Estrogen induces rapid translocation of estrogen receptor beta, but not estrogen receptor alpha, to the neuronal plasma membrane

Molecular insights into the potential effects of selective estrogen receptor β agonists in Alzheimer's and Parkinson's diseases

Alzheimer's disease (AD) and Parkinson's disease (PD) are the most common neurodegenerative disorders. Pathologically, AD and PD are characterized by the accumulation of misfolded proteins. Hence, they are also called as proteinopathy diseases. Gender is considered as one of the risk factors in both diseases. Estrogens are widely accepted to be neuroprotective in several neurodegenerative disorders. Estrogens can be produced in the central nervous system, where they are called as neurosteroids. Estrogens mediate their neuroprotective action mainly through their actions on estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ). However, ERα is mainly involved in the growth and development of the primary and secondary sexual organs in females. Hence, the activation of ERα is associated with undesired side effects such as gynecomastia and increase in the risk of breast cancer, thromboembolism, and feminization. Therefore, selective activation of ERβ is often considered to be safer. In this review, we explore the role of ERβ in regulating the expression and functions of AD- and PD-associated genes. Additionally, we discuss the association of these genes with the amyloid-beta peptide (Aβ) and α-synuclein mediated toxicity. Ultimately, we established a correlation between the importance of ERβ activation and the process underlying ERβ's neuroprotective mechanisms in AD and PD.

Surgical Menopause Impairs Retinal Conductivity and Worsens Prognosis in an Acute Model of Rat Optic Neuropathy

Deficiency of estradiol during the menopausal period is an important risk factor for neurodegenerative diseases, including various optic neuropathies. The aim of this study was to evaluate the impact of surgical menopause on the function and survival ratio of RGCs in the rat model of ONC (optic nerve crush). We used eight-week-old female Long Evans rats, divided into two main groups depending on the time between ovariectomy procedure (OVA) and euthanasia (two weeks vs. seven weeks), and subgroups—OVA, OVA + ONC, or ONC. Retinal function was assessed with electroretinography (ERG). RGC loss ratio was evaluated using immunolabelling and counting of RGCs. Seven weeks after OVA, the menopause morphologically affected interneurons but not RGC; however, when the ONC procedure was applied, RGCs appeared to be more susceptible to damage in case of deprivation of estrogens. In our analysis, PhNR (photopic negative responses) were severely diminished in the OVA + ONC group. A deprivation of estrogens in menopause results in accelerated retinal neurodegeneration that firstly involves retinal interneurons. The lack of estrogens increases the susceptibility of RGCs to insults.

Utilization of Human Induced Pluripotent Stem Cells-Derived In vitro Models for the Future Study of Sex Differences in Alzheimer's Disease

Alzheimer’s disease (AD) is an aging-dependent neurodegenerative disease that impairs cognitive function. Although the main pathologies of AD are the aggregation of amyloid-beta (Aβ) and phosphorylated Tau protein, the mechanisms that lead to these pathologies and their effects are believed to be heterogeneous among patients. Many epidemiological studies have suggested that sex is involved in disease prevalence and progression. The reduction of sex hormones contributes to the pathogenesis of AD, especially in females, suggesting that the supplementation of sex hormones could be a therapeutic intervention for AD. However, interventional studies have revealed that hormone therapy is beneficial under limited conditions in certain populations with specific administration methods. Thus, this suggests the importance of identifying crucial factors that determine hormonal effects in patients with AD. Based on these factors, it is necessary to decide which patients will receive the intervention before starting it. However, the long observational period and many uncontrollable environmental factors in clinical trials made it difficult to identify such factors, except for the APOE ε4 allele. Induced pluripotent stem cells (iPSCs) derived from patients can differentiate into neurons and recapitulate some aspects of AD pathogenesis. This in vitro model allows us to control non-cell autonomous factors, including the amount of Aβ aggregates and sex hormones. Hence, iPSCs provide opportunities to investigate sex-dependent pathogenesis and predict a suitable population for clinical trials of hormone treatment.

The role of Gα protein signaling in the membrane estrogen receptor-mediated signaling

Estrogens exert rapid, extranuclear effects by their action on the plasma membrane estrogen receptors (mERs). Gα protein associated with the cell membrane is involved in many important processes regulated by estrogens. However, the Gα's role in the mER-mediated signaling and the signaling pathways involved are poorly understood. This review aims to outline the Gα's role in the mER-mediated signaling. Immunoblotting, immunofluorescence, co-immunoprecipitation, and RNA interference were carried out using vascular endothelial cells (ECs) and human breast carcinoma cell lines as experimental models. Electrophysiology and immunocytochemistry were carried out using guinea pigs as animal models. Recent advances suggest that the signaling of mERα through Gα is required for vascular EC migration or endothelial H₂S release, while Gα₁₃ is involved in estrogen-induced breast cancer cell invasion. Besides, the Gα_q-coupled PLC-PKC-PKA pathway is critical for the neural regulation of energy homeostasis. This review summarizes the contributions of Gα to mER-mediated signaling, including cardiovascular protection, breast cancer metastasis, neural regulation of homeostatic functions, and osteogenesis.

Cell-Membrane-Localizing, Two-Photon Probe for Ratiometric Imaging of γ-Glutamyl Transpeptidase in Cancerous Cells and Tissues

γ-Glutamyl transpeptidase (GGT), a cell surface-bound protease, is associated with various diseases including cancer. The detection of the enzyme activity is an important subject, leading to about 40 activatable fluorescent probes so far. All of them, however, lack the membrane-localizing ability, raising a reliability issue in the quantitative analysis. Disclosed is the first fluorescent probe that senses the cell surface-bound enzyme, which, furthermore, is capable of ratiometric as well as two-photon imaging with desirable features. Ratiometric imaging of cancer cell lines reveals a 6.4-8.4-fold higher GGT levels than those in normal cell lines. A comparison of the enzyme activity in organ tissues of normal and tumor xenograft mice reveals notably different levels of enzyme activity depending on the kind of tissue. Normal tissues exhibited comparable levels of enzyme activity, except the kidney that has significantly higher GGT activity (2.7-4.0-fold) than the other organs. Compared with the normal tissues, considerably higher enzyme activity was observed in the tumor tissues of the thigh (4.0-fold), colon (2.5-fold), lung (3.6-fold), and liver (2.1-fold), but essentially no enhanced activity in the tumor tissues of the spleen, stomach, and pancreas and a comparable level in both the tumor and normal kidney tissues were observed. The probe offers practical means for studying GGT-associated biology in cells and tissues by one- as well as two-photon ratiometric imaging.

The role of G protein-coupled estrogen receptor 1 on neurological disorders

G protein-coupled estrogen receptor 1 (GPER) is a membrane-associated estrogen receptor (ER) associated with rapid estrogen-mediated effects. Over recent years GPER emerged has a potential therapeutic target to induce neuroprotection, avoiding the side effects elicited by the activation of classical ERs. The putative neuroprotection triggered by GPER selective activation was demonstrated in mood disorders, Alzheimer's disease or Parkinson's disease of male and female in vivo rodent models. In others, like ischemic stroke, the results are contradictory and currently there is no consensus on the role played by this receptor. However, it seems clear that sex is a biological variable that may impact the results. The major objective of this review is to provide an overview about the physiological effects of GPER in the brain and its putative contribution in neurodegenerative disorders, discussing the data about the signaling pathways involved, as well as, the diverse effects observed.

Comparative study of stress response, growth and development of uteri in post-weaning gilts challenged with zearalenone and estradiol benzoate

The objective of this study was to evaluate the effects of zearalenone (ZEA) and estradiol benzoate (EB) on stress injury and uterine development in post-weaning gilts. Thirty healthy post-weaning female gilts (Duroc × Landrace × Large White) aged 28-32 days were randomly allocated to three treatments as follows: (a) basal diet (Control), (b) basal diet plus 1.0 mg/kg purified ZEA (ZEA) and (c) basal diet plus 0.75 ml (1.5 mg) EB per pig at 3-days intervals by intramuscular injection (EB). The serum estradiol (E₂ ), the final and the increased vulvar area, uterine index, thickness of the myometrium and endometrium, and protein expression of heat shock protein 70 (HSP70) in ZEA group were higher than those in the control group (p < .05), but lower than those in the EB group (p < .05). The serum luteinizing hormone in ZEA group was lower than that of the control group (p < .05), but higher than that in the EB group (p < .05). Higher serum follicle-stimulating hormone and progesterone were observed in the ZEA and control groups than those in the EB group (p < .05). The serum glutathione peroxidase activity in the ZEA group was lower than that in the control and EB groups (p < .001), and the malondialdehyde in the ZEA group was higher than that in the control and EB groups (p < .001). Moreover, the relative mRNA and protein expression of growth hormone receptor (GHR) and relative mRNA expression of HSP70 in the ZEA and EB groups were higher than those in the control group (p < .05). In conclusion, both ZEA (1.0 mg/kg) and EB (1.5 mg at 3 days intervals by intramuscular injection) stimulated vulvar swelling and uterine hypertrophy by disordering serum hormones and up-regulating GHR expression, and induced stress by different mechanisms in this study. Furthermore, the observed up-regulating HSP70 expression challenged by ZEA or EB may be part of the mechanism to resist stress injury.

Can distinctly different rapid estrogen actions share a common mechanistic step?

Contribution to Special Issue on Fast effects of steroids. This paper reviews early evidence for the existence of rapid, non-genomic effects of estrogens on neurons, and, further, proposes that these rapid effects are often synergistic with later, genomic effects. Finally, suggestions about potential molecular mechanisms underlying the rapid effects of estrogens are offered. A mechanistic step we propose to be common among rapid estrogenic actions includes membrane ER's binding to histamine, and NMDA receptors and subsequent dimerization, and clustering (respectively) in a manner that enhances histamine and NMDA actions.

Mechanisms underlying the rapid effects of estradiol and progesterone on hippocampal memory consolidation in female rodents

Contribution to Special Issue on Fast effects of steroids. Although rapid effects of 17β‑estradiol (E₂) and progesterone on cellular functions have been observed for several decades, a proliferation of data in recent years has demonstrated the importance of these actions to cognition. In particular, an emerging literature has demonstrated that these hormones promote the consolidation of spatial and object recognition memories in rodents via rapid activation of numerous cellular events including cell signaling, histone modifications, and local protein translation in the hippocampus. This article provides an overview of the evidence demonstrating that E₂ and progesterone enhance hippocampal memory consolidation in female rodents, and then discusses numerous molecular mechanisms thus far shown to mediate the beneficial effects of these hormones on memory formation.

Differences Between Men and Women in Balance and Tremor in Relation to Plantar Fascia Laxity During the Menstrual Cycle

CONTEXT

  Although much attention has been paid to the effect of estrogen on the knee ligaments, little has been done to examine the ligaments in the foot, such as the plantar fascia, and how they may be altered during the menstrual cycle.

OBJECTIVE

  To (1) examine sex differences in plantar fascia thickness and laxity and postural sway and (2) identify any menstrual cycle effects on plantar fascia laxity, postural sway, and neuromuscular tremor between menstruation and the ovulation phase.

DESIGN

  Case-control study.

SETTING

  Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

  Fifteen healthy women (age = 25.9 ± 1.8 years) and 15 healthy men (age = 27.3 ± 2.0 years) volunteered to participate in this study.

INTERVENTION(S)

  We asked participants to perform 8 balance tasks on a force platform while we assessed postural sway and tremor.

MAIN OUTCOME MEASURE(S)

  Plantar fascia length and thickness unloaded and loaded with body weight were measured via ultrasound. Postural sway and tremor were measured using a force platform.

RESULTS

  Plantar fascia length and thickness with pressure were greater in ovulating women compared with men ( P < .001), but no differences were found between women during menstruation and men. Postural sway and tremor were greater at ovulation than during menstruation ( P < .05), and men had less sway than ovulating women on the 3 most difficult balance tasks ( P < .01).

CONCLUSIONS

  Plantar fascia laxity was increased and postural sway and tremor were decreased at ovulation compared with menstruation in women. Postural sway and tremor in men were the same as in women during menstruation. These findings support the need to be aware of the effect of sex hormones on balance to prevent lower extremity injuries during sport activities.

Rapid actions of oestrogens and their receptors on memory acquisition and consolidation in females

Increased attention has been paid in recent years to the ways in which oestrogens and oestrogen receptors rapidly affect learning and memory. These rapid effects occur within a timeframe that is too narrow for the classical genomic mode of action of oestrogen, thus suggesting nonclassical effects as underlying mechanisms. The present review examines recent developments in the study of the rapid effects of 17β-oestradiol and oestrogen receptor (ER) agonists on learning and memory tasks in female rodents, including social recognition, object recognition, object placement (spatial memory) and social learning. By comparing studies utilising systemic or intracranial treatments, as well as pre- and post-acquisition administration of oestradiol or ER agonists, the respective contributions of individual ERs within specific brain regions to various forms of learning and memory can be determined. The first part of this review explores the effects of systemic administration of 17β-oestradiol and ER agonists on memory when administered either pre- or post-acquisition. The second part not only focuses on the effects of pre- and post-acquisition infusions of 17β-oestradiol or ER agonists into the dorsal hippocampus on memory, but also discusses the contributions of other brain regions, including the medial amygdala, medial prefrontal cortex and paraventricular nucleus of the hypothalamus. The cellular mechanisms mediating the rapid effects of 17β-oestradiol on memory, including activation of intracellular signalling cascades and epigenetic processes, are discussed. Finally, the review concludes by comparing pre- and post-acquisition findings and effects of 17β-oestradiol and ER agonists in different brain regions.

Estrogen receptor α activation enhances its cell surface localization and improves myocardial redox status in ovariectomized rats

AIMS

Little is known about the role of subcellular trafficking of estrogen receptor (ER) subtypes in the acute estrogen (E₂)-mediated alleviation of oxidative stress. We tested the hypothesis that ERα migration to the cardiac myocyte membrane mediates the acute E₂-dependent improvement of cellular redox status.

MAIN METHODS

Myocardial distribution of subcellular ERα, ERβ and G-protein coupled estrogen receptor (GPER) was determined in proestrus sham-operated (SO) and in ovariectomized (OVX) rats, acutely treated with E₂ (1μg/kg) or a selective ERα (PPT), ERβ (DPN) or GPER (G1) agonist (10μg/kg), by immunofluorescence and Western blot. We measured ROS and malondialdehyde (MDA) levels, and catalase and superoxide dismutase (SOD) activities to evaluate myocardial antioxidant/redox status.

KEY FINDINGS

Compared with SO, OVX rats exhibited higher myocardial ROS and MDA levels, reduced catalase and SOD activities, along with diminished ERα, and enhanced ERβ and GPER, localization at cardiomyocyte membrane. Acute E₂ or an ERα (PPT), but not ERβ (DPN) or GPER (G1), agonist reversed these responses in OVX rats and resulted in higher ERα/ERβ and ERα/GPER ratios at the cardiomyocytes membrane. PPT or DPN enhanced myocardial Akt phosphorylation. We present the first evidence that preferential aggregation of ERα at the cardiomyocytes plasma membrane is ERα-dependent, and underlies E₂-mediated reduction in oxidative stress, at least partly, via the enhancements of myocardial catalase and SOD activities in OVX rats.

SIGNIFICANCE

The findings highlight ERα agonists as potential therapeutics for restoring the myocardial redox status following E₂ depletion in postmenopausal women.

Puerarin suppression of Aβ1-42-induced primary cortical neuron death is largely dependent on ERβ

Recent study has suggested that estrogen replacement therapy (ERT) can decrease the risk of the development of Alzheimer's disease (AD), and phytoestrogen has been proposed as a potential alternative to ERT. In this study, we investigated the protective function of puerarin (a phytoestrogen isolated from puerarin lobate) against amyloid beta (Aβ_1-42)-induced toxicity in cortical neurons and established the connection between such a protection and estrogen receptor (ER) activation. Puerarin suppressed Aβ_1-42-induced cortical neuron death in a concentration-dependent manner. Morphological examination showed that puerarin not only suppressed Aβ_1-42-induced decrease in neuron numbers, but also promoted neurite growth. In addition, we found that the neuroprotection of puerarin was dependent on the activation of estrogen receptors (ERs), as demonstrated by activation of ERE-reporter gene. Puerarin preferentially up-regulated the expression of ERβ but not ERα, and ERβ-specific siRNA significantly reduced the neuroprotection of puerarin. Taken together, our results indicated that puerarin is neuroprotective against Aβ_1-42 toxicity via the activation of estrogen receptors, and ERβ plays a key role in the process. Our novel findings provide a potential strategy for the prevention of neurodegeneration and the treatment of AD.

A clickable neurosteroid photolabel reveals selective Golgi compartmentalization with preferential impact on proximal inhibition

Anesthetic, GABA-active neurosteroids potently augment GABAA receptor function, leading to important behavioral consequences. Neurosteroids and their synthetic analogues are also models for a wide variety of cell-permeant neuroactive compounds. Cell permeation and compartmentalization raise the possibility that these compounds' actions are influenced by their cellular partitioning, but these contributions are not typically considered experimentally or therapeutically. To examine the interplay between cellular accumulation and pharmacodynamics of neurosteroids, we synthesized a novel chemical biology analogue (bio-active, clickable photolabel) of GABA-active neurosteroids. We discovered that the analogue selectively photo-labels neuronal Golgi in rat hippocampal neurons. The active analogue's selective distribution was distinct from endogenous cholesterol and not completely shared by some non-GABA active, neurosteroid-like analogues. On the other hand, the distribution was not enantioselective and did not require energy, in contrast to other recent precedents from the literature. We demonstrate that the soma-selective accumulation can act as a sink or source for steroid actions at plasma-membrane GABA receptors, altering steady-state and time course of effects at somatic GABAA receptors relative to dendritic receptors. Our results suggest a novel mechanism for compartment-selective drug actions at plasma-membrane receptors.

Effects of Estrogen and Phytoestrogen Treatment on an In Vitro Model of Recurrent Stroke on HT22 Neuronal Cell Line

An increase of stroke incidence occurs in women with the decline of estrogen levels following menopause. This ischemic damage may recur, especially soon after the first insult has occurred. We evaluated the effects of estrogen and phytoestrogen treatment on an in vitro recurrent stroke model using the HT22 neuronal cell line. HT22 cells were treated with 17β-estradiol or genistein 1 h after the beginning of the first of two oxygen and glucose deprivation/reoxygenation (OGD/R) cycles. During the second OGD, there was a deterioration of some components of the electron transport chain, such as cytochrome c oxidase subunit 1 with a subsequent increase of reactive oxygen species (ROS) production. Accordingly, there was also an increase of apoptotic phenomena demonstrated by poly(ADP-ribose) polymerase 1 cleavage, Caspase-3 activity, and Annexin V levels. The recurrent ischemic injury also raised the hypoxia-inducible factor 1α and glucose transporter 1 levels, as well as the ratio between the lipidated and cytosolic forms of microtubule-associated protein 1A/1B-light chain 3 (LC3-II/LC3-I). We found a positive effect of estradiol and genistein treatment by partially preserving the impaired cell viability after the recurrent ischemic injury; however, this positive effect does not seem to be mediated neither by blocking apoptosis processes nor by decreasing ROS production. This work contribute to the better understanding of the molecular mechanisms triggered by recurrent ischemic damage in neuronal cells and, therefore, could help with the development of an effective treatment to minimize the consequences of this pathology.

Why estrogens matter for behavior and brain health

The National Institutes of Health (NIH) has required the inclusion of women in clinical studies since 1993, which has enhanced our understanding of how biological sex affects certain medical conditions and allowed the development of sex-specific treatment protocols. However, NIH's policy did not previously apply to basic research, and the NIH recently introduced a new policy requiring all new grant applications to explicitly address sex as a biological variable. The policy itself is grounded in the results of numerous investigations in animals and humans illustrating the existence of sex differences in the brain and behavior, and the importance of sex hormones, particularly estrogens, in regulating physiology and behavior. Here, we review findings from our laboratories, and others, demonstrating how estrogens influence brain and behavior in adult females. Research from subjects throughout the adult lifespan on topics ranging from social behavior, learning and memory, to disease risk will be discussed to frame an understanding of why estrogens matter to behavioral neuroscience.

Sex steroid hormones matter for learning and memory: estrogenic regulation of hippocampal function in male and female rodents

Ample evidence has demonstrated that sex steroid hormones, such as the potent estrogen 17β-estradiol (E2), affect hippocampal morphology, plasticity, and memory in male and female rodents. Yet relatively few investigators who work with male subjects consider the effects of these hormones on learning and memory. This review describes the effects of E2 on hippocampal spinogenesis, neurogenesis, physiology, and memory, with particular attention paid to the effects of E2 in male rodents. The estrogen receptors, cell-signaling pathways, and epigenetic processes necessary for E2 to enhance memory in female rodents are also discussed in detail. Finally, practical considerations for working with female rodents are described for those investigators thinking of adding females to their experimental designs.

Signaling mechanisms mediating the regulation of synaptic plasticity and memory by estradiol

This article is part of a Special Issue "Estradiol and Cognition". Estradiol participates in the regulation of the function and plasticity of synaptic circuits in key cognitive brain regions, such as the prefrontal cortex and the hippocampus. The mechanisms elicited by estradiol are mediated by the regulation of transcriptional activity by nuclear estrogen receptors and by intracellular signaling cascades activated by estrogen receptors associated with the plasma membrane. In addition, the mechanisms include the interaction of estradiol with the signaling of other factors involved in the regulation of cognition, such as brain derived neurotrophic factor, insulin-like growth factor-1 and Wnt. Modifications in these signaling pathways by aging or by a long-lasting ovarian hormone deprivation after menopause may impair the enhancing effects of estradiol on synaptic plasticity and cognition.

Molecular mechanisms underlying the memory-enhancing effects of estradiol

This article is part of a Special Issue "Estradiol and cognition". Since the publication of the 1998 special issue of Hormones and Behavior on estrogens and cognition, substantial progress has been made towards understanding the molecular mechanisms through which 17β-estradiol (E2) regulates hippocampal plasticity and memory. Recent research has demonstrated that rapid effects of E2 on hippocampal cell signaling, epigenetic processes, and local protein synthesis are necessary for E2 to facilitate the consolidation of object recognition and spatial memories in ovariectomized female rodents. These effects appear to be mediated by non-classical actions of the intracellular estrogen receptors ERα and ERβ, and possibly by membrane-bound ERs such as the G-protein-coupled estrogen receptor (GPER). New findings also suggest a key role of hippocampally-synthesized E2 in regulating hippocampal memory formation. The present review discusses these findings in detail and suggests avenues for future study.

Cytoplasm estrogen receptor β5 as an improved prognostic factor in thymoma and thymic carcinoma progression

A number of previous studies have reported that sex steroid hormones, including estrogens, are involved in the regulation of the thymic function. The aim of the present study was to investigate the expression of estrogen receptor β5 (ERβ5) in thymic tumors and the correlation between ERβ5 expression and thymoma biological characteristics. The expression levels of ERβ5 in thymic epithelial tumors was evaluated in 103 patents using immunohistochemical staining and reverse transcription-quantitative polymerase chain reaction. In addition, an indirect immunofluorescence assay was performed to evaluate the ERβ5 expression levels in the TC1889 and T1682 cell lines. The survival outcome was estimated using Kaplan-Meier plots. The results indicated that ERβ5 expression was mainly located in the thymic tumor cell cytoplasm (87.37%; 90/103 cases) and overexpression was observed in thymic tumors compared with normal thymic tissues (P=0.001). Using the Kruskal-Wallis test, a statistically significant association was observed between cytoplasmic ERβ5 (cERβ5) expression and thymic tumor subtypes (P=0.024) and stages (P=0.003 and R=-0.376). The Kaplan-Meier plots revealed that cERβ5 expression was significantly associated with improved overall and progression-free survival (P=0.008 and P=0.004, respectively). The present study suggested that overexpression of cERβ5 may indicate an improved prognosis and may be involved in the underlying mechanism through which estrogen inhibits thymoma and thymic carcinoma development.

Learning and memory: Steroids and epigenetics

Memory formation and utilization is a complex process involving several brain structures in conjunction as the hippocampus, the amygdala and the adjacent cortical areas, usually defined as medial temporal lobe structures (MTL). The memory processes depend on the formation and modulation of synaptic connectivity affecting synaptic strength, synaptic plasticity and synaptic consolidation. The basic neurocognitive mechanisms of learning and memory are shortly recalled in the initial section of this paper. The effect of sex hormones (estrogens, androgens and progesterone) and of adrenocortical steroids on several aspects of memory processes are then analyzed on the basis of animal and human studies. A specific attention has been devoted to the different types of steroid receptors (membrane or nuclear) involved and on local metabolic transformations when required. The review is concluded by a short excursus on the steroid activated epigenetic mechanisms involved in memory formation.

Epigenetic regulation of estrogen-dependent memory

Hippocampal memory formation is highly regulated by post-translational histone modifications and DNA methylation. Accordingly, these epigenetic processes play a major role in the effects of modulatory factors, such as sex steroid hormones, on hippocampal memory. Our laboratory recently demonstrated that the ability of the potent estrogen 17β-estradiol (E2) to enhance hippocampal-dependent novel object recognition memory in ovariectomized female mice requires ERK-dependent histone H3 acetylation and DNA methylation in the dorsal hippocampus. Although these data provide valuable insight into the chromatin modifications that mediate the memory-enhancing effects of E2, epigenetic regulation of gene expression is enormously complex. Therefore, more research is needed to fully understand how E2 and other hormones employ epigenetic alterations to shape behavior. This review discusses the epigenetic alterations shown thus far to regulate hippocampal memory, briefly reviews the effects of E2 on hippocampal function, and describes in detail our work on epigenetic regulation of estrogenic memory enhancement.

A dynamic network of estrogen receptors in murine lymphocytes: fine-tuning the immune response

The actual level of circulating estrogen (17β-estradiol, E2) has a serious impact on regulation of diverse immune cell functions, where their classical cytoplasmic receptors, ERα and ERβ, act as nuclear transcriptional regulators of multiple target genes. There is growing evidence, however, for rapid, "non-nuclear" regulatory effects of E2 on lymphocytes. Such effects are likely mediated by putative membrane-associated receptor(s) (mER), but the mechanistic details and the involved signaling pathways still remained largely unknown because of their complexity. Here, we show that in lymphocytes, mERs can signalize themselves, and upon ligation, they are able to coordinate translocation of other E2Rs to the PM. Our data firmly imply existence of a complex, dynamic network of at least seven ER forms in murine lymphocytes: cytoplasmic and membrane-linked forms of ERα, ERβ, or GPR30 and a mER that can receive extracellular E2 signals. The latter mERs are likely palmitoylated, as they are enriched in lipid-raft microdomains, and their E2 binding is also cholesterol dependent. The data also support that ligation of mERs can induce rapid regulatory signals to lymphocytes and then internalize and let the E2 liberate in lysosomes. In addition, they can dynamically control the cell-surface linkage of other cytoplasmic ERs. As demonstrated by the differential effects of mER or cytoplasmic ER ligation on the proliferation of activated T and B lymphocytes, such a dynamic E2R network can be considered as a tool to manage accommodation/fine-tuning of lymphocytes to rapidly changing hormone levels.

Inhibition of estradiol synthesis impairs fear extinction in male rats

Emerging research has demonstrated that the sex hormone estradiol regulates fear extinction in female rodents and women. Estradiol may also regulate fear extinction in males, given its role in synaptic plasticity in both sexes. Here we report that inhibition of estradiol synthesis during extinction training, via the aromatase inhibitor fadrozole, significantly impairs extinction recall in male rats. This deficit in extinction recall is not due to state-dependent memory formation and is completely abolished by coadministration of estradiol. Our data suggest that estradiol may be just as important in the regulation of fear extinction in males as it is in females.

Differential ERα-mediated rapid estrogenic actions of ginsenoside Rg1 and estren in human breast cancer MCF-7 cells

Recent studies indicated that both estren and Rg1 appear to be able to activate mitogen-activated protein kinase (MAPK) pathway in estrogen responsive cells. Rg1 could lead to MAPK activation through ligand-independent activation of estrogen receptor (ER), while estren could activate the Src-MAPK pathway in an ERE-independent manner. Thus, it is important to understand the mechanistic insights on the difference in transcriptional activation between estren and Rg1. The present study also addressed the differential abilities of Rg1 and estren in terms of the ability to activate ER and the ability to induce ER translocation in MCF-7 cells. Our data indicated that Rg1 could increase pS2 gene expression, and could recruit the co-activator steroid receptor co-activator-1 (SRC-1) to the pS2 promoter. Rg1 could also induce ERα nuclear translocation as well as ERα phosphorylation at Ser118 principally in the cytoplasm in MCF-7 cells. We deduced that estren induced ERE-dependent transcriptional activity and activated ERα at Ser118 occurred in the nucleus of MCF-7 cells. However, it was found to decrease pS2 gene expression and failed to induce the recruitment of SRC-1 to the pS2 promoter in MCF-7 cells. Our results suggest that the abilities of Rg1 and estren to regulate pS2 gene expression, to recruit co-activators as well as to induce sub-cellular distribution of ERα are dramatically different.

A review of reagents for fluorescence microscopy of cellular compartments and structures, Part III: reagents for actin, tubulin, cellular membranes, and whole cell and cytoplasm

Non-antibody commercial fluorescent reagents for imaging of cytoskeletal structures have been limited primarily to tubulin and actin, with the main factor in choice based mainly on whether cells are live or fixed and permeabilized. A wider range of options exist for cell membrane dyes, and the choice of reagent primarily depends on the preferred localization in the cell (i.e., all membranes or only the plasma membrane) and usage (i.e., whether the protocol involves fixation and permeabilization). For whole-cell or cytoplasmic imaging, the choice of reagent is determined mostly by the length of time that the cells need to be visualized (hours or days) and by fixation status. Presented here is a discussion on choosing commercially available reagents for these cellular structures, with an emphasis on use for microscopic imaging, with a featured reagent for each structure, a recommended protocol, troubleshooting guide, and example image.

Phylogenetic, expression, and functional analyses of anoctamin homologs in Caenorhabditis elegans

Ca2+-activated Cl− channels (CaCCs) are critical to processes such as epithelial transport, membrane excitability, and signal transduction. Anoctamin, or TMEM16, is a family of 10 mammalian transmembrane proteins, 2 of which were recently shown to function as CaCCs. The functions of other family members have not been firmly established, and almost nothing is known about anoctamins in invertebrates. Therefore, we performed a phylogenetic analysis of anoctamins across the animal kingdom and examined the expression and function of anoctamins in the genetically tractable nematode Caenorhabditis elegans. Phylogenetic analyses support five anoctamin clades that are at least as old as the deuterostome/protosome ancestor. This includes a branch containing two Drosophila paralogs that group with mammalian ANO1 and ANO2, the two best characterized CaCCs. We identify two anoctamins in C. elegans (ANOH-1 and ANOH-2) that are also present in basal metazoans. The anoh-1 promoter is active in amphid sensory neurons that detect external chemical and nociceptive cues. Within amphid neurons, ANOH-1::GFP fusion protein is enriched within sensory cilia. RNA interference silencing of anoh-1 reduced avoidance of steep osmotic gradients without disrupting amphid cilia development, chemotaxis, or withdrawal from noxious stimuli, suggesting that ANOH-1 functions in a sensory mode-specific manner. The anoh-2 promoter is active in mechanoreceptive neurons and the spermatheca, but loss of anoh-2 had no effect on motility or brood size. Our study indicates that at least five anoctamin duplicates are evolutionarily ancient and suggests that sensory signaling may be a basal function of the anoctamin protein family.

The memory-enhancing effects of hippocampal estrogen receptor activation involve metabotropic glutamate receptor signaling

Our laboratory has demonstrated that 17β-estradiol (E2) enhances hippocampal memory consolidation via rapid activation of multiple intracellular signaling cascades, including the ERK/MAPK cascade (Fernandez et al., 2008; Fan et al., 2010). However, the receptor mechanisms responsible for these effects of E2 remain unclear. In vitro, estrogen receptor α (ERα) signaling through metabotropic glutamate receptor 1a (mGluR1a) leads to ERK-dependent CREB phosphorylation (Boulware et al., 2005), suggesting that interactions between ERs and mGluR1a may be vital to the memory-enhancing effects of E2. As such, the present study tested the roles of classical estrogen receptors (ERα and ERβ) and mGluR1a in mediating the effects of E2 on hippocampal memory consolidation. Dorsal hippocampal (DH) infusion of ERα (PPT) or ERβ (DPN) agonists enhanced novel object recognition and object placement memory in ovariectomized female mice in an ERK-dependent manner, suggesting that these receptors influence memory by rapidly activating hippocampal cell signaling. Next, DH infusion of the mGluR1a antagonist LY367385 blocked the object and spatial memory facilitation induced by E2, PPT, and DPN, demonstrating that ER/mGluR1a signaling is critical for the memory-enhancing effects of E2. Finally, we show that ERα, ERβ, mGluR1, and ERK all reside within specialized membrane microdomains of the DH, and that ERα and ERβ physically interact with mGluR1, providing a means through which ERs may activate mGluRs and downstream signaling. Together, these findings provide the first in vivo evidence demonstrating that ER/mGluR signaling can mediate the beneficial effects of E2 on hippocampal memory consolidation.

Recent evidence for rapid synthesis and action of oestrogens during auditory processing in a songbird

It is now clear that oestrogens are not only circulating reproductive hormones, but that they also have neurotransmitter-like properties in a wide range of brain circuits. The view of oestrogens as intrinsic neuromodulators that shape behaviour has been bolstered by a series of recent developments from multiple vertebrate model systems. Here, we review several recent findings from studies of songbirds showing how the identified neural circuits that govern auditory processing and sensorimotor integration are modulated by the local and acute production of oestrogens. First, studies using in vivo microdialysis demonstrate that oestrogens fluctuate in the auditory cortex (30-min time bin resolution) when songbirds are hearing song and interacting with conspecifics. Second, oestrogens rapidly boost the auditory-evoked activity of neurones in the same auditory cortical region, enhancing auditory processing. Third, local pharmacological blockade of oestrogen signalling in this region impairs auditory neuronal responsiveness, as well as behavioural song preferences. Fourth, the rapid actions of oestrogens that occur within the auditory cortex can propagate downstream (trans-synaptically) to sensorimotor circuits to enhance the neural representation of song. Lastly, we present new evidence showing that the receptor for the rapid actions of oestradiol is likely in neuronal membranes, and that traditional nuclear oestrogen receptor agonists do not mimic these rapid actions. Broadly speaking, many of these findings are observed in both males and females, emphasising the fundamental importance of oestrogens in neural circuit function. Together, these and other emergent studies provide support for rapid, brain-derived oestrogen signalling in regulating sensorimotor integration, learning and perception.

Epigenetics, oestradiol and hippocampal memory consolidation

Epigenetic alterations of histone proteins and DNA are essential for hippocampal synaptic plasticity and cognitive function, and contribute to the aetiology of psychiatric disorders and neurodegenerative diseases. Hippocampal memory formation depends on histone alterations and DNA methylation, and increasing evidence suggests that the regulation of these epigenetic processes by modulatory factors, such as environmental enrichment, stress and hormones, substantially influences memory function. Recent work from our laboratory suggests that the ability of the sex-steroid hormone 17β-oestradiol (E2 ) to enhance novel object recognition memory consolidation in young adult female mice is dependent on histone H3 acetylation and DNA methylation in the dorsal hippocampus. Our data also suggest that enzymes mediating DNA methylation and histone acetylation work in concert to regulate the effects of E2 on memory consolidation. These findings shed light on the epigenetic mechanisms that influence hormonal modulation of cognitive function, and may have important implications for understanding how hormones influence cognition in adulthood and ageing. The present review provides a brief overview of the literature on epigenetics and memory, describes in detail our findings demonstrating that epigenetic alterations regulate E2 -induced memory enhancement in female mice, and discusses future directions for research on the epigenetic regulation of E2 -induced memory enhancement.

Estrogen, predominantly via estrogen receptor α, attenuates postpartum-induced anxiety- and depression-like behaviors in female rats

Contributions from estrogen receptor (ER) subtypes (ERα and ERβ) to postpartum anxiogenic and depressive responses remain unresolved in rats. Using the elevated-plus maze (EPM) and forced swim (FS) tests, we confirmed that primiparous rats exhibited anxiogenic and depressive responses 3 weeks postpartum, improved 5 weeks postpartum (EPM), and recovered at 5 (FS) or 10 weeks postpartum (EPM) compared with diestrus nulliparous females. Immunohistochemistry suggested that these behavioral changes were temporally associated with decreased ERα but not ERβ expression in the medial amygdala (MEA). Additionally, ERα expression in the medial preoptic area (MPOA) significantly increased 10 weeks postpartum. Brain-derived neurotrophic factor (BDNF) expression was significantly elevated in the MEA 3 weeks postpartum. BDNF receptor tropomyosin-related kinase expression was significantly elevated in the MEA at 3 and 10 weeks but not at 5 weeks postpartum. The phosphorylation of ERK (pERK)-2 in the MEA, MPOA, and hippocampal CA1 region was significantly elevated 3 and 5 weeks postpartum. The effects of single daily sc injections of the ERα-selective agonist, propyl pyrazoletriol (PPT); ERβ-selective agonist, diarylpropionitrile; 17β-estradiol (E₂); and vehicle for 6 days in primiparous rats were assessed. PPT and E₂ significantly produced anxiolytic and antidepressant actions in the EPM and FS tests but PPT to a lesser degree than E₂ in the EPM test. Diarylpropionitrile affected the EPM test but was not significantly different from vehicle. BDNF expression was significantly increased 3 weeks postpartum by all treatments in the MPOA but not the CA1 and MEA. E₂ and PPT treatment significantly increased tropomyosin-related kinase and pERK1/2 expression in the MEA and MPOA and increased pERK1/2 expression in the CA1. The onset of anxiety- and depression-like behaviors in postpartum rats may be partly caused by a complex estrogen-mediated mechanism; nevertheless, changes in the ERα-related system, likely in the MEA, are predominantly involved.

Evidence for gating roles of protein kinase A and protein kinase C in estradiol-induced luteinizing hormone receptor (lhcgr) expression in zebrafish ovarian follicle cells

Estradiol (E2) stimulates luteinizing hormone receptor (lhcgr) expression in zebrafish follicle cells via nuclear estrogen receptors (nERs) that are likely expressed on the membrane, and lhcgr responds to E2 in a biphasic manner during 24-h treatment. These observations raise an interesting question on the signaling mechanism underlying E2 regulation, in particular the biphasic response of lhcgr expression. In the present study, we demonstrated that E2 regulation of lhcgr was significantly influenced by the activity of cAMP-PKA pathway. Activation of cAMP-PKA pathway by forskolin or db-cAMP suppressed E2-stimulated lhcgr expression in short-term (3 h) but enhanced its effect in long-term (24 h), suggesting differential roles of PKA at these two phases of lhcgr response. PKA inhibitor H89 showed reversed effects. In contrast, PKC pathway had consistent permissive effect on E2-induced lhcgr expression as evidenced by strong inhibition of E2 effect by PKC inhibitors GF109203X and Ro-31-8220 at both 3 and 24 h. One of the mechanisms by which PKA and PKC gated E2 effect might be through regulating nERs, particularly esr2a. Despite the strong influence of PKA and PKC, our data did not suggest direct mediating roles for these two pathways in E2 stimulation of lhcgr expression; yet they likely play critical gating roles in E2 signal transduction. As a follow-up study to our previous report on E2 regulation of gonadotropin receptors in the zebrafish ovary, the present study provides further evidence for the involvement of classical intracellular signal transduction pathways in E2 stimulation of lhcgr expression in the follicle cells.

Is basic research providing answers if adjuvant anti-estrogen treatment of breast cancer can induce cognitive impairment?

Adjuvant treatment of cancer by chemotherapy is associated with cognitive impairment in some cancer survivors. Breast cancer patients are frequently also receiving endocrine therapy with selective estrogen receptor modulators (SERMs) and/or aromatase inhibitors (AIs) to suppress the growth of estradiol sensitive breast tumors. Estrogens are well-known, however, to target brain areas involved in the regulation of cognitive behavior. In this review clinical and basic preclinical research is reviewed on the actions of estradiol, SERMs and AIs on brain and cognitive functioning to see if endocrine therapy potentially induces cognitive impairment and in that respect may contribute to the detrimental effects of chemotherapy on cognitive performance in breast cancer patients. Although many clinical studies may be underpowered to detect changes in cognitive function, current basic and clinical reports suggest that there is little evidence that AIs may have a lasting detrimental effect on cognitive performance in breast cancer patients. The clinical data on SERMs are not conclusive, but some studies do suggest that tamoxifen administration may form a risk for cognitive functioning particularly in older women. An explanation may come from basic preclinical research which indicates that tamoxifen often acts agonistic in the absence of estradiol but antagonistic in the presence of endogenous estradiol. It could be hypothesized that the negative effects of tamoxifen in older women is related to the so-called window of opportunity for estrogen. Administration of SERMs beyond this so-called window of opportunity may not be effective or might even have detrimental effects similar to estradiol.

G protein-coupled estrogen receptor in energy homeostasis and obesity pathogenesis

Obesity and its related metabolic diseases have reached a pandemic level worldwide. There are sex differences in the prevalence of obesity and its related metabolic diseases, with men being more vulnerable than women; however, the prevalence of these disorders increases dramatically in women after menopause, suggesting that sex steroid hormone estrogens play key protective roles against development of obesity and metabolic diseases. Estrogens are important regulators of several aspects of metabolism, including body weight and body fat, caloric intake and energy expenditure, and glucose and lipid metabolism in both males and females. Estrogens act in complex ways on their nuclear estrogen receptors (ERs) ERα and ERβ and transmembrane ERs such as G protein-coupled estrogen receptor. Genetic tools, such as different lines of knockout mouse models, and pharmacological agents, such as selective agonists and antagonists, are available to study function and signaling mechanisms of ERs. We provide an overview of the evidence for the physiological and cellular actions of ERs in estrogen-dependent processes in the context of energy homeostasis and body fat regulation and discuss its pathology that leads to obesity and related metabolic states.

Membrane-initiated estradiol actions mediate structural plasticity and reproduction

Over the years, our ideas about estrogen signaling have greatly expanded. In addition to estradiol having direct nuclear actions that mediate transcription and translation, more recent experiments have demonstrated membrane-initiated signaling. Both direct nuclear and estradiol membrane signaling can be mediated by the classical estrogen receptors, ERα and ERβ, which are two of the numerous putative membrane estrogen receptors. Thus far, however, only ERα has been shown to play a prominent role in regulating female reproduction and sexual behavior. Because ERα is a ligand-gated transcription factor and not a typical membrane receptor, trafficking to the cell membrane requires post-translational modifications. Two necessary modifications are palmitoylation and association with caveolins, a family of scaffolding proteins. In addition to their role in trafficking, caveolin proteins also serve to determine ERα interactions with metabotropic glutamate receptors (mGluRs). It is through these complexes that ERα, which cannot by itself activate G proteins, is able to initiate intracellular signaling. Various combinations of ERα-mGluR interactions have been demonstrated throughout the nervous system from hippocampus to striatum to hypothalamus to dorsal root ganglion (DRG) in both neurons and astrocytes. These combinations of ER and mGluR allow estradiol to have both facilitative and inhibitory actions in neurons. In hypothalamic astrocytes, the estradiol-mediated release of intracellular calcium stores regulating neurosteroid synthesis requires ERα-mGluR1a interaction. In terms of estradiol regulation of female sexual receptivity, activation of ERα-mGluR1a signaling complex leads to the release of neurotransmitters and alteration of neuronal morphology. This review will examine estradiol membrane signaling (EMS) activating a limbic-hypothalamic lordosis regulating circuit, which involves ERα trafficking, internalization, and modifications of neuronal morphology in a circuit that underlies female sexual receptivity.

Rapid control of male typical behaviors by brain-derived estrogens

Beside their genomic mode of action, estrogens also activate a variety of cellular signaling pathways through non-genomic mechanisms. Until recently, little was known regarding the functional significance of such actions in males and the mechanisms that control local estrogen concentration with a spatial and time resolution compatible with these non-genomic actions had rarely been examined. Here, we review evidence that estrogens rapidly modulate a variety of behaviors in male vertebrates. Then, we present in vitro work supporting the existence of a control mechanism of local brain estrogen synthesis by aromatase along with in vivo evidence that rapid changes in aromatase activity also occur in a region-specific manner in response to changes in the social or environmental context. Finally, we suggest that the brain estrogen provision may also play a significant role in females. Together these data bolster the hypothesis that brain-derived estrogens should be considered as neuromodulators.

Building a better hormone therapy? How understanding the rapid effects of sex steroid hormones could lead to new therapeutics for age-related memory decline

A wealth of data collected in recent decades has demonstrated that ovarian sex-steroid hormones, particularly 17β-estradiol (E2), are important trophic factors that regulate the function of cognitive regions of the brain such as the hippocampus. The loss of hormone cycling at menopause is associated with cognitive decline and dementia in women, and the onset of memory decline in animal models. However, hormone therapy is not currently recommended to prevent or treat cognitive decline, in part because of its detrimental side effects. In this article, it is proposed that investigations of the rapid effects of E2 on hippocampal function be used to further the design of new drugs that mimic the beneficial effects of E2 on memory without the side effects of current therapies. A conceptual model is presented for elucidating the molecular and biochemical mechanisms through which sex-steroid hormones modulate memory, and a specific hypothesis is proposed to account for the rapid memory-enhancing effects of E2. Empirical support for this hypothesis is discussed as a means of stimulating the consideration of new directions for the development of hormone-based therapies to preserve memory function in menopausal women.

Soy isoflavones genistein and daidzein exert anti-apoptotic actions via a selective ER-mediated mechanism in neurons following HIV-1 Tat(1-86) exposure

Background

HIV-1 viral protein Tat partially mediates the neural dysfunction and neuronal cell death associated with HIV-1 induced neurodegeneration and neurocognitive disorders. Soy isoflavones provide protection against various neurotoxic insults to maintain neuronal function and thus help preserve neurocognitive capacity.

Methodology/Principal Findings

We demonstrate in primary cortical cell cultures that 17β-estradiol or isoflavones (genistein or daidzein) attenuate Tat_1–86-induced expression of apoptotic proteins and subsequent cell death. Exposure of cultured neurons to the estrogen receptor antagonist ICI 182,780 abolished the anti-apoptotic actions of isoflavones. Use of ERα or ERβ specific antagonists determined the involvement of both ER isoforms in genistein and daidzein inhibition of caspase activity; ERβ selectively mediated downregulation of mitochondrial pro-apoptotic protein Bax. The findings suggest soy isoflavones effectively diminished HIV-1 Tat-induced apoptotic signaling.

Conclusions/Significance

Collectively, our results suggest that soy isoflavones represent an adjunctive therapeutic option with combination anti-retroviral therapy (cART) to preserve neuronal functioning and sustain neurocognitive abilities of HIV-1 infected persons.

Regulation of leptin expression by 17beta-estradiol in human placental cells involves membrane associated estrogen receptor alpha

The placenta produces a wide number of molecules that play essential roles in the establishment and maintenance of pregnancy. In this context, leptin has emerged as an important player in reproduction. The synthesis of leptin in normal trophoblastic cells is regulated by different endogenous biochemical agents, but the regulation of placental leptin expression is still poorly understood. We have previously reported that 17β-estradiol (E(2)) up-regulates placental leptin expression. To improve the understanding of estrogen receptor mechanisms in regulating leptin gene expression, in the current study we examined the effect of membrane-constrained E(2) conjugate, E-BSA, on leptin expression in human placental cells. We have found that leptin expression was induced by E-BSA both in BeWo cells and human placental explants, suggesting that E(2) also exerts its effects through membrane receptors. Moreover E-BSA rapidly activated different MAPKs and AKT pathways, and these pathways were involved in E(2) induced placental leptin expression. On the other hand we demonstrated the presence of ERα associated to the plasma membrane of BeWo cells. We showed that E(2) genomic and nongenomic actions could be mediated by ERα. Supporting this idea, the downregulation of ERα level through a specific siRNA, decreased E-BSA effects on leptin expression. Taken together, these results provide new evidence of the mechanisms whereby E(2) regulates leptin expression in placenta and support the importance of leptin in placental physiology.

Cell Models for the Study of Sex Steroid Hormone Neurobiology

To date many aspects of neurons and glia biology remain elusive, due in part to the cellular and molecular complexity of the brain. In recent decades, cell models from different brain areas have been established and proven invaluable toward understanding this complexity. In the field of steroid hormone neurobiology, an important question is: what is the profile of steroid hormone receptor expression in these specific cell lines? Currently, a clear summary of such receptor profiling is lacking. For this reason, we summarized in this review the expression of estrogen, progesterone, and androgen receptors in several widely used cell lines (glial and neuronal) derived from the forebrain and midbrain, based on our own data and that from the literature. Such information will aid in the selection of specific cell lines used to test hypotheses related to the biology of estrogens, progestins, and/or androgens.

Selective oestrogen receptor modulators differentially potentiate brain mitochondrial function

The mitochondrial energy-transducing capacity of the brain is important for long-term neurological health and is influenced by endocrine hormone responsiveness. The present study aimed to determine the role of oestrogen receptor (ER) subtypes in regulating mitochondrial function using selective agonists for ERα (propylpyrazoletriol; PPT) and ERβ (diarylpropionitrile; DPN). Ovariectomised female rats were treated with 17β-oestradiol (E(2) ), PPT, DPN or vehicle control. Both ER selective agonists significantly increased the mitochondrial respiratory control ratio and cytochrome oxidase (COX) activity relative to vehicle. Western blots of purified whole brain mitochondria detected ERα and, to a greater extent, ERβ localisation. Pre-treatment with DPN, an ERβ agonist, significantly increased ERβ association with mitochondria. In the hippocampus, DPN activated mitochondrial DNA-encoded COX I expression, whereas PPT was ineffective, indicating that mechanistically ERβ, and not ERα, activated mitochondrial transcriptional machinery. Both selective ER agonists increased protein expression of nuclear DNA-encoded COX IV, suggesting that activation of ERβ or ERα is sufficient. Selective ER agonists up-regulated a panel of bioenergetic enzymes and antioxidant defence proteins. Up-regulated proteins included pyruvate dehydrogenase, ATP synthase, manganese superoxide dismutase and peroxiredoxin V. In vitro, whole cell metabolism was assessed in live primary cultured hippocampal neurones and mixed glia. The results of analyses conducted in vitro were consistent with data obtained in vivo. Furthermore, lipid peroxides, accumulated as a result of hormone deprivation, were significantly reduced by E(2) , PPT and DPN. These findings suggest that the activation of both ERα and ERβ is differentially required to potentiate mitochondrial function in brain. As active components in hormone therapy, synthetically designed oestrogens as well as natural phyto-oestrogen cocktails can be tailored to improve brain mitochondrial endpoints.

Response of ERβ and aromatase expression in the monkey hippocampal formation to ovariectomy and menopause

Changes in the expression of estrogen-related substances in monkeys' brains at the menopausal transition, when estrogen deficit starts to occur, have not yet been examined thoroughly. In the present study, we immunohistochemically investigated the expression levels of estrogen receptor beta (ERβ) and aromatase (local estrogen synthesizing enzyme) in the hippocampal formation of premenopausal, menopausal, and ovariectomized premenopausal monkeys. In all monkeys tested, ERβ immunoreactivity was observed in interneurons located in the subiculum and the Ammon's horn, and most of these ERβ-immunoreactive neurons coexpressed a GABAergic neuron marker, parvalbumin. In the menopausal monkeys who exhibited a decline in estrogen concentration, hippocampal ERβ was highly upregulated, while aromatase expression was not markedly changed. By contrast, aromatase in the ovariectomized monkeys was significantly upregulated, while ERβ expression was not changed. In the brains of ovariectomized and menopausal monkeys, depletion of ovary-derived estrogen brought about different reactions which may be attributed to the senescence of brain aging.

Estrogen receptor β: switching to a new partner and escaping from estrogen

Estrogen receptor (ER) β, the "second" ER, plays a gatekeeper role by inhibiting cell proliferation, promoting apoptosis, and impeding the progression of prostate cancer. Ironically, its presumed ligand, 17β-estradiol, promotes cancer development in experimental models. The mechanisms underlying the interplay between estrogens and ERβ in prostate cancer remain largely unclear. Research on a previously unknown tethering partner of ERβ, Krüppel-like zinc finger transcription factor 5 (KLF5), and its downstream gene target (FOXO1) helps to unlock this puzzle. 17β-Estradiol is not required to maintain the tumor-suppressive function of ERβ in the prostate, a tissue with limited estrogen availability; moreover, the presence of 17β-estradiol abrogates ERβ- and KLF5-mediated signaling and promotes cellular proliferation. Future research into ERβ will likely involve this estrogen independency and the preference for binding nonclassical DNA elements through tethering. The development of ERβ-based therapies may lead to improved drug efficacy.

Divergent mechanisms for trophic actions of estrogens in the brain and peripheral tissues

17β-estradiol (E(2)) can enhance reproductive, cognitive, and affective functions; however, the mechanisms by which E(2) has these effects need to be better understood. Pleiotrophic effects of E(2) can occur via traditional and novel actions at various forms of estrogen receptors (ERs). In the central nervous system, trophic effects of E(2) may be related to beneficial effects of hormone replacement therapy (HRT). However, in peripheral reproductive tissues, E(2)'s capacity to evoke growth can increase risk of cancers. This review focuses on investigations aimed at elucidating divergent mechanisms of steroids to promote trophic effects in the brain, independent of effects on peripheral reproductive tissues. First, actions of estrogens via ERα or ERβ for peripheral growth (carcinogen-induced tumors, uterine growth) and hippocampus-dependent behaviors (affect, cognition) are described. Second, factors that influence these effects of estrogens are described (e.g. experience, timing/critical windows, non-ER mechanisms). Third, effects of estrogens at ERβ related to actions of progestogens, such as 5α-pregnan-3α-ol-20-one (3α,5α-THP) are described. In summary, effects of E(2) may occur via multiple mechanisms, which may underlie favorable effects in the brain with minimal peripheral trophic effects.

Estrogen receptor beta-selective agonists stimulate calcium oscillations in human and mouse embryonic stem cell-derived neurons

Estrogens are used extensively to treat hot flashes in menopausal women. Some of the beneficial effects of estrogens in hormone therapy on the brain might be due to nongenomic effects in neurons such as the rapid stimulation of calcium oscillations. Most studies have examined the nongenomic effects of estrogen receptors (ER) in primary neurons or brain slices from the rodent brain. However, these cells can not be maintained continuously in culture because neurons are post-mitotic. Neurons derived from embryonic stem cells could be a potential continuous, cell-based model to study nongenomic actions of estrogens in neurons if they are responsive to estrogens after differentiation. In this study ER-subtype specific estrogens were used to examine the role of ERα and ERβ on calcium oscillations in neurons derived from human (hES) and mouse embryonic stem cells. Unlike the undifferentiated hES cells the differentiated cells expressed neuronal markers, ERβ, but not ERα. The non-selective ER agonist 17β-estradiol (E₂) rapidly increased [Ca2+]i oscillations and synchronizations within a few minutes. No change in calcium oscillations was observed with the selective ERα agonist 4,4′,4″-(4-Propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT). In contrast, the selective ERβ agonists, 2,3-bis(4-Hydroxyphenyl)-propionitrile (DPN), MF101, and 2-(3-fluoro-4-hydroxyphenyl)-7-vinyl-1,3 benzoxazol-5-ol (ERB-041; WAY-202041) stimulated calcium oscillations similar to E₂. The ERβ agonists also increased calcium oscillations and phosphorylated PKC, AKT and ERK1/2 in neurons derived from mouse ES cells, which was inhibited by nifedipine demonstrating that ERβ activates L-type voltage gated calcium channels to regulate neuronal activity. Our results demonstrate that ERβ signaling regulates nongenomic pathways in neurons derived from ES cells, and suggest that these cells might be useful to study the nongenomic mechanisms of estrogenic compounds.

Caveolin regulation of neuronal intracellular signaling

Caveolin proteins physically interact with and compartmentalize membrane-localized signaling proteins to facilitate high-fidelity intracellular signaling. Though primarily studied outside the nervous system, recent investigations have revealed that caveolin proteins are key modulators of a variety of neuronal intracellular signaling pathways. Through both protein aggregation and segregation, caveolin proteins can exert positive and negative influences on intracellular signaling. This review will detail recent findings regarding caveolin function in the brain.

Rapid behavioural effects of oestrogens and fast regulation of their local synthesis by brain aromatase

Besides their genomic effects, oestrogens, 17beta-oestradiol in particular, also activate cellular effects that may be too rapid (seconds to minutes) to result from de novo protein synthesis. Although the existence of such nongenomic actions has been extensively demonstrated in vitro, the understanding of their behavioural significance is only emerging. Recent findings provide evidence that acute oestrogen treatments significantly affect a variety of behavioural processes, including sexual behaviour, social communication and cognition. One question arising from these results concerns the source of the oestrogens mediating nongenomic effects in vivo. In this review, data collected in vitro and in vivo are presented supporting the notion that fast modulations of local testosterone aromatisation can rapidly control the local oestrogen concentration in a time frame compatible with their rapid actions. Taken together, these data provide compelling evidence of how rapid changes in the local production and action of oestrogens can shape complex behaviours.