Timing of estrogen therapy after ovariectomy dictates the efficacy of its neuroprotective and antiinflammatory actions

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

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

Treatment with brain specific estrogen prodrug ameliorates cognitive effects of surgical menopause in mice

Menopause is an endocrine shift leading to increased vulnerability for cognitive impairment and dementia risk factors, in part due to loss of neuroprotective circulating estrogens. Systemic replacement of estrogen post-menopause has limitations, including risk for estrogen-sensitive cancers. A promising therapeutic approach therefore might be to deliver estrogen only to the brain. We examined whether we could enhance cognitive performance by delivering estrogen exclusively to the brain in ovariectomized mice (a surgical menopause model). We treated mice with the prodrug 10β,17β-dihydroxyestra-1,4-dien-3-one (DHED), which can be administered systemically but is converted to 17β-estradiol only in the brain. Young and middle-aged C57BL/6 J mice received ovariectomy and subcutaneous implant containing vehicle or DHED and underwent cognitive testing to assess memory after 1-3.5 months of treatment. Low and medium doses of DHED did not alter metabolic status in middle-aged mice. In both age groups, DHED treatment improved spatial memory in ovariectomized mice. Additional testing in middle-aged mice showed that DHED treatment improved working and recognition memory in ovariectomized mice. These results lay the foundation for future studies determining if this intervention is as efficacious in models of dementia with comorbid risk factors.

Estrogen's sex-specific effects on ischemic cell death and estrogen receptor mRNA expression in rat cortical organotypic explants

Estrogens, such as the biologically active 17-β estradiol (E2), regulate not only reproductive behaviors in adults, but also influence neurodevelopment and neuroprotection in both females and males. E2, contingent upon the timing and concentration of the therapy, is neuroprotective in female and male rodent models of stroke. In Vivo studies suggest that E2 may partially mediate this neuroprotection, particularly in the cortex, via ERα. In Vitro studies, utilizing a chemically induced ischemic injury in cortical explants from both sexes, suggest that ERα or ERβ signaling is needed to mediate the E2 protection. Since we know that the timing and concentration of E2 therapy may be sex-specific, we examined if E2 (1 nM) mediates neuroprotection when female and male cortical explants are separately isolated from postnatal day (PND) 3-4 rat. Changes in basal levels ERα, ERβ, and AR mRNA expression are compared across early post-natal development in the intact cortex and the corresponding days in vitro (DIV) for cortical explants. Following ischemic injury at 7 DIV, cell death and ERα, ERβ and AR mRNA expression was compared in female and male cortical explants. We provide evidence that E2-mediated protection is maintained in isolated cortical explants from females, but not male rats. In female cortical explants, the E2-mediated protection at 24 h occurs secondarily to a blunted transient increase in ERα mRNA at 12 h. These results suggest that cortical E2-mediated protection is influenced by sex and supports data to differentially treat females and males following ischemic injury.

The role of the brain renin-angiotensin system in Parkinson´s disease

The renin-angiotensin system (RAS) was classically considered a circulating hormonal system that regulates blood pressure. However, different tissues and organs, including the brain, have a local paracrine RAS. Mutual regulation between the dopaminergic system and RAS has been observed in several tissues. Dysregulation of these interactions leads to renal and cardiovascular diseases, as well as progression of dopaminergic neuron degeneration in a major brain center of dopamine/angiotensin interaction such as the nigrostriatal system. A decrease in the dopaminergic function induces upregulation of the angiotensin type-1 (AT1) receptor activity, leading to recovery of dopamine levels. However, AT1 receptor overactivity in dopaminergic neurons and microglial cells upregulates the cellular NADPH-oxidase-superoxide axis and Ca2+ release, which mediate several key events in oxidative stress, neuroinflammation, and α-synuclein aggregation, involved in Parkinson's disease (PD) pathogenesis. An intraneuronal antioxidative/anti-inflammatory RAS counteracts the effects of the pro-oxidative AT1 receptor overactivity. Consistent with this, an imbalance in RAS activity towards the pro-oxidative/pro-inflammatory AT1 receptor axis has been observed in the substantia nigra and striatum of several animal models of high vulnerability to dopaminergic degeneration. Interestingly, autoantibodies against angiotensin-converting enzyme 2 and AT1 receptors are increased in PD models and PD patients and contribute to blood-brain barrier (BBB) dysregulation and nigrostriatal pro-inflammatory RAS upregulation. Therapeutic strategies addressed to the modulation of brain RAS, by AT1 receptor blockers (ARBs) and/or activation of the antioxidative axis (AT2, Mas receptors), may be neuroprotective for individuals with a high risk of developing PD or in prodromal stages of PD to reduce progression of the disease.

Sex and stroke risk factors: A review of differences and impact

OBJECTIVES

There is an increase in stroke incidence risk over the lifetime of women, given their longer life expectancy. However, an alarming trend for sex disparities, particularly in certain stroke risk factors, shows a concerning need for focus on sex differences in stroke prevention and treatment for women. In this article, we are addressing sex differences in both traditional and sex-specific stroke risk factors.

METHODS

We searched PubMed from inception to December 2022 for articles related to sex differences and risk factors for stroke. We reviewed full-text articles for relevance and ultimately included 152 articles for this focused review.

RESULTS

Women are at increased risk for stroke from both traditional and non-traditional stroke risk factors. As women age, they have a higher disease burden of atrial fibrillation, increased risk of stroke related to diabetes, worsening lipid profiles, and higher prevalence of hypertension and obesity compared to men. Further, women carry sex hormone-specific risk factors for stroke, including the age of menarche, menopause, pregnancy, and its complications, as well as hormonal therapy. Men have a higher prevalence of tobacco use and atrial fibrillation, as well as an increased risk for stroke related to hyperlipidemia. Additionally, men have sex-specific risks related to low testosterone levels.

CONCLUSIONS

By identifying biological sex-specific risk factors for stroke, developing robust collaborations, researching, and applying the knowledge for risk reduction strategies, we can begin to tailor prevention and reduce the global burden of stroke morbidity and mortality.

The nongenomic neuroprotective effects of estrogen, E2-BSA, and G1 following traumatic brain injury: PI3K/Akt and histopathological study

OBJECTIVES

Studies suggest that both genomic and nongenomic pathways are involved in mediating the salutary effects of steroids following traumatic brain injury (TBI). This study investigated the nongenomic effects of 17β-estradiol (E2) mediated by the PI3K/p-Akt pathway after TBI.

METHODS

Ovariectomized rats were apportioned to E2, E2-BSA (E2 conjugated to bovine serum albumin), G1 [G-protein-coupled estrogen receptor agonist (GPER)] or their vehicle was injected following TBI, whereas ICI (classical estrogen receptor antagonist), G15 (GPER antagonist), ICI + G15, and their vehicles were injected before the induction of TBI and injection of drugs. Diffuse TBI was induced by the Marmarou model. Evans blue (EBC, 5 h), brain water contents (BWC), histopathological changes, and brain PI3K and p-Akt protein expressions were measured 24 h after TBI. The veterinary comma scale (VCS) was assessed before and at different times after TBI.

RESULTS

The results showed a reduction in BWC and EBC and increased VCS in the E2, E2-BSA, and G1 groups. Also, E2, E2-BSA, and G1 reduced brain edema, inflammation, and apoptosis. The ICI and G15 inhibited the beneficial effects of E2, E2-BSA, and G1 on these parameters. All drugs, following TBI, prevented the reduction of brain PI3K/p-Akt expression. The individual or combined use of ICI and G15 eliminated the beneficial effects of E2, E2-BSA, and G1 on PI3K/p-Akt expressions.

CONCLUSIONS

These findings indicated that PI3K/p-Akt pathway plays a critical role in mediating the salutary effects of estradiol on histopathological changes and neurological outcomes following TBI, suggesting that GPER and classic ERs are involved in regulating the expression of PI3K/p-Akt.

Brain Specific Estrogen Ameliorates Cognitive Effects of Surgical Menopause in Mice

Menopause is a major endocrinological shift that leads to an increased vulnerability to the risk factors for cognitive impairment and dementia. This is thought to be due to the loss of circulating estrogens, which exert many potent neuroprotective effects in the brain. Systemic replacement of estrogen post-menopause has many limitations, including increased risk for estrogen-sensitive cancers. A more promising therapeutic approach therefore might be to deliver estrogen only to the brain thus limiting adverse peripheral side effects. We examined whether we could enhance cognitive performance by delivering estrogen exclusively to the brain in post-menopausal mice. We modeled surgical menopause via bilateral ovariectomy (OVX). We treated mice with the pro-drug 10β,17β-dihydroxyestra-1,4-dien-3-one (DHED), which can be administered systemically but is converted to 17β-estradiol only in the brain. Young (2.5-month) and middle-aged (11-month-old) female C57BL/6J mice received ovariectomy and a subcutaneous implant containing vehicle (cholesterol) or DHED. At 3.5 months old (young group) and 14.5 months old (middle-aged group), mice underwent behavior testing to assess memory. DHED did not significantly alter metabolic status in middle-aged, post-menopausal mice. In both young and middle-aged mice, the brain-specific estrogen DHED improved spatial memory. Additional testing in middle-aged mice also showed that DHED improved working and recognition memory. These promising results lay the foundation for future studies aimed at determining if this intervention is as efficacious in models of dementia that have comorbid risk factors.

Talking about Sexuality in Stroke Individuals: The New Era of Sexual Rehabilitation

One of the largest causes of mortality and disability worldwide is stroke. In the last twenty years significant objectives have been achieved in the early and chronic treatment of motor and cognitive dysfunctions, increasing the quality of life in patients and their caregivers. However, there is an unresolved clinical issue that remains: sexual dysfunctions. Multiple etiologies, including organic (such as lesion localization, premorbid medical problems, and drugs) and psychosocial (such as fear of recurrences, loss of self-esteem, role shifts, anxiety, and depression), are associated with sexual deficits. In this perspective review, we reported the last piece of evidence about this crucial topic which drastically affects the quality of life of these patients. Indeed, although patients may often not disclose their sexual concerns, literature demonstrates that they seek help concerning this issue. On the other side, clinicians working in the rehabilitation field are not always comfortable or prepared to deal with sexuality and sexual function in neurological patients. A new phase of the training course should be launched including different physicians, nurses, rehabilitation specialists, and social workers, to learn how to deal with topics related to sexuality. As a result, professional sexual counselors should now become a structured part of stroke settings and rehabilitation with new effective tools (i.e., PLISSIT model; TDF program) for improving quality of life.

Sex differences in the inflammatory response to stroke

Ischemic stroke is a leading cause of morbidity and mortality and disproportionally affects women, in part due to their higher longevity. Older women have poorer outcomes after stroke with high rates of cognitive deficits, depression, and reduced quality of life. Post-stroke inflammatory responses are also sexually dimorphic and drive differences in infarct size and recovery. Factors that influence sex-specific immune responses can be both intrinsic and extrinsic. Differences in gonadal hormone exposure, sex chromosome compliment, and environmental/social factors can drive changes in transcriptional and metabolic profiles. In addition, how these variables interact, changes across the lifespan. After the onset of ischemic injury, necrosis and apoptosis occur, which activate microglia and other glial cells within the central nervous system, promoting the release of cytokines and chemokines and neuroinflammation. Cells involved in innate and adaptive immune responses also have dual functions after stroke as they can enhance inflammation acutely, but also contribute to suppression of the inflammatory cascade and later repair. In this review, we provide an overview of the current literature on sex-specific inflammatory responses to ischemic stroke. Understanding these differences is critical to identifying therapeutic options for both men and women.

Are the digit ratio (2D:4D) and hand grip strength related to Parkinson disease in elderly males?

BACKGROUND

Sex hormones affect the pathogenesis of Parkinson patients and it has been suggested that gender is the most important factor in the development and progression of Parkinson's disease. Studies have shown that the second to fourth digit ratio (2D:4D) is affected by the prenatal testosterone and estrogen levels and can predict predisposition to disease. In addition, decreased muscle strength in people with Parkinson's has been repeatedly reported. Hand grip strength (HGS) is a suitable measure to evaluate the musculoskeletal system among the elderly and it is considered as an indicator of the overall strength of the body. This study aimed at investigating the relationship between Parkinson's disease and HGS and 2D:4D ratio.

METHODS

In this study 117 elderly men with Parkinson disease (mean age of 61.66 ± 11.28 years) and 156 healthy control subjects (mean age of 61.86 ± 6.29 years) participated. After determining the level of disability of Parkinson patients by a neurologist (level of disability in the range of 1-4), anthropometric indices (height, weight, length of the second and fourth fingers) and maximum HGS were measured.

RESULTS

Although 2D:4D ratios (right and left hand) of male patients with Parkinson's disease were higher than those of healthy males, this difference was not statistically significant (P = 0.12, P = 0.40; respectively). Conversely, HGS for the right and left hands of Parkinson patients were significantly lower than those of healthy males (P = 0.02, P = 0.03; respectively). The results showed a significant negative relationship between Parkinson disease and the right and left HGS (R = -0.16, P = 0.005; R = -0.17, P = 0.003; respectively). Parkinson disease had no significant relationship with 2D:4D of the right hand, left hand, mean finger ratio and D_R-L 2D:4D (P > 0.05). The regression results showed that the right and left HGS were not able to predict Parkinson disease (P = 0.25, P = 0.16; respectively).

CONCLUSION

We concluded that HGS was negatively associated with the Parkinson disease, but conversely, 2D:4D may not be a valuable biomarker of elevated risk of Parkinson in elderly males.

Dietary genistein and 17β-estradiol implants differentially influence locomotor and cognitive functions following transient focal ischemia in middle-aged ovariectomized rats at different lengths of estrogen deprivation

Genistein possesses estrogenic activity and has been considered a potential replacement for estrogen replacement therapy after menopause. In the current study, we investigated the neuroprotective effects of dietary genistein at varied lengths of estrogen deprivation in middle-aged ovariectomized Sprague-Dawley rats under ischemic conditions. Two weeks of treatment with dietary genistein at 42 mg/kg but not 17β-estradiol implants improved cognitive flexibility (Morris water maze test) after short-term estrogen deprivation (2 weeks) but not long-term estrogen deprivation (12 weeks). 17β-estradiol implants but not dietary genistein improved locomotor asymmetry (cylinder test) after long-term but not short-term estrogen deprivation. Dietary genistein but not 17β-estradiol implant improved early phase motor learning (rotarod test) after long-term estrogen deprivation. Neither 17β-estradiol implant nor dietary genistein reduced infarct size after either short-term or long-term estrogen deprivation. Genistein, however, reduced ionized calcium-binding adaptor molecule-1 (Iba1) expression, a marker of brain inflammation, at the ipsilateral side of stroke injury after short-term but not long-term estrogen deprivation. This study suggests that the neuroprotective effects of dietary genistein on motor and cognitive functions are distinctly influenced by the length of estrogen deprivation following focal ischemia. SIGNIFICANCE: There is an increasing postmenopausal population opting for homeopathic medicines for the management of menopausal symptoms due to the perceived distrust in estrogen use as hormone replacement. Basic and clinical studies support the notion that early, but not delayed, hormone replacement after menopause is beneficial. Furthermore, evidence suggests that delaying hormone replacement augments the detrimental, rather than the beneficial effects of estrogens. Because of the active consideration of soy isoflavones including genistein as alternatives to estrogen replacement, it is necessary to understand the ramifications of soy isoflavones use when their administration is begun at various times after menopause.

Sex Differences in Pulmonary Hypertension

Pulmonary hypertension (PH) includes multiple diseases that share as common characteristic an elevated pulmonary artery pressure and right ventricular involvement. Sex differences are observed in practically all causes of PH. The most studied type is pulmonary arterial hypertension (PAH) which presents a gender bias regarding its prevalence, prognosis, and response to treatment. Although this disease is more frequent in women, once affected they present a better prognosis compared to men. Even if estrogens seem to be the key to understand these differences, animal models have shown contradictory results leading to the birth of the estrogen paradox. In this review we will summarize the evidence regarding sex differences in experimental animal models and, very specially, in patients suffering from PAH or PH from other etiologies.

Hormone Therapy in Menopause: Concepts, Controversies, and Approach to Treatment

Hormone therapy (HT) is an effective treatment for menopausal symptoms, including vasomotor symptoms and genitourinary syndrome of menopause. Randomized trials also demonstrate positive effects on bone health, and age-stratified analyses indicate more favorable effects on coronary heart disease and all-cause mortality in younger women (close proximity to menopause) than in women more than a decade past menopause. In the absence of contraindications or other major comorbidities, recently menopausal women with moderate or severe symptoms are appropriate candidates for HT. The Women's Health Initiative (WHI) hormone therapy trials-estrogen and progestin trial and the estrogen-alone trial-clarified the benefits and risks of HT, including how the results differed by age. A key lesson from the WHI trials, which was unfortunately lost in the posttrial cacophony, was that the risk:benefit ratio and safety profile of HT differed markedly by clinical characteristics of the participants, especially age, time since menopause, and comorbidity status. In the present review of the WHI and other recent HT trials, we aim to provide readers with an improved understanding of the importance of the timing of HT initiation, type and route of administration, and of patient-specific considerations that should be weighed when prescribing HT.

Long-term hypogonadism diminishes the neuroprotective effects of dietary genistein in young adult ovariectomized rats after transient focal ischemia

Increasing age disproportionately increases the risk of stroke among women compared to men of similar age, especially after menopause. One of the reasons for this observation is a sharp drop in circulating estrogens. However, the timing of initiation of estrogen replacement after menopause is associated with mixed beneficial and detrimental effects, hence contributing to widespread mistrust of estrogen use. Agents including soy isoflavones are being assessed as viable alternatives to estrogen therapy. In this study, we hypothesized that the neuroprotective effects of genistein, a soy isoflavone are less sensitive to the length of hypogonadism in young adult ovariectomized rats following cerebral ischemia. We expected that long-term hypogonadism will worsen motor and cognitive function, increase post-stroke inflammation with no effect on the neuroprotection of genistein. We compared the effect of treatment with dietary genistein (GEN) on short-term (2 weeks) and long-term hypogonadism (12 weeks) in young adult ovariectomized Sprague-Dawley rats on sensorimotor function, cognition and inflammation after focal ischemia. Dorsal Silastic implant of 17β-estradiol (E2) was used as a control for hormone therapy. Long-term hypogonadism stroked rats performed worse than the short-term hypogonadism stroked rats on the motor and cognitive function tests. GEN did not improve neurological assessment and motor learning after either short-term or long-term hypogonadism. GEN improved cognitive flexibility after short-term hypogonadism but not after the long-term. Both GEN and E2 reduced tissue loss after short-term hypogonadism and reduced GFAP expression at the contralateral side of ischemia after long-term hypogonadism. The length of hypogonadism may differentially influence the neuroprotective effects of both GEN and E2 on the motor and cognitive functions in young adult rats.

Electroacupuncture reactivates estrogen receptors to restore the neuroprotective effect of estrogen against cerebral ischemic stroke in long-term ovariectomized rats

BACKGROUND

Stroke is a sexually dimorphic disease and a leading cause of death and disability. Estrogen replacement therapy (ERT) confers beneficial neuroprotective effects if administered within a widely accepted time window called the "critical period." However, very few studies have explored the idea of modulating the critical period to enable long-term post-menopausal women to regain more benefits from estrogen therapy. Here, motivated by previous findings that electroacupuncture could both alter estrogen metabolism and induce significant tolerance against stroke, it was explored whether EA could restore estrogen's neuroprotection against cerebral ischemia in long-term ovariectomized (OVX) rats.

METHODS

We implemented 1 week(w)-EA pretreatment on OVX-10w or OVX-20w rats, and tested the expression of estrogen receptors, and detected the ERT's neuroprotection against stroke induced by middle cerebral artery occlusion (MCAO).

RESULTS

We found that the expression levels of phospho-ERα-S118 and estrogen receptor β (ERβ) in the striatum of OVX-10w rats were significantly decreased and ERT's neuroprotection was abolished in the OVX-10w rats. However, EA-1w pretreatment could significantly recover the expression levels of phospho-ERα-S118 and ERβ, and also restored the neuroprotective effects of ERT in OVX-10w rats. However, EA-1w pretreatment could not restore the expression of estrogen receptors and ERT's neuroprotection in OVX-20w rats.

CONCLUSION

Taken together, our study indicates that EA may be an easy intervention that can restore the efficacy of estrogen therapy during the "critical period," which has the potential to improve the stroke outcomes of an enormous number of long-term post-menopausal women. However, the time-sensitive influences for how EA and estrogen metabolism interact with each other should be considered.

Effects of 17β-Estradiol on Monocyte/Macrophage Response to Staphylococcus aureus: An In Vitro Study

To describe how 17β-estradiol (E2) influence in the monocyte/macrophage response induced by S. aureus in in vitro models of murine peritoneal macrophages (MPMs) and human peripheral blood monocytes (HPBM). MPMs (2 x 10⁵/ml) were isolated from sham (n=3) and ovariectomized (OVX) females (n = 3) and males (n = 3) after induction by thioglycolate. The MPMs obtained from OVX females and males were treated for 24 hours with 17β-estradiol (E2) (10^-7 M), and after that, inoculation with S. aureus was carried out for 6 hours. The macrophages were collected and destined to evaluate the relative gene expression of TNF-α, IL-1β, IL-6, IL-8 and TLR2. For the in vitro model of HPBMs, six men and six women of childbearing age were selected and HPBMs were isolated from samples of the volunteers’ peripheral blood. In women, blood was collected both during menstruation and in the periovulatory period. HPBMs were inoculated with S. aureus for 6 hours and the supernatant was collected for analysis of cytokines by Luminex and the HPBMs were removed for analysis of 84 genes involved in the host’s response to bacterial infections by RT-PCR array. Previous treatment with E2 decreased the gene expression and production of proinflammatory cytokines, such as TNF-α, IL-1β and IL-6 and decreased the expression of TLR2 tanto em MPMs quanto em HPBMs. The analysis of gene expression shows that E2 inhibited the NFκB pathway. It is suggested that 17β-estradiol acts as an immunoprotective in the monocyte/macrophage response induced by S. aureus.

The Hepatoprotective mechanisms of 17β-estradiol after traumatic brain injury in male rats: Classical and non-classical estrogen receptors

Protective effects of estrogen (E2) on traumatic brain injury (TBI) have been determined. In this study, the hepatoprotective effects of E2 after TBI through its receptors and oxidative stress regulation have been evaluated. Diffuse TBI induced by the Marmarou method in male rats. G15, PHTPP, MPP, and ICI182-780 as selective antagonists of E2 were injected before TBI. The results indicated that TBI induces a significant increase in liver enzymes [Alkaline phosphatase (ALP), Aspartate aminotransferase (AST), Alanine aminotransferase (ALT), Glutamyl transferase (GGT)], and oxidants levels [Malondialdehyde (MDA), Nitric oxide (NO)] and decreases in antioxidant biomarkers [Glutathione peroxidase (GPx) and Superoxide dismutase (SOD)] in the brain and liver, and plasma. We also found that E2 significantly preserved levels of these biomarkers and enzymatic activity. All antagonists inhibited the effects of E2 on increasing SOD and GPx. Also, the effects of E2 on brain MDA levels were inhibited by all antagonists, but in the liver, only ICI + G15 + E2 + TBI group was affected. The impacts of E2 on brain and liver and plasma NO levels were inhibited by all antagonists. The current findings demonstrated that E2 probably improved liver injury after TBI by modulating oxidative stress. Also, both classic (ERβ, ERα) and non-classic [G protein-coupled estrogen receptor (GPER)] receptors are affected in the protective effects of E2.

Epigenetics of the developing and aging brain: Mechanisms that regulate onset and outcomes of brain reorganization

Brain development is a life-long process that encompasses several critical periods of transition, during which significant cognitive changes occur. Embryonic development, puberty, and reproductive senescence are all periods of transition that are hypersensitive to environmental factors. Rather than isolated episodes, each transition builds upon the last and is influenced by consequential changes that occur in the transition before it. Epigenetic marks, such as DNA methylation and histone modifications, provide mechanisms by which early events can influence development, cognition, and health outcomes. For example, parental environment influences imprinting patterns in gamete cells, which ultimately impacts gene expression in the embryo which may result in hypersensitivity to poor maternal nutrition during pregnancy, raising the risks for cognitive impairment later in life. This review explores how epigenetics induce and regulate critical periods, and also discusses how early environmental interactions prime a system towards a particular health outcome and influence susceptibility to disease or cognitive impairment throughout life.

Postmenopausal hormone therapy for cardiovascular health: the evolving data

Postmenopausal (PM) hormone therapy (HT) was extremely popular for years as a treatment for many conditions, including cardiovascular (CV) disease (CVD) prevention. The adverse results from the Women's Health Initiative (WHI) ended the widespread prescriptive use of HT for nearly 20 years. The WHI findings have been broadly and unfairly applied to all hormone formulations, including modern treatments using human-identical hormones. Although CV health is indisputably linked to oestrogen status, HT involving any combination of hormones currently is not recommended for primary or secondary prevention of CVD. In the wake of more positive results from recent studies and re-evaluation of the WHI, HT has re-emerged as an issue for specialists in CVD to discuss with their patients. Rigorous scientific analysis is needed to explain the paradox of cardioprotection conferred by endogenous ovarian hormones with apparent cardiotoxicity inflicted by HT. This review will cover the origins of HT, hormone terminology and function, and key studies that contribute to our current understanding. Based on evolving evidence, if HT is to be used, we propose it be initiated immediately after cessation of ovarian hormone production and dosed as transdermal oestradiol combined with cyclic dosing of human-identical progesterone (P4).

Microglia in neurodegenerative diseases

A major feature of neurodegeneration is disruption of central nervous system homeostasis, during which microglia play diverse roles. In the central nervous system, microglia serve as the first line of immune defense and function in synapse pruning, injury repair, homeostasis maintenance, and regulation of brain development through scavenging and phagocytosis. Under pathological conditions or various stimulations, microglia proliferate, aggregate, and undergo a variety of changes in cell morphology, immunophenotype, and function. This review presents the features of microglia, especially their diversity and ability to change dynamically, and reinterprets their role as sensors for multiple stimulations and as effectors for brain aging and neurodegeneration. This review also summarizes some therapeutic approaches for neurodegenerative diseases that target microglia.

The Role of Estradiol in Traumatic Brain Injury: Mechanism and Treatment Potential

Patients surviving traumatic brain injury (TBI) face numerous neurological and neuropsychological problems significantly affecting their quality of life. Extensive studies over the past decades have investigated pharmacological treatment options in different animal models, targeting various pathological consequences of TBI. Sex and gender are known to influence the outcome of TBI in animal models and in patients, respectively. Apart from its well-known effects on reproduction, 17β-estradiol (E2) has a neuroprotective role in brain injury. Hence, in this review, we focus on the effect of E2 in TBI in humans and animals. First, we discuss the clinical classification and pathomechanism of TBI, the research in animal models, and the neuroprotective role of E2. Based on the results of animal studies and clinical trials, we discuss possible E2 targets from early to late events in the pathomechanism of TBI, including neuroinflammation and possible disturbances of the endocrine system. Finally, the potential relevance of selective estrogenic compounds in the treatment of TBI will be discussed.

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

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

Single intranasal administration of 17β-estradiol loaded gelatin nanoparticles confers neuroprotection in the post-ischemic brain

Globally, ischemic stroke is a leading cause of death and adult disability. Previous efforts to repair damaged brain tissue following ischemic events have been hindered by the relative isolation of the central nervous system. We have developed a gelatin nanoparticle-mediated intranasal drug delivery system as an efficient, non-invasive method for delivering 17β-estradiol (E2) specifically to the brain, enhancing neuroprotection, and limiting systemic side effects. Young adult male C57BL/6 J mice subjected to 30 min of middle cerebral artery occlusion (MCAO) were administered intranasal preparations of E2-GNPs, water soluble E2, or saline as control 1 h after reperfusion. Following intranasal administration of 500 ng E2-GNPs, brain E2 content rose by 5.24 fold (P<0.0001) after 30 min and remained elevated by 2.5 fold at 2 h (P<0.05). The 100 ng dose of E2-GNPs reduced mean infarct volume by 54.3% (P<0.05, n=4) in comparison to saline treated controls, demonstrating our intranasal delivery system's efficacy.

Loss of Estrogen Efficacy Against Hippocampus Damage in Long-Term OVX Mice Is Related to the Reduction of Hippocampus Local Estrogen Production and Estrogen Receptor Degradation

Postmenopausal women experience a higher risk for neurodegenerative diseases, including cognitive impairment and ischemic stroke. Many preclinical studies have indicated that estrogen replacement therapy (ERT) may provide protective effects against these neurological diseases. However, the results of Women's Health Initiative (WHI) studies have led to the proposal of "critical period hypothesis," which states that there is a precise window of opportunity for administering beneficial hormone therapy following menopause. However, the underlying molecular mechanisms require further characterization. Here, we explored the effects of ERT on cognition decline and global cerebral ischemia (GCI)-induced hippocampal neuronal damage in mice that had experienced both short-term (ovariectomized (OVX) 1 week) and long-term (OVX 10 weeks) estrogen deprivation. We also further explored the concentration of 17β-estradiol (E2) in the circulation and hippocampus and the expression of aromatase and estrogen receptors (ERα, ERα-Ser118, and ERβ). We found that the neuroprotective effectiveness of ERT against hippocampus damage exhibited in OVX1w mice was totally absent in OVX10w mice. Interestingly, the concentration of hippocampal E2 was irreversibly reduced in OVX10w mice, which was related to the decrease of aromatase expression in the hippocampus. In addition, long-term estrogen deprivation (LTED) led to a decrease in estrogen receptor proteins in the hippocampus. Thus, we concluded that the loss of ERT neuroprotection against hippocampus injury in LTED mice was related to the reduction in hippocampus E2 production and estrogen receptor degradation. These results provide several intervention targets to restore the effectiveness of ERT neuroprotection in elderly post-menopausal women.

Improving translational research in sex-specific effects of comorbidities and risk factors in ischaemic heart disease and cardioprotection: position paper and recommendations of the ESC Working Group on Cellular Biology of the Heart

Ischaemic heart disease (IHD) is a complex disorder and a leading cause of death and morbidity in both men and women. Sex, however, affects several aspects of IHD, including pathophysiology, incidence, clinical presentation, diagnosis as well as treatment and outcome. Several diseases or risk factors frequently associated with IHD can modify cellular signalling cascades, thus affecting ischaemia/reperfusion injury as well as responses to cardioprotective interventions. Importantly, the prevalence and impact of risk factors and several comorbidities differ between males and females, and their effects on IHD development and prognosis might differ according to sex. The cellular and molecular mechanisms underlying these differences are still poorly understood, and their identification might have important translational implications in the prediction or prevention of risk of IHD in men and women. Despite this, most experimental studies on IHD are still undertaken in animal models in the absence of risk factors and comorbidities, and assessment of potential sex-specific differences are largely missing. This ESC WG Position Paper will discuss: (i) the importance of sex as a biological variable in cardiovascular research, (ii) major biological mechanisms underlying sex-related differences relevant to IHD risk factors and comorbidities, (iii) prospects and pitfalls of preclinical models to investigate these associations, and finally (iv) will provide recommendations to guide future research. Although gender differences also affect IHD risk in the clinical setting, they will not be discussed in detail here.

Neuroinflammation

Neuroinflammation is implicated in contributing to a variety of neurologic and somatic illnesses including Alzheimer's disease (AD), Parkinson's disease (PD), and depression. In this chapter, we focus on the role of neuroinflammation in mediating these three illnesses and portray interactions between the immune response and the central nervous system in the context of sex differences in disease progression. The majority of this chapter is supported by clinical findings; however, we occasionally utilize preclinical models where human studies are currently lacking. We begin by detailing the pathology of neuroinflammation, distinguishing between acute and chronic inflammation, and examining contributions from the innate and adaptive immune systems. Next, we summarize potential mechanisms of immune cell mediators including interleukin-1 beta (IL-1β), tumor necrosis factor α, and IL-6 in AD, PD, and depression development. Given the strong sex bias seen in these illnesses, we additionally examine the role of sex hormones, e.g., estrogen and testosterone in mediating neuroinflammation at the cellular level. Systematically, we detail how sex hormones may contribute to distinct behavioral and clinical symptoms and prognosis between males and females with AD, PD, or depression. Finally, we highlight the possible role of exercise in alleviating neuroinflammation, as well as evidence that antiinflammatory drug therapies improve cognitive symptoms observed in brain-related diseases.

Chronic Testosterone Deprivation Sensitizes the Middle-Aged Rat Brain to Damaging Effects of Testosterone Replacement

INTRODUCTION

An increasing number of middle-aged men are being screened for low testosterone levels and the number of prescriptions for various forms of testosterone replacement therapy (TRT) has increased dramatically over the last 10 years. However, the safety of TRT has come into question with some studies suggesting increased morbidity and mortality.

OBJECTIVE

Because the benefits of estrogen replacement in postmenopausal women and ovariectomized rodents are lost if there is an extended delay between estrogen loss and replacement, we hypothesized that TRT may also be sensitive to delayed replacement.

METHODS

We compared the effects of testosterone replacement after short-term (2 weeks) and long-term testosterone deprivation (LTTD; 10 weeks) in middle-aged male rats on cerebral ischemia, oxidative stress, and cognitive function. We hypothesized that LTTD would increase oxidative stress levels and abrogate the beneficial effects of TRT.

RESULTS

Hypogonadism itself and TRT after short-term castration did not affect stroke outcome compared to intact rats. However, after long-term hypogonadism in middle-aged male Fischer 344 rats, TRT exacerbated the detrimental behavioral effects of experimental focal cerebral ischemia, whereas this detrimental effect was prevented by administration of the free-radical scavenger tempol, suggesting that TRT exacerbates oxidative stress. In contrast, TRT improved cognitive performance in non-stroked rats regardless of the length of hypogonadism. In the Morris water maze, peripheral oxidative stress was highly associated with decreased cognitive ability.

CONCLUSIONS

Taken together, these data suggest that TRT after long-term hypogonadism can exacerbate functional recovery after focal cerebral ischemia, but in the absence of injury can enhance cognition. Both of these effects are modulated by oxidative stress levels.

The Critical Period for Neuroprotection by Estrogen Replacement Therapy and the Potential Underlying Mechanisms

17β-Estradiol (estradiol or E2) is a steroid hormone that has been broadly applied as a neuroprotective therapy for a variety of neurodegenerative and cerebrovascular disorders such as ischemic stroke, Alzheimer's disease, and Parkinson's disease. Several laboratory and clinical studies have reported that Estrogen Replacement Therapy (ERT) had no effect against these diseases in elderly postmenopausal women, and at worst, increased their risk of onset and mortality. This review focuses on the growing body of data from in vitro and animal models characterizing the potential underlying mechanisms and signaling pathways that govern successful neuroprotection by ERT, including the roles of E2 receptors in mediating neuroprotection, E2 genomic regulation of apoptosis- related pathways, membrane-bound receptor-mediated non-genomic signaling pathways, and the antioxidant mechanisms of E2. Also discussed is the current evidence for a critical period of effective treatment with estrogen following natural or surgical menopause and the outcomes of E2 administration within an advantageous time period. The known mechanisms governing the duration of the critical period include depletion of E2 receptors, the switch to a ketogenic metabolic profile by neuronal mitochondria, and a decrease in acetylcholine that accompanies E2 deficiency. Also the major clinical trials and observational studies concerning postmenopausal Hormone Therapy (HT) are summarized to compare their outcomes with respect to neurological disease and discuss their relevance to the critical period hypothesis. Finally, potential controversies and future directions for this field are discussed throughout the review.

G protein-coupled estrogen receptor activates cell type-specific signaling pathways in cortical cultures: relevance to the selective loss of astrocytes

Selective activation of the G protein-coupled estrogen receptor has been proposed to avoid some of the side effects elicited by the activation of classical estrogen receptors α and β. Although its contribution to neuroprotection triggered by estradiol in brain disorders has been explored, the results regarding ischemic stroke are contradictory, and currently, there is no consensus on the role that this receptor may play. The present study aimed to investigate the role of GPER in the ischemic insult. For that, primary cortical cultures exposed to oxygen and glucose deprivation (OGD) were used as a model. Our results demonstrate that neuronal survival was strongly affected by the ischemic insult and concurrent GPER activation with G1 had no further impact. In contrast, OGD had a smaller impact on astrocytes survival but G1, alone or combined with OGD, promoted their apoptosis. This effect was prevented by the GPER antagonist G15. The results also show that ischemia did not change the expression levels of GPER in neurons and astrocytes. In this study, we also demonstrate that selective activation of GPER induced astrocyte apoptosis via the phospholipase C pathway and subsequent intracellular calcium rise, whereas in neurons, this effect was not observed. Taken together, this evidence supports a direct impact of GPER activity on the viability of astrocytes, which seems to be associated with the regulation of different signaling pathways in astrocytes and neurons.

Stroke and the neurovascular unit: glial cells, sex differences, and hypertension

A functional neurovascular unit (NVU) is central to meeting the brain's dynamic metabolic needs. Poststroke damage to the NVU within the ipsilateral hemisphere ranges from cell dysfunction to complete cell loss. Thus, understanding poststroke cell-cell communication within the NVU is of critical importance. Loss of coordinated NVU function exacerbates ischemic injury. However, particular cells of the NVU (e.g., astrocytes) and those with ancillary roles (e.g., microglia) also contribute to repair mechanisms. Epidemiological studies support the notion that infarct size and recovery outcomes are heterogeneous and greatly influenced by modifiable and nonmodifiable factors such as sex and the co-morbid condition common to stroke: hypertension. The mechanisms whereby sex and hypertension modulate NVU function are explored, to some extent, in preclinical laboratory studies. We present a review of the NVU in the context of ischemic stroke with a focus on glial contributions to NVU function and dysfunction. We explore the impact of sex and hypertension as modifiable and nonmodifiable risk factors and the underlying cellular mechanisms that may underlie heterogeneous stroke outcomes. Most of the preclinical investigative studies of poststroke NVU dysfunction are carried out primarily in male stroke models lacking underlying co-morbid conditions, which is very different from the human condition. As such, the evolution of translational medicine to target the NVU for improved stroke outcomes remains elusive; however, it is attainable with further research.

Is there a role for reproductive steroids in the etiology and treatment of affective disorders?

A variety of hormones have been shown to play a role in affective disorders. Reproductive steroids are particularly informative in our efforts to understand the pathophysiology of affective dysregulation for several reasons: i) Reproductive endocrine-related mood disorders (premenstrual dysphoric disorder, perinatal depression, perimenopausal depression) are wonderful clinical models for investigating the mechanisms by which affective state changes occur; ii) Reproductive steroids regulate virtually every system that has been implicated as disturbed in the ontogeny of affective disorders; iii) Despite the absence of a reproductive endocrinopathy a triggering role in the affective disturbance of reproductive mood disorders has been shown clearly for changes in reproductive steroids. The existing data, therefore, support a differential sensitivity to reproductive steroids in reproductive mood disorders such that an abnormal affective state is precipitated by normal changes in reproductive steroids. The therapeutic implications of these findings for affective illness are discussed.

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.

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.

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.

Is there a role for reproductive steroids in the etiology and treatment of affective disorders?

A variety of hormones have been shown to play a role in affective disorders. Reproductive steroids are particularly informative in our efforts to understand the pathophysiology of affective dysregulation for several reasons: i) Reproductive endocrine-related mood disorders (premenstrual dysphoric disorder, perinatal depression, perimenopausal depression) are wonderful clinical models for investigating the mechanisms by which affective state changes occur; ii) Reproductive steroids regulate virtually every system that has been implicated as disturbed in the ontogeny of affective disorders; iii) Despite the absence of a reproductive endocrinopathy a triggering role in the affective disturbance of reproductive mood disorders has been shown clearly for changes in reproductive steroids. The existing data, therefore, support a differential sensitivity to reproductive steroids in reproductive mood disorders such that an abnormal affective state is precipitated by normal changes in reproductive steroids. The therapeutic implications of these findings for affective illness are discussed.

Elucidating sex differences in response to cerebral ischemia: immunoregulatory mechanisms and the role of microRNAs

Cerebral ischemia remains a major cause of death and disability worldwide, yet therapeutic options remain limited. Differences in sex and age play an important role in the final outcome in response to cerebral ischemia in both experimental and clinical studies: males have a higher risk and worse outcome than females at younger ages and this trend reverses in older ages. Although the molecular mechanisms underlying sex dimorphism are complex and are still not well understood, studies suggest steroid hormones, sex chromosomes, differential cell death and immune pathways, and sex-specific microRNAs may contribute to the outcome following cerebral ischemia. This review focuses on differential effects between males and females on cell death and immunological pathways in response to cerebral ischemia, the central role of innate sex differences in steroid hormone signaling, and upstreamregulation of sexually dimorphic gene expression by microRNAs.

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.

Sex differences in Parkinson's disease: Features on clinical symptoms, treatment outcome, sexual hormones and genetics

Parkinson's disease (PD) is the second most frequent age-related neurodegenerative disorder. Sex is an important factor in the development of PD, as reflected by the fact that it is more common in men than in women by an approximate ratio of 2:1. Our hypothesis is that differences in PD among men and women are highly determined by sex-dependent differences in the nigrostriatal dopaminergic system, which arise from environmental, hormonal and genetic influences. Sex hormones, specifically estrogens, influence PD pathogenesis and might play an important role in PD differences between men and women. The objective of this review was to discuss the PD physiopathology and point out sex differences in nigrostriatal degeneration, symptoms, genetics, responsiveness to treatments and biochemical and molecular mechanisms among patients suffering from this disease. Finally, we discuss the role estrogens may have on PD sex differences.

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.

Sex steroid hormones as neuroprotective elements in ischemia models

Among sex steroid hormones, progesterone and estradiol have a wide diversity of physiological activities that target the nervous system. Not only are they carried by the blood stream, but also they are locally synthesized in the brain and for this reason, estradiol and progesterone are considered 'neurosteroids'. The physiological actions of both hormones range from brain development and neurotransmission to aging, illustrating the importance of a deep understanding of their mechanisms of action. In this review, we summarize key roles that estradiol and progesterone play in the brain. As numerous reports have confirmed a substantial neuroprotective role for estradiol in models of neurodegenerative disease, we focus this review on traumatic brain injury and stroke models. We describe updated data from receptor and signaling events triggered by both hormones, with an emphasis on the mechanisms that have been reported as 'rapid' or 'cytoplasmic actions'. Data showing the therapeutic effects of the hormones, used alone or in combination, are also summarized, with a focus on rodent models of middle cerebral artery occlusion (MCAO). Finally, we draw attention to evidence that neuroprotection by both hormones might be due to a combination of 'cytoplasmic' and 'nuclear' signaling.

Reciprocal interactions between prostaglandin E2- and estradiol-dependent signaling pathways in the injured zebra finch brain

Background

Astrocytic aromatization and consequent increases in estradiol are neuroprotective in the injured brain. In zebra finches, cyclooxygenase-activity is necessary for injury-induced aromatase expression, and increased central estradiol lowers neuroinflammation. The mechanisms underlying these influences are unknown. Here, we document injury-induced, cyclooxygenase-dependent increases in glial aromatase expression and replicate previous work in our lab showing increases in central prostaglandin E2 and estradiol following brain damage. Further, we describe injury-dependent changes in E-prostanoid and estrogen receptor expression and reveal the necessity of E-prostanoid and estrogen receptors in the injury-dependent, reciprocal interactions of neuroinflammatory and neurosteroidogenic pathways.

Methods

Adult male and female birds were shams or received bilateral injections of the appropriate drug or vehicle into contralateral telencephalic lobes.

Results

Injuries sustained in the presence of indomethacin (a cyclooxygenase inhibitor) had fewer aromatase-expressing reactive astrocytes relative to injuries injected with vehicle suggesting that cyclooxygenase activity is necessary for the induction of glial aromatase around the site of damage. Injured hemispheres had higher prostaglandin E2 and estradiol content relative to shams. Importantly, injured hemispheres injected with E-prostanoid- or estrogen receptor-antagonists showed elevated prostaglandin E2 and estradiol, respectively, but lower prostaglandin E2 or estradiol-dependent downstream activity (protein kinase A or phosphoinositide-3-kinase mRNA) suggesting that receptor antagonism did not affect injury-induced prostaglandin E2 or estradiol, but inhibited the effects of these ligands. Antagonism of E-prostanoid receptors 3 or 4 prevented injury-induced increases in neural estradiol in males and females, respectively, albeit this apparent sex-difference needs to be tested more stringently. Further, estrogen receptor-α, but not estrogen receptor-β antagonism, exaggerated neural prostaglandin E2 levels relative to the contralateral lobe in both sexes.

Conclusion

These data suggest injury-induced, sex-specific prostaglandin E2-dependent estradiol synthesis, and estrogen receptor-α dependent decreases in neuroinflammation in the vertebrate brain.

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

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

A theory of eu-estrogenemia: a unifying concept

OBJECTIVE

The aim of the study was to propose a unifying theory for the role of estrogen in postmenopausal women through examples in basic science, randomized controlled trials, observational studies, and clinical practice.

METHODS

Review and evaluation of the literature relating to estrogen.

DISCUSSION

The role of hormone therapy and ubiquitous estrogen receptors after reproductive senescence gains insight from basic science models. Observational studies and individualized patient care in clinical practice may show outcomes that are not reproduced in randomized clinical trials. The understanding gained from the timing hypothesis for atherosclerosis, the critical window theory in neurosciences, randomized controlled trials, and numerous genomic and nongenomic actions of estrogen discovered in basic science provides new explanations to clinical challenges that practitioners face. Consequences of a hypo-estrogenemic duration in women's lives are poorly understood. The Study of Women Across the Nation suggests its magnitude is greater than was previously acknowledged. We propose that the healthy user bias was the result of surgical treatment (hysterectomy with oophorectomy) for many gynecological maladies followed by pharmacological and physiological doses of estrogen to optimize patient quality of life. The past decade of research has begun to demonstrate the role of estrogen in homeostasis.

CONCLUSIONS

The theory of eu-estrogenemia provides a robust framework to unify the timing hypothesis, critical window theory, randomized controlled trials, the basic science of estrogen receptors, and clinical observations of patients over the past five decades.

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.

Brain Renin-Angiotensin System and Microglial Polarization: Implications for Aging and Neurodegeneration

Microglia can transform into proinflammatory/classically activated (M1) or anti-inflammatory/alternatively activated (M2) phenotypes following environmental signals related to physiological conditions or brain lesions. An adequate transition from the M1 (proinflammatory) to M2 (immunoregulatory) phenotype is necessary to counteract brain damage. Several factors involved in microglial polarization have already been identified. However, the effects of the brain renin-angiotensin system (RAS) on microglial polarization are less known. It is well known that there is a “classical” circulating RAS; however, a second RAS (local or tissue RAS) has been observed in many tissues, including brain. The locally formed angiotensin is involved in local pathological changes of these tissues and modulates immune cells, which are equipped with all the components of the RAS. There are also recent data showing that brain RAS plays a major role in microglial polarization. Level of microglial NADPH-oxidase (Nox) activation is a major regulator of the shift between M1/proinflammatory and M2/immunoregulatory microglial phenotypes so that Nox activation promotes the proinflammatory and inhibits the immunoregulatory phenotype. Angiotensin II (Ang II), via its type 1 receptor (AT1), is a major activator of the NADPH-oxidase complex, leading to pro-oxidative and pro-inflammatory effects. However, these effects are counteracted by a RAS opposite arm constituted by Angiotensin II/AT2 receptor signaling and Angiotensin 1–7/Mas receptor (MasR) signaling. In addition, activation of prorenin-renin receptors may contribute to activation of the proinflammatory phenotype. Aged brains showed upregulation of AT1 and downregulation of AT2 receptor expression, which may contribute to a pro-oxidative pro-inflammatory state and the increase in neuron vulnerability. Several recent studies have shown interactions between the brain RAS and different factors involved in microglial polarization, such as estrogens, Rho kinase (ROCK), insulin-like growth factor-1 (IGF-1), tumor necrosis factor α (TNF)-α, iron, peroxisome proliferator-activated receptor gamma, and toll-like receptors (TLRs). Metabolic reprogramming has recently been involved in the regulation of the neuroinflammatory response. Interestingly, we have recently observed a mitochondrial RAS, which is altered in aged brains. In conclusion, dysregulation of brain RAS plays a major role in aging-related changes and neurodegeneration by exacerbation of oxidative stress (OS) and neuroinflammation, which may be attenuated by pharmacological manipulation of RAS components.

Menopause and Parkinson's disease. Interaction between estrogens and brain renin-angiotensin system in dopaminergic degeneration

The neuroprotective effects of menopausal hormonal therapy in Parkinson's disease (PD) have not yet been clarified, and it is controversial whether there is a critical period for neuroprotection. Studies in animal models and clinical and epidemiological studies indicate that estrogens induce dopaminergic neuroprotection. Recent studies suggest that inhibition of the brain renin-angiotensin system (RAS) mediates the effects of estrogens in PD models. In the substantia nigra, ovariectomy induces a decrease in levels of estrogen receptor-α (ER-α) and increases angiotensin activity, NADPH-oxidase activity and expression of neuroinflammatory markers, which are regulated by estrogen replacement therapy. There is a critical period for the neuroprotective effect of estrogen replacement therapy, and local ER-α and RAS play a major role. Astrocytes play a major role in ER-α-induced regulation of local RAS, but neurons and microglia are also involved. Interestingly, treatment with angiotensin receptor antagonists after the critical period induced neuroprotection.