Interesting, recent studies have suggested a possibility that transcriptional factor NF-KB may play a functional role in the survival of mouse osteoclasts. However, it has not been known whether NF-KB is involved in apoptosis of and bone resorption by mature osteoclasts. Thus, using NF-KB inhibitors, we examined the functional role of NF-KB in the induction of apoptosis in rabbit mature osteoclasts. PDTC, a potent inhibitor of NF-KB, stimulated markedly apoptosis of the osteoclasts and inhibited bone resorption by these cells. These effects also was observed when three other inhibitors of NF-KB were used. And a gel mobility shift assay showed that PDTC also inhibited NF-KB binding to its consensus sequence in the cells. These results suggest a regulatory role for NF-KB in apoptosis in and bone resorption by rabbit mature osteoclasts.© 1997 Federation of European Biochemical Societies.

In this study, we demonstrate that Porphyromonas gingivalis fimbrillin, a major component of bacterial fimbriae, is one of the fibronectin-binding proteins and that fibronectin is a potent inhibitor of the adherence of the bacteria to host cells and of the pathogenesis of the bacterium that acts by binding to the fimbriae. A Western blotting (immunoblotting) assay showed that fibronectin binds strongly to P. gingivalis fimbrillin. The fimbrial binding to fibronectin was also evidenced by a binding assay involving 125 I-labeled fimbriae. Furthermore, fibronectin markedly inhibited the fimbria-induced expression of interleukin-1␤ and neutrophil-specific chemoattractant KC genes in macrophages. The inhibitory action depended on the fimbrial interaction with heparin-binding and cell attachment domains in the fibronectin structure. The binding of P. gingivalis to mouse peritoneal macrophages via its fimbriae was inhibited by fibronectin. Fibronectin also inhibited the bacterial cell-induced expression of interleukin-1␤ and KC genes in the macrophages. These results demonstrate the importance of fibronectin as a modulator of the pathogenic mechanism of P. gingivalis, a pathogen that causes adult periodontal disease.

Lipopolysaccharide (LPS) is a bacterial cell component that plays multifunctional roles in inflammatory reactions, and one of these roles is that of a powerful stimulator of bone resorption. However, the mechanism by which LPS stimulates bone resorption is not yet understood. In the present study, we show, by using mouse embryonic calvarial cells, that endogenous CD14 and interleukin-1 beta (IL-1 beta) play an important role in the LPS-mediated bone resorption and that interferon-gamma (IFN-gamma) functions as a strong inhibitor of this resorption by suppressing LPS-stimulated expression of CD14 and IL-1 beta genes in the calvarial cells. We observed that LPS-stimulated differentiation of osteoclastic cells and bone resorption were markedly neutralized by anti-mouse CD14 antibody and were clearly inhibited by anti-sense CD14 oligonucleotide treatment. In addition, because LPS stimulated CD14 gene expression in the calvarial cells, these observations demonstrate the precise role of endogenous CD14 in LPS-stimulated differentiation of osteoclastic cells and bone resorption. However, the stimulation of the differentiation of osteoclastic cells and bone resorption was also inhibited by anti-mouse IL-1 beta antibody. Interestingly, anti-sense CD14 oligonucleotide inhibited LPS-stimulated expression of the IL-1 beta gene in the calvarial cells. These observations suggest a functional role of endogenous CD14 in LPS-stimulated expression of the IL-1 beta gene in the cells. Because IFN-gamma is a potent inhibitor of bone resorption stimulated by IL-1, in additional experiments, we examined whether IFN-gamma is able to inhibit LPS-stimulated differentiation of osteoclastic cells and bone resorption. We found that IFN-gamma inhibited these stimulations by suppressing CD14 and IL-1 beta genes in the calvarial cells. The present study thus clearly demonstrates a functional role of endogenous CD14 in LPS-stimulated bone resorption.

PGs play a functional role in the early stage of Gram-negative bacterial infections, because this prostanoid is produced rapidly by epithelial cells after a bacterial infection. CD14, one of the LPS receptors, is a key molecule in triggering the response to bacterial LPS in association with a Toll-like molecule. Therefore, in this study, we investigated the effect of PG on CD14 expression in mouse macrophages. PGE1, PGE2, and PGA1 among the PGs tested strongly stimulated the expression of the CD14 gene in the cells. The stimulatory action also was observed by Western blot analysis. cAMP-elevating agents stimulated expression of CD14 gene as well. Protein kinase A inhibitor, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89), but not protein kinase C inhibitor 3-{1-[3-(dimethylamino)propyl]-1H-indol-3-yl}-4-(1H-indol-3-yl)-1H-pyrrole-2,5-dione (GF109203X), abolished the stimulated expression of CD14. A run-on assay showed that PGE2 stimulated the CD14 gene expression at the transcriptional level via protein kinase A. PGE2 also stimulated activation of AP-1, a heterodimer of c-Jun and c-Fos, because the prostanoid increased specific binding of nuclear proteins to the AP-1 consensus sequence and stimulated AP-1-promoted luciferase activity. PGE2-stimulated expression of CD14 was inhibited by antisense c-fos and c-jun oligonucleotides, but not by their sense oligonucleotides. Finally, PGE2 pretreatment synergistically stimulated LPS-induced expression of IL-1β and IL-6 genes in mouse macrophages. Therefore, the present study demonstrates that PGE2 has the ability to stimulate AP-1-mediated expression of CD14 in mouse macrophages via cAMP-dependent protein kinase A.

In a previous study, we developed a specific monoclonal antibody against Porphyromonas endodontalis lipopolysaccharide, and demonstrated that this lipopolysaccharide was detected in bacterially infected root canal fluid. We suggest here that P. endodontalis lipopolysaccharide in the infectious materials plays a stimulatory role in maxillofacial abscess formation via the expression of inflammatory cytokines. Our epidemiological study showed that this lipopolysaccharide was detected in significant levels the infectious material of patients with periapical periodontitis and odontogenic abscesses. Interestingly, infectious material-induced expression of tumor necrosis factor-alpha, interleukin-1beta, or neutrophil chemoattractant KC genes in mouse macrophages, was significantly neutralized by monoclonal antibody against the lipopolysaccharide. In addition, we also detected a significant amount of tumor necrosis factor-alpha in the infectious material. These results suggest that P. endodontalis lipopolysaccharide plays an important role in the pathogenic mechanism of maxillofacial abscess formation via the expression of inflammatory cytokines.