Estrogen stimulates osteoprotegerin expression via the suppression of miR-145 expression in MG-63 cells

Osteoprotegerin (OPG) is implicated in the pathogenesis of postmenopausal osteoporosis, and other metabolic bone diseases caused by estrogen deficiency. Previous studies have demonstrated that estrogen may stimulate OPG expression in osteoblast cells at the transcriptional level; however, whether estrogen can regulate OPG expression at a post-transcriptional level remains elusive. The present study aimed to investigate the role of microRNA (miRNA) in estrogen-mediated OPG production in human osteoblast-like MG-63 cells. The results from ELISA, western blotting and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) confirmed that estrogen may upregulate OPG expression. Mechanistic studies indicated that estrogen increased the activity of a luciferase reporter harboring the OPG 3′-untranslated region (3′-UTR). Bioinformatics analysis demonstrated that there is a potential targeting site in the OPG 3′-UTR for miRNA (miR)-145, which is associated with osteoblast differentiation. The results of an RT-qPCR suggested that estrogen suppressed miR-145 expression. In addition, dual-luciferase assay, RT-qPCR and western blot analysis indicated that miR-145 directly targets and negatively regulates OPG expression. Furthermore, transfection of cells with miR-145 mimics was able to partially inhibit the induction of OPG expression by estrogen, thus confirming the role of miR-145 in estrogen-mediated OPG induction. Taken together, the results of the present study demonstrated that estrogen may post-transcriptionally regulate OPG expression through suppression of miR-145 expression.