Caspase-1/ASC inflammasome-mediated activation of IL-1β-ROS-NF-κB pathway for control of Trypanosoma cruzi replication and survival is dispensable in NLRP3-/- macrophages

In this study, we have utilized wild-type (WT), ASC-/-, and NLRP3-/- macrophages and inhibition approaches to investigate the mechanisms of inflammasome activation and their role in Trypanosoma cruzi infection. We also probed human macrophages and analyzed published microarray datasets from human fibroblasts, and endothelial and smooth muscle cells for T. cruzi-induced changes in the expression genes included in the RT Profiler Human Inflammasome arrays. T. cruzi infection elicited a subdued and delayed activation of inflammasome-related gene expression and IL-1β production in mφs in comparison to LPS-treated controls. When WT and ASC-/- macrophages were treated with inhibitors of caspase-1, IL-1β, or NADPH oxidase, we found that IL-1β production by caspase-1/ASC inflammasome required reactive oxygen species (ROS) as a secondary signal. Moreover, IL-1β regulated NF-κB signaling of inflammatory cytokine gene expression and, subsequently, intracellular parasite replication in macrophages. NLRP3-/- macrophages, despite an inability to elicit IL-1β activation and inflammatory cytokine gene expression, exhibited a 4-fold decline in intracellular parasites in comparison to that noted in matched WT controls. NLRP3-/- macrophages were not refractory to T. cruzi, and instead exhibited a very high basal level of ROS (>100-fold higher than WT controls) that was maintained after infection in an IL-1β-independent manner and contributed to efficient parasite killing. We conclude that caspase-1/ASC inflammasomes play a significant role in the activation of IL-1β/ROS and NF-κB signaling of cytokine gene expression for T. cruzi control in human and mouse macrophages. However, NLRP3-mediated IL-1β/NFκB activation is dispensable and compensated for by ROS-mediated control of T. cruzi replication and survival in macrophages.

NOD2 contributes to Porphyromonas gingivalis-induced bone resorption

The NOD-like receptors are cytoplasmic proteins that sense microbial by-products released by invasive bacteria. Although NOD1 and NOD2 are functionally expressed in cells from oral tissues and play a role triggering immune responses, the role of NOD2 receptor in the bone resorption and in the modulation of osteoclastogenesis is still unclear. We show that in an experimental model of periodontitis with Porphyromonas gingivalis W83, NOD2(-/-) mice showed lower bone resorption when compared to wild type. Quantitative polymerase chain reaction analysis revealed that wild-type infected mice showed an elevated RANKL/OPG ratio when compared to NOD2(-/-) infected mice. Moreover, the expression of 2 osteoclast activity markers-cathepsin K and matrix metalloproteinase 9-was significantly lower in gingival tissue from NOD2(-/-) infected mice compared to WT infected ones. The in vitro study reported an increase in the expression of the NOD2 receptor 24 hr after stimulation of hematopoietic bone marrow cells with M-CSF and RANKL. We also evaluated the effect of direct activation of NOD2 receptor on osteoclastogenesis, by the activation of this receptor in preosteoclasts culture, with different concentrations of muramyl dipeptide. The results show no difference in the number of TRAP-positive cells. Although it did not alter the osteoclasts differentiation, the activation of NOD2 receptor led to a significant increase of cathepsin K expression. We confirm that this enzyme was active, since the osteoclasts resorption capacity was enhanced by muramyl dipeptide stimulation, evaluated in osteoassay plate. These results show that the lack of NOD2 receptor impairs the bone resorption, suggesting that NOD2 receptor could contribute to the progression of bone resorption in experimental model of periodontitis. The stimulation of NOD2 by its agonist, muramyl dipeptide, did not affect osteoclastogenesis, but it does favor the bone resorption capacity identified by increased osteoclast activity.

Catechins inhibit vascular endothelial growth factor production and cyclooxygenase-2 expression in human dental pulp cells

AIM

To investigate the effect of catechins on vascular endothelial growth factor (VEGF) production and cyclooxygenase-2 (COX-2) expression in human dental pulp cells (HDPC) stimulated with bacteria-derived factors or pro-inflammatory cytokines.

METHODOLOGY

Morphologically fibroblastic cells established from explant cultures of healthy human dental pulp tissues were used as HDPC. HDPC pre-treated with catechins, epigallocatechin-3-gallate (EGCG) or epicatechin gallate (ECG), were exposed to lipopolysaccharide (LPS), peptidoglycan (PG), interlukin-1β (IL-1β) or tumour necrosis factor-α (TNF-α). VEGF production was examined by enzyme-linked immunosorbent assay, and COX-2 expression was assessed by immunoblot.

RESULTS

EGCG and ECG significantly reduced LPS- or PG-mediated VEGF production in the HDPC in a dose-dependent manner. EGCG also prevented IL-1β-mediated VEGF production. Although TNF-α did not enhance VEGF production in the dental pulp cells, treatment of 20 μg mL(-1) of EGCG decreased the level of VEGF. In addition, the catechins attenuated COX-2 expression induced by LPS and IL-1β.

CONCLUSIONS

The up-regulated VEGF and COX-2 expressions in the HDPC stimulated with these bacteria-derived factors or IL-1β were diminished by the treatment of EGCG and ECG. These findings suggest that the catechins may be beneficial as an anti-inflammatory tool of the treatment for pulpal inflammation.

MiRNA-181a regulates Toll-like receptor agonist-induced inflammatory response in human fibroblasts

MicroRNAs (miRNA) regulate the synthesis of cytokines in response to Toll-like receptor (TLR) activation. Our recent microarray study comparing normal and inflamed human dental pulps showed that miRNA-181 (miR-181) family is differentially expressed in the presence of inflammation. Prior studies have reported that the dental pulp, which is composed primarily of TLR4/2+ fibroblasts, expresses elevated levels of cytokines including Interleukin-8 (IL-8) when inflamed. In this study, we employed an in-vitro model to determine the role of the miRNA 181 family in the TLR agonist-induced response in human fibroblasts. TLR4/2+ primary human dental pulp fibroblasts were stimulated with lipopolysaccharide from Porphyromonas gingivalis (Pg LPS), a known oral pathogen, and IL-8 and miR-181 expression measured. An inversely proportional relationship between IL-8 and miR-181a was observed. In-silico analysis identified a miR-181a binding site on the 3′UTR of IL-8 which was confirmed by dual-luciferase assays. MiR-181a directly binds to the 3′UTR of IL-8, an important inflammatory component of the immune response, and modulates its levels. This is the very first report demonstrating miR-181a regulation of IL-8.

NOD2 Mediates Odontoblast Differentiation and RANKL Expression

The precise regulation of odontoblast differentiation and osteoclastogenic cytokine expression in human dental pulp cells (HDPCs) is crucial for the pathology of bacteria-related pulpitis. Although the up-regulation of nucleotide-binding oligomerization domain-containing protein 2 (NOD2) has been reported in inflamed human dental pulps, the role of NOD2 in the differentiation of HDPCs remains unclear. Here, we show the involvement of NOD2 in odontoblast differentiation together with osteoclastogenic cytokine expression in HDPCs. Treatment with muramyl dipeptide (MDP), a known NOD2-agonist, significantly inhibited odontoblast differentiation of HDPCs, as revealed by reduced ALP activity, osteoblast/odontoblast marker expression, and mineralized nodule formation. Importantly, the forced down-regulation of NOD2 by small interfering RNA (siRNA) recovered MDP-down-regulated odontoblast differentiation. MDP-elicited suppression of odontoblast differentiation resulted from the increased expression of MKP-1 protein and the subsequent decline of MAPKs phosphorylation, which is a prerequisite for odontoblast differentiation. Furthermore, we found that MDP treatment elevated the expression of osteoclastogenic cytokines in HDPCs, which was also reversed by NOD2 silencing. Analysis of these data, taken together, suggests that the regulation of NOD2 expression upon MDP challenge might serve as an intrinsic mechanism that underlies the hindered dentin formation and accelerated dentin resorption in bacterial infection-mediated pulpitis.

Modulatory roles of interferon-γ through indoleamine 2, 3-dioxygenase induction in innate immune response of dental pulp cells

INTRODUCTION

Marked infiltration of inflammatory cells such as activated T cells producing interferon-γ (IFN-γ) is observed in severe pulpitis. However, the roles of IFN-γ in the innate immune response of dental pulp have not been reported. Indoleamine 2, 3-dioxygenase (IDO) is a regulator of immune responses, and the IDO expression is induced by IFN-γ in many cells whose expression in dental pulp is unknown. The purpose of this study was to determine the role of IFN-γ in the immune response through microbial pattern recognition receptors (PRRs) such as Toll-like receptors or nucleotide-binding oligomerization domain-like receptors on the production of proinflammatory cytokines such as CXCL10 and interleukin (IL)-6 and the expression of IDO in cultured human dental pulp cells (HDPCs).

METHODS

HDPCs were established from explant cultures of healthy pulp tissues. CXCL10 and IL-6 production was determined using enzyme-linked immunosorbent assay. Confirmation of IDO localization in dental pulp tissues was examined using immunohistochemistry. IDO expression in HDPCs was analyzed by immunoblot.

RESULTS

IFN-γ significantly up-regulated CXCL10 and IL-6 production in the HDPCs stimulated with ligands for PRRs in a concentration-dependent manner. The expression of IDO was detected in inflamed pulp tissue. In addition, IFN-γ in combination with the PRR ligands enhanced IDO expression in HDPCs compared with IFN-γ alone. Moreover, CXCL10 production in IFN-γ-stimulated HDPCs was inhibited by an IDO inhibitor.

CONCLUSIONS

This study showed the synergistic effects by IFN-γ on cytokine production and IDO expression in HDPCs, suggesting that IFN-γ may modulate the innate immune response of dental pulp.

Activation of toll-like receptors and inflammasome complexes in the diabetic cardiomyopathy-associated inflammation

Diabetic cardiomyopathy is defined as a ventricular dysfunction initiated by alterations in cardiac energy substrates in the absence of coronary artery disease and hypertension. Hyperglycemia, hyperlipidemia, and insulin resistance are major inducers of the chronic low-grade inflammatory state that characterizes the diabetic heart. Cardiac Toll-like receptors and inflammasome complexes may be key inducers for inflammation probably through NF-κB activation and ROS overproduction. However, metabolic dysregulated factors such as peroxisome proliferator-activated receptors and sirtuins may serve as therapeutic targets to control this response by mitigating both Toll-like receptors and inflammasome signaling.

CCL3 and CXCL12 production in vitro by dental pulp fibroblasts from permanent and deciduous teeth stimulated by Porphyromonas gingivalis LPS

OBJECTIVE

The aim of this study was to compare the production of the chemokines CCL3 and CXCL12 by cultured dental pulp fibroblasts from permanent (PDPF) and deciduous (DDPF) teeth under stimulation by Porphyromonas gingivalis LPS (PgLPS).

MATERIAL AND METHODS

Primary culture of fibroblasts from permanent (n=3) and deciduous (n=2) teeth were established using an explant technique. After the fourth passage, fibroblasts were stimulated by increasing concentrations of PgLPS (0-10 µg/mL) at 1, 6 and 24 h. The cells were tested for viability through MTT assay, and production of the chemokines CCL3 and CXCL12 was determined through ELISA. Comparisons among samples were performed using One-way ANOVA for MTT assay and Two-way ANOVA for ELISA results.

RESULTS

Cell viability was not affected by the antigen after 24 h of stimulation. PgLPS induced the production of CCL3 by dental pulp fibroblasts at similar levels for both permanent and deciduous pulp fibroblasts. Production of CXCL12, however, was significantly higher for PDPF than DDPF at 1 and 6 h. PgLPS, in turn, downregulated the production of CXCL12 by PDPF but not by DDPF.

CONCLUSION

These data suggest that dental pulp fibroblasts from permanent and deciduous teeth may present a differential behavior under PgLPS stimulation.

Pivotal role of NOD2 in inflammatory processes affecting atherosclerosis and periodontal bone loss

The purpose of this study was to elucidate the role of nucleotide binding oligomerization domain-containing protein 2 (NOD2) signaling in atherosclerosis and periodontal bone loss using an Apolipoprotein E(-/-) (ApoE(-/-)) mouse model based on the proposed role of NOD2 in inflammation. NOD2(-/-)ApoE(-/-) and ApoE(-/-) mice fed a standard chow diet were given an oral gavage of Porphyromonas gingivalis for 15 wk. NOD2(-/-)ApoE(-/-) mice exhibited significant increases in inflammatory cytokines, alveolar bone loss, cholesterol, and atherosclerotic lesions in the aorta and the heart compared with ApoE(-/-) mice. In contrast, ApoE(-/-) mice injected i.p. with Muramyl DiPeptide (MDP) to stimulate NOD2 and given an oral gavage of P. gingivalis displayed a reduction of serum inflammatory cytokines, alveolar bone loss, cholesterol, and atherosclerotic lesions in the aorta and aortic sinus compared with ApoE(-/-) mice orally challenged but injected with saline. A reduction in body weight gain was observed in ApoE(-/-) mice fed a high-fat diet (HFD) and injected with MDP compared with ApoE(-/-) mice fed a high-fat diet but injected with saline. MDP treatment of bone marrow-derived macrophages incubated with P. gingivalis increased mRNA expressions of NOD2, Toll-like receptor 2, myeloid differentiation primary response gene 88, and receptor-interacting protein-2 but reduced the expressions of inhibitor of NF-κB kinase-β, NF-κB, c-Jun N-terminal kinase 3, and TNF-α protein levels compared with saline control, highlighting pathways involved in MDP antiinflammatory effects. MDP activation of NOD2 should be considered in the treatment of inflammatory processes affecting atherosclerosis, periodontal bone loss ,and possibly, diet-induced weight gain.

CD90(+) Stromal Cells are Non-Professional Innate Immune Effectors of the Human Colonic Mucosa

Immune responses at the intestinal mucosa must allow for host protection whilst simultaneously avoiding inappropriate inflammation. Although much work has focused on the innate immune functionality of hematopoietic immune cells, non-hematopoietic cell populations – including epithelial and stromal cells – are now recognized as playing a key role in innate defense at this site. In this study we examined the innate immune capacity of primary human intestinal stromal cells (iSCs). CD90⁺ iSCs isolated from human colonic mucosa expressed a wide array of innate immune receptors and functionally responded to stimulation with bacterial ligands. iSCs also sensed infection with live Salmonella typhimurium, rapidly expressing IL-1 family cytokines via a RIPK2/p38MAPK-dependent signaling process. In addition to responding to innate immune triggers, primary iSCs exhibited a capacity for bacterial uptake, phagocytosis, and antigen processing, although to a lesser extent than professional APCs. Thus CD90⁺ iSCs represent an abundant population of “non-professional” innate immune effector cells of the human colonic mucosa and likely play an important adjunctive role in host defense and immune regulation at this site.

Fusobacterium nucleatum induces cytokine production through Toll-like-receptor-independent mechanism

AIM

To determine whether Fusobacterium nucleatum's ability to invade cells allows the bacteria to activate pro-inflammatory response through cytosolic pattern recognition receptors, independent of surface Toll-like receptors (TLRs).

METHODOLOGY

HEK293T cells, which lack endogenous TLRs, and overexpressing dominant negative myeloid differentiation primary response gene 88 (MyD88DN) protein, were infected with F. nucleatum and the production of interleukin-8 (IL-8) was determined. The necessity for intracellular invasion of the bacteria for cytokine production was also investigated by blocking bacterial invasion with cytochalasin D. The roles of NFĸB and p38 mitogen-activated protein kinase (MAPK) and nucleotide-binding oligomerization domain-1 (NOD-1) signalling pathways in F. nucleatum-induced IL-8 secretion were determined.

RESULTS

Fusobacterium nucleatum-infected HEK293T cells produced IL-8 independent of the MYD88 signalling. This response was inhibited by preventing F. nucleatum invasion into HEK293T cells. p38 MAPK but not the NFĸB signalling pathway was required for F. nucleatum-mediated IL-8 production. HEK293T cells expressed NOD-1 but not NOD-2. Yet, inhibition of NOD-1 signalling did not affect F. nucleatum-induced IL-8 secretion.

CONCLUSIONS

Fusobacterium nucleatum invasion led to cytokine production, which is mediated by the p38 MAPK signalling but independent of TLRs, NOD-1, NOD-2 and NFĸB signalling.

Intracellular adhesion molecule-1 is regulated by porphyromonas gingivalis through nucleotide binding oligomerization domain-containing proteins 1 and 2 molecules in periodontal fibroblasts

BACKGROUND

The mechanism by which Porphyromonas gingivalis regulates intracellular adhesion molecule 1 (ICAM-1) expression in human periodontal ligament cells (hPDLCs) and human gingival fibroblasts (hGFs) is unknown. The aim of this study is to investigate whether nucleotide binding oligomerization domain-containing protein (NOD) 1 and NOD2 are involved in this process and the clinical significance of ICAM-1 in periodontitis.

METHODS

hPDLCs and hGFs were treated with P. gingivalis, l-Ala-γ-d-glutamyl-mesodiaminopimelic acid (an agonist for NOD1), and muramyl dipeptide (an agonist for NOD2). Alternatively, cells transfected with small interfering RNA targeting NOD1and NOD2 were treated with P. gingivalis. ICAM-1, NOD1, and NOD2 were detected at mRNA and protein levels. In addition, clinical examinations were performed in 30 healthy controls and 40 patients with chronic periodontitis (CP) before and after treatment, and serum-soluble ICAM-1 (sICAM-1) levels in these individuals were detected by enzyme-linked immunosorbent assay.

RESULTS

This study shows that P. gingivalis caused an increase in ICAM-1, NOD1, and NOD2 expression in periodontal fibroblasts. There was a linear correlation between ICAM-1 and NOD1 and NOD2 levels. Activation of NOD1 and NOD2 by the specific agonist led to the upregulation of ICAM-1, whereas knocking down NOD1 and NOD2 caused a reduction in P. gingivalis-induced ICAM-1 production. Furthermore, sICAM-1 levels were higher in patients with CP than in healthy controls and were positively related to the clinical periodontal parameters. After periodontal treatment, sICAM-1 levels decreased significantly.

CONCLUSIONS

The present results indicate that sICAM-1 levels are correlated to the severity of periodontitis. NOD1 and NOD2 mediate P. gingivalis-induced ICAM-1 production in periodontal fibroblasts. NOD1 and NOD2 could be considered potential targets for periodontal therapy.

Characterization of NODs and TLRs in innate immune response of human cementoblast cells

OBJECTIVES

Microbial Pattern-recognition receptors (PRRs), such as Toll-like receptors (TLRs) and the nucleotide-binding oligomerization domains (NODs), are essential for mammalian innate immune response. In this study, we examined the characterization of NODs and TLRs on innate immune responses in human cementoblast (HCEM) cells.

MATERIALS AND METHODS

The gene expression of NODs and TLRs was examined by RT-PCR. Interleukin-6 (IL-6) and Interleukin-8 (IL-8) productions in culture supernatants were measured by ELISA. Western blot analysis was performed to determine the degradation of IκB-α and Mitogen activated protein kinase (MAPK) activation in response to their agonist.

RESULTS

The levels of NODs and TLRs were apparently expressed in HCEM cells. Although a few gene levels were weak in intact cells, the stimulation by their agonists increased the gene expression of TLRs. NODs and TLRs led to the production of IL-6 or IL-8 and the degradation of IκB-α and MAPK activation in HCEM cells. Combination treatment of NOD1 or NOD2 agonists with TLRs agonists did not influence the production of IL-6 and IL-8 in HCEM cells.

CONCLUSIONS

Our results indicate that NODs and TLRs are functionally expressed in HCEM cells and can trigger innate immune responses. However, NOD1 and NOD2 may not be cooperated with TLRs to elicit an immune response in HCEM cells.

Sexual dimorphism in periapical inflammation and bone loss from mitogen-activated protein kinase phosphatase-1 deficient mice

INTRODUCTION

Mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1) has been shown to be a key negative regulator of the MAPK pathways of the innate immune system. The impact of MKP-1 in an endodontic model has yet to be studied. Thus, the purpose of this study was to determine the role of MKP-1 in a bacterial-driven model of pathologic endodontic bone loss.

METHODS

Pulps were exposed in both lower first molars of 10-week-old mkp-1(+/+) and mkp-1(-/-) mice and left open to the oral environment for either 3 or 8 weeks. At death, mandibles were harvested and scanned by micro-computed tomography (μCT) to determine periapical bone loss. Histopathologic scoring was then performed on the samples to determine the amount of inflammatory infiltrate within the periapical microenvironment.

RESULTS

Significant bone loss and inflammatory infiltrate were found in all experimental groups when compared with control. No statistical difference was found between mkp-1(+/+) and mkp-1(-/-) at either time point with respect to bone loss or inflammatory infiltrate. At 8 weeks, male mkp-1(-/-) mice were found to have significantly more bone loss and inflammatory infiltrate when compared with female mkp-1(-/-) mice. There was also a significant correlation between an increase in bone loss and increase in inflammatory infiltrate.

CONCLUSIONS

A sexual dimorphism exists in the periapical inflammatory process, where male mkp-1(-/-) mice have more inflammation than female mkp-1(-/-) mice. The increase in inflammatory infiltrate correlates to more bone loss in the male mice.

Toll-like receptor 2 knockout mice showed increased periapical lesion size and osteoclast number

INTRODUCTION

The aim of this study was to characterize the formation and progression of experimentally induced periapical lesions in TLR2 knockout (TLR2 KO) mice.

METHODS

Periapical lesions were induced in molars of 28 wild type (WT) and 27 TLR2 KO mice. After 7, 21, and 42 days, the animals were euthanized, and the mandibles were subjected to histotechnical processing. Hematoxylin-eosin-stained sections were examined under conventional light microscopy for the description of pulpal, apical, and periapical features and under fluorescence microscopy for the determination of the periapical lesion size. The subsequent sections were evaluated by tartrate resistant acid phosphatase histoenzymology (osteoclasts), Brown and Brenn staining (bacteria), and immunohistochemistry (RANK, RANKL, and OPG). Data were analyzed by the Mann-Whitney U and Kruskal-Wallis tests (α = 0.05).

RESULTS

The WT group showed significant differences (P < .05) in the periapical lesion size and the osteoclast number between 7 and 42 days and between 21 and 42 days. In the TLR2 KO group, significant differences (P < .05) in the periapical lesion size and the osteoclast number were found between 7 days and the other periods. There was a significant difference (P < .05) between the 2 types of animal regarding the periapical lesion size, which was larger in the TLR2 KO animals. No significant differences (P > .05) were found between WT and TLR2 KO mice related to the pulpal, apical, and periapical features; bacteria localization; and immunohistochemical results (except for RANK expression).

CONCLUSIONS

TLR2 KO animals developed larger periapical lesions with a greater number of osteoclasts, indicating the important role of this receptor in the host's immune and inflammatory response to root canal and periradicular infection.

Peptidoglycan and lipopolysaccharide synergistically enhance bone resorption and osteoclastogenesis

BACKGROUND AND OBJECTIVE

Peptidoglycan (PGN) and lipopolysaccharide (LPS) are bacterial cell wall constituents that are able to induce bone resorption by stimulating Toll-like receptor (TLR) 2 and TLR4, respectively. The fragments of PGN also stimulate inflammatory responses via nucleotide-binding oligomerization domain (NOD) 1 and NOD2, although there are differences in the NOD-stimulatory activities between gram-positive and gram-negative PGNs. The TLR and NOD signaling pathways are known to engage in cross-talk to enhance the production of inflammatory cytokines. In the present study, we investigated the effects of gram-negative and gram-positive PGNs on bone resorption and osteoclastogenesis in the presence or absence of LPS.

MATERIAL AND METHODS

We injected Escherichia coli PGN or Staphylococcus aureus PGN with or without LPS into mouse gingiva, and histopathologically assessed alveolar bone resorption by tartrate-resistant acid phosphatase staining. We also stimulated osteoclast precursors from mouse bone marrow macrophages with these PGNs in vitro and assessed osteoclastogenesis. The cells were also stimulated with synthetic ligands for NOD1; γ-D-glutamyl-meso-DAP NOD2; muramyl dipeptide or TLR2; Pam(3) CSK(4) with or without LPS to analyse the signaling cross-talk.

RESULTS

S. aureus PGN, but not E. coli PGN, induced alveolar bone resorption, as did LPS. However, PGN from both sources significantly enhanced the bone resorption in the mice co-injected with LPS. Both types of PGNs induced osteoclastogenesis and accelerated osteoclastogenesis when the cells were co-stimulated with LPS in vitro. All synthetic ligands synergistically induced osteoclastogenesis by co-stimulation with LPS.

CONCLUSION

Gram-positive or gram-negative PGN worked synergistically with LPS to induce bone resorption and osteoclastogenesis, possibly by co-ordinating the effects of TLR2, NOD1, NOD2 and TLR4 signaling.

Nucleotide-binding oligomerization domain protein 2 deficiency enhances neointimal formation in response to vascular injury

OBJECTIVE

Nucleotide-binding oligomerization domain protein 2 (NOD2) stimulates diverse inflammatory responses resulting in differential cellular phenotypes. To identify the role of NOD2 in vascular arterial obstructive diseases, we investigated the expression and pathophysiological role of NOD2 in a vascular injury model of neointimal hyperplasia.

METHODS AND RESULTS

We first analyzed for neointimal hyperplasia following femoral artery injury in NOD2(+/+) and NOD2(-/-) mice. NOD2(-/-) mice showed a 2.86-fold increase in neointimal formation that was mainly composed of smooth muscle (SM) α-actin positive cells. NOD2 was expressed in vascular smooth muscle cells (VSMCs) and NOD2(-/-) VSMCs showed increased cell proliferation in response to mitogenic stimuli, platelet-derived growth factor-BB (PDGF-BB), or fetal bovine serum, compared with NOD2(+/+) VSMCs. Furthermore, NOD2 deficiency markedly promoted VSMCs migration in response to PDGF-BB, and this increased cell migration was attenuated by a phosphatidylinositol 3-kinase inhibitor. However, protein kinase C and c-Jun N-terminal kinase inhibitors exerted negligible effects. Moreover, muramyl dipeptide-stimulated NOD2 prevented PDGF-BB-induced VSMCs migration.

CONCLUSION

Functional NOD2 was found to be expressed in VSMCs, and NOD2 deficiency promoted VSMCs proliferation, migration, and neointimal formation after vascular injury. These results provide evidence for the involvement of NOD2 in vascular homeostasis and tissue injury, serving as a potential molecular target in the modulation of arteriosclerotic vascular disease.

NOD1 and NOD2 stimulation triggers innate immune responses of human periodontal ligament cells

Nod-like receptors (NLRs) are cytosolic sensors for microbial molecules. Nucleotide-binding oligomerization domain (NOD)1 and NOD2 recognize the peptidoglycan derivatives, meso-diaminopimelic acid (meso-DAP) and muramyl dipeptide (MDP), respectively, and trigger host innate immune responses. In the present study, we examined the function of NOD1 and NOD2 on innate immune responses in human periodontal ligament (PDL) cells. The gene expression of NOD1 and NOD2 was examined by RT-PCR. IL-6 and IL-8 production in culture supernatants was measured by ELISA. Western blot analysis was performed to determine the activation of NF-κB and MAPK in response to Tri-DAP and MDP. The genes of NOD1 and NOD2 appeared to be expressed in PDL cells. Although the levels of NOD2 expression were weak in intact cells, MDP stimulation increased the gene expression of NOD2 in PDL cells. Tri-DAP and MDP led to the production of IL-6 and IL-8 and the activation of NF-κB and MAPK in PDL cells. Toll-like receptor (TLR) stimulation led to increased gene expression of NOD1 and NOD2 in PDL cells. Pam₃CSK₄ (a TLR2 agonist) and IFN-γ synergized with Tri-DAP and MDP to produce IL-8 and IL-6 in PDL cells. Our results indicate that NOD1 and NOD2 are functionally expressed in human PDL cells and can trigger innate immune responses.

Pattern-recognition Receptors in Pulp Defense

Initial sensing of infection is mediated by germline-encoded pattern-recognition receptors (PRRs), the activation of which leads to the expression of inflammatory mediators responsible for the elimination of pathogens and infected cells. PRRs act as immune sensors that provide immediate cell responses to pathogen invasion or tissue injury. Here, we review the expression of PRRs in human dental pulp cells, namely, receptors from the Toll-like (TLR) and Nod-like NLR families, by which cells recognize bacteria. Particular attention is given to odontoblasts, which are the first cells encountered by pathogens and represent, in the tooth, the first line of defense for the host. Understanding cellular and molecular mechanisms associated with the recognition of bacterial pathogens by odontoblasts is critical for the development of therapeutic strategies that aim at preventing excessive pulp inflammation and related deleterious effects.

Expression of TRAF6 and pro-inflammatory cytokines through activation of TLR2, TLR4, NOD1, and NOD2 in human periodontal ligament fibroblasts

OBJECTIVE

Human periodontal ligament fibroblasts (HPDLFs) play a crucial role in protecting against oral bacteria in periapical tissue. Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain (NOD) are two major forms of innate immune sensors that recognize microbial pathogens and initiate pro-inflammatory signalling. Tumour necrosis factor receptor-associated factor 6 (TRAF6) is an adapter protein for TLR-mediated nuclear factor-κB (NF-κB) signalling pathway activation that induces the production of pro-inflammatory cytokines. The aim of this study was to investigate the expression of TLR2, TLR4, NOD1, and NOD2 in HPDLFs. We also investigated the expression of TRAF6 and pro-inflammatory cytokines induced by the activation of TLRs and NODs.

METHODS

The expression of TLR2, TLR4, NOD1, and NOD2 was measured by reverse transcription-polymerase chain reaction (RT-PCR), flow cytometry, and immunostaining. HPDLFs were stimulated with TLR and NOD agonists. Then, the expression of TRAF6 was measured by real-time PCR and western blot. Concentrations of IL-1β, IL-6, and IL-8 in the culture supernatants were determined by enzyme-linked immunosorbent assay (ELISA). Finally, by using small interfering RNA (siRNA) for TRAF6, we analysed the production of IL-1β, IL-6, and IL-8 in HPDLFs upon stimulation with TLRs and NODs agonists.

RESULTS

We found clear mRNA and protein expression of TLR2, TLR4, NOD1, and NOD2 in HPDLFs. The expression levels of TRAF6 and pro-inflammatory cytokines (IL-1β, IL-6, and IL-8) were markedly up-regulated upon the activation of TLRs and NODs. Furthermore, the co-activation of TLRs and NODs had synergistic effect on the production of TRAF6 and pro-inflammatory cytokines. We also found TRAF6 suppression resulted in reduced IL-1β, IL-6, and IL-8 expression upon TLR and NOD agonists challenge.

CONCLUSION

These findings indicated that TLR2, TLR4, NOD1, and NOD2 are functional receptors in HPDLFs during innate immune responses to invading bacteria, and a combination of signalling through TLRs and NODs leads to the synergistic enhancement of inflammatory reactions in HPDLFs. In addition, TLR and NOD signalling involving TRAF6 contribute to inflammatory responses in HPDLFs.

Activation of TLR2 and TLR5 did not affect tumor progression of an oral squamous cell carcinoma, YD-10B cells

BACKGROUND

Toll-like receptors (TLRs) signaling has been found to promote cell proliferation, invasiveness, and angiogenesis in a variety of cancers. This study was performed to examine whether TLR signaling is involved in tumor progression of an oral squamous cell carcinoma, YD-10B cells.

METHODS

TLRs expression was examined by reverse transcription-polymerase chain reaction (RT-PCR) in YD-10B cells. Interleukin (IL)-6 and IL-8 production by YD-10B cells in response to various TLR agonists was examined by ELISA. Cell viability and proliferation was determined by colorimetric MTT and Bromodeoxyuridine (BrdU) assay. The effect of TLR agonists on invasiveness was determined by migration and invasion assay using commercial kits. mRNA expression of vascular endothelial growth factor (VEGF) was also evaluated by RT-PCR.

RESULTS

All tested TLRs including TLR2, 3, 4, 5, 7, and 9 were expressed in YD-10B cells. IL-6 and IL-8 production was increased by Pam(3) CSK(4) , flagellin, Poly I:C, and imiquimod, but not lipopolysaccharide (LPS). Porphyromonas gingivalis LPS (Pg LPS) also led to increase of IL-8 production. However, Pam(3) CSK(4,) flagellin, and Pg LPS did not affect cell proliferation, migration, invasion, and gene expression of VEGF in YD-10B cells.

CONCLUSION

These findings indicated that TLR activation by bacterial molecules may not affect tumor progression of YD-10B cells.

Review of osteoimmunology and the host response in endodontic and periodontal lesions

Both lesions of endodontic origin and periodontal diseases involve the host response to bacteria and the formation of osteolytic lesions. Important for both is the upregulation of inflammatory cytokines that initiate and sustain the inflammatory response. Also important are chemokines that induce recruitment of leukocyte subsets and bone-resorptive factors that are largely produced by recruited inflammatory cells. However, there are differences also. Lesions of endodontic origin pose a particular challenge since that bacteria persist in a protected reservoir that is not readily accessible to the immune defenses. Thus, experiments in which the host response is inhibited in endodontic lesions tend to aggravate the formation of osteolytic lesions. In contrast, bacteria that invade the periodontium appear to be less problematic so that blocking arms of the host response tend to reduce the disease process. Interestingly, both lesions of endodontic origin and periodontitis exhibit inflammation that appears to inhibit bone formation. In periodontitis, the spatial location of the inflammation is likely to be important so that a host response that is restricted to a subepithelial space is associated with gingivitis, while a host response closer to bone is linked to bone resorption and periodontitis. However, the persistence of inflammation is also thought to be important in periodontitis since inflammation present during coupled bone formation may limit the capacity to repair the resorbed bone.

Anti-inflammatory effect of catechin on cultured human dental pulp cells affected by bacteria-derived factors

Catechins (bioactive polyphenols in green tea) are known to exhibit potent anti-inflammatory properties. However, the anti-inflammatory effects of catechins on inflamed dental pulp tissue are not known. In this study, we investigated the effect of epigallocatechin-3-gallate (EGCG) and epicatechin gallate (ECG), the major components of green tea catechins, on the expression of pro-inflammatory cytokines and adhesion molecules in human dental pulp cells stimulated with bacteria-derived factors such as lipopolysaccharide (LPS) and peptidoglycan (PG). The expression of interleukin (IL)-6 and of IL-8 was examined using the reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assays. The expression of intercellular adhesion molecule-1 (ICAM-1) and of vascular cell adhesion molecule-1 (VCAM-1) on dental pulp cells was analyzed using flow cytometry. The presence of EGCG and ECG significantly reduced, in a concentration-dependent manner, the expression of IL-6 and IL-8 in dental pulp cells exposed to LPS or PG. Increased expression of ICAM-1 and VCAM-1 on the dental pulp cells in response to bacterial components was also decreased by treatment with EGCG and ECG. These findings suggest that green tea catechins may prevent the exacerbation of pulpitis.