Noncollagenous bone matrix proteins as a part of calcific aortic valve disease regulation

Pathophysiological concepts and screening of cardiovascular disease in dialysis patients

Dialysis patients experience 10-20 times higher cardiovascular mortality than the general population. The high burden of both conventional and nontraditional risk factors attributable to loss of renal function can explain higher rates of cardiovascular disease (CVD) morbidity and death among dialysis patients. As renal function declines, uremic toxins accumulate in the blood and disrupt cell function, causing cardiovascular damage. Hemodialysis patients have many cardiovascular complications, including sudden cardiac death. Peritoneal dialysis puts dialysis patients with end-stage renal disease at increased risk of CVD complications and emergency hospitalization. The current standard of care in this population is based on observational data, which has a high potential for bias due to the paucity of dedicated randomized clinical trials. Furthermore, guidelines lack specific guidelines for these patients, often inferring them from non-dialysis patient trials. A crucial step in the prevention and treatment of CVD would be to gain better knowledge of the influence of these predisposing risk factors. This review highlights the current evidence regarding the influence of advanced chronic disease on the cardiovascular system in patients undergoing renal dialysis.

The Effect of Osteoprotectin (OPG)/Receptor Activator of Nuclear Factor-κB Ligand (RANKL)/Receptor Activator of Nuclear Factor-κB (RANK) Gene Methylation on Aortic Valve Calcified

To evaluate the effect of the methylation of osteoprotectin (OPG)/receptor activator of nuclear factor-κB ligand (RANKL)/receptor activator of nuclear factor-κB (RANK) pathway on aortic valve calcification, the aortic valve tissue was collected from 38 aortic stenosis (AS) patients who underwent valve replacement. OPG and RANKL gene methylation, RT-PCR, and ELISA were performed. Hematoxylin-eosin staining (HE), alizarin red-S staining, and immunohistochemically staining of OPG, RANKL, and CD68 were simultaneously performed. The patients were divided into noncalcified group (n = 21) and calcified group (n = 17). The methylation rate of OPG gene in noncalcified group was higher than that in calcified group (P = 0.027). The methylation degree of RANKL gene was generally lower, but the noncalcified group was still higher than that in the calcified group (P = 0.025). RT-PCR analysis showed that the mRNA expression of OPG and RANKL was higher in calcified group than in noncalcified group (P = 0.007 and P = 0.036, respectively), and the mRNA expression was negatively correlated with the gene methylation rate. The protein expression of OPG and RANKL was detected by immunohistochemistry and ELISA, showing significantly increased in calcified group (P = 0.004 and P = 0.042, respectively). Soluble RANKL (sRANKL) in CD68-positive group was significantly different from that in negative group (0.1243 ± 0.0321 vs 0.0984 ± 0.0218 pg/mL, P = 0.007). There was no significant difference in OPG value between positive group (1.9411 ± 0.4554 ng/mL) and negative group (1.8422 ± 0.5218 ng/mL, P = 0.587). In conclusion, the degree of methylation of OPG and RANKL genes may play an important role in regulating valve calcification in AS patients.

Degeneration of Aortic Valves in a Bioreactor System with Pulsatile Flow

Calcific aortic valve disease is the most common valvular heart disease in industrialized countries. Pulsatile pressure, sheer and bending stress promote initiation and progression of aortic valve degeneration. The aim of this work is to establish an ex vivo model to study the therein involved processes. Ovine aortic roots bearing aortic valve leaflets were cultivated in an elaborated bioreactor system with pulsatile flow, physiological temperature, and controlled pressure and pH values. Standard and pro-degenerative treatment were studied regarding the impact on morphology, calcification, and gene expression. In particular, differentiation, matrix remodeling, and degeneration were also compared to a static cultivation model. Bioreactor cultivation led to shrinking and thickening of the valve leaflets compared to native leaflets while gross morphology and the presence of valvular interstitial cells were preserved. Degenerative conditions induced considerable leaflet calcification. In comparison to static cultivation, collagen gene expression was stable under bioreactor cultivation, whereas expression of hypoxia-related markers was increased. Osteopontin gene expression was differentially altered compared to protein expression, indicating an enhanced protein turnover. The present ex vivo model is an adequate and effective system to analyze aortic valve degeneration under controlled physiological conditions without the need of additional growth factors.

Role of oxidative stress in calcific aortic valve disease and its therapeutic implications

Calcific aortic valve disease (CAVD) is the end result of active cellular processes that lead to the progressive fibrosis and calcification of aortic valve leaflets. In western populations, CAVD is a significant cause of cardiovascular morbidity and mortality, and in the absence of effective drugs, it will likely represent an increasing disease burden as populations age. As there are currently no pharmacological therapies available for preventing, treating, or slowing the development of CAVD, understanding the mechanisms underlying the initiation and progression of the disease is important for identifying novel therapeutic targets. Recent evidence has emerged of an important causative role for reactive oxygen species (ROS)-mediated oxidative stress in the pathophysiology of CAVD, inducing the differentiation of valve interstitial cells into myofibroblasts and then osteoblasts. In this review, we focus on the roles and sources of ROS driving CAVD and consider their potential as novel therapeutic targets for this debilitating condition.

Osteoprotegerin and Myocardial Fibrosis in Patients with Aortic Stenosis

Left ventricular myocardial fibrosis in patients with aortic stenosis (AS) confers worse prognosis. Plasma osteoprotegerin (OPG), a cytokine from the TNF receptor family, correlates with the degree of valve calcification in AS, reflecting the activity of the tissue RANKL/RANK/OPG (receptor activator of nuclear factor κΒ ligand/RANK/osteoprotegerin) axis, and is associated with poorer outcomes in AS. Its association with myocardial fibrosis is unknown. We hypothesised that OPG levels would reflect the extent of myocardial fibrosis in AS. We included 110 consecutive patients with AS who had undergone late-gadolinium contrast enhanced cardiovascular magnetic resonance (LGE-CMR). Patients were characterised according to pattern of fibrosis (no fibrosis, midwall fibrosis, or chronic myocardial infarction fibrosis). Serum OPG was measured with ELISA and compared between groups defined by valve stenosis severity. Some 36 patients had no fibrosis, 38 had midwall fibrosis, and 36 had chronic infarction. Patients with midwall fibrosis did not have higher levels of OPG compared to those without fibrosis (6.78 vs. 5.25 pmol/L, p = 0.12). There was no difference between those with midwall or chronic myocardial infarction fibrosis (6.78 vs. 6.97 pmol/L, p = 0.27). However, OPG levels in patients with chronic myocardial infarction fibrosis were significantly higher than those without fibrosis (p = 0.005).

Lymphocyte and monocyte subpopulations in severe aortic stenosis at the time of surgical intervention

INTRODUCTION

Aortic stenosis (AS) is the most common acquired valvular heart disease in adults. Immune system involvement becomes evident during AS development. We sought to investigate the role of different circulating lymphocyte and monocyte subpopulations, with focus on CD4⁺CD8⁺ and natural killer T (NKT) cells, in AS.

MATERIAL AND METHODS

Blood samples and aortic valves were obtained from patients undergoing elective aortic valve surgery. Valves were dissected and underwent genetic analyses and calcium content assessment. Lymphocytes and monocytes subsets were assessed by flow cytometry.

RESULTS

Thirty-eight AS patients were studied. Maximal transvalvular pressure gradient (PG_max) as well as mean transvalvular pressure gradient (PG_mean) correlated with the CD4⁺CD8⁺ lymphocyte count (r=0.35, P=.03 and r=0.43, P=.006, respectively) and fraction (r=0.43, P=.007 and r=0.48, P=.002, respectively). PG_max and PG_mean correlated with CD16⁺CD56⁺CD3⁺ NKT cell count (r=0.39, P=.01 and r=0.43, P=.007, respectively) and fraction (r=0.49, P=.002 and r=0.47, P=.003, respectively). The classical monocyte subpopulation increased after the surgery by 68% (P<.0001). Patients after mini-sternotomy surgery had 47% lower nonclassical monocyte counts than those with full-sternotomy (P=.03). Patients treated with statins had significantly lower postoperative levels of both classical (-25%, P=.04) and nonclassical monocytes (-37%, P=.004) than nontreated individuals.

CONCLUSIONS

In patients with severe isolated AS, CD4⁺CD8⁺ T cells and CD16⁺CD56⁺CD3⁺ NKT cells are associated with AV pressure gradients. Postoperative monocyte levels are affected by procedure invasiveness and use of statins.

Cellular Mechanisms of Aortic Valve Calcification

Comparative in vitro study examined the osteogenic potential of interstitial cells of aortic valve obtained from the patients with aortic stenosis and from control recipients of orthotopic heart transplantation with intact aortic valve. The osteogenic inductors augmented mineralization of aortic valve interstitial cells (AVIC) in patients with aortic stenosis in comparison with the control level. Native AVIC culture of aortic stenosis patients demonstrated overexpression of osteopontin gene (OPN) and underexpression of osteoprotegerin gene (OPG) in comparison with control levels. In both groups, AVIC differentiation was associated with overexpression of RUNX2 and SPRY1 genes. In AVIC of aortic stenosis patients, expression of BMP2 gene was significantly greater than the control level. The study revealed an enhanced sensitivity of AVIC to osteogenic inductors in aortic stenosis patients, which indicates probable implication of OPN, OPG, and BMP2 genes in pathogenesis of aortic valve calcification.

Pathophysiology of Aortic Stenosis and Mitral Regurgitation

The global impact of the spectrum of valve diseases is a crucial, fast-growing, and underrecognized health problem. The most prevalent valve diseases, requiring surgical intervention, are represented by calcific and degenerative processes occurring in heart valves, in particular, aortic and mitral valve. Due to the increasing elderly population, these pathologies will gain weight in the global health burden. The two most common valve diseases are aortic valve stenosis (AVS) and mitral valve regurgitation (MR). AVS is the most commonly encountered valve disease nowadays and affects almost 5% of elderly population. In particular, AVS poses a great challenge due to the multiple comorbidities and frailty of this patient subset. MR is also a common valve pathology and has an estimated prevalence of 3% in the general population, affecting more than 176 million people worldwide. This review will focus on pathophysiological changes in both these valve diseases, starting from the description of the anatomical aspects of normal valve, highlighting all the main cellular and molecular features involved in the pathological progression and cardiac consequences. This review also evaluates the main approaches in clinical management of these valve diseases, taking into account of the main published clinical guidelines. © 2017 American Physiological Society. Compr Physiol 7:799-818, 2017.

Stenotic Bicuspid and Tricuspid Aortic Valves - Micro-Computed Tomography and Biological Indices of Calcification

BACKGROUND

Valve calcification is well estimated by ex-vivo micro-computed tomography (micro-CT). The objective of this study was to investigate the associations between micro-CT findings and biological indices of calcification in aortic stenosis (AS), as well as differences between bicuspid aortic valve (BAV) and tricuspid aortic valve (TAV).Methods and Results:Aortic valves and plasma were obtained from patients undergoing valve surgery. Valves were dissected and underwent micro-CT, genetic analyses, and calcium content assessment. Plasma levels of calcification markers were measured. Forty-two patients with isolated severe AS, including 22 with BAV, were studied. BAV patients had a lower median CT value (140.0 [130.0-152.0] vs. 157.0 [147.0-176.0], P=0.002) and high-density calcification (HDC) fraction (9.3 [5.7-23.3] % vs. 21.3 [14.3-31.2] %, P=0.01), as compared with TAV. Calcification fraction (CF) correlated with AS severity (measured as maximal transvalvular pressure gradient [r=0.34, P=0.03], maximal flow velocity [r=0.38, P=0.02], and indexed aortic valve area [r=-0.37, P=0.02]). For TAV patients only, mRNA expression of integrin-binding sialoprotein correlated with CF (r=0.45, P=0.048), and the receptor activator of the nuclear factor κ-B ligand transcript correlated with HDC corrugation (r=0.54, P=0.01).

CONCLUSIONS

TAV patients with AS present more mineralized calcifications in micro-CT than BAV subjects. The relative volume of calcifications increases with the AS severity. In TAV patients, upregulated expression of genes involved in osteoblastogenesis in AS correlates with leaflet mineralization in micro-CT.

Values of osteoprotegerin in aortic valve tissue in patients with significant aortic stenosis depend on the existence of concomitant coronary artery disease

INTRODUCTION

Calcific aortic valve stenosis (CAVS) is a serious clinical problem. The strongest predictor of CAVS progression is the amount of calcium in the aortic valve. The pathogenesis of CAVS is largely consistent with the pathogenesis of atherosclerosis; however, about 50% of patients with CAVS do not exhibit significant atherosclerosis. Cardiovascular calcification is currently considered an actively regulated process, in which the important role is attributed to the RANKL/RANK/OPG (receptor activator of nuclear factor κB ligand/RANK/osteoprotegerin) axis. We measured OPG levels in the tissue of calcified, stenotic aortic valves in relation to the presence or absence of coronary artery disease (CAD).

MATERIALS AND METHODS

Aortic valve samples were collected from 105 patients with calcified, mainly severe aortic stenosis, who were divided into two groups according to the presence of CAD. In Group A (n=44), there were normal coronary artery findings, while in Group B (n=61), there was angiographically demonstrated >50% stenosis of at least one coronary artery. The control Group C (n=21) consisted of patients without aortic stenosis and with normal angiographic findings on coronary arteries.

RESULTS

The highest tissue concentrations of OPG [median (pmol/L), 25th-75th percentile] were found in Group A [6.95, 3.96-18.37], which was significantly different compared to the other two groups (P=.026 and .001, respectively). The levels of OPG in Group B [4.15, 2.47-9.16] and in Group C [2.25, 1.01-5.08] did not differ significantly (P=.078); however, the lowest concentrations of OPG were found in Group C. Neither age nor gender in our study had effect on tissue levels of OPG (P=.994 for gender; P=.848 for age).

CONCLUSION

Calcified and narrowed aortic valves, compared to the normal valves, were accompanied by a change in tissue concentrations of OPG, which is, in addition, dependent on the presence or absence of CAD. The highest tissue concentrations of OPG in our work were found in patients with significant aortic stenosis without concomitant CAD.

MicroRNA-125b and chemokine CCL4 expression are associated with calcific aortic valve disease

Calcific aortic valve disease (CAVD) is a progressive pathological condition with no effective pharmacological therapy. To identify novel molecular pathways as potential targets for pharmacotherapy, we studied microRNA (miRNA) profiles of heavily stenotic aortic valves (AS). One of the most upregulated miRNAs in AS valves compared to control valves was miR-125b (1.4-fold; P < 0.05). To identify CAVD-related changes in gene expression, DNA microarray analysis was performed, including an intermediate fibro(sclero)tic stage of the disease. This revealed changes especially in genes related to inflammation and immune response, including chemokine (C-C motif) ligand 3 (CCL3) and 4 (CCL4). CCL3 mRNA level was increased 3.9-fold (P < 0.05) when AS valves were compared to control valves, and a 2.5-fold increase (P < 0.05) in CCL4 gene expression was observed when fibro(sclero)tic valves were compared to control valves. Both CCL3 and CCL4 localized to macrophages by immunofluorescence. To identify chemokine-miRNA target pairs, data from miRNA target prediction databases were combined with valvular miRNA and mRNA expression profiles. MiR-125b was computationally predicted to target CCL4, as confirmed experimentally in cultured human THP-1 macrophages. Collectively, miR-125b and CCL4 appear to be involved in the progression of CAVD and may offer novel therapeutic and diagnostic strategies related to this disease.

Characterization of the regulatory mechanisms of activating transcription factor 3 by hypertrophic stimuli in rat cardiomyocytes

Aims

Activating transcription factor 3 (ATF3) is a stress-activated immediate early gene suggested to have both detrimental and cardioprotective role in the heart. Here we studied the mechanisms of ATF3 activation by hypertrophic stimuli and ATF3 downstream targets in rat cardiomyocytes.

Methods and Results

When neonatal rat cardiomyocytes were exposed to endothelin-1 (ET-1, 100 nM) and mechanical stretching in vitro, maximal increase in ATF3 expression occurred at 1 hour. Inhibition of extracellular signal-regulated kinase (ERK) by PD98059 decreased ET-1– and stretch–induced increase of ATF3 protein but not ATF3 mRNA levels, whereas protein kinase A (PKA) inhibitor H89 attenuated both ATF3 mRNA transcription and protein expression in response to ET-1 and stretch. To characterize further the regulatory mechanisms upstream of ATF3, p38 mitogen-activated protein kinase (MAPK) signaling was investigated using a gain-of-function approach. Adenoviral overexpression of p38α, but not p38β, increased ATF3 mRNA and protein levels as well as DNA binding activity. To investigate the role of ATF3 in hypertrophic process, we overexpressed ATF3 by adenovirus-mediated gene transfer. In vitro, ATF3 gene delivery attenuated the mRNA transcription of interleukin-6 (IL-6) and plasminogen activator inhibitor-1 (PAI-1), and enhanced nuclear factor-κB (NF-κB) and Nkx-2.5 DNA binding activities. Reduced PAI-1 expression was also detected in vivo in adult rat heart by direct intramyocardial adenovirus-mediated ATF3 gene delivery.

Conclusions

These data demonstrate that ATF3 activation by ET-1 and mechanical stretch is partly mediated through ERK and cAMP-PKA pathways, whereas p38 MAPK pathway is involved in ATF3 activation exclusively through p38α isoform. ATF3 activation caused induction of modulators of the inflammatory response NF-κB and Nkx-2.5, as well as attenuation of pro-fibrotic and pro-inflammatory proteins IL-6 and PAI-1, suggesting cardioprotective role for ATF3 in the heart.

An inducible, ligand-independent receptor activator of NF-κB gene to control osteoclast differentiation from monocytic precursors

Osteoclasts are bone-resorbing cells that are critical for the normal formation and maintenance of teeth and skeleton. Osteoclast deficiency can contribute to heterotopic ossification (HO), a pathology that is particularly detrimental to the mechanical functions of joints, valves and blood vessels. On the other hand, osteoclast over-activity is a major cause of osteoporosis. A reliable method for controlled generation of osteoclasts would be useful as a potential autologous cell therapy for HO, as well as high-throughput drug screening for anti-osteoporotic drugs. In this report, we describe the development of a cell engineering approach to control monocytic precursor cell differentiation to osteoclasts. Oligomerization of receptor activator of nuclear factor κB (RANK) is known to be essential for osteoclast differentiation from monocyte/macrophage precursors. We engineered a murine monocytic cell line, RAW264.7 to express a fusion protein comprising the intracellular RANK signaling domain and FK506-derived dimerization domains that bind to a small molecule chemical inducer of dimerization (CID). Virally infected cells expressing this fusion protein were treated with CID and dose-dependent induction of tartrate-resistant acid phosphatase activity, as well as multinucleated osteoclast formation were observed. Furthermore, NF-κB signaling was upregulated in a CID-dependent fashion, demonstrating effective RANK intracellular signaling. Functionally CID-induced osteoclasts had robust mineral resorptive activity in both two-dimensional and three-dimensional in vitro resorption assays. In addition, the CID-induced osteoclasts have the same life span as native RANKL-induced osteoclasts. Most importantly and crucially, the engineered cells differentiated into osteoclasts that were resistant to the potent osteoclast inhibitor, osteoprotegerin. Taken together, these studies are the first to describe a method for inducible control of monocytic precursor differentiation to osteoclasts that may be useful for future development of an engineered autologous cell therapy as well as high-throughput drug testing systems to treat diseases of osteoclast over-activity that are independent of osteoprotegerin.

The role of TNF-α and TNF superfamily members in the pathogenesis of calcific aortic valvular disease

Calcific aortic valve disease (CAVD) represents a slowly progressive pathologic process associated with major morbidity and mortality. The process is characterized by multiple steps: inflammation, fibrosis, and calcification. Numerous studies focalized on its physiopathology highlighting different "actors" for the multiple "acts." This paper focuses on the role of the tumor necrosis factor superfamily (TNFSF) members in the pathogenesis of CAVD. In particular, we discuss the clinical and experimental studies providing evidence of the involvement of tumor necrosis factor-alpha (TNF-α), receptor activator of nuclear factor-kappa B (NF-κB) ligand (RANKL), its membrane receptor RANK and its decoy receptor osteoprotegerin (OPG), and TNF-related apoptosis-inducing ligand (TRAIL) in valvular calcification.

Noggin attenuates the osteogenic activation of human valve interstitial cells in aortic valve sclerosis

AIMS

Aortic valve sclerosis (AVSc) is a hallmark of several cardiovascular conditions ranging from chronic heart failure and myocardial infarction to calcific aortic valve stenosis (AVS). AVSc, present in 25-30% of patients over 65 years of age, is characterized by thickening of the leaflets with marginal effects on the mechanical proprieties of the valve making its presentation asymptomatic. Despite its clinical prevalence, few studies have investigated the pathogenesis of this disease using human AVSc specimens. Here, we investigate in vitro and ex vivo BMP4-mediated transdifferentiation of human valve interstitial cells (VICs) towards an osteogenic-like phenotype in AVSc.

METHODS AND RESULTS

Human specimens from 60 patients were collected at the time of aortic valve replacement (AVS) or through the heart transplant programme (Controls and AVSc). We show that non-calcified leaflets from AVSc patients can be induced to express markers of osteogenic transdifferentiation and biomineralization through the combinatory effect of BMP4 and mechanical stimulation. We show that BMP4 antagonist Noggin attenuates VIC activation and biomineralization. Additionally, patient-derived VICs were induced to transdifferentiate using either cell culture or a Tissue Engineering (TE) Aortic Valve model. We determine that while BMP4 alone is not sufficient to induce osteogenic transdifferentiation of AVSc-derived cells, the combinatory effect of BMP4 and mechanical stretch induces VIC activation towards a phenotype typical of late calcified stage of the disease.

CONCLUSION

This work demonstrates, for the first time using AVSc specimens, that human sclerotic aortic valves can be induced to express marker of osteogenic-like phenotype typical of advanced severe aortic stenosis.

Valvular osteoclasts in calcification and aortic valve stenosis severity

BACKGROUND

Bone remodeling in calcified aortic valves is thought to originate from microfractures at multiple sites of the valve, at which osteoclasts and osteoblasts are recruited. The aim of the present study was to assess circulating mediators of bone homeostasis, correlate them to the severity of stenosis and explore the spatio-temporal distribution of bone turnover in different parts of calcified aortic valve tissue.

METHODS AND RESULTS

Plasma and explanted aortic valves were obtained from 46 patients undergoing aortic valve replacement surgery. Plasma levels of tartrate-resistant acid phosphatase (TRAP), receptor activator of nuclear-κB (RANK) ligand and Runt-related transcription factor 2 (Runx2/Cbfa1) exhibited a significant correlation to the severity of aortic stenosis. mRNA levels in normal, thickened and calcified parts of aortic valves assessed by quantitative real-time PCR were significantly elevated in calcified parts of valves for TRAP (5.08 ± 1.6-fold, P<0.001) RANK ligand (8.6 ± 4.2-fold, P<0.001) and RANK (1.98 ± 0.78-fold, P=0.015). In an age, gender and aortic valve anatomy-adjusted multivariable regression analysis the local transcript levels of TRAP correlated significantly with echocardiographic parameters quantifying stenosis severity in early stages, whereas the expression level of Runx2/Cbfa1 was a predictor of the stenosis severity in advanced stages.

CONCLUSIONS

These findings suggest a critical role of bone turnover as a determinant of aortic stenosis severity.

The Wnt5a/Ror2 pathway is associated with determination of the differentiation fate of bone marrow mesenchymal stem cells in vascular calcification

Accumulating evidence have demonstrated that mesenchymal stem cells (MSCs) are involved in the initiation and progression of various vascular diseases. Canonical Wnt signaling controls the fate of MSCs, and plays an important role in vascular calcification. However, vascular calcification can be inhibited by the non-canonical Wnt signaling pathway Wnt5a/Ror2. This study aimed to investigate whether the Wnt5a/Ror2 pathway is associated with determination of the differentiation fate of MSCs in vascular calcification. Direct co-cultures were established by seeding smooth muscle cells (SMCs) or calcified SMCs and MSCs together at ratios of SMCs or calcified SMCs 15x104; SMCs or calcified SMCs 5x104: MSCs 10x104, SMCs or calcified SMCs 10x104: MSCs 5x104. Osteosynthesis-inducing medium (OS) was added to the culture medium in the groups of MSCs with non-calcified SMCs. Cells were cultured for nine days. Osteoblastic differentiation was evaluated by cell morphology and the activity of alkaline phosphatase (ALP) in cell lysates and ALP staining. Furthermore, we investigated the inhibition of Wnt signaling, and observed that the members of the non-canonical signaling pathway Wnt5a/Ror2 were expressed in each group. Additionally, MSCs cultured in culture media with OS did not differentiate into an osteoblast phenotype when in direct contact with non-calcified SMCs, irrespective of the number of MSCs. However, an osteoblast phenotype was observed when MSCs were cultured in media without OS differentiation towards direct contact with calcified SMCs, and the levels of osteoblastic markers had a direct correlation with the number of MSCs. Of note, the Wnt5a protein was associated with the levels of calcification, thus, although rarely detected in non-calcification, Ror2 mRNA in the non-calcified groups was significantly higher compared to that in the calcified groups. Therefore, the Wnt5a/Ror2 pathway is associated with determination of the differentiation fate of bone marrow mesenchymal stem cells in vascular calcification.

Gentamicin Reduces Calcific Nodule Formation by Aortic Valve Interstitial Cells In Vitro

PURPOSE

Gentamicin is a widely employed antibiotic, but may reduce calcium uptake by eukaryotic cells. This study was conducted to determine whether gentamicin reduces calcification by porcine aortic valvular interstitial cells (pAVICs) grown in 2D culture, which is a common model for calcific aortic valve disease (CAVD).

METHODS AND RESULTS

The presence of gentamicin (up to 0.2 mM) in the medium of pAVICs cultured for 8 days significantly lowered calcification and alkaline phosphatase content in a dose-dependent manner compared to pAVICs cultured without gentamicin. Gentamicin also significantly increased cell proliferation and apoptosis at concentrations of 0.1-0.2 mM. Next, gentamicin was applied to previously calcified pAVIC cultures (grown for 8 days) to determine whether it could stop or reverse the calcification process. Daily application of gentamicin for 8 additional days significantly reduced calcification to below the pre-calcification levels.

CONCLUSIONS

These results confirm that gentamicin should be used cautiously with in vitro studies of calcification, and suggest that gentamicin may have the ability to reverse calcification by pAVICs. Given the nephrotoxicity and ototoxicity of this antibiotic, its clinical potential for the treatment of calcification in heart valves is limited. However, further investigation of the pathways through which gentamicin alters calcium uptake by valvular cells may provide insight into novel therapies for CAVD.

Matricellular proteins in cardiac adaptation and disease

The term matricellular proteins describes a family of structurally unrelated extracellular macromolecules that, unlike structural matrix proteins, do not play a primary role in tissue architecture, but are induced following injury and modulate cell-cell and cell-matrix interactions. When released to the matrix, matricellular proteins associate with growth factors, cytokines, and other bioactive effectors and bind to cell surface receptors transducing signaling cascades. Matricellular proteins are upregulated in the injured and remodeling heart and play an important role in regulation of inflammatory, reparative, fibrotic and angiogenic pathways. Thrombospondin (TSP)-1, -2, and -4 as well as tenascin-C and -X secreted protein acidic and rich in cysteine (SPARC), osteopontin, periostin, and members of the CCN family (including CCN1 and CCN2/connective tissue growth factor) are involved in a variety of cardiac pathophysiological conditions, including myocardial infarction, cardiac hypertrophy and fibrosis, aging-associated myocardial remodeling, myocarditis, diabetic cardiomyopathy, and valvular disease. This review discusses the properties and characteristics of the matricellular proteins and presents our current knowledge on their role in cardiac adaptation and disease. Understanding the role of matricellular proteins in myocardial pathophysiology and identification of the functional domains responsible for their actions may lead to design of peptides with therapeutic potential for patients with heart disease.

Osteoprotegerin levels predict mortality in patients with symptomatic aortic stenosis

OBJECTIVES

To examine the prognostic value of osteoprotegerin (OPG) levels in relation to all-cause mortality in patients with symptomatic severe aortic stenosis (AS).

DESIGN

We measured plasma OPG levels in 136 patients with symptomatic severe AS and investigated associations with transvalvular gradients, valve area, valve calcification (using ultrasonic backscatter analysis as an estimate) and measures of heart failure. Then, we assessed the prognostic value of elevated plasma OPG in determining all-cause mortality (n = 29) in these patients.

RESULTS

Elevated OPG was poorly correlated with the degree of AS but was associated with increased backscatter measurements and impaired cardiac function. Furthermore, OPG was associated with all-cause mortality in patients with symptomatic AS, even after adjustment for conventional risk markers. The strongest association was obtained by using a combination of high levels of both OPG and N-terminal pro-brain natriuretic peptide (NT-proBNP), suggesting that these markers may reflect distinct pathways in the development and progression of AS.

CONCLUSION

The level of circulating OPG is significantly associated with all-cause mortality alone and in combination with NT-proBNP in patients with severe symptomatic AS.

Cell–Matrix Interactions in the Pathobiology of Calcific Aortic Valve Disease

The hallmarks of calcific aortic valve disease (CAVD) are the significant changes that occur in the organization, composition, and mechanical properties of the extracellular matrix (ECM), ultimately resulting in stiffened stenotic leaflets that obstruct flow and compromise cardiac function. Increasing evidence suggests that ECM maladaptations are not simply a result of valve cell dysfunction; they also contribute to CAVD progression by altering cellular and molecular signaling. In this review, we summarize the ECM changes that occur in CAVD. We also discuss examples of how the ECM influences cellular processes by signaling through adhesion receptors (matricellular signaling), by regulating the presentation and availability of growth factors and cytokines to cells (matricrine signaling), and by transducing externally applied forces and resisting cell-generated tractional forces (mechanical signaling) to regulate a wide range of pathological processes, including differentiation, fibrosis, calcification, and angiogenesis. Finally, we suggest areas for future research that should lead to new insights into bidirectional cell–ECM interactions in the aortic valve, their contributions to homeostasis and pathobiology, and possible targets to slow or prevent the progression of CAVD.

Reduced sox9 function promotes heart valve calcification phenotypes in vivo

RATIONALE

Calcification of heart valve structures is the most common form of valvular disease and is characterized by the appearance of bone-like phenotypes within affected structures. Despite the clinical significance, the underlying etiology of disease onset and progression is largely unknown and valve replacement remains the most effective treatment. The SRY-related transcription factor Sox9 is expressed in developing and mature heart valves, and its function is required for expression of cartilage-associated proteins, similar to its role in chondrogenesis. In addition to cartilage-associated defects, mice with reduced sox9 function develop skeletal bone prematurely; however, the ability of sox9 deficiency to promote ectopic osteogenic phenotypes in heart valves has not been examined.

OBJECTIVE

This study aims to determine the role of Sox9 in maintaining connective tissue homeostasis in mature heart valves using in vivo and in vitro approaches.

METHODS AND RESULTS

Using histological and molecular analyses, we report that, from 3 months of age, Sox9(fl/+);Col2a1-cre mice develop calcific lesions in heart valve leaflets associated with increased expression of bone-related genes and activation of inflammation and matrix remodeling processes. Consistently, ectopic calcification is also observed following direct knockdown of Sox9 in heart valves in vitro. Furthermore, we show that retinoic acid treatment in mature heart valves is sufficient to promote calcific processes in vitro, which can be attenuated by Sox9 overexpression.

CONCLUSIONS

This study provides insight into the molecular mechanisms of heart valve calcification and identifies reduced Sox9 function as a potential genetic basis for calcific valvular disease.