Porphyromonas gingivalis Outer Membrane Vesicles-Associated DNA Triggers Inflammation by Inducing IL-6 in Astrocytes

Porphyromonas gingivalis (Pg), a key pathogen in periodontal disease, is suggested to be involved in the progression of Alzheimer's disease (AD); however, the molecular mechanism remains unclear. We previously reported that Pg-released outer membrane vesicles (OMVs) were detected in the brains of mice after intraperitoneal administration. We here investigated the effects of Pg OMVs on astrocytes, the most abundant glial cells in the central nervous system, which are involved in neuroinflammation. We demonstrated that Pg OMVs increased the expression of interleukin-6 (IL-6) mRNA, which is associated with the pathogenesis of AD, in a Toll-like receptor (TLR)2/4-independent manner in human astrocyte SVG p12 cells. Whole-genome sequencing revealed that Pg OMVs contained Pg genomic DNA, which was critical for IL-6 mRNA induction. The tracking of fluorescent-labeled Pg OMV-associated DNA revealed that Pg OMVs were transported into SVG p12 cells. Endocytosis inhibitors attenuated IL-6 mRNA expression induced by Pg OMVs, suggesting that the incorporation of Pg OMVs by endocytosis is important for IL-6 mRNA induction. Furthermore, the incorporated Pg OMV-associated DNA increased IL-6 mRNA expression via the TLR9 pathway. Our study advances understanding of the role of Pg OMVs, which may contribute to the onset and progression of AD in periodontal disease.