Association of APOE with tau-tangle pathology with and without β-amyloid

This study tested the hypothesis that the association of apolipoprotein E (APOE) with paired helical filament tau (PHF-tau) tangle pathology differs in brains with and without β-amyloid. Participants were 1056 autopsied individuals from 2 clinical-pathologic cohort studies of aging and Alzheimer's disease (AD), the Religious Orders Study, and the Rush Memory and Aging Project. Neuropathologic measures were obtained using immunohistochemistry targeting β-amyloid and PHF-tau tangles in 8 brain regions. Linear regression was used to compare the relation of APOE ε4 and ε2 to PHF-tau-tangle density in persons with β-amyloid relative to persons without β-amyloid. We found an interaction between APOE ε4 carriers and presence of β-amyloid (β = -0.968, p = 0.013) such that the association of APOE ε4 with PHF-tau tangles was much stronger in brains with β-amyloid. Stratified analysis shows that the association of APOE ε4 with PHF-tau tangles was considerably stronger among those with β-amyloid (β = 0.757, p = 1.1 × 10(-15)) compared to those without β-amyloid which was not significant (β = -0.201, p = 0.424). Separately, APOE ε2 was associated with fewer tangles in brains with β-amyloid (β = -0.425, p = 7.6 × 10(-4)) compared to those without β-amyloid which was not significant (β = -0.102, p = 0.506). Thus, the presence of APOE ε4 and ε2 alleles was not associated with PHF-tau tangles in the absence of β-amyloid. The data provide additional evidence that PHF-tau tangles in the absence of β-amyloid may reflect a pathologic process distinct from Alzheimer's disease.

Loss of Munc18-1 long splice variant in GABAergic terminals is associated with cognitive decline and increased risk of dementia in a community sample

BACKGROUND

Presynaptic terminals contribute to cognitive reserve, balancing the effects of age-related pathologies on cognitive function in the elderly. The presynaptic protein Munc18-1, alternatively spliced into long (M18L) or short (M18S) isoforms, is a critical modulator of neurotransmission. While subtle alterations in Munc18-1 have been shown to cause severe neuropsychiatric disorders with cognitive impairment, little information is known regarding the specific roles of Munc18-1 splice variants. We first investigated functional and anatomical features evidencing the divergent roles of M18L and M18S, and then evaluated their contribution to the full range of age-related cognitive impairment in the dorsolateral prefrontal cortex of a large sample of participants from a community-based aging study, including subjects with no-(NCI, n = 90), or mild-(MCI, n = 86) cognitive impairment, or with clinical dementia (n = 132). Finally, we used APP23 mutant mice to study the association between M18L/S and the time-dependent accumulation of common Alzheimer's disease pathology.

RESULTS

Using isoform-specific antibodies, M18L was localized to the synaptosomal fraction, with a distribution matching lipid raft microdomains. M18S was found widely across cytosolic and synaptosomal compartments. Immunocytochemical studies identified M18L in perisomatic, GABAergic terminals, while M18S was broadly distributed in GABAergic and glutamatergic terminals. Using regression models taking into account multiple age-related pathologies, age, education and sex, global cognitive function was associated with the level of M18L (p = 0.006) but not M18S (p = 0.88). Mean M18L in dementia cases was 51 % lower than in NCI cases (p < 0.001), and each unit of M18L was associated with a lower likelihood of dementia (odds ratio = 0.68, 95 % confidence interval = 0.50-0.90, p = 0.008). In contrast, M18S balanced across clinical and pathologically diagnosed groups. M18L loss may not be caused by age-related amyloid pathology, since APP23 mice (12- and 22-months of age) had unchanged cortical levels of M18L/S compared with wild-type animals.

CONCLUSIONS

M18L was localized to presynaptic inhibitory terminals, and was associated with cognitive function and protection from dementia in an elderly, community-based cohort. Lower M18L in inhibitory presynaptic terminals may be an early, independent contributor to cognitive decline.

Cerebral amyloid angiopathy and cognitive outcomes in community-based older persons

OBJECTIVE

We tested the hypothesis that cerebral amyloid angiopathy (CAA) is related to Alzheimer disease (AD) dementia and decline in multiple cognitive systems in old age, independent of AD plaque and tangle pathology and other common age-related neuropathologies.

METHODS

Participants (n = 1,113) came from 2 longitudinal clinical-pathologic studies of aging, the Rush Memory and Aging Project and the Religious Orders Study. All underwent annual clinical evaluations including detailed cognitive testing for a mean of 7.1 years before death. Clinical diagnoses of AD were established after reviewing all clinical data, blinded to neuropathologic information. Neuropathologic examinations provided measures of CAA, AD pathology, macroscopic infarcts, microinfarcts, and neocortical Lewy bodies. The association of CAA with AD dementia was examined using logistic regression models, and its association with cognitive decline was examined using linear mixed models.

RESULTS

CAA was common, present in 78.9% of participants, and moderately related to AD pathology (ρ = 0.401, p < 0.0001). In analyses adjusted for plaques, tangles, and other common age-related neuropathologies, CAA was associated with an increased odds of AD dementia (odds ratio = 1.237, 95% confidence interval 1.082-1.414) and an increased rate of decline in global cognition, perceptual speed, episodic memory, and semantic memory. The associations of CAA with cognitive outcomes were not driven by the presence of capillary involvement.

CONCLUSIONS

CAA is an important determinant of AD dementia and decline in multiple cognitive systems in old age.

Post-mortem brain pathology is related to declining respiratory function in community-dwelling older adults

Damage to brain structures which constitute the distributed neural network that integrates respiratory muscle and pulmonary functions, can impair adequate ventilation and its volitional control. We tested the hypothesis that the level of brain pathology in older adults is associated with declining respiratory function measured during life. 1,409 older adults had annual testing with spirometry (SPI) and respiratory muscle strength (RMS) based on maximal inspiratory and maximal expiratory pressures (MEPs). Those who died underwent structured brain autopsy. On average, during 5 years of follow-up, SPI and RMS showed progressive decline which was moderately correlated (ρ = 0.57, p < 0.001). Among decedents (N = 447), indices of brain neuropathologies showed differential associations with declining SPI and RMS. Nigral neuronal loss was associated with the person-specific decline in SPI (Estimate, −0.016 unit/year, S.E. 0.006, p = 0.009) and reduction of the slope variance was equal to 4%. By contrast, Alzheimer’s disease (AD) pathology (Estimate, −0.030 unit/year, S.E. 0.009, p < 0.001) and macroscopic infarcts (−0.033 unit/year, S.E., 0.011, p = 0.003) were associated with the person-specific decline in RMS and reduction of the slope variance was equal to 7%. These results suggest that brain pathology is associated with the rate of declining respiratory function in older adults.

GSK3β Interactions with Amyloid Genes: An Autopsy Verification and Extension

Glyocogen synthase kinase 3 (GSK3) plays an important role in the pathophysiology of Alzheimer's disease (AD) through the phosphorylation of tau. Recent work has suggested that GSK3β also plays a role in the amyloid pathway of AD through genetic interactions with APP and APBB2 on in vivo measures of amyloid. This project extends the previously identified genotype interactions to an autopsy measure of amyloid, while also testing the same interactions leveraging gene expression data quantified in the prefrontal cortex. 797 participants (251 cognitively normal, 196 mild cognitive impairment, and 350 Alzheimer's disease) were drawn from the Religious Orders Study and Rush Memory and Aging Project. A mean score of amyloid load was calculated across eight brain regions, gene expression levels from frozen sections of the dorsolateral prefrontal cortex were quantified using RNA amplification, and expression signals were generated using Beadstudio. Three SNPs previously identified in genetic interactions were genotyped using the Illumina 1M genotyping chip. Covariates included age, sex, education, and diagnosis. We were able to evaluate 2 of the 3 previously identified interactions, of which the interaction between GSK3β (rs334543) and APBB2 (rs2585590) was found in this autopsy sample (p = 0.04). We observed a comparable interaction between GSK3β and APBB2 when comparing the highest tertile of gene expression to the lowest tertile, t(1) = -2.03, p = 0.043. These results provide additional evidence of a genetic interaction between GSK3β and APBB2 and further suggest that GSK3β is involved in the pathophysiology of both of the primary neuropathologies of Alzheimer's disease.

Association of DNA methylation in the brain with age in older persons is confounded by common neuropathologies

DNA methylation plays a crucial role in the regulation of gene expression, cell differentiation and development. Previous studies have reported age-related alterations of methylation levels in the human brain across the lifespan, but little is known about whether the observed association with age is confounded by common neuropathologies among older persons. Using genome-wide DNA methylation data from 740 postmortem brains, we interrogated 420,132 CpG sites across the genome in a cohort of individuals with ages from 66 to 108 years old, a range of ages at which many neuropathologic indices become quite common. We compared the association of DNA methylation prior to and following adjustment for common neuropathologies using a series of linear regression models. In the simplest model adjusting for technical factors including batch effect and bisulfite conversion rate, we found 8156 CpGs associated with age. The number of CpGs associated with age dropped by more than 10% following adjustment for sex. Notably, after adjusting for common neuropathologies, the total number of CpGs associated with age was reduced by approximately 40%, compared to the sex-adjusted model. These data illustrate that the association of methylation changes in the brain with age is inflated if one does not account for age-related brain pathologies. This article is part of a Directed Issue entitled: Epigenetics dynamics in development and disease.

CD33 modulates TREM2: convergence of Alzheimer loci

Here, we report results from a protein quantitative trait analysis in monocytes from 226 individuals to evaluate cross-talk between Alzheimer loci. We find that the NME8 locus influences PTK2B and that the CD33 risk allele leads to greater TREM2 expression. Further, we observe (1) a decreased TREM1/TREM2 ratio with a TREM1 risk allele, (2) decreased TREM2 expression with CD33 suppression, and (3) elevated cortical TREM2 mRNA expression with amyloid pathology.

Racial Differences in Cognitive Function and Risk of Incident Stroke

BACKGROUND AND PURPOSE

Cognitive impairment is associated with increased risk of stroke; however, it is not known whether this association varies by race. Our objective was to examine the association between cognitive function and the risk of stroke among non-Hispanic blacks and whites with no history of stroke.

METHODS

Participants were from a population-based cohort study of 7205 older adults (61% black and 59% female) from Chicago's South Side. A standardized composite cognitive function score based on 3 components--global cognition (Mini-Mental State Examination), executive function (Symbol Digits Modalities test), and episodic memory (Delayed and Immediate Story Recall tests)--was used to predict risk of stroke (from Medicare hospitalization data) using a Cox model.

RESULTS

During 72,868 person-years of follow-up, 16% (N = 1185) developed stroke. After adjusting for vascular risk factors, 1 standard deviation lower composite cognitive function score was associated with increased risk of stroke in blacks (hazard ratio [HR] = 1.76; 95% confidence interval [CI], 1.66-1.88), which was twofold higher than whites (HR = 1.38; 95% CI, 1.26-1.55) (Pdifference = .002). Lower global cognition and executive function were associated with a similarly increased risk of stroke in blacks and whites. Lower episodic memory (composite of recall tests) was associated with increased risk of stroke that was twofold higher in blacks (HR = 1.12; 95% CI, 1.10-1.14) than in whites (HR = 1.06; 95% CI, 1.04-1.09).

CONCLUSIONS

Lower cognitive function was associated with increased risk of stroke and this association was stronger among blacks than whites. Future studies are needed to determine factors that can explain this finding.

Temporal course and pathologic basis of unawareness of memory loss in dementia

OBJECTIVE

To characterize the natural history and neuropathologic basis of unawareness of memory loss in late-life dementia.

METHODS

Analyses are based on 2,092 older persons from 3 longitudinal clinical-pathologic cohort studies who had no memory or cognitive impairment at baseline. Annual evaluations included clinical classification of dementia plus self-rating and performance testing of memory. At death, there was a uniform neuropathologic examination to quantify 7 dementia-related pathologies.

RESULTS

In the full group, memory ratings were modestly correlated with memory performance (intercepts r = 0.26, p < 0.001; slopes r = 0.23, p < 001) and so we regressed each person's memory performance on their memory ratings, and the residuals provided longitudinal indicators of memory awareness. In a subset of 239 persons who developed dementia, episodic memory awareness was stable until a mean of 2.6 years before dementia onset (95% credible interval -2.7, -1.6); thereafter, memory awareness declined rapidly (mean annual change -0.32, 95% credible interval -0.37, -0.28). Older age at baseline was associated with later onset of memory unawareness. In a subset of 385 persons who died and underwent neuropathologic examination, transactive response DNA-binding protein 43 (TDP-43) pathology, tau tangles, and gross cerebral infarcts were related to decline in memory awareness. In the absence of these pathologies, no decline in memory awareness was evident. Results were similar in subgroups with and without dementia.

CONCLUSIONS

Awareness of memory impairment typically begins to decline about 2-3 years before dementia onset and is associated with postmortem evidence of TDP-43 pathology, tangles, and gross cerebral infarcts.

Positive florbetapir PET amyloid imaging in a subject with frequent cortical neuritic plaques and frontotemporal lobar degeneration with TDP43-positive inclusions

Abnormal neuronal accumulation and modification of TAR DNA binding protein 43 (TDP-43) have recently been discovered to be defining histopathological features of particular subtypes of frontotemporal dementia and amyotrophic lateral sclerosis, and are also common in aging, particularly coexisting with hippocampal sclerosis and Alzheimer's disease pathology. This case report describes a 72 year old Hispanic male with no family history of neurological disease, who presented at age 59 with obsessive behavior, anxiety, agitation, and dysphasia. Positron emission tomography imaging using the amyloid ligand 18F florbetapir (Amyvid) was positive. Postmortem examination revealed frequent diffuse and neuritic amyloid plaques throughout the cerebral cortex, thalamus, and striatum, Braak stage II neurofibrillary degeneration, and frequent frontal and temporal cortex TDP-43-positive neurites with rare nuclear inclusions. The case is unusual and instructive because of the co-existence of frequent cortical and diencephalic amyloid plaques with extensive TDP-43-positive histopathology in the setting of early-onset dementia and because it demonstrates that a positive cortical amyloid imaging signal in a subject with dementia does not necessarily establish that Alzheimer's disease is the sole cause.

APOE and cerebral amyloid angiopathy in community-dwelling older persons

Both cerebral amyloid angiopathy and Alzheimer's disease pathology involve abnormal β-amyloid processing. We aim to elucidate the relationship of the apolipoprotein E (APOE) genotypes with amyloid angiopathy in the presence of variable amounts of Alzheimer's pathology. Data came from 1062 autopsied subjects from 2 community-based studies of aging. Common neuropathologies including Alzheimer's disease and amyloid angiopathy were assessed using uniform methods. APOE was genotyped by sequencing the 2 polymorphisms in codons 112 and 158 of exon 4. We examined the associations of APOE with amyloid angiopathy using ordinal logistic regression analyses, controlling for demographics and subsequently Alzheimer's and other common pathologies. Moderate to severe amyloid angiopathy was identified in 35.2% (n = 374) of the subjects; 15.3% (n = 162) of the subjects were APOE ε2 carriers; and 26.1% (n = 277) ε4 carriers. Adjusting for demographics, the presence of ε4 allele, but not ε2, was associated with more severe amyloid angiopathy. After further adjustment for Alzheimer's pathology, both ε2 (odds ratio 1.707, 95% confidence interval 1.236-2.358, p = 0.001) and ε4 (odds ratio 2.284, 95% confidence interval 1.730-3.014, p < 0.001) were independently associated with amyloid angiopathy. The results were confirmed by path analysis. Furthermore, APOE ε4 carriers, but not ε2 carriers, were more likely to have capillary amyloid angiopathy. Accounting for capillary involvement did not alter the APOE associations with amyloid angiopathy. We conclude that both APOE ε2 and ε4 alleles are associated with more severe cerebral amyloid angiopathy, and the direct effect of ε2 is masked by the allele's negative association with comorbid Alzheimer's pathology. APOE ε4, but not ε2, is associated with capillary amyloid angiopathy.

Mixed pathology is more likely in black than white decedents with Alzheimer dementia

OBJECTIVE

To compare the burden of neuropathology in black and white participants with clinical Alzheimer disease (AD).

METHODS

Participants included 122 persons enrolled in the Rush Alzheimer's Disease Clinical Core, a prospective cohort study of AD. Forty-one black decedents were matched two-to-one to 81 white decedents according to age at death, sex, years of education, and cognition proximate to death. We examined common brain pathologies related to dementia (AD, Lewy body, and macroscopic and microinfarct pathology) and arteriolar sclerosis and atherosclerosis. We calculated the frequency of each dementia pathology both alone and in combination (mixed pathologies). Racial differences in the odds of a single pathology vs mixed pathologies, and in the odds of vessel disease and its severity, were examined using logistic regression analyses.

RESULTS

AD pathology was confirmed in >93% of both black and white decedents with AD dementia. However, black decedents were less likely to have Alzheimer pathology as a single dementia pathology than white decedents (19.5% vs 42.0%), and were more likely to have AD mixed with an additional pathology (70.7% vs 50.6%), particularly Alzheimer pathology and Lewy bodies, and Alzheimer pathology, Lewy bodies, and infarcts. Black decedents also had more severe arteriolar sclerosis and atherosclerosis.

CONCLUSION

Black decedents with AD dementia are more likely to have mixed brain pathologies compared with age-, sex-, education-, and cognition-matched white decedents with AD dementia.

Central role for PICALM in amyloid-β blood-brain barrier transcytosis and clearance

PICALM is a highly validated genetic risk factor for Alzheimer's disease (AD). We found that reduced expression of PICALM in AD and murine brain endothelium correlated with amyloid-β (Aβ) pathology and cognitive impairment. Moreover, Picalm deficiency diminished Aβ clearance across the murine blood-brain barrier (BBB) and accelerated Aβ pathology in a manner that was reversible by endothelial PICALM re-expression. Using human brain endothelial monolayers, we found that PICALM regulated PICALM/clathrin-dependent internalization of Aβ bound to the low density lipoprotein receptor related protein-1, a key Aβ clearance receptor, and guided Aβ trafficking to Rab5 and Rab11, leading to Aβ endothelial transcytosis and clearance. PICALM levels and Aβ clearance were reduced in AD-derived endothelial monolayers, which was reversible by adenoviral-mediated PICALM transfer. Inducible pluripotent stem cell-derived human endothelial cells carrying the rs3851179 protective allele exhibited higher PICALM levels and enhanced Aβ clearance. Thus, PICALM regulates Aβ BBB transcytosis and clearance, which has implications for Aβ brain homeostasis and clearance therapy.

Neuropathologic correlates of regional brain volumes in a community cohort of older adults

The objective of this work was 2-fold: to generate macrostructural brain signatures of age-related neuropathologies in a community cohort of older adults and to determine the contribution of brain macrostructure to the variation in antemortem cognition after accounting for the contributions of neuropathologies and demographics. Cerebral hemispheres from 165 participants of 2 cohort studies of aging were imaged with magnetic resonance imaging ex vivo (mean age at death = 90 years; standard deviation = 6 years). The volumes of white matter and 42 gray matter regions were measured. The same hemispheres also underwent neuropathologic examination. Alzheimer's disease pathology was negatively associated with volumes of mainly temporal, frontal, and parietal gray matter regions, and with total white matter volume (p < 0.05, false discovery rate-corrected). A negative association was also detected between hippocampal sclerosis and volumes of the hippocampus, as well as other temporal and frontal gray matter regions (p < 0.05, false discovery rate-corrected). The volume of mainly medial temporal lobe regions explained an additional 5%-6% of the variation in antemortem cognition, above and beyond what was explained by neuropathologies and demographics.

Suprachiasmatic neuron numbers and rest-activity circadian rhythms in older humans

The suprachiasmatic nucleus (SCN) of the hypothalamus, the master mammalian circadian pacemaker, synchronizes endogenous rhythms with the external day-night cycle. Older humans, particularly those with Alzheimer disease (AD), often have difficulty maintaining normal circadian rhythms compared to younger adults, but the basis of this change is unknown. We report that the circadian rhythm amplitude of motor activity in both AD subjects and age-matched controls is correlated with the number of vasoactive intestinal peptide-expressing SCN neurons. AD was additionally associated with delayed circadian phase compared to cognitively healthy subjects, suggesting distinct pathologies and strategies for treating aging- and AD-related circadian disturbances.

Purpose in life and cerebral infarcts in community-dwelling older people

BACKGROUND AND PURPOSE

Purpose in life, the sense that life has meaning and direction, is associated with reduced risks of adverse health outcomes. However, it remains unknown whether purpose in life protects against the risk of cerebral infarcts among community-dwelling older people. We tested the hypothesis that greater purpose in life is associated with lower risk of cerebral infarcts.

METHODS

Participants came from the Rush Memory and Aging Project. Each participant completed a standard measure of purpose in life. Uniform neuropathologic examination identified macroscopic infarcts and microinfarcts, blinded to clinical information. Association of purpose in life with cerebral infarcts was examined in ordinal logistic regression models using a semiquantitative outcome.

RESULTS

Four hundred fifty-three participants were included in the analyses. The mean score on the measure of purpose was 3.5 (SD, 0.5; range, 2.1-5.0). Macroscopic infarcts were found in 154 (34.0%) people, and microinfarcts were found in 128 (28.3%) people. Greater purpose in life was associated with a lower odds of having more macroscopic infarcts (odds ratio, 0.535; 95% confidence interval, 0.346-0.826; P=0.005), but we did not find association with microinfarcts (odds ratio, 0.780; 95% confidence interval, 0.495-1.229; P=0.283). These results persisted after adjusting for vascular risk factors of body mass index, history of smoking, diabetes mellitus, and blood pressure, as well as measures of negative affect, physical activity, and clinical stroke. The association with macroscopic infarcts was driven by lacunar infarcts, and was independent of cerebral atherosclerosis and arteriolosclerosis.

CONCLUSIONS

Purpose in life may affect risk for cerebral infarcts, specifically macroscopic lacunar infarcts.

Vascular contributions to cognitive impairment and dementia including Alzheimer's disease

Scientific evidence continues to demonstrate the linkage of vascular contributions to cognitive impairment and dementia such as Alzheimer's disease. In December, 2013, the Alzheimer's Association, with scientific input from the National Institute of Neurological Disorders and Stroke and the National Heart, Lung and Blood Institute from the National Institutes of Health, convened scientific experts to discuss the research gaps in our understanding of how vascular factors contribute to Alzheimer's disease and related dementia. This manuscript summarizes the meeting and the resultant discussion, including an outline of next steps needed to move this area of research forward.

α-Synuclein pathology accumulates in sacral spinal visceral sensory pathways

Urinary urgency and frequency are common in α-synucleinopathies such as Parkinson disease, Lewy body dementia, and multiple system atrophy. These symptoms cannot be managed with dopamine therapy, and their underlying pathophysiology is unclear. We show that in individuals with Parkinson disease, Lewy body dementia, or multiple system atrophy, α-synuclein pathology accumulates in the lateral collateral pathway, a region of the sacral spinal dorsal horn important for the relay of pelvic visceral afferents. Deposition of α-synuclein in this region may contribute to impaired micturition and/or constipation in Parkinson disease and other α-synucleinopathies.

Residual decline in cognition after adjustment for common neuropathologic conditions

OBJECTIVE

Neurodegenerative and cerebrovascular conditions are common in old age and are associated with cognitive decline. However, considerable heterogeneity remains in residual decline (i.e., person-specific trajectories of cognitive decline adjusted for these common neuropathologic conditions). The present study aimed to characterize profiles of residual decline in late life cognition.

METHOD

Up to 19 waves of longitudinal cognitive data were collected from 876 autopsied participants from 2 ongoing clinical-pathologic cohort studies of aging. Uniform neuropathologic examinations quantified measures of Alzheimer's disease, cerebral infarcts, Lewy body disease, and hippocampal sclerosis. Random effects mixture models characterized latent profiles of residual decline in global cognition.

RESULTS

We identified 4 latent groups, and each group demonstrated distinct residual decline profiles. On average, 44% of the participants had little or no decline, 35% showed moderate decline, 13% showed severe decline and the rest (8%) had substantial within-subject fluctuation of longitudinal cognitive measures. These latent groups differed in psychological, experiential and neurobiologic factors that have been previously shown to be associated with cognitive decline. Specifically, compared with nondecliners, decliners had more depressive symptoms, were more socially isolated; were less engaged in cognitive or physical activities; and had lower density of noradrenergic neurons in locus ceruleus.

CONCLUSIONS

After controlling for common dementia related pathologies, considerable residual variability remains in cognitive aging trajectories and this variability is not random but rather is related to markers of cognitive and neural reserve. The mixture modeling approach provides a powerful tool to identify latent groups with distinct cognitive trajectories.

A TREM1 variant alters the accumulation of Alzheimer-related amyloid pathology

OBJECTIVE

Genome-wide association studies have linked variants in TREM2 (triggering receptor expressed on myeloid cells 2) and TREML2 with Alzheimer disease (AD) and AD endophenotypes. Here, we pursue a targeted analysis of the TREM locus in relation to cognitive decline and pathological features of AD.

METHODS

Clinical, cognitive, and neuropathological phenotypes were collected in 3 prospective cohorts on aging (n = 3,421 subjects). Our primary analysis was an association with neuritic plaque pathology. To functionally characterize the associated variants, we used flow cytometry to measure TREM1 expression on monocytes.

RESULTS

We provide evidence that an intronic variant, rs6910730(G) , in TREM1, is associated with an increased burden of neuritic plaques (p = 3.7 × 10(-4) ), diffuse plaques (p = 4.1 × 10(-3) ), and Aβ density (p = 2.6 × 10(-3) ) as well as an increased rate of cognitive decline (p = 5.3 × 10(-3) ). A variant upstream of TREM2, rs7759295(C) , is independently associated with an increased tau tangle density (p = 4.9 × 10(-4) ), an increased burden of neurofibrillary tangles (p = 9.1 × 10(-3) ), and an increased rate of cognitive decline (p = 2.3 × 10(-3) ). Finally, a cytometric analysis shows that the TREM1 rs6910730(G) allele is associated with decreased TREM1 expression on the surface of myeloid cells (p = 1.7 × 10(-3) ).

INTERPRETATION

We provide evidence that 2 common variants within the TREM locus are associated with pathological features of AD and aging-related cognitive decline. Our evidence suggests that these variants are likely to be independent of known AD variants and that they may work through an alteration of myeloid cell function.

Alzheimer's loci: epigenetic associations and interaction with genetic factors

OBJECTIVE

We explore the role of DNA methylation in Alzheimer's disease (AD). To elucidate where DNA methylation falls along the causal pathway linking risk factors to disease, we examine causal models to assess its role in the pathology of AD.

METHODS

DNA methylation profiles were generated in 740 brain samples using the Illumina HumanMet450K beadset. We focused our analysis on CpG sites from 11 AD susceptibility gene regions. The primary outcome was a quantitative measure of neuritic amyloid plaque (NP), a key early element of AD pathology. We tested four causal models: (1) independent associations, (2) CpG mediating the association of a variant, (3) reverse causality, and (4) genetic variant by CpG interaction.

RESULTS

Six genes regions (17 CpGs) showed evidence of CpG associations with NP, independent of genetic variation - BIN1 (5), CLU (5), MS4A6A (3), ABCA7 (2), CD2AP (1), and APOE (1). Together they explained 16.8% of the variability in NP. An interaction effect was seen in the CR1 region for two CpGs, cg10021878 (P = 0.01) and cg05922028 (P = 0.001), in relation to NP. In both cases, subjects with the risk allele rs6656401(AT) (/) (AA) display more methylation being associated with more NP burden, whereas subjects with the rs6656401(TT) protective genotype have an inverse association with more methylation being associated with less NP.

INTERPRETATION

These observations suggest that, within known AD susceptibility loci, methylation is related to pathologic processes of AD and may play a largely independent role by influencing gene expression in AD susceptibility loci.