P.G-Omvs Promote Metastasis Via Pre-Metastatic Niche Formation

Aim or purpose: Porphyromonas gingivalis (P.g) has been shown to promote tumor growth and metastasis. Outer membrane vesicles (OMVs), secreted by gram-negative bacteria, mediate intercellular communication. However, whether P.g promotes metastasis via OMVs secretion remains unknown. Materials and methods: P.g-OMVs were extracted via ultracentrifugation and characterized using transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA). qRT-PCR and ELISA were performed to detect inflammatory cytokines and macrophage chemoattractant expression in endothelial cells (ECs). Cell migration and invasion were evaluated using 2D and 3D spheroid assays. Macrophage M2 polarization was investigated using qRT-PCR and flow cytometry. In vivo, pre-metastatic niche and hematogenous metastasis models were established by intravenous P.g-OMVs injection to the C57BL/6 mice. Animal protocols were approved by Institutional Ethics Committee. Results: TEM and NTA identified that P.g-OMVs have a lipid bilayer structure with a diameter of 136 nm. P.g-OMVs significantly upregulated the expressions of IL-6, IL-8, IL-1β, TNF-α, CCL2, CCL3, and CCL22 in ECs, accompanied by the elevated CCL2 and CCL22 secretion. P.g-OMVs promoted TGF-β and Arg-1 expression, thereby accelerating M2 polarization. P.g-OMVs promoted OSCC migration and invasion. In vivo, lung tissues in the P.g-OMVs group detected a significant increase in M2 macrophage and a decrease in M1 macrophage. Moreover, statistically elevated metastatic lung foci were evaluated in the P.g-OMVs group. Conclusions: P.g-OMVs promote metastasis by forming a pre-metastatic niche in the lungs through macrophage M2 polarization.