Microarray analysis of activated mixed glial (microglia) and monocyte-derived macrophage gene expression

A critical role for Macrophage-derived Cysteinyl-Leukotrienes in HIV-1 induced neuronal injury

Macrophages (MΦ) infected with human immunodeficiency virus (HIV)-1 or activated by its envelope protein gp120 exert neurotoxicity. We found previously that signaling via p38 mitogen-activated protein kinase (p38 MAPK) is essential to the neurotoxicity of HIVgp120-stimulated MΦ. However, the associated downstream pathways remained elusive. Here we show that cysteinyl-leukotrienes (CysLT) released by HIV-infected or HIVgp120 stimulated MΦ downstream of p38 MAPK critically contribute to neurotoxicity. SiRNA-mediated or pharmacological inhibition of p38 MAPK deprives MΦ of CysLT synthase (LTC4S) and, pharmacological inhibition of the cysteinyl-leukotriene receptor 1 (CYSLTR1) protects cerebrocortical neurons against toxicity of both gp120-stimulated and HIV-infected MΦ. Components of the CysLT pathway are differentially regulated in brains of HIV-infected individuals and a transgenic mouse model of NeuroHIV (HIVgp120tg). Moreover, genetic ablation of LTC4S or CysLTR1 prevents neuronal damage and impairment of spatial memory in HIVgp120tg mice. Altogether, our findings suggest a novel critical role for cysteinyl-leukotrienes in HIV-associated brain injury.

Re-Exploring the Inflammation-Related Core Genes and Modules in Cerebral Ischemia

The genetic transcription profile of brain ischemic and reperfusion injury remains elusive. To address this, we used an integrative analysis approach including differentially expressed gene (DEG) analysis, weighted-gene co-expression network analysis (WGCNA), and pathway and biological process analysis to analyze data from the microarray studies of nine mice and five rats after middle cerebral artery occlusion (MCAO) and six primary cell transcriptional datasets in the Gene Expression Omnibus (GEO). (1) We identified 58 upregulated DEGs with more than 2-fold increase, and adj. p < 0.05 in mouse datasets. Among them, Atf3, Timp1, Cd14, Lgals3, Hmox1, Ccl2, Emp1, Ch25h, Hspb1, Adamts1, Cd44, Icam1, Anxa2, Rgs1, and Vim showed significant increases in both mouse and rat datasets. (2) Ischemic treatment and reperfusion time were the main confounding factors in gene profile changes, while sampling site and ischemic time were not. (3) WGCNA identified a reperfusion-time irrelevant and inflammation-related module and a reperfusion-time relevant and thrombo-inflammation related module. Astrocytes and microglia were the main contributors of the gene changes in these two modules. (4) Forty-four module core hub genes were identified. We validated the expression of unreported stroke-associated core hubs or human stroke-associated core hubs. Zfp36 mRNA was upregulated in permanent MCAO; Rhoj, Nfkbiz, Ms4a6d, Serpina3n, Adamts-1, Lgals3, and Spp1 mRNAs were upregulated in both transient MCAO and permanent MCAO; and NFKBIZ, ZFP3636, and MAFF proteins, unreported core hubs implicated in negative regulation of inflammation, were upregulated in permanent MCAO, but not in transient MCAO. Collectively, these results expand our knowledge of the genetic profile involved in brain ischemia and reperfusion, highlighting the crucial role of inflammatory disequilibrium in brain ischemia.

Age-differential sexual dimorphisms in CHD8-S62X-mutant mouse synapses and transcriptomes

Chd8^+/N2373K mice with a human C-terminal-truncating mutation (N2373K) display autistic-like behaviors in juvenile and adult males but not in females. In contrast, Chd8^+/S62X mice with a human N-terminal-truncating mutation (S62X) display behavioral deficits in juvenile males (not females) and adult males and females, indicative of age-differential sexually dimorphic behaviors. Excitatory synaptic transmission is suppressed and enhanced in male and female Chd8^+/S62X juveniles, respectively, but similarly enhanced in adult male and female mutants. ASD-like transcriptomic changes are stronger in newborn and juvenile (but not adult) Chd8^+/S62X males but in newborn and adult (not juvenile) Chd8^+/S62X females. These results point to age-differential sexual dimorphisms in Chd8^+/S62X mice at synaptic and transcriptomic levels, in addition to the behavioral level.

Brain region and gene dosage-differential transcriptomic changes in Shank2-mutant mice

Shank2 is an abundant excitatory postsynaptic scaffolding protein that has been implicated in various neurodevelopmental and psychiatric disorders, including autism spectrum disorder (ASD), intellectual disability, attention-deficit/hyperactivity disorder, and schizophrenia. Shank2-mutant mice show ASD-like behavioral deficits and altered synaptic and neuronal functions, but little is known about how different brain regions and gene dosages affect the transcriptomic phenotypes of these mice. Here, we performed RNA-Seq-based transcriptomic analyses of the prefrontal cortex, hippocampus, and striatum in adult Shank2 heterozygous (HT)- and homozygous (HM)-mutant mice lacking exons 6–7. The prefrontal cortical, hippocampal, and striatal regions showed distinct transcriptomic patterns associated with synapse, ribosome, mitochondria, spliceosome, and extracellular matrix (ECM). The three brain regions were also distinct in the expression of ASD-related and ASD-risk genes. These differential patterns were stronger in the prefrontal cortex where the HT transcriptome displayed increased synaptic gene expression and reverse-ASD patterns whereas the HM transcriptome showed decreased synaptic gene expression and ASD-like patterns. These results suggest brain region- and gene dosage-differential transcriptomic changes in Shank2-mutant mice.

Age, brain region, and gene dosage-differential transcriptomic changes in Shank3-mutant mice

Shank3 is an abundant excitatory postsynaptic scaffolding protein implicated in various neurodevelopmental disorders, including autism spectrum disorder (ASD), Phelan-McDermid syndrome, intellectual disability, and schizophrenia. Shank3-mutant mice show various molecular, synaptic, and behavioral deficits, but little is known about how transcriptomic phenotypes vary across different ages, brain regions, and gene dosages. Here, we report transcriptomic patterns in the forebrains of juvenile and adult homozygous Shank3-mutant mice that lack exons 14-16 and also the prefrontal, hippocampal, and striatal transcriptomes in adult heterozygous and homozygous Shank3-mutant mice. The juvenile and adult mutant transcriptomes show patterns opposite from and similar to those observed in ASD (termed reverse-ASD and ASD-like patterns), respectively. The juvenile transcriptomic changes accompany synaptic upregulations and ribosomal and mitochondrial downregulations, whereas the adult transcriptome show opposite changes. The prefrontal, hippocampal, and striatal transcriptomes show differential changes in ASD-related gene expressions and biological functions associated with synapse, ribosome, mitochondria, and spliceosome. These patterns also differ across heterozygous and homozygous Shank3-mutant mice. These results suggest age, brain region, and gene dosage-differential transcriptomic changes in Shank3-mutant mice.

Postnatal age-differential ASD-like transcriptomic, synaptic, and behavioral deficits in Myt1l-mutant mice

Myelin transcription factor 1 like (Myt1l), a zinc-finger transcription factor, promotes neuronal differentiation and is implicated in autism spectrum disorder (ASD) and intellectual disability. However, it remains unclear whether Myt1l promotes neuronal differentiation in vivo and its deficiency in mice leads to disease-related phenotypes. Here, we report that Myt1l-heterozygous mutant (Myt1l-HT) mice display postnatal age-differential ASD-related phenotypes: newborn Myt1l-HT mice, with strong Myt1l expression, show ASD-like transcriptomic changes involving decreased synaptic gene expression and prefrontal excitatory synaptic transmission and altered righting reflex. Juvenile Myt1l-HT mice, with markedly decreased Myt1l expression, display reverse ASD-like transcriptomes, increased prefrontal excitatory transmission, and largely normal behaviors. Adult Myt1l-HT mice show ASD-like transcriptomes involving astrocytic and microglial gene upregulation, increased prefrontal inhibitory transmission, and behavioral deficits. Therefore, Myt1l haploinsufficiency leads to ASD-related phenotypes in newborn mice, which are temporarily normalized in juveniles but re-appear in adults, pointing to continuing phenotypic changes long after a marked decrease of Myt1l expression in juveniles.

Early postnatal serotonin modulation prevents adult-stage deficits in Arid1b-deficient mice through synaptic transcriptional reprogramming

Autism spectrum disorder is characterized by early postnatal symptoms, although little is known about the mechanistic deviations that produce them and whether correcting them has long-lasting preventive effects on adult-stage deficits. ARID1B, a chromatin remodeler implicated in neurodevelopmental disorders, including autism spectrum disorder, exhibits strong embryonic- and early postnatal-stage expression. We report here that Arid1b-happloinsufficient (Arid1b+/-) mice display autistic-like behaviors at juvenile and adult stages accompanied by persistent decreases in excitatory synaptic density and transmission. Chronic treatment of Arid1b+/- mice with fluoxetine, a selective serotonin-reuptake inhibitor, during the first three postnatal weeks prevents synaptic and behavioral deficits in adults. Mechanistically, these rescues accompany transcriptomic changes, including upregulation of FMRP targets and normalization of HDAC4/MEF2A-related transcriptional regulation of the synaptic proteins, SynGAP1 and Arc. These results suggest that chronic modulation of serotonergic receptors during critical early postnatal periods prevents synaptic and behavioral deficits in adult Arid1b+/- mice through transcriptional reprogramming.

Arachidonic Acid Cascade and Eicosanoid Production Are Elevated While LTC4 Synthase Modulates the Lipidomics Profile in the Brain of the HIVgp120-Transgenic Mouse Model of NeuroHIV

BACKGROUND

Combination antiretroviral therapy (cART) has transformed HIV infection from a terminal disease to a manageable chronic health condition, extending patients' life expectancy to that of the general population. However, the incidence of HIV-associated neurocognitive disorders (HANDs) has persisted despite virological suppression. Patients with HIV display persistent signs of immune activation and inflammation despite cART. The arachidonic acid (AA) cascade is an important immune response system responsible for both pro- and anti-inflammatory processes.

METHODS

Lipidomics, mRNA and Western blotting analysis provide valuable insights into the molecular mechanisms surrounding arachidonic acid metabolism and the resulting inflammation caused by perturbations thereof.

RESULTS

Here, we report the presence of inflammatory eicosanoids in the brains of a transgenic mouse model of NeuroHIV that expresses soluble HIV-1 envelope glycoprotein in glial cells (HIVgp120tg mice). Additionally, we report that the effect of LTC4S knockout in HIVgp120tg mice resulted in the sexually dimorphic transcription of COX- and 5-LOX-related genes. Furthermore, the absence of LTC4S suppressed ERK1/2 and p38 MAPK signaling activity in female mice only. The mass spectrometry-based lipidomic profiling of these mice reveals beneficial alterations to lipids in the brain.

CONCLUSION

Targeting the AA cascade may hold potential in the treatment of neuroinflammation observed in NeuroHIV and HANDs.

Slc6a20a Heterozygous and Homozygous Mutant Mice Display Differential Behavioral and Transcriptomic Changes

SLC6A20A is a proline and glycine transporter known to regulate glycine homeostasis and NMDA receptor (NMDAR) function in the brain. A previous study found increases in ambient glycine levels and NMDA receptor-mediated synaptic transmission in the brains of Slc6a20a-haploinsufficient mice, but it remained unknown whether Slc6a20a deficiency leads to disease-related behavioral deficits in mice. Here, we report that Slc6a20a heterozygous and homozygous mutant mice display differential behavioral phenotypes in locomotor, repetitive behavioral, and spatial and fear memory domains. In addition, these mice show differential transcriptomic changes in synapse, ribosome, mitochondria, autism, epilepsy, and neuron-related genes. These results suggest that heterozygous and homozygous Slc6a20a deletions in mice lead to differential changes in behaviors and transcriptomes.

Early Chronic Memantine Treatment-Induced Transcriptomic Changes in Wild-Type and Shank2-Mutant Mice

Shank2 is an excitatory postsynaptic scaffolding protein strongly implicated in autism spectrum disorders (ASDs). Shank2-mutant mice with a homozygous deletion of exons 6 and 7 (Shank2-KO mice) show decreased NMDA receptor (NMDAR) function and autistic-like behaviors at juvenile [∼postnatal day (P21)] and adult (>P56) stages that are rescued by NMDAR activation. However, at ∼P14, these mice show the opposite change – increased NMDAR function; moreover, suppression of NMDAR activity with early, chronic memantine treatment during P7–21 prevents NMDAR hypofunction and autistic-like behaviors at later (∼P21 and >P56) stages. To better understand the mechanisms underlying this rescue, we performed RNA-Seq gene-set enrichment analysis of forebrain transcriptomes from wild-type (WT) and Shank2-KO juvenile (P25) mice treated early and chronically (P7–21) with vehicle or memantine. Vehicle-treated Shank2-KO mice showed upregulation of synapse-related genes and downregulation of ribosome- and mitochondria-related genes compared with vehicle-treated WT mice. They also showed a transcriptomic pattern largely opposite that observed in ASD (reverse-ASD pattern), based on ASD-related/risk genes and cell-type–specific genes. In memantine-treated Shank2-KO mice, chromatin-related genes were upregulated; mitochondria, extracellular matrix (ECM), and actin-related genes were downregulated; and the reverse-ASD pattern was weakened compared with that in vehicle-treated Shank2-KO mice. In WT mice, memantine treatment, which does not alter NMDAR function, upregulated synaptic genes and downregulated ECM genes; memantine-treated WT mice also exhibited a reverse-ASD pattern. Therefore, early chronic treatment of Shank2-KO mice with memantine alters expression of chromatin, mitochondria, ECM, actin, and ASD-related genes.

A Pathway-Based Genomic Approach to Identify Medications: Application to Alcohol Use Disorder

Chronic, excessive alcohol use alters brain gene expression patterns, which could be important for initiating, maintaining, or progressing the addicted state. It has been proposed that pharmaceuticals with opposing effects on gene expression could treat alcohol use disorder (AUD). Computational strategies comparing gene expression signatures of disease to those of pharmaceuticals show promise for nominating novel treatments. We reasoned that it may be sufficient for a treatment to target the biological pathway rather than lists of individual genes perturbed by AUD. We analyzed published and unpublished transcriptomic data using gene set enrichment of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways to identify biological pathways disrupted in AUD brain and by compounds in the Library of Network-based Cellular Signatures (LINCS L1000) and Connectivity Map (CMap) databases. Several pathways were consistently disrupted in AUD brain, including an up-regulation of genes within the Complement and Coagulation Cascade, Focal Adhesion, Systemic Lupus Erythematosus, and MAPK signaling, and a down-regulation of genes within the Oxidative Phosphorylation pathway, strengthening evidence for their importance in AUD. Over 200 compounds targeted genes within those pathways in an opposing manner, more than twenty of which have already been shown to affect alcohol consumption, providing confidence in our approach. We created a user-friendly web-interface that researchers can use to identify drugs that target pathways of interest or nominate mechanism of action for drugs. This study demonstrates a unique systems pharmacology approach that can nominate pharmaceuticals that target pathways disrupted in disease states such as AUD and identify compounds that could be repurposed for AUD if sufficient evidence is attained in preclinical studies.

Integrative network analysis reveals biological pathways associated with Williams syndrome

BACKGROUND

Williams syndrome (WS) is a neurodevelopmental disorder that has been attributed to heterozygous deletions in chromosome 7q11.23 and exhibits a variety of physical, cognitive, and behavioral features. However, the genetic basis of this phenotypic variability is unclear. In this study, we identified genetic clues underlying these complex phenotypes.

METHODS

Neurobehavioral function was assessed in WS patients and healthy controls. Total RNA was extracted from peripheral blood and subjected to microarray analysis, RNA-sequencing, and qRT-PCR. Weighted gene co-expression network analysis was performed to identify specific alterations related to intermediate disease phenotypes. To functionally interpret each WS-related module, gene ontology and disease-related gene enrichment were examined. We also investigated the micro (mi)RNA expression profiles and miRNA co-expression networks to better explain the regulation of the transcriptome in WS.

RESULTS

Our analysis identified four significant co-expression modules related to intermediate WS phenotypes. Notably, the three upregulated WS-related modules were composed exclusively of genes located outside the 7q11.23 region. They were significantly enriched in genes related to B-cell activation, RNA processing, and RNA transport. BCL11A, which is known for its association with speech disorders and intellectual disabilities, was identified as one of the hub genes in the top WS-related module. Finally, these key upregulated mRNA co-expression modules appear to be inversely correlated with a specific downregulated WS-related miRNA co-expression module.

CONCLUSIONS

Dysregulation of the mRNA/miRNA network involving genes outside of the 7q11.23 region is likely related to the complex phenotypes observed in WS patients.

Microorganisms' Footprint in Neurodegenerative Diseases

Advancement of science has gifted the human a longer life; however, as neuron cells do not regenerate, the number of people with neurodegeneration disorders rises with population aging. Neurodegeneration diseases occur as a result of neuronal cells loss caused by environmental factors, genetic mutations, proteopathies and other cellular dysfunctions. The negative direct or indirect contributions of various microorganisms in onset or severity of some neurodegeneration disorders and interaction between human immune system and pathogenic microorganisms has been portrayed in this review article. This association may explain the early onset of neurodegeneration disorders in some individuals, which can be traced through detailed study of health background of these individuals for infection with any microbial disease with neuropathogenic microorganisms (bacteria, fungi, viruses). A better understanding and recognition of the relation between microorganisms and neurodegeneration disorders may help researchers in development of novel remedies to avoid, postpone, or make neurodegeneration disorders less severe.

Reduced ENA78 levels as novel biomarker for major depressive disorder and venlafaxine efficiency: Result from a prospective longitudinal study

Although lines of evidence demonstrated that cytokines play an important role in the pathogenesis of major depressive disorder (MDD), none of the them have been established as reliable biomarkers. We use our previous whole-genome cRNA microarray data to identify epithelial cell-derived neutrophil-activating peptide 78 (ENA78), the most differentially expressed cytokine in peripheral blood between MDD patients and healthy controls; and then we confirmed the result by the quantitative reverse transcription-polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA) for mRNA and protein level, respectively, in an independent drug-naïve first-episode sample set. In addition, to replicate the role of plasma ENA 78 in MDD, and determine the role of ENA78 on the venlafaxine efficiency, we further detected the plasma ENA78 in another independent 8- week follow-up sample set. We found that both of mRNA and plasma of ENA78 decreased in MDD patients, and displayed much lower after venlafaxine treatment. We also found that venlafaxine non-responders had lower level of peripheral plasma ENA78 prior to treatment than responders. Our findings for the first time provided strong evidence that the ENA78 may play a key role of mediator in pathogenesis of MDD and in the mechanism of vinlafaxine effects on MDD indicating that reduced ENA78 may be a potential biomarker for diagnosing of MDD and predicting of response to venlafaxine.

Gene expression in human brain implicates sexually dimorphic pathways in autism spectrum disorders

Autism spectrum disorder (ASD) is more prevalent in males, and the mechanisms behind this sex-differential risk are not fully understood. Two competing, but not mutually exclusive, hypotheses are that ASD risk genes are sex-differentially regulated, or alternatively, that they interact with characteristic sexually dimorphic pathways. Here we characterized sexually dimorphic gene expression in multiple data sets from neurotypical adult and prenatal human neocortical tissue, and evaluated ASD risk genes for evidence of sex-biased expression. We find no evidence for systematic sex-differential expression of ASD risk genes. Instead, we observe that genes expressed at higher levels in males are significantly enriched for genes upregulated in post-mortem autistic brain, including astrocyte and microglia markers. This suggests that it is not sex-differential regulation of ASD risk genes, but rather naturally occurring sexually dimorphic processes, potentially including neuron–glial interactions, that modulate the impact of risk variants and contribute to the sex-skewed prevalence of ASD.

Autism spectrum disorder is approximately 4.5 times more likely to occur in boys than girls. Here, Werling, Geschwind and Parikshak characterized sexually dimorphic gene expression in the non-diseased, post-mortem, adult and prenatal human brain, and show genes expressed at higher levels in males are significantly enriched for genes upregulated in autistic brain.

Transcriptional Regulation of CXCL5 in HIV-1-Infected Macrophages and Its Functional Consequences on CNS Pathology

Human immunodeficiency virus-1 (HIV-1)-infected monocytes/macrophages and microglia release increased levels of proinflammatory cytokines and chemokines, including ELR+ (containing glutamic acid-leucine-arginine motif) chemokines. To investigate the role of HIV-1 infection on chemokine regulation, monocyte-derived macrophages (MDMs) from normal donors were infected with HIV-1 and the expression of chemokines and their downstream biological functions were evaluated. Among the tested chemokines, CXCL5 was upregulated significantly both at the mRNA and protein level in the HIV-1-infected MDMs compared with mock-infected cultures. Upregulation of CXCL5 in the HIV-1-infected MDMs is, in part, regulated by increased interleukin-1β (IL-1β) production and phosphorylation of ERK1/2. Functional analyses indicate that HIV-1-induced overexpression of CXCL5 has enhanced the ability to attract neutrophils, as observed by chemotaxis assay. However, exposure of NT2, SH-SY5Y cells, and primary neurons to HIV-1-infected MDM supernatants resulted in cell death that was not rescued by anti-CXCL5 antibody suggesting that CXCL5 does not have direct effect on neuronal death. Together, these results suggest that the increased level of CXCL5 in tissue compartments, including the central nervous system of HIV-1-infected individuals might alter the inflammatory response through the infiltration of neutrophils into tissue compartment, thus causing secondary effects on resident cells.

Microarray analysis of gene expression profiles in the rat kidney demonstrates a local inflammatory response induced by cardiopulmonary bypass

CONTEXT

Cardiopulmonary bypass (CPB) is a commonly used technique in cardiac surgery but is associated with acute, transient, renal dysfunction that has a negative impact on long-term survival.

OBJECTIVE

To unravel the molecular pathogenesis of renal injury following CPB.

DESIGN

To obtain insight into the pathogenesis of renal dysfunction following CPB, we performed a microarray analysis of renal gene expression in the rat.

SETTING

University Medical Centre Groningen.

INTERVENTION

Rats underwent CPB or a sham procedure for 60 min and were sacrificed at 60 min, 1 and 5 days after the procedure.

MAIN OUTCOME MEASURES

Renal gene expression profile as determined by microarray analysis.

RESULTS

Expression of 420 genes was significantly altered in CPB compared to the sham procedure, and in 407 genes, this was evident in the acute phase (60 min) following CPB. Gene ontology analysis revealed 28 of these genes were involved in inflammatory responses, with high expression of genes downstream of mitogen-activated protein-kinase (MAP-kinase) signalling pathways. Potent inducers identified are from the interleukin-6 cytokine family that consists of interleukin-6 and oncostatin M (OSM), which signal through the gp130-cytokine receptor complex. The plasma concentration of interleukin-6 was hugely increased by CPB as measured by ELISA. Expression of genes downstream of these signalling pathways that lead to production of chemokines, adhesion molecules and molecules involved in coagulative pathways, was upregulated.

CONCLUSION

CPB induces an acute and local inflammatory response in the kidney, which might contribute to renal injury. The signalling pathways involved identified by gene expression analysis may represent pharmacological targets to limit renal injury following CPB.

Efficient subtractive cloning of genes activated by lipopolysaccharide and interferon γ in primary-cultured cortical cells of newborn mice

Innate immune responses play a central role in neuroprotection and neurotoxicity during inflammatory processes that are triggered by pathogen-associated molecular pattern-exhibiting agents such as bacterial lipopolysaccharide (LPS) and that are modulated by inflammatory cytokines such as interferon γ (IFNγ). Recent findings describing the unexpected complexity of mammalian genomes and transcriptomes have stimulated further identification of novel transcripts involved in specific physiological and pathological processes, such as the neural innate immune response that alters the expression of many genes. We developed a system for efficient subtractive cloning that employs both sense and antisense cRNA drivers, and coupled it with in-house cDNA microarray analysis. This system enabled effective direct cloning of differentially expressed transcripts, from a small amount (0.5 µg) of total RNA. We applied this system to isolation of genes activated by LPS and IFNγ in primary-cultured cortical cells that were derived from newborn mice, to investigate the mechanisms involved in neuroprotection and neurotoxicity in maternal/perinatal infections that cause various brain injuries including periventricular leukomalacia. A number of genes involved in the immune and inflammatory response were identified, showing that neonatal neuronal/glial cells are highly responsive to LPS and IFNγ. Subsequent RNA blot analysis revealed that the identified genes were activated by LPS and IFNγ in a cooperative or distinctive manner, thereby supporting the notion that these bacterial and cellular inflammatory mediators can affect the brain through direct but complicated pathways. We also identified several novel clones of apparently non-coding RNAs that potentially harbor various regulatory functions. Characterization of the presently identified genes will give insights into mechanisms and interventions not only for perinatal infection-induced brain damage, but also for many other innate immunity-related brain disorders.

Relationship of plasma cytokines and clinical biomarkers to memory performance in HIV

Chronic systemic immune activation and inflammatory processes have been linked to brain dysfunction in medically stable HIV-infected people. We investigated the association between verbal memory performance and plasma concentrations of 13 cytokines measured using multiplexed bead array immunoassay in 74 HIV-seropositive individuals and 50 HIV-seronegative controls. Memory performance was positively related to levels of IL-8 and IFN-γ, and negatively related to IL-10 and IL-18 and to hepatitis C infection. Memory performance was not significantly related to HIV disease markers. The results indicate the importance of systemic immune and inflammatory markers to neurocognitive function in chronic and stable HIV disease.

Leukotrienes inhibit early stages of HIV-1 infection in monocyte-derived microglia-like cells

BACKGROUND

Microglia are one of the main cell types to be productively infected by HIV-1 in the central nervous system (CNS). Leukotriene B4 (LTB4) and cysteinyl-leukotrienes such as LTC4 are some of the proinflammatory molecules produced in infected individuals that contribute to neuroinflammation. We therefore sought to investigate the role of leukotrienes (LTs) in HIV-1 infection of microglial cells.

METHODS

To evaluate the role of LTs on HIV-1 infection in the CNS, monocyte-derived microglial-like cells (MDMis) were utilized in this study. Leukotriene-treated MDMis were infected with either fully replicative brain-derived HIV-1 isolates (YU2) or R5-tropic luciferase-encoding particles in order to assess viral production and expression. The efficacy of various steps of the replication cycle was evaluated by means of p24 quantification by ELISA, luciferase activity determination and quantitative real-time polymerase chain reaction (RT-PCR).

RESULTS

We report in this study that virus replication is reduced upon treatment of MDMis with LTB4 and LTC4. Additional experiments indicate that these proinflammatory molecules alter the pH-independent entry and early post-fusion events of the viral life cycle. Indeed, LT treatment induced a diminution in integrated proviral DNA while reverse-transcribed viral products remained unaffected. Furthermore, decreased C-C chemokine receptor type 5 (CCR5) surface expression was observed in LT-treated MDMis. Finally, the effect of LTs on HIV-1 infection in MDMis appears to be mediated partly via a signal transduction pathway involving protein kinase C.

CONCLUSIONS

These data show for the first time that LTs influence microglial cell infection by HIV-1, and may be a factor in the control of viral load in the CNS.

Molecular effects of activated BV-2 microglia by mitochondrial toxin 1-methyl-4-phenylpyridinium

Microglia plays an important role in inflammation-mediated neurodegeneration. Compelling evidence supports the hypothesis that microglial activation contributes to the pathogenesis of various neurodegenerative diseases. However, little is known about the molecular outcome of activated microglia. In this report, we investigate the molecular consequences of MPP(+) toxin-induced activated BV-2 microglia. Intoxication of specific mitochondrial toxin methyl-4-phenylpyridinium iodide ion (MPP(+)) to BV-2 cells induced significant mitochondrial dysfunction and increased the reactive oxygen species generation, caspase-3 activation, and poly ADP ribose polymerase proteolysis. Further, MAC-1 immunostaining in the midbrain of mice revealed a decrease in activated microglia at day 4 after intoxication with MPP(+). From this study, it was confirmed that BV-2 microglia respond to the mitochondrial toxin MPP(+) which may lead to apoptotic cell death. Understanding of the mechanistic basis of apoptotic elimination of activated microglia may help to develop new strategies for the treatment of neurodegenerative diseases.

Interactions between prostaglandins, leukotrienes and HIV-1: possible implications for the central nervous system

In HIV-1-infected individuals, there is often discordance between viremia in peripheral blood and viral load found in the central nervous system (CNS). Although the viral burden is often lower in the CNS compartment than in the plasma, neuroinflammation is present in most infected individuals, albeit attenuated by the current combined antiretroviral therapy. The HIV-1-associated neurological complications are thought to result not only from direct viral replication, but also from the subsequent neuroinflammatory processes. The eicosanoids - prostanoids and leukotrienes - are known as potent inflammatory lipid mediators. They are often present in neuroinflammatory diseases, notably HIV-1 infection. Their exact modulatory role in HIV-1 infection is, however, still poorly understood, especially in the CNS compartment. Nonetheless, a handful of studies have provided evidence as to how these lipid mediators can modulate HIV-1 infection. This review summarizes findings indicating how eicosanoids may influence the progression of neuroAIDS.

Transcriptomic analysis of autistic brain reveals convergent molecular pathology

Autism spectrum disorder (ASD) is a common, highly heritable neuro-developmental condition characterized by marked genetic heterogeneity^1–3. Thus, a fundamental question is whether autism represents an etiologically heterogeneous disorder in which the myriad genetic or environmental risk factors perturb common underlying molecular pathways in the brain⁴. Here, we demonstrate consistent differences in transcriptome organization between autistic and normal brain by gene co-expression network analysis. Remarkably, regional patterns of gene expression that typically distinguish frontal and temporal cortex are significantly attenuated in the ASD brain, suggesting abnormalities in cortical patterning. We further identify discrete modules of co-expressed genes associated with autism: a neuronal module enriched for known autism susceptibility genes, including the neuronal specific splicing factor A2BP1/FOX1, and a module enriched for immune genes and glial markers. Using high-throughput RNA-sequencing we demonstrate dysregulated splicing of A2BP1-dependent alternative exons in ASD brain. Moreover, using a published autism GWAS dataset, we show that the neuronal module is enriched for genetically associated variants, providing independent support for the causal involvement of these genes in autism. In contrast, the immune-glial module showed no enrichment for autism GWAS signals, indicating a non-genetic etiology for this process. Collectively, our results provide strong evidence for convergent molecular abnormalities in ASD, and implicate transcriptional and splicing dysregulation as underlying mechanisms of neuronal dysfunction in this disorder.

Plasma cytokine concentrations associated with HIV/hepatitis C coinfection are related to attention, executive and psychomotor functioning

Cytokine disturbances have been linked to brain dysfunction among HIV-infected people. Past studies have not simultaneously examined a large set of cytokine measures and their relationships to HIV-associated neurocognitive deficits. We hypothesized that performance on measures of attention and executive and psychomotor functions would be associated with plasma cytokine concentrations in HIV-infected individuals. Plasma samples drawn from 30 HIV-infected and 37 HIV seronegative individuals were analyzed via xMAP multiplexed bead array immunoassay to determine concentrations of 13 cytokines. Performance on Trail Making A/B, Stroop Test, Letter-Number Sequencing, Digit Symbol Coding, Symbol Search, and Grooved Pegboard tests was assessed. Statistical analyses were performed to examine group differences in cytokine concentrations, and associations between cytokine and HIV clinical variables and neurocognitive performance. Significant HIV effects were found on 7 of the 13 cytokines, primarily with respect to interleukins. HIV clinical factors (CD4 and HIV RNA levels, duration of illness, antiretroviral treatment) and hepatitis C status were associated with specific plasma cytokine concentrations. Neurocognitive measures were associated with cytokine concentrations, most consistently among the interleukins and IP-10. Generally, cytokine concentrations were among the strongest predictors of neurocognitive function relative to other clinical factors, which reinforces their potential importance in examining the neuropathological processes of HIV. The findings also point to the potential value of simultaneously examining a panel of biomarkers. The current results suggest that a complex relationship likely exists among cytokines [how?] and that these relationships are mediated not only by HIV infection but also by antiretroviral treatment and other comorbid conditions.

HIV-1 and the macrophage

Macrophages and CD4+ T cells are natural target cells for HIV-1, and both cell types contribute to the establishment of the viral reservoir that is responsible for continuous residual virus replication during antiretroviral therapy and viral load rebound upon treatment interruption. Scientific findings that support a critical role for the infected monocyte/macrophage in HIV-1-associated diseases, such as neurological disorders and cardiovascular disease, are accumulating. To prevent or treat these HIV-1-related diseases, we need to halt HIV-1 replication in the macrophage reservoir. This article describes our current knowledge of how monocytes and certain macrophage subsets are able to restrict HIV-1 infection, in addition to what makes macrophages respond less well to current antiretroviral drugs as compared with CD4+ T cells. These insights will help to find novel approaches that can be used to meet this challenge.

Role of microglia in neurotrauma

Microglia are the primary mediators of the immune defense system of the CNS and are integral to the subsequent inflammatory response. The role of microglia in the injured CNS is under scrutiny, as research has begun to fully explore how postinjury inflammation contributes to secondary damage and recovery of function. Whether microglia are good or bad is under debate, with strong support for a dual role or differential activation of microglia. Microglia release a number of factors that modulate secondary injury and recovery after injury, including pro- and anti-inflammatory cytokines, chemokines, nitric oxide, prostaglandins, growth factors, and superoxide species. Here we review experimental work on the complex and varied responses of microglia in terms of both detrimental and beneficial effects. Addressed in addition are the effects of microglial activation in two examples of CNS injury: spinal cord and traumatic brain injury. Microglial activation is integral to the response of CNS tissue to injury. In that light, future research is needed to focus on clarifying the signals and mechanisms by which microglia can be guided to promote optimal functional recovery.

Divergence of human and mouse brain transcriptome highlights Alzheimer disease pathways

Because mouse models play a crucial role in biomedical research related to the human nervous system, understanding the similarities and differences between mouse and human brain is of fundamental importance. Studies comparing transcription in human and mouse have come to varied conclusions, in part because of their relatively small sample sizes or underpowered methodologies. To better characterize gene expression differences between mouse and human, we took a systems-biology approach by using weighted gene coexpression network analysis on more than 1,000 microarrays from brain. We find that global network properties of the brain transcriptome are highly preserved between species. Furthermore, all modules of highly coexpressed genes identified in mouse were identified in human, with those related to conserved cellular functions showing the strongest between-species preservation. Modules corresponding to glial and neuronal cells were sufficiently preserved between mouse and human to permit identification of cross species cell-class marker genes. We also identify several robust human-specific modules, including one strongly correlated with measures of Alzheimer disease progression across multiple data sets, whose hubs are poorly-characterized genes likely involved in Alzheimer disease. We present multiple lines of evidence suggesting links between neurodegenerative disease and glial cell types in human, including human-specific correlation of presenilin-1 with oligodendrocyte markers, and significant enrichment for known neurodegenerative disease genes in microglial modules. Together, this work identifies convergent and divergent pathways in mouse and human, and provides a systematic framework that will be useful for understanding the applicability of mouse models for human brain disorders.

Local cell proliferation upon enucleation in Direct Retinal Brain Targets in the Visual system of the Adult Mouse

In this study we used incorporation of the DNA synthesis marker 5-bromo-2′-deoxyuridine or BrdU to visualize cell proliferation in the visual system of the adult mouse as a response to monocular enucleation. We detected new BrdU-labeled cells in different subcortical retinal target regions and we established a specific time frame in which this cell proliferation occurred. By performing immunofluorescent double stainings for BrdU and different vascular (glucose transporter type 1, collagen type IV), glial (thymosin β4, glial fibrillary acidic protein) and neuronal (Neuronal Nuclei, doublecortin) markers, we identified these proliferating cells as activated microglia. Additional immunohistochemical stainings for thymosin β4 and glial fibrillary acidic protein also revealed reactive astrocytes in the different retinorecipient nuclei and allowed us to delineate a time frame for microglial and astroglial activation. A PCR array experiment further showed increased levels of cytokines, chemokines, growth factors and enzymes that play an important role in microglial-astroglial communication during the glial activation process in response to the deafferentation.

Microglia: biology and pathology

The past 20 years have seen a gain in knowledge on microglia biology and microglia functions in disease that exceeds the expectations formulated when the microglia "immune network" was introduced. More than 10,000 articles have been published during this time. Important new research avenues of clinical importance have opened up such as the role of microglia in pain and in brain tumors. New controversies have also emerged such as the question of whether microglia are active or reactive players in neurodegenerative disease conditions, or whether they may be victims themselves. Premature commercial interests may be responsible for some of the confusion that currently surrounds microglia in both the Alzheimer and Parkinson's disease research fields. A critical review of the literature shows that the concept of "(micro)glial inflammation" is still open to interpretation, despite a prevailing slant towards a negative meaning. Perhaps the most exciting foreseeable development concerns research on the role of microglia in synaptic plasticity, which is expected to yield an answer to the question whether microglia are the brain's electricians. This review provides an analysis of the latest developments in the microglia field.

Microglia derived IL-6 suppresses neurosphere generation from adult human retinal cell suspensions

Following retinal degeneration or inflammation that disrupts tissue architecture, there is limited evidence of tissue regeneration, despite evidence of cells with progenitor properties in the adult human retina at all ages. With the prospect of tissue/cell transplantation, redressing homeostasis whilst overcoming glial barrier or gliosis remains key to successful graft versus host integration and functional recovery. Activated human retinal microglia (MG) secrete cytokines, including IL-6, which may suppress neurogenesis or cellular (photoreceptor) replacement. To investigate this hypothesis, adult human retinal explants were cultured in cytokine-conditioned media (TNFalpha, TGFbeta, LPS/IFNgamma) to activate microglia in situ. Following culture of retinal explants for 4 days, supernatant conditioned by resulting migrated microglia was collected after a further 3 days and fed to retinal cell suspensions (RCS). Neurosphere (NS) generation and survival analysis was performed after 7 and 14 days in culture, with or without addition of conditioned media and with or without concomitant IL-6 neutralisation. Neurosphere phenotype was analysed by immunohistochemistry and cell morphology. Migratory MG from retinal explants were activated (iNOS-positive) and expressed CD45, CD11b, and CD11c. LPS/IFNgamma-activated MG conditioned media (MG-CM) contained significant levels of IL-6 (1265 +/- 143) pg/ml, which inhibited neurosphere generation within RCS in the presence of optimal neurosphere generating N2-FGF2 culture medium. Neutralising IL-6 activity reinstated NS generation and the differentiation capacity was maintained in the spheres that formed. Even in the presence of high levels of IL-6, those few NS that did form demonstrated a capacity to differentiate. The data supports activated MG-derived IL-6 influence retinal cell turnover.

Matrix metalloproteinase-7 facilitates immune access to the CNS in experimental autoimmune encephalomyelitis

BACKGROUND

Metalloproteinase inhibitors can protect mice against experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis (MS). Matrix metalloproteinase-9 (MMP-9) has been implicated, but it is not clear if other MMPs are also involved, including matrilysin/MMP-7 - an enzyme capable of cleaving proteins that are essential for blood brain barrier integrity and immune suppression.

RESULTS

Here we report that MMP-7-deficient (mmp7-/-) mice on the C57Bl/6 background are resistant to EAE induced by myelin oligodendrocyte glycoprotein (MOG). Brain sections from MOG-primed mmp7-/-mice did not show signs of immune cell infiltration of the CNS, but MOG-primed wild-type mice showed extensive vascular cuffing and mononuclear cell infiltration 15 days after vaccination. At the peak of EAE wild-type mice had MMP-7 immuno-reactive cells in vascular cuffs that also expressed the macrophage markers Iba-1 and Gr-1, as well as tomato lectin. MOG-specific proliferation of splenocytes, lymphocytes, CD4+ and CD8+ cells were reduced in cells isolated from MOG-primed mmp7-/- mice, compared with MOG-primed wild-type mice. However, the adoptive transfer of splenocytes and lymphocytes from MOG-primed mmp7-/- mice induced EAE in naïve wild-type recipients, but not naïve mmp7-/- recipients. Finally, we found that recombinant MMP-7 increased permeability between endothelial cells in an in vitro blood-brain barrier model.

CONCLUSION

Our findings suggest that MMP-7 may facilitate immune cell access or re-stimulation in perivascular areas, which are critical events in EAE and multiple sclerosis, and provide a new therapeutic target to treat this disorder.

The V1-V3 region of a brain-derived HIV-1 envelope glycoprotein determines macrophage tropism, low CD4 dependence, increased fusogenicity and altered sensitivity to entry inhibitors

Background

HIV-1 infects macrophages and microglia in the brain and can cause neurological disorders in infected patients. We and others have shown that brain-derived envelope glycoproteins (Env) have lower CD4 dependence and higher avidity for CD4 than those from peripheral isolates, and we have also observed increased fusogenicity and reduced sensitivity to the fusion inhibitor T-1249. Due to the genetic differences between brain and spleen env from one individual throughout gp120 and in gp41's heptad repeat 2 (HR2), we investigated the viral determinants for the phenotypic differences by performing functional studies with chimeric and mutant Env.

Results

Chimeric Env showed that the V1/V2-C2-V3 region in brain's gp120 determines the low CD4 dependence and high avidity for CD4, as well as macrophage tropism and reduced sensitivity to the small molecule BMS-378806. Changes in brain gp41's HR2 region did not contribute to the increased fusogenicity or to the reduced sensitivity to T-1249, since a T-1249-based peptide containing residues found in brain's but not in spleen's HR2 had similar potency than T-1249 and interacted similarly with an immobilized heptad repeat 1-derived peptide in surface plasmon resonance analysis. However, the increased fusogenicity and reduced T-1249 sensitivity of brain and certain chimeric Env mostly correlated with the low CD4 dependence and high avidity for CD4 determined by brain's V1-V3 region. Remarkably, most but not all of these low CD4-dependent, macrophage tropic envelopes glycoproteins also had increased sensitivity to the novel allosteric entry inhibitor HNG-105. The gp120's C2 region asparagine 283 (N283) has been previously associated with macrophage tropism, brain infection, lower CD4 dependence and higher CD4 affinity. Therefore, we introduced the N283T mutation into an env clone from a brain-derived isolate and into a brain tissue-derived env clone, and the T283N change into a spleen-derived env from the same individual; however, we found that their phenotypes were not affected.

Conclusion

We have identified that the V1-V3 region of a brain-derived envelope glycoprotein seems to play a crucial role in determining not only the low CD4 dependence and increased macrophage tropism, but also the augmented fusogenicity and reduced sensitivity to T-1249 and BMS-378806. By contrast, increased sensitivity to HNG-105 mostly correlated with low CD4 dependence and macrophage tropism but was not determined by the presence of the brain's V1-V3 region, confirming that viral determinants of phenotypic changes in brain-derived envelope glycoproteins are likely complex and context-dependent.

CD163, a marker of perivascular macrophages, is up-regulated by microglia in simian immunodeficiency virus encephalitis after haptoglobin-hemoglobin complex stimulation and is suggestive of breakdown of the blood-brain barrier

Macrophages and microglia are the major cell types infected by human immunodeficiency virus and simian immunodeficiency virus (SIV) in the central nervous system. Microglia are likely infected in vivo, but evidence of widespread productive infection (ie, presence of viral RNA and protein) is lacking. This conclusion is controversial because, unlike lymphocytes, macrophages and microglia cannot be discreetly immunophenotyped. Of particular interest in the search for additional monocyte/macrophage-lineage cell markers is CD163; this receptor for haptoglobin-hemoglobin (Hp-Hb) complex, which forms in plasma following erythrolysis, is expressed exclusively on cells of monocyte/macrophage lineage. We examined CD163 expression in vitro and in vivo by multiple techniques and at varying times after SIV infection in macaques with or without encephalitis. In normal and acutely SIV-infected animals, and in SIV-infected animals without encephalitis, CD163 expression was detected in cells of monocyte/macrophage lineage, including perivascular macrophages, but not in parenchymal microglia. However, in chronically infected animals with encephalitis, CD163 expression was detected in activated microglia surrounding SIV encephalitis lesions in the presence of Hp-Hb complex, suggesting leakage of the blood-brain barrier. CD163 expression was also induced on microglia in vitro after stimulation with Hp-Hb complex. We conclude that CD163 is a selective marker of perivascular macrophages in normal macaques and during the early phases of SIV infection; however, later in infection in animals with encephalitis, CD163 is also expressed by microglia, which are probably activated as a result of vascular compromise.

Isolation of murine microglial cells for RNA analysis or flow cytometry

There is increasing interest in the isolation of adult microglia to study their functions at a morphological and molecular level during normal and neuroinflammatory conditions. Microglia have important roles in brain homeostasis, and in disease states they exert neuroprotective or neurodegenerative functions. To assay expression profiles or functions of microglia, we have developed a method to isolate microglial cells and infiltrating leukocytes from adult mouse brain. This protocol uses a digestion cocktail containing collagenase and dispase, and it involves separation over discontinuous percoll gradients. Isolated cells can be used for RNA analysis, including RNase protection analysis (RPA), quantitative RT-PCR, high-density microarray, proteomic or flow cytometric characterization of cell surface markers or adoptive transfer. Cell isolation can be completed in less than 4 h.

Identification of genes preferentially expressed by microglia and upregulated during cuprizone-induced inflammation

Microglia, monocytes, and peripheral macrophages share a common origin and many characteristics, but what distinguishes them from each other at the level of gene expression remains largely unknown. In this study, we compared the transcriptional profiles of freshly purified microglia, monocytes, and spleen macrophages using Affymetrix Mouse Genome arrays to identify genes predominantly expressed by microglia. Among tens of thousands of genes assayed, 127 potential candidates were found, including nine newly discovered genes encoding plasma membrane and extracellular proteins. In the brain, the latter were selectively expressed by microglia, as revealed by in situ hybridization. Three of them were confirmed to be exclusively (MSR2) or predominantly (GPR12, GPR34) expressed in the brain compared to the other tissues examined. Furthermore, all of these genes were upregulated in activated microglia after treatment with the demyelinating toxin cuprizone, suggesting that they play roles in neuroinflammation. In conclusion, this study reports the identification of new selective markers for microglia, which should prove useful not only to identify and isolate these cells, but also to better understand their distinctive properties.

cDNA microarray analysis reveals fundamental differences in the expression profiles of primary human monocytes, monocyte-derived macrophages, and alveolar macrophages

We report the systematic use of large-scale cDNA microarrays to study the gene expression profiles of primary human peripheral blood monocytes (MONO) in comparison with in vitro-differentiated, M-CSF-induced MONO-derived macrophages (MAC) and primary human alveolar MAC (AM), obtained by bronchoalveolar lavage from the lungs of normal volunteers. These studies revealed large-scale differences in the gene expression profile between both MAC types (MAC and AM) and MONO. In addition, large differences were observed in the gene expression profiles of the two MAC types. Specifically, 21% of genes on the array (2904 out of 13,582) were differentially expressed between AM and MONO, and 2229 out of 13,583 probes were differentially expressed between MAC and AM. Our expression data show remarkable differences in gene expression between different MAC subpopulations and emphasize the heterogeneity of different MAC populations. This study underscores the need to scrutinize models of MAC biology for relevance to specific disease processes.

Microarray data on gene modulation by HIV-1 in immune cells: 2000-2006

Here, we review 34 HIV microarray studies in human immune cells over the period of 2000-March 2006 with emphasis on analytical approaches used and conceptual advances on HIV modulation of target cells (CD4 T cell, macrophage) and nontargets such as NK cell, B cell, and dendritic cell subsets. Results to date address advances on gene modulation associated with immune dysregulation, susceptibility to apoptosis, virus replication, and viral persistence following in vitro or in vivo infection/exposure to HIV-1 virus or HIV-1 accessory proteins. In addition to gene modulation associated with known functional correlates of HIV infection and replication (e.g., T cell apoptosis), microarray data have yielded novel, potential mechanisms of HIV-mediated pathogenesis such as modulation of cholesterol biosynthetic genes in CD4 T cells (relevant to virus replication and infectivity) and modulation of proteasomes and histone deacetylases in chronically infected cell lines (relevant to virus latency). Intrinsic challenges in summarizing gene modulation studies remain in development of sound approaches for comparing data obtained using different platforms and analytical tools, deriving unifying concepts to distil the large volumes of data collected, and the necessity to impose a focus for validation on a small fraction of genes. Notwithstanding these challenges, the field overall continues to demonstrate progress in expanding the pool of target genes validated to date in in vitro and in vivo datasets and understanding the functional correlates of gene modulation to HIV-1 pathogenesis in vivo.

Expression of two temporally distinct microglia-related gene clusters after spinal cord injury

The dual role of microglia in cytotoxicity and neuroprotection is believed to depend on the specific, temporal expression of microglial-related genes. To better clarify this issue, we used high-density oligonucleotide microarrays to examine microglial gene expression after spinal cord injury (SCI) in rats. We compared expression changes at the lesion site, as well as in rostral and caudal regions after mild, moderate, or severe SCI. Using microglial-associated anchor genes, we identified two clusters with different temporal profiles. The first, induced by 4 h postinjury to peak between 4 and 24 h, included interleukin-1beta, interleukin-6, osteopontin, and calgranulin, among others. The second was induced 24 h after SCI, and peaked between 72 h and 7 days; it included C1qB, Galectin-3, and p22(phox). These two clusters showed similar expression profiles regardless of injury severity, albeit with slight decreases in expression in mild or severe injury vs. moderate injury. Expression was also decreased rostral and caudal to the lesion site. We validated the expression of selected cluster members at the mRNA and protein levels. In addition, we demonstrated that stimulation of purified microglia in culture induces expression of C1qB, Galectin-3, and p22(phox). Finally, inhibition of p22(phox) activity within microglial cultures significantly suppressed proliferation in response to stimulation, confirming that this gene is involved in microglial activation. Because microglial-related factors have been implicated both in secondary injury and recovery, identification of temporally distinct clusters of genes related to microglial activation may suggest distinct roles for these groups of factors.

Gene expression profile of activated microglia under conditions associated with dopamine neuronal damage

Microglia are the resident antigen-presenting cells within the central nervous system (CNS), and they serve immune-like functions in protecting the brain against injury and invading pathogens. By contrast, activated microglia can secrete numerous reactants that damage neurons. The pathogenesis of various neurodegenerative diseases has been associated with microglial activation, but the signaling pathways that program a neuronally protective or destructive phenotype in microglia are not known. To increase the understanding of microglial activation, microarray analysis was used to profile the transcriptome of BV-2 microglial cells after activation. Microglia were activated by lipopolysaccharide, the HIV neurotoxic protein TAT, and dopamine quinone, each of which has been linked to dopamine neuronal damage. We identified 210 of 9882 genes whose expression was differentially regulated by all activators (116 increased and 94 decreased in expression). Gene ontology analysis assigned up-regulated genes to a number of specific biological processes and molecular functions, including immune response, inflammation, and cytokine/chemokine activity. Genes down-regulated in expression contribute to conditions that are permissive of microglial migration, lowered adhesion to matrix, lessened phagocytosis, and reduction in receptors that oppose chemotaxis and inflammation. These results elaborate a broad profile of microglial genes whose expression is altered by conditions associated with both neurodegenerative diseases and microglial activation.

Functional expression of CCL6 by rat microglia: a possible role of CCL6 in cell-cell communication

There is growing evidence that chemokines play important roles in the immune surveillance of central nervous system (CNS). In the CNS, microglia are primary immune effector cells and secrete various chemokines in response to their microenvironment. Using the RT-PCR procedure and indirect immunofluorescence analysis, we found that CCL6 (known as C10/MRP-1 in mouse) was expressed in rat primary microglia without any stimulation, but not in primary astrocytes, although both cell types expressed CCR1 mRNA, which is a receptor for CCL6. Furthermore, immunohistochemical analysis demonstrated that microglia produced CCL6 protein in a normal brain, suggesting that microglia may be the primary source of CCL6 in a normal brain. Recombinant rat CCL6 mediated the migration of microglia and astrocytes in vitro. The CCL6-mediated cell migration was blocked by treating the cells with LY294002, a PI3-kinase inhibitor and Western blot analysis showed that the phosphorylation of Akt could be induced by treating microglia with a recombinant CCL6, suggesting that CCL6 functions by activating the PI3-kinase/Akt pathway. A proinflammatory cytokine, interferon-gamma enhanced the expression of both CCL6 mRNA and protein in microglia, while other proinflammatory cytokines, interleukin-6 and tumor necrosis factor-alpha and an anti-inflammatory cytokine, transforming growth factor-beta exerted no effect on CCL6 expression in microglia. These findings suggest that CCL6 may be a mediator released by microglia for cell-cell communication under physiological as well as pathological conditions of CNS.