The protein Nod2: an innate receptor more complex than previously assumed

MAPK signaling mediated intestinal inflammation induced by endoplasmic reticulum stress and NOD2

Endoplasmic reticulum (ER) stress is crucially involved in inflammatory bowel disease (IBD), but the mechanisms remain incompletely understood. This study aimed to elucidate how ER stress promotes inflammation in IBD. ER stress marker Grp78 and NOD2 in colon tissues of Crohn's disease (CD) patients and IBD model mice were detected by immunohistochemical analysis. THP-1 cells were exposed to ER stress and the expression of NOD2 and inflammatory cytokines was detected by PCR. We found that ER stress markers Grp78 and NOD2 were upregulated in intestinal tissues of CD patients and in THP-1 cells exposed to ER stress. ER stress inhibitor reduced Grp78 and NOD2 expression in colitis model mice and alleviated colitis. ER stress inducer cooperated with NOD2 ligand MDP to upregulate TNF-α, IL-8 and IL-1β, and activate MAPK signaling in THP-1 cells. Moreover, inhibitors of MAPK signaling led to the downregulation of IL-1β, IL-8 and TNF-α in THP-1 cells stimulated by ER stress inducer and MDP. In conclusion, ER stress upregulates NOD2 and promotes inflammation in IBD, at least partially due to the activation of MAPK pathway.

Effect of Toll-like receptor-2, -4, -5, -7, and NOD2 stimulation on potassium channel conductance in intestinal epithelial cells

Disproportionate activation of pattern recognition receptors plays a role in inflammatory bowel disease (IBD) pathophysiology. Diarrhea is a hallmark symptom of IBD, resulting at least in part from an electrolyte imbalance that may be caused by changes in potassium channel activity. We evaluated the impact of Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain 2 (NOD2) stimulation on potassium conductance of the basolateral membrane in human intestinal epithelial cells (IECs) and the role of potassium channels through electrophysiological assays under short-circuit current in Ussing chambers. TLRs and NOD2 were stimulated using specific agonists, and potassium channels were selectively blocked using triarylmethane-34 (TRAM-34), adenylyl-imidodiphosphate (AMP-PNP), and BaCl₂. Potassium conductance of the basolateral membrane decreased upon activation of TLR2, TLR4, and TLR7 in T84 cells (means ± SE, -11.2 ± 4.5, -40.4 ± 7.2, and -19.4 ± 5.9, respectively) and in Caco-2 cells (-13.1 ± 5.7, -55.7 ± 7.4, and -29.1 ± 7.2, respectively). In contrast, activation of TLR5 and NOD2 increased basolateral potassium conductance, both in T84 cells (18.0 ± 4.1 and 18.4 ± 2.8, respectively) and in Caco-2 cells (21.2 ± 8.4 and 16.0 ± 3.6, respectively). TRAM-34 and AMP-PNP induced a decrease in basolateral potassium conductance upon TLR4 stimulation in both cell lines. Both K_Ca3.1- and K_ir6-channels appear to be important mediators of this effect in IECs and could be potential targets for therapeutic agent development.NEW & NOTEWORTHY This study highlights that PRRs stimulation directly influences K⁺-channel conductance in IECs. TLR-2, -4, -7 stimulation decreased K⁺ conductance, whereas TLR5 and NOD2 stimulation had the opposite effect, leading to an increase of it instead. This study reports for the first time that K_Ca3.1- and K_ir6-channels play a role in K⁺ transport pathways triggered by TLR4 stimulation. These findings suggest that K_Ca3.1- and K_ir6-channels modulation may be a potential target for new therapeutic agents in IBD.

Analysis of miRNA Expression Profiling of RIP2 Knockdown in Chicken HD11 Cells When Infected with Avian Pathogenic E. coli (APEC)

Colibacillosis is an acute and chronic avian disease caused by avian pathogenic E. coli (APEC). Previous studies have demonstrated that RIP2 plays a significant role in APEC infection. Moreover, increasing evidence indicates that microRNAs (miRNAs) are involved in host–pathogen interactions and the immune response. However, the role of miRNAs in the host against APEC infection remains unclear. Herein, we attempted to reveal new miRNAs potentially involved in the regulation of the immune and inflammatory response against APEC infection, with a particular focus on those possibly correlated with RIP2 expression, via miRNA-seq, RT-qPCR, Western blotting, dual-luciferase reporter assay, and CCK-8. The results showed that a total of 93 and 148 differentially expressed (DE) miRNAs were identified in the knockdown of RIP2 cells following APEC infection (shRIP2+APEC) vs. knockdown of RIP2 cells (shRIP2) and shRIP2 vs. wild-type cells (WT), respectively. Among those identified DE miRNAs, the biological function of gga-miR-455-5p was investigated. It was found that gga-miR-455-5p regulated by RIP2 was involved in the immune and inflammatory response against APEC infection via targeting of IRF2 to modulate the expression of type I interferons. Additionally, RIP2 could directly regulate the production of the type I interferons. Altogether, these findings highlighted the crucial role of miRNAs, especially gga-miR-455-5p, in host defense against APEC infection.

Tofacitinib effectiveness in Blau syndrome: a case series of Chinese paediatric patients

OBJECTIVE

Blau syndrome (BS), a rare, autosomal-dominant autoinflammatory syndrome, is characterized by a clinical triad of granulomatous recurrent uveitis, dermatitis, and symmetric arthritis and associated with mutations of the nucleotide-binding oligomerization domain containing 2 (NOD2) gene. Aim of this study was to assess the efficacy of tofacitinib in Chinese paediatric patients with BS.

METHODS

Tofacitinib was regularly administered to three BS patients (Patient 1, Patient 2, and Patient 3) at different dosages: 1.7 mg/day (0.11 mg/kg), 2.5 mg/day (0.12 mg/kg), and 2.5 mg/day (0.33 mg/kg). The clinical manifestations of the patients, magnetic resonance imaging results, serological diagnoses, therapeutic measures and outcomes of treatments are described in this report.

RESULTS

The clinical characteristics and serological diagnoses of all BS patients were greatly improved after the administration of tofacitinib treatment. All patients reached clinical remission of polyarthritis and improvements in the erythrocyte sedimentation rate (ESR) and levels of C-reactive protein (CRP) and inflammatory cytokines.

CONCLUSION

Tofacitinib, a Janus kinase (JAK) inhibitor, is a promising agent for BS patients who have unsatisfactory responses to corticosteroids, traditional disease-modifying antirheumatic drugs, and biological agents.

Identification and functional analysis of NOD2 and its two splicing variants associated with a novel pattern of signal regulation in teleost fishes

The nucleotide-binding oligomerization domain 2 (NOD2) has been identified as an important sensor for microorganic invasion in both mammals and teleost fishes. In this study, two splicing variants of NOD2 (NOD2-v1 and NOD2-v2) were identified as truncating the functional domains of wild-type NOD2 in the teleost fish Schizothorax prenanti. NOD2-v1 included an intron sequence that terminated within the third leucine-rich repeat (LRR) domain, while NOD2-v2 incorporated an insertion of one and half intron sequences and truncated within the second caspase activation and recruitment domain (CARD). NOD2, NOD2-v1 and NOD2-v2 genes were ubiquitously expressed. All three genes positively responded to exposure of Aeromonas hydrophila and lipopolysaccharide stimulation in varying degrees. Using luciferase activity assays in HEK293T cells, our results revealed that NOD2 activated the NF-κB signal and recognized muramyl dipeptide (MDP). NOD2-v1 exhibited deficiency in the LRR domains and could not sense MDP, but maintained the ability to activate NF-κB and enhanced NOD2-mediated MDP recognition. Given the significant change to the functional structure, NOD2-v2 lost its capacity for NF-κB activation, but interestingly repressed NOD2-mediated MDP sensing and NF-κB activation, and even NOD2-v1-induced NF-κB activation. Altogether, our study reveals a novel pattern of signal regulation by splicing variants in teleost fishes.

Influence of NOD-like receptor 2 gene polymorphisms on muramyl dipeptide induced pro-inflammatory response in patients with active pulmonary tuberculosis and household contacts

PURPOSE

The immune response induced by nucleotide-binding oligomerization domain-2(NOD2) is associated with the production of cytokines affected by the host's genetic background. The present study aimed to examine the effects of NOD2; 802C > T, 2105G > A polymorphisms associated with altered cytokine levels in patients with active pulmonary tuberculosis disease, Latent TB subjects (household contacts(HHC) and healthy controls(HC).

METHODS

Genetic polymorphisms were analyzed by Restriction Fragment Length Polymorphism(RFLP) in 102-PTB patients, 102-HHC, and 132-HC. QuantiFERON-TB Gold In-Tube test was performed to identify latent TB infection in 60-HHC. Estimated their cytokine levels by ELISA in MDP (muramyl dipeptide) stimulated culture supernatants of all the groups. Further, we studied pre-mRNA structures by insilico analysis and relative gene expression by RT-PCR.

RESULTS

Recessive genetic models of NOD2 802C > T SNP with TT genotype and AA genotype of NOD2 2105G > A SNP were significantly associated with increased TB risk in PTB patients and HHC compared with HC. In vitro stimulations were performed with NOD2 ligand MDP in PTB patients and latent TB subjects: QuantiFERON positive household contacts (QFT + ve HHC)and QuantiFERON negative household contacts(QFT-ve HHC). The results showed that reduced TNF-α and enhanced IL-12, IL-1β indicate that these cytokines may play an essential role in the initial maintenance of cell-mediated immunity. Our study demonstrated the correlation between NOD2 polymorphism with IL-1β, TNF-α, IL-12 levels. Insilico analysis represents the pre-mRNA secondary structures affected by NOD2 SNPs. We also observed the difference in m RNA levels in variant and wild genotypes.

CONCLUSION

This finding may lead to the forthcoming development of immunotherapy and may be used as predictive markers to identify high-risk individuals for TB disease.

Bronchiolitis obliterans after allogeneic hematopoietic stem cell transplantation: The effect of NOD2/CARD15 mutations in a Tunisian population

Bronchiolitis obliterans (BO) is a serious lung complication that can develop after allogenic stem cell transplantation. It has been suggested that single nucleotide polymorphisms (SNPs) that affect the NOD2/CARD15 gene impair its function and result in an uncontrolled innate immune response in the recipient, thereby leading to BO. One hundred eighty-one donor-recipient pairs were analyzed for the association between NOD2 gene variants (SNP8 [Arg702Trp], SNP12 [Gly908Arg], and SNP13 [Leu1007fsinsC]) and the occurrence of BO. Ten patients (2.8%) developed this complication. The incidence of BO increases in recipient variant patient group from 4.7% to 23% in donor Wild-type group in SNP8 (p < 0.001). The incidence rose to 19% when the recipient carried the SNP12 variant (p < 0.001) in the Tunisian population. Analyses demonstrated that recipient NOD2CARD15 variants (SNP8 and SNP12) present a greater risk in developing BO than recipients without mutation. Our study demonstrated that NOD2/CARD15 typing may be useful in identifying patients at high risk for BO.

Nucleotide-binding and oligomerization domain (NOD)-like receptors in teleost fish: Current knowledge and future perspectives

Nucleotide-binding and oligomerization domain (NOD)-like receptors (NLRs) are a group of intracellular pathogen recognition receptors (PRRs) that play key roles in pathogen recognition and subsequent activation of innate immune signalling pathways. Expressions of several NLR subfamily members, including NOD1, NOD2, NLR-C3, NLR-C5 and NLR-X1 have been reported in many different teleost fish species. These receptors are activated by a variety of ligands, including lipopolysaccharides (LPS), peptidoglycans (PGN) and polyinosinic-polycytidylic acid [Poly(I:C)]. Synthetic dsRNA and bacterial or viral infections are known to stimulate these receptors both in vitro and in vivo. In this review, we focus on the identification, expression and function of teleost NLRs in response to bacterial or viral pathogens. Additionally, NLR ligand specificity and signalling pathways involved in the recognition of bacterial or viral stimuli are also summarized. This review focuses on current knowledge in this area and provides future perspectives regarding topics in need of additional investigation. Understanding the response of innate immune system to bacterial or viral infections in diverse species could inform the development of more effective therapies and vaccines.

Screening of Cytotoxicity and Anti-Inflammatory Properties of Feijoa Extracts Using Genetically Modified Cell Models Targeting TLR2, TLR4 and NOD2 Pathways, and the Implication for Inflammatory Bowel Disease

Feijoa has been increasingly studied in the recent decade, while investigations into its bioactivities including anti-inflammatory activity are lacking. In this article, the cytotoxicity and anti-inflammatory properties of feijoa extracts, from flesh, peel and whole fruit, from four cultivars namely APOLLO, UNIQUE, OPAL STAR and WIKI TU are presented. Three inflammatory pathways, Toll-like receptor 2 (TLR2), TLR4 and nucleotide-binding oligomerization domain-containing protein 2 (NOD2), were investigated using genetically modified cell models namely HEK-Blue™ hTLR2, HEK-Blue™ hTLR4, NOD2-WT and NOD2-G908R. Results show that feijoa peel extract induced higher cytotoxicity than flesh and whole fruit extracts, and the APOLLO cultivar was the most anti-inflammatory among the four tested cultivars. The anti-inflammatory activity of feijoa flesh was detected only through the TLR2 pathway, and the activity of feijoa peel and whole fruit was evident mainly through the TLR2 and NOD2 pathways. Most notably, feijoa anti-inflammatory activity was superior to ibuprofen particularly through the TLR2 pathway, with significantly lower secreted embryonic alkaline phosphatase IC50 concentrations (7.88, 12.81, 30.84 and 442.90 μg/mL for APOLLO flesh, peel, whole fruit extract and ibuprofen respectively). These findings indicate that feijoa has great potential to be used in the treatment and prevention of inflammation-related diseases including inflammatory bowel disease.

Expression and functional analysis of receptor-interacting serine/threonine kinase 2 (RIP2) in Japanese flounder (Paralichthys olivaceus)

Being a key adaptor protein in NOD1/2 and NF-κB signaling pathways, receptor-interacting serine/threonine kinase 2 (RIP2) plays an important role in innate immune response in vertebrates. In this study, we identified and characterized the Paralichthys olivaceus RIP2 gene (PoRIP2). Phylogenetic, alignment, and genomic analysis of PoRIP2 were conducted to determine its conservation and evolutionary relationship with other RIP2 in vertebrates. qRT-PCR results showed that the expression of PoRIP2 was high in the spleen and head kidney. Meanwhile, embryonic development expression profile revealed that it was high in the early developmental stages and hatching stage. In vivo, we examined the expression pattern in different tissues after being challenged with Edwardsiella tarda. PoRIP2 was up-regulated in tissues at different time points. In vitro, the expression of PoRIP2 was also increased after treatment with Poly I:C, PGN, and E. tarda. Transfection and overexpression experiments indicated that PoRIP2 was located in the cytoplasm of the FG-9307 cell line. The pro-inflammatory cytokines, IL-1β, IL-6, and IL-8, could be activated and up-regulated by PGN stimulation in PoRIP2 overexpressed cells. The inhibitory action was obvious in PoRIP2 overexpressed cells, and the quantity of E. tarda decreased. These findings highlight the important role of PoRIP2 in regulating innate immune in P. olivaceus. Our results indicated that PoRIP2 might be involved in immune response and the activation of the NF-κB signaling pathways. Our study can improve the knowledge on the immune system of fish and provide a theoretical basis for the study of prevention and treatment of fish diseases.

NOD2 and inflammation: current insights

The nucleotide-binding oligomerization domain (NOD) protein, NOD2, belonging to the intracellular NOD-like receptor family, detects conserved motifs in bacterial peptidoglycan and promotes their clearance through activation of a proinflammatory transcriptional program and other innate immune pathways, including autophagy and endoplasmic reticulum stress. An inactive form due to mutations or a constitutive high expression of NOD2 is associated with several inflammatory diseases, suggesting that balanced NOD2 signaling is critical for the maintenance of immune homeostasis. In this review, we discuss recent developments about the pathway and mechanisms of regulation of NOD2 and illustrate the principal functions of the gene, with particular emphasis on its central role in maintaining the equilibrium between intestinal microbiota and host immune responses to control inflammation. Furthermore, we survey recent studies illustrating the role of NOD2 in several inflammatory diseases, in particular, inflammatory bowel disease, of which it is the main susceptibility gene.

Bacterial Signaling at the Intestinal Epithelial Interface in Inflammation and Cancer

The gastrointestinal (GI) tract provides a compartmentalized interface with an enormous repertoire of immune and metabolic activities, where the multicellular structure of the mucosa has acquired mechanisms to sense luminal factors, such as nutrients, microbes, and a variety of host-derived and microbial metabolites. The GI tract is colonized by a complex ecosystem of microorganisms, which have developed a highly coevolved relationship with the host’s cellular and immune system. Intestinal epithelial pattern recognition receptors (PRRs) substantially contribute to tissue homeostasis and immune surveillance. The role of bacteria-derived signals in intestinal epithelial homeostasis and repair has been addressed in mouse models deficient in PRRs and signaling adaptors. While critical for host physiology and the fortification of barrier function, the intestinal microbiota poses a considerable health challenge. Accumulating evidence indicates that dysbiosis is associated with the pathogenesis of numerous GI tract diseases, including inflammatory bowel diseases (IBD) and colorectal cancer (CRC). Aberrant signal integration at the epithelial cell level contributes to such diseases. An increased understanding of bacterial-specific structure recognition and signaling mechanisms at the intestinal epithelial interface is of great importance in the translation to future treatment strategies. In this review, we summarize the growing understanding of the regulation and function of the intestinal epithelial barrier, and discuss microbial signaling in the dynamic host–microbe mutualism in both health and disease.

Genetic association and phenotypic correlation of TLR4 but not NOD2 variants with Tunisian inflammatory bowel disease

OBJECTIVE

The common association between NOD2/CARD15 and TLR4 gene variants with inflammatory bowel disease (IBD) has not been replicated in all studies. We studied the polymorphism of these two genes in Tunisian patients with IBD.

METHODS

Polymorphisms of NOD2 (R702W, G908R and L1007fs) and TLR4 (Asp299Gly and Thr399Ile) genes were analyzed in 106 patients with IBD (68 with ulcerative colitis [UC], 38 with Crohn's disease [CD]) and 160 healthy controls using polymerase chain reaction-restriction fragment length polymorphism. Genotypes and phenotypes were correlated.

RESULTS

The mutated allele of TLR4-Thr399Ile was strongly associated with IBD (9.4% in IBD, 7.4% in UC and 13.2% in CD vs 2.5% in controls; P = 0.0004, 0.014 and 0.00006, respectively). Heterozygous genotypes were significantly more frequent in patients with IBD (17.0%), UC (14.7%) and CD (21.1%) than in controls (5.0%) (P = 0.0012, 0.012 and 0.001, respectively). Interestingly, the wild genotype was found to be protective (odds ratio 0.24). The mutated allele of TLR4-Asp299Gly was more frequent in controls (6.8%) than in patients with IBD (2.9%). A phenotypic correlation of Asp299Gly-AG genotype with arthritis in UC patients was detected (P = 0.003). Regarding the NOD2 gene, the common variations studied were not polymorphic and there was no genetic association with IBD.

CONCLUSION

The TLR4-Thr399Ile variant was strongly associated with susceptibility to IBD, whereas TLR4-Asp299Gly seems to play a role in the clinical expression of UC. The rarity and non-association of NOD2 mutations with IBD may reveal a genetic characteristic of the population in our region.

Pattern-recognition receptors: signaling pathways and dysregulation in canine chronic enteropathies—brief review

Pattern-recognition receptors (PRRs) are expressed by innate immune cells and recognize pathogen-associated molecular patterns (PAMPs) as well as endogenous damage-associated molecular pattern (DAMP) molecules. With a large potential for synergism or convergence between their signaling pathways, PRRs orchestrate a complex interplay of cellular mediators and transcription factors, and thus play a central role in homeostasis and host defense. Aberrant activation of PRR signaling, mutations of the receptors and/or their downstream signaling molecules, and/or DAMP/PAMP complex–mediated receptor signaling can potentially lead to chronic auto-inflammatory diseases or development of cancer. PRR signaling pathways appear to also present an interesting new avenue for the modulation of inflammatory responses and to serve as potential novel therapeutic targets. Evidence for a dysregulation of the PRR toll-like receptor (TLR)2, TLR4, TLR5, and TLR9, nucleotide-binding oligomerization domain–containing protein (NOD)2, and the receptor of advanced glycation end products (RAGE) exists in dogs with chronic enteropathies. We describe the TLR, NOD2, and RAGE signaling pathways and evaluate the current veterinary literature—in comparison to human medicine—to determine the role of TLRs, NOD2, and RAGE in canine chronic enteropathies.

E3 Ubiquitin ligase ZNRF4 negatively regulates NOD2 signalling and induces tolerance to MDP

Optimal regulation of the innate immune receptor nucleotide-binding oligomerization domain-containing protein 2 (NOD2) is essential for controlling bacterial infections and inflammatory disorders. Chronic NOD2 stimulation induces non-responsiveness to restimulation, termed NOD2-induced tolerance. Although the levels of the NOD2 adaptor, RIP2, are reported to regulate both acute and chronic NOD2 signalling, how RIP2 levels are modulated is unclear. Here we show that ZNRF4 induces K48-linked ubiquitination of RIP2 and promotes RIP2 degradation. A fraction of RIP2 localizes to the endoplasmic reticulum (ER), where it interacts with ZNRF4 under either 55 unstimulated and muramyl dipeptide-stimulated conditions. Znrf4 knockdown monocytes have sustained nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation, and Znrf4 knockdown mice have reduced NOD2-induced tolerance and more effective control of Listeria monocytogenes infection. Our results thus demonstrate E3-ubiquitin ligase ZNRF4-mediated RIP2 degradation as a negative regulatory mechanism of NOD2-induced NF-κB, cytokine and anti-bacterial responses in vitro and in vivo, and identify a ZNRF4-RIP2 axis of fine-tuning NOD2 signalling to promote protective host immunity.

NOD2 in zebrafish functions in antibacterial and also antiviral responses via NF-κB, and also MDA5, RIG-I and MAVS

NOD2/RIPK2 signalling plays essential role in the modulation of innate and adaptive immunity in mammals. In this study, NOD2 was functionally characterized in zebrafish (Danio rerio), and its interaction with a receptor-interaction protein, RIPK2, and RLRs such as MDA5 and RIG-I, as well as the adaptor, MAVS was revealed in fish innate immunity. The expression of NOD2 and RIPK2 in ZF4 cells has been constitutive and can be induced by the infection of Edwardsiella tarda and SVCV. The NOD2 can sense MDP in PGN from Gram-negative and -positive bacteria. It is further revealed that the NOD2 and RIPK2 can activate NF-κB and IFN promoters, inducing significantly antiviral defense against SVCV infection. As observed in the reduced bacterial burden in RIPK2 overexpressed cells, RIPK2 also has a role in inhibiting the bacterial replication. The overexpression of NOD2 in zebrafish embryos resulted in the increase of immune gene expression, especially those encoding PRRs and cytokines involved in antiviral response such as MDA5, RIG-I, and type I IFNs, etc. Luciferase reporter assays and co-immunoprecipitation assays demonstrated that zebrafish NOD2 is associated with MDA5 and RIG-I in signalling pathway. In addition, it is further demonstrated that RIPK2 and MAVS in combination with NOD2 have an enhanced role in NOD2-mediated NF-κB and type I IFN activation. It is concluded that teleost fish NOD2 can not only sense MDP for activating innate immunity as reported in mammals, but can also interact with other PRRs to form a network in antiviral innate response.

A Novel NOD2-associated Mutation and Variant Blau Syndrome: Phenotype and Molecular Analysis

PURPOSE

To describe the clinical and molecular implications of a novel mutation in the NOD2/CARD15 gene on a family and its seven affected members.

METHODS

We reviewed the clinical presentations of family members who came to our center for refractory uveitis. Genetic testing and molecular testing was performed.

RESULTS

All affected members had adult onset recurrent non-granulomatous panuveitis. The inheritance pattern suggested an autosomal dominant disease and genetic analysis identified a novel mutation in the NOD2 gene that converted amino acid 600 from glutamate to alanine (E600A). Transfection of the E600A NOD2 into human embryonic kidney-293 (HEK293) cells revealed constitutive activation and a reduced ability to respond to the NOD2 ligand, muramyl dipeptide (MDP) as compared with wild-type NOD2.

CONCLUSIONS

The E600A mutation in the NOD2 gene may confer a higher penetrance of uveitis but a later onset of milder forms of non-ocular involvement.

Short- and long-term regulation of intestinal Na+/H+ exchange by Toll-like receptors TLR4 and TLR5

Inappropriate activation of pattern recognition receptors has been described as a potential trigger in the development of inflammatory bowel disease (IBD). In this study, we evaluated the activity and expression of Na(+)/H(+) exchanger (NHE) subtypes in T84 intestinal epithelial cells during Toll-like receptor 4 (TLR4) activation by monophosphoryl lipid A and TLR5 by flagellin. NHE activity and intracellular pH were evaluated by spectrofluorescence. Additionally, kinase activities were evaluated by ELISA, and siRNA was used to specifically inhibit adenylyl cyclase (AC). Monophosphoryl lipid A (MPLA) (0.01-50.00 μg/ml) and flagellin (10-500 ng/ml) inhibited NHE1 activity in a concentration-dependent manner (MPLA short term -25.2 ± 5.0%, long term -31.9 ± 4.0%; flagellin short term -14.9 ± 2.0%, long term -19.1 ± 2.0%). Both ligands triggered AC3, PKA, PLC, and PKC signal molecules. Long-term exposure to flagellin and MPLA induced opposite changes on NHE3 activity; flagellin increased NHE3 activity (∼10%) with overexpression of membrane protein, whereas MPLA decreased NHE3 activity (-17.3 ± 3.0%). MPLA and flagellin simultaneously had synergistic effects on NHE activity. MPLA and flagellin impaired pHi recovery after intracellular acidification. The simultaneous exposure to MPLA and flagellin induced a substantial pHi reduction (-0.55 ± 0.03 pH units). Activation of TLR4 and TLR5 exerts marked inhibition of NHE1 activity in intestinal epithelial cells. Transduction mechanisms set into motion during TLR4-mediated and long-term TLR5-mediated inhibition of NHE1 activity involve AC3, PKA, PLC, and PKC. However, short- and long-term TLR4 activation and TLR5 activation might use different signaling pathways. The physiological alterations on intestinal epithelial cells described here may be useful in the development of better IBD therapeutics.

Muramyl dipeptide enhances thermal injury-induced inflammatory cytokine production and organ function injury in rats

The bacterial infection following thermal injury is a very important factor of excessive inflammatory response and multiple organ damage. Muramyl dipeptide (MDP) is the key structure of gram-positive bacteria and gram-negative bacteria triggering the innate immune system. The aim of the present study was to determine the effect of MDP on thermal injury-induced inflammatory responses, organ function injury, and mortality in rats. Fifty male Sprague-Dawlay rats were randomly divided into three groups: normal control group, scald group, and MDP group. Scald group only suffered 20% total body surface area third-degree thermal injury. Muramyl dipeptide 5 mg·kg was administered through the femoral vein at 24 h after thermal injury in the MDP group. Plasma inflammatory cytokine levels were measured by enzyme-linked immunosorbent assay. An additional 90 male Sprague-Dawley rats were randomly divided into three groups to observe the survival rate in 72 h. Plasma levels of interleukin-6, interleukin-10, interferon-γ, and high-mobility group box 1; the white blood cell counts; the serum concentrations of alanine aminotransferase, aspartate aminotransferase, total bilirubin, creatine kinase isoenzyme-MB, blood urea nitrogen, and creatinine; and the activity of lung tissue myeloperoxidase significantly increased after thermal injury alone. Compared with the scald group, MDP led to more serious inflammatory responses and organ function damage and higher mortality (P < 0.05, respectively). These data indicate that MDP exacerbates thermal injury-induced inflammatory cytokine production, accompanied by multiple organ dysfunction syndrome and high mortality in rats.

Reduction of Mycobacterium tuberculosis infection in Bacillus Calmette Guerin immunized people is due to training of innate immunity

The currently used vaccine for prevention of tuberculosis is Bacillus Calmette Guerin, which has been associated with a protective effect of 51% against tuberculosis. New vaccination strategies based on an enhancement of adaptive T-cell based immunity have been unsuccessful in increasing the efficiency of BCG immunisation. The proposed hypothesis is that a reduction of Mycobacterium (M.) tuberculosis infection in Bacillus Calmette Guerin immunized people is due to training of innate immunity. Evidence to support the hypothesis is a systematic review, which showed that BCG protects against M. tuberculosis infection as evident from negative interferon gamma release assay results in BCG immunised exposed people. BCG has been shown to enhance innate immunity in monocytes via nucleotide binding oligomerisation domain 2 receptor activation by muramyldipeptide. An alternative hypothesis may be that T-suppressor cells induced by BCG immunisation may be the reason for the absence of an interferon gamma response mimicking absence of infection in immunized people. In order to test the primary hypothesis an ultra-low dose mouse model of M. tuberculosis infection could be used. Innate immunity could be enhanced by administration of murabutide and groups with and without murabutide enhanced BCG immunisation and with and without elimination of T-suppressor cells compared. The contribution of training of innate immunity in reduction of infection could hereby be demonstrated by treatment of mice prior to immunisation with an inhibitor of epigenetic programming. Confirmation of the hypothesis could provide the foundation of a new approach to an improved vaccine against M. tuberculosis infection.

Effect of Sulforaphane on NOD2 via NF-κB: implications for Crohn's disease

Background

Sulforaphane has well established anti-cancer properties and more recently anti-inflammatory properties have also been determined. Sulforaphane has been shown to inhibit PRR-mediated pro-inflammatory signalling by either directly targeting the receptor or their downstream signalling molecules such as the transcription factor, NF-κB. These results raise the possibility that PRR-mediated inflammation could be suppressed by specific dietary bioactives. We examined whether sulforaphane could suppress NF-κB via the NOD2 pathway.

Methods

Human embryonic kidney 293T (HEK293T) cells were stably transfected with NOD2 variants and the NF-κB reporter, pNifty2-SEAP. The cells were co-treated with sulforaphane and MDP and secreted alkaline phosphatase (SEAP) production was determined.

Results

We found that sulforaphane was able to significantly suppress the ligand-induced NF-κB activity at physiologically relevant concentrations, achievable via the consumption of broccoli within the diet.

Conclusions

These results demonstrate that the anti-inflammatory role of sulforaphane is not restricted to LPS-induced inflammatory signalling. These data add to the growing evidence that PRR activation can be inhibited by specific phytochemicals and thus suggests that diet could be a way of controlling inflammation. This is particularly important for a disease like Crohn’s disease where diet can play a key role in relieving or exacerbating symptoms.

The Concise Guide to PHARMACOLOGY 2013/14: catalytic receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full.

Catalytic receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets.

It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

Caveats and truths in genetic, clinical, autoimmune and autoinflammatory issues in Blau syndrome and early onset sarcoidosis

Blau syndrome (BS) and early onset sarcoidosis (EOS) are, respectively, the familial and sporadic forms of the pediatric granulomatous autoinflammatory disease, which belong to the group of monogenic autoinflammatory syndromes. Both of these conditions are caused by mutations in the NOD2 gene, which encodes the cytosolic NOD2 protein, one of the pivotal molecules in the regulation of innate immunity, primarily expressed in the antigen-presenting cells. Clinical onset of BS and EOS is usually in the first years of life with noncaseating epithelioid granulomas mainly affecting joints, skin, and uveal tract, variably associated with heterogeneous systemic features. The dividing line between autoinflammatory and autoimmune mechanisms is probably not so clear-cut, and the relationship existing between BS or EOS and autoimmune phenomena remains unclear. There is no established therapy for the management of BS and EOS, and the main treatment aim is to prevent ocular manifestations entailing the risk of potential blindness and to avoid joint deformities. Nonsteroidal anti-inflammatory drugs, corticosteroids and immunosuppressive drugs, such as methotrexate or azathioprine, may be helpful; when patients are unresponsive to the combination of corticosteroids and immunosuppressant agents, the tumor necrosis factor-α inhibitor infliximab should be considered. Data on anti-interleukin-1 inhibition with anakinra and canakinumab is still limited and further corroboration is required. The aim of this paper is to describe BS and EOS, focusing on their genetic, clinical, and therapeutic issues, with the ultimate goal of increasing clinicians' awareness of both of these rare but serious disorders.

Fungal chitin dampens inflammation through IL-10 induction mediated by NOD2 and TLR9 activation

Chitin is an essential structural polysaccharide of fungal pathogens and parasites, but its role in human immune responses remains largely unknown. It is the second most abundant polysaccharide in nature after cellulose and its derivatives today are widely used for medical and industrial purposes. We analysed the immunological properties of purified chitin particles derived from the opportunistic human fungal pathogen Candida albicans, which led to the selective secretion of the anti-inflammatory cytokine IL-10. We identified NOD2, TLR9 and the mannose receptor as essential fungal chitin-recognition receptors for the induction of this response. Chitin reduced LPS-induced inflammation in vivo and may therefore contribute to the resolution of the immune response once the pathogen has been defeated. Fungal chitin also induced eosinophilia in vivo, underpinning its ability to induce asthma. Polymorphisms in the identified chitin receptors, NOD2 and TLR9, predispose individuals to inflammatory conditions and dysregulated expression of chitinases and chitinase-like binding proteins, whose activity is essential to generate IL-10-inducing fungal chitin particles in vitro, have also been linked to inflammatory conditions and asthma. Chitin recognition is therefore critical for immune homeostasis and is likely to have a significant role in infectious and allergic disease.

Potential roles of nucleotide-binding oligomerization domain 2 in the pathogenesis of systemic lupus erythematosus

Nucleotide-binding oligomerization domain 2 (NOD2) is one of the most prominent member of the NOD-like receptors protein family that functions as intracellular pattern recognition receptors. Numerous studies have suggested the importance of NOD2 in defensing against microbial infections, regulation of the inflammatory process. It is shown that NOD2 contributes to the pathogenesis of various autoimmune and chronic inflammatory diseases, such as Crohn's disease, rheumatoid arthritis. The aim of this study is to summarize our current understandings of NOD2 function and the role of NOD2 in systemic lupus erythematosus (SLE). The following databases were searched: Pubmed, EMBASE and Web of Science for English-language sources, using the terms "lupus," "systemic lupus erythematosus," ''SLE," "immunity," "inflammatory" and "NOD2." Emerging data evidences that NOD2 has important biological effects in autoimmunity and inflammatory and might take part in the pathogenesis of SLE. Studies exploring the relationship between NOD2 and SLE are very limited. Whether NOD2 could be a potentially valuable therapeutic target for treatment for SLE, more understanding of the mechanism of NOD2 is needed in the future in SLE.

The Nod1, Nod2, and Rip2 axis contributes to host immune defense against intracellular Acinetobacter baumannii infection

Acinetobacter baumannii is a major extensively drug-resistant lethal human nosocomial bacterium. However, the host innate immune mechanisms controlling A. baumannii are not well understood. Although viewed as an extracellular pathogen, A. baumannii can also invade and survive intracellularly. However, whether host innate immune pathways sensing intracellular bacteria contribute to immunity against A. baumannii is not known. Here, we provide evidence for the first time that intracellular antibacterial innate immune receptors Nod1 and Nod2, and their adaptor Rip2, play critical roles in the sensing and clearance of A. baumannii by human airway epithelial cells in vitro. A. baumannii infection upregulated Rip2 expression. Silencing of Nod1, Nod2, and Rip2 expression profoundly increased intracellular invasion and prolonged the multiplication and survival of A. baumannii in lung epithelial cells. Notably, the Nod1/2-Rip2 axis did not contribute to the control of A. baumannii infection of human macrophages, indicating that they play cell type-specific roles. The Nod1/2-Rip2 axis was needed for A. baumannii infection-induced activation of NF-κB but not mitogen-activated protein kinases. Moreover, the Nod1/2-Rip2 axis was critical to induce optimal cytokine and chemokine responses to A. baumannii infection. Mechanistic studies showed that the Nod1/2 pathway contributed to the innate control of A. baumannii infection through the production of β-defensin 2 by airway epithelial cells. This study revealed new insights into the immune control of A. baumannii and may contribute to the development of effective immune therapeutics and vaccines against A. baumannii.

NOD2/CARD15 single nucleotide polymorphism 13 (3020insC) is associated with risk of sepsis and single nucleotide polymorphism 8 (2104C>T) with herpes viruses reactivation in patients after allogeneic hematopoietic stem cell transplantation

Three NOD2 polymorphisms (single nucleotide polymorphism [SNP]8 [2104C>T, Arg702Trp], SNP12 [2722G>C, Gly908Arg], and SNP13 [3020insC, Leu1007 fsins C]), identified as disease-associated variants in Crohn's disease, have recently been suggested as gene markers of the outcome of hematopoietic stem cell transplantation (HSCT). In the present multicenter study of 464 donor-recipient pairs, we focused on the effect of NOD2 mutation(s) on the risk of infections and acute graft-versus-host disease (aGVHD). The presence of SNP13 in recipients, donors, or both was more frequently seen in patients having sepsis than in those lacking sepsis (9 of 48 versus 33 of 386, P = .046). The presence of SNP8 (recipient and/or donor positive) was associated with a higher rate of Herpes viruses reactivation (17 of 21 versus 86 of 173, P = .007). In the SNP8-positive group, a trend for a higher rate of bacteremia well controlled by antibiotics was found (9 of 10 versus 47 of 81, P = .106). In contrast, the presence of SNP13 in recipient and/or donor resulted in a poor response to antibiotics (5 of 11 versus 9 of 10, P = .042). A statistically significant association between the presence of NOD2 SNPs and acute grade > II GVHD was found in a subgroup of HSCT patients who received transplants from unrelated donors with a myeloablative conditioning regimen that included antithymocyte globulin (ATG). In this subgroup of patients, donor positivity for any SNPs investigated (7 of 18 versus 17 of 113, P = .036) and, independently, only the presence of SNP8 (4 of 8 versus 20 of 123, P = .055) were associated with severe grade ≥ II aGVHD. In conclusion, SNP8 positivity in donors or recipients makes patients more prone to Herpes viruses reactivation and bacteremia but not to sepsis. Septic complications were associated with SNP13 polymorphism. SNP8 in donors constitutes a risk factor of severe aGVHD, but only if patients received transplants from unrelated donors and received ATG as part of a conditioning regimen.

The NOD2 receptor does not play a major role in the pathogenesis of Group B Streptococcus in mice

Group B Streptococcus (GBS) capsular type III is an important agent of life-threatening invasive infections. It has been previously shown that encapsulated GBS is easily internalized by dendritic cells (DCs) and this internalization has an impact on cytokine production. The intracellular receptors or pathways underlying this response are not well understood. In this work, we investigated the role of NOD2 in the pathogenesis of GBS using a mouse model of infection. NOD2(-/-) mice showed similar levels of survival and bacteremia than control mice. Interestingly, ex vivo analysis of total spleen cells from infected animals showed that the absence of NOD2 results in reduced production of inflammatory cytokines. However this abridged inflammatory response does not seem to improve mouse survival. In conclusion, we demonstrated that NOD2 is not a crucial receptor to fight GBS infection and only partially contributes to the inflammatory response.

Muramyl dipeptide responsive pathways in Crohn's disease: from NOD2 and beyond

Crohn's disease (CD) is one of main disease entities under the umbrella term chronic inflammatory bowel disease. The etiology of CD involves alterations in genetic, microbiological, and immunological factors. This review is devoted to the role of the bacterial wall compound muramyl dipeptide (MDP) for the activation of inflammatory pathways involved in the pathogenesis of CD. The importance of this molecule is underscored by the fact that (1) MDP, which is found in most Gram-negative and -positive bacteria, is able to trigger several immunological responses in the intestinal system, and (2) that alterations in several mediators of the MDP response including-but not restricted to-nucleotide oligomerization domain 2 (NOD2) are associated with CD. The normalization of MDP signaling is one of several important factors that influence the intestinal inflammatory response, a fact which emphasizes the pathogenic importance of MDP signaling for the pathogenesis of CD. The important aspects of NOD2 and non-NOD2 mediated effects of MDP for the development of CD are highlighted, as well as how alterations in these pathways might translate into the development of new therapeutic strategies.

Identification of benzimidazole diamides as selective inhibitors of the nucleotide-binding oligomerization domain 2 (NOD2) signaling pathway

NOD2 is an intracellular pattern recognition receptor that assembles with receptor-interacting protein (RIP)-2 kinase in response to the presence of bacterial muramyl dipeptide (MDP) in the host cell cytoplasm, thereby inducing signals leading to the production of pro-inflammatory cytokines. The dysregulation of NOD2 signaling has been associated with various inflammatory disorders suggesting that small-molecule inhibitors of this signaling complex may have therapeutic utility. To identify inhibitors of the NOD2 signaling pathway, we utilized a cell-based screening approach and identified a benzimidazole diamide compound designated GSK669 that selectively inhibited an MDP-stimulated, NOD2-mediated IL-8 response without directly inhibiting RIP2 kinase activity. Moreover, GSK669 failed to inhibit cytokine production in response to the activation of Toll-like receptor (TLR)-2, tumor necrosis factor receptor (TNFR)-1 and closely related NOD1, all of which share common downstream components with the NOD2 signaling pathway. While the inhibitors blocked MDP-induced NOD2 responses, they failed to block signaling induced by NOD2 over-expression or single stranded RNA, suggesting specificity for the MDP-induced signaling complex and activator-dependent differences in NOD2 signaling. Investigation of structure-activity relationship allowed the identification of more potent analogs that maintained NOD2 selectivity. The largest boost in activity was achieved by N-methylation of the C2-ethyl amide group. These findings demonstrate that the NOD2 signaling pathway is amenable to modulation by small molecules that do not target RIP2 kinase activity. The compounds we identified should prove useful tools to investigate the importance of NOD2 in various inflammatory processes and may have potential clinical utility.

Short- and long-term regulation of intestinal Na+/H+ exchange activity associated with TLR2 receptor activation is independent of nuclear factor-κB signaling

Type 2 Toll-like receptors (TLR2s) are expressed in cell membranes and recognize a wide range of pathogen-associated molecular patterns derived from bacteria, such as lipoteichoic acid (LTA). The aim of this study was to evaluate the effect of TLR2 activation by LTA on the activity of type 1 Na(+)/H(+) exchanger (NHE) in T84 intestinal epithelial cells. Short-term (0.5 hour) and long-term (18 hours) TLR2 activation significantly inhibited NHE1 activity in a concentration-dependent manner (0.01-100 µg/ml; -7 ± 3 to -21 ± 3% and 3 ± 3 to -21 ± 3% of control values, respectively). S3226 [3-[2-(3-guanidino-2-methyl-3-oxopropenyl)-5-methyl-phenyl]-N-isopropylidene-2-methyl-acrylamide dihydrochloride], an NHE3-selective inhibitor, did not affect the inhibitory effect on NHE activity. LTA-induced NHE inhibition did not occur in the presence ofethylisopropylamiloride (an NHE1 inhibitor). Long-term TLR2 activation decreased NHE1 affinity for Na(+) (Km= 64.98 ± 1.67 mM) compared with control (Km= 20.44 ± 0.54 mM) without changes in Vmax values. After TLR2 activation, we observed tyrosine-protein kinase (SRC) activation, phosphatidylinositol 3-kinase (PI3K) recruitment, and adenylyl cyclase (AC3) phosphorylation. The total amount of AC3 increased (23 ± 8% of control) after long-term treatment with LTA. Anti-AC3 small interfering RNA prevented LTA-induced NHE1 inhibition, similar to that observed with the AC3 inhibitor KH7 [(±)-2-(1H-benzimidazol-2-ylthio)propanoic acid 2-[(5-bromo-2-hydroxyphenyl)methylene]hydrazide]. A significant increase in cAMP levels (32 ± 3% and 14 ± 2% after short- and long-term stimulation, respectively) was detected, and inhibition of protein kinase A (PKA), phospholipase C (PLC), and downregulation of protein kinase C (PKC) prevented NHE1 inhibition. Inhibition of nuclear factor-κΒ (NF-κB) failed to revert NHE1 inhibition. We concluded that activation of TLR2 reduces NHE1 activity in epithelial cells through an alternative pathway that is unrelated to NF-κB, which involves SCR, PI3K, AC3, PKA, PLC, and PKC.

An evolutionary perspective on the causes and treatment of inflammatory bowel disease

PURPOSE OF REVIEW

To use insights from evolutionary biology to assess the current evidence for the causes, treatment, and prevention of inflammatory bowel disease (IBD).

RECENT FINDINGS

When analyzed in the context of evolutionary adaptation, recent assessments of genetic, microbial, and environmental associations with IBD implicate infectious causation.

SUMMARY

An evolutionary perspective provides insight into the causes of IBD, interpretation of its manifestations, and assessment of interventions. The evidence implicating infectious causation suggests that future studies of IBD would benefit from increased focus on infectious causes and interventions that prevent or inhibit them.

Adaptive redox response of mesenchymal stromal cells to stimulation with lipopolysaccharide inflammagen: mechanisms of remodeling of tissue barriers in sepsis

Acute bacterial inflammation is accompanied by excessive release of bacterial toxins and production of reactive oxygen and nitrogen species (ROS and RNS), which ultimately results in redox stress. These factors can induce damage to components of tissue barriers, including damage to ubiquitous mesenchymal stromal cells (MSCs), and thus can exacerbate the septic multiple organ dysfunctions. The mechanisms employed by MSCs in order to survive these stress conditions are still poorly understood and require clarification. In this report, we demonstrated that in vitro treatment of MSCs with lipopolysaccharide (LPS) induced inflammatory responses, which included, but not limited to, upregulation of iNOS and release of RNS and ROS. These events triggered in MSCs a cascade of responses driving adaptive remodeling and resistance to a "self-inflicted" oxidative stress. Thus, while MSCs displayed high levels of constitutively present adaptogens, for example, HSP70 and mitochondrial Sirt3, treatment with LPS induced a number of adaptive responses that included induction and nuclear translocation of redox response elements such as NFkB, TRX1, Ref1, Nrf2, FoxO3a, HO1, and activation of autophagy and mitochondrial remodeling. We propose that the above prosurvival pathways activated in MSCs in vitro could be a part of adaptive responses employed by stromal cells under septic conditions.

Impact of NOD2 polymorphisms on infectious complications following chemotherapy in patients with acute myeloid leukaemia

We sought to investigate the relationship between polymorphisms of the NOD2 gene and infectious complications following intensive induction chemotherapy in patients with acute myeloid leukaemia (AML). We hypothesised that single nucleotide polymorphisms (SNPs) of the NOD2 gene are associated with a higher rate of infections during the phase of severe neutropenia. In 131 AML patients receiving induction therapy, the presence of the three most frequent polymorphisms of NOD2 (Arg702Trp, Gly908Arg, Leu1007fsinsC) was analysed. SNP analyses by means of genomic PCR incorporating fluorescence-labelled probes with characteristic melting curves were performed using the LightCycler platform. Our data suggest a significantly lower probability of mucositis or enteritis in AML patients lacking any of the three evaluated NOD2 polymorphisms. Furthermore, bloodstream cultures of AML patients carrying either a missense or a frameshift mutation of NOD2 were significantly more frequently tested positive concerning Streptococcus spp. In contrast, the presence of NOD2 polymorphisms had no impact on such important infectious complications as systemic inflammatory response syndrome or sepsis, the rate of central venous catheter infections or the incidence of pneumonia including fungal infections. Our data represent one of the first reports investigating the impact of polymorphisms of the innate immune system on infectious complications in patients with neutropenia following chemotherapy. A correlation between NOD2 polymorphisms and infectious events in AML patients is demonstrated.

Nucleotide-binding oligomerization domain containing 2: structure, function, and diseases

OBJECTIVES

To systematically review literature about the structure and function of nucleotide-binding oligomerization domain containing 2 (NOD2) and its disease association.

METHODS

The English literature was searched using keywords "NOD2" and "disease". Relevant original and review articles were reviewed.

RESULTS

NOD2 is an intracellular protein and shares similar molecular structure with NOD1, pyrin, and cryopyrin. There are more than 100 NOD2 gene mutations, some of which have been linked to diseases such as Crohn disease, Blau syndrome, and NOD2-associated autoinflammatory disease (NAID). The NOD2 variants located in the leucine-rich repeat (LRR) region are susceptible to Crohn disease, and the variants in the nucleotide-binding domain (NBD) and in between the NBD and LRR are associated with Blau syndrome and NAID, respectively. No disease association with the gene variants has been found in rheumatoid arthritis, systemic lupus erythematosus, ankylosing spondylitis, psoriasis/psoriatic arthritis, adult sarcoidosis, granulomatous polyangiitis, or multiple sclerosis. The potential association of the NOD2 variants with graft-versus-host-disease remains controversial. NOD2 functions mainly through RICK or RIP2 to activate p38 mitogen-activated protein kinases and NF-κB, resulting in inflammatory response, and enhanced autophagic activity. Biologic therapy may be beneficial for NOD2-associated diseases, and new drug development may be realized based upon the signaling pathways.

CONCLUSIONS

NOD2 gene mutations are associated with several diseases, and some of the mutations are of diagnostic value in Blau disease and NAID. To understand the NOD2 function, disease association, and its pathogenesis is important given the ever increasing clinical significance of NOD2.

TRIM27 negatively regulates NOD2 by ubiquitination and proteasomal degradation

NOD2, the nucleotide-binding domain and leucine-rich repeat containing gene family (NLR) member 2 is involved in mediating antimicrobial responses. Dysfunctional NOD2 activity can lead to severe inflammatory disorders, but the regulation of NOD2 is still poorly understood. Recently, proteins of the tripartite motif (TRIM) protein family have emerged as regulators of innate immune responses by acting as E3 ubiquitin ligases. We identified TRIM27 as a new specific binding partner for NOD2. We show that NOD2 physically interacts with TRIM27 via the nucleotide-binding domain, and that NOD2 activation enhances this interaction. Dependent on functional TRIM27, ectopically expressed NOD2 is ubiquitinated with K48-linked ubiquitin chains followed by proteasomal degradation. Accordingly, TRIM27 affects NOD2-mediated pro-inflammatory responses. NOD2 mutations are linked to susceptibility to Crohn's disease. We found that TRIM27 expression is increased in Crohn's disease patients, underscoring a physiological role of TRIM27 in regulating NOD2 signaling. In HeLa cells, TRIM27 is partially localized in the nucleus. We revealed that ectopically expressed NOD2 can shuttle to the nucleus in a Walker A dependent manner, suggesting that NOD2 and TRIM27 might functionally cooperate in the nucleus.

We conclude that TRIM27 negatively regulates NOD2-mediated signaling by degradation of NOD2 and suggest that TRIM27 could be a new target for therapeutic intervention in NOD2-associated diseases.

The inositol phosphatase SHIP-1 inhibits NOD2-induced NF-κB activation by disturbing the interaction of XIAP with RIP2

SHIP-1 is an inositol phosphatase predominantly expressed in hematopoietic cells. Over the ten past years, SHIP-1 has been described as an important regulator of immune functions. Here, we characterize a new inhibitory function for SHIP-1 in NOD2 signaling. NOD2 is a crucial cytoplasmic bacterial sensor that activates proinflammatory and antimicrobial responses upon bacterial invasion. We observed that SHIP-1 decreases NOD2-induced NF-κB activation in macrophages. This negative regulation relies on its interaction with XIAP. Indeed, we observed that XIAP is an essential mediator of the NOD2 signaling pathway that enables proper NF-κB activation in macrophages. Upon NOD2 activation, SHIP-1 C-terminal proline rich domain (PRD) interacts with XIAP, thereby disturbing the interaction between XIAP and RIP2 in order to decrease NF-κB signaling.

Immunomodulatory properties of novel nucleotide oligomerization domain 2 (nod2) agonistic desmuramyldipeptides

There is a pressing need for the development of novel adjuvants for human use. The minimal bioactive structure of bacterial peptidoglycan (PGN), muramyldipeptide (MDP), and its derivative murabutide (MB) have long been known for their adjuvant activities. For this reason, a series of novel desmuramyldipeptides have been designed and synthesized as part of our search for therapeutically useful MDP analogues. Since nucleotide oligomerization domain 2 (Nod2) is a putative receptor for MDP, we used engineered HEK293 cells overexpressing Nod2 to screen and validate our compounds for their Nod2-agonist activity. Their immunomodulatory properties were subsequently assessed in vitro by evaluating their effect on proinflammatory cytokine production of phorbol 12-myristate 13-acetate (PMA)/ionomycin-stimulated human peripheral blood mononuclear cells (PBMCs). Herein, we present novel desmuramyldipeptides, the most active of them possessing immunoenhancing properties as a result of their potent Nod2-agonistic effect.

The c-Jun N-terminal kinase (JNK)-binding protein (JNKBP1) acts as a negative regulator of NOD2 protein signaling by inhibiting its oligomerization process

NOD2 is one of the best characterized members of the cytosolic NOD-like receptor family. NOD2 is able to sense muramyl dipeptide, a specific bacterial cell wall component, and to subsequently induce various signaling pathways leading to NF-κB activation and autophagy, both events contributing to an efficient innate and adaptive immune response. Interestingly, loss-of-function NOD2 variants were associated with a higher susceptibility for Crohn disease, which highlights the physiological importance of proper regulation of NOD2 activity. We performed a biochemical screen to search for new NOD2 regulators. We identified a new NOD2 partner, c-Jun N-terminal kinase-binding protein 1 (JNKBP1), a scaffold protein characterized by an N-terminal WD-40 domain. JNKBP1, through its WD-40 domain, binds to NOD2 following muramyl dipeptide activation. This interaction attenuates NOD2-mediated NF-κB activation and IL-8 secretion as well as NOD2 antibacterial activity. JNKBP1 exerts its repressor effect by disturbing NOD2 oligomerization and RIP2 tyrosine phosphorylation, both steps required for downstream NOD2 signaling. We furthermore showed that JNKBP1 and NOD2 are co-expressed in the human intestinal epithelium and in immune cells recruited in the lamina propria, which suggests that JNKBP1 contributes to maintain NOD2-mediated intestinal immune homeostasis.

Pathogen-mediated proteolysis of the cell death regulator RIPK1 and the host defense modulator RIPK2 in human aortic endothelial cells

Porphyromonas gingivalis is the primary etiologic agent of periodontal disease that is associated with other human chronic inflammatory diseases, including atherosclerosis. The ability of P. gingivalis to invade and persist within human aortic endothelial cells (HAEC) has been postulated to contribute to a low to moderate chronic state of inflammation, although how this is specifically achieved has not been well defined. In this study, we demonstrate that P. gingivalis infection of HAEC resulted in the rapid cleavage of receptor interacting protein 1 (RIPK1), a mediator of tumor necrosis factor (TNF) receptor-1 (TNF-R1)-induced cell activation or death, and RIPK2, a key mediator of both innate immune signaling and adaptive immunity. The cleavage of RIPK1 or RIPK2 was not observed in cells treated with apoptotic stimuli, or cells stimulated with agonists to TNF-R1, nucleotide oligomerization domain receptor 1(NOD1), NOD2, Toll-like receptor 2 (TLR2) or TLR4. P. gingivalis-induced cleavage of RIPK1 and RIPK2 was inhibited in the presence of a lysine-specific gingipain (Kgp) inhibitor. RIPK1 and RIPK2 cleavage was not observed in HAEC treated with an isogenic mutant deficient in the lysine-specific gingipain, confirming a role for Kgp in the cleavage of RIPK1 and RIPK2. Similar proteolysis of poly (ADP-ribose) polymerase (PARP) was observed. We also demonstrated direct proteolysis of RIPK2 by P. gingivalis in a cell-free system which was abrogated in the presence of a Kgp-specific protease inhibitor. Our studies thus reveal an important role for pathogen-mediated modification of cellular kinases as a potential strategy for bacterial persistence within target host cells, which is associated with low-grade chronic inflammation, a hallmark of pathogen-mediated chronic inflammatory disorders.

The impact of genomics on pediatric research and medicine

In this review, we discuss some of the most recent developments in genomics research and their relevance to the field of pediatrics. In particular, we examine 3 major approaches that are being used to identify genetic correlates of disease: genome-wide association studies, copy number variation studies, and next-generation sequencing. In the past few years, these approaches have yielded major insights into the causes and pathophysiology of a wide range of diseases but are also constrained by certain limitations. This review provides an overview of the genomic landscape in complex pediatric disorders and sets the stage for translating new discoveries into clinical practice, the future of genomic medicine.

Viral interactions with the host and microbiota in the intestine

This review explores the recent advances that have been made in our understanding of host viral interactions in the intestine. Technical advances have allowed the initial definition of intestinal viromes in a number of species including humans. Important advances in our knowledge of the host response to viral infection have shown that interferon lambda has a role that is unique from type I interferons in the intestine. Lastly, our understanding of virally induced phenotypes has expanded through new studies that show bacteria can play an important role in the outcome of viral infection in the intestine.

Miscellaneous non-inflammatory musculoskeletal conditions. Blau syndrome

Blau syndrome (BS) is a rare dominantly inherited, inflammatory syndrome characterised by the clinical triad of granulomatous dermatitis, symmetric arthritis and recurrent uveitis. The caspase recruitment domain gene CARD15/NOD2 has been identified as the gene responsible for BS. In the majority of patients, the disease is characterised by early onset, usually before 3-4 years of age. Onset is most often articular and cutaneous. Eye symptoms usually start later; however, eye involvement is the most relevant morbidity of BS. Atypical cases of BS have been reported with involvement of organs other than skin, joint and eyes. Due to its rarity and the variations in the severity and evolution of its expressions, there have been no studies on the optimal treatment for patients with BS. If the therapeutic response to corticosteroids is unsatisfactory, additional treatment with immunosuppressive agents should be tried. The results with biologic anti-cytokine agents, such as infliximab and anakinra, are variable, particularly with regard to ocular morbidity. This review will focus on the clinical and genetics aspects of the familial and the sporadic form of BS. Further, we will describe an Italian family followed by us over the past 25 years.

Messenger functions of the bacterial cell wall-derived muropeptides

Bacterial muropeptides are soluble peptidoglycan structures central to recycling of the bacterial cell wall and messengers in diverse cell signaling events. Bacteria sense muropeptides as signals that antibiotics targeting cell-wall biosynthesis are present, and eukaryotes detect muropeptides during the innate immune response to bacterial infection. This review summarizes the roles of bacterial muropeptides as messengers, with a special emphasis on bacterial muropeptide structures and the relationship of structure to the biochemical events that the muropeptides elicit. Muropeptide sensing and recycling in both Gram-positive and Gram-negative bacteria are discussed, followed by muropeptide sensing by eukaryotes as a crucial event in the innate immune response of insects (via peptidoglycan-recognition proteins) and mammals (through Nod-like receptors) to bacterial invasion.

Host-microbial interactions and regulation of intestinal epithelial barrier function: From physiology to pathology

The gastrointestinal tract is the largest reservoir of commensal bacteria in the human body, providing nutrients and space for the survival of microbes while concurrently operating mucosal barriers to confine the microbial population. The epithelial cells linked by tight junctions not only physically separate the microbiota from the lamina propria, but also secrete proinflammatory cytokines and reactive oxygen species in response to pathogen invasion and metabolic stress and serve as a sentinel to the underlying immune cells. Accumulating evidence indicates that commensal bacteria are involved in various physiological functions in the gut and microbial imbalances (dysbiosis) may cause pathology. Commensal bacteria are involved in the regulation of intestinal epithelial cell turnover, promotion of epithelial restitution and reorganization of tight junctions, all of which are pivotal for fortifying barrier function. Recent studies indicate that aberrant bacterial lipopolysaccharide-mediated signaling in gut mucosa may be involved in the pathogenesis of chronic inflammation and carcinogenesis. Our perception of enteric commensals has now changed from one of opportunistic pathogens to active participants in maintaining intestinal homeostasis. This review attempts to explain the dynamic interaction between the intestinal epithelium and commensal bacteria in disease and health status.

Assessment of the microbiota in microdissected tissues of Crohn's disease patients

The microbiota of the gastrointestinal tract is frequently mentioned as one of the key players in the etiopathogenesis of Crohn's disease (CD). Four hypotheses have been suggested: the single, still unknown bacterial pathogen, an abnormal overall composition of the bowel microbiota ("dysbiosis"), an abnormal immunological reaction to an essentially normally composed microbiota, and increased bacterial translocation. We propose that laser capture microdissection of selected microscopic structures, followed by broad-range 16S rRNA gene sequencing, is an excellent method to assess spatiotemporal alterations in the composition of the bowel microbiota in CD. Using this approach, we demonstrated significant changes of the composition, abundance, and location of the gut microbiome in this disease. Some of these abnormal findings persisted even after macroscopic mucosal healing. Further investigations along these lines may lead to a better understanding of the possible involvement of the bowel bacteria in the development of clinical Crohn's disease.