Mechanical stress enhances production of cytokines in human periodontal ligament cells induced by Porphyromonas gingivalis

Objective: We have previously reported that human periodontal ligament (hPDL) cells produced many kinds of cytokines as a result of bacterial stimulation, including stimulation with Porphyromonas gingivalis (P. gingivalis). However, the effects of mechanical stress on cytokine production in hPDL cells stimulated by periodontopathogenic bacteria are not clearly understood. In this study, we investigated the effects of mechanical stress on the production of inflammatory cytokines in hPDL cells induced by stimulation with P. gingivalis. Methods: The hPDL cells were exposed to various levels of mechanical stress (1, 6, 10 and 50 MPa) and costimulated with mechanical stress and P. gingivalis for 24 h. Cytokine mRNA expressions were determined by RT-PCR. Cytokines in the culture supernatant were assessed by ELISA, and morphologic changes in hPDL cells were observed. Results: The expressions of interleukin (IL)-6, IL-8 and tumor necrosis factor-a mRNA were observed in hPDL cells after exposure to mechanical stress. Moreover, the production of IL-6 and IL-8 increased significantly after exposure to mechanical stress ranging from 1 to 10 MPa. The amount of IL-8 in the culture supernatants of hPDL cells costimulated with P. gingivalis and mechanical stress was significantly higher than the expected additive amount. The morphology of hPDL cells did not change after exposure to 6 MPa, but these cells were partly detached from the Petri dish after exposure to SO MPa. Conclusions: These results suggest that local inflammation of the periodontal ligament may be induced mainly by periodontal bacteria, and mechanical stress may promote local inflammation. (C) 2010 Elsevier Ltd. All rights reserved.