Sex shapes experimental ischemic brain injury

The Alpha 7 Nicotinic Acetylcholine Receptor Does Not Affect Neonatal Brain Injury

Inflammation plays a central role in the development of neonatal brain injury. The alpha 7 nicotinic acetylcholine receptor (α7nAChR) can modulate inflammation and has shown promising results as a treatment target in rodent models of adult brain injury. However, little is known about the role of the α7nAChR in neonatal brain injury. Hypoxic-ischemic (HI) brain injury was induced in male and female C57BL/6 mice, α7nAChR knock-out (KO) mice and their littermate controls on postnatal day (PND) 9–10. C57BL/6 pups received i.p. injections of α7nAChR agonist PHA 568487 (8 mg/kg) or saline once daily, with the first dose given directly after HI. Caspase-3 activity and cytokine mRNA expression in the brain was analyzed 24 h after HI. Motor function was assessed 24 and 48 h after HI, and immunohistochemistry was used to assess tissue loss at 24 h and 7 days after HI and microglial activation 7 days after HI. Activation of α7nAChR with the agonist PHA 568487 significantly decreased CCL2/MCP-1, CCL5/RANTES and IL-6 gene expression in the injured brain hemisphere 24 h after HI compared with saline controls in male, but not female, pups. However, α7nAChR activation did not alter caspase-3 activity and TNFα, IL-1β and CD68 mRNA expression. Furthermore, agonist treatment did not affect motor function (24 or 48 h), neuronal tissue loss (24 h or 7 days) or microglia activation (7 days) after HI in either sex. Knock-out of α7nAChR did not influence neuronal tissue loss 7 days after HI. In conclusion, targeting the α7nAChR in neonatal brain injury shows some effect on dampening acute inflammatory responses in male pups. However, this does not lead to an effect on overall injury outcome.

Blood substitution therapy rescues the brain of mice from ischemic damage

Acute stroke causes complex, pathological, and systemic responses that have not been treatable by any single medication. In this study, using a murine transient middle cerebral artery occlusion stroke model, a novel therapeutic strategy is proposed, where blood replacement (BR) robustly reduces infarctions and improves neurological deficits in mice. Our analyses of immune cell subsets suggest that BR therapy substantially decreases neutrophils in blood following a stroke. Electrochemiluminescence detection demonstrates that BR therapy reduces cytokine storm in plasma and ELISA demonstrates reduced levels of matrix metalloproteinase-9 (MMP-9) in the plasma and brains at different time points post-stroke. Further, we have demonstrated that the addition of MMP-9 to the blood diminishes the protective effect of the BR therapy. Our study is the first to show that BR therapy leads to profoundly improved stroke outcomes in mice and that the improved outcomes are mediated via MMP-9. These results offer new insights into the mechanisms of stroke damage.

Acute stroke causes complex, pathological, and systemic responses which remain challenging to treat. Here, the authors show that substituting the blood of stroke model mice with whole-blood from naive healthy donor mice reduces infarct volume and improves neurological deficits.

Hypothermic neuroprotection against acute ischemic stroke: The 2019 update

Acute ischemic stroke is a leading cause of death and disability worldwide. Therapeutic hypothermia has long been considered as one of the most robust neuroprotective strategies. Although the neuroprotective effects of hypothermia have only been confirmed in patients with global cerebral ischemia after cardiac arrest and in neonatal hypoxic ischemic encephalopathy, establishing standardized protocols and strictly controlling the key parameters may extend its application in other brain injuries, such as acute ischemic stroke. In this review, we discuss the potential neuroprotective effects of hypothermia, its drawbacks evidenced in previous studies, and its potential clinical application for acute ischemic stroke especially in the era of reperfusion. Based on the different conditions between bench and bedside settings, we demonstrate the importance of vascular recanalization for neuroprotection of hypothermia by analyzing numerous literatures regarding hypothermia in focal cerebral ischemia. Then, we make a thorough analysis of key parameters of hypothermia and introduce novel hypothermic therapies. We advocate in favor of the process of clinical translation of intra-arterial selective cooling infusion in the era of reperfusion and provide insights into the prospects of hypothermia in acute ischemic stroke.

Systemic inflammation in hemorrhagic strokes - A novel neurological sign and therapeutic target?

Growing evidences suggest that stroke is a systemic disease affecting many organ systems beyond the brain. Stroke-related systemic inflammatory response and immune dysregulations may play an important role in brain injury, recovery, and stroke outcome. The two main phenomena in stroke-related peripheral immune dysregulations are systemic inflammation and post-stroke immunosuppression. There is emerging evidence suggesting that the spleen contracts following ischemic stroke, activates peripheral immune response and this may further potentiate brain injury. Whether similar brain-immune crosstalk occurs in hemorrhagic strokes such as intracerebral hemorrhage (ICH) and subarachnoid hemorrhage (SAH) is not established. In this review, we systematically examined animal and human evidence to date on peripheral immune responses associated with hemorrhagic strokes. Specifically, we reviewed the impact of clinical systemic inflammatory response syndrome (SIRS), inflammation- and immune-associated biomarkers, the brain-spleen interaction, and cellular mediators of peripheral immune responses to ICH and SAH including regulatory T cells (Tregs). While there is growing data suggesting that peripheral immune dysregulation following hemorrhagic strokes may be important in brain injury pathogenesis and outcome, details of this brain-immune system cross-talk remain insufficiently understood. This is an important unmet scientific need that may lead to novel therapeutic strategies in this highly morbid condition.

A new era for stroke therapy: Integrating neurovascular protection with optimal reperfusion

Recent advances in stroke reperfusion therapies have led to remarkable improvement in clinical outcomes, but many patients remain severely disabled, due in part to the lack of effective neuroprotective strategies. In this review, we show that 95% of published preclinical studies on "neuroprotectants" (1990-2018) reported positive outcomes in animal models of ischemic stroke, while none translated to successful Phase III trials. There are many complex reasons for this failure in translational research, including that the majority of clinical trials did not test early delivery of neuroprotectants in combination with successful reperfusion. In contrast to the clinical trials, >80% of recent preclinical studies examined the neuroprotectant in animal models of transient ischemia with complete reperfusion. Furthermore, only a small fraction of preclinical studies included long-term functional assessments, aged animals of both genders, and models with stroke comorbidities. Recent clinical trials demonstrate that 70%-80% of patients treated with endovascular thrombectomy achieve successful reperfusion. These successes revive the opportunity to retest previously failed approaches, including cocktail drugs that target multiple injury phases and different cell types. It is our hope that neurovascular protectants can be retested in future stroke research studies with specific criteria outlined in this review to increase translational successes.

Ischemic stroke and select adipose-derived and sex hormones: a review

Ischemic stroke is the fifth leading cause of death in the USA and is the leading cause of serious, long-term disability worldwide. The principle sex hormones (estrogen, progesterone, and testosterone), both endogenous and exogenous, have profound effects on various stroke outcomes and have become the focus of a number of studies evaluating risk factors and treatment options for ischemic stroke. In addition, the expression of other hormones that may influence stroke outcome, including select adipose-derived hormones (adiponectin, leptin, and ghrelin), can be regulated by sex hormones and are also the focus of several ischemic stroke studies. This review aims to summarize some of the preclinical and clinical studies investigating the principle sex hormones, as well as select adipose-derived hormones, as risk factors or potential treatments for ischemic stroke. In addition, the potential for relaxin, a lesser studied sex hormone, as a novel treatment option for ischemic stroke is explored.

Sex differences in neuroinflammation and neuroprotection in ischemic stroke

Stroke is not only a leading cause of mortality and morbidity worldwide it also disproportionally affects women. There are currently over 500,000 more women stroke survivors in the US than men, and elderly women bear the brunt of stroke-related disability. Stroke has dropped to the fifth leading cause of death in men, but remains the third in women. This review discusses sex differences in common stroke risk factors, the efficacy of stroke prevention therapies, acute treatment responses, and post-stroke recovery in clinical populations. Women have an increased lifetime risk of stroke compared to men, largely due to a steep increase in stroke incidence in older postmenopausal women, yet most basic science studies continue to only evaluate young male animals. Women also have an increased lifetime prevalence of many common stroke risk factors, including hypertension and atrial fibrillation, as well as abdominal obesity and metabolic syndrome. None of these age-related risk factors have been well modeled in the laboratory. Evidence from the bench has implicated genetic and epigenetic factors, differential activation of cell-death programs, cell-cell signaling pathways, and systemic immune responses as contributors to sex differences in ischemic stroke. The most recent basic scientific findings have been summarized in this review, with an emphasis on factors that differ between males and females that are pertinent to stroke outcomes. Identification and understanding of the underlying biological factors that contribute to sex differences will be critical to the development of translational targets to improve the treatment of women after stroke. © 2016 Wiley Periodicals, Inc.

Sex differences in the immune response to experimental stroke: Implications for translational research

Ischemic stroke is a leading cause of death and disability in the United States. It is known that males and females respond differently to stroke. Depending on age, the incidence, prevalence, mortality rate, and disability outcome of stroke differ between the sexes. Females generally have strokes at older ages than males and, therefore, have a worse stroke outcome. There are also major differences in how the sexes respond to stroke at the cellular level. Immune response is a critical factor in determining the progress of neurodegeneration after stroke and is fundamentally different for males and females. Additionally, females respond to stroke therapies differently from males, yet they are often left out of the basic research that is focused on developing those therapies. With a resounding failure to translate stroke therapies from the bench to the bedside, it is clearer than ever that inclusion of both sexes in stroke studies is essential for future clinical success. This Mini-Review examines sex differences in the immune response to experimental stroke and its implications for therapy development. © 2016 Wiley Periodicals, Inc.

Partial MHC class II constructs as novel immunomodulatory therapy for stroke

The worldwide prevalence of stroke continues to rise despite recent successes in treating acute ischemic stroke. With limited patient eligibility and associated risk of tPA and mechanical thrombectomy, new preventive and therapeutic modalities are needed to stave the rising wave of stroke. Inflammation plays a key role in brain damage after cerebral ischemia, and novel therapies that target pro-inflammatory cells have demonstrated promise for treatment for stroke. Partial MHC class II constructs have been shown to prevent and/or reverse clinical signs of various inflammatory diseases such as experimental autoimmune encephalomyelitis, collagen-induced arthritis and experimental autoimmune uveitis, by reducing the number and frequency of activated cells in the damaged CNS. Herein, we review the use of partial MHC class II constructs as a novel treatment for ischemic stroke. These constructs have been shown to reduce infarct volume and neurological deficit in various cerebral ischemia models in young adult and aging male and female mice. In addition, partial MHC class II constructs were shown to reverse stroke-associated splenic atrophy and promote a protective M2 macrophage/microglia phenotype in the CNS which contributes to tissue repair and recovery after stroke. By addressing remaining STAIR criteria, such as efficacy in large animal models of stroke, these constructs will be prime candidates for clinical trials of acute ischemic stroke.

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.

Rescue from Sexually Dimorphic Neuronal Cell Death by Estradiol and PI3 Kinase Activity

Responses of primary hippocampal and cortical neurons derived from male and female rats to cellular stressors were studied. It is demonstrated that 17β-estradiol (E2), a potent neuroprotectant, protected the female neurons but had no effects on the male neurons from CoCl2- and glutamate-induced toxicity. Agonists of the estrogen receptor (ER) subtypes ERα and ERβ, DPN and PPT, respectively, had similar effects to E2. By contrast, effects of E2 were abolished by the ER antagonist ICI-182780, further corroborating the neuroprotective role of ERs. In male neurons, CoCl2 predominately activated the apoptosis-inducing factor (AIF)-dependent pathway and AIF translocation from the cytosol to the nucleus. In comparison, CoCl2 activated the caspase pathway and cytochrome c release in female neurons. The inhibitors of these pathways, namely DiQ for AIF and zVAD for caspase, specifically rescued CoCl2-induced cell death in male and female neurons, respectively. When zVAD and ICI-182780, and E2 were applied in combination, it was demonstrated E2 acted on the caspase pathway leading to female-specific neuroprotection. Furthermore, the PI3 kinase (PI3K) inhibitor blocked the rescue effects of DiQ and zVAD on the male and female neurons, respectively, suggesting that PI3K is a common upstream regulator for both pathways. The present study suggested that both sex-specific and nonspecific mechanisms played a role in neuronal responses to stressors and protective reagents.

Roles of estrogen in the formation of intracranial aneurysms in ovariectomized female mice

BACKGROUND

Epidemiological studies have indicated that postmenopausal women have a higher incidence of intracranial aneurysms than men in the same age group.

OBJECTIVE

To investigate whether estrogen or estrogen receptors (ERs) mediate protective effects against the formation of intracranial aneurysms.

METHODS

Intracranial aneurysms were induced in mice by combining a single injection of elastase into the cerebrospinal fluid with deoxycorticosterone acetate salt hypertension. The mice were treated with estrogen (17β-estradiol), an ERα agonist (propyl pyrazole triol), and an ERβ agonist (diarylpropionitrile) with and without a nitric oxide synthase inhibitor.

RESULTS

The ovariectomized female mice had a significantly higher incidence of aneurysms than the male mice, which was consistent with findings in previous epidemiological studies. In ovariectomized female mice, an ERβ agonist, but not an ERα agonist or 17β-estradiol, significantly reduced the incidence of aneurysms. The protective effect of the ERβ agonist was absent in the ovariectomized ERβ knockout mice. The protective effect of the ERβ agonist was negated by treatment with a nitric oxide synthase inhibitor.

CONCLUSION

The effects of sex, menopause, and estrogen treatment observed in this animal study were consistent with previous epidemiological findings. Stimulation of estrogen receptor-β was protective against the formation of intracranial aneurysms in ovariectomized female mice.

Sex differences in microRNA expression during development in rat cortex

There are important sex differences in the risk and outcome of conditions and diseases between males and females. For example, stroke occurs with greater frequency in men than in women across diverse ethnic backgrounds and nationalities. Work from our lab and others have revealed a sex-specific sensitivity to cerebral ischemia whereby males exhibit a larger extent of brain damage following an ischemic event compared to females. Studies suggest that the difference in male and female susceptibility to ischemia may be triggered by innate variations in gene regulation and protein expression between the sexes that are independent of post-natal exposure to sex hormones. We have shown that there are differences in microRNA (miRNA) expression in adult male and female brain following focal cerebral ischemia in mouse cortex. Herein we examine a role for differential expression of miRNAs during development in male and female rat cortex as potential effectors of the phenotype that leads to sex differences to ischemia. Expression studies in male and female cortices isolated from postnatal day 0 (P0), postnatal day 7 (P7), and adult rats using TaqMan Low Density miRNA arrays and NanoString nCounter analysis revealed differential miRNA levels between males and females at each developmental stage. We focused on the miR-200 family of miRNAs that showed higher levels in females at P0, but higher levels in males at P7 that persisted into adulthood, and validated the expression of miR-200a, miR-200b, and miR-429 by individual qRT-PCR as these are clustered on chromosome 5 and may be transcriptionally co-regulated. Prediction analysis of the miR-200 miRNAs revealed that genes within the Gonadotropin releasing hormone receptor pathway are the most heavily targeted. These studies support that developmental changes in miRNA expression may influence phenotypes in adult brain that underlie sexually dimorphic responses to disease, including ischemia.

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.

Estrogen protects against intracranial aneurysm rupture in ovariectomized mice

Clinical observations suggest that postmenopausal women have a higher incidence of aneurysmal rupture than premenopausal women. We hypothesize that a relative deficiency in estrogen may increase the risks of aneurysmal growth and subarachnoid hemorrhage in postmenopausal women. We assessed the effects of estrogen and selective estrogen receptor subtype agonists on the development of aneurysmal rupture in ovariectomized female mice. We used an intracranial aneurysm mouse model that recapitulates the key features of human intracranial aneurysms, including spontaneous rupture. Ten- to 12-week-old ovariectomized female mice received treatment with estrogen, nonselective estrogen receptor antagonist, estrogen receptor-α agonist, or estrogen receptor-β agonist starting 6 days after aneurysm induction so that the treatments affected the development of aneurysmal rupture without affecting aneurysmal formation. Estrogen significantly reduced the incidence of ruptured aneurysms and rupture rates in ovariectomized mice. Nonselective estrogen receptor antagonist abolished the protective effect of estrogen. Although estrogen receptor-α agonist did not affect the incidence of ruptured aneurysms or rupture rates, estrogen receptor-β agonist prevented aneurysmal rupture without affecting the formation of aneurysms. The protective role of estrogen receptor-β agonist was abolished by the inhibition of nitric oxide synthase. We showed that estrogen prevented aneurysmal rupture in ovariectomized female mice. The protective effect of estrogen seemed to occur through the activation of estrogen receptor-β, a predominant subtype of estrogen receptor in human intracranial aneurysms and cerebral arteries.

MicroRNA responses to focal cerebral ischemia in male and female mouse brain

Stroke occurs with greater frequency in men than in women across diverse ethnic backgrounds and nationalities. Work from our lab and others have revealed a sex-specific sensitivity to cerebral ischemia whereby males exhibit a larger extent of brain damage resulting from an ischemic event compared to females. Previous studies revealed that microRNA (miRNA) expression is regulated by cerebral ischemia in males; however, no studies to date have examined the effect of ischemia on miRNA responses in females. Thus, we examined miRNA responses in male and female brain in response to cerebral ischemia using miRNA arrays. These studies revealed that in male and female brains, ischemia leads to both a universal miRNA response as well as a sexually distinct response to challenge. Target prediction analysis of the miRNAs increased in male or female ischemic brain reveal sex-specific differences in gene targets and protein pathways. These data support that the mechanisms underlying sexually dimorphic responses to cerebral ischemia includes distinct changes in miRNAs in male and female brain, in addition to a miRNA signature response to ischemia that is common to both.

Effects of chronic HIV-1 Tat exposure in the CNS: heightened vulnerability of males versus females to changes in cell numbers, synaptic integrity, and behavior

HIV-associated damage to the central nervous system results in cognitive and motor deficits. Anti-retroviral therapies reduce the severity of symptoms, yet the proportion of patients affected has remained the same or increased. Although approximately half of HIV-infected patients worldwide are women, the question of whether biological sex influences outcomes of HIV infection has received little attention. We explored this question for both behavioral and cellular/morphologic endpoints, using a transgenic mouse that inducibly expresses HIV-1 Tat in the brain. After 3 months of HIV-1 Tat exposure, both sexes showed similar reduced open field ambulation. Male Tat⁺ mice also showed reduced forelimb grip strength and enhanced anxiety in a light–dark box assay. Tat⁺ males did not improve over 12 weeks of repeated rotarod testing, indicating a motor memory deficit. Male mice also had more cellular deficits in the striatum. Neither sex showed a change in volume or total neuron numbers. Both had equally reduced oligodendroglial populations and equivalent microglial increases. However, astrogliosis and microglial nitrosative stress were higher in males. Dendrites on medium spiny neurons in male Tat⁺ mice had fewer spines, and levels of excitatory and inhibitory pre- and post-synaptic proteins were disrupted. Our results predict sex as a determinant of HIV effects in brain. Increased behavioral deficits in males correlated with glial activation and synaptic damage, both of which are implicated in cognitive/motor impairments in patients. Tat produced by residually infected cells despite antiretroviral therapy may be an important determinant of the synaptodendritic instability and behavioral deficits accompanying chronic infection.

Effects of androgens on early post-ischemic neurogenesis in mice

Although androgens are reported to affect stroke outcomes by altering ischemic tissue damage, their effect on post-injury repair is unknown. Since neurogenesis has recently been recognized as contributing to stroke outcomes, we investigated the role of androgens on stroke-induced neurogenesis. Adult male mice were subjected to transient middle cerebral artery occlusion (MCAO) and neurogenesis was examined 1 week later by quantifying BrdU/doublecortin-positive and BrdU/NeuN-positive neurons in brain germinal regions as well as the injured striatum. To elucidate the role of endogenous androgens, post-MCAO neurogenesis was examined in gonadally intact males, intact males implanted with the androgen receptor antagonist flutamide, and surgically castrated males. Surgical castration or pharmacologic androgen receptor blockade had no effects on post-ischemic neurogenesis, except that continuous androgen receptor blockade unexpectedly suppressed maturation of newborn neurons (BrdU/NeuN-positive cells) in the dentate gyrus. Post-MCAO neurogenesis was also examined in surgically castrated mice treated with continuous release implants containing testosterone or dihydrotestosterone (DHT). Testosterone and DHT robustly inhibited post-ischemic neurogenesis in the dentate gyrus, and the more potent androgen DHT virtually abolished the presence of immature newborn neurons (BrdU/doublecortin-positive cells) in the injured striatum. Our data suggest that endogenous androgens do not alter post-stroke neurogenesis quantitatively, but the presence of supra-physiological androgen stimulation profoundly suppresses early neurogenesis in germinal brain areas and reduces cellular repair in injured tissue after cerebral ischemia. These results advance the understanding of the role that androgens play in stroke outcomes.

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

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

Cerebral ischemic stroke: is gender important?

Cerebral stroke continues to be a major cause of death and the leading cause of long-term disability in developed countries. Evidence reviewed here suggests that gender influences various aspects of the clinical spectrum of ischemic stroke, in terms of influencing how a patients present with ischemic stroke through to how they respond to treatment. In addition, this review focuses on discussing the various pathologic mechanisms of ischemic stroke that may differ according to gender and compares how intrinsic and hormonal mechanisms may account for such gender differences. All clinical trials to date investigating putative neuroprotective treatments for ischemic stroke have failed, and it may be that our understanding of the injury cascade initiated after ischemic injury is incomplete. Revealing aspects of the pathophysiological consequences of ischemic stroke that are gender specific may enable gender relevant and effective neuroprotective strategies to be identified. Thus, it is possible to conclude that gender does, in fact, have an important role in ischemic stroke and must be factored into experimental and clinical investigations of ischemic stroke.

Cell death atlas of the postnatal mouse ventral forebrain and hypothalamus: effects of age and sex

Naturally occurring cell death is essential to the development of the mammalian nervous system. Although the importance of developmental cell death has been appreciated for decades, there is no comprehensive account of cell death across brain areas in the mouse. Moreover, several regional sex differences in cell death have been described for the ventral forebrain and hypothalamus, but it is not known how widespread the phenomenon is. We used immunohistochemical detection of activated caspase-3 to identify dying cells in the brains of male and female mice from postnatal day (P) 1 to P11. Cell death density, total number of dying cells, and regional volume were determined in 16 regions of the hypothalamus and ventral forebrain (the anterior hypothalamus, arcuate nucleus, anteroventral periventricular nucleus, medial preoptic nucleus, paraventricular nucleus, suprachiasmatic nucleus, and ventromedial nucleus of the hypothalamus; the basolateral, central, and medial amygdala; the lateral and principal nuclei of the bed nuclei of the stria terminalis; the caudate-putamen; the globus pallidus; the lateral septum; and the islands of Calleja). All regions showed a significant effect of age on cell death. The timing of peak cell death varied between P1 to P7, and the average rate of cell death varied tenfold among regions. Several significant sex differences in cell death and/or regional volume were detected. These data address large gaps in the developmental literature and suggest interesting region-specific differences in the prevalence and timing of cell death in the hypothalamus and ventral forebrain.

Neonatal testosterone exposure protects adult male rats from stroke

BACKGROUND

Men have a higher stroke incidence compared to women until advanced age. The contribution of hormones to these sex differences has been extensively debated. In experimental stroke, estradiol is neuroprotective, whereas androgens are detrimental. However, prior studies have only examined the effects of acute treatment paradigms; therefore, the timing and mechanism by which ischemic sexual dimorphism arises are unknown.

METHODS

The effects of exogenous neonatal androgen exposure on subsequent injury induced by middle cerebral artery occlusion in adulthood in male rats were examined. Rats were administered vehicle (oil), testosterone propionate (TP) or the non-aromatizable androgen dihydrotestosterone (DHT) for 5 days after birth. At 3 months of age, a focal stroke was induced.

RESULTS

Testosterone-treated rats (but not DHT-treated animals) had decreased infarct volumes (20 vs. 33%, p < 0.05) as well as increased estradiol levels (39.4 vs. 18.6 pg/ml, p < 0.0001) compared to oil-treated animals. TP-injected males had increased testicular aromatase (P450arom) levels (3.6 vs. 0.2 ng/ml, p < 0.0001) compared to oil-treated males. The level of X-linked inhibitor of apoptosis, the primary endogenous inhibitor of caspase-induced apoptosis, was increased in TP-treated rats compared with the oil-treated males.

CONCLUSIONS

Neonatal exposure to exogenous testosterone upregulates testicular aromatase expression in male rats and leads to adult neuroprotection secondary to changes in serum estradiol levels and cell death proteins. This study suggests that early exposure to gonadal hormones can have dramatic effects on the response to adult cerebrovascular injury.

Androgen receptor overexpression is neuroprotective in experimental stroke

Male sex is a known risk factor in human stroke. However, the role of the cognate receptor for androgens-the androgen receptor (AR)-in stroke outcome remains unclear. Here, we found that AR mRNA is downregulated in the peri-infarct tissue of gonadally intact male mice subjected to middle cerebral artery occlusion (MCAO) and 6 h reperfusion. We then used genetically engineered mice overexpressing AR in brain (AR-Tg) to compare outcomes from MCAO in intact or castrated males and to evaluate the neuroprotective role of dihydrotestosterone (DHT) replacement in AR-Tg castrates. A further evaluation of AR overexpression in ischemic paradigms was performed using rat PC12 cells transfected with human AR and treated with oxidative and apoptotic stressors. We then studied the role of DHT in cultures overexpressing AR. Our results show (1) ischemia alters the expression of AR by decreasing AR mRNA levels, (2) AR overexpression is protective in vivo against MCAO in intact and castrated AR-Tg mice and in vitro against oxidative and apoptotic stressors in AR-PC12 cells, and (3) DHT does not enhance the protection triggered by AR overexpression in AR-Tg castrated mice nor in AR-PC12 cells.

Sex-specific activation of cell death signalling pathways in cerebellar granule neurons exposed to oxygen glucose deprivation followed by reoxygenation

Neuronal death pathways following hypoxia-ischaemia are sexually dimorphic, but the underlying mechanisms are unclear. We examined cell death mechanisms during OGD (oxygen-glucose deprivation) followed by Reox (reoxygenation) in segregated male (XY) and female (XX) mouse primary CGNs (cerebellar granule neurons) that are WT (wild-type) or Parp-1 [poly(ADP-ribose) polymerase 1] KO (knockout). Exposure of CGNs to OGD (1.5 h)/Reox (7 h) caused cell death in XY and XX neurons, but cell death during Reox was greater in XX neurons. ATP levels were significantly lower after OGD/Reox in WT-XX neurons than in XY neurons; this difference was eliminated in Parp-1 KO-XX neurons. AIF (apoptosis-inducing factor) was released from mitochondria and translocated to the nucleus by 1 h exclusively in WT-XY neurons. In contrast, there was a release of Cyt C (cytochrome C) from mitochondria in WT-XX and Parp-1 KO neurons of both sexes; delayed activation of caspase 3 was observed in the same three groups. Thus deletion of Parp-1 shunted cell death towards caspase 3-dependent apoptosis. Delayed activation of caspase 8 was also observed in all groups after OGD/Reox, but was much greater in XX neurons, and caspase 8 translocated to the nucleus in XX neurons only. Caspase 8 activation may contribute to increased XX neuronal death during Reox, via caspase 3 activation. Thus, OGD/Reox induces death of XY neurons via a PARP-1-AIF-dependent mechanism, but blockade of PARP-1-AIF pathway shifts neuronal death towards a caspase-dependent mechanism. In XX neurons, OGD/Reox caused prolonged depletion of ATP and delayed activation of caspase 8 and caspase 3, culminating in greater cell death during Reox.