Sclerostin blockade inhibits bone resorption through PDGF receptor signaling in osteoblast lineage cells
Cyril Thouverey, Pierre Apostolides, Julia Brun, Joseph Caverzasio, Serge Ferrari
Cyril Thouverey, Pierre Apostolides, Julia Brun, Joseph Caverzasio, Serge Ferrari
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Research Article Bone biology

Sclerostin blockade inhibits bone resorption through PDGF receptor signaling in osteoblast lineage cells

Abstract

While sclerostin-neutralizing antibodies (Scl-Abs) transiently stimulate bone formation by activating Wnt signaling in osteoblast lineage cells, they exert sustained inhibition of bone resorption, suggesting an alternate signaling pathway by which Scl-Abs control osteoclast activity. Since sclerostin can activate platelet-derived growth factor receptors (PDGFRs) in osteoblast lineage cells in vitro and PDGFR signaling in these cells induces bone resorption through M-CSF secretion, we hypothesized that the prolonged anticatabolic effect of Scl-Abs could result from PDGFR inhibition. We show here that inhibition of PDGFR signaling in osteoblast lineage cells is sufficient and necessary to mediate prolonged Scl-Ab effects on M-CSF secretion and osteoclast activity in mice. Indeed, sclerostin coactivates PDGFRs independently of Wnt/β-catenin signaling inhibition, by forming a ternary complex with LRP6 and PDGFRs in preosteoblasts. In turn, Scl-Ab prevents sclerostin-mediated coactivation of PDGFR signaling and consequent M-CSF upregulation in preosteoblast cultures, thereby inhibiting osteoclast activity in preosteoblast/osteoclast coculture assays. These results provide a potential mechanism explaining the dissociation between anabolic and antiresorptive effects of long-term Scl-Ab.

Authors

Cyril Thouverey, Pierre Apostolides, Julia Brun, Joseph Caverzasio, Serge Ferrari

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Figure 6

Sclerostin increases Csf1 expression independently of Wnt/β-catenin signaling inhibition in preosteoblast cultures.

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Sclerostin increases Csf1 expression independently of Wnt/β-catenin sign...
(A and B) WT preosteoblasts were pretreated with Veh or 100 ng/mL Wnt1 with and without 500 ng/mL SOST for 2 hours, and treated with Veh or 25 ng/mL PDGF-BB for (A) 24 hours before measurement of Csf1 expression by quantitative RT-PCR, or (B) 48 hours before quantification of M-CSF in culture media by ELISA. Data in A and B were analyzed by 2-way ANOVA followed by Tukey’s post hoc test. (C) WT preosteoblasts were pretreated with Veh or 100 ng/mL Wnt1 with and without 500 ng/mL SOST for 2 hours, and treated with Veh or 25 ng/mL PDGF-BB for 15 minutes before evaluation of PDGFR signaling by Western blot analyses. (D) WT preosteoblasts were pretreated with DMSO or 5 μM WIKI4 (inhibitor of Wnt/β-catenin signaling), and Veh or 500 ng/mL SOST for 2 hours, and treated with Veh or 25 ng/mL PDGF-BB for 24 hours before measurement of Csf1 expression by quantitative RT-PCR. Data in D were analyzed by 2-way ANOVA followed by Tukey’s post hoc test. (E) WT preosteoblasts were pretreated with Veh, 500 ng/mL SOST, or 500 ng/mL DKK1 for 2 hours, and then treated with Veh or 25 ng/mL PDGF-BB for 24 hours before measurement of Csf1 expression by quantitative RT-PCR. Data in E were analyzed by 1-way ANOVA followed by Tukey’s post hoc test. (F) WT preosteoblasts were pretreated with Veh or 500 ng/mL DKK1 for 2 hours, and then treated with Veh or 25 ng/mL PDGF-BB for 15 minutes before evaluation of PDGFR signaling by Western blot analyses. (G) Pdgfrfl/fl and Pdgfr-cKO preosteoblasts were pretreated with Veh or 500 ng/mL SOST, and then treated with Veh or 100 ng/mL Wnt1 for 2 hours before determination of Wnt/β-catenin signaling by Western blot analyses. (H) Pdgfrfl/fl and Pdgfr-cKO preosteoblasts were pretreated with Veh or 500 ng/mL SOST, and then treated with Veh or 100 ng/mL Wnt1 for 24 hours before measurement of Wisp1 expression by quantitative RT-PCR. Data in H were analyzed by 2-way ANOVA followed by Tukey’s post hoc test.