Project description:ImportanceAllelic variation in the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism moderates increases in cerebrospinal fluid (CSF) levels of tau and phosphorylated tau 181 (p-tau181), measured using immunoassay, and cognitive decline in presymptomatic dominantly inherited Alzheimer disease (DIAD). Advances in mass spectrometry show that CSF tau phosphorylation occupancy at threonine 181 and 217 (p-tau181/tau181, p-tau217/tau217) increases with initial β-amyloid (Aβ) aggregation, while phosphorylation occupancy at threonine 205 (p-tau205/tau205) and level of total tau increase when brain atrophy and clinical symptoms become evident.ObjectiveTo determine whether site-specific tau phosphorylation occupancy (ratio of phosphorylated to unphosphorylated tau) is associated with BDNF Val66Met in presymptomatic and symptomatic DIAD.Design, setting, and participantsThis cross-sectional cohort study included participants from the Dominantly Inherited Alzheimer Network (DIAN) and Aβ-positive cognitively normal older adults in the Alzheimer's Disease Neuroimaging Initiative (ADNI). Data were collected from 2009 through 2018 at multicenter clinical sites in the United States, United Kingdom, and Australia, with no follow-up. DIAN participants provided a CSF sample and completed clinical and cognitive assessments. Data analysis was conducted between March 2020 and March 2021.Main outcomes and measuresMass spectrometry analysis was used to determine site-specific tau phosphorylation level; tau levels were also measured using immunoassay. Episodic memory and global cognitive composites were computed.ResultsOf 374 study participants, 144 were mutation noncarriers, 156 were presymptomatic mutation carriers, and 74 were symptomatic carriers. Of the 527 participants in the network, 153 were excluded because their CSF sample, BDNF status, or both were unavailable. Also included were 125 Aβ-positive cognitively normal older adults in the ADNI. The mean (SD) age of DIAD participants was 38.7 (10.9) years; 43% were women. The mean (SD) age of participants with preclinical sporadic AD was 74.8 (5.6) years; 52% were women. In presymptomatic mutation carriers, compared with Val66 homozygotes, Met66 carriers showed significantly poorer episodic memory (d = 0.62; 95% CI, 0.28-0.95), lower hippocampal volume (d = 0.40; 95% CI, 0.09-0.71), and higher p-tau217/tau217 (d = 0.64; 95% CI, 0.30-0.97), p-tau181/tau181 (d = 0.65; 95% CI, 0.32-0.99), and mass spectrometry total tau (d = 0.43; 95% CI, 0.10-0.76). In symptomatic mutation carriers, Met66 carriers showed significantly poorer global cognition (d = 1.17; 95% CI, 0.65-1.66) and higher p-tau217/tau217 (d = 0.53; 95% CI, 0.05-1.01), mass spectrometry total tau (d = 0.78; 95% CI, 0.28-1.25), and p-tau205/tau205 (d = 0.97; 95% CI, 0.46-1.45), when compared with Val66 homozygotes. In preclinical sporadic AD, Met66 carriers showed poorer episodic memory (d = 0.39; 95% CI, 0.00-0.77) and higher total tau (d = 0.45; 95% CI, 0.07-0.84) and p-tau181 (d = 0.46; 95% CI, 0.07-0.85).Conclusions and relevanceIn DIAD, clinical disease stage and BDNF Met66 were associated with cognitive impairment and levels of site-specific tau phosphorylation. This suggests that pharmacological strategies designed to increase neurotrophic support in the presymptomatic stages of AD may be beneficial.

Project description:Lifestyle-based interventions, including dietary modifications, can reduce dementia risk. In this regard, dietary supplementation with medium-chain triglycerides (MCT) shows promise against Alzheimer’s disease in humans. This effect is widely presumed to be mediated by hepatic conversion of MCT into circulating ketones. However, the physiological and cellular mechanisms underlying the benefits of MCT remain understudied, particularly in the context of Alzheimer’s disease. Here, we investigated the cellular and molecular changes occurring in the brain and systemically in response to dietary supplementation with MCT versus a classic ketogenic diet (KD). The experimental design consisted of comparing a 70% carbohydrate control diet to either a control diet supplemented with 10% MCT or a carbohydrate-free high fat KD. Diets were tested in two Alzheimer’s disease mouse models, slow-progressing 3xTg-AD mice that model pre-symptomatic/early stages and rapidly-progressing 5xFAD mice that model late stages of the disease. We found that MCT supplementation and KD both improved hippocampal-dependent spatial learning and memory, increased dendritic spine density of hippocampal neurons, and modulated hippocampal expression of genes associated with mitochondrial functions, synaptic structure, and insulin signaling in Alzheimer’s disease mouse models. However, unlike KD,MCT supplementation did not elevate circulating ketones, suggesting different mechanisms. Indeed, while MCT enhanced the peripheral insulin response of Alzheimer’s disease mice, KD conversely unveiled their latent metabolic vulnerability, increasing their hyperglycemia, body weight gain, and adiposity. The systemic metabolic disturbances of Alzheimer’s disease mice correlated with transcriptomic alterations in hepatic lipid metabolism and ketogenesis genes and increased lipid droplet accumulation. These liver metabolic abnormalities were partially reversed by both MCT supplementation and KD, but in distinct ways. Notably, KD selectively triggered hepatic neutral lipid depletion and prominent proinflammatory gene expression while MCT down-regulated expression of cholesterol-related genes. Collectively, these findings reveal that MCT supplementation in the context of Alzheimer’s disease improves cognition and systemic metabolism without elevating circulating ketone levels.

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Neural stem cells improve cognition via BDNF in a transgenic model of Alzheimer disease.

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Neural stem cells improve cognition via BDNF in a transgenic model of Alzheimer disease.

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