Cysteine proteases from Porphyromonas gingivalis and TLR ligands synergistically induce the synthesis of the cytokine IL-8 in human artery endothelial cells

Abstract

Objective: Bacterial pathogens are frequently detected in atheromatous lesions, however, their contribution to atherosclerosis remains unknown. The present study was aimed to explore the effect of the P. gingivalis cysteine protease gingipain towards the proinflammatory response of human aortic endothelial cells (HAECs).

Design: HAECs were exposed to gingipains (Rgps) extracted from the oral pathogen P. gingivalis. In addition, HAECs were co-stimulated with the TLR ligands P. gingivalis LPS, E. coli LPS or heat-killed P. gingivalis (HKPG) in combination with gingipain-active or gingipain-inactive extracts. After stimulation, IL-8 mRNA expression and protein synthesis were analysed by RT-PCR and ELISA. Means and standard errors were computed following by statistical testing (P ≤ 0.05).

Results: In HAECs, Rgps significantly increased the IL-8 mRNA (5.8 ± 1.1-fold) and protein expression (523.0 ± 57.5 pg/ml) compared to untreated controls. Co-stimulation experiments showed a significant synergistic effect for the IL-8 mRNA expression and protein synthesis when HAECs were exposed to a combination of the purified TLR ligands (P. gingivalis or E. coli LPS) or HKPG and gingipain-active extracts.

Conclusions: These results demonstrated the synergistic effects of TLR ligands and P. gingvalis cysteine proteases for the proinflammatory responses in artery vascular endothelial cells and highlight a mechanism by which bacteria may contribute to the development of atherosclerosis.