A Targeted, Differential Top-Down Proteomic Methodology for Comparison of ApoA‑I Proteoforms in Individuals with High and Low HDL Efflux Capacity

• Published in: Journal of proteome research 2018-06, Vol.17 (6), p.2156-2164
• Main Authors: Seckler, Henrique dos Santos, Fornelli, Luca, Mutharasan, R. Kannan, Thaxton, C. Shad, Fellers, Ryan, Daviglus, Martha, Sniderman, Allan, Rader, Daniel, Kelleher, Neil L, Lloyd-Jones, Donald M, Compton, Philip D, Wilkins, John T
• Format: Article
• Language: English
• Subjects: Aged; alleles; allelic variation; apolipoprotein A-I; Apolipoprotein A-I - blood; Biological Transport; blood serum; cholesterol; Cholesterol - metabolism; coronary disease; dissociation; electron transfer; Female; high density lipoprotein; Humans; Lipoproteins, HDL - metabolism; Male; mass spectrometry; Mass Spectrometry - methods; monitoring; palmitoylation; Precision Medicine; Protein Processing, Post-Translational; proteome; proteomics; Proteomics - methods; risk; Specimen Handling
• ISSN: 1535-3893; 1535-3907; 1535-3907
• DOI: 10.1021/acs.jproteome.8b00100

Top-down proteomics (TDP) allows precise determination/characterization of the different proteoforms derived from the expression of a single gene. In this study, we targeted apolipoprotein A-I (ApoA-I), a mediator of high-density-lipoprotein cholesterol efflux (HDL-E), which is inversely associated with coronary heart disease risk. Absolute ApoA-I concentration and allelic variation only partially explain interindividual HDL-E variation. Therefore, we hypothesize that differences in HDL-E are associated with the abundances of different ApoA-I proteoforms. Here, we present a targeted TDP methodology to characterize ApoA-I proteoforms in serum samples and compare their abundances between individuals. We characterized 18 ApoA-I proteoforms using selected-ion monitoring coupled to electron-transfer dissociation mass spectrometry. We then compared the abundances of these proteoforms between two groups of four participants, representing the individuals with highest and lowest HDL-E values within the Chicago Healthy Aging Study (n = 420). Six proteoforms showed significantly (p < 0.0005) higher intensity in high HDL-E individuals: canonical ApoA-I [fold difference (fd) = 1.17], carboxymethylated ApoA-I (fd = 1.24) and, with highest difference, four fatty acylated forms: palmitoylated (fd = 2.16), oleoylated (fd = 2.08), arachidonoylated (fd = 2.31) and one bearing two modifications: palmitoylation and truncation (fd = 2.13). These results demonstrate translational potential for targeted TDP in revealing, with high sensitivity, associations between interindividual proteoform variation and physiological differences underlying disease risk.