Lipopolysaccharide supports survival and fusion of preosteoclasts independent of TNF‐α, IL‐1, and RANKL

Abstract

Lipopolysaccharide (LPS), a cell component of Gram-negative bacteria, is a pathogen of inflammatory bone loss. To examine the effects of LPS on the survival and fusion of osteoclasts, mononuclear osteoclasts (preosteoclasts, pOCs) were collected from a mouse co-culture system and cultured in the presence or absence of LPS. Most pOCs died within 24 h in the absence of any stimulus. LPS as well as receptor activator of NF-kappaB ligand (RANKL) supported the survival of pOCs, and induced their fusion to form multinucleated cells (MNCs). Like authentic osteoclasts, MNCs induced by LPS expressed calcitonin receptors, and formed actin rings on culture plates. LPS-induced MNC formation in pOC cultures was observed even in the presence of osteoprotegerin and interleukin (IL)-1-receptor antagonists. MNC formation was also stimulated by LPS in pOC cultures prepared from tumor necrosis factor (TNF)-receptor-I or TNF-receptor-II deficient mice. LPS induced the degradation of IkappaB in pOCs within 20 min. Lactacystin, an inhibitor of NF-kappaB activation, and wortmannin, an inhibitor of phosphatidylinositol-3 kinase, strongly inhibited LPS-induced MNC formation in pOC cultures. LPS induced pit-forming activity of pOCs in the presence of macrophage-colony stimulating factor (M-CSF). These findings suggest that LPS stimulates the survival and fusion of pOCs, independent of RANKL, IL-1 or TNF-alpha action. Activation of NF-kappaB and phosphatidylinositol-3 kinase appeared to be involved in LPS-induced effects on pOCs. These observations suggest that LPS is involved directly in inflammatory bone loss, and also indirectly through the production of LPS-induced host factors such as IL-1 and TNF-alpha.

Suppression of Osteoprotegerin Expression by Prostaglandin E2 Is Crucially Involved in Lipopolysaccharide-Induced Osteoclast Formation

“…We previously reported that LPS and IL-1 directly stimulated the survival, fusion, and pit-forming activity of osteoclasts (47). Those results together with the results shown in this study suggest that LPS and IL-1 are involved in the stimulation of osteoclastic bone resorption in several ways: LPS and IL-1 directly stimulate osteoclast function, induce RANKL expression in osteoblasts, and suppress OPG expression through enhancement of PGE 2 production.…”

1,25 (OH)2 Vitamin D3-Stimulated Osteoclast Formation in Spleen-Osteoblast Cocultures Is Mediated in Part by Enhanced IL-1α and Receptor Activator of NF-κB Ligand Production in Osteoblasts

“…In the human monocyte cell line U-937, Vit D had no effect alone on IL-1 production, but augmented the ability of T lymphocyte-produced cytokines, PMA, or LPS to stimulate IL-1 (37-39). However, LPS directly supported survival and fusion of preosteoclast in inflammatory bone loss and this phenomenon was independent of IL-1 and RANKL action (40). In the murine macrophage cell line P388D 1 and in human peripheral monocytes (PBMs), Vit D was found to be a direct stimulator of IL-1 (41,42).…”

Infection-induced Up-regulation of the Costimulatory Molecule 4-1BB in Osteoblastic Cells and Its Inhibitory Effect on M-CSF/RANKL-induced in Vitro Osteoclastogenesis

“…59 and 60 for review). Wortmannin and LY294002, inhibitors of PI3K, strongly inhibit RANKL-induced osteoclast formation and affect proliferation and/or survival of preosteoclasts (37,61), suggesting that inhibition of RANKL-induced Akt activation by 4-1BB might account for the inhibitory effect of 4-1BB on osteoclast formation. We also found that tyrosine phosphorylation of several proteins were down-regulated by 4-1BB, suggesting that such proteins might be involved in 4-1BB-induced inhibition of osteoclastogenesis.…”