Dataset Information

The P2X7 Receptor Primes IL-1? and the NLRP3 Inflammasome in Astrocytes Exposed to Mechanical Strain.

ABSTRACT: Inflammatory responses play a key role in many neural pathologies, with localized signaling from the non-immune cells making critical contributions. The NLRP3 inflammasome is an important component of innate immune signaling and can link neural insult to chronic inflammation. The NLRP3 inflammasome requires two stages to contribute: priming and activation. The priming stage involves upregulation of inflammasome components while the activation stage results in the assembly and activation of the inflammasome complex. The priming step can be rate limiting and can connect insult to chronic inflammation, but our knowledge of the signals that regulate NLRP3 inflammasome priming in sterile inflammation is limited. This study examined the link between mechanical strain and inflammasome priming in neural systems. Transient non-ischemic elevation of intraocular pressure increased mRNA for inflammasome components IL-1?, NLRP3, ASC, and CASP1 in rat and mouse retinas. The elevation was greater 1 day after the insult, with the rise in IL-1? most pronounced. The P2X7 receptor was implicated in the mechanosensitive priming of IL-1? mRNA in vivo, as the antagonist Brilliant Blue G (BBG) blocked the increased expression, the agonist BzATP mimicked the pressure-dependent rise in IL-1?, and the rise was absent in P2X7 knockout mice. In vitro measurements from optic nerve head astrocytes demonstrated an increased expression of IL-1? following stretch or swelling. This increase in IL-1? was eliminated by degradation of extracellular ATP with apyrase, or by the block of pannexin hemichannels with carbenoxolone, probenecid, or 10panx1 peptide. The rise in IL-1? expression was also blocked by P2X7 receptor antagonists BBG, A839977 or A740003. The rise in IL-1? was prevented by blocking transcription factor NF?B with Bay 11-7082, while the swelling-dependent fall in NF?B inhibitor I?B-? was reduced by A839977 and in P2X7 knockout mice. In summary, mechanical trauma to the retina primed NLRP3 inflammasome components, but only if there was ATP release through pannexin hemichannels, and autostimulation of the P2X7 receptor. As the P2X7 receptor can also trigger stage two of inflammasome assembly and activation, the P2X7 receptor may have a central role in linking mechanical strain to neuroinflammation.

SUBMITTER: Albalawi F

PROVIDER: S-EPMC5550720 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

The P2X7 Receptor Primes IL-1β and the NLRP3 Inflammasome in Astrocytes Exposed to Mechanical Strain.

Albalawi Farraj F Lu Wennan W Beckel Jonathan M JM Lim Jason C JC McCaughey Stuart A SA Mitchell Claire H CH

Frontiers in cellular neuroscience 20170808

Inflammatory responses play a key role in many neural pathologies, with localized signaling from the non-immune cells making critical contributions. The NLRP3 inflammasome is an important component of innate immune signaling and can link neural insult to chronic inflammation. The NLRP3 inflammasome requires two stages to contribute: priming and activation. The priming stage involves upregulation of inflammasome components while the activation stage results in the assembly and activation of the i ...[more]

PMID: 28848393

Similar Datasets

Project description:Mechanical strain in neural tissues can lead to the up-regulation and release of multiple cytokines including interleukin 6 (IL-6). In the retina, the mechanosensitive release of ATP can autostimulate P2X7 receptors on both retinal ganglion cell neurons and optic nerve head astrocytes. Here, we asked whether the purinergic signaling contributed to the IL-6 response to increased intraocular pressure (IOP) in vivo, and stretch or swelling in vitro. Rat and mouse eyes were exposed to non-ischemic elevations in IOP to 50-60 mmHg for 4 h. A PCR array was used to screen cytokine changes, with quantitative (q)PCR used to confirm mRNA elevations and immunoblots used for protein levels. P2X7 antagonist Brilliant Blue G (BBG) and agonist (4-benzoyl-benzoyl)-ATP (BzATP) were injected intravitreally. ELISA was used to quantify IL-6 release from optic nerve head astrocytes or retinal ganglion cells. Receptor identity was confirmed pharmacologically and in P2X7-/- mice, acute elevation of IOP altered retinal expression of multiple cytokine genes. Elevation of IL-6 was greatest, with expression of IL1rn, IL24, Tnf, Csf1, and Lif also increased more than twofold, while expression of Tnfsf11, Gdf9, and Tnfsf4 were reduced. qPCR confirmed the rise in IL-6 and extracellular ATP marker ENTPD1, but not pro-apoptotic genes. Intravitreal injection of P2X7 receptor antagonist BBG prevented the pressure-dependent rise in IL-6 mRNA and protein in the rat retina, while injection of P2X7 receptor agonist BzATP was sufficient to elevate IL-6 expression. IOP elevation increased IL-6 in wild-type but not P2X7R knockout mice. Application of mechanical strain to isolated optic nerve head astrocytes increased IL-6 levels. This response was mimicked by agonist BzATP, but blocked by antagonists BBG and A839977. Stretch or BzATP led to IL-6 release from both astrocytes and isolated retinal ganglion cells. The mechanosensitive up-regulation and release of cytokine IL-6 from the retina involves the P2X7 receptor, with both astrocytes and neurons contributing to the response.

Project description:Neuroinflammation associated with HIV-1 infection is a problem affecting ∼50% of HIV-infected individuals. NLR family pyrin domain containing 3 (NLRP3) inflammasome has been implicated in HIV-induced microglial activation, but the mechanism(s) remain unclear. Because HIV-1 Transactivator of Transcription (Tat) protein continues to be present despite antiretroviral therapy and activates NF-kB, we hypothesized that Tat could prime the NLRP3 inflammasome. We found a dose- and time-dependent induction of NLRP3 expression in microglia exposed to Tat compared with control. Tat exposure also time-dependently increased the mature caspase-1 and IL-1β levels and enhanced the IL-1β secretion. These in vitro findings were validated in archival brain tissues from Simian Immunodeficiency Virus (SIV)-infected and uninfected rhesus macaques. Further validation of NLRP3 priming in vivo involved administration of lipopolysaccharide (LPS) to HIV transgenic (Tg) rats followed by assessment of IL-1β mRNA expression and inflammasome activation (ASC oligomers and mature IL-1β). Intriguingly, LPS potentiated upregulation of IL-1β mRNA and inflammasome activation in HIV-Tg rats compared with the wild-type controls. Interestingly, we found an inverse relationship in the expression of NLRP3 and its negative regulator, miR-223, suggesting a miR-223-mediated mechanism for Tat-induced NLRP3 priming. Furthermore, blockade of NLRP3 resulted in decreased IL-1β secretion. Collectively, these findings suggest a novel role of Tat in priming and activating the NLRP3 inflammasome. Therefore, NLRP3 can be envisioned as a therapeutic target for ameliorating Tat-mediated neuroinflammation.SIGNIFICANCE STATEMENT Despite successful suppression of viremia with increased longevity in the era of combined antiretroviral therapy, chronic inflammation with underlying neurocognitive impairment continues to afflict almost 50% of infected individuals. Viral, bacterial, and cellular products have all been implicated in promoting the chronic inflammation found in these individuals. Understanding the molecular mechanism(s) by which viral proteins such as HIV-1 Transactivator of Transcription (Tat) protein can activate microglia is thus of paramount importance. Herein, we demonstrate a novel role of Tat in priming and activating NLR family pyrin domain containing 3 (NLRP3) inflammasomes in microglial cells and in HIV-Tg rats administered lipopolysaccharide. Targeting NLRP3 inflammasome pathway mediators could thus be developed as therapeutic interventions to alleviate or prevent neuroinflammation and subsequent cognitive impairment in HIV-positive patients.

Dataset Information

The P2X7 Receptor Primes IL-1? and the NLRP3 Inflammasome in Astrocytes Exposed to Mechanical Strain.

Publications

The P2X7 Receptor Primes IL-1β and the NLRP3 Inflammasome in Astrocytes Exposed to Mechanical Strain.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets