Wolfgang Jagla

Glutaminyl cyclase inhibition attenuates pyroglutamate Aβ and Alzheimer's disease–like pathology

Because of their abundance, resistance to proteolysis, rapid aggregation and neurotoxicity, N-terminally truncated and, in particular, pyroglutamate (pE)-modified Aβ peptides have been suggested as being important in the initiation of pathological cascades resulting in the development of Alzheimers disease. We found that the N-terminal pE-formation is catalyzed by glutaminyl cyclase in vivo. Glutaminyl cyclase expression was upregulated in the cortices of individuals with Alzheimers disease and correlated with the appearance of pE-modified Aβ. Oral application of a glutaminyl cyclase inhibitor resulted in reduced Aβ3(pE)–42 burden in two different transgenic mouse models of Alzheimers disease and in a new Drosophila model. Treatment of mice was accompanied by reductions in Aβx–40/42, diminished plaque formation and gliosis and improved performance in context memory and spatial learning tests. These observations are consistent with the hypothesis that Aβ3(pE)–42 acts as a seed for Aβ aggregation by self-aggregation and co-aggregation with Aβ1–40/42. Therefore, Aβ3(pE)–40/42 peptides seem to represent Aβ forms with exceptional potency for disturbing neuronal function. The reduction of brain pE-Aβ by inhibition of glutaminyl cyclase offers a new therapeutic option for the treatment of Alzheimers disease and provides implications for other amyloidoses, such as familial Danish dementia.

Prion-like behaviour and tau-dependent cytotoxicity of pyroglutamylated amyloid-β

Extracellular plaques of amyloid-β and intraneuronal neurofibrillary tangles made from tau are the histopathological signatures of Alzheimer’s disease. Plaques comprise amyloid-β fibrils that assemble from monomeric and oligomeric intermediates, and are prognostic indicators of Alzheimer’s disease. Despite the importance of plaques to Alzheimer’s disease, oligomers are considered to be the principal toxic forms of amyloid-β. Interestingly, many adverse responses to amyloid-β, such as cytotoxicity, microtubule loss, impaired memory and learning, and neuritic degeneration, are greatly amplified by tau expression. Amino-terminally truncated, pyroglutamylated (pE) forms of amyloid-β are strongly associated with Alzheimer’s disease, are more toxic than amyloid-β, residues 1–42 (Aβ1–42) and Aβ1–40, and have been proposed as initiators of Alzheimer’s disease pathogenesis. Here we report a mechanism by which pE-Aβ may trigger Alzheimer’s disease. Aβ3(pE)–42 co-oligomerizes with excess Aβ1–42 to form metastable low-n oligomers (LNOs) that are structurally distinct and far more cytotoxic to cultured neurons than comparable LNOs made from Aβ1–42 alone. Tau is required for cytotoxicity, and LNOs comprising 5% Aβ3(pE)–42 plus 95% Aβ1–42 (5% pE-Aβ) seed new cytotoxic LNOs through multiple serial dilutions into Aβ1–42 monomers in the absence of additional Aβ3(pE)–42. LNOs isolated from human Alzheimer’s disease brain contained Aβ3(pE)–42, and enhanced Aβ3(pE)–42 formation in mice triggered neuron loss and gliosis at 3 months, but not in a tau-null background. We conclude that Aβ3(pE)–42 confers tau-dependent neuronal death and causes template-induced misfolding of Aβ1–42 into structurally distinct LNOs that propagate by a prion-like mechanism. Our results raise the possibility that Aβ3(pE)–42 acts similarly at a primary step in Alzheimer’s disease pathogenesis.

Inhibition of glutaminyl cyclase prevents pGlu‐Aβ formation after intracortical/hippocampal microinjection in vivo/in situ

Modified amyloid β (Aβ) peptides represent major constituents of the amyloid deposits in Alzheimer’s disease and Down’s syndrome. In particular, N‐terminal pyroglutamate (pGlu) following truncation renders Aβ more stable, increases hydrophobicity and the aggregation velocity. Recent evidence based on in vitro studies suggests that the cyclization of glutamic acid, leading to pGlu‐Aβ, is catalyzed by the enzyme glutaminyl cyclase (QC) following limited proteolysis of Aβ at the N‐terminus. Here, we studied the pGlu‐formation by rat QC in vitro as well as after microinjection of Aβ(1–40) and Aβ(3–40) into the rat cortex in vivo/in situ with and without pharmacological QC inhibition. Significant pGlu‐Aβ formation was observed following injection of Aβ(3–40) after 24 h, indicating a catalyzed process. The generation of pGlu‐Aβ from Aβ(3–40) was significantly inhibited by intracortical microinjection of a QC inhibitor. The study provides first evidence that generation of pGlu‐Aβ is a QC‐catalyzed process in vivo. The approach per se offers a strategy for a rapid evaluation of compounds targeting a reduction of pGlu formation at the N‐terminus of amyloid peptides.

The isoenzyme of glutaminyl cyclase is an important regulator of monocyte infiltration under inflammatory conditions

Acute and chronic inflammatory disorders are characterized by detrimental cytokine and chemokine expression. Frequently, the chemotactic activity of cytokines depends on a modified N‐terminus of the polypeptide. Among those, the N‐terminus of monocyte chemoattractant protein 1 (CCL2 and MCP‐1) is modified to a pyroglutamate (pE‐) residue protecting against degradation in vivo. Here, we show that the N‐terminal pE‐formation depends on glutaminyl cyclase activity. The pE‐residue increases stability against N‐terminal degradation by aminopeptidases and improves receptor activation and signal transduction in vitro. Genetic ablation of the glutaminyl cyclase iso‐enzymes QC (QPCT) or isoQC (QPCTL) revealed a major role of isoQC for pE1‐CCL2 formation and monocyte infiltration. Consistently, administration of QC‐inhibitors in inflammatory models, such as thioglycollate‐induced peritonitis reduced monocyte infiltration. The pharmacologic efficacy of QC/isoQC‐inhibition was assessed in accelerated atherosclerosis in ApoE3*Leiden mice, showing attenuated atherosclerotic pathology following chronic oral treatment. Current strategies targeting CCL2 are mainly based on antibodies or spiegelmers. The application of small, orally available inhibitors of glutaminyl cyclases represents an alternative therapeutic strategy to treat CCL2‐driven disorders such as atherosclerosis/restenosis and fibrosis.

Glutaminyl cyclase-mediated toxicity of pyroglutamate-beta amyloid induces striatal neurodegeneration

BackgroundPosttranslational modifications of beta amyloid (Aβ) have been shown to affect its biophysical and neurophysiological properties. One of these modifications is N-terminal pyroglutamate (pE) formation. Enzymatic glutaminyl cyclase (QC) activity catalyzes cyclization of truncated Aβ(3-x), generating pE3-Aβ. Compared to unmodified Aβ, pE3-Aβ is more hydrophobic and neurotoxic. In addition, it accelerates aggregation of other Aβ species. To directly investigate pE3-Aβ formation and toxicity in vivo, transgenic (tg) ETNA (E at the truncated N-terminus of Aβ) mice expressing truncated human Aβ(3–42) were generated and comprehensively characterized. To further investigate the role of QC in pE3-Aβ formation in vivo, ETNA mice were intercrossed with tg mice overexpressing human QC (hQC) to generate double tg ETNA-hQC mice.ResultsExpression of truncated Aβ(3–42) was detected mainly in the lateral striatum of ETNA mice, leading to progressive accumulation of pE3-Aβ. This ultimately resulted in astrocytosis, loss of DARPP-32 immunoreactivity, and neuronal loss at the sites of pE3-Aβ formation. Neuropathology in ETNA mice was associated with behavioral alterations. In particular, hyperactivity and impaired acoustic sensorimotor gating were detected. Double tg ETNA-hQC mice showed similar Aβ levels and expression sites, while pE3-Aβ were significantly increased, entailing increased astrocytosis and neuronal loss.ConclusionsETNA and ETNA-hQC mice represent novel mouse models for QC-mediated toxicity of truncated and pE-modified Aβ. Due to their significant striatal neurodegeneration these mice can also be used for analysis of striatal regulation of basal locomotor activity and sensorimotor gating, and possibly for DARPP-32-dependent neurophysiology and neuropathology. The spatio-temporal correlation of pE3-Aβ and neuropathology strongly argues for an important role of this Aβ species in neurodegenerative processes in these models.

Behavioral characterization of a new transgenic mouse model of pGlu-Aβ induced neurotoxicity: Automated, high-resolution, intra-home-cage and ethological-based phenotyping

paradigms motor function, emotion, cognition and pain. Results: Results show that TBA1 display early and distinct changes in a variety of behavioral assays. Analyzes of, for example, cognitive functions in the fear conditioning paradigm revealed differences in activity levels of both the contextual and the cued fear responses of homozygous TBA1 compared to wildtype mice. Conclusions: These data support the notion of TBA1 mice representing an excellent model for pharmacological screening of QC inhibitors. Further behavioral characterization with respect to additional paradigms and the phenotypical time course is ongoing. In conjunction with the histopathological findings, this will lead us to a comprehensive characterization allowing a deeper understanding of the pathology in this model and thus the role of pGlu neurotoxicity in Alzheimer’s disease.