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Subanesthetic isoflurane relieves zymosan-induced neutrophil inflammatory response by targeting NMDA glutamate receptor and Toll-like receptor 2 signaling.

ABSTRACT: Neutrophil release of NO/ONOO- induces endothelial cell barrier dysfunction in inflammatory acute lung injury (ALI). Previous studies using zymosan-triggered inflammation and ALI model revealed that zymosan promotes inducible NO synthase (iNOS) expression in neutrophils, and that isoflurane inhibits zymosan-induced oxidative stress and iNOS biosynthesis. However, the underlying mechanisms remain largely unknown. We found here that in zymosan-primed neutrophils, iNOS is transcriptionally activated by NF-κB, whose nuclear translocation is triggered by excessive reactive oxygen species (ROS) and consequently activated p38 MAPK. ROS production is attributed to zymosan-initiated Toll-like receptor 2 (TLR2) signaling, in which the adaptor MyD88 recruits and activates c-Src, and c-Src activates NADPH oxidase to generate ROS. Subanesthetic isoflurane counteracts the aforementioned zymosan-induced signaling by targeting N-methyl-D-aspartic acid (NMDA) glutamate receptor and thereby suppressing calcium influx and c-Src activation. Whereas iNOS accelerates NO/ONOO- production in neutrophils which eventually promote protein leak from pulmonary microvascular endothelial cells (PMVEC), isoflurane reduced NO/ONOO- release from zymosan-treated neutrophils, and thus relieves trans-PMVEC protein leak. This study provides novel insights into the roles of neutrophils and the underlying mechanisms in zymosan-induced ALI, and has implications for the therapeutic potential of subanesthetic isoflurane in attenuating inflammatory responses causing lung endothelial cell damage.

SUBMITTER: Li JT

PROVIDER: S-EPMC5077975 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Despite the characteristic etiologies and phenotypes, different brain disorders rely on common pathogenic events. Glutamate-induced neurotoxicity is a pathogenic event shared by different brain disorders. Another event occurring in different brain pathological conditions is the increase of the extracellular ATP levels, which is now recognized as a danger and harmful signal in the brain, as heralded by the ability of P2 receptors (P2Rs) to affect a wide range of brain disorders. Yet, how ATP and P2R contribute to neurodegeneration remains poorly defined. For that purpose, we now examined the contribution of extracellular ATP and P2Rs to glutamate-induced neurodegeneration. We found both in vitro and in vivo that ATP/ADP through the activation of P2Y1R contributes to glutamate-induced neuronal death in the rat hippocampus. We found in cultured rat hippocampal neurons that the exposure to glutamate (100 µM) for 30 min triggers a sustained increase of extracellular ATP levels, which contributes to NMDA receptor (NMDAR)-mediated hippocampal neuronal death through the activation of P2Y1R. We also determined that P2Y1R is involved in excitotoxicity in vivo as the blockade of P2Y1R significantly attenuated rat hippocampal neuronal death upon the systemic administration of kainic acid or upon the intrahippocampal injection of quinolinic acid. This contribution of P2Y1R fades with increasing intensity of excitotoxic conditions, which indicates that P2Y1R is not contributing directly to neurodegeneration, rather behaving as a catalyst decreasing the threshold from which glutamate becomes neurotoxic. Moreover, we unraveled that such excitotoxicity process began with an early synaptotoxicity that was also prevented/attenuated by the antagonism of P2Y1R, both in vitro and in vivo. This should rely on the observed glutamate-induced calpain-mediated axonal cytoskeleton damage, most likely favored by a P2Y1R-driven increase of NMDAR-mediated Ca2+ entry selectively in axons. This may constitute a degenerative mechanism shared by different brain diseases, particularly relevant at initial pathogenic stages.

Project description:BackgroundNeutrophil depletion improves neurologic outcomes in experimental sepsis/brain injury. We hypothesized that neutrophils may exacerbate neuronal injury through the release of neurotoxic quantities of the neurotransmitter glutamate.MethodsReal-time glutamate release by primary human neutrophils was determined using enzymatic biosensors. Bacterial and direct protein-kinase C (Phorbol 12-myristate 13-acetate; PMA) activation of neutrophils in human whole blood, isolated neutrophils or human cell lines were compared in the presence/absence of N-Methyl-d-aspartic acid receptor (NMDAR) antagonists. Bacterial and direct activation of neutrophils from wild-type and transgenic murine neutrophils deficient in NMDAR-scaffolding proteins were compared using flow cytometry (phagocytosis, reactive oxygen species (ROS) generation) and real-time respirometry (oxygen consumption).FindingsBoth glutamate and the NMDAR co-agonist d-serine are rapidly released by neutrophils in response to bacterial and PMA-induced activation. Pharmacological NMDAR blockade reduced both the autocrine release of glutamate, d-serine and the respiratory burst by activated primary human neutrophils. A highly specific small-molecule inhibitor ZL006 that limits NMDAR-mediated neuronal injury also reduced ROS by activated neutrophils in a murine model of peritonitis, via uncoupling of the NMDAR GluN2B subunit from its' scaffolding protein, postsynaptic density protein-95 (PSD-95). Genetic ablation of PSD-95 reduced ROS production by activated murine neutrophils. Pharmacological blockade of the NMDAR GluN2B subunit reduced primary human neutrophil activation induced by Pseudomonas fluorescens, a glutamate-secreting Gram-negative bacillus closely related to pathogens that cause hospital-acquired infections.InterpretationThese data suggest that release of glutamate by activated neutrophils augments ROS production in an autocrine manner via actions on NMDAR expressed by these cells. FUND: GLA: Academy Medical Sciences/Health Foundation Clinician Scientist. AVG is a Wellcome Trust Senior Research Fellow.

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Subanesthetic isoflurane relieves zymosan-induced neutrophil inflammatory response by targeting NMDA glutamate receptor and Toll-like receptor 2 signaling.

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