mTOR inhibition extends life span in multiple organisms. In mice, when metformin treatment (Met) is added to the mTOR inhibitor rapamycin (Rap), median and maximal life span is extended to a greater degree than with Rap or Met alone. Treatments that extend life span often maintain proteostasis. However, it is less clear how individual tissues, such as skeletal muscle, maintain proteostasis with life span-extending treatments. In C2C12 myotubes, we used deuterium oxide (D2O) to directly measure two primary determinants of proteostasis, protein synthesis, and degradation rates, with Rap or Met+Rap treatments. We accounted for the independent effects of cell growth and loss, and isolated the contribution of autophagy and mitochondrial fission to obtain a comprehensive assessment of protein turnover. Compared with control, both Rap and Met+Rap treatments lowered mitochondrial protein synthesis rates (p < .001) and slowed cellular proliferation (p < .01). These changes resulted in greater activation of mechanisms promoting proteostasis for Rap, but not Met+Rap. Compared with control, both Rap and Met+Rap slowed protein breakdown. Autophagy and mitochondrial fission differentially influenced the proteostatic effects of Rap and Met+Rap in C2C12 myotubes. In conclusion, we demonstrate that Met+Rap did not increase protein turnover and that these treatments do not seem to promote proteostasis through increased autophagy.

中文翻译：

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雷帕霉素和二甲双胍联合雷帕霉素对培养的骨骼肌管蛋白稳定机制的不同作用。

抑制mTOR可延长多种生物的寿命。在小鼠中，将二甲双胍治疗（Met）添加到mTOR抑制剂雷帕霉素（Rap）中时，中​​位数和最大寿命会比单独使用Rap或Met时更大。延长寿命的治疗方法通常可以维持蛋白稳态。但是，尚不清楚个体组织（例如骨骼肌）如何通过延长寿命的方法来维持蛋白稳态。在C2C12肌管中，我们使用Rap或Met + Rap处理，使用氧化氘（D2O）直接测量蛋白稳态，蛋白质合成和降解速率的两个主要决定因素。我们考虑了细胞生长和丢失的独立影响，并分离了自噬和线粒体裂变的贡献，以获得对蛋白质更新的全面评估。与对照相比，Rap和Met + Rap处理均降低了线粒体蛋白的合成速率（p <.001）和减慢了细胞增殖（p <.01）。这些改变导致了更多的促进Rap蛋白变性的机制的激活，但没有达到Met + Rap。与对照相比，Rap和Met + Rap均减慢了蛋白质的降解。自噬和线粒体裂变对C2C12肌管中Rap和Met + Rap的蛋白抑制作用有不同的影响。总之，我们证明了Met + Rap不会增加蛋白质更新，并且这些治疗似乎也不能通过增加自噬来促进蛋白稳态。Rap和Met + Rap都减慢了蛋白质的降解。自噬和线粒体裂变对C2C12肌管中Rap和Met + Rap的蛋白抑制作用有不同的影响。总之，我们证明了Met + Rap不会增加蛋白质更新，并且这些治疗似乎也不会通过增加自噬来促进蛋白稳态。Rap和Met + Rap都减慢了蛋白质的降解。自噬和线粒体裂变对C2C12肌管中Rap和Met + Rap的蛋白抑制作用有不同的影响。总之，我们证明了Met + Rap不会增加蛋白质更新，并且这些治疗似乎也不能通过增加自噬来促进蛋白稳态。