Neuro-skeletal crosstalk: brain-derived 5-HT mediates the bone-protective effects of β-Sitosterol against postmenopausal osteoporosis

Background: Postmenopausal osteoporosis (PMOP) is frequently accompanied by depression, and the underlying neuro-skeletal crosstalk remains unclear. Serotonin and sympathetic nervous system (SNS) activity are implicated in both mood and bone regulation. Objective: To investigate whether β-sitosterol (βS) alleviates PMOP-associated depression and bone loss through modulation of central 5-hydroxytryptamine (5-HT) synthesis and SNS activity. Design: An integration of in vivo and in vitro studies using mouse models and cellular assays. Methods: Ovariectomized (OVX) and 5-HT-deficient mice were treated with βS. Behavioral assessments, micro-CT, immunohistochemistry, enzyme-linked immunosorbent assays (ELISA), Western blotting (WB), and molecular docking were employed to evaluate antidepressant effects, bone parameters, and related signaling pathways. In vitro, βS effects on 5-HT production and osteogenesis were assessed in PC12 cells and BMSCs. Results: βS enhanced brain 5-HT synthesis by activating the SIRT1/NRF2/TPH2 pathway and suppressing MAO-A. It alleviated depressive-like behaviors, reduced SNS activity, and prevented bone loss in both OVX and 5-HT-deficient mice. In vitro, βS increased 5-HT secretion in PC12 cells and promoted osteogenic differentiation in BMSCs via conditioned media. Conclusion: βS restores neuro-skeletal homeostasis by boosting 5-HT-mediated suppression of SNS activity, thereby improving mood and bone health. These findings identify βS as a promising candidate for treating comorbid PMOP and depression. Our study provides the first evidence linking phytosterol therapy to neuro-skeletal regulation in bone loss.