Branched-chain amino acid and lysine deficiencies exert different effects on mammary translational regulation

Deficiencies and imbalances of specific group II essential amino acids (EAA) were created in lactating cows by an infusion subtraction protocol to explore effects on milk production and abundance and phosphorylation state of regulators of mRNA translation in the mammary glands. Five lactating cows on a diet of 11.2% crude protein were infused abomasally for 5 d with saline, 563 g/d of a complete EAA mix, or EAA mixes without the branched-chain amino acids (BCAA), Leu, or Lys in a 5 x 5 Latin square design. Milk protein yield was stimulated by EAA infusion and returned to saline levels upon subtraction of BCAA, Leu, or Lys. Mammary abundance of phosphorylated S6K1 was measured as an indicator of mammalian target of rapamycin complex 1 (mTORC1) activity and was found not to be affected by the complete EAA mix but was increased by the mixture lacking Lys. Total S6K1 abundances in mammary tissue were elevated by complete and BCAA-lacking infusions. All of the EAA treatments except the one lacking BCAA upregulated mammary eIF2B epsilon and eIF2 alpha abundances, which is stimulatory to global mRNA translation. Phosphorylation state of eIF2B epsilon tended to decrease when complete or Lys-lacking EAA mixtures were infused. Phosphorylation state of eIF2 alpha was not affected by treatment. We detected a correlation of 0.62 between phosphorylation state of S6K1 and total eIF2B epsilon abundance, and a correlation of 0.58 between phosphorylation state of S6K1 and total eIF2 alpha abundance, suggesting that mTORC1 activation may have upregulated eIF2B epsilon and eIF2 alpha expression. Despite maintenance of mammary eIF2B epsilon and eIF2 alpha abundances during Leu and Lys deficiencies, milk protein yield declined, suggesting that other factors are responsible for mediating effects of Lys and Leu. A deficiency of all 3 BCAA may impair milk protein yield through deactivation of mTORC1-mediated upregulation of eIF2B epsilon and eIF2 alpha abundances.