Abstract
BackgroundThe NLR family, pyrin domain-containing 3 (NLRP3) inflammasome plays a key role in intracerebral hemorrhage (ICH)-induced inflammatory injury, and the purinergic 2X7 receptor (P2X7R) is upstream of NLRP3 activation. This study aimed to investigate how P2X7R functions in ICH-induced inflammatory injury and how the receptor interacts with the NLRP3 inflammasome.MethodsRats were treated with P2X7R small interfering RNA (siRNA) 24 h before undergoing collagenase-induced ICH. A selective P2X7R inhibitor (blue brilliant G, BBG) or a peroxynitrite (ONOO−) decomposition catalyst (5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron(III) [FeTPPS]) was injected 30 min after ICH. Brain water content, hemorrhagic lesion volume, and neurological deficits were evaluated, and western blot, immunofluorescence, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) were carried out.ResultsStriatal P2X7R and NLRP3 inflammasomes were activated after ICH. Gene silencing of P2X7R suppressed NLRP3 inflammasome activation and interleukin (IL)-1β/IL-18 release and significantly ameliorated brain edema and neurological deficits. Additionally, enhanced NADPH oxidase 2 (NOX2, gp91phox) and inducible nitric oxide synthase (iNOS), as well as their cytotoxic product (ONOO−) were markedly attenuated by BBG treatment following ICH. This was accompanied by downregulations of the inflammasome components, IL-1β/IL-18 and myeloperoxidase (MPO, a neutrophil marker). Most importantly, inflammasome activation and IL-1β/IL-18 release were significantly inhibited by ONOO− decomposition with FeTPPS.ConclusionsOur findings implicate that P2X7R exacerbated inflammatory progression and brain damage in ICH rats possibly via NLRP3 inflammasome-dependent IL-1β/IL-18 release and neutrophil infiltration. ONOO−, a potential downstream signaling molecule of P2X7R, may play a critical role in triggering NLRP3 inflammasome activation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-015-0409-2) contains supplementary material, which is available to authorized users.
Highlights
The NLR family, pyrin domain-containing 3 (NLRP3) inflammasome plays a key role in intracerebral hemorrhage (ICH)-induced inflammatory injury, and the purinergic 2X7 receptor (P2X7R) is upstream of NLRP3 activation
P2X7R was increased and mainly expressed in microglia cells following ICH Protein content was analyzed at different time points after injection to investigate whether P2X7R would respond to collagenase-induced ICH
As shown by western blot (Fig. 1a, b), P2X7R levels were significantly elevated at 6 h after ICH (P < 0.05 vs. sham-operated animals (Sham)) and peaked at around 24 h (P < 0.01 vs. Sham) when P2X7R levels were nearly 4.5 times more than those in the Sham group
Summary
The NLR family, pyrin domain-containing 3 (NLRP3) inflammasome plays a key role in intracerebral hemorrhage (ICH)-induced inflammatory injury, and the purinergic 2X7 receptor (P2X7R) is upstream of NLRP3 activation. This study aimed to investigate how P2X7R functions in ICH-induced inflammatory injury and how the receptor interacts with the NLRP3 inflammasome. Accumulating evidence suggests that innate immunity and inflammatory responses are involved in ICH-induced secondary brain injury [1,2,3]. The intracellular Nod-like receptors have recently been shown to play a critical role in the process of innate immunity and inflammatory responses [4]. The NLR family, pyrin domain-containing 3 (NLRP3) inflammasome, the best characterized member of Nod-like receptor family, is a multiprotein complex that
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