Phytoestrogens directly inhibit TNF-α-induced bone resorption in RAW264.7 cells by suppressing c-fos-induced NFATc1 expression.
TNF-α-induced osteoclastogenesis is central to post-menopausal and inflammatory bone loss, however, the effect of phytoestrogens on TNF-α-induced bone resorption has not been studied. The phytoestrogens genistein, daidzein, and coumestrol directly suppressed TNF-α-induced osteoclastogenesis and bone resorption. TRAP positive osteoclast formation and resorption area were significantly reduced by genistein (10(-7)  M), daidzein (10(-5)  M), and coumestrol (10(-7)  M), which was prevented by the estrogen antagonist ICI 182,780. TRAP expression in mature TNF-α-induced osteoclasts was also significantly reduced by these phytoestrogen concentrations. In addition, in the presence of ICI 182,780 genistein and coumestrol (10(-5) -10(-6)  M) augmented TNF-α-induced osteoclast formation and resorption. However, this effect was not observed in the absence of estrogen antagonist indicating that genistein's and coumestrol's ER-dependent anti-osteoclastic action normally negates this pro-osteoclastic effect. To determine the mechanism mediating the anti-osteoclastic action we examined the effect of genistein, coumestrol, and daidzein on caspase 3/7 activity, cell viability and expression of key genes regulating osteoclast differentiation and fusion. While anti-osteoclastic phytoestrogen concentrations had no effect on caspase 3/7 activity or cell viability they did significantly reduce TNF-α-induced c-fos and NFATc1 expression in an ER dependent manner and also inhibited NFATc1 nuclear translocation. Significant decreases in NFκB and DC-STAMP levels were also noted. Interestingly, constitutive c-fos expression prevented the anti-osteoclastic action of phytoestrogens on differentiation, resorption and NFATc1. This suggests that phytoestrogens suppress TNF-α-induced osteoclastogenesis via inhibition of c-fos-dependent NFATc1 expression. Our data provides further evidence that phytoestrogens have a potential role in the treatment of post-menopausal and inflammatory bone loss directly inhibiting TNF-α-induced resorption.
School of Biomedical and Biological Sciences, University of Plymouth, Plymouth, UK.
Sahar
S
Karieb
Simon W
SW
Fox
D000818:Animals; D001862:Bone Resorption / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D003375:Coumestrol / Q000494:pharmacology; D019833:Genistein / Q000494:pharmacology; D007529:Isoflavones / Q000494:pharmacology; D051379:Mice; D050778:NFATC Transcription Factors / Q000378:metabolism*; D048789:Phytoestrogens / Q000494:pharmacology*; D016133:Polymerase Chain Reaction; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D007529:Isoflavones; D050778:NFATC Transcription Factors; C494005:Nfatc1 protein, mouse; D048789:Phytoestrogens; D016760:Proto-Oncogene Proteins c-fos; D014409:Tumor Necrosis Factor-alpha; C004742:daidzein; D019833:Genistein; D003375:Coumestrol