The role of FUT8‐catalyzed core fucosylation in Alzheimer’s amyloid‐β oligomer‐induced activation of human microglia

Abstract Background A previous RNA‐seq study of human Alzheimer’s disease (AD) brain samples revealed significant upregulation of FUT8 coding for α1‐6 fucosyltransferase in parahippocampal gyrus, suggesting a role of FUT8 and the core fucosylation it catalyzes in early AD. Despite the well‐recognized roles of core fucosylation in immune regulation, its significance in microglial function, especially in neurodegenerative conditions such as AD, has rarely been studied. Method Human microglia derived from induced pluripotent stem cells (iMG) were used as the model system. To simulate microglia in the early stage of AD, we stimulated iMG derived from a subject of APOE3/3 genotype with amyloid‐β oligomer (AβO, 3 μM). The degree of microglia activation was determined by cytokine induction and MAPK phosphorylation. Lectins were used in flow cytometry, cytochemical staining, and lectin blotting to determine the changes in core fucosylation. Fucosylation was also examined by MS/MS‐based N‐glycan analysis. FUT8 expression in brain or cell samples was determined by quantitative PCR and Western blotting. FUT8 inhibition was induced by siRNA‐mediated gene silencing. The transcriptional regulation of FUT8 was investigated by ChIP‐PCR using p53 antibodies. Result Human iMG responded to AβO with a pattern of pro‐inflammatory activation within 24 hours. Using two lectins specifically recognizing α1,6 core fucose, AAL and LCA, in flow cytometry and fluorescence staining, we showed that such an activation was associated with increased core fucosylation. This observation will be further verified by N‐glycomic analysis. Inhibition of fucosylation by two inhibitors, 2FF and 6‐Alk‐Fuc, as well as FUT8 knockdown by specific siRNAs suppressed AβO‐induced iMG activation. AβO‐activated iMG also showed increased protein levels of FUT8 and p53. Because p53 was previously shown to be a direct transcriptional activator of FUT8 in tumor cells, we will test whether p53 is responsible for FUT8 upregulation by ChIP‐PCR. The in vivo relevance of our results is supported by qPCR results showing increased levels of FUT8 transcript in human temporal cortex, 5xFAD mouse cortex, and microglia isolated from 5xFAD mice. Conclusion Our data suggests that FUT8‐catalyzed α1‐6 core fucosylation is required for AβO‐induced microglia activation and may play a role in the pathogenesis of AD.