Trypsin-like protease-active extracellular protein extracts from Porphyromonas gingivalis ATCC 33277 induce apoptosis in bovine aortic endothelial cells

Background and Objective: Certain virulence factors participating in periodontitis may relate to cardiovascular diseases. This study was to evaluate the pro-apoptotic effect of protein extracts from Porphyromonas gingivalis on bovine aortic endothelial cells (BAECs). Material and Methods: The BAECs were exposed to trypsin-like protease-active protein extracts from P. gingivalis, and apoptosis was examined by Hoechst 33342 staining, DNA fragmentation assay and cleaved caspase-3 detection. When BAECs were exposed to protein extracts pretreated with trypsin-like protease inhibitor (TLCK), the apoptosis rate was evaluated by Annexin V-propidium iodide staining. To further study the potential mechanism of the pro-apoptotic effect, immunoblotting was used to detect expression of alpha-tubulin, integrin beta 1 and activated ERK1/2 in BAECs treated with protein extracts or cultured in suspension. Results: After exposure to the protein extracts, BAECs exhibited loss of cell adhesion and apoptotic cell death. The pro-apoptotic effect could be delayed by TLCK pretreatment. In addition, BAECs treated with protein extracts showed decreased levels of alpha-tubulin, integrin beta 1 and activated ERK1/2. When BAECs were cultured in suspension, ERK1/2 activation was also inhibited, but the percentage decrease in ERK1/2 activation was less than that induced by protein extracts. Moreover, no significantly altered expression of alpha-tubulin was detected in suspended cells. Conclusion: Trypsin-like protease-active protein extracts from P. gingivalis could induce apoptosis of BAECs. The destruction of alpha-tubulin and integrin beta 1 and decrease of ERK1/2 activation might contribute to the pro-apoptotic effect of the protein extracts.