Modulation of protease-activated receptor expression by Porphyromonas gingivalis in human gingival epithelial cells

Background: Protease-activated receptors (PARs) are G-protein-coupled receptors with an active role in mediating inflammation, pain and other functions. The oral pathogen Porphyromonas gingivalis (P. gingivalis) secretes proteases that activate PARs. The aim of this study was to elucidate the role of PARs in the pathogenesis of chronic periodontitis by expression analysis of PARs in human gingival epithelial cells (GECs) before and after P. gingivalis supernatants treatment. Methods: GECs were isolated from healthy human gingival tissue samples. The expression of PARs in GECs was determined by reverse transcription-polymerase chain reaction (RT-PCR) and flow cytometry. The effect of P. gingivalis proteases was investigated by quantitative real-time reverse transcription polymerase chain reaction (QRT-PCR) and flow cytometry. Results: PAR-1, PAR-2, and PAR-3 were expressed in GECs. PAR-4 was not found by both RT-PCR and flow cytometry. Analysis of gene expression using QRT-PCR showed an up-regulation of PAR-2 mRNA in comparison to the untreated control cells (P < 0.05). In contrast, the mRNA expressions of PAR-1 and PAR-3 were significantly down-regulated (P > 0.05) in response to P. gingivalis supernatant compared to that in unstimulated control cells. This effect was abrogated by the protease inhibitor TLCK (P < 0.05). The results of flow cytometry indicated PARs protein levels consistent with mRNA levels in the results of QRT-PCR. Conclusions: Our study shows that PAR-1, PAR-2 and PAR-3 are expressed in GECs. P. gingivalis proteases play a role in the regulation of innate immune responses in GECs. GECs use PARs to recognize P. gingivalis and mediate cell responses involved in innate immunity.