Vinculin Regulates Osteoclast Function

Background: Vinculin, an actin-binding protein, is essential for cytoskeletal organization. Results: Vinculin deficiency in osteoclasts impairs osteoclast function, not differentiation, leading to increased bone mass in vivo. Conclusion: Vinculin expression regulates osteoclast function in a talin-dependent, v3 integrin-independent manner. Significance: This is the first demonstration that vinculin regulates osteoclast function. Osteoclastic bone resorption depends upon the cell's ability to organize its cytoskeleton. Because vinculin (VCL) is an actin-binding protein, we asked whether it participates in skeletal degradation. Thus, we mated VCLfl/fl mice with those expressing cathepsin K-Cre (CtsK-VCL) to delete the gene in mature osteoclasts or lysozyme M-Cre (LysM-VCL) to target all osteoclast lineage cells. VCL-deficient osteoclasts differentiate normally but, reflecting cytoskeletal disorganization, form small actin rings and fail to effectively resorb bone. In keeping with inhibited resorptive function, CtsK-VCL and LysM-VCL mice exhibit a doubling of bone mass. Despite cytoskeletal disorganization, the capacity of VCL-/- osteoclastic cells to normally phosphorylate c-Src in response to v3 integrin ligand is intact. Thus, integrin-activated signals are unrelated to the means by which VCL organizes the osteoclast cytoskeleton. WT VCL completely rescues actin ring formation and bone resorption, as does VCLP878A, which is incapable of interacting with Arp2/3. As expected, deletion of the VCL tail domain (VCL1-880), which binds actin, does not normalize VCL-/- osteoclasts. The same is true regarding VCLI997A, which also prevents VCL/actin binding, and VCLA50I and VCL811-1066, both of which arrest talin association. Thus, VCL binding talin, but not Arp2/3, is critical for osteoclast function, and its selective inhibition retards physiological bone loss.