Overexpression of Glutaminyl Cyclase, the Enzyme Responsible for Pyroglutamate Aβ Formation, Induces Behavioral Deficits, and Glutaminyl Cyclase Knock-out Rescues the Behavioral Phenotype in 5XFAD Mice

Abstract

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...

Pyroglutamate Amyloid-β (Aβ): A Hatchet Man in Alzheimer Disease

“…The effect of endogenous QC was studied by generating 5XFAD/QC-KO mice (homozygous for murine QC knock-out). 5XFAD/ QC-KO mice showed a significant reduction in A␤ pE3-42 levels, decreased plaque pathology, and a rescue of the behavioral phenotype (93). These data clearly demonstrate that QC is a key participant in modulating A␤ pE3-x levels in vivo and support the concept that QC is a therapeutic target for AD.…”

Pyroglutamate Amyloid β (Aβ) Aggravates Behavioral Deficits in Transgenic Amyloid Mouse Model for Alzheimer Disease

“…The TBA42 transgene was designed to preferentially liberate A␤ peptides into the neuronal secretory pathway. This allows QC to enzymatically catalyze the conversion of A␤ to A␤ pE3-42 (16,17,21).…”

“…Transgenic expression of hQC in 5XFAD mice also leads to the elevation of A␤ pE3 , thereby exacerbating behavioral deficits, increasing plaque load, and raising levels of A␤ pE3-42 but not general A␤ x-42 . It should be noted that QC has several targets besides A␤ 3-x , and these substrates could potentially influence the phenotype of the transgenic 5XFAD/hQC mice in the previous study (21). N-terminal pyroglutamate residues have been described for a number of hormones and secreted proteins (31).…”

“…Blocking QC function, either through genetic knock-out (21) or pharmacological inhibition (22), lowers A␤ pE3 levels, decreases plaque load, and ameliorates behavioral deficits in different AD mouse models. Conversely, crossing 5XFAD mice with transgenic mice expressing human QC (hQC) significantly increases levels of soluble A␤ pE3-42 peptides, raises plaque load, and intensifies motor and working memory impairment (21).…”

Oleuropein aglycone protects against pyroglutamylated-3 amyloid-ß toxicity: biochemical, epigenetic and functional correlates

“…In the AD brain, QC activity and pE-Aß levels are increased by several folds and distinct types of pE-Aß deposits, where pE3-Aß(3-42) predominates, have been identified at sites of QC-immunoreactive neurons and in target fields of QC-rich projection neurons . Chronic pharmacologic inhibition of QC or suppression of its encoding gene (Alexandru et al, 2011;Wirths et al, 2009) in transgenic mouse models of AD resulted in reduced pE-Aß peptide generation and improved performance in cognitive tasks, whereas QC overexpression worsened neuropathology and cognitive dysfunction (Jawhar et al, 2011b).…”