β-Amyloid, Cholinergic Transmission, and Cerebrovascular System - A Developmental Study in a Mouse Model of Alzheimer's Disease

Abstract

The majority of patients suffering from Alzheimer's disease (AD) demonstrate cerebral vascular changes and impaired regulation of cerebral blood flow, which has been assumed to play an important role in AD pathogenesis (vascular hypothesis of AD). There is strong evidence that both β-amyloid (Aβ) oligomers and plaques contribute to vascular injuries and functional impairments of the neurovascular unit. Vice versa, Aβ lesions can be triggered by hypertension and ischemic brain injury, while Aβ aggregates appear to have anti-angiogenic properties. Cholinergic dysfunction may result in impaired cerebral blood flow with consequences on normal function of the neurovascular unit including processing of the amyloid precursor protein (APP). To characterize in vivo the developmental relationship between Aβ formation and deposition, cortical cholinergic innervation and cerebrovascular abnormalities, transgenic Tg2576 mice that overexpress the Swedish double mutation of human APP, and demonstrate significant cerebral cortical deposition of Aβ plaques at ages from 9 months onwards, were considered as an appropriate animal model. Using the somatosensory cortex as a representative region, serial cryocut sections, were obtained from mice at ages ranging from 4 up to 18 months. These were subjected to immunohistochemistry to label vascular endothelial cells (anti-glucose transporter 1 (GluT1) immunostaining), cholinergic nerve terminals (anti-vesicular acetylcholine transporter (VAChT) immunostaining) and β-amyloid plaques (thioflavin S, and/or Solanum tuberosum lectin staining). This was followed by a thorough quantitative evaluation of the age-related spatial relationship between cerebral cortical capillaries, Aβ plaques and cholinergic terminals, using computer-assisted image analysis. The density of cholinergic terminals estimated by evaluation of VAChT immunohistochemistry in somatosensory cortical sections of wild type mice did not change with aging regardless of the cortical layer examined, while in cortical layers II/III and IV of somatosensory cortex of transgenic Tg2576 mice age-related decreases in cholinergic fiber densities were assessed. However, quantitative morphometric analysis demonstrated an age-related reduction in the number of varicosities on cholinergic fibers, particularly in layer IV, in both transgenic Tg2576 mice and non-transgenic littermates. Cholinergic innervation of microvessels in the somatosensory cortex decreased with aging in both Tg2576 mice and non-transgenic littermates, as revealed by estimating the ratio of the number of cholinergic vascular contacts and total length of blood vessel. There was no significant difference in the perivascular cholinergic innervation in areas that demonstrated significant plaque load and those with no plaque deposits regardless of the cortical layer examined. The density of blood vessels estimated in the somatosensory cortex of transgenic mice by anti-GluT-1 immunohistochemistry did not differ to that obtained in wild type mice before the onset of plaque depos...

Variants of Rab GTPase–Effector Binding Protein-2 Cause Variation in the Collateral Circulation and Severity of Stroke

“…Other genetic abnormalities have been associated with changes in capillary density, eg, Notch3 mutants with differences in pericyte coverage 16,17 and aged mice harboring the human APP-Tg2576 transgene. 18 However, expression of Notch3 was not different between CNG7BC and CNG7B6 mice (3 biological replicates done in triplicate and repeated 3 times, P > 0.8; data not shown).…”

Acute modulation of the cholinergic system in the mouse brain detected by pharmacological resting-state functional MRI

“…Furthermore, the eventual loss of cholinergic synaptic function will play a considerable role in the CBF decreases observed in AD patients and mouse models of AD (Kuznetsova and Schliebs, 2013;Ongali et al, 2010;van Beek and Claassen, 2011). The BOLD signal depends on among others cerebral blood flow (CBF), which in turn can be influenced by changes in neuronal activity at the level of the synapses or by a direct vasoactive at the level of the brain vessels.…”

Expression of vascular endothelial growth factor (VEGF) mRNA, VEGF receptor 2 (Flk‐1) mRNA, and of VEGF co‐receptor neuropilin (Nrp)‐1 mRNA in brain tissue of aging Tg2576 mice by in situ hybridization

“…Hence, to determine the effect of age‐related accumulation of Aβ on the expression level of VEGF mRNA, Flk‐1 mRNA and Nrp‐1 mRNA densitometric analysis of ISH signals in regions with high plaque load (Tg2576 mice) were compared with that in the corresponding regions of wild type mice (no plaque deposits). For this purpose, the hippocampal formation and the entorhinal cortex were selected for semiquantitative evaluation as representative brain regions displaying high plaque burden in Tg2576 mice (Kuznetsova and Schliebs, 2013).…”