Estrogen Modulation of G-protein-coupled Receptors

Effects of Oral Delta-9-Tetrahydrocannabinol in Women During the Follicular Phase of the Menstrual Cycle

Background: This study examined effects of oral delta-9-tetrahydrocannabinol (THC) in women at two phases of the menstrual cycle differing in circulating levels of estrogen (E). Pre-clinical findings indicate that E increases sensitivity to THC and other cannabinoids, raising the possibility that higher E may be a risk factor for adverse responses to THC in women. Methods: We examined subjective and behavioral responses to THC (7.5 and 15 mg oral) and placebo in women during the early follicular (EF) phase when E levels are low and the late follicular (LF) phase when E levels are higher. Outcome measures included self-report ratings of drug effects, cardiovascular measures, and biochemical verification of ovarian hormone levels. We hypothesized that women would exhibit greater responses to THC during the LF phase compared to the EF phase. Results: On most measures, responses to THC were similar during the two phases. However, on two self-report measures, "Wanting More" drug and anxiety, the effects occurred slightly earlier after drug administration in women who were tested during the EF phase. Conclusions: We conclude that the differences in levels of E occurring during the early and LF phase of the menstrual cycle do not strongly influence responses to THC. It remains to be determined whether responses are similarly stable across other cycle phases, or in women receiving exogenous hormone treatments.

The Ancestral Modulation Hypothesis: Predicting Mechanistic Control of Sexually Heteromorphic Traits Using Evolutionary History

AbstractAcross the animal kingdom there are myriad forms within a sex across, and even within, species, rendering concepts of universal sex traits moot. The mechanisms that regulate the development of these trait differences are varied, although in vertebrates, common pathways involve gonadal steroid hormones. Gonadal steroids are often associated with heteromorphic trait development, where the steroid found at higher circulating levels is the one involved in trait development for that sex. Occasionally, there are situations in which a gonadal steroid associated with heteromorphic trait development in one sex is involved in heteromorphic or monomorphic trait development in another sex. We propose a verbal hypothesis, the ancestral modulation hypothesis (AMH), that uses the evolutionary history of the trait-particularly which sex ancestrally possessed higher trait values-to predict the regulatory pathway that governs trait expression. The AMH predicts that the genomic architecture appears first to resolve sexual conflict in an initially monomorphic trait. This architecture takes advantage of existing sex-biased signals, the gonadal steroid pathway, to generate trait heteromorphism. In cases where the other sex experiences evolutionary pressure for the new phenotype, that sex will co-opt the existing architecture by altering its signal to match that of the original high-trait-value sex. We describe the integrated levels needed to produce this pattern and what the expected outcomes will be given the evolutionary history of the trait. We present this framework as a testable hypothesis for the scientific community to investigate and to create further engagement and analysis of both ultimate and proximate approaches to sexual heteromorphism.

The vital role of arcuate nociceptin/orphanin FQ neurones in mounting an oestradiol-dependent adaptive response to negative energy balance via inhibition of nearby proopiomelanocortin neurones

We tested the hypothesis that N/OFQ neurones in the arcuate nucleus (N/OFQ^ARC ) inhibit proopiomelanocortin (POMC^ARC ) neurones in a diet- and hormone-dependent manner to promote a more extensive rebound hyperphagia upon re-feeding following an 18 h fast. We utilized intact male or ovariectomized (OVX) female mice subjected to ad libitum-feeding or fasting conditions. N/OFQ^ARC neurones under negative energy balance conditions displayed heightened sensitivity as evidenced by a decreased rheobase threshold, increased firing frequency, and increased burst duration and frequency compared to ad libitum-feeding conditions. Stimulation of N/OFQ^ARC neurones more robustly inhibited POMC^ARC neurones under fasting conditions compared to ad libitum-feeding conditions. N/OFQ^ARC inhibition of POMC^ARC neurones is hormone dependent as chemostimulation of N/OFQ^ARC neurones from fasted males and OVX females produced a sizable outward current in POMC^ARC neurones. Oestradiol (E₂ ) markedly attenuated the N/OFQ-induced POMC^ARC outward current. Additionally, N/OFQ tonically inhibits POMC^ARC neurones to a greater degree under fasting conditions than in ad libitum-feeding conditions as evidenced by the abrogation of N/OFQ-nociceptin opioid peptide (NOP) receptor signalling and inhibition of N/OFQ release via chemoinhibition of N/OFQ^ARC neurones. Intra-arcuate nucleus application of N/OFQ further elevated the hyperphagic response and increased meal size during the 6 h re-feed period, and these effects were mimicked by chemostimulation of N/OFQ^ARC neurones in vivo. E₂ attenuated the robust N/OFQ-induced rebound hyperphagia seen in vehicle-treated OVX females. These data demonstrate that N/OFQ^ARC neurones play a vital role in mitigating the impact of negative energy balance by inhibiting the excitability of anorexigenic neural substrates, an effect that is diminished by E₂ in females. KEY POINTS: Nociceptin/orphanin FQ (N/OFQ) promotes increased energy intake and decreased energy expenditure under conditions of positive energy balance in a sex- and hormone-dependent manner. Here it is shown that under conditions of negative energy balance, i.e. fasting, N/OFQ inhibits anorexigenic proopiomelanocortin (POMC) neurones to a greater degree compared to homeostatic conditions due to fasting-induced hyperexcitability of N/OFQ neurones. Additionally, N/OFQ promotes a sustained increase in rebound hyperphagia and increase in meal size during the re-feed period following a fast. These results promote greater understanding of how energy balance influences the anorexigenic circuitry of the hypothalamus, and aid in understanding the neurophysiological pathways implicated in eating disorders promoting cachexia.

A novel GPER antagonist protects against the formation of estrogen-induced cholesterol gallstones in female mice

Many clinical studies and epidemiological investigations have clearly demonstrated that women are twice as likely to develop cholesterol gallstones as men, and oral contraceptives and other estrogen therapies dramatically increase that risk. Further, animal studies have revealed that estrogen promotes cholesterol gallstone formation through the estrogen receptor (ER) α, but not ERβ, pathway. More importantly, some genetic and pathophysiological studies have found that G protein-coupled estrogen receptor (GPER) 1 is a new gallstone gene, Lith18, on chromosome 5 in mice and produces additional lithogenic actions, working independently of ERα, to markedly increase cholelithogenesis in female mice. Based on computational modeling of GPER, a novel series of GPER-selective antagonists were designed, synthesized, and subsequently assessed for their therapeutic effects via calcium mobilization, cAMP, and ERα and ERβ fluorescence polarization binding assays. From this series of compounds, one new compound, 2-cyclohexyl-4-isopropyl-N-(4-methoxybenzyl)aniline (CIMBA), exhibits superior antagonism and selectivity exclusively for GPER. Furthermore, CIMBA reduces the formation of 17β-estradiol-induced gallstones in a dose-dependent manner in ovariectomized mice fed a lithogenic diet for 8 weeks. At 32 μg/day/kg CIMBA, no gallstones are found, even in ovariectomized ERα (-/-) mice treated with 6 μg/day 17β-estradiol and fed the lithogenic diet for 8 weeks. In conclusion, CIMBA treatment protects against the formation of estrogen-induced cholesterol gallstones by inhibiting the GPER signaling pathway in female mice. CIMBA may thus be a new agent for effectively treating cholesterol gallstone disease in women.

Sex steroid hormone function in the brain niche: Implications for brain metastatic colonization and progression

BACKGROUND

While sex hormones and their receptors play well-known roles in progression of primary tumors through direct action on sex steroid hormone-responsive cancer cells, emerging evidence suggest that hormones also play important roles in metastatic progression by modulating the tumor microenvironment. Estrogens and androgens synthesized in gonads and within the brain influence memory, behavior, and outcomes of brain pathologies. Yet, their impact on brain metastatic colonization and progression is just beginning to be explored.

RECENT FINDINGS

Estradiol and testosterone cross the blood-brain barrier and are synthesized de novo in astrocytes and other cells within the adult brain. Circulating and brain-synthesized estrogens have been shown to promote brain metastatic colonization of tumors lacking estrogen receptors (ERs), through mechanisms involving the upregulation of growth factors and neurotrophins in ER+ reactive astrocytes. In this review, we discuss additional mechanisms by which hormones may influence brain metastases, through modulation of brain endothelial cells, astrocytes, and microglia.

CONCLUSION

A greater understanding of hormone-brain-tumor interactions may shed further light on the mechanisms underlying the adaptation of cancer cells to the brain niche, and provide therapeutic alternatives modulating the brain metastatic niche.

G Protein-Coupled Estrogen Receptor, GPER1, Offers a Novel Target for the Treatment of Digestive Diseases

There are gender differences between men and women in many physiological functions and diseases, which indicates that female sex hormones may be important. Traditionally, estrogen exerts its biological activities by activating two classical nuclear estrogen receptors, ESR1 and ESR2. However, the roles of estrogen in the regulation of physiological functions and the pathogenesis of diseases become more complicated with the identification of the G protein-coupled estrogen receptor (GPER1). Although many GPER1-specific ligands have been developed, the therapeutic mechanisms of exclusively targeting GPER1 are not yet well understood. Translational applications and clinical trial efforts for the identified GPER1 ligands have been focused primarily on the reproductive, cardiovascular, nervous, endocrine, and immune systems. More recently, research found that GPER1 may play an important role in regulating the digestive system. Cholesterol gallstone disease, a major biliary disease, has a higher prevalence in women than in men worldwide. Emerging evidence implies that GPER1 could play an important role, independent of the classical ESR1, in the pathophysiology of cholesterol gallstones in women. This review discusses the complex signaling pathways of three estrogen receptors, highlights the development of GPER1-specific ligands, and summarizes the latest advances in the role of GPER1 in the pathogenesis of gallstone formation.

Sex differences and the neurobiology of affective disorders

Observations of the disproportionate incidence of depression in women compared with men have long preceded the recent explosion of interest in sex differences. Nonetheless, the source and implications of this epidemiologic sex difference remain unclear, as does the practical significance of the multitude of sex differences that have been reported in brain structure and function. In this article, we attempt to provide a framework for thinking about how sex and reproductive hormones (particularly estradiol as an example) might contribute to affective illness. After briefly reviewing some observed sex differences in depression, we discuss how sex might alter brain function through hormonal effects (both organizational (programmed) and activational (acute)), sex chromosome effects, and the interaction of sex with the environment. We next review sex differences in the brain at the structural, cellular, and network levels. We then focus on how sex and reproductive hormones regulate systems implicated in the pathophysiology of depression, including neuroplasticity, genetic and neural networks, the stress axis, and immune function. Finally, we suggest several models that might explain a sex-dependent differential regulation of affect and susceptibility to affective illness. As a disclaimer, the studies cited in this review are not intended to be comprehensive but rather serve as examples of the multitude of levels at which sex and reproductive hormones regulate brain structure and function. As such and despite our current ignorance regarding both the ontogeny of affective illness and the impact of sex on that ontogeny, sex differences may provide a lens through which we may better view the mechanisms underlying affective regulation and dysfunction.

Estrogen and Serotonin: Complexity of Interactions and Implications for Epileptic Seizures and Epileptogenesis

A burgeoning literature documents the confluence of ovarian steroids and central serotonergic systems in the injunction of epileptic seizures and epileptogenesis. Estrogen administration in animals reduces neuronal death from seizures by up-regulation of the prosurvival molecule i.e. Bcl-2, anti-oxidant potential and protection of NPY interneurons. Serotonin modulates epileptiform activity in either direction i.e administration of 5-HT agonists or reuptake inhibitors leads to the activation of 5-HT3 and 5-HT1A receptors tending to impede focal and generalized seizures, while depletion of brain 5-HT along with the destruction of serotonergic terminals leads to expanded neuronal excitability hence abatement of seizure threshold in experimental animal models. Serotonergic neurotransmission is influenced by the organizational activity of steroid hormones in the growing brain and the actuation effects of steroids which come in adulthood. It is further established that ovarian steroids bring induction of dendritic spine proliferation on serotonin neurons thus thawing a profound effect on serotonergic transmission. This review features 5-HT1A and 5-HT3 receptors as potential targets for ameliorating seizure-induced neurodegeneration and recurrent hypersynchronous neuronal activity. Indeed 5-HT3 receptors mediate cross-talk between estrogenic and serotonergic pathways, and could be well exploited for combinatorial drug therapy against epileptogenesis.

Distinct dynorphin expression patterns with low- and high-dose estrogen treatment in the arcuate nucleus of female rats

Kisspeptin (KISS1; encoded by Kiss1) neurons in the arcuate nucleus (ARC) coexpress tachykinin 3 (TAC3; also known as neurokinin B) and dynorphin A (PDYN). Accordingly, they are termed KNDy neurons and considered to be crucial in generating pulsatile release of gonadotropin-releasing hormone. Accumulating evidence suggests that Kiss1 and Tac3 are negatively regulated by estrogen. However, it has not been fully determined whether and how estrogen modulates Pdyn and PDYN. Here, we examined the expression of Pdyn mRNA and PDYN by in situ hybridization and immunohistochemistry, respectively, in the ARC of female rats after ovariectomy (OVX) and OVX plus low- or high-dose beta-estradiol (E2) replacement. We also investigated the effect of E2 on expression of Kiss1, KISS1, Tac3, and TAC3. Furthermore, colocalization of PDYN and estrogen receptor alpha (ESR1) was determined. Subsequently, we found that low-dose E2 treatment had no effect on Pdyn mRNA-expressing cells, but increased PDYN-immunoreactive (ir) cell numbers. In contrast, high-dose E2 treatment resulted in prominent reductions in both Pdyn mRNA-expressing and PDYN-ir cell numbers. Changes induced by low or high doses of E2 were similarly observed in the expression of Kiss1, KISS1, Tac3, and TAC3. The majority of PDYN-ir neurons coexpressed ESR1 in all groups. Our results indicate that E2 regulates the expression of PDYN, as well as KISS1 and TAC3, with regulation by E2 differing according to its levels.

Reduction of estradiol in human malignant pleural mesothelioma tissues may prevent tumour growth, as implied by in in-vivo and in-vitro models

This study aimed to investigate intratumoural estradiol and estrogen-receptors (ERα, ERβ and GPR30) in malignant pleural mesothelioma (MPM) to understand their function. Here, we report that immunohistochemistry of estradiol showed cytoplasmatic staining in 95% of fifty-seven human MPM samples with a trend toward a negative correlation between estradiol levels and the median post-diagnosis survival time. ERβ was only focally positive in 5.3% of cases, GPR30 and ERα were negative in our cases of MPM. GPR30 was detected mainly in glycosylated form in MPM cells. Moreover, G15, a GPR30 antagonist, induced MPM cell death. Altogether, these data suggest that MPM cells produce E₂ interact with glycosylated forms of GPR30, and this facilitates tumour growth. Estradiol was found in MPM cells and plasma from mice mesothelioma xenografts. Concurrent reduction in tumour mass and plasmatic estradiol levels were observed in the mice treated with exemestane, suggesting that the reduction of E₂ levels inhibit MPM growth. Thus, it appears that agents reducing estradiol levels could be useful to MPM therapy.

Pituitary Action of E2 in Prepubertal Grass Carp: Receptor Specificity and Signal Transduction for Luteinizing Hormone and Follicle-Stimulating Hormone Regulation

17β-estradiol (E2) is an important sex steroid produced by ovary and brain. In mammals, E2 plays an important role in hypothalamus-pituitary-gonad axis to regulate puberty onset, however, little is known about the functional role of E2 in teleost pituitary. Using prepubertal grass carp as model, three nuclear estrogen receptors (nERs: estrogen receptor alpha, estrogen receptor beta 1, and estrogen receptor beta 2) and two G protein-coupled estrogen receptors (GPER1: GPER1a and GPER1b) were isolated from grass carp pituitary. Tissue distribution analysis indicated that both nERs and GPERs were highly detected in grass carp pituitary, which suggested that E2 should play an important role in grass carp pituitary. Using primary cultured grass carp pituitary cells as model, high-throughput RNA-seq was used to examine the E2-induced differentially expressed genes (DEGs). Transcriptomic analysis showed that E2 could significantly upregulate the expression of 28 genes in grass carp pituitary cells, which were characterized into different functions including reproduction, gonad development, and central nervous system development. Further studies confirmed that E2 could induce luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion and mRNA expression in prepubertal grass carp pituitary in vivo and in vitro. In the pituitary, LH and FSH regulation by E2 were mediated by both ERβ and GPER1. Apparently, E2-induced LHβ and FSHβ mRNA expression were mediated by adenylyl cyclase/cAMP/protein kinase A, phospholipase C/inositol 1,4,5-triphosphate/protein kinase C, and Ca²⁺/calmodulin/CaM-dependent protein kinase II pathways. In addition to LH and FSH, E2 could also induce growth regulation by estrogen in breast cancer 1 (a novel regulator for pituitary development) mRNA expression in grass carp pituitary cells. These results, as a whole, suggested that E2 could play an important role in gonadotropin hormone release and pituitary development in prepubertal grass carp.

Neural Regulation of Paternal Behavior in Mammals: Sensory, Neuroendocrine, and Experiential Influences on the Paternal Brain

Across the animal kingdom, parents in many species devote extraordinary effort toward caring for offspring, often risking their lives and exhausting limited resources. Understanding how the brain orchestrates parental care, biasing effort over the many competing demands, is an important topic in social neuroscience. In mammals, maternal care is necessary for offspring survival and is largely mediated by changes in hormones and neuropeptides that fluctuate massively during pregnancy, parturition, and lactation (e.g., progesterone, estradiol, oxytocin, and prolactin). In the relatively small number of mammalian species in which parental care by fathers enhances offspring survival and development, males also undergo endocrine changes concurrent with birth of their offspring, but on a smaller scale than females. Thus, fathers additionally rely on sensory signals from their mates, environment, and/or offspring to orchestrate paternal behavior. Males can engage in a variety of infant-directed behaviors that range from infanticide to avoidance to care; in many species, males can display all three behaviors in their lifetime. The neural plasticity that underlies such stark changes in behavior is not well understood. In this chapter we summarize current data on the neural circuitry that has been proposed to underlie paternal care in mammals, as well as sensory, neuroendocrine, and experiential influences on paternal behavior and on the underlying circuitry. We highlight some of the gaps in our current knowledge of this system and propose future directions that will enable the development of a more comprehensive understanding of the proximate control of parenting by fathers.

Effect of Estradiol on Neurotrophin Receptors in Basal Forebrain Cholinergic Neurons: Relevance for Alzheimer's Disease

The basal forebrain is home to the largest population of cholinergic neurons in the brain. These neurons are involved in a number of cognitive functions including attention, learning and memory. Basal forebrain cholinergic neurons (BFCNs) are particularly vulnerable in a number of neurological diseases with the most notable being Alzheimer's disease, with evidence for a link between decreasing cholinergic markers and the degree of cognitive impairment. The neurotrophin growth factor system is present on these BFCNs and has been shown to promote survival and differentiation on these neurons. Clinical and animal model studies have demonstrated the neuroprotective effects of 17β-estradiol (E2) on neurodegeneration in BFCNs. It is believed that E2 interacts with neurotrophin signaling on cholinergic neurons to mediate these beneficial effects. Evidence presented in our recent study confirms that altering the levels of circulating E2 levels via ovariectomy and E2 replacement significantly affects the expression of the neurotrophin receptors on BFCN. However, we also showed that E2 differentially regulates neurotrophin receptor expression on BFCNs with effects depending on neurotrophin receptor type and neuroanatomical location. In this review, we aim to survey the current literature to understand the influence of E2 on the neurotrophin system, and the receptors and signaling pathways it mediates on BFCN. In addition, we summarize the physiological and pathophysiological significance of E2 actions on the neurotrophin system in BFCN, especially focusing on changes related to Alzheimer's disease.

Rapid steroid hormone actions via membrane receptors

Steroid hormones regulate a wide variety of physiological and developmental functions. Traditional steroid hormone signaling acts through nuclear and cytosolic receptors, altering gene transcription and subsequently regulating cellular activity. This is particularly important in hormonally-responsive cancers, where therapies that target classical steroid hormone receptors have become clinical staples in the treatment and management of disease. Much progress has been made in the last decade in detecting novel receptors and elucidating their mechanisms, particularly their rapid signaling effects and subsequent impact on tumorigenesis. Many of these receptors are membrane-bound and lack DNA-binding sites, functionally separating them from their classical cytosolic receptor counterparts. Membrane-bound receptors have been implicated in a number of pathways that disrupt the cell cycle and impact tumorigenesis. Among these are pathways that involve phospholipase D, phospholipase C, and phosphoinositide-3 kinase. The crosstalk between these pathways has been shown to affect apoptosis and proliferation in cardiac cells, osteoblasts, and chondrocytes as well as cancer cells. This review focuses on rapid signaling by 17β-estradiol and 1α,25-dihydroxy vitamin D3 to examine the integrated actions of classical and rapid steroid signaling pathways both in contrast to each other and in concert with other rapid signaling pathways. This new approach lends insight into rapid signaling by steroid hormones and its potential for use in targeted drug therapies that maximize the benefits of traditional steroid hormone-directed therapies while mitigating their less desirable effects.

Estradiol Membrane-Initiated Signaling and Female Reproduction

The discoveries of rapid, membrane-initiated steroid actions and central nervous system steroidogenesis have changed our understanding of the neuroendocrinology of reproduction. Classical nuclear actions of estradiol and progesterone steroids affecting transcription are essential. However, with the discoveries of membrane-associated steroid receptors, it is becoming clear that estradiol and progesterone have neurotransmitter-like actions activating intracellular events. Ultimately, membrane-initiated actions can influence transcription. Estradiol membrane-initiated signaling (EMS) modulates female sexual receptivity and estrogen feedback regulating the luteinizing hormone (LH) surge. In the arcuate nucleus, EMS activates a lordosis-regulating circuit that extends to the medial preoptic nucleus and subsequently to the ventromedial nucleus (VMH)--the output from the limbic and hypothalamic regions. Here, we discuss how EMS leads to an active inhibition of lordosis behavior. To stimulate ovulation, EMS facilitates astrocyte synthesis of progesterone (neuroP) in the hypothalamus. Regulation of GnRH release driving the LH surge is dependent on estradiol-sensitive kisspeptin (Kiss1) expression in the rostral periventricular nucleus of the third ventricle (RP3V). NeuroP activation of the LH surge depends on Kiss1, but the specifics of signaling have not been well elucidated. RP3V Kiss1 neurons appear to integrate estradiol and progesterone information which feeds back onto GnRH neurons to stimulate the LH surge. In a second population of Kiss1 neurons, estradiol suppresses the surge but maintains tonic LH release, another critical component of the estrous cycle. Together, evidence suggests that regulation of reproduction involves membrane action of steroids, some of which are synthesized in the brain.

Estradiol Rapidly Attenuates ORL-1 Receptor-Mediated Inhibition of Proopiomelanocortin Neurons via Gq-Coupled, Membrane-Initiated Signaling

Estradiol rapidly regulates the activity of arcuate nucleus (ARH) proopiomelanocortin (POMC) neurons that project to the medial preoptic nucleus (MPN) to regulate lordosis. Orphanin FQ/nociceptin (OFQ/N) acts via opioid receptor-like (ORL)-1 receptors to inhibit these POMC neurons. Therefore, we tested the hypothesis that estradiol excites POMC neurons by rapidly attenuating inhibitory ORL-1 signaling in these cells. Hypothalamic slices through the ARH were prepared from ovariectomized rats injected with Fluorogold into the MPN. Electrophysiological recordings were generated in ARH neurons held at or near -60 mV, and neuronal phenotype was determined post hoc by immunohistofluorescence. OFQ/N application induced robust outward currents and hyperpolarizations via G protein-gated, inwardly rectifying K+ (GIRK) channels that were attenuated by pretreatment with either 17-β estradiol (E2) or E2 conjugated to bovine serum albumin. This was blocked by the estrogen receptor (ER) antagonist ICI 182,780 and mimicked by the Gq-coupled membrane ER (Gq-mER) ligand STX and the ERα agonist PPT. Inhibiting phosphatidylinositol-3-kinase (PI3K) blocked the estrogenic attenuation of ORL-1/GIRK currents. Antagonizing either phospholipase C (PLC), protein kinase C (PKC), protein kinase A (PKA) or neuronal nitric oxide synthase (nNOS) also abrogated E2 inhibition of ORL-1/GIRK currents, whereas activation of PKC, PKA, protein kinase B (Akt) and nNOS substrate L-arginine all attenuated the OFQ/N response. This was observed in 92 MPN-projecting, POMC-positive ARH neurons. Thus, ORL-1 receptor-mediated inhibition of POMC neurons is rapidly and negatively modulated by E2, an effect which is stereoselective and membrane initiated via Gq-mER and ERα activation that signals through PLC, PKC, PKA, PI3K and nNOS.

Estrogen receptors in the central nervous system and their implication for dopamine-dependent cognition in females

This article is part of a Special Issue "Estradiol and cognition". Over the past 30 years, research has demonstrated that estrogens not only are important for female reproduction, but also play a role in a diverse array of cognitive functions. Originally, estrogens were thought to have only one receptor, localized exclusively to the cytoplasm and nucleus of cells. However, it is now known that there are at least three estrogen receptors (ERs): ERα, ERβ and G-protein coupled ER1 (GPER1). In addition to being localized to nuclei, ERα and ERβ are localized to the cell membrane, and GPER1 is also observed at the cell membrane. The mechanism through which ERs are associated with the membrane remains unclear, but palmitoylation of receptors and associations between ERs and caveolin are implicated in membrane association. ERα and ERβ are mostly observed in the nucleus using light microscopy unless they are particularly abundant. However, electron microscopy has revealed that ERs are also found at the membrane in complimentary distributions in multiple brain regions, many of which are innervated by dopamine inputs and were previously thought to contain few ERs. In particular, membrane-associated ERs are observed in the prefrontal cortex, dorsal striatum, nucleus accumbens, and hippocampus, all of which are involved in learning and memory. These findings provide a mechanism for the rapid effects of estrogens in these regions. The effects of estrogens on dopamine-dependent cognition likely result from binding at both nuclear and membrane-associated ERs, so elucidating the localization of membrane-associated ERs helps provide a more complete understanding of the cognitive effects of these hormones.

Non-invasive administration of 17β-estradiol rapidly increases aggressive behavior in non-breeding, but not breeding, male song sparrows

17β-Estradiol (E2) acts in the brain via genomic and non-genomic mechanisms to influence physiology and behavior. There is seasonal plasticity in the mechanisms by which E2 activates aggression, and non-genomic mechanisms appear to predominate during the non-breeding season. Male song sparrows (Melospiza melodia) display E2-dependent territorial aggression throughout the year. Field studies show that song sparrow aggression during a territorial intrusion is similar in the non-breeding and breeding seasons, but aggression after an intrusion ends differs seasonally. Non-breeding males stop behaving aggressively within minutes whereas breeding males remain aggressive for hours. We hypothesize that this seasonal plasticity in the persistence of aggression relates to seasonal plasticity in E2 signaling. We used a non-invasive route of E2 administration to compare the non-genomic (within 20min) effects of E2 on aggressive behavior in captive non-breeding and breeding season males. E2 rapidly increased barrier contacts (attacks) during an intrusion by 173% in non-breeding season males only. Given that these effects were observed within 20min of E2 administration, they likely occurred via a non-genomic mechanism of action. The present data, taken together with past work, suggest that environmental cues associated with the non-breeding season influence the molecular mechanisms through which E2 influences behavior. In song sparrows, transient expression of aggressive behavior during the non-breeding season is highly adaptive: it minimizes energy expenditure and maximizes the amount of time available for foraging. In all, these data suggest the intriguing possibility that aggression in the non-breeding season may be activated by a non-genomic E2 mechanism due to the fitness benefits associated with rapid and transient expression of aggression.

Exemestane blocks mesothelioma growth through downregulation of cAMP, pCREB and CD44 implicating new treatment option in patients affected by this disease

Background

Recent evidence suggests that aromatase may be involved in the pathogenesis of malignant mesothelioma. Here, we evaluated the effect of exemestane, an inhibitor of aromatase, in the treatment of mesothelioma using in vitro and in vivo preclinical models.

Results

We show a significant reduction of cell proliferation, survival, migration and block of cells in S phase of cell cycle in mesothelioma cells upon exemestane treatment. Moreover, we find that CD44, which is involved in mesothelioma cells migration, was modulated by exemestane via cAMP and pCREB. Most importantly, in mice mesothelioma xenograft exemestane causes a significant decrease in tumor size and the association pemetrexed/exemestane is more effective than pemetrexed/cisplatin.

Conclusion

The preclinical mesothelioma model suggests that exemestane might be beneficial in mesothelioma treatment.

Role of estrogen receptors and g protein-coupled estrogen receptor in regulation of hypothalamus-pituitary-testis axis and spermatogenesis

Male reproductive function is under the control of both gonadotropins and androgens through a negative feedback loop that involves the hypothalamus, pituitary, and testis known as hypothalamus-pituitary-gonadal axis (HPG). Indeed, estrogens also play an important role in regulating HPG axis but the study on relative contribution to the inhibition of gonadotropins secretion exerted by the amount of estrogens produced within the hypothalamus and/or the pituitary or by the amount of circulating estrogens is still ongoing. Moreover, it is known that the maintenance of spermatogenesis is controlled by gonadotropins and testosterone, the effects of which are modulated by a complex network of locally produced factors, including estrogens. Physiological effects of estrogens are mediated by the classical nuclear estrogen receptor alpha and estrogen receptor beta, which mediate both genomic and rapid signaling events. In addition, estrogens induce rapid non-genomic responses through a membrane-associated G protein-coupled estrogen receptor (GPER). Ours and other studies reported that, in the testis, GPER is expressed in both normal germ cells and somatic cells and it is involved in mediating the estrogen action in spermatogenesis controlling proliferative and/or apoptotic events. Interestingly, GPER expression has been revealed also in the hypothalamus and pituitary. However, its role in mediating estrogen rapid actions in this context is under investigation. Recent studies indicate that GPER is involved in modulating gonadotropin-releasing hormone (GnRH) release as well as gonadotropins secretion. In this review, we will summarize the current knowledge concerning the role of estrogen/estrogen receptors molecular pathways in regulating GnRH, follicle-stimulating hormone, and luteinizing hormone release at the hypothalamic and pituitary levels in males as well as in controlling specific testicular functions such as spermatogenesis, focusing our attention mainly on estrogen signaling mediated by GPER.

Non-classical effects of estradiol on cAMP responsive element binding protein phosphorylation in gonadotropin-releasing hormone neurons: mechanisms and role

Gonadotropin-releasing hormone (GnRH) is produced by a heterogenous neuronal population in the hypothalamus to control pituitary gonadotropin production and reproductive function in all mammalian species. Estradiol is a critical component for the communication between the gonads and the central nervous system. Resolving the mechanisms by which estradiol modulates GnRH neurons is critical for the understanding of how fertility is regulated. Extensive studies during the past decades have provided compelling evidence that estradiol has the potential to alter the intracellular signal transduction mechanisms. The common target of many signaling pathways is the phosphorylation of a key transcription factor, the cAMP response element binding protein (CREB). This review first addresses the aspects of estradiol action on CREB phosphorylation (pCREB) in GnRH neurons. Secondly, this review considers the receptors and signaling network that regulates estradiol's action on pCREB within GnRH neurons and finally it summarizes the physiological significance of CREB to estrogen feedback.

Modulation of the arcuate nucleus-medial preoptic nucleus lordosis regulating circuit: a role for GABAB receptors

Estradiol rapidly activates a microcircuit in the arcuate nucleus of the hypothalamus (ARH) that is needed for maximal female sexual receptivity. Membrane estrogen receptor-α complexes with and signals through the metabotropic glutamate receptor-1a stimulating NPY release within the ARH activating proopiomelanocortin (POMC) neurons. These POMC neurons project to the medial preoptic nucleus (MPN) and release β-endorphin. Estradiol treatment induces activation/internalization of MPN μ-opioid receptors (MOR) to inhibit lordosis. Estradiol membrane action modulates ARH gamma-aminobutyric acid receptor-B (GABAB) activity. We tested the hypothesis that ARH GABAB receptors mediate estradiol-induced MOR activation and facilitation of sexual receptivity. Double-label immunohistochemistry revealed expression of GABAB receptors in NPY, ERα and POMC expressing ARH neurons. Approximately 70% of POMC neurons expressed GABAB receptors. Because estradiol initially activates an inhibitory circuit and maintains activation of this circuit, the effects of blocking GABAB receptors were evaluated before estradiol benzoate (EB) treatment and after at the time of lordosis testing. Bilateral infusions of the GABAB receptor antagonist, CGP52432, into the ARH prior to EB treatment of ovariectomized rats prevented estradiol-induced activation/internalization of MPN MOR, and the rats remained unreceptive. However, in EB-treated rats, bilateral CGP52432 infusions 30 min before behavior testing attenuated MOR internalization and facilitated lordosis. These results indicated that GABAB receptors were located within the lordosis-regulating ARH microcircuit and are necessary for activation and maintenance of the estradiol inhibition of lordosis behavior. Although GABAB receptors positively influence estradiol signaling, they negatively regulate lordosis behavior since GABAB activity maintains the estradiol-induced inhibition.

N-3 poly-unsaturated fatty acids shift estrogen signaling to inhibit human breast cancer cell growth

Although evidence has shown the regulating effect of n-3 poly-unsaturated fatty acid (n-3 PUFA) on cell signaling transduction, it remains unknown whether n-3 PUFA treatment modulates estrogen signaling. The current study showed that docosahexaenoic acid (DHA, C22:6), eicosapentaenoic acid (EPA, C20:5) shifted the pro-survival and proliferative effect of estrogen to a pro-apoptotic effect in human breast cancer (BCa) MCF-7 and T47D cells. 17 β-estradiol (E2) enhanced the inhibitory effect of n-3 PUFAs on BCa cell growth. The IC50 of DHA or EPA in MCF-7 cells decreased when combined with E2 (10 nM) treatment (from 173 µM for DHA only to 113 µM for DHA+E2, and from 187 µm for EPA only to 130 µm for EPA+E2). E2 also augmented apoptosis in n-3 PUFA-treated BCa cells. In contrast, in cells treated with stearic acid (SA, C18:0) as well as cells not treated with fatty acid, E2 promoted breast cancer cell growth. Classical (nuclear) estrogen receptors may not be involved in the pro-apoptotic effects of E2 on the n-3 PUFA-treated BCa cells because ERα agonist failed to elicit, and ERα knockdown failed to block E2 pro-apoptotic effects. Subsequent studies reveal that G protein coupled estrogen receptor 1 (GPER1) may mediate the pro-apoptotic effect of estrogen. N-3 PUFA treatment initiated the pro-apoptotic signaling of estrogen by increasing GPER1-cAMP-PKA signaling response, and blunting EGFR, Erk 1/2, and AKT activity. These findings may not only provide the evidence to link n-3 PUFAs biologic effects and the pro-apoptotic signaling of estrogen in breast cancer cells, but also shed new insight into the potential application of n-3 PUFAs in BCa treatment.

Sexual hormones: effects on cardiac and mitochondrial activity after ischemia-reperfusion in adult rats. Gender difference

In this work we studied the influence of sex hormones on heart and mitochondrial functions, from adult castrated female and male, and intact rats. Castration was performed at their third week of life and on the fourth month animals were subjected to heart ischemia and reperfusion. Electrocardiogram and blood pressure recordings were made, cytokines levels were measured, histopathological studies were performed and thiobarbituric acid reactive species were determined. At the mitochondrial level respiratory control, transmembranal potential and calcium management were determined; Western blot of some mitochondrial components was also performed. Alterations in cardiac function were worst in intact males and castrated females as compared with those found in intact females and castrated males, cytokine levels were modulated also by hormonal status. Regarding mitochondria, in those obtained from hearts from castrated females without ischemia-reperfusion, all evaluated parameters were similar to those observed in mitochondria after ischemia-reperfusion. The results show hormonal influences on the heart at functional and mitochondrial levels.

Estradiol signaling in the regulation of reproduction and energy balance

Our knowledge of membrane estrogenic signaling mechanisms and their interactions that regulate physiology and behavior has grown rapidly over the past three decades. The discovery of novel membrane estrogen receptors and their signaling mechanisms has started to reveal the complex timing and interactions of these various signaling mechanisms with classical genomic steroid actions within the nervous system to regulate physiology and behavior. The activation of the various estrogenic signaling mechanisms is site specific and differs across the estrous cycle acting through both classical genomic mechanisms and rapid membrane-initiated signaling to coordinate reproductive behavior and physiology. This review focuses on our current understanding of estrogenic signaling mechanisms to promote: (1) sexual receptivity within the arcuate nucleus of the hypothalamus, (2) estrogen positive feedback that stimulates de novo neuroprogesterone synthesis to trigger the luteinizing hormone surge important for ovulation and estrous cyclicity, and (3) alterations in energy balance.

Potent vasodilation effect of amurensin G is mediated through the phosphorylation of endothelial nitric oxide synthase

Endothelial nitric oxide synthase (eNOS) has important regulatory functions in vascular tone, and impaired endothelium-dependent vasodilatation is a key event in diabetes and atherosclerosis. Vitis amurensis grapes containing resveratrol oligomers are consumed as wine and fruit and have antioxidative and neuroprotective effects. In this study, our goal was identify the most potent eNOS-activating compound among six stilbenes and oligostilbenes found in V. amurensis and to clarify its molecular mechanism. Among the six tested compounds, amurensin G most potently relaxed endothelium-intact aortic rings and increased eNOS phosphorylation and nitric oxide (NO) production. Amurensin G increased both estrogen receptor (ER) phosphorylation and ER-dependent gene transcription, and ERα or ERβ inhibition suppressed amurensin G-mediated eNOS phosphorylation. Amurensin G enhanced the activities of phosphatidylinositol 3-kinase (PI3K) and Src and their chemical inhibitors suppressed amurensin G-stimulated eNOS phosphorylation. Moreover, amurensin G activated AMP-activated protein kinase (AMPK), and amurensin G-stimulated eNOS phosphorylation and PI3K activation were reversed by AMPK inhibition. ER inhibition reversed AMPK-dependent PI3K activation in response to amurensin G. Amurensin G-mediated endothelium-dependent relaxation was blocked by inhibition of AMPK, ER, Src, or PI3K. These results suggest that amurensin G enhances NO production via eNOS phosphorylation in endothelial cells, and ER-dependent AMPK/PI3K pathways are required. Amurensin G would be applicable to prevent atherosclerosis.

Aggressive prostate cancer is prevented in ERαKO mice and stimulated in ERβKO TRAMP mice

Previous evidence suggests soy genistein may be protective against prostate cancer, but whether this protection involves an estrogen receptor (ER)-dependent mechanism is unknown. To test the hypothesis that phytoestrogens may act through ERα or ERβ to play a protective role against prostate cancer, we bred transgenic mice lacking functional ERα or ERβ with transgenic adenocarcinoma of mouse prostate (TRAMP) mice. Dietary genistein reduced the incidence of cancer in ER wild-type (WT)/transgenic adenocarcinoma of mouse prostate mice but not in ERα knockout (KO) or ERβKO mice. Cancer incidence was 70% in ERWT mice fed the control diet compared with 47% in ERWT mice fed low-dose genistein (300 mg/kg) and 32% on the high-dose genistein (750 mg/kg). Surprisingly, genistein only affected the well differentiated carcinoma (WDC) incidence but had no effect on poorly differentiated carcinoma (PDC). No dietary effects have been observed in either of the ERKO animals. We observed a very strong genotypic influence on PDC incidence, a protective effect in ERαKO (only 5% developed PDC), compared with 19% in the ERWT, and an increase in the incidence of PDC in ERβKO mice to 41%. Interestingly, immunohistochemical analysis showed ERα expression changing from nonnuclear in WDC to nuclear in PDC, with little change in ERβ location or expression. In conclusion, genistein is able to inhibit WDC in the presence of both ERs, but the effect of estrogen signaling on PDC is dominant over any dietary treatment, suggesting that improved differential targeting of ERα vs. ERβ would result in prevention of advanced prostate cancer.

Estrogen and Visceral Nociception at the Level of Primary Sensory Neurons

Clinical studies suggest the comorbidity of functional pain syndromes such as irritable bowel syndrome, painful bladder syndrome, chronic pelvic pain, and somatoform disorders approaches 40% to 60%. The incidence of episodic or persistent visceral pain associated with these “functional” disorders is two to three times higher in women than in men. One of the possible explanations for this phenomenon is estrogen modulation of viscerovisceral cross-sensitization. While a central site of this modulation has been shown previously, our studies suggest a peripheral site, the dorsal root ganglion (DRG). Estrogens have remarkably wide range of functions including modulation of voltage-gated calcium channels (VGCCs) and purinoreceptors (P2Xs). Significantly, inflammation dramatically alters purinoception by causing a several fold increase in ATP-activated current, alters the voltage dependence of P2X receptors, and enhances the expression of P2X receptors increasing neuronal hypersensitivity. Gonadal hormones are thought as indispensable cornerstones of the normal development and function, but it appears that no body region, no neuronal circuit, and virtually no cell is unaffected by them. Thus, increasing awareness toward estrogens appears to be obligatory.

Estradiol acts directly and indirectly on multiple signaling pathways to phosphorylate cAMP-response element binding protein in GnRH neurons

Rapid, nonclassical 17β-estradiol (E2) actions are thought to play an important role in the modulation of neuronal function. The present study addresses the intracellular signaling cascades involved in the rapid E2-induced phosphorylation of cAMP response element binding protein (CREB) in GnRH neurons. Administration of E2 to adult female mice resulted in the activation of ERK1/2 in GnRH neurons within 15 min. In vitro studies using pharmacological antagonists showed that ERK1/2 was essential for E2-induced CREB phosphorylation in GnRH neurons. Upstream to this, protein kinase A and calcium/calmodulin-dependent protein kinase type II, but not protein kinase C, were found to be necessary for E2-induced phosphorylation of ERK1/2. This rapid E2 signaling cascade in GnRH neurons was found to require both direct and indirect E2 actions. E2 failed to phosphorylate ERK1/2 and CREB in GnRH neuron-specific estrogen receptor β knockout mice in vivo. Equally, however, a cocktail of tetrodotoxin and γ-aminobutyric acid(A)/glutamate receptor antagonists also blocked E2-induced ERK1/2 phosphorylation in GnRH neurons in wild-type mice in vitro. Together, these observations indicate that E2 acts through calcium/calmodulin-dependent protein kinase type II and protein kinase A to rapidly phosphorylate ERK1/2, which then acts to phosphorylate CREB in adult female GnRH neurons. Intriguingly, these effects of E2 are dependent upon both direct ERβ mechanisms as well as indirect actions mediated by afferent inputs to GnRH neurons.

Src kinase-mediates androgen receptor-dependent non-genomic activation of signaling cascade leading to endothelial nitric oxide synthase

Our previous study has demonstrated that testosterone rapidly activates endothelial nitric oxide synthase (eNOS), enhancing nitric oxide (NO) release from endothelial cells (ECs) via the phosphatidylinositol 3-kinase/Akt (PI3-kinase/Akt) pathway. The upstream regulators of this pathway are unknown. In this study, we further investigated the non-genomic action of testosterone in human aortic ECs. Acute (30 min) activation of eNOS caused by testosterone was unaffected by pretreatment with a transcriptional inhibitor, actinomycin D. Non-permeable testosterone-BSA rapidly induced Akt and eNOS phosphorylation. In contrast, luciferase reporter assay showed that the transcriptional activity of the androgen-responsive element (ARE) was increased by testosterone, but not by testosterone-BSA at 2h after stimulation. Immunostaining displayed co-localization of androgen receptor (AR) with caveolin-1. Fractional analysis showed that AR was expressed in caveolae-enriched membrane fractions. Immunoprecipitation assays revealed the association of AR with caveolin-1 and c-Src, suggesting complex formation among them. Testosterone rapidly increased the phosphorylation of c-Src on Tyr416, which was inhibited by an AR antagonist and by siRNA for AR. PP2, a specific-inhibitor of Src kinase, abolished the testosterone-induced phosphorylation of Akt and eNOS. Our data indicate that testosterone induces rapid assembly of a membrane signaling complex among AR, caveolin-1 and c-Src, which then facilitates activation of the c-Src/ PI3-kinase/Akt cascade, resulting in activation of eNOS.

Rapid actions of plasma membrane estrogen receptors regulate motility of mouse embryonic stem cells through a profilin-1/cofilin-1-directed kinase signaling pathway

Long-term estrogen actions are vital for driving cell growth, but more recent evidence suggests that estrogen mediates more rapid cellular effects. However, the function of estradiol-17β (E(2))-BSA in mouse embryonic stem cells has not been reported. Therefore, we examined the role of E(2)-BSA in mouse embryonic stem cell motility and its related signal pathways. E(2)-BSA (10(-8) m) significantly increased motility after 24 h incubation and increased filamentous (F)-actin expression; these effects were inhibited by the estrogen receptor antagonist ICI 182,780, indicating that E(2)-BSA bound membrane estrogen receptors and initiated a signal. E(2)-BSA increased c-Src and focal adhesion kinase (FAK) phosphorylation, which was attenuated by ICI 182,780. The E(2)-BSA-induced increase in epidermal growth factor receptor (EGFR) phosphorylation was inhibited by Src inhibitor PP2. As a downstream signal molecule, E(2)-BSA activated cdc42 and increased formation of a complex with the neural Wiskott-Aldrich syndrome protein (N-WASP)/cdc42/transducer of cdc42-dependent actin assembly-1 (TOCA-1), which was inhibited by FAK small interfering RNA (siRNA) and EGFR inhibitor AG 1478. In addition, E(2)-BSA increased profilin-1 expression and cofilin-1 phosphorylation, which was blocked by cdc42 siRNA. Subsequently, E(2)-BSA induced an increase in F-actin expression, and cell motility was inhibited by each signal pathway-related siRNA molecule or inhibitors but not by cofilin-1 siRNA. A combined treatment of cofilin-1 siRNA and E(2)-BSA increased F-actin expression and cell motility more than that of E(2)-BSA alone. These data demonstrate that E(2)-BSA stimulated motility by interacting with profilin-1/cofilin-1 and F-actin through FAK- and c-Src/EGFR transactivation-dependent N-WASP/cdc42/TOCA-1 complex.

To modulate and be modulated: estrogenic influences on auditory processing of communication signals within a socio-neuro-endocrine framework

Gonadal hormones modulate behavioral responses to sexual stimuli, and communication signals can also modulate circulating hormone levels. In several species, these combined effects appear to underlie a two-way interaction between circulating gonadal hormones and behavioral responses to socially salient stimuli. Recent work in songbirds has shown that manipulating local estradiol levels in the auditory forebrain produces physiological changes that affect discrimination of conspecific vocalizations and can affect behavior. These studies provide new evidence that estrogens can directly alter auditory processing and indirectly alter the behavioral response to a stimulus. These studies show that: 1) Local estradiol action within an auditory area is necessary for socially relevant sounds to induce normal physiological responses in the brains of both sexes; 2) These physiological effects occur much more quickly than predicted by the classical time-frame for genomic effects; 3) Estradiol action within the auditory forebrain enables behavioral discrimination among socially relevant sounds in males; and 4) Estradiol is produced locally in the male brain during exposure to particular social interactions. The accumulating evidence suggests a socio-neuro-endocrinology framework in which estradiol is essential to auditory processing, is increased by a socially relevant stimulus, acts rapidly to shape perception of subsequent stimuli experienced during social interactions, and modulates behavioral responses to these stimuli. Brain estrogens are likely to function similarly in both songbird sexes because aromatase and estrogen receptors are present in both male and female forebrain. Estrogenic modulation of perception in songbirds and perhaps other animals could fine-tune male advertising signals and female ability to discriminate them, facilitating mate selection by modulating behaviors.

Menopause and Mental Well-Being: Timing of Symptoms and Timing of Hormone Treatment

In the aftermath of the Women's Health Initiative studies, both the clinical and basic science communities had to sort out divergent results among experimental findings, observational data and randomized controlled trials in order to establish a shared analysis. The scientific community formally debates the role of different HRT formulations, hormone doses, time of treatment initiation since the menopause and the age of treated women. Basic scientists demonstrated that the multiple neuroprotective effects of estrogen on brain cells may induce a differential biological response according to the time of treatment. Progesterone (but not all synthetic progestins) also has pivotal neuroactive functions in animal models of reproductive aging. Additionally, epidemiological surveys provide information regarding the detrimental role of hypogonadism on mental well-being. The present article briefly summarizes current evidence supporting the neuroactive role of estrogen, with reference to the clinical finding sustaining the intriguing hypothesis of the early female brain senescence as a highly responsive period to estrogen treatment.

17 β-estradiol rapidly increases ATP-sensitive potassium channel activity in gonadotropin-releasing hormone neurons [corrected] via a protein kinase signaling pathway

17Beta-estradiol (E2) both inhibits and excites GnRH neurons via presynaptic as well as postsynaptic mechanisms. Although it has been demonstrated that E2 can alter the excitability of GnRH neurons via direct actions, the intracellular signaling cascades mediating these actions are not well understood. Previously we have shown that the activity of one of the critical ion channels needed for maintaining GnRH neurons in a hyperpolarized state, the ATP-sensitive potassium channel (K(ATP)) channel, is augmented by E2 in ovariectomized females. However, the mRNA expression of the K(ATP) channel subunits Kir6.2 and SUR1 are unchanged with in vivo E2 treatment. Therefore, to elucidate the cellular signaling mechanism(s) modulating the channel activity, we did whole-cell patch-clamp recording of enhanced green fluorescent protein-GnRH neurons from ovariectomized female mice to study the acute effects of E2. E2 dose-dependently (EC(50) = 0.6 nM) enhanced the diazoxide (channel opener)-activated K(ATP) channel currents by 1.2- to 2.0-fold, which was antagonized by ICI 182,780. E2-BSA was equally as effective as E2, whereas 17 alpha-estradiol [corrected] had no effect. The protein kinase A (PKA) activator forskolin mimicked the effects of E2, whereas the PKA inhibitor H89 and the protein kinase C (PKC) inhibitor bisindolylmaleimide I blocked the effects of E2. Similar to E2, STX, a membrane estrogen receptor (ER) agonist that does not bind to ERalpha or ERbeta, also potentiated the diazoxide-induced K(ATP) channel current by 1.5-fold. Therefore, E2 can potentiate K(ATP) channel activity in GnRH neurons through a membrane ER-activated PKC-PKA signaling pathway.

A new MAP kinase protein involved in estradiol-stimulated reproduction of the helminth parasite Taenia crassiceps

MAP kinases (MAPK) are involved in the regulation of cellular processes such as reproduction and growth. In parasites, the role of MAPK has been scarcely studied. Here, we describe the participation of an ERK-like protein in estrogen-dependent reproduction of the helminth parasite Taenia crassiceps. Our results show that 17β-estradiol induces a concentration-dependent increase in the bud number of in vitro cultured cysticerci. If parasites are also incubated in presence of an ERK-inhibitor, the stimulatory effect of estrogen is blocked. The expression of ERK-like mRNA and its corresponding protein was detected in the parasite. The ERK-like protein was over-expressed by all treatments. Nevertheless, a strong induction of phosphorylation of this protein was observed only in response to 17β-estradiol. Cross-contamination by host cells was discarded by flow cytometry analysis. Parasite cells expressing the ERK-like protein were exclusively located at the subtegument tissue by confocal microscopy. Finally, the ERK-like protein was separated by bidimensional electrophoresis and then sequenced, showing the conserved TEY activation motif, typical of all known ERK 1/2 proteins. Our results show that an ERK-like protein is involved in the molecular signalling during the interaction between the host and T. crassiceps, and may be considered as target for anti-helminth drugs design.

Membrane-initiated actions of estrogen on the endothelium

Estrogen-induced rapid, membrane-initiated activation of numerous signal transduction cascades has been shown in animal, cellular and molecular vascular studies, which support the favorable effects of estrogen on vascular structure and function. These effects are mediated by distinct forms of estrogen receptor (ER) alpha. This includes estrogen-stimulated, rapid activation of endothelial nitric oxide synthase (eNOS), resulting in elaboration of the athero-protective, angiogenesis-promoting product nitric oxide (NO). An N-terminus truncated short isoform of ERalpha, ER46, plays a critical role in membrane-initiated, rapid responses to 17beta-estradiol (E2) in human endothelial cells (ECs). We have proposed a ER46-centered, eNOS-activating molecular complex in human EC caveolar membranes, containing c-Src, phosphatidylinositol 3-kinase (PI3K), Akt and eNOS. In this review, we describe estrogen-induced, rapid, non-genomic actions in the endothelium.

Estrogen rapidly attenuates cannabinoid-induced changes in energy homeostasis

We examined whether estrogen negatively modulates cannabinoid-induced regulation of food intake, core body temperature and neurotransmission at proopiomelanocortin (POMC) synapses. Food intake was evaluated in ovariectomized female guinea pigs abdominally implanted with thermal DataLoggers and treated s.c. with the cannabinoid CB(1)/CB(2) receptor agonist WIN 55,212-2, the CB(1) receptor antagonist AM251 or their cremephor/ethanol/0.9% saline vehicle, and with estradiol benzoate (EB) or its sesame oil vehicle. Whole-cell patch clamp recordings were performed in slices through the arcuate nucleus. WIN 55,212-2 produced dose- and time-dependent increases in food intake. EB decreased food intake 8-24h after administration, but rapidly and completely blocked the increase in consumption caused by WIN 55,212-2. EB also attenuated the WIN 55,212-2-induced decrease in core body temperature. The AM251-induced decrease in food intake was unaffected. The diminution of the WIN 55,212-2-induced increase in food intake caused by EB correlated with a marked attenuation of cannabinoid receptor-mediated decreases in glutamatergic miniature excitatory postsynaptic current frequency occurring within 10-15min of steroid application. Furthermore, EB completely blocked the depolarizing shift in the inactivation curve for the A-type K(+) current caused by WIN 55,212-2. The EB-mediated, physiologic antagonism of these presynaptic and postsynaptic actions elicited upon cannabinoid receptor activation was observed in arcuate neurons immunopositive for phenotypic markers of POMC neurons. These data reveal that estrogens negatively modulate cannabinoid-induced changes in appetite, body temperature and POMC neuronal activity. They also impart insight into the neuroanatomical substrates and effector systems upon which these counter-regulatory factors converge in the control of energy homeostasis.

Estrogen and cognitive functions

Although the effects of estrogen on sexual behavior in mammals are well known, its role on other types of behavior, including cognition, have only recently been recognized. This review summarizes work conducted in our laboratory and others with the aim of identifying the effects of estrogen on cognitive functions. The first section will briefly describe the neurobiology of estrogen. The second section will discuss the effects of estrogen on cognitive behaviors in mammals, as well as the physiological relevance of these effects and their applicability to human health and disease. The third section will detail the role of estrogen on working memory in humans and nonhuman primates, and in rodents. Finally, the concluding section will briefly describe the relationship between estrogen and the aging brain.

Low doses of bisphenol A promote human seminoma cell proliferation by activating PKA and PKG via a membrane G-protein-coupled estrogen receptor

BACKGROUND

Fetal exposure to environmental estrogens may contribute to hypofertility and/or to testicular germ cell cancer. However, many of these xenoestrogens have only a weak affinity for the classical estrogen receptors (ERs,) which is 1,000-fold less potent than the affinity of 17beta-estradiol (E(2)). Thus, several mechanisms have been suggested to explain how they could affect male germ cell proliferation at low environmental relevant concentrations.

OBJECTIVES

In this study we aimed to explore the possible promoting effect of bisphenol A (BPA) on human testicular seminoma cells. BPA is a well-recognized estrogenic endocrine disruptor used as a monomer to manufacture poly carbonate plastic and released from resin-lined food or beverage cans or from dental sealants.

METHODS AND RESULTS

BPA at very low concentrations (10(-9) to 10(-12) M) similar to those found in human fluids stimulated JKT-1 cell proliferation in vitro. BPA activated both cAMP-dependent protein kinase and cGMP-dependent protein kinase pathways and triggered a rapid (15 min) phosphorylation of the transcription factor cAMP response-element-binding protein (CREB) and the cell cycle regulator retinoblastoma protein (Rb). This nongenomic activation did not involve classical ERs because it could not be reversed by ICI 182780 (an ER antagonist) or reproduced either by E(2) or by diethylstilbestrol (a potent synthetic estrogen), which instead triggered a suppressive effect. This activation was reproduced only by E(2) coupled to bovine serum albumin (BSA), which is unable to enter the cell. As with E(2)-BSA, BPA promoted JKT-1 cell proliferation through a G-protein-coupled nonclassical membrane ER (GPCR) involving a Galpha(s) and a Galpha(i)/Galpha(q) subunit, as shown by the reversible effect observed by the corresponding inhibitors NF449 and pertussis toxin.

CONCLUSION

This GPCR-mediated nongenomic action represents--in addition to the classical ER-mediated effect--a new basis for evaluating xenoestrogens such as BPA that, at low doses and with a high affinity for this GPCR, could interfere with the developmental programming of fetal germ cell proliferation and/or differentiation when they cross the placenta.

Role of protein phosphatases and mitochondria in the neuroprotective effects of estrogens

In the present treatise, we provide evidence that the neuroprotective and mito-protective effects of estrogens are inexorably linked and involve the ability of estrogens to maintain mitochondrial function during neurotoxic stress. This is achieved by the induction of nuclear and mitochondrial gene expression, the maintenance of protein phosphatases levels in a manner that likely involves modulation of the phosphorylation state of signaling kinases and mitochondrial pro- and anti-apoptotic proteins, and the potent redox/antioxidant activity of estrogens. These estrogen actions are mediated through a combination of estrogens receptor (ER)-mediated effects on nuclear and mitochondrial transcription of protein vital to mitochondrial function, ER-mediated, non-genomic signaling and non-ER-mediated effects of estrogens on signaling and oxidative stress. Collectively, these multifaceted, coordinated action of estrogens leads to their potency in protecting neurons from a wide variety of acute insults as well as chronic neurodegenerative processes.

Ovarian-steroid modulation of locus coeruleus activity in female rats: involvement in luteinising hormone regulation

The noradrenergic nucleus locus coeruleus (LC) has been reported to regulate luteinising hormone (LH) secretion in female rats. Both oestrogen and progestin receptors have been demonstrated in LC neurones, suggesting that these cells are possibly responsive to variations in circulating levels of ovarian steroids. We therefore evaluated changes in the activity of LC neurones during the oestrous cycle and after ovarian-steroid treatment in ovariectomised (OVX) rats, as determined by immunoreactivity to Fos-related antigens (FRA), which comprises all of the known members of the Fos family. Effects of ovarian steroids on the firing rate of LC neurones were also determined in a slice preparation. The number of FRA/tyrosine hydroxylase (TH)-immunoreactive (ir) neurones in the LC increased from 14.00-16.00 h on pro-oestrus, coinciding with the onset of the LH surge and rise in plasma progesterone. FRA immunoreactivity was unaltered during dioestrus. Oestradiol-treated OVX rats (OVX+E) displayed marked reduction in FRA/TH-ir neurones in LC compared to oil-treated OVX rats. Accordingly, oestradiol superfusion significantly reduced the spontaneous firing rate of LC neurones in slices from OVX rats. Compared to OVX+E, oestradiol-treated rats injected with progesterone at 08.00 h (OVX+EP) exhibited higher number of FRA/TH-ir neurones in the LC at 10.00 h and 16.00 h, and great amplification of the LH surge. Bath application of progesterone significantly increased the spontaneous firing rate of OVX+E LC neurones. Our data suggest that ovarian steroids may physiologically modulate the activity of LC neurones in females, with possible implications for LH secretion. Moreover, oestradiol and progesterone appear to exert opposite and complementary effects (i.e. whereas oestradiol inhibits, progesterone, after oestradiol priming, stimulates LC activity).

Predator avoidance performance of larval fathead minnows (Pimephales promelas) following short-term exposure to estrogen mixtures

Aquatic organisms exposed to endocrine disrupting compounds (EDCs) at early life-stages may have reduced reproductive fitness via disruption of reproductive and non-reproductive behavioral and physiological pathways. Survival to reproductive age relies upon optimal non-reproductive trait expression, such as adequate predator avoidance responses, which may be impacted through EDC exposure. During a predator-prey confrontation, larval fish use an innate C-start escape behavior to rapidly move away from an approaching threat. We tested the hypotheses that (1) larval fathead minnows exposed to estrogens, a primary class of EDCs, singularly or in mixture, suffer a reduced ability to perform an innate C-start behavior when faced with a threat stimulus; (2) additive effects will cause greater reductions in C-start behavior; and (3) effects will differ among developmental stages. In this study, embryos (post-fertilization until hatching) were exposed for 5 days to environmentally relevant concentrations of estrone (E1), 17beta-estradiol (E2), and 17alpha-ethinylestradiol (EE2) singularly and in mixture. Exposed embryos were allowed to hatch and grow in control well water until 12 days old. Similarly, post-hatch fathead minnows were exposed for 12 days to these compounds. High-speed (1000frames/s) video recordings of escape behavior were collected and transferred to National Institutes of Health Image for frame-by-frame analysis of latency period, escape velocity, and total escape response (combination of latency period and escape velocity). When tested 12 days post-hatch, only E1 adversely affected C-start performance of larvae exposed as embryos. Conversely, larvae exposed for 12 days post-hatch did not exhibit altered escape responses when exposed to E1, while adverse responses were seen in E2 and the estrogen mixture. Ethinylestradiol exposure did not elicit changes in escape behaviors at either developmental stage. The direct impact of reduced C-start performance on survival, and ultimately, reproductive fitness provides an avenue to assess the ecological relevance of exposure in an assay of relatively short duration.

Medial preoptic area interactions with dopamine neural systems in the control of the onset and maintenance of maternal behavior in rats

The medial preoptic area (MPOA) and dopamine (DA) neural systems interact to regulate maternal behavior in rats. Two DA systems are involved: the mesolimbic DA system and the incerto-hypothalamic DA system. The hormonally primed MPOA regulates the appetitive aspects of maternal behavior by activating mesolimbic DA input to the shell region of the nucleus accumbens (NAs). DA action on MPOA via the incerto-hypothalamic system may interact with steroid and peptide hormone effects so that MPOA output to the mesolimbic DA system is facilitated. Neural oxytocin facilitates the onset of maternal behavior by actions at critical nodes in this circuitry. DA-D1 receptor agonist action on either the MPOA or NAs can substitute for the effects of estradiol in stimulating the onset of maternal behavior, suggesting an overlap in underlying cellular mechanisms between estradiol and DA. Maternal memory involves the neural plasticity effects of mesolimbic DA activity. Finally, early life stressors may affect the development of MPOA-DA interactions and maternal behavior.

Reproductive aging, sex steroids, and mood disorders

Epidemiologic studies have documented that the majority of women do not become depressed during the menopause transition. However, recent longitudinal studies suggest that in some women, the events related to the menopause transition could play a role in the onset of depression. In this article we review evidence suggesting a relationship between the menopause transition and depression. Additionally, we describe several findings that suggest a role of ovarian hormones in the onset of these depressions, including the clustering of episodes of depression during the stage of the menopause transition that is accompanied by estradiol withdrawal, and the therapeutic effects of short-term estradiol in depressed perimenopausal women. Finally, we discuss possible causes of affective disturbances during the menopause transition.

Mechanism of okadaic acid-induced neuronal death and the effect of estrogens

Serine/threonine protein phosphatases are important mediators of general cellular function as well as neurodegenerative processes. We have previously shown inhibition of protein phosphatases to be as neurotoxic as glutamate-induced neuronal death but resistant to neuroprotection by estrogens. In this study, the mechanism by which phosphatase inhibition via okadaic acid (OA) induced neurotoxicity is explored. Neurons were exposed to OA or glutamate in the presence or absence of various protein kinases inhibitors, and/or one of four estrogens. Both OA and glutamate induced cell death via increased reactive oxygen species, protein carbonylation, lipid peroxidation, caspase-3 activity, and mitochondrial dysfunction. All estrogens attenuated glutamate-mediated responses, but not OA-induced responses. In addition, inhibition of protein kinase C and mitogen-activated protein kinase pathway was neuroprotective against glutamate but not OA toxicity. Interestingly, inhibition of mitogen-activated protein kinase pathway with PD98096 or U0126 caused a decrease in reactive oxygen species production suggesting that activation of ERK1/2 could further exacerbate the oxidative stress caused by glutamate-induced toxicity; however, these inhibitors had no effect on OA-induced toxicity. Collectively, these results indicate that both glutamate and OA neurotoxicities are mediated by persistent activation of ERK1/2 and/or protein kinase C and a resulting oxidative stress, and that protein phosphatase activity is an important and necessary aspect of estrogen-mediated neuroprotection.

Vascular cell signaling by membrane estrogen receptors

The definition of estrogen's actions has expanded from transcriptional regulation to the rapid, membrane-initiated activation of numerous signal transduction cascades. Multiple biological effects of estrogen have been shown in numerous animals, cellular and molecular studies, which support the favorable effects of estrogen on vascular structure, function, and cell signaling. Work from several laboratories has shown that these effects are mediated by distinct forms of estrogen receptor (ER) alpha. This includes estrogen-stimulated rapid activation of endothelial nitric oxide synthase (eNOS), resulting in the elaboration of the athero-protective, angiogenesis-promoting product nitric oxide (NO). We have described the expression of ER46, an N-terminus truncated isoform of the ERalpha, in human endothelial cells (EC), and its critical role in membrane-initiated, rapid responses to 17beta-estradiol (E2). We have proposed an ER46-centered, eNOS activating molecular complex in human EC caveolar membranes, containing c-Src, phosphatidylinositol 3-kinase (PI3K), Akt and eNOS. Our previous studies support estrogen-induced rapid eNOS activation via a sequential c-Src/PI3K/Akt cascade in EC. In this review, we describe estrogen-induced, rapid, non-genomic actions in endothelium, driven by c-Src-ER46-caveolin-1 interactions, with consequent activation of eNOS. Amidst ongoing controversies in hormone replacement therapy, these molecular and cellular data, defining favorable estrogenic effects on the endothelium, provide a strong impetus to resolve these clinical questions.