Mechanisms Underlying Interferon-γ-Induced Priming of Microglial Reactive Oxygen Species Production

Abstract

Microglial priming and enhanced reactivity to secondary insults cause substantial neuronal damage and are hallmarks of brain aging, traumatic brain injury and neurodegenerative diseases. It is, thus, of particular interest to identify mechanisms involved in microglial priming. Here, we demonstrate that priming of microglia with interferon-γ (IFN γ) substantially enhanced production of reactive oxygen species (ROS) following stimulation of microglia with ATP. Priming of microglial ROS production was substantially reduced by inhibition of p38 MAPK activity with SB203580, by increases in intracellular glutathione levels with N-Acetyl-L-cysteine, by blockade of NADPH oxidase subunit NOX2 activity with gp91ds-tat or by inhibition of nitric oxide production with L-NAME. Together, our data indicate that priming of microglial ROS production involves reduction of intracellular glutathione levels, upregulation of NADPH oxidase subunit NOX2 and increases in nitric oxide production, and suggest that these simultaneously occurring processes result in enhanced production of neurotoxic peroxynitrite. Furthermore, IFNγ-induced priming of microglial ROS production was reduced upon blockade of Kir2.1 inward rectifier K+ channels with ML133. Inhibitory effects of ML133 on microglial priming were mediated via regulation of intracellular glutathione levels and nitric oxide production. These data suggest that microglial Kir2.1 channels may represent novel therapeutic targets to inhibit excessive ROS production by primed microglia in brain pathology.

Priming of microglia with IFN-γ slows neuronal gamma oscillations in situ

“…Indeed, it is well-established that IFN-γ is one of the most typical inducers of iNOS in macrophages and microglia (1,4,11). The moderate NO release seems to be a specific response because IFN-γ widely failed to induce reactive oxygen species production in microglia, at least, in vitro (24,56). Therefore, our data provide details for the current concept of microglial priming (20,23), i.e., the presence of an inflammatory NO component that can disturb cortical gamma oscillations.…”

“…IFN-γ serves in the priming of microglia that associates with a variety of cellular adaptations, including changes in morphology, up-regulation of receptors, and increased levels of proinflammatory cytokines (4,(18)(19)(20). Notably, priming has been generally considered to permit an exaggerated microglial response to secondary-and otherwise subthreshold-inflammatory stimuli (20)(21)(22)(23)(24). For example, bacterial lipopolysaccharide (LPS) acting through Toll-like receptor 4 (TLR4) then triggers the release of proinflammatory and cytotoxic substances, such as TNF-α, IL-6, and nitric oxide (NO), finally resulting in neuronal death (1,3,25,26).…”

Current prospects of type II interferon γ signaling and autoimmunity

“…Consequently, IFN priming elicits regulation of complex biological process via epigenetic remodeling and enrichment of STAT1-binding motifs in mice (66). For example, microglial reactive oxygen species production in response to IFNs required simultaneous modification of three mechanisms, including up-regulation of the NADPH oxidase subunit NOX2, upregulation of NO production, and the reduction of intracellular GSH levels (67).…”

Folic acid deficiency enhanced microglial immune response via the Notch1/nuclear factor kappa B p65 pathway in hippocampus following rat brain I/R injury and BV2 cells

“…The mild or moderate activation of microglial cells migrate to the ischaemic area to clear the harmful agents and maintain tissue homoeostasis . However, uncontrolled or over‐activated microglia may exacerbate tissue damage and neuronal death by producing excessive inflammatory cytokines, chemokines and oxygen/nitrogen‐free radicals, such as NO, TNF‐α, IL‐1β, IL‐6 and reactive oxygen species (ROS) . Lambertsen et al proved that microglia macrophages, especially activated microglia, were the predominant source of TNF‐α after induction of pMCAO .…”

“…34 However, uncontrolled or over-activated microglia may exacerbate tissue damage and neuronal death by producing excessive inflammatory cytokines, chemokines and oxygen/nitrogen-free radicals, such as NO, TNF-α, IL-1β, IL-6 and reactive oxygen species (ROS). 35,36 Lambertsen et al proved that microglia macrophages, especially activated microglia, were the predominant source of TNF-α after induction of pMCAO. 37 The cells that expressed IL-1β had the morphologic features of microglia and macrophages in permanent unilateral occlusion of the middle cerebral artery.…”