Using mitochondrial Ca2+ uptake as a therapeutic target for ALS

肌萎缩侧索硬化症（ALS）是一种致命的，成人发病的神经退行性疾病，其特征在于 进行性运动神经元（MN）丧失、肌肉去神经支配，并最终瘫痪。目前，没有有效的 治疗可用于停止或逆转ALS疾病进展和精确的分子机制 ALS发病机制的基础仍然是难以捉摸的。先前的研究显示线粒体呼吸链减少 MN和骨骼肌（SM）中的活性、线粒体超微结构改变和线粒体功能障碍 在ALS患者和小鼠模型中。ALS病理学的第一个迹象发生在神经肌肉接头（NMJ）， 突触前MN轴突与突触后SM终板连接。到目前为止，信号是否导致 最初NMJ损伤来自MN还是SM仍不清楚。在这个项目中，我们的目标是确定组织特异性 SM和MN中线粒体Ca 2+摄取在疾病发作和进展中的致病作用， 降低ALS小鼠线粒体Ca 2+摄取对NMJ和SM功能的功效。我们假设 SM和MN中线粒体Ca 2+处理不当均积极促进ALS疾病发病机制， 减弱线粒体Ca 2+摄取减轻了线粒体损伤并保留了NMJ/肌肉功能。到 为了验证这一假设，我们将使用具有可诱导的SM或MN特异性显性表达的转基因小鼠， 线粒体Ca 2+单向转运蛋白的负性形式，特异性和选择性地减少线粒体Ca 2+摄取 在hSOD 1G 93 A小鼠和C9-500（C9 orf 72）小鼠的SM和MN中，两种小鼠模型与大多数 ALS的遗传原因中心假设将在两个特定目标中进行检验。目标1将决定 SM或MN中线粒体Ca 2+摄取在存活、运动功能、NMJ功能和体内肌肉中的作用 在hSOD 1G 93 A和C9-500小鼠中的性能。目标2将评估组织特异性抑制对 SM或MN对NMJ和肌肉结构的线粒体Ca 2+摄取，MN存活，肌肉内在收缩 hSOD 1G 93 A和C9-500小鼠SM中的线粒体性质、线粒体结构和线粒体生物能量学。这 项目将：1）从细胞水平提供SM和NMJ功能的系统性纵向表征， 在hSOD 1G 93 A和C9-500小鼠中在疾病进展的不同阶段的整个动物水平; 2）确定在hSOD 1G 93 A和C9-500小鼠中在疾病进展的不同阶段的整个动物水平; SM或MN中线粒体Ca 2+摄取缺陷导致NMJ结构/功能改变的程度， hSOD 1G 93 A和C9-500小鼠中的疾病发作和进展; 3）提供了关于HSOD 1G 93 A和C9-500小鼠中的疾病发作和进展的第一个详细解剖。 使用相同的遗传模型，SM和MN中线粒体Ca 2+摄取在ALS表型中的相对作用， 确定导致NMJ破坏的信号的起源（来自SM或MN或两者）; 4）提供机械性 线粒体Ca 2+处理不当是否是ALS小鼠疾病进展的触发因素或靶点的证据， 不管引起突变的原因（线粒体相关或非线粒体相关）;并且最重要的是， 5)测试潜在的新治疗靶点（线粒体Ca 2+摄取，或线粒体Ca 2 + 用于治疗ALS。

Amyotrophic lateral sclerosis (ALS) is a fatal, adult-onset neurodegenerative disease characterized by progressive motor neuron (MN) loss, muscle denervation, and eventually, paralysis. Currently, no effective treatments are available to stop or reverse ALS disease progression and the precise molecular mechanisms underlie ALS pathogenesis remain elusive. Prior studies revealed decreased mitochondrial respiratory chain activity, altered mitochondrial ultrastructure, and mitochondrial dysfunction in both MN and skeletal muscle (SM) in ALS patients and mouse models. The first sign of ALS pathology occurs at the neuromuscular junction (NMJ), where presynaptic MN axons connect with postsynaptic SM end plates. To date, whether signals resulting in the initial NMJ damage are from MN or SM remain unclear. In this project, we aim to determine the tissue-specific causative role of mitochondrial Ca2+ uptake in SM and MN in disease onset and progression, and the therapeutic efficacy of reducing mitochondrial Ca2+ uptake on NMJ and SM function in ALS mice. We hypothesize that mitochondrial Ca2+ mishandling in both SM and MN actively contribute to ALS disease pathogenesis and that attenuating mitochondrial Ca2+ uptake mitigates mitochondrial damage and preserves NMJ/muscle function. To test this hypothesis, we will use transgenic mice with inducible, SM or MN-specific expression of a dominant negative form of the mitochondrial Ca2+ uniporter to specifically and selectively reduce mitochondrial Ca2+ uptake in SM and MN in hSOD1G93A mice and C9-500 (C9orf72) mice, two mouse models associated with the most prevalent genetic causes for ALS. The central hypothesis will be tested in two Specific Aims. Aim 1 will determine the role of mitochondrial Ca2+ uptake in SM or MN in survival, motor function, NMJ function and in vivo muscle performance in hSOD1G93A and C9-500 mice. Aim 2 will assess the impact of tissue-specific inhibition of mitochondrial Ca2+ uptake in SM or MN on NMJ and muscle structure, MN survival, muscle intrinsic contractile properties, mitochondrial structure and mitochondrial bioenergetics in SM of hSOD1G93A and C9-500 mice. This project will: 1) provide a systematic, longitudinal characterization of SM and NMJ function from a cellular level to whole animal level at different stages of disease progression in hSOD1G93A and C9-500 mice; 2) determine the degrees to which defects in mitochondrial Ca2+ uptake in SM or MN contribute to altered NMJ structure/function, disease onset and progression in hSOD1G93A and C9-500 mice; 3) provide the first detailed dissection on the relative role of mitochondrial Ca2+ uptake in SM and MN in ALS phenotype using the same genetic models and determine the origin of the signals that result in NMJ destruction (from SM or MN or both); 4) provide mechanistic evidence for whether mitochondrial Ca2+ mishandling is a trigger or a target for disease progression in ALS mice, regardless of the causing mutations (mitochondrial related or non-mitochondrial related); and most importantly, 5) test the validity of a potential new therapeutic target (mitochondrial Ca2+ uptake, or the mitochondrial Ca2+ uniporter) for the treatment of ALS.