The Receptor for Advanced Glycation End Products Mediates the Chemotaxis of Rabbit Smooth Muscle Cells

Abstract

Long-term incubation of proteins with glucose leads to advanced glycation end products (AGEs) with fluorescence and a brown color. We recently demonstrated immunologically the intracellular AGE accumulation in smooth muscle cell (SMC)–derived foam cells in advanced atherosclerotic lesions. To understand the mechanism of AGE accumulation in these foam cells, we have now characterized the interaction of AGE proteins with rabbit-cultured arterial SMCs. In experiments at 4°C, 125I-labeled AGE-bovine serum albumin (AGE-BSA) showed a dose-dependent saturable binding to SMCs with an apparent dissociation constant (Kd) of 4.0 μg/ml. In experiments at 37°C, AGE-BSA underwent receptor-mediated endocytosis and subsequent lysosomal degradation. The endocytic uptake of 125I-AGE-BSA was effectively inhibited by unlabeled AGE proteins such as AGE-BSA and AGE-hemoglobin, but not by acetylated LDL and oxidized LDL, well-known ligands for the macrophage scavenger receptor (MSR). Moreover, the binding of 125I-AGE-BSA to SMCs was affected neither by amphoterin, a ligand for one type of the AGE receptor, named RAGE, nor by 2-(2-furoyl)-4(5)-(2-furanyl)-1H-imidazole–hexanoic acid–BSA, a ligand for the other AGE receptors, p60 and p90. This indicates that the endocytic uptake of AGE proteins by SMCs is mediated by an AGE receptor distinct from MSR, RAGE, p60, and p90. To examine the functional role of this AGE receptor, the migratory effects of AGE-BSA on these SMCs were tested. Incubation with 1–50 μg/ml of AGE-BSA for 14 h resulted in significant dose-dependent cell migration. The AGE-BSA–induced SMC migration was chemotactic in nature and was significantly inhibited (∼80%) by an antibody against transforming growth factor-β (TGF-β), and the amount of TGF-β secreted into the culture medium from SMC by AGE-BSA was sevenfold higher than that of control, indicating that TGF-β is involved in the AGE-induced SMC chemotaxis. These data suggest that AGE may play a role in SMC migration in advanced atherosclerotic lesions.