Hippocampal Microglia Research Articles

MiR-124 Enriched Exosomes Promoted the M2 Polarization of Microglia and Enhanced Hippocampus Neurogenesis After Traumatic Brain Injury by Inhibiting TLR4 Pathway.

MicroRNA-124 (miR-124) is a brain specific miRNA that is highly expressed in microglia. The upregulation of miR-124 contributes to M2 polarization of microglia, which is beneficial to neurogenesis. Exosomes are lipid membrane vesicles that can deliver miR-124 into the brain. However, whether miR-124 enriched exosomes (Exo-miR-124) can regulate the polarization of microglia and affect hippocampus neurogenesis after traumatic brain injury (TBI) is unknown. To clarify this, the Exo-miR-124 was first constructed, and then was intravenously administrated into rats via tail vein with the dose of 3 × 109 particles/each rat at 24h post TBI. The polarization of microglia in hippocampus was evaluated through measuring the signature genes and cytokines of M1/M2 phenotype by reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immune sorbent assay (ELISA) at 7/14/21/28 days after TBI. Hippocampus neurogenesis was evaluated through detecting the proliferation marker BrdU/SOX2 and differentiation marker BrdU/NeuN by immunofluorescence (IF) at 7 and 28days after TBI respectively. Neurological function was evaluated by neurological severity score (NSS) and morris water maze (MWM) at 7/14/21/28 and 24-28days after TBI respectively. To explore the underlying mechanisms, the mRNA expression of TLR4 pathway molecules in hippocampus were measured by RT-PCR, and the polarization of microglia and the activation of TLR4 pathway in BV2 cells were measured after exosome treatment as well. Results demonstrated that Exo-miR-124 treatment promoted the M2 polarization of microglia, enhanced neurogenesis in hippocampus, and improved function recovery after TBI. The M2 polarization effect of Exo-miR-124 was produced through inhibiting TLR4 pathway, which was verified in hippocampus and BV2 microglia. In conclusion, Exo-miR-124 treatment promoted M2 polarization of microglia and improved hippocampal neurogenesis and functional recovery after brain injury, which might be a strategy to improve the outcome of TBI.

Pseudoginsenoside-F11 attenuates cognitive impairment by ameliorating oxidative stress and neuroinflammation in d‑galactose-treated mice

Oxidative stress and neuroinflammation are thought to be the two key early events during the process of mild cognitive impairment (MCI). Therefore, effective regulation of oxidative stress and neuroinflammation is an important aspect of preventing and improving MCI. We previously found that pseudoginsenoside-F11 (PF11), an ocotillol-type saponin, markedly reduced cognitive impairment in APP/PS1 mice and oAβ1–42-injected mice. In the present study, we further evaluate the effect of PF11 on learning and memory dysfunction in d‑galactose (d‑gal)-treated mice model of MCI. C57BL/6 mice received daily subcutaneous injections of d‑gal (100 mg/kg) and oral administration of PF11 (2, 4, 8, 16 mg/kg) for 9 weeks. We observed that PF11 significantly alleviated d‑gal-induced cognitive impairment, attenuated the loss of neuron and the over-activation of microglia in hippocampus of d‑gal-treated mice. The elevated levels of nod-like receptor protein 3 (NLRP3) inflammasome in hippocampus of d‑gal-treated mice were reduced by PF11 through reducing the accumulation of advanced glycation endproducts (AGEs) and the expression of the receptor of advanced glycation endproducts (RAGE). Moreover, PF11 significantly decreased H2O2 and malondialdehyde (MDA) levels, improved superoxide dismutase (SOD) activity and increased glutathione (GSH) level in d‑gal-treated mice. Finally, d‑gal treatment reduced the level of nuclear factor erythroid-related factor 2 (Nrf2) and glutathione S-transferase (GST) in hippocampus, which could reverse by PF11. Together, our findings indicated that PF11 exerts a protective effect against MCI-like pathological changes.

Perinatal exposure to nonylphenol induces microglia-mediated nitric oxide and prostaglandin E2 production in offspring hippocampus

Nonylphenol (NP) is a persistent organic pollutant (POP) that has potential for neurotoxicity. The central nervous system (CNS) of fetus and child is highly sensitive to POPs, with environmental NP exposure, in particular, receiving increasing attention. Microglia (MG) are vital resident immune cells in CNS that defend against exogenous chemicals. This makes them a potentially target of NP. We sought to explore the effects of maternal exposure to NP during pregnancy and lactation on MG in the offspring hippocampus, the production of nitric oxide (NO) and prostaglandin E2 (PGE2) by MG, and the associated underlying mechanisms. We found that maternal exposure to NP activated MG and increased the production of NO and PGE2 in the offspring hippocampus. Nuclear translocation of p65 was found to co-localize with hippocampal MG. Activation of TLR4/MyD88/NF-κB and Nrf2 signaling were observed in the offspring hippocampus. Interestingly, the inhibition of TLR4 signaling with CLI-095 partly inhibited NP-induced NO and PGE2 expression in BV2, a MG cell line. Together, our results suggested that maternal exposure to NP might increase the production of NO and PGE2 by over-activated MG in the offspring hippocampus. TLR4/MyD88/NF-κB and Nrf2 signaling pathways may be involved in the activation of MG and the increased production of NO and PGE2.

Simvastatin prevents and ameliorates depressive behaviors via neuroinflammatory regulation in mice

BackgroundStatins play a beneficial role in the treatment of coronary artery disease and are widely prescribed to prevent hypercholesterolemia. Previous studies have demonstrated that statins also have anti-inflammatory and immunomodulatory properties, and these are being explored for potential benefits in depression. However, the role of statins in the treatment of depression has not been well examined. MethodsWe investigated the effects of simvastatin on depressive behaviors and neuroinflammation in lipopolysaccharide (LPS) and chronic mild stress (CMS) induced depression model in mice. Sucrose preference test (SPT), forced swimming test (FST), novelty-suppressed feeding test (NSFT) were used to detect the depressive behaviors. The microglial activation was detected by immunohistochemistry analysis and the pro-inflammatory cytokines expressions including IL-1β, TNF-α and IL-6 were examined by Western blot analysis. ResultsOur data indicated that oral administration of simvastatin at 20 mg/kg significantly prevented and ameliorated depressive behaviors reflected by better performance in the SPT, FST and NSFT. Moreover, simvastatin markedly prevented and ameliorated LPS and CMS-induced neuroinflammation, as shown by the suppressed activation of microglia in hippocampus and decreased hippocampal pro-inflammatory cytokines expressions including IL-1β, TNF-α, IL-6, which might be mediated via the inhibition of NF-κB pathway, as shown by the decreased nuclear NF-κB p65 expression. LimitationsThe interpretation of the evidence of a positive treatment effect of simvastatin on the depressive manifestations, multifaceted etiology of depression, and confirmation of this finding from animal models to humans is needed. ConclusionThese results suggest that simvastatin has the potential to be employed as a therapy for depression associated with neuroinflammation.

Cannabinoid 1 Receptor Signaling on Hippocampal GABAergic Neurons Influences Microglial Activity.

Microglia, the resident immune cells of the brain, play important roles in defending the brain against pathogens and supporting neuronal circuit plasticity. Chronic or excessive pro-inflammatory responses of microglia damage neurons, therefore their activity is tightly regulated. Pharmacological and genetic studies revealed that cannabinoid type 1 (CB1) receptor activity influences microglial activity, although microglial CB1 receptor expression is very low and activity-dependent. The CB1 receptor is mainly expressed on neurons in the central nervous system (CNS)—with an especially high level on GABAergic interneurons. Here, we determined whether CB1 signaling on this neuronal cell type plays a role in regulating microglial activity. We compared microglia density, morphology and cytokine expression in wild-type (WT) and GABAergic neuron-specific CB1 knockout mice (GABA/CB1−/−) under control conditions (saline-treatment) and after 3 h, 24 h or repeated lipopolysaccharide (LPS)-treatment. Our results revealed that hippocampal microglia from saline-treated GABA/CB1−/− mice resembled those of LPS-treated WT mice: enhanced density and larger cell bodies, while the size and complexity of their processes was reduced. No further reduction in the size or complexity of microglia branching was detected after LPS-treatment in GABA/CB1−/− mice, suggesting that microglia in naïve GABA/CB1−/− mice were already in an activated state. This result was further supported by correlating the level of microglial tumor necrosis factor α (TNFα) with their size. Acute LPS-treatment elicited in both genotypes similar changes in the expression of pro-inflammatory cytokines (TNFα, interleukin-6 (IL-6) and interleukin 1β (IL-1β)). However, TNFα expression was still significantly elevated after repeated LPS-treatment in WT, but not in GABA/CB1−/− mice, indicating a faster development of tolerance to LPS. We also tested the possibility that the altered microglia activity in GABA/CB1−/− mice was due to an altered expression of neuron-glia interaction proteins. Indeed, the level of fractalkine (CX3CL1), a neuronal protein involved in the regulation of microglia, was reduced in hippocampal GABAergic neurons in GABA/CB1−/− mice, suggesting a disturbed neuronal control of microglial activity. Our result suggests that CB1 receptor agonists can modulate microglial activity indirectly, through CB1 receptors on GABAergic neurons. Altogether, we demonstrated that GABAergic neurons, despite their relatively low density in the hippocampus, have a specific role in the regulation of microglial activity and cannabinoid signaling plays an important role in this arrangement.

N-Methyl-D-Aspartate Receptor Link to the MAP Kinase Pathway in Cortical and Hippocampal Neurons and Microglia Is Dependent on Calcium Sensors and Is Blocked by α-Synuclein, Tau, and Phospho-Tau in Non-transgenic and Transgenic APPSw,Ind Mice.

N-methyl-D-aspartate receptors (NMDARs) respond to glutamate to allow the influx of calcium ions and the signaling to the mitogen-activated protein kinase (MAPK) cascade. Both MAPK- and Ca2+-mediated events are important for both neurotransmission and neural cell function and fate. Using a heterologous expression system, we demonstrate that NMDAR may interact with the EF-hand calcium-binding proteins calmodulin, calneuron-1, and NCS1 but not with caldendrin. NMDARs were present in primary cultures of both neurons and microglia from cortex and hippocampus. Calmodulin in microglia, and calmodulin and NCS1 in neurons, are necessary for NMDA-induced MAP kinase pathway activation. Remarkably, signaling to the MAP kinase pathway was blunted in primary cultures of cortical and hippocampal neurons and microglia from wild-type animals by proteins involved in neurodegenerative diseases: α-synuclein, Tau, and p-Tau. A similar blockade by pathogenic proteins was found using samples from the APPSw,Ind transgenic Alzheimer’s disease model. Interestingly, a very marked increase in NMDAR–NCS1 complexes was identified in neurons and a marked increase of both NMDAR–NCS1 and NMDAR–CaM complexes was identified in microglia from the transgenic mice. The results show that α-synuclein, Tau, and p-Tau disrupt the signaling of NMDAR to the MAPK pathway and that calcium sensors are important for NMDAR function both in neurons and microglia. Finally, it should be noted that the expression of receptor–calcium sensor complexes, specially those involving NCS1, is altered in neural cells from APPSw,Ind mouse embryos/pups.

The Chinese Medicine Wu-Tou Decoction Relieves Neuropathic Pain by Inhibiting Hippocampal Microglia Activation

The comorbidity between the nociceptive and mental syndromes adds to the refractoriness of neuropathic pain (NP). Wu-Tou decoction (WTD) has been prescribed for chronic pain for thousands of years in China. Recently, we reported that WTD was helpful for hippocampus and co-curative for the nociceptive, depressive and anxiety behaviors in the spinal cord ligation (SNL) mice. However, the mechanism underlying the rescue of hippocampus, as well as the roles hippocampus assumed in co-curation remain unexplored. In this study, we validated that in SNL mice, the long-lasting damages to limbic system were mainly limited to hippocampus. In addition, hippocampal neurons were proven sensitive to harms induced by microglia and rescued by WTD, which in sum indicated hippocampal microglia as the critical modulator of co-curation. To validate this hypothesis the hippocampal microglia were mal-activated in shamed mice, in which the atrophy of hippocampus and the development of NP syndromes were consolidated and proven rescued by WTD. On the contrary, in the SNL mice, the failure to control hippocampal microglia was sufficient to void all the rescues mediated by WTD. In sum, our study points out that the effective modulation of microglia in hippocampus is of pivotal importance for the co-curation by WTD.

Fibroblast Growth Factor 2 Modulates Hippocampal Microglia Activation in a Neuroinflammation Induced Model of Depression.

Recent studies indicate that disturbed structure and function of microglia can cause depression and associated neurogenesis impairments. Our previous work has demonstrated that exogenous fibroblast growth factor 2 (FGF2) reverses the depressive-like behaviors and the impaired hippocampal neurogenesis in a neuroinflammatory model of depression. However, whether and how the antidepressant effects of FGF2 involve the modulation of microglia activation has not been elucidated. In this study, to examine the effects of FGF2 on microglia activation, exogenous FGF2 was supplemented to the lateral ventricle of rats during the neuroinflammatory state induced by central lipopolysaccharides (LPS) administrations. It was found that FGF2 infusions reversed the LPS-induced depressive-like behaviors and inhibited the hippocampal microglia activation. In LPS-treated rats, FGF2 decreased the level of pro-inflammatory cytokines including interlukin-1β (IL-1β), IL-6 and tumor necrosis factor (TNF)-α, increased the level of IL-10, the anti-inflammatory cytokine and reversed the decreased expression of CX3CL1, a chemokine mainly expressed by neurons and keeping microglia in surveillance. Further, we examined the effects of inhibited FGF2 signaling by administration of SU5402, an FGFR inhibitor. It was found that SU5402 itself evoked depressive-like behaviors, induced microglia activation, increased production of pro-inflammatory cytokines including IL-1β, IL-6 and TNF-α, and decreased the expression of CX3CL1. Two lines of results that FGF2 signaling and FGFR inhibitor can effectively but oppositely modulate the regulation of microglia and the generation of depressive-like behavior, suggesting that microglia-regulated mechanisms may underlie the antidepressant role of FGF2. The present data provide novel insights into the understanding of mechanism of neuroinflammation-associated depression and may serve as a novel mechanism-based target for the treatment of inflammation-related depression.

Role of hippocampal cannabinoid receptor 2 in postoperative cognitive dysfunction in mice

Objective To investigate the role of hippocampal cannabinoid receptor 2 (CB2R) in postoperative cognitive dysfunction (POCD) in mice. Methods Fifty-four healthy male C57BL/6 mice, aged 12-16 weeks, weighing 20-30 g, were divided into 3 groups (n=18 each) using a random number table: control group (group C), group POCD and POCD plus CB2R agonist JWH133 group (group POCD+ J). The mice were subjected to an intramedullary fixation for tibial fracture under 1.5% isoflurane anesthesia to establish POCD model.In group POCD+ J, 2 mg/kg JWH133 was injected intraperitoneally at a total volume of 10 ml/kg after emergence from anesthesia and then the injection was repeated once a day until the 7th day after surgery.Open field test was carried out on 1 day before surgery and 1, 3 and 7 days after surgery to evaluate the locomotor activity.Fear conditioning test was carried out at 15 min after completion of open field test.Mice were sacrificed at 2 h after the end of behavioral test, and the hippocampus was harvested for determination of the expression of tumor necrosis factor-alpha (TNF-α), interleukin-1beta (IL-1β), monocyte chemotactic protein-1 (MCP-1) and CB2R (by Western blot) and expression of CD11b in hippocampal tissues (by immunofluorescence). Results There was no significant difference in the total exploring distance in open field test, percentage of freezing time in contextual fear conditioning test or percentage of freezing time in tone-fear conditioning text at each time point among the three groups (P>0.05). Compared with group C, the percentage of freezing time in contextual fear conditioning test was significantly decreased, and the expression of TNF-α, IL-1β, MCP-1, CD11b and CB2R was up-regulated after surgery in group S (P<0.05). Compared with group S, the percentage of freezing time in contextual fear conditioning test was significantly increased, and the expression of TNF-α, IL-1β, MCP-1, CD11b and CB2R was down-regulated after surgery in group S+ J (P<0.05). Conclusion Activation of hippocampal CB2R may be involved in the endogenous protective mechanism of POCD in mice, and the mechanism is related to inhibiting activation of hippocampal microglia and attenuating central inflammatory responses. Key words: Receptor, cannabinoid, CB2; Cognition disorders; Postoperative complications; Hippocampus

SIRT1 Mediates Apelin-13 in Ameliorating Chronic Normobaric Hypoxia-induced Anxiety-like Behavior by Suppressing NF-κB Pathway in Mice Hippocampus

We previously showed that apelin-13 ameliorates chronic normobaric hypoxia (CNH)-induced anxiety-like behavior in mice, the mechanism, however, is not well known. This study aims to investigate whether SIRT1 is involved in the anxiolytic effect of apelin-13 in CNH-treated mice, and to illustrate the potential underlying mechanism. We showed that apelin-13 treatment reversed a decrease in SIRT1 and an increase in acetylated p65 (lysine 310) proteins’ expression in hippocampus of CNH-treated mice, indicating that apelin-13 inhibited NF-κB signaling pathway by activating SIRT1. Behaviorally, apelin-13 ameliorated CNH-induced anxiety-like behavior, EX-527 blocked the beneficial effect of apelin-13, and the anxiogenic effect of CNH was attenuated by resveratrol pretreatment, suggesting that SIRT1 was involved in the effect of apelin-13 against CNH-induced anxiety-like behavior in mice. We also showed that resveratrol treatment decreased IL-1β, IL-6, TNF-ɑ, PCNA, Bcl-2, and acetyl-p65 levels, but increased Bax and caspase 3 levels in hippocampus, suggesting a suppressive effect of resveratrol on cellular neuroinflammation and proliferation while a promotive effect on apoptosis of microglia in hippocampus. Finally, blockade of NF-κB activity by PDTC diminished CNH-induced anxiety-like behavior, indicating that NF-κB was involved in CNH-induced anxiety-like behavior in mice. In conclusion, this study provides the first evidence that SIRT1 mediates the anxiolytic effect of apelin-13 in CNH-treated mice through the inhibition of NF-κB pathway. These results imply that dysfunction of the apelin-SIRT1-NF-κB axis in hippocampus represents a potential mechanism that results in the induction of neuroinflammation and reduction in neuroprotection, thus induces anxiety-like behavior in CNH-treated mice.

Maternal exposure to nonylphenol during pregnancy and lactation induces microglial cell activation and pro-inflammatory cytokine production in offspring hippocampus

Recently, environmental nonylphenol (NP) exposure in the fetus and child has received increasing attention because of its potentially deleterious effects on the central nervous system (CNS). Microglia (MG), resident immune cells in the CNS, are vital to CNS homeostasis and defense against exogenous chemicals, which makes them a potentially sensitive target of NP. The present study aims to explore the effects of maternal NP exposure during pregnancy and lactation on MG in offspring hippocampus, the production of pro-inflammatory cytokines by MG, and associated underlying mechanisms. We found that maternal NP exposure increased the production of interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in offspring hippocampus. Increases in both activation and number of MG were observed in offspring hippocampus. Increased phosphorylation of Akt was found to co-localize with hippocampal MG, while increased phosphorylation of c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK) were observed in offspring hippocampus. Activator protein 1 (AP-1), an inflammatory transcription factor, was also activated in the hippocampus of pups subjected to maternal NP exposure. These results suggest that maternal NP exposure might activate MG in offspring hippocampus. This activation seems to subsequently increase the production of IL-1β, IL-6, and TNF-α. Furthermore, Akt/MAPK/AP-1 signaling may be involved in this activation of MG and increased production of pro-inflammatory cytokines.

Intrauterine inflammation reduces postnatal neurogenesis in the hippocampal subgranular zone and leads to accumulation of hilar ectopic granule cells

Prenatal inflammation is associated with poor neurobehavioral outcomes in exposed offspring. A common route of exposure for the fetus is intrauterine infection, which is often associated with preterm birth. Hippocampal development may be particularly vulnerable to an inflammatory insult during pregnancy as this region remains highly neurogenic both prenatally and postnatally. These studies sought to determine if intrauterine inflammation specifically altered hippocampal neurogenesis and migration of newly produced granule neurons during the early postnatal period. Microglial and astroglial cell populations known to play a role in the regulation of postnatal neurogenesis were also examined. We show that intrauterine inflammation significantly reduced hippocampal neurogenesis between postnatal days 7 (P7) and P14 as well as decreased granule cell density at P28. Ectopic migration of granule cells was observed in LPS-exposed mice at P14, but not at P28. Intrauterine inflammation had no effect on hippocampal astrocyte or microglia density or on apoptosis rate at the postnatal time points examined. Thus, exposure to intrauterine inflammation disrupts early postnatal neurogenesis and leads to aberrant migration of newly born granule cells.

Sodium butyrate abolishes lipopolysaccharide-induced depression-like behaviors and hippocampal microglial activation in mice

Patients with major depressive disorder have elevated peripheral inflammation; the degree of this increase correlates with the severity of the disorder. Chronic psychological stress increases pro-inflammatory cytokines and promotes microglial activation, leading to stress vulnerability. Epigenetics, including DNA methylation and histone modification, are also related to the pathophysiology of major depressive disorder. Sodium butyrate (SB), a histone deacetylase inhibitor, exerts an antidepressant effect by altering gene expression in the hippocampus. In this study, we investigated whether lipopolysaccharide (LPS)-induced depressive-like behaviors in mice are affected by the repeated treatment with SB. Intraperitoneal injection of LPS (5 mg/kg) induced cytokines and ionized calcium-binding adaptor molecule 1(Iba1), a marker of microglial activation, in the hippocampus. It also increased the immobility time in a forced swim test, without changing locomotion. Repeated treatment with SB reduced LPS-induced alterations. These findings suggested that epigenetic regulation exist in hippocampal microglial activation, and is involved in depressive-like behaviors associated with neuro-inflammation. Further, using cDNA microarray analyses, we examined whether LPS and SB treatment affected the microglial gene profiles. Our results indicated 64 overlapping genes, between LPS-increased genes and SB-decreased genes. Among these genes, EF hand calcium binding domain 1 was a particularly distinct candidate gene.Altogether, our findings indicated that microglial activation mediated through epigenetic regulation may be involved in depressive-like behaviors. In addition, we demonstrated the effect of SB on gene information in hippocampal microglia under neuroinflammatory conditions.

Early-Life Social Isolation-Induced Depressive-Like Behavior in Rats Results in Microglial Activation and Neuronal Histone Methylation that Are Mitigated by Minocycline.

Early-life stress is a potent risk factor for development of psychiatric conditions such as depression. The underlying mechanisms remain poorly understood. Here, we used the early-life social isolation (ESI) model of early-life stress in rats to characterize development of depressive-like behavior, the role of microglia, levels of histone methylation, as well as expression of glutamate receptor subunits in the hippocampus. We found that depressive-like behavior was induced after ESI as determined by sucrose preference and forced swimming tests. Increased expression of microglial activation marker, Iba1, was observed in the hippocampus of the ESI group, while expression of the microglial CD200 receptor, which promotes microglial quiescence, significantly decreased. In addition, increased levels of proinflammatory cytokines, interleukin 1β (IL-1β), interleukin 6 (IL-6), and tumor necrosis factor-alpha (TNF-α) were observed in the hippocampus of the ESI group. Moreover, ESI increased levels of neuronal H3K9me2 (a repressive marker of transcription) and its associated "writer" enzymes, G9a and G9a-like protein, in the hippocampus. ESI also decreased expression of hippocampal NMDA receptor subunits, NR1, and AMPA receptor subunits, GluR1 and GluR2, which are involved in synaptic plasticity, but it did not affect expression of PSD95 and NR2B. Interestingly, treatment with minocycline to block microglial activation induced by ESI inhibited increases in hippocampal microglia and prevented ESI-induced depressive-like behavior as well as increases in IL-1β, IL-6, and TNF-α. Notably, minocycline also triggered downregulation of H3K9me2 expression and restored expression of NR1, GluR1, and GluR2. These results suggest that ESI induces depressive-like behavior, which may be mediated by microglial signaling.

Quantitative Analysis and Biological Efficacies regarding the Neuroprotective and Antineuroinflammatory Actions of the Herbal Formula Jodeungsan in HT22 Hippocampal Cells and BV-2 Microglia.

Jodeungsan (JDS) is a traditional herbal formula that comprises seven medicinal herbs and is broadly utilized to treat hypertension, dementia, and headache. However, the effects of JDS and its herbal components on neurodegenerative diseases have not been reported. We examined the inhibitory effects of JDS and its seven components on neuronal cell death and inflammation using HT22 hippocampal cells and BV-2 microglia, respectively. Among its seven herbal components, Uncaria sinensis (US), Chrysanthemum morifolium (CM), Zingiber officinale (ZO), Pinellia ternata (PT), Citrus unshiu (CU), and Poria cocos (PC) exhibited significant neuroprotective effects in HT22 cells. In BV-2 cells, JDS significantly suppressed the production of tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6), indicating the antineuroinflammatory activity of JDS. In addition, the herbal extracts from ZO, Panax ginseng (PG), PT, CU, and PC exhibited inhibitory effects on the inflammatory response in microglia. These data imply that the JDS effect on neurodegeneration occurs via coordination among its seven components. To establish a quality control for JDS, a simultaneous analysis using five standard compounds identified hesperidin (37.892 ± 1.228 mg/g) as the most abundant phytochemical of JDS. Further investigation of the combinatorial activities of two or more standard compounds will be necessary to verify their antineurodegenerative regulatory mechanisms.

Learned helplessness activates hippocampal microglia in rats: A potential target for the antidepressant imipramine

An accumulating body of evidence has demonstrated that inflammation is associated with the pathology of depression. We recently found that psychological stress induces inflammation in the hippocampus of the rat brain through the inflammasome, a component of the innate immune system. Microglia, the resident macrophages in the brain, play a central role in the innate immune system and express inflammasomes; thus, we hypothesized that hippocampal microglia would be key mediators in the development of depression via stress-induced inflammation. To test this hypothesis and to determine how antidepressants modulate microglial function, we used immunohistochemistry to examine the morphological changes that occur in the hippocampal microglia of rats exposed to the learned helplessness (LH) paradigm. We noted significantly increased numbers of activated microglia in the granule cell layer, hilus, CA1, and CA3 regions of the hippocampi of LH rats. Conversely, administering imipramine to LH rats for 7days produced a significant decrease in the number of activated microglia in the hilus, but not in the other examined regions. Nonetheless, there were no significant differences in the combined number of activated and non-activated microglia either in LH or LH+imipramine rats relative to control rats. In addition, treating the naïve rats with imipramine or fluvoxamine produced no discernible microglial changes. These data suggest that stress activates hippocampal microglia, while certain antidepressants decrease the number of activated microglia in the hilus, but not in other hippocampal regions. Therefore, the hilus represents a candidate target region for the antidepressant imipramine.

Preventive effects of dexmedetomidine on the development of cognitive dysfunction following systemic inflammation in aged rats.

In the present study, we examined whether and by what mechanisms dexmedetomidine (DMED) prevents the development of systemic inflammation (SI)-induced cognitive dysfunction in aged rats. Animals received a single intraperitoneal (i.p.) injection of either 5.0mg/kg lipopolysaccharide (LPS) or vehicle. LPS-treated rats were further divided into three groups: early DMED, late DMED, or midazolam (MDZ) treatment (n=12 each). Seven days after LPS injection, cognitive function was evaluated using a novel object recognition task, followed by measurement of hippocampal levels of proinflammatory cytokines and Toll-like receptor 4 (TLR-4) expression. For ex vivo experiments, microglia were isolated from the hippocampus for assessment of cytokine response to LPS. LPS-treated rats showed memory deficits, hippocampal neuroinflammation, and TLR-4 upregulation as compared to saline-treated animals. However, early DMED treatment was able to attenuate these SI-induced neurocognitive changes, whereas no benefits were observed in the MDZ and late DMED treatment groups. In ex vivo experiments, early DMED treatment prevented the development of SI-induced excessive microglial hyperactivation, which was blocked by the nonspecific α2-adrenergic receptor (AR) antagonist atipamezole or the specific α2A-AR antagonist BRL-44408, but not by the specific α2B/C-AR antagonist ARC-239. On the other hand, neither DMED nor MDZ had a direct effect on LPS-induced release of pro-inflammatory cytokines from hippocampal microglia at clinically relevant concentrations. Our findings highlight that treatment with DMED during, but not after, peripheral SI can prevent subsequent hippocampal neuroinflammation, overexpression of TLR-4 in microglia, and cognitive dysfunction, as mediated by the α2A-AR signaling pathway.

Brain omega-3 polyunsaturated fatty acids modulate microglia cell number and morphology in response to intracerebroventricular amyloid-β 1-40 in mice.

BackgroundNeuroinflammation is a proposed mechanism by which Alzheimer’s disease (AD) pathology potentiates neuronal death and cognitive decline. Consumption of omega-3 polyunsaturated fatty acids (PUFA) is associated with a decreased risk of AD in human observational studies and exerts protective effects on cognition and pathology in animal models. These fatty acids and molecules derived from them are known to have anti-inflammatory and pro-resolving properties, presenting a potential mechanism for these protective effects.MethodsHere, we explore this mechanism using fat-1 transgenic mice and their wild type littermates weaned onto either a fish oil diet (high in n-3 PUFA) or a safflower oil diet (negligible n-3 PUFA). The fat-1 mouse carries a transgene that enables it to convert omega-6 to omega-3 PUFA. At 12 weeks of age, mice underwent intracerebroventricular (icv) infusion of amyloid-β 1-40. Brains were collected between 1 and 28 days post-icv, and hippocampal microglia, astrocytes, and degenerating neurons were quantified by immunohistochemistry with epifluorescence microscopy, while microglia morphology was assessed with confocal microscopy and skeleton analysis.ResultsFat-1 mice fed with the safflower oil diet and wild type mice fed with the fish oil diet had higher brain DHA in comparison with the wild type mice fed with the safflower oil diet. Relative to the wild type mice fed with the safflower oil diet, fat-1 mice exhibited a lower peak in the number of labelled microglia, wild type mice fed with fish oil had fewer degenerating neurons, and both exhibited alterations in microglia morphology at 10 days post-surgery. There were no differences in astrocyte number at any time point and no differences in the time course of microglia or astrocyte activation following infusion of amyloid-β 1-40.ConclusionsIncreasing brain DHA, through either dietary or transgenic means, decreases some elements of the inflammatory response to amyloid-β in a mouse model of AD. This supports the hypothesis that omega-3 PUFA may be protective against AD by modulating the immune response to amyloid-β.

Abstract # 1774 Microglia mediate the anti-depressive effects of electroconvulsive shock therapy in mice exposed to chronic unpredictable stress

Electroconvulsive therapy (ECT) is one of the most effective treatments for depression. Although it has been used for decades, particularly for treatment of major depression patients with drug resistance, the mechanisms underlying ECT’s action are still elusive. Recent studies in our laboratory demonstrated that decline in the number and activation status of hippocampal microglia underlies the development of depressive-like symptoms in chronic unpredictable stress (CUS)-exposed mice. Here, we investigated whether the therapeutic effects of ECT are mediated via modulation of microglial status. We specifically assessed whether microglial inhibition (by minocycline administration), or depletion (by chronic treatment with the selective CSF1 receptor kinase inhibitor PLX5622), interferes with the therapeutic effects of ECT in CUS-exposed mice. ECT (3 sessions/week for 2.5 weeks) reversed the CUS-induced reductions in sucrose preference (anhedonia) and social exploration. These effects were microglia-dependent, evidenced by blockade of these therapeutic effects by minocycline, or by the mere absence of brain microglia. ECT-induced increases in hippocampal neurogenesis were also reduced by minocycline. Furthermore, ECT reversed the CUS-induced decrease in the total length of hippocampal microglial processes, but not the reduction in microglial number. Consistent with these morphological changes, ECT significantly altered microglia-related gene transcripts including Csfr1, P2y12r, and P2x7. In conclusion, we show that the anti-depressive therapeutic effects of ECT are dependent on the presence and activity level of microglia in the hippocampus.

Quantitative Analysis of Psoralea corylifolia Linne and its Neuroprotective and Anti-Neuroinflammatory Effects in HT22 Hippocampal Cells and BV-2 Microglia.

The seeds of Psoralea corylifolia L. (P. corylifolia), also known as “Bo-Gol-Zhee” in Korea, are used in a traditional herbal medicine for treating various skin diseases. In the present study, we performed quantitative analyses of the seven standard components of P. corylifolia: psoralen, angelicin, neobavaisoflavone, psoralidin, isobavachalcone, bavachinin, and bakuchiol, using high-performance liquid chromatography. We also investigated the neuroprotective and anti-neuroinflammation effects of P. corylifolia and its standard components in the hippocampal cell line HT22 and microglia cell line BV-2. A 70% ethanol extract of P. corylifolia was prepared and the seven standard components were separated using C-18 analytical columns by gradient solvents with acetonitrile and water, and ultraviolet detection at 215, 225 and 275 nm. The analytical method showed high linearity, with a correlation coefficient of ≥0.9999. The amounts of the standard components ranged from 0.74 to 11.71 mg/g. Among the components, bakuchiol (11.71 mg/g) was the most potent phytochemical component of P. corylifolia. Furthermore, we analyzed the inhibitory effects of the components from P. corylifolia to determine the bioactive compound needed to regulate neuronal cell changes. Angelicin, isobavachalcone, and bakuchiol suppressed lipopolysaccharide (LPS)-stimulated nitric oxide production in LPS-treated BV-2 microglia more significantly than did the other components. In HT22 hippocampal cells, neobavaisoflavone and bakuchiol had more potent inhibitory activity against hydrogen peroxide-induced cell death. Taken together of the quantification and efficacy analyses, bakuchiol appeared to be the most potent bioactive phytochemical component of P. corylifolia for the potential treatment of neurodegenerative diseases.