Brain inflammation and adult neurogenesis: the dual role of microglia

In the adult mammalian brain, neurogenesis from neural stem/progenitor cells continues in two regions: the subgranular zone in the dentate gyrus and the subventricular zone lining the lateral ventricles. The generated neuroblasts migrate to their appropriate location and differentiate to mature granule cells and olfactory bulb interneurons, respectively. Following injury such as stroke, neuroblasts generated in the subventricular zone migrate also into areas which are not normally neurogenic, e.g. striatum and cerebral cortex. In the initial studies in rodents, brain inflammation and microglia activation were found to be detrimental for the survival of the new hippocampal neurons early after they had been born. The role of inflammation for adult neurogenesis has, however, turned out to be much more complex. Recent experimental evidence indicates that microglia under certain circumstances can be beneficial and support the different steps in neurogenesis, progenitor proliferation, survival, migration, and differentiation. Here we summarize the current knowledge on the role of inflammation and in particular of microglia in adult neurogenesis in the intact and injured mammalian brain. We conclude that microglia activation, as an indicator of inflammation, is not pro- or antineurogenic per se but the net outcome is dependent on the balance between secreted molecules with pro- and antiinflammatory action.     

Modulation of Neuroimmune Responses on Glia in the Central Nervous System： Implication in Therapeutic Intervention against Neuroinflammation

It has long been known that the brain is an immunologically privileged site in normal conditions. Although the cascade of immune responses can occur as long as there is a neuronal injury or a potent immune stimulation, how the brain keeps glial cells in a quiescent state is still unclear. Increasing efforts have been made by several laboratories to elucidate how repression oi~ immune responses is achieved in the neuronal environment. The suppression factors include neurotransmitters, neurohormones, neurotrophic factors, anti-inflammatory factors, and cell-cell contact via adhesion molecules or CD200 receptor. This review discusses how these factors affect the cascade of cerebral immune responses because no single factor listed above can fully account for the immune suppression. While several factors contribute to the suppression of immune responses, activation of glial cells and their production of pro-inflammatory factors do occur as long as there is a neuronal injury, suggesting that some neuronal components facilitate immune responses. This review also discusses which signals initiate or augment cerebral immune responses so that stimulatory signals override the suppressive signals. Increasing lines of evidence have demonstrated that immune responses in the brain are not always detrimental to neurons. Attempt to simply clear off inflammatory factors in the CNS may not be appropriate for neurons in neurological disorders. Appropriate control of immune cells in the CNS may be beneficial to neurons or even neuroregeneration. Therefore, understanding the mechanisms underlying immune suppression may help us to reshape pharmacological interventions against inflammation in many neurological disorders.     

Upregulation of Shiga Toxin Receptor CD77/Gb3 and Interleukin‐1β Expression in the Brain of EHEC Patients with Hemolytic Uremic Syndrome and Neurologic Symptoms

In 2011, a large outbreak of Shiga toxin‐producing enterohemorrhagic Escherichia coli (EHEC) infections occurred in northern Germany, which mainly affected adults. Out of 3842 patients, 104 experienced a complicated course comprising hemolytic uremic syndrome and neurological complications, including cognitive impairment, aphasia, seizures and coma. T2 hyperintensities on magnet resonance imaging (MRI) bilateral in the thalami and in the dorsal pons were found suggestive of a metabolic toxic effect. Five of the 104 patients died because of toxic heart failure. In the present study, the post‐mortem neuropathological findings of the five EHEC patients are described. Histological investigation of 13 brain regions (frontal, temporal, occipital cortex, corpora mammillaria, thalamus, frontal operculum, corona radiata, gyrus angularis, pons, medulla oblongata, cerebellar vermis and cerebellar hemisphere) showed no thrombosis, ischemic changes or fresh infarctions. Further, no changes were found in electron microscopy. In comparison with five age‐matched controls, slightly increased activation of microglia and a higher neuronal expression of interleukin‐1β and of Shiga toxin receptor CD77/globotriaosylceramide 3 was observed. The findings were confirmed by Western blot analyses. It is suggested that CD77/globotriaosylceramide upregulation may be a consequence to Shiga toxin exposure, whereas increased interleukin‐1β expression may point to activation of inflammatory cascades.     

Polymorphisms of Interleukin 4 Receptor Gene and Interleukin 10 Gene are not Associated with Graves' Disease in the UK

Graves' disease (GD) is an autoimmune disorder of the thyroid gland and both environmental and genetic factors contribute to disease aetiology. Cytokines, such as interleukin 4 (IL-4) and interleukin 10 (IL-10), are involved in the immune response and may be implicated in the autoimmune disease process. Associations have been reported between single nucleotide polymorphisms (SNPs) of IL-10 and the Ile50Val polymorphism of the IL-4 receptor gene (IL-4R) gene and atopy and autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis. The autoimmune diseases cluster within families and susceptibility genes may overlap between the different disorders. Therefore, we investigated 5 SNPs (-592C/A, -657G/A, -819C/T, -1349A/G, and -2013G/A) in the promoter region of the IL-10 and the Ile50Val polymorphism (A/G) in the IL-4R in a large UK population based case-control dataset with GD. No association was found between the polymorphisms studied and GD and no significant differences were found in genotype or allele frequencies between the patients and control subjects. We conclude these polymorphisms of IL-10 and IL-4R previously associated with other immune mediated diseases, do not confer susceptibility to GD in white Caucasians in the United Kingdom.     

Uromodulin: An Immunoregulatory Glycoprotein Isolated From Pregnancy Urine That Binds to and Regulates the Activity of Interleukin 1

ABSTRACT: Uromodulin is an 85 kilodalton glycoprotein originally isolated from human pregnancy which has been shown to inhibit antigen specific T cell responses to recall antigens such as tetanus toxoid. We have also found that uromodulin is a high affinity ligand for interleukin 1 and is able to regulate the activity of interleukin 1 in vitro. Finally, we present data that free interleukin 2 receptor can be found in human pregnancy urine. We propose that a number of immunoregulatory phenomena associated with pregnancy are due to molecules able to specifically regulate interleukin 1 and interleukin 2.     

香烟烟雾暴露对未成年小鼠齿状回神经发生和小胶质细胞的影响

为探讨香烟烟雾暴露(cigarette smoking exposure,CSE)对未成年小鼠的神经发生及学习记忆的影响,本研究用亲和组织化学方法,以5-溴脱氧尿苷(5-bromodeoxyuridine,BrdU)和西非单叶豆同工凝集素-B4(Bandeirae SimplicifoliaIsolectin-B4,BSI-B4)分别标记新生细胞和小胶质细胞(microglia,MG),观察了CSE小鼠齿状回内的神经发生及MG数目的变化,并通过Morris水迷宫训练测验其空间学习能力。结果显示:CSE下小鼠齿状回内的神经发生降低,MG数目显著减少;而在水迷宫的学习中,CSE组的逃避潜伏期亦明显长于对照组(P<0.05)。上述结果表明CSE损害了未成年小鼠齿状回内的神经发生,抑制了MG的激活,同时小鼠的空间学习能力与神经发生及激活的MG数量平行变化。此结果提示CSE造成的学习能力降低可能与齿状回神经发生及MG减少有关。     

Expression of Neutral Glycosphingolipids in the Brain and Spleen of Mice Lacking TNF Receptor 1

We investigated the expression of neutral glycosphingolipids (GSLs) in the brain and spleen of mice lacking the gene for the tumor necrosis factor‐α receptor p55 (TNFR1). Neutral GSLs of the ganglio‐, globo‐, and neolacto‐series were determined in the tissues of homozygous (TNFR1 ?/?) and control heterozygous (TNFR1 +/?) animals by high performance thin layer chromatography (HPTLC) overlay immunostaining with specific antibodies. The spleen of homozygous TNFR1 knockout mice lacked glucosylceramide substituted with palmitic acid, GlcCer(C16), and showed severe reduction in the expression of GlcCer(C24). In addition, gangliotetraosylceramide substituted with palmitic acid, Gg4Cer(C16), and globotetraosylceramide, Gb4Cer, were down‐regulated in the TNFR1 ?/? spleen in comparison with the heterozygous control. The brain of both groups of animals (TNFR1 ?/? and TNFR1 +/?) did not express detectable levels of Gg4Cer, Gb5Cer and Gb4Cer, but the brain of TNFR1 knockout mice expressed abundant globotriaosylceramide, Gb3Cer, compared to no expression in control heterozygous mice. nLcCer(C24) had slightly higher (1.4 fold) expression in the brain of TNFR1 ?/? mice compared with the control animals. This study provides in vivo evidence that TNF signaling via the TNFR1 is involved in the acquisition of a divergent GSL assembly in the brain, an immunologically privileged organ, and the spleen, typical secondary lymphoid organ.     

Lectins as a Tool for Detecting Neural Stem/Progenitor Cells in the Adult Mouse Brain

Glycoconjugates are biopolymers that are broadly distributed in the central nervous system, including the cell surface of neural stem cells or neural precursor cells (NSCs/NPCs). Glycoconjugates can be recognized by carbohydrate‐binding proteins, lectins. Two lectins, Phaseolus vulgaris lectin agglutinin E‐form (PHA‐E4) and wheat germ agglutinin (WGA) have been reported to be useful in isolating NSCs/NPCs by fluorescence‐activated cell sorting (FACS) or immunopanning methods. In this study, we analyzed the lectin‐binding properties of NSCs/NPCs in two neurogenic regions of the adult mouse brain to determine whether PHA‐E4 and WGA exhibit specific binding patterns on sections and whether there are other lectins presenting the binding pattern similar to those of PHA‐E4 and WGA in lectin histochemistry. Among nine types of lectins, peanut agglutinin was localized to the white matter and four lectins bound to cells within the subventricular zone (SVZ) of the lateral ventricle. Lectin histochemistry combined with immunohistochemistry demonstrated that one lectin, Ricinus communis agglutinin, specifically detected type A neuronal precursors and that the remaining three lectins, Agaricus bisporus agglutinin (ABA), PHA‐E4, and WGA, recognized type B NSCs and type C transient amplifying cells in the SVZ. These three lectins also recognized type 1 quiescent neural progenitors and type 2a amplifying neural progenitors in the subgranular layer of the dentate gyrus. Lectin histochemistry of the neurosphere culture also yielded similar results. These observations suggest that, in addition to PHA‐E4 and WGA, ABA lectin may also be applicable in FACS or immunopanning for the isolation of NSCs/NPCs. Anat Rec, 2011. © 2010 Wiley‐Liss, Inc.     

Prevention of Escherichia coli K1 Penetration of the Blood-Brain Barrier by Counteracting the Host Cell Receptor and Signaling Molecule Involved in E. coli Invasion of Human Brain Microvascular Endothelial Cells

Escherichia coli meningitis is an important cause of mortality and morbidity, and a key contributing factor is our incomplete understanding of the pathogenesis of E. coli meningitis. We have shown that E. coli penetration into the brain requires E. coli invasion of human brain microvascular endothelial cells (HBMEC), which constitute the blood-brain barrier. E. coli invasion of HBMEC involves its interaction with HBMEC receptors, such as E. coli cytotoxic necrotizing factor 1 (CNF1) interaction with its receptor, the 67-kDa laminin receptor (67LR), and host signaling molecules including cytosolic phospholipase A₂α (cPLA₂α). In the present study, we showed that treatment with etoposide resulted in decreased expression of 67LR on HBMEC and inhibited E. coli invasion of HBMEC. Pharmacological inhibition of cysteinyl leukotrienes, lipoxygenated products of arachidonic acid released by cPLA₂α, using montelukast (an antagonist of the type 1 cysteinyl leukotriene receptor) also inhibited E. coli invasion of HBMEC. E. coli penetration into the brain was significantly decreased by etoposide as well as by montelukast, and a combination of etoposide and montelukast was significantly more effective in inhibiting E. coli K1 invasion of HBMEC than single agents alone. These findings demonstrate for the first time that counteracting the HBMEC receptor and signaling molecule involved in E. coli invasion of HBMEC provides a novel approach for prevention of E. coli penetration into the brain, the essential step required for development of E. coli meningitis.The mortality and morbidity associated with neonatal Gram-negative bacillary meningitis have remained significant despite advances in antimicrobial chemotherapy and supportive care. Inadequate knowledge of the pathogenesis has contributed to this mortality and morbidity (10-12). Escherichia coli is the most common Gram-negative organism that causes neonatal meningitis. Several lines of evidence from experimental animal models as well as human cases of E. coli meningitis indicate that E. coli penetrates into the brain initially in the cerebral vasculature (2, 13), but the underlying mechanisms contributing to E. coli penetration of the blood-brain barrier remain incompletely understood (10-12).We have developed an in vitro blood-brain barrier model by isolation and cultivation of human brain microvascular endothelial cells (HBMEC) (14, 20-22). Upon cultivation on collagen-coated Transwell inserts, the HBMEC exhibit morphological and functional properties of tight junction formation and a polarized monolayer. These properties are shown by our demonstrations of tight junction proteins (such as ZO-1), adherens junction proteins (such as β-catenin), and their spatial separation, limited permeability to propidium iodide (molecular mass, 668 Da) and inulin (molecular mass, 4,000 Da), and development of high transendothelial electrical resistance (14, 20-22). We have also developed an infant rat model of experimental hematogenous meningitis (8, 13). This animal model has important similarities to E. coli meningitis in humans, such as hematogenous infection of the meninges. Using these in vitro and in vivo models, we have shown that E. coli binding to and invasion of HBMEC are prerequisites for penetration into the brain (10-12).We have shown that E. coli K1 binding to and invasion of HBMEC require specific E. coli determinants (e.g., cytotoxic necrotizing factor 1 [CNF1] and OmpA), and these E. coli determinants contribute to HBMEC binding and invasion via interactions with their respective HBMEC receptors (10-12). For example, CNF1 contributes to E. coli K1 invasion of HBMEC via its interaction with 37-kDa laminin receptor precursor (37LRP)/67-kDa lamin receptor (67LR), while OmpA contributes to E. coli K1 binding to and invasion of HBMEC via its interaction with the HBMEC receptor, gp96 (3, 7, 9). We also showed that the E. coli determinants contributing to HBMEC binding and invasion exploit specific host signaling molecules for efficient invasion of HBMEC. For example, OmpA, NlpI, FliC, and IbeC (the E. coli structures contributing to HBMEC binding and invasion) are shown to exploit host cytosolic phospholipase A₂α (cPLA₂α) for E. coli invasion of HBMEC (4, 12, 25).We also showed that blockade of the HBMEC receptors and/or host signaling molecules was effective in preventing E. coli K1 invasion of HBMEC. For example, anti-67LR and -gp96 antibodies inhibited E. coli K1 invasion of HBMEC in a ligand-dependent manner (7, 9), and pharmacological inhibition of host cPLA₂α exhibited a dose-dependent inhibition of E. coli invasion of HBMEC (4). These findings suggest that inhibition of the HBMEC receptors and host signaling molecules involved in E. coli K1 invasion of HBMEC is likely to affect the ability of E. coli to penetrate into the brain.In screening drugs for their effects on the HBMEC receptors, we determined that etoposide (a topoisomerase inhibitor) decreased the expression of 67LR on HBMEC. cPLA₂α mediates agonist-induced release of arachidonic acid (6). We showed that the contribution of host cPLA₂α to E. coli invasion of HBMEC occurs via lipoxygenated products of arachidonic acid, cysteinyl leukotrienes (LTs), formed via LT biosynthetic pathways involving 5-lipoxygenase, and acting via the type 1 cysteinyl leukotriene receptor (CysLT1) (4, 12). More importantly, etoposide and montelukast (the CysLT1 antagonist) were additive in their prevention of E. coli K1 invasion of HBMEC and also efficient in preventing E. coli K1 penetration into the brain.     

LRIG1 Enhances Chemosensitivity by Modulating BCL-2 Expression and Receptor Tyrosine Kinase Signaling in Glioma Cells

Purpose

Leucine-rich repeats and immunoglobulin-like domains 1 (LRIG1) are an inhibitor of receptor tyrosine kinases (RTKs) that was discovered in recent years, and many studies showed that LRIG1 is a tumor suppressor gene and may be related to tumor drug resistance. In this study, we explored whether LRIG1 protein expression can improve the chemosensitivity of glioma cells and what was its mechanism.

Materials and Methods

We collected 93 cases of glioma tissues and detected the expression of LRIG1 and BCL-2. We constructed a multidrug resistance cell line U251/multidrug resistance (MDR) and examined the change of LRIG1 and BCL-2 at mRNA and protein expression levels. LRIG1 expression was upregulated in U251/MDR cells and we detected the change of multidrug resistance. Meanwhile, we changed the expression of LRIG1 and BCL-2 and explored the relationship between LRIG1 and BCL-2. Finally, we also explored the relationship between LRIG1 and RTKs.

Results

LRIG1 was negatively correlated with BCL-2 expression in glioma tissue and U251/MDR cells, and upregulation of LRIG1 can enhance chemosensitivity and inhibit BCL-2 expression. Furthermore, LRIG1 was negatively correlated with RTKs in U251/MDR cells.

Conclusion

These results demonstrated that LRIG1 can improve chemosensitivity by modulating BCL-2 expression and RTK signaling in glioma cells.     

Liver X Receptor Activation Enhances Blood–Brain Barrier Integrity in the Ischemic Brain and Increases the Abundance of ATP‐Binding Cassette Transporters ABCB1 and ABCC1 on Brain Capillary Cells

The blood–brain barrier (BBB) consists of dense contacts between endothelial cells, the tight junctions, which are complemented by membrane‐bound transporters belonging to the ATP‐binding cassette (ABC) transporter family. Liver X receptors (LXR) have previously been shown to stabilize the integrity of atherosclerotic noncerebral arteries. Their effects on ischemic cerebral vessels are still unknown. By delivering LXR agonists, T0901317 and GW3965, to mice submitted to 30 minutes intraluminal middle cerebral artery occlusion, we show that LXR activation reduces brain swelling and decreases BBB permeability by upregulating LXR's target calpastatin that deactivates calpain‐1/2, stabilizing p120 catenin. p120 catenin specifically interacts with RhoA and Cdc42, inactivating the former and overactivating the latter, thus restoring the postischemic expression, phosphorylation and interaction of the tight junction proteins occludin and zona occludens‐1. Moreover, LXR activation deactivates matrix metalloproteases‐2/9 and inhibits microvascular apoptosis by deactivating JNK1/2 and caspase‐3. In addition to the cholesterol transporters ABCA1 and ABCG1, which have previously been shown to be upregulated by LXR in noncerebral vessels, LXR activation increases the abundance of the drug transporters ABCB1 and ABCC1 on ischemic brain capillaries, as we further show. That LXR activation promotes endothelial integrity in different ways makes this receptor attractive as target for stroke therapies.     

Alterations in Immune Cells and Mediators in the Brain: It's Not Always Neuroinflammation!

Neuroinflammation was once a clearly defined term denoting pathological immune processes within the central nervous system (CNS). Historically, this term was used to indicate the four hallmarks of peripheral inflammaton that occur following severe CNS injuries, such as stroke, injury or infection. Recently, however, the definition of neuroinflammation has relaxed to the point that it is often now assumed to be present when even only a single classical hallmark of inflammation is measured. As a result, a wide range of disorders, from psychiatric to degenerative diseases, are now assumed to have an integral inflammatory component. Ironically, at the same time, research has revealed unexpected nonclassical immune actions of immune mediators and cells in the CNS in the absence of pathology, increasing the likelihood that homeostatic and adaptive immune processes in the CNS will be mistaken for neuroinflammation. Thus, we suggest reserving the term neuroinflammation for contexts where multiple signs of inflammation are present to avoid erroneously classifying disorders as inflammatory when they may instead be caused by nonimmune etiologies or secondary immune processes that serve adaptive roles.     

Temporal Patterns of Soluble Adhesion Molecules in Cerebrospinal Fluid and Plasma in Patients with the Acute Brain Infraction

The aim of this study was to define concentration changes of soluble adhesion molecules (sICAM-1, sVCAM-1 and sE-Selectin) in cerebrospinal fluid and plasma, as well as, number of peripheral blood leukocytes and the albumin coefficient in the patients with the acute brain infarction. We also, analyzed the correlation between the measured levels, the infarct volume and the degree of neurological and the functional deficit. The study included 50 patients with the acute cerebral infarction and the control group consisted of 16 patients, age and sex matched. Obtained results showed significant increase in number of leukocytes, the albumin coefficient and the level of soluble adhesion molecules within the first seven days in patients. The highest values of measured parameters were noted within the third and the fourth day after the insult, which is the suggested period of maximal intensity of inflammatory reactions. Significant correlation was found between measured parameters and the infarct volume, the degree of neurological and the functional deficit. The results suggest that investigated parameters in CSF and blood represent a dynamic index of inflammatory events as one of the fundametal mechanisms responsible for neuron damage during acute phase of brain infarction.