Wnt signalling in osteoblasts regulates expression of the receptor activator of NFkappaB ligand and inhibits osteoclastogenesis in vitro.
Reports implicating Wnt signalling in the regulation of bone mass have prompted widespread interest in the use of Wnt mimetics for the treatment of skeletal disorders. To date much of this work has focused on their anabolic effects acting on cells of the osteoblast lineage. In this study we provide evidence that Wnts also regulate osteoclast formation and bone resorption, through a mechanism involving transcriptional repression of the gene encoding the osteoclastogenic cytokine receptor activator of NFkappaB ligand (RANKL or TNFSF11) expressed by osteoblasts. In co-cultures of mouse mononuclear spleen cells and osteoblasts, inhibition of GSK3beta with LiCl or exposure to Wnt3a inhibited the formation of tartrate-resistant acid phosphatase-positive multinucleated cells compared with controls. However, these treatments had no consistent effect on the differentiation, survival or activity of osteoclasts generated in the absence of supporting stromal cells. Activation of Wnt signalling downregulated RANKL mRNA and protein expression, and overexpression of fulllength beta-catenin, but not transcriptionally inactive beta-catenin DeltaC(695-781), inhibited RANKL promoter activity. Since previous studies have demonstrated an absence of resorptive phenotype in mice lacking LRP5, we determined expression of a second Wnt co-receptor LRP6 in human osteoblasts, CD14(+) osteoclast progenitors and mature osteoclasts. LRP5 expression was undetectable in CD14-enriched cells and mature human osteoclasts, although LRP6 was expressed at high levels by these cells. Our evidence of Wnt-dependent regulation of osteoclastogenesis adds to the growing complexity of Wnt signalling mechanisms that are now known to influence skeletal function and highlights the requirement to develop novel therapeutics that differentially target anabolic and catabolic Wnt effects in bone.
Spencer
Gary J
GJ
Biomedical Tissue Research, Department of Biology, University of York, PO Box 373, York, YO10 5YW, UK. gjs6@york.ac.uk
Utting
Jennifer C
JC
Etheridge
Sharon L
SL
Arnett
Timothy R
TR
Genever
Paul G
PG
D000135:Acid Phosphatase / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D002999:Clone Cells; D018920:Coculture Techniques; D017077:Culture Media, Conditioned; D003598:Cytoskeletal Proteins; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D019204:GTP-Binding Proteins / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D026502:LDL-Receptor Related Proteins / Q000378:metabolism; D018021:Lithium Chloride / Q000494:pharmacology; D060492:Low Density Lipoprotein Receptor-Related Protein-5; D060488:Low Density Lipoprotein Receptor-Related Protein-6; D008297:Male; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D009000:Monocytes / Q000166:cytology; D009687:Nuclear Proteins; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010010:Osteoclasts / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D011401:Promoter Regions, Genetic; D053245:RANK Ligand; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D053246:Receptor Activator of Nuclear Factor-kappa B; D015398:Signal Transduction; D013154:Spleen / Q000166:cytology; D000071681:Tartrate-Resistant Acid Phosphatase; D051153:Wnt Proteins / Q000378:metabolism*; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism
D002352:Carrier Proteins; D017077:Culture Media, Conditioned; D003598:Cytoskeletal Proteins; D007527:Isoenzymes; D026502:LDL-Receptor Related Proteins; C555482:LRP5 protein, human; C555475:LRP6 protein, human; D060492:Low Density Lipoprotein Receptor-Related Protein-5; D060488:Low Density Lipoprotein Receptor-Related Protein-6; C555483:Lrp5 protein, mouse; C555476:Lrp6 protein, mouse; D008562:Membrane Glycoproteins; C512806:NIN protein, human; D009687:Nuclear Proteins; D053245:RANK Ligand; D012333:RNA, Messenger; D053246:Receptor Activator of Nuclear Factor-kappa B; C505686:TNFRSF11A protein, human; C505688:TNFSF11 protein, human; C505687:Tnfrsf11a protein, mouse; C505689:Tnfsf11 protein, mouse; D051153:Wnt Proteins; D051176:beta Catenin; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase; D019204:GTP-Binding Proteins; D018021:Lithium Chloride