Objective: To observe the effect of electroacupuncture (EA) on histopathological changes of cartilage and subchondral bone and osteoprotegerin (OPG)，receptor activator of nuclear factor-κB (RANK), and RANK ligand (RANKL) (OPG/RANK/RANKL) signaling and the expression of matrix metalloproteinase-13 (MMP-13) in ovariectomized(OVX)rats, so as to explore its mechanism underlying improvement of osteoporosis.
Methods: Three-month female SD rats were randomly divided into sham operation, model and EA groups (n＝8 in each group). The ovoariectomy model was established by resection of bilateral ovaries. Rats of the sham group were treated by simple removal of a piece of adipose tissue around the bilateral ovaries. EA (3 Hz/15 Hz, 1 mA) was applied to bilateral "Sanyinjiao" (SP 6), "Yanglingquan" (GB 34), "Yinlingquan" (SP 9) and "Zusanli" (ST 36) for 30 min, once daily (except the weekends) for 12 weeks. The histopathological changes of the subchondral bone of the right knee-joint were observed after Saffron O dyeing and evaluated by Mankin's score, and its anatomical structure including the bone volume fraction (bone volume/tissue volume, BV/TV), trabecular bone number (Tb. N) and trabecular thickness (Tb.Th), trabecular separation (Tb.Sp) was observed by using Micro CT imaging. The urine C-terminal cross-linking telopeptide of type Ⅰ collagen (CTX-Ⅰ), CTX-Ⅱ (two bone resorption markers) and serum estrogen (E 2) contents were assayed by ELISA, and the expression levels of OPG, RANKL and MMP-13 mRNAs in the cartilage tissue of the left knee-joint were detected by quantitative RT-PCR.
Results: Following modeling, the BV/TV, Tb. N and Tb.Th levels were significantly decreased (P<0.01) and Tb.Sp and Mankin's score obviously increased in the model group compared with the sham group (P<0.01), suggesting a formation of osteoporosis and degeneration of the cartilage tissue. The serum E 2 content and OPG mRNA level in the cartilagetissue were significantly down-regulated (P<0.01), and urine CTX-Ⅰ and CTX-Ⅱ contents and RANKL mRNA and MMP-13 mRNA expression levels cartilagetissue were considerably up-regulated in the model group relevant to the sham group (P<0.01). After EA intervention, modeling-induced decrease of BV/TV, Tb.N, Tb.Th, E 2 and OPG mRNA levels and OVX-induced increase of Tb.Sp, Mankin's score, CTX-Ⅰ， CTX-Ⅱ， RANKL mRNA and MMP-13 mRNA levels were all completely reversed in the EA group relevant to the model group (P<0.01，P<0.05)．.
Conclusion: EA intervention can inhibit subchondral bone osteoporosis and articular cartilage degeneration of knee-joint in OVX rats, which is closely associated with its effects in inhibiting the down-regulation of serum E 2 and OPG mRNA expression and up-regulation of CTX-Ⅰ， CTX-Ⅱ， RANKL mRNA and MMP-13 mRNA levels, including adjusting OPG/RANK/RANKL signaling.
Keywords: Bone resorption markers; Cartilage degeneration; Electroacupuncture; Knee-joint; OPG/RANK/RANKL signaling; Osteoarthritis; Subchondral bone.