Focal adhesion protein vinculin inhibits Mef2c-driven sclerostin expression in osteocytes to promote bone formation in mice

The focal adhesion (FA) is the structural basis of the cell-extracellular matrix crosstalk and plays important roles in control of organ formation and function. Here we show that expression of FA protein vinculin is dramatically reduced in osteocytes in patients with aging-related osteoporosis. Deleting vinculin using the mouse 10-kb Dmp1-Cre transgenic mice causes a severe osteopenia in both young and aged mice by impairing osteoblast function without affecting bone resorption. Vinculin loss impairs the anabolic response of skeleton to mechanical loading in mice. At the molecular level, vinculin knockdown increases, while vinculin overexpression decreases, sclerostin expression in osteocytes without impacting expression of Mef2c, a major transcriptional regulator of the Sost gene, which encodes sclerostin. Vinculin interacts with Mef2c and vinculin loss enhances Mef2c nuclear translocation and binding to the Sost enhancer ECR5 to promote sclerostin production in osteocytes. Deleting Sost expression reverses the osteopenic phenotypes caused by vinculin loss in mice. We demonstrate that estrogen is a major regulator of vinculin expression in osteocytes and that more importantly vinculin loss mediates estrogen deficiency induction of bone loss in mice. Thus, we demonstrate a novel mechanism through which vinculin inhibits the Mef2c-driven sclerostin expression in osteocytes to promote bone formation.