Oral Microbially Induced Exosomes promote Neuroinflammation and Microglial Cell Senescence

OBJECTIVES

Porphyromonas gingivalis (Pg) and its gingipain proteases contribute to Alzheimer's disease (AD) pathogenesis through yet unclear mechanisms. Cellular secretion of small extracellular vesicles or exosomes (exo) increases with aging as part of the senescence-associated secretory phenotype (SASP). We have shown that exo isolated from Pg-infected dendritic cells (PgDCexo) contain Pg antigens, transmit senescence to bystander gingival cells, and can cross the blood-brain barrier in mice. This study aims to determine the ability of PgDCexo to induce senescence and neuroinflammation in the brain using a microglial cell line in vitro.

METHODS

Isolated PgDCexo were quantitated and characterized using NTA, western blot (WB), and transmission electron microscopy (TEM). DiI labeled PgDCExo were co-cultured with murine SIMA9 microglial cells for 24 hrs, and uptake was analyzed by confocal microscopy. The effect of PgDCexo on microglial senescence and inflammation was tested using western blot, qPCR, and flow cytometry analysis (FACS).

RESULTS

DiI labeled PgDCexo were internalized in microglial cells. PgDCexo induced senescence in SIMA9 cells in a dose-dependent manner as shown by an increase in senescence biomarkers, p16 INK4A and P53 by WB and qPCR . SIMA9 cells treated with PgDCExo showed upregulated levels of IL-1β, TNFa and IL-6 by FACS and activated NLRP3 inflammasome pathway by WB.

CONCLUSIONS

Extracellular vesicles induced by P. gingivalis infection promote senescence and inflammation in microglial cells. These results suggest a potential role of Pg-induced extracellular vesicles in neuroinflammation and AD pathogenesis.

IMPLICATIONS

This study sheds light on a novel mechanism through which P.gingivalis-induced extracellular vesicles affect neurodegenerative processes in Alzheimer's disease.