What defines the seeding and cross-seeding potential of amyloid particles?

许多破坏性的人类脑部疾病，例如阿尔茨海默病（AD）、亨廷顿氏病、2型糖尿病和传染性海绵状脑病（tse），都与蛋白质的异常折叠有关。这种错误折叠的最终结果是形成大的不溶性蛋白质沉积物和小的有毒蛋白质颗粒，这种状态被称为淀粉样蛋白。聚集的蛋白质物质沉积在各种组织（如脑、肝等）是这些疾病的许多共同特征之一。重要的是，这些疾病也有相似的方法，通过这种方法，错误折叠和聚集的蛋白质在疾病条件下繁殖。在这个过程中，细胞中的不同蛋白质被触发，在结构上发生重大变化，形成高度健壮的淀粉样蛋白状态。淀粉样蛋白形成的一个关键步骤是添加预先形成的淀粉样蛋白颗粒，即种子，可以极大地加速淀粉样蛋白的生长，这种现象被称为播种。在某些情况下，这些种子颗粒被认为是具有传染性的实体，能够将疾病传播给邻近的细胞、组织或同一物种或不同物种的另一个个体，就像tse的情况一样，也可能在其他淀粉样疾病如阿尔茨海默病中。这些疾病目前和预计对人类健康和福利的影响不能被低估，但淀粉样蛋白状态如何通过播种进行繁殖的基本问题仍有待完全解决。在一些与蛋白质错误折叠相关的疾病中，可能存在一种以上的淀粉样蛋白聚集体，其中每种聚集体由具有不同氨基酸序列的蛋白质组成。例如，在阿尔茨海默病中，诊断性淀粉样蛋白和至少一种其他不同蛋白的各种淀粉样蛋白形式共存，包括传染性朊蛋白聚集体的存在。此外，最近的报告表明，朊病毒疾病的发病可能受到-淀粉样蛋白沉积的影响，并可能受到影响。两种不同的淀粉样蛋白在同一患者体内共存，可能是由于错误折叠的蛋白之间相互作用，加速了它们各自向淀粉样蛋白状态的转化。因此，淀粉样蛋白播种和交叉播种过程也可能参与淀粉样蛋白疾病的破坏性协同效应。我们的目的是研究淀粉样蛋白的基本过程，通过试管体外方法和基于细胞的体内方法相结合，以面包酵母酿酒酵母为安全且实验可处理的模型。在我们的项目中，我们将绘制具有良好特征的淀粉样蛋白种子样本的播种能力，使用天然种子或由其他淀粉样蛋白形成的种子监测淀粉样蛋白原纤维的生长，即所谓的“交叉播种”。然后，我们将研究如何“交叉播种”发生在酵母细胞使用一种新的酵母朊病毒为基础的试验。由于酵母朊病毒具有传染性但无毒，该系统使我们能够在不引起细胞死亡的情况下跟踪淀粉样蛋白的形成和繁殖，因此我们可以研究在活细胞中交叉播种的基本原理。总的来说，我们的项目将使我们能够确定错误折叠蛋白质之间潜在相互作用的性质和范围，以及在产生这种重要的疾病相关淀粉样蛋白形式时对细胞成分的依赖（如果有的话）。

A number of devastating human brain disorders, for example Alzheimer's disease (AD), Hungtington's diseases, diabetes type 2 and transmissible spongiform emcephalopathies (TSEs), are associated with the abnormal folding of proteins. The net result of this misfolding is the formation of large insoluble protein deposits and small toxic protein particles in a state called amyloid. The deposition of aggregated protein material in various tissues (e.g. brain, liver etc) is one of the many common characteristics shared by these diseases. Importantly, these disorders also share a similar method by which the misfolded and aggregated proteins are propagated in the disease conditions. In this process, different proteins in the cell are triggered to undergo a major change in their structure to form the highly robust amyloid state. One crucial step in amyloid formation is that the addition of preformed amyloid particles, the seeds, can greatly accelerate amyloid growth, and this phenomenon is called seeding. In some cases these seed particles are considered as infectious entities, capable of transmitting the disease to neighbouring cells, tissues, or another individual of the same or a different species, as in the case of the TSEs and possibly in other amyloid diseases such as Alzheimer's disease. The current and projected impact of these diseases on human health and welfare cannot be understated yet the fundamental question of how is the amyloid state propagated through seeding remains to be fully resolved. In some of the diseases associated with protein misfolding, more than one type of amyloid aggregate may exist where each type of aggregate is made of a protein with a different amino acid sequence. For example, in Alzheimer's disease the co-existence of various amyloid forms of the diagnostic amyloid-beta protein and at least one other different protein has been reported in patients including the presence of transmissible prion protein aggregates. Furthermore, recent reports have suggested that the onset of prion disease can be influenced and possibly enhanced by the presence of amyloid-beta deposits. This co-existence of two different amyloids in the same patient can be potentially explained by the interaction between misfolded proteins with each other, accelerating their respective conversions to the amyloid state. Therefore, the amyloid seeding and cross-seeding process is also potentially involved in the devastating synergetic effects in amyloid diseases.Our aim is to study the fundamental process of amyloid seeding by a combination of test tube-based in vitro approaches as well as cell-based in vivo approaches using the baker's yeast Saccharomyces cerevisiae as a safe and experimentally tractable model. In our project we will map the seeding potency of well-characterised amyloid seed samples, monitoring the growth of the amyloid fibrils using natural seeds or seeds formed from other amyloid proteins, so called "cross-seeding". We will then investigate how "cross-seeding" occurs in the yeast cell using a novel yeast prion-based assay. Since yeast prions are infectious but non-toxic, this system allows us to follow amyloid formation and propagation without causing cell death and therefore we can investigate the fundamental principles of cross-seeding in a living cell. Overall, our project will allow us to establish the nature and spectrum of the potential interactions between misfolded proteins and the dependence, if any, on cellular components in generating this important disease-associated amyloid forms.