The forgotten APOE allele: a review of the evidence and suggested mechanisms for the protective effect of APOE ɛ2

Cancer-Related Cognitive Impairment Associated with APOE rs7412 and BDNF rs6265 in Breast Cancer Survivors

OBJECTIVES

Cancer-related cognitive impairment (CRCI) is a highly prevalent and debilitating symptom reported by breast cancer survivors (BCS). The etiology of CRCI remains unclear, leading to poor symptom management. Building from prior studies, BCS with the C/C genotype of apolipoprotein E (APOE) rs7412 and the T/T genotype of brain-derived neurotrophic factor (BDNF) rs6265 were hypothesized to experience more severe CRCI. Therefore, we investigated the relationships between the severity of CRCI and polymorphisms of APOE and BDNF among BCS.

METHODS

This was a subanalysis of data from a larger descriptive, correlational, and cross-sectional study. Subjective and objective CRCI were measured using the Patient-Reported Outcomes Measurement Information System and CANTAB Cambridge Cognitive assessment, respectively. Buccal swab samples were collected to evaluate the single nucleotide polymorphisms. Multivariable generalized linear regression models were used to analyze data.

RESULTS

APOE rs7412 and BDNF rs6265 were significantly associated with lower self-reported cognitive abilities in a total of 353 BCS. Age was positively associated with self-reported cognitive scores, indicating that younger BCS perceived lower cognitive abilities. Individuals carrying genotype of C/T for APOE with the C/C or C/T for BDNF showed positive associations with cognitive abilities.

CONCLUSIONS

Younger BCS with the C/C genotype for APOE rs7412 and the T/T genotype for BDNF rs6265 may be at risk for CRCI. Knowledge regarding predictive markers for CRCI symptoms is essential for precision symptom management. Further investigation with a longitudinal and translational design is necessary to explore the etiologies for CRCI.

IMPLICATIONS FOR NURSING PRACTICE

Integrating genetic phenotyping into routine clinical practice will provide nurses with unique opportunities to understand individual susceptibilities, and how symptoms may trigger other symptoms. Further, findings from these innovative investigations will provide symptom interventionists and implementation scientists with critical data to optimize individualized strategies for symptom prevention, detection, and management.

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.

Stimulating myelin restoration with BDNF: a promising therapeutic approach for Alzheimer's disease

Alzheimer's Disease (AD) is a chronic neurodegenerative disorder constituting the most common form of dementia (60%-70% of cases). Although AD presents majorly a neurodegenerative pathology, recent clinical evidence highlights myelin impairment as a key factor in disease pathogenesis. The lack of preventive or restorative treatment is emphasizing the need to develop novel therapeutic approaches targeting to the causes of the disease. Recent studies in animals and patients have highlighted the loss of myelination of the neuronal axons as an extremely aggravating factor in AD, in addition to the formation of amyloid plaques and neurofibrillary tangles that are to date the main pathological hallmarks of the disease. Myelin breakdown represents an early stage event in AD. However, it is still unclear whether myelin loss is attributed only to exogenous factors like inflammatory processes of the tissue or to impaired oligodendrogenesis as well. Neurotrophic factors are well established protective molecules under many pathological conditions of the neural tissue, contributing also to proper myelination. Due to their inability to be used as drugs, many research efforts are focused on substituting neurotrophic activity with small molecules. Our research team has recently developed novel micromolecular synthetic neurotrophin mimetics (MNTs), selectively acting on neurotrophin receptors, and thus offering a unique opportunity for innovative therapies against neurodegenerative diseases. These small sized, lipophilic molecules address the underlying biological effect of these diseases (neuroprotective action), but also they exert significant neurogenic actions inducing neuronal replacement of the disease areas. One of the significant neurotrophin molecules in the Central Nervous System is Brain-Derived-Neurotrophin-Factor (BDNF). BDNF is a neurotrophin that not only supports neuroprotection and adult neurogenesis, but also mediates pro-myelinating effects in the CNS. BDNF binds with high-affinity on the TrkB neurotrophin receptor and enhances myelination by increasing the density of oligodendrocyte progenitor cells (OPCs) and playing an important role in CNS myelination. Conclusively, in the present review, we discuss the myelin pathophysiology in Alzheimer's Diseases, as well as the role of neurotrophins, and specifically BDNF, in myelin maintenance and restoration, revealing its valuable therapeutic potential against AD.

Alzheimer's disease genetic risk and changes in brain atrophy and white matter hyperintensities in cognitively unimpaired adults

Reduced brain volumes and more prominent white matter hyperintensities on MRI scans are commonly observed among older adults without cognitive impairment. However, it remains unclear whether rates of change in these measures among cognitively normal adults differ as a function of genetic risk for late-onset Alzheimer's disease, including APOE-ɛ4, APOE-ɛ2 and Alzheimer's disease polygenic risk scores (AD-PRS), and whether these relationships are influenced by other variables. This longitudinal study examined the trajectories of regional brain volumes and white matter hyperintensities in relationship to APOE genotypes (N = 1541) and AD-PRS (N = 1093) in a harmonized dataset of middle-aged and older individuals with normal cognition at baseline (mean baseline age = 66 years, SD = 9.6) and an average of 5.3 years of MRI follow-up (max = 24 years). Atrophy on volumetric MRI scans was quantified in three ways: (i) a composite score of regions vulnerable to Alzheimer's disease (SPARE-AD); (ii) hippocampal volume; and (iii) a composite score of regions indexing advanced non-Alzheimer's disease-related brain aging (SPARE-BA). Global white matter hyperintensity volumes were derived from fluid attenuated inversion recovery (FLAIR) MRI. Using linear mixed effects models, there was an APOE-ɛ4 gene-dose effect on atrophy in the SPARE-AD composite and hippocampus, with greatest atrophy among ɛ4/ɛ4 carriers, followed by ɛ4 heterozygouts, and lowest among ɛ3 homozygouts and ɛ2/ɛ2 and ɛ2/ɛ3 carriers, who did not differ from one another. The negative associations of APOE-ɛ4 with atrophy were reduced among those with higher education (P < 0.04) and younger baseline ages (P < 0.03). Higher AD-PRS were also associated with greater atrophy in SPARE-AD (P = 0.035) and the hippocampus (P = 0.014), independent of APOE-ɛ4 status. APOE-ɛ2 status (ɛ2/ɛ2 and ɛ2/ɛ3 combined) was not related to baseline levels or atrophy in SPARE-AD, SPARE-BA or the hippocampus, but was related to greater increases in white matter hyperintensities (P = 0.014). Additionally, there was an APOE-ɛ4 × AD-PRS interaction in relation to white matter hyperintensities (P = 0.038), with greater increases in white matter hyperintensities among APOE-ɛ4 carriers with higher AD-PRS. APOE and AD-PRS associations with MRI measures did not differ by sex. These results suggest that APOE-ɛ4 and AD-PRS independently and additively influence longitudinal declines in brain volumes sensitive to Alzheimer's disease and synergistically increase white matter hyperintensity accumulation among cognitively normal individuals. Conversely, APOE-ɛ2 primarily influences white matter hyperintensity accumulation, not brain atrophy. Results are consistent with the view that genetic factors for Alzheimer's disease influence atrophy in a regionally specific manner, likely reflecting preclinical neurodegeneration, and that Alzheimer's disease risk genes contribute to white matter hyperintensity formation.

Humanin variant P3S is associated with longevity in APOE4 carriers and resists APOE4-induced brain pathology

The APOE4 allele is recognized as a significant genetic risk factor to Alzheimer's disease (AD) and influences longevity. Nonetheless, some APOE4 carriers exhibit resistance to AD even in advanced age. Humanin, a mitochondrial-derived peptide comprising 24 amino acids, has variants linked to cognitive resilience and longevity. Our research uncovered a unique humanin variant, P3S, specifically enriched in centenarians with the APOE4 allele. Through in silico analyses and subsequent experimental validation, we demonstrated a strong affinity between humanin P3S and APOE4. Utilizing an APOE4-centric mouse model of amyloidosis (APP/PS1/APOE4), we observed that humanin P3S significantly attenuated brain amyloid-beta accumulation compared to the wild-type humanin. Transcriptomic assessments of mice treated with humanin P3S highlighted its potential mechanism involving the enhancement of amyloid beta phagocytosis. Additionally, in vitro studies corroborated humanin P3S's efficacy in promoting amyloid-beta clearance. Notably, in the temporal cortex of APOE4 carriers, humanin expression is correlated with genes associated with phagocytosis. Our findings suggest a role of the rare humanin variant P3S, especially prevalent among individuals of Ashkenazi descent, in mitigating amyloid beta pathology and facilitating phagocytosis in APOE4-linked amyloidosis, underscoring its significance in longevity and cognitive health among APOE4 carriers.

Alzheimer's diseases in America, Europe, and Asian regions: a global genetic variation

Background

Alzheimer's disease (AD) is one of the multifaceted neurodegenerative diseases influenced by many genetic and epigenetic factors. Genetic factors are merely not responsible for developing AD in the whole population. The studies of genetic variants can provide significant insights into the molecular basis of Alzheimer's disease. Our research aimed to show how genetic variants interact with environmental influences in different parts of the world.

Methodology

We searched PubMed and Google Scholar for articles exploring the relationship between genetic variations and global regions such as America, Europe, and Asia. We aimed to identify common genetic variations susceptible to AD and have no significant heterogeneity. To achieve this, we analyzed 35 single-nucleotide polymorphisms (SNPs) from 17 genes (ABCA7, APOE, BIN1, CD2AP, CD33, CLU, CR1, EPHA1, TOMM40, MS4A6A, ARID5B, SORL1, APOC1, MTHFD1L, BDNF, TFAM, and PICALM) from different regions based on previous genomic studies of AD. It has been reported that rs3865444, CD33, is the most common polymorphism in the American and European populations. From TOMM40 and APOE rs2075650, rs429358, and rs6656401, CR1 is the common investigational polymorphism in the Asian population.

Conclusion

The results of all the research conducted on AD have consistently shown a correlation between genetic variations and the incidence of AD in the populations of each region. This review is expected to be of immense value in future genetic research and precision medicine on AD, as it provides a comprehensive understanding of the genetic factors contributing to the development of this debilitating disease.

Apolipoprotein E2 Expression Alters Endosomal Pathways in a Mouse Model With Increased Brain Exosome Levels During Aging

The polymorphic APOE gene is the greatest genetic determinant of sporadic Alzheimer's disease risk: the APOE4 allele increases risk, while the APOE2 allele is neuroprotective compared with the risk-neutral APOE3 allele. The neuronal endosomal system is inherently vulnerable during aging, and APOE4 exacerbates this vulnerability by driving an enlargement of early endosomes and reducing exosome release in the brain of humans and mice. We hypothesized that the protective effects of APOE2 are, in part, mediated through the endosomal pathway. Messenger RNA analyses showed that APOE2 leads to an enrichment of endosomal pathways in the brain when compared with both APOE3 and APOE4. Moreover, we show age-dependent alterations in the recruitment of key endosomal regulatory proteins to vesicle compartments when comparing APOE2 to APOE3. In contrast to the early endosome enlargement previously shown in Alzheimer's disease and APOE4 models, we detected similar morphology and abundance of early endosomes and retromer-associated vesicles within cortical neurons of aged APOE2 targeted-replacement mice compared with APOE3. Additionally, we observed increased brain extracellular levels of endosome-derived exosomes in APOE2 compared with APOE3 mice during aging, consistent with enhanced endosomal cargo clearance by exosomes to the extracellular space. Our findings thus demonstrate that APOE2 enhances an endosomal clearance pathway, which has been shown to be impaired by APOE4 and which may be protective due to APOE2 expression during brain aging.

Impact of APOE-ε alleles on brain structure and cognitive function in healthy older adults: A VBM and DTI replication study

BACKGROUND

The Apolipoprotein E (APOE) gene has been established in the Alzheimer's disease (AD) literature to impact brain structure and function and may also show congruent effects in healthy older adults, although findings in this population are much less consistent. The current study aimed to replicate and expand the multimodal approach employed by Honea et al. Structural magnetic resonance imaging (MRI), diffusion tensor imaging (DTI), and neuropsychological measures were used to investigate the impact of APOE-ε status on grey matter structure, white matter integrity, and cognitive functioning.

METHODS

Data were obtained from the Alzheimer's Disease Initiative Phase 3 (ADNI3) database. Baseline MRI, DTI and cognitive composite scores for memory (ADNI-Mem) and executive function (ADNI-EF) were acquired from 116 healthy controls. Participants were grouped according to APOE allele presence (APOE-ε2+ N = 17, APOE-ε3ε3 N = 64, APOE-ε4+ N = 35). Voxel-based morphometry (VBM) and tract-based spatial statistics (TBSS) were used to compare grey matter volume (GMV) and white matter integrity, respectively, between APOE-ε2+ and APOE-ε3ε3 controls, and again between APOE-ε4+ and APOE-ε3ε3 controls. Multivariate analysis of covariance (MANCOVA) was used to examine the effects of APOE polymorphism on memory and EF across all APOE groups with age, sex and education as regressors of no interest. Cognitive scores were correlated (Pearson r) with imaging metrics within groups.

RESULTS

No significant differences were seen across groups, within groups in MRI metrics, or cognitive performance (p>0.05, corrected for multiple comparisons).

CONCLUSIONS

The current study partially replicated and extended previous findings from an earlier multimodal study (Honea 2009). Future studies should clarify APOE mechanisms in healthy ageing by adding other imaging, cognitive, and lifestyle metrics and longitudinal design in larger sample sizes.

Association of APOE gene with longitudinal changes of CSF amyloid beta and tau levels in Alzheimer's disease: racial differences

BACKGROUND

The Apolipoprotein E (APOE) ε4 allele is a risk factor for late-onset Alzheimer's disease (AD). However, no investigation has focused on racial differences in the longitudinal effect of APOE genotypes on CSF amyloid beta (Aβ42) and tau levels in AD.

METHODS

This study used data from the Alzheimer's Disease Neuroimaging Initiative (ADNI): 222 participants with AD, 264 with cognitive normal (CN), and 692 with mild cognitive impairment (MCI) at baseline and two years follow-up. We used a linear mixed model to investigate the effect of APOE-ε4-genotypes on longitudinal changes in the amyloid beta and tau levels.

RESULTS

Individuals with 1 or 2 APOE ε4 alleles revealed significantly higher t-Tau and p-Tau, but lower amyloid beta Aβ42 compared with individuals without APOE ε4 alleles. Significantly higher levels of log-t-Tau, log-p-Tau, and low levels of log-Aβ42 were observed in the subjects with older age, being female, and the two diagnostic groups (AD and MCI). The higher p-Tau and Aβ42 values are associated with poor Mini-Mental State Examination (MMSE) performance. Non-Hispanic Africa American (AA) and Hispanic participants were associated with decreased log-t-Tau levels (β =  - 0.154, p = 0.0112; β =  - 0.207, and p = 0.0016, respectively) as compared to those observed in Whites. Furthermore, Hispanic participants were associated with a decreased log-p-Tau level (β =  - 0.224, p = 0.0023) compared to those observed in Whites. There were no differences in Aβ42 level for non-Hispanic AA and Hispanic participants compared with White participants.

CONCLUSION

Our study, for the first time, showed that the APOE ε4 allele was associated with these biomarkers, however with differing degrees among racial groups.

Prevalence and associated factors of chemotherapy-related cognitive impairment in older breast cancer survivors

AIMS

To examine the prevalence and associated factors of chemotherapy-related cognitive impairment (CRCI) in older breast cancer survivors (BCS).

DESIGN

Systematic review.

DATA SOURCES

We searched EMBASE, PubMed, PsychInfo, CINAHL, Cochrance Library, Web of Science, CNKI and SinoMed, without language restrictions, for studies published from the establishment of the database to September 2022.

REVIEW METHODS

Two researchers independently examined the full texts, data extraction and quality assessment, and any discrepancies were resolved through discussion with a third reviewer. Quality of evidence was assessed using the Newcastle-Ottawa Scale and the Agency for Healthcare Research and Quality Scale.

RESULTS

The seven included studies showed that the estimated prevalence of CRCI in older BCS ranged from 18.6% to 27% on objective neuropsychological tests and from 7.6% to 49% on subjective cognitive assessments. The areas most affected were attention, memory, executive functioning and processing speed. CRCI was associated with 10 factors in six categories, including sociodemographic (e.g. age, education level), physiological (e.g. sleep disorders, fatigue and comorbidities), psychological (e.g. anxiety, depression), treatment modalities (e.g. chemotherapy cycles, chemotherapy regimens), genetic (e.g. APOE2, APOE4) and lifestyle factor (e.g. physical inactivity).

CONCLUSION

CRCI is multifactorial and has a relatively high prevalence. However, the results of subjective and objective cognitive examinations were inconsistent, possibly due to variations in tools used to evaluate different definitions of CRCI. Nevertheless, as there are few published studies of older BCS, this conclusion still require verification by well-designed studies in the future.

IMPACT

We found that the prevalence of CRCI in older adults is relatively high and multifactorial, providing evidence for further health care for this population.

NO PATIENT OR PUBLIC CONTRIBUTION

There was no patient or public involvement.

Investigating the synergistic effects of hormone replacement therapy, apolipoprotein E and age on brain health in the UK Biobank

Global prevalence of Alzheimer's Disease has a strong sex bias, with women representing approximately two-thirds of the patients. Yet, the role of sex-specific risk factors during midlife, including hormone replacement therapy (HRT) and their interaction with other major risk factors for Alzheimer's Disease, such as apolipoprotein E (APOE)-e4 genotype and age, on brain health remains unclear. We investigated the relationship between HRT (i.e., use, age of initiation and duration of use) and brain health (i.e., cognition and regional brain volumes). We then consider the multiplicative effects of HRT and APOE status (i.e., e2/e2, e2/e3, e3/e3, e3/e4 and e4/e4) via a two-way interaction and subsequently age of participants via a three-way interaction. Women from the UK Biobank with no self-reported neurological conditions were included (N = 207,595 women, mean age = 56.25 years, standard deviation = 8.01 years). Generalised linear regression models were computed to quantify the cross-sectional association between HRT and brain health, while controlling for APOE status, age, time since attending centre for completing brain health measure, surgical menopause status, smoking history, body mass index, education, physical activity, alcohol use, ethnicity, socioeconomic status, vascular/heart problems and diabetes diagnosed by doctor. Analyses of structural brain regions further controlled for scanner site. All brain volumes were normalised for head size. Two-way interactions between HRT and APOE status were modelled, in addition to three-way interactions including age. Results showed that women with the e4/e4 genotype who have used HRT had 1.82% lower hippocampal, 2.4% lower parahippocampal and 1.24% lower thalamus volumes than those with the e3/e3 genotype who had never used HRT. However, this interaction was not detected for measures of cognition. No clinically meaningful three-way interaction between APOE, HRT and age was detected when interpreted relative to the scales of the cognitive measures used and normative models of ageing for brain volumes in this sample. Differences in hippocampal volume between women with the e4/e4 genotype who have used HRT and those with the e3/e3 genotype who had never used HRT are equivalent to approximately 1-2 years of hippocampal atrophy observed in typical health ageing trajectories in midlife (i.e., 0.98%-1.41% per year). Effect sizes were consistent within APOE e4/e4 group post hoc sensitivity analyses, suggesting observed effects were not solely driven by APOE status and may, in part, be attributed to HRT use. Although, the design of this study means we cannot exclude the possibility that women who have used HRT may have a predisposition for poorer brain health.

Successful cognitive aging is associated with thicker anterior cingulate cortex and lower tau deposition compared to typical aging

INTRODUCTION

There is no consensus on either the definition of successful cognitive aging (SA) or the underlying neural mechanisms.

METHODS

We examined the agreement between new and existing definitions using: (1) a novel measure, the cognitive age gap (SA-CAG, cognitive-predicted age minus chronological age), (2) composite scores for episodic memory (SA-EM), (3) non-memory cognition (SA-NM), and (4) the California Verbal Learning Test (SA-CVLT).

RESULTS

Fair to moderate strength of agreement was found between the four definitions. Most SA groups showed greater cortical thickness compared to typical aging (TA), especially in the anterior cingulate and midcingulate cortices and medial temporal lobes. Greater hippocampal volume was found in all SA groups except SA-NM. Lower entorhinal 18 F-Flortaucipir (FTP) uptake was found in all SA groups.

DISCUSSION

These findings suggest that a feature of SA, regardless of its exact definition, is resistance to tau pathology and preserved cortical integrity, especially in the anterior cingulate and midcingulate cortices.

HIGHLIGHTS

Different approaches have been used to define successful cognitive aging (SA). Regardless of definition, different SA groups have similar brain features. SA individuals have greater anterior cingulate thickness and hippocampal volume. Lower entorhinal tau deposition, but not amyloid beta is related to SA. A combination of cortical integrity and resistance to tau may be features of SA.

APOE4 is a Risk Factor and Potential Therapeutic Target for Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease, the main pathological hallmark of which is the loss of neurons, resulting in cognitive and memory impairments. Sporadic late-onset AD is a prevalent form of the disease and the apolipoprotein E4 (APOE4) genotype is the strongest predictor of the disease development. The structural variations of APOE isoforms affect their roles in synaptic maintenance, lipid trafficking, energy metabolism, inflammatory response, and BBB integrity. In the context of AD, APOE isoforms variously control the key pathological elements of the disease, including Aβ plaque formation, tau aggregation, and neuroinflammation. Taking into consideration the limited number of therapy choices that can alleviate symptoms and have little impact on the AD etiology and progression to date, the precise research strategies guided by apolipoprotein E (APOE) polymorphisms are required to assess the potential risk of age-related cognitive decline in people carrying APOE4 genotype. In this review, we summarize the evidence implicating the significance of APOE isoforms on brain functions in health and pathology with the aim to identify the possible targets that should be addressed to prevent AD manifestation in individuals with the APOE4 genotype and to explore proper treatment strategies.

Feature attention graph neural network for estimating brain age and identifying important neural connections in mouse models of genetic risk for Alzheimer's disease

Alzheimer's disease (AD) remains one of the most extensively researched neurodegenerative disorders due to its widespread prevalence and complex risk factors. Age is a crucial risk factor for AD, which can be estimated by the disparity between physiological age and estimated brain age. To model AD risk more effectively, integrating biological, genetic, and cognitive markers is essential. Here, we utilized mouse models expressing the major APOE human alleles and human nitric oxide synthase 2 to replicate genetic risk for AD and a humanized innate immune response. We estimated brain age employing a multivariate dataset that includes brain connectomes, APOE genotype, subject traits such as age and sex, and behavioral data. Our methodology used Feature Attention Graph Neural Networks (FAGNN) for integrating different data types. Behavioral data were processed with a 2D Convolutional Neural Network (CNN), subject traits with a 1D CNN, brain connectomes through a Graph Neural Network using quadrant attention module. The model yielded a mean absolute error for age prediction of 31.85 days, with a root mean squared error of 41.84 days, outperforming other, reduced models. In addition, FAGNN identified key brain connections involved in the aging process. The highest weights were assigned to the connections between cingulum and corpus callosum, striatum, hippocampus, thalamus, hypothalamus, cerebellum, and piriform cortex. Our study demonstrates the feasibility of predicting brain age in models of aging and genetic risk for AD. To verify the validity of our findings, we compared Fractional Anisotropy (FA) along the tracts of regions with the highest connectivity, the Return-to-Origin Probability (RTOP), Return-to-Plane Probability (RTPP), and Return-to-Axis Probability (RTAP), which showed significant differences between young, middle-aged, and old age groups. Younger mice exhibited higher FA, RTOP, RTAP, and RTPP compared to older groups in the selected connections, suggesting that degradation of white matter tracts plays a critical role in aging and for FAGNN's selections. Our analysis suggests a potential neuroprotective role of APOE2, relative to APOE3 and APOE4, where APOE2 appears to mitigate age-related changes. Our findings highlighted a complex interplay of genetics and brain aging in the context of AD risk modeling.

Sex differences in associations between APOE ε2 and longitudinal cognitive decline

INTRODUCTION

We examined whether sex modifies the association between APOE ε2 and cognitive decline in two independent samples.

METHODS

We used observational data from cognitively unimpaired non-Hispanic White (NHW) and non-Hispanic Black (NHB) adults. Linear mixed models examined interactive associations of APOE genotype (ε2 or ε4 carrier vs. ε3/ε3) and sex on cognitive decline in NHW and NHB participants separately.

RESULTS

In both Sample 1 (N = 9766) and Sample 2 (N = 915), sex modified the association between APOE ε2 and cognitive decline in NHW participants. Specifically, relative to APOE ε3/ε3, APOE ε2 protected against cognitive decline in men but not women. Among APOE ε2 carriers, men had slower decline than women. Among APOE ε3/ε3 carriers, cognitive trajectories did not differ between sexes. There were no sex-specific associations of APOE ε2 with cognition in NHB participants (N = 2010).

DISCUSSION

In NHW adults, APOE ε2 may protect men but not women against cognitive decline.

HIGHLIGHTS

We studied sex-specific apolipoprotein E (APOE) ε2 effects on cognitive decline. In non-Hispanic White (NHW) adults, APOE ε2 selectively protects men against decline. Among men, APOE ε2 was more protective than APOE ε3/ε3. In women, APOE ε2 was no more protective than APOE ε3/ε3. Among APOE ε2 carriers, men had slower decline than women. There were no sex-specific APOE ε2 effects in non-Hispanic Black (NHB) adults.

Associations of Sex, Race, and Apolipoprotein E Alleles With Multiple Domains of Cognition Among Older Adults

Importance

Sex differences are established in associations between apolipoprotein E (APOE) ε4 and cognitive impairment in Alzheimer disease (AD). However, it is unclear whether sex-specific cognitive consequences of APOE are consistent across races and extend to the APOE ε2 allele.

Objective

To investigate whether sex and race modify APOE ε4 and ε2 associations with cognition.

Design, Setting, and Participants

This genetic association study included longitudinal cognitive data from 4 AD and cognitive aging cohorts. Participants were older than 60 years and self-identified as non-Hispanic White or non-Hispanic Black (hereafter, White and Black). Data were previously collected across multiple US locations from 1994 to 2018. Secondary analyses began December 2021 and ended September 2022.

Main Outcomes and Measures

Harmonized composite scores for memory, executive function, and language were generated using psychometric approaches. Linear regression assessed interactions between APOE ε4 or APOE ε2 and sex on baseline cognitive scores, while linear mixed-effect models assessed interactions on cognitive trajectories. The intersectional effect of race was modeled using an APOE × sex × race interaction term, assessing whether APOE × sex interactions differed by race. Models were adjusted for age at baseline and corrected for multiple comparisons.

Results

Of 32 427 participants who met inclusion criteria, there were 19 007 females (59%), 4453 Black individuals (14%), and 27 974 White individuals (86%); the mean (SD) age at baseline was 74 years (7.9). At baseline, 6048 individuals (19%) had AD, 4398 (14%) were APOE ε2 carriers, and 12 538 (38%) were APOE ε4 carriers. Participants missing APOE status were excluded (n = 9266). For APOE ε4, a robust sex interaction was observed on baseline memory (β = -0.071, SE = 0.014; P = 9.6 × 10-7), whereby the APOE ε4 negative effect was stronger in females compared with males and did not significantly differ among races. Contrastingly, despite the large sample size, no APOE ε2 × sex interactions on cognition were observed among all participants. When testing for intersectional effects of sex, APOE ε2, and race, an interaction was revealed on baseline executive function among individuals who were cognitively unimpaired (β = -0.165, SE = 0.066; P = .01), whereby the APOE ε2 protective effect was female-specific among White individuals but male-specific among Black individuals.

Conclusions and Relevance

In this study, while race did not modify sex differences in APOE ε4, the APOE ε2 protective effect could vary by race and sex. Although female sex enhanced ε4-associated risk, there was no comparable sex difference in ε2, suggesting biological pathways underlying ε4-associated risk are distinct from ε2 and likely intersect with age-related changes in sex biology.

Effect of apolipoprotein genotype and educational attainment on cognitive function in autosomal dominant Alzheimer's disease

Autosomal dominant Alzheimer's disease (ADAD) is genetically determined, but variability in age of symptom onset suggests additional factors may influence cognitive trajectories. Although apolipoprotein E (APOE) genotype and educational attainment both influence dementia onset in sporadic AD, evidence for these effects in ADAD is limited. To investigate the effects of APOE and educational attainment on age-related cognitive trajectories in ADAD, we analyzed data from 675 Presenilin-1 E280A mutation carriers and 594 non-carriers. Here we show that age-related cognitive decline is accelerated in ADAD mutation carriers who also have an APOE e4 allele compared to those who do not and delayed in mutation carriers who also have an APOE e2 allele compared to those who do not. Educational attainment is protective and moderates the effect of APOE on cognition. Despite ADAD mutation carriers being genetically determined to develop dementia, age-related cognitive decline may be influenced by other genetic and environmental factors.

Differences in resting-state brain networks and gray matter between APOE ε2 and APOE ε4 carriers in non-dementia elderly

Background

Apolipoprotein E (APOE) ε2 and APOE ε4 are the most distinct alleles among the three APOE alleles, both structurally and functionally. However, differences in cognition, brain function, and brain structure between the two alleles have not been comprehensively reported in the literature, especially in non-demented elderly individuals.

Methods

A neuropsychological test battery was used to evaluate the differences in cognitive performance in five cognitive domains. Independent component analysis (ICA) and voxel-based morphometry (VBM) were used separately to analyze resting-state functional magnetic resonance imaging (rs-fMRI) data and the structure MRI data between the two groups. Finally, correlations between differential brain regions and neuropsychological tests were calculated.

Results

APOE ε2 carriers had better cognitive performance in general cognitive, memory, attention, and executive function than APOE ε4 carriers (all p < 0.05). In ICA analyses of rs-fMRI data, the difference in the resting-state functional connectivity (rsFC) between two groups is shown in 7 brain networks. In addition, VBM analyses of the T1-weighted image revealed that APOE ε2 carriers had a larger thalamus and right postcentral gyrus volume and a smaller bilateral putamen volume than APOE ε4 carriers. Finally, differences in brain function and structure may be might be the reason that APOE ε2 carriers are better than APOE ε4 carriers in cognitive performance.

Conclusion

These findings suggest that there are significant differences in brain function and structure between APOE ε2 carriers and APOE ε4 carriers, and these significant differences are closely related to their cognitive performance.

Targeting apolipoprotein E and N-terminal amyloid β-protein precursor interaction improves cognition and reduces amyloid pathology in Alzheimer's mice

Apolipoprotein E (apoE) interaction with amyloid β-protein precursor (APP) has garnered attention as the therapeutic target for Alzheimer's disease (AD). Having discovered the apoE antagonist (6KApoEp) that blocks apoE binding to N-terminal APP, we tested the therapeutic potential of 6KApoEp on AD-relevant phenotypes in amyloid β-protein precursor/presenilin 1 (APP/PS1) mice that express each human apoE isoform of apoE2, apoE3, or apoE4 (designated APP/PS1/E2, APP/PS1/E3, or APP/PS1/E4 mice). At 12 months of age, we intraperitoneally administered 6KApoEp (250 μg/kg) or vehicle once daily for 3 months. At 15 months of age, blockage of apoE and N-terminal APP interaction by 6KApoEp treatment improved cognitive impairment in most tests of learning and memory, including novel object recognition and maze tasks in APP/PS1/E2, APP/PS1/E3, and APP/PS1/E4 mice versus each vehicle-treated mouse line and did not alter behavior in nontransgenic littermates. Moreover, 6KApoEp therapy ameliorated brain parenchymal and cerebral vascular β-amyloid deposits and decreased abundance of amyloid β-protein (Aβ) in APP/PS1/E2, APP/PS1/E3, and APP/PS1/E4 mice versus each vehicle-treated mouse group. Notably, the highest effect in Aβ-lowering by 6KApoEp treatment was observed in APP/PS1/E4 mice versus APP/PS1/E2 or APP/PS1/E3 mice. These effects occured through shifting toward lessened amyloidogenic APP processing due to decreasing APP abundance at the plasma membrane, reducing APP transcription, and inhibiting p44/42 mitogen-activated protein kinase phosphorylation. Our findings provide the preclinical evidence that 6KApoEp therapy aimed at targeting apoE and N-terminal APP interaction is a promising strategy and may be suitable for patients with AD carrying the apoE4 isoform.

Confirmed Synergy Between the ɛ4 Allele of Apolipoprotein E and the Variant K of Butyrylcholinesterase as a Risk Factor for Alzheimer's Disease: A Systematic Review and Meta-Analysis

Background

Alzheimer's disease (AD) has several risk factors. APOE4 is the main one, and it has been suggested that there may be a synergy between it and BCHE-K as a risk factor.

Objective

To investigate the association between APOE4 and BCHE-K as a risk factor for AD.

Methods

We searched PubMed, Web of Science, Embase, and Scopus on August 8, 2021 for studies that analyzed the association of APOE4 and BCHE-K with AD. The random effect model was performed in meta-analysis according to age group. A chi-square was performed with the meta-analysis data to verify if the effect found is not associated only with the E4 allele.

Results

Twenty-one studies with 6,853 subjects (3,528 AD and 3,325 Controls) were included in the meta-analysis. The quality of the evidence is moderate. There is a positive E4-K association for subjects with AD as shown by the odds ratio of 3.43. The chi-square meta test, which measures the probability that the E4-K association is due to chance, has an odds ratio of 6.155, indicating that the E4-K association is not a random event. The odds ratio of an E4-K association in subjects with AD increases to OR 4.46 for the 65- to 75-year-old group and OR 4.15 for subjects older than 75 years. The probability that the E4-K association is due to chance is ruled out by chi-square meta test values of OR 8.638 and OR 9.558.

Conclusion

The synergy between APOE4 and BCHE-K is a risk factor for late-onset AD.

The Effect of Gender and APOE ɛ4 Status on Brain Amyloid-β Deposition in Different Age Groups of Mild Cognitively Impaired Individuals: A PET-CT Study

BACKGROUND

Gender, APOE ɛ4 status and age have different effects on brain amyloid deposition in patients with mild cognitively impaired (MCI).

OBJECTIVE

To investigate the effect of gender×APOE ɛ4 status interaction on Aβ deposition in the brains of individuals with MCI in different age groups by PET scanning.

METHODS

204 individuals with MCI were classified into younger or older groups based on whether they were under or over 65 years of age. APOE genotyping, structural MRI, amyloid PET scans, and neuropsychological tests were performed. The effect of gender×APOE ɛ4 status interaction on Aβ deposition was assessed in different age groups.

RESULTS

APOE ɛ4 carriers had higher amyloid deposition than noncarriers in the whole group. Females with MCI had more amyloid deposition in the medial temporal lobe than males in the whole cohort and younger group. Older individuals with MCI had higher amyloid deposition than younger individuals. In stratified analysis by age, female APOE ɛ4 carriers had significantly increased amyloid deposition compared to their male counterparts only in the medial temporal lobe in the younger group. Amyloid deposition was increased in female APOE ɛ4 carriers compared to noncarriers in the younger group, whereas higher amyloid deposition was observed in male APOE ɛ4 carriers in the older group.

CONCLUSION

Women in the younger group with MCI who were APOE ɛ4 carriers had more amyloid deposition in the brain, while men in the older group with MCI who were APOE ɛ4 carriers had higher amyloid deposition.

Alzheimer's disease genetic risk and cognitive reserve in relationship to long-term cognitive trajectories among cognitively normal individuals

BACKGROUND

Both Alzheimer's disease (AD) genetic risk factors and indices of cognitive reserve (CR) influence risk of cognitive decline, but it remains unclear whether they interact. This study examined whether a CR index score modifies the relationship between AD genetic risk factors and long-term cognitive trajectories in a large sample of individuals with normal cognition.

METHODS

Analyses used data from the Preclinical AD Consortium, including harmonized data from 5 longitudinal cohort studies. Participants were cognitively normal at baseline (M baseline age = 64 years, 59% female) and underwent 10 years of follow-up, on average. AD genetic risk was measured by (i) apolipoprotein-E (APOE) genetic status (APOE-ε2 and APOE-ε4 vs. APOE-ε3; N = 1819) and (ii) AD polygenic risk scores (AD-PRS; N = 1175). A CR index was calculated by combining years of education and literacy scores. Longitudinal cognitive performance was measured by harmonized factor scores for global cognition, episodic memory, and executive function.

RESULTS

In mixed-effects models, higher CR index scores were associated with better baseline cognitive performance for all cognitive outcomes. APOE-ε4 genotype and AD-PRS that included the APOE region (AD-PRSAPOE) were associated with declines in all cognitive domains, whereas AD-PRS that excluded the APOE region (AD-PRSw/oAPOE) was associated with declines in executive function and global cognition, but not memory. There were significant 3-way CR index score × APOE-ε4 × time interactions for the global (p = 0.04, effect size = 0.16) and memory scores (p = 0.01, effect size = 0.22), indicating the negative effect of APOE-ε4 genotype on global and episodic memory score change was attenuated among individuals with higher CR index scores. In contrast, levels of CR did not attenuate APOE-ε4-related declines in executive function or declines associated with higher AD-PRS. APOE-ε2 genotype was unrelated to cognition.

CONCLUSIONS

These results suggest that APOE-ε4 and non-APOE-ε4 AD polygenic risk are independently associated with global cognitive and executive function declines among individuals with normal cognition at baseline, but only APOE-ε4 is associated with declines in episodic memory. Importantly, higher levels of CR may mitigate APOE-ε4-related declines in some cognitive domains. Future research is needed to address study limitations, including generalizability due to cohort demographic characteristics.

Differential Associations of APOEɛ2 and APOEɛ4 Genotypes with Cerebrospinal Fluid Biomarkers of Alzheimer's Disease in Individuals Without Dementia

BACKGROUND

The APOE genotype has emerged as the major genetic factor for AD but differs among different alleles.

OBJECTIVE

To investigate the discrepant effects of APOE genotype on AD cerebrospinal fluid (CSF) biomarkers.

METHODS

A total of 989 non-demented ADNI participants were included. The associations of APOEɛ2 and APOEɛ4 with CSF biomarkers were investigated using linear regression models. Interaction and subgroup analyses were used to investigate the effects of sex and age on these associations. Furthermore, we used mediation analyses to assess whether Aβ mediated the associations between APOE genotypes and tau.

RESULTS

APOEɛ2 carriers only showed higher Aβ levels (β [95% CI] = 0.07 [0.01, 0.13], p = 0.026). Conversely, APOEɛ4 carriers exhibited lower Aβ concentration (β [95% CI] = -0.27 [-0.31, -0.24], p < 0.001), higher t-Tau (β [95% CI] = 0.25 [0.08, 0.18], p < 0.001) and higher p-Tau (β [95% CI] = 0.31 [0.25, 0.37], p < 0.001). Subgroup analysis showed that APOE ɛ2 was significantly positively associated with Aβ only in females (β [95% CI] = 0.12 [0.04, 0.21], p = 0.005) and older people (β [95% CI] = 0.06 [0.001, 0.12], p = 0.048). But the effects of APOE ɛ4 were independent of gender and age. Besides, the associations of APOE ɛ4 with t-Tau and p-Tau were both mediated by baseline Aβ.

CONCLUSIONS

Our data suggested that APOEɛ2 could promote Aβ clearance, while the process could be modified by sex and age. However, APOEɛ4 might cause the accumulation of Aβ and tau pathology independent of sex and age.

Does the imbalance in the apolipoprotein E isoforms underlie the pathophysiological process of sporadic Alzheimer's disease?

Human apolipoprotein E (apoE) is a 299-amino acid secreted glycoprotein binding cholesterol and phospholipids, and with three common isoforms (APOE ε2, APOE ε3, and APOE ε4). The exact mechanism by which APOE gene variants increase/decrease Alzheimer's disease (AD) risk is not fully understood, but APOE isoforms differently affect brain homeostasis and neuroinflammation, blood-brain barrier (BBB) permeability, glial function, synaptogenesis, oral/gut microbiota, neural networks, amyloid beta (Aβ) deposition, and tau-mediated neurodegeneration. In this perspective, we propose a comprehensive interpretation of APOE-mediated effects within AD pathophysiology, describing some specific cellular, biochemical, and epigenetic mechanisms and updating the different APOE-targeting approaches being developed as potential AD therapies. Intracisternal adeno-associated viral-mediated delivery of APOE ε2 is being tested in AD APOE ε4/ε4 carriers, while APOE mimetics are being used in subjects with perioperative neurocognitive disorders. Other approaches including APOE ε4 antisense oligonucleotides, anti-APOE ε4 monoclonal antibodies, APOE ε4 structure correctors, and APOE-Aβ interaction inhibitors produced positive results in transgenic AD mouse models.

Effects of APOE ε2 allele on basal forebrain functional connectivity in mild cognitive impairment

BACKGROUND

Basal forebrain cholinergic system (BFCS) dysfunction is associated with cognitive decline in Alzheimer's disease (AD) and mild cognitive impairment (MCI). Apolipoprotein E (APOE) ε2 is a protective genetic factor in AD and MCI, and cholinergic sprouting depends on APOE.

OBJECTIVE

We investigated the effect of the APOE ε2 allele on BFCS functional connectivity (FC) in cognitively normal (CN) subjects and MCI patients.

METHOD

We included 60 MCI patients with APOE ε3/ε3, 18 MCI patients with APOE ε2/ε3, 73 CN subjects with APOE ε3/ε3, and 36 CN subjects with APOE ε2/ε3 genotypes who had resting-state functional magnetic resonance imaging data from the Alzheimer's disease Neuroimaging Initiative. We used BFCS subregions (Ch1-3 and Ch4) as seeds and calculated the FC with other brain areas. Using a mixed-effect analysis, we explored the interaction effects of APOE ε2 allele × cognitive status on BFCS-FC. Furthermore, we examined the relationships between imaging metrics, cognitive abilities, and AD pathology markers, controlling for sex, age, and education as covariates.

RESULTS

An interaction effect on functional connectivity was found between the right Ch4 (RCh4) and left insula (p < 0.05, corrected), and between the RCh4 and left Rolandic operculum (p < 0.05, corrected). Among all subjects and APOE ε2 carriers, RCh4-left Insula FC was associated with early tau deposition. Furthermore, no correlation was found between imaging metrics and amyloid burden. Among all subjects and APOE ε2 carriers, FC metrics were associated with cognitive performance.

CONCLUSION

The APOE ε2 genotype may play a protective role during BFCS degeneration in MCI.

Tract-specific differences in white matter microstructure between young adult APOE ε4 carriers and non-carriers: A replication and extension study

The parahippocampal cingulum bundle (PHCB) interconnects regions known to be vulnerable to early Alzheimer's disease (AD) pathology, including posteromedial cortex and medial temporal lobe. While AD-related pathology has been robustly associated with alterations in PHCB microstructure, specifically lower fractional anisotropy (FA) and higher mean diffusivity (MD), emerging evidence indicates that the reverse pattern is evident in younger adults at increased risk of AD. In one such study, Hodgetts et al. (2019) reported that healthy young adult carriers of the apolipoprotein-E (APOE) ε4 allele - the strongest common genetic risk factor for AD - showed higher FA and lower MD in the PHCB but not the inferior longitudinal fasciculus (ILF). These results are consistent with proposals claiming that heightened neural activity and intrinsic connectivity play a significant role in increasing posteromedial cortex vulnerability to amyloid-β and tau spread beyond the medial temporal lobe. Given the implications for understanding AD risk, here we sought to replicate Hodgetts et al.'s finding in a larger sample (N = 128; 40 APOE ε4 carriers, 88 APOE ε4 non-carriers) of young adults (age range = 19-33). Extending this work, we also conducted an exploratory analysis using a more advanced measure of white matter microstructure: hindrance modulated orientational anisotropy (HMOA). Contrary to the original study, we did not observe higher FA or lower MD in the PHCB of APOE ε4 carriers relative to non-carriers. Bayes factors (BFs) further revealed moderate-to-strong evidence in support of these null findings. In addition, we observed no APOE ε4-related differences in PHCB HMOA. Our findings indicate that young adult APOE ε4 carriers and non-carriers do not differ in PHCB microstructure, casting some doubt on the notion that early-life variation in PHCB tract microstructure might enhance vulnerability to amyloid-β accumulation and/or tau spread.

APOE E4 is associated with impaired self-declared cognition but not disease risk or age of onset in Nigerians with Parkinson's disease

The relationship between APOE polymorphisms and Parkinson's disease (PD) in black Africans has not been previously investigated. We evaluated the association between APOE polymorphic variability and self-declared cognition in 1100 Nigerians with PD and 1097 age-matched healthy controls. Cognition in PD was assessed using the single item cognition question (item 1.1) of the MDS-UPDRS. APOE genotype and allele frequencies did not differ between PD and controls (p > 0.05). No allelic or genotypic association was observed between APOE and age at onset of PD. In PD, APOE ε4/ε4 conferred a two-fold risk of cognitive impairment compared to one or no ε4 (HR: 2.09 (95% CI: 1.13-3.89; p = 0.02)), while APOE ε2 was associated with modest protection against cognitive impairment (HR: 0.41 (95% CI 0.19-0.99, p = 0.02)). Of 773 PD with motor phenotype and APOE characterized, tremor-dominant (TD) phenotype predominated significantly in ε2 carriers (87/135, 64.4%) compared to 22.2% in persons with postural instability/gait difficulty (PIGD) (30/135) and 13.3% in indeterminate (ID) (18/135, 13.3%) (p = 0.037). Although the frequency of the TD phenotype was highest in homozygous ε2 carriers (85.7%), the distribution of motor phenotypes across the six genotypes did not differ significantly (p = 0.18). Altogether, our findings support previous studies in other ethnicities, implying a role for APOE ε4 and ε2 as risk and protective factors, respectively, for cognitive impairment in PD.

Interaction between apolipoprotein E genotypes, excessive daytime sleepiness, and cognitive function in obstructive sleep apnea patients

BACKGROUND

Some studies show an association between the apolipoprotein E ε4 allele (ApoEε4) and obstructive sleep apnea syndrome (OSAS), and other studies, an association between ApoEε4 and excessive daytime sleepiness (EDS), but there are no data in the literature on the interaction between EDS, cognitive function, and ApoEε4 in patients with OSA.

OBJECTIVE

To examine the cognitive function of adults with and without EDS and with and without ApoEε4.

METHODS

A total of 21 male and female patients aged between 33 and 79 years, underwent a clinical interview, ApoE genotyping, neuropsychological evaluation, polysomnography, and the application of the Epworth Sleepiness Scale.

RESULTS

Excessive daytime sleepiness was associated with lower intelligence quotient (IQ; total performance) and worse immediate visual memory, regardless of the ApoE genotype. Patients carrying the ApoEε3/ε4 genotype had a worse performance in divided attention, constructional praxis, perceptual organization, and cognitive flexibility. A combination of the ε4 allele and EDS potentiates the negative effect on cognition, except for immediate visual memory. In this case, patients had a worse performance in terms of processing speed, selective attention, and visuomotor coordination.

CONCLUSIONS

Excessive daytime sleepiness and the ApoEε3/ε4 genotype are associated with worse cognitive performance in OSA patients. The combination of EDS and ε4 allele potentiates cognitive impairment.

Myelin repair in Alzheimer's disease: a review of biological pathways and potential therapeutics

This literature review investigates the significant overlap between myelin-repair signaling pathways and pathways known to contribute to hallmark pathologies of Alzheimer's disease (AD). We discuss previously investigated therapeutic targets of amyloid, tau, and ApoE, as well as other potential therapeutic targets that have been empirically shown to contribute to both remyelination and progression of AD. Current evidence shows that there are multiple AD-relevant pathways which overlap significantly with remyelination and myelin repair through the encouragement of oligodendrocyte proliferation, maturation, and myelin production. There is a present need for a single, cohesive model of myelin homeostasis in AD. While determining a causative pathway is beyond the scope of this review, it may be possible to investigate the pathological overlap of myelin repair and AD through therapeutic approaches.

A microcarrier-based protocol for scalable generation and purification of human induced pluripotent stem cell-derived neurons and astrocytes

Here, we describe a protocol for a microcarrier (MC)-based, large-scale generation and cryopreservation of human-induced pluripotent stem cell (hiPSC)-derived neurons and astrocytes. We also detail steps to isolate these populations with a high degree of purity. Finally, we describe how to cryopreserve these cell types while maintaining high levels of viability and preserving cellular function post-thaw. For complete details on the use and execution of this protocol, please refer to Brookhouser et al. (2021).

Protective effect of apolipoprotein E epsilon 3 on sporadic Alzheimer's disease in the Chinese population: a meta-analysis

Alzheimer's disease (AD) is fast becoming one of the most expensive, deadly and burdensome diseases in this century. It has the fastest-growing disease burden in China. Apolipoprotein E (APOE) polymorphic alleles are generally considered to be the primary genetic determinant of AD risk: individuals with the E4 allele are at increased risk of AD compared with individuals with the more common E3 allele. Since the intensity of the association varies among different ethnic groups, a separate meta-analysis of the Chinese population is needed. We searched Chinese and English databases to sift through literature over the past 20 years. Data on the APOE genotype and AD were collected for correlation analysis. OR was calculated according to APOE allele and genotype. A publication bias analysis and sensitivity analysis were performed, and the main results were further verified by subgroup analysis. The 116 eligible studies enrolled 23,396 patients with AD and 25,568 healthy controls. The study subjects covered at least 30 of the 34 provincial-level administrative regions (including Taiwan). The partial sex ratio was as follows: AD male/female; 10,291/11,240; control male/female, 11,304/12,428, [Formula: see text] = 0.122, P = 0.727. The results of the meta-analysis of alleles showed that I² > 50% and Q statistics were significant for all genotypes; therefore, the random effect model was selected. The frequency of the ApoE ε4 allele in AD was higher than that in healthy controls, and the difference was statistically significant (OR 2.847, 95% CI [2.611-3.101], P < 0.001). The frequencies of ApoE ε3 and ε2 in AD were lower than those in healthy controls, and the differences were statistically significant (ε3: OR 0.539, 95% CI [0.504-0.576], P < 0.001; ε2: OR 0.771, 95% CI [0.705-0.843], P < 0.001). The results of the meta-analysis of AD genotype showed that ApoE ε2/ε4 (OR 1.521, 95% CI [1.270-1.823], P < 0.001), ε3/ε4 (OR 2.491, 95% CI [2.267-2.738], P < 0.001) and ε4/ε4 (OR 5.481, 95% CI [4.801-6.257], P < 0.001) allele genotype frequencies were higher than those of the healthy controls. The differences were all statistically significant. Moreover, the ApoE ε2/ε2 (OR 0.612, 95% CI [0.504-0.743], P < 0.001), ε2/ε3 (OR 0.649, 95% CI [0.585-0.714], P < 0.001) and ε3/ε3 (OR 0.508, 95% CI [0.468-0.551], P < 0.001) genotypes were less frequent in patients with AD than in healthy controls, and the differences were statistically significant. The results of the sensitivity analysis and subgroup analysis were consistent with those of the whole model. These results provide support for the protective effect of the ApoE ε3/ε3 genotype against the development of AD. This research is the most comprehensive meta-analysis of the correlation between APOE and AD in the Chinese population by analysing the distribution of the APOE gene in patients with AD reported in the last 20 years. It was concluded that the APOE ε3 allele had a protective effect against sporadic AD in the Chinese population, with great significance, and that its protective effect was stronger than that of the ε2 allele.

Apolipoprotein E Genotype e2: Neuroprotection and Its Limits

In this review, we comprehensively, qualitatively, and critically synthesized several features of APOE-e2, a known APOE protective variant, including its associations with longevity, cognition, and neuroimaging, and neuropathology, all in humans. If e2’s protective effects—and their limits—could be elucidated, it could offer therapeutic windows for Alzheimer’s disease (AD) prevention or amelioration. Literature examining e2 within the years 1994–2021 were considered for this review. Studies on human subjects were selectively reviewed and were excluded if observation of e2 was not specified. Effects of e2 were compared with e3 and e4, separately and as a combined non-e2 group. Our examination of existing literature indicated that the most robust protective role of e2 is in longevity and AD neuropathologies, but e2’s effect on cognition and other AD imaging markers (brain structure, function, and metabolism) were inconsistent, thus inconclusive. Notably, e2 was associated with greater risk of non-AD proteinopathies and a disadvantageous cerebrovascular profile. We identified multiple methodological shortcomings of the literature on brain function and cognition that could have contributed to inconsistent and potentially misleading findings. We make careful interpretations of existing findings and provide directions for research strategies that could effectively examine the independent and unbiased effect of e2 on AD risk.

MRI Markers of Small Vessel Disease and the APOE Allele in Cognitive Impairment

Objective

The apolipoprotein E (APOE) ε4 allele is the main genetic risk factor for dementia and Alzheimer's disease (AD), but the underlying mechanism for the increased risk is not well understood. Cerebral small vessel disease (SVD) is prevalent among patients with cognitive impairment and is thought to play an important role in the pathophysiology of dementia. We aimed to investigate the association between the APOE ε genotype and magnetic resonance imaging (MRI) markers of SVD in a memory clinic population.

Material and Methods

This is a cross-sectional study with a total of 520 patients undergoing dementia investigation, including an MRI brain scan and APOE genotyping in all patients enrolled, and cerebrospinal fluid (CSF) analysis for routine AD biomarkers in 399 patients. MR images were assessed for markers of SVD: cerebral microbleeds (CMBs), cortical superficial siderosis, intracerebral hemorrhage, white matter hyperintensities, lacunar infarcts, and enlarged perivascular spaces.

Results

Apolipoprotein E carriers with AD had a higher number of CMBs when looking at all brain regions and lobar brain regions (p < 0.001). A lower number of CMBs were seen in APOE ε2 (p < 0.05), ε3 and ε3/3 carriers (p < 0.001) when looking at all brain regions. A higher number of CMBs in deep and infratentorial regions were seen in APOE ε2 and ε3 (p < 0.05). In APOE ε4/4 carriers, CMBs, cortical superficial siderosis, white matter hyperintensities, and enlarged perivascular spaces were associated with lower levels of CSF amyloid β (Aβ) 42 in the whole cohort, and in individuals with AD and mild cognitive impairment (p < 0.05).

Conclusion

Apolipoprotein E ε4 is associated with MRI markers of SVD related to amyloid pathology, specifically CMBs and Aβ42 plaque formation in the brain, as reflected by decreased CSF Aβ42 levels, whereas APOE ε3 and ε2 are associated with the markers of hypertensive arteriopathy, as reflected by the association with CMBs in deep and infratentorial brain regions.

Distinct Effects of the Apolipoprotein E ε4 Genotype on Associations Between Delayed Recall Performance and Resting-State Electroencephalography Theta Power in Elderly People Without Dementia

Background

Abnormal electroencephalography (EEG) activity has been demonstrated in mild cognitive impairment (MCI), and theta rhythm might be inversely related to memory. The apolipoprotein E (ApoE) epsilon 4 (ε4) allele, as a genetic vulnerability factor for pathologic and normal age-related cognitive decline, may influence different patterns of cognitive dysfunction. Therefore, the present study primarily aimed to verify the role of resting theta rhythm in delayed recall deficits, and further explore the effects of the ApoE genotype on the associations between the resting theta power and delayed recall performance in the elderly individuals without dementia.

Methods

A total of 47 individuals without dementia, including 23 MCI and 24 healthy subjects (HCs), participated in the study. All subjects were administered the Hopkins Verbal Learning Test–Revised (HVLT-R) to measure delayed recall performance. Power spectra based on resting-state EEG data were used to examine brain oscillations. Linear regression was used to examine the relationships between EEG power and delayed recall performance in each subgroup.

Results

The increased theta power in the bilateral central and temporal areas (P_s = 0.02–0.044, uncorrected) was found in the patients with MCI, and were negatively correlated with delayed recall performance (r_s = −0.358 to −0.306, P_s = 0.014–0.036, FDR corrected) in the elderly individuals without dementia. The worse delayed recall performance was associated with higher theta power in the left central and temporal areas, especially in ApoE ε4 non-carriers and not in carriers (r_s = −0.404 to −0.369, P_s = 0.02–0.035, uncorrected).

Conclusion

Our study suggests that theta disturbances might contribute to delayed recall memory decline. The ApoE genotype may have distinct effects on EEG-based neural correlates of episodic memory performance.

The impact of Alzheimer's disease susceptibility loci on lateral ventricular surface morphology in older adults

The enlargement of ventricular volume is a general trend in the elderly, especially in patients with Alzheimer's disease (AD). Multiple susceptibility loci have been reported to have an increased risk for AD and the morphology of brain structures are affected by the variations in the risk loci. Therefore, we hypothesized that genes contributed significantly to the ventricular surface, and the changes of ventricular surface were associated with the impairment of cognitive functions. After the quality controls (QC) and genotyping, a lateral ventricular segmentation method was employed to obtain the surface features of lateral ventricle. We evaluated the influence of 18 selected AD susceptibility loci on both volume and surface morphology across 410 subjects from Alzheimer's Disease Neuroimaging Initiative (ADNI). Correlations were conducted between radial distance (RD) and Montreal Cognitive Assessment (MoCA) subscales. Only the C allele at the rs744373 loci in BIN1 gene significantly accelerated the atrophy of lateral ventricle, including the anterior horn, body, and temporal horn of left lateral ventricle. No significant effect on lateral ventricle was found at other loci. Our results revealed that most regions of the bilateral ventricular surface were significantly negatively correlated with cognitive scores, particularly in delayed recall. Besides, small areas of surface were negatively correlated with language, orientation, and visuospatial scores. Together, our results indicated that the genetic variation affected the localized areas of lateral ventricular surface, and supported that lateral ventricle was an important brain structure associated with cognition in the elderly.

Concordance of Alzheimer’s Disease Subtypes Produced from Different Representative Morphological Measures: A Comparative Study

Background: Gray matter (GM) density and cortical thickness (CT) obtained from structural magnetic resonance imaging are representative GM morphological measures that have been commonly used in Alzheimer’s disease (AD) subtype research. However, how the two measures affect the definition of AD subtypes remains unclear. Methods: A total of 180 AD patients from the ADNI database were used to identify AD subgroups. The subtypes were identified via a data-driven strategy based on the density features and CT features, respectively. Then, the similarity between the two features in AD subtype definition was analyzed. Results: Four distinct subtypes were discovered by both density and CT features: diffuse atrophy AD, minimal atrophy AD (MAD), left temporal dominant atrophy AD (LTAD), and occipital sparing AD. The matched subtypes exhibited relatively high similarity in atrophy patterns and neuropsychological and neuropathological characteristics. They differed only in MAD and LTAD regarding the carrying of apolipoprotein E ε2. Conclusions: The results verified that different representative morphological GM measurement methods could produce similar AD subtypes. Meanwhile, the influences of apolipoprotein E genotype, asymmetric disease progression, and their interactions should be considered and included in the AD subtype definition. This study provides a valuable reference for selecting features in future studies of AD subtypes.

Perspectives on the Role of APOE4 as a Therapeutic Target for Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease that is coupled with chronic cognitive dysfunction. AD cases are mostly late onset, and genetic risk factors like the Apolipoprotein E (APOE) play a key role in this process. APOE ɛ2, APOE ɛ3, and APOE ɛ4 are three key alleles in the human APOE gene. For late onset, APOE ɛ4 has the most potent risk factor while APOE ɛ2 plays a defensive role. Several studies suggests that APOE ɛ4 causes AD via different processes like neurofibrillary tangle formation by amyloid-β accumulation, exacerbated neuroinflammation, cerebrovascular disease, and synaptic loss. But the pathway is still unclear that which actions of APOE ɛ4 lead to AD development. Since APOE was found to contribute to many AD pathways, targeting APOE ɛ4 can lead to a hopeful plan of action in development of new drugs to target AD. In this review, we focus on recent studies and perspectives, focusing on APOE ɛ4 as a key molecule in therapeutic strategies.

Genome-wide DNA methylation profiling in nonagenarians suggests an effect of PM20D1 in late onset Alzheimer's disease

Background

The aim of this study is to identify differentially methylated regions (DMRs) in the genomes of a sample of cognitively healthy individuals and a sample of individuals with LOAD, all of them nonagenarians from Costa Rica.

Methods

In this study, we compared whole blood DNA methylation profiles of 32 individuals: 21 cognitively healthy and 11 with LOAD, using the Infinium MethylationEPIC BeadChip. First, we calculated the epigenetic age of the participants based on Horvath’s epigenetic clock. DMRcate and Bumphunter were used to identify DMRs. After in silico and knowledge-based filtering of the DMRs, we performed a methylation quantitative loci (mQTL) analysis (rs708727 and rs960603).

Results

On average, the epigenetic age was 73 years in both groups, which represents a difference of over 20 years between epigenetic and chronological age in both affected and unaffected individuals. Methylation analysis revealed 11 DMRs between groups, which contain six genes and two pseudogenes. These genes are involved in cell cycle regulation, embryogenesis, synthesis of ceramides, and migration of interneurons to the cerebral cortex. One of the six genes is PM20D1, for which altered expression has been reported in LOAD. After genotyping previously reported mQTL SNPs for the gene, we found that average methylation in the PM20D1 DMR differs between genotypes for rs708727, but not for rs960603.

Conclusions

This work supports the possible role of PM20D1 in protection against AD, by showing differential methylation in blood of affected and unaffected nonagenarians. Our results also support the influence of genetic factors on PM20D1 methylation levels.

The protective gene dose effect of the APOE ε2 allele on gray matter volume in cognitively unimpaired individuals

INTRODUCTION

Harboring two copies of the apolipoprotein E (APOE) ε2 allele strongly protects against Alzheimer's disease (AD). However, the effect of this genotype on gray matter (GM) volume in cognitively unimpaired individuals has not yet been described.

METHODS

Multicenter brain magnetic resonance images (MRIs) from cognitively unimpaired ε2 homozygotes were matched (1:1) against all other APOE genotypes for relevant confounders (n = 223). GM volumes of ε2 genotypic groups were compared to each other and to the reference group (APOE ε3/ε3).

RESULTS

Carrying at least one ε2 allele was associated with larger GM volumes in brain areas typically affected by AD and also in areas associated with cognitive resilience. APOE ε2 homozygotes, but not APOE ε2 heterozygotes, showed larger GM volumes in areas related to successful aging.

DISCUSSION

In addition to the known resistance against amyloid-β deposition, the larger GM volumes in key brain regions may confer APOE ε2 homozygotes additional protection against AD-related cognitive decline.

The Amyloid-β Pathway in Alzheimer's Disease

Breakthroughs in molecular medicine have positioned the amyloid-β (Aβ) pathway at the center of Alzheimer's disease (AD) pathophysiology. While the detailed molecular mechanisms of the pathway and the spatial-temporal dynamics leading to synaptic failure, neurodegeneration, and clinical onset are still under intense investigation, the established biochemical alterations of the Aβ cycle remain the core biological hallmark of AD and are promising targets for the development of disease-modifying therapies. Here, we systematically review and update the vast state-of-the-art literature of Aβ science with evidence from basic research studies to human genetic and multi-modal biomarker investigations, which supports a crucial role of Aβ pathway dyshomeostasis in AD pathophysiological dynamics. We discuss the evidence highlighting a differentiated interaction of distinct Aβ species with other AD-related biological mechanisms, such as tau-mediated, neuroimmune and inflammatory changes, as well as a neurochemical imbalance. Through the lens of the latest development of multimodal in vivo biomarkers of AD, this cross-disciplinary review examines the compelling hypothesis- and data-driven rationale for Aβ-targeting therapeutic strategies in development for the early treatment of AD.

APOE2 mitigates disease-related phenotypes in an isogenic hiPSC-based model of Alzheimer's disease

Genome-wide association studies (GWAS) have identified polymorphism in the Apolipoprotein E gene (APOE) to be the most prominent risk factor for Alzheimer's disease (AD). Compared to individuals homozygous for the APOE3 variant, individuals with the APOE4 variant have a significantly elevated risk of AD. On the other hand, longitudinal studies have shown that the presence of the APOE2 variant reduces the lifetime risk of developing AD by 40 percent. While there has been significant research that has identified the risk-inducing effects of APOE4, the underlying mechanisms by which APOE2 influences AD onset and progression have not been extensively explored. In this study, we utilize an isogenic human induced pluripotent stem cell (hiPSC)-based system to demonstrate that conversion of APOE3 to APOE2 greatly reduced the production of amyloid-beta (Aβ) peptides in hiPSC-derived neural cultures. Mechanistically, analysis of pure populations of neurons and astrocytes derived from these neural cultures revealed that mitigating effects of APOE2 are mediated by cell autonomous and non-autonomous effects. In particular, we demonstrated the reduction in Aβ is potentially driven by a mechanism related to non-amyloidogenic processing of amyloid precursor protein (APP), suggesting a gain of the protective function of the APOE2 variant. Together, this study provides insights into the risk-modifying effects associated with the APOE2 allele and establishes a platform to probe the mechanisms by which APOE2 enhances neuroprotection against AD.

Apolipoprotein e (APOE) ε4 genotype influences memory performance following remote traumatic brain injury in U.S. military service members and veterans

The purpose of this study was to examine the association between the apolipoprotein E (APOE) ε4 allele and neurocognitive functioning following traumatic brain injury (TBI) in military service members and veterans (SMVs). Participants included 176 SMVs with a history of remote TBI (≥1 year post-injury), categorized into mild (n = 100), moderate (n = 40), and severe (n = 36) TBI groups. Participants completed a neuropsychological assessment and APOE genotyping (n = 46 ε4+, n = 130 ε4-). Neurocognitive composite scores representing memory, executive functioning, and visual processing speed were computed. ANCOVAs adjusting for race, education, combat exposure, and PTSD symptom severity showed a significant main effect of ε4 on the memory composite, such that ε4+ SMVs exhibited poorer memory performance than ε4- SMVs. When ε2 allele carriers were removed from the analyses, associations with memory were strengthened, demonstrating a possible protective effect of the ε2 allele. No main effect of TBI group was identified on any cognitive composite, nor were there any significant TBI group × ε4 status interactions for any cognitive composite. Future studies with larger samples are needed to verify these findings, but our results suggest an important relationship between ε4 status and memory functioning following remote TBI of all severities.

Race-Related Association between APOE Genotype and Alzheimer's Disease: A Systematic Review and Meta-Analysis

BACKGROUND

The global race-dependent association of Alzheimer's disease (AD) and apolipoprotein E (APOE) genotype is not well understood. Transethnic analysis of APOE could clarify the role of genetics in AD risk across populations.

OBJECTIVE

This study aims to determine how race and APOE genotype affect the risks for AD.

METHODS

We performed a systematic search of PubMed, Embase, Web of Science, and the Cochrane Library since 1993 to Aug 25, 2020. A total of 10,395 reports were identified, and 133 were eligible for analysis with data on 77,402 participants. Studies contained AD clinical diagnostic and APOE genotype data. Homogeneous data sets were pooled in case-control analyses. Odds ratios and 95% confidence intervals for developing AD were calculated for populations of different races and APOE genotypes.

RESULTS

The proportion of APOE genotypes and alleles differed between populations of different races. Results showed that APOEɛ4 was a risk factor for AD, whereas APOEɛ2 protected against it. The effects of APOEɛ4 and ɛ2 on AD risk were distinct in various races, they were substantially attenuated among Black people. Sub-group analysis found a higher frequency of APOEɛ4/ɛ4 and lower frequency of APOEɛ3/ɛ3 among early-onset AD than late-onset AD in a combined group and different races.

CONCLUSION

Our meta-analysis suggests that the association of APOE genotypes and AD differ between races. These results enhance our understanding of APOE-related risk for AD across race backgrounds and provide new insights into precision medicine for AD.

Protective association of the ε2/ε3 heterozygote with Alzheimer's disease is strengthened by TOMM40-APOE variants in men

INTRODUCTION

Despite advances, understanding the protective role of the apolipoprotein E (APOE) ε2 allele in Alzheimer's disease (AD) remains elusive.

METHODS

We examined associations of variants comprised of the TOMM40 rs8106922 and APOE rs405509, rs440446, and ε2-encoding rs7412 polymorphisms with AD in a sample of 2862 AD-affected and 169,516 AD-unaffected non-carriers of the ε4 allele.

RESULTS

Association of the ε2/ε3 heterozygote of men with AD is 38% (P = 1.65 × 10^-2 ) more beneficial when it is accompanied by rs8106922 major allele homozygote and rs405509 and rs440446 heterozygotes than by rs8106922 heterozygote and rs405509 and rs440446 major allele homozygotes. No difference in the beneficial associations of these two most common ε2/ε3-bearing variants with AD was identified in women. The role of ε2/ε3 heterozygote may be affected by different immunomodulation functions of rs8106922, rs405509, and rs440446 variants in a sex-specific manner.

DISCUSSION

Combination of TOMM40 and APOE variants defines a more homogeneous AD-protective ε2/ε3-bearing profile in men.

Interactive effects of the APOE and BDNF polymorphisms on functional brain connectivity: the Tasmanian Healthy Brain Project

Resting-state functional magnetic resonance imaging measures pathological alterations in neurodegenerative diseases, including Alzheimer’s disease. Disruption in functional connectivity may be a potential biomarker of ageing and early brain changes associated with AD-related genes, such as APOE and BDNF. The objective of this study was to identify group differences in resting-state networks between individuals with BDNF Val66Met and APOE polymorphisms in cognitively healthy older persons. Dual regression following Independent Components Analysis were performed to examine differences associated with these polymorphisms. APOE ε3 homozygotes showed stronger functional connectivity than APOE ε4 carriers. Males showed stronger functional connectivity between the Default Mode Network (DMN) and grey matter premotor cortex, while females showed stronger functional connectivity between the executive network and lateral occipital cortex and parahippocampal gyrus. Additionally, we found that with increasing cognitive reserve, functional connectivity increased within the Dorsal Attention Network (DAN), but decreased within the DMN. Interaction effects indicated stronger functional connectivity in Met/ε3 carriers than in Met/ε4 and Val/ε4 within both the DMN and DAN. APOE/BDNF interactions may therefore influence the integrity of functional brain connections in older adults, and may underlie a vulnerable phenotype for subsequent Alzheimer’s-type dementia.

Can Physical Activity Reduce the Risk of Cognitive Decline in Apolipoprotein e4 Carriers? A Systematic Review

Physical activity (PA) reduces the risk of cognitive decline (CD) in the general population. However, little is known about whether the presence of the apolipoprotein E epsilon 4 allele (APOE e4) could modify this beneficial effect. The aim of this systematic review was to analyze and synthetize the scientific evidence related to PA levels and CD risk in cognitively healthy APOE e4 carriers. Four electronic databases were analyzed. Only original articles with longitudinal study design were selected to analyze the relationship between PA and CD in APOE e4 carriers. Five studies were included in the systematic review. All studies except one stated that PA is a protective factor against CD in APOE e4 carriers. Moreover, partial support was found for the hypothesis that a greater amount and intensity of PA are more beneficial in CD prevention. The results support the idea that PA is a protective factor against CD in APOE e4 carriers. Nevertheless, it would be necessary to carry out further studies that would allow these findings to be contrasted.

Differential associations of APOE-ε2 and APOE-ε4 alleles with PET-measured amyloid-β and tau deposition in older individuals without dementia

PURPOSE

To examine associations between the APOE-ε2 and APOE-ε4 alleles and core Alzheimer's disease (AD) pathological hallmarks as measured by amyloid-β (Aβ) and tau PET in older individuals without dementia.

METHODS

We analyzed data from 462 ADNI participants without dementia who underwent Aβ ([18F]florbetapir or [18F]florbetaben) and tau ([18F]flortaucipir) PET, structural MRI, and cognitive testing. Employing APOE-ε3 homozygotes as the reference group, associations between APOE-ε2 and APOE-ε4 carriership with global Aβ PET and regional tau PET measures (entorhinal cortex (ERC), inferior temporal cortex, and Braak-V/VI neocortical composite regions) were investigated using linear regression models. In a subset of 156 participants, we also investigated associations between APOE genotype and regional tau accumulation over time using linear mixed models. Finally, we assessed whether Aβ mediated the cross-sectional and longitudinal associations between APOE genotype and tau.

RESULTS

Compared to APOE-ε3 homozygotes, APOE-ε2 carriers had lower global Aβ burden (βstd [95% confidence interval (CI)]: - 0.31 [- 0.45, - 0.16], p = 0.034) but did not differ on regional tau burden or tau accumulation over time. APOE-ε4 participants showed higher Aβ (βstd [95%CI]: 0.64 [0.42, 0.82], p < 0.001) and tau burden (βstd range: 0.27-0.51, all p < 0.006). In mediation analyses, APOE-ε4 only retained an Aβ-independent effect on tau in the ERC. APOE-ε4 showed a trend towards increased tau accumulation over time in Braak-V/VI compared to APOE-ε3 homozygotes (βstd [95%CI]: 0.10 [- 0.02, 0.18], p = 0.11), and this association was fully mediated by baseline Aβ.

CONCLUSION

Our data suggest that the established protective effect of the APOE-ε2 allele against developing clinical AD is primarily linked to resistance against Aβ deposition rather than tau pathology.

Cognition in Patients With Memory Difficulties and Dementia Relative to APOE e4 Status

The aim of this study was to investigate whether cognitive performance was equally influenced by Apolipoprotein E (APOE, with its three alleles, e2, e3, and e4) in patients with subjective cognitive decline (SCD), mild cognitive impairment (MCI), and Alzheimer’s disease (AD). In addition, we examined a group of patients with a combination of Vascular dementia (VaD) and AD (VaD/AD). We asked if the APOE e4 allele influenced cognition in these patient groups in the same way. Our study comprised data from 1,991 patients (55% women), with a mean age of 70.9 years (SD 10.8) and 12.1 years of education (SD 3.8). Of them, 1,111 (56%) had at least one APOE e4 allele; 871 (44%) had one and 240 (12%) had two e4 alleles. Three neurocognitive tests were used to measure cognition: the Mini Mental State Examination (MMSE), the 10-word test of the Consortium to Establish a Registry for Alzheimer’s Disease Word List (CERAD-WL) (immediate and delayed recall), and the Trail Making Test Part A (TMTA). The APOE genotypes were regressed against cognitive function using linear regression, adjusting for diagnosis, age, sex, and education. The interaction diagnosis^∗APOE was investigated. The allele type had the largest effect on cognitive performance assessed by the CERAD-WL delayed recall test, less for the other tests. Those without the e4 type scored 0.7 units better than those with e4 allele(s) (p < 0.001). Furthermore, there was a significant inverse dose-response pattern between number of e4 alleles and cognitive performance; those with one allele scored 0.4 units better than those with two alleles (p = 0.006), and those without e4 scored 0.7 units better than those with one e4 (p < 0.001). This pattern did not differ between the four diagnostic groups studied.

The Proportion of APOE4 Carriers Among Non-Demented Individuals: A Pooled Analysis of 389,000 Community-Dwellers

BACKGROUND

The apolipoprotein E epsilon 4 (APOE4) is the strongest genetic risk factor for sporadic Alzheimer's disease (AD). Its carriage percentage in non-demented population varies across geographic regions and ethnic groups.

OBJECTIVE

To estimate the proportion of APOE4 (2/4, 3/4, or 4/4) carriers in non-demented community-dwellers.

METHODS

PubMed, EMBASE, and China National Knowledge Infrastructure were searched from inception to April 20, 2020. Community-based studies that reported APOE polymorphisms with a sample of≥500 non-demented participants were included. Random-effects models were used to pool the results. Meta-regression and subgroup analyses were performed to test the source of heterogeneity and stratified effects. Age-standardized pooled proportion estimates (ASPPE) were calculated by direct standardization method.

RESULTS

A total of 121 studies were included, with a pooled sample of  389,000 community-dwellers from 38 countries. The global average proportion of APOE4 carriers was 23.9% (age-standardized proportion: 26.3%; 2.1% for APOE4/4, 20.6% for APOE3/4 and 2.3% for APOE2/4), and varied significantly with geographical regions (from 19.3% to 30.0%) and ethnic groups (from 19.1% to 37.5%). The proportion was highest in Africa, followed by Europe, North America, Oceania, and lowest in South America and Asia (p < 0.0001). With respect to ethnicity, it was highest in Africans, followed by Caucasians, and was lowest in Hispanics/Latinos and Chinese (p < 0.0001).

CONCLUSION

APOE4 carriers are common in communities, especially in Africans and Caucasians. Developing precision medicine strategies in this specific high-risk population is highly warranted in the future.

Effects of APOE ε2 on the Fractional Amplitude of Low-Frequency Fluctuation in Mild Cognitive Impairment: A Study Based on the Resting-State Functional MRI

BACKGROUND

Apolipoprotein E (APOE) ε2 is a protective genetic factor for Alzheimer's disease (AD). However, the potential interaction effects between the APOE ε2 allele and disease status on the intrinsic brain activity remain elusive.

METHODS

We identified 73 healthy control (HC) with APOE ε3/ε3, 61 mild cognitive impairment (MCI) subjects with APOE ε3/ε3, 24 HC with APOE ε2/ε3, and 10 MCI subjects with APOE ε2/ε3 from the ADNI database. All subjects underwent a resting-state functional MRI and Fluoro-deoxy-glucose positron emission tomography (FDG-PET). We used a fractional amplitude of low-frequency fluctuation (fALFF) to explore the spontaneous brain activity. Based on the mixed-effects analysis, we explored the interaction effects between the APOE ε2 allele versus disease status on brain activity and metabolism in a voxel-wise fashion (GRF corrected, p < 0.01), followed by post hoc two-sample t-tests (Bonferroni corrected, p < 0.05). We then investigated the relationship between the mean imaging metrics and cognitive abilities.

RESULTS

There are no significant differences in gender, age, or education among the four groups. The interaction effect on brain activity was located in the inferior parietal lobule (IPL). Post hoc analysis showed that APOE ε2/ε3 MCI had an increased IPL fALFF than APOE ε3/ε3 MCI. Regarding the APOE ε2 allele effects, we found that ε2 carriers had a decreased fALFF in the transverse temporal gyrus than non-carriers. Also, FDG-PET results showed a lower SUVR of the frontal lobe in APOE ε2 carriers than non-carriers. Furthermore, fALFF of IPL was correlated with the visuospatial function (r = -0.16, p < 0.05).

CONCLUSION

APOE ε2 carriers might have a better brain reservation when coping with AD-related pathologies.