Cellular distribution of estrogen receptor β in neonatal rat bone

Estrogens affect bone metabolism, and ovariectomy of rats results in marked bone loss caused by stimulation of osteoclastic bone resorption. Estrogen receptors (ER) have been demonstrated in osteoblasts and bone marrow stromal cells, but their presence in osteoclasts is controversial. Until recently, only one type of ER (now renamed ERα) had been identified. After the discovery of a novel ER subtype (ERβ), it became necessary to re-investigate the ER expression in human and rodent bone. In the present study we examined the expression of ER mRNA in neonatal rat bone. Expression of ER α and β mRNA (RT-PCR) was evident in femurs of 3-week-old male and female rats. In situ hybridization histochemistry of femural bones with digoxigenin labelled riboprobes, as well as radioactively labeled riboprobes, revealed that ERβ mRNA was predominantly expressed in osteoblasts covering the metaphyseal bone trabecular surface. The presence of ERβ mRNA in osteoblasts of rat bone suggests that ERβ is involved in the mechanism of action of estrogens in bone.