title: Dual modulation of osteoclast differentiation by lipopolysaccharide.
abstract: Lipopolysaccharide (LPS) modulates bone resorption by augmentation of osteoclastogenesis. It increases in osteoblasts the production of RANKL, interleukin (IL)-1, prostaglandin E2 (PGE2), and TNF-alpha, each known to induce osteoclast activity, viability, and differentiation. We examined the role of direct interactions of LPS with osteoclast precursors in promoting their differentiation. To this end, we have used bone marrow mononuclear cell preparations in the absence of osteoblasts or stromal cells. We found that LPS does not induce osteoclast differentiation in these cells. Moreover, the inclusion of LPS blocked the osteoclastogenic activity of RANKL. However, LPS is a potent inducer of osteoclastogenesis in RANKL-pretreated cells, even if present in the absence of exogenous RANKL. Osteoprotegerin (OPG), does not affect the stimulatory phase of LPS modulation of osteoclastogenesis, ruling out involvement of endogenous RANKL. LPS induces the expression of TNF-a and IL-1beta in osteoclast precursors, regardless if they were or were not pretreated with RANKL. These two cytokines induced osteoclast differentiation in RANKL-pretreated cells. To examine if these cytokines mediate LPS effect in an autocrine mechanism, we measured the effect of their neutralization on LPS osteoclastogenic activity. Although neutralization of IL-1beta did not affect LPS activity, a marked inhibition was observed when TNF-alpha was neutralized. However, TNF-a expression was increased also in conditions in which LPS inhibited RANKL osteoclastogenic activity. We found that LPS reduces the expression of RANK and macrophage colony-stimulating factor (M-CSF) receptor. In summary, LPS impacts on osteoclastogenesis also via its interactions with the precursor cells. LPS inhibits RANKL activity by reducing the expression of RANK and M-CSF receptor and stimulates osteoclastogenesis in RANKL-pretreated cells via TNF-alpha.
authors.affiliation: The H. Hubert Humphrey Center for Experimental Medicine and Cancer Research, The Hebrew University Faculty of Medicine, Jerusalem, Israel.
authors.forename: Wei
authors.initials: W
authors.lastname: Zou
authors.forename: Zvi
authors.initials: Z
authors.lastname: Bar-Shavit
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000494:pharmacology; D002454:Cell Differentiation; D015870:Gene Expression / Q000528:radiation effects; D006023:Glycoproteins / Q000235:genetics; D007375:Interleukin-1 / Q000235:genetics; D008070:Lipopolysaccharides / Q000494:pharmacology*; D016173:Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D008297:Male; D008562:Membrane Glycoproteins / Q000494:pharmacology; D051379:Mice; D008807:Mice, Inbred BALB C; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D053244:Osteoprotegerin; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics
chemical_list: D002352:Carrier Proteins; D006023:Glycoproteins; D007375:Interleukin-1; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D053244:Osteoprotegerin; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear; D018124:Receptors, Tumor Necrosis Factor; C505687:Tnfrsf11a protein, mouse; C506031:Tnfrsf11b protein, mouse; C505689:Tnfsf11 protein, mouse; D014409:Tumor Necrosis Factor-alpha; D016173:Macrophage Colony-Stimulating Factor