Methylglyoxal-modified arginine residues — a signal for receptor-mediated endocytosis and degradation of proteins by monocytic THP-1 cells

Abstract

Non-enzymatic glycosylation or glycation of proteins to form advanced glycation endproducts (AGE) has been proposed as a process which provides a signal for the degradation of proteins. Despite this, the AGE which act a recognition factor for receptor-mediated endocytosis and degradation of glycated proteins by monocytes and macrophages has not been identified. Methylglyoxal, a reactive alpha-oxoaldehyde and physiological metabolite, reacted irreversibly with arginine residues in proteins to form Ndelta-(5-hydro-5-methyl-4-imidazolon-2-yl)ornithine and Ndelta-(5-methyl-4-imidazolon-2-yl)ornithine residues. Human serum albumin minimally-modified with methylglyoxal (MG(min)-HSA) was bound by cell surface receptors of human monocytic THP-1 cells in vitro at 4 degrees C: the binding constant K(d) value was 377 +/- 35 nM and the number of receptors per cell was 5.9 +/- 0.2 X 10(5) (n = 12). N alpha-Acetyl-Ndelta-(5-hydro-5-methyl-4-imidazolon-2-yl)orni thine displaced MG(min)-HSA from THP-1 cells, suggesting that the Ndelta-(5-hydro-5-methyl-4-imidazolon-2-yl)ornithine residue was the receptor recognition factor. At 37 degrees C, MG(min)-HSA was internalised by THP-1 cells and degraded. Similar binding and degradation of human serum albumin modified by glucose-derived AGE was found but only when highly modified. MG(min)-HSA, therefore, is the first example of a protein minimally-modified by AGE-like compounds that binds specifically to monocyte receptors. The irreversible modification of proteins by methylglyoxal is a potent signal for the degradation of proteins by monocytic cells in which the arginine derivative, Ndelta-(5-hydro-5-methyl-4-imidazolon-2-yl)ornithine, is the receptor recognition factor. This factor is not present in glucose-modified proteins.

Mechanism of Perturbation of Integrin-Mediated Cell-Matrix Interactions by Reactive Carbonyl Compounds and Its Implication for Pathogenesis of Diabetic Nephropathy

“…Modification of major glomerular ECM proteins by MGO inhibits cell adhesion to these proteins. In choosing the experimental conditions for MGO treatment, we were guided by the finding that the incubation of human albumin with 0.5 mmol/l MGO for 24 h resulted in modification of ϳ1 Arg residue per molecule (38). Modification by MGO strongly inhibited endothelial cell adhesion to RGD-␣3NC1 with maximum effect achieved at 2 mmol/l MGO after 24 h (Fig.…”

Profound Mishandling of Protein Glycation Degradation Products in Uremia and Dialysis

“…MetSO residues may be reduced to methionine residues by MetSO reductase during endothelial transcytosis. MG-H1-modified proteins may be bound by activated monocytes in the dialysis session and degraded (31). The concentration of MG-H1 residues in plasma protein of PD and HD patients correlated negatively with the plasma concentration of albumin (Table 11).…”

Advanced Glycation End Products Modulate the Maturation and Function of Peripheral Blood Dendritic Cells

“…Carbonyl compounds from glycolytic intermediates of Maillard reactions (1), including glyoxal and methylglyoxal (MG), are major contributors to AGE formation. MG is the most reactive AGE precursor, and its concentration is increased in diabetic subjects (2). MG reacts irreversibly with lysine to form glycosylamine protein cross-links and with arginine to give imidazolone derivatives (3).…”

“…Glycation of albumin in vivo is consistent with only one to three glucose residues per protein molecule, making it appropriate to study such minimally glycated models in vitro (2). Proteins can be minimally glycated with MG to produce methylglyoxal-derived hydroimidazolone (MG-H) (16,17).…”