Interdisciplinary Center for Aquaculture Research (INCAR), Víctor Lamas 1290, PO Box 160-C, Concepción, Chile; Laboratorio de Biotecnologia Molecular, Departamento de Ciencias Biologicas, Facultad de Ciencias Biologicas, Universidad Andres Bello, Av. Republica 217, Santiago, Chile.
Fish Endocrinology Laboratory, Department of Biological and Environmental Sciences, University of Gothenburg, Box 463, S-40530 Gothenburg, Sweden.
Gen Comp Endocrinol. 2015 Jan 1;210:96-106. doi: 10.1016/j.ygcen.2014.10.012. Epub 2014 Nov 4.
Knowledge about the underlying mechanisms, particularly the signaling pathways that account for muscle growth in vivo in early vertebrates is still scarce. Fish (Paralichthys adspersus) were fasted for 3weeks to induce a catabolic period of strong muscle atrophy. Subsequently, fish were refed for 2weeks to induce compensatory muscle hypertrophy. During refeeding, the fish were treated daily with either rapamycin (TORC blocker), PD98059 (MEK blocker), or PBS (V; vehicle), or were untreated (C; control). Rapamycin and PD98059 differentially impaired muscle cellularity in vivo, growth performance, and the expression of growth-related genes, and the inhibition of TORC1 had a greater impact on fish muscle growth than the inhibition of MAPK. Blocking TORC1 inhibited the phosphorylation of P70S6K and 4EBP1, two downstream components activated by TORC1, thus affecting protein contents in muscle. Concomitantly, the gene expression in muscle of igf-1, 2 and igfbp-4, 5 was down-regulated while the expression of atrogin-1, murf-1, and igfbp-2, 3 was up-regulated. Muscle hypertrophy was abolished and muscle atrophy was promoted, which finally affected body weight. TORC2 complex was not affected by rapamycin. On the other hand, the PD98059 treatment triggered ERK inactivation, a downstream component activated by MEK. mRNA contents of igf-1 in muscle were down-regulated, and muscle hypertrophy was partially impaired. The present study provides the first direct data on the in vivo contribution of TORC1/P70S6K, TORC1/4EBP1, and MAPK/ERK signaling pathways in the skeletal muscle of an earlier vertebrate, and highlights the transcendental role of TORC1 in growth from the cellular to organism level.
关于潜在机制的知识，特别是在早期脊椎动物中解释肌肉生长的信号通路，仍然很少。将鱼（牙鲆）禁食 3 周以诱导强烈的肌肉萎缩分解代谢期。随后，鱼被重新喂食 2 周以诱导代偿性肌肉肥大。在重新喂食期间，鱼每天用雷帕霉素（TORC 阻断剂）、PD98059（MEK 阻断剂）或 PBS（V；载体）处理，或不处理（C；对照）。雷帕霉素和 PD98059 体内差异地损害肌肉细胞活力、生长性能和生长相关基因的表达，并且 TORC1 的抑制对鱼类肌肉生长的影响大于 MAPK 的抑制。阻断 TORC1 抑制了 TORC1 激活的两个下游成分 P70S6K 和 4EBP1 的磷酸化，从而影响肌肉中的蛋白质含量。同时，肌肉中 igf-1、2 和 igfbp-4、5 的基因表达下调，而 atrogin-1、murf-1 和 igfbp-2、3 的表达上调。肌肉肥大被消除，肌肉萎缩被促进，最终影响体重。TORC2 复合物不受雷帕霉素影响。另一方面，PD98059 处理触发 ERK 失活，这是 MEK 激活的下游成分。肌肉中 igf-1 的 mRNA 含量下调，肌肉肥大部分受损。本研究首次提供了关于 TORC1/P70S6K、TORC1/4EBP1 和 MAPK/ERK 信号通路在早期脊椎动物骨骼肌中体内作用的直接数据，并强调了 TORC1 在从细胞到生物体水平的生长中的重要作用。
