Estradiol rapidly inhibits osteoclastogenesis and RANKL expression in bone marrow cultures in postmenopausal women: a pilot study

Summary We examined RANKL expression and OCL formation in cultured bone marrow cells from eight postmenopausal women in response to E₂. E₂ treatment inhibited the ability of hematopoietic cells to form OCLs in response to RANKL, and decreased RANKL production. These changes are likely involved in the ability of E₂ to influence the development of osteoporosis. Introduction Estrogen (E₂) deficiency at menopause increases osteoclast (OCL) formation and bone resorption, predisposing women to osteoporosis. We examined receptor activator of NF-kappa B-ligand (RANKL) expression and in vitro OCL formation in cultured bone marrow cells from eight postmenopausal women before and after 3 weeks of E₂ therapy and three untreated premenopausal women. Methods TRAP staining and resorption pit assay determined OCL number and function. Flow cytometry measured the distribution of marrow cell types and expression of RANKL in the macrophage-enriched fraction (R1) and a lymphocyte-enriched fraction (R2). Results RANKL (3–100 ng/ml) produced a dose-dependent increase in in vitro OC formation and E₂ therapy significantly (p < 0.01) inhibited OCL formation by 33 to 50%. A small proportion of marrow cells bound anti- RANKL Ab (0.2–4.3%). There was no effect of E₂ on the percentage of cells binding the anti-RANKL Ab in the R1 fraction. In the R2 fraction E₂ treatment decreased the percentage of cells binding anti-RANKL Ab by 68 ± 9% (p < 0.01). Conclusion Three weeks of E₂ treatment had a dual action. It inhibited the ability of hematopoietic cells to form OCLs in response to RANKL, and decreased the production of RANKL in cells of the bone marrow. The observed changes in the osteoclastic potential of bone marrow cells are likely involved in the ability of E₂ to regulate bone mass and influence the development of osteoporosis. *Taxel and Kaneko both shared equally in this work. Supported by grants from the NOF, NIA (R03) and GCRC #M01RR06192.