Inhibition of Osteoclastogenesis by LY90009 through Notch Signaling Modulation in Osteolytic Disease Models.

Dysregulated osteoclast activity profoundly contributes to the progression of osteolytic disease, yet the extent of therapeutic intervention modalities is constrained by adverse effects. This study investigated LY900009, a γ-secretase inhibitor, and its capacity to suppress RANKL-induced osteoclastogenesis through modulation of Notch signaling. Using bone marrow-derived macrophages, we performed comprehensive in vitro evaluations of cytotoxicity, differentiation, and functional assays. Gene and protein expression analyses using qPCR and western blotting were used to elucidate the underlying molecular mechanisms. The in vivo efficacy was corroborated using a murine lipopolysaccharide-induced bone resorption model. LY900009 inhibited RANKL-induced osteoclast formation and resorptive function in a dose-dependent manner without cytotoxicity at therapeutic concentrations. This treatment significantly reduced the number of TRAP-positive osteoclasts, impaired actin belt formation, and suppressed bone matrix degradation. The expression of osteoclast markers, including NFATc1, c-Fos, cathepsin K, and TRAP, was markedly downregulated. Mechanistically, LY900009 disrupted Notch signaling and the downstream MAPK/Akt pathways. In vivo administration substantially reduced LPS-induced bone destruction, improving bone parameters and reducing osteoclast presence. These findings demonstrate that LY900009 effectively inhibits osteoclastogenesis and bone resorption by modulating the Notch/MAPK/Akt signaling axis, making it a promising therapeutic candidate for osteolytic disorders.