Changes in experimental stroke outcome across the life span

Sex Dimorphisms in Ischemic Stroke: From Experimental Studies to Clinic

Sex dimorphisms are important factors that influence the outcomes after ischemic stroke, which include basic health status, cerebrovascular anatomy, hormone levels, and unique factors such as pregnancy and menopause. It is widely recognized that male and female respond differently to stroke. Women aged 45–74 years old showed a lower risk of stroke incidence compared to age-matched man. This kind of protection is lost with aging. Hence, there is increasing requirement to get a more comprehensive understanding of sex-based factors to stroke on stroke incidence, symptoms, and treatments. This review focuses on sex-specific mechanisms in response to stroke based on experimental studies and highlights recent findings in clinical studies including sex-differential evaluation and outcomes of stroke. Sex-based personalized medicine should be promising in stroke therapies.

Antioxidant nanomedicine with cytoplasmic distribution in neuronal cells shows superior neurovascular protection properties

This study investigated whether nitroxide radical (4-amino-TEMPOL)-containing nanoparticles (RNPs; antioxidant nanomedicine) can prevent neurovascular unit impairment caused by reactive oxygen species (ROS) after cerebral ischemia-reperfusion. C57BL/6J mice underwent transient middle cerebral artery occlusion (tMCAO). The mice were randomly divided and administered intra-arterial RNPs injection (9 mg/kg, 7 μM/kg), edaravone (3 mg/kg, 17 μM/kg), or phosphate-buffered saline (control group). Survival rate and neurological score were evaluated 24 h post-injection. RNPs distribution was determined using immunofluorescence staining and blood-brain barrier (BBB) disruption using Evans blue extravasation assay. Effect of RNPs and edaravone on microglia polarization into microglia M1 and M2 was evaluated. We also determined multiple ROS-scavenging activities in brain homogenates of RNPs- and edaravone-treated animals using an electron spin resonance-based spin-trapping method. Compared with edaravone, RNPs significantly improved the survival rate and neurological deficit, inhibited BBB disruption and supported polarization of microglia into M2 microglia. RNPs were localized in endothelial cells, the perivascular space, neuronal cell cytoplasm, astrocytes, and microglia. Scavenging capacities of hydroxyl, alkoxyl, and peroxyl radicals were significantly higher in the RNPs-treated group. RNPs show promising results as a future neuroprotective nanomedicine approach for cerebral ischemia-reperfusion injury.

EMMPRIN/CD147 plays a detrimental role in clinical and experimental ischemic stroke

Background: Ischemic stroke is a devastating disease, often resulting in death or permanent neurological deficits. EMMPRIN/CD147 is a plasma membrane protein that induces the production of matrix metalloproteinases (MMPs), which contribute to secondary damage after stroke by disrupting the blood brain barrier (BBB) and facilitating peripheral leukocyte infiltration into the brain.

Results: CD147 surface expression increased significantly after stroke on infiltrating leukocytes, astrocytes and endothelial cells, but not on resident microglia. Inhibition of CD147 reduced MMP levels, decreased ischemic damage, and improved functional, cognitive and histological outcomes after experimental ischemic stroke in both young and aged mice. In stroke patients, high levels of serum CD147 24 hours after stroke predicted poor functional outcome at 12 months. Brain CD147 levels were correlated with MMP-9 and secondary hemorrhage in post-mortem samples from stroke patients.

Conclusions: Acute inhibition of CD147 decreases levels of MMP-9, limits tissue loss, and improves long-term cognitive outcomes following experimental stroke in aged mice. High serum CD147 correlates with poor outcomes in stroke patients. This study identifies CD147 as a novel, clinically relevant target in ischemic stroke.

Modeling poststroke epilepsy and preclinical development of drugs for poststroke epilepsy

Stroke is a severe clinical issue for global public health, representing the third leading cause of death and a major cause of disability in developed countries. Progresses in the pharmacological treatment of the acute stroke have given rise to a significant decrease in its mortality rate. However, as a result, there has been an increasing number of stroke survivors living with disability worldwide. Poststroke epilepsy (PSE) is a common clinical complication following stroke. Seizures can arise in close temporal association with stroke damage and/or after a variably longer interval. Overall, PSE have a good prognosis; in fact, its responding rate to antiepileptic drugs (AEDs) is higher than other types of epilepsy. However, regarding pharmacological treatment, some issues are still unresolved. To this aim, a deeper understanding of mechanisms underlying the transformation of infarcted tissue into an epileptic focus or better from a nonepileptic brain to an epileptic brain is also mandatory for PSE. However, studying epileptogenesis in patients with PSE clearly has several limitations and difficulties; therefore, modeling PSE is crucial. Until now, different experimental models have been used to study the etiopathology of cerebrovascular stroke with or without infarction, but few studies focused on poststroke epileptogenesis and PSE. In this review, we show a brief overview on the features emerging from preclinical research into experimental PSE, which could affect the discovery of biomarkers and therapy strategies for poststroke epileptogenesis. This article is part of the Special Issue "Seizures & Stroke".

Aging protects rat cortical slices against to oxygen-glucose deprivation induced damage

Objective: In present study, we aimed to clarify effect of aging on the susceptibility of brain tissue to neurodegeneration induced by ischemia.Methods: Damage induced by oxygen-glucose deprivation (OGD) followed by reoxygenation (REO) were compared in cortical slices prepared from young (3 months of age) and aged (22-24 months of age) male Sprague Dawley rats.Results: After incubation of the slices in an oxygen and glucose containing control condition, 2,3,5-triphenyl tetrazolium chloride (TTC) staining intensity was found significantly high in aged cortical slices. Although thirty minutes incubation of the slices in OGD medium followed by REO (OGD-REO) caused similar decline in TTC staining in young and aged cortical slices, staining intensity was still significantly higher in the slices prepared from aged animals. Thirty minutes of OGD-REO, on the other hand, also caused more increase in lactate dehydrogenase (LDH) leakage from young slices. While water contents of the slices were almost equal under control condition, it was significantly high in young cortical slices after OGD-REO incubations. In contrary to these findings, OGD and REO caused more increases in S100B output from aged rat cortical slices. S100B levels in brain regions including the cerebral cortex were also found higher in aged rats.Conclusion: All these results indicate that, cortical slices prepared from aged male rats are significantly less responsive to in vitro OGD-REO induced alterations. Since protein S100B outputs were almost doubled from aged cortical slices, a possible involvement of this enhanced S100B output seems to be likely.

Molecular Mechanisms of Intermittent Fasting-induced Ischemic Tolerance

Diet is a significant factor in determining human well-being. Excessive eating and/or diets with higher than needed amounts of carbohydrates, salt, and fat are known to cause metabolic disorders and functional changes in the body. To compensate the ill effects, many designer diets including the Mediterranean diet, the Okinawa diet, vegetarian/vegan diets, keto diet, anti-inflammatory diet, and the anti-oxidant diet have been introduced in the past 2 decades. While these diets are either enriched or devoid of one or more specific components, a better way to control diet is to limit the amount of food consumed. Caloric restriction (CR), which involves limiting the amount of food consumed rather than eliminating any specific type of food, as well as intermittent fasting (IF), which entails limiting the time during which food can be consumed on a given day, have gained popularity because of their positive effects on human health. While the molecular mechanisms of these 2 dietary regimens have not been fully deciphered, they are known to prolong the life span, control blood pressure, and blood glucose levels. Furthermore, CR and IF were both shown to decrease the incidence of heart attack and stroke, as well as their ill effects. In particular, IF is thought to promote metabolic switching by altering gene expression profiles leading to reduced inflammation and oxidative stress, while increasing plasticity and regeneration.

Aging exacerbates neutrophil pathogenicity in ischemic stroke

Ischemic stroke is major cause of disability and mortality worldwide, and aging is strong risk factor for poor post-stroke outcome. Neutrophils traffic rapidly to the brain following ischemic stroke, and recent evidence has suggested that aging may alter neutrophil function after tissue injury. In this study, we hypothesize that aging enhances the pro-inflammatory function of neutrophils, directly contributing to the poorer outcomes seen in aging patients. We utilized demographic data and biological specimens from ischemic stroke patients and an experimental mouse model to determine the correlation between age, neutrophil function and stroke outcomes. In ischemic stroke patients, age was associated with increased mortality and morbidity and higher levels of neutrophil-activating cytokines. In mice, aged animals had higher stroke mortality and morbidity, higher levels of neutrophil-activating cytokines and enhanced generation of neutrophil reactive oxygen species compared to young mice. Finally, depletion of neutrophils via a specific monoclonal antibody after ischemic stroke led to long-term benefits in functional outcome in aged male and female animals, with no benefit observed in young. These results demonstrate that aging is associated with augmented neutrophil pathogenicity in ischemic stroke, and that neutrophil-targeted therapies may confer greater benefit in aged subjects.

Increased Mortality and Vascular Phenotype in a Knock-In Mouse Model of Retinal Vasculopathy With Cerebral Leukoencephalopathy and Systemic Manifestations

Background and Purpose—

Retinal vasculopathy with cerebral leukoencephalopathy and systemic manifestations (RVCL-S) is an autosomal dominant small vessel disease caused by C-terminal frameshift mutations in the TREX1 gene that encodes the major mammalian 3′ to 5′ DNA exonuclease. RVCL-S is characterized by vasculopathy, especially in densely vascularized organs, progressive retinopathy, cerebral microvascular disease, white matter lesions, and migraine, but the underlying mechanisms are unknown.

Methods—

Homozygous transgenic RVCL-S knock-in mice expressing a truncated Trex1 (three prime repair exonuclease 1) protein (similar to what is seen in patients) and wild-type littermates, of various age groups, were subjected to (1) a survival analysis, (2) in vivo postocclusive reactive hyperemia and ex vivo Mulvany myograph studies to characterize the microvascular and macrovascular reactivity, and (3) experimental stroke after transient middle cerebral artery occlusion with neurological deficit assessment.

Results—

The mutant mice show increased mortality starting at midlife ( P =0.03 with hazard ratio, 3.14 [95% CI, 1.05–9.39]). The mutants also show a vascular phenotype as evidenced by attenuated postocclusive reactive hyperemia responses (across all age groups; F[1, 65]=5.7, P =0.02) and lower acetylcholine-induced relaxations in aortae (in 20- to 24-month-old mice; RVCL-S knock-in: E max : 37±8% versus WT: E max : 65±6%, P =0.01). A vascular phenotype is also suggested by the increased infarct volume seen in 12- to 14-month-old mutant mice at 24 hours after infarct onset (RVCL-S knock-in: 75.4±2.7 mm 3 versus WT: 52.9±5.6 mm 3 , P =0.01).

Conclusions—

Homozygous RVCL-S knock-in mice show increased mortality, signs of abnormal vascular function, and increased sensitivity to experimental stroke and can be instrumental to investigate the pathology seen in patients with RVCL-S.

Sensory Stimulation-Induced Astrocytic Calcium Signaling in Electrically Silent Ischemic Penumbra

Middle cerebral artery occlusion (MCAO) induces ischemia characterized by a densely ischemic focus, and a less densely ischemic penumbral zone in which neurons and astrocytes display age-dependent dynamic variations in spontaneous Ca²⁺ activities. However, it is unknown whether penumbral nerve cells respond to sensory stimulation early after stroke onset, which is critical for understanding stimulation-induced stroke therapy. In this study, we investigated the ischemic penumbra’s capacity to respond to somatosensory input. We examined adult (3- to 4-month-old) and old (18- to 24-month-old) male mice at 2–4 h after MCAO, using two-photon microscopy to record somatosensory stimulation-induced neuronal and astrocytic Ca²⁺ signals in the ischemic penumbra. In both adult and old mice, MCAO abolished spontaneous and stimulation-induced electrical activity in the penumbra, and strongly reduced stimulation-induced Ca²⁺ responses in neuronal somas (35–82%) and neuropil (92–100%) in the penumbra. In comparison, after stroke, stimulation-induced astrocytic Ca²⁺ responses in the penumbra were only moderately reduced (by 54–62%) in adult mice, and were even better preserved (reduced by 31–38%) in old mice. Our results suggest that somatosensory stimulation evokes astrocytic Ca²⁺ activity in the ischemic penumbra. We hypothesize that the relatively preserved excitability of astrocytes, most prominent in aged mice, may modulate protection from ischemic infarcts during early somatosensory activation of an ischemic cortical area. Future neuroprotective efforts in stroke may target spontaneous or stimulation-induced activity of astrocytes in the ischemic penumbra.

TRIM9-Mediated Resolution of Neuroinflammation Confers Neuroprotection upon Ischemic Stroke in Mice

Excessive and unresolved neuroinflammation is a key component of the pathological cascade in brain injuries such as ischemic stroke. Here, we report that TRIM9, a brain-specific tripartite motif (TRIM) protein, was highly expressed in the peri-infarct areas shortly after ischemic insults in mice, but expression was decreased in aged mice, which are known to have increased neuroinflammation after stroke. Mechanistically, TRIM9 sequestered β-transducin repeat-containing protein (β-TrCP) from the Skp-Cullin-F-box ubiquitin ligase complex, blocking IκBα degradation and thereby dampening nuclear factor κB (NF-κB)-dependent proinflammatory mediator production and immune cell infiltration to limit neuroinflammation. Consequently, Trim9-deficient mice were highly vulnerable to ischemia, manifesting uncontrolled neuroinflammation and exacerbated neuropathological outcomes. Systemic administration of a recombinant TRIM9 adeno-associated virus that drove brain-wide TRIM9 expression effectively resolved neuroinflammation and alleviated neuronal death, especially in aged mice. These findings reveal that TRIM9 is essential for resolving NF-κB-dependent neuroinflammation to promote recovery and repair after brain injury and may represent an attractive therapeutic target.

Hyperoxia-Induced ΔR1

Background and Purpose- Acceleration of longitudinal relaxation under hyperoxic challenge (ie, hyperoxia-induced ΔR₁) indicates oxygen accumulation and reflects baseline tissue oxygenation. We evaluated the feasibility of hyperoxia-induced ΔR₁ for evaluating cerebral oxygenation status and degree of ischemic damage in stroke. Methods- In 24-hour transient stroke rat models (n=13), hyperoxia-induced ΔR₁, ischemic severity (apparent diffusion coefficient [ADC]), vasogenic edema (R₂), total and microvascular blood volume (superparamagnetic iron oxide-driven ΔR₂* and ΔR₂, respectively), and glucose metabolism activity (¹⁸F-fluorodeoxyglucose uptake on positron emission tomography) were measured. The distribution of these parameters according to hyperoxia-induced ΔR₁ was analyzed. The partial pressure of tissue oxygen change during hyperoxic challenge was measured using fiberoptic tissue oximetry. In 4-hour stroke models (n=6), ADC and hyperoxia-induced ΔR₁ was analyzed with 2,3,5-triphenyltetrazolium chloride staining being a criterion of infarction. Results- Ischemic hemisphere showed significantly higher hyperoxia-induced ΔR₁ than nonischemic brain in a pattern depending on ADC. During hyperoxic challenge, ischemic hemisphere demonstrated uncontrolled increase of partial pressure of tissue oxygen, whereas contralateral hemisphere rapidly plateaued. Ischemic hemisphere also demonstrated significant correlation between hyperoxia-induced ΔR₁ and R₂. Hyperoxia-induced ΔR₁ showed a significant negative correlation with ¹⁸F-fluorodeoxyglucose uptake. The ADC, R₂, ΔR₂, and ¹⁸F-fluorodeoxyglucose uptake showed a dichotomized distribution according to the hyperoxia-induced ΔR₁ as their slopes and values were higher at low hyperoxia-induced ΔR₁ (<50 ms^-1) than at high ΔR₁. In 4-hour stroke rats, the distribution of ADC according to the hyperoxia-induced ΔR₁ was similar with 24-hour stroke rats. The hyperoxia-induced ΔR₁ was greater in the infarct area (47±10 ms^-1) than in peri-infarct area (16±4 ms^-1; P<0.01). Conclusions- Hyperoxia-induced ΔR₁ adequately indicates cerebral oxygenation and can be a feasible biomarker to classify the degree of ischemia-induced damage in neurovascular function and metabolism in stroke brain.

Contributions of sex to cerebrovascular function and pathology

Sex differences exist in how cerebral blood vessels function under both physiological and pathological conditions, contributing to observed sex differences in risk and outcomes of cerebrovascular diseases (CBVDs), such as vascular contributions to cognitive impairment and dementia (VCID) and stroke. Throughout most of the lifespan, women are protected from CBVDs; however, risk increases following menopause, suggesting sex hormones may play a significant role in this protection. The cerebrovasculature is a target for sex hormones, including estrogens, progestins, and androgens, where they can influence numerous vascular functions and pathologies. While there is a plethora of information on estrogen, the effects of progestins and androgens on the cerebrovasculature are less well-defined. Estrogen decreases cerebral tone and increases cerebral blood flow, while androgens increase tone. Both estrogens and androgens enhance angiogenesis/cerebrovascular remodeling. While both estrogens and androgens attenuate cerebrovascular inflammation, pro-inflammatory effects of androgens under physiological conditions have also been demonstrated. Sex hormones exert additional neuroprotective effects by attenuating oxidative stress and maintaining integrity and function of the blood brain barrier. Most animal studies utilize young, healthy, gonadectomized animals, which do not mimic the clinical conditions of aging individuals likely to get CBVDs. This is also concerning, as sex hormones appear to mediate cerebrovascular function differently based on age and disease state (e.g. metabolic syndrome). Through this review, we hope to inspire others to consider sex as a key biological variable in cerebrovascular research, as greater understanding of sex differences in cerebrovascular function will assist in developing personalized approaches to prevent and treat CBVDs.

Tetrahydrocurcumin epigenetically mitigates mitochondrial dysfunction in brain vasculature during ischemic stroke

The objectives of this study are to identify the mechanism of mitochondrial dysfunction during cerebral ischemic/reperfusion (I/R) injury and the therapeutic potential of tetrahydrocurcumin (THC) to mitigate mitochondrial dysfunction in experimental stroke model. In our study, 8-10 weeks old male C57BL/6 wild-type mice were subjected to middle cerebral artery occlusion (MCAO) for 40 min, followed by reperfusion for 72 h. THC (25mg/kg-BW/day) was injected intraperitoneally once daily for 3 days after 4 h of ischemia. The experimental groups were: (i) sham, (ii) I/R and (iii) I/R + THC. We noticed that THC treatment in ischemic mice significantly improved the functional capacity and motor co-ordination along with reduced neuroscore, infarct volume, brain edema and microvascular leakage in brain parenchyma. The study revealed that level of total homocysteine (tHcy), homocysteine metabolizing enzymes, mitochondrial oxidative stress were significantly altered in I/R mice compared to sham. We also observed alteration in mitochondrial transition pore, ATP production and O₂ consumption in the ischemic brain as compared to sham. Further, elevated matrix metalloproteinases-9 (MMP-9) activity and reduced tight junction protein expressions intensified the brain vascular impairment in I/R mice compared to sham. Interestingly, we found that levels of mitophagy markers, fusion and fission proteins were significantly altered. However THC treatment in I/R mice almost normalized the above functional and molecular changes. Mechanistic study demonstrated that DNA Methyltransferase 1 (DNMT1) expression was higher and was associated with reduced mitochondrial tissue inhibitor of metalloproteinases 2 (TIMP-2) expression through hyper-methylation of CpG island of TIMP-2 promoter in I/R mice compared to sham. However, administration of epigenetic inhibitor, 5-Azacytidine (5-Aza) abrogated I/R induced hyper-methylation of TIMP-2 promoter and maintaining the extracellular matrix (ECM) integrity. In conclusion, this study suggests that THC epigenetically ameliorates mitochondrial dysfunction in brain vasculature during Ischemic Stroke.

Sex differences in risk factors for vascular contributions to cognitive impairment & dementia

Vascular contributions to cognitive impairment and dementia (VCID) is the second most common cause of dementia. While males overall appear to be at a slightly higher risk for VCID throughout most of the lifespan (up to age 85), some risk factors for VCID more adversely affect women. These include female-specific risk factors associated with pregnancy related disorders (e.g. preeclampsia), menopause, and poorly timed hormone replacement. Further, presence of certain co-morbid risk factors, such as diabetes, obesity and hypertension, also may more adversely affect women than men. In contrast, some risk factors more greatly affect men, such as hyperlipidemia, myocardial infarction, and heart disease. Further, stroke, one of the leading risk factors for VCID, has a higher incidence in men than in women throughout much of the lifespan, though this trend is reversed at advanced ages. This review will highlight the need to take biological sex and common co-morbidities for VCID into account in both preclinical and clinical research. Given that there are currently no treatments available for VCID, it is critical that we understand how to mitigate risk factors for this devastating disease in both sexes.

Impact of C57BL/6 substrain on sex-dependent differences in mouse stroke models

We have recently found significant variation in stroke vulnerability among substrains of C57BL/6 mice, observing that commonly used N-lineage substrains exhibit larger infarcts than C57BL/6J and related substrains. Parallel variation was also seen with respect to sex differences in stroke vulnerability, in that C57BL/6 mice of the N-lineage exhibited comparable infarct sizes in males and females, whereas infarcts tended to be smaller in females than in males of J-lineage substrains. This adds to the growing list of recognized phenotypic and genetic differences among C57BL/6 substrains. Although no previous studies have explicitly compared substrains with respect to sex differences in stroke vulnerability, unrecognized background mismatch has occurred in some studies involving control and genetically modified mice. The aims of this review are to: present the evidence for associated substrain- and sex-dependent differences in a mouse permanent occlusion stroke model; examine the extent to which the published literature in other models compares with these recent results; and consider the potential impact of unrecognized heterogeneity in substrain background on the interpretation of studies investigating the impact of genetic modifications on sex differences in stroke outcome. Substrain emerges as a critical variable to be documented in any experimental stroke study in mice.

Sex differences in miRNA as therapies for ischemic stroke

MicroRNAs, a subset of non-coding RNAs, are present in virtually all tissues including body fluids and are global regulators of the transcriptome. In view of the expanding number of microRNAs and the large number of gene targets that each microRNA can potentially regulate, they have been compared to hormones in the scope of their effects. MicroRNA have been implicated as biomarkers for several diseases including stroke, as well as chronic conditions that are associated with stroke. Recent research has focused on manipulating miRNA to improve stroke outcomes. Although several miRNAs have been shown to have neuroprotective properties, the overwhelming majority of these studies have employed only male animals. This review will focus on two miRNAs, Let7f and mir363-3p, whose effectiveness as a stroke neuroprotectant is sex-specific.

Experimental models of focal and multifocal cerebral ischemia: a review

Rodent and rabbit stroke models have been instrumental in our current understanding of stroke pathophysiology; however, translational failure is a significant problem in preclinical ischemic stroke research today. There are a number of different focal cerebral ischemia models that vary in their utility, pathophysiology of causing disease, and their response to treatments. Unfortunately, despite active preclinical research using these models, treatment options for ischemic stroke have not significantly advanced since the food and drug administration approval of tissue plasminogen activator in 1996. This review aims to summarize current stroke therapies, the preclinical experimental models used to help develop stroke therapies, as well as their advantages and limitations. In addition, this review discusses the potential for naturally occurring canine ischemic stroke models to compliment current preclinical models and to help bridge the translational gap between small mammal models and human clinical trials.

The effect of age, sex and strains on the performance and outcome in animal models of stroke

Stroke is one of the leading causes of death worldwide, and the majority of cerebral stroke is caused by occlusion of cerebral circulation, which eventually leads to brain infarction. Although stroke occurs mainly in the aged population, most animal models for experimental stroke in vivo almost universally rely on young-adult rodents for the evaluation of neuropathological, neurological, or behavioral outcomes after stroke due to their greater availability, lower cost, and fewer health problems. However, it is well established that aged animals differ from young animals in terms of physiology, neurochemistry, and behavior. Stroke-induced changes are more pronounced with advancing age. Therefore, the overlooked role of age in animal models of stroke could have an impact on data quality and hinder the translation of rodent models to humans. In addition to aging, other factors also influence functional performance after ischemic stroke. In this article, we summarize the differences between young and aged animals, the impact of age, sex and animal strains on performance and outcome in animal models of stroke and emphasize age as a key factor in preclinical stroke studies.

Insulin-like Growth Factor (IGF)-1 treatment stabilizes the microvascular cytoskeleton under ischemic conditions

Our previous studies showed that Insulin-like Growth Factor (IGF)-1 reduced blood brain barrier permeability and decreased infarct volume caused by middle cerebral artery occlusion (MCAo) in middle aged female rats. Similarly, cultures of primary brain microvessel endothelial cells from middle-aged female rats and exposed to stroke-like conditions (oxygen glucose deprivation; OGD) confirmed that IGF-1 reduced dye transfer across this cell monolayer. Surprisingly, IGF-1 did not attenuate endothelial cell death caused by OGD. To reconcile these findings, the present study tested the hypothesis that, at the earliest phase of ischemia, IGF-1 promotes barrier function by increasing anchorage and stabilizing cell geometry of surviving endothelial cells. Cultures of human brain microvessel endothelial cells were subject to oxygen-glucose deprivation (OGD) in the presence of IGF-1, IGF-1 + JB-1 (IGFR inhibitor) or vehicle. OGD disrupted the cell monolayer and reduced cell-cell interactions, which was preserved in IGF-1-treated cultures and reversed by concurrent treatment with JB-1. IGF-1-mediated preservation of the endothelial monolayer was reversed with LY294002 treatment, but not by Rapamycin, indicating that IGF-1 s actions on cell-cell contacts are likely mediated via the PI3K pathway. In vivo, microvessel morphology was evaluated in middle-aged female rats that were subjected to ischemia by MCAo, and treated ICV with IGFI, IGF-1 + JB-1, or artificial CSF (aCSF; vehicle) after reperfusion. Compared to vehicle controls, IGF-1 treated animals displayed larger microvessel diameters in the peri-infarct area and increased staining density for vinculin, an anchorage protein. Both these measures were reversed by concurrent IGF-1 + JB-1 treatment. Moreover these effects were restricted to 24 h after ischemia-reperfusion and no treatment effects were seen at 5d post stroke. Collectively, these data suggest that in the earliest hours during ischemia, IGF-1 promotes receptor-mediated anchorage of endothelial cells, and its actions may be accurately characterized as vasculoprotective.

Implications for understanding ischemic stroke as a sexually dimorphic disease: the role of pial collateral circulations

We investigated structural and functional differences in primary and pial collateral circulations in adult normotensive male and female Wistar rats. Male ( n = 10) and female ( n = 7) rats were subjected to middle cerebral artery (MCA) occlusion and changes in relative cerebral blood flow in MCA and pial collateral territories were measured by multisite laser-Doppler flowmetry. Rats were then transcardially perfused with a mixture of carbon black and latex, perfusion fixed, and imaged to compare primary and pial collateral structure between male ( n = 4) and female ( n = 3) rats, including lumen diameters and number. To study pial collateral function, leptomeningeal anastomoses (LMAs) were isolated and pressurized from male ( n = 7) and female ( n = 6) rats. Myogenic tone and reactivity to pressure, vascular function to pharmacological activator, or inhibitor of ion channels was measured and compared. There was no difference between relative cerebral blood flow in both MCA and pial collateral territories during occlusion and reperfusion between groups. Compared with male LMAs, female LMAs had similar myogenic tone (24.0 ± 7.3% vs. 16.0 ± 3.7%, P > 0.05) and reactivity to increased pressure and similar vascular responses to vasoconstrictive and vasodilatory stimuli. Additionally, compared with female LMAs, male LMAs had similar numbers (21 ± 1 vs. 20 ± 2, P > 0.05) and diameters (30.5 ± 2.0 vs. 26.2 ± 0.6 μm, P > 0.05), and no sex difference was detected in the diameter of arterial segments of circle of Willis. Together, our data establish no sex difference of cerebral collateral structure or function, suggesting that the reduced severity of stroke outcome in female rats is not likely due to differences in the cerebral collateral circulation. NEW & NOTEWORTHY Our work compared the function of leptomeningeal anastomoses between male and female adult normotensive rats with no sex difference found. We also confirmed no sex difference in primary and pial collateral structure in Wistar rats. Our findings suggest that the reduced severity of stroke in premenopausal women and reproductively intact female rodents is not likely due to improved primary and pial collateral circulations.

Pretreatment with low-dose fimasartan ameliorates NLRP3 inflammasome-mediated neuroinflammation and brain injury after intracerebral hemorrhage

Nucleotide-binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, which is composed of an NLRP3 domain, the adaptor molecule apoptosis-associated speck-like protein containing a CARD (ASC) domain, and procaspase-1, plays an important role in the immune pathophysiology of the secondary damage induced by intracerebral hemorrhage (ICH). This study aims to investigate whether pre-stroke treatment with fimasartan, an angiotensin II receptor blocker, has anti-inflammatory effects on ICH by inhibiting the activation of the NLRP3 inflammasome. Sprague-Dawley rats were divided into five groups: sham, vehicle, low-dose (0.5 mg/kg) and regular-doses (1.0 and 3.0 mg/kg) fimasartan. These rats were treated for 30 days before the induction of collagenase-induced ICH and continuously 3 days after surgery. The mean blood pressure (BP) in the low-dose fimasartan group was not significantly different from that of control, and BP in the regular-dose groups was decreased in a dose-dependent manner. Pretreatment with low-dose fimasartan attenuated ICH-induced edema and improved neurological functions. Activation of the NLRP3/ASC/caspase-1 and the NF-κB pathways after ICH was markedly reduced by low-dose fimasartan. The double immunofluorescence staining of brain cells showed a significant decrease in the co-localization of NLRP3 with Iba1 (microglia marker) positive cells by fimasartan treatment. Cultured microglia cells stimulated by hemolysate demonstrated significant activation of the inflammasome, which was reduced by fimasartan. Pretreatment with a low-dose fimasartan alleviated brain damage after acute ICH by inhibiting the NLRP3 inflammasome without lowering MBP. Our study suggests pre-stroke administration of fimasartan could potentially attenuate ICH-induced secondary brain injury by targeting the inflammasome.

Profile of intravenous glyburide for the prevention of cerebral edema following large hemispheric infarction: evidence to date

Glyburide (also known as glibenclamide) is a second-generation sulfonylurea drug that inhibits sulfonylurea receptor 1 (Sur1) at nanomolar concentrations. Long used to target K_ATP (Sur1–Kir6.2) channels for the treatment of diabetes mellitus type 2, glyburide was recently repurposed to target Sur1–transient receptor potential melastatin 4 (Trpm4) channels in acute central nervous system injury. Discovered nearly two decades ago, SUR1–TRPM4 has emerged as a critical target in stroke, specifically in large hemispheric infarction, which is characterized by edema formation and life-threatening brain swelling. Following ischemia, SUR1–TRPM4 channels are transcriptionally upregulated in all cells of the neurovascular unit, including neurons, astrocytes, microglia, oligodendrocytes and microvascular endothelial cells. Work by several independent laboratories has linked SUR1–TRPM4 to edema formation, with blockade by glyburide reducing brain swelling and death in preclinical models. Recent work showed that, following ischemia, SUR1–TRPM4 co-assembles with aquaporin-4 to mediate cellular swelling of astrocytes, which contributes to brain swelling. Additionally, recent work linked SUR1–TRPM4 to secretion of matrix metalloproteinase-9 (MMP-9) induced by recombinant tissue plasminogen activator in activated brain endothelial cells, with blockade of SUR1–TRPM4 by glyburide reducing MMP-9 and hemorrhagic transformation in preclinical models with recombinant tissue plasminogen activator. The recently completed GAMES (Glyburide Advantage in Malignant Edema and Stroke) clinical trials on patients with large hemispheric infarctions treated with intravenous glyburide (RP-1127) revealed promising findings with regard to brain swelling (midline shift), MMP-9, functional outcomes and mortality. Here, we review key elements of the basic science, preclinical experiments and clinical studies, both retrospective and prospective, on glyburide in focal cerebral ischemia and stroke.

Age and Sex Are Critical Factors in Ischemic Stroke Pathology

Ischemic stroke is a devastating brain injury resulting in high mortality and substantial loss of function. Understanding the pathophysiology of ischemic stroke risk, mortality, and functional loss is critical to the development of new therapies. Age and sex have a complex and interactive effect on ischemic stroke risk and pathophysiology. Aging is the strongest nonmodifiable risk factor for ischemic stroke, and aged stroke patients have higher mortality and morbidity and poorer functional recovery than their young counterparts. Importantly, patient age modifies the influence of patient sex in ischemic stroke. Early in life, the burden of ischemic stroke is higher in men, but stroke becomes more common and debilitating for women in elderly populations. The profound effects of sex and age on clinical ischemic stroke are mirrored in the results of experimental in vivo and in vitro studies. Here, we review current knowledge on the influence of age and sex in the incidence, mortality, and functional outcome of ischemic stroke in clinical populations. We also discuss the experimental evidence for sex and age differences in stroke pathophysiology and how a better understanding of these biological variables can improve clinical care and enhance development of novel therapies.

Age-dependent Disturbances of Neuronal and Glial Protein Expression Profiles in Areas of Secondary Neurodegeneration Post-stroke

Despite the fact that approximately 80% of strokes occur in those aged over 60 years, many pre-clinical stroke studies have been conducted in younger adult rodents, raising debate about translation and generalizability of these results. We were interested in potential age differences in stroke-induced secondary neurodegeneration (SND). SND involves the death of neurons in areas remote from, but connected to, the site of infarction, as well as glial disturbances. Here we investigated potential differences in key parameters of SND in the thalamus, a major site of post-stroke SND. Protein expression profiles in young adult (2-4 months) and aged (22-23 months) mice were analyzed 28 days after a cortical stroke. Our results show that age reduced the expression of synaptic markers (PSD 95, Synapsin1) and increased Amyloid β oligomer accumulation after stroke. Protein expression of several markers of glial activity remained relatively stable across age groups post-stroke. We have identified that age exacerbates the severity of SND after stroke. Our results, however, do not support a view that microglia or astrocytes are the main contributors to the enhanced severity of SND in aged mice.

The effect of age-related risk factors and comorbidities on white matter injury and repair after ischemic stroke

White matter injury is a crucial component of human stroke, but it has often been neglected in preclinical studies. Most human stroke is associated with one or more comorbidities, including aging, hypertension, diabetes and metabolic syndrome including hyperlipidemia. The purpose of this review is to examine how age and hypertension impact stroke-induced white matter injury as well as white matter repair in both human stroke and preclinical models. It is essential that comorbidities be examined in preclinical trials as they may impact translatability to the clinic. In addition, understanding how comorbidities impact white matter injury and repair may provide new therapeutic opportunities for patients with those conditions.

Ischemic stroke across sexes: What is the status quo?

Stroke prevalence is expected to increase in the next decades due to the aging of the Western population. Ischemic stroke (IS) shows an age- and sex-dependent distribution in which men represent the most affected population within 65 years of age, being passed by post-menopausal women in older age groups. Furthermore, a sexual dimorphism concerning risk factors, presentation and treatment of IS has been widely recognized. In order to address these phenomena, a number of issue have been raised involving both socio-economical and biological factors. The latter can be either dependent on sex hormones or due to intrinsic factors. Although women have poorer outcomes and are more likely to die after a cerebrovascular event, they are still underrepresented in clinical trials and this is mirrored by the lack of sex-tailored therapies. A greater effort is needed in the future to ensure improved treatment and quality of life to both sexes.

Aging alters the immunological response to ischemic stroke

The peripheral immune system plays a critical role in aging and in the response to brain injury. Emerging data suggest inflammatory responses are exacerbated in older animals following ischemic stroke; however, our understanding of these age-related changes is poor. In this work, we demonstrate marked differences in the composition of circulating and infiltrating leukocytes recruited to the ischemic brain of old male mice after stroke compared to young male mice. Blood neutrophilia and neutrophil invasion into the brain were increased in aged animals. Relative to infiltrating monocyte populations, brain-invading neutrophils had reduced phagocytic potential, and produced higher levels of reactive oxygen species and extracellular matrix-degrading enzymes (i.e., MMP-9), which were further exacerbated with age. Hemorrhagic transformation was more pronounced in aged versus young mice relative to infarct size. High numbers of myeloperoxidase-positive neutrophils were found in postmortem human brain samples of old (> 71 years) acute ischemic stroke subjects compared to non-ischemic controls. Many of these neutrophils were found in the brain parenchyma. A large proportion of these neutrophils expressed MMP-9 and positively correlated with hemorrhage and hyperemia. MMP-9 expression and hemorrhagic transformation after stroke increased with age. These changes in the myeloid response to stroke with age led us to hypothesize that the bone marrow response to stroke is altered with age, which could be important for the development of effective therapies targeting the immune response. We generated heterochronic bone marrow chimeras as a tool to determine the contribution of peripheral immune senescence to age- and stroke-induced inflammation. Old hosts that received young bone marrow (i.e., Young → Old) had attenuation of age-related reductions in bFGF and VEGF and showed improved locomotor activity and gait dynamics compared to isochronic (Old → Old) controls. Microglia in young heterochronic mice (Old → Young) developed a senescent-like phenotype. After stroke, aged animals reconstituted with young marrow had reduced behavioral deficits compared to isochronic controls, and had significantly fewer brain-infiltrating neutrophils. Increased rates of hemorrhagic transformation were seen in young mice reconstituted with aged bone marrow. This work suggests that age alters the immunological response to stroke, and that this can be reversed by manipulation of the peripheral immune cells in the bone marrow.

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.

Ischemic stroke across sexes: what is the status quo?

Stroke prevalence is expected to increase in the next decades due to the aging of the Western population. Ischemic stroke (IS) shows an age- and sex-dependent distribution in which men represent the most affected population within 65 years of age, being passed by post-menopausal women in older age groups. Furthermore, a sexual dimorphism concerning risk factors, presentation and treatment of IS has been widely recognized. In order to address these phenomena, a number of issue have been raised involving both socio-economical and biological factors. The latter can be either dependent on sex hormones or due to intrinsic factors. Although women have poorer outcomes and are more likely to die after a cerebrovascular event, they are still underrepresented in clinical trials and this is mirrored by the lack of sex-tailored therapies. A greater effort is needed in the future to ensure improved treatment and quality of life to both sexes.

Innate immune memory in the brain shapes neurological disease hallmarks

‘Innate immune memory’ is a vital mechanism of myeloid cell plasticity that occurs in response to environmental stimuli and alters subsequent immune responses. Two types of immunological imprinting can be distinguished, training and tolerance, which are epigenetically mediated and enhance or suppress subsequent inflammation, respectively. Whether immune memory occurs in tissue-resident macrophages in vivo and how it may affect pathology remains largely unknown. Here we demonstrate that peripherally applied inflammatory stimuli induce acute immune training and tolerance in the brain and lead to differential epigenetic reprogramming of brain-resident macrophages, microglia, that persists for at least six months. Strikingly, in a mouse model of Alzheimer’s pathology, immune training exacerbates cerebral β-amyloidosis while tolerance alleviates it; similarly, peripheral immune stimulation modifies pathological features after stroke. Our results identify immune memory in the brain as an important modifier of neuropathology.

Hemicraniectomy for Ischemic and Hemorrhagic Stroke: Facts and Controversies

Malignant large artery stroke is associated with high mortality of 70% to 80% with best medical management. Decompressive craniectomy (DC) is a highly effective tool in reducing mortality. Convincing evidence has accumulated from several randomized trials, in addition to multiple retrospective studies, that demonstrate not only survival benefit but also improved functional outcome with DC in appropriately selected patients. This article explores in detail the evidence for DC, nuances regarding patient selection, and applicability of DC for supratentorial intracerebral hemorrhage and posterior fossa ischemic and hemorrhagic stroke.

Pannexin1 knockout and blockade reduces ischemic stroke injury in female, but not in male mice

The membrane channel Pannexin 1 (Panx1) mediates apoptotic and inflammatory signaling cascades in injured neurons, responses previously shown to be sexually dimorphic under ischemic conditions. We tested the hypothesis that Panx1 plays an underlying role in mediating sex differences in stroke outcome responses. Middle-aged, 8-9 month old male and female wild type and Panx1 KO mice were subjected to permanent middle cerebral artery (MCA) occlusion, and infarct size and astrocyte and microglia activation were assessed 4 days later. The sexually dimorphic nature of Panx1 deletion was also explored by testing the effect of probenecid a known Panx1 blocker to alter stroke volume. Panx1 KO females displayed significantly smaller infarct volumes (~ 50 % reduction) compared to their wild-type counterparts, whereas no such KO effect occurred in males. This sex-specific effect of Panx1 KO was recapitulated by significant reductions in peri-infarct inflammation and astrocyte reactivity, as well as smaller infarct volumes in probenecid treated females, but not males. Finally, females showed overall, higher Panx1 protein levels than males under ischemic conditions. These findings unmask a deleterious role for Panx1 in response to permanent MCA occlusion, that is unique to females, and provide several new frameworks for understanding sex differences in stroke outcome.

Calcium/calmodulin-dependent protein kinase kinase β is neuroprotective in stroke in aged mice

Stroke is a devastating neurological disease and the leading cause of long-term disability, particularly in the elderly. Calcium/calmodulin-dependent protein kinase kinase β (CaMKK β) is a major kinase activated by elevated levels of intracellular calcium. Our previous findings in young mice have suggested that CaMKK β is neuroprotective as KO mice had worse stroke outcomes. Because age is an important determinant of stroke outcome, we evaluated the functional role of CaMKK β in stroke in aged mice. We used middle cerebral artery occlusion to induce stroke in aged wild-type (WT) and CaMKK β KO male mice. Lentiviral vectors carrying CaMKK β (LV-CaMKK β) were used to overexpress CaMKK β in the mouse brain. Baseline levels of CaMKK β in the aged brain were significantly lower than those in young mice. LV-CaMKK β treatment reduced infarcts and neurological deficits assessed 3 days after stroke. In chronic survival experiments, CaMKK β KO mice showed increased tissue loss in the ipsilateral hemisphere 3 weeks after stroke. In addition, KO mice showed poorer functional recovery during the 3-week survival period, as measured by the rotarod test, corner test, locomotor activity assay, and novel object recognition test, compared with WT controls. The loss of blood-brain barrier proteins, inactivation of survival gene expression such as B-cell lymphoma 2 (Bcl-2) and an increase in inflammatory cytokines in the serum were observed after stroke with CaMKK β inhibition. We demonstrate that CaMKK β is neuroprotective in stroke in aged mice. Therefore, our data suggest that CaMKK β may be a potential target for reducing long-term disability after stroke.

SUMOylation in brain ischemia: Patterns, targets, and translational implications

Post-translational protein modification by small ubiquitin-like modifier (SUMO) regulates a myriad of homeostatic and stress responses. The SUMOylation pathway has been extensively studied in brain ischemia. Convincing evidence is now at hand to support the notion that a major increase in levels of SUMOylated proteins is capable of inducing tolerance to ischemic stress. Therefore, the SUMOylation pathway has emerged as a promising therapeutic target for neuroprotection in the face of brain ischemia. Despite this, it is prudent to acknowledge that there are many key questions still to be addressed in brain ischemia related to SUMOylation. Accordingly, herein, we provide a critical review of literature within the field to summarize current knowledge and in so doing highlight pertinent translational implications of the SUMOylation pathway in brain ischemia.

Neuroprotective effects of amiodarone in a mouse model of ischemic stroke

Background

Ion channels play a crucial role in the development of ischemic brain injury. Recent studies have reported that the blockade of various types of ion channels improves outcomes in experimental stroke models. Amiodarone, one of the most effective drugs for life-threatening arrhythmia, works as a multiple channel blocker and its characteristics cover all four Vaughan-Williams classes. Although it is known that amiodarone indirectly contributes to preventing ischemic stroke by maintaining sinus rhythm in patients with atrial fibrillation, the direct neuroprotective effect of amiodarone has not been clarified. The purpose of this study was to investigate the direct effect of amiodarone on ischemic stroke in mice.

Methods

Focal cerebral ischemia was induced via distal permanent middle cerebral artery occlusion (MCAO) in adult male mice. The amiodarone pre-treatment group received 50 mg/kg of amiodarone 1 h before MCAO; the amiodarone post-treatment groups received 50 mg/kg of amiodarone immediately after MCAO; the control group received vehicle only. In addition, the sodium channel opener veratrine and selective beta-adrenergic agonist isoprotelenol were used to elucidate the targeted pathway. Heart rate and blood pressure were monitored perioperatively. Infarct volume analysis was conducted 48 h after MCAO. The body asymmetry test and the corner test were used for neurological evaluation.

Results

Amiodarone pre-treatment and post-treatment reduced the heart rate but did not affect the blood pressure. No mice showed arrhythmia. Compared with the control group, the amiodarone pre-treatment group had smaller infarct volumes (8.9 ± 2.1% hemisphere [mean ± SD] vs. 11.2 ± 1.4%; P < 0.05) and improved functional outcomes: lower asymmetric body swing rates (52 ± 17% vs. 65 ± 18%; P < 0.05) and fewer left turns (7.1 ± 1.2 vs. 8.3 ± 1.2; P < 0.05). In contrast, amiodarone post-treatment did not improve the outcomes after MCAO. The neuroprotective effect of amiodarone pre-treatment was abolished by co-administration of veratrine but not by isoproterenol.

Conclusions

Amiodarone pre-treatment attenuated ischemic brain injury and improved functional outcomes without affecting heart rhythm and blood pressure. The present results showed that amiodarone pre-treatment has neuroprotective effects, at least in part, via blocking the sodium channels.

Ischemic stroke induces gut permeability and enhances bacterial translocation leading to sepsis in aged mice

Aging is an important risk factor for post-stroke infection, which accounts for a large proportion of stroke-associated mortality. Despite this, studies evaluating post-stroke infection rates in aged animal models are limited. In addition, few studies have assessed gut microbes as a potential source of infection following stroke. Therefore we investigated the effects of age and the role of bacterial translocation from the gut in post-stroke infection in young (8-12 weeks) and aged (18-20 months) C57Bl/6 male mice following transient middle cerebral artery occlusion (MCAO) or sham surgery. Gut permeability was examined and peripheral organs were assessed for the presence of gut-derived bacteria following stroke. Furthermore, sickness parameters and components of innate and adaptive immunity were examined. We found that while stroke induced gut permeability and bacterial translocation in both young and aged mice, only young mice were able to resolve infection. Bacterial species seeding peripheral organs also differed between young (Escherichia) and aged (Enterobacter) mice. Consequently, aged mice developed a septic response marked by persistent and exacerbated hypothermia, weight loss, and immune dysfunction compared to young mice following stroke.

Stroke sensitivity in the aged: sex chromosome complement vs. gonadal hormones

Stroke is a sexually dimorphic disease. Elderly women not only have higher stroke incidence than age-matched men, but also have poorer recovery and higher morbidity and mortality after stroke. In older, post-menopausal women, gonadal hormone levels are similar to that of men. This suggests that tissue damage and functional outcomes are influenced by biologic sex (XX vs. XY) rather than the hormonal milieu at older ages. We employed the Four Core Genotype (FCG) mouse model to study the contribution of sex chromosome complement and gonadal hormones to stroke sensitivity in aged mice in which the testis determining gene (Sry) is removed from the Y chromosome, allowing for the generation of XX males and XY females. XXF, XXM, XYF, XYM and XYwt aged mice were subjected to middle cerebral artery occlusion (MCAO). XXF and XXM mice had significantly larger infarct volumes than XYF and XYM cohorts respectively. There was no significant difference in hormone levels among aged FCG mice. XXF/XXM mice also had more robust microglial activation and higher serum levels of pro-inflammatory cytokines than XYF/XYM cohort respectively. We concluded that the sex chromosome complement contributes to ischemic sensitivity in aged animals and leads to sex differences in innate immune responses.

A Role of Endogenous Progesterone in Stroke Cerebroprotection Revealed by the Neural-Specific Deletion of Its Intracellular Receptors

Treatment with progesterone protects the male and female brain against damage after middle cerebral artery occlusion (MCAO). However, in both sexes, the brain contains significant amounts of endogenous progesterone. It is not known whether endogenously produced progesterone enhances the resistance of the brain to ischemic insult. Here, we used steroid profiling by gas chromatography-tandem mass spectrometry (GC-MS/MS) for exploring adaptive and sex-specific changes in brain levels of progesterone and its metabolites after MCAO. We show that, in the male mouse brain, progesterone is mainly metabolized via 5α-reduction leading to 5α-dihydroprogesterone (5α-DHP), also a progesterone receptor (PR) agonist ligand in neural cells, then to 3α,5α-tetrahydroprogesterone (3α,5α-THP). In the female mouse brain, levels of 5α-DHP and 3α,5α-THP are lower and levels of 20α-DHP are higher than in males. After MCAO, levels of progesterone and 5α-DHP are upregulated rapidly to pregnancy-like levels in the male but not in the female brain. To assess whether endogenous progesterone and 5α-DHP contribute to the resistance of neural cells to ischemic damage, we inactivated PR selectively in the CNS. Deletion of PR in the brain reduced its resistance to MCAO, resulting in increased infarct volumes and neurological deficits in both sexes. Importantly, endogenous PR ligands continue to protect the brain of aging mice. These results uncover the unexpected importance of endogenous progesterone and its metabolites in cerebroprotection. They also reveal that the female reproductive hormone progesterone is an endogenous cerebroprotective neurosteroid in both sexes.SIGNIFICANCE STATEMENT The brain responds to injury with protective signaling and has a remarkable capacity to protect itself. We show here that, in response to ischemic stroke, levels of progesterone and its neuroactive metabolite 5α-dihydroprogesterone are upregulated rapidly in the male mouse brain but not in the female brain. An important role of endogenous progesterone in cerebroprotection was demonstrated by the conditional inactivation of its receptor in neural cells. These results show the importance of endogenous progesterone, its metabolites, and neural progesterone receptors in acute cerebroprotection after stroke. This new concept could be exploited therapeutically by taking into account the progesterone status of patients and by supplementing and reinforcing endogenous progesterone signaling for attaining its full cerebroprotective potential.

The IMPROVE Guidelines (Ischaemia Models: Procedural Refinements Of in Vivo Experiments)

Most in vivo models of ischaemic stroke target the middle cerebral artery and a spectrum of stroke severities, from mild to substantial, can be achieved. This review describes opportunities to improve the in vivo modelling of ischaemic stroke and animal welfare. It provides a number of recommendations to minimise the level of severity in the most common rodent models of middle cerebral artery occlusion, while sustaining or improving the scientific outcomes. The recommendations cover basic requirements pre-surgery, selecting the most appropriate anaesthetic and analgesic regimen, as well as intraoperative and post-operative care. The aim is to provide support for researchers and animal care staff to refine their procedures and practices, and implement small incremental changes to improve the welfare of the animals used and to answer the scientific question under investigation. All recommendations are recapitulated in a summary poster (see supplementary information).

Age-related differences in interferon regulatory factor-4 and -5 signaling in ischemic brains of mice

Stroke is a disease that mainly affects the elderly. Since the age-related differences in stroke have not been well studied, modeling stroke in aged animals is clinically more relevant. The inflammatory responses to stroke are a fundamental pathological procedure, in which microglial activation plays an important role. Interferon regulatory factor-5 (IRF5) and IRF4 regulate M1 and M2 activation of macrophages, respectively, in peripheral inflammation; but it is unknown whether IRF5/IRF4 are also involved in cerebral inflammatory responses to stroke and whether age-related differences of the IRF5/IRF4 signaling exist in ischemic brain. Here, we investigated the influences of aging on IRF5/IRF4 signaling and post-stroke inflammation in mice. Both young (9-12 weeks) and aged (18 months) male mice were subjected to middle cerebral artery occlusion (MCAO). Morphological and biochemical changes in the ischemic brains and behavior deficits were assessed on 1, 3, and 7 d post-stroke. After MCAO, the aged mice showed smaller infarct sizes but higher neurological deficits and corner test scores than young mice. Young mice had higher levels of IRF4 and CD206 microglia in the ischemic brains, whereas the aged mice expressed more IRF5 and MHCII microglia. After MCAO, serum pro-inflammatory cytokines (TNF-α, iNOS, IL-6) were more prominently up-regulated in aged mice, whereas serum anti-inflammatory cytokines (TGF-β, IL-4, IL-10) were more prominently up-regulated in young mice. Our results demonstrate that aging has a significant influence on stroke outcomes in mice, which is probably mediated by age-specific inflammatory responses.

Gender related issues in thrombosis and hemostasis

INTRODUCTION

Many aspects of hemostasis, both primary and secondary, as well as fibrinolysis display sex differences. From a clinical viewpoint, certain differential phenotypic presentations clearly arise within various disorders of thrombosis and hemostasis. Areas covered: The present mini-review summarizes selected clinical entities where sex differences are reflected in both frequency and clinical presentation of hemostasis disorders. Sex differences are discussed within the settings of cardiovascular disease, including coronary artery disease and ischemic stroke, venous thromboembolism and inherited bleeding disorders. Moreover, pregnancy and labor present particular challenges in terms of increased thromboembolic and bleeding risk, and this is also summarized. Expert commentary: Available knowledge on sex differences in risk factors and clinical presentation of disorders within thrombosis and hemostasis is increasing. However, more evidence is needed to further clarify different risk factors and treatment effect in men and women, both as regards to cardiovascular disease and venous thromboembolism. This should facilitate improved gender guided risk stratification, and prevention and treatment of these diseases. Finally, risk assessment during pregnancy remains a challenge; this applies both to thromboembolic risk assessment during normal pregnancy and special care of women with inherited bleeding disorders during labor.

Multiparity improves outcomes after cerebral ischemia in female mice despite features of increased metabovascular risk

Females show a varying degree of ischemic sensitivity throughout their lifespan, which is not fully explained by hormonal or genetic factors. Epidemiological data suggest that sex-specific life experiences such as pregnancy increase stroke risk. This work evaluated the role of parity on stroke outcome. Age-matched virgin (i.e., nulliparous) and multiparous mice were subjected to 60 min of reversible middle cerebral artery occlusion and evaluated for infarct volume, behavioral recovery, and inflammation. Using an established mating paradigm, fetal microchimeric cells present in maternal mice were also tracked after parturition and stroke. Parity was associated with sedentary behavior, weight gain, and higher triglyceride and cholesterol levels. The multiparous brain exhibited features of immune suppression, with dampened baseline microglial activity. After acute stroke, multiparous mice had smaller infarcts, less glial activation, and less behavioral impairment in the critical recovery window of 72 h. Behavioral recovery was significantly better in multiparous females compared with nulliparous mice 1 mo after stroke. This recovery was accompanied by an increase in poststroke angiogenesis that was correlated with improved performance on sensorimotor and cognitive tests. Multiparous mice had higher levels of VEGF, both at baseline and after stroke. GFP+ fetal cells were detected in the blood and migrated to areas of tissue injury where they adopted endothelial morphology 30 d after injury. Reproductive experience has profound and complex effects on neurovascular health and disease. Inclusion of female mice with reproductive experience in preclinical studies may better reflect the life-long patterning of ischemic stroke risk in women.

Sex differences in ischaemic stroke: potential cellular mechanisms

Stroke remains a leading cause of mortality and disability worldwide. More women than men have strokes each year, in part because women live longer. Women have poorer functional outcomes, are more likely to need nursing home care and have higher rates of recurrent stroke compared with men. Despite continued advancements in primary prevention, innovative acute therapies and ongoing developments in neurorehabilitation, stroke incidence and mortality continue to increase due to the aging of the U.S.

POPULATION

Sex chromosomes (XX compared with XY), sex hormones (oestrogen and androgen), epigenetic regulation and environmental factors all contribute to sex differences. Ischaemic sensitivity varies over the lifespan, with females having an "ischaemia resistant" phenotype that wanes after menopause, which has recently been modelled in the laboratory. Pharmacological therapies for acute ischaemic stroke are limited. The only pharmacological treatment for stroke approved by the Food and Drug Administration (FDA) is tissue plasminogen activator (tPA), which must be used within hours of stroke onset and has a number of contraindications. Pre-clinical studies have identified a number of potentially efficacious neuroprotective agents; however, nothing has been effectively translated into therapy in clinical practice. This may be due, in part, to the overwhelming use of young male rodents in pre-clinical research, as well as lack of sex-specific design and analysis in clinical trials. The review will summarize the current clinical evidence for sex differences in ischaemic stroke, and will discuss sex differences in the cellular mechanisms of acute ischaemic injury, highlighting cell death and immune/inflammatory pathways that may contribute to these clinical differences.

Sex differences in stroke across the lifespan: The role of T lymphocytes

Stroke is a sexually dimorphic disease. Ischemic sensitivity changes throughout the lifespan and outcomes depend largely on variables like age, sex, hormonal status, inflammation, and other existing risk factors. Immune responses after stroke play a central role in how these factors interact. Although the post-stroke immune response has been extensively studied, the contribution of lymphocytes to stroke is still not well understood. T cells participate in both innate and adaptive immune responses at both acute and chronic stages of stroke. T cell responses also change at different ages and are modulated by hormones and sex chromosome complement. T cells have also been implicated in the development of hypertension, one of the most important risk factors for vascular disease. In this review, we highlight recent literature on the lymphocytic responses to stroke in the context of age and sex, with a focus on T cell response and the interaction with important stroke risk factors.

Sex differences in vascular physiology and pathophysiology: estrogen and androgen signaling in health and disease

Sex differences between women and men are often overlooked and underappreciated when studying the cardiovascular system. It has been long assumed that men and women are physiologically similar, and this notion has resulted in women being clinically evaluated and treated for cardiovascular pathophysiological complications as men. Currently, there is increased recognition of fundamental sex differences in cardiovascular function, anatomy, cell signaling, and pathophysiology. The National Institutes of Health have enacted guidelines expressly to gain knowledge about ways the sexes differ in both normal function and diseases at the various research levels (molecular, cellular, tissue, and organ system). Greater understanding of these sex differences will be used to steer future directions in the biomedical sciences and translational and clinical research. This review describes sex-based differences in the physiology and pathophysiology of the vasculature, with a special emphasis on sex steroid receptor (estrogen and androgen receptor) signaling and their potential impact on vascular function in health and diseases (e.g., atherosclerosis, hypertension, peripheral artery disease, abdominal aortic aneurysms, cerebral aneurysms, and stroke).

[Sex differences in acute disturbances of cerebral blood circulation]

It is shown that in the development of stroke observed sex differences, which manifest themselves both clinically and by laboratory parameters. While men have a higher incidence of stroke for most of his life, a woman in a more advanced age have a higher risk for stroke. Sex differences in the development of stroke depend on several factors, including genetic and hormonal changes throughout life. Studies sex differences in the risk of stroke is only in the initial stage, but the first results show that there are differences in neuronal cell death in males and females after experimental ischemic stroke. A better understanding of the mechanisms underlying the development of stroke in men and women will lead to more appropriate treatment strategies for patients of both sexes.

Prospects of modeling poststroke epileptogenesis

This Review describes the current status of poststroke epilepsy (PSE) with an emphasis on poststroke epileptogenesis modeling for testing new therapeutic agents. Stroke is a leading cause of epilepsy in an aging population. Late-onset "epileptic" seizures have been reported in up to 30% cases after stroke. Nevertheless, the overall prevalence of PSE is 2-4%. Rodent models of stroke have contributed to our understanding of the relationship between seizures and the underlying ischemic damage to neurons. To understand whether acutely generated stroke events lead to a chronic phenotype more closely resembling PSE with recurrent seizures, a limited variety of approaches emerged in early 2000s. These limited methods of causing an occlusion in mice and rats show different infarct size and neurological deficits. The most often employed procedure for inducing focal ischemia is the middle cerebral artery occlusion. This mimics the pathophysiology seen in humans in terms of extent of damage to cortex and striatum. Photothrombosis and endothelin-1 models can similarly evoke episodes of ischemic stroke. These models are well suited to studying mechanisms and biomarkers of epileptogenesis or optimizing novel drug discoveries. However, modeling of PSE is tedious, is highly variable, and lacks validity; therefore, it is not widely implemented in epilepsy research. Moreover, the relevance of ischemic models to specific forms of human stroke remains unclear. Stroke modeling in young male rodents lacks clinical relevance to elderly populations and especially to women, likely as a result of sex differences. Nevertheless, because of the neuronal damage and epileptogenic insult that these models trigger, they are helpful tools in studying acquired epilepsy and prophylactic drug therapy. © 2016 Wiley Periodicals, Inc.