Abstract and Introduction
Abstract
Objective: Activation of the receptor for advanced glycation end products (RAGE) in diabetic vasculature is considered to be a key mediator of atherogenesis. This study examines the effects of deletion of RAGE on the development of atherosclerosis in the diabetic apoE model of accelerated atherosclerosis.
Research Design and Methods: ApoE and RAGE/apoE double knockout mice were rendered diabetic with streptozotocin and followed for 20 weeks, at which time plaque accumulation was assessed by en face analysis.
Results: Although diabetic apoE mice showed increased plaque accumulation (14.9 ± 1.7%), diabetic RAGE/apoE mice had significantly reduced atherosclerotic plaque area (4.9 ± 0.4%) to levels not significantly different from control apoE mice (4.3 ± 0.4%). These beneficial effects on the vasculature were associated with attenuation of leukocyte recruitment; decreased expression of proinflammatory mediators, including the nuclear factor-κB subunit p65, VCAM-1, and MCP-1; and reduced oxidative stress, as reflected by staining for nitrotyrosine and reduced expression of various NADPH oxidase subunits, gp91phox, p47phox, and rac-1. Both RAGE and RAGE ligands, including S100A8/A9, high mobility group box 1 (HMGB1), and the advanced glycation end product (AGE) carboxymethyllysine were increased in plaques from diabetic apoE mice. Furthermore, the accumulation of AGEs and other ligands to RAGE was reduced in diabetic RAGE/apoE mice.
Conclusions: This study provides evidence for RAGE playing a central role in the development of accelerated atherosclerosis associated with diabetes. These findings emphasize the potential utility of strategies targeting RAGE activation in the prevention and treatment of diabetic macrovascular complications.
Introduction
The receptor for advanced glycation end products (RAGE) is a multiligand cell surface molecule belonging to the immunoglobulin superfamily. It is expressed as full-length, N-truncated, and C-truncated isoforms, generated in humans by alternative splicing. Activation of the full-length RAGE receptor has been implicated in a range of chronic diseases, including various diabetic complications and atherosclerosis. In particular, studies in RAGE mice that carry the dominant-negative form of the receptor and in RAGE-overexpressing mice have confirmed an important role of RAGE activation in the development of diabetic nephropathy, neuropathy, and impaired angiogenesis. RAGE activation has also been implicated in the acceleration of atherosclerotic lesion formation as well as in the maintenance of proinflammatory and prothrombotic mechanisms, characteristic of diabetes-accelerated atherosclerosis. RAGE also represents an important mediator of oxidative stress in diabetes. Activation of RAGE in vitro leads to increased NADPH oxidase expression, mitochondrial oxidase activity, and downregulation of endogenous antioxidant activity. RAGE mice have a suppression of neointimal proliferation after externally induced arterial injury in the absence of diabetes. Moreover, blockade of RAGE-dependent signaling by soluble RAGE (sRAGE) has been shown to inhibit the progression of atherosclerotic changes and kidney disease in diabetic mice, possibly by suppressing the activation of nuclear factor-κB (NF-κB) activation and inflammatory cytokine expression. The present study examined the role of RAGE in the development of diabetes-accelerated atherosclerosis in a model of insulin deficiency, the streptozotocin-induced diabetic RAGE/apoE mouse. Our aim was to determine the effect of global RAGE deficiency, which includes absence of both the full-length receptor and endogenous sRAGE on the development of vascular lesions in the presence and absence of diabetes. Furthermore, key mediators of the atherosclerotic process in diabetes were examined, and the effects on these pathways were assessed in these RAGE-deficient mice.