Peptidylarginine deiminase from Porphyromonas gingivalis contributes to infection of gingival fibroblasts and induction of prostaglandin E₂‐signaling pathway

Abstract

SUMMARY Porphyromonas gingivalis (Pg) expresses the enzyme peptidylarginine deiminase (PPAD), which has a strong preference for C-terminal arginines. Due to the combined activity of PPAD and Arg-specific gingipains, Pg on the cell surface is highly citrullinated. To investigate the contribution of PPAD to the interaction of Pg with primary human gingival fibroblasts (PHGF) and Pg-induced synthesis of prostaglandin E2 (PGE2), PHGF were infected with wild-type Pg ATCC 33277, an isogenic PPAD-knockout strain (Δppad) or a mutated strain (C351A) expressing an inactive enzyme in which the catalytic cysteine has been mutated to alanine (PPADC351A). Cells were infected in medium containing the mutants alone or in medium supplemented with purified, active PPAD. PHGF infection was assessed by colony-forming assay, microscopic analysis and flow cytometry. Expression of COX-2 and mPGES-1, key factors in the prostaglandin synthesis pathway, was examined by qRT-PCR, while PGE2 synthesis was evaluated by EIA. PHGF were infected more efficiently by wt-Pg than the Δppad strain, which correlated with strong induction of COX-2 and mPGES-1 expression by wt-Pg, but not by the PPAD activity-null mutant strains (ΔPPAD and C351A). The impaired ability of the ΔPPAD strain to adhere to and/or invade PHGF and both ΔPPAD and C351A to stimulate the PGE2-synthesis pathway was fully restored by the addition of purified PPAD. The latter effect was strongly inhibited by aspirin. Collectively, our results implicate PPAD activity, but not PPAD itself, as an important factor for gingival fibroblast infection and activation of PGE2 synthesis, the latter of which may strongly contribute to bone resorption and eventual tooth loss.

Metabolomic Status of The Oral Cavity in Chronic Periodontitis

“…P. gingivalis does not produce a single potent exotoxin, but is equipped with a set of enzymes, e.g. proteinases, hemolysins, peptidylarginine deiminase and cellular constituents, such as fimbriae and lipopolysaccharides, which along with toxic metabolites, have the potential to impinge upon host tissue integrity thus causing destruction of periodontal supporting tissues (5,7,(10)(11)(12). The repertoire of enzymes and metabolites that can be detrimental to the host also includes phospholipase A, prostaglandins, alkaline and acid phosphatases, etc.…”

The peptidylarginine deiminase gene is a conserved feature of Porphyromonas gingivalis

“…Additionally, a side effect of citrullination is ammonia production, which has a negative effect on neutrophil function and is protective during the acidic cleansing cycles of the mouth 7 8 . PPAD is regarded as a virulence factor because citrullination by PPAD interferes with complement activity 9 , inactivates epidermal growth factors 10 and contributes to infection of gingival fibroblasts and induction of the prostaglandin E2 synthesis 11 . Moreover, PPAD has been reported to be able to generate citrullinated forms of various arginine-containing proteins and peptides 8 , among which are human fibrinogen and human α-enolase, two candidate auto-antigens in RA 12 .…”

Periodontal disease and periodontal bacteria as triggers for rheumatoid arthritis

“…It is capable of auto-citrullinating some of its 18 arginine residues [76], although there is evidence that anti-PPAD antibodies are not directed against the citrullinated form of PPAD and that in humans, PPAD is not modified in this manner [77]. PPAD enhances cell invasion by P. gingivalis [78] and citrullinates host defence components, such as complement and LL-37, with consequent loss of function [79,80]. Human fibrinogen and -enolase, two of the proteins targeted by ACPAs in RA [74], are also PPAD substrates and antibodies against auto-citrullinated P. gingivalis enolase cross react with human -enolase autoantibodies [48].…”