Apolipoprotein E O-glycosylation is associated with amyloid plaques and APOE genotype

Although the APOE ε4 allele is the strongest genetic risk factor for sporadic Alzheimer’s disease (AD), the relationship between apolipoprotein (apoE) and AD pathophysiology is not yet fully understood. Relatively little is known about the apoE protein species, including post-translational modifications, that exist in the human periphery and CNS. To better understand these apoE species, we developed a LC-MS/MS assay that simultaneously quantifies both unmodified and O-glycosylated apoE peptides. The study cohort included 47 older individuals (age 75.6 ± 5.7 years [mean ± standard deviation]), including 23 individuals (49%) with cognitive impairment. Paired plasma and cerebrospinal fluid samples underwent analysis. We quantified O-glycosylation of two apoE protein residues – one in the hinge region and one in the C-terminal region – and found that glycosylation occupancy of the hinge region in the plasma was significantly correlated with plasma total apoE levels, APOE genotype and amyloid status as determined by CSF Aβ42/Aβ40. A model with plasma glycosylation occupancy, plasma total apoE concentration, and APOE genotype distinguished amyloid status with an AUROC of 0.89. These results suggest that plasma apoE glycosylation levels could be a marker of brain amyloidosis, and that apoE glycosylation may play a role in the pathophysiology of AD. Highlights ### Competing Interest Statement PEL reports no disclosures. JGB reports no disclosures. SES reports no disclosures. CRH reports no disclosures. NJI reports no disclosures. VK reports no disclosures. JBC reports no disclosures. YL reports no disclosures. DMH is an inventor on a patent licensed by Washington University to NextCure on the therapeutic use of anti-apoE antibodies. DMH co-founded, has equity, and is on the scientific advisory board of C2N Diagnostics. DMH is on the scientific advisory board of Denali and Cajal Neuroscience and consults for Genentech and Alector. RJB co-founded C2N Diagnostics. Washington University and RJB have equity ownership interest in C2N Diagnostics and receive royalty income based on technology (stable isotope labeling kinetics, blood plasma assay, and methods of diagnosing AD with phosphorylation changes) licensed by Washington University to C2N Diagnostics. RJB receives income from C2N Diagnostics for serving on the scientific advisory board. RJB has received research funding from Avid Radiopharmaceuticals, Janssen, Roche/Genentech, Eli Lilly, Eisai, Biogen, AbbVie, Bristol Myers Squibb, and Novartis.