No abstract

Pyroglutamate-modified amyloid-␤ (A␤ pE3 ) peptides are gaining considerable attention as potential key participants in the pathology of Alzheimer disease (AD) due to their abundance in AD brain, high aggregation propensity, stability, and cellular toxicity. Transgenic mice that produce high levels of A␤ pE3-42 show severe neuron loss. Recent in vitro and in vivo experiments have proven that the enzyme glutaminyl cyclase catalyzes the formation of A␤ pE3 . In this minireview, we summarize the current knowledge on A␤ pE3 , discussing its discovery, biochemical properties, molecular events determining formation, prevalence in the brains of AD patients, Alzheimer mouse models, and potential as a target for therapy and as a diagnostic marker.When Alois Alzheimer presented the case of his patient Auguste Deter at the Tübingen meeting of the Southwest German Psychiatrists in 1906, he did not attract much attention or stimulate any discussion in the audience. The young doctor likely would not have believed that, 100 years later, the disease that now holds his name would be the most common cause of dementia and a source of a critical medical and economical problem. At this meeting, Alzheimer presented Auguste Deter's symptoms and reported the histopathological features that are now associated with Alzheimer disease (AD) 2 : neuron loss, extracellular amyloid plaques, and intracellular neurofibrillary tangles. For more than 2 decades, the amyloid hypothesis has been the cardinal hypothesis in describing the sequence of AD etiology. The amyloid hypothesis considers amyloid-␤ (A␤) deposition to be the causative event of AD pathology and that neurofibrillary tangles, cell loss, vascular damage, and dementia occur as a consequence of it (1). However, it has been recently suggested that the extracellular formation of A␤ plaques and other AD pathological events are preceded by intraneuronal A␤ accumulation, giving rise to a modified amyloid hypothesis (2).The story of successful discoveries in modern AD research using novel molecular biological tools started with the biochemical analysis of ␤-amyloid-containing blood vessels (congophilic amyloid angiopathy) (3) and amyloid plaques consisting of A␤ (4), which led to the isolation and sequencing of the gene encoding the larger amyloid precursor protein (APP) (5, 6).In vitro and in vivo analyses of amyloid deposits in AD revealed various N-and C-terminal variants (4, 7, 8). Increased C-terminal length of A␤ (from A␤ x-40 to A␤ x-42 ) in AD enhanced aggregation and early deposition and promoted the toxicity of A␤ (9 -11). Recently, A␤ 1-43 has been discussed as a novel toxic peptide in AD (12).Beside A␤ peptides, starting with aspartate as the first amino acid (A␤ 1-x ), several N-terminally truncated and modified A␤ species have been described (4, 13-15). Among A␤ species present in AD plaques, Lewis et al. (16) reported that A␤ 4 -42 is a relatively abundant species in AD, aged control, and vascular dementia patients. Using immunoprecipitation in combination with mass spectrome...

N-terminally truncated A␤ peptides starting with pyroglutamate (A␤pE3) represent a major fraction of all A␤ peptides in the brain of Alzheimer disease (AD) patients. A␤pE3 has a higher aggregation propensity and stability and shows increased toxicity compared with full-length A␤. In the present work, we generated a novel monoclonal antibody (9D5) that selectively recognizes oligomeric assemblies of A␤pE3 and studied the potential involvement of oligomeric A␤pE3 in vivo using transgenic mouse models as well as human brains from sporadic and familial AD cases. 9D5 showed an unusual staining pattern with almost nondetectable plaques in sporadic AD patients and non-demented controls. Interestingly, in sporadic and familial AD cases prominent intraneuronal and blood vessel staining was observed. Using a novel sandwich ELISA significantly decreased levels of oligomers in plasma samples from patients with AD compared with healthy controls were identified. Moreover, passive immunization of 5XFAD mice with 9D5 significantly reduced overall A␤ plaque load and A␤pE3 levels, and normalized behavioral deficits. These data indicate that 9D5 is a therapeutically and diagnostically effective monoclonal antibody targeting low molecular weight A␤pE3 oligomers. Alzheimer disease (AD)3 represents the most frequent form of dementia and is characterized by the presence of extracellular amyloid plaques composed of amyloid-␤ (A␤) surrounded by dystrophic neurites and neurofibrillary tangles. The discovery that certain early-onset familial forms of AD may be caused by enhanced levels of A␤ peptides have led to the hypothesis that amyloidogenic A␤ is intimately involved in the AD pathogenic process (1). In the past extracellular A␤ has been regarded as the major culprit, whereas more recent evidence now points to toxic effects of A␤ in intracellular compartments (2-3). In addition, other concepts propose that the soluble oligomers and the ␤-sheet containing amyloid fibrils are the toxic forms of A␤ (4 -6). Supporting this notion, it has been demonstrated that soluble oligomeric A␤42, but not plaque-associated A␤, correlates best with cognitive dysfunction in AD (7-8). Oligomers are formed preferentially intracellulary within neuronal processes and synapses rather than extracellularly (9 -10). Besides full-length A␤ peptides starting with an aspartate at position 1, a variety of different N-truncated A␤ peptides have been identified in AD brains. Ragged peptides including phenylalanine at position 4 of A␤ have been reported as early as 1985 by Masters et al. (11). In contrast, no N-terminal sequence could be obtained from cores purified in a sodium dodecyl sulfate-containing buffer, which led to the assumption that the N terminus could be blocked (12-13). The presence of A␤pE3 (N-terminally truncated A␤ starting with pyroglutamate) in AD brain was subsequently shown using mass spectrometry of purified A␤ peptides, explaining at least partially initial difficulties in sequencing A␤ peptides purified from human brain tissue (14). The author...

Pyroglutamate-modified A␤ (A␤pE3-42) peptides are gaining considerable attention as potential key players in the pathology of Alzheimer disease (AD) due to their abundance in AD brain, high aggregation propensity, stability, and cellular toxicity. Overexpressing A␤pE3-42 induced a severe neuron loss and neurological phenotype in TBA2 mice. In vitro and in vivo experiments have recently proven that the enzyme glutaminyl cyclase (QC) catalyzes the formation of A␤pE3-42. The aim of the present work was to analyze the role of QC in an AD mouse model with abundant A␤pE3-42 formation. 5XFAD mice were crossed with transgenic mice expressing human QC (hQC) under the control of the Thy1 promoter. 5XFAD/hQC bigenic mice showed significant elevation in TBS, SDS, and formic acid-soluble A␤pE3-42 peptides and aggregation in plaques. In 6-month-old 5XFAD/hQC mice, a significant motor and working memory impairment developed compared with 5XFAD. The contribution of endogenous QC was studied by generating 5XFAD/QC-KO mice (mouse QC knock-out). 5XFAD/QC-KO mice showed a significant rescue of the wild-type mice behavioral phenotype, demonstrating the important contribution of endogenous mouse QC and transgenic overexpressed QC. These data clearly demonstrate that QC is crucial for modulating A␤pE3-42 levels in vivo and prove on a genetic base the concept that reduction of QC activity is a promising new therapeutic approach for AD. Alzheimer disease (AD)4 is a progressive neurodegenerative disorder characterized by the presence of extracellular amyloid plaques composed of amyloid-␤ (A␤) and intracellular neurofibrillary tangles. The discovery that certain early onset familial forms of AD may be caused by enhanced levels of A␤ peptides has led to the hypothesis that amyloidogenic A␤ is intimately involved in the pathogenic process (1).Besides full-length A␤ 40 and 42 isoforms starting with an aspartate at position 1, a variety of different N-truncated A␤ peptides have been identified in AD brains. Ragged peptides including phenylalanine at position 4 of A␤ have been reported as early as 1985 by Masters et al. (2). In contrast, no N-terminal sequence could be obtained from cores purified in a SDS-containing buffer, which led to the assumption that the N terminus could be blocked (3, 4).The presence of A␤pE3 (N-terminally truncated A␤ starting with pyroglutamate) in AD brain was subsequently shown using mass spectrometry of purified A␤ peptides, explaining at least partially initial difficulties in sequencing A␤ peptides purified from human brain tissue (5). The authors reported that only 10 -15% of the total A␤ isolated by this method begins at position 3 with A␤pE3. Saido et al. (6) and others (7) subsequently showed that A␤pE3 represents a dominant fraction of A␤ peptides in AD brain.Overexpression of A␤pE3-42 in neurons of TBA2 transgenic mice triggers neuron loss and an associated neurological phenotype (8). N-terminal pE formation can be catalyzed by glutaminyl cyclase (QC) and is pharmacologically inhibited by QC inhibitors, b...

The presence of Ab pE3 (N-terminal truncated Ab starting with pyroglutamate) in Alzheimer's disease (AD) has received considerable attention since the discovery that this peptide represents a dominant fraction of Ab peptides in senile plaques of AD brains. This was later confirmed by other reports investigating AD and Down's syndrome postmortem brain tissue. Importantly, Ab pE3 has a higher aggregation propensity, and stability, and shows an increased toxicity compared to full-length Ab. We have recently shown that intraneuronal accumulation of Ab pE3 peptides induces a severe neuron loss and an associated neurological phenotype in the TBA2 mouse model for AD. Given the increasing interest in Ab pE3 , we have generated two novel monoclonal antibodies which were characterized as highly specific for Ab pE3 peptides and herein used to analyze plaque deposition in APP/PS1KI mice, an AD model with severe neuron loss and learning deficits. This was compared with the plaque pattern present in brain tissue from sporadic and familial AD cases. Abundant plaques positive for Ab pE3 were present in patients with sporadic AD and familial AD including those carrying mutations in APP (arctic and Swedish) and PS1. Interestingly, in APP/PS1KI mice we observed a continuous increase in Ab pE3 plaque load with increasing age, while the density for Ab 1-x plaques declined with aging. We therefore assume that, in particular, the peptides starting with position 1 of Ab are N-truncated as disease progresses, and that, Ab pE3 positive plaques are resistant to age-dependent degradation likely due to their high stability and propensity to aggregate.