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Updated: Jun 23, 2026
Detection of MicroRNAs in Microglia by Real-time PCR in Normal CNS and During Neuroinflammation
Published on: July 23, 2012
Differential gene expression in LPS/IFNgamma activated microglia and macrophages: in vitro versus in vivo
Christoph D Schmid1, Benoit Melchior, Kokoechat Masek
1Swiss Institute of Bioinformatics, Epalinges s/Lausanne, Switzerland.
Abstract:
Two different macrophage populations contribute to CNS neuroinflammation: CNS-resident microglia and CNS-infiltrating peripheral macrophages. Markers distinguishing these two populations in tissue sections have not been identified. Therefore, we compared gene expression between LPS (lipopolysaccharide)/interferon (IFN)gamma-treated microglia from neonatal mixed glial cultures and similarly treated peritoneal macrophages. Fifteen molecules were identified by quantative PCR (qPCR) as being enriched from 2-fold to 250-fold in cultured neonatal microglia when compared with peritoneal macrophages. Only three of these molecules (C1qA, Trem2, and CXCL14) were found by qPCR to be also enriched in adult microglia isolated from LPS/IFNgamma-injected CNS when compared with infiltrating peripheral macrophages from the same CNS. The discrepancy between the in vitro and in vivo qPCR data sets was primarily because of induced expression of the 'microglial' molecules (such as the tolerance associated transcript, Tmem176b) in CNS-infiltrating macrophages. Bioinformatic analysis of the approximately 19000 mRNAs detected by TOGA gene profiling confirmed that LPS/IFNgamma-activated microglia isolated from adult CNS displayed greater similarity in total gene expression to CNS-infiltrating macrophages than to microglia isolated from unmanipulated healthy adult CNS. In situ hybridization analysis revealed that nearly all microglia expressed high levels of C1qA, while subsets of microglia expressed Trem2 and CXCL14. Expression of C1qA and Trem2 was limited to microglia, while large numbers of GABA+ neurons expressed CXCL14. These data suggest that (i) CNS-resident microglia are heterogeneous and thus a universal microglia-specific marker may not exist; (ii) the CNS micro-environment plays significant roles in determining the phenotypes of both CNS-resident microglia and CNS-infiltrating macrophages; (iii) the CNS microenvironment may contribute to immune privilege by inducing macrophage expression of anti-inflammatory molecules.
Insights
Identifying specific markers for central nervous system (CNS) microglia and infiltrating macrophages is challenging. Gene expression analysis reveals that the CNS microenvironment significantly influences macrophage phenotypes, impacting neuroinflammation.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Two distinct macrophage populations, CNS-resident microglia and peripheral macrophages, are involved in CNS neuroinflammation.
- Lack of identified markers hinders differentiation between these two cell types in tissue sections.
- Understanding these populations is crucial for developing targeted therapies for neurological disorders.
Purpose of the Study:
- To identify gene expression differences between microglia and peripheral macrophages.
- To determine if specific molecular markers can distinguish CNS-resident microglia from infiltrating macrophages in vivo.
- To investigate the influence of the CNS microenvironment on macrophage phenotype.
Main Methods:
- Comparison of gene expression using quantitative PCR (qPCR) between cultured neonatal microglia and peritoneal macrophages stimulated with lipopolysaccharide (LPS)/interferon (IFN)gamma.
- Validation of potential markers in adult microglia and infiltrating macrophages from LPS/IFNgamma-injected CNS.
- Bioinformatic analysis using TOGA gene profiling and in situ hybridization.
Main Results:
- Fifteen molecules were enriched in cultured microglia compared to peritoneal macrophages.
- Only C1qA, Trem2, and CXCL14 were enriched in adult microglia vs. infiltrating macrophages in vivo, with discrepancies attributed to induced expression in infiltrating cells.
- Activated microglia gene expression profiles were more similar to infiltrating macrophages than to resting microglia, and C1qA and Trem2 were microglia-specific, while CXCL14 was also found in neurons.
Conclusions:
- CNS-resident microglia exhibit heterogeneity, suggesting a universal microglia-specific marker may not exist.
- The CNS microenvironment significantly shapes the phenotypes of both resident microglia and infiltrating macrophages.
- The CNS microenvironment may promote immune privilege by inducing anti-inflammatory molecule expression in macrophages.
