Estrogen inhibits RANKL-stimulated osteoclastic differentiation of human monocytes through estrogen and RANKL-regulated interaction of estrogen receptor-α with BCAR1 and Traf6

Abstract

The effects of estrogen on osteoclast survival and differentiation were studied using CD14-selected mononuclear osteoclast precursors from peripheral blood. Estradiol at ~1 nM reduced RANKLdependent osteoclast differentiation by 40-50%. Osteoclast differentiation was suppressed 14 days after addition of RANKL even when estradiol was withdrawn after 18 hours. In CD14+ cells apoptosis was rare and was not augmented by RANKL or by 17-β-estradiol. Estrogen receptor-α (ERα) expression was strongly down-regulated by RANKL, whether or not estradiol was present. Mature human osteoclasts thus cannot respond to estrogen via ERα. However, ERα was present in CD14+ osteoclast progenitors, and a scaffolding protein, BCAR1, which binds ERα in the presence of estrogen, was abundant. Immunoprecipitation showed rapid (~5 minute) estrogen-dependent formation of ERα-BCAR1 complexes, which were increased by RANKL co-treatment. The RANKLsignaling intermediate Traf6, which regulates NF-κB activity, precipitated with this complex. Reduction of NF-κB nuclear localization occurred within 30 minutes of RANKL stimulation, and estradiol inhibited the phosphorylation of IκB in response to RANKL. Inhibition by estradiol was abolished by siRNA knockdown of BCAR1. We conclude that estrogen directly, but only partially, curtails human osteoclast formation. This effect requires BCAR1 and involves a non-genomic interaction with ERα. KeywordsEstrogen receptor-α; Breast cancer antiestrogen resistance-1; p130Cas; Nuclear factor-κB; TNFreceptor associated factorsOsteoclasts are multinucleated bone-degrading cells that differentiate from monocytic precursors. They are critical to bone modeling and maintenance, and mediate the release of skeletal mineral for calcium and pH homeostasis. Consequently, osteoclast differentiation and activity are regulated by several systems. Because bone loss occurs when estrogen declines at the menopause, the modulation of osteoclast formation and activity by estrogen is an important issue. The mechanisms by which estrogen regulates bone turnover remain unclear [1]. *Corresponding author: Lisa J. Robinson, 707 Scaife Hall, University of Pittsburgh, Pittsburgh, PA 15261, Tel: +1 412 647-0365, Fax: +1 412 647-4008, robinsonlj@msx.upmc.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptUnresolved issues include whether estrogen causes apoptosis of osteoclasts or osteoclast precursors, and whether estrogen suppresses osteoclast formation directly or whether effects are mediated via oth...

Blocking FSH action attenuates osteoclastogenesis

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“…The products of these two sequential amplification procedures showed that the FSHR type 2 isoform was present in PMBCs, CD14+ cells, osteoclasts prepared from CD14 cells, and ovarian control (COV) cells. A weak band was seen in CD14-negative cells, the fall-through from magnetic bead isolation of CD14+ cells [15]. This might represent type 2 FSHR in other white blood cells, but some CD14+ cells might not be captured by the magnetic beads.…”

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Apolipoprotein A-1 regulates osteoblast and lipoblast precursor cells in mice

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Long bone phenotypic analyzes of a RANK transgenic mouse line

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