Periodic 17β-estradiol pretreatment protects rat brain from cerebral ischemic damage via estrogen receptor-β

Selective estrogen receptor activation prior to global cerebral ischemia in female rats impacts microglial activation and anxiety-like behaviors without effects on CA1 neuronal injury

Estrogen receptor (ER) activation by 17-ß estradiol (E2) can attenuate neuronal injury and behavioral impairments following global cerebral ischemia (GCI) in rodents. This study sought to further examine the discrete roles of ERs through characterization of the effects of selective ER activation on post-ischemic pro-inflammatory microglial activation, hippocampal neuronal injury, and anxiety-like behaviors. Forty-six ovariectomized (OVX) adult female Wistar rats received daily s.c injections (100 μg/kg/day) of propylpyrazole triol (PPT; ERα agonist), diarylpropionitrile (DPN; ERβ agonist), G-1 (G-protein coupled ER agonist; GPER), E2 (activating all receptors), or vehicle solution (VEH) for 21 days. After final injection, rats underwent GCI via 4-vessel occlusion (n=8 per group) or sham surgery (n=6, vehicle injections). The Open Field Test (OFT), Elevated Plus Maze (EPM), and Hole Board Test (HBT) assessed anxiety-like behaviors. Microglial activation (Iba1, CD68, CD86) in the basolateral amygdala (BLA), CA1 of the hippocampus, and paraventricular nucleus of the hypothalamus (PVN) was determined 8 days post-ischemia. Compared to sham rats, Iba1 activation and CA1 neuronal injury were increased in all ischemic groups except DPN-treated rats, with PPT-treated ischemic rats also showing increased PVN Iba1-ir expression. Behaviorally, VEH ischemic rats showed slightly elevated anxiety in the EPM compared to sham counterparts, with no significant effects of agonists. While no changes were observed in the OFT, emotion regulation via grooming in the HBT was increased in G-1 rats compared to E2 rats. Our findings support selective ER activation to regulate post-ischemic microglial activation and coping strategies in the HBT, despite minimal impact on hippocampal injury.

The effects of estrogens on spatial learning and memory in female rodents - A systematic review and meta-analysis

Estrogens have inconsistent effects on learning and memory in both the clinical and preclinical literature. Preclinical literature has the advantage of investigating an array of potentially important factors contributing to the varied effects of estrogens on learning and memory, with stringently controlled studies. This study set out to identify specific factors in the animal literature that influence the effects of estrogens on cognition, for possible translation back to clinical practice. The literature was screened and studies meeting strict inclusion criteria were included in the analysis. Eligible studies included female ovariectomized rodents with an adequate vehicle for the estrogen treatment, with an outcome of spatial learning and memory in the Morris water maze. Training days of the Morris water maze were used to assess acquisition of spatial learning, and the probe trial was used to evaluate spatial memory recall. Continuous outcomes were pooled using a random effects inverse variance method and reported as standardized mean differences with 95 % confidence intervals. Subgroup analyses were developed a priori to assess important factors. The overall analysis favoured treatment for the later stages of training and for the probe trial. Factors including the type of estrogen, route, schedule of administration, age of animals, timing relative to ovariectomy, and duration of treatment were all found to be important. The subgroup analyses showed that chronic treatment with 17β-estradiol, either cyclically or continuously, to young animals improved spatial recall. These results, observed in animals, can inform and guide further clinical research on hormone replacement therapy for cognitive benefits.

Salivary cell-free HSD17B1 and HSPA1A transcripts as potential biomarkers for estrus identification in buffaloes (Bubalus bubalis)

Estrus detection is a major problem in buffaloes because of the poor expression of estrus signs leading to low reproductive efficiency. Salivary transcripts analysis is a promising tool to identify biomarkers; therefore, the present study was carried out to evaluate their potential as estrus biomarkers. The levels of HSD17B1, INHBA, HSPA1A, TES transcripts were compared in saliva during estrous cycle stages [early proestrus (day -2, EP), late proestrus (day-1, LP), estrus (E), metestrus (ME) and diestrus (DE)] of cyclic heifers (n = 8) and pluriparous (n = 8) buffaloes by employing quantitative real-time polymerase chain reaction (qRT-PCR). The levels of HSD17B1 (EP/DE 1.46-2.43 fold, LP/DE 2.49-3.06 fold; E/DE 7.21-11.9-fold p < 0.01; ME/D 1.0-1.16 fold) and HSPA1A (EP/DE 0.93-2.39 fold, LP/DE 2.68-3.23 fold; E/DE 8.52-15.18 fold p < 0.01; ME/D 0.86-1.01 fold) were significantly altered during the estrus than other estrous cycle stages in both cyclic heifers and pluriparous buffaloes. Receiver operating characteristic curve analysis revealed the ability of salivary HSD17B1 (AUC 0.96; p < 0.001) and HSPA1A (AUC 0.99; p < 0.01) to differentiate E from other stages of the estrous cycle. Significantly higher levels of HSD17B1 and HSPA1A transcripts in saliva during the estrus phase suggest their biomarkers potential for estrus detection in buffaloes.

Post-stroke periodic estrogen receptor-beta agonist improves cognition in aged female rats

Women have a higher risk of having an ischemic stroke and increased cognitive decline after stroke as compared to men. The female sex hormone 17β-estradiol (E2) is a potent neuro- and cognitive-protective agent. Periodic E2 or estrogen receptor subtype-beta (ER-β) agonist pre-treatments every 48 h before an ischemic episode ameliorated ischemic brain damage in young ovariectomized or reproductively senescent (RS) aged female rats. The current study aims to investigate the efficacy of post-stroke ER-β agonist treatments in reducing ischemic brain damage and cognitive deficits in RS female rats. Retired breeder (9-10 months) Sprague-Dawley female rats were considered RS after remaining in constant diestrus phase for more than a month. The RS rats were exposed to transient middle cerebral artery occlusion (tMCAO) for 90 min and treated with either ER-β agonist (beta 2, 3-bis(4-hydroxyphenyl) propionitrile; DPN; 1 mg/kg; s.c.) or DMSO vehicle at 4.5 h after induction of tMCAO. Subsequently, rats were treated with either ER-β agonist or DMSO vehicle every 48 h for ten injections. Forty-eight hours after the last treatment, animals were tested for contextual fear conditioning to measure post-stroke cognitive outcome. Neurobehavioral testing, infarct volume quantification, and hippocampal neuronal survival were employed to determine severity of stroke. Periodic post-stroke ER-β agonist treatment reduced infarct volume, improved recovery of cognitive capacity by increasing freezing in contextual fear conditioning, and decreased hippocampal neuronal death in RS female rats. These data suggest that periodic post-stroke ER-β agonist treatment to reduce stroke severity and improve post-stroke cognitive outcome in menopausal women has potential for future clinical investigation.

Neuroprotective Mechanism of Icariin on Hypoxic Ischemic Brain Damage in Neonatal Mice

Objective. Our previous results showed that icariin (ICA) could inhibit apoptosis and provide neuroprotection against hypoxic-ischemic brain damage (HIBD) in neonatal mice, but the specific mechanism of its neuroprotective effect remains unknown. This study aims at exploring whether ICA plays a neuroprotective role in apoptosis inhibition by regulating autophagy through the estrogen receptor α (ERα)/estrogen receptor β (ERβ) pathway in neonatal mice with HIBD. Methods. A neonatal mouse model of HIBD was constructed in vivo, and an oxygen and glucose deprivation (OGD) model in HT22 cells from the hippocampal neuronal system was constructed in vitro. The effects of ICA pretreatment on autophagy and the expression of ERα and ERβ were detected in vitro and in vivo, respectively. ICA pretreatment was also supplemented with the autophagy inhibitor 3-methyladenine (3-MA), ERα inhibitor methylpiperidino pyrazole (MPP), and ERβ inhibitor 4-(2-phenyl-5,7-bis (trifluoromethyl) pyrazolo [1,5-a] pyramidin-3-yl) phenol (PHTPP) to further detect whether ICA pretreatment can activate the ERα/ERβ pathway to promote autophagy and reduce HIBD-induced apoptosis to play a neuroprotective role against HIBD in neonatal mice. Results. ICA pretreatment significantly promoted autophagy in HIBD mice. Treatment with 3-MA significantly inhibited the increase in autophagy induced by ICA pretreatment, reversed the neuroprotective effect of ICA pretreatment, and promoted apoptosis. Moreover, ICA pretreatment significantly increased the expression levels of the ERα and ERβ proteins in HIBD newborn mice. Both MPP and PHTPP administration significantly inhibited the expression levels of the ERα and ERβ proteins activated by ICA pretreatment, reversed the neuroprotective effects of ICA pretreatment, inhibited the increase in autophagy induced by ICA pretreatment, and promoted apoptosis. Conclusion. ICA pretreatment may promote autophagy by activating the ERα and ERβ pathways, thus reducing the apoptosis induced by HIBD and exerting a neuroprotective effect on neonatal mice with HIBD.

Post-stroke low-frequency whole-body vibration improves cognition in middle-aged rats of both sexes

Low-frequency whole-body vibration (WBV; 40 Hz), a low impact form of exercise, intervention for a month following moderate transient middle-cerebral artery occlusion (tMCAO) reduces infarct volume and improves motor function in reproductively senescent, middle-aged female rats. Since post-stroke cognitive decline remains a significant problem, the current study aims to investigate the efficacy of WBV in ameliorating post-tMCAO cognitive deficits and to determine the underlying putative mechanism(s) conferring benefits of WBV in middle-aged rats. Middle-aged rats of both sexes were randomly assigned to tMCAO (90 min) or sham surgery followed by exposure to either WBV (twice a day for 15 min each for 5 days a week over a month) or no WBV treatment groups. Following the last WBV treatment, rats were tested for hippocampus-dependent learning and memory using a water maze followed by harvesting brain and blood samples for histopathological and inflammatory marker analyses, respectively. Results show that post-tMCAO WBV significantly lessens cognitive deficits in rats of both sexes. Post-tMCAO WBV significantly decreased circulating pro-inflammatory cytokines and increased serum levels of irisin, a muscle-derived hormone that may play a role in brain metabolism and inflammation regulation, which suggests putative beneficial mechanisms of WBV.

Comparative Proteome Profiling of Saliva Between Estrus and Non-Estrus Stages by Employing Label-Free Quantitation (LFQ) and Tandem Mass Tag (TMT)-LC-MS/MS Analysis: An Approach for Estrus Biomarker Identification in Bubalus bubalis

Accurate determination of estrus is essentially required for efficient reproduction management of farm animals. Buffalo is a shy breeder and does not manifest overt signs of estrus that make estrus detection difficult resulting in a poor conception rate. Therefore, identifying estrus biomarkers in easily accessible biofluid such as saliva is of utmost interest. In the current study, we generated saliva proteome profiles during proestrus (PE), estrus (E), metestrus (ME), and diestrus (DE) stages of the buffalo estrous cycle using both label-free quantitation (LFQ) and labeled (TMT) quantitation and mass spectrometry analysis. A total of 520 proteins were identified as DEPs in LFQ; among these, 59 and four proteins were upregulated (FC ≥ 1.5) and downregulated (FC ≤ 0.5) during E vs. PE, ME, and DE comparisons, respectively. Similarly, TMT-LC-MS/MS analysis identified 369 DEPs; among these, 74 and 73 proteins were upregulated and downregulated during E vs. PE, ME, and DE stages, respectively. Functional annotations of GO terms showed enrichment of glycolysis, pyruvate metabolism, endopeptidase inhibitor activity, salivary secretion, innate immune response, calcium ion binding, oocyte meiosis, and estrogen signaling. Over-expression of SERPINB1, HSPA1A, VMO1, SDF4, LCN1, OBP, and ENO3 proteins during estrus was further confirmed by Western blotting. This is the first comprehensive report on differential proteome analysis of buffalo saliva between estrus and non-estrus stages. This study generated an important panel of candidate proteins that may be considered buffalo estrus biomarkers which can be applied in the development of a diagnostic kit for estrus detection in buffalo.

Xenoestrogens impact brain estrogen receptor signaling during the female lifespan: A precursor to neurological disease?

Xenoestrogens, foreign synthetic chemicals mimicking estrogens, are lurking in our surroundings. Climate change may alter their toxicity and bioavailability. Since xenoestrogens have extremely high lipid solubility and are structurally similar to natural endogenous estrogens, they can bind to estrogen receptors (ERs) -alpha (ER-α) and -beta (ER-β). Scientific evidence accumulated over the past decades have suggested that natural 17β-estradiol (E2; a potent estrogen), via activation of its receptors, plays a pivotal role in regulation of brain development, differentiation, metabolism, synaptic plasticity, neuroprotection, cognition, anxiety, body temperature, feeding and sexual behavior. In the brain, ER-β is predominantly expressed in the various regions, including cerebral cortex and hippocampus, that have been shown to play a key role in cognition. Therefore, disturbances in function of ER-β mediated E2 signaling by xenoestrogens can lead to deleterious effects that potentiate a variety of neurological diseases starting from prenatal to post-menopause in women. The goal of this review is to identify the possible neurological effects of xenoestrogens that can alter estrogen receptor-mediated signaling in the brain during different stages of the female lifespan.

Nuclear Receptors in Myocardial and Cerebral Ischemia-Mechanisms of Action and Therapeutic Strategies

Nearly 18 million people died from cardiovascular diseases in 2019, of these 85% were due to heart attack and stroke. The available therapies although efficacious, have narrow therapeutic window and long list of contraindications. Therefore, there is still an urgent need to find novel molecular targets that could protect the brain and heart against ischemia without evoking major side effects. Nuclear receptors are one of the promising targets for anti-ischemic drugs. Modulation of estrogen receptors (ERs) and peroxisome proliferator-activated receptors (PPARs) by their ligands is known to exert neuro-, and cardioprotective effects through anti-apoptotic, anti-inflammatory or anti-oxidant action. Recently, it has been shown that the expression of aryl hydrocarbon receptor (AhR) is strongly increased after brain or heart ischemia and evokes an activation of apoptosis or inflammation in injury site. We hypothesize that activation of ERs and PPARs and inhibition of AhR signaling pathways could be a promising strategy to protect the heart and the brain against ischemia. In this Review, we will discuss currently available knowledge on the mechanisms of action of ERs, PPARs and AhR in experimental models of stroke and myocardial infarction and future perspectives to use them as novel targets in cardiovascular diseases.

Coupling of GPR30 mediated neurogenesis and protection with astroglial Aromatase-STAT3 signaling in rat hippocampus after global cerebral ischemia

Our previous study revealed that G-protein-coupled estrogen receptor-30 (GPR30) agonist G1 serves as a viable alternative neuroprotectant of 17β-estradiol (E2) to attenuate neuroinflammation and improve cognitive function after global cerebral ischemia (GCI). Aromatase, the key enzyme of E2 biosynthesis, is widely expressed in animal and human brain, and its expression and activity are mediated by selective estrogen receptor modulators. In the present study, we explored the long-term protective and reparative effects of G1 in ovariectomized rats after GCI. We used the aromatase inhibitor letrozole to elucidate whether G1 and brain-derived E2 together induce beneficial effects. Our results showed that G1 administration for 28 days a) significantly increased neurogenesis in the hippocampal sub-granular zone and CA1 regions; b) declined CA1 neuronal impairment in a long-term fashion; c) enhanced expression of synaptic proteins and cognitive function; d) and prevented reactive astrocytes loss, wherein aromatase and brain-derived estrogen levels were markedly increased. Additionally, expression and activation of transducer and activator of transcription 3 (STAT3) were increased in CA1 astrocytes of G1-treated animals. Letrozole abolished all of the observed benefits of G1. Our results suggest that GPR30 activation mediates long-term neuroprotection and neurogenesis in the hippocampus following GCI, with potential mechanism coupling with the activation of astroglial aromatase-STAT3 signaling.

Decoding signaling pathways involved in prolactin-induced neuroprotection: A review

It has been well recognized that prolactin (PRL), a pleiotropic hormone, has many functions in the brain, such as maternal behavior, neurogenesis, and neuronal plasticity, among others. Recently, it has been reported to have a significant role in neuroprotection against excitotoxicity. Glutamate excitotoxicity is a common alteration in many neurological and neurodegenerative diseases, leading to neuronal death. In this sense, several efforts have been made to decrease the progression of these pathologies. Despite various reports of PRL's neuroprotective effect against excitotoxicity, the signaling pathways that underlie this mechanism remain unclear. This review aims to describe the most recent and relevant studies on the molecular signaling pathways, particularly, PI3K/AKT, NF-κB, and JAK2/STAT5, which are currently under investigation and might be implicated in the molecular mechanisms that explain the PRL effects against excitotoxicity and neuroprotection. Remarkable neuroprotective effects of PRL might be useful in the treatment of some neurological diseases.

Participation of Glutamatergic Ionotropic Receptors in Excitotoxicity: The Neuroprotective Role of Prolactin

Glutamate (Glu) is known as the main excitatory neurotransmitter in the central nervous system. It can trigger a series of processes ranging from synaptic plasticity to neurophysiological regulation. To carry out its functions, Glu acts via interaction with its cognate receptors, which are ligand-dependent. Glutamatergic receptors include ionotropic and metabotropic categories. The first allows the passage of ions through the postsynaptic membrane, while the metabotropic subtype activates signaling cascades through second messengers. It is well known that an excess of extracellular Glu concentration induces overstimulation of ionotropic glutamatergic receptors (iGluRs), causing the excitotoxicity phenomenon that leads to neuronal damage and cell death. Excitotoxicity plays a crucial role in different brain pathologies such as brain strokes, epilepsy and neurodegenerative disorders. However, until now, there are no effective neuroprotective compounds to prevent or rescue neurons from excitotoxicity. Thus, the continuous elucidation of the molecular mechanisms underlying excitotoxicity in order to prevent damage or neuronal death is necessary. Therefore, the aim of this review was to summarize the current knowledge regarding iGluRs, while describing their structures and molecular mechanisms of action, including their role in excitotoxicity, as well as the current strategies to reduce excitotoxic damage. Particularly, strategies mediated by prolactin, a somatotropin family-related hormone that displays a significant neuroprotective effect against both Glu and kainic acid-induced excitotoxicity in the hippocampus, are described. Finally, the role of prolactin as a possible molecule in the treatment of excitotoxicity in neurological diseases is discussed.

The peri-menopause in a woman's life: a systemic inflammatory phase that enables later neurodegenerative disease

The peri-menopause or menopausal transition—the time period that surrounds the final years of a woman’s reproductive life—is associated with profound reproductive and hormonal changes in a woman’s body and exponentially increases a woman’s risk of cerebral ischemia and Alzheimer’s disease. Although our understanding of the exact timeline or definition of peri-menopause is limited, it is clear that there are two stages to the peri-menopause. These are the early menopausal transition, where menstrual cycles are mostly regular, with relatively few interruptions, and the late transition, where amenorrhea becomes more prolonged and lasts for at least 60 days, up to the final menstrual period. Emerging evidence is showing that peri-menopause is pro-inflammatory and disrupts estrogen-regulated neurological systems. Estrogen is a master regulator that functions through a network of estrogen receptors subtypes alpha (ER-α) and beta (ER-β). Estrogen receptor-beta has been shown to regulate a key component of the innate immune response known as the inflammasome, and it also is involved in regulation of neuronal mitochondrial function. This review will present an overview of the menopausal transition as an inflammatory event, with associated systemic and central nervous system inflammation, plus regulation of the innate immune response by ER-β-mediated mechanisms.

E2-BSA and G1 exert neuroprotective effects and improve behavioral abnormalities following traumatic brain injury: The role of classic and non-classic estrogen receptors

The role of classical and non-classical estrogen receptors (ERs) in mediating the neuroprotective effects of this hormone on brain edema and long-term behavioral disorders was evaluated after traumatic brain injury (TBI). Ovariectomized rats were divided as follows: E2 (17 β-estradiol), E2-BSA (E2 conjugated to bovine serum albumin), G1 [G-protein-coupled estrogen receptor agonist (GPER)] or their vehicle was injected following TBI, whereas ICI (classical estrogen receptor antagonist), G15 (GPER antagonist), ICI + G15, and their vehicle were injected before the induction of TBI and the injection of E2 and E2-BSA. Brain water (BWC) and Evans blue (EB) contents were measured 24 h and 5 h after TBI, respectively. Intracranial pressure (ICP) and cerebral perfusion pressure (CPP) were measured before and at different times after TBI. Locomotor activity, anxiety-like behavior, and spatial memory were assessed on days 3, 7, 14, and 21 after injury. E2, E2-BSA, and G1 prevented the increase of BWC and EB content after TBI, and these effects were inhibited by ICI and G15. ICI and G15 also inhibited the beneficial effects of E2, E2-BSA on ICP, as well as CPP, after trauma. E2, E2-BSA, and G1 prevented the cognitive deficiency and behavioral abnormalities induced by TBI. Similar to the above parameters, ICI and G15 also reversed this E2 and E2-BSA effects on days 3, 7, 14, and 21. Our findings indicated that the beneficial effects of E2-BSA and E2 were inhibited by both ICI and G15, suggesting that GPER and classic ERs were involved in mediating the long-term effects of E2.

Osteocalcin, ovarian senescence, and brain health

Menopause, an inevitable event in a woman's life, significantly increases risk of bone resorption and diseases such as Alzheimer's, vascular dementia, cardiac arrest, and stroke. The sole role of bones, as traditionally regarded, is to provide structural support for skeletal muscles and allow for ambulation, however this concept is becoming quickly outdated. New literature has emerged that suggests the bone cell-derived hormone osteocalcin (OCN) plays a pivotal role in cognition. OCN levels are correlated with bone mass density and bone turnover, and thus are strongly influenced by the changes associated with menopause. The goal of the current review is to discuss potential gaps in our knowledge of OCN and cognition, discrepancies in methods of OCN quantification, and therapies to enhance circulating OCN. A discussion on implementing exercise or low frequency vibration interventions at the menopausal transition to reduce risk and severity of neurological diseases and associated cognitive decline is included.

Estrogen preconditioning: A promising strategy to reduce inflammation in the ischemic brain

During the premenopausal phase of a woman's life, estrogen naturally protects against ischemic brain damage and its debilitating consequence of cognitive decline. However, the decline in estrogen at menopause exponentially increases a women's risk for cerebral ischemia and its severity. Supplementation of estrogen during menopause is the most logical solution to abate this increased risk for cerebral ischemia; however, continuous therapy has proven to be contraindicative. Studies from our laboratory over the past decade have shown that a single bolus or long-term periodic 17β-estradiol treatment(s) two days prior to ischemia mimics ischemic preconditioning-conferred protection of the brain in ovariectomized or reproductively senescent female rats. These studies also demonstrated that 17β-estradiol-induced preconditioning (EPC) requires estrogen receptor (ER)-subtype beta (ER-β) activation. ER-β is expressed throughout the brain, including in the hippocampus, which plays a key role in learning and memory. Because periodic activation of ER-β mitigates post-ischemic cognitive decline in ovariectomized female rats, it can be surmised that EPC has the potential to reduce post-ischemic damage and cognitive decline in females. Estrogens are key anti-inflammatory agents; therefore this review discusses the effects of EPC on the inflammasome. Furthermore, as we now clearly know, the brain acts differently in males and females. Indeed, neurodegenerative diseases, including cerebral ischemia, and pharmacological drugs affect males and females in different ways. Thus, inasmuch as the National Institutes of Health and the Stroke Treatment Academic Industry Roundtable (STAIR) consortium mandate inclusion of female experimental animals, this review also discusses the need to close the gap in our knowledge in future studies of EPC in female animal models of cerebral ischemia.

Estrogen and propofol combination therapy inhibits endoplasmic reticulum stress and remarkably attenuates cerebral ischemia-reperfusion injury and OGD injury in hippocampus

AIM

Endoplasmic reticulum stress (ERS) is vital in inducing apoptosis via caspase-12 and C/EBP homologous protein (CHOP) apoptotic pathway in the hippocampus after ischemia-reperfusion injury. The study aimed to estimate the efficacy of estrogen and propofol combination therapy against ERS-induced apoptosis after cerebral ischemia-reperfusion injury and oxygen-glucose deprivation (OGD) injury in the hippocampus in vivo and in vitro.

METHODS

Rat model of cerebral ischemia-reperfusion injury was generated by middle cerebral artery occlusion (MCAO) strategy with ischemic intervention for 90 min and reperfusion for 24 h. Propofol processing ischemia-reperfusion group (Propofol group) infused 50 mg/kg/h of propofol via the femoral vein at the onset of reperfusion for 30 min. Estrogen processing ischemia-reperfusion group (estrogen group) received 0.0125 mg/kg of estrogen via tail vein at 30 min prior to MCAO. Combination therapy for ischemia-reperfusion group (combination group) received simultaneous processing with propofol and estrogen. In vitro, brain slices were randomly exposed to dimethylsulfoxide (DSMO), 10 μm of propofol, 10 nm of estrogen, or propofol and estrogen. Changes in the orthodromic population spike (OPS) at the end of reoxygenation were recorded. Neurological deficit examination, Nissl staining, and 2,3,5-triphenyltetrazolium chloride (TTC) staining were employed to evaluate the level of cerebral ischemia-reperfusion injury. The expression of caspase-3, caspase-12, glucose-regulated protein 78 (GRP78), and CHOP were investigated by Western blot and immunofluorescence staining assays. Neural apoptotic rate in hippocampus was detected by the flow cytometry trial.

RESULTS

Neurological deficit score, infarct volume, the expression of caspase-3 (P <  0.05), caspase-12, GRP78, CHOP, and neural apoptotic rate of I/R group increased markedly (P <  0.01). When obtaining drug treatment, neurological deficit score (P <  0.05), infarct volume, the expression levels of caspase-12 and GRP78, and neural apoptotic rate of the propofol group decreased significantly (P <  0.01). Furthermore, neurological deficit score, infarct volume, expression levels of caspase-3, caspase-12, GRP78, and CHOP (P <  0.05), and neural apoptotic rate decreased in the estrogen group (P <  0.01) and especially in the combination group (P <  0.01). Compared with the propofol group, the neurological deficit score (P <  0.05), infarct volume, caspase-3, caspase-12, GRP78, CHOP, and neural apoptotic rate of the combination group decreased (P <  0.01). Compared with the estrogen group, the infarct volume, caspase-3 (P <  0.05), GRP78, CHOP, and neural apoptotic rate (P <  0.05) of the combination group decreased (P <  0.01). Compared with the propofol group, the infarct volume, caspase-3, caspase-12 (P <  0.05), and GRP78 (P <  0.05) of the estrogen group decreased (P <  0.01). Propofol and estrogen treatment can delay the abolishing time of OPS and increase the recovery rate and amplitude of OPS, compared with OGD group (P <  0.01), especially in the combination therapy (P <  0.01).

CONCLUSION

The neuroprotection of propofol and estrogen combination therapy inhibited excessive ERS-induced apoptosis against cerebral ischemia-reperfusion injury and OGD injury in the hippocampus of rats. Furthermore, the outcomes demonstrated that combination therapy yielded synergistic effects.

Cognitive Deficits after Cerebral Ischemia and Underlying Dysfunctional Plasticity: Potential Targets for Recovery of Cognition

Cerebral ischemia affects millions of people worldwide and survivors suffer from long-term functional and cognitive deficits. While stroke and cardiac arrest are typically considered when discussing ischemic brain injuries, there is much evidence that smaller ischemic insults underlie neurodegenerative diseases, including Alzheimer's disease. The "regenerative" capacity of the brain relies on several aspects of plasticity that are crucial for normal functioning; less affected brain areas may take over function previously performed by irreversibly damaged tissue. To harness the endogenous plasticity mechanisms of the brain to provide recovery of cognitive function, we must first understand how these mechanisms are altered after damage, such as cerebral ischemia. In this review, we discuss the long-term cognitive changes that result after cerebral ischemia and how ischemia alters several plasticity processes. We conclude with a discussion of how current and prospective therapies may restore brain plasticity and allow for recovery of cognitive function, which may be applicable to several disorders that have a disruption of cognitive processing, including traumatic brain injury and Alzheimer's disease.

[Focal cerebral ischemia in rats with estrogen deficiency and endothelial dysfunction]

AIM

To assess an effect of ovariectomy (OE) on the cerebral blood flow, endothelium-dependent vasodilation, neurological, cognitive and locomotor deficit as markers of brain damage after focal ischemia in rats.

MATERIAL AND METHODS

The study was conducted in 48 female Wistar rats. Ovariectomy was performed with ovaries and uterine body extirpation, cerebral ischemia was performed by middle cerebral artery occlusion (MCAO) in rats. To assess brain damage, Combs and Garcia scores, 'open field' test (OFT), 'extrapolatory escape test' (EET), 'passive avoidance test' (PAT), 'beam-walking test' were used. Cerebral blood flow was measured using ultrasonic flowmetry.

RESULTS AND CONCLUSION

After 7 days of MCAO, the cerebral blood flow in ovarioectomized animals was reduced by 20% compared to sham-ovariectomized animals. Ovariectomized animals with MCAO showed a three-fold endothelium-dependent vasodilation reduction (the reaction of cerebral vessels to the introduction of acetylcholine and N-L-arginine), indicating the presence of severe endothelial dysfunction. In ovarioectomized animals, the cerebral blood flow was reduced by 34% compared to sham-operated animals. MCAO and OE taken together resulted in more than 2-fold increase in neurological, motor disturbances, 3-fold decrease in motor activity of the animals in the OP test. Focal ischemia in ovarioectomized animals with endothelial dysfunction led to memory decrease by 1/5 fold in PAT and by 2-fold in EET.

Aucubin promotes angiogenesis via estrogen receptor beta in a mouse model of hindlimb ischemia

Aucubin (AU) is an iridoid glycoside that has been shown to display estrogenic properties and has various pharmacological effects. Herein, we described the angiogenic properties of AU. In the study, hindlimb ischemia was induced by ligation of femoral artery on the right leg of ovariectomized mice. AU treatment significantly accelerated perfusion recovery and reduced tissue injury in mice muscle. Quantification of CD31-positive vessels in hindlimb muscles provided evidences that AU promoted angiogenesis in peripheral ischemia. In addition, results from quantitative PCR and western blot suggested AU induced angiogenesis via vascular endothelial cell growth factor (VEGF)/Akt/endothelial nitric oxide synthase (eNOS) signaling pathway. More interestingly, AU's angiogenic effects could be completely abolished in estrogen receptor beta (ERβ) knockout mice. In conclusion, the underlying mechanisms were elucidated that AU produced pro-angiogenic effects through ERβ-mediated VEGF signaling pathways. These results expand knowledge about the beneficial effects of AU in angiogenesis and blood flow recovery. It might provide insight into the ERβ regulating neovascularisation in hindlimb ischemia and identify AU as a potent new compound used for the treatment of peripheral vascular disease.

Differential Effects of E2 on MAPK Activity in the Brain and Heart of Aged Female Rats

Aging and the coincident loss of circulating estrogens at menopause lead to increased risks for neurological and cardiovascular pathologies. Clinical studies show that estrogen therapy (ET) can be beneficial in mitigating these negative effects, in both the brain and heart, when it is initiated shortly after the perimenopausal transition. However, this same therapy is detrimental when initiated >10 years postmenopause. Importantly, the molecular mechanisms underlying this age-related switch in ET efficacy are unknown. Estrogen receptors (ERs) mediate the neuroprotective and cardioprotective functions of estrogens by modulating gene transcription or, non-genomically, by activating second messenger signaling pathways, such as mitogen activated protein kinases (MAPK). These kinases are critical regulators of cell signaling pathways and have widespread downstream effects. Our hypothesis is that age and estrogen deprivation following menopause alters the expression and activation of the MAPK family members p38 and ERK in the brain and heart. To test this hypothesis, we used a surgically induced model of menopause in 18 month old rats through bilateral ovariectomy (OVX) followed by an acute dose of 17β-estradiol (E2) administered at varying time points post-OVX (1 week, 4 weeks, 8 weeks, or 12 weeks). Age and E2 treatment differentially regulated kinase activity in both the brain and heart, and the effects were also brain region specific. MAPK signaling plays an integral role in aging, and the aberrant regulation of those signaling pathways might be involved in age-related disorders. Clinical studies show benefits of ET during early menopause but detrimental effects later, which might be reflective of changes in kinase expression and activation status.

The functions of estrogen receptor beta in the female brain: A systematic review

Females have unique and additional risk factors for neurological disorders. Among classical estrogen receptors, estrogen receptor beta (ERβ) has been suggested as a therapeutic target. However, little is known about the role of ERβ in the female brain. Six electronic databases were searched for articles evaluating the role of ERβ in the female brain and the influence of age and menopause on ERβ function. After screening 3186 titles and abstracts, 49 articles were included in the review, all of which were animal studies. Of these, 19 focused on cellular signaling, 7 on neuroendocrine pathways, 8 on neurological disorders, 4 on neuroprotection and 19 on psychological and psychiatric outcomes (6 studies evaluated two or more outcomes). Our findings showed that ERβ phosphorylated and activated intracellular second messenger proteins and regulated protein expression of genes involved in neurological functions. It also promoted neurogenesis, modulated the neuroendocrine regulation of stress response, conferred neuroprotection against ischemia and inflammation, and reduced anxiety- and depression-like behaviors. Targeting ERβ may constitute a novel treatment for menopausal symptoms, including anxiety, depression, and neurological diseases. However, to establish potential therapeutic and preventive strategies targeting ERβ, future studies should be conducted in humans to further our understanding of the importance of ERβ in women's mental and cognitive health.

Estrogen replacement therapy-induced neuroprotection against brain ischemia-reperfusion injury involves the activation of astrocytes via estrogen receptor β

The incidence of ischemic stroke is significantly increased in postmenopausal women. However, the neuroprotective effects of estrogen replacement therapy (ERT) against stroke remain controversial, and the role of astrocytes in ERT has rarely been explored. In this study, we investigated the effects of estrogen and selective estrogen receptor (ER) agonists on astrocytes activation and neuronal apoptosis in mice under conditions of cell culture oxygen and glucose deprivation and reperfusion (OGD-R), and global cerebral ischemia (GCI). We demonstrated that hippocampal astrocytes primarily express ERβ. In astrocytes, 2.5-20 nM 17β-estradiol (E2) or 10 nM DPN (ERβ agonist) not 10 nM PPT (ERα agonist), significantly increased GFAP expression. And 10 nM E2, DPN or E2+MPP (ERα antagonist), but not PPT or E2+PHTPP (ERβ antagonist), significantly reduced neuronal apoptosis following the subjection of astrocyte and neuronal cocultures to OGD-R. We also found that either 50 μg/kg E2 or 8 mg/kg DPN replacement (3 weeks) significantly increased GFAP expression and reduced GCI-induced neuronal apoptosis in hippocampal CA1 region of ovariectomized mice. These results indicate that estrogen-induced neuroprotection against ischemia-reperfusion injury involves activation of astrocytes via ERβ. Thus, the discovery and design of astrocyte-selective ERβ modulators may offer a new strategy for ERT of ischemic stroke.

Estrogen receptor beta signaling alters cellular inflammasomes activity after global cerebral ischemia in reproductively senescence female rats

Periodic treatments with estrogen receptor subtype-β (ER-β) agonist reduce post-ischemic hippocampal injury in ovariectomized rats. However, the underlying mechanism of how ER-β agonists protect the brain remains unknown. Global cerebral ischemia activates the innate immune response, and a key component of the innate immune response is the inflammasome. This study tests the hypothesis that ER-β regulates inflammasome activation in the hippocampus, thus reducing ischemic hippocampal damage in reproductively senescent female rats that received periodic ER-β agonist treatments. First, we determined the effect of hippocampal ER-β silencing on the expression of the inflammasome proteins caspase 1, apoptosis-associated speck-like protein containing a CARD (ASC), and interleukin (IL)-1β. Silencing of ER-β attenuated 17β-estradiol mediated decrease in caspase 1, ASC, and IL-1β. Next, we tested the hypothesis that periodic ER-β agonist treatment reduces inflammasome activation and ischemic damage in reproductively senescent female rats. Periodic ER-β agonist treatments significantly decreased inflammasome activation and increased post-ischemic live neuronal counts by 32% (p < 0.05) as compared to the vehicle-treated, reproductively senescent rats. Current findings demonstrated that ER-β activation regulates inflammasome activation and protects the brain from global ischemic damage in reproductively senescent female rats. Further investigation on the role of a periodic ER-β agonist regimen to reduce the innate immune response in the brain could help reduce the incidence and the impact of global cerebral ischemia in post-menopausal women. We propose that estrogen receptor subtype-β (ER-β) activation regulates inflammasome activation and protects the brain from global ischemic damage in reproductively senescent female rats.

Changes in the gene expression of estrogen receptors involved in the protective effect of estrogen in rat's trumatic brain injury

It has been demonstrated that estradiol has neuroprotective effects after traumatic brain injury (TBI) in female rats. Since estrogen receptors have an important role in estradiol effects at the cellular level and the exact mechanism(s) of estradiol-induced neuroprotection has not yet been fully clarified, the present study was designed to determine the changes in the levels of estrogen receptors mRNAs and proteins involved in this phenomenon. All experiments were carried out on female Wistar rats. The brain edema and blood-brain-barrier (BBB) disruption were assessed. The TBI method was diffuse type and induced by the Marmarou method. Semiquantitative RT-PCR and immunoblotting were used to assess ERα and ERβ gene expression. The data showed that the level of brain water content was significantly increased in TBI group. The increased water content was significantly attenuated in estradiol-treated (1mg/kg) TBI rats. Disruption of BBB after TBI was significantly inhibited just by estradiol treatment. Estrogen-treated animals showed a significant increase in ERα mRNA (18%) and protein (35%) levels in the brain tissue. Furthermore, in the brain-injured rats the levels of ERβ mRNA were lower than those in control rats. Following estrogen treatment, the protein levels of ERβ were closed to those in control group. In conclusion, the data demonstrate that estrogen treatment can protect brain against traumatic brain injury. Estrogen treatment increases ER mRNA and protein levels which were coincident with its protective effects. It seems that such phenomenon participates in the induction of neuroprotective effects of estrogen. This article is part of a Special Issue entitled 1618.

Preventive role of estradiol on kidney injury induced by renal ischemia-reperfusion in male and female rats

Background:

Renal ischemia-reperfusion (RIR) is the main cause of renal failure. The incidence of RIR injury seems to be gender-related due to female sex hormone; estrogen. This study was designed to investigate the protective role of estrogen against RIR injury in male and ovariectomized female rats.

Methods:

Thirty-nine Wistar rats were used in this study as male and ovariectomized female rats in the sham-operated, RIR, and estradiol-treated plus RIR groups. The RIR was induced by clamping the renal vessels for 45 min and then 24 h of reperfusion. All animals finally were sacrificed for the measurements.

Results:

The serum levels of creatinine and blood urea nitrogen and kidney tissue damage score significantly increased in both male and female RIR rats (P < 0.05). Estradiol however significantly attenuated theses parameters (P < 0.05) toward normal levels in female (P < 0.05), but not in male rats. Kidney weight increased in both genders and estradiol intensified it in the male rats (P < 0.05). Uterus weight was increased by estradiol in female rats (P < 0.05) and testis weight did not alter in male rats.

Conclusions:

Estradiol demonstrated a protective role against RIR injury in female rats; however, estradiol as an antioxidant could not protect the male kidney from RIR injury.

Periodic Estrogen Receptor-Beta Activation: A Novel Approach to Prevent Ischemic Brain Damage

In women, the risk for cerebral ischemia climbs rapidly after menopause. At menopause, production of ovarian hormones; i.e., progesterone and estrogen, slowly diminishes. Estrogen has been suggested to confer natural protection to premenopausal women from ischemic stroke and some of its debilitating consequences. This notion is also strongly supported by laboratory studies showing that a continuous chronic 17β-estradiol (E2; a potent estrogen) regimen protects brain from ischemic injury. However, concerns regarding the safety of the continuous intake of E2 were raised by the failed translation to the clinic. Recent studies demonstrated that repetitive periodic E2 pretreatments, in contrast to continuous E2 treatment, provided neuroprotection against cerebral ischemia in ovariectomized rats. Periodic E2 pretreatment protects hippocampal neurons through activation of estrogen receptor subtype beta (ER-β). Apart from neuroprotection, periodic activation of ER-β in ovariectomized rats significantly improves hippocampus-dependent learning and memory. Difficulties in learning and memory loss are the major consequence of ischemic brain damage. Periodic ER-β agonist pretreatment may provide pharmacological access to a protective state against ischemic stroke and its debilitating consequences. The use of ER-β-selective agonists constitutes a safer target for future research than ER-α agonist or E2, inasmuch as it lacks the ability to stimulate the proliferation of breast or endometrial tissue. In this review, we highlight ER-β signaling as a guide for future translational research to reduce cognitive decline and cerebral ischemia incidents/impact in post-menopausal women, while avoiding the side effects produced by chronic E2 treatment.

Insight into the mechanisms of action of estrogen receptor β in the breast, prostate, colon, and CNS

Estrogen and its receptors (ERs) influence many biological processes in physiology and pathology in men and women. ERs are involved in the etiology and/or progression of cancers of the prostate, breast, uterus, ovary, colon, lung, stomach, and malignancies of the immune system. In estrogen-sensitive malignancies, ERβ usually is a tumor suppressor and ERα is an oncogene. ERβ regulates genes in several key pathways including tumor suppression (p53, PTEN); metabolism (PI3K); survival (Akt); proliferation pathways (p45(Skp2), cMyc, and cyclin E); cell-cycle arresting factors (p21(WAF1), cyclin-dependent kinase inhibitor 1 (CDKN1A)), p27(Kip1), and cyclin-dependent kinases (CDKs); protection from reactive oxygen species, glutathione peroxidase. Because they are activated by small molecules, ERs are excellent targets for pharmaceuticals. ERα antagonists have been used for many years in the treatment of breast cancer and more recently pharmaceutical companies have produced agonists which are very selective for ERα or ERβ. ERβ agonists are being considered for preventing progression of cancer, treatment of anxiety and depression, as anti-inflammatory agents and as agents, which prevent or reduce the severity of neurodegenerative diseases.