Distinct Patterns Link the BDNF Val66Met Polymorphism to Alzheimer's Disease Pathology.

The brain-derived neurotropic growth factor (BDNF) gene has been linked to dementia, inflammation, and Apolipoprotein E (APOE) ɛ4 status. We used cerebrospinal fluid (CSF) amyloid-ß (Aß)42 and phosphorylated tau (p-tau) to investigate associations with BDNF polymorphisms and modifications by APOE ɛ4 or inflammation in a memory clinic population (n = 114; subjective cognitive decline, mild cognitive impairment, Alzheimer's disease). We found distinct pathways to Alzheimer's disease pathology: Val-Met displayed lower CSF-Aß42 in APOE ɛ4+ carriers, independent of p-tau, while Val-Val displayed greater p-tau at higher IL-6 and sub-threshold Aß42. This may contribute to resolving some inconsistencies in the BDNF literature and provide possible inroads to specific Aß and tau interventions depending on BDNF polymorphism.

Worry Modifies the Relationship between Locus Coeruleus Activity and Emotional Mnemonic Discrimination.

BACKGROUND: The locus coeruleus (LC) plays a critical role in modulating emotional memory performance via widespread connections to the medial temporal lobe (MTL). Interestingly, both the LC and MTL are affected during aging. Therefore, we aimed to investigate whether worry during cognitive aging changes the relationship between memory performance and the neural activity patterns during an emotional memory task. METHODS: Twenty-eight participants aged 60-83 years from the Maastricht Aging study conducted an emotional mnemonic discrimination task during a 7T fMRI-scan. We performed a robust multiple linear regression to examine the association between worry and mnemonic memory performance under different levels of arousal. Subsequently, we examined if worry modifies the relationship between neuronal activity and mnemonic memory performance. RESULTS: We observed that under low arousal, only participants with low compared to high levels of worry benefitted from additional LC activity. Under high arousal, additional LC activity was associated with lower mnemonic memory performance. CONCLUSION: Our results suggest there might be an optimal involvement of the NA-system for optimal memory discrimination performance, as we observed that under low levels of worry and with lower levels of arousal, higher LC activity might be needed to achieve similar levels of optimal memory performance as achieved under higher arousal when LC activity remained lower.

Associations between locus coeruleus integrity and nocturnal awakenings in the context of Alzheimer's disease plasma biomarkers: a 7T MRI study.

BACKGROUND: The brainstem locus coeruleus (LC) constitutes the intersection of the initial pathophysiological processes of Alzheimer's disease (AD) and sleep-wake dysregulation in the preclinical stages of the disease. However, the interplay between in vivo assessment of LC degeneration and AD-related sleep alterations remains unknown. Here, we sought to investigate whether MRI-assessed LC structural integrity relates to subjective sleep-wake measures in the context of AD plasma biomarkers, in cognitively unimpaired older individuals. METHODS: Seventy-two cognitively unimpaired older individuals aged 50-85 years (mean age = 65.2 ± 8.2 years, 37 women, 21 APOE ε4 carriers) underwent high-resolution imaging of the LC at 7 Tesla, and LC structural integrity was quantified using a data-driven approach. Reports on habitual sleep quality and nocturnal awakenings were collected using sleep questionnaires. Plasma levels of total tau, p-tau181, Aß40, and Aß42 were measured using single-molecule array technology. RESULTS: Intensity-based cluster analyses indicated two distinct LC segments, with one covering the middle-to-caudal LC and displaying lower intensity compared to the middle-to-rostral cluster (t70 = -5.12, p < 0.0001). After correction for age, sex, depression, and APOE status, lower MRI signal intensity within the middle-to-caudal LC was associated with a higher number of self-reported nocturnal awakenings (F1,63 = 6.73, pFDR = 0.03). Furthermore, this association was mostly evident in individuals with elevated levels of total tau in the plasma (F1,61 = 4.26, p = 0.04). CONCLUSION: Our findings provide in vivo evidence that worse LC structural integrity is associated with more frequent nocturnal awakenings in the context of neurodegeneration, in cognitively unimpaired older individuals. These results support the critical role of the LC for sleep-wake regulation in the preclinical stages of AD and hold promises for the identification of at-risk populations for preventive interventions.

Elevated norepinephrine metabolism is linked to cortical thickness in the context of Alzheimer's disease pathology.

Advanced Alzheimer's disease (AD) is characterized by higher noradrenaline metabolite levels that may be associated with AD pathology. The locus coeruleus (LC) is the main site for cerebral noradrenaline synthesis and LC volume loss occurs as early as Braak stage 1. This study investigates the association between noradrenergic turnover and brain morphology, and the modifying effect of AD pathology. The study sample included 77 memory clinic patients (37 cognitively unimpaired and 40 cognitively impaired (mild cognitive impairment or AD dementia)). Cortical thickness and volumetric analyses were performed using FreeSurfer. Cerebrospinal fluid was analyzed for noradrenergic metabolite 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG), Aß42 and phosphorylated tau. Higher MHPG was associated with lower cortical thickness and hippocampal volume at lower, but subthreshold, levels of Aß42 and at higher p-tau levels. These associations remained significant after adding APOE-E4 or cognitive status as covariates. Our results suggest that greater MHPG together with worse AD pathology contributes to neurodegeneration, possibly before significant amyloidosis. The noradrenergic system may play an important role in early detection of AD-related processes.

Inter-network connectivity and amyloid-beta linked to cognitive decline in preclinical Alzheimer's disease: a longitudinal cohort study.

BACKGROUND: Amyloid-beta (Aß) has a dose-response relationship with cognition in healthy adults. Additionally, the levels of functional connectivity within and between brain networks have been associated with cognitive performance in healthy adults. Aiming to explore potential synergistic effects, we investigated the relationship of inter-network functional connectivity, Aß burden, and memory decline among healthy individuals and individuals with preclinical, prodromal, or clinical Alzheimer's disease. METHODS: In this longitudinal cohort study (ADNI2), participants (55-88 years) were followed for a maximum of 5 years. We included cognitively healthy participants and patients with mild cognitive impairment (with or without elevated Aß) or Alzheimer's disease. Associations between memory decline, Aß burden, and connectivity between networks across the groups were investigated using linear and curvilinear mixed-effects models. RESULTS: We found a synergistic relationships between inter-network functional connectivity and Aß burden on memory decline. Dose-response relationships between Aß and memory decline varied as a function of directionality of inter-network connectivity across groups. When inter-network correlations were negative, the curvilinear mixed-effects models revealed that higher Aß burden was associated with greater memory decline in cognitively normal participants, but when inter-network correlations were positive, there was no association between the magnitude of Aß burden and memory decline. Opposite patterns were observed in patients with mild cognitive impairment. Combining negative inter-network correlations with Aß burden can reduce the required sample size by 88% for clinical trials aiming to slow down memory decline. CONCLUSIONS: The direction of inter-network connectivity provides additional information about Aß burden on the rate of expected memory decline, especially in the preclinical phase. These results may be valuable for optimizing patient selection and decreasing study times to assess efficacy in clinical trials.