GM‐CSF and uPA are required for Porphyromonas gingivalis‐induced alveolar bone loss in a mouse periodontitis model

Abstract

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and urokinase-type plasminogen activator (uPA) can contribute to the progression of chronic inflammatory diseases with possible involvement of macrophages. In this study, we investigated the role of both GM-CSF and uPA in Porphyromonas gingivalis-induced experimental periodontitis using GM-CSF-/- and uPA-/- mice. Intra-oral inoculation of wild-type (WT) C57BL/6 mice with P. gingivalis resulted in establishment of the pathogen in plaque and a significant increase in alveolar bone resorption. The infected mice also exhibited a CD11b(+) CD86(+) macrophage infiltrate into the gingival tissue, as well as P. gingivalis-specific pro-inflammatory cytokine and predominantly IgG2b antibody responses. In comparison, intra-oral inoculation of P. gingivalis did not induce bone resorption and there was significantly less P. gingivalis recovered from plaque in GM-CSF-/- and uPA-/- mice. Furthermore, P. gingivalis did not induce a macrophage gingival infiltrate or activate isolated peritoneal macrophages from the gene-deficient mice. Pro-inflammatory P. gingivalis-specific T-cell cytokine responses and serum interferon-gamma (IFN-γ) and IgG2b concentrations were significantly lower in GM-CSF-/- mice. In uPA-/- mice, T-cell responses were lower but serum IFN-γ and IgG2b levels were comparable with WT mice levels. These results suggest that GM-CSF and uPA are both involved in the progression of experimental periodontitis, possibly via a macrophage-dependent mechanism(s).

Porphyromonas gingivalis-derived RgpA-Kgp Complex Activates the Macrophage Urokinase Plasminogen Activator System

“…Activation of the complement cascade has been invoked as a key aspect of the role of P. gingivalis as a keystone pathogen (20). Similar to the findings in the C5aR Ϫ/Ϫ mice, which are resistant to P. gingivalis colonization and are thus protected from alveolar bone loss (53), we recently found that P. gingivalis poorly colonized the subgingival plaque in uPA Ϫ/Ϫ mice compared with wild-type mice (29). This likely explains the protection of uPA Ϫ/Ϫ mice from P. gingivalis-induced alveolar bone loss but also suggests that the pathogen depends on uPA to colonize the host and drive inflammation.…”

“…In the case of pro-uPA, the RgpAKgp complex cleaved at the major consensus sites (Lys Much of the damage to the periodontal tissue in PD is now recognized to be caused by the destructive host inflammatory response (41). We have shown that macrophages (31) and uPA (29) are important in the P. gingivalis-induced PD model. Interestingly, protection of uPA Ϫ/Ϫ mice in the P. gingivalis-induced PD model was associated with reduced numbers of macrophages in the gingival tissue (29), consistent with our data showing a critical role for uPA in promoting macrophage adhesion and motility (8).…”

“…We have shown that macrophages (31) and uPA (29) are important in the P. gingivalis-induced PD model. Interestingly, protection of uPA Ϫ/Ϫ mice in the P. gingivalis-induced PD model was associated with reduced numbers of macrophages in the gingival tissue (29), consistent with our data showing a critical role for uPA in promoting macrophage adhesion and motility (8). Indeed, we have speculated (8) that uPA may play an important role in controlling macrophage retention within certain inflammatory lesions, which may help to explain the benefit of its targeting in inflammatory disease (7,9,10,42); our prior data showing a uPA dependence for three systemic arthritis models (9,10) suggest that elevated uPA activity could be a common feature of PD and rheumatoid arthritis, perhaps helping to explain their association (43).…”

“…1A) in contrast to wild-type mice, which developed significant bone loss relative to uninoculated mice. Also uPA Ϫ/Ϫ mice had lower levels of P. gingivalis in the subgingival plaque compared with wild-type mice (data not shown), suggesting that uPA is necessary for the emergence of the pathogen (29). We have previously demonstrated that macrophage uPA conversion of plasminogen to active plasmin plays a major role in its ability to degrade matrix (8) and that depletion of macrophages protects mice from P. gingivalis-induced PD (31).…”

“…However, the role of uPA in PD has not been defined. We recently found that uPA Ϫ/Ϫ mice are resistant to experimental PD following oral infection with P. gingivalis, possibly via a macrophage-dependent mechanism(s) (29). In agreement with that study, we also showed that depletion of macrophages, which can be a major source of uPA in inflammation (30), protected mice from P. gingivalisinduced PD (31) and that uPA regulates macrophage-mediated matrix degradation (8), a hallmark of chronic PD (16,17).…”