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Influence of extracellular zinc on M1 microglial activation.

ABSTRACT: Extracellular zinc, which is released from hippocampal neurons in response to brain ischaemia, triggers morphological changes in microglia. Under ischaemic conditions, microglia exhibit two opposite activation states (M1 and M2 activation), which may be further regulated by the microenvironment. We examined the role of extracellular zinc on M1 activation of microglia. Pre-treatment of microglia with 30-60??M ZnCl2 resulted in dose-dependent increases in interleukin-1 beta (IL-1?), interleukin-6 (IL-6), and tumour necrosis factor-alpha (TNF?) secretion when M1 activation was induced by lipopolysaccharide administration. In contrast, the cell-permeable zinc chelator TPEN, the radical scavenger Trolox, and the P2X7 receptor antagonist A438079 suppressed the effects of zinc pre-treatment on microglia. Furthermore, endogenous zinc release was induced by cerebral ischaemia-reperfusion, resulting in increased expression of IL-1?, IL-6, TNF?, and the microglial M1 surface marker CD16/32, without hippocampal neuronal cell loss, in addition to impairments in object recognition memory. However, these effects were suppressed by the zinc chelator CaEDTA. These findings suggest that extracellular zinc may prime microglia to enhance production of pro-inflammatory cytokines via P2X7 receptor activation followed by reactive oxygen species generation in response to stimuli that trigger M1 activation, and that these inflammatory processes may result in deficits in object recognition memory.

SUBMITTER: Higashi Y

PROVIDER: S-EPMC5327400 | biostudies-literature | 2017 Feb

REPOSITORIES: biostudies-literature

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Influence of extracellular zinc on M1 microglial activation.

Higashi Youichirou Y Aratake Takaaki T Shimizu Shogo S Shimizu Takahiro T Nakamura Kumiko K Tsuda Masayuki M Yawata Toshio T Ueba Tetuya T Saito Motoaki M

Scientific reports 20170227

Extracellular zinc, which is released from hippocampal neurons in response to brain ischaemia, triggers morphological changes in microglia. Under ischaemic conditions, microglia exhibit two opposite activation states (M1 and M2 activation), which may be further regulated by the microenvironment. We examined the role of extracellular zinc on M1 activation of microglia. Pre-treatment of microglia with 30-60 μM ZnCl<sub>2</sub> resulted in dose-dependent increases in interleukin-1 beta (IL-1β), int ...[more]

PMID: 28240322

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Project description:Following traumatic brain injury (TBI), activation of microglia and peripherally derived inflammatory macrophages occurs in association with tissue damage. This neuroinflammatory response may have beneficial or detrimental effects on neuronal survival, depending on the functional polarization of these cells along a continuum from M1-like to M2-like activation states. The mechanisms that regulate M1-like and M2-like activation after TBI are not well understood, but appear in part to reflect the redox state of the lesion microenvironment. NADPH oxidase (NOX2) is a critical enzyme system that generates reactive oxygen species in microglia/macrophages. After TBI, NOX2 is strongly up-regulated in M1-like, but not in M2-like polarized cells. Therefore, we hypothesized that NOX2 drives M1-like neuroinflammation and contributes to neurodegeneration and loss of neurological function after TBI. In the present studies we inhibited NOX2 activity using NOX2-knockout mice or the selective peptide inhibitor gp91ds-tat. We show that NOX2 is highly up-regulated in infiltrating macrophages after injury, and that NOX2 deficiency reduces markers of M1-like activation, limits tissue loss and neurodegeneration, and improves motor recovery after moderate-level control cortical injury (CCI). NOX2 deficiency also promotes M2-like activation after CCI, through increased IL-4Rα signaling in infiltrating macrophages, suggesting that NOX2 acts as a critical switch between M1- and M2-like activation states after TBI. Administration of gp91ds-tat to wild-type CCI mice starting at 24h post-injury reduces deficits in cognitive function and increased M2-like activation in the hippocampus. Collectively, our data indicate that increased NOX2 activity after TBI drives M1-like activation that contributes to inflammatory-mediated neurodegeneration, and that inhibiting this pathway provides neuroprotection, in part by altering M1-/M2-like balance towards the M2-like neuroinflammatory response.

Dataset Information

Influence of extracellular zinc on M1 microglial activation.

Publications

Influence of extracellular zinc on M1 microglial activation.

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