TLR2 Activation by Porphyromonas gingivalis Requires Both PPAD Activity and Fimbriae

Abstract

Porphyromonas gingivalis, a keystone oral pathogen implicated in development and progression of periodontitis, may also contribute to the pathogenicity of diseases such as arthritis, atherosclerosis, and Alzheimer’s. P. gingivalis is a master manipulator of host immune responses due to production of a large variety of virulence factors. Among these, P. gingivalis peptidilarginine deiminase (PPAD), an enzyme unique to P. gingivalis, converts C-terminal Arg residues in bacterium- and host-derived proteins and peptides into citrulline. PPAD contributes to stimulation of proinflammatory responses in host cells and is essential for activation of the prostaglandin E2 (PGE2) synthesis pathway in gingival fibroblasts. Since P. gingivalis is recognized mainly by Toll-like receptor-2 (TLR2), we investigated the effects of PPAD activity on TLR2-dependent host cell responses to P. gingivalis, as well as to outer membrane vesicles (OMVs) and fimbriae produced by this organism. Using reporter cell lines, we found that PPAD activity was required for TLR2 activation by P. gingivalis cells and OMVs. We also found that fimbriae, an established TLR2 ligand, from wild-type ATCC 33277 (but not from its isogenic PPAD mutant) enhanced the proinflammatory responses of host cells. Furthermore, only fimbriae from wild-type ATCC 33277, but not from the PPAD-deficient strains, induced cytokine production and stimulated expression of genes within the PGE2 synthesis pathway in human gingival fibroblasts via activation of the NF-ĸB and MAP kinase-dependent signaling pathways. Analysis of ten clinical isolates revealed that type I FimA is preferable for TLR2 signaling enhancement. In conclusion, the data strongly suggest that both PPAD activity and fimbriae are important for TLR2-dependent cell responses to P. gingivalis infection.

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

“…U251 MG cells were used for the preparation of reporter cells transiently overexpressing TLR2, expressing firefly luciferase under the control of NF‐κB response elements, and constitutively expressing β‐galactosidase (transfection control). The transfection and reporter assay procedures are described elsewhere (Wielento et al., 2022).…”

“…In the context of periodontitis, the most important TLR2 ligands include P. gingivalis fimbriae involved in bacterial adhesion to cell surfaces, invasion of host cells, and aggregation with other bacteria during biofilm formation (Enersen et al., 2013; Hasegawa & Nagano, 2021). We previously showed that the proinflammatory response of primary human gingival fibroblasts (PHGFs) to P. gingivalis depends on the presence of fimbriae and PPAD activity, suggesting that the citrullination of a fimbrial component strongly enhances the TLR2‐activating potential of fimbriae (Wielento et al., 2022). Here we focused on the identification of specific fimbrial subunits responsible for the PPAD‐dependent augmentation of TLR2 activation.…”

Effects of Oral Inflammatory Diseases and Oral Hygiene on Atrial Fibrillation: A Systematic Review

“…Second, regarding the roles of inflammatory mediators and systemic inflammation, periodontal disease could cause a persistent inflammatory response or bacteremia, release inflammatory mediators such as C-reactive protein and interleukin-6, stimulate myocardial cell hypertrophy and apoptosis, promote myocardial fibrosis, and shorten the atrial effective refractory period, which could increase the occurrence risk and recurrence risk of atrial fibrillation [ 35 ]. As the main virulence factor of P. gingivalis , fimbriae can regulate bacterial adhesion and invasion and stimulate a long-term chronic inflammatory response, inhibit interleukin-12 expression, and reduce the host's ability to clear inflammation [ 36 ]. Third, regarding immune response, periodontal pathogens can stimulate the release of large amounts of matrix metalloproteinases (MMPs) from lymphocytes and promote the occurrence of cardiovascular diseases [ 37 ].…”

Porphyromonas gingivalis regulates atherosclerosis through an immune pathway

“…The fimbriae of P. gingivalis are divided into long fimbriae (FimA) and short fimbriae (Mfa1), both of which have enhanced inflammatory responses and evasion of host immune clearance, although each has its mechanism of action with the host. FimA acts through the characteristic P. gingivalis peptidilarginine deiminase (PPAD)-dependent activation of TLR2, induction of NF-ĸB and MAPK signaling pathways, and promotion of pro-inflammatory factor production ( 79 ). FimA interacts with complement receptor 3 (CR3) in macrophages, leading to ERK1/2 phosphorylation and inhibition of IL-12 production to promote the survival of P. gingivalis ( 80 ).…”