The Effect Of Estrogen On The Expression Of Matrix Metalloproteinases MRNA In Rabbit Osteoclasts

Objective: To observe the effect of estrogen on the expression of matrix metalloproteinases (MMPs) mRNA in rabbit osteoclasts. This study was designed to further investigate the therapeutic mechanism of estrogen on osteoporosis.Methods: Primary osteoclastic cells were obtained from the long bone of newborn New Zealand rabbit directly and cultivated in M-199 medium supplemented with 15% fetal bovine serum. Cells were incubated in absence or presence of various concentrations of estrogen(0M,10-5M,10-6M,10-7M,10-8M,10-9M,10-10M,10-11M,10-12M,10-13M), or treated with estrogen for different period according to the experimental design. Total cellular RNA was isolated with Trizol. Semiquantitative reverse transcription PCR method was used to determine the expression level of MMP-9 mRNA and MMP-8 mRNA.Results: Estrogen dose-dependently inhibited the activities of osteoclasts after 24h of treatment, especially when the concentrations of estrogen were 10-5mol/L,10-6 mol/L,10-7mol/L (P<0.05). Different concentrations of estrogen and different cultivate period showed their inhibitions on the number and area of osteoclastic bone-resorbing lacunas. Although the number and area of osteoclastic bone-resorbing lacunas increased everyday and to the extreme in the sixth day, estrogen inhibited their increase and reached its peak level at a concentration of 10-6 mol/L (P<0.05). To make clear the mechanism of estrogen inhibition on the osteoclastic bone absorption, treatment with estrogen at different concentrations downregulated the expression of MMP-9 mRNA level, especially when the concentrations of estrogen were 10-5mol/L,10-6 mol/L,10-7mol/L (P<0.05). There was no expression of MMP-8 mRNA in osteoclasts despite three repeated experiments.Conclusion: Estrogen inhibited the activities of osteoclasts time-dependently and concentration-dependently, decreasing the number and area of osteoclastic bone-absorbing lacunas. Different concentrations of estrogen reducing the expression of osteoclastic MMP-9 mRNA indicated part mechanism of the inhibitive effects of estrogen on the osteoclastic bone-absorpsion.