RESUMO
OBJECTIVE: To investigate the effect of estrogen on expression of matrix GLA protein (MGP) in ovariectomized Sprague-Dawley (SD) rats and the role of estrogen in improving postmenopausal osteoporosis. METHODS: Thirty-six SD female rats were allocated into 3 groups randomly, every 12 rats in ovariectomized group (OVX group), estrogen group (E group) and control group (sham group). Rats in OVX and E group all underwent bilateral ovariectomy, those rats in E group were given by estradiol benzoate intramuscularly after 3 weeks of ovariectomy. Rats in sham group underwent bilateral lipectomy near the ovary. All rats were kept the urine and the serum every three weeks and were sacrificed after 15 weeks. The pathology changes of uterus, lumbar vertebral bones were observed by immunohistochemistry. Bone mineral density (BMD) of lumbar vertebra of rats was determined by dual energy X ray absorptiometry (DEXA). The content of MGP in serum and urine was determined by ELISA. Expression of undercarboxylated matrix GLA Protein (MGP) was detected by immunohistochemistry. Relative quantification of MGP mRNA expression in lumbar vertebra bone was detected by Fluorescent real-time quantitative polymerase chain reaction. RESULTS: (1) After 15 weeks of ovariectomized, the endometrium of uterus and lumbar vertebra exhibit remarkable pathologic changes in OVX group. The serum estrogen of (454 ± 66) pmol/L in OVX group were lower than in (527 ± 77) pmol/L in sham group and (556 ± 80) pmol/L in E group significantly (P < 0.05). The BMD of lumbar vertebra of (0.263 ± 0.030) g/cm(2) in OVX group were lower than (0.295 ± 0.024) g/cm(2) in sham group and (0.279 ± 0.024) g/cm(2) in E group significantly (P < 0.01). (2) The serum MPG protein in OVX group and E group showed decreased trends after ovariectomized, which were (104 ± 64) ng/L in OVX group and (134 ± 6) ng/L in E group at 9 weeks, which reached statistical difference (P < 0.05). However, MGP in urine in sham group did not exhibit significant difference after 15 weeks of surgery (P > 0.05). The MGP in urine of E group showed increased trends after 12 weeks of surgery, which reached (110.0 ± 3.4) ng/L at 15 weeks, in the mean time, it was found that (86.5 ± 2.5) ng/L of MGP in urine in OVX group, which showed significant difference (P < 0.05). (3) MGP could be observed in lumbar vertebra in OVX group by immunochemistry staining. In the other two groups, the expression of MGP was not dominant. (4) Relative quantification of MGP mRNA expression in lumbar vertebra was defined as 1 in OVX group, when compared with 0.289 ± 0.260 in E group and 0.103 ± 0.098 in sham group, the difference showed statistically significant (P < 0.01). CONCLUSION: Estrogen could increase the expression of MGP mRNA and protein in ovariectomized rats and might play an important role in improving postmenopausal osteoporosis.