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病，直到尸检才被发现。这种朊病毒疾病和其他朊病毒疾病的神经毒性的主要原因是 PrP-scrapie (PrPSc) 的积累，PrPSc 是一种富含 ¿-折叠的朊病毒蛋白 (PrPC) 亚型在脑实质中的积累。怀疑有其他过程参与，但其作用机制尚不清楚。新的证据表明，铁稳态失衡是受影响大脑的一个一致特征，表明氧化还原铁与疾病相关的神经毒性有关。与阿尔茨海默氏病（AD）患病的大脑会积聚铁不同，来自sCJD和痒病感染动物模型的大脑显示出“功能性”缺铁的表型，铁摄取蛋白转铁蛋白（Tf）显着增加表明尽管脑铁水平变化很小，但铁摄取蛋白转铁蛋白（Tf）显着增加表明了这一点。此外，Tf 水平随着疾病进展而增加，与 PrPSc 直接相关，表明与疾病发病机制之间存在因果关系。令人惊讶的是，sCJD 病例的脑脊液 (CSF) 中 Tf 水平在疾病终末期之前就显着降低，而不是代偿性增加，这表明缺铁的脑实质细胞与血脑和脑 CSF 屏障之间的信号调节错误，这些屏障分别参与铁从外周循环到大脑的转运和脑 Tf 的分泌。基于这些观察结果，我们假设 sCJD 相关的脑铁调节破坏导致脑脊液中铁管理蛋白水平的特定变化，这些变化与疾病进展相关，从而为 sCJD 提供疾病特异性生物标志物。提出了两个具体目标来检验这一假设。在目标 1 中，将使用痒病感染小鼠作为模型来探索 sCJD 大脑中 CSF Tf 降低的机制。具体来说，通过追踪朊病毒疾病进展期间放射性标记铁（59Fe）从尾静脉到大脑和脑脊液室的运输，监测瘙痒病感染期间脑铁水平的变化、脑铁和PrPSc水平之间的相关性以及铁从外周循环到大脑运输的变化。大脑和脑脊液中的 59Fe 计数将与铁管理蛋白的水平相关联，以评估脑铁信号传导机制的完整性。在目标 2 中，脑脊液 Tf 和其他铁管理蛋白（“新”生物标志物）的特异性和敏感性将与“当前”的 sCJD 替代脑脊液生物标志物进行比较。将强调新生物标记物区分 sCJD 与快速进展性痴呆和 AD 的准确性，而 AD 是经常被误诊为 sCJD 的痴呆的潜在可治疗原因。新生物标志物的预后可靠性将在疾病进展过程中不同时间点收集的脑脊液样本中进行评估，这些样本来自痒病感染的小鼠和慢性消耗病感染的鹿科动物，并将确定显着变化的最早时间点。成功完成这些研究将提高我们的 了解导致 sCJD 脑脊液 Tf 降低的机制，并促进开发快速、特异且灵敏的 sCJD 死前诊断测试。 公共卫生相关性：朊病毒病是人类和动物的一组总是致命的神经退行性疾病，具有散发性和传染性。目前，对这些疾病唯一可靠的诊断测试是尸检，这存在将疾病从未确诊病例传播到健康个体的风险。我们的数据表明，散发性克雅氏病 (sCJD) 病例的脑脊液 (CSF) 中铁转运蛋白转铁蛋白减少。在此应用中，我们将研究这种变化的潜在机制，以及 CSF Tf 和其他铁管理蛋白是否可以用作 sCJD 的诊断生物标志物。

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.