In Vivo Metabolic Labeling with an Isoprenoid Probe Reveals APOE Allele-Specific Differences in the Prenylome

Prenylation is a ubiquitous process in eukaryotes consisting of the irreversible post-translational modification of proteins through the attachment of a lipophilic isoprenoid moiety to a cysteine residue near their C-terminus. Due to the important functional roles of prenylated proteins, their participation and/or dysregulation has been linked to numerous diseases, including ALS, progeria, cancer, and Alzheimer's disease (AD). In humans, the APOE4 variant is the greatest known genetic risk factor for late-onset sporadic AD with carriers of two E4 alleles having up to 15 times the risk of developing AD. To begin to unravel the potential relationship between protein prenylation, AD, and APOE variants, it is necessary to study whether different APOE genotypes affect protein prenylation systemically. In the work described here, a methodology for metabolic labeling of prenylated proteins in living mice was first developed. It was then applied to humanized mouse strains that carry human APOE3 or APOE4 alleles. Prenylomic profiling revealed that a number of prenylated proteins were present at higher levels in animals harboring the APOE4 gene compared with those with the APOE3 allele, especially in the liver─a major APOE-producing organ. Importantly, some of these proteins have links to AD neuropathology.