Regulatory circuits controlling vascular cell calcification

In Vitro Models of Cardiovascular Calcification

Cardiovascular calcification, characterized by hydroxyapatite deposition in the arterial wall and heart valves, is associated with high cardiovascular morbidity and mortality. Cardiovascular calcification is a hallmark of aging but is frequently seen in association with chronic diseases, such as chronic kidney disease (CKD), diabetes, dyslipidemia, and hypertension in the younger population as well. Currently, there is no therapeutic approach to prevent or cure cardiovascular calcification. The pathophysiology of cardiovascular calcification is highly complex and involves osteogenic differentiation of various cell types of the cardiovascular system, such as vascular smooth muscle cells and valve interstitial cells. In vitro cellular and ex vivo tissue culture models are simple and useful tools in cardiovascular calcification research. These models contributed largely to the discoveries of the numerous calcification inducers, inhibitors, and molecular mechanisms. In this review, we provide an overview of the in vitro cell culture and the ex vivo tissue culture models applied in the research of cardiovascular calcification.

The GgcxK325Q Mutation Does Not Affect the Calcium Homeostasis of the Epididymis and Male Fertility in Mice

A low-calcium microenvironment is imperative for spermatozoa maturation within the epididymis. Our previous work has shown that γ-glutamyl carboxylase (GGCX), the carboxylation enzyme of the matrix Gla protein (MGP), plays an essential role in epididymal calcium homeostasis and sperm maturation in rats and that the GGCX SNP mutation rs699664 was associated with asthenozoospermia (AZS) in humans. Here, we investigated the expression patterns of GGCX and MGP in the mouse epididymis and generated GgcxK325Q knock-in (KI) mice. We also tested the effects of this mutation on epididymal calcium homeostasis, sperm function, and male fertility in GgcxK325Q-/- mice. The results showed that both GGCX and MGP were enriched in all regions of the mouse epididymis, especially in the initial segment of the epididymis. Double immunofluorescence staining revealed that GGCX colocalized with MGP in the epithelial cells of the initial segment and caput regions as well as in the lumen of the corpus and cauda regions of the mouse epididymis. However, the GgcxK325Q-/- mice were fertile with normal epididymal morphology, sperm functions, and epididymal calcium concentration. Overall, our findings revealed that the GgcxK325Q mutation does not exert any discernible effect on male fertility in mice.

Association of desphospho-uncarboxylated matrix gla protein with incident cardiovascular disease and all-cause mortality: Results from the prospective Bruneck Study

BACKGROUND AND AIMS

Matrix Gla protein (MGP), a vitamin K-dependent protein, is a potent inhibitor of vascular calcification. Desphospho-uncarboxylated MGP (dp-ucMGP), a marker of vitamin K insufficiency, has been shown to predict cardiovascular disease (CVD) and all-cause mortality in high-risk populations. Whether the increased risk associated with dp-ucMGP also applies to the general, and especially, the elderly population has not yet been fully elucidated.

METHODS AND RESULTS

Plasma dp-ucMGP was measured in 684 individuals aged 50-89 years of the prospective population-based Bruneck Study (baseline evaluation in 2000). Baseline median dp-ucMGP was 478.4 (IQR 335.0-635.2) pmol/L. Over a median follow-up of 15.5 years, 163 CVD events occurred and 235 participants died. Age-/sex-adjusted hazard ratios (HRs) per 1-SD higher level of loge transformed dp-ucMGP were 1.30 (95%CI: 1.09-1.55; p=0.004) for incident CVD and 1.36 (95%CI: 1.17-1.57; p<0.001) for all-cause mortality. After multivariable adjustment, the associations remained significant with HRs of 1.23 (95%CI: 1.02-1.47, p=0.029) for CVD and 1.40 (95%CI: 1.20-1.64; p<0.001) for all-cause mortality. The associations remained virtually unchanged after additional adjustment for dietary quality as measured with the Alternative Healthy Eating Index. We found no association of dp-ucMGP with myocardial infarction and sudden cardiac deaths, but a strong association with other vascular deaths and non-vascular/non-cancer deaths.

CONCLUSIONS

This study shows a significant association of plasma dp-ucMGP with incident CVD and a significant and even stronger association with all-cause mortality. Clinical trials are needed to investigate whether vitamin K substitution results in improved health outcomes.

IL-1β in atherosclerotic vascular calcification: From bench to bedside

Atherosclerotic vascular calcification contributes to increased risk of death in patients with cardiovascular diseases. Assessing the type and severity of inflammation is crucial in the treatment of numerous cardiovascular conditions. IL-1β, a potent proinflammatory cytokine, plays diverse roles in the pathogenesis of atherosclerotic vascular calcification. Several large-scale, population cohort trials have shown that the incidence of cardiovascular events is clinically reduced by the administration of anti-IL-1β therapy. Anti-IL-1β therapy might reduce the incidence of cardiovascular events by affecting atherosclerotic vascular calcification, but the mechanism underlying this effect remains unclear. In this review, we summarize current knowledge on the role of IL-1β in atherosclerotic vascular calcification, and describe the latest results reported in clinical trials evaluating anti-IL-1β therapies for the treatment of cardiovascular diseases. This review will aid in improving current understanding of the pathophysiological roles of IL-1β and mechanisms underlying its activity.

A multi-omics view of the complex mechanism of vascular calcification

Vascular calcification is a high incidence and high risk disease with increasing morbidity and high mortality, which is considered the consequence of smooth muscle cell transdifferentiation initiating the mechanism of accumulation of hydroxyl calcium phosphate. Vascular calcification is also thought to be strongly associated with poor outcomes in diabetes and chronic kidney disease. Numerous studies have been accomplished; however, the specific mechanism of the disease remains unclear. Development of the genome project enhanced the understanding of life science and has entered the post-genomic era resulting in a variety of omics techniques used in studies and a large amount of available data; thus, a new perspective on data analysis has been revealed. Omics has a broader perspective and is thus advantageous over a single pathway analysis in the study of complex vascular calcification mechanisms. This paper reviews in detail various omics studies including genomics, proteomics, transcriptomics, metabolomics and multiple group studies on vascular calcification. Advances and deficiencies in the use of omics to study vascular calcification are presented in a comprehensive view. We also review the methodology of the omics studies and omics data analysis and processing. In addition, the methodology and data processing presented here can be applied to other areas. An omics landscape perspective across the boundaries between genomics, transcriptomics, proteomics and metabolomics is used to examine the mechanisms of vascular calcification. The perspective combined with various technologies also provides a direction for the subsequent exploration of clinical significance.

Molecular Aspects of Thyroid Calcification

In thyroid cancer, calcification is mainly present in classical papillary thyroid carcinoma (PTC) and in medullary thyroid carcinoma (MTC), despite being described in benign lesions and in other subtypes of thyroid carcinomas. Thyroid calcifications are classified according to their diameter and location. At ultrasonography, microcalcifications appear as hyperechoic spots ≤ 1 mm in diameter and can be named as stromal calcification, bone formation, or psammoma bodies (PBs), whereas calcifications > 1 mm are macrocalcifications. The mechanism of their formation is still poorly understood. Microcalcifications are generally accepted as a reliable indicator of malignancy as they mostly represent PBs. In order to progress in terms of the understanding of the mechanisms behind calcification occurring in thyroid tumors in general, and in PTC in particular, we decided to use histopathology as the basis of the possible cellular and molecular mechanisms of calcification formation in thyroid cancer. We explored the involvement of molecules such as runt-related transcription factor-2 (Runx-2), osteonectin/secreted protein acidic and rich in cysteine (SPARC), alkaline phosphatase (ALP), bone sialoprotein (BSP), and osteopontin (OPN) in the formation of calcification. The present review offers a novel insight into the mechanisms underlying the development of calcification in thyroid cancer.

[Quercetin attenuates Ox-LDL-induced calcification in vascular smooth muscle cells by regulating ROS-TLR4 signaling pathway]

OBJECTIVE

To determine whether quercetin inhibits oxidized low-density lipoprotein (Ox-LDL)-induced osteogenic differentiation and calcification of vascular smooth muscle cells (VSMCs) and understand the underlying mechanism.

METHODS

The calcification of human VSMCs following Ox-LDL treatment was assessed using alizarin red staining and by detecting ALP activity. The mRNA expressions of the bone-related genes including Msx2, BMP2 and Osterix, and the contractile proteins including SMA and SM22a were analyzed using qPCR. The effects of quercetin were investigated on OxLDL-induced VSMC calcification and changes in ALP activity, expressions of Msx2, BMP2, Osterix, SMA and SM22a, ROS levels and SOD activity. The effect of Toll like receptor 4 (TLR4) silencing mediated by siRNA transfection on cell calcification, ALP activity, gene expressions and ROS levels were investigated.

RESULTS

Ox-LDL treatment promoted VSMC calcification and up-regulated TLR4 expression. Quercetin treatment significantly attenuated Ox-LDL-induced VSMC calcification, reduced ALP activity, down-regulated the expression levels of Msx2, BMP2 and Osterix, and up-regulated the expressions of vascular smooth muscle contractile proteins SMA and SM22a. In addition, Quercetin treatment markedly increased SOD activity, reduced ROS levels and TLR4 expression in VSMCs. Silencing TLR4 expression using TLR4 siRNA also significantly decreased calcification of the VSMCs.

CONCLUSIONS

Quercetin inhibits Ox-LDL-induced VSMC calcification in VSMCs possibly by targeting the ROS/TLR4 signaling pathway.

Sphingosine 1-phosphate activation of ERM contributes to vascular calcification

Vascular calcification is the deposition of mineral in the artery wall by vascular smooth muscle cells (VSMCs) in response to pathological stimuli. The process is similar to bone formation and is an independent risk factor for cardiovascular disease. Given that ceramide and sphingosine 1-phosphate (S1P) are involved in cardiovascular pathophysiology and biomineralization, their role in VSMC matrix mineralization was investigated. During phosphate-induced VSMC mineralization, endogenous S1P levels increased accompanied by increased sphingosine kinase (SK) activity and increased mRNA expression of SK1 and SK2. Consistent with this, mineralization was increased by exogenous S1P, but decreased by C2-ceramide. Mechanistically, exogenous S1P stimulated ezrin-radixin-moesin (ERM) phosphorylation in VSMCs and ERM phosphorylation was increased concomitantly with endogenous S1P during mineralization. Moreover, inhibition of acid sphingomyelinase and ceramidase with desipramine prevented increased S1P levels, ERM activation, and mineralization. Finally, pharmacological inhibition of ERM phosphorylation with NSC663894 decreased mineralization induced by phosphate and exogenous S1P. Although further studies will be needed to verify these findings in vivo, this study defines a novel role for the SK-S1P-ERM pathways in phosphate-induced VSMC matrix mineralization and shows that blocking these pathways with pharmacological inhibitors reduces mineralization. These results may inform new therapeutic approaches to inhibit or delay vascular calcification.

Increased phagocytic NADPH oxidase activity associates with coronary artery calcification in asymptomatic men

Vascular calcification is a common feature in atherosclerosis and associates with cardiovascular events. Oxidative stress may be involved in the pathogenesis of vascular calcification. Previous studies have shown that the phagocytic NADPH oxidase is associated with atherosclerosis. The objective of the present study was to investigate the association between phagocytic NADPH oxidase-mediated superoxide production and coronary artery calcium (CAC). NADPH oxidase-mediated superoxide production was determined by chemiluminescence and CAC by computed tomography in 159 asymptomatic men free of overt clinical atherosclerosis. Multivariate linear regression analyses were used to assess the relationship between CAC and NADPH oxidase-mediated superoxide production. Compared with individuals in the lowest score of CAC (= 0 Agatston units), those in the upper score (>400 Agatston units) showed higher superoxide production (p < 0.05). In correlation analysis, superoxide production positively (p < 0.01) correlated with CAC, which in multivariate analysis remained significant after adjusting for age, HDL-cholesterol, triglycerides, body mass index, smoking, arterial hypertension and diabetes mellitus. In conclusion, in a population of men without clinically overt atherosclerotic disease, increased NADPH oxidase-mediated superoxide production associated with enhanced CAC. Albeit descriptive, these findings suggest a potential involvement of phagocytic NADPH oxidase-mediated oxidative stress in CAC.

Engineering Synthetic Proteins to Generate Ca2+ Signals in Mammalian Cells

The versatility of Ca²⁺ signals allows it to regulate diverse cellular processes such as migration, apoptosis, motility and exocytosis. In some receptors (e.g., VEGFR2), Ca²⁺ signals are generated upon binding their ligand(s) (e.g., VEGF-A). Here, we employed a design strategy to engineer proteins that generate a Ca²⁺ signal upon binding various extracellular stimuli by creating fusions of protein domains that oligomerize to the transmembrane domain and the cytoplasmic tail of the VEGFR2. To test the strategy, we created chimeric proteins that generate Ca²⁺ signals upon stimulation with various extracellular stimuli (e.g., rapamycin, EDTA or extracellular free Ca²⁺). By coupling these chimeric proteins that generate Ca²⁺ signals with proteins that respond to Ca²⁺ signals, we rewired, for example, dynamic cellular blebbing to increases in extracellular free Ca²⁺. Thus, using this design strategy, it is possible to engineer proteins to generate a Ca²⁺ signal to rewire a wide range of extracellular stimuli to a wide range of Ca²⁺-activated processes.

Pregnancy history and blood-borne microvesicles in middle aged women with and without coronary artery calcification

BACKGROUND AND AIMS

Having a history of preeclampsia increases the risk for future coronary artery calcification (CAC). This study evaluated the association of blood-borne, cell-derived microvesicles (MV) with CAC in middle-aged women.

METHODS

Twelve pre-selected, antigen-specific MV were measured by digital flow cytometry in the blood of age- and parity-matched women (median age 60 years) without a history of cardiovascular events, but with either a history of preeclampsia (PE, n = 39) or normotensive pregnancy (NP, n = 40). CAC was determined by computed tomography.

RESULTS

CAC scores ranged from 0 to 47 and 0-602 Agatston Units in the NP and PE groups, respectively. Waist circumference and insulin resistance were greatest in PE women with CAC. MV positive for tissue factor or stem/progenitor cell antigen (CD117) differed between NP and PE groups. In univariate analysis, those positive for tissue factor, ICAM-1, stem cells, and adipocytes (P16-set) antigens associated with CAC in the PE group. Principal components (PC) analysis reduced the MV variables to three independent dimensions. PC1 showed a modest correlation with CAC scores in the PE group (ρ = 0.31, p = 0.06) and associated with CAC in a multivariable model on pooled groups that included all 3 PC variables when adjusted for pregnancy status (p = 0.03). The association was lost when corrected for body mass index or waist circumference.

CONCLUSIONS

In women with a history of PE and elevated metabolic risk profile, a group of specific antigen-positive MV associated with CAC. These MV may reflect cellular processes associated with CAC. Their diagnostic potential for CAC remains to be determined.

Phosphate induces formation of matrix vesicles during odontoblast-initiated mineralization in vitro

Mineralization is a process of deposition of calcium phosphate crystals within a fibrous extracellular matrix (ECM). In mineralizing tissues, such as dentin, bone and hypertrophic cartilage, this process is initiated by a specific population of extracellular vesicles (EV), called matrix vesicles (MV). Although it has been proposed that MV are formed by shedding of the plasma membrane, the cellular and molecular mechanisms regulating formation of mineralization-competent MV are not fully elucidated. In these studies, 17IIA11, ST2, and MC3T3-E1 osteogenic cell lines were used to determine how formation of MV is regulated during initiation of the mineralization process. In addition, the molecular composition of MV secreted by 17IIA11 cells and exosomes from blood and B16-F10 melanoma cell line was compared to identify the molecular characteristics distinguishing MV from other EV. Western blot analyses demonstrated that MV released from 17IIA11 cells are characterized by high levels of proteins engaged in calcium and phosphate regulation, but do not express the exosomal markers CD81 and HSP70. Furthermore, we uncovered that the molecular composition of MV released by 17IIA11 cells changes upon exposure to the classical inducers of osteogenic differentiation, namely ascorbic acid and phosphate. Specifically, lysosomal proteins Lamp1 and Lamp2a were only detected in MV secreted by cells stimulated with osteogenic factors. Quantitative nanoparticle tracking analyses of MV secreted by osteogenic cells determined that standard osteogenic factors stimulate MV secretion and that phosphate is the main driver of their secretion. On the molecular level, phosphate-induced MV secretion is mediated through activation of extracellular signal-regulated kinases Erk1/2 and is accompanied by re-organization of filamentous actin. In summary, we determined that mineralization-competent MV are distinct from exosomes, and we identified a new role of phosphate in the process of ECM mineralization. These data provide novel insights into the mechanisms of MV formation during initiation of the mineralization process.

Vascular Calcification in Uremia: New-Age Concepts about an Old-Age Problem

A hallmark of aging, and major contributor to the increased prevalence of cardiovascular disease in patients with chronic kidney disease (CKD), is the progressive structural and functional deterioration of the arteries and concomitant accrual of mineral. Vascular calcification (VC) was long viewed as a degenerative age-related pathology that resulted from the passive deposition of mineral in the extracellular matrix; however, since the discovery of "bone-related" protein expression in calcified atherosclerotic plaques over 20 years ago, a plethora of studies have evoked the now widely accepted view that VC is a highly regulated and principally cell-mediated phenomenon that recapitulates many features of physiologic ossification. Central to this theory are changes in vascular smooth muscle cell (VSMC) phenotype and viability, thought to be driven by chronic exposure to a number of dystrophic stimuli characteristics of the uremic state. Here, dedifferentiated synthetic VSMCs are seen to spawn calcifying matrix vesicles that actively seed mineralization of the arterial matrix. This review provides an overview of the major epidemiological, histological, and molecular aspects of VC in the context of CKD, and a counterpoint to the prevailing paradigm that emphasizes the primacy of VSMC-mediated mechanisms. Particular focus is given to the import of protein and small molecule inhibitors in regulating physiologic and pathological mineralization and the emerging role of mineral nanoparticles and their interplay with proinflammatory processes.

Pathophysiological role of vascular smooth muscle alkaline phosphatase in medial artery calcification

Medial vascular calcification (MVC) is a pathological phenomenon that causes vascular stiffening and can lead to heart failure; it is common to a variety of conditions, including aging, chronic kidney disease, diabetes, obesity, and a variety of rare genetic diseases. These conditions share the common feature of tissue-nonspecific alkaline phosphatase (TNAP) upregulation in the vasculature. To evaluate the role of TNAP in MVC, we developed a mouse model that overexpresses human TNAP in vascular smooth muscle cells in an X-linked manner. Hemizygous overexpressor male mice (Tagln-Cre(+/-) ; Hprt(ALPL) (/Y) or TNAP-OE) show extensive vascular calcification, high blood pressure, and cardiac hypertrophy, and have a median age of death of 44 days, whereas the cardiovascular phenotype is much less pronounced and life expectancy is longer in heterozygous (Tagln-Cre(+/-) ; Hprt(ALPL) (/-) ) female TNAP-OE mice. Gene expression analysis showed upregulation of osteoblast and chondrocyte markers and decreased expression of vascular smooth muscle markers in the aortas of TNAP-OE mice. Through medicinal chemistry efforts, we developed inhibitors of TNAP with drug-like pharmacokinetic characteristics. TNAP-OE mice were treated with the prototypical TNAP inhibitor SBI-425 or vehicle to evaluate the feasibility of TNAP inhibition in vivo. Treatment with this inhibitor significantly reduced aortic calcification and cardiac hypertrophy, and extended lifespan over vehicle-treated controls, in the absence of secondary effects on the skeleton. This study shows that TNAP in the vasculature contributes to the pathology of MVC and that it is a druggable target.

Histology-directed and imaging mass spectrometry: An emerging technology in ectopic calcification

The present study was designed to demonstrate the potential of an optimized histology directed protein identification combined with imaging mass spectrometry technology to reveal and identify molecules associated to ectopic calcification in human tissue. As a proof of concept, mineralized and non-mineralized areas were compared within the same dermal tissue obtained from a patient affected by Pseudoxanthoma elasticum, a genetic disorder characterized by calcification only at specific sites of soft connective tissues. Data have been technically validated on a contralateral dermal tissue from the same subject and compared with those from control healthy skin. Results demonstrate that this approach 1) significantly reduces the effects generated by techniques that, disrupting tissue organization, blend data from affected and unaffected areas; 2) demonstrates that, abolishing differences due to inter-individual variability, mineralized and non-mineralized areas within the same sample have a specific protein profile and have a different distribution of molecules; and 3) avoiding the bias of focusing on already known molecules, reveals a number of proteins that have been never related to the disease nor to the calcification process, thus paving the way for the selection of new molecules to be validated as pathogenic or as potential pharmacological targets.

Extracellular pyrophosphate is reduced in aortic interstitial valve cells acquiring a calcifying profile: implications for aortic valve calcification

OBJECTIVES

Pyrophosphate (PPi) is a potent inhibitor of ectopic mineralization but its role during aortic valve calcification is not known.

METHODS

Anti-calcific effect of PPi was investigated by using an in vitro model of serum-driven calcification of collagen sponges and decellularized porcine aortic valve leaflets. Bovine interstitial valve cells (VIC), seeded either within the collagen matrices or in transwell chambers, were used to test cellular ability to inhibit serum-induced calcification. PPi metabolism was investigated in clonal VIC harboring different calcifying potential.

RESULTS

In a cell-free system, high serum levels induced a dose-dependent calcification of type I collagen matrices which was prevented by PPi and ATP supplementation. Blockade of serum-driven calcification by PPi and ATP was also observed when using decellularized porcine aortic valve leaflets. A similar anti-calcific effect was also seen for bovine VIC, either statically seeded into the collagen matrices or co-cultured by using a transwell system. However, when we performed co-culture experiments by using clonal VIC harboring different calcifying potential, we observed that the subset of cells acquiring a pro-calcific profile lost the ability to protect the collagen from serum-driven calcification. Pro-calcific differentiation of the clonal VIC was accompanied by increase in ALP along with significant reduction in NPP activity and ATP/PPi extracellular accumulation. These changes were not observed in the clonal subtype with lower propensity towards calcification.

CONCLUSIONS

We showed that PPi and ATP are potent inhibitors of serum-driven calcification of collagen matrix and that their extracellular accumulation is reduced in calcifying VIC.

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.

Atherogenesis and iron: from epidemiology to cellular level

Iron accumulates in human atherosclerotic lesions but whether it is a cause or simply a downstream consequence of the atheroma formation has been an open question for decades. According to the so called "iron hypothesis," iron is believed to be detrimental for the cardiovascular system, thus promoting atherosclerosis development and progression. Iron, in its catalytically active form, can participate in the generation of reactive oxygen species and induce lipid-peroxidation, triggering endothelial activation, smooth muscle cell proliferation and macrophage activation; all of these processes are considered to be proatherogenic. On the other hand, the observation that hemochromatotic patients, affected by life-long iron overload, do not show any increased incidence of atherosclerosis is perceived as the most convincing evidence against the "iron hypothesis." Epidemiological studies and data from animal models provided conflicting evidences about the role of iron in atherogenesis. Therefore, more careful studies are needed in which issues like the source and the compartmentalization of iron will be addressed. This review article summarizes what we have learnt about iron and atherosclerosis from epidemiological studies, animal models and cellular systems and highlights the rather contributory than innocent role of iron in atherogenesis.