Isoflavones possess a wide range of physiological effects. However, it is still unclear whether isoflavones can promote milk synthesis in mammary gland. This study aimed to determine the effects of a main soy isoflavone, daidzein, on milk synthesis and proliferation of mammary epithelial cells (MECs) and reveal the underlying molecular mechanism. Primary bovine MECs were treated with different concentrations of daidzein (0, 5, 10, 20, 40, and 80 μM). Daidzein dose-dependently promoted α- and β-casein and lipid synthesis, cell cycle transition, and cell amount, with the best stimulatory effect at 20 μM. Daidzein also stimulated mTOR activation and Cyclin D1 and SREBP-1c expression. Daidzein induced the expression and nuclear localization of estrogen receptor α (ERα), and ERα knockdown blocked the stimulation of daidzein on these above signaling pathways. ERα knockdown also abolished the stimulation of daidzein on NFκB1 expression and phosphorylation, and NFκB1 was required for daidzein to enhance the mTOR, Cyclin D1 and SREBP-1c signaling pathways. In summary, our findings reveal that daidzein stimulates milk synthesis and proliferation of MECs via the ERα-dependent NFκB1 activation.

异黄酮具有广泛的生理作用。但是，尚不清楚异黄酮是否能促进乳腺中的牛奶合成。这项研究旨在确定大豆异黄酮的主要成分黄豆苷元对牛奶合成和乳腺上皮细胞（MEC）增殖的影响，并揭示其潜在的分子机制。用不同浓度的大豆黄酮（0、5、10、20、40和80μM）处理初生牛MEC。大豆苷元剂量依赖性地促进α-和β-酪蛋白和脂质合成，细胞周期转变和细胞数量，在20μM时具有最佳刺激作用。大豆苷元还刺激mTOR激活以及Cyclin D1和SREBP-1c表达。大豆苷元诱导雌激素受体α（ERα）的表达和核定位，ERα的敲低阻止了大豆苷元对上述信号通路的刺激。ERα抑制还取消了大豆苷元对NFκB1表达和磷酸化的刺激作用，并且大豆苷元需要NFκB1来增强mTOR，Cyclin D1和SREBP-1c信号通路。总之，我们的发现表明，大豆苷元通过依赖于ERα的NFκB1激活刺激牛奶的合成和MEC的增殖。