Negative regulator of bone growth that acts through inhibition of Wnt signaling and bone formation. Interacts with LRP4 (via the extracellular domain); the interaction facilitates the inhibition of Wnt signaling. Interacts with LRP5 (via the first two YWTD-EGF repeat domains); the interaction inhibits Wnt-mediated signaling. Interacts with LRP6. Belongs to the sclerostin family.