Molecular Mechanisms of Rapamycin's effects on Health and longevity.

描述(申请人提供)：雷帕霉素是唯一被明确证明可以延长小鼠最长寿命的化合物。不幸的是，包括免疫抑制和心血管危险因素增加在内的副作用可能会限制该药物在人类中的应用。因此，有很大的需要和机会来了解雷帕霉素是如何发挥作用的--这既是为了开发安全有效的疗法，也是为了深入了解衰老本身的基本机制。雷帕霉素的典型靶点是mTORC1，这是一种营养感应激酶，其同源基因与低等生物的热量限制(CR)延长寿命有关。在小鼠中，mTORC1靶标S6激酶1(S6K1)的消融模拟了CR的显著特征，包括增加胰岛素敏感性、线粒体生物合成和寿命。因此，人们推测雷帕霉素通过抑制哺乳动物的mTORC1/S6K1轴来模拟CR。然而，与CR形成鲜明对比的是，雷帕霉素实际上会导致胰岛素抵抗，至少在细胞内，会抑制其他线粒体的产生和活性。考虑到胰岛素敏化和线粒体生物生成增加都被认为有助于CR诱导的寿命，这些观察结果令人惊讶，而且可能非常重要。我们最近发现，雷帕霉素诱导的胰岛素抵抗是抑制第二个靶点mTORC2的结果，而且，mTORC1的特异性抑制延长了寿命，而不会对胰岛素信号转导产生不利影响。接下来，我们计划测试在细胞中观察到的对线粒体生物生成和活性的抑制是否也在体内发生。如果是这样的话，雷帕霉素将使我们能够提供第一个明确的证据，证明线粒体的生物发生可以与寿命脱钩。在第二个实验中，我们将用雷帕霉素治疗S6K1基因敲除小鼠，以检验S6K1非依赖机制有助于其延长寿命的假设。有许多理由相信情况会是这样的。S6K1消融术在生理上会产生非常不同的变化，不会延长男性的寿命，而雷帕霉素则会。此外，mTORC2同系物调节蠕虫的寿命，我们的证明雷帕霉素破坏小鼠的mTORC2因此为S6K1非依赖性作用提供了一种候选机制。最后，我们将探索mTORC2中断的组织特异性后果。肝脏中mTORC2的丢失似乎介导了雷帕霉素对胰岛素敏感性的不利影响，缓解这些影响可能会导致补充方法来提高药物的安全性和有效性。另一方面，大脑中另一种胰岛素信号分子IRS2的丢失先前已被证明可以延长寿命，神经元mTORC2的丢失可能因此有助于雷帕霉素延长寿命的有益效果。阐明雷帕霉素能够预防或减缓年龄相关疾病的进展并延长小鼠最长存活时间的机制将为促进人类健康衰老提供重要的见解和可能的新治疗靶点。

DESCRIPTION (provided by applicant): Rapamycin is the only compound that has been unambiguously shown to extend the maximum lifespan of mice. Unfortunately, side effects including immunosuppression and the elevation of cardiovascular risk factors are likely to limit the utility of the drug in humans. Therefore, there is a great need and opportunity to understand how rapamycin works - both for the development of safe and effective therapeutics, and to gain insight into the basic mechanisms of aging itself. The canonical target of rapamycin is mTORC1, a nutrient sensing kinase whose homolog has been implicated in the extension of lifespan by caloric restriction (CR) in lower organisms. In mice, ablation of the mTORC1 target S6 kinase 1 (S6K1) mimics salient features of CR, including increases in insulin sensitivity, mitochondrial biogenesis, and lifespan. Therefore, it has been postulated that rapamycin mimics CR by inhibiting the mTORC1/S6K1 axis in mammals. In sharp contrast to CR, however, rapamycin actually causes insulin resistance and, at least in cells, inhibits oth the production and activity of mitochondria. These are surprising and potentially very important observations, given that both insulin sensitization and increased mitochondrial biogenesis have been suggested to contribute to CR-induced longevity. We recently showed that rapamycin-induced insulin resistance is the result of inhibiting a second target, mTORC2, and moreover, that specific inhibition of mTORC1 extends lifespan without detrimental effects on insulin signaling. Next, we plan to test whether the inhibition of mitochondrial biogenesi and activity that is observed in cells also occurs in vivo. If so, rapamycin will allow us to proide the first clear demonstration that mitochondrial biogenesis can be uncoupled from longevity. In a second line of experiments, we will treat S6K1 knockout mice with rapamycin to test the hypothesis that S6K1-independent mechanisms contribute to its effects on longevity. There are a number of reasons for believing that this will be the case. S6K1 ablation produces very different changes in physiology and does not extend life in males, whereas rapamycin does. Moreover, the mTORC2 homolog regulates longevity in worms, and our demonstration that rapamycin disrupts mTORC2 in mice therefore provides a candidate mechanism for S6K1-independent effects. Finally, we will explore the tissue-specific consequences of mTORC2 disruption. Loss of mTORC2 in the liver appears to mediate detrimental effects of rapamycin on insulin sensitivity, and ameliorating these effects could lead to complementary approaches to improve the safety and efficacy of the drug. On the other hand, loss of another insulin signaling molecule, IRS2, in the brain has previously been shown to extend life, and loss of neuronal mTORC2 might therefore contribute to the beneficial effect of rapamycin on lifespan. Elucidating the mechanisms by which rapamycin is able to prevent or slow progression of age-related diseases and extend the maximum survival time in mice will offer important insights, and likely new therapeutic targets, in the effort to promote healthy human aging.