Molecular Mechanisms of Organelle-based Metabolic Signaling

摘要 细胞感知营养的分子机制在很大程度上仍然未知，但它们的 阐明是我们理解正常和疾病状态下代谢调节的关键。中心 营养传感和生长调节的关键是一种古老的蛋白激酶，被称为营养传感和生长调节的机制靶点。 雷帕霉素复合物1（mTORC 1）。为了响应营养素等代谢输入的联合作用， 生长因子、能量和氧，mTORC 1从细胞质易位到溶酶体表面， 在那里它被激活。越来越多的证据表明，在溶酶体中异常的mTORC 1激活 可能是从癌症到2型糖尿病再到神经退行性疾病的驱动力。因此， 对mTORC1如何被激活，然后在对营养素的反应中失活的机制的理解可能指向 在这些疾病中找到新的治疗策略。我的实验室为 了解mTORC1通路组织，以及其功能如何与许多活动整合， 溶酶体特别是，我们已经确定了一个专门的信号通路，通过该通路，胆固醇，一个重要的 细胞膜的构建块，促进mTORC 1募集到溶酶体并激活其 下游方案。我们发现了溶酶体和内质网之间的膜接触点， 内质网是胆固醇激活mTORC 1的关键节点，因此涉及细胞器间 通信作为mTORC1调节的重要方面。此外，我们发现过量的mTORC1 由胆固醇在溶酶体中积累引起的信号传导，驱动细胞功能障碍， 力的神经退行性和代谢性疾病，尼曼-匹克C型（NPC）。 这些发现直接导致了细胞营养感测组织的深层问题， 是当前MIRA提案的核心一个关键的挑战是阐明机制和生理 脂质依赖性mTORC1调节的作用，特别是是否存在专门的胆固醇传感器， 溶酶体膜，以及它们如何将甾醇分子的丰度与mTORC 1激活和 在细胞和生物体水平的总体代谢调节。基于我们的发现， mTORC1涉及溶酶体和ER之间的物理通信，这是mTORC1的另一个主要目标。 建议是描绘介导通信和代谢物交换的机制， 溶酶体和ER，以及这种机制如何参与mTORC1的调节以及另一个主要的 代谢激酶蛋白激酶A。最后，mTORC1在鼻咽癌中的致病作用， mTORC1抑制恢复NPC细胞功能的几个参数，强烈支持mTORC1作为一个主要的 靶向神经退行性疾病。因此，我们将确定溶酶体mTORC1如何控制神经元细胞 稳态，以及失调的mTORC1信号传导如何导致神经元变性。所有这些 研究将阐明健康和疾病状态下代谢组织的基本原理。

ABSTRACT The molecular mechanisms through which cells sense nutrients remain largely unknown, but their elucidation is key to our understanding of metabolic regulation both in normal and disease states. At the center of nutrient sensing and growth regulation is an ancient protein kinase known as the mechanistic Target of Rapamycin Complex 1 (mTORC1). In response to the combined action of metabolic inputs such as nutrients, growth factors, energy and oxygen, mTORC1 translocates from the cytoplasm to the surface of lysosomes, where it becomes activated. Accumulating evidence indicates that aberrant mTORC1 activation at the lysosome could be a driving force in diseases ranging from cancer to type-2 diabetes to neurodegeneration. Thus, a deep mechanistic understanding of how mTORC1 is activated and then inactivated in response to nutrients could point the way to novel therapeutic strategies in these diseases. My lab has made important contributions to the understanding of mTORC1 pathway organization, and how its function is integrated with the many activities of the lysosome. In particular, we have identified a dedicated signaling pathway via which cholesterol, an important building block for cellular membranes, promotes mTORC1 recruitment to the lysosome and activation of its downstream programs. We have uncovered membrane contact sites between lysosomes and the endoplasmic reticulum as key nodes where mTORC1 activation by cholesterol occurs, thus implicating inter-organelle communication as an important aspect of mTORC1 regulation. Furthermore, we found that excess mTORC1 signaling, caused by cholesterol accumulation in the lysosome, drives cellular dysfunction and could be a driving force in a neurodegenerative and metabolic disease, Niemann-Pick type C (NPC). These discoveries directly lead to deep questions on the organization of cellular nutrient sensing, which are at the core of the current MIRA proposal. One key challenge is to elucidate the mechanisms and physiological roles of lipid-dependent mTORC1 regulation, specifically whether dedicated cholesterol sensors exist in the lysosomal membrane, and how they couple the abundance of sterol molecules to mTORC1 activation and to overall metabolic regulation at the cell and organism level. Based on our finding that cholesterol sensing by mTORC1 involves physical communication between the lysosome and the ER, another major goal of the proposal is to delineate the machinery that mediates communication and metabolite exchange between the lysosome and the ER, and how this machinery participates in regulation of mTORC1 as well as another major metabolic kinase, protein kinase A. Finally, the pathogenic role of dysregulated mTORC1 in NPC, and the ability of mTORC1 inhibition to restore several parameters of NPC cell function, strongly support mTORC1 as a prime target in neurodegenerative disease. We will thus determine how lysosomal mTORC1 controls neuronal cell homeostasis, and how dysregulated mTORC1 signaling contributes to neuronal degeneration. Together, these studies will shed light on fundamental principles of metabolic organization in health and disease states.