Porphyromonas gingivalis Evasion of Autophagy and Intracellular Killing by Human Myeloid Dendritic Cells Involves DC-SIGN-TLR2 Crosstalk

Abstract

Signaling via pattern recognition receptors (PRRs) expressed on professional antigen presenting cells, such as dendritic cells (DCs), is crucial to the fate of engulfed microbes. Among the many PRRs expressed by DCs are Toll-like receptors (TLRs) and C-type lectins such as DC-SIGN. DC-SIGN is targeted by several major human pathogens for immune-evasion, although its role in intracellular routing of pathogens to autophagosomes is poorly understood. Here we examined the role of DC-SIGN and TLRs in evasion of autophagy and survival of Porphyromonas gingivalis in human monocyte-derived DCs (MoDCs). We employed a panel of P. gingivalis isogenic fimbriae deficient strains with defined defects in Mfa-1 fimbriae, a DC-SIGN ligand, and FimA fimbriae, a TLR2 agonist. Our results show that DC-SIGN dependent uptake of Mfa1+P. gingivalis strains by MoDCs resulted in lower intracellular killing and higher intracellular content of P. gingivalis. Moreover, Mfa1+P. gingivalis was mostly contained within single membrane vesicles, where it survived intracellularly. Survival was decreased by activation of TLR2 and/or autophagy. Mfa1+P. gingivalis strain did not induce significant levels of Rab5, LC3-II, and LAMP1. In contrast, P. gingivalis uptake through a DC-SIGN independent manner was associated with early endosomal routing through Rab5, increased LC3-II and LAMP-1, as well as the formation of double membrane intracellular phagophores, a characteristic feature of autophagy. These results suggest that selective engagement of DC-SIGN by Mfa-1+P. gingivalis promotes evasion of antibacterial autophagy and lysosome fusion, resulting in intracellular persistence in myeloid DCs; however TLR2 activation can overcome autophagy evasion and pathogen persistence in DCs.

Role of Mfa5 in Expression of Mfa1 Fimbriae in Porphyromonas gingivalis

“…In P. gingivalis, it has been demonstrated that the accessory proteins FimC-E are essential for maintaining the structure and adhesive properties of FimA fimbriae (Nishiyama et al 2007). Binding of the C-type lectin DC-SIGN to Mfa1 fimbriae allows P. gingivalis to survive within dendritic cells (El-Awady et al 2015); the Mfa3-5 fimbrial tip complex is thought to be involved in this interaction. Therefore, our findings have implications for potential antibacterial therapeutic intervention for periodontitis.…”

Bacterial Pathogens versus Autophagy: Implications for Therapeutic Interventions

“…Porphyromonas gingivalis avoids targeting to lysosomes in human DCs and instead traffics to vesicles resembling autophagosomes where it replicates. Indeed, selective engagement of DC-SIGN by P. gingivalis during uptake promotes evasion of lysosome fusion[70]. Induction of autophagy promotes the replication of A. phagocytophilum, C. burnetii , and P. gingivalis , while inhibition of autophagy blocks the replication of these pathogens in cell culture systems[63,67,71–73].…”

Herpesvirus‐bacteria synergistic interaction in periodontitis

“…gingivalis in dendritic cells via a specific nonintegrin intercellular adhesion-grabbing molecule. 213 Porphyromonas gingivalis in association with macrophages induces toll-like receptor-2-mediated transactivation of CR3 through an inside-out pathway, and the activated CR3 interacts with P. gingivalis major fimbriae to downregulate interleukin-12, allowing P. gingivalis to enter and persist in macrophages. 189,212 Overall, P. gingivalis plays an essential role in subgingival microbial dysbiosis because of its participation in biofilm formation and modulation of host defenses, and the organism is recognized as a prototypic keystone pathogen of periodontitis.…”