Targeting NAD+ biosynthesis and excitotoxicity: two universal strategies for the treatment of amyotrophic lateral sclerosis

肌萎缩侧索硬化症（ALS）是一种毁灭性的神经退行性疾病，疾病进展迅速。患者会出现肌肉无力和瘫痪，通常在发病后3至5年死亡。尽管人们对该病的发病机制了解甚多，但到目前为止，还没有任何治疗方案可以阻止疾病的进展。然而，有充分的证据表明，能量代谢紊乱和兴奋性毒性在疾病的发病机制中起主要作用。考虑到迫切需要有效的因果疗法来治疗ALS患者，确定新的策略来防止神经元丢失，减缓甚至停止疾病进展是特别感兴趣的。目前正在进行的研究使用新的方法，如反义寡核苷酸（ASOs）或病毒基因治疗，主要集中在家族性ALS形式，即携带SOD或C9ORF72突变的患者。然而，绝大多数患者患有与特定遗传基因修饰无关的散发形式。该提案的主要目标是通过开发和临床前测试有希望的治疗策略来评估治疗散发性ALS的通用靶点，以便快速转化为临床。这也是德克萨斯大学西南医学中心转化性神经变性研究中心的核心格言，该中心将主持这个项目。在这里，我提出了两个概念，分别针对参与ALS发病机制的两种普遍途径：功能失调的NAD+生物合成和兴奋毒性。首先，根据最近的一项临床研究表明，增加NAD+水平在ALS患者中具有疾病改善特性，我们假设增强NAD+代谢可以延缓ALS动物模型的疾病进展。为了验证这一点，我将使用腺相关病毒载体基因传递增加烟酰胺磷酸核糖基转移酶（NAMPT）的表达，NAMPT是NAD+生物合成的关键限速酶。第二种策略建立在抑制钙（Ca2+）激活的磷脂超扰酶1 （PLSCR1）活性（即兴奋毒性激活）防止小胶质细胞激活和细胞内Ca2+失调的观察基础上。因此，我的目的是研究aso介导的PLSCR1抑制对临床前ALS模型中兴奋性毒性相关的运动神经元细胞死亡和疾病进展的影响。如果证明有效，测试的策略可以直接应用于临床，并有望对广泛的ALS患者有益。

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder with rapid disease progression. Patients suffer from muscle weakness and paralysis which usually result in death three to five years after disease onset. Although much is known about the disease pathogenesis, up to date, no treatment options exist to stop disease progression. However, there is ample evidence that disturbed energy metabolism and excitotoxicity majorly contribute to disease pathogenesis. Considering the urgent need for effective causal therapies to medicate ALS patients, it is of particular interest to identify new strategies to prevent neuronal loss and to slow or even stop disease progression. Ongoing studies using novel approaches, such as antisense oligonucleotides (ASOs) or viral gene therapy mainly focus on familial ALS forms, i.e. patients harboring SOD or C9ORF72 mutations. However, the vast majority of patients suffer from the sporadic form not associated with particular inherited gene modifications. The primary goal of this proposal is the evaluation of universal targets for the treatment of sporadic ALS by developing and pre-clinically testing promising treatment strategies for rapid translation into the clinic. This is also the central maxim of the Center for Translational Neurodegeneration Research at the University of Texas Southwestern Medical Center which will host this project.Here, I present two concepts targeting two universal pathways involved in the pathogenesis of ALS: dysfunctional NAD+ biosynthesis and excitotoxicity, respectively. First, based on a recent clinical study indicating that increasing NAD+ levels has disease-modifying properties in ALS patients, we hypothesize that enhancing NAD+ metabolism can delay disease progression in ALS animal models. To test this, I will increase the expression of nicotinamide phosphoribosyl transferase (NAMPT), a key rate-limiting enzyme for NAD+ biosynthesis, using adeno-associated viral vector gene delivery. The second strategy builds on the observation that suppression of calcium (Ca2+)-activated phospholipid scramblase 1 (PLSCR1) activity (i.e. excitotoxicity-activated) prevents microglial activation and intracellular Ca2+ dysregulation. Therefore, I aim to investigate the effect of ASO-mediated PLSCR1 inhibition on excitotoxicity-related motor neuron cell death and disease progression in pre-clinical ALS models. If proving effective, the tested strategies can be directly employed in the clinic and are expected to be beneficial for a wide spectrum of ALS patients.