Arterial calcification is driven by RAGE in Enpp1-/- mice

Similarities and Differences of Vascular Calcification in Diabetes and Chronic Kidney Disease

Presently, the mechanism of occurrence and development of vascular calcification (VC) is not fully understood; a range of evidence suggests a positive association between diabetes mellitus (DM) and VC. Furthermore, the increasing burden of central vascular disease in patients with chronic kidney disease (CKD) may be due, at least in part, to VC. In this review, we will review recent advances in the mechanisms of VC in the context of CKD and diabetes. The study further unveiled that VC is induced through the stimulation of pro-inflammatory factors, which in turn impairs endothelial function and triggers similar mechanisms in both disease contexts. Notably, hyperglycemia was identified as the distinctive mechanism driving calcification in DM. Conversely, in CKD, calcification is facilitated by mechanisms including mineral metabolism imbalance and the presence of uremic toxins. Additionally, we underscore the significance of investigating vascular alterations and newly identified molecular pathways as potential avenues for therapeutic intervention.

Vector potential dual effect of promoting the proliferation of chondrocytes and inhibiting the calcification process in the articular cartilage

OA commonly affects the articular cartilage of the tibia, and its calcification worsens its advancement and its prevalence has recently increased. Vector potential (VP) represents a novel physical therapy for treating OA. Since the impact of VP on articular cartilage remains unknown, we aimed to assess its effects on articular cartilage and its potential as a new treatment for OA. Here, we divided 24 male Wistar rats, 6-week-old, into control (CO, n = 12) and VP stimulus (n = 12) groups (VP conditions: volt, 67 mV; frequency, 20 kHz; current, 0.12 mA; experimental frequency, 30 min/days, 5 days/week, and 3 weeks). Articular cartilage can be classified into four layers: superficial, medial, deep, and calcified. Moreover, the number of chondrocytes in the articular cartilage was higher in the CO group compared to the VP group, although the calcified layer was thinner in the VP group. Furthermore, MKi67 exhibited higher expression in the VP group than in the CO group, while ectonucleotide pyrophosphatase/phosphodiesterase 1 was downregulated in the VP group. Our findings indicate that VP positively influenced chondrocyte proliferation and inhibited calcification in articular cartilage. Thus, VP stimulation may assist in the development of novel strategies for preventing OA.

Inflammation: a putative link between phosphate metabolism and cardiovascular disease

Dietary habits in the western world lead to increasing phosphate intake. Under physiological conditions, extraosseous precipitation of phosphate with calcium is prevented by a mineral buffering system composed of calcification inhibitors and tight control of serum phosphate levels. The coordinated hormonal regulation of serum phosphate involves fibroblast growth factor 23 (FGF23), αKlotho, parathyroid hormone (PTH) and calcitriol. A severe derangement of phosphate homeostasis is observed in patients with chronic kidney disease (CKD), a patient collective with extremely high risk of cardiovascular morbidity and mortality. Higher phosphate levels in serum have been associated with increased risk for cardiovascular disease (CVD) in CKD patients, but also in the general population. The causal connections between phosphate and CVD are currently incompletely understood. An assumed link between phosphate and cardiovascular risk is the development of medial vascular calcification, a process actively promoted and regulated by a complex mechanistic interplay involving activation of pro-inflammatory signalling. Emerging evidence indicates a link between disturbances in phosphate homeostasis and inflammation. The present review focuses on critical interactions of phosphate homeostasis, inflammation, vascular calcification and CVD. Especially, pro-inflammatory responses mediating hyperphosphatemia-related development of vascular calcification as well as FGF23 as a critical factor in the interplay between inflammation and cardiovascular alterations, beyond its phosphaturic effects, are addressed.

The Calcium Binding Protein S100A11 and Its Roles in Diseases

The calcium binding protein S100 family in humans contains 21 known members, with each possessing a molecular weight between 10 and 14 kDa. These proteins are characterized by a unique helix-loop-helix EF hand motif, and often form dimers and multimers. The S100 family mainly exists in vertebrates and exerts its biological functions both inside cells as a calcium sensor/binding protein, as well as outside cells. S100A11, a member of the S100 family, may mediate signal transduction in response to internal or external stimuli and it plays various roles in different diseases such as cancers, metabolic disease, neurological diseases, and vascular calcification. In addition, it can function as chemotactic agent in inflammatory disease. In this review, we first detail the discovery of S100 proteins and their structural features, and then specifically focus on the tissue and organ expression of S100A11. We also summarize its biological activities and roles in different disease and signaling pathways, providing an overview of S100A11 research thus far.

Homology Modeling and Virtual Screening of Proteins Related to PXE and PXE-like Diseases: Insights for Overlapping Metabolites

Background:

The molecular etiology of Pseudoxanthoma Elasticum (PXE), an autosomal recessive connective tissue disorder, has become increasingly complex as not only mutations in the ABCC6, but also in ENPP1 and GGCX, can cause resembling phenotypes.

Methods:

To get insights on the common pathway, the overlapping metabolites for these three proteins were predicted through 3D homology modeling and virtual screening. 3D homology models of ABCC6, ENPP1, and GGCX were generated by the MODELLER program, which were further validated using RAMPAGE and ERRAT servers. Substrate binding sites of ABCC6 were predicted using blind docking of reported in vitro substrates.

Results:

Virtual screening against the substrate binding site of ABCC6 using metabolites listed in Human Metabolome Databases (HMDB) revealed the best possible substrate of ABCC6. Those listed metabolites were further docked against predicted substrate binding sites of GGCX and ENPP1. Molecular docking and virtual screening revealed a list of 133 overlapping metabolites of these three proteins. Most of them are Phosphatidylinositol (PI), Phosphatidylserine (PS), Diacylglycerol (DAG), phosphatidic acid, oleanolic acid metabolites and were found to have links with calcification.

Conclusion:

These predicted overlapping metabolites may give novel insights for searching common pathomechanism for PXE and PXE-like diseases.

The role of soluble receptor for advanced glycation end-products (sRAGE) in the general population and patients with diabetes mellitus with a focus on renal function and overall outcome

Isoforms of the receptor for advanced glycation end-product (RAGE) protein, which lack the transmembrane and the signaling (soluble RAGE or sRAGE) domains are hypothesized to counteract the detrimental action of the full-length receptor by acting as a decoy, and they provide a potential tool to treat RAGE-associated diseases. Multiple studies have explored the relationship between sRAGE and endogenous secretory RAGE and its polymorphism and obesity, metabolic syndrome, atherosclerosis, kidney function, and increased mortality in the general population. In addition, sRAGE may be a key player in the pathogenesis of diabetes mellitus and its microvascular (e.g. kidney disease) as well as macrovascular (e.g. cardiovascular disease) complications. In this review, we focus on the role of sRAGE as a biomarker in these specific areas. As there is a lack of an underlying unifying hypothesis about how sRAGE changes according to the disease condition or risk factor, there is a call to incorporate all three players of the AGE-RAGE axis into a new universal biomarker/risk marker: (AGE + RAGE)/sRAGE. However, the measurement of RAGE in humans is not practical as it is a cell-bound receptor for which tissue is required for analysis. A high AGE/sRAGE ratio may be a valuable alternative and practical universal biomarker/risk marker for diseases associated with the AGE-RAGE axis, irrespective of low or high serum sRAGE concentrations.

Arterial Stiffness: A Focus on Vascular Calcification and Its Link to Bone Mineralization

This review focuses on the association between vascular calcification and arterial stiffness, highlighting the important genetic factors, systemic and local microenvironmental signals, and underlying signaling pathways and molecular regulators of vascular calcification. Elevated oxidative stress appears to be a common procalcification factor that induces osteogenic differentiation and calcification of vascular cells in a variety of disease conditions such as atherosclerosis, diabetes mellitus, and chronic kidney disease. Thus, the role of oxidative stress and oxidative stress-regulated signals in vascular smooth muscle cells and their contributions to vascular calcification are highlighted. In relation to diabetes mellitus, the regulation of both hyperglycemia and increased protein glycosylation, by AGEs (advanced glycation end products) and O-linked β-N-acetylglucosamine modification, and its role in enhancing intracellular pathophysiological signaling that promotes osteogenic differentiation and calcification of vascular smooth muscle cells are discussed. In the context of chronic kidney disease, this review details the role of calcium and phosphate homeostasis, parathyroid hormone, and specific calcification inhibitors in regulating vascular calcification. In addition, the impact of the systemic and microenvironmental factors on respective intrinsic signaling pathways that promote osteogenic differentiation and calcification of vascular smooth muscle cells and osteoblasts are compared and contrasted, aiming to dissect the commonalities and distinctions that underlie the paradoxical vascular-bone mineralization disorders in aging and diseases.

S100/RAGE-Mediated Inflammation and Modified Cholesterol Lipoproteins as Mediators of Osteoblastic Differentiation of Vascular Smooth Muscle Cells

Arterial calcification is a feature of atherosclerosis and shares many risk factors including diabetes, dyslipidemia, chronic kidney disease, hypertension, and age. Although there is overlap in risk factors, anti-atherosclerotic therapies, including statins, fail to reduce arterial, and aortic valve calcifications. This suggests that low density lipoprotein (LDL) may not be the main driver for aortic valve disease and arterial calcification. This review focuses on modified LDLs and their role in mediating foam cell formation in smooth muscle cells (SMCs), with special emphasis on enzyme modified non-oxidized LDL (ELDL). In vivo, ELDL represents one of the many forms of modified LDLs present in the atherosclerotic vessel. Phenotypic changes of macrophages and SMCs brought about by the uptake of modified LDLs overlap significantly in an atherosclerotic milieu, making it practically impossible to differentiate between the effects from oxidized LDL, ELDL, and other LDL modification. By studying in vitro-generated modifications of LDL, we were able to demonstrate marked differences in the transcriptome of human coronary artery SMCs (HCASMCs) upon uptake of ELDL, OxLDL, and native LDL, indicating that specific modifications of LDL in atherosclerotic plaques may determine the biology and functional consequences in vasculature. Enzyme-modified non-oxidized LDL (ELDL) induces calcification of SMCs and this is associated with reduced mRNA levels for genes protective for calcification (ENPP1, MGP) and upregulation of osteoblastic genes. A second focus of this review is on the synergy between hyperlipidemia and accelerated calcification In vivo in a mouse models with transgenic expression of human S100A12. We summarize mechanisms of S100A12/RAGE mediated vascular inflammation promoting vascular and valve calcification in vivo.

Comparative gene array analyses of severe elastic fiber defects in late embryonic and newborn mouse aorta

Elastic fibers provide reversible elasticity to the large arteries and are assembled during development when hemodynamic forces are increasing. Mutations in elastic fiber genes are associated with cardiovascular disease. Mice lacking expression of the elastic fiber genes elastin ( Eln-/-), fibulin-4 ( Efemp2-/-), or lysyl oxidase ( Lox-/-) die at birth with severe cardiovascular malformations. All three genetic knockout models have elastic fiber defects, aortic wall thickening, and arterial tortuosity. However, Eln-/- mice develop arterial stenoses, while Efemp2-/- and Lox-/- mice develop ascending aortic aneurysms. We performed comparative gene array analyses of these three genetic models for two vascular locations and developmental stages to determine differentially expressed genes and pathways that may explain the common and divergent phenotypes. We first examined arterial morphology and wall structure in newborn mice to confirm that the lack of elastin, fibulin-4, or lysyl oxidase expression provided the expected phenotypes. We then compared gene expression levels for each genetic model by three-way ANOVA for genotype, vascular location, and developmental stage. We found three genes upregulated by genotype in all three models, Col8a1, Igfbp2, and Thbs1, indicative of a common response to severe elastic fiber defects in developing mouse aorta. Genes that are differentially regulated by vascular location or developmental stage in all three models suggest mechanisms for location or stage-specific disease pathology. Comparison of signaling pathways enriched in all three models shows upregulation of integrins and matrix proteins involved in early wound healing, but not of mature matrix molecules such as elastic fiber proteins or fibrillar collagens.

ENPP1 enzyme replacement therapy improves blood pressure and cardiovascular function in a mouse model of generalized arterial calcification of infancy

Generalized arterial calcification of infancy (GACI) is a rare, life-threatening disorder caused by loss-of-function mutations in the gene encoding ectonucleotide pyrophosphatase phosphodiesterase 1 (ENPP1), which normally hydrolyzes extracellular ATP into AMP and pyrophosphate (PP_i). The disease is characterized by extensive arterial calcification and stenosis of large- and medium-sized vessels, leading to vascular-related complications of hypertension and heart failure. There is currently no effective treatment available, but bisphosphonates – nonhydrolyzable PP_i analogs – are being used off-label to reduce arterial calcification, although this has no reported impact on the hypertension and cardiac dysfunction features of GACI. In this study, the efficacy of a recombinant human ENPP1 protein therapeutic (rhENPP1) was tested in Enpp1^asj-2J homozygous mice (Asj-2J or Asj-2J hom), a model previously described to show extensive mineralization in the arterial vasculature, similar to GACI patients. In a disease prevention study, Asj-2J mice treated with rhENPP1 for 3 weeks showed >95% reduction in aorta calcification. Terminal hemodynamics and echocardiography imaging of Asj-2J mice also revealed that a 6-week rhENPP1 treatment normalized elevated arterial and left ventricular pressure, which translated into significant improvements in myocardial compliance, contractility, heart workload and global cardiovascular efficiency. This study suggests that ENPP1 enzyme replacement therapy could be a more effective GACI therapeutic than bisphosphonates, treating not just the vascular calcification, but also the hypertension that eventually leads to cardiac failure in GACI patients.

Summary: ENPP1 enzyme replacement therapy can have important implications for generalized arterial calcification of infancy by treating both vascular calcification and hypertension, which are the leading causes of cardiac failure and mortality in patients.

Vascular Calcification: Current Genetics Underlying This Complex Phenomenon

OBJECTIVE

Vascular calcification is the consequence of the complex interaction between genetic, environmental, and vascular factors, which ultimately lead to the deposition of calcium in the tunica intima (atherosclerotic calcification) or tunica media (Mönckenberg's sclerosis). Vascular calcification is also closely related to other pathologies, such as diabetes mellitus, dyslipidemia, and chronic kidney disease. It has been concluded that the degree of vascular calcification may vary from person to person, even if the associated pathologies and environmental factors are the same. Therefore, this suggests an important genetic contribution to the development of vascular calcification. This review aimed to find the most recent evidence about vascular calcification pathophysiology regarding the genetic aspects and molecular pathways.

DATA SOURCES

We conducted an exhaustive search in Scopus, EBSCO, and PubMed with the keywords "genetics and vascular calcification", "molecular pathways, genetic and vascular calcification" and included the main articles from January 1995 up to August 2016. We focused on the most recent evidence about vascular calcification pathophysiology regarding the genetic aspects and molecular pathways.

STUDY SELECTION

The most valuable published original and review articles related to our objective were selected.

RESULTS

Vascular calcification is a multifactorial disease; thus, its pathophysiology cannot be explained by a single specific factor, rather than by the result of the association of several genetic variants, molecular pathway interactions, and environmental factors that promote its development.

CONCLUSION

Although several molecular aspects of this mechanism have been elucidated, there is still a need for a better understanding of the factors that predispose to this disease.

Defective interplay between mTORC1 activity and endoplasmic reticulum stress-unfolded protein response in uremic vascular calcification

Vascular calcification increases the risk of cardiovascular disease and death in patients with chronic kidney disease (CKD). Increased activity of mammalian target of rapamycin complex 1 (mTORC1) and endoplasmic reticulum (ER) stress-unfolded protein response (UPR) are independently reported to partake in the pathogenesis of vascular calcification in CKD. However, the association between mTORC1 activity and ER stress-UPR remains unknown. We report here that components of the uremic state [activation of the receptor for advanced glycation end products (RAGE) and hyperphosphatemia] potentiate vascular smooth muscle cell (VSMC) calcification by inducing persistent and exaggerated activity of mTORC1. This gives rise to prolonged and excessive ER stress-UPR as well as attenuated levels of sestrin 1 ( Sesn1) and Sesn3 feeding back to inhibit mTORC1 activity. Activating transcription factor 4 arising from the UPR mediates cell death via expression of CCAAT/enhancer-binding protein (c/EBP) homologous protein (CHOP), impairs the generation of pyrophosphate, a potent inhibitor of mineralization, and potentiates VSMC transdifferentiation to the osteochondrocytic phenotype. Short-term treatment of CKD mice with rapamycin, an inhibitor of mTORC1, or tauroursodeoxycholic acid, a bile acid that restores ER homeostasis, normalized mTORC1 activity, molecular markers of UPR, and calcium content of aortas. Collectively, these data highlight that increased and/or protracted mTORC1 activity arising from the uremic state leads to dysregulated ER stress-UPR and VSMC calcification. Manipulation of the mTORC1-ER stress-UPR pathway opens up new therapeutic strategies for the prevention and treatment of vascular calcification in CKD.

Impact of magnesium:calcium ratio on calcification of the aortic wall

Objective

An inverse relationship between serum magnesium concentration and vascular calcification has been reported following observational clinical studies. Moreover, several studies have been suggesting a protective effect of magnesium on the vascular calcification. However, the exact mechanism remains elusive, and investigators have speculated among a myriad of potential actions. The effect of magnesium on calcification of the aortic wall is yet to be investigated. In the present study, the effects of magnesium and calcium on the metabolism of extracellular PPi, the main endogenous inhibitor of vascular calcification, were investigated in the rat aorta.

Approach and results

Calcium and magnesium have antagonist effects on PPi hydrolysis in the aortic wall. K_m and K_i values for PPi hydrolysis in rat aortic rings were 1.1 mmol/L magnesium and 32 μmol/L calcium, respectively, but ATP hydrolysis was not affected with calcium. Calcium deposition in the rat aortic wall dramatically increased when the magnesium concentration was increased (ratio of Mg:Ca = 1:1; 1.5 mmol/L calcium and 1.5 mmol/L magnesium) respect to low magnesium concentration (ratio Mg:Ca = 1:3, 1.5 mmol/L calcium and 0.75 mmol/L magnesium).

Conclusion

Data from observational clinical studies showing that the serum magnesium concentration is inversely correlated with vascular calcification could be reinterpreted as a compensatory regulatory mechanism that reduces both PPi hydrolysis and vascular calcification. The impact of magnesium in vascular calcification in humans could be studied in association with calcium levels, for example, as the magnesium:calcium ratio.

AGEs induce ectopic endochondral ossification in intervertebral discs

Ectopic calcifications in intervertebral discs (IVDs) are known characteristics of IVD degeneration that are not commonly reported but may be implicated in structural failure and dysfunctional IVD cell metabolic responses. This study investigated the novel hypothesis that ectopic calcifications in the IVD are associated with advanced glycation end products (AGEs) via hypertrophy and osteogenic differentiation. Histological analyses of human IVDs from several degeneration stages revealed areas of ectopic calcification within the nucleus pulposus and at the cartilage endplate. These ectopic calcifications were associated with cells positive for the AGE methylglyoxal-hydroimidazolone-1 (MG-H1). MG-H1 was also co-localised with Collagen 10 (COL10) and Osteopontin (OPN) suggesting osteogenic differentiation. Bovine nucleus pulposus and cartilaginous endplate cells in cell culture demonstrated that 200 mg/mL AGEs in low-glucose media increased ectopic calcifications after 4 d in culture and significantly increased COL10 and OPN expression. The receptor for AGE (RAGE) was involved in this differentiation process since its inhibition reduced COL10 and OPN expression. We conclude that AGE accumulation is associated with endochondral ossification in IVDs and likely acts via the AGE/RAGE axis to induce hypertrophy and osteogenic differentiation in IVD cells. We postulate that this ectopic calcification may play an important role in accelerated IVD degeneration including the initiation of structural defects. Since orally administered AGE and RAGE inhibitors are available, future investigations on AGE/RAGE and endochondral ossification may be a promising direction for developing non-invasive treatment against progression of IVD degeneration.

Vascular Calcification Revisited: A New Perspective for Phosphate Transport

Elevated serum phosphorus has emerged as a key risk factor for pathologic calcification of cardiovascular structures, or vascular calcification (VC). To prevent the formation of calciumphosphate deposits (CPD), the body uses adenosine-5’-triphosphate (ATP) to synthesize inhibitors of calcification, including proteins and inhibitors of low molecular weight. Extracellular pyrophosphate (PPi) is a potent inhibitor of VC, which is produced during extracellular hydrolysis of ATP. Loss of function in the enzymes and transporters that are involved in the cycle of extracellular ATP, including Pi transporters, leads to excessive deposition of calcium-phosphate salts. Treatment of hyperphosphatemia with Pi-binders and Injection of exogenous PPi are the effective treatments to prevent CPD in the aortic wall. The role of sodium phosphate cotransporters in ectopic calcification is contradictory and not well defined, but their important role in the control of intracellular Pi levels and the synthesis of ATP make them an important target to study.

Serum soluble RAGE levels and carotid atherosclerosis: the Northern Manhattan Study (NOMAS)

BACKGROUND

Recent cohort studies suggested that serum levels of soluble Receptor for Advanced Glycation End-products (sRAGE) are associated with the risk of cardiovascular disease. We hypothesized that sRAGE levels are associated with subclinical atherosclerosis in a racially and ethnically diverse population.

METHODS AND RESULTS

828 stroke-free participants from the Northern Manhattan Study (mean age 71.1±8.7yrs; 64% Hispanic, 19% black, and 17% white) underwent high-resolution carotid B-mode ultrasound to measure carotid plaque (present in 62% of subjects) and intima-media thickness (IMT) (mean Total=0.96±0.10 mm). Serum sRAGE was measured by ELISA and associations tested between sRAGE with IMT and plaque presence. Soluble RAGE levels were not associated with plaque presence or IMT after adjusting for sociodemographic, vascular risk factors and medication use. Stratification by race-ethnicity did not reveal any associations with carotid IMT or plaque.

CONCLUSION

In the present study, sRAGE levels were not associated with carotid atherosclerosis.

RANKL-OPG and RAGE modulation in vascular calcification and diabetes: novel targets for therapy

Type 2 diabetes is associated with increased cardiovascular morbidity and mortality and early vascular ageing. This takes the form of atherosclerosis, with progressive vascular calcification being a major complication in the pathogenesis of this disease. Current research and drug targets in diabetes have hitherto focused on atherosclerosis, but vascular calcification is now recognised as an independent predictor of cardiovascular morbidity and mortality. An emerging regulatory pathway for vascular calcification in diabetes involves the receptor activator for nuclear factor κB (RANK), RANK ligand (RANKL) and osteoprotegerin (OPG). Important novel biomarkers of calcification are related to levels of glycation and inflammation in diabetes. Several therapeutic strategies could have advantageous effects on the vasculature in patients with diabetes, including targeting the RANKL and receptor for AGE (RAGE) signalling pathways, since there has been little success-at least in macrovascular outcomes-with conventional glucose-lowering therapy. There is substantial and relevant clinical and basic science evidence to suggest that modulating RANKL-RANK-OPG signalling, RAGE signalling and the associated proinflammatory milieu alters the natural course of cardiovascular complications and outcomes in people with diabetes. However, further research is critically needed to understand the precise mechanisms underpinning these pathways, in order to translate the anti-calcification strategies into patient benefit.

Two soluble isoforms of receptors for advanced glycation end products (RAGE) in carotid atherosclerosis: the difference of soluble and endogenous secretory RAGE

BACKGROUND

Advanced glycation end products (AGEs) promote atherosclerosis through binding to their receptor, RAGE. Since soluble RAGE (sRAGE) and endogenous secretory RAGE (esRAGE) may suppress AGEs-RAGE signaling, we examined the usefulness of sRAGE and esRAGE as biomarkers of early-stage atherosclerosis.

METHODS

Serum sRAGE and esRAGE levels were measured in 284 subjects with no history of atherothrombotic diseases. The subjects were divided into high-sRAGE and low-sRAGE groups and high-esRAGE and low-esRAGE groups based on respective median values. We investigated the relationships between these parameters and the following factors: number of metabolic components, maximum intima-media thickness of the common carotid artery (IMT Cmax), carotid plaque calcification, and asymptomatic cerebral white matter lesions.

RESULTS

The low-sRAGE and low-esRAGE groups exhibited significantly more components of metabolic syndrome than the high-sRAGE and high-esRAGE groups, respectively. IMT Cmax was significantly higher in the low-sRAGE and low-esRAGE groups. Low-sRAGE levels were significantly associated with carotid plaque calcification. Multiple linear regression analysis identified body mass index (BMI), age, and high-sensitivity C-reactive protein as determinants of sRAGE, whereas only BMI was identified as a determinant of esRAGE.

CONCLUSIONS

We demonstrated that sRAGE and esRAGE are associated with atherosclerotic risk factors in early-stage atherosclerosis, suggesting that their levels evolve in correlation with those of metabolic components and inflammation. Interestingly, low-sRAGE and esRAGE levels are associated with high IMT Cmax, but only low-sRAGE levels were associated with carotid plaque calcification. Thus, sRAGE and esRAGE may reflect different aspects of atherosclerosis in its early stage.

S100/Calgranulin-mediated inflammation accelerates left ventricular hypertrophy and aortic valve sclerosis in chronic kidney disease in a receptor for advanced glycation end products-dependent manner

OBJECTIVE

S100A12 and fibroblast growth factor 23 are biomarkers of cardiovascular morbidity and mortality in patients with chronic kidney disease (CKD). We tested the hypothesis that human S100/calgranulin would accelerate cardiovascular disease in mice subjected to CKD.

APPROACH AND RESULTS

A bacterial artificial chromosome of the human S100/calgranulin gene cluster containing the genes and regulatory elements for S100A8, S100A9, and S100A12 was expressed in C57BL/6J mouse (hBAC-S100) to generate a novel humanized mouse model. CKD was induced by ureteral ligation, and hBAC-S100 mice and wild-type mice were studied after 10 weeks of chronic uremia. hBAC-S100 mice with CKD showed increased fibroblast growth factor 23 in the hearts, left ventricular hypertrophy, diastolic dysfunction, focal cartilaginous metaplasia, and calcification of the mitral and aortic valve annulus together with aortic valve sclerosis. This phenotype was not observed in wild-type mice with CKD or in hBAC-S100 mice lacking the receptor for advanced glycation end products with CKD, suggesting that the inflammatory milieu mediated by S100/receptor for advanced glycation end products promotes pathological cardiac hypertrophy in CKD. In vitro, inflammatory stimuli including interleukin-6, tumor necrosis factor-α, lipopolysaccarides, or serum from hBAC-S100 mice upregulated fibroblast growth factor 23 mRNA and protein in primary murine neonatal and adult cardiac fibroblasts.

CONCLUSIONS

Myeloid-derived human S100/calgranulin is associated with the development of cardiac hypertrophy and ectopic cardiac calcification in a receptor for advanced glycation end products-dependent manner in a mouse model of CKD. We speculate that fibroblast growth factor 23 produced by cardiac fibroblasts in response to cytokines may act in a paracrine manner to accelerate left ventricular hypertrophy and diastolic dysfunction in hBAC-S100 mice with CKD.

Mono-allelic and bi-allelic ENPP1 deficiency promote post-injury neointimal hyperplasia associated with increased C/EBP homologous protein expression

OBJECTIVE

Bi-allelic function-inactivating ENPP1 mutations cause artery media calcification (AMC) with associated severe myointimal hyperplasia in generalized arterial calcification of infancy (GACI), whereas mono-allelic ENPP1 deficiency is phenotypically normal. Here, we tested if ENPP1 deficiency promotes abnormal vascular smooth muscle cell (VSMC)-driven responses to injury, with or without calcification. The ER stress mediator C/EBP homologous protein (CHOP) affects neointimal hyperplasia and atherosclerosis, and has paradoxical effects on bone formation. Hence, we assessed relationships between ENPP1 and CHOP in VSMCs.

METHODS

We studied ENPP1-deficient mice and control littermates subjected to left carotid artery ligation, and isolated and studied VSMCs from these and Chop-/- mice, or with CHOP siRNA treatment.

RESULTS

Normal Enpp1-/+ mice, in addition to Enpp1-/- mice prior to AMC development, had accelerated neointimal hyperplasia in response to carotid artery ligation at 7-8 weeks age. Neointimal hyperplasia was linked with robust artery media CHOP expression in situ, but with marked AMC only in injured Enpp1-/- arteries. Cultured, ENPP1-deficient and CHOP-deficient VSMCs had increased migration and proliferation to PDGF. Cultured Chop-/- VSMCs demonstrated increased Pi donor-induced calcification. CHOP was significantly increased in Pi donor treated Enpp1-/- and Enpp1-/+ cultured VSMCs. CHOP siRNA treatment of Enpp1-/- VSMCs increased calcification, associated with elevated expression of tissue nonspecific alkaline phosphatase and the master osteoblastic transcription factor RUNX2.

CONCLUSIONS

Both mono-allelic and bi-allelic ENPP1 deficiency promote dysregulated VSMC function, with robust lesion CHOP expression and enhanced neointimal hyperplasia after injury in vivo, but marked post-injury calcification limited to Enpp1-/- mice. Intimal hyperplasia in GACI appears regulated by biologic effects of ENPP1 deficiency other than calcification, including ER stress. VSMC CHOP excess in ENPP1 deficiency may primarily function to limit VSMC calcification.

Plasma levels of advanced glycation endproducts are associated with type 1 diabetes and coronary artery calcification

Background

Advanced glycation endproducts (AGEs) may play a role in the development of coronary artery calcification (CAC) in type 1 diabetes (T1DM). We studied plasma AGEs in association with T1DM and CAC, and whether or not the latter association could be explained by low-grade inflammation (LGI) or endothelial dysfunction (ED).

Methods

We studied 165 individuals with and 169 without T1DM. CAC was quantified in a CAC score based on CT-scanning. Plasma levels of protein-bound pentosidine, N^ϵ-(carboxymethyl)lysine (CML) and N^ϵ-(carboxyethyl)lysine (CEL) were measured with HPLC/UPLC with fluorescence detection or tandem-mass spectrometry. Tetrahydropyrimidine (THP) was measured with ELISA, as were HsCRP, and sVCAM-1 and vWF, as markers for LGI and ED, respectively. Associations were analyzed with ANCOVA and adjusted for age, sex, BMI, waist-to-hip ratio, smoking, blood pressure, lipid profile, eGFR and T1DM.

Results

Individuals with T1DM had higher plasma levels of pentosidine, CML and THP compared with controls; means (95% CI) were 0.69 (0.65-0.73) vs. 0.51 (0.48-0.54) nmol/mmol LYS, p < 0.001; 105 (102–107) vs. 93 (90–95) nmol/mmol LYS, p < 0.001; and 126 (118–134) vs. 113 (106–120) U/mL, p = 0.03, respectively. Levels of pentosidine were higher in individuals with T1DM with a moderate to high compared with a low CAC score, means (95% CI) were 0.81 (0.70-0.93) vs. 0.67 (0.63-0.71) nmol/mmol LYS, p = 0.03, respectively. This difference was not attenuated by adjustment for LGI or ED.

Conclusions

We found a positive association between pentosidine and CAC in T1DM. These results may indicate that AGEs are possibly involved in the development of CAC in individuals with T1DM.

Regulatory circuits controlling vascular cell calcification

Vascular calcification is a common feature of chronic kidney disease, cardiovascular disease, and aging. Such abnormal calcium deposition occurs in medial and/or intimal layers of blood vessels as well as in cardiac valves. Once considered a passive and inconsequential finding, the presence of calcium deposits in the vasculature is widely accepted as a predictor of increased morbidity and mortality. Recognition of the importance of vascular calcification in health is driving research into mechanisms that govern its development, progression, and regression. Diverse, but highly interconnected factors, have been implicated, including disturbances in lipid metabolism, oxidative stress, inflammatory cytokines, and mineral and hormonal balances, which can lead to formation of osteoblast-like cells in the artery wall. A tight balance of procalcific and anticalcific regulators dictates the extent of disease. In this review, we focus on the main regulatory circuits modulating vascular cell calcification.

New insights into NPP1 function: lessons from clinical and animal studies

The recent elucidation of rare human genetic disorders resulting from mutations in ectonucleotide pyrophosphotase/phosphodiesterase (ENPP1), also known as plasma cell membrane glycoprotein 1 (PC-1), has highlighted the vital importance of this molecule in human health and disease. Generalised arterial calcification in infants (GACI), a frequently lethal disease, has been reported in recessive inactivating mutations in ENPP1. Recent findings have also linked hypophosphataemia to a lack of NPP1 function. A number of human genetic studies have indicated that NPP1 is a vital regulator that influences a wide range of tissues through various signalling pathways and when disrupted can lead to significant pathology. The function of Enpp1 has been widely studied in rodent models, where both the mutant tiptoe walking (ttw/ttw) mouse and genetically engineered Enpp1(-/-) mice show significant alterations in skeletal and soft tissue mineralisation, calcium/phosphate balance and glucose homeostasis. These models therefore provide important tools with which to study the potential mechanisms underpinning the human diseases associated with altered NPP1. This review will focus on the recent advances in our current knowledge of the actions of NPP1 in relation to bone disease, cardiovascular pathologies and diabetes. A fuller understanding of the mechanisms through which NPP1 exerts its pathological effects may stimulate the development of novel therapeutic strategies for patients at risk from the devastating clinical outcomes associated with disrupted NPP1 function.

Pioglitazone attenuates progression of aortic valve calcification via down-regulating receptor for advanced glycation end products

Receptor for advanced glycation end products (RAGE) is associated with inflammation and the progression of cardiovascular diseases. The current study tested the hypothesis that RAGE is involved in the pathogenesis of aortic valve (AV) calcification. Pioglitazone attenuated AV calcification in experimental hypercholesterolemic rabbits via down-regulation of RAGE. Male New Zealand rabbits weighing 2.5-3.0 kg were randomly divided into three groups: control group, high cholesterol + vitamin D(2) (HC + vitD(2)) group and HC + vitD(2) supplemented with pioglitazone group. Compared with HC + vitD(2) group, pioglitazone significantly inhibited the progression of AV calcification assessed by echocardiography. HC + vitD(2) diet markedly increased RAGE expression, oxidative stress, inflammatory cells infiltration and osteopontin expression. These changes were also significantly attenuated by administration of pioglitazone. Cultured porcine aortic valve interstitial cells (VICs) were used as in vitro model. We found that advanced glycation end products of bovine serum albumin markedly increased the expression of RAGE, induced high levels of production of pro-inflammatory cytokines and promoted osteoblastic differentiation of VICs. However, these effects were found to be remarkably suppressed by siRNA silencing of RAGE and pioglitazone as well. Our data provide evidence that RAGE activation-induced inflammation promotes AV calcification in hypercholesterolemic rabbits, which can be attenuated by pioglitazone treatment. This beneficial effect is associated with remarkable down-regulation of RAGE expression.

Pharmacology of ectonucleotidases: relevance for the treatment of cardiovascular disorders

ATP and other extracellular nucleotides have diverse and potent effects in different organs. Evidence indicates that extracellular nucleotides and nucleosides deliver crucial signals by acting upon a wide variety of purinergic receptors, which include 19 members separated in three families. Purinergic receptors encompass adenosine-sensitive receptors (P1) as well as the ATP and ADP-responsive receptors (P2). On the other side, P2 receptors are divided into ionotropic P2X receptors and G protein-coupled receptors P2Y. This system of purinergic signaling is made further complex by the fact that ectonucleotidases, membrane bound enzymes, participate in the metabolism of extracellular nucleotides, which are released by cells. Hence, ectonucleotidases are important modulators of purinergic receptor function. It should be pointed out that the ectonucleotidases includes enzymes with different substrate preferences and by their action generate different nucleotides and nucleosides as well as phosphate and pyrophosphate. A growing body of evidence points toward the fact that the expression pattern of different ectonucleotidases and purinergic receptors is implicated in several cardiovascular disorders. In this perspective, a short account is given on the role of ectonucleotidases into the pathobiology of some cardiovascular disorders and the need to develop a novel pharmacology based on those recent findings.

Inhibition of ectonucleotidase with ARL67156 prevents the development of calcific aortic valve disease in warfarin-treated rats

Calcific aortic valve disease is the most common heart valve disorder. So far, there is no medical treatment for calcific aortic valve disease. The expression of ectonucleotidases, which metabolize nucleotides into phosphate products, may influence the calcification of the aortic valve. In this study, we investigated if the administration of an ectonucleotidase inhibitor, ARL67156 (6-N,N-Diethyl-D-β,γ-dibromomethyleneATP trisodium salt), may prevent the calcification of the aortic valve in the warfarin-induced mineralization rat model. Male Wistar rats were treated with warfarin or warfarin+ARL67156 for 28 days. All rats had comprehensive Doppler-echocardiographic studies at 28 day. A gene profiling of ectonucleotidases expressed in aortas of rats was documented by quantitative real-time PCR. The amount of calcium was determined by quantitative method and von Kossa staining. Ex vivo cultures of rat aortas were also used to further assess the effect of ARL67156 on the calcifying process and Akt signaling. Mineralization of the aorta/aortic valve was documented in warfarin-treated rats and was accompanied by the development of aortic stenosis. These changes were paralleled by an increased of ectonucleotide pyrophosphatase/phosphodiesterase-1 (ENPP1). Administration of the ectonucleotidase inhibitor, ARL67156 prevented the development of aortic stenosis by lowering the level of apoptosis and mineralization of the aortic valve/aorta. In addition, ARL67156 normalized the level of pAkt, an important kinase involved in the survival pathway. Inhibition of ectonucleotidase activity prevented the development of calcific aortic valve disease in a rat model. On that account, ectonucleotidase may represent a novel target in the treatment of calcific aortic valve disease.

Genetic pathways of vascular calcification

Vascular calcification is an independent risk factor for cardiovascular disease. Arterial calcification of the aorta and coronary, carotid, and peripheral arteries becomes more prevalent with age. Genome-wide association studies have identified regions of the genome linked to vascular calcification, and these same regions are linked to myocardial infarction risk. The 9p21 region linked to vascular disease and inflammation also associates with vascular calcification. In addition to these common variants, rare genetic defects can serve as primary triggers of accelerated and premature calcification. Infancy-associated calcific disorders are caused by loss-of-function mutations in ENPP1, an enzyme that produces extracellular pyrophosphate. Adult-onset vascular calcification is linked to mutations in NTE5, another enzyme that regulates extracellular phosphate metabolism. Common conditions that secondarily enhance vascular calcification include atherosclerosis, metabolic dysfunction, diabetes, and impaired renal clearance. Oxidative stress and vascular inflammation, along with biophysical properties, converge with these predisposing factors to promote soft tissue mineralization. Vascular calcification is accompanied by an osteogenic profile, and this osteogenic conversion is seen within the vascular smooth muscle as well as the matrix. Here, we review the genetic causes of medial calcification in the smooth muscle layer, focusing on recent discoveries of gene mutations that regulate extracellular matrix phosphate production and the role of S100 proteins as promoters of vascular calcification.

Advanced glycation end-product Nε-carboxymethyl-Lysine accelerates progression of atherosclerotic calcification in diabetes

OBJECTIVE

Vascular calcification is an active deposition process of calcium phosphate which resembles bone formation and is highly regulated by osteoblast-like cells. Existing studies demonstrate that advanced glycation end-products (AGEs) may play a pathogenic role in the vascular calcification process. However, their mechanism remains poorly understood. The aim of our current study is to investigate how non-cross-link and non-fluorescent N(ε)-carboxymethyl-Lysine (CML), a major immunogen of AGEs, affect the progression of atherosclerotic calcification in diabetes.

METHODS

The present study consisted of an in vivo investigation and two in vitro investigations. In study I, male apoE(-/-) mice were first rendered diabetic by the administration of 5 daily intraperitoneal injections of streptozotocin (STZ, 40 mg/kg), and then given a semi-synthetic high-fat diet (HFD) plus daily injections of CML (10mg/kg/day). The mice were euthanized and analyzed at 0 month (group 0M, n = 10), 2 months (group 2M, n = 10), and 4 months (group 4M, n = 10) after the triple administrations of STZ-CML-HFD. In study II, the effects of CML on the apoptosis in macrophages were investigated. RAW264.7 cells were incubated with or without 50 μg/mL oxLDL plus various concentrations of CML for 48 h. In study III, we investigated whether A7r5 aortic smooth muscle cells were induced into osteoblast-like phenotypes by incubation with or without 80 μg/mL of RAW264.7-derived-apoptotic bodies and 50 μg/mL of oxLDL plus various concentrations of CML (or high-glucose) for 7 days. Related analyses (i.e., H&E staining, Masson staining, von Kossa staining, TUNEL staining, immunohistochemical staining, calcium content assay, annexin V-FITC/PI double-staining, and Western blot) were performed.

RESULTS

Morphological analysis showed that early atherosclerotic plaques appeared 2 months after the triple administrations of STZ-CML-HFD, and that typically advanced plaques with extensive calcification lesions, abundant cholesterol crystals, and proliferative collagen were formed 4 months after the triple administrations of STZ-CML-HFD. Furthermore, CML deposition signals and the expression of receptor for advanced glycation end-products (RAGE) in the aortic wall were mainly restricted in the atherosclerotic plaques. After the incubation of A7r5 smooth muscle cells with 10 μmol/L CML plus 50 μg/mL oxLDL, and 80 μg/mL apoptotic bodies (ABs) for 7 days, semi-quantitative analysis of bone morphogenetic protein 2 (BMP-2), core-binding factor α1 (cbfα1), and alkaline phosphatase (ALP) expression showed 5.0-, 2.0-, and 2.9-fold increases, respectively, compared with those in 50 μg/mL oxLDL and 80 μg/mL ABs. Subsequently, a similar trend was observed in the calcium deposition of the cell layer. However, high-glucose had no effects on the ALP activity and calcium deposition of A7r5 cell layer under high-lipid, apoptosis-coexisting conditions. Both animal and cell studies consistently demonstrated that the CML/RAGE axis may first initiate the apoptosis of macrophages in atherosclerotic lesions and then induce BMP-2-cbfα1-ALP-calcification cascade in a high-lipid, apoptosis-coexisting environment.

CONCLUSION

The CML/RAGE axis may play an important role in atherosclerotic calcification of diabetes through the mechanism that induces the apoptosis of macrophages followed by the osteogenic differentiation of aortic smooth muscle cells.

Genetics in arterial calcification: pieces of a puzzle and cogs in a wheel

Artery calcification reflects an admixture of factors such as ectopic osteochondral differentiation with primary host pathological conditions. We review how genetic factors, as identified by human genome-wide association studies, and incomplete correlations with various mouse studies, including knockout and strain analyses, fit into "pieces of the puzzle" in intimal calcification in human atherosclerosis, and artery tunica media calcification in aging, diabetes mellitus, and chronic kidney disease. We also describe in sharp contrast how ENPP1, CD73, and ABCC6 serve as "cogs in a wheel" of arterial calcification. Specifically, each is a minor component in the function of a much larger network of factors that exert balanced effects to promote and suppress arterial calcification. For the network to normally suppress spontaneous arterial calcification, the "cogs" ENPP1, CD73, and ABCC6 must be present and in working order. Monogenic ENPP1, CD73, and ABCC6 deficiencies each drive a molecular pathophysiology of closely related but phenotypically different diseases (generalized arterial calcification of infancy (GACI), pseudoxanthoma elasticum (PXE) and arterial calcification caused by CD73 deficiency (ACDC)), in which premature onset arterial calcification is a prominent but not the sole feature.

Calcific aortic valve stenosis: methods, models, and mechanisms

Calcific aortic valve stenosis (CAVS) is a major health problem facing aging societies. The identification of osteoblast-like and osteoclast-like cells in human tissue has led to a major paradigm shift in the field. CAVS was thought to be a passive, degenerative process, whereas now the progression of calcification in CAVS is considered to be actively regulated. Mechanistic studies examining the contributions of true ectopic osteogenesis, nonosseous calcification, and ectopic osteoblast-like cells (that appear to function differently from skeletal osteoblasts) to valvular dysfunction have been facilitated by the development of mouse models of CAVS. Recent studies also suggest that valvular fibrosis, as well as calcification, may play an important role in restricting cusp movement, and CAVS may be more appropriately viewed as a fibrocalcific disease. High-resolution echocardiography and magnetic resonance imaging have emerged as useful tools for testing the efficacy of pharmacological and genetic interventions in vivo. Key studies in humans and animals are reviewed that have shaped current paradigms in the field of CAVS, and suggest promising future areas for research.