Mechanisms Of The Regulation Of Milk Protein Synthesis By Individual Essential Amino Acid

It has now been demonstrated that AA stimulate protein synthesis, not only through mass action as substrates, but also through regulation of translation initiation and elongation via one or more cell signaling pathways. Such regulation coupled with variable mammary AA transport activity confers variable efficiency which violates the the critical fixed efficiency assumption of Mitchell and Block. The objective of the present study was to1) identify the individual EAA having effects on mTOR and GNC2 signals in bovine mammary epithelial cells, in vitro 2) investigate the independent effects of supplementation of a protein deficient diet with Leu, Ile, Met, and Thr on lactational performance in vivo.The effects of key signaling protein phosphorylation during regulating milk protein synthesis by individual EAA.mTOR phosphorylation was declined by 58% when all EAA were omitted from complete media in MAC-T cells. Omission of only Met、Ile、Val reduced phosphorylation of mTOR by 38%, 41% and 42% respectively. 4eBP1 phosphorylation declined when Met(39%), Ile(41%), Thr(36%),Lys(42%) or all EAA(59%) were omitted from media.S6K1 phosphorylation declined when Met(33%), Ile(38%), Leu(41%),Val(40%)or all EAA(53%) were omitted from media. eEF2 phosphorylation increased 18%, 20% and18% when Met, Lle and Val were omitted from media. eIF2α phosphorylation increased when EAA(49%) and Met(39%) were omitted from media. The results showed that individual EAA having effects on mTOR and GNC2 signals in bovine mammary epithelial cells, and the sensitive EAA were Met, Leu, Ile, Thr, Val, Lys.The effects of key signaling protein phosphorylation by Met, Leu, Ile, Val. Based on different EAA concentration trial, 10% EAA was chose as negative control and Met, Leu, Ile,Val were chosen for further study in a supplementation experiment in MAC-T cells.Supplementation of Leu and Ile increased phosphorylation of mTOR by 47% and 69%.Phosphorylation of 4eBP1 was increased when supplementation of Leu, Ile and Val.Supplementation two of Met, Leu, Ile, Val had additive effect on phosphorylation of signaling protein.Met, Leu, Ile or Thr effects on milk protein synthesis in lactating mice. Two studies were undertaken to assess the effects of individual EAA supplementation of a protein deficient diet on lactational performance in mice using litter growth rates as a response variable. The first was designed to establish a dietary protein response curve, and the second to determine the effects of Leu, Ile, Met, and Thr supplementation of a protein deficient diet on lactational performance. In both studies, dams were fed the test diets from parturition through d 17 of lactation when the studies were ended. Mammary tissue was collected at the end for the study from mice on the 2nd experiment and analyzed for mTOR pathway cell signaling. Supplementation with Ile, Leu, and Met increased litter weight gain by 11, 9, and10% respectively as compared to the protein deficient diet. These responses are supported by independent phosphorylation responses for mTOR and4eBP1. Supplementation of Ile, Leu,Met, and Thr increased phosphorylation of mTOR by 55, 34, 47 and 45%, respectively as compared to the low protein group. Phosphorylation of 4eBP1 increased in response to Ile,Met, and Thr supplementation by 60, 40 and 51% respectively. There were no significant effects of treatment on phosphorylation of S6K1, eIF2α, or eEF2. There was a trend for an effect of AA supplementation on blood IGF-1 concentrations, with a marked increase when the low protein diet was supplemented with Ile. The independence of litter weight gain responses are further supported by the independent responses of mTOR and Akt pathway signaling.The effects of endocrine inducing by Met and Leu on milk protein systhsis. Met and Leu supplementation of a protein deficient diet on lactational performance in mice using litter growth rates as a response variable Litter weight gain was significantly increased by Met and Leu. Met significantly increased plasma insulin level. Met and Leu significantly influenced IGF-1 concentration. Met increased insulin secration in pancreas and IGF-1secration in liver.Met and Leu mainly changed the gene expression in liver pancreas and insulin signaling pathways.In conclusion, this work demonstrated that individual EAA having effects on mTOR and GNC2 signals in bovine mammary epithelial cells, and supplementation Met, Leu, Ile and Valor two of them had additive effect on phosphorylation of signaling protein. In vivo, milk production responses to supplementation of single AA are independent. The independence of these responses are further supported by the independent responses of mTOR and Akt pathway signaling. The lack of responses in eIF2 ? phosphorylation suggest that the GCN pathway is not the primary mediator of amino acid effects on milk protein synthesis.Effects of hormon on milk protein systhsis inducing by Met and Leu are another important signals.Incorporation of a multiple limiting amino acid concept into milk protein response models will help improve milk and milk protein yield predictions, thus allowing derivation of diets that will result in increased postabsorptive N efficiency and reduce N excretion by dairy animals.