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Bone morphogenetic proteins in vascular calcification.

Vascular calcification is a common problem among the elderly and those with chronic kidney disease (CKD) and diabetes. The process of tunica media vascular calcification in CKD appears to involve a phenotypic change in the vascular smooth muscle cell (VSMC) resulting in cell-mediated mineralization of the extracellular matrix. The bone morphogenetic proteins (BMPs) are important regulators in orthotopic bone formation, and their localization at sites of vascular calcification raises the question of their role. In this review, we will discuss the actions of the BMPs in vascular calcification. Although the role of BMP-2 in vascular calcification is not proven, it has been the most studied member of the BMP family in this disease process. The role of BMP-2 may be through inducing osteoblastic differentiation of VSMCs through induction of MSX-2, or by inducing apoptosis of VSMCs, a process thought critical in the initiation of vascular calcification. Additionally, BMP-2 may be related to loss of regulation of the matrix Gla protein. A second BMP, BMP-7, less studied than BMP-2 may have opposing actions in vascular calcification. In postnatal life, BMP-7 is expressed primarily in the kidney, and expression is diminished by renal injury. BMP-7 is an important regulator of skeletal remodeling and the VSMC phenotype. BMP-7 restores skeletal anabolic balance in animal models of CKD with disordered skeletal modeling, also reducing serum phosphate in the process. BMP-7 also reverses vascular calcification in CKD, and reduction in vascular calcification is due, in part, to reduced serum phosphate, an important inducer of VSMC-mediated vascular mineralization and in part to direct actions on the VSMC.

Animals↗

Regulatory mechanisms in vascular calcification.

Vascular calcification is increasingly recognized as a significant contributor to cardiovascular morbidity and mortality as well as a biologically regulated process potentially subject to prevention and reversal. Both coronary and aortic calcification are common and influence plaque rupture, angioplasty and surgical complications, and compensatory enlargement. Aortic calcification increases aortic rigidity and contributes to cadiac ischemia, left ventricular hypertrophy, heart failure, and stroke. Calcification is also common in aortic valve leaflets further compounding adverse hemodynamic effects. Vascular calcification has often been attributed to "passive" crystallization. However, functional similarities between atherosclerotic lesions and bone contradict this view and indicate that it is no more "passive" than in embryonic bone formation or bone repair. Similarities include presence of all the major components of bone osteoid, bone regulatory factors, and subpopulations of artery wall cells that retain osteoblastic lineage potential. Several animal models for vascular calcification are available. Spontaneous vascular calcification occurs in null mice for matrix GLA protein (MGP), a small matrix protein of unknown function, and osteoprotegerin (OPG), known to modulate osteoclast differentiation. Vascular calcification may also be induced by feeding vitamin D and calcium or warfarin to normal animals, or by fat-feeding mice null for apoE or the LDL-receptor. Overall, regulation of vascular calcification is a growing field with surprising mechanisms and connections to other fields of biology.

Animals↗

[Current concepts of vascular calcification].

Vascular calcification, such as coronary and aortic calcification, is a significant feature of vascular pathology. Two distinct forms of vascular calcification are well recognized. One is medial calcification, which occurs between the cell layers of smooth muscle cells, and is related to aging, diabetes and chronic renal failure. The other is atherosclerotic calcification, which occurs in the intima during the development of atheromatous disease. It has been shown that statins inhibit the progression of calcification in the aortic valve and the coronary artery. We have found that statins inhibit calcification of human aortic smooth muscle cells, which is induced by incubating the cells in high-phosphate medium. We also found that this is mediated by inhibiting cellular apoptosis, an essential mechanism for calcification, not by inhibiting inorganic phosphate (Pi) uptake by sodium-dependent phosphate cotransporter (NPC). Besides apoptosis and Pi uptake, such proteins as osteoprotegerin (OPG), matrix Gla protein (MGP), Klotho, fetuin-A, and apoE have been shown to negatively affect vascular calcification. Many previous reports suggest that vascular calcification appears to be regulated by promoting factors, such as Pi, apoptosis, modified LDL, advanced glycation end products, oxidative stress, vitaminD3, glucocorticoid, cbfa-1, osteopontin, and inhibitory factors, such as OPG, MGP, Klotho, fetuin-A, PTH/PTHrP, pyrophosphate, statins, and bisphosphonates. The precise mechanism of vascular calcification is of interest.

Animals↗

Osteogenic regulation of vascular calcification.

Vascular calcification increasingly afflicts our aging and dysmetabolic population, predisposing patients to cardiovascular mortality and lower extremity amputation. Active osteogenic processes are evident in most histoanatomic variants, including elaboration of BMP2-Msx2 signals required for craniofacial bone formation. We developed an animal model of diet-induced diabetes, dyslipidemia, and vascular calcification. High-fat diets promote vascular calcification in male low-density lipoprotein receptor (LDLR)-deficient mice, with concomitant upregulation of aortic BMP2 and Msx2 gene expression. We wished to test if Msx2 exerts pro-calcific actions during vascular calcification, as it does in craniofacial bone. We studied CMV-Msx2Tg+;LDLR+ transgenic mice (C57Bl/6), a model previously demonstrated to recapitulate features of Msx2 signaling during craniosynostosis. After 16 weeks of fatty diets, vascular calcification was studied in CMV-Msx2Tg+ versus nontransgenic sibs. Only CMV-Msx2Tg+ mice fed high-fat diets exhibited vascular calcium accumulation by alizarin red staining, noted in the tunica media of coronary arteries and the aorta. Gene expression studies revealed that while Msx2 was expressed primarily in adventitial cells, alkaline phosphatase (ALP) expression and calcification occurred primarily in the tunica media. Msx2 promotes the elaboration of a pro-osteogenic milieu by upregulating expression of Wingless type (Wnt) ligands while downregulating the canonical antagonist, Dickkopf (Dkk1). Msx2 upregulates aortic Wnt signaling in vivo, revealed by the analysis of TOPGAL+ (Wnt reporter) versus CMV-Msx2Tg+; TOPGAL+ mice. Aortic Msx2 exerts pro-osteogenic signaling in vivo and in vitro, mediated in part via the enhancement of paracrine Wnt signaling. Strategies that selectively inhibit aortic Msx2-Wnt cascades may help diminish the initiation and progression of diabetic vascular disease.

Animals↗

Insights into the mechanism of vascular calcification.

Vascular calcification is common and clinically significant in atherosclerosis and heart failure. It was long believed to be an end-stage process of "passive" mineral precipitation. However, there is now a growing awareness that vascular calcification is a biologically regulated phenomenon. It has many similarities to bone formation, and ectopic bone is a well-documented part of vascular calcification. This implies that alterations in vascular cell differentiation, extensive or localized, are an integral part of vascular calcification. Matrix gamma-carboxylated glutamate (GLA) protein (MGP)-deficient mice develop extensive vascular calcification with replacement of the media by progressively calcifying cartilage. A potential mechanism that explains these findings is MGP interference with bone morphogenetic proteins-potent inducers of cartilage and bone.

Animals↗

Role of phosphorus and vitamin D analogs in the pathogenesis of vascular calcification.

Vascular calcification is a mortality risk factor for stage 5 chronic kidney disease patients. We investigated the role of phosphorus and vitamin D analogs in the pathogenesis of vascular calcification using in vivo, ex vivo, and in vitro models. Our results demonstrate that uremic rats receiving a hyperphosphatemia-inducing diet did not exhibit aortic calcification despite elevated levels of serum phosphorus and calcium-phosphorus (CaxP) product. The vitamin D analog 1alpha-hydroxyvitamin-D2 [1alpha(OH)D2] at 0.17 microg/kg raised serum calcium, phosphorus, CaxP product, and aortic calcification in the uremic rats, but 19-nor-1alpha,25(OH)2D2 (19-nor) at the same dose had no significant effect. At 0.67 microg/kg, both 1alpha(OH)D2 and 19-nor had similar effects on serum calcium, phosphorus, and CaxP product, but only 1alpha(OH)D2 induced significant aortic calcification. Only aortic rings from 1alpha(OH)D2-treated uremic rats exhibited a significant increase in 45Ca uptake ex vivo. When aortic rings from normal rats or a primary culture of human coronary artery smooth muscle cells were treated with phosphorus or vitamin D analogs in vitro, high phosphorus induced calcium accumulation and/or 45Ca uptake in a dose- or time-dependent manner, whereas vitamin D analogs including 1alpha(OH)D2 up to 100 nM had no significant effect despite the presence of a functional vitamin D receptor. However, serum from 1alpha(OH)D2-treated uremic rats induced 45Ca uptake into smooth muscle cells cultured in high phosphorus. These results suggest that the regulation of vascular calcification in vivo cannot be easily replicated in the ex vivo or in vitro models, and high phosphorus and some vitamin D analogs such as 1alpha(OH)D2 exert interactive effects on modulating vascular calcification.

Animals↗

Endothelin-1 is a potent regulator in vivo in vascular calcification and in vitro in calcification of vascular smooth muscle cells.

We observed changes of endothelin content and endothelin mRNA in vivo in vascular calcification and in vitro in calcification of vascular smooth muscle cells to explore the role of endothelin in vascular calcification. Calcification model in vivo was induced by administration of Vitamin D(3) plus nicotine. Calcification of vascular smooth muscle cells (VSMCs) was induced by beta-glycerophosphate. Endothelin content was measured by using radioimmunoassay. Endothelin mRNA amount was determined by using competitive quantitative RT-PCR. The results showed that calcium content, 45Ca(2+) uptake and alkaline phosphatase (ALP) activity were increased in calcified VSMCs, compared with controls, but were decreased, compared with calcified VSMCs plus BQ123 group. The endothelin content in the medium and endothelin mRNA in VSMCs were elevated by 35 and 120% (P<0.05), respectively, compared with those normal VSMCs. Calcium content, 45Ca(2+) accumulation and ALP activity in calcified arteries increased by 5.0-, 1.4-, and 1.4-fold. The endothelin levels in plasma and aorta as well as the amount of endothelin mRNA in calcified aorta were increased by 102, 103, and 22%, respectively, compared with control group. However, calcium content, 45Ca(2+) uptake and ALP activity in VDN plus bosentan group was 33, 36.7, and 40.4% lower than those in VDN group. These results indicated an upregulated endothelin gene expression as well as an increased production of endothelin in calcified aorta and VSMCs with BQ123 and bosentan significantly reducing vascular calcification. This suggested that endothelin might be involved in pathogenesis of vascular calcification.

Animals↗

[Mechanism of vascular calcification].

Vascular calcification in dialysis patients is associated with morbidity and mortality risks. Recent evidence suggests that vascular calcification is an active process resembling osteogenesis and chondrogenesis process. In this process, hyperphosphatemia is one of the important regulators. Inorganic phosphates directly regulate vascular calcification in vitro through a sodium-dependent phosphate cotransporter and promote expression of the osteoblastic differentiation markers.

Animals↗

Mechanisms of vascular calcification.

Vascular calcification is highly prevalent and correlated with high rates of cardiovascular mortality in chronic kidney disease patients. Recent evidence suggests that mineral, hormonal, and metabolic imbalances that promote phenotype change in vascular cells as well as deficiencies in specific mineralization inhibitory pathways may be important contributory factors for vascular calcification in these patients. This article reviews current mechanisms proposed for the regulation of vascular calcification and data supporting their potential contribution to this process in chronic kidney disease.

Animals↗

[Mechanism and therapy of vascular calcification].

Vascular calcification is clinically important, because it predicts a higher risk of cardiovascular event. Its pathogenesis involve atherosclerosis and regulated by mechanism which like bone metabolism. In dialysis patients, there is excess oxidative stress, shortage of scavenger, metabolic abnormality of calcium and phosphate. These factors may accelerate vascular calcification in dialysis patient. K/DOQI guideline shows the therapeutic strategy for calcium and phosphate metabolic abnormality. It is expected more progression in therapy for vascular calcification.

Animals↗

Free protein S deficiency in hemodialysis patients due to vascular calcifications?

Vascular calcifications are frequent in hemodialysis patients. Its incidence ranges from 25 to 67% depending of different series. Thirty hemodialysis patients were selected from a dialysis population of 150 patients. These 30 patients were divided into two groups: group I included 15 hemodialysis patients with severe secondary hyperparathyroidism and severe, roentgenographically visible diffuse vascular calcifications, and group II included 15 other hemodialysis patients with moderate hyperparathyroidism without radiographic evidence of arterial calcifications. The control group comprised 20 normal volunteers. In all patients, measurements of protein C activity, free protein S and intact parathyroid hormone (PTH) were performed. Statistical analysis showed that free protein S in the patients of group I had a tendency to be lower than in the patients of group II (p < 0.01) and the control group (p < 0.001). We did not find significant differences in free protein S between group II and control group patients nor a significant correlation between intact PTH and free protein S in groups I and II. Protein C activity was found to be in the normal range in both groups. Free protein S deficiency in patients of group I would suggest a synthesis defect by impaired endothelial cells-due to vascular calcifications (?). Free protein S deficiency could increase the risk of thrombotic complications in these patients.

Adult↗

Novel insights into vascular calcification.

Vascular calcification is not just a hallmark of uremic arterio- and atherosclerosis, but also a significant cardiovascular risk factor in patients with chronic kidney disease. In contrast to the previous assumption that vascular calcification predominantly occurs by passive precipitation of calcium and phosphate ions, recent research led to the insight that extraosseous calcification is a highly regulated process. High serum phosphate and calcium levels may induce a process of osteogenic 'bone-like' differentiation of vascular smooth muscle cells, while deficiencies of calcification inhibitors or a disturbed balance towards calcification inducers may have a relevant pathophysiological influence on the initiation and progression of calcified lesions. This overview summarizes some of the best explored novel risk factors for disturbances of calcium and phosphate homeostasis and points to the integral role of hyperphosphatemia as a modifiable key trigger in calcification processes.

Atherosclerosis↗

[Mechanism of vascular calcification].

Vascular calcification is an active, regulated process rather than a passive accumulation of mineral in areas of necrosis or injury including atherosclerotic plaque, aging, or damaged cardiac valves. This review describes roles of the following factors in progression of vascular calcification: (1)apoptotic cell death or chondro/osteogenic differentiation of vascular mesenchymal cells, (2)sodium-dependent phosphate co-transporter, (3)alkaline phosphatase and nucleotide triphosphate pyrophosphohydrolase (metabolism of inorganic pyrophosphate), (4)inflammatory cells such as T cells and macrophages, (5)regulatory factors including hormones, growth factors, and cytokines.

English Abstract↗

[Vascular calcification].

Vascular calcification is a pathological calcification process. Its pathogenesis involves active mineralization by chondrogenic and osteogenic cells. Since cartilaginous metaplasia has been found in several vascular diseases, this process may represent one of vascular remodeling in response to vascular injury. Endochondral ossification following cartilaginous metaplasia play an important role in the progression of vascular calcification.

Animals↗

Association of conjunctival and corneal calcification with vascular calcification in dialysis patients.

BACKGROUND: Conjunctival and corneal calcification (CCC) is a well-known and easily detectable extraskeletal calcification, but its association with vascular calcification was not investigated previously. The aim of this study is to investigate the relationship of CCC with vascular calcification and bone metabolism parameters in dialysis patients. METHODS: We evaluated 63 patients (30 men, 33 women; mean age, 43.5 +/- 13.4 years) who were on dialysis therapy for more than 6 months. Forty-four patients were on peritoneal dialysis and 19 patients were on hemodialysis therapy. The same observer evaluated the presence of CCC by using a slit-lamp microscope, and a total CCC score was recorded for each patient. Fifty-two age- and sex-matched healthy controls also were evaluated by using the same method. Biochemical data were collected from patient files. Bone mineral density (BMD) of the lumbar spine and femoral neck was measured, and the presence of vascular calcification was assessed by using x-ray examinations of the pelvis and hands. RESULTS: Mean CCC score in patients was significantly higher than that in controls (6.2 +/- 5.1 versus 1.3 +/- 1.8; P = 0.001). CCC score correlated significantly with duration of renal replacement therapy ( r s = 0.392; P = 0.002), serum phosphorus level ( r s = 0.259; P = 0.042), and calcium x phosphorus product ( r s = 0.337; P = 0.007). However, we did not find a significant correlation with calcium, parathyroid hormone, alkaline phosphatase, albumin, or C-reactive protein level or BMD. The frequency of vascular calcification was significantly greater in patients with a high CCC score (CCC score > or = 10) compared with a low CCC score (< or =3; 56.3% versus 5.6%; P = 0.002). CONCLUSION: Evaluation of CCC score is an easy, fast, and noninvasive method. It seems that CCC score can be used as an additional tool to assess the status of extraskeletal calcification in dialysis patients.

Adult↗

[Mechanism of vascular calcification].

Vascular calcification, especially in coronary artery not only serves as a surrogate marker for atherosclerosis, but also predicts a higher risk of myocardial infarction and death. Its pathogenesis involves an active mineralization process by chondrogenic and osteogenic cells as well as a passive precipitation of minerals. Since atherosclerosis is a chronic vascular inflammation, plaque calcification is conceptualized as a chondrogenic and/or osteogenic process associated with chronic vascular inflammation.

Blood Vessels↗

Vascular calcification.

Vascular calcification is an active and modifiable process involved in many disease entities, including atherosclerosis, cardiac valve disease and calcific uremic arteriolopathy. It occurs with distinct characteristics at different sites in the vessel wall. The mechanism by which calcification is induced remains uncertain; the roles of bone matrix and extracellular matrix proteins, estrogen and vitamin D are being further defined in animal models and clinical trials. Some risk factors for calcific uremic arteriolopathy and cardiac valve calcification, both disproportionately affecting chronic hemodialysis patients, have been identified in observational studies.

Animals↗

Vascular smooth muscle cell phenotypic plasticity and the regulation of vascular calcification.

Vascular smooth muscle cells (VSMCs) exhibit an extraordinary capacity to undergo phenotypic change during development, in vitro and in association with disease. Unlike other muscle cells they do not terminally differentiate. Development and maintenance of the mature contractile phenotype is regulated by a number of interacting transcription factors. In response to injury contractile VSMCs can be induced to change phenotype, proliferate and migrate to effect repair. On completion of the repair process VSMCs return to a nonproliferating contractile phenotype. In this way, in the context of atherosclerosis, a protective fibrous cap is formed and maintained at sites of injury. However in disease, when modulatory signals are perturbed, this phenotypic transition is dysregulated and VSMCs are induced to undergo inappropriate differentiation into cells with features of other mesenchymal lineages such as osteoblasts, chondrocytes and adipocytes. Moreover, evidence is accumulating that these aberrant phenotypic transitions contribute to the pathogenesis of vascular diseases such as atherosclerosis and Monckeberg's Sclerosis. Indeed, the osteo/chondrocytic conversion of VSMCs and the association of this phenotype with vascular calcification is a paradigm for how inappropriate differentiation can influence disease processes. Understanding of the mechanisms and signalling pathways involved in this particular phenotype change is well advanced offering the possibility for the design of successful therapeutic interventions in the future.

Calcinosis↗