Previous studies have shown various metabolic stressors such as saturated fatty acids (SFA) and excess insulin promote insulin resistance in metabolically meaningful cell types (such as skeletal muscle). Additionally, these stressors have been linked with suppressed mitochondrial metabolism, which is also a common characteristic of skeletal muscle of diabetics. This study characterized the individual and combined effects of excess lipid and excess insulin on myotube metabolism and related metabolic gene and protein expression. C2C12 myotubes were treated with either 500 μM palmitate (PAM), 100 nM insulin (IR), or both (PAM-IR). qRT-PCR and western blot were used to measure metabolic gene and protein expression, respectively. Oxygen consumption was used to measure mitochondrial metabolism. Glycolytic metabolism and insulin-mediated glucose uptake were measured via extracellular acidification rate. Cellular lipid and mitochondrial content were measured using Nile Red and NAO staining, respectively. IR and PAM-IR treatments led to reductions in p-Akt expression. IR treatment reduced insulin mediated glucose metabolism while PAM and PAM-IR treatment showed increases with concurrent reductions in mitochondrial metabolism. All three treatments showed suppression in mitochondrial metabolism. PAM and PAM-IR also showed increases in glycolytic metabolism. While PAM and PAM-IR significantly increased lipid content, expression of inflammatory and lipogenic proteins were unaltered. Lastly, PAM-IR reduced BCAT2 protein expression, a regulator of BCAA metabolism. Both stressors independently reduced insulin signaling, mitochondrial function, and cell metabolism, however, only PAM-IR co-treatment significantly reduced the expression of regulators of metabolism not seen with individual stressors, suggesting an additive effect of stressors on metabolic programming.

中文翻译：

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比较棕榈酸酯、胰岛素和棕榈酸酯-胰岛素联合治疗对肌管代谢和胰岛素抵抗的影响

先前的研究表明，各种代谢压力源，如饱和脂肪酸 (SFA) 和过量的胰岛素会促进具有代谢意义的细胞类型（如骨骼肌）的胰岛素抵抗。此外，这些压力源与抑制线粒体代谢有关，这也是糖尿病患者骨骼肌的共同特征。本研究描述了过量脂质和过量胰岛素对肌管代谢及相关代谢基因和蛋白质表达的单独和综合影响。用 500 μM 棕榈酸酯 (PAM)、100 nM 胰岛素 (IR) 或两者 (PAM-IR) 处理 C2C12 肌管。qRT-PCR 和蛋白质印迹分别用于测量代谢基因和蛋白质表达。耗氧量用于测量线粒体代谢。通过细胞外酸化率测量糖酵解代谢和胰岛素介导的葡萄糖摄取。分别使用尼罗红和 NAO 染色测量细胞脂质和线粒体含量。IR 和 PAM-IR 处理导致 p-Akt 表达减少。IR 治疗减少了胰岛素介导的葡萄糖代谢，而 PAM 和 PAM-IR 治疗显示增加，同时线粒体代谢减少。所有三种处理均显示线粒体代谢受到抑制。PAM 和 PAM-IR 也显示糖酵解代谢增加。虽然 PAM 和 PAM-IR 显着增加了脂质含量，但炎症和脂肪生成蛋白的表达没有改变。最后，PAM-IR 降低了 BCAT2 蛋白的表达，这是一种 BCAA 代谢的调节剂。两种压力源都独立地降低了胰岛素信号传导、线粒体功能、