Dataset Information

Microglial SIRP? regulates the emergence of CD11c+ microglia and demyelination damage in white matter.

ABSTRACT: A characteristic subset of microglia expressing CD11c appears in response to brain damage. However, the functional role of CD11c+ microglia, as well as the mechanism of its induction, are poorly understood. Here we report that the genetic ablation of signal regulatory protein ? (SIRP?), a membrane protein, induced the emergence of CD11c+ microglia in the brain white matter. Mice lacking CD47, a physiological ligand of SIRP?, and microglia-specific SIRP?-knockout mice exhibited the same phenotype, suggesting that an interaction between microglial SIRP? and CD47 on neighbouring cells suppressed the emergence of CD11c+ microglia. A lack of SIRP? did not cause detectable damage to the white matter, but resulted in the increased expression of genes whose expression is characteristic of the repair phase after demyelination. In addition, cuprizone-induced demyelination was alleviated by the microglia-specific ablation of SIRP?. Thus, microglial SIRP? suppresses the induction of CD11c+ microglia that have the potential to accelerate the repair of damaged white matter.

SUBMITTER: Sato-Hashimoto M

PROVIDER: S-EPMC6435324 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature

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Microglial SIRPα regulates the emergence of CD11c+ microglia and demyelination damage in white matter.

Sato-Hashimoto Miho M Nozu Tomomi T Toriba Riho R Horikoshi Ayano A Akaike Miho M Kawamoto Kyoko K Hirose Ayaka A Hayashi Yuriko Y Nagai Hiromi H Shimizu Wakana W Saiki Ayaka A Ishikawa Tatsuya T Elhanbly Ruwaida R Kotani Takenori T Murata Yoji Y Saito Yasuyuki Y Naruse Masae M Shibasaki Koji K Oldenborg Per-Arne PA Jung Steffen S Matozaki Takashi T Fukazawa Yugo Y Ohnishi Hiroshi H

eLife 20190326

A characteristic subset of microglia expressing CD11c appears in response to brain damage. However, the functional role of CD11c+ microglia, as well as the mechanism of its induction, are poorly understood. Here we report that the genetic ablation of signal regulatory protein α (SIRPα), a membrane protein, induced the emergence of CD11c+ microglia in the brain white matter. Mice lacking CD47, a physiological ligand of SIRPα, and microglia-specific SIRPα-knockout mice exhibi ...[more]

PMID: 30910011

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Project description:Rationale: Ischemic white matter damage frequently results in myelin loss, accompanied with microglial activation. We previously found that directing microglia towards an anti-inflammatory phenotype provided a beneficial microenvironment and helped maintain white matter integrity during chronic cerebral hypoperfusion. However, the molecular mechanisms underlying microglial polarization remain elusive. Methods: Hypoperfusion induced white matter damage mice model and lipopolysaccharide (LPS) induced primary cultured microglia were established. Autophagy activation in microglia was detected both in vivo and in vitro by immunofluorescence, Western blot and electron microscopy. Autophagy inhibitors/agonist were administrated to investigate the role of autophagic process in modulating microglial phenotypes. Quantitative real time-polymerase chain reaction and Western blot were carried out to investigate the possible pathway. Results: We identified rapid accumulation of autophagosomes in primary cultured microglia exposed to LPS and within activated microglia during white matter ischemic damage. Autophagy inhibitors switched microglial function from pro-inflammatory to anti-inflammatory phenotype. Furthermore, we found TLR4, one of the major receptors binding LPS, was most highly expressed on microglia in corpus callosum during white matter ischemic damage, and TLR4 deficiency could mimic the phenomenon in microglial functional transformation, and exhibit a protective activity in chronic cerebral hypoperfusion. Whereas, the anti-inflammatory phenotype of microglia in TLR4 deficiency group was largely abolished by the activation of autophagic process. Finally, our transcriptional analysis confirmed that the up-regulation of STAT1 and down-regulation of STAT6 in microglia exposure to LPS could be reversed by autophagy inhibition. Conclusion: These results indicated that TLR4-dependent autophagy regulates microglial polarization and induces ischemic white matter damage via STAT1/6 pathway.

Project description:Exposure to ambient air pollution has been associated with white matter damage and neurocognitive decline. However, the mechanisms of this injury are not well understood and remain largely uncharacterized in experimental models. Prior studies have shown that exposure to particulate matter (PM), a sub-fraction of air pollution, results in neuroinflammation, specifically the upregulation of inflammatory microglia. This study examines white matter and axonal injury, and characterizes microglial reactivity in the corpus callosum of mice exposed to 10 weeks (150 hours) of PM. Nanoscale particulate matter (nPM, aerodynamic diameter ≤200 nm) consisting primarily of traffic-related emissions was collected from an urban area in Los Angeles. Male C57BL/6J mice were exposed to either re-aerosolized nPM or filtered air for 5 hours/day, 3 days/week, for 10 weeks (150 hours; n = 18/group). Microglia were characterized by immunohistochemical double staining of ionized calcium-binding protein-1 (Iba-1) with inducible nitric oxide synthase (iNOS) to identify pro-inflammatory cells, and Iba-1 with arginase-1 (Arg) to identify anti-inflammatory/ homeostatic cells. Myelin injury was assessed by degraded myelin basic protein (dMBP). Oligodendrocyte cell counts were evaluated by oligodendrocyte transcription factor 2 (Olig2). Axonal injury was assessed by axonal neurofilament marker SMI-312. iNOS-expressing microglia were significantly increased in the corpus callosum of mice exposed to nPM when compared to those exposed to filtered air (2.2 fold increase; p<0.05). This was accompanied by an increase in dMBP (1.4 fold increase; p<0.05) immunofluorescent density, a decrease in oligodendrocyte cell counts (1.16 fold decrease; p<0.05), and a decrease in neurofilament SMI-312 (1.13 fold decrease; p<0.05) immunofluorescent density. Exposure to nPM results in increased inflammatory microglia, white matter injury, and axonal degradation in the corpus callosum of adult male mice. iNOS-expressing microglia release cytokines and reactive oxygen/ nitrogen species which may further contribute to the white matter damage observed in this model.

Dataset Information

Microglial SIRP? regulates the emergence of CD11c+ microglia and demyelination damage in white matter.

Publications

Microglial SIRPα regulates the emergence of CD11c<sup>+</sup> microglia and demyelination damage in white matter.

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