Ε4 Allele Research Articles

Altered patterns of brain activity during a fMRI memory task in cognitively normal adults carrying the APOE ε4 allele

AbstractBackgroundThe ε4 allele of the Apolipoprotein E gene (APOE) is a well‐established risk factor for Alzheimer’s disease (AD), ε4 carriers showing earlier onset and more severe memory impairment than non‐carriers. Neuroimaging evidence suggests that APOEε4 may modulate neural activity in AD since early stages. The purpose of this study was to determine whether APOEε4 influences brain activity in the memory circuit in older cognitively unimpaired individuals.MethodThirty cognitively unimpaired participants (n = 10 APOEε4 heterozygous carriers, age = 65± 5 years, 50% females, MMSE score = 29±1; n = 20 APOEε4 non‐carriers, age = 68±5 years, 35% females, MMSE score = 30±1) were recruited and underwent multidomain (i.e., memory, visuospatial abilities, language, attention) neuropsychological exams and functional MRI scan during an associative memory task, which consisted of two phases: (i) encoding of face‐name associations; (ii) recognition of the name associated to each face. Image preprocessing and voxel‐wise comparisons were conducted using the Statistical Parametric Mapping (SPM, v12). Clusters were considered significant at an uncorrected threshold of p<0.001.ResultParticipants were comparable for demographic and cognitive features (p>0.10) and performed similarly on the in‐scanner face‐name association memory task (p>0.10). Compared to ε4 non‐carriers, carriers showed (i) greater activation during the encoding task in the left temporo‐occipital cortex/fusiform gyrus, (ii) greater activation during the recognition task in the middle temporal gyrus/temporo‐occipital cortex bilaterally and in the right cerebellum, and (iii) lower activation during the recognition task in the medial supplementary motor area.ConclusionThese preliminary results confirm that the APOE ε4 allele is associated with a different pattern of brain functional activity during an associative memory task in cognitively unimpaired older. Given the similar cognitive performance between groups, higher activation in temporo‐occipital regions might reflect a compensatory process in regions vulnerable to AD pathology.

Relationships between KLOTHO and APOE4‐associated β‐amyloid and tau alterations across AD continuum

AbstractBackgroundApolipoprotein E ε4 allele (APOE4) is the leading genetic risk factor for Alzheimer’s disease (AD). APOE4 carriers (APOE4+) exhibit greater accumulation of the two AD neuropathological hallmarks, beta‐amyloid (β‐amyloid) and tau. KLOTHO KL‐VS heterozygosity (KL‐VSHET) attenuates APOE4‐related β‐amyloid and age‐related tau burden in cognitively normal individuals. It remains unclear whether this holds true for individuals with mild cognitive impairment (MCI) and AD. Here we investigate whether KL‐VSHET attenuates APOE4‐related cerebrospinal fluid (CSF) AD‐biomarker burden across the AD continuum.MethodMiddle‐aged and older adults (N = 396; MeanAge = 65) from the Wisconsin Registry for Alzheimer’s Prevention and Wisconsin Alzheimer’s Disease Research Center who were genotyped for KLOTHO and APOE and underwent CSF sampling were included in analyses. General linear models, covarying for sex, age, and AD family history, examined whether APOE4 yielded expected outcomes on β‐amyloid and tau burden. Follow‐up regression analyses, stratified by KL‐VS genotype [non‐carriers(KL‐VSNC,N = 293); KL‐VSHET (N = 103)], evaluated whether the APOE4 associations with β‐amyloid and tau differed between KL‐VSHET and KL‐VSNC. Analyses were stratified further by diagnosis [cognitively normal (N = 308) or MCI/AD (N = 88)] to investigate whether the relationships between APOE4 and β‐amyloid or tau differed among KL‐VSHET and KL‐VSNC in cognitively normal and MCI/AD participants.ResultResults for the entire sample, as well as stratified by KL‐VS status and diagnosis, are presented in Table 1. When the analysis was stratified by KL‐VS status, the APOE4+ effect on both β‐amyloid and tau burden was seen among KL‐VSNC but not KL‐VSHET. When further stratifying by diagnosis, the same pattern of attenuation among KL‐VSHET was observed for β‐amyloid burden in both cognitively normal individuals and MCI/AD whereas for tau burden, we only observed a non‐significant trend among cognitively normal persons (KL‐VSNC: p = 0.10; KL‐VSHET: p = 0.74).ConclusionKL‐VSHET attenuates both APOE4‐related CSF β‐amyloid and tau burden in cognitively normal individuals. This attenuation extends to CSF β‐amyloid but not tau accumulation in MCI/AD. These results add to the literature suggesting that KL‐VS heterozygosity is protective against APOE‐related biomolecular alterations that confer AD risk.

The association between cognitive reserve and age‐related neuroimaging features in homozygous APOE ε4 carriers

AbstractBackgroundAlzheimer’s disease (AD) is the most common neurodegenerative dementia syndrome, which is characterized by irreversibly progressive cognitive decline, neuropsychiatric symptoms, and impaired function of independent daily living. The majority of AD occurs in individuals aged over 65 years and is termed late‐onset AD. The apolipoprotein E (APOE) ε4 allele is the highest individual risk factor. Despite lifelong influences of APOE ε4, not all APOE ε4 carriers develop cognitive decline, some APOE ε4 carriers appear to be better than others in maintaining structural and functional properties of their brains while aging. Although previous studies showed that the AD patients with higher levels of cognitive reserve had more advanced Alzheimer’s type pathology in the comparable clinical severity, the underlying mechanism is unclear. Thus, the association between the individual’s cognitive reserve and the aging‐related brain pathologies need further investigation.MethodThis study recruited dementia free homozygous APOE ε4 allele carriers and all participants’ cognitive statuses were evaluated by neuropsychological tests. Cognitive reserve was evaluated by Cognitive Reserve Index questionnaire (CRIq). In neuroimage study, we collected brain MRI images and analyzed the severity of hippocampal atrophy and white matter hyperintensities (WMH). The relationship between different kinds of cognitive reserve and age‐related neuroimaging findings were analyzed.ResultIn total, 39 participants carrying two APOE ε4 alleles were analyzed, with an average age of 61.5 years, an education level of 13.1 years, and an average MMSE of 26.4 points. Correlation analysis showed significant associations between CRI and neuropsychological tests, especially in short‐term memory, visuospatial function, and language function tests. In neuroimaging analysis, CRI‐education was associated with hippocampal atrophy, which suggested more education might help to prevent the hippocampal atrophy. The correlation between WMH severity of brain MRI and the CRI was not statistically significant.ConclusionCognitive reserve is associated with the cognitive function in dementia free homozygous APOE ε4 allele carriers and education might prevent hippocampal atrophy.

Amyloidosis at Putamen Predicts Vulnerability to Alzheimer’s Disease

AbstractBackgroundUsing merely cortical amyloid burden in a binary approach was commonly adopted for determining if an individual is under AD pathology in both clinical trials and basic research. Subcortical amyloid, compared to cortical amyloid, showed a larger inter‐subject heterogeneity, which may provide valuable insights to their vulnerability to Alzheimer’s disease beyond cortical amyloid.MethodA total of 1344 individuals from ADNI database had 18F‐AV45 amyloid PET scans available. Regional AV45 signal was computed by averaging the signal from gray matter voxels in each region and then normalized to the mean signal in the composite reference region [1, 2]. The cortical AV45 was averaged over extensive regions consisting of frontal, anterior/posterior cingulate, lateral parietal, and lateral temporal regions. The AV45 signal in the subcortex, including putamen and caudate, were also computed. Only the participants under AD pathology, determined based on cortical amyloid positivity, were included in the analysis. The association analysis between subcortical AV45 and cognition was conducted before and after adjusting cortical AV45. A linear fitting of cortical AV45 and AV45 at putamen was conducted and participants were categorized into high (HighP), middle (MidP) and low (LowP) putamen amyloid group thresholded with ±0.5 standardized residuals. Statistical analysis was carried out to evaluate the difference of clinical diagnosis, hippocampal volume and APOE ε4 genotype. The relevance of amyloid at putamen with the rate of cognitive decline was examined.ResultPutamen, compared to caudate, had a stronger association with ADAS‐cog13 and MoCA, such an association remained exist after adjusting cortical AV45. Despite distinct AV45 at putamen, participants in LowP, MidP and HighP groups had no cortical AV45 difference. The AV45 at putamen was significantly higher in individuals with more ε4 alleles (ε4 homozygous > ε4 heterozygous > non‐ ε4) and more advance clinical stages (Dementia > MCI > CN). The individuals with higher AV45 at putamen had smaller hippocampal volume and faster cognitive decline.ConclusionOur finding suggested that amyloidosis at putamen is a valuable imaging marker beyond cortical amyloid in predicting if a participant is more vulnerable to Alzheimer’s dementia.

The Japan‐multimodal intervention trial for prevention of dementia (J‐MINT): a multi‐center, randomized, 18‐month controlled trial

AbstractBackgroundThe Japan‐multimodal intervention trial for prevention of dementia (J‐MINT) aimed to examine the efficacy of the multi‐domain intervention in the prevention of cognitive decline in older adults at high risk of dementia.MethodThe J‐MINT is an 18‐month, multi‐centered, randomized controlled trial. Participants aged 65‐85 years with mild cognitive deficits were recruited and randomized into multi‐domain intervention (management of vascular risk factors, group‐based physical exercise, nutritional counseling, and cognitive training) and control groups (health‐related information in writing every 2 months) at a 1:1 allocation ratio using the dynamic allocation method. The primary outcome was a change from baseline to 18‐month follow‐up in a composite Z score combining several neuropsychological tests, which include tests of global cognitive function (MMSE); memory (Logical memory I and II subset of the Wechsler Memory Scale‐Revised and the Free and Cued Selective Reminding Test); attention (Digit Span); executive function/processing speed (Trail Making Test, Digit Symbol Substitution Test, and Letter word fluency test).ResultBetween November 26, 2019, and December 28, 2020, 1677 participants were screened and 531 were randomly assigned to the multi‐domain intervention group (n = 265) or control group (n = 266). Four hundred and three (75.9%) participants completed the trial. The full analysis set included 433 patients who received the intervention program/health‐related information at least once. In the primary efficacy analysis, there were no significant differences in the change of composite Z score between the intervention group and the control group (mean difference 0.047 [95% CI ‐0.029 to 0.124]). In the analysis for each neuropsychological test, the score of the letter word fluency test in the intervention group significantly improved by a mean of 0.827 (95% CI = 0.356 to 1.298) points, whereas the mean difference between the intervention group and control group was not significant (mean difference 0.625 [95% CI ‐0.039 to 1.289]). In subgroup analyses, the intervention effect on composite Z score was significant among older adults with the apolipoprotein‐E (APOE) ε4 allele (mean difference 0.164 [95% CI 0.011 to 0.317]).ConclusionThe multi‐domain intervention showed significant efficacy for the prevention of cognitive decline among Japanese older adults with the APOE ε4 allele.

Clinical Manifestations.

In Alzheimer's disease (AD), a long preclinical and prodromal period precedes dementia onset in which cognition declines slowly, but at variable rates for different domains. Positive AD biomarkers, (e.g., amyloid, Tau, or APOE ε4 carriage), increase rates of cognitive decline and transition to dementia. However, the extent to which cognitive decline, identified in some older adults, reflects neurodegenerative disease or normal aging in the absence of knowledge about biomarkers or genes is not well understood. We applied a novel approach to classify cognitive decline in individuals using six cognitive composite scores (AIBL Pre-clinical Alzheimer's Cognitive Composite (AIBL-PACC), episodic recall, attention, executive function, language and recognition). We examine group-wise differences across cognitive composite scores and assessed frequencies for AD biomarker positivity amongst the novel groups. Prospective data from 1,389 Cognitively unimpaired (CU) participants from the Australian Imaging, Biomarkers and Lifestyle (AIBL) study of ageing were analysed using an unsupervised multivariate mixture modelling framework, accounting for age, gender and APOE ε4 allele status. Participants cognitive status was classified for their final visit. The cognitive profile and biomarker characteristics of adults with abnormal cognitive decline was compared. Differences in composite score values between cognitive decline and no decline groups were strongest for episodic recall (Cohen's d = 1.49) and the AIBL-PACC score (Cohen's d = 1.45, Table 1, Figure 1A). By comparison, differences in composite scores between Aβ-PET groups, or APOE ε4 allele carriers/non-carriers were of less magnitude (Table 1, Figure 1). Participants with cognitive decline were more likely to be amyloid positive, (decline: 42% vs no decline: 28%, p<0.0001), but not ε4 allele carriers (decline: 28% VS no decline: 27%, p>0.05). A measure of objective cognitive decline, created using flexible mixture models with six cognitive composite scores from AIBL, has utility for discerning participants with early changes in cognition. Based upon using the cognitive data alone, this method was able to detect amyloid positivity in those CU participants with cognitive decline.

APOE genotype‐specific lipidomic signatures in primary human hepatocytes

AbstractBackgroundApolipoprotein E (APOE) is primarily responsible for cholesterol homeostasis in the periphery and in the brain through independently regulated pathways, as it does not cross the blood‐brain barrier (BBB). Carriers of the APOE ε4 allele have a 3‐ to 15‐fold higher risk of developing Alzheimer’s disease (AD). Recently, we demonstrated that hepatic APOE4 was associated with alterations in AD‐relevant brain functions, suggesting clinical significance of plasma APOE, 90% of which is derived from the liver. How APOE genotype affects the hepatic lipidome is yet unknown. In this study, we assessed APOE genotype‐specific lipidomic profiles of primary human hepatocytes and their association with hepatic APOE.MethodWe conducted a lipidomic analysis of primary human hepatocytes isolated from 77 subjects by use of Ultra Performance Liquid Chromatography‐Tandem Mass Spectrometry. Lipid class levels over age across ε2/ε3, ε3/ε3 and ε3/ε4 genotypes were assessed using Pearson correlation analysis and between‐group comparisons for lipid class and species levels, controlled for demographic variables, were performed using one‐way ANOVA with Tukey HSD correction for multiple comparisons. We assessed hepatic APOE levels by ELISA in order to compare APOE expression between APOE genotypes and investigate correlations with lipid levels.ResultWe found APOE allele‐specific lipidomic patterns over age and between groups. APOE genotype differentially modulated the relationship between age and lipid levels across multiple lipid classes. The ε4 carriers had higher acylcarnitines (AC) and acylphosphatidylglycerol (AcylPG) as a class, as well as higher medium and long‐chain ACs, AcylPG, bis(monoacylglycerol)phosphate (BMP), monoacylglycerol and diacylglycerol species compared to ε2 carriers. Hepatocyte APOE levels decreased with age in the whole cohort, but correlated with monoacylglycerols (MG) and phosphatidylcholine (PC) only in ε4 carriers. We observed no differences in APOE hepatocyte levels specific to genotype or sex of the donor.ConclusionAPOE genotype dictates a differential lipidome in primary human hepatocytes but has no effect on APOE levels. The lipids involved suggest mitochondrial dysfunction with accompanying alterations in neutral lipid storage, reflective of a general disturbance of free fatty acid metabolism in human hepatocytes with the ε4 allele.

Predictive analysis between cytokine profile and Aβ42, p‐Tau, and p‐Tau/Aβ42 levels in the cerebrospinal fluid of older adults with and without cognitive impairment

AbstractBackgroundThe immune system activation observed in Alzheimer’s disease (AD) pathology contributes to its pathogenesis. It is proposed that ongoing interactions between β‐amyloid plaques, Tau protein, and neuroinflammatory mediators such as cytokines contribute to the maintenance of the inflammatory state in the brain. The aim was to evaluate whether cytokine profiles can predict variations in Aβ42, pTau, and pTau/Aβ42 cerebrospinal fluid (CSF) levels in older adults with and without objective cognitive impairment.MethodsEighty older adults were recruited, with a clinical diagnosis of AD dementia (36), with Mild Cognitive Impairment (MCI) (24), and without objective cognitive impairment (20). CSF levels of Aβ42, pTau, and 27 cytokines were assessed by the Luminex xMAP technique. Significant associations between Aβ42, p‐Tau, and p‐Tau/Aβ42 CSF levels and cytokines were explored in multiple linear regression analyses adjusted for age, education, and APOE ε4 carrier status.ResultsWe found that Granulocyte and Macrophage colony‐stimulating factors (GM‐CSF) (β = ‐.375; p = .010) and IL‐6 (β = ‐.370; p = .014) had a negative significant association with Aβ42, while IL‐8 (β = .452; p = .002) and IL‐4 (β = .488; p = .001) had positive significant association and higher magnitude of effect on Aβ42. For pTau, age (β = .240; p = .029), IL‐2 (β = .314; p = .012) and ε4 allele (β = 0.349; p = .002) had a positive significant association. The variable with the greatest magnitude of the effect was the presence of the ε4 allele. For the p‐Tau/Aβ42 ratio, G‐CSF (β = .423; p = .003) and GM‐CSF (β = .317; p = .019) had a significant positive association, while for IL‐8 (β = ‐.554; p = .001) and IL‐12 (β = ‐.334; p = .019) the association was significantly negative. IL‐8 had the greatest magnitude of effect on p‐Tau/Aβ42 ratio values.ConclusionThe higher levels of IL‐4 and the IL‐8 associated to a higher Aβ42 suggest their role at the beginning of the disease. On the other hand, the lower level of IL‐8 associated with a higher p‐Tau/Aβ42 suggests its inactivation as the disease progresses. Conversely, the higher levels of GM‐CSF associated with higher p‐Tau/Aβ42 suggests a more robust recruitment of the immune cell system at later stages.Reference: Aksnes, M., et al., (2021). Associations of cerebrospinal fluid amyloidogenic nanoplaques with cytokines in Alzheimer’s disease. Translational Neurodegeneration.

Effect of Adeno‐associated Viral Vector Mediated APOE Protective Variants Expression on Tau Pathology in a Tau Mouse Model

AbstractBackgroundAlzheimer’s disease (AD) is characterized by two main pathological hallmarks in the brain, namely, the presence of amyloid plaques and neurofibrillary tangles. However, the underlying mechanisms of AD pathogenesis are still largely unknown. Polymorphism in the apolipoprotein E (APOE) gene is a major genetic risk determinant of late‐onset AD, with the APOE*ε4 allele conferring an increased risk and the APOE*ε2 allele conferring protection relative to the common APOE*ε3 allele. Previous studies have shown that the presence of APOE*ε4 exacerbates tau pathology in AD patients as well as AD mouse models. uniQure is developing an AAV gene therapy approach which will simultaneously silence the risk‐increasing APOE allele and overexpress the protective APOE variant. Here, our goal is to investigate the effect of AAV‐mediated APOE protective variants expression on tau pathology in a tau mouse model.MethodProtective APOE‐variants were tested by intra‐striatal delivery of AAV vectors in a humanized tau mouse model. Vehicle or empty AAVs were injected in two separate control groups. Vector DNA, APOE mRNA and human APOE protein levels were measured in different brain areas of these mice. In addition, human tau protein levels were measured.ResultWe successfully expressed protective variants of APOE in a tau mouse model and measured human APOE protein levels in different brain areas. Furthermore, phosphorylated tau protein levels were significantly lower in AAV‐APOE‐protective variants treated tau mice compared to control groups mice indicating reduction in tau pathology in the hippocampus after protective APOE variants expression.ConclusionAAV‐mediated overexpression of protective APOE variants results in reduction of tau pathology in mice. Overexpression of protective APOE variants or in combination with a silencing approach using a new generation of therapeutic microRNAs (miRNAs) from our miQURE® platform could be an attractive treatment approach for AD.

Differences in pathology, brain atrophy, and WMHs across APOE subtypes

AbstractBackgroundThe apolipoprotein (APOE) e4 allele is a known risk factor for Alzheimer’s disease (AD), while the e2 allele is thought to be protective. As few studies have examined the relationship between brain pathologies, atrophy, and white matter hyperintensities (WMHs) and APOE status in those with the e2e4 genotype, we do so here.MethodsWe analyzed Alzheimer’s Disease Neuro Imaging participants that had APOE genotyping and at least one of the following metrics: regional WMH load (obtained using Dadar 2018); ventricle size, hippocampal (HC) and entorhinal cortex (EC) volume, amyloid level (i.e., AV‐45), and phosphorylated tau (pTau), all downloaded from LONI. Participants were divided into one of four APOE allele profiles (E4 = e4e4 or e3e4; E2 = e2e2 or e2e3; E3 = e3e3; or E24 = e2e4, Fig.1). Linear mixed effects models examined the relationship between APOE profiles and each pathology while controlling for age, sex, education, and diagnostic status.ResultsAt baseline (Fig.2), E4 exhibited increased pTau (p&lt;.001) compared to E2 and E3 and smaller HC and EC volumes than all other APOE profiles (p&lt;.01). The E24 group exhibited smaller ventricles than E3 and E4 (p&lt;.05). The E2 group exhibited less amyloid than all other APOE profiles (p&lt;.001), while E4 and E24 had more amyloid compared to E3 (p&lt;.001).Longitudinally (Fig.3), ventricular enlargement and HC atrophy significantly differed between all profiles (p&lt;.001). Furthermore, E2 was observed to have slower WMH accumulation compared to all other profiles (p&lt;.001), while E4 exhibited faster accumulation compared to E3 (p&lt;.001). The E4 group exhibited increased EC atrophy compared to E3 and E2 (p&lt;.001), and E24 exhibited more atrophy than E2 (p = .015). Amyloid increased faster in the E4 group compared to E3 and E2 (p&lt;.001), while E2 amyloid progressed slower than E3 (p = .005).ConclusionsAPOE E4 positivity is associated with increased baseline and greater accumulation of pathologies and rates of neurodegeneration. APOE E2 positivity is associated with reduced pathology burden (i.e., WMH and amyloid) and less neurodegeneration as measured by ventricle size and hippocampal and entorhinal cortex volume over time. APOE E2E4 is similar to E4 (i.e., increased neurodegeneration and pathology burden) but with a slightly slower rate of change.

Altered patterns of brain activity during a fMRI memory task in cognitively normal adults carrying the APOE ε4 allele

AbstractBackgroundThe e4 allele of the Apolipoprotein E gene (APOE) is a well‐established risk factor for Alzheimer’s disease (AD), e4 carriers showing earlier onset and more severe memory impairment than non‐carriers. Neuroimaging evidence suggests that APOEe4 may modulate neural activity in AD since early stages. The purpose of this study was to determine whether APOEe4 influences brain activity in the memory circuit in older cognitively unimpaired individuals.MethodThirty cognitively unimpaired participants (n = 10 APOEe4 heterozygous carriers, age = 65± 5 years, 50% females, MMSE score = 29±1; n = 20 APOEe4 non‐carriers, age = 68±5 years, 35% females, MMSE score = 30±1) were recruited and underwent multidomain (i.e., memory, visuospatial abilities, language, attention) neuropsychological exams and functional MRI scan during an associative memory task, which consisted of two phases: (i) encoding of face‐name associations; (ii) recognition of the name associated to each face. Image preprocessing and voxel‐wise comparisons were conducted using the Statistical Parametric Mapping (SPM, v12). Clusters were considered significant at an uncorrected threshold of p&lt;0.001.ResultParticipants were comparable for demographic and cognitive features (p&gt;0.10) and performed similarly on the in‐scanner face‐name association memory task (p&gt;0.10). Compared to e4 non‐carriers, carriers showed (i) greater activation during the encoding task in the left temporo‐occipital cortex/fusiform gyrus, (ii) greater activation during the recognition task in the middle temporal gyrus/temporo‐occipital cortex bilaterally and in the right cerebellum, and (iii) lower activation during the recognition task in the medial supplementary motor area.ConclusionThese preliminary results confirm that the APOE e4 allele is associated with a different pattern of brain functional activity during an associative memory task in cognitively unimpaired older. Given the similar cognitive performance between groups, higher activation in temporo‐occipital regions might reflect a compensatory process in regions vulnerable to AD pathology.

Amyloidosis at Putamen Predicts Vulnerability to Alzheimer’s Disease

AbstractBackgroundUsing merely cortical amyloid burden in a binary approach was commonly adopted for determining if an individual is under AD pathology in both clinical trials and basic research. Subcortical amyloid, compared to cortical amyloid, showed a larger inter‐subject heterogeneity, which may provide valuable insights to their vulnerability to Alzheimer’s disease beyond cortical amyloid.MethodA total of 1344 individuals from ADNI database had 18F‐AV45 amyloid PET scans available. Regional AV45 signal was computed by averaging the signal from gray matter voxels in each region and then normalized to the mean signal in the composite reference region [1, 2]. The cortical AV45 was averaged over extensive regions consisting of frontal, anterior/posterior cingulate, lateral parietal, and lateral temporal regions. The AV45 signal in the subcortex, including putamen and caudate, were also computed. Only the participants under AD pathology, determined based on cortical amyloid positivity, were included in the analysis. The association analysis between subcortical AV45 and cognition was conducted before and after adjusting cortical AV45. A linear fitting of cortical AV45 and AV45 at putamen was conducted and participants were categorized into high (HighP), middle (MidP) and low (LowP) putamen amyloid group thresholded with ±0.5 standardized residuals. Statistical analysis was carried out to evaluate the difference of clinical diagnosis, hippocampal volume and APOE e4 genotype. The relevance of amyloid at putamen with the rate of cognitive decline was examined.ResultPutamen, compared to caudate, had a stronger association with ADAS‐cog13 and MoCA, such an association remained exist after adjusting cortical AV45. Despite distinct AV45 at putamen, participants in LowP, MidP and HighP groups had no cortical AV45 difference. The AV45 at putamen was significantly higher in individuals with more e4 alleles (e4 homozygous &gt; e4 heterozygous &gt; non‐ e4) and more advance clinical stages (Dementia &gt; MCI &gt; CN). The individuals with higher AV45 at putamen had smaller hippocampal volume and faster cognitive decline.ConclusionOur finding suggested that amyloidosis at putamen is a valuable imaging marker beyond cortical amyloid in predicting if a participant is more vulnerable to Alzheimer’s dementia.

Developing Topics.

Alzheimer's disease (AD) is associated with the accumulation of neuropathological beta-amyloid (Ab) plaques, which is thought to be caused by an imbalance between Ab overproduction and dysfunctional Ab clearance. Both animal and human studies have shown that increased cerebrospinal fluid (CSF) levels of Ab peptides, especially Ab-40 and Ab-38 due to their high solubility, may be indicative of overall Ab dysregulation in preclinical AD, years before pathological Ab plaques begin to aggregate. The apolipoprotein E (APOE) e4 allele, which is the strongest genetic risk factor for AD, has been linked to impaired Ab clearance and disruption of the amyloid precursor protein (APP) pathway that is responsible for Ab production. However, the association between early Ab dysregulation and other genetic risk variants remains understudied. Thus, we aimed to explore whether genetic risk for AD is related to early markers of Ab overproduction by examining associations between polygenic risk scores (PRS) and CSF Ab-40 and Ab-38 in an AD-vulnerable population. We selected 88 non-demented Veterans (Age: M = 68.22, SD = 3.75 years) from the Alzheimer's Disease Neuroimaging Initiative-Department of Defense (ADNI-DOD) database with available genetic markers and CSF measures for Ab-40 and Ab-38. Genetic propensity for AD was assessed using genome-wide PRS, both with and without the APOE region, employing a p-value threshold < 0.01. CSF Ab concentrations were measured using a 2D-UPLC-tandem mass spectrometry method outlined by ADNI-DOD. Partial spearman's correlations related PRS to CSF Ab-38 and Ab-40 levels adjusting for age. CSF Ab-40 levels were positively associated with PRS for AD (rhopartial = 0.22, p = 0.037). When variants in the APOE region were excluded from the score, the relationship between CSF Ab-40 and PRS remained significant (rhopartial = 0.23, p = 0.035). The relationship between PRS for AD and CSF Ab-38 levels was not significant, regardless of whether APOE regions were included in the score (all p's > 0.1). Genetic risk for AD may lead to early Ab overproduction, as evidenced by elevated CSF Ab levels, particularly Ab-40. Other genetic variants, in addition to APOE, may play an integral role in disrupting the APP pathway and dysregulating Ab production.

APOE‐targeted epigenome therapy for late onset Alzheimer’s disease

AbstractBackgroundCarrying the APOEe4 variant significantly increases lifetime risk for LOAD. The accumulating evidence suggest that alteration of the expression of APOEe4 and APOE may hold promise as a potential therapeutics target for LOAD. In this study we developed an epigenome therapy platform to reduce APOE and APOEe4 specifically by targeted modification of the epigenome landscape within APOE locus.MethodOur approach is based on CRISPR/dCas9‐editing strategy. The novel system based on the novel bipartite repressor platform, recently developed in the laboratory. We designed targeting of APOEe4 in the allele‐discriminatory fashion, as such the editing is allele specific and precise. Furthermore, we developed a similar approach to target the regulatory elements within APOE promoter. We evaluated our platform in vitro using human hiPSC‐derived neurons and organoids, as well as in vivo by stereotactic injection of the developed system into the hippocampus of the ApoE‐humanized mice, harboring human ApoE loci replaced the mouse ortholog.ResultUsing the system, we demonstrated an efficient and precise editing of APOeE4 and APOE expressions in the hiPSC‐derived neurons and the human isogenic APOEe4 organoids. We showed that the system can robustly reduce the levels of APOE‐mRNA and the protein in both models. Importantly, the allele‐discrimination approach has resulted in no detectable editing of the e3 allele in the isogeneic hiPSC‐derived neurons, and organoids homozygous for the e3 allele. Moving onto in vivo studies, the promoter‐targeted approach using adeno‐associated‐ dCas9‐KRAB‐MeCP2 vector injected into the hippocampus of APOEe4 and APOEe3 mice, showed 50‐70% decrease in the mRNA and the protein levels. Similar effect was observed using lentivirus‐ CRISPR/Cas system targeted ApoEe4 in allele‐specific manner. Collectively, our results provided in vitro and in vivo proof‐of‐concept for the utility and efficacy of the APOE‐targeted epigenome therapy.ConclusionOur epigenome therapy strategy for fine‐tuning of APOE expression based on dCas9 technology is translational toward the development of a therapeutics approach to prevent and/or delay LOAD onset. Furthermore, the technology offers the opportunity to refine the platform for the development of gene‐specific and even allele‐ and cell‐type‐ specific therapies, and by that enables the advancement of strategies for precision medicine in LOAD.

Mechanisms of reduced Apolipoprotein E4 lipidation in iPSC‐derived astrocytes

AbstractBackgroundCarrying the apolipoprotein E ε4 (APOE4) allele is the highest known genetic risk factor for late‐onset Alzheimer’s disease (LOAD). Although how APOE4 leads to LOAD is not known, dysregulated endo‐lysosomal trafficking and lipid metabolism are key defects associated with APOE4. Cholesterol accumulation in glia instigates intracellular trafficking defects, increases cellular stress, and disrupts secretion. Additionally, enlarged endosomes were observed in the frontal lobes of APOE4‐carrying individuals, decades before the appearance of Aβ fibrilization. Therefore, we asked if cholesterol and endo‐lysosomal trafficking dysregulation in APOE4 carriers were due to differential lipidation of APOE3 and APOE4.MethodLocalization of ATP Binding Cassette Subfamily A Member 1 (ABCA1) in early, late, and recycling endosomal compartments were analyzed in human isogenic induced pluripotent stem cell (iPSC)‐derived neural cells and in cell lines treated with recombinant APOE in microscopic images. Membrane and cytoplasmic ABCA1 were compared using Western blots. Secreted high‐density lipoprotein (HDL) particles containing fluorescently tagged APOE3 or APOE4 were analyzed using ion‐mobility spectrometry. CS‐6253, an ABCA1 agonist peptide, was used to increase APOE lipidation.ResultThe protein levels of ABCA1, which mediates cholesterol and phospholipid efflux to the nascent apolipoprotein particles, were lower in APOE4/4 iPSC‐derived astrocytes compared to astrocytes derived from isogenic APOE3/3 iPSCs. Advanced image analysis revealed lower ABCA1 protein levels in Rab11+ recycling endosomes and less colocalization between ABCA1 and Rab7, a late endosome marker, in APOE4/4 astrocytes than APOE3/3 astrocytes. Consequently, less ABCA1 was detected at the cell membrane. Combined with previous data, these findings suggest APOE4 lipidation was reduced due to reduced ABCA1 activity. Additionally, BHK cells treated with recombinant APOE3 or APOE4 showed differences in ABCA1 localization that were altered by increasing APOE lipidation by activating ABCA1 via CS‐6253. Finally, fluorescently tagged APOE3 and APOE4 were incorporated in HDL particles and were secreted whose sizes were altered after CS‐6253 treatment, suggesting differences in lipidation levels.ConclusionWe demonstrated that diminished APOE4 lipidation is, at least in part, due to dysregulation of endo‐lysosomal trafficking of ABCA1 and that increasing APOE4 lipidation could alleviate cellular defects.

APOEε4 potentiates the effects of Aβ pathology on the deposition of neurofibrillary tangles via tau phosphorylation

AbstractBackgroundThe mechanisms by which the apolipoprotein E ε4 (APOEε4) allele influences Alzheimer’s disease (AD) pathophysiological progression are poorly understood. Here, we tested the association of APOEε4 carriership and amyloid‐β (Aβ) burden with longitudinal tau pathology progression.MethodWe studied 104 individuals across the aging and AD clinical spectrum from the McGill TRIAD cohort. Study participants underwent clinical assessments, APOE genotyping, magnetic resonance imaging, positron emission tomography (PET) for Aβ ([18F]AZD4694) and tau ([18F]MK6240) at baseline, as well as an additional follow‐up tau‐PET scan (mean follow‐up, 2.4 years). We further assessed longitudinal changes in tau phosphorylation (plasma phosphorylated tau at threonine 217 [p‐tau217+]), brain atrophy (gray matter density), and clinical function (clinical dementia rating scale sum of boxes).ResultWe found that APOEε4 carriership potentiates Aβ effects on longitudinal tau tangle accumulation over two years (Figure 1). Interestingly, the APOEε4‐potentiated Aβ effects on tangles were mediated by longitudinal plasma p‐tau217+ increase (Figure 2). In addition, this longitudinal tau accumulation as measured by PET was accompanied by brain atrophy and clinical decline during the follow‐up period (Figure 3).ConclusionOur results support a model in which the APOEε4 allele plays a key role in Aβ downstream effects on the aggregation of phosphorylated tau in the form of neurofibrillary tangles in the living human brain, which is a key factor in the development of dementia. These observations have important implications for the design of future trials by suggesting that the combination of therapies targeting both ApoeE4 and Aβ pathology might have the potential to synergistically halt tau progression in AD.

Sex‐specific neuropsychiatric burden distinguished by APOE4 status and cortical thickness

AbstractBackgroundThe APOE ε4 (APOE4) allele is a genetic risk factor for Alzheimer’s disease (AD). Prior work by our group found a significant association between the APOE4 allele and presence of psychosis as well as overall increased neuropsychiatric symptom (NPS) burden in female APOE4 homozygote AD patients, with no effect present in males. In this study, we sought to examine the relationship between APOE4 carrier status and sex on NPS burden from a neuroimaging perspective, with the aim to determine what brain regions may be driving this effect.MethodA cohort of 752 AD patients were selected from the National Alzheimer’s Coordinating Center (NACC) database: 104 APOE4 homozygotes (40F|64M), 304 APOE4 heterozygotes (160F|144M) and 310 APOE4 non‐carriers (131F|179M). Presence of NPS was identified using the Neuropsychiatric Inventory (NPI). Structural T1‐weighted images were downloaded from the NACC imaging dataset and cortical thickness measures corresponding to frontal, cingulate, temporal and parietal regions were assessed. Statistical analysis included a Bayesian multilevel regression where cortical thickness was modeled as an outcome variable against an interaction between sex and APOE4 homozygote status (0|1), while controlling for heterozygote status, APOE4 non‐carrier status, age, sex and MMSE as predictor variables. Within‐ and between‐groups mean differences in thickness were measured as a probability density estimate (Highest Density interval), and partial correlation was used to examine NPI correlates to thickness.ResultFemale APOE4 homozygotes displayed a high probability (&gt;90%HDI) of greater cortical thickness in the posterior cingulate and isthmus cingulate regions bilaterally and reduced cortical thickness in temporal regions (Figure 1). Cortical thickness in the fusiform cortex was positively correlated to greater NPI burden (p&lt;0.05) among female homozygotes, and negatively correlated to NPI burden among female heterozygotes. Cortical thickness in males, regardless of carrier status, did not correlate to NPI burden in any region.ConclusionThis study highlights an important relationship between the fusiform cortex and NPI burden in female APOE4 carriers, marking a female‐specific effect. Future work should further disentangle sex differences in APOE4 status and psychosis with a focus on the fusiform cortex as a potential region of interest.

Investigating the impact of APOE4 genotype on the association between cerebral blood flow and haematological properties in mid‐life adults

AbstractBackgroundCarriership of the apolipoprotein ε4 (APOE4) allele confers a heightened risk for the development of Alzheimer’s disease (AD). Cerebral blood flow (CBF) is decreased in prodromal and established AD, however findings in the preclinical stage are mixed, with some studies reporting increases. CBF can be impacted by many factors including the haematocrit. We investigated in a cohort at risk of developing AD how haematological variables relate to CBF and if this relationship is differentially moderated by APOE4.Method375 participants from the PREVENT‐Dementia study underwent arterial spin labelling (ASL) and structural 3Tesla MRI. ASL data were analysed using BASIL/FSL and structural scans with SPM12. CBF maps were corrected for partial volume effects. A vascular territory mask with nine territories, the middle, proximal and distal branches of the anterior, middle and posterior cerebral arteries (ACA, MCA, PCA) was used for region‐of‐interest analysis and registered to the native ASL space. Regional gray matter (GM) CBF values were harmonised using COMBAT. Linear regression was used to examine differences between APOE4 carriers and non‐carriers controlling for age, sex and years of education. Associations between haematological properties and CBF were examined with Pearson’s correlations. Differential relationships between CBF, haematocrit, and measures of red blood cell size and shape (distribution width (RDW) and mean corpuscular volume (MCV)) were investigated by including interaction terms of APOE4 and haematological variables in the models.ResultAPOE4 carriers had significantly higher CBF in the proximal MCA (t = 2.54, p = 0.01). Across all subjects, RDW and MCV were not associated with GM CBF, though several significant interactions were observed between APOE4 and RDW in predicting CBF (Figure 1). Haematocrit was associated with GM CBF (ρ = ‐0.19, p &lt; 0.01). No significant interactions were seen between APOE4 and haematocrit or MCV in predicting CBF.ConclusionThe variability of the size and shapes of erythrocytes was differentially associated with CBF between APOE4 carriers and non‐carriers suggesting a different response to morphological erythrocyte alterations. This could further relate to underlying factors such as inflammation, which is associated with a higher RDW. Such associations should be examined in further studies.

Investigating the impact of APOE4 genotype on the association between cerebral blood flow and haematological properties in mid‐life adults

AbstractBackgroundCarriership of the apolipoprotein ε4 (APOE4) allele confers a heightened risk for the development of Alzheimer’s disease (AD). Cerebral blood flow (CBF) is decreased in prodromal and established AD, however findings in the preclinical stage are mixed, with some studies reporting increases. CBF can be impacted by many factors including the haematocrit. We investigated in a cohort at risk of developing AD how haematological variables relate to CBF and if this relationship is differentially moderated by APOE4.Method375 participants from the PREVENT‐Dementia study underwent arterial spin labelling (ASL) and structural 3Tesla MRI. ASL data were analysed using BASIL/FSL and structural scans with SPM12. CBF maps were corrected for partial volume effects. A vascular territory mask with nine territories, the middle, proximal and distal branches of the anterior, middle and posterior cerebral arteries (ACA, MCA, PCA) was used for region‐of‐interest analysis and registered to the native ASL space. Regional gray matter (GM) CBF values were harmonised using COMBAT. Linear regression was used to examine differences between APOE4 carriers and non‐carriers controlling for age, sex and years of education. Associations between haematological properties and CBF were examined with Pearson’s correlations. Differential relationships between CBF, haematocrit, and measures of red blood cell size and shape (distribution width (RDW) and mean corpuscular volume (MCV)) were investigated by including interaction terms of APOE4 and haematological variables in the models.ResultAPOE4 carriers had significantly higher CBF in the proximal MCA (t = 2.54, p = 0.01). Across all subjects, RDW and MCV were not associated with GM CBF, though several significant interactions were observed between APOE4 and RDW in predicting CBF (Figure 1). Haematocrit was associated with GM CBF (ρ = ‐0.19, p &lt; 0.01). No significant interactions were seen between APOE4 and haematocrit or MCV in predicting CBF.ConclusionThe variability of the size and shapes of erythrocytes was differentially associated with CBF between APOE4 carriers and non‐carriers suggesting a different response to morphological erythrocyte alterations. This could further relate to underlying factors such as inflammation, which is associated with a higher RDW. Such associations should be examined in further studies.

APOE4 Genotype Relates with Body Mass and Percent Fat Mass in Cognitively Normal Older Adults

AbstractBackgroundLower body mass is related to the progression of Alzheimer’s disease (AD). Carriers of the APOE e4 (APOE4) allele have an increased risk of developing AD, and APOE4 status has been shown to be associated with decreased body mass and fat mass in AD. However, this relationship in cognitively normal older adults is unclear. We investigated whether body mass index (BMI) and body composition are related with APOE4 status in cognitively normal older adults.MethodBaseline data from 211 cognitively normal older adults in an ongoing nutrition intervention RCT (Nutrition Intervention for Cognitive Enhancement; NICE study) were analyzed. Whole blood was attained, and genetic analyses were used to determine APOE genotype. Participants with ≥ 1 APOE4 allele were classified as APOE4 carriers. BMI was calculated from weight and height. Fat mass percentage was measured using dual energy x‐ray absorptiometry. We compared means between APOE4 carriers and non‐carriers for BMI and fat mass percentage using covariate‐adjusted ordinary least squares (OLS) regression models (i.e., ANCOVA), adjusting for age and sex. Statistical analyses were performed using R (v. 4.2.2; R Foundation, Vienna, Austria). Statistical significance was set at p &lt; 0.05.ResultParticipants were 75% female with a mean age of 71.4 ± 4.9 years. 34% of participants were APOE4 carriers. Mean BMI and percent fat mass were 28.4 ± 4.6 kg/m2 and 40% ± 4.6, respectively. ApoE4 carriers had significantly lower BMI (27.5 kg/m2 ± 3.9 vs. 28.9 kg/m2 ± 4.8, p = 0.02) and lower body fat percentage (38% ± 8.0 vs. 42% ± 6.7, p &lt; 0.01) compared to non‐carriers, respectively.ConclusionIn this study, cognitively normal older adult APOE4 carriers had lower BMI and lower body fat percentage compared to non‐carriers. These findings suggest that APOE4 status may influence body weight and body composition, which may represent a way APOE4 increases the risk of symptomatic AD. Future studies are needed to explore the mechanisms underpinning the relationship of APOE4 with decreased body mass and differential body compositions and to determine if these results are consistent in different life stages.