ERbeta Expression Research Articles

Estrogen receptor (ER) beta1 and ERbetacx/beta2 inhibit ERalpha function differently in breast cancer cell line MCF7.

Estrogen receptor (ER) alpha plays an important role in the proliferation and progression of breast cancer. In order to explore the function of wild-type ERbeta (ERbeta1) and its variant form, ERbetacx/beta2, stable transformants of ERalpha-positive breast cancer MCF7 cells with ERbeta1 or ERbetacx/beta2 expression vector were established. Constitutive expression of ERbeta1 or ERbetacx/beta2 reduced the S phase population of the cell cycle in dish culture and the number of colonies in an anchorage-independent assay. DNA-protein complexes of ERE with nuclear extracts from ERbeta1 transformants were observed in the electrophoretic mobility shift assay, while no complex was observed for ERbetacx/beta2 transformants. Reporter gene assay using estrogen-responsive element (ERE)-luciferase showed less responsiveness to estrogen in these transformants compared with parental cells. Endogenous mRNA expression of two known estrogen-responsive genes, cathepsin D and IGFBP4, was weakly induced by estrogen in ERbeta1 and ERbetacx/beta2 transformants compared with parental cells. A comprehensive gene expression analysis using our custom-made cDNA microarray showed that MCF7 and ERbeta1 transformants had a similar gene expression profile, whereas ERbetacx/beta2 showed a distinct profile from others. These results indicate that ERbeta1 and ERbetacx/beta2 inhibit ERalpha function differently in MCF7 cells.

Expression of estrogen receptor-beta in normal mammary and tumor tissues: is it protective in breast carcinogenesis?

Using messenger RNA (mRNA) in situ hybridization, we investigated estrogen receptor-beta (ERbeta) mRNA levels in normal mammary, benign breast tumor (BBT), breast cancer (BC), and metastatic lymph node tissues to verify the role of ERbeta in BC development and progression. ERbeta expression was significantly decreased in BC and metastatic lymph node tissues compared with normal mammary and BBT tissues (p < 0.01). The intensity and extent of ERbeta mRNA signals were also significantly lower in BC and metastatic lymph node tissues than in the normal mammary and BBT tissues (p < 0.01). An inverse relationship was found between ERbeta mRNA level and both histologic grade (p = 0.091) and progesterone receptor expression (p = 0.052) with marginal significance, but no significant association was noted between ERbeta expression in cancer tissues and the other clinico-pathologic data. The 3-year distant relapse-free survival probability was found to be independent of ERbeta expression. Collectively, ERbeta mRNA decreases in the process of BC development, but seems to be associated with poor differentiation.

Bisphenol a induces both transient and permanent histofunctional alterations of the hypothalamic-pituitary-gonadal axis in prenatally exposed male rats.

Exposure to bisphenol A (BPA) in utero has been shown to induce alterations in the prostate of 30-d-old Wistar rats. Herein, we examine both the time course of BPA action on the rat prostate and the effects of BPA on the male hypothalamic-pituitary-gonadal axis. This was achieved by exposing rats to BPA in utero, followed by immunohistochemistry and morphometric analysis of prostatic tissue, evaluation of estrogen receptor-alpha (ERalpha) and ERbeta mRNA expression in both the preoptic area (POA) and medial basal hypothalamus, and determination of PRL, LH, and testosterone serum levels. On d 30 (peripubertal period), the prostatic periductal stroma of BPA-exposed rats demonstrated a significantly larger layer of fibroblasts than that of controls, whereas on d 120 (adulthood) no significant differences were observed. Moreover, BPA-exposed rats on d 15 exhibited an increase in stromal cellular proliferation compared with controls. Decreased expression of both androgen receptor in prostatic stromal cells and prostatic acid phosphatase in epithelial cells was observed only on d 30 in BPA-exposed males. BPA did not alter POA ERalpha mRNA expression, whereas a 4-fold increase in POA ERbeta mRNA expression was observed on both d 30 and 120. No alterations were observed in either ERalpha or ERbeta expression in the medial basal hypothalamus. BPA-exposed males exhibited increased PRL levels only on d 30, whereas a transient increase in serum testosterone levels was observed on d 15. These results support the hypothesis that prenatal exposure to environmental doses of BPA induces both transient and permanent age-dependent alterations in the male reproductive axis at different levels.

A physiologic role for testosterone in limiting estrogenic stimulation of the breast.

The normal ovary produces abundant testosterone in addition to estradiol (E(2)) and progesterone, but usually only the latter two hormones are "replaced" in the treatment of ovarian failure and menopause. Some clinical and genetic evidence suggests, however, that endogenous androgens normally inhibit estrogen-induced mammary epithelial proliferation (MEP) and thereby may protect against breast cancer. To investigate the role of endogenous androgen in regulating mammary epithelial proliferation, normal-cycling rhesus monkeys were treated with flutamide, an androgen receptor antagonist. To evaluate the effect of physiological testosterone (T) supplementation of estrogen replacement therapy, ovariectomized monkeys were treated with E(2), E(2) plus progesterone, E(2) plus T, or vehicle. We show that androgen receptor blockade in normal female monkeys results in a more than twofold increase in MEP, indicating that endogenous androgens normally inhibit MEP. Moreover, we show that addition of a small, physiological dose of T to standard estrogen therapy almost completely attenuates estrogen-induced increases in MEP in the ovariectomized monkey, suggesting that the increased breast cancer risk associated with estrogen treatment could be reduced by T supplementation. Testosterone reduces mammary epithelial estrogen receptor (ER) alpha and increases ERbeta expression, resulting in a marked reversal of the ERalpha/beta ratio found in the estrogen-treated monkey. Moreover, T treatment is associated with a significant reduction in mammary epithelial MYC expression, suggesting that T's antiestrogenic effects at the mammary gland involve alterations in ER signaling to MYC. These findings suggest that treatment with a balanced formulation including all ovarian hormones may prevent or reduce estrogenic cancer risk in the treatment of girls and women with ovarian failure.

Analysis of temporal changes in the expression of estrogen-regulated genes in the uterus.

In order to understand early events caused by estrogen in vivo, temporal uterine gene expression profiles at early stages were examined using DNA microarray analysis. Ovariectomized mice were exposed to 17beta-estradiol and the temporal mRNA expression changes of ten thousand various genes were analyzed. Clustering analysis revealed that there are at least two phases of gene activation during the period up to six hours. One involved immediate-early genes, which included certain transcription factors and growth factors as well as oncogenes. The other involved early-late genes, which included genes related to RNA and protein synthesis. In clusters of down-regulated genes, transcription factors, proteases, apoptosis and cell cycle genes were found. These hormone-inducible genes were not induced in estrogen receptor (ER) alpha knockout mice. Although expression of ERbeta is known in the uterus, these findings indicate the importance of ERalpha in the changes in gene expression in the uterus.

Clinical significance of the expression of estrogen receptors alpha and beta for endocrine therapy of breast cancer.

The assessment of the estrogen receptor (ER) alpha and the progesterone receptor (PgR) in breast cancer tissues is important for discriminating between hormone-dependent and hormone-independent tumors. ERbeta, a more recently discovered ER, may influence estrogen action through the ERalpha pathway. To evaluate the clinical significance of these receptors in the response to endocrine therapy, we investigated their expression in primary breast cancer tissues. ERalpha and PgR were evaluated using immunohistochemistry (IHC) and enzyme immunoassay (EIA) and ERbeta expression was determined using IHC and reverse transcription-polymerase chain reaction. When the cut-off level of EIA was set at 13 fmol/mg protein for ERalpha and that for IHC was set as an IHC score between 2 and 3, a significant correlation between ERalpha EIA and IHC was seen (concordance rate 88.4%). This indicates that this cut-off level of ERalpha IHC can be adopted to quantify breast cancer prognoses. Furthermore, the tumors with positive expression of ERalpha IHC or PgR IHC using this criterion were significantly related to the response to endocrine therapy. Additionally, tumors with positive expression of ERbeta wild-type tended to have a better response to endocrine therapy than negative ones, and tamoxifen responders tended to exhibit a lower ratio of ERbetacx (one of the ERbeta variants) to ERbeta wild-type than nonresponders. The results concerning ERbeta are not yet fully understood; further investigations and evaluations should analyze the role of ERbeta wild-type and variant type in breast cancer treatment.

Molecular histochemical analysis of estrogen receptor alpha and beta expressions in the mouse ovary: in situ hybridization and Southwestern histochemistry.

It is well known that estrogen plays important roles in the female reproductive organs, including the ovary, through estrogen receptors (ERalpha and ERbeta). It is suggested that selective effects of estrogen on a discrete set of genes may reside in promoters that are differentially responsive to ERalpha and ERbeta, while the relative biological significance of ERalpha and ERbeta is unclear. Therefore, for a better understanding of the physiological and pathological states of ovarian cells, it seems to be essential to analyze the cellular expression of ERalpha and ERbeta, at both the protein and mRNA levels. For this purpose, we have optimized the protocols for immunohistochemistry and nonradioactive in situ hybridization, respectively, using the mouse ovary. These techniques have been established as useful histochemical methods for the localization of specific protein and/or mRNA expression at the cellular level. Moreover, we also attempted to evaluate ERs as binding proteins to estrogen responsive elements, using Southwestern histochemistry, which permits us to analyze the localization in situ of transcription regulatory proteins. By employing these methods, more precise understanding of specific gene expression and evaluation of its biological significance in the ovary would be possible.

Expression and localisation of oestrogen and progesterone receptors in the bovine mammary gland during development, function and involution.

It is now well established that oestrogen and progesterone are absolutely essential for mammary gland development. Lactation can be induced in non-pregnant animals by sex steroid hormone treatment. Most of the genomic actions of oestrogens are mediated by two oestrogen receptors (ER)-alpha and ERbeta, and for gestagens in ruminants by the progesterone receptor (PR). Our aim was the evaluation of mRNA expression and protein (localisation and Western blotting) during mammogenesis, lactogenesis, galactopoiesis (early, middle and late) and involution (8, 24, 28, 96-108 h and 14-28 days after the end of milking) in the bovine mammary gland (total no. 53). During these stages, the mRNA was assessed by means of real-time RT-PCR (LightCycler). The protein for ERalpha, ERbeta and PR was localised by immunohistochemistry and Western blotting. The mRNA expression results indicated the existence of ERalpha, ERbeta and PR in bovine mammary gland. Both ERalpha and PR are expressed in fg/ micro g total RNA range. The highest mRNA expression was found for ERalpha and PR in the tIssue of non-pregnant heifers, followed by a significant decrease to a lower level at the time of lactogenesis with low concentrations remaining during lactation and the first 4 weeks of involution. In contrast, the expression of ERbeta was about 1000-fold lower (ag/ micro g total RNA) and showed no clear difference during the stages examined, with a significant increase only 2-4 weeks after the end of milking. Immunolocalisation for ERalpha revealed a strong positive staining in nuclei of lactocytes in non-pregnant heifers, became undetectable during pregnancy, lactogenesis and lactation, and was again detectable 14-28 days after the end of milking. In contrast, PR was localised in the nuclei of epithelial cells in the mammary tIssue of non-pregnant heifers, in primigravid animals, and during late lactation and involution. During lactogenesis, peak and mid lactation, fewer nuclei of epithelial cells were positive, but increased staining of the cytoplasm of epithelial cells was obvious. ERalpha and ERbeta protein was found in all mammary gland stages examined by Western blotting. In contrast to mRNA expression, the protein signal for ERalpha was weaker in the tIssue of non-pregnant heifers and during involution (4 weeks). ERbeta protein showed a stronger signal (two isoform bands) in non-pregnant heifers and 4 weeks after the end of milking. This correlated with the mRNA expression data. Three isoforms of PR (A, B and C) were found by Western blotting in the tIssue of non-pregnant heifers, but only isoform B remained during the following stages (lactogenesis, galactopoiesis and involution). In conclusion, the mRNA expression and protein data for ER and PR showed clear regulatory changes, suggesting involvement of these receptors in bovine mammary gland development and involution.

Localization of estrogen receptors-alpha and -beta and androgen receptor in the human growth plate at different pubertal stages.

Sex steroids are required for a normal pubertal growth spurt and fusion of the human epiphyseal growth plate. However, the localization of sex steroid receptors in the human pubertal growth plate remains controversial. We have investigated the expression of estrogen receptor (ER) alpha, ERbeta and androgen receptor (AR) in biopsies of proximal tibial growth plates obtained during epiphyseal surgery in 16 boys and eight girls. All pubertal stages were represented (Tanner stages 1-5). ERalpha, ERbeta and AR were visualized with immunohistochemistry and the number of receptor-positive cells was counted using an image analysis system. Percent receptor-positive chondrocytes were assessed in the resting, proliferative and hypertrophic zones and evaluated for sex differences and pubertal trends. Both ERalpha- and ERbeta-positive cells were detected at a greater frequency in the resting and proliferative zones than in the hypertrophic zone (64+/-2%, 64+/-2% compared with 38+/-3% for ERalpha, and 63+/-3%, 66+/-3% compared with 53+/-3% for ERbeta), whereas AR was more abundant in the resting (65+/-3%) and hypertrophic zones (58+/-3%) than in the proliferative zone (41+/-3%). No sex difference in the patterns of expression was detected. For ERalpha and AR, the percentage of receptor-positive cells was similar at all Tanner pubertal stages, whereas ERbeta showed a slight decrease in the proliferative zone during pubertal development (P<0.05). In summary, our findings suggest that ERalpha, ERbeta and AR are expressed in the human growth plate throughout pubertal development, with no difference between the sexes.

Colocalization of estrogen beta-receptor messenger RNA with orphanin FQ, vasopressin and oxytocin in the rat hypothalamic paraventricular and supraoptic nuclei.

The functional significance of the novel estrogen receptor beta in brain areas that exclusively contain the ERbeta receptor subtype such as the paraventricular (PVN) and the supraoptic (SON) nuclei of the hypothalamus is not yet fully understood. The present study attempts to characterize the peptidergic nature of the ERbeta-containing neuronal population in the PVN and the SON using the double in situ histochemistry method in the female rat. Using this method, the ERbeta mRNA coexpressions with the novel opioid neuropeptide (orphanin FQ and its receptor ORL1) mRNA in addition to the previously reported neuropeptide (arginine vasopressin-AVP, oxytocin-OXY, corticotropin releasing hormone-CRH, enkephalin-ENK) mRNAs were assessed. In the PVN, roughly half of the ERbeta expression was colocalized with the prepro-orphanin FQ mRNA, which was comparable to the colocalization observed between the ERbeta and AVP mRNAs in the same region. In addition, there was 20% overlap between the ERbeta and ORL1 receptor mRNAs, and 10% overlap between the ERbeta and OXY mRNAs in the PVN. By contrast, the coexpression between the prepro-orphanin FQ and ERbeta mRNAs was less striking in the SON. Potential interactions between the ERbeta and the well-characterized AVP-OXY neurosecretory system as well as the novel OFQ-ORL1 opioid neuropeptide system may provide new leads for the functional significance of ERbeta, specifically in stress/autonomic responses.

Expression of ERalpha and ERbeta in prostate cancer.

It has been suggested that estrogens and their receptors (ERs) may be involved in the development and progression of prostate cancer. To elucidate the significance of these receptors, expression of both ERalpha and ERbeta was measured in benign and malignant prostate tumors, as well as in cell lines. Expression of ERalpha and ERbeta was measured in prostate hyperplasia (BPH, n = 7), androgen-dependent (n = 30) as well as hormone-refractory (n = 12) prostate carcinomas, and in four prostate cancer cell lines (LNCaP, DU145, PC-3, and 22Rv1) using real-time quantitative RT-PCR. Only low-level expression of ERalpha was found in all tumor types and cell lines. The level of expression was similar to that observed in breast carcinomas found to be negative for ERalpha by immunohistochemistry. All cell lines showed low, but detectable, levels of ERbeta expression. The mean expression of ERbeta in the hormone-refractory carcinomas was about half that seen in BPH or the androgen-dependent carcinomas; however, the difference was not statistically significant. The data suggest it is unlikely that alterations in the expression of either ER are commonly involved in the progression of prostate cancer.

Expression of Estrogen Receptors α and β, Androgen Receptors and Progesterone Receptors in Human Cornea

Using immunohistochemical techniques and reverse transcription polymerase chain reaction (RT-PCR), we examined the localization of estrogen receptors alpha and beta (ER alpha, beta), androgen receptor (AR), and progesterone receptor (PR) in human corneas. Using formalin-fixed donor human cornea, we did immunohistochemical staining after making transverse sections, and examined the localization of receptors. Also, we extracted mRNA from primary culture cells of the corneal epithelium and stroma as well as the endothelial cell layer and epithelial layer of the cornea, and we performed RT-PCR and examined the expression of each receptor. Immunohistochemical staining revealed that ER alpha was localized in corneal epithelial cells as well as in corneal stromal cells, and ER beta, AR and PR were localized in corneal epithelial, stromal, and endothelial cells. ER alpha, ER beta, and AR mRNA expression was observed in cultured and in vivo epithelium and cultured stroma cells. PR mRNA was expressed not only in cultured and in vivo epithelium and in cultured stroma cells but also in endothelium. We detected the localization of estrogen receptors alpha and beta, androgen receptors, and progesterone receptors in the human cornea.

Evidence for cell-specific changes with age in expression of oestrogen receptor (ER) alpha and beta in bone fractures from men and women.

Oestrogen is recognized as important for maintaining bone mass in men and women. Oestrogen receptor (ER) alpha and the recently described ER-beta are both expressed in bone cells, but have different affinities for oestrogen agonists and plant oestrogens, which could be important in developing treatments for bone loss in both men and women. It is unclear, however, which isoform predominates in bone; cell type and age may influence their relative expression. The present study has compared ER-alpha and ER-beta expression in serial sections of human fracture callus from males (n = 19, age range 5-72 years) and females (n = 15, age range 3-86 years) by indirect immunoperoxidase. Fracture callus was used as it can be readily obtained from individuals over a wide age range and contains a variety of bone cells. Antibody specificity was confirmed by western blotting and comparison of immunoreactivity in sections of breast tumour and benign prostate hyperplasia. No gender difference in ER expression was found in bone from individuals less than 40 years old. Proliferative chondrocytes were positive for both isoforms, but few larger hypertrophic cells were immunoreactive. ER-alpha and ER-beta were co-expressed in osteoclasts, suggesting that oestrogen may act directly on these cells. Osteoblasts, osteocytes, and mesenchymal cells also expressed both isoforms. In women over 40 years of age, however, relatively fewer biopsies contained osteocytes positive for ER-alpha and ER-beta. Likewise, the proportions of osteoblasts and mesenchymal cells expressing ER-beta were reduced but ER-alpha remained unaffected. In contrast, in men over 40 years, only the proportion of biopsies containing ER-beta-positive mesenchymal cells was lower. In these older men and women, ER-alpha and ER-beta expression was retained by the small proliferative chondrocytes. These results demonstrate that gender, age, and cell type are important determinants of ER isoform expression in skeletal cells.

Selective modulation of ER-beta by estradiol and xenoestrogens in human breast cancer cell lines.

In the last decades, substances with estrogenic activity have been dispersed into the environment. Xenoestrogens act by binding to estrogen receptors, ligand-regulated transcription factors, for which two subtypes have been described, ER-alpha and ER-beta, which are often coexpressed at variable amounts in different tissues. We investigated variations in the expression of ER-alpha and ER-beta mRNAs following treatment with four xenoestrogens (bisphenol A, 4-tert octylphenol, 2-hydroxybiphenyl, 4-hydroxybiphenyl) and with 17beta-estradiol in estrogen-sensitive (T47D) and estrogen-insensitive (BT20) breast cancer cell lines. Although to a variable extent, both estradiol and the tested xenoestrogens increased the expression of ER-beta mRNA, whereas a slight effect on ER-alpha was observed only in T47D cells. Upregulation of ER-beta expression by estradiol and xenoestrogens was observed only in the presence of detectable ER-alpha protein levels. These findings indicate a regulatory role for ER-beta in ER-alpha-mediated transcription and a role for ER-beta in mediating xenoestrogen toxicity.

Estrogen modulation of left ventricular remodeling in the aged heart.

To investigate the effects of estrogen on left ventricle (LV) mass and collagen deposition, and on the expression of receptors for estrogen (ER alpha, ER beta) and Ang II (AT(2)R, AT(1)R) in the heart of aged female rats. Aged ( approximately 12 months old) intact (n=7), ovariectomized plus placebo (OVX, n=7), and estrogen-replaced (E2, n=6) as well as young ( approximately 3 months old, n=4) female Sprague-Dawley rats were used in this study. After 1 month of treatment, the left ventricular weight/body weight ratio (LVW/BW), changes in myosin heavy chain expression (MHC), matrix metalloproteinase (MMP)-2 activity, the collagen I/III ratio, and the expression of ERs and Ang II receptors in the LV were evaluated. In aged rats, OVX increased LVW/BW associated with a higher expression of beta-MHC isoform, increased collagen I/III ratio, and decreased MMP-2 activity compared to intact rats. Furthermore, the OVX group had a decrease in ERs alpha and beta as well as AT(2)R but an increase in AT(1)R expression. Estrogen replacement prevented the effects of ovariectomy on heart remodeling as well as increased further expression of ER beta and decreased AT(1)R expression. Removal of ovarian hormones increased LV remodeling in the aged rat, which could be attenuated by estrogen replacement. Moreover, regulation of Ang II receptor expression could be a mechanism by which estrogen may modulate heart remodeling.

Regulation of estrogen receptor alpha and beta expression by testosterone in the rat prostate gland.

Although ER beta is known to be expressed at high levels in the rat prostate gland, its regulation is not well understood. Here we examined ER mRNA expression and the effects of testosterone administration in male rats at 1, 4 and 9 weeks of age who were castrated and/or treated with testosterone for a week, and then sacrificed. ER alpha was the major type of ER expressed in 2 week-old animals while dominant expression of ER beta mRNA was apparent in older age groups. Interestingly while ER beta expression was diminished and ER alpha mRNA increased in the castrated group, testosterone administration reversed this effect. A time-course study indicated that induction of ER beta mRNA increased within 9 hr and ER alpha decreased in 2 days after an injection (i.p.) of testosterone. Our results suggested that 1) testosterone up-regulates ER beta mRNA expression while ER alpha is down-regulated; and that 2) great changes in ER alpha and beta expression in the prostate gland during development from the newborn to adult may be due to the influence of testosterone.

Expression of estrogen receptor alpha and beta in the uterus and vagina of immature rats treated with 17-ethinyl estradiol.

The action of estrogen on target organs has been actively studied with the discovery of estrogen receptor (ER) beta. This study was carried out to examine the expression of ERalpha and ERbeta in the uterus and the vagina of immature Sprague-Dawley rats treated with 17-ethinyl estradiol (EE). Twenty days old rats were subcutaneously treated with EE at the doses of 0 (vehicle control), 0.03, 0.3, 1.0, 3.0, and 10.0 microg/kg/day for three consecutive days. The treatment of EE at the doses of 0.3, 1.0, 3.0 and 10.0 microg/kg/day significantly increased the weights of the uterus and vagina of rats (p<0.01) and retained fluid in the uterus of rats. At the high doses of 3.0 and 10.0 microg/kg/day, the treatment of EE caused an increase in the uterine height, hypertrophy, and a decrease in the expression of ERalpha and ERbeta in the uterine luminal and glandular epithelium. The treatment of EE at the doses of 3.0 and 10.0 microg/kg/day also caused cornification and a decrease in the expression of ERalpha and ERbeta in the vaginal epithelium. These results suggest that the EE treatment decrease the expression of ERalpha and ERbeta in the uterus and vagina of immature rats and that may be associated with the morphological changes such as increase in the uterine height, hypertrophy of the uterine epithelium, and cornification of the vagina.

Temperature influences the ontogenetic expression of aromatase and oestrogen receptor mRNA in the developing tilapia (Oreochromis mossambicus) brain.

Water temperature has a differential influence on the development of central neurotransmitter systems according to the developmental period in tilapia (Oreochromis mossambicus). Aromatase and oestrogen receptors (ERs) represent important components of the mechanism of brain differentiation. Gene expression of aromatase and ERs is modulated by neurotransmitters in the developing brain. In the present study, the quantitative reverse transcription-polymerase chain reaction method was used to investigate the effects of temperature on the ontogenetic expression of aromatase and ERs in the developing tilapia brain. Before day 10 posthatching, exposure to a higher temperature (32 degrees C) resulted in a significant increase in the expression of brain aromatase; conversely, a lower temperature (20 degrees C) resulted in a decrease. ERalpha expression was depressed in accordance with the decrease of temperature, but ERbeta was unaffected by temperature. Between days 10 and 20, neither brain aromatase nor ERalpha expression was altered by temperature, whereas ERbeta expression was significantly enhanced by exposure to 32 degrees C. Between days 20 and 30, brain aromatase significantly increased at the higher temperature and decreased at 20 degrees C, but neither ERalpha nor ERbeta was affected by temperature. The expression of both brain aromatase and ERs, differentially regulated according to the temperature and to the developmental period, could be related to brain-sex differentiation.

Neuroprotective effects of estrogen and tamoxifen in vitro: a facilitative role for glia?

Selective estrogen receptor modulators (SERMs) are steroidal or nonsteroidal compounds that can exhibit either estrogen-like agonistic effects or estrogen-antagonistic effects depending on the target tissue. While SERM actions in the breast, bone, and uterus have been well characterized, their effects in the brain are considerably less well understood. Previous work by our laboratory has demonstrated a beneficial effect of tamoxifen in the reduction of ischemic stroke damage in ovariectomized female rats. The present study utilized neuronal cell culture models to attempt to understand the mechanisms of tamoxifen-mediated neuroprotection. Neither physiologic doses of 17beta-E2 nor clinically therapeutic doses of tamoxifen directly protected GT1-7 neurons or purified cultures of rat cerebrocortical neurons from several forms of cell death. Reverse transcriptase polymerase chain reaction and Western blot analysis revealed that GT1-7 neurons possessed both estrogen receptor-alpha (ERalpha) and ERbeta mRNA and protein, whereas purified embryonic rat cortical neurons only expressed appreciable levels of ERalpha transcript and protein, with little to no expression of ERbeta. In contrast to the lack of protection in the purified neuronal cultures, both 17beta- E2 and tamoxifen significantly protected mixed glial/ neuronal cortical cultures from cell death, suggesting that glia may facilitate 17beta-E2-and tamoxifen-mediated neuroprotection. Furthermore, astrocyte-conditioned media and exogenous transforming growth factor-beta1, a documented astrocyte-derived cytokine, were shown to rescue purified cortical neurons from cell death. Together, these findings support a role for astrocytes in neuroprotection and raise the intriguing possibility that astrocytes may help mediate the neuroprotective effect of 17beta-E2 and tamoxifen.

Treatment of rats with 17beta-estradiol or relaxin rapidly inhibits uterine estrogen receptor beta1 and beta2 messenger ribonucleic acid levels.

Estrogen regulates the growth and differentiation of the uterus via binding to estrogen receptors (ERs), members of the nuclear receptor family of transcription factors. Two forms of ER exist: ERalpha and ERbeta. The former is a well-characterized mediator of estrogen-induced transcription, but the function of the latter is unclear. Recent in vitro studies suggest that both splicing forms of ERbeta expressed in rat tissues, beta1 and beta2, may function as inhibitors of ERalpha transcriptional activity. To gain insight into the role of ERbeta in estrogen action, we examined the effects of estrogen and relaxin, a ligand-independent activator of ERs, on the expression of ERbeta1 and ERbeta2 mRNA in the uterus in vivo. Eighteen-day-old female rats were ovariectomized and, after recovery, treated with 17beta-estradiol, relaxin, or vehicle. Quantitative reverse transcription-polymerase chain reaction analyses of uterine RNA from estrogen-treated animals revealed marked decreases in the steady-state levels of the mRNAs for both ERbeta1 and ERbeta2 at 3, 6, and 24 h after treatment. Relaxin induced a similar effect. Neither hormone had any significant effect on ERalpha mRNA levels. To determine if endogenous estrogen exerts this effect, we examined the expression of ERbetas in the uterus during the estrous cycle. Levels of both isoforms were highest at diestrus (low estrogen), were significantly lower at early proestrus (rising estrogen), reached a nadir during late proestrus (peak estrogen), and rebounded at estrus (declining estrogen). These data suggest that down-regulation of ERbeta expression may be required for estrogen to exert its full trophic effects on the uterus.