PYPAF1, a PYRIN-containing Apaf1-like protein that assembles with ASC and regulates activation of NF-kappa B

Microglial- neuronal crosstalk in chronic viral infection through mTOR, SPP1/OPN and inflammasome pathway signaling

HIV-infection of microglia and macrophages (MMs) induces neuronal injury and chronic release of inflammatory stimuli through direct and indirect molecular pathways. A large percentage of people with HIV-associated neurologic and psychiatric co-morbidities have high levels of circulating inflammatory molecules. Microglia, given their susceptibility to HIV infection and long-lived nature, are reservoirs for persistent infection. MMs and neurons possess the molecular machinery to detect pathogen nucleic acids and proteins to activate innate immune signals. Full activation of inflammasome assembly and expression of IL-1β requires a priming event and a second signal. Many studies have demonstrated that HIV infection alone can activate inflammasome activity. Interestingly, secreted phosphoprotein-1 (SPP1/OPN) expression is highly upregulated in the CNS of people infected with HIV and neurologic dysfunction. Interestingly, all evidence thus far suggests a protective function of SPP1 signaling through mammalian target of rapamycin (mTORC1/2) pathway function to counter HIV-neuronal injury. Moreover, HIV-infected mice knocked down for SPP1 show by neuroimaging, increased neuroinflammation compared to controls. This suggests that SPP1 uses unique regulatory mechanisms to control the level of inflammatory signaling. In this mini review, we discuss the known and yet-to-be discovered biological links between SPP1-mediated stimulation of mTOR and inflammasome activity. Additional new mechanistic insights from studies in relevant experimental models will provide a greater understanding of crosstalk between microglia and neurons in the regulation of CNS homeostasis.

The Role of the NLRP3 Inflammasome in the Molecular and Biochemical Mechanisms of Cervical Ripening: A Comprehensive Review

The uterine cervix is one of the key factors involved in ensuring a proper track of gestation and labor. At the end of the gestational period, the cervix undergoes extensive changes, which can be summarized as a transformation from a non-favorable cervix to one that is soft and prone to dilation. During a process called cervical ripening, fundamental remodeling of the cervical extracellular matrix (ECM) occurs. The cervical ripening process is a derivative of many interlocking and mutually driving biochemical and molecular pathways under the strict control of mediators such as inflammatory cytokines, nitric oxide, prostaglandins, and reactive oxygen species. A thorough understanding of all these pathways and learning about possible triggering factors will allow us to develop new, better treatment algorithms and therapeutic goals that could protect women from both dysfunctional childbirth and premature birth. This review aims to present the possible role of the NLRP3 inflammasome in the cervical ripening process, emphasizing possible mechanisms of action and regulatory factors.

EEBR induces Caspase-1-dependent pyroptosis through the NF-κB/NLRP3 signalling cascade in non-small cell lung cancer

Lung cancer is a leading cause of cancer-related deaths worldwide. Recent studies have identified pyroptosis, a type of programmed cell death, as a critical process in the development and progression of lung cancer. In this study, we investigated the effect of EEBR, a new compound synthesized by our team, on pyroptosis in non-small cell lung cancer cells (NSCLC) and the underlying molecular mechanisms. Our results demonstrated that EEBR significantly reduced the proliferation and metastasis of NSCLC cells in vitro. Moreover, EEBR-induced pyroptosis in NSCLC cells, as evidenced by cell membrane rupture, the release of cytokines such as interleukin-18 and interleukin-1 beta and the promotion of Gasdermin D cleavage in a Caspase-1-dependent manner. Furthermore, EEBR promoted the nuclear translocation of NF-κB and upregulated the protein level of NLRP3. Subsequent studies revealed that EEBR-induced pyroptosis was suppressed by the inhibition of NF-κB. Finally, EEBR effectively suppressed the growth of lung cancer xenograft tumours by promoting NSCLC pyroptosis in animal models. Taken together, our findings suggest that EEBR induces Caspase-1-dependent pyroptosis through the NF-κB/NLRP3 signalling cascade in NSCLC, highlighting its potential as a candidate drug for NSCLC treatment.

Intricate confrontation: Research progress and application potential of TRIM family proteins in tumor immune escape

BACKGROUND

Tripartite motif (TRIM) family proteins have more than 80 members and are widely found in various eukaryotic cells. Most TRIM family proteins participate in the ubiquitin-proteasome degradation system as E3-ubiquitin ligases; therefore, they play pivotal regulatory roles in the occurrence and development of tumors, including tumor immune escape. Due to the diversity of functional domains of TRIM family proteins, they can extensively participate in multiple signaling pathways of tumor immune escape through different substrates. In current research and clinical contexts, immune escape has become an urgent problem. The extensive participation of TRIM family proteins in curing tumors or preventing postoperative recurrence and metastasis makes them promising targets.

AIM OF REVIEW

The aim of the review is to make up for the gap in the current research on TRIM family proteins and tumor immune escape and propose future development directions according to the current progress and problems.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This up-to-date review summarizes the characteristics and biological functions of TRIM family proteins, discusses the mechanisms of TRIM family proteins involved in tumor immune escape, and highlights the specific mechanism from the level of structure-function-molecule-pathway-phenotype, including mechanisms at the level of protein domains and functions, at the level of molecules and signaling pathways, and at the level of cells and microenvironments. We also discuss the application potential of TRIM family proteins in tumor immunotherapy, such as possible treatment strategies for combination targeting TRIM family protein drugs and checkpoint inhibitors for improving cancer treatment.

Canonical and non-canonical functions of NLRP3

BACKGROUND

Since its discovery, NLRP3 is almost never separated from its major role in the protein complex it forms with ASC, NEK7 and Caspase-1, the inflammasome. This key component of the innate immune response mediates the secretion of proinflammatory cytokines IL-1β and IL-18 involved in immune response to microbial infection and cellular damage. However, NLRP3 has also other functions that do not involve the inflammasome assembly nor the innate immune response. These non-canonical functions have been poorly studied. Nevertheless, NLRP3 is associated with different kind of diseases probably through its inflammasome dependent function as through its inflammasome independent functions.

AIM OF THE REVIEW

The study and understanding of the canonical and non-canonical functions of NLRP3 can help to better understand its involvement in various pathologies. In parallel, the description of the mechanisms of action and regulation of its various functions, can allow the identification of new therapeutic strategies.

KEY SCIENTIFIC CONCEPTS OF THE REVIEW

NLRP3 functions have mainly been studied in the context of the inflammasome, in myeloid cells and in totally deficient transgenic mice. However, for several year, the work of different teams has proven that NLRP3 is also expressed in other cell types where it has functions that are independent of the inflammasome. If these studies suggest that NLRP3 could play different roles in the cytoplasm or the nucleus of the cells, the mechanisms underlying NLRP3 non-canonical functions remain unclear. This is why we propose in this review an inventory of the canonical and non-canonical functions of NLRP3 and their impact in different pathologies.

Ox-inflammasome involvement in neuroinflammation

Neuroinflammation plays a crucial role in the onset and the progression of several neuropathologies, from neurodegenerative disorders to migraine, from Rett syndrome to post-COVID 19 neurological manifestations. Inflammasomes are cytosolic multiprotein complexes of the innate immune system that fuel inflammation. They have been under study for the last twenty years and more recently their involvement in neuro-related conditions has been of great interest as possible therapeutic target. The role of oxidative stress in inflammasome activation has been described, however the exact way of action of specific endogenous and exogenous oxidants needs to be better clarified. In this review, we provide the current knowledge on the involvement of inflammasome in the main neuropathologies, emphasizing the importance to further clarify the role of oxidative stress in its activation including the role of mitochondria in inflammasome-induced neuroinflammation.

Involvement of the SIRT1-NLRP3 pathway in the inflammatory response

The silent information regulator 2 homolog 1-NACHT, LRR and PYD domains-containing protein 3 (SIRT1-NLRP3) pathway has a crucial role in regulation of the inflammatory response, and is closely related to the occurrence and development of several inflammation-related diseases. NLRP3 is activated to produce the NLRP3 inflammasome, which leads to activation of caspase-1 and cleavage of pro-interleukin (IL)-1β and pro-IL-18 to their active forms: IL-1β and IL-18, respectively. They are proinflammatory cytokines which then cause an inflammatory response.SIRT1 can inhibit this inflammatory response through nuclear factor erythroid 2-related factor 2 and nuclear factor-kappa B pathways. This review article focuses mainly on how the SIRT1-NLRP3 pathway influences the inflammatory response and its relationship with melatonin, traumatic brain injury, neuroinflammation, depression, atherosclerosis, and liver damage. Video Abstract.

Mitochondrial-derived vesicles in skeletal muscle remodeling and adaptation

Mitochondrial remodeling is crucial to meet the bioenergetic demand to support muscle contractile activity during daily tasks and muscle regeneration following injury. A set of mitochondrial quality control (MQC) processes, including mitochondrial biogenesis, dynamics, and mitophagy, are in place to maintain a well-functioning mitochondrial network and support muscle regeneration. Alterations in any of these pathways compromises mitochondrial quality and may potentially lead to impaired myogenesis, defective muscle regeneration, and ultimately loss of muscle function. Among MQC processes, mitophagy has gained special attention for its implication in the clearance of dysfunctional mitochondria via crosstalk with the endo-lysosomal system, a major cell degradative route. Along this pathway, additional opportunities for mitochondrial disposal have been identified that may also signal at the systemic level. This communication occurs via inclusion of mitochondrial components within membranous shuttles named mitochondrial-derived vesicles (MDVs). Here, we discuss MDV generation and release as a mitophagy-complementing route for the maintenance of mitochondrial homeostasis in skeletal myocytes. We also illustrate the possible role of muscle-derived MDVs in immune signaling during muscle remodeling and adaptation.

N-Lobe of TXNIP Is Critical in the Allosteric Regulation of NLRP3 via TXNIP Binding

Inflammasomes are cytoplasmic complexes that form in response to exogenous microbial invasions and endogenous damage signals. Among the known inflammasomes, the activation of the NACHT (NAIP, CIITA, HET-E, and TP1 domain), leucine-rich repeat, and pyrin domain containing protein 3 (NLRP3) inflammasome is also primarily related to neuroinflammation and nerve cell damage. Previous studies reported that under the stimulation of dangerous signals like reactive oxygen species (ROS), the overexpression and interaction of thioredoxin-interacting protein (TXNIP) with NLRP3 may trigger the inflammatory response through the ROS/TXNIP/NLRP3 signaling pathway. This inflammatory response is the pathophysiological basis of some neurological and neurodegenerative diseases. The activation of inflammasome and apoptosis caused by TXNIP are widespread in brain diseases. Previous report has suggested the TXNIP/NLRP3 interaction interface. However, the comprehensive model of the TXNIP/NLRP3 interaction is still unclear. In this study, molecular docking experiments based on the existing crystal model of NLRP3 were performed to investigate the binding of TXNIP and NLRP3. Three in silico models of the TXNIP/NLRP3 complex were selected, and molecular dynamics simulations evaluated the binding stability of the possible interaction between the two proteins. The results revealed that the E690, E693, and D745 residues in NLRP3 and the K212 and R238 residues in TXNIP play a critical role in the TXNIP/NLRP3 interaction. N-terminal of TXNIP is essential in promoting the conformational changes of NLRP3, although it does not directly bind to NLRP3. Our findings reveal the possible binding mechanism between TXNIP and NLRP3 and the associated allosteric regulation of NLRP3. The constructed models may also be useful for inhibitor development targeting the TXNIP/NLRP3 interaction during inflammasome activation via the ROS/TXNIP/NLRP3 pathway.

Understanding the Link between Inflammasome and Apoptosis through the Response of THP-1 Cells against Drugs Using Droplet-Based Microfluidics

Droplet-based microfluidic devices are used to investigate monocytic THP-1 cells in response to drug administration. Consistent and reproducible droplets are created, each of which acts as a bioreactor to carry out single cell experiments with minimized contamination and live cell tracking under an inverted fluorescence microscope for more than 2 days. Here, the effects of three different drugs (temsirolimus, rifabutin, and BAY 11-7082) on THP-1 are examined and the results are analyzed in the context of the inflammasome and apoptosis relationship. The ASC adaptor gene tagged with GFP is monitored as the inflammasome reporter. Thus, a systematic way is presented for deciphering cell-to-cell heterogeneity, which is an important issue in cancer treatment. The drug temsirolimus, which has effects of disrupting the mTOR pathway and triggering apoptosis in tumor cells, causes THP-1 cells to express ASC and to be involved in apoptosis. Treatment with rifabutin, which inhibits proliferation and initiates apoptosis in cells, affects ASC expression by first increasing and then decreasing it. CASP-3, which has a role in apoptosis and is directly related to ASC, has an increasing level in inflammasome conditioning. Thus, the cell under the effect of rifabutin might be faced with programmed cell death faster. The drug BAY 11-7082, which is responsible for NFκB inhibition, shows similar results to temsirolimus with more than 60% of cells having high fluorescence intensity (ASC expression). The microfluidic platform presented here offers strong potential for studying newly developed small-molecule inhibitors for personalized/precision medicine.

ARMC Subfamily: Structures, Functions, Evolutions, Interactions, and Diseases

Armadillo repeat-containing proteins (ARMCs) are widely distributed in eukaryotes and have important influences on cell adhesion, signal transduction, mitochondrial function regulation, tumorigenesis, and other processes. These proteins share a similar domain consisting of tandem repeats approximately 42 amino acids in length, and this domain constitutes a substantial platform for the binding between ARMCs and other proteins. An ARMC subfamily, including ARMC1∼10, ARMC12, and ARMCX1∼6, has received increasing attention. These proteins may have many terminal regions and play a critical role in various diseases. On the one hand, based on their similar central domain of tandem repeats, this ARMC subfamily may function similarly to other ARMCs. On the other hand, the unique domains on their terminals may cause these proteins to have different functions. Here, we focus on the ARMC subfamily (ARMC1∼10, ARMC12, and ARMCX1∼6), which is relatively conserved in vertebrates and highly conserved in mammals, particularly primates. We review the structures, biological functions, evolutions, interactions, and related diseases of the ARMC subfamily, which involve more than 30 diseases and 40 bypasses, including interactions and relationships between more than 100 proteins and signaling molecules. We look forward to obtaining a clearer understanding of the ARMC subfamily to facilitate further in-depth research and treatment of related diseases.

Apoptosis-associated speck-like protein containing a CARD regulates the growth of pancreatic ductal adenocarcinoma

Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) is a key adaptor protein of inflammasomes and a proapoptotic molecule; however, its roles in signal transduction in pancreatic ductal adenocarcinoma (PDAC) cells remain unknown. Here, we clarified the role and mechanisms of action of ASC in PDAC using clinical evidence and in vitro data. ASC expression in PDAC tissues was analyzed using public tumor datasets and immunohistochemistry results of patients who underwent surgery, and PDAC prognosis was investigated using the Kaplan-Meier Plotter. ASC expression in PDAC cells was downregulated using small-interfering RNA, and gene expression was assessed by RNA sequencing. Review of the Oncomine database and immunostaining of surgically removed tissues revealed elevated ASC expression in PDAC tumors relative to non-tumor tissue, indicating poor prognosis. We observed high ASC expression in multiple PDAC cells, with ASC silencing subsequently inhibiting PDAC cell growth and altering the expression of cell cycle-related genes. Specifically, ASC silencing reduced cyclin D1 levels and stopped the cell cycle at the G1 phase but did not modulate the expression of any apoptosis-related molecules. These results show that ASC inhibited tumor progression via cell cycle modulation in PDAC cells and could be a potential therapeutic target.

Molecular biology of autoinflammatory diseases

The long battle between humans and various physical, chemical, and biological insults that cause cell injury (e.g., products of tissue damage, metabolites, and/or infections) have led to the evolution of various adaptive responses. These responses are triggered by recognition of damage-associated molecular patterns (DAMPs) and/or pathogen-associated molecular patterns (PAMPs), usually by cells of the innate immune system. DAMPs and PAMPs are recognized by pattern recognition receptors (PRRs) expressed by innate immune cells; this recognition triggers inflammation. Autoinflammatory diseases are strongly associated with dysregulation of PRR interactomes, which include inflammasomes, NF-κB-activating signalosomes, type I interferon-inducing signalosomes, and immuno-proteasome; disruptions of regulation of these interactomes leads to inflammasomopathies, relopathies, interferonopathies, and proteasome-associated autoinflammatory syndromes, respectively. In this review, we discuss the currently accepted molecular mechanisms underlying several autoinflammatory diseases.

Nlrp3 Inflammasome Signaling Regulates the Homing and Engraftment of Hematopoietic Stem Cells (HSPCs) by Enhancing Incorporation of CXCR4 Receptor into Membrane Lipid Rafts

Fast and efficient homing and engraftment of hematopoietic stem progenitor cells (HSPCs) is crucial for positive clinical outcomes from transplantation. We found that this process depends on activation of the Nlrp3 inflammasome, both in the HSPCs to be transplanted and in the cells in the recipient bone marrow (BM) microenvironment. For the first time we provide evidence that functional deficiency in the Nlrp3 inflammasome in transplanted cells or in the host microenvironment leads to defective homing and engraftment. At the molecular level, functional deficiency of the Nlrp3 inflammasome in HSPCs leads to their defective migration in response to the major BM homing chemoattractant stromal-derived factor 1 (SDF-1) and to other supportive chemoattractants, including sphingosine-1-phosphate (S1P) and extracellular adenosine triphosphate (eATP). We report that activation of the Nlrp3 inflammasome increases autocrine release of eATP, which promotes incorporation of the CXCR4 receptor into membrane lipid rafts at the leading surface of migrating cells. On the other hand, a lack of Nlrp3 inflammasome expression in BM conditioned for transplantation leads to a decrease in expression of SDF-1 and danger-associated molecular pattern molecules (DAMPs), which are responsible for activation of the complement cascade (ComC), which in turn facilitates the homing and engraftment of HSPCs.

The neutrophil inflammasome

Since inflammasomes were discovered in the early 21st century, knowledge about their biology has multiplied exponentially. These cytosolic multiprotein complexes alert the immune system about the presence of infection or tissue damage, and regulate the subsequent inflammatory responses. As inflammasome dysregulation is increasingly associated with numerous autoinflammatory disorders, there is an urgent need for further research into the inflammasome's involvement in the pathogenesis of such diseases in order to identify novel therapeutic targets and treatments. The zebrafish has become a widely used animal model to study human diseases in recent years, and has already provided relevant findings in the field of inflammasome biology including the identification of new components and pathways. We provide a detailed analysis of current knowledge on neutrophil inflammasome biology and compare its features with those of the better known macrophage inflammasome, focusing on its contribution to innate immunity and its relevance for human health. Importantly, a large body of evidence points to a link between neutrophil inflammasome dysfunction and many neutrophil-mediated human diseases, but the real contribution of the neutrophil inflammasome to the pathogenesis of these disorders is largely unknown. Although neutrophils have remained in the shadow of macrophages and monocytes in the field of inflammasome research since the discovery of these multiprotein platforms, recent studies strongly suggest that the importance of the neutrophil inflammasome has been underestimated.

Computational Modeling of NLRP3 Identifies Enhanced ATP Binding and Multimerization in Cryopyrin-Associated Periodic Syndromes

Cyropyrin-associated periodic syndromes (CAPS) are clinically distinct syndromes that encompass a phenotypic spectrum yet are caused by alterations in the same gene, NLRP3. Many CAPS cases and other NLRP3-autoinflammatory diseases (NLRP3-AIDs) are directly attributed to protein-coding alterations in NLRP3 and the subsequent dysregulation of the NLRP3 inflammasome leading to IL-1β-mediated inflammatory states. Here, we used bioinformatics tools, computational modeling, and computational assessments to explore the proteomic consequences of NLRP3 mutations, which potentially drive NLRP3 inflammasome dysregulation. We analyzed 177 mutations derived from familial cold autoinflammatory syndrome (FCAS), Muckle-Wells Syndrome (MWS), and the non-hereditary chronic infantile neurologic cutaneous and articular syndrome, also known as neonatal-onset multisystem inflammatory disease (CINCA/NOMID), as well as other NLRP3-AIDs. We found an inverse relationship between clinical severity and the severity of predicted structure changes resulting from mutations in NLRP3. Bioinformatics tools and computational modeling revealed that NLRP3 mutations that are predicted to be structurally severely-disruptive localize around the ATP binding pocket and that specific proteo-structural changes to the ATP binding pocket lead to enhanced ATP binding affinity by altering hydrogen-bond and charge interactions. Furthermore, we demonstrated that NLRP3 mutations that are predicted to be structurally mildly- or moderately-disruptive affect protein-protein interactions, such as NLRP3-ASC binding and NLRP3-NLRP3 multimerization, enhancing inflammasome formation and complex stability. Taken together, we provide evidence that proteo-structural mechanisms can explain multiple mechanisms of inflammasome activation in NLRP3-AID.

The NLRP3 inflammasome regulates adipose tissue metabolism

Adipose tissue regulates metabolic homeostasis by participating in endocrine and immune responses in addition to storing and releasing lipids from adipocytes. Obesity skews adipose tissue adipokine responses and degrades the coordination of adipocyte lipogenesis and lipolysis. These defects in adipose tissue metabolism can promote ectopic lipid deposition and inflammation in insulin-sensitive tissues such as skeletal muscle and liver. Sustained caloric excess can expand white adipose tissue to a point of maladaptation exacerbating both local and systemic inflammation. Multiple sources, instigators and propagators of adipose tissue inflammation occur during obesity. Cross-talk between professional immune cells (i.e. macrophages) and metabolic cells (i.e. adipocytes) promote adipose tissue inflammation during metabolic stress (i.e. metaflammation). Metabolic stress and endogenous danger signals can engage pathogen recognition receptors (PRRs) of the innate immune system thereby activating pro-inflammatory and stress pathways in adipose tissue. The Nod-like receptor protein 3 (NLRP3) inflammasome can act as a metabolic danger sensor to a wide range of pathogen- and damage-associated molecular patterns (PAMPs and DAMPs). Activation of the NLRP3 inflammasome facilitates caspase-1 dependent production of the pro-inflammatory cytokines IL-1β and IL-18. Activation of the NLRP3 inflammasome can promote inflammation and pyroptotic cell death, but caspase-1 is also involved in adipogenesis. This review discusses the role of the NLRP3 inflammasome in adipose tissue immunometabolism responses relevant to metabolic disease. Understanding the potential sources of NLRP3 activation and consequences of NLRP3 effectors may reveal therapeutic opportunities to break or fine-tune the connection between metabolism and inflammation in adipose tissue during obesity.

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.

The pivotal roles of the NOD-like receptors with a PYD domain, NLRPs, in oocytes and early embryo development†

Nucleotide-binding oligomerization domain (NOD)-like receptors with a pyrin domain (PYD), NLRPs, are pattern recognition receptors, well recognized for their important roles in innate immunity and apoptosis. However, several NLRPs have received attention for their new, specialized roles as maternally contributed genes important in reproduction and embryo development. Several NLRPs have been shown to be specifically expressed in oocytes and preimplantation embryos. Interestingly, and in line with divergent functions, NLRP genes reveal a complex evolutionary divergence. The most pronounced difference is the human-specific NLRP7 gene, not identified in rodents. However, mouse models have been extensively used to study maternally contributed NLRPs. The NLRP2 and NLRP5 proteins are components of the subcortical maternal complex (SCMC), which was recently identified as essential for mouse preimplantation development. The SCMC integrates multiple proteins, including KHDC3L, NLRP5, TLE6, OOEP, NLRP2, and PADI6. The NLRP5 (also known as MATER) has been extensively studied. In humans, inactivating variants in specific NLRP genes in the mother are associated with distinct phenotypes in the offspring, such as biparental hydatidiform moles (BiHMs) and preterm birth. Maternal-effect recessive mutations in KHDC3L and NLRP5 (and NLRP7) are associated with reduced reproductive outcomes, BiHM, and broad multilocus imprinting perturbations. The precise mechanisms of NLRPs are unknown, but research strongly indicates their pivotal roles in the establishment of genomic imprints and post-zygotic methylation maintenance, among other processes. Challenges for the future include translations of findings from the mouse model into human contexts and implementation in therapies and clinical fertility management.

NLRP3 Sensing of Diverse Inflammatory Stimuli Requires Distinct Structural Features

The NLRP3 inflammasome is central to host defense and implicated in various inflammatory diseases and conditions. While the favored paradigm of NLRP3 inflammasome activation stipulates a unifying signal intermediate that de-represses NLRP3, this view has not been tested. Further, structures within NLRP3 required for inflammasome activation are poorly defined. Here we demonstrate that while the NLRP3 LRRs are not auto-repressive and are not required for inflammasome activation by all agonists, distinct sequences within the NLRP3 LRRs positively and negatively modulate inflammasome activation by specific ligands. In addition, elements within the HD1/HD2 “hinge” of NLRP3 and the nucleotide-binding domain have contrasting functions depending upon the specific agonists. Further, while NLRP3 1–432 is minimally sufficient for inflammasome activation by all agonists tested, the pyrin, and linker domains (1–134) function cooperatively and are sufficient for inflammasome activation by certain agonists. Conserved cysteines 8 and 108 appear important for inflammasome activation by sterile, but not infectious insults. Our results define common and agonist-specific regions of NLRP3 that likely mediate ligand-specific responses, discount the hypothesis that NLRP3 inflammasome activation has a unified mechanism, and implicate NLRP3 as an integrator of agonist-specific, inflammasome activating signals.

NLRP12 controls arthritis severity by acting as a checkpoint inhibitor of Th17 cell differentiation

Nucleotide oligomerization domain (NOD)-like receptor-12 (NLRP12) has emerged as a negative regulator of inflammation. It is well described that the Th17 cell population increases in patients with early Rheumatoid Arthritis (RA), which correlates with the disease activity. Here, we investigated the role of NLRP12 in the differentiation of Th17 cells and the development of experimental arthritis, using the antigen-induced arthritis (AIA) murine model. We found that Nlrp12^{-/ -} mice develop severe arthritis characterized by an exacerbated Th17-mediated inflammatory response with increases in the articular hyperalgesia, knee joint swelling, and neutrophil infiltration. Adoptive transfer of Nlrp12^{-/ -} cells into WT mice recapitulated the hyperinflammatory response seen in Nlrp12^{-/ -} mice and the treatment with anti-IL-17A neutralizing antibody abrogated arthritis development in Nlrp12^{-/ -} mice, suggesting that NLRP12 works as an inhibitor of Th17 cell differentiation. Indeed, Th17 cell differentiation markedly increases in Nlrp12^-/- T cells cultured under the Th17-skewing condition. Mechanistically, we found that NLRP12 negatively regulates IL-6-induced phosphorylation of STAT3 in T cells. Finally, pharmacological inhibition of STAT3 reduced Th17 cell differentiation and abrogated hyperinflammatory arthritis observed in Nlrp12^{-/ -} mice. Thus, we described a novel role for NLRP12 as a checkpoint inhibitor of Th17 cell differentiation, which controls the severity of experimental arthritis.

Effects of PYRIN-containing Apaf1-like protein 1 on isoflurane-induced postoperative cognitive dysfunction in aged rats

Postoperative cognitive dysfunction (POCD) is a prevalent neurocognitive disorder following surgery and anesthesia, particularly in elderly patients. Isoflurane is a widely used anesthetic agent, which is associated with the development of POCD; however, the precise mechanisms remain unclear. In the present study, aged rats were exposed to 2% isoflurane to establish a POCD model. The expression of PYRIN-containing Apaf1-like protein 1 (PYPAF1) was knocked down using a lentivirus containing specific short hairpin RNA. Subsequently, the spatial learning ability of rats was assessed using the Morris water maze. In addition, mRNA and protein expression levels were detected using reverse transcription-quantitative PCR and western blot analysis, respectively. Immunofluorescence double staining was also used to determine the expression of PYPAF1 and Iba-1 in the hippocampus. Neural apoptosis was observed using TUNEL-NeuN double staining. The results revealed that isoflurane exposure impaired the spatial learning ability of rats, while PYPAF1 knockdown alleviated cognitive impairment. In addition, isoflurane exposure induced activation of the PYPAF1 inflammasome, as evidenced by elevated expression of PYPAF1 and apoptosis-associated speck-like protein containing a caspase recruitment domain, while silencing of PYPAF1 partially reversed this effect. Furthermore, isoflurane exposure promoted the activation of microglia and caspase-1, and the secretion of interleukin (IL)-1β and IL-18, all of which were alleviated following PYPAF1 silencing. Moreover, isoflurane exposure induced neuronal apoptosis, elevated the levels of Bax and cleaved caspase-3, and inhibited the expression of Bcl-2; all of these effects were partially abrogated following PYPAF1 silencing. In conclusion, the results of the present study indicated that PYPAF1 silencing partially abolished isoflurane-induced cognitive impairment, neuroinflammation and neuronal apoptosis. Therefore, PYPAF1 may be a potential therapeutic target for treatment of POCD.

Dual Role of Inflammasome Adaptor ASC in Cancer

Apoptosis-associated Speck-like protein containing a CARD (caspase activation and recruitment domain) (ASC), also called PYCARD/Target of Methylation-induced Silencing-1 (TMS1), was originally discovered as a protein that forms aggregates (“specks”) in human leukemia cells treated with chemotherapeutic agents. Its expression was found to be silenced by methylation in many human tumors, preventing tumor cells from undergoing apoptosis and supporting its role as a tumor suppressor. Subsequently, ASC was also identified as a central adaptor molecule of the inflammasome complex, which mediates the secretion of inflammatory cytokines (i.e., IL-1β and IL-18). Inflammatory cytokines have been shown to mediate tumor-promoting functions. Thus, in the context of cancer development and progression, ASC may exert opposing functions, i.e., be either tumor-suppressing by inducing tumor cell apoptosis, or tumor-promoting by favoring secretion of inflammatory cytokines (by tumor cells and/or tumor infiltrating myeloid cells) within the tumor microenvironment. Here, we report and discuss this dual role of ASC by also considering the final contribution of each of its two main functions in several cancer types, taking into consideration the correlation between ASC expression, clinical correlates, and patients’ survival. ASC and inflammasome targeting strategies are being developed. However, before the use of such treatments in clinical practice, it is fundamental to better dissect the role of ASC in different tumors, in order to privilege or avoid their use in those tumors in which ASC exerts an anti-tumor or pro-tumor function, respectively.

Inflammasome-mediated innate immunity in Alzheimer's disease

Historically neurodegenerative diseases, Alzheimer's disease (AD) in particular, have been viewed to be primarily caused and driven by neuronal mechanisms. Very recently, due to experimental, genetic, and epidemiologic evidence, immune mechanisms have entered the central stage and are now believed to contribute significantly to risk, onset, and disease progression of this class of disorders. Although immune activation of microglial cells may over time engage various signal transduction pathways, inflammasome activation, which represents a canonical and initiating pathway, seems to be one of the first responses to extracellular β-amyloid (Aβ) accumulation. Here we review the current understanding of inflammasome activation in AD.-Venegas, C., Heneka, M. T. Inflammasome-mediated innate immunity in Alzheimer's disease.

Altered inflammasome machinery as a key player in the perpetuation of Rett syndrome oxinflammation

Rett syndrome (RTT) is a progressive neurodevelopmental disorder mainly caused by mutations in the X-linked MECP2 gene. RTT patients show multisystem disturbances associated with an oxinflammatory status. Inflammasomes are multi-protein complexes, responsible for host immune responses against pathogen infections and redox-related cellular stress. Assembly of NLRP3/ASC inflammasome triggers pro-caspase-1 activation, thus, resulting in IL-1β and IL-18 maturation. However, an aberrant activation of inflammasome system has been implicated in several human diseases. Our aim was to investigate the possible role of inflammasome in the chronic subclinical inflammatory condition typical of RTT, by analyzing this complex in basal and lipopolysaccharide (LPS)+ATP-stimulated primary fibroblasts, as well as in serum from RTT patients and healthy volunteers. RTT cells showed increased levels of nuclear p65 and ASC proteins, pro-IL-1β mRNA, and NLRP3/ASC interaction in basal condition, without any further response upon the LPS + ATP stimuli. Moreover, augmented levels of circulating ASC and IL-18 proteins were found in serum of RTT patients, which are likely able to amplify the inflammatory response. Taken together, our findings suggest that RTT patients exhibited a challenged inflammasome machinery at cellular and systemic level, which may contribute to the subclinical inflammatory state feedback observed in this pathology.

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RTT cell shows a constitutive NFκB activation.

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Aberrant activation of inflammasome system is evident in RTT.

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This new evidence can explain the demonstrated subclinical inflammation in RTT.

Prdx4 limits caspase-1 activation and restricts inflammasome-mediated signaling by extracellular vesicles

Inflammasomes are cytosolic protein complexes, which orchestrate the maturation of active IL‐1β by proteolytic cleavage via caspase‐1. Although many principles of inflammasome activation have been described, mechanisms that limit inflammasome‐dependent immune responses remain poorly defined. Here, we show that the thiol‐specific peroxidase peroxiredoxin‐4 (Prdx4) directly regulates IL‐1β generation by interfering with caspase‐1 activity. We demonstrate that caspase‐1 and Prdx4 form a redox‐sensitive regulatory complex via caspase‐1 cysteine 397 that leads to caspase‐1 sequestration and inactivation. Mice lacking Prdx4 show an increased susceptibility to LPS‐induced septic shock. This effect was phenocopied in mice carrying a conditional deletion of Prdx4 in the myeloid lineage (Prdx4‐ΔLysMCre). Strikingly, we demonstrate that Prdx4 co‐localizes with inflammasome components in extracellular vesicles (EVs) from inflammasome‐activated macrophages. Purified EVs are able to transmit a robust IL‐1β‐dependent inflammatory response in vitro and also in recipient mice in vivo. Loss of Prdx4 boosts the pro‐inflammatory potential of EVs. These findings identify Prdx4 as a critical regulator of inflammasome activity and provide new insights into remote cell‐to‐cell communication function of inflammasomes via macrophage‐derived EVs.

NLRP6 deficiency aggravates liver injury after allogeneic hematopoietic stem cell transplantation

This study aims to observe the expression and role of NLRP6 in liver injury after allogeneic hematopoietic stem cell transplantation (Allo-HSCT). Allo-HSCT model was established through infusion of 5 × 10⁶ bone marrow mononuclear cells into whole body irradiated mice. On days 7, 14, 21 and 28 after transplantation, the peripheral blood was collected to detect liver function. The liver of the mice was obtained to assess the pathological changes of liver tissues after allo-HSCT by H&E staining and Mason staining. Meanwhile, expression of NLRP6, phosphorylated p38-MAPK and IκBα, caspase-1 and NLRP3 in liver were detected by Western blot. ELISA was used for detection of the level of interleukin (IL)-1β, IL-18, tumor necrosis factor (TNF)-α, IL-6, myeloperoxidase (MPO) and tumor growth factor (TGF)-β1. Increased expression of NLRP6, phosphorylated Iκbα, phosphorylated p38-MAPK, pro-caspase-1, and p20, in liver tissue with injury and fibrosis in mice after allo-HSCT were observed. Meanwhile, the level of IL-1β, IL-18, IL-6 and TNF-α was also increased. However, NLRP6^-/- mice showed more severe liver damage and liver fibrosis after transplantation together with higher level of phosphorylated Iκbα, phosphorylated p38-MAPK, Pro-caspase-1, p20 expression as well as IL-1β, IL-18, IL-6, and TNF-α secretion compared with wide-type. Interestingly, the expression of NLRP3 in the liver of NLRP6^-/- mice was significantly higher than that of wild-type. In conclusion, the expression of NLRP6 in host's liver is associated with liver injury after allo-HSCT. NLRP6 deficiency in host's liver leads to more severe liver damage, indicating a protective role of NLRP6 in host's liver to liver damage after allo-HSCT.

The NLRP3 Inflammasome: An Overview of Mechanisms of Activation and Regulation

The NLRP3 inflammasome is a critical component of the innate immune system that mediates caspase-1 activation and the secretion of proinflammatory cytokines IL-1β/IL-18 in response to microbial infection and cellular damage. However, the aberrant activation of the NLRP3 inflammasome has been linked with several inflammatory disorders, which include cryopyrin-associated periodic syndromes, Alzheimer's disease, diabetes, and atherosclerosis. The NLRP3 inflammasome is activated by diverse stimuli, and multiple molecular and cellular events, including ionic flux, mitochondrial dysfunction, and the production of reactive oxygen species, and lysosomal damage have been shown to trigger its activation. How NLRP3 responds to those signaling events and initiates the assembly of the NLRP3 inflammasome is not fully understood. In this review, we summarize our current understanding of the mechanisms of NLRP3 inflammasome activation by multiple signaling events, and its regulation by post-translational modifications and interacting partners of NLRP3.

CAPS and NLRP3

Cryopyrin-associated periodic syndrome (CAPS) is a rare inherited autoinflammatory disorder characterized by systemic, cutaneous, musculoskeletal, and central nervous system inflammation. Gain-of-function mutations in NLRP3 in CAPS patients lead to activation of the cryopyrin inflammasome, resulting in the inappropriate release of inflammatory cytokines including IL-1β and CAPS-related inflammatory symptoms. Several mechanisms have been identified that are important for the normal regulation of the cryopyrin inflammasome in order to prevent uncontrolled inflammation. Investigators have taken advantage of some of these pathways to develop and apply novel targeted therapies, which have resulted in improved quality of life for patients with this orphan disease.

Adenovirus-delivered angiopoietin-1 ameliorates phosgene-induced acute lung injury via inhibition of NLRP3 inflammasome activation

OBJECTIVE

Angiopoietin-1 (Ang1) is reported to have the ability to attenuate endothelial permeability and inflammation during the stress condition and is considered to play a critical role in vascular stabilization. The aim of this study was to investigate the mechanisms involved in the protective effects of adenovirus-delivered Ang1 in phosgene-induced acute lung injury (ALI).

METHODS

ALI was induced in rats by phosgene exposure at 8.33 g/m³ for 5 min, followed by an intravenous injection of adenovirus-Ang1 (Ad/Ang1). The histologic changes of the lung were evaluated with H&E staining. The levels of cytokines in the serum and bronchoalveolar lavage fluid (BALF) were determined by ELISA. NLRP3 inflammasome activation was assessed with immunohistochemistry, RT-PCR, Western blotting and TUNEL staining.

RESULTS

Histologic analyses suggested that reduced severity in phosgene-induced ALI with Ad/Ang1 treatment. Reduced levels of IL-1β, IL-18 and IL-33 were found in both serum and BALF samples from Ad/Ang1-treated ALI rats induced by phosgene. Moreover, immunohistochemistry analysis revealed that Ad/Ang1 treatment inhibited the NLRP3 inflammasome activation. Decreased mRNA and protein levels of NLRP3 and caspase-1 were found in phosgene-exposed rats treated with Ad/Ang1. In addition, TUNEL staining indicated a decrease in pyroptosis in phosgene-exposed rats treated with Ad/Ang1.

CONCLUSIONS

Ang1 exerts beneficial effects on phosgene-induced lung injury via inhibition of NLRP3 inflammasome activation. Disruption of NLRP3 inflammasome activation might be served as therapeutic modality for the treatment of phosgene-induced ALI.

The IL-1/IL-1 receptor axis and tumor cell released inflammasome adaptor ASC are key regulators of TSLP secretion by cancer associated fibroblasts in pancreatic cancer

BACKGROUND

The thymic stromal lymphopoietin (TSLP), a key cytokine for development of Th2 immunity, is produced by cancer associated fibroblasts (CAFs) in pancreatic cancer where predominant tumor infiltrating Th2 over Th1 cells correlates with reduced patients' survival. Which cells and molecules are mostly relevant in driving TSLP secretion by CAFs in pancreatic cancer is not defined.

METHODS

We performed in vitro, in vivo and ex-vivo analyses. For in vitro studies we used pancreatic cancer cell lines, primary CAFs cultures, and THP1 cells. TSLP secretion by CAFs was used as a read-out system to identify in vitro relevant tumor-derived inflammatory cytokines and molecules. For in vivo studies human pancreatic cancer cells and CAFs were orthotopically injected in immunodeficient mice. For ex-vivo studies immunohistochemistry was performed to detect ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain) expression in surgical samples. Bioinformatics was applied to interrogate published data sets.

RESULTS

We show in vitro that IL-1α and IL-1β released by pancreatic cancer cells and tumor cell-conditioned macrophages are crucial for TSLP secretion by CAFs. Treatment of immunodeficient mice orthotopically injected with human IL-1 positive pancreatic cancer cells plus CAFs using the IL-1R antagonist anakinra significantly reduced TSLP expression in the tumor. Importantly, we found that pancreatic cancer cells release alarmins, among which ASC, able to induce IL-1β secretion in macrophages. The relevance of ASC was confirmed ex-vivo by its expression in both tumor cells and tumor associated macrophages in pancreatic cancer surgical samples and survival data analyses showing statistically significant inverse correlation between ASC expression and survival in pancreatic cancer patients.

CONCLUSIONS

Our findings indicate that tumor released IL-1α and IL-1β and ASC are key regulators of TSLP secretion by CAFs and their targeting should ultimately dampen Th2 inflammation and improve overall survival in pancreatic cancer.

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.

Inflammasomes: Emerging Central Players in Cancer Immunology and Immunotherapy

Inflammation has an established role in cancer development and progression and is a key player in regulating the entry and exit of immune cells in the tumor microenvironment, mounting a significant impact on anti-tumor immunity. Recent studies have shed light on the role of inflammasomes in the regulation of inflammation with a focus on the subsequent effects on the immunobiology of tumors. To generate strong anti-tumor immunity, cross-talk between innate, and adaptive immune cells is necessary. Interestingly, inflammasome bridges both arms of the immune system representing a unique opportunity to manipulate the role of inflammation in favor of tumor suppression. In this review, we discuss the impact of inflammasomes on the regulation of the levels of inflammatory cytokines-chemokines and the efficacy of immunotherapy response in cancer treatment.

IAPP/amylin deposition, which is correlated with expressions of ASC and IL-1β in β-cells of Langerhans' islets, directly initiates NLRP3 inflammasome activation

Recent findings revealed that type 2 diabetes mellitus (T2D) is a chronic inflammatory disease and an islet amyloid polypeptide (IAPP)/amylin, is deposited within pancreatic islets. IAPP/amylin has been reported to activate NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome in infiltrated macrophages. NLRP3, an intracellular pattern recognition receptor, has been shown to recognize pathogens and/or metabolites and complexes with the adopter protein apoptosis-associated speck-like protein containing a caspase-recruitment domain ASC to form a huge complex, called an inflammasome, an interleukin (IL)-1β-processing platform. Although reactive oxygen species (ROS) were reported to be involved in activation of NLRP3 inflammasome, we were hypothesized that IAPP could directly activate NLRP3 inflammasome, leading to islets β-cell death. We analyzed expression of the inflammasome components ASC, NLRP3, caspase-1, IL-1β, IAPP/amylin, and insulin immunohistochemically in Langerhans' islets of autopsy cases. The initial event of NLRP3 inflammasome activation was assessed using a cell-free system consisting of NLRP3 and ASC with the amplified luminescent proximity homogeneous assay. IAPP/amylin deposition in Langerhans' islets was detected and significantly correlated with expressions of IL-1β and ASC. IAPP/amylin directly interacted with NLRP3 and initiated an interaction between NLRP3 and ASC in a cell-free system. The deposition of IAPP/amylin in β-cells of Langerhans' islets may act together with the expression level of an inflammasome component, ASC, to regulate IL-1β processing, and directly lead to the dysfunction of β-cells. The interaction between IAPP/amylin and NLRP3 could be an attractive drug target to avoid both inflammation and β-cell death for T2D therapy.

Loss of NLRP3 Function Alleviates Murine Hepatic Graft-versus-Host Disease

NLRP3 is associated with multiple risks in graft-versus-host disease, though unifying principles for these findings remain largely unknown. To explore the effects and mechanisms of the absence of NLRP3 function on hepatic graft-versus-host-disease, we established an allogeneic hematopoietic cell transplantation mice model by infusing bone marrow mononuclear cells and spleno-T cells of the BALB/c mouse into either NLRP3 knockout (NLRP3^-/- ) or wild-type C57BL/6 mice. Elevated inflammatory cell infiltration, liver fibrosis, and secretions of alanine aminotransferase (ALT) and aspartate transaminase (AST), together with weight loss, were observed in C57BL/6 recipients after transplantation. However, moderate injury pathology was detected in the liver of NLRP3^-/- recipients at day 14, which gradually improved over time. Likewise, proinflammatory cytokine IL-1β, a downstream effecter of NLRP3 inflammasome activation, showed significantly lower expression (P < .05) in the liver of NLRP3^-/- recipients relative to C57BL/6 recipients at day 7 and day 21. Moreover, compared with C57BL/6 recipients, the expression of both TNF-α and IL-1β were decreased 3-fold and 4.7-fold, respectively, at day 21 in NLRP3^-/- recipients. Interestingly, NLRP1a was expressed at a significantly reduced level in the liver of NLRP3^-/- recipients (P < .001). Furthermore, systemic inflammation was analyzed by measuring the concentration of IL-1β and adenosine triphosphate (ATP) in serum. The concentration of IL-1β achieved a maximum at day 14, then decreased at day 21 and day 28 in NLRP3^-/- recipients. In contrast, the concentration of IL-1β in C57BL/6 recipients gradually increased from day 7 to day 28. ATP levels reduced from day 7 to day 28 in NLRP3^-/- recipients, but were extremely high in C57BL/6 recipients from day 14 to day 28 (P < .01). The decreased levels of P2X7R were connected to less ATP in NLRP3^-/- recipients at day 21 and day 28. In conclusion, NLRP3 knockout in recipients could significantly relieve liver injury after transplantation and block the NLRP3 inflammasome pathway, thus providing a promising strategy for the treatment of graft-versus-host disease prophylaxis.

Inflammasome biology, molecular pathology and therapeutic implications

Inflammasomes are intracellular multiprotein signaling complexes, mainly present in myeloid cells. They commonly assemble around a cytoplasmic receptor of the nucleotide-binding leucine-rich repeat containing receptor (NLR) family, although other cytoplasmic receptors like pyrin have been shown to form inflammasomes. The nucleation of the multiprotein scaffolding platform occurs upon detection of a microbial, a danger or a homeostasis pattern by the receptor that will, most commonly, associate with the adaptor protein ASC (apoptosis-associated speck-like protein containing a CARD) through homotypic domain interactions resulting in recruitment of procaspase-1. This will lead to the autoproteolytic activation of caspase-1, which regulates the secretion of proinflammatory IL1β and IL18 cytokines and pyroptosis, a caspase-1-mediated form of cell death. Pyroptosis occurs through cleavage of Gasdermin D, a membrane pore forming protein. Recently, non-canonical inflammasomes have been described, which directly sense intracellular pathogens through caspase-4 and -5 in humans, leading to pyroptosis. Inflammasomes are important in host defense; however, a deregulated activity is associated with a number of inflammatory, immune and metabolic disorders. Furthermore, mutations in inflammasome receptor coding genes are causal for an increasing number of rare autoinflammatory diseases. Biotherapies targeting the products of inflammasome activation as well as molecules that directly or indirectly inhibit inflammasome nucleation and activation are promising therapeutic areas. This review discusses recent advances in inflammasome biology, the molecular pathology of several inflammasomes, and current therapeutic approaches in autoinflammatory diseases and in selected common multifactorial inflammasome-mediated disorders.

An NLRP3 Mutation Causes Arthropathy and Osteoporosis in Humanized Mice

The NLRP3 inflammasome plays a critical role in host defense by facilitating caspase I activation and maturation of IL-1β and IL-18, whereas dysregulation of inflammasome activity results in autoinflammatory disease. Factors regulating human NLRP3 activity that contribute to the phenotypic heterogeneity of NLRP3-related diseases have largely been inferred from the study of Nlrp3 mutant mice. By generating a mouse line in which the NLRP3 locus is humanized by syntenic replacement, we show the functioning of the human NLRP3 proteins in vivo, demonstrating the ability of the human inflammasome to orchestrate immune reactions in response to innate stimuli. Humanized mice expressing disease-associated mutations develop normally but display acute sensitivity to endotoxin and develop progressive and debilitating arthritis characterized by granulocytic infiltrates, elevated cytokines, erosion of bones, and osteoporosis. This NLRP3-dependent arthritis model provides a platform for testing therapeutic reagents targeting the human inflammasome.

TNF regulates transcription of NLRP3 inflammasome components and inflammatory molecules in cryopyrinopathies

The NLRP3 inflammasome is a protein complex responsible for caspase-1-dependent maturation of the proinflammatory cytokines IL-1β and IL-18. Gain-of-function missense mutations in NLRP3 cause the disease spectrum known as the cryopyrin-associated periodic syndromes (CAPS). In this study, we generated Nlrp3-knockin mice on various KO backgrounds including Il1b/Il18-, caspase-1-, caspase-11- (Casp1/11-), and Tnf-deficient strains. The Nlrp3L351P Il1b-/- Il18-/- mutant mice survived and grew normally until adulthood and, at 6 months of age, exhibited marked splenomegaly and leukophilia. Injection of these mice with low-dose LPS resulted in elevated serum TNF levels compared with Nlrp3L351P Casp1/11-/- mice and Il1b-/- Il18-/- littermates. Treatment of Nlrp3A350V mice with the TNF inhibitor etanercept resulted in all pups surviving to adulthood, with normal body and spleen/body weight ratios. Nlrp3A350V Tnf-/- mice showed a similar phenotypic rescue, with marked reductions in serum IL-1β and IL-18, reduced myeloid inflammatory infiltrate in the skin and spleen, and substantial decreases in splenic mRNA expression of both inflammasome components (Nlrp3, Pycard, pro-Casp1) and pro-cytokines (Il1b, Il18). Likewise, we observed a reduction in the expression of both pro-Casp1 and pro-Il1b in cultured Nlrp3A350V Tnf-/- BM-derived DCs. Our data show that TNF is an important transcriptional regulator of NLRP3 inflammasome components in murine inflammasomopathies. Moreover, these results may have therapeutic implications for CAPS patients with partial responses to IL-1-targeted therapies.

Inflammasomes in Myeloid Cells: Warriors Within

The inflammasome is a large multimeric protein complex comprising an effector protein that demonstrates specificity for a variety of activators or ligands; an adaptor molecule; and procaspase-1, which is converted to caspase-1 upon inflammasome activation. Inflammasomes are expressed primarily by myeloid cells and are located within the cell. The macromolecular inflammasome structure can be visualized by cryo-electron microscopy. This complex has been found to play a role in a variety of disease models in mice, and several have been genetically linked to human diseases. In most cases, the effector protein is a member of the NLR (nucleotide-binding domain leucine-rich repeat-containing) or NOD (nucleotide oligomerization domain)-like receptor protein family. However, other effectors have also been described, with the most notable being AIM-2 (absent in melanoma 2), which recognizes DNA to elicit inflammasome function. This review will focus on the role of the inflammasome in myeloid cells and its role in health and disease.

Posttranslational Modification as a Critical Determinant of Cytoplasmic Innate Immune Recognition

Cell surface innate immune receptors can directly detect a variety of extracellular pathogens to which cytoplasmic innate immune sensors are rarely exposed. Instead, within the cytoplasm, the environment is rife with cellular machinery and signaling pathways that are indirectly perturbed by pathogenic microbes to activate intracellular sensors, such as pyrin, NLRP1, NLRP3, or NLRC4. Therefore, subtle changes in key intracellular processes such as phosphorylation, ubiquitination, and other pathways leading to posttranslational protein modification are key determinants of innate immune recognition in the cytoplasm. This concept is critical to establish the “guard hypothesis” whereby otherwise homeostatic pathways that keep innate immune sensors at bay are released in response to alterations in their posttranslational modification status. Originally identified in plants, evidence that a similar guardlike mechanism exists in humans has recently been identified, whereby a mutation that prevents phosphorylation of the innate immune sensor pyrin triggers a dominantly inherited autoinflammatory disease. It is also noteworthy that even when a cytoplasmic innate immune sensor has a direct ligand, such as bacterial peptidoglycan (NOD1 or NOD2), RNA (RIG-I or MDA5), or DNA (cGAS or IFI16), it can still be influenced by posttranslational modification to dramatically alter its response. Therefore, due to their existence in the cytoplasmic milieu, posttranslational modification is a key determinant of intracellular innate immune receptor functionality.

Poly (I:C) and hyaluronic acid directly interact with NLRP3, resulting in the assembly of NLRP3 and ASC in a cell-free system

In the NLR family, pyrin domain containing 3 (NLRP3) is an intracellular pattern recognition receptor that activates pro-caspase-1, leading to IL-1β and IL-18 processing and activation in a large complex called the NLRP3 inflammasome. Since various pathogens or endogenous metabolites have been reported to stimulate NLRP3 inflammasome, the interaction between NLRP3 and ASC induced by these stimulants may be an attractive drug target for NLRP3-related diseases, called inflammasomopathies. However, the endogenous ligand that directly interacts with NLRP3, leading to binding to ASC, remains unclear. Therefore, we developed a cell-free system consisting of NLRP3, ASC, and pro-caspase-1 or ASC and NLRP3 with an amplified luminescent proximity homogeneous assay (ALPHA). ALPHA signals of the interaction between NLRP3 and ASC were not enhanced following an incubation without any ligand, whereas strong ALPHA signals for the interaction between NLRP3 and ASC and between NLRP3 and pro-caspase-1 with the adaptor ASC were observed upon an incubation with poly (I:C) and hyaluronic acid (HA). Poly (I:C) and HA both directly interacted with NLRP3 within a specific concentration. These results suggest that NLRP3 directly interacts with intrinsic RNA and HA, which is followed by the activation of NLRP3 inflammasome, and the cell-free system consisting of NLRP3 and ASC, or NLRP3, ASC, and pro-caspase-1 may be a useful tool for elucidating the pathogenesis of inflammasomopathies and developing target therapeutics.

The Pathogenic Role of NLRP3 Inflammasome Activation in Inflammatory Bowel Diseases of Both Mice and Humans

BACKGROUND AND AIMS

NLRP3 inflammasome is known to be involved in inflammatory bowel diseases. However, it is controversial whether it is pathogenic or beneficial. This study evaluated the roles of NLRP3 inflammasome in the pathogenesis of inflammatory bowel disease in IL-10-/- mice and humans.

METHODS

NLRP3 inflammasome in colonic mucosa, macrophages, and colonic epithelial cells were analysed by western blotting. The NLRP3 inflammasome components were studied by sucrose density gradient fractionation, chemical cross-linking, and co-immunoprecipitation. The role of NLPR3 inflammasome in the pathogenesis of colitis was extensively evaluated in IL-10-/- mice, using a specific NLPR3 inflammasome inhibitor glyburide.

RESULTS

NLRP3 inflammasome was upregulated in colonic mucosa of both IL-10-/- mice and Crohn's patients. NLRP3 inflammasome activity in IL-10-/- mice was elevated prior to colitis onset; it progressively increased as disease worsened and peaked as macroscopic disease emerged. NLRP3 inflammasome was found in both intestinal epithelial cells and colonic macrophages, as a large complex with a molecular weight of ≥ 360 kDa in size. In the absence of IL-10, NLRP3 inflammasome was spontaneously active and more robustly responsive when activated by LPS and nigericin. Glyburide markedly suppressed NLRP3 inflammasome expression/activation in IL-10-/- mice, leading to not only alleviation of ongoing colitis but also prevention/delay of disease onset. Glyburide also effectively inhibited the release of proinflammatory cytokines/chemokines by mucosal explants from Crohn's patients.

CONCLUSIONS

Abnormal activation of NLRP3 inflammasome plays a major pathogenic role in the development of chronic colitis in IL-10-/- mice and humans. Glyburide, an FDA-approved drug, may have great potential in the management of inflammatory bowel diseases.

POP1 might be recruiting its type-Ia interface for NLRP3-mediated PYD-PYD interaction: Insights from MD simulation

Inflammasomes are multiprotein caspase-activating complexes that enhance the maturation and release of proinflammatory cytokines (IL-1β and IL-18) in response to the invading pathogen and/or host-derived cellular stress. These are assembled by the sensory proteins (viz NLRC4, NLRP1, NLRP3, and AIM-2), adaptor protein (ASC), and effector molecule procaspase-1. In NLRP3-mediated inflammasome activation, ASC acts as a mediator between NLRP3 and procaspase-1 for the transmission of signals. A series of homotypic protein-protein interactions (NLRP3^PYD :ASC^PYD and ASC^CARD :CASP1^CARD ) propagates the downstream signaling for the production of proinflammatory cytokines. Pyrin-only protein 1 (POP1) is known to act as the regulator of inflammasome. It modulates the ASC-mediated inflammasome assembly by interacting with pyrin domain (PYD) of ASC. However, despite similar electrostatic surface potential, the interaction of POP1 with NLRP3^PYD is obscured till date. Herein, to explore the possible PYD-PYD interactions between NLRP3^PYD and POP1, a combined approach of protein-protein docking and molecular dynamics simulation was adapted. The current study revealed that POP1's type-Ia interface and type-Ib interface of NLRP3^PYD might be crucial for 1:1 PYD-PYD interaction. In addition to type-I mode of interaction, we also observed type-II and type-III interaction modes in two different dynamically stable heterotrimeric complexes (POP1-NLRP3-NLRP3 and POP1-NLRP3-POP1). The inter-residual/atomic distance calculation exposed several critical residues that possibly govern the said interaction, which need further investigation. Overall, the findings of this study will shed new light on hitherto concealed molecular mechanisms underlying NLRP3-mediated inflammasome, which will have strong future therapeutic implications.

[Genetics of cryopyrin-associated periodic syndrome]

Familial cold autoinflammatory syndrome (FCAS), Muckle-Wells syndrome (MWS) and chronic infantile neurological, cutaneous and articular syndrome/neonatal onset multisystem inflammatory disease (CINCA/NOMID) were originally described as three distinct diseases. After the identification of their common genetic origin in 2001 and 2002, they are now perceived as a continuum of one disease entity and labelled cryopyrin-associated periodic syndromes (CAPS). Mutations in the NLRP3 gene on chromosome 1q44 can be detected in many affected patients. These lead to the synthesis of an altered gene product named cryopyrin. This is part of the NLRP3 inflammasome and causes the activation of caspase 1 and an excess production of IL-1β, which is the driving force behind the inflammatory reactions observed in CAPS patients. In symptomatic patients, confirmation of a mutation using traditional methods of genetic analysis may not always be successful (up to 40% in the case of CINCA/NOMID phenotypes); however, in many cases somatic mutations can be found using modern methods, such as next generation sequencing (NGS) technologies. In contrast, low-penetrance NLRP3 variants may also be identified in healthy family members and are present in low frequencies in the general population. Some of the mutation carriers nevertheless present with typical signs of autoinflammation; however, their phenotype is different compared to the classical CAPS presentation. These patients display unspecific systemic inflammatory signs more frequently but show an organ involvement less often. While the detection of NLRP3 gene mutations may be viewed as confirmatory, CAPS is still predominantly a clinical diagnosis; therefore, recently published diagnostic criteria do not require the demonstration of a mutation.

Functional characterization of apoptosis-associated speck-like protein (ASC) of the goldfish (Carassius auratus L.)

Quantitative expression analysis of goldfish ASC indicated the highest and lowest mRNA levels in spleen and muscle, respectively. The ASC was differentially expressed in normal goldfish tissues and different immune cell populations. The highest ASC mRNA levels were observed in the spleen and macrophages. We generated a recombinant form of the molecule (rgfASC) and an anti-ASC IgG antibody, and report that treatment of goldfish macrophages with nigericin, an inducer of inflammasome pathway, up-regulated the expression of ASC at both mRNA and protein levels. rgfASC aggregated to form multimers in cross-linking assays, and formed speck-like structures visualized by confocal microscopy. Co-immunoprecipitation assays showed that rgfASC interacted with caspase-1 and receptor-interacting serine/threonine kinase 2 (RIP2). The dual luciferase reporter assay showed that ASC over-expression did not cause the activation of NF-κB directly, but down-regulated RIP2 ability to activate NF-κB. Goldfish ASC was found to interact with both Nod-like receptor and inflammasome signaling pathway molecules, suggesting multifunctional roles for ASC in regulation of different NLR signaling pathways and eventual proinflammatory cytokine production by activated macrophages.

The role of NLRP3 and AIM2 in inflammasome activation during Brucella abortus infection

The innate immune system is essential for the detection and elimination of bacterial pathogens. Upon inflammasome activation, caspase-1 cleaves pro-IL-1β and pro-IL-18 to their mature forms IL-1β and IL-18, respectively, and the cell undergoes inflammatory death termed pyroptosis. Here, we reviewed recent findings demonstrating that Brucella abortus ligands activate NLRP3 and AIM2 inflammasomes which lead to control of infection. This protective effect is due to the inflammatory response caused by IL-1β and IL-18 rather than cell death. Brucella DNA is sensed by AIM2 and bacteria-induced mitochondrial reactive oxygen species is detected by NLRP3. However, deregulation of pro-inflammatory cytokine production can lead to immunopathology. Nervous system invasion by bacteria of the genus Brucella results in an inflammatory disorder termed neurobrucellosis. Herein, we discuss the mechanism of caspase-1 activation and IL-1β secretion in glial cells infected with B. abortus. Our results demonstrate that the ASC inflammasome is indispensable for inducing the activation of caspase-1 and secretion of IL-1β upon infection of astrocytes and microglia with Brucella. Moreover, our results demonstrate that secretion of IL-1β by Brucella-infected glial cells depends on NLRP3 and AIM2 and leads to neurobrucellosis. Further, the inhibition of the host cell inflammasome as an immune evasion strategy has been described for bacterial pathogens. We discuss here that the bacterial type IV secretion system VirB is required for inflammasome activation in host cells during infection. Taken together, our results indicate that Brucella is sensed by ASC inflammasomes mainly NLRP3 and AIM2 that collectively orchestrate a robust caspase-1 activation and pro-inflammatory response.

Enzymatically Inactive Procaspase 1 stabilizes the ASC Pyroptosome and Supports Pyroptosome Spreading during Cell Division

Caspase-1 is a key player during the initiation of pro-inflammatory innate immune responses, activating pro-IL-1β in so-called inflammasomes. A subset of patients with recurrent febrile episodes and systemic inflammation of unknown origin harbor mutations in CASP1 encoding caspase-1. CASP1 variants result in reduced enzymatic activity of caspase-1 and impaired IL-1β secretion. The apparent paradox of reduced IL-1β secretion but systemic inflammation led to the hypothesis that CASP1 mutations may result in variable protein interaction clusters, thus activating alternative signaling pathways. To test this hypothesis, we established and characterized an in vitro system of transduced immortalized murine macrophages expressing either WT or enzymatically inactive (p.C284A) procaspase-1 fusion reporter proteins. Macrophages with variant p.C284A caspase-1 did not secrete IL-1β and exhibited reduced inflammatory cell death, referred to as pyroptosis. Caspase-1 and apoptosis-associated speck-like protein containing a CARD (ASC) formed cytosolic macromolecular complexes (so-called pyroptosomes) that were significantly increased in number and size in cells carrying the p.C284A caspase-1 variant compared with WT caspase-1. Furthermore, enzymatically inactive caspase-1 interacted with ASC longer and with increased intensity compared with WT caspase-1. Applying live cell imaging, we documented for the first time that pyroptosomes containing enzymatically inactive variant p.C284A caspase-1 spread during cell division. In conclusion, variant p.C284A caspase-1 stabilizes pyroptosome formation, potentially enhancing inflammation by two IL-1β-independent mechanisms: pyroptosomes convey an enhanced inflammatory stimulus through the recruitment of additional proteins (such as RIP2, receptor interacting protein kinase 2), which is further amplified through pyroptosome and cell division.

Guidelines for the management and treatment of periodic fever syndromes: Cryopyrin-associated periodic syndromes (cryopyrinopathies - CAPS)

OBJECTIVE

To establish guidelines based on cientific evidences for the management of cryopyrin associated periodic syndromes.

DESCRIPTION OF THE EVIDENCE COLLECTION METHOD

The Guideline was prepared from 4 clinical questions that were structured through PICO (Patient, Intervention or indicator, Comparison and Outcome), to search in key primary scientific information databases. After defining the potential studies to support the recommendations, these were graduated considering their strength of evidence and grade of recommendation.

RESULTS

1215 articles were retrieved and evaluated by title and abstract; from these, 42 articles were selected to support the recommendations.

RECOMMENDATIONS

1. The diagnosis of CAPS is based on clinical history and clinical manifestations, and later confirmed by genetic study. CAPS may manifest itself in three phenotypes: FCAS (mild form), MWS (intermediate form) and CINCA (severe form). Neurological, ophthalmic, otorhinolaryngological and radiological assessments may be highly valuable in distinguishing between syndromes; 2. The genetic diagnosis with NLRP3 gene analysis must be conducted in suspected cases of CAPS, i.e., individuals presenting before 20 years of age, recurrent episodes of inflammation expressed by a mild fever and urticaria; 3. Laboratory abnormalities include leukocytosis and elevated serum levels of inflammatory proteins; and 4. Targeted therapies directed against interleukin-1 lead to rapid remission of symptoms in most patients. However, there are important limitations on the long-term safety. None of the three anti-IL-1β inhibitors prevents progression of bone lesions.

Virulent Mycobacterium bovis Beijing Strain Activates the NLRP7 Inflammasome in THP-1 Macrophages

Mycobacterium bovis is the causative agent of tuberculosis in a wide range of mammals, including humans. Macrophages are the first line of host defense. They secrete proinflammatory cytokines, such as interleukin-1 beta (IL-1β), in response to mycobacterial infection, but the underlying mechanisms by which human macrophages are activated and release IL-1β following M. bovis infection are poorly understood. Here we show that the ‘nucleotide binding and oligomerization of domain-like receptor (NLR) family pyrin domain containing 7 protein’ (NLRP7) inflammasome is involved in IL-1β secretion and caspase-1 activation induced by M. bovis infection in THP-1 macrophages. NLRP7 inflammasome activation promotes the induction of pyroptosis as well as the expression of tumor necrosis factor alpha (TNF-α), Chemokine (C-C motif) ligand 3 (CCL3) and IL-1β mRNAs. Thus, the NLRP7 inflammasome contributes to IL-1β secretion and induction of pyroptosis in response to M. bovis infection in THP-1 macrophages.