Porphyromonas gingivalis Induces Apoptosis in Gingival Epithelial Cells

Objectives: Porphyromonas gingivalis, a Gram-negative anaerobe is considered an important pathogen in chronic periodontitis. P. gingivalis has been shown to influence apoptosis in different cell types including human gingival epithelial cells (HGECs), but the literature presents conflicting results. Here, we examined apoptosis in HGECs using different approaches and P. gingivalis strains.

Methods: HGECs were isolated from gingival biopsies of periodontally healthy patients undergoing crown lengthening procedures. When the cells reached confluence, they were washed twice with fresh media and were infected in antibiotic-free medium at MOI of 10 or 100 with live or heat-inactivated P. gingivalis ATCC 33277, with KDP128, an RgpA/RgpB/Kgp triple mutant, with P. gingivalis W50, with E8, an RgpA/RgpB double mutant, and with K1A, a Kgp mutant. Apoptosis was analyzed at 4 and 24-hour time points using DNA fragmentation, M30 epitope detection and caspase-3 activity assays.

Results: HGECs infected with high dose (MOI:100) of live P. gingivalis for 24 hours exhibited signs of apoptosis. Lower doses, shorter infection times, heat-killed bacteria and the gingipain mutants did not induce apoptosis. Furthermore, the addition of specific gingipain inhibitors abolished the ability of live P. gingivalis to induce apoptosis.

Conclusions: Gingipains produced by high doses of live P. gingivalis are essential for apoptosis in HGECs. This mechanism could be a contributing factor in the pathogenicity of this microorganism.

Supported by NIH NIDCR grant DE017384.