Powering the Brain: Understanding how Astrocytes Contribute to Energy Maintenance

大脑是人体中消耗能量最多的器官。为了提供足够的能量，神经元和神经胶质细胞利用线粒体中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高度特化的神经胶质细胞，围绕在神经元周围，约占大脑中产生的ATP的75%。星形胶质细胞强大的ATP生成支持能量消耗过程，包括细胞外离子维持、神经递质稳态和来自脑血管的能量底物运输。尽管已知星形胶质细胞产生能量的重要性，但这一过程在体内的基本方面仍不清楚。需要进一步研究这些细胞如何产生、储存和分配能量，以维持大脑细胞的结构和生理完整性。在这个发现研究项目中，我们将使用先进的体内基因传递方法，结合尖端的成像、分子和电生理学方法，研究星形胶质细胞线粒体的基本特性。******在Aim 1中，我们将使用先进的方法来表征星形胶质细胞及其细胞室（即体细胞，远端突和终足）中线粒体的大小，形状和分布。初步结果表明星形胶质细胞内存在复杂的线粒体组织。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星形胶质细胞中的线粒体运输，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、裂变/融合事件和特定室的局部招募相关。初步结果表明，线粒体在星形胶质细胞高钙动态区富集。双光子成像将用于监测完整小鼠大脑中的这些过程。******在aims 3中，我们将识别星形胶质细胞中的线粒体运输成分。我们将首先关注星形胶质细胞中的转运蛋白激酶结合1 （TRAK1）和2 （TRAK2）蛋白，这些蛋白有助于靶向神经元中的线粒体。初步结果表明，星形胶质细胞的线粒体靶向具有特定的机制。我们将确定星形胶质细胞中线粒体运输的扰动如何影响其解剖和分子特征，以及邻近神经元的生理。******这项资助将使人们对星形胶质细胞控制大脑内能量传递的机制的理解达到一个新的水平。此外，它将为有兴趣了解脑功能和体内平衡基本方面的各级受训者提供优秀的概念和技术培训。

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.