蛋氨酸对肉牛脂肪沉积的作用及其调控机制研究

Methionine is not only an essential amino acid for protein synthesis, but also able to regulate cell metabolism and other functions via serving as a methyl donor for DNA and protein methylation. Previous studies revealed opposite effects of methionine on fat deposition between rodents and swine. However, the effects of methionine on fat deposition of beef cattle is still not clear. In the present study, we will explore the effects of methionine and its regulatory mechanisms on fat deposition in beef cattle at four levels (individual, tissular, cellular and molecular) by conducting in vivo and in vitro trials. Firstly, the appropriate dietary methionine supplementation level will be determined by animal experiment. Then, the cellular morphological changes of different tissues will be analyzed by using image analysis. The mRNA and protein expression of genes related to lipid metabolism will be determined using quantitative PCR and Western blot method. Finally, the primary preadipocytes of beef cattle will be isolated and then cultured in medium containing different amount of methionine. The proliferation and differentiation of preadipocytes and lipid metabolism will be measured, which will further verify the regulatory mechanism of methionine on fat deposition of beef cattle from the cellular and molecular level. The results of this study will enrich and improve the theory that methionine can differentially regulate lipid metabolism in animals. In addition, it will also provide fundamental knowledge for the effective application of methionine in beef cattle production.

蛋氨酸不仅是合成各种蛋白质所必需的氨基酸，而且作为甲基供体通过调控DNA和功能蛋白质的甲基化修饰，进而影响细胞代谢和其他功能。基于蛋氨酸对啮齿动物和猪的脂肪沉积起到相反作用的现象以及对肉牛的影响尚不明确的问题，本项目从个体-组织-细胞-分子四个层次以及体内和体外两个角度探索蛋氨酸对肉牛脂肪沉积的作用及其调控机制。首先通过动物试验筛选出肉牛日粮蛋氨酸的适宜添加水平；然后，比较日粮蛋氨酸水平对肉牛不同组织中脂肪细胞数量及形态的影响，再利用定量PCR和Western blot方法测定脂质代谢相关基因mRNA和蛋白的表达水平；最后，分离培养肉牛原代前脂肪细胞，利用不同浓度的蛋氨酸处理，测定细胞增殖、分化和脂质代谢情况，进一步从细胞和分子水平验证蛋氨酸对肉牛脂肪沉积的调控机制。研究结果将在理论上丰富和完善蛋氨酸差异化调控动物机体脂质代谢的相关理论，在实践上为蛋氨酸在肉牛生产上的有效应用提供科学依据。

蛋氨酸不仅是合成各种蛋白质所必需的氨基酸，而且作为甲基供体通过调控DNA和功能蛋白质的甲基化修饰，进而影响细胞代谢和其他功能。基于蛋氨酸对啮齿动物和猪的脂肪沉积起到相反作用的现象以及对肉牛的影响尚不明确的问题，本项目从个体-组织-细胞-分子四个层次以及体内和体外两个角度探索蛋氨酸对肉牛脂肪沉积的作用及其调控机制。研究结果表明：1）在育肥后期日粮中添加15 g/d或30 g/d蛋氨酸羟基类似物异丙酯（HMBi）可提高肉牛的平均日增重、饲料转化效率和屠宰性能；2）日粮添加HMBi对大部分牛肉品质指标未造成显著影响，但在数值上有改善的趋势；3）日粮中添加HMBi促进了育肥后期肉牛PPARγ、FABP4、PDGFRα和CEBPα成脂相关基因的mRNA表达；4）HMBi可能是通过激活ERK1/2、PPARγ、PI3K-AKT和FABP4等相关信号通路，增加了脂肪和蛋白沉积；5）在细胞水平上，蛋氨酸可以促进牛原代脂肪细胞成脂和C2C12细胞成肌分化。本研究证实了蛋氨酸对肉牛脂肪沉积和蛋白沉积的正向调控作用，完善了蛋氨酸控动物机体脂质和蛋白代谢的相关理论；在实践上能够为蛋氨酸在肉牛生产上的有效应用提供科学依据，也为改善牛肉品质提供新的途径和有益的线索。

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