Osteoprotegerin inactivation accelerates advanced atherosclerotic lesion progression and calcification in older ApoE-/- mice

Osteoprotegerin in relation to insulin resistance and blood lipids in sub-Saharan African women with and without abdominal obesity

BACKGROUND

Osteoprotegerin (OPG), a soluble member of the tumor necrosis factor receptor superfamily that inhibits bone resorption, has been suggested as a potential marker of cardiovascular risk. This study aimed to assess the relationship between insulin resistance, lipid profile and OPG levels in obese and non-obese sub-Saharan African women.

METHODS

Sixty obese (44) and non-obese (16) volunteer women aged 18 to 40 years were recruited in this cross-sectional study. Their clinical (age, height, weight, waist circumference, systolic and diastolic blood pressures) and biochemical parameters (fasting blood glucose, total cholesterol, high density lipoprotein-cholesterol (HDL-C)) were measured using standard methods. Insulin levels were measured using an electrochemiluminescence immunoassay, while OPG levels were measured using the ELISA technique. Low density lipoprotein-cholesterol (LDL-C), body mass index (BMI) and Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) were calculated using standard methods. Abdominal obesity was defined as a waist circumference ≥ 80 cm.

RESULTS

OPG levels were higher in obese than in normal subjects, though the difference was not significant (p = 0.9). BMI, waist circumference, percent body fat and systolic blood pressure were significantly higher in obese than in non-obese subjects (p < 0.05). In these subjects, only age significantly correlated with OPG levels (r = 0.831, p = 0.003), while none of the anthropometric nor metabolic parameter did, even after adjustment for age. In obese subjects, OPG levels fairly correlated with HDL-C (r = 0.298, p = 0.058), and significantly correlated with HOMA-IR (r = -0.438, p = 0.018). After adjustment for age, OPG levels remained negatively correlated to HOMA-IR (r = -0.516, p = 0.020) and LDL-C (r = -0.535, p = 0.015) and positively correlated to HDL-C (r = 0.615, p = 0.004). In multiple linear regression analysis, age was a main determinant of OPG levels in non-obese (β = 0.647, p = 0.006) and obese (β = 0.356, p = 0.044) women. HDL-C was also associated to OPG levels in obese women (β = 0.535, p = 0.009).

CONCLUSION

The positive correlation of OPG with HDL-C and HOMA-IR, and its negative correlation with LDL-C suggest that it may be a marker of insulin sensitivity/resistance and atherogenic risk in obese African women.

Curcumin induces senescence of primary human cells building the vasculature in a DNA damage and ATM-independent manner

Curcumin is considered not only as a supplement of the diet but also as a drug in many types of diseases and even as a potential anti-aging compound. It can reduce inflammation that increases with age and accompanies almost all age-related diseases. It has been suggested that curcumin can play a beneficial role in the cardiovascular system. However, there are also data showing that curcumin can induce senescence in cancer cells, which is a beneficial effect in cancer therapy but an undesirable one in the case of normal cells. It is believed that cellular senescence accompanies age-related changes in the cardiovascular system. The aim of this study was to check if curcumin, in a certain range of concentrations, can induce senescence in cells building the vasculature. We have found that human vascular smooth muscle and endothelial cells derived from aorta are very sensitive to curcumin treatment and can senesce upon treatment with cytostatic doses. We observed characteristic senescence markers but the number of DNA damage foci decreased. Surprisingly, in vascular smooth muscle cell (VSMC) activation of DNA damage response pathway downstream of ataxia-telangiectasia mutated (ATM) was observed. ATM silencing and the supplementation of antioxidants, N-acetyl-L-cysteine (NAC) or trolox, did not reduce the number of senescent cells. Thus, we have shown that curcumin can induce senescence of cells building the vasculature, which is DNA damage and ATM independent and is not induced by increased reactive oxygen species (ROS) level. We postulate that an increase in the bioavailability of curcumin should be introduced very carefully considering senescence induction as a side effect.

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.

TNFRSF11B gene polymorphisms increased risk of peripheral arterial occlusive disease and critical limb ischemia in patients with type 2 diabetes

AIMS

Osteoprotegerin (OPG) is a secretory glycoprotein that belongs to the tumor necrosis factor receptor family and plays a role in atherosclerosis. OPG has been hypothesized to modulate vascular functions; however, its role in mediating atherosclerosis is controversial. Epidemiological data in patients with cardiovascular disease (CVD) indicate that OPG serum levels are associated with several inflammatory markers, myocardial infarction events, and calcium scores, suggesting that OPG may be causative for CVD.

METHODS

The present study aimed to evaluate whether the OPG gene (TNFRSF11B) polymorphisms are involved in the development of peripheral arterial occlusive disease (PAOD) and critical limb ischemia (CLI) in patients with type 2 diabetes. This genetic association study included 402 diabetic patients (139 males and 263 females) with peripheral arterial occlusive disease and 567 diabetic subjects without peripheral arterial occlusive disease (208 males and 359 females). The T245G, T950C, and G1181C polymorphisms of the OPG gene were analyzed by polymerase chain reaction and restriction fragment length polymorphism.

RESULTS

We found that the T245G, T950C, and G1181C gene polymorphisms of the OPG gene were significantly (27.9 vs. 12.2 %, P < 0.01; 33.6 vs. 10.4 %, P < 0.01 and 24.4 vs. 12.7 %, P < 0.01, respectively) and independently (adjusted OR 4.97 (3.12-6.91), OR 7.02 (4.96-11.67), and OR 2.85 (1.95-4.02), respectively) associated with PAOD. We also found that these three polymorphisms act synergistically in patients with PAOD and are associated with different levels of risk for PAOD and CLI, depending on the number of high-risk genotypes carried concomitantly by a given individual.

CONCLUSION

The TNFRSF11B gene polymorphisms under study are associated with PAOD, and synergistic effects between these genotypes might be potential markers for the presence and severity of atherosclerotic disorders.

MicroRNA-34a Induces Vascular Smooth Muscle Cells Senescence by SIRT1 Downregulation and Promotes the Expression of Age-Associated Pro-inflammatory Secretory Factors

Arterial aging is a major risk factor for the occurrence of cardiovascular diseases. The aged artery is characterized by endothelial dysfunction and vascular smooth muscle cells altered physiology together with low-grade chronic inflammation. MicroRNA-34a (miR-34a) has been recently implicated in cardiac, endothelial, and endothelial progenitor cell senescence; however, its contribution to aging-associated vascular smooth muscle cells phenotype has not been explored so far. We found that miR-34a was highly expressed in aortas isolated from old mice. Moreover, its well-known target, the longevity-associated protein SIRT1, was significantly downregulated during aging in both endothelial cells and vascular smooth muscle cells. Increased miR-34a as well as decreased SIRT1 expression was also observed in replicative-senescent human aortic smooth muscle cells. miR-34a overexpression in proliferative human aortic smooth muscle cells caused cell cycle arrest along with enhanced p21 protein levels and evidence of cell senescence. Furthermore, miR-34a ectopic expression induced pro-inflammatory senescence-associated secretory phenotype molecules. Finally, SIRT1 protein significantly decreased upon miR-34a overexpression and restoration of its levels rescued miR-34a-dependent human aortic smooth muscle cells senescence, but not senescence-associated secretory phenotype factors upregulation. Taken together, our findings suggest that aging-associated increase of miR-34a expression levels, by promoting vascular smooth muscle cells senescence and inflammation through SIRT1 downregulation and senescence-associated secretory phenotype factors induction, respectively, may lead to arterial dysfunctions.

Circulating osteoprotegerin is increased in the metabolic syndrome and associates with subclinical atherosclerosis and coronary arterial calcification

CONTEXT

The relationship between osteoprotegerin (OPG) a glycoprotein related to bone metabolism and the metabolic syndrome (MS) has not been established.

OBJECTIVE

The aim of this study is to evaluate OPG concentration in patients with MS and its association with subclinical atherosclerosis and coronary arterial calcification (CAC).

MATERIALS/METHODS

The study included 238 asymptomatic patients. MS was diagnosed according to the NCEP/ATPIII guidelines. OPG was measured by ELISA. All subjects underwent ultrasonography of the common carotid arteries to measure intima-media thickness (IMT) and evaluate the presence of atheroma plaques. In a subgroup (n=39) CAC was quantified by ECG-triggered cardiac computed tomography. Adipose tissue was excised from 25 patients and OPG expression by RT-PCR and immunohistochemistry was studied.

RESULTS

Patients with the MS (n=60) had higher OPG than patients without (n=178) (p<0.05). OPG correlated with IMT (r=0.2, p=0.005) and patients with atheroma plaques had higher OPG (p=0.008) and also those with coronary artery calcification (p<0.05). OPG expression was confirmed in adipose tissue (n=12) and the expression was significantly higher in patients with MS than in those without (p=0.003).

CONCLUSIONS

This study shows that OPG may potentially be a biomarker for cardiovascular risk/damage in the MS and identifies adipose tissue as a potential source of OPG.

Circulating osteoprotegerin and asymptomatic carotid atherosclerosis in postmenopausal non diabetic women

PURPOSE

Osteoprotegerin (OPG) is a bone metabolism regulator but it is also involved in vascular calcification. Its role in the development of atherosclerosis is still a subject of debate. Postmenopausal women seem to have an increased risk for cardiovascular disease. The aim of the study is to evaluate the relationship between serum OPG and asymptomatic carotid atherosclerosis in postmenopausal non-diabetic women.

MATERIAL/METHODS

Carotid artery examination was performed in 100 postmenopausal women without diabetes mellitus and overt cardiovascular disease, using B-mode ultrasonography to determine the carotid intima-media thickness (CIMT) and the presence of plaques. Serum OPG was measured in all study participants and its relationship with clinical, biochemical and vascular parameters was evaluated.

RESULTS

CIMT correlated with age (r=0.45, p<0.001), years since menopause (r=0.30, p=0.003), abdominal circumference (r=0.25, p=0.01) and OPG (r=0.23, p=0.02). Carotid plaques correlated with age (p<0.001), obesity (p=0.03), abdominal circumference (p=0.03) and CIMT (p<0.001), but not with serum OPG (p=0.86). In regression analyses the independent predictors for CIMT were age (β=0.717, p<0.001), OPG (β=0.214, p=0.02), and years since menopause (β=-0.334, p=0.04) and for the presence of carotid plaques were obesity (p=0.04, OR=3.90), CIMT (p<0.001, OR=6408.86) and smoking (p=0.02, OR=687.93).

CONCLUSION

OPG is associated with cardiovascular risk factors, CIMT, but not with the presence of asymptomatic carotid plaques in non diabetic postmenopausal women. OPG may be a marker of cardiovascular risk.

Changes of plasma concentration of osteoprotegerin and its association with endothelial dysfunction before and after hypouricemic therapy in patients with hyperuricemia

OBJECTIVE

Osteoprotegerin (OPG) is a secreted glycoprotein in the regulation of bone turnover. Recently, many studies showed that OPG acts as an important regulatory molecule in the vascular systems. Our objective was to examine the plasma OPG levels alteration and its association with endothelial function before and after hypouricemic therapy in patients with hyperuricemia.

METHODS

Thirty patients (28 males and 2 females, serum uric acid > 7.0 mg/dl) with hyperuricemia were selected. Thirty healthy individuals (28 males and 2 females) with normal serum uric acid were also selected as control. Patients were administered with hypouricemic therapy for 6 months. Plasma OPG concentration was measured in duplicate using a sandwich ELISA and high-resolution ultrasound was used to measure brachial artery diameter at rest, after reactive hyperemia and after sublingual glyceryltrinitrate.

RESULTS

Plasma OPG levels in patients with hyperuricemia before hypouricemic therapy was significantly higher than those in controls (3.39 ± 0.25 vs. 2.05 ± 0.74 ng/L, p < 0.01). After hypouricemic therapy, OPG levels decreased markedly (2.54 ± 0.38 ng/L, p < 0.01). Flow-mediated dilation (FMD) in patients with hyperuricemia was 3.07 ± 1. 23%, which was significantly lower than that in control subjects (4.62 ± 0.69%, p < 0.01), and it improved significantly after hypouricemic therapy (3.91 ± 1.37%, p < 0.01). The absolute changes in OPG showed a significant positive correlation with the changes in serum uric acid (p < 0.05) and negative correlation with the changes in FMD (p < 0.01) in patients with hyperuricemia during the course of hypouricemic therapy.

CONCLUSION

The current study demonstrates that plasma OPG levels increased significantly in patients with hyperuricemia and decreased significantly after hypouricemic therapy, and are correlated with FMD. These findings support the growing concept that elevated plasma OPG levels may be involved with the development of endothelial dysfunction in patients with hyperuricemia.

Regression of vascular calcification in chronic kidney disease - feasible or fantasy? a review of the clinical evidence

The complex relationships between cardiovascular, renal, and bone disease are increasingly recognized but not yet clearly understood. Vascular calcification (VC) represents a common end point between these interlinked systems. It is highly prevalent in chronic kidney disease (CKD) and may be responsible for some of the excess cardiovascular events seen in this condition. There is much interest in developing therapeutic agents to stop its development or reverse its progression. Traditionally considered to be due to abnormalities in calcium and phosphate metabolism alone, VC is now known to be the product of active, dynamic processes within the vessel wall. Primary prevention of VC is possible through successful prevention or reversal of progressive renal dysfunction, hypertension and hyperlipidaemia, but is challenging given the increasing global prevalence of these risk factors. Secondary prevention of VC through tight control of calcium and phosphate, can be achieved by dietary or pharmacological means. Both the modification of haemodialysis duration or methods and the use of renal transplantation have an effect. Novel drugs such as cinacalcet were hoped to halt calcification but results have been mixed, and no intervention has yet been shown to reverse calcification reliably. A new range of experimental targets involved in the putative mediatory pathways between bone and vascular disease has emerged. Aiming to manipulate the active mechanisms involved in calcium deposition, these hold hope for reversal of calcification, but are still theoretical or in early animal or human experimentation.

Osteoprotegerin and kidney disease

Vascular calcification in chronic kidney disease (CKD) patients is associated to increased mortality. Osteoprotegerin (OPG) is a soluble tumor necrosis factor (TNF) superfamily receptor that inhibits the actions of the cytokines receptor activator of nuclear factor kappa-B ligand (RANKL) and TNF-related apoptosis-inducing ligand (TRAIL) by preventing their binding to signaling receptors in the cell membrane. OPG-deficient mice display vascular calcification while OPG prevented calcification of cultured vascular smooth muscle cells and protected kidney cells from TRAIL-induced death. OPG may be a biomarker in patients with kidney disease. Circulating OPG is increased in predialysis, dialysis and transplant CKD patients and may predict vascular calcification progression and patient survival. By contrast, circulating OPG is decreased in nephrotic syndrome. In addition, free and exosome-bound urinary OPG is increased in human kidney disease. Increased urinary OPG has been associated with lupus nephritis activity. Despite the association of high OPG levels with disease, experimental functional information available suggests that OPG might be protective in kidney disease and in vascular injury in the context of uremia. Thus, tissue injury results in increased OPG, while OPG may protect from tissue injury. Recombinant OPG was safe in phase I randomized controlled trials. Further research is needed to fully define the therapeutic and biomarker potential of OPG in patients with kidney disease.

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.

RANKL inhibition with denosumab does not influence 3-year progression of aortic calcification or incidence of adverse cardiovascular events in postmenopausal women with osteoporosis and high cardiovascular risk

Atherosclerosis and osteoporosis are chronic diseases that progress with age, and studies suggest aortic calcification, an indicator of atherosclerosis, is inversely associated with bone mineral density (BMD). The osteoprotegerin (OPG)/receptor activator of NF-κB (RANK)/RANK ligand (RANKL) system has been proposed as a shared regulatory system for bone and vasculature. Denosumab (DMAb), a monoclonal antibody against RANKL, improved BMD and reduced fracture risk in the Fracture Reduction Evaluation of Denosumab in Osteoporosis Every 6 Months (FREEDOM) trial. We evaluated whether or not treatment with DMAb influenced progression of aortic calcification (AC) and incidence of cardiovascular (CV) adverse events. We included 2363 postmenopausal women with osteoporosis (1142 placebo, 1221 DMAb), selected from 7808 participants in the FREEDOM trial (3906 placebo, 3902 DMAb), at high risk of CV events according to modified Raloxifene Use for the Heart (RUTH) criteria. CV adverse events were reported by participants. AC scores were assessed using a semiquantitative method from lateral spine X-rays. Change in AC score from baseline to 12 (n = 1377), 24 (n = 1231), and 36 months (n = 1045) was calculated as AC score at follow-up minus AC score at baseline. AC progression was defined as change in AC score >0. Baseline characteristics, CV risk factors, and AC scores were similar between treatment groups. Mean age of participants was 74 years (range, 60-90), 88% were white, and 77% had AC score >0 at baseline. Frequency of AC progression over 3 years did not differ between women in placebo (22%) and DMAb (22%) groups (p = 0.98). AC progression did not differ between treatment groups when analyzed by baseline estimated glomerular filtration rate or by baseline AC scores. Frequency of CV adverse events did not differ between placebo (40%) and DMAb (38%) groups (p = 0.26). In conclusion, DMAb treatment had no effect on progression of AC or incidence of CV adverse events compared to placebo.

TWEAK/Fn14 Axis: A Promising Target for the Treatment of Cardiovascular Diseases

Cardiovascular diseases (CVD) are the first cause of mortality in Western countries. CVD include several pathologies such as coronary heart disease, stroke or cerebrovascular accident, congestive heart failure, peripheral arterial disease, and aortic aneurysm, among others. Interaction between members of the tumor necrosis factor (TNF) superfamily and their receptors elicits several biological actions that could participate in CVD. TNF-like weak inducer of apoptosis (TWEAK) and its functional receptor and fibroblast growth factor-inducible molecule 14 (Fn14) are two proteins belonging to the TNF superfamily that activate NF-κB by both canonical and non-canonical pathways and regulate several cell functions such as proliferation, migration, differentiation, cell death, inflammation, and angiogenesis. TWEAK/Fn14 axis plays a beneficial role in tissue repair after acute injury. However, persistent TWEAK/Fn14 activation mediated by blocking experiments or overexpression experiments in animal models has shown an important role of this axis in the pathological remodeling underlying CVD. In this review, we summarize the role of TWEAK/Fn14 pathway in the development of CVD, focusing on atherosclerosis and stroke and the molecular mechanisms by which TWEAK/Fn14 interaction participates in these pathologies. We also review the role of the soluble form of TWEAK as a biomarker for the diagnosis and prognosis of CVD. Finally, we highlight the results obtained with other members of the TNF superfamily that also activate canonical and non-canonical NF-κB pathway.

Osteoprotegerin (OPG) as a biomarker for diabetic cardiovascular complications

Osteoprotegerin (OPG) is a glycoprotein involved in bone metabolisms and with a regulatory role in immune, skeletal and vascular systems. Recently, circulating OPG levels have emerged as independent biomarkers of cardiovascular disease (CVD) in patients with acute or chronic heart disease, as well as in the healthy population. Furthermore, OPG has been implicated in various inflammations and linked to diabetes and poor glycaemic control. This review focuses on the relations between circulating OPG levels and cardiovascular complications, with special emphasis on diabetic patients. OPG levels were observed to increase concurrently with the severity of diabetic complications, that is, with the highest circulating OPG levels observed in diabetic patients dying from CVD. Although the clinical prognostic use of OPG may seem far away, OPG does look promising as a biomarker in order to help the cardiologist to a better risk-stratification of the patients.

Early Atherosclerosis in HIV Infected Subjects on Suppressive Antiretroviral Treatment: Role of Osteoprotegerin

Cardiovascular disease is increased in HIV-infected patients. Cytokines such as osteoprotegerin are implicated in atherosclerosis. The aim of our study was to evaluate the role of osteoprotegerin in the development and progression of atherosclerosis in HIV infected subjects on suppressive antiretroviral treatment. We enrolled 76 patients; 35 HIV infected men on suppressive Highly Active Antiretroviral Therapy with Framingham score <10%; 21 HIV negative individuals matched for age, gender, and Framingham score, and 20 subjects with Framingham score >10% as control groups. HIV positive subjects underwent echocardiography, electrocardiography, and heart multidetector computed tomography, whereas in HIV negative subjects, tomography was only performed in case of any abnormalities either in echocardiography or electrocardiography. In HIV positive patients, computed tomography showed stenosis in 51.4% of the subjects. Osteoprotegerin plasma levels were higher in HIV-infected patients than those in healthy controls but lower than in HIV negative subjects with Framingham score >10%. Higher osteoprotegerin plasma levels were found in HIV positive patients with grade I stenosis than in patients with grade II/III stenosis. In conclusion, in HIV infected subjects with Framingham score <10%, osteoprotegerin plasma concentrations are associated with atherosclerosis, in particular at the early stage of the process.

Bone Marrow– or Vessel Wall–Derived Osteoprotegerin Is Sufficient to Reduce Atherosclerotic Lesion Size and Vascular Calcification

Objective—

Osteoprotegerin (OPG) is a decoy receptor for the osteoclast differentiation factor receptor activator of NF-κB ligand. OPG regulates bone homeostasis, and its inactivation in mice results in severe osteoporosis. OPG deficiency in apolipoprotein E (ApoE) −/− mice results in increased atherosclerotic lesion size and calcification. Furthermore, receptor activator of NF-κB ligand enhances macrophage-dependent smooth muscle cell calcification in vitro. Here, we hypothesized that reconstitution of ApoE −/− OPG −/− mice with ApoE −/− OPG +/+ bone marrow (BM) would be sufficient to rescue lesion progression and vascular calcification. Conversely, reconstitution of ApoE −/− OPG +/+ mice with ApoE −/− OPG −/− BM may accelerate lesion progression and vascular calcification.

Approach and Results—

ApoE −/− OPG −/− mice transplanted with ApoE −/− OPG +/+ BM developed smaller atherosclerotic lesions and deposited less calcium in the innominate artery than that of ApoE −/− OPG −/− mice transplanted with ApoE −/− OPG −/− BM. There were no differences in lesion size and calcification in ApoE −/− OPG +/+ mice transplanted with BM from ApoE −/− OPG −/− or ApoE −/− OPG +/+ mice. The large lesions observed in the ApoE −/− OPG −/− mice transplanted with OPG −/− BM were rich in chondrocyte-like cells, collagen, and proteoglycans. Importantly, the ApoE −/− OPG −/− mice transplanted with OPG +/+ BM remained osteoporotic, and the ApoE −/− OPG +/+ mice did not show signs of bone loss regardless of the type of BM received. In coculture experiments, macrophages and mesenchymal stem cells derived from ApoE −/− OPG −/− BM induced more vascular smooth muscle cell calcification than cells derived from ApoE −/− OPG +/+ mice.

Conclusions—

These results indicate that OPG derived either from the BM or from the vessel wall is sufficient to slow down lesion progression and vascular calcification independent of bone turnover.

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.

Aortic valve calcification in chronic kidney disease

Several clinical studies reported an increased prevalence and accelerated progression of aortic valve calcification among patients with end-stage renal disease when compared with subjects with normal kidney function. Recently, mechanisms of calcific valve degeneration have been further elucidated and many of the pathways involved could be amplified in patients with decreased renal function. In particular, calcium-phosphate balance, MGP metabolism, OPG/RANK/RANKL triad, fetuin-A mineral complexes and FGF-23/Klotho axis have been shown to be impaired among patients with advanced chronic kidney disease and could play a role during vascular/valve calcification. The scope of the present review is to summarize the clinical data and the pathophysiological mechanisms potentially involved in the link between renal function decline and the progression of aortic valve disease.

Vascular calcification: an update on mechanisms and challenges in treatment

Vascular calcification is highly associated with cardiovascular disease mortality, particularly in high-risk patients with diabetes and chronic kidney diseases (CKD). In blood vessels, intimal calcification is associated with atherosclerosis, whereas medial calcification is a nonocclusive process which leads to increased vascular stiffness and reduced vascular compliance. In the valves, calcification of the leaflets can change the mechanical properties of the tissue and result in stenosis. For many decades, vascular calcification has been noted as a consequence of aging. Studies now confirm that vascular calcification is an actively regulated process and shares many features with bone development and metabolism. This review provides an update on the mechanisms of vascular calcification including the emerging roles of the RANK/RANKL/OPG triad, osteoclasts, and microRNAs. Potential treatments adapted from osteoporosis and CKD treatments that are under investigation for preventing and/or regressing vascular calcification are also reviewed.

Osteoprotegerin inhibits calcification of vascular smooth muscle cell via down regulation of the Notch1-RBP-Jκ/Msx2 signaling pathway

Objective

Vascular calcification is a common pathobiological process which occurs among the elder population and in patients with diabetes and chronic kidney disease. Osteoprotegerin, a secreted glycoprotein that regulates bone mass, has recently emerged as an important regulator of the development of vascular calcification. However, the mechanism is not fully understood. The purpose of this study is to explore novel signaling mechanisms of osteoprotegerin in the osteoblastic differentiation in rat aortic vascular smooth muscle cells (VSMCs).

Methods and Results

VSMCs were isolated from thoracic aorta of Sprague Dawley rats. Osteoblastic differentiation of VSMCs was induced by an osteogenic medium. We confirmed by Von Kossa staining and direct cellular calcium measurement that mineralization was significantly increased in VSMCs cultured in osteogenic medium; consistent with an enhanced alkaline phosphatase activity. This osteoblastic differentiation in VSMCs was significantly reduced by the addition of osteoprotegerin in a dose responsive manner. Moreover, we identified, by real-time qPCR and western blotting, that expression of Notch1 and RBP-Jκ were significantly up-regulated in VSMCs cultured in osteogenic medium at both the mRNA and protein levels, these effects were dose-dependently abolished by the treatment of osteoprotegerin. Furthermore, we identified that Msx2, a downstream target of the Notch1/RBP-Jκ signaling, was markedly down-regulated by the treatment of osteoprotegerin.

Conclusion

Osteoprotegerin inhibits vascular calcification through the down regulation of the Notch1-RBP-Jκ signaling pathway.

The role of osteoprotegerin in cardiovascular disease

Osteoprotegerin (OPG) is a 401 amino acid N-glycosylated protein, which is highly expressed in a large number of tissues. OPG mainly binds to two ligands, i.e. RANKL (receptor activator of nuclear factor κB ligand) and TRAIL (tumor necrosis factor- related apoptosis-inducing ligand). Upon binding to the former ligand, OPG inhibits the activation of osteoclasts and promotes apoptosis of osteoclasts, whereas the binding of OPG with TRAIL prevents apoptosis of tumor cells. There is now emerging evidence that OPG participates in the pathogenesis of atherosclerosis and cardiovascular diseases by amplifying the adverse effects of inflammation and several traditional risk factors such as hyperlipidemia, endothelial dysfunction, diabetes mellitus, and hypertension. Some epidemiological studies also showed a positive association between OPG levels and cardiovascular morbidity and mortality. The aim of this article is to provide an overview of the main biochemical, physiological, and pathological aspects of OPG biology in cardiovascular disease.

Cross-talk of receptor activator of nuclear factor-κB ligand signaling with renin-angiotensin system in vascular calcification

OBJECTIVE

Vascular calcification is accelerated by hypertension and also contributes to hypertension; however, it is an enigma why hypertension and vascular calcification are a vicious spiral. The present study elucidates the cross-talk between renin-angiotensin II system and receptor activator of nuclear factor-κB ligand (RANKL) system in vascular calcification.

APPROACH AND RESULTS

Angiotensin (Ang) II (10(-7) mol/L) significantly increased calcium deposition as assessed by Alizarin Red staining, associated with a significant increase in the expression of RANKL, RANK, and bone-related genes, such as cbfa1 and msx2, in human aortic vascular smooth muscle cells. Infusion of Ang II (100 ng/kg per minute) in ovariectomized ApoE(-/-) mice under high-fat diet significantly increased the expression of RANKL system and calcification in vivo, whereas administration of Ang II receptor blocker (olmesartan, 3 mg/kg per day) decreased the calcification and bone markers' expression. In addition, male OPG(-/-) mice showed a significant increase in vascular calcification followed by Ang II infusion as compared with wild type. Conversely, RANKL significantly increased Ang II type 1 receptor and angiotensin II-converting enzyme expression in vascular smooth muscle cells via extracellular signal-regulated protein kinase phosphorylation.

CONCLUSIONS

The present study demonstrated that Ang II significantly induced vascular calcification in vitro and in vivo through RANKL activation. In addition, RANKL activated renin-angiotensin II system, especially angiotensin II-converting enzyme and Ang II type 1 receptor. Cross-talk between renin-angiotensin II system and RANKL system might work as a vicious cycle to promote vascular calcification in atherosclerosis. Further studies to inhibit renin-angiotensin II system and RANKL may provide new therapeutic options to prevent and regress vascular calcification.

Correlation of plasma osteoprotegerin (OPG) and receptor activator of the nuclear factor κB ligand (RANKL) levels with clinical risk factors in patients with advanced carotid atherosclerosis

Background

Osteoprotegerin (OPG) is considered to be a crucial regulatory mediator of bone metabolism by acting as a decoy receptor of the receptor activator of nuclear factor κB ligand (RANKL). OPG and RANKL have further become the subject of intense interest for their potential role in cardiovascular disease. The present study aimed to assess the clinical implication of plasma OPG and RANKL levels in patients with advanced carotid atherosclerosis

Material/Methods

Plasma OPG and RANKL concentrations measured by solid-phase enzyme-linked immunosorbent assay (ELISA) were correlated with medical history, risk factors and medication intake in 131 patients who underwent carotid endarterectomy for vascular repair.

Results

Plasma OPG concentrations were associated with patients’ age (p=0.0258), homocysteine levels (p<0.00001), eGFR (p=0.0254), history of diabetes (p=0.0324), statins therapy (p=0.0044), hyperlipidemia (p=0.0407), smoking (p=0.0226) and CAD (p=0.0377). Plasma RANKL concentrations were associated with patients’ age (p=0.0191), homocysteine levels (p<0.00001), history of smoking (p=0.0185) and statins therapy (p=0.0004). Diabetes, CAD, smoking status, statins therapy and homocysteine were identified as independent predictors of OPG concentrations (p=0.0157, p=0.0030, p=0.0249, p=0.0047 and p=0.0072, respectively), whereas smoking showed an independent effect for RANKL (p=0.0010).

Conclusions

The present data reinforce the clinical utility of OPG in carotid atherosclerosis, whereas the clinical implication of RANKL seems uncertain.

Osteoprotegerin as a marker of atherosclerosis in diabetic patients

Atherosclerosis is the principal cause of cardiovascular disease (CVD) and has many risk factors, among which is diabetes. Osteoprotegerin (OPG) is a soluble glycoprotein, involved in bone metabolism. OPG is also found in other tissues, and studies have shown that it is expressed in vascular smooth muscle cells. OPG has been implicated in various inflammations and also has been linked to diabetes mellitus. Increased serum OPG levels were found in patients with diabetes and poor glycemic control. Furthermore, prepubertal children with type 1 diabetes have significantly increased OPG levels. Receptor activator of nuclear factor kappa-B ligand (RANKL) is not found in the vasculature in normal conditions, but may appear in calcifying areas. OPG and RANKL are important regulators of mineral metabolism in both bone and vascular tissues. Few data are available on the relationship between plasma OPG/RANKL levels and endothelial dysfunction as assessed using noninvasive methods like ultrasound indexes, neither in the general population nor, more specifically, in diabetic patients. The aim of our review study was to investigate, based on the existing data, these interrelationships in order to identify a means of predicting, via noninvasive methods, later development of endothelial dysfunction and vascular complications in diabetic patients.

Impaired fasting glucose and diabetes as predictors for radial artery calcification in end stage renal disease patients

Objective. The objective of the study was to assess the relationship between selected clinical and biochemical parameters of end stage renal disease (ESRD) patients and arterial calcification. Materials and Methods. The study comprised 59 stage 5 chronic kidney disease patients (36 hemodialyzed and 23 predialysis). The examined parameters included common carotid artery intima-media thickness (CCA-IMT), BMI, incidence of diabetes and impaired fasting glucose (IFG), dyslipidemia, hypertension, and 3-year mortality. Plasma levels asymmetric dimethylarginine (ADMA), osteopontin (OPN), osteoprotegerin (OPG), and osteocalcin (OC) were also measured. Fragments of radial artery obtained during creation of hemodialysis access were stained for calcifications using von Kossa method and alizarin red. Results. Calcification of radial artery was significantly associated with higher prevalence of IFG and diabetes (P = 0.0004) and older age (P = 0.003), as well as higher OPG (P = 0.014) and ADMA concentrations (P = 0.022). Fasting glucose >5.6 mmol/l (IFG and diabetes) significantly predicted vascular calcification in multiple logistic regression. The calcification was also associated with higher CCA-IMT (P = 0.006) and mortality (P = 0.004; OR for death 5.39 [1.20-24.1] after adjustment for dialysis status and age). Conclusion. Combination of renal insufficiency and hyperglycemic conditions exerts a synergistic effect on vascular calcification and increases the risk of death.

Association of plasma osteoprotegerin levels with stroke severity and functional outcome in acute ischaemic stroke patients

Osteoprotegerin (OPG) is known to regulate processes involved in vascular injury and inflammation. We investigated the relationship between plasma OPG levels and stroke subtype, stroke severity at admission and functional outcome at 3 months in 172 patients with acute ischaemic stroke. Patients with large artery atherosclerosis and those with multiple causes had higher plasma OPG levels than patients with lacune. Increased plasma OPG levels were independently associated with more severe stroke and poor functional outcome. These results suggest pleiotropic roles of OPG in mediating atherosclerosis and ischaemic brain injury. OPG is a potential biomarker for predicting neurologic outcome in stroke.

RANKL enhances macrophage paracrine pro-calcific activity in high phosphate-treated smooth muscle cells: dependence on IL-6 and TNF-α

BACKGROUND

Vascular calcification is highly correlated with cardiovascular disease (CVD) morbidity and mortality, and it is associated with inflammation. Receptor activator of NF-ĸB ligand (RANKL) inhibition in vivo has been shown to reduce vascular calcification in a mouse model of atherosclerosis. Therefore, we tested the hypothesis that RANKL regulates smooth muscle cell (SMC) calcification by modulating macrophage production of pro-calcific cytokines.

METHODS

We used a bone marrow-derived macrophage (BMDM)/SMC co-culture system and examined the effects of RANKL on BMDM activation and SMC matrix calcification.

RESULTS

Treatment with RANKL alone did not stimulate SMC calcification induced by elevated phosphate. BMDMs differentiated with macrophage colony-stimulating factor and placed in co-culture with SMCs increased phosphate-induced SMC calcification. RANKL added to the BMDM/SMC co-cultures further enhanced SMC calcification. Treatment of BMDMs with RANKL resulted in increased expression of IL-6 and TNF-α. Thus, increased expression of these pro-calcific cytokines in macrophages may mediate RANKL-induced SMC calcification in a paracrine fashion. Addition of neutralizing IL-6 and TNF-α antibodies together with RANKL treatment significantly reduced the RANKL induction of SMC calcification.

CONCLUSION

RANKL activation of pro-inflammatory and pro-calcific pathways in macrophages may contribute to vascular calcification and inflammation.

Smooth muscle cell-specific runx2 deficiency inhibits vascular calcification

RATIONALE

Vascular calcification is a hallmark of atherosclerosis, a major cause of morbidity and mortality in the United States. We have previously reported that the osteogenic transcription factor Runx2 is an essential and sufficient regulator of calcification of vascular smooth muscle cells (VSMC) in vitro.

OBJECTIVE

To determine the contribution of osteogenic differentiation of VSMC to the pathogenesis of vascular calcification and the function of VSMC-derived Runx2 in regulating calcification in vivo.

METHODS AND RESULTS

SMC-specific Runx2-deficient mice, generated by breeding SM22α-Cre mice with the Runx2 exon 8 floxed mice, exhibited normal aortic gross anatomy and expression levels of SMC-specific marker genes. Runx2 deficiency did not affect basal SMC markers, but inhibited oxidative stress-reduced expression of SMC markers. High-fat-diet-induced vascular calcification in vivo was markedly inhibited in the Runx2-deficient mice in comparison with their control littermates. Runx2 deficiency inhibited the expression of receptor activator of nuclear factor κB ligand, which was accompanied by decreased macrophage infiltration and formation of osteoclast-like cells in the calcified lesions. Coculture of VSMC with bone marrow-derived macrophages demonstrated that the Runx2-deficient VSMC failed to promote differentiation of macrophages into osteoclast-like cells.

CONCLUSIONS

These data have determined the importance of osteogenic differentiation of VSMC in the pathogenesis of vascular calcification in mice and defined the functional role of SMC-derived Runx2 in regulating vascular calcification and promoting infiltration of macrophages into the calcified lesion to form osteoclast-like cells. Our studies suggest that the development of vascular calcification is coupled with the formation of osteoclast-like cells, paralleling the bone remodeling process.

Osteoprotegerin Is Associated With Aneurysm Diameter and Proteolysis in Abdominal Aortic Aneurysm Disease

Objective—

Serum osteoprotegerin (OPG) concentrations have previously been associated with growth of abdominal aortic aneurysms (AAAs). In vitro experiments showed that OPG promotes matrix metalloprotease (MMP) release from monocytes and vascular smooth muscle cells. We hypothesized that OPG expression is increased in human AAAs and is associated with proteolysis.

Methods and Results—

AAA biopsies were collected from 329 patients. We assessed the concentrations of OPG, cathepsins A, B, and S as well as the activity of MMP-2 and MMP-9. The AAA wall infiltration by macrophages, lymphocytes, and plasma cells was estimated by immunohistochemistry. The concentration of OPG correlated positively with aortic diameter (<55 mm: 16.1 [5.8–28.7], 55–70 mm: 21.9 [10.2–36.0], >70 mm: 24.0 [13.5–52.9] ng OPG/mg total amount of protein, P =0.020), cathepsin A ( r =0.221, P =0.005), B ( r =0.384, P <0.001), and S ( r =0.467, P<0.001), MMP-2 ( r =0.180, P <0.001), MMP-9 ( r =0.178, P<0.001), and the number of lymphocytes ( P <0.001) and plasma cells ( P =0.001). OPG immunostaining was predominantly demonstrated in plasma cells.

Conclusion—

The concentration of aortic wall OPG is positively associated with established markers of AAA severity and pathogenesis. OPG appeared to be associated with lymphocytes and plasma cells. These human data support previous experimental data suggesting a role for OPG in AAA pathogenesis.

Osteoprotegerin as a marker of atherosclerosis: a systematic update

OBJECTIVE

Osteoprotegerin (OPG) may be involved in development of atherosclerosis. To evaluate plasma concentrations of OPG in individuals with stable coronary artery disease (CAD), acute coronary syndrome (ACS), peripheral artery disease (PAD), and cerebrovascular disease (CBVD) a systematic literature review was performed.

DESIGN AND METHODS

Studies investigating OPG concentrations in stable CAD, ACS, PAD, and CBVD were extracted from PubMed and the Cochrane Library, retrieving 280 articles. Nonrelevant articles were excluded and after thorough evaluation, and only 14 studies with clearly defined cohorts qualified for this review.

RESULTS

In 11 studies, OPG concentrations were elevated. Severity of atherosclerosis was significantly associated with higher OPG concentrations compared to healthy controls. No association between PAD and OPG concentrations was observed.

CONCLUSION

OPG concentrations are associated with the presence and severity of stable CAD, ACS, and CBVD. Larger studies are needed to reach conclusions concerning OPG concentrations in PAD. Studies addressing a putative role for OPG in suspected CAD and CBVD are warranted.

Genetic basis of atherosclerosis: insights from mice and humans

Atherosclerosis is a complex and heritable disease involving multiple cell types and the interactions of many different molecular pathways. The genetic and molecular mechanisms of atherosclerosis have, in part, been elucidated by mouse models; at least 100 different genes have been shown to influence atherosclerosis in mice. Importantly, unbiased genome-wide association studies have recently identified a number of novel loci robustly associated with atherosclerotic coronary artery disease. Here, we review the genetic data elucidated from mouse models of atherosclerosis, as well as significant associations for human coronary artery disease. Furthermore, we discuss in greater detail some of these novel human coronary artery disease loci. The combination of mouse and human genetics has the potential to identify and validate novel genes that influence atherosclerosis, some of which may be candidates for new therapeutic approaches.

Osteoprotegerin and cardiovascular mortality in patients with non-ST elevation acute coronary syndromes

OBJECTIVE

To assess the relationship between osteoprotegerin (OPG) and cardiovascular death, and the pathobiological mechanisms contributing to the association, in acute coronary syndromes (ACS).

DESIGN

Prospective observational.

SETTING

Biomarker substudy of MERLIN-TIMI 36, a randomised, placebo controlled trial of ranolazine in non-ST elevation (NSTE)-ACS.

PATIENTS

4463 patients with NSTE-ACS.

INTERVENTIONS

Ranolazine or placebo.

MAIN OUTCOME MEASURES

Incidence of cardiovascular death (CV death); additionally, heart failure (HF), cardiac arrhythmias, in-hospital ischaemia, severe recurrent ischaemia or recurrent myocardial infarction (MI).

RESULTS

During a median follow-up of 341 days, 208 patients died of cardiovascular causes. The OPG baseline concentration was strongly associated with both 30 day and 1 year incidence of CV death. After adjustment for conventional risk markers, OPG concentrations (log transformed) remained a significant predictor of CV death by 30 days (HR (95% CI) 2.32 (1.30 to 4.17); p=0.005) and by 1 year (HR 1.85 (1.33 to 2.59); p<0.001). Baseline levels of OPG were also an independent predictor of new or worsening HF at 30 days (HR 2.25 (1.38 to 3.69); p=0.001) and 1 year (HR 1.81 (1.26 to 2.58) p=0.001). By univariable analysis, higher OPG was associated with both early ischaemic and arrhythmic events. Although OPG levels were associated with recurrent MI within 12 months, this association was attenuated and no longer significant after multivariable adjustment.

CONCLUSIONS

OPG is independently associated with 30 day and 1 year risk of cardiovascular mortality and HF development after NSTE-ACS. As no independent relationship between OPG levels and recurrent ischaemia or MI was observed, myocardial dysfunction may be a more important stimulus for OPG production than ischaemia in ACS.

The effect of alendronate on the expression of osteopontin and osteoprotegerin in calcified aortic tissue of the rat

Vascular calcification is a pathobiological process which leads to high morbidity and mortality in cardiovascular disease. The association between vascular calcification and osteoporosis has been reported widely, and there are close relationships among vascular calcification, related cardiovascular disease and osteoporosis, but the biochemical mechanism of vascular calcification is presently unclear. For exploring the possible mechanism of artery calcification we established aorta calcification in an animal model with vitamin D(3) and warfarin and tested the effect of alendronate on the expression of osteopontin and osteoprotegerin in calcified aorta tissue of the rat through measuring gene and protein expression of osteopontin and osteoprotegerin respectively. The results indicated compared with control group, the aortic calcium content of calcification group was obviously increased, osteopontin mRNA and osteoprotegerin mRNA were significantly reduced, and osteoprotegerin and osteopontin protein expressions were reduced. Compared with calcification group, the aortic calcium content of alendronate group was obviously reduced, osteopontin mRNA and osteoprotegerin mRNA were significantly increased, and osteopontin and osteoprotegerin protein expression were increased. We conclude that artery calcification may reduce the expression of osteopontin and osteoprotegerin. Alendronate may inhibit rat aorta calcification by up-regulating osteopontin and osteoprotegerin expression.

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.

Mechanisms and clinical consequences of vascular calcification

Vascular calcification has severe clinical consequences and is considered an accurate predictor of future adverse cardiovascular events, including myocardial infarction and stroke. Previously vascular calcification was thought to be a passive process which involved the deposition of calcium and phosphate in arteries and cardiac valves. However, recent studies have shown that vascular calcification is a highly regulated, cell-mediated process similar to bone formation. In this article, we outline the current understanding of key mechanisms governing vascular calcification and highlight the clinical consequences. By understanding better the molecular pathways and genetic circuitry responsible for the pathological mineralization process novel drug targets may be identified and exploited to combat and reduce the detrimental effects of vascular calcification on human health.

Uridine adenosine tetraphosphate activation of the purinergic receptor P2Y enhances in vitro vascular calcification

Purinergic signaling has a crucial role in different vascular processes. The endothelial-derived vasoconstrictor uridine adenosine tetraphosphate (Up(4)A) is a potent activator of the purinoceptor P2Y and is released under pathological conditions. Here we sought to measure purinergic effects on vascular calcification and initially found that Up(4)A plasma concentrations are increased in patients with chronic kidney disease. Exploring this further we found that exogenous Up(4)A enhanced mineral deposition under calcifying conditions ex vivo in rat and mouse aortic rings and in vitro in rat vascular smooth muscle cells. The addition of Up(4)A increased the expression of different genes specific for osteochondrogenic vascular smooth muscle cells such as Cbfa1, while decreasing the expression of SM22α, a marker specific for vascular smooth muscle cells. The influence of different P2Y antagonists on Up(4)A-mediated process indicated that P2Y(2/6) receptors may be involved. Mechanisms downstream of P2Y signaling involved phosphorylation of the mitogen-activated kinases MEK and ERK1/2. Thus, Up(4)A activation of P2Y influences phenotypic transdifferentiation of vascular smooth muscle cells to osteochondrogenic cells, suggesting that purinergic signaling may be involved in vascular calcification.

Calcific aortic valve stenosis: methods, models, and mechanisms

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

The roles of lipid oxidation products and receptor activator of nuclear factor-κB signaling in atherosclerotic calcification

This review focuses on the roles of oxylipids and receptor activator of nuclear factor-κB ligand signaling in calcific cardiovascular disease. Both intimal and valvular calcifications are closely associated with atherosclerosis, leading investigators to study the role of atherogenic oxidatively modified lipids (oxylipids). Results have identified the molecular signaling through which oxylipids induce osteogenic differentiation and calcification in vascular cells. A surprising concomitant finding was that, in bona fide osteoblasts from skeletal bone, oxylipids have the opposite effect, ie, inhibiting osteoblastic maturation. This is the basis for the lipid hypothesis of osteoporosis. Oxylipids also induce resorptive osteoclastic cells within the bone environment, raising the question of whether resorptive osteoclasts can be harnessed in the vascular context for cell-based therapy to remove artery wall mineral deposits. The challenge is that vascular cells produce antiosteoclastogenic factors, including the soluble decoy receptor for receptor activator of nuclear factor-κB ligand, possibly accounting for the paucity of resorptive cells and the dominance of mineral in atherosclerotic plaque. These factors may have therapeutic use in osteoclastogenic removal of mineral deposits from arteries.

Serum osteoprotegerin and tumor necrosis factor related apoptosis inducing-ligand (TRAIL) are elevated in type 2 diabetic patients with albuminuria and serum osteoprotegerin is independently associated with the severity of diabetic nephropathy

Osteoprotegerin (OPG) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) have recently been reported to be associated with diabetic nephropathy in an in vitro study. However, the literature regarding serum OPG and TRAIL in type 2 diabetes mellitus patients is scarce. To investigate the role of OPG/TRAIL in diabetic nephropathy, we measured the serum concentrations of OPG and TRAIL in type 2 diabetes mellitus patients with different stages of nephropathy by enzyme-linked immunosorbent assay. One hundred seventy-nine subjects with type 2 diabetes mellitus were studied and stratified according to urinary microalbumin and serum creatinine measurements. The serum concentrations of OPG and TRAIL were significantly elevated in patients with microalbuminuria (OPG, 2154.2 ± 922.1 pg/mL; TRAIL, 80.2 ± 24.1 pg/mL) and macroalbuminuria (OPG, 2251.5 ± 925.7 pg/mL; TRAIL, 88.1 ± 23.8 pg/mL) as compared with patients with normoalbuminuria (OPG, 1690.1 ± 627.2 pg/mL; TRAIL, 70.7 ± 23.3 pg/mL). Serum OPG and TRAIL levels were increased in parallel and were significantly associated with each other. Using multivariate stepwise regression analysis, serum OPG was found to be an independent factor associated with the severity of diabetic nephropathy. Our results suggested that serum OPG may be a marker for the severity of diabetic nephropathy. Further studies are necessary to investigate the role of elevated serum OPG in the pathogenesis of diabetic nephropathy.