Daidzein promotes milk synthesis and proliferation of mammary epithelial cells via the estrogen receptor α-dependent NFκB1 activation

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 mu M). Daidzein dose-dependently promoted alpha- and beta-casein and lipid synthesis, cell cycle transition, and cell amount, with the best stimulatory effect at 20 mu M. Daidzein also stimulated mTOR activation and Cyclin D1 and SREBP-1c expression. Daidzein induced the expression and nuclear localization of estrogen receptor alpha (ER alpha), and ER alpha knockdown blocked the stimulation of daidzein on these above signaling pathways. ER alpha knockdown also abolished the stimulation of daidzein on NF kappa B1 expression and phosphorylation, and NF kappa B1 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 ER alpha-dependent NF kappa B1 activation.