Characterization of NLRP12 during the development of allergic airway disease in mice

The role of NLRP3 and NLRP12 inflammasomes in glioblastoma

Glioblastoma (GBM) is the deadliest malignant brain tumor, with a survival of less than 14 months after diagnosis. The highly invasive nature of GBM makes total surgical resection challenging, leading to tumor recurrence and declined survival. The heterocellular composition of the GBM reprograms its microenvironment, favoring tumor growth, proliferation, and migration. The innate immune cells in the GBM tumor microenvironment, including microglia, astrocytes, and macrophages, express pattern recognition receptors such as NLRs (Nucleotide-binding domain and leucine-rich repeat-containing) that sense pathogen- and damage-associated molecular patterns initiating inflammation. Upon activation, NLRP3 promotes inflammation by NLRP3 inflammasome formation. Auto-proteolytic cleavage and activation of Caspase-1 within the inflammasome leads to caspase-1-mediated cleavage, activation, and conversion of pro-IL-1ß and pro-IL-18 to IL-1ß and IL-18, leading to pyroptosis. In contrast, NLRP12 downregulates inflammatory responses in microglia and macrophages by regulating the NF-κB pathway. NLRP3 and NLRP12 have been implicated in the disease pathophysiology of several cancers with cell-context-dependent, pro- or anti-tumorigenic roles. In this review, we discuss the current literature on the mechanistic roles of NLRP3 and NLRP12 in GBM and the gaps in the scientific literature in the context of GBM pathophysiology with potential for targeted therapeutics.

Focus on negatively regulated NLRs in inflammation and cancer

Nucleotide-binding and oligomerization structural domain (NOD)-like receptors (NLRs) play an important role in innate immunity as cytoplasmic pattern recognition receptors (PRRs). Over the past decade, considerable progress has been made in understanding the mechanisms by which NLR family members regulate immune system function, particularly the formation of inflammasome and downstream inflammatory signals. However, recent studies have shown that some members of the NLRs, including Nlrp12, NLRX1, and NLRC3, are important in the negative regulation of inflammatory signaling and are involved in the development of various diseases, including inflammatory diseases and cancer. Based on this, in this review, we first summarize the interactions between canonical and non-canonical nuclear factor-κB (NF-κB) signaling pathways that are mainly involved in NLRs, then highlight the mechanisms by which the above NLRs negatively regulate inflammatory signaling responses as well as their roles in tumor progression, and finally summarize the synthetic and natural derivatives with therapeutic effects on these NLRs, which are considered as potential therapeutic agents for overcoming inflammatory diseases.

NF-κB Inducing Kinase Attenuates Colorectal Cancer by Regulating Noncanonical NF-κB Mediated Colonic Epithelial Cell Regeneration

BACKGROUND & AIMS

Dysregulated colonic epithelial cell (CEC) proliferation is a critical feature in the development of colorectal cancer. We show that NF-κB-inducing kinase (NIK) attenuates colorectal cancer through coordinating CEC regeneration/differentiation via noncanonical NF-κB signaling that is unique from canonical NF-kB signaling.

METHODS

Initial studies evaluated crypt morphology/functionality, organoid generation, transcriptome profiles, and the microbiome. Inflammation and inflammation-induced tumorigenesis were initiated in whole-body NIK knockout mice (Nik-/-) and conditional-knockout mice following administration of azoxymethane and dextran sulfate sodium.

RESULTS

Human transcriptomic data revealed dysregulated noncanonical NF-kB signaling. In vitro studies evaluating Nik-/- crypts and organoids derived from mature, nondividing CECs, and colonic stem cells exhibited increased accumulation and stunted growth, respectively. Transcriptomic analysis of Nik-/- cells revealed gene expression signatures associated with altered differentiation-regeneration. When assessed in vivo, Nik-/- mice exhibited more severe colitis with dextran sulfate sodium administration and an altered microbiome characterized by increased colitogenic microbiota. In the inflammation-induced tumorigenesis model, we observed both increased tumor burdens and inflammation in mice where NIK is knocked out in CECs (NikΔCEC). Interestingly, this was not recapitulated when NIK was conditionally knocked out in myeloid cells (NikΔMYE). Surprisingly, conditional knockout of the canonical pathway in myeloid cells (RelAΔMYE) revealed decreased tumor burden and inflammation and no significant changes when conditionally knocked out in CECs (RelAΔCEC).

CONCLUSIONS

Dysregulated noncanonical NF-κB signaling is associated with the development of colorectal cancer in a tissue-dependent manner and defines a critical role for NIK in regulating gastrointestinal inflammation and regeneration associated with colorectal cancer.

Cellular Context Dictates the Suppression or Augmentation of Triple-Negative Mammary Tumor Metastasis by NLRX1

Prior studies have defined multiple, but inconsistent, roles for the enigmatic pattern recognition receptor NLRX1 in regulating several cancer-associated biological functions. In this study, we explore the role of NLRX1 in the highly metastatic murine 4T1 mammary tumor model. We describe a functional dichotomy of NLRX1 between two different cellular contexts: expression in healthy host cells versus expression in the 4T1 tumor cells. Using Nlrx1-/- mice engrafted with 4T1 tumors, we demonstrate that NLRX1 functions as a tumor suppressor when expressed in the host cells. Specifically, NLRX1 in healthy host cells attenuates tumor growth and lung metastasis through suppressing characteristics of epithelial-mesenchymal transition and the lung metastatic niche. Conversely, we demonstrate that NLRX1 functions as a tumor promoter when expressed in 4T1 tumor cells using gain- and loss-of-function studies both in vitro and in vivo. Mechanistically, NLRX1 in the tumor cells augments 4T1 aggressiveness and metastasis through regulating epithelial-mesenchymal transition hallmarks, cell death, proliferation, migration, reactive oxygen species levels, and mitochondrial respiration. Collectively, we provide critical insight into NLRX1 function and establish a dichotomous role of NLRX1 in the 4T1 murine mammary carcinoma model that is dictated by cellular context.

Negative regulatory NLRs mitigate inflammation via NF-κB pathway signaling in inflammatory bowel disease

A subset of Nucleotide-binding and leucine-rich repeat-containing receptors (NLRs) function to mitigate overzealous pro-inflammatory signaling produced by NF-κB activation. Under normal pathophysiologic conditions, proper signaling by these NLRs protect against potential autoimmune responses. These NLRs associate with several different proteins within both the canonical and noncanonical NF-κB signaling pathways to either prevent activation of the pathway or inhibit signal transduction. Inhibition of the NF-κB pathways ultimately dampens the production of pro-inflammatory cytokines and activation of other downstream pro-inflammatory signaling mechanisms. Dysregulation of these NLRs, including NLRC3, NLRX1, and NLRP12, have been reported in human inflammatory bowel disease (IBD) and colorectal cancer patients, suggesting the potential of these NLRs as biomarkers for disease detection. Mouse models deficient in these NLRs also have increased susceptibility to colitis and colitis-associated colorectal cancer. While current standard of care for IBD patients and FDA-approved therapeutics function to remedy symptoms associated with IBD and chronic inflammation, these negative regulatory NLRs have yet to be explored as potential drug targets. In this review, we describe a comprehensive overview of recent studies that have evaluated the role of NLRC3, NLRX1, and NLRP12 in IBD and colitis-associated colorectal cancer.

NLRP12 attenuates ozone-induced pulmonary inflammation by regulating canonical NF-κB Pathway

Ozone (O3) is an important urban air pollutant having strong correlations with respiratory diseases. Several lines of evidence suggest that O3 exposure causes airway hyperresponsiveness (AHR) and pulmonary inflammation. Inhibitory innate immune receptors, such as NLRP12, have been demonstrated to alleviate inflammation, but the functional role for NLRP12 in O3-induced lung inflammatory inflammation remains to be reported. Here, we determined whether NLRP12 took a protective role in O3-induced AHR and pulmonary inflammation via the suppression of canonical NF-κB. C57BL/6 J mice were exposed to filtered air (FA) or 0.25, 0.50 and 1.00 ppm (3 h/day for 5 consecutive days) followed by detection of airway resistance, white blood cells, total proteins, and cytokines. Meanwhile, NLRP12 in lung tissue were detected by real time PCR. Moreover, we also examined protein expression of NLRP12 and key biomarkers of NF-κB pathway. It was shown that 24 h post O3 exposure, AHR as wells as total cells, proteins, and cytokines contents in BALF of mice were increased compare to those of FA controls in a dose-dependent manner. Notably, O3-induced AHR and lung inflammation were associated with significant decrease in pulmonary NLRP12 and upregulation of phosphorylated IRAK1, p65 and IκBα in canonical NF-κB pathway. Intratracheal administration of NLRP12-overexpresing adenovirus 4 days prior to O3 exposure alleviated AHR and lung inflammation, and inhibited canonical NF-κB pathway activation. The findings from this study indicate that NLRP12 attenuates O3-induced AHR and pulmonary inflammation, possibly through regulating canonical NF-κB pathway. This provides a novel target for the prevention and treatment of lung diseases induced by O3 exposure.

CAR-T cells targeting HLA-G as potent therapeutic strategy for EGFR-mutated and overexpressed oral cancer

Oral squamous cell carcinoma (OSCC) is a common malignancy in the world. Recently, scientists have focused on therapeutic strategies to determine the regulation of tumors and design molecules for specific targets. Some studies have demonstrated the clinical significance of human leukocyte antigen G (HLA-G) in malignancy and NLR family pyrin domain-containing 3 (NLRP3) inflammasome in promoting tumorigenesis in OSCC. This is the first study to investigate whether aberrant epidermal growth factor receptor (EGFR) induces HLA-G expression through NLRP3 inflammasome-mediated IL-1β secretion in OSCC. Our results showed that the upregulation of NLRP3 inflammasome leads to abundant HLA-G in the cytoplasm and cell membrane of FaDu cells. In addition, we also generated anti-HLA-G chimeric antigen receptor (CAR)-T cells and provided evidence for their effects in EGFR-mutated and overexpressed oral cancer. Our results may be integrated with OSCC patient data to translate basic research into clinical significance and may lead to novel EGFR-aberrant OSCC treatment.

NLRP12-expressing dendritic cells mediate both dissemination of infection and adaptive immune responses in visceral leishmaniasis

The NLR protein NLRP12 contributes to innate immunity, but the mechanism remains elusive. Infection of Nlrp12 -/- or wild-type mice with Leishmania infantum led to aberrant parasite tropism. Parasites replicated to higher levels in livers of Nlrp12 -/- mice than in the livers of WT mice and failed to disseminate to spleens. Most retained liver parasites resided in dendritic cells (DCs), with correspondingly fewer infected DCs in spleens. Furthermore, Nlrp12 -/- DCs expressed lower CCR7 than WT DCs, failed to migrate toward CCL19 or CCL21 in chemotaxis assays, and migrated poorly to draining lymph nodes after sterile inflammation. Leishmania-infected Nlpr12 -/- DCs were significantly less effective at transporting parasites to lymph nodes than WT DCs. Consistently, adaptive immune responses were also impaired in infected Nlrp12 -/- mice. We hypothesize that Nlrp12-expressing DCs are required for efficient dissemination and immune clearance of L. infantum from the site of initial infection. This is at least partly due to the defective expression of CCR7.

Small intestinal resident eosinophils maintain gut homeostasis following microbial colonization

The intestine harbors a large population of resident eosinophils, yet the function of intestinal eosinophils has not been explored. Flow cytometry and whole-mount imaging identified eosinophils residing in the lamina propria along the length of the intestine prior to postnatal microbial colonization. Microscopy, transcriptomic analysis, and mass spectrometry of intestinal tissue revealed villus blunting, altered extracellular matrix, decreased epithelial cell turnover, increased gastrointestinal motility, and decreased lipid absorption in eosinophil-deficient mice. Mechanistically, intestinal epithelial cells released IL-33 in a microbiota-dependent manner, which led to eosinophil activation. The colonization of germ-free mice demonstrated that eosinophil activation in response to microbes regulated villous size alterations, macrophage maturation, epithelial barrier integrity, and intestinal transit. Collectively, our findings demonstrate a critical role for eosinophils in facilitating the mutualistic interactions between the host and microbiota and provide a rationale for the functional significance of their early life recruitment in the small intestine.

NLRX1 Deficiency Alters the Gut Microbiome and Is Further Exacerbated by Adherence to a Gluten-Free Diet

Patients with gluten sensitivities present with dysbiosis of the gut microbiome that is further exacerbated by a strict adherence to a gluten-free diet (GFD). A subtype of patients genetically susceptible to gluten sensitivities are Celiac Disease (CeD) patients, who are carriers of the HLA DR3/DQ2 or HLA DR4/DQ8 haplotypes. Although 85-95% of all CeD patients carry HLA DQ2, up to 25-50% of the world population carry this haplotype with only a minority developing CeD. This suggests that CeD and other gluten sensitivities are mediated by factors beyond genetics. The contribution of innate immune system signaling has been generally understudied in the context of gluten sensitivities. Thus, here we examined the role of NOD-like receptors (NLRs), a subtype of pattern recognition receptors, in maintaining the composition of the gut microbiome in animals maintained on a GFD. Human transcriptomics data revealed significant increases in the gene expression of multiple NLR family members, across functional groups, in patients with active CeD compared to control specimens. However, NLRX1 was uniquely down-regulated during active disease. NLRX1 is a negative regulatory NLR that functions to suppress inflammatory signaling and has been postulate to prevent inflammation-induced dysbiosis. Using Nlrx1^-/- mice maintained on either a normal or gluten-free diet, we show that loss of NLRX1 alters the microbiome composition, and a distinctive shift further ensues following adherence to a GFD, including a reciprocal loss of beneficial microbes and increase in opportunistic bacterial populations. Finally, we evaluated the functional impact of an altered gut microbiome by assessing short- and medium-chain fatty acid production. These studies revealed significant differences in a selection of metabolic markers that when paired with 16S rRNA sequencing data could reflect an overall imbalance and loss of immune system homeostasis in the gastrointestinal system.

Neuropilin‐2 regulates airway inflammation in a neutrophilic asthma model

Background

Asthma is a heterogenous disease that can be classified into eosinophilic (type 2‐high) and noneosinophilic (type 2‐low) endotypes. The type 2‐low endotype of asthma can be characterized by the presence of neutrophilic airway inflammation that is poorly responsive to corticosteroids. Dysregulated innate immune responses to microbial products including Toll‐like receptor (TLR) ligands have been associated with the pathogenesis of neutrophilic asthma. The key molecules that regulate inflammatory responses in individuals with neutrophilic asthma remain unclear. We previously reported that the immunoregulatory receptor neuropilin‐2 (NRP2) is expressed by murine and human alveolar macrophage (AM) and suppresses lipopolysaccharide (LPS)‐induced neutrophilic airway inflammation.

Methods

Here, we investigated the immunoregulatory role of NRP2 in a mouse model of neutrophilic asthma.

Results

We found that TLR ligands, but not T helper 2 (Th2)‐promoting adjuvants, induced NRP2 expression by AM. Using an LPS‐mediated model of neutrophilic asthma, we demonstrate that NRP2 was increased in AM and other lung antigen‐presenting cells following airway challenge with antigen. Conditional deletion of NRP2 in myeloid cells exacerbated airway inflammation in a neutrophilic asthma model. In contrast, myeloid‐specific ablation of NRP2 did not affect airway inflammation in a Th2‐mediated eosinophilic asthma model. Myeloid‐specific ablation of NRP2 did not affect Th1/Th17 responses to inhaled antigens or expression of neutrophil chemokines but rather resulted in impaired efferocytosis by AM, which is necessary for effective resolution of airway inflammation.

Conclusion

Our findings suggest that NRP2 is a negative regulator of airway inflammation associated with neutrophilic asthma.

Identification of an ATP/P2X7/mast cell pathway mediating ozone-induced bronchial hyperresponsiveness

Ozone is a highly reactive environmental pollutant with well-recognized adverse effects on lung health. Bronchial hyperresponsiveness (BHR) is one consequence of ozone exposure, particularly for individuals with underlying lung disease. Our data demonstrated that ozone induced substantial ATP release from human airway epithelia in vitro and into the airways of mice in vivo and that ATP served as a potent inducer of mast cell degranulation and BHR, acting through P2X7 receptors on mast cells. Both mast cell-deficient and P2X7 receptor-deficient (P2X7-/-) mice demonstrated markedly attenuated BHR to ozone. Reconstitution of mast cell-deficient mice with WT mast cells and P2X7-/- mast cells restored ozone-induced BHR. Despite equal numbers of mast cells in reconstituted mouse lungs, mice reconstituted with P2X7-/- mast cells demonstrated significantly less robust BHR than mice reconstituted with WT mast cells. These results support a model where P2X7 on mast cells and other cell types contribute to ozone-induced BHR.

Immunological Roles of NLR in Allergic Diseases and Its Underlying Mechanisms

Our understanding on the immunological roles of pathogen recognition in innate immunity has vastly increased over the past 20 years. Nucleotide-binding oligomerization domain (NOD)-like receptors (NLR) are cytosolic pattern recognition receptors (PRR) that are responsible for sensing microbial motifs and endogenous damage signals in mammalian cytosol for immune surveillance and host defense. The accumulating discoveries on these NLR sensors in allergic diseases suggest that the pathogenesis of allergic diseases may not be confined to the adaptive immune response. Therapy targeting NLR in murine models also shields light on its potential in the treatment of allergies in man. In this review, we herein summarize the recent understanding of the role of NLR sensors and their molecular mechanisms involved in allergic inflammation, including atopic dermatitis and allergic asthma.

The Inhibitory Innate Immune Sensor NLRP12 Maintains a Threshold against Obesity by Regulating Gut Microbiota Homeostasis

In addition to high-fat diet (HFD) and inactivity, inflammation and microbiota composition contribute to obesity. Inhibitory immune receptors, such as NLRP12, dampen inflammation and are important for resolving inflammation, but their role in obesity is unknown. We show that obesity in humans correlates with reduced expression of adipose tissue NLRP12. Similarly, Nlrp12-/- mice show increased weight gain, adipose deposition, blood glucose, NF-κB/MAPK activation, and M1-macrophage polarization. Additionally, NLRP12 is required to mitigate HFD-induced inflammasome activation. Co-housing with wild-type animals, antibiotic treatment, or germ-free condition was sufficient to restrain inflammation, obesity, and insulin tolerance in Nlrp12-/- mice, implicating the microbiota. HFD-fed Nlrp12-/- mice display dysbiosis marked by increased obesity-associated Erysipelotrichaceae, but reduced Lachnospiraceae family and the associated enzymes required for short-chain fatty acid (SCFA) synthesis. Lachnospiraceae or SCFA administration attenuates obesity, inflammation, and dysbiosis. These findings reveal that Nlrp12 reduces HFD-induced obesity by maintaining beneficial microbiota.

Modulating inflammation through the negative regulation of NF-κB signaling

Immune system activation is essential to thwart the invasion of pathogens and respond appropriately to tissue damage. However, uncontrolled inflammation can result in extensive collateral damage underlying a diverse range of auto-inflammatory, hyper-inflammatory, and neoplastic diseases. The NF-κB signaling pathway lies at the heart of the immune system and functions as a master regulator of gene transcription. Thus, this signaling cascade is heavily targeted by mechanisms designed to attenuate overzealous inflammation and promote resolution. Mechanisms associated with the negative regulation of NF-κB signaling are currently under intense investigation and have yet to be fully elucidated. Here, we provide an overview of mechanisms that negatively regulate NF-κB signaling through either attenuation of signal transduction, inhibition of posttranscriptional signaling, or interference with posttranslational modifications of key pathway components. While the regulators discussed for each group are far from comprehensive, they exemplify common mechanistic approaches that inhibit this critical biochemical signaling cascade. Despite their diversity, a commonality among these regulators is their selection of specific targets at key inflection points in the pathway, such as TNF-receptor-associated factor family members or essential kinases. A better understanding of these negative regulatory mechanisms will be essential to gain greater insight related to the maintenance of immune system homeostasis and inflammation resolution. These processes are vital elements of disease pathology and have important implications for targeted therapeutic strategies.

Impaired response of the bronchial epithelium to inflammation characterizes severe equine asthma

BACKGROUND

Severe equine asthma is a naturally occurring lung inflammatory disease of mature animals characterized by neutrophilic inflammation, bronchoconstriction, mucus hypersecretion and airway remodeling. Exacerbations are triggered by inhalation of dust and microbial components. Affected animals eventually are unable of aerobic performance. In this study transcriptomic differences between asthmatic and non-asthmatic animals in the response of the bronchial epithelium to an inhaled challenge were determined.

RESULTS

Paired endobronchial biopsies were obtained pre- and post-challenge from asthmatic and non-asthmatic animals. The transcriptome, determined by RNA-seq and analyzed with edgeR, contained 111 genes differentially expressed (DE) after challenge between horses with and without asthma, and 81 of these were upregulated. Genes involved in neutrophil migration and activation were in central location in interaction networks, and related gene ontology terms were significantly overrepresented. Relative abundance of specific gene products as determined by immunohistochemistry was correlated with differential gene expression. Gene sets involved in neutrophil chemotaxis, immune and inflammatory response, secretion, blood coagulation and apoptosis were overrepresented among up-regulated genes, while the rhythmic process gene set was overrepresented among down-regulated genes. MMP1, IL8, TLR4 and MMP9 appeared to be the most important proteins in connecting the STRING protein network of DE genes.

CONCLUSIONS

Several differentially expressed genes and networks in horses with asthma also contribute to human asthma, highlighting similarities between severe human adult and equine asthma. Neutrophil activation by the bronchial epithelium is suggested as the trigger of the inflammatory cascade in equine asthma, followed by epithelial injury and impaired repair and differentiation. Circadian rhythm dysregulation and the sonic Hedgehog pathway were identified as potential novel contributory factors in equine asthma.

TIPS pentacene loaded PEO-PDLLA core-shell nanoparticles have similar cellular uptake dynamics in M1 and M2 macrophages and in corresponding in vivo microenvironments

Nanoparticle based drug delivery platforms have the potential to transform disease treatment paradigms and therapeutic strategies, especially in the context of pulmonary medicine. Once administered, nanoparticles disperse throughout the lung and many are phagocytosed by macrophages. However, there is a paucity of knowledge regarding cellular up-take dynamics of nanoparticles due largely to macrophage heterogeneity. To address this issue, we sought to better define nanoparticle up-take using polarized M1 and M2 macrophages and novel TIPS-pentacene loaded PEO-PDLLA nanoparticles. Our data reveal that primary macrophages polarized to either M1 or M2 phenotypes have similar levels of nanoparticle phagocytosis. Similarly, M1 and M2 polarized macrophages isolated from the lungs of mice following either acute (Th1) or allergic (Th2) airway inflammation also demonstrated equivalent levels of nanoparticle up-take. Together, these studies provide critical benchmark information pertaining to cellular up-take dynamics and biodistribution of nanoparticles in the context of clinically relevant inflammatory microenvironments.

Involvement of EGF receptor signaling and NLRP12 inflammasome in fine particulate matter-induced lung inflammation in mice

Epidemiological studies have shown that exposure to ambient fine particulate matter (PM_2.5 ) is associated with respiratory diseases. Lung inflammation is a central feature of many pulmonary diseases, which can be induced by PM_2.5 exposure. However, the mechanisms underlying PM_2.5 -induced lung inflammation remain unclear. To characterize the role of epidermal growth factor receptor (EGFR) and inflammasome in PM_2.5 -induced lung inflammation in mice, 30 BALB/c mice were intrabroncheally instilled with saline and PM_2.5 suspension (4.0 mg/kg b.w.) for 5 consecutive days, respectively. Bronchoalveolar lavage (BAL) was conducted and BAL fluid (BALF) was collected. The levels of reactive oxygen species (ROS), inducible nitric oxide synthase (iNOS), epidermal growth factor (EGF), CXCL1, interleukin (IL)-1β, and IL-18 in BALF were determined using ELISA. mRNA levels of IL-6, IL-1β, IL-18, CXCL1, IL-10, NLRP3, Caspase-1, and NLRP12 in lung tissues were determined by RT-PCR. Phospho-EGFR (Tyr1068) and phospho-Akt (Thr308) in lung tissues were examined using immunohistochemical staining and Western blotting, respectively. Protein levels of Caspase-1, NLRP3, NF-κB-p52/p100, and NF-κB-p65 in bronchial epithelium were examined using immunohistochemical staining. It was shown that PM_2.5 exposure induced lung inflammation. Levels of total protein, ROS, iNOS, EGF, and CXCL1 and cell number in the BALF of mice exposed to PM_2.5 were markedly elevated relative to the control. mRNA levels of CXCL1, IL-1β, and IL-18 in lung tissues of PM_2.5 -exposed mice were increased in comparison with the control. However, level of NLRP12 mRNA in lung tissues of PM_2.5 -exposed mice was reduced. Phospho-EGFR (Tyr1068) and phospho-Akt (Thr308) levels in the lungs of PM_2.5 -instilled mice were higher than those in the lungs of the control. The protein levels of NF-κB-p52/p100 and NF-κB-p65 in bronchial epithelium of PM_2.5 -exposed mice were also increased compared with the control. This study suggests that EGF-EGFR-Akt-NF-κB signaling and NLRP12 inflammasome may be associated with PM_2.5 -induced lung inflammation in mice. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1121-1134, 2017.

NLRP12 Inflammasome Expression in the Rat Brain in Response to LPS during Morphine Tolerance

Morphine, an effective but addictive analgesic, can profoundly affect the inflammatory response to pathogens, and long-term use can result in morphine tolerance. Inflammasomes are protein complexes involved in the inflammatory response. The nucleotide-binding oligomerization domain-like receptor (NLR) Family Pyrin Domain Containing (NLRP) 12 (NLRP12) inflammasome has been reported to have anti-inflammatory activity. In this study, we examined the expression of NLRP12 inflammasome related genes in the adult F344 rat brain in response to the bacterial endotoxin lipopolysaccharide (LPS) in the presence and absence of morphine tolerance. Morphine tolerance was elicited using the 2 + 4 morphine-pelleting protocol. On Day 1, the rats were pelleted subcutaneously with 2 pellets of morphine (75 mg/pellet) or a placebo; on Days 2 and 4 pellets were given. On Day 5, the animals were randomly assigned to receive either 250 µg/kg LPS or saline (i.p.). The expression of 84 inflammasome related genes in the rat brain was examined using a Ploymerase Chain Reaction (PCR) array. In response to LPS, there was a significant increase in the expression of the pro-inflammatory cytokine/chemokine genes interleukin-1 beta (Il-1β), interleukin-6 (Il-6), C-C motif chemokine ligand 2 (Ccl2), C-C motif chemokine ligand 7 (Ccl7), C-X-C motif chemokine ligand 1 (Cxcl1), and C-X-C motif chemokine ligand 3 (Cxcl3) and a significant decrease in the anti-inflammatory NLRP12 gene in both morphine-tolerant and placebo-control rats compared to saline-treated rats, although the changes were greater in the placebo-control animals. The Library of Integrated Network-Based Cellular Signatures’ (LINCS) connectivity map was used to analyze the list of affected genes to identify potential targets associated with the interactions of LPS and morphine tolerance. Our data indicate that, in the morphine tolerant state, the expression of NLRP12 and its related genes is altered in response to LPS and that the Vacuolar protein-sorting-associated protein 28 (VPS28), which is involved in the transport and sorting of proteins into sub-cellular vesicles, may be the key regulator of these alterations.

Beyond the inflammasome: regulatory NOD-like receptor modulation of the host immune response following virus exposure

A complex interaction exists between elements of the host innate immune system and viral pathogens. It is essential that the host mount a robust immune response during viral infection and effectively resolve inflammation once the pathogen has been eliminated. Members of the nucleotide-binding domain leucine-rich repeat [NBD-LRR; known as NOD-like receptor (NLR)] family of cytosolic pattern-recognition receptors are essential components of these immunological processes and have diverse functions in the host antiviral immune response. NLRs can be subgrouped based on their general function. The inflammasome-forming subgroup of NLRs are the best-characterized family members, and several have been found to modulate the maturation of IL-1β and IL-18 following virus exposure. However, the members of the regulatory NLR subgroups are significantly less characterized. These NLRs uniquely function to modulate signalling pathways initiated by other families of pattern-recognition receptors, such as Toll-like receptors and/or Rig-I-like helicase receptors. Regulatory NLRs that augment pro-inflammatory pathways include nucleotide-binding oligomerization domain-containing protein 1 (NOD1) and NOD2, which have been shown to form a multiprotein complex termed the NODosome that significantly modulates IFN and NF-κB signalling following viral infection. Conversely, a second subgroup of regulatory NLRs functions to negatively regulate inflammation. These inhibitory NLRs include NLRX1, NLRP12 and NLRC3, which have been shown to interact with TRAF molecules and various kinases to modulate diverse cellular processes. Targeting NLR signalling following infection with a virus represents a novel and promising therapeutic strategy. However, significant effort is still required to translate the current understanding of NLR biology into effective therapies.

Desflurane preconditioning protects human umbilical vein endothelial cells against anoxia/reoxygenation by upregulating NLRP12 and inhibiting non-canonical nuclear factor-κB signaling

Volatile anesthetics modulate endothelial cell apoptosis and inhibit nuclear factor-κB (NF-κB) signaling. In this study, we aimed to assess whether desflurane preconditioning protects human umbilical vein endothelial cells (HUVECs) agaist anoxia/reoxygenation (A/R) injury. HUVECs were pre-conditioned with desflurane (1.0 MAC) for 30 min, followed by a 15-min washout, then exposed to 60 min anoxia and 60 min reoxygenation (A/R), and incubated with 10 ng/ml tumor necrosis factor (TNF)-α for 60 min. HUVEC viability and apoptosis were measured by MTT assay and annexin V staining, and immunoblot analysis was used to measure the levels of Smac and cellular inhibitor of apoptosis 1 (cIAP1). NF-κB activation was assessed using the NF-κB signaling pathway real‑time PCR array, and the levels of NF-κB inducing kinase (NIK), p52, IκB kinase (IKK)α, p100, RelB and NLR family, pyrin domain containing 12 (NLRP12) were assessed by immunoblot analysis. Desflurane preconditioning attenuated the effects of A/R and/or A/R plus TNF-α on cell viability, decreasing the levels of Smac and enhancing the levels of of cIAP1 (P<0.05). Preconditioning with desflurane also enhanced the mRNA levels of interleukin (IL)-10 and NLRP12 in the cells exposed to A/R by 2.40- and 2.16‑fold, respectively. The HUVECs exposed to A/R had greater levels of NIK and p100 and reduced levels of p52 and IKKα. Desflurance preconditioning further increased p100 levels, decreased the level of NIK, further decreased p52 levels and further reduced IKKα levels. A/R in combination with TNF-α increased the NIK, IKKα, p100 and RelB levels, and this increase was significantly attenuated by desflurance preconditioning (all P<0.05). Desflurane preconditioning enhanced HUVEC survival and protected the cells against A/R injury, and our results suggested that this process involved the upregulation of NLRP12 and the inhibition of non-canonical NF-κB signaling.

Emerging significance of NLRs in inflammatory bowel disease

Pattern recognition receptors are essential mediators of host defense and inflammation in the gastrointestinal system. Recent data have revealed that toll-like receptors and nucleotide-binding domain and leucine-rich repeat-containing proteins (NLRs) function to maintain homeostasis between the host microbiome and mucosal immunity. The NLR proteins are a diverse class of cytoplasmic pattern recognition receptors. In humans, only about half of the identified NLRs have been adequately characterized. The majority of well-characterized NLRs participate in the formation of a multiprotein complex, termed the inflammasome, which is responsible for the maturation of interleukin-1β and interleukin-18. However, recent observations have also uncovered the presence of a novel subgroup of NLRs that function as positive or negative regulators of inflammation through modulating critical signaling pathways, including NF-κB. Dysregulation of specific NLRs from both proinflammatory and inhibitory subgroups have been associated with the development of inflammatory bowel disease (IBD) in genetically susceptible human populations. Our own preliminary retrospective data mining efforts have identified a diverse range of NLRs that are significantly altered at the messenger RNA level in colons from patients with IBD. Likewise, studies using genetically modified mouse strains have revealed that multiple NLR family members have the potential to dramatically modulate the immune response during IBD. Targeting NLR signaling represents a promising and novel therapeutic strategy. However, significant effort is necessary to translate the current understanding of NLR biology into effective therapies.

Inflammasome Activity in Non-Microbial Lung Inflammation

The understanding of interleukin-1 (IL-1) family cytokines in inflammatory disease has rapidly developed, due in part to the discovery and characterization of inflammasomes, which are multi-subunit intracellular protein scaffolds principally enabling recognition of a myriad of cellular stimuli, leading to the activation of caspase-1 and the processing of IL-1β and IL-18. Studies continue to elucidate the role of inflammasomes in immune responses induced by both microbes and environmental factors. This review focuses on the current understanding of inflammasome activity in the lung, with particular focus on the non-microbial instigators of inflammasome activation, including inhaled antigens, oxidants, cigarette smoke, diesel exhaust particles, mineral fibers, and engineered nanomaterials, as well as exposure to trauma and pre-existing inflammatory conditions such as metabolic syndrome. Inflammasome activity in these sterile inflammatory states contribute to diseases including asthma, chronic obstructive disease, acute lung injury, ventilator-induced lung injury, pulmonary fibrosis, and lung cancer.

Non-Inflammasome Forming NLRs in Inflammation and Tumorigenesis

Aberrant inflammation is an enabling characteristic of tumorigenesis. Thus, signaling cascades that alter inflammatory activation and resolution are of specific relevance to disease pathogenesis. Pattern recognition receptors (PRRs) are essential mediators of the host immune response and have emerged as critical elements affecting multiple facets of tumor pathobiology. The nucleotide-binding domain and leucine-rich repeat containing (NLR) proteins are intracellular PRRs that sense microbial and non-microbial products. Members of the NLR family can be divided into functional sub-groups based on their ability to either positively or negatively regulate the host immune response. Recent studies have identified a novel sub-group of non-inflammasome forming NLRs that negatively regulate diverse biological pathways associated with both inflammation and tumorigenesis. Understanding the mechanisms underlying the function of these unique NLRs will assist in the rationale design of future therapeutic strategies targeting a wide spectrum of inflammatory diseases and cancer. Here, we will discuss recent findings associated with this novel NLR sub-group and mechanisms by which these PRRs may function to alter cancer pathogenesis.

Induction of allergic airway disease using house dust mite allergen

Mouse models of allergic airway inflammation have proven essential in understanding the mechanisms and pathophysiology underling human asthma. There is a diverse range of mouse models described in the literature that typically vary slightly by allergen, duration of exposure, and route of sensitization. In general, each of these models has proven to be acceptable surrogates for studying specific aspects of the human disease, including airway inflammation, airway hyperresponsiveness (AHR), and airway remodeling. Here, we describe a highly versatile model based on nasal sensitization with house dust mite antigen (DMA). Mice receive multiple intranasal inoculations with DMA each week for a period of 4-16 weeks, which results in increased Th2-mediated airway inflammation and AHR. However, an added feature of the long--term exposures described here is the ability to more accurately evaluate the impact of chronic inflammation on airway remodeling and lung pathophysiology in response to a clinically relevant allergen.

Licensing Adaptive Immunity by NOD-Like Receptors

The innate immune system is composed of a diverse set of host defense molecules, physical barriers, and specialized leukocytes and is the primary form of immune defense against environmental insults. Another crucial role of innate immunity is to shape the long-lived adaptive immune response mediated by T and B lymphocytes. The activation of pattern recognition receptors (PRRs) from the Toll-like receptor family is now a classic example of innate immune molecules influencing adaptive immunity, resulting in effective antigen presentation to naïve T cells. More recent work suggests that the activation of another family of PRRs, the NOD-like receptors (NLRs), induces a different set of innate immune responses and accordingly, drives different aspects of adaptive immunity. Yet how this unusually diverse family of molecules (some without canonical PRR function) regulates immunity remains incompletely understood. In this review, we discuss the evidence for and against NLR activity orchestrating adaptive immune responses during infectious as well as non-infectious challenges.

NOD-Like Receptors in Lung Diseases

The lung is a particularly vulnerable organ at the interface of the body and the exterior environment. It is constantly exposed to microbes and particles by inhalation. The innate immune system needs to react promptly and adequately to potential dangers posed by these microbes and particles, while at the same time avoiding extensive tissue damage. Nucleotide-binding oligomerization domain-like receptors (NLRs) represent a group of key sensors for microbes and damage in the lung. As such they are important players in various infectious as well as acute and chronic sterile inflammatory diseases, such as pneumonia, chronic obstructive pulmonary disease (COPD), acute lung injury/acute respiratory distress syndrome, pneumoconiosis, and asthma. Activation of most known NLRs leads to the production and release of pro-inflammatory cytokines, and/or to the induction of cell death. We will review NLR functions in the lung during infection and sterile inflammation.

The cutaneous innate immune response in patients with atopic dermatitis

Orchestrating when and how the cutaneous innate immune system should respond to commensal or pathogenic microbes is a critical function of the epithelium. The cutaneous innate immune system is a key determinant of the physical, chemical, microbial, and immunologic barrier functions of the epidermis. A malfunction in this system can lead to an inadequate host response to a pathogen or a persistent inflammatory state. Atopic dermatitis is the most common inflammatory skin disorder and characterized by abnormalities in both skin barrier structures (stratum corneum and tight junctions), a robust T(H)2 response to environmental antigens, defects in innate immunity, and an altered microbiome. Many of these abnormalities may occur as the consequence of epidermal dysfunction. The epidermis directly interfaces with the environment and, not surprisingly, expresses many pattern recognition receptors that make it a key player in cutaneous innate immune responses to skin infections and injury. This review will discuss the role epidermal innate receptors play in regulation of skin barriers and, where possible, discuss the relevance of these findings for patients with atopic dermatitis.

Characterization of NLRP12 during the in vivo host immune response to Klebsiella pneumoniae and Mycobacterium tuberculosis

The majority of nucleotide binding domain leucine rich repeats-containing (NLR) family members has yet to be functionally characterized. Of the described NLRs, most are considered to be proinflammatory and facilitate IL-1β production. However, a newly defined sub-group of NLRs that function as negative regulators of inflammation have been identified based on their abilities to attenuate NF-κB signaling. NLRP12 (Monarch-1) is a prototypical member of this sub-group that negatively regulates both canonical and noncanonical NF-κB signaling in biochemical assays and in colitis and colon cancer models. The role of NLRP12 in infectious diseases has not been extensively studied. Here, we characterized the innate immune response of Nlrp12^−/− mice following airway exposure to LPS, Klebsiella pneumoniae and Mycobacterium tuberculosis. In response to E. coli LPS, Nlrp12^−/− mice showed a slight decrease in IL-1β and increase in IL-6 production, but these levels were not statistically significant. During K. pneumoniae infection, we observed subtle differences in cytokine levels and significantly reduced numbers of monocytes and lymphocytes in Nlrp12^−/− mice. However, the physiological relevance of these findings is unclear as no overt differences in the development of lung disease were observed in the Nlrp12^−/− mice. Likewise, Nlrp12^−/− mice demonstrated pathologies similar to those observed in the wild type mice following M. tuberculosis infection. Together, these data suggest that NLRP12 does not significantly contribute to the in vivo host innate immune response to LPS stimulation, Klebsiella pneumonia infection or Mycobacterium tuberculosis.

Negative regulation of human mononuclear phagocyte function

At mucosal surfaces, phagocytes such as macrophages coexist with microbial communities; highly controlled regulation of these interactions is essential for immune homeostasis. Pattern-recognition receptors (PRRs) are critical in recognizing and responding to microbial products, and they are subject to negative regulation through various mechanisms, including downregulation of PRR-activating components or induction of inhibitors. Insights into these regulatory mechanisms have been gained through human genetic disease-association studies, in vivo mouse studies utilizing disease models or targeted gene perturbations, and in vitro and ex vivo human cellular studies examining phagocytic cell functions. Although mouse models provide an important approach to study macrophage regulation, human and mouse macrophages exhibit differences, which must be considered when extrapolating mouse findings to human physiology. This review discusses inhibitory regulation of PRR-induced macrophage functions and the consequences of dysregulation of these functions and highlights mechanisms that have a role in intestinal macrophages and in human macrophage studies.

Beyond pattern recognition: NOD-like receptors in dendritic cells

Innate instruction of adaptive immunity was proposed more than 20 years ago as a mechanism by which long-lived lymphocyte responses are targeted to appropriate antigens. At the time Charles Janeway proposed this theory, most of the innate immune receptors were unknown, and the pivotal role of the dendritic cell in instructing T cell priming was debated. There is now overwhelming evidence that the innate and adaptive branches of the immune system must interact to generate immunity. Much of this work has focused on families of innate immune receptors called pattern recognition receptors (PRRs) on dendritic cells, which translate these inflammatory triggers into productive T cell responses. Nevertheless, we are only beginning to understand how these defence molecules shape the generation of immunity. We review the varied roles of one class of PRRs, the NOD-like receptors (NLRs), in immune responses and propose a new model in which adaptive immunity requires coordinated PRR activation within the dendritic cell.