AMPKα stimulates skeletal muscle fatty acid utilization during in vivo exercise in mice. Mus musculus

Existing controversy regarding the importance of AMP-activated protein kinase (AMPK) in fatty acid (FA) oxidation in skeletal muscle with contraction/exercise may to some extent pertain to redundant AMPKα1 signaling. Using a mouse model lacking both AMPKα1 and -α2 in skeletal muscle specifically (mdKO) we hypothesized that FA utilization would be impaired in skeletal muscle. Calorimetric analysis showed a similar respiratory exchange ratio (RER) of AMPKα WT and mdKO mice when fed normal chow, a high fat diet or with prolonged fasting. Though, in vivo treadmill exercise at the same relative intensity induced a higher RER in mdKO mice compared to WT (WT=0.81; mdKO=0.87; p<0.01) indicating a decreased utilization of FA. Ex vivo incubation of soleus muscle revealed that basal and contraction-induced FA oxidation was impaired in mdKO mice, suggesting that the increased RER during in vivo running exercise originated from decreased skeletal muscle FA oxidation. A decreased muscle protein expression of CD36 and FABPpm (by 17-40%) together with abolishment of TBC1D1 Ser237 phosphorylation in mdKO mice, may result in lower FA transport capacity and FA transport protein translocation to sarcolemma, respectively. In summary this study shows that the catalytically active AMPKα subunits are required for normal stimulation of FA utilization during exercise and contractions. Overall design: Four wild type and 3 AMPKα1α2 double knockout mice were used.

目前关于腺苷酸活化蛋白激酶（AMP-activated protein kinase, AMPK）在骨骼肌收缩或运动过程中对脂肪酸（fatty acid, FA）氧化的调控作用存在争议，该争议在一定程度上可能与冗余的AMPKα1信号通路相关。本研究采用骨骼肌特异性同时缺失AMPKα1与α2的小鼠模型（mdKO），提出假说：骨骼肌的脂肪酸利用能力将出现受损。量热分析结果显示，在正常饲料喂养、高脂饮食或长期禁食三种状态下，AMPKα野生型（WT）与mdKO小鼠的呼吸交换比（respiratory exchange ratio, RER）并无显著差异。不过，在相同相对强度的体内跑步机运动中，mdKO小鼠的呼吸交换比显著高于野生型小鼠（野生型=0.81；mdKO=0.87；p<0.01），这表明其脂肪酸利用能力有所下降。离体比目鱼肌孵育实验发现，mdKO小鼠的基础及收缩诱导的脂肪酸氧化均出现受损，提示体内跑步运动中呼吸交换比升高的原因在于骨骼肌脂肪酸氧化能力降低。mdKO小鼠肌肉组织中CD36与FABPpm的蛋白表达量降低17%至40%，同时TBC1D1 Ser237位点的磷酸化被消除，这两种变化可能分别导致脂肪酸转运能力下降以及脂肪酸转运蛋白向肌膜的转位受阻。综上，本研究证实，具有催化活性的AMPKα亚基对于运动及收缩过程中脂肪酸利用的正常激活是必需的。整体实验设计：本研究共使用4只野生型小鼠与3只AMPKα1α2双敲除小鼠。