Estrogen receptor-alpha is associated with the plasma membrane of astrocytes and coupled to the MAP/Src-kinase pathway

Astrocyte Reactivity and Neurodegeneration in the Female Rat Brain Following Alcohol Dependence

Recent evidence suggests that alcohol use disorder (AUD) may manifest itself differently in women compared to men. Women experience AUDs on an accelerated timeline and may have certain regional vulnerabilities. In male rats, neuronal cell death and astrocyte reactivity are noted following induction of alcohol dependence in an animal model of an AUD. However, the regional and temporal patterns of neurodegeneration and astrocyte reactivity have yet to be fully examined in females using this model. Therefore, adult female rats were exposed to a 4-day binge model of alcohol dependence followed by different periods of abstinence. Histological markers for FluoroJade B, a label of degenerating neurons, and vimentin, a marker for reactive astrocytes, were utilized. The expression of these markers in cortical and limbic regions was quantified immediately after their last dose (e.g., T0), or 2, 7, and 14 days later. Significant neuronal cell death was noted in the entorhinal cortex and the hippocampus, similar to previous reports in males, but also in several cortical regions not previously observed. Vimentin immunoreactivity was noted in the same regions as previously reported, in addition to three novel regions. Vimentin immunoreactivity also occurred at earlier and later time points in some cortical and hippocampal regions. These data suggest that both neuronal cell death and astrocyte reactivity could be more widespread in females compared to males. Therefore, this study provides a framework for specific regions and time points which should be examined in future studies of alcohol-induced damage that include female rats.

Non-genomic Effect of Estradiol on the Neurovascular Unit and Possible Involvement in the Cerebral Vascular Accident

Cerebrovascular diseases, such as ischemic cerebral vascular accident (CVA), are responsible for causing high rates of morbidity, mortality, and disability in the population. The neurovascular unit (NVU) during and after ischemic CVA plays crucial roles in cell regulation and preservation, the immune and inflammatory response, and cell and/or tissue survival and repair. Cellular responses to 17β-estradiol (E2) can be triggered by two mechanisms: one called classical or genomic, which is due to the activation of the "classical" nuclear estrogen receptors α (ERα) and β (ERβ), and the non-genomic or rapid mechanism, which is due to the activation of the G protein-coupled estrogen receptor 1 (GPER) that is located in the plasma membrane and some in intracellular membranes, such as in the Golgi apparatus and endoplasmic reticulum. Nuclear receptors can regulate gene expression and cellular functions. On the contrary, activating the GPER by E2 and/or its G-1 agonist triggers several rapid cell signaling pathways. Therefore, E2 or its G-1 agonist, by mediating GPER activation and/or expression, can influence several NVU cell types. Most studies argue that the activation of the GPER may be used as a potential therapeutic target in various pathologies, such as CVA. Thus, with this review, we aimed to summarize the existing literature on the role of GPER mediated by E2 and/or its agonist G-1 in the physiology and pathophysiology of NVU.

The interaction of membrane estradiol receptors and metabotropic glutamate receptors in adaptive and maladaptive estradiol-mediated motivated behaviors in females

Estrogen receptors were initially identified as intracellular, ligand-regulated transcription factors that result in genomic change upon ligand binding. However, rapid estrogen receptor signaling initiated outside of the nucleus was also known to occur via mechanisms that were less clear. Recent studies indicate that these traditional receptors, estrogen receptor α and estrogen receptor β, can also be trafficked to act at the surface membrane. Signaling cascades from these membrane-bound estrogen receptors (mERs) can rapidly alter cellular excitability and gene expression, particularly through the phosphorylation of CREB. A principal mechanism of neuronal mER action has been shown to occur through glutamate-independent transactivation of metabotropic glutamate receptors (mGlu), which elicits multiple signaling outcomes. The interaction of mERs with mGlu has been shown to be important in many diverse functions in females, including driving motivated behaviors. Experimental evidence suggests that a large part of estradiol-induced neuroplasticity and motivated behaviors, both adaptive and maladaptive, occurs through estradiol-dependent mER activation of mGlu. Herein we will review signaling through estrogen receptors, both "classical" nuclear receptors and membrane-bound receptors, as well as estradiol signaling through mGlu. We will focus on how the interactions of these receptors and their downstream signaling cascades are involved in driving motivated behaviors in females, discussing a representative adaptive motivated behavior (reproduction) and maladaptive motivated behavior (addiction).

Brain Volume Loss, Astrocyte Reduction, and Inflammation in Anorexia Nervosa

Anorexia nervosa is the third most common chronic disease in adolescence and is characterized by low body weight, body image distortion, weight phobia, and severe somatic consequences. Among the latter, marked brain volume reduction has been linked to astrocyte cell count reduction of about 50% in gray and white matter, while neuronal and other glial cell counts remain normal. Exact underlying mechanisms remain elusive; however, first results point to important roles of the catabolic state and the very low gonadal steroid hormones in these patients. They also appear to involve inflammatory states of "hungry astrocytes" and interactions with the gut microbiota. Functional impairments could affect the role of astrocytes in supporting neurons metabolically, neurotransmitter reuptake, and synapse formation, among others. These could be implicated in reduced learning, mood alterations, and sleep disturbances often seen in patients with AN and help explain their rigidity and difficulties in relearning processes in psychotherapy during starvation.

Estradiol Enhances Anorectic Effect of Apolipoprotein A-IV through ERα-PI3K Pathway in the Nucleus Tractus Solitarius

Estradiol (E2) enhances the anorectic action of apolipoprotein A-IV (apoA-IV), however, the intracellular mechanisms are largely unclear. Here we reported that the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway was significantly activated by E2 and apoA-IV, respectively, in primary neuronal cells isolated from rat embryonic brainstem. Importantly, the combination of E2 and apoA-IV at their subthreshold doses synergistically activated the PI3K/Akt signaling pathway. These effects, however, were significantly diminished by the pretreatment with LY294002, a selective PI3K inhibitor. E2-induced activation of the PI3K/Akt pathway was through membrane-associated ERα, because the phosphorylation of Akt was significantly increased by PPT, an ERα agonist, and by E2-BSA (E2 conjugated to bovine serum albumin) which activates estrogen receptor on the membrane. Centrally administered apoA-IV at a low dose (0.5 µg) significantly suppressed food intake and increased the phosphorylation of Akt in the nucleus tractus solitarius (NTS) of ovariectomized (OVX) rats treated with E2, but not in OVX rats treated with vehicle. These effects were blunted by pretreatment with LY294002. These results indicate that E2's regulatory role in apoA-IV's anorectic action is through the ERα-PI3K pathway in the NTS. Manipulation of the PI3K/Akt signaling activation in the NTS may provide a novel therapeutic approach for the prevention and the treatment of obesity-related disorders in females.

G Protein-Coupled Estrogen Receptor in Immune Cells and Its Role in Immune-Related Diseases

G protein-coupled estrogen receptor 1 (GPER1), is a functional estrogen receptor involved in estrogen related actions on several systems including processes of the nervous, reproductive, metabolic, cardiovascular, and immune system. Regarding the latter, GPER is expressed in peripheral B and T lymphocytes as well as in monocytes, eosinophils, and neutrophils. Several studies have implicated GPER in immune-mediated diseases like multiple sclerosis, Parkinson's disease, and atherosclerosis-related inflammation, while a recent report suggests that its deletion could be responsible for a form of familial immunodeficiency. It has also been suggested that it is a key regulator of immune-mediated events in breast, pancreatic, prostate, and hepatocellular cancer as well as in melanoma. GPER has been also reported to interact with classic ER-alpha or its splice variants in order to modify immune functions. This review aims to present current knowledge relating GPER to immune functions, the cellular and signaling pathways involved, as well as the potential clinical implications of GPER modulation in immune-related diseases.

Protein kinase inhibitors infused intraventricularly or into the ventromedial hypothalamus block short latency facilitation of lordosis by oestradiol

An injection of unesterified oestradiol (E₂ ) facilitates receptive behaviour in E₂ benzoate (EB)-primed, ovariectomised female rats when it is administered i.c.v. or systemically. The present study tested the hypothesis that inhibitors of protein kinase A (PKA), protein kinase G (PKG) or the Src/mitogen-activated protein kinase (MAPK) complex interfere with E₂ facilitation of receptive behaviour. In Experiment 1, lordosis induced by i.c.v. infusion of E₂ was significantly reduced by i.c.v. administration of Rp-cAMPS, a PKA inhibitor, KT5823, a PKG inhibitor, and PP2 and PD98059, Src and MAPK inhibitors, respectively, between 30 and 240 minutes after infusion. In Experiment 2, we determined whether the ventromedial hypothalamus (VMH) is one of the neural sites at which those intracellular pathways participate in lordosis behaviour induced by E₂ . Administration of each of the four protein kinase inhibitors into the VMH blocked facilitation of lordosis induced by infusion of E₂ also into the VMH. These data support the hypothesis that activation of several protein kinase pathways is involved in the facilitation of lordosis by E₂ in EB-primed rats.

Neurosteroids as regulators of neuroinflammation

Neuroinflammation is a physiological protective response in the context of infection and injury. However, neuroinflammation, especially if chronic, may also drive neurodegeneration. Neurodegenerative diseases, such as multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD) and traumatic brain injury (TBI), display inflammatory activation of microglia and astrocytes. Intriguingly, the central nervous system (CNS) is a highly steroidogenic environment synthesizing steroids de novo, as well as metabolizing steroids deriving from the circulation. Neurosteroid synthesis can be substantially affected by neuroinflammation, while, in turn, several steroids, such as 17β-estradiol, dehydroepiandrosterone (DHEA) and allopregnanolone, can regulate neuroinflammatory responses. Here, we review the role of neurosteroids in neuroinflammation in the context of MS, AD, PD and TBI and describe underlying molecular mechanisms. Moreover, we introduce the concept that synthetic neurosteroid analogues could be potentially utilized for the treatment of neurodegenerative diseases in the future.

[Reactive changes in morphological and morphometric parameters of immunopositive astrocytes of the amygdala in response to hormone level in absence epilepsy]

AIM

To study the changes in the morphological and morphometric parameters of immunopositive astrocytes of the amygdala in absence epilepsy depending on hormonal profile.

MATERIAL AND METHODS

Adult female WAG/Rij rats were used as experimental subjects. The astrocytes were detected on serial sections using a reaction to glial fibrillary acidic protein (GFAP) with pre-stained hematoxylin. Quantitative analysis was carried out for a 204.8´153.6 μm² field of view.

RESULTS

In the control group, astrocytes had a relatively regular stellate form and GFAP was moderately expressed in their bodies and processes. The number of astrocytes was 18.20±2.87, and their area was 164±3.29 μm². After ovariectomy, a high expression of the protein, both in the bodies and in the processes of astrocytes, increasing the cell size to 188.85±4.97 μm² (p<0.05) was observed. The astrocytes increased to 34.55±3.03 (p<0.05). In addition, the deformation of the processes and their diffuse defibration were observed. After hormone replacement therapy, a decrease in GFAP expression was detected, the area of astrocytes became smaller in comparison with the group after ovariectomy: 173.54±5.48 μm² (p<0.05). Morphological changes in glial cells were manifested as a decrease in the size of their bodies, the processes became smooth without diffuse sprouting and swelling, which is probably associated with neuroprotective functions of estradiol.

CONCLUSION

Thus, the results of our study demonstrated that the deficiency of female sex hormones led to the increase in both the amount and area of astrocytes in the anterior cortical nucleus of the amygdala, and hormone replacement therapy positively affected the structural and quantitative characteristics of astrocytes due to the endogenous protective role of estradiol.

Norepinephrine control of ventromedial hypothalamic nucleus glucoregulatory neurotransmitter expression in the female rat: Role of monocarboxylate transporter function

The ventromedial hypothalamic nucleus (VMN) is a critical component of the neural circuitry that regulates glucostasis. Astrocyte glycogen is a vital reserve of glucose and its oxidizable metabolite L-lactate. In hypoglycemic female rats, estradiol-dependent augmentation of VMN glycogen phosphorylase (GP) protein requires hindbrain catecholamine input. Research here investigated the premise that norepinephrine (NE) regulation of VMN astrocyte metabolism shapes local glucoregulatory neurotransmitter signaling in this sex. Estradiol-implanted ovariectomized rats were pretreated by intra-VMN administration of the monocarboxylate transporter inhibitor alpha-cyano-4-hydroxy-cinnamic acid (4CIN) or vehicle before NE delivery to that site. NE caused 4CIN-reversible reduction or augmentation of VMN glycogen synthase and phosphorylase expression. 4CIN prevented NE stimulation of gluco-inhibitory (glutamate decarboxylase65/67) and suppression of gluco-stimulatory (neuronal nitric oxide synthase) neuron marker proteins. These outcomes imply that effects of noradrenergic stimulation of VMN astrocyte glycogen depletion on glucoregulatory transmitter signaling may be mediated, in part, by glycogen-derived substrate fuel provision. NE control of astrocyte glycogen metabolism may involve down-regulated adrenoreceptor (AR), e.g. alpha1 and alpha2, alongside amplified beta1 AR and estrogen receptor-beta signaling. Noradrenergic hypoglycemia was refractory to 4CIN, implying that additional NE-sensitive VMN glucoregulatory neurochemicals may be insensitive to monocarboxylate uptake. Augmentation of circulating free fatty acids by combinatory NE and 4CIN, but not NE alone implies that acute hypoglycemia induced here is an insufficient stimulus for mobilization of these fuels, but is adequate when paired with diminished brain monocarboxylate fuel availability.

Norepinephrine regulation of ventromedial hypothalamic nucleus metabolic transmitter biomarker and astrocyte enzyme and receptor expression: Impact of 5' AMP-activated protein kinase

The ventromedial hypothalamic energy sensor AMP-activated protein kinase (AMPK) maintains glucostasis via neurotransmitter signals that diminish [γ-aminobutyric acid] or enhance [nitric oxide] counter-regulation. Ventromedial hypothalamic nucleus (VMN) 'fuel-inhibited' neurons are sensitive to astrocyte-generated metabolic substrate stream. Norepinephrine (NE) regulates astrocyte glycogen metabolism in vitro, and hypoglycemia intensifies VMN NE activity in vivo. Current research investigated the premise that NE elicits AMPK-dependent adjustments in VMN astrocyte glycogen metabolic enzyme [glycogen synthase (GS); glycogen phosphorylase (GP)] and gluco-regulatory neuron biomarker [glutamate decarboxylase_65/67 (GAD); neuronal nitric oxide synthase (nNOS); SF-1] protein expression in male rats. We also examined whether VMN astrocytes are directly receptive to NE and if noradrenergic input regulates cellular sensitivity to the neuro-protective steroid estradiol. Intra-VMN NE correspondingly augmented or reduced VMN tissue GAD and nNOS protein despite no change in circulating glucose, data that imply that short-term exposure to NE promotes persistent improvement in VMN nerve cell energy stability. The AMPK inhibitor Compound C (Cc) normalized VMN nNOS, GS, and GP expression in NE-treated animals. NE caused AMPK-independent down-regulation of alpha₂-, alongside Cc-reversible augmentation of beta₁-adrenergic receptor protein profiles in laser-microdissected astrocytes. NE elicited divergent adjustments in astrocyte estrogen receptor-beta (AMPK-unrelated reduction) and GPR-30 (Cc-revocable increase) proteins. Outcomes implicate AMPK in noradrenergic diminution of VMN nitrergic metabolic-deficit signaling and astrocyte glycogen shunt activity. Differentiating NE effects on VMN astrocyte adrenergic and estrogen receptor variant expression suggest that noradrenergic regulation of glycogen metabolism may be mediated, in part, by one or more receptors characterized here by sensitivity to this catecholamine.

Astrocytes Mediate Protective Actions of Estrogenic Compounds after Traumatic Brain Injury

Traumatic brain injury (TBI) is a serious public health problem. It may result in severe neurological disabilities and in a variety of cellular metabolic alterations for which available therapeutic strategies are limited. In the last decade, the use of estrogenic compounds, which activate protective mechanisms in astrocytes, has been explored as a potential experimental therapeutic approach. Previous works have suggested estradiol (E2) as a neuroprotective hormone that acts in the brain by binding to estrogen receptors (ERs). Several steroidal and nonsteroidal estrogenic compounds can imitate the effects of estradiol on ERs. These include hormonal estrogens, phytoestrogens and synthetic estrogens, such as selective ER modulators or tibolone. Current evidence of the role of astrocytes in mediating protective actions of estrogenic compounds after TBI is reviewed in this paper. We conclude that the use of estrogenic compounds to modulate astrocytic properties is a promising therapeutic approach for the treatment of TBI.

Extranuclear signaling by sex steroid receptors and clinical implications in breast cancer

Estrogen and progesterone play essential roles in the development and progression of breast cancer. Over 70% of breast cancers express estrogen receptors (ER) and progesterone receptors (PR), emphasizing the need for better understanding of ER and PR signaling. ER and PR are traditionally viewed as transcription factors that directly bind DNA to regulate gene networks. In addition to nuclear signaling, ER and PR mediate hormone-induced, rapid extranuclear signaling at the cell membrane or in the cytoplasm which triggers downstream signaling to regulate rapid or extended cellular responses. Specialized membrane and cytoplasmic proteins may also initiate hormone-induced extranuclear signaling. Rapid extranuclear signaling converges with its nuclear counterpart to amplify ER/PR transcription and specify gene regulatory networks. This review summarizes current understanding and updates on ER and PR extranuclear signaling. Further investigation of ER/PR extranuclear signaling may lead to development of novel targeted therapeutics for breast cancer management.

Estrogen Interactions With Lipid Rafts Related to Neuroprotection. Impact of Brain Ageing and Menopause

Estrogens (E2) exert a plethora of neuroprotective actions against aged-associated brain diseases, including Alzheimer's disease (AD). Part of these actions takes place through binding to estrogen receptors (ER) embedded in signalosomes, where numerous signaling proteins are clustered. Signalosomes are preferentially located in lipid rafts which are dynamic membrane microstructures characterized by a peculiar lipid composition enriched in gangliosides, saturated fatty acids, cholesterol, and sphingolipids. Rapid E2 interactions with ER-related signalosomes appear to trigger intracellular signaling ultimately leading to the activation of molecular mechanisms against AD. We have previously observed that the reduction of E2 blood levels occurring during menopause induced disruption of ER-signalosomes at frontal cortical brain areas. These molecular changes may reduce neuronal protection activities, as similar ER signalosome derangements were observed in AD brains. The molecular impairments may be associated with changes in the lipid composition of lipid rafts observed in neurons during menopause and AD. These evidences indicate that the changes in lipid raft structure during aging may be at the basis of alterations in the activity of ER and other neuroprotective proteins integrated in these membrane microstructures. Moreover, E2 is a homeostatic modulator of lipid rafts. Recent work has pointed to this relevant aspect of E2 activity to preserve brain integrity, through mechanisms affecting lipid uptake and local biosynthesis in the brain. Some evidences have demonstrated that estrogens and the docosahexaenoic acid (DHA) exert synergistic effects to stabilize brain lipid matrix. DHA is essential to enhance molecular fluidity at the plasma membrane, promoting functional macromolecular interactions in signaling platforms. In support of this, DHA detriment in neuronal lipid rafts has been associated with the most common age-associated neuropathologies, namely AD and Parkinson disease. Altogether, these findings indicate that E2 may participate in brain preservation through a dual membrane-related mechanism. On the one hand, E2 interacting with ER related signalosomes may protect against neurotoxic insults. On the other hand, E2 may exert lipostatic actions to preserve lipid balance in neuronal membrane microdomains. The different aspects of the emerging multifunctional role of estrogens in membrane-related signalosomes will be discussed in this review.

Dangguijakyak-san ameliorates memory deficits in ovariectomized mice by upregulating hippocampal estrogen synthesis

Background

Dangguijakyak-san (DJS) is an herbal formulation that has been clinically applicable for treating postmenopausal symptoms and neurological disorders. It is reported that hippocampal estrogen attenuates memory impairment via neuroprotection and synaptogenesis. However, the effect of DJS on hippocampal estrogen synthesis remains unknown. In this study, we explored the effect of DJS and its neuroprotective mechanism against memory impairment in ovariectomized (OVX) mice, with respect to hippocampal estrogen stimulation.

Methods

Cell cultures were prepared from the hippocampi of 18-day-old embryos from timed pregnant Sprague–Dawley rats. The hippocampi were dissected, collected, dissociated, and plated in 60-mm dishes. The cells were treated with DJS for 48 h and the supernatant was collected to determine estrogen levels. Female ICR mice (8-weeks-old) were housed for 1 week and ovariectomy was performed to remove the influence of ovary-synthesized estrogens. Following a 2-week post-surgical recovery period, the mice were administrated with DJS (50 and 100 mg/kg/day, p.o.) or 17β-estradiol (200 μg/kg/day, i.p.) once daily for 21 days. Hippocampal and serum estrogen levels were determined using enzyme-linked immunosorbent assay kit. Memory behavioral tests, western blot, and immunohistochemical analyses were performed to evaluate the neuroprotective effects of DJS in this model.

Results

DJS treatment promoted estrogen synthesis in primary hippocampal cells and the hippocampus of OVX mice, resulting in the amelioration of OVX-induced memory impairment. Hippocampal estrogen stimulated by DJS treatment contributed to the activation of cAMP response element-binding protein and synaptic protein in OVX mice.

Conclusion

DJS may attenuate memory deficits in postmenopausal women via hippocampal estrogen synthesis.

Electronic supplementary material

The online version of this article (10.1186/s12906-017-2015-6) contains supplementary material, which is available to authorized users.

Disruption of the Glutamate-Glutamine Cycle Involving Astrocytes in an Animal Model of Depression for Males and Females

Background: Women are twice as likely as men to develop major depression. The brain mechanisms underlying this sex disparity are not clear. Disruption of the glutamate–glutamine cycle has been implicated in psychiatric disturbances. This study identifies sex-based impairments in the glutamate–glutamine cycle involving astrocytes using an animal model of depression.

Methods: Male and female adult Long-Evans rats were exposed to chronic social defeat stress (CSDS) for 21 days, using a modified resident-intruder paradigm. Territorial aggression was used for males and maternal aggression was used for females to induce depressive-like deficits for intruders. The depressive-like phenotype was assessed with intake for saccharin solution, weight gain, estrous cycle, and corticosterone (CORT). Behaviors displayed by the intruders during daily encounters with residents were characterized. Rats with daily handling were used as controls for each sex. Ten days after the last encounter, both the intruders and controls were subjected to a no-net-flux in vivo microdialysis to assess glutamate accumulation and extracellular glutamine in the nucleus accumbens (NAc). The contralateral hemispheres were used for determining changes in astrocytic markers, including glial fibrillary acidic protein (GFAP) and glutamate transporter-1 (GLT-1).

Results: Both male and female intruders reduced saccharin intake over the course of CSDS, compared to their pre-stress period and to their respective controls. Male intruders exhibited submissive/defensive behaviors to territorial aggression by receiving sideways threats and bites. These males showed reductions in striatal GLT-1 and spontaneous glutamine in the NAc, compared to controls. Female intruders exhibited isolated behaviors to maternal aggression, including immobility, rearing, and selfgrooming. Their non-reproductive days were extended. Also, they showed reductions in prefrontal and accumbal GFAP⁺ cells and prefrontal GLT-1, compared to controls. When 10 μM of glutamate was infused, these females showed a significant accumulation of glutamate compared to controls. Infusions of glutamate reduced extracellular glutamine for both male and female intruders compared to their respective controls.

Conclusion: Twenty-one days of territorial or maternal aggression produced a depressive-like phenotype and impaired astrocytes in both male and female intruders. Disruption of the glutamate–glutamine cycle in the PFC-striatal network may be linked to depressive-like deficits more in females than in males.

Adult Neurogenesis in the Female Mouse Hypothalamus: Estradiol and High-Fat Diet Alter the Generation of Newborn Neurons Expressing Estrogen Receptor α

Estrogens and leptins act in the hypothalamus to maintain reproduction and energy homeostasis. Neurogenesis in the adult mammalian hypothalamus has been implicated in the regulation of energy homeostasis. Recently, high-fat diet (HFD) and estradiol (E2) have been shown to alter cell proliferation and the number of newborn leptin-responsive neurons in the hypothalamus of adult female mice. The current study tested the hypothesis that new cells expressing estrogen receptor α (ERα) are generated in the arcuate nucleus (ARC) and the ventromedial nucleus of the hypothalamus (VMH) of the adult female mouse, hypothalamic regions that are critical in energy homeostasis. Adult mice were ovariectomized and implanted with capsules containing E2 or oil. Within each hormone group, mice were fed an HFD or standard chow for 6 weeks and treated with BrdU to label new cells. Newborn cells that respond to estrogens were identified in the ARC and VMH, of which a subpopulation was leptin sensitive, indicating that the subpopulation consists of neurons. Moreover, there was an interaction between diet and hormone with an effect on the number of these newborn ERα-expressing neurons that respond to leptin. Regardless of hormone treatment, HFD increased the number of ERα-expressing cells in the ARC and VMH. E2 decreased hypothalamic fibroblast growth factor 10 (Fgf10) gene expression in HFD mice, suggesting a role for Fgf10 in E2 effects on neurogenesis. These findings of newly created estrogen-responsive neurons in the adult brain provide a novel mechanism by which estrogens can act in the hypothalamus to regulate energy homeostasis in females.

Tibolone protects astrocytic cells from glucose deprivation through a mechanism involving estrogen receptor beta and the upregulation of neuroglobin expression

Tibolone, a synthetic steroid used for the prevention of osteoporosis and the treatment of climacteric symptoms in post-menopausal women, may exert tissue selective estrogenic actions acting on estrogen receptors (ERs). We previously showed that tibolone protects human T98G astroglial cells against glucose deprivation (GD). In this study we have explored whether the protective effect of tibolone on these cells is mediated by ERs. Experimental studies showed that both ERα and ERβ were involved in the protection by tibolone on GD cells, being ERβ preferentially involved on these actions over ERα. Tibolone increased viability of GD cells by a mechanism fully blocked by an ERβ antagonist and partially blocked by an ERα antagonist. Furthermore, ERβ inhibition prevented the effect of tibolone on nuclear fragmentation, ROS and mitochondrial membrane potential in GD cells. The protective effect of tibolone was mediated by neuroglobin. Tibolone upregulated neuroglobin in T98G cells and primary mouse astrocytes by a mechanism involving ERβ and neuroglobin silencing prevented the protective action of tibolone on GD cells. In summary, tibolone protects T98G cells by a mechanism involving ERβ and the upregulation of neuroglobin.

Astrocytic response to cerebral ischemia is influenced by sex differences and impaired by aging

Ischemic stroke occurs more often among the elderly, and within this demographic, women are at an increased risk for stroke and have poorer functional recovery than men. This is also well replicated in animal studies where aging females are shown to have more extensive brain tissue loss as compared to adult females. Astrocytes provide nutrients for neurons, regulate glutamate levels, and release neurotrophins and thus play a key role in the events that occur following ischemia. In addition, astrocytes express receptors for gonadal hormones and synthesize several neurosteroids suggesting that the sex differences in stroke outcome may be mediated through astrocytes. This review discusses key astrocytic responses to ischemia including, reactive gliosis, excitotoxicity, and neuroinflammation. In light of the age and sex differences in stroke outcomes, this review highlights how aging and gonadal hormones influence these responses. Lastly, astrocyte specific changes in gene expression and epigenetic modifications during aging and following ischemia are discussed as possible molecular mechanisms for impaired astrocytic functioning.

Estrogen protects against dopamine neuron toxicity in primary mesencephalic cultures through an indirect P13K/Akt mediated astrocyte pathway

Astrocytes regulate neuronal homeostasis and have been implicated in affecting the viability and functioning of surrounding neurons under stressed and injured conditions. Previous data from our lab suggests indirect actions of estrogen through ERα in neighboring astroglia to protect dopamine neurons against 1-methyl-4-phenylpyridinium (MPP(+)) toxicity in mouse mesencephalic cultures. We further evaluate estrogen signaling in astrocytes and the mechanism of estrogen's indirect neuroprotective effects on dopamine neurons. Primary mesencephalic cultures pre-treated with 17β-estradiol and the membrane impermeable estrogen, E2-BSA, were both neuroprotective against MPP(+) -induced dopamine neuron toxicity, suggesting membrane-initiated neuroprotection. ERα was found in the plasma membrane of astrocyte cultures and colocalized with the lipid raft marker, flotillin-1. A 17β-estradiol time course revealed a significant increase in Akt, which was inhibited by the PI3 kinase inhibitor, LY294004. Estrogen conditioned media collected from pure astrocyte cultures rescued glial deficient mesencephalic cultures from MPP(+). This indirect estrogen-mediated neuroprotective effect in mesencephalic cultures was significantly reduced when PI3 kinase signaling in astrocytes was blocked prior to collecting estrogen-conditioned media using the irreversible PI3 kinase inhibitor, Wortmannin. Estrogen signaling via astrocytes is rapidly initiated at the membrane level and requires PI3 kinase signaling in order to protect primary mesencephalic dopamine neurons from MPP(+) neurotoxicity.

Regulation of Estrogen Receptor α Expression in the Hypothalamus by Sex Steroids: Implication in the Regulation of Energy Homeostasis

Sex differences exist in the complex regulation of energy homeostasis that utilizes central and peripheral systems. It is widely accepted that sex steroids, especially estrogens, are important physiological and pathological components in this sex-specific regulation. Estrogens exert their biological functions via estrogen receptors (ERs). ERα, a classic nuclear receptor, contributes to metabolic regulation and sexual behavior more than other ER subtypes. Physiological and molecular studies have identified multiple ERα-rich nuclei in the hypothalamus of the central nervous system (CNS) as sites of actions that mediate effects of estrogens. Much of our understanding of ERα regulation has been obtained using transgenic models such as ERα global or nuclei-specific knockout mice. A fundamental question concerning how ERα is regulated in wild-type animals, including humans, in response to alterations in steroid hormone levels, due to experimental manipulation (i.e., castration and hormone replacement) or physiological stages (i.e., puberty, pregnancy, and menopause), lacks consistent answers. This review discusses how different sex hormones affect ERα expression in the hypothalamus. This information will contribute to the knowledge of estrogen action in the CNS, further our understanding of discrepancies in correlation of altered sex hormone levels with metabolic disturbances when comparing both sexes, and improve health issues in postmenopausal women.

Omega-3 polyunsaturated fatty acids ameliorate neuroinflammation and mitigate ischemic stroke damage through interactions with astrocytes and microglia

Omega-3 polyunsaturated fatty acids (PUFA n3) provide neuroprotection due to their anti-inflammatory and anti-apoptotic properties as well as their regulatory function on growth factors and neuronal plasticity. These qualities enable PUFA n3 to ameliorate stroke outcome and limit neuronal damage. Young adult male rats received transient middle cerebral artery occlusion (tMCAO). PUFA n3 were intravenously administered into the jugular vein immediately after stroke and 12h later. We analyzed stroke volume and behavioral performance as well as the regulation of functionally-relevant genes in the penumbra. The extent of ischemic damage was reduced and behavioral performance improved subject to applied PUFA n3. Expression of Tau and growth-associated protein-43 genes were likewise restored. Ischemia-induced increase of cytokine mRNA levels was abated by PUFA n3. Using an in vitro approach, we demonstrate that cultured astroglial and microglia directly respond to PUFA n3 administration by preventing ischemia-induced increase of cyclooxygenase 2, hypoxia-inducible factor 1alpha, inducible nitric oxide synthase, and interleukin 1beta. Cultured cortical neurons also appeared as direct targets, since PUFA n3 shifted the Bcl-2-like protein 4 (Bax)/B-cell lymphoma 2 (Bcl 2) ratio towards an anti-apoptotic constellation. Thus, PUFA n3 reveal a high neuroprotective and anti-inflammatory potential in an acute ischemic stroke model by targeting astroglial and microglial function as well as improving neuronal survival strategies. Our findings signify the potential clinical feasibility of PUFA n3 therapeutic treatment in stroke and other acute neurological diseases.

Astrocyte-derived growth factors and estrogen neuroprotection: role of transforming growth factor-α in estrogen-induced upregulation of glutamate transporters in astrocytes

Extensive studies from the past decade have completely revolutionized our understanding about the role of astrocytes in the brain from merely supportive cells to an active role in various physiological functions including synaptic transmission via cross-talk with neurons and neuroprotection via releasing neurotrophic factors. Particularly, numerous studies have reported that astrocytes mediate the neuroprotective effects of 17β-estradiol (E2) and selective estrogen receptor modulators (SERMs) in various clinical and experimental models of neuronal injury. Astrocytes contain two main glutamate transporters, glutamate aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1), that play a key role in preventing excitotoxic neuronal death, a process associated with most neurodegenerative diseases. E2 has been shown to increase expression of both GLAST and GLT-1 mRNA and protein and glutamate uptake in astrocytes. Growth factors such as transforming growth factor-α (TGF-α) appear to mediate E2-induced enhancement of these transporters. These findings suggest that E2 exerts neuroprotection against excitotoxic neuronal injuries, at least in part, by enhancing astrocytic glutamate transporter levels and function. Therefore, the present review will discuss proposed mechanisms involved in astrocyte-mediated E2 neuroprotection, with a focus on glutamate transporters.

Role of astrocytes in the neuroprotective actions of 17β-estradiol and selective estrogen receptor modulators

Neuroprotective actions of 17β-estradiol (estradiol) are in part mediated by direct actions on neurons. Astrocytes, which play an essential role in the maintenance of the homeostasis of neural tissue, express estrogen receptors and are also involved in the neuroprotective actions of estradiol in the brain. Estradiol controls gliosis and regulates neuroinflammation, edema and glutamate transport acting on astrocytes. In addition, the hormone regulates the release of neurotrophic factors and other neuroprotective molecules by astrocytes. In addition, reactive astrocytes are a local source of neuroprotective estradiol for the injured brain. Since estradiol therapy is not free from peripheral risks, alternatives for the hormone have been explored. Some selective estrogen receptor modulators (SERMs), which are already in use in clinical practice for the treatment of breast cancer, osteoporosis or menopausal symptoms, exert similar actions to estradiol on astrocytes. Therefore, SERMs represent therapeutic alternatives to estradiol for the activation of astroglia-mediated neuroprotective mechanisms.

[Reactivity of perineuronal astrocytes in the prefrontal cortex in schizophrenia: an ultrastructural morphometric study]

OBJECTIVE

Previously the ultrastructural alterations of astrocytes have been reported in schizophrenia. Reduced dendritic arborization of the neurons in layer 5 of the prefrontal cortex has been found in schizophrenia. Authors hypothesized that the abnormalities in perineuronal astrocytes (PA) might contribute to these neuronal changes. It was aimed to study the ultrastructure of PA in the prefrontal cortex in schizophrenia.

MATERIAL AND METHODS

Postmortem electron microscopic morphometric study of PA was performed in layer 5, area 10 of the prefrontal cortex in 39 cases of schizophrenia and 37 controls.

RESULTS

No significant group differences were found in areas of cell, nucleus, cytoplasm, volume fraction (Vv) of lipofuscin granules and areal density of PA. However, in the subgroup of women with schizophrenia, the areal density of PA was significantly lower and the area of PA was significantly higher as compared to the subgroup of healthy women (-52%, p<0,01; +32%, p<0.05 respectively) and to the subgroup of men with schizophrenia (-56%, p<0,01; +23%, p<0,05 respectively). The area of PA nucleus was negatively correlated with the duration of disease (r= -0.37, p=0.02) and positively with the age of disease onset (ADO) (r=0,47, p<0,01). Areas of PA and of PA nucleus were significantly lower in early ADO (<21 y.o.) as compared to the adult ADO (>21 y.o.) (-24%, p<0.05). Vv of lypofuscin granules was correlated with the age in control group (r=0.52, p=0.001), but not in schizophrenia group (r=0.13, p=0.4).

CONCLUSION

Significant differences in PA reactivity in the prefrontal cortex in the schizophrenia are associated with gender and age at onset of the disease.

Estrogen, astrocytes and the neuroendocrine control of metabolism

Obesity, and its associated comorbidities such as type 2 diabetes, cardiovascular diseases, and certain cancers, represent major health challenges. Importantly, there is a sexual dimorphism with respect to the prevalence of obesity and its associated metabolic diseases, implicating a role for gonadal hormones. Specifically, estrogens have been demonstrated to regulate metabolism perhaps by acting as a leptin mimetic in the central nervous system (CNS). CNS estrogen receptors (ERs) include ER alpha (ERα) and ER beta (ERβ), which are found in nuclear, cytoplasmic and membrane sites throughout the brain. Additionally, estrogens can bind to and activate a G protein-coupled estrogen receptor (GPER), which is a membrane-associated ER. ERs are expressed on neurons as well as glia, which are known to play a major role in providing nutrient supply for neurons and have recently received increasing attention for their potentially important involvement in the CNS regulation of systemic metabolism and energy balance. This brief overview summarizes data focusing on the potential role of astrocytic estrogen action as a key component of estrogenic modulation responsible for mediating the sexual dimorphism in body weight regulation and obesity.

Neuroprotection by gonadal steroid hormones in acute brain damage requires cooperation with astroglia and microglia

The neuroactive steroids 17β-estradiol and progesterone control a broad spectrum of neural functions. Besides their roles in the regulation of classical neuroendocrine loops, they strongly influence motor and cognitive systems, behavior, and modulate brain performance at almost every level. Such a statement is underpinned by the widespread and lifelong expression pattern of all types of classical and non-classical estrogen and progesterone receptors in the CNS. The life-sustaining power of neurosteroids for tattered or seriously damaged neurons aroused interest in the scientific community in the past years to study their ability for therapeutic use under neuropathological challenges. Documented by excellent studies either performed in vitro or in adequate animal models mimicking acute toxic or chronic neurodegenerative brain disorders, both hormones revealed a high potency to protect neurons from damage and saved neural systems from collapse. Unfortunately, neurons, astroglia, microglia, and oligodendrocytes are comparably target cells for both steroid hormones. This hampers the precise assignment and understanding of neuroprotective cellular mechanisms activated by both steroids. In this article, we strive for a better comprehension of the mutual reaction between these steroid hormones and the two major glial cell types involved in the maintenance of brain homeostasis, astroglia and microglia, during acute traumatic brain injuries such as stroke and hypoxia. In particular, we attempt to summarize steroid-activated cellular signaling pathways and molecular responses in these cells and their contribution to dampening neuroinflammation and neural destruction. This article is part of a Special Issue entitled 'CSR 2013'.

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.

Neurosteroids, trigger of the LH surge

Recent experiments from our laboratory are consistent with the idea that hypothalamic astrocytes are critical components of the central nervous system (CNS) mediated estrogen positive feedback mechanism. The "astrocrine hypothesis" maintains that ovarian estradiol rapidly increases free cytoplasmic calcium concentrations ([Ca(2+)](i)) that facilitate progesterone synthesis in astrocytes. This hypothalamic neuroprogesterone along with the elevated estrogen from the ovaries allows for the surge release of gonadotropin-releasing hormone (GnRH) that triggers the pituitary luteinizing hormone (LH) surge. A narrow range of estradiol stimulated progesterone production supports an "off-on-off" mechanism regulating the transition from estrogen negative feedback to estrogen positive feedback, and back again. The rapidity of the [Ca(2+)](i) response and progesterone synthesis support a non-genomic, membrane-initiated signaling mechanism. In hypothalamic astrocytes, membrane-associated estrogen receptors (mERs) signal through transactivation of the metabotropic glutamate receptor type 1a (mGluR1a), implying that astrocytic function is influenced by surrounding glutamatergic nerve terminals. Although other putative mERs, such as mERβ, STX-activated mER-Gα(q), and G protein-coupled receptor 30 (GPR30), are present and participate in membrane-mediated signaling, their influence in reproduction is still obscure since female reproduction be it estrogen positive feedback or lordosis behavior requires mERα. The astrocrine hypothesis is also consistent with the well-known sexual dimorphism of estrogen positive feedback. In rodents, only post-pubertal females exhibit this positive feedback. Hypothalamic astrocytes cultured from females, but not males, responded to estradiol by increasing progesterone synthesis. Estrogen autoregulates its own signaling by regulating levels of mERα in the plasma membrane of female astrocytes. In male astrocytes, the estradiol-induced increase in mERα was attenuated, suggesting that membrane-initiated estradiol signaling (MIES) would also be blunted. Indeed, estradiol induced [Ca(2+)](i) release in male astrocytes, but not to levels required to stimulate progesterone synthesis. Investigation of this sexual differentiation was performed using hypothalamic astrocytes from post-pubertal four core genotype (FCG) mice. In this model, genetic sex is uncoupled from gonadal sex. We demonstrated that animals that developed testes (XYM and XXM) lacked estrogen positive feedback, strongly suggesting that the sexual differentiation of progesterone synthesis is driven by the sex steroid environment during early development. This article is part of a Special Issue entitled 'Neurosteroids'.

Estrogen and the regulation of mitochondrial structure and function in the brain

The mitochondrion is the unquestionable cellular compartment that actively preserves most of the cell functions, such as lipid metabolism, ion homeostasis, energy and ROS production, steroid biosynthesis, and control of apoptotic signaling. Thus, this cell organelle depicts a major drop-in centre for regulatory processes within a cell irrespective of the organ or tissue. However, brain tissue is unique in spite of everything due to its extremely high energy demand and sensitivity to oxidative stress. This makes brain cells, in particular neurons, considerably vulnerable against toxins and challenges that attack the mitochondrial structural organization and energetic performance. Estrogens are known to regulate a multitude of cellular functions in neural cells under physiological conditions but also play a protective role under neuropathological circumstances. In recent years, it became evident that estrogens affect distinct cellular processes by interfering with the bioenergetic mitochondrial compartment. According to the general view, estrogens indirectly regulate the mitochondrion through the control of genomic transcription of mitochondrial-located proteins and modulation of cytoplasmic signaling cascades that act upon mitochondrial physiology. More recent but still arguable data suggest that estrogens might directly signal to the mitochondrion either through classical steroid receptors or novel types of receptors/proteins associated with the mitochondrial compartment. This would allow estrogens to more rapidly modulate the function of a mitochondrion than hitherto discussed. Assuming that this novel perception of steroid action is correct, estrogen might influence the energetic control centre through long-lasting nuclear-associated processes and rapid mitochondria-intrinsic temporary mechanisms. In this article, we would like to particularly accentuate the novel conceptual approach of this duality comprising that estrogens govern the mitochondrial structural integrity and functional capacity by different cellular signaling routes. This article is part of a Special Issue entitled 'Neurosteroids'.

Signaling pathways mediating the neuroprotective effects of sex steroids and SERMs in Parkinson's disease

Studies with the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of Parkinson's disease have shown the ability of 17β-estradiol to protect the nigrostriatal dopaminergic system. This paper reviews the signaling pathways mediating the neuroprotective effect of 17β-estradiol against MPTP-induced toxicity. The mechanisms of 17β-estradiol action implicate activation of signaling pathways such as the phosphatidylinositol-3 kinase/Akt and the mitogen-activated protein kinase pathways. 17β-estradiol signaling is complex and integrates multiple interactions with signaling molecules that act to potentiate a protective effect. 17β-estradiol signaling is mediated via estrogen receptors, including GPER1, but others receptors, such as the IGF-1 receptor, are implicated in the neuroprotective effect. Glial and neuronal crosstalk is a critical factor in the maintenance of dopamine neuronal survival and in the neuroprotective action of 17β-estradiol. Compounds that stimulate GPER1 such as selective estrogen receptor modulators and phytoestrogens show neuroprotective activity and are alternatives to 17β-estradiol.

Multiple sclerosis: neuroprotective alliance of estrogen-progesterone and gender

The potential of 17β-estradiol and progesterone as neuroprotective factors is well-recognized. Persuasive data comes from in vitro and animal models reflecting a wide range of CNS disorders. These studies have endeavored to translate findings into human therapies. Nonetheless, few human studies show promising results. Evidence for neuroprotection was obtained in multiple sclerosis (MS) patients. This chronic inflammatory and demyelinating disease shows a female-to-male gender prevalence and disturbances in sex steroid production. In MS-related animal models, steroids ameliorate symptoms and protect from demyelination and neuronal damage. Both hormones operate in dampening central and brain-intrinsic immune responses and regulating local growth factor supply, oligodendrocyte and astrocyte function. This complex modulation of cell physiology and system stabilization requires the gamut of steroid-dependent signaling pathways. The identification of molecular and cellular targets of sex steroids and the understanding of cell-cell interactions in the pathogenesis will offer promise of novel therapy strategies.

Regulation of choline acetyltransferase expression by 17 β-oestradiol in NSC-34 cells and in the spinal cord

Motoneurones located in the ventral horn of the spinal cord conciliate cholinergic innervation of skeletal muscles. These neurones appear to be exceedingly affected in neurodegenerative diseases such as amyotrophic lateral sclerosis. The dysfunction of motoneurones is typically accompanied by alterations of cholinergic metabolism and signalling, as demonstrated by a decrease in choline acetyltransferase (ChAT) expression. 17 β-Oestradiol (E(2)) is generally accepted as neuroprotective factor in the brain under acute toxic and neurodegenerative conditions and also appears to exert a protective role for motoneurones. In the present study, we attempted to analyse the role of E(2) signalling on ChAT expression in the motoneurone-like cell line NSC-34 and in vivo. In a first step, we demonstrated the presence of oestrogen receptor α and β in NSC-34 cells, as well as in the cervical and lumbar parts, of the male mouse spinal cord. Subsequently, we investigated the effect of E(2) treatment on ChAT expression. The application of E(2) significantly increased the transcription of ChAT in NSC-34 cells and in the cervical but not lumbar part of the spinal cord. Our results indicate that E(2) can influence the cholinergic system by increasing ChAT expression in the mouse spinal cord. This mechanism might support motoneurones, in addition to survival-promoting mechanisms, in the temporal balance toxic or neurodegenerative challenges.

The Neurosteroid Progesterone Underlies Estrogen Positive Feedback of the LH Surge

Our understanding the steroid regulation of neural function has rapidly evolved in the past decades. Not long ago the prevailing thoughts were that peripheral steroid hormones carried information to the brain which passively responded to these steroids. These steroid actions were slow, taking hours to days to be realized because they regulated gene expression. Over the past three decades, discoveries of new steroid receptors, rapid membrane-initiated signaling mechanisms, and de novo neurosteroidogenesis have shed new light on the complexity of steroids actions within the nervous system. Sexual differentiation of the brain during development occurs predominately through timed steroid-mediated expression of proteins and long term epigenetic modifications. In contrast across the estrous cycle, estradiol release from developing ovarian follicles initially increases slowly and then at proestrus increases rapidly. This pattern of estradiol release acts through both classical genomic mechanisms and rapid membrane-initiated signaling in the brain to coordinate reproductive behavior and physiology. This review focuses on recently discovered estrogen receptor-α membrane signaling mechanisms that estradiol utilizes during estrogen positive feedback to stimulate de novo progesterone synthesis within the hypothalamus to trigger the luteinizing hormone (LH) surge important for ovulation and estrous cyclicity. The activation of these signaling pathways appears to be coordinated by the rising and waning of estradiol throughout the estrous cycle and integral to the negative and positive feedback mechanisms of estradiol. This differential responsiveness is part of the timing mechanism triggering the LH surge.

Membrane estrogen receptors stimulate intracellular calcium release and progesterone synthesis in hypothalamic astrocytes

In hypothalamic astrocytes obtained from adult female rats, estradiol rapidly increased free cytoplasmic calcium concentrations ([Ca(2+)](i)) that facilitate progesterone synthesis. The present study demonstrated that estradiol (1 nm) significantly and maximally stimulated progesterone synthesis within 5 min, supporting a rapid, nongenomic mechanism. The group I metabotropic glutamate receptor (mGluR1a) antagonist LY 367385 [(S)-(+)-a-amino-4-carboxy-2-methylbenzeneacetic acid] attenuated both the estradiol-induced [Ca(2+)](i) release and progesterone synthesis. To investigate membrane-associated estrogen receptors (mERs), agonists for ERα, ERβ, STX-activated protein, and GPR30 were compared. The selective ERα agonist propylpyrazole triole (PPT) and STX most closely mimicked the estradiol-induced [Ca(2+)](i) responses, where PPT was more potent but less efficacious than STX. Only high doses (100 nm) of selective ERβ agonist diarylpropionitrile (DPN) and GPR30 agonist G-1 induced estradiol-like [Ca(2+)](i) responses. With the exception of DPN (even at 100 nm), all agonists stimulated progesterone synthesis. The PPT- and STX-induced [Ca(2+)](i) release and progesterone synthesis were blocked by LY 367385. While the G-1-stimulated [Ca(2+)](i) release was blocked by LY 367385, progesterone synthesis was not. Since GPR30 was detected intracellularly but not in the membrane, we interpreted these results to suggest that G-1 could activate mGluR1a on the membrane and GPR30 on the smooth endoplasmic reticulum to release intracellular calcium. Although STX and G-1 maximally stimulated [Ca(2+)](i) release in astrocytes from estrogen receptor-α knock-out (ERKO) mice, estradiol in vivo did not stimulate progesterone synthesis in the ERKO mice. Together, these results indicate that mERα is mainly responsible for the rapid, membrane-initiated estradiol-signaling that leads to progesterone synthesis in hypothalamic astrocytes.

ADAM12 is expressed by astrocytes during experimental demyelination

A disintegrin and metalloproteinase (ADAM) 12 represents a member of a large family of similarly structured multi-domain proteins. In the central nervous system (CNS), ADAM12 has been suggested to play a role in brain development, glioblastoma cell proliferation, and in experimental autoimmune encephalomyelitis. Furthermore, ADAM12 was reported to be almost exclusively expressed by oligodendrocytes and could, therefore, be considered as suitable marker for this cell type. In the present study, we investigated ADAM12 expression in the healthy and pathologically altered murine CNS. As pathological paradigm, we used the cuprizone demyelination model in which myelin loss during multiple sclerosis is imitated. Besides APC(+) oligodendrocytes, SMI311(+) neurons and GFAP(+) astrocytes express ADAM12 in the adult mouse brain. ADAM12 expression was further analyzed in vitro. After the induction of demyelination, we observed that activated astrocytes are the main source of ADAM12 in brain regions affected by oligodendrocyte loss. Exposure of astrocytes in vitro to either lipopolysaccharides (LPS), tumor necrosis factor alpha (TNFalpha), glutamate, or hydrogen peroxide revealed a highly stimulus-specific regulation of ADAM12 expression which was not seen in microglial BV2 cells. It appears that LPS- and TNFalpha-induced ADAM12 expression is mediated via the classic NFkappaB pathway. In summary, we demonstrated that ADAM12 is not a suitable marker for oligodendrocytes. Our results further suggest that ADAM12 might be implicated in the course of distinct CNS diseases such as demyelinating disorders.

Estradiol-induced estrogen receptor-alpha trafficking

Estradiol has rapid actions in the CNS that are mediated by membrane estrogen receptors (ERs) and activate cell signaling pathways through interaction with metabotropic glutamate receptors (mGluRs). Membrane-initiated estradiol signaling increases the free cytoplasmic calcium concentration ([Ca(2+)](i)) that stimulates the synthesis of neuroprogesterone in astrocytes. We used surface biotinylation to demonstrate that ERalpha has an extracellular portion. In addition to the full-length ERalpha [apparent molecular weight (MW), 66 kDa], surface biotinylation labeled an ERalpha-immunoreactive protein (MW, approximately 52 kDa) identified by both COOH- and NH(2)-directed antibodies. Estradiol treatment regulated membrane levels of both proteins in parallel: within 5 min, estradiol significantly increased membrane levels of the 66 and 52 kDa ERalpha. Internalization, a measure of membrane receptor activation, was also increased by estradiol with a similar time course. Continuous treatment with estradiol for 24-48 h reduced ERalpha levels, suggesting receptor downregulation. Estradiol also increased mGluR1a trafficking and internalization, consistent with the proposed ERalpha-mGluR1a interaction. Blocking ER with ICI 182,780 or mGluR1a with LY 367385 prevented ERalpha trafficking to and from the membrane. Estradiol-induced [Ca(2+)](i) flux was also significantly increased at the time of peak ERalpha activation/internalization. These results demonstrate that ERalpha is present in the membrane and has an extracellular portion. Furthermore, membrane levels and internalization of ERalpha are regulated by estradiol and mGluR1a ligands. The pattern of trafficking into and out of the membrane suggests that the changing concentration of estradiol during the estrous cycle regulates ERalpha to augment and then terminate membrane-initiated signaling.

Neuroprotective actions of selective estrogen receptor modulators

Decreasing levels of sex hormones with aging may have a negative impact on brain function, since this decrease is associated with the progression of neurodegenerative disorders, increased depressive symptoms and other psychological disturbances. Extensive evidence from animal studies indicates that sex steroids, in particular estradiol, are neuroprotective. However, the potential benefits of estradiol therapy for the brain are counterbalanced by negative, life-threatening risks in the periphery. A potential therapeutic alternative to promote neuroprotection is the use of selective estrogen receptor modulators (SERMs), which may be designed to act with tissue selectivity as estrogen receptor agonists in the brain and not in other organs. Currently available SERMs act not only with tissue selectivity, but also with cellular selectivity within the brain and differentially modulate the activation of microglia, astroglia and neurons. Finally, SERMs may promote the interaction of estrogen receptors with the neuroprotective signaling of growth factors, such as the phosphatidylinositol 3-kinase/glycogen synthase kinase 3 pathway.

17Beta-estradiol at low concentrations acts through distinct pathways in normal versus benign prostatic hyperplasia-derived prostate stromal cells

The aim of this study was to identify differential responses to low concentrations of 17beta-estradiol (E2) in primary stromal cell cultures derived from either normal organ donors or benign prostatic hyperplasia or hypertrophy (BPH) specimens. Furthermore, we sought to identify the potential mechanism of E2 action in these cell types, through either a genomic or nongenomic mechanism. We initially treated stromal cells derived from five normal prostates or five BPH specimens with low concentrations of E2 (0.001-1.0 nM) and analyzed their growth response. To determine whether genomic or nongenomic pathways were involved, we performed studies using specific estrogen receptor antagonists to confirm transcriptional activity or MAPK inhibitors to confirm the involvement of rapid signaling. Results of these studies revealed a fundamental difference in the mechanism of the response to E2. In normal cells, we found that a nongenomic, rapid E2 signaling pathway is predominantly involved, mediated by G protein-coupled receptor-30 and the subsequent activation of ERK1/2. In BPH-derived prostate stromal cells, a genomic pathway is predominantly involved because the addition of ICI 182780 was sufficient to abrogate any estrogenic effects. In conclusion, prostate stromal cells respond to far lower concentrations of E2 than previously recognized or examined, and this response is mediated through two distinct mechanisms, depending on its origin. This may provide the basis for new insights into the causes of, and possible treatments for, BPH.

Dopamine regulates the expression of the glutamate transporter GLT1 but not GLAST in developing striatal astrocytes

Dopamine and L: -glutamate are important signals which guide the development of functional neural circuits within the striatal complex. Disequilibrium of these neurotransmitter systems is believed to be etiological for the genesis of neurological and psychiatric diseases. Since dopamine plays a crucial role for the early transmitter-regulated differentiation of striatal GABAergic neurons, we emphasized that dopaminergic transmission may also be involved in the fine tuning of intra-striatal glutamate action. In this study, we report that dopamine decreases the expression of the glutamate transporter GLT1 but not GLAST in striatal astrocytes by measuring gene and protein expression. Using glutamate-uptake approaches, we demonstrate an increase in glutamate clearance of externally added glutamate in dopamine-treated cultures compared to controls. Our findings imply that dopamine regulates the availability of L: -glutamate in the developing striatum. It is also suggested that the application of dopaminergic drugs can interfere with ontogenetic processes within the striatal complex.

17beta-estradiol and progesterone prevent cuprizone provoked demyelination of corpus callosum in male mice

Sex hormones, for example, estrogen and progesterone, are thought to affect and delay progression of multiple sclerosis (MS) in pregnant women. Although both steroid hormones are neuroprotective in the brain and elevated during pregnancy, only estrogen was tested in clinical trials. To evaluate the role of 17beta-estradiol (E) and progesterone (P) in prevention demyelination, young adult male mice were fed with cuprizone for a defined time interval and simultaneously treated with steroids by repeated injections into the neck region. The status of myelination was analyzed by magnetic resonance imaging and conventional histological staining. The individual application of E and P resulted only in a moderate prevention of demyelination in the corpus callosum (CC). The combined treatment with both steroid hormones counteracted the process of demyelination. Expression of the mature (PLP and MBP) and premature (PDGF-alpha-R) oligodendrocyte markers were significantly increased after hormone application in the affected CC. In addition, both hormones stimulated astrogliosis and the expression of IGF-1. Microglial invasion in demyelinated CC was pronounced and additionally localized in the midline of CC after hormone treatment. These data show that sex steroids can protect the brain from demyelination and stimulate remyelination. It appears that only the administration of both hormones is fully effective. The beneficial steroid effect requires interactions with oligodendrocytes possibly by preventing their degeneration or recruitment from precursor cells which are stimulated to remyelinated fibers. The positive hormonal influence on myelination in the CNS may be a future therapeutically strategy for the treatment of MS.

Impact of sex steroids on neuroinflammatory processes and experimental multiple sclerosis

Synthetic and natural estrogens as well as progestins modulate neuronal development and activity. Neurons and glia are endowed with high-affinity steroid receptors. Besides regulating brain physiology, both steroids conciliate neuroprotection against toxicity and neurodegeneration. The majority of data derive from in vitro studies, although more recently, animal models have proven the efficaciousness of steroids as neuroprotective factors. Indications for a safeguarding role also emerge from first clinical trials. Gender-specific prevalence of degenerative disorders might be associated with the loss of hormonal activity or steroid malfunctions. Our studies and evidence from the literature support the view that steroids attenuate neuroinflammation by reducing the pro-inflammatory property of astrocytes. This effect appears variable depending on the brain region and toxic condition. Both hormones can individually mediate protection, but they are more effective in cooperation. A second research line, using an animal model for multiple sclerosis, provides evidence that steroids achieve remyelination after demyelination. The underlying cellular mechanisms involve interactions with astroglia, insulin-like growth factor-1 responses, and the recruitment of oligodendrocytes.

Interaction of estrogen receptor-alpha transactivation domain with nuclear proteins of mouse brain: p68 RNA helicase shows age- and sex-specific change

Estrogen receptor (ER)-alpha interacts with nuclear proteins to mediate its multiple functions in the brain. However, it is not known which proteins interact with the ERalpha-transactivation domain (TAD) in mouse brain and whether they change with age and sex. Therefore, we have used affinity-purified GST-tagged mouse ERalpha-TAD fusion protein for interaction with nuclear proteins from the mouse brain. The pull-down assay and far-Western blotting detected four nuclear proteins of 100, 80, 68, and 50 kD. We have recently identified the 80-kD protein as MTA1 and demonstrated its decrease in old age. Here we report alteration in the interaction and expression of the 68-kD protein of adult and old mice of both sexes. This protein was identified as p68 RNA helicase through NCBI database search, immunoprecipitation, and immunoblotting. Further analysis showed that the extent of its interaction was relatively lower in old mice of both sexes and in male mice of both ages compared with their counterparts. However, the expression of p68 was significantly lower in old males compared with adult males, although other groups did not show significant changes. Such age- and sex-specific interaction of p68 suggests its implication in ERalpha-mediated brain functions during aging.

Physiology of membrane oestrogen receptor signalling in reproduction

The best characterised oestrogen receptors (ERs) that are responsible for membrane-initiated oestradiol signalling are the classic ERs, ERalpha and ERbeta. When in the nucleus, these proteins are oestradiol activated transcription factors but, when trafficked to the cell membrane, ERalpha and ERbeta rapidly activate protein kinase pathways, alter membrane electrical properties, modulate ion flux and can mediate long-term effects through gene expression. To initiate cell signalling, membrane ERs transactivate metabotropic glutamate receptors (mGluRs) to stimulate Gq signalling through pathways using PKC and calcium. In this review, we discuss the interaction of membrane ERalpha with metabotropic glutamate receptor 1a (mGluR1a) to initiate rapid oestradiol cell signalling and its critical roles in female reproduction: sexual behaviour and oestrogen positive feedback of the luteinising hormone (LH) surge. Although long considered to be regulated by the long-term actions of oestradiol on gene transcription, recent results indicate that membrane oestradiol cell signalling is vital for a full display of sexual receptivity. Similarly, the source of pre-ovulatory progesterone necessary for initiating the LH surge is hypothalamic astrocytes. Oestradiol rapidly amplifies progesterone synthesis through the release of intracellular calcium stores. The ERalpha-mGluR1a interaction is necessary for critical calcium flux. These two examples provide support for the hypothesis that membrane ERs are not themselves G-protein receptors; rather, they use mGluRs to signal.