Clearance of membrane aggregates in mutant ALS8

在先前发现的VAPB基因中，一个由丝氨酸取代的56位氨基酸突变(P56S)会导致晚发性常染色体显性遗传型肌萎缩侧索硬化症(ALS8)。VAPB是一种锚定在内质网(ER)膜上的蛋白质，内质网是由膜组成的细胞网络，是分泌和膜蛋白的入口点。ER具有质量控制功能，以确保蛋白质在离开ER前往最终目的地的途中正确折叠。VAPB-P56S的表达破坏了这一质量控制功能，并减缓了蛋白质从内质网中的退出。这会造成蛋白质交通堵塞，最终导致内质网聚集和压力。细胞有一个被称为未折叠蛋白反应或UPR的适应性过程来抵消内质网压力。UPR旨在通过以下方式减少蛋白质负荷增加的影响：(1)扩大内质网的膜容量以适应增加的负荷；(2)促进未折叠蛋白质的降解；(3)暂时停止新的蛋白质合成，以减少进入内质网的蛋白质数量。然而，如果这些对策不能缓解压力，那么导致细胞死亡的基因就会被激活，以消除受影响的细胞。我们发现，一个被称为FFAT基序的短肽序列(酸性链中的两个苯丙氨酸)可以改变VAPB的活性。它挽救了P56S突变造成的缺陷，因此蛋白质现在可以有效地离开内质网，从而缓解内质网的压力。这项研究将确定ALS8突变如何改变UPR，以及FFAT如何解析ER膜聚集体。它将探索这种方法是否可以应用于其他容易聚集的神经退行性疾病，如亨廷顿病和帕金森病。

A single amino acid mutation, proline residue at position 56 substituted by serine (P56S), in a previously identified gene named VAPB causes late-onset, autosomal dominant form of Amyotrophic Lateral Sclerosis (ALS8). VAPB is a protein anchored to the membrane of the endoplasmic reticulum (ER), a cellular network of membranes that is the entry point for secretory and membrane proteins. The ER has a quality control feature to ensure that proteins are correctly folded before they can leave the ER en route to their final destinations. Expression of VAPB-P56S disrupts this quality control feature and slows down the exit of proteins from the ER. This creates a protein traffic jam that eventually causes aggregation and stress to the ER. Cells have an adaptive process known as the unfolded protein response or UPR to counteract ER stress. UPR is designed to reduce the effect of increased protein load by (1) expanding the membrane capacity of the ER to accommodate the increased load; (2) by promoting the degradation of unfolded proteins; and (3) by temporarily shutting down new protein synthesis to reduce the amount of proteins entering the ER. However, if these countermeasures fail to relieve the stress, genes leading to cell death are then activated to eliminate the affected cell. We have discovered that a short peptide sequence known as the FFAT motif (two phenylalanines in an acidic tract) can change the activity of VAPB. It rescued the defect caused by the P56S mutation, so that proteins can now effectively leave the ER thereby relieving stress to the ER. This study will determine how the ALS8 mutation changes the UPR, and how FFAT resolves the ER membrane aggregates. It will explore whether this approach can be applied to other aggregate-prone neurodegenerative diseases such as Huntington's and Parkinson's Diseases.