NLRP3 Sensing of Diverse Inflammatory Stimuli Requires Distinct Structural Features

FUBP3 mediates the amyloid-β-induced neuronal NLRP3 expression

JOURNAL/nrgr/04.03/01300535-202507000-00028/figure1/v/2024-09-09T124005Z/r/image-tiff Alzheimer's disease is characterized by deposition of amyloid-β, which forms extracellular neuritic plaques, and accumulation of hyperphosphorylated tau, which aggregates to form intraneuronal neurofibrillary tangles, in the brain. The NLRP3 inflammasome may play a role in the transition from amyloid-β deposition to tau phosphorylation and aggregation. Because NLRP3 is primarily found in brain microglia, and tau is predominantly located in neurons, it has been suggested that NLRP3 expressed by microglia indirectly triggers tau phosphorylation by upregulating the expression of pro-inflammatory cytokines. Here, we found that neurons also express NLRP3 in vitro and in vivo, and that neuronal NLRP3 regulates tau phosphorylation. Using biochemical methods, we mapped the minimal NLRP3 promoter and identified FUBP3 as a transcription factor regulating NLRP3 expression in neurons. In primary neurons and the neuroblastoma cell line Neuro2A, FUBP3 is required for endogenous NLRP3 expression and tau phosphorylation only when amyloid-β is present. In the brains of aged wild-type mice and a mouse model of Alzheimer's disease, FUBP3 expression was markedly increased in cortical neurons. Transcriptome analysis suggested that FUBP3 plays a role in neuron-mediated immune responses. We also found that FUBP3 trimmed the 5' end of DNA fragments that it bound, implying that FUBP3 functions in stress-induced responses. These findings suggest that neuronal NLRP3 may be more directly involved in the amyloid-β-to-phospho-tau transition than microglial NLRP3, and that amyloid-β fundamentally alters the regulatory mechanism of NLRP3 expression in neurons. Given that FUBP3 was only expressed at low levels in young wild-type mice and was strongly upregulated in the brains of aged mice and Alzheimer's disease mice, FUBP3 could be a safe therapeutic target for preventing Alzheimer's disease progression.

The Emerging Role of Colchicine to Inhibit NOD-like Receptor Family, Pyrin Domain Containing 3 Inflammasome and Interleukin-1β Expression in In Vitro Models

While the beneficial effects of colchicine on inflammation and infarcted myocardium have been documented, its impact on cardiac fibroblast activation in the context of myocardial infarction (MI) remains unknown. This study aimed to investigate the effect of colchicine on the regulation of NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome activation and Interleukin-1β (IL-1β) expression in fibroblasts. 3T3 fibroblasts were exposed to 600 μM CoCl2 for 24 h to simulate hypoxia, with normoxic cells as controls. Colchicine (1 μM) was administered for 24 h. ASC-NLRP3 colocalization and IL-1β expression were evaluated using immunofluorescence and flow cytometry, respectively. Data were analyzed using t-tests and one-way ANOVA with post hoc tests. Hypoxia treatment significantly induced apoptosis-associated speck-like protein containing a CARD (ASC)-NLRP3 colocalization (p < 0.05). Colchicine treatment of hypoxic 3T3 cells reduced ASC-NLRP3 colocalization, although this reduction was not statistically significant. Additionally, IL-1β expression was significantly inhibited in colchicine-treated hypoxic 3T3 cells compared to those treated with placebo (p < 0.05). The findings of this study indicate that colchicine treatment inhibits the activation of the NLRP3 inflammasome by disrupting the colocalization of ASC and NLRP3, thereby reducing IL-1β expression in CoCl2-treated 3T3 cells.

Dendritic cells activate pyroptosis and effector-triggered apoptosis to restrict Legionella infection

The innate immune system relies on pattern recognition receptors (PRRs) to detect pathogen-associated molecular patterns (PAMPs) and guard proteins to monitor pathogen disruption of host cell processes. How different immune cell types engage PRR- and guard protein-dependent defenses in response to infection is poorly understood. Here, we show that macrophages and dendritic cells (DCs) respond in distinct ways to bacterial virulence activities. In macrophages, the bacterial pathogen Legionella pneumophila deploys its Dot/Icm type IV secretion system (T4SS) to deliver effector proteins that facilitate its robust intracellular replication. In contrast, T4SS activity triggers rapid DC death that potently restricts Legionella replication within this cell type. Intriguingly, we found that infected DCs exhibit considerable heterogeneity at the single cell level. Initially, a subset of DCs activate caspase-11 and NLRP3 inflammasome-dependent pyroptosis and release IL-1 β early during infection. At later timepoints, a separate DC population undergoes apoptosis driven by T4SS effectors that block host protein synthesis, thereby depleting the levels of the pro-survival proteins Mcl-1 and cFLIP. Together, pyroptosis and effector-triggered apoptosis robustly restrict Legionella replication in DCs. Collectively, our work suggests a model where Mcl-1 and cFLIP guard host translation in DCs, and that macrophages and DCs distinctly employ innate immune sensors and guard proteins to mount divergent responses to Legionella infection.

Active ingredients of traditional Chinese medicine inhibit NOD-like receptor protein 3 inflammasome: a novel strategy for preventing and treating heart failure

Heart failure (HF) has emerged as a significant global public health challenge owing to its high rates of morbidity and mortality. Activation of the NOD-like receptor protein 3 (NLRP3) inflammasome is regarded as a pivotal factor in the onset and progression of HF. Therefore, inhibiting the activation of the NLRP3 inflammasome may represent a promising therapeutic approach for preventing and treating HF. The active ingredients serve as the foundation for the therapeutic effects of traditional Chinese medicine (TCM). Recent research has revealed significant advantages of TCM active ingredients in inhibiting the activation of the NLRP3 inflammasome and enhancing cardiac structure and function in HF. The study aimed to explore the impact of NLRP3 inflammasome activation on the onset and progression of HF, and to review the current advancements in utilizing TCM active ingredients to inhibit the NLRP3 inflammasome for preventing and treating HF. This provides a novel perspective for the future development of precise intervention strategies targeting the NLRP3 inflammasome to prevent and treat HF.

Pharmacologic Targeting of PDIA1 Inhibits NLRP3 Inflammasome Assembly and Activation

The NLRP3 inflammasome is a cytosolic protein complex that regulates innate immune signaling in response to diverse pathogenic insults through the proteolytic processing and secretion of pro-inflammatory cytokines such as IL-1β. Hyperactivation of NLRP3 inflammasome signaling is implicated in the onset and pathogenesis of numerous diseases, motivating the discovery of new strategies to suppress NLRP3 inflammasome activity. We sought to define the potential for the proteostasis regulator AA147 to inhibit the assembly and activation of the NLRP3 inflammasome. AA147 is a pro-drug that is metabolically converted to a reactive metabolite at the endoplasmic reticulum (ER) membrane to covalently modify ER-localized proteins such as protein disulfide isomerases (PDIs). We show that AA147 inhibits NLRP3 inflammasome activity in monocytes and monocyte-derived macrophages through a mechanism involving impaired assembly of the active inflammasome complex. This inhibition is mediated through AA147-dependent covalent modification of PDIA1. Genetic depletion or treatment with other highly selective PDIA1 inhibitors similarly blocks NLRP3 inflammasome assembly and activation. Our results identify PDIA1 as a potential therapeutic target to mitigate NLRP3 inflammasome-mediated pro-inflammatory signaling implicated in etiologically diverse diseases.

Regulation of NLRPs by reactive oxygen species: A story of crosstalk

The nucleotide oligomerization domain (NOD)-like receptors containing pyrin (NLRP) family of cytosolic pattern-recognition receptors play an integral role in host defense following exposure to a diverse set of pathogenic and sterile threats. The canonical event following ligand recognition is the formation of a heterooligomeric signaling complex termed the inflammasome that produces pro-inflammatory cytokines. Dysregulation of this process is associated with many autoimmune, cardiovascular, metabolic, and neurodegenerative diseases. Despite the range of activating stimuli which affect varied cell types, recent literature makes evident that reactive oxygen species (ROS) are integral to the initiation and propagation of inflammasome signaling. Notably, ROS production and inflammasome activation act in a positive feedback loop to promote this potent immune response. While NLRP3 is by far the most extensively studied NLRP, there is also sufficient literature to make these conclusions for other NLRPs family members. In all cases, a knowledge gap exists regarding the molecular targets and effects of ROS. Future research to define these targets and to parse the order and timing of ROS-mediated NLRP activation will provide meaningful insights into inflammasome biology. This will create novel therapeutic opportunities for the numerous illnesses that are impacted by inflammasome activity.

Implication of the LRR Domain in the Regulation and Activation of the NLRP3 Inflammasome

The NLRP3 inflammasome is a critical component of the innate immune response. NLRP3 activation is a tightly controlled process involving an initial priming to express NLRP3, pro-IL-1 β, and pro-IL-18, followed by an activation signal. The precise mechanism of activation is not fully understood due to the diverse range of activators, yet it effectively orchestrates the activation of caspase-1, which subsequently triggers the release of proinflammatory cytokines IL-1β and IL-18. NLRP3 dysregulation can lead to a variety of inflammatory diseases, highlighting its significant role in immune response and disease pathogenesis. NLRP3 is divided into three domains: the PYD, the NACHT, and the LRR domains. This review focuses on the LRR domain of NLRP3, detailing its structural characteristics, its function in pathogen sensing, its role in the degradation process, and its involvement in inflammasome auto-inhibition and activation. Additionally, we discuss the impact of mutations within the LRR domain found in atypical Cryopyrin-Associated Periodic Syndromes (CAPS), highlighting the clinical relevance of this domain.

Analysis of prognostic biomarker models of TXNIP/NLRP3/IL1B inflammasome pathway in patients with acute myeloid leukemia

Background: Exploring potential biomarkers for predicting clinical outcomes and developing targeted therapies for acute myeloid leukemia (AML) is of utmost importance. This study aimed to investigate the expression pattern of the thioredoxin-interacting protein (TXNIP)/nucleotide-binding oligomerization domain (NOD)-like receptor protein 3 (NLRP3) pathway and its role in the prognosis of AML patients. Methods: In this study, we examined the prognostic value of TXNIP/NLRP3 pathway in AML patients using microarray data from Gene Expression Omnibus (GEO) and transcriptome data from the Cancer Genome Atlas (TCGA) to develop a prognostic model and validated the results by quantitative real-time PCR (qRT-PCR) in a validation cohort of 26 AML patients and 18 healthy individuals from Jinan University (JNU) database. Results: Analysis of the GSE13159 database revealed that TXNIP, interleukin 1 beta (IL1B) within the TXNIP/NLRP3 pathway were significantly upregulated and caspase1 (CASP1) was downregulated in AML patients (TXNIP, P = 0.031; IL1B, P = 0.042; CASP1, P = 0.038). Compared to high NLRP3 expression, AML patients with low NLRP3 expression had a longer overall survival (OS) in the GSE12417 dataset (P = 0.004). Moreover, both the training and validation results indicated that lower TXNIP, NLRP3, and IL1B expression were associated with favorable prognosis (GSE12417, P = 0.009; TCGA, P = 0.050; JNU, P = 0.026). According to the receiver operating characteristic curve analysis, this model demonstrated a sensitivity of 84% for predicting three-year survival. These data might provide novel predictors for AML outcome and direction for further investigation of the possibility of using TXNIP/NLRP3/IL1B genes in novel targeted therapies for AML.

Crosstalk between autophagy and inflammasomes in ricin-induced inflammatory injury

Ricin (ricin toxin, RT) has the potential to cause damage to multiple organs and systems. Currently, there are no existing antidotes, vaccinations, or effective therapies to prevent or treat RT intoxication. Apart from halting protein synthesis, RT also induces oxidative stress, inflammation and autophagy. To explore the mechanisms of RT-induced inflammatory injury and specific targets of prevention and treatment for RT poisoning, we characterized the role of cross-talk between autophagy and NLRP3 inflammasome in RT-induced damage and elucidated the underlying mechanisms. We showed that RT-induced inflammation was attributed to activation of the TLR4/MyD88/NLRP3 signaling and ROS production, evidenced by increased ASC speck formation and attenuated TXNIP/TRX-1 interaction, as well as pre-treatment with MCC950, MyD88 knockdown and NAC significantly reduced IL-1β, IL-6 and TNF-α mRNA expression. In addition, autophagy is also enhanced in RT-triggered MLE-12 cells. RT elevated the levels of ATG5, p62 and Beclin1 protein, provoked the accumulation of LC3 puncta detected by immunofluorescence staining. Treatment with rapamycin (Rapa) reversed the RT-caused TLR4/MyD88/NLRP3 signaling activation, ASC specks formation as well as the levels of IL-1β, IL-6 and TNF-α mRNA. In conclusion, RT promoted NLRP3 inflammasome activation and autophgay. Inflammation induced by RT was attenuated by autophagy activation, which suppressed the NLRP3 inflammasome. These findings suggest Rapa as a potential therapeutic drug for the treatment of RT-induced inflammation-related diseases.

The role of inflammasomes in human diseases and their potential as therapeutic targets

Inflammasomes are large protein complexes that play a major role in sensing inflammatory signals and triggering the innate immune response. Each inflammasome complex has three major components: an upstream sensor molecule that is connected to a downstream effector protein such as caspase-1 through the adapter protein ASC. Inflammasome formation typically occurs in response to infectious agents or cellular damage. The active inflammasome then triggers caspase-1 activation, followed by the secretion of pro-inflammatory cytokines and pyroptotic cell death. Aberrant inflammasome activation and activity contribute to the development of diabetes, cancer, and several cardiovascular and neurodegenerative disorders. As a result, recent research has increasingly focused on investigating the mechanisms that regulate inflammasome assembly and activation, as well as the potential of targeting inflammasomes to treat various diseases. Multiple clinical trials are currently underway to evaluate the therapeutic potential of several distinct inflammasome-targeting therapies. Therefore, understanding how different inflammasomes contribute to disease pathology may have significant implications for developing novel therapeutic strategies. In this article, we provide a summary of the biological and pathological roles of inflammasomes in health and disease. We also highlight key evidence that suggests targeting inflammasomes could be a novel strategy for developing new disease-modifying therapies that may be effective in several conditions.

What are NLRP3-ASC specks? an experimental progress of 22 years of inflammasome research

Speck assembly is the hallmark of NLRP3 inflammasome activation. The 1µm structure comprising of NLRP3 and ASC is the first observable phenotype of NLRP3 activation. While the common consensus is that the specks are the site of inflammasome activity, no direct experimental evidence exists to support this notion. In these 22 years, since the inflammasome discovery, several research studies have been published which directly or indirectly support or refute the idea of speck being the inflammasome. This review compiles the data from two decades of research to answer a long-standing question: "What are NLRP3-ASC specks?"

The NLRP3 inflammasome: activation and regulation

The NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome is a cytoplasmic supramolecular complex that is activated in response to cellular perturbations triggered by infection and sterile injury. Assembly of the NLRP3 inflammasome leads to activation of caspase-1, which induces the maturation and release of interleukin-1β (IL-1β) and IL-18, as well as cleavage of gasdermin D (GSDMD), which promotes a lytic form of cell death. Production of IL-1β via NLRP3 can contribute to the pathogenesis of inflammatory disease, whereas aberrant IL-1β secretion through inherited NLRP3 mutations causes autoinflammatory disorders. In this review, we discuss recent developments in the structure of the NLRP3 inflammasome, and the cellular processes and signaling events controlling its assembly and activation.

Chalcone: A potential scaffold for NLRP3 inflammasome inhibitors

Overactivated NLRP3 inflammasome has been shown to associate with an increasing number of disease conditions. Activation of the NLRP3 inflammasome results in caspase-1-catalyzed formation of active pro-inflammatory cytokines (IL-1β and IL-18) resulting in pyroptosis. The multi-protein composition of the NLRP3 inflammasome and its sensitivity to several damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs) make this extensively studied inflammasome an attractive target to treat chronic conditions. However, none of the known NLRP3 inhibitors has been approved for clinical use. Sulfonylurea and covalent inhibitors with electrophilic warhead (Michael acceptor) are among the prominent classes of compounds explored for their NLRP3 inhibitory effects. Chalcone, a small molecule with α, β unsaturated carbonyl group (Michael acceptor), has also been studied as a promising scaffold for the development of NLRP3 inhibitors. Low molecular weight, easy to manipulate lipophilicity and cost-effectiveness have attracted many to use chalcone scaffold for drug development. In this review, we highlight chalcone derivatives with NLRP3 inflammasome inhibitory activities. Recent developments and potential new directions summarized here will, hopefully, serve as valuable perspectives for investigators including medicinal chemists and drug discovery researchers to utilize chalcone as a scaffold for developing novel NLRP3 inflammasome inhibitors.

Phenolic and quinone methide nor-triterpenes as selective NLRP3 inflammasome inhibitors

Dysregulated inflammasome activity, particularly of the NLRP3 inflammasome, is associated with the development of several inflammatory diseases. The study of molecules directly targeting NLRP3 is an emerging field in the discovery of new therapeutic compounds for the treatment of inflammatory disorders. Friedelane triterpenes are biologically active phytochemicals having a wide range of activities including anti-inflammatory effects. In this work, we evaluated the potential anti-inflammatory activity of phenolic and quinonemethide nor-triterpenes (1-11) isolated from Maytenus retusa and some semisynthetic derivatives (12-16) through inhibition of the NLRP3 inflammasome in macrophages. Among them, we found that triterpenes 6 and 14 were the most potent, showing markedly reduced caspase-1 activity, IL-1β secretion (IC₅₀ = 1.15 µM and 0.19 µM, respectively), and pyroptosis (IC₅₀ = 2.21 µM and 0.13 µM, respectively). Further characterization confirmed their selective inhibition of NLRP3 inflammasome in both canonical and non-canonical activation pathways with no effects on AIM2 or NLRC4 inflammasome activation.

The role of NLRP3 inflammasome in digestive system malignancy

Digestive system malignancies, the most common types of cancer and a major cause of death in the worldwide, are generally characterized by high morbidity, insidious symptoms and poor prognosis. NLRP3 inflammasome, the most studied inflammasome member, is considered to be crucial in tumorigenesis. In this paper, we reviewed its pro-tumorigenic and anti-tumorigenic properties in different types of digestive system malignancy depending on the types of cells, tissues and organs involved, which would provide promising avenue for exploring new anti-cancer therapies.

The leucine-rich repeat (LRR) domain of NLRP3 is required for NLRP3 inflammasome activation in macrophages

The NLRP3 inflammasome is a critical component of innate immunity that defends the host from microbial infections. However, its aberrant activation contributes to the pathogenesis of several inflammatory diseases. Activation of the NLRP3 inflammasome induces the secretion of proinflammatory cytokines IL-1β and IL-18 and pyroptotic cell death. NLRP3 contains a leucine-rich repeat (LRR) domain at its C terminus. Although posttranslational modifications in this LRR domain have been shown to regulate NLRP3 inflammasome activation, the role of the entire LRR domain in NLRP3 inflammasome activation remains controversial. Here, we generated mouse macrophages that express an endogenous NLRP3 mutant lacking the LRR domain. Deletion of the LRR domain diminished NLRP3 inflammasome activation in macrophages. Furthermore, using NLRP3-deficient macrophages that are reconstituted with NLRP3 mutants lacking the LRR domain, we found that deletion of the LRR domain inhibited NLRP3 inflammasome activation. Mechanistically, deletion of the LRR domain inhibited NLRP3 self-association, oligomerization, and interaction with the essential regulator NEK7. Our results demonstrate a critical role for the LRR domain in NLRP3 inflammasome activation.

Identification of Potential Insect Growth Inhibitor against Aedes aegypti: A Bioinformatics Approach

Aedes aegypti is the main vector that transmits viral diseases such as dengue, hemorrhagic dengue, urban yellow fever, zika, and chikungunya. Worldwide, many cases of dengue have been reported in recent years, showing significant growth. The best way to manage diseases transmitted by Aedes aegypti is to control the vector with insecticides, which have already been shown to be toxic to humans; moreover, insects have developed resistance. Thus, the development of new insecticides is considered an emergency. One way to achieve this goal is to apply computational methods based on ligands and target information. In this study, sixteen compounds with acceptable insecticidal activities, with 100% larvicidal activity at low concentrations (2.0 to 0.001 mg·L−1), were selected from the literature. These compounds were used to build up and validate pharmacophore models. Pharmacophore model 6 (AUC = 0.78; BEDROC = 0.6) was used to filter 4793 compounds from the subset of lead-like compounds from the ZINC database; 4142 compounds (dG < 0 kcal/mol) were then aligned to the active site of the juvenile hormone receptor Aedes aegypti (PDB: 5V13), 2240 compounds (LE < −0.40 kcal/mol) were prioritized for molecular docking from the construction of a chitin deacetylase model of Aedes aegypti by the homology modeling of the Bombyx mori species (PDB: 5ZNT), which aligned 1959 compounds (dG < 0 kcal/mol), and 20 compounds (LE < −0.4 kcal/mol) were predicted for pharmacokinetic and toxicological prediction in silico (Preadmet, SwissADMET, and eMolTox programs). Finally, the theoretical routes of compounds M01, M02, M03, M04, and M05 were proposed. Compounds M01−M05 were selected, showing significant differences in pharmacokinetic and toxicological parameters in relation to positive controls and interaction with catalytic residues among key protein sites reported in the literature. For this reason, the molecules investigated here are dual inhibitors of the enzymes chitin synthase and juvenile hormonal protein from insects and humans, characterizing them as potential insecticides against the Aedes aegypti mosquito.

Dehydroisohispanolone as a Promising NLRP3 Inhibitor Agent: Bioevaluation and Molecular Docking

Dehydroisohispanolone (DIH), is a labdane diterpene that has exhibited anti-inflammatory activity via inhibition of NF-κB activation, although its potential effects on inflammasome activation remain unexplored. This study aims to elucidate whether DIH modulates NLR family pyrin domain-containing protein 3 (NLRP3) inflammasome in macrophages. Our findings show that DIH inhibited NLRP3 activation triggered by Nigericin (Nig), adenosine triphosphate (ATP) and monosodium urate (MSU) crystals, indicating broad inhibitory effects. DIH significantly attenuated caspase-1 activation and secretion of the interleukin-1β (IL-1β) in J774A.1 cells. Interestingly, the protein expressions of NLRP3, apoptosis-associated speck-like protein containing a CARD (ASC), pro-caspase-1 and pro-IL-1β were not affected by DIH treatment. Furthermore, we found that DIH pretreatment also inhibited the lipopolysaccharide (LPS)-induced NLRP3 inflammasome priming stage. In addition, DIH alleviated pyroptosis mediated by NLRP3 inflammasome activation. Similar results on IL-1β release were observed in Nig-activated bone marrow-derived macrophages (BMDMs). Covalent molecular docking analysis revealed that DIH fits well into the ATP-binding site of NLRP3 protein, forming a covalent bond with Cys415. In conclusion, our experiments show that DIH is an effective NLRP3 inflammasome inhibitor and provide new evidence for its application in the therapy of inflammation-related diseases.

Bone Marrow Mesenchymal Stem Cells (BMSCs)-Triggered Up-Regulation of miR-1297/NLR Family Pyrin Domain Containing 3 (NLRP3) Facilitates the Aggressive Proliferation of Lung Cancer Cells via Inducing Inflammatory Factor Release

miR-1297 derived from BMSC-originated exosomes participates in modulating multiple malignancies. Our study aims to clarify the effect of miR-1297 derived from BMSC-originated exosomes on the oxidative stress and inflammatory damage of lung cancer cells. miR-1297 and NLRP3 level was measured in lung cancer tissues and para-cancerous tissues, as well as in lung cancer cell lines and pulmonary epithelial cells. After miR-1297-mimics transfection or BMSC co-cultivation, cell viability was assessed by MTT and cytokines were evaluated by ELISA along with analysis of SOD activity and cell apoptosis. miR-1297 and NLRP3 were significantly elevated in lung cancer tissues and cell lines. Overexpression of miR-1297 enhanced oxidative stress and inflammatory response, along with increased cell viability and decreased apoptosis. Additionally, co-culture with BMSC protect the viability of lung cancer cells by facilitating miR-1297/NLRP3. In conclusion, a significant elevation of miR-1297 is found in lung cancer tissues and cells. Its overexpression induced the release of inflammatory factors, thereby protecting the proliferating activity of lung cancer cells and restraining apoptosis, indicating that miR-1297 may serve a promising target for early diagnosis of lung cancers.

The Role of NLRP3 Inflammasome Activation Pathway of Hepatic Macrophages in Liver Ischemia-Reperfusion Injury

Ischemia-reperfusion injury (IRI) is considered an inherent component involved in liver transplantation, which induce early organ dysfunction and failure. And the accumulating evidences indicate that the activation of host innate immune system, especially hepatic macrophages, play a pivotal role in the progression of LIRI. Inflammasomes is a kind of intracellular multimolecular complexes that actively participate in the innate immune responses and proinflammatory signaling pathways. Among them, NLRP3 inflammasome is the best characterized and correspond to regulate caspase-1 activation and the secretion of proinflammatory cytokines in response to various pathogen-derived as well as danger-associated signals. Additionally, NLRP3 is highly expressed in hepatic macrophages, and the assembly of NLRP3 inflammasome could lead to LIRI, which makes it a promising therapeutic target. However, detailed mechanisms about NLRP3 inflammasome involving in the hepatic macrophages-related LIRI is rarely summarized. Here, we review the potential role of the NLRP3 inflammasome pathway of hepatic macrophages in LIRI, with highlights on currently available therapeutic options.

Activation and Regulation of NLRP3 by Sterile and Infectious Insults

Nod-Like Receptor (NLR) is the largest family of Pathogen Recognition Receptors (PRRs) that patrols the cytosolic environment. NLR engagement drives caspase-1 activation that cleaves pro-IL-1B which then gets secreted. Released IL-1B recruits immune cells to the site of infection/injury. Caspase-1 also cleaves Gasdermin-D (GSDM-D) that forms pores within the plasma membrane driving inflammatory cell death called pyroptosis. NLRP3 is the most extensively studied NLR. The NLRP3 gene is encoded by 9 exons, where exon 1 codes for pyrin domain, exon 3 codes for NACHT domain, and Leucine Rich Repeat (LRR) domain is coded by exon 4-9. Exon 2 codes for a highly disorganized loop that connects the rest of the protein to the pyrin domain and may be involved in NLRP3 regulation. The NLRP3 inflammasome is activated by many structurally divergent agonists of microbial, environmental, and host origin. Activated NLRP3 interacts with an adaptor protein, ASC, that bridges it to pro-Caspase-1 forming a multi-protein complex called inflammasome. Dysregulation of NLRP3 inflammasome activity is a hallmark of pathogenesis in several human diseases, indicating its highly significant clinical relevance. In this review, we summarize the existing knowledge about the mechanism of activation of NLRP3 and its regulation during activation by infectious and sterile triggers.

Inflammasome Meets Centrosome: Understanding the Emerging Role of Centrosome in Controlling Inflammasome Activation

Inflammasomes are multi-protein platforms that are assembled in response to microbial and danger signals to activate proinflammatory caspase-1 for production of active form of IL-1β and induction of pyroptotic cell death. Where and how an inflammasome is assembled in cells has remained controversial. While the endoplasmic reticulum, mitochondria and Golgi apparatus have been reported to be associated with inflammasome assembly, none of these sites seems to match the morphology, number and size of activated inflammasomes that are microscopically observable as one single perinuclear micrometer-sized punctum in each cell. Recently, emerging evidence shows that NLRP3 and pyrin inflammasomes are assembled, activated and locally regulated at the centrosome, the major microtubule organizing center in mammalian cells, elegantly accounting for the singularity, size and perinuclear location of activated inflammasomes. These new exciting findings reveal the previously unappreciated importance of the centrosome in controlling inflammasome assembly and activation as well as inflammasome-related diseases.

NLRP3 cages revealed by full-length mouse NLRP3 structure control pathway activation

The NACHT-, leucine-rich-repeat- (LRR), and pyrin domain-containing protein 3 (NLRP3) is emerging to be a critical intracellular inflammasome sensor of membrane integrity and a highly important clinical target against chronic inflammation. Here, we report that an endogenous, stimulus-responsive form of full-length mouse NLRP3 is a 12- to 16-mer double-ring cage held together by LRR-LRR interactions with the pyrin domains shielded within the assembly to avoid premature activation. Surprisingly, this NLRP3 form is predominantly membrane localized, which is consistent with previously noted localization of NLRP3 at various membrane organelles. Structure-guided mutagenesis reveals that trans-Golgi network dispersion into vesicles, an early event observed for many NLRP3-activating stimuli, requires the double-ring cages of NLRP3. Double-ring-defective NLRP3 mutants abolish inflammasome punctum formation, caspase-1 processing, and cell death. Thus, our data uncover a physiological NLRP3 oligomer on the membrane that is poised to sense diverse signals to induce inflammasome activation.

The ASC Speck and NLRP3 Inflammasome Function Are Spatially and Temporally Distinct

Although considered the ternary inflammasome structure, whether the singular, perinuclear NLRP3:ASC speck is synonymous with the NLRP3 inflammasome is unclear. Herein, we report that the NLRP3:ASC speck is not required for nigericin-induced inflammasome activation but facilitates and maximizes IL-1β processing. Furthermore, the NLRP3 agonists H₂O₂ and MSU elicited IL-1β maturation without inducing specks. Notably, caspase-1 activity is spatially distinct from the speck, occurring at multiple cytoplasmic sites. Additionally, caspase-1 activity negatively regulates speck frequency and speck size, while speck numbers and IL-1β processing are negatively correlated, cyclical and can be uncoupled by NLRP3 mutations or inhibiting microtubule polymerization. Finally, when specks are present, caspase-1 is likely activated after leaving the speck structure. Thus, the speck is not the NLRP3 inflammasome itself, but is instead a dynamic structure which may amplify the NLRP3 response to weak stimuli by facilitating the formation and release of small NLRP3:ASC complexes which in turn activate caspase-1.

Mitochondria as Key Players in the Pathogenesis and Treatment of Rheumatoid Arthritis

Mitochondria are major energy-producing organelles that have central roles in cellular metabolism. They also act as important signalling hubs, and their dynamic regulation in response to stress signals helps to dictate the stress response of the cell. Rheumatoid arthritis is an inflammatory and autoimmune disease with high prevalence and complex aetiology. Mitochondrial activity affects differentiation, activation and survival of immune and non-immune cells that contribute to the pathogenesis of this disease. This review outlines what is known about the role of mitochondria in rheumatoid arthritis pathogenesis, and how current and future therapeutic strategies can function through modulation of mitochondrial activity. We also highlight areas of this topic that warrant further study. As producers of energy and of metabolites such as succinate and citrate, mitochondria help to shape the inflammatory phenotype of leukocytes during disease. Mitochondrial components can directly stimulate immune receptors by acting as damage-associated molecular patterns, which could represent an initiating factor for the development of sterile inflammation. Mitochondria are also an important source of intracellular reactive oxygen species, and facilitate the activation of the NLRP3 inflammasome, which produces cytokines linked to disease symptoms in rheumatoid arthritis. The fact that mitochondria contain their own genetic material renders them susceptible to mutation, which can propagate their dysfunction and immunostimulatory potential. Several drugs currently used for the treatment of rheumatoid arthritis regulate mitochondrial function either directly or indirectly. These actions contribute to their immunomodulatory functions, but can also lead to adverse effects. Metabolic and mitochondrial pathways are attractive targets for future anti-rheumatic drugs, however many questions still remain about the precise role of mitochondrial activity in different cell types in rheumatoid arthritis.

Development of Novel Tetrahydroquinoline Inhibitors of NLRP3 Inflammasome for Potential Treatment of DSS-Induced Mouse Colitis

The NLRP3 inflammasome is a critical component of innate immunity, which defends internal and external threats. However, inappropriate activation of the NLRP3 inflammasome induces various human diseases. In this study, we discovered and synthesized a series of tetrahydroquinoline inhibitors of NLRP3 inflammasome. Among these analogues, compound 6 exhibited optimal NLRP3 inhibitory activity. In vitro studies indicated that compound 6 directly bound to the NACHT domain of NLRP3 but not to protein pyrin domain (PYD) or LRR domain, inhibited NLRP3 ATPase activity, and blocked ASC oligomerization, thereby inhibiting NLRP3 inflammasome assembly and activation. Compound 6 specifically inhibited the NLRP3 inflammasome activation, but had no effect on the activation of NLRC4 or AIM2 inflammasomes. Furthermore, in the dextran sulfate sodium (DSS)-induced colitis mouse model, compound 6 exhibited significant anti-inflammatory activity through inhibiting NLRP3 inflammasome in vivo. Therefore, our study provides a potent NLRP3 inflammasome inhibitor, which deserves further structural optimization as a novel therapeutic candidate for NLRP3-driven diseases.