Cruz Ana Miguel, Beall Craig
Institute of Biomedical and Clinical Science, University of Exeter Medical School, Exeter, United Kingdom.
Front Physiol. 2020 Sep 25;11:567378. doi: 10.3389/fphys.2020.567378. eCollection 2020.
Saturated fatty acids such as palmitate contribute to the development of Type 2 Diabetes by reducing insulin sensitivity, increasing inflammation and potentially contributing to anabolic resistance. We hypothesized that palmitate-induced ATP release from skeletal muscle cells may increase inflammatory cytokine production and contribute to insulin/anabolic resistance in an autocrine/paracrine manner. In C2C12 myotubes differentiated at physiological glucose concentrations (5.5 mM), palmitate treatment (16 h) at concentrations greater than 250 μM increased release of ATP and inflammatory cytokines IL-6 and MIF, significantly blunted insulin and amino acid-induced signaling and reduced mitochondrial function. In contrast to our hypothesis, degradation of extracellular ATP using apyrase, did not alter palmitate-induced insulin resistance nor alter release of cytokines. Moreover, treatment with ATPγS (16 h), a non-hydrolysable ATP analog, in the absence of palmitate, did not diminish insulin sensitivity. Acute treatment with ATPγS produced insulin mimetic roles; increased phosphorylation of PKB (aka AKT), S6K1 and ERK and enhanced GLUT4-mediated glucose uptake in the absence of exogenous insulin. The increases in PKB and S6K1 phosphorylation were completely prevented by pre-incubation with broad spectrum purinergic receptor (P2R) blockers PPADs and suramin but not by P2 × 4 or P2 × 7 blockers 5-BDBD or A-438079, respectively. Moreover, ATPγS increased IL-6 yet decreased MIF release, similar to the cytokine profile produced by exercise. Acute and chronic treatment with ATPγS increased glycolytic rate in a manner that was differentially inhibited by PPADs and suramin, suggesting heterogeneous P2R activation in the control of cellular metabolism. In summary, our data suggest that the palmitate-induced increase in ATP does not contribute to insulin/anabolic resistance in a cell autonomous manner.
饱和脂肪酸（如棕榈酸酯）通过降低胰岛素敏感性、增加炎症反应并可能导致合成代谢抵抗，从而促进2型糖尿病的发展。我们推测，棕榈酸酯诱导骨骼肌细胞释放ATP可能会增加炎性细胞因子的产生，并以自分泌/旁分泌的方式导致胰岛素/合成代谢抵抗。在生理葡萄糖浓度（5.5 mM）下分化的C2C12肌管中，浓度大于250 μM的棕榈酸酯处理（16小时）会增加ATP以及炎性细胞因子IL-6和MIF的释放，显著减弱胰岛素和氨基酸诱导的信号传导，并降低线粒体功能。与我们的假设相反，使用外切核苷酸酶降解细胞外ATP并没有改变棕榈酸酯诱导的胰岛素抵抗，也没有改变细胞因子的释放。此外，在没有棕榈酸酯的情况下，用不可水解的ATP类似物ATPγS处理（16小时）并没有降低胰岛素敏感性。ATPγS的急性处理产生了胰岛素模拟作用；在没有外源性胰岛素的情况下增加了蛋白激酶B（又称AKT）、核糖体蛋白S6激酶1（S6K1）和细胞外信号调节激酶（ERK）的磷酸化，并增强了葡萄糖转运蛋白4（GLUT4）介导的葡萄糖摄取。蛋白激酶B和S6K1磷酸化的增加分别被广谱嘌呤能受体（P2R）阻滞剂PPADs和苏拉明预孵育完全阻止，但不被P2X4或P2X7阻滞剂5-BDBD或A-438079阻止。此外，ATPγS增加了IL-6的释放，但减少了MIF的释放，类似于运动产生的细胞因子谱。ATPγS的急性和慢性处理以一种被PPADs和苏拉明差异抑制的方式增加了糖酵解速率，表明在细胞代谢控制中P2R的激活存在异质性。总之，我们的数据表明，棕榈酸酯诱导的ATP增加并不会以细胞自主的方式导致胰岛素/合成代谢抵抗。
