ATP binding by NLRP7 is required for inflammasome activation in response to bacterial lipopeptides

Nucleotide-binding oligimerization domain (NOD)-like receptors (NLRs) are pattern recognition receptors (PRRs) involved in innate immune responses. NLRs encode a central nucleotide-binding domain (NBD) consisting of the NAIP, CIITA, HET-E and TP1 (NACHT) domain and the NACHT associated domain (NAD), which facilitates receptor oligomerization and downstream inflammasome signaling. The NBD contains highly conserved regions, known as Walker motifs, that are required for nucleotide binding and hydrolysis. The NLR containing a PYRIN domain (PYD) 7 (NLRP7) has been recently shown to assemble an ASC and caspase-1-containing high molecular weight inflammasome complex in response to microbial acylated lipopeptides and Staphylococcus aureus infection. However, the molecular mechanism responsible for NLRP7 inflammasome activation is still elusive. Here we demonstrate that the NBD of NLRP7 is an ATP binding domain and has ATPase activity. We further show that an intact nucleotide-binding Walker A motif is required for NBD-mediated nucleotide binding and hydrolysis, oligomerization, and NLRP7 inflammasome formation and activity. Accordingly, THP-1 cells expressing a mutated Walker A motif display defective NLRP7 inflammasome activation, interleukin (IL)-1β release and pyroptosis in response to acylated lipopeptides and S. aureus infection. Taken together, our results provide novel insights into the mechanism of NLRP7 inflammasome assembly.     

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.     

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.     

NLRP3 inflammasome is essential for the development of chronic obstructive pulmonary disease

Background: Chronic obstructive pulmonary disease (COPD) is now recognized as an inflammatory disease and the nucleotide-binding oligomerization domain-like receptor 3 (NLRP3) inflammasome was speculated to participate into its pathophysiological process, however, a direct role of NLRP3 has yet to be clearly shown. Method: COPD model was established by tobacco inhalation, COPD modeling and NLRP3 knockout mice were treated with similar dose and duration of tobacco inhalation for 12 months, the lung function, lung damage and immune responses were evaluated between control, wild type COPD and NLRP3 knock out C57B1/6 mice. Results: 10 months after tobacco inhalation, the respiratory system resistance indexes of COPD mice was significantly higher than that of control and NLRP3 knockout mice (2.8 ± 0.5 vs. 1.2 ± 0.3 and 1.3 ± 0.1 cm H₂O ml^-1 s^-1, P < 0.05); the respiratory system compliance indexes of COPD was significantly lower than that of control and NLRP3 knockout mice (0.31 ± 0.02 vs. 0.43 ± 0.04, and 0.39 ± 0.01 ml/cm H₂O); the NLRP3 knockout mice displayed no distinguishable pathological damage in the lung. Of the broncho-alveolar lavage fluid (BALF), the concentration of IL-1 and IL-18 of the COPD were significantly higher than that of control and NLRP3 knockout mice (IL-1: 286.8 ± 1.7 vs. 23.8 ± 2.1 and 24.2 ± 1.3 pg/mL, P < 0.05; IL-18: 104.5 ± 4.2 vs. 12.6 ± 2.1 and 15.7 ± 2.8 pg/mL, P < 0.05); the total numbers of macrophages, eosinophils, lymphocyte and neutrophil of control, COPD and NLRP3 knockout mice were 2.3 ± 0.4, 0.5 ± 0.2, 10.3 ± 3.4 and 2.8 ± 2.7; 8.7 ± 1.1, 12.5 ± 1.1, 45.3 ± 3.3 and 29.2 ± 4.2; and 3.2 ± 0.7, 1.8 ± 0.4, 18.1 ± 1.1 and 12.8 ± 3.4 × 10⁴ mL, respectively; the rates of NLRP3 positive macrophages in the BALF of control, COPD and NLRP3 knockout mice were 5.0 ± 1.0%, 78.1 ± 9.2% and 2.0 ± 0.9%, respectively. Conclusion: NLRP3 inflammasome is essential for the development of COPD and blockade of NLRP3 might be a possible therapeutic strategy for COPD.     

Pannexin-1 promotes NLRP3 activation during apoptosis but is dispensable for canonical or noncanonical inflammasome activation

Inflammasomes are multimeric protein complex that assemble in the cytosol upon microbial infection or cellular stress. Upon activation, inflammasomes drive the maturation of proinflammatory cytokines, IL-1β and IL-18, and also activate the pore-forming protein, gasdermin D to initiate a form of lytic cell death known as “pyroptosis”. Pannexin-1 is channel-forming glycoprotein that promotes membrane permeability and ATP release during apoptosis; and was implicated in canonical NLRP3 or noncanonical inflammasome activation. Here, by utilizing three different pannexin-1 channel inhibitors and two lines of Panx1^–/– macrophages, we provide genetic and pharmacological evidence that pannexin-1 is dispensable for canonical or noncanonical inflammasome activation. In contrast, we demonstrate that pannexin-1 cleavage and resulting channel activity during apoptosis promotes NLRP3 inflammasome activation.     

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...     

NLRP3 inflammasome is required for apoptosis of Aggregatibacter actinomycetemcomitans-infected human osteoblastic MG63 cells

Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) is a Gram-negative bacterium which is implicated in the pathogenesis of human periodontal disease and in particular aggressive periodontitis. Virulence factors from A. actinomycetemcomitans have been shown to induce apoptosis of osteoblasts, however, the underlying mechanisms of the induction of apoptosis are poorly understood. In the present study, the infection of A. actinomycetemcomitans in human osteoblastic MG63 cells was established. Accordingly, A. actinomycetemcomitans infection enhanced significant apoptosis of MG63 cells. We found that both expression levels of NLRP3 and ASC were increased dramatically after MG63 cell cultures exposed to A. actinomycetemcomitans. Moreover, the secretion of mature interleukin-1β (IL-1β) and IL-18 were extensively induced in A. actinomycetemcomitans-infected cells as compared with non-invasion group of MG63 cell cultures, indicating the activation of the NLRP3 inflammasome during infection. Finally, we found that the knockdown expression of NLRP3 by specific small interfering RNA (siRNA) attenuated apoptosis of A. actinomycetemcomitans-infected MG63 cells. Our data suggest that A. actinomycetemcomitans promotes apoptosis of human osteoblasts at least partially through the NLRP3 inflammasome.     

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.     

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。     

The NLRP3 inflammasome in fibrosis and aging: The known unknowns

Aging-related diseases such as cancer, cardiovascular diseases, diabetes, and neurodegenerative diseases are often accompanied by fibrosis. The NLRP3 inflammasome triggers the inflammatory response and subsequently promotes fibrosis through pathogen-associated molecular patterns (PAMPs). In this review, we first introduce the general background and specific mechanism of NLRP3 in fibrosis. Second, we investigate the role of NLRP3 in fibrosis in different organs/tissues. Third, we discuss the relationship between NLRP3 and fibrosis during aging. In summary, this review describes the latest progress on the roles of NLRP3 in fibrosis and aging and reveals the possibility of NLRP3 as an antifibrotic and anti-aging treatment target.     

Fatty acid-induced NLRP3-ASC inflammasome activation interferes with insulin signaling

High-fat diet (HFD) and inflammation are key contributors to insulin resistance and type 2 diabetes (T2D). Interleukin (IL)-1β plays a role in insulin resistance, yet how IL-1β is induced by the fatty acids in an HFD, and how this alters insulin signaling, is unclear. We show that the saturated fatty acid palmitate, but not unsaturated oleate, induces the activation of the NLRP3-ASC inflammasome, causing caspase-1, IL-1β and IL-18 production. This pathway involves mitochondrial reactive oxygen species and the AMP-activated protein kinase and unc-51-like kinase-1 (ULK1) autophagy signaling cascade. Inflammasome activation in hematopoietic cells impairs insulin signaling in several target tissues to reduce glucose tolerance and insulin sensitivity. Furthermore, IL-1β affects insulin sensitivity through tumor necrosis factor-independent and dependent pathways. These findings provide insights into the association of inflammation, diet and T2D.     

microRNA-520c-3p suppresses NLRP3 inflammasome activation and inflammatory cascade in preeclampsia by downregulating NLRP3

Inflammation Research - The pathogenesis of preeclampsia (PE) is suggested to be a consequence of inflammation. Previously conducted investigations on nod-like receptor pyrin domain-containing 3...     

Mechanisms of NLRP3 inflammasome activation and its role in NSAID-induced enteropathy

Nonsteroidal anti-inflammatory drugs (NSAIDs) induce cytokines, including tumor necrosis factor-α and interleukins (ILs), in the small intestine via a Toll-like receptor 4 (TLR4)-dependent pathway, leading to intestinal ulceration. Activation of the inflammasome promotes pro-caspase-1 cleavage, leading to pro-IL-1β maturation. We examined the role of NLRP3 inflammasome in NSAID-induced enteropathy. Small intestinal damage developed 3 h after indomethacin administration, accompanied by increases in IL-1β and NLRP3 mRNA expression and mature caspase-1 and IL-1β levels. In vivo blocking of IL-1β using neutralizing antibodies attenuated indomethacin-induced damage, whereas exogenous IL-1β aggravated it. NLRP3^−/− and caspase-1^−/− mice exhibited resistance to the damage with reduction of mature IL-1β production. This resistance was abolished by exogenous IL-1β. TLR4 deficiency prevented intestinal damage and inhibited upregulation of NLRP3 and IL-1β mRNAs and maturation of pro-caspase-1 and pro-IL-1β, whereas TLR4 activation by its agonists exerted opposite effects. Apyrase, an adenosine triphosphate (ATP) scavenger, or Brilliant Blue G, a purinergic P2X₇ receptor antagonist, inhibited the damage as well as caspase-1 activation and IL-1β processing, despite there being sufficient amounts of pro-IL-1β and NLRP3. These results suggest that NLRP3 inflammasome-derived IL-1β plays a crucial role in NSAID-induced enteropathy and that both TLR4- and P2X₇-dependent pathways are required for NLRP3 inflammasome activation.     

Posttranslational modifications of NLRP3 and their regulatory roles in inflammasome activation

The NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome is a multimolecular complex that plays a fundamental role in inflammation. Optimal activation of NLRP3 inflammasome is crucial for host defense against pathogens and the maintenance of immune homeostasis. Aberrant NLRP3 inflammasome activity has been implicated in various inflammatory diseases. Posttranslational modifications (PTMs) of NLRP3, a key inflammasome sensor, play critical roles in directing inflammasome activation and controlling the severity of inflammation and inflammatory diseases, such as arthritis, peritonitis, inflammatory bowel disease, atherosclerosis, and Parkinson's disease. Various NLRP3 PTMs, including phosphorylation, ubiquitination, and SUMOylation, could direct inflammasome activation and control inflammation severity by affecting the protein stability, ATPase activity, subcellular localization, and oligomerization of NLRP3 as well as the association between NLRP3 and other inflammasome components. Here, we provide an overview of the PTMs of NLRP3 and their roles in controlling inflammation and summarize potential anti-inflammatory drugs targeting NLRP3 PTMs.     

NLRP3炎性小体在动脉粥样硬化发生发展中的作用

NLRP3炎性小体是一种包含胞内受体(主要是NOD样受体)、半胱天冬氨酸前体和凋亡相关斑点样蛋白的蛋白质复合体.该复合体最初只是被描述为一种影响感染和炎症过程的复合体,它的活化引起半胱天冬氨酶-1的激活并剪切加工底物白细胞介素-1β(interleukin-1β,IL-1β)和白细胞介素-18(interleukin-18,IL-18),从而引起炎症反应;此外,炎性小体的激活过程对有氧糖酵解(瓦伯格效应,Warburg effect)有着重要的影响,这同样可以促进炎症的发生.随后的证据表明炎性小体的活化还影响很多代谢紊乱包括动脉粥样硬化(atherosclerosis, AS)、2型糖尿病、痛风和肥胖等.本综述将探讨AS与炎症、NLRP3炎性小体活化的关联性,以及瓦伯格效应如何关联炎症反应及炎性小体的激活.