title: Colony-stimulating factor-1 (CSF-1) directly inhibits receptor activator of nuclear factor-{kappa}B ligand (RANKL) expression by osteoblasts.
abstract: Colony-stimulating factor-1 (CSF-1), released by osteoblasts, stimulates the proliferation of osteoclast progenitors via the c-fms receptor (CSF-1R) and, in combination with receptor activator of nuclear factor-kappaB ligand (RANKL), leads to the formation of mature osteoclasts. Whether the CSF-1R is expressed by osteoblasts and mediates specific biological effects in osteoblasts has not been explored. Wild-type primary calvaria osteoblasts (OB) were analyzed for CSF-1R expression (RT-PCR and Western blot) and functionality (immunocomplex kinase assay). OB were serum starved for 24 h, and the effect of CSF-1 (0-100 ng/ml) on OB biological activities was determined at 48 h. In wild-type mouse bone marrow cultures, CSF-1 was tested for its effect on RANKL mRNA and osteoclast formation. Because ROS influence osteoblast RANKL expression, studies analyzed the effect of CSF-1 on reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity and Nox1 and Nox4 proteins. Results indicate that OB express CSF-1R mRNA and protein and that CSF-1R could be phosphorylated in the presence of CSF-1. In osteoblasts, CSF-1 decreased RANKL mRNA in a dose- and time-dependent manner. Incubation of bone marrow cultures with CSF-1 resulted in a significant decline in tartrate-resistant acid phosphatase (TRACP) activity and CTR expression. RANKL-decreased expression by CSF-1 was correlated with a decrease of NADPH oxidase activity as well as Nox1 and Nox4 protein levels. These findings provide the first evidence that osteoblasts express CSF-1R and are a target for CSF-1 ligand. CSF-1-mediated inhibition of RANKL expression on osteoblasts may provide an important mechanism for coupling bone formation/resorption and preventing excessive osteoclastogenesis during normal skeletal growth.
authors.affiliation: South Texas Veteran's Health Care System, Audi L. Murphy Division, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, Texas 78229, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Wittrant
authors.forename: Y
authors.initials: Y
authors.lastname: Gorin
authors.forename: S
authors.initials: S
authors.lastname: Mohan
authors.forename: B
authors.initials: B
authors.lastname: Wagner
authors.forename: S L
authors.initials: SL
authors.lastname: Abboud-Werner
mesh_terms: D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D015536:Down-Regulation; D016173:Macrophage Colony-Stimulating Factor / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D010006:Osteoblasts / Q000378:metabolism*; D053245:RANK Ligand / Q000235:genetics* / Q000378:metabolism; D016186:Receptor, Macrophage Colony-Stimulating Factor / Q000235:genetics / Q000378:metabolism
chemical_list: D053245:RANK Ligand; D016173:Macrophage Colony-Stimulating Factor; D016186:Receptor, Macrophage Colony-Stimulating Factor