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Differential transcriptional profiles identify microglial- and macrophage-specific gene markers expressed during virus-induced neuroinflammation.

ABSTRACT: BACKGROUND:In the healthy central nervous system (CNS), microglia are found in a homeostatic state and peripheral macrophages are absent from the brain. Microglia play key roles in maintaining CNS homeostasis and acting as first responders to infection and inflammation, and peripheral macrophages infiltrate the CNS during neuroinflammation. Due to their distinct origins and functions, discrimination between these cell populations is essential to the comprehension of neuroinflammatory disorders. Studies comparing the gene profiles of microglia and peripheral macrophages, or macrophages in vitro-derived from bone marrow, under non-infectious conditions of the CNS, have revealed valuable microglial-specific genes. However, studies comparing gene profiles between CNS-infiltrating macrophages and microglia, when both are isolated from the CNS during viral-induced neuroinflammation, are lacking. METHODS:We isolated, via flow cytometry, microglia and infiltrating macrophages from the brains of Theiler's murine encephalomyelitis virus-infected C57BL/6?J mice and used RNA-Seq, followed by validation with qPCR, to examine the differential transcriptional profiles of these cells. We utilized primary literature defining subcellular localization to determine whether or not particular proteins extracted from the transcriptional profiles were expressed at the cell surface. The surface expression and cellular specificity of triggering receptor expressed on myeloid cells 1 (TREM-1) protein were examined via flow cytometry. We also examined the immune response gene profile within the transcriptional profiles of these isolated microglia and infiltrating macrophages. RESULTS:We have identified and validated new microglial- and macrophage-specific genes, encoding cell surface proteins, expressed at the peak of neuroinflammation. TREM-1 protein was confirmed to be expressed by infiltrating macrophages, not microglia, at the peak of neuroinflammation. We also identified both unique and redundant immune functions, through examination of the immune response gene profiles, of microglia and infiltrating macrophages during neurotropic viral infection. CONCLUSIONS:The differential expression of cell surface-specific genes during neuroinflammation can potentially be used to discriminate between microglia and macrophages as well as provide a resource that can be further utilized to target and manipulate specific cell responses during neuroinflammation.

SUBMITTER: DePaula-Silva AB

PROVIDER: S-EPMC6642742 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature

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Differential transcriptional profiles identify microglial- and macrophage-specific gene markers expressed during virus-induced neuroinflammation.

DePaula-Silva Ana Beatriz AB Gorbea Carlos C Doty Daniel J DJ Libbey Jane E JE Sanchez John Michael S JMS Hanak Tyler J TJ Cazalla Demián D Fujinami Robert S RS

Journal of neuroinflammation 20190720 1

<h4>Background</h4>In the healthy central nervous system (CNS), microglia are found in a homeostatic state and peripheral macrophages are absent from the brain. Microglia play key roles in maintaining CNS homeostasis and acting as first responders to infection and inflammation, and peripheral macrophages infiltrate the CNS during neuroinflammation. Due to their distinct origins and functions, discrimination between these cell populations is essential to the comprehension of neuroinflammatory dis ...[more]

PMID: 31325960

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Project description:BackgroundGenome-wide association studies of Alzheimer's disease (AD) have identified a number of significant risk loci, the majority of which lie in non-coding regions of the genome. The lack of causal alleles and considerable polygenicity remains a significant barrier to translation into mechanistic understanding. This includes identifying causal variants and the cell/tissue types in which they operate. A fuller understanding of the cell types and transcriptional networks involved in AD genetic risk mechanisms will provide important insights into pathogenesis.MethodsWe assessed the significance of the overlap between genome-wide significant AD risk variants and sites of open chromatin from data sets representing diverse tissue types. We then focussed on macrophages and microglia to investigate the role of open chromatin sites containing motifs for specific transcription factors. Partitioned heritability using LDscore regression was used to investigate the contribution of specific macrophage and microglia transcription factor motif-containing open chromatin sites to the heritability of AD.ResultsAD risk single nucleotide polymorphisms (SNPs) are preferentially located at sites of open chromatin in immune cells, particularly monocytes (z score = 4.43; corrected P = 5.88 × 10- 3). Similar enrichments are observed for macrophages (z score = 4.10; corrected P < 2.40 × 10- 3) and microglia (z score = 4.34, corrected P = 0.011). In both macrophages and microglia, AD risk variants are enriched at a subset of open chromatin sites that contain DNA binding motifs for specific transcription factors, e.g. SPI1 and MEF2. Genetic variation at many of these motif-containing sites also mediate a substantial proportion of AD heritability, with SPI1-containing sites capturing the majority of the common variant SNP-chip heritability (microglia enrichment = 16.28, corrected enrichment P = 0.0044).ConclusionsAD risk alleles plausibly operate in immune cells, including microglia, and are concentrated in specific transcriptional networks. Combined with primary genetic association results, the SPI1 and MEF2 transcriptional networks appear central to AD risk mechanisms. Investigation of transcription factors targeting AD risk SNP associated regulatory elements could provide powerful insights into the molecular processes affected by AD polygenic risk. More broadly, our findings support a model of polygenic disease risk that arises from variants located in specific transcriptional networks.

Project description:Apart from their effects on mood and reward, cannabinoids exert beneficial actions such as neuroprotection and attenuation of inflammation. The immunosuppressive activity of cannabinoids has been well established. However, the underlying mechanisms are largely unknown. We previously showed that the psychoactive cannabinoid ?(9) -tetrahydrocannabinol (THC) and the non-psychoactive cannabidiol (CBD) differ in their anti-inflammatory signalling pathways.To characterize the transcriptional effects of CBD and THC, we treated BV-2 microglial cells with these compounds and performed comparative microarray analysis using the Illumina MouseRef-8 BeadChip platform. Ingenuity Pathway Analysis was performed to identify functional subsets of genes and networks regulated by CBD and/or THC.Overall, CBD altered the expression of many more genes; from the 1298 transcripts found to be differentially regulated by the treatments, 680 gene probe sets were up-regulated by CBD and 58 by THC, and 524 gene products were down-regulated by CBD and only 36 by THC. CBD-specific gene expression profile showed changes associated with oxidative stress and glutathione depletion, normally occurring under nutrient limiting conditions or proteasome inhibition and involving the GCN2/eIF2?/p8/ATF4/CHOP-TRIB3 pathway. Furthermore, CBD-stimulated genes were shown to be controlled by nuclear factors known to be involved in the regulation of stress response and inflammation, mainly via the (EpRE/ARE)-Nrf2/ATF4 system and the Nrf2/Hmox1 axis.These observations indicated that CBD, but much less than THC, induced a cellular stress response in microglial cells and suggested that this effect could underlie its anti-inflammatory activity.This article is part of a themed section on Cannabinoids in Biology and Medicine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7.

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Differential transcriptional profiles identify microglial- and macrophage-specific gene markers expressed during virus-induced neuroinflammation.

Publications

Differential transcriptional profiles identify microglial- and macrophage-specific gene markers expressed during virus-induced neuroinflammation.

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