Effects and Mechanisms of Bone Polypeptide on Improving Osteoporosis in Ovariectomized Rats via Regulation of Autophagy and Apoptosis

Objective: To investigate whether bone polypeptide (GDT) exerts protective effects against osteoporosis in rats through autophagy and apoptosis pathways. Methods: A postmenopausal osteoporosis rat model (POMP) was established via ovariectomy. Rats were randomly divided into Sham-operated, model, diethylstilbestrol (25 μg/kg), and GDT low-, medium-, and high-dose groups (50, 100, 200 mg·kg⁻¹). Intragastric administration was performed for 90 days post-surgery. Bone mineral density (BMD) was measured using dual-energy X-ray absorptiometry. Bone biomechanical properties were evaluated via three-point bending tests. Bone microstructure was analyzed by morphometry. Serum bone metabolism markers were detected using enzyme-linked immunosorbent assay (ELISA). mRNA and protein expressions of autophagy-related genes (p62, Beclin-1, LC3-II) and apoptosis-related genes (Caspase-3, Caspase-9, Bax, Bcl-2) were determined by RT-qPCR and Western blot. Results: GDT significantly increased calcium, magnesium, phosphorus, and hydroxyproline contents in bone tissues (P<0.05 or P<0.01), elevated serum parathyroid hormone (PTH) and estradiol (E2) levels, reduced osteocalcin(BGP), alkaline phosphatase (ALP), tartrate resistant acid phosphatase (TRAP), and testosterone (T) levels, and improved bone metabolism. Bone trabecular number was increased, trabecular separation was decreased, and biomechanical properties and BMD were enhanced, with improved bone microstructure. Within the 50~200 mg·kg⁻¹ dose range, GDT activated the autophagy pathway and inhibited apoptosis. mRNA and protein expressions of p62 were down regulated, while Beclin-1 and LC3-II were upregulated. Expressions of Bax, Caspase-3, and Caspase-9 were reduced, whereas Bcl-2 was increased. Significant differences were observed in the high-dose group compared to the model group (P<0.05 or P<0.01). Conclusion: GDT ameliorates osteoporosis through dual regulatory mechanisms: Activating the autophagy pathway via the Beclin-1/LC3-II axis and inhibiting mitochondrial apoptosis via the Bcl-2/Bax-Caspase cascade. This study provides a novel strategy for targeted osteoporosis therapy.