Effects Of Selenium On Gene Expression Related To Milk Fat And Protein Synthesis In Bovine Mammary Epithelial Cells

The objective of this study was to determine the effects of selenium on the antioxidative function,synthesis of milk fat and protein in bovine mammary epithelial cells(BMECs).Based on this,we used lipopolysaccharide(LPS)as the induced stress source to analysize the protective effect of selenium on LPS-induced oxidative damage and the influence on milk fat and milk protein synthesis of BMEC.Experiment 1 was conducted to study the effects of different concentrations of selenium(0,10,20,50,100,150,200 nmol/L)on BMEC activity,triglycerides(TAG)content,antioxidant enzyme activity,genes expressions related to milk fat and protein synthesis by using the completed random of single factor.The results showed that the concentration of selenium significantly improved cell proliferation,glutathione peroxidase(GPX)activity,superoxide dismutase(SOD)activity and total antioxidant capacity(T-AOC),and decreased the concentration of malondialdehyde(MDA)in a linear-dose-dependent patttern,and the addition of 50 to 100 nmol/L of selenium showed the best effect,but the addition of 150 to 200 nmol/L of selenium showed the progressive reductions.Selenium had no significant influence on TAG content,the enzyme activity of fatty acid synthase(FASN),stearyl coenzyme desaturation enzyme(SCD),A acetyl-coa carboxylase(ACACA),lipoprotein lipase(LPL),the target of rapamycin(mTOR)and p70 ribosomal protein S6 kinase 1(S6K1)in BMECs.Besides,selenium had no significant up-regulation effects on gene expression associated with milk fat such as ACACA,FASN,SCD,fatty acid binding protein 3(FABP3),LPL.peroxidase body growth activated receptor gamma(PPARG)and sterol adjusting element binding protein 1(SREBF1).Furthermore,there are no significant influence on alpha sl-casein gene(CSN1Sl1)kappa-casein(CSN3)predominate,mTOR and signal transduction and transcriptional activation factor 5(STAT5),eukaryotic translation initiation factor 4E binding protein 1(4E-BPI).eIF4E(eukaryotic initiation factor 4E),S6K1 and tyrosine kinase 2(JAK2)at different selenium concentration.In conclusion,selenium at 50-100nmol/L is better for antioxidant function,but had no effect on milk fat and milk protein synthesis in healthy BMECs.To further analysize the protective effect of selenium on the BMEC injured by LPS and the influence on milk fat and milk protein synthesis,the experiment 2 divided the BMEC into eight groups:control group(CON),LPS group(LSO)and six selenium pre-protect groups(LS10,LS20,LS50,LS100,LS150,LS200).The cells in CON group were cultured 30h in culture solution without selenium added and LPS damage.The cells in LSO group were cultured 24h in culture solution without selenium,and then added 1 μg/mL LPS to treat 6h.For selenium pre-protect groups,cells were cultured 24h in culture solution with 10,20,50,100 or 200nmol/L of selenium respectively,then added 1μg/mL LPS to treat 6h.The results showed that LPS can induce oxidative damage in BMEC and decrease cell activity and antioxidant function,and reduce the concentration of MDA,and increase activity of GPX,SOD,CAT and T-AOC.Selenium has protective effect on the oxidative damage of BMEC induced by LPS,and the protective effect is in linear-dose-dependent with selenium.LPS could lead to oxidative damage in BMEC,and reduced the gene expression of ACACA,FASN,SCD,LPL,FABP3,SREBP1 and PPARG,also it could decrease the enzyme activity of ACACA,FASN.SCD and LPL,and inhibit the synthesis of milk fat.Additionally.LPS damage down-regulated the gene expression of CSN1S1,(CSN3 associated with protein synthesis,reduced the gene expression of mTOR,STAT5,4E-BP1.eIF4E,S6K1 and JAK2 involved in mTOR and JAK/STAT signal pathway,also decreased the enzyme activity of mTOR and S6K1,and inhibited the synthesis of milk protein.Selenium relieved the inhibition due to LPS-induced oxidative damage effectively on the synthesis of milk fat and protein.and 50～200nmol/L selenium showed the best effect.In conclusion,selenium ameliorated the LPS-induced BMEC damage by improving levels of antioxidant markers and up-regulating milk fat and protein synthesis and the expression of the genes associated with milk fat and protein.