Stroke neuroprotection: oestrogen and insulin-like growth factor-1 interactions and the role of microglia

Relationship between insulin-like growth factor-1 and cerebral small vessel disease and its mechanisms: advances in the field

Insulin-like growth factor-1 (IGF-1) is an active polypeptide protein that closely resembles the structural sequence of insulin and is involved in a variety of metabolic processes in the body. Decreased IGF-1 circulation levels are associated with an increased risk of stroke and a poorer prognosis, but the relationship with cerebral small vessel disease (cSVD) is unclear. Some studies found that the level of IGF-1 in patients with cSVD was significantly reduced, but the clinical significance and underlying mechanisms are unknown. This article reviews the correlation between IGF-1 and cerebrovascular disease and explores the potential relationship and mechanism between IGF-1 and cSVD.

Microglial IL-1RA ameliorates brain injury after ischemic stroke by inhibiting astrocytic CXCL1-mediated neutrophil recruitment and microvessel occlusion

Acute ischemic stroke (AIS), one of the leading causes of mortality worldwide, is characterized by a rapid inflammatory cascade resulting in exacerbation of ischemic brain injury. Microglia are the first immune responders. However, the role of postischemic microglial activity in ischemic brain injury remains far from being fully understood. Here, using the transgenic mouse line CX₃ CR1^creER :R26^iDTR to genetically ablate microglia, we showed that microglial deletion exaggerated ischemic brain injury. Associated with this worse outcome, there were increased neutrophil recruitment, microvessel blockade and blood flow stagnation in the acute phase, accompanied by transcriptional upregulation of chemokine (C-X-C motif) ligand 1 (CXCL1). Our study showed that microglial interleukin-1 receptor antagonist (IL-1RA) suppressed astrocytic CXCL1 expression induced by oxygen and glucose deprivation and inhibited neutrophil migration. Furthermore, neutralizing antibody therapy against CXCL1 or the administration of recombinant IL-1RA protein reduced brain infarct volume and improved motor coordination performance of mice after ischemic stroke. Our study suggests that microglia protect against acute ischemic brain injury by secreting IL-1RA to inhibit astrocytic CXCL1 expression, which reduces neutrophil recruitment and neutrophil-derived microvessel occlusion.

BDNF-overexpressing MSCs delivered by hydrogel in acute ischemic stroke treatment

Background

Ischemic stroke treatment is a challenge worldwide. The efficacy and safety of mesenchymal stem cells (MSCs) for stroke have been confirmed. However, poor survival of MSCs in the ischemic environment limits the therapy efficacy. Changes in MSC status in the ischemic environment after transplantation is difficult to monitor. This study aimed to deliver brain-derived neurotrophic factor (BDNF)-overexpressing MSCs by hydrogel (H-B-MSCs) to promote recovery after ischemic stroke.

Methods

MSCs were transfected with lentivirus carrying luc2 and BDNF cassette. The properties of hydrogel were tested after synthesis with thiolated gelatin (Gel-SH), thiolated hyaluronic acid (HA-SH), and polyethylene glycol diacrylate (PEGDA). Oxygen-glucose deprivation (OGD) test was carried out to confirm the protective effects of hydrogel in the ischemic environment. Three days after stroke induction, H-B-MSCs, hydrogel carrying MSCs (H-MSCs), or phosphate-buffered saline (PBS) was injected into the brains of mice, respectively. Bioluminescence imaging (BLI) was performed at 3, 7, 14, and 21 days post-cell-transplantation to monitor the dynamic status of MSCs. In the meantime, histology, quantitative polymerase chain reaction (qPCR), enzyme-linked immunosorbent assay (ELISA), western blot, and behavior tests were carried out at different time points.

Results

Hydrogel with good biocompatibility was synthesized. Lentivirus transfection significantly increased the expression of BDNF. BDNF-MSCs could be tracked by BLI in vitro. In vitro OGD/reperfusion (OGD/R) test results suggested that MSCs carried by hydrogel could survive longer in an environment with low oxygen and glucose. H-B-MSCs significantly improved functional recovery after ischemic stroke. Furthermore, H-B-MSCs treatment promoted neurogenesis, white matter recovery, and angiogenesis after ischemic stroke. MSC dynamics could be monitored in vivo with BLI.

Conclusions

We effectively established a robust MSC delivery system with hydrogel. Prolonged survival of transplanted BDNF-MSCs with a hydrogel delivery system could promote the recovery of ischemic stroke via the continuous release of BDNF.

Galectin-3 Involvement in Cognitive Processes for New Therapeutic Considerations

Cognitive impairment may be a consequence of the normal aging process, but it may also be the hallmark of various neurodegenerative and psychiatric diseases. Early identification of individuals at particular risk for cognitive decline is critical, as it is imperative to maintain a cognitive reserve in these neuropsychiatric entities. In recent years, galectin-3 (Gal-3), a member of the galectin family, has received considerable attention with respect to aspects of neuroinflammation and neurodegeneration. The mechanisms behind the putative relationship between Gal-3 and cognitive impairment are not yet clear. Intrigued by this versatile molecule and its unique modular architecture, the latest data on this relationship are presented here. This mini-review summarizes recent findings on the mechanisms by which Gal-3 affects cognitive functioning in both animal and human models. Particular emphasis is placed on the role of Gal-3 in modulating the inflammatory response as a fine-tuner of microglia morphology and phenotype. A review of recent literature on the utility of Gal-3 as a biomarker is provided, and approaches to strategically exploit Gal-3 activities with therapeutic intentions in neuropsychiatric diseases are outlined.

Glial estradiol synthesis after brain injury

Glial cells are important contributors to the hormonal milieu of the brain, particularly following damage. In birds and mammals, neural injury induces the expression of aromatase in astroglia at and around the site of damage. This review describes the progression of our understanding about the incidence, regulation, and function of estrogens synthesized in glia. Following a quick discussion of the landmark studies that first demonstrated steroidogenesis in glia, I go on to describe how the inflammatory response following perturbation of the brain results in the transcription of aromatase and the resultant rise in local estradiol. I end with several unanswered questions, the answers to which may reveal the precise manner in which neurosteroids protect the brain from injury, both prior to and immediately following injury.

Sex differences in recovery of motor function in a rhesus monkey model of cortical injury

BACKGROUND

Stroke disproportionately affects men and women, with women over 65 years experiencing increased severity of impairment and higher mortality rates than men. Human studies have explored risk factors that contribute to these differences, but additional research is needed to investigate how sex differences affect functional recovery and hence the severity of impairment. In the present study, we used our rhesus monkey model of cortical injury and fine motor impairment to compare sex differences in the rate and degree of motor recovery following this injury.

METHODS

Aged male and female rhesus monkeys were trained on a task of fine motor function of the hand before undergoing surgery to produce a cortical lesion limited to the hand area representation of the primary motor cortex. Post-operative testing began two weeks after the surgery and continued for 12 weeks. All trials were video recorded and latency to retrieve a reward was quantitatively measured to assess the trajectory of post-operative response latency and grasp pattern compared to pre-operative levels.

RESULTS

Postmortem analysis showed no differences in lesion volume between male and female monkeys. However, female monkeys returned to their pre-operative latency and grasp patterns significantly faster than males.

CONCLUSIONS

These findings demonstrate the need for additional studies to further investigate the role of estrogens and other sex hormones that may differentially affect recovery outcomes in the primate brain.

An evidence update on the protective mechanism of tangeretin against neuroinflammation based on network pharmacology prediction and transcriptomic analysis

Although the protective effects of tangeretin on neuroinflammation have been proven in cell and animal experiments, few studies explore its underlying molecular mechanism. In this study, we used the network pharmacology method combined with the transcriptome approach to investigate its underlying anti-inflammatory mechanism in human microglial cells. Based on network pharmacology analysis, four putative target proteins and ten potential pathways were identified. Among them, vascular endothelial growth factor A (VEGFA), epidermal growth factor receptor (EGFR) and the related phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT), the mitogen-activated protein kinase (MAPK), mechanistic target of rapamycin (mTOR) signaling pathway were well-supported by transcriptome data. Meanwhile, transcriptome analysis supplemented two crucial targets: the insulin receptor (InsR) and insulin-like growth factor-I (IGF-1) receptor. Subsequently, VEGFA, EGFR, IGF-1 receptor, and InsR were further verified on the protein level. Taken together, we assumed that tangeretin could exert protective effects on neuroinflammation by decreasing the expression of VEGFA, EGFR, InsR, and IGF-1 receptor in the PI3K-AKT, MAPK, mTOR signaling pathway. More importantly, it is for the first time to show that the anti-neuroinflammatory effects of tangeretin through VEGFA, EGFR, IGF-1 receptor, InsR, and mTOR signaling pathway. These works offer new insight into the anti-neuroinflammatory functions of tangeretin and propose novel information on further anti-inflammatory mechanism studies.

Impact of ovariectomy and CO2 inhalation on microglia morphology in select brainstem and hypothalamic areas regulating breathing in female rats

The neural network that regulates breathing shows a significant sexual dimorphism. Ovarian hormones contribute to this distinction as, in rats, ovariectomy reduces the ventilatory response to CO2. Microglia are neuroimmune cells that are sensitive to neuroendocrine changes in their environment. When reacting to challenging conditions, these cells show changes in their morphology that reflect an augmented capacity for producing pro- and anti-inflammatory cytokines. Based on evidence suggesting that microglia contribute to sex-based differences in reflexive responses to hypercapnia, we hypothesized that ovariectomy and hypercapnia promote microglial reactivity in selected brain areas that regulate breathing. We used ionized calcium-binding-adapter molecule-1 (Iba1) immunolabeling to compare the density and morphology of microglia in the locus coeruleus (LC), the caudal medullary raphe, the caudal part of the nucleus of the tractus solitarius (cNTS), and the paraventricular nucleus of the hypothalamus (PVN). Tissue was obtained from SHAM (metaestrus) female rats or following ovariectomy. Rats were exposed to normocapnia or hypercapnia (5% CO2, 20 min). Ovariectomy and hypercapnia did not affect microglial density in any of the structures studied. Ovariectomy promoted a reactive phenotype in the cNTS and LC, as indicated by a larger morphological index. In these structures, hypercapnia had a relatively modest opposing effect; the medullary raphe or the PVN were not affected. We conclude that ovarian hormones attenuate microglial reactivity in CO2/H+ sensing structures. These data suggest that microglia may contribute to neurological diseases in which anomalies of respiratory control are associated with cyclic fluctuations of ovarian hormones or menopause.

Role of glial cells in the generation of sex differences in neurodegenerative diseases and brain aging

Diseases and aging-associated alterations of the nervous system often show sex-specific characteristics. Glial cells play a major role in the endogenous homeostatic response of neural tissue, and sex differences in the glial transcriptome and function have been described. Therefore, the possible role of these cells in the generation of sex differences in pathological alterations of the nervous system is reviewed here. Studies have shown that glia react to pathological insults with sex-specific neuroprotective and regenerative effects. At least three factors determine this sex-specific response of glia: sex chromosome genes, gonadal hormones and neuroactive steroid hormone metabolites. The sex chromosome complement determines differences in the transcriptional responses in glia after brain injury, while gonadal hormones and their metabolites activate sex-specific neuroprotective mechanisms in these cells. Since the sex-specific neuroprotective and regenerative activity of glial cells causes sex differences in the pathological alterations of the nervous system, glia may represent a relevant target for sex-specific therapeutic interventions.

Crosstalk between Inflammation and the BBB in Stroke

The blood-brain barrier (BBB), which is located at the interface between the central nervous system (CNS) and the circulatory system, is instrumental in establishing and maintaining the microenvironmental homeostasis of the CNS. BBB disruption following stroke promotes inflammation by enabling leukocytes, T cells and other immune cells to migrate via both the paracellular and transcellular routes across the BBB and to infiltrate the CNS parenchyma. Leukocytes promote the removal of necrotic tissues and neuronal recovery, but they also aggravate BBB injury and exacerbate stroke outcomes, especially after late reperfusion. Moreover, the swelling of astrocyte endfeet is thought to contribute to the ‘no-reflow’ phenomenon observed after cerebral ischemia, that is, blood flow cannot return to capillaries after recanalization of large blood vessels. Pericyte recruitment and subsequent coverage of endothelial cells (ECs) alleviate BBB disruption, which causes the transmigration of inflammatory cells across the BBB to be a dynamic process. Furthermore, interneurons and perivascular microglia also make contacts with ECs, astrocytes and pericytes to establish the neurovascular unit. BBB-derived factors after cerebral ischemia triggered microglial activation. During the later stage of injury, microglia remain associated with brain ECs and contribute to repair mechanisms, including postinjury angiogenesis, by acquiring a protective phenotype, which possibly occurs through the release of microglia-derived soluble factors. Taken together, we reviewed dynamic and bidirectional crosstalk between inflammation and the BBB during stroke and revealed targeted interventions based on the crosstalk between inflammation and the BBB, which will provide novel insights for developing new therapeutic strategies.

Estrogen as a Neuroprotectant in Both Sexes: Stories From the Bird Brain

Estrogens such as estradiol (E2) are potent effectors of neural structure and function via peripheral and central synthesis. In the zebra finch (Taeniopygia guttata), neural E2 synthesis is among the highest reported in homeotherms due to the abundant constitutive expression of aromatase (E-synthase) in discrete neuronal pools across the forebrain. Following penetrating or concussive trauma, E2 synthesis increases even further via the induced expression of aromatase in reactive astrocytes around the site of damage. Injury-associated astrocytic aromatization occurs in the brains of both sexes regardless of the site of injury and can remain elevated for weeks following trauma. Interestingly, penetrating injury induces astrocytic aromatase more rapidly in females compared to males, but this sex difference is not detectable 24 h posttrauma. Indeed, unilateral penetrating injury can increase E2 content 4-fold relative to the contralateral uninjured hemisphere, suggesting that glial aromatization may be a powerful source of neural E2 available to circuits. Glial aromatization is neuroprotective as inhibition of injury-induced aromatase increases neuroinflammation, gliosis, necrosis, apoptosis, and infarct size. These effects are ameliorated upon replacement with E2, suggesting that the songbird may have evolved a rapidly responsive neurosteroidogenic system to protect vulnerable brain circuits. The precise signals that induce aromatase expression in astrocytes include elements of the inflammatory cascade and underscore the sentinel role of the innate immune system as a crucial effector of trauma-associated E2 provision in the vertebrate brain. This review will describe the inductive signals of astroglial aromatase and the neuroprotective role for glial E2 synthesis in the adult songbird brains of both sexes.

The G protein-coupled oestrogen receptor, GPER1, mediates direct anti-inflammatory effects of oestrogens in human cholinergic neurones from the nucleus basalis of Meynert

It has been well established, particularly in animal models, that oestrogens exert neuroprotective effects in brain areas linked to cognitive processes. A key protective role could reside in the capacity of oestrogen to modulate the inflammatory response. However, the direct neuroprotective actions of oestrogens on neurones are complex and remain to be fully clarified. In the present study, we took advantage of a previously characterised primary culture of human cholinergic neurones (hfNBM) from the foetal nucleus basalis of Meynert, which is known to regulate hippocampal and neocortical learning and memory circuits, aiming to investigate the direct effects of oestrogens under inflammatory conditions. Exposure of cells to tumour necrosis factor (TNF)α (10 ng mL^-1 ) determined the activation of an inflammatory response, as demonstrated by nuclear factor-kappa B p65 nuclear translocation and cyclooxygenase-2 mRNA expression. These effects were inhibited by treatment with either 17β-oestradiol (E₂ ) (10 nmol L^-1 ) or G1 (100 nmol L^-1 ), the selective agonist of the G protein-coupled oestrogen receptor (GPER1). Interestingly, the GPER1 antagonist G15 abolished the effects of E₂ in TNFα-treated cells, whereas the ERα/ERβ inhibitor tamoxifen did not. Electrophysiological measurements in hfNBMs revealed a depolarising effect caused by E₂ that was specifically blocked by tamoxifen and not by G15. Conversely, G1 specifically hyperpolarised the cell membrane and also increased both inward and outward currents elicited by a depolarising stimulus, suggesting a modulatory action on hfNBM excitability by GPER1 activation. Interestingly, pretreating cells with TNFα completely blocked the effects of G1 on membrane properties and also significantly reduced GPER1 mRNA expression. In addition, we found a peculiar subcellular localisation of GPER1 to focal adhesion sites that implicates new possible mechanisms of action of GPER1 in the neuronal perception of mechanical stimuli. The results obtained in the present study indicate a modulatory functional role of GPER1 with respect to mediating the oestrogen neuroprotective effect against inflammation in brain cholinergic neurones and, accordingly, may help to identify protective strategies for preventing cognitive impairments.

Sexually dimorphic microglia and ischemic stroke

Ischemic stroke kills more women compared with men thus emphasizing a significant sexual dimorphism in ischemic pathophysiological outcomes. However, the mechanisms behind this sexual dimorphism are yet to be fully understood. It is well established that cerebral ischemia activates a variety of inflammatory cascades and that microglia are the primary immune cells of the brain. After ischemic injury, microglia are activated and play a crucial role in progression and resolution of the neuroinflammatory response. In recent years, research has focused on the role that microglia play in this sexual dimorphism that exists in the response to central nervous system (CNS) injury. Evidence suggests that the molecular mechanisms leading to microglial activation and polarization of phenotypes may be influenced by sex, therefore causing a difference in the pro/anti‐inflammatory responses after CNS injury. Here, we review advances highlighting that sex differences in microglia are an important factor in the inflammatory responses that are seen after ischemic injury. We discuss the main differences between microglia in the healthy and diseased developing, adult, and aging brain. We also focus on the dimorphism that exists between males and females in microglial‐induced inflammation and energy metabolism after CNS injury. Finally, we describe how all of the current research and literature regarding sex differences in microglia contribute to the differences in poststroke responses between males and females.

Mycoplasma contamination affects cell characteristics and decreases the sensitivity of BV2 microglia to LPS stimulation

Mycoplasma is the most common contaminant and greatly affects host cells. The influence of mycoplasma on microglia cells remains unknown. Here, we investigated the influence of mycoplasma contamination on BV2 cells (a microglia cell line). We found that mycoplasma contamination increased the phosphorylation of NF-kB and MAPK signal pathway and induced the activation of BV2 cells. These mycoplasma-contaminated BV2 cells exhibited a transition of cell morphology and slower proliferation, as well as increased gene expression and protein secretion of inflammatory factors. Furthermore, mycoplasma-contaminated BV2 cells had decreased sensitivity to lipopolysaccharide stimulation. These findings suggested that mycoplasma contamination greatly influenced the characteristics and function of microglia cells. It is important to prevent and exclude mycoplasma contamination in our research.

Ojayeonjonghwan, an oriental medicine composed of five seeds, protects against vasomotor and neurological disorders in estrogen-deficient rats

IMPACT STATEMENT

Menopausal symptoms impair the quality of life of many women, and although conventional treatments are often effective, their use is limited by adverse effects. Ojayeonjonghwan, OJa, is a traditional Oriental medicine that is used for both male and female reproductive health and has a long history of safe use. We evaluated the effectiveness of two variations of OJa (OJa1 and OJa2) for treating menopausal symptoms in ovariectomized (OVX) rats. Both OJa preparations were effective for relieving indicators of hot flashes and depression, and for preventing loss of bone mineral density and lean body mass. Only OJa 2 prevented memory dysfunction. These results show that the traditional Oriental medicine, Ojayeonjonghwan, has the potential to relieve menopausal symptoms in women and should be further evaluated in human clinical trials as an alternative to convention therapies in women for whom conventional therapies are not indicated or found to be ineffective.

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.

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.

Altered levels of circulating insulin-like growth factor I (IGF-I) following ischemic stroke are associated with outcome - a prospective observational study

Background

Insulin-like growth factor I (IGF-I) has neuroprotective effects in experimental ischemic stroke (IS). However, in patients who have suffered IS, various associations between the levels of serum IGF-I (s-IGF-I) and clinical outcome have been reported, probably reflecting differences in sampling time-points and follow-up periods. Since changes in the levels of post-stroke s-IGF-I have not been extensively explored, we investigated whether decreases in the levels of s-IGF-I between the acute time-point (median, 4 days) and 3 months (ΔIGF-I, further transformed into ΔIGF-I-quintiles, ΔIGF-I-q) are associated with IS severity and outcome.

Methods

In the Sahlgrenska Academy Study on Ischemic Stroke (SAHLSIS) conducted in Gothenburg, Sweden, patients with IS who had s-IGF-I measurements available were included (N = 354; 65% males; mean age, 55 years). Baseline stroke severity was evaluated using the National Institutes of Health Stroke Scale (NIHSS) and converted into NIHSS-quintiles (NIHSS-q). Outcomes were assessed using the modified Rankin Scale (mRS) at 3 months and 2 years.

Results

In general, the levels of s-IGF-I decreased (positive ΔIGF-I), except for those patients with the most severe NIHSS-q. After correction for sex and age, the 3rd ΔIGF-I-q showed the strongest association to mRS 0–2 [Odds Ratio (OR) 5.11, 95% confidence interval (CI) 2.18–11.9], and after 2 years, the 5th ΔIGF-I-q (OR 3.63, 95% CI 1.40–9.38) showed the strongest association to mRS 0–2. The associations remained significant after multivariate correction for diabetes, smoking, hypertension, and hyperlipidemia after 3 months, but were not significant (p = 0.057) after 2 years. The 3-month associations withstood additional correction for baseline stroke severity (p = 0.035), whereas the 2-year associations were further attenuated (p = 0.31).

Conclusions

Changes in the levels of s-IGF-I are associated primarily with temporally near 3-month outcomes, while associations with long-term 2-year outcomes are weakened and attenuated by other factors. The significance of the change in post-stroke s-IGF-I is compatible with a positive role for IGF-I in IS recovery. However, the exact mechanisms are unknown and probably reflects combinations of multiple peripheral and central actions.

Electronic supplementary material

The online version of this article (10.1186/s12883-018-1107-3) contains supplementary material, which is available to authorized users.

Estrogenic regulation of memory consolidation: A look beyond the hippocampus, ovaries, and females

The potent estrogen 17β-estradiol (E2) has long been known to regulate the hippocampus and hippocampal-dependent memories in females, and research from the past decade has begun to shed light on the molecular mechanisms through which E2 mediates memory formation in females. Although E2 can also regulate hippocampal function in males, relatively little is known about how E2 influences memory formation in males, or whether sex differences in underlying mechanisms exist. This review, based on a talk given in April 2017 at the American University symposium entitled, "Sex Differences: From Neuroscience to the Clinic and Beyond", first provides an overview of the molecular mechanisms in the dorsal hippocampus through which E2 enhances memory consolidation in ovariectomized female mice. Next, newer research is described demonstrating key roles for the prefrontal cortex and de novo hippocampal E2 synthesis to the memory-enhancing effects of E2 in females. The review then discusses the effects of de novo and exogenous E2 on hippocampal memory consolidation in both sexes, and putative sex differences in the underlying molecular mechanisms through which E2 enhances memory formation. The review concludes by discussing the importance and implications of sex differences in the molecular mechanisms underlying E2-induced memory consolidation for human health.

Brain Response to Injuries: When Microglia Go Sexist

Microglia are the principle immune cells of the brain. Once activated, microglial cells may exhibit a wide repertoire of the context-dependent profiles ranging from highly neurotoxic to more protective and pro-regenerative cellular phenotypes. While to date the mechanisms involved in the molecular regulation of the microglia polarization phenotypes remain elusive, growing evidence suggests that gender may markedly affect the inflammatory and/or glial responses following brain injuries. In the recent years, special attention has been given to the role of microglia in sexual dimorphism, both in healthy brain and diseased brain. Here, we review recent advances revealing microglia as an important determinant of gender differences under physiological conditions and in injured brain. We also discuss how microglia-driven innate immunity and signaling pathways might be involved in the sex-dependent responses following brain ischemic injury. Finally we describe how advanced methods such as live imaging techniques may help elucidate the role of microglia in the modulation of immune responses and gender difference after stroke.

Galectin-3: mediator of microglia responses in injured brain

Galectin-3 is a pleiotropic protein involved in cell activation, proliferation and migration and plays a pivotal part as an inflammatory mediator in neurodegeneration. Galectin-3 is associated with microglial activation and proliferation after ischemia. Given its putative role as a dynamic fine-tuner of microglia, activation of Galectin-3 provides molecular cues in design of new immunomodulatory strategies for stroke management. This review summarizes recent evidence on the role of Galectin-3 as a mediator of immune responses in damaged brain and mechanisms employed by Galectin-3 to affect microglial function.

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.

Rationale and design of combination of an immune modulator Fingolimod with Alteplase bridging with Mechanical Thrombectomy in Acute Ischemic Stroke (FAMTAIS) trial

Rationale In acute ischemic stroke patients with large vessel occlusion, although reperfusion within 6 h after stroke onset using combined intravenous alteplase and mechanical thrombectomy (bridging therapy) can improve functional outcome, still approximately 50% patients suffer disability which may result from reperfusion injury. Proof-of-concept clinical trials have indicated that the sphingosine-1-phosphate receptor modulator fingolimod may be efficacious in attenuating brain inflammation and improving clinical outcomes in acute ischemic stroke patients as a single therapy beyond 4.5 h of disease onset, or in combination with alteplase within 4.5 h of disease onset. Aim To assess whether the treatment of fingolimod combined with bridging therapy in large vessel occlusion acute ischemic stroke patients is effective and safe. Design and sample size estimates Fingolimod with Alteplase bridging with Mechanical Thrombectomy in Acute Ischemic Stroke (FAMTAIS) study is a randomized, open-label, multiple central trial. This study includes 98 patients with anterior circulation large vessel occlusion acute ischemic stroke who are eligible for bridging therapy, providing 80% power to reject the null hypothesis that, combined with fingolimod, the bridging therapy has an at least 15% higher penumbra tissue salvage index than receiving bridging therapy alone. Study outcomes The primary outcome is the penumbra tissue salvage index. Key secondary outcomes focus on: infarct growth and extent of clinical improvement from day 1 to day 7, frequency of parenchymal hemorrhage at day 1. Discussion If the hypothesis of FAMTAIS is confirmed, combination of fingolimod with bridging therapy is effective in attenuating reperfusion injury in patients with large vessel occlusion treated with 6 h of stroke onset.

The histone deacetylase inhibitor, sodium butyrate, exhibits neuroprotective effects for ischemic stroke in middle-aged female rats

Background

Sodium butyrate (NaB) is a histone deacetylase (HDAC) inhibitor exhibiting anti-inflammatory and neuroprotective effects in a rat ischemic model of stroke as well as a myocardial ischemia model. Although clinical evidence shows that older women are at higher risk for stroke occurrence and greater stroke severity, no studies have evaluated the effectiveness of NaB either in females or in older animals.

Methods

To determine the effects of NaB on stroke in older females, acyclic middle-aged Sprague-Dawley female rats (9–11 months old, constant diestrus) were subject to middle cerebral artery occlusion (MCAo) by intracerebral injection of recombinant endothelin-1. Rats were treated with NaB (300 mg/kg, i.p.) at 6 and 30 h following ET-1 injection. Animals were sacrificed at the early (2 days) or late (5 days) acute phase after MCAo. Serum and tissue lysates were collected for biochemical analyses.

Results

NaB treatment reduced infarct volume and ameliorated sensory motor impairment in middle-aged female rats, when measured at 2 and 5 days post MCAo. At the early acute phase (2 days post stroke), NaB treatment decreased brain lipid peroxides, and reduced serum levels of GFAP, a surrogate marker of blood-brain barrier (BBB) permeability. NaB also reduced expression of the inflammatory cytokine IL-1beta in circulation and IL-18 in the ischemic hemisphere. At the late acute phase (5 days post stroke), NaB treatment further suppressed MCAo-induced increase of IL-1beta, IL-17A, and IL-18 in brain lysates (cortex and striatum) from the ischemic hemisphere, and decreased ischemia-induced upregulation of IL-1beta and IL-18 in circulation, indicating a potent anti-inflammatory effect of the HDAC inhibitor. Moreover, NaB treatment also increased expression of IGF-1, a known neuroprotectant, in peripheral tissue including serum, liver, and spleen at the late acute phase.

Conclusions

These data provide the first evidence that delayed (>6 h) NaB treatment post-stroke is neuroprotective in older female rats. Additionally, these data also show that in addition to its well-known anti-inflammatory actions, NaB may exert a biphasic effect after stroke, operating initially to reduce BBB permeability and oxidative stress in the brain, and later, elevating IGF-1 expression in peripheral tissues.

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.

Estrogens, Neuroinflammation, and Neurodegeneration

Inflammatory activation of microglia is a hallmark of several disorders of the central nervous system. In addition to protecting the brain against inflammatory insults, microglia are neuroprotective and play a significant role in maintaining neuronal connectivity, but the prolongation of an inflammatory status may limit the beneficial functions of these immune cells. The finding that estrogen receptors are present in monocyte-derived cells and that estrogens prevent and control the inflammatory response raise the question of the role that this sex steroid plays in the manifestation and progression of pathologies that have a clear sex difference in prevalence, such as multiple sclerosis, Parkinson's disease, and Alzheimer's disease. The present review aims to provide a critical review of the current literature on the actions of estrogen in microglia and on the involvement of estrogen receptors in the manifestation of selected neurological disorders. This current understanding highlights a research area that should be expanded to identify appropriate replacement therapies to slow the progression of such diseases.

Poststroke Inflammasome Expression and Regulation in the Peri-Infarct Area by Gonadal Steroids after Transient Focal Ischemia in the Rat Brain

CNS ischemia results in locally confined and rapid tissue damage accompanied by a loss of neurons and their circuits. Early and time-delayed inflammatory responses are critical variables determining the extent of neural disintegration and regeneration. Inflammasomes are vital effectors in innate immunity. Their activation in brain-intrinsic immune cells contributes to ischemia-related brain damage. The steroids 17β-estradiol (E2) and progesterone (P) are neuroprotective and anti-inflammatory. Using a transient focal rat ischemic model, we evaluated the time response of different inflammasomes in the peri-infarct zone from the early to late phases after poststroke ischemia. We show that the different inflammasome complexes reveal a specific time-oriented sequential expression pattern with a maximum at approximately 24 h after the infarct. Within the limits of antibody availability, immunofluorescence labeling demonstrated that microglia and neurons are major sources of the locally activated inflammasomes NOD-like receptor protein-3 (NLRP3) and associated speck-like protein (ASC), respectively. E2 and P given for 24 h immediately after ischemia onset reduced hypoxia-induced mRNA expression of the inflammasomes NLRC4, AIM2 and ASC, and decreased the protein levels of ASC and NLRP3. In addition, mRNA protein levels of the cytokines interleukin-1β (IL1β), IL18 and TNFα were reduced by the steroids. The findings provide for the first time a detailed flow chart of hypoxia-driven inflammasome regulation in the peri-infarct cerebral cortex. Further, we demonstrate that E2 and P alleviate the expression of certain inflammasome components, sometimes in a hormone-specific way. Besides directly regulating other cellular neuroprotective pathways, the control of inflammasomes by these steroids might contribute to its neuroprotective potency.

Primary prevention of cardiovascular disease with hormone replacement therapy

Many peri- and postmenopausal women suffer from a reduced quality of life due to menopausal symptoms and preventable diseases. The importance of cardiovascular disease in women must be emphasized, as it is the leading cause of mortality and morbidity in women. It is well known that female hormones contribute to the later onset of cardiovascular disease in women. The effect of estrogens has for decades been understood from observational studies of postmenopausal women treated with hormone replacement therapy (HRT). Later, treatment with HRT was disregarded due to the fear of side-effects and an ambiguity of the cardiovascular advantages. Accumulating knowledge from the large number of trials and studies has elucidated the cause for the disparity in results. In this paper, the beneficial effects of HRT, with emphasis on cardiovascular disease are explained, and the relative and absolute risks of side-effects are discussed.

G protein-coupled estrogen receptor-mediated effects on cytosolic calcium and nanomechanics in brain microvascular endothelial cells

G protein-coupled estrogen receptor (GPER) is a relatively recently identified non-nuclear estrogen receptor, expressed in several tissues, including brain and blood vessels. The mechanisms elicited by GPER activation in brain microvascular endothelial cells are incompletely understood. The purpose of this work was to assess the effects of GPER activation on cytosolic Ca(2+) concentration, [Ca(2+)](i), nitric oxide production, membrane potential and cell nanomechanics in rat brain microvascular endothelial cells (RBMVEC). Extracellular but not intracellular administration of G-1, a selective GPER agonist, or extracellular administration of 17-β-estradiol and tamoxifen, increased [Ca(2+)](i) in RBMVEC. The effect of G-1 on [Ca(2+)](i) was abolished in Ca(2+) -free saline or in the presence of a L-type Ca(2+) channel blocker. G-1 increased nitric oxide production in RBMVEC; the effect was prevented by NG-nitro-l-arginine methyl ester. G-1 elicited membrane hyperpolarization that was abolished by the antagonists of small and intermediate-conductance Ca(2+) -activated K(+) channels, apamin, and charibdotoxin. GPER-mediated responses were sensitive to G-36, a GPER antagonist. In addition, atomic force microscopy studies revealed that G-1 increased the modulus of elasticity, indicative of cytoskeletal changes and increase in RBMVEC stiffness. Our results unravel the mechanisms underlying GPER-mediated effects in RBMVEC with implications for the effect of estrogen on cerebral microvasculature. Activation of the G protein-coupled estrogen receptor (GPER) in rat brain microvascular endothelial cells (RBMVEC) increases [Ca(2+)](i) by promoting Ca(2+) influx. The increase in [Ca(2+)](i) leads to membrane hyperpolarization, nitric oxide (NO) production, and to cytoskeletal changes and increased cell stiffness. Our results unravel the mechanisms underlying GPER-mediated effects in RBMVEC with implications for the effect of estrogen on cerebral microvasculature.

Changes in the BDNF-immunopositive cell population of neocortical layers I and II/III after focal cerebral ischemia in rats

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family and is widely distributed in the central nervous system, including the cerebral cortex. BDNF plays an important role in normal neural development, survival of existing neurons, and activity-dependent neuroplasticity. BDNF can also be neuroprotective and evoke neurogenesis in certain pathological conditions, such as cerebral ischemia. Neocortical layer I is an important region that can integrate feedforward and feedback information from other cortical areas and subcortical regions. In addition, it has recently been proposed as a possible source of neuronal progenitor cells after ischemia. Therefore, we investigated changes in the BDNF-immunoreactive cell population of neocortical layers I and II/III after middle cerebral artery occlusion (MCAO)-induced cerebral ischemia in rats. In unaffected condition, the number of BDNF(+) cells in layer I was significantly less than in layer II/III in the cingulate cortex and in the motor and sensory areas. The increase in the number of BDNF(+) cells in layer I 8 days after MCAO was more remarkable than layer II/III, in all regions except the area of cingulate cortex farthest from the infarct core. Only BDNF(+)-Ox-42(+) cells showed a tendency to increase consistently toward the infarct core in both layers I and II/III, implying a major source of BDNF for response to ischemic injury. The present study suggests that some beneficial effects during recovery from ischemic injury, such as increased supportive microglia/macrophages, occur owing to a sensitive response of BDNF in layer I.

Estrogens are neuroprotective factors for hypertensive encephalopathy

Estrogens are neuroprotective factors for brain diseases, including hypertensive encephalopathy. In particular, the hippocampus is highly damaged by high blood pressure, with several hippocampus functions being altered in humans and animal models of hypertension. Working with a genetic model of primary hypertension, the spontaneously hypertensive rat (SHR), we have shown that SHR present decreased dentate gyrus neurogenesis, astrogliosis, low expression of brain derived neurotrophic factor (BDNF), decreased number of neurons in the hilus of the dentate gyrus, increased basal levels of the estrogen-synthesizing enzyme aromatase, and atrophic dendritic arbor with low spine density in the CA1 region compared to normotensive Wistar Kyoto (WKY) ratsl. Changes also occur in the hypothalamus of SHR, with increased expression of the hypertensinogenic peptide arginine vasopressin (AVP) and its V1b receptor. Following chronic estradiol treatment, SHR show decreased blood pressure, enhanced hippocampus neurogenesis, decreased the reactive astrogliosis, increased BDNF mRNA and protein expression in the dentate gyrus, increased neuronal number in the hilus of the dentate gyrus, further increased the hyperexpression of aromatase and replaced spine number with remodeling of the dendritic arbor of the CA1 region. We have detected by qPCR the estradiol receptors ERα and ERβ in hippocampus from both SHR and WKY rats, suggesting direct effects of estradiol on brain cells. We hypothesize that a combination of exogenously given estrogens plus those locally synthesized by estradiol-stimulated aromatase may better alleviate the hippocampal and hypothalamic encephalopathy of SHR. This article is part of a Special Issue entitled "Sex steroids and brain disorders".

Influences of prenatal and postnatal stress on adult hippocampal neurogenesis: the double neurogenic niche hypothesis

Adult hippocampal neurogenesis (AHN) is involved in learning, memory, and stress, and plays a significant role in neurodegenerative and psychiatric disorders. As an age-dependent process, AHN is largely influenced by changes that occur during the pre- and postnatal stages of brain development, and constitutes an important field of research. This review examines the current knowledge regarding the regulators of AHN and the influence of prenatal and postnatal stress on later AHN. In addition, a hypothesis is presented suggesting that each kind of stress influences a specific neurogenic pool, developmental or postnatal, that later becomes a precursor with important repercussions for AHN. This hypothesis is referred to as "the double neurogenic niche hypothesis." Discovering what receptors, transcription factors, or genes are specifically activated by different stressors is proposed as an essential line of future research in the field. Such knowledge shall constitute an important starting point toward the goal of modifying AHN in neurodegenerative or psychiatric diseases.

The impact of microglial activation on blood-brain barrier in brain diseases

The blood-brain barrier (BBB), constituted by an extensive network of endothelial cells (ECs) together with neurons and glial cells, including microglia, forms the neurovascular unit (NVU). The crosstalk between these cells guarantees a proper environment for brain function. In this context, changes in the endothelium-microglia interactions are associated with a variety of inflammation-related diseases in brain, where BBB permeability is compromised. Increasing evidences indicate that activated microglia modulate expression of tight junctions, which are essential for BBB integrity and function. On the other hand, the endothelium can regulate the state of microglial activation. Here, we review recent advances that provide insights into interactions between the microglia and the vascular system in brain diseases such as infectious/inflammatory diseases, epilepsy, ischemic stroke and neurodegenerative disorders.

Epigenetic regulation of estrogen-dependent memory

Hippocampal memory formation is highly regulated by post-translational histone modifications and DNA methylation. Accordingly, these epigenetic processes play a major role in the effects of modulatory factors, such as sex steroid hormones, on hippocampal memory. Our laboratory recently demonstrated that the ability of the potent estrogen 17β-estradiol (E2) to enhance hippocampal-dependent novel object recognition memory in ovariectomized female mice requires ERK-dependent histone H3 acetylation and DNA methylation in the dorsal hippocampus. Although these data provide valuable insight into the chromatin modifications that mediate the memory-enhancing effects of E2, epigenetic regulation of gene expression is enormously complex. Therefore, more research is needed to fully understand how E2 and other hormones employ epigenetic alterations to shape behavior. This review discusses the epigenetic alterations shown thus far to regulate hippocampal memory, briefly reviews the effects of E2 on hippocampal function, and describes in detail our work on epigenetic regulation of estrogenic memory enhancement.

Insulin-like growth factor-1 as a prognostic marker in patients with acute ischemic stroke

Objective

Insulin-like growth factor-1 (IGF-1) has been associated with cardiovascular risk factors and atherosclerosis. The aim of the present study was to evaluate the prognostic value of IGF-1 levels in patients with acute ischemic stroke (AIS).

Methods

All patients with first-ever AIS from August 1, 2012 to August 31, 2013 were recruited to participate in the study. Clinical data were collected. The National Institutes of Health Stroke Scale (NIHSS) score was assessed on admission blinded to serum IGF-1 levels. For the assessment of functional outcome at 90 days Modified Rankin Scale (mRS) was used. On admission, serum IGF-1 levels were determined by chemiluminescence immunoassay. The influence of IGF-1 levels on functional outcome and death was assessed by multivariate logistic regression analysis.

Results

Patients with an unfavorable outcomes and non-survivors had significantly decreased serum IGF-1 levels on admission (P<0.0001 for both). IGF-1 was an independent prognostic marker of functional outcome and death [odds ratio 0.89 (0.84–0.93) and 0.90 (0.84–0.95), respectively, P<0.0001 for both, adjusted for age, NIHSS score and other predictors] in patients with ischemic stroke. Serum IGF-1 levels ≤130 ng/mL was as an value indicator for unfavorable functional outcome (OR 3.31, 95% CI:1.87–5.62; P<0.0001), after adjusting for other significant confounders.

Conclusions

We reported a significant association between low serum IGF-1 levels and unfavorable functional outcome and death.