tau蛋白正电子发射断层显像在阿尔茨海默病及其他神经退行性疾病中的研究进展

异常磷酸化的tau蛋白组成神经原纤维缠结(NFT)和β淀粉样蛋白(Aβ)聚集形成老年斑是阿尔茨海默病(AD)的主要病理改变。NFT负荷与神经元丢失、脑萎缩以及认知状况相关。正电子发射断层显像(PET)能客观显示活体脑内NFT的沉积量以及分布情况,在AD的诊断和病情评估方面具有重要参考价值。文中总结tau蛋白示踪剂的开发情况及其在AD和其他神经退行性疾病中的研究进展。     

S eladin －1表达下调与阿尔茨海默病分子机制的研究进展

阿尔茨海默病（A D ）是一种与衰老相关的神经退行性疾病,从德国神经病理学家 Alzheimer 于1906年对该病的首次报道以来,对A D的认识和研究已经进行了100余年,目前认为在A D患者的病变早期,脑内已出现明显病理学改变,包括神经元突触病理学损伤（突触减少和树突棘萎缩）［1－2］,β－淀粉样蛋白（Aβ）释放、沉积增多,老年斑形成,以及 T au蛋白过度磷酸化与神经纤维缠结（NFT ）［3－4］。但迄今为止,AD发病的细胞与分子机制仍不明了。     

蛋白质氧化与阿尔茨海默病

阿尔茨海默病（AD）是与老年相关的进展性神经变性疾病,主要分子病理学特征为脑内淀粉样蛋白（Aβ）沉积形成的老年斑和过度磷酸化tau蛋白所形成的神经纤维缠结.氧化应激是包括AD在内的神经变性病的一个重要发病机制.本文介绍了氧化应激后蛋白质发生改变的类型、AD进展期间脑内蛋白质的氧化、Aβ沉积和tau蛋白过度磷酸化的原因以及今后对AD进行预防与治疗的一些策略.     

β淀粉样蛋白25-35诱导皮质神经元tau蛋白过度磷酸化

目前阿尔茨海默病(Alzheimerdisease,AD)研究仍缺乏理想的动物模型,细胞模型通过复制AD的某些分子生化改变,可用于研究AD的发病机制和筛选治疗药物。脑内β淀粉样蛋白(Aβ)的大量沉积和tau蛋白过度磷酸化是AD的两大主要分子生化改变。淀粉样瀑布学说认为Aβ可直接诱导神经元tau     

β－分泌酶与阿尔茨海默病

阿尔茨海默病（A D ）是最常见的一种痴呆症,主要临床特点为进行性认知功能下降,最终导致身体机能的下降甚至死亡,65岁以上的老年人群多发［1］。对于年轻家族性AD患者而言,AD的发生与多基因因素相关,而对于年老的散发性AD患者,其原因是多重性的,包括基因、环境和后天造成的基因改变等因素。尽管AD的病因不明,但患者脑内β－淀粉样蛋白（Aβ）的增多可能是导致此病的首要原因。Aβ主要是由β－淀粉样前体（APP ）在β－分泌酶（BACE1）的作用下使其在β位点发生裂解而产生,这一过程在AD的病理性神经纤维缠结和淀粉样斑块形成中发挥着重要作用［2］。AD患者中BACE1的表达和活性均有显著升高［3］,已成为诊断AD的一个重要生物指标［4］。而关于BACE1的了解目前还存在很多局限,现通过以下几个方面来讨论近年BACE1在AD中的有关研究进展。     

阿尔茨海默病早期β-淀粉样斑块的PET显像诊断

阿尔茨海默病(AD)的病理特征之一是在脑中有异常β-淀粉样蛋白(Aβ)沉积。用正电子发射断层扫描(PET)技术对脑中β-淀粉样蛋白(Aβ)斑块进行显像,可以达到在活体内早期诊断AD及轻微认知障碍(MCI)的目的,并且可以用来评价和随访药物治疗的效果。本文对近年来应用不同的放射示踪剂对Aβ进行PET显像的基础及临床研究进展做简要回顾。     

胰高血糖素样多肽1-治疗糖尿病的多肽,是治疗阿尔茨海默病的新希望?

胰高血糖素样多肽l（Glucagon-like peptide,GLP）已被证明是有前景的Ⅱ型糖尿病（Type 2 diabetes mellitus,T2DM）治疗剂。阿尔茨海默病（Alzheimer’s disease,AD）和T2DM具有在淀粉样蛋白β（Amyloid β,Aβ）,tau蛋白磷酸化和葡萄糖合成酶3等方面的共同的病理生理特征。GLP-1具有神经营养特性,并能降低脑淀粉样蛋白水平。过去几十年对AD的广泛研究使我们认识到对其治疗应针对Aβ和tau蛋白。总结这些之后发现,GLP-1可能有希望用于治疗AD。本文综述了GLP-1的生物化学和生理学特征,T2DM和AD的共同的病理生理特征,以及GLP-1在治疗T2MD和改善AD某些病理变化方面的新进展。     

阿尔茨海默病患者脑内tau蛋白分布与认知组分相关性的PET显像研究

目的利用tau蛋白显像剂[18F]-APN-1607研究阿尔茨海默病(AD)患者脑内tau蛋白沉积的空间分布特点及其与各不同领域认知功能的相关性。方法回顾性分析23例AD患者和13例正常对照者的脑[18F]-APN-1607PET显像,采用基于感兴趣区(ROI)的标准摄取值比值(SUVR)方法比较AD组和对照组脑内tau蛋白分布差异,并利用偏相关分析探索脑内tau蛋白分布与成套神经心理测验各认知域评分之间的关系。结果与对照组比较,AD组有广泛的皮质tau蛋白沉积。记忆功能与全脑、额叶、颞叶、前扣带回、岛叶的tau蛋白分布呈显著负相关。视空间功能与枕叶、注意与额叶tau蛋白分布呈负相关趋势。语言和执行功能与各脑区的tau蛋白分布未见显著相关性。结论 tau蛋白显像剂[18F]-APN-1607可有效显示AD患者脑内tau蛋白沉积,特定脑区tau蛋白负荷与特定认知损害显著相关。[18F]-APN-1607有潜力用于AD诊断;其摄取分布与认知损害临床表现密切相关。     

脑淀粉样血管病的分子影像研究进展

脑淀粉样血管病(CAA)是以β-淀粉样蛋白(Aβ)沉积于脑血管壁中层及外膜为主要病理特征的一类年龄相关脑小血管病。多种分子影像技术如淀粉样蛋白正电子发射体层摄影(PET)、18F-氟脱氧葡萄糖-PET等已逐渐应用于CAA患者。其中, 淀粉样蛋白PET显像通过正电子核素标记的显像剂特异性结合病理标志物, 反映Aβ沉积的分布和负荷, 可为诊断CAA提供定性与定量信息, 然其在鉴别CAA与其他Aβ相关疾病如阿尔茨海默病方面价值有限。其他分子影像如tau-PET、单光子发射计算机体层摄影等及新型高选择性示踪剂也在被广泛研究中。文中主要就CAA分子影像进展进行综述。     

硫胺素缺乏引起脑内β淀粉样蛋白沉积和tau蛋白磷酸化的增加

目的：探讨硫胺素缺乏（TD）对脑内β淀粉样蛋白（Aβ）沉积、tau蛋白磷酸化的影响。方法：硫胺素剥夺饮食结合腹腔注射吡啶硫胺制作TD小鼠模型,正常对照组给予正常饮食及腹腔注射生理盐水。造模13d后取脑,行苏木精-伊红染色观察两组小鼠脑内易损区域病理改变,免疫组织化学染色检测脑内Aβ沉积、tau蛋白磷酸化及β-分泌酶（BACE）的表达情况。结果：苏木精-伊红染色显示TD模型组小鼠内侧丘脑出现典型的对称性针尖样出血;免疫组化显示TD模型组小鼠皮质、海马及丘脑均出现Aβ沉积,且丘脑Aβ沉积较皮质及海马更为明显,tau蛋白磷酸化及BACE的阳性细胞数显著增加。正常对照组小鼠苏木精-伊红染色脑内未见病理损伤,皮质、海马及丘脑均未发现Aβ沉积,tau蛋白磷酸化及表达BACE的阳性细胞数均明显低于TD模型组,两组差异有统计学意义（P〈0．05）。结论：TD可引起Aβ沉积、tau蛋白磷酸化增加等阿尔茨海默病的特征性病理改变,且Aβ沉积可能与上调BACE的表达有关。     

Microtubule assembly competence analysis of freshly-biopsied human tau,dephosphorylated tau,and Alzheimer tau

Phosphorylation of the microtubule-associated protein tau regulates its binding to microtubules; highly phosphorylated tau is also a prime component of paired helical filaments (PHFs) of Alzheimer's disease (AD). Tau from freshly biopsied human, monkey, and rat brain share similar electrophoretic mobility patterns and overlapping phosphorylated epitopes when compared to AD tau isolated from AD brain. We compared the microtubule reassembly competence of fresh isolates of phosphorylated tau to that of maximally dephosphorylated tau and tau from AD brain. A rapid procedure was developed which permitted the enrichment of phosphorylated and dephosphorylated tau from human biopsies in the absence of protein kinase and phosphatase activity. Microtubule assembly assays, using a spectrophotometric measure and purified bovine brain tubulin, were used to correlate assembly competence with states of tau electrophoretic mobility. Maximally dephosphorylated human biopsy-derived tau and monkey tau were assembly competent; tau from AD brain was virtually unable to direct microtubule assembly. Unmodified, biopsy-derived tau from non-AD brain was intermediate in assembly competence relative to AD tau and dephosphorylated tau. Several lines of evidence were used to correlate phosphorylation states of tau with microtubule assembly. First, in vitro dephosphorylation of human biopsy-derived tau with either PP2A or PP2B alone or in combination led to increasing assembly competence as the electrophoretic mobility of tau increased. Second, addition of the protein phosphatase inhibitor okadaic acid (10 μM) to brain-slice preparations slowed electrophoretic mobility of tau and decreased binding competence. We suggest that tau derived from freshly-biopsied brain exists in a range of phosphorylated states, and that dephosphorylation by PP2A and/or PP2B increases microtubules assembly competence. © 1996 Wiley-Liss, Inc.     

Toxic tau: structural origins of tau aggregation in Alzheimer's disease

Alzheimer’s disease is characterized by the extracellular accumulation of the amyloidβin the form of amyloid plaques and the intracellular deposition of the microtubule-associated protein tau in the form of neurofibrillary tangles.Most of the Alzheimer’s drugs targeting amyloidβhave been failed in clinical trials.Particularly,tau pathology connects greatly in the pathogenesis of Alzheimer’s disease.Tau protein enhances the stabilization of microtubules that leads to the appropriate function of the neuron.Changes in the quantity or the conformation of tau protein could affect its function as a microtubules stabilizer and some of the processes wherein it is involved.The molecular mechanisms leading to the accumulation of tau are principally signified by numerous posttranslational modifications that change its conformation and structural state.Therefore,aberrant phosphorylation,as well as truncation of tau protein,has come into focus as significant mechanisms that make tau protein in a pathological entity.Furthermore,the shape-shifting nature of tau advocates to comprehend the progression of Alzheimer’s disease precisely.In this review,we emphasize the recent studies about the toxic and shape-shifting nature of tau in the pathogenesis of Alzheimer’s disease.     

毛喉萜对tau蛋白磷酸化及聚集的影响

目的:本实验旨在细胞水平研究毛喉萜(forskolin)对tau蛋白磷酸化、聚集体形成及tau蛋白与微管结合能力的影响。方法:利用基因转染技术建立过度表达人类最长tau(tau441)的人肾母细胞瘤细胞(HEK293),免疫印迹技术检测细胞内tau蛋白的磷酸化状况,tau与微管结合能力改变;免疫荧光技术和thioflavin染色检测细胞内tau蛋白聚集体形成情况。结果:在HEK293转tau细胞株,总tau蛋白的表达没有明显改变,tau蛋白在Ser214、Ser262和Ser396/404位点过度磷酸化。与此同时,随着tau蛋白的过度磷酸化,tau蛋白与微管的结合能力下降,细胞内有磷酸化的tau蛋白聚集增加。结论:蛋白激酶A的激活可以引起tau蛋白的过度磷酸化,磷酸化的位点包括蛋白激酶A和非蛋白激酶A的磷酸化位点,而过度磷酸化的tau蛋白又损害了tau与微管结合,形成了大量细胞内聚集体,提示了蛋白激酶A的激活可能是超早期阿尔茨海默病病理发展过程的关键因素之一。     

Cellular tau pathology and immunohistochemical study of tau isoforms in sporadic tauopathies

Pathological inclusions in neurons and glial cells containing fibrillary aggregates of abnormally hyperphosphorylated tau protein are characteristic features in sporadic tauopathies. In the first part of this paper we outline the morphological features of some major sporadic tauopathies. In the second part, to better define the tau isoform composition, we report on the immunohistochemistry of tau isoforms in autopsied brains, including two cases with AD, two with diffuse neurofibrillary tangles with calcification, four with Pick’s disease with Pick bodies (PiD), seven with progressive supranuclear palsy (PSP), six with corticobasal degeneration (CBD) and seven cases with argyrophilic grain disease. We used two monoclonal antibodies, RD3 and RD4, and a polyclonal antibody for exon 10 that effectively distinguish between three‐repeat (3R) tau and four‐repeat (4R) tau. Neuronal neurofibrillary tangles (NFT) in AD and diffuse neurofibrillary tangles with calcification contained both 3R‐tau and 4R‐tau. The Pick bodies were immunopositive for 3R‐tau in two cases; however, in two other cases they were mainly immunopositive for 4R‐tau. Thus, Pick bodies demonstrated heterogeneity. 3R‐tau PiD contained 3R‐tau glial inclusions, and 4R‐tau PiD contained mainly 4R‐tau glial inclusions. Glial inclusions were more abundant in 4R‐tau PiD cases. In progressive supranuclear palsy and CBD, both neuronal and glial tau accumulation forming NFT, pretangles, tuft‐shaped astrocytes, astrocytic plaques, coiled bodies and threads demonstrated 4R‐tau in the cerebral cortices, although in the basal ganglia and brainstem neuronal and glial inclusions were occasionally immunopositive for 3R‐tau in addition to 4R‐tau. Argyrophilic grains (AG) were immunopositive for 4R‐tau, although pretangles were weakly stained for 4R‐tau. Thus the immunoreactivity for 4R‐tau was different between AG and pretangles. Therefore, the isoform composition on immunohistochemical study showed heterogeneity in PiD, and was not uniform in the basal ganglia and brain stem in PSP and CBD. It is suggested that the isoform composition of sporadic tauopathies may have a spectrum in individual cases, and cellular isoform composition may differ in various brain regions.     

Oligodendroglial tau filament formation in transgenic mice expressing G272V tau

Genetic evidence indicates that several mutations in tau, including G272V, are linked to frontotemporal dementia with parkinsonism. We expressed this mutation in mouse brains by combining a prion protein promoter-driven expression system with an autoregulatory transactivator loop that resulted in high expression of human G272V tau in neurons and in oligodendrocytes. We show that G272V tau can form filaments in murine oligodendrocytes. Electron microscopy established that the filaments were either straight or had a twisted structure; these were 17-20 nm wide and had a periodicity of approximately 75 nm. Filament formation was associated with tau phosphorylation at distinct sites, including the AT8 epitope 202/205 in vivo. Immunogold electron microscopy of sarcosyl-extracted spinal cords from G272V transgenic mice using phosphorylation-dependent antibodies AT8 or AT100 identified several sparsely gold-labelled 6-nm filaments. In the spinal cord, fibrillary inclusions were also identified by thioflavin-S fluorescent microscopy in oligodendrocytes and motor neurons. These results establish that expression of the G272V mutation in mice causes oligodendroglial fibrillary lesions that are similar to those seen in human tauopathies.     

Cerebrospinal fluid tau and phosphorylated tau protein are elevated in corticobasal syndrome

Differentiating corticobasal syndrome (CBS) from progressive supranuclear palsy (PSP) and idiopathic Parkinson's disease (PD) can be difficult. To investigate the additional value of cerebrospinal fluid (CSF) biomarkers in the diagnostic differentiation of parkinsonism, we analyzed the CSF concentrations of total protein, lactate and brain specific proteins amyloid‐β₄₂ protein, tau protein (t‐tau), and tau protein phosphorylated at Thr181 (p‐tau), in CSF samples from patients with PSP (n = 21), CBS (n = 12), and PD (n = 28). CBS patients demonstrated higher concentrations of t‐tau and p‐tau compared with PSP and PD patients. In discriminating CBS and PD, t‐tau offered the best combination of sensitivity (75%) and specificity (90.9%), followed by p‐tau (sensitivity 87.5% and specificity 75%). The p‐tau/t‐tau ratio resulted in sensitivity of 84.2% and specificity of 66.7% in discriminating PSP and CBS. In conclusion, our results suggest that CSF parameters are of additional value in the diagnostic differentiation of CBS and PD. © 2010 Movement Disorder Society     

Hyperphosphorylation-induced self assembly of murine tau: a comparison with human tau

Summary. Alzheimer’s disease-like neurofibrillary pathology is neither seen in rodents nor in transgenic animals expressing the disease causing mutant human APP or mutant human presenilins. Whether the absence of this pathology is due to inability of the murine tau to self assemble into filaments or due to some other factors is not understood. In this study, we compared recombinant murine and human taus in their ability to form filaments by AD-like hyperphosphorylation in vitro. Human and murine taus, 0N4R, were generated as recombinant proteins and phosphorylated with rat brain extract as a source of protein kinases. We found that murine tau could be hyperphosphorylated to similar stoichiometry and manner as human tau. Upon hyperphosphorylation, murine tau was able to self polymerize into bundles of paired helical filament- and straight filament-like morphology. The filaments obtained from self assembly of murine tau closely resembled those formed from identically treated human tau. Moreover, like human tau, 60–70% of murine tau aggregated on hyperphosphorylation.     

Divergent phosphorylation pattern of tau in P301L tau transgenic mice

Aggregates of hyperphosphorylated tau are prominent in brains of patients with Alzheimer's disease or frontotemporal dementia (FTD). They have been reproduced in animal models following the identification of tau mutations in familial cases of FTD. This includes our previously generated transgenic model, pR5, which expresses FTD (P301L) mutant tau in neurons. The mice are characterized by tau aggregation including tangle (NFT) formation, memory impairment and mitochondrial dysfunction. In 8-month-old mice, S422 phosphorylation of tau is linked to NFT formation, however, a detailed analysis of tau solubility, phosphorylation and aggregation has not been done nor have the mice been monitored until a high age. Here, we undertook an analysis by immunohistochemistry, Gallyas impregnation and Western blotting of brains from 3 month- up to 20 month-old mice. NFTs first appeared at 6 months in the amygdala, followed by the CA1 region of the hippocampus. As the mice get older, the solubility of tau is decreased as determined by sequential extractions. Histological analysis revealed increased phosphorylation at the AT180, AT270 and 12E8 epitopes with ageing. The numbers of AT8-positive neurons increased from 3 to 6 months old. However, whereas S422 appeared only late and concomitantly with NFT formation, the only neurons left with AT8-reactivity at 20 months were those that had undergone NFT formation. As hyperphosphorylated tau continued to accumulate, the lack of AT8-reactivity suggests regulatory mechanisms in specifically dephosphorylating the AT8 epitope in the remaining neurons. Thus, differential regulation of phosphorylation is important for NFT formation in neurodegenerative diseases with tau pathology.     

Autophagic-lysosomal perturbation enhances tau aggregation in transfectants with induced wild-type tau expression

The intracellular assembly of tau aggregates is a pathological hallmark shared by Alzheimer's disease and other neurodegenerative disorders known collectively as tauopathies. To model how tau fibrillogenesis evolves in tauopathies, we previously established transfectant M1C cultures from human neuroblastoma BE(2)-M17D cells that inducibly express human tau. In the present study, these cells were used to determine the role of the autophagic-lysosomal system in the degradation and aggregation of wild-type tau. Tau induction for 5 days led to the accumulation of tau with nominal assembly of tau aggregates within cells. When the lysosomotropic agent, chloroquine (CQ), was added following the termination of tau induction, tau clearance was delayed. Decreased tau truncation and increased levels of intact tau were observed. When present during tau induction, CQ led to tau accumulation and promoted the formation of sarkosyl-insoluble aggregates containing both truncated and full-length tau. CQ treatment significantly decreased the activities of cathepsins D, B and L, and the inhibition of cathepsins B and L mimicked the effect of CQ and increased tau levels in cells. Additionally, exposure of cells to the autophagy inhibitor, 3-methyladenine, led to tau accumulation and aggregation. These results suggest that the autophagic-lysosomal system plays a role in the clearance of tau, and that dysfunction of this system results in the formation of tau oligomers and insoluble aggregates.     

Coenzyme q induces tau aggregation, tau filaments, and Hirano bodies

Tau aggregation is a common feature of tauopathies such as Alzheimer disease (AD). In AD, tau assembles into fibrillar polymers; it may also be present in other aberrant aggregates, including Hirano bodies. The mechanisms leading to tau polymerization in vivo are not understood. In this study, we found that coenzyme Q (ubiquinone) facilitates tau aggregation after binding to tau molecules at the region of the tau molecule involved in self-assembly. Consequently, after tau-tau interactions, this region is masked in fibrillar tau polymers. Further in vitro studies showed that ubiquinone facilitates the interaction of tau protein with actin to form structures that are morphologically similar to Hirano bodies. Finally, studies in AD brains show that Hirano bodies react with an antibody raised against ubiquinone, indicating that ubiquinone is a component of Hirano bodies. Taken together, the in vitro models and findings in AD suggest that in the presence of ubiquinone, Hirano bodies may result from the interaction of actin and other proteins, including tau.