NLRP6 in infection and inflammation

Loss of NLRP6 expression increases the severity of intestinal injury after syngeneic hematopoietic stem cell transplantation

NLRP6 plays a crucial role in maintaining intestinal homeostasis by regulating the interaction between the intestinal mucosa and the microbiota. However, the impact of NLRP6 deficiency on intestinal damage following hematopoietic stem cell transplantation (HSCT) remains poorly understood. In this study, we established a syngeneic HSCT mouse model using C57BL/6 mice as donors and NLRP6-/- or C57BL/6 mice as recipients. Our findings revealed that NLRP6 deficiency had minimal influence on peripheral blood cell counts and splenic immune cell proportions in transplanted mice. However, it exacerbated pathological changes in the small intestine on day 14 post-transplantation, accompanied by increased proportions of macrophages, dendritic cells, and neutrophils. Furthermore, the NLRP6 deficiency resulted in elevated expression of MPO and CD11b, while reducing the levels mature caspase-1 and mature IL-1β in the intestine. Moreover, the NLRP6 deficiency disturbed the expression of apoptosis-related molecules and decreased the tight junction protein occludin. Notably, recipient mice with NLRP6 deficiency exhibited lower mRNA expression levels of antimicrobial genes, such as Reg3γ and Pla2g2a. The short-term increase in inflammatory cell infiltration caused by NLRP6 deficiency was associated with intestinal damage, increased apoptosis, reduced expression of antimicrobial peptides, and impaired intestinal repair. Taken together, our findings demonstrate that the loss of NLRP6 exacerbates post-transplantation intestinal damage in recipient mice.

Nod-like receptors in inflammatory arthritis

Nod-like receptors (NLRs) are innate immune receptors that play a key role in sensing components from pathogens and from damaged cells or organelles. NLRs form signaling complexes that can lead to activation of transcription factors or effector caspases - by means of inflammasome activation -Inflammatory arthritis (IA) culminating in promoting inflammation. An increasing body of research supports the role of NLRs in driving pathogenesis of IA, a collection of diseases that include rheumatoid arthritis (RA), psoriatic arthritis (PsA), ankylosing spondylitis, and pediatric arthritis. In this review, we briefly discuss the main drivers of IA diseases and dive into the evidence for - and against - various NLRs in driving these diseases. We also review the studies examining the use of NLR and inflammasome inhibitors as potential therapies for IA.

The role of the glucocorticoid receptor and its impact on steroid response in moderate-severe COVID-19 patients

The effect of corticosteroid therapy in COVID-19 patients is mediated by its suppressive effect on the regulations of inflammatory response. However, its clinical outcome is often unpredictable. This study aimed to explore the role of glucocorticoid receptors in corticosteroid response in Moderate-Severe COVID-19 patients. In this cross-sectional study, we attempted to find the relationship between the expression of the glucocorticoid receptor (encoded by NR3C1), the variation of glucocorticoid receptors isoform, and the mutations of glucocorticoid receptors exon with clinical response to corticosteroids. In addition, the relationship between glucocorticoid receptors expression and the expression of IκBα (encoded by NFKBIA) and glucocorticoid-induced leucine zipper protein (GILZ; encoded by TSC22D3) as steroid pathways was also evaluated. Thirty-four COVID-19 patients were studied. Blood was drawn before and on day 5 of corticosteroid treatment. Glucocorticoid receptors expression, isoform, and mutation were determined by RNA sequencing from white blood cells. Based on the improvement of clinical and oxygen status, patients were classified into responder and non-responder groups. Of thirty-four patients, 23 (67.6%) showed excellent responses to corticosteroids, and 11 (32.4%) were non-responders. The NR3C1 gene expression was significantly higher in the responsive group at baseline and after five days of glucocorticoid treatment. Isoform variant and mutation of glucocorticoid receptors did not correlate with clinical response. The expression of IκBα and GILZ correlated positively with glucocorticoid receptors expression. This study elucidates the relationship between glucocorticoid receptor expression with therapeutic responses to corticosteroids in moderate-severe COVID-19.

Role of the inflammasome in insulin resistance and type 2 diabetes mellitus

The inflammasome is a protein complex composed of a variety of proteins in cells and which participates in the innate immune response of the body. It can be activated by upstream signal regulation and plays an important role in pyroptosis, apoptosis, inflammation, tumor regulation, etc. In recent years, the number of metabolic syndrome patients with insulin resistance (IR) has increased year by year, and the inflammasome is closely related to the occurrence and development of metabolic diseases. The inflammasome can directly or indirectly affect conduction of the insulin signaling pathway, involvement the occurrence of IR and type 2 diabetes mellitus (T2DM). Moreover, various therapeutic agents also work through the inflammasome to treat with diabetes. This review focuses on the role of inflammasome on IR and T2DM, pointing out the association and utility value. Briefly, we have discussed the main inflammasomes, including NLRP1, NLRP3, NLRC4, NLRP6 and AIM2, as well as their structure, activation and regulation in IR were described in detail. Finally, we discussed the current therapeutic options-associated with inflammasome for the treatment of T2DM. Specially, the NLRP3-related therapeutic agents and options are widely developed. In summary, this article reviews the role of and research progress on the inflammasome in IR and T2DM.

Insights into inflammasome regulation: cellular, molecular, and pathogenic control of inflammasome activation

Maintenance of immune homeostasis is an intricate process wherein inflammasomes play a pivotal role by contributing to innate and adaptive immune responses. Inflammasomes are ensembles of adaptor proteins that can trigger a signal following innate sensing of pathogens or non-pathogens eventuating in the inductions of IL-1β and IL-18. These inflammatory cytokines substantially influence the antigen-presenting cell's costimulatory functions and T helper cell differentiation, contributing to adaptive immunity. As acute and chronic disease conditions may accompany parallel tissue damage, we analyze the critical role of extracellular factors such as cytokines, amyloids, cholesterol crystals, etc., intracellular metabolites, and signaling molecules regulating inflammasome activation/inhibition. We develop an operative framework for inflammasome function and regulation by host cell factors and pathogens. While inflammasomes influence the innate and adaptive immune components' interplay modulating the anti-pathogen adaptive immune response, pathogens may target inflammasome inhibition as a survival strategy. As trapped between health and diseases, inflammasomes serve as promising therapeutic targets and their modus operandi serves as a scientific rationale for devising better therapeutic strategies.

NLRP7: From inflammasome regulation to human disease

Nucleotide-binding oligomerization domain (NOD) and leucine-rich repeat (LRR)-containing receptors or NOD-like receptors (NLRs) are cytosolic pattern recognition receptors, which sense conserved microbial patterns and host-derived danger signals to elicit innate immune responses. The activation of several prototypic NLRs, including NLR and pyrin domain (PYD) containing (NLRP) 1, NLRP3 and NLR and caspase recruitment domain (CARD) containing (NLRC) 4, results in the assembly of inflammasomes, which are large, cytoplasmic multiprotein signalling platforms responsible for the maturation and release of the pro-inflammatory cytokines IL-1β and IL-18, and for the induction of a specialized form of inflammatory cell death called pyroptosis. However, the function of other members of the NLR family, including NLRP7, are less well understood. NLRP7 has been linked to innate immune signalling, but its precise role is still controversial as it has been shown to positively and negatively affect inflammasome responses. Inflammasomes are essential for homeostasis and host defence, but inappropriate inflammasome responses due to hereditary mutations and somatic mosaicism in inflammasome components and defective regulation have been linked to a broad spectrum of human diseases. A compelling connection between NLRP7 mutations and reproductive diseases, and in particular molar pregnancy, has been established. However, the molecular mechanisms by which NLRP7 mutations contribute to reproductive diseases are largely unknown. In this review, we focus on NLRP7 and discuss the current evidence of its role in inflammasome regulation and its implication in human reproductive diseases.

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.

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.

Transcriptome Based Profiling of the Immune Cell Gene Signature in Rat Experimental Colitis and Human IBD Tissue Samples

Chronic intestinal inflammation is characteristic of Inflammatory Bowel Disease (IBD) that is associated with the exaggerated infiltration of immune cells. A complex interplay of inflammatory mediators and different cell types in the colon are responsible for the maintenance of tissue homeostasis and affect pathological conditions. Gene expression alteration of colon biopsies from IBD patients and an in vivo rat model of colitis were examined by RNA-Seq and QPCR, while we used in silico methods, such as Ingenuity Pathway Analysis (IPA) application and the Immune Gene Signature (ImSig) package of R, to interpret whole transcriptome data and estimate immune cell composition of colon tissues. Transcriptome profiling of in vivo colitis model revealed the most significant activation of signaling pathways responsible for leukocyte recruitment and diapedesis. We observed significant alteration of genes related to glycosylation or sensing of danger signals and pro- and anti-inflammatory cytokines and chemokines, as well as adhesion molecules. We observed the elevated expression of genes that implies the accumulation of monocytes, macrophages, neutrophils and B cells in the inflamed colon tissue. In contrast, the rate of T-cells slightly decreased in the inflamed regions. Interestingly, natural killer and plasma cells do not show enrichment upon colon inflammation. In general, whole transcriptome analysis of the in vivo experimental model of colitis with subsequent bioinformatics analysis provided a better understanding of the dynamic changes in the colon tissue of IBD patients.

Cellular Stress and General Pathological Processes

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

Role of NLRP6 in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic intestinal inflammatory disease of unknown etiology. The symptoms of IBD are prone to recurrent episodes, and there is currently limited treatment and efficacy. Recently, there have been many studies showing that the nucleotide-binding oligomerization domain-like receptor containing the pyrin domain containing protein (NLR family, pyrin domain containing 6, NLRP6) regulates intestinal immunity and microorganisms in inflammatory bowel disease and related tumors. NLRP6 promotes the secretion of interleukin (IL)-18 and antimicrobial peptides, and IL-18 can inhibit the production of IL-22BP, enhance the role of IL-22, and promote the proliferation of epithelial cells through the MyD88 pathway. NLRP6 also regulates the secretion of mucoprotein 2 by goblet cells via Toll-like receptors, clears intestinal bacteria, regulates intestinal immune function, and maintains intestinal flora. Because IBD is associated with a tendency of malignant transformation, and researchers have found that NLRP6 can act on NOTCH and Wnt, activate chemokine ligand 5 and IL-6 signaling, regulate epithelial cell proliferation, and affect the development of IBD-related colorectal cancer. This article reviews the role of NLRP6 in IBD.

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.

Effects of NLRP6 in Cerebral Ischemia/Reperfusion (I/R) Injury in Rats

The NOD-like receptor protein 6 (NLRP6), an intracytoplasmic pattern recognition receptor in the nucleotide-binding domain, leucine-rich repeat-containing (NLR) innate immune receptor family, influences the inflammation reaction. The role of NLRP6 in cerebral ischemia-reperfusion (I/R) injury in rats is unclear. We explore the function of NLRP6 in cerebral I/R injury. The investigators used a middle cerebral artery occlusion/reperfusion model (MCAO) to imitate ischemic injury. We found the peak expression of NLRP6 is in 48-h post-cerebral I/R injury. The expression of NLRP6 siRNA, as well as the expression of protein and mRNA, was detected by Western blot and qRT-PCR. The degree of IL-1β and IL-18 was assessed by ELISA. After downregulating NLRP6, the expression of IL-1β, IL-18, cleaved Caspase-1, and myeloperoxidase (MPO) were reduced. In HE and Nissl staining, pathological injury of brain tissue after downregulating NLRP6 was improved. NLRP6 siRNA decreased the NLRP6-ASC binding states by CO-IP. NRP6 has a pro-inflammatory effect in cerebral I/R injury, which may provide a new target for the treatment of cerebral I/R injury.

Long noncoding RNA OIP5-AS1 aggravates cell proliferation, migration in gastric cancer by epigenetically silencing NLRP6 expression via binding EZH2

The critical role of long noncoding RNAs (lncRNAs) in the development of multiple cancers has been revealed either functioning as a tumor initiator or a cancer suppressor. A widely recognized OIP5 antisense RNA 1 (lncRNA OIP5-AS1) has been validated to be an essential regulator of the tumorigenesis of various malignancies. Whereas, the potential role and the exact mechanism of lncRNA OIP5-AS1 by which OIP5-AS1 mediates gastric cancer (GC) progression remains vague. Therefore, first our work probed its expression levels in GC cell lines and related normal cells by real-time quantitative polymerase chain reaction. The heightened level of OIP5-AS1 was detected in GC cell lines. In terms of its cellular effects, we performed a series of functional experiments and as presented in the assays, the proliferative potential and motility was diminished. However, more apoptotic cells were induced with the introduction of OIP5-AS1 silencing. Meanwhile, higher Nod-like receptor pyrin domain-containing protein 6 (NLRP6) and enhancer of zeste homolog 2 (EZH2) expression in the GC cells was monitored. Besides, OIP5-AS1 was disclosed to locate mainly in the nucleus. In terms of mechanism, OIP5-AS1 directly bound to EZH2 and obstructed NLRP6 expression, speeding up GC progression.

Microbiota and cancer: an update

The number of microbes in the human intestine is approximately 1 × 10¹⁴, while the number of eukaryotic cells in the human body is around 1 × 10¹³. As a result of co-evolution of the host mucosal immune system and the microbiota, both have developed multiple mechanisms to maintain homeostasis. Nevertheless, when these mechanisms are disturbed by pathogenic bacteria, which invade this fragile environment, the immune system responds to the microbiota and may support tumour growth in the intestine. Data advocate that the microbiota and its interactions with the host could also be implicated in carcinogenesis in other organs. It is nowadays suggested that developing methods to selectively manipulate components of the microbiota and ultimately target tumorigenesis represents a complex but exciting challenge. In this review, the main pathogenetic mechanisms of the interplay between the microbiome and the innate system, which may be implicated in tumorigenesis are discussed. Also, the importance of the gut microbiota regarding efficacy and toxicity of current chemotherapeutic agents, as well as the direct antitumor properties of the microbiota, will be reviewed.

The protective roles of NLRP6 in intestinal epithelial cells

The evolution of chronic inflammatory diseases is thought to be due to a combination of host genetic variations and environmental factors that include the alteration of intestinal flora, termed "dysbiosis." The intestinal mucosal barrier includes a chemical barrier and physical barrier that have important roles in protecting the intestine against inflammatory injury. The chemical barrier includes antimicrobial peptides (AMPs), and the physical barrier includes a mucous layer, a monolayer of intestinal epithelial cells and cell junctions. The intestinal mucosal barrier is not a static barrier, but rather, it strongly interacts with the gut microbiome and cells of the immune system. Correct expression of AMPs, together with mucus and balanced epithelial cell proliferation, prevents the occurrence of disease. NLRP6, a member of the nucleotide-binding domain, leucine-rich repeat-containing (NLR) innate immune receptor family, participates in the progression of intestinal inflammation and enteric pathogen infections. It has become apparent in recent years that NLRP6 is important in disease pathogenesis, as it responds to internal ligands that lead to the release of AMPs and mucus, thus regulating the regeneration of intestinal epithelial cells. This review summarizes the activation of NLRP6 and its protective role in the intestinal epithelial cell.

Effects of NLRP6 on the proliferation and activation of human hepatic stellate cells

Nod-like receptor pyrin domain-containing proteins (NLRPs) are known to take part in the pathogenesis of chronic liver diseases, including liver fibrosis. However, no known direct role of NLRP6, a member of NLRPs, has been reported in liver fibrosis. Here, we found that NLRP6 expression was decreased in fibrotic and cirrhotic livers. In a human hepatic stellate cell line, LX-2, overexpression of NLRP6 suppressed cell proliferation, hydroxyproline accumulation, as well as the expression of type I and type III collagens (Col-I and Col-III), α-smooth muscle actin (α-SMA) and matrix metalloproteinases (MMP2 and MMP9), whereas NLRP6 knockdown displayed reverse effects. Furthermore, NLRP6 significantly suppressed the phosphorylation of Smad2/3 (p-Smad2/3) and enhanced the expression of protein phosphatase magnesium dependent 1 A (PPM1A), the only phosphatase for Smad2/3. NLRP6 overexpression abrogated TGF-β1-stimulated hydroxyproline accumulation and p-Smad2/3. Co-immunoprecipitation assay demonstrated that NLRP6 was able to form a complex with PPM1A. NLRP6 overexpression did not change the level of p-Smad2/3 in LX-2 cells with PPM1A knockdown. These data indicated that PPM1A was required for the inhibitory effects of NLRP6 on TGF-β1/Smad2/3 signaling. In conclusion, our results suggest that NLRP6 exerts anti-fibrotic effects in LX-2 cells via regulating PPM1A/Smad2/3 and that NLRP6 may be an effective target in the treatment of liver fibrosis.

Aging and the Inflammasomes

The inflammasomes are innate immune system sensors that control the activation of caspase-1 and induce inflammation in response to infectious microbes and molecules originating from host proteins, leading to the release of pro-inflammatory cytokines, Il1b and IL18, and a particular inflammatory type of cell death termed pyroptosis. It is broadly considered that chronic inflammation may be a common link in age-related diseases, aging being the greatest risk factor for the development of chronic diseases. In this sense, we discuss the role of inflammasomes in non-infectious inflammation and their interest in aging and age-related diseases.

LRP6 targeting suppresses gastric tumorigenesis via P14ARF-Mdm2-P53-dependent cellular senescence

NLRP6, a member of the Nod-like receptor family, protects against chemically induced intestinal injury and colitis-associated colon cancer. However, the cellular mechanisms involved in this NLRP6-mediated protection remain unclear. Here, we show that NLRP6 was down-regulated in approximately 75% of primary gastric cancer cases and exhibited significant associations with advanced clinical-stage lymph node metastasis and poor overall survival. Functional studies established that ectopic overexpression or down-regulation of NLRP6 inhibited cancer cell proliferation by inducing cell cycle arrest at the G1 phase via P21 and Cyclin D1 both in vitro and in vivo. Activation of the P14^ARF-P53 pathway played a crucial role in the observed cellular senescence. We further demonstrated that ectopic overexpression of NLRP6 combined with inactivation of NF-κB(p65) and Mdm2 activates P14^ARF-P53 to promote the senescence of gastric cancer cells. These findings indicate that NLRP6 functions as a negative regulator of gastric cancer and offer a potential new option for preventing gastric cancer.

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.

NLRP6 facilitates the interaction between TAB2/3 and TRIM38 in rheumatoid arthritis fibroblast-like synoviocytes

In the present study, we investigated the role of nucleotide oligomerization domain-like receptor family pyrin domain containing 6 (NLRP6) in rheumatoid arthritis (RA) and explored the underlying mechanism. We found that both mRNA and protein levels of NLRP6 are attenuated in synovial tissues and fibroblast-like synoviocytes (FLS) of RA patients compared to patients with osteoarthritis. We also observed that pro-inflammatory cytokine production is decreased and nuclear factor-kappa B activation is inhibited in NLRP6-overexpressing RA-FLS. Furthermore, we found that NLRP6 overexpression promotes transforming growth factor-b-activated kinase 1-binding protein 2/3 lysosome-dependent degradation, and we provide evidence showing that NLRP6 plays the role of providing the docking site to facilitate the interaction between transforming growth factor-b-activated kinase 1-binding protein 2/3 and tripartite motif 38 in RA-FLS.

The NLRP3 inflammasome contributes to host protection during Sporothrix schenckii infection

Sporotrichosis is a mycosis caused by fungi from the Sporothrix schenckii species complex, whose prototypical member is Sporothrix schenckii sensu stricto. Pattern recognition receptors (PRRs) recognize and respond to pathogen-associated molecular patterns (PAMPs) and shape the following adaptive immune response. A family of PRRs most frequently associated with fungal recognition is the nucleotide-binding oligomerization domain-like receptor (NLR). After PAMP recognition, NLR family pyrin domain-containing 3 (NLRP3) binds to apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) and caspase-1 to form the NLRP3 inflammasome. When activated, this complex promotes the maturation of the pro-inflammatory cytokines interleukin-1β (IL-1β) and IL-18 and cell death through pyroptosis. In this study, we aimed to evaluate the importance of the NLRP3 inflammasome in the outcome of S. schenckii infection using the following three different knockout (KO) mice: NLRP3^-/- , ASC^-/- and caspase-1^-/- . All KO mice were more susceptible to infection than the wild-type, suggesting that NLRP3-triggered responses contribute to host protection during S. schenckii infection. Furthermore, the NLRP3 inflammasome appeared to be critical for the ex vivo release of IL-1β, IL-18 and IL-17 but not interferon-γ. Additionally, a role for the inflammasome in shaping the adaptive immune response was suggested by the lower frequencies of type 17 helper T (Th17) cells and Th1/Th17 but not Th1 cells in S. schenckii-infected KO mice. Overall, our results indicate that the NLRP3 inflammasome links the innate recognition of S. schenckii to the adaptive immune response, so contributing to protection against this infection.

Inflammatory pathway genes associated with inter-individual variability in the trajectories of morning and evening fatigue in patients receiving chemotherapy

Fatigue, a highly prevalent and distressing symptom during chemotherapy (CTX), demonstrates diurnal and interindividual variability in severity. Little is known about the associations between variations in genes involved in inflammatory processes and morning and evening fatigue severity during CTX. The purposes of this study, in a sample of oncology patients (N=543) with breast, gastrointestinal (GI), gynecological (GYN), or lung cancer who received two cycles of CTX, were to determine whether variations in genes involved in inflammatory processes were associated with inter-individual variability in initial levels as well as in the trajectories of morning and evening fatigue. Patients completed the Lee Fatigue Scale to determine morning and evening fatigue severity a total of six times over two cycles of CTX. Using a whole exome array, 309 single nucleotide polymorphisms SNPs among the 64 candidate genes that passed all quality control filters were evaluated using hierarchical linear modeling (HLM). Based on the results of the HLM analyses, the final SNPs were evaluated for their potential impact on protein function using two bioinformational tools. The following inflammatory pathways were represented: chemokines (3 genes); cytokines (12 genes); inflammasome (11 genes); Janus kinase/signal transducers and activators of transcription (JAK/STAT, 10 genes); mitogen-activated protein kinase/jun amino-terminal kinases (MAPK/JNK, 3 genes); nuclear factor-kappa beta (NFkB, 18 genes); and NFkB and MAP/JNK (7 genes). After controlling for self-reported and genomic estimates of race and ethnicity, polymorphisms in six genes from the cytokine (2 genes); inflammasome (2 genes); and NFkB (2 genes) pathways were associated with both morning and evening fatigue. Polymorphisms in six genes from the inflammasome (1 gene); JAK/STAT (1 gene); and NFkB (4 genes) pathways were associated with only morning fatigue. Polymorphisms in three genes from the inflammasome (2 genes) and the NFkB (1 gene) pathways were associated with only evening fatigue. Taken together, these findings add to the growing body of evidence that suggests that morning and evening fatigue are distinct symptoms.

The sooner the better: innate immunity as a path toward the HIV cure

To combat the diverse pathogens that infect humans, the immune system has evolved complex and diverse transcriptional signatures, which drive differential cellular and humoral responses. These signatures are induced by immune receptor sensing of pathogens and by cytokines produced at the earliest onset of infection. The specific nature of immune activation is as critical to pathogen clearance as the induction of an adaptive immune response. This is particularly true for HIV, which has developed numerous immune evasion mechanisms. In this review, we will highlight recent findings that show the differential role for early innate immune responses in promoting infection versus clearance and demonstrate the need for continued research on these pathways for development of effective HIV treatments.

Zisheng Shenqi decoction ameliorates monosodium urate crystal-induced gouty arthritis in rats through anti-inflammatory and anti-oxidative effects

Based on traditional Chinese medicinal theories on gouty arthritis, Zisheng Shenqi decoction (ZSD), a novel Chinese medicinal formula, was developed due to its multiple functions, including reinforcing renal function, promoting blood circulation and relieving pain. In the present study, the effect of ZSD on monosodium urate (MSU) crystal-induced gouty arthritis in rats was investigated and the underlying mechanisms were examined. The data from these investigations showed that the injection of MSU crystals into the ankle joint cavity caused significant elevations in ankle swelling and inflammatory cell infiltration into the synovium, whereas these abnormal changes were markedly suppressed by oral administration of ZSD (40 mg/kg) for 7 days. Mechanically, ZSD treatment prevented MSU crystal-induced inflammatory responses, as evidenced by downregulation in the expression levels of NACHT domain, leucine-rich repeat and pyrin domain containing protein (NALP) 1 and NALP6 inflammasomes, decreased serum levels of tumor necrosis factor-α and interleukin-1β, and inhibited activation of nuclear factor-κB. In addition, ZSD administration markedly enhanced the anti-oxidant status in MSU crystal-induced rats by the increase in the activities of superoxide dismutase and glutathione peroxidase, and the levels of reduced glutathione. These results indicated that ZSD effectively prevented MSU crystal-induced gouty arthritis via modulating multiple anti-oxidative and anti-inflammatory pathways, suggesting a promising herbal formula for the prevention and treatment of gouty arthritis.

Nlrp6 promotes recovery after peripheral nerve injury independently of inflammasomes

Background

NOD-like receptors (Nlrs) are key regulators of immune responses during infection and autoimmunity. A subset of Nlrs assembles inflammasomes, molecular platforms that are activated in response to endogenous danger and microbial ligands and that control release of interleukin (IL)-1β and IL-18. However, their role in response to injury in the nervous system is less understood.

Methods

In this study, we investigated the expression profile of major inflammasome components in the peripheral nervous system (PNS) and explored the physiological role of different Nlrs upon acute nerve injury in mice.

Results

While in basal conditions, predominantly members of NOD-like receptor B (Nlrb) subfamily (NLR family, apoptosis inhibitory proteins (NAIPs)) and Nlrc subfamily (ICE-protease activating factor (IPAF)/NOD) are detected in the sciatic nerve, injury causes a shift towards expression of the Nlrp family. Sterile nerve injury also leads to an increase in expression of the Nlrb subfamily, while bacteria trigger expression of the Nlrc subfamily. Interestingly, loss of Nlrp6 led to strongly impaired nerve function upon nerve crush. Loss of the inflammasome adaptor apoptosis-associated speck-like protein containing a CARD (ASC) and effector caspase-1 and caspase-11 did not affect sciatic nerve function, suggesting that Nlrp6 contributed to recovery after peripheral nerve injury independently of inflammasomes. In line with this, we did not detect release of mature IL-1β upon acute nerve injury despite potent induction of pro-IL-1β and inflammasome components Nlrp3 and Nlrp1. However, Nlrp6 deficiency was associated with increased pro-inflammatory extracellular regulated MAP kinase (ERK) signaling, suggesting that hyperinflammation in the absence of Nlrp6 exacerbated peripheral nerve injury.

Conclusions

Together, our observations suggest that Nlrp6 contributes to recovery from peripheral nerve injury by dampening inflammatory responses independently of IL-1β and inflammasomes.

IL-18 triggered by the Nlrp3 inflammasome induces host innate resistance in a pulmonary model of fungal infection

Pathogens are sensed by innate immune receptors that initiate an efficient adaptive immune response upon activation. The elements of the innate immune recognition process for Paracoccidioides brasiliensis include TLR-2, TLR-4, and dectin-1. However, there are additional receptors necessary for the host immune responses to P. brasiliensis. The nucleotide-binding oligomerization domain-like receptor (NLRs), which activate inflammasomes, are candidate receptors that deserve renewed investigation. After pathogen infection, the NLRs form large signaling platforms called inflammasomes, which lead to caspase-1 activation and maturation of proinflammatory cytokines (IL-18 and IL-1β). In this study, we showed that NLR family pyrin domain-containing 3 (Nlrp3) is required to induce caspase-1 activation and further secretion of IL-1β and IL-18 by P. brasiliensis-infected macrophages. Additionally, potassium efflux and lysosomal acidification induced by the fungus were important steps in the caspase-1 activation mechanism. Notably, Nlrp3 and caspase-1 knockout mice were more susceptible to infection than were the wild-type animals, suggesting that the Nlrp3-dependent inflammasomes contribute to host protection against P. brasiliensis. This protective effect occurred owing to the inflammatory response mediated by IL-18, as shown by an augmented fungus burden in IL-18 knockout mice. Taken together, our results show that the Nlrp3 inflammasome is essential for resistance against P. brasiliensis because it orchestrates robust caspase-1 activation and triggers an IL-18-dependent proinflammatory response.

Collaborative action of Toll-like and NOD-like receptors as modulators of the inflammatory response to pathogenic bacteria

Early sensing of pathogenic bacteria by the host immune system is important to develop effective mechanisms to kill the invader. Microbial recognition, activation of signaling pathways, and effector mechanisms are sequential events that must be highly controlled to successfully eliminate the pathogen. Host recognizes pathogens through pattern-recognition receptors (PRRs) that sense pathogen-associated molecular patterns (PAMPs). Some of these PRRs include Toll-like receptors (TLRs), nucleotide-binding oligomerization domain-like receptors (NLRs), retinoic acid-inducible gene-I- (RIG-I-) like receptors (RLRs), and C-type lectin receptors (CLRs). TLRs and NLRs are PRRs that play a key role in recognition of extracellular and intracellular bacteria and control the inflammatory response. The activation of TLRs and NLRs by their respective ligands activates downstream signaling pathways that converge on activation of transcription factors, such as nuclear factor-kappaB (NF-κB), activator protein-1 (AP-1) or interferon regulatory factors (IRFs), leading to expression of inflammatory cytokines and antimicrobial molecules. The goal of this review is to discuss how the TLRs and NRLs signaling pathways collaborate in a cooperative or synergistic manner to counteract the infectious agents. A deep knowledge of the biochemical events initiated by each of these receptors will undoubtedly have a high impact in the design of more effective strategies to control inflammation.

Antimicrobial inflammasomes: unified signalling against diverse bacterial pathogens

Inflammasomes - molecular platforms for caspase-1 activation - have emerged as common hubs for a number of pathways that detect and respond to bacterial pathogens. Caspase-1 activation results in the secretion of bioactive IL-1β and IL-18 and pyroptosis, and thus launches a systemic immune and inflammatory response. In this review we discuss signal transduction leading to 'canonical' and 'non-canonical' activation of caspase-1 through the involvement of upstream caspases. Recent studies have identified a growing number of regulatory networks involving guanylate binding proteins, protein kinases, ubiquitylation and necroptosis related pathways that modulate inflammasome responses and immunity to bacterial infection. By being able to respond to extracellular, vacuolar and cytosolic bacteria, their cytosolic toxins or ligands for cell surface receptors, inflammasomes have emerged as important sentinels of infection.

Inflammasomes

Inflammasomes are large cytosolic multiprotein complexes that assemble in response to detection of infection- or stress-associated stimuli and lead to the activation of caspase-1-mediated inflammatory responses, including cleavage and unconventional secretion of the leaderless proinflammatory cytokines IL-1β and IL-18, and initiation of an inflammatory form of cell death referred to as pyroptosis. Inflammasome activation can be induced by a wide variety of microbial pathogens and generally mediates host defense through activation of rapid inflammatory responses and restriction of pathogen replication. In addition to its role in defense against pathogens, recent studies have suggested that the inflammasome is also a critical regulator of the commensal microbiota in the intestine. Finally, inflammasomes have been widely implicated in the development and progression of various chronic diseases, such as gout, atherosclerosis, and metabolic syndrome. In this perspective, we discuss the role of inflammasomes in infectious and noninfectious inflammation and highlight areas of interest for future studies of inflammasomes in host defense and chronic disease.

The fire within: microbes inflame tumors

The immune system and the microbiota mutually interact to maintain homeostasis in the intestine. However, components of the microbiota can alter this balance and promote chronic inflammation, promoting intestinal tumor development. We review recent advances in understanding the complex interactions between the microbiota and the innate and adaptive immune systems and discuss their potential to lead us in new directions for understanding cancer biology and treatment.

Debug Your Bugs - How NLRs Shape Intestinal Host-Microbe Interactions

The host's ability to discriminate friend and foe and to establish a precise homeostasis with its associated microbiota is crucial for its survival and fitness. Among the mediators of intestinal host-microbe interactions, NOD-like receptor (NLR) proteins take center stage. They are present in the epithelial lining and innate immune cells that constantly monitor microbial activities at the intestinal barrier. Dysfunctional NLRs predispose to intestinal inflammation as well as sensitization to extra-intestinal immune-mediated diseases and are linked to the alteration of microbial communities. Here, we review advances in our understanding of their reciprocal relationship in the regulation of intestinal homeostasis and implications for intestinal health.