Function and dysfunction of prion protein in cellular iron metabolism

描述（由申请人提供）：朊病毒疾病发病机制中涉及的因素的复杂性和多样性阻碍了对有效治疗策略的研究。虽然每一个报告都提高了我们对朊病毒疾病发病机制的理解，但朊病毒蛋白（PrPC）的正常功能和疾病相关构象体PrPSc的毒性机制都不完全清楚。朊病毒感染的神经母细胞瘤细胞和小鼠模型中异常铁代谢的报道暗示了这些疾病中氧化还原铁介导的神经毒性，如已经提出的用于几种其他神经变性疾病，包括阿尔茨海默病、帕金森病、亨廷顿病等。我实验室的最新数据表明，PrPC在人神经母细胞瘤细胞中作为铁传感，摄取或转运蛋白发挥作用，PrPC中的致病性突变以特定于每个突变的方式改变细胞铁状态。我们还注意到朊病毒病影响仓鼠和人类大脑中铁代谢异常的证据，这使我们假设PrPC通过调节铁的摄取或转运来调节细胞铁的状态，并且由于疾病状态下的点突变或聚集而引起的这种功能的改变诱导神经毒性。在拟议的研究中，我们将在两个具体目标中检验这一假设。在目标1中，我们将调查是否PrPC参与细胞铁的摄取，流出，或转移到铁蛋白，并确定PrP相互作用的蛋白质或因子负责其铁调节功能。在目标2中，将评估PrP致病性突变对细胞铁状态和对自由基损伤的易感性的影响。表现出对自由基敏感性增加的细胞系将用于评价铁螯合剂和自由基清除化合物的保护作用。这些研究将在两个不同的领域提高对朊病毒疾病发病机制的理解：1）阐明朊蛋白在朊病毒疾病进展期间改变脑铁稳态中的作用，以及2）验证铁螯合在减轻朊病毒疾病相关神经毒性中的有效性。公共卫生相关性：朊病毒疾病是致命的神经退行性疾病，目前尚无治疗方法。这些疾病是传染性的、家族性的和散发性的。所有朊病毒疾病中的主要感染和致病因子包括朊病毒蛋白的富含β折叠的同种型，称为PrP-瘙痒症（PrPSc）。我们的数据表明，脑铁稳态的不平衡有助于PrPSc的产生和传播，并有助于在这些疾病中观察到的神经变性。在拟议的研究中，我们将在细胞模型中测试这一假设，并调查铁螯合是否可以作为一种治疗措施，以减轻朊病毒疾病相关的神经毒性。

DESCRIPTION (provided by applicant): The complexity and multiplicity of factors involved in prion disease pathogenesis has hampered the search for an effective therapeutic strategy. Though each report has improved our understanding of prion disease pathogenesis, neither the normal function of prion protein (PrPC) nor the mechanism of toxicity by the disease associated conformer PrPSc is entirely clear. Reports of abnormal iron metabolism in prion infected neuroblastoma cells and mouse models implicate redox-iron mediated neurotoxicity in these disorders as has been proposed for several other neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, and others. Recent data from my laboratory indicate that PrPC functions as an iron sensing, uptake, or transport protein in human neuroblastoma cells, and pathogenic mutations in PrPC alter cellular iron status in ways that are specific to each mutation. We have also noted evidence of abnormal iron metabolism in prion disease affected hamster and human brains, leading us to hypothesize that PrPC modulates cellular iron status by regulating iron uptake or transport, and alteration of this function due to point mutations or aggregation in the diseased state induces neurotoxicity. In the proposed studies we will check this hypothesis in two specific aims. In aim 1 we will investigate whether PrPC is involved in cellular iron uptake, efflux, or transfer to ferritin, and identify PrP-interacting proteins or factors responsible for its iron modulating function. In aim 2, the influence of pathogenic mutations of PrP on cellular iron status and susceptibility to free radical damage will be assessed. Cell lines exhibiting increased susceptibility to free radicals will be used to evaluate the protective effect of iron chelators and free radical scavenging compounds. These studies will improve understanding of prion disease pathogenesis in two distinct areas: 1) clarify the role of PrP in altering brain iron homeostasis during prion disease progression, and 2) validate the effectiveness of iron chelation in alleviating prion disease associated neurotoxicity. PUBLIC HEALTH RELEVANCE: Prion diseases are fatal neurodegenerative disorders for which there is currently no treatment. These disorders are infectious, familial, and sporadic in nature. The principal infectious and pathogenic agent in all prion disorders comprises of a beta-sheet rich isoform of the prion protein termed PrP-scrapie (PrPSc). Our data suggest that imbalance in brain iron homeostasis helps in the generation and propagation of PrPSc and contributes to the neurodegeneration observed in these disorders. In the proposed studies we will test this hypothesis in cell models, and investigate whether iron chelation can be used as a therapeutic measure to alleviate prion disease associated neurotoxicity.