TgCRND8 amyloid precursor protein transgenic mice exhibit an altered gamma-secretase processing and an aggressive, additive amyloid pathology subject to immunotherapeutic modulation

5xFAD mice do not have myenteric amyloidosis, dysregulation of neuromuscular transmission or gastrointestinal dysmotility

BACKGROUND

Alterations in gastrointestinal (GI) function and the gut-brain axis are associated with progression and pathology of Alzheimer's Disease (AD). Studies in AD animal models show that changes in the gut microbiome and inflammatory markers can contribute to AD development in the central nervous system (CNS). Amyloid-beta (Aβ) accumulation is a major AD pathology causing synaptic dysfunction and neuronal death. Current knowledge of the pathophysiology of AD in enteric neurons is limited, and whether Aβ accumulation directly disrupts enteric neuron function is unknown.

METHODS

In 6-month-old 5xFAD (transgenic AD) and wildtype (WT) male and female mice, GI function was assessed by colonic transit in vivo; propulsive motility and GI smooth muscle contractions ex vivo; electrochemical detection of enteric nitric oxide release in vitro, and changes in myenteric neuromuscular transmission using smooth muscle intracellular recordings. Expression of Aβ in the brain and colonic myenteric plexus in these mice was determined by immunohistochemistry staining and ELISA assay.

KEY RESULTS

At 6 months, 5xFAD mice did not show significant changes in GI motility or synaptic neurotransmission in the small intestine or colon. 5xFAD mice, but not WT mice, showed abundant Aβ accumulation in the brain. Aβ accumulation was undetectable in the colonic myenteric plexus of 5xFAD mice.

CONCLUSIONS

5xFAD AD mice are not a robust model to study amyloidosis in the gut as these mice do not mimic myenteric neuronal dysfunction in AD patients with GI dysmotility. An AD animal model with enteric amyloidosis is required for further study.

Vascular endothelial growth factor associated dissimilar cerebrovascular phenotypes in two different mouse models of Alzheimer's Disease

Vascular perturbations and cerebral hypometabolism are emerging as important components of Alzheimer's disease (AD). While various in vivo imaging modalities have been designed to detect changes of cerebral perfusion and metabolism in AD patients and animal models, study results were often heterogenous with respect to imaging techniques and animal models. We therefore evaluated cerebral perfusion and glucose metabolism of two popular transgenic AD mouse strains, TgCRND8 and 5xFAD, at 7 and 12 months-of-age under identical conditions and analyzed possible molecular mechanisms underlying heterogeneous cerebrovascular phenotypes. Results revealed disparate findings in these two strains, displaying important aspects of AD progression. TgCRND8 mice showed significantly decreased cerebral blood flow and glucose metabolism with unchanged cerebral blood volume (CBV) at 12 months-of-age whereas 5xFAD mice showed unaltered glucose metabolism with significant increase in CBV at 12 months-of-age and a biphasic pattern of early hypoperfusion followed by a rebound to normal cerebral blood flow in late disease. Finally, immunoblotting assays suggested that VEGF dependent vascular tone change may restore normoperfusion and increase CBV in 5xFAD.

Investigation of the Subcellular Neurotoxicity of Amyloid-β Using a Device Integrating Microfluidic Perfusion and Chemotactic Guidance

Alzheimer's disease (AD) is a neurodegenerative disorder with the histopathological hallmark of extracellular accumulation of amyloid-β (Aβ) peptide in brain senile plaques. Though many studies have shown the neural toxicity from various forms of Aβ peptides, the subcellular mechanisms of Aβ peptide are still not well understood, partially due to the technical challenges of isolating axons or dendrites from the cell body for localized investigation. In this study, the subcellular toxicity and localization of Aβ peptides are investigated by utilizing a microfluidic compartmentalized device, which combines physical restriction and chemotactic guidance to enable the isolation of axons and dendrites for localized pharmacological studies. It is found that Aβ peptides induced neuronal death is mostly resulted from Aβ treatment at cell body or axonal processes, but not at dendritic neurites. Simply applying Aβ to axons alone induces significant hyperactive spiking activity. Dynamic transport of Aβ aggregates is only observed between axon terminal and cell body. In addition to differential cellular uptake, more Aβ-peptide secretion is detected significantly from axons than from dendritic side. These results clearly demonstrate the existence of a localized mechanism in Aβ-induced neurotoxicity, and can potentially benefit the development of new therapeutic strategies for AD.

C-Terminal Threonine Reduces Aβ43 Amyloidogenicity Compared with Aβ42

Aβ43, a product of the proteolysis of the amyloid precursor protein APP, is related to Aβ42 by an additional Thr residue at the C-terminus. Aβ43 is typically generated at low levels compared with the predominant Aβ42 and Aβ40 forms, but it has been suggested that this longer peptide might have an impact on amyloid-β aggregation and Alzheimer's disease that is out of proportion to its brain content. Here, we report that both Aβ42 and Aβ43 spontaneously aggregate into mature amyloid fibrils via sequential appearance of the same series of oligomeric and protofibrillar intermediates, the earliest of which appears to lack β-structure. In spite of the additional β-branched amino acid at the C-terminus, Aβ43 fibrils have fewer strong backbone H-bonds than Aβ42 fibrils, some of which are lost at the C-terminus. In contrast to previous reports, we found that Aβ43 spontaneously aggregates more slowly than Aβ42. In addition, Aβ43 fibrils are very inefficient at seeding Aβ42 amyloid formation, even though Aβ42 fibrils efficiently seed amyloid formation by Aβ43 monomers. Finally, mixtures of Aβ42 and Aβ43 aggregate more slowly than Aβ42 alone. Both in this Aβ42/Aβ43 co-aggregation reaction and in cross-seeding by Aβ42 fibrils, the structure of the Aβ43 in the product fibrils is influenced by the presence of Aβ42. The results provide new details of amyloid structure and assembly pathways, an example of structural plasticity in prion-like replication, and data showing that low levels of Aβ43 in the brain are unlikely to favorably impact the aggregation of Aβ42.

Amyloid precursor protein mediated changes in intestinal epithelial phenotype in vitro

Background

Although APP and its proteolytic metabolites have been well examined in the central nervous system, there remains limited information of their functions outside of the brain. For example, amyloid precursor protein (APP) and amyloid beta (Aβ) immunoreactivity have both been demonstrated in intestinal epithelial cells. Based upon the critical role of these cells in absorption and secretion, we sought to determine whether APP or its metabolite amyloid β (Aβ), had a definable function in these cells.

Methodology/Principal Findings

The human colonic epithelial cell line, Caco-2 cells, were cultured to examine APP expression and Aβ secretion, uptake, and stimulation. Similar to human colonic epithelium stains, Caco-2 cells expressed APP. They also secreted Aβ 1-40 and Aβ 1-42, with LPS stimulating higher concentrations of Aβ 1-40 secretion. The cells also responded to Aβ 1-40 stimulation by increasing IL-6 cytokine secretion and decreasing cholesterol uptake. Conversely, stimulation with a sAPP-derived peptide increased cholesterol uptake. APP was associated with CD36 but not FATP4 in co-IP pull down experiments from the Caco-2 cells. Moreover, stimulation of APP with an agonist antibody acutely decreased CD36-mediated cholesterol uptake.

Conclusions/Significance

APP exists as part of a multi-protein complex with CD36 in human colonic epithelial cells where its proteolytic fragments have complex, reciprocal roles in regulating cholesterol uptake. A biologically active peptide fragment from the N-terminal derived, sAPP, potentiated cholesterol uptake while the β secretase generated product, Aβ1-40, attenuated it. These data suggest that APP is important in regulating intestinal cholesterol uptake in a fashion dependent upon specific proteolytic pathways. Moreover, this biology may be applicable to cells beyond the gastrointestinal tract.

Positron emission tomography imaging of fibrillar parenchymal and vascular amyloid-β in TgCRND8 mice

Few quantitative diagnostic and monitoring, tools are available to clinicians treating patients with Alzheimer's disease. Further, many of the promising quantitative imaging tools under development lack clear specificity toward different types of Amyloid-β (Aβ) pathology such as vascular or oligomeric species. Antibodies offer an opportunity to image specific types of Aβ pathology because of their excellent specificity. In this study, we developed a method to translate a panel of anti-Aβ antibodies, which show excellent histological performance, into live animal imaging contrast agents. In the TgCRND8 mouse model of Alzheimer's disease, we tested two antibodies, M64 and M116, that target parenchyma aggregated Aβ plaques and one antibody, M31, that targets vascular Aβ. All three antibodies were administered intravenously after labeling with both poly(ethylene glycol) to enhance circulation and (64)Cu to allow detection via positron emission tomography (PET) imaging. We were clearly able to differentiate TgCRND8 mice from wild type controls by PET imaging using either M116, the anti-Aβ antibody targeting parenchymal Aβ or M31, the antivascular Aβ antibody. To confirm the validity of the noninvasive imaging of specific Aβ pathology, brains were examined after imaging and showed clear evidence of binding to Aβ plaques.

The pathogenic aβ43 is enriched in familial and sporadic Alzheimer disease

The amyloid-cascade hypothesis posits that the role of amyloid β-peptide (Aβ) in Alzheimer disease (AD) involves polymerization into structures that eventually are deposited as amyloid plaques. During this process, neurotoxic oligomers are formed that induce synaptic loss and neuronal death. Several different isoforms of Aβ are produced, of which the 40 and 42 residue variants (Aβ40 and Aβ42) are the most common. Aβ42 has a strong tendency to form neurotoxic aggregates and is involved in AD pathogenesis. Longer Aβ isoforms, like the less studied Aβ43, are gaining attention for their higher propensity to aggregate into neurotoxic oligomers. To further investigate Aβ43 in AD, we conducted a quantitative study on Aβ43 levels in human brain. We homogenized human brain tissue and prepared fractions of various solubility; tris buffered saline (TBS), sodium dodecyl sulfate (SDS) and formic acid (FA). Levels of Aβ43, as well as Aβ40 and Aβ42, were quantified using ELISA. We compared quantitative data showing Aβ levels in occipital and frontal cortex from sporadic (SAD) and familial (FAD) AD cases, as well as non-demented (ND) controls. Results showed Aβ43 present in each fraction from the SAD and FAD cases, while its level was lower than the detection limit in the majority of the ND-cases. Aβ42 and Aβ43 were enriched in the less soluble fractions (SDS and FA) of SAD and FAD cases in both occipital and frontal cortex. Thus, although the total levels of Aβ43 in human brain are low compared to Aβ40 and Aβ42, we suggest that Aβ43 could initiate the formation of oligomers and amyloid plaques and thereby be crucial to AD pathogenesis.

Biochemical and morphological characterization of the AβPP/PS/tau triple transgenic mouse model and its relevance to sporadic Alzheimer's disease

Transgenic (Tg) mouse models of Alzheimer's disease (AD) have been genetically altered with human familial AD genes driven by powerful promoters. However, a Tg model must accurately mirror the pathogenesis of the human disease, not merely the signature amyloid and/or tau pathology, as such hallmarks can arise via multiple convergent or even by pathogenic mechanisms unrelated to human sporadic AD. The 3 × Tg-AD mouse simultaneously expresses 3 rare familial mutant genes that in humans independently produce devastating amyloid-β protein precursor (AβPP), presenilin-1, and frontotemporal dementias; hence, technically speaking, these mice are not a model of sporadic AD, but are informative in assessing co-evolving amyloid and tau pathologies. While end-stage amyloid and tau pathologies in 3 × Tg-AD mice are similar to those observed in sporadic AD, the pathophysiological mechanisms leading to these lesions are quite different. Comprehensive biochemical and morphological characterizations are important to gauge the predictive value of Tg mice. Investigation of AβPP, amyloid-β (Aβ), and tau in the 3 × Tg-AD model demonstrates AD-like pathology with some key differences compared to human sporadic AD. The biochemical dissection of AβPP reveals different cleavage patterns of the C-terminus of AβPP when compared to human AD, suggesting divergent pathogenic mechanisms. Human tau is concomitantly expressed with AβPP/Aβ from an early age while abundant extracellular amyloid plaques and paired helical filaments are manifested from 18 months on. Understanding the strengths and limitations of Tg mouse AD models through rigorous biochemical, pathological, and functional analyses will facilitate the derivation of models that better approximate human sporadic AD.

Potent amyloidogenicity and pathogenicity of Aβ43

The amyloid-β peptide Aβ42 is known to be a primary amyloidogenic and pathogenic agent in Alzheimer's disease. However, the role of Aβ43, which is found just as frequently in the brains of affected individuals, remains unresolved. We generated knock-in mice containing a pathogenic presenilin-1 R278I mutation that causes overproduction of Aβ43. Homozygosity was embryonic lethal, indicating that the mutation involves a loss of function. Crossing amyloid precursor protein transgenic mice with heterozygous mutant mice resulted in elevated Aβ43, impairment of short-term memory and acceleration of amyloid-β pathology, which accompanied pronounced accumulation of Aβ43 in plaque cores similar in biochemical composition to those observed in the brains of affected individuals. Consistently, Aβ43 showed a higher propensity to aggregate and was more neurotoxic than Aβ42. Other pathogenic presenilin mutations also caused overproduction of Aβ43 in a manner correlating with Aβ42 and with the age of disease onset. These findings indicate that Aβ43, an overlooked species, is potently amyloidogenic, neurotoxic and abundant in vivo.

Actions of β-amyloid protein on human neurons are expressed through the amylin receptor

Disruption of neurotoxic effects of amyloid β protein (Aβ) is one of the major, but as yet elusive, goals in the treatment of Alzheimer's disease (AD). The amylin receptor, activated by a pancreatic polypeptide isolated from diabetic patients, is a putative target for the actions of Aβ in the brain. Here we show that in primary cultures of human fetal neurons (HFNs), AC253, an amylin receptor antagonist, blocks electrophysiological effects of Aβ. Pharmacological blockade of the amylin receptor or its down-regulation using siRNA in HFNs confers neuroprotection against oligomeric Aβ-induced caspase-dependent and caspase-independent apoptotic cell death. In transgenic mice (TgCRND8) that overexpress amyloid precursor protein, amylin receptor is up-regulated in specific brain regions that also demonstrate an elevated amyloid burden. The expression of Aβ actions through the amylin receptor in human neurons and temporospatial interrelationship of Aβ and the amylin receptor in an in vivo model of AD together provide a persuasive rationale for this receptor as a novel therapeutic target in the treatment of AD.

Oral treatment with a gamma-secretase inhibitor improves long-term potentiation in a mouse model of Alzheimer's disease

The beta-amyloid peptide (Abeta) is thought to play a critical role in the pathophysiology of Alzheimer's disease (AD). To study the effects of Abeta on the brain, transgenic mouse models have been developed that express high levels of Abeta. These mice show some features of AD, including amyloid plaques and mild cognitive impairment, but not others such as progressive neurodegeneration. We investigated the age-dependent effects of Abeta on synaptic physiology in Tg2576 mice that express human Abeta. We report that both basal synaptic activity and long-term potentiation (LTP), as measured in the CA1 region of the hippocampus, were compromised by 7 months of age before plaque deposition. Despite a persistent increase in Abeta levels with age, LTP recovered in 14-month-old mice, with no further loss of basal activity compared with activity measured in 7-month-old mice. Previous work has shown that inhibitors of gamma-secretase, an enzyme critical for Abeta synthesis, can significantly reduce Abeta production and plaque formation in Tg2576 mice. Our data demonstrate that 7-month-old Tg2576 mice treated with an orally available gamma-secretase inhibitor showed a significant improvement in synaptic function and plasticity within days, and the effect was correlated with the extent and duration of Abeta reduction. These results indicate that recovery from Abeta-mediated synaptotoxicity can occur rapidly with Abeta-lowering therapies. These findings highlight some of the strengths and limitations of using Abeta-overexpressing mouse models for Alzheimer's drug discovery.

Green tea (-)-epigallocatechin-3-gallate inhibits beta-amyloid-induced cognitive dysfunction through modification of secretase activity via inhibition of ERK and NF-kappaB pathways in mice

Alzheimer's disease (AD) is characterized by the extracellular deposition of beta-amyloid peptide (Abeta) in cerebral plaques. Abeta is derived from the beta-amyloid precursor protein (APP) by the enzymes alpha-, beta- and gamma-secretase. Compounds that enhance alpha-secretase, but inhibit beta- or gamma-secretase activity, have therapeutic potential in the treatment of AD. Green tea, or its major polyphenolic compound, has been shown to have neuroprotective effects. In this study, we investigated the possible effects of (-)-epigallocatechin-3-gallate (EGCG) on memory dysfunction caused by Abeta through the change of Abeta-induced secretase activities. Mice were pretreated with EGCG (1.5 or 3 mg/kg body weight in drinking water) for 3 wk before intracerebroventricular administration of 0.5 microg Abeta(1-42). EGCG dose-dependently reduced the Abeta(1-42)-induced memory dysfunction, which was evaluated using passive avoidance and water maze tests. Abeta(1-42) induced a decrease in brain alpha-secretase and increases in both brain beta- and gamma-secretase activities, which were reduced by EGCG. In the cortex and the hippocampus, expression of the metabolic products of the beta- and gamma-secretases from APP, C99, and Abeta also were dose-dependently suppressed by EGCG. Paralleled with the suppression of beta- and gamma-secretases by EGCG, we found that EGCG inhibited the activation of extracellular signal-regulated kinase and nuclear transcription factor-kappaB in the Abeta(1-42)-injected mouse brains. In addition, EGCG inhibited Abeta(1-42)-induced apoptotic neuronal cell death in the brain. To further test the ability of EGCG to affect memory, EGCG (3 mg/kg body weight) was administered in drinking water for 1 wk to genetically developed preseniline 2 (PS2) mutant AD mice. Compared with untreated mutant PS2 AD mice, treatment with EGCG enhanced memory function and brain alpha-secretase activity but reduced brain beta- and gamma-secretase activities as well as Abeta levels. Moreover, EGCG inhibited the fibrillization of Abeta in vitro with a half maximal inhibitory concentration of 7.5 mg/L. These studies suggest that EGCG may be a beneficial agent in the prevention of development or progression of AD.

Amyloid precursor protein transgenic mouse models and Alzheimer's disease: understanding the paradigms, limitations, and contributions

Transgenic (Tg) mice that overexpress mutant familial Alzheimer's disease (AD) amyloid precursor protein (APP) genes have contributed to an understanding of dementia pathology, and support the amyloid cascade hypothesis. Although many sophisticated mice APP models exist, none recapitulates AD cellular and behavioral pathology. The morphological resemblance to AD amyloidosis is impressive, but fundamental biophysical and biochemical properties of the APP/Abeta produced in Tg mice differ substantially from those of humans. The greater resilience of Tg mice in the presence of substantial Abeta burdens suggests that levels and forms deleterious to human neurons are not as noxious in these models. Transgenic mice were widely used for testing AD therapeutic agents, and demonstrated promising results. Unfortunately, clinical trials resulted in unforeseen adverse events or negative therapeutic outcomes. The disparity between success and failure is in part attributable to evolutionary divergence between humans and rodents. These observations suggest that the pathogenesis of AD is by far more intricate than can be explained by a straightforward accumulation of Abeta.

Antibody responses, amyloid-beta peptide remnants and clinical effects of AN-1792 immunization in patients with AD in an interrupted trial

Post mortem examinations of AN-1792-vaccinated humans revealed this therapy produced focal senile plaque disruption. Despite the dispersal of substantial plaque material, vaccination did not constitute even a partial eradication of brain amyloid as water soluble amyloid-beta (Abeta) 40/42 increased in the gray matter compared to sporadic Alzheimer's disease (AD) patients and total brain Abeta levels were not decreased. Significant aspects of AD pathology were unaffected by vaccination with both vascular amyloid and hyper-phosphorylated tau deposits appeared refractory to this therapy. In addition, vaccination resulted in the consequential and drastic expansion of the white matter (WM) amyloid pool to levels without precedent in sporadic AD patients. Although vaccination disrupted amyloid plaques, this therapy did not enhance long-term cognitive function or necessarily halt neurodegeneration. The intricate involvement of vascular pathology in AD evolution and the firm recalcitrance of vessel-associated amyloid to antibody-mediated disruption suggest that immunization therapies might be more effective if administered on a prophylactic basis before vascular impairment and well ahead of any clinically evident cognitive decline. Amyloid-beta is viewed as pathological based on the postmortem correlation of senile plaques with an AD diagnosis. It remains uncertain which of the various forms of this peptide is the most toxic and whether Abeta or senile plaques themselves serve any desirable or protective functions. The long-term cognitive effects of chronic immunotherapy producing a steadily accumulating and effectively permanent pool of disrupted Abeta peptides within the human brain are unknown. In addition, the side effects of such therapy provided on a chronic basis could extend far beyond the brain. Eagerly seeking new therapies, critical knowledge gaps should prompt us to take a more wholistic perspective viewing Abeta and the amyloid cascade as aspects of complex and many-faceted physiological processes that sometimes end in AD dementia.

Abeta43 is more frequent than Abeta40 in amyloid plaque cores from Alzheimer disease brains

One hallmark of Alzheimer disease (AD) is the extracellular deposition of the amyloid beta-peptide (Abeta) in senile plaques. Two major forms of Abeta are produced, 40 (Abeta40) and 42 (Abeta42) residues long. The most abundant form of Abeta is Abeta40, while Abeta42 is more hydrophobic and more prone to form toxic oligomers and the species of particular importance in early plaque formation. Thus, the length of the hydrophobic C-terminal seems to be very important for the oligomerization and neurotoxicity of the Abeta peptide. Here we investigated which Abeta species are deposited in AD brain. We analyzed plaque cores, prepared from occipital and frontal cortex, from sporadic and familial AD cases and performed a quantitative study using Abeta standard peptides. Cyanogen bromide was used to generate C-terminal Abeta fragments, which were analyzed by HPLC coupled to an electrospray ionisation ion trap mass spectrometer. We found a longer peptide, Abeta43, to be more frequent than Abeta40. No variants longer than Abeta43 could be observed in any of the brains. Immunohistochemistry was performed and was found to be in line with our findings. Abeta1-43 polymerizes rapidly and we suggest that this variant may be of importance for AD.

Selective vulnerability in Alzheimer's disease: amyloid precursor protein and p75(NTR) interaction

OBJECTIVE

Selective neuronal vulnerability in neurodegenerative diseases is poorly understood. In Alzheimer's disease, the basal forebrain cholinergic neurons are selectively vulnerable, putatively because of their expression of the cell death mediator p75(NTR) (the common neurotrophin receptor), and its interaction with proapoptotic ligands pro-nerve growth factor and amyloid-beta peptide. However, the relation between amyloid precursor protein (APP) and p75(NTR) has not been described previously.

METHODS

APP and p75(NTR) were assayed for interaction by coimmunoprecipitation in vitro and in vivo, yeast two-hybrid assay, bioluminescence resonance energy transfer, and confocal microscopy. Effects on APP processing and signaling were studied using immunoblotting, enzyme-linked immunosorbent assays, and luciferase reporter assays.

RESULTS

The results of this study are as follows: (1) p75(NTR) and APP interact directly; (2) this interaction is modified by ligands nerve growth factor and beta-amyloid; (3) APP and p75(NTR) colocalization in vivo is modified in Alzheimer's model transgenic mice; (4) APP processing is altered by p75(NTR), and to a lesser extent, p75(NTR) processing is altered by the presence of APP; (5) APP-dependent transcription mediated by Fe65 is blocked by p75(NTR); and (6) coexpression of APP and p75(NTR) triggers cell death.

INTERPRETATION

These results provide new insight into the emerging signaling network that mediates the Alzheimer's phenotype and into the mechanism of basal forebrain cholinergic neuronal selective vulnerability. In addition, the results argue that the interaction between APP and p75(NTR) may represent a therapeutic target in Alzheimer's disease.

Intracerebroventricular amyloid-beta antibodies reduce cerebral amyloid angiopathy and associated micro-hemorrhages in aged Tg2576 mice

Although immunization against amyloid-beta (Abeta) holds promise as a disease-modifying therapy for Alzheimer disease (AD), it is associated with an undesirable accumulation of amyloid in the cerebrovasculature [i.e., cerebral amyloid angiopathy (CAA)] and a heightened risk of micro-hemorrhages. The central and peripheral mechanisms postulated to modulate amyloid with anti-Abeta immunotherapy remain largely elusive. Here, we compared the effects of prolonged intracerebroventricular (i.c.v.) versus systemic delivery of anti-Abeta antibodies on the behavioral and pathological changes in an aged Tg2576 mouse model of AD. Prolonged i.c.v. infusions of anti-Abeta antibodies dose-dependently reduced the parenchymal plaque burden, astrogliosis, and dystrophic neurites at doses 10- to 50-fold lower than used with systemic delivery of the same antibody. Both i.c.v. and systemic anti-Abeta antibodies reversed the behavioral impairment in contextual fear conditioning. More importantly, unlike systemically delivered anti-Abeta antibodies that aggravated vascular pathology, i.c.v.-infused antibodies globally reduced CAA and associated micro-hemorrhages. We present data suggesting that the divergent effects of i.c.v.-delivered anti-Abeta antibodies result from gradually engaging the local (i.e., central) mechanisms for amyloid clearance, distinct from the mechanisms engaged by high doses of anti-Abeta antibodies that circulate in the vasculature following systemic delivery. With robust efficacy in reversing AD-related pathology and an unexpected benefit in reducing CAA and associated micro-hemorrhages, i.c.v.-targeted passive immunotherapy offers a promising therapeutic approach for the long-term management of AD.

Presenilin-1 280Glu-->Ala mutation alters C-terminal APP processing yielding longer abeta peptides: implications for Alzheimer's disease

Presenilin (PS) mutations enhance the production of the Abeta42 peptide that is derived from the amyloid precursor protein (APP). The pathway(s) by which the Abeta42 species is preferentially produced has not been elucidated, nor is the mechanism by which PS mutations produce early-onset dementia established. Using a combination of histological, immunohistochemical, biochemical, and mass spectrometric methods, we examined the structural and morphological nature of the amyloid species produced in a patient expressing the PS1 280Glu-->Ala familial Alzheimer's disease mutation. Abundant diffuse plaques were observed that exhibited a staining pattern and morphology distinct from previously described PS cases, as well as discreet amyloid plaques within the white matter. In addition to finding increased amounts of CT99 and Abeta42 peptides, our investigation revealed the presence of a complex array of Abeta peptides substantially longer than 42/43 amino acid residue species. The increased hydrophobic nature of longer Abeta species retained within the membrane walls could impact the structure and function of plasma membrane and organelles. These C-terminally longer peptides may, through steric effects, dampen the rate of turnover by critical amyloid degrading enzymes such as neprilysin and insulin degrading enzyme. A complete understanding of the deleterious side effects of membrane bound Abeta as a consequence of gamma-secretase alterations is needed to understand Alzheimer's disease pathophysiology and will aid in the design of therapeutic interventions.