Microglia in the normally aged hippocampus

Sugemule-7 alleviates oxidative stress, neuroinflammation, and cell death, promoting synaptic plasticity recovery in mice with postpartum depression

Postpartum depression (PPD) profoundly impacts the mental and physical health of women globally and is an incurable psychological disorder. Traditional pharmacological treatments often have strong side effects and may adversely affect infant health through breastfeeding, underscoring the critical need for natural and gentle treatment strategies. Sugemule-7, a traditional Chinese medicine comprising multiple natural plant ingredients, represents a potentially safer and more effective alternative. To investigate its preventive effects on PPD, we established an animal model and administered the drug Sugemule-7. Our study demonstrated that varying doses of Sugemule-7 effectively alleviated depressive and anxiety-like behaviors in PPD mice, as assessed through a battery of tests, including the open field test, tail suspension test, sucrose preference test, forced swim test, novelty-suppressed feeding test, and elevated plus maze test. Furthermore, Sugemule-7 significantly improved oxidative stress levels in the serum, prefrontal cortex, and hippocampus of PPD-induced mice while also suppressing inflammatory responses and abnormal neuronal death in these brain regions. Transcriptomic sequencing of hippocampal and prefrontal cortex tissues supported our findings, revealing that differential gene expression is primarily involved in regulating synaptic plasticity. Overall, our study confirms the efficacy of Sugemule-7 in treating PPD at different concentrations, potentially alleviating depressive behaviors by enhancing synaptic plasticity, mitigating oxidative stress, reducing inflammation, and protecting neurons.

Alteration of cGAS-STING signaling pathway components in the mouse cortex and hippocampus during healthy brain aging

The cGAS-STING pathway is a pivotal element of the innate immune system, recognizing cytosolic DNA to initiate the production of type I interferons and pro-inflammatory cytokines. This study investigates the alterations of the cGAS-STING signaling components in the cortex and hippocampus of mice aged 24 and 108 weeks. In the cortex of old mice, an increase in the dsDNA sensor protein cGAS and its product 2'3'-cGAMP was observed, without corresponding activation of downstream signaling, suggesting an uncoupling of cGAS activity from STING activation. This phenomenon may be attributed to increased dsDNA concentrations in the EC neurons, potentially arising from nuclear DNA damage. Contrastingly, the hippocampus did not exhibit increased cGAS activity with aging, but there was a notable elevation in STING levels, particularly in microglia, neurons and astrocytes. This increase in STING did not correlate with enhanced IRF3 activation, indicating that brain inflammation induced by the cGAS-STING pathway may manifest extremely late in the aging process. Furthermore, we highlight the role of autophagy and its interplay with the cGAS-STING pathway, with evidence of autophagy dysfunction in aged hippocampal neurons leading to STING accumulation. These findings underscore the complexity of the cGAS-STING pathway's involvement in brain aging, with regional variations in activity and potential implications for neurodegenerative diseases.

Resveratrol prevents cognitive impairment and hippocampal inflammatory response induced by lipopolysaccharide in a mouse model of chronic neuroinflammation

BACKGROUND

Neurodegenerative disorders are associated with chronic neuroinflammation, which contributes to their pathogenesis and progression. Resveratrol (RSV) is a polyphenolic compound with strong antioxidant and anti-inflammatory properties. In the present study, we investigated whether RSV could protect against cognitive impairment and inflammatory response in a mouse model of chronic neuroinflammation induced by lipopolysaccharide (LPS).

METHOD

Mice received oral RSV (30 mg/kg) or vehicle for two weeks, and injected with LPS (0.75 mg/kg) or saline daily for the last seven days. After two weeks, mice were subjected to behavioral assessments using the Morris water maze and Y-maze. Moreover, mRNA expression of several inflammatory markers, neuronal loss, and glial density were evaluated in the hippocampus of treated mice.

RESULTS

Our findings showed that RSV treatment effectively improved spatial and working memory impairments induced by LPS. In addition, RSV significantly reduced hippocampal glial densities and neuronal loss in LPS-injected mice. Moreover, RSV treatment suppressed LPS-induced upregulation of NF-κB, IL-6, IL-1β, and GFAP in the hippocampus of treated mice.

CONCLUSION

Taken together, our results highlight the detrimental effect of systemic inflammation on the hippocampus and the potential of natural products with anti-inflammatory effects to counteract this impact.

Effects of Dietary Fiber on Short Chain Fatty Acid Receptor mRNA in Microglia and Serotonergic Neurons in the Mouse Brain

Short-chain fatty acids (SCFAs) are bioactive lipids that are released into the colon as a metabolite of bacterial fermentation of dietary fibers. Beyond their function in the gastrointestinal tract, SCFAs can also have effects inthe brain, as a part of the gut-brain axis. Recent investigations into potential therapeutic interventions via the manipulation of the gut microbiome-and thus their SCFA metabolites-has been emerging as a new branch of personalized medicine,especially for mental health conditions. The current study sought to measure and localize SCFA receptors in the mouse brain. Two cell types have been implicated in the gut-brain axis: microglia and serotonergic neurons. We used fluorescentin situhybridization in brain sections from mice fed diets with different compositions of fat and fiber to quantify the mRNA levels of known gene markers of these two cell types and colocalize each with mRNA for free fatty acid receptors that bind SCFAs. We focused onmicroglia in the hippocampus and the serotonergic neurons of the dorsal raphe. We found high colocalization of SCFA receptors in both microglia and serotonergic neurons and discovered that SCFA receptor expression in the dorsal raphe is driven by fiber solubility, while SCFA receptor expression in the hippocampus is driven by fiber amount. Higher dietary fiber was associated with decreased tyrosine hydroxylase expression. Thus, our results indicate that the amount and solubility of dietary fiber can change gene expression in the brain's microglia and serotonin neurons, potentially via sensitivity to circulating levels of SCFAs produced in the gut.

Characterizing the neuroimmune environment of offspring in a novel model of maternal allergic asthma and particulate matter exposure

Inflammation during pregnancy is associated with an increased risk for neurodevelopmental disorders (NDD). Increased gestational inflammation can be a result of an immune condition/disease, exposure to infection, and/or environmental factors. Epidemiology studies suggest that cases of NDD are on the rise. Similarly, rates of asthma are increasing, and the presence of maternal asthma during pregnancy increases the likelihood of a child being later diagnosed with NDD such as autism spectrum disorders (ASD). Particulate matter (PM), via air pollution, is an environmental factor known to worsen the symptoms of asthma, but also, PM has been associated with increased risk of neuropsychiatric disorders. Despite the links between asthma and PM with neuropsychiatric disorders, there is a lack of laboratory models investigating combined prenatal exposure to asthma and PM on offspring neurodevelopment. Thus, we developed a novel mouse model that combines exposure to maternal allergic asthma (MAA) and ultrafine iron-soot (UIS), a common component of PM. In the current study, female BALB/c mice were sensitized for allergic asthma with ovalbumin (OVA) prior to pregnancy. Following mating and beginning on gestational day 2 (GD2), dams were exposed to either aerosolized OVA to induce allergic asthma or phosphate buffered saline (PBS) for 1 h. Following the 1-h exposure, pregnant females were then exposed to UIS with a size distribution of 55 to 169 nm at an average concentration of 176 ± 45 μg/m3) (SD), or clean air for 4 h, over 8 exposure sessions. Offspring brains were collected at postnatal days (P)15 and (P)35. Cortices and hippocampal regions were then isolated and assessed for changes in cytokines using a Luminex bead-based multiplex assay. Analyses identified changes in many cytokines across treatment groups at both timepoints in the cortex, including interleukin-1 beta (IL-1β), and IL-17, which remained elevated from P15 to P35 in all treatment conditions compared to controls. There was a suppressive effect of the combined MAA plus UIS on the anti-inflammatory cytokine IL-10. Potentially shifting the cytokine balance towards more neuroinflammation. In the hippocampus at P15, elevations in cytokines were also identified across the treatment groups, namely IL-7. The combination of MAA and UIS exposure (MAA-UIS) during pregnancy resulted in an increase in microglia density in the hippocampus of offspring, as identified by IBA-1 staining. Together, these data indicate that exposure to MAA, UIS, and MAA-UIS result in changes in the neuroimmune environment of offspring that persist into adulthood.

Characterizing the Neuroimmune Environment of Offspring in a Novel Model of Maternal Allergic Asthma and Particulate Matter Exposure

Autism spectrum disorders (ASD) are neurodevelopmental disorders characterized by the presence of decreased social interactions and an increase in stereotyped and repetitive behaviors. Epidemiology studies suggest that cases of ASD are on the rise. Similarly, rates of asthma are increasing, and the presence of maternal asthma during pregnancy increases the likelihood of a child being later diagnosed with ASD. Particulate matter (PM), via air pollution, is an environmental factor known to worsen the symptoms of asthma, but also, PM has been associated with increased risk of neuropsychiatric disorders including ASD. Despite the links between asthma and PM with neuropsychiatric disorders, there is a lack of laboratory models investigating combined prenatal exposure to asthma and PM on offspring neurodevelopment. Thus, we developed a novel mouse model that combines exposure to maternal allergic asthma (MAA) and ultrafine iron-soot (UIS), a common component of PM. In the current study, female BALB/c mice were primed for allergic asthma with ovalbumin (OVA) prior to pregnancy. Following mating and beginning on gestational day 2 (GD2), dams were exposed to either aerosolized OVA or phosphate buffered saline (PBS) for 1 hour. Following the 1-hour exposure, pregnant females were then exposed to UIS or clean air for 4 hours. Offspring brains were collected at postnatal days (P)15 and (P)35. Cortices and hippocampal regions were then isolated and assessed for changes in cytokines using a Luminex bead-based multiplex assay. Analyses identified changes in many cytokines across treatment groups at both timepoints in the cortex, including interleukin-1 beta (IL-1β), IL-2, IL-13, and IL-17, which remained elevated from P15 to P35 in all treatment conditions compared to controls. In the hippocampus at P15, elevations in cytokines were also identified across the treatment groups, namely interferon gamma (IFNγ) and IL-7. The combination of MAA and UIS exposure (MAA-UIS) during pregnancy resulted in an increase in microglia density in the hippocampus of offspring, as identified by IBA-1 staining. Together, these data indicate that exposure to MAA, UIS, and MAA-UIS result in changes in the neuroimmune environment of offspring that persist into adulthood.

Long-term high-fat diet consumption by mice throughout adulthood induces neurobehavioral alterations and hippocampal neuronal remodeling accompanied by augmented microglial lipid accumulation

High-fat diet (HFD) consumption is generally associated with an increased risk of cognitive and emotional dysfunctions that constitute a sizeable worldwide health burden with profound social and economic consequences. Middle age is a critical time period that affects one's health later in life; pertinently, the prevalence of HFD consumption is increasing among mature adults. Given the growing health-related economic burden imposed globally by increasing rates of noncommunicable diseases in rapidly aging populations, along with the pervasive but insidious health impairments associated with HFD consumption, it is critically important to understand the effects of long-term HFD consumption on brain function and to gain insights into their potential underlying mechanisms. In the present study, adult male C57BL/6J mice were randomly assigned a control diet (CD, 10 kJ% from fat) or an HFD (60 kJ% from fat) for 6 months (6 M) or 9 months (9 M) followed by behavioral tests, serum biochemical analysis, and histological examinations of both the dorsal and ventral regions of the hippocampus. In both the 6 M and 9 M cohorts, mice that consumed an HFD exhibited poorer memory performance in the Morris water maze test (MWM) and greater depression- and anxiety-like behavior during the open field test (OFT), sucrose preference test (SPT) and forced swim test (FST) than control mice. Compared with age-matched mice in the CD group, mice in the HFD group showed abnormal hippocampal neuronal morphology, which was particularly evident in the ventral hippocampus. Hippocampal microglia in mice in the HFD group generally had a more activated phenotype evidenced by a smaller microglial territory area and increased cluster of differentiation 68 (CD68, a marker of phagocytic activity) immunoreactivity, while the microglial density in the dentate gyrus (DG) was decreased, indicating microglial decline. The engulfment of postsynaptic density 95 (PSD95, a general postsynaptic marker) puncta by microglia was increased in the HFD groups. Histological analysis of neutral lipids using a fluorescent probe (BODIPY) revealed that the total neutral lipid content in regions of interests (ROIs) and the lipid load in microglia were increased in the HFD group relative to the age-matched CD group. In summary, our results demonstrated that chronic HFD consumption from young adulthood to middle age induced anxiety- and depression-like behavior as well as memory impairment. The negative influence of chronic HFD consumption on behavioral and hippocampal neuroplasticity appears to be linked to a change in microglial phenotype that is accompanied by a remarkable increase in cellular lipid accumulation. These observations highlighting the potential to target lipid metabolism deficits to reduce the risk of HFD-associated emotional dysfunctions.

Maternal separation leads to regional hippocampal microglial activation and alters the behavior in the adolescence in a sex-specific manner

Early life adversities during childhood (such as maltreatment, abuse, neglect, or parental deprivation) may increase the vulnerability to cognitive disturbances and emotional disorders in both, adolescence and adulthood. Maternal separation (MS) is a widely used model to study stress-related changes in brain and behavior in rodents. In this study, we investigated the effect of MS (postnatal day 2–14, 3 ​h/day) in both, female and male adolescent mice. Specifically, we evaluated (i) the spatial working memory, anxiety and depressive-like behavior, (ii) the hippocampal synaptic gene expression, and (iii) the hippocampal neuroinflammatory response.

Our results show that MS significantly increased depressive-like behavior in adolescent female mice and altered the spatial memory in adolescent male mice. In addition, MS led to decreased expression of genes related to synaptic function (5ht6r, Synaptophysin, and Cox-2) and induced an exacerbated microglial activation in dentate gyrus (DG), CA1, and CA3. However, while the levels of hippocampal inflammatory cytokines were not modified by MS, they did follow a sex-specific expression in adolescent mice.

Taken together, our results suggest that MS induces long-term changes in hippocampal microglia and synaptic gene expression, alters the spatial memory, and induces depressive-like behavior in the adolescent mice, in a sex-specific manner.

In wildtype adolescent mice (6 weeks of age):•

Maternal separation alters spatial working memory in males and induces depressive-like behavior in females.

•

Maternal separation changes hippocampal synaptic gene expression.

•

Maternal separation activates microglia in dentate gyrus, CA1, and CA3 but does not affect hippocampal cytokine levels. However, males present higher levels of cytokines compared to females.

Accelerated age-related decline in hippocampal neurogenesis in mice with noise-induced hearing loss is associated with hippocampal microglial degeneration

Large-scale epidemiological surveys suggest that hearing loss (HL) is a significant risk factor for dementia. We previously showed that noise-induced HL (NIHL) impairs hippocampal cognitive function and decreases hippocampal neurogenesis and neuronal complexity, suggesting a causal role of HL in dementia. To further investigate the influence of acquired peripheral HL on hippocampal neurogenesis with the aging process as well as the underlying mechanism, we produced NIHL in male CBA/J mice and assessed hippocampal neurogenesis and microglial morphology in the auditory brain and hippocampus at 4 days post-noise exposure (DPN) or 1, 3, 6, or 12 months post-noise exposure (MPN) by immunofluorescence labeling. We found that the age-related decline in hippocampal neurogenesis was accelerated in mice with NIHL. Furthermore, in mice with NIHL, prolonged microglial activation occurred from 1 MPN to 12 MPN across multiple auditory nuclei, while aggravated microglial deterioration occurred in the hippocampus and correlated with the age-related decline in hippocampal neurogenesis. These results suggest that acquired peripheral HL accelerates the age-related decline in hippocampal neurogenesis and that hippocampal microglial degeneration may contribute to the development of neurodegeneration following acquired peripheral HL.

Role of Chronic Administration of Antidepressant Drugs in the Prenatal Stress-Evoked Inflammatory Response in the Brain of Adult Offspring Rats: Involvement of the NLRP3 Inflammasome-Related Pathway

Evidence indicates that adverse experiences in early life may be a factor for immune disturbances leading to the depression in adulthood. Recently, a pivotal role in the pathogenesis of depression has been assigned to the activation of the brain Nod-like receptor pyrin-containing 3 (NLRP3) inflammasome. We investigated the impact of chronic treatment with antidepressant drugs on the behavioral disturbances and the levels of proinflammatory factors in the hippocampus and frontal cortex of adult male rats after prenatal stress exposure. Next, we explored the involvement of the NLRP3 inflammasome-related pathways in the mechanism of antidepressant action. Our study confirmed that chronic antidepressant treatment attenuated depression-like disturbances and exerted an anxiolytic action. All antidepressants diminished the prenatal stress-induced increase in IL-1β in both brain areas, while IL-18 only in the hippocampus. Moreover, tianeptine administration diminished the increase in CCR2 levels in both brain areas, while in the hippocampus, tianeptine, along with venlafaxine CCL2 and iNOS levels. Next, we observed that in the hippocampus, tianeptine and fluoxetine suppressed upregulation of TLR4. Furthermore, venlafaxine suppressed NFкB p65-subunit phosphorylation, while fluoxetine enhanced the IкB level. Importantly, in the hippocampus, all antidepressants normalized evoked by stress changes in caspase-1 level, while tianeptine and venlafaxine also affect the levels of ASC and NLRP3 subunits. Our results provide new evidence that chronic administration of antidepressants exerts anti-inflammatory effects more pronounced in the hippocampus, through suppression of the NLRP3 inflammasome activation. These effects are accompanied by an improvement in the behavioral dysfunctions evoked by prenatal stress.

Early chronic exposure to low-level lead alters total hippocampal microglia in pre-adolescent mice

Developmental lead (Pb) exposure alters brain function through mechanisms that are not yet understood. A previous study showed that early lead exposure reduced microglia number in the dentate gyrus region of the hippocampus. Given the critical role of microglia in brain development, it is important to determine whether these differences are unique to the dentate gyrus, or occur throughout the hippocampus. Unbiased stereology was used to quantify microglia mean cell body number in total hippocampus, and compare the proportion of microglia in the ventral vs. dorsal regions. Total hippocampal volume was also measured and compared. The study included brain tissue from 30 pre-adolescent C57BL/6 J mice, exposed to 30 ppm Pb acetate (n = 10, mean BLL 3.4 μg/dL at sacrifice), 330 ppm Pb acetate (n = 10, mean BLL 14.1 μg/dL at sacrifice), or 0 ppm Pb acetate (n = 10, negative controls). In lead exposed animals, microglia mean cell body number was reduced in total hippocampus; total hippocampal volume was reduced. Importantly, effects in low- and high-dose exposure groups did not differ. Contrary to study hypotheses, the distribution of hippocampal microglia in the ventral vs. dorsal hippocampal regions did not differ. Overall, lowest and higher levels of lead exposure during development had strikingly similar disruptive effects in the neuroimmune system. Studies are needed to determine the immune and other mechanisms responsible for these effects. Future studies would benefit from larger samples to determine whether in fact there is a group by sex interaction driving the effects of early lead exposure on microglia.

Phloroglucinol ameliorates cognitive impairments by reducing the amyloid β peptide burden and pro-inflammatory cytokines in the hippocampus of 5XFAD mice

Among the various causative factors involved in the pathogenesis of Alzheimer's disease (AD), oxidative stress has emerged as an important factor. Phloroglucinol is a polyphenol component of phlorotannin, which is found at sufficient levels in Ecklonia cava (E. cava). Phloroglucinol has been reported to exert antioxidant activities in various tissues. Previously, we reported that the stereotaxic injection of phloroglucinol regulated synaptic plasticity in an AD mouse model. In this study, we aimed to investigate the effects of oral administration of phloroglucinol in AD. The oral administration of phloroglucinol for 2 months attenuated the impairments in cognitive function observed in 6-month-old 5X familial AD (5XFAD) mice, as assessed with the T-maze and Y-maze tests. The administration of phloroglucinol for 2 months in 5XFAD mice caused a reduction in the number of amyloid plaques and in the protein level of BACE1, a major amyloid precursor protein cleavage enzyme, together with γ-secretase. Phloroglucinol also restored the reduction in dendritic spine density and the number of mature spines in the hippocampi of 5XFAD mice. In addition, phloroglucinol-administered 5XFAD mice displayed lower protein levels of GFAP and Iba-1 and mRNA levels of TNF-α and IL-6 compared with vehicle-administered 5XFAD mice. These results demonstrated that phloroglucinol alleviated the neuropathological features and behavioral phenotypes in the 5XFAD mouse model. Taken together, our results suggest that phloroglucinol has therapeutic potential for AD treatment.

Sexually divergent induction of microglial-associated neuroinflammation with hippocampal aging

Background

The necessity of including both males and females in molecular neuroscience research is now well understood. However, there is relatively limited basic biological data on brain sex differences across the lifespan despite the differences in age-related neurological dysfunction and disease between males and females.

Methods

Whole genome gene expression of young (3 months), adult (12 months), and old (24 months) male and female C57BL6 mice hippocampus was analyzed. Subsequent bioinformatic analyses and confirmations of age-related changes and sex differences in hippocampal gene and protein expression were performed.

Results

Males and females demonstrate both common expression changes with aging and marked sex differences in the nature and magnitude of the aging responses. Age-related hippocampal induction of neuroinflammatory gene expression was sexually divergent and enriched for microglia-specific genes such as complement pathway components. Sexually divergent C1q protein expression was confirmed by immunoblotting and immunohistochemistry. Similar patterns of cortical sexually divergent gene expression were also evident. Additionally, inter-animal gene expression variability increased with aging in males, but not females.

Conclusions

These findings demonstrate sexually divergent neuroinflammation with aging that may contribute to sex differences in age-related neurological diseases such as stroke and Alzheimer’s, specifically in the complement system. The increased expression variability in males suggests a loss of fidelity in gene expression regulation with aging. These findings reveal a central role of sex in the transcriptomic response of the hippocampus to aging that warrants further, in depth, investigations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0920-8) contains supplementary material, which is available to authorized users.

Effects of long‑term post‑ischemic treadmill exercise on gliosis in the aged gerbil hippocampus induced by transient cerebral ischemia

Therapeutic exercise is an integral component of the rehabilitation of patients who have suffered a stroke. The objective of the present study was to use immunohistochemistry to investigate the effects of post-ischemic exercise on neuronal damage or death and gliosis in the aged gerbil hippocampus following transient cerebral ischemia. Aged gerbils (male; age, 22–24 months) underwent ischemia and were subjected to treadmill exercise for 1 or 4 weeks. Neuronal death was detected in the stratum pyramidale of the hippocampal CA1 region and in the polymorphic layer of the dentate gyrus using cresyl violet and Fluoro-Jade B histofluorescence staining. No significant difference in neuronal death was identified following 1 or 4 weeks of post-ischemic treadmill exercise. However, post-ischemic treadmill exercise affected gliosis (the activation of astrocytes and microglia). Glial fibrillary acidic protein-immunoreactive astrocytes and ionized calcium binding adaptor molecule 1-immunoreactive microglia were activated in the CA1 and polymorphic layer of the dentate gyrus of the group without treadmill exercise. Conversely, 4 weeks of treadmill exercise significantly alleviated ischemia-induced astrocyte and microglial activation; however, 1 week of treadmill exercise did not alleviate gliosis. These findings suggest that long-term post-ischemic treadmill exercise following transient cerebral ischemia does not influence neuronal protection; however, it may effectively alleviate transient cerebral ischemia-induced astrocyte and microglial activation in the aged hippocampus.

Microglia across the lifespan: from origin to function in brain development, plasticity and cognition

Microglia are the only immune cells that permanently reside in the central nervous system (CNS) alongside neurons and other types of glial cells. The past decade has witnessed a revolution in our understanding of their roles during normal physiological conditions. Cutting-edge techniques revealed that these resident immune cells are critical for proper brain development, actively maintain health in the mature brain, and rapidly adapt their function to physiological or pathophysiological needs. In this review, we highlight recent studies on microglial origin (from the embryonic yolk sac) and the factors regulating their differentiation and homeostasis upon brain invasion. Elegant experiments tracking microglia in the CNS allowed studies of their unique roles compared with other types of resident macrophages. Here we review the emerging roles of microglia in brain development, plasticity and cognition, and discuss the implications of the depletion or dysfunction of microglia for our understanding of disease pathogenesis. Immune activation, inflammation and various other conditions resulting in undesirable microglial activity at different stages of life could severely impair learning, memory and other essential cognitive functions. The diversity of microglial phenotypes across the lifespan, between compartments of the CNS, and sexes, as well as their crosstalk with the body and external environment, is also emphasised. Understanding what defines particular microglial phenotypes is of major importance for future development of innovative therapies controlling their effector functions, with consequences for cognition across chronic stress, ageing, neuropsychiatric and neurological diseases.

Beneficial impact of intracerebroventricular fractalkine administration on behavioral and biochemical changes induced by prenatal stress in adult rats: Possible role of NLRP3 inflammasome pathway

Several lines of evidence indicate that adverse experience in early life may be a triggering factor for pathological inflammatory processes and lead to the development of depression. Fractalkine (CX3CL1), a chemokine, plays an important role not only in the migration, differentiation and proliferation of neuronal and glial cells but also in the regulation of neuronal-microglial signaling and the production of pro-inflammatory factors. In the present study, we examined the impact of a prenatal stress procedure on the expression of fractalkine in the hippocampus and frontal cortex of young and adult male rats. Furthermore, we measured the age-dependent effect of stress during pregnancy on the expression of pro-inflammatory factors IL-1β, IL-18, TNF-α, IL-6, and CCL2 in both brain structures. Next, to illustrate the link between fractalkine signaling and the behavioral and biochemical changes induced by prenatal stress, adult prenatally stressed offspring were injected intracerebroventricularly (icv) with exogenous fractalkine. We reported that prenatal stress leads to long-lasting deficits in fractalkine signaling and enhanced inflammatory activation. The study demonstrates that icv administration of fractalkine attenuates the behavioural changes evoked by prenatal stress procedure in adult animals. Moreover, fractalkine administration, exhibits anti-inflammatory action, mainly in the frontal cortex of adult prenatally stressed rats. The effect of fractalkine is related to inhibition of NLRP3 inflammasome. However, its action on the other members of NOD-like receptor family (NLR) cannot be excluded. These findings provide new in vivo evidence that the behavioral and inflammatory disturbances observed in adult prenatally stressed rats may be related to long-lasting malfunctions in fractalkine signaling.

Chronic Intermittent Hypoxia Induces Chronic Low-Grade Neuroinflammation in the Dorsal Hippocampus of Mice

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) induces cognitive impairment that involves intermittent hypoxia (IH). Because OSA is recognized as a low-grade systemic inflammatory disease and only some patients develop cognitive deficits, we investigated whether IH-related brain consequences shared similar pathophysiology and required additional factors such as systemic inflammation to develop.

DESIGN

Nine-week-old male C57BL/6J mice were exposed to 1 day, 6 or 24 w of IH (alternating 21-5% FiO2 every 30 sec, 8 h/day) or normoxia. Microglial changes were assessed in the functionally distinct dorsal (dH) and ventral (vH) regions of the hippocampus using Iba1 immunolabeling. Then the study concerned dH, as vH only tended to be lately affected. Seven proinflammatory and anti-inflammatory cytokine messenger RNA (mRNA) were assessed at all time points using semiquantitative real-time reverse transcription polymerase chain reaction (RT-PCR). Similar mRNA analysis was performed after 6 w IH or normoxia associated for the past 3 w with repeated intraperitoneal low-dose lipopolysaccharide or saline.

MEASUREMENTS AND RESULTS

Chronic (6, 24 w) but not acute IH induced significant microglial changes in dH only, including increased density and morphological features of microglia priming. In dH, acute but not chronic IH increased IL-1β and RANTES/CCL5 mRNA, whereas the other cytokines remained unchanged. In contrast, chronic IH plus lipopolysaccharide increased interleukin (IL)-6 and IL10 mRNA whereas lipopolysaccharide alone did not affect these cytokines.

CONCLUSION

The obstructive sleep apnea component intermittent hypoxia (IH) causes low-grade neuroinflammation in the dorsal hippocampus of mice, including early but transient cytokine elevations, delayed but long-term microglial changes, and cytokine response alterations to lipopolysaccharide inflammatory challenge. These changes may contribute to IH-induced cognitive impairment and pathological brain aging.

Network Comparison of Inflammation in Colorectal Cancer and Alzheimer's Disease

Recently, a large clinical study revealed an inverse correlation of individual risk of cancer versus Alzheimer's disease (AD). However, no explanation exists for this anticorrelation at the molecular level; however, inflammation is crucial to the pathogenesis of both diseases, necessitating a need to understand differing signaling usage during inflammatory responses distinct to both diseases. Using a subpathway analysis approach, we identified numerous well-known and previously unknown pathways enriched in datasets from both diseases. Here, we present the quantitative importance of the inflammatory response in the two disease pathologies and summarize signal transduction pathways common to both diseases that are affected by inflammation.

The role of inflammation and microglial activation in the pathophysiology of psychiatric disorders

Psychiatric disorders, including major depressive disorder (MDD), bipolar disorder (BD) and schizophrenia, affect a significant percentage of the world population. These disorders are associated with educational difficulties, decreased productivity and reduced quality of life, but their underlying pathophysiological mechanisms are not fully elucidated. Recently, studies have suggested that psychiatric disorders could be considered as inflammatory disorders, even though the exact mechanisms underlying this association are not known. An increase in inflammatory response and oxidative stress may lead to inflammation, which in turn can stimulate microglia in the brain. Microglial activation is roused by the M1 phenotype, which is associated with an increase in interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). On the contrary, M2 phenotype is associated with a release of anti-inflammatory cytokines. Thus, it is possible that the inflammatory response from microglial activation can contribute to brain pathology, as well as influence treatment responses. This review will highlight the role of inflammation in the pathophysiology of psychiatric disorders, such as MDD, BD, schizophrenia, and autism. More specifically, the role of microglial activation and associated molecular cascades will also be discussed as a means by which these neuroinflammatory mechanisms take place, when appropriate.

Physiological and psychosocial age-related changes associated with reduced food intake in older persons

Dietary intake changes during the course of aging. Normally an increase in food intake is observed around 55 years of age, which is followed by a reduction in food intake in individuals over 65 years of age. This reduction in dietary intake results in lowered levels of body fat and body weight, a phenomenon known as anorexia of aging. Anorexia of aging has a variety of consequences, including a decline in functional status, impaired muscle function, decreased bone mass, micronutrient deficiencies, reduced cognitive functions, increased hospital admission and even premature death. Several changes during lifetime have been implicated to play a role in the reduction in food intake and the development of anorexia of aging. These changes are both physiological, involving peripheral hormones, senses and central brain regulation and non-physiological, with differences in psychological and social factors. In the present review, we will focus on age-related changes in physiological and especially non-physiological factors, that play a role in the age-related changes in food intake and in the etiology of anorexia of aging. At the end we conclude with suggestions for future nutritional research to gain greater understanding of the development of anorexia of aging which could lead to earlier detection and better prevention.

NADPH oxidase-dependent oxidative stress and mitochondrial damage in hippocampus of D-galactose-induced aging rats

Mitochondrial DNA (mtDNA) common deletion (CD) plays a significant role in aging and age-related diseases. In this study, we used D-galactose (D-gal) to generate an animal model of aging and the involvement and causative mechanisms of mitochondrial damage in such a model were investigated. Twenty 5-week-old male Sprague-Dawley rats were randomly divided into two groups: D-gal group (n=10) and control group (n=10). The quantity of the mtDNA CD in the hippocampus was determined using a TaqMan real-time PCR assay. Transmission electron microscopy was used to observe the mitochondrial ultrastructure in the hippocampus. Western blot was used to detect the protein levels of NADPH oxidase (NOX) and uncoupling protein 2 (UCP2). We found that the level of mtDNA CD was significantly higher in the hippocampus of D-gal-induced aging rats than in control rats. In comparison with the control group, the mitochondrial ultrastructure in the hippocampus of D-gal-treated rats was damaged, and the protein levels of NOX and UCP2 were significantly increased in the hippocampus of D-gal-induced aging rats. This study demonstrated that the levels of mtDNA CD and NOX protein expression were significantly increased in the hippocampus of D-gal-induced aging rats. These findings indicate that NOX-dependent reactive oxygen species generation may contribute to D-gal-induced mitochondrial damage.

Spatial regulation of interleukin-6 signaling in response to neurodegenerative stressors in the retina

Neuroinflammation, defined as the induction of immune-related processes within the central nervous system, is recognized as a component of many neurodegenerative disorders, including glaucomatous degeneration of retinal ganglion cells (RGCs). Previous work in vitro identified IL-6 as a potential neuroprotective factor for RGCs, particularly those challenged by glaucoma-related stressors. Here we examined the temporal and spatial characteristics of IL-6 signaling in response to two stressors related to RGC neurodegeneration: age and elevated intraocular pressure (IOP). Using ELISA, immunoblotting, immunolabeling and quantitative microscopy, we measured and compared whole retina and RGC-related expression of IL-6 and IL-6Rα in normal retina (young C57), retina susceptible to glaucomatous neurodegeneration (young DBA/2), aging retina (aged C57) and aging retina challenged by elevated IOP (aged DBA/2). We found that: 1) neurodegenerative stressors induce alterations in whole retina expression of IL-6 and IL-6Rα, 2) these whole retina changes do not reflect the immediate milieu of RGCs, where IL-6 and IL-6Rα expression is spatially variable and 3) the extent and magnitude of this spatial variability is stressor-dependent. Our data provide the first evidence that neurodegenerative stressors produce microenvironments of IL-6 signaling in retina and that the nature and magnitude of spatial regulation is dependent on the identity of the stressor.