Estradiol enhances apoptosis in bovine mammary epithelial cells in vitro

Previous studies conducted on mid- or late-lactation dairy cows showed that the administration of exogenous estradiol induced a severe decrease in milk yield and accelerated mammary gland involution. However, the effects of estradiol on mammary epithelial cells remained unknown. The aims of this study were to investigate the in vitro effects of estradiol (i) on a bovine mammary epithelial cell line (Mac-T) and (ii) on apoptose-induced bovine mammary epithelial cells. In the first part of this study, the Mac-T cells were treated with increasing doses of estradiol (10−6, 10−5, 10−4, and 10−3 M), during increasing times (6h, 12h, 24h and 48h). It appeared that the higher treatment doses of estradiol (10−4 and 10−3M) reduced the cell proliferation by 8 and 19% respectively at 24h and by 5 and 10% respectively at 48h, and induced apoptosis of the mammary epithelial cells. In the second part of this study, the Mac-T cells were either treated with estradiol (E2, 10−4M) or with camptothecin (Ct, 10 μM) to induce apoptosis or with camptothecin combine with estradiol (Ct+ E2), during increasing times (2h, 6h, 24h and 48h). After 6h of treatment, we observed an increase in apoptotic markers (Caspase 3 activity and Annexin V-positive cell rate) in both Ct and Ct+ E2 treatment batches. This increase was more important in the Ct+ E2 treatment batch at 6h (+ 61.5%) and 24h (+ 9.8%) compared with the Ct treatment batch. Taken together, these results suggest that estradiol reduces mammary epithelial cells expansion and enhances apoptosis pathways in vitro.