Sarsasapogenin stimulates angiogenesis and osteogenesis coupling to treat estrogen deficiency-induced osteoporosis by activating the GPX4/SLIT3/ROBO1 axis.

BACKGROUND: Promoting the coupling of osteogenesis and angiogenesis is a crucial strategy for the treatment of postmenopausal osteoporosis (PMOP). Estrogen deficiency induces ferroptosis, which is closely associated with the pathophysiology of PMOP. Sarsasapogenin (SAR) is a natural sapogenin with anti-oxidative effects. However, it is unclear whether SAR has a protective role against the impaired osteogenesis and angiogenesis coupling in PMOP. In this study, we evaluated the efficacy of SAR in estrogen deficiency-induced osteoporosis and explored the underlying mechanisms.

METHODS: Bone marrow mesenchymal stem cells (BMSCs) and human umbilical vein endothelial cells (HUVECs) were utilized to assess the in vitro effects of SAR on the coupling of osteogenesis and angiogenesis. In vivo experiments involved bilateral ovariectomy (OVX)-induced osteoporosis in mice and glutathione peroxidase 4 (GPX4)-knockout (KO) mice. Mice were orally administered SAR (5 or 10 mg/kg/d) for a duration of 12 weeks. The direct target of SAR was investigated through molecular docking, a cellular thermal shift assay, and surface plasmon resonance. Additionally, RNA sequencing was employed to elucidate the underlying mechanisms.

RESULTS: SAR treatment improved cell viability and osteogenic differentiation while inhibiting ferroptosis in iron dextran-induced BMSCs. Furthermore, SAR enhanced the production of slit guidance ligand 3 (SLIT3) in these cells, which stimulated angiogenesis by activating its receptor, roundabout human homolog 1 (ROBO1), in HUVECs. An in vitro model of ferroptosis induced by erastin demonstrated that SAR promoted the coupling of osteogenesis and angiogenesis by upregulating the BMSCs-SLIT3/HUVECs-ROBO1 axis. Activation of GPX4 was identified as a contributing factor to the effects of SAR on this coupling. Transfection of GPX4 small interfering RNA (siRNA) in BMSCs negated the impact of SAR on the BMSCs-SLIT3/HUVECs-ROBO1 axis. Additionally, SAR was found to directly interact with GPX4, enhancing protein stability, with an equilibrium dissociation constant of 44.6 μM. Notably, SAR did not increase SLIT3, ROBO1, or indicators of osteogenesis or angiogenesis in GPX4-KO mice.

CONCLUSIONS: These findings underscore the significance of restoring the GPX4/SLIT3/ROBO1 axis in promoting the coupling of angiogenesis and osteogenesis. SAR mitigates PMOP, in part, by activating the BMSCs-SLIT3/HUVECs-ROBO1 axis, with GPX4 serving as an upstream signaling modulator responsible for SLIT3 production. Our observations provide experimental evidence supporting the clinical application of SAR in the treatment of PMOP.