Regulation of Mitochondrial Fission and Fusion

神经遗传学分支细胞生物学部分的研究重点是一些神经退行性疾病的分子机制，包括线粒体疾病，帕金森病，周围神经病和遗传性痉挛性截瘫（HSP）。 这些疾病共同折磨着数百万美国人，在数年内不知不觉地恶化，其中绝大多数人的治疗选择有限。 我们的实验室正在研究这些疾病的遗传形式，使用分子和细胞生物学方法来研究疾病基因的突变如何最终导致细胞功能障碍。 在这个项目中，我们强调研究细胞内线粒体形态的调节。事实上，调节线粒体形态的融合和裂变事件对于适当的线粒体功能是必不可少的，并且它们的调节在多种细胞功能中越来越多地被认识到。 哺乳动物的线粒体分裂事件由至少两种蛋白质协调：动力蛋白相关蛋白Drp 1和膜整合蛋白Fis 1。 线粒体融合的相互过程也需要发动蛋白超家族的大GTP酶：OPA 1和线粒体融合蛋白Mfn 1和Mfn 2。 由于在遗传性神经系统疾病患者中发现了Drp 1、Mfn 2和OPA 1的突变，并且在程序性细胞死亡过程中存在线粒体的显著片段化，因此对这些过程的调控的了解在临床上具有高度相关性。 在过去，我们发表了一项关于Drp 1 A395 D突变的研究，该突变由于线粒体分裂明显减少而导致了致命的线粒体疾病。 在这个项目中，我们能够证明这种突变导致Drp 1蛋白的高阶多聚体相互作用的丧失。在补充研究中，我们现在已经确定了Drp 1中的突变，这些突变显着稳定了高阶Drp 1结构。最后，在与一些合作者正在进行的研究中，我们已经确定了一些Drp 1相互作用的蛋白质，这些蛋白质可能参与细胞内线粒体的正确分布，以及通过未知机制调节线粒体分裂/融合平衡的新蛋白质。我们将继续评估患有这些类型疾病的患者，这些研究将刺激更多的机制研究。 最近，我们一直专注于线粒体动力学和功能在某些形式的遗传性痉挛性截瘫，特别是SPG 11，SPG 15和SPG 48。2018年，我们与Xuo-Jun Li博士合作在Human Molecular Genetics上发表了一项研究，表明诱导多能干细胞（iPSC）衍生的神经元在轴突内的线粒体结构和功能方面存在损伤，可以通过抑制线粒体分裂来抑制。此外，我们已经与Richard Wade-Martins博士启动了一个新项目，研究遗传形式帕金森病患者iPSCs中的线粒体功能，该项目的工作将很快提交出版。 最后，我们最近完成并发表了一项与Chuang-Rung Chang博士的研究，确定了线粒体分裂GTd 1/Drp 1和肌动蛋白调节蛋白Srv 2/CAP在酵母线粒体中的相互作用。Srv 2的缺失导致线粒体延长-超灌注，并降低酵母细胞中保留的呼吸能力。我们的研究结果进一步证明srv 2细胞中不规则的网络形态来自于线粒体上肌动蛋白组装的破坏。我们认为，Srv 2功能作为一个促分裂因子在塑造线粒体动力学和调节活动，通过其肌动蛋白调节作用。最后，我们最近完成并提交了一项研究，该研究的重点是毫无头绪的蛋白质在将Drp 1招募到线粒体中的作用。 总之，这些研究继续为神经元内线粒体形态的调节提供重要见解，这是一个具有明确临床相关性和重要性的领域。

Research in the Cell Biology Section, Neurogenetics Branch focuses on the molecular mechanisms underlying a number of neurodegenerative disorders, including mitochondrial disorders, Parkinson disease, peripheral neuropathies, and the hereditary spastic paraplegias (HSPs). These disorders, which together afflict millions of Americans, worsen insidiously over a number of years, and treatment options are limited for the vast majority of them. Our laboratory is investigating inherited forms of these disorders, using molecular and cell biology approaches to study how mutations in disease genes ultimately result in cellular dysfunction. In this project, we are emphasizing investigations into the regulation of mitochondrial morphology within cells. Indeed, fusion and fission events that regulate mitochondrial morphology are essential for proper mitochondrial function, and their regulation is increasingly recognized in diverse cellular functions. Mitochondrial fission events in mammals are orchestrated by at least two proteins; the dynamin-related protein Drp1 and the integral membrane protein Fis1. The reciprocal process of mitochondrial fusion also requires large GTPases of the dynamin superfamily: OPA1 and the mitofusins Mfn1 and Mfn2. Since mutations in Drp1, Mfn2, and OPA1 have been identified in patients with inherited neurological disorders, and there is prominent fragmentation of mitochondria during programmed cell death, insights into the regulation of these processes is highly relevant clinically. In the past, we published a study of the Drp1 A395D mutation that caused a neonatally fatal mitochondrial disorder due to markedly diminished mitochondrial fission. In this project, we were able to show that this mutation resulted in loss of higher-order multimeric interactions of the Drp1 protein. In complementary studies, we have now identified mutations in Drp1 that dramatically stabilizes higher-order Drp1 structures. Lastly, in ongoing studies with a number of collaborators we have identified a number of Drp1-interacting proteins that may be involved in the proper distribution of mitochondria within cells as well as novel proteins that regulate the mitochondrial fission/fusion balance through unknown mechanisms. We continue to evaluate patients with these types of disorders, and these studies will spur additional mechanistic investigations. More recently, we have been focusing our efforts on mitochondrial dynamics and function in certain forms of hereditary spastic paraplegia, most notably SPG11, SPG15 and SPG48. In 2018, we published a study in Human Molecular Genetics in collaboration with Dr. Xue-Jun Li, showing that induced pluripotent stem cell (iPSC)-derived neurons have impairments in mitochondrial structure and function within axons that can be suppressed by inhibition of mitochondrial fission. Also, we have initiated a new project with Dr. Richard Wade-Martins investigating mitochondrial function in iPSCs from patients with genetic forms of Parkinson disease, and work on this project will be submitted for publication shortly. Finally, we have recently completed and published a study with Dr. Chuang-Rung Chang identifying an interaction between the mitochondrial fission GTPase Dnm1/Drp1 and the actin-regulatory protein Srv2/CAP at mitochondria in yeast. Deletion of Srv2 causes elongated-hyperfused mitochondria and reduces the reserved respiration capacity in yeast cells. Our results further demonstrate that the irregular network morphology in srv2 cells derives from disrupted actin assembly at mitochondria. We suggest that Srv2 functions as a pro-fission factor in shaping mitochondrial dynamics and regulating activity through its actin-regulatory effects. Finally, we have very recently completed and submitted a study for publication that focuses on the role of the clueless protein in recruiting Drp1 to mitochondria. Together, these studies are continuing to provide critical insights into the regulation of mitochondrial morphology within neurons, an area of clear clinical relevance and importance.