Different engagement of TLR2 and TLR4 in Porphyromonas gingivalis vs. ligature-induced periodontal bone loss

The associations of two novel inflammation indexes, systemic immune-inflammation index (SII) and system inflammation response index (SIRI), with periodontitis: evidence from NHANES 2009-2014

OBJECTIVES

The research's goal is to look for any potential relationships between the systemic immune-inflammation index (SII) and the system inflammation response index (SIRI), along with inflammation indicators and the likelihood of periodontitis.

METHODS

Ten thousand two hundred eighty-two individuals in sum were determined to be eligible for this cross-sectional study from the National Health and Nutrition Examination Survey (NHANES) between 2009 and 2014. Multiple logistic regression, generalized additive model, smooth curve fitting, subgroup analysis, and interaction tests were done for analyzing the association between periodontitis and SII, SIRI, and other inflammatory indicators.

RESULTS

The analysis, adjusted for population weighting, revealed that individuals with moderate/severe periodontitis had SII levels of 545.46 (95% CI (529.10, 561.82), P = 0.0044) and SIRI levels of 1.33 (95% CI (1.29, 1.37), P < 0.0001). In a fully adjusted multivariate logistic regression model, SII was not sensibly associated with moderate/severe periodontitis among the continuous and quartile Q1-Q4 groups (OR = 0.97, 95% CI (0.91, 1.02)). The continuous variable of SIRI (OR = 1.11, 95% CI (1.06, 1.17)) and the quartile Q4 group (OR = 1.58, 95% CI (1.28, 1.94)) had a deemed significant positive association with moderate to severe periodontitis. In addition, other inflammatory indicators, especially NLR, PPN, PLR, MLR, PC, NC, and MC were observed to be notably involved moderate/severe periodontist in this research.

CONCLUSION

We explored the association between periodontitis and two novel comprehensive markers of inflammation (SII and SIRI).

CLINICAL RELEVANCE

These inflammatory markers are expected to serve as tools to assist clinicians in diagnosing periodontitis.

Mouse gingival single-cell transcriptomic atlas identified a novel fibroblast subpopulation activated to guide oral barrier immunity in periodontitis

Periodontitis, one of the most common non-communicable diseases, is characterized by chronic oral inflammation and uncontrolled tooth supporting alveolar bone resorption. Its underlying mechanism to initiate aberrant oral barrier immunity has yet to be delineated. Here, we report a unique fibroblast subpopulation activated to guide oral inflammation (AG fibroblasts) identified in a single-cell RNA sequencing gingival cell atlas constructed from the mouse periodontitis models. AG fibroblasts localized beneath the gingival epithelium and in the cervical periodontal ligament responded to the ligature placement and to the discrete topical application of Toll-like receptor stimulants to mouse maxillary tissue. The upregulated chemokines and ligands of AG fibroblasts linked to the putative receptors of neutrophils in the early stages of periodontitis. In the established chronic inflammation, neutrophils, together with AG fibroblasts, appeared to induce type 3 innate lymphoid cells (ILC3s) that were the primary source of interleukin-17 cytokines. The comparative analysis of Rag2-/- and Rag2-/-Il2rg-/- mice suggested that ILC3 contributed to the cervical alveolar bone resorption interfacing the gingival inflammation. We propose the AG fibroblast-neutrophil-ILC3 axis as a previously unrecognized mechanism which could be involved in the complex interplay between oral barrier immune cells contributing to pathological inflammation in periodontitis.

Oral Microbial Signature of Rheumatoid Arthritis in Female Patients

This study aimed to identify the oral microbial signature of Kazakh female rheumatoid arthritis (RA) patients. A total of 75 female patients who met the American College of Rheumatology 2010 classification criteria for RA and 114 healthy volunteers were included in the study. Amplicons of the 16S rRNA gene were sequenced to analyze the microbial composition. We identified significant differences in bacterial diversity and abundance between the RA and control groups, as measured by Shannon (p value = 0.0205) and Simpson (p value = 0.00152) indices. The oral samples from RA patients had higher bacterial diversity than those from non-RA volunteers. The RA samples had a higher relative abundance of Prevotellaceae and Leptotrichiaceae, but a lower content of butyrate and propionate-producing bacteria compared to the control group. The samples from patients in remission had a higher abundance of Treponema sp. and Absconditabacteriales (SR1), whereas those with low disease activity had higher levels of Porphyromonas and those with high RA activity had higher levels of Staphylococcus. A positive correlation was found between the taxa Prevotella_9 and serum levels of antibodies to cyclic citrullinated peptide (ACPA) and rheumatoid factor (RF). The predicted functional pattern of the ACPA+/RF- and ACPA+/RF+ seropositive groups was characterized by increased ascorbate metabolism, degradation of glycosaminoglycans, and reduced biodegradation of xenobiotics. These findings suggest that the functional pattern of the microflora should be considered when selecting a therapeutic strategy for RA in order to provide a personalized approach.

NLRC5 modulates bone metabolism and plays a role in periodontitis

INTRODUCTION

NOD-like receptor C5 (NLRC5) plays a significant role in the immune system, and is one of the largest members of the pattern recognition receptor family. Previous studies have found that NLRC5 might be involved in the regulation of various diseases, such as fibrotic diseases and cancers; however, its effect on bone metabolism-related diseases has not been reported.

METHODS

Skeletons of Nlrc5^-/- mice generated by CRISPR/Cas9 and wild-type (WT) mice were compared using X-ray, micro-computed tomography, double labeling, and histological examination. Tartrate-resistant acid phosphatase and pit-absorption assays were performed to evaluate the effect of NLRC5 on osteoclasts differentiation and osteoclastic capacity. The influence of NLRC5 on osteoblasts differentiation and bone formation were studied using alkaline phosphatase and alizarin red staining, respectively. Experimental periodontitis was induced by Porphyromonas gingivalis infection and ligature to investigate the role of NLRC5 in inflammatory periodontal bone loss.

RESULTS

Adenovirus-mediated NLRC5 overexpression in human bone marrow mesenchymal stem cells regulated osteogenesis positively. The femoral osteogenesis ability was significantly weakened in Nlrc5^-/- mice. Histology showed that the area of the femoral trabeculae in the Nlrc5^-/- mice was less than that in the WT mice, and radiology suggested that the Nlrc5^-/- mice had fewer trabeculae and a thinner bone cortex than those of the WT mice. Nlrc5 knockout decreased osteoblast mineralization and increased osteoclastogenesis in vitro. NLRC5 was downregulated in periodontitis and P. gingivalis infection. In the experimental periodontitis model, the alveolar bone loss, inflammatory cell infiltration, and inflammatory cytokines secretion (interleukin [IL]-1β, IL-6, and tumor necrosis factor alpha [TNF-α]) in the Nlrc5^-/- mice were significantly enhanced compared to WT mice.

CONCLUSION

We verified a novel role of NLRC5 in bone metabolism by regulating both osteoclasts activity and osteoblasts activity. Our results revealed a protective effect of NLRC5 against periodontal inflammation and alveolar bone destruction. NLRC5 could be a novel treatment target to prevent periodontal bone destruction.

Does Oral Endotoxin Contribute to Systemic Inflammation?

The oral microbiome, with a unique emphasis on Porphyromonas gingivalis has been associated with a constellation of inflammatory diseases such as cardiovascular disease, rheumatoid arthritis, Alzheimer's disease, type II diabetes, and non-alcoholic associated fatty liver disease. Periodontal disease has also been shown to induce “leaky gut” leading to metabolic endotoxemia. Several recent studies investigating the habitants of the blood microbiome have found the majority of species appear to be derived from oral and skin bacterial communities in otherwise healthy individuals. Many of the same pathologies associated with perturbations of oral health, such as cardiovascular disease, show alterations to the composition of the blood microbiome as well as circulating neutrophil phenotypes. Gingival inflammation is associated with activated blood neutrophil phenotypes that can exacerbate a distal inflammatory insult which may explain the connection between oral and systemic inflammatory conditions. While in the oral cavity, neutrophils encounter oral microbes that are adept in manipulating neutrophil activity which can re-enter the vasculature thereafter. Endotoxin from oral microbes can differ significantly depending on bacterial community and state of oral health to alter cellular LPS tolerance mechanisms which may contribute to the primed neutrophil phenotype seen in periodontitis and provide a mechanism by which the oral-microbes can affect systemic health outcomes. This review synthesizes the studies between inflammatory diseases and oral health with emphasis on microbiome and corresponding lipopolysaccharides in immune tolerance and activation.

Nano-emulsion of mangosteen rind extract in a mucoadhesive patch for periodontitis regenerative treatment: An in vivo study

Objective

To investigate the therapeutic potential of nano-emulsion of mangosteen rind extract in a mucoadhesive gingival patch on periodontitis, and its effect on tumor necrosis factor alpha (TNF-α), receptor activator of nuclear factor kappa Β ligand (RANKL), and interleukin 10 (IL-10) expression.

Methods

Sixty Wistar rats were divided into four groups: positive control group (mucoadhesive patch with doxycycline), negative control group (mucoadhesive patch), treatment group I (mucoadhesive patch with mangosteen rind extract), and treatment group II (mucoadhesive patch with nano-emulsion of mangosteen rind extract). An experimental model of Porphyromonas gingivalis-induced periodontitis was established in rats by treatment with 0.03 mL bacteria locally (1 × 10¹⁰ colony-forming units) seven times at 2-day intervals in the gingival sulcus of mandibular anterior teeth. Treatment was 1 h/day for 3 days. On days 3, 5, and 7, five rats from each group were killed. TNF-α, IL-10, and RANKL expression was determined by dissecting the lower jaw for immunohistochemistry.

Results

The mucoadhesive patch with nano-emulsion mangosteen rind extract significantly decreased TNF-α and RANKL expression and increased IL-10 expression (p < 0.05) compared to the treatment I, positive and negative control groups.

Conclusion

A mucoadhesive gingival patch with nano-emulsion of mangosteen rind extract has the potential to treat periodontitis by decreasing TNF-α, RANKL, and increasing IL-10 expression.

Differential involvement of the canonical and noncanonical inflammasomes in the immune response against infection by the periodontal bacteria Porphyromonas gingivalis and Fusobacterium nucleatum

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The canonical P2 × 7-Caspase-1 pathway is necessary for secretion of IL-1β in oral tissues and macrophages infected with P. gingivalis.

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P2 × 7 receptor controls bacterial load of F. nucleatum and P. gingivalis in macrophages and in mice.

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Caspase-11 is essential for F. nucleatum-induced secretion of IL-1β in macrophages, limits F. nucleatum infection in macrophages and in mice, and is required for cell death induced by F. nucleatum infection.

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The canonical inflammasome is activated preferentially in response to P. gingivalis infection, while the noncanonical inflammasome plays a predominant role during F. nucleatum infection.

We examined the involvement of the P2 × 7 receptor and the canonical and noncanonical inflammasomes in the control of single-species or dual-species infection by the periodontal bacteria Porphyromonas gingivalis and Fusobacterium nucleatum in cells and mice. Stimulation of the P2 × 7 receptor leads to activation of the canonical NLRP3 inflammasome and activation of caspase-1, which leads to cleavage of pro-IL-1β to IL-1β, a key cytokine in the host inflammatory response in periodontal disease. The non-canonical inflammasome pathway involves caspase-11. Thus, wildtype (WT), P2 × 7^−/−, caspase-11^−/− and caspase-1/11^−/− mice were co-infected with both bacterial species. In parallel, bone marrow-derived macrophages (BMDMs) from WT mice and the different knockout mice were infected with P. gingivalis and/or F. nucleatum, and treated or not with extracellular ATP, which is recognized by P2 × 7. F. nucleatum infection alone promoted secretion of IL-1β in BMDMs. Conversely, the canonical pathway involving P2 × 7 and caspase-1 was necessary for secretion of IL-1β in BMDMs infected with P. gingivalis and in the mandible of mice coinfected with P. gingivalis and F. nucleatum. The P2 × 7 pathway can limit bacterial load in single-species and dual-species infection with P. gingivalis and F. nucleatum in BMDMs and in mice. The non-canonical pathway involving caspase-11 was required for secretion of IL-1β induced by F. nucleatum infection in BMDMs, without treatment with ATP. Caspase-11 was also required for induction of cell death during infection with F. nucleatum and contributed to limiting bacterial load during F. nucleatum infection in BMDMs and in the gingival tissue of mice coinfected with P. gingivalis and F. nucleatum. Together, these data suggest that the P2 × 7-caspase-1 and caspase-11 pathways are involved in the immune response against infection by P. gingivalis and F. nucleatum, respectively.

Application of Ligature-Induced Periodontitis in Mice to Explore the Molecular Mechanism of Periodontal Disease

Periodontitis is an inflammatory disease characterized by the destruction of the periodontium. In the last decade, a new murine model of periodontitis has been widely used to simulate alveolar bone resorption and periodontal soft tissue destruction by ligation. Typically, 3-0 to 9-0 silks are selected for ligation around the molars in mice, and significant bone loss and inflammatory infiltration are observed within a week. The ligature-maintained period can vary according to specific aims. We reviewed the findings on the interaction of systemic diseases with periodontitis, periodontal tissue destruction, the immunological and bacteriological responses, and new treatments. In these studies, the activation of osteoclasts, upregulation of pro-inflammatory factors, and excessive immune response have been considered as major factors in periodontal disruption. Multiple genes identified in periodontal tissues partly reflect the complexity of the pathogenesis of periodontitis. The effects of novel treatment methods on periodontitis have also been evaluated in a ligature-induced periodontitis model in mice. This model cannot completely represent all aspects of periodontitis in humans but is considered an effective method for the exploration of its mechanisms. Through this review, we aimed to provide evidence and enlightenment for future studies planning to use this model.

Effects of Erythromycin on Osteoclasts and Bone Resorption via DEL-1 Induction in Mice

Macrolides are used to treat various infectious diseases, including periodontitis. Furthermore, macrolides are known to have immunomodulatory effects; however, the underlying mechanism of their action remains unclear. DEL-1 has emerged as an important factor in homeostatic immunity and osteoclastogenesis. Specifically, DEL-1 is downregulated in periodontitis tissues. Therefore, in the present study, we investigated whether the osteoclastogenesis inhibitory effects of erythromycin (ERM) are mediated through upregulation of DEL-1 expression. We used a ligature-induced periodontitis model in C57BL/6Ncrl wild-type or DEL-1-deficient mice and in vitro cell-based mechanistic studies to investigate how ERM inhibits alveolar bone resorption. As a result of measuring alveolar bone resorption and gene expression in the tooth ligation model, ERM treatment reduced bone loss by increasing DEL-1 expression and decreasing the expression of osteoclast-related factors in wild-type mice. In DEL-1-deficient mice, ERM failed to suppress bone loss and gene expression of osteoclast-related factors. In addition, ERM treatment downregulated osteoclast differentiation and calcium resorption in in vitro experiments with mouse bone marrow-derived macrophages. In conclusion, ERM promotes the induction of DEL-1 in periodontal tissue, which may regulate osteoclastogenesis and decrease inflammatory bone resorption. These findings suggest that ERM may exert immunomodulatory effects in a DEL-1-dependent manner.

TLR2 and TLR4 Differentially Regulate the Osteogenic Capacity of Human Periodontal Ligament Fibroblasts

AIMS

To test that the osteogenic capacity of periodontal ligament (PDL) fibroblasts can be mediated by TLR2 and TLR4 activation.

MATERIALS AND METHODS

Human PDL fibroblasts were cultured in osteogenic medium and treated with TLR2 and TLR4 agonists (Pam3CSK4 and monophosphoryl Lipid A (MPLA), respectively). Cell proliferation was measured by MTT and BrdU incorporation. Osteogenic differentiation was measured by alkaline phosphatase (ALP) activity. Nodule formation was measured for osteoblast function. The expression of markers of potential signaling pathways (RUNX2, OCN, BSP and Osterix) was evaluated by quantitative PCR.

RESULTS

PDL fibroblasts grew at the same rate during the first 5 days in response to both Pam3CSK5 and MPLA. On day 7, cells cultured in the presence of Pam3CSK4 had a significantly higher rate of DNA replication, while cells in MPLA group had a significantly lower DNA replication rate (one-third) compared to the control (p less than 0.05). Pam3CSK4 induced significantly higher ALP activity and larger calcified nodules. TLR4 activation significantly reduced the expression of RUNX2 and osterix and enhanced OCN. Neither TLR2 nor TLR4 affected BSP expression.

CONCLUSIONS

These data suggest that the activation of TLR2 and TLR4 differentially and perhaps antagonistically modulate osteogenesis by human PDL fibroblasts and have a direct role of TLR-mediated PDL function during periodontal regeneration as a potential target for therapeutics.

Autophagy and its significance in periodontal disease

Autophagy is an evolutionarily conserved process essential for cellular homeostasis and human health. As a lysosome-dependent degradation pathway, autophagy acts as a modulator of the pathogenesis of diverse diseases. The relationship between autophagy and oral diseases has been explored in recent years, and there is increasing interest in the role of autophagy in periodontal disease. Periodontal disease is a prevalent chronic inflammatory disorder characterized by the destruction of periodontal tissues. It is initiated through pathogenic bacterial infection and interacts with the host immune defense, leading to inflammation and alveolar bone resorption. In this review, we outline the machinery of autophagy and present an overview of work on the significance of autophagy in regulating pathogen invasion, the immune response, inflammation, and alveolar bone homeostasis of periodontal disease. Existing data provide support for the importance of autophagy as a multi-dimensional regulator in the pathogenesis of periodontal disease and demonstrate the importance of future research on the potential roles of autophagy in periodontal disease.

Vitamin D decreases Porphyromonas gingivalis internalized into macrophages by promoting autophagy

OBJECTIVES

This paper aims to study the effect of the active form of vitamin D (calcitriol) on the internalized Porphyromonas gingivalis in macrophages and to assess the role of autophagy during this process.

MATERIALS AND METHODS

Quantitative RT-PCR and bacteria culture were used to quantify live P. gingivalis internalized into U937-derived macrophages. Western blot assays were performed to detect the effect of P. gingivalis and calcitriol on autophagy in macrophages. Transmission electron microscope was used to observe the effect of calcitriol on the status of internalized P. gingivalis. Colocalization of P. gingivalis with the autophagosome and lysosome markers was observed by confocal laser scanning microscopy.

RESULTS

Calcitriol caused a dose-dependent decrease in live P. gingivalis numbers and promoted both the endogenous and P. gingivalis-induced autophagy in macrophages. Calcitriol significantly promoted the destruction of P. gingivalis and the colocalization of P. gingivalis with autophagosome and lysosome markers. Conversely, with 3-MA, live P. gingivalis numbers in macrophages increased significantly and inhibition effect of calcitriol on the number of live P. gingivalis was attenuated.

CONCLUSION

In U937-derived macrophages, calcitriol may promote colocalization of P. gingivalis with autophagosomes and lysosomes, namely autophagy process, to degrade live P. gingivalis.

Chronic Exposure of Gingival Fibroblasts to TLR2 or TLR4 Agonist Inhibits Osteoclastogenesis but Does Not Affect Osteogenesis

Chronic exposure to periodontopathogenic bacteria such as Porphyromonas gingivalis and the products of these bacteria that interact with the cells of the tooth surrounding tissues can ultimately result in periodontitis. This is a disease that is characterized by inflammation-related alveolar bone degradation by the bone-resorbing cells, the osteoclasts. Interactions of bacterial products with Toll-like receptors (TLRs), in particular TLR2 and TLR4, play a significant role in this chronic inflammatory reaction, which possibly affects osteoclastic activity and osteogenic capacity. Little is known about how chronic exposure to specific TLR activators affects these two antagonistic activities. Here, we studied the effect of TLR activation on gingival fibroblasts (GF), cells that are anatomically close to infiltrating bacterial products in the mouth. These were co-cultured with naive osteoclast precursor cells (i.e., monocytes), as part of the peripheral blood mononuclear cells (PBMCs). Activation of GF co-cultures (GF + PBMCs) with TLR2 or TLR4 agonists resulted in a weak reduction of the osteoclastogenic potential of these cultures, predominantly due to TLR2. Interestingly, chronic exposure, especially to TLR2 agonist, resulted in increased release of TNF-α at early time points. This effect, was reversed at later time points, thus suggesting an adaptation to chronic exposure. Monocyte cultures primed with M-CSF + RANKL, led to the formation of bone-resorbing osteoclasts, irrespective of being activated with TLR agonists. Late activation of these co-cultures with TLR2 and with TLR4 agonists led to a slight decrease in bone resorption. Activation of GF with TLR2 and TLR4 agonists did not affect the osteogenic capacity of the GF cells. In conclusion, chronic exposure leads to diverse reactions; inhibitory with naive osteoclast precursors, not effecting already formed (pre-)osteoclasts. We suggest that early encounter of naive monocytes with TLR agonists may result in differentiation toward the macrophage lineage, desirable for clearing bacterial products. Once (pre-)osteoclasts are formed, these cells may be relatively insensitive for direct TLR stimulation. Possibly, TLR activation of periodontal cells indirectly stimulates osteoclasts, by secreting osteoclastogenesis stimulating inflammatory cytokines.

Response of Human Mesenchymal Stromal Cells from Periodontal Tissue to LPS Depends on the Purity but Not on the LPS Source

Human periodontal ligament stromal cells (hPDLSCs) and gingival mesenchymal stromal cells (hGMSCs) are resident mesenchymal stromal cells (MSCs) of the periodontal tissue. The lipopolysaccharide (LPS) from Porphyromonas gingivalis is structurally distinct from that of other Gram-negative bacteria, and earlier studies linked this structural difference to a distinct virulence activity and the ability to activate toll-like receptor 2 (TLR-2), besides TLR-4 as commonly occurring upon LPS challenge. Later studies, in contrast, argue that TLR-2 activation by P. gingivalis LPS is due to lipoprotein contamination. In the present study, we aimed to define the influence of structure versus purity of P. gingivalis LPS on the immune response of hPDLSCs and hGMSCs. Cells were stimulated with commercially available "standard" P. gingivalis LPS, "ultrapure" P. gingivalis LPS, or "ultrapure" Escherichia coli LPS, and the expression of interleukin- (IL-) 8, IL-6, monocyte chemoattractant protein- (MCP-) 1, TLR-2, and TLR-4 was evaluated. The contribution of TLR-4 to the LPS-induced response was assessed using the specific TLR-4 inhibitor TAK-242. "Standard" P. gingivalis LPS induced significantly higher IL-8, IL-6, and MCP-1 production compared to the "ultrapure" LPS preparations, with no significant difference detectable for "ultrapure" LPS from P. gingivalis and E. coli. By using TAK-242, the response of hPDLSCs and hGMSCs to "ultrapure" LPS preparations was effectively inhibited to the levels comparable to those of nonstimulated controls. In contrast, high levels of response to "standard" LPS were observed, even in the presence of TAK-242. Our data show that the response of MSCs from periodontal tissue to LPS depends more on the purity of the LPS preparation than on the LPS source. Even a small amount of contaminating lipoproteins can drastically enhance the hPDLSCs' and hGMSCs; responsiveness to P. gingivalis LPS, which might also contribute to the progression of periodontal disease.

Toll-Like Receptor Signaling and Immune Regulatory Lymphocytes in Periodontal Disease

Periodontitis is known to be initiated by periodontal microbiota derived from biofilm formation. The microbial dysbiotic changes in the biofilm trigger the host immune and inflammatory responses that can be both beneficial for the protection of the host from infection, and detrimental to the host, causing tissue destruction. During this process, recognition of Pathogen-Associated Molecular Patterns (PAMPs) by the host Pattern Recognition Receptors (PRRs) such as Toll-like receptors (TLRs) play an essential role in the host–microbe interaction and the subsequent innate as well as adaptive responses. If persistent, the adverse interaction triggered by the host immune response to the microorganisms associated with periodontal biofilms is a direct cause of periodontal inflammation and bone loss. A large number of T and B lymphocytes are infiltrated in the diseased gingival tissues, which can secrete inflammatory mediators and activate the osteolytic pathways, promoting periodontal inflammation and bone resorption. On the other hand, there is evidence showing that immune regulatory T and B cells are present in the diseased tissue and can be induced for the enhancement of their anti-inflammatory effects. Changes and distribution of the T/B lymphocytes phenotype seem to be a key determinant of the periodontal disease outcome, as the functional activities of these cells not only shape up the overall immune response pattern, but may directly regulate the osteoimmunological balance. Therefore, interventional strategies targeting TLR signaling and immune regulatory T/B cells may be a promising approach to rebalance the immune response and alleviate bone loss in periodontal disease. In this review, we will examine the etiological role of TLR signaling and immune cell osteoclastogenic activity in the pathogenesis of periodontitis. More importantly, the protective effects of immune regulatory lymphocytes, particularly the activation and functional role of IL-10 expressing regulatory B cells, will be discussed.

TLR4 mediates alveolar bone resorption in experimental peri-implantitis through regulation of CD45+ cell infiltration, RANKL/OPG ratio, and inflammatory cytokine production

BACKGROUND

The present study was to determine the role of Toll-like receptor 4 (TLR4) signaling in inflammation and alveolar bone resorption using a murine model of Porphyromonas gingivalis-associated ligature-induced peri-implantitis.

METHODS

Smooth surface titanium implants were placed in the left maxilla alveolar bone 6 weeks after extraction of first and second molars in Wild-type (WT) and TLR4^-/- (TLR4 KO) mice. Silk ligatures immersed with P. gingivalis were tied around the implants 4 weeks after the implant placement and confirmation of osteointegration. Two weeks after the ligation, bone resorption, osteoclastogenesis, cellular inflammatory responses, and gingival mRNA expression levels of cytokines were assessed by micro-computed tomography, tartrate-resistant acid phosphatase (TRAP) staining, immunobiological examination and Real-time quantitative polymerase chain reaction, respectively.

RESULTS

In both WT and TLR4 KO mice, the bone resorption around implants was significantly increased in the P. gingivalis/ligation group compared with control group. In P. gingivalis/ligation group, the levels of bone resorption, TRAP+ cell formation, and gingival CD3+ and CD45+ cell infiltration were significantly decreased in TLR4 KO mice compared with that in WT mice. Receptor activator of nuclear factor-kappa B ligand /osteoprotegerin (RANKL/OPG) ratio was significantly increased after P. gingivalis/ligation treatment in WT mice not in TLR4 KO mice. When comparing the P. gingivalis/ligation group with the respective control group, gingival mRNA expressions of IL-1β, IFN-γ, and 1L-17 were significantly increased in TLR4 KO mice.

CONCLUSION

This study suggests that TLR4 mediates alveolar bone resorption in P. gingivalis associated ligature-induced peri-implantitis through regulation of immune B cell infiltration, RANKL/OPG expression ratio, and differential inflammatory cytokine production.

RANKL blockade alleviates peri-implant bone loss and is enhanced by anti-inflammatory microRNA-146a through TLR2/4 signaling

BACKGROUND

The present study was to determine the effect of local anti-RANKL antibody administration in the presence or absence of microRNA-146a on ligature-induced peri-implant bone resorption, and the potential role of TLR2/4 signaling in such effect.

RESULTS

Titanium implants were placed in the left maxilla alveolar bone 6 weeks after extraction of first and second molars in C57/BL6 wild-type (WT) and TLR2-/- TLR4-/- (TLR2/4 KO) mice. Silk ligatures were tied around the implants 4 weeks after implantation. Anti-RANKL antibody (500 μg/mL) with or without microRNA 146a (miR-146a) (100 nM) was injected into palatal gingiva around implant on days 3, 6, and 9 during 2 weeks of ligation period. Bone resorption around the implants was assessed by 2D imaging using area measurement and 3D imaging using micro-computed tomography (μCT). Real-time quantitative PCR (RT-qPCR) was used to determine the peri-implant gingival mRNA expression levels of pro-inflammatory cytokines (TNF-α) and osteoclastogenesis-related cytokines (RANKL). In both WT and TLR2/4 KO mice, the bone resorption around implants was significantly increased in the ligation only group when compared to the non-ligation group, but TLR2/4 KO mice showed significantly less bone loss compared to WT mice after ligation. As expected, gingival injection of anti-RANKL antibody significantly reduced bone loss compared with the ligation only group in both WT and TLR2/4 KO mice. Moreover, injection of miR-146a in addition to anti-RANKL antibody significantly enhanced the inhibition of bone loss in WT mice but not in TLR2/4 KO mice. Gingival mRNA expressions of RANKL were significantly reduced by anti-RANKL antibody treatment in both WT and TLR2/4 KO mice but were not affected by the additional miR-146a treatment. Gingival mRNA expression of TNF-α was significantly reduced by miR-146a treatment in WT mice but not in TLR2/4 KO mice. The number of gingival inflammatory cell infiltration and peri-implant TRAP-positive cell formation was significantly reduced by the additional miR-146a treatment in WT mice but not in TLR2/4 KO mice.

CONCLUSIONS

This study suggests that anti-inflammatory miR-146a enhance anti-RANKL-induced inhibition of peri-implant bone resorption through the regulation of TLR2/4 signaling and inhibition of TNF-α expression.

Toll-like receptor-2 and -4 responses regulate neutrophil infiltration into the junctional epithelium and significantly contribute to the composition of the oral microbiota

BACKGROUND

Oral gingival tissue, especially the junctional epithelium (JE), is constantly exposed to sub-gingival plaque. A key component of gingival health is the regulation of the number of neutrophils that migrate into the gingival crevice to counteract its harmful effects. This report investigates the contribution of innate defense receptors, Toll-like receptor (TLR)2, TLR4, and both (TLR2/4) to the maintenance of neutrophil homeostasis in the JE.

METHODS

Bacterial composition was analyzed from whole oral swabs collected from 12- to 14-week-old TLR2, TLR4, TLR2/4 double knock-out (KO) mice using a MiSeq platform targeting the V3-V4 region of the 16S ribosomal RNA gene. Mandibles were histologically examined for quantification of neutrophils in the JE and bone loss. Lastly, total bacterial load was quantitated using quantitative real-time PCR.

RESULTS

Compared with wild-type, all TLR KO mice displayed significantly increased recruitment of neutrophils (P = 0.0079) into the JE. In addition, TLR4 and TLR2/4 KO mice demonstrated a significant increase in the number of bacteria (P = 0.0022 and P = 0.0152, respectively). Lastly, comparative compositional analyses of the oral microbiome revealed that each KO strain harbored unique microbial communities that are distinct from each other but maintained similar levels of alveolar bone.

CONCLUSIONS

Neutrophil migration into healthy mouse JE does not require TLR2 or TLR4. However, a significant increase in the number of neutrophils as well as a significant change in the oral microbial composition in both TLR2 and TLR4 KO mice demonstrate that these TLRs contribute to the homeostatic relationship between bacteria and the host in healthy mice periodontal tissue.

The Influence of TLR4, CD14, OPG, and RANKL Polymorphisms in Periodontitis: A Case-Control Study

The pathogenesis of periodontitis involves a complex interaction between the microbial challenge and the host immune response. The individual immunoinflammatory response has a great contribution in the pathogenesis of the disease and becomes a trigger in the process of bone remodeling which is a characteristic of the disease. Thus, the aim of this study was to evaluate the influence of the TLR4 A896G (rs4986790), TLR4 C1196T (rs4986791), CD14 C-260T (rs2569190), RANKL (TNFSF11, rs2277438), and OPG (TNFSF11B C163T, rs3102735) polymorphisms in periodontitis. A case-control study was conducted on patients with periodontitis (N = 203) and controls (N = 213) over 30 years of age, without diabetes mellitus, acute infections, and osteoarthritis, and patients without aggressive periodontitis, i.e., stage IV and C degree of periodontitis, and any periodontal treatment performed in the last 6 months. Genotypes were determined by the PCR-RFLP and sequencing method. The frequency comparisons between case and controls were performed using the chi-square test and logistic regression (OpenEpi and SNPStats software). The risk (OR) was evaluated for values of P < 0.05. Differences in TLR4, CD14, RANKL, and OPG genotype and allele frequency distributions were not observed between patients and controls. However, some variants were a risk factor for the development of periodontitis when considering gender and smoking habits. The TLR4 896 A/G genotype was a risk factor for periodontitis in males (OR = 2.86), and the TLR4 1196C/C genotype was a risk factor for nonsmoking males (OR = 1.85) when compared to women. The RANKL A/A and the OPG T/C genotype was associated with the risk of the disease in nonsmoking men compared to nonsmoking women with the same genotype (OR = 1.96 and OR = 2.9, respectively). In conclusion, TLR4, CD14, RANKL, and OPG variants were not associated with periodontitis. However, TLR4, RANKL, and OPG polymorphisms could be a risk for periodontitis in males regardless of smoking habits.