Expression and localization of estrogen receptor-β in murine and human bone

Estrogens have profound effects on bone metabolism. Cellular responses to estrogens are mediated by estrogen receptors (ERs) which belong to the nuclear receptor superfamily. Two estrogen receptors, ER alpha and ER beta, have been cloned. Previously expression of ER alpha has been shown in osteoblasts. Here we demonstrate that the transcript for ER beta can be detected in the human osteosarcoma cell lines (MG-63 and SaOS-2) and in cultured human osteoblast-like cells. We also show that ER beta protein is present in nuclear extracts from these cells. Furthermore, ER beta immunoreactivity is found in sections of murine and human bone. Murine and human osteoblast and osteocyte nuclei are immunoreactive for ER beta. Osteoclasts are also ER beta immunoreactive but the staining is mainly cytoplasmic. The present study demonstrates that ER beta is present in all the cellular compartments involved in bone formation and bone resorption, both in human and in murine bone tissue.