Amyloid Deposition In Alzheimer's Disease Research Articles

P205: The effect of APOE e4 genotype on cognition, brain volume, glucose metabolism and amyloid deposition in AD

Objective:Many previous studies have shown that the APOE e4 genotype affects cognition, brain volume, glucose metabolism and amyloid deposition. However, these studies were conducted separately, and few studies simultaneously investigated the effects of the APOE e4 genotype on cognition, brain volume, glucose metabolism and amyloid deposition in Alzheimer disease (AD). The purpose of this study is to simultaneously investigate the association of the APOE e4 genotype with cognition, brain volume, glucose metabolism and amyloid deposition in patients with AD.Methods:This is a cross-sectional study of 69 subjects with Alzheimer’s disease (AD). All subjects were divided into carriers and noncarriers of the ε4 allele. Forty APOE ε4 carriers and 29 APOE ε4 non-carriers underwent neuropsychological, structural magnetic resonance imaging, 18F-fluorodeoxyglucose positron emission tomography scans (18F-FDG-PET) and 18F-Florbetaben amyloid positron emission tomography scans (amyloid PET). Analysis of covariance (ANCOVA) was conducted to compare the differences on cognition, brain volume, glucose metabolism and amyloid deposition between APOE ε4 carriers and non-carriers after controlling demographics.Results:APOE ε4 carriers had 50% lower scores of SVLT_delayed recall compared to non-carriers (0.88 ± 1.65 vs 1.76 ± 1.75). However, APOE ε4 carriers performed better on other cognitive tests than non- carriers (K-BNT (11.04 ± 2.55 vs 9.66 ± 2.82), RCFT (25.73 ± 8.56 vs 20.15 ± 10.82), and Stroop test_color response (48.28 ± 26.33 vs 31.56 ± 27.03)). APOE ε4 carriers had slightly smaller hippocampal volume than non-carriers (3.09 ± 0.38 vs 3.32 ± 0.38), but greater total brain cortical thickness (1.45 ± 1.55 vs 1.37 ± 1.24).Conclusions:We found that APOE e4 genotype is associated with cognition, brain volume in AD, suggesting that APOE e4 genotype can play a very important role in the underlying pathogenesis of AD.

A Novel Near-Infrared Fluorescence Probe THK-565 Enables In Vivo Detection of Amyloid Deposits in Alzheimer’s Disease Mouse Model

PurposeNoninvasive imaging of protein aggregates in the brain is critical for the early diagnosis, disease monitoring, and evaluation of the effectiveness of novel therapies for Alzheimer’s disease (AD). Near-infrared fluorescence (NIRF) imaging with specific probes is a promising technique for the in vivo detection of protein deposits without radiation exposure. Comprehensive screening of fluorescent compounds identified a novel compound, THK-565, for the in vivo imaging of amyloid-β (Aβ) deposits in the mouse brain. This study assessed whether THK-565 could detect amyloid-β deposits in vivo in the AD mouse model.ProceduresThe fluorescent properties of THK-565 were evaluated in the presence and absence of Aβ fibrils. APP knock-in (APP-KI) mice were used as an animal model of AD. In vivo NIRF images were acquired after the intravenous administration of THK-565 and THK-265 in mice. The binding selectivity of THK-565 to Aβ was evaluated using brain slices obtained from these mouse models.ResultsThe fluorescence intensity of the THK-565 solution substantially increased by mixing with Aβ fibrils. The maximum emission wavelength of the complex of THK-565 and Aβ fibrils was 704 nm, which was within the optical window range. THK-565 selectively bound to amyloid deposits in brain sections of APP-KI mice After the intravenous administration of THK-565, the fluorescence signal in the head of APP-KI mice was significantly higher than that of wild-type mice and higher than that after administration of THK-265. Ex vivo analysis confirmed that the THK-565 signal corresponded to Aβ immunostaining in the brain sections of these mice.ConclusionsA novel NIRF probe, THK-565, enabled the in vivo detection of Aβ deposits in the brains of the AD mouse model, suggesting that NIRF imaging with THK-565 could non-invasively assess disease-specific pathology in AD.

Structures of brain-derived 42-residue amyloid-β fibril polymorphs with unusual molecular conformations and intermolecular interactions

Fibrils formed by the 42-residue amyloid-β peptide (Aβ42), a main component of amyloid deposits in Alzheimer's disease (AD), are known to be polymorphic, i.e., to contain multiple possible molecular structures. Previous studies of Aβ42 fibrils, including fibrils prepared entirely invitro or extracted from brain tissue and using solid-state NMR (ssNMR) or cryogenic electron microscopy (cryo-EM) methods, have found polymorphs with differences in amino acid sidechain orientations, lengths of structurally ordered segments, and contacts between cross-β subunit pairs within a single filament. Despite these differences, Aβ42 molecules adopt a common S-shaped conformation in all previously described high-resolution Aβ42 fibril structures. Here we report two cryo-EM-based structures of Aβ42 fibrils that are qualitatively different, in samples derived from AD brain tissue by seeded growth. In type A fibrils, residues 12 to 42 adopt a ν-shaped conformation, with both intra-subunit and intersubunit hydrophobic contacts to form a compact core. In type B fibrils, residues 2 to 42 adopt an υ-shaped conformation, with only intersubunit contacts and internal pores. Type A and type B fibrils have opposite helical handedness. Cryo-EM density maps and molecular dynamics simulations indicate intersubunit K16-A42 salt bridges in type B fibrils and partially occupied K28-A42 salt bridges in type A fibrils. The coexistence of two predominant polymorphs, with differences in N-terminal dynamics, is supported by ssNMR data, as is faithful propagation of structures from first-generation to second-generation brain-seeded Aβ42 fibril samples. These results demonstrate that Aβ42 fibrils can exhibit a greater range of structural variations than seen in previous studies.

Spontaneous intracerebral haemorrhage associated with early-onset cerebral amyloid angiopathy and Alzheimer’s disease neuropathological changes five decades after cadaveric dura mater graft

Cerebral amyloid angiopathy (CAA) is a small vessel disease, causing spontaneous intracerebral hemorrhage (ICH) in the elderly. It is strongly associated with Alzheimer disease (AD), as most CAA patients show deposition of Aβ—i.e. the basic component of parenchymal Alzheimer amyloid deposits—in the cerebral vessels. Iatrogenic early-onset CAA has been recently identified in patients with a history of traumatic brain injury or other cerebral as well as extra-cerebral lesions that led to neurosurgery or other medical procedures as intravascular embolization by cadaveric dura mater extracts many years before the first ICH event. In those patients, a transmission of Aβ seeds from neurosurgical instruments or from cadaveric dura mater exposure was suggested. We report a 51-year-old woman with unremarkable family history who presented abruptly with aphasia and right hemiparesis. A cerebral left lobar haemorrhagic stroke was documented by neuroimaging. Accurate anamnesis revealed a neurosurgical procedure with cadaveric dura mater graft at the age of 2 years for an arachnoid cyst. The neuropathological examination of the cerebral parietal biopsy showed severe amyloid angiopathy in many leptomeningeal and cortical vessels, as well as abundant parenchymal Aβ deposits, neurofibrillary tangles and neuropil threads. The mechanism involved in the human-to-human transmission of the Aβ proteinopathy remains to be clarified. In our patient the cadaver derived dura used for grafting is a very strong candidate as the source of the transmission. A systematic monitoring of individuals who have had neurosurgical procedures in early life, especially those involving cadaveric dural grafts, is required to determine the ratio of those affected by CAA many years later and unaffected. Moreover, our report confirms that in addition to vascular and parenchymal Aβ pathology, neurofibrillary changes indistinguishable from AD may develop in specific conditions with long latency period from the neurosurgical or embolization procedure.

How Naturalistic Driving Compares to Aβ‐related CSF and Plasma Biomarkers in the Detection of Amyloid PET Positivity: A Machine Learning Approach

AbstractBackgroundIdentifying individuals with Alzheimer disease (AD) pathology a decade or more before the onset of dementia symptoms can be achieved with amyloid positron emission tomography (PET), cerebrospinal fluid (CSF) biomarkers, or blood biomarkers. This study compares driving behavior with CSF and blood biomarkers to identify amyloid deposition in AD, as defined by the “gold standard” PET‐amyloid.MethodWe used commercial‐in‐vehicle‐GPS dataloggers to study naturalistic driving behaviors among 101 cognitively normal older drivers (aged 65+). All participants had blood, CSF, and PET biomarker data. The cohort included 37 individuals with and 64 without PET‐amyloid positivity.Driving variables included total number of trips, number of trips with a distance less than 1‐mile, trips in evening rush hour, trips with hard acceleration, speeding events, and average speed. Three Multi‐layer Perceptron (MLP) classifiers were trained with three sets of inputs: (1) driving variables, (2) driving variables and age, and (3) driving variables, age, and APOE ε4 status. Additionally, plasma Aβ42/Aβ40 < 0.1013, CSF Aβ42/Aβ40 < 0.0673, or Amyloid Probability Score (APS) (modeled score incorporating plasma Aβ42/40, age, and APOE ε4 status) > 15 were used to detect PET‐amyloid positivity. The driving models were trained on 80% of the data and all biomarkers were evaluated on the remaining 20% of the data. Specificity (Spe), sensitivity (Sen), F1‐score (F1), and area under the receiver operating curve (AUC) were compared across the three driving models and three fluid‐based biomarkers.ResultFor predicting PET‐amyloid positivity, CSF Aβ42/Aβ40 achieved the highest performance (Spe=0.96, Sen=0.98, F1=0.97) followed by the MLP model with driving variables, age, and APOE ε4 status (Spe=0.93, Sen=0.91, and F1=0.92), MLP model with driving variables and age (Spe=0.88, Sen=0.85, and F1=0.86), APS (Spe=0.82, Sen=0.84, and F1=0.81), plasma Aβ42/Aβ40 (Spe=0.79, Sen=0.80, and F1=0.76), and MLP model with driving variables (Spe=0.71, Sen=0.72, and F1=0.71). The AUC from driving variables was 0.800, and improved by adding age to 0.933, and age and APOE ε4 status to 0.977. Furthermore, AUC scores were 0.986, 0.911, and 0.873 for CSF Aβ42/Aβ40, APS, and plasma Aβ42/Aβ40, respectively.ConclusionDriving is a useful neurobehavioral marker in predicting PET‐amyloid positivity among cognitively normal older drivers.

Enhanced Brain Retention of Aβ4‐x Proteoforms and its Contribution to Amyloid Deposits in Alzheimer’s Disease

The deposition of amyloid‐β (Aβ) in brain parenchyma and cerebral vasculature together with intraneuronal neurofibrillary tangles and the gradual loss of synapsis are central neuropathological hallmarks of Alzheimer’s disease (AD). Although it remains unclear what primarily triggers and drives the progression of AD, different lines of investigation point out to a central role of oligomeric Aβ conformations for the disease pathogenesis. Recent studies revealed that the molecular heterogeneity of Aβ deposits is significantly more complex than originally anticipated, extending well beyond the classic Aβ1‐40/Aβ1‐42 dichotomy and being substantially expanded by the presence of multiple post‐translational modifications that increase the proteome diversity. Although N‐terminal truncations at glutamates 3 and 11 and their subsequent cyclation to pyroglutamate are perhaps the most extensively studied modifications, many others have been reported, with species beginning at phenylalanine 4 and bearing an intact C‐terminus being especially relevant. Indeed, Aβ4‐42 peptides were reported as major components of amyloid plaque cores and the limited studies available seem to indicate their relative abundance in patients with AD, Down’s syndrome, and vascular dementia. In this work we assessed the topographic distribution of these species with in‐house‐generated anti‐Aβ4‐x monoclonal 18H6 – specific for Aβ species starting at position 4 and blind for the full‐length Aβ40 and Aβ42 – and used in conjunction with thioflavin S and antibodies specific for the C‐terminus 40 and 42 in confirmed AD cases. All types of Aβ deposits – parenchymal plaques, pre‐amyloid lesions and CAA – contained the Aβ epitopes tested, albeit expressed in different proportions. These co‐localizations were further stressed by combining double immunohistochemical analysis with Thioflavin S staining, showing the preferential location of Aβ4‐x species in CAA and cored plaques with fibrillar amyloid conformation, strongly suggesting poor clearance characteristics. To investigate the brain clearance of Aβ4‐x species in comparison with full‐length Aβ40 and Aβ42 homologues, peptides were synthesized, biochemically and biophysically characterized, radiolabeled with [125I]Na and utilized for in vivo brain clearance experiments in 5–6‐week‐old C57Bl/6 mice. Brain efflux of all monomeric Aβ species tested was fast, with >80% cleared within the 60 min duration of the experiment whereas retention of oligomeric preparations was consistently higher than that of monomeric forms. Notably, clearance of Aβ4‐40 and Aβ4‐42 was significantly lower (<45%) than the full‐length counterparts (61% ‐ 68%), further supporting a pathogenic role for Aβ oligomerization in AD and specifically highlighting the importance of oligomeric Aβ4‐x species exhibiting higher brain retention compared to their full‐length counterparts. Since the process of multimerization is concentration dependent, failing to remove these oligomeric forms of Aβ from the brain will further contribute to exacerbate the amyloidogenic loop and the persistence of amyloid deposits.

Evidence against altered excitatory/inhibitory balance in the posteromedial cortex of young adult APOE E4 carriers: A resting state 1H-MRS study

A strategy to gain insight into early changes that may predispose people to Alzheimer's disease (AD) is to study the brains of younger cognitively healthy people that are at increased genetic risk of AD. The Apolipoprotein (APOE) E4 allele is the strongest genetic risk factor for AD, and several neuroimaging studies comparing APOE E4 carriers with non-carriers at age ∼20–30 years have detected hyperactivity (or reduced deactivation) in posteromedial cortex (PMC), a key hub of the default network (DN), which has a high susceptibility to early amyloid deposition in AD. Transgenic mouse models suggest such early network activity alterations may result from altered excitatory/inhibitory (E/I) balance, but this is yet to be examined in humans. Here we test the hypothesis that PMC fMRI hyperactivity could be underpinned by altered levels of excitatory (glutamate) and/or inhibitory (GABA) neurotransmitters in this brain region. Forty-seven participants (20 APOE E4 carriers and 27 non-carriers) aged 18–25 years underwent resting-state proton magnetic resonance spectroscopy (1H-MRS), a non-invasive neuroimaging technique to measure glutamate and GABA in vivo. Metabolites were measured in a PMC voxel of interest and in a comparison voxel in the occipital cortex (OCC). There was no difference in either glutamate or GABA between the E4 carriers and non-carriers in either MRS voxel, or in the ratio of glutamate to GABA, a measure of E/I balance. Default Bayesian t-tests revealed evidence in support of this null finding. Our findings suggest that PMC hyperactivity in APOE E4 carriers is unlikely to be associated with, or possibly may precede, alterations in local resting-state PMC neurotransmitters, thus informing our understanding of the spatio-temporal sequence of early network alterations underlying APOE E4 related AD risk.

Donanemab (LY3002813) dose-escalation study in Alzheimer's disease.

IntroductionThis study explored the safety and tolerability features of donanemab (LY3002813) in patients with mild cognitive impairment due to Alzheimer's disease (AD) or mild to moderate AD dementia.MethodsPatients with AD were enrolled into the single‐ascending dose phase and were administered a single, intravenous (IV) dose of donanemab (five dosing cohorts from 0.1 to 10 mg/kg) or placebo followed by a 12‐week follow‐up period for each dose level. After the follow‐up period, the same patients proceeded into the multiple‐ascending dose (MAD) phase (five cohorts) and were administered IV doses of donanemab (0.3 to 10 mg/kg) or placebo approximately once per month for up to four doses depending on the initial doses (only cohort 1 went from 0.1 mg/kg to a higher dose of 0.3 mg/kg during the MAD phase). This phase concluded with a 12‐week follow‐up period. The relative exposure assessment of an unblinded, single, subcutaneous 3‐mg/kg dose of donanemab in patients with AD was also performed, followed by a 12‐week follow‐up period. One cohort of healthy subjects received an unblinded, single, IV 1‐mg/kg dose of donanemab. These two cohorts did not continue to the MAD phase.ResultsDonanemab was generally well tolerated up to 10 mg/kg. After single‐dose administration from 0.1 to 3.0 mg/kg, the mean terminal elimination half‐life was ≈4 days, increasing to ≈10 days at 10 mg/kg. Only the 10‐mg/kg dose showed changes in amyloid positron emission tomography. Amyloid reduction of 40% to 50% was achieved. Approximately 90% of subjects developed anti‐drug antibodies at 3 months after a single intravenous dose.DiscussionIntravenous donanemab 10 mg/kg can reduce amyloid deposits in AD despite having a shorter than expected half‐life.

Extracellular Amyloid Deposits in Alzheimer’s and Creutzfeldt–Jakob Disease: Similar Behavior of Different Proteins?

Neurodegenerative diseases are characterized by the deposition of specific protein aggregates, both intracellularly and/or extracellularly, depending on the type of disease. The extracellular occurrence of tridimensional structures formed by amyloidogenic proteins defines Alzheimer’s disease, in which plaques are composed of amyloid β-protein, while in prionoses, the same term “amyloid” refers to the amyloid prion protein. In this review, we focused on providing a detailed didactic description and differentiation of diffuse, neuritic, and burnt-out plaques found in Alzheimer’s disease and kuru-like, florid, multicentric, and neuritic plaques in human transmissible spongiform encephalopathies, followed by a systematic classification of the morphological similarities and differences between the extracellular amyloid deposits in these disorders. Both conditions are accompanied by the extracellular deposits that share certain signs, including neuritic degeneration, suggesting a particular role for amyloid protein toxicity.

Switching on Brain PET to Light Up Amyloid Pathology In Vivo.

An article entitled “In Vivo Imaging of Amyloid Deposition in Alzheimer Disease Using the Radioligand 18F-AV-45 (Florbetapir F 18),” by Wong et al., was published in The Journal of Nuclear Medicine in 2010 ([1][1]). It became one of the most-cited publications of this journal from that period.

Autophagy modulates Aβ accumulation and formation of aggregates in yeast

Intracellular accumulation of amyloid-β protein (Aβ) is an early event in Alzheimer's disease (AD). The autophagy-lysosomal pathway is an important pathway for maintaining cellular proteostasis and for the removal of damaged organelles and protein aggregates in all eukaryotes. Despite mounting evidence showing that modulating autophagy promotes clearance of Aβ aggregates, the regulatory mechanisms and signalling pathways underlying this process remain poorly understood. In order to gain better insight we used our previously characterised yeast model expressing GFP-Aβ42 to identify genes that regulate the removal of Aβ42 aggregates by autophagy. We report that GFP-Aβ42 is sequestered and is selectively transported to vacuole for degradation and that autophagy is the prominent pathway for clearance of aggregates. Next, to identify genes that selectively promote the removal of Aβ42 aggregates, we screened levels of GFP-Aβ42 and non-aggregating GFP-Aβ42 (19:34) proteins in a panel of 192 autophagy mutants lacking genes involved in regulation and initiation of the pathway, cargo selection and degradation processes. The nutrient and stress signalling genes RRD1, SNF4, GCN4 and SSE1 were identified. Deletion of these genes impaired GFP-Aβ42 clearance and their overexpression reduced GFP-Aβ42 levels in yeast. Overall, our findings identify a novel role for these nutrient and stress signalling genes in the targeted elimination of Aβ42 aggregates, which offer a promising avenue for developing autophagy based therapies to suppress amyloid deposition in AD.

Systemic LPS-induced A\u03b2-solubilization and clearance in A\u03b2PP-transgenic mice is diminished by heparanase overexpression

Amyloid-β (Aβ) is the main constituent of amyloid deposits in Alzheimer’s disease (AD). The neuropathology is associated with neuroinflammation. Here, we investigated effects of systemic lipopolysaccharide (LPS)-treatment on neuroinflammation and Aβ deposition in AβPP-mice and double-transgenic mice with brain expression of AβPP and heparanase, an enzyme that degrades HS and generates an attenuated LPS-response. At 13 months of age, the mice received a single intraperitoneal injection of 50 µg LPS or vehicle, and were sacrificed 1.5 months thereafter. Aβ in the brain was analyzed histologically and biochemically after sequential detergent extraction. Neuroinflammation was assessed by CD45 immunostaining and mesoscale cytokine/chemokine ELISA. In single-transgenic mice, LPS-treatment reduced total Aβ deposition and increased Tween-soluble Aβ. This was associated with a reduced CXCL1, IL-1β, TNF-α-level and microgliosis, which correlated with amyloid deposition and total Aβ. In contrast, LPS did not change Aβ accumulation or inflammation marker in the double-transgenic mice. Our findings suggest that a single pro-inflammatory LPS-stimulus, if given sufficient time to act, triggers Aβ-clearance in AβPP-transgenic mouse brain. The effects depend on HS and heparanase.

REGION-SPECIFIC ATROPHY AS MEASURED BY CORTICAL GRAY MATTER VOLUME IS ASSOCIATED WITH BOTH REGIONAL AND TOTAL CORTICAL AMYLOID-BETA BURDEN IN COGNITIVELY NORMAL INDIVIDUALS AT RISK FOR ALZHEIMER'S DISEASE

Introduction Models of preclinical Alzheimer's disease (AD) have proposed that cerebral amyloidosis and subsequent neurodegeneration may occur years, if not decades prior to observable cognitive decline. We previously demonstrated that total cortical amyloid-beta burden was inversely associated with cortical gray matter volume but not episodic memory in a sample of cognitively normal, middle-aged participants, with a first-degree family history and varying genetic risks of AD (Mecca et al., 2018). The current study utilizes an exploratory approach to determine the regional contribution of cortical amyloid deposition to gray matter volume and neuropsychological test performance in pre-symptomatic individuals at varying genetic risk for AD. Methods As described previously (Mecca et al., 2018), cognitively normal participants aged 50-66 with a first-degree family history for AD were genetically screened to select three groups: APOE genotype e4e4 (n=15), e3e4 (n=15), and e3e3 (n=15), matched for age and sex. Participants were then studied with [11C]PiB PET, MRI, and neuropsychological testing. PET and MR images were co-registered for application of a ROI template (AAL for SPM2) to generate regional time-activity curves with cerebellum as the reference region. MRI images were segmented into gray matter, white matter, and CSF. Mask images of these segments were smoothed to the system resolution (∼6mm), and gray matter values of BPND were partial volume corrected (PVC). PVC-BPND was then computed using SRTM2 for frontal, posterior cingulate, precuneus, lateral parietal, lateral temporal, medial temporal, occipital, and basal ganglia ROIs. A cortical BPND (cortical amyloid) was also calculated by taking a weighted average of only the frontal, posterior cingulate, precuneus, lateral parietal, and lateral temporal regions. To quantify GM within each ROI, we applied inverse transformations of the AAL from MNI to subject space and calculated GM fraction as the number of voxels segmenting a GM divided by the total number of voxels in a region. Results The study sample consisted of 24 females and 21 males with an average age of 59.12 (SD 4.72) and 16.33 (SD 1.86) years of education. Participants demonstrated an average MMSE score of 29.66 (SD 0.91), GDS score of 0.71 (SD 1.25), WAIS-III FSIQ score of 115.04 (SD 13.32), and WRAT-3 Reading score of 109.47 (SD 9.64). As previously reported, mean cortical BPND was 0.145 ± 0.131 for APOE-e3e3, 0.297 ± 0.299 for APOE-e3e4, and 0.389 ± 0.222 for APOE-e4e4 participants. An exploratory analysis was performed to examine the regional contributions to the association between cortical amyloid burden and gray matter volume. There were significant inverse associations between gray matter fraction and cortical amyloid in the frontal (spearman r=-0.459, p=0.002), lateral temporal (spearman r=-0.546, p Conclusions Based on our regional exploratory analyses, the inverse association between cortical amyloid burden and gray matter volume is strongest in the frontal, lateral, and medial temporal lobes. This is consistent with models of preclinical AD in which neurodegeneration occurs early in the disease process and before manifest cognitive decline. Interestingly, although the occipital lobeis traditionally thought to be a region of low amyloid deposition, we find the regional gray matter volume is significantly correlated with both regional and cortical amyloid. This perhaps implicates the occipital lobe as part of the cortical signature of AD, at least in cognitively normal middle-aged individuals with an increased risk of developing AD. It is also noted that medial temporal lobe atrophy isn't associated with regional amyloid, but instead significantly correlated with total cortical amyloid deposition. This is expected given the medial temporal lobe's reputation as a known area of early atrophy but not amyloid deposition in AD. This research was funded by This research was supported by the Alzheimer's Association IIRG-07-60026 (CHvD) and National Institute on Aging (P50-AG047270). APM was supported in part by the NIH/NIA K23-AG057794. RSO was supported in part by the NIMH R25 IMPORT grant (#R25MH071584).

Knockout of Amyloid β Protein Precursor (APP) Expression Alters Synaptogenesis, Neurite Branching and Axonal Morphology of Hippocampal Neurons.

The function of the β-A4 amyloid protein precursor (APP) of Alzheimer's disease (AD) remains unclear. APP has a number of putative roles in neuronal differentiation, survival, synaptogenesis and cell adhesion. In this study, we examined the development of axons, dendrites and synapses in cultures of hippocampus neutrons derived from APP knockout (KO) mice. We report that loss of APP function reduces the branching of cultured hippocampal neurons, resulting in reduced synapse formation. Using a compartmentalised culture approach, we found reduced axonal outgrowth in cultured hippocampal neurons and we also identified abnormal growth characteristics of isolated hippocampal neuron axons. Although APP has previously been suggested to play an important role in promoting cell adhesion, we surprisingly found that APPKO hippocampal neurons adhered more strongly to a poly-L-lysine substrate and their neurites displayed an increased density of focal adhesion puncta. The findings suggest that the function of APP has an important role in both dendritic and axonal growth and that endogenous APP may regulate substrate adhesion of hippocampal neurons. The results may explain neuronal and synaptic morphological abnormalities in APPKO mice and the presence of abnormal APP expression in dystrophic neurites around amyloid deposits in AD.

Alzheimer disease: Risk variants associated with amyloid deposition in Alzheimer disease.

Alzheimer disease: Risk variants associated with amyloid deposition in Alzheimer disease.

Lack of BACE1 S-palmitoylation reduces amyloid burden and mitigates memory deficits in transgenic mouse models of Alzheimer’s disease

Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by pathological brain lesions and a decline in cognitive function. β-Amyloid peptides (Aβ), derived from proteolytic processing of amyloid precursor protein (APP), play a central role in AD pathogenesis. β-Site APP cleaving enzyme 1 (BACE1), the transmembrane aspartyl protease which initiates Aβ production, is axonally transported in neurons and accumulates in dystrophic neurites near cerebral amyloid deposits in AD. BACE1 is modified by S-palmitoylation at four juxtamembrane cysteine residues. S-palmitoylation is a dynamic posttranslational modification that is important for trafficking and function of several synaptic proteins. Here, we investigated the in vivo significance of BACE1 S-palmitoylation through the analysis of knock-in mice with cysteine-to-alanine substitution at the palmitoylated residues (4CA mice). BACE1 expression, as well as processing of APP and other neuronal substrates, was unaltered in 4CA mice despite the lack of BACE1 S-palmitoylation and reduced lipid raft association. Whereas steady-state Aβ levels were similar, synaptic activity-induced endogenous Aβ production was not observed in 4CA mice. Furthermore, we report a significant reduction of cerebral amyloid burden and BACE1 accumulation in dystrophic neurites in the absence of BACE1 S-palmitoylation in mouse models of AD amyloidosis. Studies in cultured neurons suggest that S-palmitoylation is required for dendritic spine localization and axonal targeting of BACE1. Finally, the lack of BACE1 S-palmitoylation mitigates cognitive deficits in 5XFAD mice. Using transgenic mouse models, these results demonstrate that intrinsic posttranslational S-palmitoylation of BACE1 has a significant impact on amyloid pathogenesis and the consequent cognitive decline.

GENOME-WIDE ASSOCIATION STUDY OF A MULTIMODAL IMAGING BIOMARKER IN THE ADNI COHORT

Genome-wide association studies (GWAS) in Alzheimer's disease (AD) using neuroimaging-based phenotypes are typically derived from a single imaging modality. However, AD is a complex disorder involving different inter-linked pathogenic pathways. To explore genetic influences on disease progression, we generated a novel disease progression score (DPS) comprising cortical β-amyloid levels and hippocampal volume, then using it as a quantitative phenotype in GWAS. Study participants were part of the AD Neuroimaging Initiative (ADNI). Hippocampal volumes were computed with FreeSurfer from T1-weighted MRI scans. Cortical Aβ42 levels were computed as standardised uptake values ratio (SUVR) from florbetapir PET scans. The AD-DPS was computed by jointly modelling the long-term time evolution of hippocampal volume and cortical SUVR for 1088 individuals, using the growth models via alternating conditional expectation (GRACE) algorithm. We used this DPS as a continuous phenotype for a GWAS in 846 subjects of Caucasian ancestry, covarying for sex, age, APOE4 status, baseline SUVR and 2 principal components of population structure. Additionally, we repeated the analysis stratified by APOE4 status. Progression curves were in good agreement with proposed models of AD biomarker evolution (Figures 1–2). A genome-wide significant association with AD-DPS was found on chromosome 4 for rs3733541 (p=9.45e-09), located 300 kbp upstream of the KIT gene (Figure 3). This association was not found when testing hippocampal volume and Aβ42 burden separately. There were no genome-wide significant SNPs in the stratified analyses. However, the standardised effect size for rs3733541 was greater in APOE4 non-carriers (β=-0.11± 0.02, p=9.5e-5) than in APOE4 carriers (β=-0.08±0.02, p=3e-3). We describe the first use of a DPS derived from multiple imaging modalities in a quantitative trait-GWAS. The KIT gene and its ligand stem cell factor (SCF) are involved in a pathway leading to migration and differentiation of neural stem cells to sites of brain injury. Significantly lower levels of SCF have been found in the plasma and CSF of patients with early AD. If validated in future studies, this novel susceptibility locus may influence the joint occurrence of hippocampal atrophy and amyloid deposition in AD. Long-term progression curves for two AD biomarkers. Left, florbetapir PET SUVR; right, bilateral hippocampal volume. Disease progression score stratified by diagnostic group (left) and by MCI progression status (right). Manhattan plots for the GWAS of hippocampal volume (top), amyloid burden (middle), disease progression score (bottom). The blue line is the threshold for suggestive associations at p = 1e-5; the red line is the threshold for genome-wide significant associations at p = 5e-8.

AQP4 Association with Amyloid Deposition and Astrocyte Pathology in the Tg-ArcSwe Mouse Model of Alzheimer's Disease.

Amyloid-β deposition in senile plaques is one of the main pathological changes in Alzheimer's disease (AD). We previously reported that aquaporin-4 (AQP4) is redistributed within the astrocytes in cerebral amyloid angiopathy in the tg-ArcSwe mouse model of AD, suggesting that AQP4 may participate in amyloid-β deposition. However, the role of AQP4 in plaque formation is not currently clear. The objective of the current study was to explore the AQP4 distribution within plaques in the tg-ArcSwe mice in more depth by the combined application of immunofluorescence cytochemistry and immunogold electron microscopy. In addition, the astrocyte marker, glial fibrillary acidic protein (GFAP), was studied in association with AQP4. We demonstrated a robust upregulation of AQP4 expression in areas of plaques. Compared to GFAP, AQP4 appeared predominantly at later stages of plaque formation, in older mice, and within the processes of astrocytes. In combination with GFAP, AQP4 differentiated plaques into three progression stages under light microscopy. This suggests that AQP4 expression was associated with amyloid deposition and astrocyte pathology in the Tg-ArcSwe mouse model of AD. This provides novel proof for the involvement of AQP4 in the process of amyloid deposition in AD.

Plasma Exosomes Spread and Cluster Around β-Amyloid Plaques in an Animal Model of Alzheimer's Disease.

Exosomes, a type of extracellular vesicle, have been shown to be involved in many disorders, including Alzheimer’s disease (AD). Exosomes may contribute to the spread of misfolded proteins such as amyloid-β (Aβ) and α-synuclein. However, the specific diffusion process of exosomes and their final destination in brain are still unclear. In the present study, we isolated exosomes from peripheral plasma and injected them into the hippocampus of an AD mouse model, and investigated exosome diffusion. We found that injected exosomes can spread from the dentate gyrus (DG) to other regions of hippocampus and to the cortex. Exosomes targeted microglia preferentially; this phenomenon is stable and is not affected by age. In AD mice, microglia take up lower levels of exosomes. More interestingly, plasma exosomes cluster around the Aβ plaques and are engulfed by activated microglia nearby. Our data indicate that exosomes can diffuse throughout the brain and may play a role in the dynamics of amyloid deposition in AD through microglia.

Potential Therapeutic Effects of Oleuropein Aglycone in Alzheimer's Disease.

Alzheimer's disease (AD) is an age-associated neurodegenerative amyloid disease and is considered a social and clinical problem the last decades, particularly in the Western countries. Amyloid diseases are characterized by the deposition of typically aggregated protein/peptides in tissues that are associated with brain degeneration and progressive cognitive impairment. The amyloid plaques and neurofibrillary tangles arise as a result of self-assembly into fibrillar material of amyloid-β protein and hyperphosphorylated tau, respectively. Moreover, mounting evidence shows that oxidative and nitrosative stress plays a central role in the pathogenesis of neurodegenerative disorders such as AD. Oleuropein belongs to a specific group of polyphenols, the secoiridoids, which are abundant in Oleaceae. Oleuropein aglycone is abundant in extra virgin olive oil and it is generated as a product of a glucosidase released when olive fruits are crushed. This secoiridoid compound has radical-scavenging activity and antioxidative effects and it is considered a promising target to prevent amyloid toxicity as an inhibitor of the oligomer nucleation and growth. The neuroprotective and antioxidant effects of flavonoids have been found to strongly depend on their structure and functional groups. Oleuropein aglycone counteracts amyloid aggregation and toxicity affecting different pathways: amyloid precursor protein processing, amyloid-β peptide and tau aggregation, autophagy impairment, and neuroinflammation. In the current work, available literature on oleuropein aglycone effects as antioxidant and inhibitor of amyloid deposits in AD is reviewed. Moreover, we discuss the chemistry, food sources and bioavailability of oleuropein aglycone.