Division of Exercise Physiology, West Virginia University School of Medicine, Morgantown, West Virginia, USA.
Am J Physiol Regul Integr Comp Physiol. 2010 Dec;299(6):R1546-54. doi: 10.1152/ajpregu.00337.2010. Epub 2010 Sep 15.
The aim of this study was to determine the effect of 14 days of 5-aminoimidazole-4-carboxamide-1β-4-ribofuranoside (AICAR) treatment on mammalian target of rapamycin (mTOR) signaling and mTOR-regulated processes (i.e., translation initiation) in obese mouse skeletal muscle. Our hypothesis was that daily treatment (14 days) with AICAR would normalize obesity-induced alterations in skeletal muscle mTOR signaling and mTOR-regulated processes to lean levels and positively affect muscle mass. Fourteen-week-old male, lean (L; 31.3 g body wt) wild-type and ob/ob (O; 59.6 g body wt) mice were injected with the AMP-activated kinase (AMPK) activator AICAR (A) at 0.5 mg·g body wt(-1)·day(-1) or saline control (C) for 14 days. At 24 h after the last injection (including a 12-h fast), all mice were killed, and the plantar flexor complex muscle (gastrocnemius, soleus, and plantaris) was excised for analysis. Muscle mass was lower in OC (159 ± 12 mg) than LC, LA, and OA (176 ± 10, 178 ± 9, and 166 ± 16 mg, respectively) mice, independent of a body weight change. A decrease in obese muscle mass corresponded with higher muscle cross section staining intensity for lipid and glycogen, higher blood glucose and insulin levels, and lower nuclear-enriched fractions for peroxisome proliferator-activated receptor-γ coactivator-1α protein expression in OC skeletal muscle, which was normalized with AICAR treatment. AMPK and acetyl-cocarboxylase phosphorylation was reduced in OC mice and augmented by AICAR treatment in OA mice. Conversely, OC mice displayed higher activation of downstream targets (S6 kinase-1 and ribosomal protein S6) of mTOR and lower raptor-associated mTOR than LC mice, which were reciprocally altered after 14 days of AICAR treatment. Dysregulation of translational capacity was improved in OA mice, as assessed by sucrose density gradient fractionation of ribosomes, total and ribosome-associated RNA content, eukaryotic initiation factor 4F complex formation, and eukaryotic initiation factor 4G phosphorylation. These data show that short-term (14 days) AMPK agonist treatment augments regulatory processes in atrophic obese mouse skeletal muscle through the normalization of mTOR signaling and mRNA translation closer to lean levels.
本研究旨在确定 14 天 5-氨基咪唑-4-甲酰胺-1β-D-核糖呋喃核苷（AICAR）治疗对肥胖小鼠骨骼肌中雷帕霉素靶蛋白（mTOR）信号及其调控过程（即翻译起始）的影响。我们的假设是，每天用 AICAR 治疗（14 天）可以使肥胖引起的骨骼肌 mTOR 信号及其调控过程恢复正常，使其接近瘦体水平，并对肌肉质量产生积极影响。14 周龄雄性、瘦体（L；31.3g 体重）野生型和 ob/ob（O；59.6g 体重）小鼠以 0.5mg·g 体重·天-1·d-1 的剂量注射 AMP 激活的蛋白激酶（AMPK）激动剂 AICAR（A）或生理盐水对照（C）14 天。在最后一次注射后 24 小时（包括 12 小时禁食），所有小鼠均被处死，取出跖屈肌复合体（比目鱼肌、跖肌和趾长屈肌）进行分析。OC（159±12mg）小鼠的肌肉质量低于 LC、LA 和 OA（176±10、178±9 和 166±16mg）小鼠，与体重变化无关。肥胖肌肉质量的下降与肌肉横截面脂质和糖原染色强度增加、血糖和胰岛素水平升高以及过氧化物酶体增殖物激活受体-γ共激活因子-1α蛋白核富集分数降低有关，而这些变化在 AICAR 治疗后得到了纠正。OC 小鼠的 AMPK 和乙酰基辅酶 A 磷酸化减少，OA 小鼠的 AICAR 治疗增加了这一过程。相反，OC 小鼠的 mTOR 下游靶标（S6 激酶-1 和核糖体蛋白 S6）的激活水平高于 LC 小鼠，而经过 14 天的 AICAR 治疗后，这一情况发生了逆转。OA 小鼠的翻译能力失调得到了改善，通过核糖体蔗糖密度梯度分级分离、总 RNA 和核糖体相关 RNA 含量、真核起始因子 4F 复合物形成和真核起始因子 4G 磷酸化来评估。这些数据表明，短期（14 天）AMPK 激动剂治疗通过使 mTOR 信号及其 mRNA 翻译更接近瘦体水平，增强了萎缩性肥胖小鼠骨骼肌中的调节过程。
