Temporal expression of IL-1beta protein and mRNA in the brain after systemic LPS injection is affected by age and estrogen

Ovary removal modifies liver message RNA profiles in single Comb White Leghorn chickens

Ovaries produce sex hormones, and ovariectomized animals are often used as models for ovarian dysfunction. The liver is a vital organ involved in metabolism and immunity. In the present study, we conducted experiments to investigate the effects of ovariectomy on transcription and metabolic processes in the liver in chicken. Eight Single Comb White Leghorn (SCWL) female chickens were ovariectomized at 17 wk of age, and 8 intact SCWL females served as controls. At 100 wk of age, all chickens were euthanized. High-throughput transcriptome sequencing was performed on liver RNA obtained from ovariectomized and intact females. A total of 267 differentially expressed genes (DEG) were identified in our study. After analysis using DAVID functional annotation tool, one significant Kyoto Encyclopedia of Genes and Genomes pathway, the phosphatidylinositol signaling pathway, was clustered. Gene Ontology enrichment analysis yielded 46 significant Gene Ontology terms. Among terms describing biological processes, the glycerolipid metabolic and lipid localization processes were dominant. The anabolic genes, PEPCK and GK5, and the catabolic genes, VTG1; VTG2; PLD5; DGKQ; DGKE; and FABP3, were detected in ovariectomized chickens. Differentially expressed genes such as ENSGALG00000000162, IL-1Β, SVOPL, and CA12 implied that livers in ovariectomized chickens were subjected to strong inflammatory reactions, whereas defenses against endogenous materials were compromised. A comprehensive view of gene expression in the liver of ovariectomized chickens would advance our understanding of lipid metabolism, glycometabolism, and their relationships to pathologies induced by absence of the ovary. The identified DEG indicated that ovariectomy disturbed lipid metabolism in the liver and was accompanied by an increase in hepatic gluconeogenesis and reductions in phosphatidic acid synthesis and lipid carrier capacity.

NOD-like receptor protein 3 inflammasome drives postoperative mechanical pain in a sex-dependent manner

Postoperative pain management continues to be suboptimal because of the lack of effective nonopioid therapies and absence of understanding of sex-driven differences. Here, we asked how the NLRP3 inflammasome contributes to postoperative pain. Inflammasomes are mediators of the innate immune system that are responsible for activation and secretion of IL-1β upon stimulation by specific molecular signals. Peripheral IL-1β is known to contribute to the mechanical sensitization induced by surgical incision. However, it is not known which inflammasome mediates the IL-1β release after surgical incision. Among the 9 known inflammasomes, the NLRP3 inflammasome is ideally positioned to drive postoperative pain through IL-1β production because NLRP3 can be activated by factors that are released by incision. Here, we show that male mice that lack NLRP3 (NLRP3) recover from surgery-induced behavioral and neuronal mechanical sensitization faster and display less surgical site inflammation than mice expressing NLRP3 (wild-type). By contrast, female NLRP3 mice exhibit minimal attenuation of the postoperative mechanical hypersensitivity and no change in postoperative inflammation compared with wild-type controls. Sensory neuron-specific deletion of NLRP3 revealed that in males, NLRP3 expressed in non-neuronal cells and potentially sensory neurons drives postoperative pain. However, in females, only the NLRP3 that may be expressed in sensory neurons contributes to postoperative pain where the non-neuronal cell contribution is NLRP3 independent. This is the first evidence of a key role for NLRP3 in postoperative pain and reveals immune-mediated sex differences in postoperative pain.

Age and Sex Influence the Hippocampal Response and Recovery Following Sepsis

Although in-hospital mortality rates for sepsis have decreased, survivors often experience lasting physical and cognitive deficits. Moreover, older adults are more vulnerable to long-term complications associated with sepsis. We employed a murine model to examine the influence of age and sex on the brain’s response and recovery following sepsis. Young (~ 4 months) and old (~ 20 months) mice (C57BL/6) of both sexes underwent cecal ligation and puncture (CLP) with restraint stress. The hippocampal transcriptome was examined in age- and sex-matched controls at 1 and 4 days post-CLP. In general, immune- and stress-related genes increased, while neuronal, synaptic, and glial genes decreased 1 day after CLP-induced sepsis. However, specific age and sex differences were observed for the initial responsiveness to sepsis as well as the rate of recovery examined on day 4. Young females exhibited a muted transcriptional response relative to young males and old females. Old females exhibited a robust shift in gene transcription on day 1, and while most genes recovered, genes linked to neurogenesis and myelination continued to be downregulated by day 4. In contrast, old males exhibited a more delayed or prolonged response to sepsis, such that neuronal and synaptic genes continued to decrease while immune response genes continued to increase on day 4. These results suggest that aging is associated with delayed recovery from sepsis, which is particularly evident in males.

Estrogen-IGF-1 interactions in neuroprotection: ischemic stroke as a case study

The steroid hormone 17b-estradiol and the peptide hormone insulin-like growth factor (IGF)-1 independently exert neuroprotective actions in neurologic diseases such as stroke. Only a few studies have directly addressed the interaction between the two hormone systems, however, there is a large literature that indicates potentially greater interactions between the 17b-estradiol and IGF-1 systems. The present review focuses on key issues related to this interaction including IGF-1 and sex differences and common activation of second messenger systems. Using ischemic stroke as a case study, this review also focuses on independent and cooperative actions of estrogen and IGF-1 on neuroprotection, blood brain barrier integrity, angiogenesis, inflammation and post-stroke epilepsy. Finally, the review also focuses on the astrocyte, a key mediator of post stroke repair, as a local source of 17b-estradiol and IGF-1. This review thus highlights areas where significant new research is needed to clarify the interactions between these two neuroprotectants.

Effects of hormone therapy on cognition and mood

OBJECTIVE

Results of the Women's Health Initiative (WHI) and Women's Health Initiative Memory Study (WHIMS) suggested that hormone therapy (HT) may be detrimental to cognitive health. This article reviews clinical studies that address issues relevant to those results.

DESIGN

Literature review.

INTERVENTION(S)

A search of Pubmed and Web of Science was conducted using the search terms HT and cognition, HT and mood. Clinical and observational studies were selected if they were published after the year 2000. Theories of HT mechanisms of action, pharmacology, biology, and observational and clinical trials are discussed.

RESULT(S)

Although observational and clinical trials show conflicting findings, methodologic considerations must be acknowledged. HT formulation and dose, route of administration, timing of initiation, length of treatment, and health of participants all contribute to inconsistencies in results. Transdermal estradiol and micronized progesterone administered at time of menopause are generally associated with cognitive and affective benefit.

CONCLUSION(S)

At the present time, results from existing studies are equivocal regarding the benefits of HT on cognition and affect. Future studies, such as the Kronos Early Estrogen Prevention Study (KEEPS), should address methodologic inconsistencies to provide clearer answers to this important question.

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

Oestrogen has been shown to be neuroprotective for stroke and other neural injury models. Oestrogen promotes a neuroprotective phenotype through myriad actions, including stimulating neurogenesis, promoting neuronal differentiation and survival, suppressing neuroinflammation and maintaining the integrity of the blood-brain barrier. At the molecular level, oestrogen directly modulates genes that are beneficial for repair and regeneration via the canonical oestrogen receptor. Increasingly, evidence indicates that oestrogen acts in concert with growth factors to initiate neuroprotection. Oestrogen and insulin-like growth factor (IGF)-1 act cooperatively to influence cell survival, and combined steroid hormone/growth factor interaction has been well documented in the context of neurones and astrocytes. Here, we summarise the evidence that oestrogen-mediated neuroprotection is critically dependent on IGF-1 signalling, and specifically focus on microglia as the source of IGF-1 and the locus of oestrogen-IGF-1 interactions in stroke neuroprotection.

Age-related changes in brain support cells: Implications for stroke severity

Stroke is one of the leading causes of adult disability and the fourth leading cause of mortality in the US. Stroke disproportionately occurs among the elderly, where the disease is more likely to be fatal or lead to long-term supportive care. Animal models, where the ischemic insult can be controlled more precisely, also confirm that aged animals sustain more severe strokes as compared to young animals. Furthermore, the neuroprotection usually seen in younger females when compared to young males is not observed in older females. The preclinical literature thus provides a valuable resource for understanding why the aging brain is more susceptible to severe infarction. In this review, we discuss the hypothesis that stroke severity in the aging brain may be associated with reduced functional capacity of critical support cells. Specifically, we focus on astrocytes, that are critical for detoxification of the brain microenvironment and endothelial cells, which play a crucial role in maintaining the blood brain barrier. In view of the sex difference in stroke severity, this review also discusses studies of middle-aged acyclic females as well as the effects of the estrogen on astrocytes and endothelial cells.

Role and interactions of annexin A1 and oestrogens in the manifestation of sexual dimorphisms in cerebral and systemic inflammation

BACKGROUND AND PURPOSE

Gender differences in inflammation are well described, with females often showing more robust, oestrogen-associated responses. Here, we investigated the influence of gender, oestrogen and the anti-inflammatory protein annexin A1 (AnxA1) on lipopolysaccharide (LPS)-induced leukocyte-endothelial cell interactions in murine cerebral and mesenteric microvascular beds.

EXPERIMENTAL APPROACH

Intravital microscopy was used to visualize and quantify the effects of LPS (10 μg·per mouse i.p.) on leukocyte-endothelial interactions in male and female wild-type (WT) mice. The effects of ovariectomy ± oestrogen replacement were examined in WT and AnxA1-null (AnxA1(-/-) ) female mice.

KEY RESULTS

LPS increased leukocyte adherence in the cerebral and mesenteric beds of both male and female WT mice; females showed exacerbated responses in the brain versus males, but not the mesentery. Ovariectomy further enhanced LPS-induced adhesion in the brain but not the mesentery; its effects were reversed by oestrogen treatment. OVX AnxA1(-/-) mice also showed exaggerated adhesive responses to LPS in the brain. However, these were unresponsive to ovariectomy and, paradoxically, responded to oestrogen with a pronounced increase in basal and LPS-induced leukocyte adhesion in the cerebrovasculature.

CONCLUSIONS AND IMPLICATIONS

Our data confirm the fundamental role of AnxA1 in limiting the inflammatory response in the central and peripheral microvasculature. They also (i) show that oestrogen acts via an AnxA1-dependent mechanism to protect the cerebral, but not the mesenteric, vasculature from the damaging effects of LPS and (ii) reveal a paradoxical and potentially toxic effect of the steroid in potentiating the central response to LPS in the absence of AnxA1.

Decisive role of Reelin signaling during early stages of Alzheimer's disease

Alzheimer's disease (AD) is one of the largest unmet medical concerns of our society. Around 25 million patients worldwide together with their families are still waiting for an effective treatment. We have recently initiated a re-evaluation of our knowledge of the molecular and cellular mechanisms underlying sporadic AD. Based on the existing literature, we have proposed a mechanistic explanation of how the late-onset form of the disease may evolve on the cellular level. Here, we expand this hypothesis by addressing the pathophysiological changes underlying the early and almost invariant appearance of the neurofibrillary tangles, the only reliable correlate of the cognitive status, in distinct brain areas and their consistent "spread" along interconnected neurons as the disease advances. In this review we present and discuss novel evidence that the extracellular signaling protein Reelin, expressed along the olfactory and limbic pathways in the adult brain, might hold a key to understand the earliest steps of the disease, highlighting the olfactory pathway as the brain's Achilles heel involved in the initiation of the pathophysiological characteristic of late-onset AD.

Cytokine signaling modulates blood-brain barrier function

The blood-brain barrier (BBB) provides a vast interface for cytokines to affect CNS function. The BBB is a target for therapeutic intervention. It is essential, therefore, to understand how cytokines interact with each other at the level of the BBB and how secondary signals modulate CNS functions beyond the BBB. The interactions between cytokines and lipids, however, have not been fully addressed at the level of the BBB. Here, we summarize current understanding of the localization of cytokine receptors and transporters in specific membrane microdomains, particularly lipid rafts, on the luminal (apical) surface of the microvascular endothelial cells composing the BBB. We then illustrate the clinical context of cytokine effects on the BBB by neuroendocrine regulation and amplification of inflammatory signals. Two unusual aspects discussed are signaling crosstalk by different classes of cytokines and genetic regulation of drug efflux transporters. We also introduce a novel area of focus on how cytokines may act through nuclear hormone receptors to modulate efflux transporters and other targets. A specific example discussed is the ATP-binding cassette transporter-1 (ABCA-1) that regulates lipid metabolism. Overall, cytokine signaling at the level of the BBB is a crucial feature of the dynamic regulation that can rapidly change BBB function and affect brain health and disease.

A lack of ovarian function increases neuroinflammation in aged mice

Although several lines of evidence have indicated that menopause is associated with increased susceptibility to neurological disorders, the mechanisms involved in this phenomenon remain to be elucidated. Because neuroinflammation is a common feature of a number of brain diseases, we hypothesized that the cessation of ovarian functions and the consequent decrease in estrogen receptor (ER)-mediated antiinflammatory activity may represent a trigger for postmenopausal brain dysfunctions. The aim of the present study was to investigate the effects of aging and surgical menopause on the activity of ER in neuroinflammation. The present study shows that ER genes are expressed in the hippocampus, but ER transcriptional activity decreases significantly beginning at 12 months of age in intact and ovariectomized mice. With ovariectomy, we observe an age-dependent accumulation of mRNA encoding inflammatory mediators (e.g. TNFα, IL1β, and macrophage inflammatory protein-2) and changes in the morphology of astroglia and microglia. In addition, we show that aging itself is coupled with an exaggerated response to acute inflammatory stimuli with a major accumulation of TNFα, IL1β, macrophage inflammatory protein-2, and macrophage chemoattractant protein-1 mRNA in response to lipopolysaccharide administration. The response to acute inflammatory stimuli appears to be differentially modulated by the duration of hormone deprivation in 12-month-old mice. Taken together, the present results show that aging is associated with decreased ER activity, despite continuous ER synthesis, and that age-dependent neuroinflammation is strongly influenced by hormone deprivation.

Attractiveness of illness-associated odorant cues in female rats is modulated by ovarian hormones, but not associated with pro-inflammatory cytokine levels

Odorant cues released by rodents play a key role in mate preference/selection. The goal of the following series of studies was to determine the impact of acute illness, and the potential role of the inflammatory response, on the release of illness-associated odor cues from female rats. Adult female Sprague-Dawley rats were injected with lipopolysaccharide (LPS, 100 μg/kg) and their soiled bedding was used as a stimulus to naïve male odor recipients. While odored bedding from sick males elicited a robust avoidance response evidenced by decreased sniffing, avoidance and burying behavior, odored bedding from sick females elicited only a reduction in sniffing, indicating a reduction in odor attractiveness. Odor cues from ovariectomized, but not sham-operated females decreased sniffing behavior and increased avoidance in male odor recipients. Acute estradiol benzoate (EB, 20 μg/kg) replacement into ovariectomized females restored the investigatory response of male recipients toward odor cues, while LPS administration into ovariectomized oil or EB treated females had little impact on odor attractiveness. Measurement of cytokines in both brain (the paraventricular nucleus of the hypothalamus) and blood from female odor donors indicated increased expression of TNF-α, IL-1β, and IL-6 following LPS, which was not affected by EB treatment. These findings illustrate a critical sexual dimorphism by demonstrating that acute illness reduces the attractiveness of female odor, whereas odor cues from sick males are highly aversive. Moreover, the attractiveness of female odor appears to be associated with circulating ovarian hormone levels, but not central or peripheral inflammatory cytokines.

Sex hormones, aging, and Alzheimer's disease

A promising strategy to delay and perhaps prevent Alzheimer's disease (AD) is to identify the age-related changes that put the brain at risk for the disease. A significant normal age change known to result in tissue-specific dysfunction is the depletion of sex hormones. In women, menopause results in a relatively rapid loss of estradiol and progesterone. In men, aging is associated with a comparatively gradual yet significant decrease in testosterone. We review a broad literature that indicates age-related losses of estrogens in women and testosterone in men are risk factors for AD. Both estrogens and androgens exert a wide range of protective actions that improve multiple aspects of neural health, suggesting that hormone therapies have the potential to combat AD pathogenesis. However, translation of experimental findings into effective therapies has proven challenging. One emerging treatment option is the development of novel hormone mimetics termed selective estrogen and androgen receptor modulators. Continued research of sex hormones and their roles in the aging brain is expected to yield valuable approaches to reducing the risk of AD.

Sex hormones, aging, and Alzheimer's disease

A promising strategy to delay and perhaps prevent Alzheimer's disease (AD) is to identify the age-related changes that put the brain at risk for the disease. A significant normal age change known to result in tissue-specific dysfunction is the depletion of sex hormones. In women, menopause results in a relatively rapid loss of estradiol and progesterone. In men, aging is associated with a comparatively gradual yet significant decrease in testosterone. We review a broad literature that indicates age-related losses of estrogens in women and testosterone in men are risk factors for AD. Both estrogens and androgens exert a wide range of protective actions that improve multiple aspects of neural health, suggesting that hormone therapies have the potential to combat AD pathogenesis. However, translation of experimental findings into effective therapies has proven challenging. One emerging treatment option is the development of novel hormone mimetics termed selective estrogen and androgen receptor modulators. Continued research of sex hormones and their roles in the aging brain is expected to yield valuable approaches to reducing the risk of AD.

Dopaminergic neuroprotection of hormonal replacement therapy in young and aged menopausal rats: role of the brain angiotensin system

There is a lack of consensus about the effects of the type of menopause (surgical or natural) and of oestrogen replacement therapy on Parkinson's disease. The effects of the timing of replacement therapy and the female's age may explain the observed differences in such effects. However, the mechanisms involved are poorly understood. The renin-angiotensin system mediates the beneficial effects of oestrogen in several tissues, and we have previously shown that dopaminergic cell loss is enhanced by angiotensin via type 1 receptors, which is activated by ageing. In rats, we compared the effects of oestrogen replacement therapy on 6-hydroxydopamine-induced dopaminergic degeneration, nigral renin-angiotensin system activity, activation of the nicotinamide adenine dinucleotide phosphate oxidase complex and levels of the proinflammatory cytokine interleukin-1β in young (surgical) menopausal rats and aged menopausal rats. In young surgically menopausal rats, the renin-angiotensin system activity was higher (i.e. higher angiotensin converting enzyme activity, higher angiotensin type-1 receptor expression and lower angiotensin type-2 receptor expression) than in surgically menopausal rats treated with oestrogen; the nicotinamide adenine dinucleotide phosphate oxidase activity and interleukin-1β expression were also higher in the first group than in the second group. In aged menopausal rats, the levels of nigral renin-angiotensin and nicotinamide adenine dinucleotide phosphate oxidase activity were similar to those observed in surgically menopausal rats. However, oestrogen replacement therapy significantly reduced 6-hydroxydopamine-induced dopaminergic cell loss in young menopausal rats but not in aged rats. Treatment with oestrogen also led to a more marked reduction in nigral renin-angiotensin and nicotinamide adenine dinucleotide phosphate oxidase activity in young surgically menopausal rats (treated either immediately or after a period of hypo-oestrogenicity) than in aged menopausal rats. Interestingly, treatment with the angiotensin type-1 receptor antagonist candesartan led to remarkable reduction in renin-angiotensin system activity and dopaminergic neuron loss in both groups of menopausal rats. This suggests that manipulation of the brain renin-angiotensin system may be an efficient approach for the prevention or treatment of Parkinson's disease in oestrogen-deficient females, together with or instead of oestrogen replacement therapy.

Production of proinflammatory cytokines and chemokines during neuroinflammation: novel roles for estrogen receptors alpha and beta

Neuroinflammation is a common feature of many neurological disorders, and it is often accompanied by the release of proinflammatory cytokines and chemokines. Estradiol-17β (E2) exhibits antiinflammatory properties, including the suppression of proinflammatory cytokines, in the central nervous system. However, the mechanisms employed by E2 and the role(s) of estrogen receptors (ERs) ERα and ERβ are unclear. To investigate these mechanisms, we employed an in vivo lipopolysaccharide (LPS) model of systemic inflammation in ovariectomized (OVX) and OVX and E2-treated (OVX+E2) mice. Brain levels of proinflammatory cytokines (IL-1β, IL-6, and IL-12p40) and chemokines (CCL2/MCP-1, CCL3/MIP-1α, CCL5/RANTES, and CXCL1/KC) were quantified in mice at 0 (sham), 3, 6, 12, and 24 h after infection using multiplex protein analysis. E2 treatment inhibited LPS-induced increases in all cytokines. In contrast, E2 treatment only suppressed CCL/RANTES chemokine concentrations. To determine whether ERα and ERβ regulate brain cytokine and chemokine levels, parallel experiments were conducted using ERα knockout and ERβ knockout mice. Our results revealed that both ERα and ERβ regulated proinflammatory cytokine and chemokine production through E2-dependent and E2-independent mechanisms. To assess whether breakdown of the blood-brain barrier is an additional target of E2 against LPS-induced neuroinflammation, we measured Evan's blue extravasation and identified distinct roles for ERα and ERβ. Taken together, these studies identify a dramatic cytokine- and chemokine-mediated neuroinflammatory response that is regulated through ERα- and ERβ-mediated ligand-dependent and ligand-independent mechanisms.

A high cholesterol diet elevates hippocampal cytokine expression in an age and estrogen-dependent manner in female rats

BACKGROUND

While the effects of a proatherogenic diet have been widely studied in the context of systemic inflammation, much less is known about its effects on central or brain inflammation and its modulation with age. In this study, we examined the effect of a high cholesterol/choline diet in adult and older acyclic females to assess its impact on systemic and central inflammatory markers. Moreover, since the loss of ovarian hormones at menopause may predispose women to increased production of pro-inflammatory cytokines, we also tested the impact of estrogen replacement to adult and older females in diet-induced inflammation.

METHODS

Ovariectomized adult female rats and older (reproductive senescent) female rats were replaced with estrogen or a control pellet and maintained thereafter on a diet containing either 4% cholesterol/1% choline or control chow for 10 weeks. Interleukin 1beta (IL-1beta) expression in the liver was used as a marker of systemic inflammation, while a panel of cytokine/chemokines were used to examine the effects of diet on the hippocampus.

RESULTS

IL-1beta expression was elevated in the liver of adult and reproductive senescent females fed with the high cholesterol diet, although this was restricted to groups that were ovariectomized and not replaced with estrogen. Estrogen-treated animals of both ages did not have elevated IL-1beta levels when fed the high cholesterol diet. Diet-induced changes in cytokine/chemokine expression in the hippocampus however were critically age dependent and restricted to the reproductive senescent females. In this group, the high cholesterol diet led to an increase in interleukin (IL)-4, IL-6, IL-12p70, IL-13, RANTES (Regulated on Activation, Normal T Expressed and Secreted) and VEGF (vascular endothelial growth factor). Moreover, estrogen treatment to reproductive senescent females suppressed diet-induced expression of specific cytokines (RANTES, VEGF, IL-6) and attenuated the expression of others (IL-4, IL-12p70, and IL-13).

CONCLUSIONS

These data indicate that a proatherogenic diet presents a significant risk for central inflammation in older females that are deprived of estrogen treatment.

Estradiol regulation of lipocalin-type prostaglandin D synthase promoter activity: evidence for direct and indirect mechanisms

In the CNS, lipocalin-type prostaglandin D synthase (L-PGDS) is predominantly a non-neuronal enzyme responsible for the production of PGD(2), an endogenous sleep promoting substance. We have previously demonstrated that estradiol differentially regulates L-PGDS transcript levels in the rodent brain. In hypothalamic nuclei, estradiol increases L-PGDS transcript expression, whereas in the ventrolateral preoptic area L-PGDS gene expression is reduced after estradiol treatment. In the present study, we have used an immortalized glioma cell line transfected with a L-PGDS reporter construct and estrogen receptor (ER) alpha and ERbeta expression plasmids to further elucidate the mechanisms underlying estradiol regulation of L-PGDS gene expression. We found that physiologically relevant concentrations of estradiol evoked an inverted U response in cells expressing ERalpha. The most effective concentration of estradiol (10(-11)M) increased the promoter activity 3-fold over baseline. Expression of ERbeta did not increase activity over control and when ERbeta was co-expressed with ERalpha there was a significant attenuation of the promoter activity. While ERalpha significantly increased L-PGDS promoter activity, our previous in vivo studies demonstrate a greater magnitude of change in L-PGDS gene expression in the presences of estradiol. This led us to ask whether estradiol is signaling via a paracrine factor released by the neighboring neurons. Conditioned media from estradiol treated neurons applied to the glioma cell line resulted in a significant 7-fold increase in L-PGDS promoter activity supporting the possibility that neuronal-glial interactions are involved in estradiol regulation of L-PGDS.

Sickness-related odor communication signals as determinants of social behavior in rat: a role for inflammatory processes

Infected animals are avoided by conspecifics, suggesting that the inflammatory cascade may play a significant role in odor communication. Injection of male rats with the bacterial mimetic, lipopolysaccharide (LPS, 100 microg/kg, i.p.), decreased investigation through a wire-mesh partition between healthy male partners. This avoidance response was observed in adult males in response to soiled bedding collected from sick rats, regardless of whether LPS was injected peripherally (100 microg/kg, i.p.) or centrally (0.25 or 2.5 microg, icv). The release of sickness-related odor cues was dose-dependently blocked by icv infusion of the anti-inflammatory cytokine, interleukin-10 (IL-10; 20 or 200 ng), and reproduced by icv infusion of pro-inflammatory cytokine, IL-1beta (5 or 50 ng). Subcutaneous pretreatment with either estradiol benzoate (20 microg/kg) or testosterone propionate (50 or 500 microg/kg) to adult males that were administered LPS inhibited release of aversive odor cues, but these hormones alone did not influence odor properties. Importantly, the avoidance response to sickness-related odor was not associated with changes in plasma corticosterone, testosterone, or IL-6 levels of odor donors. However, plasma IL-1beta concentrations of sick animals was in fact predictive of aversive responses in conspecifics, suggesting that the inflammatory cascade, but not plasma steroid hormones, is likely to mediate aversive properties in odor that functions to signal illness state to conspecifics.

LPS-induced iNOS expression in Bv-2 cells is suppressed by an oxidative mechanism acting on the JNK pathway--a potential role for neuroprotection

Activated microglia cells, observed during chronic inflammation, produce and secrete compounds that at high concentrations or during sustained production might cause neuronal cell death. Inducible nitric oxide synthase (iNOS) is expressed in response to various immunological stimuli and catalyses the formation of the free radical nitric oxide (NO), that at low and regulated levels participate in cell signaling and cytoprotective events, whereas its higher and unregulated production can promote neurotoxicity in cells or in tissues. Regulation of NO production is therefore central for maintaining NO-levels within a safe window. We have analyzed iNOS protein expression and NO production, in murine microglial Bv-2 cells after 16h treatment with the bacterial endotoxin lipopolysaccharide (LPS). We have further analyzed three MAPK pathways, by co-treating the cells with LPS and the inhibitors of ERK1/2, p38 or JNK MAPK activities. To investigate participation of an oxidative regulatory mechanism, cells were also treated with the antioxidant N-acetyl-L-cysteine (NAC). Our results show that LPS-induced iNOS expression in Bv-2 cells is mainly mediated through JNK MAPK. In addition, co-treatment of the Bv-2 cells with LPS and NAC surprisingly further increased the iNOS expression, an effect also found to be mediated through the JNK MAPK pathway. The level of phosphorylated JNK MAPK (p46) was strongly increased by LPS alone and was further increased when combined with NAC. Our data indicate that iNOS and NO production are suppressed by an oxidative mechanism acting on the JNK MAPK pathway and we speculate that it might constitute a potential regulatory mechanism controlling the NO level.

Regulation of cytokine signaling and T-cell recruitment in the aging mouse brain in response to central inflammatory challenge

Aging is often accompanied by increased levels of inflammatory molecules in the organism, but age-related changes in the brain response to inflammatory challenges still require clarification. We here investigated in mice whether cytokine signaling and T-cell neuroinvasion undergo age-related changes. We first analyzed the expression of molecules involved in T-cell infiltration and cytokine signaling regulation in the septum and hippocampus of 2-3 months and 20- to 24-month-old mice at 4h after intracerebroventricular injections of tumor necrosis factor (TNF)-alpha or interferon-gammaversus saline injections. Transcripts of the chemokine CXCL9, intercellular adhesion molecule (ICAM)-1 and suppressor of cytokine signaling molecules (SOCS) 1 and 3 were increased in both age groups after cytokine injection; microglia-derived matrix metalloproteinase (MMP) 12 mRNA was induced in old mice also after control saline injections. Age-related changes in ICAM-1 protein expression and T-cell infiltration were then analyzed in mice of 3-4, 8-9 and 15-16 months at 48h after TNF-alpha injections. ICAM-1 immunoreactivity, and Western blotting in striatum, septum, hippocampus and hypothalamus showed progressive age-related enhancement of TNF-alpha-elicited ICAM-1 upregulation. Double immunofluorescence revealed ICAM-1 expression in microglia and astrocytic processes. CD3(+), CD4(+) and CD8(+) T-cells exhibited progressive age-related increases in brain parenchyma and choroid plexus after cytokine exposure. The findings indicate that the brain responses to inflammatory challenges are not only preserved with advancing age, but also include gradual amplification of ICAM-1 expression and T-cell recruitment. The data highlight molecular and cellular correlates of age-related increase of brain sensitivity to inflammatory stimuli, which could be involved in altered brain vulnerability during aging.

Protective actions of sex steroid hormones in Alzheimer's disease

Risk for Alzheimer's disease (AD) is associated with age-related loss of sex steroid hormones in both women and men. In post-menopausal women, the precipitous depletion of estrogens and progestogens is hypothesized to increase susceptibility to AD pathogenesis, a concept largely supported by epidemiological evidence but refuted by some clinical findings. Experimental evidence suggests that estrogens have numerous neuroprotective actions relevant to prevention of AD, in particular promotion of neuron viability and reduction of beta-amyloid accumulation, a critical factor in the initiation and progression of AD. Recent findings suggest neural responsiveness to estrogen can diminish with age, reducing neuroprotective actions of estrogen and, consequently, potentially limiting the utility of hormone therapies in aged women. In addition, estrogen neuroprotective actions are also modulated by progestogens. Specifically, continuous progestogen exposure is associated with inhibition of estrogen actions whereas cyclic delivery of progestogens may enhance neural benefits of estrogen. In recent years, emerging literature has begun to elucidate a parallel relationship of sex steroid hormones and AD risk in men. Normal age-related testosterone loss in men is associated with increased risk to several diseases including AD. Like estrogen, testosterone has been established as an endogenous neuroprotective factor that not only increases neuronal resilience against AD-related insults, but also reduces beta-amyloid accumulation. Androgen neuroprotective effects are mediated both directly by activation of androgen pathways and indirectly by aromatization to estradiol and initiation of protective estrogen signaling mechanisms. The successful use of hormone therapies in aging men and women to delay, prevent, and or treat AD will require additional research to optimize key parameters of hormone therapy and may benefit from the continuing development of selective estrogen and androgen receptor modulators.

Influence of continuous infusion of interleukin-1beta on depression-related processes in mice: corticosterone, circulating cytokines, brain monoamines, and cytokine mRNA expression

RATIONALE

Activation of the immune system typically occurs on a subchronic or chronic basis (e.g., in response to bacterial or viral insults). However, analyses of the effects of cytokine treatments have typically involved acute treatments, and limited data are available concerning the behavioral and central neurochemical impact of subchronic interleukin-1beta (IL-1beta) administration.

OBJECTIVES

Several peripheral and central effects of IL-1beta treatment were assessed following single or repeated bolus injections or after infusion of the cytokine (through Alzet minipumps) over several days.

RESULTS

The impact of an acute bolus injection of IL-1beta (1.0 microg) on plasma corticosterone and on circulating IL-1beta, IL-6, and TNF-alpha were diminished following 5-day IL-1beta treatment, although high levels of sickness were still apparent. When IL-1beta (1.0 or 2.0 mug/day) was continuously infused over 3 days, plasma corticosterone and sickness were elevated, but these effects were attenuated after 7 days (subchronic) of treatment. As well, the effects of IL-1beta treatment on diurnal variations of motor activity diminished over days. Despite the diminution of the behavioral and neuroendocrine effects of the cytokine after treatment 7 days, subchronic IL-1beta infusion altered prefrontal cortical and hippocampal serotonin and norepinephrine utilization, and within these regions, the messenger RNA (mRNA) expression of IL-1beta, IL-6, TNF-alpha, and their receptors, as well as that of 5-HT(2C), 5-HT(1B) receptors, and p11, was increased.

DISCUSSION

The findings indicate that peripheral cytokine infusion markedly influences central cytokine mRNA expression and also influences 5-HT turnover, which might contribute to behavioral changes elicited by IL-1beta.

Effects of estrogen on temporal expressions of IL-1beta and IL-1ra in rat organotypic hippocampal slices exposed to oxygen-glucose deprivation

Anti-inflammatory action of estrogen is involved in neuroprotection but the effects of estrogen on IL-1beta and its endogenous antagonist (IL-1 ra) have not been clearly defined in the ischemic brain. This study was performed to evaluate whether estrogen affects the expression of IL-1beta or IL-1ra and the ratio of the two in the ischemic hippocampus. Rat organotypic hippocampal slices were treated with 17beta estradiol (E2, 1 nM) for 7 days, exposed to oxygen-glucose deprivation (OGD) for 30 min, and then reperfused for 72 h. CA1 neuronal death quantified by propidium iodide (PI) staining and expressions of IL-1beta and IL-1ra in slices measured by real-time PCR and Western blotting were examined. PI intensities in CA1 in slices treated with E2 were significantly reduced at 24 h and 72 h post-OGD, and IL-1beta mRNA expressions were reduced at 6 h and 24 h post-OGD. In addition, IL-1ra mRNA was significantly overexpressed and the ratio of IL-1beta to IL-1ra mRNA expression was reduced by E2 especially at 24 h. In terms of protein levels, E2 downregulated IL-1beta but upregulated IL-1ra and thereby decreased the IL-1beta/IL-1 ra ratio at 24h. These findings demonstrate that estrogen-induced protection is associated with a decrease in IL-1beta and an increase in IL-1ra expression in the ischemic hippocampus during early reperfusion periods, which suggests that modulation of IL-1beta/IL-1ra might be a part of anti-inflammatory effects of estrogen.

Effects of estrogen receptor agonists on regulation of the inflammatory response in astrocytes from young adult and middle-aged female rats

Estrogen has been shown to attenuate the inflammatory response following injury or lipopolysaccharide treatment in several organ systems. Estrogen's actions are transduced through two estrogen receptor sub-types, estrogen receptor (ER) -alpha and estrogen receptor-beta, whose actions may be overlapping or independent of each other. The present study examined the effects of ERalpha- and ERbeta-specific ligands in regulating the inflammatory response in primary astrocyte cultures. Pre-treatment with 17beta-estradiol (ERalpha/ERbeta agonist), HPTE (ERalpha agonist/ERbeta antagonist) and DPN (ERbeta agonist) led to attenuation of IL-1beta, TNFalpha, and MMP-9 in astrocyte media derived from young adult (3-4 mos.) and reproductive senescent female (9-11 mos., acyclic) astrocyte cultures, while pretreatment with PPT (ERalpha agonist) attenuated IL-1beta (but not MMP-9) in both young and senescent-derived astrocyte cultures. Our previous work determined that 17beta-estradiol was unable to attenuate the LPS-induced increase in IL-1beta in olfactory bulb primary microglial cultures derived from either young adult or reproductive senescent females. In young adult-derived microglial cultures, the LPS-induced increase in IL-1beta was not attenuated by pre-treatment with 17beta-estradiol, PPT or HPTE. Interestingly, the ERbeta agonist, DPN significantly decreased IL-1beta following LPS treatment in young adult-derived microglia. Thus while both microglia and astrocytes synthesize and release inflammatory mediators, the present data shows that compounds which bind ERbeta are more effective in attenuating proinflammatory cytokines in both cell types and may therefore be a more effective agent for future therapeutic use.

More than a decade of estrogen neuroprotection

Considerable evidence has emerged through more than a decade of research supporting the neuroprotective and cognition-preserving effects of estrogens. Such basic research coupled with various epidemiological studies led quickly to the assessment of Premarin for the treatment of mild to moderate Alzheimer's disease (AD), initiated by the Alzheimer's Disease Cooperative Study Group and headed by Dr. Leon Thal. While this and subsequent trials with Premarin (Wyeth Research, Monmouth Junction, New Jersey) and PremPro (Wyeth Research), a conjugated equine estrogen preparation plus medoxyprogresterone acetate, have not supported the use of estrogens in treating advanced AD, considerable inferences have been made from these placebo controlled trials of estrogens. Here, we aimed to put these AD trials of estrogens in perspective by considering the potential mechanisms of these potent neuroprotective estrogens, the role of estrogens in other neurodegenerative conditions, such as cerebral ischemia, and based on our current understanding of estrogen neurobiology, offer insight into the design of future clinical trails of estrogens for neuronal protection.

The function of microglia, either neuroprotection or neurotoxicity, is determined by the equilibrium among factors released from activated microglia in vitro

Opposing functions of activated microglia, namely neuroprotection or neurotrophy versus neurodestruction or neurotoxicity, have been observed in a number of experimental models of neurotrauma and neurodegenerative diseases. However, the mechanism(s) involved in the determination of which function activated microglia execute under a given set of conditions still remains to be elucidated. Our current in vitro study has revealed that a neuroprotective/neurotrophic or a neurodestructive/neurotoxic microglial function may be configured by the equilibrium among various microglial factors released into the microenvironment. When NSC-34 neurons were treated with lower concentrations of lipopolysaccharide-stimulated BV-2 microglial conditioned medium (LPS-BVCM), viability of the NSC-34 neurons increased, outgrowth of neuronal processes was promoted, and the formation of 2,5-hexanedione-induced aggregates was prevented. However, when NSC-34 neurons were treated with higher concentrations of the same LPS-BVCM, neuronal viability was reduced, apoptosis was induced and outgrowth of neuronal processes was prevented. Measurement of the cytokines tumor necrotic factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and IL-6 in the LPS-BVCM has shown that the upregulation in expression for each cytokine varied both temporally and quantitatively. It is postulated that an alteration in the concentration of the LPS-BVCM might significantly affect the functional balance of microglial factors in the microenvironment with a resultant different microglial function.

Microglia-mediated neurotoxicity: uncovering the molecular mechanisms

Mounting evidence indicates that microglial activation contributes to neuronal damage in neurodegenerative diseases. Recent studies show that in response to certain environmental toxins and endogenous proteins, microglia can enter an overactivated state and release reactive oxygen species (ROS) that cause neurotoxicity. Pattern recognition receptors expressed on the microglial surface seem to be one of the primary, common pathways by which diverse toxin signals are transduced into ROS production. Overactivated microglia can be detected using imaging techniques and therefore this knowledge offers an opportunity not only for early diagnosis but, importantly, for the development of targeted anti-inflammatory therapies that might slow or halt the progression of neurodegenerative disease.

Evidence to Implicate Early Modulation of Interleukin‐1β Expression in the Neuroprotection Afforded by 17β‐Estradiol in Male Rats Undergone Transient Middle Cerebral Artery Occlusion

Neuroprotection exerted by 17beta-estradiol (17beta-E(2)) has been widely investigated in animal models of acute cerebral ischemia. Estrogens interact with intracellular receptors (ERalpha and ERbeta) to modulate the transcription of target genes, including those implicated in neuronal survival. Neuroprotection may also occur via interaction with ER-like membrane receptors mediating rapid, non-genomic, actions or via receptor-independent mechanisms. There is also evidence that blockade of inflammatory factors may represent an important mechanism involved in estrogenic neuroprotection. Here we investigate whether reduced brain damage by acute pharmacological treatment with 17beta-E(2) in male rats subjected to transient (2h) middle cerebral artery occlusion (tMCAo) involves modulation of interleukin-1beta (IL-1beta), a proinflammatory cytokine strongly implicated in the pathophysiology of ischemic stroke. Administration of 17beta-E(2) (0.2mg/kg, i.p., 1h before tMCAo) results in significant reduction of brain infarct volume, and this is reverted by the ER antagonist ICI 182,780 (0.25mg/kg, i.p.) administered 1h before 17beta-E(2). Two hours MCAo followed by 2-h reperfusion results in a significant, threefold increase of IL-1beta levels in the cortical tissue ipsilateral to the ischemic damage. Interestingly, a pretreatment with a neuroprotective dose of 17beta-E(2) attenuates the cytokine elevation and this appears to occur through ER activation. In addition, neuroprotection by 17beta-E(2) is accompanied by reduced cytochrome c translocation both in the striatum and in the cortex as revealed by Western blotting 3h after reperfusion. In conclusion, we report the original observation that neuroprotection exerted by 17beta-E(2) in a rat model of transient focal brain ischemia is accompanied by reduced cytochrome c translocation to the cytosol and involves early modulation of IL-1beta production.