Inhibition of epithelial cell apoptosis by Porphyromonas gingivalis

Porphyromonas gingivalis is periodontal pathogen that is capable of invading gingival epithelial cells (GECs). Apoptotic responses of primary cultures of GECs to P. gingivalis were investigated with a DNA fragmentation ELISA assay. P. gingivalis induced a transient increase in GEC DNA fragmentation; however, after prolonged incubation GECs did not undergo apoptosis. Furthermore, P. gingivalis blocked apoptosis in GECs following stimulation with camptothecin. Immunoblotting of GECs with Bcl-2 or Bax antibodies showed that P. gingivalis up-regulated Bcl-2 levels in GECs, whereas Bax levels were transiently elevated and declined after 24 h stimulation. Streptococcus gordonii did not affect levels of either molecule. RT-PCR demonstrated that induction of Bcl-2 occurs at the transcriptional level. The results suggest that P. gingivalis can inhibit apoptosis in GECs by up-regulation of the anti-apoptotic molecule Bcl-2. The prevention of host cell apoptosis may represent a strategy for P. gingivalis survival within invaded GECs.