Valine enhances intramuscular fat deposition through activating autophagy and fatty acid metabolism pathways in C2C12 myoblasts

The branched-chain amino acids (BCAA) are essential to animal growth and intramuscular fat deposition, and also metabolic health (circulating level elevated in obesity and diabetes). However, the molecular role and effect of valine on muscle growth and fat deposition were less explored. Valine supplementation significantly affected mouse muscle growth, increasing the abdominal fat but decreasing the back fat. In the leg muscle, the expression levels of genes related to autophagy and fat deposition were significantly disturbed. Furthermore, valine promotes lipid deposition in myoblasts in a dose-dependent manner, and co-treatment of valine and palmitic acid can act in concert to enhance lipid deposition in myoblast. Moreover, transcriptome sequencing on myoblasts revealed that the signaling pathways such as mTOR, PI3K-AKT and fatty acid metabolism were activated after valine treatment, and palmitic acid additionally stimulated signaling pathways related to lipid metabolism in myoblasts. Therefore, valine could independently activate the autophagy pathway, and the fatty acid metabolism pathway to enhance intramuscular fat deposition Overall design: C2C12 cells of mice were taken as samples and sequenced and divided into control group (Control group), labeled C1-C6; 0.45 mM valine treatment group (Valine group), labeled as V1-V6; 0.45 mM+75 µ M Palmitic acid treatment group (Val+PA group), marked as VP1-VP6, randomly selected 3 samples from each group of six samples and sent them to the company for sequencing.

支链氨基酸（branched-chain amino acids, BCAA）是动物生长与肌内脂肪沉积所必需的营养物质，同时与代谢健康紧密相关（其循环水平在肥胖与糖尿病患者体内会升高）。然而，缬氨酸（valine）在肌肉生长及脂肪沉积过程中的分子作用与调控效应，目前尚未得到充分探究。缬氨酸干预可显著影响小鼠肌肉生长，能够增加腹部脂肪含量同时降低背部脂肪沉积；在腿部肌肉组织中，自噬与脂肪沉积相关基因的表达水平发生了显著紊乱。进一步研究表明，缬氨酸可通过剂量依赖性方式促进成肌细胞内的脂质沉积，且缬氨酸与棕榈酸（palmitic acid, PA）联合处理可产生协同效应，进一步增强成肌细胞的脂质沉积。对成肌细胞进行转录组测序的结果显示，经缬氨酸处理后，mTOR、PI3K-AKT及脂肪酸代谢等信号通路被激活；而棕榈酸可额外激活成肌细胞内与脂质代谢相关的信号通路。综上，缬氨酸可独立激活自噬通路与脂肪酸代谢通路，从而促进肌内脂肪沉积。整体实验设计：以小鼠C2C12细胞作为实验样本进行转录组测序，实验分为三组：对照组（Control group），编号为C1-C6；0.45 mM缬氨酸处理组（Valine group），编号为V1-V6；0.45 mM缬氨酸+75 μM棕榈酸处理组（Val+PA group），编号为VP1-VP6。每组6个样本中随机选取3个送至公司进行测序。