Effects Of Estrogen On Apoptosis Of Mice Bone Marrow Mesenchymal Stem Cells(mBMMSCs) And Relevant Mechanism

Estrogen deficiency is an important cause in the pathogenesis ofpostmenopausal osteoporosis, followed by imbalance between bone resorbtionand bone formation and loss of bone mass. In orthodontics, changes of boneturnover always affect teeth movement. Estrogen can regulate bone remodelingin different ways, including affecting cells in bone directly and indirectly. Bonemarrow mesenchymal stem cells（BMMSCs） are pluripotent stem cells, and thequantity and differentiation of BMMSCs are key events to keep bone remoldingnormal. In patients with osteoporosis, the quantity and differentiation ofBMMSCs both change. It is reported that, estrogen could increase differentiationfrom BMMSCs to osteoblasts, and decrease differentiation from BMMSCs tolipoblasts. In conclusion, low estrogen level induces low bone density. But therelation between estrogen and apoptosis of BMMSCs is unknown. In this study, we isolate BMMSCs from both ovariectomied and sham-operated C57/BL miceand culture them in vitro, to determine their apoptosis. Besides, we also isolateBMMSCs from normal C57/BL mice, and culture them in differentconcentrations of estrogen, then to determine their apoptosis. Finally, we studythe relevant mechanism in preliminary. This study provides the basis for furtherstudies. This study could be divided as follows,1. Establish the ovariectomied mice model with osteoporosis and isolate,culture and identify the mBMMSCs.In order to determine the relation between estrogen and apoptosis ofBMMSCs, we have established the ovariectomied C57/BL mice model tosimulate postmenopausal osteoporosis. We have isolated, cultured, andidentified the cells we got from the bone marrow of mice. The result showedthat we get both the osteoporosis model and mBMMSCs successfully.2. The effects of estrogen on the apoptosis of mBMMSCs.In order to determine the relation between estrogen and apoptosis ofBMMSCs, we isolate BMMSCs from both ovariectomied and sham-operatedC57/BL mice and culture them in vitro. We also culture normal BMMSCs in themedium added three different estrogen concentrations respectively to furtherconfirm the relation between estrogen and apoptosis in BMMSCs, including0mol/L,10-9mol/L, and10-7mol/L. Their apoptosis are observed by FCM andCaspase3Activity Test. As a result, in the rank of the percentage of apoptosis,the percentage of apoptosis in ovariectomied group is higher than thesham-operated group, and the group of BMMSCs cultured in0mol/L estrogenhas the highest rate, followed by the group cultured in10-9mol/L estrogen, andthe group cultured in10^-7mol/L estrogen has the lowest rate of apoptosis. Inconclusion, BMMSCs from ovariectomied mice with low estrogen are more sensitive to apoptosis, and in vitro, the percentage of apoptosis reduced whilethe concentration of estrogen rose.3. Study the relevant mechanism in preliminaryEstrogen can play different roles with apoptosis in different cells.Researchers in our lab compared the microRNA expression level of BMMSCsbetween ovariectomied and sham-operated C57/BL mice. The result is there areseveral microRNAs aberrantly expressing in ovariectomied C57/BL mice. Wefocus on miR-21, which has the largest difference in quantity. In this study, weobserve the relation between estrogen and miR-21by qTR-PCR. As a result, theexpression of miR-21in ovariectomied group is lower than the sham-operatedgroup, and the expression of miR-21is up-regulated, while the concentration ofestrogen rose. To sum up, it suggests that estrogen may suppress apoptosis ofBMMSCs by up-regulating miR-21.