Interaction of Porphyromonas gingivalis with low-density lipoproteins:: implications for a role for periodontitis in atherosclerosis

Objective: The association of periodontitis with atherosclerosis has been suggested from epidemiological studies. Recently, we have reported that macrophages stimulated by Porphyromonas gingivalis formed foam cells in the presence of low-density lipoproteins (LDL). In this study, we examined the direct interactions between LDL and P. gingivalis. Methods: We investigated the aggregation of LDL with P. gingivalis and its outer membrane vesicles (OMVs), degradation of the apo B-100 protein of LDL by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blot analyses, as well as the effects of protease inhibitors or activators on the mobility of LDL by agarose gel shift assays. The binding of P. gingivalis or its OMVs with LDL was demonstrated by western blot analysis. We also examined whether or not the aggregated LDL induced foam cell formation from murine macrophages. Results: LDL was aggregated in a dose-dependent manner with P. gingivalis and its OMVs. Moreover, degradation of the apo B-100 protein of LDL was directly demonstrated in the presence of P. gingivalis or its OMVs. Furthermore, the gel shift assays indicated that the mobility of LDL was increased in the presence of P. gingivalis. This alteration was attenuated in the presence of the protease inhibitors TLCK and leupeptin and increased in the presence of reducing agents. Moreover, LDL was bound to specific proteins of P. gingivalis suggesting that these proteins may also play a role in aggregation. Finally, the aggregated LDL induced murine macrophages to form foam cells. Conclusions: These results suggest that P. gingivalis may stimulate foam cell formation, in part, by aggregating LDL by proteolysis of apo B-100.