Effects Of Vitamin A And Acetic Acid On Gene Expression Related To Milk Fat And Protein Synthesis In Bovine Mammary Epithelial Cells

The experiment was conducted to investigate the effects of V_A on gene expression related to milk fat and protein synthesis in bovine mammary epithelial cells(BMECs),and to observe if V_A have a interaction effect with acetic acid in milk components synthesis under the supplement of milk fat precursor.Furthermore,the study was looking forward to dscussing the mechanism of V_A influencing milk fat and protein synthesis,and providing a basis for the addition of proper V_A in diets and improvement of milk fat and protein synthesis of dairy cows.Experiment 1 was designed as a single factor randomized trial,and cells were randomly divided into 6 groups with 6 repeats each group,the control group was cultured in RA-free medium,meanwhile treatment group were added 0.05,0.1,0.2,1.0,2.0 ?g/mL RA respectively based on control medium for 24 h.At the end of the experiment the cells were harvested for detection of related parameters.The results showed that 1,2 ?g/mL V_A significantly enhanced cell vitality and intracellular triacylglycerols(TG)content;V_A up-regulated mRNA expression of peroxisome proliferator-activated receptor y(PPARG),sterol regulatory element-binding protein(SREBP1),stearoyl-CoA desaturase(SCD),as well as promoted mRNA expression of signal transducers and activators of transcription(STAT5),a-casein(CSNIS1)and ?-casein(CSN3)involved in milk protein synthesis.Experiment 2 was designed as two factors randomized trial,cells were randomly divided into 6 groups with 6 repeats each group,the control group was cultured in RA-free medium,meanwhile treatment group were added 0 V_A+6 acetic acid,0 V_A?10 acetic acid,1 V_A+0 acetic acid,1 V_A+6 acetic acid,I V_A+10 acetic acid(?g/mL+mmol/L)respectively based on control medium for 24h.At the end of the experiment the cells were harvested for detection of related parameters.Results indicated that acetic acid and V_A had the interaction effects on milk fat synthesis,and acetic acid up-regulated TG content,however acetic acid inhibited TG synthesis when added with V_A together;acetic acid up-regulated acetyl-coenzymeA carboxylase(ACACA),fatty acid synthase(FASN)enzymatic activity and PPARG mRNA expression in BMECs,but acetic acid inhibited those enzymatic activity and mRNA expression when added with V_A.The results also suggested that acetic acid could enhance CSN3 mRNA expression and mammalian target of rapamycin(mTOR)content,p70 ribosomal protein S6 kinase(S6K1)activity in BMECs;and acetic acid and V_A had the interaction effects on relieving the down-regulation of mTOR and?-casein(CSN2)gene expression which induced by adding V_A or acetic acid alone.Overall consideration,the effects of ehancing milk fat synthesis was preferable at 0 V_A+10 acetic acid group,but inferior at 1 V_A+10 acetic acid;the effects on promoting milk protein synthesis was preferable at 0 V_AA+6 acetic acid group,but inferior at 1 V_A+6 acetic acid group.