Clearance of membrane aggregates in mutant ALS8

先前鉴定的 VAPB 基因中的单个氨基酸突变（第 56 位脯氨酸残基被丝氨酸取代（P56S））会导致晚发、常染色体显性形式的肌萎缩侧索硬化症 (ALS8)。 VAPB 是一种锚定在内质网 (ER) 膜上的蛋白质，内质网是一种细胞膜网络，是分泌蛋白和膜蛋白的入口点。 ER 具有质量控制功能，可确保蛋白质在离开 ER 前往最终目的地之前正确折叠。 VAPB-P56S 的表达破坏了这种质量控制功能，并减慢了蛋白质从内质网的排出。这会造成蛋白质交通堵塞，最终导致聚集并对内质网造成压力。细胞有一个称为未折叠蛋白反应或 UPR 的适应性过程来抵消 ER 应激。 UPR 旨在通过以下方式减少蛋白质负荷增加的影响：(1) 扩大 ER 的膜容量以适应增加的负荷； (2)通过促进未折叠蛋白的降解； (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，如果这些对策无法缓解压力，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，称为 FFAT 基序（酸性区中的两个苯丙氨酸）的短肽序列可以改变 VAPB 的活性。它挽救了P56S突变引起的缺陷，使蛋白质现在可以有效地离开内质网，从而减轻内质网的压力。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易聚集的神经退行性疾病，例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.