Powering the Brain: Understanding how Astrocytes Contribute to Energy Maintenance

大脑是人体内能量最昂贵的器官。为了提供足够的能量，神经元和神经胶质细胞利用线粒体的氧化磷酸化来产生细胞生理所需的高达90%的ATP。值得注意的是，星形胶质细胞是一种围绕神经元的高度专业化的胶质细胞，约占大脑产生的ATP的75%。星形胶质细胞产生的强大的ATP支持耗能的过程，包括细胞外离子维持、神经递质动态平衡和脑血管系统的能量底物运输。尽管星形胶质细胞产生能量的重要性已为人所知，但在体内这一过程的基本方面仍然不清楚。需要进一步的研究来解决这些细胞如何创造、储存和分配能量，以维持大脑中细胞的结构和生理完整性。在这个发现研究计划中，我们将使用先进的体内基因传递方法结合最先进的成像、分子和电生理学方法来研究星形胶质细胞线粒体的基本特性。在目标1中，我们将使用先进的方法来表征线粒体的大小、形状和在星形胶质细胞及其细胞间隔(即胞体、远端突起和末端足部)中的分布，使用尖端的光学和电子显微镜方法。初步结果表明，原位星形胶质细胞内存在复杂的线粒体结构。拟议的实验结果将首次描述大脑中单个星形胶质细胞内线粒体的三维组织。*在目标2中，我们将使用实时成像方法原位监测线粒体在星形胶质细胞中的运输，并确定星形胶质细胞中的神经活动和细胞内钙动力学如何与线粒体运输、分裂/融合事件和局部招募到特定的隔室有关。初步结果表明，星形胶质细胞的线粒体在高钙动力学区域得到了丰富。双光子成像将被用来监测完整的小鼠大脑中的这些过程。*在目标3中，我们将识别星形胶质细胞中的线粒体运输成分。我们首先将重点放在星形胶质细胞中帮助靶向神经元线粒体的运输蛋白运动蛋白结合1(TRAK1)和2(TRAK2)蛋白。初步结果表明，在星形胶质细胞中线粒体靶向使用了特定的机制。我们将确定星形胶质细胞线粒体运输的扰动如何影响它们的解剖和分子特征，以及邻近神经元的生理学。*这项拨款将创造一个新的水平，理解星形胶质细胞控制大脑内能量传递的机制。此外，它将为对了解大脑功能和动态平衡的基本方面感兴趣的各级受训人员提供出色的概念和技术培训。

The brain is the most energy expensive organ in the human body. To provide sufficient energy, neurons and glial cells harness oxidative phosphorylation in mitochondria to produce up to 90% of ATP required for cellular physiology. Remarkably, astrocytes, a highly specialized glial cell surrounding neurons, account for approximately 75% of ATP produced in the brain. The robust ATP production by astrocytes supports energy-consuming processing including extracellular ion maintenance, neurotransmitter homeostasis, and energy substrate transport from cerebrovasculature. Despite the known importance of energy production by astrocytes, fundamental aspects of this process in vivo remain unclear. Further investigation is need to resolve how these cells create, store, and distribute energy to maintain the structural and physiological integrity of cells in the brain. In this Discovery Research Program, we will study fundamental properties of astrocyte mitochondria using advanced in vivo gene delivery methods combined with cutting-edge imaging, molecular, and electrophysiology approaches.******In Aim 1, we will use advanced methods to characterize mitochondria size, shape, and distribution in astrocytes and their cellular compartments (i.e. soma, distal processes, and endfeet) using cutting-edge light and electron microscopy approaches. Preliminary results indicate a complex organization of mitochondria in astrocytes in situ. Results from the proposed experiments will describe for the first time the 3-dimensional organization of mitochondria within individual astrocytes in the brain.******In Aim 2, we will use live imaging approaches to monitor mitochondrial trafficking in astrocytes in situ and determine how neural activity and intracellular calcium dynamics in astrocytes relates to mitochondrial transport, fission/fusion events, and local recruitment to specific compartments. Preliminary results suggest that mitochondria are enriched at areas of high calcium dynamics in astrocytes. 2-photon imaging will be used to monitor these processes in the intact mouse brain.******In Aim 3, we will identify mitochondrial trafficking components in astrocytes. We will initially focus on the trafficking protein kinesin binding 1 (TRAK1) and 2 (TRAK2) proteins in astrocytes that help target mitochondria in neurons. Preliminary results indicate specific mechanisms are used for mitochondrial targeting in astrocytes. We will determine how perturbation of mitochondrial trafficking in astrocytes impacts their anatomy and molecular features, as well as, the physiology of neighboring neurons.******This grant will create a new level of understanding of astrocyte mechanisms that control energy delivery within the brain. Moreover, it will provide excellent conceptual and technical training for trainees at all levels interested in understanding fundamental aspects of brain function and homeostasis.