Lysine glycation of apolipoprotein A-I impairs its anti-inflammatory function in type 2 diabetes mellitus

J Mol Cell Cardiol. 2018 Sep:122:47-57. doi: 10.1016/j.yjmcc.2018.08.001. Epub 2018 Aug 7.

Abstract

Apolipoprotein A-I (apoA-I), the major protein compontent of high-density lipoprotein (HDL), exerts many anti-atherogenic functions. This study aimed to reveal whether nonenzymatic glycation of specific sites of apoA-I impaired its anti-inflammatory effects in type 2 diabetes mellitus (T2DM). LC-MS/MS was used to analyze the specific sites and the extent of apoA-I glycation either modified by glucose in vitro or isolated from T2DM patients. Cytokine release in THP-1 monocyte-derived macrophages was tested by ELISA. Activation of NF-kappa B pathway was detected by western blot. The binding affinity of apoA-I to THP-1 cells was measured using 125I-labeled apoA-I. We identified seven specific lysine (Lys, K) residues of apoA-I (K12, K23, K40, K96, K106, K107 and K238) that were susceptible to be glycated either in vitro or in vivo. Glycation of apoA-I impaired its abilities to inhibit the release of TNF-α and IL-1β against lipopolysaccharide (LPS) in THP-1 cells. Besides, the glycation levels of these seven K sites in apoA-I were inversely correlated with its anti-inflammatory abilities. Furthermore, glycated apoA-I had a lower affinity to THP-1 cells than native apoA-I had. We generated mutant apoA-I (K107E, M-apoA-I) with a substitution of glutamic acid (Glu, E) for lysine at the 107th site, and found that compared to wild type apoA-I (WT-apoA-I), M-apoA-I decreased its anti-inflammatory effects in THP-1 cells. We also modeled the location of these seven K residues on apoA-I which allowed us to infer the conformational alteration of glycated apoA-I and HDL. In summary, glycation of these seven K residues altered the conformation of apoA-I and consequently impaired the protective effects of apoA-I, which may partly account for the increased risk of cardiovascular disease (CVD) in diabetic subjects.

Keywords: Apolipoprotein; Glycation; HDL; Inflammation; Proteomics.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Amino Acid Substitution
  • Analysis of Variance
  • Apolipoprotein A-I / metabolism*
  • Chromatography, Liquid
  • Diabetes Mellitus, Type 2 / blood*
  • Glucose
  • Glutamic Acid / genetics
  • Glycosylation
  • Humans
  • Inflammation / metabolism*
  • Interleukin-1beta / metabolism
  • Lipopolysaccharides / pharmacology
  • Lipoproteins, HDL / metabolism
  • Lysine / genetics
  • Lysine / metabolism*
  • Middle Aged
  • NF-kappa B / metabolism
  • Protein Conformation
  • Protein Disulfide-Isomerases
  • THP-1 Cells
  • Tandem Mass Spectrometry
  • Tumor Necrosis Factor-alpha / metabolism

Substances

  • APOA1 protein, human
  • Apolipoprotein A-I
  • Interleukin-1beta
  • Lipopolysaccharides
  • Lipoproteins, HDL
  • NF-kappa B
  • TNF protein, human
  • Tumor Necrosis Factor-alpha
  • Glutamic Acid
  • Protein Disulfide-Isomerases
  • Glucose
  • Lysine