Virus sensing receptors in cellular infectivity of influenza A virus.

An innate immune response is essential to mobilize protective immunity upon the infection of respiratory epithelial cells with influenza A virus (IAV). The response is classified as early (nonspecific effectors), local systematic (effector cells recruitment) and late (antigen to lymphoid organ transport, naive B and T cells recognition, effector cells clonal expansion and differentiation). Virus particles are detected by the host cells as non-self by various sensors that are present on the cell surface, endosomes and cytosol. These sensors are collectively termed as pattern recognition receptors (PRRs). The PRRs distinguish unique molecular signatures known as pathogen-associated molecular pattern, which are present either on the cell surface or within intracellular compartments. PRRs have been classified into five major groups: C-Type Lectin Receptor (CLR), Toll-like receptor (TLR), Nod-like receptor (NLR), Retinoic acid-inducible gene-I-like receptor (RLR), which play a role in innate immunity to IAV infection, and the pyrin and hematopoietic interferon-inducible nuclear (PYHIN) domain protein. Here, we discuss the role of PRRs in cellular infectivity of IAV and highlight the recent progress.

Deletion or Inhibition of NOD1 Favors Plaque Stability and Attenuates Atherothrombosis in Advanced Atherogenesis †.

Atherothrombosis, the main cause of acute coronary syndromes (ACS), is characterized by the rupture of the atherosclerotic plaque followed by the formation of thrombi. Fatal plaque rupture sites show large necrotic cores combined with high levels of inflammation and thin layers of collagen. Plaque necrosis due to the death of macrophages and smooth muscle cells (SMCs) remains critical in the process. To determine the contribution of the innate immunity receptor NOD1 to the stability of atherosclerotic plaque, Apoe-/- and Apoe-/- Nod1-/- atherosclerosis prone mice were placed on a high-fat diet for 16 weeks to assess post-mortem advanced atherosclerosis in the aortic sinus. The proliferation and apoptosis activity were analyzed, as well as the foam cell formation capacity in these lesions and in primary cultures of macrophages and vascular SMCs obtained from both groups of mice. Our results reinforce the preeminent role for NOD1 in human atherosclerosis. Advanced plaque analysis in the Apoe-/- atherosclerosis model suggests that NOD1 deficiency may decrease the risk of atherothrombosis by decreasing leukocyte infiltration and reducing macrophage apoptosis. Furthermore, Nod1-/- SMCs exhibit higher proliferation rates and decreased apoptotic activity, contributing to thicker fibrous caps with reduced content of pro-thrombotic collagen. These findings demonstrate a direct link between NOD1 and plaque vulnerability through effects on both macrophages and SMCs, suggesting promising insights for early detection of biomarkers for treating patients before ACS occurs.

RIPK2 Dictates Insulin Responses to Tyrosine Kinase Inhibitors in Obese Male Mice.

Tyrosine kinase inhibitors (TKIs) used in cancer are also being investigated in diabetes. TKIs can improve blood glucose control in diabetic cancer patients, but the specific kinases that alter blood glucose or insulin are not clear. We sought to define the role of Receptor Interacting Serine/Threonine Kinase 2 (RIPK2) in mouse models of insulin resistance. We tested the TKI gefitinib, which inhibits RIPK2 activity, in wild-type (WT), Nod1-/-, Nod2-/-, and Ripk2-/- mice fed an obesogenic high-fat diet. Gefitinib lowered blood glucose during a glucose tolerance test (GTT) in a nucleotide-binding oligomerization domain (NOD)-RIPK2-independent manner in all obese mice. However, gefitinib lowered glucose-stimulated insulin secretion only in obese Ripk2-/- mice. Gefitinib had no effect on insulin secretion in obese WT, Nod1-/-, or Nod2-/- mice. Hence, genetic deletion of Ripk2 promoted the insulin-sensitizing potential of gefitinib, since this TKI lowered both blood glucose and insulin only in Ripk2-/- mice. Gefitinib did not alter the inflammatory profile of pancreas, adipose, liver, or muscle tissues in obese Ripk2-/- mice compared with obese WT mice. We also tested imatinib, a TKI that does not inhibit RIPK2 activity, in obese WT mice. Imatinib lowered blood glucose during a GTT, consistent with TKIs lowering blood glucose independently of RIPK2. However, imatinib increased glucose-stimulated insulin secretion during the glucose challenge. These data show that multiple TKIs lower blood glucose, where actions of TKIs on RIPK2 dictate divergent insulin responses, independent of tissue inflammation. Our data show that RIPK2 limits the insulin sensitizing effect of gefitinib, whereas imatinib increased insulin secretion.

Activation of the pattern recognition receptor NOD1 augments colon cancer metastasis.

While emerging data suggest nucleotide oligomerization domain receptor 1 (NOD1), a cytoplasmic pattern recognition receptor, may play an important and complementary role in the immune response to bacterial infection, its role in cancer metastasis is entirely unknown. Hence, we sought to determine the effects of NOD1 on metastasis. NOD1 expression in paired human primary colon cancer, human and murine colon cancer cells were determined using immunohistochemistry and immunoblotting (WB). Clinical significance of NOD1 was assessed using TCGA survival data. A series of in vitro and in vivo functional assays, including adhesion, migration, and metastasis, was conducted to assess the effect of NOD1. C12-iE-DAP, a highly selective NOD1 ligand derived from gram-negative bacteria, was used to activate NOD1. ML130, a specific NOD1 inhibitor, was used to block C12-iE-DAP stimulation. Stable knockdown (KD) of NOD1 in human colon cancer cells (HT29) was constructed with shRNA lentiviral transduction and the functional assays were thus repeated. Lastly, the predominant signaling pathway of NOD1-activation was identified using WB and functional assays in the presence of specific kinase inhibitors. Our data demonstrate that NOD1 is highly expressed in human colorectal cancer (CRC) and human and murine CRC cell lines. Clinically, we demonstrate that this increased NOD1 expression negatively impacts survival in patients with CRC. Subsequently, we identify NOD1 activation by C12-iE-DAP augments CRC cell adhesion, migration and metastasis. These effects are predominantly mediated via the p38 mitogen activated protein kinase (MAPK) pathway. This is the first study implicating NOD1 in cancer metastasis, and thus identifying this receptor as a putative therapeutic target.

Potential Role of Gut Microbiota in Induction and Regulation of Innate Immune Memory.

The gut microbiota significantly regulates the development and function of the innate and adaptive immune system. The attribute of immunological memory has long been linked only with adaptive immunity. Recent evidence indicates that memory is also present in the innate immune cells such as monocytes/macrophages and natural killer cells. These cells exhibit pattern recognition receptors (PRRs) that recognize microbe- or pathogen-associated molecular patterns (MAMPs or PAMPs) expressed by the microbes. Interaction between PRRs and MAMPs is quite crucial since it triggers the sequence of signaling events and epigenetic rewiring that not only play a cardinal role in modulating the activation and function of the innate cells but also impart a sense of memory response. We discuss here how gut microbiota can influence the generation of innate memory and functional reprogramming of bone marrow progenitors that helps in protection against infections. This article will broaden our current perspective of association between the gut microbiome and innate memory. In the future, this knowledge may pave avenues for development and designing of novel immunotherapies and vaccination strategies.

Activation of the Endoplasmic Reticulum Stress Response Impacts the NOD1 Signaling Pathway.

Nucleotide-binding oligomerization domain 1 (NOD1) is an intracellular pattern recognition receptor (PRR) responsible for sensing bacterial peptidoglycan fragments. Stimulation of NOD1 leads to a robust innate immune response via activation of the major transcription factor NF-κB. In addition to peptidoglycan sensing, NOD1 and the closely related PRR NOD2 have been linked to inflammation by responding to the endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR). Here we show that differential ER stress induction renders cells more susceptible to Salmonella enterica serovar Typhimurium infection in a NOD1-dependent manner, measured by increased NF-κB activation and cytokine expression. In HeLa57A cells stably transfected with an NF-κB::luciferase reporter, we show that cells undergoing ER stress induced by thapsigargin display a significant increase in NF-κB activation in response to NOD1 stimulation by C12-iE-DAP (acylated derivative of the iE-DAP dipeptide [gamma-d-glutamyl-meso-diaminopimelic acid]) and the S Typhimurium effector protein SopE. Tunicamycin-induced ER stress had no effect on NOD1-stimulated NF-κB activation. We further show that the mouse intestinal epithelial cell line MODE-K and RAW264.7 macrophages are more responsive to Salmonella infection when treated with thapsigargin but not with tunicamycin. These profound differences between thapsigargin- and tunicamycin-treated cells upon inflammation suggest that different components downstream of the UPR contribute to NOD1 activation. We found that the NOD1-induced inflammatory response is dependent on protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) activation in conjunction with stimulation of the inositol triphosphate receptor (IP3R). Together, these results suggest that differential UPR activation makes cells more responsive to bacterial infections in a NOD1-dependent manner.

Nod1 Imprints Inflammatory and Carcinogenic Responses toward the Gastric Pathogen Helicobacter pylori.

Helicobacter pylori (H. pylori) is the strongest known risk for gastric cancer. The H. pylori cag type IV secretion system is an oncogenic locus that translocates peptidoglycan into host cells, where it is recognized by NOD1, an innate immune receptor. Beyond this, the role of NOD1 in H. pylori-induced cancer remains undefined. To address this knowledge gap, we infected two genetic models of Nod1 deficiency with the H. pylori cag + strain PMSS1: C57BL/6 mice, which rarely develop cancer, and INS-GAS FVB/N mice, which commonly develop cancer. Infected C57BL/6 Nod1-/- and INS-GAS Nod1-/- mice acutely developed more severe gastritis, and INS-GAS Nod1-/- mice developed gastric dysplasia more frequently compared with Nod1+/+ mice. Because Nod1 genotype status did not alter microbial phenotypes of in vivo-adapted H. pylori, we investigated host immunologic responses. H. pylori infection of Nod1-/- mice led to significantly increased gastric mucosal levels of Th1, Th17, and Th2 cytokines compared with Nod1 wild-type (WT) mice. To define the role of specific innate immune cells, we quantified cytokine secretion from H. pylori-infected primary gastric organoids generated from WT or Nod1-/- mice that were cocultured with or without WT or Nod1-/- macrophages. Infection increased cytokine production from gastric epithelial cells and macrophages and elevations were significantly increased with Nod1 deficiency. Furthermore, H. pylori infection altered the polarization status of Nod1-/- macrophages compared with Nod1+/+ macrophages. Collectively, these studies demonstrate that loss of Nod1 augments inflammatory and injury responses to H. pylori. Nod1 may exert its restrictive role by altering macrophage polarization, leading to immune evasion and microbial persistence. SIGNIFICANCE: These findings suggest that manipulation of NOD1 may represent a novel strategy to prevent or treat pathologic outcomes induced by H. pylori infection.

Nucleotide-binding oligomerization domain 1 (NOD1) modulates liver ischemia reperfusion through the expression adhesion molecules.

BACKGROUND & AIMS: In liver transplantation, organ shortage leads to the use of marginal grafts that are more susceptible to ischemia-reperfusion (IR) injury. We identified nucleotide-binding oligomerization domain 1 (NOD1) as an important modulator of polymorphonuclear neutrophil (PMN)-induced liver injury, which occurs in IR. Herein, we aimed to elucidate the role of NOD1 in IR injury, particularly focusing on its effects on the endothelium and hepatocytes. METHOD: Nod1 WT and KO mice were treated with NOD1 agonists and subjected to liver IR. Expression of adhesion molecules was analyzed in total liver, isolated hepatocytes and endothelial cells. Interactions between PMNs and hepatocytes were studied in an ex vivo co-culture model using electron microscopy and lactate dehydrogenase levels. We generated NOD1 antagonist-loaded nanoparticles (np ALINO). RESULTS: NOD1 agonist treatment increased liver injury, PMN tissue infiltration and upregulated ICAM-1 and VCAM-1 expression 20 hours after reperfusion. NOD1 agonist treatment without IR increased expression of adhesion molecules (ICAM-1, VCAM-1) in total liver and more particularly in WT hepatocytes, but not in Nod1 KO hepatocytes. This induction is dependent of p38 and ERK signaling pathways. Compared to untreated hepatocytes, a NOD1 agonist markedly increased hepatocyte lysis in co-culture with PMNs as shown by the increase of lactate dehydrogenase in supernatants. Interaction between hepatocytes and PMNs was confirmed by electron microscopy. In a mouse model of liver IR, treatment with np ALINO significantly reduced the area of necrosis, aminotransferase levels and ICAM-1 expression. CONCLUSION: NOD1 regulates liver IR injury through induction of adhesion molecules and modulation of hepatocyte-PMN interactions. NOD1 antagonist-loaded nanoparticles reduced liver IR injury and provide a potential approach to prevent IR, especially in the context of liver transplantation. LAY SUMMARY: Nucleotide-binding oligomerization domain 1 (NOD1) is as an important modulator of polymorphonuclear neutrophil (PMN)-induced liver injury, which occurs in ischemia-reperfusion. Here, we show that the NOD1 pathway targets liver adhesion molecule expression on the endothelium and on hepatocytes through p38 and ERK signaling pathways. The early increase of adhesion molecule expression after reperfusion emphasizes the importance of adhesion molecules in liver injury. In this study we generated nanoparticles loaded with NOD1 antagonist. These nanoparticles reduced liver necrosis by reducing PMN liver infiltration and adhesion molecule expression.

Neisseria gonorrhoeae PBP3 and PBP4 Facilitate NOD1 Agonist Peptidoglycan Fragment Release and Survival in Stationary Phase.

Neisseria gonorrhoeae releases peptidoglycan fragments during growth, and these molecules induce an inflammatory response in the human host. The proinflammatory molecules include peptidoglycan monomers, peptidoglycan dimers, and free peptides. These molecules can be released by the actions of lytic transglycosylases or an amidase. However, >40% of the gonococcal cell wall is cross-linked, where the peptide stem on one peptidoglycan strand is linked to the peptide stem on a neighboring strand, suggesting that endopeptidases may be required for the release of many peptidoglycan fragments. Therefore, we characterized mutants with individual or combined mutations in genes for the low-molecular-mass penicillin-binding proteins PBP3 and PBP4. Mutations in either dacB, encoding PBP3, or pbpG, encoding PBP4, did not significantly reduce the release of peptidoglycan monomers or free peptides. A mutation in dacB caused the appearance of a larger-sized peptidoglycan monomer, the pentapeptide monomer, and an increased release of peptidoglycan dimers, suggesting the involvement of this enzyme in both the removal of C-terminal d-Ala residues from stem peptides and the cleavage of cross-linked peptidoglycan. Mutation of both dacB and pbpG eliminated the release of tripeptide-containing peptidoglycan fragments concomitantly with the appearance of pentapeptide and dipeptide peptidoglycan fragments and higher-molecular-weight peptidoglycan dimers. In accord with the loss of tripeptide peptidoglycan fragments, the level of human NOD1 activation by the dacB pbpG mutants was significantly lower than that by the wild type. We conclude that PBP3 and PBP4 overlap in function for cross-link cleavage and that these endopeptidases act in the normal release of peptidoglycan fragments during growth.

Hematopoiesis and the bacterial microbiome.

Recent studies have revealed that the intestinal bacterial microbiome plays an important role in the regulation of hematopoiesis. A correlation between adverse hematologic effects and imbalance of the intestinal microbiome, or dysbiosis, is evident in several human conditions, such as inflammatory bowel disease, obesity, and, critically, in the setting of antibiotic exposure. Here we review the effects of gut dysbiosis on the hematological compartment and our current understanding of the mechanisms through which changes in the bacterial microbiome affect hematopoiesis.

Infection of human intestinal epithelial cells by invasive bacteria activates NF-κB and increases ICAM-1 expression through NOD1.

BACKGROUND/AIMS: Nucleotide-binding oligomerization domain 1 (NOD1) is required for primary intestinal epithelial cells (IECs) to respond to natural mucopeptides secreted by gram-negative bacteria. Infection of human IECs with invasive bacteria up-regulates intercellular adhesion molecule-1 (ICAM-1) expression. However, the role of NOD family members in host defense has been largely unknown. The aim of this study was to determine whether there is a functional role for NOD1 in the up-regulation of ICAM-1 expression in invasive bacteria-infected IECs. METHODS: ICAM-1 mRNA expression was compared between controls, Caco-2 or HT29 cells transfected with an empty vector, and IECs stably transfected with a dominant-negative (DN) NOD1. Expression was compared using qualitative reverse transcription polymerase chain reaction (RT-PCR), real-time RT-PCR, and flow cytometry after infection with enteroinvasive Escherichia coli O29:NM or Shigella flexneri. Nuclear factor kB (NF-κB) activation was determined by electrophoretic mobility shift assays. RESULTS: DN NOD1 significantly inhibited the up-regulation of ICAM-1 expression in response to an enteroinvasive bacterial infection. The Caco-2 cells transfected with DN NOD1 manifested marked inhibition of NF-kB activation in response to E. coli O29:NM infection. CONCLUSIONS: Signaling through NOD1 may play an essential role in neutrophil trafficking following infection with enteroinvasive bacteria.

NLR Nod1 signaling promotes survival of BCR-engaged mature B cells through up-regulated Nod1 as a positive outcome.

Although B cell development requires expression of the B cell antigen receptor (BCR), it remains unclear whether engagement of self-antigen provides a positive impact for most B cells. Here, we show that BCR engagement by self-ligand during development in vivo results in up-regulation of the Nod-like receptor member Nod1, which recognizes the products of intestinal commensal bacteria. In anti-thymocyte/Thy-1 autoreactive BCR knock-in mice lacking self-Thy-1 ligand, immunoglobulin light chain editing occurred, generating B cells with up-regulated Nod1, including follicular and marginal zone B cells with natural autoreactivity. This BCR editing with increased Nod1 resulted in preferential survival. In normal adult mice, most mature B cells are enriched for Nod1 up-regulated cells, and signaling through Nod1 promotes competitive survival of mature B cells. These findings demonstrate a role for microbial products in promoting survival of mature B cells through up-regulated Nod1, providing a positive effect of BCR engagement on development of most B cells.

Role of NOD1 in Heart Failure Progression via Regulation of Ca2+ Handling.

BACKGROUND: Heart failure (HF) is a complex syndrome associated with a maladaptive innate immune system response that leads to deleterious cardiac remodeling. However, the underlying mechanisms of this syndrome are poorly understood. Nucleotide-binding oligomerization domain-containing protein 1 (NOD1) is a newly recognized innate immune sensor involved in cardiovascular diseases. OBJECTIVES: This study evaluated the role of NOD1 in HF progression. METHODS: NOD1 was examined in human failing myocardium and in a post-myocardial infarction (PMI) HF model evaluated in wild-type (wt-PMI) and Nod1-/- mice (Nod1-/--PMI). RESULTS: The NOD1 pathway was up-regulated in human and murine failing myocardia. Compared with wt-PMI, hearts from Nod1-/--PMI mice had better cardiac function and attenuated structural remodeling. Ameliorated cardiac function in Nod1-/--PMI mice was associated with prevention of Ca2+ dynamic impairment linked to HF, including smaller and longer intracellular Ca2+ concentration transients and a lesser sarcoplasmic reticulum Ca2+ load due to a down-regulation of the sarcoplasmic reticulum Ca2+-adenosine triphosphatase pump and by augmented levels of the Na+/Ca2+ exchanger. Increased diastolic Ca2+ release in wt-PMI cardiomyocytes was related to hyperphosphorylation of ryanodine receptors, which was blunted in Nod1-/--PMI cardiomyocytes. Pharmacological blockade of NOD1 also prevented Ca2+ mishandling in wt-PMI mice. Nod1-/--PMI mice showed significantly fewer ventricular arrhythmias and lower mortality after isoproterenol administration. These effects were associated with lower aberrant systolic Ca2+ release and with a prevention of the hyperphosphorylation of ryanodine receptors under isoproterenol administration in Nod1-/--PMI mice. CONCLUSIONS: NOD1 modulated intracellular Ca2+ mishandling in HF, emerging as a new target for HF therapy.

Role of nucleotide-binding oligomerization domain 1 (NOD1) and its variants in human cytomegalovirus control in vitro and in vivo.

Induction of nucleotide-binding oligomerization domain 2 (NOD2) and downstream receptor-interacting serine/threonine-protein kinase 2 (RIPK2) by human cytomegalovirus (HCMV) is known to up-regulate antiviral responses and suppress virus replication. We investigated the role of nucleotide-binding oligomerization domain 1 (NOD1), which also signals through RIPK2, in HCMV control. NOD1 activation by Tri-DAP (NOD1 agonist) suppressed HCMV and induced IFN-ß. Mouse CMV was also inhibited through NOD1 activation. NOD1 knockdown (KD) or inhibition of its activity with small molecule ML130 enhanced HCMV replication in vitro. NOD1 mutations displayed differential effects on HCMV replication and antiviral responses. In cells overexpressing the E56K mutation in the caspase activation and recruitment domain, virus replication was enhanced, but in cells overexpressing the E266K mutation in the nucleotide-binding domain or the wild-type NOD1, HCMV was inhibited, changes that correlated with IFN-ß expression. The interaction of NOD1 and RIPK2 determined the outcome of virus replication, as evidenced by enhanced virus growth in NOD1 E56K mutant cells (which failed to interact with RIPK2). NOD1 activities were executed through IFN-ß, given that IFN-ß KD reduced the inhibitory effect of Tri-DAP on HCMV. Signaling through NOD1 resulting in HCMV suppression was IKKα-dependent and correlated with nuclear translocation and phosphorylation of IRF3. Finally, NOD1 polymorphisms were significantly associated with the risk of HCMV infection in women who were infected with HCMV during participation in a glycoprotein B vaccine trial. Collectively, our data indicate a role for NOD1 in HCMV control via RIPK2- IKKα-IRF3 and suggest that its polymorphisms predict the risk of infection.

Cardiopulmonary Bypass Down-Regulates NOD Signaling and Inflammatory Response in Children with Congenital Heart Disease.

In the present study, we aimed to examine the impact of cardiopulmonary bypass (CPB) on expression and function of NOD1 and NOD2 in children with congenital heart disease (CHD), in an attempt to clarify whether NOD1 and NOD2 signaling is involved in the modulation of host innate immunity against postoperative infection in pediatric CHD patients. Peripheral blood samples were collected from pediatric CHD patients at five different time points: before CPB, immediately after CPB, and 1, 3, and 7 days after CPB. Real-time PCR, Western blot, and ELISA were performed to measure the expression of NOD1 and NOD2, their downstream signaling pathways, and inflammatory cytokines at various time points. Proinflammatory cytokine IL-6 and TNF-α levels in response to stimulation with either the NOD1 agonist Tri-DAP or the NOD2 agonist MDP were significantly reduced after CPB compared with those before CPB, which is consistent with a suppressed inflammatory response postoperatively. The expression of phosphorylated RIP2 and activation of the downstream signaling pathways NF-κB p65 and MAPK p38 upon Tri-DAP or MDP stimulation in PBMCs were substantially inhibited after CPB. The mRNA level of NOD1 and protein levels of NOD1 and NOD2 were also markedly decreased after CPB. Our results demonstrated that NOD-mediated signaling pathways were substantially inhibited after CPB, which correlates with the suppressed inflammatory response and may account, at least in part, for the increased risk of postoperative infection in pediatric CHD patients.

Peptidoglycan from the gut microbiota governs the lifespan of circulating phagocytes at homeostasis.

Maintenance of myeloid cell homeostasis requires continuous turnover of phagocytes from the bloodstream, yet whether environmental signals influence phagocyte longevity in the absence of inflammation remains unknown. Here, we show that the gut microbiota regulates the steady-state cellular lifespan of neutrophils and inflammatory monocytes, the 2 most abundant circulating myeloid cells and key contributors to inflammatory responses. Treatment of mice with broad-spectrum antibiotics, or with the gut-restricted aminoglycoside neomycin alone, accelerated phagocyte turnover and increased the rates of their spontaneous apoptosis. Metagenomic analyses revealed that neomycin altered the abundance of intestinal bacteria bearing γ-d-glutamyl-meso-diaminopimelic acid, a ligand for the intracellular peptidoglycan sensor Nod1. Accordingly, signaling through Nod1 was both necessary and sufficient to mediate the stimulatory influence of the flora on myeloid cell longevity. Stimulation of Nod1 signaling increased the frequency of lymphocytes in the murine intestine producing the proinflammatory cytokine interleukin 17A (IL-17A), and liberation of IL-17A was required for transmission of Nod1-dependent signals to circulating phagocytes. Together, these results define a mechanism through which intestinal microbes govern a central component of myeloid homeostasis and suggest perturbations of commensal communities can influence steady-state regulation of cell fate.

Cdx2 Expression and Intestinal Metaplasia Induced by H. pylori Infection of Gastric Cells Is Regulated by NOD1-Mediated Innate Immune Responses.

Chronic infection with the bacterial Helicobacter pylori is a major cause of gastric and duodenal ulcer disease, gastric mucosal atrophy, and cancer. H. pylori-induced expression of the intestinal epithelial-specific transcription factor caudal-related homeobox 2 (Cdx2) contributes to intestinal metaplasia, a precursor event to gastric cancer. Given a role for the bacterial pattern recognition molecule nucleotide-binding oligomerization domain 1 (NOD1) in the innate immune response to bacterial infection, we investigated mechanisms used by NOD1 to regulate H. pylori infection and its propensity towards the development of intestinal metaplasia. We found that Cdx2 was induced by H. pylori infection in both normal and neoplastic gastric epithelial cells in a manner that was inversely related to NOD1 signaling. Mechanistic investigations revealed that Cdx2 induction relied upon activation of NF-κB but was suppressed by NOD1-mediated activation of TRAF3, a negative regulator of NF-κB. In vivo, prolonged infection of NOD1-deficient mice with H. pylori led to increased Cdx2 expression and intestinal metaplasia. Furthermore, gastric epithelial cells from these mice exhibited increased nuclear expression of the NF-κB p65 subunit and decreased expression of TRAF3. Overall, our findings illuminated a role for NOD1 signaling in attenuating H. pylori-induced Cdx2 expression in gastric epithelial cells, suggesting a rationale to augment NOD1 signaling in H. pylori-infected patients to limit their risks of accumulating precancerous gastric lesions.

Ischemia as a factor affecting innate immune responses in kidney transplantation.

PURPOSE OF REVIEW: Ischemic injury inevitably occurs during the procurement of organs for transplantation, and the injury is worsened by inflammation following reperfusion. The purpose of this review is to describe the role of the innate immune system in ischemia-induced renal injury in kidneys procured for transplantation. The key role of pattern recognition receptors in immune responses to ischemia is described. Innate immune receptors are emerging novel targets for the amelioration of ischemic injury of donor kidneys. RECENT FINDINGS: Several families of pattern recognition receptors are direct mediators of early injurious events during kidney procurement, and also innate and adaptive immune responses after transplantation. The deleterious events associated with the activation of the innate immune system in donor kidneys significantly contribute to short and long-term allograft outcomes. SUMMARY: Although a number of therapies have been proposed to decrease ischemic donor kidney injury, targeting the innate immune system is an exciting new area that is gaining significant interest in transplantation. As we learn more about how these important receptors are regulated by ischemia, strategies will likely evolve to allow their modulation in ischemic renal injury.

An Overview of Pathogen Recognition Receptors for Innate Immunity in Dental Pulp.

Pathogen recognition receptors (PRRs) are a class of germ line-encoded receptors that recognize pathogen-associated molecular patterns (PAMPs). The activation of PRRs is crucial for the initiation of innate immunity, which plays a key role in first-line defense until more specific adaptive immunity is developed. PRRs differ in the signaling cascades and host responses activated by their engagement and in their tissue distribution. Currently identified PRR families are the Toll-like receptors (TLRs), the C-type lectin receptors (CLRs), the nucleotide-binding oligomerization domain-like receptors (NLRs), the retinoic acid-inducible gene-I-like receptors (RLRs), and the AIM2-like receptor (ALR). The environment of the dental pulp is substantially different from that of other tissues of the body. Dental pulp resides in a low compliance root canal system that limits the expansion of pulpal tissues during inflammatory processes. An understanding of the PRRs in dental pulp is important for immunomodulation and hence for developing therapeutic targets in the field of endodontics. Here we comprehensively review recent finding on the PRRs and the mechanisms by which innate immunity is activated. We focus on the PRRs expressed on dental pulp and periapical tissues and their role in dental pulp inflammation.

NLRs Challenge Impacts Tight Junction Claudins In Sertoli Cells.

AIM: The present study aims to investigate the NALP3 system and its effect on claudins in Sertoli cells using a mouse adult Sertoli cell line as a model. We focus on the Sertoli cell biology looking for the possible implications for male reproductive functions. MATERIALS AND METHODS: Adult Sertoli cells were transfected with NAPL3 siRNA and treated with NOD1 (ie-DAP) and NOD2 (MDP) receptor ligands. Two dimensional gel electrophoresis was performed on lysates of non-challenged and MDP-treated Sertoli cells. RESULTS: There were positive claudin-5 and claudin-11 expression levels on transcript (RT-qPCR) levels. Specific protein spots in 2D gels were detected after bioinformatics analysis. This study demonstrates direct induction of tight-junction proteins probably favouring junction stability. CONCLUSIONS: The innate immunity and tight-junction pathway integration probably have a protective role for both blood-testis immune barrier and spermatogenesis compartmentalisation maintained by the very same barrier. This integration also points the way for mechanistic research of the disturbances inflicted during an inflammatory response in the testis niche.