Effects of retinoic acid on the synthesis of selenoprotein and the antioxidative indices of bovine mammary epithelial cells in vitro

The present study was conducted to examine the effects of retinoic acid (RA) on the synthesis of selenoprotein and the antioxidative indices of bovine mammary epithelial cells (BMEC) in vitro and to explore the antioxidative mechanisms of RA in the BMEC. The subconfluenced BMEC were divided into six treatments with six replicates per treatment and cultured in a Dulbecco’s Modified Eagle’s Medium/F12 media (10% fetal bovine serum, 5 μg/ml ovine prolactin, 10 ng/ml epidermal growth factor, 1 g/ml hydrocortisone, 0.5% insulin-transferrin-selenium) containing different levels of RA (0 (control), 0.05, 0.1, 0.2, 1 or 2 mg/ml) for 24 h. Addition of RA promoted the proliferation of BMEC, increased the activities of catalase, superoxide dismutase, total antioxidant capacity, glutathione peroxidase (GPX), thioredoxin reductase (TRXR), and the content of selenoprotein P (SELP) in a dose-dependent manner (P < 0.05). The optimal RA dose was 1 μg/ml. However, positive effect of RA tended to be suppressed when RA was increased to 2 μg/ml. The expressions of mRNA and protein of GPX in BMEC were up-regulated by RA in a quadratic dose-response relationship (P < 0.01), and the addition of 1 μg/ml RA showed the best effect. The mRNA expressions of TRXR1 and SELP as well as the protein expression of TRXR1 were higher at 1–2 μg/ml RA. These results suggested that RA promoted antioxidant function of BMEC by regulating the synthesis of selenoprotein including GPX, TRXR, and SELP in vitro.