The impact of dynamic actin polymerization on mitochondrial dynamics and function

“肌动蛋白细胞骨架”不是一个结构，而是许多不同的结构组装和拆卸， 不同的目的在哺乳动物细胞中，一些丰富且易于识别的结构占据了我们的视野 肌动蛋白细胞骨架的结构，包括：应力纤维，板状伪足和丝状伪足。然而，越来越多的 已经揭示了丰富的和/或高度瞬时的肌动蛋白基结构，控制着重要的细胞 流程.两种这样的肌动蛋白结构是本申请的主题：1）CIA，钙诱导的肌动蛋白;和2） ADA，急性去极化诱导肌动蛋白。虽然高度短暂，但这两种结构在胞质溶胶中广泛存在 并影响重要的过程。此外，CIA和ADA都影响线粒体的结构和功能。 CIA依赖于钙激活的α蛋白INF 2，它刺激肌动蛋白聚合在细胞膜上。 内质网和整个胞质溶胶。CIA的下游影响包括增加线粒体 钙和线粒体分裂增加。CIA的重要性是由INF 2突变的事实说明， 与两种疾病有关，即局灶节段性肾小球硬化症（FSGS）和腓骨肌萎缩症（CMTD）。 ADA由线粒体去极化（药理学诱导或缺氧诱导）触发， 激活两条平行的途径：1）线粒体钙释放激活蛋白激酶C-κ B，依次激活 Rac、WAVE复合物和Arp 2/3复合物; 2）ATP减少激活AMP依赖性蛋白激酶 （AMPK）通过LKB 1，依次激活Cdc 42和FMNL formins。ADA肌动蛋白网络与 与线粒体。一个令人兴奋的新结果是，ADA的一个直接后果是快速刺激 糖酵解此外，ADA暂时抑制线粒体去极化的长期后果， 线粒体重组和线粒体自噬蛋白帕金的募集。本资助期内的目标 阐明CIA和ADA的触发机制及其下游效应。这些目标 将使用细胞方法（活细胞显微镜，蛋白质组学，代谢 分析）和生物化学方法（无细胞重建，在模型脂质上分析纯化的蛋白质 膜）。要问的问题包括以下几个方面。1)INF 2是如何通过增加钙激活的？ 2)肌球蛋白II和肌成束蛋白是如何将INF 2聚合的纤维组织成网络的？3)中情局是怎么 与已知的线粒体分裂蛋白如Mff和Drp 1的接口来刺激分裂？4)PKC如何 和AMPK激活Rac和Cdc 42，分别在ADA？5)Arp 2/3复合物和FMNL是如何形成蛋白的 在ADA期间一起工作6)ADA如何刺激糖酵解？这些问题涉及基本的 机械问题的重要性，广泛的哺乳动物细胞，并占据了令人兴奋的前沿之间 细胞骨架生物学、线粒体生物学和代谢。 1

The ‘actin cytoskeleton’ is not one structure but a number of distinct structures assembled and disassembled for different purposes. In mammalian cells, a few abundant and easily recognizable structures dominate our view of the actin cytoskeleton, including: stress fibers, lamellipodia and filopodia. However, a growing number of less abundant and/or highly transient actin-based structures have been revealed, controlling important cellular processes. Two such actin structures are the subject of this application: 1) CIA, calcium-induced actin; and 2) ADA, acute depolarization-induced actin. Though highly transient, both structures are extensive in the cytosol and affect important processes. In addition, both CIA and ADA impact the structure and function of mitochondria. CIA depends on calcium activation of the formin protein INF2, which stimulates actin polymerization on the endoplasmic reticulum and throughout the cytosol. Downstream effects of CIA include increased mitochondrial calcium and increased mitochondrial fission. The importance of CIA is illustrated by the fact that INF2 mutations link to two diseases, focal segmental glomerulosclerosis (FSGS) and Charcot-Marie-Tooth disease (CMTD). ADA is triggered by mitochondrial depolarization (either pharmacologically-induced or hypoxia-induced), which activates two parallel pathways: 1) mitochondrial calcium release activates protein kinase C-, activating in turn Rac, WAVE complex, and Arp2/3 complex; and 2) decreased ATP activates AMP-dependent protein kinase (AMPK) through LKB1, activating in turn Cdc42 and FMNL formins. The ADA actin network is tightly associated with mitochondria. An exciting new result is that one immediate consequence of ADA is rapid stimulation of glycolysis. Additionally, ADA temporarily inhibits longer-term consequences of mitochondrial depolarization such as mitochondrial reorganization and recruitment of the mitophagy protein Parkin. The goals in this grant period are to elucidate both the mechanisms triggering CIA and ADA, as well as their downstream effects. These goals will be accomplished using a combination of cellular approaches (live-cell microscopy, proteomics, metabolic analysis) and biochemical approaches (cell-free reconstitution, analysis of purified proteins on model lipid membranes). The questions to be asked include the following. 1) How is INF2 activated by increased calcium? 2) How are INF2-polymerized filaments organized into a network by myosin II and fascin? 3) How does CIA interface with known mitochondrial fission proteins such as Mff and Drp1 to stimulate fission? 4) How do PKC and AMPK activate Rac and Cdc42, respectively, during ADA? 5) How do Arp2/3 complex and FMNL formins work together during ADA? 6) How does ADA stimulate glycolysis? These questions address fundamental mechanistic questions important to a wide range of mammalian cells, and occupy an exciting frontier between cytoskeletal biology, mitochondrial biology, and metabolism. 1