Transmission of NLRP3-IL-1β Signals in Cerebral Ischemia and Reperfusion Injury: from Microglia to Adjacent Neuron and Endothelial Cells via IL-1β/IL-1R1/TRAF6.

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The pyrin domain-containing protein 3 (NLRP3) inflammasome drives the profound cerebral ischemia and reperfusion injury (I/R) and mediates the secretion of IL-1β (interleukin-1β), which exerts a subsequent cascade of inflammatory injury. The NLRP3-activated-microglial manipulation in adjacent neuronal and endothelial NLRP3 activation has been confirmed in our previous studies. In the present study, we extended the cognition of how microglia mediated neuronal and endothelial NLRP3-IL-1β signaling during cerebral ischemia and reperfusion injury. In vitro, Neuro-2a and bEND3 cells were cultured alone or co-cultured with BV2 cells and oxygen-glucose deprivation/reoxygenation (OGD/R) was performed. In vivo, transient middle cerebral artery occlusion (tMCAO) rat models and lentiviral silencing targeting IL-1R1 were performed. The NLRP3 inflammasome activation was evaluated by enzyme-linked immunosorbent assay, western blotting, immunoprecipitation, immunohistochemistry, and immunofluorescence. In the co-culture system after OGD/R treatment, NLRP3 inflammasomes in neurons and endothelial cells were activated by microglial IL-1β via IL-1β/IL-1R1/TRAF6 signaling pathway, with the basal protein level of NLRP3. In addition, ruptured lysosomes engulfing ASC specks which were possibly secreted from microglia triggered the enhanced NLRP3 expression. In cortices of tMCAO rats at 24h of reperfusion, silencing IL-1R1, mainly presented in neurons and endothelial cells, was efficient to block the subsequent inflammatory damage and leukocyte brain infiltration, leading to better neurological outcome. Neuronal and endothelial NLRP3 inflammasomes were activated by microglia in cerebral ischemia and reperfusion injury mainly via IL-1β/IL-1R1/TRAF6 signaling, which might be therapeutically targetable.