title: Essential role of nuclear factor of activated T cells (NFAT)-mediated Wnt signaling in osteoblast differentiation induced by strontium ranelate.
abstract: The antiosteoporotic treatment strontium ranelate (SrRan) was shown to increase bone mass and strength by dissociating bone resorption and bone formation. To identify the molecular mechanisms of action of SrRan on osteoblasts, we investigated its effects on calcineurin-NFAT (nuclear factor of activated T cells) signaling, an important calcium sensitive pathway controlling bone formation. Using murine MC3T3-E1 and primary murine osteoblasts, we demonstrate that SrRan induces NFATc1 nuclear translocation, as shown by immunocytochemical and Western blot analyses. Molecular analysis showed that SrRan increased NFATc1 transactivation in osteoblasts, an effect that was fully abrogated by the calcineurin inhibitors cyclosporin A or FK506, confirming that SrRan activates NFATc1 signaling in osteoblasts. This has functional implications because calcineurin inhibitors blunted the enhanced osteoblast replication and expression of the osteoblast phenotypic markers Runx2, alkaline phosphatase, and type I collagen induced by SrRan. We further found that SrRan increased the expression of Wnt3a and Wnt5a as well as beta-catenin transcriptional activity in osteoblasts, and these effects were abolished by calcineurin inhibitors. The Wnt inhibitors sFRP1 and DKK1 abolished SrRan-induced osteoblast gene expression. Furthermore, blunting the Wnt5a receptor Ryk or RhoA that acts downstream of Ryk abrogated cell proliferation and osteoblast gene expression induced by SrRan. These results indicate that activation of NFATc1 and downstream canonical and non-canonical Wnt signaling pathways mediate SrRan-induced osteoblastic cell replication and differentiation, which provides novel insights into the mechanisms of action of this antiosteoporotic agent in osteoblastogenesis.
authors.affiliation: Laboratory of Osteoblast Biology and Pathology, INSERM U606, 75475 Paris cedex 10, USA.
authors.forename: Olivia
authors.initials: O
authors.lastname: Fromigué
authors.forename: Eric
authors.initials: E
authors.lastname: Haÿ
authors.forename: Alain
authors.initials: A
authors.lastname: Barbara
authors.forename: Pierre J
authors.initials: PJ
authors.lastname: Marie
mesh_terms: D000818:Animals; D015153:Blotting, Western; D065095:Calcineurin Inhibitors; D002454:Cell Differentiation / Q000187:drug effects* / Q000235:genetics; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D016572:Cyclosporine / Q000494:pharmacology; D007150:Immunohistochemistry; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology; D051379:Mice; D050778:NFATC Transcription Factors / Q000235:genetics / Q000378:metabolism*; D009942:Organometallic Compounds / Q000494:pharmacology*; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D016559:Tacrolimus / Q000494:pharmacology; D013876:Thiophenes / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000235:genetics; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism*; D000071818:Wnt-5a Protein; D060508:Wnt3 Protein; D060509:Wnt3A Protein; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism; D000094742:Secreted Frizzled-Related Proteins
chemical_list: D065095:Calcineurin Inhibitors; D016572:Cyclosporine; D036341:Intercellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D050778:NFATC Transcription Factors; D009942:Organometallic Compounds; D011518:Proto-Oncogene Proteins; D016559:Tacrolimus; D013876:Thiophenes; D051153:Wnt Proteins; D000071818:Wnt-5a Protein; D060508:Wnt3 Protein; D060509:Wnt3A Protein; D051176:beta Catenin; C501127:Dkk1 protein, mouse; C485539:Sfrp1 protein, mouse; D000094742:Secreted Frizzled-Related Proteins; C555510:WNT3A protein, human; C085389:WNT5A protein, human; C555511:Wnt3a protein, mouse; C081587:strontium ranelate