Fujita Satoshi, Dreyer Hans C, Drummond Micah J, Glynn Erin L, Cadenas Jerson G, Yoshizawa Fumiaki, Volpi Elena, Rasmussen Blake B
University of Texas Medical Branch, Department of Internal Medicine, Galveston, TX 77555-1144, USA.
J Physiol. 2007 Jul 15;582(Pt 2):813-23. doi: 10.1113/jphysiol.2007.134593. Epub 2007 May 3.
The mammalian target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK) are important nutrient- and energy-sensing and signalling proteins in skeletal muscle. AMPK activation decreases muscle protein synthesis by inhibiting mTOR signalling to regulatory proteins associated with translation initiation and elongation. On the other hand, essential amino acids (leucine in particular) and insulin stimulate mTOR signalling and protein synthesis. We hypothesized that anabolic nutrients would be sensed by both AMPK and mTOR, resulting in an acute and potent stimulation of human skeletal muscle protein synthesis via enhanced translation initiation and elongation. We measured muscle protein synthesis and mTOR-associated upstream and downstream signalling proteins in young male subjects (n=14) using stable isotopic and immunoblotting techniques. Following a first muscle biopsy, subjects in the 'Nutrition' group ingested a leucine-enriched essential amino acid-carbohydrate mixture (EAC). Subjects in the Control group did not consume nutrients. A second biopsy was obtained 1 h later. Ingestion of EAC significantly increased muscle protein synthesis, modestly reduced AMPK phosphorylation, and increased Akt/PKB (protein kinase B) and mTOR phosphorylation (P<0.05). mTOR signalling to its downstream effectors (S6 kinase 1 (S6K1) and 4E-binding protein 1 (4E-BP1) phosphorylation status) was also increased (P<0.05). In addition, eukaryotic elongation factor 2 (eEF2) phosphorylation was significantly reduced (P<0.05). Protein synthesis and cell signalling (phosphorylation status) was unchanged in the control group (P>0.05). We conclude that anabolic nutrients alter the phosphorylation status of both AMPK- and mTOR-associated signalling proteins in human muscle, in association with an increase in protein synthesis not only via enhanced translation initiation but also through signalling promoting translation elongation.
雷帕霉素哺乳动物靶点（mTOR）和AMP激活的蛋白激酶（AMPK）是骨骼肌中重要的营养和能量传感及信号蛋白。AMPK激活通过抑制mTOR向与翻译起始和延伸相关的调节蛋白的信号传导来降低肌肉蛋白质合成。另一方面，必需氨基酸（特别是亮氨酸）和胰岛素刺激mTOR信号传导和蛋白质合成。我们假设合成代谢营养素会被AMPK和mTOR感知，通过增强翻译起始和延伸，导致对人骨骼肌蛋白质合成的急性和强效刺激。我们使用稳定同位素和免疫印迹技术测量了年轻男性受试者（n = 14）的肌肉蛋白质合成以及与mTOR相关的上游和下游信号蛋白。在第一次肌肉活检后，“营养”组的受试者摄入了富含亮氨酸的必需氨基酸 - 碳水化合物混合物（EAC）。对照组的受试者不摄入营养素。1小时后进行第二次活检。摄入EAC显著增加了肌肉蛋白质合成，适度降低了AMPK磷酸化，并增加了Akt / PKB（蛋白激酶B）和mTOR磷酸化（P < 0.05）。mTOR向其下游效应器（S6激酶1（S6K1）和4E - 结合蛋白1（4E - BP1）磷酸化状态）的信号传导也增加了（P < 0.05）。此外，真核延伸因子2（eEF2）磷酸化显著降低（P < 0.05）。对照组的蛋白质合成和细胞信号传导（磷酸化状态）没有变化（P>0.05）。我们得出结论，合成代谢营养素改变了人肌肉中与AMPK和mTOR相关的信号蛋白的磷酸化状态，不仅通过增强翻译起始，还通过促进翻译延伸的信号传导增加了蛋白质合成。
