INSERM, U1060, IFR62, Oullins, F-69921, France.
Mol Cell Endocrinol. 2011 Mar 30;335(2):166-76. doi: 10.1016/j.mce.2011.01.008. Epub 2011 Jan 15.
The protein deacetylase SIRT1, and its activator resveratrol, exert beneficial effects on glucose metabolism. Different SIRT1 targets have been identified, including PTP1B, AMPK, FOXO, PGC-1α and IRS2. The latter may underscore a tight link between SIRT1 and insulin signaling components. However, whether SIRT1 has a direct effect on insulin resistance and whether resveratrol acts directly or indirectly in this context is still a matter of controversy and this question has not been addressed in muscle cells. Here, we show that SIRT1 protein expression is decreased in muscle biopsies and primary myotubes derived from type 2 diabetic patients, suggesting a contribution of diminished SIRT1 in the determination of muscle insulin resistance. To investigate the functional impact of SIRT1 on the insulin pathway, the activation of insulin downstream effector PKB was evaluated after SIRT1 inactivation by RNAi, SIRT1 overexpression, or resveratrol treatments. In muscle cells and HEK293 cells, downregulation of SIRT1 reduced, while overexpression increased, insulin-induced PKB activatory phosphorylation. Further molecular characterisation revealed that SIRT1 interacts in an insulin-independent manner with the PI3K adapter subunit p85. We then investigated whether resveratrol may improve insulin signaling in muscle cells via SIRT1, or alternative targets. Incubation of muscle cells with resveratrol reverted the insulin-resistant state induced by prolonged TNFα or insulin treatment. Resveratrol-dependent improvement of insulin-resistance occurred through inhibition of serine phosphorylation of IRS1/2, implicating resveratrol as a serine kinase inhibitor. Finally, a functional interaction between PI3K and SIRT1 was demonstrated in C. elegans, where constitutively active PI3K - mimicking increased IIS signaling - lead to shortened lifespan, while removal of sir-2.1 abolished PI3K-induced lifespan shortening. Our data identify SIRT1 as a positive modulator of insulin signaling in muscle cells through PI3K, and this mechanism appears to be conserved from C. elegans through humans.
蛋白去乙酰化酶 SIRT1 及其激活剂白藜芦醇对葡萄糖代谢有有益影响。已经确定了不同的 SIRT1 靶标，包括 PTP1B、AMPK、FOXO、PGC-1α 和 IRS2。后者可能强调了 SIRT1 与胰岛素信号成分之间的紧密联系。然而，SIRT1 是否对胰岛素抵抗有直接影响，以及白藜芦醇在这种情况下是直接还是间接起作用，仍然存在争议，这个问题在肌肉细胞中尚未得到解决。在这里，我们表明 SIRT1 蛋白表达在 2 型糖尿病患者的肌肉活检和原代肌管中降低，表明 SIRT1 减少对肌肉胰岛素抵抗的决定有贡献。为了研究 SIRT1 对胰岛素途径的功能影响，在用 RNAi、SIRT1 过表达或白藜芦醇处理来失活 SIRT1 后，评估了胰岛素下游效应物 PKB 的激活。在肌肉细胞和 HEK293 细胞中，下调 SIRT1 减少了胰岛素诱导的 PKB 激活性磷酸化，而上调 SIRT1 则增加了胰岛素诱导的 PKB 激活性磷酸化。进一步的分子特征表明，SIRT1 以胰岛素非依赖性的方式与 PI3K 接头亚基 p85 相互作用。然后，我们研究了白藜芦醇是否可以通过 SIRT1 或其他靶标改善肌肉细胞中的胰岛素信号。用白藜芦醇孵育肌肉细胞可逆转由 TNFα 或胰岛素处理延长引起的胰岛素抵抗状态。白藜芦醇依赖的胰岛素抵抗改善是通过抑制 IRS1/2 的丝氨酸磷酸化来实现的，这表明白藜芦醇是一种丝氨酸激酶抑制剂。最后，在秀丽隐杆线虫中证明了 PI3K 和 SIRT1 之间的功能相互作用，其中组成型激活的 PI3K - 模拟增加的 IIS 信号 - 导致寿命缩短，而去除 sir-2.1 则消除了 PI3K 诱导的寿命缩短。我们的数据表明，SIRT1 通过 PI3K 成为肌肉细胞中胰岛素信号的正调节剂，并且这种机制似乎从秀丽隐杆线虫到人类都是保守的。
