Internal prostaglandin synthesis augments osteoprotegerin production in human gingival fibroblasts stimulated by tipopolysaccharide

Periodontitis is an inflammatory bone disease caused by Gram-negative anaerobic bacteria. Osteoclast differentiation is regulated by the balance between receptor activator of nuclear factor kappa B ligand (RANKL) and osteoprotegerin (OPG). The purpose of this study was to examine the mechanism of OPG production in human gingival fibroblasts (HGF) stimulated by lipopolysaccharide (LPS) from periodontopathic bacteria. The expressions of Toll-like receptor 2 (TLR-2) and TLR-4 in HGF were examined using flow-cytometry. HGF were stimulated with whole cell extracts or LPS from Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis with or without polymyxin B, a LPS inhibitor. In addition, HGF were stimulated with LPS, prostaglandin E-2 (PGE(2)), various agonists of PGE receptors (EP1, EP2, EP3 and EP4 agonists) with or without indomethacin (IND), a prostaglandin synthesis inhibitor. OPG and PGE2 production was measured using an enzyme-linked immunosorbent assay (ELISA). HGF expressed both TLR-2 and TLR-4. Both A. actinomycetemcomitans and R gingivalis LPS augmented OPG expression in HGE Whole cell extracts from A. actinomycetemcomitans and P. gingivalis augmented OPG production by HGF; the augmentation was suppressed by polyrnyxin B. IND suppressed OPG production in LPSstimulated HGF. PGE2 stimulated HGF to produce OPG. EP1 and EP2 agonists, but not EP3 and EP4 agonists, increased OPG production by HGE These results suggest that LPS-induced OPG production by HGF is regulated via EP1 and/or EP2 receptors by endogenously generated PGE(2).