Segetalin B promotes bone formation in ovariectomized mice by activating PLD1/SIRT1 signaling to inhibit γ-secretase-mediated Notch1 overactivation.

Segetalin B (SB) has shown promise in mitigating osteoporosis in ovariectomized (OVX) mice, though its underlying mechanisms remain unclear. This study investigates how SB promotes bone formation through Phospholipase D1 (PLD1) activation in OVX models. In vitro, bone marrow-derived mesenchymal stem cells (BMSCs) from OVX mice were cultured for osteogenic differentiation. The effects of SB, PLD1 inhibitor VU0359595, SIRT1 inhibitor EX527, and γ-secretase inhibitor LY-411575 were examined. In vivo, the impact of SB and LY-411575 on osteoporosis in OVX mice was evaluated. SB significantly increased PLD1 phosphorylation, enhancing osteogenic differentiation and SIRT1 activity. Blocking PLD1 with VU0359595 reversed these effects. Inhibiting SIRT1 with EX527 restored γ-secretase activity and Notch1 signaling but did not alter PLD1 activation. Notch1 overexpression weakened SB's promotion of osteogenesis and activation of the Wnt/β-catenin pathway. In vivo, SB combined with LY-411575 showed stronger anti-bone loss effects compared to SB alone. These findings suggest that SB may directly activates PLD1, which enhances SIRT1 activity and suppresses Notch1 signaling overactivation via γ-secretase inhibition. This cascade promotes bone formation by upregulating Wnt/β-catenin signaling. Combining SB with LY-411575 may offer a novel therapeutic strategy for postmenopausal osteoporosis.