Enhanced osteoblast proliferation and collagen gene expression by estradiol.
Estrogens play a crucial role in the development of postmenopausal osteoporosis. However, the mechanism by which estrogens exert their effects on bone is unknown. To examine possible direct effects of 17 beta-estradiol on bone-forming cells, we used pure rat osteoblast-like cells in vitro as a model. Osteoblast-like cells prepared from calvaria of newborn rats were cultured serum-free in methylcellulose-containing medium for 21 days. Osteoblast-like cells proliferate selectively into clonally derived cell clusters of spherical morphology. 17 beta-Estradiol at concentrations of 0.1 nM and 1 nM enhanced osteoblast-like cell proliferation by 41% and 68% above vehicle-treated controls. The biologically inactive stereoisomer 17 alpha-estradiol (same concentrations) had no effect. Moreover, the antiestrogen tamoxifen abolished the stimulation of osteoblast-like cell proliferation by 17 beta-estradiol. After 21 days of culture, RNA was prepared and analyzed in a dot-hybridization assay for the abundance of pro alpha 1(I) collagen mRNA. Steady-state mRNA levels were increased in cultures treated with 17 beta-estradiol in a dose-dependent manner with maximal stimulation at 1 nM and 10 nM. At the same concentrations, the percentage of synthesized protein (labeled by [3H]proline pulse) that was digestible by collagenase was increased, indicating that 17 beta-estradiol acts at pretranslational levels to enhance synthesis of bone collagen. These data show that the osteoblast is a direct target for 17 beta-estradiol.
Ernst
M
M
Department of Medicine, University Hospital of Zurich, Switzerland.
Schmid
C
C
Froesch
E R
ER
D000818:Animals; D000831:Animals, Newborn; D002455:Cell Division / Q000187:drug effects; D003094:Collagen / Q000096:biosynthesis* / Q000235:genetics; D004958:Estradiol / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects*; D010637:Phenolsulfonphthalein / Q000494:pharmacology; D051381:Rats; D013629:Tamoxifen / Q000494:pharmacology
D013629:Tamoxifen; D004958:Estradiol; D003094:Collagen; D010637:Phenolsulfonphthalein