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

Although the APOE {varepsilon}4 allele is the strongest genetic risk factor for sporadic Alzheimers 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 A{beta}42/A{beta}40. 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. HighlightsO_LISimultaneous quantification of unmodified and O-glycosylated apoE via LC-MS/MS. C_LIO_LITotal plasma apoE varies by APOE genotype in an isoform, dose-dependent fashion. C_LIO_LICNS-derived apoE is more extensively O-glycosylated than peripherally derived apoE. C_LIO_LIHinge region glycosylation occupancy of plasma apoE is associated with amyloidosis. C_LI