Accumulation of abnormally phosphorylated tau precedes the formation of neurofibrillary tangles in Alzheimer's disease

The intraneuronal accumulation of paired helical filaments in the form of neurofibrillary tangles is one hallmark of the brain pathology in Alzheimer's disease. At certain predilection sites, a small number of similar lesions are also present in the brains of the majority of aged non-demented individuals. As suggested by several studies before, these abnormal cytoskeletal structures contain determinants of microtubule-associated protein tau and ubiquitin. The present study uses a morphological classification of neurofibrillary tangles into different stages of maturation, as suggested by Alzheimer in 1911, and shows by quantitative immunocytochemistry that early stages of neurofibrillary degeneration contain abnormally phosphorylated tau. Immunoreactivity for the altered tau is seen not only in tangles but also in the cytoplasm of some nerve cells lacking neurofibrillary tangles. Similar numbers of such immunoreactive neurons without tangles are present in age-matched non-demented individuals as in Alzheimer cases, but are absent in young controls. In contrast, incorporation of an epitope, recognized by a monoclonal antibody (3-39) raised to paired helical filaments, which is directed against a determinant residing in the 50-65 amino acid residue region of ubiquitin occurs late in the process of tangle maturation and is most pronounced in extracellular 'ghost tangles'. It is suggested that the accumulation of abnormally phosphorylated tau is one of the earliest cytoskeletal changes in the process of tangle formation. Exposure of certain ubiquitin epitopes in the pathological fibers may reflect an unsuccessful attempt of proteolytic degradation.     

Dystrophic neurites infiltrate extracellular neurofibrillary tangles in Alzheimer disease

The neurotrophic activity of β-amyloid protein (β-AP) has been suggested to be responsible for the dystrophic neurites that surround β-AP deposits in senile plaques of Alzheimer disease. The recent finding that neurofibrillary tangles (NFT) that remain as remnants in the extracellular space (E-NFT) after the death of the neuron contain β-AP, suggested that dystrophic neurites might also be associated with E-NFT. In this study, we use a probe for E-NFT, basic fibroblast growth factor (bFGF)-binding to show that E-NFT do contain dystrophic neurites. Since these neurites contain the amyloid precursor protein whose cleavage can lead to β-AP, they may also play a role in further β-AP deposition in the E-NFT.     

Increased neurofibrillary tangles in patients with Alzheimer disease with comorbid depression.

OBJECTIVE: Recent evidence suggests that a history of major depression may lead to increases in hippocampal neuropathology in Alzheimer disease (AD). The authors tested the hypothesis that neuritic plaques and neurofibrillary tangles are more pronounced in the brains of patients with AD with comorbid depression as compared with patients with AD without depression. METHODS: Brain samples from patients were selected from the U.S. National Alzheimer's Coordinating Center database. The primary analysis included 7164 individuals: 6468 had AD as the primary neuropathologic diagnosis and 696 were considered neuropathologically normal. Depression at study inclusion was rated as present or absent in consensus conferences. Neuropathologic ratings from the Consortium to Establish a Registry in Alzheimer's Disease rating of neuritic plaques and Braak staging of neurofibrillary tangles were used for between-group analyses. RESULTS: Brains of patients with AD with comorbid depression showed higher levels of cortical tangle formation than brains of patients with AD without comorbid depression. Results remained stable when controlling for age, gender, level of education, and cognitive status. Within patients with AD, comorbid depression increased the odds for advanced neuropathologic disease stage (odds ratio: 1.47; 95% confidence interval: 1.03-2.08). CONCLUSION: In AD, the presence of depression comorbidity corresponds to increases in AD-related neuropathologic changes beyond age, gender, level of education, and cognitive status, suggesting an interaction between depression and the neuropathologic processes in AD.     

Genes associated with the progression of neurofibrillary tangles in Alzheimer's disease

The spreading of neurofibrillary tangles (NFTs), intraneuronal aggregates of highly phosphorylated microtubule-associated protein tau, across the human brain is correlated with the cognitive severity of Alzheimer''s disease (AD). To identify genes relevant to NFT expansion defined by the Braak stage, we conducted whole-genome exon array analysis with an exploratory sample set consisting of 213 human post-mortem brain tissue specimens from the entorinal, temporal and frontal cortices of 71 brain-donor subjects: Braak NFT stages 0 (N=13), I–II (N=20), III–IV (N=19) and V–VI (N=19). We identified eight genes, RELN, PTGS2, MYO5C, TRIL, DCHS2, GRB14, NPAS4 and PHYHD1, associated with the Braak stage. The expression levels of three genes, PHYHD1, MYO5C and GRB14, exhibited reproducible association on real-time quantitative PCR analysis. In another sample set, including control subjects (N=30), and in patients with late-onset AD (N=37), dementia with Lewy bodies (N=17) and Parkinson disease (N=36), the expression levels of two genes, PHYHD1 and MYO5C, were obviously associated with late-onset AD. Protein–protein interaction network analysis with a public database revealed that PHYHD1 interacts with MYO5C via POT1, and PHYHD1 directly interacts with amyloid beta-peptide 42. It is thus likely that functional failure of PHYHD1 and MYO5C could lead to AD development.     

Neuronal loss correlates with but exceeds neurofibrillary tangles in Alzheimer's disease

To assess the relationship between dementia, neuronal loss, and neuropathological findings in Alzheimer's disease (AD), we counted the number of neurons, senile plaques, and neurofibrillary tangles in a high-order association cortex. We studied the superior temporal sulcus of 34 individuals with AD and 17 nondemented control subjects, using statistically unbiased, stereological counting techniques. The number of superior temporal sulcus neurons in nondemented control subjects was stable across the sixth to ninth decades. In AD, more than 50% of the neurons were lost. Both neuronal loss and neurofibrillary tangles increased in parallel with the duration and severity of illness, but the amount of neuronal loss exceeded by manyfold the amount of neurofibrillary tangles accumulated. In contrast to the correlation between neurofibrillary tangels and neuronal loss, the number of senile plaques and the percentage of the superior temporal sulcus that was covered by Aβ (amyloid burden) were not related to neuronal loss, number of neurofibrillary tangles, or duration of disease. Neither the amount nor the rate of neuronal loss in the superior temporal sulcus in AD correlated with apolipoprotein E genotype. These data suggest that neuronal loss in association areas such as the superior temporal sulcus contributes directly to cognitive impairment in AD.     

阿尔茨海默病患者脑中双螺旋丝的体外去磷酸化作用

目的探讨阿尔茨海默病（ＡＤ）脑损伤逆转的可能性及其途径。方法用去磷酸化和免疫印迹法研究ＡＤ脑损伤可逆性。结果蛋白磷酸酯酶（ＰＰ）２Ａ和ＰＰ２Ｂ可使ＡＤ神经原纤维缠结中的Ｉ型双螺旋丝（ＰＨＦＩｔａｕ）在Ｓｅｒ１９９／Ｓｅｒ２０２去磷酸化，Ｓｅｒ３９６／Ｓｅｒ４０４部分去磷酸化；此外，ＰＰ２Ａ和ＰＰ２Ｂ可分别使ＰＨＦＩＩｔａｕ的Ｓｅｒ４６和Ｓｅｒ２３５去磷酸化；去磷酸化后ＰＨＦＩＩｔａｕ的相对电泳迁移率加快。Ｍｎ２＋和Ｍｇ２＋可增加上述酶对ＰＨＦＩＩｔａｕ的去磷酸化作用。酶的去磷酸化作用具有浓度依赖性，随着酶浓度的增加，去磷酸化作用增强。结论因为ｔａｕ蛋白异常过度磷酸化并形成ＰＨＦ被认为是ＡＤ神经原纤维退化的基础，ＰＨＦ可在体外被蛋白磷酸酯酶去磷酸化的结果提示，ＡＤ脑损伤可能是可逆的。     

Microglia are associated with the extracellular neurofibrillary tangles of Alzheimer disease.

When neurons die, the filaments of neurofibrillary tangles (NFT) undergo structural and antigenic modifications. The exact mechanism of this modification is unknown, but glial cells could play an important role. Previous studies have shown that astroglial processes infiltrate extracellular NFT. In this study we use double immunolabelling to show that microglia also infiltrate extracellular NFT. Therefore, along with the previously identified astroglia, the microglia could be responsible for the modification of extracellular NFT.     

Severity of dementia in Alzheimer disease and neurofibrillary tangles in multiple brain regions

We studied the relationship of numbers of neurofibrillary tangles (NFTs) in selected cortical and subcortical sites to the duration of clinical disease and severity of dementia. Sixteen patients with a clinical diagnosis of "probable" Alzheimer disease were screened with standardized neuropsychological instruments to estimate the severity of dementia. Tissues were obtained at autopsy from the subiculum, four neocortical areas, and the nucleus basalis of Meynert: NFT counts were assessed with the thioflavin S stain. Overall, the subiculum showed the most NFTs, followed by visual association and premotor cortices, primary cortex (motor and visual), and the nucleus basalis. NFT counts were significantly positively correlated with the duration of disease in the nucleus basalis and less strongly in the motor cortex. Neuropsychological impairment was significantly correlated with NFT counts only in the nucleus basalis. In turn, counts in the nucleus basalis were reliably correlated with those in all other brain regions except the subiculum. Counts in the subiculum showed no correlation with any other area. Numbers of NFTs within functionally related sites, the primary motor and premotor cortices or primary and visual association cortices, were significantly or near-significantly correlated, whereas motor and visual cortical counts showed no intercorrelation. Our results indicate that although there is less NFT accumulation in the nucleus basalis than in many other brain regions, counts in this structure bear a close relationship to disease severity and duration and to NFT accumulation in other regions.     

14-3-3 protein beta isoform is associated with 3-repeat tau neurofibrillary tangles in Alzheimer's disease

14-3-3 proteins play roles in phosphorylation of tau proteins in neurofibrillary tangles (NFT) in Alzheimer's disease (AD). Tau is phosphorylated at serine (pSer) and threonine (pThr) in NFT, and NFT morphology varies according to phosphorylated sites and tau isoform. The roles of 14-3-3 proteins in NFT morphology remain unknown. This study was performed to examine the relationships between 14 and 3-3 proteins and tau phosphorylation of NFT. NFT were labeled with Gallyas impregnation, tau and 14-3-3 immunohistochemistry in paraffin-embedded hippocampal sections from seven AD and three control brains. Anti-tau antisera included monoclonal antisera that recognize pSer262 (pSer262), pSer422 (pSer422), pSer202/pThr205 (AT8), Thr231 (AT180), three-repeat (RD3) and four-repeat (RD4) tau isoform. Anti-14-3-3 protein isoform antisera included polyclonal antisera to beta, gamma, zeta, epsilon, tau, mu and sigma isoforms and monoclonal antiserum to beta antiserum (H8-beta). NFT density was obtained by counting labeled NFT in cornu ammonis (CA) 1-CA4, subiculum and entorhinal cortex. H8-beta and zeta isoforms were strongly expressed in NFT. Regional densities of NFT positive for pSer262, AT8, AT180, and Gallyas impregnation were similar to RD3-positive NFT density with high densities in CA1 and entorhinal cortex. NFT positive for pSer422 showed a similar regional distribution to RD4-positive NFT with high NFT density in CA2-CA4. H8-beta-positive NFT showed a similar regional distribution to RD3-positive NFT. In contrast, zeta isoform-positive NFT showed no specific distribution. In conclusion, H8-beta isoform is associated with development of 3-repeats NFT but a role of 14-3-3 zeta isoform in NFT could not be specified.     

Distribution of neurofibrillary tangles in diffuse neurofibrillary tangles with calcification

Aims:  In this study, the appearance and distribution of neurofibrillary tangles (NFT) in diffuse neurofibrillary tangles with calcification (DNTC) were investigated neuropathologically in order to elucidate the detailed distribution pattern in this disease.
Methods:  The distribution of NFT in six cases neuropathologically diagnosed as DNTC (two men and four women) was studied using Gallyas–Braak silver stain. The age at death ranged from 56 to 73, with an average of 63.5 ± 7.5 years.
Results:  NFT were seen throughout the cerebral cortex, and were especially marked in the temporal and limbic cortices. The distribution pattern of NFT in the limbic lobe was similar to that in Alzheimer's disease as reported in the previous studies. In the temporal lobe, more NFT were distributed in the anterior than in the posterior area, which was confirmed in all six cases. The temporal pole showed the highest density of NFT including ghost tangles.
Conclusions:  The diffuse appearance of NFT in the cerebral cortex with the highest severity in the temporal pole was found to be a neuropathological characteristic of DNTC.     

Immunoreactivity patterns in neurofibrillary tangles of the inferior temporal cortex in Alzheimer disease

The distributions of various immunohistochemical markers of neurofibrillary tangles (NFT) were compared to that of a normal nerve cell cytoskeletal marker, SMI32, in the inferior temporal cortex of Alzheimer brains and normal aged controls. NFT markers included antibodies to the microtubule-associated proteins tau, ubiquitin, or amyloid P component (AP). The results showed that, in our group of patients, the decrease of SMI32 immunoreactivity in the Alzheimer temporal cortex is paralleled by an increase in AP immunoreactivity in neurons and neurofibrillary tangles. This suggests that AP may play an important role in NFT formation or evolution in Alzheimer disease.     

磷酸酶和糖苷酶对Alzheimer神经原纤维缠结的作用

目的　探讨Alzheimer病 (AD)神经原纤维缠结形成的可能机制及逆转AD神经元变性的可能性和途径。方法　去磷酸化 ,去糖基化 ,负染电子显微镜和放免印迹图像定量分析技术。结果( 1)磷酸酶 2A、 2B的去磷酸化作用可使AD神经原纤维缠结中的Ⅱ型双螺旋丝 (PHFⅡ )结构松解 ,释放游离tau蛋白的量比对照组高 2 5 % (P <0 .0 0 1) ,去磷酸化可恢复PHFⅡ tau促微管组装的生物学功能 ;( 2 )糖苷酶的去糖基化作用则使PHFⅡ的螺旋消失 ,在电子显微镜下呈直径 ( 2 .5± 0 .5 )nm的束状线性纤微丝结构 ;( 3 )单纯去糖基化不能明显恢复tau的生物学功能 ,也不促使tau蛋白的释放 ,但去糖基化可使随后的去磷酸化从PHFⅡ结构中释放游离tau蛋白的量增高 3 5 % (P <0 .0 5 )。结论( 1)异常磷酸化可能直接参与AD神经元PHF的形成和tau生物学活性的丧失 ;( 2 )异常糖基化可能通过维持PHF的螺旋结构而使其更为稳定 ;( 3 )磷酸酶可从结构和功能上直接抑制和逆转AD的神经元变性 ,而糖苷酶可促进磷酸酶对AD脑损伤的保护作用。     

Comparison of the neurofibrillary pathology in Alzheimer’s disease and familial presenile dementia with tangles

Alzheimer’s disease (AD) is characterised neuropathologically by the presence of abundant extracellular β-amyloid deposits and intracellular neurofibrillary lesions consisting of neurofibrillary tangles, neuropil threads and senile plaque neurites which contain paired helical filaments (PHFs) made of hyperphosphorylated microtubule-associated protein tau. A new familial form of presenile dementia with neurofibrillary pathology and no β-amyloid deposits has been described recently [Sumi et al. (1992) Neurology 42: 120–127]. We have compared the tau pathology in this familial form of presenile dementia with that of AD. To this end we have used electron microscopy, immunoblotting and immunohistochemistry with phosphorylation-dependent (PHF1, AT8, AT100, AT180, AT270, 12E8) and phosphorylation-independent (BR133, BR134) anti-tau antibodies. We show that in the two diseases dispersed PHFs are structurally, biochemically and immunologically identical; they are stained by all anti-tau antibodies used and on immunoblots PHF-tau appears as three major bands of 60, 64 and 68 kDa. However, while the anti-tau antibodies stain neurofibrillary tangles, neuropil threads and neuritic plaques in AD brain, no neuritic plaques are found in familial presenile dementia. These results indicate that in the two diseases tau undergoes the same modifications; they confirm that neurofibrillary tangles and neuropil threads like those in AD can exist independently of β-amyloid deposits and that their presence is associated with dementia.     

Efficacy and safety of immunization with phosphorylated tau against neurofibrillary tangles in mice

As an abnormally folded and aggregated protein, tau composed of neurofibrillary tangles (NFTs) in Alzheimer's disease and other tauopathies seems to be a candidate for immunotherapy. Yet, the encephalitogenicity of full-length tau protein, recently reported by us in immunized mice, demands to carefully and selectively target pathological tau and address both efficacy (anti-NFT effect) and safety (free of encephalitis). We immunized NFT mice with NFT-related phosphorylated (phos) tau peptides, using an immunization protocol aimed to predispose a proinflammatory milieu in CNS as a set up to detect biohazard, an approach we used when the neurotoxicity of full-length tau was detected [use of complete Freund adjuvant (CFA) with pertussis toxin (PT)]. A decrease of about 40% in NFT burden in CNS was demonstrated and was accompanied with an increase in microglial burden. Anti-phos-tau antibodies were detected in serum and blood vessels in the CNS, while no encephalitogenicity (free of clinical neurological deficits, of adverse effects on brain inflammatory cells and of axonal damage) was recorded. The level of the lysosomal proteases, cathepsins D and L, was affected in the immunized mice suggesting the possible involvement of the lysosomal system in the decrease of NFTs. The robust anti-NFT effect and the lack of encephalitogenicity in NFT mice immunized with phos-tau peptides, even though CFA with PT was included in vaccine, point to their anti-NFT therapeutic potential.     

Visualization of newly deposited tau in neurofibrillary tangles and neuropil threads

Neurofibrillary tangles (NFTs) and neuropil threads (NTs), the major hallmark of Alzheimer disease (AD), are composed of the microtubule-associated protein tau that has undergone posttranslational modifications, including deamidation and isomerization on asparaginyl or aspartyl residues. Because such modifications represent protein aging, we generated 2 antibodies, TM4, specific for Asp-387 of tau, and iD387, specific for isoAsp-387 of tau, to investigate the evolution of NFTs and NTs. On Western blots of Sarkosyl-insoluble fractions, TM4 strongly labeled paired helical filament-tau (PHF-tau), whereas iD387 preferentially labeled PHF smear. Thus, it is reasonable to postulate that TM4-labeled tau (unmodified tau species) represents more recent deposition, and iD387-labeled tau (modified tau species) represents earlier deposition. Unexpectedly, TM4 immunostained even highly evolved NFTs, suggesting that deposition of newly produced tau continues until neuronal death. iD387 labeled the whole profile of NFTs up to distal dendritic branches, whereas TM4 staining was localized to particular portions of NFTs in proximal dendrites and neuronal perikarya. In NTs, TM4 preferentially labeled the outer portion, whereas iD387 intensely labeled the core portion. Based on TM4-positive NFT counts and total NFT counts, we speculate that NFTs in the human hippocampus are produced at a constant rate irrespective of the disease stage.     

Abnormal phosphorylation of tau precedes ubiquitination in neurofibrillary pathology of Alzheimer disease

On tissue sections of Alzheimer brain, 4 antibodies to tau immunolabel not only neurofibrillary tangles, neuritic plaques and neuropil threads but also the tangle-free cytoplasm of a subset of hippocampal and cortical neurons we believe to be at a stage of alteration preceding the formation of paired helical filaments (PHF). Pretreatment of tissue sections with alkaline phosphatase leads to an increase in staining intensity and in number of immunoreactive lesions with antibodies directed to an amino terminal and to a mid-region of the tau molecule. The diffuse neuronal staining could not be observed with any of 7 monoclonal antibodies recognizing ubiquitin. We conclude (1) that abnormal phosphorylation of tau occurs prior to its incorporation into PHF and leads to its accumulation in the nerve cell body and (2) that ubiquitin is seen associated only when a neurofibrillary tangle is already formed.     

Scanning electron microscopical study of the neurofibrillary tangles of Alzheimer’s disease

Neurofibrillary tangles (NFTs) have been ultrastructually studied by various methods, leading to several three-dimensional models of paired helical filaments (PHFs). In this study, we present the scanning electron microscopic findings of NFTs in an autopsy case of Alzheimer’s disease and clarify the three-dimensional structures of NFTs. NFTs were clearly defined in freeze-cracked nerve cells and consisted of two types of filamentous structures, straight and helical filaments. Straight filaments measured from 20 to 25 nm in diameter and had a smooth surface. They were slightly bent but mostly straight with no constrictions. One type of straight filaments ran in a bundle in the same direction, another was intertwined to each other. Most of the helical profiles of filaments usually measured about 28 nm in diameter, with a distance of 100 nm between periodic constrictions. They seemed to consist of a pair of isodiametric filaments of 10 nm in diameter. In addition, two unusual types of helical filaments were occasionally observed. One comprised thick filaments of about 38 nm in diameter, with a distance of 100 nm between constrictions; these helical filaments appeared to consist of two or more strands. The other comprised thin helical filaments of about 20 nm in diameter and regularly constricted at an interval of 50 nm. All types of the helical filaments examined in this case were leotropic. This result supports a protofilament model of PHFs. Scanning electron microscopy using the freeze-cracked and maceration method is a useful and simple method for three-dimensional observation of the filamentous structures in NFTs. Received: 10 October 1996 / Revised, accepted: 15 January 1997     

Apolipoprotein E immunoreactivity within neurofibrillary tangles: relationship to tau and PHF in Alzheimer's disease

The present immunohistochemical study determined the relationship between ApoE and the expression of the cytoskeletal protein tau (Taut) and paired helical filaments (PHF), within the magnocellular neurons of the nucleus basalis of Meynert and layer II stellate neurons of the entorhinal cortex in Alzheimer's disease (AD). Although nearly all ApoE immunoreactive perikarya within these two brain regions were PHF immunoreactive, not all PHF and Tau2 containing neurons stained for ApoE in AD. Moreover, more Tau2-immunostained neurons, as compared to PHF, were ApoE immunonegative. This was particularly evident in a population of control subjects which exhibited AD-like pathology intermediate between the AD and normal aged individuals. Thus, neurons within the nucleus basalis of Meynert and entorhinal cortex layer II stellate exhibit evidence of cytoskeletal pathology prior to displaying ApoE. These observations suggest that (1) ApoE plays a secondary role in NFT formation or (2) this protein is accumulated within these neurons in response to reparative process(es) induced by NFT-associated neuronal damage.     

Localization of neurofibrillary tangles and beta-amyloid plaques in the brains of living patients with Alzheimer disease.

The authors used 2-(1-(6-[(2-[18F]fluoroethyl)(methyl)amino]-2-naphthyl)ethylidene)malononitrile ([18F]FDDNP), a hydrophobic radiofluorinated derivative of 2-(1-[6-(dimethylamino)-2-naphthyl]ethylidene)malononitrile (DDNP), in conjunction with positron emission tomography to determine the localization and load of neurofibrillary tangles (NFTs) and beta-amyloid senile plaques (APs) in the brains of living Alzheimer disease (AD) patients. Previous work illustrated the in vitro binding characteristics of [18F]FDDNP to synthetic beta-amyloid(1-40) fibrils and to NFTs and APs in human AD brain specimens. In the present study, greater accumulation and slower clearance was observed in AP- and NFT-dense brain areas and correlated with lower memory performance scores. The relative residence time of the probe in brain regions affected by AD was significantly greater in patients with AD (n=9) than in control subjects (n=7; p=0.0007). This noninvasive technique for monitoring AP and NFT development is expected to facilitate diagnostic assessment of patients with AD and assist in response-monitoring during experimental treatments.