title: Roles of stromal cell RANKL, OPG, and M-CSF expression in biphasic TGF-beta regulation of osteoclast differentiation.
abstract: To better understand the complex roles of transforming growth factor-beta (TGF-beta) in bone metabolism, we examined the impact of a range of TGF-beta concentrations on osteoclast differentiation. In co-cultures of support cells and spleen or marrow osteoclast precursors, low TGF-beta concentrations stimulated while high concentrations inhibited differentiation. We investigated the influences of TGF-beta on macrophage colony stimulating factor (M-CSF), receptor activator of NF-kappaB ligand (RANKL), and osteoprotegerin (OPG) expression and found a dose dependent inhibition of M-CSF expression. RANKL expression was elevated at low TGF-beta concentrations with a less dramatic increase in OPG. Addition of OPG blocked differentiation at the stimulatory TGF-beta dose. Thus, low TGF-beta concentrations elevated the RANKL/OPG ratio while high concentrations did not, supporting that, at low TGF-beta concentrations, there is sufficient M-CSF and a high RANKL/OPG ratio to stimulate differentiation. At high TGF-beta concentrations, the RANKL/OPG ratio and M-CSF expression were both repressed and there was no differentiation. We examined whether TGF-beta-mediated repression of osteoclasts differentiation is due to these changes by adding M-CSF and/or RANKL and did not observe any impact on differentiation repression. We studied direct TGF-beta impacts on osteoclast precursors by culturing spleen or marrow cells with M-CSF and RANKL. TGF-beta treatment dose-dependently stimulated osteoclast differentiation. These data indicate that low TGF-beta levels stimulate osteoclast differentiation by impacting the RANKL/OPG ratio while high TGF-beta levels repress osteoclast differentiation by multiple avenues including mechanisms independent of the RANKL/OPG ratio or M-CSF expression regulation.
authors.affiliation: Department of Biology, University of Minnesota, Duluth, Minnesota, USA.
authors.forename: Mary
authors.initials: M
authors.lastname: Karst
authors.forename: Genevieve
authors.initials: G
authors.lastname: Gorny
authors.forename: Rachelle J Sells
authors.initials: RJ
authors.lastname: Galvin
authors.forename: Merry Jo
authors.initials: MJ
authors.lastname: Oursler
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology; D002352:Carrier Proteins / Q000378:metabolism*; D002454:Cell Differentiation; D002478:Cells, Cultured; D018920:Coculture Techniques; D004305:Dose-Response Relationship, Drug; D005260:Female; D005786:Gene Expression Regulation; D006023:Glycoproteins / Q000378:metabolism*; D016173:Macrophage Colony-Stimulating Factor / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D010010:Osteoclasts / Q000166:cytology* / Q000187:drug effects; D053244:Osteoprotegerin; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D018124:Receptors, Tumor Necrosis Factor; D013154:Spleen / Q000166:cytology; D017154:Stromal Cells / Q000166:cytology / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism* / Q000494:pharmacology; D053773:Transforming Growth Factor beta1; D053781:Transforming Growth Factor beta2
chemical_list: D002352:Carrier Proteins; D006023:Glycoproteins; 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; C508961:Tgfb1 protein, mouse; C505687:Tnfrsf11a protein, mouse; C506031:Tnfrsf11b protein, mouse; C505689:Tnfsf11 protein, mouse; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D053781:Transforming Growth Factor beta2; D016173:Macrophage Colony-Stimulating Factor