Abstract T MP71: Estrogen Attenuates NLRP3 Inflammasome Activation Following Global Cerebral Ischemia

Abstract

NLRP3 inflammasome formation and activation have recently been reported to be involved in several types of ischemic injury, including middle cerebral artery occlusion (MCAO)-induced cerebral ischemia. However, it is unknown whether or not NLRP3 inflammasome is involved in brain injury following global cerebral ischemia (GCI) in ovariectomized rats, and whether its activation can be regulated by 17β-Estradiol (E2) replacement. As part of its activation, NLRP3 can bind the apoptosis speck protein (ASC) to assemble an NLRP3-ASC-Caspase-1 inflammasome and induce caspase-1 activation, followed by subsequent activation of IL-1β and IL-18. IL-1β and IL-18 are implicated in neurodegeneration in diverse forms of experimental brain injury, including ischemic brain injury. In this study, confocal microscopic analysis revealed that NLRP3 expression was initially highly induced in hippocampal CA1 neurons at 1-day reperfusion in the placebo-treated rats following 10-min GCI. Interestingly, at later time-points (3-7 days reperfusion) NLRP3 became highly expressed in GFAP-positive astrocytes in the hippocampal CA1 region. Additionally, ASC was similarly highly induced in astrocytes and co-localized with NLRP3 at the late reperfusion stage (3-7 day). E2 replacement initiated at the time of ovariectomy (7 days before GCI) blocked the induction of NLRP3 and ASC in astrocytes. In addition, caspase-1 activity was found to be highly induced at 1-day reperfusion, and significantly attenuated following E2 replacement. Cleaved-IL-1β expression was also enhanced in neurons at 1-day reperfusion and in astrocytes at 3-7 day reperfusion - effects that were blocked by E2 replacement. Taken as a whole, the results suggest that NLRP3 inflammasome formation and activation is markedly enhanced in the hippocampal CA1 region following GCI, which may contribute to neuronal injury. Furthermore, E2 replacement markedly attenuated NLRP3 inflammation activation and cytokine induction after GCI, which may contribute to E2 neuroprotective effects following GCI.