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Estrogens have been shown to be essential for maintaining a sufficiently high bone mineral density and ER alpha expression has been demonstrated in bone cells. Recently, a novel estrogen receptor, estrogen receptor beta (ERbeta) has been identified. Here we demonstrate that also ERbeta is expressed in human osteoblasts, and that ER alpha and ERbeta are differentially expressed during human osteoblast differentiation. ERbeta mRNA expression increased gradually during osteoblast culture, resulting in an average increase of 9.9+/-5.3 fold (mean+/-S.D., n=3) at day 21 (mineralization phase) as compared to day 6 (proliferation phase). In contrast, ER alpha mRNA expression levels increased only slightly until day 10 (2.3+/-1.7 fold) and then remained constant. The observed differential regulation of ER alpha and beta is suggestive for an additional functional role of ERbeta to ER alpha in bone metabolism.
Arts et al. (Sat,) studied this question.