Temporal expression of estrogen receptor alpha in rat bone marrow mesenchymal stem cells

Estrogen responsiveness of bone formation is mediated by the estrogen receptor alpha (ERα) in osteoblastic lineage. As osteoblasts arise from the multipotent bone marrow stromal (mesenchymal) cells, this study was undertaken to observe the ERα in primary female adult rat bone marrow mesenchymal stem cells (BMSCs). The ERα was localized using immunocytochemical analysis in identified primary BMSCs. Then, using real-time PCR analysis, we measured the expression of ERα messenger RNA (mRNA) in BMSCs. ERα transcripts showed different trends between untreated cultures (control group) and osteogenic-induced cultures (treated group). In the control group, ERα mRNA climbed at peak levels at a confluence stage and decreased until day 20, whereas, in the treated group, the ERα mRNA kept climbing from a low level until day 20. Thus, the observed developmental expression of ERα mRNA correlates with progressive BMSCs growth and osteogenic differentiation and BMSCs may be a primary target cell for estrogen in maintaining bone formation.