The NLRP1 inflammasomes

Gaussian Embedding for Large-scale Gene Set Analysis

Gene sets, including protein complexes and signaling pathways, have proliferated greatly, in large part as a result of high-throughput biological data. Leveraging gene sets to gain insight into biological discovery requires computational methods for converting them into a useful form for available machine learning models. Here, we study the problem of embedding gene sets as compact features that are compatible with available machine learning codes. We present Set2Gaussian, a novel network-based gene set embedding approach, which represents each gene set as a multivariate Gaussian distribution rather than a single point in the low-dimensional space, according to the proximity of these genes in a protein-protein interaction network. We demonstrate that Set2Gaussian improves gene set member identification, accurately stratifies tumors, and finds concise gene sets for gene set enrichment analysis. We further show how Set2Gaussian allows us to identify a previously unknown clinical prognostic and predictive subnetwork around NEFM in sarcoma, which we validate in independent cohorts.

CD147 Aggravated Inflammatory Bowel Disease by Triggering NF-κB-Mediated Pyroptosis

BACKGROUND

Pyroptosis, a novel form of inflammatory programmed cell death, was recently found to be a cause of mucosal barrier defect. In our pervious study, CD147 expression was documented to increase in intestinal tissue of inflammatory bowel disease (IBD).

OBJECTIVE

The aim of this study was to determine the function of serum CD147 in pyroptosis.

METHODS

The study group consisted of 96 cases. The centration of CD147, IL-1β, and IL-18 levels in serum was assessed by ELISA. Real-time PCR and WB were performed to analyze the effect of CD147 on pyroptosis.

RESULTS

In this study, our results showed that CD147 induced cell pyroptosis in intestinal epithelial cells (IECs) by enhancement of IL-1β and IL-18 expression and secretion in IECs, which is attributed to activation of inflammasomes, including caspase-1 and GSDMD as well as GSDME, leading to aggregate inflammatory reaction. Mechanically, CD147 promoted phosphorylation of NF-κB p65 in IECs, while inhibition of NF-κB activity by the NF-κB inhibitor BAY11-7082 reversed the effect of CD147 on IL-1β and IL-18 secretion. Most importantly, serum CD147 level is slightly clinically correlated with IL-1β, but not IL-18 level.

CONCLUSION

These findings revealed a critical role of CD147 in the patients with IBD, suggesting that blockade of CD147 may be a novel therapeutic strategy for the patients with IBD.

Immunostimulatory efficacy and protective potential of putative TgERK7 protein in mice experimentally infected by Toxoplasma gondii

The extracellular signal-regulated kinases (ERKs) serve as important determinants of cellular signal transduction pathways, and hence may play important roles during infections. Previous work suggested that putative ERK7 of Toxoplasma gondii is required for efficient intracellular replication of the parasite. However, the antigenic and immunostimulatory properties of TgERK7 protein remain unknown. The objective of this study was to produce a recombinant TgERK7 protein in vitro and to evaluate its effect on the induction of humoral and T cell-mediated immune responses against T. gondii infection in BALB/c mice. Immunization using TgERK7 mixed with Freund's adjuvants significantly increased the ratio of CD3e⁺CD4⁺ T/CD3e⁺CD8a⁺ T lymphocytes in spleen and elevated serum cytokines (IFN-γ, IL-2, IL-4, IL-10, IL-12p70, IL-23, MCP-1, and TNF-α) in immunized mice compared to control mice. On the contrary, immunization did not induce high levels of serum IgG antibodies. Five predicted peptides of TgERK7 were synthesized and conjugated with KLH and used to analyze the antibody specificity in the sera of immunized mice. We detected a progressive increase in the antibody level only against TgERK7 peptide A (DEVDKHVLRKYD). Antibody raised against this peptide significantly decreased intracellular proliferation of T. gondii in vitro, suggesting that peptide A can potentially induce a protective antibody response. We also showed that immunization improved the survival rate of mice challenged with a virulent strain and significantly reduced the parasite cyst burden within the brains of chronically infected mice. Our data show that TgERK7-based immunization induced TgERK7 peptide A-specific immune responses that can impart protective immunity against T. gondii infection. The therapeutic potential of targeting ERK7 signaling pathway for future toxoplasmosis treatment is warranted.

Cepharanthine attenuates cerebral ischemia/reperfusion injury by reducing NLRP3 inflammasome-induced inflammation and oxidative stress via inhibiting 12/15-LOX signaling

Cepharanthine (CEP) is a potential candidate for treatment of cerebral ischemia/reperfusion (I/R) injury, due to its anti-inflammatory and anti-oxidative properties. To investigate the effect of CEP on cerebral I/R injury, we established a mouse model of transient middle cerebral artery occlusion (tMCAO) and a microglia cell model of oxygen and glucose deprivation/reoxygenation (OGD/R). Administration of CEP attenuated neurological deficits, reduced infarct volume and edema, and decreased microglia activation in MCAO mice. Immunofluorescence staining showed an up-regulation in NLR Family Pyrin Domain Containing 3 (NLRP3) immunoreactivity in Iba1-labled microglia together with total Iba1 and NLRP3 expression in the brain following tMCAO, while down-regulated by CEP treatment. In both tMCAO-induced mice and OGD/R-treated BV-2 cells, CEP exhibited dose-dependent inhibition on the expression of NLRP3, ASC and cleaved caspase-1. Importantly, CEP attenuated tMCAO or OGD/R-induced overproduction of M1 microglia-regulated pro-inflammation cytokines IL-1β and IL-18, suggesting that CEP might involve in suppressing microglia polarization to M1 phenotype in vivo and in vitro. Moreover, CEP dose-dependently inhibited tMCAO-induced arachidonate 15 lipoxygenase (ALOX15) together with Iba1-labled microglia. The subsequent ALOX15-mediated oxidative stress was decreased by CEP treatment in vivo and in vitro, as evidenced by reduced ROS generation and MDA level, and increased SOD activity. Taken together, we demonstrate that CEP attenuates cerebral I/R injury probably by inhibiting microglia activation and NLRP3 inflammasome-induced inflammation and reducing oxidative stress via suppressing 12/15-LOX signaling.

Characterization of the inflammasome component SmASC in turbot (Scophthalmus maximus)

Apoptosis-associated speck-like protein containing a C-terminal caspase recruit domain (ASC) is an important adapter protein in the inflammasome complex that mediates inflammatory caspase activation and host innate immunity in mammals. However, the function of inflammasome components in lower vertebrate remains poorly understood. In this study, full length of SmASC was cloned from turbot (Scophthalmus maximus). Through bioinformatic analysis, we found that SmASC shares relatively high identity with ASC in bony fish. Furthermore, we found that the intact SmASC can form an oligomeric speck-like structure, while the PYD segment of SmASC can form the filamentous structure. Moreover, expression of SmASC was induced after intraperitoneal injection of Edwardsiella piscicida (E. piscicida) in vivo. To further explore the role of SmASC during infection, we constructed SmASC knockdown and overexpression models by administration of siRNA and overexpression plasmids in vivo, respectively. Expression of SmASC decreased the propagation of E. piscicida in different immune organs. In summary, our results characterize the function of SmASC in S. maximus, suggesting that the SmASC plays a critical role in turbot immune responses.

Role of inflammasomes in the pathogenesis of periodontal disease and therapeutics

Inflammasomes are a group of multimolecular intracellular complexes assembled around several innate immune proteins. Recognition of a diverse range of microbial, stress and damage signals by inflammasomes results in direct activation of caspase‐1, which subsequently induces the only known form of secretion of active interleukin‐1β and interleukin‐18. Although the importance of interleukin‐1β in the periodontium is not questioned, the impact of inflammasomes in periodontal disease and its potential for therapeutics in periodontology is still in its very early stages. Increasing evidence in preclinical models and human data strongly implicate the involvement of inflammasomes in a number of inflammatory, autoinflammatory and autoimmune disorders. Here we review: (a) the currently known inflammasome functions, (b) clinical/preclinical data supporting inflammasome involvement in the context of periodontal and comorbid diseases and (c) potential therapies targeting inflammasomes. To clarify further the inflammasome involvement in periodontitis, we present analyses of data from a large clinical study (n = 5809) that measured the gingival crevicular fluid‐interleukin‐1β and grouped the participants based on current periodontal disease classifications. We review data on 4910 European‐Americans that correlate 16 polymorphisms in the interleukin‐1B region with high gingival crevicular fluid‐interleukin‐1β levels. We show that inflammasome components are increased in diseased periodontal tissues and that the caspase‐1 inhibitor, VX‐765, inhibits ~50% of alveolar bone loss in experimental periodontitis. The literature review further supports that although patients clinically present with the same phenotype, the disease that develops probably has different underlying biological pathways. The current data indicate that inflammasomes have a role in periodontal disease pathogenesis. Understanding the contribution of different inflammasomes to disease development and distinct patient susceptibility will probably translate into improved, personalized therapies.

Inflammasome activation by NLRP1 and NLRC4 in patients with coronary stenosis

OBJECTIVE AND DESIGN

We performed an experimental, analytical and prospective study to evaluate the systemic activation of inflammasome in atherosclerosis' patients, in order to shed light into responsible mechanisms for plaque formation.

SUBJECTS

We included sixty individuals distributed into 3 groups: 2 groups based on the report from the angiography (severe lesions - SL and primary lesions - PL) and 1 group enclosing healthy individuals (HC).

METHODS

The expression assays of inflammasome genes NLRP1, NLRC4, CASP-1 and IL-1β were performed using Real Time qPCR, with specific Taqman Assays. IL-1β serum levels were analysed by commercial kit. Were applied the Shapiro-Wilk and Student's T-test as statistical tests. Statistical significance was set to p ≤ 0.05.

RESULTS

Upregulation of NLRP1 (+3.47 FC, p = 0.0001), NLRC4 (+7.06 FC, p = 6.792 × 10^-09) and IL-1β (+2.43 FC, p = 0.005) was observed in all atherosclerosis patients when compared to HC. According to stenosis severity, patients with primary lesions showed upregulation of inflammasome genes NLRP1 (+2.87 FC, p = 0.0008), NLRC4 (+6.34 FC, p = 4.134 × 10^-07) and IL-1β (+3.39 FC, p = 0.0012) with respect to the HC group. No statistical difference was found in IL-1β serum levels according the assessed groups.

CONCLUSIONS

Inflammasome activation in atherosclerosis's patients can be systemic altered and may be triggered by NLRP1 and NLRC4 receptors. IL-1β gene expression was identified in our study as an important systemic detectable marker of plaque severity.

Inflammasome Activation in Response to Intracellular Protozoan Parasites

Inflammasomes are cytosolic complexes that assemble in response to cellular stress or upon sensing microbial molecules, culminating in cytokine processing and an inflammatory form of cell death called pyroptosis. Inflammasomes are usually composed of a sensor molecule, an adaptor protein, and an inflammatory caspase, such as Caspase-1, which cleaves and activates multiple substrates, including Gasdermin-D, pro-IL-1β, and pro-IL-18. Ultimately, inflammasome activation promotes inflammation and restriction of the microbial infection. In recent years, many studies have addressed the role of inflammasomes during fungal, bacterial, viral, and parasitic diseases, revealing sophisticated aspects of the host-pathogen interaction. In this review, we summarize recent advances on inflammasome activation in response to intracellular parasites, including Leishmania spp., Plasmodium spp., Trypanosoma cruzi, and Toxoplasma gondii.

Exploring the ring potential of 2,4-diaminopyrimidine derivatives towards the identification of novel caspase-1 inhibitors in Alzheimer's disease therapy

Pro-inflammatory activation of caspase-1 in the neurodegenerative pathway has been associated with age-dependent cognitive impairment and Alzheimer's disease (AD) in humans. A recent report highlighted 2,4-diaminopyrimidine ring as an essential fragment in the inhibition of human caspase-1. However, the role of the ring and its enzyme inhibitory mechanism is not thoroughly investigated at the molecular level. The purpose of this study is therefore in twofold: (1) to understand the enzyme binding mechanism of the 2,4-diaminopyrimidine ring and (2) to search for more potent caspase-1 inhibitors that contain the ring, using integrative per-residue energy decomposition (PRED) pharmacophore modeling. Ligand interaction profile of a reference compound revealed a peculiar hydrogen formation of the amino group of 2,4-diaminopyrimidine with active site residue Arg341, possibly forming the bases for its inhibitory prowess against caspase-1. A generated pharmacophore model for structure-based virtual screening identified compounds, ZINC724667, ZINC09908119, and ZINC09933770, as potential caspase-1 inhibitors that possessed desirable pharmacokinetic and physiochemical properties. Further analyses revealed active site residues, Arg179, Ser236, Cys285, Gln283, Ser339, and Arg341, as crucial to inhibitor binding by stabilizing and forming hydrogen bonds, hydrophobic, and pi-pi interactions with the 2,4-diaminopyrimidine rings. Common interaction patterns of the hits could have accounted for their selective and high-affinity ligand binding, which was characterized by notable disruptions in caspase-1 structural architecture. These compounds could further be explored as potential leads in the development of novel caspase-1 inhibitors.

Pyroptosis: The missing puzzle among innate and adaptive immunity crosstalk

Pyroptosis is a newly discovered programmed cell death with inflammasome formation. Pattern recognition receptors that identify repetitive motifs of prospective pathogens such as LPS of gram-negative bacteria are crucial to pyroptosis. Upon stimulation by pathogen-associated molecular patterns or damage-associated molecular patterns, proinflammatory cytokines, mainly IL-1 family members IL-1β and IL-18, are released through pyroptosis specific pore-forming protein, gasdermin D. Even though IL-1 family members are mainly involved in innate immunity, they can be factors in adaptive immunity. Given the importance of IL-1 family members in health and diseases, deciphering the role of pyroptosis in the regulation of innate and adaptive immunity is of great importance, especially with the recent progress in identifying the exact mechanism of such a pathway. In this review, we will focus on how the innate inflammatory mediators can regulate the adaptive immune system and vice versa via pyroptosis.

Cellular Stress and General Pathological Processes

From the viewpoint of the general pathology, most of the human diseases are associated with a limited number of pathogenic processes such as inflammation, tumor growth, thrombosis, necrosis, fibrosis, atrophy, pathological hypertrophy, dysplasia and metaplasia. The phenomenon of chronic low-grade inflammation could be attributed to non-classical forms of inflammation, which include many neurodegenerative processes, pathological variants of insulin resistance, atherosclerosis, and other manifestations of the endothelial dysfunction. Individual and universal manifestations of cellular stress could be considered as a basic element of all these pathologies, which has both physiological and pathophysiological significance. The review examines the causes, main phenomena, developmental directions and outcomes of cellular stress using a phylogenetically conservative set of genes and their activation pathways, as well as tissue stress and its role in inflammatory and para-inflammatory processes. The main ways towards the realization of cellular stress and its functional blocks were outlined. The main stages of tissue stress and the classification of its typical manifestations, as well as its participation in the development of the classical and non-classical variants of the inflammatory process, were also described. The mechanisms of cellular and tissue stress are structured into the complex systems, which include networks that enable the exchange of information with multidirectional signaling pathways which together make these systems internally contradictory, and the result of their effects is often unpredictable. However, the possible solutions require new theoretical and methodological approaches, one of which includes the transition to integral criteria, which plausibly reflect the holistic image of these processes.

Cellular Interplay as a Consequence of Inflammatory Signals Leading to Liver Fibrosis Development

Inflammation has been known to be an important driver of fibrogenesis in the liver and onset of hepatic fibrosis. It starts off as a process meant to protect the liver from further damage, but it can become the main promoter of liver fibrosis. There are many inflammation-related pathways activated during liver fibrosis that lead to hepatic stellate cells (HSCs) activation and collagen-deposition in the liver. Such events are mostly modulated upstream of HSCs and involve signals from hepatocytes and innate immune cells. One particular event is represented by cell death during liver injury that generates multiple inflammatory signals that further trigger sterile inflammation and enhancement of inflammatory response. The assembly of inflammasome that responds to danger-associated molecular patterns (DAMPs) stimulates the release of pro-inflammatory cytokines and at the same time, initiates programmed cell death called pyroptosis. This review focuses on cellular and molecular mechanisms responsible for initiation and progress of inflammation in the liver.

miR-590-3p Inhibits Pyroptosis in Diabetic Retinopathy by Targeting NLRP1 and Inactivating the NOX4 Signaling Pathway

Purpose

To elucidate the mechanism whereby miR-590-3p regulates pyroptosis in diabetic retinopathy (DR).

Methods

Human retinal microvascular endothelial cells (HRMECs) incubated with high glucose (HG) were used to establish cell models, and the expression levels of miR-590-3p, caspase-1, IL-1β, NLRP1, NOX4, TXNIP, NLRP3, and ROS were determined. Additionally, miR-590-3p was altered using a mimic or an inhibitor, and siRNAs targeting NLRP1 and NOX4 were applied to explore the regulatory mechanism of miR-590-3p in DR. The relationships between miR-590-3p and NLRP1/NOX4 also were investigated using a luciferase reporter assay. Furthermore, vitreous tissue samples were collected to confirm pyroptosis in clinical DR.

Results

Downregulated miR-590-3p and upregulated NLRP1/NOX4 levels were observed in a cell culture model of DR. Inhibiting miR-590-3p upregulated NLRP1, the NOX4/ROS/TXNIP/NLRP3 pathway, and caspase-1. NLRP1 and NOX4 were confirmed as direct target genes of miR-590-3p. The overexpression of miR-590-3p or knockdown of NLRP1 and NOX4 increased cell activity and suppressed pyroptosis. Intriguingly, the upregulation of IL-1β induced the downregulation of miR-590-3p by lowering the DNA promoter activity of pri-miR-590.

Conclusions

HG induced pyroptosis in a cell culture model of DR, and the downregulation of miR-590-3p promoted pyroptotic death by targeting NLRP1 and activating the NOX4/ROS/TXNIP/NLRP3 pathway via an IL-1β-mediated positive feedback loop.

A genetic origin for acid-base imbalance triggers the mitochondrial damage that explains the autoimmune response and drives to gastric neuroendocrine tumours

BACKGROUND

Type I gastric neuroendocrine tumors (gNETs) arise from hypergastrinemia in patients with autoimmune chronic atrophic gastritis. According to the classical model, the gastric H+/K+ ATPase was the causative autoantigen recognized by CD4+ T cells in chronic autoimmune scenario that secretes IL-17 and correlates with parietal cell (PC) atrophy, which drives to gastric achlorhydria and increases the risk for gastric neoplasms. However, the mechanism by which the inflammatory response correlates with PC atrophy is not clearly defined.

METHODS

Recently, we found that the ATP4A^p.R703C mutation impaired PC function and gastric acidification, which drove familial gNET. Our group constructed a knock-in mouse model for the ATP4A mutation, which has served us to better understand the relation between impaired capability to export protons across the plasma membrane of PCs and tumor progression.

RESULTS

The ATP4A^p.R703C mutation drives gastric achlorhydria, but also deregulates the acid-base balance within PCs, affecting mitochondrial biogenesis. Mitochondrial malfunction activates ROS signaling, which triggers caspase-3-mediated apoptosis of parietal cells. In addition, when gastric euchlorhydria was restored, mitochondrial function is recovered. Infection by H. pylori promotes destabilization of the mitochondria of the PCs by a mechanism similar to that described for APT4A^p.R703C carriers.

CONCLUSIONS

A genetic origin that drives mitochondria alteration would initiate the gastric chronic inflammation instead of the classical IL-17 secretion-mediated mechanism explanation. Gastric euchlorhydria restoration is suggested to be indicated for mitochondrial recover. Our results open a new window to understand gastric neoplasms formation but also the inflammatory mechanisms and autoimmune disorders conducted by genetic origin that composes a premalignant scenario.

Fiery Cell Death: Pyroptosis in the Central Nervous System

Pyroptosis ('fiery death') is an inflammatory type of regulated cell death (RCD), which occurs downstream of inflammasome activation. Pyroptosis is mediated directly by the recently identified family of pore-forming proteins known as gasdermins, the best characterized of which is gasdermin D (GSDMD). Recent investigations implicate pyroptosis in the pathogenesis of multiple neurological diseases. In this review, we discuss molecular mechanisms that drive pyroptosis, evidence for pyroptosis within the CNS, and emerging therapeutic strategies for its inhibition in the context of neurological disease.

Host inflammatory responses to intracellular invaders: Review study

As soon as a pathogen invades through the physical barriers of its corresponding host, host mounts a series of protective immune response to get rid of the invading pathogen. Host's pattern recognition receptors (PRR), localized at the cellular surface, cytoplasm and also in the nucleus; recognises pathogen associated molecular patterns (PAMPs) and plays crucial role in directing the immune response to be specific. Inflammatory responses are among the earliest strategies to tackle the pathogen by the host and are tightly regulated by multiple molecular pathways. Inflammasomes are multi-subunit protein complex consisting of a receptor molecule viz. NLRP3, an adaptor molecule- Apoptosis-associated speck-like protein containing a CARD (ASC) and an executioner caspase. Upon infection and/or injury; inflammasome components assemble and oligomerizes leading to the auto cleavage of the pro-caspase-1 to its active form. The activated caspase-1 cleaves immature form of the pro-inflammatory cytokines to their mature form e.g. IL1-β and IL-18 which mount inflammatory response. Moreover, C-terminal end of the Gasdermin D molecule is also cleaved by the caspase-1. The activated N-terminal Gasdermin D molecule form pores in the infected cells leading to their pyroptosis. Hence, inflammasomes drive inflammation during infection and controls the establishment of the pathogen by mounting inflammatory response and activation of the pyroptotic cell death.

Emerging insights into molecular mechanisms underlying pyroptosis and functions of inflammasomes in diseases

Pyroptosis is a form of necrotic and inflammatory programmed cell death, which could be characterized by cell swelling, pore formation on plasma membranes, and release of proinflammatory cytokines (IL-1β and IL-18). The process of pyroptosis presents as dual effects: protecting multicellular organisms from microbial infection and endogenous dangers; leading to pathological inflammation if overactivated. Two pathways have been found to trigger pyroptosis: caspase-1 mediated inflammasome pathway with the involvement of NLRP1-, NLRP3-, NLRC4-, AIM2-, pyrin-inflammasome (canonical inflammasome pathway) and caspase-4/5/11-mediated inflammasome pathway (noncanonical inflammasome pathway). Gasdermin D (GSDMD) has been proved to be a substrate of inflammatory caspases (caspase-1/4/5/11), and the cleaved N-terminal domain of GSDMD oligomerizes to form cytotoxic pores on the plasma membrane. Here, we mainly reviewed the up to date mechanisms of pyroptosis, and began with the inflammasomes as the activator of caspase-1/caspase-11, 4, and 5. We further discussed these inflammasomes functions in diseases, including infectious diseases, sepsis, inflammatory autoimmune diseases, and neuroinflammatory diseases.

HSC70 regulates cold-induced caspase-1 hyperactivation by an autoinflammation-causing mutant of cytoplasmic immune receptor NLRC4

NLRC4 [nucleotide-binding domain and leucine-rich repeat (NLR) family, caspase recruitment domain (CARD) containing 4] is an innate immune receptor, which, upon detection of certain pathogens or internal distress signals, initiates caspase-1-mediated interleukin-1β maturation and an inflammatory response. A gain-of-function mutation, H443P in NLRC4, causes familial cold autoinflammatory syndrome (FCAS) characterized by cold-induced hyperactivation of caspase-1, enhanced interleukin-1β maturation, and inflammation. Although the H443P mutant shows constitutive activity, the mechanism involved in hyperactivation of caspase-1 by NLRC4-H443P upon exposure of cells to lower temperature is not known. Here, we show that heat shock cognate protein 70 (HSC70) complexes with NLRC4 and negatively regulates caspase-1 activation by NLRC4-H443P in human cells. Compared with NLRC4, the structurally altered NLRC4-H443P shows enhanced interaction with HSC70. Nucleotide binding- and leucine-rich repeat domains of NLRC4, but not its CARD, can engage in complex formation with HSC70. Knockdown of HSC70 enhances apoptosis-associated speck-like protein containing a CARD (ASC)-speck formation and caspase-1 activation by NLRC4-H443P. Exposure to subnormal temperature results in reduced interaction of NLRC4-H443P with HSC70, and an increase in its ability to form ASC specks and activate caspase-1. Unlike the NLRC4-H443P mutant, another constitutively active mutant (NLRC4-V341A) associated with autoinflammatory diseases, but not FCAS, showed neither enhanced interaction with HSC70 nor an increase in inflammasome formation upon exposure to subnormal temperature. Our results identify HSC70 as a negative regulator of caspase-1 activation by the temperature-sensitive NLRC4-H443P mutant. We also show that low-temperature-induced hyperactivation of caspase-1 by NLRC4-H443P is due to loss of inhibition by HSC70.

Homozygous NLRP1 gain-of-function mutation in siblings with a syndromic form of recurrent respiratory papillomatosis

Juvenile-onset recurrent respiratory papillomatosis (JRRP) is a rare and debilitating childhood disease that presents with recurrent growth of papillomas in the upper airway. Two common human papillomaviruses (HPVs), HPV-6 and -11, are implicated in most cases, but it is still not understood why only a small proportion of children develop JRRP following exposure to these common viruses. We report 2 siblings with a syndromic form of JRRP associated with mild dermatologic abnormalities. Whole-exome sequencing of the patients revealed a private homozygous mutation in NLRP1, encoding Nucleotide-Binding Domain Leucine-Rich Repeat Family Pyrin Domain-Containing 1. We find the NLRP1 mutant allele to be gain of function (GOF) for inflammasome activation, as demonstrated by the induction of inflammasome complex oligomerization and IL-1β secretion in an overexpression system. Moreover, patient-derived keratinocytes secrete elevated levels of IL-1β at baseline. Finally, both patients displayed elevated levels of inflammasome-induced cytokines in the serum. Six NLRP1 GOF mutations have previously been described to underlie 3 allelic Mendelian diseases with differing phenotypes and modes of inheritance. Our results demonstrate that an autosomal recessive, syndromic form of JRRP can be associated with an NLRP1 GOF mutation.

Inflammasomes and autoimmune and rheumatic diseases: A comprehensive review

Inflammasomes are a multi-protein platform forming a part of the innate immune system. Inflammasomes are at standby status and can be activated when needed. Inflammasome activation is an important mechanism for the production of active interleukin (IL)-1β and IL-18, which have important roles to instruct adaptive immunity. Active forms of inflammasomes trigger a series of inflammatory cascades and lead to the differentiation and polarization of naïve T cells and secretion of various cytokines, which can induce various kinds of autoimmune and rheumatic diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), gout, Sjögren's syndrome, Behçet's disease, anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis and IgA vasculitis (former Henoch-Schönlein purpura ). In this review, we summarize studies published on inflammasomes and review their roles in various autoimmune diseases. Understanding of the role of inflammasomes may facilitate the diagnosis of autoimmune diseases and the development of tailored therapies in the future.

The effect of NLRP inflammasome on the regulation of AGEs-induced inflammatory response in human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Diabetes influences the frequency and development of periodontitis. Inflammation of human periodontal ligament cells (HPDLCs) participates in this pathologic process. Hence, this study aims to explore whether advanced glycation end products (AGEs), by-products of diabetes, could exaggerate inflammation induced by muramyl dipeptide (MDP) in HPDLCs, and whether nucleotide-binding oligomerization domain-like receptors (NLRs) signaling pathway was involved.

MATERIAL AND METHODS

Human periodontal ligament cells were pre-treated with 100 μg/mL AGEs for 24 hours and stimulated with 10 μg/mL MDP for 24 hours. IL-6, IL-1β, and RAGE were detected, and the activation of NF-κB signaling pathway was observed. The expression of NLRs was evaluated with or without silencing RAGE or blocking NF-κB pathway under AGEs stimulation. Statistical analyses were performed by using independent sample t test.

RESULTS

Advanced glycation end products induced significant increase of inflammatory cytokines in HPDLCs (P < 0.05). Results of western blot (WB) showed that after 45 minutes stimulation of AGEs, p-p65/p65 ratio peaked; AGEs promoted the expression of NLRP1, NLRP3, and apoptosis-associated speck-like protein containing a CARD (ASC). After silencing RAGE or blocking NF-κB pathway, the up-regulation of NLRs protein caused by AGEs was attenuated. Additionally, AGEs pre-treatment could enhance the inflammatory response of MDP and the expression of NLRs, which were demonstrated by more expression of IL-6, IL-1β, NOD2, NLRP1, NLRP3, and ASC.

CONCLUSION

Advanced glycation end products induced inflammatory response in HPDLCs via NLRP1-inflammasome and NLRP3-inflammasome activation in which NF-κB signal pathway was involved. Besides, AGEs promoted the inflammatory response of MDP via NOD2, NLRP1-inflammasome, and NLRP3-inflammasome.

The Canonical Inflammasome: A Macromolecular Complex Driving Inflammation

The inflammasome is a multi-molecular platform crucial to the induction of an inflammatory response to cellular danger. Recognition in the cytoplasm of endogenously and exogenously derived ligands initiates conformational change in sensor proteins, such as NLRP3, that permits the subsequent rapid recruitment of adaptor proteins, like ASC, and the resulting assembly of a large-scale inflammatory signalling platform. The assembly process is driven by sensor-sensor interactions as well as sensor-adaptor and adaptor-adaptor interactions. The resulting complex, which can reach diameters of around 1 micron, has a variable composition and stoichiometry. The inflammasome complex functions as a platform for the proximity induced activation of effector caspases, such as caspase-1 and caspase-8. This ultimately leads to the processing of the inflammatory cytokines pro-IL1β and pro-IL18 into their active forms, along with the cleavage of Gasdermin D, a key activator of cell death via pyroptosis.

Programmed necrotic cell death of macrophages: Focus on pyroptosis, necroptosis, and parthanatos

Macrophages are highly plastic cells of the innate immune system. Macrophages play central roles in immunity against microbes and contribute to a wide array of pathologies. The processes of macrophage activation and their functions have attracted considerable attention from life scientists. Although macrophages are highly resistant to many toxic stimuli, including oxidative stress, macrophage death has been reported in certain diseases, such as viral infections, tuberculosis, atherosclerotic plaque development, inflammation, and sepsis. While most studies on macrophage death focused on apoptosis, a significant body of data indicates that programmed necrotic cell death forms may be equally important modes of macrophage death. Three such regulated necrotic cell death modalities in macrophages contribute to different pathologies, including necroptosis, pyroptosis, and parthanatos. Various reactive oxygen and nitrogen species, such as superoxide, hydrogen peroxide, and peroxynitrite have been shown to act as triggers, mediators, or modulators in regulated necrotic cell death pathways. Here we discuss recent advances in necroptosis, pyroptosis, and parthanatos, with a strong focus on the role of redox homeostasis in the regulation of these events.

The Role of Neuronal NLRP1 Inflammasome in Alzheimer's Disease: Bringing Neurons into the Neuroinflammation Game

The innate immune system and inflammatory response in the brain have critical impacts on the pathogenesis of many neurodegenerative diseases including Alzheimer's disease (AD). In the central nervous system (CNS), the innate immune response is primarily mediated by microglia. However, non-glial cells such as neurons could also partake in inflammatory response independently through inflammasome signalling. The NLR family pyrin domain-containing 1 (NLRP1) inflammasome in the CNS is primarily expressed by pyramidal neurons and oligodendrocytes. NLRP1 is activated in response to amyloid-β (Aβ) aggregates, and its activation subsequently cleaves caspase-1 into its active subunits. The activated caspase-1 proteolytically processes interleukin-1β (IL-1β) and interleukin-18 (IL-18) into maturation whilst co-ordinately triggers caspase-6 which is responsible for apoptosis and axonal degeneration. In addition, caspase-1 activation induces pyroptosis, an inflammatory form of programmed cell death. Studies in murine AD models indicate that the Nlrp1 inflammasome is indeed upregulated in AD and neuronal death is observed leading to cognitive decline. However, the mechanism of NLRP1 inflammasome activation in AD is particularly elusive, given its structural and functional complexities. In this review, we examine the implications of the human NLRP1 inflammasome and its signalling pathways in driving neuroinflammation in AD.

The NLRP1 inflammasome: new mechanistic insights and unresolved mysteries

Nucleotide-binding domain, leucine-rich repeat (NLR) proteins constitute a diverse class of innate immune sensors that detect pathogens or stress-associated stimuli in plants and animals. Some NLRs are activated upon direct binding to pathogen-derived ligands. In contrast, we focus here on a vertebrate NLR called NLRP1 that responds to the enzymatic activities of pathogen effectors. We discuss a newly proposed 'functional degradation' mechanism that explains activation and assembly of NLRP1 into an oligomeric complex called an inflammasome. We also discuss how NLRP1 is activated by non-pathogen-associated triggers such as the anti-cancer drug Val-boroPro, or by human disease-associated mutations. Finally, we discuss how research on NLRP1 has led to additional biological insights, including the unexpected discovery of a new CARD8 inflammasome.

NOD-like receptors: major players (and targets) in the interface between innate immunity and cancer

Innate immunity comprises several inflammation-related modulatory pathways which receive signals from an array of membrane-bound and cytoplasmic pattern recognition receptors (PRRs). The NLRs (NACHT (NAIP (neuronal apoptosis inhibitor protein), C2TA (MHC class 2 transcription activator), HET-E (incompatibility locus protein from Podospora anserina) and TP1 (telomerase-associated protein) and Leucine-Rich Repeat (LRR) domain containing proteins) relate to a large family of cytosolic innate receptors, involved in detection of intracellular pathogens and endogenous byproducts of tissue injury. These receptors may recognize pathogen-associated molecular patterns (PAMPs) and/or danger-associated molecular patterns (DAMPs), activating host responses against pathogen infection and cellular stress. NLR-driven downstream signals trigger a number of signaling circuitries, which may either initiate the formation of inflammasomes and/or activate nuclear factor κB (NF-κB), stress kinases, interferon response factors (IRFs), inflammatory caspases and autophagy. Disruption of those signals may lead to a number of pro-inflammatory conditions, eventually promoting the onset of human malignancies. In this review, we describe the structures and functions of the most well-defined NLR proteins and highlight their association and biological impact on a diverse number of cancers.

The MC4 receptor agonist RO27-3225 inhibits NLRP1-dependent neuronal pyroptosis via the ASK1/JNK/p38 MAPK pathway in a mouse model of intracerebral haemorrhage

BACKGROUND AND PURPOSE

Inflammasome-mediated pyroptosis is an important neuronal cell death mechanism. Previous studies reported that activation of melanocortin MC₄ receptor exerted neuroprotection in several neurological diseases. Here, we have investigated the role of MC₄ receptor activation with RO27-3225 in suppressing neuronal pyroptosis after experimental intracerebral haemorrhage (ICH) and the underlying mechanism.

EXPERIMENTAL APPROACH

One hundred and sixty-nine male CD1 mice were used. ICH was induced by injection of bacterial collagenase into the right-side basal ganglia. RO27-3225, a selective agonist of MC₄ receptor, was injected intraperitoneally at 1 hr after ICH. To elucidate the underlying mechanism, we used the specific MC₄ receptor antagonist HS024 and NQDI-1, a specific inhibitor of the apoptosis signalling-regulating kinase 1 (ASK1). Neurological tests, Western blot, Fluoro-Jade C, TUNEL, and immunofluorescence staining were conducted.

KEY RESULTS

Expression of MC₄ receptor and the NOD-like receptor family, pyrin domain containing 1 (NLRP1) inflammasome in brain were increased after ICH. RO27-3225 treatment decreased neuronal pyroptosis and neurobehavioural deficits at 24 and 72 hr after ICH. RO27-3225 reduced the expression of p-ASK1, p-JNK, p-p38 MAPK, NLRP1 inflammasome, cleaved caspase-1, and IL-1β after ICH. HS024 pretreatment prevented the effects of RO27-3225. Similar to RO27-3225, NQDI-1 alone improved neurological functions and down-regulated ASK1/JNK/p38MAPK expression after ICH.

CONCLUSIONS AND IMPLICATIONS

RO27-3225 suppressed NLRP1-dependent neuronal pyroptosis and improved neurological function, possibly mediated by activation of MC₄ receptor and inhibition of ASK1/JNK/p38 MAPK signalling pathways, after experimental ICH in mice. The MC₄ receptor may be a promising therapeutic target for the management of ICH.

Diverging inflammasome signals in tumorigenesis and potential targeting

Inflammasomes are molecular platforms that assemble upon sensing various intracellular stimuli. Inflammasome assembly leads to activation of caspase 1, thereby promoting the secretion of bioactive interleukin-1β (IL-1β) and IL-18 and inducing an inflammatory cell death called pyroptosis. Effectors of the inflammasome efficiently drive an immune response, primarily providing protection against microbial infections and mediating control over sterile insults. However, aberrant inflammasome signalling is associated with pathogenesis of inflammatory and metabolic diseases, neurodegeneration and malignancies. Chronic inflammation perpetuated by inflammasome activation plays a central role in all stages of tumorigenesis, including immunosuppression, proliferation, angiogenesis and metastasis. Conversely, inflammasome signalling also contributes to tumour suppression by maintaining intestinal barrier integrity, which portrays the diverse roles of inflammasomes in tumorigenesis. Studies have underscored the importance of environmental factors, such as diet and gut microbiota, in inflammasome signalling, which in turn influences tumorigenesis. In this Review, we deliver an overview of the interplay between inflammasomes and tumorigenesis and discuss their potential as therapeutic targets.

Functional degradation: A mechanism of NLRP1 inflammasome activation by diverse pathogen enzymes

Inflammasomes are multiprotein platforms that initiate innate immunity by recruitment and activation of caspase-1. The NLRP1B inflammasome is activated upon direct cleavage by the anthrax lethal toxin protease. However, the mechanism by which cleavage results in NLRP1B activation is unknown. In this study, we find that cleavage results in proteasome-mediated degradation of the amino-terminal domains of NLRP1B, liberating a carboxyl-terminal fragment that is a potent caspase-1 activator. Proteasome-mediated degradation of NLRP1B is both necessary and sufficient for NLRP1B activation. Consistent with our functional degradation model, we identify IpaH7.8, a Shigella flexneri ubiquitin ligase secreted effector, as an enzyme that induces NLRP1B degradation and activation. Our results provide a unified mechanism for NLRP1B activation by diverse pathogen-encoded enzymatic activities.

Inflammasomes, Autophagy, and Cell Death: The Trinity of Innate Host Defense against Intracellular Bacteria

Inflammasome activation is an innate host defense mechanism initiated upon sensing pathogens or danger in the cytosol. Both autophagy and cell death are cell autonomous processes important in development, as well as in host defense against intracellular bacteria. Inflammasome, autophagy, and cell death pathways can be activated by pathogens, pathogen-associated molecular patterns (PAMPs), cell stress, and host-derived damage-associated molecular patterns (DAMPs). Phagocytosis and toll-like receptor (TLR) signaling induce reactive oxygen species (ROS), type I IFN, NFκB activation of proinflammatory cytokines, and the mitogen-activated protein kinase cascade. ROS and IFNγ are also prominent inducers of autophagy. Pathogens, PAMPs, and DAMPs activate TLRs and intracellular inflammasomes, inducing apoptotic and inflammatory caspases in a context-dependent manner to promote various forms of cell death to eliminate pathogens. Common downstream signaling molecules of inflammasomes, autophagy, and cell death pathways interact to initiate appropriate measures against pathogens and determine host survival as well as pathological consequences of infection. The integration of inflammasome activation, autophagy, and cell death is central to pathogen clearance. Various pathogens produce virulence factors to control inflammasomes, subvert autophagy, and modulate host cell death in order to evade host defense. This review highlights the interaction of inflammasomes, autophagy, and host cell death pathways in counteracting Burkholderia pseudomallei, the causative agent of melioidosis. Contrasting evasion strategies used by B. pseudomallei, Mycobacterium tuberculosis, and Legionella pneumophila to avoid and dampen these innate immune responses will be discussed.

Polymorphisms in NLRP1 Gene Are Associated with Type 1 Diabetes

OBJECTIVE

The aim of this study was to clarify the association of two single-nucleotide polymorphisms (SNPs) (rs11651270 and rs2670660) in the NLRP1 (NLR family pyrin domain containing 1) gene with type 1 diabetes (T1D) in the Chinese Han population. We hypothesize that mutations in the NLRP1 gene may affect the susceptibility to T1D.

MATERIALS AND METHODS

A case control study was designed, and participants fulfilling the diagnostic criteria of classical T1D as well as nondiabetic controls were enrolled in the study. The polymorphisms rs11651270 and rs2670660 were genotyped by polymerase chain reaction (PCR) and Sanger sequencing. Chi-squared test and logistic regression analysis were performed to compare the distributions of the allele and genotype between cases and controls. Kruskal-Wallis one-way ANOVA was used to compare the characteristics of different genotypes in participants with T1D.

RESULTS

A total of 510 participants with classical T1D as well as 531 nondiabetic controls were enrolled in the study. The two groups were matched in sex (p = 0.418). The age (p < 0.001) and BMI (p < 0.001) were significantly lower in cases compared to controls. Significantly higher values were observed for fasting plasma glucose (FPG) (p < 0.001) and 2 h postprandial plasma glucose (PPG) (p < 0.001) in individuals with T1D. Regarding the allelic model, the minor allele C of rs11651270 was significantly associated with lower risk of T1D compared with the T allele (OR = 0.714, 95% CI = 0.579-0.882). Both rs11651270 and rs2670660 polymorphisms were associated with T1D in the Chinese Han population under a dominant model (OR = 0.648, 95% CI = 0.503-0.834 and OR = 0.716, 95% CI = 0.549-0.934, respectively) and an overdominant model (OR = 0.663, 95% CI = 0.511-0.860 and OR = 0.711, 95% CI = 0.541-0.935, respectively). Additionally, the polymorphism rs11651270 was also related to T1D in an additive model (OR = 0.719, 95% CI = 0.583-0.887). Most importantly, when we analyzed the clinical characteristics of T1D individuals with different genotypes, we found that the age of onset with the TT genotype at rs11651270 was younger than those with the other two genotypes (p = 0.001).

CONCLUSIONS

SNPs in the NLRP1 gene were associated with T1D, as well as the age of onset in the Chinese Han T1D individuals. Our study indicated that the NLRP1 gene might play a pivotal role in the etiopathogenesis of T1D and could be applied to genetic screening of T1D in the Chinese Han population.

Inflammasomes: Pandora's box for sepsis

Sepsis was known to ancient Greeks since the time of great physician Hippocrates (460-377 BC) without exact information regarding its pathogenesis. With time and medical advances, it is now considered as a condition associated with organ dysfunction occurring in the presence of systemic infection as a result of dysregulation of the immune response. Still with this advancement, we are struggling for the development of target-based therapeutic approach for the management of sepsis. The advancement in understanding the immune system and its working has led to novel discoveries in the last 50 years, including different pattern recognition receptors. Inflammasomes are also part of these novel discoveries in the field of immunology which are <20 years old in terms of their first identification. They serve as important cytosolic pattern recognition receptors required for recognizing cytosolic pathogens, and their pathogen-associated molecular patterns play an important role in the pathogenesis of sepsis. The activation of both canonical and non-canonical inflammasome signaling pathways is involved in mounting a proinflammatory immune response via regulating the generation of IL-1β, IL-18, IL-33 cytokines and pyroptosis. In addition to pathogens and their pathogen-associated molecular patterns, death/damage-associated molecular patterns and other proinflammatory molecules involved in the pathogenesis of sepsis affect inflammasomes and vice versa. Thus, the present review is mainly focused on the inflammasomes, their role in the regulation of immune response associated with sepsis, and their targeting as a novel therapeutic approach.

The inflammasome in leprosy skin lesions: an immunohistochemical evaluation

Objective

Leprosy is a chronic infectious disease presenting with a spectrum of clinical manifestations that correspond to the type of immune response that develops in the host. Factors that may be involved in this process include inflammasomes, cytosolic proteins responsible for the activation of caspase 1, IL-1β and IL-18 secretion, and induction of a type of death called pyroptosis.

Patients and methods

We evaluated the expression of inflammasome markers (nucleotide-binding oligomerization domain-like receptor containing pyrin domain 1 [NLRP1], nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 [NLRP3], caspase 1, IL-1β, and IL-18) by immunohistochemistry in 43 samples of skin lesions of leprosy patients from the groups indeterminate (I) leprosy (13 patients), tuberculoid (TT) leprosy (15 patients), and lepromatous leprosy (LL; 15 patients).

Results

The evaluated markers were most upregulated in LL lesions, followed by lesions of TT leprosy and I leprosy. Differences were statistically significant between the I leprosy and LL leprosy forms and between the I leprosy and TT leprosy forms. Positive and significant correlations were found between IL-18 and caspase 1 in LL (r=0.7516, P=0.0012) and TT leprosy (r=0.7366, P=0.0017). In I leprosy, correlations were detected between caspase 1 and IL-1β (r=0.6412, P=0.0182), NLRP1 and IL-18 (r=0.5585, P=0.473), NLRP3 and IL-18 (r=0.6873, P=0.0094), and NLRP1 and NLRP3 (r=0.8040, P=0.0009).

Conclusion

The expression of inflammasome markers in LL lesions indicates the ineffectiveness of this protein complex in controlling the infection. Caspase 1 may be involved in the pyroptotic cell death in the lepromatous form of the disease. Inflammasomes may act together in the initial phase of I leprosy; this phenomenon may influence the clinical outcome of the disease.

Oxidized hemoglobin forms contribute to NLRP3 inflammasome-driven IL-1β production upon intravascular hemolysis

Damage associated molecular patterns (DAMPs) are released form red blood cells (RBCs) during intravascular hemolysis (IVH). Extracellular heme, with its pro-oxidant, pro-inflammatory and cytotoxic effects, is sensed by innate immune cells through pattern recognition receptors such as toll-like receptor 4 and nucleotide-binding domain and leucine rich repeat containing family, pyrin domain containing 3 (NLRP3), while free availability of heme is strictly controlled. Here we investigated the involvement of different hemoglobin (Hb) forms in hemolysis-associated inflammatory responses. We found that after IVH most of the extracellular heme molecules are localized in oxidized Hb forms. IVH was associated with caspase-1 activation and formation of mature IL-1β in plasma and in the liver of C57BL/6 mice. We showed that ferrylHb (FHb) induces active IL-1β production in LPS-primed macrophages in vitro and triggered intraperitoneal recruitment of neutrophils and monocytes, caspase-1 activation and active IL-1β formation in the liver of C57BL/6 mice. NLRP3 deficiency provided a survival advantage upon IVH, without influencing the extent of RBC lysis or the accumulation of oxidized Hb forms. However, both hemolysis-induced and FHb-induced pro-inflammatory responses were largely attenuated in Nlrp3^-/- mice. Taken together, FHb is a potent trigger of NLRP3 activation and production of IL-1β in vitro and in vivo, suggesting that FHb may contribute to hemolysis-induced inflammation. Identification of RBC-derived DAMPs might allow us to develop new therapeutic approaches for hemolytic diseases.

Characterization of an NLRP1 Inflammasome from Zebrafish Reveals a Unique Sequential Activation Mechanism Underlying Inflammatory Caspases in Ancient Vertebrates

NLRP1 inflammasome is one of the best-characterized inflammasomes in humans and other mammals. However, the existence of this inflammasome in nonmammalian species remains poorly understood. In this study, we report the molecular and functional identification of an NLRP1 homolog, Danio rerio NLRP1 (DrNLRP1) from a zebrafish (D. rerio) model. This DrNLRP1 possesses similar structural architecture to mammalian NLRP1s. It can trigger the formation of a classical inflammasome for the activation of zebrafish inflammatory caspases (D. rerio Caspase [DrCaspase]-A and DrCaspase-B) and maturation of D. rerio IL-1β in a D. rerio ASC (DrASC)-dependent manner. In this process, DrNLRP1 promotes the aggregation of DrASC into a filament with DrASC^CARD core and DrASC^PYD cluster. The assembly of DrNLRP1 inflammasome depends on the CARD-CARD homotypic interaction between DrNLRP1 and DrASC^CARD core, and PYD-PYD interaction between DrCaspase-A/B and DrASC^PYD cluster. The FIIND domain in DrNLRP1 is necessary for inflammasome assembly. To understand the mechanism of how the two DrCaspases are coordinated in DrNLRP1 inflammasome, we propose a two-step sequential activation model. In this model, the recruitment and activation of DrCaspase-A/B in the inflammasome is shown in an alternate manner, with a preference for DrCaspase-A followed by a subsequent selection for DrCaspase-B. By using morpholino oligonucleotide-based knockdown assays, the DrNLRP1 inflammasome was verified to play important functional roles in antibacterial innate immunity in vivo. These observations demonstrate that the NLRP1 inflammasome originated as early as in teleost fish. This finding not only gives insights into the evolutionary history of inflammasomes but also provides a favorable animal model for the study of NLRP1 inflammasome-mediated immunology and diseases.

Inflammasomes in Tissue Damages and Immune Disorders After Trauma

Trauma remains a leading cause of death worldwide. Hemorrhagic shock and direct injury to vital organs are responsible for early mortality whereas most delayed deaths are secondary to complex pathophysiological processes. These processes result from imbalanced systemic reactions to the multiple aggressions associated with trauma. Trauma results in the uncontrolled local and systemic release of endogenous mediators acting as danger signals [damage-associated molecular patterns (DAMPs)]. Their recognition by the innate immune system triggers a pro-inflammatory immune response paradoxically associated with concomitant immunosuppression. These responses, ranging in intensity from inappropriate to overwhelming, promote the propagation of injuries to remote organs, leading to multiple organ failure and death. Some of the numerous DAMPs released after trauma trigger the assembly of intracellular multiprotein complexes named inflammasomes. Once activated by a ligand, inflammasomes lead to the activation of a caspase. Activated caspases allow the release of mature forms of interleukin-1β and interleukin-18 and trigger a specific pro-inflammatory cell death termed pyroptosis. Accumulating data suggest that inflammasomes, mainly NLRP3, NLRP1, and AIM2, are involved in the generation of tissue damage and immune dysfunction after trauma. Following trauma-induced DAMP(s) recognition, inflammasomes participate in multiple ways in the development of exaggerated systemic and organ-specific inflammatory response, contributing to organ damage. Inflammasomes are involved in the innate responses to traumatic brain injury and contribute to the development of acute respiratory distress syndrome. Inflammasomes may also play a role in post-trauma immunosuppression mediated by dysregulated monocyte functions. Characterizing the involvement of inflammasomes in the pathogenesis of post-trauma syndrome is a key issue as they may be potential therapeutic targets. This review summarizes the current knowledge on the roles of inflammasomes in trauma.

Inhibition of ER stress-related IRE1α/CREB/NLRP1 pathway promotes the apoptosis of human chronic myelogenous leukemia cell

Endoplasmic reticulum (ER) stress is induced in chronic myelogenous leukemia (CML) cells. As an important sensor of ER stress, inositol-requiring protein-1α (IRE1α) promotes the survival of acute myeloid leukemia. NLRP1 inflammasome activation promotes metastatic melanoma growth and that IRE1α can increase NLRP1 inflammasome gene expression. This study aimed to investigate the role and molecular mechanism of IRE1α in CML cell growth. We found that overexpression of IRE1α or NLRP1 significantly promoted the proliferation and decreased the apoptosis of CML cells, whereas downregulation of these two genes showed the opposite effects. 4-phenylbutyric acid (4-PBA), an ER stress inhibitor, reduced the expression of IRE1α and NLRP1. IRE1α elevated NLRP1 expression via cAMP responsive element binding protein (CREB) phosphorylation. NLRP1 inflammasome was activated in CML cells and its activation partly reversed ER stress inhibitor-induced cell apoptosis. Furthermore, inhibition of IRE1α/NLRP1 pathway sensitized CML cells to imatinib-mediated apoptosis. Additionally, IRE1α expression was elevated and NLRP1 inflammasome was activated in primary cells from CML patients. Downregulation of IRE1α or NLRP1 suppressed the proliferation and elevated the apoptosis of primary CML cells. Collectively, this study demonstrated that the IRE1α/CREB/NLRP1 pathway contributes to the progression of CML and the development of imatinib resistance. Hence, targeting ER stress-related IRE1α expression or NLRP1 inflammasome activation may block CML development.

Control of Inflammasome Activation by Phosphorylation

Inflammasomes are cytosolic protein complexes composed of innate immune sensors, the adaptor protein ASC, and the cysteine protease caspase-1. In response to microbial infection or 'danger signals', inflammasomes play critical roles in host defense or contribute to the pathogenesis of various inflammatory diseases. Recent studies have provided abundant evidence for a vital role of phosphorylation in the regulation of inflammasome assembly and activation. This review integrates previous observations and discoveries for inflammasome regulation by protein phosphorylation with the most recent findings. Additionally, the timely application and clinical prospects in the treatment of inflammatory diseases, by targeting related protein kinases or phosphatases, are also discussed.

Inflammasomes in livestock and wildlife: Insights into the intersection of pathogens and natural host species

The inflammasome serves as a mechanism by which the body senses damage or danger. These multiprotein complexes form in the cytosol of myeloid, epithelial and potentially other cell types to drive caspase-1 cleavage and the secretion of the pro-inflammatory cytokines IL-1β and IL-18. Different types of inflammasomes, centered on (and named after) their cytosolic NLRs, respond to signals from bacteria, fungi, and viruses, as well as "sterile inflammatory" triggers. Despite the large body of research accumulated on rodent and human inflammasomes over the past 15 years, only recently have studies expanded to consider the role of inflammasomes in veterinary and wildlife species. Due to the key role of inflammasomes in mediating inflammatory responses observed in humans and rodents, characterization of the similarities and differences between humans/rodents and veterinary species is required to identify genetic and evolutionary influences on disease responses and to develop therapeutic candidates for use in veterinary inflammatory syndromes. Here, we summarize recent findings on inflammasomes in swine, cattle, dogs, bats, small ruminants, and birds. We describe current gaps in our knowledge and highlight promising areas for future research.

PYNOD reduces microglial inflammation and consequent neurotoxicity upon lipopolysaccharides stimulation

PYNOD, a nod-like receptors (NLR)-like protein, was indicated to inhibit NF-κB activation, caspase-1-mediated interleukin (IL)-1β release and cell apoptosis in a dose-dependent manner. Exogenous addition of recombinant PYNOD to mixed glial cultures may suppress caspase-1 activation and IL-1β secretion induced by Aβ. However, to the best of our knowledge, there no study has focused on the immunoregulatory effects of PYNOD specifically in microglia. The present study aimed to explore the roles of PYNOD involved in the lipopolysaccharides (LPS)-induced microglial inflammation and consequent neurotoxicity. Murine microglial BV-2 cells were transfected with pEGFP-C2-PYNOD (0–5.0 µg/ml) for 24 h and incubated with or without LPS (1 µg/ml) for a further 24 h. Cell viability was determined using MTT assay and the secretion of nitric oxide (NO), IL-1β and caspase-1 was measured using the Griess method or ELISA. Protein expression levels of NF-κB p65 and inducible nitric oxide synthase (iNOS) were detected by immunofluorescent staining and/or western blot analysis. Co-culture of BV-2 cells with human neuroblastoma cell line SK-N-SH was performed in Transwell plates and the cell viability and apoptosis (using flow cytometry) of SK-N-SH cells were determined. Results indicated that PYNOD overexpression inhibited NO secretion and iNOS protein expression induced by LPS in BV-2 cells, with no detectable cytotoxicity. PYNOD overexpression also reduced the secretion of IL-1β and caspase-1 from BV-2 cells upon LPS stimulation. These effects were dose-dependent. Additionally, PYNOD overexpression prevented LPS-induced nuclear translocation of NF-κB p65 in BV-2 cells. The growth-inhibitory and apoptosis-promoting effects of BV-2 cells towards SK-N-SH cells were alleviated as a result of PYNOD overexpression. In conclusion, PYNOD may mitigate microglial inflammation and consequent neurotoxicity.

HIV replication is associated to inflammasomes activation, IL-1β, IL-18 and caspase-1 expression in GALT and peripheral blood

BACKGROUND

Human immunodeficiency virus (HIV) promotes an inflammatory process, leading to the progressive loss of the functional capacity of the immune system. The HIV infection induces alterations in several tissues, but mainly in the gut-associated lymphoid tissue (GALT). However, the degree of GALT deterioration varies among infected individuals. In fact, it has been shown that HIV-controllers, who spontaneously control viral replication, exhibit a lower inflammatory response, and a relative normal frequency and function of most of the immune cells. Inflammasomes are molecular complexes involved in the inflammatory response, being NLRP1, NLRP3, NLRC4, AIM2 and Pyrin inflammasomes, the best characterized so far. These complexes regulate the maturation of cytokines of the IL-1 family, including IL-1β and IL-18. These cytokines have been associated with immune activation and expansion of HIV target cells, promoting viral replication. Interesting, some reports indicate that HIV induces the activation of the NLRP3 inflammasome, but the role of this, and other inflammasomes during HIV infection, especially in GALT, remains unclear.

OBJECTIVE

To compare the relative expression of inflammasome components and the proinflammatory response related to their activity, between HIV-progressors and HIV-controllers.

METHODS

GALT biopsies and peripheral blood mononuclear cells (PBMCs) from 15 HIV-controllers and 15 HIV-progressors were obtained. The relative expression of the following inflammasome components were evaluated by RT-PCR: NLRP3, NLRC4, NLRP1, AIM2, ASC, Caspase-1, IL-1β and IL-18. In addition, plasma concentration of IL-18 was evaluated as an indicator of baseline proinflammatory status. Finally, in supernatants of PBMCs in vitro stimulated with inflammasome agonists, the concentrations of IL-1β and IL-18 were quantified by ELISA.

RESULTS

HIV-progressors exhibited higher expression of IL-1β, IL-18 and caspase-1 genes in GALT and PBMCs compared with HIV-controllers. In addition, HIV-progressors had also increased expression of ASC in PBMCs. When plasma levels were evaluated, IL-18 was increased in HIV-progressors. Interesting, these patients also showed an increased production of IL-1β in supernatants of PBMCs stimulated in vitro with the agonists of AIM2, NLRP1 and NLRC4 inflammasomes. Finally, the expression of caspase-1, NLRP1, IL-1β and IL-18 in GALT or peripheral blood was correlated with CD4+ T-cell count and viral load.

CONCLUSION

Our results suggest that during HIV-infection, the required signals to induce the expression of different components of the inflammasomes are produced, both in GALT and in periphery. The activation of these molecular complexes could increase the number of target cells, favoring HIV replication and cell death, promoting the disease progression.

Expression profile of pattern recognition receptors in skeletal muscle of SOD1(G93A) amyotrophic lateral sclerosis (ALS) mice and sporadic ALS patients

AIMS

Amyotrophic lateral sclerosis (ALS) is characterized by degeneration of motoneurons and progressive muscle wasting. Inflammatory processes, mediated by non-neuronal cells, such as glial cells, are known to contribute to disease progression. Inflammasomes consist of pattern recognition receptors (PRRs), apoptosis-associated speck-like protein (ASC) and caspase 1 and are essential for interleukin (IL) processing and a rapid immune response after tissue damage. Recently, we described inflammasome activation in the spinal cord of ALS patients and in SOD1^(G93A) ALS mice. Since pathological changes in the skeletal muscle are early events in ALS, we hypothesized that PRRs might be abnormally expressed in muscle fibre degeneration.

METHODS

Western blot analysis, real-time PCR and immunohistochemistry were performed with muscle tissue from presymptomatic and early-symptomatic male SOD1^(G93A) mice and with muscle biopsies of control and sporadic ALS (sALS) patients. Analysed PRRs include nucleotide-binding oligomerization domain-like (NOD-like) receptor protein 1 (NLRP1), NLR protein 3 (NLRP3), NLR family CARD domain-containing 4 (NLRC4) and absent in melanoma 2. Additionally, expression levels of ASC, caspase 1, interleukin 1 beta (IL1β) and interleukin 18 (IL18) were evaluated.

RESULTS

Expression of PRRs and ASC was detected in murine and human tissue. The PRR NLRC4, caspase 1 and IL1β were significantly elevated in denervated muscle of SOD1^(G93A) mice and sALS patients. Furthermore, levels of caspase 1 and IL1β were already increased in presymptomatic animals.

CONCLUSION

Our findings suggest that increased inflammasome activation may be involved in skeletal muscle pathology in ALS. Furthermore, elevated levels of NLRC4, caspase 1 and IL1β reflect early changes in the skeletal muscle and may contribute to the denervation process.