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      Advanced Glycation End Products Induce Calcification of Vascular Smooth Muscle Cells through RAGE/p38 MAPK

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          Background: Mönckeberg’s calcification in diabetes, known as medial artery calcification, is an independent predictor of cardiovascular mortality. However, the mechanism underlying this phenomenon remains to be elucidated. We demonstrate that advanced glycation end products (AGEs) induce calcification of vascular smooth muscle cells through the receptor for AGE (RAGE)/p38 mitogen-activated protein kinase (MAPK) signaling pathway. Methods: We detected vascular calcification by von Kossa staining. Alkaline phosphatase (ALP) activity was determined by measuring p-nitrophenol. Osteocalcin concentrations were measured using ELISA. Western blotting for protein phosphorylation and real-time RT-PCR for expression of mRNA were used. Results: AGEs induced calcification of vascular smooth muscle cells. AGEs also induced the expression of Runx2 mRNA. In addition, AGEs increased ALP activity and osteocalcin secretion. Furthermore, AGEs induced phosphorylation of p38 MAPK, and this phosphorylation was inhibited by the anti-RAGE blocking antibody. Increased ALP activity was inhibited by the p38 MAPK inhibitor or anti-RAGE blocking antibody. Furthermore, the p38 MAPK inhibitor and anti-RAGE blocking antibody both inhibited AGE-induced calcification of vascular smooth muscle cells. Diabetic serum induced calcification of smooth muscle cells and the calcification was inhibited by RAGE blocking. Conclusion: Our findings indicate that AGEs induce calcification of vascular smooth muscle cells by osteoblast-like differentiation of smooth muscle cells through RAGE/p38 MAPK.

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          Most cited references 16

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          Electron beam computed tomography in the evaluation of cardiac calcification in chronic dialysis patients.

          The purpose of this study was to assess the value of electron beam computed tomography in the detection of cardiac calcifications in coronaries and valves of dialysis patients and to determine the rate at which calcification progresses. Forty-nine chronic hemodialysis patients aged 28 to 74 years were compared with 102 non-dialysis patients aged 32 to 73 years with documented or suspected coronary artery disease, all of whom underwent coronary angiography. We used high-resolution electron beam computed tomography scanning to make 30 axial slices with a distance of 3 mm between each slice. The number of calcifications, the surface area, and the average and highest density values were measured. We calculated a quantitative coronary artery calcium score and assessed calcification of mitral and aortic valves. In dialysis patients, the measurements were repeated after 12 months. The coronary artery calcium score was from 2.5-fold to fivefold higher in the dialysis patients than in the non-dialysis patients. Hypertensive dialysis patients had higher calcium scores than non-hypertensive dialysis patients (P < 0.05). A stepwise, multiple regression analysis confirmed the importance of age and hypertension. No correlation between calcium, phosphate, or parathyroid hormone values and the coronary calcium score was identified; however, the calcium score was inversely correlated with bone mass in the dialysis patients (r = 0.47, P < 0.05). The mitral valve was calcified in 59% of dialysis patients, while the aortic valve was calcified in 55%. The coronary artery calcium score was correlated with aortic valvular, but not mitral valvular calcification. A repeat examination of the dialysis patients at an interval of 1 year showed a disturbing tendency for progression. Our data under-score the frequency and severity of coronary and valvular calcifications in dialysis patients, and illustrate the rapid progression of this calcification. Finally, they draw attention to hypertension as an important risk factor in this process.
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            Osteogenic regulation of vascular calcification: an early perspective.

            Cardiovascular calcification is a common consequence of aging, diabetes, hypercholesterolemia, mechanically abnormal valve function, and chronic renal insufficiency. Although vascular calcification may appear to be a uniform response to vascular insult, it is a heterogenous disorder, with overlapping yet distinct mechanisms of initiation and progression. A minimum of four histoanatomic variants-atherosclerotic (fibrotic) calcification, cardiac valve calcification, medial artery calcification, and vascular calciphylaxis-arise in response to metabolic, mechanical, infectious, and inflammatory injuries. Common to the first three variants is a variable degree of vascular infiltration by T cells and macrophages. Once thought benign, the deleterious clinical consequences of calcific vasculopathy are now becoming clear; stroke, amputation, ischemic heart disease, and increased mortality are portended by the anatomy and extent of calcific vasculopathy. Along with dystrophic calcium deposition in dying cells and lipoprotein deposits, active endochondral and intramembranous (nonendochondral) ossification processes contribute to vascular calcium load. Thus vascular calcification is subject to regulation by osteotropic hormones and skeletal morphogens in addition to key inhibitors of passive tissue mineralization. In response to oxidized lipids, inflammation, and mechanical injury, the microvascular smooth muscle cell becomes activated. Orthotopically, proliferating stromal myofibroblasts provide osteoprogenitors for skeletal growth and fracture repair; however, in valves and arteries, vascular myofibroblasts contribute to cardiovascular ossification. Current data suggest that paracrine signals are provided by bone morphogenetic protein-2, Wnts, parathyroid hormone-related polypeptide, osteopontin, osteoprotegerin, and matrix Gla protein, all entrained to endocrine, metabolic, inflammatory, and mechanical cues. In end-stage renal disease, a "perfect storm" of vascular calcification often occurs, with hyperglycemia, hyperphosphatemia, hypercholesterolemia, hypertension, parathyroid hormone resistance, and iatrogenic calcitriol excess contributing to severe calcific vasculopathy. This brief review recounts emerging themes in the pathobiology of vascular calcification and highlights some fundamental deficiencies in our understanding of vascular endocrinology and metabolism that are immediately relevant to human health and health care.
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              Protein glycation: a firm link to endothelial cell dysfunction.

              The advanced glycation end products (AGEs) are a heterogeneous class of molecules, including the following main subgroups: bis(lysyl)imidazolium cross-links, hydroimidazolones, 3-deoxyglucosone derivatives, and monolysyl adducts. AGEs are increased in diabetes, renal failure, and aging. Microvascular lesions correlate with the accumulation of AGEs, as demonstrated in diabetic retinopathy or renal glomerulosclerosis. On endothelial cells, ligation of receptor for AGE (RAGE) by AGEs induces the expression of cell adhesion molecules, tissue factor, cytokines such as interleukin-6, and monocyte chemoattractant protein-1. A chief means by which AGEs via RAGE exert their effects is by generation of reactive oxygen species, at least in part via stimulation of NADPH oxidase. Diabetes-associated vascular dysfunction in vivo can be prevented by blockade of RAGE. Thus, agents that limit AGE formation, increase the catabolism of these species, or antagonize their binding to RAGE may provide new targets for vascular protection in diabetes.

                Author and article information

                J Vasc Res
                Journal of Vascular Research
                S. Karger AG
                October 2009
                30 June 2009
                : 46
                : 6
                : 572-580
                First Department of Internal Medicine, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan
                226225 J Vasc Res 2009;46:572–580
                © 2009 S. Karger AG, Basel

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                Page count
                Figures: 6, References: 39, Pages: 9
                Research Paper


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