Effects Of Estrogen On The Expressions Of Autophagy-related Gene In Bone With Ovariectomized Rats

Objective:This study was to evaluate the effect of estrogen(E2) on bone metabolism and the expression of Atg5, Atg7, Ulk1 and p62 in tibia and to explore whether estrogen influences the bone mass by changing the level of autophagy. Method:Six-month-old female Sprague-Dawley rats(n=27) were randomly divided into the following groups: ovariectomy untreated group(OVX);sham-operated group(Sham);ovariectomy 17β-estradiol(0.1mg/kg·wk) treated group(E2). The rats in OVX and Sham groups were treated with normal saline of the same quantity. Select three rats randomly from each group to survey their bone mineral density by DEXA before and after the treatment; The left tibias of these rats were also used to make HE staining biopsy and then be scanned by optical microscope. The ratio between the mean trabecular area and marrow cavity were analyzed by Image-Pro Plus 6.0. The remaining 6 rats’ left tibias from each group were used to measure the levels of Atg5, Atg7, Ulk1 and p62 m RNA by quantitative real-time reverse transcription PCR(q RT-PCR). Results:1. The body weights of all the rats were not significantly different before the treatment(all P>0.05). By the end of the 24-week experiment, all of the rats had increased their body weights. The rats in OVX group tended to gain more weight than those in Sham and E2 group(P<0.01).The difference between Sham and E2 group was not statistically significant(P>0.05).2. Before the treatment, bone mineral density of each group was not significantly different(P>0.05). By the end of the 24-week experiment, Bone mineral density of OVX group was significantly decreased compared to the Sham and E2 group(P<0.05). Trabecular density in the Sham and the E2 group was more compact than in the OVX group. The Image-Pro Plus 6.0 showed that the ratio between the trabecular area and marrow cavity in Sham and the E2 group were significantly higher than the OVX(P<0.01).3. The consequence of RT-PCR indicates: OVX group caused a significant increase in Atg5, Ulk1 m RNA levels as compared with the Sham and E2 group( P<0.01); Its Atg7 m RNA level was also higher than the other two groups(P<0.05); Its p62 m RNA level was lower than Sham group(P<0.05), but had no difference with E2 group(P>0.05). The m RNA levels of Atg5, Atg7, Ulk1 and p62 caused no difference between the rats in Sham group and E2 group(P>0.05). Conclusion:1. The replication animal model of osteoporosis was successful.2. The autophagy level increased in ovariectomized rats. Treatment with estrogen reversed the increased autophagy level to recover bone mass.