Signaling of Serum Amyloid A Through Receptor for Advanced Glycation End Products as a Possible Mechanism for Uremia-Related Atherosclerosis

Abstract

Objective-Cardiovascular disease is the leading cause of death in patients with end-stage renal disease. Serum amyloid A (SAA) is an acute phase protein and a binding partner for the multiligand receptor for advanced glycation end products (RAGE). We investigated the role of the interaction between SAA and RAGE in uremia-related atherogenesis. Approach and Results-We used a mouse model of uremic vasculopathy, induced by 5 of 6 nephrectomy in the Apoe −/− background. Sham-operated mice were used as controls. Primary cultures of Ager +/+ and Ager −/− vascular smooth muscle cells (VSMCs) were stimulated with recombinant SAA, S100B, or vehicle alone. Relevance to human disease was assessed with human VSMCs. The surface area of atherosclerotic lesions at the aortic roots was larger in uremic Apoe −/− than in sham-operated Apoe −/− mice (P<0.001). Furthermore, atherosclerotic lesions displayed intense immunostaining for RAGE and SAA, with a pattern similar to that of α-SMA. Ager transcript levels in the aorta were 6× higher in uremic animals than in controls (P<0.0001). Serum SAA concentrations were higher in uremic mice, not only after 4 weeks of uremia but also at 8 and 12 weeks of uremia, than in sham-operated animals. We investigated the functional role of RAGE in uremia-induced atherosclerosis further, in animals lacking RAGE. We found that the induction of uremia in Apoe −/− Ager −/− mice did not accelerate atherosclerosis. In vitro, the stimulation of Ager +/+ but not of Ager −/− VSMCs with SAA or S100B significantly induced the production of reactive oxygen species, the phosphorylation of AKT and mitogenactivated protein kinase-extracellular signal-regulated kinases and cell migration. Reactive oxygen species inhibition with N-acetyl cysteine significantly inhibited both the phosphorylation of AKT and the migration of VSMCs. Similar results were obtained for human VSMCs, except that the phosphorylation of mitogen-activated protein kinase-extracellular signal-regulated kinases, rather than of AKT, was subject to specific redox-regulation by SAA and S100B. Furthermore, human aortic atherosclerotic sections were positively stained for RAGE and SAA. Conclusions-Uremia upregulates SAA and RAGE expression in the aortic wall and in atherosclerotic lesions in mice. Ager −/− animals are protected against the uremia-induced acceleration of atherosclerosis. SAA modulates the functions of murine and human VSMCs in vitro in a RAGE-dependent manner. This study, therefore, identifies SAA as a potential new uremic toxin involved in uremia-related atherosclerosis through interaction with RAGE. This manuscript was sent to Ryozo Nagai, Consulting Editor, for review by expert referees, editorial decision, and final disposition. marker of cardiovascular risk. 6 High levels have been reported in uremic patients and are independently associated with cardiovascular mortality.7 SAA has also been reported to play an active role in the atherogenic process. 6,8,9 First, SAA has been detected in the atherosclerotic lesions of hyperlipidem...

RAGE Mediates Cholesterol Efflux Impairment in Macrophages Caused by Human Advanced Glycated Albumin

“…Interestingly, glycated albumin is enhanced in those animals’ serum and acts similarly to glycated albumin drawn from DM subjects. RAGE is overexpressed in the uremic aortic wall, and Ager null animals are protected from the uremia-induced acceleration of atherosclerosis [ 37 ]. Thus, RAGE inhibition may contribute to abrogating the deleterious effects of AGE albumin in a range of metabolic conditions where carbonyl stress prevails.…”

2016 ATVB Plenary Lecture

“…Uremic conditions are linked to highly increased accumulation of RAGE ligand AGEs 22 . In animal models, performance of the “5/6 nephrectomy” in Apoe null mice resulted in accelerated atherosclerosis in mice expressing Ager but not in mice devoid of Ager 23 . RAGE ligands serum amyloid A (SAA) and S100B increased significantly in the uremic environment and upon stimulation of SMCs with these ligands, prominent increases in production of reactive oxygen species (ROS) were observed in a RAGE-dependent manner 23 .…”

Serum Amyloid A and Immunomodulation

“…Inhibition of RAGE by a RAGE competitor, by soluble RAGE, and by anti-RAGE IgG reduced the SAAstimulated tissue factor expression [63]. RAGE is also reported to mediate the proinflammatory activity of SAA in uremia-related atherosclerosis, based on a study using the Apoe −/− and Ager −/− mice [95]. These studies identify RAGE as an endothelial and monocyte-expressed molecule that mediates selected activities of SAA.…”