Genistein induces oestrogen receptor-α gene expression in osteoblasts through the activation of mitogen- activated protein kinases/NF-κB/activator protein-1 and promotes cell mineralisation

Oestrogen and oestrogen receptors (ER) play critical roles in the maintenance of bone remodelling. Genistein, structurally similar to 17-oestradiol, is a phyto-oestrogen that may be beneficial for treating osteoporosis. In the present study, we evaluated the effects of genistein on the regulation of ER gene expression and osteoblast mineralisation using MC3T3-E1 cells and primary rat calvarial osteoblasts as our experimental models. Exposure of MC3T3-E1 cells and primary rat osteoblasts to genistein at 10m for 24h did not affect the cell morphology or viability. However, treatment of MC3T3-E1 cells with 10m-genistein enhanced the phosphorylation of extracellular signal-regulated kinase 1/2, p38 mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase 1/2 in a time-dependent manner. Sequentially, genistein increased the translocation of NF-B and c-Jun from the cytoplasm to the nucleus. Consequently, exposure of MC3T3-E1 cells to genistein induced ER mRNA expression in concentration- and time-dependent manners. In parallel, the amounts of cytosolic and nuclear ER in MC3T3-E1 cells were increased following genistein administration. Additionally, genistein also increased the levels of ER mRNA and nuclear ER protein in rat calvarial osteoblasts. A bioinformatic search revealed that there are several ER-specific DNA-binding elements in the 5-promoter regions of the bone morphogenetic protein-6, collagen type I and osteocalcin genes. As a result, genistein could induce the expressions of these osteoblast differentiation-related genes in primary rat osteoblasts. Co-treatment with genistein and traditional differentiation reagents synergistically increased osteoblast mineralisation. Therefore, the present study showed that genistein can induce ER gene expression via the activation of MAPK/NF-B/activator protein-1 and accordingly stimulates differentiation-related gene expressions and osteoblast mineralisation.