The role of prion heterogeneity in transmission and transport

仅蛋白质假说认为，传染性普恩病毒由细胞内普恩蛋白(PrPC)的错误折叠异构体(PrPSc)组成，不编码核酸，这代表了一种特殊的生物学原理。PrP通过诱导主要为a-螺旋的PrPC构象转换为具有b-折叠结构的PrPSc进行复制，这使得PrPSc易于聚集，并对蛋白水解性消化具有弹性。PrPSc的构象可以改变，尽管一级结构相同，这些构象变异被称为Prion菌株。Prion菌株可以通过具有不同PrPC一级结构的不同宿主进化或选择，或者在同一宿主物种中表达PrPC的物种特异性等位变异，这些变异是由多态密码子和随后的单一氨基酸替换引起的。PrPSc由不同分子量的PrPSc聚集体组成，分别代表单体PrPSc、寡聚PrPSc或纤维状PrPSc的不同部分。当将寡聚PrPSc聚合体注射到普恩病毒病的啮齿动物模型中时，其传染性水平最高。然而，PrPSc聚集体大小在外周身体部位自然感染中的作用，以及宿主因素对PrP基因聚集谱的影响尚未被研究，但对于全面了解可传递信息是如何由PrP编码的至关重要。有趣的是，我们的初步数据表明PrPSc聚合大小在针对特定大脑区域进行复制方面起到了作用。我们建议的研究计划解决的基本问题是，哪些信息是由PrPSc聚合体的子集存储和传递的，以及这些信息是如何在与宿主有机体的相互作用中进行调节的。*慢性消耗性疾病(CWD)颈鹿的Prion是一个高度相关的模型，因为该疾病正在北美和两个欧洲国家的野生鹿群中传播，并威胁到加拿大濒危的驯鹿种群。我们将使用我们新产生的独特的敲入小鼠模型，在内源性PrP启动子的控制下表达Cervid PrP的野生型和选定的等位变异，以感染大小不同的PrPSc聚合体。这些将由创新的细胞培养、原代神经元和体外PrP扩增模型来补充，以解决三个目标：(1)确定Cervid PrPC的特定多态对Prion转换的细胞先决条件的影响；(2)分析CWD分离株的PrPSc聚集体大小分布及其在Prion运输和感染性中的作用；(3)研究PrPSc聚集体大小遗传及其在大脑中宿主细胞选择中的作用。*这项研究的结果将对我们了解Pron-宿主相互作用和可由蛋白质结构编码的信息范围产生重大影响。**

The protein-only hypothesis states that infectious prions consist of a misfolded isoform (PrPSc) of the cellular prion protein (PrPC) without encoding nucleic acid which represents an exceptional biological principle. Prions replicate by inducing conformational conversion of the mainly a-helical PrPC into PrPSc with b-sheet structure, which makes it prone to aggregation and resilient to proteolytic digestion. The conformation of PrPSc can vary despite identical primary structure, and these conformational variants are termed prion strains. Prion strains can evolve or be selected upon passage through different hosts with distinct PrPC primary structures, or in the same host species expressing species-specific allelic variants of PrPC arising from polymorphic codons and subsequent single amino acid substitutions. Prion strains encode and inherit their biological and biochemical properties in their conformations, and consist of a mixture of PrPSc aggregates of different molecular weights, representing fractions of monomeric, oligomeric or fibrillary PrPSc. Oligomeric PrPSc aggregates contain the highest levels of infectivity when injected intracerebrally into rodent models of prion disease. However, the role of PrPSc aggregate size in natural infection at peripheral body sites, and the impact of host factors on the aggregate profile such as the PrP genotype have not been investigated but are critically important to gain a full understanding of how transmissible information is encoded by prions. Interestingly, our preliminary data indicate a role of PrPSc aggregate size in targeting specific brain regions for replication. Our proposed research program addresses the basic questions which information is stored and transmitted by the subsets of PrPSc aggregates that compose prion strains, and how this information is modulated upon interaction with the host organism.***Chronic wasting disease (CWD) prions of cervids are a highly relevant model as the disease is spreading among wild cervids in North America and two European countries, and threatens endangered caribou populations in Canada. We will use our newly generated, unique knock-in mouse models expressing wild-type and selected allelic variants of cervid PrP under control of the endogenous PrP promoter for infection with size-fractionated PrPSc aggregates. These will be complemented by innovative cell culture, primary neuron and in vitro prion amplification models to address three objectives: (1) to determine the impact of specific polymorphisms in cervid PrPC on cellular prerequisites for prion conversion, (2) to analyse PrPSc aggregate size profiles of CWD isolates and the role in prion transport and infectivity and (3) to investigate PrPSc aggregate size inheritance and its role in host cell selection in the brain.***Results from this research will have a significant impact on our knowledge about prion-host interaction and the range of information that can be encoded by protein structure.**