Estrogen receptors alpha and beta are differentially expressed in developing human bone

Estrogen plays an essential role in the development and maintenance of the skeleton; its effects are mediated via interactions with two estrogen recep tor (ER) subtypes, alpha and beta. The aim of this study was to establish t he cellular distribution of ER alpha and ER beta in neonatal human rib bone . ER alpha and ER beta immunoreactivity was seen in proliferative and prehy pertrophic chondrocytes in the growth plate, with lower levels of expressio n in the late hypertrophic zone. Different patterns of expression of the tw o ERs were seen in bone. In cortical bone, intense staining for ER alpha wa s observed in osteoblasts and osteocytes adjacent to the periosteal-forming surface and in osteoclasts on the opposing resorbing surface. In cancellou s bone, ER beta was strongly expressed in both osteoblasts and osteocytes, whereas only low expression of ER alpha was seen in these areas. Nuclear an d cytoplasmic staining for ER beta was apparent in osteoclasts. These obser vations demonstrate distinct patterns of expression for the two ER subtypes in developing human bone and indicate functions in both the growth plate a nd mineralized bone. In the latter, ER alpha is predominantly expressed in cortical bone, whereas ER beta shows higher levels of expression in cancell ous bone.