The role of estrogen receptors in the differentiation of osteoblast and bone regeneration

Two different types of estrogen receptors, usually referred to as estrogen receptor-α (ER-α) and estrogen receptor-β (ER-β), are widely expressed in different tissue types. However, the expression patterns vary among different tissues. Estrogen receptors are members of the steroid/thyroid hormone receptor superfamily of ligand-activated transcription factors, and ER-α and ER-β have been shown to be differentially activated by various ligands. It has been suggested that ER-α and ER-β are related to the function of the osteoblasts. Studies have shown that mice lacking estrogen receptors showed defects in bone formation. Other studies have also shown that the observed developmental expression of estrogen receptors' mRNA correlates with progressive osteoblast differentiation, and have suggested that estrogen receptors may play a role in the differential regulation of bone cell gene expression. In this paper, an extensive review of the role of estrogen receptors will be performed using in vitro and in vivo studies. The clinical implications of estrogen receptors will be also be discussed.