Vascular Smooth Muscle Cell Activation by Glycated Albumin (Amadori Adducts)

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Abstract
Nonenzymatic glycation is increased in diabetes. The role of advanced glycation end products has been implicated in many of the complications of diabetes, whereas the effects of early-glycation Amadori-modified proteins on vascular cells alone are poorly defined. In the present study, we show that glycated serum albumin (GSA) induces a parallel activation of the redox-responsive transcription factors (nuclear factor κB) and AP-1 and increases activity of mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinase (ERK), and p38 MAPK in vascular smooth muscle cells (VSMCs). GSA increased expression of early response genes, c- fos and c- jun , and inflammatory genes, monocyte chemoattractant peptide (MCP-1), and interleukin (IL)-6. These effects were comparable to bacterial lipopolysaccharide, tumor necrosis factor-αa, (TNF-αa), IL-1αb, angiotensin II, epidermal growth factor, and the phorbol ester PMA. One of signaling pathways by which GSA activates VSMCs appears to be via nuclear factor κB activation, leading to induction of MCP-1 and IL-6 gene expression, comparable to the effects of lipopolysaccharide, TNF-αa, and IL-1αb. Another signaling cascade by which GSA activates VSMCs is the ERK→c-Fos→AP-1 pathway, which may lead to stimulation of cell proliferation and migration. These effects are comparable to the effects of angiotensin II, epidermal growth factor, and PMA. Incubation of VSMCs with the antioxidant N -acetylcysteine suppressed GSA-elicited mRNA induction of MCP-1 and IL-6. Inhibition of p38 MAPK but not ERK caused attenuation of MCP-1 and IL-6 mRNA induction. Finally, GSA caused a significant stimulation of VSMC growth and migration. These findings suggest that GSA may play a role in diabetic atherogenesis by activating VSMCs, leading to induction of inflammatory mediators in the vessel wall, as well as proliferation and migration of VSMCs.