Conditional deletion of Wnt5a in myeloid osteoclast precursors results in low bone mass via disruption of osteoblast migration and focal adhesion dynamics

Bone remodeling relies on the coordinated signaling between bone-resorbing osteoclasts and bone-forming osteoblasts through locally secreted coupling factors, including WNT5A. Although osteoblast-derived WNT5A is known to promote osteoclastogenesis, the contribution of osteoclast-derived WNT5A to bone homeostasis remains poorly defined. We previously showed that conditional deletion of Wnt5a in mature osteoclasts using the Ctsk-Cre driver results in low bone mass, suggesting an anabolic role for osteoclast-derived WNT5A. However, Ctsk expression in other cell types, including periosteal cells, precluded definitive attribution. Here, we used the more specific LysM-Cre line to validate the osteoclast-specific function of Wnt5a in vivo. LysM-Cre; Wnt5aF/F mice displayed significantly reduced trabecular bone driven by decreased osteoblast number and activity, while osteoclast number and resorptive function were preserved. Transcriptomic profiling of osteoblast-enriched cells revealed dysregulation of genes involved in cell adhesion, integrin binding, and cell communication, alongside upregulation of stress-related genes. Histological analyses and functional assays showed that loss of osteoclast-derived Wnt5a led to impaired extracellular matrix maturation together with defective osteoblast focal adhesion assembly and migration, respectively. Collectively, these data provide a mechanistic link between Wnt5a and osteoblast function. In summary, our study establishes osteoclast-derived Wnt5a as a clastokine supporting bone formation through regulation of osteoblast migration and adhesion dynamics, highlighting the context-dependent and cell-specific roles of WNT5A in skeletal homeostasis.