Mass Spectrometric Studies of Apolipoprotein Proteoforms and Their Role in Lipid Metabolism and Type 2 Diabetes

Abstract

Apolipoproteins function as structural components of lipoprotein particles, cofactors for enzymes, and ligands for cell-surface receptors. Most of the apoliporoteins exhibit proteoforms, arising from single nucleotide polymorphisms (SNPs) and post-translational modifications such as glycosylation, oxidation, and sequence truncations. Reviewed here are recent studies correlating apolipoproteins proteoforms with the specific clinical measures of lipid metabolism and cardiometabolic risk. Targeted mass spectrometric immunoassays toward apolipoproteins A-I, A-II, and C-III were applied on large cross-sectional and longitudinal clinical cohorts. Several correlations were observed, including greater apolipoprotein A-I and A-II oxidation in patients with diabetes and cardiovascular disease, and a divergent apoC-III proteoforms association with plasma triglycerides, indicating significant differences in the metabolism of the individual apoC-III proteoforms. These are the first studies of their kind, correlating specific proteoforms with clinical measures in order to determine their utility as potential clinical biomarkers for disease diagnosis, risk stratification, and therapy decisions. Such studies provide the impetus for the further development and clinical translation of MS-based protein tests.

Simple and Fast Assay for Apolipoprotein E Phenotyping and Glycotyping: Discovering Isoform-Specific Glycosylation in Plasma and Cerebrospinal Fluid

“…The assay was comprised of two steps: 1) immunocapture of apoE from samples using anti-apoE antibody immobilized within a porous microcolumn inside a pipettor tip, and 2) elution and detection of the captured intact apoE with MALDI-TOF MS. This method has been utilized for the analysis of several other proteins [33,34]. The workflow for the assay is shown in Fig.…”

Emerging evidences for the opposite role of apolipoprotein C3 and apolipoprotein A5 in lipid metabolism and coronary artery disease

“…The rest other three all have a core glycan chain made of an O-linked disaccharide galactose linked to N-acetylgalactosamine. ApoC3 0b is the proteoform that just contain the glycan core, while apoC3 1 and apoC3 2 contain additional one and two sialic acid residues, respectively [45]. Moreover, four major proteoforms of apoC3 differentially correlated to fasting TG levels.…”

“…Moreover, four major proteoforms of apoC3 differentially correlated to fasting TG levels. It has been found that, using mass spectrometric immunoassay measurement, plasma apoC3 0a , apoC3 0b , and apoC3 1 had positive while apoC3 2 had negative relationship with fasting plasma TG [45], suggesting that analysis of individual isoforms of apoC3 could provide more comprehensive information than total plasma apoC3 concentration only.…”

“…Consistently, in a cohort of 75,725 participants, the cumulative incidences of ischemic vascular disease and ischemic heart disease were reduced in heterozygotes for loss-of-function mutations in APOC3 (R19X or A43T or IVS2 + 1G → A) as compared with noncarriers, with corresponding risk reductions of 41% and 36% [4]. Noticeably, it has been reported that there was also a trend for fewer major adverse cardiovascular disease events in patients with higher apoC3 2 proteoform, while these associations were not detected for the other apoC3 proteoforms, suggesting apoC3 2 is more like a loss-of-function proteoform [45].…”

Proteomic Toolbox To Standardize the Separation of Extracellular Vesicles and Lipoprotein Particles

“…Lastly, both EVs and LPs carry glycosylated proteins with a different pattern of glycosylation. 31,32 Lectins are proteins that can reversibly and highly specifically bind glycoproteins, giving credence to use immobilized lectin, ConA, for potential EVs and LPs separation.…”