Centre de Recherche de l’Institut du Cerveau et de la Moelle Épiniere (CRICM), Paris, France.
Hum Mol Genet. 2013 Jun 15;22(12):2350-60. doi: 10.1093/hmg/ddt080. Epub 2013 Feb 26.
The mutations P56S and T46I in the gene encoding vesicle-associated membrane protein-associated protein B/C (VAPB) cause ALS8, a familial form of amyotrophic lateral sclerosis (ALS). Overexpression of mutant forms of VAPB leads to cytosolic aggregates, suggesting a gain of function of the mutant protein. However, recent work suggested that the loss of VAPB function could be the major mechanism leading to ALS8. Here, we used multiple genetic and experimental approaches to study whether VAPB loss of function might be sufficient to trigger motor neuron degeneration. In order to identify additional ALS-associated VAPB mutations, we screened the entire VAPB gene in a cohort of ALS patients and detected two mutations (A145V and S160Δ). To directly address the contribution of VAPB loss of function in ALS, we generated zebrafish and mouse models with either a decreased or a complete loss of Vapb expression. Vapb knockdown in zebrafish led to swimming deficits. Mice knocked-out for Vapb showed mild motor deficits after 18 months of age yet had innervated neuromuscular junctions (NMJs). Importantly, overexpression of VAPB mutations were unable to rescue the motor deficit caused by Vapb knockdown in zebrafish and failed to cause a toxic gain-of-function defect on their own. Thus, Vapb loss of function weakens the motor system of vertebrate animal models but is on its own unable to lead to a complete ALS phenotype. Our findings are consistent with the notion that VAPB mutations constitute a risk factor for motor neuron disease through a loss of VAPB function.
编码囊泡相关膜蛋白相关蛋白 B/C（VAPB）的基因突变 P56S 和 T46I 导致 ALS8，这是一种家族性肌萎缩侧索硬化症（ALS）。突变型 VAPB 的过表达会导致细胞溶质聚集，表明突变蛋白具有功能获得。然而，最近的研究表明，VAPB 功能丧失可能是导致 ALS8 的主要机制。在这里，我们使用多种遗传和实验方法研究 VAPB 功能丧失是否足以引发运动神经元变性。为了鉴定额外的与 ALS 相关的 VAPB 突变，我们在一组 ALS 患者中筛选了整个 VAPB 基因，并检测到两种突变（A145V 和 S160Δ）。为了直接研究 VAPB 功能丧失在 ALS 中的作用，我们生成了具有 Vapb 表达减少或完全缺失的斑马鱼和小鼠模型。斑马鱼中 Vapb 的敲低导致游泳能力缺陷。Vapb 敲除的小鼠在 18 个月后表现出轻微的运动缺陷，但具有神经肌肉接头（NMJs）。重要的是，VAPB 突变体的过表达无法挽救 Vapb 敲低引起的斑马鱼运动缺陷，并且它们本身无法引起毒性功能获得缺陷。因此，Vapb 功能丧失削弱了脊椎动物动物模型的运动系统，但本身不足以导致完全的 ALS 表型。我们的研究结果与 VAPB 突变通过 VAPB 功能丧失构成运动神经元疾病风险因素的观点一致。
