The first two authors contributed equally to this work.
Sclerostin Regulates Release of Bone Mineral by Osteocytes by Induction of Carbonic Anhydrase 2
Article first published online: 19 NOV 2013
© 2013 American Society for Bone and Mineral Research
Journal of Bone and Mineral Research
Volume 28, Issue 12, pages 2436–2448, December 2013
How to Cite
Kogawa, M., Wijenayaka, A. R., Ormsby, R. T., Thomas, G. P., Anderson, P. H., Bonewald, L. F., Findlay, D. M. and Atkins, G. J. (2013), Sclerostin Regulates Release of Bone Mineral by Osteocytes by Induction of Carbonic Anhydrase 2. J Bone Miner Res, 28: 2436–2448. doi: 10.1002/jbmr.2003
For a Commentary on this article, please see Arnett (J Bone Miner Res. 2013;28:2433–2435. DOI: 10.1002/jbmr.2119).
- Issue published online: 19 NOV 2013
- Article first published online: 19 NOV 2013
- Accepted manuscript online: 5 JUN 2013 05:36AM EST
- Manuscript Accepted: 17 MAY 2013
- Manuscript Revised: 6 MAY 2013
- Manuscript Received: 4 OCT 2012
- National Health and Medical Research Council of Australia (NHMRC). Grant Numbers: 565372, 1004871
- CARBONIC ANHYDRASE 2;
- OSTEOCYTIC OSTEOLYSIS
The osteocyte product sclerostin is emerging as an important paracrine regulator of bone mass. It has recently been shown that osteocyte production of receptor activator of NF-κB ligand (RANKL) is important in osteoclastic bone resorption, and we reported that exogenous treatment of osteocytes with sclerostin can increase RANKL-mediated osteoclast activity. There is good evidence that osteocytes can themselves liberate mineral from bone in a process known as osteocytic osteolysis. In the current study, we investigated sclerostin-stimulated mineral dissolution by human primary osteocyte-like cells (hOCy) and mouse MLO-Y4 cells. We found that sclerostin upregulated osteocyte expression of carbonic anhydrase 2 (CA2/Car2), cathepsin K (CTSK/Ctsk), and tartrate-resistant acid phosphatase (ACP5/Acp5). Because acidification of the extracellular matrix is a critical step in the release of mineral from bone, we further examined the regulation by sclerostin of CA2. Sclerostin stimulated CA2 mRNA and protein expression in hOCy and in MLO-Y4 cells. Sclerostin induced a decrease in intracellular pH (pHi) in both cell types as well as a decrease in extracellular pH (pHo) and the release of calcium ions from mineralized substrate. These effects were reversed in the co-presence of the carbonic anhydrase inhibitor, acetozolamide. Car2-siRNA knockdown in MLO-Y4 cells significantly inhibited the ability of sclerostin to both reduce the pHo and release calcium from a mineralized substrate. Knockdown in MLO-Y4 cells of each of the putative sclerostin receptors, Lrp4, Lrp5 and Lrp6, using siRNA, inhibited the sclerostin induction of Car2, Catk and Acp5 mRNA, as well as pHo and calcium release. Consistent with this activity of sclerostin resulting in osteocytic osteolysis, human trabecular bone samples treated ex vivo with recombinant human sclerostin for 7 days exhibited an increased osteocyte lacunar area, an effect that was reversed by the co-addition of acetozolamide. These findings suggest a new role for sclerostin in the regulation of perilacunar mineral by osteocytes. © 2013 American Society for Bone and Mineral Research.