The in vivo topography of cortical changes in healthy aging and prodromal Alzheimer's disease

Diet enriched in omega-3 fatty acids alleviates olfactory system deficits in APOE4 transgenic mice

Olfactory dysfunction is observed in several neurological disorders including Mild Cognitive Impairment (MCI) and Alzheimer disease (AD). These deficits occur early and correlate with global cognitive performance, depression and degeneration of olfactory regions in the brain. Despite extensive human studies, there has been little characterization of the olfactory system in models of AD. In order to determine if olfactory structural and/or molecular phenotypes are observed in a model expressing a genetic risk factor for AD, we assessed the olfactory bulb (OB) in APOE4 transgenic mice. A significant decrease in OB weight was observed at 12 months of age in APOE4 mice concurrent with inflammation and decreased NeuN expression. In order to determine if a diet rich in omega-3s may alleviate the olfactory system phenotypes observed, we assessed WT and APOE4 mice on a docosahexaenoic acid (DHA) diet. APOE4 mice on a DHA diet did not present with atrophy of the OB, and the alterations in NeuN and IBA-1 expression were alleviated. Furthermore, alterations in caspase mRNA and protein expression in the APOE4 OB were not observed with a DHA diet. Similar to the human AD condition, OB atrophy is an early phenotype in the APOE4 mice and concurrent with inflammation. These data support a link between the structural olfactory brain region atrophy and the olfactory dysfunction observed in AD and suggest that inflammation and cell death pathways may contribute to the olfactory deficits observed. Furthermore, the results suggest that diets enriched in DHA may provide benefit to APOE4 allele carriers.

The C677T variant in MTHFR modulates associations between brain integrity, mood, and cognitive functioning in old age

INTRODUCTION

The C677T functional variant in the methylene-tetrahydrofolate reductase (MTHFR) gene leads to reduced enzymatic activity and elevated blood levels of homocysteine. Hyperhomocysteinemia has been linked with higher rates of cardiovascular diseases, cognitive decline, and late-life depression.

METHODS AND MATERIALS

Here, 3D magnetic resonance imaging data was analyzed from 738 individuals (age: 75.5 ± 6.8 years; 438 men/300 women) including 173 Alzheimer's patients, 359 subjects with mild cognitive impairment, and 206 healthy older adults, scanned as part of the Alzheimer's Disease Neuroimaging Initiative (ADNI).

RESULTS

We found that this variant associates with localized brain atrophy, after controlling for age, sex, and dementia status, in brain regions implicated in both intellectual and emotional functioning, notably the medial orbitofrontal cortices. The medial orbitofrontal cortex is involved in the cognitive modulation of emotional processes, and localized atrophy in this region was previously linked with both cognitive impairment and depressive symptoms. Here, we report that increased plasma homocysteine mediates the association between MTHFR genotype and lower medial orbitofrontal volumes, and that these volumes mediate the association between cognitive decline and depressed mood in this elderly cohort. We additionally show that vitamin B12 deficiency interacts with the C677T variant in the etiology of hyperhomocysteinemia.

CONCLUSION

This study sheds light on important relationships between vascular risk factors, age-related cognitive decline, and late-life depression, and represents a significant advance in our understanding of clinically relevant associations relating to MTHFR genotype.

Frontal delta event-related oscillations relate to frontal volume in mild cognitive impairment and healthy controls

Amnesic mild cognitive impairment (MCI) represents a risk of developing Alzheimer's disease (AD), but not all MCI subjects progress to dementia of AD type. Magnetic resonance imaging (MRI) of cortical and hippocampal atrophy supports early diagnosis of AD in MCI subjects, while frontal event-related oscillations (EROs) at delta frequencies (<4Hz) are appealing markers for this purpose, as they are both cost-effective and largely available. The present study tested the hypothesis that these EROs reflect cortical frontal neurodegeneration in the continuum between normal and amnesic MCI subjects. EROs and volumetric MRI data were recorded in 28 amnesic MCI and in 28 healthy elderly controls (HCs). EROs were collected during a standard visual oddball paradigm including frequent (66.6%) and rare (33.3%; targets to be mentally counted) stimuli. Peak-to-peak amplitude of delta target EROs (<4Hz) was measured. Volume of frontal cortex was estimated from MRIs. Frontal volume was lower in MCI compared to the HC group. Furthermore, widespread delta target EROs were lower in amplitude in the former than in the latter group. Finally, there was a positive correlation between frontal volume and frontal delta target EROs in MCI and HC subjects as a whole group. These results suggest that frontal delta EROs reflect frontal neurodegeneration in the continuum between normal and amnesic MCI subjects.