APOE ɛ4 exacerbates age-dependent deficits in cortical microstructure

Association between diffusion MRI-based measures of neurite microstructure and risk of Alzheimer's disease

Early detection of Alzheimer's disease (AD) is crucial for intervention, but traditional MRI and cognitive assessments may miss pre-symptomatic changes. Advanced diffusion MRI (dMRI) methods, such as Neurite Orientation Dispersion and Density Imaging (NODDI), show promise in identifying early brain changes. We analyzed 65 cognitively unimpaired older adults (25 APOE-e4 carriers, 40 non-carriers) from the ADNI3 dataset. NODDI's neurite density index (NDI) and orientation dispersion index (ODI), volumetric MRI and cognition (MoCA) were analyzed in key brain regions like the hippocampus, fusiform gyrus, and entorhinal cortex. Statistical analyses included linear regression and t-tests, with FDR correction. NDI differed significantly between carriers and non-carriers and correlated with MoCA scores. ODI differed only in the CA1 hippocampal subfield. Volumetric MRI measures showed no group differences. Significant APOE-e4 group differences were observed in NDI for the left fusiform gyrus (β = 0.015, p = 0.02), right fusiform gyrus (β = 0.018, p = 0.02), left entorhinal cortex (β = 0.018, p = 0.04), right entorhinal cortex (β = 0.018, p = 0.03), left CA1 (β = 0.03, p = 0.02), and left CA2-3 (β = 0.03, p = 0.02). ODI differences were observed only in left CA1 (β = 0.037, p = 0.008). No volumetric measures differed significantly. MoCA correlated with NDI in bilateral entorhinal cortices (p = 0.001-0.05), left fusiform gyrus (p = 0.02), and right CA2-3 (p = 0.02). NODDI metrics, particularly NDI, could help detect early APOE-e4-related microstructural changes, while traditional volumetric MRI measures remain uninformative at early stages.

Cortical microstructural abnormalities in dementia with Lewy bodies and their associations with Alzheimer's disease copathologies

Dementia with Lewy bodies (DLB) frequently coexists with Alzheimer's disease pathology, yet the pattern of cortical microstructural injury and its relationship with amyloid, tau, and cerebrovascular pathologies remains unclear. We applied neurite orientation dispersion and density imaging (NODDI) to assess cortical microstructural integrity in 57 individuals within the DLB spectrum and 57 age- and sex-matched cognitively unimpaired controls by quantifying mean diffusivity (MD), tissue-weighted neurite density index (tNDI), orientation dispersion index (ODI), and free water fraction (FWF). Amyloid and tau levels were measured using PiB and Flortaucipir PET imaging. Compared to controls, DLB exhibited increased MD and FWF, reduced tNDI across multiple regions, and focal ODI reductions in the occipital cortex. Structural equation modeling revealed that APOE genotype influenced amyloid levels, which elevated tau, leading to microstructural injury. These findings highlight the role of AD pathology in DLB neurodegeneration, advocating for multi-target therapeutic approaches addressing both AD and DLB-specific pathologies.

Hypothalamic volume, sleep, and APOE genotype in cognitively healthy adults

INTRODUCTION

Sleep dysfunction in those at higher risk of dementia may be associated with early structural changes to the hypothalamus.

METHODS

We used multivariate regression to analyze self-reported sleep (Pittsburgh Sleep Quality Index [PSQI]) from cognitively healthy participants in the PREVENT Dementia and Alzheimer's and Families (ALFA) studies (n = 1939), stratified by apolipoprotein E (APOE) genotype as homozygotes, heterozygotes, and non-carriers. FreeSurfer was used to extract hypothalamic subunit volumes from T1-weighted magnetic resonance images.

RESULTS

APOE ε4 homozygotes had a larger anterior-superior hypothalamus compared to heterozygotes and non-carriers, an effect which was driven by younger people in the cohort. APOE ε4 carriers had a higher PSQI global score after age 55, and smaller anterior-superior and tubular-superior subunits were associated with more sleep disturbances. Sleep duration and efficiency worsened with age, but only in participants with a small anterior-inferior hypothalamus.

DISCUSSION

This suggests that aging and APOE ε4 are associated with hypothalamic changes, highlighting mechanisms linking sleep dysfunction to dementia.

HIGHLIGHTS

Apolipoprotein E (APOE) ε4 homozygotes ha a larger anterior-superior hypothalamus. APOE ε4 carriers have worse sleep, but only after age 55. Worse sleep in APOE ε4 carriers was associated with smaller hypothalamic subunits. Higher age was associated with worse sleep in people with a small hypothalamus.

Influence of alpha-synuclein on glucose metabolism in Alzheimer's disease continuum: Analyses of α-synuclein seed amplification assay and FDG-PET

INTRODUCTION

We investigated the association between alpha-synuclein (α-syn) pathology and brain glucose metabolism across the cognitive spectrum of Alzheimer's disease (AD) co-pathologies.

METHODS

Fluorodeoxyglucose positron emission tomography (FDG-PET) data from 829 Alzheimer's Disease Neuroimaging Initiative participants (648 cognitively impaired [CI], 181 unimpaired [CU]) were compared between α-syn seed amplification assay (SAA) positive and negative groups. Interactions with cerebrospinal fluid (CSF) AD biomarkers were examined.

RESULTS

SAA+ was associated with widespread hypometabolism among CI individuals, particularly in posterior cortical regions, independent of CSF amyloid and tau levels in the occipital lobes. Regional hypometabolism mediated the effect of α-syn SAA on disease severity in CI individuals, independent of CSF amyloid and tau levels. There were no influences of SAA on FDG-PET in CU individuals.

DISCUSSION

This study supports a model in which α-syn aggregation influences metabolic dysfunction, which then influences clinical disease severity, independent of AD. SAA+ could help optimize participant selection and outcome measures for clinical trials in AD.

HIGHLIGHTS

α-synuclein seed amplification positivity (SAA+) was associated with hypometabolism in cognitively impaired individuals. Hypometabolism mediated the influence of α-synuclein on disease severity. Occipital hypometabolism in SAA+ was independent of cerebrospinal fluid levels of Alzheimer's disease pathology. These findings can optimize future clinical trials targeting α-synuclein pathology.

Brain age gap, dementia risk factors and cognition in middle age

Brain Age Gap has been associated with dementia in old age. Less is known relating brain age gap to dementia risk-factors or cognitive performance in middle-age. Cognitively healthy, middle-aged subjects from PREVENT-Dementia had comprehensive neuropsychological, neuroimaging and genetic assessments. Brain Ages were predicted from T1-weighted 3T MRI scans. Cognition was assessed using the COGNITO computerized test battery. 552 middle-aged participants (median [interquartile range] age 52.8 [8.7] years, 60.0% female) had baseline data, of whom 95 had amyloid PET data. Brain age gap in middle-age was associated with hypertension (P = 0.007) and alcohol intake (P = 0.008) but not apolipoprotein E epsilon 4 allele (P = 0.14), amyloid centiloids (P = 0.39) or cognitive performance (P = 0.74). Brain age gap in middle-age is associated with modifiable dementia risk-factors, but not with genetic risk for Alzheimer's disease, amyloid deposition or cognitive performance. These results are important for understanding brain-age in middle-aged populations, which might be optimally targeted by future dementia-preventing therapies.

Texture-based morphometry in relation to apolipoprotein ε4 genotype, ageing and sex in a midlife population

Brain atrophy and cortical thinning are typically observed in people with Alzheimer's disease (AD) and, to a lesser extent, in those with mild cognitive impairment. In asymptomatic middle-aged apolipoprotein ε4 (ΑPOE4) carriers, who are at higher risk of future AD, study reports are discordant with limited evidence of brain structural differences between carriers and non-carriers of the ε4 allele. Alternative imaging markers with higher sensitivity at the presymptomatic stage, ideally quantified using typically acquired structural MRI scans, would thus be of great benefit for the detection of early disease, disease monitoring and subject stratification. In the present cross-sectional study, we investigated textural properties of T1-weighted 3T MRI scans in relation to APOE4 genotype, age and sex. We pooled together data from the PREVENT-Dementia and ALFA studies focused on midlife healthy populations with dementia risk factors (analysable cohort: 1585 participants; mean age 56.2 ± 7.4 years). Voxel-based and texture (examined features: contrast, entropy, energy, homogeneity) based morphometry was used to identify areas of volumetric and textural differences between APOE4 carriers and non-carriers. Textural maps were generated and were subsequently harmonised using voxel-wise COMBAT. For all analyses, APOE4, sex, age and years of education were used as model predictors. Interactions between APOE4 and age were further examined. There were no group differences in regional brain volume or texture based on APOE4 carriership or when age × APOE4 interactions were examined. Older people tended to have a less homogeneous textural profile in grey and white matter and a more homogeneous profile in the ventricles. A more heterogeneous textural profile was observed for females in areas such as the ventricles, frontal and parietal lobes and for males in the brainstem, cerebellum, precuneus and cingulate. Overall, we have shown the absence of volumetric and textural differences between APOE4 carriers and non-carriers at midlife and have established associations of textural features with ageing and sex.