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KMID : 1012320050080030159
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Nutritional Sciences
2005 Volume.8 No. 3 p.159 ~ p.168
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Yak-kong and Soybean Induced Expression of Osteoprotegerin in MG-63 Human Osteoblastic Cells Requires Estrogen Receptor- β
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Kim Jin-Young
Cho Yun-Hi
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Abstract
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Phytoestrogens, especially Yak-kong or soybean-derived isoflavones have been traditionally used as a supplement of estrogen for preventing postmemopausal osteoporosis in oriental folk medicine. In our previous study, the treatment of Yak-kong and soybean increased estrogen receptor-a (ERa) expression and proliferation of MG-63 osteoblastic cells. In contrast, the increase of estrogen receptor-β(ERβ) expression in proliferating MG-63 cells with Yak-kong and soybean treatment was less pronounced, which suggested that ERβ may play a role rather in the regulation of bone cell differentiation To determine the role of ERβ in Yak-kong or soybean mediated regulation of bone cell differentiation, we established MG-63 cell lines stably expressing either ERβ or antisense ERβ RNAs. Increased expression of ERβ did not affect ERa expression and proliferation of MG-63 cells. However, increased expression of ERβ in MG-63 cells (ERβ-MG63 cells) selectively enhanced Yak-kong or soybean induced expression of osteoprotegerin (OPG), a novel soluble glycoprotein which is secreted from osteoblasts and mediates the signal for osteoclast differentiation. Inhibition of ERβ expression by antisense ERβ RNAs (As-ERβ-MG63) caused these cells to insensitize Yak-kong or soybean induced expression of OPG but increased MG-63 cell proliferation. Furthermore, the comparable effects between Yak-kong and the combined treatment of genistein and daidzein at 0.5×10-8 M, which is a concentration of these two isoflavones similar to Yak-kong at 0.001 mg/mL, on OPG expression in ERβ -MG63 cell demonstrate that the enhanced expression of OPG with Yak-kong treatment is mediated by the synergistic effect of low leveled isoflavones in the extracts. Together, coupled with low level of ER expression in osteoclasts, our data demonstrate that ERβ in osteoblasts plays an important role in Yak-kong and soybean mediated inhibition of osteoclast differentiation indirectly by enhancing the expression of OPG.
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KEYWORD
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Osteoprotegerin, Yak-kong, Soybean, MG-63 cells
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