Paracrine osteogenic signals via bone morphogenetic protein-2 accelerate the atherosclerotic intimal calcification in vivo

Association between plasma BMP-2 and in-stent restenosis in patients with coronary artery disease

OBJECTIVE

This study aimed to assess the association between plasma bone morphogenetic protein-2 (BMP-2) level and in-stent restenosis in patients with coronary artery disease.

METHODS

A total of 96 patients who underwent percutaneous coronary intervention (PCI) and were followed up after PCI were enrolled in this study. 47 patients diagnosed with in-stent restenosis (ISR) were recruited to ISR group and 49 patients without ISR were recruited to Control group according to the results of coronary angiography (CAG). Baseline characteristic data were collected, and plasma BMP-2 level was evaluated. The results were analyzed using logistic regression.

RESULTS

There were 47 patients in the ISR group and 49 patients in the Control group. Plasma levels of BMP-2 were higher in the ISR group than in the non-ISR group [20.96 (18.44, 27.05) pg/ml vs. 29.53 (25.03, 34.07) pg/ml, P<0.01]. Furthermore, the ISR group had significantly longer stent lengths and lower stent diameters than the Control group (P<0.01 and P<0.01, respectively). In multivariate analysis, BMP-2 level, diabetes, stent length and stent diameter were independently associated with ISR [odds ratio (OR)=1.11, 95% confidence interval (CI)=1.03-1.18, P<0.01; OR=4.75, 95% CI=(1.44-15.61), P=0.01; OR=1.06, 95% CI=(1.02-1.11), P<0.01; and OR=0.15, 95% CI=(0.02-0.95), P=0.04, respectively].

CONCLUSIONS

Increased BMP-2 levels were independently associated with ISR in patients with coronary artery disease. Plasma BMP-2 may be useful in predicting ISR.

Characterization of new bone morphogenetic protein (Bmp)-2 regulatory alleles

Bone morphogenetic protein 2 (BMP2, HGNC:1069, GeneID: 650) is a classical morphogen; a molecule that acts at a distance and whose concentration influences cell proliferation, differentiation, and apoptosis. Key events requiring precise Bmp2 regulation include heart specification and morphogenesis and neural development. In mesenchymal cells, the concentration of BMP2 influences myogenesis, adipogenesis, chondrogenesis, and osteogenesis. Because the amount, timing, and location of BMP2 synthesis influence pattern formation and organogenesis, the mechanisms that regulate Bmp2 are crucial. A sequence within the 3'UTR of the Bmp2 mRNA termed the "ultra-conserved sequence" (UCS) has been largely unchanged since fishes and mammals diverged. Cre-lox mediated deletion of the UCS in a reporter transgene revealed that the UCS may repress Bmp2 in proepicardium, epicardium, and epicardium-derived cells (EPDC) and in tissues with known epicardial contributions (coronary vessels and valves). The UCS also repressed the transgene in the aorta, outlet septum, posterior cardiac plexus, cardiac and extra-cardiac nerves, and neural ganglia. We used homologous recombination and conditional deletion to generate three new alleles in which the Bmp2 3'UTR was altered as follows: a UCS flanked by loxP sites with or without a neomycin resistance targeting vector, or a deleted UCS. Deletion of the UCS was associated with elevated Bmp2 mRNA and BMP signaling levels, reduced fitness, and embryonic malformations.

Nedd4 Deficiency in Vascular Smooth Muscle Promotes Vascular Calcification by Stabilizing pSmad1

The nonosseous calcification process such as atherosclerosis is one of the major complications in several types of metabolic diseases. In a previous study, we uncovered that aberrant activity of transforming growth factor β (TGF-β) signaling pathway could contribute to the vascular smooth muscle cells' (VSMCs) calcification process. Also, we identified NEDD4 E3 ligase as a key suppressor of bone morphogenetic protein (BMP)/Smad pathway via a polyubiquitination-dependent selective degradation of C-terminal phosphorylated Smad1 (pSmad1) activated by TGF-β. Here, we further validated and confirmed the role of Nedd4 in in vivo vascular calcification progression. First, Nedd4 deletion in SM22α-positive mouse tissues (Nedd4^fl/fl ;SM22α-Cre) showed deformed aortic structures with disarranged elastin fibers at 24 weeks after birth. Second, vitamin D-induced aorta vascular calcification rate in Nedd4^fl/fl ;SM22α-Cre mice was significantly higher than their wild-type littermates. Nedd4^fl/fl ;SM22α-Cre mice showed a development of vascular calcification even at very low-level injection of vitamin D, but this was not exhibited in wild-type littermates. Third, we confirmed that TGF-β1-induced pSmad1 levels were elevated in Nedd4-deficient primary VSMCs isolated from Nedd4^fl/fl ;SM22α-Cre mice. Fourth, we further found that Nedd4^fl/fl ;SM22α-Cre mVSMCs gained mesenchymal cell properties toward osteoblast-like differentiation by a stable isotope labeling in cell culture (SILAC)-based proteomics analysis. Finally, epigenetic analysis revealed that methylation levels of human NEDD4 gene promoter were significantly increased in atherosclerosis patients. Collectively, abnormal expression or dysfunction of Nedd4 E3 ligase could be involved in vascular calcification of VSMCs by activating bone-forming signals during atherosclerosis progression. © 2016 American Society for Bone and Mineral Research.

Endoplasmic Reticulum Stress in Arterial Smooth Muscle Cells: A Novel Regulator of Vascular Disease

Cardiovascular disease continues to be the leading cause of death in industrialised societies. The idea that the arterial smooth muscle cell (ASMC) plays a key role in regulating many vascular pathologies has been gaining importance, as has the realisation that not enough is known about the pathological cellular mechanisms regulating ASMC function in vascular remodelling. In the past decade endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) have been recognised as a stress response underlying many physiological and pathological processes in various vascular cell types. Here we summarise what is known about how ER stress signalling regulates phenotypic switching, trans/dedifferentiation and apoptosis of ASMCs and contributes to atherosclerosis, hypertension, aneurysms and vascular calcification.

A novel role of bone morphogenetic protein-7 in the regulation of adhesion and migration of human monocytic cells

BACKGROUND

Bone morphogenetic protein (BMP) 7 is abundant in atherosclerotic plaques and increases monocyte pro-coagulant activity by enhancing tissue factor (TF) expression. While several members of the BMP superfamily are able to serve as chemotactic agents for monocytes, the role of BMP-7 in regulation of monocyte motility is not known.

AIMS

To assess the effect of BMP-7 on adhesive and migratory properties of human monocytes.

METHODS

Chemokinesis, adhesion, and transendothelial migration of BMP-7-treated THP-1 cells and human monocytes were analysed using live-cell imaging, orbital shear, and Boyden chamber assays. Surface presentation of β2 integrins and phosphorylation status of Akt & focal adhesion kinase (FAK) were studied by flow cytometry and Western blot.

RESULTS

High levels of BMP-7 protein were detectable in intimal regions of atherosclerotic plaques; BMP-7 significantly enhanced THP-1 and monocyte chemokinetic properties in vitro (1.21+0.01 and 1.76+0.21 fold increase in crawling distance, respectively). Under orbital shear, adhesion of monocytic cells to microvascular endothelial cell (MVEC) monolayers was also significantly increased by BMP-7 (3.89+1.56 and 2.57+0.97 fold over vehicle). Moreover, BMP-7 accelerated transendothelial migration of THP-1 cells and monocytes towards MCP-1 (5.91+0.88 and 2.96±0.65 fold increase, respectively). BMP-7 enhanced cell surface presentation of β2 integrins in the active conformation. Observed effects were determined to be Akt and FAK dependent, as shown by pharmacological inhibition.

CONCLUSION

BMP-7 directly upregulates adhesion and migration of human monocytic cells via activation of β2 integrins, Akt, and FAK. Our findings suggest that BMP-7 may serve as a novel contributor to atherogenesis.

Yap/Taz transcriptional activity in endothelial cells promotes intramembranous ossification via the BMP pathway

Osteogenesis is categorized into two groups based on developmental histology, intramembranous and endochondral ossification. The role of blood vessels during endochondral ossification is well known, while their role in intramembranous ossification, especially the intertissue pathway, is poorly understood. Here, we demonstrate endothelial Yap/Taz is a novel regulator of intramembranous ossification in zebrafish. Appropriate blood flow is required for Yap/Taz transcriptional activation in endothelial cells and intramembranous ossification. Additionally, Yap/Taz transcriptional activity in endothelial cells specifically promotes intramembranous ossification. BMP expression by Yap/Taz transactivation in endothelial cells is also identified as a bridging factor between blood vessels and intramembranous ossification. Furthermore, the expression of Runx2 in pre-osteoblast cells is a downstream target of Yap/Taz transcriptional activity in endothelial cells. Our results provide novel insight into the relationship between blood flow and ossification by demonstrating intertissue regulation.

Calcification of Vascular Smooth Muscle Cells and Imaging of Aortic Calcification and Inflammation

Cardiovascular disease is the leading cause of morbidity and mortality in the world. Atherosclerotic plaques, consisting of lipid-laden macrophages and calcification, develop in the coronary arteries, aortic valve, aorta, and peripheral conduit arteries and are the hallmark of cardiovascular disease. In humans, imaging with computed tomography allows for the quantification of vascular calcification; the presence of vascular calcification is a strong predictor of future cardiovascular events. Development of novel therapies in cardiovascular disease relies critically on improving our understanding of the underlying molecular mechanisms of atherosclerosis. Advancing our knowledge of atherosclerotic mechanisms relies on murine and cell-based models. Here, a method for imaging aortic calcification and macrophage infiltration using two spectrally distinct near-infrared fluorescent imaging probes is detailed. Near-infrared fluorescent imaging allows for the ex vivo quantification of calcification and macrophage accumulation in the entire aorta and can be used to further our understanding of the mechanistic relationship between inflammation and calcification in atherosclerosis. Additionally, a method for isolating and culturing animal aortic vascular smooth muscle cells and a protocol for inducing calcification in cultured smooth muscle cells from either murine aortas or from human coronary arteries is described. This in vitro method of modeling vascular calcification can be used to identify and characterize the signaling pathways likely important for the development of vascular disease, in the hopes of discovering novel targets for therapy.

Protective Role of Smad6 in Inflammation-Induced Valvular Cell Calcification

Calcific aortic vascular and valvular disease (CAVD) is associated with hyperlipidemia, the effects of which occur through chronic inflammation. Evidence suggests that inhibitory small mothers against decapentaplegic (I-Smads; Smad6 and 7) regulate valve embryogenesis and may serve as a mitigating factor in CAVD. However, whether I-Smads regulate inflammation-induced calcific vasculopathy is not clear. Therefore, we investigated the role of I-Smads in atherosclerotic calcification. Results showed that expression of Smad6, but not Smad7, was reduced in aortic and valve tissues of hyperlipidemic compared with normolipemic mice, while expression of tumor necrosis factor alpha (TNF-α) was upregulated. To test whether the effects are in response to inflammatory cytokines, we isolated murine aortic valve leaflets and cultured valvular interstitial cells (mVIC) from the normolipemic mice. By immunochemistry, mVICs were strongly positive for vimentin, weakly positive for smooth muscle α actin, and negative for an endothelial cell marker. TNF-α upregulated alkaline phosphatase (ALP) activity and matrix mineralization in mVICs. By gene expression analysis, TNF-α significantly upregulated bone morphogenetic protein 2 (BMP-2) expression while downregulating Smad6 expression. Smad7 expression was not significantly affected. To further test the role of Smad6 on TNF-α-induced valvular cell calcification, we knocked down Smad6 expression using lentiviral transfection. In cells transfected with Smad6 shRNA, TNF-α further augmented ALP activity, expression of BMP-2, Wnt- and redox-regulated genes, and matrix mineralization compared with the control cells. These findings suggest that TNF-α induces valvular and vascular cell calcification, in part, by specifically reducing the expression of a BMP-2 signaling inhibitor, Smad6.

A novel role for the mineralocorticoid receptor in glucocorticoid driven vascular calcification

Vascular calcification, which is common in the elderly and in patients with atherosclerosis, diabetes and chronic renal disease, increases the risk of cardiovascular morbidity and mortality. It is a complex, active and highly regulated cellular process that resembles physiological bone formation. It has previously been established that pharmacological doses of glucocorticoids facilitate arterial calcification. However, the consequences for vascular calcification of endogenous glucocorticoid elevation have yet to be established. Glucocorticoids (cortisol, corticosterone) are released from the adrenal gland, but can also be generated within cells from 11-keto metabolites of glucocorticoids (cortisone, 11-dehydrocorticosterone [11-DHC]) by the enzyme, 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). In the current study we hypothesized that endogenous glucocorticoids facilitate vascular smooth muscle cell (VSMC) calcification and investigated the receptor-mediated mechanism underpinning this process.

In vitro studies revealed increased phosphate-induced calcification in mouse VSMCs following treatment for 7 days with corticosterone (100 nM; 7.98 fold; P < 0.01), 11-DHC (100 nM; 7.14 fold; P < 0.05) and dexamethasone (10 nM; 7.16 fold; P < 0.05), a synthetic glucocorticoid used as a positive control. Inhibition of 11β-HSD isoenzymes by 10 μM carbenoxolone reduced the calcification induced by 11-DHC (0.37 fold compared to treatment with 11-DHC alone; P < 0.05). The glucocorticoid receptor (GR) antagonist mifepristone (10 μM) had no effect on VSMC calcification in response to corticosterone or 11-DHC. In contrast, the mineralocorticoid receptor (MR) antagonist eplerenone (10 μM) significantly decreased corticosterone- (0.81 fold compared to treatment with corticosterone alone; P < 0.01) and 11-DHC-driven (0.64 fold compared to treatment with 11-DHC alone; P < 0.01) VSMC calcification, suggesting this glucocorticoid effect is MR-driven and not GR-driven. Neither corticosterone nor 11-DHC altered the mRNA levels of the osteogenic markers PiT-1, Osx and Bmp2. However, DAPI staining of pyknotic nuclei and flow cytometry analysis of surface Annexin V expression showed that corticosterone induced apoptosis in VSMCs.

This study suggests that in mouse VSMCs, corticosterone acts through the MR to induce pro-calcification effects, and identifies 11β-HSD-inhibition as a novel potential treatment for vascular calcification.

Mechanisms of Vascular Calcification: The Pivotal Role of Pyruvate Dehydrogenase Kinase 4

Vascular calcification, abnormal mineralization of the vessel wall, is frequently associated with aging, atherosclerosis, diabetes mellitus, and chronic kidney disease. Vascular calcification is a key risk factor for many adverse clinical outcomes, including ischemic cardiac events and subsequent cardiovascular mortality. Vascular calcification was long considered to be a passive degenerative process, but it is now recognized as an active and highly regulated process similar to bone formation. However, despite numerous studies on the pathogenesis of vascular calcification, the mechanisms driving this process remain poorly understood. Pyruvate dehydrogenase kinases (PDKs) play an important role in the regulation of cellular metabolism and mitochondrial function. Recent studies show that PDK4 is an attractive therapeutic target for the treatment of various metabolic diseases. In this review, we summarize our current knowledge regarding the mechanisms of vascular calcification and describe the role of PDK4 in the osteogenic differentiation of vascular smooth muscle cells and development of vascular calcification. Further studies aimed at understanding the molecular mechanisms of vascular calcification will be critical for the development of novel therapeutic strategies.

Bone morphogenetic proteins in inflammation, glucose homeostasis and adipose tissue energy metabolism

Bore morphogenetic proteins (BMPs) are members of the transforming growth factor (TGF)-β superfamily, a group of secreted proteins that regulate embryonic development. This review summarizes the effects of BMPs on physiological processes not exclusively linked to the musculoskeletal system. Specifically, we focus on the involvement of BMPs in inflammatory disorders, e.g. fibrosis, inflammatory bowel disease, anchylosing spondylitis, rheumatoid arthritis. Moreover, we discuss the role of BMPs in the context of vascular disorders, and explore the role of these signalling proteins in iron homeostasis (anaemia, hemochromatosis) and oxidative damage. The second and third parts of this review focus on BMPs in the development of metabolic pathologies such as type-2 diabetes mellitus and obesity. The pancreatic beta cells are the sole source of the hormone insulin and BMPs have recently been implicated in pancreas development as well as control of adult glucose homeostasis. Lastly, we review the recently recognized role of BMPs in brown adipose tissue formation and their consequences for energy expenditure and adiposity. In summary, BMPs play a pivotal role in metabolism beyond their role in skeletal homeostasis. However, increased understanding of these pleiotropic functions also highlights the necessity of tissue-specific strategies when harnessing BMP action as a therapeutic target.

Bone morphogenetic protein 6 and oxidized low-density lipoprotein synergistically recruit osteogenic differentiation in endothelial cells

AIMS

Vascular calcification contributes to mortality and morbidity in atherosclerosis, chronic kidney disease, and diabetes. Vascular calcific lesions contain osteoblast- and chondroblast-like cells, suggesting a process of endochondral or membranous ossification thought to result from the phenotypic plasticity of vascular cells. Bone morphogenetic protein (BMP) signalling potentiates atherosclerotic calcification, whereas BMP inhibition attenuates vascular inflammation and calcification in atherogenic mice. We hypothesized endothelial cells (ECs) may undergo osteogenic differentiation in response to BMP signalling and pro-atherogenic stimuli.

METHODS AND RESULTS

Among various BMP ligands tested, BMP6 and BMP9 elicited the most potent signalling in bovine aortic endothelial cells (BAEC), however, only BMP6 induced osteogenic differentiation. BMP6 and oxidized low-density lipoprotein (oxLDL) independently and synergistically induced osteogenic differentiation and mineralization, in a manner consistent with endothelial-to-mesenchymal transition. Treatment of ECs with BMP6 or oxLDL individually induced osteogenic and chondrogenic transcription factors Runx2 and Msx2, whereas treatment with BMP6 and oxLDL synergistically up-regulated Osterix and Osteopontin. Production of H2O2 was necessary for oxLDL-induced regulation of Runx2, Msx2, and Osterix in BAEC, and H2O2 was sufficient by itself to up-regulate these genes. Mineralization of ECs in response to BMP6 or oxLDL was abrogated by scavenging reactive oxygen species or inhibiting BMP type I receptor kinases. Similar synergistic effects of BMP and oxLDL upon osteogenic and chondrogenic transcription and phenotypic plasticity in human aortic endothelial cells were observed.

CONCLUSION

These findings provide a potential mechanism for the observed interactions of BMP signalling, oxidative stress, and inflammation in recruiting vascular calcification associated with atherosclerosis.

[The matrix-gla protein awakening may lead to the demise of vascular calcification]

Matrix-gla-protein (MGP) is mainly secreted by chondrocytes and smooth vascular muscle cells. This potent inhibitor of vascular calcification need to undergo 2 post-transcriptional steps to be fully active: one phosphorylation of 3 serine residues (on 5) and a carboxylation of 5 glutamate residues (on 9). Like other "Gla" proteins, this carboxylation is vitamin K dependant. Several forms of MGP thus circulate in the plasma, some of them being totally inactive (the unphosphorylated and uncarboxylated MGP), some others being partially or fully active, according to the number of phosphorylated or carboxylated sites. A theoretical link exists between MGP, vitamin K, vascular calcifications and cardiovascular diseases. This link is even more evident in patients suffering from chronic kidney diseases (CKD), and notably hemodialysis patients. If this link has been demonstrated in different experimental studies, clinical studies are mainly observational and their results must be interpreted accordingly. MGP concentrations are definitely not yet a surrogate to estimate the levels of vascular calcification, but could allow the monitoring of vitamin K treatment. Modulation of MGP concentrations may reduce vascular calcification in hemodialyzed patients, if the large ongoing trials show an efficiency of this treatment. In this review, we will summarize the role of MGP in the vascular calcifications process, describe the problems linked to the analytical determination of MGP in plasma and finally describe the different clinical studies on MGP and vascular calcifications in the general population and in CKD patients.

Increased plasma BMP-2 levels are associated with atherosclerosis burden and coronary calcification in type 2 diabetic patients

BACKGROUND

Although Bone morphogenetic protein-2 (BMP-2) is a known mediator of bone regeneration and vascular calcification, to date no study has investigated the relationship between BMP-2 and type 2 diabetes mellitus (T2DM) and its possible role in coronary artery disease (CAD). The purpose of this study is to evaluate the relationship of BMP-2 with atherosclerosis and calcification in patients with T2DM.

METHODS

124 subjects were enrolled in this study: 29 patients with T2DM and CAD; 26 patients with T2DM and without CAD; 36 patients with CAD and without T2DMand 34 without T2DM or CAD (control group). Severity of coronary lesions was assessed using coronary angiography and intravascular ultrasound (IVUS). Plasma BMP-2 levels were quantified using a commercially available ELISA kit.

RESULTS

Compared to the control group, the mean plasma BMP-2 level was significantly higher in T2DM patients with or without CAD (20.1 ± 1.7 or 19.3 ± 1.5 pg/ml, vs 17.2 ± 3.3 pg/ml, P < 0.001). In a multivariable linear regression analysis, both T2DM and CAD were significantly and positively associated with BMP-2 (Estimate, 0.249; standard error (SE), 0.063; p <0.0001; Estimate, 0.400; SE, 0.06; p < 0.0001). Plasma BMP-2 was also strongly correlated with glycosylated hemoglobin A1c (HbA1c) (Spearman ρ = -0.31; p = 0.0005). SYNTAX score was also significantly associated with BMP-2 (Spearman ρ = 0.46; p = 0.0002). Using the results from IVUS, plasma BMP-2 levels were shown to positively correlate with plaque burden (Spearman ρ = 0.38, P = 0.002) and plaque calcification (Spearman ρ =0.44, P = 0.0003) and to negatively correlate with lumen volume (Spearman ρ =0.31, P = 0.01).

CONCLUSIONS

Our study demonstrates that patients with T2DM had higher circulating levels of BMP-2 than normal controls. Plasma BMP-2 levels correlated positively with plaque burden and calcification in patients with T2DM.

Between Rho(k) and a hard place: the relation between vessel wall stiffness, endothelial contractility, and cardiovascular disease

Vascular stiffness is a mechanical property of the vessel wall that affects blood pressure, permeability, and inflammation. As a result, vascular stiffness is a key driver of (chronic) human disorders, including pulmonary arterial hypertension, kidney disease, and atherosclerosis. Responses of the endothelium to stiffening involve integration of mechanical cues from various sources, including the extracellular matrix, smooth muscle cells, and the forces that derive from shear stress of blood. This response in turn affects endothelial cell contractility, which is an important property that regulates endothelial stiffness, permeability, and leukocyte-vessel wall interactions. Moreover, endothelial stiffening reduces nitric oxide production, which promotes smooth muscle cell contraction and vasoconstriction. In fact, vessel wall stiffening, and microcirculatory endothelial dysfunction, precedes hypertension and thus underlies the development of vascular disease. Here, we review the cross talk among vessel wall stiffening, endothelial contractility, and vascular disease, which is controlled by Rho-driven actomyosin contractility and cellular mechanotransduction. In addition to discussing the various inputs and relevant molecular events in the endothelium, we address which actomyosin-regulated changes at cell adhesion complexes are genetically associated with human cardiovascular disease. Finally, we discuss recent findings that broaden therapeutic options for targeting this important mechanical signaling pathway in vascular pathogenesis.

Wnt16 attenuates TGFβ-induced chondrogenic transformation in vascular smooth muscle

OBJECTIVE

Phenotypic plasticity of vascular smooth muscle cells (VSMCs) contributes to cardiovascular disease. Chondrocyte-like transformation of VSMCs associates with vascular calcification and underlies the formation of aortic cartilaginous metaplasia induced in mice by genetic loss of matrix Gla protein (MGP). Previous microarray analysis identified a dramatic downregulation of Wnt16 in calcified MGP-null aortae, suggesting an antagonistic role for Wnt16 in the chondrogenic transformation of VSMCs.

APPROACH AND RESULTS

Wnt16 is significantly downregulated in MGP-null aortae, before the histological appearance of cartilaginous metaplasia, and in primary MGP-null VSMCs. In contrast, intrinsic TGFβ is activated in MGP-null VSMCs and is necessary for spontaneous chondrogenesis of these cells in high-density micromass cultures. TGFβ3-induced chondrogenic transformation in wild-type VSMCs associates with Smad2/3-dependent Wnt16 downregulation, but Wnt16 does not suppress TGFβ3-induced Smad activation. In addition, TGFβ3 inhibits Notch signaling in wild-type VSMCs, and this pathway is downregulated in MGP-null aortae. Exogenous Wnt16 stimulates Notch activity and attenuates TGFβ3-induced downregulation of Notch in wild-type VSMCs, prevents chondrogenesis in MGP-null and TGFβ3-treated wild-type VSMCs, and stabilizes expression of contractile markers of differentiated VSMCs.

CONCLUSIONS

We describe a novel TGFβ-Wnt16-Notch signaling conduit in the chondrocyte-like transformation of VSMCs and identify endogenous TGFβ activity in MGP-null VSMCs as a critical mediator of chondrogenesis. Our proposed model suggests that the activated TGFβ pathway inhibits expression of Wnt16, which is a positive regulator of Notch signaling and a stabilizer of VSMC phenotype. These data advance the comprehensive mechanistic understanding of VSMC transformation and may identify a novel potential therapeutic target in vascular calcification.

Inhibition of bone morphogenetic protein signal transduction prevents the medial vascular calcification associated with matrix Gla protein deficiency

OBJECTIVE

Matrix Gla protein (MGP) is reported to inhibit bone morphogenetic protein (BMP) signal transduction. MGP deficiency is associated with medial calcification of the arterial wall, in a process that involves both osteogenic transdifferentiation of vascular smooth muscle cells (VSMCs) and mesenchymal transition of endothelial cells (EndMT). In this study, we investigated the contribution of BMP signal transduction to the medial calcification that develops in MGP-deficient mice.

APPROACH AND RESULTS

MGP-deficient mice (MGP(-/-)) were treated with one of two BMP signaling inhibitors, LDN-193189 or ALK3-Fc, beginning one day after birth. Aortic calcification was assessed in 28-day-old mice by measuring the uptake of a fluorescent bisphosphonate probe and by staining tissue sections with Alizarin red. Aortic calcification was 80% less in MGP(-/-) mice treated with LDN-193189 or ALK3-Fc compared with vehicle-treated control animals (P<0.001 for both). LDN-193189-treated MGP(-/-) mice survived longer than vehicle-treated MGP(-/-) mice. Levels of phosphorylated Smad1/5 and Id1 mRNA (markers of BMP signaling) did not differ in the aortas from MGP(-/-) and wild-type mice. Markers of EndMT and osteogenesis were increased in MGP(-/-) aortas, an effect that was prevented by LDN-193189. Calcification of isolated VSMCs was also inhibited by LDN-193189.

CONCLUSIONS

Inhibition of BMP signaling leads to reduced vascular calcification and improved survival in MGP(-/-) mice. The EndMT and osteogenic transdifferentiation associated with MGP deficiency is dependent upon BMP signaling. These results suggest that BMP signal transduction has critical roles in the development of vascular calcification in MGP-deficient mice.

Loss of apoptosis regulator through modulating IAP expression (ARIA) protects blood vessels from atherosclerosis

Atherosclerosis is the primary cause for cardiovascular disease. Here we identified a novel mechanism underlying atherosclerosis, which is provided by ARIA (apoptosis regulator through modulating IAP expression), the transmembrane protein that we recently identified. ARIA is expressed in macrophages present in human atherosclerotic plaque as well as in mouse peritoneal macrophages. When challenged with acetylated LDL, peritoneal macrophages isolated from ARIA-deficient mice showed substantially reduced foam cell formation, whereas the uptake did not differ from that in wild-type macrophages. Mechanistically, loss of ARIA enhanced PI3K/Akt signaling and consequently reduced the expression of acyl coenzyme A:cholesterol acyltransferase-1 (ACAT-1), an enzyme that esterifies cholesterol and promotes its storage, in macrophages. Inhibition of PI3K abolished the reduction in ACAT-1 expression and foam cell formation in ARIA-deficient macrophages. In contrast, overexpression of ARIA reduced Akt activity and enhanced foam cell formation in RAW264.7 macrophages, which was abrogated by treatment with ACAT inhibitor. Of note, genetic deletion of ARIA significantly reduced the atherosclerosis in ApoE-deficient mice. Oil red-O-positive lipid-rich lesion was reduced, which was accompanied by an increase of collagen fiber and decrease of necrotic core lesion in atherosclerotic plaque in ARIA/ApoE double-deficient mice. Analysis of bone marrow chimeric mice revealed that loss of ARIA in bone marrow cells was sufficient to reduce the atherosclerogenesis in ApoE-deficient mice. Together, we identified a unique role of ARIA in the pathogenesis of atherosclerosis at least partly by modulating macrophage foam cell formation. Our results indicate that ARIA could serve as a novel pharmacotherapeutic target for the treatment of atherosclerotic diseases.

BMP-9 regulates the osteoblastic differentiation and calcification of vascular smooth muscle cells through an ALK1 mediated pathway

The process of vascular calcification shares many similarities with that of physiological skeletal mineralization, and involves the deposition of hydroxyapatite crystals in arteries. However, the cellular mechanisms responsible have yet to be fully explained. Bone morphogenetic protein (BMP-9) has been shown to exert direct effects on both bone development and vascular function. In the present study, we have investigated the role of BMP-9 in vascular smooth muscle cell (VSMC) calcification. Vessel calcification in chronic kidney disease (CKD) begins pre-dialysis, with factors specific to the dialysis milieu triggering accelerated calcification. Intriguingly, BMP-9 was markedly elevated in serum from CKD children on dialysis. Furthermore, in vitro studies revealed that BMP-9 treatment causes a significant increase in VSMC calcium content, alkaline phosphatase (ALP) activity and mRNA expression of osteogenic markers. BMP-9-induced calcium deposition was significantly reduced following treatment with the ALP inhibitor 2,5-Dimethoxy-N-(quinolin-3-yl) benzenesulfonamide confirming the mediatory role of ALP in this process. The inhibition of ALK1 signalling using a soluble chimeric protein significantly reduced calcium deposition and ALP activity, confirming that BMP-9 is a physiological ALK1 ligand. Signal transduction studies revealed that BMP-9 induced Smad2, Smad3 and Smad1/5/8 phosphorylation. As these Smad proteins directly bind to Smad4 to activate target genes, siRNA studies were subsequently undertaken to examine the functional role of Smad4 in VSMC calcification. Smad4-siRNA transfection induced a significant reduction in ALP activity and calcium deposition. These novel data demonstrate that BMP-9 induces VSMC osteogenic differentiation and calcification via ALK1, Smad and ALP dependent mechanisms. This may identify new potential therapeutic strategies for clinical intervention.

Evaluation of the cellular origins of heterotopic ossification

Heterotopic ossification (HO), acquired or hereditary, is featured by the formation of bone outside of the normal skeleton. Typical acquired HO is a common, debilitating condition associated with traumatic events. Cardiovascular calcification, an atypical form of acquired HO, is prevalent and associated with high rates of cardiovascular mortality. Hereditary HO syndromes, such as fibrodysplasia ossificans progressiva and progressive osseous heteroplasia, are rare, progressive, life-threatening disorders. The cellular origins of HO remain elusive. Some bona fide contributing cell populations have been found through genetic lineage tracing and other experiments in vivo, and various other candidate populations have been proposed. Nevertheless, because of the difficulties in establishing cellular phenotypes in vivo and other confounding factors, the true identities of these populations are still uncertain. This review critically evaluates the accumulating data in the field. The major focus is on the candidate populations that may give rise to osteochondrogenic lineage cells directly, not the populations that may contribute to HO indirectly. This issue is important not solely because of the clinical implications, but also because it highlights the basic biological processes that govern bone formation.

Does the calcification of adamantinomatous craniopharyngioma resemble the calcium deposition of osteogenesis/odontogenesis?

AIMS

Calcification in adamantinomatous craniopharyngioma (ACP) is troublesome for surgical intervention. The aim of this study was to examine the osteogenic proteins that play important roles in the calcium deposition of the odontogenic/osteogenic tissues in craniopharyngioma.

METHODS AND RESULTS

Craniopharyngiomas (n = 89) were investigated for the presence and expression pattern of the osteoinductive/odontoinductive factor bone morphogenetic protein-2 (Bmp2) and two osteoblastic differentiation makers, Runt-related transcription factor-2 (Runx2) and Osterix, using immunohistochemistry and Western blotting. Our results showed that Bmp2, Runx2 and Osterix levels increased in cases with high calcification and correlated positively with the degree of calcification in ACP, whereas they showed little or no expression in squamous papillary craniopharyngioma. In ACP, Bmp2 was expressed primarily in the stellate reticulum and whorl-like array cells; Runx2 and Osterix tended to be expressed in calcification-related epithelia, including whorl-like array cells and epithelia in/around wet keratin and calcification lesions.

CONCLUSIONS

Our study indicated, for the first time, that osteogenic factor Bmp2 may play an important role in the calcification of ACP via autocrine or paracrine mechanisms. Given the presence of osteogenic markers (Runx2 and Osterix), craniopharyngioma cells could differentiate into an osteoblast-like lineage, and the process of craniopharyngioma calcification resembles that which occurs in osteogenesis/odontogenesis.

Ceramide mediates Ox-LDL-induced human vascular smooth muscle cell calcification via p38 mitogen-activated protein kinase signaling

Vascular calcification is associated with significant cardiovascular morbidity and mortality, and has been demonstrated as an actively regulated process resembling bone formation. Oxidized low density lipoprotein (Ox-LDL) has been identified as a regulatory factor involved in calcification of vascular smooth muscle cells (VSMCs). Additionally, over-expression of recombinant human neutral sphingomyelinase (N-SMase) has been shown to stimulate VSMC apoptosis, which plays an important role in the progression of vascular calcification. The aim of this study is to investigate whether ceramide regulates Ox-LDL-induced calcification of VSMCs via activation of p38 mitogen-activated protein kinase (MAPK) pathway. Ox-LDL increased the activity of N-SMase and the level of ceramide in cultured VSMCs. Calcification and the osteogenic transcription factor, Msx2 mRNA expression were reduced by N-SMase inhibitor, GW4869 in the presence of Ox-LDL. Usage of GW4869 inhibited Ox-LDL-induced apoptosis in VSMCs, an effect which was reversed by C2-ceramide. Additionally, C2-ceramide treatment accelerated VSMC calcification, with a concomitant increase in ALP activity. Furthermore, C2-ceramide treatment enhanced Ox-LDL-induced VSMC calcification. Addition of caspase inhibitor, ZVAD-fmk attenuated Ox-LDL-induced calcification. Both Ox-LDL and C2-ceramide treatment increased the phosphorylation of p38 MAPK. Inhibition of p38 MAPK by SB203580 attenuated Ox-LDL-induced calcification of VSMCs. These data suggest that Ox-LDL activates N-SMase-ceramide signaling pathway, and stimulates phosphorylation of p38 MAPK, leading to apoptosis in VSMCs, which initiates VSMC calcification.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Gene expression in the vascular wall of the aortic arch in spontaneously hypertensive hyperlipidemic model rats using DNA microarray analysis

AIMS

In recent years, there has been an increase in patients with arteriosclerosis and the risk of lifestyle-related diseases. However, the pathogenesis and medication of atherosclerosis have not been elucidated. We developed a rat model of lifestyle-related diseases by feeding a high-fat diet and 30% sucrose solution (HFDS) to spontaneously hypertensive hyperlipidemic rats (SHHR) and reported that this model is a useful model of early atherosclerosis. In order to elucidate the pathogenesis of early atherosclerosis, we searched for atherosclerosis-related genes by microarray analysis using the aortic arch rat model of lifestyle-related diseases.

MAIN METHODS

Four-month-old male Sprague-Dawley rats and SHHR were each divided into two normal diet (ND) groups and two HFDS groups. After a four-month treatment, the expression of mRNA in the aortic arch was detected using the oligo DNA microarray one-color method and quantified using real-time PCR.

KEY FINDINGS

In this study, we detected 39 genes in microarray analysis. Esm1, Retnlb Mkks, and Grem2 showed particularly marked changes in gene expression in the SHHR-HFDS group. Compared with the SD-ND group, the SHHR-HFDS group had an increase in Mkks gene expression of about 26-fold and an approximately 22-fold increase in the expression of Grem2. Similarly, the expression of Esm1 increased by about 12-fold and that of Retnlg by about 10-fold as shown by quantitative real-time PCR.

SIGNIFICANCE

This study suggested that these four genes might be important in early atherosclerosis development.

A role for the endothelium in vascular calcification

RATIONALE

Vascular calcification is a regulated process that involves osteoprogenitor cells and frequently complicates common vascular disease, such as atherosclerosis and diabetic vasculopathy. However, it is not clear whether the vascular endothelium has a role in contributing osteoprogenitor cells to the calcific lesions.

OBJECTIVE

To determine whether the vascular endothelium contributes osteoprogenitor cells to vascular calcification.

METHODS AND RESULTS

In this study, we use 2 mouse models of vascular calcification, mice with gene deletion of matrix Gla protein, a bone morphogenetic protein (BMP)-inhibitor, and Ins2Akita/+ mice, a diabetes model. We show that enhanced BMP signaling in both types of mice stimulates the vascular endothelium to contribute osteoprogenitor cells to the vascular calcification. The enhanced BMP signaling results in endothelial-mesenchymal transitions and the emergence of multipotent cells, followed by osteoinduction. Endothelial markers colocalize with multipotent and osteogenic markers in calcified arteries by immunostaining and fluorescence-activated cell sorting. Lineage tracing using Tie2-Gfp transgenic mice supports an endothelial origin of the osteogenic cells. Enhancement of matrix Gla protein expression in Ins2Akita/+ mice, as mediated by an Mgp transgene, limits the generation of multipotent cells. Moreover, matrix Gla protein-depleted human aortic endothelial cells in vitro acquire multipotency rendering the cells susceptible to osteoinduction by BMP and high glucose.

CONCLUSIONS

Our data suggest that the endothelium is a source of osteoprogenitor cells in vascular calcification that occurs in disorders with high BMP activation, such as deficiency of BMP-inhibitors and diabetes mellitus.

Development of a model of elevated intraocular pressure in rats by gene transfer of bone morphogenetic protein 2

PURPOSE

To determine whether inducing calcification in the trabecular meshwork results in elevated IOP in living rats. To use this property to create an elevated IOP animal model by gene transfer of bone morphogenetic protein 2 (BMP2).

METHODS

Calcification was assessed by alizarin red staining in primary human trabecular meshwork (HTM) cells and alkaline phosphatase (ALP) activity in the angle tissue. Brown Norway (BN) and Wistar rats were intracamerally injected with Ad5BMP2 (OS) and control Ad5.CMV-Null (OD). IOPs were taken twice a week and expressed as mean integral pressures. Morphology was assessed on fixed, paraffin-embedded anterior segments. Retinal ganglion cells (RGCs) were quantified on retrograde and Brn-3a-labeled flat mounts using MetaMorph software.

RESULTS

BMP2-treated cells displayed marked increase in calcification. Trabecular meshwork tissue showed moderate ALP activity at 13 days postinjection. Fifty-four of 55 BN and 15 of 19 Wistar rats displayed significantly elevated IOP. In a representative 29-day experiment, the integral IOP difference between treated and control eyes was 367.7 ± 83 mm Hg-days (P = 0.007). Morphological evaluation revealed a well-organized trabecular meshwork tissue, exhibiting denser matrix in the treated eyes. The Ad5BMP2-treated eye showed 34.4% ± 4.8% (P = 0.00002) loss of peripheral RGC over controls.

CONCLUSIONS

Gene transfer of the calcification inducer BMP2 gene to the trabecular meshwork induces elevated IOP in living rats without altering the basic structure of the tissue. This strategy generates an elevated IOP model in rats that would be useful for evaluation of glaucoma drugs targeting the outflow pathway.

Association between circulating osteoblast progenitor cells and aortic calcifications in women with postmenopausal osteoporosis

BACKGROUND AND AIMS

Ectopic artery calcification has been documented in women with postmenopausal osteoporosis, in whom an imbalance in the number of circulating osteoprogenitor cells (OPCs) has been identified. Circulating OPCs form calcified nodules in vitro; however, it remains unknown whether an association exists between the number of circulating OPCs and aortic calcifications. We investigated the relationship between OPCs and aortic calcifications in women with postmenopausal osteoporosis.

METHODS AND RESULTS

The number of circulating OPCs was quantified by FACS analysis in 50 osteoporotic postmenopausal women. OPCs were defined as CD15-/alkaline-phosphatase(AP)+ cells coexpressing or not CD34. Participants underwent measurement of markers of bone metabolism, bone mineral density and abdominal aortic calcium (AAC) by 64-slice computed tomography. Patients with AAC were older, had lower 25(OH)vitamin D levels and higher circulating CD15-/AP+/CD34- cells than those without AAC. Significant correlates of AAC included age (rho = 0.38 p = 0.006), calcium (rho = 0.35 p = 0.01), 25(OH)vitamin D (rho = -0.31, p = 0.03) and the number of CD15-/AP+/CD34- cells (rho = 0.55 p < 0.001). In regression analyses, the log-transformed number of CD15-/AP+/CD34- cells was associated with the presence (OR = 6.45, 95% CI 1.03-40.1, p = 0.04) and severity (β = 0.43, p < 0.001) of AAC, independent of age, 25(OH)vitamin D, calcium and other potential confounders. Patients with low 25(OH)vitamin D and high CD15-/AP+/CD34- cells had higher median AAC than other patients (1927/μL, 862-2714/μL vs 147/μL, 0-1665/μL, p = 0.003).

CONCLUSION

In women with postmenopausal osteoporosis, the number of circulating CD15-/AP+/CD34- cells is significantly associated with increased aortic calcifications, that appear to be correlated also with reduced 25(OH)vitamin D levels.

Vitamin K-dependent carboxylation of matrix Gla-protein: a crucial switch to control ectopic mineralization

Vascular mineralization has recently emerged as a risk factor for cardiovascular morbidity and mortality. Previously regarded as a passive end-stage process, vascular mineralization is currently recognized as an actively regulated process with cellular and humoral contributions. The discovery that the vitamin K-dependent matrix Gla-protein (MGP) is a strong inhibitor of vascular calcification has propelled our mechanistic understanding of this process and opened novel avenues for diagnosis and treatment. This review focuses on molecular mechanisms of vascular mineralization involving MGP and discusses the potential for treatments and biomarkers to monitor patients at risk for vascular mineralization.

Malnutrition, a new inducer for arterial calcification in hemodialysis patients?

BACKGROUND

Arterial calcification is a significant cardiovascular risk factor in hemodialysis patients. A series of factors are involved in the process of arterial calcification; however, the relationship between malnutrition and arterial calcification is still unclear.

METHODS

68 hemodialysis patients were enrolled in this study. Nutrition status was evaluated using modified quantitative subjective global assessment (MQSGA). Related serum biochemical parameters were measured. And the radial artery samples were collected during the arteriovenous fistula surgeries. Hematoxylin/eosin stain was used to observe the arterial structures while Alizarin red stain to observe calcified depositions and classify calcified degree. The expressions of bone morphogenetic protein 2 (BMP2) and matrix Gla protein (MGP) were detected by immunohistochemistry and western blot methods.

RESULTS

66.18% hemodialysis patients were malnutrition. In hemodialysis patients, the calcified depositions were mainly located in the medial layer of the radial arteries and the expressions of BMP2 and MGP were both increased in the calcified areas. The levels of serum albumin were negatively associated with calcification score and the expressions of BMP2 and MGP. While MQSGA score, serum phosphorus and calcium × phosphorus product showed positive relationships with calcification score and the expressions of BMP2 and MGP.

CONCLUSIONS

Malnutrition is prevalent in hemodialysis patients and is associated with arterial calcification and the expressions of BMP2 and MGP in calcified radial arteries. Malnutrition may be a new inducer candidate for arterial calcification in hemodialysis patients.

The factor VII-activating protease (FSAP) enhances the activity of bone morphogenetic protein-2 (BMP-2)

Factor VII-activating protease (FSAP) is a circulating protease involved in the pathogenesis of atherosclerosis, calcification, and fibrotic processes. To understand how FSAP controls the balance of local growth factors, we have investigated its effect on the regulation of bone morphogenetic proteins (BMPs). BMP-2 is produced as a large pro-form and secreted as a mature heparin-binding growth factor after intracellular processing by pro-protein convertases (PCs). In this study, we discovered that FSAP enhances the biological activity of mature BMP-2 as well as its pro-form, as shown by osteogenic differentiation of C2C12 myoblasts. These findings were complemented by knockdown of FSAP in hepatocytes, which revealed BMP-2 processing by endogenous FSAP. N-terminal sequencing indicated that pro-BMP-2 was cleaved by FSAP at the canonical PC cleavage site, giving rise to mature BMP-2 (Arg(282)↓Gln(283)), as well as in the N-terminal heparin binding region of mature BMP-2, generating a truncated mature BMP-2 peptide (Arg(289)↓Lys(290)). Similarly, mature BMP-2 was also cleaved to a truncated peptide within its N-terminal region (Arg(289)↓Lys(290)). Plasmin exhibited a similar activity, but it was weaker compared with FSAP. Thrombin, Factor VIIa, Factor Xa, and activated protein C were not effective. These results were further supported by the observation that the mutation of the heparin binding region of BMP-2 inhibited the processing by FSAP but not by PC. Thus, the proteolysis and activation of pro-BMP-2 and mature BMP-2 by FSAP can regulate cell differentiation and calcification in vasculature and may explain why polymorphisms in the gene encoding for FSAP are related to vascular diseases.

Targeting of the osteoclastogenic RANKL-RANK axis prevents osteoporotic bone loss and soft tissue calcification in coxsackievirus B3-infected mice

Bone mineralization is a normal physiological process, whereas ectopic calcification of soft tissues is a pathological process that leads to irreversible tissue damage. We have established a coxsackievirus B3 (CVB3)-infected mouse model that manifests both osteoporosis and ectopic calcification specifically in heart, pancreas, and lung. The CVB3-infected mice showed increased serum concentrations of both cytokines including IL-1β, TNF-α, and the receptor activator of NF-κB ligand (RANKL) that stimulate osteoclast formation and of the osteoclast-derived protein tartrate-resistant acid phosphatase 5b. They exhibited more osteoclasts in bone, with no change in the number of osteoblasts, and a decrease in bone formation and the serum concentration of osteoblast-produced osteocalcin. These results indicate that CVB3-induced osteoporosis is likely due to upregulation of osteoclast formation and function, in addition to decreased osteoblast activity. In addition, the serum in the CVB3-infected mice contained a high inorganic phosphate content, which causes ectopic calcification. RANKL treatment induced an increase in the in vitro cardiac fibroblast calcification by inorganic phosphate via the upregulation of osteogenic BMP2, SPARC, Runx2, Fra-1, and NF-κB signaling. We finally observed that i.p. administration of RANK-Fc, a recombinant antagonist of RANKL, prevented bone loss as well as ectopic calcification in CVB3-infected mice. Thus, our results indicate that RANKL may contribute to both abnormal calcium deposition in soft tissues and calcium depletion in bone. In addition, our animal model should provide a tool for the development of new therapeutic agents for calcium disturbance in soft and hard tissues.

Mechanisms of arterial remodeling: lessons from genetic diseases

Vascular disease is still the leading cause of morbidity and mortality in the Western world, and the primary cause of myocardial infarction, stroke, and ischemia. The biology of vascular disease is complex and still poorly understood in terms of causes and consequences. Vascular function is determined by structural and functional properties of the arterial vascular wall. Arterial stiffness, that is a pathological alteration of the vascular wall, ultimately results in target-organ damage and increased mortality. Arterial remodeling is accelerated under conditions that adversely affect the balance between arterial function and structure such as hypertension, atherosclerosis, diabetes mellitus, chronic kidney disease, inflammatory disease, lifestyle aspects (smoking), drugs (vitamin K antagonists), and genetic abnormalities [e.g., pseudoxanthoma elasticum (PXE), Marfan's disease]. The aim of this review is to provide an overview of the complex mechanisms and different factors that underlie arterial remodeling, learning from single gene defect diseases like PXE, and PXE-like, Marfan's disease and Keutel syndrome in vascular remodeling.

Mechanistic insights into vascular calcification in CKD

Cardiovascular disease begins early in the course of renal decline and is a life-limiting problem in patients with CKD. The increased burden of cardiovascular disease is due, at least in part, to calcification of the vessel wall. The uremic milieu provides a perfect storm of risk factors for accelerated calcification, but elevated calcium and phosphate levels remain key to the initiation and progression of vascular smooth muscle cell calcification in CKD. Vascular calcification is a highly regulated process that involves a complex interplay between promoters and inhibitors of calcification and has many similarities to bone ossification. Here, we discuss current understanding of the process of vascular calcification, focusing specifically on the discrete and synergistic effects of calcium and phosphate in mediating vascular smooth muscle cell apoptosis, osteochondrocytic differentiation, vesicle release, calcification inhibitor expression, senescence, and death. Using our model of intact human vessels, factors initiating vascular calcification in vivo and the role of calcium and phosphate in driving accelerated calcification ex vivo are described. This work allows us to link clinical and basic research into a working theoretical model to explain the pathway of development of vascular calcification in CKD.

Vitamin K-antagonists accelerate atherosclerotic calcification and induce a vulnerable plaque phenotype

BACKGROUND

Vitamin K-antagonists (VKA) are treatment of choice and standard care for patients with venous thrombosis and thromboembolic risk. In experimental animal models as well as humans, VKA have been shown to promote medial elastocalcinosis. As vascular calcification is considered an independent risk factor for plaque instability, we here investigated the effect of VKA on coronary calcification in patients and on calcification of atherosclerotic plaques in the ApoE(-/-) model of atherosclerosis.

METHODOLOGY/PRINCIPAL FINDINGS

A total of 266 patients (133 VKA users and 133 gender and Framingham Risk Score matched non-VKA users) underwent 64-slice MDCT to assess the degree of coronary artery disease (CAD). VKA-users developed significantly more calcified coronary plaques as compared to non-VKA users. ApoE(-/-) mice (10 weeks) received a Western type diet (WTD) for 12 weeks, after which mice were fed a WTD supplemented with vitamin K(1) (VK(1), 1.5 mg/g) or vitamin K(1) and warfarin (VK(1)&W; 1.5 mg/g & 3.0 mg/g) for 1 or 4 weeks, after which mice were sacrificed. Warfarin significantly increased frequency and extent of vascular calcification. Also, plaque calcification comprised microcalcification of the intimal layer. Furthermore, warfarin treatment decreased plaque expression of calcification regulatory protein carboxylated matrix Gla-protein, increased apoptosis and, surprisingly outward plaque remodeling, without affecting overall plaque burden.

CONCLUSIONS/SIGNIFICANCE

VKA use is associated with coronary artery plaque calcification in patients with suspected CAD and causes changes in plaque morphology with features of plaque vulnerability in ApoE(-/-) mice. Our findings underscore the need for alternative anticoagulants that do not interfere with the vitamin K cycle.

Macrophages play a unique role in the plaque calcification by enhancing the osteogenic signals exerted by vascular smooth muscle cells

Vascular calcification is a major risk factor for the cardiovascular disease, yet its underlying molecular mechanisms remain to be elucidated. Recently, we identified that osteogenic signals via bone morphogenetic protein (BMP)-2 exerted by vascular smooth muscle cells (VSMCs) play a crucial role in the formation of atherosclerotic plaque calcification. Here we report a synergistic interaction between macrophages and VSMCs with respect to plaque calcification. Treatment with conditioned medium (CM) of macrophages dramatically enhanced BMP-2 expression in VSMCs, while it substantially reduced the expression of matrix Gla-protein (MGP) that inhibits the BMP-2 osteogenic signaling. As a result, macrophages significantly accelerated the osteoblastic differentiation of C2C12 cells induced by VSMC-CM. In contrast, macrophage-CM did not enhance the osteoblastic gene expressions in VSMCs, indicating that macrophages unlikely induced the osteoblastic trans-differentiation of VSMCs. We then examined the effect of recombinant TNF-α and IL-1β on the VSMC-derived osteogenic signals. Similar to the macrophage-CM, both cytokines enhanced BMP-2 expression and reduced MGP expression in VSMCs. Nevertheless, only the neutralization of TNF-α but not IL-1β attenuated the effect of macrophage-CM on the expression of these genes in VSMCs, due to the very low concentration of IL-1β in the macrophage-CM. On the other hand, VSMCs significantly enhanced IL-1β expression in macrophages, which might in turn accelerate the VSMC-mediated osteogenic signals. Together, we identified a unique role of macrophages in the formation of plaque calcification in coordination with VSMCs. This interaction between macrophages and VSMCs is a potential therapeutic target to treat and prevent the atherosclerotic plaque calcification.

Osteocalcin positive CD133+/CD34-/KDR+ progenitor cells as an independent marker for unstable atherosclerosis

AIMS

For the characterization of endothelial progenitor cells (EPCs), commonly the markers CD34 and KDR have been used. CD133+/CD34-/KDR+ cells may represent more immature 'early' progenitors. In patients with coronary artery disease (CAD), a large fraction of EPCs carry the osteoblastic marker osteocalcin (OCN), which may mediate vascular calcification and abnormal repair. The aim of this study was to evaluate the expression of OCN+ 'early' EPCs in patients with risk factors (RFs) and a history of stable (history of stenting/coronary artery bypass grafting) or unstable CAD (myocardial infarction).

METHODS AND RESULTS

Medical history and blood samples from 282 patients (age 58 ± 16 years) with CAD or at least one RF (mean 2.5 ± 1.5) were analysed. For the analysis of EPC markers (CD133, CD34, KDR) and OCN, the flow cytometry of peripheral blood mononuclear cells was performed. Circulating OCN+/CD133+/CD34-/KDR+ cells (median counts [interquartile range] per 100 000 events) were 15 [4-41] in patients with RF (n = 199), 26 [1-136] in those with a history of stable (n = 57), and 246 [105-308] in those with a history of unstable CAD (n = 26; P < 0.001). The association with unstable CAD remained highly significant even after multivariate adjusting for RFs and the different characteristics of the groups. Osteocalcin positive 'early' EPCs trend to predict further events [HR for each doubling of the cell number: 1.20 (95% CI: 1.00-1.46), P = 0.06].

CONCLUSION

Circulating OCN+ 'early' EPCs are strongly associated with unstable CAD. Therefore, this particular subset of EPCs could mediate abnormal vascular repair and may help identifying patients with a more unstable phenotype of atherosclerosis.

Vascular tissues are a primary source of BMP2 expression during bone formation induced by distraction osteogenesis

Prior studies showed that bone regeneration during distraction osteogenesis (DO) was dependent on vascular tissue development and that inhibition of VEGFR signaling diminished the expression of BMP2. A combination of micro-computed tomography (μCT) analysis of vascular and skeletal tissues, immunohistological and histological analysis of transgenic mice containing a BAC transgene in which β-galactosidase had been inserted into the coding region of BMP2 and qRT-PCR analysis, was used to examine how the spatial temporal expression of the morphogenetic signals that drive skeletal and vascular tissue development is coordinated during DO. These results showed that BMP2 expression was induced in smooth muscle and vascular endothelial cells of arteries and veins, capillary endothelial cells, hypertrophic chondrocytes and osteocytes. BMP2 was not expressed by lymphatic vessels or macrophages. Separate peaks of BMP2 mRNA expression were induced in the surrounding muscular tissues and the distraction gap and corresponded first with large vessel collateralization and arteriole remodeling followed by periods of angiogenesis in the gap region. Immunohistological and qRT-PCR analysis of VEGF receptors and ligands showed that mesenchymal cells, lining cells and chondrocytes, expressed VEGFA, although PlGF expression was only seen in mesenchymal cells within the gap region. On the other hand VEGFR2 appeared to be predominantly expressed by vascular endothelial and hematopoietic cells. These results suggest that bone and vascular tissue formation is coordinated via a mutually supporting set of paracrine loops in which blood vessels primarily synthesize the morphogens that promote bone formation while mesenchymal cells primarily synthesize the morphogens that promote vascular tissue formation.

Transfer of bone-marrow-derived mesenchymal stem cells influences vascular remodeling and calcification after balloon injury in hyperlipidemic rats

Bone-marrow-derived mesenchymal stem cells (BM-MSCs) were found to markedly increase atherosclerotic lesion size. The aim of this paper was to investigate whether BM-MSCs contribute to vascular remodeling and calcification after balloon injury in hyperlipidemic rats. Labeled BM-MSCs were found in the lesion of hyperlipidemic rats after balloon injury. Comparing injury group, transferred BM-MSCs significantly triggered vascular negative remodeling, characterized by the changes of remodeling index (0.628 ± 0.0293 versus 0.544 ± 0.0217), neointimal area (0.078 ± 0.015 mm² versus 0.098 ± 0.019 mm²), PCNA index (23.91 ± 6.59% versus 43.11 ± 5.31%), and percentage of stenosis (18.20 ± 1.09% versus 30.58 ± 1.21%). Apparent vascular calcification was detected in medial layers at 6 weeks after balloon angioplasty, which may be associated with upregulation of bone morphogenetic protein-2 (BMP-2). Our data indicated that unselected BM-MSCs transfer may induce vascular remodeling and calcification after balloon injury in hyperlipidemic rats.

BMPs are mediators in tissue crosstalk of the regenerating musculoskeletal system

The musculoskeletal system is a tight network of many tissues. Coordinated interplay at a biochemical level between tissues is essential for development and repair. Traumatic injury usually affects several tissues and represents a large challenge in clinical settings. The current demand for potent growth factors in such applications thus accompanies the keen interest in molecular mechanisms and orchestration of tissue formation. Of special interest are multitasking growth factors that act as signals in a variety of cell types, both in a paracrine and in an autocrine manner, thereby inducing cell differentiation and coordinating not only tissue assembly at specific sites but also maturation and homeostasis. We concentrate here on bone morphogenetic proteins (BMPs), which are important crosstalk mediators known for their irreplaceable roles in vertebrate development. The molecular crosstalk during embryonic musculoskeletal tissue formation is recapitulated in adult repair. BMPs act at different levels from the initiation to maturation of newly formed tissue. Interestingly, this is influenced by the spatiotemporal expression of different BMPs, their receptors and co-factors at the site of repair. Thus, the regenerative potential of BMPs needs to be evaluated in the context of highly connected tissues such as muscle and bone and might indeed be different in more poorly connected tissues such as cartilage. This highlights the need for an understanding of BMP signaling across tissues in order to eventually improve BMP regenerative potential in clinical applications. In this review, the distinct members of the BMP family and their individual contribution to musculoskeletal tissue repair are summarized by focusing on their paracrine and autocrine functions.

Inhibition of bone morphogenetic protein signaling reduces vascular calcification and atherosclerosis

OBJECTIVE

The expression of bone morphogenetic proteins (BMPs) is enhanced in human atherosclerotic and calcific vascular lesions. Although genetic gain- and loss-of-function experiments in mice have supported a causal role of BMP signaling in atherosclerosis and vascular calcification, it remains uncertain whether BMP signaling might be targeted pharmacologically to ameliorate both of these processes.

METHODS AND RESULTS

We tested the impact of pharmacological BMP inhibition on atherosclerosis and calcification in LDL receptor-deficient (LDLR-/-) mice. LDLR-/- mice fed a high-fat diet developed abundant vascular calcification within 20 weeks. Prolonged treatment of LDLR-/- mice with the small molecule BMP inhibitor LDN-193189 was well-tolerated and potently inhibited development of atheroma, as well as associated vascular inflammation, osteogenic activity, and calcification. Administration of recombinant BMP antagonist ALK3-Fc replicated the antiatherosclerotic and anti-inflammatory effects of LDN-193189. Treatment of human aortic endothelial cells with LDN-193189 or ALK3-Fc abrogated the production of reactive oxygen species induced by oxidized LDL, a known early event in atherogenesis. Unexpectedly, treatment of mice with LDN-193189 lowered LDL serum cholesterol by 35% and markedly decreased hepatosteatosis without inhibiting HMG-CoA reductase activity. Treatment with BMP2 increased, whereas LDN-193189 or ALK3-Fc inhibited apolipoprotein B100 secretion in HepG2 cells, suggesting that BMP signaling contributes to the regulation of cholesterol biosynthesis.

CONCLUSION

These results definitively implicate BMP signaling in atherosclerosis and calcification, while uncovering a previously unidentified role for BMP signaling in LDL cholesterol metabolism. BMP inhibition may be helpful in the treatment of atherosclerosis and associated vascular calcification.

TGFβ signaling and cardiovascular diseases

Transforming growth factor β (TGFβ) family members are involved in a wide range of diverse functions and play key roles in embryogenesis, development and tissue homeostasis. Perturbation of TGFβ signaling may lead to vascular and other diseases. In vitro studies have provided evidence that TGFβ family members have a wide range of diverse effects on vascular cells, which are highly dependent on cellular context. Consistent with these observations genetic studies in mice and humans showed that TGFβ family members have ambiguous effects on the function of the cardiovascular system. In this review we discuss the recent advances on TGFβ signaling in (cardio)vascular diseases, and describe the value of TGFβ signaling as both a disease marker and therapeutic target for (cardio)vascular diseases.

The regulation of valvular and vascular sclerosis by osteogenic morphogens

Vascular calcification increasingly afflicts our aging, dysmetabolic population. Once considered only a passive process of dead and dying cells, vascular calcification has now emerged as a highly regulated form of biomineralization organized by collagenous and elastin extracellular matrices. During skeletal bone formation, paracrine epithelial-mesenchymal and endothelial-mesenchymal interactions control osteochondrocytic differentiation of multipotent mesenchymal progenitor cells. These paracrine osteogenic signals, mediated by potent morphogens of the bone morphogenetic protein and wingless-type MMTV integration site family member (Wnt) superfamilies, are also active in the programming of arterial osteoprogenitor cells during vascular and valve calcification. Inflammatory cytokines, reactive oxygen species, and oxylipids-increased in the clinical settings of atherosclerosis, diabetes, and uremia that promote arteriosclerotic calcification-elicit the ectopic vascular activation of osteogenic morphogens. Specific extracellular and intracellular inhibitors of bone morphogenetic protein-Wnt signaling have been identified as contributing to the regulation of osteogenic mineralization during development and disease. These inhibitory pathways and their regulators afford the development of novel therapeutic strategies to prevent and treat valve and vascular sclerosis.