Porphyromonas gingivalis Phosphatidylethanolamine Lipids Inhibit LL-37 Production in Epithelial Cells

OBJECTIVES: Antimicrobial peptides play an important role in controlling colonization of microorganisms and the resulting infection at the host mucosal surfaces. Genetic deficiency of the antimicrobial peptide LL-37 in human saliva is associated with severe periodontitis. Therefore, the objective of this study was to determine whether the periodontal pathogen, Porphyromonas gingivalis (Pg), effects LL-37 expression by human gingival epithelial cells (GEC) in response to stimulation with other strains of periodontal pathogens.

METHODS: Immortalized GEC line, OBA-9, was stimulated with 5 different types of heat-killed bacteria, Pg W83, A. actinomycetemcomitans (Aa), F. nucleatum, P. intermedia and E. corrodens (107/ml, respectively), in DMEM with 10% FBS. In another assay, Pg phosphatidylethanolamine lipids (1 ug/ml), Pg LPS (1 ug/ml), Pg autoclave supernatant (x100 dilution of Pg W83, 109/ml autoclaved in PBS), or whole fixed Pg W83 (107/ml) was applied to OBA9 co-cultured with fixed Aa. After different periods of incubation, culture supernatants were harvested and subjected to LL-37 ELISA.

RESULTS: OBA-9 cells produced LL-37 in response to stimulation with Aa, F. nucleatum, P. intermedia and E. corrodens, whereas Pg did not induce such LL-37 expression in OBA9 cells. The LL-37 induced by stimulation with Aa was suppressed by the presence of whole Pg and Pg autoclave supernatant. In general, autoclave treatment of bacteria destroys the bacterial protein antigens, while most carbohydrate components remain intact. Autoclave-resistant Pg phosphatidylethanolamine lipids, but not Pg LPS, suppressed LL-37 expression by Aa-stimulated OBA9, indicating that phosphoethanolamine lipids are responsible for Pg-mediated inhibition of LL37 production by GEC.

CONCLUSION: Pg appeared to possess a property inhibiting LL-37 production by GEC due to their production of phosphatidylethanolamine lipids which are structurally distinct from Pg LPS (Nichols, et al. J Lipid Res 2006; 47(4):844-53).

This study was supported by NIDCR DE18310.