Regulation Of Parathyroid Hormone Gene Expression By Ovariectomy And Prophylactic Administration Of Estrogen In Rat

Parathyroid gland is one of the endocrine glands of the body.The main function of the parathyroid gland is to secrete parathyroid hormone?PTH?.Estrogen is a steroid hormone secreted by ovaries.The decrease of estrogen can cause disruption of calcium and phosphorus balance,which results in osteoporosis.PTH is the main determinant of bone turnover rate in the body.However,there is still a lack of evidence that estrogen could directly regulate PTH secretion and the regulation mechanism is unclear.In the present study,we established the rat model of postmenopausal osteoporosis?PMOP?by bilateral ovariectomy.We observed the histopathology of femur,tibia,uterus,duodenum,renal cortex and renal medulla by paraffin section and H&E staining.We measured the changes of estrogen in serum by enzyme-linked immunosorbent assay?ELISA?.After parathyroid was collected from SD rats,Real-time Quantitative Polymerase Chain Reaction?Real-time qPCR?was used to detect PTH mRNA,estrogen receptor?ER?,calcium sensing receptor?CaSR?,vitamin D receptor?VDR?,fibroblast growth factor-23?FGF-23?,FGF-23 receptor 1?fibroblast growth factor receptor 1,FGFR1?,Klotho and early growth response gene 1?Egr1?expression.The regulation role of ovariectomy and prophylactic administration of estrogen on PTH was investigated.The histomorphological observation of organs and bone showed that osteoporosis was found in the femur and tibia of the ovariectomized?OVX?group,showing trabecular cracked and space larger.The ?-estradiol-treated OVX?OVX/E2?group did not show significant change.Comparing with the sham-operated?Sham?group,there was no significant pathological lesion in the duodenum,renal cortex and renal medulla both in the OVX group and the OVX/E2 group.Comparing with the Sham group,the endometrium of the OVX group was significantly thicken and the uterine glands became larger and more in the lamina propria.Comparing with the OVX group,the uterine glands became smaller and more complete,the endometrial hyperplasia did not occur in the OVX/E2 group.These results indicated that injection of small doses of ?-estradiol could prevent the occurrence of osteoporosis,and there was no uterine cancer occurrence in the OVX/E2 group.The results of ELISA showed that there was no significant difference in serum estrogen among the three different treatment groups.Comparing with the Sham group,absorption photometry detection of serum Ca²⁺ was significantly higher in OVX/E2 group,and comparing with the OVX group,there was no significant difference in the Sham group and the OVX group.The results of Real-time qPCR showed that the expression of PTH was decreased in ovariectomized rats,and the prophylactic injection of ?-estradiol caused the increase of PTH expression.The ER-? expression was present in the parathyroid gland,and the expression of ER-? was increased after ovariectomy,the prophylactic injection of E2 caused the decrease of ER-? expression.These results indicated that ER-? in the parathyroid gland can respond to a slight change in estrogen,and participates in the regulation of PTH expression.After ovariectomy,the expression of VDR in the parathyroid was increased,and the expression of VDR in the parathyroid was decreased after prophylactic injection of ?-estradiol.This suggested that VDR might inhibit the expression of PTH.Comparing with Sham group,serum Ca²⁺ increases slightly and the expression of CaSR in parathyroid gland were significantly decreased in the OVX group.Comparing with the OVX group,serum Ca²⁺ was increased slightly and the expression of CaSR in parathyroid gland was significantly higher in the OVX/E2 group.This suggested that the Ca²⁺/CaSR regulatory system may be involved in the regulation of PTH expression.Comparing with the Sham group,the expression of FGF-23,FGFR1,Klotho and Egr1 in parathyroid gland were significantly decreased in the OVX group.Comparing with OVX group,the expression of FGF-23,Klotho and Egr1 in parathyroid gland were significantly decreased in OVX/E2 group.The expression of FGFR1 in the parathyroid was increased after prophylactic injection of ?-estradiol.It indicated that the inhibitory effect on PTH was decreased by FGFRs/Klotho receptor regulatory system of FGF-23 in the ovariectomy rats,but the regulating role was weaker by the prophylactic injection of ?-estradiol.These results suggested that ovariectomized and the prophylactic injection of ?-estradiol could affect ER-? expression,VDR signaling regulator,the Ca²⁺/CaSR regulatory system,and also the FGFRs/Klotho receptor regulatory system of FGF-23,which could finally affect the expression of PTH.