Estradiol protects against ischemic injury

The cerebellum as a target for estrogen action

This review focuses on the effects of estrogens upon the cerebellum, a brain region long ignored as a site of estrogen action. Highlighted are the diverse effects of estradiol within the cerebellum, emphasizing the importance of estradiol signaling in cerebellar development, modulation of synaptic neurotransmission in the adult, and the potential influence of estrogens on various health and disease states. We also provide new data, consistent with previous studies, in which locally synthesized estradiol modulates cerebellar glutamatergic neurotransmission, providing one underlying mechanism by which the actions of estradiol can affect this brain region.

Neuroprotection and estrogen receptors

This review is intended to assess the state of current knowledge on the role of estrogen receptors (ERs) in the neuroprotective effects of estrogens in models for acute neuronal injury and death. We evaluate the overall evidence that estrogens are neuroprotective in acute injury and critically assess the role of ERα, ERβ, GPR 30, and nonreceptor-mediated mechanisms in these robust neuroprotective effects of this ovarian steroid hormone. We conclude that all three receptors, as well as nonreceptor-mediated mechanisms can be involved in neuroprotection, depending on the model used, the level of estrogen administrated, and the mode of administration of the steroid. Also, the signaling pathways used by both ER-dependent and ER-independent mechanisms to exert neuroprotection are considered. Finally, further studies that are needed to parse out the relative contribution of receptor versus nonreceptor-mediated signaling are discussed.

Estrogen and neuroprotection: from clinical observations to molecular mechanisms

We now appreciate that estrogen is a pleiotropic gonadal steroid that exerts profound effects on the plasticity and cell survival of the adult brain. Over the past century, the life span of women has increased, but the age of the menopause remains constant. This means that women may now live over one third of their lives in a hypoestrogenic, postmenopausal state. The impact of prolonged hypoestrogenicity on the brain is now a critical health concern as we realize that these women may suffer an increased risk of cognitive dysfunction and neurodegeneration due to a variety of diseases. Accumulating evidence from both clinical and basic science studies indicates that estrogen exerts critical protective actions against neurodegenerative conditions such as Alzheimer's disease and stroke. Here, we review the discoveries that comprise our current understanding of estrogen action against neurodegeneration. These findings carry far-reaching possibilities for improving the quality of life in our aging population.

Blood glutamate scavenging: insight into neuroprotection

Brain insults are characterized by a multitude of complex processes, of which glutamate release plays a major role. Deleterious excess of glutamate in the brain's extracellular fluids stimulates glutamate receptors, which in turn lead to cell swelling, apoptosis, and neuronal death. These exacerbate neurological outcome. Approaches aimed at antagonizing the astrocytic and glial glutamate receptors have failed to demonstrate clinical benefit. Alternatively, eliminating excess glutamate from brain interstitial fluids by making use of the naturally occurring brain-to-blood glutamate efflux has been shown to be effective in various animal studies. This is facilitated by gradient driven transport across brain capillary endothelial glutamate transporters. Blood glutamate scavengers enhance this naturally occurring mechanism by reducing the blood glutamate concentration, thus increasing the rate at which excess glutamate is cleared. Blood glutamate scavenging is achieved by several mechanisms including: catalyzation of the enzymatic process involved in glutamate metabolism, redistribution of glutamate into tissue, and acute stress response. Regardless of the mechanism involved, decreased blood glutamate concentration is associated with improved neurological outcome. This review focuses on the physiological, mechanistic and clinical roles of blood glutamate scavenging, particularly in the context of acute and chronic CNS injury. We discuss the details of brain-to-blood glutamate efflux, auto-regulation mechanisms of blood glutamate, natural and exogenous blood glutamate scavenging systems, and redistribution of glutamate. We then propose different applied methodologies to reduce blood and brain glutamate concentrations and discuss the neuroprotective role of blood glutamate scavenging.

17β-Estradiol inhibits apoptotic cell death of oligodendrocytes by inhibiting RhoA-JNK3 activation after spinal cord injury

A delayed oligodendrocyte cell death after spinal cord injury (SCI) contributes to chronic demyelination of spared axons, leading to a permanent neurological deficit. Therefore, therapeutic approaches to prevent oligodendrocyte cell death after SCI should be considered. Estrogens are well known to have a broad neuroprotective effect, but the protective effect of estrogens on oligodendrocytes after injury is largely unknown. Here, we demonstrated that 17β-estradiol attenuates apoptosis of oligodendrocytes by inhibiting RhoA and c-Jun-N-terminal kinase activation after SCI. Estrogen receptor (ER)-α and -β were expressed in oligodendrocytes of the spinal cord, and 17β-estradiol treatment significantly inhibited oligodendrocyte cell death at 7 d after injury as compared with vehicle (cyclodextrin) control. 17β-Estradiol also attenuated caspase-3 and -9 activation at 7 d and reduced the loss of axons from progressive degeneration. In addition, 17β-estradiol inhibited RhoA and JNK3 activation, which were activated and peaked at 3 and/or 5 d after injury. Furthermore, administration of Rho inhibitor, PEP-1-C3 exoenzyme, inhibited RhoA and JNK3 activation, and decreased phosphorylated c-Jun level at 5 d after injury. Additionally, the attenuation of RhoA and JNK3 activation as well as oligodendrocyte cell death by 17β-estradiol was reversed by ER antagonist, ICI182780. Our results thus indicate that 17β-estradiol treatment improves functional recovery after SCI in part by reducing oligodendrocyte cell death via inhibition of RhoA and JNK3 activation, which were ER dependent. Furthermore, improvement of hindlimb motor function by posttreatment of 17β-estradiol suggests its potential as a therapeutic agent for SCI patients.

Neuroprotective effects of nonfeminizing estrogens in retinal photoreceptor neurons

PURPOSE

Retinal diseases such as macular degeneration and glaucoma are disorders that target specific retinal neurons that can ultimately lead to vision loss. Under these conditions and pathologies, retinal neurons can die via apoptosis that may be due to increased oxidative stress. The neuroprotective effects of 17β-estradiol (E2) and three synthetic nonfeminizing estrogen analogs (ZYC-26, ZYC-23, and ZYC-3) were investigated to examine their abilities to protect retinal neurons against glutamate toxicity.

METHODS

Using an in vitro model of glutamate-induced cell death in 661W cells, a mouse cone photoreceptor cell line, shown to express both estrogen receptors (ERs) via immunoblotting, was pretreated with E2 and its analogs and cell viability were assessed.

RESULTS

It was observed that E2 and estrogen analogs, ZYC-26 and ZYC-3, were protective against a 5 mM glutamate insult in 661W cells. The neuroprotective abilities of ZYC-26 and ZYC-3 were autonomous of estrogen receptor-α (ERα) and ERβ demonstrated by their ability to protect in the presence of ICI 182780, a pan-ER antagonist with a high affinity for the estrogen receptor. Treatment with PPT and DPN, ERα- and ERβ-specific agonists, respectively, did not protect the 661W cells from the glutamate insult. Studying the membrane ER (mER) or GPR30 did show that activation of the receptor by G1 protected the retinal neuron from insult, whereas G15, an antagonist of the mER was not able to antagonize the protection previously seen.

CONCLUSIONS

These data demonstrate that nonfeminizing estrogens may emerge as useful compounds for neuroprotection of retinal cells.

Post-ischemic estradiol treatment reduced glial response and triggers distinct cortical and hippocampal signaling in a rat model of cerebral ischemia

BACKGROUND

Estradiol has been shown to exert neuroprotective effects in several neurodegenerative conditions, including cerebral ischemia. The presence of this hormone prior to ischemia attenuates the damage associated with such events in a rodent model (middle cerebral artery occlusion (MCAO)), although its therapeutic value when administered post-ischemia has not been assessed. Hence, we evaluated the effects of estradiol treatment after permanent MCAO (pMCAO) was induced in rats, studying the PI3K/AKT/GSK3/β-catenin survival pathway and the activation of SAPK-JNK in two brain areas differently affected by pMCAO: the cortex and hippocampus. In addition, we analyzed the effect of estradiol on the glial response to injury.

METHODS

Male rats were subjected to pMCAO and estradiol (0.04 mg/kg) was administered 6, 24, and 48 h after surgery. The animals were sacrificed 6 h after the last treatment, and brain damage was evaluated by immunohistochemical quantification of 'reactive gliosis' using antibodies against GFAP and Iba1. In addition, Akt, phospho-Akt(Ser473), phospho-Akt(Thr308), GSK3, phospho-GSK3(Ser21/9), β-catenin, SAPK-JNK, and pSAPK-JNK(Thr183/Tyr185) levels were determined in western blots of the ipsilateral cerebral cortex and hippocampus, and regional differences in neuronal phospho-Akt expression were determined by immunohistochemistry.

RESULTS

The increases in the percentage of GFAP- (5.25-fold) and Iba1- (1.8-fold) labeled cells in the cortex and hippocampus indicate that pMCAO induced 'reactive gliosis'. This effect was prevented by post-ischemic estradiol treatment; diminished the number of these cells to those comparable with control animals. pMCAO down-regulated the PI3K/AkT/GSK3/β-catenin survival pathway to different extents in the cortex and hippocampus, the activity of which was restored by estradiol treatment more efficiently in the cerebral cortex (the most affected region) than in the hippocampus. No changes in the phosphorylation of SAPK-JNK were observed 54 h after inducing pMCAO, whereas pMCAO did significantly decrease the phospho-Akt(Ser473) in neurons, an effect that was reversed by estradiol.

CONCLUSION

The present study demonstrates that post-pMCAO estradiol treatment attenuates ischemic injury in both neurons and glia, events in which the PI3K/AKT/GSK3/β-catenin pathway is at least partly involved. These findings indicate that estradiol is a potentially useful treatment to enhance recovery after human ischemic stroke.

Worsened outcome from middle cerebral artery occlusion in aged rats receiving 17β-estradiol

Although estrogens are neuroprotective in young adult animal models of stroke, clinical trials demonstrate that estrogens increase the incidence and severity of stroke in aged women. We have previously shown that experimental stroke pathophysiology differs between young adult and aged rats. The aim of this study was to determine the effects of 17β-estradiol after middle cerebral artery occlusion and reperfusion in young adult and aged female rats. Focal embolic stroke was performed by middle cerebral artery occlusion with fibrin clot followed by reperfusion with i.v. human recombinant tissue plasminogen activator. Histological and functional outcomes were measured at 24 h after middle cerebral artery occlusion with fibrin clot. Aged rats treated with 17β-estradiol had significantly increased infarct volumes compared with placebo-treated aged rats. Young adult rats treated with 17β-estradiol had significantly decreased infarct volumes and improved functional outcome compared with ovariectomized young adult rats. Our results suggest that 17β-estradiol may act in an age-dependent manner in the postischemic rat brain. In young adult rats, it is neuroprotective; chronic treatment with 17β-estradiol during aging leads to worsened ischemic brain injury in aged female rats.

Age-related severity of focal ischemia in female rats is associated with impaired astrocyte function

In middle-aged female rats, focal ischemia leads to a larger cortical infarction as compared with younger females. To determine if stroke-induced cytotoxicity in middle-aged females was associated with impaired astrocyte function, astrocytes were harvested and cultured from the ischemic cortex of young and middle-aged female rats. Middle-aged astrocytes cleared significantly less glutamate from media as compared with young female astrocytes. Furthermore, astrocyte-conditioned media from middle-aged female astrocytes induced greater migration of peripheral blood monocyte cells (PBMCs) and expressed higher levels of the chemoattractant macrophage inflammatory protein-1 (MIP-1). Middle-aged astrocytes also induced greater migration of neural progenitor cells (NPCs), however, their ability to promote neuronal differentiation of neural progenitor cells was similar to young astrocytes. In males, where cortical infarct volume is similar in young and middle-aged animals, no age-related impairment was observed in astrocyte function. These studies show that the aging astrocyte may directly contribute to infarct severity by inefficient glutamate clearance and enhanced cytokine production and suggest a cellular target for improved stroke therapy among older females.

17β-Estradiol prevents cell death and mitochondrial dysfunction by an estrogen receptor-dependent mechanism in astrocytes after oxygen-glucose deprivation/reperfusion

17β-Estradiol (E2) has been shown to protect against ischemic brain injury, yet its targets and the mechanisms are unclear. E2 may exert multiple regulatory actions on astrocytes that may greatly contribute to its ability to protect the brain. Mitochondria are recognized as playing central roles in the development of injury during ischemia. Increasing evidence indicates that mitochondrial mechanisms are critically involved in E2-mediated protection. In this study, the effects of E2 and the role of mitochondria were evaluated in primary cultures of astrocytes subjected to an ischemia-like condition of oxygen-glucose deprivation (OGD)/reperfusion. We showed that E2 treatment significantly protects against OGD/reperfusion-induced cell death as determined by cell viability, apoptosis, and lactate dehydrogenase leakage. The protective effects of E2 on astrocytic survival were blocked by an estrogen receptor (ER) antagonist (ICI-182,780) and were mimicked by an ER agonist selective for ERα (PPT), but not by an ER agonist selective for ERβ (DPN). OGD/reperfusion provoked mitochondrial dysfunction as manifested by an increase in cellular reactive oxygen species production, loss of mitochondrial membrane potential, and depletion of ATP. E2 pretreatment significantly inhibited OGD/reperfusion-induced mitochondrial dysfunction, and this effect was also blocked by ICI-182,780. Therefore, we conclude that E2 provides direct protection to astrocytes from ischemic injury by an ER-dependent mechanism, highlighting an important role for ERα. Estrogen protects against mitochondrial dysfunction at the early phase of ischemic injury. However, overall implications for protection against brain ischemia and its complex sequelae await further exploration.

An antagomir to microRNA Let7f promotes neuroprotection in an ischemic stroke model

We previously showed that middle-aged female rats sustain a larger infarct following experimental stroke as compared to younger female rats, and paradoxically, estrogen treatment to the older group is neurotoxic. Plasma and brain insulin-like growth factor-1 (IGF-1) levels decrease with age. However, IGF-1 infusion following stroke, prevents estrogen neurotoxicity in middle-aged female rats. IGF1 is neuroprotective and well tolerated, but also has potentially undesirable side effects. We hypothesized that microRNAs (miRNAs) that target the IGF-1 signaling family for translation repression could be alternatively suppressed to promote IGF-1-like neuroprotection. Here, we report that two conserved IGF pathway regulatory microRNAs, Let7f and miR1, can be inhibited to mimic and even extend the neuroprotection afforded by IGF-1. Anti-mir1 treatment, as late as 4 hours following ischemia, significantly reduced cortical infarct volume in adult female rats, while anti-Let7 robustly reduced both cortical and striatal infarcts, and preserved sensorimotor function and interhemispheric neural integration. No neuroprotection was observed in animals treated with a brain specific miRNA unrelated to IGF-1 (anti-miR124). Remarkably, anti-Let7f was only effective in intact females but not males or ovariectomized females indicating that the gonadal steroid environment critically modifies miRNA action. Let7f is preferentially expressed in microglia in the ischemic hemisphere and confirmed in ex vivo cultures of microglia obtained from the cortex. While IGF-1 was undetectable in microglia harvested from the non-ischemic hemisphere, IGF-1 was expressed by microglia obtained from the ischemic cortex and was further elevated by anti-Let7f treatment. Collectively these data support a novel miRNA-based therapeutic strategy for neuroprotection following stroke.

Estradiol protects against hippocampal damage and impairments in fear conditioning resulting from transient global ischemia in mice

Estradiol protects against hippocampal damage and some learning impairments resulting from transient global ischemia in rats. Here, we seek to validate a mouse model of transient global ischemia and evaluate the effects of estradiol on ischemia-induced hippocampal damage and behavioral impairments. Female C57Bl6/J mice were ovariectomized and implanted with estradiol- or oil-secreting capsules. One week later, mice experienced 15-min of 2-vessel occlusion (2-VO) or sham surgical procedures. Five days later, mice were exposed to a fear conditioning protocol in which a specific context and novel tone were paired with mild footshock. Twenty-four hours following conditioning, contextual fear was assessed by measuring freezing behavior in the conditioned context (in the absence of the tone). This was followed by assessment of cue fear by measuring freezing behavior to the conditioned tone presented in a new context. When tested in the conditioned context, oil-treated mice that experienced 2-VO exhibited a significant reduction in freezing behavior whereas estradiol-treated mice that experienced 2-VO showed no disruption in freezing behavior. Freezing behavior when presented with the conditioned tone was unaffected by either surgery or hormone treatment. These findings suggest that global ischemia causes impairments in performance on the hippocampally-dependent contextual fear task but not conditioned cue-based fear. Furthermore, estradiol prevented the ischemia-induced impairment in contextual fear conditioning. Fluoro-Jade (FJ) staining revealed neuronal degeneration throughout the dorsal hippocampus of mice that experienced 2-VO. Estradiol treatment reduced the number of FJ+ cells in CA1 and CA2, but not in CA3 or in the dentate gyrus. Together, these findings suggest that 15 min of global ischemia causes extensive hippocampal neurodegeneration and disrupts contextual fear conditioning processes in mice and that estradiol protects against these adverse effects.

Estrogen receptors and type 1 metabotropic glutamate receptors are interdependent in protecting cortical neurons against β-amyloid toxicity

We examined the interaction between estrogen receptors (ERs) and type 1 metabotropic glutamate receptors (mGlu1 receptors) in mechanisms of neurodegeneration/neuroprotection using mixed cultures of cortical cells challenged with β-amyloid peptide. Both receptors were present in neurons, whereas only ERα but not mGlu1 receptors were found in astrocytes. Addition of 17β-estradiol (17βE2) protected cultured neurons against amyloid toxicity, and its action was mimicked by the selective ERα agonist, 1,3,5-tris(4-hydroxyphenyl)-4-propyl-1H-pyrazole (PPT) as well as by a cell-impermeable bovine serum albumin conjugate of 17βE2. The selective ERβ agonist, diarylpropionitrile (DPN), was only slightly neuroprotective. The mGlu1/5 receptor agonist, 3,5-dihydroxyphenylglycine (DHPG), was also neuroprotective against amyloid toxicity, and its action was abolished by the mGlu1 receptor antagonist, (3,4-dihydro-2H-pyrano[2,3-b]quinolin-7-yl)-(cis-4-methoxycyclohexyl)-methanone (JNJ 16259685). Neuroprotection by 17βΕ2 or PPT (but not DPN) and DHPG was less than additive, suggesting that ERα and mGlu1 receptors activate the same pathway of cell survival. More important, neuroprotection by 17βΕ2 was abolished not only by the ER antagonist fulvestrant (ICI 182,780) but also by JNJ 16259685, and neuroprotection by DHPG was abolished by ICI 182,780. ERα and mGlu1 receptors were also interdependent in activating the phosphatidylinositol-3-kinase pathway, and pharmacological blockade of this pathway abolished neuroprotection by 17βE2, DHPG, or their combination. These data provide the first evidence that ERα and mGlu1 receptors critically interact in promoting neuroprotection, information that should be taken into account when the impact of estrogen on neurodegeneration associated with central nervous system disorders is examined.

Estrogen neuroprotection and the critical period hypothesis

17β-Estradiol (estradiol or E2) is implicated as a neuroprotective factor in a variety of neurodegenerative disorders. This review focuses on the mechanisms underlying E2 neuroprotection in cerebral ischemia, as well as emerging evidence from basic science and clinical studies, which suggests that there is a "critical period" for estradiol's beneficial effect in the brain. Potential mechanisms underlying the critical period are discussed, as are the neurological consequences of long-term E2 deprivation (LTED) in animals and in humans after natural menopause or surgical menopause. We also summarize the major clinical trials concerning postmenopausal hormone therapy (HT), comparing their outcomes with respect to cardiovascular and neurological disease and discussing their relevance to the critical period hypothesis. Finally, potential caveats, controversies and future directions for the field are highlighted and discussed throughout the review.

Expression of Estrogen Receptor α and β in Rat Astrocytes in Primary Culture: Effects of Hypoxia and Glucose Deprivation

Estrogen replacement therapy could play a role in the reduction of injury associated with cerebral ischemia in vivo, which could be, at least partially, a consequence of estrogen influence of glutamate buffering by astrocytes during hypoxia/ischemia. Estrogen exerts biological effects through interaction with its two receptors: estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ), which are both expressed in astrocytes. This study explored effects of hypoxia and glucose deprivation (HGD), alone or followed by 1 h recovery, on ERα and ERβ expression in primary rat astrocyte cultures following 1 h exposure to: a) 5 % CO2 in air (control group-CG); b) 2 % O2/5 % CO2 in N2 with glucose deprivation (HGD group-HGDG); or c) the HGDG protocol followed by 1 h CG protocol (recovery group-RG). ERα mRNA expression decreased in HGDG. At the protein level, full-length ERα (67 kDa) and three ERα-immunoreactive protein bands (63, 60 and 52 kDa) were detected. A significant decrease in the 52 kDa band was seen in HGDG, while a significant decrease in expression of the full length ERα was seen in the RG. ERβ mRNA and protein expression (a 54 kDa single band) did not change. The observed decrease in ERα protein may limit estrogen-mediated signalling in astrocytes during hypoxia and recovery.

Effect of estrogens on blood glutamate levels in relation to neurological outcome after TBI in male rats

PURPOSE

Estrogen has been shown to possess neuroprotective properties both in vitro and in vivo. Traumatic brain injury (TBI) in ovulating females results in favorable neurological outcomes when compared to males with similar insults. The brain-to-blood glutamate gradient removes excess glutamate from brain extracellular fluids (ECF). Enhancing this gradient leads to improved neurological outcomes following TBI. In this study we investigate the effect of female gonadal steroids on blood glutamate levels and neurological outcomes.

METHODS

Forty male Sprague-Dawley rats were assigned to one of five groups: (1) sham, (2) Premarin treatment, (3) TBI, (4) TBI + Premarin treatment, and (5) TBI + Premarin pretreatment. TBI was induced, and estrogen and glutamate levels were determined at 0, 60, 120, 135, and 150 min. Neurological recovery was evaluated using the Neurological Severity Score (NSS) at 1 h and reassessed at 24 h post TBI.

RESULTS

Premarin treatment groups demonstrated a decline in blood glutamate levels by 60 min. This decline was found to be more pronounced in the TBI + Premarin group, which maintained the decline throughout the experiment. At 120 min, the difference between groups was most pronounced (TBI + Premarin 99 ± 36 μM/l vs. control 200 ± 46 μM/l, p < 0.01). Neurological recovery was significantly better in the Premarin treatment group (NSS at 24 h 6 ± 1 vs. control 11 ± 1).

CONCLUSIONS

Premarin injected into male rats significantly decreases blood glutamate levels in rats suffering TBI. This decrease is associated with improved neurological outcomes, thus implicating the role of estrogen in neuroprotection.

The potential for estrogens in preventing Alzheimer's disease and vascular dementia

Estrogens are the best-studied class of drugs for potential use in the prevention of Alzheimer's disease (AD). These steroids have been shown to be potent neuroprotectants both in vitro and in vivo, and to exert effects that are consistent with their potential use in prevention of AD. These include the prevention of the processing of amyloid precursor protein (APP) into beta-amyloid (Aß), the reduction in tau hyperphosphorylation, and the elimination of catastrophic attempts at neuronal mitosis. Further, epidemiological data support the efficacy of early postmenopausal use of estrogens for the delay or prevention of AD. Collectively, this evidence supports the further development of estrogen-like compounds for prevention of AD. Several approaches to enhance brain specificity of estrogen action are now underway in an attempt to reduce the side effects of chronic estrogen therapy in AD.

Estradiol suppresses recovery of REM sleep following sleep deprivation in ovariectomized female rats

Sleep complaints such as insufficient sleep and insomnia are twice as prevalent in women. Symptoms of sleep disruption are often coincident with changes in the gonadal hormone profile across a women's lifespan. Data from a number of different species, including humans, non-human primates and rodents strongly implicate a role for gonadal hormones in the modulation of sleep. In female rats, increased levels of circulating estradiol increase wakefulness and reduce sleep in the dark phase. In this study, we asked whether this reduction in sleep is driven by estradiol-dependent reduction in sleep need during the dark phase by assessing sleep before and after sleep deprivation (SD). Ovariectomized rats implanted with EEG telemetry transmitters were given Silastic capsules containing either 17-β estradiol in sesame oil (E2) or sesame oil alone. After a 24-hour baseline, animals were sleep-deprived via gentle handling for the entire 12-hour light phase, and then allowed to recover. E2 treatment suppressed baseline REM sleep duration in the dark phase, but not NREM or Wake duration, within three days. While SD induced a compensatory increase in REM duration in both groups, this increase was smaller in E2-treated rats compared to oils, as measured in absolute duration as well as by relative increase over baseline. Thus, E2 suppressed REM sleep in the dark phase both before and after SD. E2 also suppressed NREM and increased waking in the early- to mid-dark phase on the day after SD. NREM delta power tracked NREM sleep before and after SD, with small hormone-dependent reductions in delta power in recovery, but not spontaneous sleep. These results demonstrate that E2 powerfully and specifically suppresses spontaneous and recovery REM sleep in the dark phase, and suggest that ovarian steroids may consolidate circadian sleep-wake rhythms.

Investigation of the temperature stability of premarin intravenous using liquid chromatography-mass spectrometry

Stability of Premarin(®)Intravenous was investigated in dry and reconstituted forms by monitoring major components in samples for a period of six months, using liquid chromatography-mass spectrometry. The components, largely comprising a series of estrogen and steroid hormone sulfates, were considered to be fairly stable (variation≤10%) for dry samples stored at room temperature and at 38°C (100°F) during the experimental time frame. However, significant variation, especially after 2 months of storage, was observed in reconstituted solutions. This variation was significantly larger for samples stored at elevated vs. room temperature. It was interesting to note that the concentration of equilenin sulfate increased over time, whereas that of other major components were seen to fluctuate and decrease. This phenomenon was partially explained by the conversion of equilin compounds into their corresponding equilenin forms, a phenomenon which was further investigated through a storage study with pure standard solutions and by tandem mass spectrometry.

Effects of estradiol on ischemic factor-induced astrocyte swelling and AQP4 protein abundance

In the early hours of ischemic stroke, cerebral edema forms as Na, Cl, and water are secreted across the blood-brain barrier (BBB) and astrocytes swell. We have shown previously that ischemic factors, including hypoxia, aglycemia, and arginine vasopressin (AVP), stimulate BBB Na-K-Cl cotransporter (NKCC) and Na/H exchanger (NHE) activities and that inhibiting NKCC and/or NHE by intravenous bumetanide and/or HOE-642 reduces edema and infarct in a rat model of ischemic stroke. Estradiol also reduces edema and infarct in this model and abolishes ischemic factor stimulation of BBB NKCC and NHE. There is evidence that NKCC and NHE also participate in ischemia-induced swelling of astrocytes. However, little is known about estradiol effects on astrocyte cell volume. In this study, we evaluated the effects of AVP (100 nM), hypoxia (7.5% O(2)), aglycemia, hypoxia (2%)/aglycemia [oxygen glucose deprivation (OGD)], and estradiol (1-100 nM) on astrocyte cell volume using 3-O-methyl-d-[(3)H]glucose equilibration methods. We found that AVP, hypoxia, aglycemia, and OGD (30 min to 5 h) each significantly increased astrocyte cell volume, and that estradiol (30-180 min) abolished swelling induced by AVP or hypoxia, but not by aglycemia or OGD. Bumetanide and/or HOE-642 also abolished swelling induced by AVP but not aglycemia. Abundance of aquaporin-4, known to participate in ischemia-induced astrocyte swelling, was significantly reduced following 7-day but not 2- or 3-h estradiol exposures. Our findings suggest that hypoxia, aglycemia, and AVP each contribute to ischemia-induced astrocyte swelling, and that the edema-attenuating effects of estradiol include reduction of hypoxia- and AVP-induced astrocyte swelling and also reduction of aquaporin-4 abundance.

Decrease of Tau hyperphosphorylation by 17β estradiol requires sphingosine kinase in a glutamate toxicity model

Several studies have linked estrogens with sphingosine kinase (SphK) activity, enzyme responsible of sphingosine-1-phosphate synthesis (S-1P), however their possible interaction in the nervous system is not documented yet. In the present study, we developed a glutamate toxicity model in SH-SY5Y cells to evaluate the possible effect of the inhibition of SphK activity on the protective capability of 17β-estradiol (E2). Glutamate induced cytoskeletal actin changes associated to cytotoxic stress, significant increase of apoptotic-like nuclear fragmentation, Tau hyperphosphorylation and increase of p25/p35 cleavage. These effects were prevented by E2 pre-treatment during 24 h. Although the inhibition of SphK did not block this protective effect, significantly increased Tau hyperphosphorylation by glutamate, in a way that was not reverted by E2. Our results suggest that the decrease of glutamate-induced Tau hyperphosphorylation by 17β-estradiol requires SphK.

Biologic and plastic effects of experimental traumatic brain injury treatment paradigms and their relevance to clinical rehabilitation

Neuroplastic changes, whether induced by traumatic brain injury (TBI) or therapeutic interventions, alter neurobehavioral outcome. Here we present several treatment strategies that have been evaluated by using experimental TBI models and discuss potential mechanisms of action (ie, plasticity) and how such changes affect function.

Potential age-dependent effects of estrogen on neural injury

In 2000, approximately 10 million women were receiving hormone replacement therapy (HRT) for alleviation of menopausal symptoms. A number of prior animal studies suggested that HRT may be neuroprotective and cardioprotective. Then, in 2003, reports from the Women's Health Initiative (WHI) indicated that long-term estrogen/progestin supplementation led to increased incidence of stroke. A second branch of the WHI in women with prior hysterectomy found an even stronger correlation between estrogen supplementation alone and stroke incidence. Follow-up analyses of the data, as well as data from other smaller clinical trials, have also demonstrated increased stroke severity in women receiving HRT or estrogen alone. This review examines the studies indicating that estrogen is neuroprotectant in animal models and explores potential reasons why this may not be true in postmenopausal women. Specifically, age-related differences in estrogen receptors and estrogenic actions in the brain are discussed, with the conclusion that animal models of disease must closely mimic human disease to produce clinically relevant results.

Sexual dimorphism in ischemic stroke: lessons from the laboratory

Ischemic stroke is emerging as a major health problem for elderly women. Women have lower stroke incidence than men until an advanced age, when the epidemiology of ischemic stroke shifts and incidence rises dramatically in women. Experimental models of rodent stroke have replicated this clinical epidemiology, with exacerbated injury in older compared with young female rodents. Many of the detrimental effects of aging on ischemic stroke outcome in females can be replicated by ovariectomy, suggesting that hormones such as estrogen play a neuroprotective role. However, emerging data suggest that the molecular mechanisms leading to ischemic cell death differ in the two sexes, and these effects may be independent of circulating hormone levels. This article highlights recent clinical and experimental literature on sex differences in stroke outcomes and mechanisms.

The assessment of non-feminizing estrogens for use in neuroprotection

Menopause is associated with a precipitous decline in circulating estrogens and a resulting loss of the neuroprotective actions of this steroid hormone. In view of the results of the Women's Health Initiative and the preceding knowledge that orally administered estrogens has a variety of adverse side effects, likely through actions on peripheral estrogen receptor alpha (ERα), we initiated a program of research to synthesis and assess a group of non-feminizing estrogens that lack ability to interact with ERs but retain much of the neuroprotective action of feminizing estrogens. This program of research is aimed at the identification of compounds which do not stimulate ERs but are potentially neuroprotective in vitro and in animal models of neuronal cell death. We discovered that the most effective non-feminizing estrogens were those with large bulky groups in the 2 and/or 4 carbon of the phenolic A ring of the steroid. These compounds were 8- to 114-fold more potent than 17 β-estradiol (βE2), but lacked ER binding capacity in vitro and feminizing effects in vivo. The success of this program of research suggests that strategies to optimize non-feminizing estrogens for use in postmenopausal women can be successful.

Estrogen protection against mitochondrial toxin-induced cell death in hippocampal neurons: antagonism by progesterone

Previously we demonstrated that mitochondrial dysfunction plays a critical role in the pathogenesis of Alzheimer's disease. Further, we have shown that the neuroprotective effects of 17β-estradiol (E2) are dependent upon mitochondrial function. In the current study, we sought to identify mitochondrial sites of E2 action that mediate neuroprotection by assessing the efficacy of E2 to protect neurons against inhibitors of mitochondrial respiration which target specific complexes within the respiratory chain. Subsequently, the impact of progesterone (P4) on E2-induced prevention against mitochondrial toxins was investigated. Mitochondrial inhibitors, rotenone, 3-NPA, antimycin, KCN, and oligomycin, exhibited concentration dependent toxicity in primary hippocampal neurons. The concentration inducing 30% cell death (LD30) was selected for analyses assessing the neuroprotective efficacy of ovarian hormones (E2 and P4). Pretreatment of hippocampal neurons with E2 significantly protected against 3-NPA (7.5mM) and antimycin (125 μM) induced cell death and was moderately neuroprotective against rotenone (3 μM). E2 was ineffective against KCN and oligomycin-induced cell death. Pretreatment with P4 was without effect against these mitochondrial inhibitors. Co-administration of P4 with E2 abolished E2 induced neuroprotection against 3-NPA and antimycin. Additional metabolic analyses indicated that E2 and P4 separately increased mitochondrial respiratory capacity whereas the co-administration of E2 and P4 resulted in diminished mitochondrial respiration. These findings indicate that E2 protects against mitochondrial toxins that target complexes I, II and III whereas P4 was without effect. The data also predict that continuous combined co-administration of estrogen and progesterone common to many hormone therapy regimens is unlikely to prevent the deficits in mitochondrial function.

Estrogen receptor-alpha gene expression in the cortex: sex differences during development and in adulthood

17β-estradiol is a hormone with far-reaching organizational, activational and protective actions in both male and female brains. The organizational effects of early estrogen exposure are essential for long-lasting behavioral and cognitive functions. Estradiol mediates many of its effects through the intracellular receptors, estrogen receptor-alpha (ERα) and estrogen receptor-beta (ERβ). In the rodent cerebral cortex, estrogen receptor expression is high early in postnatal life and declines dramatically as the animal approaches puberty. This decline is accompanied by decreased expression of ERα mRNA. This change in expression is the same in both males and females in the developing isocortex and hippocampus. An understanding of the molecular mechanisms involved in the regulation of estrogen receptor alpha (ERα) gene expression is critical for understanding the developmental, as well as changes in postpubertal expression of the estrogen receptor. One mechanism of suppressing gene expression is by the epigenetic modification of the promoter regions by DNA methylation that results in gene silencing. The decrease in ERα mRNA expression during development is accompanied by an increase in promoter methylation. Another example of regulation of ERα gene expression in the adult cortex is the changes that occur following neuronal injury. Many animal studies have demonstrated that the endogenous estrogen, 17β-estradiol, is neuroprotective. Specifically, low levels of estradiol protect the cortex from neuronal death following middle cerebral artery occlusion (MCAO). In females, this protection is mediated through an ERα-dependent mechanism. ERα expression is rapidly increased following MCAO in females, but not in males. This increase is accompanied by a decrease in methylation of the promoter suggesting a return to the developmental program of gene expression within neurons. Taken together, during development and in adulthood, regulation of ERα gene expression in the cortex can occur by DNA methylation and in a sex-dependent fashion in the adult brain.

Chronic estradiol exposure induces oxidative stress in the hypothalamus to decrease hypothalamic dopamine and cause hyperprolactinemia

Estrogens are known to cause hyperprolactinemia, most probably by acting on the tuberoinfundibular dopaminergic (TIDA) system of the hypothalamus. Dopamine (DA) produced by TIDA neurons directly inhibits prolactin secretion and, therefore, to stimulate prolactin secretion, estrogens inhibit TIDA neurons to decrease DA production. However, the mechanism by which estrogen produces this effect is not clear. In the present study, we used a paradigm involving chronic exposure to low levels of estradiol-17β (E(2)) to mimic prolonged exposures to environmental and endogenous estrogens. We hypothesized that chronic exposure to low levels of E(2) induces oxidative stress in the arcuate nucleus (AN) of the hypothalamus that contains TIDA neurons and causes nitration of tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of DA. This results in a significant decrease in DA and consequently, hyperprolactinemia. To investigate this, adult, intact female cycling rats were implanted with slow-release E(2) pellets (20 ng/day) for 30, 60, or 90 days and were compared with old (16-18 mo old) constant estrous (OCE) rats. Chronic E(2) exposure significantly increased the expression of glial fibrillary acidic protein and the concentrations of interleukin-1β (IL-1β) and nitrate in the AN that contains perikarya of TIDA neurons and increased nitration of TH in the median eminence (ME) that contains the terminals. These levels were comparable to those seen in OCE rats. We observed a significant decrease in DA concentrations in the ME and hyperprolactinemia in an exposure-dependent manner similar to that seen in OCE rats. It was concluded that chronic exposure to low levels of E(2) evokes oxidative stress in the AN to inhibit TIDA neuronal function, most probably leading to hyperprolactinemia.

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

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

Effects of estrogens and endocrine-disrupting chemicals on cell differentiation-survival-proliferation in brain: contributions of neuronal cell lines

Estrogens and estrogen receptors (ER) are key actors in the control of differentiation and survival and act on extrareproductive tissues such as brain. Thus, estrogens may display neuritogenic effects during development and neuroprotective effects in the pathophysiological context of brain ischemia and neurodegenerative pathologies like Alzheimer's disease or Parkinson's disease. Some of these effects require classical transcriptional "genomic" mechanisms through ER, whereas other effects appear to rely clearly on "membrane-initiated mechanisms" through cytoplasmic signal transduction pathways. Disturbances of these mechanisms by endocrine-disrupting chemicals (EDC) may exert adverse effects on brain. Some EDC may act via ER-independent mechanisms but might cross-react with endogenous estrogen. Other EDC may act through ER-dependent mechanisms and display agonistic/antagonistic estrogenic properties. Because of these potential effects of EDC, it is necessary to establish sensitive cell-based assays to determine EDC effects on brain. In the present review, some effects of estrogens and EDC are described with focus on ER-mediated effects in neuronal cells. Particular attention is given to PC12 cells, an interesting model to study the mechanisms underlying ER-mediated differentiating and neuroprotective effects of estrogens.

Age and 17β-estradiol effects on blood-brain barrier tight junction and estrogen receptor proteins in ovariectomized rats

Age and estrogen levels alter blood-brain barrier (BBB) tight junction (TJ) regulation, impacting brain homeostasis and pathological outcomes. This examination evaluated BBB TJ and estrogen receptor (ER) protein expression changes in young (8-10 week) and middle-aged (10-12 month) ovariectomized female Fisher-344 rats with chronic 17β-estradiol or placebo treatment. Middle-aged rats showed decreased protein expression of occludin with 17β-estradiol (55 kDa band) or placebo (45, 55, 60 kDa bands) treatment compared to respective young. In young animals, 17β-estradiol treatment increased expression of the occludin 55 kDa band over placebo; however, this effect was lost in the middle-aged animals. In both young and middle-aged animals, expression of claudin-5 (23, 32 kDa bands) and ERα (66 kDa) increased with 17β-estradiol treatment, while junctional adhesion molecule-A showed no change across all groups. However, ERα expression (66 kDa) was significantly reduced in the middle-aged animals compared to young placebo treated animals. Measurement of BBB TJ permeability via in situ perfusion of (14)C-sucrose showed no change with age or treatment. Our results show that increasing age and 17β-estradiol treatment alters the expression of ERα and distinct BBB TJ protein isoforms without altering functional paracellular permeability.

Simultaneous quantification of four native estrogen hormones at trace levels in human cerebrospinal fluid using liquid chromatography-tandem mass spectrometry

Estrogens are known to exhibit neuroprotective effects on the brain. Their importance in this regard and in others has been emphasized in many recent studies, which increases the need to develop reliable analytical methods for the measurement of estrogen hormones. A heart-cutting two-dimensional liquid chromatography separation method coupled with electrospray ionization-tandem mass spectrometry (ESI-MS/MS) has been developed for simultaneous measurement of four estrogens, including estriol (E3), estrone (E1), 17β-estradiol (17β-E2), and 17α-estradiol (17α-E2), in human cerebrospinal fluid (CSF). The method was based on liquid-liquid extraction and derivatization of estrogens with dansyl chloride to enhance the sensitivity of ESI-based detection in conjunction with tandem mass spectrometry. Dansylated estriol and estrone were separated in the first dimension by an amide-C18 column, while dansylated 17β- and 17α-estradiol were resolved on the second dimension by two C18 columns (175 mm total length) connected in series. This is the first report of a method for simultaneous quantification of all four endogenous estrogen compounds in their dansylated form. The detection limits for E1, 17α-E2, 17β-E2, and E3 were 19, 35, 26, and 61pg/mL, respectively. Due to matrix effects, validation and calibration was carried out in charcoal-stripped CSF. The precision and accuracy were more than 86% for the two E2 compounds and 79% for E1 and E3 while the extraction recovery ranged from 91% to 104%. The method was applied to measure estrogens obtained in a clinical setting, from the CSF of ischemic trauma patients. While 17β-estradiol was present at a significant level in the CSF of some samples, other estrogens were present at lower levels or were undetectable.

17beta-estradiol attenuates programmed cell death in cortical pericontusional zone following traumatic brain injury via upregulation of ERalpha and inhibition of caspase-3 activation

Pericontusional zone (PCZ) of traumatic cerebral contusion is a target of pharmacological intervention. It is well studied that 17beta-estradiol has a protective role in ischemic brain injury, but its role in brain protection of traumatic brain damage deserves further investigation, especially in pericontusional zone. Here we show that 17beta-estradiol enhances the protein expression and mRNA induction of estrogen alpha receptor (ERalpha) and prevents from programmed cell death in cortical pericontusional zone. ERalpha specific antagonist blocks this protective effect of 17beta-estradiol. Caspase-3 activation occurs in cortical pericontusional zone of the oil-treated injured rat brain and its activation is inhibited by 17beta-estradiol treatment. Additionally, ERalpha specific antagonist reverses this inhibition. Pan-caspase inhibitor also protect cortical pericontusional zone from programmed cell death. Our present study indicates 17beta-estradiol protects from programmed cell death in cortical pericontusional zone via enhancement of ERalpha and decrease of caspase-3 activation.

The effects of estrogen and progesterone on blood glutamate levels: evidence from changes of blood glutamate levels during the menstrual cycle in women

The gonadal steroids estrogen and progesterone have been shown to have neuroprotective properties against various neurodegenerative conditions. Excessive concentrations of glutamate have been found to exert neurotoxic properties. We hypothesize that estrogen and progesterone provide neuroprotection by the autoregulation of blood and brain glutamate levels. Venous blood samples (10 ml) were taken from 31 men and 45 women to determine blood glutamate, estrogen, progesterone, glucose, glutamate-pyruvate transaminase (GPT), and glutamate-oxaloacetate transaminase (GOT) levels, collected on Days 1, 7, 12, and 21 of the female participants' menstrual cycle. Blood glutamate concentrations were higher in men than in women at the start of menstruation (P < 0.05). Blood glutamate levels in women decreased significantly on Days 7 (P < 0.01), 12 (P < 0.001), and 21 (P < 0.001) in comparison with blood glutamate levels on Day 1. There was a significant decrease in blood glutamate levels on Days 12 (P < 0.001) and 21 (P < 0.001) in comparison with blood glutamate levels on Day 7. Furthermore, there was an increase in blood glutamate levels on Day 21 compared with Day 12 (P < 0.05). In women, there were elevated levels of estrogen on Days 7 (P < 0.05), 12, and 21 (P < 0.001), and elevated levels of progesterone on Days 12 and 21 (P < 0.001). There were no differences between men and women with respect to blood glucose concentrations. Concentrations of GOT (P < 0.05) and GPT (P < 0.001) were significantly higher in men than in women during the entire cycle. The results of this study demonstrate that blood glutamate levels are inversely correlated to levels of plasma estrogen and progesterone.

Sustained levels of progesterone prior to the onset of cerebral ischemia are not beneficial to female mice

Female gender, which is abolished following ovariectomy and reproductive senescence, is associated with improved outcome following cerebral stroke. Estrogen replacement partially restores this benefit of the female gender but the effect of progesterone in hormone-deficient animals is currently unknown. We evaluated various outcomes following middle cerebral artery occlusion (MCAO) in ovariectomised female mice, with a physiologically relevant restoration of progesterone levels. Ovariectomised female mice had significantly elevated plasma (P=<0.05) and brain progesterone levels (P=<0.01) following implantation of a 21-day release pellet (50mg) compared with mice that received placebo implants 7 days prior to undergoing 60 min MCAO. Assessment of well-being (body weight recovery) and neurological score at 24h and 48h post-MCAO indicated that MCAO significantly worsened outcome compared with sham-operated mice but progesterone had no effect. MCAO resulted in a substantial lesion formation and a significant increase (P<0.05) in ipsilateral brain water content, both of which were not affected by progesterone treatment. Furthermore, there was no significant alteration in ipsilateral Aquaporin-4 (AQP4) expression following MCAO or progesterone treatment. The present study indicates that sustained physiologically relevant levels of progesterone prior to cerebral ischemia neither benefited nor worsened outcomes in previously ovariectomised female mice.

Reproductive age modulates the impact of focal ischemia on the forebrain as well as the effects of estrogen treatment in female rats

While human observational studies and animal studies report a neuroprotective role for estrogen therapy in stroke, the multicenter placebo-controlled Women's Health Initiative (WHI) study concluded that hormone therapy increased the risk for stroke in postmenopausal women. The present study therefore tested the hypothesis that estrogen replacement would increase the severity of a stroke-like injury in females when this replacement occurs after a prolonged hypoestrogenic period, such as the menopause or reproductive senescence, but not when given to females that were normally cycling immediately prior to the hormone replacement. Two groups of female rats were used: multiparous females with normal but lengthened estrus cycles (mature adults), and older multiparous females currently in a persistent acyclic state (reproductive senescent). Animals were either used intact, or were bilaterally ovariectomized and immediately replaced with a 17beta-estradiol pellet or control pellet. Animals were subject to a forelimb placing test (a test for sensorimotor deficit) and thereafter to middle cerebral artery occlusion (MCAo) by stereotaxic injection of the vasoconstrictive peptide endothelin-1, adjacent to the MCA. One week after stroke, behavioral tests were performed again. Cortical and striatal infarct volume, measured from brain slices, was significantly greater in intact reproductive senescent females as compared to intact mature adults. Furthermore, estrogen treatment to ovariectomized mature adult females significantly reduced the cortical infarct volume. Paradoxically, estrogen treatment to ovariectomized reproductive senescent females significantly increased cortical and striatal infarct volumes as compared to control pellet replaced senescent females. Significant post-stroke behavioral deficit was observed in all groups on the side contralateral to the lesion, while senescent females also exhibited deficits on the ipsilateral side, in the cross-midline forelimb placement test. Using an animal model that approximates the natural ovarian aging process, these findings strongly support the hypothesis that the effectiveness of estrogen therapy in protecting brain health may depend critically on the time of initiation with respect to a female's reproductive status.

Estrogen receptor α genetic variants and the risk of stroke in a South Indian population from Andhra Pradesh

BACKGROUND

Stroke is a complex disease caused by combination of multiple risk factors. Recent findings have suggested that stroke has a strong genetic component. Evidence suggests that variations in the estrogen receptor α (ESR1) gene may influence stroke risk.

AIMS

The present study was carried out to investigate the role of ESR1 gene polymorphisms [PvuII (rs 2234693) and XbaI (rs 9340799)] with stroke in a South Indian population from Andhra Pradesh. The relationship between ESR1 genotypes with estradiol levels was also investigated in pre- and postmenopausal women.

METHODS

Four hundred patients with ischemic stroke and three hundred and eighty subjects were enrolled in this case-control study. Ischemic stroke subtypes were classified according to TOAST (Trial of Org 10172 in Acute Stroke Treatment) classification. The ESR1 PvuII and XbaI genotypes were determined by PCR-RFLP method. Serum estradiol was measured by ELISA.

RESULTS

In case of PvuII polymorphism statistically significant difference was observed in the genotypic and allelic frequencies between patients and controls (joint analysis of men and women) (p=0.003 and 0.004 respectively). However, the XbaI genotypes and alleles did not show an association with stroke in the study population. When the analysis was carried out separately for men and women, the PvuII polymorphism did not show significant association with stroke in men; women showed a significant association. Further when women were grouped in to premenopausal and postmenopausal, the premenopausal group did not show a significant association with the polymorphism but significant association with stroke was found in postmenopausal women. A stepwise multiple logistic regression analysis confirmed these findings. Women with pp genotype had low estradiol levels in comparison with PP genotypic individuals (p<0.05). Further evaluating the association of this polymorphism with stroke subtypes, we found significant association of PvuII polymorphism with extracranial atherosclerosis, lacunar and cardioembolic stroke.

CONCLUSION

In conclusion our results suggest the PvuII gene polymorphism is significantly associated with stroke in postmenopausal women in a South Indian population from Andhra Pradesh. The pp genotypes have average 17β estradiol levels which are significantly low in comparison with PP genotypes. Therefore postmenopausal women with a high frequency of pp genotype are more predisposed to ischemic stroke. However, this is a preliminary study and the results need to be confirmed in a larger cohort.

17beta-estradiol protects male mice from cuprizone-induced demyelination and oligodendrocyte loss

In addition to regulating reproductive functions in the brain and periphery, estrogen has tropic and neuroprotective functions in the central nervous system (CNS). Estrogen administration has been demonstrated to provide protection in several animal models of CNS disorders, including stroke, brain injury, epilepsy, Parkinson's disease, Alzheimer's disease, age-related cognitive decline and multiple sclerosis. Here, we use a model of toxin-induced oligodendrocyte death which results in demyelination, reactive gliosis, recruitment of oligodendrocyte precursor cells and subsequent remyelination to study the potential benefit of 17beta-estradiol (E2) administration in male mice. The results indicate that E2 partially ameliorates loss of oligodendrocytes and demyelination in the corpus callosum. This protection is accompanied by a delay in microglia accumulation as well as reduced mRNA expression of the pro-inflammatory cytokine, tumor necrosis factor alpha (TNFalpha), and insulin-like growth factor-1 (IGF-1). E2 did not significantly alter the accumulation of astrocytes or oligodendrocyte precursor cells, or remyelination. These data obtained from a toxin-induced, T cell-independent model using male mice provide an expanded view of the beneficial effects of estrogen on oligodendrocyte and myelin preservation.

Possible involvement of DNA methylation in NKCC1 gene expression during postnatal development and in response to ischemia

In CNS, GABA(A) receptor-mediated responses switch from depolarization to hyperpolarization during postnatal development. This switch is mediated by developmental down-regulation of inwardly directed Na(+)-K(+)-2Cl(-) co-transporter type 1 (NKCC1) and up-regulation of outwardly directed K(+)-Cl(-) co-transporter type 2. While several factors have been shown to regulate K(+)-Cl(-) co-transporter type 2 expression, little is known about the mechanisms by which the expression of NKCC1 is regulated during postnatal development. Here, we report a novel epigenetic mechanism underlying the developmental regulation of NKCC1 gene expression in the rat cerebral cortex. In vitro DNA methylation of the NKCC1 promoter region, which contains a high density of cytosine-phosphodiester-guanine islands, significantly decreased the expression of NKCC1 mRNA, and the degree of methylation of the NKCC1 promoter region significantly increased during postnatal development. In addition, treatment with 5-aza-2'-deoxycytidine, a specific DNA methyltransferase inhibitor, elicited an increase in the expression of NKCC1 mRNA and protein in cortical slice cultures. Focal ischemic injury induced by the occlusion of the middle cerebral artery led to the re-expression of NKCC1 mRNA and protein even in the mature rat cortex. The re-expression of NKCC1 mRNA and protein in the injured cerebral cortex was related to a decrease in the methylation status of the NKCC1 promoter region. Our results indicate that epigenetic mechanisms, such as DNA methylation, might be involved in the regulation of NKCC1 gene expression during postnatal development as well as under pathological conditions.

The neurotoxic effects of estrogen on ischemic stroke in older female rats is associated with age-dependent loss of insulin-like growth factor-1

Hormone therapy to postmenopausal females increases the risk and severity of ischemic stroke. Our previous work using an animal model of menopause (reproductive senescence) shows that middle cerebral artery occlusion (MCAo) causes a larger cortical-striatal infarct in this older acyclic group compared with younger females. Moreover, although estrogen treatment is neuroprotective in younger females, estrogen paradoxically increases infarct volume in acyclic females. We hypothesized that the neurotoxic effects of estrogen in older females occurs because of decreased availability of IGF-1, a neuroprotectant that decreases with advancing age and is downregulated by estrogen treatment. Our data show that plasma IGF-1 levels are significantly reduced in reproductive senescent females and further reduced by estrogen at all ages. The neuroprotective effect of estrogen on MCAo-induced cortical infarct volume in mature adult female is reversed by intracerebroventricular injections of IGF-1 receptor antagonist JB-1. Similarly, estrogens neurotoxic effects on cortical infarct volume in senescent females is attenuated by concurrent IGF-1 treatment, and reversed when IGF-1 is infused 4 h after the onset of ischemia (delayed IGF-1 treatment). Delayed IGF-1/estrogen treatment also suppressed ischemia-induced ERK1 phosphorylation, reduced protein oxidation, and stimulated an early increase in prostaglandin E(2) at the infarct site. IGF-1 treatment was only protective in senescent females that received estrogen, indicating that the neuroprotective actions of this peptide require interaction with the steroid hormone receptor. These data support the hypothesis that stroke severity in older females is associated with decreased IGF-1 and further indicate that short-term postischemic IGF-1 therapy may be beneficial for stroke.

Extranuclear estrogen receptors mediate the neuroprotective effects of estrogen in the rat hippocampus

BACKGROUND

17beta-estradiol (E2) has been implicated to exert neuroprotective effects in the brain following cerebral ischemia. Classically, E2 is thought to exert its effects via genomic signaling mediated by interaction with nuclear estrogen receptors. However, the role and contribution of extranuclear estrogen receptors (ER) is unclear and was the subject of the current study.

METHODOLOGY/PRINCIPAL FINDINGS

To accomplish this goal, we employed two E2 conjugates (E2 dendrimer, EDC, and E2-BSA) that can interact with extranuclear ER and exert rapid nongenomic signaling, but lack the ability to interact with nuclear ER due to their inability to enter the nucleus. EDC or E2-BSA (10 microM) was injected icv 60 min prior to global cerebral ischemia (GCI). FITC-tagged EDC or E2-BSA revealed high uptake in the hippocampal CA1 region after icv injection, with a membrane (extranuclear) localization pattern in cells. Both EDC and E2-BSA exerted robust neuroprotection in the CA1 against GCI, and the effect was blocked by the ER antagonist, ICI182,780. EDC and E2-BSA both rapidly enhanced activation of the prosurvival kinases, ERK and Akt, while attenuating activation of the proapoptotic kinase, JNK following GCI, effects that were blocked by ICI182,780. Administration of an MEK or PI3K inhibitor blocked the neuroprotective effects of EDC and E2-BSA. Further studies showed that EDC increased p-CREB and BDNF in the CA1 region in an ERK- and Akt-dependent manner, and that cognitive outcome after GCI was preserved by EDC in an ER-dependent manner.

CONCLUSIONS/SIGNIFICANCE

In conclusion, the current study demonstrates that activation of extranuclear ER results in induction of ERK-Akt-CREB-BDNF signaling in the hippocampal CA1 region, which significantly reduces ischemic neuronal injury and preserves cognitive function following GCI. The study adds to a growing literature that suggests that extranuclear ER can have important actions in the brain.

Identification of proteins regulated by estradiol in focal cerebral ischemic injury--a proteomics approach

Estradiol protects neuronal cells against permanent and focal ischemic brain damage. We identified the proteins that are expressed following estradiol administration during cerebral ischemia in an animal model. Adult female rats were ovariectomized and treated with oil or estradiol prior to middle cerebral artery occlusion (MCAO) to induce cerebral ischemia, and brains were collected 24h after MCAO. Protein analysis was performed on the cerebral cortex using two-dimensional gel electrophoresis. Protein spots with difference in intensity between oil- and estradiol-treated groups were identified by mass spectrometry. Among these proteins, levels of protein phosphatase 2A (PP2A) and astrocytic phosphoprotein PEA-15 were significantly decreased in the oil-treated group in comparison to the estradiol-treated group. Moreover, Western blot analysis demonstrated that estradiol treatment prevents injury-induced decrease of PP2A and PEA-15 levels during both MCAO-induced injury and glutamate exposure in HT22 cells. In contrast, levels of the 60kDa heat shock protein (Hsp 60) were significantly increased in oil-treated animals, while estradiol prevented the injury-induced increase of Hsp 60. The results of this study provide an evidence that estradiol protects neuronal cells against ischemic brain injury through the up- and down-modulation of specific proteins.

Effects of 17beta-estradiol replacement on the apoptotic effects caused by ovariectomy in the rat hippocampus

AIMS

The aim of the present study was to investigate the effects of different periods of ovariectomy and 17beta-estradiol replacement on apoptotic cell death and expression of members of the Bcl-2 family in the rat hippocampus.

MAIN METHODS

Hippocampi were obtained from rats in proestrus, ovariectomized (15 days, 21 days and 36 days), ovariectomized for 15 days and then treated with 17beta-estradiol for 7 or 21 days, and rats ovariectomized and immediately treated with 17beta-estradiol for 21 days. The expression of Bcl-2 and Bax and the number of apoptotic cells were determined.

KEY FINDINGS

Ovariectomy decreased Bcl-2 expression and increased Bax expression and the number of apoptotic cells. Replacement with 17beta-estradiol (21 days) throughout the post-ovariectomy period reduced the number of apoptotic cells to the control levels, and prevented the effects of ovariectomy on Bax expression, but only partially restored the Bcl-2 expression. After 15 days of ovariectomy, the replacement with 17beta-estradiol for 21 days, but not for 7 days, restored the Bcl-2 and Bax expression and the percentage of apoptotic cells to the levels found in the proestrus control.

SIGNIFICANCE

The present results show that a physiological concentration of 17beta-estradiol may help maintain long-term neuronal viability by regulating the expression of members of the Bcl-2 family. Even after a period of hormonal deprivation, treatment with 17beta-estradiol is able to restore the expression of Bax and Bcl-2 to control levels, but the duration of the treatment is a key factor to obtain the desired effect. These data provide new understanding into the mechanisms contributing to the neuroprotective action of estrogen.

Epigenetic regulation of estrogen receptor alpha gene expression in the mouse cortex during early postnatal development

Estrogens play a critical role in brain development by acting on areas that express estrogen receptors. In the rodent cortex, estrogen receptor alpha (ER alpha) mRNA expression is high early in postnatal development but declines starting at postnatal day (PND) 10 and is virtually absent in the adult cortex. The mechanisms controlling this regulation are largely unknown. Methylation is important for gene silencing during development in many tissues, including the brain. In the present study, we examined the methylation status of ER alpha 5' untranslated exons during early postnatal development in male and female mice using methylation-specific PCR and pyrosequencing. Several regions of ER alpha promoter displayed a significant increase in methylation at PND 18 and 25 compared with PND 4. DNA methyltransferases (DNMT) are important for the initiation and maintenance of methylation. Real-time PCR showed that DNMT3A, the de novo DNMT peaked at PND 10 and was decreased by PND 25. DNMT1, which is important for maintenance of methylation, increased across development and stayed high in adult cortex. The methyl-CpG-binding protein 2 (MeCP2) is also important for stabilization of methylation. A chromatin immunoprecipitation assay showed a correlation between association of MeCP2 with ER alpha promoter and the increase in methylation and decrease in ER alpha expression after PND 10. In mice containing a mutant MeCP2 protein, ER alpha mRNA expression and promoter methylation patterns across development were different compared with wild-type mice. These data suggest that methylation of ER alpha promoters regulates ER alpha mRNA expression in the cortex during postnatal development in a MeCP2-dependent fashion.