Gender-linked brain injury in experimental stroke

In Situ Pluripotency Factor Expression Promotes Functional Recovery From Cerebral Ischemia

Recovery from ischemic tissue injury can be promoted by cell proliferation and neovascularization. Transient expression of four pluripotency factors (Pou5f1, Sox2, Myc, and Klf4) has been used to convert cell types but never been tested as a means to promote functional recovery from ischemic injury. Here we aimed to determine whether transient in situ pluripotency factor expression can improve neurobehavioral function. Cerebral ischemia was induced by transient bilateral common carotid artery occlusion, after which the four pluripotency factors were expressed through either doxycycline administration into the lateral ventricle in transgenic mice in which the four factors are expressed in a doxycycline-inducible manner. Histologic evaluation showed that this transient expression induced the proliferative generation of astrocytes and/or neural progenitors, but not neurons or glial scar, and increased neovascularization with upregulation of angiogenic factors. Furthermore, in vivo pluripotency factor expression caused neuroprotective effects such as increased numbers of mature neurons and levels of synaptic markers in the striatum. Dysplasia or tumor development was not observed. Importantly, neurobehavioral evaluations such as rotarod and ladder walking tests showed that the expression of the four factors dramatically promoted functional restoration from ischemic injury. These results provide a basis for novel therapeutic modality development for cerebral ischemia.

Gender disparities and thrombolysis use among patient with first-ever ischemic stroke in Malaysia

OBJECTIVE

Gender as an independent predictor in stroke has been well documented. However, data on gender differences among first-ever ischemic stroke in developing country are limited. We aim to describe gender effects on clinical characteristics, thrombolysis treatment received, and outcomes of patients with first-ever ischemic stroke.

METHODS

Data were extracted from the prospective multiethnic stroke registry, National Neurology Registry (NNEUR). Descriptive analysis and logistic regression were performed.

RESULTS

A total of 4762 first-ever ischemic stroke patients admitted to 13 government hospitals from July 2009 to June 2015 were available for this study. Slightly over half were male (55.1%), and they were 1.7 years younger than female (mean age, 63.6 versus 61.9 years, p < 0.001). Gender-age-adjusted incidence was observed to be higher in females (66.7 per 100,000) compared to males (57.4 per 100,000). First-ever ischemic stroke incidence increased by 24.3 and 11.2% among female and male annually. Female experienced significantly poorer functional outcome and greater 30-day in-hospital mortality compared to male. In subgroup analysis, only 31 (0.65%) patients were treated with thrombolysis.

DISCUSSION

First-ever ischemic stroke incidence increased by 24.3 and 11.2% among female and male annually. There were distinct symptoms at hospital presentation between genders. All our patients discharged home regardless of genders. In summary, Malaysian female first-ever ischemic stroke was older, present with severe stroke, greater number of risk factors and poorer functional outcome and 30-day in-hospital mortality compared to male.

Why estrogens matter for behavior and brain health

The National Institutes of Health (NIH) has required the inclusion of women in clinical studies since 1993, which has enhanced our understanding of how biological sex affects certain medical conditions and allowed the development of sex-specific treatment protocols. However, NIH's policy did not previously apply to basic research, and the NIH recently introduced a new policy requiring all new grant applications to explicitly address sex as a biological variable. The policy itself is grounded in the results of numerous investigations in animals and humans illustrating the existence of sex differences in the brain and behavior, and the importance of sex hormones, particularly estrogens, in regulating physiology and behavior. Here, we review findings from our laboratories, and others, demonstrating how estrogens influence brain and behavior in adult females. Research from subjects throughout the adult lifespan on topics ranging from social behavior, learning and memory, to disease risk will be discussed to frame an understanding of why estrogens matter to behavioral neuroscience.

High-dose estrogen treatment at reperfusion reduces lesion volume and accelerates recovery of sensorimotor function after experimental ischemic stroke

Estrogens have previously been shown to protect the brain against acute ischemic insults, by potentially augmenting cerebrovascular function after ischemic stroke. The current study hypothesized that treatment with sustained release of high-dose 17β-estradiol (E2) at the time of reperfusion from middle cerebral artery occlusion (MCAO) in rats would attenuate reperfusion injury, augment post-stroke angiogenesis and cerebral blood flow, and attenuate lesion volume. Female Wistar rats underwent ovariectomy, followed two weeks later by transient, two-hour right MCAO (tMCAO) and treatment with E2 (n=13) or placebo (P; n=12) pellets starting at reperfusion. E2 treatment resulted in significantly smaller total lesion volume, smaller lesions within striatal and cortical brain regions, and less atrophy of the ipsilateral hemisphere after six weeks of recovery. E2-treated animals exhibited accelerated recovery of contralateral forelimb sensorimotor function in the cylinder test. Magnetic resonance imaging (MRI) showed that E2 treatment reduced the formation of lesion cysts, decreased lesion volume, and increased lesional cerebral blood flow (CBF). K(trans), a measure of vascular permeability, was increased in the lesions. This finding, which represents lesion neovascularization, was not altered by E2 treatment. Ischemic stroke-related angiogenesis and vessel formation was confirmed with immunolabeling of brain tissue and was not altered with E2 treatment. In summary, E2 treatment administered immediately following reperfusion significantly reduced lesion size, cyst formation, and brain atrophy while improving lesional CBF and accelerating recovery of functional deficits in a rat model of ischemic stroke.

A Comparative Study of Variables Influencing Ischemic Injury in the Longa and Koizumi Methods of Intraluminal Filament Middle Cerebral Artery Occlusion in Mice

The intraluminal filament model of middle cerebral artery occlusion (MCAO) in mice and rats has been plagued by inconsistency, owing in part to the multitude of variables requiring control. In this study we investigated the impact of several major variables on survival rate, lesion volume, neurological scores, cerebral blood flow (CBF) and body weight including filament width, time after reperfusion, occlusion time and the choice of surgical method. Using the Koizumi method, we found ischemic injury can be detected as early as 30 min after reperfusion, to a degree that is not statistically different from 24 h post-perfusion, using 2,3,5-Triphenyltetrazolium chloride (TTC) staining. We also found a distinct increase in total lesion volume with increasing occlusion time, with 30–45 min a critical time for the development of large, reproducible lesions. Furthermore, although we found no significant difference in total lesion volume generated by the Koizumi and Longa methods of MCAO, nor were survival rates appreciably different between the two at 4 h after reperfusion, the Longa method produces significantly greater reperfusion. Finally, we found no statistical evidence to support the exclusion of data from animals experiencing a CBF reduction of <70% in the MCA territory following MCAO, using laser-Doppler flowmetry. Instead we suggest the main usefulness of laser-Doppler flowmetry is for guiding filament placement and the identification of subarachnoid haemorrhages and premature reperfusion. In summary, this study provides detailed evaluation of the Koizumi method of intraluminal filament MCAO in mice and a direct comparison to the Longa method.

The Importance of Considering Sex Differences in Translational Stroke Research

Stroke is the second leading cause of death worldwide, and differences between men and women have been documented in incidence, prevalence, and outcome. Here, we reviewed the literature on sex differences in stroke severity, mortality, functional outcome, and response to therapies after ischemic stroke. Many of the sex differences in stroke severity and mortality are explained by differences in baseline demographics such as older age in women. However, women account for more stroke deaths, consistently suffer from worse stroke outcomes, and are more often institutionalized and permanently disabled than men. These sex differences in functional outcome are equalized after treatment with tissue plasminogen activator (tPA) and women may benefit more from treatment than men. However, this may depend on race, as African-American women have less of a response to tPA than other groups. Regarding endovascular treatments, the few existing studies that have investigated sex differences in stroke outcome point to equal benefit in both sexes; however, many clinical trials are relatively underpowered to detect sex differences. Further, we considered sex-specific effects in animal models of stroke and present recommendations for the performance of stroke studies in female animals. The male-biased use of research animals is distinguished from the clinical situation where there is a disproportionate and growing female stroke population. Stroke in women is greatly understudied, and including both sexes is especially important in both preclinical and clinical studies that evaluate potential stroke therapies.

Human Motor Cortex Functional Changes in Acute Stroke: Gender Effects

The acute phase of stroke is accompanied by functional changes in the activity and interplay of both hemispheres. In healthy subjects, gender is known to impact the functional brain organization. We investigated whether gender influences also acute stroke functional changes. In thirty-five ischemic stroke patients, we evaluated the excitability of the affected (AH) and unaffected hemisphere (UH) by measuring resting and active motor threshold (AMT) and motor-evoked potential amplitude under baseline conditions and after intermittent theta burst stimulation (iTBS) of AH. We also computed an index of the excitability balance between the hemispheres, laterality indexes (LI), to evidence hemispheric asymmetry. AMT differed significantly between AH and UH only in the male group (p = 0.004), not in females (p > 0.200), and both LIAMT and LIRMT were significantly higher in males than in females (respectively p = 0.033 and p = 0.042). LTP-like activity induced by iTBS in AH was more frequent in females. Gender influences the functional excitability changes that take place after human stroke and the level of LTP that can be induced by repetitive stimulation. This knowledge is of high value in the attempt of individualizing to different genders any non-invasive stimulation strategy designed to foster stroke recovery.

Cerebrolysin dose-dependently improves neurological outcome in rats after acute stroke: A prospective, randomized, blinded, and placebo-controlled study

BACKGROUND

Cerebrolysin is a mixture of neuropeptides and free amino acids that is clinically used for the treatment of stroke. To further standardize treatment schemes, we assessed the dose response of Cerebrolysin on sensorimotor outcome in a rat model of ischemic stroke.

METHODS

This study was a prospective, blinded, placebo-controlled, preclinical experiment. Male and female Wistar rats, subjected to embolic middle cerebral artery occlusion, were randomly treated with Cerebrolysin doses of 0.8, 2.5, 5.0, 7.5 ml/kg or placebo, 4 h after middle cerebral artery occlusion for a total of 10 consecutive days.

RESULTS

The primary outcome was neurologic improvement at day 28, lesion volume, mortality, and animal weight were secondary and safety outcomes, respectively. There was a significant (p < 0.001) dose effect of Cerebrolysin on neurological outcome. Cerebrolysin at a dose of ≥ 2.5 ml/kg significantly (p < 0.001) improved neurological outcome (Mean Estimate (95% CL): 0.8 ml/kg: 6.2 (-6.0/18.4), 2.5 ml/kg: -28.9 (-41.6/-16.2), 5.0 ml/kg: -33.4 (-45.0/-21.7), 7.5 ml/kg: -36.3 (-48.2/-24.4). Higher doses (≥ 2.5 ml/kg) resulted in better recovery; however, differences between effective doses were not significant. Treatment with 5 ml/kg reduced lesion volume (p = 0.016). No treatment gender interactions were found and there were no differences in death or weight loss.

CONCLUSION

Collectively, these data on Cerebrolysin efficacy demonstrate the feasibility of a preclinical study setup following a randomized, placebo-controlled, and blinded design with a clinical relevant treatment scheme. Cerebrolysin at doses of ≥ 2.5 ml/kg improved functional outcome and at a dose of 5 ml/kg reduced infarct volume.

Estrogen receptors alpha mediates postischemic inflammation in chronically estrogen-deprived mice

Estrogens are known to exert neuroprotective and immuneomodulatory effects after stroke. However, at present, little is known about the role of estrogens and its receptors in postischemic inflammation after menopause. Here, we provide important in vivo evidence of a distinct shift in microglial phenotypes in the model of postmenopause brain. Using a model-system for live imaging of microglial activation in the context of chronic estrogen- and ERα-deficiency associated with aging, we observed a marked deregulation of the TLR2 signals and/or microglial activation in ovariectomized and/or ERα knockout mice. Further analysis revealed a 5.7-fold increase in IL-6, a 4.7-fold increase in phospho-Stat3 levels suggesting an overactivation of JAK/STAT3 pathway and significantly larger infarction in ERα knockouts chronically deprived of estrogen. Taken together, our results suggest that in the experimental model of menopause and/or aging, ERα mediates innate immune responses and/or microglial activation, and ischemia-induced production of IL-6. Based on our results, we propose that the loss of functional ERα may lead to deregulation of postischemic inflammatory responses and increased vulnerability to ischemic injury in aging female brains.

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

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

Regional cortical thinning of the orbitofrontal cortex in medication-naïve female patients with major depressive disorder is not associated with MAOA-uVNTR polymorphism

BACKGROUND

Orbitofrontal cortex alterations have been suggested to underlie the impaired mood regulation in depression. MAOA-uVNTR (monoamine oxidase A-upstream variable number of tandem repeats) polymorphism has been reported to be associated with major depressive disorder by various studies. The influence of MAOA-uVNTR genotype on function and structure of the orbitofrontal cortex has previously been reported. In this study, we investigated the difference in orbitofrontal cortex thickness between medication-naïve female patients with major depressive disorder and healthy controls, and the influence of MAOA-uVNTR genotype on orbitofrontal cortex thickness in depression.

METHODS

Thirty-one patients with major depressive disorder and 43 healthy controls were included. All participants were subjected to T1-weighted structural magnetic resonance imaging and genotyped for MAOA-uVNTR polymorphism. An automated procedure of FreeSurfer was used to analyze difference in orbitofrontal cortex thickness.

RESULTS

Patients showed a significantly thinner left orbitofrontal cortex (F_(1,71) = 7.941, p = 0.006) and right orbitofrontal cortex (F_(1,71) = 17.447, p < 0.001). For the orbitofrontal cortex sub-region analysis, patients showed a significantly thinner left medial orbitofrontal cortex (F_(1,71) = 8.117, p = 0.006), right medial orbitofrontal cortex (F_(1,71) = 21.795, p < 0.001) and right lateral orbitofrontal cortex (F_(1,71) = 9.932, p = 0.002) compared to healthy controls. No significant interaction of diagnosis and MAOA-uVNTR genotype on orbitofrontal cortex thickness was revealed.

CONCLUSIONS

Our results suggest that structural alterations of the orbitofrontal cortex may be associated with the pathophysiology of major depressive disorder. Future studies with larger sample sizes are needed to detect a possible association between MAOA-uVNTR genotype and orbitofrontal cortex thickness in depression.

The impact of gender on stroke pathology and treatment

Cerebral ischemic stroke is a leading cause of mortality and functional disability. However, unfortunately few effective treatments exist to counteract the deleterious pathological mechanisms triggered following an ischemic event. Epidemiological and experimental studies have revealed a significant difference in the vulnerability of males versus females to both the incidence of stroke and amount of resulting pathology following an ischemic stroke which is also dependent on the stage of lifespan. Here we review the evidence for gender differences in both the overall pathology and cellular mechanisms of injury following ischemic stroke. In addition, we discuss the evidence for any gender differences that may occur in the effectiveness of treatments and how this supports the need for the investigation and development of gender-specific therapies.

Role for microglia in sex differences after ischemic stroke: importance of M2

Inflammation plays a critical role in the pathogenesis of ischemic stroke. This process depends, in part, upon proinflammatory factors released by activated resident central nervous system (CNS) microglia (MG). Previous studies demonstrated that transfer of IL-10(+) B-cells reduced infarct volumes in male C57BL/6 J recipient mice when given 24 h prior to or therapeutically at 4 or 24 h after experimental stroke induced by 60 min middle cerebral artery occlusion (MCAO). The present study assesses possible sex differences in immunoregulation by IL-10(+) B-cells on primary male vs. female MG cultured from naïve and ischemic stroke-induced mice. Thus, MG cultures were treated with recombinant (r)IL-10, rIL-4 or IL-10(+) B-cells after lipopolysaccharide (LPS) activation and evaluated by flow cytometry for production of proinflammatory and anti-inflammatory factors. We found that IL-10(+) B-cells significantly reduced MG production of TNF-α, IL-1β and CCL3 post-MCAO and increased their expression of the anti-inflammatory M2 marker, CD206, by cell-cell interactions. Moreover, MG from female vs. male mice had higher expression of IL-4 and IL-10 receptors and increased production of IL-4, especially after treatment with IL-10(+) B-cells. These findings indicate that IL-10-producing B-cells play a crucial role in regulating MG activation, proinflammatory cytokine release and M2 phenotype induction, post-MCAO, with heightened sensitivity of female MG to IL-4 and IL-10. This study, coupled with our previous demonstration of increased numbers of transferred IL-10(+) B-cells in the ischemic hemisphere, provide a mechanistic basis for local regulation by secreted IL-10 and IL-4 as well as direct B-cell/MG interactions that promote M2-MG.

Ginkgo biloba Extract Prevents Female Mice from Ischemic Brain Damage and the Mechanism Is Independent of the HO1/Wnt Pathway

It is well known that gender differences exist in experimental or clinical stroke with respect to brain damage and loss of functional outcome. We have previously reported neuroprotective properties of Ginkgo biloba/EGb 761® (EGb 761) in transient and permanent mouse models of brain ischemia using male mice, and the mechanism of action was attributed to the upregulation of the heme oxygenase 1 (HO1)/Wnt pathway. Here, we sought to investigate whether EGb 761's protective effect in ovariectomized female mice following stroke is also mediated by the HO1/Wnt pathway. Female mice were ovariectomized (OVX) to remove the protective effect of estrogen and were treated with EGb 761 for 7 days prior to inducing permanent middle cerebral artery occlusion (pMCAO) and allowed to survive for an additional 7 days. At day 8, animals were sacrificed, and the brains were harvested for infarct volume analysis, western blots, and immunohistochemistry. The OVX female mice treated with EGb 761 showed significantly lower infarct size as compared to Veh/OVX animals. EGb 761 treatment in female mice inhibited apoptosis by preventing caspase-3 cleavage and blocking the extrinsic apoptotic pathway. EGb 761 pretreatment significantly enhanced neurogenesis in OVX mice as compared to the Veh/OVX group and significantly upregulated androgen receptor expression with no changes in HO1/Wnt signaling. These results suggest that EGb 761 prevented brain damage in OVX female mice by improving grip strength and neurological deficits, and the mechanism of action is not through HO1/Wnt but via blocking the extrinsic apoptotic pathway.

Proline-, glutamic acid-, and leucine-rich protein 1 mediates estrogen rapid signaling and neuroprotection in the brain

17-β estradiol (E2) has been implicated as neuroprotective in a variety of neurodegenerative disorders. However, the underlying mechanism remains unknown. Here, we provide genetic evidence, using forebrain-specific knockout (FBKO) mice, that proline-, glutamic acid-, and leucine-rich protein 1 (PELP1), an estrogen receptor coregulator protein, is essential for the extranuclear signaling and neuroprotective actions of E2 in the hippocampal CA1 region after global cerebral ischemia (GCI). E2-mediated extranuclear signaling (including activation of extracellular signal-regulated kinase and Akt) and antiapoptotic effects [such as attenuation of JNK signaling and increase in phosphorylation of glycogen synthase kinase-3β (GSK3β)] after GCI were compromised in PELP1 FBKO mice. Mechanistic studies revealed that PELP1 interacts with GSK3β, E2 modulates interaction of PELP1 with GSK3β, and PELP1 is a novel substrate for GSK3β. RNA-seq analysis of control and PELP1 FBKO mice after ischemia demonstrated alterations in several genes related to inflammation, metabolism, and survival in PELP1 FBKO mice, as well as a significant reduction in the activation of the Wnt/β-catenin signaling pathway. In addition, PELP1 FBKO studies revealed that PELP1 is required for E2-mediated neuroprotection and for E2-mediated preservation of cognitive function after GCI. Collectively, our data provide the first direct in vivo evidence, to our knowledge, of an essential role for PELP1 in E2-mediated rapid extranuclear signaling, neuroprotection, and cognitive function in the brain.

Sirtuin-2 mediates male specific neuronal injury following experimental cardiac arrest through activation of TRPM2 ion channels

OBJECTIVE

Sirtuins (Sirt) are a class of deacetylase enzymes that play an important role in cell proliferation. Sirt2 activation produces O-acetylated-ADPribose (OAADPr) which can act as a ligand for transient receptor potential cation channel, M2 (TRPM2). We tested the hypothesis that Sirt2 is activated following global cerebral ischemia and contributes to neuronal injury through activation of TRPM2.

METHODS

Adult male and female mice (8-12 weeks old) C57Bl/6 and TRPM2 knock-out mice were subjected to 8 min of cardiac arrest followed by cardiopulmonary resuscitation (CA/CPR). The Sirt2 inhibitor AGK-2 was administered intravenously 30 min after resuscitation. Hippocampal CA1 injury was analyzed at 3 days after CA/CPR. Acute Sirt2 activity was analyzed at 3 and 24 h after CA/CPR. Long-term hippocampal function was assessed using slice electrophysiology 7 days after CA/CPR.

RESULTS

AGK-2 significantly reduced CA1 injury in WT but not TRPM2 knock-out males and had no effect on CA1 injury in females. Elevated Sirt2 activity was observed in hippocampal tissue from males at 24 h after cardiac arrest and was reduced by AGK-2. In contrast, Sirt2 activity in females was increased at 3 but not 24 h. Finally, we observed long-term benefit of AGK-2 on hippocampal function, with a protection of long-term potentiation at CA1 synapses at 7 and 30 days after ischemia.

CONCLUSIONS

In summary, we observed a male specific activation of Sirt2 that contributes to neuronal injury and functional deficits after ischemia specifically in males. These results are consistent with a role of Sirt2 in activating TRPM2 following global ischemia in a sex specific manner. These results support the growing body of literature showing that oxidative stress mechanisms predominate in males and converge on TRPM2 activation as a mediator of cell death.

Demethylation of Circulating Estrogen Receptor Alpha Gene in Cerebral Ischemic Stroke

Background

Estrogen is involved in neuron plasticity and can promote neuronal survival in stroke. Its actions are mostly exerted via estrogen receptor alpha (ERα). Previous animal studies have shown that ERα is upregulated by DNA demethylation following ischemic injury. This study investigated the methylation levels in the ERα promoter in the peripheral blood of ischemic stroke patients.

Methods

The study included 201 ischemic stroke patients, and 217 age- and sex-comparable healthy controls. The quantitative methylation level in the 14 CpG sites of the ERα promoter was measured by pyrosequencing in each participant. Multivariate regression model was used to adjust for stroke traditional risk factors. Stroke subtypes and sex-specific analysis were also conducted.

Results

The results demonstrated that the stroke cases had a lower ERα methylation level than controls in all 14 CpG sites, and site13 and site14 had significant adjusted p-values of 0.035 and 0.026, respectively. Stroke subtypes analysis showed that large-artery atherosclerosis and cardio-embolic subtypes had significantly lower methylation levels than the healthy controls at CpG site5, site9, site12, site13 and site14 with adjusted p = 0.039, 0.009, 0.025, 0.046 and 0.027 respectively. However, the methylation level for the patients with small vessel subtype was not significant. We combined the methylation data from the above five sites for further sex-specific analysis. The results showed that the significant association only existed in women (adjusted p = 0.011), but not in men (adjusted p = 0.300).

Conclusions

Female stroke cases have lower ERα methylation levels than those in the controls, especially in large-artery and cardio-embolic stroke subtypes. The study implies that women suffering from ischemic stroke of specific subtype may undergo different protective mechanisms to reduce the brain injury.

Adoptive transfer of immune subsets prior to MCAO does not exacerbate stroke outcome in splenectomized mice

The peripheral immune response contributes to neurologic impairment after stroke and the extent of initial damage is greater in males than females. We have previously shown that spleen cells directly contribute to ischemic damage in males, as splenectomy prior to experimental stroke eliminates the sex differences in infarct volume. This study aims to determine which specific subset of immune cells exert pathogenic effects when injected 24 hours before MCAO induction into splenectomized male and female WT mice. The results demonstrate that CD4/CD8/CD11b treated mice had no significant effect on infarct volumes vs. vehicle-treated control mice after MCAO. However, there were significant alterations to the resident peripheral immune composition. These results suggest that there are regulatory factors resulting from splenectomy or other possible influences that inhibit peripheral immune cell contribution to neuroinflammation and thus contributing to differential effects of the spleen on stroke outcome in males and female mice.

Impact of Sex Difference on Severity and Functional Outcome in Patients with Cardioembolic Stroke

INTRODUCTION

Female sex is a risk factor for thromboembolic events in Caucasian, but not in Japanese, patients with nonvalvular atrial fibrillation. However, it remains unclear whether the female sex is also a risk factor for severe stroke and unfavorable functional outcome in patients with cardioembolic (CE) stroke.

METHODS

Three hundred fifty-five consecutive patients with CE stroke within 48 hours after onset and with a modified Rankin Scale (mRS) score of 1 or lower before onset were studied. We compared basic characteristics, stroke severity, and functional outcome between female (n = 157) and male (n = 198) patients.

RESULTS

The mean age was higher in female than in male patients (80 ± 8 versus 75 ± 9 years, P < .00001). The congestive heart failure, hypertension, age [≥ 75 years], diabetes, stroke/transient ischemic attack [TIA] (CHADS2) score before onset was similar between the two groups (median, 3 [2-4] in both groups). Stroke severity on admission, assessed by the National Institutes of Health Stroke Scale (NIHSS), was higher in female than in male patients (13 [5-20] versus 8 [3-16], P = .0009). Functional outcome at discharge, assessed by mRS, was unfavorable in female than in male patients (3 [1-5] versus 2 [1-4], P = .005). An mRS score of 3 or higher at discharge was found more in female than in male patients (59% versus 39%, P = .0001). Multivariate analyses confirmed that female sex was a significant determinant of severe stroke (NIHSS ≥ 8) on admission (odds ratio [OR] to male = 1.97; 95% confidence interval [CI]; 1.24-3.15, P = .004) and for the mRS score of 3 or higher at discharge (OR = 1.83; 95% CI, 1.16-2.89; P = .01). Similar results were obtained by propensity-score matching analysis.

CONCLUSIONS

Female sex is a risk factor for severe stroke on admission and unfavorable functional outcome at discharge in Japanese patients with CE stroke.

Resveratrol neuroprotection in stroke and traumatic CNS injury

Resveratrol, a stilbene formed in many plants in response to various stressors, elicits multiple beneficial effects in vertebrates. Particularly, resveratrol was shown to have therapeutic properties in cancer, atherosclerosis and neurodegeneration. Resveratrol-induced benefits are modulated by multiple synergistic pathways that control oxidative stress, inflammation and cell death. Despite the lack of a definitive mechanism, both in vivo and in vitro studies suggest that resveratrol can induce a neuroprotective state when administered acutely or prior to experimental injury to the CNS. In this review, we discuss the neuroprotective potential of resveratrol in stroke, traumatic brain injury and spinal cord injury, with a focus on the molecular pathways responsible for this protection.

The Zinc Ion Chelating Agent TPEN Attenuates Neuronal Death/apoptosis Caused by Hypoxia/ischemia Via Mediating the Pathophysiological Cascade Including Excitotoxicity, Oxidative Stress, and Inflammation

AIMS

We aim to determine the significant effect of TPEN, a Zn(2+) chelator, in mediating the pathophysiological cascade in neuron death/apoptosis induced by hypoxia/ischemia.

METHODS

We conducted both in vivo and in vitro experiments in this study. PC12 cells were used to establish hypoxia/ischemia model by applying oxygen-glucose deprivation (OGD). SHR-SP rats were used to establish an acute ischemic model by electrocoagulating middle cerebral artery occlusion. The effect of TPEN on neuron death/apoptosis was evaluated. In addition, the relative biomarks of excitotoxicity, oxidative stress, and inflammation reactions in hypoxia/ischemia PC12 cell model as well as in SHR-SP rat hypoxia/ischemia model were also assessed.

RESULTS

TPEN significantly attenuates the neurological deficit, reduced the cerebral infarction area and the ratio of apoptotic neurons, and increased the expression of GluR2 in the rat hypoxia/ischemia brain. TPEN also increased blood SOD activity, decreased blood NOS activity and blood MDA and IL-6 contents in rats under hypoxia/ischemia. In addition, TPEN significantly inhibited the death and apoptosis of cells and attenuated the alteration of GluR2 and NR2 expression caused by OGD or OGD plus high Zn(2+) treatments.

CONCLUSIONS

Zn(2+) is involved in neural cell apoptosis and/or death caused by hypoxia/ischemia via mediating excitotoxicity, oxidative stress, and inflammation.

Effect of sex and age interactions on functional outcome after stroke

Stroke is one of the leading causes of death and disability worldwide. Experimental and clinical studies showed that sex and age play an important role in deciding the outcome after stroke. At younger ages, males were shown to have a higher risk for stroke than females. However, this trend reverses in older ages particularly when females reach menopause. Many preclinical studies indicate that steroid hormones modulate the age-dependent differential stroke outcome. In addition, patterns of cell death pathways activated following cerebral ischemia are distinct between males and females, but independent of steroid hormones. Recent studies also indicate that microRNAs play important roles in mediating sex-specific stroke outcome by regulating stroke-related genes. This review discusses the contribution of sex and age to outcome after stroke with particular emphasis on the experimental studies that examined the effects of steroid hormones, differential cell death pathways, and involvement of sex-specific microRNAs following cerebral ischemia. Current understanding of the role of thrombolytic agents in stroke therapy is also discussed.

Sex-associated differences in the modulation of vascular risk in patients with asymptomatic carotid stenosis

In this study, we aimed to identify determinants of the different sex-related stroke risk in subjects with asymptomatic internal carotid artery (ICA) stenosis. In all, 492 women (44.4%) and 617 men (55.6%), with unilateral ⩾ 60% asymptomatic ICA stenosis, were prospectively evaluated with a median follow-up of 37 months (interquartile range, 26 to 43). Vascular risk profile, plaque characteristics, stenosis progression, and common carotid artery intima-media thickness were investigated. Outcome measure was the occurrence of ischemic stroke ipsilateral to ICA stenosis. Myocardial infarction, contralateral stroke and transient ischemic attack were considered as competing events. The incidence rate of ipsilateral stroke over the entire follow-up period was 0.16%: 0.09% (95% confidence interval (CI) 0.05 to 0.15) in women and 0.22% (95% CI 0.17 to 0.29) in men (log-rank test, P<0.001). Stenosis progression significantly influenced the risk of ipsilateral stroke in both men (subhazard ratio, SHR, 8.99) and women (SHR 4.89). Stenosis degree (71% to 90%, SHR 2.35; 91% to 99%, SHR 3.38) and irregular plaque surface (SHR 2.32) were relevant risk factors for ipsilateral stroke only in men. Our findings suggest that characteristics of the stenosis and plaque exert a different effect in modulating vascular risk in the two sexes. Understanding sex differences in cardiovascular disease could help to target sex-specific future therapies.

U0126 attenuates cerebral vasoconstriction and improves long-term neurologic outcome after stroke in female rats

Sex differences are well known in cerebral ischemia and may impact the effect of stroke treatments. In male rats, the MEK1/2 inhibitor U0126 reduces ischemia-induced endothelin type B (ETB) receptor upregulation, infarct size and improves acute neurologic function after experimental stroke. However, responses to this treatment in females and long-term effects on outcome are not known. Initial experiments used in vitro organ culture of cerebral arteries, confirming ERK1/2 activation and increased ETB receptor-mediated vasoconstriction in female cerebral arteries. Transient middle cerebral artery occlusion (tMCAO, 120 minutes) was induced in female Wistar rats, with U0126 (30 mg/kg intraperitoneally) or vehicle administered at 0 and 24 hours of reperfusion, or with no treatment. Infarct volumes were determined and neurologic function was assessed by 6-point and 28-point neuroscores. ETB receptor-mediated contraction was studied with myograph and protein expression with immunohistochemistry. In vitro organ culture and tMCAO resulted in vascular ETB receptor upregulation and activation of ERK1/2 that was prevented by U0126. Although no effect on infarct size, U0126 improved the long-term neurologic function after experimental stroke in female rats. In conclusion, early prevention of the ERK1/2 activation and ETB receptor-mediated vasoconstriction in the cerebral vasculature after ischemic stroke in female rats improves the long-term neurologic outcome.

Sex differences in ischemic stroke sensitivity are influenced by gonadal hormones, not by sex chromosome complement

Epidemiologic studies have shown sex differences in ischemic stroke. The four core genotype (FCG) mouse model, in which the testes determining gene, Sry, has been moved from Y chromosome to an autosome, was used to dissociate the effects of sex hormones from sex chromosome in ischemic stroke outcome. Middle cerebral artery occlusion (MCAO) in gonad intact FCG mice revealed that gonadal males (XXM and XYM) had significantly higher infarct volumes as compared with gonadal females (XXF and XYF). Serum testosterone levels were equivalent in adult XXM and XYM, as was serum estrogen in XXF and XYF mice. To remove the effects of gonadal hormones, gonadectomized FCG mice were subjected to MCAO. Gonadectomy significantly increased infarct volumes in females, while no change was seen in gonadectomized males, indicating that estrogen loss increases ischemic sensitivity. Estradiol supplementation in gonadectomized FCG mice rescued this phenotype. Interestingly, FCG male mice were less sensitive to effects of hormones. This may be due to enhanced expression of the transgene Sry in brains of FCG male mice. Sex differences in ischemic stroke sensitivity appear to be shaped by organizational and activational effects of sex hormones, rather than sex chromosomal complement.

Soluble epoxide hydrolase gene deletion improves blood flow and reduces infarct size after cerebral ischemia in reproductively senescent female mice

Soluble epoxide hydrolase (sEH), a key enzyme in the metabolism of vasodilatory epoxyeicosatrienoic acids (EETs), is sexually dimorphic, suppressed by estrogen, and contributes to underlying sex differences in cerebral blood flow and injury after cerebral ischemia. We tested the hypothesis that sEH inhibition or gene deletion in reproductively senescent (RS) female mice would increase cerebral perfusion and decrease infarct size following stroke. RS (15–18 month old) and young (3–4 month old) female sEH knockout (sEHKO) mice and wild type (WT) mice were subjected to 45 min middle cerebral artery occlusion (MCAO) with laser Doppler perfusion monitoring. WT mice were treated with vehicle or a sEH inhibitor t-AUCB at the time of reperfusion and every 24 h thereafter for 3 days. Differences in regional cerebral blood flow were measured in vivo using optical microangiography (OMAG). Infarct size was measured 3 days after reperfusion. Infarct size and cerebral perfusion 24 h after MCAO were not altered by age. Both sEH gene deletion and sEH inhibition increased cortical perfusion 24 h after MCAO. Neither sEH gene deletion nor sEH inhibition reduced infarct size in young mice. However, sEH gene deletion, but not sEH inhibition of the hydrolase domain of the enzyme, decreased infarct size in RS mice. Results of these studies show that sEH gene deletion and sEH inhibition enhance cortical perfusion following MCAO and sEH gene deletion reduces damage after ischemia in RS female mice; however this neuroprotection in absent is young mice.

Sex-Based Differences in Multiple Sclerosis (MS): Part II: Rising Incidence of Multiple Sclerosis in Women and the Vulnerability of Men to Progression of this Disease

It is well known that a number of autoimmune diseases including multiple sclerosis (MS) predominantly affect women and there has been much attention directed toward understanding why this is the case. Past research has revealed a number of sex differences in autoimmune responses that can account for the female bias in MS. However, much less is known about why the incidence of MS has increased exclusively in women over the past half century. The recency of this increase suggests that changing environmental or lifestyle factors are interacting with biological sex to increase MS risk predominantly in females. Indeed, a number of recent studies have identified sex-specific differences in the effect of environmental factors on MS incidence. The first part of this chapter will overview this evidence and will discuss the possible scenarios of how the environment may be interacting with autoimmune mechanisms to contribute to the preferential rise in MS incidence in women. Despite the strong female bias in MS incidence, culminating evidence from natural history studies, and imaging and pathology studies suggests that males who develop MS may exhibit a more rapid decline in disability and cognitive functioning than women. Very little is known about the biological basis of this more rapid deterioration, but some insights have been provided by studies in rodent models of demyelination/remyelination. The second part of this chapter will overview the evidence that males with relapsing-onset MS undergo a more rapid progression of disease than females and will discuss potential biological mechanisms that account for this sex difference.

Estrogen-IGF-1 interactions in neuroprotection: ischemic stroke as a case study

The steroid hormone 17b-estradiol and the peptide hormone insulin-like growth factor (IGF)-1 independently exert neuroprotective actions in neurologic diseases such as stroke. Only a few studies have directly addressed the interaction between the two hormone systems, however, there is a large literature that indicates potentially greater interactions between the 17b-estradiol and IGF-1 systems. The present review focuses on key issues related to this interaction including IGF-1 and sex differences and common activation of second messenger systems. Using ischemic stroke as a case study, this review also focuses on independent and cooperative actions of estrogen and IGF-1 on neuroprotection, blood brain barrier integrity, angiogenesis, inflammation and post-stroke epilepsy. Finally, the review also focuses on the astrocyte, a key mediator of post stroke repair, as a local source of 17b-estradiol and IGF-1. This review thus highlights areas where significant new research is needed to clarify the interactions between these two neuroprotectants.

Plasma Estrogen Levels Are Associated With Severity of Injury and Outcomes After Aneurysmal Subarachnoid Hemorrhage

BACKGROUND

Biochemical mediators alter cerebral perfusion and have been implicated in delayed cerebral ischemia (DCI) and poor outcomes after aneurysmal subarachnoid hemorrhage (aSAH). Estrogens (estrone [E1] and estradiol [E2]) are mediators with neuroprotective properties that could play a role in DCI. This study explored associations between plasma estrogen levels and outcomes following aSAH.

METHODS

Plasma samples from 1-4, 4-6, and 7-10 days after hemorrhage from 99 adult aSAH patients were analyzed for estrogen levels using liquid chromatography tandem mass spectrometry. DCI was operationalized as radiographic/ultrasonic evidence of impaired cerebral blood flow accompanied by neurological deterioration. Outcomes were assessed using the Modified Rankin Scale at 3 and 12 months after hemorrhage. Statistical analysis included correlation, regression, and group-based trajectory.

RESULTS

Higher E1 and E2 levels were associated with higher Hunt and Hess grade (E1, p = .01; E2, p = .03), the presence of DCI (E1, p = .02; E2, p = .02), and poor 3-month outcomes (E1, p = .002; E2, p = .002). Trajectory analysis identified distinct populations over time for E1 (61% E1 high) and E2 (68% E2 high). Patients in higher trajectory groups had higher Fisher grades (E1, p = .008; E2, p = .01), more frequent DCI (E1, p = .04; E2, p = .08), and worse 3-month outcomes (E1, p = .01; E2, p = .004) than low groups.

CONCLUSIONS

These results provide the first clinical evidence that plasma E1 and E2 concentrations are associated with severity of injury and outcomes after aSAH.

Splenectomy reduces infarct volume and neuroinflammation in male but not female mice in experimental stroke

The peripheral immune response contributes to neurodegeneration after stroke yet little is known about how this process differs between males and females. The current study demonstrates that splenectomy prior to experimental stroke eliminates sex differences in infarct volume and activated brain monocytes/microglia. In the periphery of both sexes, activated T cells correlate directly with stroke outcome while monocytes are reduced by splenectomy only in males. This study provides new information about the sex specific mechanisms of the peripheral immune response in neurodegeneration after stroke and demonstrates the need for representation of both sexes in basic and clinical stroke research.

Sex Steroids Do Not Modulate TRPM2-Mediated Injury in Females following Middle Cerebral Artery Occlusion(1,2,3)

TRPM2 is an ion channel that is activated by ischemia in stroke and contributes to neuronal injury only in males. We tested whether the lack of TRPM2 activation following stroke in females is caused by differences in sex steroids.

Calcium-permeable transient receptor potential M2 (TRPM2) ion channel activation contributes to cerebral ischemic injury specifically in males. In male mice, circulating androgens are required for TRPM2 inhibition with clotrimazole (CTZ) to provide protection following experimental stroke. Sufficient levels of circulating androgens are necessary to support ischemia-induced activation of poly ADP ribose polymerase (PARP) and consequent activation of TRPM2 channels. In this study, we tested whether differences in sex steroids contribute to the lack of CTZ neuroprotection in females. Middle cerebral artery occlusion (MCAO) was performed using adult female mice that were hormonally intact, ovariectomized (OVX) or dihydrotestosterone (DHT) treated. CTZ or vehicle was administered at the time of reperfusion, animals were euthanized 24 h later and brains and serum were collected. Infarct analysis revealed no effect of CTZ in intact females or females lacking endogenous sex steroids (OVX). Interestingly, treatment of female mice with the potent androgen receptor agonist DHT had no effect on ischemic injury and did not permit CTZ neuroprotection. Similarly, DHT-treated females did not exhibit increased levels of ADPribose, the TRPM2 ligand generated by PARP, following ischemia. No differences in TRPM2 or androgen receptor expression were observed between males and females. These data suggest that the lack of TRPM2 activation in females following experimental stroke is not due to the presence of estrogen or the absence of androgens. In conclusion, our data demonstrate that while circulating androgens are necessary for PARP-mediated TRPM2 injury in males, they are not sufficient to produce TRPM2 activation in females.

Microglial activation occurs in the absence of anxiety-like behavior following microembolic stroke in female, but not male, rats

Background

The incidence of depression and anxiety disorders is twice as high in women than men; however, females exhibit less neuronal damage following an equivalent ischemic event. Microembolic stroke increases anxiety- and depressive-like behaviors in male rats but the behavioral repercussions in females are unknown.

Findings

Given the relative neuronal protection from stroke in ovary-intact females, female rats exposed to microembolic stroke may be behaviorally protected as compared to males. The data presented demonstrate that anxiety-like behavior is increased in males despite a comparable increase in microglial activation following microembolic stroke in both males and females.

Conclusions

These data suggest that males may be more behaviorally susceptible to the effects of microembolic stroke and further illustrate a dissociation between neuroinflammation and behavior in females.

A novel atherothrombotic model of ischemic stroke induced by injection of collagen into the cerebral vasculature

BACKGROUND

Most ischemic strokes in humans are caused by ruptured arterial atheroma, which activate platelets and produce thrombi that occlude cerebral vessels.

METHODS

To simulate these events, we threaded a catheter through the internal carotid artery toward the middle cerebral artery (MCA) orifice and injected collagen directly into the cerebral circulation of male C57Bl/6 mice and Wistar rats.

RESULTS

Laser-Doppler flowmetry demonstrated reductions in cerebral blood flow (CBF) of ∼80% in mice and ∼60% in rats. CBF spontaneously increased but remained depressed after catheter withdrawal. Magnetic resonance imaging showed that ipsilateral CBF was reduced at 3h after collagen injection and markedly improved at 48 h. Micro-computed tomography revealed reduced blood vessel density in the ipsilateral MCA territory at 3 h. Gross examination of excised brains revealed thrombi within ipsilateral cerebral arteries at 3 h, but not 24 h, after collagen injection. Immunofluorescence microscopy confirmed that platelets and fibrinogen/fibrin were major components of these thrombi at both macrovascular and microvascular levels. Cerebral infarcts comprising ∼30% of hemispheric volume and neurobehavioral deficits were observed 48 h after ischemic injury in both mice and rats.

COMPARISON WITH EXISTING METHODS

Collagen injection caused brain injury that was similar in magnitude and variability to mechanical MCA occlusion or injection of a pre-formed clot; however, alterations in CBF and the mechanism of vascular occlusion were more consistent with clinical ischemic stroke.

CONCLUSION

This novel rodent model of ischemic stroke has pathophysiologic characteristics consistent with clinical atherothrombotic stroke, is technically feasible, and creates reproducible brain injury.

Dying neurons in thalamus of asphyxiated term newborns and rats are autophagic

OBJECTIVE

Neonatal hypoxic-ischemic encephalopathy (HIE) still carries a high burden by its mortality and long-term neurological morbidity in survivors. Apart from hypothermia, there is no acknowledged therapy for HIE, reflecting the lack of mechanistic understanding of its pathophysiology. (Macro)autophagy, a physiological intracellular process of lysosomal degradation, has been proposed to be excessively activated in excitotoxic conditions such as HIE. The present study examines whether neuronal autophagy in the thalamus of asphyxiated human newborns or P7 rats is enhanced and related to neuronal death processes.

METHODS

Neuronal autophagy and cell death were evaluated in the thalamus (frequently injured in severe HIE) of both human newborns who died after severe HIE (n = 5) and P7 hypoxic-ischemic rats (Rice-Vannuci model). Autophagic (LC3, p62), lysosomal (LAMP1, cathepsins), and cell death (TUNEL, caspase-3) markers were studied by immunohistochemistry in human and rat brain sections, and by additional methods in rats (immunoblotting, histochemistry, and electron microscopy).

RESULTS

Following severe perinatal asphyxia in both humans and rats, thalamic neurons displayed up to 10-fold (p < 0.001) higher numbers of autophagosomes and lysosomes, implying an enhanced autophagic flux. The highly autophagic neurons presented strong features of apoptosis. These findings were confirmed and elucidated in more detail in rats.

INTERPRETATION

These results show for the first time that autophagy is enhanced in severe HIE in dying thalamic neurons of human newborns, as in rats. Experimental neuroprotective strategies targeting autophagy could thus be a promising lead to follow for the development of future therapeutic approaches.

Possible roles of astrocytes in estrogen neuroprotection during cerebral ischemia

17β-Estradiol (E2), one of female sex hormones, has well-documented neuroprotective effects in a variety of clinical and experimental disorders of the central cerebral ischemia, including stroke and neurodegenerative diseases. The cellular mechanisms that underlie these protective effects of E2 are uncertain because a number of different cell types express estrogen receptors in the central nervous system. Astrocytes are the most abundant cells in the central nervous system and provide structural and nutritive support of neurons. They interact with neurons by cross-talk, both physiologically and pathologically. Proper astrocyte function is particularly important for neuronal survival under ischemic conditions. Dysfunction of astrocytes resulting from ischemia significantly influences the responses of other brain cells to injury. Recent studies demonstrate that estrogen receptors are expressed in astrocytes, indicating that E2 may exert multiple regulatory actions on astrocytes. Cerebral ischemia induced changes in the expression of estrogen receptors in astrocytes. In the present review, we summarize the data in support of possible roles for astrocytes in the mediation of neuroprotection by E2 against cerebral ischemia.

Animal models of stroke: translational potential at present and in 2050

Translation from basic science bench research in ischemic stroke to bedside treatment of patients suffering ischemic stroke remains a difficult challenge. Despite literally hundreds of compounds and interventions that provide benefit in experimental models of cerebral ischemia, efficacy in humans remains to be demonstrated. The reasons for failure to translate the extensive positive basic science findings to successful clinical trials have been the focus of discussion for years. Some attribute the failure to flaws in clinical trial design, others question the predictive value of current animal models and some question the quality of preclinical data. It is likely that a combination of all these shortcomings have ultimately led to the failure. The purpose of this review is to analyze the commonly used animal models used in the field today, provide a framework for understanding the current state of basic science research in the ischemic stroke field and discuss a path forward.

Traumatic brain injury dysregulates microRNAs to modulate cell signaling in rat hippocampus

Traumatic brain injury (TBI) is a common cause for cognitive and communication problems, but the molecular and cellular mechanisms are not well understood. Epigenetic modifications, such as microRNA (miRNA) dysregulation, may underlie altered gene expression in the brain, especially hippocampus that plays a major role in spatial learning and memory and is vulnerable to TBI. To advance our understanding of miRNA in pathophysiological processes of TBI, we carried out a time-course microarray analysis of microRNA expression profile in rat ipsilateral hippocampus and examined histological changes, apoptosis and synapse ultrastructure of hippocampus post moderate TBI. We found that 10 out of 156 reliably detected miRNAs were significantly and consistently altered from one hour to seven days after injury. Bioinformatic and gene ontology analyses revealed 107 putative target genes, as well as several biological processes that might be initiated by those dysregulated miRNAs. Among those differentially expressed microRNAs, miR-144, miR-153 and miR-340-5p were confirmed to be elevated at all five time points after TBI by quantitative RT-PCR. Western blots showed three of the predicated target proteins, calcium/calmodulin-dependent serine protein kinase (CASK), nuclear factor erythroid 2-related factor 2 (NRF2) and alpha-synuclein (SNCA), were concurrently down- regulated, suggesting that miR-144, miR-153 and miR-340-5p may play important roles collaboratively in the pathogenesis of TBI-induced cognitive and memory impairments. These microRNAs might serve as potential targets for progress assessment and intervention against TBI to mitigate secondary damage to the brain.

Sex differences in cognitive impairment and Alzheimer's disease

Studies have shown differences in specific cognitive ability domains and risk of Alzheimer's disease between the men and women at later age. However it is important to know that sex differences in cognitive function during adulthood may have their basis in both organizational effects, i.e., occurring as early as during the neuronal development period, as well as in activational effects, where the influence of the sex steroids influence brain function in adulthood. Further, the rate of cognitive decline with aging is also different between the sexes. Understanding the biology of sex differences in cognitive function will not only provide insight into Alzheimer's disease prevention, but also is integral to the development of personalized, gender-specific medicine. This review draws on epidemiological, translational, clinical, and basic science studies to assess the impact of sex differences in cognitive function from young to old, and examines the effects of sex hormone treatments on Alzheimer's disease in men and women.

Mechanism of the sex difference in endothelial dysfunction after stroke

Stroke, the number four cause of death in the United States, is a greatly debilitating event resulting from insufficient blood supply to the brain (cerebral ischemia). Endothelial dysfunction, primarily characterized by dampened endothelial- dependent vasodilation, is a major contributor to the development and outcome of stroke. This review discusses the role of soluble epoxide hydrolase (sEH), an enzyme responsible for the degradation of vasoprotective eicosatrienoic acids (EETs), in the context of the cerebral vasculature and its contribution to the sexual dimorphic nature of stroke.

Biological sex and mechanisms of ischemic brain injury

Cerebrovascular disease is a leading cause of death-from-disease and of disability worldwide, affecting some 15 million people. The incidence of stroke or "brain attack" is unlikely to recede for a decade at minimum by most predictions, despite large public health initiatives in stroke prevention. It has been well established that stroke is also one of the most strikingly sex-specific diseases in its epidemiology, and in some cases, in patient outcomes. For example, women sustain lower rates of ischemic stroke relative to men, even beyond their menopausal years. In contrast, outcomes are worse in women in many clinical studies. The biological basis for this sexual dimorphism is a compelling story, and both hormone-dependent and hormone-independent factors are involved, the latter of which is the subject of this brief review. Understanding the molecular and cell-based mechanisms underlying sex differences in ischemic brain injury is an important step toward personalized medicine and effective therapeutic interventions in patients of both sexes.

Phenotypic changes in immune cell subsets reflect increased infarct volume in male vs. female mice

Inflammatory responses in the brain after cerebral ischemia have been studied extensively in male mice, but not female mice, thus potentially giving a less-than-accurate view of gender associated pathological processes. In humans, cerebral infarcts are typically smaller in premenopausal females than in age-matched males. In the current study, we confirmed smaller infarcts in female vs. male mice after middle cerebral artery occlusion and 96 h of reperfusion. Moreover, we explored immunological alterations related to this difference and found that the percentage of CD4+ T lymphocytes was significantly higher in spleens in males than females, with increased expression of the activation markers, CD69 and CD44. In contrast, the percentage of CD8+ T lymphocytes was significantly higher in spleens of females than males, leading to the identification of a small but distinct population of IL-10-secreting CD8+CD122+ suppressor T cells that were also increased in females. Finally, we observed that males have a greater percentage of activated macrophages/microglia in the brain than females, as well as increased expression of the VLA-4 adhesion molecule in both brain and spleen. This new information suggesting gender-dependent immunological mechanisms in stroke implies that effective treatments for human stroke may also be gender specific.

Circulating miRNA profiles provide a biomarker for severity of stroke outcomes associated with age and sex in a rat model

Small non-coding RNA [miRNA (microRNA)] found in the circulation have been used successfully as biomarkers and mechanistic targets for chronic and acute disease. The present study investigated the impact of age and sex on miRNA expression following ischaemic stroke in an animal model. Adult (6 month) and middle-aged (11-12 months) female and male rats were subject to MCAo (middle cerebral artery occlusion) using ET-1 (endothelin-1). Circulating miRNAs were analysed in blood samples at 2 and 5 days post-stroke, and brain miRNAs were analysed at 5 days post-stroke. Although stroke-associated infarction was observed in all groups, infarct volume and sensory-motor deficits were significantly reduced in adult females compared with middle-aged females, adult males or middle-aged males. At 2 days post-stroke, 21 circulating miRNAs were differentially regulated and PCA (principal component analysis) confirmed that most of the variance was due to age. At 5 days post-stroke, 78 circulating miRNAs exhibited significantly different regulation, and most of the variance was associated with sex. A small cohort (five) of miRNAs, miR-15a, miR-19b, miR-32 miR-136 and miR-199a-3p, were found to be highly expressed exclusively in adult females compared with middle-aged females, adult males and middle-aged males. Predicted gene targets for these five miRNAs analysed for KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways revealed that the top ten KEGG pathways were related to growth factor signalling, cell structure and PI3K (phosphoinositide 3-kinase)/Akt and mTOR (mammalian target of rapamycin) signalling. Overall, the pattern of circulating miRNA expression suggests an early influence of age in stroke pathology, with a later emergence of sex as a factor for stroke severity.

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.

Clinical characteristics of acute lacunar stroke in women: emphasis on gender differences

There are few studies analyzing features of ischemic stroke subtypes in women. We assessed gender differences in lacunar stroke subtype based on data collected from a prospective stroke registry in Barcelona, Spain. Lacunar ischemic stroke was diagnosed in 310 (8.1 %) women and 423 (11.1 %) men of a total of 3,808 consecutive stroke patients included in a prospective hospital-based stroke registry, in Barcelona, Catalonia (Spain), over a period of 19 years. Independent factors for lacunar stroke in women were assessed by multivariate analysis. Women accounted for 42 % of all lacunar stroke patients (n = 733) in the registry and 11.4 % of all patients with ischemic stroke (n = 2,704). Very old age (85 years or older) was found in 20.3 % in women versus 11.1 % in men (P < 0.0001). In the logistic regression analysis, obesity [odds ratio (OR) = 4.24], prolonged hospital stay (>12 days) (OR = 1.59), arterial hypertension (OR = 1.50), and age (OR = 1.06) were significant variables independently associated with lacunar stoke in women, whereas peripheral vascular disease (OR = 0.51), chronic obstructive pulmonary disease (OR = 0.46), renal dysfunction (OR = 0.13), and heavy smoking (OR = 0.04) were independent variables for lacunar stroke in men. Women with lacunar stroke were remarkably older and presented with obesity and hypertension more frequently than did men. Lacunar stroke severity was similar in men and women. These findings in lacunar stroke patients could be explained by differences in gender for ischemic stroke in general.

Brain-derived estrogen exerts anti-inflammatory and neuroprotective actions in the rat hippocampus

17β-estradiol (E2) has been implicated to play a critical role in neuroprotection, synaptic plasticity, and cognitive function. Classically, the role of gonadal-derived E2 in these events is well established, but the role of brain-derived E2 is less clear. To address this issue, we investigated the expression, localization, and modulation of aromatase and local E2 levels in the hippocampus following global cerebral ischemia (GCI) in adult ovariectomized rats. Immunohistochemistry (IHC) revealed that the hippocampal regions CA1, CA3 and dentate gyrus (DG) exhibited high levels of immunoreactive aromatase staining, with aromatase being co-localized primarily in neurons in non-ischemic animals. Following GCI, aromatase became highly expressed in GFAP-positive astrocytes in the hippocampal CA1 region at 2-3 days post GCI reperfusion. An ELISA for E2 and IHC for E2 confirmed the GCI-induced elevation of local E2 in the CA1 region and that the increase in local E2 occurred in astrocytes. Furthermore, central administration of aromatase antisense (AS) oligonucleotides, but not missense (MS) oligonucleotides, blocked the increase in aromatase and local E2 in astrocytes after GCI, and resulted in a significant increase in GCI-induced hippocampal CA1 region neuronal cell death and neuroinflammation. As a whole, these results suggest that brain-derived E2 exerts important neuroprotective and anti-inflammatory actions in the hippocampal CA1 region following GCI.

Novel humanized recombinant T cell receptor ligands protect the female brain after experimental stroke

Transmigration of peripheral leukocytes to the brain is a major contributor to cerebral ischemic cell death mechanisms. Humanized partial major histocompatibility complex class II constructs (pMHC), covalently linked to myelin peptides, are effective for treating experimental stroke in males, but new evidence suggests that some inflammatory cell death mechanisms after brain injury are sex-specific. We here demonstrate that treatment with pMHC constructs also improves outcomes in female mice with middle cerebral artery occlusion (MCAO). HLA-DR2 transgenic female mice with MCAO were treated with RTL1000 (HLA-DR2 moiety linked to human MOG-35-55 peptide), HLA-DRa1-MOG-35-55, or vehicle (VEH) at 3, 24, 48, and 72 h after reperfusion and were recovered for 96 h or 2 weeks post-injury for measurement of histology (TTC staining) or behavioral testing. RTL1000- and DRa1-MOG-treated mice had profoundly reduced infarct volumes as compared to the VEH group, although higher doses of DRa1-MOG were needed for females vs. males evaluated previously. RTL1000-treated females also exhibited strongly improved functional recovery in a standard cylinder test. In novel studies of post-ischemic ultrasonic vocalization (USV), as measured by animal calls to their cage mates, we modeled in mice the post-stroke speech deficits common in human stroke survivors. The number of calls was reduced in injured animals relative to pre-MCAO baseline regardless of RTL1000 treatment status. However, call duration was significantly improved by RTL1000 treatment, suggesting benefit to the animal’s recovery of vocalization capability. We conclude that both the parent RTL1000 molecule and the novel non-polymorphic DRα1-MOG-35-55 construct were highly effective immunotherapies for treatment of transient cerebral ischemia in females.