Gingivalis Peptidylarginine Deiminase Research Articles

Accessory fimbrial subunits and PPAD are necessary for TLR2 activation by Porphyromonas gingivalis.

Porphyromonas gingivalis is an oral pathogen that promotes dysbiosis by quenching the bactericidal activity of the host immune system while maintaining chronic inflammation, leading to periodontitis. This involves the secretion of virulence factors such as P. gingivalis peptidyl arginine deiminase (PPAD), which converts the C-terminal Arg residues of bacterial and host-derived proteins and peptides into citrulline. We have previously shown that PPAD activity and major fimbriae (containing FimA) are necessary for P. gingivalis to activate Toll-like receptor 2 (TLR2). TLR2 is an important component of the innate immune system and plays a predominant role in the recognition of P. gingivalis by host cells. Here, we extend those findings to show that P. gingivalis strains deficient for PPAD and fimbriae induced almost identical transcriptional profiles in infected primary human gingival fibroblasts (PHGFs), but these differed substantially from the transcriptome elicited by the wild-type ATCC 33277 strain. Apparently, PPAD-modified fimbriae trigger the host cell response to P. gingivalis, as confirmed by showing that the proinflammatory host cell response mediated by TLR2 is dependent on PPAD activity and the presence of fimbriae, with type I fimbriae as the most potent TLR2 activators. We also found that PPAD-modified accessory fimbrial subunits (FimC, FimD, and FimE) alone or in combination are TLR2 ligands in a reporter cell line. Although FimA polymerization to form the fimbrial shaft was not required for TLR2 activation, the secretion and proteolytic maturation of FimA were necessary for signaling by accessory Fim proteins. This was supported by showing that the proinflammatory activation of PHGFs is dependent on PPAD and accessory fimbrial subunits. We conclude that accessory fimbrial subunits are modified by PPAD and stimulate the response to P. gingivalis infection in a TLR2-dependent manner.

Implications of Porphyromonas gingivalis peptidyl arginine deiminase and gingipain R in human health and diseases.

Porphyromonas gingivalis is a major pathogenic bacterium involved in the pathogenesis of periodontitis. Citrullination has been reported as the underlying mechanism of the pathogenesis, which relies on the interplay between two virulence factors of the bacterium, namely gingipain R and the bacterial peptidyl arginine deiminase. Gingipain R cleaves host proteins to expose the C-terminal arginines for peptidyl arginine deiminase to citrullinate and generate citrullinated proteins. Apart from carrying out citrullination in the periodontium, the bacterium is found capable of citrullinating proteins present in the host synovial tissues, atherosclerotic plaques and neurons. Studies have suggested that both virulence factors are the key factors that trigger distal effects mediated by citrullination, leading to the development of some non-communicable diseases, such as rheumatoid arthritis, atherosclerosis, and Alzheimer’s disease. Thus, inhibition of these virulence factors not only can mitigate periodontitis, but also can provide new therapeutic solutions for systematic diseases involving bacterial citrullination. Herein, we described both these proteins in terms of their unique structural conformations and biological relevance to different human diseases. Moreover, investigations of inhibitory actions on the enzymes are also enumerated. New approaches for identifying inhibitors for peptidyl arginine deiminase through drug repurposing and virtual screening are also discussed.

Are Viral Infections Key Inducers of Autoimmune Diseases? Focus on Epstein-Barr Virus.

It is generally accepted that certain viral infections can trigger the development of autoimmune diseases. However, the exact mechanisms by which these viruses induce autoimmunity are still not understood. In this review, we first describe hypothetical mechanisms by which viruses induce some representative autoimmune diseases. Then, we focus on Epstein–Barr virus (EBV) and discuss its role in the pathogenesis of rheumatoid arthritis (RA). The discussion is mainly based on our own previous findings that (A) EBV DNA and its products EBV-encoded small RNA (EBER) and latent membrane protein 1 (LMP1) are present in the synovial lesions of RA, (B) mRNA expression of the signaling lymphocytic activation molecule-associated protein (SAP)/SH2D1A gene that plays a critical role in cellular immune responses to EBV is reduced in the peripheral T cells of patients with RA, and (C) EBV infection of mice reconstituted with human immune system components (humanized mice) induced erosive arthritis that is pathologically similar to RA. Additionally, environmental factors may contribute to EBV reactivation as follows: Porphyromonas gingivalis peptidylarginine deiminase (PAD), an enzyme required for citrullination, engenders antigens leading to the production of citrullinated peptides both in the gingiva and synovium. Anti-citrullinated peptides autoantibody is an important marker for diagnosis and disease activity of RA. These findings, as well as various results obtained by other researchers, strongly suggest that EBV is directly involved in the pathogenesis of RA, a typical autoimmune disease.

Porphyromonas gingivalis exacerbates ulcerative colitis via Porphyromonas gingivalis peptidylarginine deiminase

Ulcerative Colitis (UC) has been reported to be related to Porphyromonas gingivalis (P. gingivalis). Porphyromonas gingivalis peptidylarginine deiminase (PPAD), a virulence factor released by P. gingivalis, is known to induce inflammatory responses. To explore the pathological relationships between PPAD and UC, we used homologous recombination technology to construct a P. gingivalis strain in which the PPAD gene was deleted (Δppad) and a Δppad strain in which the PPAD gene was restored (comΔppad). C57BL/6 mice were orally gavaged with saline, P. gingivalis, Δppad, or comΔppad twice a week for the entire 40 days (days 0−40), and then, UC was induced by dextran sodium sulfate (DSS) solution for 10 days (days 31−40). P. gingivalis and comΔppad exacerbated DDS-induced colitis, which was determined by assessing the parameters of colon length, disease activity index, and histological activity index, but Δppad failed to exacerbate DDS-induced colitis. Flow cytometry and ELISA revealed that compared with Δppad, P. gingivalis, and comΔppad increased T helper 17 (Th17) cell numbers and interleukin (IL)-17 production but decreased regulatory T cells (Tregs) numbers and IL-10 production in the spleens of mice with UC. We also cocultured P. gingivalis, Δppad, or comΔppad with T lymphocytes in vitro and found that P. gingivalis and comΔppad significantly increased Th17 cell numbers and decreased Treg cell numbers. Immunofluorescence staining of colon tissue paraffin sections also confirmed these results. The results suggested that P. gingivalis exacerbated the severity of UC in part via PPAD.

Impact of chronic gingivitis management on the cytokine and anti‐PPAD expressions in juvenile systemic lupus erythematosus: A six‐month follow‐up

To evaluate how chronic gingivitis treatment impacts the oral and circulating cytokine expressions after six-month follow-up in patients with juvenile systemic lupus erythematosus (jSLE) and also to evaluate the circulating expression of anti-Porphyromonas gingivalis peptidylarginine deiminase antibodies (anti-PPAD) before and after treatment. Juvenile systemic lupus erythematosus patients present a worse periodontal condition associated with higher gingival crevicular fluid (GCF) levels of interleukin (IL)-1β, IL-8, granulocyte colony-stimulating factor (G-CSF), interferon-γ and monocyte chemoattractant protein (MCP)-1. Twenty-one adolescents with jSLE (mean age: 16.2±1.5years) were recruited. Participants were rheumatologically and periodontally examined. All individuals were clinically diagnosed with gingival inflammation. Chronic gingivitis treatment consisted of supragingival scaling, prophylaxis and oral hygiene instructions. The cytokine levels were determined by bead-based multiplex assays and the anti-PPAD levels by ELISA. Gingival crevicular fluid (GCF) and serum samples were collected at baseline and 6months after treatment. We observed a reduction in attachment loss, SLE Disease Activity Index (SLEDAI), IL-1β, IL-10 and MCP-1 GCF levels, and the IL-4 and IL-5serum levels 6months after periodontal treatment. On the contrary, a significant increase in GCF expression of IL-4, IL-12, IL-17, IFN-γ and serum levels of anti-PPAD antibody was observed. Juvenile systemic lupus erythematosus patients seem to positively benefit from periodontal treatment by a significantly reduced CAL, a GCF reduction of pro-inflammatory cytokines and an increasing of anti-inflammatory ones. However, an increase in the GCF expression of IL-17 and the serum expression of anti-PPAD antibody 6months after periodontal treatment might negatively affect the treatment outcome of such patients in the long term.

The P. gingivalis Autocitrullinome Is Not a Target for ACPA in Early Rheumatoid Arthritis

Rheumatoid arthritis (RA), a chronic inflammatory disease affecting primarily the joints, is frequently characterized by the presence of autoimmune anticitrullinated protein antibodies (ACPA) during preclinical stages of disease and accumulation of hypercitrullinated proteins in arthritic joints. A strong association has been reported between RA and periodontal disease, and Porphyromonas gingivalis, a known driver of periodontitis, has been proposed as the microbial link underlying this association. We recently demonstrated P. gingivalis–mediated gut barrier breakdown and exacerbation of joint inflammation during inflammatory arthritis. In the present study, we investigated another potential role for P. gingivalis in RA etiopathogenesis, based on the generation of ACPA through the activity of a unique P. gingivalis peptidylarginine deiminase (PPAD) produced by this bacterium, which is capable of protein citrullination. Using a novel P. gingivalis W50 PPAD mutant strain, incapable of protein citrullination, and serum from disease-modifying antirheumatic drug–naïve early arthritis patients, we assessed whether autocitrullinated proteins in the P. gingivalis proteome serve as cross-activation targets in the initiation of ACPA production. We found no evidence for patient antibody activity specific to autocitrullinated P. gingivalis proteins. Moreover, deletion of PPAD did not prevent P. gingivalis–mediated intestinal barrier breakdown and exacerbation of disease during inflammatory arthritis in a murine model. Together, these findings suggest that the enzymatic activity of PPAD is not a major virulence mechanism during early stages of inflammatory arthritis.

PR296: Porphyromonas gingivalis peptidylarginine deiminase as a risk factor for the response to cytokine targeted therapy in patients with rheumatoid arthritis

PR296: Porphyromonas gingivalis peptidylarginine deiminase as a risk factor for the response to cytokine targeted therapy in patients with rheumatoid arthritis

Porphyromonas gingivalis Peptidyl Arginine Deiminase Can Modulate Neutrophil Activity via Infection of Human Dental Stem Cells

Periodontitis (PD) is a widespread chronic inflammatory disease in the human population. Porphyromonas gingivalis is associated with PD and can citrullinate host proteins via P. gingivalis peptidyl arginine deiminase (PPAD). Here, we hypothesized that infection of human dental follicle stem cells (hDFSCs) with P. gingivalis and subsequent interaction with neutrophils will alter the neutrophil phenotype. To test this hypothesis, we established and analyzed a triple-culture system of neutrophils and hDFSCs primed with P. gingivalis. Mitogen-activated pathway blocking reagents were applied to gain insight into stem cell signaling after infection. Naïve hDFSCs do not influence the neutrophil phenotype. However, infection of hDFSCs with P. gingivalis prolongs the survival of neutrophils and increases their migration. These phenotypic changes depend on direct cellular contacts and PPAD expression by P. gingivalis. Active JNK and ERK pathways in primed hDFSCs are essential for the phenotypic changes in neutrophils. Collectively, our results confirm that P. gingivalis modifies hDFSCs, thereby causing an immune imbalance.

Generation and characterisation of Porphyromonas gingivalis mutant lacking peptidylarginine deiminase activity

ABSTRACTPorphyromonas gingivalis peptidylarginine deiminase (PPAD) is the focus of several studies due to its ability to citrullinate in vitro human proteins, which have been linked to the aetiopathogenesis of rheumatoid arthritis (RA). The aim of this work was the generation by homologous recombination and characterisation of a P. gingivalis W50 mutant lacking pad gene (PG1424) to study the role of PPAD in RA. To confirm the absence of PPAD activity in P. gingivalis PG1424, cells were incubated with arginine-containing substrates and citrullination of L-arginine measured using a colorimetric assay and thin-layer chromatography. Furthermore, arginine and lysine protease (gingipain) activities were assessed and immunoblotting was performed using monoclonal antibody 1B5 (mAb1B5) and a commercial anti-modified citrulline antibody (AMC) to detect differences in virulence factor expression. The deletion of pad gene in P. gingivalis PG1424 completely abolished the ability to autocitrullinate P. gingivalis proteins in the mutant strain and also the citrullination of used substrates but not free L-arginine. Moreover, the wild-type and mutant strains had similar total gingipain activities and reactivity with mAb1B5. In conclusion, this work has produced a well-characterised PPAD-deleted P. gingivalis strain, which can be used to help determine the role of citrullination by this microorganism in RA.

Theoretical insights into the protonation states of active site cysteine and citrullination mechanism of Porphyromonas gingivalis peptidylarginine deiminase.

Porphyromonas gingivalis peptidylarginine deiminase (PPAD) catalyzes the citrullination of peptidylarginine, which plays a critical role in the rheumatoid arthritis (RA) and gene regulation. For a better understanding of citrullination mechanism of PPAD, it is required to establish the protonation states of active site cysteine, which is still a controversial issue for the members of guanidino-group-modifying enzyme superfamily. In this work, we first explored the transformation between the two states: State N (both C351 and H236 are neutral) and State I (both residues exist as a thiolate-imidazolium ion pair), and then investigated the citrullination reaction of peptidylarginine, using a combined QM/MM approach. State N is calculated to be more stable than State I by 8.46 kcal/mol, and State N can transform to State I via two steps of substrate-assisted proton transfer. Citrullination of the peptidylarginine contains deamination and hydrolysis. Starting from State N, the deamination reaction corresponds to an energy barrier of 18.82 kcal/mol. The deprotonated C351 initiates the nucleophilic attack to the substrate, which is the key step for deamination reaction. The hydrolysis reaction contains two chemical steps. Both the deprotonated D238 and H236 can act as the bases to activate the hydrolytic water, which correspond to similar energy barriers (∼17 kcal/mol). On the basis of our calculations, C351, D238, and H236 constitute a catalytic triad, and their protonation states are critical for both the deamination and hydrolysis processes. In view of the sequence similarity, these findings may be shared with human PAD1-PAD4 and other guanidino-group-modifying enzymes. Proteins 2017; 85:1518-1528. © 2017 Wiley Periodicals, Inc.

Effects by periodontitis on pristane-induced arthritis in rats.

BackgroundAn infection-immune association of periodontal disease with rheumatoid arthritis has been suggested. This study aimed to investigate the effect of pre-existing periodontitis on the development and the immune/inflammatory response of pristane-induced arthritis.MethodsWe investigated the effect of periodontitis induced by ligature placement and Porphyromonas gingivalis (P. gingivalis) infection, in combination with Fusobacterium nucleatum to promote its colonization, on the development of pristane-induced arthritis (PIA) in rats (Dark Agouti). Disease progression and severity of periodontitis and arthritis was monitored using clinical assessment, micro-computed tomography (micro-CT)/intraoral radiographs, antibody response, the inflammatory markers such as α-1-acid glycoprotein (α-1-AGP) and c-reactive protein (CRP) as well as cytokine multiplex profiling at different time intervals after induction.ResultsExperimentally induced periodontitis manifested clinically (P < 0.05) prior to pristane injection and progressed steadily until the end of experiments (15 weeks), as compared to the non-ligated arthritis group. Injection of pristane 8 weeks after periodontitis-induction led to severe arthritis in all rats demonstrating that the severity of arthritis was not affected by the pre-existence of periodontitis. Endpoint analysis showed that 89% of the periodontitis-affected animals were positive for antibodies against arginine gingipain B and furthermore, the plasma antibody levels to a citrullinated P. gingivalis peptidylarginine deiminase (PPAD) peptide (denoted CPP3) were significantly (P < 0.05) higher in periodontitis rats with PIA. Additionally, there was a trend towards increased pro-inflammatory and anti-inflammatory cytokine levels, and increased α-1-AGP levels in plasma from periodontitis-challenged PIA rats.ConclusionsPre-existence of periodontitis induced antibodies against citrullinated peptide derived from PPAD in rats with PIA. However, there were no differences in the development or severity of PIA between periodontitis challenged and periodontitis free rats.Electronic supplementary materialThe online version of this article (doi:10.1186/s12967-016-1067-6) contains supplementary material, which is available to authorized users.

Concentration of antibodies against Porphyromonas gingivalis is increased before the onset of symptoms of rheumatoid arthritis.

BackgroundThe periodontal pathogen Porphyromonas gingivalis is hypothesized to be important in rheumatoid arthritis (RA) aetiology by inducing production of anti-citrullinated protein antibodies (ACPA). We have shown that ACPA precede RA onset by years, and that anti-P. gingivalis antibody levels are elevated in RA patients. The aim of this study was to investigate whether anti-P. gingivalis antibodies pre-date symptom onset and ACPA production.MethodsA case–control study (251 cases, 198 controls) was performed within the Biobank of Northern Sweden. Cases had donated blood samples (n = 422) before the onset of RA symptoms by 5.2 (6.2) years (median (interquartile range)). Blood was also collected from 192 RA patients following diagnosis. Antibodies against P. gingivalis virulence factor arginine gingipainB (RgpB), and a citrullinated peptide (CPP3) derived from the P. gingivalis peptidylarginine deiminase enzyme, were analysed by ELISA.ResultsAnti-RgpB IgG levels were significantly increased in pre-symptomatic individuals (mean ± SEM; 152.7 ± 14.8 AU/ml) and in RA patients (114.4 ± 16.9 AU/ml), compared with controls (p < 0.001). Anti-CPP3 antibodies were detected in 5 % of pre-symptomatic individuals and in 8 % of RA patients, with elevated levels in both subsets (4.33 ± 0.59 and 9.29 ± 1.81 AU/ml, respectively) compared with controls (p < 0.001). Anti-CPP3 antibodies followed the ACPA response, with increasing concentrations over time, whilst anti-RgpB antibodies were elevated and stable in the pre-symptomatic individuals with a trend towards lower levels after RA diagnosis.ConclusionsAnti-P. gingivalis antibody concentrations were significantly increased in RA patients compared with controls, and were detectable years before onset of symptoms of RA, supporting an aetiological role for P. gingivalis in the development of RA.Electronic supplementary materialThe online version of this article (doi:10.1186/s13075-016-1100-4) contains supplementary material, which is available to authorized users.

Serum Immunoglobulin G Levels to Porphyromonas gingivalis Peptidylarginine Deiminase Affect Clinical Response to Biological Disease-Modifying Antirheumatic Drug in Rheumatoid Arthritis.

ObjectivesTo determine whether serum immunity to Porphyromonas gingivalis peptidylarginine deiminase (PPAD) affects the clinical response to biological disease-modifying antirheumatic drug (bDMARD) in patients with rheumatoid arthritis (RA).MethodsIn a retrospective study, rheumatologic and periodontal conditions of 60 patients with RA who had been treated with conventional synthetic DMARD were evaluated before (baseline) and after 3 and 6 months of bDMARD therapy. After serum levels of anti-PPAD immunoglobulin G (IgG) were determined at baseline, the patients were respectively divided into two groups for high and low anti-PPAD IgG titers according to the median measurements. Genotypes at 8 functional single nucleotide polymorphisms (SNPs) related to RA were also determined.ResultsAfter 3 and 6 months of therapy, patients with low anti-PPAD IgG titers showed a significantly greater decrease in changes in the Disease Activity Score including 28 joints using C-reactive protein (DAS28-CRP) (P = 0.04 for both) and anti-cyclic citrullinated peptide (CCP) IgG levels (P = 0.03 and P = 0.04) than patients with high anti-PPAD IgG titers, although these parameter values were comparable at baseline. The anti-PPAD IgG titers were significantly positively correlated with changes in the DAS28-CRP (P = 0.01 for both) and the anti-CCP IgG levels (P = 0.02 for both) from baseline to 3 and 6 months later. A multiple regression analysis revealed a significantly positive association between the anti-PPAD IgG titers and changes in the DAS28-CRP after 6 months of bDMARD therapy (P = 0.006), after adjusting for age, gender, smoking, periodontal condition, and RA-related SNPs.ConclusionThe serum IgG levels to PPAD affect the clinical response to bDMARD in patients with RA.

The peptidylarginine deiminase gene is a conserved feature of Porphyromonas gingivalis.

Periodontitis is an infective process that ultimately leads to destruction of the soft and hard tissues that support the teeth (the periodontium). Periodontitis has been proposed as a candidate risk factor for development of the autoimmune disease rheumatoid arthritis (RA). Porphyromonas gingivalis, a major periodontal pathogen, is the only known prokaryote expressing a peptidyl arginine deiminase (PAD) enzyme necessary for protein citrullination. Antibodies to citrullinated proteins (anti-citrullinated protein antibodies, ACPA) are highly specific for RA and precede disease onset. Objective of this study was to assess P. gingivalis PAD (PPAD) gene expression and citrullination patterns in representative samples of P. gingivalis clinical isolates derived from periodontitis patients with and without RA and in related microbes of the Porphyromonas genus. Our findings indicate that PPAD is omnipresent in P. gingivalis, but absent in related species. No significant differences were found in the composition and expression of the PPAD gene of P. gingivalis regardless of the presence of RA or periodontal disease phenotypes. From this study it can be concluded that if P. gingivalis plays a role in RA, it is unlikely to originate from a variation in PPAD gene expression.

Expression of anti-Porphyromonas gingivalis peptidylarginine deiminase immunoglobulin G and peptidylarginine deiminase-4 in patients with rheumatoid arthritis and periodontitis.

Autoimmunity against citrullinated proteins through peptidylarginine deiminase (PAD) may be involved in the pathophysiology of rheumatoid arthritis (RA). The present study evaluated the serum levels of antibodies to citrullinated proteins and to Porphyromonas gingivalis PAD (PPAD), and the endogenous expression of PAD-4, in individuals with and without RA, as well as before and after periodontal treatment. The study participants consisted of 52 patients with RA (RA group) and 26 age-, gender- and smoking status-matched healthy controls (non-RA group). Of the 52 patients, 26 were randomly assigned to receive oral hygiene instruction and supragingival scaling (RA subgroup). After periodontal and rheumatologic assessments, the serum levels of anti-cyclic citrullinated peptide (CCP) immunoglobulin G (IgG), anti-PPAD IgG and PAD-4 were determined using ELISA. The serum levels of anti-CCP IgG and anti-PPAD IgG were significantly higher in the RA group than in the non-RA group (p < 0.001 and p = 0.03). A significant, positive correlation was observed between the serum levels of anti-PPAD IgG and anti-CCP IgG (p = 0.04), but not between the serum levels of PAD-4 and anti-CCP IgG. Multiple logistic regression analyses revealed a significant association between anti-PPAD IgG responses and RA after adjustment for age, gender and smoking (p = 0.004). Supragingival scaling significantly improved the periodontal condition and disease activity of RA (p < 0.05), but failed to decrease the serum levels of anti-CCP IgG, anti-PPAD IgG and PAD-4 after 2 mo of treatment. These results might suggest an association between anti-PPAD IgG and anti-CCP IgG responses, implicating a role for PPAD in protein citrullination in patients with RA and periodontitis.

Porphyromonas gingivalis peptidylarginine deiminase, a key contributor in the pathogenesis of experimental periodontal disease and experimental arthritis.

ObjectivesTo investigate the suggested role of Porphyromonas gingivalis peptidylarginine deiminase (PAD) in the relationship between the aetiology of periodontal disease and experimentally induced arthritis and the possible association between these two conditions.MethodsA genetically modified PAD-deficient strain of P. gingivalis W50 was produced. The effect of this strain, compared to the wild type, in an established murine model for experimental periodontitis and experimental arthritis was assessed. Experimental periodontitis was induced following oral inoculation with the PAD-deficient and wild type strains of P. gingivalis. Experimental arthritis was induced via the collagen antibody induction process and was monitored by assessment of paw swelling and micro-CT analysis of the radio-carpal joints. Experimental periodontitis was monitored by micro CT scans of the mandible and histological assessment of the periodontal tissues around the mandibular molars. Serum levels of anti-citrullinated protein antibodies (ACPA) and P. gingivalis were assessed by ELISA.ResultsThe development of experimental periodontitis was significantly reduced in the presence of the PAD-deficient P. gingivalis strain. When experimental arthritis was induced in the presence of the PAD-deficient strain there was less paw swelling, less erosive bone damage to the joints and reduced serum ACPA levels when compared to the wild type P. gingivalis inoculated group.ConclusionThis study has demonstrated that a PAD-deficient strain of P. gingivalis was associated with significantly reduced periodontal inflammation. In addition the extent of experimental arthritis was significantly reduced in animals exposed to prior induction of periodontal disease through oral inoculation of the PAD-deficient strain versus the wild type. This adds further evidence to the potential role for P. gingivalis and its PAD in the pathogenesis of periodontitis and exacerbation of arthritis. Further studies are now needed to elucidate the mechanisms which drive these processes.

Defining the role of Porphyromonas gingivalis peptidylarginine deiminase (PPAD) in rheumatoid arthritis through the study of PPAD biology

BackgroundAntibodies to citrullinated proteins are a hallmark of rheumatoid arthritis (RA). Porphyromonas gingivalis peptidylarginine deiminase (PPAD) has been implicated in the initiation of RA by generating citrullinated neoantigens and due...

The Link Between Periodontal Disease and Rheumatoid Arthritis: An Updated Review

Porphyromonas gingivalis is a leading pathogen in chronic periodontitis, a disease process involving progressive destruction of the tissues that support the teeth. Recently, the organism has been reported to produce a unique bacterial enzyme, P. gingivalis peptidyl-arginine deiminase (PPAD), which has the ability to convert arginine residues in proteins to citrulline. Protein citrullination alters protein structure and function; hence, PPAD may be involved in deregulation of the host’s signalling network and immune evasion. Further, accumulating evidence suggests a role for autoimmunity against citrullinated proteins in the development of rheumatoid arthritis (RA). As inflammatory conditions in the lungs of cigarette smokers contribute to the breakdown of immune tolerance to citrullinated epitopes, chronic exposure to citrullinated proteins at periodontitis sites may also predispose susceptible individuals to the development of autoantibodies and the initiation of RA. In this review, we discuss evidence that PPAD may represent a mechanistic link between periodontitis and RA, diseases that are known to be significantly associated at the epidemiological level.

Porphyromonas gingivalis Facilitates the Development and Progression of Destructive Arthritis through Its Unique Bacterial Peptidylarginine Deiminase (PAD)

Rheumatoid arthritis and periodontitis are two prevalent chronic inflammatory diseases in humans and are associated with each other both clinically and epidemiologically. Recent findings suggest a causative link between periodontal infection and rheumatoid arthritis via bacteria-dependent induction of a pathogenic autoimmune response to citrullinated epitopes. Here we showed that infection with viable periodontal pathogen Porphyromonas gingivalis strain W83 exacerbated collagen-induced arthritis (CIA) in a mouse model, as manifested by earlier onset, accelerated progression and enhanced severity of the disease, including significantly increased bone and cartilage destruction. The ability of P. gingivalis to augment CIA was dependent on the expression of a unique P. gingivalis peptidylarginine deiminase (PPAD), which converts arginine residues in proteins to citrulline. Infection with wild type P. gingivalis was responsible for significantly increased levels of autoantibodies to collagen type II and citrullinated epitopes as a PPAD-null mutant did not elicit similar host response. High level of citrullinated proteins was also detected at the site of infection with wild-type P. gingivalis. Together, these results suggest bacterial PAD as the mechanistic link between P. gingivalis periodontal infection and rheumatoid arthritis.

Effect of Porphyromonas gingivalis on Citrullination of Proteins by Macrophages In Vitro

Citrullination of proteins within inflamed periodontal tissues may provide an important link between periodontitis and rheumatoid arthritis. The aim of this study is to determine whether the presence of Porphyromonas gingivalis peptidylarginine deiminase (PPAD) can influence citrullination of proteins by either increasing the amount of local citrullinated protein or influencing the peptidylarginine deiminase (PAD) enzymes found in the monocyte/macrophage population. Human peripheral blood monocytes and macrophages were incubated in the presence of live or heat-killed P. gingivalis. Expression of PAD2 and PAD4, PPAD, and citrullinated proteins were assessed by either a combination of real-time polymerase chain reaction, Western blotting, or a colorimetric assay. PPAD was detected only in mononuclear cells incubated in the presence of live P. gingivalis and resulted in increased extracellular citrullination. Endogenous PAD (mRNA and protein) expression was detected in monocytes and macrophages but was not affected by P. gingivalis. Although P. gingivalis produces a PAD that can citrullinate extracellular proteins and may contribute to the citrullinated protein load in gingival tissues, it does not appear to affect PAD expression or citrullination by host monocytes or macrophages.