine epithelial secretory response

17Beta-estradiol (E2) acts through the estrogen receptor (ER) to regulate uterine epithelial cell growth, proliferation, differentiation, and secretory protein production. We have previously shown that E2-induced uterine epithelial proliferation is mediated indirectly by ER alpha-positive stroma; epithelial ER alpha is neither necessary nor sufficient for E2-induced uterine epithelial mitogenesis. In the present study, we addressed the question of whether production of uterine epithelial secretory proteins and their messenger RNAs (mRNAs) requires ER alpha in stroma, epithelium, or both by analyzing tissue recombinations composed of uterine tissue from adult ER alpha knockout (ko) and neonatal BALB/c (wt) mice. Stroma (S) and epithelium (E) were separated by trypsinization, and four types of uterine tissue recombinants were prepared: wt-S + wt-E, wt-S + ko-E, ko-S + wt-E, and ko-S + ko-E. These tissue recombinants were grown as subrenal capsule grafts in intact female nude mice for 4 weeks, at which time the hosts were ovariectomized. To assess the production of secretory proteins and their mRNAs, 1 week after ovariectomy the hosts were given three daily injections of oil or E2 (100 ng), and then 24 h later the grafts were recovered and used for either ER or lactoferrin (LF) immunohistochemistry. To assess steady state mRNA levels by Northern blotting, hosts received one injection of oil or E2 24 h before harvest. ER immunohistochemistry was used to monitor the completeness of tissue separation. In wt-S + wt-E tissue recombinants from E2-treated hosts, the epithelium stained intensely for LF (an abundant E2-dependent uterine secretory protein), whereas similar tissue recombinants from oil-treated hosts showed minimal immunostaining. Conversely, LF immunostaining was minimal in wt-S + ko-E grafts from both oil- and E2-treated hosts. LF staining was also minimal in ko-S + ko-E and ko-S + wt-E tissue recombinants regardless of hormone treatment. For Northern analyses, the epithelial content of the tissue recombinants was monitored using the reference epithelial transcript, E-cadherin. While all tissue recombinant groups expressed E-cadherin mRNA, wt-S + wt-E tissue recombinants from E2-treated hosts produced a strong, single 2.6-kb band of LF mRNA. LF transcripts were minimal or absent in all other tissue recombinant types. Northern blotting results identical to those seen for LF were also observed for the uterine secretory protein complement component C3. Our data demonstrate that both stromal and epithelial ER alpha are required for the production of LF protein and of LF or C3 mRNAs in response to E2. Thus, in contrast to E2-induced epithelial mitogenesis, which requires only stromal ER alpha, both epithelial and stromal ER alpha are necessary for the production of E2-dependent epithelial secretory proteins.