The binding of advanced glycation end-products (AGE) to the receptor for AGE (RAGE) is known to deteriorate various cell functions and is implicated in the pathogenesis of diabetic vascular complications. In the present study, we show that the cellular constituents of small vessels, endothelial cells (EC) and pericytes express novel splice variants of RAGE mRNA coding for the isoforms that lack the N-terminal V-type immunoglobulin-like domain (N-truncated) or the C-terminal transmembrane domain (C-truncated), as well as the known full-length mRNA. The ratio of the expression of the three variants was different between EC and pericytes; the content of the C-truncated form was highest in EC, whereas the full-length form was the most abundant in pericytes. Transfection experiments with COS-7 cells demonstrated that those variant mRNAs were translated into proteins as deduced; C-truncated RAGE was efficiently secreted into the culture media, and N-truncated RAGE was located mainly on the plasma membrane. The three isoforms were also detected in primary cultured human EC and pericytes. Further, full-length and C-truncated forms of RAGE bound to an AGE-conjugated column, whereas N-truncated RAGE did not. The AGE induction of extracellular-signal-related kinase phosphorylation and vascular endothelial growth factor in EC and of the growth and cord-like structure formation of EC was abolished completely by C-truncated RAGE, indicating that this endogenous secretory receptor (endogenous secretory RAGE) is cytoprotective against AGE. The results may contribute to our understanding of the molecular basis for the diversity of cellular responses to AGE and for individual variations in the susceptibility to diabetic vascular complications.

No abstract

Objectives-Advanced glycation endproducts, AGEs, and its specific receptor, RAGE, are involved in diabetic vascular complications. Endogenous secretory RAGE, esRAGE, has been identified as an alternatively spliced form of RAGE, and shown to act as a decoy receptor for AGE. Here, we measured plasma esRAGE level with a recently developed enzyme-linked immunosorbent assay (ELISA) and examined its association with atherosclerosis in age-and gender-matched 203 type 2 diabetic and 134 nondiabetic subjects. Methods and Results-Plasma esRAGE was inversely associated with carotid or femoral atherosclerosis, as quantitatively measured as intimal-medial thickness (IMT) by arterial ultrasound. Stepwise regression analyses revealed that plasma esRAGE was the third strongest and independent factor associated with carotid IMT, following age and systolic blood pressure. Plasma esRAGE was significantly lower in diabetic patients (0.176Ϯ0.092 ng/mL) than nondiabetic controls (0.253Ϯ0.111). Of note, in all, diabetic or nondiabetic group, plasma esRAGE was significantly and inversely correlated with components of the metabolic syndrome including body mass index, blood pressure, triglyceride, HbA1c, or an insulin resistance index. Stepwise regression analyses showed that body mass index or insulin resistance index was the major factor determining plasma esRAGE in all, nondiabetic or diabetic population. Conclusions-esRAGE is a novel and potential protective factor for the metabolic syndrome and atherosclerosis. Key Words: pathophysiology Ⅲ risk factors Ⅲ type 2 diabetes U nder hyperglycemic conditions, endogenous nonenzymatic glycoxidation of proteins and lipids leads to the formation of heterogeneous products, collectively termed advanced glycation end products (AGEs). 1 AGE engagement of cell surface the receptor for AGE (RAGE) results in cellular signaling including activation of nuclear factor-B, increased expression of cytokines and adhesion molecules, and induction of oxidative stress. 2,3 Transgenic mice overexpressing human RAGE in vascular cells developed advanced nephropathy when they were made diabetic. 4 Thus, the AGE-RAGE system has been thought to play a pivotal role in the development of diabetic microvascular complications.Accumulating evidence suggests that RAGE is also involved in macrovascular complications in diabetes. 5,6 RAGE expression is shown to be upregulated in atherosclerotic plaques of diabetic animals. 7 Some of the human studies also implicate the involvement of RAGE in diabetic vasculopathy. 8,9 Moreover, the group of Stern and Schmidt has shown that augmentation of atherosclerosis in diabetic mice is inhibited by the competition of RAGE with its soluble truncated form termed soluble RAGE (sRAGE), lacking the transmembrane and cytoplasmic domains, produced by recombinant gene engineering. 7,10 Recently, an endogenous secretory RAGE (esRAGE) has been identified as a novel splice variant that directs the synthesis of RAGE proteins carrying all of the extracellular domains but devoid of the transmembrane...

No abstract