Effect of the ratios of acetate and β-hydroxybutyrate on the expression of milk fat- and protein-related genes in bovine mammary epithelial cells

The objective of this study was to evaluate the effects of the different ratios of acetate and β-hydroxybutyrate (BHBA) on cell viability, triacylglycerol (TAG) content, and mRNA expression of the genes related to lipid and protein synthesis in bovine mammary epithelial cells (BMECs). Primary cells were isolated from the mammary glands of Holstein dairy cows and were passaged twice. Then, the cells were cultured with different ratios of acetate and BHBA (1 : 3, 1 : 2, 1 : 1, 2 : 1, 3 : 1, 4 : 1, and 1 : 1, Group 1 to Group 7, respectively) for 48 h, and the fetal bovine serum in the culture media was replaced with fatty acid-free bovine serum albumin (BSA) (1 g/l). The control culture media contained only fatty acid-free BSA without unsaturated fatty acids (0mM). Cell viability was not affected by adding different ratios of acetate and BHBA, but TAG accumulation was significantly influenced by supplementing the culture media with different ratios of acetate and BHBA. The expression levels of genes related to milk fat (FASN, ACACA, CD36, SCD, FABP3, LPL, PPARG, and SPEBF1) and milk protein-related genes (CSN1S1, CSN3, mTOR, 4E-BP1, S6KB1, STAT5, JAK2, and LEPTIN) were significantly affected by the addition of different ratios of acetate and BHBA to the BMECs. Our results suggested that Groups 3 and 4 (1 : 1 and 2 : 1) had a stronger acceleration of milk fat synthesis, and Group 4 (2 : 1) had the strongest effect. The expression of the CSN1S1 and LEPTIN mRNAs was more effectively promoted in Groups 3 and 4 (1 : 1 and 2 : 1), and Group 3 (1 : 1) had the strongest acceleration. Expressions of genes related to milk protein synthesis (mTOR, 4E-BP1, S6KB1, JAK2, and STAT5) were up-regulated using a ratio of acetate and BHBA of 2 : 1. Taken together, the 2 : 1 ratio of acetate and BHBA had the best effect for both the milk fat synthesis and milk protein synthesis genes. However, further studies are necessary to elucidate the mechanism for regulating milk fat and protein synthesis by different ratios of acetate and BHBA.