Estrogen is neuroprotective via an apolipoprotein E-dependent mechanism in a mouse model of global ischemia

Preventing development of post-stroke hyperexcitability by optogenetic or pharmacological stimulation of cortical excitatory activity

Stroke is the most common cause of acquired epilepsy, but treatment for preventing the development of post-stroke epilepsy is still unavailable. Since stroke results in neuronal damage and death as well as initial loss of activity in the affected brain region, homeostatic plasticity may be trigged and contribute to an increase in network hyperexcitability that underlies epileptogenesis. Correspondingly, enhancing brain activity may inhibit hyperexcitability from enhanced homeostatic plasticity and prevent post-stroke epileptogenesis. To test these hypotheses, we first used in vivo two-photon and mesoscopic imaging of activity of cortical pyramidal neurons in Thy1-GCaMP6 transgenic mice to determine longitudinal changes in excitatory activity after a photothrombotic ischemic stroke. At 3-days post-stroke, there was a significant loss of neuronal activity in the peri-injury area as indicated by reductions in the frequency of calcium spikes and percentage of active neurons, which recovered to baseline level at day 7, supporting a homeostatic activity regulation of the surviving neurons in the peri-injury area. We further used optogenetic stimulation to specifically stimulate activity of pyramidal neurons in the peri-injury area of Thy-1 channelrhodopsin transgenic mice from day 5 to day 15 after stroke. Using pentylenetetrazole test to evaluate seizure susceptibility, we showed that stroke mice are more susceptible to Racine stage V seizures (time latency 54.3 ± 12.9 min) compared to sham mice (107.1 ± 13.6 min), but optogenetic stimulation reversed the increase in seizure susceptibility (114.0 ± 9.2 min) in mice with stroke. Similarly, administration of D-cycloserine, a partial N-methyl-d-aspartate (NMDA) receptor agonist that can mildly enhance neuronal activity without causing post-stroke seizure, from day 5 to day 15 after a stroke significantly reversed the increase in seizure susceptibility. The treatment also resulted in an increased survival of glutamic acid decarboxylase 67 (GAD67) positive interneurons and a reduced activation of glial fibrillary acidic protein (GFAP) positive reactive astrocytes. Thus, this study supports the involvement of homeostatic activity regulation in the development of post-stroke hyperexcitability and potential application of activity enhancement as a novel strategy to prevent post-stroke late-onset seizure and epilepsy through regulating cortical homeostatic plasticity.

Targeting 17β-estradiol biosynthesis in neural stem cells improves stroke outcome

Dax-1 (dosage-sensitive sex reversal adrenal hypoplasia congenital region on X-chromosome gene 1) blocks 17β-estradiol biosynthesis and its knockdown would be expected to increase 17β-estradiol production. We hypothesized that knockdown of Dax-1 in a conditionally immortalized neural stem cell (NSC) line, MHP36, is a useful approach to increase 17β-estradiol production. Short hairpin (sh) RNA targeted to Dax-1 in NSCs, namely MHP36-Dax1KD cells, resulted in the degradation of Dax-1 RNA and attenuation of Dax-1 protein expression. In vitro, MHP36-Dax1KD cells exhibited overexpression of aromatase and increased 17β-estradiol secretion compared to MHP36 cells. As 17β-estradiol has been shown to promote the efficacy of cell therapy, we interrogated the application of 17β-estradiol-enriched NSCs in a relevant in vivo disease model. We hypothesized that MHP36-Dax1KD cells will enhance functional recovery after transplantation in a stroke model. C57BL/6 male adult mice underwent ischemia/reperfusion by left middle cerebral artery occlusion for 45 min using an intraluminal thread. Two days later male mice randomly received vehicle, MHP36 cells, MHP36-Dax1KD cells, and MHP36 cells suspended in 17β-estradiol (100 nm) or 17β-estradiol alone (100 nm) with serial behavioral testing over 28 days followed by post-mortem histology and blinded analysis. Recovery of sensorimotor function was accelerated and enhanced, and lesion volume was reduced by MHP36-Dax1KD transplants. Regarding mechanisms, immunofluorescence indicated increased synaptic plasticity and neuronal differentiation after MHP36-Dax1KD transplants. In conclusion, knockdown of Dax-1 is a useful target to increase 17β-estradiol biosynthesis in NSCs and improves functional recovery after stroke in vivo, possibly mediated through neuroprotection and improved synaptic plasticity. Therefore, targeting 17β-estradiol biosynthesis in stem cells may be a promising therapeutic strategy for enhancing the efficacy of stem cell-based therapies for stroke.

Moderators of gene-outcome associations following traumatic brain injury

The field of genomics is the principal avenue in the ongoing development of precision/personalised medicine for a variety of health conditions. However, relating genes to outcomes is notoriously complex, especially when considering that other variables can change, or moderate, gene-outcome associations. Here, we comprehensively discuss moderation of gene-outcome associations in the context of traumatic brain injury (TBI), a common, chronically debilitating, and costly neurological condition that is under complex polygenic influence. We focus our narrative review on single nucleotide polymorphisms (SNPs) of three of the most studied genes (apolipoprotein E, brain-derived neurotrophic factor, and catechol-O-methyltransferase) and on three demographic variables believed to moderate associations between these SNPs and TBI outcomes (age, biological sex, and ethnicity). We speculate on the mechanisms which may underlie these moderating effects, drawing widely from biomolecular and behavioural research (n = 175 scientific reports) within the TBI population (n = 72) and other neurological, healthy, ageing, and psychiatric populations (n = 103). We conclude with methodological recommendations for improved exploration of moderators in future genetics research in TBI and other populations.

Gender Differences of Dementia in Response to Intensive Self-Administered Transcranial and Intraocular Near-Infrared Stimulation

Background

Transcranial near-infrared (tNIR) stimulation was proven to be a safe, reliable, and effective treatment for cognitive and behavioral symptoms of dementia. Dementia patients of different genders differ in terms of gross anatomy, biochemistry, genetic profile, clinical presentations, and socio-psychological status. Studies of the tNIR effect on dementia have thus far been gender-neutral, with dementia subjects being grouped based on diagnoses or dementia severity. This trial hereby investigated how dementia subjects of different sex respond to tNIR treatment.

Methods

A total of 60 patient-caregiver dyads were enrolled and randomized to this double-blind, sham-controlled clinical trial. The tNIR light has a wavelength of 1,060 nm to 1,080 nm and was delivered via a photobiomodulation (PBM) unit. The active PBM unit emits near-infrared (NIR) light while the sham unit does not. The treatment consists of a six-minute tNIR light stimulation session twice daily for eight weeks. Neuropsychological assessments conducted at baseline (week 0) and endline (week 8) were compared within the female and male group and between different sex, respectively.

Results

Over the course of treatment, active-arm female subjects had a 20.2% improvement in Mini‐Mental State Exam (MMSE) (mean 4.8 points increase, p < 0.001) and active-arm male cohort had 19.3% improvement (p < 0.001). Control-arm female subjects had a 6.5% improvement in MMSE (mean 1.5 points increase, p < 0.03) and control-arm male subjects had 5.9% improvement (p = 0.35) with no significant differences in the mean MMSE between female and male subjects in both arms respectively. Other comparison of assessments including Clock Copying and Drawing Test, Logical Memory Test - immediate and delayed recall yielded nominal but not statistically significant differences. No significant differences were observed in the mean MMSE between female and male subjects in both arms respectively before treatment implementation (active arm, p = 0.12; control arm, p = 0.50) at week 0, or after treatment completion (active arm, p = 0.11; control arm, p = 0.74) at week 8.

Conclusion

Despite differences between female and male dementia subjects, the response to tNIR light stimulation does not demonstrate gender-based differences. Further studies are warranted to refine the tNIR treatment protocol for subjects suffering from dementia or dementia-related symptoms.

Sex-dependent effect of APOE on Alzheimer's disease and other age-related neurodegenerative disorders

The importance of apolipoprotein E (APOE) in late-onset Alzheimer's disease (LOAD) has been firmly established, but the mechanisms through which it exerts its pathogenic effects remain elusive. In addition, the sex-dependent effects of APOE on LOAD risk and endophenotypes have yet to be explained. In this Review, we revisit the different aspects of APOE involvement in neurodegeneration and neurological diseases, with particular attention to sex differences in the contribution of APOE to LOAD susceptibility. We discuss the role of APOE in a broader range of age-related neurodegenerative diseases, and summarize the biological factors linking APOE to sex hormones, drawing on supportive findings from rodent models to identify major mechanistic themes underlying the exacerbation of LOAD-associated neurodegeneration and pathology in the female brain. Additionally, we list sex-by-genotype interactions identified across neurodegenerative diseases, proposing APOE variants as a shared etiology for sex differences in the manifestation of these diseases. Finally, we present recent advancements in 'omics' technologies, which provide a new platform for more in-depth investigations of how dysregulation of this gene affects the development and progression of neurodegenerative diseases. Collectively, the evidence summarized in this Review highlights the interplay between APOE and sex as a key factor in the etiology of LOAD and other age-related neurodegenerative diseases. We emphasize the importance of careful examination of sex as a contributing factor in studying the underpinning genetics of neurodegenerative diseases in general, but particularly for LOAD.

Sex and Gender Driven Modifiers of Alzheimer's: The Role for Estrogenic Control Across Age, Race, Medical, and Lifestyle Risks

Research indicates that after advanced age, the major risk factor for late-onset Alzheimer’s disease (AD) is female sex. Out of every three AD patients, two are females with postmenopausal women contributing to over 60% of all those affected. Sex- and gender-related differences in AD have been widely researched and several emerging lines of evidence point to different vulnerabilities that contribute to dementia risk. Among those being considered, it is becoming widely accepted that gonadal steroids contribute to the gender disparity in AD, as evidenced by the “estrogen hypothesis.” This posits that sex hormones, 17β-estradiol in particular, exert a neuroprotective effect by shielding females’ brains from disease development. This theory is further supported by recent findings that the onset of menopause is associated with the emergence of AD-related brain changes in women in contrast to men of the same age. In this review, we discuss genetic, medical, societal, and lifestyle risk factors known to increase AD risk differently between the genders, with a focus on the role of hormonal changes, particularly declines in 17β-estradiol during the menopause transition (MT) as key underlying mechanisms.

Estrogen and insulin synergistically promote endometrial cancer progression via crosstalk between their receptor signaling pathways

Objective

Despite evidence that estrogens and insulin are involved in the development and progression of many cancers, their synergistic role in endometrial carcinoma (EC) has not been analyzed yet.

Methods

Here, we investigated how estrogens act synergistically with insulin to promote EC progression. Cell growth in vitro and in vivo, effects of estradiol and insulin on apoptosis and cell cycle distribution, and expression and activation of estrogen receptor (ER), insulin receptor (InsR), and key proteins in the PI3K and MAPK pathways were examined after combined stimulation with estradiol and insulin.

Results

Compared to EC cells treated with estradiol or insulin alone, those treated with both estradiol and insulin exhibited stronger stimulation. Estradiol significantly induced phosphorylation of InsR-β and IRS-1, whereas insulin significantly induced phosphorylation of ER-α. In addition, treatment with both insulin and estradiol together significantly increased the expression and phosphorylation of Akt, MAPK, and ERK. Notably, InsR-β inhibition had a limited effect on estradiol-dependent proliferation, cell cycle, and apoptosis, whereas ER-α inhibition had a limited insulin-dependent effect, in EC cell lines. Insulin and estradiol individually and synergistically promoted EC xenograft growth in mice.

Conclusions

Estrogen and insulin play synergistic roles in EC carcinogenesis and progression by activating InsR-β and ER-α, promoting a crosstalk between them, and thereby resulting in the activation of downstream PI3K/Akt and MAPK/ERK signaling pathways.

Estrogens as neuroprotectants: Estrogenic actions in the context of cognitive aging and brain injury

There is ample empirical evidence to support the notion that the biological impacts of estrogen extend beyond the gonads to other bodily systems, including the brain and behavior. Converging preclinical findings have indicated a neuroprotective role for estrogen in a variety of experimental models of cognitive function and brain insult. However, the surprising null or even detrimental findings of several large clinical trials evaluating the ability of estrogen-containing hormone treatments to protect against age-related brain changes and insults, including cognitive aging and brain injury, led to hesitation by both clinicians and patients in the use of exogenous estrogenic treatments for nervous system outcomes. That estrogen-containing therapies are used by tens of millions of women for a variety of health-related applications across the lifespan has made identifying conditions under which benefits with estrogen treatment will be realized an important public health issue. Here we provide a summary of the biological actions of estrogen and estrogen-containing formulations in the context of aging, cognition, stroke, and traumatic brain injury. We have devoted special attention to highlighting the notion that estrogen appears to be a conditional neuroprotectant whose efficacy is modulated by several interacting factors. By developing criteria standards for desired beneficial peripheral and neuroprotective outcomes among unique patient populations, we can optimize estrogen treatments for attenuating the consequences of, and perhaps even preventing, cognitive aging and brain injury.

Physiological and functional changes in the stratum corneum restored by oestrogen in an ovariectomized mice model of climacterium

Significant decreases in hormonal levels at menopause induce physiological and functional discomfort in the skin. Representative changes at menopause are based on so-called dry skin. However, there is no evidence to explain the mechanism, even though hydration of the stratum corneum (SC) in women at menopause is comparable with that at premenopause but is enhanced by hormone replacement therapy. This study objective was to evaluate structural and functional changes in the SC in ovariectomized mice model of menopause. Hydration of the SC, recovery of the permeability barrier function, integrity and cohesion of the SC, and irritant dermatitis were analysed in mice that underwent ovariectomy with or without replacement of 17ß-estradiol. In ovariectomized mice, hydration of the SC was reduced, recovery of permeability barrier function after acute disruption was impaired, and integrity of the SC was weakened and was associated with increased cohesion and increased levels of irritant dermatitis. Oestrogen replacement treatment restored all changes. Immunohistochemistry revealed reduced levels of expression of desmoglein-1 and differentiation markers of epidermis in ovariectomized mice compared with control mice and mice with oestrogen replacement treatment. These changes might be directly associated with weakened integrity and impaired permeability barrier function of the SC in ovariectomized mice. This study results reveal that so-called dry skin at menopause is caused by not only lower hydration of the SC but also complicated structural and functional changes in the SC and skin.

Estrogen Stimulates Homing of Endothelial Progenitor Cells to Endometriotic Lesions

The incorporation of endothelial progenitor cells (EPCs) into microvessels contributes to the vascularization of endometriotic lesions. Herein, we analyzed whether this vasculogenic process is regulated by estrogen. Estrogen- and vehicle-treated human EPCs were analyzed for migration and tube formation. Endometriotic lesions were induced in irradiated FVB/N mice, which were reconstituted with bone marrow from FVB/N-TgN (Tie2/green fluorescent protein) 287 Sato mice. The animals were treated with 100 μg/kg β-estradiol 17-valerate or vehicle (control) over 7 and 28 days. Lesion growth, cyst formation, homing of green fluorescent protein(+)/Tie2(+) EPCs, vascularization, cell proliferation, and apoptosis were analyzed by high-resolution ultrasonography, caliper measurements, histology, and immunohistochemistry. Numbers of blood circulating EPCs were assessed by flow cytometry. In vitro, estrogen-treated EPCs exhibited a higher migratory and tube-forming capacity when compared with controls. In vivo, numbers of circulating EPCs were not affected by estrogen. However, estrogen significantly increased the number of EPCs incorporated into the lesions' microvasculature, resulting in an improved early vascularization. Estrogen further stimulated the growth of lesions, which exhibited massively dilated glands with a flattened layer of stroma. This was mainly because of an increased glandular secretory activity, whereas cell proliferation and apoptosis were not markedly affected. These findings indicate that vasculogenesis in endometriotic lesions is dependent on estrogen, which adds a novel hormonally regulated mechanism to the complex pathophysiology of endometriosis.

Exploring the effect of the apolipoprotein E (APOE) gene on executive function, working memory, and processing speed during the early recovery period following traumatic brain injury

INTRODUCTION

There is evidence that the e4 allele of the apolipoprotein E (APOE) gene is detrimental to cognitive function, but results from traumatic brain injury (TBI) populations are mixed. A possible explanation is that APOEe2 carriers have routinely been incorporated into APOEe4 and non-e4 groups, despite APOEe2 being proposed to have an ameliorative effect. Our primary aim was to investigate the influence of APOEe4 on cognitive impairment during early recovery following TBI, excluding the potential confound of APOEe2 possession. A secondary objective was to explore whether APOEe4 displays more pronounced effects in moderate to severe TBI and to consider the potential postinjury protective influence of the APOEe2 allele.

METHOD

Participants who recently sustained a TBI (posttraumatic amnesia > 5 minutes) were assessed on measures of information processing speed, executive function, and working memory upon remission of posttraumatic amnesia. APOE genotype was determined by buccal saliva DNA extraction (APOEe4 n = 37, APOEe3 n = 92, APOEe2 n = 13).

RESULTS

Stepwise multiple regressions were performed to compare APOEe4 carriers to APOEe3 homozygotes, with injury severity, age, and estimated premorbid IQ included in the first step. This model was found to significantly predict performance on all tasks, accounting for 17.3-24.3% of the variance. When APOEe4 status was added for the second step, there were no significant changes on any tasks (additional variance <1%). The effect of APOEe4 in moderate to severe TBI and the effect of APOEe2 were explored by analysis of covariance (ANCOVA), with no significant effects revealed.

CONCLUSIONS

It is unlikely that APOE genotype influences cognitive function in the initial recovery period following TBI, regardless of injury severity. However, a more nuanced and long-term exploration of the effect of APOE genotype in the TBI population is warranted.

Sex-related neurogenesis decrease in hippocampal dentate gyrus with depressive-like behaviors in sigma-1 receptor knockout mice

Male sigma-1 receptor knockout (σ1R(-/-)) mice showed depressive-like phenotype with deficit in the survival of newly generated neuronal cells in the hippocampal dentate gyrus (DG), but female σ1R(-/-) mice did not. The level of serum estradiol (E2) at proestrus or diestrus did not differ between female σ1R(-/-) mice and wild-type (WT) mice. Ovariectomized (OVX) female σ1R(-/-) mice, but not WT mice, presented the same depressive-like behaviors and neurogenesis decrease as male σ1R(-/-) mice. Treatment of male σ1R(-/-) mice with E2 could alleviate the depressive-like behaviors and rescue the neurogenesis decrease. In addition, E2 could correct the decline in the density of NMDA-activated current (INMDA) in granular cells of DG and the phosphorylation of NMDA receptor (NMDAr) subtype 2B (NR2B) in male σ1R(-/-) mice, which was associated with the elevation of Src phosphorylation. The neuroprotection and antidepressant effects of E2 in male σ1R(-/-) mice were blocked by the inhibitor of Src or NR2B. The NMDAr agonist showed also the neuroprotection and antidepressant effects in male σ1R(-/-) mice, which were insensitive to the Src inhibitor. On the other hand, either the deprivation of E2 or the inhibition of Src in female σ1R(-/-) mice rather than WT mice led to a distinct decline in INMDA and NR2B phosphorylation. Similarly, the Src inhibitor could cause neurogenesis decrease and depressive-like behaviors in female σ1R(-/-) mice, but not in WT mice. These results indicate that the σ1R deficiency impairs neurogenesis leading to a depressive-like phenotype, which is alleviated by the neuroprotection of E2.

Neurite outgrowth promoting effect of 17-β estradiol is mediated through estrogen receptor alpha in an olfactory epithelium culture

Olfactory deficits are observed early in the course of chronic neurological disorders including Alzheimer's disease (AD). Estrogen treatment in post-menopausal women reduced the incidence of olfactory dysfunction, raising the possibility that estrogen treatment can cure olfactory deficits in preclinical stages of AD. In this study, we examined the estradiol׳s effects on neurite outgrowth in explant cultures of mouse olfactory epithelium (OE). We found that neurons in OE cultures treated with 100 pM 17-β estradiol (estradiol) had significantly longer neurite outgrowth than cultures treated with ethanol alone (vehicle). The OE neurons expressed estrogen receptors alpha (ERα) and ER beta (ERβ). Estrogen treatment upregulated both ERα and ERβ expression in OE culture. Treatment of OE cultures with propyl pyrazole triol (PPT), a selective agonist for ERα increased neurite outgrowth to comparable extent as estradiol treatment. In contrast, 2,3-bis-4-hydroxyphenyl (DPN), a specific agonist for ERβ, had no effect on neurite outgrowth. Furthermore, estradiol treatment increased neurite outgrowth in OE cultures derived from ERβ-deficient/knockout mice and wild-type littermates, but not in ERα-deficient/knockout mice. These data suggest that ERα mediates the neurite outgrowth promoting effects of estradiol in OE cultures. We propose that olfactory dysfunction in chronic neurological disorders, where estrogen deficiency is a risk factor, is an indicator of compromised axonal regeneration of olfactory sensory neurons.

Sex and gender differences in the causes of dementia: a narrative review

This is a narrative review of new ideas and concepts related to differences between men and women in their risk of developing dementia or Alzheimer's disease (AD). We introduce the concept of dimorphic neurology and the distinction between sex and gender. We then provide three examples of risk factors related to sex and gender from the literature. Apolipoprotein E genotype is equally common in men and women but has a stronger effect in women. Apolipoprotein E genotype is a biological factor that cannot be modified but interacts with sex or gender related factors that can be modified. Low education has a similar harmful effect in men and women but has been historically more common in women. Education is a social factor related to gender that can be modified. Finally, bilateral oophorectomy is a factor restricted to women. Bilateral oophorectomy is a surgical practice related to sex that can be modified. Consideration of risk and protective factors in men and women separately may accelerate etiologic research for neurological diseases in general, and for dementia and AD in particular. Similarly, future preventive interventions for dementia should be tailored to men and women separately.

rLOAD: does sex mediate the effect of acute antiplatelet loading on stroke outcome

BACKGROUND

Biologic sex can influence response to pharmacologic therapy. The purpose of this proof-of-concept study was to evaluate the medicating effects of estrogen in the efficacy of acute antiplatelet loading therapy on stroke outcome in the rabbit small clot embolic model.

METHODS

Female and male (20/group) New Zealand White rabbits were embolized to produce embolic stroke by injecting small blood clots into the middle cerebral artery via an internal carotid artery catheter. Two hours after embolization, rabbits were treated with standard dose antiplatelet loading (aspirin 10 mg/kg plus clopidogrel 10 mg/kg). Primary outcome measures were platelet inhibition, behavioral outcome P 50 (the weight of microclots (mg) that produces neurologic dysfunction in 50% of a group of animals), and effect of endogenous estrogen on outcome.

RESULTS

For the first time in a non-rodent model of stroke, it was found that higher endogenous estrogen levels resulted in significantly better behavioral outcome in female subjects (r s -0.70, p < 0.011). Platelet inhibition in response to collagen, arachidonic acid, and adenosine diphosphate (ADP) was not significantly different in females with higher vs. lower estrogen levels.

CONCLUSIONS

Behavioral outcomes are improved with females with higher endogenous estrogen levels treated with standard dose antiplatelet loading. This is the first non-rodent study to demonstrate that higher endogenous estrogen levels in female rabbits appear to be neuroprotective in ischemic stroke. This research supports the further study of the effect of endogenous estrogen levels on outcome with standard dose antiplatelet loading in stroke patients not eligible for revascularization therapies.

Sex differences in the response to poly(ADP-ribose) polymerase-1 deletion and caspase inhibition after stroke

BACKGROUND AND PURPOSE

Emerging data suggest that the molecular cell death pathways triggered by ischemic insults differ in the male and female brain. Cell death in males is initiated by poly(ADP-ribose) polymerase-1 (PARP-1) activation; however, manipulation of this pathway paradoxically increases ischemic damage in females. In contrast, females are exquisitely sensitive to caspase-mediated cell death. The effect of caspase inhibition in PARP-1 knockout mice was evaluated to determine if the detrimental effects of PARP deletion in females were secondary to increased caspase activation.

METHODS

Focal stroke was induced by transient or permanent middle cerebral artery occlusion (MCAO) in wild-type (WT) and PARP-1(-/-) mice of both sexes. The pan-caspase inhibitor, quinoline-Val-Asp(Ome)-CH2-O-phenoxy (Q-VD-OPh), was administered 90 minutes after middle cerebral artery occlusion. Infarct size and neurological sores were assessed. Separate cohorts were used for protein analysis for PAR, Apoptosis inducing factor (AIF), caspase-9, and caspase-3.

RESULTS

WT mice of both sexes had increased nuclear AIF after stroke compared to PARP-1(-/-) mice. PARP-1(-/-) females had higher mitochondrial cytochrome C and activated caspase-9 and -3 levels than WT female mice. PARP-1(-/-) females also had an increase in stroke-induced cytosolic cytochrome C release compared with WT females, which was not seen in males. Q-VD-OPh decreased caspase-9 in both males and females but only led to reduction of infarct in females. PARP-1(-/-) males had smaller infarcts, whereas PARP-1(-/-) females had larger strokes compared with WT. Q-VD-OPh significantly decreased infarct in both WT and PARP-1(-/-) females in both transient and permanent MCAO models, but had no effect in males.

CONCLUSIONS

Deletion of PARP-1 reduces infarct in males but exacerbates injury in females. PARP-1(-/-) females have enhanced caspase activation. The detrimental effects of PARP loss in females can be reversed with caspase inhibition.

Acute responses to estradiol replacement in the olfactory system of apoE-deficient and wild-type mice

Epidemiological studies suggest that estrogen therapy protects against clinical expression of chronic neurological diseases. These beneficial effects of estrogen therapy are highly modified by apolipoprotein E (apoE) through an unknown mechanism. We examined the short-term effects of estradiol replacement in ovariectomized mice on apoE expression and markers for cell proliferation, reactive gliosis, neuronal maturation, and synaptogenesis in the primary olfactory pathway of wild-type (WT) and apoE knockout (KO) mice. Three days of estradiol replacement increased apoE expression in the olfactory nerve and in the glomerular layer. Estradiol treatment also increased cell proliferation, total cell numbers, number of mature neurons in the olfactory epithelium, and reactive astrocyte numbers in the olfactory bulb (OB) in both WT and KO mice. We also found that estradiol increased glomerular synaptophysin (Syn), but the magnitude of increase was potentiated by the presence of apoE. These data suggest that apoE may be necessary to elicit the complete effect of estradiol on Syn upregulation.

Complexities of oestrogen in stroke

Evidence exists for the potential protective effects of circulating ovarian hormones in stroke, and oestrogen reduces brain damage in animal ischaemia models. However, a recent clinical trial indicated that HRT (hormone-replacement therapy) increased the incidence of stroke in post-menopausal women, and detrimental effects of oestrogen on stroke outcome have been identified in a meta-analysis of HRT trials and in pre-clinical research studies. Therefore oestrogen is not an agent that can be promoted as a potential stroke therapy. Many published reviews have reported the neuroprotective effects of oestrogen in stroke, but have failed to include information on the detrimental effects. This issue is addressed in the present review, along with potential mechanisms of action, and the translational capacity of pre-clinical research.

Genetic and hormonal factors modulate spreading depression and transient hemiparesis in mouse models of familial hemiplegic migraine type 1

Familial hemiplegic migraine type 1 (FHM1) is an autosomal dominant subtype of migraine with aura that is associated with hemiparesis. As with other types of migraine, it affects women more frequently than men. FHM1 is caused by mutations in the CACNA1A gene, which encodes the alpha1A subunit of Cav2.1 channels; the R192Q mutation in CACNA1A causes a mild form of FHM1, whereas the S218L mutation causes a severe, often lethal phenotype. Spreading depression (SD), a slowly propagating neuronal and glial cell depolarization that leads to depression of neuronal activity, is the most likely cause of migraine aura. Here, we have shown that transgenic mice expressing R192Q or S218L FHM1 mutations have increased SD frequency and propagation speed; enhanced corticostriatal propagation; and, similar to the human FHM1 phenotype, more severe and prolonged post-SD neurological deficits. The susceptibility to SD and neurological deficits is affected by allele dosage and is higher in S218L than R192Q mutants. Further, female S218L and R192Q mutant mice were more susceptible to SD and neurological deficits than males. This sex difference was abrogated by ovariectomy and senescence and was partially restored by estrogen replacement, implicating ovarian hormones in the observed sex differences in humans with FHM1. These findings demonstrate that genetic and hormonal factors modulate susceptibility to SD and neurological deficits in FHM1 mutant mice, providing a potential mechanism for the phenotypic diversity of human migraine and aura.

Long-term effects of bilateral oophorectomy on brain aging: unanswered questions from the Mayo Clinic Cohort Study of Oophorectomy and Aging

In the Mayo Clinic Cohort Study of Oophorectomy and Aging, women who had both ovaries removed before reaching natural menopause experienced a long-term increased risk of parkinsonism, cognitive impairment or dementia, and depressive and anxiety symptoms. Here, we discuss five possible mechanistic interpretations of the observed associations; first, the associations may be non-causal because they result from the confounding effect of genetic variants or of other risk factors; second, the associations may be mediated by an abrupt reduction in levels of circulating estrogen; third, the associations may be mediated by an abrupt reduction in levels of circulating progesterone or testosterone; fourth, the associations may be mediated by an increased release of gonadotropins by the pituitary gland; and fifth, genetic variants may modify the hormonal effects of bilateral oophorectomy through simple or more complex interactions. Results from other studies are cited as evidence for or against each possible mechanism. These putative causal mechanisms are probably intertwined, and their clarification is a research priority.

Apolipoprotein E polymorphism and gender difference in outcome after severe traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is one of the most common causes of death and dismal outcome among children and young adults. The morbidity and mortality differ but more aggressive monitoring and more designated neuro intensive care units have improved the results. Studies have demonstrated a connection between apolipoprotein E (APOE) genotype and outcome after TBI, but few are prospective and none is from northern Europe. APOE has three alleles: epsilon2, epsilon3 and epsilon4.

METHODS

A total of 96 patients with Glasgow coma score (GCS) < or =8 were prospectively and consecutively included. APOE genotypes were all analyzed at the same laboratory from blood samples by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

All patients were assessed at 1 year with Glasgow outcome scale extended (GOSE), National Institute of Health Stroke Scale (NIHSS) and the Barthel daily living index. The genotype was available in all patients. Twenty-six patients expressed APOE epsilon4 while 70 patients did not. Outcome demonstrated that patients with APOE epsilon4 had worse outcome vs. those lacking this allele. When subdividing patients into gender, males with APOE epsilon4 did worse, a difference not detected among female patients.

CONCLUSIONS

APOE epsilon4 correlated to worse outcome in TBI patients. We also found that males with APOE epsilon4 had poor outcome while females did not. Thus, the results indicate that genetic polymorphism may influence outcome after TBI.

Role of Dickkopf-1, an antagonist of the Wnt/beta-catenin signaling pathway, in estrogen-induced neuroprotection and attenuation of tau phosphorylation

17beta-Estradiol (E2) has been implicated to be neuroprotective in a variety of neurodegenerative disorders, although the mechanism remains poorly understood. The current study sheds light on this issue by demonstrating that low physiological levels of E2 protects the hippocampus CA1 against global cerebral ischemia by preventing elevation of dickkopf-1 (Dkk1), an antagonist of the Wnt/beta-catenin signaling pathway, which is a principal mediator of neurodegeneration in cerebral ischemia and Alzheimer's disease. E2 inhibition of Dkk1 elevation correlated with a reduction of phospho-beta-catenin and elevation of nuclear beta-catenin levels, as well as enhancement of Wnt-3, suggesting E2 activation of the Wnt/beta-catenin signaling pathway. In agreement, the beta-catenin downstream prosurvival factor, survivin, was induced by E2 at 24 and 48 h after cerebral ischemia, an effect observed only in surviving neurons because degenerating neurons lacked survivin expression. E2 suppression of Dkk1 elevation was found to be caused by attenuation of upstream c-Jun N-terminal protein kinase (JNK)/c-Jun signaling, as E2 attenuation of JNK/c-Jun activation and a JNK inhibitor significantly blocked Dkk1 induction. Tau hyperphosphorylation has been implicated to have a prodeath role in Alzheimer's disease and cerebral ischemia, and E2 attenuates tau hyperphosphorylation. Our study demonstrates that tau hyperphosphorylation is strongly induced after global cerebral ischemia, and that E2 inhibits tau hyperphosphorylation by suppressing activation of the JNK/c-Jun/Dkk1 signaling pathway. Finally, exogenous Dkk1 replacement via intracerebroventricular administration completely reversed E2-induced neuroprotection, nuclear beta-catenin induction, and phospho-tau attenuation, further suggesting that E2 inhibition of Dkk1 is a critical mechanism underlying its neuroprotective and phospho-tau regulatory effects after cerebral ischemia.

Gender and the injured brain

Anesthesiologists are frequently confronted with patients who are at risk for neurological complications due to perioperative stroke or prior traumatic brain injury. In this review, we address the growing and fascinating body of data that suggests gender and sex steroids influence the pathophysiology of injury and outcome for these patients. Cerebral ischemia, traumatic brain injury, and epilepsy are reviewed in the context of potential sex differences in mechanisms and outcomes of brain injury and the role of estrogen, progesterone, and androgens in shaping these processes. Lastly, implications for current and future perioperative and intensive care are identified.

Estrogen Action in Neuroprotection and Brain Inflammation

The fertile period of women's life compared to menopause is associated with a lower incidence of degenerative inflammatory diseases. In brain, estrogens ameliorate brain performance and have positive effects on selected neural pathologies characterized by a strong inflammatory component. We thus hypothesized that the inflammatory response is a target of estrogen action; several studies including ours provided strong evidence to support this prediction. Microglia, the brain's inflammatory cells, and circulating monocytes express the estrogen receptors ER-alpha and ER-beta and their responsiveness in vivo and in vitro to pro-inflammatory agents, such as lipopolysaccharide (LPS), is controlled by 17beta-estradiol (E(2)). Susceptibility of central nervous system (CNS) macrophage cells to E(2) is also preserved in animal models of neuroinflammatory diseases, in which ER-alpha seems to be specifically involved. At the molecular level, induction of inflammatory gene expression is blocked by E(2). We recently observed that, differently from conventional anti-inflammatory drugs, E(2) stimulates a nongenomic event that interferes with the LPS signal transduction from the plasma membrane to cytoskeleton and intracellular effectors, which results in the inhibition of the nuclear translocation of NF-kappaB, a transcription factor of inflammatory genes. Interference with NF-kappaB intracellular trafficking is selectively mediated by ER-alpha. In summary, evidence from basic research strongly indicates that the use of estrogenic drugs that can mimic the anti-inflammatory activity of E(2) might trigger beneficial effects against neurodegeneration in addition to carrying out their specific therapeutic function.

Estrogens and experimental ischemic stroke: a systematic review

Estrogens are believed to provide females with endogenous protection against cerebrovascular events although clinical trials studying long-term hormone replacement have yielded disappointing results. In contrast, estrogens might be neuroprotective after experimental ischemia. We performed a systematic review of controlled experimental studies that administered estrogens before, or after, cerebral ischemia and measured lesion volume. Relevant studies were found from searching PubMed, Embase and Web of Science. From 161 identified publications, 27 studies using 1,304 experimental subjects were analyzed using the Cochrane Review Manager software. Estrogens reduced lesion volume in a dose-dependent manner, after either transient (P<0.001) or permanent (P<0.001) ischemia and whether administered before or up to 4 h after ischemia onset; no studies assessed efficacy for later time periods. The effect size for estrogens decreased with increasing quality scores for studies of transient ischemia. Estrogens reduced lesion volume when administered to ovariectomized females and young adult males, but had no effect in intact females. Limited data were present for aged animals and the full dose-response relationship was not available in all experimental groups. On the basis of these data, estrogens are a candidate treatment for ischemic stroke, although further preclinical studies are also warranted.

Inducible nitric oxide synthase contributes to gender differences in ischemic brain injury

Estrogens have antiinflammatory actions and protect the brain from ischemic injury. Cerebral ischemia is accompanied by an inflammatory reaction that contributes to the tissue damage, an effect mediated in part by toxic amounts of nitric oxide (NO) produced by the inducible isoform of NO synthase (iNOS). Therefore, estrogens may protect the female brain by modulating postischemic iNOS expression. To test this hypothesis, we studied whether iNOS plays a role in the mechanisms of the reduced susceptibility to ischemic injury observed in female mice. The middle cerebral artery was occluded for 20 mins using an intraluminal filament in C57Bl/6 mice, and infarct volume was assessed 3 days later in cresyl violet-stained sections. Infarcts were 53% smaller in female mice than in males (P < 0.05), a reduction abolished by ovariectomy (OVX) and reinstated by estrogen replacement. In normal female mice, postischemic iNOS mRNA was lower than in males (P < 0.05). Ovariectomy increased iNOS mRNA after ischemia and estrogen replacement blocked this effect. Furthermore, the iNOS inhibitor aminoguanidine reduced infarct volume in male, but not in female, mice. Similarly, male iNOS-null mice had smaller infarcts than wild-type mice, but female iNOS nulls were not protected. Ovariectomy and OVX with estrogen replacement did not affect infarct volume in iNOS-null female mice. The findings suggest that the neuroprotection conferred by estrogens is, in part, related to attenuation of iNOS expression. Such attenuation could result from the potent antiinflammatory effects of estrogens that downregulate iNOS expression via transcriptional or posttranscriptional mechanisms.

Acute and chronic estradiol treatments reduce memory deficits induced by transient global ischemia in female rats

Transient global ischemia induces selective, delayed neuronal death in the hippocampal CA1 and delayed cognitive deficits. Estrogen treatment ameliorates hippocampal injury associated with global ischemia. Although much is known about the impact of estrogen on neuronal survival, relatively little is known about its impact on functional outcome assessed behaviorally. We investigated whether long-term estradiol (21-day pellets implanted 14 days prior to ischemia) or acute estradiol (50 microg infused into the lateral ventricles immediately after ischemia) attenuates ischemia-induced cell loss and improves visual and spatial working memory in ovariectomized female rats. Global ischemia significantly impaired visual and spatial memory, assessed by object recognition and object placement tests at 6-9 days. Global ischemia did not affect locomotion, exploration, or anxiety-related behaviors, assessed by an open-field test at 6 days. Long-term estradiol prevented the ischemia-induced deficit in visual working memory, maintaining normal performance in tests with retention intervals of up to 1 h. Long-term estradiol also prevented ischemia-induced deficits in spatial memory tests with short (1 and 7 min), but not longer (15 min), retention intervals. Acute estradiol significantly improved visual memory assessed with short retention intervals, but did not prevent deficits in spatial memory. Acute estradiol significantly increased the number of surviving CA1 neurons, assessed either at 7 days after ischemia or after the completion of behavioral testing 9 days after ischemia. In contrast, chronic estradiol did not reduce CA1 cell death 9 days after ischemia. Thus, long-term estradiol at near physiological levels and acute estradiol administered after ischemic insult improve functional recovery after global ischemia. These findings have important implications for intervention in the neurological sequellae associated with global ischemia.

Endogenous and exogenous hormone exposure and risk of cognitive impairment in Swedish twins: a preliminary study

PURPOSE

To analyze the risk of cognitive impairment among female Swedish Twins with regard to endogenous and exogenous hormone exposure.

DESIGN AND SETTING

A cross-sectional analysis of data from the HARMONY Study, a population-based cohort study of cognitive impairment in the Swedish Twin Registry.

METHODS

Information regarding age at menarche and menopause, parity, and length and type of hormone therapy (HT) was collected via a telephone interview from 6604 women, aged 65-84. Cognitive impairment was assessed with the TELE, a brief telephone cognitive screen.

RESULTS

Length of reproductive period was inversely associated with risk of cognitive impairment (p<0.01). The OR was 1.15 (CI 95% 0.96-1.36) for women with reproductive periods <35 years and 0.82 (CI 95% 0.66-1.00) for women with reproductive periods >39 years. Age at menopause was inversely associated with risk of cognitive impairment. Use of HT was associated with average 40% decline in the risk of cognitive impairment, independent of type and timing of treatment.

CONCLUSION

Our results suggest that both increased length of reproductive period and HT are associated with reduced risk of cognitive impairment.

Estrogen can act via estrogen receptor alpha and beta to protect hippocampal neurons against global ischemia-induced cell death

Estradiol at physiological concentrations intervenes in apoptotic death cascades and ameliorates neuronal death in experimental models of focal and global ischemia. The cellular targets that mediate estradiol protection of hippocampal neurons in global ischemia are, however, unclear. The present study examined the hypothesis that estradiol protects hippocampal neurons in ovariectomized rats via estrogen receptor (ER)alpha and/or beta. Estradiol (14 d pretreatment) afforded robust protection of CA1 neurons against global ischemia-induced death. The broad-spectrum ER antagonist ICI 182,780 (intracerebroventricularly, 0 and 12 h after ischemia) abolished estrogen protection, consistent with a role for ERs. To evaluate the potential roles of ERalpha vs. ERbeta in estrogen protection, we administered subtype-selective agonists for 14 d before and 7 d after ischemia. The ERalpha-selective agonist propyl pyrazole triol (PPT, 10 mg/kg) and ERbeta-selective agonist WAY 200070-3 (1 mg/kg) produced nearly complete protection of CA1 neurons in approximately 50% of the animals. PPT, but not WAY 200070-3, at doses used for protection, elicited lordosis, induced negative feedback inhibition of LH release, and reduced weight gain. These findings establish the efficacy of the PPT dose in neuroendocrine assays and specificity of WAY 200070-3 for ERbeta. We also examined the ability of estradiol and neuronal injury to regulate ERalpha and ERbeta expression. Both estradiol and global ischemia markedly increased ERalpha, but not ERbeta, protein in CA1. These data indicate that estradiol can act via ERalpha and ERbeta to protect CA1 neurons from global ischemia-induced death and that both estradiol and global ischemia modulate ERalpha expression in hippocampal CA1.

Neuroprotection by a selective estrogen receptor beta agonist in a mouse model of global ischemia

The present study employs selective estrogen receptor (ER) agonists to determine whether 17beta-estradiol-induced neuroprotection in global ischemia is receptor mediated and, if so, which subtype of receptor (ERalpha or ERbeta) is predominantly responsible. Halothane-anesthetized female C57Bl/6J mice were ovariectomized, and osmotic minipumps containing ERbeta agonist diarylpropiolnitrile (DPN) (8 mg.kg(-1).day(-1), n = 12) or vehicle (50% DMSO in 0.9% saline) (n = 9) or ERalpha agonist propyl pyrazole triol (PPT) (2 mg.kg(-1).day(-1), n = 13) or vehicle (50% DMSO in 0.9% saline) (n = 10) were implanted subcutaneously. One week later transient global ischemia was induced by bilateral carotid artery occlusion under halothane anesthesia, and the mice were perfusion fixed 72 h later. ERbeta agonist DPN significantly reduced ischemic damage by 70% in the caudate nucleus and 55% in the CA1 region compared with vehicle controls (P < 0.05, Mann-Whitney U-statistic). In contrast, pretreatment with the ERalpha agonist PPT had no effect on the extent of neuronal damage compared with controls. The data indicate a significant estrogen receptor-mediated neuroprotection in a global cerebral ischemia model involving ERbeta.

Differential effects of 17beta-estradiol upon stroke damage in stroke prone and normotensive rats

We previously reported that during pro-estrus (high endogenous estrogen levels), brain damage after middle cerebral artery occlusion (MCAO) was reduced in stroke-prone spontaneously hypertensive rats (SHRSP) but not in normotensive Wistar Kyoto rat (WKY). In the present study, we examined the effect of exogenous estrogen on brain damage after MCAO in SHRSP and WKY. A 17beta-estradiol (0.025 mg or 0.25 mg, 21 day release) or matching placebo pellet was implanted into ovariectomized WKY and SHRSP (3 to 4 months old) who then underwent distal diathermy-induced MCAO 2 weeks later. Plasma 17beta-estradiol levels for placebo and 17beta-estradiol groups were as follows: WKY 0.025 mg 16.4 +/- 8.5 (pg/mL, mean +/- SD) and 25.85 +/- 12.6; WKY 0.25 mg 18.2 +/- 9.0 and 69.8 +/- 27.4; SHRSP 0.25 mg 20.7 +/- 8.8 and 81.0 +/- 16.9. In SHRSP, infarct volumes at 24 hours after MCAO were similar in placebo and 17beta-estradiol groups: SHRSP 0.025 mg 126.7 +/- 15.3 mm (n = 6) and 114.0 +/- 14.1 mm (n = 8) (not significant); SHRSP 0.25 mg 113.5 +/- 22.3 mm (n = 8) and 129.7 +/- 26.2 mm (n = 7) (not significant), respectively. In WKY, 17beta-estradiol significantly increased infarct volume by 65% with 0.025 mg dose [36.1 +/- 20.7 mm (n = 8) and 59.7 +/- 19.3 mm (n = 8) (P = 0.033, unpaired t-test)] and by 96% with 0.25 mg dose [55.9 +/- 36.4 mm (n = 8) and 109.7 +/- 6.7 mm (n = 4) (P = 0.017)]. Thus, 17beta-estradiol increased stroke damage in normotensive rats with no significant effect in stroke-prone rats. Despite being contrary to our hypothesis, our findings add substance to the recently reported negative effects of 17beta-estradiol in clinical studies.

Estrogen and selective estrogen receptor modulators: neuroprotection in the Women's Health Initiative era

Estrogen has been comprehensively studied as a neuroprotective agent in women, animals, and a variety of in vitro models of neural injury and degeneration. Most data suggest that estrogen can benefit the ischemic brain and reduce cell death. However, recent data from the Women's Health Initiative have raised concerns about the utility and safety of chronic estrogen use in women. While estrogen is a potent and reproducible neuroprotectant in animals and in vitro, its current administration in women has had unanticipated and paradoxical effects. Nonetheless, estrogen's diverse actions make it an ideal prototype for developing new neuroprotectants such as selective estrogen receptor modulators (SERMs). SERMs represent a class of drugs with mixed estrogen agonistic and antagonistic activity. Experimental and clinical data suggest a neuroprotective role for SERMs in normal and injured brain. The discrepancy among observational studies, preclinical data, and clinical trials emphasizes the need for further study of the mechanisms leading to the increased incidence of stroke observed in postmenopausal women. Research is still needed to optimize combined or estrogen alone hormone replacement therapy options as well as the prevention/management of cerebrovascular/ central nervous system disorders. This review critiques estrogen and SERMs' neuroprotective potential in experimental and clinical studies of stroke and cerebrovascular disease.