Effects of Lysine Dipeptides on the Expression of Genes Related to Milk Protein Synthesis and Amino Acid Transporters in Bovine Mammary Tissue

The study was carried out to investigate the effects of various lysine (Lys) dipeptides on gene expression related to milk protein and amino acid transporters in bovine mammary tissue.Mammary tissues were obtained from midlactating Holstein dairy cows and cultured under lactogenic hormones (prolactin, hydrocortisone and insulin) with different ratios of various Lys-peptide (Lys-Lys (KK), Lys-His (KH), Lys-Phe (KF), Lys-Leu (KL)and Lys-Thr (KT)).They isometrically substituted 0, 5%, 10%, 15% and 20% of free Lys (total concentration of Lys was 210 μg/mL), respectively.After 48 h treatment, mammary tissues were harvested for gene expression analysis by Real-time PCR.The results showed that:Compared with the free Lys group with no Lys substitution, when the KH replaced Lys at ratio of 15%, the KF replacement ratio was 10%, KK, KL and KT replacement ratio was 5%, the CSN1S1 mRNA abundance were the highest (P<0.05);When the KK replaced Lys at ratios of 5%, 10%, 15% and 20%, KH replacement ratios were 10% and 15%, KF replacement ratio was 15%, KL replacement ratios were 5% and 20% and KT replacement ratios were 5%, 10% and 15%, the SLC15A2 gene expression was significantly enhanced (P<0.05); when the KH replaced lysine at ratio of 15%, KK and KL replacement ratio was 10%, KF and KT replacement ratio was 5%, the abundance of SLC6A14⁺ mRNA was the highest (P<0.05);When the KH replaced Lys at ratio of 15% and 20%, KK replacement ratios were 5%, 10% and 15%, KL replacement ratio was 5% and 10%, the mRNA abundance of mTOR was significantly increased (P<0.05).The results indicated that the Lys dipeptides might be able to promote amino acid uptake and milk protein related gene expression in bovine mammary gland tissues.