A Sialidase‐Deficient Porphyromonas gingivalis Mutant Strain Induces Less Interleukin‐1&bgr; and Tumor Necrosis Factor‐&agr; in Epi4 Cells Than W83 Strain Through Regulation of c‐Jun N‐Terminal Kinase Pathway

BACKGROUND Porphyromonas gingivalis is one of the major periodontal pathogens. In a previous study, a mouse abscess model showed that sialidase deficiency of P. gingivalis weakened its virulence, but the mechanism behind this observation remains unknown. METHODS A sialidase-deficient mutant strain (△PG0352) and a complemented strain (com△PG0352) were constructed. Epi4 cells were stimulated by wild-type strain P. gingivalis W83, △PG0352, or com△PG0352. Real-time polymerase chain reaction was carried out to detect expression of virulent genes in P. gingivalis and interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor (TNF)-α in epi4 cells. Activities of sialidase, gingipains, and lipopolysaccharide (LPS) were compared among the different P. gingivalis strains. Levels of IL-1β and TNF-α in the epi4 cells supernatant were detected by enzyme-linked immunosorbent assay and levels of p38, extracellular signal-regulated kinase, c-Jun N-terminal kinase (JNK), and phospho-c-Jun were detected by western blotting. RESULTS Compared with P. gingivalis W83 and com△PG0352, activities of Kgp and Rgp gingipains and amount of LPS decreased in △PG0352, whereas there were no differences in LPS activity among these three strains. Level of phospho-JNK was lower in epi4 cells stimulated by △PG0352. △pG0352 induced less IL-1β and TNF-α and more IL-8 in epi4 cells; differences in IL-1β and TNF-α could not be detected after JNK blocking. CONCLUSION A sialidase-deficient P. gingivalis mutant strain induces less IL-1β and TNF-α in epi4 cells than W83 strain through regulation of JNK pathway.