HDL Glycoprotein Composition and Site-Specific Glycosylation Differentiates Between Clinical Groups and Affects IL-6 Secretion in Lipopolysaccharide-Stimulated Monocytes

Abstract

The goal of this pilot study was to determine whether HDL glycoprotein composition affects HDL’s immunomodulatory function. HDL were purified from healthy controls (n = 13), subjects with metabolic syndrome (MetS) (n = 13), and diabetic hemodialysis (HD) patients (n = 24). Concentrations of HDL-bound serum amyloid A (SAA), lipopolysaccharide binding protein (LBP), apolipoprotein A-I (ApoA-I), apolipoprotein C-III (ApoC-III), α-1-antitrypsin (A1AT), and α-2-HS-glycoprotein (A2HSG); and the site-specific glycovariations of ApoC-III, A1AT, and A2HSG were measured. Secretion of interleukin 6 (IL-6) in lipopolysaccharide-stimulated monocytes was used as a prototypical assay of HDL’s immunomodulatory capacity. HDL from HD patients were enriched in SAA, LBP, ApoC-III, di-sialylated ApoC-III (ApoC-III2) and desialylated A2HSG. HDL that increased IL-6 secretion were enriched in ApoC-III, di-sialylated glycans at multiple A1AT glycosylation sites and desialylated A2HSG, and depleted in mono-sialylated ApoC-III (ApoC-III1). Subgroup analysis on HD patients who experienced an infectious hospitalization event within 60 days (HD+) (n = 12), vs. those with no event (HD−) (n = 12) showed that HDL from HD+ patients were enriched in SAA but had lower levels of sialylation across glycoproteins. Our results demonstrate that HDL glycoprotein composition, including the site-specific glycosylation, differentiate between clinical groups, correlate with HDL’s immunomodulatory capacity, and may be predictive of HDL’s ability to protect from infection.

Site-Specific Glycoprofiles of HDL-Associated ApoE are Correlated with HDL Functional Capacity and Unaffected by Short-Term Diet

“…In our previous study, the glycan ApoC3_74_O_1102, which decreased after FF and increased after Med in this study, was found to be 2-fold higher in HDL compared to plasma, 10 and was elevated in hemodialysis patients, but decreased in MetS patients compared to healthy human controls. 12 Although the glycan ApoC3_74_O_2230, which increased after FF and decreased after Med in this study, was not detected in our previous study, another non-sialylated ApoC-III glycan, ApoC3_74_O_0300, was found to be decreased in hemodialysis patients and elevated in MetS patients. 12 Di-sialylated ApoC-III is enriched in small dense LDL in hemodialysis patients with dyslipidemia, 42 and was found to be reduced across lipoprotein classes in MetS patients.…”

“…11 Importantly, key HDL proteins are differentially glycosylated in multiple disease states vs. healthy individuals, and site-specific glycosylation of HDL-associated proteins is associated with HDL's immunomodulatory capacity. 12 Apolipoprotein E (ApoE) genotype is one of the most important risk factors for a number of ageassociated diseases, 13 and the single greatest genetic risk factor for Alzheimer's Disease. 14 ApoE is a component of HDL particles that is involved in mediating HDL functional capacity.…”

Glycosylation of human plasma lipoproteins reveals a high level of diversity, which directly impacts their functional properties

“…Similar differences were found between patients with metabolic syndrome and healthy subjects [27]. Furthermore, HDL glycoprotein composition differentiates between clinical groups, correlating with immunomodulatory capacity of HDL [28].…”

“…Given that ABCA1 preferentially effluxes cholesterol to small relative to large HDL [59], such effect should have resulted in the elevated cholesterol efflux capacity of the desialylated particles, which was not the case, suggesting that other factors, including HDL charge, were more important for this functional alteration. We interpret these data to hypothesise that the N-glycome of HDL proteins, including fetuin A, alpha-1-antitripsin, angiotensinogen [26,28,29], LCAT [24] and possibly apoA-I [57,58], can be affected by neuroaminidaseinduced desialylation and that these modifications bear a potential to reduce electronegativity and LCAT activity of HDL to concomitantly contribute to the diminished capacity of HDL to efflux cellular cholesterol via ABCA1, counteracting potentially beneficial effects of the diminished HDL size.…”

“…As N-and O-glycosylation of human apoA-I was recently reported [57,58], desialylation might equally alter interactions of apoA-I with cellular proteins, including ABCA1. The question of apoA-I glycosylation remains controversial though as apoA-I-associated glycans were not detected in several studies employing LC/MS/MS [26,28,29].…”