APOE Ε4 Carriers Research Articles

Exploring mitochondrial blood-based and genetic markers in older adults with mild cognitive impairment and remitted major depressive disorder

Mild cognitive impairment (MCI) is a prodromal stage in aging to possible progression to Alzheimer’s disease and related dementia (ADRD), where co-occurrence of major depressive disorder (MDD) accelerates the progression. Metabolic and mitochondrial abnormalities in ADRD and other neurodegenerative disorders have been widely suggested, while possible mitochondrial dysfunction has been associated with etiopathology of both MCI and MDD. Hence, investigation of mitochondrial markers in MCI, MDD, and presence of both conditions is warranted. In total, 332 older adult participants were included: 168 with MCI, 108 with MCI plus remitted MDD (rMDD), and 56 with rMDD but without MCI. We measured plasma circulating mitochondrial DNA (ccf-mtDNA), lactate, and extracted nuclear mitochondrial encoded (NMt) single-nucleotide variants (SNVs) (n = 312). Non-parametric statistical tests on ccf-mtDNA and lactate levels were performed on the diagnosis, clinical and cardiometabolic variables. Binary sequence kernel association test (SKAT-O) and burden test were performed on NMt-SNV, adjusted for age, race, gender, type II diabetes, and APOE genotype. Lower level of lactate was observed in MCI (KW χ2 = 14.8, P = 0.0024), more specifically, significant differences of lower plasma lactate between MCI only and rMDD, but not between MCI+rMDD and MCI were found, suggesting potential roles in MCI driving lactate lower levels. While higher levels of ccf-mtDNA were observed in APOE-ε4 carrier (χ2 = 5.04, P = 0.05). This relationship was present only in MCI (P = 0.043) and MCI+rMDD groups (P = 0.023). No significant nuclear-encoded mitochondrial gene associations were observed with MCI or MDD. The results suggest decreased level of plasma lactate in individuals with MCI and MCI+rMDD, with inverse correlation with ccf-mtDNA, in addition to effect of APOE-ε4 in further increasing ccf-mtDNA specifically in participants with cognitive impairment. These findings contribute to a deeper understanding of the mitochondrial markers in MCI and MDD, warranting further research to explore the precise roles of mitochondrial abnormalities in the development and progression of MCI.

Association of modifiable risk factors with progression to dementia in relation to amyloid and tau pathology

BackgroundDementia preventive interventions targeting multiple modifiable risk factors are a promising approach. However, the impact of modifiable risk factors in the presence of beta-amyloid or phosphorylated-tau (p-tau) pathology is unclear.MethodsThe objective of the study was to examine the role of modifiable risk factors (vascular factors, depression, and smoking) in the progression to mild cognitive impairment (MCI) or dementia among 434 cognitively unimpaired (CU) and 611 individuals with MCI from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. Vascular risk factors were summarized with the Cardiovascular Risk Factors, Aging, and Dementia (CAIDE) score, dichotomized into higher versus lower risk. Depression and smoking (yes/no) were categorised according to medical history or current symptoms. Analyses were stratified by beta-amyloid negative (A-) and positive (A +), p-tau negative (T-) and positive (T +), or beta-amyloid and p-tau negative (A-T-) and positive (A + T +) biomarker status. Cox proportional hazard models were adjusted for age, sex, education, baseline MMSE score, baseline hippocampal volume and ApoE4 carrier status.ResultsHigher CAIDE score was associated with increased risk of progression to all-cause dementia in most MCI subgroups: adjusted hazard ratios (aHR) [95% CI] were 3.1 [1.43; 6.53] in the A- subgroup, 1.7 [1.20–2.27] in T + , 2.6 [1.06–6.59] in A-T-, and 1.6 [1.15–2.22] in the A + T + subgroup. Smoking (yes/no) was associated with increased dementia aHR in the A + MCI subgroup: 1.6 [1.07–2.34]. Depression increased dementia aHR in the T + MCI subgroup: 1.5 [1.06–2.02]. No significant associations were found in the CU biomarker subgroups.ConclusionAddressing modifiable risk factors carries an important potential for reducing the risk of dementia even after the onset of Alzheimer's pathology. Knowledge of biomarker status can further optimize prevention strategies.

Hypercholesterolemia and Alzheimer's Disease: Unraveling the Connection and Assessing the Efficacy of Lipid-Lowering Therapies.

This article examines the relationship between cholesterol levels and Alzheimer's disease (AD), beginning with the early observation that individuals who died from heart attacks often had brain amyloid deposition. Subsequent animal model research proved that high cholesterol could hasten amyloid accumulation. In contrast, cholesterol-lowering treatments appeared to counteract this effect. Human autopsy studies reinforced the cholesterol-AD connection, revealing that higher cholesterol levels during midlife significantly correlated with higher brain amyloid pathology. This effect was especially pronounced in individuals aged 40 to 55. Epidemiological data supported animal research and human tissue observations and suggested that managing cholesterol levels in midlife could reduce the risk of developing AD. We analyze the main observational studies and clinical trials on the efficacy of statins. While observational data often suggest a potential protective effect against AD, clinical trials have not consistently shown benefit. The failure of these trials to demonstrate a clear advantage is partially attributed to multiple factors, including the timing of statin therapy, the type of statin and the appropriate selection of patients for treatment. Many studies failed to target individuals who might benefit most from early intervention, such as high-risk patients like APOE4 carriers. The review addresses how cholesterol is implicated in AD through various biological pathways, the potential preventive role of cholesterol management as suggested by observational studies, and the difficulties encountered in clinical trials, particularly related to statin use. The paper highlights the need to explore alternate therapeutic targets and mechanisms that escape statin intervention.

APOE 𝜀4-related blood-brain barrier breakdown is associated with microstructural abnormalities.

Blood-brain barrier (BBB) dysfunction occurs in Alzheimer's disease (AD). Yet, the stage at which it appears along the AD time course and whether it contributes to neurodegeneration remain unclear. Older adults (61 to 90 years) from cognitively normal (CN) to mildly cognitively impaired (CI), enriched for APOE 𝜀4 and amyloid positivity, underwent dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) and diffusion MRI to measure BBB permeability and brain microstructure. Analysis of variance compared BBB permeability according to cognitive status, amyloid beta (Aβ), and APOE4. Linear regressions assessed associations of BBB permeability with brain microstructure and interactions with Aβ and APOE4. BBB permeability was elevated for APOE4 carriers across the cortical gray matter, with the strongest differences among CN amyloid-negative individuals. Associations between entorhinal BBB permeability and microstructure interacted with Aβ and APOE4, with the strongest relationships in amyloid-positive individuals and APOE4 carriers. APOE4 may drive widespread BBB dysfunction in preclinical AD, which may contribute to neurodegenerative changes early along the AD cascade. Gray matter blood-brain barrier (BBB) permeability is elevated for APOE4 carriers. APOE4-related BBB breakdown appears in the absence of cognitive decline or amyloid. BBB leakage correlates with entorhinal cortex microstructural injury. Associations with microstructure are strongest for amyloid-positive APOE4 carriers.

Lower activity of cholesteryl ester transfer protein (CETP) and the risk of dementia: a Mendelian randomization analysis

BackgroundElevated concentrations of low-density lipoprotein cholesterol (LDL-C) are linked to dementia risk, and conversely, increased plasma concentrations of high-density lipoprotein cholesterol (HDL-C) and apolipoprotein-A1 (Apo-A1) associate with decreased dementia risk. Inhibition of cholesteryl ester transfer protein (CETP) meaningfully affects the concentrations of these blood lipids and may therefore provide an opportunity to treat dementia.MethodsDrug target Mendelian randomization (MR) was employed to anticipate the on-target effects of lower CETP concentration (μg/mL) on plasma lipids, cardiovascular disease outcomes, autopsy confirmed Lewy body dementia (LBD), as well as Parkinson’s dementia.ResultsMR analysis of lower CETP concentration recapitulated the blood lipid effects observed in clinical trials of CETP-inhibitors, as well as protective effects on coronary heart disease (odds ratio (OR) 0.92, 95% confidence interval (CI) 0.89; 0.96), heart failure, abdominal aortic aneurysm, any stroke, ischemic stroke, and small vessel stroke (0.90, 95%CI 0.85; 0.96). Consideration of dementia related traits indicated that lower CETP concentrations were associated higher total brain volume (0.04 per standard deviation, 95%CI 0.02; 0.06), lower risk of LBD (OR 0.81, 95%CI 0.74; 0.89) and Parkinson’s dementia risk (OR 0.26, 95%CI 0.14; 0.48). APOE4 stratified analyses suggested the LBD effect was most pronounced in APOE-ε4 + participants (OR 0.61 95%CI 0.51; 0.73), compared to APOE-ε4- (OR 0.89 95%CI 0.79; 1.01); interaction p-value 5.81 × 10− 4.ConclusionsThese results suggest that inhibition of CETP may be a viable strategy to treat dementia, with a more pronounced effect expected in APOE-ε4 carriers.

Longitudinal trajectories of general cognitive and daily functions in data-driven subtypes of MCI: A longitudinal cohort analysis of older adults

ObjectivesTo derive data-driven subtypes of mild cognitive impairment (MCI) and characterize the complicated changes of general cognitive and daily functions over time in MCI subtypes. MethodsA total of 813 subjects diagnosed as MCI at baseline from the Alzheimer's Disease Neuroimaging Initiative (ADNI) were included. Data-driven MCI subtypes were derived from group-based multi-trajectory modeling (GBMTM) analyses using longitudinal measurement scores in the cognitive domains of visuospatial function, language, and executive function. General cognitive and daily functions were measured by the Mini-Mental State Examination (MMSE) and the Functional Assessment Questionnaire (FAQ), respectively, whose longitudinal trajectory changes were depicted by Linear mixed models. ResultsThree MCI subtypes were derived, which were defined as “Cognitive decline group”, “Mild cognitive decline group” and “No cognitive decline group”. The “Mild cognitive decline group” had the highest percentage in the sample (46.2 %), followed by the “No cognitive decline group” (35.2 %). Patients in the “Cognitive decline group” had the highest mean age (74.69 years) at baseline, the highest APOE ε4 carriers (63.2 %), and the greatest dementia conversion rate (77.0 %). The changes in MMSE and FAQ score trajectories were fastest in the “Cognitive decline group” in the first 36 months and most slowly in the “No cognitive decline group”. ConclusionMCI individuals could be subdivided into more fine-grained cognitive subtypes, and identifying these distinct MCI subtypes and their different trajectories of cognitive decline may have important prognostic value for improving clinical course prediction.

IPSC-derived blood-brain barrier modeling reveals APOE isoform-dependent interactions with amyloid beta

BackgroundThree common isoforms of the apolipoprotein E (APOE) gene - APOE2, APOE3, and APOE4 - hold varying significance in Alzheimer’s Disease (AD) risk. The APOE4 allele is the strongest known genetic risk factor for late-onset Alzheimer’s Disease (AD), and its expression has been shown to correlate with increased central nervous system (CNS) amyloid deposition and accelerated neurodegeneration. Conversely, APOE2 is associated with reduced AD risk and lower CNS amyloid burden. Recent clinical data have suggested that increased blood-brain barrier (BBB) leakage is commonly observed among AD patients and APOE4 carriers. However, it remains unclear how different APOE isoforms may impact AD-related pathologies at the BBB.MethodsTo explore potential impacts of APOE genotypes on BBB properties and BBB interactions with amyloid beta, we differentiated isogenic human induced pluripotent stem cell (iPSC) lines with different APOE genotypes into both brain microvascular endothelial cell-like cells (BMEC-like cells) and brain pericyte-like cells. We then compared the effect of different APOE isoforms on BBB-related and AD-related phenotypes. Statistical significance was determined via ANOVA with Tukey’s post hoc testing as appropriate.ResultsIsogenic BMEC-like cells with different APOE genotypes had similar trans-endothelial electrical resistance, tight junction integrity and efflux transporter gene expression. However, recombinant APOE4 protein significantly impeded the “brain-to-blood” amyloid beta 1–40 (Aβ40) transport capabilities of BMEC-like cells, suggesting a role in diminished amyloid clearance. Conversely, APOE2 increased amyloid beta 1–42 (Aβ42) transport in the model. Furthermore, we demonstrated that APOE-mediated amyloid transport by BMEC-like cells is dependent on LRP1 and p-glycoprotein pathways, mirroring in vivo findings. Pericyte-like cells exhibited similar APOE secretion levels across genotypes, yet APOE4 pericyte-like cells showed heightened extracellular amyloid deposition, while APOE2 pericyte-like cells displayed the least amyloid deposition, an observation in line with vascular pathologies in AD patients.ConclusionsWhile APOE genotype did not directly impact general BMEC or pericyte properties, APOE4 exacerbated amyloid clearance and deposition at the model BBB. Conversely, APOE2 demonstrated a potentially protective role by increasing amyloid transport and decreasing deposition. Our findings highlight that iPSC-derived BBB models can potentially capture amyloid pathologies at the BBB, motivating further development of such in vitro models in AD modeling and drug development.

Relationships between APOE, Type 2 Diabetes, and Cardiovascular Disease in Postmenopausal Women.

The Apolipoprotein E (APOE) ε4 allele, type 2 diabetes mellitus (T2DM), and cardiovascular disease (CVD) are well-established risk factors for dementia. Relationships between APOE and incidence of T2DM and CVD are not fully understood but may shed light on the mechanisms underlying dementia pathogenesis. Postmenopausal women (N=6,795) from the Women's Health Initiative hormone therapy clinical trial with APOE genotyping and no prior diagnosis of T2DM or CVD were included. We examined associations of APOE status (APOE2+ [ε2/ε2, ε2/ε3], APOE3 [ε3/ε3], and APOE4+ [ε4/ε4, ε3/ε4] carriers) with incidence of T2DM, coronary heart disease (CHD), stroke, and total CVD events using Cox regression. CVD outcomes were examined in baseline non-statin users and adjusted for statin initiation over follow-up to account for possible confounding by statins. Among all participants (mean age 66.7±6.5 years, 100% non-Hispanic white), 451 (6.6%) were using statins at baseline. Over the follow-up (mean 14.9 and 16.0 years for T2DM and CVD, respectively), 1,564 participants developed T2DM and 1,578 developed CVD. T2DM incidence did not differ significantly by APOE status (ps≥0.09). Among non-statin users, APOE4+ had higher incidence of total CVD (hazard ratio [95% confidence interval]=1.18 [1.02-1.38], p=0.03) compared to APOE3 carriers, but risks for CHD (1.09 [0.87-1.36], p=0.47) and stroke (1.14 [0.91-1.44], p=0.27) were not significantly elevated when examined individually. CVD outcomes did not differ between APOE2+ and APOE3 carriers (ps≥0.11). T2DM risk did not differ by APOE status among postmenopausal women, but APOE4+ carriers not using statins had an increased risk of total CVD events.

APOE4 and Infectious Diseases Jointly Contribute to Brain Glucose Hypometabolism, a Biomarker of Alzheimer's Pathology: New Findings from the ADNI.

Impaired brain glucose metabolism is a preclinical feature of neurodegenerative diseases such as Alzheimer's disease (AD). Infections may promote AD-related pathology. Therefore, we investigated the interplay between infections and APOE4, a strong genetic risk factor for AD. We analyzed data on 1,509 participants in the Alzheimer's Disease Neuroimaging Initiative (ADNI) database using multivariate linear regression models. The outcomes were rank-normalized hypometabolic convergence index (HCI), statistical regions of interest (SROI) for AD, and mild cognitive impairment (MCI). Marginal mean estimates for infections, stratified by APOE4 carrier status, were then computed. Prior infections were associated with greater HCI [β=0.15, 95% CI: 0.03, 0.27, p=0.01]. The combined effects of infections and APOE4 carriers on HCI levels were significantly greater than either variable alone. Among APOE4 carriers, the estimated marginal mean was 0.62, rising to 0.77, with infections (p<0.001), indicating an interaction effect. Carriers with multiple infections showed greater hypometabolism (higher HCI), with an estimate of 0.44 (p=0.01) compared to 0.11 (p=0.08) for those with a single infection, revealing a dose-response relationship. The estimates for the association of infections with SROI AD and SROI MCI were β=-0.01 (p=0.02) and β=-0.01 (p=0.04), respectively. Our findings suggest that infections and APOE4 jointly contribute to brain glucose hypometabolism and AD pathology, supporting a "multi-hit" mechanism in AD development.

Sex-Dependent Effects of Cardiometabolic Health and APOE4 on Brain Age: A Longitudinal Cohort Study.

The aging population is growing faster than all other demographic strata. With older age comes a greater risk of health conditions such as obesity and high blood pressure (BP). These cardiometabolic risk factors (CMRs) exhibit prominent sex differences in midlife and aging, yet their influence on brain health in females vs males is largely unexplored. In this study, we investigated sex differences in relationships between BP, body mass index (BMI), and brain age over time and tested for interactions with APOE ε4 genotype (APOE4), a known genetic risk factor of Alzheimer disease. The sample included participants from 2 United Kingdom-based longitudinal birth cohorts, the Lothian Birth Cohort (1936) and Insight 46 (1946). Participants with MRI data from at least 1 time point were included to evaluate sex differences in associations between CMRs and brain age. The open-access software package brainageR 2.1 was used to estimate brain age for each participant. Linear mixed-effects models were used to assess the relationships between brain age, BMI, BP, and APOE4 status (i.e., carrier vs noncarrier) in males and females over time. The combined sample comprised 1,120 participants (48% female) with a mean age (SD) of 73 (0.72) years in the Lothian Birth Cohort and 71 (0.68) years in Insight 46 at the time point 1 assessment. Approximately 30% of participants were APOE4 carriers. Higher systolic and diastolic BP was significantly associated with older brain age in females only (β = 0.43-0.56, p < 0.05). Among males, higher BMI was associated with older brain age across time points and APOE4 groups (β = 0.72-0.77, p < 0.05). In females, higher BMI was linked to older brain age among APOE4 noncarriers (β = 0.68-0.99, p < 0.05), whereas higher BMI was linked to younger brain age among carriers, particularly at the last time point (β = -1.75, p < 0.05). This study indicates sex-dependent and time-dependent relationships between CMRs, APOE4 status, and brain age. Our findings highlight the necessity of sex-stratified analyses to elucidate the role of CMRs in individual aging trajectories, providing a basis for developing personalized preventive interventions.

Elevated blood glucose levels are associated with the progression of brain hypometabolism, and HDL-C and APOE4 add to this association.

Brain glucose hypometabolism has consistently been found in neurodegenerative disorders, including Alzheimer's disease (AD). High blood glucose and HDL cholesterol (HDL-C) levels have also been linked to neurodegeneration and AD. However, there is limited understanding of the relationships between dementia-related risk factors in the brain and blood. A linear mixed model was used to examine the relationship between blood glucose and HDL-C levels and the progression of brain hypometabolism, adjusting for APOE4 and other clinical covariates. The hypometabolic convergence index (HCI) was measured by fluorodeoxyglucose-18 (FDG) positron emission tomography (PET) in participants from the Alzheimer's Disease Neuroimaging Initiative (ADNI). Data visualizations were generated to understand the joint effects of plasma glucose, HDL-C, and APOE4 on HCI. There were 336 individuals (781 observations), of whom 22.62% had AD. The majority were male (63.98%) and of white race, and 48.51% were carriers of APOE4. Over time, high blood glucose level was associated with the progression of brain glucose hypometabolism (β=0.33, 95% CI: 0.02, 0.64, p<0.05). A high plasma HDL-C level (β=1.22, 95% CI: 0.09, 2.35, p<0.05), more study visits (β=1.67, 95% CI: 1.37, 1.98, p<0.001), and being an APOE4 allele carrier (β=1.29, 95% CI: 0.15, 2.42, p<0.05) were also significant predictors of brain hypometabolism progression. APOE4 carrier status and number of visits account for the largest proportion of the variance from the fixed effects model. Random effects due to participant characteristics and fixed effects together accounted for 95.2% of the model variance. Subgroup analysis revealed that these effects were observed only in those without AD. High plasma glucose levels facilitated the progression of brain hypometabolism. The effect was more prominent in the APOE4 double-carriers with elevated HDL-C. Elevated blood glucose may reflect systemic insulin resistance, which could impair brain glucose uptake, resulting in brain hypometabolism. Controlling blood glucose and HDL-C levels in APOE4 carriers may improve brain metabolism, potentially delaying the onset of dementia.

Exploring the causal effects of serum lipids and lipidomes on lewy body dementia: a Mendelian randomization study.

Lewy body dementia (LBD) is a neurodegenerative disorder characterized by the accumulation of Lewy bodies, which primarily composed of misfolded alpha-synuclein (αS). The development of LBD and APOE4 subtypes is thought to be associated with disorders of lipid metabolism. In this study, we investigated the causal relationship between serum lipids, liposomes and LBD using a two-sample Mendelian randomization (TSMR) method. A TSMR analysis of genome-wide association study (GWAS) data for 8 serum lipids, 179 lipidomes components, LBD and its subtypes was performed, using inverse variance weighted as the primary outcome. To ensure robustness, the sensitivity analyses including MR Pleiotropy RESidual Sum and Outlier, Cochran's test, leave-one-out method and funnel plots were performed. In this study, we found that low-density lipoprotein cholesterol (LDL-C) (OR=1.45, 95% CI=1.19-1.77, P<0.001) and remnant cholesterol (RC) (OR=2.64, 95% CI=1.64-4.28, P<0.001) had significant positive causal effects on LBD, and RC also had a positive effect on LBD in carriers of the APOE4 gene. The results of lipidome analysis showed that phosphatidylcholine (PC) (O-16:0_20:4) levels (OR=0.86, 95% CI=0.75-0.98, P=0.02) and PC (O-18:1_20:4) levels (OR=0.76, 95% CI=0.65-0.89, P <0.001) had negative causal effects on LBD, whereas phosphatidylinositol (PI) (18:1_20:4) levels had a positive causal effect on LBD (OR=1.19, 95% CI=1.02-1.39, P=0.03). For LBD with APOE4 carriers, high levels of PC (16:1_18:0) and PC (O-18:2_18:1) had a significant positive effect, while high levels of PC (O-16:1_18:0), phosphatidylethanolamine (PE) (O-18:2_18:1), sphingomyelin (SM) (d38:2), and triacylglycerol (TAG) (56:5) significantly reduced the risk. No heterogeneity and horizontal pleiotropy were observed in sensitivity analysis. Elevated LDL-C and RC levels are significant risk factors for LBD, with RC also impacting APOE4-carrying LBD. Glycerophospholipids play a crucial role in the pathogenesis of LBD, but the specific components that play a role differ from those with the APOE4 carries. These findings highlight the importance of lipid metabolism in LBD and APOE4 subtypes.

The influences of ApoE isoforms on endothelial adherens junctions and actin cytoskeleton responding to mCRP.

Apolipoprotein E4 (ApoE4) plays an important role responding to monomeric C-reactive protein (mCRP) via binding to CD31 leading to cerebrovascular damage and Alzheimer's disease (AD). Using phosphor-proteomic profiling, we found altered cytoskeleton proteins in the microvasculature of AD brains, including increased levels of hyperphosphorylated tau (pTau) and the actin-related protein, LIMA1. To address the hypothesis that cytoskeletal changes serve as early pathological signatures linked with CD31 in brain endothelia in ApoE4 carriers, ApoE4 knock-in mice intraperitoneal injected with mCRP revealed that mCRP increased the expressions of phosphorylated CD31 (pCD31) and LIMA1, and facilitate the binding of pCD31 to LIMA1. mCRP combined with recombinant APOE4 protein decreased interaction of CD31 and VE-Cadherin at adherens junctions (AJs), along with altered the expression of various actin cytoskeleton proteins, causing microvasculature damage. Notably, the APOE2 protein attenuated these changes. Overall, our study demonstrates that ApoE4 responds to mCRP to disrupt the endothelial AJs which link with the actin cytoskeleton and this pathway could play a key role in the barrier dysfunction leading to AD risk.

Lifestyle, biological, and genetic factors related to brain iron accumulation across adulthood

Iron is necessary for many neurobiological mechanisms, but its overaccumulation can be harmful. Factors triggering age-related brain iron accumulation remain largely unknown and longitudinal data are insufficient. We examined associations between brain iron load and accumulation and, blood markers of iron metabolism, cardiovascular health, lifestyle factors (smoking, alcohol use, physical activity, diet), and ApoE status using longitudinal data from the IronAge study (n = 208, age = 20–79, mean follow-up time = 2.75 years). Iron in cortex and basal ganglia was estimated with magnetic resonance imaging using quantitative susceptibility mapping (QSM). Our results showed that (1) higher peripheral iron levels (i.e., composite score of blood iron markers) were related to greater iron load in the basal ganglia; (2) healthier diet was related to higher iron levels in the cortex and basal ganglia, although for the latter the association was significant only in younger adults (age = 20–39); (3) worsening cardiovascular health was related to increased iron accumulation; (4) younger ApoE ε4 carriers accumulated more iron in basal ganglia than younger non-carriers. Our results demonstrate that modifiable factors, including lifestyle, cardiovascular, and physiological ones, are linked to age-related brain iron content and accumulation, contributing novel information on potential targets for interventions in preventing brain iron-overload.

Apolipoprotein E4 and Alzheimer's disease causality under adverse environments and potential intervention by senolytic nutrients

Apolipoprotein E (apoE) has a pivotal role in Alzheimer's Disease (AD) pathophysiology. APOE4 has been recognized as a risk factor for developing late-onset AD. Recently, APOE4 homozygosity was regarded as a new familial genetic trait of AD. In this opinion paper, we summarized the potential pleiotropic antagonism role of APOE4 in children living under early life adversity and afflicted with enteric infection/malnutrition-related pathogenic exposome. APOE4 was found to be neuroprotective early in life despite its increasing risk for AD with aging. We call for awareness of the potential burden this can bring to the public health system when APOE4 carriers, raised under adverse environmental conditions in early life and then aging with unhealthy lifestyles in later life may be at special risk for cognitive impairments and acquired AD. We postulate the importance of anti-senescence therapies to protect these individuals and remediate aging-related chronic illnesses.

Differences in Grey Matter Concentrations and Functional Connectivity between Young Carriers and Non-Carriers of the APOE ε4 Genotype.

Background: The pathophysiology of Alzheimer's disease (AD) may begin developing years or even decades prior to the manifestation of its first symptoms. The APOE ε4 genotype is a prominent genetic risk for AD that has been found to be associated with brain changes across the lifespan since early adulthood. Thus, studying brain changes that may occur in young adults with an APOE ε4 status is highly relevant. Objective: Examine potential differences in grey matter (GM) and functional connectivity (FC) in brains of cognitively healthy young APOE ε4 carriers and non-carriers, denoted here as ε4(+) and ε4(-), respectively. Methods: Three Tesla magnetic resonance imaging (MRI) brain scans were acquired from cognitively healthy young participants aged approximately 20 years (n = 151). Voxel-based morphometry (VBM) analysis was employed to identify potential structural differences in GM between ε4(+) and ε4(-). In a subsequent seed-based connectivity (SBC) analysis, brain regions that structurally differed in the VBM analysis were considered as seeds and correlated with all the remaining voxels across the brains to then measure the differences in FC between groups. Results: The VBM analysis suggested that ε4(+) (n = 28) had greater GM densities relative to ε4(-) (n = 123) in the left hippocampus and the left posterior insula (puncorr < 0.001). However, the effect did not survive the correction for multiple comparisons, suggesting minimal structural differences in this age range. In contrast, the SBC analysis indicated that ε4(+) exhibited significantly decreased FC between the left hippocampus and areas of the left middle temporal gyrus (n = 27) compared to ε4(-) (n = 102). These results remained significant after multiple comparisons (pFDR < 0.05). Lastly, no statistically significant differences in FC between groups were observed for the left insular seed (pFDR > 0.05). Discussion: These results suggest early structural and functional brain changes associated with the APOE ε4 genotype on young adults. Yet, they must be cautiously interpreted and contrasted with both older adults with genetic risk for AD and patients diagnosed with AD.

The Interaction Effects of Sex, Age, APOE and Common Health Risk Factors on Human Brain Functions.

Nonlinear changes in brain function during aging are shaped by a complex interplay of factors, including sex, age, genetics, and modifiable health risk factors. However, the combined effects and underlying mechanisms of these factors on brain functional connectivity remain poorly understood. To comprehensively investigate the combined associations of sex, age, APOE genotypes, and ten common modifiable health risk factors with brain functional connectivities during aging. This analysis used data from 36,630 UK Biobank participants, aged 44-81, who were assessed for sex, age, APOE genotypes, 10 health risk factors, and brain functional connectivities through resting-state functional magnetic resonance imaging. Brain functional connectivities were evaluated through within- and between-network functional connectivities and connectivity strength. Associations between risk factors and brain functional connectivities, including their interaction effects, were analyzed. Hypertension, BMI, and education were the top three influential factors. Sex-specific effects were also observed in interactions involving APOE4 gene, smoking, alcohol consumption, diabetes, BMI, and education. Notably, a negative sex-excessive alcohol interaction showed a stronger negative effect on functional connectivities in males, particularly between the dorsal attention network and the language network, while moderate alcohol consumption appeared to have protective effects. A significant negative interaction between sex and APOE4 revealed a greater reduction in functional connectivity between the cingulo-opercular network and the posterior multimodal network in male APOE4 carriers. Additional findings included a negative age-BMI interaction between the visual and dorsal attention networks, and a positive age-hypertension interaction between the frontoparietal and default mode networks. The findings highlight significant sex disparities in the associations between age, the APOE-ε4 gene, modifiable health risk factors, and brain functional connectivity, emphasizing the necessity of jointly considering these factors to gain a deeper understanding of the complex processes underlying brain aging.

Associations of Microbleeds and Their Topography With Imaging and CSF Biomarkers of Alzheimer Pathology in Individuals With Down Syndrome.

Cerebral hemorrhages are an exclusion criterion and potential adverse effect of antiamyloid agents. It is, therefore, critical to characterize the natural history of cerebral microbleeds in populations genetically predisposed to Alzheimer disease (AD), such as Down syndrome (DS). We aimed to assess microbleed emergence in adults with DS across the AD spectrum, defining their topography and associations with clinical variables, cognitive outcomes, and fluid and neuroimaging biomarkers. This cross-sectional study included participants aged 18 years or older from the Down-Alzheimer Barcelona Neuroimaging Initiative and Sant Pau Initiative on Neurodegeneration with T1-weighted and susceptibility-weighted images. Participants underwent comprehensive assessments, including apolipoprotein E (APOE) genotyping; fluid and plasma determinations of beta-amyloid, tau, and neurofilament light; cognitive outcomes (Cambridge Cognitive Examination and modified Cued Recall Test); and vascular risk factors (hypertension, diabetes mellitus, and dyslipidemia). We manually segmented microbleeds and characterized their topography. Associations between microbleed severity and AD biomarkers were explored using between-group comparisons (none vs 1 vs 2+) and multivariate linear models. We included 276 individuals with DS and 158 healthy euploid controls (mean age = 47.8 years, 50.92% female). Individuals with DS were more likely to have microbleeds than controls (20% vs 8.9%, p < 0.001), with more severe presentation (12% with 2+ vs 1.9%). Microbleeds increased with age (12% 20-30 years vs 60% > 60 years) and AD clinical stage (12.42% asymptomatic, 27.9% prodromal, 35.09% dementia) were more common in APOEε4 carriers (26% vs 18.3% noncarriers, p = 0.008), but not associated with vascular risk factors (p > 0.05). Microbleeds were predominantly posterior (cerebellum 33.66%; occipital 14.85%; temporal 21.29%) in participants with DS. Associations with microbleed severity were found for neuroimaging and fluid AD biomarkers, but only hippocampal volumes (standardized β = -0.18 [-0.31, -0.06], p < 0.005) and CSF p-tau-181 concentrations (β = 0.26 [0.12, 0.41], p < 0.005) survived regression controlling for age and disease stage, respectively. Microbleeds had limited effect on cognitive outcomes. In participants with DS, microbleeds present with a posterior, lobar predominance, are associated with disease severity, but do not affect cognitive performance. These results suggest an interplay between AD pathology and vascular lesions, implicating microbleeds as a risk factor limiting the use of antiamyloid agents in this population.

Serum proteomics reveal APOE-ε4-dependent and APOE-ε4-independent protein signatures in Alzheimer's disease.

A deeper understanding of the molecular processes underlying late-onset Alzheimer's disease (LOAD) could aid in biomarker and drug target discovery. Using high-throughput serum proteomics in the prospective population-based Age, Gene/Environment Susceptibility-Reykjavik Study (AGES) cohort of 5,127 older Icelandic adults (mean age, 76.6 ± 5.6 years), we identified 303 proteins associated with incident LOAD over a median follow-up of 12.8 years. Over 40% of these proteins were associated with LOAD independently of APOE-ε4 carrier status, were implicated in neuronal processes and overlapped with LOAD protein signatures in brain and cerebrospinal fluid. We identified 17 proteins whose associations with LOAD were strongly dependent on APOE-ε4 carrier status, with mostly consistent associations in cerebrospinal fluid. Remarkably, four of these proteins (TBCA, ARL2, S100A13 and IRF6) were downregulated by APOE-ε4 yet upregulated due to LOAD, a finding replicated in external cohorts and possibly reflecting a response to disease onset. These findings highlight dysregulated pathways at the preclinical stages of LOAD, including those both independent of and dependent on APOE-ε4 status.

Comparison of subjective cognitive decline and polygenic risk score in the prediction of all-cause dementia, Alzheimer’s disease and vascular dementia

BackgroundPolygenic risk scores (PRS) and subjective cognitive decline (SCD) are associated with the risk of developing dementia. It remains to examine whether they can improve the established cardiovascular risk factors aging and dementia (CAIDE) model and how their predictive abilities compare.MethodsThe CAIDE model was applied to a sub-sample of a large, population-based cohort study (n = 5,360; aged 50–75) and evaluated for the outcomes of all-cause dementia, Alzheimer’s disease (AD) and vascular dementia (VD) by calculating Akaike’s information criterion (AIC) and the area under the curve (AUC). The improvement of the CAIDE model by PRS and SCD was further examined using the net reclassification improvement (NRI) method and integrated discrimination improvement (IDI).ResultsDuring 17 years of follow-up, 410 participants were diagnosed with dementia, including 139 AD and 152 VD diagnoses. Overall, the CAIDE model showed high discriminative ability for all outcomes, reaching AUCs of 0.785, 0.793, and 0.789 for all-cause dementia, AD, and VD, respectively. Adding information on SCD significantly increased NRI for all-cause dementia (4.4%, p = 0.04) and VD (7.7%, p = 0.01). In contrast, prediction models for AD further improved when PRS was added to the model (NRI, 8.4%, p = 0.03). When APOE ε4 carrier status was included (CAIDE Model 2), AUCs increased, but PRS and SCD did not further improve the prediction.ConclusionsUnlike PRS, information on SCD can be assessed more efficiently, and thus, the model including SCD can be more easily transferred to the clinical setting. Nevertheless, the two variables seem negligible if APOE ε4 carrier status is available.