[Mechanisms of electroacupuncture underlying treatment of osteoporosis based on HDAC2-mediated osteoblast differentiation pathway].

Objective: To observe the effect of electroacupuncture (EA) on expression of histone deacetylase 2 (HDAC2), histone H3, bone formation related genes and proteins in osteoporosis rats, so as to reveal its mechanisms underlying improvement of osteoporosis.

Methods: Female SD rats were randomly divided into 4 groups: sham operation, model, EA and medication (＝ 10 rats in each group). The osteoporosis model was established by castration. EA (2 Hz, 1 mA) was applied to bilateral "Shenshu" (BL23) and "Pishu" (BL20) for 10 min, once every other day for 8 weeks. Rats of the medication group received subcutaneous injection of 17 β-estradiol (100 µg/kg, 20 µg/mL). The bone quality and quantity including the cortical bone mineral density (CBMD), trabecular bone mineral density (TBMD), ratio of bone volume /total volume (BV /TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), trabecular separation (Tb. Sp), trabecular bone pattern factor (Tb.Pf), and structure model index (SMI) of the right thigh-bone were detected by using a micro-computed tomography. Serum alkaline phosphatase (ALP) and estrogen 2 (E2) contents were assayed by using colorimetry and ELISA, expression levels of HDAC2, histone H3 and Runx2 in the thigh-bone were detected using Western blot, and that of Runx2 mRNA was detected using quantitative real-time PCR, separately. The co-expression of Ac-histone H3/Runx2 and Runx2/ALP was observed by using immunofluorescence histochemical staining.

Results: After modeling, the levels of TBMD, BV/TV, Tb.Th, and Tb.N, serum E2 and ALP, and expression of Runx2 protein and mRNA, Ac-histone and ALP proteins were significantly lower (<0.01), and those of Tb.Sp, Tb.Pf and SMI, HDAC2 and histone H3 proteins were significantly higher (<0.01) in the model group than those in the sham operation group. After the interventions, the decrease of TBMD, BV/TV, Tb.N，Runx2 protein and mRNA，ALP in both EA and medication groups, serum E2 in the medication group, and Ac-histone H3 in the EA group, and the increase of Tb.Sp in the medication group, Tb.Pf, SMI, and HDAC2 in both EA and medication groups, and histone H3 in the EA group were reversed (<0.01, <0.05). No significant changes were found in the levels of CBMD after modeling relevant to the sham operation group, and after EA and medication interventions (>0.05). The effects of EA were significantly superior to 17 β-estradiol in down-regulating the expression of HDAC2 and histone H3 proteins and in up-regulating expression of Ac-histone H3 protein (<0.01，<0.05)．.

Conclusion: EA treatment can increase bone density, increase bone mass and trabecular bone, and promote trabecular bone rod-like changes in plate shape in osteoporosis rats, which is related to its effect in up-regulating the expression of Ac-histone H3 protein, and down-regulating the expression of bone formation-related proteins.