Porphyromonas gingivalis outer membrane vesicles promote alveolar bone resorption by increasing the local RANKL/OPG ratio in experimental periodontitis model rats

Abstract

Abstract Outer membrane vesicles (OMVs) released by bacteria contain bacteria-specific nucleic acids and proteins. Porphyromonas gingivalis ( Pg )-OMVs exert various effects on periodontal tissue cells; however, their involvement in bone metabolism remains unclear. Therefore, this study aimed to investigate the effects of Pg -OMVs on osteoclasts and osteoblasts in vitro and elucidate their involvement in alveolar bone resorption in vivo using experimental periodontitis model rats. Tartrate-resistant acid phosphatase staining and Western blotting revealed that Pg -OMVs promoted osteoclast differentiation and increased the levels of several osteoclast differentiation markers, respectively, in RAW264.7 cells. Quantitative reverse transcription-polymerase chain reaction and Western blotting revealed that Pg -OMVs increased the receptor activator of nuclear factor-kappa B (NF-κB) ligand (RANKL) levels and decreased osteoprotegerin (OPG) levels in MC3T3-E1 cells. Pg -OMVs reduced alkaline phosphatase activity and calcified nodule formation in a concentration-dependent manner. Rats were divided into four groups (healthy control, Pg -OMV administration, ligature-induced periodontitis, and ligature-induced periodontitis with Pg -OMV administration groups), and the alveolar bone resorption degree was measured via micro-computed tomography. Pg -OMVs administration significantly promoted alveolar bone resorption and increased the RANKL/OPG ratio in periodontal tissues. Our results suggest that Pg -OMVs contribute to alveolar bone resorption by promoting osteoclast differentiation, suppressing osteoblast mineralization, and increasing the RANKL/OPG ratio.