The objective of this R21 application is to investigate at the atomic level, the mechanism of action of sclerostin, an osteocyte-derived, secreted, cystine-knot protein that inhibits bone formation by examining how sclerostin interacts with proteins that play an essential role in mediating its activity. Because the disruption of sclerostin expression or activity increases bone mass insights developed through our studies may be useful in devising treatments for osteoporosis, a disease affecting 10 million Americans. Bone morphogenetic protein 6 (BMP6), cysteine-rich protein 61 (Cyr61) and low-density-lipoprotein receptor-related protein 5 (LRP5) are key sclerostin-associating proteins reported to mediate sclerostin activity. No structural data exists for these protein complexes. Moreover, preliminary docking studies suggest that the conformations observed in two sclerostin NMR solution-structures must be altered to affect binding to these three proteins. We hypothesize that in contrast to its highly disordered structure in the solution-state, the "loop 2" region of sclerostin (amino acids G86-R109) becomes highly structured when sclerostin binds proteins such as BMP6, Cyr61 and LRP5 whose functions it modulates. If true, sclerostin activity might be antagonized by allosteric modulation and by targeting its interaction site(s), through the use of orally effective, small molecules that would generate new bone in patients.
In Aim 1 we will determine the molecular mechanism of sclerostin interaction with BMP6;
in Aim 2 we will determine the molecular mechanism of sclerostin interaction with Cyr61 C-terminal domain and in Aim 3 we will identify crystallization conditions for the sclerostin complex with LRP5 extracellular domain.
In Aims 1 -2, our proposed mechanism for sclerostin interaction will be probed by x-ray crystallography followed by analysis of binding-affinities of structure-guided mutants through the use of surface plasmon resonance.
In Aim 3 conditions for crystallizing sclerostin-LRP5 1st ?-propeller complexes will be established. Significance: Osteoporosis is a significant medical health problem associated with fractures and considerable morbidity, prevalent particularly in aging and post-menopausal women. While effective bone anti-resorptive drugs are available for osteoporosis treatment, they have little effect on bone formation. The only anabolic agent available now is teriparatide that must be administered parenterally. Sclerostin is an osteocyte derived protein that inhibits bone formation. Antagonizing its function is a potential therapeutic strategy to increase high quality bone. Our studies will allow an atomic-level understanding of the interface between sclerostin and three protein partners that mediate sclerostin function. We anticipate this knowledge would provide a strong basis for development of antagonistic drugs that can be administrated orally, especially if structural results suggest sclerostin might be amenable to allosteric modulation by small-molecules.

Public Health Relevance

Orally effective drugs that build bone are required for the treatment of osteoporosis. By determining the structures of complexes of sclerostin (a bone inhibitory protein) with other proteins with which it interacts, we will be able to obtain the information that will allow the design of such drugs. This effort will greatly help women and men with osteoporosis and osteoporosis-related fractures.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Exploratory/Developmental Grants (R21)
Project #
Application #
Study Section
Skeletal Biology Structure and Regeneration Study Section (SBSR)
Program Officer
Chen, Faye H
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Mayo Clinic, Rochester
United States
Zip Code
Ryan, Zachary C; Craig, Theodore A; McGee-Lawrence, Meghan et al. (2015) Alterations in vitamin D metabolite, parathyroid hormone and fibroblast growth factor-23 concentrations in sclerostin-deficient mice permit the maintenance of a high bone mass. J Steroid Biochem Mol Biol 148:225-31
Ryan, Zachary C; Craig, Theodore A; Salisbury, Jeffrey L et al. (2014) Enhanced prostacyclin formation and Wnt signaling in sclerostin deficient osteocytes and bone. Biochem Biophys Res Commun 448:83-8
Kumar, Rajiv; Vallon, Volker (2014) Reduced renal calcium excretion in the absence of sclerostin expression: evidence for a novel calcium-regulating bone kidney axis. J Am Soc Nephrol 25:2159-68
Craig, Theodore A; Zhang, Yuji; Magis, Andrew T et al. (2014) Detection of 1?,25-dihydroxyvitamin D-regulated miRNAs in zebrafish by whole transcriptome sequencing. Zebrafish 11:207-18
Craig, Theodore A; Ramachandran, Pradeep L; Bergen 3rd, H Robert et al. (2013) The regulation of apoptosis by the downstream regulatory element antagonist modulator/potassium channel interacting protein 3 (DREAM/KChIP3) through interactions with hexokinase I. Biochem Biophys Res Commun 433:508-12
McGee-Lawrence, Meghan E; Ryan, Zachary C; Carpio, Lomeli R et al. (2013) Sclerostin deficient mice rapidly heal bone defects by activating *-catenin and increasing intramembranous ossification. Biochem Biophys Res Commun 441:886-90
Devarajan-Ketha, Hemamalini; Craig, Theodore A; Madden, Benjamin J et al. (2012) The sclerostin-bone protein interactome. Biochem Biophys Res Commun 417:830-5
Tebben, Peter J; Milliner, Dawn S; Horst, Ronald L et al. (2012) Hypercalcemia, hypercalciuria, and elevated calcitriol concentrations with autosomal dominant transmission due to CYP24A1 mutations: effects of ketoconazole therapy. J Clin Endocrinol Metab 97:E423-7