Dysregulation of Inflammasomes in Human Dental Pulp Cells Exposed to Porphyromonas gingivalis and Fusobacterium nucleatum

INTRODUCTION: Interleukin-1β (IL-1β) is a major proinflammatory cytokine that plays a significant role in pulpal inflammation. The regulation of IL-1β as well as different cytokines and chemokines is controlled by multiprotein complexes named inflammasomes, which are known to be involved in pulpal inflammation. The goal of this study was to evaluate the effects of well-established endodontic bacteria and periodontal pathogens Fusobacterium nucleatum and Porphyromonas gingivalis on NLRP3 and AIM2 inflammasomes; the inflammasome regulatory proteins POP1, CARD16, and TRIM16; inflammasome components ASC and caspase-1; and IL-1β levels in human dental pulp cells (HDPCs) in vitro.

METHODS: HDPCs were exposed to either F. nucleatum or P. gingivalis or to the combination of both with an additional 30 minutes of 5 mmol/L adenosine triphosphate (ATP) incubation for 24 hours. Escherichia coli lipopolysaccharide exposure was used as a control. Gene expression of NLRP3, AIM2, POP1, CARD16, TRIM16, ASC and caspase-1, and IL-1β were evaluated by reverse transcription polymerase chain reaction. The presence and levels of pro- and mature IL-1β were monitored by immunocytochemistry and the release with enzyme-linked immunosorbent assay.

RESULTS: Up-regulation of NLRP3 and AIM2 was detected in all exposure groups. IL-1β was up-regulated in all groups, except for the F. nucleatum + ATP group. CARD16 was significantly down-regulated by F. nucleatum or P. gingivalis with or without ATP; however, POP1 was down-regulated only in P. gingivalis and E. coli LPS + ATP groups. P. gingivalis alone significantly increased intracellular pro- and mature IL-1β levels.

CONCLUSIONS: P. gingivalis and F. nucleatum in the presence of ATP may play a significant role in IL-1β-induced pulpal inflammation by dysregulating inflammasomes and their regulators.