No influence of OPG and its ligands, RANKL and TRAIL, on proliferation and regulation of the calcification process in primary human vascular smooth muscle cells

The role of OPG/RANKL in the pathogenesis of diabetic cardiovascular disease

Cardiovascular (CV) disease is the leading cause of mortality in patients with type 2 diabetes mellitus. A major factor in the pathogenesis of CV disease is vascular calcification (VC), which is accelerated in type 2 diabetes mellitus. Calcification of the vessel wall contributes to vascular stiffness and left ventricular hypertrophy whereas intimal calcification may predispose to plaque rupture and CV death. The pathogenesis of VC is complex but appears to be regulated by the osteoprotegerin (OPG)/receptor activator of nuclear factor-κB ligand (RANKL) signaling pathway, which is involved in bone remodeling. Within the bone, OPG prevents RANKL from binding to receptor activator of nuclear factor-κB and inhibiting bone resorption. Outside of the bone, the clinical significance of OPG blocking RANKL is not well understood, but OPG knockout mice that lack OPG develop early and severe VC. This minireview outlines some of the research on OPG/RANKL in the pathogenesis of VC and discusses potential therapies, which may reduce VC and CV burden in humans.

TRAIL attenuates RANKL-mediated osteoblastic signalling in vascular cell mono-culture and co-culture models

Background and objectives

Vascular calcification (VC) is a major risk factor for elevated cardiovascular morbidity/mortality. Underlying this process is osteoblastic signalling within the vessel wall involving complex and interlinked roles for receptor-activator of nuclear factor-κB ligand (RANKL), osteoprotegerin (OPG), and tumour necrosis factor-related apoptosis-inducing ligand (TRAIL). RANKL promotes vascular cell osteoblastic differentiation, whilst OPG acts as a neutralizing decoy receptor for RANKL (and TRAIL). With respect to TRAIL, much recent evidence points to a vasoprotective role for this ligand, albeit via unknown mechanisms. In order to shed more light on TRAILs vasoprotective role therefore, we employed in vitro cell models to test the hypothesis that TRAIL can counteract the RANKL-mediated signalling that occurs between the vascular cells that comprise the vessel wall.

Methods and results

Human aortic endothelial and smooth muscle cell mono-cultures (HAECs, HASMCs) were treated with RANKL (0–25 ng/mL ± 5 ng/mL TRAIL) for 72 hr. Furthermore, to better recapitulate the paracrine signalling that exists between endothelial and smooth muscle cells within the vessel wall, non-contact transwell HAEC:HASMC co-cultures were also employed and involved RANKL treatment of HAECs (±TRAIL), subsequently followed by analysis of pro-calcific markers in the underlying subluminal HASMCs. RANKL elicited robust osteoblastic signalling across both mono- and co-culture models (e.g. increased BMP-2, alkaline phosphatase/ALP, Runx2, and Sox9, in conjunction with decreased OPG). Importantly, several RANKL actions (e.g. increased BMP-2 release from mono-cultured HAECs or increased ALP/Sox9 levels in co-cultured HASMCs) could be strongly blocked by co-incubation with TRAIL. In summary, this paper clearly demonstrates that RANKL can elicit pro-osteoblastic signalling in HAECs and HASMCs both directly and across paracrine signalling axes. Moreover, within these contexts we present clear evidence that TRAIL can block several key signalling actions of RANKL in vascular cells, providing further evidence of its vasoprotective potential.

Methylation and expression of RECK, P53 and RUNX genes in patients with esophageal cancer

The methylation and expression of RECK, P53 and RUNX genes in patients with esophageal cancer was investigated. In order to achieve this aim, a sample of 58 patients with esophageal cancer, treated between February 2013 and February 2014, were considered as the observation group. Additionally, a sample of 42 healthy individuals was selected as the control group. Methylation status of RECK, P53 and RUNX genes from the observation and control groups were detected by MSP. Reverse transcriptase-quantitative PCR (RT-qPCR), enzyme-linked immunosorbent assay (ELISA), western blot and immunohistochemistry were used to detect the mRNA and protein levels of RECK, P53 and RUNX in both the observation and the control groups. Results showed that the methylation rates of RECK, P53 and RUNX genes in patients with esophageal cancer were 72.4% (42/58), 1.7% (1/58) and 3.4% (2/58), respectively, which were significantly different from those in the control group [7.1% (3/42), 90.5 (38/42), and 83.3% (35/42), respectively]. The mRNA expression level of RECK is only equal to the 2.3% of that in the control group, while the mRNA expression levels of P53 and RUNX were 65.1 and 47.2 times higher than those in the control group, respectively (p<0.05). ELISA showed that RECK protein level in the observation group (0.12±0.05) µg/l, was significantly lower than the control group (3.46±0.08) µg/l (p<0.05), while, P53 and RUNX protein levels in observation group were significantly higher than that in healthy people (6.43±0.12 µg/l vs. 0.64±0.06 µg/l and 4.32±0.14 µg/l vs. 0.53±0.09 µg/l, respectively), and the results were similar to western blot. The data of immunohistochemistry showed that the proportion of RECK protein positive cells in the observation group was significantly lower than that in the control group (9.5 vs. 82.3%, P<0.05), while the proportions of P53 and RUNX protein positive cell in the observation group were significantly higher than those in the control group (78.4 vs. 11.1% and 87.3 vs. 9.06%), respectively, (P<0.05). This study concluded that, in patients with esophageal cancer, the methylation of RECK gene is increased and the expression of RECK gene is inhibited, while methylation of RUNX gene decreased and their expression was increased. This change in methylation of these genes may promote the occurrence and development of esophageal cancer.

Mechanism of genistein regulating the differentiation of vascular smooth muscle cells into osteoblasts via the OPG/RANKL pathway

Objective

The present study aimed to investigate the mechanism of genistein, a tyrosine kinase inhibitor, regulating the differentiation of vascular smooth muscle cells (VSMCs) into osteoblasts via the OPG/RANKL (Osteoprotegerin/Receptor Activator of Nuclear Factor-κB Ligand) pathway.

Methods

The mouse VSMCs were isolated, purified and cultured. We constructed the LV5-Tnfrsf11b overexpression lentiviral vector and LV3-OPG-309 interference lentiviral vector. The OPG overexpression was induced and the growth of VSMCs infected with the lentiviral vector was observed. The VSMC calcification and control group were treated with different doses of genistein. The mRNA and protein expression levels of OPG, α-SM-actin (smooth muscle actin), ALP (alkaline phosphatase) and OPN (osteopontin) were detected in VSMCs after treatment using RT-PCR and Western Blot.

Result

We induced OPG overexpression and performed lentiviral vector infection of the VSMCs to suppress OPG expression, respectively, which was followed by treatment with genistein. The results showed that the relative expression of OPG was the highest in the VSMC calcification +genistein +OPG overexpression-inducing treatment group. It was the lowest in the VSMC calcification +OPG expression-suppressing treatment group. The relative expression of ALP was the highest in the VSMC calcification +OPG expression-suppressing treatment group, and the lowest in the VSMCs+genistein treatment group.

Conclusion

OPG gene plays an important regulatory role in the growth of VSMCs, by suppressing the calcification of VSMCs. Genistein could regulate the differentiation of VSMCs into osteoblasts via the OPG/RANKL pathway in a dose-dependent manner.

Fibroblast growth factor 21 plays an inhibitory role in vascular calcification in vitro through OPG/RANKL system

Vascular calcification is prevalent and associated with adverse outcome without available therapy. The benefits of fibroblast growth factor (FGF)-21 on metabolism and atherosclerosis make it a promising therapeutic agent for vascular calcification. We investigated the effects of FGF21 on vascular smooth muscle cell (VSMC) calcification by culturing rat VSMCs in a calcifying medium for 9days. FGF21 markedly attenuated mineral deposition and apoptosis at the indicated time points. In the presence of FGF21, the expression levels of osteoblastic protein including bone morphogenic protein-2, alkaline phosphatase(ALP), runt-related transcription factor(RUNX)-2 and nuclear factor-kappa B ligand (RANKL) were down-regulated, whereas the expression of osteoprotegerin (OPG) increased. Knockdown of OPG significantly impaired inhibition of FGF21 on apoptosis and the expression of pro-apoptotic genes including caspase-3 and Bax and osteoblastic -promoting markers including ALP, RUNX-2 and RANKL. Furthermore, FGF21 facilitated the phosphoryl of AKT but suppressed P38, while OPG knockdown attenuated the effects. LY29400 (inhibitor of PI3K) abrogated the activation of PI3K/AKT and SB203580 (inhibitor of P38) abolished the inhibition of FGF21 on P38, while alteration was observed in the expression of RUNX-2. FGF21 inhibited VSMCs calcification via OPG/RANKL system, and through P38 andPI3K/AKT pathways.

Deletion of a Distal RANKL Gene Enhancer Delays Progression of Atherosclerotic Plaque Calcification in Hypercholesterolemic Mice

Receptor activator of NF-κB ligand (RANKL) is a TNF-like cytokine which mediates diverse physiological functions including bone remodeling and immune regulation. RANKL has been identified in atherosclerotic lesions; however, its role in atherosclerotic plaque development remains elusive. An enhancer located 75 kb upstream of the murine Rankl gene's transcription start site designated D5 is important for its calciotropic hormone- and cytokine-mediated expression. Here, we determined the impact of RANKL levels in atherosclerotic plaque development in the D5 enhancer-null (D5^-/- ) mice in an atherogenic Apoe^-/- background fed a high-fat diet (HFD). Rankl mRNA transcripts were increased in aortic arches and thoracic aortae of Apoe^-/- mice; however, this increase was blunted in Apoe^-/- ;D5^-/- mice. Similarly, higher Rankl transcripts were identified in splenic T lymphocytes in Apoe^-/- mice, and their levels were reduced in Apoe^-/- ;D5^-/- mice. When analyzed by micro-computed tomography (µCT), atherosclerotic plaque calcification was identified in six out of eight Apoe^-/- mice, whereas only one out of eight Apoe^-/- ;D5^-/- mice developed plaque calcification after 12 weeks of HFD. However, following 18 weeks of HFD challenge, all of Apoe^-/- and Apoe^-/- ;D5^-/- animals developed atherosclerotic plaque calcification. Likewise, atherosclerotic lesion sizes were site-specifically reduced in the aortic arch of Apoe^-/- ;D5^-/- mice at initial stage of atherosclerosis and this effect was diminished as atherosclerosis proceeded to a more advanced stage. Our data suggest that deletion of the RANKL D5 enhancer delays the progression of atherosclerotic plaque development and plaque calcification in hypercholesterolemic mice. This work provides important insight into RANKL's regulatory role in atherosclerosis. J. Cell. Biochem. 118: 4240-4253, 2017. © 2017 Wiley Periodicals, Inc.

From bones to blood pressure, developing novel biologic approaches targeting the osteoprotegein pathway for pulmonary vascular disease

Osteoprotegerin (tnfsf11b, OPG) is a soluble member of the TNF superfamily originally described as an important regulator of osteoclastogenesis almost 20 years ago. OPG is a heparin-binding secreted glycoprotein that exists as a 55–62 kDa monomer or a 110–120 kDa disulphide-linked homodimer. Acting as a soluble decoy receptor for RANKL, OPG actively regulates RANK signalling, and thereby osteoclastogenesis. OPG has subsequently been shown to also be a decoy receptor TNF related apoptosis inducing-ligand (tnfsf10, TRAIL, Apo2L). TRAIL is a type II transmembrane protein that is widely expressed in a variety of human tissues, including the spleen, lung, and prostate. Through binding to TRAIL, OPG can inhibit TRAIL-induced apoptosis of cancer cells. More recently, OPG has been demonstrated to be secreted by, and influence, vascular smooth muscle cells phenotype particularly related to vascular calcification and pulmonary vascular remodelling. In pulmonary artery smooth muscle cell (PASMC) suppression of BMP, induction of 5-HT and IL-1 signalling have been shown to stimulate the release of OPG in vitro, which causes cell migration and proliferation. Patients with idiopathic PAH (IPAH) demonstrate increased circulating and tissue levels of OPG, and circulating serum levels predict survival. In pre-clinical models, OPG levels correlate with disease severity. Since OPG is a naturally circulating protein, we are investigating the potential of novel biologic antibody therapies to rescue PAH phenotype in disease models. Further pre-clinical and mechanistic data are forthcoming, but we believe current published data identify OPG as an exciting and novel therapeutic target in PAH.

RANKL promotes osteoblastic activity in vascular smooth muscle cells by upregulating endothelial BMP-2 release

INTRODUCTION

Receptor activator of nuclear factor kappa beta-ligand (RANKL) is thought to promote vascular calcification (VC) by inducing osteoblastic behaviour in vascular smooth muscle cells (VSMC) in an ill-defined process. The present study assessed whether RANKL affects pro-osteoblastic paracrine signalling between human aortic endothelial cells (HAEC) and human aortic smooth muscle cells (HASMC) using both conditioned media transfer and cell co-culture experimental approaches.

METHODS AND RESULTS

For initial experiments (6-well format), HAEC-conditioned media was harvested following 72h exposure to RANKL, and transferred to reporter HASMCs with/without noggin, an inhibitor of pro-osteoblastic bone morphogenetic protein (BMP) paracrine signalling. In further experiments, HAECs and HASMCs were co-cultured within the CellMax(®) Duo, a perfusing bioreactor unit that mimics the flow-mediated co-interaction of these cells within the arterial wall, and RANKL was added to the perfusing media for 72h. At the conclusion of each experiment markers of osteoblastic activity were measured in HASMCs, including alkaline phosphatase (ALP) activity, mRNA levels of ALP and Runx2, as well as BMP-2 and BMP-4 concentrations. RANKL increased BMP-2 release from HAECs, while exposure of HASMCs to RANKL-treated HAEC-conditioned media induced osteoblastic behaviour in HASMCs, an effect prevented by noggin. Within the CellMax(®) Duo bioreactor, the addition of RANKL to the intraluminal HAECs also produced an increase in BMP-2 and increased osteoblastic behaviour within the co-cultured HASMC population.

CONCLUSIONS

RANKL promotes VC by inducing BMP-2 release from HAECs, which in turn appears to act in a paracrine fashion on the adjacent HASMC population to increase osteoblastic activity.

Transdifferentiation of human endothelial progenitors into smooth muscle cells

Access to smooth muscle cells (SMC) would create opportunities for tissue engineering, drug testing, and disease modeling. Herein we report the direct conversion of human endothelial progenitor cells (EPC) to induced smooth muscle cells (iSMC) by induced expression of MYOCD. The EPC undergo a cytoskeletal rearrangement resembling that of mesenchymal cells within 3 days post initiation of MYOCD expression. By day 7, the reprogrammed cells show upregulation of smooth muscle markers ACTA2, MYH11, and TAGLN by qRT-PCR and ACTA2 and MYH11 expression by immunofluorescence. By two weeks, they resemble umbilical artery SMC in microarray gene expression analysis. The iSMC, in contrast to EPC control, show calcium transients in response to phenylephrine stimulation and a contractility an order of magnitude higher than that of EPC as determined by traction force microscopy. Tissue-engineered blood vessels constructed using iSMC show functionality with respect to flow- and drug-mediated vasodilation and vasoconstriction.

Targeting local vascular and systemic consequences of inflammation on vascular and cardiac valve calcification

INTRODUCTION

Cardiac valve calcification and vascular calcification (VC) are associated with cardiovascular mortality in the general population and in patients with chronic kidney disease (CKD). CKD, diabetes mellitus, and atherosclerosis are among the causes of systemic inflammation that are associated with VC.

AREAS COVERED

This review collates clinical and experimental evidence that inflammation accelerates VC progression. Specifically, we review the actions of key pro-inflammatory cytokines and inflammation-related transcription factors on VC, and the role played by senescence. Inflammatory cytokines, such as the TNF superfamily and IL-6 superfamily, and inflammation-related transcription factor NF-κB promote calcification in cultured vascular smooth muscle cells, valvular interstitial cells, or experimental animal models through direct effects, but also indirectly by decreasing circulating Fetuin A or Klotho levels.

EXPERT OPINION

Experimental evidence suggests a causal link between inflammation and VC that would change the clinical approach to prevention and treatment of VC. However, the molecular basis remains unclear and little is known about VC in humans treated with drugs targeting inflammatory cytokines. The effect of biologicals targeting TNF-α, RANKL, IL-6, and other inflammatory mediators on VC, in addition to the impact of dietary phosphate in patients with chronic systemic inflammation, requires study.

Vascular calcification: from pathophysiology to biomarkers

The link between vascular calcification (VC) and increased mortality is now well established. Over time, as clinical importance of this phenomenon has begun to be fully considered, scientists have highlighted more and more physiopathological mechanisms and signaling pathways that underlie VC. Several conditions such as diabetes, dyslipidemia and renal diseases are undoubtedly identified as predisposing factors. But even if the process is better understood, many questions still remain unanswered. This review briefly develops the various theories that attempt to explain mineralization genesis. Nonetheless, the main purpose of the article is to provide a profile of the various existing biomarkers of VC. Indeed, in the past years, a lot of inhibitors and promoters, which form a dense and interconnected network, were identified. Given importance to assess and control mineralization process, a focusing on accumulated knowledge of each marker seemed to be necessary. Therefore, we tried to define their respective role in the physiopathology and how they can contribute to calcification risk assessment. Among these, Klotho/fibroblast growth factor-23, fetuin-A, Matrix Gla protein, Bone morphogenetic protein-2, osteoprotegerin, osteopontin, osteonectin, osteocalcin, pyrophosphate and sclerostin are specifically discussed.

Role of osteoprotegerin and its gene polymorphisms in the occurrence of left ventricular hypertrophy in essential hypertensive patients

The aim of the study was to investigate the role of osteoprotegerin (OPG) in left ventricular hypertrophy (LVH) development in patients with essential hypertension (EH). A total of 1092 patients diagnosed with EH were recruited. The LVHs were determined and OPG gene polymorphisms were genotyped. Patients with LVH had a significantly higher mean serum OPG level than those without LVH. The 1181CC genotype carriers had significantly lower risk for LVH compared with GC and GG genotype carriers. The serum OPG level and OPG 1181 G>C polymorphism were found to be independent risk factors for the occurrence of LVH in hypertensive patients. In vitro study shows that OPG overexpression upregulates cell surface size, protein synthesis per cell, and hypertrophy- and fibrosis-related proteins in both cardiomyocytes and cardiac fibroblasts, whereas OPG inhibition can abolish the above-mentioned changes. Consistent with the in vitro data, our in vivo study revealed that the OPG administration induced the LVH in hypertensive rats. This study is the first to report the close association between OPG and LVH development in EH patients and the regulatory effect of OPG on cardiomyocytes and cardiac fibroblasts.

Tumor necrosis factor-related apoptosis-inducing ligand in vascular inflammation and atherosclerosis: a protector or culprit?

In addition to inducing tumor cell apoptosis, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) shows broad biological functions both in vitro and in vivo. TRAIL gene deletion enhanced atherogenesis in hyperlipidemic mice, supporting that endogenous TRAIL has protective actions in maintaining blood vessel homeostasis and repressing atherosclerosis. The mechanisms of this beneficial effect are not understood. It remains to be determined whether the athero-protective action of TRAIL is via direct impacts on residential vascular cells or indirectly by modulating systemic immune functions. However, in vitro experiments indicate that excessive TRAIL may stimulate endothelial cell apoptosis, smooth muscle proliferation and migration, and inflammatory responses. Moreover, TRAIL can stimulate lipid uptake and foam cell formation in cultured macrophages. Here we provide a critical review on the potential relationships between TRAIL and atherosclerosis. We propose that increased TRAIL production may also have potential detrimental effects on vascular inflammation and atherosclerosis. Further in vivo experiments are warranted to elucidate the effects of exogenous TRAIL on atherogenesis.

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.

Below-knee arterial calcification in type 2 diabetes: association with receptor activator of nuclear factor κB ligand, osteoprotegerin, and neuropathy

CONTEXT

Calcification of the arterial wall in diabetes contributes to the arterial occlusive process occurring below the knee. The osteoprotegerin (OPG)/receptor activator of nuclear factor κB ligand (RANKL) system is suspected to be involved in the calcification process.

OBJECTIVE

The aim of the study was to investigate whether there is a link between arterial calcification in type 2 diabetes and 1) conventional cardiovascular risk factors, 2) serum RANKL and OPG levels, and 3) neuropathy.

PATIENTS AND METHODS

We objectively scored, in a cross-sectional study, infrapopliteal vascular calcification using computed tomography scanning in 198 patients with type 2 diabetes, a high cardiovascular risk, and a glomerular filtration rate >30 mL/min. Color duplex ultrasonography was performed to assess peripheral arterial occlusive disease, and mediacalcosis. Peripheral neuropathy was defined by a neuropathy disability score >6. RANKL and OPG were measured in the serum by routine chemistry.

RESULTS

Below-knee arterial calcification was associated with arterial occlusive disease. In multivariate logistic regression analysis, the variables significantly and independently associated with the calcification score were age (odds ratio [OR] = 1.08; 95% confidence interval [CI] = 1.04-1.13; P < .0001), male gender (OR = 3.53; 95% CI = 1.54-8.08; P = .003), previous cardiovascular disease (OR = 2.78; 95% CI = 1.39-5.59; P = .005), and neuropathy disability score (per 1 point, OR = 1.21; 95% CI = 1.05-1.38; P = .006). The association with ln OPG, significantly associated with calcification score in univariate analysis (OR = 3.14; 95% CI = 1.05-9.40; P = .045), was no longer significant in multivariate analysis. RANKL and OPG/RANKL were not significantly associated with the calcification score.

CONCLUSIONS

Below-knee arterial calcification severity is clearly correlated with peripheral neuropathy severity and with several usual cardiovascular risk factors, but not with serum RANKL level.

Age and menopausal status affect osteoprotegerin and osteocalcin levels in women differently, irrespective of thyroid function

Osteoprotegerin (OPG) and osteocalcin (OC) are essential bone proteins. Recent studies have demonstrated that they are not secreted solely by bone cells; they play roles in the vascular function and energy metabolism, and they are influenced by multiple factors. The aim of the current study was to investigate the influence of menopause and age on OPG and OC in women with different thyroid-stimulating hormone (TSH) levels.

Increased calcification in osteoprotegerin-deficient smooth muscle cells: Dependence on receptor activator of NF-κB ligand and interleukin 6

OBJECTIVE

Vascular calcification is highly correlated with cardiovascular disease morbidity and mortality. Osteoprotegerin (OPG) is a secreted decoy receptor for receptor activator of NF-κB ligand (RANKL). Inactivation of OPG in apolipoprotein E-deficient (ApoE-/-) mice increases lesion size and calcification. The mechanism(s) by which OPG is atheroprotective and anticalcific have not been entirely determined. We investigated whether OPG-deficient vascular smooth muscle cells (VSMCs) are more susceptible to mineralization and whether RANKL mediates this process.

RESULTS

Lesion-free aortas from 12-week-old ApoE-/-OPG-/- mice had spotty calcification, an appearance of osteochondrogenic factors and a decrease of smooth muscle markers when compared to ApoE-/-OPG+/+ aortas. In osteogenic conditions, VSMCs isolated from ApoE-/-OPG-/- (KO-VSMC) mice deposited more calcium than VSMCs isolated from ApoE-/-OPG+/+ (WT-VSMC) mice. Gene expression and biochemical analysis indicated accelerated osteochondrogenic differentiation. Ablation of RANKL signaling in KO-VSMCs rescued the accelerated calcification. While WT-VSMCs did not respond to RANKL treatment, KO-VSMCs responded with enhanced calcification and the upregulation of osteochondrogenic genes. RANKL strongly induced interleukin 6 (IL-6), which partially mediated RANKL-dependent calcification and gene expression in KO-VSMCs.

CONCLUSIONS

OPG inhibits vascular calcification by regulating the procalcific effects of RANKL on VSMCs and is thus a possible target for therapeutic intervention.

TRAIL-deficiency accelerates vascular calcification in atherosclerosis via modulation of RANKL

The osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) cytokine system, not only controls bone homeostasis, but has been implicated in regulating vascular calcification. TNF–related apoptosis-inducing ligand (TRAIL) is a second ligand for OPG, and although its effect in vascular calcification in vitro is controversial, its role in vivo is not yet established. This study aimed to investigate the role of TRAIL in vascular calcification in vitro using vascular smooth muscle cells (VSMCs) isolated from TRAIL^−/− and wild-type mice, as well as in vivo, in advanced atherosclerotic lesions of TRAIL^−/−ApoE^−/− mice. The involvement of OPG and RANKL in this process was also examined. TRAIL dose-dependently inhibited calcium-induced calcification of human VSMCs, while TRAIL^−/− VSMCs demonstrated accelerated calcification induced by multiple concentrations of calcium compared to wild-type cells. Consistent with this, RANKL mRNA was significantly elevated with 24 h calcium treatment, while OPG and TRAIL expression in human VSMCs was inhibited. Brachiocephalic arteries from TRAIL^−/−ApoE^−/− and ApoE^−/− mice fed a high fat diet for 12 w demonstrated increased chondrocyte-like cells in atherosclerotic plaque, as well as increased aortic collagen II mRNA expression in TRAIL^−/−ApoE^−/− mice, with significant increases in calcification observed at 20 w. TRAIL^−/−ApoE^−/− aortas also had significantly elevated RANKL, BMP-2, IL-1β, and PPAR-γ expression at 12 w. Our data provides the first evidence that TRAIL deficiency results in accelerated cartilaginous metaplasia and calcification in atherosclerosis, and that TRAIL plays an important role in the regulation of RANKL and inflammatory markers mediating bone turn over in the vasculature.

An ELISA for the quantitation of von Willebrand factor: osteoprotegerin complexes in plasma

BACKGROUND

Von Willebrand factor (VWF) is pivotal in arterial thrombosis, and osteoprotegerin (OPG) is besides being a bone protein also related to cardiovascular diseases. OPG can bind VWF, but the significance of this interaction is not known.

OBJECTIVES

The aim was to develop an assay for measurement of von Willebrand factor-osteoprotegerin complex (VWF:OPG) in human plasma. Furthermore, the significance of VWF:OPG complex as a marker of cardiovascular disease (CVD) was evaluated.

PATIENTS/METHODS

A sandwich ELISA for quantification of VWF:OPG was developed using a polyclonal rabbit anti-human VWF capturing antibody and a monoclonal anti-human OPG detecting antibody. Samples were quantified relative to a standard curve obtained from dilutions of a plasma pool from healthy individuals. The assay was evaluated in two groups of patients with CVD and two groups of asymptomatic individuals with and without documented coronary calcification (total n=118).

RESULTS AND CONCLUSIONS

The assay detected VWF:OPG complexes in human plasma, while no significant signal was observed when testing solutions containing VWF or recombinant OPG alone. Importantly, the ELISA assay was able to detect in vitro formed complexes between human VWF and recombinant OPG in a dose-dependent manner. There was a large inter-individual variation in plasma VWF:OPG levels, but we found no significant differences in the level of VWF:OPG complexes between the four groups. Thus, we conclude that increasing OPG plasma levels in atherosclerotic CVD are not derived from increased levels of complexed form of VWF and OPG, but are more likely due to increased amounts of OPG secreted into the circulation.

Enhanced mineralization potential of vascular cells from SM22α-Rankl (tg) mice

Vascular calcification, prevalent in diabetes and chronic kidney disease, contributes to morbidity and mortality. To investigate the effect of receptor activator of NF-kB ligand (RANKL) on vascular calcification in vivo, transgenic mice, where RANKL expression was targeted to vascular smooth muscle cells using the SM22α promoter (SM22α-Rankl ( tg )), were created. Sixteen-month-old male SM22α-Rankl ( tg ) mice had higher body weight and higher serum calcium levels but lower lumbar bone mineral density (BMD) compared with age- and gender-matched wild-type (WT) littermates. BMD of long bones, body fat (percent of weight) of the leg, and serum levels of phosphate and RANKL were not significantly different. No significant differences in these parameters were observed in female mice. Histological analysis did not reveal calcium deposits in the aortic roots of SM22α-Rankl ( tg ) mice. To analyze the osteoblastic differentiation and mineralization potentials of vascular cells, aortic smooth muscle cells (SMCs) were isolated and cultured. Results showed that SM22α-Rankl ( tg ) SMCs had higher baseline alkaline phosphatase (ALP) activity but not baseline matrix calcification. When induced by the PKA agonist forskolin, ALP activity was greater in SM22α-Rankl ( tg ) than in WT SMCs. Real-time RT-qPCR revealed higher baseline expression of ALP and ankylosis genes but lower osteoprotegerin gene in SM22α-Rankl ( tg ) SMCs. Matrix mineralization induced by inorganic phosphate or forskolin was greater in SM22α-Rankl ( tg ) than in WT SMCs. Treatment of these cells with the ALP inhibitor levamisole abolished forskolin-induced matrix mineralization but not inorganic phosphate-induced matrix mineralization. These findings suggest that RANKL overexpression in the vasculature may promote mineralization potential.