Crosstalk of Human Oral Keratinocytes with Commensal and Pathogenic Bacteria

Objectives: Periodontal disease is initiated by a microbial shift from commensal plaque biofilm to pathogenic one which results in destructive inflammatory response. Hitherto only sparse data are available on the molecular mechanisms which govern the harmonious bacteria-host interaction in healthy status and regulate the microbial shift concerned. This preliminary study aimed to investigate the molecular mechanisms by which commensal and periodontopathic bacteria communicate with human oral keratinocytes (HOKs), and to determine the effects of bacterial DNA on the cytokine expression in HOKs.

Methods: Commensal bacteria Streptococcus mutans (Sm), Actinomyces israelii (Ai) and periodontopathic bacteria Actinomyces actinomycetemcomitans (Aa), Porphyromonas gingivalis (Pg) were used in the study. Sm and Aa as well as the purified DNAs of Sm, Ai, Aa and Pg were co-cultured with HOKs respectively. IL-6, IL-8 and TNF-alpha were analyzed by ELISA. The effects of Aa- and Pg DNA on the expression of Toll-like receptors (TLRs) related signal transduction pathways in HOKs were examined by western blots, qPCR and PCR array.

Results: Sm and Aa up-regulated the expression of IL-6 and IL-8 in HOKs through different signaling pathways. Aa induced p65 MAPK pathway after 30 min co-culture with HOKs. The DNAs of Sm, Ai, Aa and Pg enhanced the expression of IL-6 and IL-8 in HOKs. Pg DNA activated TLR signaling pathway.

Conclusion: This study suggests that commensal and pathogenic bacteria or bacterial DNAs may differentially affect the expression of IL-6 and IL-8 and the related TLR signaling pathway in HOKs. (Supported by RGC/HKU766909M and HKU/Seed Funding/201007159003).