Early activation of mTORC1 signalling in response to mechanical overload is independent of phosphoinositide 3-kinase/Akt signalling
Early activation of mTORC1 signalling in response to mechanical overload is independent of phosphoinositide 3-kinase/Akt signalling
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DOI：
10.1113/jphysiol.2011.205658
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发表时间：
2011-04-01
影响因子：
5.5
通讯作者：
Esser, Karyn A.
中科院分区：
文献类型：
--
作者：
Miyazaki, Mitsunori;McCarthy, John J.;Esser, Karyn A.
非技术概述阻力运动引起的骨骼肌肥大与蛋白质合成速率显著增加有关。蛋白激酶mTORC1已被证明是一个关键的信号中枢，不同的合成代谢因子(即生长因子、营养物质和机械应变)通过它参与蛋白质合成的调节。在这项研究中，我们使用肌肉肥大的活体模型来描述不同的输入通路对mTORC1的调节作用。我们发现胰岛素/胰岛素样生长因子1通路对于mTORC1信号的早期激活并不是必需的，但这可能是通过激活ERK/TSC2通路来实现的。了解在体内调节mTORC1活性的关键上游通路将为开发维持骨骼肌质量的新治疗策略提供必要的基础。哺乳动物靶标雷帕霉素复合体1(MTORC1)是调节蛋白质代谢和细胞生长的一系列信号的中央整合因子。然而，调节骨骼肌中mTORC1活性的单个通路的作用尚不清楚。本研究的目的是确定在机械超负荷诱导的骨骼肌肥大过程中，mTORC1激活的调节机制。与以前的研究一致，机械超负荷导致足底肌肉进行性肥大，这与总RNA含量和蛋白质代谢的显著增加有关。T389和T421/S424的S6K1磷酸化水平显著增加，表明mTORC1在一天的超负荷后被激活。相反，通过Akt磷酸化状态(T308和S473)、直接下游靶标的磷酸化(糖原合成酶激酶3β、富含Pro的Akt底物40 kDa和结节性硬化症2(TSC2))和一种激酶分析来评估Akt活性，直到超负荷2-3天才显著增加。Wortmannin对磷脂酰肌醇3-激酶(PI3K)活性的抑制足以阻断胰岛素依赖的信号转导，但不能阻止mTORC1在超负荷时的早期激活。我们发现有丝分裂原激活的蛋白激酶(MEK)/细胞外信号调节激酶(ERK)依赖的通路在超负荷后第1天被激活。此外，MEK/ERK信号转导的靶点-S664处TSC2的磷酸化也在这一早期时间点增加。这些观察结果表明，在活体内，骨骼肌机械超负荷早期的mTORC1激活不依赖于PI3K/Akt信号通路，并提供了证据表明MEK/ERK通路可能通过TSC2的磷酸化参与mTORC1的激活。
Non-technical summaryHypertrophy of skeletal muscle in response to resistance exercise is associated with significantly elevated rates of protein synthesis. The protein kinase mTORC1 has been shown to be a key signalling hub through which different anabolic factors (i.e. growth factors, nutrients and mechanical strain) contribute to the regulation of protein synthesis. In this study, we use an in vivo model of muscle hypertrophy to delineate the contribution of different input pathways regulating mTORC1. We found that the insulin/insulin like growth factor 1 pathway is not necessary for early activation of mTORC1 signalling but this probably occurs through activation of the ERK/TSC2 pathway. Knowledge of the key upstream pathways that modulate mTORC1 activity in vivo will provide the necessary foundation for the development of new therapeutic strategies for the maintenance of skeletal muscle mass.The mammalian target of rapamycin complex 1 (mTORC1) functions as a central integrator of a wide range of signals that modulate protein metabolism and cell growth. However, the contributions of individual pathways regulating mTORC1 activity in skeletal muscle are poorly defined. The purpose of this study was to determine the regulatory mechanisms that contribute to mTORC1 activation during mechanical overload-induced skeletal muscle hypertrophy. Consistent with previous studies, mechanical overload induced progressive hypertrophy of the plantaris muscle which was associated with significant increases in total RNA content and protein metabolism. mTORC1 was activated after a single day of overload as indicated by a significant increase in S6K1 phosphorylation at T389 and T421/S424. In contrast, Akt activity, as assessed by Akt phosphorylation status (T308 and S473), phosphorylation of direct downstream targets (glycogen synthase kinase 3 beta, proline-rich Akt substrate 40 kDa and tuberous sclerosis 2 (TSC2)) and a kinase assay, was not significantly increased until 2-3 days of overload. Inhibition of phosphoinositide 3-kinase (PI3K) activity by wortmannin was sufficient to block insulin-dependent signalling but did not prevent the early activation of mTORC1 in response to overload. We identified that the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK)-dependent pathway was activated at day 1 after overload. In addition, a target of MEK/ERK signalling, phosphorylation of TSC2 at S664, was also increased at this early time point. These observations demonstrate that in vivo, mTORC1 activation at the early phase of mechanical overload in skeletal muscle occurs independently of PI3K/Akt signalling and provide evidence that the MEK/ERK pathway may contribute to mTORC1 activation through phosphorylation of TSC2.