The Proteolytic Activity of Porphyromonas gingivalis Is Critical in a Murine Model of Periodontitis

Background: Porphyromonas gingivalis ( Pg ), a periodontal pathogen, has interstrain variability in virulence. The aim of this study is to determine the contribution of the cell invasion ability and proteolytic activity of Pg to its virulence in a murine model of periodontitis. Methods: Three clinical isolates: KUMC‐P1 (P1: low cell invasion ability and low proteolytic activity); KUMC‐P4 (P4: low cell invasion ability and high proteolytic activity); and KUMC‐P8 (P8: high cell invasion ability and low proteolytic activity), were orally administered into mice. Alveolar bone loss (ABL) and bacterial invasion of gingival tissues were measured. Additionally, effects of the three strains on transepithelial electrical resistance (TER) and the levels of tight‐junction proteins in gingival epithelial cells were evaluated in vitro. Results: ABL induced by the three strains was in the sequence P4 > P8 > P1, and the difference between P8 and P1 was not significant. Amounts of Pg detected within the gingival tissues were increased by all three strains compared with the sham group, and bacterial level was positively correlated with ABL. In vitro, P4 had a greater effect than the other strains on epithelial barrier disruption, as evidenced by the reduced levels of tight‐junction proteins and TER. Conclusion: The proteolytic activity of Pg was more critical than the cell invasion ability for inducing experimental periodontitis in mice, which could be attributed to the paracellular pathway dependence of gingival tissue invasion by bacteria in the mice.