Rapamycin has a biphasic effect on insulin sensitivity in C2C12 myotubes due to sequential disruption of mTORC1 and mTORC2.
Rapamycin has a biphasic effect on insulin sensitivity in C2C12 myotubes due to sequential disruption of mTORC1 and mTORC2.
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DOI：
10.3389/fgene.2012.00177
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发表时间：
2012
影响因子：
3.7
通讯作者：
Baur JA
中科院分区：
文献类型：
--
作者：
Ye L;Varamini B;Lamming DW;Sabatini DM;Baur JA
雷帕霉素是一种mTOR复合体1(MTORC1)的抑制剂，在体外和体内的急性研究中，通过破坏S6激酶介导的负反馈回路来改善胰岛素敏感性。我们发现，雷帕霉素对C2C12肌管的胰岛素敏感性有明显的双相效应，在24-48小时后几乎完全胰岛素抵抗的第一个小时内反应性增强。我们和其他人最近观察到，慢性雷帕霉素治疗诱导啮齿动物胰岛素抵抗，至少部分是由于mTORC2的破坏，mTORC2是一种含有mTOR的复合体，对药物不是很敏感。慢性雷帕霉素治疗也可能通过抑制依赖mTORC1的线粒体的生物发生和活性来削弱胰岛素的作用，这可能导致已知触发胰岛素抵抗的脂质中间产物的积聚。我们证实，雷帕霉素抑制关键的线粒体转录因子pGC-1α的表达，并显著降低肌管的呼吸频率。然而，雷帕霉素不能刺激PKCθ的磷酸化，PKC DNA是脂质诱导的胰岛素抵抗的中心介质。相反，我们发现mTORC2的戏剧性中断，这与胰岛素抵抗的开始不谋而合。通过shRNA介导的特定成分(分别为Raptor和Rictor)的敲除来选择性地抑制mTORC1或mTORC2，证实了雷帕霉素的线粒体效应是mTORC1依赖的，而胰岛素抵抗仅通过敲除mTORC2来重现。因此，mTORC2的破坏，而不是线粒体的抑制，导致了雷帕霉素处理的肌管中的胰岛素抵抗，这个系统可以作为一个有用的模型来理解雷帕霉素对体内mTOR信号的影响。
Rapamycin, an inhibitor of mTOR complex 1 (mTORC1), improves insulin sensitivity in acute studies in vitro and in vivo by disrupting a negative feedback loop mediated by S6 kinase. We find that rapamycin has a clear biphasic effect on insulin sensitivity in C2C12 myotubes, with enhanced responsiveness during the first hour that declines to almost complete insulin resistance by 24–48 h. We and others have recently observed that chronic rapamycin treatment induces insulin resistance in rodents, at least in part due to disruption of mTORC2, an mTOR-containing complex that is not acutely sensitive to the drug. Chronic rapamycin treatment may also impair insulin action via the inhibition of mTORC1-dependent mitochondrial biogenesis and activity, which could result in a buildup of lipid intermediates that are known to trigger insulin resistance. We confirmed that rapamycin inhibits expression of PGC-1α, a key mitochondrial transcription factor, and acutely reduces respiration rate in myotubes. However, rapamycin did not stimulate phosphorylation of PKCθ, a central mediator of lipid-induced insulin resistance. Instead, we found dramatic disruption of mTORC2, which coincided with the onset of insulin resistance. Selective inhibition of mTORC1 or mTORC2 by shRNA-mediated knockdown of specific components (Raptor and Rictor, respectively) confirmed that mitochondrial effects of rapamycin are mTORC1-dependent, whereas insulin resistance was recapitulated only by knockdown of mTORC2. Thus, mTORC2 disruption, rather than inhibition of mitochondria, causes insulin resistance in rapamycin-treated myotubes, and this system may serve as a useful model to understand the effects of rapamycin on mTOR signaling in vivo.