title: FLT3 ligand can substitute for macrophage colony-stimulating factor in support of osteoclast differentiation and function.
abstract: Although bone resorption and osteoclast numbers are reduced in osteopetrotic (op/op) mice, osteoclasts are nevertheless present and functional, despite the absence of macrophage colony-stimulating factor (M-CSF). This suggests that alternative factors can partly compensate for the crucial actions of M-CSF in osteoclast induction. It was found that when nonadherent bone marrow cells were incubated in RANKL with Flt3 ligand (FL) without exogenous M-CSF, tartrate-resistance acid phosphatase (TRAP)-positive cells were formed, and bone resorption occurred. Without FL, only macrophagelike TRAP-negative cells were present. Granulocyte-macrophage CSF, stem cell factor, interleukin-3, and vascular endothelial growth factor could not similarly replace the need for M-CSF. TRAP-positive cell induction in FL was not due to synergy with M-CSF produced by the bone marrow cells themselves because FL also enabled their formation from the hemopoietic cells of op/op mice, which lack any M-CSF. FL appeared to substitute for M-CSF by supporting the differentiation of adherent cells that express mRNA for RANK and responsiveness to RANKL. To determine whether FL can account for the compensation for M-CSF deficiency that occurs in vivo, FL signaling was blockaded in op/op mice by the injection of soluble recombinant Flt3. It was found that the soluble receptor induced a substantial decrease in osteoclast number, strongly suggesting that FL is responsible for the partial compensation for M-CSF deficiency that occurs in these mice.
authors.affiliation: Department of Cellular Pathology, St George's Hospital Medical School, London, United Kingdom.
authors.forename: J M
authors.initials: JM
authors.lastname: Lean
authors.forename: K
authors.initials: K
authors.lastname: Fuller
authors.forename: T J
authors.initials: TJ
authors.lastname: Chambers
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology; D001862:Bone Resorption; D002352:Carrier Proteins / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D004347:Drug Interactions; D005269:Femur / Q000166:cytology; D006023:Glycoproteins / Q000235:genetics; D006412:Hematopoietic Stem Cells / Q000187:drug effects; D016173:Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D008297:Male; D008562:Membrane Glycoproteins / Q000494:pharmacology; D008565:Membrane Proteins / Q000494:pharmacology*; D051379:Mice; D008815:Mice, Inbred Strains; D010010:Osteoclasts / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D053244:Osteoprotegerin; D053245:RANK Ligand; D012333:RNA, Messenger / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics; D018124:Receptors, Tumor Necrosis Factor; D013154:Spleen / Q000166:cytology
chemical_list: D002352:Carrier Proteins; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D053244:Osteoprotegerin; D053245:RANK Ligand; D012333:RNA, Messenger; 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; C506032:Tnfrsf11b protein, rat; C505689:Tnfsf11 protein, mouse; C084881:flt3 ligand protein; D016173:Macrophage Colony-Stimulating Factor