The influence of APOE ε4 on the pTau interactome in sporadic Alzheimer's disease.

APOE ε4 is the major genetic risk factor for sporadic Alzheimer's disease (AD). Although APOE ε4 is known to promote Aβ pathology, recent data also support an effect of APOE polymorphism on phosphorylated Tau (pTau) pathology. To elucidate these potential effects, the pTau interactome was analyzed across APOE genotypes in the frontal cortex of 10 advanced AD cases (n = 5 APOE ε3/ε3 and n = 5 APOE ε4/ε4 ), using a combination of anti-pTau pS396/pS404 (PHF1) immunoprecipitation (IP) and mass spectrometry (MS). This proteomic approach was complemented by an analysis of anti-pTau PHF1 and anti-Aβ 4G8 immunohistochemistry, performed in the frontal cortex of 21 advanced AD cases (n = 11 APOE ε3/ε3 and n = 10 APOE ε4/ε4 ). Our dataset includes 1130 and 1330 proteins enriched in IP PHF1 samples from APOE ε3/ε3 and APOE ε4/ε4 groups (fold change ≥ 1.50, IP PHF1 vs IP IgG ctrl ). We identified 80 and 68 proteins as probable pTau interactors in APOE ε3/ε3 and APOE ε4/ε4 groups, respectively (SAINT score ≥ 0.80; false discovery rate (FDR) ≤ 5%). A total of 47/80 proteins were identified as more likely to interact with pTau in APOE ε3/ε3 vs APOE ε4/ε4 cases. Functional enrichment analyses showed that they were significantly associated with the nucleoplasm compartment and involved in RNA processing. In contrast, 35/68 proteins were identified as more likely to interact with pTau in APOE ε4/ε4 vs APOE ε3/ε3 cases. They were significantly associated with the synaptic compartment and involved in cellular transport. A characterization of Tau pathology in the frontal cortex showed a higher density of plaque-associated neuritic crowns, made of dystrophic axons and synapses, in APOE ε4 carriers. Cerebral amyloid angiopathy was more frequent and severe in APOE ε4/ε4 cases. Our study supports an influence of APOE genotype on pTau-subcellular location in AD. These results suggest a facilitation of pTau progression to Aβ-affected brain regions in APOE ε4 carriers, paving the way to the identification of new therapeutic targets.