Sensing damage by the NLRP3 inflammasome

The NLRP3 inflammasome is activated in response to a variety of signals that are indicative of damage to the host including tissue damage, metabolic stress, and infection. Upon activation, the NLRP3 inflammasome serves as a platform for activation of the cysteine protease caspase-1, which leads to the processing and secretion of the proinflammatory cytokines interleukin-1β (IL-1β) and IL-18. Dysregulated NLRP3 inflammasome activation is associated with both heritable and acquired inflammatory diseases. Here, we review new insights into the mechanism of NLRP3 inflammasome activation and its role in disease pathogenesis.     

Inhibition of the NLRP3 inflammasome by HSP90 inhibitors

Excessive and dysregulated inflammation is known to contribute to disease progression. HSP90 is an intracellular chaperone known to regulate inflammatory processes including the NLRP3 inflammasome and secretion of the pro‐inflammatory cytokine interleukin(IL)‐1β. Here, primarily using an in vitro inflammasome ASC speck assay, and an in vivo model of murine peritonitis, we tested the utility of HSP90 inhibitors as anti‐inflammatory molecules. We report that the HSP90 inhibitor EC144 effectively inhibited inflammatory processes including priming and activation of NLRP3 in vitro and in vivo. A specific inhibitor of the β HSP90 isoform was ineffective suggesting the importance of the α isoform in inflammatory signalling. EC144 inhibited IL‐1β and IL‐6 in vivo when administered orally, and was brain‐penetrant. These data suggest that HSP90 inhibitors may be useful for targeting inflammation in diverse diseases that are worsened by the presence of inflammation.     

NLRP3 inflammasome activation downstream of cytoplasmic LPS recognition by both caspase‐4 and caspase‐5

Humans encode two inflammatory caspases that detect cytoplasmic LPS, caspase‐4 and caspase‐5. When activated, these trigger pyroptotic cell death and caspase‐1‐dependent IL‐1β production; however the mechanism underlying this process is not yet confirmed. We now show that a specific NLRP3 inhibitor, MCC950, prevents caspase‐4/5‐dependent IL‐1β production elicited by transfected LPS. Given that both caspase‐4 and caspase‐5 can detect cytoplasmic LPS, it is possible that these proteins exhibit some degree of redundancy. Therefore, we generated human monocytic cell lines in which caspase‐4 and caspase‐5 were genetically deleted either individually or together. We found that the deletion of caspase‐4 suppressed cell death and IL‐1β production following transfection of LPS into the cytoplasm, or in response to infection with Salmonella typhimurium. Although deletion of caspase‐5 did not confer protection against transfected LPS, cell death and IL‐1β production were reduced after infection with Salmonella. Furthermore, double deletion of caspase‐4 and caspase‐5 had a synergistic effect in the context of Salmonella infection. Our results identify the NLRP3 inflammasome as the specific platform for IL‐1β maturation, downstream of cytoplasmic LPS detection by caspase‐4/5. We also show that both caspase‐4 and caspase‐5 are functionally important for appropriate responses to intracellular Gram‐negative bacteria.     

Listeria monocytogenes is sensed by the NLRP3 and AIM2 inflammasome

The inflammasome pathway functions to regulate caspase‐1 activation in response to a broad range of stimuli. Caspase‐1 activation is required for the maturation of the pivotal pro‐inflammatory cytokines of the pro‐IL‐1β family. In addition, caspase‐1 activation leads to a certain type of cell death known as pyroptosis. Activation of the inflammasome has been shown to play a critical role in the recognition and containment of various microbial pathogens, including the intracellularly replicating Listeria monocytogenes; however, the inflammasome pathways activated during L. monocytogenes infection are only poorly defined. Here, we demonstrate that L. monocytogenes activates both the NLRP3 and the AIM2 inflammasome, with a predominant involvement of the AIM2 inflammasome. In addition, L. monocytogenes‐triggered cell death was diminished in the absence of both AIM2 and NLRP3, and is concomitant with increased intracellular replication of L. monocytogenes. Altogether, these data establish a role for DNA sensing through the AIM2 inflammasome in the detection of intracellularly replicating bacteria.     

Caspase‐4 mediates non‐canonical activation of the NLRP3 inflammasome in human myeloid cells

Inflammasome activation culminates in activation of caspase‐1, which leads to the maturation and subsequent release of cytokines of the interleukin 1 (IL‐1) family and results in a particular form of cell death known as pyroptosis. In addition, in the murine system, a so‐called non‐canonical inflammasome involving caspase‐11 has been described that directly responds to cytosolic LPS. Here, we show that the human monocytic cell line THP1 activates the inflammasome in response to cytosolic LPS in a TLR4‐independent fashion. This response is mediated by caspase‐4 and accompanied by caspase‐1 activation, pyroptosis, and IL‐1β maturation. In addition to caspase‐4, efficient IL‐1β conversion upon intracellular LPS delivery relies on potassium efflux, NLRP3, ASC, and caspase‐1, indicating that although caspase‐4 activation alone is sufficient to induce pyroptosis, this process depends on the NLRP3 inflammasome activation to drive IL‐1β maturation. Altogether, this study provides evidence for the presence of a non‐canonical inflammasome in humans and its dependence on caspase‐4.     

Initiation and perpetuation of NLRP3 inflammasome activation and assembly

The NLRP3 (NOD-like receptor family, pyrin domain containing 3) inflammasome is a multiprotein complex that orchestrates innate immune responses to infection and cell stress through activation of caspase-1 and maturation of inflammatory cytokines pro-interleukin-1β (pro-IL-1β) and pro-IL-18. Activation of the inflammasome during infection can be protective, but unregulated NLRP3 inflammasome activation in response to non-pathogenic endogenous or exogenous stimuli can lead to unintended pathology. NLRP3 associates with mitochondria and mitochondrial molecules, and activation of the NLRP3 inflammasome in response to diverse stimuli requires cation flux, mitochondrial Ca²⁺ uptake, and mitochondrial reactive oxygen species accumulation. It remains uncertain whether NLRP3 surveys mitochondrial integrity and senses mitochondrial damage, or whether mitochondria simply serve as a physical platform for inflammasome assembly. The structure of the active, caspase-1-processing NLRP3 inflammasome also requires further clarification, but recent studies describing the prion-like properties of ASC have advanced the understanding of how inflammasome assembly and caspase-1 activation occur while raising new questions regarding the propagation and resolution of NLRP3 inflammasome activation. Here, we review the mechanisms and pathways regulating NLRP3 inflammasome activation, discuss emerging concepts in NLRP3 complex organization, and expose the knowledge gaps hindering a comprehensive understanding of NLRP3 activation.     

AMPK通过抑制NLRP3炎症小体参与延缓衰老过程

<正>衰老是在细胞、组织和器官水平上发生的生理性内稳态的渐进性损害过程。就代谢角度而言,该过程主要表现为体成分、胰岛素抵抗、自噬功能障碍、线粒体和炎症反应的变化,其中涉及生长激素、胰岛素/胰岛素样生长因子1及各种能量感应系统如AMP活化蛋白激酶(AMP-activated protein kinase,AMPK)、沉默信息调节因子(silent information regula‐tors,SIRTs)等多条信号通路的变化^[1]。而从临床角     

NLRP3炎症小体与溃疡性结肠炎的研究进展

溃疡性结肠炎是肠道慢性炎性反应性疾病,遗传易感性、肠道菌群和黏膜免疫功能失调在溃疡性结肠炎的发生发展过程中起重要作用.目前研究显示NLRP3基因与溃疡性结肠炎的易感性相关,NLRP3炎症小体可维持肠道内环境稳定,对实验性结肠炎具有保护作用,其功能缺陷可能导致对溃疡性结肠炎易感.NLRP3炎症小体有可能成为溃疡性结肠炎治疗的新靶点.     

Priming of NLRP3 inflammasome activation by Msn kinase MINK1 in macrophages

The nucleotide-binding domain, leucine-rich-repeat containing family, pyrin domain-containing 3 (NLRP3) inflammasome is essential in inflammation and inflammatory disorders. Phosphorylation at various sites on NLRP3 differentially regulates inflammasome activation. The Ser725 phosphorylation site on NLRP3 is depicted in multiple inflammasome activation scenarios, but the importance and regulation of this site has not been clarified. The present study revealed that the phosphorylation of Ser725 was an essential step for the priming of the NLRP3 inflammasome in macrophages. We also showed that Ser725 was directly phosphorylated by misshapen (Msn)/NIK-related kinase 1 (MINK1), depending on the direct interaction between MINK1 and the NLRP3 LRR domain. MINK1 deficiency reduced NLRP3 activation and suppressed inflammatory responses in mouse models of acute sepsis and peritonitis. Reactive oxygen species (ROS) upregulated the kinase activity of MINK1 and subsequently promoted inflammasome priming via NLRP3 Ser725 phosphorylation. Eliminating ROS suppressed NLRP3 activation and reduced sepsis and peritonitis symptoms in a MINK1-dependent manner. Altogether, our study reveals a direct regulation of the NLRP3 inflammasome by Msn family kinase MINK1 and suggests that modulation of MINK1 activity is a potential intervention strategy for inflammasome-related diseases.     

Negative regulation of NLRP3 inflammasome by SIRT1 in vascular endothelial cells

NLRP3 inflammasome not only functions as a critical effector in innate immunity, but also triggers the production of proinflammatory cytokines involved in inflammation-associated diseases. Sirtuin 1 (SIRT1) plays an important role in the regulation of cellular inflammation. However, whether the activation of NLRP3 inflammasome is regulated by SIRT1 remains unknown. In this study, we investigated the regulatory effect of SIRT1 on NLRP3 inflammasome and the underlying mechanisms. We found that lipopolysaccharide (LPS) and adenosine triphosphate (ATP)-induced the activation of NLRP3 inflammasome in human umbilical vein endothelial cells (HUVECs). Activation of SIRT1 inhibited NLRP3 inflammasome activation and subsequent caspase-1 cleavage as well as interleukin (IL)-1β secretion, whereas SIRT1 knockdown obviously enhanced the activation of NLRP3 inflammasome in HUVECs. Importantly, gene silencing of SIRT1 abrogated the inhibitory effect of SIRT1 activator on NLRP3 inflammasome formation and IL-1β production in HUVECs stimulated with LPS plus ATP. Further study indicated that cluster of differentiation 40 (CD40) may be involved in the regulation of NLRP3 inflammasome by SIRT1. In vivo studies indicated that implantation of the periarterial carotid collar increased the arterial expression levels of CD40 and CD40 Ligand (CD40L), but inhibited arterial SIRT1 expression in the rabbits. Moreover, treatment with SIRT1 activator decreased CD40 and CD40L levels in collared arteries. Meanwhile, serum IL-1β level, the marker of inflammasome activation, was also inhibited by SIRT1 activation. Taken together, these findings revealed a novel regulatory mechanism of NLRP3 inflammasome by SIRT1, which may be related to suppression of CD40.     

Molecular mechanisms regulating NLRP3 inflammasome activation

Inflammasomes are multi-protein signaling complexes that trigger the activation of inflammatory caspases and the maturation of interleukin-1β. Among various inflammasome complexes, the NLRP3 inflammasome is best characterized and has been linked with various human autoinflammatory and autoimmune diseases. Thus, the NLRP3 inflammasome may be a promising target for anti-inflammatory therapies. In this review, we summarize the current understanding of the mechanisms by which the NLRP3 inflammasome is activated in the cytosol. We also describe the binding partners of NLRP3 inflammasome complexes activating or inhibiting the inflammasome assembly. Our knowledge of the mechanisms regulating NLRP3 inflammasome signaling and how these influence inflammatory responses offers further insight into potential therapeutic strategies to treat inflammatory diseases associated with dysregulation of the NLRP3 inflammasome.     

Acupuncture inhibits NLRP3 inflammasome activation in the prefrontal cortex of a chronic stress rat model of depression

The Nod-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome-driven inflammatory response plays a key role in the pathophysiology of depression. Mounting evidence suggests that acupuncture is an effective treatment for depression. In this study, we investigated the effects of acupuncture treatment at the acupoints Baihui (GV20) and Yintang (GV29) on NLRP3 inflammasome in the prefrontal cortex (PFC) of an animal model of depression. Rats that underwent chronic unpredictable mild stress (CUMS) for 6 weeks showed depressive-like behaviors, which were confirmed by sucrose preference and locomotor activity in the open field test. The protein levels of NLRP3, apoptotic speck-containing protein with a card (ASC), and cysteinyl aspartate specific proteinase-1 (Caspase-1) in the PFC were detected by Western blot analysis. The mRNA and protein expressions of interleukin-1β (IL-1β) and interleukin-18 (IL-18) in the PFC were measured by the real-time polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. Our results showed that the depressive-like behaviors in stressed rats were reversed by acupuncture treatment. Compared with control rats, the protein expression of NLRP3, ASC, and Caspase-1 and the mRNA and protein expressions of IL-1β and IL-18 in the PFC were markedly increased in CUMS rats. Acupuncture treatment significantly decreased the levels of NLRP3 inflammasome components and inflammatory cytokines in the PFC. Acupuncture treatment also reduced the number of TUNEL-positive cells in the PFC. These results suggested that acupuncture has antidepressant-like effects, and its mechanism appears to be involved in the inhibition of NLRP3 inflammasome activation and apoptosis in the PFC.     

NLRP3炎症小体激活的调控机制研究进展

NLRP3炎症小体是固有免疫系统的重要组成部分,在抵抗病原体感染及危险信号刺激过程中发挥关键作用。同时,NLRP3炎症小体的异常激活也与糖尿病、阿尔茨海默病、红斑狼疮等疾病密切相关。因此,调控和干预炎症小体激活过程对维持机体免疫稳态和发挥免疫功能有重要作用。本文从NLRP3的翻译后修饰、互作分子、细胞器和细胞定位改变以及与NLRP3功能相关的代谢过程和代谢物等多个方面综述了NLRP3炎症小体激活的调控机制研究进展,以期为理解炎症小体激活和炎症反应的发生,以及治疗炎症相关疾病提供新的借鉴。     

NLRP3 inflammasome activation and cell death

The NLRP3 inflammasome is a cytosolic multiprotein complex composed of the innate immune receptor protein NLRP3, adapter protein ASC, and inflammatory protease caspase-1 that responds to microbial infection, endogenous danger signals, and environmental stimuli. The assembled NLRP3 inflammasome can activate the protease caspase‐1 to induce gasdermin D-dependent pyroptosis and facilitate the release of IL-1β and IL-18, which contribute to innate immune defense and homeostatic maintenance. However, aberrant activation of the NLRP3 inflammasome is associated with the pathogenesis of various inflammatory diseases, such as diabetes, cancer, and Alzheimer’s disease. Recent studies have revealed that NLRP3 inflammasome activation contributes to not only pyroptosis but also other types of cell death, including apoptosis, necroptosis, and ferroptosis. In addition, various effectors of cell death have been reported to regulate NLRP3 inflammasome activation, suggesting that cell death is closely related to NLRP3 inflammasome activation. In this review, we summarize the inextricable link between NLRP3 inflammasome activation and cell death and discuss potential therapeutics that target cell death effectors in NLRP3 inflammasome-associated diseases.     

The NLRP3 inflammasome: a therapeutic target for inflammation-associated cancers

ABSTRACT

Introduction: Inflammasomes are large multimeric intracellular complexes that are capable of maturation and secretion of pro-inflammatory cytokines, IL-1β and IL-18, in response to danger signal molecules. As a member of the inflammasome family, the NLRP3 inflammasome has recently been under intense investigation revealing its possible role in several human diseases especially cancers.

Areas covered: In this review, we will discuss the biology and mechanism of NLRP3 inflammasome activation, its role in specific types of tumors and the novel therapeutic modalities targeting this complex.

Expert opinion: The NLRP3 inflammasome and its components including the adapter apoptosis-associated speck-like (ASC) protein and caspase-1 impose different and sometimes contrasting effects in tumorigenesis depending on various contexts. Considering the novel role of this complex in the initiation and progression of neoplasia, the NLRP3 inflammasome and its pathways provide desirable therapeutic targets for prevention, treatment, and prognosis of certain types of cancer. To date, several agents have been introduced for this purpose, some of which have shown promising results in the clinic.     

NLRP3炎症小体活化促进上皮细胞焦亡诱导变应性鼻炎

目的 研究NLRP3炎症小体激活在变异性鼻炎的发生发展中的作用,并试图探讨其潜在的机制.方法 利用野生型(wide-type,WT)和NLRP3基因敲除(knock out,KO)小鼠构建卵清蛋白(ovalbumin,OVA)诱导的变异性鼻炎模型.按照体质量将小鼠随机分为4组:WT、WT-OVA、NLRP3 KO、NL...     

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

While interleukin (IL)-1β plays an important role in combating the invading pathogen as part of the innate immune response, its dysregulation is responsible for a number of autoinflammatory disorders. Large IL-1β activating platforms, known as inflammasomes, can assemble in response to the detection of endogenous host and pathogen-associated danger molecules. Formation of these protein complexes results in the autocatalysis and activation of caspase-1, which processes precursor IL-1β into its secreted biologically active form. Inflammasome and IL-1β activity is required to efficiently control viral, bacterial and fungal pathogen infections. Conversely, excess IL-1β activity contributes to human disease, and its inhibition has proved therapeutically beneficial in the treatment of a spectrum of serious, yet relatively rare, heritable inflammasomopathies. Recently, inflammasome function has been implicated in more common human conditions, such as gout, type II diabetes and cancer. This raises the possibility that anti-IL-1 therapeutics may have broader applications than anticipated previously, and may be utilized across diverse disease states that are linked insidiously through unwanted or heightened inflammasome activity.