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Influence of extracellular zinc on M1 microglial activation
Youichirou Higashi1, Takaaki Aratake1, Shogo Shimizu1
1Department of Pharmacology, Kochi Medical School, Kochi University, Kohasu, Okoh-cho, Nankoku 783-8505, Japan.
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 μM ZnCl2 resulted in dose-dependent increases in interleukin-1 beta (IL-1β), interleukin-6 (IL-6), and tumour necrosis factor-alpha (TNFα) 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-1β, IL-6, TNFα, 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.
Insights
Extracellular zinc released during brain ischemia primes microglia, increasing pro-inflammatory cytokine production and impairing memory. Zinc chelation reverses these effects, highlighting zinc
Area of Science:
- Neuroscience
- Immunology
- Biochemistry
Background:
- Microglia, the immune cells of the brain, adopt M1 and M2 activation states under ischemic conditions.
- Extracellular zinc released from neurons during brain ischemia influences microglial behavior.
- The specific role of extracellular zinc in microglial M1 activation requires further investigation.
Purpose of the Study:
- To investigate the role of extracellular zinc in promoting M1 activation of microglia.
- To elucidate the mechanisms by which zinc influences pro-inflammatory cytokine production in microglia.
- To determine the impact of zinc-mediated microglial activation on cognitive function after cerebral ischemia-reperfusion.
Main Methods:
- In vitro studies involving microglia pre-treated with zinc chloride (ZnCl2) and stimulated with lipopolysaccharide.
- Assessment of cytokine secretion (IL-1β, IL-6, TNFα) and microglial surface marker expression (CD16/32).
- In vivo studies using a cerebral ischemia-reperfusion model in rodents, with and without zinc chelation (CaEDTA).
- Evaluation of cognitive function using object recognition memory tests.
Main Results:
- Zinc pre-treatment dose-dependently increased secretion of IL-1β, IL-6, and TNFα in M1-activated microglia.
- The effects of zinc were attenuated by a zinc chelator (TPEN), a radical scavenger (Trolox), and a P2X7 receptor antagonist (A438079).
- Cerebral ischemia-reperfusion induced endogenous zinc release, increasing M1 markers and pro-inflammatory cytokines, leading to memory deficits.
- Zinc chelation with CaEDTA suppressed these ischemia-reperfusion-induced effects.
Conclusions:
- Extracellular zinc primes microglia for enhanced pro-inflammatory cytokine production via P2X7 receptor activation and reactive oxygen species generation.
- Zinc-induced M1 microglial activation contributes to cognitive deficits, specifically in object recognition memory, following cerebral ischemia-reperfusion.
- Targeting extracellular zinc may offer a therapeutic strategy to mitigate neuroinflammation and memory impairments after ischemic brain injury.
