Bone Abstracts

Notch signaling plays a central role in various cell fate decisions, including skeletal development. Recently, Notch signaling was implicated in osteoclast differentiation and maturation, including the resorption activity of osteoclasts. However, the specific involvement of notch signaling in resorption activity was not fully investigated. Here, we investigated the roles of Notch signaling in the resorption activity of osteoclasts by use of the γ-secretase inhibitor dibenzazepine (DBZ). Attenuating Notch signaling by DBZ suppressed the expression of NFATc1, a master transcription factor for osteoclast differentiation. However, overexpression of a constitutively active form of NFATc1 did not fully rescue the effects of DBZ. DBZ suppressed the autophosphorylation of PYK2, which is essential for the formation of the podosome belt and sealing zone, with reduced c-Src/PYK2 interaction. We further observed increased PYK2 activation by RANKL accompanied by increased NICD2 production. These results confirmed that overexpression of NICD2 rescued DBZ-mediated suppression of resorption activity with promotion of PYK2 autophosphorylation, PYK2/c-Src interaction, and microtubule acetylation. Consistent with the in vitro results, DBZ strongly suppressed bone destruction in an interleukin-1-induced bone loss model. Collectively, these results demonstrate that Notch 2 in osteoclasts plays a role in the control of resorption activity via the PYK2-c-Src-microtubule signaling pathway.