亮氨酸对老年前期小鼠血浆游离氨基酸的影响

Effect of Dietary Leucine Supplementation on Plasma Free Amino Acids in Pre-senile Mice

目的:探讨补充亮氨酸对老年前期小鼠血浆游离氨基酸的影响及其可能机制。方法:13月龄小鼠分别给予5%亮氨酸和3.4%丙氨酸添加8周。血糖仪测血糖,ELISA法测血清胰岛素,氨基酸分析仪测血浆氨基酸谱,RT-PCR测腓肠肌氨基酸转运蛋白LAT1、CD98、PAT1、SNAT2与GCN2基因表达,BCA法蛋白定量,免疫印迹法测mTOR磷酸化率。结果:亮氨酸添加未致血糖、胰岛素水平显著变化;氨基酸谱仅亮氨酸含量显著增加,丙氨酸、谷氨酸、甘氨酸含量显著下降,其他氨基酸水平无差异;LAT1、CD98基因表达显著上调,其他表达未见差异;肌肉蛋白总量与mTOR磷酸化率均显著增加。结论:膳食添加亮氨酸通过增加血浆游离亮氨酸含量活化LAT1、CD98,增加胞内氨基酸可利用性并与mTOR关联,促进肌肉蛋白合成。

The objective of this study was to investigate the effect of leucine supplementation on plasma free amino acids in pre--senile mice and the possible mechanism. Thirteen-month-old mice were treated with normal chow diet supplemented with 5% leucine and 3.4% alanine respectively for 8 weeks. The blood glucose was determined with a portable blood glu- cose meter, serum insulin concentration was determined by ELISA. Plasma free amino acids were determined with an ami- no acid analyzer, mRNA expression of LAT1, CD98, PAT1, SNAT2 and GCN2 were evaluated by Real-time quantitative RT-PCR. BCA method was used to detect the gastrocnemius protein content. Phosphorylation rate of mammalian target of rapamycin （roTOR） were detected by the method of Western blotting. The results showed that leueine supplementation did not change the level of blood glucose and serum insulin. The content of leucine increased significantly but alanine, glu- tamic acid and glycine dropped dramatically. Other amino acids were unchanged. As for the mRNA expression, lustLAT1 and CD98 elevated significantly while the others were unchanged. The protein content and phosphorylation rate of mTOR in gastrocnemius were both significantly in- creased. It could be concluded that diet leucine supplemen- tation elevated amino acids availability in skeletal muscle cells through the activated LAT1 and CD98 which were in- fluenced by increased plasma free leucine. Meanwhile, these two amino acid transporters, coupled with the activa- tion of roTOR and finally promoted the protein synthesis inskeletal muscle.