Targeting thymidine phosphorylase as a potential therapy for bone loss associated periprosthetic osteolysis

The aim of this study was to identify macrophage-derived factors that promote osteoclast differentiation and periprosthetic bone destruction. To achieve this, we examined the effects of 12 macrophage-derived factors that were identified by RNA-seq analysis of stimulated macrophages on osteoclast differentiation. TYMP was found to trigger significant number of osteoclasts that exhibited resorbing activities on dentine slices. TYMP were detected in serum and synovial tissues of patients that had been diagnosed with aseptic loosening. RNA-seq for TYMP-induced-osteoclasts was then performed in an effort to understand action mode of TYMP. TYMP stimulation appeared to activate the tyrosine kinase FYN signaling associated with osteoclast formation. Oral administration of saracatinib, a FYN kinase inhibitor, significantly suppressed formation of bone osteolytic lesions in a polyethylene debris-induced osteolysis model. Our findings highlight a novel molecular target for therapeutic intervention in periprosthetic osteolysis. Overall design: RNA-seq for macrophages stimulated by macrophage colony-stimulating factor, receptor activator of nuclear factor kappa-b ligand and thymidine phosphorylase