Genetic control of susceptibility to Porphyromonas gingivalis-induced alveolar bone loss in mice

Alterations in salivary biomarkers in relation to periodontal health and obesity among Hong Kong adolescents

OBJECTIVES

To explore the association among salivary biomarkers, periodontal inflammation, and adiposity status in adolescents.

METHODS

This study included 180 Hong Kong adolescents aged 12-15 years. Anthropometric measurements including central obesity surrogate, waist-to-height ratio (WHtR), and dental examinations were conducted. The participants were classified into four groups as follows: with normal WHtR and less extensive periodontal inflammation (NW+LP); with high WHtR and less extensive periodontal inflammation (HW+LP); with normal WHtR and more extensive periodontal inflammation (NW+P); and with high WHtR and more extensive periodontal inflammation (HW+P). Saliva were collected to measure salivary physicochemical parameters, total bacterial load, and levels of protein biomarkers including secretory phospholipase A2 group IIA (sPLA2-IIA) and interleukin-6 (IL-6). Data were analysed by Kruskal-Wallis test and Spearman correlation coefficient.

RESULTS

Salivary IL-6 levels and sPLA2-IIA and IL-6 output differed significantly between groups (P = 0.041, 0.027, and 0.043, respectively). The NW+P group had significantly higher salivary IL-6 output than the NW+LP group (P = 0.034) and significantly lower salivary sPLA2-IIA output than the HW+LP group (P = 0.038). Salivary IL-6 levels were negatively correlated with the number of sextants with healthy gingivae and positively correlated with salivary sPLA2-IIA levels in participants with normal WHtR. Salivary sPLA2-IIA levels were negatively correlated with total salivary bacterial load in participants with high WHtR.

CONCLUSIONS

Salivary IL-6 levels were associated with the extent of periodontal inflammation in participants with normal WHtR but not in those with high WHtR. Adolescents with different adiposity status may have different mechanisms of periodontal inflammation.

CLINICAL SIGNIFICANCE

Investigating salivary biomarkers of periodontal health holds potential benefits in identifying individuals at risk and customizing oral health promotion strategies for individuals with varying levels of adiposity, even as early as adolescence.

Erythropoietin receptor signal is crucial for periodontal ligament stem cell-based tissue reconstruction in periodontal disease

Alveolar bone loss caused by periodontal disease eventually leads to tooth loss. Periodontal ligament stem cells (PDLSCs) are the tissue-specific cells for maintaining and repairing the periodontal ligament, cementum, and alveolar bone. Here, we investigated the role of erythropoietin receptor (EPOR), which regulates the microenvironment-modulating function of mesenchymal stem cells, in PDLSC-based periodontal therapy. We isolated PDLSCs from patients with chronic periodontal disease and healthy donors, referred to as PD-PDLSCs and Cont-PDLSCs, respectively. PD-PDLSCs exhibited reduced potency of periodontal tissue regeneration and lower expression of EPOR compared to Cont-PDLSCs. EPOR-silencing suppressed the potency of Cont-PDLSCs mimicking PD-PDLSCs, whereas EPO-mediated EPOR activation rejuvenated the reduced potency of PD-PDLSCs. Furthermore, we locally transplanted EPOR-silenced and EPOR-activated PDLSCs into the gingiva around the teeth of ligament-induced periodontitis model mice and demonstrated that EPOR in PDLSCs participated in the regeneration of the periodontal ligament, cementum, and alveolar bone in the ligated teeth. The EPOR-mediated paracrine function of PDLSCs maintains periodontal immune suppression and bone metabolic balance via osteoclasts and osteoblasts in the periodontitis model mice. Taken together, these results suggest that EPOR signaling is crucial for PDLSC-based periodontal regeneration and paves the way for the development of novel options for periodontal therapy.

A novel macrolide-Del-1 axis to regenerate bone in old age

Aging is associated with increased susceptibility to chronic inflammatory bone loss disorders, such as periodontitis, in large part due to the impaired regenerative potential of aging tissues. DEL-1 exerts osteogenic activity and promotes bone regeneration. However, DEL-1 expression declines with age. Here we show that systemically administered macrolide antibiotics and a non-antibiotic erythromycin derivative, EM-523, restore DEL-1 expression in 18-month-old ("aged") mice while promoting regeneration of bone lost due to naturally occurring age-related periodontitis. These compounds failed to induce bone regeneration in age-matched DEL-1-deficient mice. Consequently, these drugs promoted DEL-1-dependent functions, including alkaline phosphatase activity and osteogenic gene expression in the periodontal tissue while inhibiting osteoclastogenesis, leading to net bone growth. Macrolide-treated aged mice exhibited increased skeletal bone mass, suggesting that this treatment may be pertinent to systemic bone loss disorders. In conclusion, we identified a macrolide-DEL-1 axis that can regenerate bone lost due to aging-related disease.

Nisin lantibiotic prevents NAFLD liver steatosis and mitochondrial oxidative stress following periodontal disease by abrogating oral, gut and liver dysbiosis

Oral microbiome dysbiosis mediates chronic periodontal disease, gut microbial dysbiosis, and mucosal barrier disfunction that leads to steatohepatitis via the enterohepatic circulation. Improving this dysbiosis towards health may improve liver disease. Treatment with antibiotics and probiotics have been used to modulate the microbial, immunological, and clinical landscape of periodontal disease with some success. The aim of the present investigation was to evaluate the potential for nisin, an antimicrobial peptide produced by Lactococcus lactis, to counteract the periodontitis-associated gut dysbiosis and to modulate the glycolipid-metabolism and inflammation in the liver. Periodontal pathogens, namely Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia and Fusobacterium nucleatum, were administrated topically onto the oral cavity to establish polymicrobial periodontal disease in mice. In the context of disease, nisin treatment significantly shifted the microbiome towards a new composition, commensurate with health while preventing the harmful inflammation in the small intestine concomitant with decreased villi structural integrity, and heightened hepatic exposure to bacteria and lipid and malondialdehyde accumulation in the liver. Validation with RNA Seq analyses, confirmed the significant infection-related alteration of several genes involved in mitochondrial dysregulation, oxidative phosphorylation, and metal/iron binding and their restitution following nisin treatment. In support of these in vivo findings indicating that periodontopathogens induce gastrointestinal and liver distant organ lesions, human autopsy specimens demonstrated a correlation between tooth loss and severity of liver disease. Nisin's ability to shift the gut and liver microbiome towards a new state commensurate with health while mitigating enteritis, represents a novel approach to treating NAFLD-steatohepatitis-associated periodontal disease.

Current concepts in the pathogenesis of periodontitis: from symbiosis to dysbiosis

The primary etiological agent for the initiation and progression of periodontal disease is the dental plaque biofilm which is an organized aggregation of microorganisms residing within a complex intercellular matrix. The non-specific plaque hypothesis was the first attempt to explain the role of the dental biofilm in the pathogenesis of periodontal diseases. However, the introduction of sophisticated diagnostic and laboratory assays has led to the realisation that the development of periodontitis requires more than a mere increase in the biomass of dental plaque. Indeed, multispecies biofilms exhibit complex interactions between the bacteria and the host. In addition, not all resident microorganisms within the biofilm are pathogenic, since beneficial bacteria exist that serve to maintain a symbiotic relationship between the plaque microbiome and the host’s immune-inflammatory response, preventing the emergence of pathogenic microorganisms and the development of dysbiosis. This review aims to highlight the development and structure of the dental plaque biofilm and to explore current literature on the transition from a healthy (symbiotic) to a diseased (dysbiotic) biofilm in periodontitis and the associated immune-inflammatory responses that drive periodontal tissue destruction and form mechanistic pathways that impact other systemic non-communicable diseases.

Chronological analysis of periodontal bone loss in experimental periodontitis in mice

OBJECTIVES

Periodontal disease is understood to be a result of dysbiotic interactions between the host and the biofilm, causing a unique reaction for each individual, which in turn characterizes their susceptibility. The objective of this study was to chronologically evaluate periodontal tissue destruction induced by systemic bacterial challenge in known susceptible (BALB/c) and resistant (C57BL/6) mouse lineages.

MATERIAL AND METHODS

Animals, 6-8 weeks old, were allocated into three experimental groups: Negative control (C), Gavage with sterile carboxymethyl cellulose 2%-without bacteria (Sham), and Gavage with carboxymethyl cellulose 2% + Porphyromonas gingivalis (Pg-W83). Before infection, all animals received antibiotic treatment (sulfamethoxazole/trimethoprim, 400/80 mg/5 mL) for 7 days, followed by 3 days of rest. Microbial challenge was performed 3 times per week for 1, 2, or 3 weeks. After that, the animals were kept until the completion of 42 days of experiments, when they were euthanized. The alveolar bone microarchitecture was assessed by computed microtomography.

RESULTS

Both C57BL/6 and BALB/c mice exhibited significant bone volume loss and lower trabecular thickness as well as greater bone porosity compared to the (C) and (Sham) groups after 1 week of microbial challenge (p < .001). When comparing only the gavage groups regarding disease implantation, time and lineage, it was possible to observe that within 1 week of induction the disease was more established in BALB/c than in C57BL/6 (p < .05).

CONCLUSIONS

Our results reflected that after 1 week of microbial challenge, there was evidence of alveolar bone loss for both lineages, with the loss observed in BALB/c mice being more pronounced.

Repurposing Metformin for periodontal disease management as a form of oral-systemic preventive medicine

BACKGROUND

Despite the improvements in treatment over the last decades, periodontal disease (PD) affects millions of people around the world and the only treatment available is based on controlling microbial load. Diabetes is known to increase the risk of PD establishment and progression, and recently, glucose metabolism modulation by pharmaceutical or dietarian means has been emphasised as a significant modulator of non-communicable disease development.

METHODS

The impact of pharmaceutically controlling glucose metabolism in non-diabetic animals and humans (REBEC, UTN code: U1111-1276-1942) was investigated by repurposing Metformin, as a mean to manage periodontal disease and its associated systemic risk factors.

RESULTS

We found that glucose metabolism control via use of Metformin aimed at PD management resulted in significant prevention of bone loss during induced periodontal disease and age-related bone loss in vivo. Metformin also influenced the bacterial species present in the oral environment and impacted the metabolic epithelial and stromal responses to bacterial dysbiosis at a single cell level. Systemically, Metformin controlled blood glucose levels and age-related weight gain when used long-term. Translationally, our pilot randomized control trial indicated that systemic Metformin was safe to use in non-diabetic patients and affected the periodontal tissues. During the medication window, patients showed stable levels of systemic blood glucose, lower circulating hsCRP and lower insulin levels after periodontal treatment when compared to placebo. Finally, patients treated with Metformin had improved periodontal parameters when compared to placebo treated patients.

CONCLUSION

This is the first study to demonstrate that systemic interventions using Metformin in non-diabetic individuals aimed at PD prevention have oral-systemic effects constituting a possible novel form of preventive medicine for oral-systemic disease management.

Immunometabolic capacities of nutritional fatty acids in regulation of inflammatory bone cell interaction and systemic impact of periodontal infection

Introduction

Novel preventive strategies in periodontal disease target the bacterial-induced inflammatory host response to reduce associated tissue destruction. Strategies focus on the modulation of tissue-destroying inflammatory host response, particularly the reduction of inflammation and promotion of resolution. Thereby, nutrition is a potent immunometabolic non-pharmacological intervention. Human studies have demonstrated the benefit of olive oil-containing Mediterranean-style diets (MDs), the main component of which being mono-unsaturated fatty acid (FA) oleic acid (OA (C18:1)). Hence, nutritional OA strengthened the microarchitecture of alveolar trabecular bone and increased circulating pro-resolving lipid mediators following bacterial inoculation with periodontal pathogen Porphyromonas gingivalis, contrary to saturated FA palmitic acid (PA (C16:0)), which is abundant in Western-style diets. Additionally, the generalized distribution of inflammatory pathway mediators can occur in response to bacterial infection and compromise systemic tissue metabolism and bone homeostasis distant from the side of infection. Whether specific FA-enriched nutrition and periodontal inoculation are factors in systemic pathology that can be immune-modulatory targeted through dietary substitution is unknown and of clinical relevance.

Methods

Normal-weight C57BL/6-mice received OA-or PA-enriched diets (PA-ED, OA-ED, PA/OA-ED) or a normal-standard diet (n=12/group) for 16 weeks and were orally infected with P. gingivalis/placebo to induce periodontal disease. Using histomorphometry and LC-MS/MS, systemic bone morphology, incorporated immunometabolic FA-species, serological markers of bone metabolism, and stress response were determined in addition to bone cell inflammation and interaction in vitro.

Results

In contrast to OA-ED, PA-ED reduced systemic bone microarchitecture paralleled by increased lipotoxic PA-containing metabolite accumulation in bone. Substitution with OA reversed the bone-destructive impact of PA, which was accompanied by reduced diacylglycerols (DAG) and saturated ceramide levels. Further, PA-associated reduction in mineralization activity and concomitant pro-inflammatory activation of primary osteoblasts were diminished in cultures where PA was replaced with OA, which impacted cellular interaction with osteoclasts. Additionally, PA-ED increased osteoclast numbers in femurs in response to oral P. gingivalis infection, whereas OA-ED reduced osteoclast occurrence, which was paralleled by serologically increased levels of the stress-reducing lipokine PI(18:1/18:1).

Conclusion

OA substitution reverses the bone-destructive and pro-inflammatory effects of PA and eliminates incorporated lipotoxic PA metabolites. This supports Mediterranean-style OA-based diets as a preventive intervention to target the accumulation of PA-associated lipotoxic metabolites and thereby supports systemic bone tissue resilience after oral bacterial P. gingivalis infection.

Ligature-Induced Periodontitis Drives Colorectal Cancer: An Experimental Model in Mice

Periodontitis is a prevalent inflammatory oral disease associated with an increased risk of colorectal cancer. Experimental animal models are critical tools to investigate the effects and mechanisms of periodontitis on colorectal cancer. Several murine periodontitis models have been used in research, including oral gavage, periodontal pathogen injection, and ligature models. The role of experimental periodontitis caused by silk ligation in colorectal cancer remains unclear. In this study, we used an experimental periodontitis model on a colitis-associated colorectal cancer model and a spontaneous model, respectively. We observed the promotion of colorectal cancer in ligature-induced periodontitis mice compared to those control mice in 2 different models, as assessed by tumor number, tumor size, and tumor load. Since bacterial dysbiosis is an important feature of periodontitis, we next analyzed the oral and gut microbiomes using 16S ribosomal RNA gene sequencing. We found that the experimental periodontitis model reshaped the microbial community in the oral cavity and gut. In addition, we found a higher extent of programmed death 1 (PD-1)-positive CD8⁺ T-cell infiltration in tumor samples of the periodontitis group than in controls by immunofluorescence staining. Regarding the potential molecular mechanism, we transplanted the fecal microbiota of the periodontitis patient into mice and observed a tumor-promoting effect in the periodontitis group, assessed by tumor volume and tumor weight, together with a low level of INF-γ⁺ CD8⁺ T-cell infiltration in subcutaneous tumor mice. Taken together, we show that ligature-induced periodontitis model promotes colorectal cancer by microbiota remodeling and suppression of the immune response.

Mediterranean diet component oleic acid increases protective lipid mediators and improves trabecular bone in a Porphyromonas gingivalis inoculation model

AIM

Therapeutic modulation of bacterial-induced inflammatory host response is being investigated in gingival inflammation and periodontal disease pathology. Therefore, dietary intake of the monounsaturated fatty acid (FA) oleic acid (OA (C18:1)), which is the main component of Mediterranean-style diets, and saturated FA palmitic acid (PA (C16:0)), which is a component of Western-style diets, was investigated for their modifying potential in an oral inoculation model of Porphyromonas gingivalis.

MATERIALS AND METHODS

Normal-weight C57BL/6-mice received OA- or PA-enriched diets (PA-ED, OA-ED, PA/OA-ED) or normal standard diet for 16 weeks and were inoculated with P. gingivalis/placebo (n = 12/group). Gingival inflammation, alveolar bone structure, circulating lipid mediators, and in vitro cellular response were determined.

RESULTS

FA treatment of P. gingivalis-lipopolysaccharide-incubated gingival fibroblasts (GFbs) modified inflammatory activation, which only PA exacerbated with concomitant TNF-α stimulation. Mice exhibited no signs of acute inflammation in gingiva or serum and no inoculation- or nutrition-associated changes of the crestal alveolar bone. However, following P. gingivalis inoculation, OA-ED improved oral trabecular bone micro-architecture and enhanced circulating pro-resolving mediators resolvin D4 (RvD4) and 4-hydroxydocosahexaenoic acid (4-HDHA), whereas PA-ED did not. In vitro experiments demonstrated significantly improved differentiation in RvD4- and 4-HDHA-treated primary osteoblast cultures and reduced the expression of osteoclastogenic factors in GF. Further, P. gingivalis infection of OA-ED animals led to a serum composition that suppressed osteoclastic differentiation in vitro.

CONCLUSIONS

Our results underline the preventive impact of Mediterranean-style OA-EDs by indicating their pro-resolving nature beyond anti-inflammatory properties.

The interaction of CD300lf and ceramide reduces the development of periodontitis by inhibiting osteoclast differentiation

AIM

The regulation of osteoclasts (OCs) by inhibitory immunoreceptors maintains bone homeostasis and is considered an important determinant of the extent of periodontal pathology. The aim of this study was to investigate the role of the inhibitory immunoreceptor CD300lf and its ligand ceramide in osteoclastogenesis in periodontitis.

MATERIALS AND METHODS

The expression of CD300lf was measured in vitro and in a ligature-induced periodontitis model. The effect of CD300lf ablation on osteoclastogenesis was examined in ligature-retained and ligature removal periodontitis models. The effect of ceramide, the ligand of CD300lf, was examined in osteoclastogenesis in vitro and in vivo by smearing 20 μg of ceramide dissolved in carboxymethylcellulose on teeth and gingiva every other day in an experimental periodontitis model and ligature removal model.

RESULTS

CD300lf expression was downregulated during osteoclastogenesis. Ablation of CD300lf in the ligature-induced periodontitis model increased the number of OCs and exacerbated bone damage. Bone resorption caused by CD300lf ablation was reversible following ligature removal. CD300lf-ceramide binding suppressed osteoclastogenesis in vitro and inhibited alveolar bone loss in a mouse periodontitis model.

CONCLUSIONS

Our findings reveal that CD300lf-ceramide binding plays a critical negative role in alveolar bone loss in periodontitis by inhibiting OCs differentiation.

TRAF3IP2-IL-17 Axis Strengthens the Gingival Defense against Pathogens

Recent genome-wide association studies have suggested novel risk loci associated with periodontitis, which is initiated by dysbiosis in subgingival plaque and leads to destruction of teeth-supporting structures. One such genetic locus was the tumor necrosis factor receptor-associated factor 3 interacting protein 2 (TRAF3IP2), a gene encoding the gate-keeping interleukin (IL)-17 receptor adaptor. In this study, we first determined that carriers of the lead exonic variant rs13190932 within the TRAF3IP2 locus combined with a high plaque microbial burden was associated with more severe periodontitis than noncarriers. We then demonstrated that TRAF3IP2 is essential in the IL-17-mediated CCL2 and IL-8 chemokine production in primary gingival epithelial cells. Further analysis suggested that rs13190932 may serve a surrogate variant for a genuine loss-of-function variant rs33980500 within the same gene. Traf3ip2 null mice (Traf3ip2^-/-) were more susceptible than wild-type (WT) mice to the Porphyromonas gingivalis-induced periodontal alveolar bone loss. Such bone loss was associated with a delayed P. gingivalis clearance and an attenuated neutrophil recruitment in the gingiva of Traf3ip2^-/- mice. Transcriptomic data showed decreased expression of antimicrobial genes, including Lcn2, S100a8, and Defb1, in the Traf3ip2^-/- mouse gingiva in comparison to WT mice prior to or upon P. gingivalis oral challenge. Further 16S ribosomal RNA sequencing analysis identified a distinct microbial community in the Traf3ip2^-/- mouse oral plaque, which was featured by a reduced microbial diversity and an overabundance of Streptococcus genus bacteria. More P. gingivalis was observed in the Traf3ip2^-/- mouse gingiva than WT control animals in a ligature-promoted P. gingivalis invasion model. In agreement, neutrophil depletion resulted in more local gingival tissue invasion by P. gingivalis. Thus, we identified a homeostatic IL-17-TRAF3IP2-neutrophil axis underpinning host defense against a keystone periodontal pathogen.

Pathobiont-responsive Th17 cells in gut-mouth axis provoke inflammatory oral disease and are modulated by intestinal microbiome

Host immune response via Th17 cells against oral pathobionts is a key mediator in periodontitis development. However, where and how the Th17-type immune response is induced during the development of periodontitis is not well understood. Here, we demonstrate that gut translocation of the oral pathobiont Porphyromonas gingivalis (Pg) exacerbates oral pathobiont-induced periodontitis with enhanced Th17 cell differentiation. The oral pathobiont-responsive Th17 cells are differentiated in Peyer's patches and translocated systemically in the peripheral immune tissues. They are also capable of migrating to and accumulating in the mouth upon oral infection. Development of periodontitis via the oral pathobiont-responsive Th17 cells is regulated by the intestinal microbiome, and altering the intestinal microbiome composition with antibiotics affects the development of periodontitis. Our study highlights that pathobiont-responsive Th17 cells in the gut-mouth axis and the intestinal microbiome work together to provoke inflammatory oral diseases, including periodontitis.

Oral Microbiome Using Colocasia antiquorum var. esculenta Extract Varnish in a Mouse Model with Oral Gavage of P. gingivalis ATCC 53978

Background and Objective: There is increasing interest in preventing periodontitis using natural products. The purpose of this study was to investigate the effect of Colocasia antiquorum var. esculenta (CA) varnish on the oral microbiome and alveolar bone loss in a mouse periodontitis model. Materials and Methods: Antibacterial activity against Porphyromonas gingivalis (P. gingivalis) ATCC 53978 and cell cytotoxicity using CCK-8 on L929 cells were measured. Balb/c mice were assigned into five groups (negative control, positive control, CA in drinking water, varnish, and CA varnish). P. gingivalis was administered to the mice by oral gavage three times. After sacrifice, the oral microbiome and the levels of the inflammatory cytokine IL-1β and matrix metalloproteinase-9 were analyzed. Alveolar bone loss was measured using micro-computed tomography. Results: CA extract showed an antibacterial effect against P. gingivalis (p < 0.05) and showed no cytotoxicity at that concentration (p > 0.05). Although alpha diversity of the oral microbiome did not statistically differ between the groups (p > 0.05), the relative abundance of dominant bacteria tended to be different between the groups. The inflammatory cytokine IL-1β was reduced in the CA varnish group (p < 0.05), and no difference was observed in MMP-9 expression and alveolar bone loss (p > 0.05). Conclusions: CA varnish did not affect the overall microflora and exhibited an anti-inflammatory effect, suggesting that it is possibility a suitable candidate for improving periodontitis.

Periodontal Infection Aggravates C1q-Mediated Microglial Activation and Synapse Pruning in Alzheimer's Mice

Periodontitis is a dysbiotic infectious disease that leads to the destruction of tooth supporting tissues. There is increasing evidence that periodontitis may affect the development and severity of Alzheimer's disease (AD). However, the mechanism(s) by which periodontal infection impacts the neurodegenerative process in AD remains unclear. In the present study, using an amyloid precursor protein (APP) knock-in (App KI) AD mouse model, we showed that oral infection with Porphyromonas gingivalis (Pg), a keystone pathogen of periodontitis, worsened behavioral and cognitive impairment and accelerated amyloid beta (Aβ) accumulation in AD mice, thus unquestionably and significantly aggravating AD. We also provide new evidence that the neuroinflammatory status established by AD, is greatly complicated by periodontal infection and the consequential entry of Pg into the brain via Aβ-primed microglial activation, and that Pg-induced brain overactivation of complement C1q is critical for periodontitis-associated acceleration of AD progression by amplifying microglial activation, neuroinflammation, and tagging synapses for microglial engulfment. Our study renders support for the importance of periodontal infection in the innate immune regulation of AD and the possibility of targeting microbial etiology and periodontal treatment to ameliorate the clinical manifestation of AD and lower AD prevalence.

Loss of Neutrophil Homing to the Periodontal Tissues Modulates the Composition and Disease Potential of the Oral Microbiota

Periodontal disease is considered to arise from an imbalance in the interplay between the host and its commensal microbiota, characterized by inflammation, destructive periodontal bone loss, and a dysbiotic oral microbial community. The neutrophil is a key component of defense of the periodontium: defects in their number or efficacy of function predisposes individuals to development of periodontal disease. Paradoxically, neutrophil activity, as part of a deregulated inflammatory response, is considered an important element in the destructive disease process. In this investigation, we examined the role the neutrophil plays in the regulation of the oral microbiota by analysis of the microbiome composition in mice lacking the CXCR2 neutrophil receptor required for recruitment to the periodontal tissues. A breeding protocol was employed that ensured that only the oral microbiota of wild-type (CXCR2^+/+) mice was transferred to subsequent generations of wild-type, heterozygote, and homozygote littermates. In the absence of neutrophils, the microbiome undergoes a significant shift in total load and composition compared to when normal levels of neutrophil recruitment into the gingival tissues occur, and this is accompanied by a significant increase in periodontal bone pathology. However, transfer of the oral microbiome of CXCR2^-/- mice into germfree CXCR2^+/+ mice led to restoration of the microbiome to the wild-type CXCR2^+/+ composition and the absence of pathology. These data demonstrate that the composition of the oral microbiome is inherently flexible and is governed to a significant extent by the genetics and resultant phenotype of the host organism.

Episymbiotic Saccharibacteria suppresses gingival inflammation and bone loss in mice through host bacterial modulation

Saccharibacteria (TM7) are obligate epibionts living on the surface of their host bacteria and are strongly correlated with dysbiotic microbiomes during periodontitis and other inflammatory diseases, suggesting they are putative pathogens. However, due to the recalcitrance of TM7 cultivation, causal research to investigate their role in inflammatory diseases is lacking. Here, we isolated multiple TM7 species on their host bacteria from periodontitis patients. These TM7 species reduce inflammation and consequential bone loss by modulating host bacterial pathogenicity in a mouse ligature-induced periodontitis model. Two host bacterial functions involved in collagen binding and utilization of eukaryotic sialic acid are required for inducing bone loss and are altered by TM7 association. This TM7-mediated downregulation of host bacterial pathogenicity is shown for multiple TM7/host bacteria pairs, suggesting that, in contrast to their suspected pathogenic role, TM7 could protect mammalian hosts from inflammatory damage induced by their host bacteria.

B-Cell Deficiency Exacerbates Inflammation and Bone Loss in Ligature-Induced Experimental Periodontitis in Mice

Objective

Periodontitis, one of the most prevalent chronic oral infectious diseases in humans, is induced by the breakdown in the balance between the biofilm and host immune system. Previous studies have shown the presence of large numbers of B cells in periodontitis lesions, implicating that B lymphocytes play a predominant role during the pathogenesis of periodontitis. This study aimed to investigate the role of all B cells in the initiation of periodontitis.

Methods

Experimental periodontitis was induced in B cell-deficient (CD19Cre) mice and wild-type (WT) control mice by 5-0 silk ligation around the maxillary second molar. Four weeks after ligation, alveolar bone loss was determined by micro-computed tomography. The levels of inflammatory cytokines and receptor activator of NF-κB ligand (RANKL)/osteoprotegerin in periodontal lesions were analyzed using real-time quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, and immunohistochemistry. Lymphocyte populations in the cervical lymph nodes and spleen and among the peripheral blood mononuclear cells were detected by flow cytometry.

Results

B-cell deficiency resulted in increased severity of alveolar bone loss in mouse experimental periodontitis, which was associated with increased osteoclast activity and upregulated RANKL expression in the periodontal lesions. In addition, gingiva cytokine expression profiles were shifted to T helper type 1 (Th1) and Th17 in the CD19Cre mice with ligature-induced periodontitis compared with WT mice. In addition, a reduced CD4⁺/CD8⁺ T cell ratio was observed in the CD19Cre mice.

Conclusion

B-cell deficiency exacerbates the inflammation and alveolar bone loss in ligature-induced experimental periodontitis in mice, implicating that B cells may overall play a protective role in the initiation of periodontitis.

Effects of Colocasia antiquorum var. Esculenta Extract In Vitro and In Vivo against Periodontal Disease

Background and Objectives: Periodontal disease is a chronic inflammatory disease in which gradual destruction of tissues around teeth is caused by plaque formed by pathogenic bacteria. The purpose of this study was to evaluate the potential of 75% ethanol extract of Colocasia antiquorum var. esculenta (CA) as a prophylactic and improvement agent for periodontal disease in vitro and in vivo. Materials and Methods: The antimicrobial efficacy of CA against Porphyromonas gingivalis (P. gingivalis, ATCC 33277) was evaluated using minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) test, and cytotoxicity was confirmed by CCK-8 assay. For the in vivo study, P. gingivalis was applied by oral gavage to BALB/c mice. Forty-two days after the first inoculation of P. gingivalis, intraoral swabs were taken for microbiome analysis, and the mice were sacrificed to evaluate the alveolar bone loss. Results: The MIC of CA against P. gingivalis was 31.3 μg/mL, the MBC was 62.5 μg/mL, with no cytotoxicity. The diversity of the oral microbiome decreased in the positive control group, while those of the VA (varnish) and VCA (varnish added with CA) groups increased as much as in the negative control group, although the alveolar bone loss was not induced in the mouse model. Conclusions: CA showed antibacterial effects in vitro, and the VA and VCA groups exhibited increased diversity in the oral microbiome, suggesting that CA has potential for improving periodontal disease.

Porphyromonas gingivalis induces entero-hepatic metabolic derangements with alteration of gut microbiota in a type 2 diabetes mouse model

Periodontal infection induces systemic inflammation; therefore, aggravating diabetes. Orally administered periodontal pathogens may directly alter the gut microbiota. We orally treated obese db/db diabetes mice using Porphyromonas gingivalis (Pg). We screened for Pg-specific peptides in the intestinal fecal specimens and examined whether Pg localization influenced the intestinal microbiota profile, in turn altering the levels of the gut metabolites. We evaluated whether the deterioration in fasting hyperglycemia was related to the changes in the intrahepatic glucose metabolism, using proteome and metabolome analyses. Oral Pg treatment aggravated both fasting and postprandial hyperglycemia (P < 0.05), with a significant (P < 0.01) increase in dental alveolar bone resorption. Pg-specific peptides were identified in fecal specimens following oral Pg treatment. The intestinal Pg profoundly altered the gut microbiome profiles at the phylum, family, and genus levels; Prevotella exhibited the largest increase in abundance. In addition, Pg-treatment significantly altered intestinal metabolite levels. Fasting hyperglycemia was associated with the increase in the levels of gluconeogenesis-related enzymes and metabolites without changes in the expression of proinflammatory cytokines and insulin resistance. Oral Pg administration induced gut microbiota changes, leading to entero-hepatic metabolic derangements, thus aggravating hyperglycemia in an obese type 2 diabetes mouse model.

PRMT5 inhibition modulates murine dendritic cells activation by inhibiting the metabolism switch: a new therapeutic target in periodontitis

Background

Protein arginine methyltransferase 5 (PRMT5) catalyzes the methylation of arginine residues in multiple proteins. Recent reports have highlighted the anti-inflammatory role of PRMT5. Dendritic cells (DCs) are well-known professional antigen-presenting cells that are crucial for immune response initiation. However, whether PRMT5 participates in DC immunity processes is unknown.

Methods

In an in vitro experiment, a PRMT5 inhibitor (EPZ015666) was used to inhibit PRMT5 expression, and lipopolysaccharide (LPS) stimulation was applied to mimic the inflammation context. Proinflammatory cytokine production, interferon-stimulated genes (ISGs), costimulatory molecules, major histocompatibility complex (MHC) expression and DC metabolism were measured following PRMT5 inhibition and LPS stimulation. In an in vivo study, we first tested PRMT5 mRNA and protein expression in a BALB/c mouse ligature-induced periodontitis model. Then, we evaluated changes in periodontal tissue and DC migration to cervical lymph nodes after local treatment with the PRMT5 inhibitor.

Results

The in vitro results revealed that PRMT5 inhibition attenuated DC activation and maturation by inhibiting the expression of proinflammatory cytokines, ISGs, costimulatory molecules, and MHC induced by LPS stimulation. We also found that inhibition of PRMT5 blocked the DC metabolic switch to glycolysis. In the in vivo study, we found that PRMT5 inhibition reversed the severity of the lesions and slowed the migration of DCs to cervical lymph nodes.

Conclusions

The results show a critical role of PRMT5 in the control of DC activation through inhibition of the metabolic switch and indicate that PRMT5 is a promising therapeutic target in periodontitis.

Antibiofilm Peptides: Relevant Preclinical Animal Infection Models and Translational Potential

Biofilm-forming bacteria may be 10-1000 times more resistant to antibiotics than planktonic bacteria and represent about 75% of bacterial infections in humans. Antibiofilm treatments are scarce, and no effective therapies have been reported so far. In this context, antibiofilm peptides (ABPs) represent an exciting class of agents with potent activity against biofilms both in vitro and in vivo. Moreover, murine models of bacterial biofilm infections have been used to evaluate the in vivo effectiveness of ABPs. Therefore, here we highlight the translational potential of ABPs and provide an overview of the different clinically relevant murine models to assess ABP efficacy, including wound, foreign body, chronic lung, and oral models of infection. We discuss key challenges to translate ABPs to the clinic and the pros and cons of the existing murine biofilm models for reliable assessment of the efficacy of ABPs.

A cross-species interaction with a symbiotic commensal enables cell-density-dependent growth and in vivo virulence of an oral pathogen

Recent studies describe in detail the shifts in composition of human-associated polymicrobial communities from health to disease. However, the specific processes that drive the colonization and overgrowth of pathogens within these communities remain incompletely understood. We used in vitro culture systems and a disease-relevant mouse model to show that population size, which determines the availability of an endogenous diffusible small molecule, limits the growth, colonization, and in vivo virulence of the human oral pathogen Porphyromonas gingivalis. This bacterial pathogen overcomes the requirement for an endogenous cue by utilizing a cell-density dependent, growth-promoting, soluble molecule provided by the symbiotic early colonizer Veillonella parvula, but not produced by other commensals tested. Our work shows that exchange of cell-density-dependent diffusible cues between specific early and late colonizing species in a polymicrobial community drives microbial successions, pathogen colonization and disease development, representing a target process for manipulation of the microbiome towards the healthy state.

Frontline Science: Activation of metabolic nuclear receptors restores periodontal tissue homeostasis in mice with leukocyte adhesion deficiency-1

β2 Integrins mediate neutrophil-endothelial adhesion and recruitment of neutrophils to sites of inflammation. The diminished expression of β2 integrins in patients with mutations in the ITGB2 (CD18) gene (leukocyte adhesion deficiency-Type 1; LAD1) results in few or no neutrophils in peripheral tissues. In the periodontium, neutrophil paucity is associated with up-regulation of IL-23 and IL-17, which drive inflammatory bone loss. Using a relevant mouse model, we investigated whether diminished efferocytosis (owing to neutrophil scarcity) is associated with LAD1 periodontitis pathogenesis and aimed to develop approaches to restore the missing efferocytosis signals. We first showed that CD18^-/- mice phenocopied human LAD1 in terms of IL-23/IL-17-driven inflammatory bone loss. Ab-mediated blockade of c-Mer tyrosine kinase (Mer), a major efferocytic receptor, mimicked LAD1-associated up-regulation of gingival IL-23 and IL-17 mRNA expression in wild-type (WT) mice. Consistently, soluble Mer-Fc reversed the inhibitory effect of efferocytosis on IL-23 expression in LPS-activated Mϕs. Adoptive transfer of WT neutrophils to CD18^-/- mice down-regulated IL-23 and IL-17 expression to normal levels, but not when CD18^-/- mice were treated with blocking anti-Mer Ab. Synthetic agonist-induced activation of liver X receptors (LXR) and peroxisome proliferator-activated receptors (PPAR), which link efferocytosis to generation of homeostatic signals, inhibited the expression of IL-23 and IL-17 and favorably affected the bone levels of CD18^-/- mice. Therefore, our data link diminished efferocytosis-associated signaling due to impaired neutrophil recruitment to dysregulation of the IL-23-IL-17 axis and, moreover, suggest LXR and PPAR as potential therapeutic targets for treating LAD1 periodontitis.

IL-10 Dampens an IL-17-Mediated Periodontitis-Associated Inflammatory Network

Emerging evidence suggests comprehensive immune profiling represents a highly promising, yet insufficiently tapped approach to identify potentially prognostic signatures for periodontitis. In this report, we agnostically identified a periodontitis-associated inflammatory expression network with multiple biomarkers identified within gingival crevicular fluid samples from study participants by applying principal component analysis. We identified an IL-17-dominated trait that is associated with periodontal disease and is inversely modified by the level of IL-10. IL-10 mitigated chemokine CXCL5 and CXCL1 expressions in IL-17-stimulated peripheral blood monocytic cells and peripheral blood monocytic cell-derived macrophages. Il10-deficient mice presented more bone loss, which was associated with more Il17 and IL-17-mediated chemokine and cytokine expression at the transcriptional levels in comparison with control wild-type mice in both the Porphyromonas gingivalis-induced experimental murine periodontitis and ligature-induced alveolar bone-loss models. The dampening effect of IL-10 on the excessive signaling of IL-17 appeared to be mediated by innate immune cells populations rather than by gingival epithelial cells, which are the major cell target for IL-17 signaling. Additionally, elevated IL-17 response in Il10-deficient mice specifically elicited an M1-skewing macrophage phenotype in the gingiva that was associated with the advanced bone loss in the ligature model. In summary, IL-17 dominated an inflammatory network characteristic of periodontitis, and IL-10 dampens this excessive IL-17-mediated periodontitis trait.

Polymicrobial periodontal disease triggers a wide radius of effect and unique virome

Periodontal disease is a microbially-mediated inflammatory disease of tooth-supporting tissues that leads to bone and tissue loss around teeth. Although bacterially-mediated mechanisms of alveolar bone destruction have been widely studied, the effects of a polymicrobial infection on the periodontal ligament and microbiome/virome have not been well explored. Therefore, the current investigation introduced a new mouse model of periodontal disease to examine the effects of a polymicrobial infection on periodontal ligament (PDL) properties, changes in bone loss, the host immune response, and the microbiome/virome using shotgun sequencing. Periodontal pathogens, namely Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia, and Fusobacterium nucleatum were used as the polymicrobial oral inoculum in BALB/cByJ mice. The polymicrobial infection triggered significant alveolar bone loss, a heightened antibody response, an elevated cytokine immune response, a significant shift in viral diversity and virome composition, and a widening of the PDL space; the latter two findings have not been previously reported in periodontal disease models. Changes in the PDL space were present at sites far away from the site of insult, indicating that the polymicrobial radius of effect extends beyond the bone loss areas and site of initial infection and wider than previously appreciated. Associations were found between bone loss, specific viral and bacterial species, immune genes, and PDL space changes. These findings may have significant implications for the pathogenesis of periodontal disease and biomechanical properties of the periodontium. This new polymicrobial mouse model of periodontal disease in a common mouse strain is useful for evaluating the features of periodontal disease.

Horizontal and Vertical Transfer of Oral Microbial Dysbiosis and Periodontal Disease

One of the hallmark features of destructive periodontal disease, well documented over the last 50 y, is a change to the quantitative and qualitative composition of the associated microbiology. These alterations are now generally viewed as transformational shifts of the microbial populations associated with health leading to the emergence of bacterial species, which are only present in low abundance in health and a proportionate decrease in the abundance of others. The role of this dysbiosis of the health associated microbiota in the development of disease remains controversial: is this altered microbiology the driving agent of disease or merely a consequence of the altered environmental conditions that invariably accompany destructive disease? In this work, we aimed to address this controversy through controlled transmission experiments in the mouse in which a dysbiotic oral microbiome was transferred either horizontally or vertically into healthy recipient mice. The results of these murine studies demonstrate conclusively that natural transfer of the dysbiotic oral microbiome from a periodontally diseased individual into a healthy individual will lead to establishment of the dysbiotic community in the recipient and concomitant transmission of the disease phenotype. The inherent resilience of the dysbiotic microbial community structure in diseased animals was further demonstrated by analysis of the effects of antibiotic therapy on periodontally diseased mice. Although antibiotic treatment led to a reversal of dysbiosis of the oral microbiome, in terms of both microbial load and community structure, dysbiosis of the microbiome was reestablished following cessation of therapy. Collectively, these data suggest that an oral dysbiotic microbial community structure is stable to transfer and can act in a similar manner to a conventional transmissible infectious disease agent with concomitant effects on pathology. These findings have implications to our understanding of the role of microbial dysbiosis in the development and progression of human periodontal disease.

Plant-Derived Exosomal Nanoparticles Inhibit Pathogenicity of Porphyromonas gingivalis

Plant exosomes protect plants against infection; however, whether edible plant exosomes can protect mammalian hosts against infection is not known. In this study, we show that ginger exosome-like nanoparticles (GELNs) are selectively taken up by the periodontal pathogen Porphyromonas gingivalis in a GELN phosphatidic acid (PA) dependent manner via interactions with hemin-binding protein 35 (HBP35) on the surface of P. gingivalis. Compared with PA (34:2), PA (34:1) did not interact with HBP35, indicating that the degree of unsaturation of PA plays a critical role in GELN-mediated interaction with HBP35. On binding to HBP35, pathogenic mechanisms of P. gingivalis were significantly reduced following interaction with GELN cargo molecules, including PA and miRs. These cargo molecules interacted with multiple pathogenic factors in the recipient bacteria simultaneously. Using edible plant exosome-like nanoparticles as a potential therapeutic agent to prevent/treat chronic periodontitis was further demonstrated in a mouse model.

A Potential Role of Phospholipase 2 Group IIA (PLA2-IIA) in P. gingivalis-Induced Oral Dysbiosis

Porphyromonas gingivalis is an oral pathogen with the ability to induce oral dysbiosis and periodontal disease. Nevertheless, the mechanisms by which P. gingivalis could abrogate the host-microbe symbiotic relationship leading to oral dysbiosis remain unclear. We have recently demonstrated that P. gingivalis specifically increased the antimicrobial properties of oral epithelial cells, through a strong induction of the expression of PLA₂-IIA in a mechanism that involves activation of the Notch-1 receptor. Moreover, gingival expression of PLA₂-IIA was significantly increased during initiation and progression of periodontal disease in non-human primates and interestingly, those PLA₂-IIA expression changes were concurrent with oral dysbiosis. In this chapter, we present an innovative hypothesis of a potential mechanism involved in P. gingivalis-induced oral dysbiosis and inflammation based on our previous observations and a robust body of literature that supports the antimicrobial and proinflammatory properties of PLA₂-IIA as well as its role in other chronic inflammatory diseases.

Porphyromonas gingivalis induces depression via downregulating p75NTR-mediated BDNF maturation in astrocytes

Many cross-sectional epidemiological studies have shown the incidence of periodontitis is positive correlated with that of depression. However, their causal relationship and underlying mechanism are largely unknown. Porphyromonas gingivalis (Pg) is the main pathogen for periodontitis. Employing female mice treated with Pg every other day for 4 weeks, we found that Pg-mice showed obvious depression-like behavior, an increased number of activated astrocytes and decreased levels of mature brain derived neurotrophic factor (BDNF) and astrocytic p75NTR in the hippocampus. Both hippocampal injection of BDNF and overexpression of p75NTR in astrocytes alleviated Pg-induced depression-like behavior in mice. Moreover, Pg-lipopolysaccharides (LPS) generated similar phenotypes, which were reversed by the TLR-4 inhibitor TAK242. Our results suggest that Pg-LPS decreases the level of astrocytic p75NTR and then downregulates BDNF maturation, leading to depression-like behavior in mice. Our study provides the first evidence that Pg is a modifiable risk factor for depression and uncovers a novel therapeutic target for the treatment of depression.

Fetal Weight Outcomes in C57BL/6J and C57BL/6NCrl Mice after Oral Colonization with Porphyromonas gingivalis

Porphyromonas gingivalis is considered a keystone pathogen that contributes to the initiation and progression of periodontitis in humans. P. gingivalis has also been detected in human placentas associated with adverse pregnancy outcomes. The spread of P. gingivalis from the oral cavity to the reproductive tract thus represents a potential mechanism whereby periodontitis can lead to adverse pregnancy outcomes. In a murine model of pregnancy and oral infection with P. gingivalis, C57BL/6J mice developed low fetal weight, whereas C57BL/6NCrl mice did not. Although C57BL/6NCrl mice harbor segmented filamentous bacteria that drive a Th17 response, fetal weight was independent of frequency of Th17 or Th1 in either substrain. Low fetal weight was instead correlated with increasing amounts of P. gingivalis DNA in the placentas of the C57BL/6J dams. In contrast, fetal weight in C57BL/6NCrl mice was independent of P. gingivalis in the placenta. Differences in genetics or microbiome that influence the ability of P. gingivalis to colonize the placenta may drive differential fetal weight outcomes between C57BL/6J and C57BL/6NCrl mice and, potentially, between diverse human populations.

Efficient protocols and methods for high-throughput utilization of the Collaborative Cross mouse model for dissecting the genetic basis of complex traits

The Collaborative Cross (CC) mouse model is a next-generation mouse genetic reference population (GRP) designated for a high-resolution quantitative trait loci (QTL) mapping of complex traits during health and disease. The CC lines were generated from reciprocal crosses of eight divergent mouse founder strains composed of five classical and three wild-derived strains. Complex traits are defined to be controlled by variations within multiple genes and the gene/environment interactions. In this article, we introduce and present variety of protocols and results of studying the host response to infectious and chronic diseases, including type 2 diabetes and metabolic diseases, body composition, immune response, colorectal cancer, susceptibility to Aspergillus fumigatus, Klebsiella pneumoniae, Pseudomonas aeruginosa, sepsis, and mixed infections of Porphyromonas gingivalis and Fusobacterium nucleatum, which were conducted at our laboratory using the CC mouse population. These traits are observed at multiple levels of the body systems, including metabolism, body weight, immune profile, susceptibility or resistance to the development and progress of infectious or chronic diseases. Herein, we present full protocols and step-by-step methods, implemented in our laboratory for the phenotypic and genotypic characterization of the different CC lines, mapping the gene underlying the host response to these infections and chronic diseases. The CC mouse model is a unique and powerful GRP for dissecting the host genetic architectures underlying complex traits, including chronic and infectious diseases.

An experimental murine model to study periodontitis

Periodontal disease (PD) is a common dental disease associated with the interaction between dysbiotic oral microbiota and host immunity. It is a prevalent disease, resulting in loss of gingival tissue, periodontal ligament, cementum and alveolar bone. PD is a major form of tooth loss in the adult population. Experimental animal models have enabled the study of PD pathogenesis and are used to test new therapeutic approaches for treating the disease. The ligature-induced periodontitis model has several advantages as compared with other models, including rapid disease induction, predictable bone loss and the capacity to study periodontal tissue and alveolar bone regeneration because the model is established within the periodontal apparatus. Although mice are the most convenient and versatile animal models used in research, ligature-induced periodontitis has been more frequently used in large animals. This is mostly due to the technical challenges involved in consistently placing ligatures around murine teeth. To reduce the technical challenge associated with the traditional ligature model, we previously developed a simplified method to easily install a bacterially retentive ligature between two molars for inducing periodontitis. In this protocol, we provide detailed instructions for placement of the ligature and demonstrate how the model can be used to evaluate gingival tissue inflammation and alveolar bone loss over a period of 18 d after ligature placement. This model can also be used on germ-free mice to investigate the role of human oral bacteria in periodontitis in vivo. In conclusion, this protocol enables the mechanistic study of the pathogenesis of periodontitis in vivo.

Influence of Porphyromonas gingivalis in gut microbiota of streptozotocin-induced diabetic mice

OBJECTIVES

Increasing evidence suggests that periodontitis can exacerbate diabetes, and gut bacterial dysbiosis appears to be linked with the diabetic condition. The present study examined the effects of oral administration of the periodontopathic bacterium, Porphyromonas gingivalis, on the gut microbiota and systemic conditions in streptozotocin-induced diabetic mice.

MATERIALS AND METHODS

Diabetes was induced by streptozotocin injection in C57BL/6J male mice (STZ). STZ and wild-type (WT) mice were orally administered P. gingivalis (STZPg, WTPg) or saline (STZco, WTco). Feces were collected, and the gut microbiome was examined by 16S rRNA gene sequencing. The expression of genes related to inflammation, epithelial tight junctions, and glucose/fatty acid metabolism in the ileum or liver were examined by quantitative PCR.

RESULTS

The relative abundance of several genera, including Brevibacterium, Corynebacterium, and Facklamia, was significantly increased in STZco mice compared to WTco mice. The relative abundances of Staphylococcus and Turicibacter in the gut microbiome were altered by oral administration of P. gingivalis in STZ mice. STZPg mice showed higher concentrations of fasting blood glucose and inflammatory genes levels in the ileum, compared to STZco mice.

CONCLUSIONS

Oral administration of P. gingivalis altered the gut microbiota and aggravated glycemic control in streptozotocin-induced diabetic mice.

Genomewide Association Study Identifies Cxcl Family Members as Partial Mediators of LPS-Induced Periodontitis

Periodontitis (PD) is characterized by bacterial infection and inflammation of tooth-supporting structures and can lead to tooth loss. PD affects ∼47% of the US population over age 30 years and has a heritability of about 50%. Although the host immunoinflammatory response and genetic background play a role, little is known of the underlying genetic factors. We examined natural genetic variation in lipopolysaccharide (LPS)-induced PD across a panel of inbred mouse strains, the hybrid mouse diversity panel (HMDP). We observed a strain-dependent sixfold difference in LPS-induced bone loss across the HMDP with a heritability of 53%. We performed a genomewide association study (GWAS) using FAST-LMM, which corrects for population structure, and identified loci significantly associated with PD. We examined candidate genes at a locus on chromosome 5, which suggested a relationship between LPS-induced bone loss and, together with expression data, identified Cxcl family members as associated with PD. We observed an increase in Cxcl10 protein, as well as immune cells and pro-inflammatory cytokines in C57BL/6J (high bone loss strain) but not in A/J (low bone loss strain) after LPS injections. Genetic deletion of CXCR3 (Cxcl9 and10 receptor) demonstrated a ∼50% reduction in bone loss and reduced osteoclasts after LPS injections. Furthermore, WT mice treated with AMG-487 (a CXCR3 antagonist) showed a ∼45% reduction in bone loss and decreased osteoclasts after LPS injections. We conclude that CXCR3 is a strong candidate for modulating the host response in individuals susceptible to PD. © 2018 American Society for Bone and Mineral Research.

Keratinocyte-specific ablation of protease-activated receptor 2 prevents gingival inflammation and bone loss in a mouse model of periodontal disease

Chronic periodontitis is characterised by gingival inflammation and alveolar bone loss. A major aetiological agent is Porphyromonas gingivalis, which secretes proteases that activate protease-activated receptor 2 (PAR₂ ). PAR₂ expressed on oral keratinocytes is activated by proteases released by P. gingivalis, inducing secretion of interleukin 6 (IL-6), and global knockout of PAR₂ prevents bone loss and inflammation in a periodontal disease model in mice. To test the hypothesis that PAR₂ expressed on gingival keratinocytes is required for periodontal disease pathology, keratinocyte-specific PAR₂ -null mice were generated using K14-Cre targeted deletion of the PAR₂ gene (F2rl1). These mice were subjected to a model of periodontitis involving placement of a ligature around a tooth, combined with P. gingivalis infection ("Lig + Inf"). The intervention caused a significant 44% decrease in alveolar bone volume (assessed by microcomputed tomography) in wildtype (K14-Cre:F2rl1^wt/wt ), but not littermate keratinocyte-specific PAR₂ -null (K14-Cre:F2rl1^fl/fl ) mice. Keratinocyte-specific ablation of PAR₂ prevented the significant Lig + Inf-induced increase (2.8-fold) in the number of osteoclasts in alveolar bone and the significant up-regulation (2.4-4-fold) of the inflammatory markers IL-6, IL-1β, interferon-γ, myeloperoxidase, and CD11b in gingival tissue. These data suggest that PAR₂ expressed on oral epithelial cells is a critical regulator of periodontitis-induced bone loss and will help in designing novel therapies with which to treat the disease.

Activation of Notch-1 in oral epithelial cells by P. gingivalis triggers the expression of the antimicrobial protein PLA2-IIA

P. gingivalis (Pg) is an oral pathogen with the ability to induce oral dysbiosis and periodontal disease. Nevertheless, the mechanisms by which mucosal responses to the oral microbiota in the presence of specific pathogens such as Pg could abrogate the host-microbe symbiotic relationship leading to periodontitis remain unclear. Herein, we identified the Notch-1/PLA2-IIA axis as a new molecular pathway through which Pg could be specifically modulating oral epithelial antimicrobial and inflammatory responses. Pg activated Notch-1, and inhibition or silencing of Notch-1 completely abrogated Pg-induced PLA2-IIA in oral epithelial cells (OECs). Activation of Notch-1 and PLA2-IIA production were associated with Pg-produced gingipains. Other oral Gram-positive and Gram-negative species failed to induce similar responses. Pg enhanced OEC antimicrobial activity through PLA2-IIA. Increased Notch-1 activation correlated with higher PLA2-IIA gingival expression and changes in the abundance of specific oral bacteria phyla during periodontal disease. Oral bacterial species exhibited differential antimicrobial susceptibility to PLA2-IIA. These findings support previous evidence suggesting an important role for epithelial Notch-1 activation and PLA2-IIA production during health and disease at mucosal surfaces, and provide new mechanistic information concerning the regulation of epithelial antimicrobial and pro-inflammatory responses modulated by oral pathogenic bacteria associated with periodontal disease.

Chronic biofilm-based infections: skewing of the immune response

Many of the deadliest bacterial diseases that plague humanity in the modern age are caused by bacterial biofilms that produce chronic infections. However, most of our knowledge of the host immune response comes from the study of planktonic pathogens. While there are similarities in the host response to planktonic and biofilm bacteria, specific immune responses toward biofilms have not been well studied; the only apparent difference is the inability to clear the bacteria allowing the biofilm infection to become chronic. In some cases, the biofilms skew T-cell response toward a balance that allows a stalemate between the host and the pathogen, in which the infection can become persistent. In this minireview, we will summarize well-known examples of this phenomena as well as some emerging studies that may indicate that this situation is much more common than initially thought.

Inhibition of 5-lipoxygenase attenuates inflammation and BONE resorption in lipopolysaccharide-induced periodontal disease

BACKGROUND

Arachidonate-5-lipoxygenase (5-LO) activity and increased leukotriene B4 (LTB4) production have been implicated in various inflammatory conditions. Increased production of leukotrienes has been associated with periodontal diseases; however, their relative contribution to tissue destruction is unknown. In this study, an orally active specific 5-LO inhibitor is used to assess its role in inflammation and bone resorption in a murine model of lipopolysaccharide (LPS)-induced periodontal disease.

METHODS

Periodontal disease was induced in Balb/c mice by direct injections of LPS into the palatal gingival tissues adjacent to the maxillary first molars three times per week for 4 weeks. Animals were treated with biochemical inhibitor (2 mg/kg/daily) or the same volume of the vehicle by oral gavage. Microcomputed tomography analysis was used to assess bone resorption. Enzyme immunoassay determined LTB4, and enzyme-linked immunosorbent assays quantified tumor necrosis factor (TNF), interleukin (IL)-12, and IL-10 in gingival tissues. Histologic sections were used for the morphometric analysis (number of neutrophils and mononuclear cells). Osteoclasts were counted in tartrate-resistant acid phosphatase-stained sections.

RESULTS

Administration of 5-LO inhibitor effectively reduced production of LTB4 (23.7% decrease) and significantly reduced TNF and IL-12 levels in gingival tissues. Moreover, reduction of LTB4 levels in gingival tissues was associated with a significant decrease in bone resorption and a marked reduction in number of osteoclasts and inflammatory cells.

CONCLUSION

5-LO activity plays a relevant role in inflammation and bone resorption associated with the LPS model of experimental periodontal disease.

Genes Critical for Developing Periodontitis: Lessons from Mouse Models

Since the etiology of periodontitis in humans is not fully understood, genetic mouse models may pinpoint indispensable genes for optimal immunological protection of the periodontium against tissue destruction. This review describes the current knowledge of genes that are involved for a proper maintenance of a healthy periodontium in mice. Null mutations of genes required for leukocyte cell–cell recognition and extravasation (e.g., Icam-1, P-selectin, Beta2-integrin/Cd18), for pathogen recognition and killing (e.g., Tlr2, Tlr4, Lamp-2), immune modulatory molecules (e.g., Cxcr2, Ccr4, IL-10, Opg, IL1RA, Tnf-α receptor, IL-17 receptor, Socs3, Foxo1), and proteolytic enzymes (e.g., Mmp8, Plasmin) cause periodontitis, most likely due to an inefficient clearance of bacteria and bacterial products. Several mechanisms resulting in periodontitis can be recognized: (1) inefficient bacterial control by the polymorphonuclear neutrophils (defective migration, killing), (2) inadequate antigen presentation by dendritic cells, or (3) exaggerated production of pro-inflammatory cytokines. In all these cases, the local immune reaction is skewed toward a Th1/Th17 (and insufficient activation of the Th2/Treg) with subsequent osteoclast activation. Finally, genotypes are described that protect the mice from periodontitis: the SCID mouse, and mice lacking Tlr2/Tlr4, the Ccr1/Ccr5, the Tnf-α receptor p55, and Cathepsin K by attenuating the inflammatory reaction and the osteoclastogenic response.

Rapamycin treatment attenuates age-associated periodontitis in mice

Interventions that target biological mechanisms of aging have great potential to enhance quality of life by delaying morbidity and mortality. The FDA-approved drug rapamycin is a compelling candidate for such an intervention. In a previous study, it was reported that 3 months of rapamycin treatment is sufficient to increase life expectancy and remodel the gut microbiome in aged mice. Transient treatment with rapamycin or a rapamycin derivative has also been shown to delay immune stem cell senescence and rejuvenate immune function in aged mice and elderly people. Periodontal disease is an important age-related disease involving altered immune function, pathological changes to the oral microbiome, and systemic inflammation. Periodontal disease is defined clinically by loss of alveolar bone and by connective tissue degeneration. Here, we describe significant alveolar bone loss during aging in two different mouse strain backgrounds and report that rapamycin treatment is sufficient to reverse age-associated periodontal disease in mice. Partial restoration of youthful levels of alveolar bone is observed in 22-month-old rapamycin-treated mice as rapidly as 8 weeks after initiation of treatment. To the best of our knowledge, this represents the first intervention shown to substantially prevent or reverse age-associated alveolar bone loss. These findings suggest the possibility that inhibition of mTOR with rapamycin or other pharmacological agents may be useful to treat a clinically relevant condition for which there is currently no effective treatment.

Development of a root canal treatment model in the rat

Root canal treatment is performed to treat apical periodontitis, and various procedures and techniques are currently used. Although animal models have been used in the developmental research of root canal treatment, little of this research has used small animals such as rats, because of their small size. In this study, root canal treatment was performed on the rat mandibular first molar, which had four root canals, using a microscope, and the therapeutic effect was evaluated bacteriologically, radiologically and histopathologically. By performing root canal treatment, the level of bacteria in the mesial root of the treated teeth was reduced by 75% compared with the control. Additionally, the volume of the periapical lesions of the treated teeth as measured by micro-computed tomography decreased significantly 2 weeks after the root canal treatment when compared with the control. Histological evidence of healing was observed in the treatment group 8 weeks after root canal treatment. These results suggest that a root canal treatment model using rats can be used in developmental research for novel methods of root canal treatment.

Dissection of Host Susceptibility to Bacterial Infections and Its Toxins

Infection is one of the leading causes of human mortality and morbidity. Exposure to microbial agents is obviously required. However, also non-microbial environmental and host factors play a key role in the onset, development and outcome of infectious disease, resulting in large of clinical variability between individuals in a population infected with the same microbe. Controlled and standardized investigations of the genetics of susceptibility to infectious disease are almost impossible to perform in humans whereas mouse models allow application of powerful genomic techniques to identify and validate causative genes underlying human diseases with complex etiologies. Most of current animal models used in complex traits diseases genetic mapping have limited genetic diversity. This limitation impedes the ability to create incorporated network using genetic interactions, epigenetics, environmental factors, microbiota, and other phenotypes. A novel mouse genetic reference population for high-resolution mapping and subsequently identifying genes underlying the QTL, namely the Collaborative Cross (CC) mouse genetic reference population (GRP) was recently developed. In this chapter, we discuss a variety of approaches using CC mice for mapping genes underlying quantitative trait loci (QTL) to dissect the host response to polygenic traits, including infectious disease caused by bacterial agents and its toxins.

Porphyromonas gingivalis suppresses adaptive immunity in periodontitis, atherosclerosis, and Alzheimer's disease

Porphyromonas gingivalis, a keystone pathogen in chronic periodontitis, has been found to associate with remote body organ inflammatory pathologies, including atherosclerosis and Alzheimer’s disease (AD). Although P. gingivalis has a plethora of virulence factors, much of its pathogenicity is surprisingly related to the overall immunosuppression of the host. This review focuses on P. gingivalis aiding suppression of the host’s adaptive immune system involving manipulation of cellular immunological responses, specifically T cells and B cells in periodontitis and related conditions. In periodontitis, this bacterium inhibits the synthesis of IL-2 and increases humoral responses. This reduces the inflammatory responses related to T- and B-cell activation, and subsequent IFN-γ secretion by a subset of T cells. The T cells further suppress upregulation of programmed cell death-1 (PD-1)-receptor on CD⁺cells and its ligand PD-L1 on CD11b⁺-subset of T cells. IL-2 downregulates genes regulated by immune response and induces a cytokine pattern in which the Th17 lineage is favored, thereby modulating the Th17/T-regulatory cell (Treg) imbalance. The suppression of IFN-γ-stimulated release of interferon-inducible protein-10 (IP-10) chemokine ligands [ITAC (CXCL11) and Mig (CXCL9)] by P. gingivalis capsular serotypes triggers distinct T cell responses and contributes to local immune evasion by release of its outer membrane vesicles. In atherosclerosis, P. gingivalis reduces Tregs, transforms growth factor beta-1 (TGFβ-1), and causes imbalance in the Th17 lineage of the Treg population. In AD, P. gingivalis may affect the blood–brain barrier permeability and inhibit local IFN-γ response by preventing entry of immune cells into the brain. The scarcity of adaptive immune cells in AD neuropathology implies P. gingivalis infection of the brain likely causing impaired clearance of insoluble amyloid and inducing immunosuppression. By the effective manipulation of the armory of adaptive immune suppression through a plethora of virulence factors, P. gingivalis may act as a keystone organism in periodontitis and in related systemic diseases and other remote body inflammatory pathologies.