Abundance of Amino Acid Transporters and mTOR Pathway Components in the Gastrointestinal Tract of Lactating Holstein Cows

Abstract

Data from non-ruminants indicate that amino acid (AA) transport into cells can regulate mTOR pathway activity and protein synthesis. Whether mTOR is expressed in the ruminant gastrointestinal tract (GIT) and how it may be related to AA transporters and the AA concentrations in the tissue is unknown. Ruminal papillae and the epithelia of the duodenum, jejunum, and ileum collected at slaughter from eight clinically healthy Holstein in mid-lactation were used. Metabolites and RNA were extracted from tissue for liquid chromatography–mass spectrometry and RT-qPCR analysis. The glycine and asparagine concentrations in the rumen were greater than those in the intestine (p < 0.05), but the concentrations of other AAs were greater in the small intestine than those in the rumen. Among the 20 AAs identified, the concentrations of glutamate, alanine, and glycine were the greatest. The mRNA abundances of AKT1 and MTOR were greater in the small intestine than those in the rumen (p < 0.05). Similarly, the SLC1A1, SLC6A6, SLC7A8, SLC38A1, SLC38A7, and SLC43A2 mRNA abundances were greater (p < 0.05) in the small intestine than those in the rumen. The mRNA abundances of SLC1A5, SLC3A2, and SLC7A5 were greater in the rumen than those in the small intestine (p < 0.05). Overall, the present study provides fundamental data on the relationship between mTOR pathway components and the transport of AAs in different sections of the gastrointestinal tract.

Leucine-Mediated SLC7A5 Promotes Milk Protein and Milk Fat Synthesis through mTOR Signaling Pathway in Goat Mammary Epithelial Cells

“…In the rescue assay, the inhibition of mTOR activity using Torin1 weakened the promotion of milk protein synthesis by SLC7A5 , whereas the activation of mTOR using MHY1485 failed to rescue the inhibitory effect of interference with milk protein synthesis by SLC7A5 . In addition, probably due to the off-target effects, the role of MHY1485 did not meet expectations . Indeed, studies suggest that SLC7A5 and mTOR can form a feedback loop that SLC7A5 is a transporter mediating the import of leucine, which activates the AKT/mTOR pathway; on the other hand, IGF2BP2 -mediated upregulation of SLC7A5 expression through AKT/mTOR pathway activation .…”

“…In addition, probably due to the off-target effects, the role of MHY1485 did not meet expectations. 38 Indeed, studies suggest that SLC7A5 and mTOR can form a feedback loop that SLC7A5 is a transporter mediating the import of leucine, which activates the AKT/mTOR pathway; on the other hand, IGF2BP2-mediated upregulation of SLC7A5 expression through AKT/mTOR pathway activation. 39 This observation suggests that the lack of AA limits the synthesis of milk protein.…”

dCas9‐guided demethylation of the AKT1 promoter improves milk protein synthesis in a bovine mastitis mammary gland epithelial model induced by using Staphylococcus aureus

“…or inactivation through phosphorylation of TSC2 that results in upregulation of mTORC1 activity, and further phosphorylation of eIF4EBP and p70S6K1 (Jiang et al, 2023;Zhang et al, 2018). In the present study, we examined the expression of genes involved in milk protein synthesis, such as AKT1, mTOR, and p70S6K1 in BMMECs and observed that their protein levels decreased.…”