University of Perpignan Via Domitia, Laboratoire Européen Performance Santé Altitude (LEPSA), EA4604, Department of Sports Sciences, 7 avenue Pierre de Coubertin, 66120 Font-Romeu, France.
Faculty of Sports Science, University of Montpellier, 700 avenue du Pic Saint Loup, 34090 Montpellier, France; INRA, UMR866 Dynamique Musculaire et Métabolisme, Université Montpellier, 2 Place Viala, 34060 Montpellier, France.
Biochem Biophys Res Commun. 2018 May 15;499(3):493-498. doi: 10.1016/j.bbrc.2018.03.176. Epub 2018 Mar 30.
AMP-activated protein kinase (AMPK) is a critical enzyme in conditions of cellular energy deficit such as exercise, hypoxia or nutritional stress. AMPK is well known to regulate protein degradation pathways notably through FOXO-related axis. In this study, we investigated the implication of AMPK activation in FOXO3 expression and stability in skeletal muscle primary myotubes. First, time course and dose response studies revealed optimal AICAR treatment duration and dose in skeletal muscle cells. Then, experiments with cycloheximide treatment of primary myotubes highlighted that AICAR infusion extends FOXO3 protein half-life. Our results also showed that AICAR treatment or nutrient depletion increases FOXO3 expression in primary myotubes and the expression of the mitochondrial E3 ligase Mul1 involved in mitochondrial turnover (mitophagy). In AMPK KO cells, nutrient depletion failed to alter the level of some FOXO3-dependent atrophic genes, including LC3B, BNIP3, and the mitochondrial E3 ligase Mul1, but not the expression of other genes (i.e. FOXO1, Gabarapl1, MAFbx, MuRF1). In summary, our data highlight that AMPK stabilizes FOXO3 and suggest a role in the first initiation step of mitochondrial segregation in muscle cells.
AMP 激活的蛋白激酶（AMPK）是细胞能量亏缺（如运动、缺氧或营养应激）条件下的关键酶。AMPK 通过 FOXO 相关轴，调控蛋白降解途径是众所周知的。在这项研究中，我们研究了 AMPK 激活在骨骼肌原代肌管中 FOXO3 表达和稳定性中的作用。首先，时间过程和剂量反应研究揭示了骨骼肌细胞中 AICAR 的最佳处理时间和剂量。然后，用环己酰亚胺处理原代肌管的实验表明，AICAR 输注可延长 FOXO3 蛋白半衰期。我们的结果还表明，AICAR 处理或营养耗竭增加了原代肌管中的 FOXO3 表达和参与线粒体周转（自噬）的线粒体 E3 连接酶 Mul1 的表达。在 AMPK KO 细胞中，营养耗竭未能改变某些依赖 FOXO3 的萎缩基因（包括 LC3B、BNIP3 和线粒体 E3 连接酶 Mul1）的水平，但不改变其他基因（即 FOXO1、Gabarapl1、MAFbx、MuRF1）的水平。总之，我们的数据强调了 AMPK 稳定 FOXO3，并提示其在肌细胞中线粒体分离的初始步骤中起作用。
