17β-Estradiol Regulates Microglia Activation and Polarization in the Hippocampus Following Global Cerebral Ischemia

Microglial Sp1 induced LRRK2 upregulation in response to manganese exposure, and 17β-estradiol afforded protection against this manganese toxicity

Chronic exposure to elevated levels of manganese (Mn) causes a neurological disorder referred to as manganism, presenting symptoms similar to those of Parkinson's disease (PD), yet the mechanisms by which Mn induces its neurotoxicity are not completely understood. 17β-estradiol (E2) affords neuroprotection against Mn toxicity in various neural cell types including microglia. Our previous studies have shown that leucine-rich repeat kinase 2 (LRRK2) mediates Mn-induced inflammatory toxicity in microglia. The LRRK2 promoter sequences contain three putative binding sites of the transcription factor (TF), specificity protein 1 (Sp1), which increases LRRK2 promoter activity. In the present study, we tested if the Sp1-LRRK2 pathway plays a role in both Mn toxicity and the protection afforded by E2 against Mn toxicity in BV2 microglial cells. The results showed that Mn induced cytotoxicity, oxidative stress, and tumor necrosis factor-α production, which were attenuated by an LRRK2 inhibitor, GSK2578215A. The overexpression of Sp1 increased LRRK2 promoter activity, mRNA and protein levels, while inhibition of Sp1 with its pharmacological inhibitor, mithramycin A, attenuated the Mn-induced increases in LRRK2 expression. Furthermore, E2 attenuated the Mn-induced Sp1 expression by decreasing the expression of Sp1 via the promotion of the ubiquitin-dependent degradation pathway, which was accompanied by increased protein levels of RING finger protein 4, the E3-ligase of Sp1, Sp1 ubiquitination, and SUMOylation. Taken together, our novel findings suggest that Sp1 serves as a critical TF in Mn-induced LRRK2 expression as well as in the protection afforded by E2 against Mn toxicity through reduction of LRRK2 expression in microglia.

Sex Dependent Disparities in the Central Innate Immune Response after Moderate Spinal Cord Contusion in Rat

Subacute spinal cord injury (SCI) displays a complex pathophysiology associated with pro-inflammation and ensuing tissue damage. Microglia, the resident innate immune cells of the CNS, in concert with infiltrating macrophages, are the primary contributors to SCI-induced inflammation. However, subpopulations of activated microglia can also possess immunomodulatory activities that are essential for tissue remodeling and repair, including the production of anti-inflammatory cytokines and growth factors that are vital for SCI recovery. Recently, reports have provided convincing evidence that sex-dependent differences exist in how microglia function during CNS pathologies and the extent to which these cells contribute to neurorepair and endogenous recovery. Herein we employed flow cytometry and immunohistochemical methods to characterize the phenotype and population dynamics of activated innate immune cells within the injured spinal cord of age-matched male and female rats within the first week (7 days) following thoracic SCI contusion. This assessment included the analysis of pro- and anti-inflammatory markers, as well as the expression of critical immunomodulatory kinases, including P38 MAPK, and transcription factors, such as NFκB, which play pivotal roles in injury-induced inflammation. We demonstrate that activated microglia from the injured spinal cord of female rats exhibited a significantly diminutive pro-inflammatory response, but enhanced anti-inflammatory activity compared to males. These changes included lower levels of iNOS and TLR4 expression but increased levels of ARG-1 and CD68 in females after SCI. The altered expression of these markers is indicative of a disparate secretome between the microglia of males and females after SCI and that the female microglia possesses higher phagocytic capabilities (increased CD68). The examination of immunoregulatory kinases and transcription factors revealed that female microglia had higher levels of phosphorylated P38Thr180/Tyr182 MAPK and nuclear NFκB pp50Ser337 but lower amounts of nuclear NFκB pp65Ser536, suggestive of an attenuated pro-inflammatory phenotype in females compared to males after SCI. Collectively, this work provides novel insight into some of the sex disparities that exist in the innate immune response after SCI and indicates that sex is an important variable when designing and testing new therapeutic interventions or interpretating positive or negative responses to an intervention.

Subsecond Codetection of Dopamine and Estradiol at a Modified Sharkfin Waveform

17β-Estradiol (E2) is a ubiquitously expressed hormone that is active in a wide range of neuroprotective and regenerative roles throughout the brain. In particular, it is a well-known dopamine (DA) regulator and is responsible for modulating the expression of dopaminergic receptors and transporters. Recent studies point to E2 release occurring on a rapid time scale and having impacts on DA activity within seconds to minutes. As such, tools capable of monitoring the release of both E2 and DA in real time are essential for developing an accurate understanding of their interactive roles in neurotransmission and regulation. Currently, no analytical techniques capable of codetection of both analytes with high sensitivity, spatiotemporal resolution, extended monitoring, and minimal tissue damage exist. We describe a modified waveform using fast-scan cyclic voltammetry that is capable of low nanomolar detection of both DA and E2 on a subsecond time scale. Both analytes have limits of detection at or below 30 nM and high sensitivity: 11.31 ± 0.55 nA/μM for DA and 9.47 ± 0.36 nA/μM for E2. The waveform is validated in a tissue matrix, confirming its viability for measurement in a biologically relevant setting. This is the first method capable of codetection of fluctuations in DA and E2 with the temporal, spatial, and sensitivity requirements necessary for studying real-time neurochemical signaling.

Sex hormone signaling and regulation of immune function

Immune responses to antigens, including innocuous, self, tumor, microbial, and vaccine antigens, differ between males and females. The quest to uncover the mechanisms for biological sex differences in the immune system has intensified, with considerable literature pointing toward sex hormonal influences on immune cell function. Sex steroids, including estrogens, androgens, and progestins, have profound effects on immune function. As such, drastic changes in sex steroid concentrations that occur with aging (e.g., after puberty or during the menopause transition) or pregnancy impact immune responses and the pathogenesis of immune-related diseases. The effect of sex steroids on immunity involves both the concentration of the ligand and the density and distribution of genomic and nongenomic receptors that serve as transcriptional regulators of immune cellular responses to affect autoimmunity, allergy, infectious diseases, cancers, and responses to vaccines. The next frontier will be harnessing these effects of sex steroids to improve therapeutic outcomes.

Estrogen plays an important role by influencing the NLRP3 inflammasome

The nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome is an important part of the natural immune system that plays an important role in many diseases. Estrogen is a sex hormone that plays an important role in controlling reproduction and regulates many physiological and pathological processes. Recent studies have indicated that estrogen is associated with disease progression. Estrogen can ameliorate some diseases (e. g, sepsis, mood disturbances, cerebral ischemia, some hepatopathy, Parkinson's disease, amyotrophic lateral sclerosis, inflammatory bowel disease, spinal cord injury, multiple sclerosis, myocardial ischemia/reperfusion injury, osteoarthritis, and renal fibrosis) by inhibiting the NLRP3 inflammasome. Estrogen can also promote the development of diseases (e.g., ovarian endometriosis, dry eye disease, and systemic lupus erythematosus) by upregulating the NLRP3 inflammasome. In addition, estrogen has a dual effect on the development of cancers and asthma. However, the mechanism of these effects is not summarized. This article reviewed the progress in understanding the effects of estrogen on the NLRP3 inflammasome and its mechanisms in recent years to provide a theoretical basis for an in-depth study.

Complexity of Sex Differences and Their Impact on Alzheimer's Disease

Sex differences are present in brain morphology, sex hormones, aging processes and immune responses. These differences need to be considered for proper modelling of neurological diseases with clear sex differences. This is the case for Alzheimer's disease (AD), a fatal neurodegenerative disorder with two-thirds of cases diagnosed in women. It is becoming clear that there is a complex interplay between the immune system, sex hormones and AD. Microglia are major players in the neuroinflammatory process occurring in AD and have been shown to be directly affected by sex hormones. However, many unanswered questions remain as the importance of including both sexes in research studies has only recently started receiving attention. In this review, we provide a summary of sex differences and their implications in AD, with a focus on microglia action. Furthermore, we discuss current available study models, including emerging complex microfluidic and 3D cellular models and their usefulness for studying hormonal effects in this disease.

Non-genomic Effect of Estradiol on the Neurovascular Unit and Possible Involvement in the Cerebral Vascular Accident

Cerebrovascular diseases, such as ischemic cerebral vascular accident (CVA), are responsible for causing high rates of morbidity, mortality, and disability in the population. The neurovascular unit (NVU) during and after ischemic CVA plays crucial roles in cell regulation and preservation, the immune and inflammatory response, and cell and/or tissue survival and repair. Cellular responses to 17β-estradiol (E2) can be triggered by two mechanisms: one called classical or genomic, which is due to the activation of the "classical" nuclear estrogen receptors α (ERα) and β (ERβ), and the non-genomic or rapid mechanism, which is due to the activation of the G protein-coupled estrogen receptor 1 (GPER) that is located in the plasma membrane and some in intracellular membranes, such as in the Golgi apparatus and endoplasmic reticulum. Nuclear receptors can regulate gene expression and cellular functions. On the contrary, activating the GPER by E2 and/or its G-1 agonist triggers several rapid cell signaling pathways. Therefore, E2 or its G-1 agonist, by mediating GPER activation and/or expression, can influence several NVU cell types. Most studies argue that the activation of the GPER may be used as a potential therapeutic target in various pathologies, such as CVA. Thus, with this review, we aimed to summarize the existing literature on the role of GPER mediated by E2 and/or its agonist G-1 in the physiology and pathophysiology of NVU.

NLRP3 Inflammasome’s Activation in Acute and Chronic Brain Diseases—An Update on Pathogenetic Mechanisms and Therapeutic Perspectives with Respect to Other Inflammasomes

Increasingly prevalent acute and chronic human brain diseases are scourges for the elderly. Besides the lack of therapies, these ailments share a neuroinflammation that is triggered/sustained by different innate immunity-related protein oligomers called inflammasomes. Relevant neuroinflammation players such as microglia/monocytes typically exhibit a strong NLRP3 inflammasome activation. Hence the idea that NLRP3 suppression might solve neurodegenerative ailments. Here we review the recent Literature about this topic. First, we update conditions and mechanisms, including RNAs, extracellular vesicles/exosomes, endogenous compounds, and ethnic/pharmacological agents/extracts regulating NLRP3 function. Second, we pinpoint NLRP3-activating mechanisms and known NLRP3 inhibition effects in acute (ischemia, stroke, hemorrhage), chronic (Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, MS, ALS), and virus-induced (Zika, SARS-CoV-2, and others) human brain diseases. The available data show that (i) disease-specific divergent mechanisms activate the (mainly animal) brains NLRP3; (ii) no evidence proves that NLRP3 inhibition modifies human brain diseases (yet ad hoc trials are ongoing); and (iii) no findings exclude that concurrently activated other-than-NLRP3 inflammasomes might functionally replace the inhibited NLRP3. Finally, we highlight that among the causes of the persistent lack of therapies are the species difference problem in disease models and a preference for symptomatic over etiologic therapeutic approaches. Therefore, we posit that human neural cell-based disease models could drive etiological, pathogenetic, and therapeutic advances, including NLRP3’s and other inflammasomes’ regulation, while minimizing failure risks in candidate drug trials.

Anti-Inflammatory Actions of G-Protein-Coupled Estrogen Receptor 1 (GPER) and Brain-Derived Estrogen Following Cerebral Ischemia in Ovariectomized Rats

Global cerebral ischemia can elicit rapid innate neuroprotective mechanisms that protect against delayed neuronal death. Brain-derived 17β-estradiol (BDE2), an endogenous neuroprotectant, is synthesized from testosterone by the enzyme aromatase (Aro) and is upregulated by brain ischemia and inflammation. Our recent study revealed that G1, a specific G-protein-coupled estrogen receptor 1 (GPER) agonist, exerts anti-inflammatory and anti-apoptotic roles after global cerebral ischemia (GCI). Herein, we aimed to elucidate whether G1 modulates the early inflammatory process and the potential underlying mechanisms in the ovariectomized rat hippocampal CA1 region. G1 was found to markedly reduce pro-inflammatory (iNOS, MHCII, and CD68) and to enhance anti-inflammatory (CD206, Arginase 1, IL1RA, PPARγ, and BDNF) markers after 1 and 3 days of reperfusion after GCI. Intriguingly, the neuroprotection of G1 was blocked by the Aro inhibitor, letrozole. Conversely, the GPER antagonist, G36, inhibited Aro-BDE2 signaling and exacerbated neuronal damage. As a whole, this work demonstrates a novel anti-inflammatory role of GPER, involving a synergistic mediation with BDE2 during the early stage of GCI.

Sex differences in a double-blind randomized clinical trial with minocycline in treatment-resistant depressed patients: CRP and IL-6 as sex-specific predictors of treatment response

Background

Inflammation is a well-known risk factor for depression. Specifically, patients who do not respond to antidepressant treatment show higher levels of inflammatory biomarkers compared with responders. Thus, several studies have investigated the efficacy of anti-inflammatory add-on treatment in this population. However, major depressive disorder is more prevalent in females than in males, with sex differences present in antidepressant treatment response and in immune system regulation. To explore sex differences in inflammatory profiles and treatment responses, we investigated a cohort of patients with treatment resistant depression (TRD), for which they received an adjunctive, anti-inflammatory treatment with minocycline - the Minocycline in Depression (MINDEP) study.

Methods

The MINDEP study is a 4-week double-blind, randomised, placebo-controlled clinical trial (stratified by sex) with 39 TRD participants, which demonstrated the efficacy of minocycline, an antibiotic with anti-inflammatory properties, in TRD patients with major depressive disorder (MDD) and evidence of low-grade inflammation measured with C-reactive protein (CRP) ≥ 3 mg/L. In these secondary analyses, we investigated the differential effects of minocycline in females (N = 22, 10 randomised to minocycline and 12 randomised to placebo) and in males (N = 17, 8 randomised to minocycline and 9 randomised to placebo) on changes in depressive symptoms (Δ- Hamilton Rating Scale for Depression (HAMD)-17), taking also into consideration CRP levels (CRP ≥3 mg/L vs. CRP <3 mg/L). Additionally, we investigated the role of serum IL-6 in predicting treatment response to minocycline, using sex-specific medians of IL-6, in novel exploratory analyses.

Results

Sex differences in Δ-HAMD-17 indicate that only females (F = 10.49, p = 0.005), but not males (F = 1.64, p = 0.22), presented an effect of CRP levels on the response to minocycline. Also, we detected sex differences in the relationship between serum CRP and IL-6 levels: CRP was strongly correlated with IL-6 in females (Spearman's ρ = 0.658, P < 0.001) but not in males (ρ = 0.007, p = 0.979). Exploratory analyses found that IL-6 was indeed a better predictor of response than minocycline than CRP, as we found an interaction between study arms and IL-6 groups (above and below the IL-6 sex-specific median) in females (F = 4.435 p = 0.050) and, at trend statistical level, in males (F = 4.258 p = 0.060). Moreover, Δ-HAMD-17 was numerically comparable in the two high-IL-6 group taking minocycline (females, mean 9.20 ± SD 7.80; males, mean 8.80 ± SD 5.97), confirming that high IL-6, differently from high CRP, identified responders to minocycline both in males and females.

Conclusion

Our findings highlight the need of sex-specific inflammatory biomarkers in predicting antidepressant response to anti-inflammatories in TRD patients, with the possibility of CRP being a relevant predictor of treatment response only for females, and IL-6 being relevant for both sexes.

Icaritin inhibits neuroinflammation in a rat cerebral ischemia model by regulating microglial polarization through the GPER-ERK-NF-κB signaling pathway

BACKGROUND

Activated microglia play a key role in initiating the inflammatory cascade following ischemic stroke and exert proinflammatory or anti-inflammatory effects, depending on whether they are polarized toward the M1 or M2 phenotype. The present study investigated the regulatory effect of icaritin (ICT) on microglial polarization in rats after cerebral ischemia/reperfusion injury (CI/RI) and explored the possible anti-inflammatory mechanisms of ICT.

METHODS

A rat model of transient middle cerebral artery occlusion (tMCAO) was established. Following treatment with ICT, a G protein-coupled estrogen receptor (GPER) inhibitor or an extracellular signal-regulated kinase (ERK) inhibitor, the Garcia scale and rotarod test were used to assess neurological and locomotor function. 2,3,5-Triphenyltetrazolium chloride (TTC) and Fluoro-Jade C (FJC) staining were used to evaluate the infarct volume and neuronal death. The levels of inflammatory factors in the ischemic penumbra were evaluated using enzyme-linked immunosorbent assays (ELISAs). In addition, western blotting, immunofluorescence staining and quantitative PCR (qPCR) were performed to measure the expression levels of markers of different microglial phenotypes and proteins related to the GPER-ERK-nuclear factor kappa B (NF-κB) signaling pathway.

RESULTS

ICT treatment significantly decreased the cerebral infarct volume, brain water content and fluorescence intensity of FJC; improved the Garcia score; increased the latency to fall and rotation speed in the rotarod test; decreased the levels of interleukin-1 beta (IL-1β), tumor necrosis factor-alpha (TNF-α), Iba1, CD40, CD68 and p-P65-NF-κB; and increased the levels of CD206 and p-ERK. U0126 (an inhibitor of ERK) and G15 (a selective antagonist of GPER) antagonized these effects.

CONCLUSIONS

These findings indicate that ICT plays roles in inhibiting the inflammatory response and achieving neuroprotection by regulating GPER-ERK-NF-κB signaling and then inhibiting microglial activation and M1 polarization while promoting M2 polarization, which provides a new therapeutic for against cerebral ischemic stroke.

Activation of LRP1 Ameliorates Cerebral Ischemia/Reperfusion Injury and Cognitive Decline by Suppressing Neuroinflammation and Oxidative Stress through TXNIP/NLRP3 Signaling Pathway in Mice

Cerebral ischemia/reperfusion (I/R) injury is a clinical event associated with high morbidity and mortality. Neuroinflammation plays a crucial role in the pathogenesis of I/R-induced brain injury and cognitive decline. Low-density lipoprotein receptor-related protein-1 (LRP1) can exert strong neuroprotection in experimental intracerebral hemorrhage. However, whether LRP1 can confer neuroprotective effects after cerebral I/R is yet to be elucidated. The present study is aimed at investigating the effects of LRP1 activation on cerebral I/R injury and deducing the underlying mechanism involving TXNIP/NLRP3 signaling pathway. Cerebral I/R injury was induced in mice by bilateral common carotid artery occlusion. LPR1 ligand, apoE-mimic peptide COG1410, was administered intraperitoneally. To elucidate the underlying mechanism, overexpression of TXNIP was achieved via the hippocampal injection of AAV-TXNIP before COG1410 treatment. Neurobehavioral tests, brain water content, immunofluorescence, Western blot, enzyme-linked immunosorbent assay, HE, and terminal deoxynucleotidyl transferase dUTP nick end labeling staining were performed. Our results showed that the expressions of endogenous LRP1, TXNIP, NLRP3, procaspase-1, and cleaved caspase-1 were increased after cerebral I/R. COG1410 significantly ameliorated cerebral I/R-induced neurobehavioral deficits, brain edema, histopathological damage, and poor survival rate. Interestingly, COG1410 inhibited microglia proinflammatory polarization and promoted anti-inflammatory polarization, decreased oxidative stress, attenuated apoptosis, and inhibited the expression of the TXNIP/NLRP3 signaling pathway. However, the benefits of COG1410 were abolished by TXNIP overexpression. Thus, our study suggested that LRP1 activation with COG1410 attenuated cerebral I/R injury at least partially related to modulating microglial polarization through TXNIP/NLRP3 signaling pathway in mice. Thus, COG1410 treatment might serve as a promising therapeutic approach in the management of cerebral I/R patients.

[18F]ROStrace detects oxidative stress in vivo and predicts progression of Alzheimer's disease pathology in APP/PS1 mice

BACKGROUND

Oxidative stress is implicated in the pathogenesis of the most common neurodegenerative diseases, such as Alzheimer's disease (AD). However, tracking oxidative stress in the brain has proven difficult and impeded its use as a biomarker. Herein, we investigate the utility of a novel positron emission tomography (PET) tracer, [¹⁸F]ROStrace, as a biomarker of oxidative stress throughout the course of AD in the well-established APP/PS1 double-mutant mouse model. PET imaging studies were conducted in wild-type (WT) and APP/PS1 mice at 3 different time points, representing early (5 mo.), middle (10 mo.), and advanced (16 mo.) life (n = 6-12, per sex). Semi-quantitation SUVRs of the plateau phase (40-60 min post-injection; SUVR_40-60) of ten brain subregions were designated by the Mirrione atlas and analyzed by Pmod. Statistical parametric mapping (SPM) was used to distinguish brain regions with elevated ROS in APP/PS1 relative to WT in both sexes. The PET studies were validated by ex vivo autoradiography and immunofluorescence with the parent compound, dihydroethidium.

RESULTS

[¹⁸F]ROStrace retention was increased in the APP/PS1 brain compared to age-matched controls by 10 mo. of age (p < 0.0001) and preceded the accumulation of oxidative damage in APP/PS1 neurons at 16 mo. (p < 0.005). [¹⁸F]ROStrace retention and oxidative damages were higher and occurred earlier in female APP/PS1 mice as measured by PET (p < 0.001), autoradiography, and immunohistochemistry (p < 0.05). [¹⁸F]ROStrace differences emerged midlife, temporally and spatially correlating with increased Aβ burden (r² = 0.36; p = 0.0003), which was also greatest in the female brain (p < 0.001).

CONCLUSIONS

[¹⁸F]ROStrace identifies increased oxidative stress and neuroinflammation in APP/PS1 female mice, concurrent with increased amyloid burden midlife. Differences in oxidative stress during this crucial time may partially explain the sexual dimorphism in AD. [¹⁸F]ROStrace may provide a long-awaited tool to stratify at-risk patients who may benefit from antioxidant therapy prior to irreparable neurodegeneration.

Sex Differences in Poststroke Inflammation: a Focus on Microglia Across the Lifespan

Stroke is one of the leading causes of death worldwide and currently only few therapeutic options are available. Stroke is a sexually dimorphic disease contributing to the difficulty in finding efficient treatments. Poststroke neuroinflammation is geared largely by brain microglia and infiltrating peripheral immune cells and largely contributes to sex differences in the outcome of stroke. Microglia, since very early in the development, are sexually divergent, imprinting specific sex-related features. The diversity in terms of microglial density, morphology, and transcriptomic and proteomic profiles between sexes remains in the adulthood and is likely to contribute to the observed sex-differences on the postischemic inflammation. The impact of sexual hormones is fundamental: changes in terms of risk and severity have been observed for females before and after menopause underlining the importance of altered circulating sexual hormones. Moreover, aging is a driving force for changes that interact with sex, shifting the inflammatory response in a sex-dependent manner. This review summarizes the present literature on sex differences in stroke-induced inflammatory responses, with the focus on different microglial responses along lifespan.

Premarin Reduces Neurodegeneration and Promotes Improvement of Function in an Animal Model of Spinal Cord Injury

Spinal cord injury (SCI) causes significant mortality and morbidity. Currently, no FDA-approved pharmacotherapy is available for treating SCI. Previously, low doses of estrogen (17β-estradiol, E2) were shown to improve the post-injury outcome in a rat SCI model. However, the range of associated side effects makes advocating its therapeutic use difficult. Therefore, this study aimed at investigating the therapeutic efficacy of Premarin (PRM) in SCI. PRM is an FDA-approved E2 (10%) formulation, which is used for hormone replacement therapy with minimal risk of serious side effects. The effects of PRM on SCI were examined by magnetic resonance imaging, immunofluorescent staining, and western blot analysis in a rat model. SCI animals treated with vehicle alone, PRM, E2 receptor antagonist (ICI), or PRM + ICI were graded in a blinded way for locomotor function by using the Basso–Beattie–Bresnahan (BBB) locomotor scale. PRM treatment for 7 days decreased post-SCI lesion volume and attenuated neuronal cell death, inflammation, and axonal damage. PRM also altered the balance of pro- and anti-apoptotic proteins in favor of cell survival and improved angiogenesis and microvascular growth. Increased expression of estrogen receptors (ERs) ERα and ERβ following PRM treatment and their inhibition by ER inhibitor indicated that the neuroprotection associated with PRM treatment might be E2-receptor mediated. The attenuation of glial activation with decreased inflammation and cell death, and increased angiogenesis by PRM led to improved functional outcome as determined by the BBB locomotor scale. These results suggest that PRM treatment has significant therapeutic implications for the improvement of post-SCI outcome.

Xenoestrogens impact brain estrogen receptor signaling during the female lifespan: A precursor to neurological disease?

Xenoestrogens, foreign synthetic chemicals mimicking estrogens, are lurking in our surroundings. Climate change may alter their toxicity and bioavailability. Since xenoestrogens have extremely high lipid solubility and are structurally similar to natural endogenous estrogens, they can bind to estrogen receptors (ERs) -alpha (ER-α) and -beta (ER-β). Scientific evidence accumulated over the past decades have suggested that natural 17β-estradiol (E2; a potent estrogen), via activation of its receptors, plays a pivotal role in regulation of brain development, differentiation, metabolism, synaptic plasticity, neuroprotection, cognition, anxiety, body temperature, feeding and sexual behavior. In the brain, ER-β is predominantly expressed in the various regions, including cerebral cortex and hippocampus, that have been shown to play a key role in cognition. Therefore, disturbances in function of ER-β mediated E2 signaling by xenoestrogens can lead to deleterious effects that potentiate a variety of neurological diseases starting from prenatal to post-menopause in women. The goal of this review is to identify the possible neurological effects of xenoestrogens that can alter estrogen receptor-mediated signaling in the brain during different stages of the female lifespan.

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.

17β-Estradiol Abrogates Oxidative Stress and Neuroinflammation after Cortical Stab Wound Injury

Disruptions in brain energy metabolism, oxidative damage, and neuroinflammation are commonly seen in traumatic brain injury (TBI). Microglial activation is the hallmark of neuroinflammation. After brain injury, microglia also act as a double-edged sword with distinctive phenotypic changes. Therefore, therapeutic applications to potentiate microglia towards pro-inflammatory response following brain injury have become the focus of attention in recent years. Here, in the current study, we investigated the hypothesis that 17β-estradiol could rescue the mouse brain against apoptotic cell death and neurodegeneration by suppressing deleterious proinflammatory response probably by abrogating metabolic stress and oxidative damage after brain injury. Male C57BL/6N mice were used to establish a cortical stab wound injury (SWI) model. Immediately after brain injury, the mice were treated with 17β-estradiol (10 mg/kg, once every day via i.p. injection) for one week. Immunoblotting and immunohistochemical analysis was performed to examine the cortical and hippocampal brain regions. For the evaluation of reactive oxygen species (ROS), reduced glutathione (GSH), and oxidized glutathione (GSSG), we used specific kits. Our findings revealed that 17β-estradiol treatment significantly alleviated SWI-induced energy dyshomeostasis and oxidative stress by increasing the activity of phospho-AMPK (Thr172) and by regulating the expression of an antioxidant gene (Nrf2) and cytoprotective enzymes (HO-1 and GSH) to mitigate ROS. Importantly, 17β-estradiol treatment downregulated gliosis and proinflammatory markers (iNOS and CD64) while significantly augmenting an anti-inflammatory response as evidenced by the robust expression of TGF-β and IGF-1 after brain injury. The treatment with 17β-estradiol also reduced inflammatory mediators (Tnf-α, IL-1β, and COX-2) in the injured mouse. Moreover, 17β-estradiol administration rescued p53-associated apoptotic cell death in the SWI model by regulating the expression of Bcl-2 family proteins (Bax and Bcl-2) and caspase-3 activation. Finally, SWI + 17β-estradiol-treated mice illustrated reduced brain lesion volume and enhanced neurotrophic effect and the expression of synaptic proteins. These findings suggest that 17β-estradiol is an effective therapy against the brain secondary injury-induced pathological cascade following trauma, although further studies may be conducted to explore the exact mechanisms.

17β-Estradiol Attenuates Intracerebral Hemorrhage-Induced Blood-Brain Barrier Injury and Oxidative Stress Through SRC3-Mediated PI3K/Akt Signaling Pathway in a Mouse Model

Estrogen is neuroprotective in brain injury models, and steroid receptor cofactor 3 (SRC3) mediates estrogen signaling. We aimed to investigate whether and how SRC3 is involved in the neuroprotective effects of 17ß-estradiol (E2) in a mouse model of intracerebral hemorrhage (ICH). Ovariectomized female mice were treated with E2 after autologous blood injection-induced ICH. Brain damage was assessed by neurological deficit score, brain water content, and oxidative stress levels. Blood–brain barrier (BBB) integrity was evaluated by Evan's blue extravasation and claudin-5, ZO-1, and occludin levels. SRC3 expression and PI3K/Akt signaling pathway were examined in ICH mice treated with E2. The effect of SRC3 on E2-mediated neuroprotection was determined by examining neurological outcomes in SRC3-deficient mice undergone ICH and E2 treatment. We found that E2 alleviated ICH-induced brain edema and neurological deficits, protected BBB integrity, and suppressed oxidative stress. E2 enhanced SRC3 expression and PI3K-/Akt signaling pathway. SRC3 deficiency abolished the protective effects of E2 on ICH-induced neurological deficits, brain edema, and BBB integrity. Our results suggest that E2 suppresses ICH-induced brain injury and SRC3 plays a critical role in E2-mediated neuroprotection.

Platinum nanoparticles Protect Against Lipopolysaccharide-Induced Inflammation in Microglial BV-2 Cells via Decreased Oxidative Damage and Increased Phagocytosis

Neuroinflammation and oxidative stress cooperate to compromise the function of the central nervous system (CNS). Colloidal platinum nanoparticles (Pt NPs) are ideal candidates for reducing the deleterious effects of neuroinflammation since they act as free radical scavengers. Here we evaluated the effects of Pt NPs on several markers of lipopolysaccharide (LPS)-induced inflammation in cultured BV-2 microglial cells. BV-2 cells were treated with increased dilutions (1-100 ppm) of Colloidal Pt and/or LPS (1-10 µg/mL) at different exposure times. Three different protocols of exposure were used combining Pt NPs and LPS: (a) conditioning-protective effect (pre-post-treat), (b) therapeutic effect (co-treat) and (c) conditioning-therapeutic effect (pre-co-treat). After exposure to LPS for 24 h, cells were used for assessment of cell viability, reactive oxygen species (ROS) generation, lactate dehydrogenase (LDH) activity, apoptosis and caspase-3 levels, cell proliferation, mitochondrial membrane potential, inducible nitric oxide (iNOS) activity, pro-inflammatory cytokine (IL-1β, TNF-α and IL-6) levels, and phagocytic activity. Low concentrations (below or equal to 10 ppm) of Colloidal Pt prevented or ameliorated the LPS-induced increase in ROS formation, loss of mitochondrial membrane potential, induction of apoptosis, increase in LDH release, increase in pro-inflammatory cytokines and iNOS, inhibition of phagocytosis linked to microglial persistence in the M1 phase phenotype, loss of cell adhesion, differentiation and/or proliferation, as well as loss of cell viability. These protective effects were evident when cells were preconditioned with Pt NPs prior to LPS treatment. Collectively, the findings demonstrate that at low concentrations, Pt NPs can regulate the function and phenotype of BV-2 cells, activating protective mechanisms to maintain the microglial homeostasis and reduce inflammatory events triggered by the inflammatory insults induced by LPS. These preventive/protective effects on the LPS pro-inflammatory model are linked to the antioxidant properties and phagocytic activity of these NPs.

Triggering Innate Immune Receptors as New Therapies in Alzheimer's Disease and Multiple Sclerosis

Multiple sclerosis and Alzheimer's disease are two complex neurodegenerative diseases involving the immune system. So far, available treatments provide at best mild improvements to patients' conditions. For decades now, a new set of molecules have been used to modulate and regulate the innate immunity in these pathologies. Most studies have been carried out in rodents and some of them have reported tremendous beneficial effects on the disease course. The modulation of innate immune cells is of great interest since it provides new hope for patients. In this review, we will briefly overview the therapeutic potential of some molecules and receptors in multiple sclerosis and Alzheimer's disease and how they could be used to exploit new therapeutic avenues.

Tetramethoxystilbene Inhibits NLRP3 Inflammasome Assembly via Blocking the Oligomerization of Apoptosis-Associated Speck-like Protein Containing Caspase Recruitment Domain: In Vitro and In Vivo Evaluation

Nucleotide-binding domain leucine-rich repeat family pyrin domain containing 3 (NLRP3) inflammasome complex regulates the caspase-1 activity and subsequent processing of interleukin-1β (IL-1β). Various inflammatory diseases involve the activation of inflammasome complexes; thus, the intervention in complex formation via small molecules offers a new therapeutic opportunity. The structure-guided design and synthesis of a series of methoxystilbenes and methoxy-2-phenylnaphthalenes identified new inhibitors of NLRP3 inflammasome complex. The tetramethoxystilbene 4o and trimethoxy 2-phenylnaphthalene 1t inhibit the release of a mature form of IL-1β in J774A.1 cells with IC50 values of 1.39 and 2.07 μM, respectively. Mechanistic investigation revealed that tetramethoxystilbene 4o blocks the oligomerization of apoptosis-associated speck-like protein (ASC), which is the vital step in the formation of NLRP3 inflammasome assembly, thus preventing the activation of caspase-1 and the IL-1β release. Treatment of LPS+ATP challenged mice with 20 mg/kg of 4o significantly suppressed the levels of IL-1β. The data presented herein warrant further investigation of methoxystilbenes in disease-specific models of inflammatory diseases.

Gualou Guizhi Granule Suppresses LPS-Induced Inflammatory Response of Microglia and Protects against Microglia-Mediated Neurotoxicity in HT-22 via Akt/NF-κB Signaling Pathways

Neuroinflammation plays a crucial part in the commencement and advancement of ischemic stroke. Gualou Guizhi granule (GLGZG) is known to well exhibit neuroprotective effect, but it is not known whether GLGZG can regulate the inflammatory process at the cellular level in BV2 microglia cells and protect against microglia-mediated neurotoxicity in neurons. Herein, we aimed to investigate the anti-inflammatory effects of GLGZG on BV2 microglia cells and protection against microglia-mediated neurotoxicity in neurons. Methods. The cell model of neuroinflammation was constructed by lipopolysaccharide (LPS) to observe the effect of GLGZG in the presence or absence of GLGZG. The production of nitric oxide (NO), inflammatory mediators, was detected. Moreover, potential mechanisms associated with the anti-inflammatory effect, such as inhibition of microglial activation and nuclear factor kappa B (NF-κB), were also investigated. In addition, to prove whether GLGZG protects against microglia-mediated neurotoxicity, neuronal HT-22 cells were cultured in the conditioned medium. And cell survivability and neuronal apoptosis of HT-22 were evaluated. Results. It was found that a main regulator of inflammation, NO, is suppressed by GLGZG in BV2 microglial cells. Moreover, GLGZG dose dependently decreased the mRNA and protein levels of inducible NO synthase (iNOS) in LPS-stimulated BV2 cells. Additionally, GLGZG inhibited the expression and secretion of proinflammatory cytokines in BV2 microglial cells. Also, GLGZG inhibited LPS-activated nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) in BV2 microglial cells at the intracellular level. GLGZG significantly affected Akt phosphorylation: phosphorylated forms of Akt increased. To check whether GLGZG protects against microglia-mediated neurotoxicity, neuronal HT-22 cells were incubated in the conditioned medium. GLGZG showed a neuroprotective effect by promoting cell survivability and suppressing neuronal apoptosis. Conclusions. GLGZG exerted its potential effects on suppressing inflammatory responses in LPS-induced BV2 cells by regulating NF-κB and Akt pathways. In addition, GLGZG could protect against microglia-mediated neurotoxicity in HT-22.

Cellular and molecular pathophysiology in the progression of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder etiologically linked to the loss of substantia nigra (SN) dopaminergic neurons in the mid-brain. The etiopathology of sporadic PD is still unclear; however, the interaction of extrinsic and intrinsic factors may play a critical role in the onset and progression of the disease. Studies in animal models and human post-mortem tissue have identified distinct cellular and molecular changes in the diseased brain, suggesting complex interactions between different glial cell types and various molecular pathways. Small changes in the expression of specific genes in a single pathway or cell type possibly influence others at the cellular and system levels. These molecular and cellular signatures like neuroinflammation, oxidative stress, and autophagy have been observed in PD patients' brain tissue. While the etiopathology of PD is still poorly understood, the interplay between glial cells and molecular events may play a crucial role in disease onset and progression.

Decoding signaling pathways involved in prolactin-induced neuroprotection: A review

It has been well recognized that prolactin (PRL), a pleiotropic hormone, has many functions in the brain, such as maternal behavior, neurogenesis, and neuronal plasticity, among others. Recently, it has been reported to have a significant role in neuroprotection against excitotoxicity. Glutamate excitotoxicity is a common alteration in many neurological and neurodegenerative diseases, leading to neuronal death. In this sense, several efforts have been made to decrease the progression of these pathologies. Despite various reports of PRL's neuroprotective effect against excitotoxicity, the signaling pathways that underlie this mechanism remain unclear. This review aims to describe the most recent and relevant studies on the molecular signaling pathways, particularly, PI3K/AKT, NF-κB, and JAK2/STAT5, which are currently under investigation and might be implicated in the molecular mechanisms that explain the PRL effects against excitotoxicity and neuroprotection. Remarkable neuroprotective effects of PRL might be useful in the treatment of some neurological diseases.

Tamoxifen suppresses brain metastasis of estrogen receptor-deficient breast cancer by skewing microglia polarization and enhancing their immune functions

Background

Brain metastasis of breast cancer exhibits exceedingly poor prognosis, and both triple negative (TN) and Her2⁺ subtypes have the highest incidence of brain metastasis. Although estrogen blockers are considered to be ineffective for their treatment, recent evidence indicates that estrogen blockade using tamoxifen showed certain efficacy. However, how estrogen affects brain metastasis of triple negative breast cancer (TNBC) remains elusive.

Methods

To examine the effect of estrogen on brain metastasis progression, nude mice were implanted with brain metastatic cells and treated with either estrogen supplement, tamoxifen, or ovariectomy for estrogen depletion. For clinical validation study, brain metastasis specimens from pre- and post-menopause breast cancer patients were examined for microglia polarization by immunohistochemistry. To examine the estrogen-induced M2 microglia polarization, microglia cells were treated with estrogen, and the M1/M2 microglia polarization was detected by qRT-PCR and FACS. The estrogen receptor-deficient brain metastatic cells, SkBrM and 231BrM, were treated with conditioned medium (CM) derived from microglia that were treated with estrogen in the presence or absence of tamoxifen. The effect of microglia-derived CM on tumor cells was examined by colony formation assay and sphere forming ability.

Results

We found that M2 microglia were abundantly infiltrated in brain metastasis of pre-menopausal breast cancer patients. A similar observation was made in vivo, when we treated mice systemically with estrogen. Blocking of estrogen signaling either by tamoxifen treatment or surgical resection of mice ovaries suppressed M2 microglial polarization and decreased the secretion of C-C motif chemokine ligand 5, resulting in suppression of brain metastasis. The estrogen modulation also suppressed stemness in TNBC cells in vitro. Importantly, estrogen enhanced the expression of signal regulatory protein α on microglia and restricted their phagocytic ability.

Conclusions

Our results indicate that estrogen promotes brain metastasis by skewing polarity of M2 microglia and inhibiting their phagocytic ability, while tamoxifen suppresses brain metastasis by blocking the M2 polarization of microglia and increasing their anti-tumor phagocytic ability. Our results also highlight a potential therapeutic utility of tamoxifen for treating brain metastasis of hormone receptor-deficient breast cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13058-021-01412-z.

Genistein-3'-sodium sulfonate Attenuates Neuroinflammation in Stroke Rats by Down-Regulating Microglial M1 Polarization through α7nAChR-NF-κB Signaling Pathway

Microglial M1 depolarization mediated prolonged inflammation contributing to brain injury in ischemic stroke. Our previous study revealed that Genistein-3'-sodium sulfonate (GSS) exerted neuroprotective effects in ischemic stroke. This study aimed to explore whether GSS protected against brain injury in ischemic stroke by regulating microglial M1 depolarization and its underlying mechanisms. We established transient middle cerebral artery occlusion and reperfusion (tMCAO) model in rats and used lipopolysaccharide (LPS)-stimulated BV2 microglial cells as in vitro model. Our results showed that GSS treatment significantly reduced the brain infarcted volume and improved the neurological function in tMCAO rats. Meanwhile, GSS treatment also dramatically reduced microglia M1 depolarization and IL-1β level, reversed α7nAChR expression, and inhibited the activation of NF-κB signaling in the ischemic penumbra brain regions. These effects of GSS were further verified in LPS-induced M1 depolarization of BV2 cells. Furthermore, pretreatment of α7nAChR inhibitor (α-BTX) significantly restrained the neuroprotective effect of GSS treatment in tMCAO rats. α-BTX also blunted the regulating effects of GSS on neuroinflammation, M1 depolarization and NF-κB signaling activation. This study demonstrates that GSS protects against brain injury in ischemic stroke by reducing microglia M1 depolarization to suppress neuroinflammation in peri-infarcted brain regions through upregulating α7nAChR and thereby inhibition of NF-κB signaling. Our findings uncover a potential molecular mechanism for GSS treatment in ischemic stroke.

Astaxanthin inhibits microglia M1 activation against inflammatory injury triggered by lipopolysaccharide through down-regulating miR-31-5p

AIMS

Astaxanthin is a natural carotenoid, can readily cross the blood-brain barrier and exerts a powerful neuroprotective effect. In this study, experiments were performed to explore the underlying molecular mechanisms of which Astaxanthin inhibiting the microglia M1 activation.

MAIN METHODS

BV2 cells and mice were pre-treated with Astaxanthin and treated by Lipopolysaccharide (LPS). The expressions of M1-related factors (pro-inflammatory cytokines and M1 markers) were measured by RT-qPCR and western blot. The target association between miR-31-5p and Numb was explored via luciferase activity assay. MiR-31-5p mimic was transfected into BV2 cells, then the cells were treated with Astaxanthin in combination with LPS. The expression of M1-related factors and Notch pathway-related molecules were measured via RT-qPCR, western blot and immunofluorescence assay.

KEY FINDINGS

Precondition of BV2 cells with Astaxanthin inhibited the expression of M1-related factors triggered by LPS. In addition, Astaxanthin decreased the number of Iba1-positive microglia and downregulated the levels of M1-related factors in hippocampus in LPS-treated mice. Further investigation revealed that Astaxanthin-mediated suppression of M1-related factors levels was reversed by miR-31-5p mimic in BV2 cells stimulated by LPS. Subsequently, we verified that miR-31-5p repressed Numb expression by binding to the 3'-UTR of Numb mRNA. Also, Astaxanthin suppressed the expression of Notch1, Hes1 and Hes5 and improved the expression of Numb in BV2 cells challenged by LPS, but this alteration can be reversed by miR-31-5p mimic.

SIGNIFICANCE

Our study demonstrated that down-regulating miR-31-5p by Astaxanthin could be a potential therapeutic approach to suppress neuroinflammation via regulating microglia M1 activation.

Astrocyte-Derived Estrogen Regulates Reactive Astrogliosis and is Neuroprotective following Ischemic Brain Injury

Expression of the 17β-estradiol (E2) synthesis enzyme aromatase is highly upregulated in astrocytes following brain injury. However, the precise role of astrocyte-derived E2 in the injured brain remains unclear. In the current study, we generated a glial fibrillary acidic protein (GFAP) promoter-driven aromatase knock-out (GFAP-ARO-KO) mouse model to deplete astrocyte-derived E2 in the brain and determine its roles after global cerebral ischemia (GCI) in male and female mice. GFAP-ARO-KO mice were viable and fertile, with normal gross brain structure, normal morphology, intensity and distribution of astrocytes, normal aromatase expression in neurons, and normal cognitive function basally. In contrast, after GCI, GFAP-ARO-KO mice: (1) lacked the normal elevation of astrocyte aromatase and hippocampal E2 levels; (2) had significantly attenuated reactive astrogliosis; and (3) displayed enhanced neuronal damage, microglia activation, and cognitive deficits. RNA-sequencing (RNA-seq) analysis revealed that the ischemic GFAP-ARO-KO mouse hippocampus failed to upregulate the "A2" panel of reactive astrocyte genes. In addition, the JAK-STAT3 pathway, which is critical for the induction of reactive astrogliosis, was significantly downregulated in the GFAP-ARO-KO hippocampus following GCI. Finally, exogenous E2 administration fully rescued the compromised JAK-STAT3 pathway and reactive astrogliosis, and reversed the enhanced neuronal damage and microglial activation in the GFAP-ARO-KO mice after GCI, suggesting that the defects in the KO mice are because of a loss of E2 rather than an increase in precursor androgens. In conclusion, the current study provides novel genetic evidence for a beneficial role of astrocyte-derived E2 in reactive astrogliosis, microglial activation, and neuroprotection following an ischemic injury to the brain.SIGNIFICANCE STATEMENT Following cerebral ischemia, reactive astrocytes express the enzyme aromatase and produce 17β-estradiol (E2), although the precise role of astrocyte-derived E2 is poorly understood. In this study, we generated a glial fibrillary acidic protein (GFAP) promoter-driven aromatase knock-out (GFAP-ARO-KO) mouse to deplete astrocyte-derived E2 and elucidate its roles after global cerebral ischemia (GCI). The GFAP-ARO-KO mice exhibited significantly attenuated reactive astrogliosis, as well as enhanced microglial activation, neuronal damage, and cognitive dysfunction after GCI. Transcriptome analysis further revealed that astrocyte-derived E2 was critical for the induction of the JAK-STAT3 signaling pathway, as well as the A2 reactive astrocyte phenotype after ischemia. Collectively, these findings indicate that astrocyte-derived E2 has a key role in the regulation of reactive astrogliosis, microglial activation, and neuroprotection after cerebral ischemia.

Modulatory effect of 17β-estradiol on myeloid cell infiltration into the male rat brain after ischemic stroke

Ischemic stroke is the leading cause of human disability and mortality in the world. Neuroinflammation is the main pathological event following ischemia which contributes to secondary brain tissue damage and is driven by infiltration of circulating immune cells such as macrophages. Because of neuroprotective properties against ischemic brain damage, estrogens have the potential to become of therapeutic interest. However, the exact mechanisms of neuroprotection and signaling pathways is not completely understood. In the current study, 12-week-old male Wistar rats underwent an experimental ischemia by occluding the middle cerebral artery transiently (tMCAO) for 1 h. Male rats subjected to tMCAO were randomly assigned to receive 17β-estradiol or vehicle treatment. The animals were sacrificed 72 h post tMCAO, transcardially perfused and the brains were proceeded either for TTC staining and gene analysis or for flow cytometry (CD45, CD11b, CD11c, CD40). We found that 17β-estradiol substitution significantly reduced the cortical infarct which was paralleled by an improved Garcia test scoring. Flow cytometry revealed that CD45+ cells as well as CD45+CD11b+CD11c+ cells were massively increased in tMCAO animals and numbers were nearly restored to sham levels after 17β-estradiol treatment. Gene expression analysis showed a reperfusion time-dependent upregulation of the markers CD45, CD11b and the activation marker CD40. The reduction in gene expression after 72 h of reperfusion and simultaneous 17β-estradiol substitution did not reach statistical significance. These data indicate that 17β-estradiol alleviated the cerebral ischemia-reperfusion injury and selectively suppressed the activation of the neuroinflammatory cascade via reduction of the number of activated microglia or infiltrated monocyte-derived macrophages in brain.

Higher CSF sTREM2 and microglia activation are associated with slower rates of beta-amyloid accumulation

Microglia activation is the brain's major immune response to amyloid plaques in Alzheimer's disease (AD). Both cerebrospinal fluid (CSF) levels of soluble TREM2 (sTREM2), a biomarker of microglia activation, and microglia PET are increased in AD; however, whether an increase in these biomarkers is associated with reduced amyloid-beta (Aβ) accumulation remains unclear. To address this question, we pursued a two-pronged translational approach. Firstly, in non-demented and demented individuals, we tested CSF sTREM2 at baseline to predict (i) amyloid PET changes over ∼2 years and (ii) tau PET cross-sectionally assessed in a subset of patients. We found higher CSF sTREM2 associated with attenuated amyloid PET increase and lower tau PET. Secondly, in the App^NL-G-F mouse model of amyloidosis, we studied baseline ¹⁸ F-GE180 microglia PET and longitudinal amyloid PET to test the microglia vs. Aβ association, without any confounding co-pathologies often present in AD patients. Higher microglia PET at age 5 months was associated with a slower amyloid PET increase between ages 5-to-10 months. In conclusion, higher microglia activation as determined by CSF sTREM2 or microglia PET shows protective effects on subsequent amyloid accumulation.

Gonadal Hormones E2 and P Mitigate Cerebral Ischemia-Induced Upregulation of the AIM2 and NLRC4 Inflammasomes in Rats

Acute ischemic stroke (AIS) is a devastating neurological condition with a lack of neuroprotective therapeutic options, despite the reperfusion modalities thrombolysis and thrombectomy. Post-ischemic brain damage is aggravated by an excessive inflammatory cascade involving the activation and regulation of the pro-inflammatory cytokines IL-1β and IL-18 by inflammasomes. However, the role of AIM2 and NLRC4 inflammasomes and the influence of the neuroprotective steroids 17β-estradiol (E2) and progesterone (P) on their regulation after ischemic stroke have not yet been conclusively elucidated. To address the latter, we subjected a total of 65 rats to 1 h of transient Middle Cerebral Artery occlusion (tMCAO) followed by a reperfusion period of 72 h. Moreover, we evaluated the expression and regulation of AIM2 and NLRC4 in glial single-cell cultures (astroglia and microglia) after oxygen–glucose deprivation (OGD). The administration of E2 and P decreased both infarct sizes and neurological impairments after cerebral ischemia in rats. We detected a time-dependent elevation of gene and protein levels (Western Blot/immunohistochemistry) of the AIM2 and NLRC4 inflammasomes in the post-ischemic brains. E2 or P selectively mitigated the stroke-induced increase of AIM2 and NLRC4. While both inflammasomes seemed to be exclusively abundant in neurons under physiological and ischemic conditions in vivo, single-cell cultures of cortical astrocytes and microglia equally expressed both inflammasomes. In line with the in vivo data, E and P selectively reduced AIM2 and NLRC4 in primary cortical astrocytes and microglial cells after OGD. In conclusion, the post-ischemic elevation of AIM2 and NLRC4 and their down-regulation by E2 and P may shed more light on the anti-inflammatory effects of both gonadal hormones after stroke.

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.

The NLRP3-Mediated Neuroinflammatory Responses to CdTe Quantum Dots and the Protection of ZnS Shell

Introduction

Since CdTe quantum dots (QDs) are still widely considered as advanced fluorescent probes because of their far superior optical performance and fluorescence efficiency over non-cadmium QDs, it is important to find ways to control their toxicity.

Methods

In this study, the adverse effects of two cadmium-containing QDs, ie, CdTe QDs and CdTe@ZnS QDs, on the nervous system of nematode C. elegans, the hippocampus of mice, and cultured microglia were measured in order to evaluate the neuroinflammation caused by cadmium-containing QDs and the potential mechanisms.

Results

Firstly, we observed that cadmium-containing QD exposure-induced immune responses and neurobehavioral deficit in nematode C. elegans. In the mice treated with QDs, neuroinflammatory responses to QDs in the hippocampus, including microglial activation and IL-1ß release, occurred as well. When investigating the mechanisms of cadmium-containing QDs causing IL-1ß-mediated inflammation, the findings suggested that cadmium-containing QDs activated the NLRP3 inflammasome by causing excessive ROS generation, and resulted in IL-1ß release.

Discussion

Even though the milder immune responses and neurotoxicity of CdTe@ZnS QDs compared with CdTe QDs indicated the protective role of ZnS coating, the inhibitions of NLRP3 expression and ROS production completely reduced the IL-1ß-mediated inflammation. This provided valuable information that inhibiting target molecules is an effective and efficient way to alleviate  the toxicity of cadmium-containing QDs, so it is important to evaluate QDs through a mechanism-based risk assessment.

Sex steroid hormone function in the brain niche: Implications for brain metastatic colonization and progression

BACKGROUND

While sex hormones and their receptors play well-known roles in progression of primary tumors through direct action on sex steroid hormone-responsive cancer cells, emerging evidence suggest that hormones also play important roles in metastatic progression by modulating the tumor microenvironment. Estrogens and androgens synthesized in gonads and within the brain influence memory, behavior, and outcomes of brain pathologies. Yet, their impact on brain metastatic colonization and progression is just beginning to be explored.

RECENT FINDINGS

Estradiol and testosterone cross the blood-brain barrier and are synthesized de novo in astrocytes and other cells within the adult brain. Circulating and brain-synthesized estrogens have been shown to promote brain metastatic colonization of tumors lacking estrogen receptors (ERs), through mechanisms involving the upregulation of growth factors and neurotrophins in ER+ reactive astrocytes. In this review, we discuss additional mechanisms by which hormones may influence brain metastases, through modulation of brain endothelial cells, astrocytes, and microglia.

CONCLUSION

A greater understanding of hormone-brain-tumor interactions may shed further light on the mechanisms underlying the adaptation of cancer cells to the brain niche, and provide therapeutic alternatives modulating the brain metastatic niche.

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.

Discovery of benzo[cd]indol-2-one and benzylidene-thiazolidine-2,4-dione as new classes of NLRP3 inflammasome inhibitors via ER-β structure based virtual screening

The structure-guided virtual screening (VS) has proved to be successful strategy in identification of new scaffolds for biological targets. The overactivity of NLRP3 inflammasome has been implicated in variety of inflammatory diseases including Alzheimer's disease. The up-regulation of estrogen-receptor β (ER-β) activity has been directly linked with inhibition of NLRP3 inflammasome activity. In the present study, we report discovery of new NLRP3 inflammasome inhibitors via ER-β crystal structure (PDB: 5TOA) guided virtual screening of 20,000 compound library. For experimental validation, top 10 ligands were selected based on structure novelty, docking score, prime MMGB/SA binding affinity and interaction pattern analysis. Amongst the tested compounds, three thiazolidin-4-ones IIIM-1268, IIIM-1269 and IIIM-1270 and benzo[cd]indol-2-one IIIM-1266 have shown 73, 69, 75 and 77% suppression of IL-1β release in mouse macrophages (J774A.1 cells) at 10 µM. Benzylidene-thiazolidine-2,4-diones IIIM-1268 and IIIM-1270 inhibited IL-1β release with IC₅₀ of 2.3 and 3.5 µM and also significantly decreased the protein expression level of mature form of IL-1β in western-blot analysis. IIIM-1266 and IIIM-1270 displayed bidentate H-bonding with Arg 346 and Glu 305 residues in the active site of ER-β; and they also strongly occupied the ADP-binding site of NLRP3 protein. The results presented herein, indicate that ER-β guided VS can be successfully used to identify new NLRP3 inflammasome inhibitors, which may have potential in the development of novel anti-Alzheimer agents.

The glycolytic shift was involved in CdTe/ZnS quantum dots inducing microglial activation mediated through the mTOR signaling pathway

The excellent optical property and relatively low toxicity of CdTe/ZnS core/shell quantum dots (QDs) make them an advanced fluorescent probe in the application of biomedicines, particularly in neuroscience. Thus, it is important to evaluate the biosafety of CdTe/ZnS QDs on the central nervous system (CNS). Our previous studies have suggested that the high possibility of CdTe/ZnS QDs being transported into the brain across the blood-brain barrier resulted in microglial activation and a shift of glycometabolism, but their underlying mechanism remains unclear. In this study, when mice were injected intravenously with CdTe/ZnS QDs through tail veins, the microglial activation, polarized into both M1 phenotype and M2 phenotype, and the neuronal impairment were observed in the hippocampus. Meanwhile, the increased pro- and anti-inflammatory cytokines released from BV2 microglial cells treated with CdTe/ZnS QDs also indicated that QD exposure was capable of inducing microglial activation in vitro. We further demonstrated that the glycolytic shift from oxidative phosphorylation switching into aerobic glycolysis was required in the microglial activation into M1 phenotype induced by CdTe/ZnS QD treatment, which was mediated through the mTOR signaling pathway. The findings, taken together, provide a mechanistic insight regarding the CdTe/ZnS QDs inducing microglial activation and the role of the glycolytic shift in it.

The role of NLRP3 inflammasome activation in the neuroinflammatory responses to Ag2Se quantum dots in microglia

Silver selenide quantum dots (Ag₂Se QDs) provide bright prospects for the application of QDs in the field of biomedicine because they contain low-toxic compounds and show great advantages in the imaging of deep tissues and tiny vascular structures. However, the biosafety of these novel QDs has not been thoroughly evaluated, especially in one main target for toxicity-the central nervous system (CNS). Our previous studies have suggested severe inflammatory responses to cadmium-containing QDs in the hippocampus, which gives us a hint regarding the risk assessment of Ag₂Se QDs. In this study, microglial activation followed by enhanced levels of pro-inflammatory cytokines was observed in the hippocampus of mice intravenously injected with Ag₂Se QDs. When using the microglial BV2 cells to investigate the underlying mechanisms, we found that the NLRP3 inflammasome activation was involved in the IL-1β-mediated inflammation induced by Ag₂Se QDs. On the one hand, Ag₂Se QD-activated NF-κB participated in the NLRP3 inflammasome priming and assembly as well as the pro-IL-1β upregulation. On the other hand, Ag₂Se QD-induced ROS generation, particularly mtROS, triggered the NLRP3 inflammasome activation and resulted in active caspase-1 to process pro-IL-1β into mature IL-1β release. These findings not only indicated that it is important to evaluate the biosafety of novel QDs, even those containing low-toxic compounds, but also provided an unbiased and mechanism-based risk assessment of similar nanoparticles.

Berberine Facilitates Angiogenesis Against Ischemic Stroke Through Modulating Microglial Polarization via AMPK Signaling

Evidence suggests that microglia/macrophages can change their phenotype to M1 or M2 and participate in tissue damage or repair. Berberine (BBR) has shown promise in experimental stroke models, but its effects on microglial polarization and long-term recovery after stroke are elusive. Here, we investigated the effects of BBR on angiogenesis and microglial polarization through AMPK signaling after stroke. In the present study, C57BL/6 mice were subjected to transient middle cerebral artery occlusion (tMCAO), intragastrically administrated with BBR at 50 mg/kg/day. Neo-angiogenesis was observed by ⁶⁸Ga-NODAGA-RGD micro-PET/CT and immunohistochemistry. Immunofluorescent staining further exhibited an increase of M2 microglia and a reduction of M1 microglia at 14 days after stroke. In vitro studies, the lipopolysaccharide (LPS)-induced BV2 microglial cells were used to confirm the AMPK activation effect of BBR. RT-PCR, Flow cytometry, and ELISA all demonstrated that BBR could inhibit M1 polarization and promote M2 polarization. Furthermore, treatment of human umbilical vein endothelial cells (HUVEC) with conditioned media collected from BBR-treated BV2 cells promoted angiogenesis. All effects stated above were reversed by AMPK inhibitor (Compound C) and AMPK siRNA. In conclusion, BBR treatment improves functional recovery and promotes angiogenesis following tMCAO via AMPK-dependent microglial M2 polarization.