Inflammasome in Gingival Epithelial Cells Infected By Porphyromonas gingivalis

Production of IL-1beta by macrophages typically requires two separate signals. The first signal, from a pathogen associated molecular pattern (PAMP) such as LPS, promotes production and intracellular accumulation of the immature cytokine. The second signal, usually derived from a “danger signal” such as extracellular ATP (ATPe), results in activation of an inflammasome, and processing and secretion of the mature cytokine. The inflammasome component, Nalp3/cryopyrin, was previously shown to be responsive to P2X7 ligation by ATPe. Primary gingival epithelial cells (GECs) are an important component of the innate immune response to periodontal bacteria and we had shown that they express functional P2X7 receptor, but the ability of GECs to secrete IL-1beta during infection remains poorly characterized. Objective: This study investigated whether GECs can secrete IL-1beta following treatment with LPS or infection with the periodontal bacteria Porphyromonas gingivalis. The expression and effect of Nalp3 on IL-1beta secretion was examined in cells treated with ATPe. Methods: Expression of Nalp3 in GECs was analyzed by PCR. GECs were stimulated by the P2X7 agonist, ATPe, with or without pre-infection with P. gingivalis or pretreatment with LPS. Production and secretion of IL-1beta protein was measured by fluorescence microscopy and ELISA. Results: GECs express the Nalp3 gene. Treatment of cells with LPS alone or infection with P. gingivalis induced expression of the il-1beta gene and intracellular accumulation of IL-1beta protein. However, IL-1beta protein was not secreted unless the LPS-treated or infected cells were subsequently stimulated with ATPe. Conclusion: P. gingivalis-infected GECs do not secrete IL-1beta unless they are stimulated with ATPe. The Nalp3 inflammasome is therefore likely to be an important mediator of the inflammatory response in GECs.

This work supported by NIDCR grant R01DE016593.