TLR4, NOD1 and NOD2 mediate immune recognition of putative newly identified periodontal pathogens

The oral-gut microbiome axis in health and disease

The human body hosts trillions of microorganisms throughout many diverse habitats with different physico-chemical characteristics. Among them, the oral cavity and the gut harbour some of the most dense and diverse microbial communities. Although these two sites are physiologically distinct, they are directly connected and can influence each other in several ways. For example, oral microorganisms can reach and colonize the gastrointestinal tract, particularly in the context of gut dysbiosis. However, the mechanisms of colonization and the role that the oral microbiome plays in causing or exacerbating diseases in other organs have not yet been fully elucidated. Here, we describe recent advances in our understanding of how the oral and intestinal microbiota interplay in relation to their impact on human health and disease.

NOD2 contributes to Parvimonas micra-induced bone resorption in diabetic rats with experimental periodontitis

BACKGROUND

Type 2 diabetes mellitus (T2DM) may affect the oral microbial community, exacerbating periodontal inflammation; however, its pathogenic mechanisms remain unclear. As nucleotide-binding oligomerization domain 2 (NOD2) plays a crucial role in the activation during periodontitis (PD), it is hypothesized that changes in the oral microbial community due to diabetes enhance periodontal inflammation through the activation of NOD2.

METHODS

We collected subgingival plaque from 180 subjects who were categorized into two groups based on the presence or absence of T2DM. The composition of oral microbiota was detected by 16S rRNA high-throughput sequencing. In animal models of PD with or without T2DM, we assessed alveolar bone resorption by micro-computerized tomography and used immunohistochemistry to detect NOD2 expression in alveolar bone. Primary osteoblasts were cultured in osteogenic induction medium with high or normal glucose and treated with inactivated bacteria. After 24 h of inactivated bacteria intervention, the osteogenic differentiation ability was detected by alkaline phosphatase (ALP) staining, and the expressions of NOD2 and interleukin-12 (IL-6) were detected by western blot.

RESULTS

The relative abundance of Parvimonas and Filifactor in the T2DM group was increased compared to the group without T2DM. In animal models, alveolar bone mass was decreased in PD, particularly in T2DM with PD (DMPD) group, compared to controls. Immunohistochemistry revealed NOD2 in osteoblasts from the alveolar bone in both the PD group and DMPD group, especially in the DMPD group. In vitro, intervention with inactivated Parvimonas significantly reduced ALP secretion of primary osteoblasts in high glucose medium, accompanied by increased expression of NOD2 and IL-6.

CONCLUSIONS

The results suggest that T2DM leading to PD may be associated with the activation of NOD2 by Parvimonas.

Global trends in research on aging associated with periodontitis from 2002 to 2023: a bibliometric analysis

Background

Aging has been implicated in many chronic inflammatory diseases, including periodontitis. Periodontitis is an inflammatory disease caused by long-term irritation of the periodontal tissues by the plaque biofilm on the surface of the teeth. However, only a few bibliometric analyses have systematically studied this field to date. This work sought to visualize research hot spots and trends in aging associated with periodontitis from 2002 to 2023 through bibliometric approaches.

Methods

Graphpad prism v8.0.2 was used to analyse and plot annual papers, national publication trends and national publication heat maps. In addition, CtieSpace (6.1.6R (64-bit) Advanced Edition) and VOSviewer (version 1.6.18) were used to analyse these data and visualize the scientific knowledge graph.

Results

The number of documents related to aging associated with periodontitis has steadily increased over 21 years. With six of the top ten institutions in terms of publications coming from the US, the US is a major driver of research in this area. journal of periodontology is the most published journal in the field. Tonetti MS is the most prolific authors and co-cited authors in the field. Journal of Periodontology and Journal of Clinical Periodontology are the most popular journals in the field with the largest literature. Periodontitis, Alzheimer's disease, and peri-implantitis are current hot topics and trends in the field. Inflammation, biomarkers, oxidative stress cytokines are current research hotspots in this field.

Conclusion

Our research found that global publications regarding research on aging associated with periodontitis increased dramatically and were expected to continue increasing. Inflammation and aging, and the relationship between periodontitis and systemic diseases, are topics worthy of attention.

Parvimonas micra can translocate from the subgingival sulcus of the human oral cavity to colorectal adenocarcinoma

Oral and intestinal samples from a cohort of 93 colorectal cancer (CRC) patients and 30 healthy controls (non-CRC) were collected for microbiome analysis. Saliva (28 non-CRC and 94 CRC), feces (30 non-CRC and 97 CRC), subgingival fluid (20 CRC), and tumor tissue samples (20 CRC) were used for 16S metabarcoding and/or RNA sequencing (RNAseq) approaches. A differential analysis of the abundance, performed with the ANCOM-BC package, adjusting the P-values by the Holm-Bonferroni method, revealed that Parvimonas was significantly over-represented in feces from CRC patients (P-value < 0.001) compared to healthy controls. A total of 11 Parvimonas micra isolates were obtained from the oral cavity and adenocarcinoma of CRC patients. Genome analysis identified a pair of isolates from the same patient that shared 99.2% identity, demonstrating that P. micra can translocate from the subgingival cavity to the gut. The data suggest that P. micra could migrate in a synergistic consortium with other periodontal bacteria. Metatranscriptomics confirmed that oral bacteria were more active in tumor than in non-neoplastic tissues. We suggest that P. micra could be considered as a CRC biomarker detected in non-invasive samples such as feces.

Metagenomic analysis of healthy and diseased peri-implant microbiome under different periodontal conditions: a cross-sectional study

BACKGROUND

Peri-implantitis is a polybacterial infection that can lead to the failure of dental implant rehabilitation. This study aimed to profile the microbiome of the peri-implant plaque and estimate the effect of periodontitis on it among 40 Chinese participants with dental implant prostheses and presenting with varying peri-implant and periodontal health states.

METHODS

Submucosal plaque samples were collected from four distinct clinical categories based on both their implant and periodontal health status at sampling point. Clinical examinations of dental implant and remaining teeth were carried out. Metagenomic analysis was then performed.

RESULTS

The microbiome of the peri-implantitis sites differed from that of healthy implant sites, both taxonomically and functionally. Moreover, the predominant species in peri-implantitis sites were slightly affected by the presence of periodontitis. T. forsythia, P. gingivalis, T. denticola, and P. endodontalis were consistently associated with peri-implantitis and inflammatory clinical parameters regardless of the presence of periodontitis. Prevotella spp. and P. endodontalis showed significant differences in the peri-implantitis cohorts under different periodontal conditions. The most distinguishing function between diseased and healthy implants is related to flagellar assembly, which plays an important role in epithelial cell invasion.

CONCLUSIONS

The composition of the peri-implant microbiome varied in the diseased and healthy states of implants and is affected by individual periodontal conditions. Based on their correlations with clinical parameters, certain species are associated with disease and healthy implants. Flagellar assembly may play a vital role in the process of peri-implantitis.

DAMPs and alarmin gene expression patterns in aging healthy and diseased mucosal tissues

Introduction

Periodontitis is delineated by a dysbiotic microbiome at sites of lesions accompanied by a dysregulated persistent inflammatory response that undermines the integrity of the periodontium. The interplay of the altered microbial ecology and warning signals from host cells would be a critical feature for maintaining or re-establishing homeostasis in these tissues.

Methods

This study used a nonhuman primate model (Macaca mulatta) with naturally-occurring periodontitis (n = 34) and experimental ligature-induced periodontitis (n = 36) to describe the features of gene expression for an array of damage-associate molecular patterns (DAMPs) or alarmins within the gingival tissues. The animals were age stratified into: ≤3 years (Young), 7-12 years (Adolescent), 12-15 years (Adult) and 17-23 years (Aged). Gingival tissue biopsies were examined via microarray. The analysis focused on 51 genes representative of the DAMPs/alarmins family of host cell warning factors and 18 genes associated with tissue destructive processed in the gingival tissues. Bacterial plaque samples were collected by curette sampling and 16S rRNA gene sequences used to describe the oral microbiome.

Results

A subset of DAMPs/alarmins were expressed in healthy and naturally-occurring periodontitis tissues in the animals and suggested local effects on gingival tissues leading to altered levels of DAMPs/alarmins related to age and disease. Significant differences from adult healthy levels were most frequently observed in the young and adolescent animals with few representatives in this gene array altered in the healthy aged gingival tissues. Of the 51 target genes, only approximately ⅓ were altered by ≥1.5-fold in any of the age groups of animals during disease, with those increases observed during disease initiation. Distinctive positive and negative correlations were noted with the DAMP/alarmin gene levels and comparative expression changes of tissue destructive molecules during disease across the age groups. Finally, specific correlations of DAMP/alarmin genes and relative abundance of particular microbes were observed in health and resolution samples in younger animals, while increased correlations during disease in the older groups were noted.

Conclusions

Thus, using this human-like preclinical model of induced periodontitis, we demonstrated the dynamics of the activation of the DAMP/alarmin warning system in the gingival tissues that showed some specific differences based on age.

New putative periodontopathogens and periodontal health-associated species: A systematic review and meta-analysis

To investigate the existence of any association between new putative periodontal pathogens and periodontitis. Two independent reviewers conducted electronic literature searches in the MEDLINE (PubMed), EMBASE, DOSS and Google Scholar databases as well as a manual search to identify eligible clinical studies prior to November 2022. Studies comparing the prevalence of microorganisms other than the already-known periodontal pathogens in subgingival plaque and/or saliva samples between subjects with periodontitis and subject with periodontal health were included. Meta-analyses were performed on data provided by the included studies. Fifty studies including a total of 2739 periodontitis subjects and 1747 subjects with periodontal health were included. The Archaea domain and 25 bacterial species (Anaeroglobus geminatus, Bacteroidales [G-2] bacterium HMT 274, Desulfobulbus sp. HMT 041, Dialister invisus, Dialister pneumosintes, Eubacterium brachy, Enterococcus faecalis, Eubacterium nodatum, Eubacterium saphenum, Filifactor alocis, Fretibacterium sp. HMT 360, Fretibacterium sp. HMT 362, Mogibacterium timidum, Peptoniphilaceae sp. HMT 113, Peptostreptococcus stomatis, Porphyromonas endodontalis, Slackia exigua, Streptococcus gordonii, Selenomonas sputigena, Treponema amylovorum, Treponema lecithinolyticum, Treponema maltophilum, Treponema medium, Treponema parvum and Treponema socranskii) were found to be statistically significantly associated with periodontitis. Network studies should be conducted to investigate the role of these newly identified periodontitis-associated microorganisms through interspecies interaction and host-microbe crosstalk analyses.

The Roles of Periodontal Bacteria in Atherosclerosis

Atherosclerosis (AS) is an inflammatory vascular disease that constitutes a major underlying cause of cardiovascular diseases (CVD) and stroke. Infection is a contributing risk factor for AS. Epidemiological evidence has implicated individuals afflicted by periodontitis displaying an increased susceptibility to AS and CVD. This review concisely outlines several prevalent periodontal pathogens identified within atherosclerotic plaques, including Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, and Fusobacterium nucleatum. We review the existing epidemiological evidence elucidating the association between these pathogens and AS-related diseases, and the diverse mechanisms for which these pathogens may engage in AS, such as endothelial barrier disruption, immune system activation, facilitation of monocyte adhesion and aggregation, and promotion of foam cell formation, all of which contribute to the progression and destabilization of atherosclerotic plaques. Notably, the intricate interplay among bacteria underscores the complex impact of periodontitis on AS. In conclusion, advancing our understanding of the relationship between periodontal pathogens and AS will undoubtedly offer invaluable insights and potential therapeutic avenues for the prevention and management of AS.

Periodontal treatment and microbiome-targeted therapy in management of periodontitis-related nonalcoholic fatty liver disease with oral and gut dysbiosis

A growing body of evidence from multiple areas proposes that periodontal disease, accompanied by oral inflammation and pathological changes in the microbiome, induces gut dysbiosis and is involved in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). A subgroup of NAFLD patients have a severely progressive form, namely nonalcoholic steatohepatitis (NASH), which is characterized by histological findings that include inflammatory cell infiltration and fibrosis. NASH has a high risk of further progression to cirrhosis and hepatocellular carcinoma. The oral microbiota may serve as an endogenous reservoir for gut microbiota, and transport of oral bacteria through the gastro-intestinal tract can set up a gut microbiome dysbiosis. Gut dysbiosis increases the production of potential hepatotoxins, including lipopolysaccharide, ethanol, and other volatile organic compounds such as acetone, phenol and cyclopentane. Moreover, gut dysbiosis increases intestinal permeability by disrupting tight junctions in the intestinal wall, leading to enhanced translocation of these hepatotoxins and enteric bacteria into the liver through the portal circulation. In particular, many animal studies support that oral administration of Porphyromonas gingivalis, a typical periodontopathic bacterium, induces disturbances in glycolipid metabolism and inflammation in the liver with gut dysbiosis. NAFLD, also known as the hepatic phenotype of metabolic syndrome, is strongly associated with metabolic complications, such as obesity and diabetes. Periodontal disease also has a bidirectional relationship with metabolic syndrome, and both diseases may induce oral and gut microbiome dysbiosis with insulin resistance and systemic chronic inflammation cooperatively. In this review, we will describe the link between periodontal disease and NAFLD with a focus on basic, epidemiological, and clinical studies, and discuss potential mechanisms linking the two diseases and possible therapeutic approaches focused on the microbiome. In conclusion, it is presumed that the pathogenesis of NAFLD involves a complex crosstalk between periodontal disease, gut microbiota, and metabolic syndrome. Thus, the conventional periodontal treatment and novel microbiome-targeted therapies that include probiotics, prebiotics and bacteriocins would hold great promise for preventing the onset and progression of NAFLD and subsequent complications in patients with periodontal disease.

Shift in the submucosal microbiome of diseased peri-implant sites after non-surgical mechanical debridement treatment

Objectives

The object of this prospective study was to assess the submucosal microbiome shifts in diseased peri-implant sites after non-surgical mechanical debridement therapy.

Materials and methods

Submucosal plaques were collected from 14 healthy implants and 42 diseased implants before and eight weeks after treatment in this prospective study. Mechanical debridement was performed using titanium curettes, followed by irrigation with 0.2% (w/v) chlorhexidine. Subsequently, 16S rRNA gene sequencing was used to analyze the changes in the submucosal microbiome before and after the non-surgical treatment.

Results

Clinical parameters and the submucosal microbiome were statistically comparable before and after mechanical debridement. The Alpha diversity decreased significantly after mechanical debridement. However, the microbial richness varied between the post-treatment and healthy groups. In network analysis, the post-treatment increased the complexity of the network compared to pre-treatment. The relative abundances of some pathogenic species, such as Porphyromonas gingivalis, Tannerella forsythia, Peptostreptococcaceae XIG-6 nodatum, Filifactor alocis, Porphyromonas endodontalis, TM7 sp., and Desulfobulbus sp. HMT 041, decreased significantly following the non-surgical treatment.

Conclusions

Non-surgical treatment for peri-implant diseases using mechanical debridement could provide clinical and microbiological benefits. The microbial community profile tended to shift towards a healthy profile, and submucosal dysbiosis was relieved following mechanical debridement.

Prevotella genus and its related NOD-like receptor signaling pathway in young males with stage III periodontitis

Background

As periodontitis progresses, the oral microbiota community changes dynamically. In this study, we evaluated the dominant bacteria and their roles in the potential pathway in young males with stage III periodontitis.

Methods

16S rRNA sequencing was performed to evaluate variations in the composition of oral bacteria between males with stage I and III periodontitis and identify the dominant bacteria of each group. Function prediction was obtained based on 16S rRNA sequencing data. The inhibitor of the predominant pathway for stage III periodontitis was used to investigate the role of the dominant bacteria in periodontitis in vivo and in vitro.

Results

Chao1 index, Observed Species and Phylogenetic Diversity (PD) whole tree values were significantly higher in the stage III periodontitis group. β-diversity suggested that samples could be divided according to the stages of periodontitis. The dominant bacteria in stage III periodontitis were Prevotella, Prevotella_7, and Dialister, whereas that in stage I periodontitis was Cardiobacterium. KEGG analysis predicted that variations in the oral microbiome may be related to the NOD-like receptor signaling pathway. The inhibitor of this pathway, NOD-IN-1, decreased P. intermedia -induced Tnf-α mRNA expression and increased P. intermedia -induced Il-6 mRNA expression, consistent with the ELISA results. Immunohistochemistry confirmed the down-regulation of TNF-α and IL-6 expressions by NOD-IN-1 in P. intermedia-induced periodontitis.

Conclusion

The composition of the oral bacteria in young males varied according to the stage of periodontitis. The species richness of oral microtia was greater in young males with stage III periodontitis than those with stage I periodontitis. Prevotella was the dominant bacteria in young males with stage III periodontitis, and inhibition of the NOD-like receptor signaling pathway can decrease the periodontal inflammation induced by P. intermedia.

Oral biofilm dysbiosis during experimental periodontitis

OBJECTIVES

We have previously characterized the main osteoimmunological events that occur during ligature periodontitis. This study aims to determine the polymicrobial community shifts that occur during disease development.

METHODS

Periodontitis was induced in C57BL/6 mice using the ligature-induced periodontitis model. Healthy oral mucosa swabs and ligatures were collected every 3 days from 0 to 18 days post-ligature placement. Biofilm samples were evaluated by 16SrRNA gene sequencing (Illumina MiSeq) and QIIME. Time-course changes were determined by relative abundance, diversity, and rank analyses (PERMANOVA, Bonferroni-adjusted).

RESULTS

Microbial differences between health and periodontal inflammation were observed at all phylogenic levels. An evident microbial community shift occurred in 25 genera during the advancement of "gingivitis" (3-6 days) to periodontitis (9-18 days). From day 0 to 18, dramatic changes were identified in Streptococcus levels, with an overall decrease (54.04%-0.02%) as well an overall increase of Enterococcus and Lactobacillus (23.7%-73.1% and 10.1%-70.2%, respectively). Alpha-diversity decreased to its lowest at 3 days, followed by an increase in diversity as disease advancement. Beta-diversity increased after ligature placement, indicating that bone loss develops in response to a greater microbial variability (p = 0.001). Levels of facultative and strict anaerobic bacteria augmented over the course of disease progression, with a total of eight species significantly different during the 18-day period.

CONCLUSION

The data supports that murine gingival inflammation and alveolar bone loss develop in response to microbiome shifts. Bacterial diversity increased during progression to bone loss. These findings further support the utilization of the periodontitis ligature model for microbial shift analysis under different experimental conditions.

Lipopolysaccharide from Porphyromonas gingivalis, but Not from Porphyromonas endodontalis, Induces Macrophage M1 Profile

Apical Lesions of Endodontic Origin (ALEO) are initiated by polymicrobial endodontic canal infection. Porphyromonas gingivalis (Pg) and Porphyromonas endodontalis (Pe) lipopolysaccharides (LPS) can induce a pro-inflammatory macrophage response through their recognition by TLR2 and TLR4. However, polarization responses induced by Pg and/or Pe LPS in macrophages are not fully understood. We aimed to characterize the polarization profiles of macrophages differentiated from THP-1 cells following Pg and/or Pe LPS stimulation from reference strain and clinical isolates. A modified LPS purification protocol was implemented and the electrophoretic LPS profiles were characterized. THP-1 human monocytes differentiated to macrophages were stimulated with Pg and Pe LPS. Polarization profiles were characterized through cell surface markers and secreted cytokines levels after 24 h of stimulation. TLR2 and TLR4 cell surfaces and transcriptional levels were determined after 24 or 2 h of LPS stimulation, respectively. LPS from Pg induced a predominant M1 profile in macrophages evidenced by changes in the expression of the surface marker CD64 and pro-inflammatory cytokine profiles, TNF-α, IL-1β, IL-6, and IL-12. Pe LPS was unable to induce a significant response. TLR2 and TLR4 expressions were neither modified by Pg or Pe LPS. Pg LPS, but not Pe LPS, induced a macrophage M1 Profile.

Super-taxon in human microbiome are identified to be associated with colorectal cancer

Background

Microbial communities in the human body, also known as human microbiota, impact human health, such as colorectal cancer (CRC). However, the different roles that microbial communities play in healthy and disease hosts remain largely unknown. The microbial communities are typically recorded through the taxa counts of operational taxonomic units (OTUs). The sparsity and high correlations among OTUs pose major challenges for understanding the microbiota-disease relation. Furthermore, the taxa data are structured in the sense that OTUs are related evolutionarily by a hierarchical structure.

Results

In this study, we borrow the idea of super-variant from statistical genetics, and propose a new concept called super-taxon to exploit hierarchical structure of taxa for microbiome studies, which is essentially a combination of taxonomic units. Specifically, we model a genus which consists of a set of OTUs at low hierarchy and is designed to reflect both marginal and joint effects of OTUs associated with the risk of CRC to address these issues. We first demonstrate the power of super-taxon in detecting highly correlated OTUs. Then, we identify CRC-associated OTUs in two publicly available datasets via a discovery-validation procedure. Specifically, four species of two genera are found to be associated with CRC: Parvimonas micra, Parvimonas sp., Peptostreptococcus stomatis, and Peptostreptococcus anaerobius. More importantly, for the first time, we report the joint effect of Parvimonas micra and Parvimonas sp. (p = 0.0084) as well as that of Peptostrepto-coccus stomatis and Peptostreptococcus anaerobius (p = 8.21e-06) on CRC. The proposed approach provides a novel and useful tool for identifying disease-related microbes by taking the hierarchical structure of taxa into account and further sheds new lights on their potential joint effects as a community in disease development.

Conclusions

Our work shows that proposed approaches are effective to study the microbiota-disease relation taking into account for the sparsity, hierarchical and correlated structure among microbes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12859-022-04786-9.

Discrimination of Bacterial Community Structures among Healthy, Gingivitis, and Periodontitis Statuses through Integrated Metatranscriptomic and Network Analyses

Periodontal disease is an inflammatory condition caused by polymicrobial infection. The inflammation is initiated at the gingiva (gingivitis) and then extends to the alveolar bone, leading to tooth loss (periodontitis). Previous studies have shown differences in bacterial composition between periodontal healthy and diseased sites. However, bacterial metabolic activities during the health-to-periodontitis microbiome shift are still inadequately understood. This study was performed to investigate the bacterial characteristics of healthy, gingivitis, and periodontitis statuses through metatranscriptomic analysis. Subgingival plaque samples of healthy, gingivitis, and periodontitis sites in the same oral cavity were collected from 21 patients. Bacterial compositions were then determined based on 16S rRNA reads; taxonomic and functional profiles derived from genes based on mRNA reads were estimated. The results showed clear differences in bacterial compositions and functional profiles between healthy and periodontitis sites. Co-occurrence networks were constructed for each group by connecting two bacterial species if their mRNA abundances were positively correlated. The clustering coefficient values were 0.536 for healthy, 0.600 for gingivitis, and 0.371 for periodontitis sites; thus, network complexity increased during gingivitis development, whereas it decreased during progression to periodontitis. Taxa, including Eubacterium nodatum, Eubacterium saphenum, Filifactor alocis, and Fretibacterium fastidiosum, showed greater transcriptional activities than those of red complex bacteria, in conjunction with disease progression. These taxa were associated with periodontal disease progression, and the health-to-periodontitis microbiome shift was accompanied by alterations in bacterial network structure and complexity.

IMPORTANCE The characteristics of the periodontal microbiome influence clinical periodontal status. Gingivitis involves reversible gingival inflammation without alveolar bone resorption. In contrast, periodontitis is an irreversible disease characterized by inflammatory destruction in both soft and hard tissues. An imbalance of the microbiome is present in both gingivitis and periodontitis. However, differences in microbiomes and their functional activities in the healthy, gingivitis, and periodontitis statuses are still inadequately understood. Furthermore, some inflamed gingival statuses do not consistently cause attachment loss. In this study, metatranscriptomic analyses were used to investigate the specific bacterial composition and gene expression patterns of the microbiomes of the healthy, gingivitis, and periodontitis statuses. In addition, co-occurrence network analysis revealed that the gingivitis site included features of networks observed in both the healthy and periodontitis sites. These results provide transcriptomic evidence to support gingivitis as an intermediate state between the healthy and periodontitis statuses.

Bacteriophage manipulation of the microbiome associated with tumour microenvironments-can this improve cancer therapeutic response?

Some cancer treatment failures have been attributed to the tumour microbiota, with implications that microbiota manipulation may improve treatment efficacy. While antibiotics have been used to control bacterial growth, their dysbiotic effects on the microbiome, failure to penetrate biofilms and decreased efficacy due to increasing antimicrobial resistance by bacteria, suggest alternatives are needed. Bacteriophages may provide a precise means for targeting oncobacteria whose relative abundance is increased in tumour tissue microbiomes. Fusobacterium, Streptococcus, Peptostreptococcus, Prevotella, Parvimonas, and Treponema species are prevalent in tumour tissue microbiomes of some cancers. They may promote cancer growth by dampening immunity, stimulating release of proinflammatory cytokines, and directly interacting with cancer cells to stimulate proliferation. Lytic bacteriophages against some of these oncobacteria have been isolated and characterised. The search continues for others. The possibility exists for their testing as adjuncts to complement existing therapies. In this review, we highlight the role of oncobacteria, specifically those whose relative abundance in the intra-tumour microbiome is increased, and discuss the potential for bacteriophages against these micro-organisms to augment existing cancer therapies. The capacity for bacteriophages to modulate immunity and kill specific bacteria makes them suitable candidates to manipulate the tumour microbiome and negate the effects of these oncobacteria.

Porphyromonas gingivalis lipopolysaccharide affects oral epithelial connections via pyroptosis

Background/purpose

Pyroptosis is a form of programmed cell death dependent on the activation of caspase-1. Porphyromonas gingivalis (P. gingivalis) is a major pathogenic bacterium in periodontitis and its lipopolysaccharide (LPS) can trigger inflammation. However, whether P. gingivalis-LPS affects epithelial connections or triggers pyroptosis in the gingival epithelium is unknown.

Materials and methods

Gingival samples from human donors were collected and the expression levels of E-cadherin, nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3), caspase-1/4/5, interleukin (IL)-18, and IL-1β were examined. P. gingivalis-LPS was injected into rat gingival sulcus to establish gingivitis models, and the expression levels of E-cadherin, NLRP3, caspase-1/11, IL-18, and IL-1β were compared via immunohistochemistry. The mRNA levels of E-cadherin, caspase-1, IL-18, and IL-1β were evaluated in oral mucosa epithelial cells (OMECs) and rat gingival tissues.

Results

In the present study, NLRP3 (p < 0.01), caspase-1 (p < 0.01), caspase-4 (p = 0.044), and IL-18 (p = 0.036) expression was greater in the human inflammatory gingival samples, whereas E-cadherin (p = 0.045) had the opposite presentation. Gingivitis models were successfully established in rats with the injection of P. gingivalis-LPS. NLRP3 (p = 0.015), caspase-1 (p < 0.01), caspase-11 (p < 0.01), and IL-18 (p = 0.041) were upregulated, whereas E-cadherin (p = 0.038) expression was decreased. Furthermore, E-cadherin mRNA was decreased while caspase-1, IL-18, and IL-1β mRNA levels were increased. The addition of a caspase-1 inhibitor reversed the expression changes.

Conclusion

P. gingivalis-LPS may effectively destroy the epithelial connection by triggering pyroptosis.

Association between metabolic syndrome and periodontitis: The role of lipids, inflammatory cytokines, altered host response, and the microbiome

Periodontitis has been associated with many systemic diseases and conditions, including metabolic syndrome. Metabolic syndrome is a cluster of conditions that occur concomitantly and together they increase the risk of cardiovascular disease and double the risk of type 2 diabetes. In this review, we focus on the association between metabolic syndrome and periodontitis; however, we also include information on diabetes mellitus and cardiovascular disease, since these two conditions are significantly intertwined with metabolic syndrome. With regard to periodontitis and metabolic syndrome, to date, the vast majority of studies point to an association between these two conditions and also demonstrate that periodontitis can contribute to the development of, or can worsen, metabolic syndrome. Evaluating the effect of metabolic syndrome on the salivary microbiome, data presented herein support the hypothesis that the salivary bacterial profile is altered in metabolic syndrome patients compared with healthy patients. Considering periodontitis and these three conditions, the vast majority of human and animal studies point to an association between periodontitis and metabolic syndrome, diabetes, and cardiovascular disease. Moreover, there is evidence to suggest that metabolic syndrome and diabetes can alter the oral microbiome. However, more studies are needed to fully understand the influence these conditions have on each other.

NOD1-Targeted Immunonutrition Approaches: On the Way from Disease to Health

Immunonutrition appears as a field with great potential in modern medicine. Since the immune system can trigger serious pathophysiological disorders, it is essential to study and implement a type of nutrition aimed at improving immune system functioning and reinforcing it individually for each patient. In this sense, the nucleotide-binding oligomerization domain-1 (NOD1), one of the members of the pattern recognition receptors (PRRs) family of innate immunity, has been related to numerous pathologies, such as cancer, diabetes, or cardiovascular diseases. NOD1, which is activated by bacterial-derived peptidoglycans, is known to be present in immune cells and to contribute to inflammation and other important pathways, such as fibrosis, upon recognition of its ligands. Since immunonutrition is a significant developing research area with much to discover, we propose NOD1 as a possible target to consider in this field. It is relevant to understand the cellular and molecular mechanisms that modulate the immune system and involve the activation of NOD1 in the context of immunonutrition and associated pathological conditions. Surgical or pharmacological treatments could clearly benefit from the synergy with specific and personalized nutrition that even considers the health status of each subject.

Parvimonas micra as a putative non-invasive faecal biomarker for colorectal cancer

The use of faecal microbial markers as non-invasive biomarkers for colorectal cancer (CRC) has been suggested, but not fully elucidated. Here, we have evaluated the importance of Parvimonas micra as a potential non-invasive faecal biomarker in CRC and its relation to other microbial biomarkers. The levels of P. micra, F. nucleatum and clbA + bacteria were quantified using qPCR in faecal samples from a population-based cohort of patients undergoing colonoscopy due to symptoms from the large bowel. The study included 38 CRC patients, 128 patients with dysplasia and 63 controls. The results were validated in a second consecutive CRC cohort including faecal samples from 238 CRC patients and 94 controls. We found significantly higher levels of P. micra in faecal samples from CRC patients compared to controls. A test for P. micra could detect CRC with a specificity of 87.3% and a sensitivity of 60.5%. In addition, we found that combining P. micra with other microbial markers, could further enhance test sensitivity. Our findings support the potential use of P. micra as a non-invasive biomarker for CRC. Together with other microbial faecal markers, P. micra may identify patients with "high risk" microbial patterns, indicating increased risk and incidence of cancer.

LncRNA MAFG-AS1 regulates human periodontal ligament stem cell proliferation and Toll-like receptor 4 expression

LncRNA MAFG-AS1 is predicted to interact with miR-146a, which can target Toll-like receptor 4 (TLR4), a key player in periodontitis. This study aimed to investigate the roles of MAFG-AS1 in periodontitis. It was observed that MAFG-AS1 was downregulated in the human periodontal ligament stem cells (PDLSCs) derived from periodontitis-affected teeth. Dual-luciferase assay revealed that co-transfection of MAFG-AS1 expression vector and miR-146a mimic showed significantly lower relative luciferase activity comparing to co-transfection of MAFG-AS1 expression vector and negative control (NC) miRNA. However, MAFG-AS1 and miR-146a failed to affect each other. Interestingly, MAFG-AS1 overexpression led to the upregulated TLR4. In addition, MAFG-AS1 overexpression also led to the inhibited proliferation of PDLSCs. Therefore, MAFG-AS1 may regulate the proliferation of PDLSCs and the expression of TLR4 to participate in periodontitis.

Alteration of the abundance of Parvimonas micra in the gut along the adenoma-carcinoma sequence

Parvimonas micra (P. micra) is reported to be associated with colorectal cancer (CRC). However, its association with colorectal adenoma (CRA) and its role in the initiation of colorectal tumors remain unknown. The present study aimed to clarify the relationship between P. micra and CRA and CRC by exploring the changes of P. micra abundance in an adenoma-carcinoma sequence in a new cohort and 4 public sequencing datasets. To investigate the alterations of P. micra abundance in the gut along the adenoma-carcinoma sequence, quantitative PCR (qPCR) was conducted to measure the relative abundance of P. micra in fecal samples from 277 subjects (128 patients with CRA, 66 patients with CRC and 83 healthy individuals, as controls) who underwent colonoscopy as outpatients. Then, the relative abundance of P. micra was analyzed in fecal samples from 596 subjects (185 healthy controls, 158 CRC, 253 CRA) in four public 16S rRNA sequencing datasets. The qPCR results demonstrated that the CRA group had an abundance of P. micra (P=0.2) similar to that of the healthy control group, while the CRC group had a significantly increased abundance (P=8.2×10⁻¹¹). The level of P. micra effectively discriminated patients with CRC from healthy controls, while it poorly discriminated patients with CRA from healthy controls; with an area under the receiver operating characteristic curve of 0.867 for patients with CRC and 0.554 for patients with CRA. The same pattern of the alteration of P. micra abundance, which was low in healthy controls and patients with CRA but elevated in patients with CRC, was found in all four public sequencing datasets. These results suggested that P. micra was closely associated with, and may serve as a diagnostic marker for, CRC but not CRA. Moreover, it was indicated that P. micra may be an opportunistic pathogen of CRC, which may promote CRC development but serve a limited role in tumorigenesis.

Whole Transcriptome Analysis Reveals That Filifactor alocis Modulates TNFα-Stimulated MAPK Activation in Human Neutrophils

Periodontitis is an irreversible, bacteria-induced, chronic inflammatory disease that compromises the integrity of tooth-supporting tissues and adversely affects systemic health. As the immune system's first line of defense against bacteria, neutrophils use their microbicidal functions in the oral cavity to protect the host against periodontal disease. However, periodontal pathogens have adapted to resist neutrophil microbicidal mechanisms while still propagating inflammation, which provides essential nutrients for the bacteria to proliferate and cause disease. Advances in sequencing technologies have recognized several newly appreciated bacteria associated with periodontal lesions such as the Gram-positive anaerobic rod, Filifactor alocis. With the discovery of these oral bacterial species, there is also a growing need to assess their pathogenic potential and determine their contribution to disease progression. Currently, few studies have addressed the pathogenic mechanisms used by oral bacteria to manipulate the neutrophil functional responses at the level of the transcriptome. Thus, this study aims to characterize the global changes at the gene expression level in human neutrophils during infection with F. alocis. Our results indicate that the challenge of human neutrophils with F. alocis results in the differential expression of genes involved in multiple neutrophil effector functions such as chemotaxis, cytokine and chemokine signaling pathways, and apoptosis. Moreover, F. alocis challenges affected the expression of components from the TNF and MAPK kinase signaling pathways. This resulted in transient, dampened p38 MAPK activation by secondary stimuli TNFα but not by fMLF. Functionally, the F. alocis-mediated inhibition of p38 activation by TNFα resulted in decreased cytokine production but had no effect on the priming of the respiratory burst response or the delay of apoptosis by TNFα. Since the modulatory effect was characteristic of viable F. alocis only, we propose this as one of F. alocis' mechanisms to control neutrophils and their functional responses.

Microbiome in Colorectal Cancer: How to Get from Meta-omics to Mechanism?

Mounting evidence from metagenomic analyses suggests that a state of pathological microbial imbalance or dysbiosis is prevalent in the gut of patients with colorectal cancer. Several bacterial taxa have been identified of which representative isolate cultures interact with human cancer cells in vitro and trigger disease pathways in animal models. However, how the complex interrelationships in dysbiotic communities may be involved in cancer pathogenesis remains a crucial question. Here, we provide a survey of current knowledge of the gut microbiome in colorectal cancer. Moving beyond observational studies, we outline new experimental approaches for gaining ecosystem-level mechanistic understanding of the gut microbiome's role in cancer pathogenesis.

Salivary concentrations of macrophage activation-related chemokines are influenced by non-surgical periodontal treatment: a 12-week follow-up study

Background: During periodontal inflammation, bacteria induces chemokine expression and migration of various inflammatory cells. The aim of the study was to learn if periodontal treatment alters salivary concentrations of macrophage activation-related chemokines and if such alterations correlate with abundance of periodontitis-associated bacteria. Methods: Twenty-five patients with periodontitis completed the study (NCT02913248 at clinicaltrials.gov). Periodontal parameters and stimulated saliva samples were obtained at baseline and 2, 6 and 12 weeks after non-surgical periodontal treatment. Salivary concentrations of monocyte chemoattractant proteins (MCP-1-4), macrophage-derived chemokine (MDC), macrophage migration inhibitory factor (MIF), monokine induced by interferon-gamma (MIG), macrophage inflammatory protein (MIP-1α) and interferon-inducible protein (IP-10) were quantified using the Luminex® xMAP™ technique and abundance of bacteria was quantified using next-generation sequencing. Results: The treatment improved all periodontal parameters and caused an increase in the concentrations of MCP-2, MDC and MIP-1α at week 12 compared to baseline, week 2 and week 6, respectively. Salivary concentrations of MCP-1-2, MDC, MIG, MIP-1α and IP-10 correlated with the abundance of specific periodontitis-associated bacteria. Conclusions: Periodontal treatment impacts salivary concentrations of MCP-2, MDC and MIP-1α, which correlate with the abundance of specific periodontitis-associated bacteria. This indicates that these chemokines reflect periodontal status and possess potential in illustrating a response to treatment.

Effect of poly(3-hydroxyalkanoates) as natural polymers on mesenchymal stem cells

Mesenchymal stem cells (MSCs) are stromal multipotent stem cells that can differentiate into multiple cell types, including fibroblasts, osteoblasts, chondrocytes, adipocytes, and myoblasts, thus allowing them to contribute to the regeneration of various tissues, especially bone tissue. MSCs are now considered one of the most promising cell types in the field of tissue engineering. Traditional petri dish-based culture of MSCs generate heterogeneity, which leads to inconsistent efficacy of MSC applications. Biodegradable and biocompatible polymers, poly(3-hydroxyalkanoates) (PHAs), are actively used for the manufacture of scaffolds that serve as carriers for MSC growth. The growth and differentiation of MSCs grown on PHA scaffolds depend on the physicochemical properties of the polymers, the 3D and surface microstructure of the scaffolds, and the biological activity of PHAs, which was discovered in a series of investigations. The mechanisms of the biological activity of PHAs in relation to MSCs remain insufficiently studied. We suggest that this effect on MSCs could be associated with the natural properties of bacteria-derived PHAs, especially the most widespread representative poly(3-hydroxybutyrate) (PHB). This biopolymer is present in the bacteria of mammalian microbiota, whereas endogenous poly(3-hydroxybutyrate) is found in mammalian tissues. The possible association of PHA effects on MSCs with various biological functions of poly(3-hydroxybutyrate) in bacteria and eukaryotes, including in humans, is discussed in this paper.

LncRNA papillary thyroid carcinoma susceptibility candidate 3 (PTCSC3) regulates the proliferation of human periodontal ligament stem cells and toll-like receptor 4 (TLR4) expression to improve periodontitis

Background

LncRNA PTCSC3 is a known tumor suppressor, while its roles in other human diseases are unclear.

Methods

All participants were admitted by The second Affiliated Hospital, School of Medicine, Zhejiang University from January 2016 to January 2018. RT-qPCR, Vectors, cell transfection, In vitro cell proliferation assay and western blot were using to carry out the experiment.

Results

In this study we found that PTCSC3 was downregulated, while toll-like receptor 4 (TLR4) was upregulated in periodontal ligament stem cells (PDLSCs) isolated from periodontitis affected teeth that in PDLSCs isolated from healthy teeth. Expression levels of PTCSC3 and TLR4 were only significantly and inversely correlated in PDLSCs isolated from periodontitis affected teeth but not in PDLSCs isolated from healthy teeth. PTCSC3 overexpression led to the downregulation of TLR4 in PDLSCs isolated from periodontitis affected teeth, while TLR4 overexpression failed to significantly affect PTCSC3. PTCSC3 overexpression also led to the inhibited proliferation of periodontitis-affected PDLSCs.

Conclusions

Therefore, lncRNA PTCSC3 may regulate the proliferation of PDLSCs and TLR4 expression to improve periodontitis.

The synergistic effect of NOD2 and TLR4 on the activation of autophagy in human submandibular gland inflammation

BACKGROUND

Sialadenitis is a nonneoplastic disease that causes salivary dysfunction. Autophagy may be involved in helping protect salivary function when the salivary gland is impaired; this process is primarily activated by sensors of innate immunity, such as Toll-like receptors and nucleotide-binding oligomerization domain (NOD)-like receptors. The role of these pattern recognition receptors (PRRs) in the regulation of salivary gland tissue defense and homeostasis has been underappreciated. This study hypothesized that NOD2 and TLR4 have a synergistic effect on the activation of autophagy in human submandibular gland (HSG) inflammation.

METHODS

Submandibular gland inflammation was modeled by treating HSG cell lines in vitro with muramyl dipeptide (MDP) and lipopolysaccharide (LPS) for 24 hours. The mRNA and protein expression of NOD2, TLR4 and autophagy-related proteins (ATG5, LC3, Beclin1) were evaluated by real-time PCR and Western blot. Immunohistochemistry and double immunofluorescence were used to analyze the presence, distribution and colocalization of the aforementioned indicators in HSG tissues.

RESULT

The mRNA and protein expression of autophagy-related proteins were significantly increased in HSG cells costimulated with LPS and MDP for 24 hours. NOD2, TLR4 and the autophagy-related proteins were also highly expressed in residual acini and dilated ducts of chronic submandibular sialadenitis tissues. In addition, PRRs and autophagy markers were obviously colocalized in chronic submandibular sialadenitis tissues and HSG cells.

CONCLUSION

TLR4 and NOD2 have unique expression sites in salivary glands, and they may synergistically activate autophagy in salivary glands under conditions of inflammation.

NLRP6 Induces Pyroptosis by Activation of Caspase-1 in Gingival Fibroblasts

NLRP6, a member of the nucleotide-binding domain, leucine-rich repeat-containing (NLR) innate immune receptor family, has been reported to participate in inflammasome formation. Activation of inflammasome triggers a caspase-1-dependent programming cell death called pyroptosis. However, whether NLRP6 induces pyroptosis has not been investigated. In this study, we showed that NLRP6 overexpression activated caspase-1 and gasdermin-D and then induced pyroptosis of human gingival fibroblasts, resulting in release of proinflammatory mediators interleukin (IL)-1β and IL-18. Moreover, NLRP6 was highly expressed in gingival tissue of periodontitis compared with healthy controls. Porphyromonas gingivalis, which is a commensal bacterium and has periodontopathic potential, induced pyroptosis of gingival fibroblasts by activation of NLRP6. Together, we, for the first time, identified that NLRP6 could induce pyroptosis of gingival fibroblasts by activation of caspase-1 and may play a role in periodontitis.

Oral Bacterial and Fungal Microbiome Impacts Colorectal Carcinogenesis

Host's physiology is significantly influenced by microbiota colonizing the epithelial surfaces. Complex microbial communities contribute to proper mucosal barrier function, immune response, and prevention of pathogen invasion and have many other crucial functions. The oral cavity and large intestine are distant parts of the digestive tract, both heavily colonized by commensal microbiota. Nevertheless, they feature different proportions of major bacterial and fungal phyla, mostly due to distinct epithelial layers organization and different oxygen levels. A few obligate anaerobic strains inhabiting the oral cavity are involved in the pathogenesis of oral diseases. Interestingly, these microbiota components are also enriched in gut inflammatory and tumor tissue. An altered microbiota composition - dysbiosis - and formation of polymicrobial biofilms seem to play important roles in the development of oral diseases and colorectal cancer. In this review, we describe the differences in composition of commensal microbiota in the oral cavity and large intestine and the mechanisms by which microbiota affect the inflammatory and carcinogenic response of the host.

Immune response profiling of primary monocytes and oral keratinocytes to different Tannerella forsythia strains and their cell surface mutants

The oral pathogen Tannerella forsythia possesses a unique surface (S-) layer with a complex O-glycan containing a bacterial sialic acid mimic in the form of either pseudaminic acid or legionaminic acid at its terminal position. We hypothesize that different T. forsythia strains employ these stereoisomeric sugar acids for interacting with the immune system and resident host tissues in the periodontium. Here, we show how T. forsythia strains ATCC 43037 and UB4 displaying pseudaminic acid and legionaminic acid, respectively, and selected cell surface mutants of these strains modulate the immune response in monocytes and human oral keratinocytes (HOK) using a multiplex immunoassay. When challenged with T. forsythia, monocytes secrete proinflammatory cytokines, chemokines and vascular endothelial growth factor (VEGF) with the release of interleukin-1β (IL-1β) and IL-7 being differentially regulated by the two T. forsythia wild-type strains. Truncation of the bacteria's O-glycan leads to significant reduction of IL-1β and regulates macrophage inflammatory protein-1. HOK infected with T. forsythia produce IL-1Ra, chemokines and VEGF. Although the two wild-type strains elicit preferential immune responses for IL-8, both truncation of the O-glycan and deletion of the S-layer result in significantly increased release of IL-8, granulocyte-macrophage colony-stimulating factor and monocyte chemoattractant protein-1. Through immunofluorescence and confocal laser scanning microscopy of infected HOK we additionally show that T. forsythia is highly invasive and tends to localize to the perinuclear region. This indicates, that the T. forsythia S-layer and attached sugars, particularly pseudaminic acid in ATCC 43037, contribute to dampening the response of epithelial tissues to initial infection and hence play a pivotal role in orchestrating the bacterium's virulence.

Exploring the microbiome of healthy and diseased peri-implant sites using Illumina sequencing

AIM

To compare the microbiome of healthy (H) and diseased (P) peri-implant sites and determine the core peri-implant microbiome.

MATERIALS AND METHODS

Submucosal biofilms from 32 H and 35 P sites were analysed using 16S rRNA sequencing (MiSeq, Illumina), QIIME and HOMINGS. Differences between groups were determined using principal coordinate analysis (PCoA), t tests and Wilcoxon rank sum test and FDR-adjusted. The peri-implant core microbiome was determined.

RESULTS

PCoA showed partitioning between H and P at all taxonomic levels. Bacteroidetes, Spirochetes and Synergistetes were higher in P, while Actinobacteria prevailed in H (p < .05). Porphyromonas and Treponema were more abundant in P while Rothia and Neisseria were higher in H (p < .05). The core peri-implant microbiome contained Fusobacterium, Parvimonas and Campylobacter sp. T. denticola, and P. gingivalis levels were higher in P, as well as F. alocis, F. fastidiosum and T. maltophilum (p < .05).

CONCLUSION

The peri-implantitis microbiome is commensal-depleted and pathogen-enriched, harbouring traditional and new pathogens. The core peri-implant microbiome harbours taxa from genera often associated with periodontal inflammation.

Quantification by qPCR of Pathobionts in Chronic Periodontitis: Development of Predictive Models of Disease Severity at Site-Specific Level

Currently, there is little evidence available on the development of predictive models for the diagnosis or prognosis of chronic periodontitis based on the qPCR quantification of subgingival pathobionts. Our objectives were to: (1) analyze and internally validate pathobiont-based models that could be used to distinguish different periodontal conditions at site-specific level within the same patient with chronic periodontitis; (2) develop nomograms derived from predictive models. Subgingival plaque samples were obtained from control and periodontal sites (probing pocket depth and clinical attachment loss <4 mm and >4 mm, respectively) from 40 patients with moderate-severe generalized chronic periodontitis. The samples were analyzed by qPCR using TaqMan probes and specific primers to determine the concentrations of Actinobacillus actinomycetemcomitans (Aa), Fusobacterium nucleatum (Fn), Parvimonas micra (Pm), Porphyromonas gingivalis (Pg), Prevotella intermedia (Pi), Tannerella forsythia (Tf), and Treponema denticola (Td). The pathobiont-based models were obtained using multivariate binary logistic regression. The best models were selected according to specified criteria. The discrimination was assessed using receiver operating characteristic curves and numerous classification measures were thus obtained. The nomograms were built based on the best predictive models. Eight bacterial cluster-based models showed an area under the curve (AUC) ≥0.760 and a sensitivity and specificity ≥75.0%. The PiTfFn cluster showed an AUC of 0.773 (sensitivity and specificity = 75.0%). When Pm and AaPm were incorporated in the TdPiTfFn cluster, we detected the two best predictive models with an AUC of 0.788 and 0.789, respectively (sensitivity and specificity = 77.5%). The TdPiTfAa cluster had an AUC of 0.785 (sensitivity and specificity = 75.0%). When Pm was incorporated in this cluster, a new predictive model appeared with better AUC and specificity values (0.787 and 80.0%, respectively). Distinct clusters formed by species with different etiopathogenic role (belonging to different Socransky’s complexes) had a good predictive accuracy for distinguishing a site with periodontal destruction in a periodontal patient. The predictive clusters with the lowest number of bacteria were PiTfFn and TdPiTfAa, while TdPiTfAaFnPm had the highest number. In all the developed nomograms, high concentrations of these clusters were associated with an increased probability of having a periodontal site in a patient with chronic periodontitis.

Interplay of Toll-Like Receptor 9, Myeloid Cells, and Deubiquitinase A20 in Periodontal Inflammation

Toll-like receptor 9 (TLR9)-deficient (TLR9^-/-) mice are resistant to periodontitis, a disease characterized by a dysbiotic microbiota and deregulated immune response and resulting in tooth loss and various systemic conditions. However, the mechanisms and biological pathways by which TLR9 instigates periodontal inflammation are yet to be identified. In a ligature-induced model of periodontitis, we demonstrate that TLR9^-/- mice exhibited significantly less alveolar bone loss than their wild-type (WT) counterparts. Consistent with the disease phenotype, gingival tissues showed significantly more inflammatory cell infiltration in the WT ligated but not in the TLR9^-/- ligated mice compared to the unligated controls. The peritoneal infection model using Porphyromonas gingivalis, a keystone pathogen for periodontitis, revealed reduced neutrophils in TLR9^-/- mice on day 1 postinfection compared to the levels in WT mice. Transcriptomics analyses showed increased expression of A20 (tumor necrosis factor alpha [TNF-α]-induced protein 3 [TNFAIP3]), an inhibitor of the NF-κB pathway and a negative regulator of TLR signaling, in ligated TLR9^-/- mouse gingival tissues compared to its expression in the WT. Ex vivo, TLR9^-/- bone marrow-derived macrophages produced more A20 than WT cells following P. gingivalis challenge. Clinically, A20 was modestly upregulated in human gingival tissue specimens from chronic periodontitis patients, further confirming the biological relevance of A20 in periodontal inflammation. We conclude that TLR9 modulates periodontal disease progression at both the cellular and molecular level and identify A20 as a novel downstream signaling molecule in the course of periodontal inflammation. Understanding the regulation of the TLR9 signaling pathway and the involvement of A20 as a limiting factor of inflammation will uncover alternative therapeutic targets to treat periodontitis and other chronic inflammatory diseases.

Human neutrophils and oral microbiota: a constant tug-of-war between a harmonious and a discordant coexistence

Neutrophils are a major component of the innate host response, and the outcome of the interaction between the oral microbiota and neutrophils is a key determinant of oral health status. The composition of the oral microbiome is very complex and different in health and disease. Neutrophils are constantly recruited to the oral cavity, and their protective role is highlighted in cases where their number or functional responses are impeded, resulting in different forms of periodontal disease. Periodontitis, one of the more severe and irreversible forms of periodontal disease, is a microbial-induced chronic inflammatory disease that affects the gingival tissues supporting the tooth. This chronic inflammatory disease is the result of a shift of the oral bacterial symbiotic community to a dysbiotic more complex community. Chronic inflammatory infectious diseases such as periodontitis can occur because the pathogens are able to evade or disable the innate immune system. In this review, we discuss how human neutrophils interact with both the symbiotic and the dysbiotic oral community; an understanding of which is essential to increase our knowledge of the periodontal disease process.