Resumen de The Proteolytic Activity of Porphyromonas gingivalis Is Critical in a Murine Model of Periodontitis
Keum Jin Baek, Yun Sik Choi, Cheol Keun Kang, Youngnim Choi
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.
Periodontitis is a chronic inflammatory disease of the periodontium caused by loss of homeostasis between a subgingival biofilm and its host.1 With the accumulation of plaque bacteria, amounts of immune-evasive and/or invasive periodontal pathogens, such as Porphyromonas gingivalis (Pg), Treponema denticola, and Tannerella forsythia, are increased,2 and bacterial invasion into gingival tissues may have a crucial role in the development of chronic periodontitis.3,4 The gingival epithelia form physical, chemical, and immunologic barriers against invading plaque-associated bacteria and provide the first line of host defense.4 Gingival epithelial cells are connected to each other by protein complexes consisting of cytoskeletal, cytosolic, and transmembrane proteins.5,6 Among these proteins, zonula occludens (ZO), junctional adhesion molecules (JAMs), occludin, and claudins assemble tight junction-like structures that regulate transport of ions, solutes, and water through the paracellular pathway.7,8 The function of the physical barrier is modulated by the expression and localization of tight-junction proteins.9 A number of chemicals and pathogens are known to modulate epithelial barrier function.4 Application of a barrier-disrupting chemical, dextran sulfate sodium, to the gingival mucosa has been shown to induce alveolar bone loss (ABL) in mice.3 Pg has the capacity to invade the gingival epithelia through both transcellular and paracellular pathways. It can efficiently invade gingival epithelial cells and spread into neighboring cells.10,11 In addition, gingipains, the potent cysteine proteinases of Pg, modulate expression of epithelial junctional proteins, such as ZO-1, occludin, claudins, and E-cadherin, disrupting epithelial barrier function.3,12-14 Gingipains also hydrolyze various immune components, including immunoglobulins, complement proteins, and cytokines/chemokines, suggesting that Pg may be able to modulate the host immune response to its benefit.15-19 Pg clinical isolates exhibit variable proteolytic and cell invasion activities.20-22 Evaluation of the heterogenic virulence of Pg clinical isolates in a mouse abscess model has revealed associations with both cell invasion and proteolytic activities.22 Recently, it has been reported that the cell invasion ability, but not the cytokine proteolytic activity, of Pg has strong positive correlations with the clinical parameters of patients who harbor isolates.20 However, supporting experimental evidence is lacking. Thus, the aim of this study was to determine the contribution of the cell invasion ability and proteolytic activity of Pg to its virulence in a murine model of periodontitis.
