Zhou Jia, Yue Shuangming, Xue Benchu, Wang Zhisheng, Wang Lizhi, Peng Quanhui, Xue Bai
Animal Nutrition Institute, Sichuan Agricultural University, Chengdu 611130, China.
Department of Bioengineering, Sichuan Water Conservancy Vocation College, Chengdu 611845, China.
J Anim Sci Technol. 2021 Sep;63(5):1126-1141. doi: 10.5187/jast.2021.e93. Epub 2021 Sep 30.
Recent evidence has shown that methionine (Met) supplementation can improve milk protein synthesis under hyperthermia (which reduces milk production). To explore the mechanism by which milk protein synthesis is affected by Met supplementation under hyperthermia, mammary alveolar (MAC-T) cells were incubated at a hyperthermic temperature of 42°C for 6 h in media with different concentrations of Met. While the control group (CON) contained a normal amino acid concentration profile (60 μg/mL of Met), the three treatment groups were supplemented with Met at concentrations of 10 μg/mL (MET70, 70 μg/mL of Met), 20 μg/mL (MET80, 80 μg/mL of Met), and 30 μg/mL (MET90,90 μg/mL of Met). Our results show that additional Met supplementation increases the mRNA and protein levels of BCL2 (B-cell lymphoma-2, an anti-apoptosis agent), and decreases the mRNA and protein levels of BAX (Bcl-2-associated X protein, a pro-apoptosis agent), especially at an additional supplementary concentration of 20 μg/mL (group Met80). Supplementation with higher concentrations of Met decreased the mRNA levels of - and -, and increased protein levels of heat shock protein (HSP70). The total protein levels of the mechanistic target of rapamycin (mTOR) and the mTOR signalling pathway-related proteins, AKT, ribosomal protein S6 kinase B1 (RPS6KB1), and ribosomal protein S6 (RPS6), increased with increasing Met supplementation, and peaked at 80 μg/mL Met (group Met80). In addition, we also found that additional Met supplementation upregulated the gene expression of αS1-casein (), β-casein (), and the amino acid transporter genes , which are known to be mTOR targets. Additional Met supplementation, however, had no effect on the gene expression of κ-casein () and solute carrier family 34 member 2 (). Our results suggest that additional Met supplementation with 20 μg/mL may promote the synthesis of milk proteins in bovine mammary epithelial cells under hyperthermia by inhibiting apoptosis, activating the AKT-mTOR-RPS6KB1 signalling pathway, and regulating the entry of amino acids into these cells.
最近的证据表明，补充蛋氨酸（Met）可以在高温环境下（高温会降低产奶量）改善乳蛋白合成。为了探究高温环境下补充Met影响乳蛋白合成的机制，将乳腺泡（MAC-T）细胞在含有不同浓度Met的培养基中于42°C的高温下孵育6小时。对照组（CON）含有正常的氨基酸浓度分布（60μg/mL的Met），三个处理组分别补充浓度为10μg/mL（MET70，70μg/mL的Met）、20μg/mL（MET80，80μg/mL的Met）和30μg/mL（MET90，90μg/mL的Met）的Met。我们的结果表明，额外补充Met会增加抗凋亡因子BCL2（B细胞淋巴瘤-2）的mRNA和蛋白水平，并降低促凋亡因子BAX（Bcl-2相关X蛋白）的mRNA和蛋白水平，尤其是在额外补充浓度为20μg/mL时（Met80组）。补充更高浓度的Met会降低-和-的mRNA水平，并增加热休克蛋白（HSP70）的蛋白水平。雷帕霉素机制靶点（mTOR）以及mTOR信号通路相关蛋白AKT、核糖体蛋白S6激酶B1（RPS6KB1）和核糖体蛋白S6（RPS6）的总蛋白水平随着Met补充量的增加而升高，并在Met浓度为80μg/mL时达到峰值（Met80组）。此外，我们还发现额外补充Met会上调αS1-酪蛋白（）、β-酪蛋白（）以及已知为mTOR靶点的氨基酸转运蛋白基因和的基因表达。然而，额外补充Met对κ-酪蛋白（）和溶质载体家族34成员2（）的基因表达没有影响。我们的结果表明，在高温环境下，额外补充20μg/mL的Met可能通过抑制细胞凋亡、激活AKT-mTOR-RPS6KB1信号通路以及调节氨基酸进入这些细胞，从而促进牛乳腺上皮细胞中乳蛋白的合成。
