Electroacupuncture at the governor vessel and bladder meridian acupoints improves postmenopausal osteoporosis through osteoprotegerin/RANKL/RANK and Wnt/β-catenin signaling pathways

摘要

Previous studies have demonstrated that pretreatment with electroacupuncture (EA) at the zusanli/ST36 and sanyinjiao/SP6 acupoints prevents ovariectomy-induced osteoporosis in rats; however, the therapeutic effects of EA at the governor vessel (GV) and bladder meridian (BL) acupoints remain unclear. In the present study, the effects of EA at the GV4, GV6, BL20 and BL23 acupoints on the bones of ovariectomized (OVX) rats were investigated to identify the pathways that mediate the action of EA on the bones. A postmenopausal osteoporosis model was established by performing an ovariectomy in six-month-old female Sprague Dawley rats. Following the ovariectomy, EA treatment was administered once per day for 90 days, with an interval of 5 days per 10 days. The changes in the serum levels of estradiol (E2) and the bone turnover markers, osteocalcin (OC) and tartrate-resistant acid phosphatase 5b (TRACP 5b), were determined, while the bone mineral density (BMD) of the lumbar vertebra and the histomorphology of the femur were observed. Furthermore, the expression of osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL), which are involved in the OPG/RANKL pathway, were detected by ELISA. In addition, the protein expression levels of low-density lipoprotein receptor-related protein (LRP) 5, β-catenin and runt-related transcription factor (Runx) 2, which are involved in the Wnt/β-catenin signaling pathway, were detected by western blot analysis. The results revealed that the GV and BL EA treatment groups significantly increased the serum levels of E2 and OC, decreased the serum levels of TRACP 5b and increased the BMD of the lumbar vertebra when compared with the OVX group. With regard to the histomorphology of the bone tissue, an ordered arrangement and a slight thinning of the trabeculae, with no evident hairline fractures, was observed in the femurs following EA treatment in the OVX rats. Furthermore, histomorphological analysis revealed that EA treatment significantly increased the values of the bone histomorphometry indices, trabecular area percentage, trabecular thickness and trabecular number, and reduced the value of trabecular separation, as compared with the OVX group. In addition, the ratio of OPG/RANKL expression was significantly upregulated, and the expression levels of LRP5, β-catenin and Runx2 were significantly upregulated in the EA treatment groups. Therefore, these results demonstrated that long-term stimulation with EA treatment at the GV and BL acupoints was able to alleviate osteoporosis induced by an ovariectomy through regulating the OPG/RANKL and Wnt/β-catenin signaling pathways.