Novel role of lipopolysaccharide derived from Aggregatibacter actinomycetemcomitans in periodontitis

Objective: Aggregatibacter actinomycetemcomitans (A.a) is frequently associated with aggressive periodontitis in children and adolescence. Although, it is well understood that lipopolysaccharide (LPS) derived from A.a stimulates host-immune system and induces osteocrastic differentiation, it is still unknown that the effect of LPS on bone formation and cell to cell communication via gap junction in osteoblast.

Methods: Mouse osteoblastic cell line MC3T3-E1 were used in the present study, and LPS was extracted from A.a ATCC43717. The expressions of mRNA of differentiation markers were measured by real-time RT-PCR using TaqMan probes. The gap junctional intercellular communication was assayed by scrape loading/dye transfer?assay. To neutralize inflammatory cytokines induced by LPS, antibodies were added to growth medium of MC3T3-E1.

Results: LPS derived from A.a inhibited osteoblastic differentiation and cell to cell communication via gap junction significantly. Furthermore, once polymyxin B was added to the medium, the inhibition caused by LPS was disappeared completely. While neutralizing antibodies of cytokines had no effect on LPS.

Conclusion: The present study revealed that LPS derived from A.a effects on differentiation and cell to cell communication in osteoblast and this inhibition was not caused by autocrine inflammatory cytokines induce by LPS. The present results could indicate the novel role of lipopolysaccharide derived from A.a in alveolar bone loss.