Department of Exercise Science, High Point University, One University Parkway, High Point, NC, 27262-3598, USA.
School of Health Sciences, Lindenwood University, St. Charles, MO, 63301, USA.
Mol Cell Biochem. 2020 May;468(1-2):169-183. doi: 10.1007/s11010-020-03720-y. Epub 2020 Mar 28.
Population data have consistently demonstrated a correlation between circulating branched-chain amino acids (BCAA) and insulin resistance. Most recently valine catabolite, 3-hydroxyisobutyrate, has emerged as a potential cause of BCAA-mediated insulin resistance; however, it is unclear if valine independently promotes insulin resistance. It is also unclear if excess valine influences the ability of cells to degrade BCAA. Therefore, this study investigated the effect of valine on muscle insulin signaling and related metabolism in vitro. C2C12 myotubes were treated with varying concentrations (0.5 mM-2 mM) of valine for up to 48 h. qRT-PCR and western blot were used to measure metabolic gene and protein expression, respectively. Insulin sensitivity (indicated by pAkt:Akt), metabolic gene and protein expression, and cell metabolism were also measured following valine treatment both with and without varying levels of insulin resistance. Mitochondrial and glycolytic metabolism were measured via oxygen consumption and extracellular acidification rate, respectively. Valine did not alter regulators of mitochondrial biogenesis or glycolysis; however, valine reduced branched-chain alpha-keto acid dehydrogenase a (Bckdha) mRNA (but not protein) expression which was exacerbated by insulin resistance. Valine treatment had no effect on pAkt:Akt following either acute or 48-h treatment, regardless of insulin stimulation or varying levels of insulin resistance. In conclusion, despite consistent population data demonstrating a relationship between circulating BCAA (and related metabolites) and insulin resistance, valine does not appear to independently alter insulin sensitivity or worsen insulin resistance in the myotube model of skeletal muscle.
人群数据一直表明循环支链氨基酸 (BCAA) 与胰岛素抵抗之间存在相关性。最近，支链氨基酸代谢物 3-羟基异丁酸已成为 BCAA 介导的胰岛素抵抗的潜在原因；然而，尚不清楚缬氨酸是否独立促进胰岛素抵抗。也不清楚过量的缬氨酸是否会影响细胞降解 BCAA 的能力。因此，本研究在体外研究了缬氨酸对肌肉胰岛素信号转导和相关代谢的影响。用不同浓度（0.5 mM-2 mM）的缬氨酸处理 C2C12 肌管长达 48 小时。qRT-PCR 和 Western blot 分别用于测量代谢基因和蛋白质表达。还测量了缬氨酸处理后（有无不同程度的胰岛素抵抗）肌肉胰岛素敏感性（由 pAkt:Akt 表示）、代谢基因和蛋白质表达以及细胞代谢。通过耗氧量和细胞外酸化率分别测量线粒体和糖酵解代谢。缬氨酸不会改变线粒体生物发生或糖酵解的调节剂；然而，缬氨酸降低了支链α-酮酸脱氢酶 a (Bckdha) mRNA（但不是蛋白质）表达，这种表达在存在胰岛素抵抗时加剧。无论是否存在胰岛素刺激或不同程度的胰岛素抵抗，急性或 48 小时处理后，缬氨酸处理对 pAkt:Akt 均无影响。总之，尽管人群数据一直表明循环 BCAA（和相关代谢物）与胰岛素抵抗之间存在关系，但在骨骼肌肌管模型中，缬氨酸似乎不会独立改变胰岛素敏感性或加重胰岛素抵抗。
