Department of Exercise Science, High Point University, High Point, NC, USA.
Endocrine. 2022 Apr;76(1):18-28. doi: 10.1007/s12020-021-02939-z. Epub 2021 Nov 22.
Branched-chain amino acids (BCAA) have been shown to enhance several cellular signaling pathways including protein synthesis and mitochondrial biogenesis, yet population data demonstrate a correlation between circulating BCAA and severity of insulin resistance which has been hypothesized to be, in part, a byproduct of BCAA inhibition of mitochondrial function. The purpose of this study is to examine the effect of a BCAA mixture on muscle metabolism and related gene expression in vitro.
C2C12 myotubes were treated with a BCAA mixture containing leucine:isoleucine:valine at a ratio of 2:1:1 at 0.2, 2, or 20 mM (based on leucine content) for 6 days. qRT-PCR was used to measure metabolic gene expression. Oxygen consumption and extracellular acidification were used to assess mitochondrial and glycolytic metabolism, respectively. Mitochondrial content was determined via mitochondrial-specific staining.
Despite significantly elevated mitochondrial staining, 6-day BCAA treatment reduced basal mitochondrial metabolism at a supraphysiological concentration (20 mM) in both insulin sensitive and resistant cells. Peak mitochondrial capacity was also reduced in insulin-resistant (but not insulin sensitive) cells. Conversely, basal glycolytic metabolism was elevated following 20 mM BCAA treatment, regardless of insulin resistance. In addition, insulin-resistant cells treated with 20 mM BCAA exhibited reduced gene expression of Ppargc1a, Cytc, Atp5b, Glut4, and several glycolytic enzymes versus insulin sensitive cells treated with 20 mM BCAA.
Collectively, these findings suggest BCAA at supraphysiologically high levels may negatively alter mitochondrial metabolism, and concurrent insulin resistance may also diminish peak mitochondrial capacity, as well as impede molecular adaptations that support a transition to a glycolytic preference/compensation.
支链氨基酸（BCAA）已被证明可增强多种细胞信号通路，包括蛋白质合成和线粒体生物发生，然而人群数据表明循环 BCAA 与胰岛素抵抗的严重程度之间存在相关性，这部分被假设为 BCAA 抑制线粒体功能的副产物。本研究旨在体外研究 BCAA 混合物对肌肉代谢和相关基因表达的影响。
用含有亮氨酸：异亮氨酸：缬氨酸比例为 2:1:1 的 BCAA 混合物处理 C2C12 肌管，浓度分别为 0.2、2 或 20mM（基于亮氨酸含量），持续 6 天。qRT-PCR 用于测量代谢基因表达。耗氧量和细胞外酸化分别用于评估线粒体和糖酵解代谢。通过线粒体特异性染色来确定线粒体含量。
尽管线粒体染色明显升高，但在胰岛素敏感和抵抗细胞中，6 天的 BCAA 处理在超生理浓度（20mM）下降低了基础线粒体代谢。峰值线粒体容量也在胰岛素抵抗细胞（但不是胰岛素敏感细胞）中降低。相反，无论胰岛素抵抗如何，20mM BCAA 处理后基础糖酵解代谢均升高。此外，与胰岛素敏感细胞相比，用 20mM BCAA 处理的胰岛素抵抗细胞的 Ppargc1a、Cytc、Atp5b、Glut4 和几种糖酵解酶的基因表达降低。
总之，这些发现表明，高生理水平的 BCAA 可能会负面改变线粒体代谢，同时胰岛素抵抗也可能降低峰值线粒体容量，并阻碍支持向糖酵解偏好/补偿转变的分子适应。
