Abstract: Objective： To explore the effect of gamma secretase inhibitor (Semagacestat) on osteoclast formation and bone resorption induced by RANKL and its mechanism. Methods：Bone marrow cavity macrophages of 5 weeks old C57 mice were extracted for culture. IC50 of Semagacestat on macrophages was calculated by MTT to determine the safe drug concentration.The effect of Semagacestat on osteoclast formation was evaluated by osteoclast formation, TRAP staining and bone resorption test.RT-PCR was used to detect gene expression related to osteoclast formation.Western blot analysis of expression of proteins associated with Notch signaling pathway was also tested. Results：The 24h, 48h and 96h IC50 of Simasit on macrophages were 6.03, 5.79 and 5.18μmol/L, respectively. Trap staining showed that the number of osteoclasts formed was (209±8) for each well in the control group, and (183±14) for each well, (91±10) for each well, and (22±7) for each well in the Semagacestat 100, 200, and 400 nmol/L dosing groups, respectively(P < 0.05). In vitro bone resorption results showed that the percentage of bone resorption area in blank control group was (93.3±3.0)%, and the percentage of bone resorption area in Semagacestat 100, 200 and 400 nmol/L dosing groups was (80.6±6.6)%, (52.2±6.6)%, (27.4±5.8)%, respectively (P<0.05). RT-PCR results showed that the expressions of osteoclast related gene: C-fos, TRAP, Cath-K and NFATC1 were significantly decreased with the increase of the concentration of Semagacestat (P<0.05). Western Blot results showed that Cleaved-Notch1, NFATc1, and Hes1 expression decreased in the Semagacestat group compared to the control group (P<0.05). Conclusions:By inhibiting the activation of Notch pathway, Semagacestat inhibits the formation and bone resorption of osteoclasts, and may have a potential therapeutic effect on osteoarthritis.

Key words: Semagacestat, osteoarthritis, osteoblast, bone resorption, Notch signaling