Glycans are a novel biomarker of chronological and biological ages

Abstract

Fine structural details of glycans attached to the conserved N-glycosylation site significantly not only affect function of individual immunoglobulin G (IgG) molecules but also mediate inflammation at the systemic level. By analyzing IgG glycosylation in 5,117 individuals from four European populations, we have revealed very complex patterns of changes in IgG glycosylation with age. Several IgG glycans (including FA2B, FA2G2, and FA2BG2) changed considerably with age and the combination of these three glycans can explain up to 58% of variance in chronological age, significantly more than other markers of biological age like telomere lengths. The remaining variance in these glycans strongly correlated with physiological parameters associated with biological age. Thus, IgG glycosylation appears to be closely linked with both chronological and biological ages. Considering the important role of IgG glycans in inflammation, and because the observed changes with age promote inflammation, changes in IgG glycosylation also seem to represent a factor contributing to aging.

Significance statement: Glycosylation is the key posttranslational mechanism that regulates function of immunoglobulins, with multiple systemic repercussions to the immune system. Our study of IgG glycosylation in 5,117 individuals from four European populations has revealed very extensive and complex changes in IgG glycosylation with age. The combined index composed of only three glycans explained up to 58% of variance in age, considerably more than other biomarkers of age like telomere lengths. The remaining variance in these glycans strongly correlated with physiological parameters associated with biological age; thus, IgG glycosylation appears to be closely linked with both chronological and biological ages. The ability to measure human biological aging using molecular profiling has practical applications for diverse fields such as disease prevention and treatment, or forensics.

Keywords: Aging; Glycome; Glycosylation; Immunoglobulin G; Inflammation..

Figure 1.

UPLC analysis of immunoglobulin G (IgG) glycosylation. Each IgG contains one conserved N-glycosylation site on Asn₁₉₇ of its heavy chain. Different glycans can be attached to this site and the process seems to be highly regulated. UPLC analysis can reveal composition of the glycome attached to a population of IgG molecules by separating total IgG N-glycome into 24 chromatographic glycan peaks (GP1–GP24), mostly corresponding to individual glycan structures.

Figure 2.

Relationship between age and selected glycan structures. Plots indicate associations between the individual contributions of four selected glycan structures to the total immunoglobulin G glycome and chronological age in four different human populations. Blue and red curves are fitted local regression models describing gender-specific relationship between age and glycan structure. The shaded region is a pointwise 95% confidence interval on the fitted values (there is 95% confidence that the true regression curve lies within the shaded region).

Figure 3.

Individual changes in immunoglobulin G (IgG) glycans with age. Two time points of relative levels of glycans (percentages of individual glycan structures within the total IgG glycome), which associated strongly with age within an individual, are presented on the background showing levels of the same glycans for different individuals from the same population.

Figure 4.

Prediction of chronological age from measured immunoglobulin G glycans. Using the simplified GlycanAge model, predicted age was calculated for 2,035 individuals from the Orkney cohort and plotted against real chronological age of the same individual (A). The prediction of age was further improved by inclusion of forced expiratory volume and systolic blood pressure (B).