An estrogen receptor-alpha knock-in mutation provides evidence of ligand-independent signaling and allows modulation of ligand-induced pathways in vivo

High-intensity interval training improves long-term memory and increases hippocampal antioxidant activity and BDNF levels in ovariectomized Wistar rats

Menopause is the period in which women cease to produce the hormone estrogen, which can trigger physiological, cognitive, and behavioral changes. In this context, alternatives are needed that can reduce the effects provided by menopause, specifically in terms of cognitive and behavioral aspects. High-intensity interval training (HIIT) is an exercise protocol that has shown the potential to improve cognition by promoting an increase in antioxidant defenses and BDNF levels. Therefore, the aim of this study was to evaluate the effects of HIIT on behavior and hippocampal neurochemistry in ovariectomized adult rats. Four groups of rats were divided into: females without ovariectomy surgery and sedentary (SHAM-SED); females with ovariectomy surgery and sedentary (OVX-SED); females without ovariectomy surgery and trained (SHAM-HIIT); females with ovariectomy surgery and trained (OVX-HIIT). After the surgical procedure and the HIIT protocol, the animals underwent anxiety (elevated plus maze and open field) and memory (novel object recognition) tests. Corticosterone was measured in blood and BDNF levels and redox status were evaluated in the hippocampus. The OVX-SED group showed low BDNF levels and antioxidant enzymes, which may be linked to the observed memory impairments. The HIIT protocol (SHAM-HIIT and OVX-HIIT groups) increased the BDNF levels and antioxidant enzymes in the hippocampus, improving the animals' memory. However, HIIT also led to increased plasma corticosterone and anxiety-like behaviors. The ovariectomy procedure induced memory impairment probably due to reductions in hippocampal BDNF levels and redox imbalance. The HIIT protocol demonstrates promising results as an alternative to improve memory in ovariectomized rats.

The emerging role of estrogen's non-nuclear signaling in the cardiovascular disease

Sexual dimorphism exists in the epidemiology of cardiovascular disease (CVD), which indicates the involvement of sexual hormones in the pathophysiology of CVD. In particular, ample evidence has demonstrated estrogen's protective effect on the cardiovascular system. While estrogen receptors, bound to estrogen, act as a transcription factor which regulates gene expressions by binding to the specific DNA sequence, a subpopulation of estrogen receptors localized at the plasma membrane induces activation of intracellular signaling, called "non-nuclear signaling" or "membrane-initiated steroid signaling of estrogen". Although the precise molecular mechanism of non-nuclear signaling as well as its physiological impact was unclear for a long time, recent development of genetically modified animal models and pathway-selective estrogen receptor stimulant bring new insights into this pathway. We review the published experimental studies on non-nuclear signaling of estrogen, and summarize its role in cardiovascular system, especially focusing on: (1) the molecular mechanism of non-nuclear signaling; (2) the design of genetically modified animals and pathway-selective stimulant of estrogen receptor.

Rosetta Stone for Cancer Cure: Comparison of the Anticancer Capacity of Endogenous Estrogens, Synthetic Estrogens and Antiestrogens

This work presents the history of the recognition of principal regulatory capacities of estrogen hormones having been mistakenly regarded as breast cancer promoting agents for more than 120 years. Comprehensive analysis of the results of clinical, epidemiological, immunological and molecular studies justified that endogenous estrogens are the principal regulators of embryonic development, survival and reproduction via orchestrating appropriate expression and even edition of all genes in mammalians. Medical use of chemically modified synthetic estrogens caused toxic complications; thromboembolic events and increased cancer risk in female organs as they proved to be endocrine disruptors deregulating estrogen receptors (ERs) rather than their activators. Synthetic estrogen treatment exhibits ambiguous correlations with cancer risk at different sites, which may be attributed to an inhibition of the unliganded activation of estrogen receptors (ERs) coupled with compensatory liganded activation. The principle of estrogen induced breast cancer led to the introduction of antiestrogen therapies against this tumor; inhibition of the liganded activation of estrogen receptors and aromatase enzyme activity. The initial enthusiasm turned into disappointment as the majority of breast cancers proved to be primarily resistant to antiestrogens. In addition, nearly all patients showing earlier good tumor responses to endocrine therapy, later experienced secondary resistance leading to metastatic disease and fatal outcome. Studying the molecular events in tumors responsive and unresponsive to antiestrogen therapy, it was illuminated that a complete inhibition of liganded ER activation stimulates the growth of cancers, while a successful compensatory upregulation of estrogen signal may achieve DNA restoration, tumor regression and patient's survival. Recognition of the principal role of endogenous estrogens in gene expression, gene edition and DNA repair, estrogen treatment and stimulation of ER expression in patients may bring about a great turn in medical practice.

Role of Seipin in Human Diseases and Experimental Animal Models

Seipin, a protein encoded by the Berardinelli-Seip congenital lipodystrophy type 2 (BSCL2) gene, is famous for its key role in the biogenesis of lipid droplets and type 2 congenital generalised lipodystrophy (CGL2). BSCL2 gene mutations result in genetic diseases including CGL2, progressive encephalopathy with or without lipodystrophy (also called Celia’s encephalopathy), and BSCL2-associated motor neuron diseases. Abnormal expression of seipin has also been found in hepatic steatosis, neurodegenerative diseases, glioblastoma stroke, cardiac hypertrophy, and other diseases. In the current study, we comprehensively summarise phenotypes, underlying mechanisms, and treatment of human diseases caused by BSCL2 gene mutations, paralleled by animal studies including systemic or specific Bscl2 gene knockout, or Bscl2 gene overexpression. In various animal models representing diseases that are not related to Bscl2 mutations, differential expression patterns and functional roles of seipin are also described. Furthermore, we highlight the potential therapeutic approaches by targeting seipin or its upstream and downstream signalling pathways. Taken together, restoring adipose tissue function and targeting seipin-related pathways are effective strategies for CGL2 treatment. Meanwhile, seipin-related pathways are also considered to have potential therapeutic value in diseases that are not caused by BSCL2 gene mutations.

Estrogen Biosynthesis and Signal Transduction in Ovarian Disease

Estrogen mainly binds to estrogen receptors (ERs) to regulate menstrual cycles and reproduction. The expression of ERalpha (ERα), ERbeta (ERβ), and G-protein-coupled estrogen receptor (GPER) mRNA could be detected in ovary, suggesting that they play an important role in estrogen signal transduction in ovary. And many studies have revealed that abnormal expression of estrogen and its receptors is closely related to ovarian disease or malignant tumors. With the continuous development and research of animal models, tissue-specific roles of both ERα and ERβ have been demonstrated in animals, which enable people to have a deeper understanding of the potential role of ER in regulating female reproductive diseases. Nevertheless, our current understanding of ERs expression and function in ovarian disease is, however, incomplete. To elucidate the biological mechanism behind ERs in the ovary, this review will focus on the role of ERα and ERβ in polycystic ovary syndrome (PCOS), ovarian cancer and premature ovarian failure (POF) and discuss the major challenges of existing therapies to provide a reference for the treatment of estrogen target tissue ovarian diseases.

Segregation of nuclear and membrane-initiated actions of estrogen receptor using genetically modified animals and pharmacological tools

Estrogen receptor alpha (ERα) and beta (ERβ) are members of the nuclear receptor superfamily, playing widespread functions in reproductive and non-reproductive tissues. Beside the canonical function of ERs as nuclear receptors, in this review, we summarize our current understanding of extra-nuclear, membrane-initiated functions of ERs with a specific focus on ERα. Over the last decade, in vivo evidence has accumulated to demonstrate the physiological relevance of this ERα membrane-initiated-signaling from mouse models to selective pharmacological tools. Finally, we discuss the perspectives and future challenges opened by the integration of extra-nuclear ERα signaling in physiology and pathology of estrogens.

Estrogen receptor agonists induce anti‑edema effects by altering α and β estrogen receptor gene expression

The present study aimed to examine whether the attenuation of estrogen receptor expression is prevented by propyl pyrazole triol (PPT), an agonist for estrogen receptor α (ERα) or and diarypropiolnitrile (DPN), an agonist for estrogen receptor β (ERβ) after traumatic brain injury (TBI). The tests performed on ovariectomized female Wistar rats included sham group, vehicle group, and treated groups: PPT, DPN, and PPT+DPN 30 minutes after TBI. Blood‑brain barrier (BBB) disruption and brain water content were estimated. RT‑PCR and\r\nwestern blotting were utilized to evaluate ESR1 and ESR2 gene and protein expression. The data indicated that PPT, DPN, and PPT+DPN attenuated TBI‑induced brain edema. Also, BBB disruption after TBI was prevented in PPT, DPN, and PPT+DPN‑treated TBI animals. Estrogen agonist‑treated animals showed a significant elevation in Esr1 mRNA and protein expression levels in the brain tissue of TBI rats. In addition, the data indicated a significant elevation of Esr2 mRNA and protein expression levels in the brain tissue of estrogen agonist‑treated TBI rats. The data shows that both ESR1 and ESR2 agonists can enhance ER mRNA and protein levels in TBI animals' brain. It appears that this effect contributes to the neuroprotective function of ER agonists.

Estrogen receptor-α signaling in post-natal mammary development and breast cancers

17β-estradiol controls post-natal mammary gland development and exerts its effects through Estrogen Receptor ERα, a member of the nuclear receptor family. ERα is also critical for breast cancer progression and remains a central therapeutic target for hormone-dependent breast cancers. In this review, we summarize the current understanding of the complex ERα signaling pathways that involve either classical nuclear “genomic” or membrane “non-genomic” actions and regulate in concert with other hormones the different stages of mammary development. We describe the cellular and molecular features of the luminal cell lineage expressing ERα and provide an overview of the transgenic mouse models impacting ERα signaling, highlighting the pivotal role of ERα in mammary gland morphogenesis and function and its implication in the tumorigenic processes. Finally, we describe the main features of the ERα-positive luminal breast cancers and their modeling in mice.

Estrogens and development of the rete testis, efferent ductules, epididymis and vas deferens

Estrogen has always been considered the female hormone and testosterone the male hormone. However, estrogen's presence in the testis and deleterious effects of estrogen treatment during development have been known for nearly 90 years, long before estrogen receptors (ESRs) were discovered. Eventually it was learned that testes actually synthesize high levels of estradiol (E2) and sequester high concentrations in the reproductive tract lumen, which seems contradictory to the overwhelming number of studies showing reproductive pathology following exogenous estrogen exposures. For too long, the developmental pathology of estrogen has dominated our thinking, even resulting in the "estrogen hypothesis" as related to the testicular dysgenesis syndrome. However, these early studies and the development of an Esr1 knockout mouse led to a deluge of research into estrogen's potential role in and disruption of development and function of the male reproductive system. What is new is that estrogen action in the male cannot be divorced from that of androgen. This paper presents what is known about components of the estrogen pathway, including its synthesis and target receptors, and the need to achieve a balance between androgen- and estrogen-action in male reproductive tract differentiation and adult functions. The review focuses on what is known regarding development of the male reproductive tract, from the rete testis to the vas deferens, and examines the expression of estrogen receptors and presence of aromatase in the male reproductive system, traces the evidence provided by estrogen-associated knockout and transgenic animal models and discusses the effects of fetal and postnatal exposures to estrogens. Hopefully, there will be enough here to stimulate discussions and new investigations of the androgen:estrogen balance that seems to be essential for development of the male reproductive tract.

Beneficial effects of minocycline on the ovary of polycystic ovary syndrome mouse model: Molecular docking analysis and evaluation of TNF-α, TNFR2, TLR-4 gene expression

Polycystic ovary syndrome (PCOS) is the most common cause of ovulatory infertility. Inflammation may be involved in the pathogenesis and development of PCOS. We investigated the anti-inflammatory effect of minocycline on TNF-α, TNFR2, and TLR4 expression levels and the key features of PCOS in a mouse model. Molecular docking was performed by Molecular Operating Environment software. PCOS was induced by estradiol valerate injection (EV) (2 mg/kg/day) in 40 mice. After 28 days, the mice were divided into five groups, including control, PCOS, minocycline control, minocycline PCOS model (50 mg/kg), and letrozole PCOS (0.5 mg/kg). The Levels of FSH, LH, E2, and testosterone were determined by ELISA. H&E staining was used for histological analysis in the ovarian tissues. Docking scores were -10.35, -10.57, and -12.45 kcal/mol for TNFα, TLR-4, and TNFR2, respectively. The expression levels of TNF-α, TNFR2, and TLR4 were detected by Real-Time PCR. PCOS models exhibited acyclicity, a significant increase in E2 levels (P < 0.01), and no difference in FSH, LH, and testosterone. The expression levels of TNF-α, TNFR2, and TLR-4 significantly increased in PCOS (2.70, 7.90, and 14.83-fold, respectively). EV treatment significantly increased graafian follicles (P < 0.001) and decreased corpus luteum (CL) (P < 0.01). Minocycline treatment in PCOS led to a significant decrease in E2 (P < 0.01) and graafian follicles (P < 0.001) and a significant increase in the CL numbers (P < 0.05). Our findings showed the positive effects of minocycline on estradiol level, CL and graafian follicles counts, suggesting that minocycline might inhibit these proteins and improve ovulation in our mouse model of PCOS.

Estrogen in the male: a historical perspective

Estrogens have traditionally been considered female hormones. Nevertheless, the presence of estrogen in males has been known for over 90 years. Initial studies suggested that estrogen was deleterious to male reproduction because exogenous treatments induced developmental abnormalities. However, demonstrations of estrogen synthesis in the testis and high concentrations of 17β-estradiol in rete testis fluid suggested that the female hormone might have a function in normal male reproduction. Identification of estrogen receptors and development of biological radioisotope methods to assess estradiol binding revealed that the male reproductive tract expresses estrogen receptor extensively from the neonatal period to adulthood. This indicated a role for estrogens in normal development, especially in efferent ductules, whose epithelium is the first in the male reproductive tract to express estrogen receptor during development and a site of exceedingly high expression. In the 1990s, a paradigm shift occurred in our understanding of estrogen function in the male, ushered in by knockout mouse models where estrogen production or expression of its receptors was not present. These knockout animals revealed that estrogen's main receptor (estrogen receptor 1 [ESR1]) is essential for male fertility and development of efferent ductules, epididymis, and prostate, and that loss of only the membrane fraction of ESR1 was sufficient to induce extensive male reproductive abnormalities and infertility. This review provides perspectives on the major discoveries and developments that led to our current knowledge of estrogen's importance in the male reproductive tract and shaped our evolving concept of estrogen's physiological role in the male.

Non-genomic Effects of Estrogen on Cell Homeostasis and Remodeling With Special Focus on Cardiac Ischemia/Reperfusion Injury

This review takes into consideration the main mechanisms involved in cellular remodeling following an ischemic injury, with special focus on the possible role played by non-genomic estrogen effects. Sex differences have also been considered. In fact, cardiac ischemic events induce damage to different cellular components of the heart, such as cardiomyocytes, vascular cells, endothelial cells, and cardiac fibroblasts. The ability of the cardiovascular system to counteract an ischemic insult is orchestrated by these cell types and is carried out thanks to a number of complex molecular pathways, including genomic (slow) or non-genomic (fast) effects of estrogen. These pathways are probably responsible for differences observed between the two sexes. Literature suggests that male and female hearts, and, more in general, cardiovascular system cells, show significant differences in many parameters under both physiological and pathological conditions. In particular, many experimental studies dealing with sex differences in the cardiovascular system suggest a higher ability of females to respond to environmental insults in comparison with males. For instance, as cells from females are more effective in counteracting the ischemia/reperfusion injury if compared with males, a role for estrogen in this sex disparity has been hypothesized. However, the possible involvement of estrogen-dependent non-genomic effects on the cardiovascular system is still under debate. Further experimental studies, including sex-specific studies, are needed in order to shed further light on this matter.

Estrogen Receptors: New Directions in the New Millennium

Nineteen years have passed since our previous review in this journal in 1999 regarding estrogen receptors. At that time, we described the current assessments of the physiological activities of estrogen and estrogen receptors. Since that time there has been an explosion of progress in our understanding of details of estrogen receptor-mediated processes from the molecular and cellular level to the whole organism. In this review we discuss the basic understanding of estrogen signaling and then elaborate on the progress and current understanding of estrogen receptor actions that have developed using new models and continuing clinical studies.

Estrogen Receptors Are Involved in the Neuroprotective Effect of Silibinin in Aβ1-42-Treated Rats

Alzheimer's disease (AD) is a progressive neurodegenerative disease that is characterized by a cascade of pathologic changes. A widely discussed theory indicates that amyloid β (Aβ) peptides are the causative agents of AD. Silibinin, a flavonoid derived from milk thistle, is well known for its hepato-protective activities and we have reported the neuroprotective effects of silibinin. In this study, we investigated the role of estrogen receptors (ERs) in silibinin's neuroprotective effect on Aβ_1-42-injected rats. Results of Morris water maze and novel object-recognition tests demonstrated that silibinin significantly attenuated Aβ_1-42-induced memory impairment. Silibinin attenuated ERs and PI3K-Akt pathways, as well as modulated mitogen-activated protein kinases in the hippocampus of Aβ_1-42-injected rats. Taken together, silibinin is a potential candidate in the treatment of Alzheimer's disease.

Genome-Wide Mapping of In Vivo ERα-Binding Sites in Male Mouse Efferent Ductules

As an important nuclear hormone receptor, estrogen receptor α (ERα), which is encoded by the Esr1 gene, regulates the expression of hundreds of genes in a stimulus-specific, temporal, and tissue-specific fashion, mainly by binding to specific DNA sequences called estrogen response elements (EREs). As an important estrogen target tissue in males, the function of the efferent ductules relies on the presence of the ERα protein, but the underlying regulatory mechanisms are poorly illustrated. In this study, genome-wide ERα-binding sites in mouse efferent ductules were mapped by chromatin immunoprecipitation sequencing. In total, 12,105 peaks were identified, and a majority of them were located far from the annotated gene transcription start site. Motif analysis revealed that ∼80% of the ERα-binding peaks harbored at least one ERE, whereas androgen response element-like sequences were the most overrepresented motif in the peaks without any EREs. A number of candidate transcription factor motifs adjacent to the EREs were significantly enriched, including AP2 and GRE, implying the involvement of these putative adjacent factors in the global regulation of ERα target genes. Unexpectedly, more than 50% of the ERα-binding peaks in mouse efferent ductules overlapped with those binding peaks previously identified in mouse uterus, suggesting the conserved mechanism of ERα action in these two tissues. Cobinding of ERα target genes by androgen receptor was further confirmed for Slc9a3 gene, which was responsible for fluid resorption in the efferent ductules. Taken together, our study provides a useful reference set for future work aimed at exploring the mechanism of ERα action in physiological conditions.

Estrogen and cigarette sidestream smoke particulate matter exhibit ERα-dependent tumor-promoting effects in lung adenocarcinoma cells

Estrogen and secondhand smoke are key risk factors for nonsmoking female lung cancer patients who frequently have lung adenocarcinoma and show tumor estrogen receptor α (ERα) expression. We speculated that estrogen and secondhand smoke might cause harmful effects via ERα signaling. Our results showed that 17β-estradiol (E2), the primary form of endogenous estrogen, exacerbated proliferation, migration, and granzyme B resistance of lung adenocarcinoma cells in an ERα-dependent manner. Cigarette sidestream smoke particulate matter (CSSP), the major component of secondhand smoke, could activate ERα activity dose dependently in human lung adenocarcinoma cells. The estrogenic activity of CSSP was abolished by an ERα-selective antagonist. CSSP regulated the nuclear entry, phosphorylation, and turnover of ERα similarly to E2. Furthermore, CSSP enhanced E2-stimulated ERα activity and Ser118 phosphorylation even when ERα became saturated with E2. Activation of ERα by CSSP required GSK3β activity, but not involving polycyclic aromatic hydrocarbons, reactive oxygen species, calcium, epidermal growth factor receptor, and PI3K/Akt. Although CSSP possessed cytotoxicity, ERα-expressing cells grew and migrated faster than nonexpressing cells on recovery from CSSP exposure as observed in E2-pretreated cells. Knockdown of ERα by siRNA diminished E2- and CSSP-stimulated cell migration. Twenty-one genes, including SERPINB9, were identified to be upregulated by both E2 and CSSP via ERα. Increased SERPINB9 expression was accompanied with increased resistance to granzyme B-mediated apoptosis. This study demonstrates that estrogen has ERα-dependent tumor-promoting activity. CSSP acts like estrogen and shows a potential to enhance estrogen-induced ERα action.

Estrogen Hormone Biology

The hormone estrogen is involved in both female and male reproduction, as well as numerous other biological systems including the neuroendocrine, vascular, skeletal, and immune systems. Therefore, it is also implicated in many different diseases and conditions such as infertility, obesity, osteoporosis, endometriosis, and a variety of cancers. Estrogen works through its two distinct nuclear receptors, estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ). Various transcriptional regulation mechanisms have been identified as the mode of action for estrogen, mainly the classical mechanism with direct DNA binding but also a nongenomic mode of action and one using tethered or indirect binding. The expression profiles of ERα and ERβ are unique with the primary sites of ERα expression being the uterus and pituitary gland and the main site of ERβ expression being the granulosa cells of the ovary. Mouse models with knockout or mutation of Esr1 and Esr2 have furthered our understanding of the role of each individual receptor plays in physiology. From these studies, it is known that the primary roles for ERα are in the uterus and neuroendocrine system, as female mice lacking ERα are infertile due to impaired ovarian and uterine function, whereas female mice lacking ERβ are subfertile due to ovarian defects. The development of effective therapies for estrogen-related diseases has relied on an understanding of the physiological roles and mechanistic functionalities of ERα and ERβ in human health and disease.

Control of Germline Stem Cell Lineages by Diet and Physiology

Tight coupling of reproduction to environmental factors and physiological status is key to long-term species survival. In particular, highly conserved pathways modulate germline stem cell lineages according to nutrient availability. This chapter focuses on recent in vivo studies in genetic model organisms that shed light on how diet-dependent signals control the proliferation, maintenance, and survival of adult germline stem cells and their progeny. These signaling pathways can operate intrinsically in the germ line, modulate the niche, or act through intermediate organs to influence stem cells and their differentiating progeny. In addition to illustrating the extent of dietary regulation of reproduction, findings from these studies have implications for fertility during aging or disease states.

Regulation of gene expression by 17β-estradiol in the arcuate nucleus of the mouse through ERE-dependent and ERE-independent mechanisms

17β-Estradiol (E2) modulates gene expression in the hypothalamic arcuate nucleus (ARC) to control homeostatic functions. In the ARC, estrogen receptor (ER) α is highly expressed and is an important contributor to E2's actions, controlling gene expression through estrogen response element (ERE)-dependent and -independent mechanisms. The objective of this study was to determine if known E2-regulated genes are regulated through these mechanisms. The selected genes have been shown to regulate homeostasis and have been separated into three subsections: channels, receptors, and neuropeptides. To determine if ERE-dependent or ERE-independent mechanisms regulate gene expression, two transgenic mouse models, an ERα knock-out (ERKO) and an ERα knock-in/knock-out (KIKO), which lacks a functional ERE binding domain, were used in addition to their wild-type littermates. Females of all genotypes were ovariectomized and injected with oil or estradiol benzoate (E2B). Our results suggest that E2B regulates multiple genes through these mechanisms. Of note, Cacna1g and Kcnmb1 channel expression was increased by E2B in WT females only, suggesting an ERE-dependent regulation. Furthermore, the NKB receptor, Tac3r, was suppressed by E2B in WT and KIKO females but not ERKO females, suggesting that ERα-dependent, ERE-independent signaling is necessary for Tac3r regulation. The adrenergic receptor Adra1b was suppressed by E2B in all genotypes indicating that ERα is not the primary receptor for E2B's actions. The neuropeptide Tac2 was suppressed by E2B through ERE-dependent mechanisms. These results indicate that E2B activates both ERα-dependent and independent signaling in the ARC through ERE-dependent and ERE-independent mechanisms to control gene expression.

What's new in estrogen receptor action in the female reproductive tract

Estrogen receptor alpha (ERα) is a critical player in development and function of the female reproductive system. Perturbations in ERα response can affect wide-ranging aspects of health in humans as well as in livestock and wildlife. Because of its long-known and broad impact, ERα mechanisms of action continue to be the focus on cutting-edge research efforts. Consequently, novel insights have greatly advanced understanding of every aspect of estrogen signaling. In this review, we attempt to briefly outline the current understanding of ERα mediated mechanisms in the context of the female reproductive system.

Treating gynecologic malignancies with selective estrogen receptor downregulators (SERDs): promise and challenges

Endometrial and ovarian cancers are estrogen-dependent gynecologic malignancies. Although many are estrogen receptor (ER) positive, treatment with the selective estrogen receptor modulator (SERM) tamoxifen, a tissue selective partial-agonist, has demonstrated only modest clinical benefit. Selective estrogen receptor downregulators (SERDs) are pure ER antagonists showing a benefit for advanced ER positive breast cancer, which has bolstered their potential use for ER positive gynecologic malignancies. We summarize these preclinical and clinical data, suggesting that a subpopulation of patients with endometrial or ovarian cancer exists in which treatment with SERDs results in improved outcome. However, the full potential of SERDs for a gynecologic malignancies will be realized only when the appropriate predictive biomarkers are identified. Additionally, a further understanding ER signaling in the context of ovarian and endometrial tissues that appear to involve c-Src and other kinase pathways is needed to successfully address the emergence of resistance with rationally designed combination therapies.

Changes in the gene expression of estrogen receptors involved in the protective effect of estrogen in rat's trumatic brain injury

It has been demonstrated that estradiol has neuroprotective effects after traumatic brain injury (TBI) in female rats. Since estrogen receptors have an important role in estradiol effects at the cellular level and the exact mechanism(s) of estradiol-induced neuroprotection has not yet been fully clarified, the present study was designed to determine the changes in the levels of estrogen receptors mRNAs and proteins involved in this phenomenon. All experiments were carried out on female Wistar rats. The brain edema and blood-brain-barrier (BBB) disruption were assessed. The TBI method was diffuse type and induced by the Marmarou method. Semiquantitative RT-PCR and immunoblotting were used to assess ERα and ERβ gene expression. The data showed that the level of brain water content was significantly increased in TBI group. The increased water content was significantly attenuated in estradiol-treated (1mg/kg) TBI rats. Disruption of BBB after TBI was significantly inhibited just by estradiol treatment. Estrogen-treated animals showed a significant increase in ERα mRNA (18%) and protein (35%) levels in the brain tissue. Furthermore, in the brain-injured rats the levels of ERβ mRNA were lower than those in control rats. Following estrogen treatment, the protein levels of ERβ were closed to those in control group. In conclusion, the data demonstrate that estrogen treatment can protect brain against traumatic brain injury. Estrogen treatment increases ER mRNA and protein levels which were coincident with its protective effects. It seems that such phenomenon participates in the induction of neuroprotective effects of estrogen. This article is part of a Special Issue entitled 1618.

Development of phenotypic and transcriptional biomarkers to evaluate relative activity of potentially estrogenic chemicals in ovariectomized mice

BACKGROUND

Concerns regarding potential endocrine-disrupting chemicals (EDCs) have led to a need for methods to evaluate candidate estrogenic chemicals. Our previous evaluations of two such EDCs revealed a response similar to that of estradiol (E2) at 2 hr, but a less robust response at 24 hr, similar to the short-acting estrogen estriol (E3).

OBJECTIVES

Microarray analysis using tools to recognize patterns of response have been utilized in the cancer field to develop biomarker panels of transcripts for diagnosis and selection of treatments most likely to be effective. Biological effects elicited by long- versus short-acting estrogens greatly affect the risks associated with exposures; therefore, we sought to develop tools to predict the ability of chemicals to maintain estrogenic responses.

METHODS

We used biological end points in uterine tissue and a signature pattern-recognizing tool that identified coexpressed transcripts to develop and test a panel of transcripts in order to classify potentially estrogenic compounds using an in vivo system. The end points used are relevant to uterine tissue, but the resulting classification of the compounds is important for other sensitive tissues and species.

RESULTS

We evaluated biological and transcriptional end points with proven short- and long-acting estrogens and verified the use of our approach using a phytoestrogen. With our model, we were able to classify the diarylheptanoid D3 as a short-acting estrogen.

CONCLUSIONS

We have developed a panel of transcripts as biomarkers which, together with biological end points, might be used to screen and evaluate potentially estrogenic chemicals and infer mode of activity.

Maternal exposure to diethylstilbestrol during pregnancy and increased breast cancer risk in daughters

The idea that susceptibility to breast cancer is determined not only through inherited germline mutations but also by epigenetic changes induced by alterations in hormonal environment during fetal development is gaining increasing support. Using findings obtained in human and animal studies, this review addresses the mechanisms that may explain why daughters of mothers who took synthetic estrogen diethylstilbestrol (DES) during pregnancy have two times higher breast cancer risk than women who were not exposed to it. The mechanisms likely involve epigenetic alterations, such as increased DNA methylation and modifications in histones and microRNA expression. Further, these alterations may target genes that regulate stem cells and prevent differentiation of their daughter cells. Recent findings in a preclinical model suggest that not only are women exposed to DES in utero at an increased risk of developing breast cancer, but this risk may extend to their daughters and granddaughters as well. It is critical, therefore, to determine if the increased risk is driven by epigenetic alterations in genes that increase susceptibility to breast cancer and if these alterations are reversible.

Minireview: Tipping the balance: ligand-independent activation of steroid receptors

Steroid receptors are prototypical ligand-dependent transcription factors and a textbook example for allosteric regulation. According to this canonical model, binding of cognate steroid is an absolute requirement for transcriptional activation. Remarkably, the simple one ligand-one receptor model could not be farther from the truth. Steroid receptors, notably the sex steroid receptors, can receive multiple inputs. Activation of steroid receptors by other signals, working through their own signaling pathways, in the absence of the cognate steroids, represents the most extreme form of signaling cross talk. Compared with cognate steroids, ligand-independent activation pathways produce similar but not identical outputs. Here we review the phenomena and discuss what is known about the underlying molecular mechanisms and the biological significance. We hypothesize that steroid receptors may have evolved to be trigger happy. In addition to their cognate steroids, many posttranslational modifications and interactors, modulated by other signals, may be able to tip the balance.

Modeling prolactin actions in breast cancer in vivo: insights from the NRL-PRL mouse

Elevated exposure to prolactin (PRL) is epidemiologically associated with an increased risk of aggressive ER+ breast cancer. To understand the underlying mechanisms and crosstalk with other oncogenic factors, we developed the NRL-PRL mouse. In this model, mammary expression of a rat prolactin transgene raises local exposure to PRL without altering estrous cycling. Nulliparous females develop metastatic, histotypically diverse mammary carcinomas independent from ovarian steroids, and most are ER+. These characteristics resemble the human clinical disease, facilitating study of tumorigenesis, and identification of novel preventive and therapeutic approaches.

Small tubules, surprising discoveries: from efferent ductules in the turkey to the discovery that estrogen receptor alpha is essential for fertility in the male

Efferent ductules are small, delicate tubules that connect rete testis with the head of the epididymis, first identified by de Graaf in 1668. Although difficult to find in routine dissection, the ductules are an essential component of the male reproductive tract and in larger mammals occupy up more than 50% of the caput epididymidis. My introduction to research began with the study of efferent ductules in the domestic turkey, and to my surprise these small structures with kidney-like function become the core for numerous discoveries throughout my scientific career. In this review, only two discoveries that I found interesting will be discussed: cilia that line the efferent ductule lumen and estrogen receptors that play an essential role in regulating fluid reabsorption. A potential link between these two discoveries was uncovered in the study of efferent ductule effects observed in the estrogen receptor knockout mouse and following toxic exposure to the fungicide benomyl.

Disruption of estrogen receptor signaling and similar pathways in the efferent ductules and initial segment of the epididymis

Seminiferous tubular atrophy may involve indirectly the disruption of estrogen receptor-α (ESR1) function in efferent ductules of the testis. ESR1 helps to maintain fluid resorption by the ductal epithelium and the inhibition or stimulation of this activity in rodent species will lead to fluid accumulation in the lumen. If not resolved, the abnormal buildup of fluid in the head of the epididymis and efferent ductules becomes a serious problem for the testis, as it leads to an increase in testis weight, tubular dilation and seminiferous epithelial degeneration, as well as testicular atrophy. The same sequence of pathogenesis occurs if the efferent ductule lumen becomes occluded. This review provides an introduction to the role of estrogen in the male reproductive tract but focuses on the various overlapping mechanisms that could induce efferent ductule dysfunction and fluid backpressure histopathology. Although efferent ductules are difficult to find, their inclusion in routine histological evaluations is recommended, as morphological images of these delicate tubules may be essential for understanding the mechanism of testicular injury, especially if dilations are observed in the rete testis and/or seminiferous tubules.

Signature Lesion:

The rete testis and efferent ductules can appear dilated, as if the lumens were greatly expanded with excess fluid or the accumulation of sperm. Because the efferent ductules resorb most of the fluid arriving from the rete testis lumen, one of two mechanisms is likely to be involved: a) reduced fluid uptake, which has been caused by the disruption in estrogen receptor signaling or associated pathways; or b) an increased rate of fluid resorption, which results in luminal occlusion. Both mechanisms can lead to a temporary increase in testicular weight, tubular dilation and atrophy of the seminiferous tubules.

Segregated responses of mammary gland development and vaginal opening to prepubertal genistein exposure in Bscl2(-/-) female mice with lipodystrophy

Berardinelli-Seip congenital lipodystrophy 2-deficient (Bscl2(-/-)) mice recapitulate human BSCL2 disease with lipodystrophy. Bscl2-encoded seipin is detected in adipocytes and epithelium of mammary gland. Postnatal mammary gland growth spurt and vaginal opening signify pubertal onset in female mice. Bscl2(-/-) females have longer and dilated mammary gland ducts at 5-week old and delayed vaginal opening. Prepubertal exposure to 500ppm genistein diet increases mammary gland area and accelerates vaginal opening in both control and Bscl2(-/-) females. However, genistein treatment increases ductal length in control but not Bscl2(-/-) females. Neither prepubertal genistein treatment nor Bscl2-deficiency affects phospho-estrogen receptor α or progesterone receptor expression patterns in 5-week old mammary gland. Interestingly, Bscl2-deficiency specifically reduces estrogen receptor β expression in mammary gland ductal epithelium. In summary, Bscl2(-/-) females have accelerated postnatal mammary ductal development but delayed vaginal opening; they display segregated responses in mammary gland development and vaginal opening to prepubertal genistein treatment.

Ductuli efferentes of the male Golden Syrian hamster reproductive tract

Efferent ductules are responsible for the transportation of spermatozoa from the testis to the epididymis and their epithelium is responsible for the reabsorption of over 90% of the luminal fluid. The purpose of this research was to characterize the gross morphology and histology of efferent ductules in the male Golden Syrian hamster. The efferent ductules emerge from rete testis with a unique polarity at the apex or cephalic pole of the testis. The number of efferent ductules varied from 3 to 10 with an average of 6.0 and blind ending ducts were observed in approximately 56% of the males. The ductules merged into a single common duct prior to entering the caput epididymidis. The proximal efferent ductule lumen was wider than the distal (conus and common ducts), consistent with reabsorption of most of the luminal fluid, as was morphology of the ductal epithelium. Non-ciliated cells in the proximal region had prominent endocytic apparatuses, showing both coated pits and apical tubules in the apical cytoplasm. Large basolateral, intercellular spaces were also present in the epithelium of the proximal region. Distal non-ciliated cells had an abundance of large endosomes and lysosomal granules. Localisation of sodium/hydrogen exchanger-3 (NHE3; SLC9A3) and aquaporins 1 and 9 (AQP1, AQP9) along the microvillus border was also consistent with ion transport and fluid reabsorption by this epithelium. In comparison, the caput epididymidis epithelium expressed only AQP9 immunostaining. Another unusual feature of the hamster efferent ductules was the presence of glycogen aggregates in the basal cytoplasm of small groups of epithelial cells, but only in the proximal ducts near the rete testis. Androgen (AR), estrogen (ESR1 and ESR2) and vitamin D receptors (VDR) were also abundant in epithelial nuclei of proximal and distal efferent ductules. In comparison, caput epididymidis showed very little immunostaining for ESR1.

Estrogen Receptor Alpha Binding to ERE is Required for Full Tlr7- and Tlr9-Induced Inflammation

We previously found that a maximum innate inflammatory response induced by stimulation of Toll-like receptors (TLRs) 3, 7 and 9 requires ERα, but does not require estrogen in multiple cell types from both control and lupus-prone mice. Given the estrogen-independence, we hypothesized that ERα mediates TLR signaling by tethering to, and enhancing, the activity of downstream transcription factors such as NFκB, rather than acting classically by binding EREs on target genes. To investigate the mechanism of ERα impact on TLR signaling, we utilized mice with a knock-in ERα mutant that is unable to bind ERE. After stimulation with TLR ligands, both ex vivo spleen cells and bone marrow-derived dendritic cells (BM-DCs) isolated from mutant ERα ("KIKO") mice produced significantly less IL-6 compared with cells from wild-type (WT) littermates. These results suggest that ERα modulation of TLR signaling does indeed require ERE binding for its effect on the innate immune response.

Estrogen hormone physiology: reproductive findings from estrogen receptor mutant mice

Estrogen receptors (ERs) play a crucial role in reproduction and normal physiology. The two sub-types of ER (ERα and β) are expressed in various levels in different tissues and selective cell types. Gene targeting technology allowed us to produce lines of mice with disrupted ERα (αERKO) and ERβ genes (βERKO) as well as a compound αβERKO in the whole body. Male and female αERKO mice are infertile. Estrogen, EGF and IGF-1 treatments failed to induce uterine growth and DNA synthesis in αERKO uteri. αERKO females are infertile due to hypoplastic uteri and hyperemic ovaries with no corpora lutea due to persistent LH stimulation from loss of negative feedback. αERKO males are infertile, with testicular atrophy and seminiferous tubule dysmorphogenesis producing decreased spermatogenesis and inactive sperm. βERKO females show arrested folliculogenesis and subfertility. Ovarian analyses indicate differential gene expression related to ovulatory stimulation deficits including lack of LH, PR, Cyp19 and Cox2 expression. A unique ovarian phenotype is found only in αβERKO females showing transdifferentiation of granulosa cells to Sertoli cells. We describe here several novel mouse models which possess ERα gene modification. To understand ERα function in uterine endometrial epithelial cells, we generated a tissue selective ERα gene disrupted mouse model, the uterine epithelial-specific ERα knockout (UtEpiαERKO). To understand the physiological role of ERα functional domains, we generated a mouse model with a mutation in the ligand dependent transcription activation domain of ERα (AF2ERKI). Findings from the ERα mutant mice suggest that the absence of functional ERα is not lethal and results in significant endocrine effects and altered physiological processes.

Prolactin activates ERα in the absence of ligand in female mammary development and carcinogenesis in vivo

Resistance of estrogen receptor positive (ERα+) breast cancers to antiestrogens is a major factor in the mortality of this disease. Although activation of ERα in the absence of ligand is hypothesized to contribute to this resistance, the potency of this mechanism in vivo is not clear. Epidemiologic studies have strongly linked prolactin (PRL) to both development of ERα+ breast cancer and resistance to endocrine therapies. Here we employed genetically modified mouse models to examine the ability of PRL and cross talk with TGFα to activate ERα, using a mutated ERα, ERα(G525L), which is refractory to endogenous estrogens. We demonstrate that PRL promotes pubertal ERα-dependent mammary ductal elongation and gene expression in the absence of estrogen, which are abrogated by the antiestrogen, ICI 182,780 (ICI). PRL and TGFα together reduce sensitivity to estrogen, and 30% of their combined stimulation of ductal proliferation is inhibited by ICI, implicating ligand-independent activation of ERα as a component of their interaction. However, PRL/TGFα-induced heterogeneous ERα+ tumors developed more rapidly in the presence of ICI and contained altered transcripts for surface markers associated with epithelial subpopulations and increased signal transducer and activator of transcription 5b expression. Together, these data support strong interactions between PRL and estrogen on multiple levels. Ligand-independent activation of ERα suggests that PRL may contribute to resistance to antiestrogen therapies. However, these studies also underscore ERα-mediated moderation of tumor phenotype. In light of the high expression of PRL receptors in ERα+ cancers, understanding the actions of PRL and cross talk with other oncogenic factors and ERα itself has important implications for therapeutic strategies.

PET imaging of oestrogen receptors in patients with breast cancer

Oestrogen receptors are overexpressed in around 70% of all breast cancers, and are a target for endocrine therapy. These receptors can be visualised on PET with use of 16α-[(18)F]-fluoro-17β-oestradiol ((18)F-FES) as a tracer. Compared with biopsy, which enables assessment of individual sites, whole-body (18)F-FES-PET enables quantification of oestrogen-receptor expression in all metastases. In several studies, measurement of tumour protein expression in oestrogen receptors by (18)F-FES-PET, concurrent with biopsy, detected oestrogen-receptor-positive tumour lesions with a sensitivity of 84% and specificity of 98%. Roughly 45% of patients with metastatic breast cancer have discordant oestrogen-receptor expression across lesions (ie, (18)F-FES-positive and (18)F-FES-negative metastases). Low tumour (18)F-FES uptake in metastases can predict failure of hormonal therapy in patients with oestrogen-receptor-positive primary tumours. Finally, (18)F-FES-PET has shown that oestrogen-receptor binding capacity changes after intervention with hormonal drugs, but findings need to be confirmed. Factors other than oestrogen-receptor expression, including menopausal status and concomitant therapies, that can affect tumour (18)F-FES uptake must be taken into account.

Estrogen responsiveness of the TFIID subunit TAF4B in the normal mouse ovary and in ovarian tumors

Estrogen signaling in the ovary is a fundamental component of normal ovarian function, and evidence also indicates that excessive estrogen is a risk factor for ovarian cancer. We have previously demonstrated that the gonadally enriched TFIID subunit TAF4B, a paralog of the general transcription factor TAF4A, is required for fertility in mice and for the proliferation of ovarian granulosa cells following hormonal stimulation. However, the relationship between TAF4B and estrogen signaling in the normal ovary or during ovarian tumor initiation and progression has yet to be defined. Herein, we show that Taf4b mRNA and TAF4B protein, but not Taf4a mRNA or TAF4A protein, are increased in whole ovaries and granulosa cells of the ovary after exposure to 17beta-estradiol or the synthetic estrogen diethylstilbestrol and that this response occurs within hours after stimulation. Furthermore, this increase occurs via nuclear estrogen receptors both in vivo and in a mouse granulosa cancer cell line, NT-1. We observe a significant increase in Taf4b mRNA in estrogen-supplemented mouse ovarian tumors, which correlates with diminished survival of these mice. These data highlight the novel response of the general transcription factor TAF4B to estrogen in the normal ovary and during ovarian tumor progression in the mouse, suggesting its potential role in regulating actions downstream of estrogen stimulation.

The AF-1 activation function of estrogen receptor α is necessary and sufficient for uterine epithelial cell proliferation in vivo

Estrogen receptor-α (ERα) regulates gene transcription through the 2 activation functions (AFs) AF-1 and AF-2. The crucial role of ERαAF-2 was previously demonstrated for endometrial proliferative action of 17β-estradiol (E2). Here, we investigated the role of ERαAF-1 in the regulation of gene transcription and cell proliferation in the uterus. We show that acute treatment with E2 or tamoxifen, which selectively activates ERαAF-1, similarly regulate the expression of a uterine set of estrogen-dependent genes as well as epithelial cell proliferation in the uterus of wild-type mice. These effects were abrogated in mice lacking ERαAF-1 (ERαAF-1(0)). Four weeks of E2 treatment led to uterine hypertrophy and sustained luminal epithelial and stromal cell proliferation in wild-type mice, but not in ERαAF-1(0) mice. However, ERαAF-1(0) mice still presented a moderate uterine hypertrophy essentially due to a stromal edema, potentially due to the persistence of Vegf-a induction. Epithelial apoptosis is largely decreased in these ERαAF-1(0) uteri, and response to progesterone is also altered. Finally, E2-induced proliferation of an ERα-positive epithelial cancer cell line was also inhibited by overexpression of an inducible ERα isoform lacking AF-1. Altogether, these data highlight the crucial role of ERαAF-1 in the E2-induced proliferative response in vitro and in vivo. Because ERαAF-1 was previously reported to be dispensable for several E2 extrareproductive protective effects, an optimal ERα modulation could be obtained using molecules activating ERα with a minimal ERαAF-1 action.

Exposures to synthetic estrogens at different times during the life, and their effect on breast cancer risk

Women are using estrogens for many purposes, such as to prevent pregnancy or miscarriage, or to treat menopausal symptoms. Estrogens also have been used to treat breast cancer which seems puzzling, since there is convincing evidence to support a link between high lifetime estrogen exposure and increased breast cancer risk. In this review, we discuss the findings that maternal exposure to the synthetic estrogen diethylstilbestrol during pregnancy increases breast cancer risk in both exposed mothers and their daughters. In addition, we review data regarding the use of estrogens in oral contraceptives and as postmenopausal hormone therapy and discuss the opposing effects on breast cancer risk based upon timing of exposure. We place particular emphasis on studies investigating how maternal estrogenic exposures during pregnancy increase breast cancer risk among daughters. New data suggest that these exposures induce epigenetic modifications in the mammary gland and germ cells, thereby causing an inheritable increase in breast cancer risk for multiple generations.

Estrogen receptor-beta agonist diarylpropionitrile counteracts the estrogenic activity of estrogen receptor-alpha agonist propylpyrazole-triol in the mammary gland of ovariectomized Sprague Dawley rats

Although estrogen can bind both types of estrogen receptors, estrogen receptor-alpha (ERα) is dominant in mediating estrogenic activity in the mammary gland and uterus. Excessive estrogenic activity such as estrogen-based postmenopausal hormone replacement therapy increases the risk for breast and endometrial cancers. The adverse effect of estrogen on uterine endometrium can be opposed by progestins; however, estrogen-plus-progestin regimen imposes substantially greater risk for breast cancer than estrogen alone. In this study, we used ERα-selective agonist propylpyrazole-triol (PPT) and ERβ-selective agonist diarylpropionitrile (DPN) to activate ERα and estrogen receptor-beta (ERβ) separately in an ovariectomized rat model and determined whether PPT-activated ERα function in the mammary gland can be suppressed by DPN activated ERβ. Ovariectomized rats were randomly divided into six groups and treated with DMSO (control), DPN, PPT, PPT/DPN, PPT/Progesterone, and PPT/Progesterone/DPN, respectively. In the mammary gland, PPT but not DPN increased cell proliferation and amphiregulin gene expression; importantly, the stimulatory effect of PPT on mammary cell proliferation and amphiregulin gene expression can be suppressed by DPN. In the uterus, the effect of PPT on uterine weight and endometrial cell proliferation was not inhibited by DPN but can be inhibited by progesterone. These data provide in vivo evidence that PPT activated ERα activity in the mammary gland can be opposed by ERβ-selective agonist DPN, which may be explored for the development of better hormone replacement therapy regimen with less risk for breast cancer.

Estrogen receptors mediate rapid activation of phospholipase C pathway in the rat endometrium

The aim of the present study was to investigate the activation of rapid signaling events by 17β-estradiol in the rat uterus. 17β-Estradiol induced a rapid increase of total [3H]-inositol phosphate accumulation in the whole uterus and endometrium, but not in the myometrium. The effect of 17β-estradiol in the endometrium was blocked by phospholipase C (PLC) inhibitor (U73122), estrogen receptors antagonist (ICI 182,780), exportin CRM1 inhibitor (leptomycin B) and selective inhibitor of the SRC family of protein tyrosine kinases (PP2). Furthermore, a selective agonist of ESR1 (PPT) and a selective agonist of GPER (G-1) also induced a rapid increase of total [(3)H]-inositol phosphate accumulation in the endometrium. The G-1 effects were blocked by GPER antagonist (G-15). 17β-Estradiol and G-1 promoted an additive effect on total [3H]-inositol phosphate accumulation. In conclusion, the present results indicate that a rapid activation of the PLC-mediated phosphoinositide hydrolysis occurred in the rat endometrium after 17β-estradiol stimulation, and this effect was mediated by ESR1 that underwent nuclear export after hormone stimulation, and that GPER activation may play an additive role for this response. These rapid actions might be one of the key steps that mediate the estrogen-dependent activation of cellular events in the endometrium.

Estrogen signaling and cardiovascular disease

Estrogen has pleiotropic effects on the cardiovascular system. The mechanisms by which estrogen confers these pleiotropic effects are undergoing active investigation. Until a decade ago, all estrogen signaling was thought to occur by estrogen binding to nuclear estrogen receptors (estrogen receptor-α and estrogen receptor-β), which bind to DNA and function as ligand-activated transcription factors. Estrogen binding to the receptor alters gene expression, thereby altering cell function. Estrogen also binds to nuclear estrogen receptors that are tethered to the plasma membrane, resulting in acute activation of signaling kinases such as PI3K. An orphan G-protein-coupled receptor, G-protein-coupled receptor 30, can also bind estrogen and activate acute signaling pathways. Thus, estrogen can alter cell function by binding to different estrogen receptors. This article reviews the different estrogen receptors and their signaling mechanisms, discusses mechanisms that regulate estrogen receptor levels and locations, and considers the cardiovascular effects of estrogen signaling.

The effects of 17β-estradiol and a selective estrogen receptor modulator, bazedoxifene, on ovarian carcinogenesis

OBJECTIVE

To test if estrogen promotes carcinogenesis in vitro and in a genetic mouse model of ovarian cancer and whether its effects can be inhibited by a novel selective estrogen receptor modulator (SERM), bazedoxifene.

METHODS

Bazedoxifene was synthesized and it was confirmed that the drug abrogated the uterine stimulatory effect of 17β-estradiol in mice. To determine if hormones alter tumorigenesis in vivo LSL-K-ras(G12D/+)Pten(loxP/loxP) mice were treated with vehicle control, 17β-estradiol or bazedoxifene. Hormone receptor status of a cell line established from LSL-K-ras(G12D/+)Pten(loxP/loxP) mouse ovarian tumors was characterized using Western blotting and immunohistochemistry. The cell line was treated with hormones and invasion assays were performed using Boyden chambers and proliferation was assessed using MTT assays.

RESULTS

In vitro 17β-estradiol increased both the invasion and proliferation of ovarian cancer cells and bazedoxifene reversed these effects. However, in the genetic mouse model neither treatment with 17β-estradiol nor bazedoxifene changed mean tumor burden when compared to treatment with placebo. The mice in all treatment groups had similar tumor incidence, metastatic nodules and ascites.

CONCLUSION

While 17β-estradiol increases the invasion and proliferation of ovarian cancer cells, these effects do not translate into increased tumor burden in a genetic mouse model of endometrioid ovarian cancer. Likewise, while the SERM reversed the detrimental effects of estrogen in vitro, there was no change in tumor burden in mice treated with bazedoxifene. These findings demonstrate the complex interplay between hormones and ovarian carcinogenesis.

Neonatal diethylstilbestrol exposure disrupts female reproductive tract structure/function via both direct and indirect mechanisms in the hamster

We assessed neonatal diethylstilbestrol (DES)-induced disruption at various endocrine levels in the hamster. In particular, we used organ transplantation into the hamster cheek pouch to determine whether abnormalities observed in the post-pubertal ovary are due to: (a) a direct (early) mechanism or (b) an indirect (late) mechanism that involves altered development and function of the hypothalamus and/or pituitary. Of the various disruption endpoints and attributes assessed: (1) some were consistent with the direct mechanism (altered uterine and cervical dimensions/organization, ovarian polyovular follicles, vaginal hypospadius, endometrial hyperplasia/dysplasia); (2) some were consistent with the indirect mechanism (ovarian/oviductal salpingitis, cystic ovarian follicles); (3) some were consistent with a combination of the direct and indirect mechanisms (altered endocrine status); and (4) the mechanism(s) for one (lack of corpora lutea) was uncertain. This study also generated some surprising observations regarding vaginal estrous assessments as a means to monitor periodicity of ovarian function in the hamster.

Estrogen receptor α AF-2 mutation results in antagonist reversal and reveals tissue selective function of estrogen receptor modulators

The estrogen receptor (ER) is a ligand-dependent transcription factor containing two transcriptional activation domains. AF-1 is in the N terminus of the receptor protein and AF-2 activity is dependent on helix 12 of the C-terminal ligand-binding domain. Two point mutations of leucines 543 and 544 to alanines (L543A, L544A) in helix 12 minimized estrogen-dependent transcriptional activation and reversed the activity of the estrogen antagonists ICI182780 (ICI) and tamoxifen (TAM) into agonists in a similar manner that TAM activated WT ERα through AF-1 activation. To evaluate the physiological role of AF-1 and AF-2 for the tissue-selective function of TAM, we generated an AF-2-mutated ERα knock-in (AF2ERKI) mouse model. AF2ERKI homozygote female mice have hypoplastic uterine tissue and rudimentary mammary glands similar to ERα-KO mice. Female mice were infertile as a result of anovulation from hemorrhagic cystic ovaries and elevated serum LH and E2 levels, although the mutant ERα protein is expressed in the AF2ERKI model. The AF2ERKI phenotype suggests that AF-1 is not activated independently, even with high serum E2 levels. ICI and TAM induced uterotropic and ER-mediated gene responses in ovariectomized AF2ERKI female mice in the same manner as in TAM- and E2-treated WT mice. In contrast, ICI and TAM did not act as agonists to regulate negative feedback of serum LH or stimulate pituitary prolactin gene expression in a different manner than TAM- or E2-treated WT mice. The functionality of the mutant ERα in the pituitary appears to be different from that in the uterus, indicating that ERα uses AF-1 differently in the uterus and the pituitary for TAM action.

Ex3αERKO male infertility phenotype recapitulates the αERKO male phenotype

Disruption of the Esr1 gene encoding estrogen receptor α (ERα) by insertion of a neomycin resistance gene (neo) into exon 2 (αERKO mice) was shown previously to cause infertility in male mice. While full-length ERα protein was not expressed in αERKO mice, alternative splicing resulted in the low-level expression of a truncated form lacking the N-terminus A/B domain and containing the DNA- and ligand-binding domains. Thus, it was unclear whether the reproductive phenotype in αERKO males was only due to the lack of full-length ERα or was affected by the presence of the variant ERα isoform. The present study examined male mice with deletion of exon 3 of Esr1 gene, lacking the DNA-binding domain, and null for ERα (Ex3αERKO). Dilation of some seminiferous tubules was apparent in male Ex3αERKO mice as early as postnatal day 10 and was pronounced in all tubules from day 20 onward. At 6 weeks of age, sperm numbers and sperm motility were lower in Ex3αERKO mice than in wild-type (WT) mice, and the rete testis and efferent ductules were dilated. Mating studies determined that adult Ex3αERKO males were infertile and failed to produce copulatory plugs. Serum testosterone levels and Hsd17b3 and Cyp17a1 transcript levels were significantly higher, but serum estradiol, progesterone, LH, and FSH levels and Cyp19a1 transcript levels were not significantly different from those in WT mice. These results confirm and extend those seen in other studies on male mice with deletion of exon 3 of Esr1 gene. In addition, the reproductive phenotype of male Ex3αERKO mice recapitulated the phenotype of αERKO mice, strongly suggesting that the αERKO male infertility was not due to the presence of the DNA-binding domain in the truncated form of ERα and that full-length ERα is essential for maintenance of male fertility.

Estrogen, efferent ductules, and the epididymis

Estrogen's presence in the male reproductive system has been known for over 60 years, but its potential function in the epididymis remains an important area of investigation. Estrogen is synthesized by germ cells, producing a relatively high concentration in rete testis fluid. There are two estrogen receptors (ESR), the presence of which in the head of the epididymis is well documented and consistent between species; however, in other regions of the epididymis, their expression appears to be isotype, species, and cell specific. ESR1 is expressed constitutively in the epididymis; however, its presence is downregulated by high doses of estrogen, making the design of experiments complicated, as the phenotype of the Cyp19a1(-/-) mouse does not resemble that of the Esr1(-/-) mouse. Ligand-independent and DNA-binding Esr1 mutant models further demonstrate the complexity and importance of both signaling pathways in maintenance of efferent ductules and epididymis. Data now reveal the presence of not only classical nuclear receptors, but also cytoplasmic ESR and rapid responding membrane receptors; however, their importance in the epididymis remains undetermined. ESR1 regulates ion transport and water reabsorption in the efferent ducts and epididymis, and its regulation of other associated genes is continually being uncovered. In the male, some genes, such as Aqp9 and Slc9a3, contain both androgen and estrogen response elements and are dually regulated by these hormones. While estrogen pathways are a necessity for fertility in the male, future studies are needed to understand the interplay between androgens and estrogens in epididymal tissues, particularly in cell types that contain both receptors and their cofactors.

Proteome analysis and genome-wide regulatory motif prediction identify novel potentially sex-hormone regulated proteins in rat efferent ducts

The efferent ducts are a series of tubules that conduct sperm from the rete testis to the epididymis. They absorb most fluid and proteins originating from the rete testis during concentration of spermatozoa prior to their entry into the epididymis. Proteome analysis of micro-dissected efferent duct samples from adult rats was combined with genome-wide computational prediction of conserved hormone response elements to identify factors likely regulated by oestrogens and androgens. We identified 165 proteins and found subsets of the promoters controlling their corresponding genes to contain androgen- and oestrogen response elements (ARE/EREs) at similar frequencies. Moreover, EREs were significantly enriched among the loci identified compared with their genome-wide occurrence. The expression and localization of Anxa6, Ckb, Krt19, Park7, Pdzk1 and Tpt1 in the efferent ducts and other related hormone controlled tissues was further validated at the RNA or protein level. This study identifies many novel proteins predicted to play roles in sperm maturation and male fertility and provides significant computational evidence that the efferent ducts express genes transcriptionally controlled by sex hormones.

Oestrogens and spermatogenesis

The role of oestrogens in male reproductive tract physiology has for a long time been a subject of debate. The testis produces significant amounts of oestrogenic hormones, via aromatase, and oestrogen receptors (ERs)alpha (ESR1) and ERbeta (ESR2) are selectively expressed in cells of the testis as well as the epididymal epithelium, depending upon species. This review summarizes the current knowledge concerning the presence and activity of aromatase and ERs in testis and sperm and the potential roles that oestrogens may have in mammalian spermatogenesis. Data show that physiology of the male gonad is in part under the control of a balance of androgens and oestrogens, with aromatase serving as a modulator.