Decreased expression of the NLRP6 inflammasome is associated with increased intestinal permeability and inflammation in obesity with type 2 diabetes

BACKGROUND

Obesity-associated dysfunctional intestinal permeability contributes to systemic chronic inflammation leading to the development of metabolic diseases. The inflammasomes constitute essential components in the regulation of intestinal homeostasis. We aimed to determine the impact of the inflammasomes in the regulation of gut barrier dysfunction and metabolic inflammation in the context of obesity and type 2 diabetes (T2D).

METHODS

Blood samples obtained from 80 volunteers (n = 20 normal weight, n = 21 OB without T2D, n = 39 OB with T2D) and a subgroup of jejunum samples were used in a case-control study. Circulating levels of intestinal damage markers and expression levels of inflammasomes as well as their main effectors (IL-1β and IL-18) and key inflammation-related genes were analyzed. The impact of inflammation-related factors, different metabolites and Akkermansia muciniphila in the regulation of inflammasomes and intestinal integrity genes was evaluated. The effect of blocking NLRP6 by using siRNA in inflammation was also studied.

RESULTS

Increased circulating levels (P < 0.01) of the intestinal damage markers endotoxin, LBP, and zonulin in patients with obesity decreased (P < 0.05) after weight loss. Patients with obesity and T2D exhibited decreased (P < 0.05) jejunum gene expression levels of NLRP6 and its main effector IL18 together with increased (P < 0.05) mRNA levels of inflammatory markers. We further showed that while NLRP6 was primarily localized in goblet cells, NLRP3 was localized in the intestinal epithelial cells. Additionally, decreased (P < 0.05) mRNA levels of Nlrp1, Nlrp3 and Nlrp6 in the small intestinal tract obtained from rats with diet-induced obesity were found. NLRP6 expression was regulated by taurine, parthenolide and A. muciniphila in the human enterocyte cell line CCL-241. Finally, a significant decrease (P < 0.01) in the expression and release of MUC2 after the knockdown of NLRP6 was observed.

CONCLUSIONS

The increased levels of intestinal damage markers together with the downregulation of NLRP6 and IL18 in the jejunum in obesity-associated T2D suggest a defective inflammasome sensing, driving to an impaired epithelial intestinal barrier that may regulate the progression of multiple obesity-associated comorbidities.

Transcriptome and Pathway Analysis Reveals that Adipose-derived Stem Cells Target Inflammatory Factors and Delay the Progression of Diabetic Liver Disease

BACKGROUND

Diabetic liver disease is one of the main complications that leads to the aggravation of diabetes, but it has not received sufficient attention. This study aimed to provide a better understanding of the altered molecular networks in in diabetic rats with liver damage after stem cell therapy. To a certain extent, our research would be instructive, since almost no studies of this kind have been performed on patients with diabetic liver disease after stem cell therapy.

METHODS

Streptozotocin-induced diabetic rats were treated with adipose-derived stem cells. RNA-Seq analysis was performed on the liver tissues of these animals, and key pathway factors were further identified and validated.

RESULTS

RNA-Seq analysis revealed numerous affected signaling pathways and functional categories. The results showed that the network of dual specificity phosphatase 1 (DUSP1), an oxidative stress-related gene, was prominently activated in the liver after stem cell therapy, and the enrichment of genes associated with liver damage, steatosis and fibrosis was also detected. The extracellular regulated protein kinase (ERK)/signal transducer and activator of transcription 3 (STAT3) signaling pathway may be involved in this process by regulating the nucleotide-binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome.

CONCLUSIONS

These data provide novel insights into liver biology, suggest common alterations in the molecular networks during diabetic liver damage, and show the advantages of stem cell therapy, indicating its further application potential for early treatment of diabetic liver damage and delaying the progression of liver fibrosis in the later stage.

Inflammasome activation by viral infection: mechanisms of activation and regulation

Viral diseases are the most common problems threatening human health, livestock, and poultry industries worldwide. Viral infection is a complex and competitive dynamic biological process between a virus and a host/target cell. During viral infection, inflammasomes play important roles in the host and confer defense mechanisms against the virus. Inflammasomes are polymeric protein complexes and are considered important components of the innate immune system. These immune factors recognize the signals of cell damage or pathogenic microbial infection after activation by the canonical pathway or non-canonical pathway and transmit signals to the immune system to initiate the inflammatory responses. However, some viruses inhibit the activation of the inflammasomes in order to replicate and proliferate in the host. In recent years, the role of inflammasome activation and/or inhibition during viral infection has been increasingly recognized. Therefore, in this review, we describe the biological properties of the inflammasome associated with viral infection, discuss the potential mechanisms that activate and/or inhibit NLRP1, NLRP3, and AIM2 inflammasomes by different viruses, and summarize the reciprocal regulatory effects of viral infection on the NLRP3 inflammasome in order to explore the relationship between viral infection and inflammasomes. This review will pave the way for future studies on the activation mechanisms of inflammasomes and provide novel insights for the development of antiviral therapies.

Pyroptosis and Sarcopenia: Frontier Perspective of Disease Mechanism

With global ageing, sarcopenia, as an age-related disease, has brought a heavy burden to individuals and society. Increasing attention has been given to further exploring the morbidity mechanism and intervention measures for sarcopenia. Pyroptosis, also known as cellular inflammatory necrosis, is a kind of regulated cell death that plays a role in the ageing progress at the cellular level. It is closely related to age-related diseases such as cardiovascular diseases, Alzheimer’s disease, osteoarthritis, and sarcopenia. In the process of ageing, aggravated oxidative stress and poor skeletal muscle perfusion in ageing muscle tissues can activate the nod-like receptor (NLRP) family to trigger pyroptosis. Chronic inflammation is a representative characteristic of ageing. The levels of inflammatory factors such as TNF-α may activate the signaling pathways of pyroptosis by the NF-κB-GSDMD axis, which remains to be further studied. Autophagy is a protective mechanism in maintaining the integrity of intracellular organelles and the survival of cells in adverse conditions. The autophagy of skeletal muscle cells can inhibit the activation of the pyroptosis pathway to some extent. A profound understanding of the mechanism of pyroptosis in sarcopenia may help to identify new therapeutic targets in the future. This review article focuses on the role of pyroptosis in the development and progression of sarcopenia.

Modulation of TLR/NF-κB/NLRP Signaling by Bioactive Phytocompounds: A Promising Strategy to Augment Cancer Chemotherapy and Immunotherapy

Background

Tumors often progress to a more aggressive phenotype to resist drugs. Multiple dysregulated pathways are behind this tumor behavior which is known as cancer chemoresistance. Thus, there is an emerging need to discover pivotal signaling pathways involved in the resistance to chemotherapeutic agents and cancer immunotherapy. Reports indicate the critical role of the toll-like receptor (TLR)/nuclear factor-κB (NF-κB)/Nod-like receptor pyrin domain-containing (NLRP) pathway in cancer initiation, progression, and development. Therefore, targeting TLR/NF-κB/NLRP signaling is a promising strategy to augment cancer chemotherapy and immunotherapy and to combat chemoresistance. Considering the potential of phytochemicals in the regulation of multiple dysregulated pathways during cancer initiation, promotion, and progression, such compounds could be suitable candidates against cancer chemoresistance.

Objectives

This is the first comprehensive and systematic review regarding the role of phytochemicals in the mitigation of chemoresistance by regulating the TLR/NF-κB/NLRP signaling pathway in chemotherapy and immunotherapy.

Methods

A comprehensive and systematic review was designed based on Web of Science, PubMed, Scopus, and Cochrane electronic databases. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed to include papers on TLR/NF-κB/NLRP and chemotherapy/immunotherapy/chemoresistance by phytochemicals.

Results

Phytochemicals are promising multi-targeting candidates against the TLR/NF-κB/NLRP signaling pathway and interconnected mediators. Employing phenolic compounds, alkaloids, terpenoids, and sulfur compounds could be a promising strategy for managing cancer chemoresistance through the modulation of the TLR/NF-κB/NLRP signaling pathway. Novel delivery systems of phytochemicals in cancer chemotherapy/immunotherapy are also highlighted.

Conclusion

Targeting TLR/NF-κB/NLRP signaling with bioactive phytocompounds reverses chemoresistance and improves the outcome for chemotherapy and immunotherapy in both preclinical and clinical stages.

Molecular Docking and Dynamics Simulations Studies of a Dataset of NLRP3 Inflammasome Inhibitors

BACKGROUND

The organism's defense against aggressive agents is performed by the innate immune system, via activation of pattern-recognition receptors (PRRs). Initially, these agents are recognized by the immune system, resulting in the inflammatory response that activates the pathogen elimination and tissue repair. Inflammasomes are macromolecules related to the host's response to endo or exogenous aggressive agents. Thus, inflammation mediated by inflammasomes plays an important role in the pathogenesis of diseases, such as neurodegenerative disorders, autoimmune diseases, and type 2 diabetes, justifying their attractiveness as drug targets. One of the most important tasks remains in the ATPase nucleotide-binding oligomerization domain nucleotide-binding domain leucine-rich repeat-containing receptors protein 3 (NLRP3), in which the blocking of its oligomerization is related to the functional inhibition of inflammasomes. Here, we performed molecular docking and dynamics simulations for NP3-146, an analog of MCC950, and to obtain information about the complex stability and main interactions with amino acid residues from NLRP3.

METHODS

Using the crystalized structure recently deposited in the protein data bank (7alv), molecular docking in GOLD software and Molecular dynamics simulations in GROMACS software were performed, to generate the RMSD, RMSF, Rg, SASA, and H-bond plots.

RESULTS

The results of RMSD, RMSF, Rg, SASA, and H-bond plots of both complexes confirmed the stability at the active site. Besides, the analyses of the most stable conformation showed that the main interactions are performed with Ala227, Ala228, Pro352, Ile411, Phe575, and Arg578 residues.

CONCLUSION

This report confirmed the stability of NP3-146, similar to the know inhibitor MCC950, and provides various information useful to design NLRP3 inhibitors.

NOD2 and reproduction-associated NOD-like receptors have been lost during the evolution of pangolins

NOD-like receptors (NLRs) are sensors of pathogen-associated molecular patterns with critical roles in the control of immune responses and programmed cell death. Recent studies have revealed inter-species differences in mammalian innate immune genes and a particular degeneration of nucleic acid sensing pathways in pangolins, which are currently investigated as potential hosts for zoonotic pathogens. Here, we used comparative genomics to determine which NLR genes are conserved or lost in pangolins and related mammals. We show that NOD2, which is implicated in sensing bacterial muramyl dipeptide and viral RNA, is a pseudogene in pangolins, but not in any other mammalian species investigated. NLRC4 and NAIP are absent in pangolins and canine carnivorans, suggesting convergent loss of cytoplasmic sensing of bacterial flagellin in these taxa. Among NLR family pyrin domain containing proteins (NLRPs), skin barrier-related NLRP10 has been lost in pangolins after the evolutionary divergence from Carnivora. Strikingly, pangolins lack all NLRPs associated with reproduction (germ cells and embryonic development) in other mammals, i.e., NLRP2, 4, 5, 7, 8, 9, 11, 13, and 14. Taken together, our study shows a massive degeneration of NLR genes in pangolins and suggests that these endangered mammals may have unique adaptations of innate immunity and reproductive cell biology.

Evidence That a TRPA1-Mediated Murine Model of Temporomandibular Joint Pain Involves NLRP3 Inflammasome Activation

This study investigates the role of transient receptor potential ankyrin 1 (TRPA1) in murine temporomandibular joint (TMJ) inflammatory hyperalgesia and the influence of the NLR family pyrin domain-containing 3 (NLRP3) inflammasome. Two distinct murine models of TMJ pain and inflammation (zymosan and CFA) were established. Spontaneous pain-like behaviours were observed as unilateral front paw cheek wipes. Ipsilateral cheek blood flow was used as a measure of ongoing inflammation, which, to our knowledge, is a novel approach to assessing real-time inflammation in the TMJ. Joint tissue and trigeminal ganglia were collected for ex vivo investigation. Both zymosan and CFA induced a time-dependent increase in hyperalgesia and inflammation biomarkers. Zymosan induced a significant effect after 4 h, correlating with a significantly increased IL-1β protein expression. CFA (50 µg) induced a more sustained response. The TRPA1 receptor antagonist A967079 significantly inhibited hyper-nociception. The NLRP3 inhibitor MCC950 similarly inhibited hyper-nociception, also attenuating inflammatory markers. In the trigeminal ganglia, CFA-induced CGRP expression showed trends of inhibition by A967079, whilst lba1 immunofluorescence was significantly inhibited by A967079 and MCC950, where the effect of TRPA1 inhibition lasted up to 14 days. Our results show that stimulation of TRPA1 is key to the TMJ pain. However, the inflammasome inhibitor exhibited similar properties in attenuating these pain-like behaviours, in addition to some inflammatory markers. This indicates that in addition to the therapeutic targeting of TRPA1, NLRP3 inhibition may provide a novel therapeutic strategy for TMJ inflammation and pain.

Pathophysiological Implication of Pattern Recognition Receptors in Fetal Membranes Rupture: RAGE and NLRP Inflammasome

Preterm prelabor ruptures of fetal membranes (pPROM) are a pregnancy complication responsible for 30% of all preterm births. This pathology currently appears more as a consequence of early and uncontrolled process runaway activation, which is usually implicated in the physiologic rupture at term: inflammation. This phenomenon can be septic but also sterile. In this latter case, the inflammation depends on some specific molecules called “alarmins” or “damage-associated molecular patterns” (DAMPs) that are recognized by pattern recognition receptors (PRRs), leading to a microbial-free inflammatory response. Recent data clarify how this activation works and which receptor translates this inflammatory signaling into fetal membranes (FM) to manage a successful rupture after 37 weeks of gestation. In this context, this review focused on two PRRs: the receptor for advanced glycation end-products (RAGE) and the NLRP7 inflammasome.

Somatic Mutation of NLRP Genes in Gastric and Colonic Cancers

Nucleotide-binding and leucine-rich repeat protein (NLRP) genes are involved in inflammasome formation that plays a role in inflammation/host defense and cell death. Both cell death and inflammation are crucial for cancer development, but the roles of NLRPs in cancer are partially known. In this study, we analyzed mononucleotide repeats in coding sequences of NLRP1, NLRP2, NLRP4 and NLRP9, and found 1, 1, 1 and 8 frameshift mutation (s) in gastric (GC) and colonic cancers (CRC), respectively. Five of the 32 high microsatellite instability (MSI-H) GCs (15.5%) and 6 of 113 MSI-H CRCs (5.5%) exhibited the frameshift mutations. There was no NLRP frameshift mutations in microsatellite stable (MSS) GCs and CRCs. We also discovered that 2 of 16 CRCs (12.5%) harbored intratumoral heterogeneity (ITH) of the NLRP9 frameshift mutations in one or more areas. In both GC and CRC with MSI-H, NLRP9 expression in NLRP9-mutated cases was significantly lower than that in NLRP9-non-mutated cases. Our data indicate that NLRP9 is altered at multiple levels (frameshift mutation, mutational ITH and loss of expression), which together could contribute to pathogenesis of MSI-H GC and CRC.

The Differential Expression of the Inflammasomes in Adipose Tissue and Colon Influences the Development of Colon Cancer in a Context of Obesity by Regulating Intestinal Inflammation

BACKGROUND

Inflammasomes maintain tissue homeostasis and their altered regulation in the colon, and the adipose tissue (AT) leads to chronic activation of inflammatory pathways promoting colon cancer (CC) development. We aimed to analyze the potential involvement of inflammasomes in obesity-associated CC.

METHODS

Ninety-nine volunteers [61 with obesity (OB) and 38 normoponderal (NP)] further subclassified according to the approved protocol for the diagnosis of CC (58 without CC and 41 with CC) were included in the case-control study.

RESULTS

CC (P<0.01) and obesity (P<0.01) were accompanied by increased mRNA levels of NLRP3, NLRP6, ASC, IL1B and NOD2 in VAT. Contrarily, patients with CC exhibited a downregulation of NLRP6 and IL18 in their colon. Additionally, we revealed that the decreased Nlrp1 (P<0.05), Nlrp3 (P<0.01) and Nlrp6 (P<0.01) mRNA levels in the colon from obese rats significantly increase (P<0.05) after caloric restriction. Adipocyte-conditioned media obtained from subjects with obesity reduced (P<0.01) the mRNA of NLRP3 as well as molecules involved in maintaining the intestinal integrity (MUC2, CLDN1 and TJP1) and the anti-inflammatory factors FGF21, KLF4, and IL33 and in HT-29 cells. We also found that the knockdown of NLRP6 in HT-29 cells significantly upregulated (P<0.05) the mRNA of NLRP1 and NLRP3 and inhibited (P<0.05) the expression levels of MUC2. Finally, we showed that the incubation of HT-29 with Akkermansia muciniphila influence (P<0.05) the inflammasome expression profile as well as intestinal integrity-related genes and aberrant inflammation.

CONCLUSIONS

These findings provide evidence that the downregulated levels of NLRP6 and IL18 in the colon from patients with CC may be responsible for a reduced intestinal-barrier integrity, triggering local inflammation, which in turn acts on the dysfunctional AT in obesity, increasing the expression of different inflammasome components and flaring up a vicious cycle of uncontrollable inflammatory cascades that favours a pro-tumorigenic microenvironment.

ATP-Binding and Hydrolysis in Inflammasome Activation

The prototypical model for NOD-like receptor (NLR) inflammasome assembly includes nucleotide-dependent activation of the NLR downstream of pathogen- or danger-associated molecular pattern (PAMP or DAMP) recognition, followed by nucleation of hetero-oligomeric platforms that lie upstream of inflammatory responses associated with innate immunity. As members of the STAND ATPases, the NLRs are generally thought to share a similar model of ATP-dependent activation and effect. However, recent observations have challenged this paradigm to reveal novel and complex biochemical processes to discern NLRs from other STAND proteins. In this review, we highlight past findings that identify the regulatory importance of conserved ATP-binding and hydrolysis motifs within the nucleotide-binding NACHT domain of NLRs and explore recent breakthroughs that generate connections between NLR protein structure and function. Indeed, newly deposited NLR structures for NLRC4 and NLRP3 have provided unique perspectives on the ATP-dependency of inflammasome activation. Novel molecular dynamic simulations of NLRP3 examined the active site of ADP- and ATP-bound models. The findings support distinctions in nucleotide-binding domain topology with occupancy of ATP or ADP that are in turn disseminated on to the global protein structure. Ultimately, studies continue to reveal how the ATP-binding and hydrolysis properties of NACHT domains in different NLRs integrate with signaling modules and binding partners to control innate immune responses at the molecular level.

Exposure to environmental black carbon exacerbates nasal epithelial inflammation via the reactive oxygen species (ROS)-nucleotide-binding, oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3)-caspase-1-interleukin 1β (IL-1β) pathway

BACKGROUND

Allergic rhinitis(AR) is an increasing challenge to public health worldwide. Exposure to environmental black carbon (BC) is associated with increased risk of allergic rhinitis, but the molecular mechanisms underlying its toxicity have not been fully elucidated. The aims of the present study were therefore to determine the effect of BC on the expression of interleukin 1β (IL-1β) and to investigate the mechanism underlying BC-induced IL-1β production in pollen-sensitized human nasal epithelial cells (hNECs).

METHODS

Nasal mucosal samples collected from 10 patients undergoing nasal surgery were used to isolate and culture epithelial cells as air-liquid interface (ALI) cultures. Cultures exposed to BC ± pollen allergen for 24 hours were assessed for the presence of IL-1β, the production of reactive oxygen species (ROS), and activation of the nucleotide-binding, oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome. Furthermore, the mechanisms underlying BC ± pollen allergen-induced IL-1β in hNECs were evaluated.

RESULTS

Exposure to BC significantly increased the production of IL-1β and ROS and the expression of NLRP3 in hNECs, compared with control, all of which were significantly increased further by exposure to a combination of BC and pollen. Incubation of hNECs with N-acetyl-L-cysteine (NAC) significantly attenuated BC ± pollen-induced expression of ROS, NLRP3, and IL-1β. NLRP3 and Caspase-1 inhibitors (MCC950 and YVAD) significantly inhibited IL-1β expression and NLRP3 activation, but not NLRP3 expression following exposure to BC ± pollen.

CONCLUSION

These findings suggest that exposure to BC and pollen can exaggerate oxidative stress and significantly increase the expression of IL-1β in hNECs, and that this may involve a pathway integrating ROS-NLRP3-Caspase-1-IL-1β signaling.

A Fatal Alliance between Microglia, Inflammasomes, and Central Pain

Microglia are the resident immune cells in the CNS, which survey the brain parenchyma for pathogens, initiate inflammatory responses, secrete inflammatory mediators, and phagocyte debris. Besides, they play a role in the regulation of brain ion homeostasis and in pruning synaptic contacts and thereby modulating neural networks. More recent work shows that microglia are embedded in brain response related to stress phenomena, the development of major depressive disorders, and pain-associated neural processing. The microglia phenotype varies between activated-toxic-neuroinflammatory to non-activated-protective-tissue remodeling, depending on the challenges and regulatory signals. Increased inflammatory reactions result from brain damage, such as stroke, encephalitis, as well as chronic dysfunctions, including stress and pain. The dimension of damage/toxic stimuli defines the amplitude of inflammation, ranging from an on-off event to low but continuous simmering to uncontrollable. Pain, either acute or chronic, involves inflammasome activation at the point of origin, the different relay stations, and the sensory and processing cortical areas. This short review aimed at identifying a sinister role of the microglia-inflammasome platform for the development and perpetuation of acute and chronic central pain and its association with changes in CNS physiology.

The Role of Inflammasomes in Atherosclerosis and Stroke Pathogenesis

Inflammation is a devastating outcome of cerebrovascular diseases (CVD), namely stroke and atherosclerosis. Numerous studies over the decade have shown that inflammasomes play a role in mediating inflammatory reactions post cellular injury occurring after a stroke or a rupture of an atherosclerotic plaque. In view of this, targeting these inflammatory pathways using different pharmacological therapies may improve outcomes in patients with CVD. Here, we review the mechanisms by which inflammasomes drive the pathogenesis of stroke and atherosclerosis. Also, discussed here are the possible treatment strategies available for inhibiting inflammasomes or their up-stream/down-stream mediators.

Schwann cell transplantation exerts neuroprotective roles in rat model of spinal cord injury by combating inflammasome activation and improving motor recovery and remyelination

Inflammasome activation in the traumatic central nervous system (CNS) injuries is responsible for propagation of an inflammatory circuit and neuronal cell death resulting in sensory/motor deficiencies. NLRP1 and NLRP3 are known as activators of inflammasome complex in the spinal cord injury (SCI). In this study, cell therapy using Schwann cells (SCs) was applied for targeting NLRP inflammasome complexes outcomes in the motor recovery. These cells were chosen due to their regenerative roles for CNS injuries. SCs were isolated from sciatic nerves and transplanted to the contusive SCI-induced Wistar rats. NLRP1 and NLRP3 inflammasome complexes and their related pro-inflammatory cytokines were assayed in both mRNA and protein levels. Neuronal cell survival (Nissl staining), motor recovery and myelination (Luxol fast blue/LFB) were also evaluated. The groups were laminectomy, SCI, vehicle and treatment. The treatment group received Schwann cells, and the vehicle group received solvent for the cells. SCI caused increased expressions for both NLRP1 and NLRP3 inflammasome complexes along with their related pro-inflammatory cytokines, all of which were abrogated after administration of SCs (except for IL-18 protein showing no change to the cell therapy). Motor deficits in the hind limb, neuronal cell death and demyelination were also found in the SCI group, which were counteracted in the treatment group. From our findings we conclude promising role for cell therapy with SCs for targeting axonal demyelination and degeneration possibly through attenuation of the activity for inflammasome complexes and related inflammatory circuit.

Application of immobilized ATP to the study of NLRP inflammasomes

The NLRP proteins are a subfamily of the NOD-like receptor (NLR) innate immune sensors that possess an ATP-binding NACHT domain. As the most well studied member, NLRP3 can initiate the assembly process of a multiprotein complex, termed the inflammasome, upon detection of a wide range of microbial products and endogenous danger signals and results in the activation of pro-caspase-1, a cysteine protease that regulates multiple host defense pathways including cytokine maturation. Dysregulated NLRP3 activation contributes to inflammation and the pathogenesis of several chronic diseases, and the ATP-binding properties of NLRPs are thought to be critical for inflammasome activation. In light of this, we examined the utility of immobilized ATP matrices in the study of NLRP inflammasomes. Using NLRP3 as the prototypical member of the family, P-linked ATP Sepharose was determined to be a highly-effective capture agent. In subsequent examinations, P-linked ATP Sepharose was used as an enrichment tool to enable the effective profiling of NLRP3-biomarker signatures with selected reaction monitoring-mass spectrometry (SRM-MS). Finally, ATP Sepharose was used in combination with a fluorescence-linked enzyme chemoproteomic strategy (FLECS) screen to identify potential competitive inhibitors of NLRP3. The identification of a novel benzo[d]imidazol-2-one inhibitor that specifically targets the ATP-binding and hydrolysis properties of the NLRP3 protein implies that ATP Sepharose and FLECS could be applied other NLRPs as well.

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.

What do we know about the inflammasome in humans?

The inflammasome complex is part of the innate immune system, which serves to protect the host against harm from pathogens and damaged cells. It is a term first proposed by Tschopp's group in 2002, with numerous original research articles and reviews published on the topic since. There have been many types of inflammasome identified, but all result in the common pathway of activation of caspases and interleukin 1β along with possible cell death called pyroptosis. Despite a growing body of research investigating the structure and function of the inflammasome in animal models, there is still limited evidence identifying inflammasome components in human physiology and disease. In this review, we explore the molecular structure and mechanism of activation of the inflammasome with a particular focus on inflammasome complexes expressed in humans. Inflammasome components have been identified in several human peripheral and brain tissues using both in vivo and ex vivo work, and the inflammasome complex has been shown to be associated with several genetic and acquired inflammatory and neoplastic disorders. We discuss the strengths and weaknesses of the information available on the inflammasome with an emphasis on the importance of prioritizing work on human tissue. There is a huge demand for more effective treatments for a number of inflammatory and neurodegenerative diseases. Modulation of the inflammasome has been proposed as a novel treatment for several of these diseases and there are currently clinical trials ongoing to test this theory.

Negative regulation of the inflammasome: keeping inflammation under control

In addition to its roles in controlling infection and tissue repair, inflammation plays a critical role in diverse and distinct chronic diseases, such as cancer, metabolic syndrome, and neurodegenerative disorders, underscoring the harmful effect of an uncontrolled inflammatory response. Regardless of the nature of the stimulus, initiation of the inflammatory response is mediated by assembly of a multimolecular protein complex called the inflammasome, which is responsible for the production of inflammatory cytokines, such as interleukin-1β (IL-1β) and IL-18. The different stimuli and mechanisms that control inflammasome activation are fairly well understood, but the mechanisms underlying the control of undesired inflammasome activation and its inactivation remain largely unknown. Here, we review recent advances in our understanding of the molecular mechanisms that negatively regulate inflammasome activation to prevent unwanted activation in the resting state, as well as those involved in terminating the inflammatory response after a specific insult to maintain homeostasis.

Inflammasomes in neuroinflammation and changes in brain function: a focused review

Recent literature has pointed to the existence of inflammasome-mediated inflammatory pathways in central nervous system (CNS) disorders and associated changes in behavior. Neuroinflammation, which is an innate immune response in the CNS against harmful and irritable stimuli such as pathogens and metabolic toxic waste, as well as to chronic mild stress, is mediated by protein complexes known as inflammasomes. Inflammasomes activate pro-inflammatory caspases 1 and 5, which then cleave the precursor forms of pro-inflammatory cytokines IL-1β, IL-18, and IL-33 into their active forms. These pro-inflammatory cytokines have been shown to promote a variety of innate immune processes associated with infection, inflammation, and autoimmunity, and thereby play an instrumental role in the instigation of neuroinflammation during old age and subsequent occurrence of neurodegenerative diseases, cognitive impairment, and dementia. In particular, NLRP inflammasomes may also have a role in the etiologies of depression, Alzheimer's disease (AD) and in metabolic disorders, such as Type II diabetes, obesity and cardiovascular diseases that have been shown to be co-morbid with psychiatric illnesses. It has been reported that while these inflammasomes may be activated through TNF-α dependent pathways, other cytokines, like IFN-γ, may assist in inhibiting their activation and thus delay disease progression. Furthermore, some other cytokines, including IL-6, may not have a direct role in inflammasome-mediated diseases. An array of recent research suggests that NLRP inflammasomes targeted therapies could be used for alleviating neuroinflammation and for treatment of associated psychiatric illnesses, although this still remains a challenge and necessitates further extensive research. This review examines the complex inflammatory signaling pathways involved in the activation of NLRP inflammasomes and the role they play in promoting neuroinflammation and subsequent behavioral changes.

NLRPs, microbiota, and gut homeostasis: unravelling the connection

Within the NOD-like receptor (NLR) family, there are several NLRP (NLR family, pyrin domain-containing) proteins that are involved in the formation of inflammasomes. These multi-protein complexes are a key part of the network of cellular events required for secretion of the pro-inflammatory cytokines IL-1β and IL-18. The NLRP3 inflammasome is the best-characterized member of the family and has recently been implicated in gut homeostasis and determining the severity of inflammation in inflammatory bowel disease (IBD) and inflammation-associated colorectal cancer. This led to the discovery that NLRP6 and NLRP12 also contribute to the maintenance of intestinal homeostasis and modulation of the gut microbiota, which in turn influences the intestine and distant organs. In this review, we bring together the latest data on the potential roles of NLRP family members in gut health and disease and identify the most pressing questions that remain to be answered to further our understanding of human diseases including IBD, inflammation-associated cancers, and metabolic syndromes linked with obesity.

Biochemical and structural aspects of the ATP-binding domain in inflammasome-forming human NLRP proteins

Nucleotide-binding domain and leucine-rich repeat-containing receptors (NLRs) regulate innate immunity by activating inflammatory responses in a variety of biological systems following the recognition of pathogen- or disease-associated molecular patterns. NLRs are characterized by a central nucleotide-binding and oligomerization (NACHT) domain found in P-loop NTPases. In this review, we detail the functional and structural properties of the NACHT domain of a subfamily of NLRs, the NLRPs (NLR containing a pyrin domain), based on previous studies, sequence analysis, homology modeling, and structure predictions. Several NLRPs have been found to regulate inflammatory responses through the assembly of oligomeric caspase 1-activating platforms known as inflammasomes, the 3-dimensional structure of the NLRP NACHT domain has still not been solved. Homology modeling suggests that sequence variability within the NACHT domains of different NLRP family members may alter the topology of the ATP-binding pocket. Based on this finding, we discuss the potential therapeutic prospects aligned with the NACHT domain and the development of selective inhibitors of inflammasome activity.

Trichothecene mycotoxins activate NLRP3 inflammasome through a P2X7 receptor and Src tyrosine kinase dependent pathway

Inflammasome is an intracellular molecular platform of the innate immunity that is a key mediator of inflammation. The inflammasome complex detects pathogens and different danger signals, and triggers cysteine protease caspase-1-dependent processing of pro-inflammatory cytokines IL-1β, and IL-18 in dendritic cells and macrophages. Previously, we have shown that water-damaged building associated trichothecene mycotoxins, including roridin A, trigger IL-1β and IL-18 secretion in human macrophages. However, the molecular basis as well as mechanism behind this trichothecene-induced cytokine secretion has remained uncharacterized. Here, we show that the trichothecene-induced IL-1β secretion is dependent on NLRP3 inflammasome in human primary macrophages. Pharmacological inhibition and small interfering RNA approach showed that the trichothecene-induced NLRP3 inflammasome activation is mediated through ATP-gated P2X7 receptor. Moreover, we show that trichothecene-triggered NLRP3 inflammasome activation is dependent on Src tyrosine kinase activity. In addition, gene silencing of c-Cbl, a negative autophagy-related regulator of c-Src, resulted in enhanced secretion of IL-1β and IL-18 in response to trichothecene mycotoxin stimulation in human macrophages. In conclusion, our results suggest that roridin A, a fungal trichothecene mycotoxin, acts as microbial danger signals that trigger activation of NLRP3 inflammasome through P2X7R and Src tyrosine kinase signaling dependent pathway in human primary macrophages.

ER stress-induced cell death mechanisms

The endoplasmic-reticulum (ER) stress response constitutes a cellular process that is triggered by a variety of conditions that disturb folding of proteins in the ER. Eukaryotic cells have developed an evolutionarily conserved adaptive mechanism, the unfolded protein response (UPR), which aims to clear unfolded proteins and restore ER homeostasis. In cases where ER stress cannot be reversed, cellular functions deteriorate, often leading to cell death. Accumulating evidence implicates ER stress-induced cellular dysfunction and cell death as major contributors to many diseases, making modulators of ER stress pathways potentially attractive targets for therapeutics discovery. Here, we summarize recent advances in understanding the diversity of molecular mechanisms that govern ER stress signaling in health and disease. This article is part of a Special Section entitled: Cell Death Pathways.

Role of innate immunity in diabetes and metabolism: recent progress in the study of inflammasomes

Type 1 diabetes is one of the classical examples of organ- specific autoimmune diseases characterized by lymphocytic infiltration or inflammation in pancreatic islets called 'insulitis'. In contrast, type 2 diabetes has been traditionally regarded as a metabolic disorder with a pathogenesis that is totally different from that of type 1 diabetes. However, recent investigation has revealed contribution of chronic inflammation in the pathogenesis of type 2 diabetes. In addition to type 2 diabetes, the role of chronic inflammation is being appreciated in a wide variety of metabolic disorders such as obesity, metabolic syndrome, and atherosclerosis. In this review, we will cover the role of innate immunity in the pathogenesis of metabolic disorders with an emphasis on NLRP3.