The role of prion heterogeneity in transmission and transport

纯蛋白质假说指出，感染性朊病毒由细胞朊病毒蛋白（PrPC）的错误折叠同种型（PrPSc）组成，而不编码核酸，这代表了一种特殊的生物学原理。朊病毒通过诱导主要为a-螺旋的PrPC构象转化为具有b-折叠结构的PrPSc来复制，这使得其易于聚集并对蛋白水解消化有弹性。尽管一级结构相同，但PrPSc的构象可以变化，这些构象变体被称为朊病毒株。朊病毒株可在通过具有不同PrPC一级结构的不同宿主时进化或被选择，或在表达由多态性密码子和随后的单个氨基酸取代产生的PrPC的物种特异性等位基因变体的相同宿主物种中进化或被选择。朊病毒菌株在其构象中编码并继承其生物学和生物化学性质，并且由不同分子量的PrPSc聚集体的混合物组成，所述聚集体代表单体、寡聚体或非单体PrPSc的部分。当脑内注射到朊病毒疾病的啮齿动物模型中时，寡聚PrPSc聚集体含有最高水平的感染性。然而，PrPSc聚集体大小在外周体部位自然感染中的作用，以及宿主因素对聚集体特征（如PrP基因型）的影响尚未研究，但对于充分了解朊病毒如何编码可传播信息至关重要。有趣的是，我们的初步数据表明PrPSc聚集体大小在靶向特定大脑区域进行复制中的作用。我们提出的研究计划解决了以下基本问题：组成朊病毒株的PrPSc聚集体的子集存储和传输哪些信息，以及这些信息如何在与宿主生物相互作用时被调节。鹿科动物的慢性消耗性疾病（CWD）朊病毒是一种高度相关的模型，因为该疾病正在北美和两个欧洲国家的野生鹿科动物中传播，并威胁着加拿大濒临灭绝的驯鹿种群。我们将使用我们新产生的，独特的基因敲入小鼠模型表达野生型和选定的等位基因变异的cervid PrP的控制下的内源性PrP启动子感染的大小分级的PrPSc聚集体。这些将通过创新的细胞培养、原代神经元和体外朊病毒扩增模型来补充，以实现三个目标：（1）确定鹿PrPC中特定多态性对朊病毒转化的细胞先决条件的影响，（2）分析慢性消耗病分离株的PrPSc聚集体大小特征以及在朊病毒转运和感染性中的作用，以及（3）研究PrPSc聚集体大小遗传及其在脑中宿主细胞选择中的作用。这项研究的结果将对我们关于朊病毒-宿主相互作用以及蛋白质结构编码的信息范围的知识产生重大影响。

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.**