The iron modulatory function of prion protein and prion disorders

 描述（由申请人提供）：朊病毒蛋白（PrPC）是一种普遍表达的细胞表面糖蛋白，已知主要作为PrP-瘙痒病（PrPSc）的底物，PrPSc是与散发性克雅氏病（sCJD）和其他朊病毒疾病发病机制有关的主要神经毒性剂。然而，对PrPC的生理功能或PrPSc的神经毒性机制缺乏共识。最近的报告表明，PrPC介导的细胞铁摄取功能作为二价金属转运铁还原酶（FR）的合作伙伴。敲除小鼠中PrPC的缺乏（PrP-/-）诱导所有全身器官和脑中的铁缺乏，表明在铁摄取中的非冗余作用，以及其他铁调节蛋白不能补偿其缺乏。因此，在sCJD和羊瘙痒症感染的动物大脑中观察到的铁缺乏症可能是由于聚集导致PrPC功能丧失的结果，该铁缺乏症随着疾病进展而增加并与PrPSc相关。sCJD脑中总铁和氧化还原活性铁的伴随增加令人困惑，这可能是由于铁以生物不可用的形式在蛋白酶抗性和洗涤剂不溶性铁蛋白聚集体中被螯合。铁调节蛋白的相关变化以疾病特异性的方式反映在脑脊液（CSF）中，在区分sCJD和其他痴呆方面提供了92.5%的特异性。然而，当神经炎症和相关的小胶质细胞增生和星形细胞增生发生时，这种特异性可能会被掩盖，导致铁在神经元，小胶质细胞和星形胶质细胞中的活跃积累。基于这些观察结果，我们提出，损失或颠覆的PrPC介导的细胞铁摄取结合螯合的铁在PrPSc-铁蛋白复合物诱导的主要变化，脑铁代谢的神经炎症的继发性影响进行修改。提出了两个广泛的目标来检验这一假设。在目的1中，我们将研究原代神经元和星形胶质细胞、转化细胞系和相关小鼠模型中PrPC的FR活性在铁摄取中的意义。将鉴定PrPC相互作用的二价金属转运蛋白，并研究体外PrPC聚集和体内羊瘙痒病感染对细胞铁摄取的破坏。在目标2中，羊瘙痒症感染和炎症的小鼠模型将用于鉴定羊瘙痒症感染特异性的脑铁代谢的变化，以及由伴随或随后的神经炎症和相关的小胶质细胞增生和星形细胞增生诱导的脑铁代谢的变化。将在疾病进展期间研究PrPSc和叠加的小胶质细胞增生和星形细胞增生对铁蛋白的铁含量和生化特征的影响，以了解sCJD脑中富含铁的聚集铁蛋白的原因。这些研究的成功完成将阐明朊病毒疾病中脑铁稳态异常的机制，并将有助于区分脑铁稳态中sCJD特异性改变与神经炎症的继发性影响。这些信息对于开发疾病特异性治疗方案至关重要，这些治疗方案可以在疾病过程的早期阻止铁稳态异常。

 DESCRIPTION (provided by applicant): Prion protein (PrPC) is a ubiquitously expressed cell surface glycoprotein known mostly for its role as the substrate for PrP-scrapie (PrPSc), the principal neurotoxic agent implicated in the pathogenesis of sporadic- Creutzfeldt-Jakob disease (sCJD) and other prion disorders. Consensus on the physiological function of PrPC or the mechanism of neurotoxicity by PrPSc, however, is lacking. Recent reports suggest that PrPC mediates cellular iron uptake by functioning as a ferrireductase (FR) partner for divalent metal transporters. Absence of PrPC in knockout mice (PrP-/-) induces iron deficiency in all systemic organs and the brain, indicating a non- redundant role in iron uptake, and the inability of other iron modulating proteins to compensate for its absence. It is therefore likely that the iron deficiency observed in sCJD and scrapie-infected animal brains that increases with disease progression and correlates with PrPSc is a result of loss of function of PrPC due to aggregation. The accompanying increase in total and redox-active iron in sCJD brains is perplexing, and is probably due to the sequestration of iron in a biological unavailable form in protease-resistant and detergent-insoluble ferritin aggregates. The associated changes in iron modulating proteins are reflected in the cerebrospinal fluid (CSF) in a disease-specific manner, providing a specificity of 92.5% in discriminating sCJD from other dementias. However, this specificity is likely to be obscured when neuroinflammation and associated microgliosis and astrocytosis supervene, causing active accumulation of iron in the neurons, microglia, and astrocytes. Based on these observations, we propose that loss or subversion of PrPC-mediated cellular iron uptake combined with sequestration of iron in PrPSc-ferritin complexes induces primary changes in brain iron metabolism that are modified by the secondary effects of neuroinflammation. Two broad aims are proposed to test this hypothesis. In aim 1 we will investigate the significance of FR activity of PrPC in iron uptake by primary neurons and astrocytes, transformed cell lines, and relevant mouse models. PrPC- interacting divalent metal transporters will be identified, and disruption of cellular iron uptake by aggregation of PrPC in vitro and scrapie infection in vivo will be investigated. In aim 2, mouse models of scrapie infection and inflammation will be used to identify changes in brain iron metabolism that are specific to scrapie infection, and those induced by concomitant or subsequent neuroinflammation and associated microgliosis and astrocytosis. The influence of PrPSc and super-imposed microgliosis and astrocytosis on the iron content and biochemical characteristics of ferritin will be investigated during disease progression to understand the cause of iron-rich, aggregated ferritin in sCJD brains. Successful completion of these studies will clarify the mechanism of brain iron dyshomeostasis in prion disorders, and will help in distinguishing sCJD-specific alterations in brain iron homeostasis form the secondary effects of neuroinflammation. This information is critical for the development of disease-specific therapeutic options that can arrest iron dyshomeostasis early in the disease course.