Aims

The aim was to explore the combined effect of APOE and BDNF Val66Met polymorphisms on spatial navigation and volumes of navigation-related brain structures in individuals with amnestic mild cognitive impairment (aMCI).

Methods

116 older adults with aMCI from the Czech Brain Aging Study were stratified based on the APOE and BDNF Val66Met polymorphisms into four groups: ε4^-BDNF^Val/Val (n=29), ε4^-BDNF^Met (n=11), ε4⁺BDNF^Val/Val (n=52), ε4⁺BDNF^Met (n=24). All participants underwent clinical examination, comprehensive neuropsychological examination, brain MRI and spatial navigation testing in a real-space human analogue of the Morris water maze.

Results

The ɛ4⁺/BDNF^Met group, although similar to other polymorphism groups in demographic characteristics and global cognition (MMSE = 26), had significantly worse egocentric navigation performance than all other polymorphism groups (ps≤.045), and worse episodic memory compared to ɛ4–/BDNF^{Val/Val Val} (p<0.026). The ɛ4⁺/BDNF^Met group had smaller volumes of the left hippocampus and entorhinal cortex compared to the ɛ4–/BDNF^Val/Val (ps≤.019) and ɛ4–/BDNF^Met (ps≤.020) groups and smaller volumes of the right hippocampus and entorhinal cortex compared to the ɛ4–/BDNF^Met group (ps≤.038).

Conclusions

The combination of APOE ɛ4 and BDNF^Met polymorphisms is associated with more pronounced egocentric spatial navigation impairment, a typical feature of early AD, and atrophy of the medial temporal lobe in individuals with aMCI.

Aims

We investigated dose effects of the apolipoprotein E (APOE) genotype on the cerebrospinal fluid (CSF) proteome in prodromal Alzheimer’s disease (AD) individuals.

Methods

We selected 49 prodromal AD individuals (67±7 years old, 22 (45%) female) from the Amsterdam Dementia Cohort, equally distributed among APOE Ɛ3Ɛ3, Ɛ3Ɛ4 and Ɛ4Ɛ4 genotypes, and measured CSF proteomics data with Olink multiplex panels.

In total, 661 proteins were detected in at least 10 individuals per genotype and considered for further analysis. Associations between z-transformed protein concentrations and APOE-genotype were tested with linear regressions adjusting for age and sex.

Results

Amyloid-β 1-42 concentrations were comparable amongst APOE-genotype subgroups, whilst total tau was most often abnormal in APOE Ɛ4Ɛ4 compared to Ɛ3Ɛ3 (88% vs. 41%, p=0.04). In total, 17 of 661 (2.6%) proteins were differentially expressed in one of the APOE-genotype subgroups (all p<.05). Eleven proteins were upregulated in the APOE Ɛ4Ɛ4 group compared to the Ɛ3Ɛ3 group, with Ɛ3Ɛ4 showing intermediate values (see figure). Three proteins were lowest in APOE Ɛ3Ɛ4 and highest in Ɛ4Ɛ4. Two proteins were increased in APOE Ɛ3Ɛ3 compared to Ɛ3Ɛ4 and Ɛ4Ɛ4. Altered proteins showed involvement in biological processes of the immune system, lipid metabolism and signal transduction. One protein, pleiotrophin, was related to synaptic plasticity.

Conclusions

The CSF proteome in prodromal AD individuals shows APOE Ɛ4 dose-dependent alterations that were related to biological processes of lipid metabolism, immune system, signal transduction and synaptic plasticity. These results suggest that this APOE Ɛ4 dose-dependent effect may need to be taken into account in therapy development.

Aims

Recent studies have determined the ways APOE^ε4 differs from APOE^ε3, however, little is known about the ways these two alleles interact to affect risk for AD. Here we describe the creation of a new set of humanized APOE alleles and test our hypothesis that APOE^ε3/ε4 modifies risk for AD and related dementias in ways distinct from APOE^ε4/ε4.

Methods

A new series of humanized APOE mice that includes APOE^ε4/ε4 and APOE^ε3/ε3 mice were generated by MODEL-AD. Female and male APOE^ε3/ε3, APOE^ε3/ε4 and APOE^ε4/ε4 mice were characterized at 2 months. Two voluntary running cohorts (4 months and 12 months) were included to determine whether the effects of exercise are modified by APOE genotype. A battery of assays included blood lipid profiles, novel spatial memory, metabolic assessment, immunofluorescence and cortical transcriptional profiling. Linear modeling and WGCNA were used to identify effects of sex, genotype, and running in gene expression data.

Results

Cholesterol and triglyceride composition were significantly influenced by APOE genotype at 2 months and 4 months, respectively. Linear modeling identified genes significantly different between mice carrying one or two APOE^ε4 alleles compared to the reference APOE^ε3/ε3 genotype as early as 2 months. Genotype-specific differences in cerebrovascular proteins were observed at 12 months. Preliminary analyses of 12 month data indicate genotype-, sex- and activity-specific effects.

Conclusions

Our study predicts differences between APOE^ε3/ε4 and APOE^ε4/ε4 genotypes on AD-relevant phenotypes, suggesting therapies aimed at modifying APOE biology to treat dementias may need to be targeted to specific APOE genotypes.

Aims

ApolipoproteinE (APOE) ε4 is the primary genetic risk factor for late-onset Alzheimer's disease (AD). While early research implicated APOEε4 in aggregation and defective clearance of amyloid-beta, more recent work has uncovered novel roles in other AD relevant pathology, namely endosomal-lysosomal dysfunction and lipid imbalances. Herein, we aimed to determine to (co)dominant effect of APOEε4 expression in regional brain lipid composition in aged mice.

Methods

We performed targeted mass-spectometry (MS) lipidomics analysis on entorhinal cortex (EC), a brain region vulnerable in AD, and primary visual cortex (PVC) from 14–15 month-old APOE targeted replacement mice (APOE ε4/ε4, APOE ε3/ε4 and APOEε3/ε3 mice). Next, we validated the contribution of neuronal cells to APOE-mediated lipid dysregulation by profiling cultured primary neurons treated with conditioned media from APOE ε4/ε4 vs. APOEε3/ε3 astrocytes.

Results

Our results confirm an increased susceptibility of EC to APOE ε4 pathology versus the PVC. APOE ε4 expression showed a dominant effect in decreasing diacylglycerol levels (DAG) and a semi-dominant additive effect in upregulation of multiple ceramide, glycosylated sphingolipids and bis(monoacylglycerol)phosphate (BMP) species, lipids known to accumulate as a result of endolysosomal dysfunction. Neurons treated with conditioned media from APOE ε4 astrocytes also showed inversed regulation of DAG and BMP species.

Conclusions

Our results suggest APOEε4 expression differentially modulates regional lipid signatures which may underlie increased susceptibility of EC to AD-relevant pathology, namely defects in endosomal-lysosomal flux and onset of neurofibrillary tangles. These findings support future experiments aiming lipid manipulation as a novel therapeutical avenue in AD and related neurodegenerative disorders.

Aims

Objectives:

To unravel the effects of distinct apoE3 and apoE4 particles of different densities on the cholesterol efflux from astrocytes, and absorption into neurons.

Methods

Methods:

ApoE preparation: the conditioned media of primary and cell line's apoE3 and apoE4 astrocytes were subjected to sucrose gradient ultra-centrifugation and the resulting fractions were collected according to their respective densities.

Cholesterol efflux: human apoE3/E4 immortalized astrocytes were labeled with fluorescent cholesterol, after which, the efflux of the fluorescent cholesterol was measured in the presence and absence of the different apoE particles.

Absorption: Differentiated neuroblastoma cells were incubated with the above efflux media which contained fluorescent cholesterol and apoE particles. The extent to which the cholesterol was reabsorbed into the cells was measured.

Results

Results:

The low density apoE particles (highly lipidated) were more effective than the high density in inducing both efflux and absorption. These effects were similar between apoE3 and apoE4 suggesting that the extent of lipidation of apoE particles is a key dominating factor for cholesterol transport.

Conclusions

Conclusions:

a. These results suggest that the extent of lipidation of apoE particles is a key factor in determining the effect of cholesterol transport, suggesting that counteracting apoE4 pathology may be possible, with increased lipidation of the particles.

b. The effects of lipidation are dominant over apoE4 genotype, resulting in the same effects of apoE3 and apoE4, when similarly lipidated.

Aims

As the strongest genetic risk factor for late-onset Alzheimer’s disease (AD), the ε4 variant of apolipoprotein E (ApoE4) is known to perturb both lipid homeostasis and energy metabolism in brain. However, the cell type-specific mechanism of ApoE4 polymorphism in modulating brain lipid metabolism is unclear.

Methods

Using humanized ApoE3 and ApoE4 mice, here we describe a loss-of-function role of ApoE4 in regulating fatty acid (FA) metabolism across neuron and astrocyte in tandem with their distinct mitochondrial phenotypes.

Results

ApoE4 disrupts neuronal function partially by decreasing the sequestering of FA in neuronal lipid droplets (LDs). Sequestered neuronal FAs are exported and internalized by astrocytes, with ApoE4 in either cell types diminishing the transport efficiency. In ApoE4 astrocytes, increased mitochondrial fission underlies a metabolic shift towards enhanced glucose metabolism and reduced mitochondrial β-oxidation capacity, which further elicits astrocytic LD accumulation. Importantly, diminished capacity of ApoE4 astrocytes in eliminating neuronal lipids and performing FA degradation accounts for their compromised metabolic- and synaptic support to neurons.

Conclusions

These data support the coupling of neuron lipid homeostasis and astrocytic FA degradation with cell type-specific mitochondrial function, which is essential to protect neurons from energy deficit and lipotoxicity. Our findings reveal the mechanistic basis of ApoE4 in disrupting brain lipid homeostasis and bioenergetic capacity, which could underlie the accelerated lipid dysregulation, exacerbated energy deficits, and increased AD risk for ApoE4 carriers.

Aims

The association of Apolipoprotein E (APOE) ɛ4 with Alzheimer's disease risk is well-established however, the impact of APOE ɛ4 on human brain cell function remains unclear. We hypothesized that human APOE ε4/ε4 genotype contributes to disease risk through cell autonomous and non-cell autonomous mechanisms in a human specific manner.

Methods

Global transcriptomic analysis (pathway, network and cell type deconvolution) were performed on brain cell types, astrocytes, microglia, mixed cortical cultures (neurons and astrocytes) and brain microvascular endothelial cells, derived from human induced pluripotent stem cells (population and isogenic cells), post-mortem brains and APOE targeted replacement mice. For in vitro mechanistic study, filipin staining, Gas Chromatography/Mass Spectrometry (GC/MS), live cell imaging, immunocytochemistry, and Luminex multiplex immunoassays were utilized for lipid trafficking, the measurement of intracellular cholesterol level, localization, and cytokine/chemokine secretion.

Results

Global transcriptomic analyses identified human specific APOE ε4-driven lipid metabolic dysregulation in astrocytes and microglia. Decoupled cholesterol metabolism in APOE ε4 glia is due to lysosomal cholesterol sequestration; despite increased intracellular cholesterol leads to elevated de novo synthesis and decreased efflux. The most significant upregulated signal in post-mortem APOE ε4 AD brains is matrisome associated with chemotaxis, glial activation and lipid biosynthesis, which derives from astrocytes, paralleled pathways uncovered in astrocytes when co-cultured with neurons. Further, APOE ε4 astrocytes show enhanced chemokine/proinflammatory factors production when communicating with neurons.

Conclusions

Human APOE ε4 initiates human glia-specific cell autonomous and non-cell autonomous dysregulation that may increase AD risk.

Aims

To unravel the extent to which the pathological effects of apoE4 in AD are driven by downregulation and impaired trafficking of distinct membrane receptors and to investigate the mechanisms underlying this effect.

Methods

Primary neuronal cultures were prepared from APOE3 and APOE4 transgenic mice. The cultures were maintained for 14-21 days. Afterward, the levels and spatial distribution of selected receptors were determined. Utilizing specific markers for a distinct intracellular domain, enabled us to determine the intracellular location of these receptors, its' effects on various phenotypes, and the extent to which it can be affected by novel treatments.

Results

The results obtained show that the levels of apoE receptors (apoER2 and LRP-1), non-apoE receptors (VEGFR2 and InsulinR), and apoE lipidating transporter ABCA1 were down-regulated by the APOE4, and that the intracellular distribution and translocations are determined by apoE genotype, and are receptor-specific. Accordingly, the results show that while the downregulation of apoER2 and VEGFR2 were associated with their accumulation in the early endosome, LRP-1 was downregulated in all intracellular compartments, and InsulinR yields an intermediate pattern.

Conclusions

The effects observed in this study suggest that normal activity of neurons is impaired by the presence of apoE4 via downregulation and impaired trafficking of distinct receptors. The diversity of these receptors could help explain the wide spectrum of pathologies induced by apoE4. Moreover, this system can also be used as a model to examine the efficacy of apoE4-related anti AD therapies.