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

INTRODUCTION: Bone remodeling depends on coordinated signaling between bone-resorbing osteoclasts and bone-forming osteoblasts through locally secreted coupling factors. Disruption of this balance leads to decreased bone mass, resulting in conditions such as osteoporosis. Osteoclast-derived anabolic factors, or clastokines, have emerged as attractive therapeutic candidates with the potential of selectively enhancing bone formation without suppressing resorption. Osteoblast-derived WNT5A is an established coupling factor promoting osteoclastogenesis; however, osteoclast-derived WNT5A specific contribution to bone homeostasis and the downstream mechanism by which it acts on osteoblasts remains undefined. METHODS: This study aimed to address this gap using a myeloid-specific conditional knockout mouse that selectively targets osteoclast-derived WNT5A while leaving osteoblast-derived WNT5A intact. Wnt5a was conditionally deleted in osteoclast precursors and their progeny using LysM-Cre; Wnt5aF/F mice and both male and female knockout mice were characterized by μCT, histomorphometry, serum bone turnover markers, transcriptomic profiling of osteoblast-enriched cells, and in vitro focal adhesion and migration assays. RESULTS: Both male and female knockout mice displayed significantly reduced trabecular volume compared with controls. This low bone mass phenotype was driven by decreased osteoblast number and activity, with no significant changes in osteoclast number or resorptive function. Transcriptomic profiling of osteoblast-enriched cells revealed dysregulation of genes involved in focal adhesion, integrin binding, and cell communication, alongside upregulation of stress-related gene networks. Histological and functional analyses demonstrated that loss of osteoclast-derived WNT5A impaired extracellular matrix maturation and disrupted osteoblast focal adhesion assembly and migration. DISCUSSION: Together, our study establishes osteoclast-derived WNT5A as a clastokine that promotes bone formation in vivo by regulating osteoblast migration and adhesion dynamics. These findings establish a mechanistic link between osteoclast secretory activity and osteoblast function and highlight the context-dependent and cell-of-origin specific roles of WNT5A in skeletal homeostasis.