Molecular Basis of Iron Imbalance in sCJD Brain and CSF

描述（由申请人提供）：散发性克雅氏病（sCJD）是一种致命的人类朊病毒疾病，直到尸检才会被发现。在这种和其他朊病毒疾病中，神经毒性的主要原因是PrP-scrapie （PrPSc）的积累，PrPSc是朊病毒蛋白（PrPC）在脑实质中的一种富片状异构体。怀疑其他进程的参与，但其作用机制尚不清楚。新出现的证据表明，铁稳态失衡是受影响大脑的一贯特征，暗示氧化还原铁与疾病相关的神经毒性有关。与阿尔茨海默病（AD）不同，患病的大脑会积累铁，sCJD和痒病感染动物模型的大脑显示出“功能性”铁缺乏的表型，这表明尽管脑铁水平变化很小，但铁摄取蛋白转铁蛋白（Tf）显著增加。此外，Tf水平随疾病进展而升高，与PrPSc直接相关，提示与疾病发病机制存在因果关系。令人惊讶的是，sCJD患者的脑脊液（CSF）中的Tf水平在终末期疾病之前就显著降低，而不是代偿性增加，这表明缺铁脑实质细胞与血脑和脑-CSF屏障之间的信号调节失调，这些屏障分别参与铁从外周循环运输到大脑和脑Tf的分泌。基于这些观察结果，我们假设sCJD相关的脑铁调节中断导致与疾病进展相关的CSF铁管理蛋白水平的特异性变化，为sCJD提供疾病特异性生物标志物。为了验证这一假设，提出了两个具体目标。在目的1中，将以瘙痒病感染小鼠为模型，探讨sCJD脑CSF Tf减少的机制。具体而言，瘙痒病感染期间脑铁水平的变化、脑铁与PrPSc水平的相关性以及铁从外周循环到脑的运输变化将通过跟踪放射性标记铁（59Fe）在朊病毒疾病进展期间从尾静脉到脑和脑脊液室的运输来监测。脑和脑脊液中的铁计数将与铁管理蛋白的水平相关，以评估脑铁信号机制的完整性。在目标2中，CSF Tf和其他铁管理蛋白（“新的”生物标志物）的特异性和敏感性将与sCJD的“现有”替代CSF生物标志物进行比较。将强调区分sCJD与快速进展性痴呆和AD的新生物标志物的准确性，AD是痴呆症的潜在可治疗原因，经常被误诊为sCJD。新生物标志物的预后可靠性将在瘙痒病感染小鼠和慢性消耗性疾病感染小鼠疾病进展过程中不同时间点采集的脑脊液样本中进行评估，并确定显著变化的最早时间点。顺利完成这些学习将提高我们的素质

DESCRIPTION (provided by applicant): Sporadic Creutzfeldt-Jakob disease (sCJD) is a fatal prion disorder of humans that escapes detection until autopsy. The principal cause of neurotoxicity in this and other prion disorders is accumulation of PrP-scrapie (PrPSc), a ¿-sheet rich isoform of prion protein (PrPC) in the brain parenchyma. Participation of other processes is suspected, but their mechanism of action is unclear. Emerging evidence indicates that imbalance of iron homeostasis is a consistent feature of affected brains, implicating redox-iron in disease associated neurotoxicity. Unlike Alzheimer's disease (AD) where diseased brains accumulate iron, brains from sCJD and scrapie infected animal models reveal a phenotype of 'functional' iron deficiency as suggested by a significant increase in the iron uptake protein transferrin (Tf) despite minimal change in brain iron levels. Moreover, Tf levels increase with disease progression in direct correlation with PrPSc, suggesting a cause and effect relationship with disease pathogenesis. Surprisingly, instead of a compensatory increase, levels of Tf are significantly decreased in the cerebrospinal-fluid (CSF) of sCJD cases much before end-stage disease, indicating mis-regulation of signaling between iron starved brain parenchymal cells and the blood-brain and brain-CSF barriers involved in iron transport from the peripheral circulation to the brain and secretion of brain Tf respectively. Based on these observations, we hypothesize that sCJD associated disruption of brain iron regulation causes specific changes in CSF levels of iron management proteins that correlate with disease progression, providing disease specific biomarker(s) for sCJD. Two specific aims are proposed to test this hypothesis. In aim 1, the mechanism underlying decreased CSF Tf in sCJD brains will be explored using scrapie infected mice as models. Specifically, change in brain iron levels during scrapie infection, correlation between brain iron and PrPSc levels, and change in iron transport from the peripheral circulation to the brain will be monitored by tracking transport of radiolabeled iron (59Fe) from the tail vein to the brain and CSF compartments during prion disease progression. 59Fe counts in the brain and CSF will be correlated with levels of iron management proteins to evaluate the integrity of brain iron signaling mechanisms. In aim 2, the specificity and sensitivity of CSF Tf and other iron management proteins, the 'new' biomarkers, will be compared with 'current' surrogate CSF biomarkers of sCJD. The accuracy of new biomarkers in differentiating sCJD from rapidly progressive dementia and AD, potentially treatable causes of dementias often misdiagnosed as sCJD, will be emphasized. The prognostic reliability of new biomarkers will be assessed in CSF samples collected at different time points during disease progression from scrapie infected mice and Chronic Wasting Disease infected cervids, and the earliest time-point of a significant change will be identified. Successful completion of these studies will improve our understanding of the mechanism leading to decreased CSF Tf in sCJD, and facilitate the development of a rapid, specific, and sensitive pre-mortem diagnostic test for sCJD. PUBLIC HEALTH RELEVANCE: Prion disorders are a group of invariably fatal neurodegenerative conditions of humans and animals that are sporadic and infectious in nature. Currently, the only reliable diagnostic test for these disorders is post- mortem, posing a risk of disease transmission from undiagnosed cases to healthy individuals. Our data indicate that the iron transport protein transferrin is decreased in the cerebrospinal fluid (CSF) of sporadic Creutzfeldt-Jakob disease (sCJD) cases. In this application we will investigate the underlying mechanism of this change, and whether CSF Tf and other iron management proteins can be used as a diagnostic biomarker for sCJD.