Inflammasome activation has an important role in the development of spontaneous colitis

Divergent Roles for the IL-1 Family in Gastrointestinal Homeostasis and Inflammation

Inflammatory disorders of the gastro-intestinal tract are a major cause of morbidity and significant burden from a health and economic perspective in industrialized countries. While the incidence of such conditions has a strong environmental component, in particular dietary composition, epidemiological studies have identified specific hereditary mutations which result in disequilibrium between pro- and anti-inflammatory factors. The IL-1 super-family of cytokines and receptors is highly pleiotropic and plays a fundamental role in the pathogenesis of several auto-inflammatory conditions including rheumatoid arthritis, multiple sclerosis and psoriasis. However, the role of this super-family in the etiology of inflammatory bowel diseases remains incompletely resolved despite extensive research. Herein, we highlight the currently accepted paradigms as they pertain to specific IL-1 family members and focus on some recently described non-classical roles for these pathways in the gastrointestinal tract. Finally, we address some of the shortcomings and sources of variance in the field which to date have yielded several conflicting results from similar studies and discuss the potential effect of these factors on data interpretation.

Stable IL- 1β-Activation in an Inflammasome Signalling Model Depends on Positive and Negative Feedbacks and Tight Regulation of Protein Production

INTRODUCTION

NLRP3-dependent inflammasome signalling is a key pathway during inflammatory processes and its deregulation is implicated in several diseases. NLRP3-inflammasome pathway activation leads to the rapid, phosphorylation-driven NF$\kappa$κB-pathway signalling, subsequently proceeds via slower transcription/translation process for producing pro-enzymes, and finally leads to the medium-speed enzymatic activation of the central inflammatory mediator IL-$1\beta$1β[1] . We here were interested in how the timing of the rate-limiting step of transcription/translation and the presence of a positive and negative auto-regulation would pose conditions for meaningful and stable IL-$1\beta$1β-activation.

METHODS

We extracted the essential topology of the inflammasome pathway network using a linear chain of first-order reaction and a second-order reaction for inhibitory feedback. We then performed an analytical treatment of the resulting ODE set to obtain closed-form formulae. We therefore looked for the steady states and characterized their stability by using a Jacobian-based, local analysis. We employed the Small Gain Theorem from Control Theory as recently applied by us [2] and the Gershgorin Circle Theorem to obtain mathematically exact conditions for a positive ON state and stabilities for ON and OFF steady states.

RESULTS

We identified an ON- and one OFF- steady state whose properties we characterized in terms of the kinetic parameters by closed-form formulae. We found that under the assumption of a first-order information flow through the network, the existence of a biologically reasonable ON steady state required the simultaneous presence of the positive and the negative feedback. Assuming non-competitivity between IL-$1\beta$1β entities binding to different receptors, we found that a minimum kinetics for protein production is required to sustain a steady state with IL-$1\beta$1β activation. Assuming competitivity between IL-$1\beta$1β entities introduced additional restrictions on the maximum protein production speed to guarantee a biologically reasonable ON steady state. Finally, for both models, we ruled out bistability, suggesting that IL-$1\beta$1β activation would undergo a smooth change upon alterations of its parameters.

CONCLUSION

Exemplified by the core pathway of NLRP3-inflammasome signalling, we here demonstrate that a mostly linear activation cascade containing an intermediate rate limiting step poses kinetic restrictions on this step and requires positive and negative autoregulation for obtaining a meaningful ON steady state. Due to the generality of our framework, our results are important for a wide class of receptor mediated-pathways, where a fast initial phosphorylation cascade is followed by a (slower) transcriptional response and subsequent autoregulation. Our results may further provide important design principles for synthetic biological networks involving biochemical activation and transcription/translation, by relating timing considerations and autoregulation to stable pathway activation.

Pretreatment with a Heat-Killed Probiotic Modulates the NLRP3 Inflammasome and Attenuates Colitis-Associated Colorectal Cancer in Mice

Colorectal cancer (CRC) is one of the most common malignancies worldwide. Inflammation contributes to cancer development and inflammatory bowel disease is an important risk factor for CRC. The aim of this study is to assess whether a widely used probiotic Enterococcus faecalis can modulate the NLRP3 inflammasome and protect against colitis and colitis-associated CRC. We studied the effect of heat-killed cells of E. faecalis on NLRP3 inflammasome activation in THP-1-derived macrophages. Pretreatment of E. faecalis or NLRP3 siRNA can inhibit NLRP3 inflammasome activation in macrophages in response to fecal content or commensal microbes, P. mirabilis or E. coli, according to the reduction of caspase-1 activation and IL-1β maturation. Mechanistically, E. faecalis attenuates the phagocytosis that is required for the full activation of the NLRP3 inflammasome. In in vivo mouse experiments, E. faecalis can ameliorate the severity of intestinal inflammation and thereby protect mice from dextran sodium sulfate (DSS)-induced colitis and the formation of CRC in wild type mice. On the other hand, E. faecalis cannot prevent DSS-induced colitis in NLRP3 knockout mice. Our findings indicate that application of the inactivated probiotic, E. faecalis, may be a useful and safe strategy for attenuation of NLRP3-mediated colitis and inflammation-associated colon carcinogenesis.

Myosin 1F Regulates M1-Polarization by Stimulating Intercellular Adhesion in Macrophages

Intestinal macrophages are highly mobile cells with extraordinary plasticity and actively contribute to cytokine-mediated epithelial cell damage. The mechanisms triggering macrophage polarization into a proinflammatory phenotype are unknown. Here, we report that during inflammation macrophages enhance its intercellular adhesion properties in order to acquire a M1-phenotype. Using in vitro and in vivo models we demonstrate that intercellular adhesion is mediated by integrin-αVβ3 and relies in the presence of the unconventional class I myosin 1F (Myo1F). Intercellular adhesion mediated by αVβ3 stimulates M1-like phenotype in macrophages through hyperactivation of STAT1 and STAT3 downstream of ILK/Akt/mTOR signaling. Inhibition of integrin-αVβ3, Akt/mTOR, or lack of Myo1F attenuated the commitment of macrophages into a pro-inflammatory phenotype. In a model of colitis, Myo1F deficiency strongly reduces the secretion of proinflammatory cytokines, decreases epithelial damage, ameliorates disease activity, and enhances tissue repair. Together our findings uncover an unknown role for Myo1F as part of the machinery that regulates intercellular adhesion and polarization in macrophages.

A decrease in anaerobic bacteria promotes Candida glabrata overgrowth while β-glucan treatment restores the gut microbiota and attenuates colitis

Background

The intestinal microbiota plays a crucial role in the maintenance of gut homeostasis. Changes in crosstalk between the intestinal epithelial cells, immune cells and the microbiota are critically involved in the development of inflammatory bowel disease. In the experimental mouse model, the development of colitis induced by dextran sulfate sodium (DSS) promotes overgrowth of the opportunistic yeast pathogen Candida glabrata. Conversely, fungal colonization aggravates inflammatory parameters. In the present study, we explored the effect of C. glabrata colonization on the diversity of the gut microbiota in a DSS-induced colitis model, and determined the impact of soluble β-glucans on C. glabrata-host interactions.

Results

Mice were administered a single inoculum of C. glabrata and were exposed to DSS treatment for 2 weeks in order to induce acute colitis. For β-glucan treatment, mice were administered with soluble β-glucans purified from C. glabrata (3 mg per mouse), orally and daily, for 5 days, starting on day 1. The number of C. glabrata colonies and changes in microbiota diversity were assessed in freshly collected stool samples from each tagged mouse, using traditional culture methods based on agar plates. An increase in Escherichia coli and Enterococcus faecalis populations and a reduction in Lactobacillus johnsonii and Bacteroides thetaiotaomicron were observed during colitis development. This decrease in L. johnsonii was significantly accentuated by C. glabrata overgrowth. Oral administration of β-glucans to mice decreased the overgrowth of aerobic bacteria and IL-1β expression while L. johnsonii and B. thetaiotaomicron populations increased significantly. β-glucan treatment increased IL-10 production via PPARγ sensing, promoting the attenuation of colitis and C. glabrata elimination.

Conclusions

This study shows that the colonic inflammation alters the microbial balance, while β-glucan treatment increases the anaerobic bacteria and promotes colitis attenuation and C. glabrata elimination.

A Comparative Study on the Efficacy of NLRP3 Inflammasome Signaling Inhibitors in a Pre-clinical Model of Bowel Inflammation

Nucleotide-binding oligomerization domain leucine rich repeat and pyrin domain-containing protein 3 (NLRP3) inflammasome is pivotal in maintaining intestinal homeostasis and sustaining enteric immune responses in the setting of inflammatory bowel diseases. Drugs acting as NLRP3 blockers could represent innovative strategies for treatment of bowel inflammation. This study was performed in rats with dinitrobenzenesulfonic acid (DNBS)-induced colitis, to investigate how the direct blockade of NLRP3 inflammasome with an irreversible inhibitor (INF39) compares with Ac-YVAD-cmk (YVAD, caspase-1 inhibitor) and anakinra (IL-1β receptor antagonist), acting downstream on NLRP3 signaling. Animals with DNBS-colitis received YVAD (3 mg/kg) or anakinra (100 mg/Kg) intraperitoneally, and INF39 (25 mg/kg) or dexamethasone (DEX, 1 mg/kg) orally for 6 days, starting on the same day of colitis induction. Under colitis, there was a body weight decrease, which was attenuated by YVAD, anakinra or INF39, but not DEX. All test drugs counteracted the increase in spleen weight. The colonic shortening and morphological colonic alterations associated with colitis were counteracted by INF39, anakinra and DEX, while YVAD was without effects. Tissue increments of myeloperoxidase, tumor necrosis factor and interleukin-1β were more effectively counteracted by INF39 and DEX, than YVAD and anakinra. These findings indicate that: (1) direct inhibition of NLRP3 inflammasome with INF39 is more effective than caspase-1 inhibition or IL-1β receptor blockade in reducing systemic and bowel inflammatory alterations; (2) direct NLRP3 inhibition can be a suitable strategy for treatment of bowel inflammation.

Growth differentiation factor 11 ameliorates experimental colitis by inhibiting NLRP3 inflammasome activation

Growth differentiation factor 11 (GDF11) has an anti-inflammatory effect in the mouse model of atherosclerosis and Alzheimer's disease, but how GDF11 regulates intestinal inflammation during ulcerative colitis (UC) is poorly defined. The Nod-like receptor family pyrin domain-1 containing 3 (NLRP3) inflammasome is closely associated with intestinal inflammation because of its ability to increase IL-1β secretion. Our aim is to determine whether GDF11 has an effect on attenuating experimental colitis in mice. In this study, using a dextran sodium sulfate (DSS)-induced acute colitis mouse model, we reported that GDF11 treatment attenuated loss of body weight, the severity of the disease activity index, shortening of the colon, and histological changes in the colon. GDF11 remarkably suppressed IL-1β secretion and NLRP3 inflammasome activation in colon samples and RAW 264.7 cells, such as the levels of NLRP3 and activated caspase-1. Furthermore, we found that GDF11 inhibited NLRP3 inflammasome activation by downregulating the Toll-like receptor 4/NF-κB p65 pathway and reactive oxygen species production via the typical Smad2/3 pathway. Thus, our research shows that GDF11 alleviates DSS-induced colitis by inhibiting NLRP3 inflammasome activation, providing some basis for its potential use in the treatment of UC. NEW & NOTEWORTHY Here, we identify a new role for growth differentiation factor 11 (GDF11), which ameliorates dextran sodium sulfate-induced acute colitis. Meanwhile, we discover a new phenomenon of GDF11 inhibiting IL-1β secretion and Nod-like receptor family pyrin domain-1 containing 3 (NLRP3) inflammasome activation. These findings reveal that GDF11 is a new potential candidate for the treatment of ulcerative colitis patients with a hyperactive NLRP3 inflammasome.

The Role of NLRP3 and IL-1β in the Pathogenesis of Inflammatory Bowel Disease

It is logical to assume that a major pro-inflammatory mechanism, i.e., the NLRP3 inflammasome would play a prominent role in the pathogenesis of the Inflammatory Bowel Disease (IBD) in humans. However, while both studies of murine models of gut disease and patients provide data that the main cytokine product generated by this inflammasome, IL-1β, does in fact contribute to inflammation in IBD, there is no evidence that IL-1β plays a decisive or prominent role in "ordinary" patients with IBD (Crohn's disease). On the other hand, there are several definable point mutations that result in over-active NLRP3 inflammasome activity and in these cases, the gut inflammation is driven by IL-1β and is treatable by biologic agents that block the effects of this cytokine.

Environmental Factors Modify the Severity of Acute DSS Colitis in Caspase-11-Deficient Mice

BACKGROUND

Human and mouse studies implicate the inflammasome in the pathogenesis of inflammatory bowel diseases, though the effects in mice are variable. The noncanonical inflammasome activator caspase-11 (Casp11) reportedly attenuates acute dextran sodium sulfate (DSS) colitis in mice. However, the effects of Casp11 on chronic experimental colitis and factors that influence the impact of Casp11 on acute DSS colitis are unknown.

METHODS

We studied the role of Casp11 in Il10-/- mice and acute and chronic DSS colitis mouse models. We quantified colonic Casp11 mRNA using quantative polymerase chain reaction and colitis using weight loss, blinded histological scoring, IL-12/23p40 secretion by colonic explants, and fecal lipocalin-2. We determined fecal microbial composition using 16S amplicon sequencing.

RESULTS

We detected increased colonic Casp11 mRNA in Il10-/- mice with chronic colitis, but not in mice with DSS colitis. The presence of Casp11 did not alter the severity of chronic colitis in DSS-treated or Il10-/- mice. Contrary to prior reports, we initially observed that Casp11 exacerbates acute DSS colitis. Subsequent experiments in the same animal facility revealed no effect of Casp11 on acute DSS colitis. There were pronounced stochastic changes in the fecal microbiome over this time. The majority of bacterial taxa that changed over time in wild-type vs Casp11-/- mice belong to the Clostridiales.

CONCLUSIONS

Casp11 does not impact chronic experimental colitis, and its effects on acute DSS colitis vary with environmental factors including the microbiota, particularly Clostridiales. Stochastic drifts in intestinal microbiota composition, even in mice in the same housing facility, should be considered when interpreting studies of acute DSS colitis models.

Preventive effect of bergenin against the development of TNBS-induced acute colitis in rats is associated with inflammatory mediators inhibition and NLRP3/ASC inflammasome signaling pathways

Ulcerative colitis is an idiopathic inflammatory bowel disease characterized by intestinal inflammation; blocking this inflammatory process may be the key to the development of new naturally occurring anti-inflammatory drugs, with greater efficiency and lower side effects. The objective of this study is to explore the effects of bergenin (BG) in TNBS (2,4,6-trinitrobenzenesulfonic acid)-induced acute colitis model in rats in order to assist in the studies for the development of novel natural product therapies for inflammatory bowel disease. 48 Wistar rats were randomized into six groups: (i) Control and (ii) TNBS control; (iii) 5-ASA 100 mg/kg/day (iv) BG 12 mg/kg/day (v) BG 25 mg/kg/day and (vi) BG 50 mg/kg/day. Colitis was induced by instillation of TNBS. Colitis was evaluated by an independent observer who was blinded to the treatment. Our results revealed that bergenin decreased the macroscopic and microscopic damage signs of colitis, and reduced the degree of neutrophilic infiltration in the colon tissue; also, it was capable to down-regulate COX-2, iNOS, IkB-α, and pSTAT3 protein expression. Similarly, using a protocol for indirect ELISA quantification of cytokines, bergenin treatment reduced IL-1β, IFN-γ and IL-10 levels, and inhibited both canonical (IL-1) and non-canonical (IL-11) NLRP3/ASC inflammasome signaling pathways in TNBS-induced acute colitis. Conclusion: Our study has provided evidence that administration of bergenin reduced the damage caused by TNBS in an experimental model of acute colitis in rats, reduced levels of pro-inflammatory proteins and cytokines probably by modulation of pSTAT3 and NF-κB signaling and blocking canonical and non-canonical NLRP3/ASC inflammasome pathways.

Milk Fat Globule Membrane Inhibits NLRP3 Inflammasome Activation and Enhances Intestinal Barrier Function in a Rat Model of Short Bowel

BACKGROUND

The milk fat globule membrane (MFGM) contains various bioactive components which have been shown to maintain gut barrier integrity. This study aimed to evaluate the protective effects of MFGM on intestinal barrier function and its possible mechanisms in a rat model of short bowel syndrome (SBS).

MATERIALS AND METHODS

Five-week-old male Sprague-Dawley rats were divided into 3 groups (n = 8 per group), consisting of Sham group and rats submitted to massive small-bowel resection then supplemented with either water (SBS) or 1.5g/kg/d MFGM (SBS+MFGM) by daily gavage. Rats were sacrificed on day 15 postoperation. Intestinal adaptation, gut permeability, bacterial translocation (BT), expression of tight junction proteins, mucin 1 (MUC1), and nucleotide-binding oligomerization domain leucine-rich repeat and pyrin domain-containing protein 3 (NLRP3) pathway in the ileum were evaluated.

RESULTS

Both SBS+MFGM and SBS groups exhibited lower body weight and higher ileum villus height than Sham group, but no difference was detected between each other. SBS group had significantly higher intestinal permeability and BT rate than other groups (P < .05). Compared with SBS rats, SBS+MFGM group showed higher expression of tight junction proteins and MUC1, lower expression of NLRP3 and caspase-1 in the ileum, as well as lower interleukin (IL)-1β but higher IL-18 levels in ileum tissue.

CONCLUSIONS

Supplementation of MFGM helps to modulate NLRP3 inflammasome activation and enhances gut barrier integrity in rats after massive small-bowel resection, which provides experimental support for potential applications of MGFM in intestinal barrier dysfunction, although further studies are needed.

Norisoboldine, a natural aryl hydrocarbon receptor agonist, alleviates TNBS-induced colitis in mice, by inhibiting the activation of NLRP3 inflammasome

Although the etiology of inflammatory bowel disease is still uncertain, increasing evidence indicates that the excessive activation of NLRP3 inflammasome plays a major role. Norisoboldine (NOR), an alkaloid isolated from Radix Linderae, has previously been demonstrated to inhibit inflammation and IL-1β production. The present study was to examine the effect of NOR on colitis and the underlying mechanism related to NLRP3 inflammasome activation. Our results showed that NOR alleviated colitis symptom in mice induced by 2, 4, 6-trinitrobenzene sulfonic acid (TNBS). Moreover, it significantly reduced expressions of cleaved IL-1β, NLRP3 and cleaved Caspase-1 but not ASC in colons of mice. In THP-1 cells, NOR suppressed the expressions of NLRP3, cleaved Caspase-1 and cleaved IL-1β but not ASC induced by lipopolysaccharide (LPS) and adenosine triphosphate (ATP). Furthermore, NOR could activate aryl hydrocarbon receptor (AhR) in THP-1 cells, inducing CYP1A1 mRNA expression, and promoting dissociation of AhR/HSP90 complexes, association of AhR and ARNT, AhR nuclear translocation, XRE reporter activity and binding activity of AhR/ARNT/XRE. Both siAhR and α-naphthoflavone (α-NF) markedly diminished the inhibition of NOR on NLRP3 inflammasome activation. In addition, NOR elevated Nrf2 level and reduced ROS level in LPS- and ATP-stimulated THP-1 cells, which was reversed by either siAhR or α-NF treatment. Finally, correlations between activation of AhR and attenuation of colitis, inhibition of NLRP3 inflammasome activation and up-regulation of Nrf2 level in colons were validated in mice with TNBS-induced colitis. Taken together, NOR ameliorated TNBS-induced colitis in mice through inhibiting NLRP3 inflammasome activation via regulating AhR/Nrf2/ROS signaling pathway.

Molecular Targets in Hepatocarcinogenesis and Implications for Therapy

Hepatocarcinogenesis comprises of multiple, complex steps that occur after liver injury and usually involve several pathways, including telomere dysfunction, cell cycle, WNT/β-catenin signaling, oxidative stress and mitochondria dysfunction, autophagy, apoptosis, and AKT/mTOR signaling. Following liver injury, gene mutations, accumulation of oxidative stress, and local inflammation lead to cell proliferation, differentiation, apoptosis, and necrosis. The persistence of this vicious cycle in turn leads to further gene mutation and dysregulation of pro- and anti-inflammatory cytokines, such as interleukin (IL)-1β, IL-6, IL-10, IL-12, IL-13, IL-18, and transforming growth factor (TGF)-β, resulting in immune escape by means of the NF-κB and inflammasome signaling pathways. In this review, we summarize studies focusing on the roles of hepatocarcinogenesis and the immune system in liver cancer. In addition, we furnish an overview of recent basic and clinical studies to provide a strong foundation to develop novel anti-carcinogenesis targets for further treatment interventions.

MCC950, a specific small molecule inhibitor of NLRP3 inflammasome attenuates colonic inflammation in spontaneous colitis mice

MCC950 a potent, highly specific small molecule inhibitor of canonical and noncanonical activation of NLRP3 inflammasome has been evaluated in a multitude of NLRP3 driven inflammatory diseases. However, the effect of MCC950 on colonic inflammation has not yet been reported. In the present study we investigated the effect of MCC950 in a spontaneous chronic colitis mouse model Winnie, which mimics human ulcerative colitis. Oral administration of 40 mg/kg MCC950 commencing at Winnie week seven for three weeks significantly improved body weight gain, colon length, colon weight to body weight ratio, disease activity index and histopathological scores. MCC950 significantly suppressed release of proinflammatory cytokines IL-1β, IL-18, IL1-α, IFNγ, TNF-α, IL6, IL17, chemokine MIP1a and Nitric Oxide in colonic explants. Moreover, MCC950 resulted in a significant decrease of IL-1β release and activation of caspase-1 in colonic explants and macrophage cells isolated from Winnie. Complete inhibition with MCC950 in Winnie colonic explants shows, for the first time, the contribution of inflammatory effects resulting exclusively from canonical and noncanonical NLRP3 inflammasome activation in colitis. Taken together, our results illustrate the efficacy of MCC950 in the treatment of murine ulcerative colitis and provides avenue for a potential novel therapeutic agent for human inflammatory bowel diseases.

Loss-of-function CARD8 mutation causes NLRP3 inflammasome activation and Crohn's disease

In these studies, we evaluated the contribution of the NLRP3 inflammasome to Crohn's disease (CD) in a kindred containing individuals having a missense mutation in CARD8, a protein known to inhibit this inflammasome. Whole exome sequencing and PCR studies identified the affected individuals as having a V44I mutation in a single allele of the T60 isoform of CARD8. The serum levels of IL-1β in the affected individuals were increased compared with those in healthy controls, and their peripheral monocytes produced increased amounts of IL-1β when stimulated by NLRP3 activators. Immunoblot studies probing the basis of these findings showed that mutated T60 CARD8 failed to downregulate the NLRP3 inflammasome because it did not bind to NLRP3 and inhibit its oligomerization. In addition, these studies showed that mutated T60 CARD8 exerted a dominant-negative effect by its capacity to bind to and form oligomers with unmutated T60 or T48 CARD8 that impeded their binding to NLRP3. Finally, inflammasome activation studies revealed that intact but not mutated CARD8 prevented NLRP3 deubiquitination and serine dephosphorylation. CD due to a CARD8 mutation was not effectively treated by anti-TNF-α, but did respond to IL-1β inhibitors. Thus, patients with anti-TNF-α-resistant CD may respond to this treatment option.

Microbiota Normalization Reveals that Canonical Caspase-1 Activation Exacerbates Chemically Induced Intestinal Inflammation

Inflammasomes play a central role in regulating intestinal barrier function and immunity during steady state and disease. Because the discoveries of a passenger mutation and a colitogenic microbiota in the widely used caspase-1-deficient mouse strain have cast doubt on previously identified direct functions of caspase-1, we reassessed the role of caspase-1 in the intestine. To this end, we generated Casp1^-/- and Casp11^-/- mice and rederived them into an enhanced barrier facility to standardize the microbiota. We found that caspase-11 does not influence caspase-1-dependent processing of IL-18 in homeostasis and during DSS colitis. Deficiency of caspase-1, but not caspase-11, ameliorated the severity of DSS colitis independent of microbiota composition. Ablation of caspase-1 in intestinal epithelial cells was sufficient to protect mice against DSS colitis. Moreover, Casp1^-/- mice developed fewer inflammation-induced intestinal tumors than control mice. These data show that canonical inflammasome activation controls caspase-1 activity, contributing to exacerbation of chemical-induced colitis.

The Goldilocks Conundrum: NLR Inflammasome Modulation of Gastrointestinal Inflammation during Inflammatory Bowel Disease

Recent advances have revealed significant insight into inflammatory bowel disease (IBD) pathobiology. Ulcerative colitis and Crohn's disease, the chronic relapsing clinical manifestations of IBD, are complex disorders with genetic and environmental influences. These diseases are associated with the dysregulation of immune tolerance, excessive inflammation, and damage to the epithelial cell barrier. Increasing evidence indicates that pattern recognition receptors, including Toll-like receptors (TLRs) and nucleotide-binding domain and leucine-rich repeat-containing proteins (NLRs), function to maintain immune system homeostasis, modulate the gastrointestinal microbiome, and promote proper intestinal epithelial cell regeneration and repair. New insights have revealed that NLR family members are essential components in maintaining this immune system homeostasis. To date, the vast majority of studies associated with NLRs have focused on family members that form a multiprotein signaling platform called the inflammasome. These signaling complexes are responsible for the cleavage and activation of the potent pleotropic cytokines IL-1β and IL-18, and they facilitate a unique form of cell death defined as pyroptosis. In this review, we summarize the current paradigms associated with NLR inflammasome maintenance of immune system homeostasis in the gastrointestinal system. New concepts related to canonical and noncanonical inflammasome signaling, as well as the implications of classical and alternative inflammasomes in IBD pathogenesis, are also reviewed.

Substance-P Ameliorates Dextran Sodium Sulfate-Induced Intestinal Damage by Preserving Tissue Barrier Function

Intestinal inflammation alters immune responses in the mucosa and destroys colon architecture, leading to serious diseases such as inflammatory bowel disease. Thus, the modulation of intestinal integrity and immune responses in IBD can be the critical factor to be considered to reduce the severity of damages. Substance-P (SP), endogenous peptide to be involved in cell proliferation, migration and immune modulation, can exert the therapeutic effect on diverse diseases including cornea damage, rheumatoid arthritis and diabetic complications. SP was found to elevate expression of junctional molecule. Considering the function of SP reported previously, it was inferred that SP is capable of exert the beneficial effect of SP on intestinal diseases by controlling intestinal structure as well as immune responses. In this study, we explored the therapeutic effect of SP on dextran sodium sulfate-induced intestine damage by injecting SP. The effects of SP were evaluated by analyzing crypt structures, proliferating cell pool and infiltration of immune cells. DSS treatment provoked abnormal immune response and disruption of intestine epithelial barrier. However, co-treatment of SP obviously blocked the development of intestinal damages by declining inflammatory responses and sustaining intestinal structure more intact. The treatment of SP to chronic damages also promoted intestinal regeneration by preserving the integrity of colon tissue. Moreover, DSS-induced reduction of epithelial junctional molecule was obviously inhibited by SP treatment in vitro. Taken together, our data indicate that SP can reduce intestinal damages, possibly by modulating barrier structure and immune response. Our results propose SP as candidate therapeutics in intestinal damages.

Characterization of Growth Hormone Resistance in Experimental and Ulcerative Colitis

Growth hormone (GH) resistance may develop as a consequence of inflammation during conditions such as inflammatory bowel disease, encompassing ulcerative colitis (UC). However, the specific role of the GH–insulin growth factor (IGF)-1-axis and/or the functional consequences of GH resistance in this condition are unclear. In situ hybridization targeting the GH receptor (GHR) and relevant transcriptional analyses were performed in patients with UC and in IL-10 knock-out mice with piroxicam accelerated colitis (PAC). Using cultured primary epithelial cells, the effects of inflammation on the molecular mechanisms governing GH resistance was verified. Also, the therapeutic potential of GH on mucosal healing was tested in the PAC model. Inflammation induced intestinal GH resistance in UC and experimental colitis by down-regulating GHR expression and up-regulating suppressor of cytokine signalling (SOCS) proteins. These effects are driven by pro-inflammatory mediators (tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6) as confirmed using primary epithelial cells. Treatment of experimental colitis with GH increased IGF-1 and body weight of the mice, but had no effects on colonic inflammation or mucosal healing. The high transcriptional similarity between UC and experimental colitis accentuates the formation of intestinal GH resistance during inflammation. Inflammation-induced GH resistance not only impairs general growth but induces a state of local resistance, which potentially impairs the actions of GH on mucosal healing during colitis when using long-acting GH therapy.

Inflammasomes and Cancer: The Dynamic Role of the Inflammasome in Tumor Development

Chronic Inflammation in tumor microenvironments is not only associated with various stages of tumor development, but also has significant impacts on tumor immunity and immunotherapy. Inflammasome are an important innate immune pathway critical for the production of active IL-1β and interleukin 18, as well as the induction of pyroptosis. Although extensive studies have demonstrated that inflammasomes play a vital role in infectious and autoimmune diseases, their role in tumor progression remains elusive. Multiple studies using a colitis-associated colon cancer model show that inflammasome components provide protection against the development of colon cancer. However, very recent studies demonstrate that inflammasomes promote tumor progression in skin and breast cancer. These results indicate that inflammasomes can promote and suppress tumor development depending on types of tumors, specific inflammasomes involved, and downstream effector molecules. The complicated role of inflammasomes raises new opportunities and challenges to manipulate inflammasome pathways in the treatment of cancer.

PTPN22 regulates NLRP3-mediated IL1B secretion in an autophagy-dependent manner

A variant within the gene locus encoding PTPN22 (protein tyrosine phosphatase, non-receptor type 22) emerged as an important risk factor for auto-inflammatory disorders, including rheumatoid arthritis, systemic lupus erythematosus and type 1 diabetes, but at the same time protects from Crohn disease, one of the 2 main forms of inflammatory bowel diseases. We have previously shown that loss of PTPN22 results in decreased NLRP3 (NLR family pyrin domain containing 3) activation and that this effect is mediated via enhanced NLRP3 phosphorylation. However, it is unclear how phosphorylation of NLRP3 mediates its inhibition. Here, we demonstrate that loss of macroautophagy/autophagy abrogates the inhibitory effect on NLRP3 activation observed upon loss of PTPN22. Phosphorylated, but not nonphosphorylated NLRP3 is found in autophagosomes, indicating that NLRP3 phosphorylation mediates its inactivation via promoting sequestration into phagophores, the precursors to autophagosomes. This finding shows that autophagy and NLRP3 inflammasome activation are connected, and that PTPN22 plays a key role in the regulation of those 2 pathways. Given its role in inflammatory disorders, PTPN22 might be an attractive therapeutic target, and understanding the cellular mechanisms modulated by PTPN22 is of crucial importance.

Comparison of Cytokine and Efflux Transporter Expression in Pediatric Versus Adult-onset Ulcerative Colitis

OBJECTIVES

Ulcerative colitis (UC), a chronic inflammation of the colon, is often more severe in children than adults. Identification of altered expression of efflux transporters, cytokines, and suppressor of cytokine signaling (SOCS) molecules in pediatric versus adult patients could provide insight into the differential molecular patterns related to the age and disease pathology.

METHODS

Mucosal samples from terminal ileum and colon in pediatric (9 UC-New, 4 UC-Remission) and adult (9 UC-New, 8 UC-Remission) patients were compared with healthy subjects (15 children and 10 adults) for mRNA expressions of several efflux transporters, cytokines, and SOCS molecules.

RESULTS

The inflamed colon interleukin (IL)-6, IL-17A, and interferon-γ levels were elevated in UC-New subgroups but close to control values in UC-Remission. IL-1β expression was increased only in UC-New children. Interestingly, uninflamed ileum also showed increased IL-6 and IL-1β levels in UC-New subgroups. SOCS1/SOCS3 expression pattern followed a trend observed for inflammatory cytokines only in children. Both children and adults had decreased multidrug resistance protein 1 expression in colon, which inversely correlated with disease score, IL-6 and interferon-γ levels in UC-New children. IL-2 expression was upregulated in UC-Remission, compared with controls.

CONCLUSIONS

Efflux transporter expression varies between UC children and adults except for decreased multidrug resistance protein 1. UC is characterized by a dysregulated TH1 and TH17 cytokine response irrespective of age at disease onset, with higher cytokine levels detected in children. Increased IL-2 levels in remission imply a protective role for regulatory T cells (Tregs).

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.

In Vivo and In Vitro Study on the Efficacy of Terpinen-4-ol in Dextran Sulfate Sodium-Induced Mice Experimental Colitis

The purpose of this study was to investigate the protective effects of Terpinen-4-ol (TER) on dextran sulfate sodium (DSS)-induced experimental colitis and clarify the possible mechanisms. In vivo, an acute colitis model was used to confirm the anti-inflammatory activity and the possible mechanisms of TER in C57BL/6 and NLRP3-/- mice. In vitro, we performed further study, using RAW264.7 cells and Caco-2 cells, to confirm the molecular mechanisms of TER on inflammatory response. In C57BL/6 mice, TER alleviated DSS-induced disease activity index (DAI), colon length shortening, colonic pathological damage, and myeloperoxidase (MPO) activities. The production of pro-inflammatory mediators was significantly decreased by TER. Furthermore, TER inhibited NF-κB and NLRP3 inflammasome activation. Surprisingly, TER reduced the plasmatic lipopolysaccharide (LPS) concentration and re-balanced Escherichia coli (E. coli) and Lactobacillus levels. In addition, TER prevented the impairment of colon epithelium barrier by regulating the expression of zonula occludens-1 and occludin. In vitro, the results showed that TER significantly suppressed NLRP3 inflammasome activation in LPS-stimulated RAW264.7 cells, as indicated by decreased expression of NLRP3 and caspase-1, and lowered interleukin-1β secretion. In contrast, mice deficient for NLRP3 were less sensitive to DSS-induced acute colitis, and TER treatment exerted little protective effect on DSS-induced intestinal inflammation in NLRP3-/- mice. The protective effect of TER may be largely attributed to its inhibition of NLRP3 inflammasome activation in colon. Taken together, our findings showed that TER might be a potential agent for the treatment of ulcerative colitis.

Myeloid-derived miR-223 regulates intestinal inflammation via repression of the NLRP3 inflammasome

Neudecker et al. define a role for a microRNA, miR-223, in regulating the inflammatory tone of the intestine by constraining nlrp3 inflammasome activation in CCR2⁺ monocytes and attenuating excessive IL-1β–driven inflammation. Therapeutic nanoparticle delivery of miR-223 mimetics limits experimental colitis.

MicroRNA (miRNA)-mediated RNA interference regulates many immune processes, but how miRNA circuits orchestrate aberrant intestinal inflammation during inflammatory bowel disease (IBD) is poorly defined. Here, we report that miR-223 limits intestinal inflammation by constraining the nlrp3 inflammasome. miR-223 was increased in intestinal biopsies from patients with active IBD and in preclinical models of intestinal inflammation. miR-223^-/y mice presented with exacerbated myeloid-driven experimental colitis with heightened clinical, histopathological, and cytokine readouts. Mechanistically, enhanced NLRP3 inflammasome expression with elevated IL-1β was a predominant feature during the initiation of colitis with miR-223 deficiency. Depletion of CCR2⁺ inflammatory monocytes and pharmacologic blockade of IL-1β or NLRP3 abrogated this phenotype. Generation of a novel mouse line, with deletion of the miR-223 binding site in the NLRP3 3′ untranslated region, phenocopied the characteristics of miR-223^-/y mice. Finally, nanoparticle-mediated overexpression of miR-223 attenuated experimental colitis, NLRP3 levels, and IL-1β release. Collectively, our data reveal a previously unappreciated role for miR-223 in regulating the innate immune response during intestinal inflammation.

In Vivo Study of the Efficacy of the Essential Oil of Zanthoxylum bungeanum Pericarp in Dextran Sulfate Sodium-Induced Murine Experimental Colitis

The purpose of this study was to investigate the protective effects and mechanisms of the essential oil of Zanthoxylum bungeanum pericarp (ZBEO) on dextran sulfate sodium (DSS)-induced experimental colitis in mice. ZBEO decreased DSS-induced body weight loss, the disease activity index, colon length shortening, colonic pathological damage, and myeloperoxidase activities. The production of pro-inflammatory mediators was significantly alleviated by ZBEO. Further mechanistic analysis showed that ZBEO inhibited inflammation by regulating NF-κB and PPARγ pathways. ZBEO also inhibited NLRP3 activation in colitis in mice. Furthermore, ZBEO contributed to the maintenance of tight junction architecture by regulating the expression of zonula occludens-1 during colitis. Surprisingly, treatment with ZBEO increased levels of the commensal bacteria containing Lactobacillus and Bifidobacteria but reduced Escherichia coli levels in the feces of mice. These results suggested that supplementation with ZBEO might provide a new dietary strategy for the prevention of ulcerative colitis.

HBV inhibits LPS-induced NLRP3 inflammasome activation and IL-1β production via suppressing the NF-κB pathway and ROS production

BACKGROUND & AIMS

Hepatitis B virus (HBV) has developed strategies to evade immune responses. However, the mechanisms involved remain unclear. The NLRP3 inflammasome plays crucial roles in antiviral host defense and its downstream factor IL-1β has been shown to inhibit HBV infection in vivo. This study aims to assess whether HBV can affect the NLRP3 inflammasome signaling pathways and shed light on the underlying mechanisms HBV utilizes to evade host innate immune responses.

METHODS

HBV inhibition of the lipopolysaccharide (LPS)-induced NLRP3 inflammasome activation was evaluated by Western blot, quantitative RT-PCR, flow cytometry and immunofluorescence.

RESULTS

Kupffer cells expressed significantly more NLRP3 and IL-1β after LPS stimulation; whereas, chronic HBV infection suppressed LPS-induced NLRP3 and pro-IL-1β expression as well as IL-1β maturation. This inhibitory activity is mediated by HBeAg, and is involved in the inhibition of NF-κB signal pathway and reactive oxygen species (ROS) production. The inhibitory effect of HBeAg was confirmed in patients with chronic hepatitis B (CHB) and hepatocellular carcinoma by comparing the levels of IL-1β and NLRP3-related proteins in para-carcinoma tissues from HBeAg-positive or negative patients. Moreover, chronic HBV infection increases the susceptibility of mice to S. typhimurium infection, possibly via inhibiting the NLRP3 inflammasome activation and IL-1β production.

CONCLUSIONS

HBeAg inhibits LPS-induced NLRP3 inflammasome activation and IL-1β production via suppressing NF-κB pathway and ROS production. This finding provides a novel mechanism for HBV-mediated suppression of innate immune responses, and identifies new therapeutic targets for chronic HBV infection and related diseases.

LAY SUMMARY

HBeAg suppresses LPS-induced NLRP3 inflammasome activation and IL-1β production in two ways, one is to repress NLRP3 and pro-IL-1β expression via inhibiting NF-κB phosphorylation, and the other is to repress caspase-1 activation and IL-1β maturation via inhibiting ROS production. This effect contributes to the HBV persistence and immune tolerance.

The RNA-binding protein Tristetraprolin (TTP) is a critical negative regulator of the NLRP3 inflammasome

The NLRP3 inflammasome is a central regulator of inflammation in many common diseases, including atherosclerosis and type 2 diabetes, driving the production of pro-inflammatory mediators such as IL-1β and IL-18. Due to its function as an inflammatory gatekeeper, expression and activation of NLRP3 need to be tightly regulated. In this study, we highlight novel post-transcriptional mechanisms that can modulate NLRP3 expression. We have identified the RNA-binding protein Tristetraprolin (TTP) as a negative regulator of NLRP3 in human macrophages. TTP targets AU-rich elements in the NLRP3 3'-untranslated region (UTR) and represses NLRP3 expression. Knocking down TTP in primary macrophages leads to an increased induction of NLRP3 by LPS, which is also accompanied by increased Caspase-1 and IL-1β cleavage upon NLRP3, but not AIM2 or NLRC4 inflammasome activation. Furthermore, we found that human NLRP3 can be alternatively polyadenylated, producing a short 3'-UTR isoform that excludes regulatory elements, including the TTP- and miRNA-223-binding sites. Because TTP also represses IL-1β expression, it is a dual inhibitor of the IL-1β system, regulating expression of the cytokine and the upstream controller NLRP3.

Canonical and Non-Canonical Activation of NLRP3 Inflammasome at the Crossroad between Immune Tolerance and Intestinal Inflammation

Several lines of evidence point out the relevance of nucleotide-binding oligomerization domain leucine rich repeat and pyrin domain-containing protein 3 (NLRP3) inflammasome as a pivotal player in regulating the integrity of intestinal homeostasis and shaping innate immune responses during bowel inflammation. Intensive research efforts are being made to achieve an integrated view about the protective/detrimental role of canonical and non-canonical NLRP3 inflammasome activation in the maintenance of intestinal microenvironment integrity. Evidence is also emerging that the pharmacological modulation of NLRP3 inflammasome could represent a promising molecular target for the therapeutic management of inflammatory immune-mediated gut diseases. The present review has been intended to provide a critical appraisal of the available knowledge about the role of canonical and non-canonical NLRP3 inflammasome activation in the dynamic interplay between microbiota, intestinal epithelium, and innate immune system, taken together as a whole integrated network regulating the maintenance/breakdown of intestinal homeostasis. Moreover, special attention has been paid to the pharmacological modulation of NLRP3 inflammasome, emphasizing the concept that this multiprotein complex could represent a suitable target for the management of inflammatory bowel diseases.

The mito-DAMP cardiolipin blocks IL-10 production causing persistent inflammation during bacterial pneumonia

Bacterial pneumonia is a significant healthcare burden worldwide. Failure to resolve inflammation after infection precipitates lung injury and an increase in morbidity and mortality. Gram-negative bacteria are common in pneumonia and increased levels of the mito-damage-associated molecular pattern (DAMP) cardiolipin can be detected in the lungs. Here we show that mice infected with Klebsiella pneumoniae develop lung injury with accumulation of cardiolipin. Cardiolipin inhibits resolution of inflammation by suppressing production of anti-inflammatory IL-10 by lung CD11b⁺Ly6G^intLy6C^loF4/80⁺ cells. Cardiolipin induces PPARγ SUMOylation, which causes recruitment of a repressive NCOR/HDAC3 complex to the IL-10 promoter, but not the TNF promoter, thereby tipping the balance towards inflammation rather than resolution. Inhibition of HDAC activity by sodium butyrate enhances recruitment of acetylated histone 3 to the IL-10 promoter and increases the concentration of IL-10 in the lungs. These findings identify a mechanism of persistent inflammation during pneumonia and indicate the potential of HDAC inhibition as a therapy.

Non-resolving bacterial pneumonia results in lung tissue damage owing to overactive inflammation. Here the authors show that the mitochondrial DAMP cardiolipin contributes to persistent inflammation by SUMOylating PPARγ, which promotes binding of the corepressor NCOR/HDAC3 complex to the IL-10 promoter.

Signal transduction analysis of the NLRP3-inflammasome pathway after cellular damage and its paracrine regulation

Activation of the NLRP3-inflammasome pathway and production of the inflammatory cytokine IL-1B after cellular damage caused by infarct or infection is a key process in several diseases such as acute myocardial infarction and inflammatory bowel disease. However, while the molecular triggers of the NLRP3-pathway after cellular damage are well known, the mechanisms that sustain or confine its activity are currently under investigation. We present here an Ordinary Differential Equation-based model that investigates the mechanisms of inflammasome activation and regulation in monocytes to predict IL-1β activation kinetics upon a two-step activation by Damage-Associate-Molecular-Particles (DAMP) and extracellular ATP. Assuming both activation signals to be concomitantly present or present with a delay of 12h, the model predicted a transient IL-1β activation at different concentration levels dependent on signal synchronisation. Introducing a positive feedback loop mediated by active IL-1β resulted in a sustained IL-1β activation, hence arguing for a paracrine signalling between inflammatory cells to guarantee a temporally stable inflammatory response. We then investigate mechanisms that control termination of inflammation using two recently identified molecular intervention points in the inflammasome pathway. We found that a more upstream regulation, by attenuating production of the IL-1β-proform, was more potent in attenuating active IL-1β production than direct inhibition of the NLRP3-inflammasome. Interestingly, ablating this upstream negative feedback led to a high variability of IL-1β production in monocytes from different subjects, consistent with a recent pre-clinical study. We finally discuss the relevance and implications of our findings in disease models of acute myocardial infarction and spontaneous colitis.

Interleukin 1β Mediates Intestinal Inflammation in Mice and Patients With Interleukin 10 Receptor Deficiency

Interleukin 10 receptor (IL10R)-deficient mice develop spontaneous colitis and, similarly, patients with loss-of-function mutations in IL10R develop severe infant-onset inflammatory bowel disease. Loss of IL10R signaling in mouse and human macrophages is associated with increased production of interleukin 1β. We demonstrated that innate immune production of IL1β mediates colitis in IL10R-deficient mice. Transfer of Il1r1-/- CD4+ T cells into Rag1-/-/Il10rb-/- mice reduced the severity of their colitis (compared to mice that received CD4+ T cells that express IL1R), accompanied by decreased production of interferon gamma, tumor necrosis factor-α, and IL17A. In macrophages from mice without disruption of IL10R signaling or from healthy humans (controls), incubation with IL10 reduced canonical activation of the inflammasome and production of IL1β through transcriptional and post-translational regulation of NLRP3. Lipopolysaccharide and adenosine triphosphate stimulation of macrophages from Il10rb-/- mice or IL10R-deficient patients resulted in increased production of IL1β. Moreover, in human IL10R-deficient macrophages, lipopolysaccharide stimulation alone triggered IL1β secretion via non-canonical, caspase 8-dependent activation of the inflammasome. We treated 2 IL10R-deficient patients with severe and treatment-refractory infant-onset inflammatory bowel disease with the IL1-receptor antagonist anakinra. Both patients had marked clinical, endoscopic, and histologic responses after 4-7 weeks. This treatment served as successful bridge to allogeneic hematopoietic stem cell transplantation in 1 patient. Our findings indicate that loss of IL10 signaling leads to intestinal inflammation, at least in part, through increased production of IL1 by innate immune cells, leading to activation of CD4+ T cells. Agents that block IL1 signaling might be used to treat patients with inflammatory bowel disease resulting from IL10R deficiency.

Deoxycholic Acid Triggers NLRP3 Inflammasome Activation and Aggravates DSS-Induced Colitis in Mice

A westernized high-fat diet (HFD) is associated with the development of inflammatory bowel disease (IBD). High-level fecal deoxycholic acid (DCA) caused by HFD contributes to the colonic inflammatory injury of IBD; however, the mechanism concerning the initiation of inflammatory response by DCA remains unclear. In this study, we sought to investigate the role and mechanism of DCA in the induction of inflammation via promoting NLRP3 inflammasome activation. Here, we, for the first time, showed that DCA dose-dependently induced NLRP3 inflammasome activation and highly pro-inflammatory cytokine-IL-1β production in macrophages. Mechanistically, DCA-triggered NLRP3 inflammasome activation by promoting cathepsin B release at least partially through sphingosine-1-phosphate receptor 2. Colorectal instillation of DCA significantly increased mature IL-1β level in colonic tissue and exacerbated DSS-induced colitis, while in vivo blockage of NLRP3 inflammasome or macrophage depletion dramatically reduced the mature IL-1β production and ameliorated the aggravated inflammatory injury imposed by DCA. Thus, our findings show that high-level fecal DCA may serve as an endogenous danger signal to activate NLRP3 inflammasome and contribute to HFD-related colonic inflammation. NLRP3 inflammasome may represent a new potential therapeutical target for treatment of IBD.

Targeting inflammasome/IL-1 pathways for cancer immunotherapy

The inflammatory microenvironment has been shown to play important roles in various stages of tumor development including initiation, growth, and metastasis. The inflammasome is a critical innate immune pathway for the production of active IL-1β, a potent inflammatory cytokine. Although inflammasomes are essential for host defense against pathogens and contribute to autoimmune diseases, their role in tumor progression remains controversial. Here, our results demonstrate that the inflammasome and IL-1β pathway promoted tumor growth and metastasis in animal and human breast cancer models. We found that tumor progression was associated with the activation of inflammasome and elevated levels of IL-1β at primary and metastatic sites. Mice deficient for inflammasome components exhibited significantly reduced tumor growth and lung metastasis. Furthermore, inflammasome activation promoted the infiltration of myeloid cells such as myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) into tumor microenvironments. Importantly, blocking IL-1R with IL-1R antagonist (IL-Ra) inhibited tumor growth and metastasis accompanied by decreased myeloid cell accumulation. Our results suggest that targeting the inflammasome/IL-1 pathway in tumor microenvironments may provide a novel approach for the treatment of cancer.

ER Stress-induced Inflammasome Activation Contributes to Hepatic Inflammation and Steatosis

Endoplasmic reticulum (ER) stress functions as a protein folding and quality control mechanism to maintain cell homeostasis. Emerging evidence indicates that ER stress is also involved in metabolic and inflammatory diseases. However, the link between ER stress and inflammation remains not well characterized. In this study, we have demonstrated that ER stress-induced inflammasome activation plays a critical role in the pathogenesis of hepatic steatosis. By utilizing genetic and pharmacological agent-induced hepatic steatosis animal models, we found that hepatic steatosis was associated with inflammasome activation and ER stress. Our results show that caspase-1 ablation alleviated liver inflammation and injury. Liver tissues from caspase-1 KO mice had significantly reduced production of IL-1β under ER stress conditions. We also found that ER stress promoted inflammasome activation and IL-1β processing in both hepatocytes and Kupffer cells/macrophages. Moreover, lack of caspase-1 ameliorated cell death or pyropoptosis of hepatocytes induced by ER stress. Taken together, our findings suggest that ER stress-induced inflammasome activation and IL-1β production generate a positive feedback loop to amplify inflammatory response, eventually leading to liver steatosis and injury.

Defective Intestinal Mucin-Type O-Glycosylation Causes Spontaneous Colitis-Associated Cancer in Mice

BACKGROUND & AIMS

Core 1- and core 3-derived mucin-type O-linked oligosaccharides (O-glycans) are major components of the colonic mucus layer. Defective forms of colonic O-glycans, such as the Thomsen-nouveau (Tn) antigen, frequently are observed in patients with ulcerative colitis and colorectal cancer, but it is not clear if they contribute to their pathogenesis. We investigated whether and how impaired O-glycosylation contributes to the development of colitis-associated colorectal cancer using mice lacking intestinal core 1- and core 3-derived O-glycans.

METHODS

We generated mice that lack core 1- and core 3-derived intestinal O-glycans (DKO mice) and analyzed them, along with mice that singly lack intestinal epithelial core 1 O-glycans (IEC C1galt1(-/-) mice) or core 3 O-glycans (C3Gnt(-/-) mice). Intestinal tissues were collected at different time points and analyzed for levels of mucin and Tn antigen, development of colitis, and tumor formation using imaging, quantitative polymerase chain reaction, immunoblot, and enzyme-linked immunosorbent assay techniques. We also used cellular and genetic approaches, as well as intestinal microbiota depletion, to identify inflammatory mediators and pathways that contribute to disease in DKO and wild-type littermates (controls).

RESULTS

Intestinal tissues from DKO mice contained higher levels of Tn antigen and had more severe spontaneous chronic colitis than tissues from IEC C1galt1(-/-) mice, whereas spontaneous colitis was absent in C3GnT(-/-) and control mice. IEC C1galt1(-/-) mice and DKO mice developed spontaneous colorectal tumors, although the onset of tumors in the DKO mice occurred earlier (age, 8-9 months) than that in IEC C1galt1(-/-) mice (15 months old). Antibiotic depletion of the microbiota did not cause loss of Tn antigen but did reduce the development of colitis and cancer formation in DKO mice. Colon tissues from DKO mice, but not control mice, contained active forms of caspase 1 and increased caspase 11, which were reduced after antibiotic administration. Supernatants from colon tissues of DKO mice contained increased levels of interleukin-1β and interleukin-18, compared with those from control mice. Disruption of the caspase 1 and caspase 11 genes in DKO mice (DKO/Casp1/11(-/-) mice) decreased the development of colitis and cancer, characterized by reduced colonic thickening, hyperplasia, inflammatory infiltrate, and tumors compared with DKO mice.

CONCLUSIONS

Impaired expression of O-glycans causes colonic mucus barrier breach and subsequent microbiota-mediated activation of caspase 1-dependent inflammasomes in colonic epithelial cells of mice. These processes could contribute to colitis-associated colon cancer in humans.

Mechanisms of NLRP3 inflammasome activation and its role in NSAID-induced enteropathy

Nonsteroidal anti-inflammatory drugs (NSAIDs) induce cytokines, including tumor necrosis factor-α and interleukins (ILs), in the small intestine via a Toll-like receptor 4 (TLR4)-dependent pathway, leading to intestinal ulceration. Activation of the inflammasome promotes pro-caspase-1 cleavage, leading to pro-IL-1β maturation. We examined the role of NLRP3 inflammasome in NSAID-induced enteropathy. Small intestinal damage developed 3 h after indomethacin administration, accompanied by increases in IL-1β and NLRP3 mRNA expression and mature caspase-1 and IL-1β levels. In vivo blocking of IL-1β using neutralizing antibodies attenuated indomethacin-induced damage, whereas exogenous IL-1β aggravated it. NLRP3(-/-) and caspase-1(-/-) mice exhibited resistance to the damage with reduction of mature IL-1β production. This resistance was abolished by exogenous IL-1β. TLR4 deficiency prevented intestinal damage and inhibited upregulation of NLRP3 and IL-1β mRNAs and maturation of pro-caspase-1 and pro-IL-1β, whereas TLR4 activation by its agonists exerted opposite effects. Apyrase, an adenosine triphosphate (ATP) scavenger, or Brilliant Blue G, a purinergic P2X7 receptor antagonist, inhibited the damage as well as caspase-1 activation and IL-1β processing, despite there being sufficient amounts of pro-IL-1β and NLRP3. These results suggest that NLRP3 inflammasome-derived IL-1β plays a crucial role in NSAID-induced enteropathy and that both TLR4- and P2X7-dependent pathways are required for NLRP3 inflammasome activation.

IL-10 Modulates Th17 Pathogenicity during Autoimmune Diseases

The immune system is essential for host defense against pathogen infections; however dysregulated immune response may lead to inflammatory or autoimmune diseases. Elevated activation of both innate immune cells and T cells such as Th17 cells are linked to many autoimmune diseases, including Multiple Sclerosis (MS), arthritis and inflammatory bowel disease (IBD). To keep immune homeostasis, the immune system develops a number of negative feedback mechanisms, such as the production of anti-inflammatory cytokine IL-10, to dampen excessive production of inflammatory cytokines and uncontrolled activation of immune cells. Our recent studies uncover a novel immunoregulatory function of interferon (IFN) pathways on the innate and antigen-specific immune response. Our results show that IFNα/β induced IL-10 production from macrophages and Th17 cells, which in turn negatively regulated Th17 function in autoimmune diseases such as Experimental Allergic Encephalomyelitis (EAE), an animal model of human MS. In a chronic colitis model resembling human IBD, we also found that IL-10 inhibited inflammasome/IL-1 pathway, and the pathogenicity of Th17 cells, leading to reduced chronic intestinal inflammation. Results from our and other studies further suggest that IL-10 produced by both macrophages and regulatory T cells may shift Th17 into more regulatory phenotypes, leading to reduced inflammatory response.

Activity of SHIP, Which Prevents Expression of Interleukin 1β, Is Reduced in Patients With Crohn's Disease

BACKGROUND & AIMS

Crohn's disease (CD) is associated with a dysregulated immune response to commensal micro-organisms in the intestine. Mice deficient in inositol polyphosphate 5'-phosphatase D (INPP5D, also known as SHIP) develop intestinal inflammation resembling that of patients with CD. SHIP is a negative regulator of PI3Kp110α activity. We investigated mechanisms of intestinal inflammation in Inpp5d(-/-) mice (SHIP-null mice), and SHIP levels and activity in intestinal tissues of subjects with CD.

METHODS

We collected intestines from SHIP-null mice, as well as Inpp5d(+/+) mice (controls), and measured levels of cytokines of the interleukin 1 (IL1) family (IL1α, IL1β, IL1ra, and IL6) by enzyme-linked immunosorbent assay. Macrophages were isolated from lamina propria cells of mice, IL1β production was measured, and mechanisms of increased IL1β production were investigated. Macrophages were incubated with pan-phosphatidylinositol 3-kinase inhibitors or PI3Kp110α-specific inhibitors. Some mice were given an antagonist of the IL1 receptor; macrophages were depleted from ilea of mice using clodronate-containing liposomes. We obtained ileal biopsies from sites of inflammation and peripheral blood mononuclear cells (PBMCs) from treatment-naïve subjects with CD or without CD (controls), and measured SHIP levels and activity. PBMCs were incubated with lipopolysaccharide and adenosine triphosphate, and levels of IL1β production were measured.

RESULTS

Inflamed intestinal tissues and intestinal macrophages from SHIP-null mice produced higher levels of IL1B and IL18 than intestinal tissues from control mice. We found PI3Kp110α to be required for macrophage transcription of Il1b. Macrophage depletion or injection of an IL1 receptor antagonist reduced ileal inflammation in SHIP-null mice. Inflamed ileal tissues and PBMCs from patients with CD had lower levels of SHIP protein than controls (P < .0001 and P < .0002, respectively). There was an inverse correlation between levels of SHIP activity in PBMCs and induction of IL1β production by lipopolysaccharide and adenosine triphosphate (R(2) = .88).

CONCLUSIONS

Macrophages from SHIP-deficient mice have increased PI3Kp110α-mediated transcription of Il1b, which contributes to spontaneous ileal inflammation. SHIP levels and activity are lower in intestinal tissues and peripheral blood samples from patients with CD than controls. There is an inverse correlation between SHIP activity and induction of IL1β production by lipopolysaccharide and adenosine triphosphate in PBMCs. Strategies to reduce IL1B might be developed to treat patients with CD found to have low SHIP activity.

Apigenin supplementation protects the development of dextran sulfate sodium-induced murine experimental colitis by inhibiting canonical and non-canonical inflammasome signaling pathways

The present study was designed to elucidate the protective effects of dietary apigenin (API) enrichment in a chronic colitis model induced by DSS in mice. Inflammatory mediators and the possible role of canonical and non-canonical NLRP3 inflammasome signaling pathways in the beneficial effects of API under chronic inflammatory conditions were also explored. Six-week-old mice were randomized in four dietary groups: sham and control groups received standard diet (SD), and other two groups were fed with API at 0.1%. After 30days, all groups except sham received 3% DSS in drinking water for 5days followed by a regime of 21days of water. Our results revealed that dietary API supplementation decreased the macroscopic and microscopic damage signs of colitis; also, it was capable to down-regulate mPGES, COX-2 and iNOS enzyme colonic expressions and to decrease serum matrix metalloproteinase (MMP-3) levels. Similarly, API diet reduced IL-1β and TNF-α proinflammatory cytokine secretions in primary LPS-stimulated splenocytes. Furthermore, we demonstrated that API anti-inflammatory activity was related with an inhibition of both canonical and non-canonical NLRP3 inflammasome pathways by decreasing proinflammatory IL-1β and IL-18 cytokine levels as a consequence of regulation of cleaved caspase-1 and caspase-11 enzymes. We conclude that API supplement might provide a basis for developing a new dietary strategy for the prevention of chronic ulcerative colitis.

Magnesium lithospermate B acts against dextran sodiumsulfate-induced ulcerative colitis by inhibiting activation of the NRLP3/ASC/Caspase-1 pathway

This study aimed to observe the therapeutic effects of magnesium lithospermate B on acute and chronic colitis induced by dextran sodiumsulfate (DSS) and the role of inflammasome complex (NOD-like receptor protein, NLRP; apoptosis-associated speck-like protein containing, ASC; caspase-1). Establishment of acute and chronic colitis models were by using 5% DSS oral administration in BALB/C male mice. Magnesium lithospermate B (240 mg/kg body weight) was given by subcutaneous injection. Samples were collected for biomarker assay, histological examination, immunohistochemical evaluation and western blot. There was obvious increase in TNF-α level and NLPR3, ASC, and caspase-1 expressions in acute and chronic colitis groups compared with the normal control. Significant decrease of the tumor necrosis factor-α level and the expressions of NLPR3, ASC, and caspase-1 were observed after treatment with magnesium lithospermate B. This study showed that magnesium lithospermate B could be used to treat acute and chronic colitis by inhibiting the activation of the NLRP3/ASC/Caspase-1 pathway.

Complement activation promotes colitis-associated carcinogenesis through activating intestinal IL-1β/IL-17A axis

Colitis-associated colorectal cancer (CAC) is the most serious complication of inflammatory bowel disease (IBD). Excessive complement activation has been shown to be involved in the pathogenesis of IBD. However, its role in the development of CAC is largely unknown. Here, using a CAC model induced by combined administration of azoxymethane (AOM) and dextran sulfate sodium (DSS), we demonstrated that complement activation was required for CAC pathogenesis. Deficiency in key components of complement (e.g., C3, C5, or C5a receptor) rendered tumor repression in mice subjected to AOM/DSS. Mechanistic investigation revealed that complement ablation dramatically reduced proinflammatory cytokine interleukin (IL)-1β levels in the colonic tissues that was mainly produced by infiltrating neutrophils. IL-1β promoted colon carcinogenesis by eliciting IL-17 response in intestinal myeloid cells. Furthermore, complement-activation product C5a represented a potent inducer for IL-1β in neutrophil, accounting for downregulation of IL-1β levels in the employed complement-deficient mice. Overall, our study proposes a protumorigenic role of complement in inflammation-related colorectal cancer and that the therapeutic strategies targeting complement may be beneficial for the treatment of CAC in clinic.

Heterogeneity of subordination of the IL-18/IFN-γ axis to caspase-1 among patients with Crohn's disease

In Crohn's disease (CD), hierarchical architecture of the inflammatory network, including subordination of IL-18, an IFN-γ-inducing cytokine, to the inflammasome, have remained undeciphered. Heterogeneity among patients of such a subordination cannot be evaluated by animal models, monofactorial in their etiology and homogenous in disease progression. To address these issues, we set up an ex vivo model of inflamed mucosa explant cultures from patients with active long-standing CD. Th1 cytokine production, especially IFN-γ and IL-18, was assessed in relation with inflammation intensity. Subordination of the Th1 response to caspase-1, effector of the inflammasome, was determined in explant cultures subjected to pharmacological inhibition of caspase-1 by YVAD. We showed a correlation between secreted IFN-γ/IL-18 levels, and caspase-1 activation, with inflammation intensity of intestinal CD mucosa explants. Inhibition of caspase-1 activation using the specific inhibitor YVAD identified a homogenous non responder group featuring a caspase-1-independent IL-18/IFN-γ response, and a heterogenous responder group, in which both IL-18 and IFN-γ responses were caspase-1-dependent, with a 40-70% range of inhibition by YVAD. These findings bring out the concept of heterogeneity of subordination of the Th1 response to inflammasome activation among CD patients. This ex vivo model should have therapeutic relevance in allowing to determine eligibility of CD patients for new targeted therapies.

Chronic TLR Stimulation Controls NLRP3 Inflammasome Activation through IL-10 Mediated Regulation of NLRP3 Expression and Caspase-8 Activation

While the molecular mechanisms promoting activation of the Nod-like Receptor (NLR) family member NLRP3 inflammasome are beginning to be defined, little is known about the mechanisms that regulate the NLRP3 inflammasome. Acute (up to 4 hours) LPS stimulation, followed by ATP is frequently used to activate the NLRP3 inflammasome in macrophages. Interestingly, we observed that the ability of LPS to license NLRP3 is transient, as prolonged (12 to 24 hours) LPS exposure was a relatively ineffective priming stimulus. This suggests that relative to acute LPS, chronic LPS exposure triggers regulatory mechanisms to dampen NLRP3 activation. Transfer of culture supernatants from macrophages stimulated with LPS for 24 hours dramatically reduced ATP- and nigericin-induced NLRP3 inflammasome activation in naïve macrophages. We further identified IL-10 as the secreted inflammasome-tolerizing factor that acts in an autocrine manner to control activation of the NLRP3 inflammasome. Finally, we demonstrated that IL-10 dampens NLRP3 expression to control NLRP3 inflammasome activation and subsequent caspase-8 activation. In conclusion, we have uncovered a mechanism by which chronic, but not acute, LPS exposure induces IL-10 to dampen NLRP3 inflammasome activation to avoid overt inflammation.

Properdin Regulation of Complement Activation Affects Colitis in Interleukin 10 Gene-Deficient Mice

BACKGROUND

Interleukin 10-deficient mice (IL-10(-/-)) are a popular model used to dissect the mechanisms underlying inflammatory bowel diseases. The role of complement, a host defense mechanism that bridges the innate and adaptive immune systems, has not been described in this model. We therefore studied the effect of deficiency of properdin, a positive regulator of complement, on colitis in mice with the IL-10(-/-) background.

METHODS

For acute colitis, IL-10(-/-) and IL-10/properdin double knockout (DKO) or radiation bone marrow-reconstituted chimeric mice, had piroxicam added to their powdered chow for 14 days. For chronic colitis, 2.5% dextran sodium sulfate was added to the animals' water for 4 days then the mice were killed 8 weeks later. Colons were assessed for inflammation, cell infiltration, and cytokine and complement measurements. Bacterial translocation was measured by cultivating bacteria from organs on Luria broth agar plates.

RESULTS

C3a and C5a levels and C9 deposition were all increased in piroxicam-fed IL-10(-/-) mice compared with mice not fed piroxicam. Piroxicam-fed DKO mice lacked increased C5a and C9 deposition combined with exacerbated colitis, reduced numbers of infiltrating neutrophils, and markedly higher local and systemic bacterial numbers compared with IL-10(-/-) mice. Bone marrow cells from IL-10(-/-) mice were sufficient to restore protection against the heightened colitis in piroxicam-fed DKO mice.

CONCLUSIONS

Complement is activated in the IL-10(-/-) mouse mucosa in a properdin-dependent manner. In the absence of terminal complement activation, the inflammation is heightened, likely due to a lack of neutrophil control over microbes escaping from the intestines.

Proneness of TLR5 deficient mice to develop colitis is microbiota dependent

Alterations in the gut microbiota have been implicated to play a role in potentiating inflammatory bowel diseases in both humans and mice. Mice lacking the flagellin receptor, toll-like receptor 5 (TLR5), are prone to develop spontaneous gut inflammation, but are significantly protected when treated with antibiotics or maintained in germ-free conditions. However, given that the incidence of spontaneous inflammation in TLR5KO mice is quite variable in conventional conditions (typically ∼10% show clear colitis), this result is far from definitive and does not rule out that TLR5KO mice might be prone to develop inflammation even in the absence of a microbiota. Herein, we demonstrate that neutralization of IL10 signaling induces colitis in 100% of TLR5KO mice which provide a more rigorous approach to evaluate the role of microbiota in gut inflammation. Mice treated with antibiotics or maintained in germ-free condition are substantially protected against IL-10R neutralization-induced colitis, underscoring that gut inflammation in TLR5KO mice is dependent upon the presence of a gut microbiota.

Tr1 Cells, but Not Foxp3+ Regulatory T Cells, Suppress NLRP3 Inflammasome Activation via an IL-10-Dependent Mechanism

The two best-characterized types of CD4(+) regulatory T cells (Tregs) are Foxp3(+) Tregs and Foxp3(-) type 1 regulatory (Tr1) cells. The ability of Foxp3(+) Tregs and Tr1 cells to suppress adaptive immune responses is well known, but how these cells regulate innate immunity is less defined. We discovered that CD44(hi)Foxp3(-) T cells from unmanipulated mice are enriched in Tr1 cell precursors, enabling differentiation of cells that express IL-10, as well as Tr1-associated cell surface markers, CD49b and LAG-3, and transcription factors, cMaf, Blimp-1, and AhR. We compared the ability of Tr1 cells versus Foxp3(+) Tregs to suppress IL-1β production from macrophages following LPS and ATP stimulation. Surprisingly, Tr1 cells, but not Foxp3(+) Tregs, inhibited the transcription of pro-IL-1β mRNA, inflammasome-mediated activation of caspase-1, and secretion of mature IL-1β. Consistent with the role for IL-10 in Tr1 cell-mediated suppression, inhibition of inflammasome activation and IL-1β secretion was abrogated in IL-10R-deficient macrophages. Moreover, IL-1β production from macrophages derived from Nlrp3(A350V) knockin mice, which carry a mutation found in cryopyrin-associated periodic syndrome patients, was suppressed by Tr1 cells but not Foxp3(+) Tregs. Using an adoptive transfer model, we found a direct correlation between Tr1 cell engraftment and protection from weight loss in mice expressing a gain-of-function NLRP3. Collectively, these data provide the first evidence for a differential role of Tr1 cells and Foxp3(+) Tregs in regulating innate immune responses. Through their capacity to produce high amounts of IL-10, Tr1 cells may have unique therapeutic effects in disease-associated inflammasome activation.

Differential regulation of proinflammatory mediators following LPS- and ATP-induced activation of monocytes from patients with antiphospholipid syndrome

Antiphospholipid syndrome (APS) is an acquired autoimmune disorder characterized by recurrent thrombosis and pregnancy morbidity in association with the presence of antiphospholipid antibodies. Growing evidence supports the involvement of monocytes in APS pathogenesis. Inflammatory activation of monocytes promotes thrombus formation and other APS complications. However, mechanisms underlying their activation are poorly investigated. We aimed to determine transcriptional activity of monocytes after exposing them to low concentrations of lipopolysaccharide (LPS) and LPS + adenosine triphosphate (ATP) using comparative qRT-PCR. The results showed that LPS significantly increased transcriptional levels of TLR2, IL-23, CCL2, CXCL10, IL-1β, and IL-6 in APS cells, while, in cells from healthy donors, LPS resulted in IL-6 and STAT3 elevated mRNAs. Double stimulation of the cells resulted in decreased mRNA levels of NLRP3 in monocytes isolated from healthy donors and CCL2, IL-1β in APS cells. By contrast, TLR2 mRNAs were elevated in both investigated groups after culture of the cells with LPS + ATP. Thus, the findings indicate increased sensitivity of APS cells to LPS that may contribute to thrombus formation and enhance development or progression of autoimmune processes. Low concentrations of ATP diminish LPS-induced inflammatory state of APS monocytes which might be a potential mechanism which regulates inflammatory state of the cells.