Regulation of brain microglia by female gonadal steroids

Inflammatory signalling during the perinatal period: Implications for short- and long-term disease risk

During pregnancy and the postpartum, there are dynamic fluctuations in steroid and peptide hormone levels as well as inflammatory signalling. These changes are required for a healthy pregnancy and can persist well beyond the postpartum. Many of the same hormone and inflammatory signalling changes observed during the perinatal period also play a role in symptoms related to autoimmune disorders, psychiatric disorders, and perhaps neurodegenerative disease later in life. In this review, we outline hormonal and immunological shifts linked to pregnancy and the postpartum and discuss the possible role of these shifts in increasing psychiatric, neurodegenerative disease risk and autoimmune symptoms during and following pregnancy. Furthermore, we discuss how key variables such as the number of births (parity) and sex of the fetus can influence inflammatory signalling, and possibly future disease risk, but are not often studied. We conclude by discussing the importance of studying female experiences such as pregnancy and parenting on physiology and disease.

Role of the gut microbiome in mediating sex-specific differences in the pathophysiology of Alzheimer's disease

Alzheimer's disease (AD) presents distinct pathophysiological features influenced by biological sex, with women disproportionately affected due to sex-specific genetic, hormonal, and epigenetic factors. This review delves into three critical areas of sex differences in AD: First, we explore how genetic predisposition and hormonal changes, particularly those involving sex-specific modifications, influence susceptibility and progression of the disease. Second, we examine the neuroimmune dynamics in AD, emphasizing variations in microglial activity between sexes during crucial developmental stages and the effects of hormonal interventions on disease outcomes. Crucially, this review highlights the significant role of gut microbiome perturbations in shaping AD pathophysiology in a sex-specific manner, suggesting that these alterations can further influence microglial activity and overall disease trajectory. Third, we provide a viewpoint that advocates for personalized therapeutic strategies that integrate the understanding of hormonal fluctuations and microbiome dynamics into treatment plans in order to optimize patient outcomes.

Toward discovering a novel family of peptides targeting neuroinflammatory states of brain microglia and astrocytes

Microglia are immune-derived cells critical to the development and healthy function of the brain and spinal cord, yet are implicated in the active pathology of many neuropsychiatric disorders. A range of functional phenotypes associated with the healthy brain or disease states has been suggested from in vivo work and were modeled in vitro as surveying, reactive, and primed sub-types of primary rat microglia and mixed microglia/astrocytes. It was hypothesized that the biomolecular profile of these cells undergoes a phenotypical change as well, and these functional phenotypes were explored for potential novel peptide binders using a custom 7 amino acid-presenting M13 phage library (SX7) to identify unique peptides that bind differentially to these respective cell types. Surveying glia were untreated, reactive were induced with a lipopolysaccharide treatment, recovery was modeled with a potent anti-inflammatory treatment dexamethasone, and priming was determined by subsequently challenging the cells with interferon gamma. Microglial function was profiled by determining the secretion of cytokines and nitric oxide, and expression of inducible nitric oxide synthase. After incubation with the SX7 phage library, populations of SX7-positive microglia and/or astrocytes were collected using fluorescence-activated cell sorting, SX7 phage was amplified in Escherichia coli culture, and phage DNA was sequenced via next-generation sequencing. Binding validation was done with synthesized peptides via in-cell westerns. Fifty-eight unique peptides were discovered, and their potential functions were assessed using a basic local alignment search tool. Peptides potentially originated from proteins ranging in function from a variety of supportive glial roles, including synapse support and pruning, to inflammatory incitement including cytokine and interleukin activation, and potential regulation in neurodegenerative and neuropsychiatric disorders.

Chronic Variable Stress and Cafeteria Diet Combination Exacerbate Microglia and c-fos Activation but Not Experimental Anxiety or Depression in a Menopause Model

The menopause transition is a vulnerable period for developing both psychiatric and metabolic disorders, and both can be enhanced by stressful events worsening their effects. The present study aimed to evaluate whether a cafeteria diet (CAF) combined with chronic variable stress (CVS) exacerbates anxious- or depressive-like behavior and neuronal activation, cell proliferation and survival, and microglia activation in middle-aged ovariectomized (OVX) rats. In addition, body weight, lipid profile, insulin resistance, and corticosterone as an index of metabolic changes or hypothalamus-pituitary-adrenal (HPA) axis activation, and the serum pro-inflammatory cytokines IL-6, IL-β, and TNFα were measured. A CAF diet increased body weight, lipid profile, and insulin resistance. CVS increased corticosterone and reduced HDL. A CAF produced anxiety-like behaviors, whereas CVS induced depressive-like behaviors. CVS increased serum TNFα independently of diet. A CAF and CVS separately enhanced the percentage of Iba-positive cells in the hippocampus; the combination of factors further increased Iba-positive cells in the ventral hippocampus. A CAF and CVS increased the c-fos-positive cells in the hippocampus; the combination of factors increased the number of positive cells expressing c-fos in the ventral hippocampus even more. The combination of a CAF and CVS generates a slight neuroinflammation process and neuronal activation in a hippocampal region-specific manner and differentially affects the behavior.

Low-Dose Radiation Therapy Impacts Microglial Inflammatory Response without Modulating Amyloid Load in Female TgF344-AD Rats

Background

Low-dose radiation therapy (LD-RT) has demonstrated in preclinical and clinical studies interesting properties in the perspective of targeting Alzheimer's disease (AD), including anti-amyloid and anti-inflammatory effects. Nevertheless, studies were highly heterogenous with respect to total doses, fractionation protocols, sex, age at the time of treatment and delay post treatment. Recently, we demonstrated that LD-RT reduced amyloid peptides and inflammatory markers in 9-month-old TgF344-AD (TgAD) males.

Objective

As multiple studies demonstrated a sex effect in AD, we wanted to validate that LD-RT benefits are also observed in TgAD females analyzed at the same age.

Methods

Females were bilaterally treated with 2 Gy×5 daily fractions, 2 Gy×5 weekly fractions, or 10 fractions of 1 Gy delivered twice a week. The effect of each treatment on amyloid load and inflammation was evaluated using immunohistology and biochemistry.

Results

A daily treatment did not affect amyloid and reduced only microglial-mediated inflammation markers, the opposite of the results obtained in our previous male study. Moreover, altered fractionations (2 Gy×5 weekly fractions or 10 fractions of 1 Gy delivered twice a week) did not influence the amyloid load or neuroinflammatory response in females.

Conclusions

A daily treatment consequently appears to be the most efficient for AD. This study also shows that the anti-amyloid and anti-inflammatory response to LD-RT are, at least partly, two distinct mechanisms. It also emphasizes the necessity to assess the sex impact when evaluating responses in ongoing pilot clinical trials testing LD-RT against AD.

CD46 expression in the central nervous system of male and female pubescent mice

CD46 is a complementary regulatory protein ubiquitously expressed in human cells, controlling complement system activation. CD46 has further been identified to have several other functions including regulatory T cell induction and intestinal epithelial (IEC) barrier regulation. Activation of CD46 in the IEC can impact intestinal barrier permeability and immune system functioning. CD46 has only been identified in the spermatozoa and retina of mice. In other murine cells, the homologue CRRY is identified to function as the complementary regulator. Due to the identification of CRRY across other wild-type mouse cells and the development of mouse strains transgenic for human CD46, no recent research has been conducted to determine if CD46 is present in non-transgenic mouse strains. Therefore, the current study investigated if CD46 is expressed in the substantia nigra (SN) and caudate putamen (CP) of pubescent CD1 mice and examined the acute effects of pubertal antimicrobial and lipopolysaccharide (LPS) treatment on CD46 expression in the brain. As of 5 weeks of age, mice were administered mixed antimicrobial solution or water with oral gavage twice daily for 7 days. At 6 weeks of age, mice received an intraperitoneal injection of LPS or saline. Mice were euthanized 8 h post-injection and brain samples were collected. Our results indicate that pubescent CD-1 mice express CD46 in the SN and CP. However, LPS-treated mice displayed significantly less CD46 expression in the SN in comparison to saline-treated mice. Furthermore, males displayed more CD46 in the CP compared to females, regardless of LPS and antimicrobial treatments. Our data suggest CD46 is present in CD1 mice and that LPS and antimicrobial treatments impact CD46 protein expression in a sex-dependent manner. These results have important implications for the expression of CD46 in the mouse brain and the understanding of its role in immune system regulation.

Abnormal Microglial Density and Morphology in the Brain of Cyclooxygenase 2 Knockin Mice

Prostaglandin E2 (PGE2) is a signaling molecule produced by cyclooxygenase-2 (COX-2) that is important in healthy brain development. Anomalies in the COX-2/PGE2 pathway due to genetic or environmental factors have been linked to Autism Spectrum Disorders (ASD). Our previous studies showed that COX-2 deficient (COX-2-KI) mice exhibit sex-dependent molecular changes in the brain and associated autism-related behaviors. Here, we aim to determine the effect of COX-2-KI on microglial density and morphology in the developing brain. Microglia normally transition between an amoeboid or ramified morphology depending on their surroundings and are important for the development of the healthy brain, assisting with synaptogenesis, synaptic pruning, and phagocytosis. We use COX-2-KI male and female mice to evaluate microglia density, morphology, and branch length and number in five brain regions (cerebellum, hippocampus, olfactory bulb, prefrontal cortex, and thalamus) at the gestational day 19 (G19) and postnatal day 25 (PN25). We discovered that COX2-KI females were affected at G19 with increased microglial density, altered percentage of amoeboid and ramified microglia, affected branch length, and decreased branching networks in a region-specific manner; these effects persisted to PN25 in select regions. Interestingly, while limited changes were found in G19 COX-2-KI males, at PN25 we found increased microglial density, higher percentages of ramified microglia, and increased branch counts, and length observed in nearly all brain regions tested. Overall, we show for the first time that the COX-2 deficiency in our ASD mouse model influences microglia morphology in a sex- and region- and stage-dependent manner.

Impact of Sex on Neuroimmune contributions to Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. Inflammation has been observed in both the idiopathic and familial forms of PD. Importantly, PD is reported more often in men than in women, men having at least 1.5- fold higher risk to develop PD than women. This review summarizes the impact of biological sex and sex hormones on the neuroimmune contributions to PD and its investigation in animal models of PD. Innate and peripheral immune systems participate in the brain neuroinflammation of PD patients and is reproduced in neurotoxin, genetic and alpha-synuclein based models of PD. Microglia and astrocytes are the main cells of the innate immune system in the central nervous system and are the first to react to restore homeostasis in the brain. Analysis of serum immunoprofiles in female and male control and PD patients show that a great proportion of these markers differ between male and female. The relationship between CSF inflammatory markers and PD clinical characteristics or PD biomarkers shows sex differences. Conversely, in animal models of PD, sex differences in inflammation are well documented and the beneficial effects of endogenous and exogenous estrogenic modulation in inflammation have been reported. Targeting neuroinflammation in PD is an emerging therapeutic option but gonadal drugs have not yet been investigated in this respect, thus offering new opportunities for sex specific treatments.

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.

Three-Dimensional Analysis of Sex- and Gonadal Status- Dependent Microglial Activation in a Mouse Model of Parkinson’s Disease

Parkinson’s disease (PD) is characterized by neurodegeneration and neuroinflammation. PD prevalence and incidence are higher in men than in women and modulation of gonadal hormones could have an impact on the disease course. This was investigated in male and female gonadectomized (GDX) and SHAM operated (SHAM) mice. Dutasteride (DUT), a 5α-reductase inhibitor, was administered to these mice for 10 days to modulate their gonadal sex hormones. On the fifth day of DUT treatment, mice received 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to model PD. We have previously shown in these mice the toxic effect of MPTP in SHAM and GDX males and in GDX females on dopamine markers and astrogliosis whereas SHAM females were protected by their female sex hormones. In SHAM males, DUT protected against MPTP toxicity. In the present study, microglial density and the number of doublets, representative of a microglial proliferation, were increased by the MPTP lesion only in male mice and prevented by DUT in SHAM males. A three-dimensional morphological microglial analysis showed that MPTP changed microglial morphology from quiescent to activated only in male mice and was not prevented by DUT. In conclusion, microgliosis can be modulated by sex hormone-dependent and independent factors in a mice model of PD.

Inhibition of Pro-Inflammatory Microglia with Minocycline Improves Cognitive and Sleep-Wake Dysfunction Under Respiratory Stress in a Sporadic Model for Alzheimer's Disease

BACKGROUND

Neuroinflammation in Alzheimer's disease (AD) can occur due to excessive activation of microglia in response to the accumulation of amyloid-β peptide (Aβ). Previously, we demonstrated an increased expression of this peptide in the locus coeruleus (LC) in a sporadic model for AD (streptozotocin, STZ; 2 mg/kg, ICV). We hypothesized that the STZ-AD model exhibits neuroinflammation, and treatment with an inhibitor of microglia (minocycline) can reverse the cognitive, respiratory, sleep, and molecular disorders of this model.

OBJECTIVE

To evaluate the effect of minocycline treatment in STZ model disorders.

METHODS

We treated control and STZ-treated rats for five days with minocycline (30 mg/kg, IP) and evaluated cognitive performance, chemoreflex response to hypercapnia and hypoxia, and total sleep time. Additionally, quantification of Aβ, microglia analyses, and relative expression of cytokines in the LC were performed.

RESULTS

Minocycline treatment improved learning and memory, which was concomitant with a decrease in microglial cell density and re-establishment of morphological changes induced by STZ in the LC region. Minocycline did not reverse the STZ-induced increase in CO2 sensitivity during wakefulness. However, it restored the daytime sleep-wake cycle in STZ-treated animals to the same levels as those observed in control animals. In the LC, levels of A and expression of Il10, Il1b, and Mcp1 mRNA remained unaffected by minocycline, but we found a strong trend of minocycline effect on Tnf- α.

CONCLUSION

Our findings suggest that minocycline effectively reduces microglial recruitment and the inflammatory morphological profile in the LC, while it recovers cognitive performance and restores the sleep-wake pattern impaired by STZ.

Microglial angiotensin type 2 receptors mediate sex-specific expression of inflammatory cytokines independently of circulating estrogen

There are sex differences in microglia, which can maintain sex-related gene expression and functional differences in the absence of circulating sex steroids. The angiotensin type 2 (AT2) receptors mediate anti-inflammatory actions in different tissues, including brain. In mice, we performed RT-PCR analysis of microglia isolated from adult brains and RNA scope in situ hybridization from males, females, ovariectomized females, orchiectomized males and brain masculinized females. We also compared wild type and AT2 knockout mice. The expression of AT2 receptors in microglial cells showed sex differences with much higher AT2 mRNA expression in females than in males, and this was not dependent on circulating gonadal hormones, as observed using ovariectomized females, brain masculinized females and orchiectomized males. These results suggest genomic reasons, possibly related to sex chromosome complement, for sex differences in AT2 expression in microglia, as the AT2 receptor gene is located in the X chromosome. Furthermore, sex differences in expression of AT2 receptors were associated to sex differences in microglial expression of key anti-inflammatory cytokines such as interleukin-10 and pro-inflammatory cytokines such as interleukin-1β and interleukin-6. In conclusion, sex differences in microglial AT2 receptor expression appear as a major factor contributing to sex differences in the neuroinflammatory responses beyond the effects of circulating steroids.

Aerobic exercise alleviates pyroptosis-related diseases by regulating NLRP3 inflammasome

Pyroptosis plays a crucial role in a variety of human diseases, including atherosclerosis, obesity, diabetes, depression, and Alzheimer’s disease, which usually release pyroptosis-related cytokines due to inflammation. Many studies have demonstrated that aerobic exercise is a good option for decreasing the release of pyroptosis-related cytokines. However, the molecular mechanisms of aerobic exercise on pyroptosis-related diseases remain unknown. In this review, the effects of aerobic exercise on pyroptosis in endothelial cells, adipocytes and hippocampal cells, and their potential mechanisms are summarized. In endothelial cells, aerobic exercise could inhibit NOD-like receptor protein 3 (NLRP3) inflammasome-mediated pyroptosis by improving the endothelial function, while reducing vascular inflammation and oxidative stress. In adipocytes, aerobic exercise has been shown to inhibit pyroptosis by ameliorating inflammation and insulin resistance. Moreover, aerobic exercise could restrict pyroptosis by attenuating microglial activation, neuroinflammation, and amyloid-beta deposition in hippocampal cells. In summary, aerobic exercise alleviates the pyroptosis-related diseases by regulating the NLRP3 inflammation si0067naling.

The effects of antimicrobials and lipopolysaccharide on acute immune responsivity in pubertal male and female CD1 mice

Exposure to stress during critical periods of development—such as puberty—is associated with long-term disruptions in brain function and neuro-immune responsivity. However, the mechanisms underlying the effect of stress on the pubertal neuro-immune response has yet to be elucidated. Therefore, the objective of the current study was to investigate the effect antimicrobial and lipopolysaccharide (LPS) treatments on acute immune responsivity in pubertal male and female mice. Moreover, the potential for probiotic supplementation to mitigate these effects was also examined. 240 male and female CD1 mice were treated with one week of antimicrobial treatment (mixed antimicrobials or water) and probiotic treatment (L. rhamnosis R0011 and L. helveticus R0052 or L. helveticus R0052 and B. longum R0175) or placebo at five weeks of age. At six weeks of age (pubertal stress-sensitive period), the mice received a single injection of LPS or saline. Sickness behaviours were assessed, and mice were euthanized 8 h post-injection. Brain, blood, and intestinal samples were collected. The results indicated that the antimicrobial treatment reduced sickness behaviours, and potentiated LPS-induced plasma cytokine concentrations and pro-inflammatory markers in the pre-frontal cortex (PFC) and hippocampus, in a sex-dependent manner. However, probiotics reduced LPS-induced plasma cytokine concentrations along with hippocampal and PFC pro-inflammatory markers in a sex-dependent manner. L. rhamnosis R0011 and L. helveticus R0052 treatment also mitigated antimicrobial-induced plasma cytokine concentrations and sickness behaviours. These findings suggest that the microbiome is an important modulator of the pro-inflammatory immune response during puberty.

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Pubertal dysbiosis increases LPS-induced neuroinflammation.

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Pubertal dysbiosis increases LPS-induced plasma cytokine concentrations.

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Pubertal probiotic treatment reduces LPS-induced neuroinflammation.

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Pubertal probiotic treatment reduces LPS-induced plasma cytokine concentrations.

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Pubertal probiotic treatment reduces LPS-induced sickness.

Immune System Alterations and Postpartum Mental Illness: Evidence From Basic and Clinical Research

The postpartum period is a time associated with high rates of depression and anxiety as well as greater risk for psychosis in some women. A growing number of studies point to aberrations in immune system function as contributing to postpartum mental illness. Here we review evidence from both clinical and animal models suggesting an immune component to postpartum depression, postpartum anxiety, and postpartum psychosis. Thus far, clinical data primarily highlights changes in peripheral cytokine signaling in disease etiology, while animal models have begun to provide insight into the immune environment of the maternal brain and how central inflammation may also be contributing to postpartum mental illnesses. Further research investigating peripheral and central immune function, along with neural and endocrine interactions, will be important in successfully developing novel prevention and treatment strategies for these serious disorders that impact a large portion of new mothers.

Raloxifene, a cannabinoid type-2 receptor inverse agonist, mitigates visual deficits and pathology and modulates microglia after ocular blast

Visual deficits after ocular blast injury (OBI) are common, but pharmacological approaches to improve long-term outcomes have not been identified. Blast forces frequently damage the retina and optic nerves, and work on experimental animals has shown the pro-inflammatory actions of microglia can further exacerbate such injuries. Cannabinoid type-2 receptor (CB2) inverse agonists specifically target activated microglia, biasing them away from the harmful pro-inflammatory M1 state toward the helpful reparative M2 state. We previously found that treating mice with CB2 inverse agonists after traumatic brain injury, produced by either focal cranial air blast or dorsal cranial impact, greatly attenuated the visual deficits and pathology that otherwise resulted. Here we examined the consequences of single and repeat OBI and the benefit provided by raloxifene, an FDA-approved estrogen receptor drug that possesses noteworthy CB2 inverse agonism. After single OBI, although the amplitudes of the A- and B-waves of the electroretinogram and pupil light response appeared to be normal, the mice showed hints of deficits in contrast sensitivity and visual acuity, a trend toward optic nerve axon loss, and significantly increased light aversion, which were reversed by 2 weeks of daily treatment with raloxifene. Mice subjected to repeat OBI (5 blasts spaced 1 min apart), exhibited more severe visual deficits, including decreases in contrast sensitivity, visual acuity, the amplitudes of the A- and B-waves of the electroretinogram, light aversion, and resting pupil diameter (i.e. hyperconstriction), accompanied by the loss of photoreceptor cells and optic nerve axons, nearly all of which were mitigated by raloxifene. Interestingly, optic nerve axon abundance was strongly correlated with contrast sensitivity and visual acuity across all groups of experimental mice in the repeat OBI study, suggesting optic nerve axon loss with rOBI and its attenuation with raloxifene are associated with the extent of these two deficits while photoreceptor abundance was highly correlated with A-wave amplitude and resting pupil size, suggesting a prominent role for photoreceptors in these two deficits. Quantitative PCR (qPCR) showed levels of M1-type microglial markers (e.g. iNOS, IL1β, TNFα, and CD32) in retina, optic nerve, and thalamus were increased 3 days after repeat OBI. With raloxifene treatment, the overall expression of M1 markers was more similar to that in sham mice. Raloxifene treatment was also associated with the elevation of IL10 transcripts in all three tissues compared to repeat OBI alone, but the results for the three other M2 microglial markers we examined were more varied. Taken together, the qPCR results suggest that raloxifene benefit for visual function and pathology was associated with a lessening of the pro-inflammatory actions of microglia. The benefit we find for raloxifene following OBI provides a strong basis for phase-2 efficacy testing in human clinical trials for treating ocular injury.

Raloxifene Modulates Microglia and Rescues Visual Deficits and Pathology After Impact Traumatic Brain Injury

Mild traumatic brain injury (TBI) involves widespread axonal injury and activation of microglia, which initiates secondary processes that worsen the TBI outcome. The upregulation of cannabinoid type-2 receptors (CB2) when microglia become activated allows CB2-binding drugs to selectively target microglia. CB2 inverse agonists modulate activated microglia by shifting them away from the harmful pro-inflammatory M1 state toward the helpful reparative M2 state and thus can stem secondary injury cascades. We previously found that treatment with the CB2 inverse agonist SMM-189 after mild TBI in mice produced by focal cranial blast rescues visual deficits and the optic nerve axon loss that would otherwise result. We have further shown that raloxifene, which is Food and Drug Administration (FDA)-approved as an estrogen receptor modulator to treat osteoporosis, but also possesses CB2 inverse agonism, yields similar benefit in this TBI model through its modulation of microglia. As many different traumatic events produce TBI in humans, it is widely acknowledged that diverse animal models must be used in evaluating possible therapies. Here we examine the consequences of TBI created by blunt impact to the mouse head for visual function and associated pathologies and assess raloxifene benefit. We found that mice subjected to impact TBI exhibited decreases in contrast sensitivity and the B-wave of the electroretinogram, increases in light aversion and resting pupil diameter, and optic nerve axon loss, which were rescued by daily injection of raloxifene at 5 or 10 mg/ml for 2 weeks. Raloxifene treatment was associated with reduced M1 activation and/or enhanced M2 activation in retina, optic nerve, and optic tract after impact TBI. Our results suggest that the higher raloxifene dose, in particular, may be therapeutic for the optic nerve by enhancing the phagocytosis of axonal debris that would otherwise promote inflammation, thereby salvaging less damaged axons. Our current work, together with our prior studies, shows that microglial activation drives secondary injury processes after both impact and cranial blast TBI and raloxifene mitigates microglial activation and visual system injury in both cases. The results thus provide a strong basis for phase 2 human clinical trials evaluating raloxifene as a TBI therapy.

Estrogen receptor agonists induce anti‑edema effects by altering α and β estrogen receptor gene expression

The present study aimed to examine whether the attenuation of estrogen receptor expression is prevented by propyl pyrazole triol (PPT), an agonist for estrogen receptor α (ERα) or and diarypropiolnitrile (DPN), an agonist for estrogen receptor β (ERβ) after traumatic brain injury (TBI). The tests performed on ovariectomized female Wistar rats included sham group, vehicle group, and treated groups: PPT, DPN, and PPT+DPN 30 minutes after TBI. Blood‑brain barrier (BBB) disruption and brain water content were estimated. RT‑PCR and\r\nwestern blotting were utilized to evaluate ESR1 and ESR2 gene and protein expression. The data indicated that PPT, DPN, and PPT+DPN attenuated TBI‑induced brain edema. Also, BBB disruption after TBI was prevented in PPT, DPN, and PPT+DPN‑treated TBI animals. Estrogen agonist‑treated animals showed a significant elevation in Esr1 mRNA and protein expression levels in the brain tissue of TBI rats. In addition, the data indicated a significant elevation of Esr2 mRNA and protein expression levels in the brain tissue of estrogen agonist‑treated TBI rats. The data shows that both ESR1 and ESR2 agonists can enhance ER mRNA and protein levels in TBI animals' brain. It appears that this effect contributes to the neuroprotective function of ER agonists.

Nanoparticulate matter exposure results in white matter damage and an inflammatory microglial response in an experimental murine model

Exposure to ambient air pollution has been associated with white matter damage and neurocognitive decline. However, the mechanisms of this injury are not well understood and remain largely uncharacterized in experimental models. Prior studies have shown that exposure to particulate matter (PM), a sub-fraction of air pollution, results in neuroinflammation, specifically the upregulation of inflammatory microglia. This study examines white matter and axonal injury, and characterizes microglial reactivity in the corpus callosum of mice exposed to 10 weeks (150 hours) of PM. Nanoscale particulate matter (nPM, aerodynamic diameter ≤200 nm) consisting primarily of traffic-related emissions was collected from an urban area in Los Angeles. Male C57BL/6J mice were exposed to either re-aerosolized nPM or filtered air for 5 hours/day, 3 days/week, for 10 weeks (150 hours; n = 18/group). Microglia were characterized by immunohistochemical double staining of ionized calcium-binding protein-1 (Iba-1) with inducible nitric oxide synthase (iNOS) to identify pro-inflammatory cells, and Iba-1 with arginase-1 (Arg) to identify anti-inflammatory/ homeostatic cells. Myelin injury was assessed by degraded myelin basic protein (dMBP). Oligodendrocyte cell counts were evaluated by oligodendrocyte transcription factor 2 (Olig2). Axonal injury was assessed by axonal neurofilament marker SMI-312. iNOS-expressing microglia were significantly increased in the corpus callosum of mice exposed to nPM when compared to those exposed to filtered air (2.2 fold increase; p<0.05). This was accompanied by an increase in dMBP (1.4 fold increase; p<0.05) immunofluorescent density, a decrease in oligodendrocyte cell counts (1.16 fold decrease; p<0.05), and a decrease in neurofilament SMI-312 (1.13 fold decrease; p<0.05) immunofluorescent density. Exposure to nPM results in increased inflammatory microglia, white matter injury, and axonal degradation in the corpus callosum of adult male mice. iNOS-expressing microglia release cytokines and reactive oxygen/ nitrogen species which may further contribute to the white matter damage observed in this model.

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.

Glia-Driven Neuroinflammation and Systemic Inflammation in Alzheimer's Disease

The neuroinflammatory hypothesis of Alzheimer's disease (AD) was proposed more than 30 years ago. The involvement of the two main types of glial cells microglia and astrocytes, in neuroinflammation, was suggested early on. In this review, we highlight that the exact contributions of reactive glia to AD pathogenesis remain difficult to define, likely due to the heterogeneity of glia populations and alterations in their activation states through the stages of AD progression. In the case of microglia, it is becoming apparent that both beneficially and adversely activated cell populations can be identified at various stages of AD, which could be selectively targeted to either limit their damaging actions or enhance beneficial functions. In the case of astrocytes, less information is available about potential subpopulations of reactive cells; it also remains elusive whether astrocytes contribute to the neuropathology of AD by mainly gaining neurotoxic functions or losing their ability to support neurons due to astrocyte damage. We identify L-type calcium channel blocker, nimodipine, as a candidate drug for AD, which potentially targets both astrocytes and microglia. It has already shown consistent beneficial effects in basic experimental and clinical studies. We also highlight the recent evidence linking peripheral inflammation and neuroinflammation. Several chronic systemic inflammatory diseases, such as obesity, type 2 diabetes mellitus, and periodontitis, can cause immune priming or adverse activation of glia, thus exacerbating neuroinflammation and increasing risk or facilitating the progression of AD. Therefore, reducing peripheral inflammation is a potentially effective strategy for lowering AD prevalence.

Microglial Responses to Brain Injury and Disease: Functional Diversity and New Opportunities

As an integral part of the innate immune system of the brain, resident microglia must react rapidly to the onset of brain injury and neurological disease. These dynamic cells then continue to shift their phenotype along a multidimensional continuum with overlapping pro- and anti-inflammatory states, allowing them to adapt to microenvironmental changes during the progression of brain disorders. However, the ability of microglia to shift phenotype through nimble molecular, structural, and functional changes comes at a cost, as the extreme pro-inflammatory states may prevent these professional phagocytes from clearing toxic debris and secreting tissue-repairing neurotrophic factors. Evolution has strongly favored heterogeneity in microglia in both the spatial and temporal dimensions-they can assume diverse roles in different brain regions, throughout the course of brain development and aging, and during the spatiotemporal progression of brain injuries and neurological diseases. Age and sex differences add further diversity to microglia functional status under physiological and pathological conditions. This article reviews recent advances in our knowledge of microglia with emphases on molecular mediators of phenotype shifts and functional diversity. We describe microglia-targeted therapeutic opportunities, including pharmacologic modulation of phenotype and repopulation of the brain with fresh microglia. With the advent of powerful new tools, research on microglia has recently accelerated in pace and may translate into potential therapeutics against brain injury and neurological disease.

Arctigenin protects against depression by inhibiting microglial activation and neuroinflammation via HMGB1/TLR4/NF-κB and TNF-α/TNFR1/NF-κB pathways

BACKGROUND AND PURPOSE

Arctigenin, a major bioactive component of Fructus arctii, has been reported to have antidepressant-like effects. However, the mechanisms underlying these effects are still unclear. Neuroinflammation can be caused by excessive production of proinflammatory cytokines in microglia via high-mobility group box 1 (HMGB1)/TLR4/NF-κB and TNF-α/TNFR1/NF-κB signalling pathways, leading to depression. In this study, we have investigated the antidepressant mechanism of arctigenin by conducting in vitro and in vivo studies.

EXPERIMENTAL APPROACH

The effects of chronic unpredictable mild stress (CUMS) on wild-type (WT) and TLR4^-/- mice were examined. Antidepressant-like effects of arctigenin were tested using the CUMS-induced model of depression in WT mice. The effects of arctigenin were assessed on the HMGB1/TLR4/NF-κB and TNF-α/TNFR1/NF-κB signalling pathways in the prefrontal cortex (PFC) of mouse brain and HMGB1- or TNF-α-stimulated primary cultured microglia. The interaction between HMGB1 and TLR4 or TNF-α and TNFR1 with or without arctigenin was examined by localized surface plasmon resonance (LSPR) and co-immunoprecipitation assays.

KEY RESULTS

The immobility times in the tail suspension test (TST) and forced swimming test (FST) were reduced in TLR4^-/- mice, compared with WT mice. Arctigenin exhibited antidepressant-like effects. Arctigenin also inhibited microglia activation and inflammatory responses in the PFC of mouse brain. Arctigenin inhibited HMGB1 and TLR4 or TNF-α and TNFR1 interactions, and suppressed both HMGB1/TLR4/NF-κB and TNF-α/TNFR1/NF-κB signalling pathways.

CONCLUSIONS AND IMPLICATIONS

Arctigenin has antidepressant-like effects by attenuating excessive microglial activation and neuroinflammation through the HMGB1/TLR4/NF-κB and TNF-α/TNFR1/NF-κB signalling pathways. This suggests that arctigenin has potential as a new drug candidate suitable for clinical trials to treat depression.

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.

COVID-19: Pain Management in Patients with SARS-CoV-2 Infection-Molecular Mechanisms, Challenges, and Perspectives

Since the end of 2019, the whole world has been struggling with the pandemic of the new Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV-2). Available evidence suggests that pain is a common symptom during Coronavirus Disease 2019 (COVID-19). According to the World Health Organization, many patients suffer from muscle pain (myalgia) and/or joint pain (arthralgia), sore throat and headache. The exact mechanisms of headache and myalgia during viral infection are still unknown. Moreover, many patients with respiratory failure get admitted to the intensive care unit (ICU) for ventilatory support. Pain in ICU patients can be associated with viral disease itself (myalgia, arthralgia, peripheral neuropathies), may be caused by continuous pain and discomfort associated with ICU treatment, intermittent procedural pain and chronic pain present before admission to the ICU. Undertreatment of pain, especially when sedation and neuromuscular blocking agents are used, prone positioning during mechanical ventilation or extracorporeal membrane oxygenation (ECMO) may trigger delirium and cause peripheral neuropathies. This narrative review summarizes current knowledge regarding challenges associated with pain assessment and management in COVID-19 patients. A structured prospective evaluation should be undertaken to analyze the probability, severity, sources and adequate treatment of pain in patients with COVID-19 infection.

Microglia: A Central Player in Depression

Microglia are the major immune cells in the central nervous system and play a key role in the normal function of the brain. Microglia exhibit functional diversity, and they control the inflammation in central nervous system through releasing inflammatory cytokine, clearing apoptotic cells via phagocytosis, regulating synaptic plasticity and the formation of neural network by synapse pruning. Recent studies have strongly indicated that the microglial dysfunction is associated with a variety of neuropsychiatric diseases such as depression, which have been termed as "microgliopathy". The emergency of advanced technologies and tools has enabled us to comprehensively understand the role of microglia in physiology and pathology, and growing studies have targetted microglia to explore the treatment of neuropsychiatric diseases. Here, we describe the key progress of microglia research, and review the recent developments in the understanding of the role of microglia in physiology and etiology of depression.

A Fatal Alliance between Microglia, Inflammasomes, and Central Pain

Microglia are the resident immune cells in the CNS, which survey the brain parenchyma for pathogens, initiate inflammatory responses, secrete inflammatory mediators, and phagocyte debris. Besides, they play a role in the regulation of brain ion homeostasis and in pruning synaptic contacts and thereby modulating neural networks. More recent work shows that microglia are embedded in brain response related to stress phenomena, the development of major depressive disorders, and pain-associated neural processing. The microglia phenotype varies between activated-toxic-neuroinflammatory to non-activated-protective-tissue remodeling, depending on the challenges and regulatory signals. Increased inflammatory reactions result from brain damage, such as stroke, encephalitis, as well as chronic dysfunctions, including stress and pain. The dimension of damage/toxic stimuli defines the amplitude of inflammation, ranging from an on-off event to low but continuous simmering to uncontrollable. Pain, either acute or chronic, involves inflammasome activation at the point of origin, the different relay stations, and the sensory and processing cortical areas. This short review aimed at identifying a sinister role of the microglia-inflammasome platform for the development and perpetuation of acute and chronic central pain and its association with changes in CNS physiology.

Benefits of progesterone on brain immaturity and white matter injury induced by chronic hypoxia in neonatal rats

OBJECTIVES

This study aims to evaluate the protective effects of progesterone on white matter injury and brain immaturity in neonatal rats with chronic hypoxia.

METHODS

Three-day old Sprague-Dawley rats were randomly divided into 3 groups: (1) control (n = 48), rats were exposed to normoxia (fraction of inspired oxygen: 21% ± 0%); (2) chronic hypoxia (n = 48), rats were exposed to hypoxia (fraction of inspired oxygen: 10.5% ± 1.0%); and (3) progesterone (n = 48), rats were exposed to hypoxia and administrated with progesterone (8 mg/kg/d). Hematoxylin-eosin staining, immunohistochemistry, real-time quantitative polymerase chain reaction, and Western blot analyses were compared on postnatal day 14 in different groups. Motor skill and coordination abilities of rats were assessed via rotation experiments.

RESULTS

Increased brain weights (P < .05), narrowed ventricular sizes (P < .01), and rotarod experiment scores (P < .01) were better in the progesterone group than in the chronic hypoxia group. The number of mature oligodendrocytes and myelin basic protein expression increased in the progesterone group compared with the chronic hypoxia group (P < .01). The polarization of M1 microglia cells in the corpus callosum of chronic hypoxia-induced hypomyelination rats was significantly increased, whereas there were fewer M2 microglia cells. Conversely, progesterone therapy had an opposite effect and caused an increase in M2 microglia polarization versus a reduction in M1 microglia cells.

CONCLUSIONS

Progesterone could prevent white matter injury and improve brain maturation in a neonatal hypoxic rat model; this may be associated with inducing a switch from M1 to M2 in microglia.

NLRP3 Depletion Fails to Mitigate Inflammation but Restores Diminished Phagocytosis in BV-2 Cells After In Vitro Hypoxia

Post-hypoxic/ischemic neuroinflammation is selectively driven by sterile inflammation, which implies the interplay of brain-intrinsic immune cells with other neural cells and immigrated peripheral immune cells. The resultant inflammatory cascade evolves extra- and intracellular pathogen and danger-associated receptors. The latter interacts with multiprotein complexes termed inflammasomes. The NLRP3 inflammasome is one of the best-described inflammasomes. However, its impact on post-ischemic neuroinflammation and its role in neuroprotection after ischemic stroke are still under debate. Microglial cells are known to be the main source of neuroinflammation; hence, we depleted NLRP3 in BV-2 microglial cells using shRNA to investigate its role in IL-1β maturation and phagocytosis after hypoxia (oxygen-glucose-deprivation (OGD)). We also examined the expression profiles of other inflammasomes (NLRC4, AIM2, ASC) and caspase-1 activity after OGD. OGD triggered caspase-1 activity and increased IL-1β secretion in BV-2 cells with no alteration after NLRP3 depletion. The expression of the AIM2 inflammasome was significantly higher after OGD in NLRP3-depleted cells, whereas NLRC4 was unaltered in all groups. Interestingly, OGD induced a complete inactivation of phagocytic activity in wild-type cells, while in NLRP3-depleted BV-2, this inactivity was restored after hypoxia. Our findings indicate a minor role of NLRP3 in the inflammatory response after hypoxic/ischemic stimulus. However, NLRP3 seems to play a pivotal role in the regulation of post-ischemic phagocytosis. This might be a prerequisite for the putative neuroprotective effect.

Regulatory Control of Microglial Phagocytosis by Estradiol and Prostaglandin E2 in the Developing Rat Cerebellum

Microglia are essential to sculpting the developing brain, and they achieve this in part through the process of phagocytosis which is regulated by microenvironmental signals associated with cell death and synaptic connectivity. In the rat cerebellum, microglial phagocytosis reaches its highest activity during the third postnatal week of development but the factors regulating this activity are unknown. A signaling pathway, involving prostaglandin E₂ (PGE₂) stimulation of the estrogen synthetic enzyme aromatase, peaks during the 2nd postnatal week and is a critical regulator of Purkinje cell maturation. We explored the relationship between the PGE₂-estradiol pathway and microglia in the maturing cerebellum. Toward that end, we treated developing rat pups with pharmacological inhibitors of estradiol and PGE₂ synthesis and then stained microglia with the universal marker Iba1 and quantified microglia engaged in phagocytosis as well as phagocytic cups in the vermis and cerebellar hemispheres. Inhibition of aromatase reduced the number of phagocytic cups in the vermis, but not in the cerebellar hemisphere at postnatal day 17. Similar results were found after treatment with nimesulide and indomethacin, inhibitors of the PGE₂-producing enzymes cyclooxygenase 1 and 2. In contrast, treatment with estradiol or PGE₂ had little effect on microglial phagocytosis in the developing cerebellum. Thus, endogenous estrogens and prostaglandins upregulate the phagocytic activity of microglia during a select window of postnatal cerebellar development, but exogenous treatment with these same signaling molecules does not further increase the already high levels of phagocytosis. This may be due to an upper threshold or evidence of resistance to exogenous perturbation.

Sex-specific effects of prenatal valproic acid exposure on sociability and neuroinflammation: Relevance for susceptibility and resilience in autism

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders with an incidence four times higher in boys than in girls. By analyzing the effect of sex in a mouse model of ASD, we were able to identify immune alterations that could underlie this sex bias. Pregnant mice were injected subcutaneously with 600 mg/kg of valproic acid (VPA) or saline at gestational day 12.5. Their male and female offspring were evaluated in a social interaction test at adulthood, and only male VPA mice showed reduced sociability levels and a lack of preference for the social stimulus over a novel object. We then analyzed the corticosterone (CORT) response to an inflammatory stimulus, as a measure of the hypothalamus-pituitary-adrenal (HPA) function, and the neuroinflammatory state in adult and young animals. Adult VPA males exhibited increased basal CORT levels, while VPA females showed levels comparable to controls. As male mice showed a blunted CORT response at PD21 when compared to female mice, we propose that this early dimorphism could explain the different effects of VPA on HPA function. In addition, prenatal VPA exposure resulted in altered astroglial and microglial cell density levels in the cerebellum and dentate gyrus of adult mice. These neuroinflammatory effects were more pronounced in females than males, and appeared at early developmental stages. Hence, these postnatal glial density differences could underlie the behavioral alterations observed in adulthood, when only males show a social deficit. Our work contributes to the understanding of biological mechanisms affected by VPA on male and female rodents and shed light on the study of possible resilience mechanisms in the female population and/or susceptibility to ASD in boys.

Sex differences in traumatic brain injury: a multi-dimensional exploration in genes, hormones, cells, individuals, and society

Traumatic brain injury (TBI) is exceptionally prevalent in society and often imposes a massive burden on patients' families and poor prognosis. The evidence reviewed here suggests that gender can influence clinical outcomes of TBI in many aspects, ranges from patients' mortality and short-term outcome to their long-term outcome, as well as the incidence of cognitive impairment. We mainly focused on the causes and mechanisms underlying the differences between male and female after TBI, from both biological and sociological views. As it turns out that multiple factors contribute to the gender differences after TBI, not merely the perspective of gender and sex hormones. Centered on this, we discussed how female steroid hormones exert neuroprotective effects through the anti-inflammatory and antioxidant mechanism, along with the cognitive impairment and the social integration problems it caused. As to the treatment, both instant and long-term treatment of TBI requires adjustments according to gender. A further study with more focus on this topic is therefore suggested to provide better treatment options for these patients.

The Importance of Restoring Body Fat Mass in the Treatment of Anorexia Nervosa: An Expert Commentary

Anorexia nervosa is a severe mental disorder that is characterised by dietary restriction, low weight and widespread endocrine abnormalities. Whilst the importance of weight restoration has been recognised in recent guidelines, the significance of normalising body fat mass has received less attention. A recent systematic review and meta-analysis found that a minimum of 20.5% body fat mass is necessary for regular menses in women with anorexia nervosa of reproductive age. This has significant implications for both treatment and research. It is important to help the patient and carers understand that a certain level of body fat percentage is essential for optimal health, such as the return of menstruation. Further research is needed into how best to use this information to help motivation to change as part of treatment. The benefit of the return of menstruation goes beyond improved fertility: it signals the normalisation of sexual hormones, which have a widespread impact on the body and multiple pathways in the brain. Given the complex functions of adipocytes in various organs of the body, the metabolic effects of the normal body fat tissue should not be underestimated. Further research is needed to elucidate the mechanisms behind the link between minimum body fat mass, menstruation, bone and brain health in anorexia nervosa.

Glucocorticoids mediate stress induction of the alarmin HMGB1 and reduction of the microglia checkpoint receptor CD200R1 in limbic brain structures

Exposure to stressors primes neuroinflammatory responses to subsequent immune challenges and stress-induced glucocorticoids (GCs) play a mediating role in this phenomenon of neuroinflammatory priming. Recent evidence also suggests that the alarmin high-mobility group box-1 (HMGB1) and the microglial checkpoint receptor CD200R1 serve as proximal mechanisms of stress-induced neuroinflammatory priming. However, it is unclear whether stress-induced GCs play a causal role in these proximal mechanisms of neuroinflammatory priming; this forms the focus of the present investigation. Here, we found that exposure to a severe acute stressor (inescapable tailshock) induced HMGB1 and reduced CD200R1 expression in limbic brain regions and pharmacological blockade of GC signaling (RU486) mitigated these effects of stress. To confirm these effects of RU486, adrenalectomy (ADX) with basal corticosterone (CORT) replacement was used to block the stress-induced increase in GCs as well as effects on HMGB1 and CD200R1. As with RU486, ADX mitigated the effects of stress on HMGB1 and CD200R1. Subsequently, exogenous CORT was administered to determine whether GCs are sufficient to recapitulate the effects of stress. Indeed, exogenous CORT induced expression of HMGB1 and reduced expression of CD200R1. In addition, exposure of primary microglia to CORT also recapitulated the effects of stress on CD200R1 suggesting that CORT acts directly on microglia to reduce expression of CD200R1. Taken together, these findings suggest that GCs mediate the effects of stress on these proximal mechanisms of neuroinflammatory priming.

Neuroimmunology of the female brain across the lifespan: Plasticity to psychopathology

The female brain is highly dynamic and can fundamentally remodel throughout the normal ovarian cycle as well as in critical life stages including perinatal development, pregnancy and old-age. As such, females are particularly vulnerable to infections, psychological disorders, certain cancers, and cognitive impairments. We will present the latest evidence on the female brain; how it develops through the neonatal period; how it changes through the ovarian cycle in normal individuals; how it adapts to pregnancy and postpartum; how it responds to illness and disease, particularly cancer; and, finally, how it is shaped by old age. Throughout, we will highlight female vulnerability to and resilience against disease and dysfunction in the face of environmental challenges.

Steroids in Stroke with Special Reference to Progesterone

Both sex and steroid hormones are important to consider in human ischemic stroke and its experimental models. Stroke initiates a cascade of changes that lead to neural cell death, but also activates endogenous protective processes that counter the deleterious consequences of ischemia. Steroids may be part of these cerebroprotective processes. One option to provide cerebroprotection is to reinforce these intrinsic protective mechanisms. In the current review, we first summarize studies describing sex differences and the influence of steroid hormones in stroke. We then present and discuss our recent results concerning differential changes in endogenous steroid levels in the brains of male and female mice and the importance of progesterone receptors (PR) during the early phase after stroke. In the third part, we give an overview of experimental studies, including ours, that provide evidence for the pleiotropic beneficial effects of progesterone and its promising cerebroprotective potential in stroke. We also highlight the key role of PR signaling as well as potential additional mechanisms by which progesterone may provide cerebroprotection.

The long and short term effects of motherhood on the brain

Becoming a mother is associated with dramatic changes in physiology, endocrinology, immune function, and behaviour that begins during pregnancy and persists into the postpartum. Evidence also suggests that motherhood is accompanied by long-term changes in brain function. In this review, we summarize the short (pregnancy and postpartum) and long-term (beyond the postpartum and into middle age) effects of pregnancy and motherhood on cognition, neuroplasticity, and neuroimmune signalling. We also discuss the effects of previous history of pregnancy and motherhood (parity) on brain health and disease (neurodegenerative diseases and stroke outcomes) and on efficacy of hormone and antidepressant treatments. Finally, we argue that pregnancy and motherhood are unique female experiences that need to be taken into account to better understand female brain function and aging.

Cerebroprotection by progesterone following ischemic stroke: Multiple effects and role of the neural progesterone receptors

Treatment with progesterone limits brain damage after stroke. However, the cellular bases of the cerebroprotective effects of progesterone are not well documented. The aims of this study were to determine neural cells and functions that are affected by progesterone treatment and the role of neural progesterone receptors (PR) after stroke. Adult male PR^NesCre mice, selectively lacking PR in the central nervous system, and their control PR^loxP/loxP littermates were subjected to transient ischemia by middle cerebral artery occlusion (MCAO) for 30 min. Mice received either progesterone (8 mg/kg) or vehicle at 1-, 6- and 24- hrs post-MCAO and outcomes were analyzed at 48 h post-MCAO. In PR^loxP/loxP mice, progesterone exerted multiple effects on different neural cell types, improved motor functional outcomes and reduced total infarct volumes. In the peri-infarct, progesterone increased the density of neurons (NeuN⁺ cells), of cells of the oligodendroglial lineage (Olig2⁺ cells) and of oligodendrocyte progenitors (OP, NG2⁺ cells). Progesterone decreased the density of activated astrocytes (GFAP⁺ cells) and reactive microglia (Iba1⁺ cells) coexpressing the mannose receptor type 1 CD206 marker. Progesterone also reduced the expression of aquaporin 4 (AQP4), the water channel involved in both edema formation and resorption. The beneficial effects of progesterone were not observed in PR^NesCre mice. Our findings show that progesterone treatment exerts beneficial effects on neurons, oligodendroglial cells and neuroinflammatory responses via PR. These findings demonstrate that progesterone is a pleiotropic cerebroprotective agent and that neural PR represent a therapeutic target for stroke cerebroprotection.

Estrogen Promotes Pro-resolving Microglial Behavior and Phagocytic Cell Clearance Through the Actions of Annexin A1

Local production of estrogen rapidly follows brain tissue injury, but the role this hormone plays in regulating the response to neural damage or in the modulation of mediators regulating inflammation is in many ways unclear. Using the murine BV2 microglia model as well as primary microglia from wild-type and annexin A1 (AnxA1) null mice, we have identified two related mechanisms whereby estradiol can modulate microglial behavior in a receptor specific fashion. Firstly, estradiol, via estrogen receptor β (ERβ), enhanced the phagocytic clearance of apoptotic cells, acting through increased production and release of the protein AnxA1. Secondly, stimulation of either ERβ or the G protein coupled estrogen receptor GPER promoted the adoption of an anti-inflammatory/pro-resolving phenotype, an action similarly mediated through AnxA1. Together, these data suggest the hypothesis that locally produced estrogen acts through AnxA1 to exert powerful pro-resolving actions, controlling and limiting brain inflammation and ultimately protecting this highly vulnerable organ. Given the high degree of receptor selectivity in evoking these responses, we suggest that the use of selective estrogen receptor ligands may hold therapeutic promise in the treatment of neuroinflammation, avoiding unwanted generalized effects.

Estrogen nuclear receptors affect cell migration by altering sublocalization of AQP2 in glioma cell lines

Glioblastomas are capable of infiltrating into neighboring brain tissues. The prognosis of a male patient is worse than that of women. Here, we demonstrate the effects of estrogen on invasion of glioma cells via regulating estrogen nuclear receptors (ERα and ERβ) combined with aquaporin 2 (AQP2). In our study, we conclude that AQP2 was located mainly in the nuclei of the glioma cell lines and is capable of inhibiting cell invasion. According to the gene ontology analysis, out of 138 screened genes, three genes of ankyrin repeat and FYVE domain containing 1 (ANKFY1), lymphocyte transmembrane adaptor 1 (LAX1), and latent transforming growth factor beta-binding protein 1 (LTBP1) were found to be regulating the ERα and ERβ. The expression of ERα was found to be high, whereas the expression of both ERβ and AQP2 was low in glioma cells from patient tissues and glioblastoma cell lines. The expression levels of AQP2, ANKFY1, LAX1, and LTBP1 were upregulated by both ERα small interfering RNA (siRNA) and overexpression of ERβ. AQP2 inhibition of cell invasion was inversely influenced by LAX1siRNA. The luciferase report system indicated that AQP2 promoted the transcriptional activity of LAX1 and inhibited cell invasion. These data suggest that ERβ may function as AQP promoter in the nucleus to sustain cells' stability by promoting AQP production, while ERα acts as an antagonist of AQP2. The ratio between ERα and ERβ is likely to affect the distribution of AQP2 in the nucleus. Low level of ERβ reduces the inhibition of invasion of glioma cells influenced by high level of LAX1 expression, leading to an increase in the invasion ability of glioma cells.

Multimodal antidepressant vortioxetine causes analgesia in a mouse model of chronic neuropathic pain

Vortioxetine is a multimodal antidepressant that potently antagonizes 5-HT3 serotonin receptors, inhibits the high-affinity serotonin transporter, activates 5-HT1A and 5-HT1B receptors, and antagonizes 5-HT1D and 5-HT7 receptors. 5-HT3 receptors largely mediate the hyperalgesic activity of serotonin that occurs in response to nerve injury. Activation of 5-HT3 receptors contributes to explain why selective serotonin reuptake inhibitors, such as fluoxetine, are not indicated in the treatment of neuropathic pain. Here, we studied the analgesic action of vortioxetine in the chronic constriction injury model of neuropathic pain in mice. Vortioxetine was injected once a day for 27 days at doses (10 mg/kg, intraperitoneally) that determine >90% 5-HT3 receptor occupancy in the central nervous system. The action of vortioxetine was compared to the action of equal doses of the serotonin-noradrenaline reuptake inhibitor, venlafaxine (one of the gold standard drugs in the treatment of neuropathic pain), and fluoxetine. Vortioxetine caused a robust analgesia in chronic constriction injury mice, and its effect was identical to that produced by venlafaxine. In contrast, fluoxetine was inactive in chronic constriction injury mice. Vortioxetine enhanced mechanical pain thresholds in chronic constriction injury mice without changing motor activity, as assessed by the open-field and horizontal bar tests. None of the three antidepressants caused analgesia in the complete Freund’s adjuvant model of chronic inflammatory pain. These findings raise the attractive possibility that vortioxetine can be effective in the treatment of neuropathic pain, particularly in patients with comorbid depression and cognitive dysfunction.

Impact of steroid hormones E2 and P on the NLRP3/ASC/Casp1 axis in primary mouse astroglia and BV-2 cells after in vitro hypoxia

Clinical and animal model studies have demonstrated the neuroprotective and anti-inflammatory effects of 17beta-estradiol (E2) and progesterone (P) in different disease models of the central nervous system (CNS) including ischemic stroke. Inflammasomes are involved in the interleukin-1 beta (IL1beta) maturation, in particular, NLRP3, the adaptor protein apoptosis-associated speck-like protein containing a CARD (ASC) and the active caspase-1 (Casp1) form. Recently, we showed that administration of E2 or P selectively regulated these components after experimental ischemic stroke in rats. Therefore, we investigated the impact of E2 and P on the NLRP3/ASC/Casp1 axis in the murine microglia-like cell line BV-2 cells and primary astrocytes after short-term in vitro hypoxia. The inflammatory cytokine IL1beta but not IL18 was increased after short-term hypoxia in astroglia and BV-2 cells. The same applied to NLPR3 and ASC. Casp1 activity was also elevated in astroglia and BV-2 cells after hypoxia. The administration of E2 or P selectively dampened IL1beta, ASC and NLRP3 expression mainly in BV-2 cells. Both steroid hormones failed to reduce Casp1 activity after hypoxia. We conclude that E2- and P-mediated anti-inflammatory mechanisms occur upstream of Casp1 through the regulation of NLRP3 and its adaptor ASC.

Sex differences in depression-like behavior and neuroinflammation in rats post-MI: role of estrogens

Patients with heart failure (HF) have a high prevalence of depression associated with a worse prognosis, particularly in older women. The present study evaluated whether sex and estrogens affect depression-like behavior and associated neuroinflammation induced by myocardial infarction (MI) in rats. MI was induced by occlusion of the left anterior descending artery in young adult male and female Wistar rats or in ovariectomized (OVX) female rats without and with estrogen [17β-estradiol (E₂)] replacement. MI groups showed a comparable degree of cardiac dysfunction. Eight weeks post-MI, male rats with HF exhibited depression-like behaviors, including anhedonia and higher immobility in the sucrose preference and forced swim tests, which were not observed in female rats with HF. In the cued fear conditioning test, male but not female rats with HF froze more than sham rats. After OVX, female sham rats developed mild depression-like behaviors that were pronounced in OVX female rats post-MI and were largely prevented by E₂ replacement. Cytokine levels in the plasma and paraventricular nucleus increased in both sexes with HF, but only male rats with HF showed an increase in cytokine levels in the prefrontal cortex. OVX alone did not affect cytokine levels, but OVX-MI caused significant increases in the prefrontal cortex, which were shifted to an anti-inflammatory pattern by E₂ replacement. These results suggest that estrogens prevent depression-like behavior induced by HF post-MI in young adult female rats by inhibiting proinflammatory cytokine production and actions in the prefrontal cortex. NEW & NOTEWORTHY In contrast to male rats, female rats with heart failure after myocardial infarction do not develop depression-like behavior or increases in prefrontal cortex cytokines. However, after ovariectomy, female rats exhibit similar changes, which are prevented by 17β-estradiol replacement. Neuroinflammation in the prefrontal cortex in male subjects may contribute to depression-like behavior, whereas its estrogen-dependent absence in female subjects may protect against depression.

Spatial Distribution and Expression of Ectonucleotidases in Rat Hippocampus After Removal of Ovaries and Estradiol Replacement

Purinergic signaling is the main synaptic and non-synaptic signaling system in brain. ATP acts as a fast excitatory transmitter, while adenosine sets a global inhibitory tone within hippocampal neuronal networks. ATP and adenosine are interconnected by ectonucleotidase enzymes, which convert ATP to adenosine. Existing data point to the converging roles of ovarian steroids and purinergic signaling in synapse formation and refinement and synapse activity in the hippocampus. Therefore, in the present study, we have used enzyme histochemistry and expression analysis to obtain data on spatial distribution and expression of ecto-enzymes NTPDase1, NTPDase2, and ecto-5'-nucleotidase (eN) after removal of ovaries (OVX) and estradiol replacement (E2) in female rat hippocampus. The results show that target ectonucleotidases are predominantly localized in synapse-rich hippocampal layers. The most represented NTPDase in the hippocampal tissue is NTPDase2, being at the same time the mostly affected ectonucleotidase by OVX and E2. Specifically, OVX decreases the expression of NTPDase2 and eN, whereas E2 restores their expression to control level. Impact of OVX and E2 on ectonucleotidase expression was also examined in purified synaptosome (SYN) and gliosome (GLIO) fractions. Data reveal that SYN expresses NTPDase1 and NTPDase2, both of which are reduced following OVX and restored with E2. GLIO exhibits NTPDase2-mediated ATP hydrolysis, which falls in OVX, and recovers by E2. These changes in the activity occur without parallel changes in NTPDase2-protein abundance. The same holds for eN. The lack of correlation between NTPDase2 and eN activities and their respective protein abundances suggest a non-genomic mode of E2 action, which is studied further in primary astrocyte culture. Since ovarian steroids shape hippocampal synaptic networks and regulate ectonucleotidase activities, it is possible that cognitive deficits seen after ovary removal may arise from the loss of E2 modulatory actions on ectonucleotidase expression in the hippocampus.

Deciphering sex differences in the immune system and depression

Certain mood disorders and autoimmune diseases are predominately female diseases but we do not know why. Here, we explore the relationship between depression and the immune system from a sex-based perspective. This review characterizes sex differences in the immune system in health and disease. We explore the contribution of gonadal and stress hormones to immune function at the cellular and molecular level in the brain and body. We propose hormonal and genetic sex specific immune mechanisms that may contribute to the etiology of mood disorders.

Sex Steroids, Adult Neurogenesis, and Inflammation in CNS Homeostasis, Degeneration, and Repair

Sex steroidal hormones coordinate the development and maintenance of tissue architecture in many organs, including the central nervous systems (CNS). Within the CNS, sex steroids regulate the morphology, physiology, and behavior of a wide variety of neural cells including, but not limited to, neurons, glia, endothelial cells, and immune cells. Sex steroids spatially and temporally control distinct molecular networks, that, in turn modulate neural activity, synaptic plasticity, growth factor expression and function, nutrient exchange, cellular proliferation, and apoptosis. Over the last several decades, it has become increasingly evident that sex steroids, often in conjunction with neuroinflammation, have profound impact on the occurrence and severity of neuropsychiatric and neurodegenerative disorders. Here, I review the foundational discoveries that established the regulatory role of sex steroids in the CNS and highlight recent advances toward elucidating the complex interaction between sex steroids, neuroinflammation, and CNS regeneration through adult neurogenesis. The majority of recent work has focused on neuroinflammatory responses following acute physical damage, chronic degeneration, or pharmacological insult. Few studies directly assess the role of immune cells in regulating adult neurogenesis under healthy, homeostatic conditions. As such, I also introduce tractable, non-traditional models for examining the role of neuroimmune cells in natural neuronal turnover, seasonal plasticity of neural circuits, and extreme CNS regeneration.

Estrogen serum concentration affects blood immune cell composition and polarization in human females under controlled ovarian stimulation

Estrogens modulate the immune system and possess anti-inflammatory properties. In line, immune cells express a variety of estrogen receptors (ER) including ER-alpha and -beta. In the present study, we examined the influence of 17beta-estradiol (E2) serum concentrations on blood leukocyte composition and their ex vivo polarization/activation status by FACS analysis in sub-fertile human females under controlled ovarian stimulation (COS). Using a set of cell-type and polarization-specific markers, we demonstrate that increased 17ß-estradiol (E2) serum concentrations yield an overall increase in leukocytes, neutrophils and monocytes but decreased lymphocytes. There was a clear ratio shift towards an increase in M2 monocytes with a protective quality and an increase in T-helper cells compared to a decrease in cytotoxic T-cells. These data support experimental findings and clinical trials, i.e. related to multiple sclerosis and other autoimmune-related diseases, that have shown a down-regulation of CD8(+) T cells and up-regulation of T-regulatory cells. Further studies have to pinpoint to which extent the immune system/-responsiveness of otherwise healthy female patients is affected by medium-term systemic E2 variations.

The Synthetic Steroid Tibolone Decreases Reactive Gliosis and Neuronal Death in the Cerebral Cortex of Female Mice After a Stab Wound Injury

Previous studies have shown that estradiol reduces reactive gliosis after a stab wound injury in the cerebral cortex. Since the therapeutic use of estradiol is limited by its peripheral hormonal effects, it is of interest to determine whether synthetic estrogenic compounds with tissue-specific actions regulate reactive gliosis. Tibolone is a synthetic steroid that is widely used for the treatment of climacteric symptoms and/or the prevention of osteoporosis. In this study, we have assessed the effect of tibolone on reactive gliosis in the cerebral cortex after a stab wound brain injury in ovariectomized adult female mice. By 7 days after brain injury, tibolone reduced the number of glial fibrillary acidic protein (GFAP) immunoreactive astrocytes, the number of ionized calcium binding adaptor molecule 1 (Iba1) immunoreactive microglia, and the number of microglial cells with a reactive phenotype in comparison to vehicle-injected animals. These effects on gliosis were associated with a reduction in neuronal loss in the proximity to the wound, suggesting that tibolone exerts beneficial homeostatic actions in the cerebral cortex after an acute brain injury.