West Daniel W D, Baehr Leslie M, Marcotte George R, Chason Courtney M, Tolento Luis, Gomes Aldrin V, Bodine Sue C, Baar Keith
Department of Physiology & Membrane Biology, University of California Davis, Davis, CA, USA.
Department of Neurobiology, Physiology & Behavior, University of California Davis, Davis, CA, USA.
J Physiol. 2016 Jan 15;594(2):453-68. doi: 10.1113/JP271365. Epub 2015 Dec 15.
Ribosome biogenesis is the primary determinant of translational capacity, but its regulation in skeletal muscle following acute resistance exercise is poorly understood. Resistance exercise increases muscle protein synthesis acutely, and muscle mass with training, but the role of translational capacity in these processes is unclear. Here, we show that acute resistance exercise activated pathways controlling translational activity and capacity through both rapamycin-sensitive and -insensitive mechanisms. Transcription factor c-Myc and its downstream targets, which are known to regulate ribosome biogenesis in other cell types, were upregulated after resistance exercise in a rapamycin-independent manner and may play a role in determining translational capacity in skeletal muscle. Local inhibition of myostatin was also not affected by rapamycin and may contribute to the rapamycin-independent effects of resistance exercise.
This study aimed to determine (1) the effect of acute resistance exercise on mechanisms of ribosome biogenesis, and (2) the impact of mammalian target of rapamycin on ribosome biogenesis, and muscle protein synthesis (MPS) and degradation. Female F344BN rats underwent unilateral electrical stimulation of the sciatic nerve to mimic resistance exercise in the tibialis anterior (TA) muscle. TA muscles were collected at intervals over the 36 h of exercise recovery (REx); separate groups of animals were administered rapamycin pre-exercise (REx+Rapamycin). Resistance exercise led to a prolonged (6-36 h) elevation (30-50%) of MPS that was fully blocked by rapamycin at 6 h but only partially at 18 h. REx also altered pathways that regulate protein homeostasis and mRNA translation in a manner that was both rapamycin-sensitive (proteasome activity; phosphorylation of S6K1 and rpS6) and rapamycin-insensitive (phosphorylation of eEF2, ERK1/2 and UBF; gene expression of the myostatin target Mighty as well as c-Myc and its targets involved in ribosome biogenesis). The role of c-Myc was tested in vitro using the inhibitor 10058-F4, which, over time, decreased basal RNA and MPS in a dose-dependent manner (correlation of RNA and MPS, r(2) = 0.98), even though it had no effect on the acute stimulation of protein synthesis. In conclusion, acute resistance exercise stimulated rapamycin-sensitive and -insensitive mechanisms that regulate translation activity and capacity.
核糖体生物合成是翻译能力的主要决定因素，但急性抗阻运动后其在骨骼肌中的调节机制尚不清楚。抗阻运动可急性增加肌肉蛋白质合成，并通过训练增加肌肉质量，但翻译能力在这些过程中的作用尚不清楚。在此，我们表明急性抗阻运动通过雷帕霉素敏感和不敏感机制激活了控制翻译活性和能力的途径。转录因子c-Myc及其下游靶点在其他细胞类型中已知可调节核糖体生物合成，在抗阻运动后以雷帕霉素非依赖方式上调，可能在决定骨骼肌翻译能力中发挥作用。肌肉生长抑制素的局部抑制也不受雷帕霉素影响，可能有助于抗阻运动的雷帕霉素非依赖效应。
本研究旨在确定（1）急性抗阻运动对核糖体生物合成机制的影响，以及（2）雷帕霉素靶蛋白对核糖体生物合成、肌肉蛋白质合成（MPS）和降解的影响。雌性F344BN大鼠接受坐骨神经单侧电刺激，以模拟胫骨前肌（TA）的抗阻运动。在运动恢复（REx）的36小时内间隔采集TA肌肉；单独的动物组在运动前给予雷帕霉素（REx+雷帕霉素）。抗阻运动导致MPS持续升高（6-36小时）（升高30-50%），雷帕霉素在6小时时完全阻断了这种升高，但在18小时时仅部分阻断。REx还以雷帕霉素敏感（蛋白酶体活性；S6K1和rpS6的磷酸化）和雷帕霉素不敏感（eEF2、ERK1/2和UBF的磷酸化；肌肉生长抑制素靶点Mighty以及c-Myc及其参与核糖体生物合成的靶点的基因表达）的方式改变了调节蛋白质稳态和mRNA翻译的途径。使用抑制剂10058-F4在体外测试了c-Myc的作用，随着时间的推移，该抑制剂以剂量依赖方式降低基础RNA和MPS（RNA和MPS的相关性，r(2)=0.98），尽管它对蛋白质合成的急性刺激没有影响。总之，急性抗阻运动刺激了调节翻译活性和能力的雷帕霉素敏感和不敏感机制。
