SCOPE: Understanding the regulatory mechanism of milk protein synthesis is important to develop strategies to improve milk protein and enhance lactation performance. The mammalian target of rapamycin (mTOR) pathway is a crucial modulator of protein synthesis. In this study, we want to investigate if T1R1/T1R3 can regulate milk protein synthesis and mediate the mTOR pathway in the mice mammary gland in vivo. METHODS AND RESULTS: T1R1 knockout mice, WT mice, and mammary explants were used. The weigh-suckle-weigh method was used to quantify the milk yield. The expression level of β-casein and AA transporter mRNA were analyzed by qPCR. Western blot was used to analyze protein abundance of members of the mTOR pathway. As expected, the knockout of T1R1 not only reduced the total milk yield in the mice mammary glands, but also repressed β-casein synthesis. Additionally, the phosphorylation of 4EBP1 and S6K was significantly decreased in T1R1 knockout mice. The T1R1 knockout also increased the protein abundance of the AA transporter SLC3A2 and mRNA expression of SLC7A5/SLC3A2 and SLC1A5. Activation of the mTOR pathway was repressed by inhibition of T1R3 or T1R1 knockout in mammary gland explants. CONCLUSION: T1R1/T1R3 modulates the mTOR pathway to regulate milk protein synthesis in the mouse mammary gland in vivo.
SCOPE: Understanding the regulatory mechanism of milk protein synthesis is important to develop strategies to improve milk protein and enhance lactation performance. The mammalian target of rapamycin (mTOR) pathway is a crucial modulator of protein synthesis. In this study, we want to investigate if T1R1/T1R3 can regulate milk protein synthesis and mediate the mTOR pathway in the mice mammary gland in vivo. METHODS AND RESULTS:T1R1 knockout mice, WT mice, and mammary explants were used. The weigh-suckle-weigh method was used to quantify the milk yield. The expression level of β-casein and AA transporter mRNA were analyzed by qPCR. Western blot was used to analyze protein abundance of members of the mTOR pathway. As expected, the knockout of T1R1 not only reduced the total milk yield in the mice mammary glands, but also repressed β-casein synthesis. Additionally, the phosphorylation of 4EBP1 and S6K was significantly decreased in T1R1 knockout mice. The T1R1 knockout also increased the protein abundance of the AA transporter SLC3A2 and mRNA expression of SLC7A5/SLC3A2 and SLC1A5. Activation of the mTOR pathway was repressed by inhibition of T1R3 or T1R1 knockout in mammary gland explants. CONCLUSION:T1R1/T1R3 modulates the mTOR pathway to regulate milk protein synthesis in the mouse mammary gland in vivo.