The NLRP3 inflammasome in health and disease: the good, the bad and the ugly

Pattern-recognition receptors and gastric cancer

Chronic inflammation has been associated with an increased risk of several human malignancies, a classic example being gastric adenocarcinoma (GC). Development of GC is known to result from infection of the gastric mucosa by Helicobacter pylori, which initially induces acute inflammation and, in a subset of patients, progresses over time to chronic inflammation, gastric atrophy, intestinal metaplasia, dysplasia, and finally intestinal-type GC. Germ-line encoded receptors known as pattern-recognition receptors (PRRs) are critical for generating mature pro-inflammatory cytokines that are crucial for both Th1 and Th2 responses. Given that H. pylori is initially targeted by PRRs, it is conceivable that dysfunction within genes of this arm of the immune system could modulate the host response against H. pylori infection, and subsequently influence the emergence of GC. Current evidence suggests that Toll-like receptors (TLRs) (TLR2, TLR3, TLR4, TLR5, and TLR9), nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) (NOD1, NOD2, and NLRP3), a C-type lectin receptor (DC-SIGN), and retinoic acid-inducible gene (RIG)-I-like receptors (RIG-I and MDA-5), are involved in both the recognition of H. pylori and gastric carcinogenesis. In addition, polymorphisms in genes involved in the TLR (TLR1, TLR2, TLR4, TLR5, TLR9, and CD14) and NLR (NOD1, NOD2, NLRP3, NLRP12, NLRX1, CASP1, ASC, and CARD8) signaling pathways have been shown to modulate the risk of H. pylori infection, gastric precancerous lesions, and/or GC. Further, the modulation of PRRs has been suggested to suppress H. pylori-induced inflammation and enhance GC cell apoptosis, highlighting their potential relevance in GC therapeutics. In this review, we present current advances in our understanding of the role of the TLR and NLR signaling pathways in the pathogenesis of GC, address the involvement of other recently identified PRRs in GC, and discuss the potential implications of PRRs in GC immunotherapy.

TXNIP mediates NLRP3 inflammasome activation in cardiac microvascular endothelial cells as a novel mechanism in myocardial ischemia/reperfusion injury

NLRP3 inflammasome is necessary for initiating acute sterile inflammation. Recent studies have demonstrated that NLRP3 inflammasome is up-regulated and mediates myocardial ischemia/reperfusion (MI/R) injury. However, the signaling pathways that lead to the activation of NLRP3 inflammasome by MI/R injury have not been fully elucidated. C57BL/6J mice were subjected to 30 min ischemia and 3 or 24 h reperfusion. The ischemic heart exhibited enhanced inflammasome activation as evidenced by increased NLRP3 expression and caspase-1 activity and increased IL-1β and IL-18 production. Intramyocardial NLRP3 siRNA injection or an intraperitoneal injection of BAY 11-7028, an inflammasome inhibitor, attenuated macrophage and neutrophil infiltration and decreased MI/R injury, as measured by cardiomyocyte apoptosis and infarct size. The ischemic heart also exhibited enhanced interaction between Txnip and NLRP3, which has been shown to be a mechanism for activating NLRP3. Intramyocardial Txnip siRNA injection also decreased infarct size and NLRP3 activation. In vitro experiments revealed that NLRP3 was expressed in cardiac microvascular endothelial cells (CMECs), but was hardly expressed in cardiomyocytes. Simulated ischemia/reperfusion (SI/R) stimulated NLRP3 inflammasome activation in CMECs, but not in cardiomyocytes. Moreover, CMECs subjected to SI/R injury increased interactions between Txnip and NLRP3. Txnip siRNA diminished NLRP3 inflammasome activation and SI/R-induced injury, as measured by LDH release and caspase-3 activity in CMECs. ROS scavenger dissociated TXNIP from NLRP3 and inhibited the activation of NLRP3 inflammasome in the CMECs. For the first time, we demonstrated that TXNIP-mediated NLRP3 inflammasome activation in CMECs was a novel mechanism of MI/R injury. Interventions that block Txnip/NLRP3 signaling to inhibit the activation of NLRP3 inflammasomes may be novel therapies for mitigating MI/R injury.

Leukocyte infiltration and activation of the NLRP3 inflammasome in white adipose tissue following thermal injury

OBJECTIVES

Severe thermal injury is associated with extreme and prolonged inflammatory and hypermetabolic responses, resulting in significant catabolism that delays recovery or even leads to multiple organ failure and death. Burned patients exhibit many symptoms of stress-induced diabetes, including hyperglycemia, hyperinsulinemia, and hyperlipidemia. Recently, the nucleotide-binding domain, leucine-rich family (NLR), pyrin-containing 3 (NLRP3) inflammasome has received much attention as the sensor of endogenous "danger signals" and mediator of "sterile inflammation" in type II diabetes. Therefore, we investigated whether the NLRP3 inflammasome is activated in the adipose tissue of burned patients, as we hypothesize that, similar to the scenario observed in chronic diabetes, the cytokines produced by the inflammasome mediate insulin resistance and metabolic dysfunction.

DESIGN

Prospective cohort study.

SETTING

Ross Tilley Burn Centre & Sunnybrook Research Institute.

PATIENTS

We enrolled 76 patients with burn sizes ranging from 1% to 70% total body surface area. All severely burned patients exhibited burn-induced insulin resistance and hyperglycemia.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We examined the adipose tissue of control and burned patients and found, via flow cytometry and gene expression studies, increased infiltration of leukocytes-especially macrophages-and evidence of inflammasome priming and activation. Furthermore, we observed increased levels of interleukin-1β in the plasma of burned patients when compared to controls.

CONCLUSIONS

In summary, our study is the first to show activation of the inflammasome in burned humans, and our results provide impetus for further investigation of the role of the inflammasome in burn-induced hypermetabolism and, potentially, developing novel therapies targeting this protein complex for the treatment of stress-induced diabetes.

Intravascular immunity as a key to systemic vasculitis: a work in progress, gaining momentum

Vascular inflammation contributes to the defence against invading microbes and to the repair of injured tissues. In most cases it resolves before becoming apparent. Vasculitis comprises heterogeneous clinical entities that are characterized by the persistence of vascular inflammation after it has served its homeostatic function. Most underlying mechanisms have so far remained elusive. Intravascular immunity refers to the surveillance of the vasculature by leucocytes that sense microbial or sterile threats to vessel integrity and initiate protective responses that entail most events that determine the clinical manifestations of vasculitis, such as end-organ ischaemia, neutrophil extracellular traps generation and thrombosis, leucocyte extravasation and degranulation. Understanding how the resolution of vascular inflammation goes awry in patients with systemic vasculitis will facilitate the identification of novel pharmacological targets and bring us a step closer in each patient to the selection of more effective and less toxic treatments.

Inflammasomes: molecular regulation and implications for metabolic and cognitive diseases

Inflammasomes are specialized signaling platforms critical for the regulation of innate immune and inflammatory responses. Various NLR family members (i.e., NLRP1, NLRP3, and IPAF) as well as the PYHIN family member AIM2 can form inflammasome complexes. These multi-protein complexes activate inflammatory caspases (i.e., caspase-1) which in turn catalyze the maturation of select pro-inflammatory cytokines, including interleukin (IL)-1β and IL-18. Activation of the NLRP3 inflammasome typically requires two initiating signals. Toll-like receptor (TLR) and NOD-like receptor (NLR) agonists activate the transcription of pro-inflammatory cytokine genes through an NF-κB-dependent priming signal. Following exposure to extracellular ATP, stimulation of the P2X purinoreceptor-7 (P2X7R), which results in K(+) efflux, is required as a second signal for NLRP3 inflammasome formation. Alternative models for NLRP3 activation involve lysosomal destabilization and phagocytic NADPH oxidase and/or mitochondria-dependent reactive oxygen species (ROS) production. In this review we examine regulatory mechanisms that activate the NLRP3 inflammasome pathway. Furthermore, we discuss the potential roles of NLRP3 in metabolic and cognitive diseases, including obesity, type 2 diabetes mellitus, Alzheimer's disease, and major depressive disorder. Novel therapeutics involving inflammasome activation may result in possible clinical applications in the near future.

NLRP3 inflammasome is activated in fibromyalgia: the effect of coenzyme Q10

AIMS

Fibromyalgia (FM) is a prevalent chronic pain syndrome characterized by generalized hyperalgesia associated with a wide spectrum of symptoms such as fatigue and joint stiffness. Diagnosis of FM is difficult due to the lack of reliable diagnostic biomarkers, while treatment is largely inadequate. We have investigated the role of coenzyme Q10 (CoQ10) deficiency and mitochondrial dysfunction in inflammasome activation in blood cells from FM patients, and in vitro and in vivo CoQ10 deficiency models.

RESULTS

Mitochondrial dysfunction was accompanied by increased protein expression of interleukin (IL)-1β, NLRP3 (NOD-like receptor family, pyrin domain containing 3) and caspase-1 activation, and an increase of serum levels of proinflammatory cytokines (IL-1β and IL-18). CoQ10 deficiency induced by p-aminobenzoate treatment in blood mononuclear cells and mice showed NLRP3 inflammasome activation with marked algesia. A placebo-controlled trial of CoQ10 in FM patients has shown a reduced NLRP3 inflammasome activation and IL-1β and IL-18 serum levels.

INNOVATION

These results show an important role for the NLRP3 inflammasome in the pathogenesis of FM, and the capacity of CoQ10 in the control of inflammasome.

CONCLUSION

These findings provide new insights into the pathogenesis of FM and suggest that NLRP3 inflammasome inhibition represents a new therapeutic intervention for the disease.

Uncontrolled sepsis: a systematic review of translational immunology studies in intensive care medicine

BACKGROUND

The design of clinical immunology studies in sepsis presents several fundamental challenges to improving the translational understanding of pathologic mechanisms. We undertook a systematic review of bed-to-benchside studies to test the hypothesis that variable clinical design methodologies used to investigate immunologic function in sepsis contribute to apparently conflicting laboratory data, and identify potential alternatives that overcome various obstacles to improve experimental design.

METHODS

We performed a systematic review of the design methodology employed to study neutrophil function (respiratory burst), monocyte endotoxin tolerance and lymphocyte apoptosis in the intensive care setting, over the past 15 years. We specifically focussed on how control samples were defined, taking into account age, gender, ethnicity, concomitant therapies, timing of sample collection and the criteria used to diagnose sepsis.

RESULTS

We identified 57 eligible studies, the majority of which (74%) used case-control methodology. Healthy volunteers represented the control population selected in 83% of studies. Comprehensive demographic data on age, gender and ethnicity were provided in ≤48% of case control studies. Documentation of diseases associated with immunosuppression, malignancy and immunomodulatory therapies was rare. Less than half (44%) of studies undertook independent adjudication for the diagnosis of sepsis while 68% provided microbiological data. The timing of sample collection was defined by highly variable clinical criteria. By contrast, surgical studies avoided many such confounders, although only one study in surgical patients monitored the study group for development of sepsis.

CONCLUSIONS

We found several important and common limitations in the clinical design of translational immunologic studies in human sepsis. Major elective surgery overcame many of these methodological limitations. The failure of adequate clinical design in mechanistic studies may contribute to the lack of translational therapeutic progress in intensive care medicine.

Autoinflammatory syndromes

Autoinflammatory syndromes comprise a diagnostically challenging group of systemic inflammatory disorders uniquely related by (1) dysregulation of innate immunity, (2) inflammasome activation, (3) dramatic clinical features (high fevers, neutrophilic rashes, and bone or synovial involvement), (4) impressive acute phase responses, and (5) effective treatment with cytokine inhibitors. This review details some of the more common autoinflammatory disorders, their distinguishing features and dermatologic manifestations, and how an accurate diagnosis can be established in patients presenting with periodic or intermittent febrile disorders.

NLRP3 inflammasome is activated in mononuclear blood cells from patients with major depressive disorder

INTRODUCTION

Major depressive disorder (MDD) is a very prevalent disease which pathogenic mechanism remains elusive. There are some hypotheses and pilot studies suggesting that cytokines may play an important role in MDD. In this respect, we have investigated the role of NLRP3 inflammasome complex in the maturation of caspase-1 and the processing of its substrates, IL-1β and IL-18, in blood cells from MDD patients.

METHODS

Forty MDD patients were selected for this study, twenty without treatments and twenty treated with amitriptyline, a common tricyclic antidepressant. Blood samples from twenty healthy volunteers were included in the study. The inflammasome activation was studied by Western blot and real-time PCR of NLRP3 and caspase 1 and serum levels of IL-1β and 18.

RESULTS

We observed increased gene expression of NLRP3 and caspase-1 in blood cells, and increased serum levels of IL-1β and IL-18 in non-treated patients. IL-1β and IL-18 correlated with Beck Depression Inventory (BDI) scores of MDD patients. Interestingly, amitriptyline treatment reduced NLRP3 and caspase-1 gene expression, and IL-1β and IL-18 serum levels. As it is well established that oxidative stress is associated with NLRP3 inflammasome activation, we next studied mitochondrial ROS and lipid peroxidation (LPO) levels in MDD patients. Increased levels of mitochondrial ROS and LPO were observed in MDD patients, however oxidative damage was higher in MDD patients treated with amitriptyline.

CONCLUSIONS

These findings provide new insight into the pathogenesis of MDD and the effects of amitriptyline treatment on NLRP3 inflammasome activation and IL-1β and IL-18 serum levels.

The nature, significance, and glucagon-like peptide-1 analog treatment of brain insulin resistance in Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease leading over the course of decades to the most common form of dementia. Many of its pathologic features and cognitive deficits may be due in part to brain insulin resistance recently demonstrated in the insulin receptor→insulin receptor substrate-1 (IRS-1) signaling pathway. The proximal cause of such resistance in AD dementia and amnestic mild cognitive impairment (aMCI) appears to be serine inhibition of IRS-1, a phenomenon likely due to microglial release of inflammatory cytokines triggered by oligomeric Aβ. Studies on animal models of AD and on human brain tissue from MCI cases at high risk of AD dementia have shown that brain insulin resistance and many other pathologic features and symptoms of AD may be greatly reduced or even reversed by treatment with FDA-approved glucagon-like peptide-1 (GLP-1) analogs such as liraglutide (Victoza). These findings call attention to the need for further basic, translational, and clinical studies on GLP-1 analogs as promising AD therapeutics.

Programmed cell death in Legionella infection

ABSTRACT: The causative agent of Legionnaires’ disease, Legionella pneumophila, resides within alveolar macrophages by exporting 295 bacterial virulence proteins (effectors) to modulate host cell processes. This leads to the formation of a unique vacuolar niche and the suppression of macrophage cell death pathways, which, in turn, promote bacterial survival and allow sufficient time for replication. However, once nutrients within the vacuole are depleted, Legionella must act to induce host cell death in order to facilitate bacterial egress and reinfect new cells. Intracellular Legionella also evade detection by the host cell’s innate immune system, which seeks to destroy invading pathogens by activating inflammasome complexes, thereby promoting proinflammatory cytokine activation and pyroptotic cell death. Understanding how different forms of programmed cell death contribute to Legionella infectivity and are manipulated by Legionella effector proteins will be important for identifying novel antibacterial therapeutic targets.

Nonmicrobial-mediated inflammatory airway diseases--an update

In lungs, airways are in constant contact with air, microbes, allergens, and environmental pollutants. The airway epithelium represents the first line of lung defense through different mechanisms, which facilitate clearance of inhaled pathogens and environmental particles while minimizing an inflammatory response. The innate immune system facilitates immediate recognition of both foreign pathogens and tissue damage through toll-like receptor, which acts as a gateway for all intracellular events leading to inflammation. In the absence of microbial stimulus, the immune system is capable of detecting a wide range of insults against the host. This review focuses on various molecular mechanisms involved in pathophysiology of airway inflammation mediated by environmental factors, cellular stress, and pharmacological and clinical agents.

Involvement of inflammasome activation in lipopolysaccharide-induced mice depressive-like behaviors

AIMS

The NLRP3 inflammasome is a cytoplasmic multiprotein complex of the innate immune system that regulates the cleavage of interleukin-1β and interleukin-18 precursors. It can detect a wide range of danger signals and trigger a series of immune-inflammatory reactions. There were plenty of studies indicating that activation of the immune system played pivotal roles in depression. However, the underlying mechanisms of immune-depression interactions remained elusive and there was no report about the involvement of inflammasome activation in depression.

METHODS

We established an acute depression mouse model with lipopolysaccharide to explore the involvement of inflammasome activation in depression.

RESULTS

The lipopolysaccharide-treated mice displayed depressive-like behaviors and pro-inflammatory cytokine interleukin-1β protein and mRNA levels significantly increased. The NLRP3 inflammasome mRNA expression level also significantly elevated in depressed mice brain. Pretreatment with the NLRP3 inflammasome inhibitor Ac-YVAD-CMK significantly abrogated the depressive-like behaviors induced by lipopolysaccharide.

CONCLUSION

These data suggest for the first time that the NLRP3 inflammasome is involved in lipopolysaccharide-induced mice depressive-like behaviors. The NLRP3 inflammasome may be a central mediator between immune activation and depression, which raises the possibility that it may be a more specific target for the depression treatments in the near future.

Crosstalk between autophagy and inflammasomes

A variety of cellular stresses activate the autophagy pathway, which is fundamentally important in protection against injurious stimuli. Defects in the autophagy process are associated with a variety of human diseases, including inflammatory and metabolic diseases. The inflammasomes are emerging as key signaling platforms directing the maturation and secretion of interleukin-1 family cytokines in response to pathogenic and sterile stimuli. Recent studies have identified the critical role of inflammasome activation in host defense and inflammation. Delineation of the relationship between autophagy and inflammasome activation is now being greatly facilitated by the use of mice models of autophagy gene deficiency and clinical studies. We surveyed the recent research regarding the contribution of autophagy to the control of inflammation, in particular the association between autophagy and inflammasomes. Understanding the mechanisms by which autophagy balances inflammation might facilitate the development of autophagy-based therapeutic modalities for infectious and inflammatory diseases.

NLRP3 polymorphisms are associated with late-onset Alzheimer's disease in Han Chinese

The innate immunity and inflammatory response plays an important role in AD pathogenesis. Recently, a wealth of information linking the activation of NLRP3 inflammasome to Alzheimer's disease (AD) pathogenesis has emerged. Considering the pivotal role of NLRP3 in the inflammatory process and in AD, we hypothesized that variations in NLRP3 gene may also affect susceptibility to AD. Three selected functional single-nucleotide polymorphisms (SNPs) in NLRP3 gene (rs2027432, rs10754558, rs35829419) were genotyped in 1133 late-onset AD (LOAD) patients and 1159 healthy controls in a large Northern Han Chinese population. Among them, the 5'-flanking rs2027432 polymorphism seemed to be most associated with LOAD risk even after adjusting for age, gender, and ApoE ε4 status. For rs10754558, the genotype frequency differed significantly only in ApoE ε4 carriers. On the other hand, the minor A allele of rs35829419 (Q705K) polymorphism appeared to exert a protective effect against the development of LOAD. Our data support the notion that genetic variation in NLRP3 gene may contribute to LOAD risk in Northern Han Chinese.

Host response to respiratory bacterial pathogens as identified by integrated analysis of human gene expression data

Respiratory bacterial pathogens are one of the leading causes of infectious death in the world and a major health concern complicated by the rise of multi-antibiotic resistant strains. Therapeutics that modulate host genes essential for pathogen infectivity could potentially avoid multi-drug resistance and provide a wider scope of treatment options. Here, we perform an integrative analysis of published human gene expression data generated under challenges from the gram-negative and Gram-positive bacteria pathogens, Pseudomonas aeruginosa and Streptococcus pneumoniae, respectively. We applied a previously described differential gene and pathway enrichment analysis pipeline to publicly available host mRNA GEO datasets resulting from exposure to bacterial infection. We found 72 canonical human pathways common between four GEO datasets, representing P. aeruginosa and S. pneumoniae. Although the majority of these pathways are known to be involved with immune response, we found several interesting new interactions such as the SUMO1 pathway that might have a role in bacterial infections. Furthermore, 36 host-bacterial pathways were also shared with our previous results for respiratory virus host gene expression. Based on our pathway analysis we propose several drug-repurposing opportunities supported by the literature.

Synovium and the innate inflammatory network in osteoarthritis progression

This review focuses on the recent advancements in the understanding of innate immunity in the pathogenesis of osteoarthritis, particularly with attention to the roles of damage-associated molecular patterns (DAMPs), pattern recognition receptors (PPRs), and complement in synovitis development and cartilage degradation. Endogenous molecular products derived from cellular stress and extracellular matrix disruption can function as DAMPs to induce inflammatory responses and pro-catabolic events in vitro and promote synovitis and cartilage degradation in vivo via PRRs. Some of the DAMPs and PRRs display various capacities in driving synovitis and/or cartilage degradation in different models of animal studies. New findings reveal that the inflammatory complement cascade plays a key in the pathogenesis of OA. Crosstalk between joint tissues such as synovium and cartilage communicated at the cellular level within the innate immune inflammatory network is implicated to play an important role in OA progression. Further studies on how the innate immune inflammatory network impacts the OA disease process at different stages of progression will lead to the development of new therapeutic strategies.

Ambiguities in NLRP3 inflammasome regulation: is there a role for mitochondria?

BACKGROUND

The NLRP3 inflammasome is a sensor of specific pathogen, host and environmental danger molecules. Upon activation NLRP3 recruits caspase-1, which cleaves and thereby activates precursor interleukin-1β (IL-1β) and IL-18 to initiate immune responses. Several recent studies have posited that the mitochondria are a central regulator of NLRP3 function.

SCOPE OF REVIEW

Mitochondrial reactive oxygen species (mtROS) production, mitochondrial apoptosis, mitochondrial DNA (mtDNA) release, mitophagy, calcium induced mitochondrial damage and mitochondrial co-ordination of NLRP3 localization have all been implicated in regulating NLRP3 activity. In this article we review the literature both for and against these models of NLRP3 inflammasome activation, and highlight other recent contentious issues concerning NLRP3 functioning.

MAJOR CONCLUSIONS

Although many mechanisms have been proposed for activating NLRP3, no unified model has yet to gain acceptance. Further research is required to clarify how the mitochondria might influence NLRP3 activity.

GENERAL SIGNIFICANCE

While the NLRP3 inflammasome is important for host protection against microbial infection, rare genetic mutations in NLRP3 also cause severe auto-inflammatory diseases. More recent research has implicated NLRP3 activity in pathologies such as atherosclerosis, cancer, type 2 diabetes and Alzheimer's disease. Understanding the mechanisms of NLRP3 inflammasome formation and regulation therefore has the potential to uncover new inflammasome and disease specific therapeutic targets. This article is part of a Special Issue entitled Frontiers of Mitochondrial Research.

Chronic alcohol-induced microRNA-155 contributes to neuroinflammation in a TLR4-dependent manner in mice

Introduction

Alcohol-induced neuroinflammation is mediated by pro-inflammatory cytokines and chemokines including tumor necrosis factor-α (TNFα), monocyte chemotactic protein-1 (MCP1) and interleukin-1-beta (IL-1β). Toll-like receptor-4 (TLR4) pathway induced nuclear factor-κB (NF-κB) activation is involved in the pathogenesis of alcohol-induced neuroinflammation. Inflammation is a highly regulated process. Recent studies suggest that microRNAs (miRNAs) play crucial role in fine tuning gene expression and miR-155 is a major regulator of inflammation in immune cells after TLR stimulation.

Aim

To evaluate the role of miR-155 in the pathogenesis of alcohol-induced neuroinflammation.

Methods

Wild type (WT), miR-155- and TLR4-knockout (KO) mice received 5% ethanol-containing or isocaloric control diet for 5 weeks. Microglia markers were measured by q-RTPCR; inflammasome activation was measured by enzyme activity; TNFα, MCP1, IL-1β mRNA and protein were measured by q-RTPCR and ELISA; phospho-p65 protein and NF-κB were measured by Western-blotting and EMSA; miRNAs were measured by q-PCR in the cerebellum. MiR-155 was measured in immortalized and primary mouse microglia after lipopolysaccharide and ethanol stimulation.

Results

Chronic ethanol feeding up-regulated miR-155 and miR-132 expression in mouse cerebellum. Deficiency in miR-155 protected mice from alcohol-induced increase in inflammatory cytokines; TNFα, MCP1 protein and TNFα, MCP1, pro-IL-1β and pro-caspase-1 mRNA levels were reduced in miR-155 KO alcohol-fed mice. NF-κB was activated in WT but not in miR-155 KO alcohol-fed mice. However increases in cerebellar caspase-1 activity and IL-1β levels were similar in alcohol-fed miR-155-KO and WT mice. Alcohol-fed TLR4-KO mice were protected from the induction of miR-155. NF-κB activation measured by phosphorylation of p65 and neuroinflammation were reduced in alcohol-fed TLR4-KO compared to control mice. TLR4 stimulation with lipopolysaccharide in primary or immortalized mouse microglia resulted in increased miR-155.

Conclusion

Chronic alcohol induces miR-155 in the cerebellum in a TLR4-dependent manner. Alcohol-induced miR-155 regulates TNFα and MCP1 expression but not caspase-dependent IL-1β increase in neuroinflammation.

Antroquinonol mitigates an accelerated and progressive IgA nephropathy model in mice by activating the Nrf2 pathway and inhibiting T cells and NLRP3 inflammasome

High levels of reactive oxygen species (ROS), systemic T cell activation, and macrophage infiltration in the kidney are implicated in the acceleration and progression of IgA nephropathy (IgAN), the most frequent type of primary glomerulonephritis. However, the pathogenic mechanism of IgAN is still little understood, and it remains a challenge to establish a specific therapeutic strategy for this type of glomerular disorder. Recently, we showed that antroquinonol (Antroq), a pure active compound from Antrodia camphorata mycelium, inhibits renal inflammation and reduces oxidative stress in a mouse model of renal fibrosis. But the anti-inflammatory and immune-regulatory effects of Antroq on the acceleration and progression of primary glomerular disorders have not been determined. In this study, we show that Antroq administration substantially impeded the development of severe renal lesions, such as intense glomerular proliferation, crescents, sclerosis, and periglomerular interstitial inflammation, in mice with induced accelerated and progressive IgAN (AcP-IgAN). Further mechanistic analysis in AcP-IgAN mice showed that, early in the developmental stage of the AcP-IgAN model, Antroq promoted the Nrf2 antioxidant pathway and inhibited the activation of T cells and NLRP3 inflammasome. Significantly improved proteinuria/renal function and histopathology in AcP-IgAN mice of an established stage supported potential therapeutic effects of Antroq on the disease. In addition, Antroq was shown to inhibit activation of NLRP3 inflammasome in vitro by an IgA immune complex (IC) partly involving a reduced ROS production in IgA-IC-primed macrophages, and this finding may be helpful in the understanding of the mode of action of Antroq in the treated AcP-IgAN mice.

The role of the immune response in age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in developed countries; with the aging population, the negative health impacts and costs of the disease will increase dramatically over the next decade. Although the exact cause of AMD is unknown, genetic studies have implicated the complement system as well as other immune responses in disease pathogenesis and severity. Furthermore, histologic studies have shown the presence of macrophages, lymphocytes, and mast cells, as well as fibroblasts, in both atrophic lesions and with retinal neovascularization. This review summarizes discussions from the fifth annual conference of the Arnold and Mabel Beckman Initiative for Macular Research by the Inflammation and Immune Response Task Force. These deliberations focused on the role of inflammatory immune responses, including complement, inflammasomes, adaptive immune responses, and para-inflammation, unanswered questions and studies to address these questions, and potential immune-related therapeutic targets for AMD.

New pathways to control inflammatory responses in adipose tissue

Obesity is characterized by the presence of chronic inflammation in adipose tissue, particularly in the visceral compartment, that has been causally linked to development of obesity-associated comorbidities. This link can be either direct or indirect, through induction of insulin resistance. This review summarizes recent evidence on potential pharmacological targets of adipose tissue inflammation, with emphasis on mediators that are being studied for intervention in chronic inflammatory diseases and are therefore viable therapeutical candidates. Specifically, we discuss evidence on the role of the inflammasome and its downstream products as a potential target for anti-inflammatory strategies as well as T regulatory (Treg) cells and mediators involved in the resolution phase of inflammation such as resolvins, protectins, annexin A1 (ANXA1) and galectins as potential targets for novel agonist therapies.

NLRP3 deletion protects from hyperoxia-induced acute lung injury

Inspiration of a high concentration of oxygen, a therapy for acute lung injury (ALI), could unexpectedly lead to reactive oxygen species (ROS) production and hyperoxia-induced acute lung injury (HALI). Nucleotide-binding domain and leucine-rich repeat PYD-containing protein 3 (NLRP3) senses the ROS, triggering inflammasome activation and interleukin-1β (IL-1β) production and secretion. However, the role of NLRP3 inflammasome in HALI is unclear. The main aim of this study is to determine the effect of NLRP3 gene deletion on inflammatory response and lung epithelial cell death. Wild-type (WT) and NLRP3(-/-) mice were exposed to 100% O2 for 48-72 h. Bronchoalveolar lavage fluid and lung tissues were examined for proinflammatory cytokine production and lung inflammation. Hyperoxia-induced lung pathological score was suppressed in NLRP3(-/-) mice compared with WT mice. Hyperoxia-induced recruitment of inflammatory cells and elevation of IL-1β, TNFα, macrophage inflammatory protein-2, and monocyte chemoattractant protein-1 were attenuated in NLRP3(-/-) mice. NLRP3 deletion decreased lung epithelial cell death and caspase-3 levels and a suppressed NF-κB levels compared with WT controls. Taken together, this research demonstrates for the first time that NLRP3-deficient mice have suppressed inflammatory response and blunted lung epithelial cell apoptosis to HALI.

Alcohol-induced IL-1β in the brain is mediated by NLRP3/ASC inflammasome activation that amplifies neuroinflammation

Alcohol-induced neuroinflammation is mediated by proinflammatory cytokines, including IL-1β. IL-1β production requires caspase-1 activation by inflammasomes-multiprotein complexes that are assembled in response to danger signals. We hypothesized that alcohol-induced inflammasome activation contributes to increased IL-1β in the brain. WT and TLR4-, NLRP3-, and ASC-deficient (KO) mice received an ethanol-containing or isocaloric control diet for 5 weeks, and some received the rIL-1ra, anakinra, or saline treatment. Inflammasome activation, proinflammatory cytokines, endotoxin, and HMGB1 were measured in the cerebellum. Expression of inflammasome components (NLRP1, NLRP3, ASC) and proinflammatory cytokines (TNF-α, MCP-1) was increased in brains of alcohol-fed compared with control mice. Increased caspase-1 activity and IL-1β protein in ethanol-fed mice indicated inflammasome activation. TLR4 deficiency protected from TNF-α, MCP-1, and attenuated alcohol-induced IL-1β increases. The TLR4 ligand, LPS, was not increased in the cerebellum. However, we found up-regulation of acetylated and phosphorylated HMGB1 and increased expression of the HMGB1 receptors (TLR2, TLR4, TLR9, RAGE) in alcohol-fed mice. NLRP3- or ASC-deficient mice were protected from caspase-1 activation and alcohol-induced IL-1β increase in the brain. Furthermore, in vivo treatment with rIL-1ra prevented alcohol-induced inflammasome activation and IL-1β, TNF-α, and acetylated HMGB1 increases in the cerebellum. Conversely, intracranial IL-1β administration induced TNF-α and MCP-1 in the cerebellum. In conclusion, alcohol up-regulates and activates the NLRP3/ASC inflammasome, leading to caspase-1 activation and IL-1β increase in the cerebellum. IL-1β amplifies neuroinflammation, and disruption of IL-1/IL-1R signaling prevents alcohol-induced inflammasome activation and neuroinflammation. Increased levels of acetylated and phosphorylated HMGB1 may contribute to alcoholic neuroinflammation.

Chemical genetics reveals a kinase-independent role for protein kinase R in pyroptosis

Formation of the inflammasome, a scaffolding complex that activates caspase-1, is important in numerous diseases. Pyroptotic cell death induced by anthrax lethal toxin (LT) is a model for inflammasome-mediated caspase-1 activation. We discovered 7-desacetoxy-6,7-dehydrogedunin (7DG) in a phenotypic screen as a small molecule that protects macrophages from LT-induced death. Using chemical proteomics, we identified protein kinase R (PKR) as the target of 7DG and show that RNAi knockdown of PKR phenocopies treatment with 7DG. Further, we show that PKR's role in ASC assembly and caspase-1 activation induced by several different inflammasome stimuli is independent of PKR's kinase activity, demonstrating that PKR has a previously uncharacterized role in caspase-1 activation and pyroptosis that is distinct from its reported kinase-dependent roles in apoptosis and inflammasome formation in lipopolysaccharide-primed cells. Remarkably, PKR has different roles in two distinct cell death pathways and has a broad role in inflammasome function relevant in other diseases.

Inflammation links excess fat to insulin resistance: the role of the interleukin-1 family

A growing body of evidence suggests that cytokines of the interleukin-1 (IL-1) family, particularly IL-1β but also IL-1Ra and IL-18, are involved in obesity-associated inflammation. IL-1β is produced via cleavage of pro-IL-1β by caspase-1, which in turn is activated by a multiprotein complex called the inflammasome. The components of the NLRP3 inflammasome are involved in sensing obesity-associated danger signals, both in mice and in human (obese) subjects, with caspase-1 seemingly the most crucial regulator. Autophagy is upregulated in obesity and may function as a mechanism to control IL-1β gene expression in adipose tissue to mitigate chronic inflammation. All these mechanisms are operative in human adipose tissue and appear to be more pronounced in human visceral compared to subcutaneous tissue. In animal studies, blocking caspase-1 activity results in decreased weight gain, decreased inflammation, and improved insulin sensitivity. Human intervention studies with IL-1Ra (anakinra) have reported beneficial effects in patients with diabetes, yet without significant changes in insulin sensitivity. Clearly, the IL-1 family of cytokines, especially IL-1β, plays an important role in obesity-associated inflammation and insulin resistance and may represent a therapeutic target to reverse the detrimental metabolic consequences of obesity.

The inflammasome and danger associated molecular patterns (DAMPs) are implicated in cytokine and chemokine responses following stressor exposure

Exposure to stressors or trauma in the absence of pathogenic challenge can stimulate a systemic sterile inflammatory response characterized by high concentrations of blood and tissue cytokines, chemokines, and danger associated molecular patterns (DAMPs) such as heat shock protein-72 (Hsp72), and uric acid. The signaling pathways responsible for these responses remain unclear, however, the inflammasome may play a role. In vitro, DAMPs are known to stimulate the inflammasome in the presence of LPS to activate caspase-1 which cleaves immature precursors of interleukin (IL)-1β and IL-18 into their mature releasable forms. Furthermore, in vivo neutralization of the LPS selectively attenuates the stress-induced increase in the inflammasome-dependent cytokines IL-1β and IL-18. Thus, the current experiments tested the hypothesis that inflammasome-mediated processes are necessary for a systemic stress-induced inflammatory response to an acute stressor. The data presented (1) establish that male F344 rats exposed to an acute severe stressor (100 tail shocks) have elevated plasma concentrations of inflammatory proteins (IL-1β, IL-18, IL-6, IL-10, and monocyte chemotactic protein (MCP)-1), and DAMPs (uric acid and Hsp72); (2) demonstrate that inhibiting caspase-1 in vivo, using the caspase-1 inhibitor ac-YVAD-cmk, attenuates stress-induced production of IL-1β, IL-18, and IL-6 in both the circulation and peripheral tissues; and (3) implicates the DAMPs uric acid and Hsp72 as important signals contributing to inflammasome-dependent inflammatory responses using a stepwise multiple regression. The results increase our mechanistic understanding of systemic sterile inflammatory responses, and provide novel evidence that the inflammasome may be an important pharmacological target for treatment of these conditions.

The role of interleukin-1 in allergy-related disorders

PURPOSE OF REVIEW

Interleukin-1β (IL-1β) is a potent proinflammatory cytokine, which is involved in many inflammatory conditions including autoinflammatory and allergic disorders. This review provides insights into recent advances of our understanding of the pathogenesis of IL-1β-associated allergy-related disorders.

RECENT FINDINGS

In autoinflammatory as well as allergic diseases such as contact hypersensitivity, atopic dermatitis and bronchial asthma, dysfunctional inflammasome processing has been demonstrated to account for IL-1β-induced inflammation. IL-1-neutralizing drugs have been shown to completely suppress or markedly reduce inflammatory responses in clinical studies and experimental models of urticarial autoinflammatory diseases as well as common allergic disorders.

SUMMARY

The recent findings support a crucial role for IL-1β and inflammasome components in a variety of allergy-related disorders.

NLRP3 Inflammasome and MS/EAE

Inflammasomes are cytosolic sensors that detect pathogens and danger signals in the innate immune system. The NLRP3 inflammasome is currently the most fully characterized inflammasome and is known to detect a wide array of microbes and endogenous damage-associated molecules. Possible involvement of the NLRP3 inflammasome (or inflammasomes) in the development of multiple sclerosis (MS) was suggested in a number of studies. Recent studies showed that the NLRP3 inflammasome exacerbates experimental autoimmune encephalomyelitis (EAE), an animal model of MS, although EAE can also develop without the NLRP3 inflammasome. In this paper, we discuss the NLRP3 inflammasome in MS and EAE development.

Commensal bacteria and MAMPs are necessary for stress-induced increases in IL-1β and IL-18 but not IL-6, IL-10 or MCP-1

Regular interactions between commensal bacteria and the enteric mucosal immune environment are necessary for normal immunity. Alterations of the commensal bacterial communities or mucosal barrier can disrupt immune function. Chronic stress interferes with bacterial community structure (specifically, α-diversity) and the integrity of the intestinal barrier. These interferences can contribute to chronic stress-induced increases in systemic IL-6 and TNF-α. Chronic stress, however, produces many physiological changes that could indirectly influence immune activity. In addition to IL-6 and TNF-α, exposure to acute stressors upregulates a plethora of inflammatory proteins, each having unique synthesis and release mechanisms. We therefore tested the hypothesis that acute stress-induced inflammatory protein responses are dependent on the commensal bacteria, and more specifically, lipopolysaccharide (LPS) shed from Gram-negative intestinal commensal bacteria. We present evidence that both reducing commensal bacteria using antibiotics and neutralizing LPS using endotoxin inhibitor (EI) attenuates increases in some (inflammasome dependent, IL-1 and IL-18), but not all (inflammasome independent, IL-6, IL-10, and MCP-1) inflammatory proteins in the blood of male F344 rats exposed to an acute tail shock stressor. Acute stress did not impact α- or β- diversity measured using 16S rRNA diversity analyses, but selectively reduced the relative abundance of Prevotella. These findings indicate that commensal bacteria contribute to acute stress-induced inflammatory protein responses, and support the presence of LPS-mediated signaling in stress-evoked cytokine and chemokine production. The selectivity of the commensal bacteria in stress-evoked IL-1β and IL-18 responses may implicate the inflammasome in this response.

Nanovectorized radiotherapy: a new strategy to induce anti-tumor immunity

Recent experimental findings show that activation of the host immune system is required for the success of chemo- and radiotherapy. However, clinically apparent tumors have already developed multiple mechanisms to escape anti-tumor immunity. The fact that tumors are able to induce a state of tolerance and immunosuppression is a major obstacle in immunotherapy. Hence, there is an overwhelming need to develop new strategies that overcome this state of immune tolerance and induce an anti-tumor immune response both at primary and metastatic sites. Nanovectorized radiotherapy that combines ionizing radiation and nanodevices, is one strategy that could boost the quality and magnitude of an immune response in a predictable and designable fashion. The potential benefits of this emerging treatment may be based on the unique combination of immunostimulatory properties of nanoparticles with the ability of ionizing radiation to induce immunogenic tumor cell death. In this review, we will discuss available data and propose that the nanovectorized radiotherapy could be a powerful new strategy to induce anti-tumor immunity required for positive patient outcome.

Type I IFN-mediated regulation of IL-1 production in inflammatory disorders

Although contributing to inflammatory responses and to the development of certain autoimmune pathologies, type I interferons (IFNs) are used for the treatment of viral, malignant, and even inflammatory diseases. Interleukin-1 (IL-1) is a strongly pyrogenic cytokine and its importance in the development of several inflammatory diseases is clearly established. While the therapeutic use of IL-1 blocking agents is particularly successful in the treatment of innate-driven inflammatory disorders, IFN treatment has mostly been appreciated in the management of multiple sclerosis. Interestingly, type I IFNs exert multifaceted immunomodulatory effects, including the reduction of IL-1 production, an outcome that could contribute to its efficacy in the treatment of inflammatory diseases. In this review, we summarize the current knowledge on IL-1 and IFN effects in different inflammatory disorders, the influence of IFNs on IL-1 production, and discuss possible therapeutic avenues based on these observations.

IL-1 signal affects both protection and pathogenesis of virus-induced chronic CNS demyelinating disease

Background

Theiler’s virus infection induces chronic demyelinating disease in mice and has been investigated as an infectious model for multiple sclerosis (MS). IL-1 plays an important role in the pathogenesis of both the autoimmune disease model (EAE) and this viral model for MS. However, IL-1 is known to play an important protective role against certain viral infections. Therefore, it is unclear whether IL-1-mediated signaling plays a protective or pathogenic role in the development of TMEV-induced demyelinating disease.

Methods

Female C57BL/6 mice and B6.129S7-Il1r1^tm1Imx/J mice (IL-1R KO) were infected with Theiler’s murine encephalomyelitis virus (1 x 10⁶ PFU). Differences in the development of demyelinating disease and changes in the histopathology were compared. Viral persistence, cytokine production, and immune responses in the CNS of infected mice were analyzed using quantitative PCR, ELISA, and flow cytometry.

Results

Administration of IL-1β, thereby rending resistant B6 mice susceptible to TMEV-induced demyelinating disease, induced a high level of Th17 response. Interestingly, infection of TMEV into IL-1R-deficient resistant C57BL/6 (B6) mice also induced TMEV-induced demyelinating disease. High viral persistence was found in the late stage of viral infection in IL-1R-deficient mice, although there were few differences in the initial anti-viral immune responses and viral persistent levels between the WT B6 and IL-1R-deficiecent mice. The initial type I IFN responses and the expression of PDL-1 and Tim-3 were higher in the CNS of TMEV-infected IL-1R-deficient mice, leading to deficiencies in T cell function that permit viral persistence.

Conclusions

These results suggest that the presence of high IL-1 level exerts the pathogenic role by elevating pathogenic Th17 responses, whereas the lack of IL-1 signals promotes viral persistence in the spinal cord due to insufficient T cell activation by elevating the production of inhibitory cytokines and regulatory molecules. Therefore, the balance of IL-1 signaling appears to be extremely important for the protection from TMEV-induced demyelinating disease, and either too much or too little signaling promotes the development of disease.

The involvement of microglial cells in Japanese encephalitis infections

Despite the availability of effective vaccines, Japanese encephalitis virus (JEV) infections remain a leading cause of encephalitis in many Asian countries. The virus is transmitted to humans by Culex mosquitoes, and, while the majority of human infections are asymptomatic, up to 30% of JE cases admitted to hospital die and 50% of the survivors suffer from neurological sequelae. Microglia are brain-resident macrophages that play key roles in both the innate and adaptive immune responses in the CNS and are thus of importance in determining the pathology of encephalitis as a result of JEV infection.

Dangerous liaisons: mitochondrial DNA meets the NLRP3 inflammasome

Danger signals released by damaged organelles can promote inflammation. In this issue of Immunity, Shimada et al. (2012) report that oxidized DNA, released by mitochondria, directly binds and activates the NLRP3 inflammasome.

Inhibitor of apoptosis proteins limit RIP3 kinase-dependent interleukin-1 activation

Interleukin-1β (IL-1β) is a potent inflammatory cytokine that is usually cleaved and activated by inflammasome-associated caspase-1. To determine whether IL-1β activation is regulated by inhibitor of apoptosis (IAP) proteins, we treated macrophages with an IAP-antagonist "Smac mimetic" compound or genetically deleted the genes that encode the three IAP family members cIAP1, cIAP2, and XIAP. After Toll-like receptor priming, IAP inhibition triggered cleavage of IL-1β that was mediated not only by the NLRP3-caspase-1 inflammasome, but also by caspase-8 in a caspase-1-independent manner. In the absence of IAPs, rapid and full generation of active IL-1β by the NLRP3-caspase-1 inflammasome, or by caspase-8, required the kinase RIP3 and reactive oxygen species production. These results demonstrate that activation of the cell death-inducing ripoptosome platform and RIP3 can generate bioactive IL-1β and implicate them as additional targets for the treatment of pathological IL-1-driven inflammatory responses.

Identification of common biological pathways and drug targets across multiple respiratory viruses based on human host gene expression analysis

BACKGROUND

Pandemic and seasonal respiratory viruses are a major global health concern. Given the genetic diversity of respiratory viruses and the emergence of drug resistant strains, the targeted disruption of human host-virus interactions is a potential therapeutic strategy for treating multi-viral infections. The availability of large-scale genomic datasets focused on host-pathogen interactions can be used to discover novel drug targets as well as potential opportunities for drug repositioning.

METHODS/RESULTS

In this study, we performed a large-scale analysis of microarray datasets involving host response to infections by influenza A virus, respiratory syncytial virus, rhinovirus, SARS-coronavirus, metapneumonia virus, coxsackievirus and cytomegalovirus. Common genes and pathways were found through a rigorous, iterative analysis pipeline where relevant host mRNA expression datasets were identified, analyzed for quality and gene differential expression, then mapped to pathways for enrichment analysis. Possible repurposed drugs targets were found through database and literature searches. A total of 67 common biological pathways were identified among the seven different respiratory viruses analyzed, representing fifteen laboratories, nine different cell types, and seven different array platforms. A large overlap in the general immune response was observed among the top twenty of these 67 pathways, adding validation to our analysis strategy. Of the top five pathways, we found 53 differentially expressed genes affected by at least five of the seven viruses. We suggest five new therapeutic indications for existing small molecules or biological agents targeting proteins encoded by the genes F3, IL1B, TNF, CASP1 and MMP9. Pathway enrichment analysis also identified a potential novel host response, the Parkin-Ubiquitin Proteasomal System (Parkin-UPS) pathway, which is known to be involved in the progression of neurodegenerative Parkinson's disease.

CONCLUSIONS

Our study suggests that multiple and diverse respiratory viruses invoke several common host response pathways. Further analysis of these pathways suggests potential opportunities for therapeutic intervention.

TLR-induced NF-κB activation regulates NLRP3 expression in murine macrophages

NLRP3 inflammasome plays a critical role in the activation of caspase-1 and maturation of IL-1β. However, the specific cis- and trans-regulatory elements that determine the extent of NLRP3 expression are not well defined. In this study, we found NLRP3 expression was induced by TLR agonists in murine macrophages in a NF-κB dependent manner. Furthermore, the corresponding NF-κB binding sites (nt -1303 to -1292 and -1238 to -1228) were identified in the NLRP3 promoter. Finally, EMSA and ChIP assays demonstrated LPS-induced NF-κB binding to the NLRP3 promoter. Therefore, out results delineated the molecular mechanisms involved in TLR-induced transcriptional regulation of NLRP3.

Pattern recognition receptors in immune disorders affecting the skin

Pattern recognition receptors (PRRs) evolved to protect organisms against pathogens, but excessive signaling can induce immune responses that are harmful to the host. Putative PRR dysfunction is associated with numerous immune disorders that affect the skin, such as systemic lupus erythematosus, cryopyrin-associated periodic syndrome, and primary inflammatory skin diseases including psoriasis and atopic dermatitis. As yet, the evidence is often confined to genetic association studies without additional proof of a causal relationship. However, insight into the role of PRRs in the pathophysiology of some disorders has already resulted in new therapeutic approaches based on immunomodulation of PRRs.

Chronic inflammation in cancer development

Chronic inflammatory mediators exert pleiotropic effects in the development of cancer. On the one hand, inflammation favors carcinogenesis, malignant transformation, tumor growth, invasion, and metastatic spread; on the other hand inflammation can stimulate immune effector mechanisms that might limit tumor growth. The link between cancer and inflammation depends on intrinsic and extrinsic pathways. Both pathways result in the activation of transcription factors such as NF-κB, STAT-3, and HIF-1 and in accumulation of tumorigenic factors in tumor and microenvironment. STAT-3 and NF-κB interact at multiple levels and thereby boost tumor-associated inflammation which can suppress anti-tumor immune responses. These factors also promote tumor growth, progression, and metastatic spread. IL-1, IL-6, TNF, and PGHS-2 are key mediators of an inflammatory milieu by modulating the expression of tumor-promoting factors. In this review we concentrate on the crucial role of pro-inflammatory mediators in inflammation-driven carcinogenesis and outline molecular mechanisms of IL-1 signaling in tumors. In addition, we elucidate the dual roles of stress proteins as danger signals in the development of anti-cancer immunity and anti-apoptotic functions.