Inserm, UMR-S 872, Centre de Recherche des Cordeliers, Paris 75006, France.
Diabetologia. 2012 Jan;55(1):204-14. doi: 10.1007/s00125-011-2328-9. Epub 2011 Oct 18.
AIMS/HYPOTHESIS: Recent experiments in liver and adipocyte cell lines indicate that palmitate can induce endoplasmic reticulum (ER) stress. Since it has been shown that ER stress can interfere with insulin signalling, our hypothesis was that the deleterious action of palmitate on the insulin signalling pathway in muscle cells could also involve ER stress.
We used C2C12 and human myotubes that were treated either with palmitate or tunicamycin. Total lysates and RNA were prepared for western blotting or quantitative RT-PCR respectively. Glycogen synthesis was assessed by [¹⁴C]glucose incorporation.
Incubation of myotubes with palmitate or tunicamycin inhibited insulin-stimulated protein kinase B (PKB)/ v-akt murine thymoma viral oncogene homologue 1 (Akt). In parallel, an increase in ER stress markers was observed. Pre-incubation with chemical chaperones that reduce ER stress only prevented tunicamycin but not palmitate-induced insulin resistance. We hypothesised that ER stress activation levels induced by palmitate may not be high enough to induce insulin resistance, in contrast with tunicamycin-induced ER stress. Indeed, tunicamycin induced a robust activation of the inositol-requiring enzyme 1 (IRE-1)/c-JUN NH₂-terminal kinase (JNK) pathway, leading to serine phosphorylation of insulin receptor substrate 1 (IRS-1) and a decrease in IRS-1 tyrosine phosphorylation. In contrast, palmitate only induced a very weak activation of the IRE1/JNK pathway, with no IRS1 serine phosphorylation.
CONCLUSIONS/INTERPRETATION: These data show that insulin resistance induced by palmitate is not related to ER stress in muscle cells.
目的/假设：最近在肝和脂肪细胞系中的实验表明，棕榈酸可以诱导内质网（ER）应激。由于已经表明 ER 应激可以干扰胰岛素信号，我们的假设是，棕榈酸对肌肉细胞中胰岛素信号通路的有害作用也可能涉及 ER 应激。
我们使用 C2C12 和人肌管，分别用棕榈酸或衣霉素处理。分别提取总蛋白裂解物和 RNA，进行 Western blot 或定量 RT-PCR。通过[¹⁴C]葡萄糖掺入评估糖原合成。
肌管孵育棕榈酸或衣霉素抑制胰岛素刺激的蛋白激酶 B（PKB）/ v-akt 鼠胸腺瘤病毒致癌基因同源物 1（Akt）。同时，观察到 ER 应激标志物增加。用化学伴侣预处理，仅能预防衣霉素诱导的胰岛素抵抗，但不能预防棕榈酸诱导的胰岛素抵抗。我们假设，棕榈酸诱导的 ER 应激激活水平可能不足以诱导胰岛素抵抗，与衣霉素诱导的 ER 应激不同。事实上，衣霉素诱导了强烈的肌醇需求酶 1（IRE-1）/ c-JUN NH₂-末端激酶（JNK）途径的激活，导致胰岛素受体底物 1（IRS-1）的丝氨酸磷酸化和 IRS-1 酪氨酸磷酸化减少。相比之下，棕榈酸仅诱导 IRE1/JNK 途径的非常弱的激活，没有 IRS1 丝氨酸磷酸化。
结论/解释：这些数据表明，棕榈酸诱导的胰岛素抵抗与肌肉细胞中的 ER 应激无关。
