Membrane-initiated actions of estradiol that regulate reproduction, energy balance and body temperature

Peering into the Brain's Estrogen Receptors: PET Tracers for Visualization of Nuclear and Extranuclear Estrogen Receptors in Brain Disorders

Estrogen receptors (ERs) play a multitude of roles in brain function and are implicated in various brain disorders. The use of positron emission tomography (PET) tracers for the visualization of ERs' intricate landscape has shown promise in oncology but remains limited in the context of brain disorders. Despite recent progress in the identification and development of more selective ligands for various ERs subtypes, further optimization is necessary to enable the reliable and efficient imaging of these receptors. In this perspective, we briefly touch upon the significance of estrogen signaling in the brain and raise the setbacks associated with the development of PET tracers for identification of specific ERs subtypes in the brain. We then propose avenues for developing efficient PET tracers to non-invasively study the dynamics of ERs in the brain, as well as neuropsychiatric diseases associated with their malfunction in a longitudinal manner. This perspective puts several potential candidates on the table and highlights the unmet needs and areas requiring further research to unlock the full potential of PET tracers for ERs imaging, ultimately aiding in deepening our understanding of ERs and forging new avenues for potential therapeutic strategies.

Polycystic Ovary Syndrome and the Neuroendocrine Consequences of Androgen Excess

Polycystic ovary syndrome (PCOS) is a major endocrine disorder strongly associated with androgen excess and frequently leading to female infertility. Although classically considered an ovarian disease, altered neuroendocrine control of gonadotropin-releasing hormone (GnRH) neurons in the brain and abnormal gonadotropin secretion may underpin PCOS presentation. Defective regulation of GnRH pulse generation in PCOS promotes high luteinizing hormone (LH) pulsatile secretion, which in turn overstimulates ovarian androgen production. Early and emerging evidence from preclinical models suggests that maternal androgen excess programs abnormalities in developing neuroendocrine circuits that are associated with PCOS pathology, and that these abnormalities are sustained by postpubertal elevation of endogenous androgen levels. This article will discuss experimental evidence, from the clinic and in preclinical animal models, that has significantly contributed to our understanding of how androgen excess influences the assembly and maintenance of neuroendocrine impairments in the female brain. Abnormal central gamma-aminobutyric acid (GABA) signaling has been identified in both patients and preclinical models as a possible link between androgen excess and elevated GnRH/LH secretion. Enhanced GABAergic innervation and drive to GnRH neurons is suspected to contribute to the pathogenesis and early manifestation of neuroendocrine derangement in PCOS. Accordingly, this article also provides an overview of GABA regulation of GnRH neuron function from prenatal development to adulthood to discuss possible avenues for future discovery research and therapeutic interventions. © 2022 American Physiological Society. Compr Physiol 12:3347-3369, 2022.

Deletion of Stim1 in Hypothalamic Arcuate Nucleus Kiss1 Neurons Potentiates Synchronous GCaMP Activity and Protects against Diet-Induced Obesity

Kisspeptin (Kiss1) neurons are essential for reproduction, but their role in the control of energy balance and other homeostatic functions remains unclear. High-frequency firing of hypothalamic arcuate Kiss1 (Kiss1^ARH) neurons releases kisspeptin into the median eminence, and neurokinin B (NKB) and dynorphin onto neighboring Kiss1^ARH neurons to generate a slow EPSP mediated by TRPC5 channels that entrains intermittent, synchronous firing of Kiss1^ARH neurons. High-frequency optogenetic stimulation of Kiss1^ARH neurons also releases glutamate to excite the anorexigenic proopiomelanocortin (POMC) neurons and inhibit the orexigenic neuropeptide Y/agouti-related peptide (AgRP) neurons via metabotropic glutamate receptors. At the molecular level, the endoplasmic reticulum (ER) calcium-sensing protein stromal interaction molecule 1 (STIM1) is critically involved in the regulation of neuronal Ca²⁺ signaling and neuronal excitability through its interaction with plasma membrane (PM) calcium (e.g., TRPC) channels. Therefore, we hypothesized that deletion of Stim1 in Kiss1^ARH neurons would increase neuronal excitability and their synchronous firing, which ultimately would affect energy homeostasis. Using optogenetics in combination with whole-cell recording and GCaMP6 imaging in slices, we discovered that deletion of Stim1 in Kiss1 neurons significantly increased the amplitude and duration of the slow EPSP and augmented synchronous [Ca²⁺]i oscillations in Kiss1^ARH neurons. Deletion of Stim1 in Kiss1^ARH neurons amplified the actions of NKB and protected ovariectomized female mice from developing obesity and glucose intolerance with high-fat dieting (HFD). Therefore, STIM1 appears to play a critical role in regulating synchronous firing of Kiss1^ARH neurons, which ultimately affects the coordination between energy homeostasis and reproduction.SIGNIFICANCE STATEMENT Hypothalamic arcuate kisspeptin (Kiss1^ARH) neurons are essential for stimulating the pulsatile release of gonadotropin-releasing hormone (GnRH) and maintaining fertility. However, Kiss1^ARH neurons appear to be a key player in coordinating energy balance with reproduction. The regulation of calcium channels and hence calcium signaling is critically dependent on the endoplasmic reticulum (ER) calcium-sensing protein stromal interaction molecule 1 (STIM1), which interacts with the plasma membrane (PM) calcium channels. We have conditionally deleted Stim1 in Kiss1^ARH neurons and found that it significantly increased the excitability of Kiss1^ARH neurons and protected ovariectomized female mice from developing obesity and glucose intolerance with high-fat dieting (HFD).

Sleep and Methylation of Estrogen Receptor Genes, ESR1 and GPER, in Healthy Middle-Aged and Older Women: Findings from the Women 40+ Healthy Aging Study

PURPOSE

Sleep problems in middle-aged and older women are very common and have been associated with menopause-related changes in estrogen levels. However, not all women experience sleep problems as they enter perimenopause, and epigenetic mechanisms might contribute to the differences in sleep quality within this population. In this study, we hypothesized that increased methylation of two estrogen receptor (ER) genes (ESR1 and GPER) would be associated with increased sleep problems in healthy pre-, peri-, and postmenopausal women, either directly or indirectly through the experience of vasomotor symptoms (VMS).

MATERIALS AND METHODS

In 130 healthy women aged 40-73 years, we assessed DNA methylation from dried blood spots (DBS). Women rated their sleep quality using the Pittsburgh Sleep Quality Index (PSQI), and VMS using the Menopause Rating Scale (MRS).

RESULTS

Higher percentage methylation of ESR1 was associated with increased sleep problems, mediated by VMS, even after controlling for age, menopausal status, body mass index, estradiol levels, depressive symptoms, and caffeine consumption. There was no significant association between GPER methylation and either sleep problems or VMS.

CONCLUSION

The study findings support an association between increased ESR1 methylation and sleep problems through increased VMS among healthy women aged 40-73 years.

A plurality of molecular targets: The receptor ecosystem for bisphenol-A (BPA)

Bisphenol-A (BPA) is a well-known endocrine disrupting compound (EDC), capable of affecting the normal function and development of the reproductive system, brain, adipose tissue, and more. In spite of these diverse and well characterized effects, there is often comparatively little known about the molecular mechanisms which bring them about. BPA has traditionally been regarded as a primarily estrogenic EDC, and this perspective is often what guides research into the effects of BPA. However, emerging data from in-vitro and in-silico models show that BPA binds with a significant number of hormone receptors, including a number of nuclear and membrane-bound estrogen receptors, androgen receptors, as well as the thyroid hormone receptor, glucocorticoid receptor, and PPARγ. With this increased diversity of receptor targets, it may be possible to explain some of the more puzzling aspects of BPA pharmacology, including its non-monotonic dose-response curve, as well as experimental results which disagree with estrogenic positive controls. This paper reviews the receptors for which BPA has a known interaction, and discusses the implications of taking these receptors into account when studying the disruptive effects of BPA on growth and development.

Local Estrogen Synthesis Regulates Parallel Fiber-Purkinje Cell Neurotransmission Within the Cerebellar Cortex

Estrogens affect cerebellar activity and cerebellum-based behaviors. Within the adult rodent cerebellum, the best-characterized action of estradiol is to enhance glutamatergic signaling. However, the mechanisms by which estradiol promotes glutamatergic neurotransmission remain unknown. Within the mouse cerebellum, we found that estrogen receptor activation of metabotropic glutamate receptor type 1a strongly enhances neurotransmission at the parallel fiber-Purkinje cell synapse. The blockade of local estrogen synthesis within the cerebellum results in a diminution of glutamatergic neurotransmission. Correspondingly, decreased estrogen availability via gonadectomy or blockade of aromatase activity negatively affects locomotor performance. These data indicate that locally derived, and not just gonad-derived, estrogens affect cerebellar physiology and function. In addition, estrogens were found to facilitate parallel fiber-Purkinje cell synaptic transmission in both sexes. As such, the actions of estradiol to support cerebellar neurotransmission and cerebellum-based behaviors might be fundamental to understanding the normal processing of activity within the cerebellar cortex.

The Arcuate Estrogen-Regulated Transcriptome: Estrogen Response Element-Dependent and -Independent Signaling of ERα in Female Mice

To influence energy homeostasis and reproduction, 17β-estradiol (E2) controls the arcuate nucleus (ARC) through multiple receptor-mediated mechanisms, but primarily via estrogen receptor (ER) α, which signals through both estrogen response element (ERE)-dependent and -independent mechanisms. To determine ERα-mediated, ERE-dependent, and ERE-independent E2 signaling in the ARC, we examined the differential regulation of the mouse arcuate transcriptome by E2 using three mice genotypes: (1) wild-type, (2) ERα knock-in/knockout (ERE-independent mechanisms), and (3) total ERα knockout (ERα-independent mechanisms). Females were ovariectomized and injected with oil or E2, and RNA sequencing on the ARC was used to identify E2-regulated genes in each genotype. Our results show that E2 regulates numerous genes involved in cell signaling, cytoskeleton structure, inflammation, neurotransmission, neuropeptide production, and transcription. Furthermore, ERE-independent signaling regulates ARC genes expressed in kisspeptin neurons and transcription factors that control the hypothalamic/pituitary/gonadal axis. Interestingly, a few genes involved in mitochondrial oxidative respiration were regulated by E2 through ERα-independent signaling. A comparison within oil- and E2-treated females across the three genotypes suggests that genes involved in cell growth and proliferation, extracellular matrices, neuropeptides, receptors, and transcription are differentially expressed across the genotypes. Comparing with previously published chromatin immunoprecipitation sequencing analysis, we found that ERE-independent regulation in the ARC is mainly mediated by tethering of ERα, which is consistent with previous findings. We conclude that the mouse arcuate estrogen-regulated transcriptome is regulated by multiple receptor-mediated mechanisms to modulate the central control of energy homeostasis and reproduction, including novel E2-responsive pathways.

Gq Protein-Coupled Membrane-Initiated Estrogen Signaling Rapidly Excites Corticotropin-Releasing Hormone Neurons in the Hypothalamic Paraventricular Nucleus in Female Mice

CRH neurons in the hypothalamic paraventricular nucleus (PVN) play a central role in regulating the hypothalamus-pituitary-adrenal (HPA) axis and are directly influenced by 17β-estradiol (E2). Although compelling evidence has suggested the existence of membrane-associated estrogen receptors (mERs) in hypothalamic and other central nervous system neurons, it remains unknown whether E2 impacts CRH neuronal excitability through this mechanism. The purpose of the current study is to examine the existence and function of mER signaling in PVN CRH neurons. Whole-cell recordings were made from CRH neurons identified by Alexa Fluor 594 labeling and post hoc immunostaining in ovariectomized female mice. E2 (100nM) rapidly suppressed the M-current (a voltage-dependent K(+) current) and potentiated glutamatergic excitatory postsynaptic currents. The putative Gq-coupled mER (Gq-mER) characterized in hypothalamic proopiomelanocortin neurons initiates a phospholipase C-protein kinase C-protein kinase A pathway; therefore, we examined the involvement of this pathway using selective inhibitors. Indeed, the ER antagonist ICI 182780 and inhibitors of Gq-phospholipase C-protein kinase C-protein kinase A blocked E2's actions, suggesting dependence on the Gq-mER. Furthermore, STX, a selective ligand for the Gq-mER, mimicked E2's actions. Finally, to examine the in vivo effect of Gq-mER activation, E2 or STX injection increased c-fos expression in CRH neurons in the PVN, suggesting CRH neuronal activation. This corresponded to an increase in plasma corticosterone. We conclude that the Gq-mER plays a critical role in the rapid regulation of CRH neuronal activity and the HPA axis. Our findings provide a potential underlying mechanism for E2's involvement in the pathophysiology of HPA-associated mood disorders.

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.

Estrogen Receptor Beta and 2-arachidonoylglycerol Mediate the Suppressive Effects of Estradiol on Frequency of Postsynaptic Currents in Gonadotropin-Releasing Hormone Neurons of Metestrous Mice: An Acute Slice Electrophysiological Study

Gonadotropin-releasing hormone (GnRH) neurons are controlled by 17β-estradiol (E2) contributing to the steroid feedback regulation of the reproductive axis. In rodents, E2 exerts a negative feedback effect upon GnRH neurons throughout the estrus-diestrus phase of the ovarian cycle. The present study was undertaken to reveal the role of estrogen receptor subtypes in the mediation of the E2 signal and elucidate the downstream molecular machinery of suppression. The effect of E2 administration at low physiological concentration (10 pM) on GnRH neurons in acute brain slices obtained from metestrous GnRH-green fluorescent protein (GFP) mice was studied under paradigms of blocking or activating estrogen receptor subtypes and interfering with retrograde 2-arachidonoylglycerol (2-AG) signaling. Whole-cell patch clamp recordings revealed that E2 significantly diminished the frequency of spontaneous postsynaptic currents (sPSCs) in GnRH neurons (49.62 ± 7.6%) which effect was abolished by application of the estrogen receptor (ER) α/β blocker Faslodex (1 μM). Pretreatment of the brain slices with cannabinoid receptor type 1 (CB1) inverse agonist AM251 (1 μM) and intracellularly applied endocannabinoid synthesis blocker THL (10 μM) significantly attenuated the effect of E2 on the sPSCs. E2 remained effective in the presence of tetrodotoxin (TTX) indicating a direct action of E2 on GnRH cells. The ERβ specific agonist DPN (10 pM) also significantly decreased the frequency of miniature postsynaptic currents (mPSCs) in GnRH neurons. In addition, the suppressive effect of E2 was completely blocked by the selective ERβ antagonist PHTPP (1 μM) indicating that ERβ is required for the observed rapid effect of the E2. In contrast, the ERα agonist PPT (10 pM) or the membrane-associated G protein-coupled estrogen receptor (GPR30) agonist G1 (10 pM) had no significant effect on the frequency of mPSCs in these neurons. AM251 and tetrahydrolipstatin (THL) significantly abolished the effect of E2 whereas AM251 eliminated the action of DPN on the mPSCs. These data suggest the involvement of the retrograde endocannabinoid mechanism in the rapid direct effect of E2. These results collectively indicate that estrogen receptor beta and 2-AG/CB1 signaling mechanisms are coupled and play an important role in the mediation of the negative estradiol feedback on GnRH neurons in acute slice preparation obtained from intact, metestrous mice.

The dual action of estrogen hypothesis

Estradiol (E2) can act in the brain in a relatively fast manner (i.e., seconds to minutes) usually through signaling initiated at the cell membrane. Brain-derived E2 has thus been considered as another type of neurotransmitter. Recent work found that behaviors indicative of male sexual motivation are activated by estrogenic metabolites of testosterone (T) in a fast manner, while sexual performance (copulatory behavior per se) is regulated by brain E2 in a slower manner via nucleus-initiated actions. This functional division between these two types of action appears to generalize to other behavioral systems regulated by E2. We propose the dual action of estrogen hypothesis to explain this functional distinction between these two different modes of action.

Prolonged infusion of estradiol benzoate into the stalk median eminence stimulates release of GnRH and kisspeptin in ovariectomized female rhesus macaques

Our recent study indicates that a brief infusion (20 min) of estradiol (E2) benzoate (EB) into the stalk-median eminence (S-ME) stimulates GnRH release with a latency of approximately 10 minutes. In contrast to the effect induced by a brief infusion of EB, it has previously been shown that systemic EB administration suppresses release of GnRH, kisspeptin, and LH with a latency of several hours, which is known as the negative feedback action of E2. We speculated that the differential results by these 2 modes of EB administration are due to the length of E2 exposure. Therefore, in the present study, the effects of EB infusion for periods of 20 minutes, 4 hours, or 7 hours into the S-ME of ovariectomized female monkeys on the release of GnRH and kisspeptin were examined using a microdialysis method. To assess the effects of the EB infusion on LH release, serum samples were also collected. The results show that similar to the results with 20-minute infusion, both 4- and 7-hour infusions of EB consistently stimulated release of GnRH and kisspeptin from the S-ME accompanied by LH release in the general circulation. In contrast, sc injection of EB suppressed all 3 hormones (GnRH, kisspeptin, and LH) measured. It is concluded that regardless of the exposure period, direct E2 action on GnRH and kisspeptin neurons in the S-ME, where their neuroterminals are present, is stimulatory, and the E2-negative feedback effects do not occur at the S-ME level.

Membrane-initiated non-genomic signaling by estrogens in the hypothalamus: cross-talk with glucocorticoids with implications for behavior

The estrogen receptor and glucocorticoid receptor are members of the nuclear receptor superfamily that can signal using both non-genomic and genomic transcriptional modes. Though genomic modes of signaling have been well characterized and several behaviors attributed to this signaling mechanism, the physiological significance of non-genomic modes of signaling has not been well understood. This has partly been due to the controversy regarding the identity of the membrane ER (mER) or membrane GR (mGR) that may mediate rapid, non-genomic signaling and the downstream signaling cascades that may result as a consequence of steroid ligands binding the mER or the mGR. Both estrogens and glucocorticoids exert a number of actions on the hypothalamus, including feedback. This review focuses on the various candidates for the mER or mGR in the hypothalamus and the contribution of non-genomic signaling to classical hypothalamically driven behaviors and changes in neuronal morphology. It also attempts to categorize some of the possible functions of non-genomic signaling at both the cellular level and at the organismal level that are relevant for behavior, including some behaviors that are regulated by both estrogens and glucocorticoids in a potentially synergistic manner. Lastly, it attempts to show that steroid signaling via non-genomic modes may provide the organism with rapid behavioral responses to stimuli.

Regulation of local steroidogenesis in the brain and in prostate cancer: lessons learned from interdisciplinary collaboration

Sex steroids play critical roles in the regulation of the brain and many other organs. Traditionally, researchers have focused on sex steroid signaling that involves travel from the gonads via the circulation to intracellular receptors in target tissues. This classic concept has been challenged, however, by the growing number of cases in which steroids are synthesized locally and act locally within diverse tissues. For example, the brain and prostate carcinoma were previously considered targets of gonadal sex steroids, but under certain circumstances, these tissues can upregulate their steroidogenic potential, particularly when circulating sex steroid concentrations are low. We review some of the similarities and differences between local sex steroid synthesis in the brain and prostate cancer. We also share five lessons that we have learned during the course of our interdisciplinary collaboration, which brought together neuroendocrinologists and cancer biologists. These lessons have important implications for future research in both fields.

Research resource: Gene profiling of G protein-coupled receptors in the arcuate nucleus of the female

The hypothalamic arcuate nucleus controls many critical homeostatic functions including energy homeostasis, reproduction, and motivated behavior. Although G protein-coupled receptors (GPCRs) are involved in the regulation of these functions, relatively few of the GPCRs have been identified specifically within the arcuate nucleus. Here, using TaqMan low-density arrays we quantified the mRNA expression of nonolfactory GPCRs in mouse arcuate nucleus. An unprecedented number of GPCRs (total of 292) were found to be expressed, of which 183 were known and 109 were orphan GPCRs. The known GPCR genes expressed were classified into several functional clusters including hormone/neurotransmitter, growth factor, angiogenesis and vasoactivity, inflammation and immune system, and lipid messenger receptors. The plethora of orphan genes expressed in the arcuate nucleus were classified into 5 structure-related classes including class A (rhodopsin-like), class B (adhesion), class C (other GPCRs), nonsignaling 7-transmembrane chemokine-binding proteins, and other 7-transmembrane proteins. Therefore, for the first time, we provide a quantitative estimate of the numerous GPCRs expressed in the hypothalamic arcuate nucleus. Finally, as proof of principle, we documented the expression and function of one of these receptor genes, the glucagon-like peptide 1 receptor (Glp1r), which was highly expressed in the arcuate nucleus. Single-cell RT-PCR revealed that Glp1r mRNA was localized in proopiomelanocortin neurons, and using whole-cell recording we found that the glucagon-like peptide 1-selective agonist exendin-4 robustly excited proopiomelanocortin neurons. Thus, the quantitative GPCR data emphasize the complexity of the hypothalamic arcuate nucleus and furthermore provide a valuable resource for future neuroendocrine/endocrine-related experiments.

Gonadal steroid hormones and the hypothalamo-pituitary-adrenal axis

The hypothalamo-pituitary-adrenal (HPA) axis represents a complex neuroendocrine feedback loop controlling the secretion of adrenal glucocorticoid hormones. Central to its function is the paraventricular nucleus of the hypothalamus (PVN) where neurons expressing corticotropin releasing factor reside. These HPA motor neurons are a primary site of integration leading to graded endocrine responses to physical and psychological stressors. An important regulatory factor that must be considered, prior to generating an appropriate response is the animal's reproductive status. Thus, PVN neurons express androgen and estrogen receptors and receive input from sites that also express these receptors. Consequently, changes in reproduction and gonadal steroid levels modulate the stress response and this underlies sex differences in HPA axis function. This review examines the make up of the HPA axis and hypothalamo-pituitary-gonadal (HPG) axis and the interactions between the two that should be considered when exploring normal and pathological responses to environmental stressors.

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.

Molecular mechanisms underlying the rapid arrhythmogenic action of bisphenol A in female rat hearts

Previously we showed that bisphenol A (BPA), an environmental estrogenic endocrine disruptor, rapidly altered Ca(2+) handling and promoted arrhythmias in female rat hearts. The underlying molecular mechanism was not known. Here we examined the cardiac-specific signaling mechanism mediating the rapid impact of low-dose BPA in female rat ventricular myocytes. We showed that protein kinase A (PKA) and Ca(2+)/CaM-dependent protein kinase II (CAMKII) signaling pathways are the two major pathways activated by BPA. Exposure to 1 nM BPA rapidly increased production of cAMP and rapidly but transiently increased the phosphorylation of the ryanodine receptors by PKA but not by CAMKII. BPA also rapidly increased the phosphorylation of phospholamban (PLN), a key regulator protein of sarcoplasmic reticulum Ca(2+) reuptake, by CAMKII but not PKA. The increase in CAMKII phosphorylation of PLN was mediated by phospholipase C and inositol trisphosphate receptor-mediated Ca(2+) release, likely from the endoplasmic reticulum Ca(2+) storage. These two pathways are likely localized, impacting only their respective target proteins. The rapid impacts of BPA on ryanodine receptors and PLN phosphorylation were mediated by estrogen receptor-β but not estrogen receptor-α. BPA's rapid signaling in cardiac myocytes did not involve activation of ERK1/2. Functional analysis showed that PKA but not CAMKII activation contributed to BPA-induced sarcoplasmic reticulum Ca(2+) leak, and both PKA and CAMKII were necessary contributors to the stimulatory effect of BPA on arrhythmogenesis. These results provide mechanistic insight into BPA's rapid proarrhythmic actions in female cardiac myocytes and contribute to the assessment of the consequence and potential cardiac toxicity of BPA exposure.

Rapid control of reproductive behaviour by locally synthesised oestrogens: focus on aromatase

Oestrogens activate nucleus- and membrane-initiated signalling. Nucleus-initiated events control a wide array of physiological and behavioural responses. These effects generally take place within relatively long periods of time (several hours to days). By contrast, membrane-initiated signalling affects a multitude of cellular functions in a much shorter timeframe (seconds to minutes). However, much less is known about their functional significance. Furthermore, the origin of the oestrogens able to trigger these acute effects is rarely examined. Finally, these two distinct types of oestrogenic actions have often been studied independently such that we do not exactly know how they cooperate to control the same response. The present review presents a synthesis of recent work carried out in our laboratory that aimed to address these issues in the context of the study of male sexual behaviour in Japanese quail, which is a considered as a suitable species for tackling these issues. The first section presents data indicating that 17β-oestradiol, or its membrane impermeable analogues, acutely enhances measures of male sexual motivation but does not affect copulatory behaviour. These effects depend on the activation of membrane-initiated events and local oestrogen production. The second part of this review discusses the regulation of brain oestrogen synthesis through post-translational modifications of the enzyme aromatase. Initially discovered in vitro, these rapid and reversible enzymatic modulations occur in vivo following variations in the social and environment context and therefore provide a mechanism of acute regulation of local oestrogen provision with a spatial and time resolution compatible with the rapid effects observed on male sexual behaviour. Finally, we discuss how these distinct modes of oestrogenic action (membrane- versus nucleus-initiated) acting in different time frames (short- versus long-term) interact to control different components (motivation versus performance) of the same behavioural response and improve reproductive fitness.

Nuclear receptor coactivators: regulators of steroid action in brain and behaviour

Steroid hormones act in specific regions of the brain to alter behaviour and physiology. Although it has been well established that the bioavailability of the steroid and the expression of its receptor is critical for understanding steroid action in the brain, the importance of nuclear receptor coactivators in the brain is becoming more apparent. The present review focuses on the function of the p160 family of coactivators, which includes steroid receptor coactivator-1 (SRC-1), SRC-2 and SRC-3, in steroid receptor action in the brain. The expression, regulation and function of these coactivators in steroid-dependent gene expression in both brain and behaviour are discussed.

Survivin Is a transcriptional target of STAT3 critical to estradiol neuroprotection in global ischemia

Transient global ischemia causes selective, delayed death of hippocampal CA1 pyramidal neurons in humans and animals. It is well established that estrogens ameliorate neuronal death in animal models of focal and global ischemia. However, the role of signal transducer and activator of transcription-3 (STAT3) and its target genes in estradiol neuroprotection in global ischemia remains unclear. Here we show that a single intracerebral injection of 17β-estradiol to ovariectomized female rats immediately after ischemia rescues CA1 neurons destined to die. Ischemia promotes activation of STAT3 signaling, association of STAT3 with the promoters of target genes, and STAT3-dependent mRNA and protein expression of prosurvival proteins in the selectively vulnerable CA1. In animals subjected to ischemia, acute postischemic estradiol further enhances activation and nuclear translocation of STAT3 and STAT3-dependent transcription of target genes. Importantly, we show that STAT3 is critical to estradiol neuroprotection, as evidenced by the ability of STAT3 inhibitor peptide and STAT3 shRNA delivered directly into the CA1 of living animals to abolish neuroprotection. In addition, we identify survivin, a member of the inhibitor-of-apoptosis family of proteins and known gene target of STAT3, as essential to estradiol neuroprotection, as evidenced by the ability of shRNA to survivin to reverse neuroprotection. These findings indicate that ischemia and estradiol act synergistically to promote activation of STAT3 and STAT3-dependent transcription of survivin in insulted CA1 neurons and identify STAT3 and survivin as potentially important therapeutic targets in an in vivo model of global ischemia.

Mechanism of formation of the major estradiol product ions following collisional activation of the molecular anion in a tandem quadrupole mass spectrometer

The importance of the mass spectral product ion structure is highlighted in quantitative assays, which typically use multiple reaction monitoring (MRM), and in the discovery of novel metabolites. Estradiol is an important sex steroid whose quantitation and metabolite identification using tandem mass spectrometry has been widely employed in numerous clinical studies. Negative electrospray ionization tandem mass spectrometry of estradiol (E2) results in several product ions, including the abundant m/z 183 and 169. Although m/z 183 is one of the most abundant product ions used in many quantitative assays, the structure of m/z 183 has not been rigorously examined. We suggest a structure for m/z 183 and a mechanism of formation consistent with collision induced dissociation (CID) of E2 and several stable isotopes ([D4]-E2, [(13)C6]-E2, and [D1]-E2). An additional product ion from E2, namely m/z 169, has also been examined. MS(3) experiments indicated that both m/z 183 and m/z 169 originate from only E2 [M - H](-) m/z 271. These ions, m/z 183 and m/z 169, were also present in the collision induced decomposition mass spectra of other prominent estrogens, estrone (E1) and estriol (E3), indicating that these two product ions could be used to elucidate the estrogenic origin of novel metabolites. We propose two fragmentation schemes to explain the CID data and suggest a structure of m/z 183 and m/z 169 consistent with several isotopic variants and high resolution mass spectrometric measurements.

The membrane estrogen receptor ligand STX rapidly enhances GABAergic signaling in NPY/AgRP neurons: role in mediating the anorexigenic effects of 17β-estradiol

Besides its quintessential role in reproduction, 17β-estradiol (E2) is a potent anorexigenic hormone. E2 and the selective Gq-coupled membrane estrogen receptor (Gq-mER) ligand STX rapidly increase membrane excitability in proopiomelanocortin (POMC) neurons by desensitizing the coupling of GABAB receptors to G protein-coupled inwardly rectifying K(+) channels (GIRKs), which upon activation elicit a hyperpolarizing outward current. However, it is unknown whether E2 and STX can modulate GABAB signaling in neuropeptide Y (NPY)/agouti-related peptide (AgRP) neurons. We used single-cell RT-PCR and whole cell patch clamping with selective pharmacological reagents to show that NPY/AgRP cells of mice express the GABAB-R1 and -R2 receptors and are hyperpolarized by the GABAB agonist baclofen in an E2-dependent manner. In males, E2 rapidly attenuated the coupling of GABAB receptors to GIRKs, which was blocked by the general PI3K inhibitors wortmannin and LY-294002 or the selective p110β subunit inhibitor TGX-221. The ERα-selective agonist propyl pyrazole triol mimicked the effects of E2. STX, in contrast, enhanced the GABAB response in males, which was abrogated by the estrogen receptor (ER) antagonist ICI 182,780. In gonadectomized mice of both sexes, E2 enhanced or attenuated the GABAB response in different NPY/AgRP cells. Coperfusing wortmannin with E2 or simply applying STX always enhanced the GABAB response. Thus, in NPY/AgRP neurons, activation of the Gq-mER by E2 or STX enhances the GABAergic postsynaptic response, whereas activation of ERα by E2 attenuates it. These findings demonstrate a clear functional dichotomy of rapid E2 membrane-initiated signaling via ERα vs. Gq-mER in a CNS neuron vital for regulating energy homeostasis.