Dysregulation of RNA processing as a driver of motor neuron dysfunction in Amyotrophic Lateral Sclerosis

肌萎缩性侧索硬化症（ALS）（也称为运动神经元疾病）是由运动神经或神经元的丧失引起的。这些运动神经将来自大脑和脊髓的信号传递到周围肌肉，从而实现日常运动。这些患者的运动神经丧失导致进行性肌肉麻痹，并最终因允许我们呼吸的肌肉衰竭而死亡。大约10-15%的ALS病例有家族史，已知几个具有不同功能的基因的特定缺陷（称为突变）会导致ALS。然而，驱动运动神经元丧失的过程尚不清楚。虽然肌萎缩侧索硬化症的病因尚不清楚，但这些患者受影响的许多神经都表现出一个共同的特征。这种特征涉及到一种叫做TDP43的蛋白质从细胞核内部错误地迁移到细胞质外部。细胞核是细胞的指挥中心，它包含了我们的DNA，以及如何制造不同蛋白质的特定指令，蛋白质是细胞中的主力。细胞质是细胞内的凝胶状液体，含有细胞核并具有制造蛋白质的机制。每个细胞核和细胞质都有明确的作用，这些作用取决于特定蛋白质的精确可用性。因此，蛋白质位置的任何变化都会干扰神经细胞的正常活动，导致它们死亡。TDP43蛋白从细胞核到细胞质的重新定位，也称为错位，扰乱了神经细胞的正常功能，导致它们死亡。我们已经开发了一种新的方法，在培养皿中触发人类神经细胞中TDP43蛋白的错误定位。这将使我们能够详细地研究这种迁移的后果。随着一种被称为重编程的新干细胞技术的出现，来自患者的皮肤或血细胞可以转化为胚胎状态。这些重新编程的细胞被称为诱导多能干细胞（iPSC），有可能转化为体内任何类型的细胞。因此，来自肌萎缩侧索硬化症患者的iPSC现在可以被诱导成运动神经，也就是说，与肌萎缩侧索硬化症患者丢失的细胞相同。这项技术可以在培养皿中培育ALS的人体模型，使科学家能够探究这些细胞中出现的问题，从而导致ALS患者死亡。利用这些模型，我们发现神经细胞存活所需的重要分子过程RNA剪接在ALS中存在缺陷。利用RNA剪接的过程，神经细胞产生了正常功能所需的许多不同类型的蛋白质。错误地执行这个过程会导致产生无效的蛋白质，这可能导致神经细胞的结构和功能出现问题。在本课题中，我们将利用iPSC技术生成运动神经，并利用这些神经来了解TDP43错位如何导致RNA剪接缺陷以及RNA剪接在ALS中的作用。这项研究的结果将对肌萎缩侧索硬化症运动神经死亡的原因产生更深入的见解，并为我们对抗肌萎缩侧索硬化症开发治疗药物提供新的途径。

Amyotrophic Lateral Sclerosis (ALS) (also known as motor neuron disease), is caused by a loss of motor nerves or neurons. These motor nerves carry signals from the brain and spinal cord to the peripheral muscles allowing everyday movements. Loss of motor nerves in these patients leads to progressive muscle paralysis and eventual death due to failure of muscles that allow us to breath. About ~10-15% of ALS cases have a family history and specific defects, called mutations, in several genes with diverse functions are known to cause ALS. However, the processes driving motor neuron loss are poorly understood. Though the cause of ALS is unknown, many of the nerves affected in these patients show a common feature. This feature involves incorrect migration of a protein called TDP43 from within the nucleus of a cell, outside into its cytoplasm. The nucleus is the command centre of the cell and contains our DNA with specific instructions on how to make different proteins, the workhorses in a cell. The cytoplasm is the gel-like liquid within the cell that contains the nucleus and has the machinery to make proteins. Each of the nucleus and the cytoplasm have defined roles that are dependent on precise availability of specific proteins. Thus, any change in the proteins' locations will interfere with the normal activity of nerve cells resulting in their death. Relocation, also called mislocalization, of TDP43 protein from the nucleus to the cytoplasm perturbs the normal function of the nerve cells causing them to die. We have developed a new way to trigger TDP43 protein mislocalization in human nerve cells in a dish. This will allow us to look at the consequences of this relocation in detail. With the advent of a new stem cell technology called reprogramming, skin or blood cells from patients can be converted into an embryonic state. These reprogrammed cells are called induced pluripotent stem cells (iPSC) and have the potential to be converted to any type of cell in the body. Consequently, iPSC's from ALS patients can now be coaxed to become motor nerves i.e., the same kind of cells that are lost in ALS patients. This technology enables the development of human models of ALS in a dish, allowing scientists to interrogate what goes wrong within these cells to cause them to die in ALS. Using such models, we have uncovered that an important molecular process required for nerve cell survival called RNA splicing is defective in ALS. Using the process of RNA splicing, nerve cells create many different types of proteins that are required for normal function. Incorrect execution of this process leads to the generation of ineffective proteins, which can lead to problems in the structure and function of nerve cells. In this proposal, we will use the iPSC technology to generate motor nerves and use these nerves to understand how TDP43 mislocalization causes RNA splicing defects and the role of RNA splicing in ALS. The results of this study will generate deeper insights into why ALS motor nerves die and highlight new ways to develop therapeutic drugs in our fight against ALS.