Inhibiting Inflammasome Activation Research Articles

Knockdown of GPER in Cardiomyocytes Activates NLRP3 Pathways

IntroductionImmune activation and subsequent low‐grade inflammation have emerged as important factors in the progression of heart failure, particularly among postmenopausal women. The molecular underpinnings of this effect are not clear but might involve the loss of estrogenic control on mitochondrial reactive oxygen species (ROS), with subsequent activation of the cardiac NLRP3 inflammasome; a component of the innate immune system. We've shown that activation of the G‐protein coupled estrogen receptor (GPER), by its specific agonist G1, prevents cardiac remodeling and dysfunction from estrogen deficiency, aging and hypertension, and that genetic deactivation of cardiac GPER leads to LV dysfunction. Others report that GPER has anti‐atherogenic effects partly due to suppression of toll‐like receptors. Taken together, we hypothesize that cardiac GPER has a key role in both the maintenance of cardiac mitochondrial resilience and suppression of inflammasome activation in the female heart, and that deactivation by E2 loss unbridles vulnerabilities to aging and hemodynamic stress. To study this potential GPER‐to‐cardiac mitochondrial induced‐inflammatory interaction, we characterized changes in mitochondrial ROS and innate immunity gene transcripts in hearts from cardiomyocyte specific GPER knockout (KO) female mice and GPER‐intact wild type (WT).MethodsGPER KO and WT littermates (n=6/group, 6 months old) underwent echocardiographic evaluations prior to sacrifice. Using real‐time qPCR, HPLC‐coulometric electrochemical detection, and RT2 Profiler™ PCR Array assays, frozen cardiac tissue was processed, respectively, for measures of: 1) BNP mRNA; 2) mitochondrial resilience ‐ defined by reduced glutathione‐to‐oxidized glutathione ratios (GSH/GSSG), and mRNA levels of Sirt3 and SOD2; and 3) inflammatory transcript markers of innate immunity. Data were analyzed by Student's t‐test (significance P<0.05).ResultsAs expected, GPER knockdown resulted in 40% and 34% reductions in fractional shortening (%FS) and myocardial relaxation (e′), respectively, and a 4.5‐fold increase in BNP mRNA expression (P<0.01). Oxidative stress was increased in GPER KO, as indicated by reductions in redox status and gene transcript levels of Sirt3 and its mitochondrial deacetylation substrate SOD2 (Fig. 1). Cardiac NOD‐like receptors (NLRP3, Naip5, and NLRP5) caspase‐1, caspase‐12, IL‐18, IL‐12b, and IL‐6, were all increased by 3‐fold or more when compared to WT, and this occurred independent of changes in expression of the NF‐κB gene family (Fig. 2).ConclusionAbsence of cardiac GPER allows activation of inflammatory pathways expressing as loss of mitochondrial quality control programs, such as Sirt3 and SOD2, with subsequent increases in mitochondrial ROS in association with cardiac inflammasome activation. Given that NF‐κB expression was not affected by GPER KO, it is less likely that NRLP3 is transcriptionally regulated in this model. Future studies will determine whether GPER activation by G1 blunts the NLRP3 inflammasome through a Sirt3‐mediated mitochondrial “surveillance” mechanism to limit the progression of LV dysfunction after estrogen loss and during states of pressure overload.Support or Funding InformationNIH AG033727 (LG) NIH HL051952 (CMF and LG)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Historical aspects of studies on roles of the inflammasome in the pathogenesis of periodontal diseases.

The proinflammatory cytokine interleukin-1β (IL-1β) is produced as inactive proIL-1β and then processed by caspase-1 to become active. In 2002, it was demonstrated that the intracellular multiprotein complex known as the inflammasome functions as a molecular platform to trigger activation of caspase-1. Inflammasomes are known to function as intracellular sensors for a broad spectrum of various pathogen-associated and damage-associated molecular patterns. In 1985, it was demonstrated that Porphyromonas gingivalis, a representative bacterium causing chronic periodontitis, induces IL-1 production by murine peritoneal macrophages. Since then, many studies have suggested that IL-1, particularly IL-1β plays key roles in the pathogenesis of periodontal diseases. However, the term "inflammasome" was not used until the involvement of inflammasomes in periodontal disease was suggested in 2009. Several subsequent studies on the roles of the inflammasome in the pathogenesis of periodontal diseases have been published. Interestingly, two contradictory reports on the modulation of inflammasomes by P.gingivalis have been published. Some papers have described how P.gingivalis activates the inflammasome to produce IL-1β whereas some stated that P.gingivalis inhibits inflammasome activation to subvert immune responses. Several lines of evidence have suggested that the inflammasome activation is modulated by periodontopathic bacteria other than P.gingivalis. Hence, studies on the roles of inflammasomes in the pathogenesis of periodontal diseases began only 8years ago and many pathological roles of inflammasomes remain to be clarified.

A hot-water extract of Sanguisorba officinalis ameliorates endotoxin-induced septic shock by inhibiting inflammasome activation.

The inflammasome is a multiprotein signaling complex that mediates inflammatory innate immune responses through caspase 1 activation and subsequent IL-1β secretion. However, because its aberrant activation often leads to inflammatory diseases, targeting the inflammasome holds promise for the treatment of inflammation-related diseases. In this study, it was found that a hot-water extract of Sanguisorba officinalis (HSO) suppresses inflammasome activation triggered by adenosine 5'-triphosphate, nigericin, microbial pathogens, and double stranded DNA in bone marrow-derived macrophages. HSO was found to significantly suppress IL-1β production in a dose-dependent manner; this effect correlated well with small amounts of caspase 1 and little ASC pyroptosome formation in HSO-treated cells. The anti-inflammatory activity of HSO was further confirmed in a mouse model of endotoxin-induced septic shock. Oral administration of HSO reduced IL-1β titers in the serum and peritoneal cavity, increasing the survival rate. Taken together, our results suggest that HSO is an inhibits inflammasome activation through nucleotide-binding domain and leucine-rich repeat pyrin domain 3, nucleotide-binding domain and leucine-rich repeat caspase recruitment domain 4 and absent in melanoma 2 pathways, and may be useful for treatment of inflammasome-mediated diseases.

Artemisia Extract Suppresses NLRP3 and AIM2 Inflammasome Activation by Inhibition of ASC Phosphorylation.

Artemisia princeps var. orientalis (Asteraceae, A. princeps) is a well-known traditional medicinal herb used for treating various inflammatory disorders in Korea, Japan, China, and other Asian countries. In the present study, we investigated the effects of A. princeps extract (APO) on interleukin- (IL-) 1β regulation and inflammasome activation in bone marrow-derived macrophages (BMDMs) and monosodium urate- (MSU-) induced peritonitis mouse model in vivo. The APO treatment to BMDMs primed with lipopolysaccharide (LPS) attenuated the NLRP3 and AIM2 inflammasome activation induced by danger signals, such as ATP, nigericin, silica crystals, and poly (dA:dT), respectively. Mechanistic study revealed that APO suppressed the ASC oligomerization and speck formation, which are required for inflammasome activation. APO treatment also reduced the ASC phosphorylation induced by the combination of LPS and a tyrosine phosphatase inhibitor. In vivo evaluation revealed that intraperitoneal administration of APO reduced IL-1β levels, significantly (p < 0.05) and dose dependently, in the MSU-induced peritonitis mouse model. In conclusion, our study is the first to report that the extract of A. princeps inhibits inflammasome activation through the modulation of ASC phosphorylation. Therefore, APO might be developed as therapeutic potential in the treatment of inflammasome-mediated inflammatory disorders, such as gouty arthritis.

Cytoprotective activated protein C averts Nlrp3 inflammasome–induced ischemia-reperfusion injury via mTORC1 inhibition

AbstractCytoprotection by activated protein C (aPC) after ischemia-reperfusion injury (IRI) is associated with apoptosis inhibition. However, IRI is hallmarked by inflammation, and hence, cell-death forms disjunct from immunologically silent apoptosis are, in theory, more likely to be relevant. Because pyroptosis (ie, cell death resulting from inflammasome activation) is typically observed in IRI, we speculated that aPC ameliorates IRI by inhibiting inflammasome activation. Here we analyzed the impact of aPC on inflammasome activity in myocardial and renal IRIs. aPC treatment before or after myocardial IRI reduced infarct size and Nlrp3 inflammasome activation in mice. Kinetic in vivo analyses revealed that Nlrp3 inflammasome activation preceded myocardial injury and apoptosis, corroborating a pathogenic role of the Nlrp3 inflammasome. The constitutively active Nlrp3A350V mutation abolished the protective effect of aPC, demonstrating that Nlrp3 suppression is required for aPC-mediated protection from IRI. In vitro aPC inhibited inflammasome activation in macrophages, cardiomyocytes, and cardiac fibroblasts via proteinase-activated receptor 1 (PAR-1) and mammalian target of rapamycin complex 1 (mTORC1) signaling. Accordingly, inhibiting PAR-1 signaling, but not the anticoagulant properties of aPC, abolished the ability of aPC to restrict Nlrp3 inflammasome activity and tissue damage in myocardial IRI. Targeting biased PAR-1 signaling via parmodulin-2 restricted mTORC1 and Nlrp3 inflammasome activation and limited myocardial IRI as efficiently as aPC. The relevance of aPC-mediated Nlrp3 inflammasome suppression after IRI was corroborated in renal IRI, where the tissue protective effect of aPC was likewise dependent on Nlrp3 inflammasome suppression. These studies reveal that aPC protects from IRI by restricting mTORC1-dependent inflammasome activation and that mimicking biased aPC PAR-1 signaling using parmodulins may be a feasible therapeutic approach to combat IRI.

Ginsenoside Rg1 inhibits inflammatory responses via modulation of the nuclear factor‑κB pathway and inhibition of inflammasome activation in alcoholic hepatitis.

Ginsenoside Rg1 (G-Rg1) is an active ingredient of Panax ginseng, which has previously been reported to attenuate alcohol-induced hepatic damage; however, the underlying mechanisms remain largely unknown. The present study aimed to investigate the protective effects of G-Rg1 on alcohol-induced cell injury in vitro and on a rat model of alcoholic hepatitis in vivo. For the in vitro model, L-O2 cells were incubated with ethanol in the presence or absence of G-Rg1. For the in vivo model, rats were administered ethanol by intragastric injection and were treated with G-Rg1, or dexamethasone as a control. The results indicated that serum biochemical parameters, including alanine aminotransferase, aspartate aminotransferase and total bilirubin, as well as the expression of nuclear factor (NF)-κB pathway-associated inflammatory cytokines, including interleukin (IL)-6, tumor necrosis factor-α and IL-1β, were elevated in response to alcohol; however, they were significantly decreased by G-Rg1 treatment. Furthermore, NF-κB pathway activation was reduced by treatment with G-Rg1. G-Rg1 also decreased oxidative stress by inhibiting cytochrome P450 2E1 expression and reactive oxygen species production, and promoting glutathione peroxidase expression. Furthermore, G-Rg1 inhibited the expression levels of caspase-3 and -8, which may be associated with decreased hepatocyte apoptosis. These data suggested that G-Rg1 may protect hepatocytes against alcohol-induced injury, through preventing excessive inflammation and hepatocellular apoptosis.

Teaching an old pathway new tricks: Targeting BTK to block NLRP3

A proteomics screen identified BTK as a novel inflammasome regulator and demonstrated that blocking BTK can inhibit inflammasome activity.

MyD88-dependent inflammasome activation and autophagy inhibition contributes to Ehrlichia-induced liver injury and toxic shock.

Severe hepatic inflammation is a common cause of acute liver injury following systemic infection with Ehrlichia, obligate Gram-negative intracellular bacteria that lack lipopolysaccharide (LPS). We have previously shown that type I IFN (IFN-I) and inflammasome activation are key host-pathogenic mediators that promote excessive inflammation and liver damage following fatal Ehrlichia infection. However, the underlying signals and mechanisms that regulate protective immunity and immunopathology during Ehrlichia infection are not well understood. To address this issue, we compared susceptibility to lethal Ixodes ovatus Ehrlichia (IOE) infection between wild type (WT) and MyD88-deficient (MyD88-/-) mice. We show here that MyD88-/- mice exhibited decreased inflammasome activation, attenuated liver injury, and were more resistant to lethal infection than WT mice, despite suppressed protective immunity and increased bacterial burden in the liver. MyD88-dependent inflammasome activation was also dependent on activation of the metabolic checkpoint kinase mammalian target of rapamycin complex 1 (mTORC1), inhibition of autophagic flux, and defective mitophagy in macrophages. Blocking mTORC1 signaling in infected WT mice and primary macrophages enhanced bacterial replication and attenuated inflammasome activation, suggesting autophagy promotes bacterial replication while inhibiting inflammasome activation. Finally, our data suggest TLR9 and IFN-I are upstream signaling mechanisms triggering MyD88-mediated mTORC1 and inflammasome activation in macrophages following Ehrlichia infection. This study reveals that Ehrlichia-induced liver injury and toxic shock are mediated by MyD88-dependent inflammasome activation and autophagy inhibition.

NLRP3 inflammasome activation contributes to VSMC phenotypic transformation and proliferation in hypertension

Inflammation is involved in pathogenesis of hypertension. NLRP3 inflammasome activation is a powerful mediator of inflammatory response via caspase-1 activation. The present study was designed to determine the roles and mechanisms of NLRP3 inflammasome in phenotypic modulation and proliferation of vascular smooth muscle cells (VSMCs) in hypertension. Experiments were conducted in spontaneously hypertensive rats (SHR) and primary aortic VSMCs. NLRP3 inflammasome activation was observed in the media of aorta in SHR and in the VSMCs from SHR. Knockdown of NLRP3 inhibited inflammasome activation, VSMC phenotypic transformation and proliferation in SHR-derived VSMCs. Increased NFκB activation, histone acetylation and histone acetyltransferase expression were observed in SHR-derived VSMCs and in media of aorta in SHR. Chromatin immunoprecipitation analysis revealed the increased histone acetylation, p65-NFκB and Pol II occupancy at the NLRP3 promoter in vivo and in vitro. Inhibition of NFκB with BAY11-7082 or inhibition of histone acetyltransferase with curcumin prevented the NLRP3 inflammasome activation, VSMC phenotype switching and proliferation in VSMCs from SHR. Moreover, curcumin repressed NFκB activation. Silencing of NLRP3 gene ameliorated hypertension, vascular remodeling, NLRP3 inflammasome activation and phenotype switching in the aorta of SHR. These results indicate that NLRP3 inflammasome activation response to histone acetylation and NFκB activation contributes to VSMC phenotype switching and proliferation and vascular remodeling in hypertension.

Inflammation: Activated protein C inhibits inflammasome activation in IRI.

Inflammation: Activated protein C inhibits inflammasome activation in IRI.

Aggravated Postinfarct Heart Failure in Type 2 Diabetes Is Associated with Impaired Mitophagy and Exaggerated Inflammasome Activation

Type 2 diabetes mellitus (T2DM) is a major risk factor for heart disease. Mortality rates after myocardial infarction (MI) are significantly increased in T2DM patients because of dysfunctional left ventricle (LV). However, molecular pathways underlying accelerated heart failure (HF) after MI in T2DM remain unclear. We investigated the underlying mechanisms by inducing MI in a well-established model of T2DM and control mice. Cardiac imaging revealed a significantly decreased global left ventricular ejection fraction in parallel with increased mortality after MI in T2DM mice compared with control mice. Genome-wide mRNA sequencing, immunoblot, electron microscopy, together with immunofluorescence staining for LC3 and p62 indicated an impaired mitophagy in peri-infarct regions of LV in T2DM mice compared with control mice. Furthermore, defective mitophagy was associated with an increased release of mitochondrial DNA, resulting in Aim2 and NLRC4 inflammasome and caspase-I hyperactivation in cardiomyocytes and cardiac macrophages in peri-infarct regions of LV in T2DM mice. Consistent with inflammasome and caspase-I hyperactivation, cardiomyocyte death and IL-18 secretion were increased in T2DM mice. Our results indicate that T2DM aggravates HF after MI through defective mitophagy, associated exaggerated inflammasome activation, cell death, and IL-18 secretion, suggesting that restoring mitophagy and inhibiting inflammasome activation may serve as novel targets for the prevention and treatment of HF in T2DM.

Dietary PUFAs attenuate NLRP3 inflammasome activation via enhancing macrophage autophagy

Dietary PUFAs reduce atherosclerosis and macrophage inflammation, but how nucleotide-binding oligomerization domain leucine-rich repeat-containing receptor protein (NLRP3) inflammasome activation and autophagy influence PUFA-mediated atheroprotection is poorly understood. We fed Ldlr−/− mice diets containing 10% (calories) palm oil (PO) and 0.2% cholesterol, supplemented with an additional 10% of calories as PO, fish oil (FO), echium oil (EO, containing 18:4 n-3), or borage oil (BO, containing 18:3 n-6). Inflammasome activation, autophagic flux, and mitochondrial function were measured in peritoneal macrophages, blood monocytes, or liver from diet-fed mice. Compared with PO, dietary PUFAs (FO, EO, or BO) markedly inhibited inflammasome activation, shown by 1) less macrophage IL-1β secretion and caspase-1 cleavage in response to NLRP3 inflammasome activators, 2) less IL-1β secretion and caspase-1 cleavage from liver or hepatocytes in response to lipopolysaccharide (LPS), and 3) attenuated caspase-1 activity in blood monocytes. Furthermore, PUFA-enriched diets increased LC3-II expression in macrophage, aorta, and liver samples and reduced numbers of dysfunctional mitochondria in macrophages in response to LPS and palmitate, suggesting enhanced autophagic activation. Dietary PUFAs did not attenuate NLRP3 inflammasome activation in atg5-deficient macrophages, indicating that autophagic activation is critical for the PUFA-mediated inflammasome inactivation. In conclusion, dietary PUFAs reduce atherosclerosis, in part, by activation of macrophage autophagy and attenuation of NLRP3 inflammasome activation.

The Ketone Body β-Hydroxybutyrate Does Not Inhibit Synuclein Mediated Inflammasome Activation in Microglia.

Parkinson's disease (PD) is recognized as the most common neurodegenerative movement disorder and results in debilitating motor deficits. The accumulation and spread of neurotoxic synuclein aggregates in the form of Lewy bodies is a key pathological feature of PD. Chronic activation of the NLRP3 inflammasome by protein aggregates is emerging as a major pathogenic mechanism in progressive neurodegenerative disorders and is considered an important therapeutic target. Recently the ketone body, β-hydroxy butyrate (BHB), was shown to efficiently inhibit the NLRP3 inflammasome in macrophages, and in vivo models of inflammatory disease. Furthermore, BHB can readily cross the blood brain barrier suggesting that it could have therapeutic benefits for the management of PD. In this study, we evaluated if BHB could inhibit chronic microglial inflammasome activation induced by pathological fibrillar synuclein aggregates. Interestingly, we found that BHB treatment almost completely blocked all aspects of inflammasome activation and pyroptosis induced by ATP and monosodium urate (MSU) crystals, consistent with previously published reports in macrophages. Surprisingly however, BHB did not inhibit inflammasome activation and release of IL-1β or caspase-1 induced by synuclein fibrils. Our results demonstrate that BHB does not block the upstream pathways regulating inflammasome activation by synuclein fibrils and suggest that synuclein mediated inflammasome activation proceeds via distinct mechanisms compared to traditional NLRP3 activators such as ATP and MSU.

NOVEL NLRP3 INFLAMMASOME INHIBITORS: EVALUATION IN IL-1β RELEASE AND HIGH-CONTENT ASC-SPECK CELLULAR ASSAYS

Clinical studies have identified activation of microglia in early stage Alzheimer's disease (AD) patients and shown upregulation of pro inflammatory mediators in patients’ brain and CSF. One of these mediators is IL-1β, which is upregulated in microglia associated with amyloid plaques. The NLRP3 inflammasome in microglia is activated by fibrillary Aβ and controls the processing of pro-IL-1β by caspase 1 and its subsequent release. The NLRP3 inflammasome is formed when NRLP3 is activated and multimerises the ASC adapter protein, which recruits and activates caspase 1 triggering the processing of pro-IL-1β to the secreted form. In the APP/PS1 mouse model, knock out of NLRP3 abolished the cognitive deficit and reduced plaque burden suggesting NLRP3 could represent a new therapeutic target. We have developed a high content imaging assay to monitor inflammasome formation, using the GE healthcare IN Cell Analyzer 2000. The monocytic cell line THP-1 stably overexpressing a Cyan Fluorescent Protein (CFP) - ASC chimera was provided by Prof Eicke Latz (University of Bonn). Using this cell line we have developed an algorithm to detect CFP-ASC oligomerisation following priming with LPS and activation with nigericin. This algorithm identifies and quantifies specks formed when the CFP-ASC multimerises. A discrete panel of tool inhibitors, including derivatives of the boron containing 2-APB, which has been shown to inhibit inflammasome activity via IL-1β release assays, was used to inhibit observable speck formation. We have established a 96 well assay format assay for monitoring the inhibition of inflammasome formation by small molecule inhibitors. Using a discrete panel of tool inhibitors we have validated that this assay can detect and discriminate between potential NLRP3 inhibitors of varying potency. In addition to inhibiting speck formation in THP-1 cells, we established that the tool compounds effectively inhibited IL-1β release from primary cultures of glia. Inhibition of the NLRP3 inflammasome represents a potential therapeutic target for AD. This new assay would provide mechanistic in vitro data disease phenotype relevant data. Such data can be used to inform decisions regarding the use of tool compounds within in vivo models or to support a medicinal chemistry program.

Melatonin alleviates inflammasome-induced pyroptosis through inhibiting NF-κB/GSDMD signal in mice adipose tissue.

Pyroptosis is a proinflammatory form of cell death that is associated with pathogenesis of many chronic inflammatory diseases. Melatonin is substantially reported to possess anti-inflammatory properties by inhibiting inflammasome activation. However, the effects of melatonin on inflammasome-induced pyroptosis in adipocytes remain elusive. Here, we demonstrated that melatonin alleviated lipopolysaccharides (LPS)-induced inflammation and NLRP3 inflammasome formation in mice adipose tissue. The NLRP3 inflammasome-mediated pyroptosis was also inhibited by melatonin in adipocytes. Further analysis revealed that gasdermin D (GSDMD), the key executioner of pyroptosis, was the target for melatonin inhibition of adipocyte pyroptosis. Importantly, we determined that nuclear factor κB (NF-κB) signal was required for the GSDMD-mediated pyroptosis in adipocytes. We also confirmed that melatonin alleviated adipocyte pyroptosis by transcriptional suppression of GSDMD. Moreover, GSDMD physically interacted with interferon regulatory factor 7 (IRF7) and subsequently formed a complex to promote adipocyte pyroptosis. Melatonin also attenuated NLRP3 inflammasome activation and pyroptosis, which was induced by LPS or obesity. In summary, our results demonstrate that melatonin alleviates inflammasome-induced pyroptosis by blocking NF-κB/GSDMD signal in mice adipose tissue. Our data reveal a novel function of melatonin on adipocyte pyroptosis, suggesting a new potential therapy for melatonin to prevent and treat obesity caused systemic inflammatory response.

Abstract 43: Cholesterol Efflux Pathways Suppress Inflammasome Activation in Mice and Humans

Plasma high-density-lipoprotein (HDL) has several anti-atherogenic properties, including its key role in functioning as acceptor for ATP-binding cassette A1 and G1 (ABCA1 and ABCG1) mediated cholesterol efflux. We have shown previously that macrophage Abca1/g1 deficiency accelerates atherosclerosis, by enhancing foam cell formation and inflammatory cytokine expression in atherosclerotic plaques. Macrophage cholesterol accumulation activates the inflammasome, leading to caspase-1 cleavage, required for IL-1β and IL-18 secretion. Several studies have suggested that inflammasome activation accelerates atherogenesis. We hypothesized that macrophage Abca1/g1 deficiency activates the inflammasome. In Ldlr -/- mice fed a Western type diet (WTD), macrophage Abca1/g1 deficiency increased IL-1β and IL-18 plasma levels (2-fold; P &lt;0.001), and induced caspase-1 cleavage. Deficiency of the inflammasome components Nlrp3 or caspase-1 in macrophage Abca1/g1 knockouts reversed the increase in plasma IL-18 levels ( P &lt;0.001), indicating these changes were inflammasome dependent. We found that macrophage Abca1/g1 deficiency induced caspase-1 cleavage in splenic CD115 + monocytes and CD11b + macrophages. While mitochondrial ROS production or lysosomal function were not affected, macrophage Abca1/g1 deficiency led to an increased splenic population of monocytes (2.5-fold; P &lt;0.01). Monocytes secrete ATP, and as a result, ATP secretion from total splenic cells was increased (2.5-fold; P &lt;0.01), likely contributing to inflammasome activation. Caspase-1 deficiency decreased atherosclerosis in macrophage Abca1/g1 deficient Ldlr -/- mice fed WTD for 8 weeks (225822 vs 138606 μm 2 ; P &lt;0.05). Of therapeutic interest, one injection of reconstituted HDL (100 mg/kg) in macrophage Abca1/g1 knockouts decreased plasma IL-18 levels ( P &lt;0.05). Tangier disease patients, with a homozygous loss-of-function for ABCA1, showed increased IL-1β and IL-18 plasma levels (3-fold; P &lt;0.001), suggesting that cholesterol efflux pathways also suppress inflammasome activation in humans. These findings suggest that macrophage cholesterol efflux pathways suppress inflammasome activation, possibly contributing to the anti-atherogenic effects of HDL treatment.

Binding of small molecule to ASC leads to the suppression of NLRP3 inflammasome and acute gout symptoms

Abstract The NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome, which is composed of NLRP3, the adaptor protein ASC, and caspase-1, is closely linked to the pathogenesis of metabolic diseases. We investigated whether caffeic acid phenethyl ester (CAPE), an anti-inflammatory phytochemical, could modulate the activation of NLRP3 inflammasome and have beneficial effects on the related disease such as acute gout. In primary mouse macrophages, CAPE blocked NLRP3 inflammasome activation induced by monosodium uric acid (MSU) crystals. In a mouse air pouch inflammation model and an acute gout model, oral administration of CAPE suppressed MSU-induced caspase-1 activation and interleukin (IL)-1b production, correlating with the attenuation of inflammatory symptoms. CAPE inhibited inflammasome activation induced by ASC, but not NLRP3 nor caspase-1. CAPE directly associated with ASC, resulting in the blockade of NLRP3-ASC interaction. These results demonstrate a novel inhibitory mechanism by which small molecules regulate NLRP3 inflammasome targeting ASC, suggesting the therapeutic strategy for NLRP3-related inflammatory diseases.

Opposing effects of Nrf2 and Nrf2-activating compounds on the NLRP3 inflammasome independent of Nrf2-mediated gene expression.

The transcription factor Nrf2 regulates the expression of genes required for protection from xenobiotic and oxidative stress. Under normal conditions Nrf2 is constantly degraded upon ubiquitination, mediated by the Nrf2 inhibitor Keap1. Inflammasomes represent stress-induced protein complexes. They are critically involved in acute and chronic inflammation through caspase-1-mediated activation of pro-inflammatory cytokines. Here, we demonstrate that Nrf2 is a positive regulator of the NLRP3 inflammasome. In contrast, Nrf2-activating compounds, including the anti-inflammatory drug dimethyl fumarate (DMF), inhibit inflammasome activation. Both effects are independent of the transcriptional activity of Nrf2 and, at least in part, not interdependent. On the other hand, NLRP3 inflammasome activation induces a rapid and partly caspase-1- and Keap1-independent degradation of Nrf2. These data argue against a simultaneous activation of both stress-related pathways. Finally, we provide evidence that the cross-regulation of both pathways is controlled by a physical interaction between the Nrf2/Keap1 and NLRP3 complexes.

Progress on mechanisms for pathogensto evade NOD-like receptor and Toll-like receptor signaling pathways

The innate immune system provides a first line of defense against invading pathogens, in which the pattern recognition receptors (PRR) recognize pathogen-associated molecular patterns (PAMP) and initiate the downstream signaling pathways to eliminate the encountered pathogens. There are two main classes of such signaling pathways: NOD-like receptor (NLR) signaling pathway and Toll-like receptor (TLR) signaling pathway. The microbial pathogens under selective pressure have evolved numerous mechanisms to avoid and/or manipulate the NLR and TLR signal transduction for survival and replication. To evade the NLR signaling pathway, pathogens interfere and/or inhibit inflammasome activation in innate immune cells by producing virulence factors or reducing PAMPs expression. The mechanisms for pathogens to evade TLR signaling pathway include: inhibition of mitogen activated protein kinases (MAPKs) cascade reaction, inhibition of NF-КB activation, and interference of down-stream signal transduction by producing Toll/interleukin-1 receptor (TIR)-containing proteins which bind directly with TLRs or adaptor proteins in the signaling pathway.

Protective effects of Cinnamomum cassia (Lamaceae) against gout and septic responses via attenuation of inflammasome activation in experimental models

Ethnopharmacological relevanceCinnamomum cassia (C. cassia, Lauraceae family), commonly used for treating dyspepsia, gastritis, blood circulation, and inflammatory diseases is considered as one of the 50 fundamental herbs in traditional Chinese medicine. Aim of the studyThe anti-inflammatory action of an ethanol extract of C. cassia (CA), and its underlying mechanisms were explored in both in vitro cellular and in vivo murine models. Materials and methodsBone marrow-derived macrophages (BMDMs) were used to study the regulatory effect of CA on inflammasome activation. A lipopolysaccharide (LPS)-induced sepsis mouse model and a monosodium urate (MSU)-induced gout model were employed to study the effect of CA on in vivo efficacy. ResultsCA improved the survival rate in the LPS-induced septic shock mouse model and inhibited inflammasome activation including NLRP3, NLRC4, and AIM2, leading to suppression of interleukin-1β secretion. Further, ASC oligomerization and its speck formation in cytosol were attenuated by CA treatment. Furthermore, CA improved both survival rate of LPS-induced septic shock and gout murine model. ConclusionsCA treatment significantly attenuated danger signals-induced inflammatory responses via regulation of inflammasome activation, substantiating the traditional claims of its use in the treatment of inflammation-related disorders.