Effects of aging on stem cell function through systemic signals and mTOR

我的主要抱负是作为一名独立研究员研究新陈代谢和衰老之间的关系。我对新陈代谢的兴趣始于我在大学里上的代谢途径课程，在研究生院开始学习有关卡路里限制和延长寿命的文献时，我的兴趣得到了巩固。对卡路里限制的了解让我思考细胞和身体作为一个整体是如何对全身能量水平做出反应的。正因为如此，我决定把我在约翰·霍普金斯医学院的研究生工作集中在研究全身营养通量是如何被细胞感知并在新陈代谢的调节中起作用的。出于对细胞如何对外界信号做出反应的同样兴趣，我在哈佛医学院/DFCI的博士后工作重点是研究激素信号转导的动力学。为了扩大我科学培训的深度和广度，我决定与斯坦福医学院的托马斯·兰多博士合作，在衰老和干细胞生物学领域获得进一步的专业知识。兰多博士和我都有一个共同的观点，那就是在很多方面，衰老可以被认为是一种系统性疾病。像代谢性疾病一样，衰老的许多方面，如果不是大多数方面，可能是由于细胞对改变和功能失调的系统环境的反应。了解衰老的系统环境以及细胞如何对这种环境做出反应，可能会产生改善或预防许多衰老病理的治疗方法。将我在新陈代谢和信号传递方面的专业知识与我在与兰多博士合作期间开发的衰老研究和干细胞生物学方面的技能结合在一起，使我处于一个独特的位置，能够研究衰老如何以前所未有的方式影响干细胞、组织和机体功能。众所周知，随着年龄的增长，组织的动态平衡会下降。成体干细胞的主要功能是通过提供细胞和遗传物质来维持组织的动态平衡，以确保适当的组织功能。然而，随着年龄的增长，干细胞功能的下降是与年龄相关的组织功能障碍的一个主要因素。在这里，我们将使用成人肌肉干细胞(卫星细胞)作为模型来研究干细胞如何应对衰老。这一建议的基础是基于我们的观察，来自老年动物的卫星细胞具有mTORC1信号的异常诱导。MTORC1信号复合体是细胞对外界代谢和激素信号反应的主要中介，被广泛认为是衰老和寿命的一个因素。因此，我们在这个提议中有两个主要目标：1)了解mTORC1信号在卫星细胞中的功能作用；2)确定导致老年动物卫星细胞mTORC1活性异常的上游信号。利用卫星细胞特有的遗传模型来调节mTORC1的活性，我们的初步数据显示，mTORC1的诱导足以概括一系列与年龄相关的卫星细胞功能变化：数量减少，自我更新丧失，肌肉再生能力降低。此外，我们还发现，HGF，一种已知在衰老过程中升高的血清激素，足以在静止的卫星细胞中诱导mTORC1活性。这些数据表明，在衰老过程中，系统性因素HGF会导致卫星细胞mTORC1活动的慢性诱导，从而导致与年龄相关的功能下降。在这项提议中，我们将通过使用遗传学和药理学方法来测试他的模型，以抑制卫星细胞中的mTORC1和HGF信号，以防止与年龄相关的卫星细胞功能障碍。这项工作的意义将是识别参与衰老对干细胞功能影响的新途径及其作用的分子机制，为我未来在独立职业生涯中的工作提供基础。这项建议的长期目标包括针对mTORC1或HGF的简单饮食或药物干预的治疗性使用，以纠正干细胞功能障碍和改善与年龄相关的组织病理。这项提议的目标将得到兰多博士提供的环境和指导的大力帮助。作为斯坦福大学格伦老龄化研究基金会的一部分，兰多实验室与安妮·布鲁内特博士和史蒂夫·阿坦迪博士一起为衰老和干细胞研究培养了一个富有成效和创造性的环境。我聘请了巴克老龄化研究所的布莱恩·肯尼迪博士作为共同导师，阿文德·拉马纳坦博士作为合作者，感谢他们在与衰老相关的新陈代谢和TOR信号领域的指导和专业知识。这里提出的工作将给我提供资源和机会，以进一步发展我的研究战略和目标，以顺利过渡到独立的职业生涯。这将得到兰多和肯尼迪博士的指导，他们将在作为独立调查员的后勤、哲学和伦理问题上指导我。此外，兰多博士和肯尼迪博士将利用他们庞大的学术网络帮助我确定合适的教职空缺，并就如何选择最好的研究所/环境开始我的独立研究生涯向我提供建议。

My driving ambition is to study the relationship between metabolism and aging as an independent investigator. My interest in metabolism started with the metabolic pathways courses I took in college and was cemented in graduate school when I began to study the literature on calorie restriction and life span extension. Learning about calorie restriction made me think about how cells and the body as a whole respond to systemic energy levels. Because of this I decided to concentrate my graduate work at Johns Hopkins School of Medicine on studying how systemic nutrient fluxes are sensed by cells and act in regulation of metabolism. Following this same interest on how cells respond to external signals, I concentrated my postdoctoral work at Harvard Medical School/DFCI on studying the dynamics of hormonal signal transduction. To expand the depth and breadth of my scientific training I have decided to work with Dr. Thomas Rando at Stanford Medical School to gain further expertise in the fields of aging and stem cell biology. Dr. Rando and I share a common view that in many ways aging can be thought of as a systemic condition. Like metabolic diseases, many, if not most aspects of aging may be due to the cellular response to an altered and dysfunctional systemic environment. Understanding the aged systemic environment and how cells respond to this environment will likely yield treatments to ameliorate or prevent many pathologies of aging. Combining my expertise in metabolism and signaling with the skills in aging research and stem cell biology I am developing while working with Dr. Rando puts me in a unique position to be able to study how aging impacts stem cell, tissue, and organismal function in ways that have not been done before. It is well known that with aging there is a decline in tissue homeostasis. The primary function of adult stem cells is to maintain tissue homeostasis by providing the cellular and genetic material that ensures proper tissue function. However, decline in stem cell function with aging is a major contributing factor in age-related tissue dysfunction. Here, we will use adult muscle stem cells (satellite cells) as a model to study how stem cells respond to aging. The foundation of this proposal is based on our observation that satellite cells from aged animals have an aberrant induction of mTORC1 signaling. The mTORC1 signaling complex is a major mediator of the cellular response to external metabolic and hormonal signals and has been widely implicated as a factor in aging and life span. Therefore, we have two major goals in this proposal: 1) to understand the functional role of mTORC1 signaling in satellite cells and 2) to identify the upstream signals which contribute to aberrant mTORC1 activity in satellite cells from aged animals. Using satellite cell specific genetic models to modulate mTORC1 activity our preliminary data show that induction of mTORC1 is sufficient to recapitulate a host of the age-associated satellite cell functional changes: decline in number, loss of self-renewal, and reduced capacity for muscle regeneration. Additionally, we have found that HGF, a serum hormone known to be elevated in aging, is sufficient to induce mTORC1 activity in quiescent satellite cells. These data suggest a model where in aging, systemic factors, HGF, lead to chronic induction of mTORC1 activity in satellite cells which contributes to age related functional decline. In this proposal we will test his model by using genetic and pharmacologic approaches to suppress mTORC1 and HGF signaling in satellite cells to prevent age-related satellite cell dysfunction. The implications ofthis work will be the identification of novel pathways involved in the effects of aging on stem cell function and the molecular mechanisms by which they act, providing a basis for future work in my independent career. Long term goals of this proposal include the therapeutic use of simple dietary or pharmacologic interventions targeting mTORC1 or HGF to correct stem cell dysfunction and ameliorate age related tissue pathologies. The goals of this proposal will be strongly aided by the environment and mentorship provided by Dr. Rando. The Rando lab as part of the Glenn Foundation for Aging Research at Stanford with Drs. Anne Brunet and Steve Artandi cultivate a productive and creative environment for aging and stem cell research. I have enlisted Dr. Brian Kennedy of The Buck Institute for Research on Aging as a co-mentor and Dr. Arvind Ramanathan as a collaborator for their guidance and expertise in the fields of metabolism and TOR signaling as they relate to aging. The work proposed here will give me the resources and opportunity to further develop my research strategy and goals for a smooth transition into an independent career. This will be facilitated by the mentorship of Drs. Rando and Kennedy who will guide me on the logistical, philosophical, and ethical issues of being an independent investigator. Additionally, Drs. Rando and Kennedy will support this transition by using their large network in academic science to help me identify appropriate faculty position openings and will advise me with decisions on how to choose the best institute/environment to start my independent research career.