Osteogenesis associates with inflammation in early-stage atherosclerosis evaluated by molecular imaging in vivo

Arterial calcification: Finger-pointing at resident and circulating stem cells

The term ‘‘Stammzelle’’ (stem cells) originally appeared in 1868 in the works of Ernst Haeckel who used it to describe the ancestor unicellular organism from which he presumed all multicellular organisms evolved. Since then stem cells have been studied in a wide spectrum of normal and pathological conditions; it is remarkable to note that ectopic arterial calcification was considered a passive deposit of calcium since its original discovering in 1877; in the last decades, resident and circulating stem cells were imaged to drive arterial calcification through chondro-osteogenic differentiation thus opening the idea that an active mechanism could be at the basis of the process that clinically shows a Janus effect: calcifications either lead to the stabilization or rupture of the atherosclerotic plaques. A review of the literature underlines that 130 years after stem cell discovery, antigenic markers of stem cells are still debated and the identification of the osteoprogenitor phenotype is even more elusive due to tissue degradation occurring at processing and manipulation. It is necessary to find a consensus to perform comparable studies that implies phenotypic recognition of stem cells antigens. A hypothesis is based on the singular morphology and amitotic mechanism of division of osteoclasts: it constitutes the opening to a new approach on osteoprogenitors markers and recognition. Our aim was to highlight all the present evidences of the active calcification process, summarize the different cellular types involved, and discuss a novel approach to discover osteoprogenitor phenotypes in arterial wall.

Endothelial microparticles mediate inflammation-induced vascular calcification

Stimulation of endothelial cells (ECs) with TNF-α causes an increase in the expression of bone morphogenetic protein-2 (BMP-2) and the production of endothelial microparticles (EMPs). BMP-2 is known to produce osteogenic differentiation of vascular smooth muscle cells (VSMCs). It was found that EMPs from TNF-α-stimulated endothelial cells (HUVECs) contained a significant amount of BMP-2 and were able to enhance VSMC osteogenesis and calcification. Calcium content was greater in VSMCs exposed to EMPs from TNF-α-treated HUVECs than EMPs from nontreated HUVECs (3.56 ± 0.57 vs. 1.48 ± 0.56 µg/mg protein; P < 0.05). The increase in calcification was accompanied by up-regulation of Cbfa1 (osteogenic transcription factor) and down-regulation of SM22α (VSMC lineage marker). Inhibition of BMP-2 by small interfering RNA reduced the VSMC calcification induced by EMPs from TNF-α-treated HUVECs. Similar osteogenic capability was observed in EMPs from both patients with chronic kidney disease and senescent cells, which also presented a high level of BMP-2 expression. Labeling of EMPs with CellTracker shows that EMPs are phagocytized by VSMCs under all conditions (with or without high phosphate, control, and EMPs from TNF-α-treated HUVECs). Our data suggest that EC damage results in the release of EMPs with a high content of calcium and BMP-2 that are able to induce calcification and osteogenic differentiation of VSMCs.

Well-organized neointima of large-pore poly(L-lactic acid) vascular graft coated with poly(L-lactic-co-ε-caprolactone) prevents calcific deposition compared to small-pore electrospun poly(L-lactic acid) graft in a mouse aortic implantation model

OBJECTIVE

Tissue engineering techniques have emerged that allow bioresorbable grafts to be implanted that restore function and transform into biologically active arteries. However, these implants are susceptible to calcification during the remodeling process. The objective of this study was to evaluate the role of pore size of bioabsorbable grafts in the development of calcification.

METHODS

Two types of grafts were prepared: a large-pore graft constructed of poly(L-lactic acid) (PLA) fibers coated with poly(L-lactide-co-ε-caprolactone) (PLCL) (PLA-PLCL), and a small-pore graft made of electrospun PLA nanofibers (PLA-nano). Twenty-eight PLA-PLCL grafts and twenty-five PLA-nano grafts were implanted as infra-renal aortic interposition conduits in 8-week-old female SCID/Bg mice, and followed for 12 months after implantation.

RESULTS

Large-pore PLA-PLCL grafts induced a well-organized neointima after 12 months, and Alizarin Red S staining showed neointimal calcification only in the thin neointima of small-pore PLA-nano grafts. At 12 months, macrophage infiltration, evaluated by F4/80 staining, was observed in the thin neointima of the PLA-nano graft, and there were few vascular smooth muscle cells (VSMCs) in this layer. On the other hand, the neointima of the PLA-PLCL graft was composed of abundant VSMCs, and a lower density of macrophages (F4/80 positive cells, PLA-PLCL; 68.1 ± 41.4/mm(2) vs PLA-nano; 188.3 ± 41.9/mm(2), p = 0.007). The VSMCs of PLA-PLCL graft expressed transcription factors of both osteoblasts and osteoclasts.

CONCLUSION

These findings demonstrate that in mouse arterial circulation, large-pore PLA-PLCL grafts created a well-organized neointima and prevented calcific deposition compared to small-pore, electrospun PLA-nano grafts.

Small entities with large impact: microcalcifications and atherosclerotic plaque vulnerability

PURPOSE OF REVIEW

Atherosclerotic plaque rupture and subsequent acute events, such as myocardial infarction and stroke, contribute to the majority of cardiovascular-related deaths. Calcification has emerged as a significant predictor of cardiovascular morbidity and mortality, challenging previously held notions that calcifications stabilize atherosclerotic plaques. In this review, we address this discrepancy through recent findings that not all calcifications are equivalent in determining plaque stability.

RECENT FINDINGS

The risk associated with calcification is inversely associated with calcification density. As opposed to large calcifications that potentially stabilize the plaque, biomechanical modeling indicates that small microcalcifications within the plaque fibrous cap can lead to sufficient stress accumulation to cause plaque rupture. Microcalcifications appear to derive from matrix vesicles enriched in calcium-binding proteins that are released by cells within the plaque. Clinical detection of microcalcifications has been hampered by the lack of imaging resolution required for in-vivo visualization; however, recent studies have demonstrated promising new techniques to predict the presence of microcalcifications.

SUMMARY

Microcalcifications play a major role in destabilizing atherosclerotic plaques. The identification of critical characteristics that lead to instability along with new imaging modalities to detect their presence in vivo may allow early identification and prevention of acute cardiovascular events.

Coronary and Abdominal Aorta Calcification in Rheumatoid Arthritis: Relationships with Traditional Cardiovascular Risk Factors, Disease Characteristics, and Concomitant Treatments

Objective.

To assess the influence of traditional cardiovascular (CV) risk factors, disease characteristics, and concomitant treatments in patients with rheumatoid arthritis (RA) on coronary artery calcification (CAC) and abdominal aorta calcification (AAC).

Methods.

In our cross-sectional study, 75 patients with RA were compared with 75 age-matched and sex-matched control participants. The CAC and AAC scores were measured by computed tomography in patients with no clinical evidence of coronary artery disease. The relationships between the presence or absence of CAC and AAC and traditional CV risk factors, disease characteristics, and concomitant treatments in patients with RA were assessed in a multiple logistic regression analysis.

Results.

The RA and control groups did not differ significantly in terms of age, sex composition, or the prevalence of traditional CV risk factors. AAC and CAC were more prevalent and severe in patients with RA than in controls. Older age (OR = 1.15, p < 0.01) and hypertension (OR = 3.77, p = 0.04) were found to be independently associated with CAC, whereas current use of methotrexate (MTX; OR = 0.12, p = 0.01) was found to be associated with the absence of CAC. Older age (OR per yr = 1.17, p < 0.001) and erosive arthritis (OR = 3.78, p = 0.03) were found to be independently associated with AAC.

Conclusion.

Our study demonstrates that in patients with RA, (1) CAC and AAC are more prevalent and more severe compared with age-matched and sex-matched control participants, (2) current use of MTX is a major determinant of the absence of CAC, and (3) erosive arthritis is a major determinant of AAC.

Prevalence, extent and composition of coronary plaque in patients with rheumatoid arthritis without symptoms or prior diagnosis of coronary artery disease

OBJECTIVES

Accelerated cardiovascular morbidity and mortality occur in patients with rheumatoid arthritis (RA). We evaluated the presence, burden and compositional differences of coronary plaque in patients with RA without symptoms or diagnosis of coronary artery disease (CAD) compared against controls.

METHODS

One hundred and fifty patients with RA and 150 matched controls underwent 64-slice CT angiography (CTA) for evaluation of coronary plaque. Numbers of segments with plaque per patient (Segment involvement score (SIS)), degree of segment stenosis (stenosis severity score (SSS)), plaque size (plaque burden score (PBS)), and composition were assessed using a standardised American Heart Association 15-segment model. Lesions were classified as non-calcified plaque (NCP), mixed (MP), and fully calcified plaque (CP).

RESULTS

 Higher proportion of patients with RA had plaque when compared with controls (71% vs 45%, p<0.0001); 13.5% of total RA segments harboured plaque compared with 6% in controls (p<0.0001), and all plaque types were higher (p<0.001). Multivessel disease, both non-obstructive and obstructive, was more prevalent, and quantitative measures of stenotic plaque severity (SSS) and extent (PBS) were higher in RA, even after adjustments for cardiac risk factors (p<0.01 for all). A steeper progression of plaque with age was seen in RA. Disease activity associated only with presence of NCP and MP, whereas patient age was the only predictor of fully CP.

CONCLUSIONS

RA patients without CAD have higher prevalence, extent, and severity of all types of coronary plaque. Residual disease activity associates with presence of higher risk NCP and MP potentially contributing to future adverse cardiac events.

Phosphonated near-infrared fluorophores for biomedical imaging of bone

The conventional method for creating targeted contrast agents is to conjugate separate targeting and fluorophore domains. A new strategy is based on the incorporation of targeting moieties into the non-delocalized structure of pentamethine and heptamethine indocyanines. Using the known affinity of phosphonates for bone minerals in a model system, two families of bifunctional molecules that target bone without requiring a traditional bisphosphonate are synthesized. With peak fluorescence emissions at approximately 700 or 800 nm, these molecules can be used for fluorescence-assisted resection and exploration (FLARE) dual-channel imaging. Longitudinal FLARE studies in mice demonstrate that phosphonated near-infrared fluorophores remain stable in bone for over five weeks, and histological analysis confirms their incorporation into the bone matrix. Taken together, a new strategy for creating ultra-compact, targeted near-infrared fluorophores for various bioimaging applications is described.

Ankle-brachial index and bone turnover in patients on dialysis

An association between atherosclerosis and osteoporosis has been reported in several studies. This association could result from local intraosseous atherosclerosis and ischemia, which is shown by limb osteoporosis in patients with peripheral artery disease (PAD), but also could result from bidirectional communication between the skeleton and blood vessels. Systemic bone disorders and PAD are frequent in ESRD. Here, we investigated the possible interaction of these disorders. For 65 prevalent nondiabetic patients on hemodialysis, we measured ankle-brachial pressure index (ABix) and evaluated mineral and bone disorders with bone histomorphometry. In prevalent patients on hemodialysis, PAD (ABix<0.9 or >1.4/incompressible) was associated with low bone turnover and pronounced osteoblast resistance to parathyroid hormone (PTH), which is indicated by decreased double-labeled surface and osteoblast surface (P<0.001). Higher osteoblast resistance to PTH in patients with PAD was characterized by weaker correlation coefficients (slopes) between serum PTH and double-labeled surface (P=0.02) or osteoblast surface (P=0.03). The correlations between osteoclast number or eroded surface and serum mineral parameters, including PTH, did not differ for subjects with normal ABix and PAD. Common vascular risk factors (dyslipidemia, smoking, and sex) were similar for normal, low, and incompressible ABix. Patients with PAD were older and had high C-reactive protein levels and longer hemodialysis vintage. These results indicate that, in prevalent nondiabetic patients with ESRD, PAD associates with low bone turnover and pronounced osteoblast resistance to PTH.

Total calcium-sensing receptor expression in circulating monocytes is increased in rheumatoid arthritis patients with severe coronary artery calcification

Introduction

Human circulating monocytes express the calcium-sensing receptor (CaSR) and are involved in atherosclerosis. This study investigated the potential association between vascular calcification in rheumatoid arthritis (RA) and CaSR expression in circulating monocytes.

Methods

In this cross-sectional study, 50 RA patients were compared to 25 control subjects matched for age and gender. Isolation of peripheral blood mononuclear cells and flow cytometry analysis were performed to study the surface and total CaSR expression in circulating monocytes. Coronary artery calcium (CAC) and abdominal aortic calcification (AAC) scores were evaluated by computed tomography and an association between these scores and the surface and/or total CaSR expression in circulating monocytes in RA patients was investigated.

Results

The two groups were similar in terms of age (RA: 60.9 ± 8.3 years, versus controls: 59.6 ± 5.3 years) and gender (RA: 74.0% females versus 72.0% females). We did not find a higher prevalence and greater burden of CAC or AAC in RA patients versus age- and gender-matched controls. When compared with control subjects, RA patients did not exhibit greater total CaSR (101.6% ± 28.8 vs. 99.9% ± 22.0) or surface CaSR (104.6% ± 20.4 vs. 99.9% ± 13.7) expression, but total CaSR expression in circulating monocytes was significantly higher in RA patients with severe CAC (Agatston score ≥200, n = 11) than in patients with mild-to-moderate CAC (1 to 199, n = 21) (P = 0.01).

Conclusions

This study demonstrates for the first time that total CaSR expression in human circulating monocytes is increased in RA patients with severe coronary artery calcification.

Imaging subclinical atherosclerosis: is it ready for prime time? A review

Imaging subclinical atherosclerosis holds the promise of individualized cardiovascular (CV) risk assessment. The large arsenal of noninvasive imaging techniques available today is playing an increasingly important role in the diagnosis and monitoring of subclinical atherosclerosis. However, there is a debate about the advisability of clinical screens for subclinical atherosclerosis and which modality is the most appropriate for monitoring risk and atherosclerosis progression. This article offers an overview of the traditional and emerging noninvasive imaging modalities used to detect early atherosclerosis, surveys population studies addressing the value of subclinical atherosclerosis detection, and also examines guideline recommendations for their clinical implementation. The clinical relevance of this manuscript lies in the potential of current imaging technology to improve CV risk prediction based on traditional risk factors and the present recommendations for subclinical atherosclerosis assessment. Noninvasive imaging will also help to identify individuals at high CV who would benefit from intensive prevention or therapeutic interventions.

Medial vascular calcification revisited: review and perspectives

Vascular calcifications (VCs) are actively regulated biological processes associated with crystallization of hydroxyapatite in the extracellular matrix and in cells of the media (VCm) or intima (VCi) of the arterial wall. Both patterns of VC often coincide and occur in patients with type II diabetes, chronic kidney disease, and other less frequent disorders; VCs are also typical in senile degeneration. In this article, we review the current state of knowledge about the pathology, molecular biology, and nosology of VCm, expand on potential mechanisms responsible for poor prognosis, and expose some of the directions for future research in this area.

Inflammation and its resolution as determinants of acute coronary syndromes

Inflammation contributes to many of the characteristics of plaques implicated in the pathogenesis of acute coronary syndromes. Moreover, inflammatory pathways not only regulate the properties of plaques that precipitate acute coronary syndromes but also modulate the clinical consequences of the thrombotic complications of atherosclerosis. This synthesis will provide an update on the fundamental mechanisms of inflammatory responses that govern acute coronary syndromes and also highlight the ongoing balance between proinflammatory mechanisms and endogenous pathways that can promote the resolution of inflammation. An appreciation of the countervailing mechanisms that modulate inflammation in relation to acute coronary syndromes enriches our fundamental understanding of the pathophysiology of this important manifestation of atherosclerosis. In addition, these insights provide glimpses into potential novel therapeutic interventions to forestall this ultimate complication of the disease.

Fetuin-A and albumin alter cytotoxic effects of calcium phosphate nanoparticles on human vascular smooth muscle cells

Calcification is a detrimental process in vascular ageing and in diseases such as atherosclerosis and arthritis. In particular, small calcium phosphate (CaP) crystal deposits are associated with inflammation and atherosclerotic plaque de-stabilisation. We previously reported that CaP particles caused human vascular smooth muscle cell (VSMC) death and that serum reduced the toxic effects of the particles. Here, we found that the serum proteins fetuin-A and albumin (≥ 1 µM) reduced intracellular Ca2+ elevations and cell death in VSMCs in response to CaP particles. In addition, CaP particles functionalised with fetuin-A, but not albumin, were less toxic than naked CaP particles. Electron microscopic studies revealed that CaP particles were internalised in different ways; via macropinocytosis, membrane invagination or plasma membrane damage, which occurred within 10 minutes of exposure to particles. However, cell death did not occur until approximately 30 minutes, suggesting that plasma membrane repair and survival mechanisms were activated. In the presence of fetuin-A, CaP particle-induced damage was inhibited and CaP/plasma membrane interactions and particle uptake were delayed. Fetuin-A also reduced dissolution of CaP particles under acidic conditions, which may contribute to its cytoprotective effects after CaP particle exposure to VSMCs. These studies are particularly relevant to the calcification observed in blood vessels in patients with kidney disease, where circulating levels of fetuin-A and albumin are low, and in pathological situations where CaP crystal formation outweighs calcification-inhibitory mechanisms.

Cardiovascular biomarkers in patients with psoriasis

Psoriasis is a systemic inflammatory disease of the skin with associated comorbidity. Severe forms of psoriasis are associated with increased mortality, which might be due to cardiovascular (CV) comorbidity. In this study, we investigated in 79 patients with psoriasis compared to 80 healthy volunteers different biomarkers that play a role in vascular disease and inflammation, such as C-reactive protein (CRP), human soluble CD40 ligand (sCD40L), oxidized low-density lipoprotein (ox-LDL), human matrix Gla protein (MGP) and fetuin-A. Our results showed that CRP (P < 0.0001), sCD40L (P < 0.0001) and MGP (P < 0.0001) were increased in the patient cohort. Fetuin-A showed decreased serum levels in patients with psoriasis (P < 0.0001), whereas ox-LDL did not show any significant difference. In multivariate analyses controlling for sex, age and BMI, these findings were confirmed. Thus, CV biomarkers are altered in patients with psoriasis. If the decrease in fetuin-A as well as the increase in sCD40L can be proven in further studies, these biomarkers may help to characterize a subgroup of patients who are at risk to develop CVD and/or monitor the effect of therapeutic antipsoriatic strategies on concomitant diseases. This knowledge may be useful in the management of high-need patients with psoriasis.

Procoagulant activity of circulating microparticles is associated with the presence of moderate calcified plaque burden detected by multislice computed tomography

BACKGROUND

Circulating microparticles (MPs) have been reported to be associated with coronary artery disease (CAD). In this study, we explored the relationship between MPs procoagulant activity and characteristics of atherosclerotic plaque detected by 64-slice computed tomography angiography (CTA).

METHODS

In 127 consecutive patients with CAD but without acute coronary syndrome and who underwent 64-slice CTA, MPs procoagulant activity in plasma (by a thrombin generation test), soluble form of lectin-like oxidized low-density lipoprotein receptor-1 (sLOX-1) and N(epsilon)-(carboxymethyl) lysine (CML) circulating levels (by ELISA) were measured. A quantitative volumetric analysis of the lumen and plaque burden of the vessel wall (soft and calcific components), for the three major coronary vessels, was performed. The patients were classified in three groups according to the presence of calcium volume: non-calcified plaque (NCP) group (calcium volume (%) = 0), moderate calcified plaque (MCP) group (0 < calcium volume (%) < 1), and calcified plaque (CP) group (calcium volume (%) ≥ 1).

RESULTS

MPs procoagulant activity and CML levels were higher in MCP group than in CP or NCP group (P = 0.009 and P = 0.027, respectively). MPs procoagulant activity was positively associated with CML (r = 0.317, P < 0.0001) and sLOX-1 levels (r = 0.216, P = 0.0025).

CONCLUSIONS

MPs procoagulant activity was higher in the MCP patient group and correlated positively with sLOX-1 and CML levels, suggesting that it may characterize a state of blood vulnerability that may locally precipitate plaque instability and increase the risk of subsequent major cardiovascular events.

Inflammatory, metabolic, and genetic mechanisms of vascular calcification

This review centers on updating the active research area of vascular calcification. This pathology underlies substantial cardiovascular morbidity and mortality, through adverse mechanical effects on vascular compliance, vasomotion, and, most likely, plaque stability. Biomineralization is a complex, regulated process occurring widely throughout nature. Decades ago, its presence in the vasculature was considered a mere curiosity and an unregulated, dystrophic process that does not involve biological mechanisms. Although it remains controversial whether the process has any adaptive value or past evolutionary advantage, substantial advances have been made in understanding the biological mechanisms driving the process. Different types of calcific vasculopathy, such as inflammatory versus metabolic, have parallel mechanisms in skeletal bone calcification, such as intramembranous and endochondral ossification. Recent work has identified important regulatory roles for inflammation, oxidized lipids, elastin, alkaline phosphatase, osteoprogenitor cells, matrix γ-carboxyglutamic acid protein, transglutaminase, osteoclastic regulatory factors, phosphate regulatory hormones and receptors, apoptosis, prelamin A, autophagy, and microvesicles or microparticles similar to the matrix vesicles of skeletal bone. Recent work has uncovered fascinating interactions between matrix γ-carboxyglutamic acid protein, vitamin K, warfarin, and transport proteins. And, lastly, recent breakthroughs in inherited forms of calcific vasculopathy have identified the genes responsible as well as an unexpected overlap of phenotypes. Until recently, vascular calcification was considered a purely degenerative, unregulated process. Since then, investigative groups around the world have identified a wide range of causative mechanisms and regulatory pathways, and some of the recent developments are highlighted in this review.

Potential drug targets for calcific aortic valve disease

Calcific aortic valve disease (CAVD) is a major contributor to cardiovascular morbidity and mortality and, given its association with age, the prevalence of CAVD is expected to continue to rise as global life expectancy increases. No drug strategies currently exist to prevent or treat CAVD. Given that valve replacement is the only available clinical option, patients often cope with a deteriorating quality of life until diminished valve function demands intervention. The recognition that CAVD results from active cellular mechanisms suggests that the underlying pathways might be targeted to treat the condition. However, no such therapeutic strategy has been successfully developed to date. One hope was that drugs already used to treat vascular complications might also improve CAVD outcomes, but the mechanisms of CAVD progression and the desired therapeutic outcomes are often different from those of vascular diseases. Therefore, we discuss the benchmarks that must be met by a CAVD treatment approach, and highlight advances in the understanding of CAVD mechanisms to identify potential novel therapeutic targets.

Multisystemic functions of alkaline phosphatases

Human and mouse alkaline phosphatases (AP) are encoded by a multigene family expressed ubiquitously in multiple tissues. Gene knockout (KO) findings have helped define some of the precise exocytic functions of individual isozymes in bone, teeth, the central nervous system, and in the gut. For instance, deficiency in tissue-nonspecific alkaline phosphatase (TNAP) in mice (Alpl (-/-) mice) and humans leads to hypophosphatasia (HPP), an inborn error of metabolism characterized by epileptic seizures in the most severe cases, caused by abnormal metabolism of pyridoxal-5'-phosphate (the predominant form of vitamin B6) and by hypomineralization of the skeleton and teeth featuring rickets and early loss of teeth in children or osteomalacia and dental problems in adults caused by accumulation of inorganic pyrophosphate (PPi). Enzyme replacement therapy with mineral-targeting TNAP prevented all the manifestations of HPP in mice, and clinical trials with this protein therapeutic are showing promising results in rescuing life-threatening HPP in infants. Conversely, TNAP induction in the vasculature during generalized arterial calcification of infancy (GACI), type II diabetes, obesity, and aging can cause medial vascular calcification. TNAP inhibitors, discussed extensively in this book, are in development to prevent pathological arterial calcification. The brush border enzyme intestinal alkaline phosphatase (IAP) plays an important role in fatty acid (FA) absorption, in protecting gut barrier function, and in determining the composition of the gut microbiota via its ability to dephosphorylate lipopolysaccharide (LPS). Knockout mice (Akp3 (-/-)) deficient in duodenal-specific IAP (dIAP) become obese, and develop hyperlipidemia and hepatic steatosis when fed a high-fat diet (HFD). These changes are accompanied by upregulation in the jejunal-ileal expression of the Akp6 IAP isozyme (global IAP, or gIAP) and concomitant upregulation of FAT/CD36, a phosphorylated fatty acid translocase thought to play a role in facilitating the transport of long-chain fatty acids into cells. gIAP, but not dIAP, is able to modulate the phosphorylation status of FAT/CD36. dIAP, even though it is expressed in the duodenum, is shed into the gut lumen and is active in LPS dephosphorylation throughout the gut lumen and in the feces. Akp3 (-/-) mice display gut dysbiosis and are more prone to dextran sodium sulfate-induced colitis than wild-type mice. Of relevance, oral administration of recombinant calf IAP prevents the dysbiosis and protects the gut from chronic colitis. Analogous to the role of IAP in the gut, TNAP expression in the liver may have a proactive role from bacterial endotoxin insult. Finally, more recent studies suggest that neuronal death in Alzheimer's disease may also be associated with TNAP function on certain brain-specific phosphoproteins. This review recounts the established roles of TNAP and IAP and briefly discusses new areas of investigation related to multisystemic functions of these isozymes.

Instrumentation in Diffuse Optical Imaging

Diffuse optical imaging is highly versatile and has a very broad range of applications in biology and medicine. It covers diffuse optical tomography, fluorescence diffuse optical tomography, bioluminescence, and a number of other new imaging methods. These methods of diffuse optical imaging have diversified instrument configurations but share the same core physical principle – light propagation in highly diffusive media, i.e., the biological tissue. In this review, the author summarizes the latest development in instrumentation and methodology available to diffuse optical imaging in terms of system architecture, light source, photo-detection, spectral separation, signal modulation, and lastly imaging contrast.

Plasma fetuin-A levels are reduced in patients with hypothyroidism

OBJECTIVE

To determine plasma fetuin-A levels in hypothyroid patients before and after treatment with l-thyroxine (T4) and to determine the relation between plasma fetuin-A levels with cardiovascular risk factors.

DESIGN

A prospective, controlled, single-blind study.

METHODS

Forty-four treatment-naive female patients diagnosed with hypothyroidism and 39 age- and sex-matched control subjects were enrolled. Anthropometric measurements, blood pressure, plasma TSH, fetuin-A, free T4, LDL-cholesterol, triglyceride, C-reactive protein, fibrinogen levels, and brachial artery flow-mediated dilatation were measured. All measurements were repeated after 3 months in the control group and 3 months after the attainment of euthyroidism with l-T4 replacement in the hypothyroid group. Baseline data were compared between the two groups. Posttreatment plasma fetuin-A levels of hypothyroid patients were compared with baseline levels of both groups. The relationship between plasma fetuin-A, TSH levels, and other cardiovascular risk factors was evaluated.

RESULTS

Plasma fetuin-A levels were ∼20% lower in hypothyroid female patients compared with the controls (P=0.0001). Fetuin-A levels increased by ∼20% in hypothyroid patients after achievement of euthyroidism (P=0.0001) and were no longer different compared with controls (P=0.38). There was a negative correlation between plasma TSH and fetuin-A levels (r=-0.79; P=0.001). There was no significant correlation between plasma fetuin-A levels and cardiovascular risk factors within or between groups. The fetuin-A levels were normalized with thyroid hormone treatment.

CONCLUSION

Plasma fetuin-A levels are reduced in female patients with hypothyroidism, which are restored to normal during restoration of euthyroidism. There was no relation with cardiovascular risk factors.

18F-fluoride positron emission tomography for identification of ruptured and high-risk coronary atherosclerotic plaques: a prospective clinical trial

BACKGROUND

The use of non-invasive imaging to identify ruptured or high-risk coronary atherosclerotic plaques would represent a major clinical advance for prevention and treatment of coronary artery disease. We used combined PET and CT to identify ruptured and high-risk atherosclerotic plaques using the radioactive tracers (18)F-sodium fluoride ((18)F-NaF) and (18)F-fluorodeoxyglucose ((18)F-FDG).

METHODS

In this prospective clinical trial, patients with myocardial infarction (n=40) and stable angina (n=40) underwent (18)F-NaF and (18)F-FDG PET-CT, and invasive coronary angiography. (18)F-NaF uptake was compared with histology in carotid endarterectomy specimens from patients with symptomatic carotid disease, and with intravascular ultrasound in patients with stable angina. The primary endpoint was the comparison of (18)F-fluoride tissue-to-background ratios of culprit and non-culprit coronary plaques of patients with acute myocardial infarction.

FINDINGS

In 37 (93%) patients with myocardial infarction, the highest coronary (18)F-NaF uptake was seen in the culprit plaque (median maximum tissue-to-background ratio: culprit 1·66 [IQR 1·40-2·25] vs highest non-culprit 1·24 [1·06-1·38], p<0·0001). By contrast, coronary (18)F-FDG uptake was commonly obscured by myocardial uptake and where discernible, there were no differences between culprit and non-culprit plaques (1·71 [1·40-2·13] vs 1·58 [1·28-2·01], p=0·34). Marked (18)F-NaF uptake occurred at the site of all carotid plaque ruptures and was associated with histological evidence of active calcification, macrophage infiltration, apoptosis, and necrosis. 18 (45%) patients with stable angina had plaques with focal (18)F-NaF uptake (maximum tissue-to-background ratio 1·90 [IQR 1·61-2·17]) that were associated with more high-risk features on intravascular ultrasound than those without uptake: positive remodelling (remodelling index 1·12 [1·09-1·19] vs 1·01 [0·94-1·06]; p=0·0004), microcalcification (73% vs 21%, p=0·002), and necrotic core (25% [21-29] vs 18% [14-22], p=0·001).

INTERPRETATION

(18)F-NaF PET-CT is the first non-invasive imaging method to identify and localise ruptured and high-risk coronary plaque. Future studies are needed to establish whether this method can improve the management and treatment of patients with coronary artery disease.

FUNDING

Chief Scientist Office Scotland and British Heart Foundation.

Alendronate and risk of lower limb ischemic vascular events: a population-based cohort study

While alendronate inhibits atherosclerosis experimentally, its effect on lower limb ischemia risk is unknown. Our results suggest that alendronate reduces the risk of lower limb ischemic vascular events requiring surgical interventions, including amputation. Our results are relevant for patients at risk of lower limb ischemia undergoing fragility fracture treatment.

INTRODUCTION

This study aimed to determine the association between alendronate therapy and the risk of lower limb ischemic vascular events (i.e., bypass surgery, endovascular stenting, and major lower limb amputation for lower limb ischemia).

METHODS

We used a nationwide population-based cohort of patients aged over 50 years diagnosed with a vertebral or hip fracture between January 1999 and June 2010. We compared the risk of lower limb ischemic vascular events between patients undergoing treatment with alendronate (n = 3,731) and an age- and sex-matched comparison group (n = 7,462) over 5 years of follow-up. Hazard ratios (HR) were estimated using Cox proportional regression analysis with adjustment for treatment status, comorbidities, and other variables.

RESULTS

Ten patients (0.3 %) in the alendronate treatment group had a lower limb ischemic vascular event compared with 51 patients (0.7 %) in the comparison group. The incidence of lower limb ischemic vascular events was 8.4 (95 % CI, 4.0-15.5) per 10,000 person-years in the alendronate group and 21.8 (95 % CI, 16.2-28.7) per 10,000 person-years in the comparison group. The risk of a lower limb ischemic vascular event in the alendronate treatment group was lower (adjusted HR, 0.41; 95 % CI, 0.21-0.82).

CONCLUSION

Alendronate treatment was associated with a reduced risk of lower limb ischemic vascular events among hip or vertebral fragility fracture patients.

Cystathionine γ-lyase accelerates osteoclast differentiation: identification of a novel regulator of osteoclastogenesis by proteomic analysis

OBJECTIVE

Clinical evidence has linked vascular calcification in advanced atherosclerotic plaques with overt cardiovascular disease and mortality. Bone resorbing monocyte-derived osteoclast-like cells are sparse in these plaques, indicating that their differentiation capability could be suppressed. Here, we seek to characterize the process of osteoclastogenesis by identifying novel regulators and pathways, with the aim of exploring possible strategies to reduce calcification.

APPROACH AND RESULTS

We used a quantitative mass spectrometry strategy, tandem mass tagging, to quantify changes in the proteome of osteoclast-like cells differentiated from RAW264.7 cells in response to, receptor activator of nuclear factor κ-B ligand induction, a common in vitro model for osteogenesis. More than 4000 proteins were quantified, of which 138 were identified as novel osteoclast-related proteins. We selected 5 proteins for subsequent analysis (cystathionine γ-lyase [Cth/CSE], EGF-like repeat and discoidin I-like domain-containing protein 3, integrin α FG-GAP repeat containing 3, adseverin, and serpinb6b) and show that gene expression levels are also increased. Further analysis of the CSE transcript profile reveals an early onset of an mRNA increase. Silencing of CSE by siRNA and dl-propargylglycine, a CSE inhibitor, attenuated receptor activator of nuclear factor κ-B ligand-induced tartrate-resistant acid phosphatase type 5 activity and pit formation, suggesting that CSE is a potent inducer of calcium resorption. Moreover, knockdown of CSE suppressed expression of osteoclast differentiation markers.

CONCLUSIONS

Our large-scale proteomics study identified novel candidate regulators or markers for osteoclastogenesis and demonstrated that CSE may act in early stages of osteoclastogenesis.

Positron emission tomography of the vulnerable atherosclerotic plaque in man--a contemporary review

Atherosclerosis is the primary underlying cause of cardiovascular disease (CVD). It is the leading cause of morbidity and mortality in the Western world today and is set to become the prevailing disease and major cause of death worldwide by 2020. In the 1950s surgical intervention was introduced to treat symptomatic patients with high-grade carotid artery stenosis due to atherosclerosis – a procedure known as carotid endarterectomy (CEA). By removing the atherosclerotic plaque from the affected carotid artery of these patients, CEA is beneficial by preventing subsequent ipsilateral ischemic stroke. However, it is known that patients with low to intermediate artery stenosis may still experience ischemic events, leading clinicians to consider plaque composition as an important feature of atherosclerosis. Today molecular imaging can be used for characterization, visualization and quantification of cellular and subcellular physiological processes as they take place in vivo; using this technology we can obtain valuable information on atherosclerostic plaque composition. Applying molecular imaging clinically to atherosclerotic disease therefore has the potential to identify atherosclerotic plaques vulnerable to rupture. This could prove to be an important tool for the selection of patients for CEA surgery in a health system increasingly focused on individualized treatment. This review focuses on current advances and future developments of in vivo atherosclerosis PET imaging in man.

Mechanisms of arterial calcifications and consequences for cardiovascular function

Cardiovascular complications are the leading cause of mortality in chronic (CKD) and end-stage renal disease (ESRD). The risk of developing cardiovascular complications is associated with changes in the structure and function of the arterial system, which are in many aspects similar to those occurring with aging. The presence of traditional risk factors does not fully explain the extension and severity of arterial disease. Therefore, other factors associated with CKD and ESRD must also be involved. Arterial calcification (AC) is a common complication of CKD and ESRD, and the extent of AC in general population as well as in patients with CKD is predictive of subsequent cardiovascular mortality beyond established conventional risk factors. AC is an active process similar to bone formation that implicates a variety of proteins involved in bone and mineral metabolism and is considered part of a systemic dysfunction defined as CKD-associated mineral and bone disorder (CKD-MBD).

MR imaging of the arterial vessel wall: molecular imaging from bench to bedside

Cardiovascular diseases remain the leading cause of morbidity and mortality in the Western world and developing countries. In clinical practice, in vivo characterization of atherosclerotic lesions causing myocardial infarction, ischemic stroke, and other complications remains challenging. Imaging methods, limited to the assessment luminal stenosis, are the current reference standard for the assessment of clinically significant coronary and carotid artery disease and the guidance of treatment. These techniques do not allow distinction between stable and potentially vulnerable atherosclerotic plaque. Magnetic resonance (MR) imaging is a modality well suited for visualization and characterization of the relatively thin arterial vessel wall, because it allows imaging with high spatial resolution and excellent soft-tissue contrast. In clinical practice, atherosclerotic plaque components of the carotid artery and aorta may be differentiated and characterized by using unenhanced vessel wall MR imaging. Additional information can be gained by using clinically approved nonspecific contrast agents. With the advent of targeted MR contrast agents, which enhance specific molecules or cells, pathologic processes can be visualized at a molecular level with high spatial resolution. In this article, the pathophysiologic changes of the arterial vessel wall underlying the development of atherosclerosis will be first reviewed. Then basic principles and properties of molecular MR imaging contrast agents will be introduced. Additionally, recent advances in preclinical molecular vessel wall imaging will be reviewed. Finally, the clinical feasibility of arterial vessel wall imaging at unenhanced and contrast material-enhanced MR imaging of the aortic, carotid, and coronary vessel wall will be discussed.

Molecular imaging of inflammation in atherosclerosis

Acute rupture of vulnerable plaques frequently leads to myocardial infarction and stroke. Within the last decades, several cellular and molecular players have been identified that promote atherosclerotic lesion formation, maturation and plaque rupture. It is now widely recognized that inflammation of the vessel wall and distinct leukocyte subsets are involved throughout all phases of atherosclerotic lesion development. The mechanisms that render a stable plaque unstable and prone to rupture, however, remain unknown and the identification of the vulnerable plaque remains a major challenge in cardiovascular medicine. Imaging technologies used in the clinic offer minimal information about the underlying biology and potential risk for rupture. New imaging technologies are therefore being developed, and in the preclinical setting have enabled new and dynamic insights into the vessel wall for a better understanding of this complex disease. Molecular imaging has the potential to track biological processes, such as the activity of cellular and molecular biomarkers in vivo and over time. Similarly, novel imaging technologies specifically detect effects of therapies that aim to stabilize vulnerable plaques and silence vascular inflammation. Here we will review the potential of established and new molecular imaging technologies in the setting of atherosclerosis, and discuss the cumbersome steps required for translating molecular imaging approaches into the clinic.

Membrane vesicles nucleate mineralo-organic nanoparticles and induce carbonate apatite precipitation in human body fluids

Recent studies indicate that membrane vesicles (MVs) secreted by various cells are associated with human diseases, including arthritis, atherosclerosis, cancer, and chronic kidney disease. The possibility that MVs may induce the formation of mineralo-organic nanoparticles (NPs) and ectopic calcification has not been investigated so far. Here, we isolated MVs ranging in size between 20 and 400 nm from human serum and FBS using ultracentrifugation and sucrose gradient centrifugation. The MV preparations consisted of phospholipid-bound vesicles containing the serum proteins albumin, fetuin-A, and apolipoprotein A1; the mineralization-associated enzyme alkaline phosphatase; and the exosome proteins TNFR1 and CD63. Notably, we observed that MVs induced mineral precipitation following inoculation and incubation in cell culture medium. The mineral precipitates consisted of round, mineralo-organic NPs containing carbonate hydroxyapatite, similar to previous descriptions of the so-called nanobacteria. Annexin V-immunogold staining revealed that the calcium-binding lipid phosphatidylserine (PS) was exposed on the external surface of serum MVs. Treatment of MVs with an anti-PS antibody significantly decreased their mineral seeding activity, suggesting that PS may provide nucleating sites for calcium phosphate deposition on the vesicles. These results indicate that MVs may represent nucleating agents that induce the formation of mineral NPs in body fluids. Given that mineralo-organic NPs represent precursors of calcification in vivo, our results suggest that MVs may initiate ectopic calcification in the human body.

High-resolution molecular imaging via intravital microscopy: illuminating vascular biology in vivo

Complications of atherosclerosis and thrombosis are leading causes of death worldwide. While experimental investigations have yielded valuable insights into key molecular and cellular phenomena in these diseases of medium- and large-sized vessels, direct visualization of relevant in vivo biological processes has been limited. However, recent developments in molecular imaging technology, specifically fluorescence imaging agents coupled with high-resolution, high-speed intravital microscopy (IVM), are now enabling dynamic and longitudinal investigations into the mechanisms and progression of many vascular diseases. Here we review recent advances in IVM that have provided new in vivo biological insights into atherosclerosis and thrombosis.

Changing views of the biomechanics of vulnerable plaque rupture: a review

This review examines changing perspectives on the biomechanics of vulnerable plaque rupture over the past 25 years from the first finite element analyses (FEA) showing that the presence of a lipid pool significantly increases the local tissue stress in the atheroma cap to the latest imaging and 3D FEA studies revealing numerous microcalcifications in the cap proper and a new paradigm for cap rupture. The first part of the review summarizes studies describing the role of the fibrous cap thickness, tissue properties, and lesion geometry as main determinants of the risk of rupture. Advantages and limitations of current imaging technologies for assessment of vulnerable plaques are also discussed. However, the basic paradoxes as to why ruptures frequently did not coincide with location of PCS and why caps >65 μm thickness could rupture at tissue stresses significantly below the 300 kPa critical threshold still remained unresolved. The second part of the review describes recent studies in the role of microcalcifications, their origin, shape, and clustering in explaining these unresolved issues including the actual mechanism of rupture due to the explosive growth of tiny voids (cavitation) in local regions of high stress concentration between closely spaced microinclusions oriented along their tensile axis.

Focal arterial inflammation precedes subsequent calcification in the same location: a longitudinal FDG-PET/CT study

BACKGROUND

Arterial calcium (Ca) deposition has been identified as an active inflammatory process. We sought to test the hypothesis that local vascular inflammation predisposes to subsequent arterial calcium deposition in humans.

METHODS AND RESULTS

From a hospital database, we identified 137 patients (age, 61 ± 13 years; 48.1% men) who underwent serial positron-emission tomography/computed tomography (1-5 years apart). Focal arterial inflammation was prospectively determined by measuring 18F-flourodeoxyglucose uptake (using baseline positron-emission tomography) within predetermined locations of the thoracic aortic wall and was reported as a standardized uptake value. A separate, blinded investigator evaluated calcium deposition (on the baseline and follow-up computed tomographic scans) along the same standardized sections of the aorta. New calcification was prospectively defined using square root-transformed difference of calcium volume score, with a cutoff value of 2.5. Accordingly, vascular segment was classified as either with or without subsequent calcification. Overall, 67 (9%) of aortic segments demonstrated subsequent calcification. Baseline median (interquartile range) standardized uptake value was higher in segments with versus without subsequent calcification (2.09 [1.84-2.44] versus 1.92 [1.72-2.20], P=0.002). This was also true in the subset of segments with Ca present at baseline (2.08 [1.81-2.40] versus 1.86 [1.66-2.09], P=0.02), as well as those without (2.17 [1.87-2.51] versus 1.93 [1.73-2.20], P=0.04). Furthermore, across all patients, subsequent Ca deposition was associated with the underlying 18F-flourodeoxyglucose uptake (inflammatory signal), measured as standardized uptake value (odds ratio [95% confidence interval]=2.94 [1.27-6.89], P=0.01) or target-to-background ratio (2.59 [1.18-5.70], =0.02), after adjusting for traditional cardiovascular risk factors.

CONCLUSIONS

Here, we provide first-in-man evidence that arterial inflammation precedes subsequent Ca deposition, a marker of plaque progression, within the underlying location in the artery wall.

Macrophage-derived matrix vesicles: an alternative novel mechanism for microcalcification in atherosclerotic plaques

RATIONALE

We previously showed that early calcification of atherosclerotic plaques associates with macrophage accumulation. Chronic renal disease and mineral imbalance accelerate calcification and the subsequent release of matrix vesicles (MVs), precursors of microcalcification.

OBJECTIVE

We tested the hypothesis that macrophage-derived MVs contribute directly to microcalcification.

METHODS AND RESULTS

Macrophages associated with regions of calcified vesicular structures in human carotid plaques (n=136 patients). In vitro, macrophages released MVs with high calcification and aggregation potential. MVs expressed exosomal markers (CD9 and TSG101) and contained S100A9 and annexin V. Silencing S100A9 in vitro and genetic deficiency in S100A9-/- mice reduced MV calcification, whereas stimulation with S100A9 increased calcification potential. Externalization of phosphatidylserine after Ca/P stimulation and interaction of S100A9 and annexin V indicated that a phosphatidylserine-annexin V-S100A9 membrane complex facilitates hydroxyapatite nucleation within the macrophage-derived MV membrane.

CONCLUSIONS

Our results support the novel concept that macrophages release calcifying MVs enriched in S100A9 and annexin V, which contribute to accelerated microcalcification in chronic renal disease.

Role of extracellular vesicles in de novo mineralization: an additional novel mechanism of cardiovascular calcification

Extracellular vesicles are membrane micro/nanovesicles secreted by many cell types into the circulation and the extracellular milieu in physiological and pathological conditions. Evidence suggests that extracellular vesicles, known as matrix vesicles, play a role in the mineralization of skeletal tissue, but emerging ultrastructural and in vitro studies have demonstrated their contribution to cardiovascular calcification as well. Cells involved in the progression of cardiovascular calcification release active vesicles capable of nucleating hydroxyapatite on their membranes. This review discusses the role of extracellular vesicles in cardiovascular calcification and elaborates on this additional mechanism of calcification as an alternative pathway to the currently accepted mechanism of biomineralization via osteogenic differentiation.

Biological imaging of atherosclerosis: moving beyond anatomy

Biological or molecular imaging is now providing exciting new strategies to study atherosclerosis in both animals and humans. These technologies hold the promise to provide disease-specific, molecular information within the context of a systemic or organ-specific disease beyond traditional anatomical-based imaging. By integration of biological, chemical, and anatomical imaging knowledge into diagnostic strategies, a more comprehensive and predictive picture of atherosclerosis is likely to emerge. As such, biological imaging is well positioned to study different stages of atherosclerosis and its treatment, including the sequence of atheroma initiation, progression, and plaque rupture. In this review, we describe the evolving concepts in atherosclerosis imaging with a focus on coronary artery disease, and we provide an overview of recent exciting translational developments in biological imaging. The illuminated examples and discussions will highlight how biological imaging is providing new clinical approaches to identify high-risk plaques, and to streamline the development process of new atherosclerosis therapies.

Revised microcalcification hypothesis for fibrous cap rupture in human coronary arteries

Using 2.1-µm high-resolution microcomputed tomography, we have examined the spatial distribution, clustering, and shape of nearly 35,000 microcalcifications (µCalcs) ≥ 5 µm in the fibrous caps of 22 nonruptured human atherosclerotic plaques. The vast majority of these µCalcs were <15 µm and invisible at the previously used 6.7-µm resolution. A greatly simplified 3D finite element analysis has made it possible to quickly analyze which of these thousands of minute inclusions are potentially dangerous. We show that the enhancement of the local tissue stress caused by particle clustering increases rapidly for gap between particle pairs (h)/particle diameter (D) < 0.4 if particles are oriented along the tensile axis of the cap. Of the thousands of µCalcs observed, there were 193 particle pairs with h/D ≤ 2 (tissue stress factor > 2), but only 3 of these pairs had h/D ≤ 0.4, where the local tissue stress could increase a factor > 5. Using nondecalcified histology, we also show that nearly all caps have µCalcs between 0.5 and 5 µm and that the µCalcs ≥ 5 µm observed in high-resolution microcomputed tomography are agglomerations of smaller calcified matrix vesicles. µCalcs < 5 µm are predicted to be not harmful, because the tiny voids associated with these very small particles will not explosively grow under tensile forces because of their large surface energy. These observations strongly support the hypothesis that nearly all fibrous caps have µCalcs, but only a small subset has the potential for rupture.

Pulmonary hypertension with extensive calcification in small pulmonary vessels and alveolar capillary wall in a chronic hemodialysis patient

We report a case of a 41-year-old male with end-stage renal disease receiving chronic hemodialysis who was referred to this hospital because of dyspnea. He had been on a regular dialysis for 20 years due to chronic glomerulonephritis. His transthoracic echocardiography revealed severe pulmonary hypertension (PH), and cardiac catheterization confirmed this diagnosis. From clinical examination and review of the chest X-ray and computed tomography images, we thought PH was due to multifactorial mechanisms typical of hemodialysis patients. However, microscopic examination of lung tissue from autopsy specimen revealed extensive calcium deposits not only in alveolar septal wall but also in alveolar capillaries and small vessels, which had diffuse intimal thickening causing the narrowing of the lumens. These pathological findings suggest that pulmonary vascular calcification contributed to the PH in this patient. <Learning objective: Pulmonary hypertension (PH) is prevalent and associated with mortality in patients with end-stage renal disease (ESRD). However, the pathogenesis of PH with ESRD remains uncertain. Here we report a PH case receiving long-term hemodialysis, and whose pathological findings revealed extensive calcification in small pulmonary vessels and alveolar capillaries. This case will provide evidence indicating the causative role of pulmonary calcification for the development of PH in dialysis patients.>.

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

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

MicroRNA in cardiovascular calcification: focus on targets and extracellular vesicle delivery mechanisms

Cardiovascular calcification is a prominent feature of chronic inflammatory disorders-such as chronic kidney disease, type 2 diabetes mellitus, and atherosclerosis-that associate with significant morbidity and mortality. The concept that similar pathways control both bone remodeling and vascular calcification is widely accepted, but the precise mechanisms of calcification remain largely unknown. The central role of microRNAs (miRNA) as fine-tune regulators in the cardiovascular system and bone biology has gained acceptance and has raised the possibility for novel therapeutic targets. Additionally, circulating miRNAs have been proposed as biomarkers for a wide range of cardiovascular diseases, but knowledge of miRNA biology in cardiovascular calcification is very limited. This review focuses on the role of miRNAs in cardiovascular disease, with emphasis on osteogenic processes. Herein, we discuss the current understanding of miRNAs in cardiovascular calcification. Furthermore, we identify a set of miRNAs common to diseases associated with cardiovascular calcification (chronic kidney disease, type 2 diabetes mellitus, and atherosclerosis), and we hypothesize that these miRNAs may provide a molecular signature for calcification. Finally, we discuss this novel hypothesis with emphasis on known biological and pathological osteogenic processes (eg, osteogenic differentiation, release of calcifying matrix vesicles). The aim of this review is to provide an organized discussion of the known links between miRNA and calcification that provide emerging concepts for future studies on miRNA biology in cardiovascular calcification, which will be critical for developing new therapeutic strategies.