Metabolic regulation by p66Shc determines stem cell fate and neuronal survival

哺乳动物细胞使用称为线粒体的特殊细胞器来分解营养物质，并在一个依赖于氧气存在的过程中产生高水平的ATP，这是一种化学形式的能量。然而，氧自由基是线粒体代谢过程中产生的潜在有害副产物。在衰老过程中，哺乳动物经常表现出氧自由基的产生增加，或解毒能力下降，特别是在被称为神经元的特殊脑细胞中。由于其高代谢状态，神经元特别容易受到线粒体产生的氧自由基的影响。因此，大脑中的神经元必须能够建立足够的抗氧化防御，以维持一个人的一生。或者，为了补充神经细胞的死亡，成年干细胞可以在一个称为分化的过程中产生功能神经元。对干细胞分化的精确调控和神经元的抗氧化防御，对于终生维持大脑功能至关重要。最近的研究表明，在暴露于某种形式的压力后，一种名为p66Shc的独特信号蛋白可以从细胞液(细胞的主要液体部分)移动到线粒体。一旦进入线粒体，p66Shc就会触发氧自由基的增加，从而促进一系列结果，包括神经元分化或细胞死亡。然而，p66Shc控制这些细胞过程的确切机制还知之甚少。我的实验室最近的研究表明，p66Shc可以作为一个开关，关闭糖酵解，而开启线粒体代谢。糖酵解是一种不产生氧自由基的代谢形式。此外，p66Shc还抑制一种名为Nrf2的关键蛋白的激活，Nrf2是表达抗氧化基因所必需的。利用培养的小鼠胚胎干细胞和神经元样细胞，我们将探索p66Shc诱导的线粒体代谢和氧自由基产生影响干细胞分化能力的假设，并形成神经元以安装适当的抗氧化反应。此外，我们还将确定p66Shc诱导的氧自由基产生时发生氧化修饰的特定蛋白质的类型。作为一个长期目标，我们还将在成年脑干细胞或神经元中产生p66Shc基因缺失的小鼠。这项拟议的研究结果将为控制干细胞分化的分子机制以及神经元如何对压力做出反应提供新的见解；这些事件对于一生中最佳的大脑功能至关重要。

Mammalian cells used specialized organelles called mitochondria to break down nutrients and generate high levels of ATP, a chemical form of energy, in a process dependent on the presence of oxygen. However, oxygen radicals are potentially harmful by-products that arise during mitochondrial metabolism. During the aging process, mammals frequently exhibit increased production of oxygen radicals, or the decreased ability to detoxify them, particularly in specialized brain cells called neurons. Due to their high metabolic state, neurons are particularly vulnerable to mitochondrial generated oxygen radicals. Thus, neurons in the brain must be able to mount a sufficient antioxidant defense to maintain survival throughout one's lifespan. Alternatively, to replenish neuron cell death, adult stem cells can give rise to functional neurons, in a process called differentiation. The precise regulation of stem cell differentiation, and antioxidant defense in neurons, is critical to maintain brain function throughout life. Recent studies have shown that a unique signaling protein called p66Shc can move from the cytosol, the main fluid containing portion of a cell, into mitochondria following exposure to certain forms of stress. Once in the mitochondria, p66Shc triggers increased oxygen radical formation that can then promote a variety of outcomes, including neuronal differentiation or cell death. However, the precise mechanism by which p66Shc controls these cellular processes is poorly understood. Recent studies in my lab have revealed that p66Shc can act as a "switch" which turns off glycolysis, a form of metabolism that does not generate oxygen radicals, while turning on mitochondrial metabolism. In addition, p66Shc also suppresses the activation of a key protein called Nrf2 that is required for expression of antioxidant genes. Using both cultured mouse embryonic stem cells and neuron-like cells, we will explore the hypothesis that p66Shc induced mitochondrial metabolism and oxygen radical production affects the ability of stem cells to differentiate, and form neurons to mount an appropriate antioxidant response. In addition, we will identify the types of specific proteins that become oxidatively modified in response to p66Shc induced oxygen radical production. As a long-term goal, we will also generate mice in which the p66Shc gene is deleted in either adult brain stem cells or neurons. The results of the proposed study will provide novel insight into the molecular mechanisms controlling stem cell differentiation and how neurons respond to stress; events critical for optimal brain function throughout life.