Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 116, Issue 28, Pages 14138-14143Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1900881116
Keywords
Sfrp4; Ror2/Jnk; endocortical remodeling; Pyle's disease; Wnt signaling
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Funding
- NIH-National Institute of Arthritis and Musculoskeletal and Skin Diseases [R01AR064724]
- China Scholarship Council [201606160044]
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Loss-of-function mutations in the Wnt inhibitor secreted frizzled receptor protein 4 (SFRP4) cause Pyle's disease (OMIM 265900), a rare skeletal disorder characterized by wide metaphyses, significant thinning of cortical bone, and fragility fractures. In mice, we have shown that the cortical thinning seen in the absence of Sfrp4 is associated with decreased periosteal and endosteal bone formation and increased endocortical resorption. While the increase in Rankl/Opg in cortical bone of mice lacking Sfrp4 suggests an osteoblast-dependent effect on endocortical osteoclast (OC) activity, whether Sfrp4 can cell-autonomously affect OCs is not known. We found that Sfrp4 is expressed during bone marrow macrophage OC differentiation and that Sfrp4 significantly suppresses the ability of early and late OC precursors to respond to Rankl-induced OC differentiation. Sfrp4 deletion in OCs resulted in activation of canonical Wnt/beta-catenin and noncanonical Wnt/Ror2/Jnk signaling cascades. However, while inhibition of canonical Wnt/beta-catenin signaling did not alter the effect of Sfrp4 on OCgenesis, blocking the noncanonical Wnt/Ror2/Jnk cascade markedly suppressed its regulation of OC differentiation in vitro. Importantly, we report that deletion of Ror2 exclusively in OCs (CtskCreRor2(fl/fl)) in Sfrp4 null mice significantly reversed the increased number of endosteal OCs seen in these mice and reduced their cortical thinning. Altogether, these data show autocrine and paracrine effects of Sfrp4 in regulating OCgenesis and demonstrate that the increase in endosteal OCs seen in Sfrp4(-/-) mice is a consequence of noncanonical Wnt/Ror2/Jnk signaling activation in OCs overriding the negative effect that activation of canonical Wnt/beta-catenin signaling has on OCgenesis.
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