TREM2 AD risk variants impact pTau and microglia and astrocyte related biomarkers in cognitively unimpaired subjects

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AbstractBackgroundIn the central nervous system, Triggering Receptor Expressed on Myeloid Cells 2 (TREM2) is expressed primarily in microglia. TREM2 receptors are important for microglial functions including phagocytosis, lipid metabolism and inflammatory responses. TREM2 coding variants (e.g. R47H rs75932628 and R62H rs143332484) increase the risk of late onset Alzheimer’s Diseases (AD). However, the impact of TREM2 risk variants on microglial cell functions in humans remains to be elucidated.MethodCSF and plasma samples were collected from AD patients (n = 120) and cognitively unimpaired control subjects (n = 53) with subjective complaints who do not meet biomarker‐based criteria for AD diagnosis. TREM2 AD risk variant carriers (n = 52) were screened from over 6000 samples of the Amsterdam dementia cohort using a combination of genotype array and exome sequencing. We performed extensive biomarker analysis of CSF and plasma samples with multidisciplinary approaches. We compared the effect of TREM2 mutations on AD disease and microglial and astrocytic biomarkers in AD patients and in cognitively unimpaired control subjects, respectively. A linear model was used with age and gender adjusted for the data analysis.ResultWe found higher levels of pTau181 and pTau231 in CSF and plasma in cognitively unimpaired TREM2 mutation carriers compared to non‐carriers, while no difference was observed between TREM2 genotype among the AD patients. Microglia and astrocyte biomarkers including sTREM2, FABP3, OLR1, YKL40 and GFAP were higher in the CSF from cognitively unimpaired TREM2 mutation carriers compared to non‐carriers, but no difference was detected between TREM2 genotype among the AD patients. We also found different levels of lipid metabolites in CSF and plasma samples from the TREM2 mutation carriers compared to non‐carriers in both AD patients and cognitively unimpaired control subjects.ConclusionTREM2 AD risk variants in cognitively unimpaired subjects increase pTau biomarkers and microglial and astrocytic related biomarkers. In AD patients, the biomarker differences between TREM2 genotype are diminished likely due to the extensive microglial responses to AD pathology. Moreover, our data indicates TREM2 AD risk variants may impact lipid‐metabolic processes in microglial cells. These data provide the biomarker insights on how TREM2 mutations may increase the risk of AD.