The vinculin-β-catenin axis promotes bone formation and repair: an essential prerequisite for the anti-osteoporotic efficacy of sclerostin-neutralizing antibody.

Currently, targeting the Wnt/β-catenin pathway to promote bone formation is a primary strategy for the development of osteoporosis drugs. Here, we demonstrate that vinculin promotes bone mass increase and fracture repair by elevating the β-catenin protein levels in mesenchymal stem cells (MSCs). Furthermore, it is revealed that vinculin is required for sclerostin-neutralizing antibody (Scl-Ab) to increase the bone mass in mice. We find that promoter accessibility and the expression of the Vcl gene, which encodes vinculin, are reduced in the MSCs from elderly human individuals, and vinculin knockdown impairs osteoblast differentiation in vitro. Genetic deletion of Vcl in Prx1-expressing cells in mice leads to pronounced bone loss in weight-bearing long bones, but not in the non-weight-bearing skull, primarily attributed to severely impaired bone formation, characterized by reduced osteoblastic and increased adipogenic differentiation. Unexpectedly, vinculin loss decreases the β-catenin protein levels by approximately 80% in MSCs in vitro and in the bone. Mechanistically, vinculin binds to β-catenin and blocks GSK-3 phosphorylation and the subsequent ubiquitin-proteasomal degradation of β-catenin, thereby stabilizing β-catenin. Thus, mutating the β-catenin GSK-3 phosphorylation sites abolishes the ability of vinculin deficiency to destabilize β-catenin, and the pharmacological inhibition of GSK-3 activity restores the bone loss induced by vinculin ablation in mice. Furthermore, deleting vinculin expression in chondrocytes impairs bone fracture healing, while a hydrogel containing MSCs overexpressing vinculin in mice promotes fracture healing. Importantly, vinculin loss abolishes the ability of sclerostin-neutralizing antibody Scl-Ab, a current primary anti-osteoporotic treatment, to increase bone mass in mice. Thus, we demonstrate that the vinculin-β-catenin axis in MSCs promotes bone formation and fracture healing and is essential for the effectiveness of current osteoporosis drugs.