Plasma N-Glycoproteomics in monozygotic twin pairs discordant for body mass index reveals an obesity signature related to inflammation and iron metabolism.

Abstract

Background: N-glycosylation is a complex, post-translational modification which influences protein function and is sensitive to physiological changes. Obesity is associated with alterations in protein function; however, little is known about the glycoproteome in obesity beyond observations of association with types and structures of selected glycopeptides. Most often, due to technical challenges, glycan composition and structure information are missing. Here, we combined label-free data-independent proteomics and targeted quantitative glycoproteomics to study N-glycosylation of plasma proteins in obesity. Using a monozygotic twin study design, we controlled for genetic variation and focused only on the acquired effects of obesity.

Methods: Using plasma samples of 48 monozygotic twin pairs discordant for BMI (intrapair difference > 2.5 kg/m²), we identified using mass spectrometry, differential protein and glycopeptide levels between heavier and leaner co-twins. We used a within-twin paired analysis model and considered p < 0.05 as significant.

Results: We identified 48 protein and 33 N-glycosylation expression differences (p < 0.05) between co-twins. These differences occurred either both in the protein expression and glycoprotein (sometimes in opposing directions) or independently from each other. Haptoglobin protein was upregulated (Fold Change = 1.10, p = 0.001) in heavier co-twins along with seven upregulated glycan compositions at N-glycosylation site Asn241. The complement protein C3 was upregulated (Fold Change = 1.08, p = 0.014) along with one upregulated glycopeptide at Asn85. Additionally, many glycopeptides were upregulated despite non-significant differences in protein-backbone plasma levels.

Conclusion: Differential protein expression related to cholesterol biosynthesis and acute phase signalling as well as N-glycosylation of proteins related to iron metabolism and inflammation can be linked to acquired obesity.