Eicosapentaenoic Acid Is Associated with Decreased Incidence of Alzheimer's Dementia in the Oldest Old

BACKGROUND

Omega-3 (n-3) and omega-6 (n-6) polyunsaturated fatty acids (PUFAs) may have different effects on cognitive health due to their anti- or pro-inflammatory properties.

METHODS

We aimed to prospectively examine the relationships between n-3 and n-6 PUFA contents in serum phospholipids with incident all-cause dementia and Alzheimer's disease dementia (AD). We included 1264 non-demented participants aged 84 ± 3 years from the German Study on Ageing, Cognition, and Dementia in Primary Care Patients (AgeCoDe) multicenter-cohort study. We investigated whether fatty acid concentrations in serum phospholipids, especially eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), alpha-linolenic acid (ALA), linoleic acid (LA), dihomo-γ-linolenic acid (DGLA), and arachidonic acid (AA), were associated with risk of incident all-cause dementia and AD.

RESULTS

During the follow-up window of seven years, 233 participants developed dementia. Higher concentrations of EPA were associated with a lower incidence of AD (hazard ratio (HR) 0.76 (95% CI 0.63; 0.93)). We also observed that higher concentrations of EPA were associated with a decreased risk for all-cause dementia (HR 0.76 (95% CI 0.61; 0.94)) and AD (HR 0.66 (95% CI 0.51; 0.85)) among apolipoprotein E ε4 (APOE ε4) non-carriers but not among APOE ε4 carriers. No other fatty acids were significantly associated with AD or dementia.

CONCLUSIONS

Higher concentrations of EPA were associated with a lower risk of incident AD. This further supports a beneficial role of n-3 PUFAs for cognitive health in old age.

PLCG2 protective variant p.P522R modulates tau pathology and disease progression in patients with mild cognitive impairment

A rare coding variant (rs72824905, p.P522R) conferring protection against Alzheimer’s disease (AD) was identified in the gene encoding the enzyme phospholipase-C-γ2 (PLCG2) that is highly expressed in microglia. To explore the protective nature of this variant, we employed latent process linear mixed models to examine the association of p.P522R with longitudinal cognitive decline in 3595 MCI patients, and in 10,097 individuals from population-based studies. Furthermore, association with CSF levels of pTau₁₈₁, total tau, and Aβ_1-42 was assessed in 1261 MCI patients. We found that MCI patients who carried the p.P522R variant showed a slower rate of cognitive decline compared to non-carriers and that this effect was mediated by lower pTau₁₈₁ levels in CSF. The effect size of the association of p.P522R with the cognitive decline and pTau₁₈₁ was similar to that of APOE-ε4, the strongest genetic risk factor for AD. Interestingly, the protective effect of p.P522R was more pronounced in MCI patients with low Aβ_1-42 levels suggesting a role of PLCG2 in the response to amyloid pathology. In line with this hypothesis, we observed no protective effect of the PLCG2 variant on the cognitive decline in population-based studies probably due to the lower prevalence of amyloid positivity in these samples compared to MCI patients. Concerning the potential biological underpinnings, we identified a network of co-expressed proteins connecting PLCG2 to APOE and TREM2 using unsupervised co-regulatory network analysis. The network was highly enriched for the complement cascade and genes differentially expressed in disease-associated microglia. Our data show that p.P522R in PLCG2 reduces AD disease progression by mitigating tau pathology in the presence of amyloid pathology and, as a consequence, maintains cognitive function. Targeting the enzyme PLCG2 might provide a new therapeutic approach for treating AD.

Genetik der Alzheimer-Krankheit

Die Alzheimer-Erkrankung („Alzheimer’s disease“, AD) ist die häufigste Ursache der neurodegenerativen Demenzen. Im Gegensatz zu monogenen und meist frühmanifesten Formen der AD, welche auf hochpenetrante Mutationen in den Genen APP, PSEN1 und PSEN2 zurückzuführen sind, wird die Suszeptibilität für die sporadische, oft spätmanifeste Form der AD durch eine komplexe Wechselwirkung zwischen genetischen und epigenetischen Faktoren wie auch umwelt- und lebensstilbedingten Faktoren bestimmt. Obgleich APOE ε4 der stärkste genetische Risikofaktor für die AD ist, macht der Effekt des APOE ε4 lediglich 27,3 % der geschätzten Heritabilität von 58–79 % aus. Durch den kontinuierlichen technischen Fortschritt von GWAS (genomweite Assoziationsstudien) und automatisierten Sequenziermethoden der nächsten Generation gelingt es Wissenschaftlern in groß angelegten Kollaborationen sukzessive die fehlende Heritabilität aufzudecken. Wichtige Erkenntnisse aus GWAS und Signalweganalysen suggerieren, dass Mikroglia, die residenten Immunzellen des ZNS, eine entscheidende Rolle bei der Pathogenese der AD spielen. Eine beachtliche Anzahl der in genetischen Studien identifizierten Risikogene weisen immunsystembezogene Funktionen auf und werden in höchstem Maße von Mikroglia exprimiert. Durch die Beschreibung von Risikovarianten in CR1, CLU, SPI1, CD33, MS4A, ABCA7, EPHA1, HLA-DRB5/1, INPP5D, TYROBP, TREM2, PLCG2 und ABI3 nimmt die Mikroglia vermittelte Immunantwort bei der Pathogenese der AD eine zentrale Rolle ein. Von besonderer Bedeutung könnte sein, dass die PLCγ2-Variante p.P522R einen protektiven Effekt auf die LOAD („late-onset“ AD; spätmanifeste Form der AD) ausübt und als Enzym ein klassisches Ziel für eine therapeutische Modulation von komplexen Formen der AD darstellt.

Genetic estimators of DNA methylation provide insights into the molecular basis of polygenic traits

The large biological distance between genetic risk loci and their mechanistic consequences in the tissue of interest limits the ability to establish functionality of susceptibility variants for genetically complex traits. Such a biological gap may be reduced through the systematic study of molecular mediators of genomic action, such as epigenetic modification. Here, we report the identification of robust genetic estimators of whole-blood CpG methylation, which can serve as intermediate molecular traits amenable to association testing with other genetically complex traits. We describe the relationship between these estimators and gene expression, demonstrate their genome-wide applicability to association testing even in the absence of individual genotypic data, and show that these estimators powerfully identify methylation-related genomic loci associated with polygenic traits and common diseases, such as schizophrenia. The use of genetic estimators for blood DNA methylation, which are made publically available, can serve as a valuable tool for the identification of epigenetic underpinnings of complex traits.