Ershiwuwei Guijiu Pill Activates PI3K/Akt/mTOR-mediated Autophagy to Alleviate Osteoporosis in Ovariectomized Rats

Abstract:

Objective To investigate the mechanism of Ershiwuwei Guijiu pill in preventing and treating postmenopausal osteoporosis （PMOP） by activating the phosphatidylinositol 3-kinase （PI3K）/protein kinase B （Akt）/mammalian target of rapamycin （mTOR） signaling pathway and inhibiting excessive autophagy.Method Female SD rats were ovariectomized and randomly divided into the sham operation group （Sham）， the operation group （OVX）， the Ershiwuwei Guijiu pill （GJ） group， and the raloxifene hydrochloride （RLX） group， with 10 rats in each group. Enzyme-linked immunosorbent assay （ELISA） and colorimetric methods were used to detect the levels of estrogen， bone metabolism markers in serum， and total superoxide dismutase （T-SOD）， malondialdehyde （MDA）， and glutathione peroxidase （GSH-Px） in tibial tissue. Flow cytometry was used to detect reactive oxygen species （ROS） levels in bone marrow mesenchymal stem cells. Masson staining was used to observe pathological changes in the proximal tibia， and micro-computed tomography （Micro-CT） was used to observe changes in tibial microstructural parameters. Real-time fluorescence quantitative polymerase chain reaction （Real-time PCR） and Western blot were used to detect the expression of autophagy-related proteins Beclin1， microtubule-associated protein 1A/1B-light chain 3 （LC3）， autophagy-related 5 （Atg5）， as well as PI3K， Akt， and mTOR in tibial tissue.Result Compared with the Sham group， the OVX group showed a significant decrease in serum levels of estradiol （E₂） and calcium ion （Ca²⁺）， and T-SOD， GSH-Px， PI3K， Akt， and mTOR mRNA levels in bone tissue （P<0.05， P<0.01）， significantly reduced bone mineral density （BMD）， bone surface/bone volume （BS/BV）， trabecular thickness （Tb.Th）， trabecular number （Tb.N）， and trabecular connectivity （Con） in the tibia （P<0.05， P<0.01）， thinner epiphyseal growth plate， and the bone marrow cavity filled with fat vacuoles. Moreover， the levels of phosphorus （P）， MDA， ROS， and mRNA and protein expression of Beclin1， LC3， and Atg5， as well as trabecular separation （Tb.Sp） were significantly elevated （P<0.05， P<0.01）. Compared with the OVX group， the GJ and RLX groups showed significant increases in serum E₂ and Ca²⁺， and bone tissue levels of SOD， GSH-Px， and the mRNA levels of PI3K， Akt， and mTOR （P<0.05， P<0.01）， significantly increased BMD， BS/BV， Tb.Th， Tb.N， and Con in the tibia， thickened epiphyseal growth plate， and significantly reduced fat vacuoles in the bone marrow cavity （P<0.05， P<0.01）. Additionally， the levels of P， MDA， ROS， Beclin1， LC3， Atg5 mRNA and proteins， and Tb.Sp were significantly decreased （P<0.05， P<0.01）. The ratios of p-PI3K/PI3K， p-Akt/Akt， and p-mTOR/mTOR， which were significantly reduced in the OVX group （P<0.01）， were significantly increased in the GJ and RLX groups （P<0.01）.Conclusion The Ershiwuwei Guijiu pill reduces oxidative stress and inhibits autophagy， thereby preventing and treating postmenopausal osteoporosis. Its mechanism may be related to the activation of the PI3K/Akt/mTOR signaling pathway， which inhibits autophagy.