Milk protein produced from mammary gland of dairy cows provides good protein nutrition for humans. As one limiting amino acid (AA) for dairy cows, methionine (Met) plays a crucial regulatory role in milk protein production. Although it has been identified that Met regulates casein synthesis mainly through mTOR signaling pathway in bovine mammary gland, the underlying mechanism remains further examined. Here the primary bovine mammary epithelial cells (BMECs) were used in the whole study. First, compared with Met deprivation group (-Met), Met supplementation (+0.6 mM Met) significantly upregulated the expression of ASCT2 gene (sodium-dependent neutral amino acid transporter (P &lt; 0.05) and seryl-tRNA synthetase (SARS) protein (P &lt; 0.05) in BMECs. Furthermore, with the inhibitor of ASCT2 (GPNA) and SARS inhibition, cells were treated with Met-starved and Met-sufficient medium (0.6 mM Met) for 6 h to evaluate the related gene and protein abundance. When Met was deprived, there was a reduction in β-casein synthesis (P &lt; 0.05), and this reduction was further exacerbated when Met transport (ASCT2 activity) was inhibited or when SARS expression was depressed in BMECs (P &lt; 0.05). In addition, when the protein expression of ASCT2 or SARS was depressed, the other one’s protein abundance was decreased (P &lt; 0.05) under Met deprivation or Met supplementation. This work suggests that ASCT2 is involved in the SARS-mediated Met-stimulation of β-casein synthesis in BMECs, and this stimulation may be regulated by higher mammary Met uptake. The study expanded the understanding of the mechanisms underlying AA regulation of milk protein synthesis in mammary gland.

ASCT2 and SARS are involved in Met-stimulated β-casein synthesis in bovine mammary epithelial cells

2019 Fall National Meeting

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