Abstract
Osteocytes play a critical role in bone remodeling through the secretion of paracrine factors regulating the differentiation and activity of osteoblasts and osteoclasts. Sclerostin is a key osteocyte-derived factor that suppresses bone formation and promotes bone resorption, therefore regulators of sclerostin secretion are a likely source of new therapeutic strategies for treatment of skeletal disorders. Here, we demonstrate that protein kinase CK2 (casein kinase 2) controls sclerostin expression in osteocytes via the deubiquitinase ubiquitin-specific peptidase 4 (USP4)-mediated stabilization of Sirtuin1 (SIRT1). Deletion of CK2 regulatory subunit, Csnk2b, in osteocytes (Csnk2bDmp1) results in low bone mass due to elevated levels of sclerostin. This phenotype in Csnk2bDmp1 mice was partly reversed when sclerostin expression was downregulated by a single intravenous injection with bone-targeting adeno-associated virus 9 (AAV9) carrying an artificial-microRNA that targets Sost. Mechanistically, CK2-induced phosphorylation of USP4 is important for stabilization of SIRT1 by suppressing ubiquitin-dependent proteasomal degradation. Upregulated expression of SIRT1 inhibits sclerostin transcription in osteocytes. Collectively, the CK2-USP4-SIRT1 pathway is crucial for the regulation of sclerostin expression in osteocytes to maintain bone homeostasis.
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Data supporting the findings of this manuscript are available from the corresponding author upon reasonable request.
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Acknowledgements
We would like to thank Drs. Paola Divieti Pajevic and Marc Wein for providing Ocy454 osteocytic cell line. We also thank the many individuals who provided valuable reagents. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2014R1A6A3A03055719, J.M.K.). This project was also supported by the Center for Skeletal Research Imaging and Biomechanical Testing Core for biomechanical testing (NIH P30AR066261) and Career Award for Medical Scientists from the Burroughs Wellcome Fund, the NIH under awards DP5OD021351 and R01AR075585, and a Pershing Square Sohn Cancer Research Alliance award to M.B.G. J.H.S holds support from NIAMS of the NIH under R01AR068983 and R21AR077557 and the AAVAA Therapeutics.
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J.M.K. designed, executed, and interpreted the experiments. Y.Y.S, J.K., and O.L. performed histology, immunohistochemistry, dynamic histomorphometry, and micro-CT analyses. J.X., and G.G. generated rAAV. J.H., and H.C. performed transcriptome analysis. B.B., and O.F. generated and provided Csnk2b floxed mice, respectively. M.B.G. helped skeletal analysis of mice. J.H.S. supervised the research and participated in the manuscript preparation.
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JHS is a scientific co-founder of the AAVAA Therapeutics and holds equity in this company. GG is a scientific co-founder of AAVAA Therapeutics, Voyager Therapeutics, and Aspa Therapeutics and holds equity in these companies. GG is an inventor on patents with potential royalties licensed to Voyager Therapeutics, Aspa Therapeutics Inc., and other biopharmaceutical companies. Other authors declare no competing interests.
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Kim, JM., Yang, YS., Xie, J. et al. Regulation of sclerostin by the SIRT1 stabilization pathway in osteocytes. Cell Death Differ 29, 1625–1638 (2022). https://doi.org/10.1038/s41418-022-00952-x
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DOI: https://doi.org/10.1038/s41418-022-00952-x
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