Role of NLRP3 inflammasome in inflammatory bowel diseases

Inflammasomes are multiprotein intracellular complexes which are responsible for the activation of inflammatory responses. Among various subtypes of inflammasomes, NLRP3 has been a subject of intensive investigation. NLRP3 is considered to be a sensor of microbial and other danger signals and plays a crucial role in mucosal immune responses, promoting the maturation of proinflammatory cytokines interleukin 1β(IL-1β) and IL-18. NLRP3 inflammasome has been associated with a variety of inflammatory and autoimmune conditions, including inflammatory bowel diseases(IBD). The role of NLRP3 in IBD is not yet fully elucidated as it seems to demonstrate both pathogenic and protective effects. Studies have shown a relationship between genetic variants and mutations in NLRP3 gene with IBD pathogenesis. A complex interaction between the NLRP3 inflammasome and the mucosal immune response has been reported. Activation of the inflammasome is a key function mediated by the innate immune response and in parallel the signaling through IL-1β and IL-18 is implicated in adaptive immunity. Further research is needed to delineate the precise mechanisms of NLRP3 function in regulating immune responses. Targeting NLRP3 inflammasome and its downstream signaling will provide new insights into the development of future therapeutic strategies.     

病毒感染与NLRP3炎性小体

炎性小体是一类由多蛋白组成的复合物,通常由NOD样受体蛋白家族(NLRs)、凋亡相关斑点样蛋白(ASC)及半胱氨酸天冬氨酸蛋白酶-1(caspase-1)组成,是固有免疫系统的一个重要组成部分。机体受到刺激(内源性刺激或外源性刺激),启动炎性小体的激活,caspase-1活化,进而促使下游炎性因子(IL-18、IL-1β)成熟与分泌来参与炎症的发生及发展。近年来研究最为广泛的是NLRP3炎性小体。本文就NLRP3炎性小体的结构、激活及在病毒感染时NLRP3炎性小体的激活与调控作一综述。     

Impaired quality control of mitochondria: Aging from a new perspective

Mitochondria fulfill a number of essential cellular functions and play a key role in the aging process. Reactive oxygen species (ROS) are predominantly generated in this organelle but next to inducing oxidative damage they act as signaling molecules. Autophagy is regulated by signaling ROS and is known to affect aging as well as neurodegenerative diseases. Many cellular components that influence autophagy are linked to longevity such as members of the sirtuin protein family. Recent studies further link mitochondrial dynamics to the removal of dysfunctional mitochondria by mitophagy, thereby representing a novel mechanism for the quality control of mitochondria. Here we summarize the current views on how mitochondrial function is linked to aging and we propose that quality control of mitochondria has a crucial role in counteracting the aging process.     

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.     

Mitochondrial alterations, cellular response to oxidative stress and defective degradation of proteins in aging

Respiratory function decline and increase ofoxidative stress in mitochondria have beenproposed as important contributors to humanaging. A wide spectrum of alterations in agedindividuals and senescent cells are similar andare correlated to cellular response tosublethal dose of oxidative stress. Thesealterations and responses include: (1) declinein mitochondrial respiratory function; (2)increase in the rate of production of reactiveoxygen species (ROS); (3) accumulation ofmitochondrial DNA (mtDNA) mutations; (4)increase in the levels of oxidative damage toDNA, protein, and lipids; and (5) decrease inthe capacities of degradation of oxidativelydamaged proteins and other macromolecules. Responses to oxidative stress and theirsubsequent interactions in tissues result inthe deleterious effect of ROS on the cellularfunction, which culminate in aging anddegenerative diseases. In this review, wefocus on the roles that ROS play in age-relatedoxidative damage to mtDNA and proteins andoxidative stress responses at the molecular andcellular levels. The alterations of geneexpression profiles elicited by oxidativestress in aging animals are discussed. Wesuggest that the increase in mitochondrialproduction of ROS and decline in the cellularcapacity to cope with oxidative stress andsubsequent accumulation of mtDNA mutations andoxidized proteins play an important role in theaging process.     

NLRP3炎性体在心肌病和心律失常中的作用及研究进展

NLRP3炎性体是先天免疫反应的参与者，通过相关激活信号来触发炎症。NLRP3炎性体在心肌细胞和心脏成纤维细胞中表达，通过水解含半胱氨酸的天冬氨酸蛋白水解酶(caspase-1)前体生成caspase-1促使白介素（IL）-1β、IL-18的成熟和释放而导致细胞焦亡，其浸润影响到心肌病和心律失常等心血管疾病的发生发展过程。在这篇综述中，我们介绍了NLRP3炎性体在心肌病和心律失常中的作用及相关机制，对探索针对NLRP3炎症体在此类疾病中的治疗方案有重要意义。     

Role of NLRP3 and NLRP1 inflammasomes signaling pathways in pathogenesis of rheumatoid arthritis

Objective:To investigate the role of NLRP3 and NLRP1 inflammasomes signaling pathways in rheumatoid arthritis(RA).Methods:A total of 36 patients with RA were selected,peripheral blood mononuclear cell(PBMC)and granulocyte were separated from venous blood.RT-qPCR method was used to detect the expression level and diversity of NLRP3 and NLRP1 in PBMC and granulocyte mRNA in patieuts with RA.and detect the mRNA expression of downstream factor IL-1β.The correlation between RA and the expression of NLRP3 aud NLRP1 was analyzed.Normal 30 cases were set as control group.Results:Expression levels of NLRP1.and caspase-1mRNA in PBMC of RA group were significautly lower than those of control group(P0.05).while there was no significant differeuee in expression levels of NLRP3,ASC.IL-1βmRNA between these two groups(P0.05);NLRP3,caspase-1,and ASC mRNA expression in granulocyte of RA patients were significantly lower than those in control group(P0.05).There was no currelation between rheumatoid factor and expression levels of NLRP3.ASC.caspase-1 mRNA in RA group(P0.05);NLRP1,IL-1βmRNA expression level had a negative corrlation with anti-rheunatoid factor antibody(P=0.0332,0.0340).Conclusions:NLRP3 and NLRP1 inflammasomes signaling pathways are involved in RA inflammatory reaction process as protective factors,and play an important role in RA inflammatory mechanisms.     

Upregulated NLRP3 inflammasome activation is attenuated by anthocyanins in patients with nonalcoholic fatty liver disease: A case-control and an intervention study

ObjectivesDespite the recent attention focused on the roles of the NLRP3 inflammasome in the pathogenesis of metabolic and inflammatory diseases, little is known about the activation status of NLRP3 inflammasome in patients with nonalcoholic fatty liver disease (NAFLD). The present study aimed to investigate whether inflammasomes activation is upregulated in patients with NAFLD and the upregulation can be attenuated by anthocyanins, which are polyphenols with known anti-inflammatory activities.MethodsThis study included a case-control study and a randomized controlled intervention trial. In the first part, NAFLD patients and healthy controls were recruited from a cohort of railroad workers. In the second part, NAFLD patients were randomly assigned to receive either capsules of anthocyanins (320 mg daily) or placebo for 12 weeks. A series of genes and factors associated with activation of NLRP3 inflammasome in subjects’ plasma and peripheral blood mononuclear cells (PBMCs) were analyzed.ResultsCompared with healthy controls, the mRNA levels of NLRP3 inflammasome components (NLRP3, caspase-1, interleukin (IL)-1β, and IL-18) were significantly upregulated in the PBMCs of NAFLD patients. Consistently, plasma levels of mature IL-1β and IL-18 in NAFLD patients were significantly higher than in controls. After anthocyanin administration, both mRNA expression of NLRP3 inflammasome components (caspase-1, IL-1β, and IL-18) in PBMCs and plasma levels of IL-1β and IL-18 decreased dramatically in NAFLD patients compared with controls.ConclusionsThis study has demonstrated that the activation of NLRP3 inflammasome is highly increased in NAFLD patients, but it can be markedly suppressed by anthocyanins, which provides a rationale for the development of anti-inflammatory therapies in NAFLD.     

Oxidative stress, mitochondria and mtDNA-mutator mice

The oxidative stress theory of aging, an expansion of the mitochondrial theory of aging, is based around the idea of a vicious cycle, in which somatic mutations of mitochondrial DNA (mtDNA) provoke respiratory chain dysfunction leading to enhanced ROS production and in turn to the accumulation of further mtDNA mutations. Mitochondrial dysfunction and mtDNA mutations are amplified during the course of aging. Recently, results obtained from mtDNA-mutator mice further strengthen the role of mitochondria in the aging process. However, lack of increased oxidative stress in the mtDNA-mutator mice raises doubts in the direct connection of mtDNA mutations with increased ROS production, challenging the oxidative stress theory of aging. The purpose of this short review is to highlight several studies that provide direct evidence that accelerated aging is linked to mtDNA mutations, without an increase in oxidative damage.     

TLR-induced PAI-2 expression suppresses IL-1β processing via increasing autophagy and NLRP3 degradation

The NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome, a multiprotein complex, triggers caspase-1 activation and maturation of the proinflammatory cytokines IL-1β and IL-18 upon sensing a wide range of pathogen- and damage-associated molecules. Dysregulation of NLRP3 inflammasome activity contributes to the pathogenesis of many diseases, but its regulation remains poorly defined. Here we show that depletion of plasminogen activator inhibitor type 2 (PAI-2), a serine protease inhibitor, resulted in NLRP3- and ASC (apoptosis-associated Speck-like protein containing a C-terminal caspase recruitment domain)‐dependent caspase-1 activation and IL-1β secretion in macrophages upon Toll-like receptor 2 (TLR2) and TLR4 engagement. TLR2 or TLR4 agonist induced PAI-2 expression, which subsequently stabilized the autophagic protein Beclin 1 to promote autophagy, resulting in decreases in mitochondrial reactive oxygen species, NLRP3 protein level, and pro–IL-1β processing. Likewise, overexpressing Beclin 1 in PAI-2–deficient cells rescued the suppression of NLRP3 activation in response to LPS. Together, our data identify a tier of TLR signaling in controlling NLRP3 inflammasome activation and reveal a cell-autonomous mechanism which inversely regulates TLR- or Escherichia coli-induced mitochondrial dysfunction, oxidative stress, and IL-1β–driven inflammation.Innate immunity, the first line of host defense against pathogen infection, is composed of diverse germ line-encoded pattern-recognition receptors, such as Toll-like receptors (TLRs) and NOD-like receptors (NLRs), that recognize pathogen-associated molecular patterns (PAMPs) from pathogens or danger-associated molecular patterns from damaged tissue (1, 2). TLRs recognize a variety of PAMPs from microbes to induce autophagy and cytokine production for host defense against microbial infections. Inflammasomes, multiple protein complexes containing NLR proteins or AIM2, mediate caspase-1 activation leading to the processing of the proinflammatory cytokines IL-1β and IL-18 (3). The inflammasome/caspase-1 complexes also may target additional effector molecules to regulate diverse physiological functions, such as pyroptosis and tissue repair (4). Among the identified inflammasomes, the NLRP3 inflammasome has been studied extensively and has been shown to be activated by a large variety of activators that share no structural similarity (2). For this reason, it has been suggested that the NLRP3 inflammasome is activated through a secondary mediator, such as potassium (K⁺) efflux, reactive oxygen species (ROS), or lysosomal proteases (1). The inflammasomes play a critical role in the clearance of microbial pathogens and tissue repair (2, 5). However, dysregulation of inflammasome activation has been associated with a variety of human diseases, including autoinflammatory diseases, metabolic disorders, and cancer (3, 6).Autophagy, an evolutionarily conserved cellular catabolic process, facilitates the recycling of damaged proteins and organelles (7). Increasing evidence indicates that autophagy is involved in the regulation of immune responses and inflammation (7). Macrophages treated with an autophagy inhibitor or with the deletion of several autophagic components, including Atg16L1, Beclin 1, and LC3, induced greater caspase-1 activation and IL-1β secretion in response to LPS or LPS plus an NLRP3 agonist (8, 9). These data strongly suggest that the NLRP3 inflammasome activity is negatively regulated by autophagy, but the underlying mechanism is poorly understood.Plasminogen activator inhibitor type 2 (PAI-2), a serine proteinase inhibitor (SERPIN), originally was identified as an inhibitor of the urokinase-type plasminogen activator (uPA) involved in cellular invasion and tissue remodeling (10). Recently, PAI-2 has been associated with newly identified uPA-independent biological functions, probably through targeting an as yet uncharacterized intracellular molecule (11). In addition, PAI-2 is one of the major molecules up-regulated in macrophages in response to TLR4 activators or inflammatory mediators, suggesting its function in the regulation of innate immunity (12, 13).Macrophages treated with LPS alone do not release mature IL-1β and IL-18 unless accompanied by a second stimulus, such as ATP or crystals (8, 14). LPS activates TLR4 to induce the synthesis of pro–IL-1β and the inflammasome component NLRP3 via IκB kinase (IKK)/NF-κB activation; a second stimulus is required for inflammasome assembly and caspase-1 activation to cleave pro–IL-1β and pro–IL-18 to their mature forms. Nevertheless, previous work showed that LPS alone is sufficient to induce mature IL-1β production in IKKβ-deficient macrophages because of enhanced pro–IL-1β processing (15). Additionally, LPS-induced PAI-2 expression is blunted in IKKβ-deficient macrophages, and reintroduction of PAI-2 blocks IL-1β maturation in a caspase-1–dependent manner, suggesting that PAI-2 inhibits pro–IL-1β processing upon LPS stimulation; however, the underlying mechanism is unknown.Here, we show that depletion of PAI-2 in macrophages induces caspase-1 activation and IL-1β production in response to TLR agonists and Escherichia coli with no need of a second stimulus. TLR engagement induced PAI-2 expression and enhanced association of PAI-2 with Beclin 1, leading to an increase in autophagy, which then caused reduced mitochondrial ROS (mROS) and increased NLRP3 degradation, resulting in decreased IL-1β maturation. Inflammatory cytokines and cellular ROS play vital roles in innate immunity, but prolonged and excess production of these mediators can be detrimental. Our results suggest that PAI-2 is a cell-autonomous mechanism that counteracts the detrimental effects caused by TLR2/4- and E. coli-triggered cellular stress by reducing ROS production and the inflammasome activation, thereby resulting in less inflammation and tissue damage.     

炎性小体在脑缺血中的作用

固有免疫在脑缺血后炎性损伤中发挥重要作用,其中炎性小体被认为是一个关键因素.炎性小体是一种大分子蛋白质复合物,可识别各种病原体相关分子模式和损伤相关分子模式介导免疫炎性反应.研究显示,脑缺血或脑缺血再灌注可诱导NLRP1和NLRP3炎性小体激活.文章对炎性小体的结构、活化、调控以及在脑缺血中的作用进行了综述.     

Contribution of impaired mitochondrial autophagy to cardiac aging: mechanisms and therapeutic opportunities

The prevalence of cardiovascular disease increases with advancing age. Although long-term exposure to cardiovascular risk factors plays a major role in the etiopathogenesis of cardiovascular disease, intrinsic cardiac aging enhances the susceptibility to developing heart pathologies in late life. The progressive decline of cardiomyocyte mitochondrial function is considered a major mechanism underlying heart senescence. Damaged mitochondria not only produce less ATP but also generate increased amounts of reactive oxygen species and display a greater propensity to trigger apoptosis. Given the postmitotic nature of cardiomyocytes, the efficient removal of dysfunctional mitochondria is critical for the maintenance of cell homeostasis, because damaged organelles cannot be diluted by cell proliferation. The only known mechanism whereby mitochondria are turned over is through macroautophagy. The efficiency of this process declines with advancing age, which may play a critical role in heart senescence and age-related cardiovascular disease. The present review illustrates the putative mechanisms whereby alterations in the autophagic removal of damaged mitochondria intervene in the process of cardiac aging and in the pathogenesis of specific heart diseases that are especially prevalent in late life (eg, left ventricular hypertrophy, ischemic heart disease, heart failure, and diabetic cardiomyopathy). Interventions proposed to counteract cardiac aging through improvements in macroautophagy (eg, calorie restriction and calorie restriction mimetics) are also presented.     

Same molecule but different expression: aging and sepsis trigger NLRP3 inflammasome activation,a target of melatonin

The connection between the innate immune system, clock genes, and mitochondrial bioenergetics was analyzed during aging and sepsis in mouse heart. Our results suggest that the sole NF‐κB activation does not explain the inflammatory process underlying aging; the former also triggers the NLRP3 inflammasome that enhances caspase‐1‐dependent maturation of IL‐1β. In this way, aged mice enter into a vicious cycle as IL‐1β further activates the NF‐κB/NLRP3 inflammasome link. The origin of NF‐κB activation was related to the age‐dependent Bmal1/Clock/RORα/Rev‐Erbα loop disruption, which lowers NAD⁺ levels, reducing the SIRT1 deacetylase ability to inactivate NF‐κB. Consequently, NF‐κB binding to DNA increases, raising the formation of proinflammatory mediators and inducing mitochondrial impairment. The cycle is then closed with the subsequent NLRP3 inflammasome activation. This paired contribution of the innate immune pathways serves as a catalyst to magnify the response to sepsis in aged compared with young mice. Melatonin administration blunted the septic response, reducing inflammation and oxidative stress, and enhancing mitochondrial function at the levels of nonseptic aged mice, but it did not counteract the age‐related inflammation. Together, our results suggest that, although with different strengths, chronoinflammaging constitutes the biochemical substrate of aging and sepsis, and identifies the NLRP3 inflammasome as a new molecular target for melatonin, providing a rationale for its use in NLRP3‐dependent diseases.     

Pharmacological activation of AMPK prevents Drp1-mediated mitochondrial fission and alleviates endoplasmic reticulum stress-associated endothelial dysfunction

Background and purposeThis study aims to investigate whether and how pharmacological activation of AMP-activated protein kinase (AMPK) improves endothelial function by suppressing mitochondrial ROS-associated endoplasmic reticulum stress (ER stress) in the endothelium.Experimental approachPalmitate stimulation induced mitochondrial fission and ER stress-associated endothelial dysfunction. The effects of AMPK activators salicylate and AICA riboside (AICAR) on mitochondrial ROS production, Drp1 phosphorylation, mitochondrial fission, ER stress, thioredoxin-interacting protein (TXNIP)/NLRP3 inflammasome activation, inflammation, cell apoptosis and endothelium-dependent vasodilation were observed.Key results“Silencing” of TXNIP by RNA interference inhibited NLRP3 inflammasome activation in response to ER stress, indicating that TXNIP was a key link between ER stress and NLRP3 inflammasome activation. AMPK activators salicylate and AICAR prevented ROS-induced mitochondrial fission by enhancing dynamin-related protein 1 (Drp1) phosphorylation (Ser 637) and thereby attenuated IRE-1α and PERK phosphorylation, but their actions were blocked by knockdown of AMPK. Salicylate and AICAR reduced TXNIP induction and inhibited NLRP3 inflammasome activation by reducing NLRP3 and caspase-1 expression, leading to a reduction in IL-1β secretion. As a result, salicylate and AICAR inhibited inflammation and reduced cell apoptosis. Meanwhile, salicylate and AICAR enhanced eNOS phosphorylation and restored the loss of endothelium-dependent vasodilation in the rat aorta. Immunohistochemistry staining showed that AMPK activation inhibited ER stress and NLRP3 inflammasome activation in the vascular endothelium.Conclusion and implicationsPharmacological activation of AMPK regulated mitochondrial morphology and ameliorated endothelial dysfunction by suppression of mitochondrial ROS-associated ER stress and subsequent TXNIP/NLRP3 inflammasome activation. These findings suggested that regulation of Drp1 phosphorylation by AMPK activation contributed to suppression of ER stress and thus presented a potential therapeutic strategy for AMPK activation in the regulation of endothelium homeostasis.     

FMDV Leader Protein Interacts with the NACHT and LRR Domains of NLRP3 to Promote IL-1β Production

Foot-and-mouth disease virus (FMDV) infection causes inflammatory clinical symptoms, such as high fever and vesicular lesions, even death of animals. Interleukin-1β (IL-1β) is an inflammatory cytokine that plays an essential role in inflammatory responses against viral infection. The viruses have developed multiple strategies to induce the inflammatory responses, including regulation of IL-1β production. However, the molecular mechanism underlying the induction of IL-1β by FMDV remains not fully understood. Here, we found that FMDV robustly induced IL-1β production in macrophages and pigs. Infection of Casp-1 inhibitor-treated cells and NOD-, LRR- and pyrin domain-containing 3 (NLRP3)-knockdown cells indicated that NLRP3 is essential for FMDV-induced IL-1β secretion. More importantly, we found that FMDV L^pro associates with the NACHT and LRR domains of NLRP3 to promote NLRP3 inflammasome assembly and IL-1β secretion. Moreover, FMDV L^pro induces calcium influx and potassium efflux, which trigger NLRP3 activation. Our data revealed the mechanism underlying the activation of the NLRP3 inflammasome after FMDV L^pro expression, thus providing insights for the control of FMDV infection-induced inflammation.     

Kir6.2 knockout aggravates lipopolysaccharide-induced mouse liver injury via enhancing NLRP3 inflammasome activation

Background

ATP-sensitive potassium (K-ATP) channels couple cellular metabolism to electric activity. Although Kir6.2-composed K-ATP channel (Kir6.2/K-ATP channel) has been demonstrated to regulate inflammation, a common cause of most liver diseases, its role in liver injury remains elusive.

Methods

Kir6.2 knockout mice were used to prepared LPS-induced liver injury model so as to investigate the role of Kir6.2/K-ATP channels in the injury. Histochemistry was applied to evaluate the extent of liver injury. Proinflammatory cytokines were analyzed by ELISA. Endoplasmic reticulum (ER) stress and autophagy were assessed by western blotting.

Results

We showed that Kir6.2 knockout markedly promoted the infiltration of lymphocytes and neutrophils in liver and significantly elevated serum levels of alanine transaminase (ALT) in respond to LPS treatment. We further found that Kir6.2 deficiency enhanced the activation of NF-κB and NLRP3 inflammasome following LPS challenge, and thereby increased the levels of pro-inflammatory cytokines IL-1β, IL-18 and TNF-α. Treatment of wild-type mice with the K-ATP channel opener iptakalim (IPT) could protect against LPS-induced liver injury through attenuating NLRP3 inflammasome-mediated inflammatory responses. Furthermore, Kir6.2 knockout-induced activation of NLRP3 inflammasome aggravated endoplasmic reticulum (ER) stress, autophagy and subsequent hepatocyte death.

Conclusion

Kir6.2 deficiency exacerbated LPS-induced liver injury by enhancing NLRP3 inflammasome-mediated inflammatory response. Thus, Kir6.2/K-ATP channel may be a potential candidate target for the treatment and prevention of liver injury.     

NLRP3炎症小体与肺部疾病

NLRP3炎症小体是细胞内固有免疫系统的感受器,是-类通过活化caspase-1来间接调控IL-18与IL-18的成熟和分泌的蛋白复合体。作为机体固有免疫及应激系统的重要防御成分,NLRP3炎症小体参与了多种疾病发生和进展。近年发现NLRP3炎症小体与肺部疾病关系密切。本文就NLRP3炎症小体的组成、活化机制及其在肺炎、肺结核、COPD及哮喘等肺部疾病中的研究作一综述。     

Influenza A Virus Infection Activates NLRP3 Inflammasome through Trans-Golgi Network Dispersion

The NLRP3 inflammasome consists of NLRP3, ASC, and pro-caspase-1 and is an important arm of the innate immune response against influenza A virus (IAV) infection. Upon infection, the inflammasome is activated, resulting in the production of IL-1β and IL-18, which recruits other immune cells to the site of infection. It has been suggested that in the presence of stress molecules such as nigericin, the trans-Golgi network (TGN) disperses into small puncta-like structures where NLRP3 is recruited and activated. Here, we investigated whether IAV infection could lead to TGN dispersion, whether dispersed TGN (dTGN) is responsible for NLRP3 inflammasome activation, and which viral protein is involved in this process. We showed that the IAV causes dTGN formation, which serves as one of the mechanisms of NLRP3 inflammasome activation in response to IAV infection. Furthermore, we generated a series of mutant IAVs that carry mutations in the M2 protein. We demonstrated the M2 proton channel activity, specifically His37 and Trp41 are pivotal for the dispersion of TGN, NLRP3 conformational change, and IL-1β induction. The results revealed a novel mechanism behind the activation and regulation of the NLRP3 inflammasome in IAV infection.     

Mitochondrial protein mitofusin 2 is required for NLRP3 inflammasome activation after RNA virus infection

Nod-like receptor family, pyrin domain-containing 3 (NLRP3), is involved in the early stages of the inflammatory response by sensing cellular damage or distress due to viral or bacterial infection. Activation of NLRP3 triggers its assembly into a multimolecular protein complex, termed “NLRP3 inflammasome.” This event leads to the activation of the downstream molecule caspase-1 that cleaves the precursor forms of proinflammatory cytokines, such as interleukin 1 beta (IL-1β) and IL-18, and initiates the immune response. Recent studies indicate that the reactive oxygen species produced by mitochondrial respiration is critical for the activation of the NLRP3 inflammasome by monosodium urate, alum, and ATP. However, the precise mechanism by which RNA viruses activate the NLRP3 inflammasome is not well understood. Here, we show that loss of mitochondrial membrane potential [ΔΨ(m)] dramatically reduced IL-1β secretion after infection with influenza, measles, or encephalomyocarditis virus (EMCV). Reduced IL-1β secretion was also observed following overexpression of the mitochondrial inner membrane protein, uncoupling protein-2, which induces mitochondrial proton leakage and dissipates ΔΨ(m). ΔΨ(m) was required for association between the NLRP3 and mitofusin 2, a mediator of mitochondrial fusion, after infection with influenza virus or EMCV. Importantly, the knockdown of mitofusin 2 significantly reduced the secretion of IL-1β after infection with influenza virus or EMCV. Our results provide insight into the roles of mitochondria in NLRP3 inflammasome activation.Nod-like receptor family, pyrin domain-containing 3 (NLRP3) can be activated by a wide variety of stimuli, such as endogenous danger signals from damaged cells, bacterial components, environmental irritants, and DNA and RNA viruses (1). It forms a multiprotein complex called the NLRP3 inflammasome, which includes an adaptor protein apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) and procaspase-1. The NLRP3 inflammasome-mediated cytokine release requires two signaling pathways (2). The first signal is induced by Toll-like receptors (TLRs), interleukin 1 receptor (IL-1R), or tumor necrosis factor receptor, and leads to the synthesis of inactive NLRP3, pro–IL-1β, and pro–IL-18 in the cytosol. The second signal is triggered by NLRP3 agonists, which induce the activation of caspase-1. Caspase-1 catalyzes the proteolytic processing of pro–IL-1β and pro–IL-18, and their conversion to mature forms, and stimulates their secretion across the plasma membrane (1). These inflammasome-dependent cytokines play a key role in the induction of adaptive immunity and the initiation of tissue healing after influenza virus infection (3–5). Migration of dendritic cells (DCs) to the draining lymph nodes and priming of CD8 T cells during influenza virus infection require IL-1R signaling in respiratory DCs (6). By contrast, chronic activation of the NLRP3 inflammasome has been linked to many inflammatory diseases (7, 8). Therefore, increasing the number of studies dedicated to the investigation of the molecular mechanisms of NLRP3 inflammasome activation will be crucial for improving our understanding of the pathogenesis of infectious and autoinflammatory diseases.Mitochondria are compartmentalized by two membrane bilayers (outer and inner membranes) and are involved in a wide variety of functions in eukaryotic cells. Within the past decade, novel functions of mitochondria have been discovered demonstrating their crucial role in innate antiviral immunity in vertebrates (9). A direct link between mitochondria and innate immunity was first highlighted with the finding that an adaptor protein, mitochondrial antiviral signaling (MAVS; also known as IPS-1, VISA, or Cardif) (10–13), triggered retinoic acid-inducible gene 1 (RIG-I) and melanoma differentiation-associated protein 5-mediated type I interferon (IFN) induction. In addition to their role in antiviral immunity, mitochondria also function as a platform for the activation of the NLRP3 inflammasome by producing mitochondrial reactive oxygen species (mROS) (14, 15). In this context, NLRP3 agonists trigger the generation of mROS from damaged mitochondria, resulting in the dissociation of thioredoxin (TRX) from TRX-interacting protein, which associates with NLRP3 to facilitate inflammasome formation (16). Furthermore, cytosolic mitochondrial DNA (mtDNA) released from damaged mitochondria has been reported to activate the NLRP3 inflammasome (17) and absent in melanoma 2 inflammasome (15), recently identified as a cytoplasmic DNA sensor for the inflammasome (18–21). Although mitochondria are essential for host-cell defense, the mechanism of their involvement in the activation of the NLRP3 inflammasome is still unclear. In the present study, we demonstrate that the mitofusin 2 (Mfn2) is required for the full activation of the NLRP3 inflammasomes in macrophages.