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

BACKGROUND: Posttranslational modifications of beta amyloid (Aß) 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 Aß(3-x), generating pE3-Aß. Compared to unmodified Aß, pE3-Aß is more hydrophobic and neurotoxic. In addition, it accelerates aggregation of other Aß species. To directly investigate pE3-Aß formation and toxicity in vivo, transgenic (tg) ETNA (E at the truncated N-terminus of Aß) mice expressing truncated human Aß(3-42) were generated and comprehensively characterized. To further investigate the role of QC in pE3-Aß formation in vivo, ETNA mice were intercrossed with tg mice overexpressing human QC (hQC) to generate double tg ETNA-hQC mice. RESULTS: Expression of truncated Aß(3-42) was detected mainly in the lateral striatum of ETNA mice, leading to progressive accumulation of pE3-Aß. This ultimately resulted in astrocytosis, loss of DARPP-32 immunoreactivity, and neuronal loss at the sites of pE3-Aß 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 Aß levels and expression sites, while pE3-Aß were significantly increased, entailing increased astrocytosis and neuronal loss. CONCLUSIONS: ETNA and ETNA-hQC mice represent novel mouse models for QC-mediated toxicity of truncated and pE-modified Aß. 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-Aß and neuropathology strongly argues for an important role of this Aß species in neurodegenerative processes in these models.

Prion-like behaviour and tau-dependent cytotoxicity of pyroglutamylated amyloid-ß.

Extracellular plaques of amyloid-ß and intraneuronal neurofibrillary tangles made from tau are the histopathological signatures of Alzheimer's disease. Plaques comprise amyloid-ß 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-ß. Interestingly, many adverse responses to amyloid-ß, 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-ß are strongly associated with Alzheimer's disease, are more toxic than amyloid-ß, residues 1-42 (Aß(1-42)) and Aß(1-40), and have been proposed as initiators of Alzheimer's disease pathogenesis. Here we report a mechanism by which pE-Aß may trigger Alzheimer's disease. Aß(3(pE)-42) co-oligomerizes with excess Aß(1-42) to form metastable low-n oligomers (LNOs) that are structurally distinct and far more cytotoxic to cultured neurons than comparable LNOs made from Aß(1-42) alone. Tau is required for cytotoxicity, and LNOs comprising 5% Aß(3(pE)-42) plus 95% Aß(1-42) (5% pE-Aß) seed new cytotoxic LNOs through multiple serial dilutions into Aß(1-42) monomers in the absence of additional Aß(3(pE)-42). LNOs isolated from human Alzheimer's disease brain contained Aß(3(pE)-42), and enhanced Aß(3(pE)-42) formation in mice triggered neuron loss and gliosis at 3 months, but not in a tau-null background. We conclude that Aß(3(pE)-42) confers tau-dependent neuronal death and causes template-induced misfolding of Aß(1-42) into structurally distinct LNOs that propagate by a prion-like mechanism. Our results raise the possibility that Aß(3(pE)-42) acts similarly at a primary step in Alzheimer's disease pathogenesis.

Selective hippocampal neurodegeneration in transgenic mice expressing small amounts of truncated Aß is induced by pyroglutamate-Aß formation.

Posttranslational amyloid-ß (Aß) modification is considered to play an important role in Alzheimer's disease (AD) etiology. An N-terminally modified Aß species, pyroglutamate-amyloid-ß (pE3-Aß), has been described as a major constituent of Aß deposits specific to human AD but absent in normal aging. Formed via cyclization of truncated Aß species by glutaminyl cyclase (QC; QPCT) and/or its isoenzyme (isoQC; QPCTL), pE3-Aß aggregates rapidly and is known to seed additional Aß aggregation. To directly investigate pE3-Aß toxicity in vivo, we generated and characterized transgenic TBA2.1 and TBA2.2 mice, which express truncated mutant human Aß. Along with a rapidly developing behavioral phenotype, these mice showed progressively accumulating Aß and pE3-Aß deposits in brain regions of neuronal loss, impaired long-term potentiation, microglial activation, and astrocytosis. Illustrating a threshold for pE3-Aß neurotoxicity, this phenotype was not found in heterozygous animals but in homozygous TBA2.1 or double-heterozygous TBA2.1/2.2 animals only. A significant amount of pE3-Aß formation was shown to be QC-dependent, because crossbreeding of TBA2.1 with QC knock-out, but not isoQC knock-out, mice significantly reduced pE3-Aß levels. Hence, lowering the rate of QC-dependent posttranslational pE3-Aß formation can, in turn, lower the amount of neurotoxic Aß species in AD.