Abstract
Pathogenic variants disrupting the binding between sclerostin (encoded by SOST) and its receptor LRP4 have previously been described to cause sclerosteosis, a rare high bone mass disorder. The sclerostin-LRP4 complex inhibits canonical WNT signaling, a key pathway regulating osteoblastic bone formation and a promising therapeutic target for common bone disorders, such as osteoporosis. In the current study, we crossed mice deficient for Sost (Sost−/−) with our p.Arg1170Gln Lrp4 knock-in (Lrp4KI/KI) mouse model to create double mutant Sost−/−;Lrp4KI/KI mice. We compared the phenotype of Sost−/− mice with that of Sost−/−;Lrp4KI/KI mice, to investigate a possible synergistic effect of the disease-causing p.Arg1170Trp variant in Lrp4 on Sost deficiency. Interestingly, presence of Lrp4KI alleles partially mitigated the Sost−/− phenotype. Cellular and dynamic histomorphometry did not reveal mechanistic insights into the observed phenotypic differences. We therefore determined the molecular effect of the Lrp4KI allele by performing bulk RNA sequencing on Lrp4KI/KI primary osteoblasts. Unexpectedly, mostly genes related to bone resorption or remodeling (Acp5, Rankl, Mmp9) were upregulated in Lrp4KI/KI primary osteoblasts. Verification of these markers in Lrp4KI/KI, Sost−/− and Sost−/−;Lrp4KI/KI mice revealed that sclerostin deficiency counteracts this Lrp4KI/KI effect in Sost−/−;Lrp4KI/KI mice. We therefore hypothesize that models with two inactivating Lrp4KI alleles rather activate bone remodeling, with a net gain in bone mass, whereas sclerostin deficiency has more robust anabolic effects on bone formation. Moreover, these effects of sclerostin and Lrp4 are stronger in female mice, contributing to a more severe phenotype than in males and more detectable phenotypic differences among different genotypes.
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Funding
This research was funded by grants of the Fund for Scientific Research Flanders (FWO grant G031915N), a personal grant to EB (FWO personal grant 12A3814N), a research grant of the University of Antwerp (Methusalem—OEC grant—“GENOMED”; FFB190208) and the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 602300 (SYBIL).
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Conceptualization, GH, EB and WVH; Data curation, GH and EB; Formal analysis, GH, EB, LM and TAY; and Methodology, GH, EB, LM, TAY and ES; Supervision, WVH; Validation, GH, EB and LM; Writing—original draft, GH and WVH; Writing—review & editing, GH, EB, LM, TAY, ES, MK, IK, GM, TS and WVH. All authors listed have made a substantial, direct, and intellectual contribution to the work and have approved it for publication. All authors have read and agreed to the published version of the manuscript.
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GH, EB, LM, TAY, ES, GM, TS and WVH declare that they have no conflict of interest. MK and IK are employees of Novartis Institutes for BioMedical Research.
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All animal experimental procedures were carried out in compliance with the ARRIVE guidelines and European Commission Council Directive 2010/63/EU on protecting animals for scientific purposes and ethical approval for all procedures was obtained by the University of Antwerp Ethics Committee (Reference Number 2017-60).
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All animal experimental procedures were carried out in compliance with the ARRIVE guidelines and were approved by the University of Antwerp Ethics Committee (reference number 2017-60).
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Hendrickx, G., Boudin, E., Mateiu, L. et al. An Additional Lrp4 High Bone Mass Mutation Mitigates the Sost-Knockout Phenotype in Mice by Increasing Bone Remodeling. Calcif Tissue Int 114, 171–181 (2024). https://doi.org/10.1007/s00223-023-01158-0
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DOI: https://doi.org/10.1007/s00223-023-01158-0