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

Abstract

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.

Opportunistic pathogen Porphyromonas gingivalis targets the LC3B-ceramide complex and mediates lethal mitophagy resistance in oral tumors

“…This work provides previously unknown details of the ceramide-LC3B complex, which includes ANXA2, 46 as decreased ANXA2-ceramide association by P. gingivalis or shRNA-mediated knockdown prevented ceramide-dependent mitophagy. Our data also showed that bacterial FimA protein 47 , 48 is key to targeting and inhibiting the formation of ANXA2-ceramide-LC3B by FimA-ANXA2 interaction in response to P. gingivalis infection in OSCC cells. FimA is a unique type V fimbria distinct to P. gingivalis, which is used in biofilm formation, adhesion to host molecules, host cell invasion, and enhancing proliferation in human primary epithelial cells.…”

“…In this study, we only utilized the 33277 strain (a type strain), which has been one of the most characterized strains for the host pathogenesis of P. gingivalis . 48 , 56 Therefore, future studies that use low-passage clinical strains might be warranted to reach deeper conclusions. Nevertheless, our study provides a mechanism by which P. gingivalis infection results in resistance to ceramide-dependent mitophagy by targeting the ANXA2-ceramide-LC3B complex via bacterial FimA-ANXA2 association.…”

Porphyromonas gingivalis Peptidyl Arginine Deiminase (PPAD) in the Context of the Feed-Forward Loop of Inflammation in Periodontitis

“…IL-6 is another important pro-inflammatory cytokine implicated in the progression of periodontal disease [ 35 , 36 ]. Compared with PMNs infected with WT P. gingivalis, PMNs infected with the PPAD mutant strain showed reduced secretion of IL-6 after 3, 24, and 48 h ( Figure 3 b).…”

“…Overall, these results suggested that PPAD possesses strong immune-modulatory activity due to its regulation of pro-inflammatory cytokine release. IL-6 is another important pro-inflammatory cytokine implicated in the progression of periodontal disease [35,36]. Compared with PMNs infected with WT P. gingivalis, PMNs infected with the PPAD mutant strain showed reduced secretion of IL-6 after 3, 24, and 48 h (Figure 3b).…”

Frankincense (Boswellia serrata) Extract Effects on Growth and Biofilm Formation of Porphyromonas gingivalis, and Its Intracellular Infection in Human Gingival Epithelial Cells

“…Interestingly, P. gingivalis and F. nucleatum use different mechanisms to modulate the host immune response and contribute to biofilm formation and dissemination [13][14][15][16]. P. gingivalis and F. nucleatum are intracellular pathogens and have been described to evade the host immune response via several virulence factors [9,14,[16][17][18][19][20][21][22].…”