Early Upregulation of NLRP3 in the Brain of Neonatal Mice Exposed to Hypoxia-Ischemia: No Early Neuroprotective Effects of NLRP3 Deficiency

Abstract

Background: The NLRP3 inflammasome acts as an early mediator of inflammation by cleaving and releasing IL-1β and IL-18 from their proforms. Objective: The aim of this study was to describe NLRP3 activation and evaluate whether deficiency of NLRP3 protects against neonatal hypoxic ischemic brain damage. Methods: C57BL/6 and NLRP3^-/- mice at P9 were subjected to unilateral common carotid ligation followed by hypoxia. RT-PCR was used on mRNA in five different subregions of the brain. Brain infarction was evaluated by histopathology and 2,3,5-triphenyltetrazolium chloride staining. Plasma levels of IL-18 were measured by ELISA. Double labeling immunohistochemistry was used to examine cell-specific NLRP3 expression. Results: NLRP3 was upregulated 24 h after hypoxia-ischemia (HI) in the hippocampus (2.6-fold), striatum (2.2-fold) and thalamus (2.3-fold). Brain infarction volumes were not statistically significantly different in NLRP3^-/- mice compared to WT mice 24 h after HI, accompanied by no significant changes in plasma IL-18 levels. Three hours after HI, NLRP3 expression occurred in astrocytes located in the hippocampus and habenular nucleus of the thalamus. Microglia only showed scarce expression at this time point, but prominent NLRP3 expression 72 h after HI. Conclusion: Astrocytes are early mediators of NLRP3 activity. No early neuroprotective effect of NLRP3 deficiency in neonatal HI brain damage was shown.

Neuromodulatory Effect of NLRP3 and ASC in Neonatal Hypoxic Ischemic Encephalopathy

“…We previously reported that NLRP3 is upregulated after neonatal hypoxia-ischemia and that early expression is seen in astrocytes (3 h), while microglial expression of NLRP3 is evident after 24–72 h [6]. However, we did not find any difference in early infarction volume (24 h) between NLRP3-deficient mice and wild-type (Wt) mice after hypoxia-ischemia.…”

“…Circulating levels of IL-1β, IL-18, and tumor necrosis factor (TNF) were measured in plasma as previously described [6], using Meso Scale technology (MesoScale, Diagnostics) and Bio-Plex suspension array (Bio-Rad Laboratories Inc.) according to the manufacturer’s protocol.…”

Inflammasome Priming in Sterile Inflammatory Disease

“…Nlrp3 RNA expression and protein levels were also increased in the brain following hypoxia-ischemia (HI) in a mouse model [22]. At earlier time points following HI, NLRP3 expression was detected in astrocytes in the hippocampus and the thalamus, and at later time points both astrocytes and microglia showed increased NLRP3 expression [22] .…”

“…Nlrp3 RNA expression and protein levels were also increased in the brain following hypoxia-ischemia (HI) in a mouse model [22]. At earlier time points following HI, NLRP3 expression was detected in astrocytes in the hippocampus and the thalamus, and at later time points both astrocytes and microglia showed increased NLRP3 expression [22] . Furthermore, hypoxic exposure was found to increase the levels of NLRP3, AIM2, and pro-IL-1 in human prostate epithelial cells, in prostate cancer cell lines, and in THP-1 cells, and was targeted using an NF-κB inhibitor [23] .…”

Ginkgolide B ameliorates NLRP3 inflammasome activation after hypoxic‐ischemic brain injury in the neonatal male rat

“…In particular, the secretion of IL‐1β and IL‐18 requires the NOD (nucleotide‐binding oligomerization domain)‐like receptor (NLR) Pyrin domain containing 3 (NLRP3) inflammasome (Singh and Jha, 2018; Song et al, 2017). NLRP3 activation has been reported to mediate injury in various CNS disorders including HIE (Ystgaard et al, 2015; Chen et al, 2018). The up‐regulation of NLRP3 was found in several regions of the brain at 24 h after neonatal HI (Ystgaard et al, 2015; Chen et al, 2018).…”