Liao Xian-Dong, Zhou Chang-Hai, Zhang Jing, Shen Jing-Lin, Wang Ya-Jing, Jin Yong-Cheng, Li Sheng-Li
Department of Animal Science, College of Animal Science, Jilin University, Changchun 130062, China.
State Key Laboratory of Animal Nutrition, Beijing Engineering Technology Research Center of Raw Milk Quality and Safety Control, College of Animal Science and Technology, China Agricultural University, Beijing 100193, China.
Asian-Australas J Anim Sci. 2020 Jun;33(6):1012-1022. doi: 10.5713/ajas.19.0315. Epub 2019 Aug 23.
Caseins and fatty acids of milk are synthesized and secreted by the epithelial cells of the mammary gland. All-trans retinoic acid (ATRA), an active metabolite of vitamin A, has been shown to promote mammary development. This study was conducted to determine the effect of ATRA on casein synthesis and fatty acid composition in MAC-T cells.
MAC-T cells were allowed to differentiate for 4 d, treated with ATRA (0, 1.0, 1.5, and 2.0 μM), and incubated for 3 d. We analyzed the fatty acid composition, the mRNA expression of casein and fatty acid synthesis-related genes, and the phosphorylation of casein synthesis-related proteins of MAC-T cells by gas chromatography, quantitative polymerase chain reaction, and western blotting, respectively.
In MAC-T cells, ATRA increased the mRNA levels of αS1-casein and β-casein, janus kinase 2 (JAK2) and E74-like factor 5 of the signal transducer and activator of transcription 5 β (STAT5-β) pathway, ribosomal protein S6 kinase beta-1 (S6K1) and eukaryotic translation initiation factor 4E binding protein 1 of the mammalian target of rapamycin (mTOR) pathway, inhibited the mRNA expression of phosphoinositide 3-kinase and eukaryotic initiation factor 4E of the mTOR pathway, and promoted the phosphorylation of STAT5-β and S6K1 proteins. Additionally, ATRA increased the de novo synthesis of fatty acids, reduced the content of long-chain fatty acids, the ratio of monounsaturated fatty acids to saturated fatty acids (SFA), the ratio of polyunsaturated fatty acids (PUFA) to SFA, and the ratio of ω-6 to ω-3 PUFA. The mRNA levels of acetyl-CoA carboxylase 1, fatty acid synthase, lipoprotein lipase, stearoyl-CoA desaturase, peroxisome proliferator-activated receptor gamma, and sterol regulatory element-binding protein 1 (SREBP1) were enhanced by ATRA.
ATRA promotes the synthesis of casein by regulating JAK2/STAT5 pathway and downstream mTOR signaling pathway, and it improves the fatty acid composition of MAC-T cells by regulating SREBP1-related genes.
乳腺上皮细胞合成并分泌牛奶中的酪蛋白和脂肪酸。全反式维甲酸（ATRA）是维生素A的一种活性代谢产物，已被证明可促进乳腺发育。本研究旨在确定ATRA对MAC-T细胞中酪蛋白合成及脂肪酸组成的影响。
使MAC-T细胞分化4天，用ATRA（0、1.0、1.5和2.0μM）处理，并孵育3天。我们分别通过气相色谱法、定量聚合酶链反应和蛋白质免疫印迹法分析了MAC-T细胞的脂肪酸组成、酪蛋白和脂肪酸合成相关基因的mRNA表达以及酪蛋白合成相关蛋白的磷酸化情况。
在MAC-T细胞中，ATRA增加了αS1-酪蛋白和β-酪蛋白、信号转导子和转录激活子5β（STAT5-β）途径的janus激酶2（JAK2）和E74样因子5、雷帕霉素靶蛋白（mTOR）途径的核糖体蛋白S6激酶β-1（S6K1）和真核翻译起始因子4E结合蛋白1的mRNA水平，抑制了mTOR途径的磷酸肌醇3激酶和真核起始因子4E的mRNA表达，并促进了STAT5-β和S6K1蛋白的磷酸化。此外，ATRA增加了脂肪酸的从头合成，降低了长链脂肪酸的含量、单不饱和脂肪酸与饱和脂肪酸（SFA）的比例、多不饱和脂肪酸（PUFA）与SFA的比例以及ω-6与ω-3 PUFA的比例。ATRA提高了乙酰辅酶A羧化酶1、脂肪酸合酶、脂蛋白脂肪酶、硬脂酰辅酶A去饱和酶、过氧化物酶体增殖物激活受体γ和固醇调节元件结合蛋白1（SREBP1）的mRNA水平。
ATRA通过调节JAK2/STAT5途径和下游mTOR信号通路促进酪蛋白合成，并通过调节SREBP1相关基因改善MAC-T细胞的脂肪酸组成。
