Pyroglutamylated amyloid-ß is associated with hyperphosphorylated tau and severity of Alzheimer's disease.

Pyroglutamylated amyloid-ß (pE(3)-Aß) has been suggested to play a major role in Alzheimer's disease (AD) pathogenesis as amyloid-ß (Aß) oligomers containing pE(3)-Aß might initiate tau-dependent cytotoxicity. We aimed to further elucidate the associations among pE(3)-Aß, full-length Aß and hyperphosphorylated tau (HP-τ) in human brain tissue. We examined 41 post mortem brains of both AD (n = 18) and controls. Sections from frontal and entorhinal cortices were stained with pE(3)-Aß, HP-τ and full-length Aß antibodies. The respective loads were assessed using image analysis and western blot analysis was performed in a subset of cases. All loads were significantly higher in AD, but when using Aß loads as independent variables only frontal pE(3)-Aß load predicted AD. In frontal and entorhinal cortices pE(3)-Aß load independently predicted HP-τ load while non-pE(3)-Aß failed to do so. All loads correlated with the severity of AD neuropathology. However, partial correlation analysis revealed respective correlations in the frontal cortex only for pE(3)-Aß load only while in the entorhinal cortex respective correlations were seen for both HP-τ and non-pE(3)-Aß loads. Mini Mental State Examination scores were independently predicted by entorhinal HP-τ load and by frontal pE(3)-Aß load. Here, we report an association between pE(3)-Aß and HP-τ in human brain tissue and an influence of frontal pE(3)-Aß on both the severity of AD neuropathology and clinical dementia. Our findings further support the notion that pE(3)-Aß may represent an important link between Aß and HP-τ, and investigations into its role as diagnostic and therapeutic target in AD are warranted.

Transgenic expression of intraneuronal Aß42 but not Aß40 leads to cellular Aß lesions, degeneration, and functional impairment without typical Alzheimer's disease pathology.

An early role of amyloid-ß peptide (Aß) aggregation in Alzheimer's disease pathogenesis is well established. However, the contribution of intracellular or extracellular forms of Aß to the neurodegenerative process is a subject of considerable debate. We here describe transgenic mice expressing Aß1-40 (APP47) and Aß1-42 (APP48) with a cleaved signal sequence to insert both peptides during synthesis into the endoplasmic reticulum. Although lower in transgene mRNA, APP48 mice reach a higher brain Aß concentration. The reduced solubility and increased aggregation of Aß1-42 may impair its degradation. APP48 mice develop intracellular Aß lesions in dendrites and lysosomes. The hippocampal neuron number is reduced already at young age. The brain weight decreases during aging in conjunction with severe white matter atrophy. The mice show a motor impairment. Only very few Aß1-40 lesions are found in APP47 mice. Neither APP47 nor APP48 nor the bigenic mice develop extracellular amyloid plaques. While intracellular membrane expression of Aß1-42 in APP48 mice does not lead to the AD-typical lesions, Aß aggregates develop within cells accompanied by considerable neurodegeneration.

Pathology of clinical and preclinical Alzheimer's disease.

Alzheimer's disease (AD) is characterized neuropathologically by the presence of amyloid plaques, neuritic plaques, and neurofibrillary tangles (NFTs). These lesions occur not only in demented individuals with AD but also in non-demented persons. In non-demented individuals, amyloid and neuritic plaques are usually accompanied with NFTs and are considered to represent asymptomatic or preclinical AD (pre-AD) pathology. Here, we defined and characterized neuropathological differences between clinical AD, non-demented pre-AD, and non-AD control cases. Our results show that clinical AD may be defined as cases exhibiting late stages of NFT, amyloid, and neuritic plaque pathology. This is in contrast to the neuropathological changes characteristic of pre-AD, which display early stages of these lesions. Both AD and pre-AD cases often exhibit cerebral amyloid angiopathy (CAA) and granulovacuolar degeneration (GVD), and when they do, these AD-related pathologies were at early stages in pre-AD cases and at late stages in symptomatic AD. Importantly, NFTs, GVD, and CAA were also observed in non-AD cases, i.e., in cases without amyloid plaque pathology. Moreover, soluble and dispersible, high-molecular-weight amyloid ß-protein (Aß) aggregates detected by blue-native polyacrylamide gel electrophoresis were elevated in clinical AD compared to that in pre-AD and non-AD cases. Detection of NFTs, GVD, and CAA in cases without amyloid plaques, presently classified as non-AD, is consistent with the idea that NFTs, GVD, and CAA may precede amyloid plaque pathology and may represent a pre-amyloid plaque stage of pre-AD not yet considered in the current recommendations for the neuropathological diagnosis of AD. Our finding of early stages of AD-related NFT, amyloid, and GVD pathology provides a more clear definition of pre-AD cases that is in contrast to the changes in clinical AD, which is characterized by late stages of these AD-related pathologies. The observed elevation of soluble/dispersible Aß aggregates from pre-AD compared to that in AD cases suggests that, in addition to more widespread AD-related pathologies, soluble/dispersible Aß aggregates in the neuropil play a role in the conversion of pre-AD to clinical AD.

High-molecular weight Aß oligomers and protofibrils are the predominant Aß species in the native soluble protein fraction of the AD brain.

Alzheimer's disease (AD) is characterized by the aggregation and deposition of amyloid ß protein (Aß) in the brain. Soluble Aß oligomers are thought to be toxic. To investigate the predominant species of Aß protein that may play a role in AD pathogenesis, we performed biochemical analysis of AD and control brains. Sucrose buffer-soluble brain lysates were characterized in native form using blue native (BN)-PAGE and also in denatured form using SDS-PAGE followed by Western blot analysis. BN-PAGE analysis revealed a high-molecular weight smear (>1000 kD) of Aß(42) -positive material in the AD brain, whereas low-molecular weight and monomeric Aß species were not detected. SDS-PAGE analysis, on the other hand, allowed the detection of prominent Aß monomer and dimer bands in AD cases but not in controls. Immunoelectron microscopy of immunoprecipitated oligomers and protofibrils/fibrils showed spherical and protofibrillar Aß-positive material, thereby confirming the presence of high-molecular weight Aß (hiMWAß) aggregates in the AD brain. In vitro analysis of synthetic Aß(40) - and Aß(42) preparations revealed Aß fibrils, protofibrils, and hiMWAß oligomers that were detectable at the electron microscopic level and after BN-PAGE. Further, BN-PAGE analysis exhibited a monomer band and less prominent low-molecular weight Aß (loMWAß) oligomers. In contrast, SDS-PAGE showed large amounts of loMWAß but no hiMWAß(40) and strikingly reduced levels of hiMWAß(42) . These results indicate that hiMWAß aggregates, particularly Aß(42) species, are most prevalent in the soluble fraction of the AD brain. Thus, soluble hiMWAß aggregates may play an important role in the pathogenesis of AD either independently or as a reservoir for release of loMWAß oligomers.

Amyloid-ß protein modulates the perivascular clearance of neuronal apolipoprotein E in mouse models of Alzheimer's disease.

The deposition of amyloid-ß protein (Aß) in the brain is a hallmark of Alzheimer's disease (AD). Apolipoprotein E (apoE) is involved in the clearance of Aß from brain and the APOE ε4 allele is a major risk factor for sporadic AD. We have recently shown that apoE is drained into the perivascular space (PVS), where it co-localizes with Aß. To further clarify the role of apoE in perivascular clearance of Aß, we studied apoE-transgenic mice over-expressing human apoE4 either in astrocytes (GE4) or in neurons (TE4). These animals were crossbred with amyloid precursor protein (APP)-transgenic mice and with APP-presenilin-1 (APP-PS1) double transgenic mice. Using an antibody that specifically detects human apoE (h-apoE), we observed that astroglial expression of h-apoE in GE4 mice leads to its perivascular drainage, whereas neuronal expression in TE4 mice does not, indicating that neuron-derived apoE is usually not the subject of perivascular drainage. However, h-apoE was observed not only in the PVS of APP-GE4 and APP-PS1-GE4 mice, but also in that of APP-TE4 and APP-PS1-TE4 mice. In all these mouse lines, we found co-localization of neuron-derived h-apoE and Aß in the PVS. Aß and h-apoE were also found in the cytoplasm of perivascular astrocytes indicating that astrocytes take up the neuron-derived apoE bound to Aß, presumably prior to its clearance into the PVS. The uptake of apoE-Aß complexes into glial cells was further investigated in glioblastoma cells. It was mediated by α(2)macroglobulin receptor/low density lipoprotein receptor-related protein (LRP-1) and inhibited by adding receptor-associated protein (RAP). It results in endosomal Aß accumulation within these cells. These results suggest that neuronal apoE-Aß complexes, but not neuronal apoE alone, are substrates for LRP-1-mediated astroglial uptake, transcytosis, and subsequent perivascular drainage. Thus, the production of Aß and its interaction with apoE lead to the pathological perivascular drainage of neuronal apoE and provide insight into the pathological interactions of Aß with neuronal apoE metabolism.

Correction to: Different aspects of Alzheimer's disease-related amyloid ß-peptide pathology and their relationship to amyloid positron emission tomography imaging and dementia.

An amendment to this paper has been published and can be accessed via the original article.

Cerebral small vessel disease-induced apolipoprotein E leakage is associated with Alzheimer disease and the accumulation of amyloid beta-protein in perivascular astrocytes.

Apolipoprotein E (apoE) plays a role in the pathogenesis of Alzheimer disease (AD). It is involved in the receptor-mediated cellular clearance of the amyloid beta-protein (Abeta) and in the perivascular drainage of the extracellular fluid. Microvascular changes are also associated with AD and have been discussed as a possible reason for altered perivascular drainage. To further clarify the role of apoE in the perivascular and vascular pathology in AD patients, we studied its occurrence and distribution in the perivascular space, the perivascular neuropil, and in the vessel wall of AD and control cases with and without small vessel disease (SVD). Apolipoprotein E was found in the perivascular space and in the neuropil around arteries of the basal ganglia from control and AD cases disclosing no major differences. Western blot analysis of basal ganglia tissue also revealed no significant differences pertaining to the amount of full-length and C-terminal truncated apoE in AD cases compared with controls. In contrast, Abeta occurred in apoE-positive perivascular astrocytes in AD cases but not in controls. In blood vessels, apoE and immunoglobulin G were detected within the SVD-altered vessel wall. The severity of SVD was associated with the occurrence of apoE in the vessel wall and with that of Abeta in perivascular astrocytes. These results point to an important role of apoE in the perivascular clearance of Abeta in the human brain. The occurrence of apoE and immunoglobulin G in SVD lesions and in the perivascular space suggests that the presence of SVD results in plasma-protein leakage into the brain. It is therefore tempting to speculate that apoE represents a pathogenetic link between SVD and AD.