The iron modulatory function of prion protein and prion disorders

描述（由申请人提供）：朊病毒蛋白（PrPC）是一种正常糖蛋白，与朊病毒疾病（一组人类和动物的致命性神经退行性疾病）的发病机制有关。PrPC构象变化为聚集的PrP-羊瘙痒症（PrPSc）形式被认为是这些疾病中神经毒性的主要原因。最近，我们证明，PrPC在细胞铁的摄取和运输中起着重要作用，PrP基因敲除（PrPKO）小鼠中PrPC的选择性缺失诱导这些动物相对于野生型（wt）对照的全身性铁缺乏状态。具体而言，PrPKO小鼠显示经口引入的铁从十二指肠到血流的转运受损，以及造血前体细胞和主要器官的实质细胞对血浆铁的摄取效率低下。连同我们最近的报告证明了与朊病毒病影响的脑中PrPSc沉积相关的铁缺乏表型，这些观察结果表明，由于聚集成PrPSc形式而导致的PrPC正常功能的丧失可能是患病脑中脑铁稳态失调的原因。在本申请中，我们将集中在铁调节的机制，并假设，PrPC是一种新的铁的摄取和运输蛋白，并调节细胞铁代谢直接或通过与其他铁转运蛋白（S）。拟定的研究将使用两种互补的方法来检验这一假设：1）通过评价在同一组织中利用不同转运途径的不同铁源的转运，2）通过研究利用不同摄取和转运途径的相同铁源跨组织的转运。将使用不表达PrPC（PrPKO）、表达wt水平（wt）和表达比wt水平高10倍的PrPC（PrPKO）的小鼠模型进行该分析。这种方法将允许通过PrPC识别铁转运的途径，以及PrPC与已知铁代谢途径的交叉点。为实现这些目标，提出了三个具体目标。在目标1中，PrPC在脑铁代谢中的功能作用将在WT、PrPKO和PrP小鼠中进行评估，并将在表达铁转运缺陷的PrP正常和突变形式的神经母细胞瘤细胞中研究其潜在机制。此外，将在羊瘙痒病感染的野生型和朊病毒感染的小鼠中评估PrPC、PrPSc和脑铁状态之间的相关性。在目标2中，将在从wt、PrPKO和PrP小鼠分离的造血和网状内皮细胞中检查不同来源的铁的转运，并将在用正常和突变PrP形式转染的K562红白血病细胞中研究潜在的机制。在目标3中，将在wt、PrPKO和PrkD小鼠中检查不同来源的铁穿过肠上皮的摄取和转运，并与上述目标2进行比较。基于体内结果，极化Caco-2细胞转染表达PrPC或突变的PrP形式将被用作吸收肠上皮细胞的模型，以了解铁转运PrPC的机制。这些研究的成功完成将揭示PrPC调节铁的新途径，并提高我们对朊病毒疾病中脑铁失衡和相关神经毒性机制的理解。 公共卫生相关性：本申请的长期目标是了解朊病毒蛋白（PrPC）在铁吸收、转运和利用中的作用。从我的实验室的初步数据表明，PrPC参与铁的吸收和运输，并在朊病毒疾病的脑铁稳态异常的这一功能的损失。成功完成拟议的研究将提高我们对PrPC在铁代谢中的功能作用以及朊病毒疾病中脑铁失衡的根本原因的理解。

DESCRIPTION (provided by applicant): Prion protein (PrPC) is a normal glycoprotein implicated in the pathogenesis of prion disorders, a group of fatal neurodegenerative conditions of humans and animals. A change in the conformation of PrPC to an aggregated, PrP-scrapie (PrPSc) form is believed to be the principal cause of neurotoxicity in these disorders. Recently, we demonstrated that PrPC plays a functional role in cellular iron uptake and transport, and selective deletion of PrPC in PrP knock-out (PrPKO) mice induces a state of systemic iron deficiency in these animals relative to wild-type (wt) controls. Specifically, PrPKO mice show impaired transport of orally introduced iron from the duodenum to the blood stream, and inefficient uptake of plasma iron by hematopoietic precursor cells and parenchymal cells of major organs. Together with our recent report demonstrating a phenotype of iron deficiency that correlates with PrPSc deposits in prion disease affected brains, these observations suggest that loss of normal function of PrPC due to aggregation to the PrPSc form may be responsible for brain iron dys- homeostasis in diseased brains. In this application, we will focus on the mechanism of iron modulation by PrPC, and hypothesize that PrPC is a novel iron uptake and transport protein, and modulates cellular iron metabolism either directly or by interacting with other iron transport protein(s). The proposed studies will test this hypothesis using two complementary approaches: 1) by evaluating the transport of different sources of iron that utilize distinct pathways of transport in the same tissue, and 2) by investigating the transport of same source of iron across tissues that utilize distinct pathways of uptake and transport. Mouse models that express no PrPC (PrPKO), wt levels (wt), and 10-fold higher than wt levels of PrPC (PrPOV) will be used for this analysis. This approach will allow identification of pathways of iron transport by PrPC, and the point where PrPC intersects with known pathways of iron metabolism. Three specific aims are proposed to accomplish these goals. In aim 1, the functional role of PrPC in brain iron metabolism will be evaluated in wt, PrPKO, and PrPOV mice, and the underlying mechanism will be investigated in neuroblastoma cells expressing normal and mutant forms of PrP defective in iron transport. In addition, the correlation between PrPC, PrPSc, and brain iron status will be assessed in scrapie infected wt and PrPOV mice. In aim 2, the transport of different sources of iron will be checked in hematopoietic and reticuloendothelial cells isolated from wt, PrPKO, and PrPOV mice, and the underlying mechanism will be investigated in K562 erythroleukemia cells transfected with normal and mutant PrP forms. In aim 3, the uptake and transport of different sources of iron across the intestinal epithelium will be checked in wt, PrPKO, and PrPOV mice, and compared with aim 2 above. Based on in vivo results, polarized Caco-2 cells transfected to express PrPC or mutant PrP forms will be used as models of absorptive enterocytes to understand the mechanism of iron transport by PrPC. Successful completion of these studies will uncover novel pathway(s) of iron modulation by PrPC, and improve our understanding of the mechanism(s) underlying brain iron imbalance and associated neurotoxicity in prion disorders. PUBLIC HEALTH RELEVANCE: The long term goal of this application is to understand the role of prion protein (PrPC) in iron uptake, transport, and utilization. Preliminary data from my laboratory demonstrate that PrPC is involved in iron uptake and transport, and loss of this function contributes to brain iron dyshomeostasis in prion disorders. Successful completion of the proposed studies will improve our understanding of the functional role of PrPC in iron metabolism, and the underlying cause of brain iron imbalance in prion disorders.