tau蛋白异常翻译后修饰在阿尔茨海默病中的作用

在阿尔茨海默病（A1zheimer’s disease,AD）中微管相关蛋白tau能够产生许多异常翻译后修饰并聚集形成配对螺旋丝（paired helical filament,PHF）。这些tau的修饰包括过磷酸化、异常糖基化、截断等,其中,过磷酸化和异常糖基化是阿尔茨海默氏病等神经退行性疾病神经元纤维化的主要分子发病机制。     

Tau蛋白在阿尔茨海默病神经细胞退行性变性中的作用

Tau是神经细胞中含量最高的微管相关蛋白质,其主要生物学功能是促进微管组装和维持微管的稳定性。已发现tau蛋白异常与20余种神经退行性疾病有关。该结合作研究组近年来的工作,介绍tau蛋白在阿尔茨海默病神经细胞退行性变性中的可能作用及其机制,并对神经细胞退行性变性的本质提出了一些新见解。     

丝氨酸/苏氨酸蛋白磷酸酯酶在tau蛋白异常磷酸化中的作用

Tau蛋白过度磷酸化在阿尔采末病（Alzheimer’s disease,AD）发病过程中发挥重要作用,抑制蛋白磷酸酯酶活性,可诱导tau的过度磷酸化和聚积。本文拟就近年来蛋白磷酸酯酶在tau蛋白异常磷酸化中的作用作一综述。     

Tau蛋白寡聚体与阿尔茨海默病

阿尔茨海默病（AD）是严重影响老年人健康的一种神经退行性疾病。AD主要两个病理特征是tau蛋白组成的神经原纤维缠结和β淀粉样蛋白组成的Aβ斑块。Tau蛋白是目前研究AD机制和防治药物的一个重要靶点。Tau蛋白的寡聚体形式被认为是最具神经毒性的,并且其能在神经元之间传播,诱导胞内的正常tau蛋白聚集。本综述结合近年来的文献报道,对tau寡聚体的制备手段、形成机理、神经毒性、传播机制以及治疗前景等方面做了系统总结和讨论,为人们深入认识tau寡聚体提供参考。     

Tau 蛋白磷酸化在阿尔茨海默病中所处的地位

阿尔茨海默病(Alzheimer’s disease,AD)是一种老年人常见的神经系统退行性疾病,是痴呆最常见的病因。AD患者越来越多,给家属及社会带来严重负担造成了巨大的家庭和社会负担,这就迫使我们进一步探讨AD发病机制。在AD的众多发病机制中,tau蛋白假说倍受青睐。在蛋白磷酸酯酶2A(protein phosphatase 2A,PP2A)、糖原合酶激酶-3β(glycogen synthase kinase-3β,GSK-3β)、细胞周期依赖性蛋白激酶-5(cyclin-dependent kinase 5,CDK-5)和Bcl-2等蛋白酶及调节蛋白作用下,微管相关蛋白tau蛋白以其异常磷酸化结构或是形成二聚体、寡聚体和神经原纤维缠结等形式,参与到AD的病理过程。Tau蛋白及其相关结构,可能启动或促进了AD的凋亡,亦可能抑制了急性凋亡却促进了慢性的神经细胞变性。揭开这一谜底,可能揭开AD病理改变的神秘面纱。     

阿尔兹海默病中tau蛋白磷酸化调节

细胞内高度磷酸化tau蛋白形成的神经纤维缠结是阿尔兹海默病的主要病理特征之一。过度磷酸化的tau蛋白将引起细胞内微管的紊乱,从而造成神经元突触连接的丢失。Tau蛋白的磷酸化受到多种因素的影响,这些因素的失常将会导致tau蛋白的异常磷酸化。Tau蛋白的基本功能和结构、翻译后的主要修饰以及蛋白激酶和磷酸酯酶的调节,在阿尔兹海默病理以及预防治疗中发挥重要作用。     

脑脊液β-淀粉样蛋白/磷酸化tau蛋白比值在鉴别诊断阿尔茨海默病与血管性痴呆中的价值

目的:探讨脑脊液Aβ1-42、t-tau蛋白及p-tau181蛋白以及Aβ1-42/t-tau和Aβ1-12/p-tau181比值鉴别诊断阿尔茨海默病(AD)与血管性痴呆(VD)的临床应用价值.方法:采用酶联免疫吸附法检测AD患者、VD患者和正常对照组(NC)脑脊液中Aβ1-42、t-tau蛋白及P-tau181蛋白浓度的变化.结果:An组患者脑脊液Aβ1-42越浓度显著低于VD组和NC组,t-tan蛋白及p-tau181蛋白浓度显著高于VD组和NC组.当Aβ1-42/p-tau181比值分界值为11.3时,鉴别诊断AD与VD的敏感性和特异性分别为95%和94%.结论:脑脊液Aβ1-42、t-tau蛋白及p-tau181蛋白浓度的变化,尤其是Aβ1-42/p-tau181比值是很好的AD与VD鉴别诊断的生物学指标.     

Tau蛋白——Alzheimer病研究的新热点

Ｔａｕ蛋白——Ａｌｚｈｅｉｍｅｒ病研究的新热点顾琪贺林（上海生命科学研究中心,上海２０００３１）关键词Ｔａｕ蛋白Ａｌｚｈｅｉｍｅｒ病Ｔａｕ蛋白是一种神经原微管相关蛋白。处于异常磷酸化状态的Ｔａｕ蛋白集合成双股螺旋纤丝（ｐａｉｒｅｄｈｅｌｉｃａｌｆｉｌ...     

Tau蛋白在阿尔兹海默病治疗中的研究进展

阿尔兹海默病中一个重要的病理特点是神经原纤维缠结(NFTs),其与Tau蛋白具有密切的关系。Tau蛋白是含量最高的微管相关蛋白。正常Tau蛋白可与微管蛋白结合促进其有效聚合形成微管。而过度磷酸化的Tau蛋白则会自我聚集,进而导致NFTs的形成。近年来,国内外就Tau为主要靶点治疗AD有了很大进展。本文就Tau蛋白在AD中的病理学意义,与Aβ蛋白的相互作用以及以Tau为主要切入点对AD进行治疗的方法作一综述。     

Tau蛋白高度磷酸化致阿尔茨海默病动物模型研究进展

阿尔茨海默病（Alzheimer＇sdisease,AD）是老年人中最常见的神经退行性疾病,以过度磷酸化tau蛋白为核心形成的神经原纤维缠结为AD的主要病理特征之一。近年来对tau蛋白磷酸化的研究备受关注。在AD的实验研究中,探索理想的AD动物模型对于明确AD的病因、发病机制及药物的研发等方面起关键作用。本文对Tau蛋白磷酸化致AD主要动物模型的研究进展进行了综述,包括Tau转基因动物模型、激酶和磷酸化酶系统失衡致Tau蛋白过度磷酸化损伤模型、降低Tau蛋白糖基化致Tau过度磷酸化模型等。     

Hierarchical Phosphorylation of Recombinant Tau by the Paired-Helical Filament-Associated Protein Kinase Is Dependent on Cyclic AMP-Dependent Protein Kinase

Abstract : Immunoaffinity-purified paired helical filaments (PHFs) from Alzheimer's disease (AD) brain homogenates contain an associated protein kinase activity that is able to induce the phosphorylation of PHF proteins on addition of exogenous MgCl₂ and ATP. PHF kinase activity is shown to be present in immunoaffinity-purified PHFs from both sporadic and familial AD, Down's syndrome, and Pick's disease but not from normal brain homogenates. Although initial studies failed to show that the kinase was able to induce the phosphorylation of tau, additional studies presented in this article show that only cyclic AMP-dependent protein kinase-pretreated recombinant tau is a substrate for the PHF kinase activity. Deletional mutagenesis, phosphopeptide mapping, and site-directed mutagenesis have identified the PHF kinase phosphorylation sites as amino acids Thr³⁶¹ and Ser⁴¹² in htau40. In addition, the cyclic AMP-dependent protein kinase phosphorylation sites that direct the PHF kinase have been mapped to amino acids Ser³⁵⁶ and Ser⁴⁰⁹ in htau40. Additional data demonstrate that these hierarchical phosphorylations in the extreme C terminus of tau allow for the incorporation of recombinant tau into exogenously added AD-derived PHFs, providing evidence that certain unique phosphorylations of tau may play a role in the pathogenesis of neurofibrillary pathology in AD.     

New Phosphorylation Sites Identified in Hyperphosphorylated Tau (Paired Helical Filament-Tau) from Alzheimer's Disease Brain Using Nanoelectrospray Mass Spectrometry

Abstract: Paired helical filaments (PHFs) are the structural constituents of neurofibrillary tangles in Alzheimer's disease and are composed of hyperphosphorylated forms of the microtubule-associated protein tau (PHF-tau). Pathological hyperphosphorylation of tau is believed to be an important contributor to the destabilisation of microtubules and their subsequent disappearance from tangle-bearing neurons in Alzheimer's disease, making elucidation of the mechanisms that regulate tau phosphorylation an important research goal. Thus, it is essential to identify, preferably by direct sequencing, all of the sites in PHF-tau that are phosphorylated, a task that is incomplete because of the difficulty to date of purifying insoluble PHF-tau to homogeneity and in sufficient quantities for structural analysis. Here we describe the solubilisation of PHF-tau followed by its purification by Mono Q chromatography and reversed-phase HPLC. Phosphopeptides from proteolytically digested PHF-tau were sequenced by nanoelectrospray mass spectrometry. We identified 22 phosphorylation sites in PHF-tau, including five sites not previously identified. The combination of our new data with previous reports shows that PHF-tau can be phosphorylated on at least 25 different sites.     

A Conformation- and Phosphorylation-Dependent Antibody Recognizing the Paired Helical Filaments of Alzheimer's Disease

Abstract: Hyperphosphorylated tau (PHF-tau) is the major constituent of paired helical filaments (PHFs) from Alzheimer's disease (AD) brains. This conclusion has been based largely on the creation and characterization of monoclonal antibodies raised against PHFs, which can be classified in three categories: (a) those recognizing unmodified primary sequences of tau, (b) those recognizing phosphorylation-dependent epitopes on tau, and (c) those recognizing conformation-dependent epitopes on tau. Recent studies have suggested that the antibodies recognizing primary sequence and phosphorylation-dependent epitopes on tau are unable to distinguish between normal adult biopsy tau and PHF-tau. We now present evidence for a new fourth class of monoclonal antibodies recognizing conformation-dependent phosphoepitopes on tau, typified by TG-3, a monoclonal antibody raised to PHFs from AD brain homogenates. Studies using a series of deletional tau mutants, site-directed tau mutants, and synthetic peptides enable the precise epitope mapping of TG-3. Additional studies demonstrate that TG-3 reacts with neonatal mouse tau and PHF-tau but does not recognize adult mouse tau or tau derived from normal human autopsy or biopsy tissue. Further investigation reveals that TG-3 recognizes a unique conformation of tau found almost exclusively in PHFs from AD brains.     

综述:环境因素与Tau蛋白的异常磷酸化

神经纤维缠结是阿尔茨海默病(Alzheimer's disease,AD)的重要病理特征之一,其发生发展因素一直是相关研究领域的热点问题．神经纤维缠结由异常磷酸化的Tau蛋白错误折叠、聚集所形成,因此对诱发Tau蛋白异常磷酸化的因素进行探究显得尤为重要．Tau蛋白异常磷酸化逐渐形成神经缠结是AD早期发生的病理过程之一,本文就Tau蛋白异常磷酸化发生的环境影响因素进行了讨论．     

Characterization of In Vitro Glycation Sites of Tau

Abstract: Tau is a microtubule-associated protein that loses microtubule binding activity and aggregates into paired helical filaments (PHFs) in Alzheimer's disease. Nonenzymic glycation is one of the posttranslational modifications detected in PHF-tau, but not in normal tau. PHF-tau has reduced ability to bind to microtubules. To determine whether glycation of tau occurs in its microtubule binding domains, we have characterized in vitro glycation sites of the longest isoform of tau, which has four microtubule binding domains (Tau-4). The identified glycation sites are Lys-87, 132, 150, 163, 174, 225, 234, 259, 280, 281, 347, 353, and 369. We have also studied glycation of another isoform of tau, which has only three microtubule binding domains (Tau-3). This isoform is modified by glucose 15–20% more slowly than Tau-4. However, the glycation sites appear to be the same in both isoforms, except for Lys-280 and 281; these are located in the second microtubule binding domain, which is missing in Tau-3. Lys-150, 163, and 174 are located within or proximal to the sequence of tau that is involved in the microtubule nucleation activity, and Lys-259, 280, 281, 347, 353, and 369 are located in the microtubule binding domains. Glycation at these sites can affect the functional properties of tau, and advanced glycation at these sites might lead to the formation of insoluble aggregates similar to the ones seen in Alzheimer's disease.     

乙醛对人类神经tau磷酸化的影响

用乙醛对人类神经tau进行醛胺化,通过NCLK(neuronal cdc2-like protein kinase)和［γ-³²P］ATP对其磷酸化.磷酸化的产物经胃蛋白酶降解及HPLC(C-18)分析降解片段,发现醛胺化tau的降解物中有两个新的磷酸化肽段(A4和A6).     

综述:Tau蛋白过度磷酸化机制及其在阿尔茨海默病神经元变性中的作用

Tau蛋白是神经元中含量最高的微管相关蛋白,其经典生物学功能是促进微管组装和维持微管的稳定性．在阿尔茨海默病(Alzheimer's disease,AD)患者,异常过度磷酸化的Tau蛋白以配对螺旋丝结构形成神经原纤维缠结并在神经元内聚积．大量研究提示,Tau蛋白异常在AD患者神经变性和学习记忆障碍的发生发展中起重要作用．本课题组对Tau蛋白异常磷酸化的机制及其对细胞的影响进行了系列研究,发现Tau蛋白表达和磷酸化具有调节细胞生存命运的新功能,并由此对AD神经细胞变性的本质提出了新见解．本文主要综述作者实验室有关Tau蛋白的部分研究结果．     

Distinctly Phosphorylated Neurofilaments in Different Classes of Neurons

Abstract: Recent immunohistochemical experiments revealed that specific anti-neurofilament monoclonal antibodies yield distinct patterns in different types of neurons. This led to the suggestion that neurofilaments are a family of heterogeneous molecules whose occurrence and distribution are a function of cell type. In the present study we examined the hypothesis that this heterogeneity is due to differences in the extent of phosphorylation of neurofilament proteins in distinct types of neurons. In view of the large number of potential phosphorylation sites on the heavy neurofilament protein (NF-H), we focused on this protein and examined its extent of phosphorylation in different types of neurons. This was performed using neurofilaments isolated from axons of the cholinergic bovine ventral root motor neurons and of the chemically heterogeneous bovine dorsal root neurons. Two-dimensional gel electrophoresis revealed that the isoelectric point of ventral root NF-H (pl 5.10) was ∼0.2 pl units more acidic than that of dorsal root NH-F. This difference was abolished by treating the neurofilaments with alkaline phosphatase, suggesting that the excess negative charge of ventral root NF-H is due to increased levels of phosphorylation. Amino acid analysis confirmed that the phosphoserine content of ventral root NF-H (27.2 ± 2.5% of the serines) is markedly higher than that of dorsal root NF-H (15.5 ± 6.2% of the serines). These findings provide a novel system for studying the biochemistry and function of distinctly phosphorylated neurofilaments in different types of neurons.     

Cross-Linking Sites of the Human Tau Protein, Probed by Reactions with Human Transglutaminase

Abstract: A portion of the neurofibrillary tangles of Alzheimer's disease has the characteristics of cross-linked protein. Because the principal component of these lesions is the microtubule-associated protein tau, and because a major source of cross-linking activity within neurons is supplied by tissue transglutaminase (TGase), it has been postulated that isopeptide bond formation is a major posttranslational modification leading to the formation of insoluble neurofibrillary tangles. Here we have mapped the sites on two isoforms of human tau protein (τ23 and τ40) capable of participating in human TGase-mediated isopeptide bond formation. Using dansyl-labeled fluorescent probes, it was shown that eight Gln residues can function as amine acceptor residues, with two major sites being Gln³⁵¹ and Gln⁴²⁴. In addition, 10 Lys residues were identified as amine donors, most of which are clustered adjacent to the microtubule-binding repeats of tau in regions known to be solvent accessible in filamentous tau. The distribution of amine donors correlated closely with that of Arg residues, suggesting a link between neighboring positive charge and the TGase selectivity for donor sites in the protein substrate. Apart from revealing the sites that can be cross-linked during the TGase-catalyzed assembly of tau filaments, the results suggest a topography for the tau monomers so assembled.     

Is tau a suitable therapeutical target in tauopathies?

Tau is an intracellular protein, found mainly in neurons, but it can also be found in the extracellular space in pathological situations. Here we discuss whether intracellular tau, in aggregated form or modified by phosphorylation, could be toxic inside a neuron. On the other hand, it has been proposed that extracellular tau could be toxic. In this review, we address the question if the elimination of tau would be a possible therapeutic method to avoid tauopathy disorder and we suggest ways to eliminate intracellular and extracellular tau as treatment.